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for Multi-Task Learning Searching Across Diverse Network Topologies/08f871aa-0255-4d39-aee9-94ac7465f9f8_content_list.json @@ -0,0 +1,1644 @@ +[ + { + "type": "text", + "text": "Dynamic Neural Network for Multi-Task Learning Searching across Diverse Network Topologies", + "text_level": 1, + "bbox": [ + 228, + 130, + 743, + 176 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Wonhyeok Choi, Sunghoon Im* \nDepartment of Electrical Engineering & Computer Science, DGIST, Daegu, Korea \n{smu06117, sunghoonim}@dgist.ac.kr", + "bbox": [ + 158, + 203, + 810, + 256 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 291, + 313, + 306 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "In this paper, we present a new MTL framework that searches for structures optimized for multiple tasks with diverse graph topologies and shares features among tasks. We design a restricted DAG-based central network with read-in/read-out layers to build topologically diverse task-adaptive structures while limiting search space and time. We search for a single optimized network that serves as multiple task adaptive sub-networks using our three-stage training process. To make the network compact and discretized, we propose a flow-based reduction algorithm and a squeeze loss used in the training process. We evaluate our optimized network on various public MTL datasets and show ours achieves state-of-the-art performance. An extensive ablation study experimentally validates the effectiveness of the sub-module and schemes in our framework.", + "bbox": [ + 75, + 316, + 472, + 542 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 551, + 209, + 566 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Multi-task learning (MTL), which learns multiple tasks simultaneously with a single model has gained increasing attention [3, 13, 14]. MTL improves the generalization performance of tasks while limiting the total number of network parameters to a lower level by sharing representations across tasks. However, as the number of tasks increases, it becomes more difficult for the model to learn the shared representations, and improper sharing between less related tasks causes negative transfers that sacrifice the performance of multiple tasks [15,36]. To mitigate the negative transfer in MTL, some works [6, 25, 32] separate the shared and task-specific parameters on the network.", + "bbox": [ + 75, + 577, + 468, + 758 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "More recent works [21, 29, 38] have been proposed to dynamically control the ratio of shared parameters across tasks using a Dynamic Neural Network (DNN) to construct a task adaptive network. These works mainly apply the cell-based architecture search [19, 27, 41] for fast search times, so that the optimized sub-networks of each task consist of fixed or simple structures whose layers are simply branched, as shown in Fig. 1a. They primarily focus on finding branching", + "bbox": [ + 75, + 758, + 470, + 878 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "patterns in specific aspects of the architecture, and feature-sharing ratios across tasks. However, exploring optimized structures in restricted network topologies has the potential to cause performance degradation in heterogeneous MTL scenarios due to unbalanced task complexity.", + "bbox": [ + 500, + 292, + 890, + 368 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "We present a new MTL framework searching for subnetwork structures, optimized for each task across diverse network topologies in a single network. To search the graph topologies from richer search space, we apply Directed Acyclic Graph (DAG) for the homo/heterogeneous MTL frameworks, inspired by the work in NAS [19, 27, 40]. The MTL in the DAG search space causes a scalability issue, where the number of parameters and search time increase quadratically as the number of hidden states increases.", + "bbox": [ + 496, + 369, + 892, + 505 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "To solve this problem, we design a restricted DAG-based central network with read-in/read-out layers that allow our MTL framework to search across diverse graph topologies while limiting the search space and search time. Our flow-restriction eliminates the low-importance long skip connection among network structures for each task, and creates the required number of parameters from $O(N^2)$ to $O(N)$ . The read-in layer is the layer that directly connects all the hidden states from the input state, and the read-out layer is the layer that connects all the hidden states to the last feature layer. These are key to having various network topological representations, such as polytree structures, with early-exiting and multi-embedding.", + "bbox": [ + 496, + 506, + 893, + 702 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Then, we optimize the central network to have compact task-adaptive sub-networks using a three-stage training procedure. To accomplish this, we propose a squeeze loss and a flow-based reduction algorithm. The squeeze loss limits the upper bound on the number of parameters. The reduction algorithm prunes the network based on the weighted adjacency matrix measured by the amount of information flow in each layer. In the end, our MTL framework constructs a compact single network that serves as multiple task-specific networks with unique structures, such as chain, polytree, and parallel diverse topologies, as presented in Fig. 1b. It also dynamically controls the amount of sharing representation among tasks.", + "bbox": [ + 496, + 704, + 893, + 900 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Corresponding author", + "bbox": [ + 94, + 887, + 220, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "3779", + "bbox": [ + 482, + 945, + 514, + 955 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/9eb6ce8f6581a330c427eb55ebf2cd59425057164ae3c0f36d0ca7d895b92f9c.jpg", + "image_caption": [ + "(i). Mixture-of-Experts" + ], + "image_footnote": [ + "- - $\\rightarrow$ : inactivated operation" + ], + "bbox": [ + 117, + 112, + 343, + 193 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/b84c484c0785246c528c2a3d6dfba93cfef10f4f82c3fcabc523efc749b5c989.jpg", + "image_caption": [ + "(iii).Ours", + "$\\bigcirc$ : hidden states" + ], + "image_footnote": [ + ":activated operation" + ], + "bbox": [ + 364, + 112, + 586, + 193 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/1550a4d2ebad536df6871564cb9f1497878b6bc1ec58b4c6c76dbc8442d41bd3.jpg", + "image_caption": [ + "(ii).Skip-or-Select" + ], + "image_footnote": [ + "non-operation", + "(a) Graph representation of existing DNN-based methods (i)-(ii). for MTL and ours (iii)." + ], + "bbox": [ + 117, + 214, + 343, + 287 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/39d42af6da39011dc02e3a7ef353edb2d31e23f99d2a7f9bbcbf2bb2e7ebd470.jpg", + "image_caption": [ + "(i). Complete Directed Acyclic Graph", + "(ii). Subgraph topologies" + ], + "image_footnote": [], + "bbox": [ + 635, + 109, + 831, + 159 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/3c6b6df501bf8ac240961a679f1310c740d90d88269fcdb9d7e78b56e1a539f5.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 617, + 199, + 725, + 215 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/d1e1ca9da298354661df86545538e16c8587665db2355972770a8659a247c58c.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 745, + 183, + 852, + 234 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/b6f1c6cc4b029196914b5ffa78bc7cfe23e2cb25ca979e4a0b58f4491ce669ff.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 622, + 238, + 720, + 297 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/9b5373f39e249d7c971cccf8d768072d1e69a52df2a972445c412e32e775154e.jpg", + "image_caption": [ + "Figure 1. Graph representation of various neural networks. (a) Graph representation of existing dynamic neural network for multitask learning and ours. (b) Topologies of a completed Directed Acyclic Graph (DAG) and the output sub-graph of DAG structure." + ], + "image_footnote": [ + "(b) Topologies of DAG (i). and its sub-graph (ii)." + ], + "bbox": [ + 745, + 239, + 851, + 299 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "The experiments demonstrate that our framework successfully searches the task-adaptive network topologies of each task and leverages the knowledge among tasks to make a generalized feature. The proposed method outperforms state-of-the-art methods on all common benchmark datasets for MTL. Our contributions can be summarized as follows:", + "bbox": [ + 75, + 373, + 468, + 463 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- We present for the first time an MTL framework that searches both task-adaptive structures and sharing patterns among tasks. It achieves state-of-the-art performance on all public MTL datasets.", + "- We propose a new DAG-based central network composed of a flow restriction scheme and read-in/out layers, that has diverse graph topologies in a reasonably restricted search space.", + "- We introduce a new training procedure that optimizes the MTL framework for compactly constructing various task-specific sub-networks in a single network." + ], + "bbox": [ + 94, + 473, + 468, + 650 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Works", + "text_level": 1, + "bbox": [ + 76, + 664, + 225, + 679 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Neural Architecture Search (NAS) Neural Architecture Search is a method that automates neural architecture engineering [8]. Early works [2, 40, 41] use reinforcement learning based on rewarding the model accuracy of the generated architecture. Alternative approaches [24, 30, 37] employ evolutionary algorithms to optimize both the neural architecture and its weights. These methods search for an adequate neural architecture in a large discrete space. Gradient-based NAS methods [4, 19, 39] of formulating operations in a differentiable search space are proposed to alleviate the scalability issues. They generally use the convex combination from a set of operations instead of determining a single operation. Most NAS approaches [19, 27, 40] adopt the complete DAG as a search space, to find the architecture", + "bbox": [ + 75, + 688, + 468, + 900 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "in the various network topologies. However, DAG-based MTL frameworks have not been proposed, because of their considerably high computational demands.", + "bbox": [ + 496, + 373, + 890, + 417 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Multi-Task Learning (MTL) Multi-task learning in deep neural networks can be categorized into hard and soft parameter sharing types [31]. Hard parameter sharing [3, 13, 14], also known as shared-bottom, is the most commonly used approach to MTL. This scheme improves generalization performance while reducing the computational cost of the network, by using shared hidden layers between all tasks. However, it typically struggles with the negative transfer problem [15, 36] which degrades performance due to improper sharing between less relevant tasks.", + "bbox": [ + 496, + 419, + 892, + 568 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "On the other hand, soft-parameter sharing [25, 32] alleviate the negative transfer problem by changing the shared parameter ratio. These approaches mitigate the negative transfer by flexibly modifying shared information, but they cannot maintain the computational advantage on the classic shared-bottom model. Recently, advanced approaches have been proposed to adjust shared parameters using a dynamic neural network [21, 22, 29, 38] and NAS [10].", + "bbox": [ + 496, + 568, + 890, + 688 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "NAS-style MTL MTL frameworks using a dynamic neural network (DNN) can be divided into two categories. One employs the Mixture-of-Experts (MoE) [33], which is designed for conditional computation of per-sample, to MTL by determining the experts of each task [9, 21, 22]. They have a fixed depth finalized task-specific sub-network, because they choose experts from a fixed number of modular layers. This causes a critical issue with task-balancing in the heterogeneous MTL. The other adopts the skip-or-select policy to select task-specific blocks from the set of residual blocks [38] or a shared block per layer [12, 29]. These methods only create a simple serial path in the finalized subnetwork of each task, and a parallel link cannot be reproduced. Moreover, they heuristically address the unbalanced", + "bbox": [ + 496, + 688, + 892, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "3780", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "task-wise complexity issues in the heterogenous MTL (e.g. manually changing the balancing parameters based on the task complexity [29,38]). Thus, none of the aforementioned works focus on finding the optimal task-specific structure in the MTL scenario.", + "bbox": [ + 75, + 90, + 468, + 165 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Method", + "text_level": 1, + "bbox": [ + 76, + 179, + 166, + 194 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We describe our MTL framework, which searches for optimized network structures tailored to each task across diverse graph topologies, while limiting search time. Sec. 3.1 describes the composition of the searchable space of our central network and our flow-restriction method for efficiently balancing the topological diversity of task-specific sub-networks and searching space. Sec. 3.2 introduces our mechanism to determine the task-adaptive sub-network in the central network and describes the overall training process and loss function. The overall pipeline of our method is illustrated in Fig. 2.", + "bbox": [ + 75, + 204, + 470, + 369 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. The Central Network with Diverse Topologies", + "text_level": 1, + "bbox": [ + 76, + 378, + 465, + 395 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Our central network composes a graph $G = (V, E)$ with layers $E$ in which the $N$ hidden states $V = \\{v_1, \\dots, v_N\\}$ are topologically sorted:", + "bbox": [ + 75, + 402, + 468, + 446 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nE = \\left\\{e _ {i j} \\right\\} _ {i, j \\in \\{1, \\dots , N \\}}, \\text {w h e r e} i < j, \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 150, + 457, + 468, + 474 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\ne _ {i j} (\\cdot ; \\theta_ {i j}): \\mathbb {R} ^ {N ^ {v _ {i}}} \\rightarrow \\mathbb {R} ^ {N ^ {v _ {j}}}, \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 176, + 476, + 468, + 494 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $e_{ij}$ is the operation that transfers the state $v_{i}$ to $v_{j}$ with the weight parameters $\\theta_{ij} \\in \\Theta$ , and $N^{v_k}$ is the number of the elements of hidden state $v_{k}$ , respectively. We adopt the DAG structure [19, 27, 40] for the network. However, the optimized structure from DAG is searched from $2^{N(N - 1) / 2}$ network topologies, which are too large to be optimized in time. To address the issue while maintaining diversity, we propose a flow-restriction and read-in/read-out layers.", + "bbox": [ + 75, + 503, + 468, + 625 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Flow-restriction The flow-restriction eliminates the low-importance long skip connection among network structures for each task by restricting $j - i \\leq M$ where $M$ is the flow constant. Regulating the searchable edges in the graph reduces the required number of parameters and searching time from $O(N^2)$ to $O(N)$ , but it sacrifices the diversity and capacity of the network topologies.", + "bbox": [ + 75, + 625, + 468, + 729 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "To explain the topological diversity and task capacity of sub-networks, we define the three components of network topology, as follows:", + "bbox": [ + 75, + 731, + 468, + 775 + ], + "page_idx": 2 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "1. $\\mathcal{D}(G) = \\max (\\{\\mathrm{Distance}(v_i,v_j)\\}_{v_i,v_j\\in V}),$", + "2. $\\mathcal{W}(G) = \\max (\\{\\mathrm{Out}_{v_i}\\}_{v_i\\in V}),$", + "3. $S(G_{s},G) = |E_{s}| / |E|$" + ], + "bbox": [ + 88, + 782, + 392, + 848 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\mathrm{Out}_{v_i}$ is the out-degree of the vertex $v_i$ and $\\mathrm{Distance}(\\cdot)$ is the operation that counts the number of layers (or edges) between two connected vertices. The network", + "bbox": [ + 75, + 854, + 468, + 900 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "depth $\\mathcal{D}(G)$ is equal to the longest distance between two vertices in the graph $G$ . The network width $\\mathcal{W}(G)$ is equal to the maximum value of the out-degrees of hidden states in the graph $G$ . The sparsity $\\mathcal{S}(G_s, G)$ of the sub-graph $G_s$ is the ratio of finalized edges $|E_s|$ over entire edges $|E|$ . The first two components are measurements of the topological diversity of the finalized sub-network, while the last one is for the sub-network capacity. While a complete DAG has the full range of depth and width components, the flow-restricted DAG has the properties of depth and width components as follows:", + "bbox": [ + 496, + 90, + 890, + 257 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\text {P r o p e r t y 1 .} \\min (\\{\\mathcal {D} (G _ {s}) \\} _ {G _ {s} \\subseteq G}) = \\lceil (| V | / M) \\rceil ,\n$$\n", + "text_format": "latex", + "bbox": [ + 498, + 267, + 825, + 284 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\text {P r o p e r t y 2 .} \\max (\\{\\mathcal {W} (G _ {s}) \\} _ {G _ {s} \\subseteq G}) = M,\n$$\n", + "text_format": "latex", + "bbox": [ + 500, + 292, + 774, + 309 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\{G_s\\}$ is the entire sub-graph of $G$ . The min-depth property (Prop. 1) can cause the over-parameterized problem when the capacity of the task is extremely low. The max-width property (Prop. 2) directly sacrifices the diversity of network topologies in the search space.", + "bbox": [ + 496, + 318, + 890, + 393 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Read-in/Read-out layers We design read-in/read-out layers to mitigate these problems. The read-in layer embeds the input state $v_{0}$ into all hidden states $v_{i} \\in V$ with task-specific weights $\\alpha_{i}^{k} \\in \\mathcal{A}$ for all $K$ tasks $\\mathcal{T} = \\{T_k\\}_{k \\in \\{1, \\dots, K\\}}$ as follows:", + "bbox": [ + 498, + 393, + 890, + 470 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nv _ {i} ^ {k} = \\sigma \\left(\\alpha_ {i} ^ {k}\\right) \\cdot v _ {0}, \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 637, + 482, + 890, + 501 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\sigma (\\cdot)$ is the sigmoid function. Then, the central network sequentially updates the hidden state $v_{1}^{k}$ to $v_{N}^{k}$ with the task-specific weights $\\gamma_{ij}^{k}\\in \\Gamma$ that correspond to $e_{ij}^{k}$ :", + "bbox": [ + 496, + 507, + 890, + 556 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nv _ {j} ^ {k} = \\frac {1}{\\operatorname {I n} _ {v _ {j} ^ {k}}} \\sum_ {e _ {i j} \\in E} \\left(\\sigma \\left(\\gamma_ {i j} ^ {k}\\right) \\cdot e _ {i j} \\left(v _ {i} ^ {k}; \\theta_ {i j}\\right)\\right), \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 563, + 566, + 890, + 604 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\operatorname{In}_{v_j^k}$ is the in-degree of $v_{j}^{k}$ . Note that $\\Gamma$ is the adjacency matrix of graph $G$ . Finally, the read-out layer aggregates all hidden state features $\\{v_{i}^{k}\\}_{i\\in \\{1,\\dots,N\\}}$ with the task-specific weights $\\beta_i^k\\in \\mathcal{B}$ and produces the last layer feature $v_{L}^{k}$ for each task $k$ as follows:", + "bbox": [ + 496, + 617, + 890, + 696 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nv _ {L} ^ {k} = \\sum_ {i \\in \\{1, \\dots , N \\}} \\left(\\sigma \\left(\\beta_ {i} ^ {k}\\right) \\cdot v _ {i} ^ {k}\\right). \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 596, + 708, + 890, + 742 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The final prediction $\\hat{\\mathbf{y}}_k$ for each task $T_{k}$ is computed by passing the aggregated features $v_{L}^{k}$ through the task-specific head $H^{k}(\\cdot)$ as follows:", + "bbox": [ + 496, + 753, + 890, + 799 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {\\mathbf {y}} ^ {k} = H ^ {k} \\left(v _ {L} ^ {k}\\right). \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 642, + 809, + 890, + 829 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "All upper-level parameters $\\mathcal{A},\\mathcal{B}$ , and $\\Gamma$ are learnable parameters, and their learning process is described in Sec. 3.2. The read-in/read-out layers enable the optimized network to have a multi-input/output sub-network. The read-out layer", + "bbox": [ + 496, + 839, + 890, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "3781", + "bbox": [ + 482, + 944, + 513, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/545018b5d6911594acd54e953845adfeb62cea15ae128f78ddf76ec4c89429e8.jpg", + "image_caption": [ + "Figure 2. Overall pipeline. Our central network follows a DAG-based structure with read-in/out layers, and task-specific heads. The long skip connection is cut by our flow-restriction. Our framework with a 3-task MTL learning scenario consists of three stages including warm-up, search, and fine-tuning stages. The warm-up stage only learns the parameters of the main network $\\Theta$ and task-specific weights. The search stage learns the upper-level parameters $\\mathcal{A},\\mathcal{B},\\Gamma$ , and task-specific weights. Then, flow-based reduction eliminates the low-importance edges from the network. The fine-tuning stage re-trains the network with the remaining important parameters." + ], + "image_footnote": [], + "bbox": [ + 99, + 90, + 883, + 380 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "aggregates all hidden states of the central network during the search stage, allowing a specific task to use the early hidden states to output predictions while ignoring the last few layers. These early-exit structures help alleviate the over-parameterized problem in simple tasks.", + "bbox": [ + 75, + 486, + 468, + 561 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. Network Optimization and Training Procedure", + "text_level": 1, + "bbox": [ + 76, + 569, + 468, + 585 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We describe the entire training process for our MTL framework, which consists of three stages, including warm-up, search, and fine-tuning stages.", + "bbox": [ + 75, + 592, + 468, + 638 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Warm-up stage As with other gradient-based NAS, our framework has upper-level parameters that determine the network structure and parameters. This bilevel optimization with a complex objective function in an MTL setup makes the training process unstable. For better convergence, we initially train all network parameters across tasks for a few iterations. We train the weight parameters of the central network $\\Theta$ that shares all operations $E$ across tasks. We fix all values of the upper-level parameters $\\mathcal{A},\\mathcal{B}$ , and $\\Gamma$ as 0, which becomes 0.5 after the sigmoid function $\\sigma (\\cdot)$ , and freeze them. We train the network parameters $\\Theta$ in Eq. 4 with a task loss as follows:", + "bbox": [ + 75, + 638, + 468, + 818 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\text {t a s k}} = \\sum_ {k = 0} ^ {K} \\mathcal {L} _ {T _ {k}} \\left(\\hat {\\mathbf {y}} _ {T _ {k}}, \\mathbf {y} _ {T _ {k}}\\right), \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 174, + 823, + 468, + 864 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\mathcal{L}_{T_k}$ is the task-specific loss, which is the unique loss function for each task.", + "bbox": [ + 76, + 869, + 468, + 898 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Search stage After the warm-up stage, we unfreeze the upper-level parameters $\\mathcal{A},\\mathcal{B}$ , and $\\Gamma$ and search the network topologies appropriate to each task. We train all these parameters and network parameters $\\Theta$ simultaneously by minimizing the task loss and the proposed squeeze loss $\\mathcal{L}_{sq}$ as follows:", + "bbox": [ + 496, + 486, + 890, + 575 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\text {t r a i n}} = \\mathcal {L} _ {\\text {t a s k}} + \\lambda_ {s q} \\mathcal {L} _ {s q}, \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 604, + 585, + 890, + 604 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {s q} = \\sum_ {k = 0} ^ {K} \\left(\\max \\left(\\left(\\sum_ {\\gamma_ {i j} \\in \\Gamma} \\left(\\sigma \\left(\\gamma_ {i j}\\right)\\right) - \\kappa\\right), 0\\right)\\right), \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 553, + 607, + 890, + 650 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\lambda_{sq}$ is the balancing hyperparameter, and $\\kappa$ is a constant number called the budget, that directly reduces the sparsity of the central network. This auxiliary loss is designed to encourage the model to save computational resources.", + "bbox": [ + 496, + 659, + 890, + 733 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Fine-tuning stage. Lastly, we perform a fine-tuning stage to construct a compact and discretized network structure using the trained upper-level parameters $\\mathcal{A},\\mathcal{B}$ , and $\\Gamma$ . To do so, we design a flow-based reduction algorithm that allows the network to obtain high computational speed by omitting low-importance operations, as described in Alg. 1. It measures the amount of information flow of each layer $e_{ij}$ in the central network by calculating the ratio of edge weight with respect to other related edges weight. Then, it sequentially removes the edge which has the lowest information flow. Alg. 1 stops when the edge selected to be deleted is", + "bbox": [ + 496, + 734, + 892, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "3782", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 3 + }, + { + "type": "code", + "sub_type": "algorithm", + "code_caption": [ + "Algorithm 1: Flow-based Reduction" + ], + "code_body": "Input: $\\Gamma \\in \\mathbb{R}^{N\\times N}$ $\\mathcal{A}\\in \\mathbb{R}^N$ $\\mathcal{B}\\in \\mathbb{R}^N$ Output: $\\hat{\\Gamma},\\hat{\\mathcal{A}},\\hat{\\mathcal{B}} / /$ Discretized params. \n1 initialize zero matrix $\\Psi ,\\hat{\\Psi}\\in \\mathbb{R}^{(N + 2)\\times (N + 2)}$ \n2 $N_{\\alpha} = \\mathrm{argmax}(\\mathcal{A})$ \n3 $N_{\\beta} = \\max (N_{\\alpha} + 1,\\mathrm{argmax}(\\mathcal{B}))$ \n4 $\\Gamma [:N_{\\alpha},:)]\\gets 0 / /$ remove edges $< N_{\\alpha}$ \n5 $\\Gamma [:,N_{\\beta}]:\\gets 0 / /$ remove edges $>N_{\\beta}$ \n6 $\\Psi [1:N,1:N]\\gets \\Gamma /$ merge $\\Gamma ,A,B$ into $\\Psi$ \n7 $\\Psi [0,N_{\\alpha} + 1:N_{\\beta} + 1]\\gets A[N_{\\alpha}:N_{\\beta}]$ \n8 $\\Psi [N_{\\alpha} + 1:N_{\\beta} + 1,N + 1]\\gets B[N_{\\alpha}:N_{\\beta}]$ \n9 while True do \n10 initialize zero matrix $S\\in \\mathbb{R}^{(N + 2)\\times (N + 2)}$ \nfor $i\\gets 0$ to $\\{N + 1\\}$ do \nfor $j\\gets 0$ to $\\{N + 1\\}$ do \n $S[i,j]\\gets$ $\\psi_{ij}\\left(\\frac{1}{\\ln v_i}\\sum_{\\psi_{ki}\\in \\Psi}(\\psi_{ki}) / \\sum_{\\psi_{ik}\\in \\Psi}(\\psi_{ik})+\\right.$ $\\left.\\frac{1}{\\mathrm{Out}_v_j}\\sum_{\\psi_{jk}\\in \\Psi}(\\psi_{jk}) / \\sum_{\\psi_{kj}\\in \\Psi}(\\psi_{kj})\\right)$ $\\psi_{ij}\\gets 0$ where $S[i,j]$ is nonzero min value \nif graph built from $\\Psi$ is reachable then \n $\\hat{\\Psi}\\gets \\Psi$ \nelse \n $\\hat{\\Psi} [\\hat{\\Psi} >0]\\gets 1 / /$ discretization \n $\\hat{\\Gamma}\\gets \\hat{\\Psi}[1:N,1:N] / /$ split into $\\Gamma ,A,B$ $\\hat{\\mathcal{A}}\\gets \\hat{\\Psi}[0,1:N]$ $\\hat{\\mathcal{B}}\\gets \\hat{\\Psi}[1:N,N + 1]$ \nreturn $\\hat{\\Gamma},\\hat{\\mathcal{A}},\\hat{\\mathcal{B}}$", + "bbox": [ + 78, + 111, + 473, + 556 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "the only edge that can reach the graph. We use the simple Depth-first search algorithm to check the reachability of $\\hat{\\Gamma}$ between hidden state $v_{N_{\\alpha}}$ to $v_{N_{\\beta}}$ . All the output $\\hat{A}, \\hat{B}, \\hat{\\Gamma}$ in Alg. 1, which is the discretized binary adjacency matrix, represent the truncated task-adaptive sub-network. After the reduction, we fix the upper-level parameters and only re-train the network parameters $\\Theta$ , and we do not use the sigmoid function in Eq. 3-5", + "bbox": [ + 75, + 575, + 468, + 696 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 76, + 708, + 207, + 724 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We first describe the experimental setup in Sec. 4.1. We compare our method to state-of-the-art MTL frameworks on various benchmark datasets for MTL in Sec. 4.2. We also conduct extensive experiments and ablation studies to validate our proposed method in Sec. 4.3-4.5.", + "bbox": [ + 75, + 733, + 468, + 809 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.1. Experimental Settings", + "text_level": 1, + "bbox": [ + 76, + 816, + 284, + 833 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Dataset We use four public datasets for multi-task scenarios including Omniglot [17], NYU-v2 [34], Cityscapes [7], and PASCAL-Context [26]. We use these datasets, configured by previous MTL works [29, 38], not their original sources.", + "bbox": [ + 75, + 839, + 468, + 902 + ], + "page_idx": 4 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- Omniglot Omniglot is a classification dataset consisting of 50 different alphabets, and each of them consists of a number of characters with 20 handwritten images per character.", + "- NYU-v2 NYU-v2 comprises images of indoor scenes, fully labeled for joint semantic segmentation, depth estimation, and surface normal estimation.", + "- Cityscapes Cityscapes dataset collected from urban driving scenes in European cities consists of two tasks: joint semantic segmentation and depth estimation.", + "- PASCAL-Context PASCAL-Context datasets contain PASCAL VOC 2010 [34] with semantic segmentation, human parts segmentation, and saliency maps, as well as additional annotations for surface normals and edge maps." + ], + "bbox": [ + 517, + 90, + 893, + 342 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Competitive methods We compare the proposed framework with state-of-the-art methods [1, 11, 12, 18, 20, 22, 23, 25, 28, 29, 32, 38] and various baselines including a single task and a shared-bottom. The single-task baseline trains each task independently using a task-specific encoder and task-specific head for each task. The shared-bottom baseline trains multiple tasks simultaneously with a shared encoder and separated task-specific heads.", + "bbox": [ + 496, + 354, + 890, + 474 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We compare our method with MoE-based approaches, including Soft Ordering [23], Routing [28], and Gumbel-Matrix [22], as well as a NAS approach [18] on Omniglot datasets. CMTR [18] can modify parameter count, similar to our method. We compare our method with other soft-parameter sharing methods including Cross-Stitch [25], Sluice network [32], and NDDR-CNN [11] and the dynamic neural network (DNN)-based methods including MTAN [20], DEN [1], and Adashare [38] for the other three datasets. We provide the evaluation results of two recent works, LTB [12] and PHN [29] for PASCAL-Context datasets because only the results are reported in their papers, but no source codes are provided.", + "bbox": [ + 496, + 477, + 892, + 672 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Multi-task scenarios We set up multi-task scenarios with the combination of several tasks out of a total of seven tasks, including classification $\\mathcal{T}_{cls}$ , semantic segmentation $\\mathcal{T}_{sem}$ , depth estimation $\\mathcal{T}_{dep}$ , surface normal prediction $\\mathcal{T}_{norm}$ , human-part segmentation $\\mathcal{T}_{part}$ , saliency detection $\\mathcal{T}_{sal}$ , and edge detection $\\mathcal{T}_{edge}$ . We follow the MTL setup in [38] for three datasets including Omniglot, NYU-v2, and cityscapes, and [29] for PASCAL-Context. We simulate a homogeneous MTL scenario of a 20-way classification task in a multi-task setup using Omniglot datasets by following [23]. Each task predicts a class of characters in a single alphabet set. We use the other three datasets for heterogeneous MTL. We set three tasks including segmentation, depth estimation, and normal estimation for NYU-v2 and two with segmentation, depth estimation for Cityscapes.", + "bbox": [ + 496, + 674, + 892, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "3783", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/456132b189e2b87c449fc271ee5c02701d79c2d050ad204f0f08ab81ea2a5749.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodTest Acc. (%)# of Param ↓
Soft Ordering [23]66.590.27
CMTR [18]87.19-
MoE [28]92.199.08
Gumbel-Matrix [22]93.529.08
Single Task93.4820.00
Shared Bottom93.251.00
Ours (M=3)94.990.91
Ours (M=5)95.711.37
Ours (M=7)95.681.46
", + "bbox": [ + 84, + 88, + 460, + 267 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/65edecee36b206bacf039ce5e69afa9cbb05a017ed4765b2720a7bf56698011e.jpg", + "table_caption": [ + "Table 1. Evaluation on Omniglot datasets." + ], + "table_footnote": [], + "table_body": "
MethodΔsem↑Δnorm↑Δdep↑Δ↑# of Param ↓
Single-Task0.00.00.00.03.00
Shared Bottom-7.6+7.5+5.2+1.71.00
Cross-Stitch [25]-4.9+4.2+4.7+1.33.00
Sluice [32]-8.4+2.9+4.1-0.53.00
NDDR-CNN [11]-15.0+2.9-3.5-5.23.15
MTAN [20]-4.2+8.7+3.8+2.73.11
DEN [1]-9.9+1.7-35.2-14.51.12
AdaShare [38]+8.8+7.9+10.1+8.91.00
Ours (M=5)+11.9+7.9+8.8+9.51.04
Ours (M=7)+13.4+9.2+10.7+11.11.31
Ours (M=9)+13.2+9.0+10.9+11.01.63
", + "bbox": [ + 81, + 305, + 465, + 450 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We set five tasks $\\mathcal{T}_{sem}$ , $\\mathcal{T}_{part}$ , $\\mathcal{T}_{norm}$ , $\\mathcal{T}_{sal}$ , and $\\mathcal{T}_{edge}$ as used in [29] for PASCAL-Context datasets.", + "bbox": [ + 76, + 488, + 468, + 517 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Evaluation metrics We follow the common evaluation metrics utilized in the competitive methods. We use an accuracy metric for the classification task. The semantic segmentation task is measured by mean Intersection over Union (mIoU) and pixel accuracy. We use the mean absolute and mean relative errors, and relative difference as the percentage of $\\delta = \\max (\\hat{\\mathbf{d}} /\\mathbf{d},\\mathbf{d} / \\hat{\\mathbf{d}})$ within thresholds $1.25^{\\{1,2,3\\}}$ for the depth estimation task. For the evaluation of the PASCAL-Context datasets, we follow the same metrics used in [29] for all tasks. As reported in [38], we report a single relative performance $\\Delta_{\\mathcal{T}_i}$ in Tab. 1-4 for each task $\\mathcal{T}_i$ with respect to the single-task baseline, which defined as:", + "bbox": [ + 76, + 518, + 468, + 700 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\Delta_ {\\mathcal {T} _ {i}} = \\frac {1 0 0}{| \\mathcal {M} |} \\sum_ {j = 0} ^ {| \\mathcal {M} |} (- 1) ^ {l _ {j}} \\frac {\\left(\\mathcal {M} _ {\\mathcal {T} _ {i} , j} - \\mathcal {M} _ {\\mathcal {T} _ {i} , j} ^ {\\text {s i n g l e}}\\right)}{\\mathcal {M} _ {\\mathcal {T} _ {i} , j} ^ {\\text {s i n g l e}}}, \\tag {10}\n$$\n", + "text_format": "latex", + "bbox": [ + 109, + 705, + 468, + 750 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $\\mathcal{M}_{\\mathcal{T}_i,j}$ and $\\mathcal{M}_{\\mathcal{T}_i,j}^{single}$ are the $j$ -th metric of $i$ -th task $\\mathcal{T}_i$ from each method and the single task baseline, respectively. The constant $l_j$ is 1 if a lower value represents better for the metric $\\mathcal{M}_{\\mathcal{T}_i,j}$ and 0 otherwise. The averaged relative performance for all tasks $\\mathcal{T}$ is defined as:", + "bbox": [ + 76, + 758, + 468, + 835 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\Delta_ {\\mathcal {T}} = \\frac {1}{| \\mathcal {T} |} \\sum_ {i = 1} ^ {| \\mathcal {T} |} \\Delta_ {\\mathcal {T} _ {i}}. \\tag {11}\n$$\n", + "text_format": "latex", + "bbox": [ + 202, + 854, + 468, + 897 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/afabb8b55366ef66d4c16b772be3715c89783ac951c502d40119370f3c5bcd7e.jpg", + "table_caption": [ + "Table 2. Evaluation on NYU-v2 datasets." + ], + "table_footnote": [], + "table_body": "
MethodΔTsem↑ΔTdep↑ΔT↑# of Param ↓
Single-Task0.00.00.02.00
Shared Bottom-3.7-0.5-2.11.00
Cross-Stitch [25]-0.1+5.8+2.82.00
Sluice [32]-0.8+4.0+1.62.00
NDDR-CNN [11]+1.3+3.3+2.32.07
MTAN [20]+0.5+4.8+2.72.41
DEN [1]-3.1-1.6-2.41.12
AdaShare [38]+1.8+3.8+2.81.00
Ours (M=5)+3.5+3.9+3.70.96
Ours (M=7)+7.5+3.1+5.31.16
Ours (M=9)+8.3+4.8+6.61.31
", + "bbox": [ + 501, + 88, + 890, + 263 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/ee9d07809961af3321c5ba1681436f17fb810c74891503437fc637d608fdf9b8.jpg", + "table_caption": [ + "Table 3. Evaluation on Cityscapes datasets." + ], + "table_footnote": [], + "table_body": "
MethodΔTsem↑ΔTpart↑ΔTmal↑ΔTnorm↓ΔTedge↑ΔT↑# of Param ↓
Single-Task0.00.00.00.00.00.05.00
Shared Bottom-6.6-0.7-3.4-14.30.0-5.01.00
Cross-Stitch [25]-1.3+3.6-0.2-1.40.0+0.15.00
Sluice [32]-1.6-1.2-0.5-2.9-6.0-2.45.00
NDDR-CNN [11]-1.1-2.60.0-5.00.0-1.75.61
MTAN [20]-3.6-0.7-0.3-5.0-6.0-3.15.21
AdaShare [38]-1.4+4.0-0.5-0.70.0+0.31.00
LTB [12]-6.9-1.9+0.2-1.40.0-2.03.19
PHN [29]-6.6-1.6-1.00.00.0-1.82.51
Ours (M=5)-0.3+3.4+0.90.00.0+0.81.93
Ours (M=7)0.0-0.2+1.7+1.40.0+0.61.91
Ours (M=9)0.0+3.6+1.8+1.40.0+1.42.31
", + "bbox": [ + 501, + 301, + 888, + 425 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 4. Evaluation on PASCAL-Context datasets.", + "bbox": [ + 539, + 435, + 849, + 448 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "The absolute task performance for all metrics is reported in the supplementary material.", + "bbox": [ + 496, + 460, + 890, + 491 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Network and training details For our central network, we set 8 hidden states, the same as the existing MoE-based works [22, 28] and use the same classification head for Omniglot datasets. We set 12 hidden states, the same as the VGG-16 [35], except for the max-pooled state, and use the Deeplab-v2 [5] decoder structure as all task heads for all the other datasets, respectively. We use the Adam [16] optimizer to update both upper-level parameters and network parameters. We use cross-entropy loss for semantic segmentation and L2 loss for the other tasks. For a fair comparison, we train our central network from scratch without pre-training for all experiments. We describe more details on the network structure and hyperparameter settings in the supplementary material.", + "bbox": [ + 496, + 491, + 892, + 703 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.2. Comparison to State-of-the-art Methods", + "text_level": 1, + "bbox": [ + 500, + 710, + 844, + 727 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We report the performance of the proposed method with different flow constants $M$ and compare it with state-ofthe-art methods in Tab. 1-4 with four different MTL scenarios. Tab. 1 shows that our framework with any flow constant $M$ outperforms all the competitive methods for the homogeneous MTL scenario with Omniglot datasets. Ours has a similar number of parameters to the shared-bottom baseline. All the other experiments for heterogeneous MTL scenarios in Tab. 2-4 show that our frameworks achieve the best performance among all state-ofthe-art works. Even with the flow constant $M = 5$ , our", + "bbox": [ + 496, + 734, + 890, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "3784", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/b9685fc639f8cf3ef3d889b2c17580fad8d4d6bf2fd04b5b1b7f9cb8e4242d44.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 81, + 89, + 243, + 166 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/47c4569c23e0b786adbd892f548d4f896abd54ff24f7b3f69c338fe9853a76c8.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 80, + 167, + 245, + 239 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/db07d5fcda95a6f169df26e4072f6548b53451779bc202cb3145862b24a625a9.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 80, + 241, + 245, + 316 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/210b57c0800e83ece8e609cc462da0656d882da0fb11737a55c07efdb041758a.jpg", + "image_caption": [ + "Figure 3. Graph Representation of Task-adaptive Sub-network The finalized sub-network topologies ( $M = 7$ ) trained with NYUv2 datasets is illustrated as graph. (a-c) The task-adaptive subnetwork of semantic segmentation, depth estimation, and surface normal, respectively. (d) The adjacency matrix where color represents the discretized value for the activated edge of each task." + ], + "image_footnote": [], + "bbox": [ + 245, + 90, + 446, + 313 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/810b8c438afb9117b8309cc1f814647c725de3b4711a5d2b4438e182a3a64478.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
TaskDWS
Semantic Seg.530.103
Depth730.192
Surface normal720.128
", + "bbox": [ + 148, + 424, + 398, + 501 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 5. Topologies analysis on NYU-v2 datasets.", + "bbox": [ + 120, + 511, + 423, + 526 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "model outperforms AdaShare [38] for both the NYU-v2 and Cityscapes datasets, while keeping almost the same number of parameters (NYU-v2: 1.00 vs. 1.04 and Cityscapes 1.00 vs. 0.96). With the flow constant $M = 7,9$ , our method outperforms all the baselines by a large margin. The results from the PASCAL-Context datasets in Tab. 4 show that all baselines suffer from negative transfer in several tasks, as the number of tasks increases. Only Adashare and Cross Stitch slightly outperform the single-task baseline (see the performance $\\Delta_{\\mathcal{T}}$ ). On the other hand, ours with $M = 9$ achieves the best performance without any negative transfers for all tasks.", + "bbox": [ + 75, + 537, + 468, + 718 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Interestingly, the required parameters of the search space increase almost in proportion to the increase of the flow constant, but there is no significant difference in the number of parameters of the finalized networks. For example, the required number of parameters for the network with the flow constant $M = 3,5,7$ is 2.77, 4.23, and 5.38, respectively. This demonstrates that the proposed flow-based reduction algorithm is effective in removing low-relative parameters while maintaining performance. Specifically, we observe that the total performance of our framework with $M = 7$ is slightly better than the $M = 9$ setup in Tab. 2 despite its smaller architecture search space. To investigate this,", + "bbox": [ + 75, + 719, + 470, + 901 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "we further analyze the tendency in performance and computational complexity with respect to the flow constant in Sec. 4.4.", + "bbox": [ + 498, + 90, + 890, + 135 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.3. Analysis of Topologies and Task Correlation", + "text_level": 1, + "bbox": [ + 498, + 146, + 872, + 162 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "To demonstrate the effectiveness of the proposed learning mechanism, we visualize our finalized sub-network topologies in Fig. 3-(a-c) and the adjacency matrix for NYU-v2 3-task learning in Fig. 3-(d). We also analyze the diversity and capacity of task-adaptive network topologies in Tab. 5 with network depth $\\mathcal{D}$ , width $\\mathcal{W}$ , and sparsity $\\mathcal{S}$ described in Sec. 3.1. These analyses provide three key observations on our task-adaptive network and the correlation among tasks.", + "bbox": [ + 496, + 170, + 890, + 306 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "First, the tasks of segmentation and surface normal hardly share network parameters. Various task-sharing patterns are configured at the edge, but there is only one sharing layer between the two tasks. This experiment shows a low relationship between tasks, as it is widely known that the proportion of shared parameters between tasks indicates task correlation [22, 29, 38].", + "bbox": [ + 496, + 306, + 890, + 412 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Second, long skip connections are mostly lost. The length of the longest skip connection in the finalized network is 5, and the number of these connections is 2 out of 18 layers, even with the flow constant of 7. This phenomenon is observed not only in NYU-v2 datasets but also in the other MTL datasets. This can be evidence that the proposed flow-restriction reduces search time while maintaining high performance even by eliminating the long skip connection in the DAG-based central network.", + "bbox": [ + 496, + 412, + 890, + 547 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Lastly, Depth estimation task requires more network resources than segmentation and surface normal estimation tasks. We analyze the network topologies of the finalized sub-network of each task in NYU-v2 datasets using three components defined in Sec. 3. The depth $\\mathcal{D}$ and width $\\mathcal{W}$ of the sub-network increase in the order of semantic segmentation, surface normal prediction, and depth estimation tasks. Likewise, the sparsity $\\mathcal{S}$ of the depth network is the highest. This experiment shows that the depth network is the task that requires the most network resources.", + "bbox": [ + 496, + 549, + 890, + 700 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.4. Performance w.r.t. Flow-restriction", + "text_level": 1, + "bbox": [ + 500, + 710, + 815, + 724 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We analyze performance and computational complexity with respect to the flow constant $M$ for the NYU-v2 and Cityscapes datasets. We report the rate of performance degradation with respect to the complete DAG search space in Fig. 4. We observe that the reduction rate of the final performance does not exceed $3\\%$ even with considerably lower flow constants. The performance is saturated at a flow constant of about 7 or more. This means that the proposed method optimizes the task adaptive sub-network regardless of the size of the network search space, if it satisfies the minimum required size.", + "bbox": [ + 496, + 734, + 890, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "3785", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/f99b551058ea1a5578eff9d3380fbed19b51679d90f7b930038f2cedc89aaeff.jpg", + "image_caption": [ + "Figure 4. Model performance with respect to the proposed flow-restriction. We plot the degradation ratio of the performance (left y-axis) and parameter (right y-axis) by changing the flow constant $M$ . We measure the final averaged task performance with NYU-v2 and Cityscapes datasets marked by purple and pink circle markers, respectively. We also measure the number of parameters marked by gray square markers." + ], + "image_footnote": [], + "bbox": [ + 89, + 111, + 460, + 287 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "To demonstrate the effectiveness of our flow-based reduction (FBR) algorithm, we compare it to two other reduction algorithms (random and threshold) for Cityscapes datasets in Fig. 5. The random reduction literally removes the edges randomly, and the thresholding method sequentially removes the edge which has the lowest value in the adjacency matrix $\\Gamma$ . We measure the rate of performance degradation of the pruned network of each reduction algorithm with respect to the non-reduced network while changing the sparsity $S$ . Note that our method automatically determines the sparsity, so for this experiment only, we add a termination condition that stops the network search when a certain sparsity is met. The results show that the proposed flow-reduction method retains performance even with a low sparsity rate. This means that our method efficiently prunes the low-related edge of the network compared to the other methods.", + "bbox": [ + 75, + 409, + 470, + 667 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.5. Ablation Study on Proposed Modules", + "text_level": 1, + "bbox": [ + 76, + 679, + 400, + 696 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We conduct ablation studies on the four key components of our framework; the flow-restriction, read-in/out layers, flow-based reduction, and squeeze loss. We report the relative task performance and the number of parameters of the finalized network with/without the components in Tab. 6. The results show that our framework, including all components, achieves the lowest number of parameters and the second-best performance. Our method without flow-based reduction achieves the best performance. However, the finalized network from this setup has about a five-times larger number of parameters than ours because the network has never been pruned in a training process. This demonstrates that our restricted DAG-based central network is optimized", + "bbox": [ + 75, + 704, + 470, + 902 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/b5d16cf1a474ad815b6d8330a98a0086d8abf203cd0b4aa0d44f4069098427e6.jpg", + "image_caption": [ + "Figure 5. Model Performance with respect to the network sparsity. We plot the performance degradation rate by changing network sparsity. We compare our flow-based reduction algorithm to two other schemes; random selection and thresholding." + ], + "image_footnote": [], + "bbox": [ + 517, + 108, + 846, + 280 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/20a1ac497d403b80340cd9bc418ad2f62606116570126c7c923ce431773d48fd.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodΔTsem↑ΔTdep↑ΔTnorm↑ΔT# of Param ↓
Ours (M=7)+13.4+9.2+10.7+11.11.31
w/o flow-restriction+13.2+9.2+10.4+11.01.80
w/o read-in/out+11.7+8.3+10.4+10.11.43
w/o flow-based reduction+14.2+9.2+11.1+11.56.50
w/o Lsq+13.2+8.8+10.7+10.91.38
", + "bbox": [ + 501, + 364, + 888, + 441 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 6. Ablation study on the proposed modules (NYU-v2).", + "bbox": [ + 504, + 450, + 883, + 465 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "to build compact task-adaptive sub-networks with performance close to the optimized sub-network from a complete DAG-based network.", + "bbox": [ + 498, + 476, + 890, + 521 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusions", + "text_level": 1, + "bbox": [ + 500, + 534, + 627, + 550 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this paper, we present a new MTL framework to search for task-adaptive network structures across diverse network topologies in a single network. We propose flow restriction to solve the scalability issue in a complete DAG search space while maintaining the diverse network topological representation of the DAG search space by adopting read-in/out layers. We also introduce a flow-based reduction algorithm that prunes the network efficiently while maintaining overall task performance and squeeze loss, limiting the upper bound on the number of network parameters. The extensive experiments demonstrate that the submodule and schemes of our framework efficiently improve both the performance and compactness of the network. Our method compactly constructs various task-specific subnetworks in a single network and achieves the best performance among all the competitive methods on four MTL benchmark datasets.", + "bbox": [ + 496, + 559, + 890, + 816 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgement", + "text_level": 1, + "bbox": [ + 500, + 829, + 660, + 847 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. RS-2023-00210908).", + "bbox": [ + 498, + 854, + 890, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "3786", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Chanho Ahn, Eunwoo Kim, and Songhwai Oh. 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In Proceedings of the IEEE conference on computer vision and pattern recognition, pages 8697-8710, 2018. 1, 2" + ], + "bbox": [ + 78, + 90, + 470, + 882 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "3788", + "bbox": [ + 482, + 945, + 514, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/Dynamic Neural Network for Multi-Task Learning Searching Across Diverse Network Topologies/08f871aa-0255-4d39-aee9-94ac7465f9f8_model.json b/2023/Dynamic Neural Network for Multi-Task Learning Searching Across Diverse Network Topologies/08f871aa-0255-4d39-aee9-94ac7465f9f8_model.json new file mode 100644 index 0000000000000000000000000000000000000000..9c4528fd2842f00764e00a85f635fa5dd099efcb --- /dev/null +++ b/2023/Dynamic Neural Network for Multi-Task Learning Searching Across Diverse Network Topologies/08f871aa-0255-4d39-aee9-94ac7465f9f8_model.json @@ -0,0 +1,2277 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.23, + 0.131, + 0.744, + 0.177 + ], + "angle": 0, + "content": "Dynamic Neural Network for Multi-Task Learning Searching across Diverse Network Topologies" + }, + { + "type": "text", + "bbox": [ + 0.16, + 0.204, + 0.812, + 0.257 + ], + "angle": 0, + "content": "Wonhyeok Choi, Sunghoon Im* \nDepartment of Electrical Engineering & Computer Science, DGIST, Daegu, Korea \n{smu06117, sunghoonim}@dgist.ac.kr" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.292, + 0.314, + 0.308 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.317, + 0.473, + 0.543 + ], + "angle": 0, + "content": "In this paper, we present a new MTL framework that searches for structures optimized for multiple tasks with diverse graph topologies and shares features among tasks. We design a restricted DAG-based central network with read-in/read-out layers to build topologically diverse task-adaptive structures while limiting search space and time. We search for a single optimized network that serves as multiple task adaptive sub-networks using our three-stage training process. To make the network compact and discretized, we propose a flow-based reduction algorithm and a squeeze loss used in the training process. We evaluate our optimized network on various public MTL datasets and show ours achieves state-of-the-art performance. An extensive ablation study experimentally validates the effectiveness of the sub-module and schemes in our framework." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.552, + 0.21, + 0.568 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.578, + 0.47, + 0.759 + ], + "angle": 0, + "content": "Multi-task learning (MTL), which learns multiple tasks simultaneously with a single model has gained increasing attention [3, 13, 14]. MTL improves the generalization performance of tasks while limiting the total number of network parameters to a lower level by sharing representations across tasks. However, as the number of tasks increases, it becomes more difficult for the model to learn the shared representations, and improper sharing between less related tasks causes negative transfers that sacrifice the performance of multiple tasks [15,36]. To mitigate the negative transfer in MTL, some works [6, 25, 32] separate the shared and task-specific parameters on the network." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.759, + 0.471, + 0.88 + ], + "angle": 0, + "content": "More recent works [21, 29, 38] have been proposed to dynamically control the ratio of shared parameters across tasks using a Dynamic Neural Network (DNN) to construct a task adaptive network. These works mainly apply the cell-based architecture search [19, 27, 41] for fast search times, so that the optimized sub-networks of each task consist of fixed or simple structures whose layers are simply branched, as shown in Fig. 1a. They primarily focus on finding branching" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.293, + 0.892, + 0.369 + ], + "angle": 0, + "content": "patterns in specific aspects of the architecture, and feature-sharing ratios across tasks. However, exploring optimized structures in restricted network topologies has the potential to cause performance degradation in heterogeneous MTL scenarios due to unbalanced task complexity." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.37, + 0.893, + 0.506 + ], + "angle": 0, + "content": "We present a new MTL framework searching for subnetwork structures, optimized for each task across diverse network topologies in a single network. To search the graph topologies from richer search space, we apply Directed Acyclic Graph (DAG) for the homo/heterogeneous MTL frameworks, inspired by the work in NAS [19, 27, 40]. The MTL in the DAG search space causes a scalability issue, where the number of parameters and search time increase quadratically as the number of hidden states increases." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.507, + 0.895, + 0.703 + ], + "angle": 0, + "content": "To solve this problem, we design a restricted DAG-based central network with read-in/read-out layers that allow our MTL framework to search across diverse graph topologies while limiting the search space and search time. Our flow-restriction eliminates the low-importance long skip connection among network structures for each task, and creates the required number of parameters from \\( O(N^2) \\) to \\( O(N) \\). The read-in layer is the layer that directly connects all the hidden states from the input state, and the read-out layer is the layer that connects all the hidden states to the last feature layer. These are key to having various network topological representations, such as polytree structures, with early-exiting and multi-embedding." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.705, + 0.895, + 0.901 + ], + "angle": 0, + "content": "Then, we optimize the central network to have compact task-adaptive sub-networks using a three-stage training procedure. To accomplish this, we propose a squeeze loss and a flow-based reduction algorithm. The squeeze loss limits the upper bound on the number of parameters. The reduction algorithm prunes the network based on the weighted adjacency matrix measured by the amount of information flow in each layer. In the end, our MTL framework constructs a compact single network that serves as multiple task-specific networks with unique structures, such as chain, polytree, and parallel diverse topologies, as presented in Fig. 1b. It also dynamically controls the amount of sharing representation among tasks." + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.888, + 0.221, + 0.9 + ], + "angle": 0, + "content": "*Corresponding author" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.946, + 0.516, + 0.957 + ], + "angle": 0, + "content": "3779" + } + ], + [ + { + "type": "image_caption", + "bbox": [ + 0.117, + 0.099, + 0.227, + 0.111 + ], + "angle": 0, + "content": "(i). Mixture-of-Experts" + }, + { + "type": "image", + "bbox": [ + 0.118, + 0.113, + 0.344, + 0.194 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.36, + 0.099, + 0.409, + 0.11 + ], + "angle": 0, + "content": "(iii).Ours" + }, + { + "type": "image", + "bbox": [ + 0.365, + 0.113, + 0.588, + 0.194 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.117, + 0.203, + 0.207, + 0.215 + ], + "angle": 0, + "content": "(ii).Skip-or-Select" + }, + { + "type": "image", + "bbox": [ + 0.118, + 0.215, + 0.344, + 0.289 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.389, + 0.214, + 0.493, + 0.228 + ], + "angle": 0, + "content": "\\(\\bigcirc\\) : hidden states" + }, + { + "type": "image_footnote", + "bbox": [ + 0.379, + 0.234, + 0.533, + 0.246 + ], + "angle": 0, + "content": "- - \\(\\rightarrow\\) : inactivated operation" + }, + { + "type": "image_footnote", + "bbox": [ + 0.379, + 0.252, + 0.523, + 0.263 + ], + "angle": 0, + "content": ":activated operation" + }, + { + "type": "image_footnote", + "bbox": [ + 0.379, + 0.27, + 0.498, + 0.281 + ], + "angle": 0, + "content": "non-operation" + }, + { + "type": "list", + "bbox": [ + 0.379, + 0.214, + 0.533, + 0.281 + ], + "angle": 0, + "content": null + }, + { + "type": "image_footnote", + "bbox": [ + 0.118, + 0.306, + 0.587, + 0.32 + ], + "angle": 0, + "content": "(a) Graph representation of existing DNN-based methods (i)-(ii). for MTL and ours (iii)." + }, + { + "type": "image_caption", + "bbox": [ + 0.606, + 0.093, + 0.776, + 0.105 + ], + "angle": 0, + "content": "(i). Complete Directed Acyclic Graph" + }, + { + "type": "image", + "bbox": [ + 0.636, + 0.111, + 0.832, + 0.16 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.607, + 0.17, + 0.719, + 0.182 + ], + "angle": 0, + "content": "(ii). Subgraph topologies" + }, + { + "type": "image", + "bbox": [ + 0.619, + 0.2, + 0.726, + 0.217 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.746, + 0.184, + 0.853, + 0.235 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.624, + 0.239, + 0.721, + 0.298 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.746, + 0.24, + 0.852, + 0.3 + ], + "angle": 0, + "content": null + }, + { + "type": "image_footnote", + "bbox": [ + 0.601, + 0.306, + 0.859, + 0.32 + ], + "angle": 0, + "content": "(b) Topologies of DAG (i). and its sub-graph (ii)." + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.331, + 0.892, + 0.36 + ], + "angle": 0, + "content": "Figure 1. Graph representation of various neural networks. (a) Graph representation of existing dynamic neural network for multitask learning and ours. (b) Topologies of a completed Directed Acyclic Graph (DAG) and the output sub-graph of DAG structure." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.374, + 0.47, + 0.464 + ], + "angle": 0, + "content": "The experiments demonstrate that our framework successfully searches the task-adaptive network topologies of each task and leverages the knowledge among tasks to make a generalized feature. The proposed method outperforms state-of-the-art methods on all common benchmark datasets for MTL. Our contributions can be summarized as follows:" + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.474, + 0.469, + 0.534 + ], + "angle": 0, + "content": "- We present for the first time an MTL framework that searches both task-adaptive structures and sharing patterns among tasks. It achieves state-of-the-art performance on all public MTL datasets." + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.54, + 0.469, + 0.6 + ], + "angle": 0, + "content": "- We propose a new DAG-based central network composed of a flow restriction scheme and read-in/out layers, that has diverse graph topologies in a reasonably restricted search space." + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.606, + 0.468, + 0.651 + ], + "angle": 0, + "content": "- We introduce a new training procedure that optimizes the MTL framework for compactly constructing various task-specific sub-networks in a single network." + }, + { + "type": "list", + "bbox": [ + 0.096, + 0.474, + 0.469, + 0.651 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.665, + 0.227, + 0.68 + ], + "angle": 0, + "content": "2. Related Works" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.689, + 0.47, + 0.901 + ], + "angle": 0, + "content": "Neural Architecture Search (NAS) Neural Architecture Search is a method that automates neural architecture engineering [8]. Early works [2, 40, 41] use reinforcement learning based on rewarding the model accuracy of the generated architecture. Alternative approaches [24, 30, 37] employ evolutionary algorithms to optimize both the neural architecture and its weights. These methods search for an adequate neural architecture in a large discrete space. Gradient-based NAS methods [4, 19, 39] of formulating operations in a differentiable search space are proposed to alleviate the scalability issues. They generally use the convex combination from a set of operations instead of determining a single operation. Most NAS approaches [19, 27, 40] adopt the complete DAG as a search space, to find the architecture" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.374, + 0.892, + 0.418 + ], + "angle": 0, + "content": "in the various network topologies. However, DAG-based MTL frameworks have not been proposed, because of their considerably high computational demands." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.42, + 0.893, + 0.569 + ], + "angle": 0, + "content": "Multi-Task Learning (MTL) Multi-task learning in deep neural networks can be categorized into hard and soft parameter sharing types [31]. Hard parameter sharing [3, 13, 14], also known as shared-bottom, is the most commonly used approach to MTL. This scheme improves generalization performance while reducing the computational cost of the network, by using shared hidden layers between all tasks. However, it typically struggles with the negative transfer problem [15, 36] which degrades performance due to improper sharing between less relevant tasks." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.569, + 0.892, + 0.689 + ], + "angle": 0, + "content": "On the other hand, soft-parameter sharing [25, 32] alleviate the negative transfer problem by changing the shared parameter ratio. These approaches mitigate the negative transfer by flexibly modifying shared information, but they cannot maintain the computational advantage on the classic shared-bottom model. Recently, advanced approaches have been proposed to adjust shared parameters using a dynamic neural network [21, 22, 29, 38] and NAS [10]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.689, + 0.893, + 0.901 + ], + "angle": 0, + "content": "NAS-style MTL MTL frameworks using a dynamic neural network (DNN) can be divided into two categories. One employs the Mixture-of-Experts (MoE) [33], which is designed for conditional computation of per-sample, to MTL by determining the experts of each task [9, 21, 22]. They have a fixed depth finalized task-specific sub-network, because they choose experts from a fixed number of modular layers. This causes a critical issue with task-balancing in the heterogeneous MTL. The other adopts the skip-or-select policy to select task-specific blocks from the set of residual blocks [38] or a shared block per layer [12, 29]. These methods only create a simple serial path in the finalized subnetwork of each task, and a parallel link cannot be reproduced. Moreover, they heuristically address the unbalanced" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "3780" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.166 + ], + "angle": 0, + "content": "task-wise complexity issues in the heterogenous MTL (e.g. manually changing the balancing parameters based on the task complexity [29,38]). Thus, none of the aforementioned works focus on finding the optimal task-specific structure in the MTL scenario." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.18, + 0.168, + 0.195 + ], + "angle": 0, + "content": "3. Method" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.205, + 0.471, + 0.371 + ], + "angle": 0, + "content": "We describe our MTL framework, which searches for optimized network structures tailored to each task across diverse graph topologies, while limiting search time. Sec. 3.1 describes the composition of the searchable space of our central network and our flow-restriction method for efficiently balancing the topological diversity of task-specific sub-networks and searching space. Sec. 3.2 introduces our mechanism to determine the task-adaptive sub-network in the central network and describes the overall training process and loss function. The overall pipeline of our method is illustrated in Fig. 2." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.379, + 0.466, + 0.396 + ], + "angle": 0, + "content": "3.1. The Central Network with Diverse Topologies" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.403, + 0.47, + 0.448 + ], + "angle": 0, + "content": "Our central network composes a graph \\( G = (V, E) \\) with layers \\( E \\) in which the \\( N \\) hidden states \\( V = \\{v_1, \\dots, v_N\\} \\) are topologically sorted:" + }, + { + "type": "equation", + "bbox": [ + 0.151, + 0.458, + 0.469, + 0.475 + ], + "angle": 0, + "content": "\\[\nE = \\left\\{e _ {i j} \\right\\} _ {i, j \\in \\{1, \\dots , N \\}}, \\text {w h e r e} i < j, \\tag {1}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.178, + 0.477, + 0.469, + 0.496 + ], + "angle": 0, + "content": "\\[\ne _ {i j} (\\cdot ; \\theta_ {i j}): \\mathbb {R} ^ {N ^ {v _ {i}}} \\rightarrow \\mathbb {R} ^ {N ^ {v _ {j}}}, \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.505, + 0.469, + 0.625 + ], + "angle": 0, + "content": "where \\( e_{ij} \\) is the operation that transfers the state \\( v_{i} \\) to \\( v_{j} \\) with the weight parameters \\( \\theta_{ij} \\in \\Theta \\), and \\( N^{v_k} \\) is the number of the elements of hidden state \\( v_{k} \\), respectively. We adopt the DAG structure [19, 27, 40] for the network. However, the optimized structure from DAG is searched from \\( 2^{N(N - 1) / 2} \\) network topologies, which are too large to be optimized in time. To address the issue while maintaining diversity, we propose a flow-restriction and read-in/read-out layers." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.626, + 0.469, + 0.731 + ], + "angle": 0, + "content": "Flow-restriction The flow-restriction eliminates the low-importance long skip connection among network structures for each task by restricting \\( j - i \\leq M \\) where \\( M \\) is the flow constant. Regulating the searchable edges in the graph reduces the required number of parameters and searching time from \\( O(N^2) \\) to \\( O(N) \\), but it sacrifices the diversity and capacity of the network topologies." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.732, + 0.47, + 0.776 + ], + "angle": 0, + "content": "To explain the topological diversity and task capacity of sub-networks, we define the three components of network topology, as follows:" + }, + { + "type": "text", + "bbox": [ + 0.09, + 0.784, + 0.393, + 0.802 + ], + "angle": 0, + "content": "1. \\(\\mathcal{D}(G) = \\max (\\{\\mathrm{Distance}(v_i,v_j)\\}_{v_i,v_j\\in V}),\\)" + }, + { + "type": "text", + "bbox": [ + 0.089, + 0.808, + 0.312, + 0.825 + ], + "angle": 0, + "content": "2. \\(\\mathcal{W}(G) = \\max (\\{\\mathrm{Out}_{v_i}\\}_{v_i\\in V}),\\)" + }, + { + "type": "text", + "bbox": [ + 0.089, + 0.832, + 0.263, + 0.849 + ], + "angle": 0, + "content": "3. \\(S(G_{s},G) = |E_{s}| / |E|\\)" + }, + { + "type": "list", + "bbox": [ + 0.089, + 0.784, + 0.393, + 0.849 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.47, + 0.901 + ], + "angle": 0, + "content": "where \\(\\mathrm{Out}_{v_i}\\) is the out-degree of the vertex \\(v_i\\) and \\(\\mathrm{Distance}(\\cdot)\\) is the operation that counts the number of layers (or edges) between two connected vertices. The network" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.258 + ], + "angle": 0, + "content": "depth \\(\\mathcal{D}(G)\\) is equal to the longest distance between two vertices in the graph \\(G\\). The network width \\(\\mathcal{W}(G)\\) is equal to the maximum value of the out-degrees of hidden states in the graph \\(G\\). The sparsity \\(\\mathcal{S}(G_s, G)\\) of the sub-graph \\(G_s\\) is the ratio of finalized edges \\(|E_s|\\) over entire edges \\(|E|\\). The first two components are measurements of the topological diversity of the finalized sub-network, while the last one is for the sub-network capacity. While a complete DAG has the full range of depth and width components, the flow-restricted DAG has the properties of depth and width components as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.499, + 0.268, + 0.826, + 0.285 + ], + "angle": 0, + "content": "\\[\n\\text {P r o p e r t y 1 .} \\min (\\{\\mathcal {D} (G _ {s}) \\} _ {G _ {s} \\subseteq G}) = \\lceil (| V | / M) \\rceil ,\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.5, + 0.293, + 0.776, + 0.31 + ], + "angle": 0, + "content": "\\[\n\\text {P r o p e r t y 2 .} \\max (\\{\\mathcal {W} (G _ {s}) \\} _ {G _ {s} \\subseteq G}) = M,\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.319, + 0.892, + 0.395 + ], + "angle": 0, + "content": "where \\(\\{G_s\\}\\) is the entire sub-graph of \\(G\\). The min-depth property (Prop. 1) can cause the over-parameterized problem when the capacity of the task is extremely low. The max-width property (Prop. 2) directly sacrifices the diversity of network topologies in the search space." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.395, + 0.892, + 0.472 + ], + "angle": 0, + "content": "Read-in/Read-out layers We design read-in/read-out layers to mitigate these problems. The read-in layer embeds the input state \\( v_{0} \\) into all hidden states \\( v_{i} \\in V \\) with task-specific weights \\( \\alpha_{i}^{k} \\in \\mathcal{A} \\) for all \\( K \\) tasks \\( \\mathcal{T} = \\{T_k\\}_{k \\in \\{1, \\dots, K\\}} \\) as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.638, + 0.483, + 0.891, + 0.502 + ], + "angle": 0, + "content": "\\[\nv _ {i} ^ {k} = \\sigma \\left(\\alpha_ {i} ^ {k}\\right) \\cdot v _ {0}, \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.508, + 0.892, + 0.557 + ], + "angle": 0, + "content": "where \\(\\sigma (\\cdot)\\) is the sigmoid function. Then, the central network sequentially updates the hidden state \\(v_{1}^{k}\\) to \\(v_{N}^{k}\\) with the task-specific weights \\(\\gamma_{ij}^{k}\\in \\Gamma\\) that correspond to \\(e_{ij}^{k}\\):" + }, + { + "type": "equation", + "bbox": [ + 0.565, + 0.567, + 0.891, + 0.605 + ], + "angle": 0, + "content": "\\[\nv _ {j} ^ {k} = \\frac {1}{\\operatorname {I n} _ {v _ {j} ^ {k}}} \\sum_ {e _ {i j} \\in E} \\left(\\sigma \\left(\\gamma_ {i j} ^ {k}\\right) \\cdot e _ {i j} \\left(v _ {i} ^ {k}; \\theta_ {i j}\\right)\\right), \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.618, + 0.892, + 0.698 + ], + "angle": 0, + "content": "where \\(\\operatorname{In}_{v_j^k}\\) is the in-degree of \\(v_{j}^{k}\\). Note that \\(\\Gamma\\) is the adjacency matrix of graph \\(G\\). Finally, the read-out layer aggregates all hidden state features \\(\\{v_{i}^{k}\\}_{i\\in \\{1,\\dots,N\\}}\\) with the task-specific weights \\(\\beta_i^k\\in \\mathcal{B}\\) and produces the last layer feature \\(v_{L}^{k}\\) for each task \\(k\\) as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.598, + 0.709, + 0.891, + 0.743 + ], + "angle": 0, + "content": "\\[\nv _ {L} ^ {k} = \\sum_ {i \\in \\{1, \\dots , N \\}} \\left(\\sigma \\left(\\beta_ {i} ^ {k}\\right) \\cdot v _ {i} ^ {k}\\right). \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.755, + 0.891, + 0.8 + ], + "angle": 0, + "content": "The final prediction \\(\\hat{\\mathbf{y}}_k\\) for each task \\(T_{k}\\) is computed by passing the aggregated features \\(v_{L}^{k}\\) through the task-specific head \\(H^{k}(\\cdot)\\) as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.643, + 0.81, + 0.891, + 0.83 + ], + "angle": 0, + "content": "\\[\n\\hat {\\mathbf {y}} ^ {k} = H ^ {k} \\left(v _ {L} ^ {k}\\right). \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.892, + 0.901 + ], + "angle": 0, + "content": "All upper-level parameters \\(\\mathcal{A},\\mathcal{B}\\), and \\(\\Gamma\\) are learnable parameters, and their learning process is described in Sec. 3.2. The read-in/read-out layers enable the optimized network to have a multi-input/output sub-network. The read-out layer" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.514, + 0.957 + ], + "angle": 0, + "content": "3781" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.1, + 0.092, + 0.885, + 0.381 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.394, + 0.893, + 0.466 + ], + "angle": 0, + "content": "Figure 2. Overall pipeline. Our central network follows a DAG-based structure with read-in/out layers, and task-specific heads. The long skip connection is cut by our flow-restriction. Our framework with a 3-task MTL learning scenario consists of three stages including warm-up, search, and fine-tuning stages. The warm-up stage only learns the parameters of the main network \\(\\Theta\\) and task-specific weights. The search stage learns the upper-level parameters \\(\\mathcal{A},\\mathcal{B},\\Gamma\\), and task-specific weights. Then, flow-based reduction eliminates the low-importance edges from the network. The fine-tuning stage re-trains the network with the remaining important parameters." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.487, + 0.47, + 0.563 + ], + "angle": 0, + "content": "aggregates all hidden states of the central network during the search stage, allowing a specific task to use the early hidden states to output predictions while ignoring the last few layers. These early-exit structures help alleviate the over-parameterized problem in simple tasks." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.57, + 0.469, + 0.587 + ], + "angle": 0, + "content": "3.2. Network Optimization and Training Procedure" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.593, + 0.469, + 0.639 + ], + "angle": 0, + "content": "We describe the entire training process for our MTL framework, which consists of three stages, including warm-up, search, and fine-tuning stages." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.64, + 0.469, + 0.819 + ], + "angle": 0, + "content": "Warm-up stage As with other gradient-based NAS, our framework has upper-level parameters that determine the network structure and parameters. This bilevel optimization with a complex objective function in an MTL setup makes the training process unstable. For better convergence, we initially train all network parameters across tasks for a few iterations. We train the weight parameters of the central network \\(\\Theta\\) that shares all operations \\(E\\) across tasks. We fix all values of the upper-level parameters \\(\\mathcal{A},\\mathcal{B}\\), and \\(\\Gamma\\) as 0, which becomes 0.5 after the sigmoid function \\(\\sigma (\\cdot)\\), and freeze them. We train the network parameters \\(\\Theta\\) in Eq. 4 with a task loss as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.175, + 0.824, + 0.469, + 0.865 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\text {t a s k}} = \\sum_ {k = 0} ^ {K} \\mathcal {L} _ {T _ {k}} \\left(\\hat {\\mathbf {y}} _ {T _ {k}}, \\mathbf {y} _ {T _ {k}}\\right), \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.469, + 0.9 + ], + "angle": 0, + "content": "where \\(\\mathcal{L}_{T_k}\\) is the task-specific loss, which is the unique loss function for each task." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.487, + 0.892, + 0.576 + ], + "angle": 0, + "content": "Search stage After the warm-up stage, we unfreeze the upper-level parameters \\(\\mathcal{A},\\mathcal{B}\\), and \\(\\Gamma\\) and search the network topologies appropriate to each task. We train all these parameters and network parameters \\(\\Theta\\) simultaneously by minimizing the task loss and the proposed squeeze loss \\(\\mathcal{L}_{sq}\\) as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.606, + 0.587, + 0.891, + 0.605 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\text {t r a i n}} = \\mathcal {L} _ {\\text {t a s k}} + \\lambda_ {s q} \\mathcal {L} _ {s q}, \\tag {8}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.555, + 0.608, + 0.891, + 0.651 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {s q} = \\sum_ {k = 0} ^ {K} \\left(\\max \\left(\\left(\\sum_ {\\gamma_ {i j} \\in \\Gamma} \\left(\\sigma \\left(\\gamma_ {i j}\\right)\\right) - \\kappa\\right), 0\\right)\\right), \\tag {9}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.66, + 0.892, + 0.734 + ], + "angle": 0, + "content": "where \\(\\lambda_{sq}\\) is the balancing hyperparameter, and \\(\\kappa\\) is a constant number called the budget, that directly reduces the sparsity of the central network. This auxiliary loss is designed to encourage the model to save computational resources." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.735, + 0.893, + 0.901 + ], + "angle": 0, + "content": "Fine-tuning stage. Lastly, we perform a fine-tuning stage to construct a compact and discretized network structure using the trained upper-level parameters \\(\\mathcal{A},\\mathcal{B}\\), and \\(\\Gamma\\). To do so, we design a flow-based reduction algorithm that allows the network to obtain high computational speed by omitting low-importance operations, as described in Alg. 1. It measures the amount of information flow of each layer \\(e_{ij}\\) in the central network by calculating the ratio of edge weight with respect to other related edges weight. Then, it sequentially removes the edge which has the lowest information flow. Alg. 1 stops when the edge selected to be deleted is" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "3782" + } + ], + [ + { + "type": "code_caption", + "bbox": [ + 0.088, + 0.096, + 0.333, + 0.11 + ], + "angle": 0, + "content": "Algorithm 1: Flow-based Reduction" + }, + { + "type": "algorithm", + "bbox": [ + 0.08, + 0.112, + 0.475, + 0.558 + ], + "angle": 0, + "content": "Input: \\(\\Gamma \\in \\mathbb{R}^{N\\times N}\\) \\(\\mathcal{A}\\in \\mathbb{R}^N\\) \\(\\mathcal{B}\\in \\mathbb{R}^N\\) Output: \\(\\hat{\\Gamma},\\hat{\\mathcal{A}},\\hat{\\mathcal{B}} / /\\) Discretized params. \n1 initialize zero matrix \\(\\Psi ,\\hat{\\Psi}\\in \\mathbb{R}^{(N + 2)\\times (N + 2)}\\) \n2 \\(N_{\\alpha} = \\mathrm{argmax}(\\mathcal{A})\\) \n3 \\(N_{\\beta} = \\max (N_{\\alpha} + 1,\\mathrm{argmax}(\\mathcal{B}))\\) \n4 \\(\\Gamma [:N_{\\alpha},:)]\\gets 0 / /\\) remove edges \\(< N_{\\alpha}\\) \n5 \\(\\Gamma [:,N_{\\beta}]:\\gets 0 / /\\) remove edges \\(>N_{\\beta}\\) \n6 \\(\\Psi [1:N,1:N]\\gets \\Gamma /\\) merge \\(\\Gamma ,A,B\\) into \\(\\Psi\\) \n7 \\(\\Psi [0,N_{\\alpha} + 1:N_{\\beta} + 1]\\gets A[N_{\\alpha}:N_{\\beta}]\\) \n8 \\(\\Psi [N_{\\alpha} + 1:N_{\\beta} + 1,N + 1]\\gets B[N_{\\alpha}:N_{\\beta}]\\) \n9 while True do \n10 initialize zero matrix \\(S\\in \\mathbb{R}^{(N + 2)\\times (N + 2)}\\) \nfor \\(i\\gets 0\\) to \\(\\{N + 1\\}\\) do \nfor \\(j\\gets 0\\) to \\(\\{N + 1\\}\\) do \n\\(S[i,j]\\gets\\) \\(\\psi_{ij}\\left(\\frac{1}{\\ln v_i}\\sum_{\\psi_{ki}\\in \\Psi}(\\psi_{ki}) / \\sum_{\\psi_{ik}\\in \\Psi}(\\psi_{ik})+\\right.\\) \\(\\left.\\frac{1}{\\mathrm{Out}_v_j}\\sum_{\\psi_{jk}\\in \\Psi}(\\psi_{jk}) / \\sum_{\\psi_{kj}\\in \\Psi}(\\psi_{kj})\\right)\\) \n\\(\\psi_{ij}\\gets 0\\) where \\(S[i,j]\\) is nonzero min value \nif graph built from \\(\\Psi\\) is reachable then \n\\(\\hat{\\Psi}\\gets \\Psi\\) \nelse \n\\(\\hat{\\Psi} [\\hat{\\Psi} >0]\\gets 1 / /\\) discretization \n\\(\\hat{\\Gamma}\\gets \\hat{\\Psi}[1:N,1:N] / /\\) split into \\(\\Gamma ,A,B\\) \n\\(\\hat{\\mathcal{A}}\\gets \\hat{\\Psi}[0,1:N]\\) \n\\(\\hat{\\mathcal{B}}\\gets \\hat{\\Psi}[1:N,N + 1]\\) \nreturn \\(\\hat{\\Gamma},\\hat{\\mathcal{A}},\\hat{\\mathcal{B}}\\)" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.576, + 0.47, + 0.697 + ], + "angle": 0, + "content": "the only edge that can reach the graph. We use the simple Depth-first search algorithm to check the reachability of \\(\\hat{\\Gamma}\\) between hidden state \\(v_{N_{\\alpha}}\\) to \\(v_{N_{\\beta}}\\). All the output \\(\\hat{A}, \\hat{B}, \\hat{\\Gamma}\\) in Alg. 1, which is the discretized binary adjacency matrix, represent the truncated task-adaptive sub-network. After the reduction, we fix the upper-level parameters and only re-train the network parameters \\(\\Theta\\), and we do not use the sigmoid function in Eq. 3-5" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.709, + 0.209, + 0.725 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.734, + 0.47, + 0.81 + ], + "angle": 0, + "content": "We first describe the experimental setup in Sec. 4.1. We compare our method to state-of-the-art MTL frameworks on various benchmark datasets for MTL in Sec. 4.2. We also conduct extensive experiments and ablation studies to validate our proposed method in Sec. 4.3-4.5." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.818, + 0.285, + 0.834 + ], + "angle": 0, + "content": "4.1. Experimental Settings" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.47, + 0.903 + ], + "angle": 0, + "content": "Dataset We use four public datasets for multi-task scenarios including Omniglot [17], NYU-v2 [34], Cityscapes [7], and PASCAL-Context [26]. We use these datasets, configured by previous MTL works [29, 38], not their original sources." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.092, + 0.892, + 0.152 + ], + "angle": 0, + "content": "- Omniglot Omniglot is a classification dataset consisting of 50 different alphabets, and each of them consists of a number of characters with 20 handwritten images per character." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.16, + 0.894, + 0.205 + ], + "angle": 0, + "content": "- NYU-v2 NYU-v2 comprises images of indoor scenes, fully labeled for joint semantic segmentation, depth estimation, and surface normal estimation." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.214, + 0.892, + 0.26 + ], + "angle": 0, + "content": "- Cityscapes Cityscapes dataset collected from urban driving scenes in European cities consists of two tasks: joint semantic segmentation and depth estimation." + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.267, + 0.892, + 0.343 + ], + "angle": 0, + "content": "- PASCAL-Context PASCAL-Context datasets contain PASCAL VOC 2010 [34] with semantic segmentation, human parts segmentation, and saliency maps, as well as additional annotations for surface normals and edge maps." + }, + { + "type": "list", + "bbox": [ + 0.518, + 0.092, + 0.894, + 0.343 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.355, + 0.892, + 0.476 + ], + "angle": 0, + "content": "Competitive methods We compare the proposed framework with state-of-the-art methods [1, 11, 12, 18, 20, 22, 23, 25, 28, 29, 32, 38] and various baselines including a single task and a shared-bottom. The single-task baseline trains each task independently using a task-specific encoder and task-specific head for each task. The shared-bottom baseline trains multiple tasks simultaneously with a shared encoder and separated task-specific heads." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.478, + 0.893, + 0.674 + ], + "angle": 0, + "content": "We compare our method with MoE-based approaches, including Soft Ordering [23], Routing [28], and Gumbel-Matrix [22], as well as a NAS approach [18] on Omniglot datasets. CMTR [18] can modify parameter count, similar to our method. We compare our method with other soft-parameter sharing methods including Cross-Stitch [25], Sluice network [32], and NDDR-CNN [11] and the dynamic neural network (DNN)-based methods including MTAN [20], DEN [1], and Adashare [38] for the other three datasets. We provide the evaluation results of two recent works, LTB [12] and PHN [29] for PASCAL-Context datasets because only the results are reported in their papers, but no source codes are provided." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.675, + 0.893, + 0.901 + ], + "angle": 0, + "content": "Multi-task scenarios We set up multi-task scenarios with the combination of several tasks out of a total of seven tasks, including classification \\(\\mathcal{T}_{cls}\\), semantic segmentation \\(\\mathcal{T}_{sem}\\), depth estimation \\(\\mathcal{T}_{dep}\\), surface normal prediction \\(\\mathcal{T}_{norm}\\), human-part segmentation \\(\\mathcal{T}_{part}\\), saliency detection \\(\\mathcal{T}_{sal}\\), and edge detection \\(\\mathcal{T}_{edge}\\). We follow the MTL setup in [38] for three datasets including Omniglot, NYU-v2, and cityscapes, and [29] for PASCAL-Context. We simulate a homogeneous MTL scenario of a 20-way classification task in a multi-task setup using Omniglot datasets by following [23]. Each task predicts a class of characters in a single alphabet set. We use the other three datasets for heterogeneous MTL. We set three tasks including segmentation, depth estimation, and normal estimation for NYU-v2 and two with segmentation, depth estimation for Cityscapes." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "3783" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.086, + 0.089, + 0.462, + 0.268 + ], + "angle": 0, + "content": "
MethodTest Acc. (%)# of Param ↓
Soft Ordering [23]66.590.27
CMTR [18]87.19-
MoE [28]92.199.08
Gumbel-Matrix [22]93.529.08
Single Task93.4820.00
Shared Bottom93.251.00
Ours (M=3)94.990.91
Ours (M=5)95.711.37
Ours (M=7)95.681.46
" + }, + { + "type": "table_caption", + "bbox": [ + 0.144, + 0.28, + 0.402, + 0.294 + ], + "angle": 0, + "content": "Table 1. Evaluation on Omniglot datasets." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.306, + 0.467, + 0.452 + ], + "angle": 0, + "content": "
MethodΔsem↑Δnorm↑Δdep↑Δ↑# of Param ↓
Single-Task0.00.00.00.03.00
Shared Bottom-7.6+7.5+5.2+1.71.00
Cross-Stitch [25]-4.9+4.2+4.7+1.33.00
Sluice [32]-8.4+2.9+4.1-0.53.00
NDDR-CNN [11]-15.0+2.9-3.5-5.23.15
MTAN [20]-4.2+8.7+3.8+2.73.11
DEN [1]-9.9+1.7-35.2-14.51.12
AdaShare [38]+8.8+7.9+10.1+8.91.00
Ours (M=5)+11.9+7.9+8.8+9.51.04
Ours (M=7)+13.4+9.2+10.7+11.11.31
Ours (M=9)+13.2+9.0+10.9+11.01.63
" + }, + { + "type": "table_caption", + "bbox": [ + 0.147, + 0.463, + 0.398, + 0.476 + ], + "angle": 0, + "content": "Table 2. Evaluation on NYU-v2 datasets." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.489, + 0.469, + 0.518 + ], + "angle": 0, + "content": "We set five tasks \\(\\mathcal{T}_{sem}\\), \\(\\mathcal{T}_{part}\\), \\(\\mathcal{T}_{norm}\\), \\(\\mathcal{T}_{sal}\\), and \\(\\mathcal{T}_{edge}\\) as used in [29] for PASCAL-Context datasets." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.519, + 0.469, + 0.701 + ], + "angle": 0, + "content": "Evaluation metrics We follow the common evaluation metrics utilized in the competitive methods. We use an accuracy metric for the classification task. The semantic segmentation task is measured by mean Intersection over Union (mIoU) and pixel accuracy. We use the mean absolute and mean relative errors, and relative difference as the percentage of \\(\\delta = \\max (\\hat{\\mathbf{d}} /\\mathbf{d},\\mathbf{d} / \\hat{\\mathbf{d}})\\) within thresholds \\(1.25^{\\{1,2,3\\}}\\) for the depth estimation task. For the evaluation of the PASCAL-Context datasets, we follow the same metrics used in [29] for all tasks. As reported in [38], we report a single relative performance \\(\\Delta_{\\mathcal{T}_i}\\) in Tab. 1-4 for each task \\(\\mathcal{T}_i\\) with respect to the single-task baseline, which defined as:" + }, + { + "type": "equation", + "bbox": [ + 0.11, + 0.707, + 0.469, + 0.751 + ], + "angle": 0, + "content": "\\[\n\\Delta_ {\\mathcal {T} _ {i}} = \\frac {1 0 0}{| \\mathcal {M} |} \\sum_ {j = 0} ^ {| \\mathcal {M} |} (- 1) ^ {l _ {j}} \\frac {\\left(\\mathcal {M} _ {\\mathcal {T} _ {i} , j} - \\mathcal {M} _ {\\mathcal {T} _ {i} , j} ^ {\\text {s i n g l e}}\\right)}{\\mathcal {M} _ {\\mathcal {T} _ {i} , j} ^ {\\text {s i n g l e}}}, \\tag {10}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.759, + 0.469, + 0.837 + ], + "angle": 0, + "content": "where \\(\\mathcal{M}_{\\mathcal{T}_i,j}\\) and \\(\\mathcal{M}_{\\mathcal{T}_i,j}^{single}\\) are the \\(j\\)-th metric of \\(i\\)-th task \\(\\mathcal{T}_i\\) from each method and the single task baseline, respectively. The constant \\(l_j\\) is 1 if a lower value represents better for the metric \\(\\mathcal{M}_{\\mathcal{T}_i,j}\\) and 0 otherwise. The averaged relative performance for all tasks \\(\\mathcal{T}\\) is defined as:" + }, + { + "type": "equation", + "bbox": [ + 0.204, + 0.855, + 0.469, + 0.898 + ], + "angle": 0, + "content": "\\[\n\\Delta_ {\\mathcal {T}} = \\frac {1}{| \\mathcal {T} |} \\sum_ {i = 1} ^ {| \\mathcal {T} |} \\Delta_ {\\mathcal {T} _ {i}}. \\tag {11}\n\\]" + }, + { + "type": "table", + "bbox": [ + 0.503, + 0.089, + 0.892, + 0.264 + ], + "angle": 0, + "content": "
MethodΔTsem↑ΔTdep↑ΔT↑# of Param ↓
Single-Task0.00.00.02.00
Shared Bottom-3.7-0.5-2.11.00
Cross-Stitch [25]-0.1+5.8+2.82.00
Sluice [32]-0.8+4.0+1.62.00
NDDR-CNN [11]+1.3+3.3+2.32.07
MTAN [20]+0.5+4.8+2.72.41
DEN [1]-3.1-1.6-2.41.12
AdaShare [38]+1.8+3.8+2.81.00
Ours (M=5)+3.5+3.9+3.70.96
Ours (M=7)+7.5+3.1+5.31.16
Ours (M=9)+8.3+4.8+6.61.31
" + }, + { + "type": "table_caption", + "bbox": [ + 0.563, + 0.275, + 0.828, + 0.289 + ], + "angle": 0, + "content": "Table 3. Evaluation on Cityscapes datasets." + }, + { + "type": "table", + "bbox": [ + 0.502, + 0.302, + 0.89, + 0.426 + ], + "angle": 0, + "content": "
MethodΔTsem↑ΔTpart↑ΔTmal↑ΔTnorm↓ΔTedge↑ΔT↑# of Param ↓
Single-Task0.00.00.00.00.00.05.00
Shared Bottom-6.6-0.7-3.4-14.30.0-5.01.00
Cross-Stitch [25]-1.3+3.6-0.2-1.40.0+0.15.00
Sluice [32]-1.6-1.2-0.5-2.9-6.0-2.45.00
NDDR-CNN [11]-1.1-2.60.0-5.00.0-1.75.61
MTAN [20]-3.6-0.7-0.3-5.0-6.0-3.15.21
AdaShare [38]-1.4+4.0-0.5-0.70.0+0.31.00
LTB [12]-6.9-1.9+0.2-1.40.0-2.03.19
PHN [29]-6.6-1.6-1.00.00.0-1.82.51
Ours (M=5)-0.3+3.4+0.90.00.0+0.81.93
Ours (M=7)0.0-0.2+1.7+1.40.0+0.61.91
Ours (M=9)0.0+3.6+1.8+1.40.0+1.42.31
" + }, + { + "type": "table_caption", + "bbox": [ + 0.54, + 0.436, + 0.851, + 0.449 + ], + "angle": 0, + "content": "Table 4. Evaluation on PASCAL-Context datasets." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.461, + 0.892, + 0.492 + ], + "angle": 0, + "content": "The absolute task performance for all metrics is reported in the supplementary material." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.492, + 0.893, + 0.704 + ], + "angle": 0, + "content": "Network and training details For our central network, we set 8 hidden states, the same as the existing MoE-based works [22, 28] and use the same classification head for Omniglot datasets. We set 12 hidden states, the same as the VGG-16 [35], except for the max-pooled state, and use the Deeplab-v2 [5] decoder structure as all task heads for all the other datasets, respectively. We use the Adam [16] optimizer to update both upper-level parameters and network parameters. We use cross-entropy loss for semantic segmentation and L2 loss for the other tasks. For a fair comparison, we train our central network from scratch without pre-training for all experiments. We describe more details on the network structure and hyperparameter settings in the supplementary material." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.712, + 0.845, + 0.728 + ], + "angle": 0, + "content": "4.2. Comparison to State-of-the-art Methods" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.735, + 0.892, + 0.901 + ], + "angle": 0, + "content": "We report the performance of the proposed method with different flow constants \\(M\\) and compare it with state-ofthe-art methods in Tab. 1-4 with four different MTL scenarios. Tab. 1 shows that our framework with any flow constant \\(M\\) outperforms all the competitive methods for the homogeneous MTL scenario with Omniglot datasets. Ours has a similar number of parameters to the shared-bottom baseline. All the other experiments for heterogeneous MTL scenarios in Tab. 2-4 show that our frameworks achieve the best performance among all state-ofthe-art works. Even with the flow constant \\(M = 5\\), our" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "3784" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.083, + 0.09, + 0.245, + 0.167 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.081, + 0.168, + 0.246, + 0.24 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.081, + 0.242, + 0.246, + 0.317 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.246, + 0.092, + 0.447, + 0.314 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.328, + 0.47, + 0.412 + ], + "angle": 0, + "content": "Figure 3. Graph Representation of Task-adaptive Sub-network The finalized sub-network topologies (\\(M = 7\\)) trained with NYUv2 datasets is illustrated as graph. (a-c) The task-adaptive subnetwork of semantic segmentation, depth estimation, and surface normal, respectively. (d) The adjacency matrix where color represents the discretized value for the activated edge of each task." + }, + { + "type": "table", + "bbox": [ + 0.149, + 0.425, + 0.4, + 0.502 + ], + "angle": 0, + "content": "
TaskDWS
Semantic Seg.530.103
Depth730.192
Surface normal720.128
" + }, + { + "type": "table_caption", + "bbox": [ + 0.121, + 0.512, + 0.424, + 0.527 + ], + "angle": 0, + "content": "Table 5. Topologies analysis on NYU-v2 datasets." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.538, + 0.47, + 0.719 + ], + "angle": 0, + "content": "model outperforms AdaShare [38] for both the NYU-v2 and Cityscapes datasets, while keeping almost the same number of parameters (NYU-v2: 1.00 vs. 1.04 and Cityscapes 1.00 vs. 0.96). With the flow constant \\( M = 7,9 \\), our method outperforms all the baselines by a large margin. The results from the PASCAL-Context datasets in Tab. 4 show that all baselines suffer from negative transfer in several tasks, as the number of tasks increases. Only Adashare and Cross Stitch slightly outperform the single-task baseline (see the performance \\( \\Delta_{\\mathcal{T}} \\)). On the other hand, ours with \\( M = 9 \\) achieves the best performance without any negative transfers for all tasks." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.72, + 0.471, + 0.902 + ], + "angle": 0, + "content": "Interestingly, the required parameters of the search space increase almost in proportion to the increase of the flow constant, but there is no significant difference in the number of parameters of the finalized networks. For example, the required number of parameters for the network with the flow constant \\( M = 3,5,7 \\) is 2.77, 4.23, and 5.38, respectively. This demonstrates that the proposed flow-based reduction algorithm is effective in removing low-relative parameters while maintaining performance. Specifically, we observe that the total performance of our framework with \\( M = 7 \\) is slightly better than the \\( M = 9 \\) setup in Tab. 2 despite its smaller architecture search space. To investigate this," + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.092, + 0.892, + 0.136 + ], + "angle": 0, + "content": "we further analyze the tendency in performance and computational complexity with respect to the flow constant in Sec. 4.4." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.147, + 0.874, + 0.164 + ], + "angle": 0, + "content": "4.3. Analysis of Topologies and Task Correlation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.171, + 0.892, + 0.307 + ], + "angle": 0, + "content": "To demonstrate the effectiveness of the proposed learning mechanism, we visualize our finalized sub-network topologies in Fig. 3-(a-c) and the adjacency matrix for NYU-v2 3-task learning in Fig. 3-(d). We also analyze the diversity and capacity of task-adaptive network topologies in Tab. 5 with network depth \\(\\mathcal{D}\\), width \\(\\mathcal{W}\\), and sparsity \\(\\mathcal{S}\\) described in Sec. 3.1. These analyses provide three key observations on our task-adaptive network and the correlation among tasks." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.308, + 0.892, + 0.413 + ], + "angle": 0, + "content": "First, the tasks of segmentation and surface normal hardly share network parameters. Various task-sharing patterns are configured at the edge, but there is only one sharing layer between the two tasks. This experiment shows a low relationship between tasks, as it is widely known that the proportion of shared parameters between tasks indicates task correlation [22, 29, 38]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.414, + 0.892, + 0.548 + ], + "angle": 0, + "content": "Second, long skip connections are mostly lost. The length of the longest skip connection in the finalized network is 5, and the number of these connections is 2 out of 18 layers, even with the flow constant of 7. This phenomenon is observed not only in NYU-v2 datasets but also in the other MTL datasets. This can be evidence that the proposed flow-restriction reduces search time while maintaining high performance even by eliminating the long skip connection in the DAG-based central network." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.55, + 0.892, + 0.701 + ], + "angle": 0, + "content": "Lastly, Depth estimation task requires more network resources than segmentation and surface normal estimation tasks. We analyze the network topologies of the finalized sub-network of each task in NYU-v2 datasets using three components defined in Sec. 3. The depth \\(\\mathcal{D}\\) and width \\(\\mathcal{W}\\) of the sub-network increase in the order of semantic segmentation, surface normal prediction, and depth estimation tasks. Likewise, the sparsity \\(\\mathcal{S}\\) of the depth network is the highest. This experiment shows that the depth network is the task that requires the most network resources." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.711, + 0.816, + 0.726 + ], + "angle": 0, + "content": "4.4. Performance w.r.t. Flow-restriction" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.735, + 0.892, + 0.901 + ], + "angle": 0, + "content": "We analyze performance and computational complexity with respect to the flow constant \\( M \\) for the NYU-v2 and Cityscapes datasets. We report the rate of performance degradation with respect to the complete DAG search space in Fig. 4. We observe that the reduction rate of the final performance does not exceed \\( 3\\% \\) even with considerably lower flow constants. The performance is saturated at a flow constant of about 7 or more. This means that the proposed method optimizes the task adaptive sub-network regardless of the size of the network search space, if it satisfies the minimum required size." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "3785" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.09, + 0.112, + 0.462, + 0.288 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.303, + 0.472, + 0.403 + ], + "angle": 0, + "content": "Figure 4. Model performance with respect to the proposed flow-restriction. We plot the degradation ratio of the performance (left y-axis) and parameter (right y-axis) by changing the flow constant \\( M \\). We measure the final averaged task performance with NYU-v2 and Cityscapes datasets marked by purple and pink circle markers, respectively. We also measure the number of parameters marked by gray square markers." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.41, + 0.472, + 0.668 + ], + "angle": 0, + "content": "To demonstrate the effectiveness of our flow-based reduction (FBR) algorithm, we compare it to two other reduction algorithms (random and threshold) for Cityscapes datasets in Fig. 5. The random reduction literally removes the edges randomly, and the thresholding method sequentially removes the edge which has the lowest value in the adjacency matrix \\(\\Gamma\\). We measure the rate of performance degradation of the pruned network of each reduction algorithm with respect to the non-reduced network while changing the sparsity \\(S\\). Note that our method automatically determines the sparsity, so for this experiment only, we add a termination condition that stops the network search when a certain sparsity is met. The results show that the proposed flow-reduction method retains performance even with a low sparsity rate. This means that our method efficiently prunes the low-related edge of the network compared to the other methods." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.68, + 0.401, + 0.697 + ], + "angle": 0, + "content": "4.5. Ablation Study on Proposed Modules" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.705, + 0.472, + 0.903 + ], + "angle": 0, + "content": "We conduct ablation studies on the four key components of our framework; the flow-restriction, read-in/out layers, flow-based reduction, and squeeze loss. We report the relative task performance and the number of parameters of the finalized network with/without the components in Tab. 6. The results show that our framework, including all components, achieves the lowest number of parameters and the second-best performance. Our method without flow-based reduction achieves the best performance. However, the finalized network from this setup has about a five-times larger number of parameters than ours because the network has never been pruned in a training process. This demonstrates that our restricted DAG-based central network is optimized" + }, + { + "type": "image", + "bbox": [ + 0.518, + 0.109, + 0.848, + 0.281 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.296, + 0.892, + 0.353 + ], + "angle": 0, + "content": "Figure 5. Model Performance with respect to the network sparsity. We plot the performance degradation rate by changing network sparsity. We compare our flow-based reduction algorithm to two other schemes; random selection and thresholding." + }, + { + "type": "table", + "bbox": [ + 0.502, + 0.365, + 0.89, + 0.442 + ], + "angle": 0, + "content": "
MethodΔTsem↑ΔTdep↑ΔTnorm↑ΔT# of Param ↓
Ours (M=7)+13.4+9.2+10.7+11.11.31
w/o flow-restriction+13.2+9.2+10.4+11.01.80
w/o read-in/out+11.7+8.3+10.4+10.11.43
w/o flow-based reduction+14.2+9.2+11.1+11.56.50
w/o Lsq+13.2+8.8+10.7+10.91.38
" + }, + { + "type": "table_caption", + "bbox": [ + 0.506, + 0.452, + 0.884, + 0.467 + ], + "angle": 0, + "content": "Table 6. Ablation study on the proposed modules (NYU-v2)." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.477, + 0.892, + 0.522 + ], + "angle": 0, + "content": "to build compact task-adaptive sub-networks with performance close to the optimized sub-network from a complete DAG-based network." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.535, + 0.628, + 0.551 + ], + "angle": 0, + "content": "5. Conclusions" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.56, + 0.892, + 0.817 + ], + "angle": 0, + "content": "In this paper, we present a new MTL framework to search for task-adaptive network structures across diverse network topologies in a single network. We propose flow restriction to solve the scalability issue in a complete DAG search space while maintaining the diverse network topological representation of the DAG search space by adopting read-in/out layers. We also introduce a flow-based reduction algorithm that prunes the network efficiently while maintaining overall task performance and squeeze loss, limiting the upper bound on the number of network parameters. The extensive experiments demonstrate that the submodule and schemes of our framework efficiently improve both the performance and compactness of the network. Our method compactly constructs various task-specific subnetworks in a single network and achieves the best performance among all the competitive methods on four MTL benchmark datasets." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.83, + 0.661, + 0.848 + ], + "angle": 0, + "content": "Acknowledgement" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.855, + 0.892, + 0.901 + ], + "angle": 0, + "content": "This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. RS-2023-00210908)." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.956 + ], + "angle": 0, + "content": "3786" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.116, + 0.47, + 0.171 + ], + "angle": 0, + "content": "[1] Chanho Ahn, Eunwoo Kim, and Songhwai Oh. 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In Proceedings of the IEEE conference on computer vision and pattern recognition, pages 8697-8710, 2018. 1, 2" + }, + { + "type": "list", + "bbox": [ + 0.08, + 0.092, + 0.472, + 0.883 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.946, + 0.516, + 0.956 + ], + "angle": 0, + "content": "3788" + } + ] +] \ No newline at end of file diff --git a/2023/Dynamic Neural Network for Multi-Task Learning Searching Across Diverse Network Topologies/08f871aa-0255-4d39-aee9-94ac7465f9f8_origin.pdf b/2023/Dynamic Neural Network for Multi-Task Learning Searching Across Diverse Network Topologies/08f871aa-0255-4d39-aee9-94ac7465f9f8_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..86736cd959b1f77857e63eee559ed702413905d9 --- /dev/null +++ b/2023/Dynamic Neural Network for Multi-Task Learning Searching Across Diverse Network Topologies/08f871aa-0255-4d39-aee9-94ac7465f9f8_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:25acb563a3e2cba6f1cd26d50a72813901ca6ebe7aa6e4cbe0f0ee70d8d67a2e +size 1248275 diff --git a/2023/Dynamic Neural Network for Multi-Task Learning Searching Across Diverse Network Topologies/full.md b/2023/Dynamic Neural Network for Multi-Task Learning Searching Across Diverse Network Topologies/full.md new file mode 100644 index 0000000000000000000000000000000000000000..d101582c531910e34f83494876ff24bfe6288f89 --- /dev/null +++ b/2023/Dynamic Neural Network for Multi-Task Learning Searching Across Diverse Network Topologies/full.md @@ -0,0 +1,354 @@ +# Dynamic Neural Network for Multi-Task Learning Searching across Diverse Network Topologies + +Wonhyeok Choi, Sunghoon Im* +Department of Electrical Engineering & Computer Science, DGIST, Daegu, Korea +{smu06117, sunghoonim}@dgist.ac.kr + +# Abstract + +In this paper, we present a new MTL framework that searches for structures optimized for multiple tasks with diverse graph topologies and shares features among tasks. We design a restricted DAG-based central network with read-in/read-out layers to build topologically diverse task-adaptive structures while limiting search space and time. We search for a single optimized network that serves as multiple task adaptive sub-networks using our three-stage training process. To make the network compact and discretized, we propose a flow-based reduction algorithm and a squeeze loss used in the training process. We evaluate our optimized network on various public MTL datasets and show ours achieves state-of-the-art performance. An extensive ablation study experimentally validates the effectiveness of the sub-module and schemes in our framework. + +# 1. Introduction + +Multi-task learning (MTL), which learns multiple tasks simultaneously with a single model has gained increasing attention [3, 13, 14]. MTL improves the generalization performance of tasks while limiting the total number of network parameters to a lower level by sharing representations across tasks. However, as the number of tasks increases, it becomes more difficult for the model to learn the shared representations, and improper sharing between less related tasks causes negative transfers that sacrifice the performance of multiple tasks [15,36]. To mitigate the negative transfer in MTL, some works [6, 25, 32] separate the shared and task-specific parameters on the network. + +More recent works [21, 29, 38] have been proposed to dynamically control the ratio of shared parameters across tasks using a Dynamic Neural Network (DNN) to construct a task adaptive network. These works mainly apply the cell-based architecture search [19, 27, 41] for fast search times, so that the optimized sub-networks of each task consist of fixed or simple structures whose layers are simply branched, as shown in Fig. 1a. They primarily focus on finding branching + +patterns in specific aspects of the architecture, and feature-sharing ratios across tasks. However, exploring optimized structures in restricted network topologies has the potential to cause performance degradation in heterogeneous MTL scenarios due to unbalanced task complexity. + +We present a new MTL framework searching for subnetwork structures, optimized for each task across diverse network topologies in a single network. To search the graph topologies from richer search space, we apply Directed Acyclic Graph (DAG) for the homo/heterogeneous MTL frameworks, inspired by the work in NAS [19, 27, 40]. The MTL in the DAG search space causes a scalability issue, where the number of parameters and search time increase quadratically as the number of hidden states increases. + +To solve this problem, we design a restricted DAG-based central network with read-in/read-out layers that allow our MTL framework to search across diverse graph topologies while limiting the search space and search time. Our flow-restriction eliminates the low-importance long skip connection among network structures for each task, and creates the required number of parameters from $O(N^2)$ to $O(N)$ . The read-in layer is the layer that directly connects all the hidden states from the input state, and the read-out layer is the layer that connects all the hidden states to the last feature layer. These are key to having various network topological representations, such as polytree structures, with early-exiting and multi-embedding. + +Then, we optimize the central network to have compact task-adaptive sub-networks using a three-stage training procedure. To accomplish this, we propose a squeeze loss and a flow-based reduction algorithm. The squeeze loss limits the upper bound on the number of parameters. The reduction algorithm prunes the network based on the weighted adjacency matrix measured by the amount of information flow in each layer. In the end, our MTL framework constructs a compact single network that serves as multiple task-specific networks with unique structures, such as chain, polytree, and parallel diverse topologies, as presented in Fig. 1b. It also dynamically controls the amount of sharing representation among tasks. + +(i). Mixture-of-Experts +![](images/9eb6ce8f6581a330c427eb55ebf2cd59425057164ae3c0f36d0ca7d895b92f9c.jpg) +- - $\rightarrow$ : inactivated operation + +(iii).Ours +$\bigcirc$ : hidden states +![](images/b84c484c0785246c528c2a3d6dfba93cfef10f4f82c3fcabc523efc749b5c989.jpg) +:activated operation + +(ii).Skip-or-Select +![](images/1550a4d2ebad536df6871564cb9f1497878b6bc1ec58b4c6c76dbc8442d41bd3.jpg) +non-operation +(a) Graph representation of existing DNN-based methods (i)-(ii). for MTL and ours (iii). + +![](images/39d42af6da39011dc02e3a7ef353edb2d31e23f99d2a7f9bbcbf2bb2e7ebd470.jpg) +(i). Complete Directed Acyclic Graph +(ii). Subgraph topologies + +![](images/3c6b6df501bf8ac240961a679f1310c740d90d88269fcdb9d7e78b56e1a539f5.jpg) + +![](images/d1e1ca9da298354661df86545538e16c8587665db2355972770a8659a247c58c.jpg) + +![](images/b6f1c6cc4b029196914b5ffa78bc7cfe23e2cb25ca979e4a0b58f4491ce669ff.jpg) + +Figure 1. Graph representation of various neural networks. (a) Graph representation of existing dynamic neural network for multitask learning and ours. (b) Topologies of a completed Directed Acyclic Graph (DAG) and the output sub-graph of DAG structure. +![](images/9b5373f39e249d7c971cccf8d768072d1e69a52df2a972445c412e32e775154e.jpg) +(b) Topologies of DAG (i). and its sub-graph (ii). + +The experiments demonstrate that our framework successfully searches the task-adaptive network topologies of each task and leverages the knowledge among tasks to make a generalized feature. The proposed method outperforms state-of-the-art methods on all common benchmark datasets for MTL. Our contributions can be summarized as follows: + +- We present for the first time an MTL framework that searches both task-adaptive structures and sharing patterns among tasks. It achieves state-of-the-art performance on all public MTL datasets. +- We propose a new DAG-based central network composed of a flow restriction scheme and read-in/out layers, that has diverse graph topologies in a reasonably restricted search space. +- We introduce a new training procedure that optimizes the MTL framework for compactly constructing various task-specific sub-networks in a single network. + +# 2. Related Works + +Neural Architecture Search (NAS) Neural Architecture Search is a method that automates neural architecture engineering [8]. Early works [2, 40, 41] use reinforcement learning based on rewarding the model accuracy of the generated architecture. Alternative approaches [24, 30, 37] employ evolutionary algorithms to optimize both the neural architecture and its weights. These methods search for an adequate neural architecture in a large discrete space. Gradient-based NAS methods [4, 19, 39] of formulating operations in a differentiable search space are proposed to alleviate the scalability issues. They generally use the convex combination from a set of operations instead of determining a single operation. Most NAS approaches [19, 27, 40] adopt the complete DAG as a search space, to find the architecture + +in the various network topologies. However, DAG-based MTL frameworks have not been proposed, because of their considerably high computational demands. + +Multi-Task Learning (MTL) Multi-task learning in deep neural networks can be categorized into hard and soft parameter sharing types [31]. Hard parameter sharing [3, 13, 14], also known as shared-bottom, is the most commonly used approach to MTL. This scheme improves generalization performance while reducing the computational cost of the network, by using shared hidden layers between all tasks. However, it typically struggles with the negative transfer problem [15, 36] which degrades performance due to improper sharing between less relevant tasks. + +On the other hand, soft-parameter sharing [25, 32] alleviate the negative transfer problem by changing the shared parameter ratio. These approaches mitigate the negative transfer by flexibly modifying shared information, but they cannot maintain the computational advantage on the classic shared-bottom model. Recently, advanced approaches have been proposed to adjust shared parameters using a dynamic neural network [21, 22, 29, 38] and NAS [10]. + +NAS-style MTL MTL frameworks using a dynamic neural network (DNN) can be divided into two categories. One employs the Mixture-of-Experts (MoE) [33], which is designed for conditional computation of per-sample, to MTL by determining the experts of each task [9, 21, 22]. They have a fixed depth finalized task-specific sub-network, because they choose experts from a fixed number of modular layers. This causes a critical issue with task-balancing in the heterogeneous MTL. The other adopts the skip-or-select policy to select task-specific blocks from the set of residual blocks [38] or a shared block per layer [12, 29]. These methods only create a simple serial path in the finalized subnetwork of each task, and a parallel link cannot be reproduced. Moreover, they heuristically address the unbalanced + +task-wise complexity issues in the heterogenous MTL (e.g. manually changing the balancing parameters based on the task complexity [29,38]). Thus, none of the aforementioned works focus on finding the optimal task-specific structure in the MTL scenario. + +# 3. Method + +We describe our MTL framework, which searches for optimized network structures tailored to each task across diverse graph topologies, while limiting search time. Sec. 3.1 describes the composition of the searchable space of our central network and our flow-restriction method for efficiently balancing the topological diversity of task-specific sub-networks and searching space. Sec. 3.2 introduces our mechanism to determine the task-adaptive sub-network in the central network and describes the overall training process and loss function. The overall pipeline of our method is illustrated in Fig. 2. + +# 3.1. The Central Network with Diverse Topologies + +Our central network composes a graph $G = (V, E)$ with layers $E$ in which the $N$ hidden states $V = \{v_1, \dots, v_N\}$ are topologically sorted: + +$$ +E = \left\{e _ {i j} \right\} _ {i, j \in \{1, \dots , N \}}, \text {w h e r e} i < j, \tag {1} +$$ + +$$ +e _ {i j} (\cdot ; \theta_ {i j}): \mathbb {R} ^ {N ^ {v _ {i}}} \rightarrow \mathbb {R} ^ {N ^ {v _ {j}}}, \tag {2} +$$ + +where $e_{ij}$ is the operation that transfers the state $v_{i}$ to $v_{j}$ with the weight parameters $\theta_{ij} \in \Theta$ , and $N^{v_k}$ is the number of the elements of hidden state $v_{k}$ , respectively. We adopt the DAG structure [19, 27, 40] for the network. However, the optimized structure from DAG is searched from $2^{N(N - 1) / 2}$ network topologies, which are too large to be optimized in time. To address the issue while maintaining diversity, we propose a flow-restriction and read-in/read-out layers. + +Flow-restriction The flow-restriction eliminates the low-importance long skip connection among network structures for each task by restricting $j - i \leq M$ where $M$ is the flow constant. Regulating the searchable edges in the graph reduces the required number of parameters and searching time from $O(N^2)$ to $O(N)$ , but it sacrifices the diversity and capacity of the network topologies. + +To explain the topological diversity and task capacity of sub-networks, we define the three components of network topology, as follows: + +1. $\mathcal{D}(G) = \max (\{\mathrm{Distance}(v_i,v_j)\}_{v_i,v_j\in V}),$ +2. $\mathcal{W}(G) = \max (\{\mathrm{Out}_{v_i}\}_{v_i\in V}),$ +3. $S(G_{s},G) = |E_{s}| / |E|$ + +where $\mathrm{Out}_{v_i}$ is the out-degree of the vertex $v_i$ and $\mathrm{Distance}(\cdot)$ is the operation that counts the number of layers (or edges) between two connected vertices. The network + +depth $\mathcal{D}(G)$ is equal to the longest distance between two vertices in the graph $G$ . The network width $\mathcal{W}(G)$ is equal to the maximum value of the out-degrees of hidden states in the graph $G$ . The sparsity $\mathcal{S}(G_s, G)$ of the sub-graph $G_s$ is the ratio of finalized edges $|E_s|$ over entire edges $|E|$ . The first two components are measurements of the topological diversity of the finalized sub-network, while the last one is for the sub-network capacity. While a complete DAG has the full range of depth and width components, the flow-restricted DAG has the properties of depth and width components as follows: + +$$ +\text {P r o p e r t y 1 .} \min (\{\mathcal {D} (G _ {s}) \} _ {G _ {s} \subseteq G}) = \lceil (| V | / M) \rceil , +$$ + +$$ +\text {P r o p e r t y 2 .} \max (\{\mathcal {W} (G _ {s}) \} _ {G _ {s} \subseteq G}) = M, +$$ + +where $\{G_s\}$ is the entire sub-graph of $G$ . The min-depth property (Prop. 1) can cause the over-parameterized problem when the capacity of the task is extremely low. The max-width property (Prop. 2) directly sacrifices the diversity of network topologies in the search space. + +Read-in/Read-out layers We design read-in/read-out layers to mitigate these problems. The read-in layer embeds the input state $v_{0}$ into all hidden states $v_{i} \in V$ with task-specific weights $\alpha_{i}^{k} \in \mathcal{A}$ for all $K$ tasks $\mathcal{T} = \{T_k\}_{k \in \{1, \dots, K\}}$ as follows: + +$$ +v _ {i} ^ {k} = \sigma \left(\alpha_ {i} ^ {k}\right) \cdot v _ {0}, \tag {3} +$$ + +where $\sigma (\cdot)$ is the sigmoid function. Then, the central network sequentially updates the hidden state $v_{1}^{k}$ to $v_{N}^{k}$ with the task-specific weights $\gamma_{ij}^{k}\in \Gamma$ that correspond to $e_{ij}^{k}$ : + +$$ +v _ {j} ^ {k} = \frac {1}{\operatorname {I n} _ {v _ {j} ^ {k}}} \sum_ {e _ {i j} \in E} \left(\sigma \left(\gamma_ {i j} ^ {k}\right) \cdot e _ {i j} \left(v _ {i} ^ {k}; \theta_ {i j}\right)\right), \tag {4} +$$ + +where $\operatorname{In}_{v_j^k}$ is the in-degree of $v_{j}^{k}$ . Note that $\Gamma$ is the adjacency matrix of graph $G$ . Finally, the read-out layer aggregates all hidden state features $\{v_{i}^{k}\}_{i\in \{1,\dots,N\}}$ with the task-specific weights $\beta_i^k\in \mathcal{B}$ and produces the last layer feature $v_{L}^{k}$ for each task $k$ as follows: + +$$ +v _ {L} ^ {k} = \sum_ {i \in \{1, \dots , N \}} \left(\sigma \left(\beta_ {i} ^ {k}\right) \cdot v _ {i} ^ {k}\right). \tag {5} +$$ + +The final prediction $\hat{\mathbf{y}}_k$ for each task $T_{k}$ is computed by passing the aggregated features $v_{L}^{k}$ through the task-specific head $H^{k}(\cdot)$ as follows: + +$$ +\hat {\mathbf {y}} ^ {k} = H ^ {k} \left(v _ {L} ^ {k}\right). \tag {6} +$$ + +All upper-level parameters $\mathcal{A},\mathcal{B}$ , and $\Gamma$ are learnable parameters, and their learning process is described in Sec. 3.2. The read-in/read-out layers enable the optimized network to have a multi-input/output sub-network. The read-out layer + +![](images/545018b5d6911594acd54e953845adfeb62cea15ae128f78ddf76ec4c89429e8.jpg) +Figure 2. Overall pipeline. Our central network follows a DAG-based structure with read-in/out layers, and task-specific heads. The long skip connection is cut by our flow-restriction. Our framework with a 3-task MTL learning scenario consists of three stages including warm-up, search, and fine-tuning stages. The warm-up stage only learns the parameters of the main network $\Theta$ and task-specific weights. The search stage learns the upper-level parameters $\mathcal{A},\mathcal{B},\Gamma$ , and task-specific weights. Then, flow-based reduction eliminates the low-importance edges from the network. The fine-tuning stage re-trains the network with the remaining important parameters. + +aggregates all hidden states of the central network during the search stage, allowing a specific task to use the early hidden states to output predictions while ignoring the last few layers. These early-exit structures help alleviate the over-parameterized problem in simple tasks. + +# 3.2. Network Optimization and Training Procedure + +We describe the entire training process for our MTL framework, which consists of three stages, including warm-up, search, and fine-tuning stages. + +Warm-up stage As with other gradient-based NAS, our framework has upper-level parameters that determine the network structure and parameters. This bilevel optimization with a complex objective function in an MTL setup makes the training process unstable. For better convergence, we initially train all network parameters across tasks for a few iterations. We train the weight parameters of the central network $\Theta$ that shares all operations $E$ across tasks. We fix all values of the upper-level parameters $\mathcal{A},\mathcal{B}$ , and $\Gamma$ as 0, which becomes 0.5 after the sigmoid function $\sigma (\cdot)$ , and freeze them. We train the network parameters $\Theta$ in Eq. 4 with a task loss as follows: + +$$ +\mathcal {L} _ {\text {t a s k}} = \sum_ {k = 0} ^ {K} \mathcal {L} _ {T _ {k}} \left(\hat {\mathbf {y}} _ {T _ {k}}, \mathbf {y} _ {T _ {k}}\right), \tag {7} +$$ + +where $\mathcal{L}_{T_k}$ is the task-specific loss, which is the unique loss function for each task. + +Search stage After the warm-up stage, we unfreeze the upper-level parameters $\mathcal{A},\mathcal{B}$ , and $\Gamma$ and search the network topologies appropriate to each task. We train all these parameters and network parameters $\Theta$ simultaneously by minimizing the task loss and the proposed squeeze loss $\mathcal{L}_{sq}$ as follows: + +$$ +\mathcal {L} _ {\text {t r a i n}} = \mathcal {L} _ {\text {t a s k}} + \lambda_ {s q} \mathcal {L} _ {s q}, \tag {8} +$$ + +$$ +\mathcal {L} _ {s q} = \sum_ {k = 0} ^ {K} \left(\max \left(\left(\sum_ {\gamma_ {i j} \in \Gamma} \left(\sigma \left(\gamma_ {i j}\right)\right) - \kappa\right), 0\right)\right), \tag {9} +$$ + +where $\lambda_{sq}$ is the balancing hyperparameter, and $\kappa$ is a constant number called the budget, that directly reduces the sparsity of the central network. This auxiliary loss is designed to encourage the model to save computational resources. + +Fine-tuning stage. Lastly, we perform a fine-tuning stage to construct a compact and discretized network structure using the trained upper-level parameters $\mathcal{A},\mathcal{B}$ , and $\Gamma$ . To do so, we design a flow-based reduction algorithm that allows the network to obtain high computational speed by omitting low-importance operations, as described in Alg. 1. It measures the amount of information flow of each layer $e_{ij}$ in the central network by calculating the ratio of edge weight with respect to other related edges weight. Then, it sequentially removes the edge which has the lowest information flow. Alg. 1 stops when the edge selected to be deleted is + +Algorithm 1: Flow-based Reduction +Input: $\Gamma \in \mathbb{R}^{N\times N}$ $\mathcal{A}\in \mathbb{R}^N$ $\mathcal{B}\in \mathbb{R}^N$ Output: $\hat{\Gamma},\hat{\mathcal{A}},\hat{\mathcal{B}} / /$ Discretized params. +1 initialize zero matrix $\Psi ,\hat{\Psi}\in \mathbb{R}^{(N + 2)\times (N + 2)}$ +2 $N_{\alpha} = \mathrm{argmax}(\mathcal{A})$ +3 $N_{\beta} = \max (N_{\alpha} + 1,\mathrm{argmax}(\mathcal{B}))$ +4 $\Gamma [:N_{\alpha},:)]\gets 0 / /$ remove edges $< N_{\alpha}$ +5 $\Gamma [:,N_{\beta}]:\gets 0 / /$ remove edges $>N_{\beta}$ +6 $\Psi [1:N,1:N]\gets \Gamma /$ merge $\Gamma ,A,B$ into $\Psi$ +7 $\Psi [0,N_{\alpha} + 1:N_{\beta} + 1]\gets A[N_{\alpha}:N_{\beta}]$ +8 $\Psi [N_{\alpha} + 1:N_{\beta} + 1,N + 1]\gets B[N_{\alpha}:N_{\beta}]$ +9 while True do +10 initialize zero matrix $S\in \mathbb{R}^{(N + 2)\times (N + 2)}$ +for $i\gets 0$ to $\{N + 1\}$ do +for $j\gets 0$ to $\{N + 1\}$ do + $S[i,j]\gets$ $\psi_{ij}\left(\frac{1}{\ln v_i}\sum_{\psi_{ki}\in \Psi}(\psi_{ki}) / \sum_{\psi_{ik}\in \Psi}(\psi_{ik})+\right.$ $\left.\frac{1}{\mathrm{Out}_v_j}\sum_{\psi_{jk}\in \Psi}(\psi_{jk}) / \sum_{\psi_{kj}\in \Psi}(\psi_{kj})\right)$ $\psi_{ij}\gets 0$ where $S[i,j]$ is nonzero min value +if graph built from $\Psi$ is reachable then + $\hat{\Psi}\gets \Psi$ +else + $\hat{\Psi} [\hat{\Psi} >0]\gets 1 / /$ discretization + $\hat{\Gamma}\gets \hat{\Psi}[1:N,1:N] / /$ split into $\Gamma ,A,B$ $\hat{\mathcal{A}}\gets \hat{\Psi}[0,1:N]$ $\hat{\mathcal{B}}\gets \hat{\Psi}[1:N,N + 1]$ +return $\hat{\Gamma},\hat{\mathcal{A}},\hat{\mathcal{B}}$ + +the only edge that can reach the graph. We use the simple Depth-first search algorithm to check the reachability of $\hat{\Gamma}$ between hidden state $v_{N_{\alpha}}$ to $v_{N_{\beta}}$ . All the output $\hat{A}, \hat{B}, \hat{\Gamma}$ in Alg. 1, which is the discretized binary adjacency matrix, represent the truncated task-adaptive sub-network. After the reduction, we fix the upper-level parameters and only re-train the network parameters $\Theta$ , and we do not use the sigmoid function in Eq. 3-5 + +# 4. Experiments + +We first describe the experimental setup in Sec. 4.1. We compare our method to state-of-the-art MTL frameworks on various benchmark datasets for MTL in Sec. 4.2. We also conduct extensive experiments and ablation studies to validate our proposed method in Sec. 4.3-4.5. + +# 4.1. Experimental Settings + +Dataset We use four public datasets for multi-task scenarios including Omniglot [17], NYU-v2 [34], Cityscapes [7], and PASCAL-Context [26]. We use these datasets, configured by previous MTL works [29, 38], not their original sources. + +- Omniglot Omniglot is a classification dataset consisting of 50 different alphabets, and each of them consists of a number of characters with 20 handwritten images per character. +- NYU-v2 NYU-v2 comprises images of indoor scenes, fully labeled for joint semantic segmentation, depth estimation, and surface normal estimation. +- Cityscapes Cityscapes dataset collected from urban driving scenes in European cities consists of two tasks: joint semantic segmentation and depth estimation. +- PASCAL-Context PASCAL-Context datasets contain PASCAL VOC 2010 [34] with semantic segmentation, human parts segmentation, and saliency maps, as well as additional annotations for surface normals and edge maps. + +Competitive methods We compare the proposed framework with state-of-the-art methods [1, 11, 12, 18, 20, 22, 23, 25, 28, 29, 32, 38] and various baselines including a single task and a shared-bottom. The single-task baseline trains each task independently using a task-specific encoder and task-specific head for each task. The shared-bottom baseline trains multiple tasks simultaneously with a shared encoder and separated task-specific heads. + +We compare our method with MoE-based approaches, including Soft Ordering [23], Routing [28], and Gumbel-Matrix [22], as well as a NAS approach [18] on Omniglot datasets. CMTR [18] can modify parameter count, similar to our method. We compare our method with other soft-parameter sharing methods including Cross-Stitch [25], Sluice network [32], and NDDR-CNN [11] and the dynamic neural network (DNN)-based methods including MTAN [20], DEN [1], and Adashare [38] for the other three datasets. We provide the evaluation results of two recent works, LTB [12] and PHN [29] for PASCAL-Context datasets because only the results are reported in their papers, but no source codes are provided. + +Multi-task scenarios We set up multi-task scenarios with the combination of several tasks out of a total of seven tasks, including classification $\mathcal{T}_{cls}$ , semantic segmentation $\mathcal{T}_{sem}$ , depth estimation $\mathcal{T}_{dep}$ , surface normal prediction $\mathcal{T}_{norm}$ , human-part segmentation $\mathcal{T}_{part}$ , saliency detection $\mathcal{T}_{sal}$ , and edge detection $\mathcal{T}_{edge}$ . We follow the MTL setup in [38] for three datasets including Omniglot, NYU-v2, and cityscapes, and [29] for PASCAL-Context. We simulate a homogeneous MTL scenario of a 20-way classification task in a multi-task setup using Omniglot datasets by following [23]. Each task predicts a class of characters in a single alphabet set. We use the other three datasets for heterogeneous MTL. We set three tasks including segmentation, depth estimation, and normal estimation for NYU-v2 and two with segmentation, depth estimation for Cityscapes. + +
MethodTest Acc. (%)# of Param ↓
Soft Ordering [23]66.590.27
CMTR [18]87.19-
MoE [28]92.199.08
Gumbel-Matrix [22]93.529.08
Single Task93.4820.00
Shared Bottom93.251.00
Ours (M=3)94.990.91
Ours (M=5)95.711.37
Ours (M=7)95.681.46
+ +Table 1. Evaluation on Omniglot datasets. + +
MethodΔsem↑Δnorm↑Δdep↑Δ↑# of Param ↓
Single-Task0.00.00.00.03.00
Shared Bottom-7.6+7.5+5.2+1.71.00
Cross-Stitch [25]-4.9+4.2+4.7+1.33.00
Sluice [32]-8.4+2.9+4.1-0.53.00
NDDR-CNN [11]-15.0+2.9-3.5-5.23.15
MTAN [20]-4.2+8.7+3.8+2.73.11
DEN [1]-9.9+1.7-35.2-14.51.12
AdaShare [38]+8.8+7.9+10.1+8.91.00
Ours (M=5)+11.9+7.9+8.8+9.51.04
Ours (M=7)+13.4+9.2+10.7+11.11.31
Ours (M=9)+13.2+9.0+10.9+11.01.63
+ +We set five tasks $\mathcal{T}_{sem}$ , $\mathcal{T}_{part}$ , $\mathcal{T}_{norm}$ , $\mathcal{T}_{sal}$ , and $\mathcal{T}_{edge}$ as used in [29] for PASCAL-Context datasets. + +Evaluation metrics We follow the common evaluation metrics utilized in the competitive methods. We use an accuracy metric for the classification task. The semantic segmentation task is measured by mean Intersection over Union (mIoU) and pixel accuracy. We use the mean absolute and mean relative errors, and relative difference as the percentage of $\delta = \max (\hat{\mathbf{d}} /\mathbf{d},\mathbf{d} / \hat{\mathbf{d}})$ within thresholds $1.25^{\{1,2,3\}}$ for the depth estimation task. For the evaluation of the PASCAL-Context datasets, we follow the same metrics used in [29] for all tasks. As reported in [38], we report a single relative performance $\Delta_{\mathcal{T}_i}$ in Tab. 1-4 for each task $\mathcal{T}_i$ with respect to the single-task baseline, which defined as: + +$$ +\Delta_ {\mathcal {T} _ {i}} = \frac {1 0 0}{| \mathcal {M} |} \sum_ {j = 0} ^ {| \mathcal {M} |} (- 1) ^ {l _ {j}} \frac {\left(\mathcal {M} _ {\mathcal {T} _ {i} , j} - \mathcal {M} _ {\mathcal {T} _ {i} , j} ^ {\text {s i n g l e}}\right)}{\mathcal {M} _ {\mathcal {T} _ {i} , j} ^ {\text {s i n g l e}}}, \tag {10} +$$ + +where $\mathcal{M}_{\mathcal{T}_i,j}$ and $\mathcal{M}_{\mathcal{T}_i,j}^{single}$ are the $j$ -th metric of $i$ -th task $\mathcal{T}_i$ from each method and the single task baseline, respectively. The constant $l_j$ is 1 if a lower value represents better for the metric $\mathcal{M}_{\mathcal{T}_i,j}$ and 0 otherwise. The averaged relative performance for all tasks $\mathcal{T}$ is defined as: + +$$ +\Delta_ {\mathcal {T}} = \frac {1}{| \mathcal {T} |} \sum_ {i = 1} ^ {| \mathcal {T} |} \Delta_ {\mathcal {T} _ {i}}. \tag {11} +$$ + +Table 2. Evaluation on NYU-v2 datasets. + +
MethodΔTsem↑ΔTdep↑ΔT↑# of Param ↓
Single-Task0.00.00.02.00
Shared Bottom-3.7-0.5-2.11.00
Cross-Stitch [25]-0.1+5.8+2.82.00
Sluice [32]-0.8+4.0+1.62.00
NDDR-CNN [11]+1.3+3.3+2.32.07
MTAN [20]+0.5+4.8+2.72.41
DEN [1]-3.1-1.6-2.41.12
AdaShare [38]+1.8+3.8+2.81.00
Ours (M=5)+3.5+3.9+3.70.96
Ours (M=7)+7.5+3.1+5.31.16
Ours (M=9)+8.3+4.8+6.61.31
+ +Table 3. Evaluation on Cityscapes datasets. + +
MethodΔTsem↑ΔTpart↑ΔTmal↑ΔTnorm↓ΔTedge↑ΔT↑# of Param ↓
Single-Task0.00.00.00.00.00.05.00
Shared Bottom-6.6-0.7-3.4-14.30.0-5.01.00
Cross-Stitch [25]-1.3+3.6-0.2-1.40.0+0.15.00
Sluice [32]-1.6-1.2-0.5-2.9-6.0-2.45.00
NDDR-CNN [11]-1.1-2.60.0-5.00.0-1.75.61
MTAN [20]-3.6-0.7-0.3-5.0-6.0-3.15.21
AdaShare [38]-1.4+4.0-0.5-0.70.0+0.31.00
LTB [12]-6.9-1.9+0.2-1.40.0-2.03.19
PHN [29]-6.6-1.6-1.00.00.0-1.82.51
Ours (M=5)-0.3+3.4+0.90.00.0+0.81.93
Ours (M=7)0.0-0.2+1.7+1.40.0+0.61.91
Ours (M=9)0.0+3.6+1.8+1.40.0+1.42.31
+ +Table 4. Evaluation on PASCAL-Context datasets. + +The absolute task performance for all metrics is reported in the supplementary material. + +Network and training details For our central network, we set 8 hidden states, the same as the existing MoE-based works [22, 28] and use the same classification head for Omniglot datasets. We set 12 hidden states, the same as the VGG-16 [35], except for the max-pooled state, and use the Deeplab-v2 [5] decoder structure as all task heads for all the other datasets, respectively. We use the Adam [16] optimizer to update both upper-level parameters and network parameters. We use cross-entropy loss for semantic segmentation and L2 loss for the other tasks. For a fair comparison, we train our central network from scratch without pre-training for all experiments. We describe more details on the network structure and hyperparameter settings in the supplementary material. + +# 4.2. Comparison to State-of-the-art Methods + +We report the performance of the proposed method with different flow constants $M$ and compare it with state-ofthe-art methods in Tab. 1-4 with four different MTL scenarios. Tab. 1 shows that our framework with any flow constant $M$ outperforms all the competitive methods for the homogeneous MTL scenario with Omniglot datasets. Ours has a similar number of parameters to the shared-bottom baseline. All the other experiments for heterogeneous MTL scenarios in Tab. 2-4 show that our frameworks achieve the best performance among all state-ofthe-art works. Even with the flow constant $M = 5$ , our + +![](images/b9685fc639f8cf3ef3d889b2c17580fad8d4d6bf2fd04b5b1b7f9cb8e4242d44.jpg) + +![](images/47c4569c23e0b786adbd892f548d4f896abd54ff24f7b3f69c338fe9853a76c8.jpg) + +![](images/db07d5fcda95a6f169df26e4072f6548b53451779bc202cb3145862b24a625a9.jpg) + +![](images/210b57c0800e83ece8e609cc462da0656d882da0fb11737a55c07efdb041758a.jpg) +Figure 3. Graph Representation of Task-adaptive Sub-network The finalized sub-network topologies ( $M = 7$ ) trained with NYUv2 datasets is illustrated as graph. (a-c) The task-adaptive subnetwork of semantic segmentation, depth estimation, and surface normal, respectively. (d) The adjacency matrix where color represents the discretized value for the activated edge of each task. + +
TaskDWS
Semantic Seg.530.103
Depth730.192
Surface normal720.128
+ +Table 5. Topologies analysis on NYU-v2 datasets. + +model outperforms AdaShare [38] for both the NYU-v2 and Cityscapes datasets, while keeping almost the same number of parameters (NYU-v2: 1.00 vs. 1.04 and Cityscapes 1.00 vs. 0.96). With the flow constant $M = 7,9$ , our method outperforms all the baselines by a large margin. The results from the PASCAL-Context datasets in Tab. 4 show that all baselines suffer from negative transfer in several tasks, as the number of tasks increases. Only Adashare and Cross Stitch slightly outperform the single-task baseline (see the performance $\Delta_{\mathcal{T}}$ ). On the other hand, ours with $M = 9$ achieves the best performance without any negative transfers for all tasks. + +Interestingly, the required parameters of the search space increase almost in proportion to the increase of the flow constant, but there is no significant difference in the number of parameters of the finalized networks. For example, the required number of parameters for the network with the flow constant $M = 3,5,7$ is 2.77, 4.23, and 5.38, respectively. This demonstrates that the proposed flow-based reduction algorithm is effective in removing low-relative parameters while maintaining performance. Specifically, we observe that the total performance of our framework with $M = 7$ is slightly better than the $M = 9$ setup in Tab. 2 despite its smaller architecture search space. To investigate this, + +we further analyze the tendency in performance and computational complexity with respect to the flow constant in Sec. 4.4. + +# 4.3. Analysis of Topologies and Task Correlation + +To demonstrate the effectiveness of the proposed learning mechanism, we visualize our finalized sub-network topologies in Fig. 3-(a-c) and the adjacency matrix for NYU-v2 3-task learning in Fig. 3-(d). We also analyze the diversity and capacity of task-adaptive network topologies in Tab. 5 with network depth $\mathcal{D}$ , width $\mathcal{W}$ , and sparsity $\mathcal{S}$ described in Sec. 3.1. These analyses provide three key observations on our task-adaptive network and the correlation among tasks. + +First, the tasks of segmentation and surface normal hardly share network parameters. Various task-sharing patterns are configured at the edge, but there is only one sharing layer between the two tasks. This experiment shows a low relationship between tasks, as it is widely known that the proportion of shared parameters between tasks indicates task correlation [22, 29, 38]. + +Second, long skip connections are mostly lost. The length of the longest skip connection in the finalized network is 5, and the number of these connections is 2 out of 18 layers, even with the flow constant of 7. This phenomenon is observed not only in NYU-v2 datasets but also in the other MTL datasets. This can be evidence that the proposed flow-restriction reduces search time while maintaining high performance even by eliminating the long skip connection in the DAG-based central network. + +Lastly, Depth estimation task requires more network resources than segmentation and surface normal estimation tasks. We analyze the network topologies of the finalized sub-network of each task in NYU-v2 datasets using three components defined in Sec. 3. The depth $\mathcal{D}$ and width $\mathcal{W}$ of the sub-network increase in the order of semantic segmentation, surface normal prediction, and depth estimation tasks. Likewise, the sparsity $\mathcal{S}$ of the depth network is the highest. This experiment shows that the depth network is the task that requires the most network resources. + +# 4.4. Performance w.r.t. Flow-restriction + +We analyze performance and computational complexity with respect to the flow constant $M$ for the NYU-v2 and Cityscapes datasets. We report the rate of performance degradation with respect to the complete DAG search space in Fig. 4. We observe that the reduction rate of the final performance does not exceed $3\%$ even with considerably lower flow constants. The performance is saturated at a flow constant of about 7 or more. This means that the proposed method optimizes the task adaptive sub-network regardless of the size of the network search space, if it satisfies the minimum required size. + +![](images/f99b551058ea1a5578eff9d3380fbed19b51679d90f7b930038f2cedc89aaeff.jpg) +Figure 4. Model performance with respect to the proposed flow-restriction. We plot the degradation ratio of the performance (left y-axis) and parameter (right y-axis) by changing the flow constant $M$ . We measure the final averaged task performance with NYU-v2 and Cityscapes datasets marked by purple and pink circle markers, respectively. We also measure the number of parameters marked by gray square markers. + +To demonstrate the effectiveness of our flow-based reduction (FBR) algorithm, we compare it to two other reduction algorithms (random and threshold) for Cityscapes datasets in Fig. 5. The random reduction literally removes the edges randomly, and the thresholding method sequentially removes the edge which has the lowest value in the adjacency matrix $\Gamma$ . We measure the rate of performance degradation of the pruned network of each reduction algorithm with respect to the non-reduced network while changing the sparsity $S$ . Note that our method automatically determines the sparsity, so for this experiment only, we add a termination condition that stops the network search when a certain sparsity is met. The results show that the proposed flow-reduction method retains performance even with a low sparsity rate. This means that our method efficiently prunes the low-related edge of the network compared to the other methods. + +# 4.5. Ablation Study on Proposed Modules + +We conduct ablation studies on the four key components of our framework; the flow-restriction, read-in/out layers, flow-based reduction, and squeeze loss. We report the relative task performance and the number of parameters of the finalized network with/without the components in Tab. 6. The results show that our framework, including all components, achieves the lowest number of parameters and the second-best performance. Our method without flow-based reduction achieves the best performance. However, the finalized network from this setup has about a five-times larger number of parameters than ours because the network has never been pruned in a training process. This demonstrates that our restricted DAG-based central network is optimized + +![](images/b5d16cf1a474ad815b6d8330a98a0086d8abf203cd0b4aa0d44f4069098427e6.jpg) +Figure 5. Model Performance with respect to the network sparsity. We plot the performance degradation rate by changing network sparsity. We compare our flow-based reduction algorithm to two other schemes; random selection and thresholding. + +
MethodΔTsem↑ΔTdep↑ΔTnorm↑ΔT# of Param ↓
Ours (M=7)+13.4+9.2+10.7+11.11.31
w/o flow-restriction+13.2+9.2+10.4+11.01.80
w/o read-in/out+11.7+8.3+10.4+10.11.43
w/o flow-based reduction+14.2+9.2+11.1+11.56.50
w/o Lsq+13.2+8.8+10.7+10.91.38
+ +Table 6. Ablation study on the proposed modules (NYU-v2). + +to build compact task-adaptive sub-networks with performance close to the optimized sub-network from a complete DAG-based network. + +# 5. Conclusions + +In this paper, we present a new MTL framework to search for task-adaptive network structures across diverse network topologies in a single network. We propose flow restriction to solve the scalability issue in a complete DAG search space while maintaining the diverse network topological representation of the DAG search space by adopting read-in/out layers. We also introduce a flow-based reduction algorithm that prunes the network efficiently while maintaining overall task performance and squeeze loss, limiting the upper bound on the number of network parameters. The extensive experiments demonstrate that the submodule and schemes of our framework efficiently improve both the performance and compactness of the network. Our method compactly constructs various task-specific subnetworks in a single network and achieves the best performance among all the competitive methods on four MTL benchmark datasets. + +# Acknowledgement + +This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. RS-2023-00210908). + +# References + +[1] Chanho Ahn, Eunwoo Kim, and Songhwai Oh. Deep elastic networks with model selection for multi-task learning. In Proceedings of the IEEE/CVF international conference on computer vision, pages 6529-6538, 2019. 5, 6 +[2] Bowen Baker, Otkrist Gupta, Nikhil Naik, and Ramesh Raskar. Designing neural network architectures using reinforcement learning. arXiv preprint arXiv:1611.02167, 2016. 2 +[3] Hakan Bilen and Andrea Vedaldi. Integrated perception with recurrent multi-task neural networks. Advances in neural information processing systems, 29, 2016. 1, 2 +[4] Han Cai, Ligeng Zhu, and Song Han. 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Introduction" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 457, + 287, + 601 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 457, + 287, + 601 + ], + "spans": [ + { + "bbox": [ + 46, + 457, + 287, + 601 + ], + "type": "text", + "content": "Multi-task learning (MTL), which learns multiple tasks simultaneously with a single model has gained increasing attention [3, 13, 14]. MTL improves the generalization performance of tasks while limiting the total number of network parameters to a lower level by sharing representations across tasks. However, as the number of tasks increases, it becomes more difficult for the model to learn the shared representations, and improper sharing between less related tasks causes negative transfers that sacrifice the performance of multiple tasks [15,36]. 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They primarily focus on finding branching" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 232, + 545, + 292 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 232, + 545, + 292 + ], + "spans": [ + { + "bbox": [ + 306, + 232, + 545, + 292 + ], + "type": "text", + "content": "patterns in specific aspects of the architecture, and feature-sharing ratios across tasks. However, exploring optimized structures in restricted network topologies has the potential to cause performance degradation in heterogeneous MTL scenarios due to unbalanced task complexity." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 293, + 546, + 400 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 293, + 546, + 400 + ], + "spans": [ + { + "bbox": [ + 304, + 293, + 546, + 400 + ], + "type": "text", + "content": "We present a new MTL framework searching for subnetwork structures, optimized for each task across diverse network topologies in a single network. To search the graph topologies from richer search space, we apply Directed Acyclic Graph (DAG) for the homo/heterogeneous MTL frameworks, inspired by the work in NAS [19, 27, 40]. The MTL in the DAG search space causes a scalability issue, where the number of parameters and search time increase quadratically as the number of hidden states increases." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 401, + 547, + 556 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 401, + 547, + 556 + ], + "spans": [ + { + "bbox": [ + 304, + 401, + 547, + 556 + ], + "type": "text", + "content": "To solve this problem, we design a restricted DAG-based central network with read-in/read-out layers that allow our MTL framework to search across diverse graph topologies while limiting the search space and search time. Our flow-restriction eliminates the low-importance long skip connection among network structures for each task, and creates the required number of parameters from " + }, + { + "bbox": [ + 304, + 401, + 547, + 556 + ], + "type": "inline_equation", + "content": "O(N^2)" + }, + { + "bbox": [ + 304, + 401, + 547, + 556 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 304, + 401, + 547, + 556 + ], + "type": "inline_equation", + "content": "O(N)" + }, + { + "bbox": [ + 304, + 401, + 547, + 556 + ], + "type": "text", + "content": ". The read-in layer is the layer that directly connects all the hidden states from the input state, and the read-out layer is the layer that connects all the hidden states to the last feature layer. These are key to having various network topological representations, such as polytree structures, with early-exiting and multi-embedding." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 558, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 558, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 558, + 547, + 713 + ], + "type": "text", + "content": "Then, we optimize the central network to have compact task-adaptive sub-networks using a three-stage training procedure. To accomplish this, we propose a squeeze loss and a flow-based reduction algorithm. The squeeze loss limits the upper bound on the number of parameters. The reduction algorithm prunes the network based on the weighted adjacency matrix measured by the amount of information flow in each layer. In the end, our MTL framework constructs a compact single network that serves as multiple task-specific networks with unique structures, such as chain, polytree, and parallel diverse topologies, as presented in Fig. 1b. It also dynamically controls the amount of sharing representation among tasks." + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 703, + 135, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 703, + 135, + 712 + ], + "spans": [ + { + "bbox": [ + 58, + 703, + 135, + 712 + ], + "type": "text", + "content": "*Corresponding author" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "type": "text", + "content": "3779" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 72, + 89, + 210, + 153 + ], + "blocks": [ + { + "bbox": [ + 71, + 78, + 138, + 87 + ], + "lines": [ + { + "bbox": [ + 71, + 78, + 138, + 87 + ], + "spans": [ + { + "bbox": [ + 71, + 78, + 138, + 87 + ], + "type": "text", + "content": "(i). 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Graph representation of various neural networks. (a) Graph representation of existing dynamic neural network for multitask learning and ours. (b) Topologies of a completed Directed Acyclic Graph (DAG) and the output sub-graph of DAG structure." + } + ] + } + ], + "index": 20, + "angle": 0, + "type": "image_caption" + } + ], + "index": 18 + }, + { + "bbox": [ + 46, + 296, + 287, + 367 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 296, + 287, + 367 + ], + "spans": [ + { + "bbox": [ + 46, + 296, + 287, + 367 + ], + "type": "text", + "content": "The experiments demonstrate that our framework successfully searches the task-adaptive network topologies of each task and leverages the knowledge among tasks to make a generalized feature. The proposed method outperforms state-of-the-art methods on all common benchmark datasets for MTL. Our contributions can be summarized as follows:" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 58, + 375, + 287, + 515 + ], + "type": "list", + "angle": 0, + "index": 25, + "blocks": [ + { + "bbox": [ + 58, + 375, + 287, + 422 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 375, + 287, + 422 + ], + "spans": [ + { + "bbox": [ + 58, + 375, + 287, + 422 + ], + "type": "text", + "content": "- We present for the first time an MTL framework that searches both task-adaptive structures and sharing patterns among tasks. It achieves state-of-the-art performance on all public MTL datasets." + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 58, + 427, + 287, + 475 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 427, + 287, + 475 + ], + "spans": [ + { + "bbox": [ + 58, + 427, + 287, + 475 + ], + "type": "text", + "content": "- We propose a new DAG-based central network composed of a flow restriction scheme and read-in/out layers, that has diverse graph topologies in a reasonably restricted search space." + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 58, + 479, + 286, + 515 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 479, + 286, + 515 + ], + "spans": [ + { + "bbox": [ + 58, + 479, + 286, + 515 + ], + "type": "text", + "content": "- We introduce a new training procedure that optimizes the MTL framework for compactly constructing various task-specific sub-networks in a single network." + } + ] + } + ], + "index": 24 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 47, + 526, + 138, + 538 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 526, + 138, + 538 + ], + "spans": [ + { + "bbox": [ + 47, + 526, + 138, + 538 + ], + "type": "text", + "content": "2. Related Works" + } + ] + } + ], + "index": 26 + }, + { + "bbox": [ + 46, + 545, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 545, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 545, + 287, + 713 + ], + "type": "text", + "content": "Neural Architecture Search (NAS) Neural Architecture Search is a method that automates neural architecture engineering [8]. Early works [2, 40, 41] use reinforcement learning based on rewarding the model accuracy of the generated architecture. Alternative approaches [24, 30, 37] employ evolutionary algorithms to optimize both the neural architecture and its weights. These methods search for an adequate neural architecture in a large discrete space. Gradient-based NAS methods [4, 19, 39] of formulating operations in a differentiable search space are proposed to alleviate the scalability issues. They generally use the convex combination from a set of operations instead of determining a single operation. Most NAS approaches [19, 27, 40] adopt the complete DAG as a search space, to find the architecture" + } + ] + } + ], + "index": 27 + }, + { + "bbox": [ + 304, + 296, + 545, + 331 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 296, + 545, + 331 + ], + "spans": [ + { + "bbox": [ + 304, + 296, + 545, + 331 + ], + "type": "text", + "content": "in the various network topologies. However, DAG-based MTL frameworks have not been proposed, because of their considerably high computational demands." + } + ] + } + ], + "index": 28 + }, + { + "bbox": [ + 304, + 332, + 546, + 450 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 332, + 546, + 450 + ], + "spans": [ + { + "bbox": [ + 304, + 332, + 546, + 450 + ], + "type": "text", + "content": "Multi-Task Learning (MTL) Multi-task learning in deep neural networks can be categorized into hard and soft parameter sharing types [31]. Hard parameter sharing [3, 13, 14], also known as shared-bottom, is the most commonly used approach to MTL. This scheme improves generalization performance while reducing the computational cost of the network, by using shared hidden layers between all tasks. However, it typically struggles with the negative transfer problem [15, 36] which degrades performance due to improper sharing between less relevant tasks." + } + ] + } + ], + "index": 29 + }, + { + "bbox": [ + 304, + 450, + 545, + 545 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 450, + 545, + 545 + ], + "spans": [ + { + "bbox": [ + 304, + 450, + 545, + 545 + ], + "type": "text", + "content": "On the other hand, soft-parameter sharing [25, 32] alleviate the negative transfer problem by changing the shared parameter ratio. These approaches mitigate the negative transfer by flexibly modifying shared information, but they cannot maintain the computational advantage on the classic shared-bottom model. Recently, advanced approaches have been proposed to adjust shared parameters using a dynamic neural network [21, 22, 29, 38] and NAS [10]." + } + ] + } + ], + "index": 30 + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "text", + "content": "NAS-style MTL MTL frameworks using a dynamic neural network (DNN) can be divided into two categories. One employs the Mixture-of-Experts (MoE) [33], which is designed for conditional computation of per-sample, to MTL by determining the experts of each task [9, 21, 22]. They have a fixed depth finalized task-specific sub-network, because they choose experts from a fixed number of modular layers. This causes a critical issue with task-balancing in the heterogeneous MTL. The other adopts the skip-or-select policy to select task-specific blocks from the set of residual blocks [38] or a shared block per layer [12, 29]. These methods only create a simple serial path in the finalized subnetwork of each task, and a parallel link cannot be reproduced. Moreover, they heuristically address the unbalanced" + } + ] + } + ], + "index": 31 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "3780" + } + ] + } + ], + "index": 32 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 131 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 131 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 131 + ], + "type": "text", + "content": "task-wise complexity issues in the heterogenous MTL (e.g. manually changing the balancing parameters based on the task complexity [29,38]). Thus, none of the aforementioned works focus on finding the optimal task-specific structure in the MTL scenario." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 142, + 102, + 154 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 142, + 102, + 154 + ], + "spans": [ + { + "bbox": [ + 47, + 142, + 102, + 154 + ], + "type": "text", + "content": "3. Method" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 162, + 288, + 293 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 162, + 288, + 293 + ], + "spans": [ + { + "bbox": [ + 46, + 162, + 288, + 293 + ], + "type": "text", + "content": "We describe our MTL framework, which searches for optimized network structures tailored to each task across diverse graph topologies, while limiting search time. Sec. 3.1 describes the composition of the searchable space of our central network and our flow-restriction method for efficiently balancing the topological diversity of task-specific sub-networks and searching space. Sec. 3.2 introduces our mechanism to determine the task-adaptive sub-network in the central network and describes the overall training process and loss function. The overall pipeline of our method is illustrated in Fig. 2." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 300, + 285, + 313 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 300, + 285, + 313 + ], + "spans": [ + { + "bbox": [ + 47, + 300, + 285, + 313 + ], + "type": "text", + "content": "3.1. The Central Network with Diverse Topologies" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 319, + 287, + 354 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 319, + 287, + 354 + ], + "spans": [ + { + "bbox": [ + 46, + 319, + 287, + 354 + ], + "type": "text", + "content": "Our central network composes a graph " + }, + { + "bbox": [ + 46, + 319, + 287, + 354 + ], + "type": "inline_equation", + "content": "G = (V, E)" + }, + { + "bbox": [ + 46, + 319, + 287, + 354 + ], + "type": "text", + "content": " with layers " + }, + { + "bbox": [ + 46, + 319, + 287, + 354 + ], + "type": "inline_equation", + "content": "E" + }, + { + "bbox": [ + 46, + 319, + 287, + 354 + ], + "type": "text", + "content": " in which the " + }, + { + "bbox": [ + 46, + 319, + 287, + 354 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 319, + 287, + 354 + ], + "type": "text", + "content": " hidden states " + }, + { + "bbox": [ + 46, + 319, + 287, + 354 + ], + "type": "inline_equation", + "content": "V = \\{v_1, \\dots, v_N\\}" + }, + { + "bbox": [ + 46, + 319, + 287, + 354 + ], + "type": "text", + "content": " are topologically sorted:" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 92, + 362, + 287, + 376 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 92, + 362, + 287, + 376 + ], + "spans": [ + { + "bbox": [ + 92, + 362, + 287, + 376 + ], + "type": "interline_equation", + "content": "E = \\left\\{e _ {i j} \\right\\} _ {i, j \\in \\{1, \\dots , N \\}}, \\text {w h e r e} i < j, \\tag {1}", + "image_path": "f3e361eeeb7a8b8940a97398cc7a016f4e2e7a85c498c002554bf0e2eaa371b5.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 108, + 377, + 287, + 392 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 108, + 377, + 287, + 392 + ], + "spans": [ + { + "bbox": [ + 108, + 377, + 287, + 392 + ], + "type": "interline_equation", + "content": "e _ {i j} (\\cdot ; \\theta_ {i j}): \\mathbb {R} ^ {N ^ {v _ {i}}} \\rightarrow \\mathbb {R} ^ {N ^ {v _ {j}}}, \\tag {2}", + "image_path": "9dca3b19e97440d3be7c738f42eae8b5b0eef5d9b56698d95d883058784fe942.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 399, + 287, + 495 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 399, + 287, + 495 + ], + "spans": [ + { + "bbox": [ + 46, + 399, + 287, + 495 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 399, + 287, + 495 + ], + "type": "inline_equation", + "content": "e_{ij}" + }, + { + "bbox": [ + 46, + 399, + 287, + 495 + ], + "type": "text", + "content": " is the operation that transfers the state " + }, + { + "bbox": [ + 46, + 399, + 287, + 495 + ], + "type": "inline_equation", + "content": "v_{i}" + }, + { + "bbox": [ + 46, + 399, + 287, + 495 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 46, + 399, + 287, + 495 + ], + "type": "inline_equation", + "content": "v_{j}" + }, + { + "bbox": [ + 46, + 399, + 287, + 495 + ], + "type": "text", + "content": " with the weight parameters " + }, + { + "bbox": [ + 46, + 399, + 287, + 495 + ], + "type": "inline_equation", + "content": "\\theta_{ij} \\in \\Theta" + }, + { + "bbox": [ + 46, + 399, + 287, + 495 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 46, + 399, + 287, + 495 + ], + "type": "inline_equation", + "content": "N^{v_k}" + }, + { + "bbox": [ + 46, + 399, + 287, + 495 + ], + "type": "text", + "content": " is the number of the elements of hidden state " + }, + { + "bbox": [ + 46, + 399, + 287, + 495 + ], + "type": "inline_equation", + "content": "v_{k}" + }, + { + "bbox": [ + 46, + 399, + 287, + 495 + ], + "type": "text", + "content": ", respectively. We adopt the DAG structure [19, 27, 40] for the network. However, the optimized structure from DAG is searched from " + }, + { + "bbox": [ + 46, + 399, + 287, + 495 + ], + "type": "inline_equation", + "content": "2^{N(N - 1) / 2}" + }, + { + "bbox": [ + 46, + 399, + 287, + 495 + ], + "type": "text", + "content": " network topologies, which are too large to be optimized in time. To address the issue while maintaining diversity, we propose a flow-restriction and read-in/read-out layers." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 495, + 287, + 578 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 495, + 287, + 578 + ], + "spans": [ + { + "bbox": [ + 46, + 495, + 287, + 578 + ], + "type": "text", + "content": "Flow-restriction The flow-restriction eliminates the low-importance long skip connection among network structures for each task by restricting " + }, + { + "bbox": [ + 46, + 495, + 287, + 578 + ], + "type": "inline_equation", + "content": "j - i \\leq M" + }, + { + "bbox": [ + 46, + 495, + 287, + 578 + ], + "type": "text", + "content": " where " + }, + { + "bbox": [ + 46, + 495, + 287, + 578 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 46, + 495, + 287, + 578 + ], + "type": "text", + "content": " is the flow constant. Regulating the searchable edges in the graph reduces the required number of parameters and searching time from " + }, + { + "bbox": [ + 46, + 495, + 287, + 578 + ], + "type": "inline_equation", + "content": "O(N^2)" + }, + { + "bbox": [ + 46, + 495, + 287, + 578 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 46, + 495, + 287, + 578 + ], + "type": "inline_equation", + "content": "O(N)" + }, + { + "bbox": [ + 46, + 495, + 287, + 578 + ], + "type": "text", + "content": ", but it sacrifices the diversity and capacity of the network topologies." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 579, + 287, + 614 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 579, + 287, + 614 + ], + "spans": [ + { + "bbox": [ + 46, + 579, + 287, + 614 + ], + "type": "text", + "content": "To explain the topological diversity and task capacity of sub-networks, we define the three components of network topology, as follows:" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 54, + 620, + 240, + 672 + ], + "type": "list", + "angle": 0, + "index": 13, + "blocks": [ + { + "bbox": [ + 55, + 620, + 240, + 635 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 55, + 620, + 240, + 635 + ], + "spans": [ + { + "bbox": [ + 55, + 620, + 240, + 635 + ], + "type": "text", + "content": "1. " + }, + { + "bbox": [ + 55, + 620, + 240, + 635 + ], + "type": "inline_equation", + "content": "\\mathcal{D}(G) = \\max (\\{\\mathrm{Distance}(v_i,v_j)\\}_{v_i,v_j\\in V})," + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 54, + 639, + 190, + 653 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 54, + 639, + 190, + 653 + ], + "spans": [ + { + "bbox": [ + 54, + 639, + 190, + 653 + ], + "type": "text", + "content": "2. " + }, + { + "bbox": [ + 54, + 639, + 190, + 653 + ], + "type": "inline_equation", + "content": "\\mathcal{W}(G) = \\max (\\{\\mathrm{Out}_{v_i}\\}_{v_i\\in V})," + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 54, + 658, + 160, + 672 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 54, + 658, + 160, + 672 + ], + "spans": [ + { + "bbox": [ + 54, + 658, + 160, + 672 + ], + "type": "text", + "content": "3. " + }, + { + "bbox": [ + 54, + 658, + 160, + 672 + ], + "type": "inline_equation", + "content": "S(G_{s},G) = |E_{s}| / |E|" + } + ] + } + ], + "index": 12 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\mathrm{Out}_{v_i}" + }, + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "text", + "content": " is the out-degree of the vertex " + }, + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "inline_equation", + "content": "v_i" + }, + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\mathrm{Distance}(\\cdot)" + }, + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "text", + "content": " is the operation that counts the number of layers (or edges) between two connected vertices. The network" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 72, + 545, + 204 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 204 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 204 + ], + "type": "text", + "content": "depth " + }, + { + "bbox": [ + 304, + 72, + 545, + 204 + ], + "type": "inline_equation", + "content": "\\mathcal{D}(G)" + }, + { + "bbox": [ + 304, + 72, + 545, + 204 + ], + "type": "text", + "content": " is equal to the longest distance between two vertices in the graph " + }, + { + "bbox": [ + 304, + 72, + 545, + 204 + ], + "type": "inline_equation", + "content": "G" + }, + { + "bbox": [ + 304, + 72, + 545, + 204 + ], + "type": "text", + "content": ". The network width " + }, + { + "bbox": [ + 304, + 72, + 545, + 204 + ], + "type": "inline_equation", + "content": "\\mathcal{W}(G)" + }, + { + "bbox": [ + 304, + 72, + 545, + 204 + ], + "type": "text", + "content": " is equal to the maximum value of the out-degrees of hidden states in the graph " + }, + { + "bbox": [ + 304, + 72, + 545, + 204 + ], + "type": "inline_equation", + "content": "G" + }, + { + "bbox": [ + 304, + 72, + 545, + 204 + ], + "type": "text", + "content": ". The sparsity " + }, + { + "bbox": [ + 304, + 72, + 545, + 204 + ], + "type": "inline_equation", + "content": "\\mathcal{S}(G_s, G)" + }, + { + "bbox": [ + 304, + 72, + 545, + 204 + ], + "type": "text", + "content": " of the sub-graph " + }, + { + "bbox": [ + 304, + 72, + 545, + 204 + ], + "type": "inline_equation", + "content": "G_s" + }, + { + "bbox": [ + 304, + 72, + 545, + 204 + ], + "type": "text", + "content": " is the ratio of finalized edges " + }, + { + "bbox": [ + 304, + 72, + 545, + 204 + ], + "type": "inline_equation", + "content": "|E_s|" + }, + { + "bbox": [ + 304, + 72, + 545, + 204 + ], + "type": "text", + "content": " over entire edges " + }, + { + "bbox": [ + 304, + 72, + 545, + 204 + ], + "type": "inline_equation", + "content": "|E|" + }, + { + "bbox": [ + 304, + 72, + 545, + 204 + ], + "type": "text", + "content": ". The first two components are measurements of the topological diversity of the finalized sub-network, while the last one is for the sub-network capacity. While a complete DAG has the full range of depth and width components, the flow-restricted DAG has the properties of depth and width components as follows:" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 212, + 505, + 225 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 212, + 505, + 225 + ], + "spans": [ + { + "bbox": [ + 305, + 212, + 505, + 225 + ], + "type": "interline_equation", + "content": "\\text {P r o p e r t y 1 .} \\min (\\{\\mathcal {D} (G _ {s}) \\} _ {G _ {s} \\subseteq G}) = \\lceil (| V | / M) \\rceil ,", + "image_path": "622ca9016ce444c49a60045a5a0e6ee57faef7c456ca18ce75db7105d8535c8e.jpg" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 232, + 474, + 245 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 232, + 474, + 245 + ], + "spans": [ + { + "bbox": [ + 306, + 232, + 474, + 245 + ], + "type": "interline_equation", + "content": "\\text {P r o p e r t y 2 .} \\max (\\{\\mathcal {W} (G _ {s}) \\} _ {G _ {s} \\subseteq G}) = M,", + "image_path": "2a154d722775fba2abc527c9a93068f2c12d6181b7d66bb57b030601287320fe.jpg" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 252, + 545, + 312 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 252, + 545, + 312 + ], + "spans": [ + { + "bbox": [ + 304, + 252, + 545, + 312 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 252, + 545, + 312 + ], + "type": "inline_equation", + "content": "\\{G_s\\}" + }, + { + "bbox": [ + 304, + 252, + 545, + 312 + ], + "type": "text", + "content": " is the entire sub-graph of " + }, + { + "bbox": [ + 304, + 252, + 545, + 312 + ], + "type": "inline_equation", + "content": "G" + }, + { + "bbox": [ + 304, + 252, + 545, + 312 + ], + "type": "text", + "content": ". The min-depth property (Prop. 1) can cause the over-parameterized problem when the capacity of the task is extremely low. The max-width property (Prop. 2) directly sacrifices the diversity of network topologies in the search space." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 305, + 312, + 545, + 373 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 312, + 545, + 373 + ], + "spans": [ + { + "bbox": [ + 305, + 312, + 545, + 373 + ], + "type": "text", + "content": "Read-in/Read-out layers We design read-in/read-out layers to mitigate these problems. The read-in layer embeds the input state " + }, + { + "bbox": [ + 305, + 312, + 545, + 373 + ], + "type": "inline_equation", + "content": "v_{0}" + }, + { + "bbox": [ + 305, + 312, + 545, + 373 + ], + "type": "text", + "content": " into all hidden states " + }, + { + "bbox": [ + 305, + 312, + 545, + 373 + ], + "type": "inline_equation", + "content": "v_{i} \\in V" + }, + { + "bbox": [ + 305, + 312, + 545, + 373 + ], + "type": "text", + "content": " with task-specific weights " + }, + { + "bbox": [ + 305, + 312, + 545, + 373 + ], + "type": "inline_equation", + "content": "\\alpha_{i}^{k} \\in \\mathcal{A}" + }, + { + "bbox": [ + 305, + 312, + 545, + 373 + ], + "type": "text", + "content": " for all " + }, + { + "bbox": [ + 305, + 312, + 545, + 373 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 305, + 312, + 545, + 373 + ], + "type": "text", + "content": " tasks " + }, + { + "bbox": [ + 305, + 312, + 545, + 373 + ], + "type": "inline_equation", + "content": "\\mathcal{T} = \\{T_k\\}_{k \\in \\{1, \\dots, K\\}}" + }, + { + "bbox": [ + 305, + 312, + 545, + 373 + ], + "type": "text", + "content": " as follows:" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 390, + 382, + 545, + 397 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 390, + 382, + 545, + 397 + ], + "spans": [ + { + "bbox": [ + 390, + 382, + 545, + 397 + ], + "type": "interline_equation", + "content": "v _ {i} ^ {k} = \\sigma \\left(\\alpha_ {i} ^ {k}\\right) \\cdot v _ {0}, \\tag {3}", + "image_path": "31a6075800a94d2fbe26eab26f0c5de18f36fc36c3eec850ab6142218e2508e9.jpg" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 304, + 402, + 545, + 441 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 402, + 545, + 441 + ], + "spans": [ + { + "bbox": [ + 304, + 402, + 545, + 441 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 402, + 545, + 441 + ], + "type": "inline_equation", + "content": "\\sigma (\\cdot)" + }, + { + "bbox": [ + 304, + 402, + 545, + 441 + ], + "type": "text", + "content": " is the sigmoid function. Then, the central network sequentially updates the hidden state " + }, + { + "bbox": [ + 304, + 402, + 545, + 441 + ], + "type": "inline_equation", + "content": "v_{1}^{k}" + }, + { + "bbox": [ + 304, + 402, + 545, + 441 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 304, + 402, + 545, + 441 + ], + "type": "inline_equation", + "content": "v_{N}^{k}" + }, + { + "bbox": [ + 304, + 402, + 545, + 441 + ], + "type": "text", + "content": " with the task-specific weights " + }, + { + "bbox": [ + 304, + 402, + 545, + 441 + ], + "type": "inline_equation", + "content": "\\gamma_{ij}^{k}\\in \\Gamma" + }, + { + "bbox": [ + 304, + 402, + 545, + 441 + ], + "type": "text", + "content": " that correspond to " + }, + { + "bbox": [ + 304, + 402, + 545, + 441 + ], + "type": "inline_equation", + "content": "e_{ij}^{k}" + }, + { + "bbox": [ + 304, + 402, + 545, + 441 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 345, + 449, + 545, + 479 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 345, + 449, + 545, + 479 + ], + "spans": [ + { + "bbox": [ + 345, + 449, + 545, + 479 + ], + "type": "interline_equation", + "content": "v _ {j} ^ {k} = \\frac {1}{\\operatorname {I n} _ {v _ {j} ^ {k}}} \\sum_ {e _ {i j} \\in E} \\left(\\sigma \\left(\\gamma_ {i j} ^ {k}\\right) \\cdot e _ {i j} \\left(v _ {i} ^ {k}; \\theta_ {i j}\\right)\\right), \\tag {4}", + "image_path": "56647c02e7a30690a05ebd7bea731a877d66c67d871715f37d05092dd1d05432.jpg" + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 304, + 489, + 545, + 552 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 489, + 545, + 552 + ], + "spans": [ + { + "bbox": [ + 304, + 489, + 545, + 552 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 489, + 545, + 552 + ], + "type": "inline_equation", + "content": "\\operatorname{In}_{v_j^k}" + }, + { + "bbox": [ + 304, + 489, + 545, + 552 + ], + "type": "text", + "content": " is the in-degree of " + }, + { + "bbox": [ + 304, + 489, + 545, + 552 + ], + "type": "inline_equation", + "content": "v_{j}^{k}" + }, + { + "bbox": [ + 304, + 489, + 545, + 552 + ], + "type": "text", + "content": ". Note that " + }, + { + "bbox": [ + 304, + 489, + 545, + 552 + ], + "type": "inline_equation", + "content": "\\Gamma" + }, + { + "bbox": [ + 304, + 489, + 545, + 552 + ], + "type": "text", + "content": " is the adjacency matrix of graph " + }, + { + "bbox": [ + 304, + 489, + 545, + 552 + ], + "type": "inline_equation", + "content": "G" + }, + { + "bbox": [ + 304, + 489, + 545, + 552 + ], + "type": "text", + "content": ". Finally, the read-out layer aggregates all hidden state features " + }, + { + "bbox": [ + 304, + 489, + 545, + 552 + ], + "type": "inline_equation", + "content": "\\{v_{i}^{k}\\}_{i\\in \\{1,\\dots,N\\}}" + }, + { + "bbox": [ + 304, + 489, + 545, + 552 + ], + "type": "text", + "content": " with the task-specific weights " + }, + { + "bbox": [ + 304, + 489, + 545, + 552 + ], + "type": "inline_equation", + "content": "\\beta_i^k\\in \\mathcal{B}" + }, + { + "bbox": [ + 304, + 489, + 545, + 552 + ], + "type": "text", + "content": " and produces the last layer feature " + }, + { + "bbox": [ + 304, + 489, + 545, + 552 + ], + "type": "inline_equation", + "content": "v_{L}^{k}" + }, + { + "bbox": [ + 304, + 489, + 545, + 552 + ], + "type": "text", + "content": " for each task " + }, + { + "bbox": [ + 304, + 489, + 545, + 552 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 304, + 489, + 545, + 552 + ], + "type": "text", + "content": " as follows:" + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 365, + 561, + 545, + 588 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 365, + 561, + 545, + 588 + ], + "spans": [ + { + "bbox": [ + 365, + 561, + 545, + 588 + ], + "type": "interline_equation", + "content": "v _ {L} ^ {k} = \\sum_ {i \\in \\{1, \\dots , N \\}} \\left(\\sigma \\left(\\beta_ {i} ^ {k}\\right) \\cdot v _ {i} ^ {k}\\right). \\tag {5}", + "image_path": "72f130547c63fdc730548fbeb55decc9de276c127058ec00baa24ab8bb0aaaac.jpg" + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 304, + 597, + 545, + 633 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 597, + 545, + 633 + ], + "spans": [ + { + "bbox": [ + 304, + 597, + 545, + 633 + ], + "type": "text", + "content": "The final prediction " + }, + { + "bbox": [ + 304, + 597, + 545, + 633 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{y}}_k" + }, + { + "bbox": [ + 304, + 597, + 545, + 633 + ], + "type": "text", + "content": " for each task " + }, + { + "bbox": [ + 304, + 597, + 545, + 633 + ], + "type": "inline_equation", + "content": "T_{k}" + }, + { + "bbox": [ + 304, + 597, + 545, + 633 + ], + "type": "text", + "content": " is computed by passing the aggregated features " + }, + { + "bbox": [ + 304, + 597, + 545, + 633 + ], + "type": "inline_equation", + "content": "v_{L}^{k}" + }, + { + "bbox": [ + 304, + 597, + 545, + 633 + ], + "type": "text", + "content": " through the task-specific head " + }, + { + "bbox": [ + 304, + 597, + 545, + 633 + ], + "type": "inline_equation", + "content": "H^{k}(\\cdot)" + }, + { + "bbox": [ + 304, + 597, + 545, + 633 + ], + "type": "text", + "content": " as follows:" + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 393, + 641, + 545, + 657 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 393, + 641, + 545, + 657 + ], + "spans": [ + { + "bbox": [ + 393, + 641, + 545, + 657 + ], + "type": "interline_equation", + "content": "\\hat {\\mathbf {y}} ^ {k} = H ^ {k} \\left(v _ {L} ^ {k}\\right). \\tag {6}", + "image_path": "223f169fa1738ea389bfd94e429f1fdb2ec8587e42bf21caff3f9feda8581291.jpg" + } + ] + } + ], + "index": 26 + }, + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "content": "All upper-level parameters " + }, + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{A},\\mathcal{B}" + }, + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\Gamma" + }, + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "content": " are learnable parameters, and their learning process is described in Sec. 3.2. The read-in/read-out layers enable the optimized network to have a multi-input/output sub-network. The read-out layer" + } + ] + } + ], + "index": 27 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "type": "text", + "content": "3781" + } + ] + } + ], + "index": 28 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 61, + 72, + 541, + 301 + ], + "blocks": [ + { + "bbox": [ + 61, + 72, + 541, + 301 + ], + "lines": [ + { + "bbox": [ + 61, + 72, + 541, + 301 + ], + "spans": [ + { + "bbox": [ + 61, + 72, + 541, + 301 + ], + "type": "image", + "image_path": "545018b5d6911594acd54e953845adfeb62cea15ae128f78ddf76ec4c89429e8.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 312, + 546, + 369 + ], + "lines": [ + { + "bbox": [ + 46, + 312, + 546, + 369 + ], + "spans": [ + { + "bbox": [ + 46, + 312, + 546, + 369 + ], + "type": "text", + "content": "Figure 2. Overall pipeline. Our central network follows a DAG-based structure with read-in/out layers, and task-specific heads. The long skip connection is cut by our flow-restriction. Our framework with a 3-task MTL learning scenario consists of three stages including warm-up, search, and fine-tuning stages. The warm-up stage only learns the parameters of the main network " + }, + { + "bbox": [ + 46, + 312, + 546, + 369 + ], + "type": "inline_equation", + "content": "\\Theta" + }, + { + "bbox": [ + 46, + 312, + 546, + 369 + ], + "type": "text", + "content": " and task-specific weights. The search stage learns the upper-level parameters " + }, + { + "bbox": [ + 46, + 312, + 546, + 369 + ], + "type": "inline_equation", + "content": "\\mathcal{A},\\mathcal{B},\\Gamma" + }, + { + "bbox": [ + 46, + 312, + 546, + 369 + ], + "type": "text", + "content": ", and task-specific weights. Then, flow-based reduction eliminates the low-importance edges from the network. The fine-tuning stage re-trains the network with the remaining important parameters." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 385, + 287, + 445 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 385, + 287, + 445 + ], + "spans": [ + { + "bbox": [ + 46, + 385, + 287, + 445 + ], + "type": "text", + "content": "aggregates all hidden states of the central network during the search stage, allowing a specific task to use the early hidden states to output predictions while ignoring the last few layers. These early-exit structures help alleviate the over-parameterized problem in simple tasks." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 451, + 287, + 464 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 451, + 287, + 464 + ], + "spans": [ + { + "bbox": [ + 47, + 451, + 287, + 464 + ], + "type": "text", + "content": "3.2. Network Optimization and Training Procedure" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 469, + 287, + 506 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 469, + 287, + 506 + ], + "spans": [ + { + "bbox": [ + 46, + 469, + 287, + 506 + ], + "type": "text", + "content": "We describe the entire training process for our MTL framework, which consists of three stages, including warm-up, search, and fine-tuning stages." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 506, + 287, + 648 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 506, + 287, + 648 + ], + "spans": [ + { + "bbox": [ + 46, + 506, + 287, + 648 + ], + "type": "text", + "content": "Warm-up stage As with other gradient-based NAS, our framework has upper-level parameters that determine the network structure and parameters. This bilevel optimization with a complex objective function in an MTL setup makes the training process unstable. For better convergence, we initially train all network parameters across tasks for a few iterations. We train the weight parameters of the central network " + }, + { + "bbox": [ + 46, + 506, + 287, + 648 + ], + "type": "inline_equation", + "content": "\\Theta" + }, + { + "bbox": [ + 46, + 506, + 287, + 648 + ], + "type": "text", + "content": " that shares all operations " + }, + { + "bbox": [ + 46, + 506, + 287, + 648 + ], + "type": "inline_equation", + "content": "E" + }, + { + "bbox": [ + 46, + 506, + 287, + 648 + ], + "type": "text", + "content": " across tasks. We fix all values of the upper-level parameters " + }, + { + "bbox": [ + 46, + 506, + 287, + 648 + ], + "type": "inline_equation", + "content": "\\mathcal{A},\\mathcal{B}" + }, + { + "bbox": [ + 46, + 506, + 287, + 648 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 46, + 506, + 287, + 648 + ], + "type": "inline_equation", + "content": "\\Gamma" + }, + { + "bbox": [ + 46, + 506, + 287, + 648 + ], + "type": "text", + "content": " as 0, which becomes 0.5 after the sigmoid function " + }, + { + "bbox": [ + 46, + 506, + 287, + 648 + ], + "type": "inline_equation", + "content": "\\sigma (\\cdot)" + }, + { + "bbox": [ + 46, + 506, + 287, + 648 + ], + "type": "text", + "content": ", and freeze them. We train the network parameters " + }, + { + "bbox": [ + 46, + 506, + 287, + 648 + ], + "type": "inline_equation", + "content": "\\Theta" + }, + { + "bbox": [ + 46, + 506, + 287, + 648 + ], + "type": "text", + "content": " in Eq. 4 with a task loss as follows:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 107, + 652, + 287, + 685 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 107, + 652, + 287, + 685 + ], + "spans": [ + { + "bbox": [ + 107, + 652, + 287, + 685 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\text {t a s k}} = \\sum_ {k = 0} ^ {K} \\mathcal {L} _ {T _ {k}} \\left(\\hat {\\mathbf {y}} _ {T _ {k}}, \\mathbf {y} _ {T _ {k}}\\right), \\tag {7}", + "image_path": "a3a447d486c43f45019b66255d1125f409cd50a56f22424faf540082e5f84ce0.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 689, + 287, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 712 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 712 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 689, + 287, + 712 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{T_k}" + }, + { + "bbox": [ + 47, + 689, + 287, + 712 + ], + "type": "text", + "content": " is the task-specific loss, which is the unique loss function for each task." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 385, + 545, + 456 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 385, + 545, + 456 + ], + "spans": [ + { + "bbox": [ + 304, + 385, + 545, + 456 + ], + "type": "text", + "content": "Search stage After the warm-up stage, we unfreeze the upper-level parameters " + }, + { + "bbox": [ + 304, + 385, + 545, + 456 + ], + "type": "inline_equation", + "content": "\\mathcal{A},\\mathcal{B}" + }, + { + "bbox": [ + 304, + 385, + 545, + 456 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 304, + 385, + 545, + 456 + ], + "type": "inline_equation", + "content": "\\Gamma" + }, + { + "bbox": [ + 304, + 385, + 545, + 456 + ], + "type": "text", + "content": " and search the network topologies appropriate to each task. We train all these parameters and network parameters " + }, + { + "bbox": [ + 304, + 385, + 545, + 456 + ], + "type": "inline_equation", + "content": "\\Theta" + }, + { + "bbox": [ + 304, + 385, + 545, + 456 + ], + "type": "text", + "content": " simultaneously by minimizing the task loss and the proposed squeeze loss " + }, + { + "bbox": [ + 304, + 385, + 545, + 456 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{sq}" + }, + { + "bbox": [ + 304, + 385, + 545, + 456 + ], + "type": "text", + "content": " as follows:" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 370, + 464, + 545, + 479 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 370, + 464, + 545, + 479 + ], + "spans": [ + { + "bbox": [ + 370, + 464, + 545, + 479 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\text {t r a i n}} = \\mathcal {L} _ {\\text {t a s k}} + \\lambda_ {s q} \\mathcal {L} _ {s q}, \\tag {8}", + "image_path": "e2925606ee2babaa7d9df9632f4f86f03c0cdd59b2f74b3b2d8812943b47b725.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 339, + 481, + 545, + 515 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 339, + 481, + 545, + 515 + ], + "spans": [ + { + "bbox": [ + 339, + 481, + 545, + 515 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {s q} = \\sum_ {k = 0} ^ {K} \\left(\\max \\left(\\left(\\sum_ {\\gamma_ {i j} \\in \\Gamma} \\left(\\sigma \\left(\\gamma_ {i j}\\right)\\right) - \\kappa\\right), 0\\right)\\right), \\tag {9}", + "image_path": "86d4dabb3b3e58fa28d0b468fd342fb6d5725cf3cb81f4eb7afe1987062f1fd9.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 522, + 545, + 581 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 522, + 545, + 581 + ], + "spans": [ + { + "bbox": [ + 304, + 522, + 545, + 581 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 522, + 545, + 581 + ], + "type": "inline_equation", + "content": "\\lambda_{sq}" + }, + { + "bbox": [ + 304, + 522, + 545, + 581 + ], + "type": "text", + "content": " is the balancing hyperparameter, and " + }, + { + "bbox": [ + 304, + 522, + 545, + 581 + ], + "type": "inline_equation", + "content": "\\kappa" + }, + { + "bbox": [ + 304, + 522, + 545, + 581 + ], + "type": "text", + "content": " is a constant number called the budget, that directly reduces the sparsity of the central network. This auxiliary loss is designed to encourage the model to save computational resources." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 582, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 546, + 713 + ], + "type": "text", + "content": "Fine-tuning stage. Lastly, we perform a fine-tuning stage to construct a compact and discretized network structure using the trained upper-level parameters " + }, + { + "bbox": [ + 304, + 582, + 546, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{A},\\mathcal{B}" + }, + { + "bbox": [ + 304, + 582, + 546, + 713 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 304, + 582, + 546, + 713 + ], + "type": "inline_equation", + "content": "\\Gamma" + }, + { + "bbox": [ + 304, + 582, + 546, + 713 + ], + "type": "text", + "content": ". To do so, we design a flow-based reduction algorithm that allows the network to obtain high computational speed by omitting low-importance operations, as described in Alg. 1. It measures the amount of information flow of each layer " + }, + { + "bbox": [ + 304, + 582, + 546, + 713 + ], + "type": "inline_equation", + "content": "e_{ij}" + }, + { + "bbox": [ + 304, + 582, + 546, + 713 + ], + "type": "text", + "content": " in the central network by calculating the ratio of edge weight with respect to other related edges weight. Then, it sequentially removes the edge which has the lowest information flow. Alg. 1 stops when the edge selected to be deleted is" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "3782" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "code", + "bbox": [ + 48, + 88, + 290, + 441 + ], + "blocks": [ + { + "bbox": [ + 53, + 76, + 203, + 87 + ], + "lines": [ + { + "bbox": [ + 53, + 76, + 203, + 87 + ], + "spans": [ + { + "bbox": [ + 53, + 76, + 203, + 87 + ], + "type": "text", + "content": "Algorithm 1: Flow-based Reduction" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "code_caption" + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "lines": [ + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "spans": [ + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "text", + "content": "Input: " + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "inline_equation", + "content": "\\Gamma \\in \\mathbb{R}^{N\\times N}" + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "inline_equation", + "content": "\\mathcal{A}\\in \\mathbb{R}^N" + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "inline_equation", + "content": "\\mathcal{B}\\in \\mathbb{R}^N" + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "text", + "content": " Output: " + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "inline_equation", + "content": "\\hat{\\Gamma},\\hat{\\mathcal{A}},\\hat{\\mathcal{B}} / /" + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "text", + "content": " Discretized params. \n1 initialize zero matrix " + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "inline_equation", + "content": "\\Psi ,\\hat{\\Psi}\\in \\mathbb{R}^{(N + 2)\\times (N + 2)}" + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "text", + "content": " \n2 " + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "inline_equation", + "content": "N_{\\alpha} = \\mathrm{argmax}(\\mathcal{A})" + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "text", + "content": " \n3 " + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "inline_equation", + "content": "N_{\\beta} = \\max (N_{\\alpha} + 1,\\mathrm{argmax}(\\mathcal{B}))" + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "text", + "content": " \n4 " + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "inline_equation", + "content": "\\Gamma [:N_{\\alpha},:)]\\gets 0 / /" + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "text", + "content": " remove edges " + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "inline_equation", + "content": "< N_{\\alpha}" + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "text", + "content": " \n5 " + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "inline_equation", + "content": "\\Gamma [:,N_{\\beta}]:\\gets 0 / /" + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "text", + "content": " remove edges " + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "inline_equation", + "content": ">N_{\\beta}" + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "text", + "content": " \n6 " + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "inline_equation", + "content": "\\Psi [1:N,1:N]\\gets \\Gamma /" + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "text", + "content": " merge " + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "inline_equation", + "content": "\\Gamma ,A,B" + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "text", + "content": " into " + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "inline_equation", + "content": "\\Psi" + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "text", + "content": " \n7 " + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "inline_equation", + "content": "\\Psi [0,N_{\\alpha} + 1:N_{\\beta} + 1]\\gets A[N_{\\alpha}:N_{\\beta}]" + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "text", + "content": " \n8 " + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "inline_equation", + "content": "\\Psi [N_{\\alpha} + 1:N_{\\beta} + 1,N + 1]\\gets B[N_{\\alpha}:N_{\\beta}]" + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "text", + "content": " \n9 while True do \n10 initialize zero matrix " + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "inline_equation", + "content": "S\\in \\mathbb{R}^{(N + 2)\\times (N + 2)}" + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "text", + "content": " \nfor " + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "inline_equation", + "content": "i\\gets 0" + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "inline_equation", + "content": "\\{N + 1\\}" + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "text", + "content": " do \nfor " + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "inline_equation", + "content": "j\\gets 0" + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "inline_equation", + "content": "\\{N + 1\\}" + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "text", + "content": " do \n" + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "inline_equation", + "content": "S[i,j]\\gets" + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "inline_equation", + "content": "\\psi_{ij}\\left(\\frac{1}{\\ln v_i}\\sum_{\\psi_{ki}\\in \\Psi}(\\psi_{ki}) / \\sum_{\\psi_{ik}\\in \\Psi}(\\psi_{ik})+\\right." + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "inline_equation", + "content": "\\left.\\frac{1}{\\mathrm{Out}_v_j}\\sum_{\\psi_{jk}\\in \\Psi}(\\psi_{jk}) / \\sum_{\\psi_{kj}\\in \\Psi}(\\psi_{kj})\\right)" + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "inline_equation", + "content": "\\psi_{ij}\\gets 0" + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "text", + "content": " where " + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "inline_equation", + "content": "S[i,j]" + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "text", + "content": " is nonzero min value \nif graph built from " + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "inline_equation", + "content": "\\Psi" + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "text", + "content": " is reachable then \n" + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "inline_equation", + "content": "\\hat{\\Psi}\\gets \\Psi" + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "text", + "content": " \nelse \n" + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "inline_equation", + "content": "\\hat{\\Psi} [\\hat{\\Psi} >0]\\gets 1 / /" + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "text", + "content": " discretization \n" + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "inline_equation", + "content": "\\hat{\\Gamma}\\gets \\hat{\\Psi}[1:N,1:N] / /" + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "text", + "content": " split into " + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "inline_equation", + "content": "\\Gamma ,A,B" + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "inline_equation", + "content": "\\hat{\\mathcal{A}}\\gets \\hat{\\Psi}[0,1:N]" + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "inline_equation", + "content": "\\hat{\\mathcal{B}}\\gets \\hat{\\Psi}[1:N,N + 1]" + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "text", + "content": " \nreturn " + }, + { + "bbox": [ + 48, + 88, + 290, + 441 + ], + "type": "inline_equation", + "content": "\\hat{\\Gamma},\\hat{\\mathcal{A}},\\hat{\\mathcal{B}}" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "code_body" + } + ], + "index": 1, + "sub_type": "algorithm" + }, + { + "bbox": [ + 46, + 456, + 287, + 552 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 456, + 287, + 552 + ], + "spans": [ + { + "bbox": [ + 46, + 456, + 287, + 552 + ], + "type": "text", + "content": "the only edge that can reach the graph. We use the simple Depth-first search algorithm to check the reachability of " + }, + { + "bbox": [ + 46, + 456, + 287, + 552 + ], + "type": "inline_equation", + "content": "\\hat{\\Gamma}" + }, + { + "bbox": [ + 46, + 456, + 287, + 552 + ], + "type": "text", + "content": " between hidden state " + }, + { + "bbox": [ + 46, + 456, + 287, + 552 + ], + "type": "inline_equation", + "content": "v_{N_{\\alpha}}" + }, + { + "bbox": [ + 46, + 456, + 287, + 552 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 46, + 456, + 287, + 552 + ], + "type": "inline_equation", + "content": "v_{N_{\\beta}}" + }, + { + "bbox": [ + 46, + 456, + 287, + 552 + ], + "type": "text", + "content": ". All the output " + }, + { + "bbox": [ + 46, + 456, + 287, + 552 + ], + "type": "inline_equation", + "content": "\\hat{A}, \\hat{B}, \\hat{\\Gamma}" + }, + { + "bbox": [ + 46, + 456, + 287, + 552 + ], + "type": "text", + "content": " in Alg. 1, which is the discretized binary adjacency matrix, represent the truncated task-adaptive sub-network. After the reduction, we fix the upper-level parameters and only re-train the network parameters " + }, + { + "bbox": [ + 46, + 456, + 287, + 552 + ], + "type": "inline_equation", + "content": "\\Theta" + }, + { + "bbox": [ + 46, + 456, + 287, + 552 + ], + "type": "text", + "content": ", and we do not use the sigmoid function in Eq. 3-5" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 561, + 127, + 574 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 561, + 127, + 574 + ], + "spans": [ + { + "bbox": [ + 47, + 561, + 127, + 574 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 581, + 287, + 641 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 581, + 287, + 641 + ], + "spans": [ + { + "bbox": [ + 46, + 581, + 287, + 641 + ], + "type": "text", + "content": "We first describe the experimental setup in Sec. 4.1. We compare our method to state-of-the-art MTL frameworks on various benchmark datasets for MTL in Sec. 4.2. We also conduct extensive experiments and ablation studies to validate our proposed method in Sec. 4.3-4.5." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 647, + 174, + 660 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 647, + 174, + 660 + ], + "spans": [ + { + "bbox": [ + 47, + 647, + 174, + 660 + ], + "type": "text", + "content": "4.1. Experimental Settings" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 665, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 287, + 715 + ], + "type": "text", + "content": "Dataset We use four public datasets for multi-task scenarios including Omniglot [17], NYU-v2 [34], Cityscapes [7], and PASCAL-Context [26]. We use these datasets, configured by previous MTL works [29, 38], not their original sources." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 317, + 72, + 547, + 271 + ], + "type": "list", + "angle": 0, + "index": 11, + "blocks": [ + { + "bbox": [ + 317, + 72, + 545, + 120 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 72, + 545, + 120 + ], + "spans": [ + { + "bbox": [ + 317, + 72, + 545, + 120 + ], + "type": "text", + "content": "- Omniglot Omniglot is a classification dataset consisting of 50 different alphabets, and each of them consists of a number of characters with 20 handwritten images per character." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 317, + 126, + 547, + 162 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 126, + 547, + 162 + ], + "spans": [ + { + "bbox": [ + 317, + 126, + 547, + 162 + ], + "type": "text", + "content": "- NYU-v2 NYU-v2 comprises images of indoor scenes, fully labeled for joint semantic segmentation, depth estimation, and surface normal estimation." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 317, + 169, + 545, + 205 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 169, + 545, + 205 + ], + "spans": [ + { + "bbox": [ + 317, + 169, + 545, + 205 + ], + "type": "text", + "content": "- Cityscapes Cityscapes dataset collected from urban driving scenes in European cities consists of two tasks: joint semantic segmentation and depth estimation." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 317, + 211, + 545, + 271 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 211, + 545, + 271 + ], + "spans": [ + { + "bbox": [ + 317, + 211, + 545, + 271 + ], + "type": "text", + "content": "- PASCAL-Context PASCAL-Context datasets contain PASCAL VOC 2010 [34] with semantic segmentation, human parts segmentation, and saliency maps, as well as additional annotations for surface normals and edge maps." + } + ] + } + ], + "index": 10 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 304, + 281, + 545, + 376 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 281, + 545, + 376 + ], + "spans": [ + { + "bbox": [ + 304, + 281, + 545, + 376 + ], + "type": "text", + "content": "Competitive methods We compare the proposed framework with state-of-the-art methods [1, 11, 12, 18, 20, 22, 23, 25, 28, 29, 32, 38] and various baselines including a single task and a shared-bottom. The single-task baseline trains each task independently using a task-specific encoder and task-specific head for each task. The shared-bottom baseline trains multiple tasks simultaneously with a shared encoder and separated task-specific heads." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 378, + 546, + 533 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 378, + 546, + 533 + ], + "spans": [ + { + "bbox": [ + 304, + 378, + 546, + 533 + ], + "type": "text", + "content": "We compare our method with MoE-based approaches, including Soft Ordering [23], Routing [28], and Gumbel-Matrix [22], as well as a NAS approach [18] on Omniglot datasets. CMTR [18] can modify parameter count, similar to our method. We compare our method with other soft-parameter sharing methods including Cross-Stitch [25], Sluice network [32], and NDDR-CNN [11] and the dynamic neural network (DNN)-based methods including MTAN [20], DEN [1], and Adashare [38] for the other three datasets. We provide the evaluation results of two recent works, LTB [12] and PHN [29] for PASCAL-Context datasets because only the results are reported in their papers, but no source codes are provided." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 534, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 534, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 534, + 546, + 713 + ], + "type": "text", + "content": "Multi-task scenarios We set up multi-task scenarios with the combination of several tasks out of a total of seven tasks, including classification " + }, + { + "bbox": [ + 304, + 534, + 546, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{T}_{cls}" + }, + { + "bbox": [ + 304, + 534, + 546, + 713 + ], + "type": "text", + "content": ", semantic segmentation " + }, + { + "bbox": [ + 304, + 534, + 546, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{T}_{sem}" + }, + { + "bbox": [ + 304, + 534, + 546, + 713 + ], + "type": "text", + "content": ", depth estimation " + }, + { + "bbox": [ + 304, + 534, + 546, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{T}_{dep}" + }, + { + "bbox": [ + 304, + 534, + 546, + 713 + ], + "type": "text", + "content": ", surface normal prediction " + }, + { + "bbox": [ + 304, + 534, + 546, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{T}_{norm}" + }, + { + "bbox": [ + 304, + 534, + 546, + 713 + ], + "type": "text", + "content": ", human-part segmentation " + }, + { + "bbox": [ + 304, + 534, + 546, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{T}_{part}" + }, + { + "bbox": [ + 304, + 534, + 546, + 713 + ], + "type": "text", + "content": ", saliency detection " + }, + { + "bbox": [ + 304, + 534, + 546, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{T}_{sal}" + }, + { + "bbox": [ + 304, + 534, + 546, + 713 + ], + "type": "text", + "content": ", and edge detection " + }, + { + "bbox": [ + 304, + 534, + 546, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{T}_{edge}" + }, + { + "bbox": [ + 304, + 534, + 546, + 713 + ], + "type": "text", + "content": ". We follow the MTL setup in [38] for three datasets including Omniglot, NYU-v2, and cityscapes, and [29] for PASCAL-Context. We simulate a homogeneous MTL scenario of a 20-way classification task in a multi-task setup using Omniglot datasets by following [23]. Each task predicts a class of characters in a single alphabet set. We use the other three datasets for heterogeneous MTL. We set three tasks including segmentation, depth estimation, and normal estimation for NYU-v2 and two with segmentation, depth estimation for Cityscapes." + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "3783" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 52, + 70, + 282, + 212 + ], + "blocks": [ + { + "bbox": [ + 52, + 70, + 282, + 212 + ], + "lines": [ + { + "bbox": [ + 52, + 70, + 282, + 212 + ], + "spans": [ + { + "bbox": [ + 52, + 70, + 282, + 212 + ], + "type": "table", + "html": "
MethodTest Acc. (%)# of Param ↓
Soft Ordering [23]66.590.27
CMTR [18]87.19-
MoE [28]92.199.08
Gumbel-Matrix [22]93.529.08
Single Task93.4820.00
Shared Bottom93.251.00
Ours (M=3)94.990.91
Ours (M=5)95.711.37
Ours (M=7)95.681.46
", + "image_path": "456132b189e2b87c449fc271ee5c02701d79c2d050ad204f0f08ab81ea2a5749.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 50, + 242, + 285, + 357 + ], + "blocks": [ + { + "bbox": [ + 88, + 221, + 246, + 232 + ], + "lines": [ + { + "bbox": [ + 88, + 221, + 246, + 232 + ], + "spans": [ + { + "bbox": [ + 88, + 221, + 246, + 232 + ], + "type": "text", + "content": "Table 1. Evaluation on Omniglot datasets." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 50, + 242, + 285, + 357 + ], + "lines": [ + { + "bbox": [ + 50, + 242, + 285, + 357 + ], + "spans": [ + { + "bbox": [ + 50, + 242, + 285, + 357 + ], + "type": "table", + "html": "
MethodΔsem↑Δnorm↑Δdep↑Δ↑# of Param ↓
Single-Task0.00.00.00.03.00
Shared Bottom-7.6+7.5+5.2+1.71.00
Cross-Stitch [25]-4.9+4.2+4.7+1.33.00
Sluice [32]-8.4+2.9+4.1-0.53.00
NDDR-CNN [11]-15.0+2.9-3.5-5.23.15
MTAN [20]-4.2+8.7+3.8+2.73.11
DEN [1]-9.9+1.7-35.2-14.51.12
AdaShare [38]+8.8+7.9+10.1+8.91.00
Ours (M=5)+11.9+7.9+8.8+9.51.04
Ours (M=7)+13.4+9.2+10.7+11.11.31
Ours (M=9)+13.2+9.0+10.9+11.01.63
", + "image_path": "65edecee36b206bacf039ce5e69afa9cbb05a017ed4765b2720a7bf56698011e.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 387, + 287, + 410 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 387, + 287, + 410 + ], + "spans": [ + { + "bbox": [ + 47, + 387, + 287, + 410 + ], + "type": "text", + "content": "We set five tasks " + }, + { + "bbox": [ + 47, + 387, + 287, + 410 + ], + "type": "inline_equation", + "content": "\\mathcal{T}_{sem}" + }, + { + "bbox": [ + 47, + 387, + 287, + 410 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 387, + 287, + 410 + ], + "type": "inline_equation", + "content": "\\mathcal{T}_{part}" + }, + { + "bbox": [ + 47, + 387, + 287, + 410 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 387, + 287, + 410 + ], + "type": "inline_equation", + "content": "\\mathcal{T}_{norm}" + }, + { + "bbox": [ + 47, + 387, + 287, + 410 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 387, + 287, + 410 + ], + "type": "inline_equation", + "content": "\\mathcal{T}_{sal}" + }, + { + "bbox": [ + 47, + 387, + 287, + 410 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 47, + 387, + 287, + 410 + ], + "type": "inline_equation", + "content": "\\mathcal{T}_{edge}" + }, + { + "bbox": [ + 47, + 387, + 287, + 410 + ], + "type": "text", + "content": " as used in [29] for PASCAL-Context datasets." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 411, + 287, + 555 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 411, + 287, + 555 + ], + "spans": [ + { + "bbox": [ + 47, + 411, + 287, + 555 + ], + "type": "text", + "content": "Evaluation metrics We follow the common evaluation metrics utilized in the competitive methods. We use an accuracy metric for the classification task. The semantic segmentation task is measured by mean Intersection over Union (mIoU) and pixel accuracy. We use the mean absolute and mean relative errors, and relative difference as the percentage of " + }, + { + "bbox": [ + 47, + 411, + 287, + 555 + ], + "type": "inline_equation", + "content": "\\delta = \\max (\\hat{\\mathbf{d}} /\\mathbf{d},\\mathbf{d} / \\hat{\\mathbf{d}})" + }, + { + "bbox": [ + 47, + 411, + 287, + 555 + ], + "type": "text", + "content": " within thresholds " + }, + { + "bbox": [ + 47, + 411, + 287, + 555 + ], + "type": "inline_equation", + "content": "1.25^{\\{1,2,3\\}}" + }, + { + "bbox": [ + 47, + 411, + 287, + 555 + ], + "type": "text", + "content": " for the depth estimation task. For the evaluation of the PASCAL-Context datasets, we follow the same metrics used in [29] for all tasks. As reported in [38], we report a single relative performance " + }, + { + "bbox": [ + 47, + 411, + 287, + 555 + ], + "type": "inline_equation", + "content": "\\Delta_{\\mathcal{T}_i}" + }, + { + "bbox": [ + 47, + 411, + 287, + 555 + ], + "type": "text", + "content": " in Tab. 1-4 for each task " + }, + { + "bbox": [ + 47, + 411, + 287, + 555 + ], + "type": "inline_equation", + "content": "\\mathcal{T}_i" + }, + { + "bbox": [ + 47, + 411, + 287, + 555 + ], + "type": "text", + "content": " with respect to the single-task baseline, which defined as:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 67, + 559, + 287, + 594 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 67, + 559, + 287, + 594 + ], + "spans": [ + { + "bbox": [ + 67, + 559, + 287, + 594 + ], + "type": "interline_equation", + "content": "\\Delta_ {\\mathcal {T} _ {i}} = \\frac {1 0 0}{| \\mathcal {M} |} \\sum_ {j = 0} ^ {| \\mathcal {M} |} (- 1) ^ {l _ {j}} \\frac {\\left(\\mathcal {M} _ {\\mathcal {T} _ {i} , j} - \\mathcal {M} _ {\\mathcal {T} _ {i} , j} ^ {\\text {s i n g l e}}\\right)}{\\mathcal {M} _ {\\mathcal {T} _ {i} , j} ^ {\\text {s i n g l e}}}, \\tag {10}", + "image_path": "b6775ca343603dc58eddd2bad9800f2b095c4a1bac500a6f96d59bd9ef803ee7.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 601, + 287, + 662 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 601, + 287, + 662 + ], + "spans": [ + { + "bbox": [ + 47, + 601, + 287, + 662 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 601, + 287, + 662 + ], + "type": "inline_equation", + "content": "\\mathcal{M}_{\\mathcal{T}_i,j}" + }, + { + "bbox": [ + 47, + 601, + 287, + 662 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 601, + 287, + 662 + ], + "type": "inline_equation", + "content": "\\mathcal{M}_{\\mathcal{T}_i,j}^{single}" + }, + { + "bbox": [ + 47, + 601, + 287, + 662 + ], + "type": "text", + "content": " are the " + }, + { + "bbox": [ + 47, + 601, + 287, + 662 + ], + "type": "inline_equation", + "content": "j" + }, + { + "bbox": [ + 47, + 601, + 287, + 662 + ], + "type": "text", + "content": "-th metric of " + }, + { + "bbox": [ + 47, + 601, + 287, + 662 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 47, + 601, + 287, + 662 + ], + "type": "text", + "content": "-th task " + }, + { + "bbox": [ + 47, + 601, + 287, + 662 + ], + "type": "inline_equation", + "content": "\\mathcal{T}_i" + }, + { + "bbox": [ + 47, + 601, + 287, + 662 + ], + "type": "text", + "content": " from each method and the single task baseline, respectively. The constant " + }, + { + "bbox": [ + 47, + 601, + 287, + 662 + ], + "type": "inline_equation", + "content": "l_j" + }, + { + "bbox": [ + 47, + 601, + 287, + 662 + ], + "type": "text", + "content": " is 1 if a lower value represents better for the metric " + }, + { + "bbox": [ + 47, + 601, + 287, + 662 + ], + "type": "inline_equation", + "content": "\\mathcal{M}_{\\mathcal{T}_i,j}" + }, + { + "bbox": [ + 47, + 601, + 287, + 662 + ], + "type": "text", + "content": " and 0 otherwise. The averaged relative performance for all tasks " + }, + { + "bbox": [ + 47, + 601, + 287, + 662 + ], + "type": "inline_equation", + "content": "\\mathcal{T}" + }, + { + "bbox": [ + 47, + 601, + 287, + 662 + ], + "type": "text", + "content": " is defined as:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 124, + 677, + 287, + 711 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 124, + 677, + 287, + 711 + ], + "spans": [ + { + "bbox": [ + 124, + 677, + 287, + 711 + ], + "type": "interline_equation", + "content": "\\Delta_ {\\mathcal {T}} = \\frac {1}{| \\mathcal {T} |} \\sum_ {i = 1} ^ {| \\mathcal {T} |} \\Delta_ {\\mathcal {T} _ {i}}. \\tag {11}", + "image_path": "471b5f7d9f454c044900e97cc5151a8fc23803b0d410555c09e495b87fca203c.jpg" + } + ] + } + ], + "index": 8 + }, + { + "type": "table", + "bbox": [ + 307, + 70, + 545, + 209 + ], + "blocks": [ + { + "bbox": [ + 89, + 366, + 243, + 376 + ], + "lines": [ + { + "bbox": [ + 89, + 366, + 243, + 376 + ], + "spans": [ + { + "bbox": [ + 89, + 366, + 243, + 376 + ], + "type": "text", + "content": "Table 2. Evaluation on NYU-v2 datasets." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 307, + 70, + 545, + 209 + ], + "lines": [ + { + "bbox": [ + 307, + 70, + 545, + 209 + ], + "spans": [ + { + "bbox": [ + 307, + 70, + 545, + 209 + ], + "type": "table", + "html": "
MethodΔTsem↑ΔTdep↑ΔT↑# of Param ↓
Single-Task0.00.00.02.00
Shared Bottom-3.7-0.5-2.11.00
Cross-Stitch [25]-0.1+5.8+2.82.00
Sluice [32]-0.8+4.0+1.62.00
NDDR-CNN [11]+1.3+3.3+2.32.07
MTAN [20]+0.5+4.8+2.72.41
DEN [1]-3.1-1.6-2.41.12
AdaShare [38]+1.8+3.8+2.81.00
Ours (M=5)+3.5+3.9+3.70.96
Ours (M=7)+7.5+3.1+5.31.16
Ours (M=9)+8.3+4.8+6.61.31
", + "image_path": "afabb8b55366ef66d4c16b772be3715c89783ac951c502d40119370f3c5bcd7e.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "table_body" + } + ], + "index": 9 + }, + { + "type": "table", + "bbox": [ + 307, + 239, + 544, + 337 + ], + "blocks": [ + { + "bbox": [ + 344, + 217, + 506, + 228 + ], + "lines": [ + { + "bbox": [ + 344, + 217, + 506, + 228 + ], + "spans": [ + { + "bbox": [ + 344, + 217, + 506, + 228 + ], + "type": "text", + "content": "Table 3. Evaluation on Cityscapes datasets." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 307, + 239, + 544, + 337 + ], + "lines": [ + { + "bbox": [ + 307, + 239, + 544, + 337 + ], + "spans": [ + { + "bbox": [ + 307, + 239, + 544, + 337 + ], + "type": "table", + "html": "
MethodΔTsem↑ΔTpart↑ΔTmal↑ΔTnorm↓ΔTedge↑ΔT↑# of Param ↓
Single-Task0.00.00.00.00.00.05.00
Shared Bottom-6.6-0.7-3.4-14.30.0-5.01.00
Cross-Stitch [25]-1.3+3.6-0.2-1.40.0+0.15.00
Sluice [32]-1.6-1.2-0.5-2.9-6.0-2.45.00
NDDR-CNN [11]-1.1-2.60.0-5.00.0-1.75.61
MTAN [20]-3.6-0.7-0.3-5.0-6.0-3.15.21
AdaShare [38]-1.4+4.0-0.5-0.70.0+0.31.00
LTB [12]-6.9-1.9+0.2-1.40.0-2.03.19
PHN [29]-6.6-1.6-1.00.00.0-1.82.51
Ours (M=5)-0.3+3.4+0.90.00.0+0.81.93
Ours (M=7)0.0-0.2+1.7+1.40.0+0.61.91
Ours (M=9)0.0+3.6+1.8+1.40.0+1.42.31
", + "image_path": "ee9d07809961af3321c5ba1681436f17fb810c74891503437fc637d608fdf9b8.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "table_body" + } + ], + "index": 11 + }, + { + "bbox": [ + 330, + 345, + 520, + 355 + ], + "lines": [ + { + "bbox": [ + 330, + 345, + 520, + 355 + ], + "spans": [ + { + "bbox": [ + 330, + 345, + 520, + 355 + ], + "type": "text", + "content": "Table 4. Evaluation on PASCAL-Context datasets." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 304, + 365, + 545, + 389 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 365, + 545, + 389 + ], + "spans": [ + { + "bbox": [ + 304, + 365, + 545, + 389 + ], + "type": "text", + "content": "The absolute task performance for all metrics is reported in the supplementary material." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 389, + 546, + 557 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 389, + 546, + 557 + ], + "spans": [ + { + "bbox": [ + 304, + 389, + 546, + 557 + ], + "type": "text", + "content": "Network and training details For our central network, we set 8 hidden states, the same as the existing MoE-based works [22, 28] and use the same classification head for Omniglot datasets. We set 12 hidden states, the same as the VGG-16 [35], except for the max-pooled state, and use the Deeplab-v2 [5] decoder structure as all task heads for all the other datasets, respectively. We use the Adam [16] optimizer to update both upper-level parameters and network parameters. We use cross-entropy loss for semantic segmentation and L2 loss for the other tasks. For a fair comparison, we train our central network from scratch without pre-training for all experiments. We describe more details on the network structure and hyperparameter settings in the supplementary material." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 563, + 517, + 576 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 563, + 517, + 576 + ], + "spans": [ + { + "bbox": [ + 306, + 563, + 517, + 576 + ], + "type": "text", + "content": "4.2. Comparison to State-of-the-art Methods" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "content": "We report the performance of the proposed method with different flow constants " + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "content": " and compare it with state-ofthe-art methods in Tab. 1-4 with four different MTL scenarios. Tab. 1 shows that our framework with any flow constant " + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "content": " outperforms all the competitive methods for the homogeneous MTL scenario with Omniglot datasets. Ours has a similar number of parameters to the shared-bottom baseline. All the other experiments for heterogeneous MTL scenarios in Tab. 2-4 show that our frameworks achieve the best performance among all state-ofthe-art works. Even with the flow constant " + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "inline_equation", + "content": "M = 5" + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "content": ", our" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "3784" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 50, + 71, + 149, + 132 + ], + "blocks": [ + { + "bbox": [ + 50, + 71, + 149, + 132 + ], + "lines": [ + { + "bbox": [ + 50, + 71, + 149, + 132 + ], + "spans": [ + { + "bbox": [ + 50, + 71, + 149, + 132 + ], + "type": "image", + "image_path": "b9685fc639f8cf3ef3d889b2c17580fad8d4d6bf2fd04b5b1b7f9cb8e4242d44.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 49, + 133, + 150, + 190 + ], + "blocks": [ + { + "bbox": [ + 49, + 133, + 150, + 190 + ], + "lines": [ + { + "bbox": [ + 49, + 133, + 150, + 190 + ], + "spans": [ + { + "bbox": [ + 49, + 133, + 150, + 190 + ], + "type": "image", + "image_path": "47c4569c23e0b786adbd892f548d4f896abd54ff24f7b3f69c338fe9853a76c8.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 49, + 191, + 150, + 251 + ], + "blocks": [ + { + "bbox": [ + 49, + 191, + 150, + 251 + ], + "lines": [ + { + "bbox": [ + 49, + 191, + 150, + 251 + ], + "spans": [ + { + "bbox": [ + 49, + 191, + 150, + 251 + ], + "type": "image", + "image_path": "db07d5fcda95a6f169df26e4072f6548b53451779bc202cb3145862b24a625a9.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 150, + 72, + 273, + 248 + ], + "blocks": [ + { + "bbox": [ + 150, + 72, + 273, + 248 + ], + "lines": [ + { + "bbox": [ + 150, + 72, + 273, + 248 + ], + "spans": [ + { + "bbox": [ + 150, + 72, + 273, + 248 + ], + "type": "image", + "image_path": "210b57c0800e83ece8e609cc462da0656d882da0fb11737a55c07efdb041758a.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 259, + 287, + 326 + ], + "lines": [ + { + "bbox": [ + 46, + 259, + 287, + 326 + ], + "spans": [ + { + "bbox": [ + 46, + 259, + 287, + 326 + ], + "type": "text", + "content": "Figure 3. Graph Representation of Task-adaptive Sub-network The finalized sub-network topologies (" + }, + { + "bbox": [ + 46, + 259, + 287, + 326 + ], + "type": "inline_equation", + "content": "M = 7" + }, + { + "bbox": [ + 46, + 259, + 287, + 326 + ], + "type": "text", + "content": ") trained with NYUv2 datasets is illustrated as graph. (a-c) The task-adaptive subnetwork of semantic segmentation, depth estimation, and surface normal, respectively. (d) The adjacency matrix where color represents the discretized value for the activated edge of each task." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_caption" + } + ], + "index": 3 + }, + { + "type": "table", + "bbox": [ + 91, + 336, + 244, + 397 + ], + "blocks": [ + { + "bbox": [ + 91, + 336, + 244, + 397 + ], + "lines": [ + { + "bbox": [ + 91, + 336, + 244, + 397 + ], + "spans": [ + { + "bbox": [ + 91, + 336, + 244, + 397 + ], + "type": "table", + "html": "
TaskDWS
Semantic Seg.530.103
Depth730.192
Surface normal720.128
", + "image_path": "810b8c438afb9117b8309cc1f814647c725de3b4711a5d2b4438e182a3a64478.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "table_body" + } + ], + "index": 5 + }, + { + "bbox": [ + 74, + 405, + 259, + 417 + ], + "lines": [ + { + "bbox": [ + 74, + 405, + 259, + 417 + ], + "spans": [ + { + "bbox": [ + 74, + 405, + 259, + 417 + ], + "type": "text", + "content": "Table 5. Topologies analysis on NYU-v2 datasets." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 426, + 287, + 569 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 426, + 287, + 569 + ], + "spans": [ + { + "bbox": [ + 46, + 426, + 287, + 569 + ], + "type": "text", + "content": "model outperforms AdaShare [38] for both the NYU-v2 and Cityscapes datasets, while keeping almost the same number of parameters (NYU-v2: 1.00 vs. 1.04 and Cityscapes 1.00 vs. 0.96). With the flow constant " + }, + { + "bbox": [ + 46, + 426, + 287, + 569 + ], + "type": "inline_equation", + "content": "M = 7,9" + }, + { + "bbox": [ + 46, + 426, + 287, + 569 + ], + "type": "text", + "content": ", our method outperforms all the baselines by a large margin. The results from the PASCAL-Context datasets in Tab. 4 show that all baselines suffer from negative transfer in several tasks, as the number of tasks increases. Only Adashare and Cross Stitch slightly outperform the single-task baseline (see the performance " + }, + { + "bbox": [ + 46, + 426, + 287, + 569 + ], + "type": "inline_equation", + "content": "\\Delta_{\\mathcal{T}}" + }, + { + "bbox": [ + 46, + 426, + 287, + 569 + ], + "type": "text", + "content": "). On the other hand, ours with " + }, + { + "bbox": [ + 46, + 426, + 287, + 569 + ], + "type": "inline_equation", + "content": "M = 9" + }, + { + "bbox": [ + 46, + 426, + 287, + 569 + ], + "type": "text", + "content": " achieves the best performance without any negative transfers for all tasks." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 570, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 570, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 570, + 288, + 714 + ], + "type": "text", + "content": "Interestingly, the required parameters of the search space increase almost in proportion to the increase of the flow constant, but there is no significant difference in the number of parameters of the finalized networks. For example, the required number of parameters for the network with the flow constant " + }, + { + "bbox": [ + 46, + 570, + 288, + 714 + ], + "type": "inline_equation", + "content": "M = 3,5,7" + }, + { + "bbox": [ + 46, + 570, + 288, + 714 + ], + "type": "text", + "content": " is 2.77, 4.23, and 5.38, respectively. This demonstrates that the proposed flow-based reduction algorithm is effective in removing low-relative parameters while maintaining performance. Specifically, we observe that the total performance of our framework with " + }, + { + "bbox": [ + 46, + 570, + 288, + 714 + ], + "type": "inline_equation", + "content": "M = 7" + }, + { + "bbox": [ + 46, + 570, + 288, + 714 + ], + "type": "text", + "content": " is slightly better than the " + }, + { + "bbox": [ + 46, + 570, + 288, + 714 + ], + "type": "inline_equation", + "content": "M = 9" + }, + { + "bbox": [ + 46, + 570, + 288, + 714 + ], + "type": "text", + "content": " setup in Tab. 2 despite its smaller architecture search space. To investigate this," + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 72, + 545, + 107 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 545, + 107 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 545, + 107 + ], + "type": "text", + "content": "we further analyze the tendency in performance and computational complexity with respect to the flow constant in Sec. 4.4." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 116, + 534, + 129 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 116, + 534, + 129 + ], + "spans": [ + { + "bbox": [ + 305, + 116, + 534, + 129 + ], + "type": "text", + "content": "4.3. Analysis of Topologies and Task Correlation" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 135, + 545, + 243 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 135, + 545, + 243 + ], + "spans": [ + { + "bbox": [ + 304, + 135, + 545, + 243 + ], + "type": "text", + "content": "To demonstrate the effectiveness of the proposed learning mechanism, we visualize our finalized sub-network topologies in Fig. 3-(a-c) and the adjacency matrix for NYU-v2 3-task learning in Fig. 3-(d). We also analyze the diversity and capacity of task-adaptive network topologies in Tab. 5 with network depth " + }, + { + "bbox": [ + 304, + 135, + 545, + 243 + ], + "type": "inline_equation", + "content": "\\mathcal{D}" + }, + { + "bbox": [ + 304, + 135, + 545, + 243 + ], + "type": "text", + "content": ", width " + }, + { + "bbox": [ + 304, + 135, + 545, + 243 + ], + "type": "inline_equation", + "content": "\\mathcal{W}" + }, + { + "bbox": [ + 304, + 135, + 545, + 243 + ], + "type": "text", + "content": ", and sparsity " + }, + { + "bbox": [ + 304, + 135, + 545, + 243 + ], + "type": "inline_equation", + "content": "\\mathcal{S}" + }, + { + "bbox": [ + 304, + 135, + 545, + 243 + ], + "type": "text", + "content": " described in Sec. 3.1. These analyses provide three key observations on our task-adaptive network and the correlation among tasks." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 243, + 545, + 327 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 243, + 545, + 327 + ], + "spans": [ + { + "bbox": [ + 304, + 243, + 545, + 327 + ], + "type": "text", + "content": "First, the tasks of segmentation and surface normal hardly share network parameters. Various task-sharing patterns are configured at the edge, but there is only one sharing layer between the two tasks. This experiment shows a low relationship between tasks, as it is widely known that the proportion of shared parameters between tasks indicates task correlation [22, 29, 38]." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 327, + 545, + 434 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 327, + 545, + 434 + ], + "spans": [ + { + "bbox": [ + 304, + 327, + 545, + 434 + ], + "type": "text", + "content": "Second, long skip connections are mostly lost. The length of the longest skip connection in the finalized network is 5, and the number of these connections is 2 out of 18 layers, even with the flow constant of 7. This phenomenon is observed not only in NYU-v2 datasets but also in the other MTL datasets. This can be evidence that the proposed flow-restriction reduces search time while maintaining high performance even by eliminating the long skip connection in the DAG-based central network." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 435, + 545, + 555 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 435, + 545, + 555 + ], + "spans": [ + { + "bbox": [ + 304, + 435, + 545, + 555 + ], + "type": "text", + "content": "Lastly, Depth estimation task requires more network resources than segmentation and surface normal estimation tasks. We analyze the network topologies of the finalized sub-network of each task in NYU-v2 datasets using three components defined in Sec. 3. The depth " + }, + { + "bbox": [ + 304, + 435, + 545, + 555 + ], + "type": "inline_equation", + "content": "\\mathcal{D}" + }, + { + "bbox": [ + 304, + 435, + 545, + 555 + ], + "type": "text", + "content": " and width " + }, + { + "bbox": [ + 304, + 435, + 545, + 555 + ], + "type": "inline_equation", + "content": "\\mathcal{W}" + }, + { + "bbox": [ + 304, + 435, + 545, + 555 + ], + "type": "text", + "content": " of the sub-network increase in the order of semantic segmentation, surface normal prediction, and depth estimation tasks. Likewise, the sparsity " + }, + { + "bbox": [ + 304, + 435, + 545, + 555 + ], + "type": "inline_equation", + "content": "\\mathcal{S}" + }, + { + "bbox": [ + 304, + 435, + 545, + 555 + ], + "type": "text", + "content": " of the depth network is the highest. This experiment shows that the depth network is the task that requires the most network resources." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 563, + 499, + 574 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 563, + 499, + 574 + ], + "spans": [ + { + "bbox": [ + 306, + 563, + 499, + 574 + ], + "type": "text", + "content": "4.4. Performance w.r.t. Flow-restriction" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "content": "We analyze performance and computational complexity with respect to the flow constant " + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "content": " for the NYU-v2 and Cityscapes datasets. We report the rate of performance degradation with respect to the complete DAG search space in Fig. 4. We observe that the reduction rate of the final performance does not exceed " + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "inline_equation", + "content": "3\\%" + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "content": " even with considerably lower flow constants. The performance is saturated at a flow constant of about 7 or more. This means that the proposed method optimizes the task adaptive sub-network regardless of the size of the network search space, if it satisfies the minimum required size." + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "3785" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 55, + 88, + 282, + 228 + ], + "blocks": [ + { + "bbox": [ + 55, + 88, + 282, + 228 + ], + "lines": [ + { + "bbox": [ + 55, + 88, + 282, + 228 + ], + "spans": [ + { + "bbox": [ + 55, + 88, + 282, + 228 + ], + "type": "image", + "image_path": "f99b551058ea1a5578eff9d3380fbed19b51679d90f7b930038f2cedc89aaeff.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 239, + 288, + 319 + ], + "lines": [ + { + "bbox": [ + 46, + 239, + 288, + 319 + ], + "spans": [ + { + "bbox": [ + 46, + 239, + 288, + 319 + ], + "type": "text", + "content": "Figure 4. Model performance with respect to the proposed flow-restriction. We plot the degradation ratio of the performance (left y-axis) and parameter (right y-axis) by changing the flow constant " + }, + { + "bbox": [ + 46, + 239, + 288, + 319 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 46, + 239, + 288, + 319 + ], + "type": "text", + "content": ". We measure the final averaged task performance with NYU-v2 and Cityscapes datasets marked by purple and pink circle markers, respectively. We also measure the number of parameters marked by gray square markers." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 324, + 288, + 529 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 324, + 288, + 529 + ], + "spans": [ + { + "bbox": [ + 46, + 324, + 288, + 529 + ], + "type": "text", + "content": "To demonstrate the effectiveness of our flow-based reduction (FBR) algorithm, we compare it to two other reduction algorithms (random and threshold) for Cityscapes datasets in Fig. 5. The random reduction literally removes the edges randomly, and the thresholding method sequentially removes the edge which has the lowest value in the adjacency matrix " + }, + { + "bbox": [ + 46, + 324, + 288, + 529 + ], + "type": "inline_equation", + "content": "\\Gamma" + }, + { + "bbox": [ + 46, + 324, + 288, + 529 + ], + "type": "text", + "content": ". We measure the rate of performance degradation of the pruned network of each reduction algorithm with respect to the non-reduced network while changing the sparsity " + }, + { + "bbox": [ + 46, + 324, + 288, + 529 + ], + "type": "inline_equation", + "content": "S" + }, + { + "bbox": [ + 46, + 324, + 288, + 529 + ], + "type": "text", + "content": ". Note that our method automatically determines the sparsity, so for this experiment only, we add a termination condition that stops the network search when a certain sparsity is met. The results show that the proposed flow-reduction method retains performance even with a low sparsity rate. This means that our method efficiently prunes the low-related edge of the network compared to the other methods." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 538, + 245, + 552 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 538, + 245, + 552 + ], + "spans": [ + { + "bbox": [ + 47, + 538, + 245, + 552 + ], + "type": "text", + "content": "4.5. Ablation Study on Proposed Modules" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 558, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 558, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 558, + 288, + 715 + ], + "type": "text", + "content": "We conduct ablation studies on the four key components of our framework; the flow-restriction, read-in/out layers, flow-based reduction, and squeeze loss. We report the relative task performance and the number of parameters of the finalized network with/without the components in Tab. 6. The results show that our framework, including all components, achieves the lowest number of parameters and the second-best performance. Our method without flow-based reduction achieves the best performance. However, the finalized network from this setup has about a five-times larger number of parameters than ours because the network has never been pruned in a training process. This demonstrates that our restricted DAG-based central network is optimized" + } + ] + } + ], + "index": 4 + }, + { + "type": "image", + "bbox": [ + 317, + 86, + 518, + 222 + ], + "blocks": [ + { + "bbox": [ + 317, + 86, + 518, + 222 + ], + "lines": [ + { + "bbox": [ + 317, + 86, + 518, + 222 + ], + "spans": [ + { + "bbox": [ + 317, + 86, + 518, + 222 + ], + "type": "image", + "image_path": "b5d16cf1a474ad815b6d8330a98a0086d8abf203cd0b4aa0d44f4069098427e6.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 234, + 545, + 279 + ], + "lines": [ + { + "bbox": [ + 305, + 234, + 545, + 279 + ], + "spans": [ + { + "bbox": [ + 305, + 234, + 545, + 279 + ], + "type": "text", + "content": "Figure 5. Model Performance with respect to the network sparsity. We plot the performance degradation rate by changing network sparsity. We compare our flow-based reduction algorithm to two other schemes; random selection and thresholding." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_caption" + } + ], + "index": 5 + }, + { + "type": "table", + "bbox": [ + 307, + 289, + 544, + 350 + ], + "blocks": [ + { + "bbox": [ + 307, + 289, + 544, + 350 + ], + "lines": [ + { + "bbox": [ + 307, + 289, + 544, + 350 + ], + "spans": [ + { + "bbox": [ + 307, + 289, + 544, + 350 + ], + "type": "table", + "html": "
MethodΔTsem↑ΔTdep↑ΔTnorm↑ΔT# of Param ↓
Ours (M=7)+13.4+9.2+10.7+11.11.31
w/o flow-restriction+13.2+9.2+10.4+11.01.80
w/o read-in/out+11.7+8.3+10.4+10.11.43
w/o flow-based reduction+14.2+9.2+11.1+11.56.50
w/o Lsq+13.2+8.8+10.7+10.91.38
", + "image_path": "20a1ac497d403b80340cd9bc418ad2f62606116570126c7c923ce431773d48fd.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "table_body" + } + ], + "index": 7 + }, + { + "bbox": [ + 309, + 357, + 541, + 369 + ], + "lines": [ + { + "bbox": [ + 309, + 357, + 541, + 369 + ], + "spans": [ + { + "bbox": [ + 309, + 357, + 541, + 369 + ], + "type": "text", + "content": "Table 6. Ablation study on the proposed modules (NYU-v2)." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 305, + 377, + 545, + 413 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 377, + 545, + 413 + ], + "spans": [ + { + "bbox": [ + 305, + 377, + 545, + 413 + ], + "type": "text", + "content": "to build compact task-adaptive sub-networks with performance close to the optimized sub-network from a complete DAG-based network." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 423, + 384, + 436 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 423, + 384, + 436 + ], + "spans": [ + { + "bbox": [ + 306, + 423, + 384, + 436 + ], + "type": "text", + "content": "5. Conclusions" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 443, + 545, + 647 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 443, + 545, + 647 + ], + "spans": [ + { + "bbox": [ + 304, + 443, + 545, + 647 + ], + "type": "text", + "content": "In this paper, we present a new MTL framework to search for task-adaptive network structures across diverse network topologies in a single network. We propose flow restriction to solve the scalability issue in a complete DAG search space while maintaining the diverse network topological representation of the DAG search space by adopting read-in/out layers. We also introduce a flow-based reduction algorithm that prunes the network efficiently while maintaining overall task performance and squeeze loss, limiting the upper bound on the number of network parameters. The extensive experiments demonstrate that the submodule and schemes of our framework efficiently improve both the performance and compactness of the network. Our method compactly constructs various task-specific subnetworks in a single network and achieves the best performance among all the competitive methods on four MTL benchmark datasets." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 657, + 404, + 671 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 657, + 404, + 671 + ], + "spans": [ + { + "bbox": [ + 306, + 657, + 404, + 671 + ], + "type": "text", + "content": "Acknowledgement" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 677, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 677, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 677, + 545, + 713 + ], + "type": "text", + "content": "This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. RS-2023-00210908)." + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "3786" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 288, + 712 + ], + "type": "list", + "angle": 0, + "index": 14, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 135 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 135 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 135 + ], + "type": "text", + "content": "[1] Chanho Ahn, Eunwoo Kim, and Songhwai Oh. 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In Proceedings of the IEEE conference on computer vision and pattern recognition, pages 8697-8710, 2018. 1, 2" + } + ] + } + ], + "index": 13 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "type": "text", + "content": "3788" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 9 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/DynamicDet_ A Unified Dynamic Architecture for Object Detection/a2c8ee28-6898-4bb7-b856-836c2ee0fe1f_content_list.json b/2023/DynamicDet_ A Unified Dynamic Architecture for Object Detection/a2c8ee28-6898-4bb7-b856-836c2ee0fe1f_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..981711b44761883c08c88ce629a0ffb66b2ecbbf --- /dev/null +++ b/2023/DynamicDet_ A Unified Dynamic Architecture for Object Detection/a2c8ee28-6898-4bb7-b856-836c2ee0fe1f_content_list.json @@ -0,0 +1,1841 @@ +[ + { + "type": "text", + "text": "DynamicDet: A Unified Dynamic Architecture for Object Detection", + "text_level": 1, + "bbox": [ + 143, + 130, + 825, + 152 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Zhihao Lin Yongtao Wang† Jinhe Zhang Xiaojie Chu Wangxuan Institute of Computer Technology, Peking University", + "bbox": [ + 228, + 180, + 738, + 217 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "linzhihao@stu.pku.edu.cn, wyt@stu.edu.cn \njinhezhang17@gmail.com, chuxiaojie@stu.pku.edu.cn", + "bbox": [ + 264, + 219, + 699, + 251 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 286, + 313, + 301 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Dynamic neural network is an emerging research topic in deep learning. With adaptive inference, dynamic models can achieve remarkable accuracy and computational efficiency. However, it is challenging to design a powerful dynamic detector, because of no suitable dynamic architecture and exiting criterion for object detection. To tackle these difficulties, we propose a dynamic framework for object detection, named DynamicDet. Firstly, we carefully design a dynamic architecture based on the nature of the object detection task. Then, we propose an adaptive router to analyze the multi-scale information and to decide the inference route automatically. We also present a novel optimization strategy with an exiting criterion based on the detection losses for our dynamic detectors. Last, we present a variable-speed inference strategy, which helps to realize a wide range of accuracy-speed trade-offs with only one dynamic detector. Extensive experiments conducted on the COCO benchmark demonstrate that the proposed DynamicDet achieves new state-of-the-art accuracy-speed trade-offs. For instance, with comparable accuracy, the inference speed of our dynamic detector Dy-YOLOv7-W6 surpasses YOLOv7-E6 by $12\\%$ , YOLOv7-D6 by $17\\%$ , and YOLOv7-E6E by $39\\%$ . The code is available at https://github.com/VDIGPKU/DynamicDet.", + "bbox": [ + 75, + 315, + 473, + 678 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 688, + 209, + 704 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Object detection is an essential topic in computer vision, as it is a fundamental component for other vision tasks, e.g., autonomous driving [26, 40, 56], multi-object tracking [52,57], intelligent transportation [36,55], etc. In recent years, tremendous progress has been made toward more accurate and faster detectors, such as Network Architecture Search (NAS)-based detectors [10,25,48] and YOLO series models [2,9,11,21,44,45]. However, these methods need to design and train multiple models to achieve a few good trade-offs between accuracy and speed, which is not flexible enough for various application scenarios. To alleviate this", + "bbox": [ + 75, + 708, + 470, + 875 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/e58d5c4029fef6ed42e9d09d96b19e2fa2dcf95ea87589fe9afbcdee9ea37d45.jpg", + "image_caption": [ + "Figure 1. Comparison of the proposed dynamic detectors and other efficient object detectors. Our method can achieve a wide range of state-of-the-art trade-offs between accuracy and speed with a single model." + ], + "image_footnote": [], + "bbox": [ + 519, + 287, + 870, + 478 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/00fc6387c9f69629a483f0e524e5208ab324529c9b179d89c50a215e1d0bae9a.jpg", + "image_caption": [ + "\"Easy\" image", + "Figure 2. Examples of \"easy\" and \"hard\" images for the object detection task." + ], + "image_footnote": [], + "bbox": [ + 526, + 558, + 691, + 643 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/296e29e46b6febb73647721df8769cc4fb3e29ce00473a49b9d95eb18cc6bc66.jpg", + "image_caption": [ + "\"Hard\" image" + ], + "image_footnote": [], + "bbox": [ + 697, + 558, + 862, + 643 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "problem, we focus on dynamic inference for the object detection task, and attempt to use only one dynamic detector to achieve a wide range of good accuracy-speed trade-offs, as shown in Fig. 1.", + "bbox": [ + 496, + 700, + 893, + 762 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "The human brain inspires many fields of deep learning, and the dynamic neural network [12] is a typical one. As two examples shown in Fig. 2, we can quickly identify all objects on the left \"easy\" image, while we need more time to achieve the same effect for the right one. In other words, the processing speeds of images are different in our brains [18, 34], which depend on the difficulties of the images. This property motivates the image-wise dynamic neural network, and many exciting works have been proposed", + "bbox": [ + 496, + 763, + 893, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 810, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "† Corresponding author.", + "bbox": [ + 94, + 886, + 220, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "6282", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "(e.g., Branchynet [43], MSDNet [17], DVT [50]). Although these approaches have achieved remarkable performance, they are all designed specifically for the image classification task and are not suitable for other vision tasks, especially for the object detection [12]. The main difficulties in designing an image-wise dynamic detector are as follows.", + "bbox": [ + 75, + 90, + 467, + 181 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Dynamic detectors cannot utilize the existing dynamic architectures. Most existing dynamic architectures are cascaded with multiple stages (i.e., a stack of multiple layers) [17, 20, 33, 54], and predict whether to stop the inference at each exiting point. Such a paradigm is feasible in image classification but is ineffective in object detection, since an image has multiple objects and each object usually has different categories and scales, as shown in Fig. 2. Hence, almost all detectors depend heavily on multi-scale information, utilizing the features on different scales to detect objects of different sizes (which are obtained by fusing the multi-scale features of the backbone with a detection neck, i.e., FPN [27]). In this case, the exiting points for detectors can only be placed behind the last stage. Consequently, the entire backbone module has to be run completely [58], and it is impossible to achieve dynamic inference on multiple cascaded stages.", + "bbox": [ + 75, + 181, + 467, + 436 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Dynamic detectors cannot exploit the existing exiting criteria for image classification. For the image classification task, the threshold of top-1 accuracy is a widely used criterion for decision-making [17, 50]. Notably, it only needs one fully connected layer to predict the top-1 accuracy at intermediate layer, which is easy and costless. However, object detection task requires the neck and the head to predict the categories and locations of the object instances [3, 14, 27, 39]. Hence, the existing exiting criteria for image classification is not suitable for object detection.", + "bbox": [ + 75, + 439, + 467, + 589 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To deal with the above difficulties, we propose a dynamic framework to achieve dynamic inference for object detection, named DynamicDet. Firstly, We design a dynamic architecture for the object detection task, which can exit with multi-scale information during the inference. Then, we propose an adaptive router to choose the best route for each image automatically. Besides, we present the corresponding optimization and inference strategies for the proposed DynamicDet.", + "bbox": [ + 75, + 590, + 467, + 724 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Our main contributions are as follows:", + "bbox": [ + 96, + 726, + 351, + 739 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- We propose a dynamic architecture for object detection, named DynamicDet, which consists of two cascaded detectors and a router. This dynamic architecture can be easily adapted to mainstream detectors, e.g., Faster R-CNN andYOLO.", + "- We propose an adaptive router to predict the difficulty scores of the images based on the multi-scale features, and achieve automatic decision-making. In addition, we propose a hyperparameter-free optimization strategy and a variable-speed inference strategy for our dy" + ], + "bbox": [ + 94, + 744, + 467, + 900 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "namic architecture.", + "bbox": [ + 532, + 92, + 661, + 104 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "- Extensive experiments show that DynamicDet can obtain a wide range of accuracy-speed trade-offs with only one dynamic detector. We also achieve new state-of-the-art trade-offs for real-time object detection (i.e., $56.8\\%$ AP at 46 FPS).", + "bbox": [ + 517, + 109, + 890, + 184 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related work", + "text_level": 1, + "bbox": [ + 500, + 198, + 635, + 213 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.1. Backbone design on object detection", + "text_level": 1, + "bbox": [ + 500, + 220, + 813, + 236 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Backbones play a crucial role in object detectors since the performance of detectors highly relies on the multiscale features extracted by the backbones [4]. ResNet [15] and its variants (e.g., ResNeXt [51], Res2Net [8]) introduce the residual connection to neural networks, providing a high-quality backbone architecture family for all vision tasks. Further, to reduce the calculation load, CSPNet [46] cuts down the duplicate gradient information to reduce the heavy inference, improving the efficiency significantly. Its effective architecture also inspires many lightweight detectors (e.g.,YOLO series models [2, 9, 11, 21, 44, 45]). Then, some transformer-based backbones (e.g.,PVT [47], Swin Transformer [31]) are proposed to learn the global information better. In addition, many auto-designed backbones [4,6,19,41] for object detection are proposed. For example, DetNAS [4] utilizes the one-shot supernet to search the optimal backbone, with the guidance of the object detection task.", + "bbox": [ + 496, + 239, + 890, + 510 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Although many kinds of backbones have been proposed, almost all of them are single-pass architectures, which sequentially produce one set of multi-scale features. Thus, all stages of them cannot be skipped. Fortunately, some works propose the architectures of multiple cascaded backbones, which have the potential to be converted as a dynamic backbone for object detection. For example, CBNet [24, 30] groups multiple identical backbones with composite connections, constructing a more powerful composite backbone. Since these backbones have multiple sub-backbones and each of them can produce intermediate multi-scale features, we can add some exiting points after each subbackbone for dynamic inference.", + "bbox": [ + 496, + 511, + 890, + 708 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.2. Accuracy-speed trade-off on object detection", + "text_level": 1, + "bbox": [ + 500, + 714, + 879, + 729 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Almost all detection methods are designed for a better accuracy-speed trade-off, i.e., more accurate and faster. With a given detector, the simplest way to obtain an accuracy-speed trade-off is to adopt the model scaling techniques [42, 44, 45] (e.g., increasing the channel size or repeating the layers). EfficientDet [42] uniformly scales the resolution, depth, and width for all modules simultaneously, achieving remarkable efficiency on real-time detectors. Scaled-YOLOv4 [44] modifies not only the depth, width, and resolution but also the structure of the network to pursue a better trade-off. YOLOv7 [45] designs a", + "bbox": [ + 496, + 734, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "6283", + "bbox": [ + 482, + 945, + 514, + 955 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/838871ccf0a606b6b2fb17b9d427ca0cf03613139a6bd0ff8bf3cd99f83c71d9.jpg", + "image_caption": [ + "Figure 3. Illustration of the architecture of DynamicDet. The first backbone extracts the multi-scale features from the input image firstly. Then, the router will be fed with these multi-scale features to predict the difficulty of image and to decide the inference route. Notably, the \"easy\" images will be processed by only one backbone, while the \"hard\" images will be processed by two." + ], + "image_footnote": [], + "bbox": [ + 176, + 97, + 794, + 287 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "compound scaling method for concatenation-based models, achieving new state-of-the-art trade-offs. EAutoDet [48] constructs a supernet and adopts Network Architecture Search (NAS) to automatically search for suitable scaling factors under different hardware constraints. However, all the above methods need to train multiple detectors for the best trade-offs (e.g., one tiny model for real-time detection and another large model for accurate detection), leading to colossal training resources. In this paper, we focus on dynamic inference, aiming to achieve a wide range of best accuracy-speed trade-offs with only one dynamic detector.", + "bbox": [ + 75, + 342, + 472, + 508 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "2.3. Dynamic neural network", + "text_level": 1, + "bbox": [ + 76, + 517, + 305, + 532 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The dynamic neural network can achieve adaptive computation for different images (i.e., image-wise [17, 20, 22, 23, 43, 49, 50, 54]) or pixels (i.e., spatial-wise [7, 13, 37]). SACT [7] is a classic spatial-wise dynamic network, which adaptively adjusts the number of executed layers for the regions of the image, to improve the efficiency of networks. Its practical speed-up performance highly relies on the hardware-software co-design [12]. However, the current deep learning hardware and libraries [1, 35] are not friendly to these spatial-wise dynamic networks [12]. On the contrary, image-wise dynamic networks do not rely on sparse computing and can be easily accelerated on the conventional CPUs and GPUs [5]. Branchynet [43] introduces the early exiting strategy, which enables the model to exit from the intermediate layer whenever the model is confident enough. MSDNet [17] and its variants [23, 54] develop a multi-classifier architecture for the image classification task. DVT [50] cascades multiple transformers with increasing numbers of tokens and activates them sequentially to achieve dynamic inference. However, these methods are all designed specifically for the image classification task and cannot be applied to other vision tasks, such as object detection.", + "bbox": [ + 75, + 537, + 472, + 883 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The closest work to our DynamicDet is Adaptive Feed", + "bbox": [ + 96, + 885, + 468, + 900 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "ing [58]. In Adaptive Feeding [58], each image is detected by a lightweight detector (e.g., TinyYOLO [38]) and then classified as easy or hard by a linear support vector machine (SVM) with those detected results. Then, the easy images will go through a fast detector (e.g., SSD300 [29]), while the hard images will go through a more accurate but slower one (e.g., SSD500 [29]). Adaptive Feeding [58] introduces the above multi-stage process for dynamic inference, which is inefficient and not elegant. In comparison, the proposed DynamicDet cascades two detectors and a classifier (i.e., the router), yielding a more unified and efficient dynamic detector.", + "bbox": [ + 496, + 342, + 893, + 523 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Approach", + "text_level": 1, + "bbox": [ + 498, + 534, + 609, + 551 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In the following, we elaborate on our dynamic architecture for object detection. We first introduce the overall architecture in Sec. 3.1. Then, we state the proposed adaptive router, i.e., the decision maker of DynamicDet in Sec. 3.2. Finally, we introduce the optimization strategy and a variable-speed inference strategy in Secs. 3.3 and 3.4.", + "bbox": [ + 496, + 556, + 893, + 648 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Overall architecture", + "text_level": 1, + "bbox": [ + 498, + 655, + 692, + 669 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The overall architecture of our dynamic detector is shown in Fig. 3. Inspired by CBNet [24, 30], our dynamic architecture consists of two detectors and one router. For an input image $\\mathbf{x}$ , we initially extract its multi-scale features $F_{1}$ with the first backbone $\\mathcal{B}_1$ as", + "bbox": [ + 496, + 676, + 893, + 751 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nF _ {1} = \\mathcal {B} _ {1} (\\mathbf {x}) = \\left[ f _ {1} ^ {\\{1 \\}}, f _ {1} ^ {\\{2 \\}}, \\dots , f _ {1} ^ {\\{L \\}} \\right], \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 575, + 755, + 890, + 773 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $L$ denotes the number of stages, i.e., the number of multi-scale features. Then, the router $\\mathcal{R}$ will be fed with these features $F_{1}$ to predict a difficulty score $\\phi \\in (0,1)$ for this image as", + "bbox": [ + 496, + 780, + 893, + 840 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\phi = \\mathcal {R} \\left(F _ {1}\\right). \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 655, + 838, + 890, + 853 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Generally speaking, the \"easy\" images exit at the first backbone, while the \"hard\" images require the further processing. Specifically, if the router classifies the input image as", + "bbox": [ + 496, + 854, + 893, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "6284", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "an \"easy\" one, the followed neck and head $\\mathcal{D}_1$ will output the detection results $\\mathbf{y}$ as", + "bbox": [ + 76, + 90, + 468, + 121 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {y} = \\mathcal {D} _ {1} \\left(F _ {1}\\right). \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 228, + 128, + 468, + 143 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "On the contrary, if the router classifies the input image as a \"hard\" one, the multi-scale features will need further enhancement by the second backbone, instead of immediately decoded by $\\mathcal{D}_1$ . In particular, we embed the multi-scale features $F_{1}$ into $H$ by a composite connection module $\\mathcal{G}$ as", + "bbox": [ + 76, + 151, + 468, + 227 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nH = \\mathcal {G} \\left(F _ {1}\\right) = \\left[ h ^ {\\{1 \\}}, h ^ {\\{2 \\}}, \\dots , h ^ {\\{L \\}} \\right], \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 155, + 232, + 468, + 250 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\mathcal{G}$ is the DHLC of CBNet [24, 30] in our implementation. Then, we feed the input image $\\mathbf{x}$ into the second backbone and enhance the features of the second backbone via summing the corresponding elements of $H$ at each stage sequentially, denoted as", + "bbox": [ + 76, + 257, + 468, + 332 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nF _ {2} = \\mathcal {B} _ {2} (\\mathbf {x}, H) = \\left[ f _ {2} ^ {\\{1 \\}}, f _ {2} ^ {\\{2 \\}}, \\dots , f _ {2} ^ {\\{L \\}} \\right], \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 143, + 339, + 468, + 357 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "and the detection results will be obtained by the second head and neck $\\mathcal{D}_2$ as", + "bbox": [ + 76, + 364, + 468, + 393 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {y} = \\mathcal {D} _ {2} \\left(F _ {2}\\right). \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 228, + 393, + 468, + 407 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Through the above process, the \"easy\" images will be processed by only one backbone, while the \"hard\" images will be processed by two. Obviously, with such an architecture, trades-offs between computation (i.e., speed) and accuracy can be achieved.", + "bbox": [ + 76, + 410, + 468, + 484 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. Adaptive router", + "text_level": 1, + "bbox": [ + 76, + 492, + 235, + 508 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In mainstream object detectors, different scale features play different roles. Generally, the features of the shallow layers, with strong spatial information and small receptive fields, are more used to detect small objects. In contrast, the features of the deep layers, with strong semantic information and large receptive fields, are more used to detect large objects. This property makes it necessary to consider multi-scale information when predicting the difficulty score of an image. According to this, we design an adaptive router based on the multi-scale features, that is, a simple yet effective decision-maker for the dynamic detector.", + "bbox": [ + 76, + 513, + 468, + 679 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Inspired by the squeeze-and-excitation (SE) module [16], we first pool the multi-scale features $F_{1}$ independently and concatenate them all as", + "bbox": [ + 76, + 680, + 468, + 724 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\widetilde {F} _ {1} = \\mathcal {C} ([ \\mathcal {P} (f _ {1} ^ {\\{1 \\}}), \\mathcal {P} (f _ {1} ^ {\\{2 \\}}), \\dots , \\mathcal {P} (f _ {1} ^ {\\{L \\}}) ]), \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 137, + 731, + 468, + 750 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\mathcal{P}$ denotes the global average pooling and $\\mathcal{C}$ denotes the channel-wise concatenation. With this operation, we compress the multi-scale features $F_{1}$ into a vector $\\widetilde{F}_1\\in \\mathbb{R}^d$ of dimension $d$ . Then, we map this vector to a difficulty score $\\phi \\in (0,1)$ via two learnable fully connected layers as", + "bbox": [ + 76, + 756, + 468, + 832 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\phi = \\sigma \\left(W _ {2} \\left(\\delta \\left(W _ {1} \\widetilde {F} _ {1} + b _ {1}\\right)\\right) + b _ {2}\\right), \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 166, + 837, + 468, + 853 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\delta, \\sigma$ denote the ReLU and Sigmoid activation functions respectively, and $W_{1}, W_{2}, b_{1}, b_{2}$ are learnable parameters. Following [59], we reduce the feature dimension to", + "bbox": [ + 76, + 854, + 468, + 900 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "$\\lfloor d / 4 \\rfloor$ in the first fully connected layer, and exploit the second fully connected layer with a Sigmoid function to generate the predicted score. It is worth noting that the computational burden of our router can be negligible since we first pool all multi-scale features to one vector.", + "bbox": [ + 498, + 90, + 890, + 167 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.3. Optimization strategy", + "text_level": 1, + "bbox": [ + 500, + 176, + 705, + 191 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In this section, we describe the optimization strategy for the above dynamic architecture.", + "bbox": [ + 500, + 199, + 890, + 228 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Firstly, we jointly train the cascaded detectors, and the training objective is", + "bbox": [ + 500, + 229, + 890, + 258 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\min _ {\\Theta_ {1}, \\Theta_ {2}} \\left(\\mathcal {L} _ {d e t} ^ {\\{1 \\}} (\\mathbf {x}, \\mathbf {y} | \\Theta_ {1}) + \\mathcal {L} _ {d e t} ^ {\\{2 \\}} (\\mathbf {x}, \\mathbf {y} | \\Theta_ {2})\\right), \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 565, + 265, + 890, + 289 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\mathbf{x},\\mathbf{y}$ denote the input image and the ground truth respectively, $\\Theta_{i}$ denotes the learnable parameters of the detector $i$ and $\\mathcal{L}_{det}^{\\{i\\}}$ denotes the training loss for detector $i$ (e.g., bounding box regression loss and classification loss). After the above training phase, these two detectors will be able to detect the objects, and we freeze their parameters $\\Theta_{1},\\Theta_{2}$ during the later training.", + "bbox": [ + 498, + 296, + 890, + 402 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Then, we train the adaptive router to automatically distinguish the difficulty of the image. Here, we assume the parameters of the router are $\\Theta_{\\mathcal{R}}$ and the predicted difficulty score obtained from the Eq. (8) is $\\phi$ . We hope the router can assign the \"easy\" images (i.e., with lower $\\phi$ ) to the faster detector (i.e., the first detector) and the \"hard\" images (i.e., with higher $\\phi$ ) to the more accurate detector (i.e., the second detector).", + "bbox": [ + 498, + 404, + 890, + 523 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "However, it is non-trivial to implement that in practice. If we directly optimize the router without any constraints as", + "bbox": [ + 500, + 523, + 890, + 555 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\min _ {\\Theta_ {\\mathcal {R}}} \\left((1 - \\phi) \\mathcal {L} _ {d e t} ^ {\\{1 \\}} (\\mathbf {x}, \\mathbf {y} | \\Theta_ {1}) + \\phi \\mathcal {L} _ {d e t} ^ {\\{2 \\}} (\\mathbf {x}, \\mathbf {y} | \\Theta_ {2})\\right), \\tag {10}\n$$\n", + "text_format": "latex", + "bbox": [ + 527, + 563, + 890, + 587 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "the router will always choose the most accurate detector as it allows for a lower training loss. Furthermore, if we naively add hardware constraints to the training objective as", + "bbox": [ + 498, + 597, + 890, + 642 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\min _ {\\Theta_ {\\mathcal {R}}} \\left((1 - \\phi) \\mathcal {L} _ {d e t} ^ {\\{1 \\}} (\\mathbf {x}, \\mathbf {y} | \\Theta_ {1}) \\right. \\tag {11} \\\\ + \\phi \\mathcal {L} _ {\\det } ^ {\\{2 \\}} (\\mathbf {x}, \\mathbf {y} | \\Theta_ {2}) + \\lambda \\phi), \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 578, + 648, + 890, + 694 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "we will have to adjust the hyperparameter $\\lambda$ by try and error, leading to huge workforce consumption.", + "bbox": [ + 498, + 704, + 890, + 734 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "To overcome the above challenges, we propose a hyperparameter-free optimization strategy for our adaptive router. First, we define the difficulty criterion based on the corresponding training loss difference between two detectors of an image, as shown in Fig. 4. Specifically, we assume that if the loss difference of an image between two detectors is small enough, this image can be classified as an \"easy\" image. Instead, if the loss difference is large enough, it should be classified as a \"hard\" image. Ideally, for a balanced situation, we hope the easier half of all images go through the first detector, and the harder half go through the", + "bbox": [ + 496, + 734, + 890, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "6285", + "bbox": [ + 482, + 945, + 514, + 955 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/c87c12f27aa4df54ce02c10e3a34e24fcf159bcd50f1a454e1eb63c7592641e6.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 166, + 92, + 323, + 189 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/652de6e2eae6db9ba228cd6c079f2146e4a21c19bf3aa1a57ee2060e51842ba1.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 334, + 93, + 493, + 186 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/840745a6b4ee977605a4113364649562b952bfbddda0189c9ee3bc65a58430f5.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 504, + 93, + 660, + 186 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/e19632608de35955eea25ed022085fdc70a168b5e0131a1a94d01335c454ae59.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 669, + 123, + 797, + 181 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/edbe03cbfa8097748a9b5299898919a9dc32b8b496129657678ce3850bee9bfd.jpg", + "image_caption": [ + "Figure 4. Illustration of the difficulty criterion based on the training loss difference between two cascaded detectors. For the top image, the loss difference between the first detector and the second detector is very small, so it should be classified as an \"easy\" image. On the contrary, the loss difference of the bottom image is large, so it should be classified as a \"hard\" image." + ], + "image_footnote": [], + "bbox": [ + 166, + 205, + 323, + 289 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/59d5ce7642d1797840a469c41ae0c827741824c8c78baa9927f25ad1924ebb0c.jpg", + "image_caption": [ + "$\\mathcal{L}_{det}^{\\{1\\}} = 0.27$", + "$\\mathcal{L}_{det}^{\\{1\\}} = 0.57$" + ], + "image_footnote": [], + "bbox": [ + 336, + 205, + 491, + 289 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/ef82ec2b8d9024e02eabe318525496e70da2f16943caf59d360950f9a73d1bb1.jpg", + "image_caption": [ + "$\\mathcal{L}_{det}^{\\{2\\}} = 0.25$", + "$\\mathcal{L}_{det}^{\\{2\\}} = 0.33$" + ], + "image_footnote": [], + "bbox": [ + 504, + 205, + 660, + 289 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/e2b5e720778b29fd7f5152af3158ca06c68c6d3fd8448c9bcaa545ecf372fb7d.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 669, + 228, + 795, + 284 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/11636b696b83613f719e1f7a10f33a5fce3ea1567e75108d08f331df28b41e0f.jpg", + "image_caption": [ + "Figure 5. Qualitative analysis of the loss of two cascaded detectors on the images with different difficulties. With the proposed adaptive offset in our optimization strategy, the loss curves of two detectors intersect and reveal the optimal curve of DynamicDet." + ], + "image_footnote": [], + "bbox": [ + 106, + 378, + 434, + 522 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "second one. To achieve this, we introduce an adaptive offset to balance the losses of two detectors and optimize our router via gradient descent. In practice, we first calculate the median of the training loss difference $\\Delta$ between the first and the second detector on the training set. Then, the training objective of our router can be formulated as", + "bbox": [ + 75, + 606, + 468, + 698 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\min _ {\\Theta_ {\\mathcal {R}}} \\left((1 - \\phi) \\left(\\mathcal {L} _ {d e t} ^ {\\{1 \\}} (\\mathbf {x}, \\mathbf {y} \\mid \\Theta_ {1}) - \\Delta / 2\\right) \\right. \\tag {12} \\\\ + \\phi (\\mathcal {L} _ {\\det } ^ {\\{2 \\}} (\\mathbf {x}, \\mathbf {y} | \\Theta_ {2}) + \\Delta / 2)), \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 145, + 708, + 467, + 753 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\Delta / 2$ is used to reward the first detector and punish the second detector, respectively. As the qualitative analysis shown in Fig. 5, without this reward and penalty, the losses of the second detector are always smaller than the first detector. When the reward and penalty are conducted, their loss curves intersect and reveal the optimal curve.", + "bbox": [ + 75, + 763, + 467, + 854 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Our training objective provides a means to optimize the adaptive router by introducing the following gradient through the difficulty score $\\phi$ to all parameters $\\Theta_{\\mathcal{R}}$ of the", + "bbox": [ + 75, + 854, + 468, + 900 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "router as", + "bbox": [ + 500, + 378, + 560, + 388 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\frac {\\partial \\mathcal {L}}{\\partial \\Theta_ {\\mathcal {R}}} = \\frac {\\partial \\mathcal {L}}{\\partial \\phi} \\frac {\\partial \\phi}{\\partial \\Theta_ {\\mathcal {R}}} = - \\frac {\\partial \\phi}{\\partial \\Theta_ {\\mathcal {R}}} \\left(\\mathcal {L} _ {d e t} ^ {\\{1 \\}} - \\mathcal {L} _ {d e t} ^ {\\{2 \\}} - \\Delta\\right). \\tag {13}\n$$\n", + "text_format": "latex", + "bbox": [ + 519, + 395, + 890, + 424 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "To distinguish between \"easy\" and \"hard\" images better, we expect the optimization direction of the router to be related to the difficulty of the image, i.e., the difference in loss between the two detectors. Obviously, the gradient at Eq. (13) enable such expectation.", + "bbox": [ + 498, + 431, + 890, + 506 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.4. Variable-speed inference", + "text_level": 1, + "bbox": [ + 500, + 517, + 725, + 532 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We further propose a simple and effective method to determine the difficulty score thresholds to achieve variable-speed inference with only one dynamic detector. Specifically, our adaptive router will output a difficulty score and decide which detector to go through based on a certain threshold during inference. Therefore, we can set different thresholds to achieve different accuracy-speed trade-offs. Firstly, we count the difficulty scores $S_{val}$ of the validation set. Then, based on the actual needs (e.g., the target latency), we can obtain the corresponding threshold for our router. For example, assuming the latency of the first detector is $lat_1$ , the latency of the cascaded two detectors is $lat_2$ and the target latency is $lat_t$ , we can calculate the maximum allowable proportion of the \"hard\" images $k$ as", + "bbox": [ + 496, + 540, + 890, + 752 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nk = \\frac {l a t _ {t} - l a t _ {1}}{l a t _ {2} - l a t _ {1}}, \\quad l a t _ {1} \\leq l a t _ {t} \\leq l a t _ {2}, \\tag {14}\n$$\n", + "text_format": "latex", + "bbox": [ + 571, + 758, + 890, + 787 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "and then the threshold $\\tau_{val}$ will be", + "bbox": [ + 500, + 792, + 728, + 808 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\tau_ {v a l} = \\operatorname {p e r c e n t i l e} \\left(S _ {v a l}, k\\right), \\tag {15}\n$$\n", + "text_format": "latex", + "bbox": [ + 609, + 816, + 890, + 830 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where percentile $(\\cdot, k)$ means to compute the $k$ -th quantile of the data. It is worth noting that this threshold $\\tau_{val}$ is robust in both validation set and test set because these two sets are independent and identically distributed (i.e., i.i.d.).", + "bbox": [ + 496, + 839, + 890, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "6286", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/309f662c4fdbb111e8afaaf0cc391bda26dbd9dde3fcadd2dc857f8c055be219.jpg", + "table_caption": [], + "table_footnote": [ + "1 The FPS marked with $\\dagger$ are from the corresponding papers, and others are measured on the same machine with 1 NVIDIA V100 GPU.", + "Table 1. Comparison with the state-of-the-art real-time object detectors on COCO test-dev." + ], + "table_body": "
ModelSizeFLOPsFPSAP
EAutoDet-X [48]640225.3G41†49.2
YOLOX-L [9]640155.6G69†50.1
YOLOX-X [9]640281.9G58†51.5
YOLOv5-L (r6.2) [11]640109.1G11449.0
YOLOv5-X (r6.2) [11]640205.7G10050.9
YOLOv6-M [21]64082.2G10949.6
YOLOv6-L [21]640144.0G7652.4
PP-YOLOE+-M [53]64049.9G123†50.0
PP-YOLOE+-L [53]640110.1G78†53.3
PP-YOLOE+-X [53]640206.6G45†54.9
YOLOv7 [45]640104.7G11451.4
Dy-YOLOv7/10640112.4G11052.1
Dy-YOLOv7/50640143.2G9653.3
Dy-YOLOv7/90640174.0G8553.8
Dy-YOLOv7/100640181.7G8353.9
YOLOv7-X [45]640189.9G10553.1
Dy-YOLOv7-X/10640201.7G9853.3
Dy-YOLOv7-X/50640248.9G7854.4
Dy-YOLOv7-X/90640296.1G6555.0
Dy-YOLOv7-X/100640307.9G6455.0
YOLOv5-M6 (r6.2) [11]1280200.0G9651.4
YOLOv5-L6 (r6.2) [11]1280445.6G6553.8
YOLOv5-X6 (r6.2) [11]1280839.2G3955.0
YOLOv7-W6 [45]1280360.0G7854.9
YOLOv7-E6 [45]1280515.2G5256.0
YOLOv7-D6 [45]1280806.8G4156.6
YOLOv7-E6E [45]1280843.2G3356.8
Dy-YOLOv7-W6/101280384.2G7455.2
Dy-YOLOv7-W6/501280480.8G5856.1
Dy-YOLOv7-W6/901280577.4G4856.7
Dy-YOLOv7-W6/1001280601.6G4656.8
", + "bbox": [ + 81, + 88, + 465, + 608 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Based on the above strategy, one dynamic detector can directly cover the accuracy-speed trade-offs from the single to double detectors, avoiding redesigning and training multiple detectors under different hardware constraints.", + "bbox": [ + 75, + 685, + 467, + 744 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 76, + 757, + 207, + 773 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "In this section, we evaluate our DynamicDet through extensive experiments. In Sec. 4.1, we detail the experimental setups. In Sec. 4.2, we compare our DynamicDet with the state-of-the-art real-time detectors. In Sec. 4.3, we present the experimental results on two-stage detectors with CNN and transformer-based backbones to demonstrate the generality of DynamicDet over different backbones and detectors. In Sec. 4.4, we ablate each component of DynamicDet", + "bbox": [ + 75, + 779, + 467, + 900 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "in detail. In Sec. 4.5, we visualize the \"easy\" and the \"hard\" images determined by the adaptive router.", + "bbox": [ + 498, + 90, + 888, + 119 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.1. Experimental setups", + "text_level": 1, + "bbox": [ + 500, + 125, + 692, + 140 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We conduct experiments on the COCO [28] benchmark. All the models presented are trained on the 118k training images, and tested on the 5k minival images and 20k test-dev images. We choose the YOLOv7 [45] series models as the real-time detector baseline, and the Faster R-CNN [39] (ResNet [15]) and the Mask R-CNN [14] (Swin Transformer [31]) as the two-stage detector baselines. All dynamic detectors are trained with the same hyper-parameters of their corresponding baselines. We use brief notation to indicate the easy-hard proportion for each dynamic detector: for instance, \"Dy-YOLOv7-X/10\" means the dynamic YOLOv7-X model with $10\\%$ images are classified as \"hard\" and the rest are classified as \"easy\". The training of the adaptive router is conducted on a single GPU with batchsize 1 and two epochs, utilizing the AdamW [32] optimizer with a constant learning rate $1 \\times 10^{-5}$ and weight decay $5 \\times 10^{-3}$ . The reported FLOPs for dynamic detectors are the average FLOPs on the corresponding dataset. The speed performance is measured on a machine with 1 NVIDIA V100 GPU unless otherwise stated. The implementation of Dy-YOLOv7 is developed by the YOLOv7 [45] framework, with two identical detectors. The implementation of dynamic two-stage detectors is developed by the open-source CBNet [24] framework, with two identical backbones and a shared neck and head.", + "bbox": [ + 496, + 143, + 890, + 521 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.2. Comparison with the state-of-the-arts", + "text_level": 1, + "bbox": [ + 500, + 525, + 823, + 540 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "As shown in Tab. 1, compared with the state-of-the-art high-performance real-time object detectors, our dynamic detectors obtain better results and achieve the new state-of-the-art accuracy-speed trade-offs. Specifically, DyYOLOv7-W6 / 50 achieves $56.1\\%$ AP with 58 FPS, which is $0.1\\%$ more accurate and $12\\%$ faster than YOLOv7-E6. Dy-YOLOv7-W6 / 100 achieves $56.8\\%$ AP with 46 FPS, which is $39\\%$ faster than YOLOv7-E6E with a similar accuracy. It is worth noting that these trade-offs are obtained by only one dynamic detector instead of multiple independent models.", + "bbox": [ + 496, + 545, + 890, + 710 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.3. Generality for two-stage detectors", + "text_level": 1, + "bbox": [ + 500, + 714, + 795, + 729 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We conduct experiments on two classic two-stage detectors (i.e., Faster R-CNN [39], Mask R-CNN [14]) to show the generality of our DynamicDet. As shown in Tab. 2, our method is compatible with two-stage detectors and can also improve the accuracy-speed performance of baselines. For example, Dy-Faster R-CNN ResNet50 / 90 boosts the bbox AP by $1\\%$ with the comparable inference speed for Faster R-CNN ResNet101. Furthermore, DynamicDet is also compatible with transformer-based backbones (e.g., Swin Transformer [31]). Dy-Mask R-CNN Swin-T / 90 improves the bbox AP to $49.9\\%$ with the comparable inference", + "bbox": [ + 496, + 734, + 890, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "6287", + "bbox": [ + 482, + 945, + 514, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/2af7fa10586c53514e026f99ad6d98bb258f5f138148b6a17974f1d27509402c.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
ModelFLOPsFPSAPboxAPmask
Faster R-CNN ResNet50 [15, 39]207.1G2337.4-
Faster R-CNN ResNet101 [15, 39]283.1G1839.4-
Dy-Faster R-CNN ResNet50 / 50245.4G2039.5-
Dy-Faster R-CNN ResNet50 / 90276.0G1740.4-
Mask R-CNN Swin-T [14, 31]263.8G1546.041.6
Mask R-CNN Swin-S [14, 31]353.8G1248.243.2
Dy-Mask R-CNN Swin-T / 50310.6G1248.743.6
Dy-Mask R-CNN Swin-T / 90348.0G1149.944.2
", + "bbox": [ + 81, + 88, + 460, + 234 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/20d16858f67a13a72af9d2dbad9cd55f48a8f43b8a1472acbd7744c8a4c3abca.jpg", + "image_caption": [ + "Figure 6. Bounding box mAP v.s. inference speed for two-stage detectors on COCO minival." + ], + "image_footnote": [], + "bbox": [ + 84, + 267, + 455, + 443 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "speed of Mask R-CNN Swin-S. Notably, our two-stage dynamic detector can also perform variable-speed inference as illustrated in Fig. 6.", + "bbox": [ + 75, + 488, + 467, + 532 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.4. Ablation study", + "text_level": 1, + "bbox": [ + 76, + 540, + 225, + 556 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.4.1 Lightweight adaptive router", + "text_level": 1, + "bbox": [ + 76, + 564, + 326, + 579 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "The FLOPs ratios for the adaptive router in different models are presented in Tab. 3. We can find that this ratio is less than $0.002\\%$ in all models, demonstrating that the computational burden of the adaptive router can be negligible. This lightweight router avoids slowing down the detection process and ensures the fast decision-making for dynamic inference.", + "bbox": [ + 75, + 584, + 467, + 688 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.4.2 Effective training strategy for adaptive router", + "text_level": 1, + "bbox": [ + 76, + 699, + 447, + 714 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We ablate the effectiveness of the proposed training and optimization strategy for adaptive router. We first train a Mask R-CNN [14] with cascaded Swin-T [31] as our baseline detector. Then, we apply three strategies to achieve the decision-making for router: random, AP-based (i.e., dividing \"easy\" and \"hard\" images based on the validation accuracy and using them to train the router, similar to Adaptive Feeding [58]), and our proposed strategy. As shown in Fig. 7, we compare the bbox AP on the test-dev set of different training strategies. It is shown that our optimization strategy outperforms another two strategies under all latency constraints. Taking the detector with $84.5\\mathrm{ms}$ la", + "bbox": [ + 75, + 719, + 467, + 900 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/bad2a21494d648733e3da7df5b7a0b2e2aa3986533e1cafeb72b34dfd87df3eb.jpg", + "table_caption": [ + "Table 2. Comparison with two-stage detectors on COCO minival." + ], + "table_footnote": [], + "table_body": "
ModelRouterTotalRatio
Dy-YOLOv72.1M104.7G0.0020%
Dy-YOLOv7-W61.9M360.0G0.0005%
Dy-Faster R-CNN ResNet503.7M283.7G0.0013%
Dy-Mask R-CNN Swin-T0.5M357.4G0.0001%
", + "bbox": [ + 500, + 88, + 887, + 179 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 3. Comparison of the adaptive router's FLOPs and the total FLOPs in different dynamic models.", + "bbox": [ + 498, + 186, + 890, + 215 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/e6dd069a60c275cd8825a7a86211f867ab10d89897c056b291e1f2cff0010104.jpg", + "image_caption": [ + "Figure 7. Comparison of the proposed strategy and other two decision-making strategies." + ], + "image_footnote": [], + "bbox": [ + 527, + 229, + 859, + 404 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "tency (i.e., $50\\%$ easy and $50\\%$ hard) as an example, our strategy exceeds random selection $0.9\\%$ AP and AP-based strategy $0.7\\%$ AP. This proves that our optimization strategy effectively improves the discrimination accuracy of the router and outperforms AP-based strategy [58].", + "bbox": [ + 496, + 450, + 890, + 527 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.4.3 Robust variable-speed inference strategy", + "text_level": 1, + "bbox": [ + 498, + 535, + 836, + 550 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "To achieve variable-speed inference for a dynamic detector, we count the difficulty scores on the validation set and directly adopt the corresponding thresholds for the test set. This strategy requires the validation set to be large enough. However, with custom datasets, this is not always sufficient. To demonstrate the robustness of our variable-speed inference strategy, we analyze the impact of the validation set size on the threshold consistency between the validation set and test set. Taking the Dy-Mask R-CNN Swin-T on COCO [28] dataset as an example, its threshold for $50\\%$ quantile on the test set is 0.62. Then, we count the thresholds for $50\\%$ quantile on the validation set of different sizes (i.e., $0.5\\mathrm{k}$ , $1\\mathrm{k}$ , ..., $5\\mathrm{k}$ ). As shown in Fig. 9, the threshold obtained from $5\\mathrm{k}$ validation images is consistent with the threshold of the test set, which confirms our assumption in Sec. 3.4. Later, as the data size decreases, the thresholds of the validation set change within a small range. However, when the data size is less than $1.5\\mathrm{k}$ , the threshold of the validation set and the test set will occur a large deviation (i.e., 0.11 at $1\\mathrm{k}$ ). Overall, our variable-speed inference strategy is stable when the validation set size is relatively sufficient (e.g., about $2\\mathrm{k}$ validation images for the $20\\mathrm{k}$ test set on COCO [28]).", + "bbox": [ + 496, + 553, + 890, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "6288", + "bbox": [ + 482, + 945, + 514, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/fa011afe1afb13eaf8464c89f3ac1e730022cababa4383be608b1aba1fed37f6.jpg", + "image_caption": [ + "Figure 8. Visualization of the \"easy\" and the \"hard\" images. The horizontal direction corresponds to the difficulty scores predicted by our adaptive router in Dy-Mask R-CNN Swin-T." + ], + "image_footnote": [], + "bbox": [ + 122, + 97, + 267, + 257 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/3c57b4f1596c3835ffc2418e5a78b1efae89b211944cdc2e94d3aacb2212b078.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 272, + 98, + 406, + 257 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/753b2b3d021adc5b696f23a6348ce24e5d63533e714f0a00fa109cce3468199f.jpg", + "image_caption": [ + "Difficulty score" + ], + "image_footnote": [], + "bbox": [ + 413, + 98, + 547, + 257 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/dc2f37bd9ec0096463d18d76ee878c7b6ef90581554d89f924e2860150e01fc4.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 553, + 98, + 687, + 257 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/b0856eb2cff187efa5b6c57e769487d74de7ff14c30f349d4b156edf4c4852e4.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 694, + 98, + 828, + 257 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/d3079eafb4ddf953b5b366ef5922c413435bdb2635c8a385ea5c4bda725a36fb.jpg", + "image_caption": [ + "Figure 9. Comparison of the thresholds obtained from the test set and the validation sets of different sizes." + ], + "image_footnote": [], + "bbox": [ + 116, + 316, + 428, + 479 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.4.4 Comparison with the trade-offs obtained by adjusting the input resolution", + "text_level": 1, + "bbox": [ + 76, + 526, + 468, + 558 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "For a well-trained detector, changing its input resolution can also quickly obtain a series of accuracy-speed trade-offs. Here we compare this method with our dynamic detector. As shown in Fig. 10, we compare our Dy-YOLOv7-W6 and the YOLOv7-D6 with different input resolutions (i.e., $640\\sim 1280$ ), and we observe that our dynamic detector achieves better accuracy-speed trade-offs. For example, our Dy-YOLOv7-W6 achieves $55.2\\%$ AP at 74 FPS (13.5 ms), while YOLOv7-D6 with 640 input resolution only achieves $52.2\\%$ AP at an even slower inference speed.", + "bbox": [ + 75, + 565, + 468, + 717 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.5. Visualization of images with different difficulty scores", + "text_level": 1, + "bbox": [ + 76, + 726, + 468, + 756 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We depict the images with different predicted difficulty scores in Fig. 8, ascending from left to right. That is, the images on the left are considered as the \"easy\" images, while those on the right are considered as the \"hard\" images. We can observe that the \"easy\" images usually contain fewer objects, with the usual camera viewpoint and the clean background. In contrast, the \"hard\" images usually have more complex scenes with severe occlusion and much more small objects.", + "bbox": [ + 75, + 763, + 470, + 902 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/413422f95248967b7ee9cb64d40f17b1d4bb7be470d768bf22d2664da7c135e4.jpg", + "image_caption": [ + "Figure 10. Comparison of the trade-offs obtained from our DyYOLOv7-W6 and YOLOv7-D6 with different resolutions." + ], + "image_footnote": [], + "bbox": [ + 545, + 316, + 846, + 479 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 523, + 619, + 540 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this paper, we present a unified dynamic architecture for object detection, DynamicDet. We first design a dynamic architecture to support dynamic inference on mainstream detectors. Then, we propose an adaptive router to predict the difficulty score of each image and determine the inference route. With the above architecture and router, we then propose a hyperparameter-free optimization strategy with an adaptive offset to training our dynamic detectors. Last, we present a variable-speed inference strategy. With the settable threshold for dynamic inference, we can achieve a wide range of accuracy-speed trade-offs with only one dynamic detector. Extensive experimental results demonstrate the superiority of the proposed DynamicDet in accuracy and efficiency, and new state-of-the-art accuracy-speed trade-offs are achieved.", + "bbox": [ + 496, + 550, + 893, + 777 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgments", + "text_level": 1, + "bbox": [ + 500, + 790, + 658, + 808 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "This work was supported by National Natural Science Foundation of China under Grant 62176007. This work was also a research achievement of Key Laboratory of Science, Technology and Standard in Press Industry (Key Laboratory of Intelligent Press Media Technology).", + "bbox": [ + 496, + 815, + 893, + 893 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "6289", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 174, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Martin Abadi, Paul Barham, Jianmin Chen, Zhifeng Chen, Andy Davis, Jeffrey Dean, Matthieu Devin, Sanjay Ghemawat, Geoffrey Irving, Michael Isard, et al. Tensorflow: a system for large-scale machine learning. In 12th USENIX symposium on operating systems design and implementation (OSDI 16), pages 265-283, 2016. 3", + "[2] Alexey Bochkovskiy, Chien-Yao Wang, and Hong-Yuan Mark Liao. 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Dynamic feature pyramid networks for object detection. arXiv preprint arXiv:2012.00779, 2020. 4" + ], + "bbox": [ + 501, + 90, + 890, + 757 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "6291", + "bbox": [ + 482, + 945, + 513, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/DynamicDet_ A Unified Dynamic Architecture for Object Detection/a2c8ee28-6898-4bb7-b856-836c2ee0fe1f_model.json b/2023/DynamicDet_ A Unified Dynamic Architecture for Object Detection/a2c8ee28-6898-4bb7-b856-836c2ee0fe1f_model.json new file mode 100644 index 0000000000000000000000000000000000000000..d6970cb819c1269d1f86c69069cd10eda54144e8 --- /dev/null +++ b/2023/DynamicDet_ A Unified Dynamic Architecture for Object Detection/a2c8ee28-6898-4bb7-b856-836c2ee0fe1f_model.json @@ -0,0 +1,2563 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.001, + 0.812, + 0.047 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.145, + 0.131, + 0.826, + 0.154 + ], + "angle": 0, + "content": "DynamicDet: A Unified Dynamic Architecture for Object Detection" + }, + { + "type": "text", + "bbox": [ + 0.23, + 0.181, + 0.74, + 0.218 + ], + "angle": 0, + "content": "Zhihao Lin Yongtao Wang† Jinhe Zhang Xiaojie Chu Wangxuan Institute of Computer Technology, Peking University" + }, + { + "type": "text", + "bbox": [ + 0.266, + 0.22, + 0.7, + 0.252 + ], + "angle": 0, + "content": "linzhihao@stu.pku.edu.cn, wyt@stu.edu.cn \njinhezhang17@gmail.com, chuxiaojie@stu.pku.edu.cn" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.287, + 0.314, + 0.303 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.316, + 0.474, + 0.679 + ], + "angle": 0, + "content": "Dynamic neural network is an emerging research topic in deep learning. With adaptive inference, dynamic models can achieve remarkable accuracy and computational efficiency. However, it is challenging to design a powerful dynamic detector, because of no suitable dynamic architecture and exiting criterion for object detection. To tackle these difficulties, we propose a dynamic framework for object detection, named DynamicDet. Firstly, we carefully design a dynamic architecture based on the nature of the object detection task. Then, we propose an adaptive router to analyze the multi-scale information and to decide the inference route automatically. We also present a novel optimization strategy with an exiting criterion based on the detection losses for our dynamic detectors. Last, we present a variable-speed inference strategy, which helps to realize a wide range of accuracy-speed trade-offs with only one dynamic detector. Extensive experiments conducted on the COCO benchmark demonstrate that the proposed DynamicDet achieves new state-of-the-art accuracy-speed trade-offs. For instance, with comparable accuracy, the inference speed of our dynamic detector Dy-YOLOv7-W6 surpasses YOLOv7-E6 by \\(12\\%\\), YOLOv7-D6 by \\(17\\%\\), and YOLOv7-E6E by \\(39\\%\\). The code is available at https://github.com/VDIGPKU/DynamicDet." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.689, + 0.21, + 0.705 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.709, + 0.471, + 0.876 + ], + "angle": 0, + "content": "Object detection is an essential topic in computer vision, as it is a fundamental component for other vision tasks, e.g., autonomous driving [26, 40, 56], multi-object tracking [52,57], intelligent transportation [36,55], etc. In recent years, tremendous progress has been made toward more accurate and faster detectors, such as Network Architecture Search (NAS)-based detectors [10,25,48] and YOLO series models [2,9,11,21,44,45]. However, these methods need to design and train multiple models to achieve a few good trade-offs between accuracy and speed, which is not flexible enough for various application scenarios. To alleviate this" + }, + { + "type": "image", + "bbox": [ + 0.52, + 0.289, + 0.871, + 0.479 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.487, + 0.895, + 0.543 + ], + "angle": 0, + "content": "Figure 1. Comparison of the proposed dynamic detectors and other efficient object detectors. Our method can achieve a wide range of state-of-the-art trade-offs between accuracy and speed with a single model." + }, + { + "type": "image", + "bbox": [ + 0.527, + 0.559, + 0.692, + 0.644 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.574, + 0.645, + 0.645, + 0.657 + ], + "angle": 0, + "content": "\"Easy\" image" + }, + { + "type": "image", + "bbox": [ + 0.699, + 0.559, + 0.863, + 0.644 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.746, + 0.645, + 0.817, + 0.657 + ], + "angle": 0, + "content": "\"Hard\" image" + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.663, + 0.892, + 0.69 + ], + "angle": 0, + "content": "Figure 2. Examples of \"easy\" and \"hard\" images for the object detection task." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.702, + 0.894, + 0.763 + ], + "angle": 0, + "content": "problem, we focus on dynamic inference for the object detection task, and attempt to use only one dynamic detector to achieve a wide range of good accuracy-speed trade-offs, as shown in Fig. 1." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.895, + 0.903 + ], + "angle": 0, + "content": "The human brain inspires many fields of deep learning, and the dynamic neural network [12] is a typical one. As two examples shown in Fig. 2, we can quickly identify all objects on the left \"easy\" image, while we need more time to achieve the same effect for the right one. In other words, the processing speeds of images are different in our brains [18, 34], which depend on the difficulties of the images. This property motivates the image-wise dynamic neural network, and many exciting works have been proposed" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.887, + 0.222, + 0.9 + ], + "angle": 0, + "content": "† Corresponding author." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "6282" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.468, + 0.182 + ], + "angle": 0, + "content": "(e.g., Branchynet [43], MSDNet [17], DVT [50]). Although these approaches have achieved remarkable performance, they are all designed specifically for the image classification task and are not suitable for other vision tasks, especially for the object detection [12]. The main difficulties in designing an image-wise dynamic detector are as follows." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.183, + 0.468, + 0.438 + ], + "angle": 0, + "content": "Dynamic detectors cannot utilize the existing dynamic architectures. Most existing dynamic architectures are cascaded with multiple stages (i.e., a stack of multiple layers) [17, 20, 33, 54], and predict whether to stop the inference at each exiting point. Such a paradigm is feasible in image classification but is ineffective in object detection, since an image has multiple objects and each object usually has different categories and scales, as shown in Fig. 2. Hence, almost all detectors depend heavily on multi-scale information, utilizing the features on different scales to detect objects of different sizes (which are obtained by fusing the multi-scale features of the backbone with a detection neck, i.e., FPN [27]). In this case, the exiting points for detectors can only be placed behind the last stage. Consequently, the entire backbone module has to be run completely [58], and it is impossible to achieve dynamic inference on multiple cascaded stages." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.44, + 0.468, + 0.59 + ], + "angle": 0, + "content": "Dynamic detectors cannot exploit the existing exiting criteria for image classification. For the image classification task, the threshold of top-1 accuracy is a widely used criterion for decision-making [17, 50]. Notably, it only needs one fully connected layer to predict the top-1 accuracy at intermediate layer, which is easy and costless. However, object detection task requires the neck and the head to predict the categories and locations of the object instances [3, 14, 27, 39]. Hence, the existing exiting criteria for image classification is not suitable for object detection." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.591, + 0.468, + 0.725 + ], + "angle": 0, + "content": "To deal with the above difficulties, we propose a dynamic framework to achieve dynamic inference for object detection, named DynamicDet. Firstly, We design a dynamic architecture for the object detection task, which can exit with multi-scale information during the inference. Then, we propose an adaptive router to choose the best route for each image automatically. Besides, we present the corresponding optimization and inference strategies for the proposed DynamicDet." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.727, + 0.352, + 0.74 + ], + "angle": 0, + "content": "Our main contributions are as follows:" + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.746, + 0.468, + 0.82 + ], + "angle": 0, + "content": "- We propose a dynamic architecture for object detection, named DynamicDet, which consists of two cascaded detectors and a router. This dynamic architecture can be easily adapted to mainstream detectors, e.g., Faster R-CNN andYOLO." + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.826, + 0.468, + 0.901 + ], + "angle": 0, + "content": "- We propose an adaptive router to predict the difficulty scores of the images based on the multi-scale features, and achieve automatic decision-making. In addition, we propose a hyperparameter-free optimization strategy and a variable-speed inference strategy for our dy" + }, + { + "type": "list", + "bbox": [ + 0.096, + 0.746, + 0.468, + 0.901 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.533, + 0.093, + 0.662, + 0.106 + ], + "angle": 0, + "content": "namic architecture." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.11, + 0.892, + 0.185 + ], + "angle": 0, + "content": "- Extensive experiments show that DynamicDet can obtain a wide range of accuracy-speed trade-offs with only one dynamic detector. We also achieve new state-of-the-art trade-offs for real-time object detection (i.e., \\(56.8\\%\\) AP at 46 FPS)." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.199, + 0.637, + 0.214 + ], + "angle": 0, + "content": "2. Related work" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.221, + 0.815, + 0.237 + ], + "angle": 0, + "content": "2.1. Backbone design on object detection" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.241, + 0.892, + 0.511 + ], + "angle": 0, + "content": "Backbones play a crucial role in object detectors since the performance of detectors highly relies on the multiscale features extracted by the backbones [4]. ResNet [15] and its variants (e.g., ResNeXt [51], Res2Net [8]) introduce the residual connection to neural networks, providing a high-quality backbone architecture family for all vision tasks. Further, to reduce the calculation load, CSPNet [46] cuts down the duplicate gradient information to reduce the heavy inference, improving the efficiency significantly. Its effective architecture also inspires many lightweight detectors (e.g.,YOLO series models [2, 9, 11, 21, 44, 45]). Then, some transformer-based backbones (e.g.,PVT [47], Swin Transformer [31]) are proposed to learn the global information better. In addition, many auto-designed backbones [4,6,19,41] for object detection are proposed. For example, DetNAS [4] utilizes the one-shot supernet to search the optimal backbone, with the guidance of the object detection task." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.512, + 0.892, + 0.709 + ], + "angle": 0, + "content": "Although many kinds of backbones have been proposed, almost all of them are single-pass architectures, which sequentially produce one set of multi-scale features. Thus, all stages of them cannot be skipped. Fortunately, some works propose the architectures of multiple cascaded backbones, which have the potential to be converted as a dynamic backbone for object detection. For example, CBNet [24, 30] groups multiple identical backbones with composite connections, constructing a more powerful composite backbone. Since these backbones have multiple sub-backbones and each of them can produce intermediate multi-scale features, we can add some exiting points after each subbackbone for dynamic inference." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.715, + 0.88, + 0.731 + ], + "angle": 0, + "content": "2.2. Accuracy-speed trade-off on object detection" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.735, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Almost all detection methods are designed for a better accuracy-speed trade-off, i.e., more accurate and faster. With a given detector, the simplest way to obtain an accuracy-speed trade-off is to adopt the model scaling techniques [42, 44, 45] (e.g., increasing the channel size or repeating the layers). EfficientDet [42] uniformly scales the resolution, depth, and width for all modules simultaneously, achieving remarkable efficiency on real-time detectors. Scaled-YOLOv4 [44] modifies not only the depth, width, and resolution but also the structure of the network to pursue a better trade-off. YOLOv7 [45] designs a" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.946, + 0.516, + 0.957 + ], + "angle": 0, + "content": "6283" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.178, + 0.098, + 0.795, + 0.288 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.293, + 0.895, + 0.337 + ], + "angle": 0, + "content": "Figure 3. Illustration of the architecture of DynamicDet. The first backbone extracts the multi-scale features from the input image firstly. Then, the router will be fed with these multi-scale features to predict the difficulty of image and to decide the inference route. Notably, the \"easy\" images will be processed by only one backbone, while the \"hard\" images will be processed by two." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.343, + 0.473, + 0.51 + ], + "angle": 0, + "content": "compound scaling method for concatenation-based models, achieving new state-of-the-art trade-offs. EAutoDet [48] constructs a supernet and adopts Network Architecture Search (NAS) to automatically search for suitable scaling factors under different hardware constraints. However, all the above methods need to train multiple detectors for the best trade-offs (e.g., one tiny model for real-time detection and another large model for accurate detection), leading to colossal training resources. In this paper, we focus on dynamic inference, aiming to achieve a wide range of best accuracy-speed trade-offs with only one dynamic detector." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.518, + 0.307, + 0.533 + ], + "angle": 0, + "content": "2.3. Dynamic neural network" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.538, + 0.473, + 0.884 + ], + "angle": 0, + "content": "The dynamic neural network can achieve adaptive computation for different images (i.e., image-wise [17, 20, 22, 23, 43, 49, 50, 54]) or pixels (i.e., spatial-wise [7, 13, 37]). SACT [7] is a classic spatial-wise dynamic network, which adaptively adjusts the number of executed layers for the regions of the image, to improve the efficiency of networks. Its practical speed-up performance highly relies on the hardware-software co-design [12]. However, the current deep learning hardware and libraries [1, 35] are not friendly to these spatial-wise dynamic networks [12]. On the contrary, image-wise dynamic networks do not rely on sparse computing and can be easily accelerated on the conventional CPUs and GPUs [5]. Branchynet [43] introduces the early exiting strategy, which enables the model to exit from the intermediate layer whenever the model is confident enough. MSDNet [17] and its variants [23, 54] develop a multi-classifier architecture for the image classification task. DVT [50] cascades multiple transformers with increasing numbers of tokens and activates them sequentially to achieve dynamic inference. However, these methods are all designed specifically for the image classification task and cannot be applied to other vision tasks, such as object detection." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.886, + 0.47, + 0.901 + ], + "angle": 0, + "content": "The closest work to our DynamicDet is Adaptive Feed" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.343, + 0.895, + 0.525 + ], + "angle": 0, + "content": "ing [58]. In Adaptive Feeding [58], each image is detected by a lightweight detector (e.g., TinyYOLO [38]) and then classified as easy or hard by a linear support vector machine (SVM) with those detected results. Then, the easy images will go through a fast detector (e.g., SSD300 [29]), while the hard images will go through a more accurate but slower one (e.g., SSD500 [29]). Adaptive Feeding [58] introduces the above multi-stage process for dynamic inference, which is inefficient and not elegant. In comparison, the proposed DynamicDet cascades two detectors and a classifier (i.e., the router), yielding a more unified and efficient dynamic detector." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.535, + 0.611, + 0.553 + ], + "angle": 0, + "content": "3. Approach" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.558, + 0.894, + 0.65 + ], + "angle": 0, + "content": "In the following, we elaborate on our dynamic architecture for object detection. We first introduce the overall architecture in Sec. 3.1. Then, we state the proposed adaptive router, i.e., the decision maker of DynamicDet in Sec. 3.2. Finally, we introduce the optimization strategy and a variable-speed inference strategy in Secs. 3.3 and 3.4." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.656, + 0.694, + 0.67 + ], + "angle": 0, + "content": "3.1. Overall architecture" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.677, + 0.894, + 0.752 + ], + "angle": 0, + "content": "The overall architecture of our dynamic detector is shown in Fig. 3. Inspired by CBNet [24, 30], our dynamic architecture consists of two detectors and one router. For an input image \\(\\mathbf{x}\\), we initially extract its multi-scale features \\(F_{1}\\) with the first backbone \\(\\mathcal{B}_1\\) as" + }, + { + "type": "equation", + "bbox": [ + 0.576, + 0.756, + 0.892, + 0.775 + ], + "angle": 0, + "content": "\\[\nF _ {1} = \\mathcal {B} _ {1} (\\mathbf {x}) = \\left[ f _ {1} ^ {\\{1 \\}}, f _ {1} ^ {\\{2 \\}}, \\dots , f _ {1} ^ {\\{L \\}} \\right], \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.781, + 0.895, + 0.841 + ], + "angle": 0, + "content": "where \\(L\\) denotes the number of stages, i.e., the number of multi-scale features. Then, the router \\(\\mathcal{R}\\) will be fed with these features \\(F_{1}\\) to predict a difficulty score \\(\\phi \\in (0,1)\\) for this image as" + }, + { + "type": "equation", + "bbox": [ + 0.656, + 0.839, + 0.892, + 0.854 + ], + "angle": 0, + "content": "\\[\n\\phi = \\mathcal {R} \\left(F _ {1}\\right). \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.856, + 0.894, + 0.901 + ], + "angle": 0, + "content": "Generally speaking, the \"easy\" images exit at the first backbone, while the \"hard\" images require the further processing. Specifically, if the router classifies the input image as" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "6284" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.47, + 0.122 + ], + "angle": 0, + "content": "an \"easy\" one, the followed neck and head \\(\\mathcal{D}_1\\) will output the detection results \\(\\mathbf{y}\\) as" + }, + { + "type": "equation", + "bbox": [ + 0.23, + 0.13, + 0.47, + 0.145 + ], + "angle": 0, + "content": "\\[\n\\mathbf {y} = \\mathcal {D} _ {1} \\left(F _ {1}\\right). \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.152, + 0.469, + 0.228 + ], + "angle": 0, + "content": "On the contrary, if the router classifies the input image as a \"hard\" one, the multi-scale features will need further enhancement by the second backbone, instead of immediately decoded by \\(\\mathcal{D}_1\\). In particular, we embed the multi-scale features \\(F_{1}\\) into \\(H\\) by a composite connection module \\(\\mathcal{G}\\) as" + }, + { + "type": "equation", + "bbox": [ + 0.156, + 0.233, + 0.469, + 0.251 + ], + "angle": 0, + "content": "\\[\nH = \\mathcal {G} \\left(F _ {1}\\right) = \\left[ h ^ {\\{1 \\}}, h ^ {\\{2 \\}}, \\dots , h ^ {\\{L \\}} \\right], \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.258, + 0.469, + 0.333 + ], + "angle": 0, + "content": "where \\(\\mathcal{G}\\) is the DHLC of CBNet [24, 30] in our implementation. Then, we feed the input image \\(\\mathbf{x}\\) into the second backbone and enhance the features of the second backbone via summing the corresponding elements of \\(H\\) at each stage sequentially, denoted as" + }, + { + "type": "equation", + "bbox": [ + 0.144, + 0.34, + 0.469, + 0.358 + ], + "angle": 0, + "content": "\\[\nF _ {2} = \\mathcal {B} _ {2} (\\mathbf {x}, H) = \\left[ f _ {2} ^ {\\{1 \\}}, f _ {2} ^ {\\{2 \\}}, \\dots , f _ {2} ^ {\\{L \\}} \\right], \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.366, + 0.469, + 0.395 + ], + "angle": 0, + "content": "and the detection results will be obtained by the second head and neck \\(\\mathcal{D}_2\\) as" + }, + { + "type": "equation", + "bbox": [ + 0.23, + 0.394, + 0.469, + 0.408 + ], + "angle": 0, + "content": "\\[\n\\mathbf {y} = \\mathcal {D} _ {2} \\left(F _ {2}\\right). \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.411, + 0.469, + 0.486 + ], + "angle": 0, + "content": "Through the above process, the \"easy\" images will be processed by only one backbone, while the \"hard\" images will be processed by two. Obviously, with such an architecture, trades-offs between computation (i.e., speed) and accuracy can be achieved." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.493, + 0.236, + 0.509 + ], + "angle": 0, + "content": "3.2. Adaptive router" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.514, + 0.469, + 0.68 + ], + "angle": 0, + "content": "In mainstream object detectors, different scale features play different roles. Generally, the features of the shallow layers, with strong spatial information and small receptive fields, are more used to detect small objects. In contrast, the features of the deep layers, with strong semantic information and large receptive fields, are more used to detect large objects. This property makes it necessary to consider multi-scale information when predicting the difficulty score of an image. According to this, we design an adaptive router based on the multi-scale features, that is, a simple yet effective decision-maker for the dynamic detector." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.681, + 0.469, + 0.725 + ], + "angle": 0, + "content": "Inspired by the squeeze-and-excitation (SE) module [16], we first pool the multi-scale features \\(F_{1}\\) independently and concatenate them all as" + }, + { + "type": "equation", + "bbox": [ + 0.138, + 0.732, + 0.469, + 0.751 + ], + "angle": 0, + "content": "\\[\n\\widetilde {F} _ {1} = \\mathcal {C} ([ \\mathcal {P} (f _ {1} ^ {\\{1 \\}}), \\mathcal {P} (f _ {1} ^ {\\{2 \\}}), \\dots , \\mathcal {P} (f _ {1} ^ {\\{L \\}}) ]), \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.757, + 0.469, + 0.833 + ], + "angle": 0, + "content": "where \\(\\mathcal{P}\\) denotes the global average pooling and \\(\\mathcal{C}\\) denotes the channel-wise concatenation. With this operation, we compress the multi-scale features \\(F_{1}\\) into a vector \\(\\widetilde{F}_1\\in \\mathbb{R}^d\\) of dimension \\(d\\). Then, we map this vector to a difficulty score \\(\\phi \\in (0,1)\\) via two learnable fully connected layers as" + }, + { + "type": "equation", + "bbox": [ + 0.168, + 0.838, + 0.469, + 0.854 + ], + "angle": 0, + "content": "\\[\n\\phi = \\sigma \\left(W _ {2} \\left(\\delta \\left(W _ {1} \\widetilde {F} _ {1} + b _ {1}\\right)\\right) + b _ {2}\\right), \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.856, + 0.469, + 0.901 + ], + "angle": 0, + "content": "where \\(\\delta, \\sigma\\) denote the ReLU and Sigmoid activation functions respectively, and \\(W_{1}, W_{2}, b_{1}, b_{2}\\) are learnable parameters. Following [59], we reduce the feature dimension to" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.092, + 0.892, + 0.168 + ], + "angle": 0, + "content": "\\(\\lfloor d / 4 \\rfloor\\) in the first fully connected layer, and exploit the second fully connected layer with a Sigmoid function to generate the predicted score. It is worth noting that the computational burden of our router can be negligible since we first pool all multi-scale features to one vector." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.177, + 0.706, + 0.193 + ], + "angle": 0, + "content": "3.3. Optimization strategy" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.2, + 0.892, + 0.229 + ], + "angle": 0, + "content": "In this section, we describe the optimization strategy for the above dynamic architecture." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.23, + 0.892, + 0.26 + ], + "angle": 0, + "content": "Firstly, we jointly train the cascaded detectors, and the training objective is" + }, + { + "type": "equation", + "bbox": [ + 0.566, + 0.266, + 0.892, + 0.29 + ], + "angle": 0, + "content": "\\[\n\\min _ {\\Theta_ {1}, \\Theta_ {2}} \\left(\\mathcal {L} _ {d e t} ^ {\\{1 \\}} (\\mathbf {x}, \\mathbf {y} | \\Theta_ {1}) + \\mathcal {L} _ {d e t} ^ {\\{2 \\}} (\\mathbf {x}, \\mathbf {y} | \\Theta_ {2})\\right), \\tag {9}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.297, + 0.892, + 0.404 + ], + "angle": 0, + "content": "where \\(\\mathbf{x},\\mathbf{y}\\) denote the input image and the ground truth respectively, \\(\\Theta_{i}\\) denotes the learnable parameters of the detector \\(i\\) and \\(\\mathcal{L}_{det}^{\\{i\\}}\\) denotes the training loss for detector \\(i\\) (e.g., bounding box regression loss and classification loss). After the above training phase, these two detectors will be able to detect the objects, and we freeze their parameters \\(\\Theta_{1},\\Theta_{2}\\) during the later training." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.405, + 0.892, + 0.524 + ], + "angle": 0, + "content": "Then, we train the adaptive router to automatically distinguish the difficulty of the image. Here, we assume the parameters of the router are \\(\\Theta_{\\mathcal{R}}\\) and the predicted difficulty score obtained from the Eq. (8) is \\(\\phi\\). We hope the router can assign the \"easy\" images (i.e., with lower \\(\\phi\\)) to the faster detector (i.e., the first detector) and the \"hard\" images (i.e., with higher \\(\\phi\\)) to the more accurate detector (i.e., the second detector)." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.525, + 0.892, + 0.556 + ], + "angle": 0, + "content": "However, it is non-trivial to implement that in practice. If we directly optimize the router without any constraints as" + }, + { + "type": "equation", + "bbox": [ + 0.529, + 0.564, + 0.891, + 0.588 + ], + "angle": 0, + "content": "\\[\n\\min _ {\\Theta_ {\\mathcal {R}}} \\left((1 - \\phi) \\mathcal {L} _ {d e t} ^ {\\{1 \\}} (\\mathbf {x}, \\mathbf {y} | \\Theta_ {1}) + \\phi \\mathcal {L} _ {d e t} ^ {\\{2 \\}} (\\mathbf {x}, \\mathbf {y} | \\Theta_ {2})\\right), \\tag {10}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.598, + 0.892, + 0.643 + ], + "angle": 0, + "content": "the router will always choose the most accurate detector as it allows for a lower training loss. Furthermore, if we naively add hardware constraints to the training objective as" + }, + { + "type": "equation", + "bbox": [ + 0.58, + 0.65, + 0.891, + 0.695 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\min _ {\\Theta_ {\\mathcal {R}}} \\left((1 - \\phi) \\mathcal {L} _ {d e t} ^ {\\{1 \\}} (\\mathbf {x}, \\mathbf {y} | \\Theta_ {1}) \\right. \\tag {11} \\\\ + \\phi \\mathcal {L} _ {\\det } ^ {\\{2 \\}} (\\mathbf {x}, \\mathbf {y} | \\Theta_ {2}) + \\lambda \\phi), \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.705, + 0.891, + 0.735 + ], + "angle": 0, + "content": "we will have to adjust the hyperparameter \\(\\lambda\\) by try and error, leading to huge workforce consumption." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.736, + 0.892, + 0.901 + ], + "angle": 0, + "content": "To overcome the above challenges, we propose a hyperparameter-free optimization strategy for our adaptive router. First, we define the difficulty criterion based on the corresponding training loss difference between two detectors of an image, as shown in Fig. 4. Specifically, we assume that if the loss difference of an image between two detectors is small enough, this image can be classified as an \"easy\" image. Instead, if the loss difference is large enough, it should be classified as a \"hard\" image. Ideally, for a balanced situation, we hope the easier half of all images go through the first detector, and the harder half go through the" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.946, + 0.515, + 0.957 + ], + "angle": 0, + "content": "6285" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.168, + 0.093, + 0.325, + 0.19 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.336, + 0.094, + 0.494, + 0.188 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.377, + 0.189, + 0.452, + 0.206 + ], + "angle": 0, + "content": "\\(\\mathcal{L}_{det}^{\\{1\\}} = 0.27\\)" + }, + { + "type": "image", + "bbox": [ + 0.506, + 0.094, + 0.661, + 0.188 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.545, + 0.189, + 0.621, + 0.206 + ], + "angle": 0, + "content": "\\(\\mathcal{L}_{det}^{\\{2\\}} = 0.25\\)" + }, + { + "type": "image", + "bbox": [ + 0.671, + 0.124, + 0.798, + 0.182 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.168, + 0.207, + 0.325, + 0.29 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.338, + 0.207, + 0.493, + 0.29 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.377, + 0.29, + 0.452, + 0.308 + ], + "angle": 0, + "content": "\\(\\mathcal{L}_{det}^{\\{1\\}} = 0.57\\)" + }, + { + "type": "image", + "bbox": [ + 0.506, + 0.207, + 0.661, + 0.29 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.545, + 0.29, + 0.621, + 0.308 + ], + "angle": 0, + "content": "\\(\\mathcal{L}_{det}^{\\{2\\}} = 0.33\\)" + }, + { + "type": "image", + "bbox": [ + 0.671, + 0.229, + 0.797, + 0.285 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.315, + 0.894, + 0.358 + ], + "angle": 0, + "content": "Figure 4. Illustration of the difficulty criterion based on the training loss difference between two cascaded detectors. For the top image, the loss difference between the first detector and the second detector is very small, so it should be classified as an \"easy\" image. On the contrary, the loss difference of the bottom image is large, so it should be classified as a \"hard\" image." + }, + { + "type": "image", + "bbox": [ + 0.107, + 0.38, + 0.435, + 0.523 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.531, + 0.47, + 0.587 + ], + "angle": 0, + "content": "Figure 5. Qualitative analysis of the loss of two cascaded detectors on the images with different difficulties. With the proposed adaptive offset in our optimization strategy, the loss curves of two detectors intersect and reveal the optimal curve of DynamicDet." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.607, + 0.47, + 0.699 + ], + "angle": 0, + "content": "second one. To achieve this, we introduce an adaptive offset to balance the losses of two detectors and optimize our router via gradient descent. In practice, we first calculate the median of the training loss difference \\(\\Delta\\) between the first and the second detector on the training set. Then, the training objective of our router can be formulated as" + }, + { + "type": "equation", + "bbox": [ + 0.146, + 0.709, + 0.468, + 0.754 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\min _ {\\Theta_ {\\mathcal {R}}} \\left((1 - \\phi) \\left(\\mathcal {L} _ {d e t} ^ {\\{1 \\}} (\\mathbf {x}, \\mathbf {y} \\mid \\Theta_ {1}) - \\Delta / 2\\right) \\right. \\tag {12} \\\\ + \\phi (\\mathcal {L} _ {\\det } ^ {\\{2 \\}} (\\mathbf {x}, \\mathbf {y} | \\Theta_ {2}) + \\Delta / 2)), \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.765, + 0.468, + 0.856 + ], + "angle": 0, + "content": "where \\(\\Delta / 2\\) is used to reward the first detector and punish the second detector, respectively. As the qualitative analysis shown in Fig. 5, without this reward and penalty, the losses of the second detector are always smaller than the first detector. When the reward and penalty are conducted, their loss curves intersect and reveal the optimal curve." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.469, + 0.901 + ], + "angle": 0, + "content": "Our training objective provides a means to optimize the adaptive router by introducing the following gradient through the difficulty score \\(\\phi\\) to all parameters \\(\\Theta_{\\mathcal{R}}\\) of the" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.38, + 0.562, + 0.39 + ], + "angle": 0, + "content": "router as" + }, + { + "type": "equation", + "bbox": [ + 0.521, + 0.396, + 0.892, + 0.425 + ], + "angle": 0, + "content": "\\[\n\\frac {\\partial \\mathcal {L}}{\\partial \\Theta_ {\\mathcal {R}}} = \\frac {\\partial \\mathcal {L}}{\\partial \\phi} \\frac {\\partial \\phi}{\\partial \\Theta_ {\\mathcal {R}}} = - \\frac {\\partial \\phi}{\\partial \\Theta_ {\\mathcal {R}}} \\left(\\mathcal {L} _ {d e t} ^ {\\{1 \\}} - \\mathcal {L} _ {d e t} ^ {\\{2 \\}} - \\Delta\\right). \\tag {13}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.432, + 0.892, + 0.507 + ], + "angle": 0, + "content": "To distinguish between \"easy\" and \"hard\" images better, we expect the optimization direction of the router to be related to the difficulty of the image, i.e., the difference in loss between the two detectors. Obviously, the gradient at Eq. (13) enable such expectation." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.518, + 0.726, + 0.534 + ], + "angle": 0, + "content": "3.4. Variable-speed inference" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.541, + 0.892, + 0.753 + ], + "angle": 0, + "content": "We further propose a simple and effective method to determine the difficulty score thresholds to achieve variable-speed inference with only one dynamic detector. Specifically, our adaptive router will output a difficulty score and decide which detector to go through based on a certain threshold during inference. Therefore, we can set different thresholds to achieve different accuracy-speed trade-offs. Firstly, we count the difficulty scores \\( S_{val} \\) of the validation set. Then, based on the actual needs (e.g., the target latency), we can obtain the corresponding threshold for our router. For example, assuming the latency of the first detector is \\( lat_1 \\), the latency of the cascaded two detectors is \\( lat_2 \\) and the target latency is \\( lat_t \\), we can calculate the maximum allowable proportion of the \"hard\" images \\( k \\) as" + }, + { + "type": "equation", + "bbox": [ + 0.573, + 0.759, + 0.892, + 0.788 + ], + "angle": 0, + "content": "\\[\nk = \\frac {l a t _ {t} - l a t _ {1}}{l a t _ {2} - l a t _ {1}}, \\quad l a t _ {1} \\leq l a t _ {t} \\leq l a t _ {2}, \\tag {14}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.793, + 0.729, + 0.809 + ], + "angle": 0, + "content": "and then the threshold \\(\\tau_{val}\\) will be" + }, + { + "type": "equation", + "bbox": [ + 0.61, + 0.817, + 0.892, + 0.832 + ], + "angle": 0, + "content": "\\[\n\\tau_ {v a l} = \\operatorname {p e r c e n t i l e} \\left(S _ {v a l}, k\\right), \\tag {15}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.892, + 0.901 + ], + "angle": 0, + "content": "where percentile \\((\\cdot, k)\\) means to compute the \\(k\\)-th quantile of the data. It is worth noting that this threshold \\(\\tau_{val}\\) is robust in both validation set and test set because these two sets are independent and identically distributed (i.e., i.i.d.)." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.956 + ], + "angle": 0, + "content": "6286" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.082, + 0.089, + 0.467, + 0.609 + ], + "angle": 0, + "content": "
ModelSizeFLOPsFPSAP
EAutoDet-X [48]640225.3G41†49.2
YOLOX-L [9]640155.6G69†50.1
YOLOX-X [9]640281.9G58†51.5
YOLOv5-L (r6.2) [11]640109.1G11449.0
YOLOv5-X (r6.2) [11]640205.7G10050.9
YOLOv6-M [21]64082.2G10949.6
YOLOv6-L [21]640144.0G7652.4
PP-YOLOE+-M [53]64049.9G123†50.0
PP-YOLOE+-L [53]640110.1G78†53.3
PP-YOLOE+-X [53]640206.6G45†54.9
YOLOv7 [45]640104.7G11451.4
Dy-YOLOv7/10640112.4G11052.1
Dy-YOLOv7/50640143.2G9653.3
Dy-YOLOv7/90640174.0G8553.8
Dy-YOLOv7/100640181.7G8353.9
YOLOv7-X [45]640189.9G10553.1
Dy-YOLOv7-X/10640201.7G9853.3
Dy-YOLOv7-X/50640248.9G7854.4
Dy-YOLOv7-X/90640296.1G6555.0
Dy-YOLOv7-X/100640307.9G6455.0
YOLOv5-M6 (r6.2) [11]1280200.0G9651.4
YOLOv5-L6 (r6.2) [11]1280445.6G6553.8
YOLOv5-X6 (r6.2) [11]1280839.2G3955.0
YOLOv7-W6 [45]1280360.0G7854.9
YOLOv7-E6 [45]1280515.2G5256.0
YOLOv7-D6 [45]1280806.8G4156.6
YOLOv7-E6E [45]1280843.2G3356.8
Dy-YOLOv7-W6/101280384.2G7455.2
Dy-YOLOv7-W6/501280480.8G5856.1
Dy-YOLOv7-W6/901280577.4G4856.7
Dy-YOLOv7-W6/1001280601.6G4656.8
" + }, + { + "type": "table_footnote", + "bbox": [ + 0.097, + 0.611, + 0.465, + 0.635 + ], + "angle": 0, + "content": "1 The FPS marked with \\(\\dagger\\) are from the corresponding papers, and others are measured on the same machine with 1 NVIDIA V100 GPU." + }, + { + "type": "table_footnote", + "bbox": [ + 0.077, + 0.644, + 0.468, + 0.671 + ], + "angle": 0, + "content": "Table 1. Comparison with the state-of-the-art real-time object detectors on COCO test-dev." + }, + { + "type": "list", + "bbox": [ + 0.077, + 0.611, + 0.468, + 0.671 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.686, + 0.468, + 0.745 + ], + "angle": 0, + "content": "Based on the above strategy, one dynamic detector can directly cover the accuracy-speed trade-offs from the single to double detectors, avoiding redesigning and training multiple detectors under different hardware constraints." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.758, + 0.208, + 0.775 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.78, + 0.468, + 0.901 + ], + "angle": 0, + "content": "In this section, we evaluate our DynamicDet through extensive experiments. In Sec. 4.1, we detail the experimental setups. In Sec. 4.2, we compare our DynamicDet with the state-of-the-art real-time detectors. In Sec. 4.3, we present the experimental results on two-stage detectors with CNN and transformer-based backbones to demonstrate the generality of DynamicDet over different backbones and detectors. In Sec. 4.4, we ablate each component of DynamicDet" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.092, + 0.89, + 0.121 + ], + "angle": 0, + "content": "in detail. In Sec. 4.5, we visualize the \"easy\" and the \"hard\" images determined by the adaptive router." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.126, + 0.694, + 0.141 + ], + "angle": 0, + "content": "4.1. Experimental setups" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.145, + 0.892, + 0.522 + ], + "angle": 0, + "content": "We conduct experiments on the COCO [28] benchmark. All the models presented are trained on the 118k training images, and tested on the 5k minival images and 20k test-dev images. We choose the YOLOv7 [45] series models as the real-time detector baseline, and the Faster R-CNN [39] (ResNet [15]) and the Mask R-CNN [14] (Swin Transformer [31]) as the two-stage detector baselines. All dynamic detectors are trained with the same hyper-parameters of their corresponding baselines. We use brief notation to indicate the easy-hard proportion for each dynamic detector: for instance, \"Dy-YOLOv7-X/10\" means the dynamic YOLOv7-X model with \\(10\\%\\) images are classified as \"hard\" and the rest are classified as \"easy\". The training of the adaptive router is conducted on a single GPU with batchsize 1 and two epochs, utilizing the AdamW [32] optimizer with a constant learning rate \\(1 \\times 10^{-5}\\) and weight decay \\(5 \\times 10^{-3}\\). The reported FLOPs for dynamic detectors are the average FLOPs on the corresponding dataset. The speed performance is measured on a machine with 1 NVIDIA V100 GPU unless otherwise stated. The implementation of Dy-YOLOv7 is developed by the YOLOv7 [45] framework, with two identical detectors. The implementation of dynamic two-stage detectors is developed by the open-source CBNet [24] framework, with two identical backbones and a shared neck and head." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.526, + 0.825, + 0.541 + ], + "angle": 0, + "content": "4.2. Comparison with the state-of-the-arts" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.546, + 0.892, + 0.711 + ], + "angle": 0, + "content": "As shown in Tab. 1, compared with the state-of-the-art high-performance real-time object detectors, our dynamic detectors obtain better results and achieve the new state-of-the-art accuracy-speed trade-offs. Specifically, DyYOLOv7-W6 / 50 achieves \\(56.1\\%\\) AP with 58 FPS, which is \\(0.1\\%\\) more accurate and \\(12\\%\\) faster than YOLOv7-E6. Dy-YOLOv7-W6 / 100 achieves \\(56.8\\%\\) AP with 46 FPS, which is \\(39\\%\\) faster than YOLOv7-E6E with a similar accuracy. It is worth noting that these trade-offs are obtained by only one dynamic detector instead of multiple independent models." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.715, + 0.797, + 0.731 + ], + "angle": 0, + "content": "4.3. Generality for two-stage detectors" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.735, + 0.892, + 0.901 + ], + "angle": 0, + "content": "We conduct experiments on two classic two-stage detectors (i.e., Faster R-CNN [39], Mask R-CNN [14]) to show the generality of our DynamicDet. As shown in Tab. 2, our method is compatible with two-stage detectors and can also improve the accuracy-speed performance of baselines. For example, Dy-Faster R-CNN ResNet50 / 90 boosts the bbox AP by \\(1\\%\\) with the comparable inference speed for Faster R-CNN ResNet101. Furthermore, DynamicDet is also compatible with transformer-based backbones (e.g., Swin Transformer [31]). Dy-Mask R-CNN Swin-T / 90 improves the bbox AP to \\(49.9\\%\\) with the comparable inference" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.946, + 0.516, + 0.957 + ], + "angle": 0, + "content": "6287" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.082, + 0.089, + 0.462, + 0.235 + ], + "angle": 0, + "content": "
ModelFLOPsFPSAPboxAPmask
Faster R-CNN ResNet50 [15, 39]207.1G2337.4-
Faster R-CNN ResNet101 [15, 39]283.1G1839.4-
Dy-Faster R-CNN ResNet50 / 50245.4G2039.5-
Dy-Faster R-CNN ResNet50 / 90276.0G1740.4-
Mask R-CNN Swin-T [14, 31]263.8G1546.041.6
Mask R-CNN Swin-S [14, 31]353.8G1248.243.2
Dy-Mask R-CNN Swin-T / 50310.6G1248.743.6
Dy-Mask R-CNN Swin-T / 90348.0G1149.944.2
" + }, + { + "type": "table_caption", + "bbox": [ + 0.081, + 0.244, + 0.467, + 0.258 + ], + "angle": 0, + "content": "Table 2. Comparison with two-stage detectors on COCO minival." + }, + { + "type": "image", + "bbox": [ + 0.086, + 0.268, + 0.456, + 0.444 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.448, + 0.468, + 0.476 + ], + "angle": 0, + "content": "Figure 6. Bounding box mAP v.s. inference speed for two-stage detectors on COCO minival." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.489, + 0.468, + 0.534 + ], + "angle": 0, + "content": "speed of Mask R-CNN Swin-S. Notably, our two-stage dynamic detector can also perform variable-speed inference as illustrated in Fig. 6." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.541, + 0.227, + 0.557 + ], + "angle": 0, + "content": "4.4. Ablation study" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.565, + 0.327, + 0.58 + ], + "angle": 0, + "content": "4.4.1 Lightweight adaptive router" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.585, + 0.468, + 0.689 + ], + "angle": 0, + "content": "The FLOPs ratios for the adaptive router in different models are presented in Tab. 3. We can find that this ratio is less than \\(0.002\\%\\) in all models, demonstrating that the computational burden of the adaptive router can be negligible. This lightweight router avoids slowing down the detection process and ensures the fast decision-making for dynamic inference." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.7, + 0.449, + 0.715 + ], + "angle": 0, + "content": "4.4.2 Effective training strategy for adaptive router" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.72, + 0.468, + 0.901 + ], + "angle": 0, + "content": "We ablate the effectiveness of the proposed training and optimization strategy for adaptive router. We first train a Mask R-CNN [14] with cascaded Swin-T [31] as our baseline detector. Then, we apply three strategies to achieve the decision-making for router: random, AP-based (i.e., dividing \"easy\" and \"hard\" images based on the validation accuracy and using them to train the router, similar to Adaptive Feeding [58]), and our proposed strategy. As shown in Fig. 7, we compare the bbox AP on the test-dev set of different training strategies. It is shown that our optimization strategy outperforms another two strategies under all latency constraints. Taking the detector with \\(84.5\\mathrm{ms}\\) la" + }, + { + "type": "table", + "bbox": [ + 0.501, + 0.089, + 0.888, + 0.18 + ], + "angle": 0, + "content": "
ModelRouterTotalRatio
Dy-YOLOv72.1M104.7G0.0020%
Dy-YOLOv7-W61.9M360.0G0.0005%
Dy-Faster R-CNN ResNet503.7M283.7G0.0013%
Dy-Mask R-CNN Swin-T0.5M357.4G0.0001%
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.188, + 0.892, + 0.216 + ], + "angle": 0, + "content": "Table 3. Comparison of the adaptive router's FLOPs and the total FLOPs in different dynamic models." + }, + { + "type": "image", + "bbox": [ + 0.529, + 0.231, + 0.861, + 0.405 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.41, + 0.892, + 0.438 + ], + "angle": 0, + "content": "Figure 7. Comparison of the proposed strategy and other two decision-making strategies." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.452, + 0.892, + 0.528 + ], + "angle": 0, + "content": "tency (i.e., \\(50\\%\\) easy and \\(50\\%\\) hard) as an example, our strategy exceeds random selection \\(0.9\\%\\) AP and AP-based strategy \\(0.7\\%\\) AP. This proves that our optimization strategy effectively improves the discrimination accuracy of the router and outperforms AP-based strategy [58]." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.536, + 0.837, + 0.551 + ], + "angle": 0, + "content": "4.4.3 Robust variable-speed inference strategy" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.554, + 0.892, + 0.901 + ], + "angle": 0, + "content": "To achieve variable-speed inference for a dynamic detector, we count the difficulty scores on the validation set and directly adopt the corresponding thresholds for the test set. This strategy requires the validation set to be large enough. However, with custom datasets, this is not always sufficient. To demonstrate the robustness of our variable-speed inference strategy, we analyze the impact of the validation set size on the threshold consistency between the validation set and test set. Taking the Dy-Mask R-CNN Swin-T on COCO [28] dataset as an example, its threshold for \\(50\\%\\) quantile on the test set is 0.62. Then, we count the thresholds for \\(50\\%\\) quantile on the validation set of different sizes (i.e., \\(0.5\\mathrm{k}\\), \\(1\\mathrm{k}\\), ..., \\(5\\mathrm{k}\\)). As shown in Fig. 9, the threshold obtained from \\(5\\mathrm{k}\\) validation images is consistent with the threshold of the test set, which confirms our assumption in Sec. 3.4. Later, as the data size decreases, the thresholds of the validation set change within a small range. However, when the data size is less than \\(1.5\\mathrm{k}\\), the threshold of the validation set and the test set will occur a large deviation (i.e., 0.11 at \\(1\\mathrm{k}\\)). Overall, our variable-speed inference strategy is stable when the validation set size is relatively sufficient (e.g., about \\(2\\mathrm{k}\\) validation images for the \\(20\\mathrm{k}\\) test set on COCO [28])." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.946, + 0.516, + 0.957 + ], + "angle": 0, + "content": "6288" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.123, + 0.098, + 0.268, + 0.258 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.274, + 0.099, + 0.408, + 0.258 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.414, + 0.099, + 0.548, + 0.258 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.555, + 0.099, + 0.688, + 0.258 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.695, + 0.099, + 0.829, + 0.258 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.429, + 0.26, + 0.538, + 0.273 + ], + "angle": 0, + "content": "Difficulty score" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.277, + 0.895, + 0.307 + ], + "angle": 0, + "content": "Figure 8. Visualization of the \"easy\" and the \"hard\" images. The horizontal direction corresponds to the difficulty scores predicted by our adaptive router in Dy-Mask R-CNN Swin-T." + }, + { + "type": "image", + "bbox": [ + 0.117, + 0.318, + 0.429, + 0.481 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.485, + 0.471, + 0.513 + ], + "angle": 0, + "content": "Figure 9. Comparison of the thresholds obtained from the test set and the validation sets of different sizes." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.527, + 0.47, + 0.559 + ], + "angle": 0, + "content": "4.4.4 Comparison with the trade-offs obtained by adjusting the input resolution" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.566, + 0.47, + 0.718 + ], + "angle": 0, + "content": "For a well-trained detector, changing its input resolution can also quickly obtain a series of accuracy-speed trade-offs. Here we compare this method with our dynamic detector. As shown in Fig. 10, we compare our Dy-YOLOv7-W6 and the YOLOv7-D6 with different input resolutions (i.e., \\(640\\sim 1280\\)), and we observe that our dynamic detector achieves better accuracy-speed trade-offs. For example, our Dy-YOLOv7-W6 achieves \\(55.2\\%\\) AP at 74 FPS (13.5 ms), while YOLOv7-D6 with 640 input resolution only achieves \\(52.2\\%\\) AP at an even slower inference speed." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.727, + 0.469, + 0.757 + ], + "angle": 0, + "content": "4.5. Visualization of images with different difficulty scores" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.765, + 0.471, + 0.903 + ], + "angle": 0, + "content": "We depict the images with different predicted difficulty scores in Fig. 8, ascending from left to right. That is, the images on the left are considered as the \"easy\" images, while those on the right are considered as the \"hard\" images. We can observe that the \"easy\" images usually contain fewer objects, with the usual camera viewpoint and the clean background. In contrast, the \"hard\" images usually have more complex scenes with severe occlusion and much more small objects." + }, + { + "type": "image", + "bbox": [ + 0.546, + 0.318, + 0.847, + 0.481 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.5, + 0.485, + 0.892, + 0.513 + ], + "angle": 0, + "content": "Figure 10. Comparison of the trade-offs obtained from our DyYOLOv7-W6 and YOLOv7-D6 with different resolutions." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.525, + 0.62, + 0.541 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.551, + 0.895, + 0.779 + ], + "angle": 0, + "content": "In this paper, we present a unified dynamic architecture for object detection, DynamicDet. We first design a dynamic architecture to support dynamic inference on mainstream detectors. Then, we propose an adaptive router to predict the difficulty score of each image and determine the inference route. With the above architecture and router, we then propose a hyperparameter-free optimization strategy with an adaptive offset to training our dynamic detectors. Last, we present a variable-speed inference strategy. With the settable threshold for dynamic inference, we can achieve a wide range of accuracy-speed trade-offs with only one dynamic detector. Extensive experimental results demonstrate the superiority of the proposed DynamicDet in accuracy and efficiency, and new state-of-the-art accuracy-speed trade-offs are achieved." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.791, + 0.66, + 0.809 + ], + "angle": 0, + "content": "Acknowledgments" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.816, + 0.894, + 0.894 + ], + "angle": 0, + "content": "This work was supported by National Natural Science Foundation of China under Grant 62176007. This work was also a research achievement of Key Laboratory of Science, Technology and Standard in Press Industry (Key Laboratory of Intelligent Press Media Technology)." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "6289" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.175, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.116, + 0.47, + 0.198 + ], + "angle": 0, + "content": "[1] Martin Abadi, Paul Barham, Jianmin Chen, Zhifeng Chen, Andy Davis, Jeffrey Dean, Matthieu Devin, Sanjay Ghemawat, Geoffrey Irving, Michael Isard, et al. Tensorflow: a system for large-scale machine learning. 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With adaptive inference, dynamic models can achieve remarkable accuracy and computational efficiency. However, it is challenging to design a powerful dynamic detector, because of no suitable dynamic architecture and exiting criterion for object detection. To tackle these difficulties, we propose a dynamic framework for object detection, named DynamicDet. Firstly, we carefully design a dynamic architecture based on the nature of the object detection task. Then, we propose an adaptive router to analyze the multi-scale information and to decide the inference route automatically. We also present a novel optimization strategy with an exiting criterion based on the detection losses for our dynamic detectors. Last, we present a variable-speed inference strategy, which helps to realize a wide range of accuracy-speed trade-offs with only one dynamic detector. Extensive experiments conducted on the COCO benchmark demonstrate that the proposed DynamicDet achieves new state-of-the-art accuracy-speed trade-offs. For instance, with comparable accuracy, the inference speed of our dynamic detector Dy-YOLOv7-W6 surpasses YOLOv7-E6 by $12\%$ , YOLOv7-D6 by $17\%$ , and YOLOv7-E6E by $39\%$ . The code is available at https://github.com/VDIGPKU/DynamicDet. + +# 1. Introduction + +Object detection is an essential topic in computer vision, as it is a fundamental component for other vision tasks, e.g., autonomous driving [26, 40, 56], multi-object tracking [52,57], intelligent transportation [36,55], etc. In recent years, tremendous progress has been made toward more accurate and faster detectors, such as Network Architecture Search (NAS)-based detectors [10,25,48] and YOLO series models [2,9,11,21,44,45]. However, these methods need to design and train multiple models to achieve a few good trade-offs between accuracy and speed, which is not flexible enough for various application scenarios. To alleviate this + +![](images/e58d5c4029fef6ed42e9d09d96b19e2fa2dcf95ea87589fe9afbcdee9ea37d45.jpg) +Figure 1. Comparison of the proposed dynamic detectors and other efficient object detectors. Our method can achieve a wide range of state-of-the-art trade-offs between accuracy and speed with a single model. + +![](images/00fc6387c9f69629a483f0e524e5208ab324529c9b179d89c50a215e1d0bae9a.jpg) +"Easy" image +Figure 2. Examples of "easy" and "hard" images for the object detection task. + +![](images/296e29e46b6febb73647721df8769cc4fb3e29ce00473a49b9d95eb18cc6bc66.jpg) +"Hard" image + +problem, we focus on dynamic inference for the object detection task, and attempt to use only one dynamic detector to achieve a wide range of good accuracy-speed trade-offs, as shown in Fig. 1. + +The human brain inspires many fields of deep learning, and the dynamic neural network [12] is a typical one. As two examples shown in Fig. 2, we can quickly identify all objects on the left "easy" image, while we need more time to achieve the same effect for the right one. In other words, the processing speeds of images are different in our brains [18, 34], which depend on the difficulties of the images. This property motivates the image-wise dynamic neural network, and many exciting works have been proposed + +(e.g., Branchynet [43], MSDNet [17], DVT [50]). Although these approaches have achieved remarkable performance, they are all designed specifically for the image classification task and are not suitable for other vision tasks, especially for the object detection [12]. The main difficulties in designing an image-wise dynamic detector are as follows. + +Dynamic detectors cannot utilize the existing dynamic architectures. Most existing dynamic architectures are cascaded with multiple stages (i.e., a stack of multiple layers) [17, 20, 33, 54], and predict whether to stop the inference at each exiting point. Such a paradigm is feasible in image classification but is ineffective in object detection, since an image has multiple objects and each object usually has different categories and scales, as shown in Fig. 2. Hence, almost all detectors depend heavily on multi-scale information, utilizing the features on different scales to detect objects of different sizes (which are obtained by fusing the multi-scale features of the backbone with a detection neck, i.e., FPN [27]). In this case, the exiting points for detectors can only be placed behind the last stage. Consequently, the entire backbone module has to be run completely [58], and it is impossible to achieve dynamic inference on multiple cascaded stages. + +Dynamic detectors cannot exploit the existing exiting criteria for image classification. For the image classification task, the threshold of top-1 accuracy is a widely used criterion for decision-making [17, 50]. Notably, it only needs one fully connected layer to predict the top-1 accuracy at intermediate layer, which is easy and costless. However, object detection task requires the neck and the head to predict the categories and locations of the object instances [3, 14, 27, 39]. Hence, the existing exiting criteria for image classification is not suitable for object detection. + +To deal with the above difficulties, we propose a dynamic framework to achieve dynamic inference for object detection, named DynamicDet. Firstly, We design a dynamic architecture for the object detection task, which can exit with multi-scale information during the inference. Then, we propose an adaptive router to choose the best route for each image automatically. Besides, we present the corresponding optimization and inference strategies for the proposed DynamicDet. + +Our main contributions are as follows: + +- We propose a dynamic architecture for object detection, named DynamicDet, which consists of two cascaded detectors and a router. This dynamic architecture can be easily adapted to mainstream detectors, e.g., Faster R-CNN andYOLO. +- We propose an adaptive router to predict the difficulty scores of the images based on the multi-scale features, and achieve automatic decision-making. In addition, we propose a hyperparameter-free optimization strategy and a variable-speed inference strategy for our dy + +namic architecture. + +- Extensive experiments show that DynamicDet can obtain a wide range of accuracy-speed trade-offs with only one dynamic detector. We also achieve new state-of-the-art trade-offs for real-time object detection (i.e., $56.8\%$ AP at 46 FPS). + +# 2. Related work + +# 2.1. Backbone design on object detection + +Backbones play a crucial role in object detectors since the performance of detectors highly relies on the multiscale features extracted by the backbones [4]. ResNet [15] and its variants (e.g., ResNeXt [51], Res2Net [8]) introduce the residual connection to neural networks, providing a high-quality backbone architecture family for all vision tasks. Further, to reduce the calculation load, CSPNet [46] cuts down the duplicate gradient information to reduce the heavy inference, improving the efficiency significantly. Its effective architecture also inspires many lightweight detectors (e.g.,YOLO series models [2, 9, 11, 21, 44, 45]). Then, some transformer-based backbones (e.g.,PVT [47], Swin Transformer [31]) are proposed to learn the global information better. In addition, many auto-designed backbones [4,6,19,41] for object detection are proposed. For example, DetNAS [4] utilizes the one-shot supernet to search the optimal backbone, with the guidance of the object detection task. + +Although many kinds of backbones have been proposed, almost all of them are single-pass architectures, which sequentially produce one set of multi-scale features. Thus, all stages of them cannot be skipped. Fortunately, some works propose the architectures of multiple cascaded backbones, which have the potential to be converted as a dynamic backbone for object detection. For example, CBNet [24, 30] groups multiple identical backbones with composite connections, constructing a more powerful composite backbone. Since these backbones have multiple sub-backbones and each of them can produce intermediate multi-scale features, we can add some exiting points after each subbackbone for dynamic inference. + +# 2.2. Accuracy-speed trade-off on object detection + +Almost all detection methods are designed for a better accuracy-speed trade-off, i.e., more accurate and faster. With a given detector, the simplest way to obtain an accuracy-speed trade-off is to adopt the model scaling techniques [42, 44, 45] (e.g., increasing the channel size or repeating the layers). EfficientDet [42] uniformly scales the resolution, depth, and width for all modules simultaneously, achieving remarkable efficiency on real-time detectors. Scaled-YOLOv4 [44] modifies not only the depth, width, and resolution but also the structure of the network to pursue a better trade-off. YOLOv7 [45] designs a + +![](images/838871ccf0a606b6b2fb17b9d427ca0cf03613139a6bd0ff8bf3cd99f83c71d9.jpg) +Figure 3. Illustration of the architecture of DynamicDet. The first backbone extracts the multi-scale features from the input image firstly. Then, the router will be fed with these multi-scale features to predict the difficulty of image and to decide the inference route. Notably, the "easy" images will be processed by only one backbone, while the "hard" images will be processed by two. + +compound scaling method for concatenation-based models, achieving new state-of-the-art trade-offs. EAutoDet [48] constructs a supernet and adopts Network Architecture Search (NAS) to automatically search for suitable scaling factors under different hardware constraints. However, all the above methods need to train multiple detectors for the best trade-offs (e.g., one tiny model for real-time detection and another large model for accurate detection), leading to colossal training resources. In this paper, we focus on dynamic inference, aiming to achieve a wide range of best accuracy-speed trade-offs with only one dynamic detector. + +# 2.3. Dynamic neural network + +The dynamic neural network can achieve adaptive computation for different images (i.e., image-wise [17, 20, 22, 23, 43, 49, 50, 54]) or pixels (i.e., spatial-wise [7, 13, 37]). SACT [7] is a classic spatial-wise dynamic network, which adaptively adjusts the number of executed layers for the regions of the image, to improve the efficiency of networks. Its practical speed-up performance highly relies on the hardware-software co-design [12]. However, the current deep learning hardware and libraries [1, 35] are not friendly to these spatial-wise dynamic networks [12]. On the contrary, image-wise dynamic networks do not rely on sparse computing and can be easily accelerated on the conventional CPUs and GPUs [5]. Branchynet [43] introduces the early exiting strategy, which enables the model to exit from the intermediate layer whenever the model is confident enough. MSDNet [17] and its variants [23, 54] develop a multi-classifier architecture for the image classification task. DVT [50] cascades multiple transformers with increasing numbers of tokens and activates them sequentially to achieve dynamic inference. However, these methods are all designed specifically for the image classification task and cannot be applied to other vision tasks, such as object detection. + +The closest work to our DynamicDet is Adaptive Feed + +ing [58]. In Adaptive Feeding [58], each image is detected by a lightweight detector (e.g., TinyYOLO [38]) and then classified as easy or hard by a linear support vector machine (SVM) with those detected results. Then, the easy images will go through a fast detector (e.g., SSD300 [29]), while the hard images will go through a more accurate but slower one (e.g., SSD500 [29]). Adaptive Feeding [58] introduces the above multi-stage process for dynamic inference, which is inefficient and not elegant. In comparison, the proposed DynamicDet cascades two detectors and a classifier (i.e., the router), yielding a more unified and efficient dynamic detector. + +# 3. Approach + +In the following, we elaborate on our dynamic architecture for object detection. We first introduce the overall architecture in Sec. 3.1. Then, we state the proposed adaptive router, i.e., the decision maker of DynamicDet in Sec. 3.2. Finally, we introduce the optimization strategy and a variable-speed inference strategy in Secs. 3.3 and 3.4. + +# 3.1. Overall architecture + +The overall architecture of our dynamic detector is shown in Fig. 3. Inspired by CBNet [24, 30], our dynamic architecture consists of two detectors and one router. For an input image $\mathbf{x}$ , we initially extract its multi-scale features $F_{1}$ with the first backbone $\mathcal{B}_1$ as + +$$ +F _ {1} = \mathcal {B} _ {1} (\mathbf {x}) = \left[ f _ {1} ^ {\{1 \}}, f _ {1} ^ {\{2 \}}, \dots , f _ {1} ^ {\{L \}} \right], \tag {1} +$$ + +where $L$ denotes the number of stages, i.e., the number of multi-scale features. Then, the router $\mathcal{R}$ will be fed with these features $F_{1}$ to predict a difficulty score $\phi \in (0,1)$ for this image as + +$$ +\phi = \mathcal {R} \left(F _ {1}\right). \tag {2} +$$ + +Generally speaking, the "easy" images exit at the first backbone, while the "hard" images require the further processing. Specifically, if the router classifies the input image as + +an "easy" one, the followed neck and head $\mathcal{D}_1$ will output the detection results $\mathbf{y}$ as + +$$ +\mathbf {y} = \mathcal {D} _ {1} \left(F _ {1}\right). \tag {3} +$$ + +On the contrary, if the router classifies the input image as a "hard" one, the multi-scale features will need further enhancement by the second backbone, instead of immediately decoded by $\mathcal{D}_1$ . In particular, we embed the multi-scale features $F_{1}$ into $H$ by a composite connection module $\mathcal{G}$ as + +$$ +H = \mathcal {G} \left(F _ {1}\right) = \left[ h ^ {\{1 \}}, h ^ {\{2 \}}, \dots , h ^ {\{L \}} \right], \tag {4} +$$ + +where $\mathcal{G}$ is the DHLC of CBNet [24, 30] in our implementation. Then, we feed the input image $\mathbf{x}$ into the second backbone and enhance the features of the second backbone via summing the corresponding elements of $H$ at each stage sequentially, denoted as + +$$ +F _ {2} = \mathcal {B} _ {2} (\mathbf {x}, H) = \left[ f _ {2} ^ {\{1 \}}, f _ {2} ^ {\{2 \}}, \dots , f _ {2} ^ {\{L \}} \right], \tag {5} +$$ + +and the detection results will be obtained by the second head and neck $\mathcal{D}_2$ as + +$$ +\mathbf {y} = \mathcal {D} _ {2} \left(F _ {2}\right). \tag {6} +$$ + +Through the above process, the "easy" images will be processed by only one backbone, while the "hard" images will be processed by two. Obviously, with such an architecture, trades-offs between computation (i.e., speed) and accuracy can be achieved. + +# 3.2. Adaptive router + +In mainstream object detectors, different scale features play different roles. Generally, the features of the shallow layers, with strong spatial information and small receptive fields, are more used to detect small objects. In contrast, the features of the deep layers, with strong semantic information and large receptive fields, are more used to detect large objects. This property makes it necessary to consider multi-scale information when predicting the difficulty score of an image. According to this, we design an adaptive router based on the multi-scale features, that is, a simple yet effective decision-maker for the dynamic detector. + +Inspired by the squeeze-and-excitation (SE) module [16], we first pool the multi-scale features $F_{1}$ independently and concatenate them all as + +$$ +\widetilde {F} _ {1} = \mathcal {C} ([ \mathcal {P} (f _ {1} ^ {\{1 \}}), \mathcal {P} (f _ {1} ^ {\{2 \}}), \dots , \mathcal {P} (f _ {1} ^ {\{L \}}) ]), \tag {7} +$$ + +where $\mathcal{P}$ denotes the global average pooling and $\mathcal{C}$ denotes the channel-wise concatenation. With this operation, we compress the multi-scale features $F_{1}$ into a vector $\widetilde{F}_1\in \mathbb{R}^d$ of dimension $d$ . Then, we map this vector to a difficulty score $\phi \in (0,1)$ via two learnable fully connected layers as + +$$ +\phi = \sigma \left(W _ {2} \left(\delta \left(W _ {1} \widetilde {F} _ {1} + b _ {1}\right)\right) + b _ {2}\right), \tag {8} +$$ + +where $\delta, \sigma$ denote the ReLU and Sigmoid activation functions respectively, and $W_{1}, W_{2}, b_{1}, b_{2}$ are learnable parameters. Following [59], we reduce the feature dimension to + +$\lfloor d / 4 \rfloor$ in the first fully connected layer, and exploit the second fully connected layer with a Sigmoid function to generate the predicted score. It is worth noting that the computational burden of our router can be negligible since we first pool all multi-scale features to one vector. + +# 3.3. Optimization strategy + +In this section, we describe the optimization strategy for the above dynamic architecture. + +Firstly, we jointly train the cascaded detectors, and the training objective is + +$$ +\min _ {\Theta_ {1}, \Theta_ {2}} \left(\mathcal {L} _ {d e t} ^ {\{1 \}} (\mathbf {x}, \mathbf {y} | \Theta_ {1}) + \mathcal {L} _ {d e t} ^ {\{2 \}} (\mathbf {x}, \mathbf {y} | \Theta_ {2})\right), \tag {9} +$$ + +where $\mathbf{x},\mathbf{y}$ denote the input image and the ground truth respectively, $\Theta_{i}$ denotes the learnable parameters of the detector $i$ and $\mathcal{L}_{det}^{\{i\}}$ denotes the training loss for detector $i$ (e.g., bounding box regression loss and classification loss). After the above training phase, these two detectors will be able to detect the objects, and we freeze their parameters $\Theta_{1},\Theta_{2}$ during the later training. + +Then, we train the adaptive router to automatically distinguish the difficulty of the image. Here, we assume the parameters of the router are $\Theta_{\mathcal{R}}$ and the predicted difficulty score obtained from the Eq. (8) is $\phi$ . We hope the router can assign the "easy" images (i.e., with lower $\phi$ ) to the faster detector (i.e., the first detector) and the "hard" images (i.e., with higher $\phi$ ) to the more accurate detector (i.e., the second detector). + +However, it is non-trivial to implement that in practice. If we directly optimize the router without any constraints as + +$$ +\min _ {\Theta_ {\mathcal {R}}} \left((1 - \phi) \mathcal {L} _ {d e t} ^ {\{1 \}} (\mathbf {x}, \mathbf {y} | \Theta_ {1}) + \phi \mathcal {L} _ {d e t} ^ {\{2 \}} (\mathbf {x}, \mathbf {y} | \Theta_ {2})\right), \tag {10} +$$ + +the router will always choose the most accurate detector as it allows for a lower training loss. Furthermore, if we naively add hardware constraints to the training objective as + +$$ +\begin{array}{l} \min _ {\Theta_ {\mathcal {R}}} \left((1 - \phi) \mathcal {L} _ {d e t} ^ {\{1 \}} (\mathbf {x}, \mathbf {y} | \Theta_ {1}) \right. \tag {11} \\ + \phi \mathcal {L} _ {\det } ^ {\{2 \}} (\mathbf {x}, \mathbf {y} | \Theta_ {2}) + \lambda \phi), \\ \end{array} +$$ + +we will have to adjust the hyperparameter $\lambda$ by try and error, leading to huge workforce consumption. + +To overcome the above challenges, we propose a hyperparameter-free optimization strategy for our adaptive router. First, we define the difficulty criterion based on the corresponding training loss difference between two detectors of an image, as shown in Fig. 4. Specifically, we assume that if the loss difference of an image between two detectors is small enough, this image can be classified as an "easy" image. Instead, if the loss difference is large enough, it should be classified as a "hard" image. Ideally, for a balanced situation, we hope the easier half of all images go through the first detector, and the harder half go through the + +![](images/c87c12f27aa4df54ce02c10e3a34e24fcf159bcd50f1a454e1eb63c7592641e6.jpg) + +![](images/652de6e2eae6db9ba228cd6c079f2146e4a21c19bf3aa1a57ee2060e51842ba1.jpg) + +![](images/840745a6b4ee977605a4113364649562b952bfbddda0189c9ee3bc65a58430f5.jpg) + +![](images/e19632608de35955eea25ed022085fdc70a168b5e0131a1a94d01335c454ae59.jpg) + +![](images/edbe03cbfa8097748a9b5299898919a9dc32b8b496129657678ce3850bee9bfd.jpg) +Figure 4. Illustration of the difficulty criterion based on the training loss difference between two cascaded detectors. For the top image, the loss difference between the first detector and the second detector is very small, so it should be classified as an "easy" image. On the contrary, the loss difference of the bottom image is large, so it should be classified as a "hard" image. + +![](images/59d5ce7642d1797840a469c41ae0c827741824c8c78baa9927f25ad1924ebb0c.jpg) +$\mathcal{L}_{det}^{\{1\}} = 0.27$ +$\mathcal{L}_{det}^{\{1\}} = 0.57$ + +![](images/ef82ec2b8d9024e02eabe318525496e70da2f16943caf59d360950f9a73d1bb1.jpg) +$\mathcal{L}_{det}^{\{2\}} = 0.25$ +$\mathcal{L}_{det}^{\{2\}} = 0.33$ + +![](images/e2b5e720778b29fd7f5152af3158ca06c68c6d3fd8448c9bcaa545ecf372fb7d.jpg) + +![](images/11636b696b83613f719e1f7a10f33a5fce3ea1567e75108d08f331df28b41e0f.jpg) +Figure 5. Qualitative analysis of the loss of two cascaded detectors on the images with different difficulties. With the proposed adaptive offset in our optimization strategy, the loss curves of two detectors intersect and reveal the optimal curve of DynamicDet. + +second one. To achieve this, we introduce an adaptive offset to balance the losses of two detectors and optimize our router via gradient descent. In practice, we first calculate the median of the training loss difference $\Delta$ between the first and the second detector on the training set. Then, the training objective of our router can be formulated as + +$$ +\begin{array}{l} \min _ {\Theta_ {\mathcal {R}}} \left((1 - \phi) \left(\mathcal {L} _ {d e t} ^ {\{1 \}} (\mathbf {x}, \mathbf {y} \mid \Theta_ {1}) - \Delta / 2\right) \right. \tag {12} \\ + \phi (\mathcal {L} _ {\det } ^ {\{2 \}} (\mathbf {x}, \mathbf {y} | \Theta_ {2}) + \Delta / 2)), \\ \end{array} +$$ + +where $\Delta / 2$ is used to reward the first detector and punish the second detector, respectively. As the qualitative analysis shown in Fig. 5, without this reward and penalty, the losses of the second detector are always smaller than the first detector. When the reward and penalty are conducted, their loss curves intersect and reveal the optimal curve. + +Our training objective provides a means to optimize the adaptive router by introducing the following gradient through the difficulty score $\phi$ to all parameters $\Theta_{\mathcal{R}}$ of the + +router as + +$$ +\frac {\partial \mathcal {L}}{\partial \Theta_ {\mathcal {R}}} = \frac {\partial \mathcal {L}}{\partial \phi} \frac {\partial \phi}{\partial \Theta_ {\mathcal {R}}} = - \frac {\partial \phi}{\partial \Theta_ {\mathcal {R}}} \left(\mathcal {L} _ {d e t} ^ {\{1 \}} - \mathcal {L} _ {d e t} ^ {\{2 \}} - \Delta\right). \tag {13} +$$ + +To distinguish between "easy" and "hard" images better, we expect the optimization direction of the router to be related to the difficulty of the image, i.e., the difference in loss between the two detectors. Obviously, the gradient at Eq. (13) enable such expectation. + +# 3.4. Variable-speed inference + +We further propose a simple and effective method to determine the difficulty score thresholds to achieve variable-speed inference with only one dynamic detector. Specifically, our adaptive router will output a difficulty score and decide which detector to go through based on a certain threshold during inference. Therefore, we can set different thresholds to achieve different accuracy-speed trade-offs. Firstly, we count the difficulty scores $S_{val}$ of the validation set. Then, based on the actual needs (e.g., the target latency), we can obtain the corresponding threshold for our router. For example, assuming the latency of the first detector is $lat_1$ , the latency of the cascaded two detectors is $lat_2$ and the target latency is $lat_t$ , we can calculate the maximum allowable proportion of the "hard" images $k$ as + +$$ +k = \frac {l a t _ {t} - l a t _ {1}}{l a t _ {2} - l a t _ {1}}, \quad l a t _ {1} \leq l a t _ {t} \leq l a t _ {2}, \tag {14} +$$ + +and then the threshold $\tau_{val}$ will be + +$$ +\tau_ {v a l} = \operatorname {p e r c e n t i l e} \left(S _ {v a l}, k\right), \tag {15} +$$ + +where percentile $(\cdot, k)$ means to compute the $k$ -th quantile of the data. It is worth noting that this threshold $\tau_{val}$ is robust in both validation set and test set because these two sets are independent and identically distributed (i.e., i.i.d.). + +
ModelSizeFLOPsFPSAP
EAutoDet-X [48]640225.3G41†49.2
YOLOX-L [9]640155.6G69†50.1
YOLOX-X [9]640281.9G58†51.5
YOLOv5-L (r6.2) [11]640109.1G11449.0
YOLOv5-X (r6.2) [11]640205.7G10050.9
YOLOv6-M [21]64082.2G10949.6
YOLOv6-L [21]640144.0G7652.4
PP-YOLOE+-M [53]64049.9G123†50.0
PP-YOLOE+-L [53]640110.1G78†53.3
PP-YOLOE+-X [53]640206.6G45†54.9
YOLOv7 [45]640104.7G11451.4
Dy-YOLOv7/10640112.4G11052.1
Dy-YOLOv7/50640143.2G9653.3
Dy-YOLOv7/90640174.0G8553.8
Dy-YOLOv7/100640181.7G8353.9
YOLOv7-X [45]640189.9G10553.1
Dy-YOLOv7-X/10640201.7G9853.3
Dy-YOLOv7-X/50640248.9G7854.4
Dy-YOLOv7-X/90640296.1G6555.0
Dy-YOLOv7-X/100640307.9G6455.0
YOLOv5-M6 (r6.2) [11]1280200.0G9651.4
YOLOv5-L6 (r6.2) [11]1280445.6G6553.8
YOLOv5-X6 (r6.2) [11]1280839.2G3955.0
YOLOv7-W6 [45]1280360.0G7854.9
YOLOv7-E6 [45]1280515.2G5256.0
YOLOv7-D6 [45]1280806.8G4156.6
YOLOv7-E6E [45]1280843.2G3356.8
Dy-YOLOv7-W6/101280384.2G7455.2
Dy-YOLOv7-W6/501280480.8G5856.1
Dy-YOLOv7-W6/901280577.4G4856.7
Dy-YOLOv7-W6/1001280601.6G4656.8
+ +1 The FPS marked with $\dagger$ are from the corresponding papers, and others are measured on the same machine with 1 NVIDIA V100 GPU. +Table 1. Comparison with the state-of-the-art real-time object detectors on COCO test-dev. + +Based on the above strategy, one dynamic detector can directly cover the accuracy-speed trade-offs from the single to double detectors, avoiding redesigning and training multiple detectors under different hardware constraints. + +# 4. Experiments + +In this section, we evaluate our DynamicDet through extensive experiments. In Sec. 4.1, we detail the experimental setups. In Sec. 4.2, we compare our DynamicDet with the state-of-the-art real-time detectors. In Sec. 4.3, we present the experimental results on two-stage detectors with CNN and transformer-based backbones to demonstrate the generality of DynamicDet over different backbones and detectors. In Sec. 4.4, we ablate each component of DynamicDet + +in detail. In Sec. 4.5, we visualize the "easy" and the "hard" images determined by the adaptive router. + +# 4.1. Experimental setups + +We conduct experiments on the COCO [28] benchmark. All the models presented are trained on the 118k training images, and tested on the 5k minival images and 20k test-dev images. We choose the YOLOv7 [45] series models as the real-time detector baseline, and the Faster R-CNN [39] (ResNet [15]) and the Mask R-CNN [14] (Swin Transformer [31]) as the two-stage detector baselines. All dynamic detectors are trained with the same hyper-parameters of their corresponding baselines. We use brief notation to indicate the easy-hard proportion for each dynamic detector: for instance, "Dy-YOLOv7-X/10" means the dynamic YOLOv7-X model with $10\%$ images are classified as "hard" and the rest are classified as "easy". The training of the adaptive router is conducted on a single GPU with batchsize 1 and two epochs, utilizing the AdamW [32] optimizer with a constant learning rate $1 \times 10^{-5}$ and weight decay $5 \times 10^{-3}$ . The reported FLOPs for dynamic detectors are the average FLOPs on the corresponding dataset. The speed performance is measured on a machine with 1 NVIDIA V100 GPU unless otherwise stated. The implementation of Dy-YOLOv7 is developed by the YOLOv7 [45] framework, with two identical detectors. The implementation of dynamic two-stage detectors is developed by the open-source CBNet [24] framework, with two identical backbones and a shared neck and head. + +# 4.2. Comparison with the state-of-the-arts + +As shown in Tab. 1, compared with the state-of-the-art high-performance real-time object detectors, our dynamic detectors obtain better results and achieve the new state-of-the-art accuracy-speed trade-offs. Specifically, DyYOLOv7-W6 / 50 achieves $56.1\%$ AP with 58 FPS, which is $0.1\%$ more accurate and $12\%$ faster than YOLOv7-E6. Dy-YOLOv7-W6 / 100 achieves $56.8\%$ AP with 46 FPS, which is $39\%$ faster than YOLOv7-E6E with a similar accuracy. It is worth noting that these trade-offs are obtained by only one dynamic detector instead of multiple independent models. + +# 4.3. Generality for two-stage detectors + +We conduct experiments on two classic two-stage detectors (i.e., Faster R-CNN [39], Mask R-CNN [14]) to show the generality of our DynamicDet. As shown in Tab. 2, our method is compatible with two-stage detectors and can also improve the accuracy-speed performance of baselines. For example, Dy-Faster R-CNN ResNet50 / 90 boosts the bbox AP by $1\%$ with the comparable inference speed for Faster R-CNN ResNet101. Furthermore, DynamicDet is also compatible with transformer-based backbones (e.g., Swin Transformer [31]). Dy-Mask R-CNN Swin-T / 90 improves the bbox AP to $49.9\%$ with the comparable inference + +
ModelFLOPsFPSAPboxAPmask
Faster R-CNN ResNet50 [15, 39]207.1G2337.4-
Faster R-CNN ResNet101 [15, 39]283.1G1839.4-
Dy-Faster R-CNN ResNet50 / 50245.4G2039.5-
Dy-Faster R-CNN ResNet50 / 90276.0G1740.4-
Mask R-CNN Swin-T [14, 31]263.8G1546.041.6
Mask R-CNN Swin-S [14, 31]353.8G1248.243.2
Dy-Mask R-CNN Swin-T / 50310.6G1248.743.6
Dy-Mask R-CNN Swin-T / 90348.0G1149.944.2
+ +![](images/20d16858f67a13a72af9d2dbad9cd55f48a8f43b8a1472acbd7744c8a4c3abca.jpg) +Figure 6. Bounding box mAP v.s. inference speed for two-stage detectors on COCO minival. + +speed of Mask R-CNN Swin-S. Notably, our two-stage dynamic detector can also perform variable-speed inference as illustrated in Fig. 6. + +# 4.4. Ablation study + +# 4.4.1 Lightweight adaptive router + +The FLOPs ratios for the adaptive router in different models are presented in Tab. 3. We can find that this ratio is less than $0.002\%$ in all models, demonstrating that the computational burden of the adaptive router can be negligible. This lightweight router avoids slowing down the detection process and ensures the fast decision-making for dynamic inference. + +# 4.4.2 Effective training strategy for adaptive router + +We ablate the effectiveness of the proposed training and optimization strategy for adaptive router. We first train a Mask R-CNN [14] with cascaded Swin-T [31] as our baseline detector. Then, we apply three strategies to achieve the decision-making for router: random, AP-based (i.e., dividing "easy" and "hard" images based on the validation accuracy and using them to train the router, similar to Adaptive Feeding [58]), and our proposed strategy. As shown in Fig. 7, we compare the bbox AP on the test-dev set of different training strategies. It is shown that our optimization strategy outperforms another two strategies under all latency constraints. Taking the detector with $84.5\mathrm{ms}$ la + +Table 2. Comparison with two-stage detectors on COCO minival. + +
ModelRouterTotalRatio
Dy-YOLOv72.1M104.7G0.0020%
Dy-YOLOv7-W61.9M360.0G0.0005%
Dy-Faster R-CNN ResNet503.7M283.7G0.0013%
Dy-Mask R-CNN Swin-T0.5M357.4G0.0001%
+ +Table 3. Comparison of the adaptive router's FLOPs and the total FLOPs in different dynamic models. + +![](images/e6dd069a60c275cd8825a7a86211f867ab10d89897c056b291e1f2cff0010104.jpg) +Figure 7. Comparison of the proposed strategy and other two decision-making strategies. + +tency (i.e., $50\%$ easy and $50\%$ hard) as an example, our strategy exceeds random selection $0.9\%$ AP and AP-based strategy $0.7\%$ AP. This proves that our optimization strategy effectively improves the discrimination accuracy of the router and outperforms AP-based strategy [58]. + +# 4.4.3 Robust variable-speed inference strategy + +To achieve variable-speed inference for a dynamic detector, we count the difficulty scores on the validation set and directly adopt the corresponding thresholds for the test set. This strategy requires the validation set to be large enough. However, with custom datasets, this is not always sufficient. To demonstrate the robustness of our variable-speed inference strategy, we analyze the impact of the validation set size on the threshold consistency between the validation set and test set. Taking the Dy-Mask R-CNN Swin-T on COCO [28] dataset as an example, its threshold for $50\%$ quantile on the test set is 0.62. Then, we count the thresholds for $50\%$ quantile on the validation set of different sizes (i.e., $0.5\mathrm{k}$ , $1\mathrm{k}$ , ..., $5\mathrm{k}$ ). As shown in Fig. 9, the threshold obtained from $5\mathrm{k}$ validation images is consistent with the threshold of the test set, which confirms our assumption in Sec. 3.4. Later, as the data size decreases, the thresholds of the validation set change within a small range. However, when the data size is less than $1.5\mathrm{k}$ , the threshold of the validation set and the test set will occur a large deviation (i.e., 0.11 at $1\mathrm{k}$ ). Overall, our variable-speed inference strategy is stable when the validation set size is relatively sufficient (e.g., about $2\mathrm{k}$ validation images for the $20\mathrm{k}$ test set on COCO [28]). + +![](images/fa011afe1afb13eaf8464c89f3ac1e730022cababa4383be608b1aba1fed37f6.jpg) +Figure 8. Visualization of the "easy" and the "hard" images. The horizontal direction corresponds to the difficulty scores predicted by our adaptive router in Dy-Mask R-CNN Swin-T. + +![](images/3c57b4f1596c3835ffc2418e5a78b1efae89b211944cdc2e94d3aacb2212b078.jpg) + +![](images/753b2b3d021adc5b696f23a6348ce24e5d63533e714f0a00fa109cce3468199f.jpg) +Difficulty score + +![](images/dc2f37bd9ec0096463d18d76ee878c7b6ef90581554d89f924e2860150e01fc4.jpg) + +![](images/b0856eb2cff187efa5b6c57e769487d74de7ff14c30f349d4b156edf4c4852e4.jpg) + +![](images/d3079eafb4ddf953b5b366ef5922c413435bdb2635c8a385ea5c4bda725a36fb.jpg) +Figure 9. Comparison of the thresholds obtained from the test set and the validation sets of different sizes. + +# 4.4.4 Comparison with the trade-offs obtained by adjusting the input resolution + +For a well-trained detector, changing its input resolution can also quickly obtain a series of accuracy-speed trade-offs. Here we compare this method with our dynamic detector. As shown in Fig. 10, we compare our Dy-YOLOv7-W6 and the YOLOv7-D6 with different input resolutions (i.e., $640\sim 1280$ ), and we observe that our dynamic detector achieves better accuracy-speed trade-offs. For example, our Dy-YOLOv7-W6 achieves $55.2\%$ AP at 74 FPS (13.5 ms), while YOLOv7-D6 with 640 input resolution only achieves $52.2\%$ AP at an even slower inference speed. + +# 4.5. Visualization of images with different difficulty scores + +We depict the images with different predicted difficulty scores in Fig. 8, ascending from left to right. That is, the images on the left are considered as the "easy" images, while those on the right are considered as the "hard" images. We can observe that the "easy" images usually contain fewer objects, with the usual camera viewpoint and the clean background. In contrast, the "hard" images usually have more complex scenes with severe occlusion and much more small objects. + +![](images/413422f95248967b7ee9cb64d40f17b1d4bb7be470d768bf22d2664da7c135e4.jpg) +Figure 10. Comparison of the trade-offs obtained from our DyYOLOv7-W6 and YOLOv7-D6 with different resolutions. + +# 5. Conclusion + +In this paper, we present a unified dynamic architecture for object detection, DynamicDet. We first design a dynamic architecture to support dynamic inference on mainstream detectors. Then, we propose an adaptive router to predict the difficulty score of each image and determine the inference route. With the above architecture and router, we then propose a hyperparameter-free optimization strategy with an adaptive offset to training our dynamic detectors. Last, we present a variable-speed inference strategy. With the settable threshold for dynamic inference, we can achieve a wide range of accuracy-speed trade-offs with only one dynamic detector. Extensive experimental results demonstrate the superiority of the proposed DynamicDet in accuracy and efficiency, and new state-of-the-art accuracy-speed trade-offs are achieved. + +# Acknowledgments + +This work was supported by National Natural Science Foundation of China under Grant 62176007. This work was also a research achievement of Key Laboratory of Science, Technology and Standard in Press Industry (Key Laboratory of Intelligent Press Media Technology). + +# References + +[1] Martin Abadi, Paul Barham, Jianmin Chen, Zhifeng Chen, Andy Davis, Jeffrey Dean, Matthieu Devin, Sanjay Ghemawat, Geoffrey Irving, Michael Isard, et al. 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Dynamic feature pyramid networks for object detection. arXiv preprint arXiv:2012.00779, 2020. 4 \ No newline at end of file diff --git a/2023/DynamicDet_ A Unified Dynamic Architecture for Object Detection/images.zip b/2023/DynamicDet_ A Unified Dynamic Architecture for Object Detection/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..f0ae3ed3680a9d4d4950243cfb6e4643efbecfaf --- /dev/null +++ b/2023/DynamicDet_ A Unified Dynamic Architecture for Object Detection/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:dd37513bc9b1e52a320ab80a78632382eedb0a94628caa855683707ff076d661 +size 671976 diff --git a/2023/DynamicDet_ A Unified Dynamic Architecture for Object Detection/layout.json b/2023/DynamicDet_ A Unified Dynamic Architecture for Object Detection/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..e5cfba7d1d614a8dc9d0d4da2cb0e9638b3a5aa7 --- /dev/null +++ b/2023/DynamicDet_ A Unified Dynamic Architecture for Object Detection/layout.json @@ -0,0 +1,9619 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 88, + 103, + 505, + 121 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 88, + 103, + 505, + 121 + ], + "spans": [ + { + "bbox": [ + 88, + 103, + 505, + 121 + ], + "type": "text", + "content": "DynamicDet: A Unified Dynamic Architecture for Object Detection" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 140, + 143, + 452, + 172 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 140, + 143, + 452, + 172 + ], + "spans": [ + { + "bbox": [ + 140, + 143, + 452, + 172 + ], + "type": "text", + "content": "Zhihao Lin Yongtao Wang† Jinhe Zhang Xiaojie Chu Wangxuan Institute of Computer Technology, Peking University" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 162, + 174, + 428, + 199 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 162, + 174, + 428, + 199 + ], + "spans": [ + { + "bbox": [ + 162, + 174, + 428, + 199 + ], + "type": "text", + "content": "linzhihao@stu.pku.edu.cn, wyt@stu.edu.cn \njinhezhang17@gmail.com, chuxiaojie@stu.pku.edu.cn" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 143, + 227, + 192, + 239 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 227, + 192, + 239 + ], + "spans": [ + { + "bbox": [ + 143, + 227, + 192, + 239 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 250, + 290, + 537 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 250, + 290, + 537 + ], + "spans": [ + { + "bbox": [ + 46, + 250, + 290, + 537 + ], + "type": "text", + "content": "Dynamic neural network is an emerging research topic in deep learning. With adaptive inference, dynamic models can achieve remarkable accuracy and computational efficiency. However, it is challenging to design a powerful dynamic detector, because of no suitable dynamic architecture and exiting criterion for object detection. To tackle these difficulties, we propose a dynamic framework for object detection, named DynamicDet. Firstly, we carefully design a dynamic architecture based on the nature of the object detection task. Then, we propose an adaptive router to analyze the multi-scale information and to decide the inference route automatically. We also present a novel optimization strategy with an exiting criterion based on the detection losses for our dynamic detectors. Last, we present a variable-speed inference strategy, which helps to realize a wide range of accuracy-speed trade-offs with only one dynamic detector. Extensive experiments conducted on the COCO benchmark demonstrate that the proposed DynamicDet achieves new state-of-the-art accuracy-speed trade-offs. For instance, with comparable accuracy, the inference speed of our dynamic detector Dy-YOLOv7-W6 surpasses YOLOv7-E6 by " + }, + { + "bbox": [ + 46, + 250, + 290, + 537 + ], + "type": "inline_equation", + "content": "12\\%" + }, + { + "bbox": [ + 46, + 250, + 290, + 537 + ], + "type": "text", + "content": ", YOLOv7-D6 by " + }, + { + "bbox": [ + 46, + 250, + 290, + 537 + ], + "type": "inline_equation", + "content": "17\\%" + }, + { + "bbox": [ + 46, + 250, + 290, + 537 + ], + "type": "text", + "content": ", and YOLOv7-E6E by " + }, + { + "bbox": [ + 46, + 250, + 290, + 537 + ], + "type": "inline_equation", + "content": "39\\%" + }, + { + "bbox": [ + 46, + 250, + 290, + 537 + ], + "type": "text", + "content": ". The code is available at https://github.com/VDIGPKU/DynamicDet." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 545, + 128, + 558 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 545, + 128, + 558 + ], + "spans": [ + { + "bbox": [ + 47, + 545, + 128, + 558 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 561, + 288, + 693 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 561, + 288, + 693 + ], + "spans": [ + { + "bbox": [ + 46, + 561, + 288, + 693 + ], + "type": "text", + "content": "Object detection is an essential topic in computer vision, as it is a fundamental component for other vision tasks, e.g., autonomous driving [26, 40, 56], multi-object tracking [52,57], intelligent transportation [36,55], etc. In recent years, tremendous progress has been made toward more accurate and faster detectors, such as Network Architecture Search (NAS)-based detectors [10,25,48] and YOLO series models [2,9,11,21,44,45]. However, these methods need to design and train multiple models to achieve a few good trade-offs between accuracy and speed, which is not flexible enough for various application scenarios. To alleviate this" + } + ] + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 318, + 228, + 533, + 379 + ], + "blocks": [ + { + "bbox": [ + 318, + 228, + 533, + 379 + ], + "lines": [ + { + "bbox": [ + 318, + 228, + 533, + 379 + ], + "spans": [ + { + "bbox": [ + 318, + 228, + 533, + 379 + ], + "type": "image", + "image_path": "e58d5c4029fef6ed42e9d09d96b19e2fa2dcf95ea87589fe9afbcdee9ea37d45.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 385, + 547, + 430 + ], + "lines": [ + { + "bbox": [ + 304, + 385, + 547, + 430 + ], + "spans": [ + { + "bbox": [ + 304, + 385, + 547, + 430 + ], + "type": "text", + "content": "Figure 1. Comparison of the proposed dynamic detectors and other efficient object detectors. Our method can achieve a wide range of state-of-the-art trade-offs between accuracy and speed with a single model." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 322, + 442, + 423, + 510 + ], + "blocks": [ + { + "bbox": [ + 322, + 442, + 423, + 510 + ], + "lines": [ + { + "bbox": [ + 322, + 442, + 423, + 510 + ], + "spans": [ + { + "bbox": [ + 322, + 442, + 423, + 510 + ], + "type": "image", + "image_path": "00fc6387c9f69629a483f0e524e5208ab324529c9b179d89c50a215e1d0bae9a.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 351, + 510, + 394, + 520 + ], + "lines": [ + { + "bbox": [ + 351, + 510, + 394, + 520 + ], + "spans": [ + { + "bbox": [ + 351, + 510, + 394, + 520 + ], + "type": "text", + "content": "\"Easy\" image" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 304, + 525, + 545, + 546 + ], + "lines": [ + { + "bbox": [ + 304, + 525, + 545, + 546 + ], + "spans": [ + { + "bbox": [ + 304, + 525, + 545, + 546 + ], + "type": "text", + "content": "Figure 2. Examples of \"easy\" and \"hard\" images for the object detection task." + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_caption" + } + ], + "index": 11 + }, + { + "type": "image", + "bbox": [ + 427, + 442, + 528, + 510 + ], + "blocks": [ + { + "bbox": [ + 427, + 442, + 528, + 510 + ], + "lines": [ + { + "bbox": [ + 427, + 442, + 528, + 510 + ], + "spans": [ + { + "bbox": [ + 427, + 442, + 528, + 510 + ], + "type": "image", + "image_path": "296e29e46b6febb73647721df8769cc4fb3e29ce00473a49b9d95eb18cc6bc66.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 456, + 510, + 500, + 520 + ], + "lines": [ + { + "bbox": [ + 456, + 510, + 500, + 520 + ], + "spans": [ + { + "bbox": [ + 456, + 510, + 500, + 520 + ], + "type": "text", + "content": "\"Hard\" image" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_caption" + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 555, + 547, + 604 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 555, + 547, + 604 + ], + "spans": [ + { + "bbox": [ + 304, + 555, + 547, + 604 + ], + "type": "text", + "content": "problem, we focus on dynamic inference for the object detection task, and attempt to use only one dynamic detector to achieve a wide range of good accuracy-speed trade-offs, as shown in Fig. 1." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 605, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 547, + 715 + ], + "type": "text", + "content": "The human brain inspires many fields of deep learning, and the dynamic neural network [12] is a typical one. As two examples shown in Fig. 2, we can quickly identify all objects on the left \"easy\" image, while we need more time to achieve the same effect for the right one. In other words, the processing speeds of images are different in our brains [18, 34], which depend on the difficulties of the images. This property motivates the image-wise dynamic neural network, and many exciting works have been proposed" + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 702, + 135, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 702, + 135, + 712 + ], + "spans": [ + { + "bbox": [ + 58, + 702, + 135, + 712 + ], + "type": "text", + "content": "† Corresponding author." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "6282" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 286, + 144 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 286, + 144 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 286, + 144 + ], + "type": "text", + "content": "(e.g., Branchynet [43], MSDNet [17], DVT [50]). Although these approaches have achieved remarkable performance, they are all designed specifically for the image classification task and are not suitable for other vision tasks, especially for the object detection [12]. The main difficulties in designing an image-wise dynamic detector are as follows." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 144, + 286, + 346 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 144, + 286, + 346 + ], + "spans": [ + { + "bbox": [ + 46, + 144, + 286, + 346 + ], + "type": "text", + "content": "Dynamic detectors cannot utilize the existing dynamic architectures. Most existing dynamic architectures are cascaded with multiple stages (i.e., a stack of multiple layers) [17, 20, 33, 54], and predict whether to stop the inference at each exiting point. Such a paradigm is feasible in image classification but is ineffective in object detection, since an image has multiple objects and each object usually has different categories and scales, as shown in Fig. 2. Hence, almost all detectors depend heavily on multi-scale information, utilizing the features on different scales to detect objects of different sizes (which are obtained by fusing the multi-scale features of the backbone with a detection neck, i.e., FPN [27]). In this case, the exiting points for detectors can only be placed behind the last stage. Consequently, the entire backbone module has to be run completely [58], and it is impossible to achieve dynamic inference on multiple cascaded stages." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 348, + 286, + 467 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 348, + 286, + 467 + ], + "spans": [ + { + "bbox": [ + 46, + 348, + 286, + 467 + ], + "type": "text", + "content": "Dynamic detectors cannot exploit the existing exiting criteria for image classification. For the image classification task, the threshold of top-1 accuracy is a widely used criterion for decision-making [17, 50]. Notably, it only needs one fully connected layer to predict the top-1 accuracy at intermediate layer, which is easy and costless. However, object detection task requires the neck and the head to predict the categories and locations of the object instances [3, 14, 27, 39]. Hence, the existing exiting criteria for image classification is not suitable for object detection." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 468, + 286, + 574 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 468, + 286, + 574 + ], + "spans": [ + { + "bbox": [ + 46, + 468, + 286, + 574 + ], + "type": "text", + "content": "To deal with the above difficulties, we propose a dynamic framework to achieve dynamic inference for object detection, named DynamicDet. Firstly, We design a dynamic architecture for the object detection task, which can exit with multi-scale information during the inference. Then, we propose an adaptive router to choose the best route for each image automatically. Besides, we present the corresponding optimization and inference strategies for the proposed DynamicDet." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 59, + 575, + 215, + 586 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 575, + 215, + 586 + ], + "spans": [ + { + "bbox": [ + 59, + 575, + 215, + 586 + ], + "type": "text", + "content": "Our main contributions are as follows:" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 58, + 590, + 286, + 713 + ], + "type": "list", + "angle": 0, + "index": 7, + "blocks": [ + { + "bbox": [ + 58, + 590, + 286, + 649 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 590, + 286, + 649 + ], + "spans": [ + { + "bbox": [ + 58, + 590, + 286, + 649 + ], + "type": "text", + "content": "- We propose a dynamic architecture for object detection, named DynamicDet, which consists of two cascaded detectors and a router. This dynamic architecture can be easily adapted to mainstream detectors, e.g., Faster R-CNN andYOLO." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 58, + 654, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 654, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 58, + 654, + 286, + 713 + ], + "type": "text", + "content": "- We propose an adaptive router to predict the difficulty scores of the images based on the multi-scale features, and achieve automatic decision-making. In addition, we propose a hyperparameter-free optimization strategy and a variable-speed inference strategy for our dy" + } + ] + } + ], + "index": 6 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 326, + 73, + 405, + 83 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 326, + 73, + 405, + 83 + ], + "spans": [ + { + "bbox": [ + 326, + 73, + 405, + 83 + ], + "type": "text", + "content": "namic architecture." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 317, + 87, + 545, + 146 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 87, + 545, + 146 + ], + "spans": [ + { + "bbox": [ + 317, + 87, + 545, + 146 + ], + "type": "text", + "content": "- Extensive experiments show that DynamicDet can obtain a wide range of accuracy-speed trade-offs with only one dynamic detector. We also achieve new state-of-the-art trade-offs for real-time object detection (i.e., " + }, + { + "bbox": [ + 317, + 87, + 545, + 146 + ], + "type": "inline_equation", + "content": "56.8\\%" + }, + { + "bbox": [ + 317, + 87, + 545, + 146 + ], + "type": "text", + "content": " AP at 46 FPS)." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 157, + 389, + 169 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 157, + 389, + 169 + ], + "spans": [ + { + "bbox": [ + 306, + 157, + 389, + 169 + ], + "type": "text", + "content": "2. Related work" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 175, + 498, + 187 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 175, + 498, + 187 + ], + "spans": [ + { + "bbox": [ + 306, + 175, + 498, + 187 + ], + "type": "text", + "content": "2.1. Backbone design on object detection" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 190, + 545, + 404 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 190, + 545, + 404 + ], + "spans": [ + { + "bbox": [ + 304, + 190, + 545, + 404 + ], + "type": "text", + "content": "Backbones play a crucial role in object detectors since the performance of detectors highly relies on the multiscale features extracted by the backbones [4]. ResNet [15] and its variants (e.g., ResNeXt [51], Res2Net [8]) introduce the residual connection to neural networks, providing a high-quality backbone architecture family for all vision tasks. Further, to reduce the calculation load, CSPNet [46] cuts down the duplicate gradient information to reduce the heavy inference, improving the efficiency significantly. Its effective architecture also inspires many lightweight detectors (e.g.,YOLO series models [2, 9, 11, 21, 44, 45]). Then, some transformer-based backbones (e.g.,PVT [47], Swin Transformer [31]) are proposed to learn the global information better. In addition, many auto-designed backbones [4,6,19,41] for object detection are proposed. For example, DetNAS [4] utilizes the one-shot supernet to search the optimal backbone, with the guidance of the object detection task." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 405, + 545, + 561 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 405, + 545, + 561 + ], + "spans": [ + { + "bbox": [ + 304, + 405, + 545, + 561 + ], + "type": "text", + "content": "Although many kinds of backbones have been proposed, almost all of them are single-pass architectures, which sequentially produce one set of multi-scale features. Thus, all stages of them cannot be skipped. Fortunately, some works propose the architectures of multiple cascaded backbones, which have the potential to be converted as a dynamic backbone for object detection. For example, CBNet [24, 30] groups multiple identical backbones with composite connections, constructing a more powerful composite backbone. Since these backbones have multiple sub-backbones and each of them can produce intermediate multi-scale features, we can add some exiting points after each subbackbone for dynamic inference." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 566, + 538, + 578 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 566, + 538, + 578 + ], + "spans": [ + { + "bbox": [ + 306, + 566, + 538, + 578 + ], + "type": "text", + "content": "2.2. Accuracy-speed trade-off on object detection" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "content": "Almost all detection methods are designed for a better accuracy-speed trade-off, i.e., more accurate and faster. With a given detector, the simplest way to obtain an accuracy-speed trade-off is to adopt the model scaling techniques [42, 44, 45] (e.g., increasing the channel size or repeating the layers). EfficientDet [42] uniformly scales the resolution, depth, and width for all modules simultaneously, achieving remarkable efficiency on real-time detectors. Scaled-YOLOv4 [44] modifies not only the depth, width, and resolution but also the structure of the network to pursue a better trade-off. YOLOv7 [45] designs a" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "type": "text", + "content": "6283" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 108, + 77, + 486, + 228 + ], + "blocks": [ + { + "bbox": [ + 108, + 77, + 486, + 228 + ], + "lines": [ + { + "bbox": [ + 108, + 77, + 486, + 228 + ], + "spans": [ + { + "bbox": [ + 108, + 77, + 486, + 228 + ], + "type": "image", + "image_path": "838871ccf0a606b6b2fb17b9d427ca0cf03613139a6bd0ff8bf3cd99f83c71d9.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 232, + 547, + 266 + ], + "lines": [ + { + "bbox": [ + 46, + 232, + 547, + 266 + ], + "spans": [ + { + "bbox": [ + 46, + 232, + 547, + 266 + ], + "type": "text", + "content": "Figure 3. Illustration of the architecture of DynamicDet. The first backbone extracts the multi-scale features from the input image firstly. Then, the router will be fed with these multi-scale features to predict the difficulty of image and to decide the inference route. Notably, the \"easy\" images will be processed by only one backbone, while the \"hard\" images will be processed by two." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 271, + 289, + 403 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 271, + 289, + 403 + ], + "spans": [ + { + "bbox": [ + 46, + 271, + 289, + 403 + ], + "type": "text", + "content": "compound scaling method for concatenation-based models, achieving new state-of-the-art trade-offs. EAutoDet [48] constructs a supernet and adopts Network Architecture Search (NAS) to automatically search for suitable scaling factors under different hardware constraints. However, all the above methods need to train multiple detectors for the best trade-offs (e.g., one tiny model for real-time detection and another large model for accurate detection), leading to colossal training resources. In this paper, we focus on dynamic inference, aiming to achieve a wide range of best accuracy-speed trade-offs with only one dynamic detector." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 410, + 187, + 422 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 410, + 187, + 422 + ], + "spans": [ + { + "bbox": [ + 47, + 410, + 187, + 422 + ], + "type": "text", + "content": "2.3. Dynamic neural network" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 426, + 289, + 700 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 426, + 289, + 700 + ], + "spans": [ + { + "bbox": [ + 46, + 426, + 289, + 700 + ], + "type": "text", + "content": "The dynamic neural network can achieve adaptive computation for different images (i.e., image-wise [17, 20, 22, 23, 43, 49, 50, 54]) or pixels (i.e., spatial-wise [7, 13, 37]). SACT [7] is a classic spatial-wise dynamic network, which adaptively adjusts the number of executed layers for the regions of the image, to improve the efficiency of networks. Its practical speed-up performance highly relies on the hardware-software co-design [12]. However, the current deep learning hardware and libraries [1, 35] are not friendly to these spatial-wise dynamic networks [12]. On the contrary, image-wise dynamic networks do not rely on sparse computing and can be easily accelerated on the conventional CPUs and GPUs [5]. Branchynet [43] introduces the early exiting strategy, which enables the model to exit from the intermediate layer whenever the model is confident enough. MSDNet [17] and its variants [23, 54] develop a multi-classifier architecture for the image classification task. DVT [50] cascades multiple transformers with increasing numbers of tokens and activates them sequentially to achieve dynamic inference. However, these methods are all designed specifically for the image classification task and cannot be applied to other vision tasks, such as object detection." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 59, + 701, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 701, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 59, + 701, + 287, + 713 + ], + "type": "text", + "content": "The closest work to our DynamicDet is Adaptive Feed" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 271, + 547, + 415 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 271, + 547, + 415 + ], + "spans": [ + { + "bbox": [ + 304, + 271, + 547, + 415 + ], + "type": "text", + "content": "ing [58]. In Adaptive Feeding [58], each image is detected by a lightweight detector (e.g., TinyYOLO [38]) and then classified as easy or hard by a linear support vector machine (SVM) with those detected results. Then, the easy images will go through a fast detector (e.g., SSD300 [29]), while the hard images will go through a more accurate but slower one (e.g., SSD500 [29]). Adaptive Feeding [58] introduces the above multi-stage process for dynamic inference, which is inefficient and not elegant. In comparison, the proposed DynamicDet cascades two detectors and a classifier (i.e., the router), yielding a more unified and efficient dynamic detector." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 305, + 423, + 373, + 437 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 423, + 373, + 437 + ], + "spans": [ + { + "bbox": [ + 305, + 423, + 373, + 437 + ], + "type": "text", + "content": "3. Approach" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 441, + 547, + 514 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 441, + 547, + 514 + ], + "spans": [ + { + "bbox": [ + 304, + 441, + 547, + 514 + ], + "type": "text", + "content": "In the following, we elaborate on our dynamic architecture for object detection. We first introduce the overall architecture in Sec. 3.1. Then, we state the proposed adaptive router, i.e., the decision maker of DynamicDet in Sec. 3.2. Finally, we introduce the optimization strategy and a variable-speed inference strategy in Secs. 3.3 and 3.4." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 519, + 424, + 530 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 519, + 424, + 530 + ], + "spans": [ + { + "bbox": [ + 305, + 519, + 424, + 530 + ], + "type": "text", + "content": "3.1. Overall architecture" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 536, + 547, + 595 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 536, + 547, + 595 + ], + "spans": [ + { + "bbox": [ + 304, + 536, + 547, + 595 + ], + "type": "text", + "content": "The overall architecture of our dynamic detector is shown in Fig. 3. Inspired by CBNet [24, 30], our dynamic architecture consists of two detectors and one router. For an input image " + }, + { + "bbox": [ + 304, + 536, + 547, + 595 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 304, + 536, + 547, + 595 + ], + "type": "text", + "content": ", we initially extract its multi-scale features " + }, + { + "bbox": [ + 304, + 536, + 547, + 595 + ], + "type": "inline_equation", + "content": "F_{1}" + }, + { + "bbox": [ + 304, + 536, + 547, + 595 + ], + "type": "text", + "content": " with the first backbone " + }, + { + "bbox": [ + 304, + 536, + 547, + 595 + ], + "type": "inline_equation", + "content": "\\mathcal{B}_1" + }, + { + "bbox": [ + 304, + 536, + 547, + 595 + ], + "type": "text", + "content": " as" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 352, + 598, + 545, + 613 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 352, + 598, + 545, + 613 + ], + "spans": [ + { + "bbox": [ + 352, + 598, + 545, + 613 + ], + "type": "interline_equation", + "content": "F _ {1} = \\mathcal {B} _ {1} (\\mathbf {x}) = \\left[ f _ {1} ^ {\\{1 \\}}, f _ {1} ^ {\\{2 \\}}, \\dots , f _ {1} ^ {\\{L \\}} \\right], \\tag {1}", + "image_path": "1c2849aebc01741436701a3e53ed2f942ba3d49f37e9b9b7ceee2896e07d3f00.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 618, + 547, + 666 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 618, + 547, + 666 + ], + "spans": [ + { + "bbox": [ + 304, + 618, + 547, + 666 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 618, + 547, + 666 + ], + "type": "inline_equation", + "content": "L" + }, + { + "bbox": [ + 304, + 618, + 547, + 666 + ], + "type": "text", + "content": " denotes the number of stages, i.e., the number of multi-scale features. Then, the router " + }, + { + "bbox": [ + 304, + 618, + 547, + 666 + ], + "type": "inline_equation", + "content": "\\mathcal{R}" + }, + { + "bbox": [ + 304, + 618, + 547, + 666 + ], + "type": "text", + "content": " will be fed with these features " + }, + { + "bbox": [ + 304, + 618, + 547, + 666 + ], + "type": "inline_equation", + "content": "F_{1}" + }, + { + "bbox": [ + 304, + 618, + 547, + 666 + ], + "type": "text", + "content": " to predict a difficulty score " + }, + { + "bbox": [ + 304, + 618, + 547, + 666 + ], + "type": "inline_equation", + "content": "\\phi \\in (0,1)" + }, + { + "bbox": [ + 304, + 618, + 547, + 666 + ], + "type": "text", + "content": " for this image as" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 401, + 664, + 545, + 676 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 401, + 664, + 545, + 676 + ], + "spans": [ + { + "bbox": [ + 401, + 664, + 545, + 676 + ], + "type": "interline_equation", + "content": "\\phi = \\mathcal {R} \\left(F _ {1}\\right). \\tag {2}", + "image_path": "92fc0c05e32604085cb1f741c4225fcf38f19b187aacfc6abb31c3698c4e92e2.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 677, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 547, + 713 + ], + "type": "text", + "content": "Generally speaking, the \"easy\" images exit at the first backbone, while the \"hard\" images require the further processing. Specifically, if the router classifies the input image as" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "6284" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 287, + 96 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 287, + 96 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 287, + 96 + ], + "type": "text", + "content": "an \"easy\" one, the followed neck and head " + }, + { + "bbox": [ + 47, + 72, + 287, + 96 + ], + "type": "inline_equation", + "content": "\\mathcal{D}_1" + }, + { + "bbox": [ + 47, + 72, + 287, + 96 + ], + "type": "text", + "content": " will output the detection results " + }, + { + "bbox": [ + 47, + 72, + 287, + 96 + ], + "type": "inline_equation", + "content": "\\mathbf{y}" + }, + { + "bbox": [ + 47, + 72, + 287, + 96 + ], + "type": "text", + "content": " as" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 140, + 102, + 287, + 114 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 140, + 102, + 287, + 114 + ], + "spans": [ + { + "bbox": [ + 140, + 102, + 287, + 114 + ], + "type": "interline_equation", + "content": "\\mathbf {y} = \\mathcal {D} _ {1} \\left(F _ {1}\\right). \\tag {3}", + "image_path": "5edc55ea109bcfee8a746d85db35ffcd75f5fdfb21d66103c1f8902ac5c13f7e.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 120, + 287, + 180 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 120, + 287, + 180 + ], + "spans": [ + { + "bbox": [ + 47, + 120, + 287, + 180 + ], + "type": "text", + "content": "On the contrary, if the router classifies the input image as a \"hard\" one, the multi-scale features will need further enhancement by the second backbone, instead of immediately decoded by " + }, + { + "bbox": [ + 47, + 120, + 287, + 180 + ], + "type": "inline_equation", + "content": "\\mathcal{D}_1" + }, + { + "bbox": [ + 47, + 120, + 287, + 180 + ], + "type": "text", + "content": ". In particular, we embed the multi-scale features " + }, + { + "bbox": [ + 47, + 120, + 287, + 180 + ], + "type": "inline_equation", + "content": "F_{1}" + }, + { + "bbox": [ + 47, + 120, + 287, + 180 + ], + "type": "text", + "content": " into " + }, + { + "bbox": [ + 47, + 120, + 287, + 180 + ], + "type": "inline_equation", + "content": "H" + }, + { + "bbox": [ + 47, + 120, + 287, + 180 + ], + "type": "text", + "content": " by a composite connection module " + }, + { + "bbox": [ + 47, + 120, + 287, + 180 + ], + "type": "inline_equation", + "content": "\\mathcal{G}" + }, + { + "bbox": [ + 47, + 120, + 287, + 180 + ], + "type": "text", + "content": " as" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 95, + 184, + 287, + 198 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 95, + 184, + 287, + 198 + ], + "spans": [ + { + "bbox": [ + 95, + 184, + 287, + 198 + ], + "type": "interline_equation", + "content": "H = \\mathcal {G} \\left(F _ {1}\\right) = \\left[ h ^ {\\{1 \\}}, h ^ {\\{2 \\}}, \\dots , h ^ {\\{L \\}} \\right], \\tag {4}", + "image_path": "812c73dea454e8650048e2fcef3aa4ce492408e61ed13604a23452f408561b42.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 204, + 287, + 263 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 204, + 287, + 263 + ], + "spans": [ + { + "bbox": [ + 47, + 204, + 287, + 263 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 204, + 287, + 263 + ], + "type": "inline_equation", + "content": "\\mathcal{G}" + }, + { + "bbox": [ + 47, + 204, + 287, + 263 + ], + "type": "text", + "content": " is the DHLC of CBNet [24, 30] in our implementation. Then, we feed the input image " + }, + { + "bbox": [ + 47, + 204, + 287, + 263 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 47, + 204, + 287, + 263 + ], + "type": "text", + "content": " into the second backbone and enhance the features of the second backbone via summing the corresponding elements of " + }, + { + "bbox": [ + 47, + 204, + 287, + 263 + ], + "type": "inline_equation", + "content": "H" + }, + { + "bbox": [ + 47, + 204, + 287, + 263 + ], + "type": "text", + "content": " at each stage sequentially, denoted as" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 88, + 269, + 287, + 283 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 88, + 269, + 287, + 283 + ], + "spans": [ + { + "bbox": [ + 88, + 269, + 287, + 283 + ], + "type": "interline_equation", + "content": "F _ {2} = \\mathcal {B} _ {2} (\\mathbf {x}, H) = \\left[ f _ {2} ^ {\\{1 \\}}, f _ {2} ^ {\\{2 \\}}, \\dots , f _ {2} ^ {\\{L \\}} \\right], \\tag {5}", + "image_path": "7dd729581d9560b4c471da75109b6384aa636ae8e6193b7ac5ea4fb1af332b98.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 289, + 287, + 312 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 289, + 287, + 312 + ], + "spans": [ + { + "bbox": [ + 47, + 289, + 287, + 312 + ], + "type": "text", + "content": "and the detection results will be obtained by the second head and neck " + }, + { + "bbox": [ + 47, + 289, + 287, + 312 + ], + "type": "inline_equation", + "content": "\\mathcal{D}_2" + }, + { + "bbox": [ + 47, + 289, + 287, + 312 + ], + "type": "text", + "content": " as" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 140, + 312, + 287, + 323 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 140, + 312, + 287, + 323 + ], + "spans": [ + { + "bbox": [ + 140, + 312, + 287, + 323 + ], + "type": "interline_equation", + "content": "\\mathbf {y} = \\mathcal {D} _ {2} \\left(F _ {2}\\right). \\tag {6}", + "image_path": "a845cbfbc4b851e2ce026d00b7df1e5fe5ca4fd0c2b0fc4666b250e49ce39df6.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 325, + 287, + 384 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 325, + 287, + 384 + ], + "spans": [ + { + "bbox": [ + 47, + 325, + 287, + 384 + ], + "type": "text", + "content": "Through the above process, the \"easy\" images will be processed by only one backbone, while the \"hard\" images will be processed by two. Obviously, with such an architecture, trades-offs between computation (i.e., speed) and accuracy can be achieved." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 390, + 144, + 403 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 390, + 144, + 403 + ], + "spans": [ + { + "bbox": [ + 47, + 390, + 144, + 403 + ], + "type": "text", + "content": "3.2. Adaptive router" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 407, + 287, + 538 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 407, + 287, + 538 + ], + "spans": [ + { + "bbox": [ + 47, + 407, + 287, + 538 + ], + "type": "text", + "content": "In mainstream object detectors, different scale features play different roles. Generally, the features of the shallow layers, with strong spatial information and small receptive fields, are more used to detect small objects. In contrast, the features of the deep layers, with strong semantic information and large receptive fields, are more used to detect large objects. This property makes it necessary to consider multi-scale information when predicting the difficulty score of an image. According to this, we design an adaptive router based on the multi-scale features, that is, a simple yet effective decision-maker for the dynamic detector." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 47, + 539, + 287, + 574 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 539, + 287, + 574 + ], + "spans": [ + { + "bbox": [ + 47, + 539, + 287, + 574 + ], + "type": "text", + "content": "Inspired by the squeeze-and-excitation (SE) module [16], we first pool the multi-scale features " + }, + { + "bbox": [ + 47, + 539, + 287, + 574 + ], + "type": "inline_equation", + "content": "F_{1}" + }, + { + "bbox": [ + 47, + 539, + 287, + 574 + ], + "type": "text", + "content": " independently and concatenate them all as" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 84, + 579, + 287, + 594 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 84, + 579, + 287, + 594 + ], + "spans": [ + { + "bbox": [ + 84, + 579, + 287, + 594 + ], + "type": "interline_equation", + "content": "\\widetilde {F} _ {1} = \\mathcal {C} ([ \\mathcal {P} (f _ {1} ^ {\\{1 \\}}), \\mathcal {P} (f _ {1} ^ {\\{2 \\}}), \\dots , \\mathcal {P} (f _ {1} ^ {\\{L \\}}) ]), \\tag {7}", + "image_path": "a09ac0e63f3a55715081aa0345dd809210ba7e3614e97ac0156ddf86940e0da6.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 47, + 599, + 287, + 659 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 599, + 287, + 659 + ], + "spans": [ + { + "bbox": [ + 47, + 599, + 287, + 659 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 599, + 287, + 659 + ], + "type": "inline_equation", + "content": "\\mathcal{P}" + }, + { + "bbox": [ + 47, + 599, + 287, + 659 + ], + "type": "text", + "content": " denotes the global average pooling and " + }, + { + "bbox": [ + 47, + 599, + 287, + 659 + ], + "type": "inline_equation", + "content": "\\mathcal{C}" + }, + { + "bbox": [ + 47, + 599, + 287, + 659 + ], + "type": "text", + "content": " denotes the channel-wise concatenation. With this operation, we compress the multi-scale features " + }, + { + "bbox": [ + 47, + 599, + 287, + 659 + ], + "type": "inline_equation", + "content": "F_{1}" + }, + { + "bbox": [ + 47, + 599, + 287, + 659 + ], + "type": "text", + "content": " into a vector " + }, + { + "bbox": [ + 47, + 599, + 287, + 659 + ], + "type": "inline_equation", + "content": "\\widetilde{F}_1\\in \\mathbb{R}^d" + }, + { + "bbox": [ + 47, + 599, + 287, + 659 + ], + "type": "text", + "content": " of dimension " + }, + { + "bbox": [ + 47, + 599, + 287, + 659 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 47, + 599, + 287, + 659 + ], + "type": "text", + "content": ". Then, we map this vector to a difficulty score " + }, + { + "bbox": [ + 47, + 599, + 287, + 659 + ], + "type": "inline_equation", + "content": "\\phi \\in (0,1)" + }, + { + "bbox": [ + 47, + 599, + 287, + 659 + ], + "type": "text", + "content": " via two learnable fully connected layers as" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 102, + 663, + 287, + 676 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 102, + 663, + 287, + 676 + ], + "spans": [ + { + "bbox": [ + 102, + 663, + 287, + 676 + ], + "type": "interline_equation", + "content": "\\phi = \\sigma \\left(W _ {2} \\left(\\delta \\left(W _ {1} \\widetilde {F} _ {1} + b _ {1}\\right)\\right) + b _ {2}\\right), \\tag {8}", + "image_path": "14619e4d70cb7571f31f7e7a0d4c32bd118341e259b0f0f709048019b29f78fc.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 47, + 677, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 677, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 677, + 287, + 713 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 677, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\delta, \\sigma" + }, + { + "bbox": [ + 47, + 677, + 287, + 713 + ], + "type": "text", + "content": " denote the ReLU and Sigmoid activation functions respectively, and " + }, + { + "bbox": [ + 47, + 677, + 287, + 713 + ], + "type": "inline_equation", + "content": "W_{1}, W_{2}, b_{1}, b_{2}" + }, + { + "bbox": [ + 47, + 677, + 287, + 713 + ], + "type": "text", + "content": " are learnable parameters. Following [59], we reduce the feature dimension to" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 72, + 545, + 133 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 545, + 133 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 545, + 133 + ], + "type": "inline_equation", + "content": "\\lfloor d / 4 \\rfloor" + }, + { + "bbox": [ + 305, + 72, + 545, + 133 + ], + "type": "text", + "content": " in the first fully connected layer, and exploit the second fully connected layer with a Sigmoid function to generate the predicted score. It is worth noting that the computational burden of our router can be negligible since we first pool all multi-scale features to one vector." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 140, + 432, + 152 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 140, + 432, + 152 + ], + "spans": [ + { + "bbox": [ + 306, + 140, + 432, + 152 + ], + "type": "text", + "content": "3.3. Optimization strategy" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 306, + 158, + 545, + 181 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 158, + 545, + 181 + ], + "spans": [ + { + "bbox": [ + 306, + 158, + 545, + 181 + ], + "type": "text", + "content": "In this section, we describe the optimization strategy for the above dynamic architecture." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 306, + 182, + 545, + 205 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 182, + 545, + 205 + ], + "spans": [ + { + "bbox": [ + 306, + 182, + 545, + 205 + ], + "type": "text", + "content": "Firstly, we jointly train the cascaded detectors, and the training objective is" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 346, + 210, + 545, + 229 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 346, + 210, + 545, + 229 + ], + "spans": [ + { + "bbox": [ + 346, + 210, + 545, + 229 + ], + "type": "interline_equation", + "content": "\\min _ {\\Theta_ {1}, \\Theta_ {2}} \\left(\\mathcal {L} _ {d e t} ^ {\\{1 \\}} (\\mathbf {x}, \\mathbf {y} | \\Theta_ {1}) + \\mathcal {L} _ {d e t} ^ {\\{2 \\}} (\\mathbf {x}, \\mathbf {y} | \\Theta_ {2})\\right), \\tag {9}", + "image_path": "33883436387efd6904592b538bfbf06e706090be6fcae8db1abbe04041775de4.jpg" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 305, + 235, + 545, + 319 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 235, + 545, + 319 + ], + "spans": [ + { + "bbox": [ + 305, + 235, + 545, + 319 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 235, + 545, + 319 + ], + "type": "inline_equation", + "content": "\\mathbf{x},\\mathbf{y}" + }, + { + "bbox": [ + 305, + 235, + 545, + 319 + ], + "type": "text", + "content": " denote the input image and the ground truth respectively, " + }, + { + "bbox": [ + 305, + 235, + 545, + 319 + ], + "type": "inline_equation", + "content": "\\Theta_{i}" + }, + { + "bbox": [ + 305, + 235, + 545, + 319 + ], + "type": "text", + "content": " denotes the learnable parameters of the detector " + }, + { + "bbox": [ + 305, + 235, + 545, + 319 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 305, + 235, + 545, + 319 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 235, + 545, + 319 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{det}^{\\{i\\}}" + }, + { + "bbox": [ + 305, + 235, + 545, + 319 + ], + "type": "text", + "content": " denotes the training loss for detector " + }, + { + "bbox": [ + 305, + 235, + 545, + 319 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 305, + 235, + 545, + 319 + ], + "type": "text", + "content": " (e.g., bounding box regression loss and classification loss). After the above training phase, these two detectors will be able to detect the objects, and we freeze their parameters " + }, + { + "bbox": [ + 305, + 235, + 545, + 319 + ], + "type": "inline_equation", + "content": "\\Theta_{1},\\Theta_{2}" + }, + { + "bbox": [ + 305, + 235, + 545, + 319 + ], + "type": "text", + "content": " during the later training." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 305, + 320, + 545, + 415 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 320, + 545, + 415 + ], + "spans": [ + { + "bbox": [ + 305, + 320, + 545, + 415 + ], + "type": "text", + "content": "Then, we train the adaptive router to automatically distinguish the difficulty of the image. Here, we assume the parameters of the router are " + }, + { + "bbox": [ + 305, + 320, + 545, + 415 + ], + "type": "inline_equation", + "content": "\\Theta_{\\mathcal{R}}" + }, + { + "bbox": [ + 305, + 320, + 545, + 415 + ], + "type": "text", + "content": " and the predicted difficulty score obtained from the Eq. (8) is " + }, + { + "bbox": [ + 305, + 320, + 545, + 415 + ], + "type": "inline_equation", + "content": "\\phi" + }, + { + "bbox": [ + 305, + 320, + 545, + 415 + ], + "type": "text", + "content": ". We hope the router can assign the \"easy\" images (i.e., with lower " + }, + { + "bbox": [ + 305, + 320, + 545, + 415 + ], + "type": "inline_equation", + "content": "\\phi" + }, + { + "bbox": [ + 305, + 320, + 545, + 415 + ], + "type": "text", + "content": ") to the faster detector (i.e., the first detector) and the \"hard\" images (i.e., with higher " + }, + { + "bbox": [ + 305, + 320, + 545, + 415 + ], + "type": "inline_equation", + "content": "\\phi" + }, + { + "bbox": [ + 305, + 320, + 545, + 415 + ], + "type": "text", + "content": ") to the more accurate detector (i.e., the second detector)." + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 306, + 415, + 545, + 440 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 415, + 545, + 440 + ], + "spans": [ + { + "bbox": [ + 306, + 415, + 545, + 440 + ], + "type": "text", + "content": "However, it is non-trivial to implement that in practice. If we directly optimize the router without any constraints as" + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 323, + 446, + 545, + 465 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 323, + 446, + 545, + 465 + ], + "spans": [ + { + "bbox": [ + 323, + 446, + 545, + 465 + ], + "type": "interline_equation", + "content": "\\min _ {\\Theta_ {\\mathcal {R}}} \\left((1 - \\phi) \\mathcal {L} _ {d e t} ^ {\\{1 \\}} (\\mathbf {x}, \\mathbf {y} | \\Theta_ {1}) + \\phi \\mathcal {L} _ {d e t} ^ {\\{2 \\}} (\\mathbf {x}, \\mathbf {y} | \\Theta_ {2})\\right), \\tag {10}", + "image_path": "b05647e79ee0ade69c027d9a5e0c83ac68f064e6deb77107c0f5e29eb0382484.jpg" + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 305, + 473, + 545, + 509 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 473, + 545, + 509 + ], + "spans": [ + { + "bbox": [ + 305, + 473, + 545, + 509 + ], + "type": "text", + "content": "the router will always choose the most accurate detector as it allows for a lower training loss. Furthermore, if we naively add hardware constraints to the training objective as" + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 354, + 514, + 545, + 550 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 354, + 514, + 545, + 550 + ], + "spans": [ + { + "bbox": [ + 354, + 514, + 545, + 550 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\min _ {\\Theta_ {\\mathcal {R}}} \\left((1 - \\phi) \\mathcal {L} _ {d e t} ^ {\\{1 \\}} (\\mathbf {x}, \\mathbf {y} | \\Theta_ {1}) \\right. \\tag {11} \\\\ + \\phi \\mathcal {L} _ {\\det } ^ {\\{2 \\}} (\\mathbf {x}, \\mathbf {y} | \\Theta_ {2}) + \\lambda \\phi), \\\\ \\end{array}", + "image_path": "145cd52d836f2564b5f262668b373b3e1a6fd6a4e61e6a0f3fb4fbde2d46a7d4.jpg" + } + ] + } + ], + "index": 26 + }, + { + "bbox": [ + 305, + 558, + 545, + 582 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 558, + 545, + 582 + ], + "spans": [ + { + "bbox": [ + 305, + 558, + 545, + 582 + ], + "type": "text", + "content": "we will have to adjust the hyperparameter " + }, + { + "bbox": [ + 305, + 558, + 545, + 582 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 305, + 558, + 545, + 582 + ], + "type": "text", + "content": " by try and error, leading to huge workforce consumption." + } + ] + } + ], + "index": 27 + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "content": "To overcome the above challenges, we propose a hyperparameter-free optimization strategy for our adaptive router. First, we define the difficulty criterion based on the corresponding training loss difference between two detectors of an image, as shown in Fig. 4. Specifically, we assume that if the loss difference of an image between two detectors is small enough, this image can be classified as an \"easy\" image. Instead, if the loss difference is large enough, it should be classified as a \"hard\" image. Ideally, for a balanced situation, we hope the easier half of all images go through the first detector, and the harder half go through the" + } + ] + } + ], + "index": 28 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "type": "text", + "content": "6285" + } + ] + } + ], + "index": 29 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 102, + 73, + 198, + 150 + ], + "blocks": [ + { + "bbox": [ + 102, + 73, + 198, + 150 + ], + "lines": [ + { + "bbox": [ + 102, + 73, + 198, + 150 + ], + "spans": [ + { + "bbox": [ + 102, + 73, + 198, + 150 + ], + "type": "image", + "image_path": "c87c12f27aa4df54ce02c10e3a34e24fcf159bcd50f1a454e1eb63c7592641e6.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 205, + 74, + 302, + 148 + ], + "blocks": [ + { + "bbox": [ + 205, + 74, + 302, + 148 + ], + "lines": [ + { + "bbox": [ + 205, + 74, + 302, + 148 + ], + "spans": [ + { + "bbox": [ + 205, + 74, + 302, + 148 + ], + "type": "image", + "image_path": "652de6e2eae6db9ba228cd6c079f2146e4a21c19bf3aa1a57ee2060e51842ba1.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 309, + 74, + 404, + 148 + ], + "blocks": [ + { + "bbox": [ + 309, + 74, + 404, + 148 + ], + "lines": [ + { + "bbox": [ + 309, + 74, + 404, + 148 + ], + "spans": [ + { + "bbox": [ + 309, + 74, + 404, + 148 + ], + "type": "image", + "image_path": "840745a6b4ee977605a4113364649562b952bfbddda0189c9ee3bc65a58430f5.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + } + ], + "index": 3 + }, + { + "type": "image", + "bbox": [ + 410, + 98, + 488, + 144 + ], + "blocks": [ + { + "bbox": [ + 410, + 98, + 488, + 144 + ], + "lines": [ + { + "bbox": [ + 410, + 98, + 488, + 144 + ], + "spans": [ + { + "bbox": [ + 410, + 98, + 488, + 144 + ], + "type": "image", + "image_path": "e19632608de35955eea25ed022085fdc70a168b5e0131a1a94d01335c454ae59.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_body" + } + ], + "index": 5 + }, + { + "type": "image", + "bbox": [ + 102, + 163, + 198, + 229 + ], + "blocks": [ + { + "bbox": [ + 102, + 163, + 198, + 229 + ], + "lines": [ + { + "bbox": [ + 102, + 163, + 198, + 229 + ], + "spans": [ + { + "bbox": [ + 102, + 163, + 198, + 229 + ], + "type": "image", + "image_path": "edbe03cbfa8097748a9b5299898919a9dc32b8b496129657678ce3850bee9bfd.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 249, + 547, + 283 + ], + "lines": [ + { + "bbox": [ + 46, + 249, + 547, + 283 + ], + "spans": [ + { + "bbox": [ + 46, + 249, + 547, + 283 + ], + "type": "text", + "content": "Figure 4. Illustration of the difficulty criterion based on the training loss difference between two cascaded detectors. For the top image, the loss difference between the first detector and the second detector is very small, so it should be classified as an \"easy\" image. On the contrary, the loss difference of the bottom image is large, so it should be classified as a \"hard\" image." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 206, + 163, + 301, + 229 + ], + "blocks": [ + { + "bbox": [ + 230, + 149, + 276, + 163 + ], + "lines": [ + { + "bbox": [ + 230, + 149, + 276, + 163 + ], + "spans": [ + { + "bbox": [ + 230, + 149, + 276, + 163 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{det}^{\\{1\\}} = 0.27" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 206, + 163, + 301, + 229 + ], + "lines": [ + { + "bbox": [ + 206, + 163, + 301, + 229 + ], + "spans": [ + { + "bbox": [ + 206, + 163, + 301, + 229 + ], + "type": "image", + "image_path": "59d5ce7642d1797840a469c41ae0c827741824c8c78baa9927f25ad1924ebb0c.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 230, + 229, + 276, + 243 + ], + "lines": [ + { + "bbox": [ + 230, + 229, + 276, + 243 + ], + "spans": [ + { + "bbox": [ + 230, + 229, + 276, + 243 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{det}^{\\{1\\}} = 0.57" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_caption" + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 309, + 163, + 404, + 229 + ], + "blocks": [ + { + "bbox": [ + 333, + 149, + 380, + 163 + ], + "lines": [ + { + "bbox": [ + 333, + 149, + 380, + 163 + ], + "spans": [ + { + "bbox": [ + 333, + 149, + 380, + 163 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{det}^{\\{2\\}} = 0.25" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 309, + 163, + 404, + 229 + ], + "lines": [ + { + "bbox": [ + 309, + 163, + 404, + 229 + ], + "spans": [ + { + "bbox": [ + 309, + 163, + 404, + 229 + ], + "type": "image", + "image_path": "ef82ec2b8d9024e02eabe318525496e70da2f16943caf59d360950f9a73d1bb1.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 333, + 229, + 380, + 243 + ], + "lines": [ + { + "bbox": [ + 333, + 229, + 380, + 243 + ], + "spans": [ + { + "bbox": [ + 333, + 229, + 380, + 243 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{det}^{\\{2\\}} = 0.33" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 410, + 181, + 487, + 225 + ], + "blocks": [ + { + "bbox": [ + 410, + 181, + 487, + 225 + ], + "lines": [ + { + "bbox": [ + 410, + 181, + 487, + 225 + ], + "spans": [ + { + "bbox": [ + 410, + 181, + 487, + 225 + ], + "type": "image", + "image_path": "e2b5e720778b29fd7f5152af3158ca06c68c6d3fd8448c9bcaa545ecf372fb7d.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + } + ], + "index": 11 + }, + { + "type": "image", + "bbox": [ + 65, + 300, + 266, + 414 + ], + "blocks": [ + { + "bbox": [ + 65, + 300, + 266, + 414 + ], + "lines": [ + { + "bbox": [ + 65, + 300, + 266, + 414 + ], + "spans": [ + { + "bbox": [ + 65, + 300, + 266, + 414 + ], + "type": "image", + "image_path": "11636b696b83613f719e1f7a10f33a5fce3ea1567e75108d08f331df28b41e0f.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 420, + 287, + 464 + ], + "lines": [ + { + "bbox": [ + 46, + 420, + 287, + 464 + ], + "spans": [ + { + "bbox": [ + 46, + 420, + 287, + 464 + ], + "type": "text", + "content": "Figure 5. Qualitative analysis of the loss of two cascaded detectors on the images with different difficulties. With the proposed adaptive offset in our optimization strategy, the loss curves of two detectors intersect and reveal the optimal curve of DynamicDet." + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_caption" + } + ], + "index": 13 + }, + { + "bbox": [ + 46, + 480, + 287, + 553 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 480, + 287, + 553 + ], + "spans": [ + { + "bbox": [ + 46, + 480, + 287, + 553 + ], + "type": "text", + "content": "second one. To achieve this, we introduce an adaptive offset to balance the losses of two detectors and optimize our router via gradient descent. In practice, we first calculate the median of the training loss difference " + }, + { + "bbox": [ + 46, + 480, + 287, + 553 + ], + "type": "inline_equation", + "content": "\\Delta" + }, + { + "bbox": [ + 46, + 480, + 287, + 553 + ], + "type": "text", + "content": " between the first and the second detector on the training set. Then, the training objective of our router can be formulated as" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 89, + 561, + 286, + 597 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 89, + 561, + 286, + 597 + ], + "spans": [ + { + "bbox": [ + 89, + 561, + 286, + 597 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\min _ {\\Theta_ {\\mathcal {R}}} \\left((1 - \\phi) \\left(\\mathcal {L} _ {d e t} ^ {\\{1 \\}} (\\mathbf {x}, \\mathbf {y} \\mid \\Theta_ {1}) - \\Delta / 2\\right) \\right. \\tag {12} \\\\ + \\phi (\\mathcal {L} _ {\\det } ^ {\\{2 \\}} (\\mathbf {x}, \\mathbf {y} | \\Theta_ {2}) + \\Delta / 2)), \\\\ \\end{array}", + "image_path": "54ae126a9217da7232533d708ade0d212b159e864548bd6bfd756dae10bae947.jpg" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 46, + 605, + 286, + 677 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 605, + 286, + 677 + ], + "spans": [ + { + "bbox": [ + 46, + 605, + 286, + 677 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 605, + 286, + 677 + ], + "type": "inline_equation", + "content": "\\Delta / 2" + }, + { + "bbox": [ + 46, + 605, + 286, + 677 + ], + "type": "text", + "content": " is used to reward the first detector and punish the second detector, respectively. As the qualitative analysis shown in Fig. 5, without this reward and penalty, the losses of the second detector are always smaller than the first detector. When the reward and penalty are conducted, their loss curves intersect and reveal the optimal curve." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "text", + "content": "Our training objective provides a means to optimize the adaptive router by introducing the following gradient through the difficulty score " + }, + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\phi" + }, + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "text", + "content": " to all parameters " + }, + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\Theta_{\\mathcal{R}}" + }, + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "text", + "content": " of the" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 306, + 300, + 343, + 308 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 300, + 343, + 308 + ], + "spans": [ + { + "bbox": [ + 306, + 300, + 343, + 308 + ], + "type": "text", + "content": "router as" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 318, + 313, + 545, + 336 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 318, + 313, + 545, + 336 + ], + "spans": [ + { + "bbox": [ + 318, + 313, + 545, + 336 + ], + "type": "interline_equation", + "content": "\\frac {\\partial \\mathcal {L}}{\\partial \\Theta_ {\\mathcal {R}}} = \\frac {\\partial \\mathcal {L}}{\\partial \\phi} \\frac {\\partial \\phi}{\\partial \\Theta_ {\\mathcal {R}}} = - \\frac {\\partial \\phi}{\\partial \\Theta_ {\\mathcal {R}}} \\left(\\mathcal {L} _ {d e t} ^ {\\{1 \\}} - \\mathcal {L} _ {d e t} ^ {\\{2 \\}} - \\Delta\\right). \\tag {13}", + "image_path": "4a80049b675f33762a947183da4efcff81db1d77919e79e05e213a2a5558a365.jpg" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 305, + 342, + 545, + 401 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 342, + 545, + 401 + ], + "spans": [ + { + "bbox": [ + 305, + 342, + 545, + 401 + ], + "type": "text", + "content": "To distinguish between \"easy\" and \"hard\" images better, we expect the optimization direction of the router to be related to the difficulty of the image, i.e., the difference in loss between the two detectors. Obviously, the gradient at Eq. (13) enable such expectation." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 306, + 410, + 444, + 422 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 410, + 444, + 422 + ], + "spans": [ + { + "bbox": [ + 306, + 410, + 444, + 422 + ], + "type": "text", + "content": "3.4. Variable-speed inference" + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 304, + 428, + 545, + 596 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 428, + 545, + 596 + ], + "spans": [ + { + "bbox": [ + 304, + 428, + 545, + 596 + ], + "type": "text", + "content": "We further propose a simple and effective method to determine the difficulty score thresholds to achieve variable-speed inference with only one dynamic detector. Specifically, our adaptive router will output a difficulty score and decide which detector to go through based on a certain threshold during inference. Therefore, we can set different thresholds to achieve different accuracy-speed trade-offs. Firstly, we count the difficulty scores " + }, + { + "bbox": [ + 304, + 428, + 545, + 596 + ], + "type": "inline_equation", + "content": "S_{val}" + }, + { + "bbox": [ + 304, + 428, + 545, + 596 + ], + "type": "text", + "content": " of the validation set. Then, based on the actual needs (e.g., the target latency), we can obtain the corresponding threshold for our router. For example, assuming the latency of the first detector is " + }, + { + "bbox": [ + 304, + 428, + 545, + 596 + ], + "type": "inline_equation", + "content": "lat_1" + }, + { + "bbox": [ + 304, + 428, + 545, + 596 + ], + "type": "text", + "content": ", the latency of the cascaded two detectors is " + }, + { + "bbox": [ + 304, + 428, + 545, + 596 + ], + "type": "inline_equation", + "content": "lat_2" + }, + { + "bbox": [ + 304, + 428, + 545, + 596 + ], + "type": "text", + "content": " and the target latency is " + }, + { + "bbox": [ + 304, + 428, + 545, + 596 + ], + "type": "inline_equation", + "content": "lat_t" + }, + { + "bbox": [ + 304, + 428, + 545, + 596 + ], + "type": "text", + "content": ", we can calculate the maximum allowable proportion of the \"hard\" images " + }, + { + "bbox": [ + 304, + 428, + 545, + 596 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 304, + 428, + 545, + 596 + ], + "type": "text", + "content": " as" + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 350, + 601, + 545, + 624 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 350, + 601, + 545, + 624 + ], + "spans": [ + { + "bbox": [ + 350, + 601, + 545, + 624 + ], + "type": "interline_equation", + "content": "k = \\frac {l a t _ {t} - l a t _ {1}}{l a t _ {2} - l a t _ {1}}, \\quad l a t _ {1} \\leq l a t _ {t} \\leq l a t _ {2}, \\tag {14}", + "image_path": "d2887452657fad181c0a6080abd88f0407073712d4761bc5bee9fd8673551a79.jpg" + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 306, + 628, + 446, + 640 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 628, + 446, + 640 + ], + "spans": [ + { + "bbox": [ + 306, + 628, + 446, + 640 + ], + "type": "text", + "content": "and then the threshold " + }, + { + "bbox": [ + 306, + 628, + 446, + 640 + ], + "type": "inline_equation", + "content": "\\tau_{val}" + }, + { + "bbox": [ + 306, + 628, + 446, + 640 + ], + "type": "text", + "content": " will be" + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 373, + 647, + 545, + 658 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 373, + 647, + 545, + 658 + ], + "spans": [ + { + "bbox": [ + 373, + 647, + 545, + 658 + ], + "type": "interline_equation", + "content": "\\tau_ {v a l} = \\operatorname {p e r c e n t i l e} \\left(S _ {v a l}, k\\right), \\tag {15}", + "image_path": "93cd68c76de37cb4adc0ff443428702142349cdaff1f476abb19eaec606e3e30.jpg" + } + ] + } + ], + "index": 26 + }, + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "content": "where percentile " + }, + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "inline_equation", + "content": "(\\cdot, k)" + }, + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "content": " means to compute the " + }, + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "content": "-th quantile of the data. It is worth noting that this threshold " + }, + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\tau_{val}" + }, + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "content": " is robust in both validation set and test set because these two sets are independent and identically distributed (i.e., i.i.d.)." + } + ] + } + ], + "index": 27 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "6286" + } + ] + } + ], + "index": 28 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 50, + 70, + 285, + 482 + ], + "blocks": [ + { + "bbox": [ + 50, + 70, + 285, + 482 + ], + "lines": [ + { + "bbox": [ + 50, + 70, + 285, + 482 + ], + "spans": [ + { + "bbox": [ + 50, + 70, + 285, + 482 + ], + "type": "table", + "html": "
ModelSizeFLOPsFPSAP
EAutoDet-X [48]640225.3G41†49.2
YOLOX-L [9]640155.6G69†50.1
YOLOX-X [9]640281.9G58†51.5
YOLOv5-L (r6.2) [11]640109.1G11449.0
YOLOv5-X (r6.2) [11]640205.7G10050.9
YOLOv6-M [21]64082.2G10949.6
YOLOv6-L [21]640144.0G7652.4
PP-YOLOE+-M [53]64049.9G123†50.0
PP-YOLOE+-L [53]640110.1G78†53.3
PP-YOLOE+-X [53]640206.6G45†54.9
YOLOv7 [45]640104.7G11451.4
Dy-YOLOv7/10640112.4G11052.1
Dy-YOLOv7/50640143.2G9653.3
Dy-YOLOv7/90640174.0G8553.8
Dy-YOLOv7/100640181.7G8353.9
YOLOv7-X [45]640189.9G10553.1
Dy-YOLOv7-X/10640201.7G9853.3
Dy-YOLOv7-X/50640248.9G7854.4
Dy-YOLOv7-X/90640296.1G6555.0
Dy-YOLOv7-X/100640307.9G6455.0
YOLOv5-M6 (r6.2) [11]1280200.0G9651.4
YOLOv5-L6 (r6.2) [11]1280445.6G6553.8
YOLOv5-X6 (r6.2) [11]1280839.2G3955.0
YOLOv7-W6 [45]1280360.0G7854.9
YOLOv7-E6 [45]1280515.2G5256.0
YOLOv7-D6 [45]1280806.8G4156.6
YOLOv7-E6E [45]1280843.2G3356.8
Dy-YOLOv7-W6/101280384.2G7455.2
Dy-YOLOv7-W6/501280480.8G5856.1
Dy-YOLOv7-W6/901280577.4G4856.7
Dy-YOLOv7-W6/1001280601.6G4656.8
", + "image_path": "309f662c4fdbb111e8afaaf0cc391bda26dbd9dde3fcadd2dc857f8c055be219.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + }, + { + "bbox": [ + 59, + 483, + 284, + 502 + ], + "lines": [ + { + "bbox": [ + 59, + 483, + 284, + 502 + ], + "spans": [ + { + "bbox": [ + 59, + 483, + 284, + 502 + ], + "type": "text", + "content": "1 The FPS marked with " + }, + { + "bbox": [ + 59, + 483, + 284, + 502 + ], + "type": "inline_equation", + "content": "\\dagger" + }, + { + "bbox": [ + 59, + 483, + 284, + 502 + ], + "type": "text", + "content": " are from the corresponding papers, and others are measured on the same machine with 1 NVIDIA V100 GPU." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_footnote" + }, + { + "bbox": [ + 47, + 510, + 286, + 531 + ], + "lines": [ + { + "bbox": [ + 47, + 510, + 286, + 531 + ], + "spans": [ + { + "bbox": [ + 47, + 510, + 286, + 531 + ], + "type": "text", + "content": "Table 1. Comparison with the state-of-the-art real-time object detectors on COCO test-dev." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_footnote" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 543, + 286, + 590 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 543, + 286, + 590 + ], + "spans": [ + { + "bbox": [ + 46, + 543, + 286, + 590 + ], + "type": "text", + "content": "Based on the above strategy, one dynamic detector can directly cover the accuracy-speed trade-offs from the single to double detectors, avoiding redesigning and training multiple detectors under different hardware constraints." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 600, + 127, + 613 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 600, + 127, + 613 + ], + "spans": [ + { + "bbox": [ + 47, + 600, + 127, + 613 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 617, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 617, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 617, + 286, + 713 + ], + "type": "text", + "content": "In this section, we evaluate our DynamicDet through extensive experiments. In Sec. 4.1, we detail the experimental setups. In Sec. 4.2, we compare our DynamicDet with the state-of-the-art real-time detectors. In Sec. 4.3, we present the experimental results on two-stage detectors with CNN and transformer-based backbones to demonstrate the generality of DynamicDet over different backbones and detectors. In Sec. 4.4, we ablate each component of DynamicDet" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 305, + 72, + 544, + 95 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 544, + 95 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 544, + 95 + ], + "type": "text", + "content": "in detail. In Sec. 4.5, we visualize the \"easy\" and the \"hard\" images determined by the adaptive router." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 99, + 424, + 111 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 99, + 424, + 111 + ], + "spans": [ + { + "bbox": [ + 306, + 99, + 424, + 111 + ], + "type": "text", + "content": "4.1. Experimental setups" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 114, + 545, + 413 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 114, + 545, + 413 + ], + "spans": [ + { + "bbox": [ + 304, + 114, + 545, + 413 + ], + "type": "text", + "content": "We conduct experiments on the COCO [28] benchmark. All the models presented are trained on the 118k training images, and tested on the 5k minival images and 20k test-dev images. We choose the YOLOv7 [45] series models as the real-time detector baseline, and the Faster R-CNN [39] (ResNet [15]) and the Mask R-CNN [14] (Swin Transformer [31]) as the two-stage detector baselines. All dynamic detectors are trained with the same hyper-parameters of their corresponding baselines. We use brief notation to indicate the easy-hard proportion for each dynamic detector: for instance, \"Dy-YOLOv7-X/10\" means the dynamic YOLOv7-X model with " + }, + { + "bbox": [ + 304, + 114, + 545, + 413 + ], + "type": "inline_equation", + "content": "10\\%" + }, + { + "bbox": [ + 304, + 114, + 545, + 413 + ], + "type": "text", + "content": " images are classified as \"hard\" and the rest are classified as \"easy\". The training of the adaptive router is conducted on a single GPU with batchsize 1 and two epochs, utilizing the AdamW [32] optimizer with a constant learning rate " + }, + { + "bbox": [ + 304, + 114, + 545, + 413 + ], + "type": "inline_equation", + "content": "1 \\times 10^{-5}" + }, + { + "bbox": [ + 304, + 114, + 545, + 413 + ], + "type": "text", + "content": " and weight decay " + }, + { + "bbox": [ + 304, + 114, + 545, + 413 + ], + "type": "inline_equation", + "content": "5 \\times 10^{-3}" + }, + { + "bbox": [ + 304, + 114, + 545, + 413 + ], + "type": "text", + "content": ". The reported FLOPs for dynamic detectors are the average FLOPs on the corresponding dataset. The speed performance is measured on a machine with 1 NVIDIA V100 GPU unless otherwise stated. The implementation of Dy-YOLOv7 is developed by the YOLOv7 [45] framework, with two identical detectors. The implementation of dynamic two-stage detectors is developed by the open-source CBNet [24] framework, with two identical backbones and a shared neck and head." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 416, + 504, + 428 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 416, + 504, + 428 + ], + "spans": [ + { + "bbox": [ + 306, + 416, + 504, + 428 + ], + "type": "text", + "content": "4.2. Comparison with the state-of-the-arts" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 432, + 545, + 563 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 432, + 545, + 563 + ], + "spans": [ + { + "bbox": [ + 304, + 432, + 545, + 563 + ], + "type": "text", + "content": "As shown in Tab. 1, compared with the state-of-the-art high-performance real-time object detectors, our dynamic detectors obtain better results and achieve the new state-of-the-art accuracy-speed trade-offs. Specifically, DyYOLOv7-W6 / 50 achieves " + }, + { + "bbox": [ + 304, + 432, + 545, + 563 + ], + "type": "inline_equation", + "content": "56.1\\%" + }, + { + "bbox": [ + 304, + 432, + 545, + 563 + ], + "type": "text", + "content": " AP with 58 FPS, which is " + }, + { + "bbox": [ + 304, + 432, + 545, + 563 + ], + "type": "inline_equation", + "content": "0.1\\%" + }, + { + "bbox": [ + 304, + 432, + 545, + 563 + ], + "type": "text", + "content": " more accurate and " + }, + { + "bbox": [ + 304, + 432, + 545, + 563 + ], + "type": "inline_equation", + "content": "12\\%" + }, + { + "bbox": [ + 304, + 432, + 545, + 563 + ], + "type": "text", + "content": " faster than YOLOv7-E6. Dy-YOLOv7-W6 / 100 achieves " + }, + { + "bbox": [ + 304, + 432, + 545, + 563 + ], + "type": "inline_equation", + "content": "56.8\\%" + }, + { + "bbox": [ + 304, + 432, + 545, + 563 + ], + "type": "text", + "content": " AP with 46 FPS, which is " + }, + { + "bbox": [ + 304, + 432, + 545, + 563 + ], + "type": "inline_equation", + "content": "39\\%" + }, + { + "bbox": [ + 304, + 432, + 545, + 563 + ], + "type": "text", + "content": " faster than YOLOv7-E6E with a similar accuracy. It is worth noting that these trade-offs are obtained by only one dynamic detector instead of multiple independent models." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 566, + 487, + 578 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 566, + 487, + 578 + ], + "spans": [ + { + "bbox": [ + 306, + 566, + 487, + 578 + ], + "type": "text", + "content": "4.3. Generality for two-stage detectors" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "content": "We conduct experiments on two classic two-stage detectors (i.e., Faster R-CNN [39], Mask R-CNN [14]) to show the generality of our DynamicDet. As shown in Tab. 2, our method is compatible with two-stage detectors and can also improve the accuracy-speed performance of baselines. For example, Dy-Faster R-CNN ResNet50 / 90 boosts the bbox AP by " + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "inline_equation", + "content": "1\\%" + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "content": " with the comparable inference speed for Faster R-CNN ResNet101. Furthermore, DynamicDet is also compatible with transformer-based backbones (e.g., Swin Transformer [31]). Dy-Mask R-CNN Swin-T / 90 improves the bbox AP to " + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "inline_equation", + "content": "49.9\\%" + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "content": " with the comparable inference" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "type": "text", + "content": "6287" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 50, + 70, + 282, + 186 + ], + "blocks": [ + { + "bbox": [ + 50, + 70, + 282, + 186 + ], + "lines": [ + { + "bbox": [ + 50, + 70, + 282, + 186 + ], + "spans": [ + { + "bbox": [ + 50, + 70, + 282, + 186 + ], + "type": "table", + "html": "
ModelFLOPsFPSAPboxAPmask
Faster R-CNN ResNet50 [15, 39]207.1G2337.4-
Faster R-CNN ResNet101 [15, 39]283.1G1839.4-
Dy-Faster R-CNN ResNet50 / 50245.4G2039.5-
Dy-Faster R-CNN ResNet50 / 90276.0G1740.4-
Mask R-CNN Swin-T [14, 31]263.8G1546.041.6
Mask R-CNN Swin-S [14, 31]353.8G1248.243.2
Dy-Mask R-CNN Swin-T / 50310.6G1248.743.6
Dy-Mask R-CNN Swin-T / 90348.0G1149.944.2
", + "image_path": "2af7fa10586c53514e026f99ad6d98bb258f5f138148b6a17974f1d27509402c.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 52, + 212, + 279, + 351 + ], + "blocks": [ + { + "bbox": [ + 52, + 212, + 279, + 351 + ], + "lines": [ + { + "bbox": [ + 52, + 212, + 279, + 351 + ], + "spans": [ + { + "bbox": [ + 52, + 212, + 279, + 351 + ], + "type": "image", + "image_path": "20d16858f67a13a72af9d2dbad9cd55f48a8f43b8a1472acbd7744c8a4c3abca.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 354, + 286, + 376 + ], + "lines": [ + { + "bbox": [ + 46, + 354, + 286, + 376 + ], + "spans": [ + { + "bbox": [ + 46, + 354, + 286, + 376 + ], + "type": "text", + "content": "Figure 6. Bounding box mAP v.s. inference speed for two-stage detectors on COCO minival." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 387, + 286, + 422 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 387, + 286, + 422 + ], + "spans": [ + { + "bbox": [ + 46, + 387, + 286, + 422 + ], + "type": "text", + "content": "speed of Mask R-CNN Swin-S. Notably, our two-stage dynamic detector can also perform variable-speed inference as illustrated in Fig. 6." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 428, + 138, + 441 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 428, + 138, + 441 + ], + "spans": [ + { + "bbox": [ + 47, + 428, + 138, + 441 + ], + "type": "text", + "content": "4.4. Ablation study" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 447, + 200, + 459 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 447, + 200, + 459 + ], + "spans": [ + { + "bbox": [ + 47, + 447, + 200, + 459 + ], + "type": "text", + "content": "4.4.1 Lightweight adaptive router" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 463, + 286, + 545 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 463, + 286, + 545 + ], + "spans": [ + { + "bbox": [ + 46, + 463, + 286, + 545 + ], + "type": "text", + "content": "The FLOPs ratios for the adaptive router in different models are presented in Tab. 3. We can find that this ratio is less than " + }, + { + "bbox": [ + 46, + 463, + 286, + 545 + ], + "type": "inline_equation", + "content": "0.002\\%" + }, + { + "bbox": [ + 46, + 463, + 286, + 545 + ], + "type": "text", + "content": " in all models, demonstrating that the computational burden of the adaptive router can be negligible. This lightweight router avoids slowing down the detection process and ensures the fast decision-making for dynamic inference." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 554, + 274, + 566 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 554, + 274, + 566 + ], + "spans": [ + { + "bbox": [ + 47, + 554, + 274, + 566 + ], + "type": "text", + "content": "4.4.2 Effective training strategy for adaptive router" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 570, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 570, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 570, + 286, + 713 + ], + "type": "text", + "content": "We ablate the effectiveness of the proposed training and optimization strategy for adaptive router. We first train a Mask R-CNN [14] with cascaded Swin-T [31] as our baseline detector. Then, we apply three strategies to achieve the decision-making for router: random, AP-based (i.e., dividing \"easy\" and \"hard\" images based on the validation accuracy and using them to train the router, similar to Adaptive Feeding [58]), and our proposed strategy. As shown in Fig. 7, we compare the bbox AP on the test-dev set of different training strategies. It is shown that our optimization strategy outperforms another two strategies under all latency constraints. Taking the detector with " + }, + { + "bbox": [ + 46, + 570, + 286, + 713 + ], + "type": "inline_equation", + "content": "84.5\\mathrm{ms}" + }, + { + "bbox": [ + 46, + 570, + 286, + 713 + ], + "type": "text", + "content": " la" + } + ] + } + ], + "index": 9 + }, + { + "type": "table", + "bbox": [ + 306, + 70, + 543, + 142 + ], + "blocks": [ + { + "bbox": [ + 49, + 193, + 285, + 204 + ], + "lines": [ + { + "bbox": [ + 49, + 193, + 285, + 204 + ], + "spans": [ + { + "bbox": [ + 49, + 193, + 285, + 204 + ], + "type": "text", + "content": "Table 2. Comparison with two-stage detectors on COCO minival." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 306, + 70, + 543, + 142 + ], + "lines": [ + { + "bbox": [ + 306, + 70, + 543, + 142 + ], + "spans": [ + { + "bbox": [ + 306, + 70, + 543, + 142 + ], + "type": "table", + "html": "
ModelRouterTotalRatio
Dy-YOLOv72.1M104.7G0.0020%
Dy-YOLOv7-W61.9M360.0G0.0005%
Dy-Faster R-CNN ResNet503.7M283.7G0.0013%
Dy-Mask R-CNN Swin-T0.5M357.4G0.0001%
", + "image_path": "bad2a21494d648733e3da7df5b7a0b2e2aa3986533e1cafeb72b34dfd87df3eb.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "table_body" + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 148, + 545, + 171 + ], + "lines": [ + { + "bbox": [ + 305, + 148, + 545, + 171 + ], + "spans": [ + { + "bbox": [ + 305, + 148, + 545, + 171 + ], + "type": "text", + "content": "Table 3. Comparison of the adaptive router's FLOPs and the total FLOPs in different dynamic models." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "text" + }, + { + "type": "image", + "bbox": [ + 323, + 182, + 526, + 320 + ], + "blocks": [ + { + "bbox": [ + 323, + 182, + 526, + 320 + ], + "lines": [ + { + "bbox": [ + 323, + 182, + 526, + 320 + ], + "spans": [ + { + "bbox": [ + 323, + 182, + 526, + 320 + ], + "type": "image", + "image_path": "e6dd069a60c275cd8825a7a86211f867ab10d89897c056b291e1f2cff0010104.jpg" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 324, + 545, + 346 + ], + "lines": [ + { + "bbox": [ + 305, + 324, + 545, + 346 + ], + "spans": [ + { + "bbox": [ + 305, + 324, + 545, + 346 + ], + "type": "text", + "content": "Figure 7. Comparison of the proposed strategy and other two decision-making strategies." + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_caption" + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 357, + 545, + 418 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 357, + 545, + 418 + ], + "spans": [ + { + "bbox": [ + 304, + 357, + 545, + 418 + ], + "type": "text", + "content": "tency (i.e., " + }, + { + "bbox": [ + 304, + 357, + 545, + 418 + ], + "type": "inline_equation", + "content": "50\\%" + }, + { + "bbox": [ + 304, + 357, + 545, + 418 + ], + "type": "text", + "content": " easy and " + }, + { + "bbox": [ + 304, + 357, + 545, + 418 + ], + "type": "inline_equation", + "content": "50\\%" + }, + { + "bbox": [ + 304, + 357, + 545, + 418 + ], + "type": "text", + "content": " hard) as an example, our strategy exceeds random selection " + }, + { + "bbox": [ + 304, + 357, + 545, + 418 + ], + "type": "inline_equation", + "content": "0.9\\%" + }, + { + "bbox": [ + 304, + 357, + 545, + 418 + ], + "type": "text", + "content": " AP and AP-based strategy " + }, + { + "bbox": [ + 304, + 357, + 545, + 418 + ], + "type": "inline_equation", + "content": "0.7\\%" + }, + { + "bbox": [ + 304, + 357, + 545, + 418 + ], + "type": "text", + "content": " AP. This proves that our optimization strategy effectively improves the discrimination accuracy of the router and outperforms AP-based strategy [58]." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 424, + 512, + 436 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 424, + 512, + 436 + ], + "spans": [ + { + "bbox": [ + 305, + 424, + 512, + 436 + ], + "type": "text", + "content": "4.4.3 Robust variable-speed inference strategy" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 438, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 438, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 438, + 545, + 713 + ], + "type": "text", + "content": "To achieve variable-speed inference for a dynamic detector, we count the difficulty scores on the validation set and directly adopt the corresponding thresholds for the test set. This strategy requires the validation set to be large enough. However, with custom datasets, this is not always sufficient. To demonstrate the robustness of our variable-speed inference strategy, we analyze the impact of the validation set size on the threshold consistency between the validation set and test set. Taking the Dy-Mask R-CNN Swin-T on COCO [28] dataset as an example, its threshold for " + }, + { + "bbox": [ + 304, + 438, + 545, + 713 + ], + "type": "inline_equation", + "content": "50\\%" + }, + { + "bbox": [ + 304, + 438, + 545, + 713 + ], + "type": "text", + "content": " quantile on the test set is 0.62. Then, we count the thresholds for " + }, + { + "bbox": [ + 304, + 438, + 545, + 713 + ], + "type": "inline_equation", + "content": "50\\%" + }, + { + "bbox": [ + 304, + 438, + 545, + 713 + ], + "type": "text", + "content": " quantile on the validation set of different sizes (i.e., " + }, + { + "bbox": [ + 304, + 438, + 545, + 713 + ], + "type": "inline_equation", + "content": "0.5\\mathrm{k}" + }, + { + "bbox": [ + 304, + 438, + 545, + 713 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 438, + 545, + 713 + ], + "type": "inline_equation", + "content": "1\\mathrm{k}" + }, + { + "bbox": [ + 304, + 438, + 545, + 713 + ], + "type": "text", + "content": ", ..., " + }, + { + "bbox": [ + 304, + 438, + 545, + 713 + ], + "type": "inline_equation", + "content": "5\\mathrm{k}" + }, + { + "bbox": [ + 304, + 438, + 545, + 713 + ], + "type": "text", + "content": "). As shown in Fig. 9, the threshold obtained from " + }, + { + "bbox": [ + 304, + 438, + 545, + 713 + ], + "type": "inline_equation", + "content": "5\\mathrm{k}" + }, + { + "bbox": [ + 304, + 438, + 545, + 713 + ], + "type": "text", + "content": " validation images is consistent with the threshold of the test set, which confirms our assumption in Sec. 3.4. Later, as the data size decreases, the thresholds of the validation set change within a small range. However, when the data size is less than " + }, + { + "bbox": [ + 304, + 438, + 545, + 713 + ], + "type": "inline_equation", + "content": "1.5\\mathrm{k}" + }, + { + "bbox": [ + 304, + 438, + 545, + 713 + ], + "type": "text", + "content": ", the threshold of the validation set and the test set will occur a large deviation (i.e., 0.11 at " + }, + { + "bbox": [ + 304, + 438, + 545, + 713 + ], + "type": "inline_equation", + "content": "1\\mathrm{k}" + }, + { + "bbox": [ + 304, + 438, + 545, + 713 + ], + "type": "text", + "content": "). Overall, our variable-speed inference strategy is stable when the validation set size is relatively sufficient (e.g., about " + }, + { + "bbox": [ + 304, + 438, + 545, + 713 + ], + "type": "inline_equation", + "content": "2\\mathrm{k}" + }, + { + "bbox": [ + 304, + 438, + 545, + 713 + ], + "type": "text", + "content": " validation images for the " + }, + { + "bbox": [ + 304, + 438, + 545, + 713 + ], + "type": "inline_equation", + "content": "20\\mathrm{k}" + }, + { + "bbox": [ + 304, + 438, + 545, + 713 + ], + "type": "text", + "content": " test set on COCO [28])." + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "type": "text", + "content": "6288" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 75, + 77, + 164, + 204 + ], + "blocks": [ + { + "bbox": [ + 75, + 77, + 164, + 204 + ], + "lines": [ + { + "bbox": [ + 75, + 77, + 164, + 204 + ], + "spans": [ + { + "bbox": [ + 75, + 77, + 164, + 204 + ], + "type": "image", + "image_path": "fa011afe1afb13eaf8464c89f3ac1e730022cababa4383be608b1aba1fed37f6.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 219, + 547, + 243 + ], + "lines": [ + { + "bbox": [ + 46, + 219, + 547, + 243 + ], + "spans": [ + { + "bbox": [ + 46, + 219, + 547, + 243 + ], + "type": "text", + "content": "Figure 8. Visualization of the \"easy\" and the \"hard\" images. The horizontal direction corresponds to the difficulty scores predicted by our adaptive router in Dy-Mask R-CNN Swin-T." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 167, + 78, + 249, + 204 + ], + "blocks": [ + { + "bbox": [ + 167, + 78, + 249, + 204 + ], + "lines": [ + { + "bbox": [ + 167, + 78, + 249, + 204 + ], + "spans": [ + { + "bbox": [ + 167, + 78, + 249, + 204 + ], + "type": "image", + "image_path": "3c57b4f1596c3835ffc2418e5a78b1efae89b211944cdc2e94d3aacb2212b078.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 253, + 78, + 335, + 204 + ], + "blocks": [ + { + "bbox": [ + 253, + 78, + 335, + 204 + ], + "lines": [ + { + "bbox": [ + 253, + 78, + 335, + 204 + ], + "spans": [ + { + "bbox": [ + 253, + 78, + 335, + 204 + ], + "type": "image", + "image_path": "753b2b3d021adc5b696f23a6348ce24e5d63533e714f0a00fa109cce3468199f.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 262, + 205, + 329, + 216 + ], + "lines": [ + { + "bbox": [ + 262, + 205, + 329, + 216 + ], + "spans": [ + { + "bbox": [ + 262, + 205, + 329, + 216 + ], + "type": "text", + "content": "Difficulty score" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 339, + 78, + 421, + 204 + ], + "blocks": [ + { + "bbox": [ + 339, + 78, + 421, + 204 + ], + "lines": [ + { + "bbox": [ + 339, + 78, + 421, + 204 + ], + "spans": [ + { + "bbox": [ + 339, + 78, + 421, + 204 + ], + "type": "image", + "image_path": "dc2f37bd9ec0096463d18d76ee878c7b6ef90581554d89f924e2860150e01fc4.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + } + ], + "index": 3 + }, + { + "type": "image", + "bbox": [ + 425, + 78, + 507, + 204 + ], + "blocks": [ + { + "bbox": [ + 425, + 78, + 507, + 204 + ], + "lines": [ + { + "bbox": [ + 425, + 78, + 507, + 204 + ], + "spans": [ + { + "bbox": [ + 425, + 78, + 507, + 204 + ], + "type": "image", + "image_path": "b0856eb2cff187efa5b6c57e769487d74de7ff14c30f349d4b156edf4c4852e4.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + } + ], + "index": 4 + }, + { + "type": "image", + "bbox": [ + 71, + 251, + 262, + 380 + ], + "blocks": [ + { + "bbox": [ + 71, + 251, + 262, + 380 + ], + "lines": [ + { + "bbox": [ + 71, + 251, + 262, + 380 + ], + "spans": [ + { + "bbox": [ + 71, + 251, + 262, + 380 + ], + "type": "image", + "image_path": "d3079eafb4ddf953b5b366ef5922c413435bdb2635c8a385ea5c4bda725a36fb.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 47, + 384, + 288, + 406 + ], + "lines": [ + { + "bbox": [ + 47, + 384, + 288, + 406 + ], + "spans": [ + { + "bbox": [ + 47, + 384, + 288, + 406 + ], + "type": "text", + "content": "Figure 9. Comparison of the thresholds obtained from the test set and the validation sets of different sizes." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_caption" + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 417, + 287, + 442 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 417, + 287, + 442 + ], + "spans": [ + { + "bbox": [ + 47, + 417, + 287, + 442 + ], + "type": "text", + "content": "4.4.4 Comparison with the trade-offs obtained by adjusting the input resolution" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 448, + 287, + 568 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 448, + 287, + 568 + ], + "spans": [ + { + "bbox": [ + 46, + 448, + 287, + 568 + ], + "type": "text", + "content": "For a well-trained detector, changing its input resolution can also quickly obtain a series of accuracy-speed trade-offs. Here we compare this method with our dynamic detector. As shown in Fig. 10, we compare our Dy-YOLOv7-W6 and the YOLOv7-D6 with different input resolutions (i.e., " + }, + { + "bbox": [ + 46, + 448, + 287, + 568 + ], + "type": "inline_equation", + "content": "640\\sim 1280" + }, + { + "bbox": [ + 46, + 448, + 287, + 568 + ], + "type": "text", + "content": "), and we observe that our dynamic detector achieves better accuracy-speed trade-offs. For example, our Dy-YOLOv7-W6 achieves " + }, + { + "bbox": [ + 46, + 448, + 287, + 568 + ], + "type": "inline_equation", + "content": "55.2\\%" + }, + { + "bbox": [ + 46, + 448, + 287, + 568 + ], + "type": "text", + "content": " AP at 74 FPS (13.5 ms), while YOLOv7-D6 with 640 input resolution only achieves " + }, + { + "bbox": [ + 46, + 448, + 287, + 568 + ], + "type": "inline_equation", + "content": "52.2\\%" + }, + { + "bbox": [ + 46, + 448, + 287, + 568 + ], + "type": "text", + "content": " AP at an even slower inference speed." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 47, + 575, + 287, + 599 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 575, + 287, + 599 + ], + "spans": [ + { + "bbox": [ + 47, + 575, + 287, + 599 + ], + "type": "text", + "content": "4.5. Visualization of images with different difficulty scores" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "text", + "content": "We depict the images with different predicted difficulty scores in Fig. 8, ascending from left to right. That is, the images on the left are considered as the \"easy\" images, while those on the right are considered as the \"hard\" images. We can observe that the \"easy\" images usually contain fewer objects, with the usual camera viewpoint and the clean background. In contrast, the \"hard\" images usually have more complex scenes with severe occlusion and much more small objects." + } + ] + } + ], + "index": 12 + }, + { + "type": "image", + "bbox": [ + 334, + 251, + 518, + 380 + ], + "blocks": [ + { + "bbox": [ + 334, + 251, + 518, + 380 + ], + "lines": [ + { + "bbox": [ + 334, + 251, + 518, + 380 + ], + "spans": [ + { + "bbox": [ + 334, + 251, + 518, + 380 + ], + "type": "image", + "image_path": "413422f95248967b7ee9cb64d40f17b1d4bb7be470d768bf22d2664da7c135e4.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 306, + 384, + 545, + 406 + ], + "lines": [ + { + "bbox": [ + 306, + 384, + 545, + 406 + ], + "spans": [ + { + "bbox": [ + 306, + 384, + 545, + 406 + ], + "type": "text", + "content": "Figure 10. Comparison of the trade-offs obtained from our DyYOLOv7-W6 and YOLOv7-D6 with different resolutions." + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_caption" + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 415, + 379, + 428 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 415, + 379, + 428 + ], + "spans": [ + { + "bbox": [ + 306, + 415, + 379, + 428 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 436, + 547, + 616 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 436, + 547, + 616 + ], + "spans": [ + { + "bbox": [ + 304, + 436, + 547, + 616 + ], + "type": "text", + "content": "In this paper, we present a unified dynamic architecture for object detection, DynamicDet. We first design a dynamic architecture to support dynamic inference on mainstream detectors. Then, we propose an adaptive router to predict the difficulty score of each image and determine the inference route. With the above architecture and router, we then propose a hyperparameter-free optimization strategy with an adaptive offset to training our dynamic detectors. Last, we present a variable-speed inference strategy. With the settable threshold for dynamic inference, we can achieve a wide range of accuracy-speed trade-offs with only one dynamic detector. Extensive experimental results demonstrate the superiority of the proposed DynamicDet in accuracy and efficiency, and new state-of-the-art accuracy-speed trade-offs are achieved." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 626, + 403, + 640 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 626, + 403, + 640 + ], + "spans": [ + { + "bbox": [ + 306, + 626, + 403, + 640 + ], + "type": "text", + "content": "Acknowledgments" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 646, + 547, + 708 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 646, + 547, + 708 + ], + "spans": [ + { + "bbox": [ + 304, + 646, + 547, + 708 + ], + "type": "text", + "content": "This work was supported by National Natural Science Foundation of China under Grant 62176007. 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Dynamic Replica and DynamicStereo. In this work, we (a) introduce a new synthetic stereo video dataset (Dynamic Replica) to train and benchmark temporally consistent disparity estimators for dynamic scenes with people and animals, and (b) propose a method (DynamicStereo) exploiting recent advances in transformer architectures that performs efficient stereo matching at the level of videos." + ], + "image_footnote": [], + "bbox": [ + 86, + 387, + 184, + 472 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/d5553136ac43c56e7f6157c6b1f2a2c3b72c09086fccfecc01e2fc2866268267.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 187, + 387, + 285, + 472 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/1517f73660bca214c2037384d40c11a3c6490b8a198dd0589c6a5472fbc3330b.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 287, + 387, + 385, + 472 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/6f8ff3f0e0789e3efa8cf229d37d7bf3842ccbecb6e0125f2a1d9e6c92c3178f.jpg", + "image_caption": [ + "DynamicStereo:", + "temporally-consistent depth from stereo prediction", + "input: dynamic sequence of stereo pairs" + ], + "image_footnote": [], + "bbox": [ + 501, + 314, + 630, + 349 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/b1e5e44f027395d127e39f5c2578131a6c313814d17eb268ea1a7d89302712a2.jpg", + "image_caption": [ + "prediction: dynamic sequence of consistent disparity maps" + ], + "image_footnote": [], + "bbox": [ + 630, + 315, + 758, + 351 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/3e239b74b1b88d494ed4f8b054d6cd97d9355fb53948c5154288c7c7a5b9c464.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 403, + 359, + 620, + 446 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/0640c24746eadba5ff494cf157113c15f7bd99a9bc43ce6676ca8996038ea993.jpg", + "image_caption": [ + "qualitative results on a real-world stereo video (rendered from the original and a novel viewpoints)" + ], + "image_footnote": [], + "bbox": [ + 625, + 359, + 794, + 448 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/4c6cd4b10cc0f5f02b6445fcdc98ad47aff18862a330b5659ead0e0565983234.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 794, + 359, + 880, + 448 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 551, + 313, + 568 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "We consider the problem of reconstructing a dynamic scene observed from a stereo camera. Most existing methods for depth from stereo treat different stereo frames independently, leading to temporally inconsistent depth predictions. Temporal consistency is especially important for immersive AR or VR scenarios, where flickering greatly diminishes the user experience. We propose DynamicStereo, a novel transformer-based architecture to estimate disparity for stereo videos. The network learns to pool information from neighboring frames to improve the temporal consistency of its predictions. Our architecture is designed to process stereo videos efficiently through divided attention layers. We also introduce Dynamic Replica, a new benchmark dataset containing synthetic videos of people and animals in scanned environments, which provides complementary training and evaluation data for dynamic stereo closer to real applications than existing datasets. Training with this dataset further improves the quality of predictions of our proposed DynamicStereo as well as prior methods. Finally, it acts as a benchmark for consistent stereo methods. Project page: https://dynamic-stereo.github.io/", + "bbox": [ + 75, + 585, + 472, + 902 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 501, + 551, + 630, + 568 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Estimating depth from stereo is a fundamental computer vision problem, with applications in 3D reconstruction, robot navigation, and human motion capture, among others. With the advent of consumer devices featuring multiple cameras, such as AR glasses and smartphones, stereo can simplify the 3D reconstruction of everyday scenes, extracting them as content to be experienced in virtual or mixed reality, or for mixed reality pass-through.", + "bbox": [ + 496, + 580, + 890, + 700 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Depth from stereo takes as input two images capturing the same scene from different viewpoints. It then finds pairs of matching points, a problem known as disparity estimation. Since the two cameras are calibrated, the matched points can be projected into 3D using triangulation. While this process is robust, it is suboptimal when applied to video data, as it can only reconstruct stereo frames individually, ignoring the fact that the observations infer properties of the same underlying objects over time. Even if the camera moves or the scene deforms non-rigidly, the instantaneous 3D reconstructions are highly correlated and disregarding this fact can result in inconsistencies.", + "bbox": [ + 496, + 703, + 892, + 883 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "In this paper, we thus consider the problem of dynamic", + "bbox": [ + 517, + 887, + 890, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "13229", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "depth from stereo to improve the temporal consistency of stereo reconstruction from video data.", + "bbox": [ + 76, + 90, + 468, + 119 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Traditional approaches to stereo compute the matching costs between local image patches, aggregating those in an objective function, and optimizing the latter together with a regularization term to infer disparities. Examples of such approaches include max-flow [35] and graph-cut [15]. More recently, stereo methods have used deep networks learned from a large number of image pairs annotated with ground-truth disparities [12, 14, 18, 23]. They usually follow an approach similar to the traditional methods, but using deep CNN features for computing the matching costs, and replacing the per-image optimization by a pre-trained regression deep network, which processes the cost volume and outputs the estimated disparities.", + "bbox": [ + 75, + 122, + 467, + 318 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In the video setting, matching quality can potentially be improved by looking for matches across space and time. For instance, points occluded in one camera at a given point in time may be visible from both cameras at other times.", + "bbox": [ + 76, + 321, + 467, + 381 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Transformer architectures have shown that attention can be a powerful and flexible method for pooling information over a range of contexts [6, 8, 9, 42]. Our DynamicStereo model incorporates self- and cross-attention to extract relevant information across space, time and stereo pairs. Our architecture relies on divided attention [3] to allow efficient processing of this high-dimensional space.", + "bbox": [ + 75, + 383, + 467, + 488 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "As a learning-based approach, we wish to learn priors from data representative of real-life 3D dynamic reconstruction applications, where videos depict people or animals moving and interacting with objects. There are several synthetic video datasets [10,27,41] commonly used for training stereo and optical flow methods, but they contain abstract scenes with several layers of moving objects that share little resemblance to real-life. More realistic stereo datasets also exist [45, 49], but they either do not contain video sequences or are focused on static scenes. Given these limitations, as an additional contribution we propose a new synthetic stereo dataset showing moving human and animal characters inside realistic physical spaces from the Replica dataset [40]. We call this new dataset Dynamic Replica (DR), and we use it for learning dynamic stereo matches. DR contains 524 videos of virtual humans and animals embedded in realistic digital scans of physical environments (see Tab. 1 and Fig. 2). We show that DR can significantly boost the quality of dynamic stereo methods compared to training them only on existing depth-from-stereo datasets.", + "bbox": [ + 75, + 491, + 467, + 792 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To summarise, we make three contributions. (1) We introduce DynamicStereo, a transformer-based architecture that improves dynamic depth from stereo by jointly processing stereo videos. (2) We release Dynamic Replica, a new benchmark dataset for learning and evaluating models for dynamic depth from stereo. (3) We demonstrate state-of-the-art dynamic stereo results in a variety of benchmarks.", + "bbox": [ + 75, + 795, + 467, + 900 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/0bce1e19626a427b8fddff3e1d2ed6a0b2984dbd47dd0d52fe47cde59802cdeb.jpg", + "image_caption": [ + "SceneFlow" + ], + "image_footnote": [], + "bbox": [ + 504, + 88, + 625, + 141 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/58f21ce3775f4c1e67fd9df57369ec75d8922791a0777c3a09a8ac7998f18791.jpg", + "image_caption": [ + "KITTI" + ], + "image_footnote": [], + "bbox": [ + 625, + 88, + 785, + 141 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/9871f2242953995286c3c3b0387205b2501533f64b5d82beb40b32cb805011b2.jpg", + "image_caption": [ + "Middlebury" + ], + "image_footnote": [], + "bbox": [ + 787, + 88, + 888, + 141 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/4ee63bb9be0b8eccf1d4ac21292dfa288f05b3cad4beff8433e41c798dea9a9f.jpg", + "image_caption": [ + "Sintel" + ], + "image_footnote": [], + "bbox": [ + 504, + 152, + 629, + 207 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/c6ed9a43e5fd011fa59876676ca001e33a035a70887bc0d7408f9488259cd577.jpg", + "image_caption": [ + "ETH3D", + "Dynamic Replica (ours)" + ], + "image_footnote": [], + "bbox": [ + 630, + 152, + 763, + 207 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/a7607f9f919f409917f6e609763a807be45fd4aebe3182403c5f672b57e0125b.jpg", + "image_caption": [ + "Figure 2. Example frames from depth-from-stereo datasets. We visually compare current datasets to Dynamic Replica, which contains renderings of every-day scenes with people and animals and differs from existing datasets in size, realism, and content." + ], + "image_footnote": [], + "bbox": [ + 764, + 152, + 887, + 207 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related work", + "text_level": 1, + "bbox": [ + 500, + 314, + 635, + 330 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Depth from stereo. Stereo matching is a classic problem in computer vision. The traditional way of solving it is to compute local matching costs between image patches and then either perform local aggregation [4, 13, 46, 56], or a global optimization based on an energy function featuring data and regularization terms [15, 35].", + "bbox": [ + 496, + 340, + 890, + 430 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "More recently, deep learning has become the dominant approach to stereo matching. Zbontar and LeCun [52] proposed to use a CNN to compute the matching cost between image patches. Then Mayer et al. [27] introduced the first fully learning-based approach to stereo estimation. Inspired by traditional stereo algorithms, the next line of work [7, 12, 14, 51, 53, 54] applied 3D convolutions in their fully learning-based approaches. They construct a dense 3D cost volume between the left and the right 2D feature-maps before filtering it with a 3D-CNN. These approaches often fail to generalize to data that they were not trained on.", + "bbox": [ + 496, + 431, + 890, + 595 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "More recent works focused on improving the computational efficiency of stereo estimation [1,22,23,43]. Inspired by RAFT [44] which constructs a 4D cost volume between all pairs of pixels for optical flow, RAFT-Stereo [23] restricts this volume to 3D by collapsing it to the epipolar line. Similarly to RAFT, it iteratively updates the prediction at high resolution allowing to maintain global context and recover details. These updates are performed by a GRU [2] that operates at multiple resolutions.", + "bbox": [ + 496, + 598, + 890, + 733 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "CRE-Stereo [18] proposes to gradually increase resolution during iterative updates which simplifies the architecture. However, the lack of information propagation from lower to higher resolution may result in a loss of context. Our architecture also refines disparity in a coarse-to-fine manner, but unlike CRE-Stereo, we fuse low-resolution and high-resolution features together and propagate them to the final prediction. This allows high-resolution layers to use these features and keep track of previous states.", + "bbox": [ + 496, + 734, + 890, + 869 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Some recent works incorporate attention [47]. Stereo Transformer [19] replaces cost volume with dense pixel", + "bbox": [ + 500, + 869, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "13230", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 1 + }, + { + "type": "table", + "img_path": "images/354fa4011d1cdb4a421778f13554a4ee39e9ca421e5cd5650bcd2b9f750724e1.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
Dataset propertyMPI Sintel [5]KITTI [28]SceneFlow [27]Falling Things [45]TartanAir [50]Dynamic Replica (ours)
#Training frames1064194+2003480160200296000145200
#Test frames564195+2004248006000+18000
#Training sequences25194+2002256(330)1037484
Resolution1024×4361242×375960×540960×540640×4801280×720
Disparity/Depth✓sparse✓✓✓✓
Optical flow✓(sparse)✓X✓✓
Segmentation✓X✓✓✓✓
Non-rigid objects✓X(✓)X(X)✓
Realism(✓)✓X(✓)(✓)(✓)
", + "bbox": [ + 101, + 88, + 870, + 238 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Table 1. Comparison of depth-from-stereo datasets. Dynamic Replica is larger than previous datasets in both resolution and number of frames. A main aspect is that it contains non-rigid objects such as animals and people, which is not available at scale in prior datasets.", + "bbox": [ + 75, + 248, + 893, + 276 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "matching using attention. LoFTR [42] and SuperGlue [36] use combinations of self and cross-attention layers for sparse feature matching. Inspired by these methods, CRE-Stereo [18] uses self and cross-attention to improve convolutional features. These works focus on disparity estimation for individual frames. As we predict disparity for videos, we apply attention across time, space, and stereo frames.", + "bbox": [ + 75, + 301, + 470, + 409 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Dynamic video depth. Monocular depth estimators like MiDaS [30, 31] attempt to estimate depth from a single image. Due to the ambiguity of this task, they tend to be far less accurate than methods that use stereo. Recent works have proposed to extend these methods to use monocular videos instead, relying on motion parallax in static areas [21] or fusing information extracted from all the frames of a video, in an off-line fashion.", + "bbox": [ + 75, + 415, + 468, + 536 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Consistent Video Depth (CVD) [25] assumes that objects move almost rigidly across neighboring frames. Robust CVD (RCVD) [16] excludes dynamic objects from the optimization objective. Dynamic VD (DVD) [55] explicitly models motion of non-rigid objects with a scene-flow network. All these methods require fine-tuning a monocular depth predictor like MiDAS on a specific video, a process that must be carried out from scratch for each new video.", + "bbox": [ + 75, + 539, + 468, + 660 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Dynamic depth from stereo. The work of Li et al. (CODD) [20] is the closest to ours. It is based on three different networks: stereo, motion, and fusion, that are trained separately. During inference, consistency is achieved by extracting information from the memory state that is updated after each iteration. It is an online approach that assumes no access to future frames and thus does not allow global optimization over the whole sequence. Our network does not need a memory state and learns consistency from data. It can be applied in both online and offline settings.", + "bbox": [ + 75, + 667, + 468, + 819 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Datasets for learning depth from stereo. Training data is an important factor for learning-based stereo algorithms. It is challenging to collect real data for this task because disparity is extremely difficult to annotate. [28, 48] Active sensors such as time-of-flight cameras can provide ground", + "bbox": [ + 75, + 824, + 468, + 902 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "truth depth. KITTI [28] shows that converting such ground truth depth to pixel-accurate annotations is still challenging for dynamic objects due to the low frame rate and imprecise estimations. Synthetic datasets [17, 32, 33] can simplify the data collection process. SceneFlow [27] is the first large-scale synthetic dataset for disparity and optical flow estimation. It allowed training fully learning-based methods for these tasks. SceneFlow is less realistic compared to MPI Sintel [5], a much smaller dataset with optical flow and disparity annotations. Falling Things [45] is realistic and relatively large but does not contain non-rigid objects. TartanAir [49] is a realistic SLAM dataset with ground-truth stereo information but only few non-rigid objects.", + "bbox": [ + 496, + 301, + 890, + 498 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "To the best of our knowledge, we are the first to introduce a large-scale semi-realistic synthetic dataset with a focus on non-rigid objects for disparity estimation.", + "bbox": [ + 496, + 500, + 890, + 544 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Method", + "text_level": 1, + "bbox": [ + 500, + 558, + 589, + 573 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We first formalize the dynamic depth from stereo problem. Given a sequence $S = [(I_t^L, I_t^R)]_{1 \\leq t \\leq T} \\in \\mathbb{R}^{2 \\times 3 \\times H \\times W}$ of $T$ rectified stereo frames, the task is to predict a sequence of disparity maps $\\hat{D} = [D_t]_{1 \\leq t \\leq T} \\in \\mathbb{R}^{H \\times W}$ aligned with the left frames $I_t^L$ . While most disparity estimation methods operate on single frames $\\hat{D}_t = \\Phi(S_t)$ , here we learn a model that operates on sequences of length $T$ , constructing a function $\\hat{D} = \\Phi(S)$ . This has the advantage that the model can fuse information along time and thus improve its temporal consistency.", + "bbox": [ + 496, + 583, + 890, + 733 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The challenge is to design an architecture that can pass information across such a large volume of data efficiently. We achieve this via an encoder-decoder design (Fig. 3), building on prior work [11, 18, 34]. The encoder extracts features independently from all the frames and obtains a multi-scale representation of their content. The decoder then matches progressively more detailed features to recover the disparities from coarse to fine. Low-resolution matches easily spot large displacements of large image regions, capturing the rough structure of the disparity map, whereas high-resolution matches recover the details.", + "bbox": [ + 496, + 734, + 890, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "13231", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/8e462895edc154bdce3928ea071b06725fc4bbdb9f9e3feb28573296d9a6cd4a.jpg", + "image_caption": [ + "Figure 3. Proposed architecture of DynamicStereo. Our method consists of three main components. A convolutional encoder produces feature maps at three scales. As data spans time, space and stereo views, the SST-Block operating at the smallest resolution, ensures information exchange across all dimensions. Finally, the prediction is generated by a decoder composed of an iterative update function $g$ ." + ], + "image_footnote": [], + "bbox": [ + 76, + 89, + 893, + 261 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "For efficiency, matches are always carried out along epipolar lines. The task of exchanging information across space, view and time is delegated to two mechanisms. First, the encoder terminates in a transformer network that updates the lowest-resolution feature by running attention across these three dimensions in turn. This is efficient because it is done only for the lowest-resolution features. Second, the decoder further propagates information as it matches features to recover the disparities. The decoder itself consists of update blocks (Fig. 4a) that use both space and time information to gradually refine the disparity.", + "bbox": [ + 75, + 340, + 472, + 508 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.1. Encoder", + "text_level": 1, + "bbox": [ + 76, + 521, + 181, + 535 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The encoder starts by extracting features from every frame $I_{t}^{v}, v \\in \\{L, R\\}$ , $t \\in \\{1, \\dots, T\\}$ of the stereo video independently by applying the same CNN $F$ to them. As it is typical for CNN backbones, the resolution of the output feature map is lower than the resolution of the input image. Features are extracted with minimum stride $k = 4$ and are further down-sampled with average pooling to obtain features at 1/8 and 1/16 of the original resolution. Overall, this results in the feature maps $\\phi(I_{t}^{v})_{k} \\in \\mathbb{R}^{d \\times \\frac{H}{k} \\times \\frac{W}{k}}$ , $k \\in \\{4, 8, 16\\}$ . We will use the symbol $\\phi_{k} \\in \\mathbb{R}^{T \\times 2 \\times d \\times \\frac{H}{k} \\times \\frac{W}{k}}$ to refer to the combined five-dimensional (temporal, stereo and spatial) feature volume at resolution $k$ .", + "bbox": [ + 75, + 546, + 468, + 731 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Information Propagation. The backbone $F$ processes frames independently, so we require a different mechanism to exchange of information between left and right views $v$ and different timestamps $t$ . We do so by passing the features to a transformer network that uses self and cross-attention. Ideally, attention should compare feature maps across views, time, and space. However, it is computationally demanding to apply attention jointly even with linear [42] space and stereo attention. We thus rely on divided attention [3] to attend these three dimensions individually. We call this a Space-Stereo-Time attention block", + "bbox": [ + 75, + 734, + 470, + 902 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "(SST, Fig. 4b) and we repeat it four times. Since attention remains computationally expensive, we only apply SST to the lowest-resolution feature map $\\phi_{16}$ only.", + "bbox": [ + 496, + 340, + 893, + 388 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. Decoder", + "text_level": 1, + "bbox": [ + 500, + 393, + 601, + 409 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The output of the encoder is a multi-resolution feature volume, where the lowest resolution features incorporate information across time, view and space dimensions due to the SST block described above. The task of the decoder is to convert this feature volume into the final disparity values.", + "bbox": [ + 496, + 417, + 890, + 492 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The decoder is based on three ideas: (1) Disparities are updated from coarse to fine [18], using features of increasing resolution to update earlier estimates. (2) At each resolution, a feature correlation volume is computed and correspondences are refined iteratively [44] with reference to this volume. (3) Similar to the SST attention blocks in the encoder, information is exchanged between the three dimensions (space, view and time) throughout decoding. We describe next each component in detail.", + "bbox": [ + 496, + 493, + 890, + 628 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Iterative correspondence updates. Our model produces a sequence of progressively more accurate disparity estimates $\\hat{D} = \\hat{D}^{(m)} \\in \\mathbb{R}^{\\frac{H}{k} \\times \\frac{W}{k}}$ , $0 \\leq m \\leq M$ starting from $\\hat{D}^{(0)} = 0$ and then applying $M$ times the update rule:", + "bbox": [ + 496, + 632, + 893, + 694 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {D} ^ {(m + 1)} = \\hat {D} ^ {(m)} + g (\\hat {D} ^ {(m)}, \\phi). \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 586, + 696, + 890, + 718 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We apply the rule $\\frac{M}{4}$ times to obtain disparities $\\hat{D}^{(m)}$ at the coarser resolution $(\\frac{H}{16},\\frac{W}{16})$ . We then upsample $\\hat{D}^{(\\frac{M}{4})}$ to resolution $(\\frac{H}{8},\\frac{W}{8})$ , apply the update rule $\\frac{M}{4}$ more times to obtain $\\hat{D}^{(\\frac{M}{2})}$ , upsample the disparity again, and apply the update $\\frac{M}{2}$ more times to obtain $\\hat{D}^{(M)}$ at resolution $(\\frac{H}{4},\\frac{W}{4})$ . Finally, we upsample the predicted disparity $\\hat{D}^{(M)}$ to $(H,W)$ . Different versions of the function $g$ are trained for each of the three resolutions and upsampling uses the same mechanism as in RAFT.", + "bbox": [ + 496, + 720, + 890, + 869 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The detailed structure of the update network $g$ is illustrated in Fig. 4a and described below.", + "bbox": [ + 496, + 869, + 890, + 901 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "13232", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/01daee62dac09ac60d37fdb60d3eb6e85a2fd2f80e8583efcbd38ced04cdff2d.jpg", + "image_caption": [ + "Figure 4. The proposed architecture of (a) update block $g$ and (b) SST-Block." + ], + "image_footnote": [ + "(a) Update block $g$ . We use the current disparity estimate $\\hat{D}^{(m)}$ to sample the corresponding point and its epipolar neighbourhood from the correlation volume $C$ at different resolutions. The resulting correlation estimate $\\hat{C}^{(m)}$ is fused with the disparity $\\hat{D}^{(m)}$ and with a part of feature map $\\phi^L$ . We then apply space-time attention before passing the fused output to the 3D GRU that updates the disparity." + ], + "bbox": [ + 81, + 88, + 488, + 309 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/fbde85f350c6c7a32e433847a66c9c61d420904b1f28a064a4b2ae45303ad616.jpg", + "image_caption": [], + "image_footnote": [ + "(b) SST-Block: combines all dimensions of the input spatial, stereo and temporal attention layers. Divided attention greatly reduces computational complexity of the network." + ], + "bbox": [ + 509, + 172, + 867, + 271 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Correlation volume. Similar to classical disparity estimation methods, $g$ starts by computing the correlation volumes between left and right features $C_{t,s,k} = \\mathrm{corr}(\\phi_{t,s,k}^{L},\\phi_{t,s,k}^{R})\\in \\mathbb{R}^{\\frac{H}{sk}\\times \\frac{W}{sk}\\times \\frac{W}{sk}}$ for each feature resolution $k$ and at different scales $s\\in \\{1,2,4,8\\}$ . The correlation is computed along epipolar lines, which correspond to image rows as the input images are rectified. Each element $(h,w,w^{\\prime})$ of $C_{t,s,k}$ is the inner product between feature vectors of $\\phi_{t,s,k}^{L}$ and $\\phi_{t,s,k}^{R}$ :", + "bbox": [ + 75, + 364, + 468, + 505 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nC _ {t, s, k} (h, w, w ^ {\\prime}) = \\frac {1}{\\sqrt {d}} \\langle \\phi_ {t, s, k} ^ {L} (h, w), \\phi_ {t, s, k} ^ {R} (h, w ^ {\\prime}) \\rangle . (2)\n$$\n", + "text_format": "latex", + "bbox": [ + 91, + 513, + 468, + 546 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Thus, $C_{t,s,k}(h,w,w')$ is proportional to how well the left image point $(h,w)$ matches the right image point $(h,w')$ . As the correlation volume does not depend on the update iteration $m$ , it is computed only once.", + "bbox": [ + 75, + 551, + 468, + 613 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Correlation lookup. The function $g$ updates the disparity at location $(h, w)$ by observing the correlation volume in a local neighbourhood centered on the current disparity value $\\hat{D}_t^{(m)}(h, w)$ . The necessary samples are collected and stacked as feature channels of the tensor", + "bbox": [ + 75, + 616, + 468, + 694 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {C} _ {t, k} ^ {(m)} (h, w) = \\underset {s, \\delta} {\\operatorname {c a t}} \\left[ C _ {t, s, k} \\left(\\frac {h}{s}, \\frac {w}{s}, \\frac {w + \\hat {D} _ {t} ^ {(m)} (h , w)}{s} + \\delta\\right) \\right]. \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 81, + 699, + 467, + 752 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The current correlation estimate $\\hat{C}_{t,k}^{(m)}\\in \\mathbb{R}^{\\frac{H}{k}\\times \\frac{W}{k}\\times 4(2\\Delta +1)}$ captures the correlation volume across all four scales and in a neighborhood $\\delta \\in \\{-\\Delta ,\\dots ,\\Delta \\}$ for additional context, with cat representing the concatenation operation.", + "bbox": [ + 75, + 752, + 467, + 815 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Modality fusion. The estimated correlation, disparity, and feature maps need to be combined to provide the update block with enough information to update the disparity. Using a late fusion scheme, we encode correlation $\\hat{C}_{t,k}^{(m)}$ and disparity $\\hat{D}_t^{(m)}$ separately, before concatenating them with", + "bbox": [ + 75, + 816, + 467, + 901 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "the feature map of the left frame $\\phi_{t,k}^{L}$ , as it is the reference frame. To incorporate temporal and spatial information, we apply self-attention across time $(T)$ and space $\\left(\\frac{H}{k},\\frac{W}{k}\\right)$ to the output of the modality fusion step. For efficiency, we do it only for $k = 16$ . Architecture details can be found in Fig. 4 and the supplementary material.", + "bbox": [ + 496, + 364, + 890, + 455 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3D CNN-based GRU. The update function $g$ is implemented using a 3D convolutional GRU.", + "bbox": [ + 498, + 458, + 890, + 488 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "At each step $m$ , the GRU takes as input the fused features and a hidden state that is initialized with the reference feature map $\\phi^L$ . All internal operations of the GRU are implemented as separable 3D convolutions across space and time to propagate temporal and spatial information. The output of each iteration is an update to the current disparity estimate as in eq. (1). Each subsequent iteration is preceded by correlation lookup and modality fusion.", + "bbox": [ + 496, + 489, + 890, + 611 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.3. Training", + "text_level": 1, + "bbox": [ + 500, + 623, + 604, + 638 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Due to its iterative nature, the proposed model generates $M$ predictions for every timestamp. During training, we supervise the network over the full sequence of predictions $\\hat{D}_t^{(m)}$ , with exponentially increasing weights towards the final estimate at step $M$ as follows:", + "bbox": [ + 500, + 647, + 890, + 724 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} (\\hat {D}, D) = \\sum_ {t = 1} ^ {T} \\sum_ {m = 1} ^ {M} \\gamma^ {M - m} \\| \\hat {D} _ {t} ^ {(m)} - D _ {t} \\|, \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 552, + 739, + 890, + 781 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\gamma = 0.9$ and $D$ is the ground truth disparity sequence. Lower resolution disparity estimates are up-sampled to ground truth resolution.", + "bbox": [ + 498, + 787, + 890, + 834 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.4. Inference", + "text_level": 1, + "bbox": [ + 500, + 845, + 609, + 859 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The model is trained on stereo sequences with a fixed length of $T$ . To increase the temporal coherence at test time,", + "bbox": [ + 500, + 869, + 890, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "13233", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/9b1437151b21ac9a5b7b7f5a4d034e611030a87761f6b1e107fb6dd7c14332cd.jpg", + "image_caption": [ + "Table 2. Dynamic Replica. Example video frames and disparity maps from our proposed dataset. The proposed dataset contains diverse indoor scenes filled with animated people and animals to provide a benchmark for disparity estimation in close-to-real environments." + ], + "image_footnote": [], + "bbox": [ + 109, + 87, + 251, + 330 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/319a66435e6641088731d142233b8e0cf4ebc2f87559026e1f08192885709196.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 259, + 87, + 403, + 330 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/dd84241bdd771f7ad3e71b94868c2b791657be0e0e887add7308ebb6132b6ed4.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 411, + 87, + 553, + 330 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/8a337af419a1afb87a7615195f630b1cb26411f6e0e6c06a66918ea60e831d5c.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 562, + 88, + 705, + 330 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/e424cbcfa48e594276f6dfb2cb3637084ede4b9c6b1d0403d6ae0ff14de1b5db.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 712, + 88, + 856, + 330 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "we apply it to videos of arbitrary length using a sliding window approach with overlap, where we discard the predictions in overlapping time steps. For details see supp. mat. Videos shorter than $T$ time steps can be used by repeating the first or the last frame up to the minimal length $T$ . This corresponds to a static scene without moving camera and is well within the training distribution of the model.", + "bbox": [ + 75, + 398, + 472, + 506 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4. Dynamic Replica: dynamic stereo dataset", + "text_level": 1, + "bbox": [ + 76, + 518, + 449, + 537 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Training temporally consistent models requires a dataset with stereo videos and dense ground-truth annotations. While the SceneFlow dataset [26] fulfils both criteria, it is comprised of very short sequences of randomly textured objects moving. In this paper, we introduce a more realistic synthetic dataset and benchmark of animated humans and animals in every-day scenes: Dynamic Replica.", + "bbox": [ + 75, + 545, + 468, + 651 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "The dataset consists of 524 videos of synthetic humans and animals performing actions in virtual environments (see Tab. 2). Training and validation videos are 10 seconds long and each contain 300 frames. There are 484 training and 20 validation videos. Our test split consists of 20 videos of length 30 seconds to benchmark models on longer videos.", + "bbox": [ + 75, + 651, + 468, + 742 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Videos are rendered at a resolution of $1280 \\times 720$ . This is close to the resolution of modern screens and higher than the resolution of such popular stereo datasets as Intel $(1024 \\times 536)$ and SceneFlow $(960 \\times 540)$ .", + "bbox": [ + 75, + 742, + 468, + 801 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "The dataset is based on Facebook Replica [40] reconstructions of indoor spaces. We take 375 3D scans of humans from the RenderPeople1 dataset and animate them using motion capture sequences from real humans scans. We use artist-created animated 3D models of animals from 13", + "bbox": [ + 75, + 803, + 470, + 878 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "categories (chimp, dog, horse, sheep, etc.). We use different environments, scans, textures and motions for training, validation and test splits to evaluate generalization to unseen environments and dynamic objects.", + "bbox": [ + 496, + 398, + 890, + 459 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We randomize camera baselines in our training subset to ensure generalization across different stereo setups. Baselines are sampled uniformly between $4\\mathrm{cm}$ and $30\\mathrm{cm}$ .", + "bbox": [ + 496, + 460, + 890, + 505 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "For each scene we generate a camera trajectory imitating a person filming the scene with their mobile phone or AR glasses. These virtual cameras have smooth trajectories and are located approximately at $1.25\\mathrm{m}$ above the ground.", + "bbox": [ + 496, + 506, + 890, + 566 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "All samples in the dataset contain ground-truth depth maps, optical flow, foreground / background segmentation masks and camera parameters for both stereo views.", + "bbox": [ + 496, + 566, + 890, + 612 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5. Experiments", + "text_level": 1, + "bbox": [ + 500, + 628, + 633, + 645 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We structure the experiments as follows. First, we evaluate the Dynamic Replica dataset by comparing generalization performance of prior models trained on other datasets and on Dynamic Replica. Then we evaluate our model and compare it to the state of the art in temporal consistency. Finally, we ablate design choices in the model architecture and verify the importance of its individual components.", + "bbox": [ + 496, + 654, + 890, + 760 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Implementation Details. We implement DynamicStereo in PyTorch [29] and train on 8 NVIDIA TESLA Volta V100 32GB GPUs. The SF version is trained for 70k iterations with a batch size 8. We train the $\\mathrm{DR + SF}$ version for 120k iterations which takes about 4 days.", + "bbox": [ + 496, + 763, + 890, + 839 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Both models are trained on random $384 \\times 512$ crops of sequences of length $T = 5$ and evaluated in the original resolution with $T = 20$ and overlapping windows of size 10. During training, we use the AdamW optimizer [24] and set", + "bbox": [ + 496, + 839, + 893, + 901 + ], + "page_idx": 5 + }, + { + "type": "page_footnote", + "text": "1 http://renderpeople.com/", + "bbox": [ + 94, + 886, + 235, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "13234", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/3bae9f4d73ab36569fafd2e2165030ac2eb9aece09b805622d1d4520253239c8.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
Mtd DataKITTIMiddleburyETH3DSintelStereoDR
fullhalfquarterCleanFinalfull
[23] DR7.2519.5113.1313.863.787.3613.042.90
[23] SF5.5517.7612.809.643.055.899.204.01
[23] (DR+SF)/25.6315.0810.369.243.025.969.122.20
[18] DR6.0431.9423.8215.933.9415.0319.354.13
[18] SF6.2223.9515.6410.503.957.5111.016.59
[18] (DR+SF)/25.3522.0213.698.963.536.969.983.49
", + "bbox": [ + 78, + 88, + 472, + 218 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 3. Dynamic Replica generalization - non-temporal disparity estimation. SF - SceneFlow [27], DR - Dynamic Replica (ours). For $(\\mathrm{DR} + \\mathrm{SF}) / 2$ , we replace half of SF with samples from DR. The performance improves over pure SF training, showing that DR is valuable for generalization, compared to training only with SF data. Errors are the percent of pixels with end-point-error greater than the specified threshold. We average across 3 runs with different seeds and use the standard evaluation thresholds: 3px for KITTI 2015 [28] and Sintel Stereo [5], 2px for Middlebury [37], 1px for ETH3D [38] and DR.", + "bbox": [ + 75, + 234, + 472, + 375 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "the number of iterative updates $M = 20$ . We train with one-cycle learning rate schedule [39] with a maximum learning rate $3 \\cdot 10^{-4}$ . We set the lookup neighborhood $\\Delta = 4$ (see Sec. 3.2). For attention layers we use positional encoding in both space and time. We apply linear attention [42] for space and use standard quadratic attention for time. For other implementation details, please see supp. mat.", + "bbox": [ + 75, + 398, + 470, + 505 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.1. Dynamic Replica", + "text_level": 1, + "bbox": [ + 76, + 513, + 243, + 529 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "In Tab. 3 we show results obtained by training two recent state-of-the-art models, RAFT-Stereo [23] and CRE-Stereo [18] on SceneFlow, our dataset and their combination and testing the models' generalization to other disparity estimation datasets. While the main objective of our method is to produce temporally consistent disparity estimates, here we train state-of-the-art disparity estimation models to evaluate the usefulness of the dataset in this setting.", + "bbox": [ + 75, + 536, + 468, + 656 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "SceneFlow is an abstract dataset of moving shapes on colorful backgrounds. It aims at generalization through domain randomization, while our dataset consists of more realistic home and office scenes with people. Thus, while training on Dynamic Replica alone improves performance on the DR test set, it does not generalize as well as models trained on SceneFlow. However, combining both datasets boosts performance across both, datasets and models.", + "bbox": [ + 75, + 657, + 468, + 777 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "This highlights the benefits of including Dynamic Replica in the standard set of disparity estimation training datasets, even if its main goal is to enable training of temporally consistent models on longer sequences.", + "bbox": [ + 75, + 777, + 470, + 839 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.2. Temporal Consistency", + "text_level": 1, + "bbox": [ + 76, + 847, + 284, + 864 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "The main objective of our method and dataset is to enable training of temporally consistent disparity estimators.", + "bbox": [ + 76, + 869, + 468, + 901 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/c8e0cd66c67a97d14175302687fae87848e30fd1f283f9894fb15bb1ca96501e.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 506, + 88, + 633, + 145 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/cea7e63d00d59308988534dad86175a2206b8cb98f068f3adc4a639f801b6f1f.jpg", + "image_caption": [ + "(mean image)" + ], + "image_footnote": [], + "bbox": [ + 506, + 143, + 633, + 199 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/d0b513f27f12341df97e947898f633439ee7e15793130324510acf7e13e90a8f.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 638, + 88, + 766, + 145 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/3dce11bf36f34a11839149ef4a7174d6f0b92ec5e4b732b11b0842024d878697.jpg", + "image_caption": [ + "RAFT Stereo [23]" + ], + "image_footnote": [], + "bbox": [ + 638, + 143, + 764, + 199 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/ded0d55971c87fb304d707f6b39121c0990fb32a2ba58d123e3910e1bb1f91ca.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 774, + 88, + 901, + 145 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/41e6e1476b848996b58a8d0112c80d02775a8538120ea8f9c14f59557aa475e4.jpg", + "image_caption": [ + "DynamicStereo", + "Table 4. Temporal consistency. Mean and variance of a 40-frame reconstructed static video, visualized. Both models are trained on DR & SF. We predict depth for each frame and convert it to globally aligned point clouds. Render combined point cloud with a camera displaced by 15 angles. Finally, we compute mean and variance across all images. Pixels with variance higher than $50\\mathrm{px}^2$ are shown in red. Our method has lower variance." + ], + "image_footnote": [], + "bbox": [ + 774, + 143, + 900, + 199 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "To evaluate temporal consistency, we compute the temporal end-point-error (TEPE) defined as follows:", + "bbox": [ + 498, + 354, + 890, + 383 + ], + "page_idx": 6 + }, + { + "type": "equation", + "text": "\n$$\n\\operatorname {T E P E} (\\hat {D}, D) = \\sqrt {\\sum_ {t = 1} ^ {T - 1} \\left(\\left(\\hat {D} _ {t} - \\hat {D} _ {t + 1}\\right) - \\left(D _ {t} - D _ {t + 1}\\right)\\right) ^ {2}}. \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 509, + 397, + 890, + 445 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "This effectively measures the variation of the end-point-error across time. Lower values mean greater temporal consistency. In Tab. 5 we show that our model is more temporally consistent than prior methods across training datasets and benchmarks. It is even better than CRE-Stereo [18] that is trained on a combination of seven datasets. Additionally, models trained with Dynamic Replica are more consistent than models trained on SceneFlow alone.", + "bbox": [ + 496, + 455, + 890, + 575 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "With the above experiments, we have shown that Dynamic Replica is a useful dataset for training temporally consistent disparity estimators as well as standard stereoframe models, and that our proposed model improves over the state of the art in both tasks when trained on our dataset.", + "bbox": [ + 496, + 578, + 890, + 652 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "In Tab. 4, we show a qualitative comparison of the temporal consistency between our model and RAFT-Stereo on a real-world sequence. We show the mean reconstruction over time of the sequence and color each pixel more red, the higher its variance across time. Our model significantly reduces the flickering that single-timestep models such as RAFT-Stereo produce. For more qualitative results and videos, please see the supplementary material.", + "bbox": [ + 496, + 654, + 890, + 776 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.3. Ablation Studies", + "text_level": 1, + "bbox": [ + 500, + 786, + 663, + 800 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "In this section, we validate our method by ablating the design choices of our model. We train the model on Scene-Flow [27] for 50k iterations with the hyper-parameters described in Implementation Details (see Sec. 5). We evaluate these models on the clean pass of Sintel [5] and on the test split of Dynamic Replica. We measure both accuracy and", + "bbox": [ + 496, + 810, + 890, + 901 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "13235", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/f7f9451c553bb296a8a19ed0eadebd3cd9fd2c9e3146d7a9d5e7945a2e1c89fb.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
Training dataMethodSintel StereoDynamic Replica
CleanFinalFirst 150 frames
@δ3pxTEPE±δ1pxδt3px@δ3pxTEPE±δ1pxδt3px@δ1px
SFCODD [20]8.681.4410.785.6517.462.3218.569.796.59
RAFT-Stereo [23]6.120.929.334.5110.402.1013.697.085.51
Ours6.100.778.413.938.971.4511.955.983.44
DR+SFRAFT-Stereo [23]5.710.849.154.409.162.2713.457.171.89
Ours5.770.768.463.938.681.4211.935.923.32
SF+M+KCODD [20]9.111.3312.166.2311.902.0116.168.6410.03
SF+MRAFT-Stereo [23]5.860.858.794.138.471.6312.406.233.46
7 datasets (incl. Sintel)CRE-Stereo [18]4.580.676.363.268.171.9012.296.871.75
DR+SFOurs5.770.768.463.938.681.4211.935.923.32
", + "bbox": [ + 78, + 88, + 898, + 327 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/428065a80a85e862e720ceba607fb614535f00addcf68279e19c81f940dd15af.jpg", + "table_caption": [ + "Table 5. Accuracy $⑥$ and Temporal consistency $①$ . SF - SceneFlow [27], K - KITTI [28], M - Middlebury [37], DR - Dynamic Replica (ours). Temporal end-point error (TEPE) measures the consistency of the disparity estimation over time. We also compute $\\delta_{1px}^{t}$ and $\\delta_{3px}^{t}$ that show the proportion of pixels with TEPE higher than the threshold. Our model is more consistent than prior work and models. Additionally, other methods trained on our dataset also improve in temporal consistency. As CRE Stereo trains on Sintel and disparity estimation is evaluated on the training set of Sintel, CRE Stereo results are training set results and cannot be directly compared." + ], + "table_footnote": [], + "table_body": "
MethodSintel CleanDynamic Replica
δ3pxTEPEδ1pxTEPE
shared weights6.600.9086.480.101
sep. weights6.240.8234.760.126
", + "bbox": [ + 96, + 430, + 450, + 513 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/6ebbc21b9407320ad35c181e6e9630e121d60e45e951f6a03190d5c923e2d79c.jpg", + "table_caption": [ + "Table 6. Update Block Weight sharing. Learning separate update blocks—one per resolution—consistently improves the results compared to weight sharing across all update blocks." + ], + "table_footnote": [], + "table_body": "
MethodSintel CleanDynamic Replica
δ3pxTEPEδ1pxTEPE
Conv2D6.461.057.310.140
Conv3D6.240.8234.760.126
", + "bbox": [ + 120, + 585, + 424, + 670 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 7. Update Block Convolution. A GRU with a 3D convolution across space and time improves the performance over the 2D variant, especially in terms of the temporal metric TEPE.", + "bbox": [ + 75, + 680, + 468, + 722 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "temporal consistency. For accuracy, we use an end-point-error threshold of 3px for Sintel and 1px for DR. This shows the proportion of pixels with an end-point-error higher than 3px. For consistency, we use TEPE (see Sec. 5.2).", + "bbox": [ + 75, + 755, + 468, + 816 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Update Block. In Tab. 6 we compare sharing weights of the three blocks across the three resolutions of the decoder to learning separate update blocks. As different scales exploit features of different resolutions, learning separate update blocks improves the results over weight-sharing.", + "bbox": [ + 75, + 821, + 468, + 898 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Update Block Convolution. While prior works such as CRE Stereo use 2D convolutions in the iterative update block as they operate on single time steps, we find it beneficial to extend the processing of the update block across time (Tab. 7). This results in a general improvement but shows especially large improvements in temporal consistency.", + "bbox": [ + 496, + 433, + 890, + 523 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Please see the supplement for additional analysis.", + "bbox": [ + 519, + 525, + 846, + 540 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "6. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 556, + 617, + 571 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this paper, we make two main contributions. We introduce a new stereo video dataset—Dynamic Replica—that allows training temporally consistent disparity estimators. Additionally, we introduce a new method that is able to improve over the state of the art in temporally consistent stereo estimation using the new dataset.", + "bbox": [ + 496, + 584, + 890, + 674 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We show that other methods benefit from training on this new dataset as it contains realistic scenes and can thus reduce the domain gap between the real world and typical synthetic, abstract training datasets such as SceneFlow. Our combines spatial, temporal, and stereo information, enabling precise and consistent predictions across time. In extensive ablation studies, we show that each component of the model contributes to the final performance.", + "bbox": [ + 496, + 676, + 890, + 796 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgements", + "text_level": 1, + "bbox": [ + 500, + 814, + 666, + 830 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "C. R. is supported by VisualAI EP/T028572/1. We would like to thank Filippos Kokkinos for helping to capture test videos, Roman Shapovalov and Luke Melas-Kyriazi for insightful discussions.", + "bbox": [ + 496, + 839, + 890, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "13236", + "bbox": [ + 480, + 945, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Abhishek Badki, Alejandro Troccoli, Kihwan Kim, Jan Kautz, Pradeep Sen, and Orazio Gallo. Bi3d: Stereo depth estimation via binary classifications. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 1600-1608, 2020. 2", + "[2] Nicolas Ballas, Li Yao, Chris Pal, and Aaron C. Courville. Delving deeper into convolutional networks for learning video representations. 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Dynamic Replica and DynamicStereo. In this work, we (a) introduce a new synthetic stereo video dataset (Dynamic Replica) to train and benchmark temporally consistent disparity estimators for dynamic scenes with people and animals, and (b) propose a method (DynamicStereo) exploiting recent advances in transformer architectures that performs efficient stereo matching at the level of videos." + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.553, + 0.314, + 0.569 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.586, + 0.473, + 0.903 + ], + "angle": 0, + "content": "We consider the problem of reconstructing a dynamic scene observed from a stereo camera. Most existing methods for depth from stereo treat different stereo frames independently, leading to temporally inconsistent depth predictions. Temporal consistency is especially important for immersive AR or VR scenarios, where flickering greatly diminishes the user experience. We propose DynamicStereo, a novel transformer-based architecture to estimate disparity for stereo videos. The network learns to pool information from neighboring frames to improve the temporal consistency of its predictions. Our architecture is designed to process stereo videos efficiently through divided attention layers. We also introduce Dynamic Replica, a new benchmark dataset containing synthetic videos of people and animals in scanned environments, which provides complementary training and evaluation data for dynamic stereo closer to real applications than existing datasets. Training with this dataset further improves the quality of predictions of our proposed DynamicStereo as well as prior methods. Finally, it acts as a benchmark for consistent stereo methods. Project page: https://dynamic-stereo.github.io/" + }, + { + "type": "title", + "bbox": [ + 0.502, + 0.553, + 0.631, + 0.569 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.581, + 0.892, + 0.702 + ], + "angle": 0, + "content": "Estimating depth from stereo is a fundamental computer vision problem, with applications in 3D reconstruction, robot navigation, and human motion capture, among others. With the advent of consumer devices featuring multiple cameras, such as AR glasses and smartphones, stereo can simplify the 3D reconstruction of everyday scenes, extracting them as content to be experienced in virtual or mixed reality, or for mixed reality pass-through." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.704, + 0.893, + 0.884 + ], + "angle": 0, + "content": "Depth from stereo takes as input two images capturing the same scene from different viewpoints. It then finds pairs of matching points, a problem known as disparity estimation. Since the two cameras are calibrated, the matched points can be projected into 3D using triangulation. While this process is robust, it is suboptimal when applied to video data, as it can only reconstruct stereo frames individually, ignoring the fact that the observations infer properties of the same underlying objects over time. Even if the camera moves or the scene deforms non-rigidly, the instantaneous 3D reconstructions are highly correlated and disregarding this fact can result in inconsistencies." + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.888, + 0.892, + 0.903 + ], + "angle": 0, + "content": "In this paper, we thus consider the problem of dynamic" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "13229" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.47, + 0.121 + ], + "angle": 0, + "content": "depth from stereo to improve the temporal consistency of stereo reconstruction from video data." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.123, + 0.468, + 0.319 + ], + "angle": 0, + "content": "Traditional approaches to stereo compute the matching costs between local image patches, aggregating those in an objective function, and optimizing the latter together with a regularization term to infer disparities. Examples of such approaches include max-flow [35] and graph-cut [15]. More recently, stereo methods have used deep networks learned from a large number of image pairs annotated with ground-truth disparities [12, 14, 18, 23]. They usually follow an approach similar to the traditional methods, but using deep CNN features for computing the matching costs, and replacing the per-image optimization by a pre-trained regression deep network, which processes the cost volume and outputs the estimated disparities." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.322, + 0.468, + 0.382 + ], + "angle": 0, + "content": "In the video setting, matching quality can potentially be improved by looking for matches across space and time. For instance, points occluded in one camera at a given point in time may be visible from both cameras at other times." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.384, + 0.468, + 0.489 + ], + "angle": 0, + "content": "Transformer architectures have shown that attention can be a powerful and flexible method for pooling information over a range of contexts [6, 8, 9, 42]. Our DynamicStereo model incorporates self- and cross-attention to extract relevant information across space, time and stereo pairs. Our architecture relies on divided attention [3] to allow efficient processing of this high-dimensional space." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.492, + 0.468, + 0.793 + ], + "angle": 0, + "content": "As a learning-based approach, we wish to learn priors from data representative of real-life 3D dynamic reconstruction applications, where videos depict people or animals moving and interacting with objects. There are several synthetic video datasets [10,27,41] commonly used for training stereo and optical flow methods, but they contain abstract scenes with several layers of moving objects that share little resemblance to real-life. More realistic stereo datasets also exist [45, 49], but they either do not contain video sequences or are focused on static scenes. Given these limitations, as an additional contribution we propose a new synthetic stereo dataset showing moving human and animal characters inside realistic physical spaces from the Replica dataset [40]. We call this new dataset Dynamic Replica (DR), and we use it for learning dynamic stereo matches. DR contains 524 videos of virtual humans and animals embedded in realistic digital scans of physical environments (see Tab. 1 and Fig. 2). We show that DR can significantly boost the quality of dynamic stereo methods compared to training them only on existing depth-from-stereo datasets." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.796, + 0.468, + 0.901 + ], + "angle": 0, + "content": "To summarise, we make three contributions. (1) We introduce DynamicStereo, a transformer-based architecture that improves dynamic depth from stereo by jointly processing stereo videos. (2) We release Dynamic Replica, a new benchmark dataset for learning and evaluating models for dynamic depth from stereo. (3) We demonstrate state-of-the-art dynamic stereo results in a variety of benchmarks." + }, + { + "type": "image", + "bbox": [ + 0.505, + 0.089, + 0.626, + 0.142 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.538, + 0.143, + 0.59, + 0.151 + ], + "angle": 0, + "content": "SceneFlow" + }, + { + "type": "image", + "bbox": [ + 0.627, + 0.089, + 0.786, + 0.142 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.692, + 0.143, + 0.725, + 0.151 + ], + "angle": 0, + "content": "KITTI" + }, + { + "type": "image", + "bbox": [ + 0.788, + 0.089, + 0.889, + 0.142 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.81, + 0.143, + 0.867, + 0.152 + ], + "angle": 0, + "content": "Middlebury" + }, + { + "type": "image", + "bbox": [ + 0.505, + 0.153, + 0.63, + 0.208 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.551, + 0.211, + 0.582, + 0.219 + ], + "angle": 0, + "content": "Sintel" + }, + { + "type": "image", + "bbox": [ + 0.631, + 0.153, + 0.764, + 0.208 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.68, + 0.21, + 0.719, + 0.219 + ], + "angle": 0, + "content": "ETH3D" + }, + { + "type": "image", + "bbox": [ + 0.765, + 0.153, + 0.888, + 0.208 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.765, + 0.209, + 0.889, + 0.219 + ], + "angle": 0, + "content": "Dynamic Replica (ours)" + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.233, + 0.892, + 0.289 + ], + "angle": 0, + "content": "Figure 2. Example frames from depth-from-stereo datasets. We visually compare current datasets to Dynamic Replica, which contains renderings of every-day scenes with people and animals and differs from existing datasets in size, realism, and content." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.315, + 0.637, + 0.331 + ], + "angle": 0, + "content": "2. Related work" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.341, + 0.892, + 0.431 + ], + "angle": 0, + "content": "Depth from stereo. Stereo matching is a classic problem in computer vision. The traditional way of solving it is to compute local matching costs between image patches and then either perform local aggregation [4, 13, 46, 56], or a global optimization based on an energy function featuring data and regularization terms [15, 35]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.432, + 0.892, + 0.597 + ], + "angle": 0, + "content": "More recently, deep learning has become the dominant approach to stereo matching. Zbontar and LeCun [52] proposed to use a CNN to compute the matching cost between image patches. Then Mayer et al. [27] introduced the first fully learning-based approach to stereo estimation. Inspired by traditional stereo algorithms, the next line of work [7, 12, 14, 51, 53, 54] applied 3D convolutions in their fully learning-based approaches. They construct a dense 3D cost volume between the left and the right 2D feature-maps before filtering it with a 3D-CNN. These approaches often fail to generalize to data that they were not trained on." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.599, + 0.892, + 0.734 + ], + "angle": 0, + "content": "More recent works focused on improving the computational efficiency of stereo estimation [1,22,23,43]. Inspired by RAFT [44] which constructs a 4D cost volume between all pairs of pixels for optical flow, RAFT-Stereo [23] restricts this volume to 3D by collapsing it to the epipolar line. Similarly to RAFT, it iteratively updates the prediction at high resolution allowing to maintain global context and recover details. These updates are performed by a GRU [2] that operates at multiple resolutions." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.735, + 0.892, + 0.87 + ], + "angle": 0, + "content": "CRE-Stereo [18] proposes to gradually increase resolution during iterative updates which simplifies the architecture. However, the lack of information propagation from lower to higher resolution may result in a loss of context. Our architecture also refines disparity in a coarse-to-fine manner, but unlike CRE-Stereo, we fuse low-resolution and high-resolution features together and propagate them to the final prediction. This allows high-resolution layers to use these features and keep track of previous states." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.871, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Some recent works incorporate attention [47]. Stereo Transformer [19] replaces cost volume with dense pixel" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "13230" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.102, + 0.089, + 0.872, + 0.239 + ], + "angle": 0, + "content": "
Dataset propertyMPI Sintel [5]KITTI [28]SceneFlow [27]Falling Things [45]TartanAir [50]Dynamic Replica (ours)
#Training frames1064194+2003480160200296000145200
#Test frames564195+2004248006000+18000
#Training sequences25194+2002256(330)1037484
Resolution1024×4361242×375960×540960×540640×4801280×720
Disparity/Depth✓sparse✓✓✓✓
Optical flow✓(sparse)✓X✓✓
Segmentation✓X✓✓✓✓
Non-rigid objects✓X(✓)X(X)✓
Realism(✓)✓X(✓)(✓)(✓)
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.249, + 0.894, + 0.277 + ], + "angle": 0, + "content": "Table 1. Comparison of depth-from-stereo datasets. Dynamic Replica is larger than previous datasets in both resolution and number of frames. A main aspect is that it contains non-rigid objects such as animals and people, which is not available at scale in prior datasets." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.303, + 0.471, + 0.41 + ], + "angle": 0, + "content": "matching using attention. LoFTR [42] and SuperGlue [36] use combinations of self and cross-attention layers for sparse feature matching. Inspired by these methods, CRE-Stereo [18] uses self and cross-attention to improve convolutional features. These works focus on disparity estimation for individual frames. As we predict disparity for videos, we apply attention across time, space, and stereo frames." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.416, + 0.47, + 0.537 + ], + "angle": 0, + "content": "Dynamic video depth. Monocular depth estimators like MiDaS [30, 31] attempt to estimate depth from a single image. Due to the ambiguity of this task, they tend to be far less accurate than methods that use stereo. Recent works have proposed to extend these methods to use monocular videos instead, relying on motion parallax in static areas [21] or fusing information extracted from all the frames of a video, in an off-line fashion." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.54, + 0.47, + 0.661 + ], + "angle": 0, + "content": "Consistent Video Depth (CVD) [25] assumes that objects move almost rigidly across neighboring frames. Robust CVD (RCVD) [16] excludes dynamic objects from the optimization objective. Dynamic VD (DVD) [55] explicitly models motion of non-rigid objects with a scene-flow network. All these methods require fine-tuning a monocular depth predictor like MiDAS on a specific video, a process that must be carried out from scratch for each new video." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.668, + 0.47, + 0.82 + ], + "angle": 0, + "content": "Dynamic depth from stereo. The work of Li et al. (CODD) [20] is the closest to ours. It is based on three different networks: stereo, motion, and fusion, that are trained separately. During inference, consistency is achieved by extracting information from the memory state that is updated after each iteration. It is an online approach that assumes no access to future frames and thus does not allow global optimization over the whole sequence. Our network does not need a memory state and learns consistency from data. It can be applied in both online and offline settings." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.825, + 0.47, + 0.903 + ], + "angle": 0, + "content": "Datasets for learning depth from stereo. Training data is an important factor for learning-based stereo algorithms. It is challenging to collect real data for this task because disparity is extremely difficult to annotate. [28, 48] Active sensors such as time-of-flight cameras can provide ground" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.303, + 0.892, + 0.499 + ], + "angle": 0, + "content": "truth depth. KITTI [28] shows that converting such ground truth depth to pixel-accurate annotations is still challenging for dynamic objects due to the low frame rate and imprecise estimations. Synthetic datasets [17, 32, 33] can simplify the data collection process. SceneFlow [27] is the first large-scale synthetic dataset for disparity and optical flow estimation. It allowed training fully learning-based methods for these tasks. SceneFlow is less realistic compared to MPI Sintel [5], a much smaller dataset with optical flow and disparity annotations. Falling Things [45] is realistic and relatively large but does not contain non-rigid objects. TartanAir [49] is a realistic SLAM dataset with ground-truth stereo information but only few non-rigid objects." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.5, + 0.892, + 0.545 + ], + "angle": 0, + "content": "To the best of our knowledge, we are the first to introduce a large-scale semi-realistic synthetic dataset with a focus on non-rigid objects for disparity estimation." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.559, + 0.591, + 0.574 + ], + "angle": 0, + "content": "3. Method" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.584, + 0.892, + 0.734 + ], + "angle": 0, + "content": "We first formalize the dynamic depth from stereo problem. Given a sequence \\( S = [(I_t^L, I_t^R)]_{1 \\leq t \\leq T} \\in \\mathbb{R}^{2 \\times 3 \\times H \\times W} \\) of \\( T \\) rectified stereo frames, the task is to predict a sequence of disparity maps \\( \\hat{D} = [D_t]_{1 \\leq t \\leq T} \\in \\mathbb{R}^{H \\times W} \\) aligned with the left frames \\( I_t^L \\). While most disparity estimation methods operate on single frames \\( \\hat{D}_t = \\Phi(S_t) \\), here we learn a model that operates on sequences of length \\( T \\), constructing a function \\( \\hat{D} = \\Phi(S) \\). This has the advantage that the model can fuse information along time and thus improve its temporal consistency." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.735, + 0.892, + 0.901 + ], + "angle": 0, + "content": "The challenge is to design an architecture that can pass information across such a large volume of data efficiently. We achieve this via an encoder-decoder design (Fig. 3), building on prior work [11, 18, 34]. The encoder extracts features independently from all the frames and obtains a multi-scale representation of their content. The decoder then matches progressively more detailed features to recover the disparities from coarse to fine. Low-resolution matches easily spot large displacements of large image regions, capturing the rough structure of the disparity map, whereas high-resolution matches recover the details." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "13231" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.078, + 0.09, + 0.895, + 0.262 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.273, + 0.895, + 0.318 + ], + "angle": 0, + "content": "Figure 3. Proposed architecture of DynamicStereo. Our method consists of three main components. A convolutional encoder produces feature maps at three scales. As data spans time, space and stereo views, the SST-Block operating at the smallest resolution, ensures information exchange across all dimensions. Finally, the prediction is generated by a decoder composed of an iterative update function \\( g \\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.342, + 0.473, + 0.51 + ], + "angle": 0, + "content": "For efficiency, matches are always carried out along epipolar lines. The task of exchanging information across space, view and time is delegated to two mechanisms. First, the encoder terminates in a transformer network that updates the lowest-resolution feature by running attention across these three dimensions in turn. This is efficient because it is done only for the lowest-resolution features. Second, the decoder further propagates information as it matches features to recover the disparities. The decoder itself consists of update blocks (Fig. 4a) that use both space and time information to gradually refine the disparity." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.522, + 0.182, + 0.536 + ], + "angle": 0, + "content": "3.1. Encoder" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.547, + 0.47, + 0.732 + ], + "angle": 0, + "content": "The encoder starts by extracting features from every frame \\( I_{t}^{v}, v \\in \\{L, R\\} \\), \\( t \\in \\{1, \\dots, T\\} \\) of the stereo video independently by applying the same CNN \\( F \\) to them. As it is typical for CNN backbones, the resolution of the output feature map is lower than the resolution of the input image. Features are extracted with minimum stride \\( k = 4 \\) and are further down-sampled with average pooling to obtain features at 1/8 and 1/16 of the original resolution. Overall, this results in the feature maps \\( \\phi(I_{t}^{v})_{k} \\in \\mathbb{R}^{d \\times \\frac{H}{k} \\times \\frac{W}{k}} \\), \\( k \\in \\{4, 8, 16\\} \\). We will use the symbol \\( \\phi_{k} \\in \\mathbb{R}^{T \\times 2 \\times d \\times \\frac{H}{k} \\times \\frac{W}{k}} \\) to refer to the combined five-dimensional (temporal, stereo and spatial) feature volume at resolution \\( k \\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.735, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Information Propagation. The backbone \\( F \\) processes frames independently, so we require a different mechanism to exchange of information between left and right views \\( v \\) and different timestamps \\( t \\). We do so by passing the features to a transformer network that uses self and cross-attention. Ideally, attention should compare feature maps across views, time, and space. However, it is computationally demanding to apply attention jointly even with linear [42] space and stereo attention. We thus rely on divided attention [3] to attend these three dimensions individually. We call this a Space-Stereo-Time attention block" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.342, + 0.895, + 0.389 + ], + "angle": 0, + "content": "(SST, Fig. 4b) and we repeat it four times. Since attention remains computationally expensive, we only apply SST to the lowest-resolution feature map \\(\\phi_{16}\\) only." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.395, + 0.602, + 0.41 + ], + "angle": 0, + "content": "3.2. Decoder" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.418, + 0.892, + 0.493 + ], + "angle": 0, + "content": "The output of the encoder is a multi-resolution feature volume, where the lowest resolution features incorporate information across time, view and space dimensions due to the SST block described above. The task of the decoder is to convert this feature volume into the final disparity values." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.494, + 0.892, + 0.63 + ], + "angle": 0, + "content": "The decoder is based on three ideas: (1) Disparities are updated from coarse to fine [18], using features of increasing resolution to update earlier estimates. (2) At each resolution, a feature correlation volume is computed and correspondences are refined iteratively [44] with reference to this volume. (3) Similar to the SST attention blocks in the encoder, information is exchanged between the three dimensions (space, view and time) throughout decoding. We describe next each component in detail." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.633, + 0.894, + 0.695 + ], + "angle": 0, + "content": "Iterative correspondence updates. Our model produces a sequence of progressively more accurate disparity estimates \\(\\hat{D} = \\hat{D}^{(m)} \\in \\mathbb{R}^{\\frac{H}{k} \\times \\frac{W}{k}}\\), \\(0 \\leq m \\leq M\\) starting from \\(\\hat{D}^{(0)} = 0\\) and then applying \\(M\\) times the update rule:" + }, + { + "type": "equation", + "bbox": [ + 0.588, + 0.698, + 0.891, + 0.719 + ], + "angle": 0, + "content": "\\[\n\\hat {D} ^ {(m + 1)} = \\hat {D} ^ {(m)} + g (\\hat {D} ^ {(m)}, \\phi). \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.722, + 0.892, + 0.87 + ], + "angle": 0, + "content": "We apply the rule \\(\\frac{M}{4}\\) times to obtain disparities \\(\\hat{D}^{(m)}\\) at the coarser resolution \\((\\frac{H}{16},\\frac{W}{16})\\). We then upsample \\(\\hat{D}^{(\\frac{M}{4})}\\) to resolution \\((\\frac{H}{8},\\frac{W}{8})\\), apply the update rule \\(\\frac{M}{4}\\) more times to obtain \\(\\hat{D}^{(\\frac{M}{2})}\\), upsample the disparity again, and apply the update \\(\\frac{M}{2}\\) more times to obtain \\(\\hat{D}^{(M)}\\) at resolution \\((\\frac{H}{4},\\frac{W}{4})\\). Finally, we upsample the predicted disparity \\(\\hat{D}^{(M)}\\) to \\((H,W)\\). Different versions of the function \\(g\\) are trained for each of the three resolutions and upsampling uses the same mechanism as in RAFT." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.871, + 0.892, + 0.902 + ], + "angle": 0, + "content": "The detailed structure of the update network \\(g\\) is illustrated in Fig. 4a and described below." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "13232" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.089, + 0.49, + 0.31 + ], + "angle": 0, + "content": null + }, + { + "type": "image_footnote", + "bbox": [ + 0.492, + 0.089, + 0.889, + 0.165 + ], + "angle": 0, + "content": "(a) Update block \\( g \\). We use the current disparity estimate \\( \\hat{D}^{(m)} \\) to sample the corresponding point and its epipolar neighbourhood from the correlation volume \\( C \\) at different resolutions. The resulting correlation estimate \\( \\hat{C}^{(m)} \\) is fused with the disparity \\( \\hat{D}^{(m)} \\) and with a part of feature map \\( \\phi^L \\). We then apply space-time attention before passing the fused output to the 3D GRU that updates the disparity." + }, + { + "type": "image", + "bbox": [ + 0.511, + 0.173, + 0.868, + 0.272 + ], + "angle": 0, + "content": null + }, + { + "type": "image_footnote", + "bbox": [ + 0.492, + 0.276, + 0.889, + 0.314 + ], + "angle": 0, + "content": "(b) SST-Block: combines all dimensions of the input spatial, stereo and temporal attention layers. Divided attention greatly reduces computational complexity of the network." + }, + { + "type": "image_caption", + "bbox": [ + 0.24, + 0.324, + 0.724, + 0.339 + ], + "angle": 0, + "content": "Figure 4. The proposed architecture of (a) update block \\( g \\) and (b) SST-Block." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.365, + 0.47, + 0.506 + ], + "angle": 0, + "content": "Correlation volume. Similar to classical disparity estimation methods, \\(g\\) starts by computing the correlation volumes between left and right features \\(C_{t,s,k} = \\mathrm{corr}(\\phi_{t,s,k}^{L},\\phi_{t,s,k}^{R})\\in \\mathbb{R}^{\\frac{H}{sk}\\times \\frac{W}{sk}\\times \\frac{W}{sk}}\\) for each feature resolution \\(k\\) and at different scales \\(s\\in \\{1,2,4,8\\}\\). The correlation is computed along epipolar lines, which correspond to image rows as the input images are rectified. Each element \\((h,w,w^{\\prime})\\) of \\(C_{t,s,k}\\) is the inner product between feature vectors of \\(\\phi_{t,s,k}^{L}\\) and \\(\\phi_{t,s,k}^{R}\\):" + }, + { + "type": "equation", + "bbox": [ + 0.092, + 0.514, + 0.47, + 0.547 + ], + "angle": 0, + "content": "\\[\nC _ {t, s, k} (h, w, w ^ {\\prime}) = \\frac {1}{\\sqrt {d}} \\langle \\phi_ {t, s, k} ^ {L} (h, w), \\phi_ {t, s, k} ^ {R} (h, w ^ {\\prime}) \\rangle . (2)\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.553, + 0.47, + 0.614 + ], + "angle": 0, + "content": "Thus, \\( C_{t,s,k}(h,w,w') \\) is proportional to how well the left image point \\( (h,w) \\) matches the right image point \\( (h,w') \\). As the correlation volume does not depend on the update iteration \\( m \\), it is computed only once." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.617, + 0.47, + 0.695 + ], + "angle": 0, + "content": "Correlation lookup. The function \\( g \\) updates the disparity at location \\( (h, w) \\) by observing the correlation volume in a local neighbourhood centered on the current disparity value \\( \\hat{D}_t^{(m)}(h, w) \\). The necessary samples are collected and stacked as feature channels of the tensor" + }, + { + "type": "equation", + "bbox": [ + 0.082, + 0.7, + 0.468, + 0.753 + ], + "angle": 0, + "content": "\\[\n\\hat {C} _ {t, k} ^ {(m)} (h, w) = \\underset {s, \\delta} {\\operatorname {c a t}} \\left[ C _ {t, s, k} \\left(\\frac {h}{s}, \\frac {w}{s}, \\frac {w + \\hat {D} _ {t} ^ {(m)} (h , w)}{s} + \\delta\\right) \\right]. \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.753, + 0.468, + 0.816 + ], + "angle": 0, + "content": "The current correlation estimate \\(\\hat{C}_{t,k}^{(m)}\\in \\mathbb{R}^{\\frac{H}{k}\\times \\frac{W}{k}\\times 4(2\\Delta +1)}\\) captures the correlation volume across all four scales and in a neighborhood \\(\\delta \\in \\{-\\Delta ,\\dots ,\\Delta \\}\\) for additional context, with cat representing the concatenation operation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.818, + 0.468, + 0.902 + ], + "angle": 0, + "content": "Modality fusion. The estimated correlation, disparity, and feature maps need to be combined to provide the update block with enough information to update the disparity. Using a late fusion scheme, we encode correlation \\(\\hat{C}_{t,k}^{(m)}\\) and disparity \\(\\hat{D}_t^{(m)}\\) separately, before concatenating them with" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.365, + 0.892, + 0.456 + ], + "angle": 0, + "content": "the feature map of the left frame \\(\\phi_{t,k}^{L}\\), as it is the reference frame. To incorporate temporal and spatial information, we apply self-attention across time \\((T)\\) and space \\(\\left(\\frac{H}{k},\\frac{W}{k}\\right)\\) to the output of the modality fusion step. For efficiency, we do it only for \\(k = 16\\). Architecture details can be found in Fig. 4 and the supplementary material." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.459, + 0.892, + 0.489 + ], + "angle": 0, + "content": "3D CNN-based GRU. The update function \\( g \\) is implemented using a 3D convolutional GRU." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.491, + 0.892, + 0.612 + ], + "angle": 0, + "content": "At each step \\(m\\), the GRU takes as input the fused features and a hidden state that is initialized with the reference feature map \\(\\phi^L\\). All internal operations of the GRU are implemented as separable 3D convolutions across space and time to propagate temporal and spatial information. The output of each iteration is an update to the current disparity estimate as in eq. (1). Each subsequent iteration is preceded by correlation lookup and modality fusion." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.624, + 0.605, + 0.64 + ], + "angle": 0, + "content": "3.3. Training" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.648, + 0.892, + 0.726 + ], + "angle": 0, + "content": "Due to its iterative nature, the proposed model generates \\(M\\) predictions for every timestamp. During training, we supervise the network over the full sequence of predictions \\(\\hat{D}_t^{(m)}\\), with exponentially increasing weights towards the final estimate at step \\(M\\) as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.553, + 0.74, + 0.892, + 0.782 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} (\\hat {D}, D) = \\sum_ {t = 1} ^ {T} \\sum_ {m = 1} ^ {M} \\gamma^ {M - m} \\| \\hat {D} _ {t} ^ {(m)} - D _ {t} \\|, \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.789, + 0.892, + 0.835 + ], + "angle": 0, + "content": "where \\(\\gamma = 0.9\\) and \\(D\\) is the ground truth disparity sequence. Lower resolution disparity estimates are up-sampled to ground truth resolution." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.847, + 0.61, + 0.861 + ], + "angle": 0, + "content": "3.4. Inference" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.871, + 0.892, + 0.901 + ], + "angle": 0, + "content": "The model is trained on stereo sequences with a fixed length of \\( T \\). To increase the temporal coherence at test time," + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "13233" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.111, + 0.088, + 0.253, + 0.332 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.261, + 0.088, + 0.404, + 0.331 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.413, + 0.088, + 0.554, + 0.331 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.563, + 0.089, + 0.706, + 0.331 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.714, + 0.089, + 0.857, + 0.331 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.345, + 0.895, + 0.375 + ], + "angle": 0, + "content": "Table 2. Dynamic Replica. Example video frames and disparity maps from our proposed dataset. The proposed dataset contains diverse indoor scenes filled with animated people and animals to provide a benchmark for disparity estimation in close-to-real environments." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.399, + 0.473, + 0.507 + ], + "angle": 0, + "content": "we apply it to videos of arbitrary length using a sliding window approach with overlap, where we discard the predictions in overlapping time steps. For details see supp. mat. Videos shorter than \\( T \\) time steps can be used by repeating the first or the last frame up to the minimal length \\( T \\). This corresponds to a static scene without moving camera and is well within the training distribution of the model." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.52, + 0.45, + 0.538 + ], + "angle": 0, + "content": "4. Dynamic Replica: dynamic stereo dataset" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.546, + 0.47, + 0.652 + ], + "angle": 0, + "content": "Training temporally consistent models requires a dataset with stereo videos and dense ground-truth annotations. While the SceneFlow dataset [26] fulfils both criteria, it is comprised of very short sequences of randomly textured objects moving. In this paper, we introduce a more realistic synthetic dataset and benchmark of animated humans and animals in every-day scenes: Dynamic Replica." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.652, + 0.47, + 0.743 + ], + "angle": 0, + "content": "The dataset consists of 524 videos of synthetic humans and animals performing actions in virtual environments (see Tab. 2). Training and validation videos are 10 seconds long and each contain 300 frames. There are 484 training and 20 validation videos. Our test split consists of 20 videos of length 30 seconds to benchmark models on longer videos." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.743, + 0.47, + 0.803 + ], + "angle": 0, + "content": "Videos are rendered at a resolution of \\(1280 \\times 720\\). This is close to the resolution of modern screens and higher than the resolution of such popular stereo datasets as Intel \\((1024 \\times 536)\\) and SceneFlow \\((960 \\times 540)\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.804, + 0.471, + 0.879 + ], + "angle": 0, + "content": "The dataset is based on Facebook Replica [40] reconstructions of indoor spaces. We take 375 3D scans of humans from the RenderPeople1 dataset and animate them using motion capture sequences from real humans scans. We use artist-created animated 3D models of animals from 13" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.4, + 0.892, + 0.46 + ], + "angle": 0, + "content": "categories (chimp, dog, horse, sheep, etc.). We use different environments, scans, textures and motions for training, validation and test splits to evaluate generalization to unseen environments and dynamic objects." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.461, + 0.892, + 0.506 + ], + "angle": 0, + "content": "We randomize camera baselines in our training subset to ensure generalization across different stereo setups. Baselines are sampled uniformly between \\(4\\mathrm{cm}\\) and \\(30\\mathrm{cm}\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.507, + 0.892, + 0.568 + ], + "angle": 0, + "content": "For each scene we generate a camera trajectory imitating a person filming the scene with their mobile phone or AR glasses. These virtual cameras have smooth trajectories and are located approximately at \\(1.25\\mathrm{m}\\) above the ground." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.568, + 0.892, + 0.613 + ], + "angle": 0, + "content": "All samples in the dataset contain ground-truth depth maps, optical flow, foreground / background segmentation masks and camera parameters for both stereo views." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.629, + 0.634, + 0.646 + ], + "angle": 0, + "content": "5. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.655, + 0.892, + 0.761 + ], + "angle": 0, + "content": "We structure the experiments as follows. First, we evaluate the Dynamic Replica dataset by comparing generalization performance of prior models trained on other datasets and on Dynamic Replica. Then we evaluate our model and compare it to the state of the art in temporal consistency. Finally, we ablate design choices in the model architecture and verify the importance of its individual components." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.892, + 0.84 + ], + "angle": 0, + "content": "Implementation Details. We implement DynamicStereo in PyTorch [29] and train on 8 NVIDIA TESLA Volta V100 32GB GPUs. The SF version is trained for 70k iterations with a batch size 8. We train the \\(\\mathrm{DR + SF}\\) version for 120k iterations which takes about 4 days." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.894, + 0.902 + ], + "angle": 0, + "content": "Both models are trained on random \\(384 \\times 512\\) crops of sequences of length \\(T = 5\\) and evaluated in the original resolution with \\(T = 20\\) and overlapping windows of size 10. During training, we use the AdamW optimizer [24] and set" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.887, + 0.236, + 0.901 + ], + "angle": 0, + "content": "1 http://renderpeople.com/" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "13234" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.08, + 0.089, + 0.473, + 0.219 + ], + "angle": 0, + "content": "
Mtd DataKITTIMiddleburyETH3DSintelStereoDR
fullhalfquarterCleanFinalfull
[23] DR7.2519.5113.1313.863.787.3613.042.90
[23] SF5.5517.7612.809.643.055.899.204.01
[23] (DR+SF)/25.6315.0810.369.243.025.969.122.20
[18] DR6.0431.9423.8215.933.9415.0319.354.13
[18] SF6.2223.9515.6410.503.957.5111.016.59
[18] (DR+SF)/25.3522.0213.698.963.536.969.983.49
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.235, + 0.473, + 0.375 + ], + "angle": 0, + "content": "Table 3. Dynamic Replica generalization - non-temporal disparity estimation. SF - SceneFlow [27], DR - Dynamic Replica (ours). For \\((\\mathrm{DR} + \\mathrm{SF}) / 2\\), we replace half of SF with samples from DR. The performance improves over pure SF training, showing that DR is valuable for generalization, compared to training only with SF data. Errors are the percent of pixels with end-point-error greater than the specified threshold. We average across 3 runs with different seeds and use the standard evaluation thresholds: 3px for KITTI 2015 [28] and Sintel Stereo [5], 2px for Middlebury [37], 1px for ETH3D [38] and DR." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.399, + 0.471, + 0.506 + ], + "angle": 0, + "content": "the number of iterative updates \\( M = 20 \\). We train with one-cycle learning rate schedule [39] with a maximum learning rate \\( 3 \\cdot 10^{-4} \\). We set the lookup neighborhood \\( \\Delta = 4 \\) (see Sec. 3.2). For attention layers we use positional encoding in both space and time. We apply linear attention [42] for space and use standard quadratic attention for time. For other implementation details, please see supp. mat." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.514, + 0.245, + 0.53 + ], + "angle": 0, + "content": "5.1. Dynamic Replica" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.537, + 0.47, + 0.657 + ], + "angle": 0, + "content": "In Tab. 3 we show results obtained by training two recent state-of-the-art models, RAFT-Stereo [23] and CRE-Stereo [18] on SceneFlow, our dataset and their combination and testing the models' generalization to other disparity estimation datasets. While the main objective of our method is to produce temporally consistent disparity estimates, here we train state-of-the-art disparity estimation models to evaluate the usefulness of the dataset in this setting." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.658, + 0.47, + 0.778 + ], + "angle": 0, + "content": "SceneFlow is an abstract dataset of moving shapes on colorful backgrounds. It aims at generalization through domain randomization, while our dataset consists of more realistic home and office scenes with people. Thus, while training on Dynamic Replica alone improves performance on the DR test set, it does not generalize as well as models trained on SceneFlow. However, combining both datasets boosts performance across both, datasets and models." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.779, + 0.471, + 0.84 + ], + "angle": 0, + "content": "This highlights the benefits of including Dynamic Replica in the standard set of disparity estimation training datasets, even if its main goal is to enable training of temporally consistent models on longer sequences." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.848, + 0.285, + 0.865 + ], + "angle": 0, + "content": "5.2. Temporal Consistency" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.469, + 0.902 + ], + "angle": 0, + "content": "The main objective of our method and dataset is to enable training of temporally consistent disparity estimators." + }, + { + "type": "image", + "bbox": [ + 0.507, + 0.089, + 0.635, + 0.146 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.508, + 0.145, + 0.634, + 0.2 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.528, + 0.204, + 0.612, + 0.217 + ], + "angle": 0, + "content": "(mean image)" + }, + { + "type": "image", + "bbox": [ + 0.64, + 0.089, + 0.767, + 0.146 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.64, + 0.145, + 0.766, + 0.2 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.649, + 0.203, + 0.758, + 0.217 + ], + "angle": 0, + "content": "RAFT Stereo [23]" + }, + { + "type": "image", + "bbox": [ + 0.775, + 0.089, + 0.903, + 0.146 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.775, + 0.145, + 0.901, + 0.2 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.789, + 0.203, + 0.888, + 0.217 + ], + "angle": 0, + "content": "DynamicStereo" + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.23, + 0.894, + 0.327 + ], + "angle": 0, + "content": "Table 4. Temporal consistency. Mean and variance of a 40-frame reconstructed static video, visualized. Both models are trained on DR & SF. We predict depth for each frame and convert it to globally aligned point clouds. Render combined point cloud with a camera displaced by 15 angles. Finally, we compute mean and variance across all images. Pixels with variance higher than \\(50\\mathrm{px}^2\\) are shown in red. Our method has lower variance." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.355, + 0.892, + 0.385 + ], + "angle": 0, + "content": "To evaluate temporal consistency, we compute the temporal end-point-error (TEPE) defined as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.51, + 0.398, + 0.892, + 0.446 + ], + "angle": 0, + "content": "\\[\n\\operatorname {T E P E} (\\hat {D}, D) = \\sqrt {\\sum_ {t = 1} ^ {T - 1} \\left(\\left(\\hat {D} _ {t} - \\hat {D} _ {t + 1}\\right) - \\left(D _ {t} - D _ {t + 1}\\right)\\right) ^ {2}}. \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.457, + 0.892, + 0.577 + ], + "angle": 0, + "content": "This effectively measures the variation of the end-point-error across time. Lower values mean greater temporal consistency. In Tab. 5 we show that our model is more temporally consistent than prior methods across training datasets and benchmarks. It is even better than CRE-Stereo [18] that is trained on a combination of seven datasets. Additionally, models trained with Dynamic Replica are more consistent than models trained on SceneFlow alone." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.579, + 0.892, + 0.654 + ], + "angle": 0, + "content": "With the above experiments, we have shown that Dynamic Replica is a useful dataset for training temporally consistent disparity estimators as well as standard stereoframe models, and that our proposed model improves over the state of the art in both tasks when trained on our dataset." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.655, + 0.892, + 0.777 + ], + "angle": 0, + "content": "In Tab. 4, we show a qualitative comparison of the temporal consistency between our model and RAFT-Stereo on a real-world sequence. We show the mean reconstruction over time of the sequence and color each pixel more red, the higher its variance across time. Our model significantly reduces the flickering that single-timestep models such as RAFT-Stereo produce. For more qualitative results and videos, please see the supplementary material." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.787, + 0.665, + 0.801 + ], + "angle": 0, + "content": "5.3. Ablation Studies" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.811, + 0.892, + 0.902 + ], + "angle": 0, + "content": "In this section, we validate our method by ablating the design choices of our model. We train the model on Scene-Flow [27] for 50k iterations with the hyper-parameters described in Implementation Details (see Sec. 5). We evaluate these models on the clean pass of Sintel [5] and on the test split of Dynamic Replica. We measure both accuracy and" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "13235" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.079, + 0.089, + 0.899, + 0.328 + ], + "angle": 0, + "content": "
Training dataMethodSintel StereoDynamic Replica
CleanFinalFirst 150 frames
@δ3pxTEPE±δ1pxδt3px@δ3pxTEPE±δ1pxδt3px@δ1px
SFCODD [20]8.681.4410.785.6517.462.3218.569.796.59
RAFT-Stereo [23]6.120.929.334.5110.402.1013.697.085.51
Ours6.100.778.413.938.971.4511.955.983.44
DR+SFRAFT-Stereo [23]5.710.849.154.409.162.2713.457.171.89
Ours5.770.768.463.938.681.4211.935.923.32
SF+M+KCODD [20]9.111.3312.166.2311.902.0116.168.6410.03
SF+MRAFT-Stereo [23]5.860.858.794.138.471.6312.406.233.46
7 datasets (incl. Sintel)CRE-Stereo [18]4.580.676.363.268.171.9012.296.871.75
DR+SFOurs5.770.768.463.938.681.4211.935.923.32
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.337, + 0.894, + 0.409 + ], + "angle": 0, + "content": "Table 5. Accuracy \\(⑥\\) and Temporal consistency \\(①\\). SF - SceneFlow [27], K - KITTI [28], M - Middlebury [37], DR - Dynamic Replica (ours). Temporal end-point error (TEPE) measures the consistency of the disparity estimation over time. We also compute \\(\\delta_{1px}^{t}\\) and \\(\\delta_{3px}^{t}\\) that show the proportion of pixels with TEPE higher than the threshold. Our model is more consistent than prior work and models. Additionally, other methods trained on our dataset also improve in temporal consistency. As CRE Stereo trains on Sintel and disparity estimation is evaluated on the training set of Sintel, CRE Stereo results are training set results and cannot be directly compared." + }, + { + "type": "table", + "bbox": [ + 0.098, + 0.431, + 0.451, + 0.515 + ], + "angle": 0, + "content": "
MethodSintel CleanDynamic Replica
δ3pxTEPEδ1pxTEPE
shared weights6.600.9086.480.101
sep. weights6.240.8234.760.126
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.525, + 0.47, + 0.568 + ], + "angle": 0, + "content": "Table 6. Update Block Weight sharing. Learning separate update blocks—one per resolution—consistently improves the results compared to weight sharing across all update blocks." + }, + { + "type": "table", + "bbox": [ + 0.122, + 0.587, + 0.426, + 0.671 + ], + "angle": 0, + "content": "
MethodSintel CleanDynamic Replica
δ3pxTEPEδ1pxTEPE
Conv2D6.461.057.310.140
Conv3D6.240.8234.760.126
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.681, + 0.47, + 0.723 + ], + "angle": 0, + "content": "Table 7. Update Block Convolution. A GRU with a 3D convolution across space and time improves the performance over the 2D variant, especially in terms of the temporal metric TEPE." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.756, + 0.469, + 0.817 + ], + "angle": 0, + "content": "temporal consistency. For accuracy, we use an end-point-error threshold of 3px for Sintel and 1px for DR. This shows the proportion of pixels with an end-point-error higher than 3px. For consistency, we use TEPE (see Sec. 5.2)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.822, + 0.47, + 0.899 + ], + "angle": 0, + "content": "Update Block. In Tab. 6 we compare sharing weights of the three blocks across the three resolutions of the decoder to learning separate update blocks. As different scales exploit features of different resolutions, learning separate update blocks improves the results over weight-sharing." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.434, + 0.892, + 0.525 + ], + "angle": 0, + "content": "Update Block Convolution. While prior works such as CRE Stereo use 2D convolutions in the iterative update block as they operate on single time steps, we find it beneficial to extend the processing of the update block across time (Tab. 7). This results in a general improvement but shows especially large improvements in temporal consistency." + }, + { + "type": "text", + "bbox": [ + 0.52, + 0.526, + 0.847, + 0.541 + ], + "angle": 0, + "content": "Please see the supplement for additional analysis." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.558, + 0.619, + 0.573 + ], + "angle": 0, + "content": "6. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.585, + 0.892, + 0.675 + ], + "angle": 0, + "content": "In this paper, we make two main contributions. We introduce a new stereo video dataset—Dynamic Replica—that allows training temporally consistent disparity estimators. Additionally, we introduce a new method that is able to improve over the state of the art in temporally consistent stereo estimation using the new dataset." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.677, + 0.892, + 0.797 + ], + "angle": 0, + "content": "We show that other methods benefit from training on this new dataset as it contains realistic scenes and can thus reduce the domain gap between the real world and typical synthetic, abstract training datasets such as SceneFlow. Our combines spatial, temporal, and stereo information, enabling precise and consistent predictions across time. In extensive ablation studies, we show that each component of the model contributes to the final performance." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.815, + 0.667, + 0.831 + ], + "angle": 0, + "content": "Acknowledgements" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.892, + 0.901 + ], + "angle": 0, + "content": "C. R. is supported by VisualAI EP/T028572/1. We would like to thank Filippos Kokkinos for helping to capture test videos, Roman Shapovalov and Luke Melas-Kyriazi for insightful discussions." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.946, + 0.519, + 0.957 + ], + "angle": 0, + "content": "13236" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.116, + 0.473, + 0.187 + ], + "angle": 0, + "content": "[1] Abhishek Badki, Alejandro Troccoli, Kihwan Kim, Jan Kautz, Pradeep Sen, and Orazio Gallo. 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Dynamic Replica and DynamicStereo. In this work, we (a) introduce a new synthetic stereo video dataset (Dynamic Replica) to train and benchmark temporally consistent disparity estimators for dynamic scenes with people and animals, and (b) propose a method (DynamicStereo) exploiting recent advances in transformer architectures that performs efficient stereo matching at the level of videos. + +![](images/d5553136ac43c56e7f6157c6b1f2a2c3b72c09086fccfecc01e2fc2866268267.jpg) + +![](images/1517f73660bca214c2037384d40c11a3c6490b8a198dd0589c6a5472fbc3330b.jpg) + +![](images/6f8ff3f0e0789e3efa8cf229d37d7bf3842ccbecb6e0125f2a1d9e6c92c3178f.jpg) +DynamicStereo: +temporally-consistent depth from stereo prediction +input: dynamic sequence of stereo pairs + +![](images/b1e5e44f027395d127e39f5c2578131a6c313814d17eb268ea1a7d89302712a2.jpg) +prediction: dynamic sequence of consistent disparity maps + +![](images/3e239b74b1b88d494ed4f8b054d6cd97d9355fb53948c5154288c7c7a5b9c464.jpg) + +![](images/0640c24746eadba5ff494cf157113c15f7bd99a9bc43ce6676ca8996038ea993.jpg) +qualitative results on a real-world stereo video (rendered from the original and a novel viewpoints) + +![](images/4c6cd4b10cc0f5f02b6445fcdc98ad47aff18862a330b5659ead0e0565983234.jpg) + +# Abstract + +We consider the problem of reconstructing a dynamic scene observed from a stereo camera. Most existing methods for depth from stereo treat different stereo frames independently, leading to temporally inconsistent depth predictions. Temporal consistency is especially important for immersive AR or VR scenarios, where flickering greatly diminishes the user experience. We propose DynamicStereo, a novel transformer-based architecture to estimate disparity for stereo videos. The network learns to pool information from neighboring frames to improve the temporal consistency of its predictions. Our architecture is designed to process stereo videos efficiently through divided attention layers. We also introduce Dynamic Replica, a new benchmark dataset containing synthetic videos of people and animals in scanned environments, which provides complementary training and evaluation data for dynamic stereo closer to real applications than existing datasets. Training with this dataset further improves the quality of predictions of our proposed DynamicStereo as well as prior methods. Finally, it acts as a benchmark for consistent stereo methods. Project page: https://dynamic-stereo.github.io/ + +# 1. Introduction + +Estimating depth from stereo is a fundamental computer vision problem, with applications in 3D reconstruction, robot navigation, and human motion capture, among others. With the advent of consumer devices featuring multiple cameras, such as AR glasses and smartphones, stereo can simplify the 3D reconstruction of everyday scenes, extracting them as content to be experienced in virtual or mixed reality, or for mixed reality pass-through. + +Depth from stereo takes as input two images capturing the same scene from different viewpoints. It then finds pairs of matching points, a problem known as disparity estimation. Since the two cameras are calibrated, the matched points can be projected into 3D using triangulation. While this process is robust, it is suboptimal when applied to video data, as it can only reconstruct stereo frames individually, ignoring the fact that the observations infer properties of the same underlying objects over time. Even if the camera moves or the scene deforms non-rigidly, the instantaneous 3D reconstructions are highly correlated and disregarding this fact can result in inconsistencies. + +In this paper, we thus consider the problem of dynamic + +depth from stereo to improve the temporal consistency of stereo reconstruction from video data. + +Traditional approaches to stereo compute the matching costs between local image patches, aggregating those in an objective function, and optimizing the latter together with a regularization term to infer disparities. Examples of such approaches include max-flow [35] and graph-cut [15]. More recently, stereo methods have used deep networks learned from a large number of image pairs annotated with ground-truth disparities [12, 14, 18, 23]. They usually follow an approach similar to the traditional methods, but using deep CNN features for computing the matching costs, and replacing the per-image optimization by a pre-trained regression deep network, which processes the cost volume and outputs the estimated disparities. + +In the video setting, matching quality can potentially be improved by looking for matches across space and time. For instance, points occluded in one camera at a given point in time may be visible from both cameras at other times. + +Transformer architectures have shown that attention can be a powerful and flexible method for pooling information over a range of contexts [6, 8, 9, 42]. Our DynamicStereo model incorporates self- and cross-attention to extract relevant information across space, time and stereo pairs. Our architecture relies on divided attention [3] to allow efficient processing of this high-dimensional space. + +As a learning-based approach, we wish to learn priors from data representative of real-life 3D dynamic reconstruction applications, where videos depict people or animals moving and interacting with objects. There are several synthetic video datasets [10,27,41] commonly used for training stereo and optical flow methods, but they contain abstract scenes with several layers of moving objects that share little resemblance to real-life. More realistic stereo datasets also exist [45, 49], but they either do not contain video sequences or are focused on static scenes. Given these limitations, as an additional contribution we propose a new synthetic stereo dataset showing moving human and animal characters inside realistic physical spaces from the Replica dataset [40]. We call this new dataset Dynamic Replica (DR), and we use it for learning dynamic stereo matches. DR contains 524 videos of virtual humans and animals embedded in realistic digital scans of physical environments (see Tab. 1 and Fig. 2). We show that DR can significantly boost the quality of dynamic stereo methods compared to training them only on existing depth-from-stereo datasets. + +To summarise, we make three contributions. (1) We introduce DynamicStereo, a transformer-based architecture that improves dynamic depth from stereo by jointly processing stereo videos. (2) We release Dynamic Replica, a new benchmark dataset for learning and evaluating models for dynamic depth from stereo. (3) We demonstrate state-of-the-art dynamic stereo results in a variety of benchmarks. + +![](images/0bce1e19626a427b8fddff3e1d2ed6a0b2984dbd47dd0d52fe47cde59802cdeb.jpg) +SceneFlow + +![](images/58f21ce3775f4c1e67fd9df57369ec75d8922791a0777c3a09a8ac7998f18791.jpg) +KITTI + +![](images/9871f2242953995286c3c3b0387205b2501533f64b5d82beb40b32cb805011b2.jpg) +Middlebury + +![](images/4ee63bb9be0b8eccf1d4ac21292dfa288f05b3cad4beff8433e41c798dea9a9f.jpg) +Sintel + +![](images/c6ed9a43e5fd011fa59876676ca001e33a035a70887bc0d7408f9488259cd577.jpg) +ETH3D +Dynamic Replica (ours) + +![](images/a7607f9f919f409917f6e609763a807be45fd4aebe3182403c5f672b57e0125b.jpg) +Figure 2. Example frames from depth-from-stereo datasets. We visually compare current datasets to Dynamic Replica, which contains renderings of every-day scenes with people and animals and differs from existing datasets in size, realism, and content. + +# 2. Related work + +Depth from stereo. Stereo matching is a classic problem in computer vision. The traditional way of solving it is to compute local matching costs between image patches and then either perform local aggregation [4, 13, 46, 56], or a global optimization based on an energy function featuring data and regularization terms [15, 35]. + +More recently, deep learning has become the dominant approach to stereo matching. Zbontar and LeCun [52] proposed to use a CNN to compute the matching cost between image patches. Then Mayer et al. [27] introduced the first fully learning-based approach to stereo estimation. Inspired by traditional stereo algorithms, the next line of work [7, 12, 14, 51, 53, 54] applied 3D convolutions in their fully learning-based approaches. They construct a dense 3D cost volume between the left and the right 2D feature-maps before filtering it with a 3D-CNN. These approaches often fail to generalize to data that they were not trained on. + +More recent works focused on improving the computational efficiency of stereo estimation [1,22,23,43]. Inspired by RAFT [44] which constructs a 4D cost volume between all pairs of pixels for optical flow, RAFT-Stereo [23] restricts this volume to 3D by collapsing it to the epipolar line. Similarly to RAFT, it iteratively updates the prediction at high resolution allowing to maintain global context and recover details. These updates are performed by a GRU [2] that operates at multiple resolutions. + +CRE-Stereo [18] proposes to gradually increase resolution during iterative updates which simplifies the architecture. However, the lack of information propagation from lower to higher resolution may result in a loss of context. Our architecture also refines disparity in a coarse-to-fine manner, but unlike CRE-Stereo, we fuse low-resolution and high-resolution features together and propagate them to the final prediction. This allows high-resolution layers to use these features and keep track of previous states. + +Some recent works incorporate attention [47]. Stereo Transformer [19] replaces cost volume with dense pixel + +
Dataset propertyMPI Sintel [5]KITTI [28]SceneFlow [27]Falling Things [45]TartanAir [50]Dynamic Replica (ours)
#Training frames1064194+2003480160200296000145200
#Test frames564195+2004248006000+18000
#Training sequences25194+2002256(330)1037484
Resolution1024×4361242×375960×540960×540640×4801280×720
Disparity/Depth✓sparse✓✓✓✓
Optical flow✓(sparse)✓X✓✓
Segmentation✓X✓✓✓✓
Non-rigid objects✓X(✓)X(X)✓
Realism(✓)✓X(✓)(✓)(✓)
+ +Table 1. Comparison of depth-from-stereo datasets. Dynamic Replica is larger than previous datasets in both resolution and number of frames. A main aspect is that it contains non-rigid objects such as animals and people, which is not available at scale in prior datasets. + +matching using attention. LoFTR [42] and SuperGlue [36] use combinations of self and cross-attention layers for sparse feature matching. Inspired by these methods, CRE-Stereo [18] uses self and cross-attention to improve convolutional features. These works focus on disparity estimation for individual frames. As we predict disparity for videos, we apply attention across time, space, and stereo frames. + +Dynamic video depth. Monocular depth estimators like MiDaS [30, 31] attempt to estimate depth from a single image. Due to the ambiguity of this task, they tend to be far less accurate than methods that use stereo. Recent works have proposed to extend these methods to use monocular videos instead, relying on motion parallax in static areas [21] or fusing information extracted from all the frames of a video, in an off-line fashion. + +Consistent Video Depth (CVD) [25] assumes that objects move almost rigidly across neighboring frames. Robust CVD (RCVD) [16] excludes dynamic objects from the optimization objective. Dynamic VD (DVD) [55] explicitly models motion of non-rigid objects with a scene-flow network. All these methods require fine-tuning a monocular depth predictor like MiDAS on a specific video, a process that must be carried out from scratch for each new video. + +Dynamic depth from stereo. The work of Li et al. (CODD) [20] is the closest to ours. It is based on three different networks: stereo, motion, and fusion, that are trained separately. During inference, consistency is achieved by extracting information from the memory state that is updated after each iteration. It is an online approach that assumes no access to future frames and thus does not allow global optimization over the whole sequence. Our network does not need a memory state and learns consistency from data. It can be applied in both online and offline settings. + +Datasets for learning depth from stereo. Training data is an important factor for learning-based stereo algorithms. It is challenging to collect real data for this task because disparity is extremely difficult to annotate. [28, 48] Active sensors such as time-of-flight cameras can provide ground + +truth depth. KITTI [28] shows that converting such ground truth depth to pixel-accurate annotations is still challenging for dynamic objects due to the low frame rate and imprecise estimations. Synthetic datasets [17, 32, 33] can simplify the data collection process. SceneFlow [27] is the first large-scale synthetic dataset for disparity and optical flow estimation. It allowed training fully learning-based methods for these tasks. SceneFlow is less realistic compared to MPI Sintel [5], a much smaller dataset with optical flow and disparity annotations. Falling Things [45] is realistic and relatively large but does not contain non-rigid objects. TartanAir [49] is a realistic SLAM dataset with ground-truth stereo information but only few non-rigid objects. + +To the best of our knowledge, we are the first to introduce a large-scale semi-realistic synthetic dataset with a focus on non-rigid objects for disparity estimation. + +# 3. Method + +We first formalize the dynamic depth from stereo problem. Given a sequence $S = [(I_t^L, I_t^R)]_{1 \leq t \leq T} \in \mathbb{R}^{2 \times 3 \times H \times W}$ of $T$ rectified stereo frames, the task is to predict a sequence of disparity maps $\hat{D} = [D_t]_{1 \leq t \leq T} \in \mathbb{R}^{H \times W}$ aligned with the left frames $I_t^L$ . While most disparity estimation methods operate on single frames $\hat{D}_t = \Phi(S_t)$ , here we learn a model that operates on sequences of length $T$ , constructing a function $\hat{D} = \Phi(S)$ . This has the advantage that the model can fuse information along time and thus improve its temporal consistency. + +The challenge is to design an architecture that can pass information across such a large volume of data efficiently. We achieve this via an encoder-decoder design (Fig. 3), building on prior work [11, 18, 34]. The encoder extracts features independently from all the frames and obtains a multi-scale representation of their content. The decoder then matches progressively more detailed features to recover the disparities from coarse to fine. Low-resolution matches easily spot large displacements of large image regions, capturing the rough structure of the disparity map, whereas high-resolution matches recover the details. + +![](images/8e462895edc154bdce3928ea071b06725fc4bbdb9f9e3feb28573296d9a6cd4a.jpg) +Figure 3. Proposed architecture of DynamicStereo. Our method consists of three main components. A convolutional encoder produces feature maps at three scales. As data spans time, space and stereo views, the SST-Block operating at the smallest resolution, ensures information exchange across all dimensions. Finally, the prediction is generated by a decoder composed of an iterative update function $g$ . + +For efficiency, matches are always carried out along epipolar lines. The task of exchanging information across space, view and time is delegated to two mechanisms. First, the encoder terminates in a transformer network that updates the lowest-resolution feature by running attention across these three dimensions in turn. This is efficient because it is done only for the lowest-resolution features. Second, the decoder further propagates information as it matches features to recover the disparities. The decoder itself consists of update blocks (Fig. 4a) that use both space and time information to gradually refine the disparity. + +# 3.1. Encoder + +The encoder starts by extracting features from every frame $I_{t}^{v}, v \in \{L, R\}$ , $t \in \{1, \dots, T\}$ of the stereo video independently by applying the same CNN $F$ to them. As it is typical for CNN backbones, the resolution of the output feature map is lower than the resolution of the input image. Features are extracted with minimum stride $k = 4$ and are further down-sampled with average pooling to obtain features at 1/8 and 1/16 of the original resolution. Overall, this results in the feature maps $\phi(I_{t}^{v})_{k} \in \mathbb{R}^{d \times \frac{H}{k} \times \frac{W}{k}}$ , $k \in \{4, 8, 16\}$ . We will use the symbol $\phi_{k} \in \mathbb{R}^{T \times 2 \times d \times \frac{H}{k} \times \frac{W}{k}}$ to refer to the combined five-dimensional (temporal, stereo and spatial) feature volume at resolution $k$ . + +Information Propagation. The backbone $F$ processes frames independently, so we require a different mechanism to exchange of information between left and right views $v$ and different timestamps $t$ . We do so by passing the features to a transformer network that uses self and cross-attention. Ideally, attention should compare feature maps across views, time, and space. However, it is computationally demanding to apply attention jointly even with linear [42] space and stereo attention. We thus rely on divided attention [3] to attend these three dimensions individually. We call this a Space-Stereo-Time attention block + +(SST, Fig. 4b) and we repeat it four times. Since attention remains computationally expensive, we only apply SST to the lowest-resolution feature map $\phi_{16}$ only. + +# 3.2. Decoder + +The output of the encoder is a multi-resolution feature volume, where the lowest resolution features incorporate information across time, view and space dimensions due to the SST block described above. The task of the decoder is to convert this feature volume into the final disparity values. + +The decoder is based on three ideas: (1) Disparities are updated from coarse to fine [18], using features of increasing resolution to update earlier estimates. (2) At each resolution, a feature correlation volume is computed and correspondences are refined iteratively [44] with reference to this volume. (3) Similar to the SST attention blocks in the encoder, information is exchanged between the three dimensions (space, view and time) throughout decoding. We describe next each component in detail. + +Iterative correspondence updates. Our model produces a sequence of progressively more accurate disparity estimates $\hat{D} = \hat{D}^{(m)} \in \mathbb{R}^{\frac{H}{k} \times \frac{W}{k}}$ , $0 \leq m \leq M$ starting from $\hat{D}^{(0)} = 0$ and then applying $M$ times the update rule: + +$$ +\hat {D} ^ {(m + 1)} = \hat {D} ^ {(m)} + g (\hat {D} ^ {(m)}, \phi). \tag {1} +$$ + +We apply the rule $\frac{M}{4}$ times to obtain disparities $\hat{D}^{(m)}$ at the coarser resolution $(\frac{H}{16},\frac{W}{16})$ . We then upsample $\hat{D}^{(\frac{M}{4})}$ to resolution $(\frac{H}{8},\frac{W}{8})$ , apply the update rule $\frac{M}{4}$ more times to obtain $\hat{D}^{(\frac{M}{2})}$ , upsample the disparity again, and apply the update $\frac{M}{2}$ more times to obtain $\hat{D}^{(M)}$ at resolution $(\frac{H}{4},\frac{W}{4})$ . Finally, we upsample the predicted disparity $\hat{D}^{(M)}$ to $(H,W)$ . Different versions of the function $g$ are trained for each of the three resolutions and upsampling uses the same mechanism as in RAFT. + +The detailed structure of the update network $g$ is illustrated in Fig. 4a and described below. + +Figure 4. The proposed architecture of (a) update block $g$ and (b) SST-Block. +![](images/01daee62dac09ac60d37fdb60d3eb6e85a2fd2f80e8583efcbd38ced04cdff2d.jpg) +(a) Update block $g$ . We use the current disparity estimate $\hat{D}^{(m)}$ to sample the corresponding point and its epipolar neighbourhood from the correlation volume $C$ at different resolutions. The resulting correlation estimate $\hat{C}^{(m)}$ is fused with the disparity $\hat{D}^{(m)}$ and with a part of feature map $\phi^L$ . We then apply space-time attention before passing the fused output to the 3D GRU that updates the disparity. + +![](images/fbde85f350c6c7a32e433847a66c9c61d420904b1f28a064a4b2ae45303ad616.jpg) +(b) SST-Block: combines all dimensions of the input spatial, stereo and temporal attention layers. Divided attention greatly reduces computational complexity of the network. + +Correlation volume. Similar to classical disparity estimation methods, $g$ starts by computing the correlation volumes between left and right features $C_{t,s,k} = \mathrm{corr}(\phi_{t,s,k}^{L},\phi_{t,s,k}^{R})\in \mathbb{R}^{\frac{H}{sk}\times \frac{W}{sk}\times \frac{W}{sk}}$ for each feature resolution $k$ and at different scales $s\in \{1,2,4,8\}$ . The correlation is computed along epipolar lines, which correspond to image rows as the input images are rectified. Each element $(h,w,w^{\prime})$ of $C_{t,s,k}$ is the inner product between feature vectors of $\phi_{t,s,k}^{L}$ and $\phi_{t,s,k}^{R}$ : + +$$ +C _ {t, s, k} (h, w, w ^ {\prime}) = \frac {1}{\sqrt {d}} \langle \phi_ {t, s, k} ^ {L} (h, w), \phi_ {t, s, k} ^ {R} (h, w ^ {\prime}) \rangle . (2) +$$ + +Thus, $C_{t,s,k}(h,w,w')$ is proportional to how well the left image point $(h,w)$ matches the right image point $(h,w')$ . As the correlation volume does not depend on the update iteration $m$ , it is computed only once. + +Correlation lookup. The function $g$ updates the disparity at location $(h, w)$ by observing the correlation volume in a local neighbourhood centered on the current disparity value $\hat{D}_t^{(m)}(h, w)$ . The necessary samples are collected and stacked as feature channels of the tensor + +$$ +\hat {C} _ {t, k} ^ {(m)} (h, w) = \underset {s, \delta} {\operatorname {c a t}} \left[ C _ {t, s, k} \left(\frac {h}{s}, \frac {w}{s}, \frac {w + \hat {D} _ {t} ^ {(m)} (h , w)}{s} + \delta\right) \right]. \tag {3} +$$ + +The current correlation estimate $\hat{C}_{t,k}^{(m)}\in \mathbb{R}^{\frac{H}{k}\times \frac{W}{k}\times 4(2\Delta +1)}$ captures the correlation volume across all four scales and in a neighborhood $\delta \in \{-\Delta ,\dots ,\Delta \}$ for additional context, with cat representing the concatenation operation. + +Modality fusion. The estimated correlation, disparity, and feature maps need to be combined to provide the update block with enough information to update the disparity. Using a late fusion scheme, we encode correlation $\hat{C}_{t,k}^{(m)}$ and disparity $\hat{D}_t^{(m)}$ separately, before concatenating them with + +the feature map of the left frame $\phi_{t,k}^{L}$ , as it is the reference frame. To incorporate temporal and spatial information, we apply self-attention across time $(T)$ and space $\left(\frac{H}{k},\frac{W}{k}\right)$ to the output of the modality fusion step. For efficiency, we do it only for $k = 16$ . Architecture details can be found in Fig. 4 and the supplementary material. + +3D CNN-based GRU. The update function $g$ is implemented using a 3D convolutional GRU. + +At each step $m$ , the GRU takes as input the fused features and a hidden state that is initialized with the reference feature map $\phi^L$ . All internal operations of the GRU are implemented as separable 3D convolutions across space and time to propagate temporal and spatial information. The output of each iteration is an update to the current disparity estimate as in eq. (1). Each subsequent iteration is preceded by correlation lookup and modality fusion. + +# 3.3. Training + +Due to its iterative nature, the proposed model generates $M$ predictions for every timestamp. During training, we supervise the network over the full sequence of predictions $\hat{D}_t^{(m)}$ , with exponentially increasing weights towards the final estimate at step $M$ as follows: + +$$ +\mathcal {L} (\hat {D}, D) = \sum_ {t = 1} ^ {T} \sum_ {m = 1} ^ {M} \gamma^ {M - m} \| \hat {D} _ {t} ^ {(m)} - D _ {t} \|, \tag {4} +$$ + +where $\gamma = 0.9$ and $D$ is the ground truth disparity sequence. Lower resolution disparity estimates are up-sampled to ground truth resolution. + +# 3.4. Inference + +The model is trained on stereo sequences with a fixed length of $T$ . To increase the temporal coherence at test time, + +![](images/9b1437151b21ac9a5b7b7f5a4d034e611030a87761f6b1e107fb6dd7c14332cd.jpg) +Table 2. Dynamic Replica. Example video frames and disparity maps from our proposed dataset. The proposed dataset contains diverse indoor scenes filled with animated people and animals to provide a benchmark for disparity estimation in close-to-real environments. + +![](images/319a66435e6641088731d142233b8e0cf4ebc2f87559026e1f08192885709196.jpg) + +![](images/dd84241bdd771f7ad3e71b94868c2b791657be0e0e887add7308ebb6132b6ed4.jpg) + +![](images/8a337af419a1afb87a7615195f630b1cb26411f6e0e6c06a66918ea60e831d5c.jpg) + +![](images/e424cbcfa48e594276f6dfb2cb3637084ede4b9c6b1d0403d6ae0ff14de1b5db.jpg) + +we apply it to videos of arbitrary length using a sliding window approach with overlap, where we discard the predictions in overlapping time steps. For details see supp. mat. Videos shorter than $T$ time steps can be used by repeating the first or the last frame up to the minimal length $T$ . This corresponds to a static scene without moving camera and is well within the training distribution of the model. + +# 4. Dynamic Replica: dynamic stereo dataset + +Training temporally consistent models requires a dataset with stereo videos and dense ground-truth annotations. While the SceneFlow dataset [26] fulfils both criteria, it is comprised of very short sequences of randomly textured objects moving. In this paper, we introduce a more realistic synthetic dataset and benchmark of animated humans and animals in every-day scenes: Dynamic Replica. + +The dataset consists of 524 videos of synthetic humans and animals performing actions in virtual environments (see Tab. 2). Training and validation videos are 10 seconds long and each contain 300 frames. There are 484 training and 20 validation videos. Our test split consists of 20 videos of length 30 seconds to benchmark models on longer videos. + +Videos are rendered at a resolution of $1280 \times 720$ . This is close to the resolution of modern screens and higher than the resolution of such popular stereo datasets as Intel $(1024 \times 536)$ and SceneFlow $(960 \times 540)$ . + +The dataset is based on Facebook Replica [40] reconstructions of indoor spaces. We take 375 3D scans of humans from the RenderPeople1 dataset and animate them using motion capture sequences from real humans scans. We use artist-created animated 3D models of animals from 13 + +categories (chimp, dog, horse, sheep, etc.). We use different environments, scans, textures and motions for training, validation and test splits to evaluate generalization to unseen environments and dynamic objects. + +We randomize camera baselines in our training subset to ensure generalization across different stereo setups. Baselines are sampled uniformly between $4\mathrm{cm}$ and $30\mathrm{cm}$ . + +For each scene we generate a camera trajectory imitating a person filming the scene with their mobile phone or AR glasses. These virtual cameras have smooth trajectories and are located approximately at $1.25\mathrm{m}$ above the ground. + +All samples in the dataset contain ground-truth depth maps, optical flow, foreground / background segmentation masks and camera parameters for both stereo views. + +# 5. Experiments + +We structure the experiments as follows. First, we evaluate the Dynamic Replica dataset by comparing generalization performance of prior models trained on other datasets and on Dynamic Replica. Then we evaluate our model and compare it to the state of the art in temporal consistency. Finally, we ablate design choices in the model architecture and verify the importance of its individual components. + +Implementation Details. We implement DynamicStereo in PyTorch [29] and train on 8 NVIDIA TESLA Volta V100 32GB GPUs. The SF version is trained for 70k iterations with a batch size 8. We train the $\mathrm{DR + SF}$ version for 120k iterations which takes about 4 days. + +Both models are trained on random $384 \times 512$ crops of sequences of length $T = 5$ and evaluated in the original resolution with $T = 20$ and overlapping windows of size 10. During training, we use the AdamW optimizer [24] and set + +
Mtd DataKITTIMiddleburyETH3DSintelStereoDR
fullhalfquarterCleanFinalfull
[23] DR7.2519.5113.1313.863.787.3613.042.90
[23] SF5.5517.7612.809.643.055.899.204.01
[23] (DR+SF)/25.6315.0810.369.243.025.969.122.20
[18] DR6.0431.9423.8215.933.9415.0319.354.13
[18] SF6.2223.9515.6410.503.957.5111.016.59
[18] (DR+SF)/25.3522.0213.698.963.536.969.983.49
+ +Table 3. Dynamic Replica generalization - non-temporal disparity estimation. SF - SceneFlow [27], DR - Dynamic Replica (ours). For $(\mathrm{DR} + \mathrm{SF}) / 2$ , we replace half of SF with samples from DR. The performance improves over pure SF training, showing that DR is valuable for generalization, compared to training only with SF data. Errors are the percent of pixels with end-point-error greater than the specified threshold. We average across 3 runs with different seeds and use the standard evaluation thresholds: 3px for KITTI 2015 [28] and Sintel Stereo [5], 2px for Middlebury [37], 1px for ETH3D [38] and DR. + +the number of iterative updates $M = 20$ . We train with one-cycle learning rate schedule [39] with a maximum learning rate $3 \cdot 10^{-4}$ . We set the lookup neighborhood $\Delta = 4$ (see Sec. 3.2). For attention layers we use positional encoding in both space and time. We apply linear attention [42] for space and use standard quadratic attention for time. For other implementation details, please see supp. mat. + +# 5.1. Dynamic Replica + +In Tab. 3 we show results obtained by training two recent state-of-the-art models, RAFT-Stereo [23] and CRE-Stereo [18] on SceneFlow, our dataset and their combination and testing the models' generalization to other disparity estimation datasets. While the main objective of our method is to produce temporally consistent disparity estimates, here we train state-of-the-art disparity estimation models to evaluate the usefulness of the dataset in this setting. + +SceneFlow is an abstract dataset of moving shapes on colorful backgrounds. It aims at generalization through domain randomization, while our dataset consists of more realistic home and office scenes with people. Thus, while training on Dynamic Replica alone improves performance on the DR test set, it does not generalize as well as models trained on SceneFlow. However, combining both datasets boosts performance across both, datasets and models. + +This highlights the benefits of including Dynamic Replica in the standard set of disparity estimation training datasets, even if its main goal is to enable training of temporally consistent models on longer sequences. + +# 5.2. Temporal Consistency + +The main objective of our method and dataset is to enable training of temporally consistent disparity estimators. + +![](images/c8e0cd66c67a97d14175302687fae87848e30fd1f283f9894fb15bb1ca96501e.jpg) + +![](images/cea7e63d00d59308988534dad86175a2206b8cb98f068f3adc4a639f801b6f1f.jpg) +(mean image) + +![](images/d0b513f27f12341df97e947898f633439ee7e15793130324510acf7e13e90a8f.jpg) + +![](images/3dce11bf36f34a11839149ef4a7174d6f0b92ec5e4b732b11b0842024d878697.jpg) +RAFT Stereo [23] + +![](images/ded0d55971c87fb304d707f6b39121c0990fb32a2ba58d123e3910e1bb1f91ca.jpg) + +![](images/41e6e1476b848996b58a8d0112c80d02775a8538120ea8f9c14f59557aa475e4.jpg) +DynamicStereo +Table 4. Temporal consistency. Mean and variance of a 40-frame reconstructed static video, visualized. Both models are trained on DR & SF. We predict depth for each frame and convert it to globally aligned point clouds. Render combined point cloud with a camera displaced by 15 angles. Finally, we compute mean and variance across all images. Pixels with variance higher than $50\mathrm{px}^2$ are shown in red. Our method has lower variance. + +To evaluate temporal consistency, we compute the temporal end-point-error (TEPE) defined as follows: + +$$ +\operatorname {T E P E} (\hat {D}, D) = \sqrt {\sum_ {t = 1} ^ {T - 1} \left(\left(\hat {D} _ {t} - \hat {D} _ {t + 1}\right) - \left(D _ {t} - D _ {t + 1}\right)\right) ^ {2}}. \tag {5} +$$ + +This effectively measures the variation of the end-point-error across time. Lower values mean greater temporal consistency. In Tab. 5 we show that our model is more temporally consistent than prior methods across training datasets and benchmarks. It is even better than CRE-Stereo [18] that is trained on a combination of seven datasets. Additionally, models trained with Dynamic Replica are more consistent than models trained on SceneFlow alone. + +With the above experiments, we have shown that Dynamic Replica is a useful dataset for training temporally consistent disparity estimators as well as standard stereoframe models, and that our proposed model improves over the state of the art in both tasks when trained on our dataset. + +In Tab. 4, we show a qualitative comparison of the temporal consistency between our model and RAFT-Stereo on a real-world sequence. We show the mean reconstruction over time of the sequence and color each pixel more red, the higher its variance across time. Our model significantly reduces the flickering that single-timestep models such as RAFT-Stereo produce. For more qualitative results and videos, please see the supplementary material. + +# 5.3. Ablation Studies + +In this section, we validate our method by ablating the design choices of our model. We train the model on Scene-Flow [27] for 50k iterations with the hyper-parameters described in Implementation Details (see Sec. 5). We evaluate these models on the clean pass of Sintel [5] and on the test split of Dynamic Replica. We measure both accuracy and + +
Training dataMethodSintel StereoDynamic Replica
CleanFinalFirst 150 frames
@δ3pxTEPE±δ1pxδt3px@δ3pxTEPE±δ1pxδt3px@δ1px
SFCODD [20]8.681.4410.785.6517.462.3218.569.796.59
RAFT-Stereo [23]6.120.929.334.5110.402.1013.697.085.51
Ours6.100.778.413.938.971.4511.955.983.44
DR+SFRAFT-Stereo [23]5.710.849.154.409.162.2713.457.171.89
Ours5.770.768.463.938.681.4211.935.923.32
SF+M+KCODD [20]9.111.3312.166.2311.902.0116.168.6410.03
SF+MRAFT-Stereo [23]5.860.858.794.138.471.6312.406.233.46
7 datasets (incl. Sintel)CRE-Stereo [18]4.580.676.363.268.171.9012.296.871.75
DR+SFOurs5.770.768.463.938.681.4211.935.923.32
+ +Table 5. Accuracy $⑥$ and Temporal consistency $①$ . SF - SceneFlow [27], K - KITTI [28], M - Middlebury [37], DR - Dynamic Replica (ours). Temporal end-point error (TEPE) measures the consistency of the disparity estimation over time. We also compute $\delta_{1px}^{t}$ and $\delta_{3px}^{t}$ that show the proportion of pixels with TEPE higher than the threshold. Our model is more consistent than prior work and models. Additionally, other methods trained on our dataset also improve in temporal consistency. As CRE Stereo trains on Sintel and disparity estimation is evaluated on the training set of Sintel, CRE Stereo results are training set results and cannot be directly compared. + +
MethodSintel CleanDynamic Replica
δ3pxTEPEδ1pxTEPE
shared weights6.600.9086.480.101
sep. weights6.240.8234.760.126
+ +Table 6. Update Block Weight sharing. Learning separate update blocks—one per resolution—consistently improves the results compared to weight sharing across all update blocks. + +
MethodSintel CleanDynamic Replica
δ3pxTEPEδ1pxTEPE
Conv2D6.461.057.310.140
Conv3D6.240.8234.760.126
+ +Table 7. Update Block Convolution. A GRU with a 3D convolution across space and time improves the performance over the 2D variant, especially in terms of the temporal metric TEPE. + +temporal consistency. For accuracy, we use an end-point-error threshold of 3px for Sintel and 1px for DR. This shows the proportion of pixels with an end-point-error higher than 3px. For consistency, we use TEPE (see Sec. 5.2). + +Update Block. In Tab. 6 we compare sharing weights of the three blocks across the three resolutions of the decoder to learning separate update blocks. As different scales exploit features of different resolutions, learning separate update blocks improves the results over weight-sharing. + +Update Block Convolution. While prior works such as CRE Stereo use 2D convolutions in the iterative update block as they operate on single time steps, we find it beneficial to extend the processing of the update block across time (Tab. 7). This results in a general improvement but shows especially large improvements in temporal consistency. + +Please see the supplement for additional analysis. + +# 6. Conclusion + +In this paper, we make two main contributions. We introduce a new stereo video dataset—Dynamic Replica—that allows training temporally consistent disparity estimators. Additionally, we introduce a new method that is able to improve over the state of the art in temporally consistent stereo estimation using the new dataset. + +We show that other methods benefit from training on this new dataset as it contains realistic scenes and can thus reduce the domain gap between the real world and typical synthetic, abstract training datasets such as SceneFlow. Our combines spatial, temporal, and stereo information, enabling precise and consistent predictions across time. In extensive ablation studies, we show that each component of the model contributes to the final performance. + +# Acknowledgements + +C. 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Most existing methods for depth from stereo treat different stereo frames independently, leading to temporally inconsistent depth predictions. Temporal consistency is especially important for immersive AR or VR scenarios, where flickering greatly diminishes the user experience. We propose DynamicStereo, a novel transformer-based architecture to estimate disparity for stereo videos. The network learns to pool information from neighboring frames to improve the temporal consistency of its predictions. Our architecture is designed to process stereo videos efficiently through divided attention layers. We also introduce Dynamic Replica, a new benchmark dataset containing synthetic videos of people and animals in scanned environments, which provides complementary training and evaluation data for dynamic stereo closer to real applications than existing datasets. Training with this dataset further improves the quality of predictions of our proposed DynamicStereo as well as prior methods. Finally, it acts as a benchmark for consistent stereo methods. Project page: https://dynamic-stereo.github.io/" + } + ] + } + ], + "index": 31 + }, + { + "bbox": [ + 307, + 437, + 386, + 450 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 307, + 437, + 386, + 450 + ], + "spans": [ + { + "bbox": [ + 307, + 437, + 386, + 450 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 32 + }, + { + "bbox": [ + 304, + 460, + 545, + 555 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 460, + 545, + 555 + ], + "spans": [ + { + "bbox": [ + 304, + 460, + 545, + 555 + ], + "type": "text", + "content": "Estimating depth from stereo is a fundamental computer vision problem, with applications in 3D reconstruction, robot navigation, and human motion capture, among others. With the advent of consumer devices featuring multiple cameras, such as AR glasses and smartphones, stereo can simplify the 3D reconstruction of everyday scenes, extracting them as content to be experienced in virtual or mixed reality, or for mixed reality pass-through." + } + ] + } + ], + "index": 33 + }, + { + "bbox": [ + 304, + 557, + 546, + 700 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 557, + 546, + 700 + ], + "spans": [ + { + "bbox": [ + 304, + 557, + 546, + 700 + ], + "type": "text", + "content": "Depth from stereo takes as input two images capturing the same scene from different viewpoints. It then finds pairs of matching points, a problem known as disparity estimation. Since the two cameras are calibrated, the matched points can be projected into 3D using triangulation. While this process is robust, it is suboptimal when applied to video data, as it can only reconstruct stereo frames individually, ignoring the fact that the observations infer properties of the same underlying objects over time. Even if the camera moves or the scene deforms non-rigidly, the instantaneous 3D reconstructions are highly correlated and disregarding this fact can result in inconsistencies." + } + ] + } + ], + "index": 34 + }, + { + "bbox": [ + 317, + 703, + 545, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 703, + 545, + 715 + ], + "spans": [ + { + "bbox": [ + 317, + 703, + 545, + 715 + ], + "type": "text", + "content": "In this paper, we thus consider the problem of dynamic" + } + ] + } + ], + "index": 35 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "13229" + } + ] + } + ], + "index": 36 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 287, + 95 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 287, + 95 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 287, + 95 + ], + "type": "text", + "content": "depth from stereo to improve the temporal consistency of stereo reconstruction from video data." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 97, + 286, + 252 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 97, + 286, + 252 + ], + "spans": [ + { + "bbox": [ + 46, + 97, + 286, + 252 + ], + "type": "text", + "content": "Traditional approaches to stereo compute the matching costs between local image patches, aggregating those in an objective function, and optimizing the latter together with a regularization term to infer disparities. Examples of such approaches include max-flow [35] and graph-cut [15]. More recently, stereo methods have used deep networks learned from a large number of image pairs annotated with ground-truth disparities [12, 14, 18, 23]. They usually follow an approach similar to the traditional methods, but using deep CNN features for computing the matching costs, and replacing the per-image optimization by a pre-trained regression deep network, which processes the cost volume and outputs the estimated disparities." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 255, + 286, + 302 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 255, + 286, + 302 + ], + "spans": [ + { + "bbox": [ + 47, + 255, + 286, + 302 + ], + "type": "text", + "content": "In the video setting, matching quality can potentially be improved by looking for matches across space and time. For instance, points occluded in one camera at a given point in time may be visible from both cameras at other times." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 304, + 286, + 387 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 304, + 286, + 387 + ], + "spans": [ + { + "bbox": [ + 46, + 304, + 286, + 387 + ], + "type": "text", + "content": "Transformer architectures have shown that attention can be a powerful and flexible method for pooling information over a range of contexts [6, 8, 9, 42]. Our DynamicStereo model incorporates self- and cross-attention to extract relevant information across space, time and stereo pairs. Our architecture relies on divided attention [3] to allow efficient processing of this high-dimensional space." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 389, + 286, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 389, + 286, + 628 + ], + "spans": [ + { + "bbox": [ + 46, + 389, + 286, + 628 + ], + "type": "text", + "content": "As a learning-based approach, we wish to learn priors from data representative of real-life 3D dynamic reconstruction applications, where videos depict people or animals moving and interacting with objects. There are several synthetic video datasets [10,27,41] commonly used for training stereo and optical flow methods, but they contain abstract scenes with several layers of moving objects that share little resemblance to real-life. More realistic stereo datasets also exist [45, 49], but they either do not contain video sequences or are focused on static scenes. Given these limitations, as an additional contribution we propose a new synthetic stereo dataset showing moving human and animal characters inside realistic physical spaces from the Replica dataset [40]. We call this new dataset Dynamic Replica (DR), and we use it for learning dynamic stereo matches. DR contains 524 videos of virtual humans and animals embedded in realistic digital scans of physical environments (see Tab. 1 and Fig. 2). We show that DR can significantly boost the quality of dynamic stereo methods compared to training them only on existing depth-from-stereo datasets." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 630, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 630, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 630, + 286, + 713 + ], + "type": "text", + "content": "To summarise, we make three contributions. (1) We introduce DynamicStereo, a transformer-based architecture that improves dynamic depth from stereo by jointly processing stereo videos. (2) We release Dynamic Replica, a new benchmark dataset for learning and evaluating models for dynamic depth from stereo. (3) We demonstrate state-of-the-art dynamic stereo results in a variety of benchmarks." + } + ] + } + ], + "index": 5 + }, + { + "type": "image", + "bbox": [ + 309, + 70, + 383, + 112 + ], + "blocks": [ + { + "bbox": [ + 309, + 70, + 383, + 112 + ], + "lines": [ + { + "bbox": [ + 309, + 70, + 383, + 112 + ], + "spans": [ + { + "bbox": [ + 309, + 70, + 383, + 112 + ], + "type": "image", + "image_path": "0bce1e19626a427b8fddff3e1d2ed6a0b2984dbd47dd0d52fe47cde59802cdeb.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 329, + 113, + 361, + 119 + ], + "lines": [ + { + "bbox": [ + 329, + 113, + 361, + 119 + ], + "spans": [ + { + "bbox": [ + 329, + 113, + 361, + 119 + ], + "type": "text", + "content": "SceneFlow" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_caption" + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 383, + 70, + 481, + 112 + ], + "blocks": [ + { + "bbox": [ + 383, + 70, + 481, + 112 + ], + "lines": [ + { + "bbox": [ + 383, + 70, + 481, + 112 + ], + "spans": [ + { + "bbox": [ + 383, + 70, + 481, + 112 + ], + "type": "image", + "image_path": "58f21ce3775f4c1e67fd9df57369ec75d8922791a0777c3a09a8ac7998f18791.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 423, + 113, + 443, + 119 + ], + "lines": [ + { + "bbox": [ + 423, + 113, + 443, + 119 + ], + "spans": [ + { + "bbox": [ + 423, + 113, + 443, + 119 + ], + "type": "text", + "content": "KITTI" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 482, + 70, + 544, + 112 + ], + "blocks": [ + { + "bbox": [ + 482, + 70, + 544, + 112 + ], + "lines": [ + { + "bbox": [ + 482, + 70, + 544, + 112 + ], + "spans": [ + { + "bbox": [ + 482, + 70, + 544, + 112 + ], + "type": "image", + "image_path": "9871f2242953995286c3c3b0387205b2501533f64b5d82beb40b32cb805011b2.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 495, + 113, + 530, + 120 + ], + "lines": [ + { + "bbox": [ + 495, + 113, + 530, + 120 + ], + "spans": [ + { + "bbox": [ + 495, + 113, + 530, + 120 + ], + "type": "text", + "content": "Middlebury" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 309, + 121, + 385, + 164 + ], + "blocks": [ + { + "bbox": [ + 309, + 121, + 385, + 164 + ], + "lines": [ + { + "bbox": [ + 309, + 121, + 385, + 164 + ], + "spans": [ + { + "bbox": [ + 309, + 121, + 385, + 164 + ], + "type": "image", + "image_path": "4ee63bb9be0b8eccf1d4ac21292dfa288f05b3cad4beff8433e41c798dea9a9f.jpg" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 337, + 167, + 356, + 173 + ], + "lines": [ + { + "bbox": [ + 337, + 167, + 356, + 173 + ], + "spans": [ + { + "bbox": [ + 337, + 167, + 356, + 173 + ], + "type": "text", + "content": "Sintel" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_caption" + } + ], + "index": 12 + }, + { + "type": "image", + "bbox": [ + 386, + 121, + 467, + 164 + ], + "blocks": [ + { + "bbox": [ + 386, + 121, + 467, + 164 + ], + "lines": [ + { + "bbox": [ + 386, + 121, + 467, + 164 + ], + "spans": [ + { + "bbox": [ + 386, + 121, + 467, + 164 + ], + "type": "image", + "image_path": "c6ed9a43e5fd011fa59876676ca001e33a035a70887bc0d7408f9488259cd577.jpg" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 416, + 166, + 440, + 173 + ], + "lines": [ + { + "bbox": [ + 416, + 166, + 440, + 173 + ], + "spans": [ + { + "bbox": [ + 416, + 166, + 440, + 173 + ], + "type": "text", + "content": "ETH3D" + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 468, + 165, + 544, + 173 + ], + "lines": [ + { + "bbox": [ + 468, + 165, + 544, + 173 + ], + "spans": [ + { + "bbox": [ + 468, + 165, + 544, + 173 + ], + "type": "text", + "content": "Dynamic Replica (ours)" + } + ] + } + ], + "index": 17, + "angle": 0, + "type": "image_caption" + } + ], + "index": 14 + }, + { + "type": "image", + "bbox": [ + 468, + 121, + 543, + 164 + ], + "blocks": [ + { + "bbox": [ + 468, + 121, + 543, + 164 + ], + "lines": [ + { + "bbox": [ + 468, + 121, + 543, + 164 + ], + "spans": [ + { + "bbox": [ + 468, + 121, + 543, + 164 + ], + "type": "image", + "image_path": "a7607f9f919f409917f6e609763a807be45fd4aebe3182403c5f672b57e0125b.jpg" + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 184, + 545, + 228 + ], + "lines": [ + { + "bbox": [ + 305, + 184, + 545, + 228 + ], + "spans": [ + { + "bbox": [ + 305, + 184, + 545, + 228 + ], + "type": "text", + "content": "Figure 2. Example frames from depth-from-stereo datasets. We visually compare current datasets to Dynamic Replica, which contains renderings of every-day scenes with people and animals and differs from existing datasets in size, realism, and content." + } + ] + } + ], + "index": 18, + "angle": 0, + "type": "image_caption" + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 249, + 389, + 262 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 249, + 389, + 262 + ], + "spans": [ + { + "bbox": [ + 306, + 249, + 389, + 262 + ], + "type": "text", + "content": "2. Related work" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 270, + 545, + 341 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 270, + 545, + 341 + ], + "spans": [ + { + "bbox": [ + 304, + 270, + 545, + 341 + ], + "type": "text", + "content": "Depth from stereo. Stereo matching is a classic problem in computer vision. The traditional way of solving it is to compute local matching costs between image patches and then either perform local aggregation [4, 13, 46, 56], or a global optimization based on an energy function featuring data and regularization terms [15, 35]." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 304, + 342, + 545, + 472 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 342, + 545, + 472 + ], + "spans": [ + { + "bbox": [ + 304, + 342, + 545, + 472 + ], + "type": "text", + "content": "More recently, deep learning has become the dominant approach to stereo matching. Zbontar and LeCun [52] proposed to use a CNN to compute the matching cost between image patches. Then Mayer et al. [27] introduced the first fully learning-based approach to stereo estimation. Inspired by traditional stereo algorithms, the next line of work [7, 12, 14, 51, 53, 54] applied 3D convolutions in their fully learning-based approaches. They construct a dense 3D cost volume between the left and the right 2D feature-maps before filtering it with a 3D-CNN. These approaches often fail to generalize to data that they were not trained on." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 304, + 474, + 545, + 581 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 474, + 545, + 581 + ], + "spans": [ + { + "bbox": [ + 304, + 474, + 545, + 581 + ], + "type": "text", + "content": "More recent works focused on improving the computational efficiency of stereo estimation [1,22,23,43]. Inspired by RAFT [44] which constructs a 4D cost volume between all pairs of pixels for optical flow, RAFT-Stereo [23] restricts this volume to 3D by collapsing it to the epipolar line. Similarly to RAFT, it iteratively updates the prediction at high resolution allowing to maintain global context and recover details. These updates are performed by a GRU [2] that operates at multiple resolutions." + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 304, + 582, + 545, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 545, + 689 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 545, + 689 + ], + "type": "text", + "content": "CRE-Stereo [18] proposes to gradually increase resolution during iterative updates which simplifies the architecture. However, the lack of information propagation from lower to higher resolution may result in a loss of context. Our architecture also refines disparity in a coarse-to-fine manner, but unlike CRE-Stereo, we fuse low-resolution and high-resolution features together and propagate them to the final prediction. This allows high-resolution layers to use these features and keep track of previous states." + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "text", + "content": "Some recent works incorporate attention [47]. Stereo Transformer [19] replaces cost volume with dense pixel" + } + ] + } + ], + "index": 24 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "13230" + } + ] + } + ], + "index": 25 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 62, + 70, + 533, + 189 + ], + "blocks": [ + { + "bbox": [ + 62, + 70, + 533, + 189 + ], + "lines": [ + { + "bbox": [ + 62, + 70, + 533, + 189 + ], + "spans": [ + { + "bbox": [ + 62, + 70, + 533, + 189 + ], + "type": "table", + "html": "
Dataset propertyMPI Sintel [5]KITTI [28]SceneFlow [27]Falling Things [45]TartanAir [50]Dynamic Replica (ours)
#Training frames1064194+2003480160200296000145200
#Test frames564195+2004248006000+18000
#Training sequences25194+2002256(330)1037484
Resolution1024×4361242×375960×540960×540640×4801280×720
Disparity/Depth✓sparse✓✓✓✓
Optical flow✓(sparse)✓X✓✓
Segmentation✓X✓✓✓✓
Non-rigid objects✓X(✓)X(X)✓
Realism(✓)✓X(✓)(✓)(✓)
", + "image_path": "354fa4011d1cdb4a421778f13554a4ee39e9ca421e5cd5650bcd2b9f750724e1.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 197, + 547, + 219 + ], + "lines": [ + { + "bbox": [ + 46, + 197, + 547, + 219 + ], + "spans": [ + { + "bbox": [ + 46, + 197, + 547, + 219 + ], + "type": "text", + "content": "Table 1. Comparison of depth-from-stereo datasets. Dynamic Replica is larger than previous datasets in both resolution and number of frames. A main aspect is that it contains non-rigid objects such as animals and people, which is not available at scale in prior datasets." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 239, + 288, + 324 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 239, + 288, + 324 + ], + "spans": [ + { + "bbox": [ + 46, + 239, + 288, + 324 + ], + "type": "text", + "content": "matching using attention. LoFTR [42] and SuperGlue [36] use combinations of self and cross-attention layers for sparse feature matching. Inspired by these methods, CRE-Stereo [18] uses self and cross-attention to improve convolutional features. These works focus on disparity estimation for individual frames. As we predict disparity for videos, we apply attention across time, space, and stereo frames." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 329, + 287, + 425 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 329, + 287, + 425 + ], + "spans": [ + { + "bbox": [ + 46, + 329, + 287, + 425 + ], + "type": "text", + "content": "Dynamic video depth. Monocular depth estimators like MiDaS [30, 31] attempt to estimate depth from a single image. Due to the ambiguity of this task, they tend to be far less accurate than methods that use stereo. Recent works have proposed to extend these methods to use monocular videos instead, relying on motion parallax in static areas [21] or fusing information extracted from all the frames of a video, in an off-line fashion." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 427, + 287, + 523 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 427, + 287, + 523 + ], + "spans": [ + { + "bbox": [ + 46, + 427, + 287, + 523 + ], + "type": "text", + "content": "Consistent Video Depth (CVD) [25] assumes that objects move almost rigidly across neighboring frames. Robust CVD (RCVD) [16] excludes dynamic objects from the optimization objective. Dynamic VD (DVD) [55] explicitly models motion of non-rigid objects with a scene-flow network. All these methods require fine-tuning a monocular depth predictor like MiDAS on a specific video, a process that must be carried out from scratch for each new video." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 529, + 287, + 649 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 529, + 287, + 649 + ], + "spans": [ + { + "bbox": [ + 46, + 529, + 287, + 649 + ], + "type": "text", + "content": "Dynamic depth from stereo. The work of Li et al. (CODD) [20] is the closest to ours. It is based on three different networks: stereo, motion, and fusion, that are trained separately. During inference, consistency is achieved by extracting information from the memory state that is updated after each iteration. It is an online approach that assumes no access to future frames and thus does not allow global optimization over the whole sequence. Our network does not need a memory state and learns consistency from data. It can be applied in both online and offline settings." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "type": "text", + "content": "Datasets for learning depth from stereo. Training data is an important factor for learning-based stereo algorithms. It is challenging to collect real data for this task because disparity is extremely difficult to annotate. [28, 48] Active sensors such as time-of-flight cameras can provide ground" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 239, + 545, + 395 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 239, + 545, + 395 + ], + "spans": [ + { + "bbox": [ + 304, + 239, + 545, + 395 + ], + "type": "text", + "content": "truth depth. KITTI [28] shows that converting such ground truth depth to pixel-accurate annotations is still challenging for dynamic objects due to the low frame rate and imprecise estimations. Synthetic datasets [17, 32, 33] can simplify the data collection process. SceneFlow [27] is the first large-scale synthetic dataset for disparity and optical flow estimation. It allowed training fully learning-based methods for these tasks. SceneFlow is less realistic compared to MPI Sintel [5], a much smaller dataset with optical flow and disparity annotations. Falling Things [45] is realistic and relatively large but does not contain non-rigid objects. TartanAir [49] is a realistic SLAM dataset with ground-truth stereo information but only few non-rigid objects." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 396, + 545, + 431 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 396, + 545, + 431 + ], + "spans": [ + { + "bbox": [ + 304, + 396, + 545, + 431 + ], + "type": "text", + "content": "To the best of our knowledge, we are the first to introduce a large-scale semi-realistic synthetic dataset with a focus on non-rigid objects for disparity estimation." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 442, + 361, + 454 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 442, + 361, + 454 + ], + "spans": [ + { + "bbox": [ + 306, + 442, + 361, + 454 + ], + "type": "text", + "content": "3. Method" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 462, + 545, + 581 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 462, + 545, + 581 + ], + "spans": [ + { + "bbox": [ + 304, + 462, + 545, + 581 + ], + "type": "text", + "content": "We first formalize the dynamic depth from stereo problem. Given a sequence " + }, + { + "bbox": [ + 304, + 462, + 545, + 581 + ], + "type": "inline_equation", + "content": "S = [(I_t^L, I_t^R)]_{1 \\leq t \\leq T} \\in \\mathbb{R}^{2 \\times 3 \\times H \\times W}" + }, + { + "bbox": [ + 304, + 462, + 545, + 581 + ], + "type": "text", + "content": " of " + }, + { + "bbox": [ + 304, + 462, + 545, + 581 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 304, + 462, + 545, + 581 + ], + "type": "text", + "content": " rectified stereo frames, the task is to predict a sequence of disparity maps " + }, + { + "bbox": [ + 304, + 462, + 545, + 581 + ], + "type": "inline_equation", + "content": "\\hat{D} = [D_t]_{1 \\leq t \\leq T} \\in \\mathbb{R}^{H \\times W}" + }, + { + "bbox": [ + 304, + 462, + 545, + 581 + ], + "type": "text", + "content": " aligned with the left frames " + }, + { + "bbox": [ + 304, + 462, + 545, + 581 + ], + "type": "inline_equation", + "content": "I_t^L" + }, + { + "bbox": [ + 304, + 462, + 545, + 581 + ], + "type": "text", + "content": ". While most disparity estimation methods operate on single frames " + }, + { + "bbox": [ + 304, + 462, + 545, + 581 + ], + "type": "inline_equation", + "content": "\\hat{D}_t = \\Phi(S_t)" + }, + { + "bbox": [ + 304, + 462, + 545, + 581 + ], + "type": "text", + "content": ", here we learn a model that operates on sequences of length " + }, + { + "bbox": [ + 304, + 462, + 545, + 581 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 304, + 462, + 545, + 581 + ], + "type": "text", + "content": ", constructing a function " + }, + { + "bbox": [ + 304, + 462, + 545, + 581 + ], + "type": "inline_equation", + "content": "\\hat{D} = \\Phi(S)" + }, + { + "bbox": [ + 304, + 462, + 545, + 581 + ], + "type": "text", + "content": ". This has the advantage that the model can fuse information along time and thus improve its temporal consistency." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "content": "The challenge is to design an architecture that can pass information across such a large volume of data efficiently. We achieve this via an encoder-decoder design (Fig. 3), building on prior work [11, 18, 34]. The encoder extracts features independently from all the frames and obtains a multi-scale representation of their content. The decoder then matches progressively more detailed features to recover the disparities from coarse to fine. Low-resolution matches easily spot large displacements of large image regions, capturing the rough structure of the disparity map, whereas high-resolution matches recover the details." + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "13231" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 47, + 71, + 547, + 207 + ], + "blocks": [ + { + "bbox": [ + 47, + 71, + 547, + 207 + ], + "lines": [ + { + "bbox": [ + 47, + 71, + 547, + 207 + ], + "spans": [ + { + "bbox": [ + 47, + 71, + 547, + 207 + ], + "type": "image", + "image_path": "8e462895edc154bdce3928ea071b06725fc4bbdb9f9e3feb28573296d9a6cd4a.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 216, + 547, + 251 + ], + "lines": [ + { + "bbox": [ + 46, + 216, + 547, + 251 + ], + "spans": [ + { + "bbox": [ + 46, + 216, + 547, + 251 + ], + "type": "text", + "content": "Figure 3. Proposed architecture of DynamicStereo. Our method consists of three main components. A convolutional encoder produces feature maps at three scales. As data spans time, space and stereo views, the SST-Block operating at the smallest resolution, ensures information exchange across all dimensions. Finally, the prediction is generated by a decoder composed of an iterative update function " + }, + { + "bbox": [ + 46, + 216, + 547, + 251 + ], + "type": "inline_equation", + "content": "g" + }, + { + "bbox": [ + 46, + 216, + 547, + 251 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 270, + 289, + 403 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 270, + 289, + 403 + ], + "spans": [ + { + "bbox": [ + 46, + 270, + 289, + 403 + ], + "type": "text", + "content": "For efficiency, matches are always carried out along epipolar lines. The task of exchanging information across space, view and time is delegated to two mechanisms. First, the encoder terminates in a transformer network that updates the lowest-resolution feature by running attention across these three dimensions in turn. This is efficient because it is done only for the lowest-resolution features. Second, the decoder further propagates information as it matches features to recover the disparities. The decoder itself consists of update blocks (Fig. 4a) that use both space and time information to gradually refine the disparity." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 413, + 111, + 424 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 413, + 111, + 424 + ], + "spans": [ + { + "bbox": [ + 47, + 413, + 111, + 424 + ], + "type": "text", + "content": "3.1. Encoder" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 433, + 287, + 579 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 433, + 287, + 579 + ], + "spans": [ + { + "bbox": [ + 46, + 433, + 287, + 579 + ], + "type": "text", + "content": "The encoder starts by extracting features from every frame " + }, + { + "bbox": [ + 46, + 433, + 287, + 579 + ], + "type": "inline_equation", + "content": "I_{t}^{v}, v \\in \\{L, R\\}" + }, + { + "bbox": [ + 46, + 433, + 287, + 579 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 433, + 287, + 579 + ], + "type": "inline_equation", + "content": "t \\in \\{1, \\dots, T\\}" + }, + { + "bbox": [ + 46, + 433, + 287, + 579 + ], + "type": "text", + "content": " of the stereo video independently by applying the same CNN " + }, + { + "bbox": [ + 46, + 433, + 287, + 579 + ], + "type": "inline_equation", + "content": "F" + }, + { + "bbox": [ + 46, + 433, + 287, + 579 + ], + "type": "text", + "content": " to them. As it is typical for CNN backbones, the resolution of the output feature map is lower than the resolution of the input image. Features are extracted with minimum stride " + }, + { + "bbox": [ + 46, + 433, + 287, + 579 + ], + "type": "inline_equation", + "content": "k = 4" + }, + { + "bbox": [ + 46, + 433, + 287, + 579 + ], + "type": "text", + "content": " and are further down-sampled with average pooling to obtain features at 1/8 and 1/16 of the original resolution. Overall, this results in the feature maps " + }, + { + "bbox": [ + 46, + 433, + 287, + 579 + ], + "type": "inline_equation", + "content": "\\phi(I_{t}^{v})_{k} \\in \\mathbb{R}^{d \\times \\frac{H}{k} \\times \\frac{W}{k}}" + }, + { + "bbox": [ + 46, + 433, + 287, + 579 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 433, + 287, + 579 + ], + "type": "inline_equation", + "content": "k \\in \\{4, 8, 16\\}" + }, + { + "bbox": [ + 46, + 433, + 287, + 579 + ], + "type": "text", + "content": ". We will use the symbol " + }, + { + "bbox": [ + 46, + 433, + 287, + 579 + ], + "type": "inline_equation", + "content": "\\phi_{k} \\in \\mathbb{R}^{T \\times 2 \\times d \\times \\frac{H}{k} \\times \\frac{W}{k}}" + }, + { + "bbox": [ + 46, + 433, + 287, + 579 + ], + "type": "text", + "content": " to refer to the combined five-dimensional (temporal, stereo and spatial) feature volume at resolution " + }, + { + "bbox": [ + 46, + 433, + 287, + 579 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 433, + 287, + 579 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "content": "Information Propagation. The backbone " + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "inline_equation", + "content": "F" + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "content": " processes frames independently, so we require a different mechanism to exchange of information between left and right views " + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "inline_equation", + "content": "v" + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "content": " and different timestamps " + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "content": ". We do so by passing the features to a transformer network that uses self and cross-attention. Ideally, attention should compare feature maps across views, time, and space. However, it is computationally demanding to apply attention jointly even with linear [42] space and stereo attention. We thus rely on divided attention [3] to attend these three dimensions individually. We call this a Space-Stereo-Time attention block" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 270, + 547, + 308 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 270, + 547, + 308 + ], + "spans": [ + { + "bbox": [ + 304, + 270, + 547, + 308 + ], + "type": "text", + "content": "(SST, Fig. 4b) and we repeat it four times. Since attention remains computationally expensive, we only apply SST to the lowest-resolution feature map " + }, + { + "bbox": [ + 304, + 270, + 547, + 308 + ], + "type": "inline_equation", + "content": "\\phi_{16}" + }, + { + "bbox": [ + 304, + 270, + 547, + 308 + ], + "type": "text", + "content": " only." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 312, + 368, + 324 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 312, + 368, + 324 + ], + "spans": [ + { + "bbox": [ + 306, + 312, + 368, + 324 + ], + "type": "text", + "content": "3.2. Decoder" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 331, + 545, + 390 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 331, + 545, + 390 + ], + "spans": [ + { + "bbox": [ + 304, + 331, + 545, + 390 + ], + "type": "text", + "content": "The output of the encoder is a multi-resolution feature volume, where the lowest resolution features incorporate information across time, view and space dimensions due to the SST block described above. The task of the decoder is to convert this feature volume into the final disparity values." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 391, + 545, + 498 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 391, + 545, + 498 + ], + "spans": [ + { + "bbox": [ + 304, + 391, + 545, + 498 + ], + "type": "text", + "content": "The decoder is based on three ideas: (1) Disparities are updated from coarse to fine [18], using features of increasing resolution to update earlier estimates. (2) At each resolution, a feature correlation volume is computed and correspondences are refined iteratively [44] with reference to this volume. (3) Similar to the SST attention blocks in the encoder, information is exchanged between the three dimensions (space, view and time) throughout decoding. We describe next each component in detail." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 501, + 547, + 550 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 501, + 547, + 550 + ], + "spans": [ + { + "bbox": [ + 304, + 501, + 547, + 550 + ], + "type": "text", + "content": "Iterative correspondence updates. Our model produces a sequence of progressively more accurate disparity estimates " + }, + { + "bbox": [ + 304, + 501, + 547, + 550 + ], + "type": "inline_equation", + "content": "\\hat{D} = \\hat{D}^{(m)} \\in \\mathbb{R}^{\\frac{H}{k} \\times \\frac{W}{k}}" + }, + { + "bbox": [ + 304, + 501, + 547, + 550 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 501, + 547, + 550 + ], + "type": "inline_equation", + "content": "0 \\leq m \\leq M" + }, + { + "bbox": [ + 304, + 501, + 547, + 550 + ], + "type": "text", + "content": " starting from " + }, + { + "bbox": [ + 304, + 501, + 547, + 550 + ], + "type": "inline_equation", + "content": "\\hat{D}^{(0)} = 0" + }, + { + "bbox": [ + 304, + 501, + 547, + 550 + ], + "type": "text", + "content": " and then applying " + }, + { + "bbox": [ + 304, + 501, + 547, + 550 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 304, + 501, + 547, + 550 + ], + "type": "text", + "content": " times the update rule:" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 359, + 552, + 545, + 569 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 359, + 552, + 545, + 569 + ], + "spans": [ + { + "bbox": [ + 359, + 552, + 545, + 569 + ], + "type": "interline_equation", + "content": "\\hat {D} ^ {(m + 1)} = \\hat {D} ^ {(m)} + g (\\hat {D} ^ {(m)}, \\phi). \\tag {1}", + "image_path": "5a527a5e54c8161079f3ce9a3434b36c52e92e3c95973117fb05680edc772112.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 571, + 545, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 571, + 545, + 689 + ], + "spans": [ + { + "bbox": [ + 304, + 571, + 545, + 689 + ], + "type": "text", + "content": "We apply the rule " + }, + { + "bbox": [ + 304, + 571, + 545, + 689 + ], + "type": "inline_equation", + "content": "\\frac{M}{4}" + }, + { + "bbox": [ + 304, + 571, + 545, + 689 + ], + "type": "text", + "content": " times to obtain disparities " + }, + { + "bbox": [ + 304, + 571, + 545, + 689 + ], + "type": "inline_equation", + "content": "\\hat{D}^{(m)}" + }, + { + "bbox": [ + 304, + 571, + 545, + 689 + ], + "type": "text", + "content": " at the coarser resolution " + }, + { + "bbox": [ + 304, + 571, + 545, + 689 + ], + "type": "inline_equation", + "content": "(\\frac{H}{16},\\frac{W}{16})" + }, + { + "bbox": [ + 304, + 571, + 545, + 689 + ], + "type": "text", + "content": ". We then upsample " + }, + { + "bbox": [ + 304, + 571, + 545, + 689 + ], + "type": "inline_equation", + "content": "\\hat{D}^{(\\frac{M}{4})}" + }, + { + "bbox": [ + 304, + 571, + 545, + 689 + ], + "type": "text", + "content": " to resolution " + }, + { + "bbox": [ + 304, + 571, + 545, + 689 + ], + "type": "inline_equation", + "content": "(\\frac{H}{8},\\frac{W}{8})" + }, + { + "bbox": [ + 304, + 571, + 545, + 689 + ], + "type": "text", + "content": ", apply the update rule " + }, + { + "bbox": [ + 304, + 571, + 545, + 689 + ], + "type": "inline_equation", + "content": "\\frac{M}{4}" + }, + { + "bbox": [ + 304, + 571, + 545, + 689 + ], + "type": "text", + "content": " more times to obtain " + }, + { + "bbox": [ + 304, + 571, + 545, + 689 + ], + "type": "inline_equation", + "content": "\\hat{D}^{(\\frac{M}{2})}" + }, + { + "bbox": [ + 304, + 571, + 545, + 689 + ], + "type": "text", + "content": ", upsample the disparity again, and apply the update " + }, + { + "bbox": [ + 304, + 571, + 545, + 689 + ], + "type": "inline_equation", + "content": "\\frac{M}{2}" + }, + { + "bbox": [ + 304, + 571, + 545, + 689 + ], + "type": "text", + "content": " more times to obtain " + }, + { + "bbox": [ + 304, + 571, + 545, + 689 + ], + "type": "inline_equation", + "content": "\\hat{D}^{(M)}" + }, + { + "bbox": [ + 304, + 571, + 545, + 689 + ], + "type": "text", + "content": " at resolution " + }, + { + "bbox": [ + 304, + 571, + 545, + 689 + ], + "type": "inline_equation", + "content": "(\\frac{H}{4},\\frac{W}{4})" + }, + { + "bbox": [ + 304, + 571, + 545, + 689 + ], + "type": "text", + "content": ". Finally, we upsample the predicted disparity " + }, + { + "bbox": [ + 304, + 571, + 545, + 689 + ], + "type": "inline_equation", + "content": "\\hat{D}^{(M)}" + }, + { + "bbox": [ + 304, + 571, + 545, + 689 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 304, + 571, + 545, + 689 + ], + "type": "inline_equation", + "content": "(H,W)" + }, + { + "bbox": [ + 304, + 571, + 545, + 689 + ], + "type": "text", + "content": ". Different versions of the function " + }, + { + "bbox": [ + 304, + 571, + 545, + 689 + ], + "type": "inline_equation", + "content": "g" + }, + { + "bbox": [ + 304, + 571, + 545, + 689 + ], + "type": "text", + "content": " are trained for each of the three resolutions and upsampling uses the same mechanism as in RAFT." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 689, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 689, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 689, + 545, + 714 + ], + "type": "text", + "content": "The detailed structure of the update network " + }, + { + "bbox": [ + 304, + 689, + 545, + 714 + ], + "type": "inline_equation", + "content": "g" + }, + { + "bbox": [ + 304, + 689, + 545, + 714 + ], + "type": "text", + "content": " is illustrated in Fig. 4a and described below." + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "13232" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 50, + 70, + 299, + 245 + ], + "blocks": [ + { + "bbox": [ + 50, + 70, + 299, + 245 + ], + "lines": [ + { + "bbox": [ + 50, + 70, + 299, + 245 + ], + "spans": [ + { + "bbox": [ + 50, + 70, + 299, + 245 + ], + "type": "image", + "image_path": "01daee62dac09ac60d37fdb60d3eb6e85a2fd2f80e8583efcbd38ced04cdff2d.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 301, + 70, + 544, + 130 + ], + "lines": [ + { + "bbox": [ + 301, + 70, + 544, + 130 + ], + "spans": [ + { + "bbox": [ + 301, + 70, + 544, + 130 + ], + "type": "text", + "content": "(a) Update block " + }, + { + "bbox": [ + 301, + 70, + 544, + 130 + ], + "type": "inline_equation", + "content": "g" + }, + { + "bbox": [ + 301, + 70, + 544, + 130 + ], + "type": "text", + "content": ". We use the current disparity estimate " + }, + { + "bbox": [ + 301, + 70, + 544, + 130 + ], + "type": "inline_equation", + "content": "\\hat{D}^{(m)}" + }, + { + "bbox": [ + 301, + 70, + 544, + 130 + ], + "type": "text", + "content": " to sample the corresponding point and its epipolar neighbourhood from the correlation volume " + }, + { + "bbox": [ + 301, + 70, + 544, + 130 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 301, + 70, + 544, + 130 + ], + "type": "text", + "content": " at different resolutions. The resulting correlation estimate " + }, + { + "bbox": [ + 301, + 70, + 544, + 130 + ], + "type": "inline_equation", + "content": "\\hat{C}^{(m)}" + }, + { + "bbox": [ + 301, + 70, + 544, + 130 + ], + "type": "text", + "content": " is fused with the disparity " + }, + { + "bbox": [ + 301, + 70, + 544, + 130 + ], + "type": "inline_equation", + "content": "\\hat{D}^{(m)}" + }, + { + "bbox": [ + 301, + 70, + 544, + 130 + ], + "type": "text", + "content": " and with a part of feature map " + }, + { + "bbox": [ + 301, + 70, + 544, + 130 + ], + "type": "inline_equation", + "content": "\\phi^L" + }, + { + "bbox": [ + 301, + 70, + 544, + 130 + ], + "type": "text", + "content": ". We then apply space-time attention before passing the fused output to the 3D GRU that updates the disparity." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_footnote" + }, + { + "bbox": [ + 146, + 256, + 443, + 268 + ], + "lines": [ + { + "bbox": [ + 146, + 256, + 443, + 268 + ], + "spans": [ + { + "bbox": [ + 146, + 256, + 443, + 268 + ], + "type": "text", + "content": "Figure 4. The proposed architecture of (a) update block " + }, + { + "bbox": [ + 146, + 256, + 443, + 268 + ], + "type": "inline_equation", + "content": "g" + }, + { + "bbox": [ + 146, + 256, + 443, + 268 + ], + "type": "text", + "content": " and (b) SST-Block." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 312, + 137, + 531, + 215 + ], + "blocks": [ + { + "bbox": [ + 312, + 137, + 531, + 215 + ], + "lines": [ + { + "bbox": [ + 312, + 137, + 531, + 215 + ], + "spans": [ + { + "bbox": [ + 312, + 137, + 531, + 215 + ], + "type": "image", + "image_path": "fbde85f350c6c7a32e433847a66c9c61d420904b1f28a064a4b2ae45303ad616.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 301, + 218, + 544, + 248 + ], + "lines": [ + { + "bbox": [ + 301, + 218, + 544, + 248 + ], + "spans": [ + { + "bbox": [ + 301, + 218, + 544, + 248 + ], + "type": "text", + "content": "(b) SST-Block: combines all dimensions of the input spatial, stereo and temporal attention layers. Divided attention greatly reduces computational complexity of the network." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_footnote" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 289, + 287, + 400 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 289, + 287, + 400 + ], + "spans": [ + { + "bbox": [ + 46, + 289, + 287, + 400 + ], + "type": "text", + "content": "Correlation volume. Similar to classical disparity estimation methods, " + }, + { + "bbox": [ + 46, + 289, + 287, + 400 + ], + "type": "inline_equation", + "content": "g" + }, + { + "bbox": [ + 46, + 289, + 287, + 400 + ], + "type": "text", + "content": " starts by computing the correlation volumes between left and right features " + }, + { + "bbox": [ + 46, + 289, + 287, + 400 + ], + "type": "inline_equation", + "content": "C_{t,s,k} = \\mathrm{corr}(\\phi_{t,s,k}^{L},\\phi_{t,s,k}^{R})\\in \\mathbb{R}^{\\frac{H}{sk}\\times \\frac{W}{sk}\\times \\frac{W}{sk}}" + }, + { + "bbox": [ + 46, + 289, + 287, + 400 + ], + "type": "text", + "content": " for each feature resolution " + }, + { + "bbox": [ + 46, + 289, + 287, + 400 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 289, + 287, + 400 + ], + "type": "text", + "content": " and at different scales " + }, + { + "bbox": [ + 46, + 289, + 287, + 400 + ], + "type": "inline_equation", + "content": "s\\in \\{1,2,4,8\\}" + }, + { + "bbox": [ + 46, + 289, + 287, + 400 + ], + "type": "text", + "content": ". The correlation is computed along epipolar lines, which correspond to image rows as the input images are rectified. Each element " + }, + { + "bbox": [ + 46, + 289, + 287, + 400 + ], + "type": "inline_equation", + "content": "(h,w,w^{\\prime})" + }, + { + "bbox": [ + 46, + 289, + 287, + 400 + ], + "type": "text", + "content": " of " + }, + { + "bbox": [ + 46, + 289, + 287, + 400 + ], + "type": "inline_equation", + "content": "C_{t,s,k}" + }, + { + "bbox": [ + 46, + 289, + 287, + 400 + ], + "type": "text", + "content": " is the inner product between feature vectors of " + }, + { + "bbox": [ + 46, + 289, + 287, + 400 + ], + "type": "inline_equation", + "content": "\\phi_{t,s,k}^{L}" + }, + { + "bbox": [ + 46, + 289, + 287, + 400 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 289, + 287, + 400 + ], + "type": "inline_equation", + "content": "\\phi_{t,s,k}^{R}" + }, + { + "bbox": [ + 46, + 289, + 287, + 400 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 56, + 407, + 287, + 433 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 56, + 407, + 287, + 433 + ], + "spans": [ + { + "bbox": [ + 56, + 407, + 287, + 433 + ], + "type": "interline_equation", + "content": "C _ {t, s, k} (h, w, w ^ {\\prime}) = \\frac {1}{\\sqrt {d}} \\langle \\phi_ {t, s, k} ^ {L} (h, w), \\phi_ {t, s, k} ^ {R} (h, w ^ {\\prime}) \\rangle . (2)", + "image_path": "cc8ed68bcfe2ca498d61566341a817f2bc7372a5b33675ebd4cca12ca621726e.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 437, + 287, + 486 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 437, + 287, + 486 + ], + "spans": [ + { + "bbox": [ + 46, + 437, + 287, + 486 + ], + "type": "text", + "content": "Thus, " + }, + { + "bbox": [ + 46, + 437, + 287, + 486 + ], + "type": "inline_equation", + "content": "C_{t,s,k}(h,w,w')" + }, + { + "bbox": [ + 46, + 437, + 287, + 486 + ], + "type": "text", + "content": " is proportional to how well the left image point " + }, + { + "bbox": [ + 46, + 437, + 287, + 486 + ], + "type": "inline_equation", + "content": "(h,w)" + }, + { + "bbox": [ + 46, + 437, + 287, + 486 + ], + "type": "text", + "content": " matches the right image point " + }, + { + "bbox": [ + 46, + 437, + 287, + 486 + ], + "type": "inline_equation", + "content": "(h,w')" + }, + { + "bbox": [ + 46, + 437, + 287, + 486 + ], + "type": "text", + "content": ". As the correlation volume does not depend on the update iteration " + }, + { + "bbox": [ + 46, + 437, + 287, + 486 + ], + "type": "inline_equation", + "content": "m" + }, + { + "bbox": [ + 46, + 437, + 287, + 486 + ], + "type": "text", + "content": ", it is computed only once." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 488, + 287, + 550 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 488, + 287, + 550 + ], + "spans": [ + { + "bbox": [ + 46, + 488, + 287, + 550 + ], + "type": "text", + "content": "Correlation lookup. The function " + }, + { + "bbox": [ + 46, + 488, + 287, + 550 + ], + "type": "inline_equation", + "content": "g" + }, + { + "bbox": [ + 46, + 488, + 287, + 550 + ], + "type": "text", + "content": " updates the disparity at location " + }, + { + "bbox": [ + 46, + 488, + 287, + 550 + ], + "type": "inline_equation", + "content": "(h, w)" + }, + { + "bbox": [ + 46, + 488, + 287, + 550 + ], + "type": "text", + "content": " by observing the correlation volume in a local neighbourhood centered on the current disparity value " + }, + { + "bbox": [ + 46, + 488, + 287, + 550 + ], + "type": "inline_equation", + "content": "\\hat{D}_t^{(m)}(h, w)" + }, + { + "bbox": [ + 46, + 488, + 287, + 550 + ], + "type": "text", + "content": ". The necessary samples are collected and stacked as feature channels of the tensor" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 50, + 554, + 286, + 596 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 50, + 554, + 286, + 596 + ], + "spans": [ + { + "bbox": [ + 50, + 554, + 286, + 596 + ], + "type": "interline_equation", + "content": "\\hat {C} _ {t, k} ^ {(m)} (h, w) = \\underset {s, \\delta} {\\operatorname {c a t}} \\left[ C _ {t, s, k} \\left(\\frac {h}{s}, \\frac {w}{s}, \\frac {w + \\hat {D} _ {t} ^ {(m)} (h , w)}{s} + \\delta\\right) \\right]. \\tag {3}", + "image_path": "b9af405729a7cd5f327051e2862baaf0a0d0df9001ca144e8aa3580da80386ed.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 596, + 286, + 646 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 596, + 286, + 646 + ], + "spans": [ + { + "bbox": [ + 46, + 596, + 286, + 646 + ], + "type": "text", + "content": "The current correlation estimate " + }, + { + "bbox": [ + 46, + 596, + 286, + 646 + ], + "type": "inline_equation", + "content": "\\hat{C}_{t,k}^{(m)}\\in \\mathbb{R}^{\\frac{H}{k}\\times \\frac{W}{k}\\times 4(2\\Delta +1)}" + }, + { + "bbox": [ + 46, + 596, + 286, + 646 + ], + "type": "text", + "content": " captures the correlation volume across all four scales and in a neighborhood " + }, + { + "bbox": [ + 46, + 596, + 286, + 646 + ], + "type": "inline_equation", + "content": "\\delta \\in \\{-\\Delta ,\\dots ,\\Delta \\}" + }, + { + "bbox": [ + 46, + 596, + 286, + 646 + ], + "type": "text", + "content": " for additional context, with cat representing the concatenation operation." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 647, + 286, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 647, + 286, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 647, + 286, + 714 + ], + "type": "text", + "content": "Modality fusion. The estimated correlation, disparity, and feature maps need to be combined to provide the update block with enough information to update the disparity. Using a late fusion scheme, we encode correlation " + }, + { + "bbox": [ + 46, + 647, + 286, + 714 + ], + "type": "inline_equation", + "content": "\\hat{C}_{t,k}^{(m)}" + }, + { + "bbox": [ + 46, + 647, + 286, + 714 + ], + "type": "text", + "content": " and disparity " + }, + { + "bbox": [ + 46, + 647, + 286, + 714 + ], + "type": "inline_equation", + "content": "\\hat{D}_t^{(m)}" + }, + { + "bbox": [ + 46, + 647, + 286, + 714 + ], + "type": "text", + "content": " separately, before concatenating them with" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 289, + 545, + 361 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 289, + 545, + 361 + ], + "spans": [ + { + "bbox": [ + 304, + 289, + 545, + 361 + ], + "type": "text", + "content": "the feature map of the left frame " + }, + { + "bbox": [ + 304, + 289, + 545, + 361 + ], + "type": "inline_equation", + "content": "\\phi_{t,k}^{L}" + }, + { + "bbox": [ + 304, + 289, + 545, + 361 + ], + "type": "text", + "content": ", as it is the reference frame. To incorporate temporal and spatial information, we apply self-attention across time " + }, + { + "bbox": [ + 304, + 289, + 545, + 361 + ], + "type": "inline_equation", + "content": "(T)" + }, + { + "bbox": [ + 304, + 289, + 545, + 361 + ], + "type": "text", + "content": " and space " + }, + { + "bbox": [ + 304, + 289, + 545, + 361 + ], + "type": "inline_equation", + "content": "\\left(\\frac{H}{k},\\frac{W}{k}\\right)" + }, + { + "bbox": [ + 304, + 289, + 545, + 361 + ], + "type": "text", + "content": " to the output of the modality fusion step. For efficiency, we do it only for " + }, + { + "bbox": [ + 304, + 289, + 545, + 361 + ], + "type": "inline_equation", + "content": "k = 16" + }, + { + "bbox": [ + 304, + 289, + 545, + 361 + ], + "type": "text", + "content": ". Architecture details can be found in Fig. 4 and the supplementary material." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 363, + 545, + 387 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 363, + 545, + 387 + ], + "spans": [ + { + "bbox": [ + 305, + 363, + 545, + 387 + ], + "type": "text", + "content": "3D CNN-based GRU. The update function " + }, + { + "bbox": [ + 305, + 363, + 545, + 387 + ], + "type": "inline_equation", + "content": "g" + }, + { + "bbox": [ + 305, + 363, + 545, + 387 + ], + "type": "text", + "content": " is implemented using a 3D convolutional GRU." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 388, + 545, + 484 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 388, + 545, + 484 + ], + "spans": [ + { + "bbox": [ + 304, + 388, + 545, + 484 + ], + "type": "text", + "content": "At each step " + }, + { + "bbox": [ + 304, + 388, + 545, + 484 + ], + "type": "inline_equation", + "content": "m" + }, + { + "bbox": [ + 304, + 388, + 545, + 484 + ], + "type": "text", + "content": ", the GRU takes as input the fused features and a hidden state that is initialized with the reference feature map " + }, + { + "bbox": [ + 304, + 388, + 545, + 484 + ], + "type": "inline_equation", + "content": "\\phi^L" + }, + { + "bbox": [ + 304, + 388, + 545, + 484 + ], + "type": "text", + "content": ". All internal operations of the GRU are implemented as separable 3D convolutions across space and time to propagate temporal and spatial information. The output of each iteration is an update to the current disparity estimate as in eq. (1). Each subsequent iteration is preceded by correlation lookup and modality fusion." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 494, + 370, + 506 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 494, + 370, + 506 + ], + "spans": [ + { + "bbox": [ + 306, + 494, + 370, + 506 + ], + "type": "text", + "content": "3.3. Training" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 306, + 513, + 545, + 574 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 513, + 545, + 574 + ], + "spans": [ + { + "bbox": [ + 306, + 513, + 545, + 574 + ], + "type": "text", + "content": "Due to its iterative nature, the proposed model generates " + }, + { + "bbox": [ + 306, + 513, + 545, + 574 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 306, + 513, + 545, + 574 + ], + "type": "text", + "content": " predictions for every timestamp. 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Lower resolution disparity estimates are up-sampled to ground truth resolution." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 306, + 670, + 373, + 681 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 670, + 373, + 681 + ], + "spans": [ + { + "bbox": [ + 306, + 670, + 373, + 681 + ], + "type": "text", + "content": "3.4. Inference" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "text", + "content": "The model is trained on stereo sequences with a fixed length of " + }, + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "text", + "content": ". 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Dynamic Replica. Example video frames and disparity maps from our proposed dataset. The proposed dataset contains diverse indoor scenes filled with animated people and animals to provide a benchmark for disparity estimation in close-to-real environments." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 159, + 69, + 247, + 262 + ], + "blocks": [ + { + "bbox": [ + 159, + 69, + 247, + 262 + ], + "lines": [ + { + "bbox": [ + 159, + 69, + 247, + 262 + ], + "spans": [ + { + "bbox": [ + 159, + 69, + 247, + 262 + ], + "type": "image", + "image_path": "319a66435e6641088731d142233b8e0cf4ebc2f87559026e1f08192885709196.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 252, + 69, + 339, + 262 + ], + "blocks": [ + { + "bbox": [ + 252, + 69, + 339, + 262 + ], + "lines": [ + { + "bbox": [ + 252, + 69, + 339, + 262 + ], + "spans": [ + { + "bbox": [ + 252, + 69, + 339, + 262 + ], + "type": "image", + "image_path": "dd84241bdd771f7ad3e71b94868c2b791657be0e0e887add7308ebb6132b6ed4.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 344, + 70, + 432, + 262 + ], + "blocks": [ + { + "bbox": [ + 344, + 70, + 432, + 262 + ], + "lines": [ + { + "bbox": [ + 344, + 70, + 432, + 262 + ], + "spans": [ + { + "bbox": [ + 344, + 70, + 432, + 262 + ], + "type": "image", + "image_path": "8a337af419a1afb87a7615195f630b1cb26411f6e0e6c06a66918ea60e831d5c.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + } + ], + "index": 3 + }, + { + "type": "image", + "bbox": [ + 436, + 70, + 524, + 262 + ], + "blocks": [ + { + "bbox": [ + 436, + 70, + 524, + 262 + ], + "lines": [ + { + "bbox": [ + 436, + 70, + 524, + 262 + ], + "spans": [ + { + "bbox": [ + 436, + 70, + 524, + 262 + ], + "type": "image", + "image_path": "e424cbcfa48e594276f6dfb2cb3637084ede4b9c6b1d0403d6ae0ff14de1b5db.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 316, + 289, + 401 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 316, + 289, + 401 + ], + "spans": [ + { + "bbox": [ + 46, + 316, + 289, + 401 + ], + "type": "text", + "content": "we apply it to videos of arbitrary length using a sliding window approach with overlap, where we discard the predictions in overlapping time steps. For details see supp. mat. Videos shorter than " + }, + { + "bbox": [ + 46, + 316, + 289, + 401 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 46, + 316, + 289, + 401 + ], + "type": "text", + "content": " time steps can be used by repeating the first or the last frame up to the minimal length " + }, + { + "bbox": [ + 46, + 316, + 289, + 401 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 46, + 316, + 289, + 401 + ], + "type": "text", + "content": ". This corresponds to a static scene without moving camera and is well within the training distribution of the model." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 411, + 275, + 426 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 411, + 275, + 426 + ], + "spans": [ + { + "bbox": [ + 47, + 411, + 275, + 426 + ], + "type": "text", + "content": "4. Dynamic Replica: dynamic stereo dataset" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 432, + 287, + 516 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 432, + 287, + 516 + ], + "spans": [ + { + "bbox": [ + 46, + 432, + 287, + 516 + ], + "type": "text", + "content": "Training temporally consistent models requires a dataset with stereo videos and dense ground-truth annotations. While the SceneFlow dataset [26] fulfils both criteria, it is comprised of very short sequences of randomly textured objects moving. In this paper, we introduce a more realistic synthetic dataset and benchmark of animated humans and animals in every-day scenes: Dynamic Replica." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 516, + 287, + 588 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 516, + 287, + 588 + ], + "spans": [ + { + "bbox": [ + 46, + 516, + 287, + 588 + ], + "type": "text", + "content": "The dataset consists of 524 videos of synthetic humans and animals performing actions in virtual environments (see Tab. 2). Training and validation videos are 10 seconds long and each contain 300 frames. There are 484 training and 20 validation videos. Our test split consists of 20 videos of length 30 seconds to benchmark models on longer videos." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 588, + 287, + 635 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 588, + 287, + 635 + ], + "spans": [ + { + "bbox": [ + 46, + 588, + 287, + 635 + ], + "type": "text", + "content": "Videos are rendered at a resolution of " + }, + { + "bbox": [ + 46, + 588, + 287, + 635 + ], + "type": "inline_equation", + "content": "1280 \\times 720" + }, + { + "bbox": [ + 46, + 588, + 287, + 635 + ], + "type": "text", + "content": ". This is close to the resolution of modern screens and higher than the resolution of such popular stereo datasets as Intel " + }, + { + "bbox": [ + 46, + 588, + 287, + 635 + ], + "type": "inline_equation", + "content": "(1024 \\times 536)" + }, + { + "bbox": [ + 46, + 588, + 287, + 635 + ], + "type": "text", + "content": " and SceneFlow " + }, + { + "bbox": [ + 46, + 588, + 287, + 635 + ], + "type": "inline_equation", + "content": "(960 \\times 540)" + }, + { + "bbox": [ + 46, + 588, + 287, + 635 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 636, + 288, + 696 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 636, + 288, + 696 + ], + "spans": [ + { + "bbox": [ + 46, + 636, + 288, + 696 + ], + "type": "text", + "content": "The dataset is based on Facebook Replica [40] reconstructions of indoor spaces. We take 375 3D scans of humans from the RenderPeople1 dataset and animate them using motion capture sequences from real humans scans. We use artist-created animated 3D models of animals from 13" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 316, + 545, + 364 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 316, + 545, + 364 + ], + "spans": [ + { + "bbox": [ + 304, + 316, + 545, + 364 + ], + "type": "text", + "content": "categories (chimp, dog, horse, sheep, etc.). We use different environments, scans, textures and motions for training, validation and test splits to evaluate generalization to unseen environments and dynamic objects." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 365, + 545, + 400 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 365, + 545, + 400 + ], + "spans": [ + { + "bbox": [ + 304, + 365, + 545, + 400 + ], + "type": "text", + "content": "We randomize camera baselines in our training subset to ensure generalization across different stereo setups. Baselines are sampled uniformly between " + }, + { + "bbox": [ + 304, + 365, + 545, + 400 + ], + "type": "inline_equation", + "content": "4\\mathrm{cm}" + }, + { + "bbox": [ + 304, + 365, + 545, + 400 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 365, + 545, + 400 + ], + "type": "inline_equation", + "content": "30\\mathrm{cm}" + }, + { + "bbox": [ + 304, + 365, + 545, + 400 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 401, + 545, + 449 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 401, + 545, + 449 + ], + "spans": [ + { + "bbox": [ + 304, + 401, + 545, + 449 + ], + "type": "text", + "content": "For each scene we generate a camera trajectory imitating a person filming the scene with their mobile phone or AR glasses. These virtual cameras have smooth trajectories and are located approximately at " + }, + { + "bbox": [ + 304, + 401, + 545, + 449 + ], + "type": "inline_equation", + "content": "1.25\\mathrm{m}" + }, + { + "bbox": [ + 304, + 401, + 545, + 449 + ], + "type": "text", + "content": " above the ground." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 449, + 545, + 485 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 449, + 545, + 485 + ], + "spans": [ + { + "bbox": [ + 304, + 449, + 545, + 485 + ], + "type": "text", + "content": "All samples in the dataset contain ground-truth depth maps, optical flow, foreground / background segmentation masks and camera parameters for both stereo views." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 306, + 498, + 388, + 511 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 498, + 388, + 511 + ], + "spans": [ + { + "bbox": [ + 306, + 498, + 388, + 511 + ], + "type": "text", + "content": "5. Experiments" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 518, + 545, + 602 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 518, + 545, + 602 + ], + "spans": [ + { + "bbox": [ + 304, + 518, + 545, + 602 + ], + "type": "text", + "content": "We structure the experiments as follows. First, we evaluate the Dynamic Replica dataset by comparing generalization performance of prior models trained on other datasets and on Dynamic Replica. Then we evaluate our model and compare it to the state of the art in temporal consistency. Finally, we ablate design choices in the model architecture and verify the importance of its individual components." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 605, + 545, + 665 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 545, + 665 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 545, + 665 + ], + "type": "text", + "content": "Implementation Details. We implement DynamicStereo in PyTorch [29] and train on 8 NVIDIA TESLA Volta V100 32GB GPUs. The SF version is trained for 70k iterations with a batch size 8. We train the " + }, + { + "bbox": [ + 304, + 605, + 545, + 665 + ], + "type": "inline_equation", + "content": "\\mathrm{DR + SF}" + }, + { + "bbox": [ + 304, + 605, + 545, + 665 + ], + "type": "text", + "content": " version for 120k iterations which takes about 4 days." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 665, + 547, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 547, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 547, + 714 + ], + "type": "text", + "content": "Both models are trained on random " + }, + { + "bbox": [ + 304, + 665, + 547, + 714 + ], + "type": "inline_equation", + "content": "384 \\times 512" + }, + { + "bbox": [ + 304, + 665, + 547, + 714 + ], + "type": "text", + "content": " crops of sequences of length " + }, + { + "bbox": [ + 304, + 665, + 547, + 714 + ], + "type": "inline_equation", + "content": "T = 5" + }, + { + "bbox": [ + 304, + 665, + 547, + 714 + ], + "type": "text", + "content": " and evaluated in the original resolution with " + }, + { + "bbox": [ + 304, + 665, + 547, + 714 + ], + "type": "inline_equation", + "content": "T = 20" + }, + { + "bbox": [ + 304, + 665, + 547, + 714 + ], + "type": "text", + "content": " and overlapping windows of size 10. During training, we use the AdamW optimizer [24] and set" + } + ] + } + ], + "index": 19 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 58, + 702, + 144, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 702, + 144, + 713 + ], + "spans": [ + { + "bbox": [ + 58, + 702, + 144, + 713 + ], + "type": "text", + "content": "1 http://renderpeople.com/" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "13234" + } + ] + } + ], + "index": 21 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 48, + 70, + 289, + 173 + ], + "blocks": [ + { + "bbox": [ + 48, + 70, + 289, + 173 + ], + "lines": [ + { + "bbox": [ + 48, + 70, + 289, + 173 + ], + "spans": [ + { + "bbox": [ + 48, + 70, + 289, + 173 + ], + "type": "table", + "html": "
Mtd DataKITTIMiddleburyETH3DSintelStereoDR
fullhalfquarterCleanFinalfull
[23] DR7.2519.5113.1313.863.787.3613.042.90
[23] SF5.5517.7612.809.643.055.899.204.01
[23] (DR+SF)/25.6315.0810.369.243.025.969.122.20
[18] DR6.0431.9423.8215.933.9415.0319.354.13
[18] SF6.2223.9515.6410.503.957.5111.016.59
[18] (DR+SF)/25.3522.0213.698.963.536.969.983.49
", + "image_path": "3bae9f4d73ab36569fafd2e2165030ac2eb9aece09b805622d1d4520253239c8.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 186, + 289, + 297 + ], + "lines": [ + { + "bbox": [ + 46, + 186, + 289, + 297 + ], + "spans": [ + { + "bbox": [ + 46, + 186, + 289, + 297 + ], + "type": "text", + "content": "Table 3. Dynamic Replica generalization - non-temporal disparity estimation. SF - SceneFlow [27], DR - Dynamic Replica (ours). For " + }, + { + "bbox": [ + 46, + 186, + 289, + 297 + ], + "type": "inline_equation", + "content": "(\\mathrm{DR} + \\mathrm{SF}) / 2" + }, + { + "bbox": [ + 46, + 186, + 289, + 297 + ], + "type": "text", + "content": ", we replace half of SF with samples from DR. The performance improves over pure SF training, showing that DR is valuable for generalization, compared to training only with SF data. Errors are the percent of pixels with end-point-error greater than the specified threshold. We average across 3 runs with different seeds and use the standard evaluation thresholds: 3px for KITTI 2015 [28] and Sintel Stereo [5], 2px for Middlebury [37], 1px for ETH3D [38] and DR." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 316, + 288, + 400 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 316, + 288, + 400 + ], + "spans": [ + { + "bbox": [ + 46, + 316, + 288, + 400 + ], + "type": "text", + "content": "the number of iterative updates " + }, + { + "bbox": [ + 46, + 316, + 288, + 400 + ], + "type": "inline_equation", + "content": "M = 20" + }, + { + "bbox": [ + 46, + 316, + 288, + 400 + ], + "type": "text", + "content": ". We train with one-cycle learning rate schedule [39] with a maximum learning rate " + }, + { + "bbox": [ + 46, + 316, + 288, + 400 + ], + "type": "inline_equation", + "content": "3 \\cdot 10^{-4}" + }, + { + "bbox": [ + 46, + 316, + 288, + 400 + ], + "type": "text", + "content": ". We set the lookup neighborhood " + }, + { + "bbox": [ + 46, + 316, + 288, + 400 + ], + "type": "inline_equation", + "content": "\\Delta = 4" + }, + { + "bbox": [ + 46, + 316, + 288, + 400 + ], + "type": "text", + "content": " (see Sec. 3.2). For attention layers we use positional encoding in both space and time. We apply linear attention [42] for space and use standard quadratic attention for time. For other implementation details, please see supp. mat." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 407, + 149, + 419 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 407, + 149, + 419 + ], + "spans": [ + { + "bbox": [ + 47, + 407, + 149, + 419 + ], + "type": "text", + "content": "5.1. Dynamic Replica" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 425, + 287, + 520 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 425, + 287, + 520 + ], + "spans": [ + { + "bbox": [ + 46, + 425, + 287, + 520 + ], + "type": "text", + "content": "In Tab. 3 we show results obtained by training two recent state-of-the-art models, RAFT-Stereo [23] and CRE-Stereo [18] on SceneFlow, our dataset and their combination and testing the models' generalization to other disparity estimation datasets. While the main objective of our method is to produce temporally consistent disparity estimates, here we train state-of-the-art disparity estimation models to evaluate the usefulness of the dataset in this setting." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 521, + 287, + 616 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 521, + 287, + 616 + ], + "spans": [ + { + "bbox": [ + 46, + 521, + 287, + 616 + ], + "type": "text", + "content": "SceneFlow is an abstract dataset of moving shapes on colorful backgrounds. It aims at generalization through domain randomization, while our dataset consists of more realistic home and office scenes with people. Thus, while training on Dynamic Replica alone improves performance on the DR test set, it does not generalize as well as models trained on SceneFlow. However, combining both datasets boosts performance across both, datasets and models." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 616, + 288, + 665 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 616, + 288, + 665 + ], + "spans": [ + { + "bbox": [ + 46, + 616, + 288, + 665 + ], + "type": "text", + "content": "This highlights the benefits of including Dynamic Replica in the standard set of disparity estimation training datasets, even if its main goal is to enable training of temporally consistent models on longer sequences." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 671, + 174, + 685 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 671, + 174, + 685 + ], + "spans": [ + { + "bbox": [ + 47, + 671, + 174, + 685 + ], + "type": "text", + "content": "5.2. Temporal Consistency" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "text", + "content": "The main objective of our method and dataset is to enable training of temporally consistent disparity estimators." + } + ] + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 310, + 70, + 388, + 115 + ], + "blocks": [ + { + "bbox": [ + 310, + 70, + 388, + 115 + ], + "lines": [ + { + "bbox": [ + 310, + 70, + 388, + 115 + ], + "spans": [ + { + "bbox": [ + 310, + 70, + 388, + 115 + ], + "type": "image", + "image_path": "c8e0cd66c67a97d14175302687fae87848e30fd1f283f9894fb15bb1ca96501e.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 310, + 114, + 388, + 158 + ], + "blocks": [ + { + "bbox": [ + 310, + 114, + 388, + 158 + ], + "lines": [ + { + "bbox": [ + 310, + 114, + 388, + 158 + ], + "spans": [ + { + "bbox": [ + 310, + 114, + 388, + 158 + ], + "type": "image", + "image_path": "cea7e63d00d59308988534dad86175a2206b8cb98f068f3adc4a639f801b6f1f.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 323, + 161, + 374, + 171 + ], + "lines": [ + { + "bbox": [ + 323, + 161, + 374, + 171 + ], + "spans": [ + { + "bbox": [ + 323, + 161, + 374, + 171 + ], + "type": "text", + "content": "(mean image)" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 391, + 70, + 469, + 115 + ], + "blocks": [ + { + "bbox": [ + 391, + 70, + 469, + 115 + ], + "lines": [ + { + "bbox": [ + 391, + 70, + 469, + 115 + ], + "spans": [ + { + "bbox": [ + 391, + 70, + 469, + 115 + ], + "type": "image", + "image_path": "d0b513f27f12341df97e947898f633439ee7e15793130324510acf7e13e90a8f.jpg" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_body" + } + ], + "index": 12 + }, + { + "type": "image", + "bbox": [ + 391, + 114, + 468, + 158 + ], + "blocks": [ + { + "bbox": [ + 391, + 114, + 468, + 158 + ], + "lines": [ + { + "bbox": [ + 391, + 114, + 468, + 158 + ], + "spans": [ + { + "bbox": [ + 391, + 114, + 468, + 158 + ], + "type": "image", + "image_path": "3dce11bf36f34a11839149ef4a7174d6f0b92ec5e4b732b11b0842024d878697.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 397, + 160, + 463, + 171 + ], + "lines": [ + { + "bbox": [ + 397, + 160, + 463, + 171 + ], + "spans": [ + { + "bbox": [ + 397, + 160, + 463, + 171 + ], + "type": "text", + "content": "RAFT Stereo [23]" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_caption" + } + ], + "index": 13 + }, + { + "type": "image", + "bbox": [ + 474, + 70, + 552, + 115 + ], + "blocks": [ + { + "bbox": [ + 474, + 70, + 552, + 115 + ], + "lines": [ + { + "bbox": [ + 474, + 70, + 552, + 115 + ], + "spans": [ + { + "bbox": [ + 474, + 70, + 552, + 115 + ], + "type": "image", + "image_path": "ded0d55971c87fb304d707f6b39121c0990fb32a2ba58d123e3910e1bb1f91ca.jpg" + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_body" + } + ], + "index": 15 + }, + { + "type": "image", + "bbox": [ + 474, + 114, + 551, + 158 + ], + "blocks": [ + { + "bbox": [ + 474, + 114, + 551, + 158 + ], + "lines": [ + { + "bbox": [ + 474, + 114, + 551, + 158 + ], + "spans": [ + { + "bbox": [ + 474, + 114, + 551, + 158 + ], + "type": "image", + "image_path": "41e6e1476b848996b58a8d0112c80d02775a8538120ea8f9c14f59557aa475e4.jpg" + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 482, + 160, + 543, + 171 + ], + "lines": [ + { + "bbox": [ + 482, + 160, + 543, + 171 + ], + "spans": [ + { + "bbox": [ + 482, + 160, + 543, + 171 + ], + "type": "text", + "content": "DynamicStereo" + } + ] + } + ], + "index": 17, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 305, + 182, + 547, + 258 + ], + "lines": [ + { + "bbox": [ + 305, + 182, + 547, + 258 + ], + "spans": [ + { + "bbox": [ + 305, + 182, + 547, + 258 + ], + "type": "text", + "content": "Table 4. Temporal consistency. Mean and variance of a 40-frame reconstructed static video, visualized. Both models are trained on DR & SF. We predict depth for each frame and convert it to globally aligned point clouds. Render combined point cloud with a camera displaced by 15 angles. Finally, we compute mean and variance across all images. Pixels with variance higher than " + }, + { + "bbox": [ + 305, + 182, + 547, + 258 + ], + "type": "inline_equation", + "content": "50\\mathrm{px}^2" + }, + { + "bbox": [ + 305, + 182, + 547, + 258 + ], + "type": "text", + "content": " are shown in red. Our method has lower variance." + } + ] + } + ], + "index": 18, + "angle": 0, + "type": "image_caption" + } + ], + "index": 16 + }, + { + "bbox": [ + 305, + 281, + 545, + 304 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 281, + 545, + 304 + ], + "spans": [ + { + "bbox": [ + 305, + 281, + 545, + 304 + ], + "type": "text", + "content": "To evaluate temporal consistency, we compute the temporal end-point-error (TEPE) defined as follows:" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 312, + 315, + 545, + 353 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 315, + 545, + 353 + ], + "spans": [ + { + "bbox": [ + 312, + 315, + 545, + 353 + ], + "type": "interline_equation", + "content": "\\operatorname {T E P E} (\\hat {D}, D) = \\sqrt {\\sum_ {t = 1} ^ {T - 1} \\left(\\left(\\hat {D} _ {t} - \\hat {D} _ {t + 1}\\right) - \\left(D _ {t} - D _ {t + 1}\\right)\\right) ^ {2}}. \\tag {5}", + "image_path": "2f3b1f4a596ac638f1d7cbb36dfea95409ea63b361a7d50695839125c99478cc.jpg" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 304, + 361, + 545, + 456 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 361, + 545, + 456 + ], + "spans": [ + { + "bbox": [ + 304, + 361, + 545, + 456 + ], + "type": "text", + "content": "This effectively measures the variation of the end-point-error across time. Lower values mean greater temporal consistency. In Tab. 5 we show that our model is more temporally consistent than prior methods across training datasets and benchmarks. It is even better than CRE-Stereo [18] that is trained on a combination of seven datasets. Additionally, models trained with Dynamic Replica are more consistent than models trained on SceneFlow alone." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 304, + 458, + 545, + 517 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 458, + 545, + 517 + ], + "spans": [ + { + "bbox": [ + 304, + 458, + 545, + 517 + ], + "type": "text", + "content": "With the above experiments, we have shown that Dynamic Replica is a useful dataset for training temporally consistent disparity estimators as well as standard stereoframe models, and that our proposed model improves over the state of the art in both tasks when trained on our dataset." + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 304, + 518, + 545, + 615 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 518, + 545, + 615 + ], + "spans": [ + { + "bbox": [ + 304, + 518, + 545, + 615 + ], + "type": "text", + "content": "In Tab. 4, we show a qualitative comparison of the temporal consistency between our model and RAFT-Stereo on a real-world sequence. We show the mean reconstruction over time of the sequence and color each pixel more red, the higher its variance across time. Our model significantly reduces the flickering that single-timestep models such as RAFT-Stereo produce. For more qualitative results and videos, please see the supplementary material." + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 306, + 623, + 406, + 634 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 623, + 406, + 634 + ], + "spans": [ + { + "bbox": [ + 306, + 623, + 406, + 634 + ], + "type": "text", + "content": "5.3. Ablation Studies" + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 304, + 642, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 642, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 642, + 545, + 714 + ], + "type": "text", + "content": "In this section, we validate our method by ablating the design choices of our model. We train the model on Scene-Flow [27] for 50k iterations with the hyper-parameters described in Implementation Details (see Sec. 5). We evaluate these models on the clean pass of Sintel [5] and on the test split of Dynamic Replica. We measure both accuracy and" + } + ] + } + ], + "index": 25 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "13235" + } + ] + } + ], + "index": 26 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 48, + 70, + 550, + 259 + ], + "blocks": [ + { + "bbox": [ + 48, + 70, + 550, + 259 + ], + "lines": [ + { + "bbox": [ + 48, + 70, + 550, + 259 + ], + "spans": [ + { + "bbox": [ + 48, + 70, + 550, + 259 + ], + "type": "table", + "html": "
Training dataMethodSintel StereoDynamic Replica
CleanFinalFirst 150 frames
@δ3pxTEPE±δ1pxδt3px@δ3pxTEPE±δ1pxδt3px@δ1px
SFCODD [20]8.681.4410.785.6517.462.3218.569.796.59
RAFT-Stereo [23]6.120.929.334.5110.402.1013.697.085.51
Ours6.100.778.413.938.971.4511.955.983.44
DR+SFRAFT-Stereo [23]5.710.849.154.409.162.2713.457.171.89
Ours5.770.768.463.938.681.4211.935.923.32
SF+M+KCODD [20]9.111.3312.166.2311.902.0116.168.6410.03
SF+MRAFT-Stereo [23]5.860.858.794.138.471.6312.406.233.46
7 datasets (incl. Sintel)CRE-Stereo [18]4.580.676.363.268.171.9012.296.871.75
DR+SFOurs5.770.768.463.938.681.4211.935.923.32
", + "image_path": "f7f9451c553bb296a8a19ed0eadebd3cd9fd2c9e3146d7a9d5e7945a2e1c89fb.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 59, + 341, + 276, + 407 + ], + "blocks": [ + { + "bbox": [ + 46, + 266, + 547, + 323 + ], + "lines": [ + { + "bbox": [ + 46, + 266, + 547, + 323 + ], + "spans": [ + { + "bbox": [ + 46, + 266, + 547, + 323 + ], + "type": "text", + "content": "Table 5. Accuracy " + }, + { + "bbox": [ + 46, + 266, + 547, + 323 + ], + "type": "inline_equation", + "content": "⑥" + }, + { + "bbox": [ + 46, + 266, + 547, + 323 + ], + "type": "text", + "content": " and Temporal consistency " + }, + { + "bbox": [ + 46, + 266, + 547, + 323 + ], + "type": "inline_equation", + "content": "①" + }, + { + "bbox": [ + 46, + 266, + 547, + 323 + ], + "type": "text", + "content": ". SF - SceneFlow [27], K - KITTI [28], M - Middlebury [37], DR - Dynamic Replica (ours). Temporal end-point error (TEPE) measures the consistency of the disparity estimation over time. We also compute " + }, + { + "bbox": [ + 46, + 266, + 547, + 323 + ], + "type": "inline_equation", + "content": "\\delta_{1px}^{t}" + }, + { + "bbox": [ + 46, + 266, + 547, + 323 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 266, + 547, + 323 + ], + "type": "inline_equation", + "content": "\\delta_{3px}^{t}" + }, + { + "bbox": [ + 46, + 266, + 547, + 323 + ], + "type": "text", + "content": " that show the proportion of pixels with TEPE higher than the threshold. Our model is more consistent than prior work and models. Additionally, other methods trained on our dataset also improve in temporal consistency. As CRE Stereo trains on Sintel and disparity estimation is evaluated on the training set of Sintel, CRE Stereo results are training set results and cannot be directly compared." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 59, + 341, + 276, + 407 + ], + "lines": [ + { + "bbox": [ + 59, + 341, + 276, + 407 + ], + "spans": [ + { + "bbox": [ + 59, + 341, + 276, + 407 + ], + "type": "table", + "html": "
MethodSintel CleanDynamic Replica
δ3pxTEPEδ1pxTEPE
shared weights6.600.9086.480.101
sep. weights6.240.8234.760.126
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MethodSintel CleanDynamic Replica
δ3pxTEPEδ1pxTEPE
Conv2D6.461.057.310.140
Conv3D6.240.8234.760.126
", + "image_path": "6ebbc21b9407320ad35c181e6e9630e121d60e45e951f6a03190d5c923e2d79c.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_body" + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 539, + 287, + 572 + ], + "lines": [ + { + "bbox": [ + 46, + 539, + 287, + 572 + ], + "spans": [ + { + "bbox": [ + 46, + 539, + 287, + 572 + ], + "type": "text", + "content": "Table 7. Update Block Convolution. A GRU with a 3D convolution across space and time improves the performance over the 2D variant, especially in terms of the temporal metric TEPE." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 598, + 287, + 647 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 598, + 287, + 647 + ], + "spans": [ + { + "bbox": [ + 46, + 598, + 287, + 647 + ], + "type": "text", + "content": "temporal consistency. For accuracy, we use an end-point-error threshold of 3px for Sintel and 1px for DR. This shows the proportion of pixels with an end-point-error higher than 3px. For consistency, we use TEPE (see Sec. 5.2)." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 651, + 287, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 651, + 287, + 712 + ], + "spans": [ + { + "bbox": [ + 46, + 651, + 287, + 712 + ], + "type": "text", + "content": "Update Block. In Tab. 6 we compare sharing weights of the three blocks across the three resolutions of the decoder to learning separate update blocks. As different scales exploit features of different resolutions, learning separate update blocks improves the results over weight-sharing." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 343, + 545, + 415 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 343, + 545, + 415 + ], + "spans": [ + { + "bbox": [ + 304, + 343, + 545, + 415 + ], + "type": "text", + "content": "Update Block Convolution. While prior works such as CRE Stereo use 2D convolutions in the iterative update block as they operate on single time steps, we find it beneficial to extend the processing of the update block across time (Tab. 7). This results in a general improvement but shows especially large improvements in temporal consistency." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 318, + 416, + 518, + 428 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 318, + 416, + 518, + 428 + ], + "spans": [ + { + "bbox": [ + 318, + 416, + 518, + 428 + ], + "type": "text", + "content": "Please see the supplement for additional analysis." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 441, + 378, + 453 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 441, + 378, + 453 + ], + "spans": [ + { + "bbox": [ + 306, + 441, + 378, + 453 + ], + "type": "text", + "content": "6. Conclusion" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 463, + 545, + 534 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 463, + 545, + 534 + ], + "spans": [ + { + "bbox": [ + 304, + 463, + 545, + 534 + ], + "type": "text", + "content": "In this paper, we make two main contributions. We introduce a new stereo video dataset—Dynamic Replica—that allows training temporally consistent disparity estimators. Additionally, we introduce a new method that is able to improve over the state of the art in temporally consistent stereo estimation using the new dataset." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 536, + 545, + 631 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 536, + 545, + 631 + ], + "spans": [ + { + "bbox": [ + 304, + 536, + 545, + 631 + ], + "type": "text", + "content": "We show that other methods benefit from training on this new dataset as it contains realistic scenes and can thus reduce the domain gap between the real world and typical synthetic, abstract training datasets such as SceneFlow. Our combines spatial, temporal, and stereo information, enabling precise and consistent predictions across time. In extensive ablation studies, we show that each component of the model contributes to the final performance." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 645, + 408, + 658 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 645, + 408, + 658 + ], + "spans": [ + { + "bbox": [ + 306, + 645, + 408, + 658 + ], + "type": "text", + "content": "Acknowledgements" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "content": "C. R. is supported by VisualAI EP/T028572/1. We would like to thank Filippos Kokkinos for helping to capture test videos, Roman Shapovalov and Luke Melas-Kyriazi for insightful discussions." + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "type": "text", + "content": "13236" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 289, + 712 + ], + "type": "list", + "angle": 0, + "index": 12, + "blocks": [ + { + "bbox": [ + 53, + 91, + 289, + 148 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 289, + 148 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 289, + 148 + ], + "type": "text", + "content": "[1] Abhishek Badki, Alejandro Troccoli, Kihwan Kim, Jan Kautz, Pradeep Sen, and Orazio Gallo. 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IEEE Transactions on pattern analysis and machine intelligence, 22(7), 2000. 2" + } + ] + } + ], + "index": 10 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 749, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 749, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 749, + 318, + 757 + ], + "type": "text", + "content": "13239" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 10 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Dynamically Instance-Guided Adaptation_ A Backward-Free Approach for Test-Time Domain Adaptive Semantic Segmentation/8fab8469-0a5d-4f13-bb47-6165f5c91b04_content_list.json b/2023/Dynamically Instance-Guided Adaptation_ A Backward-Free Approach for Test-Time Domain Adaptive Semantic Segmentation/8fab8469-0a5d-4f13-bb47-6165f5c91b04_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..1677fc49e0bbe62c76a774a15ebb3b67f583430c --- /dev/null +++ b/2023/Dynamically Instance-Guided Adaptation_ A Backward-Free Approach for Test-Time Domain Adaptive Semantic Segmentation/8fab8469-0a5d-4f13-bb47-6165f5c91b04_content_list.json @@ -0,0 +1,1467 @@ +[ + { + "type": "text", + "text": "Dynamically Instance-Guided Adaptation: A Backward-free Approach for Test-Time Domain Adaptive Semantic Segmentation", + "text_level": 1, + "bbox": [ + 109, + 130, + 859, + 176 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Wei Wang $^{1}$ , Zhun Zhong $^{2}$ , Weijie Wang $^{2}$ , Xi Chen $^{3}$ , Charles Ling $^{1}$ , Boyu Wang $^{1*}$ , Nicu Sebe $^{2}$ $^{1}$ Western University $^{2}$ University of Trento $^{3}$ Huawei Noah's Ark Lab", + "bbox": [ + 109, + 202, + 857, + 239 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/ff8531033168e900ef0eb98e27c170abe9809915ab5b4aadcd0737d6ab6d3197.jpg", + "image_caption": [ + "Figure 1. Top: Illustration of test-time domain adaptive semantic segmentation (TTDA-Seg). Bottom: Comparison with different TTDA methods. The proposed DIGA is a holistic method that has the properties of effectiveness (distribution&semantic adaptation and avoid unstable training&error accumulation) and efficiency (backward-free)." + ], + "image_footnote": [], + "bbox": [ + 89, + 255, + 890, + 531 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 587, + 313, + 602 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "In this paper, we study the application of Test-time domain adaptation in semantic segmentation (TTDA-Seg) where both efficiency and effectiveness are crucial. Existing methods either have low efficiency (e.g., backward optimization) or ignore semantic adaptation (e.g., distribution alignment). Besides, they would suffer from the accumulated errors caused by unstable optimization and abnormal distributions. To solve these problems, we propose a novel backward-free approach for TTDA-Seg, called Dynamically Instance-Guided Adaptation (DIGA). Our principle is utilizing each instance to dynamically guide its own adaptation in a non-parametric way, which avoids the error accumulation issue and expensive optimizing cost. Specifically, DIGA is composed of a distribution adaptation module (DAM) and a semantic adaptation module (SAM), enabling us to jointly adapt the model in two indispensable aspects. DAM mixes the instance and source BN statistics to", + "bbox": [ + 75, + 619, + 473, + 876 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "encourage the model to capture robust representation. SAM combines the historical prototypes with instance-level prototypes to adjust semantic predictions, which can be associated with the parametric classifier to mutually benefit the final results. Extensive experiments evaluated on five target domains demonstrate the effectiveness and efficiency of the proposed method. Our DIGA establishes new state-of-the-art performance in TTDA-Seg. Source code is available at: https://github.com/Waybaba/DIGA.", + "bbox": [ + 496, + 589, + 893, + 724 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 500, + 753, + 632, + 768 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Semantic segmentation (Seg) [3, 40, 45, 46, 49] is a fundamental task in computer vision, which is an important step in the visual-based robot, autonomous driving and etc. Modern deep-learning techniques have achieved impressive success in segmentation. However, one serious drawback of them is that the segmentation models trained on one dataset (source domain) may undergo catastrophic performance degradation when applied to another dataset sam", + "bbox": [ + 496, + 779, + 893, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Corresponding author", + "bbox": [ + 94, + 887, + 220, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "24090", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "pled from a different distribution. This phenomenon will be even more serious under complex and ever-changing contexts, e.g., autonomous driving.", + "bbox": [ + 75, + 90, + 468, + 136 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To solve this well-known problem caused by domain shifts, researchers have devoted great effort to domain generalization (DG) [6,11,18,19,21,30] and domain adaptation (DA) [23,47,47,50]. Specifically, DG aims to learn generalized models with only labeled source data. Traditional DA attempts to adapt the model on the target domain by using both labeled source data and unlabeled target data. However, both learning paradigms have their own disadvantages. The performance of DG is limited especially when evaluated on a domain with a large gap from the source since it does not leverage target data [11]. DA assumes that the unlabeled target data are available in advance and can be chronically exploited to improve target performance. This assumption, however, can not always be satisfied in real-world applications. For example, when driving in a new city, the data are incoming sequentially and we expect the system to dynamically adapt to the ever-changing scenario.", + "bbox": [ + 75, + 138, + 468, + 396 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To meet the real-world applications, [41] introduces the test-time domain adaptation (TTDA), which aims at adapting the model during the testing phase in an online fashion (see Fig. 1 Top). Generally, existing methods can be divided into two categories: backward-based methods [1,22,27,37, 41] and backward-free methods [15,25,28,33]. The former category (see Fig. 1 (a)) focuses on optimizing the parameters of models with self-supervision losses, such as entropy loss [27, 41]. In this way, both distribution adaptation and semantic adaptation can be achieved, which however has the following drawbacks. (1) Low-Efficiency : Due to the requirement of back-propagation, the computation cost will be multiplied, leading to low efficiency. (2) Unstable Optimization & Error Accumulation: Since the gradient is calculated with single sample by weak supervision, the randomness could be high thus leading to unstable optimization. Although this problem can be mitigated in some certain by increasing the testing batch size, it still cannot be solved well. In such cases, the accumulated errors may lead the model to forget the original well-learned knowledge and thus cause performance degradation.", + "bbox": [ + 75, + 398, + 470, + 717 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "The second category aims to adapt the model in the distribution level by updating statistics in batch normalization (BN) [25] layers, which is very efficient as it is directly implemented in forward propagation with a light computation cost. Instance normalization [28] (see Fig. 1 (b)) directly replaces the source statistics with those from each instance, which is sensitive to the target variations due to discarding the basic source knowledge and thus is unstable. Mirza et al [25] (see Fig. 1 (c)) study the impacts of updating the historical statistics by instance statistics with fixed momentum or dynamically fluctuating momentum. However, these methods also suffer from the error accumulation is", + "bbox": [ + 75, + 719, + 468, + 900 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/5e0b116703992dc731840b17314624c7c6c6750cb4e0ec3afbcbf0be9e76675c.jpg", + "image_caption": [ + "Figure 2. Illustration of the implementation of our DIGA. Given a source model, our DIGA can be readily equipped with only access to the BN layers, classifier head and feature head." + ], + "image_footnote": [], + "bbox": [ + 521, + 88, + 877, + 193 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "sue caused by abnormal target distributions as well as the neglect of semantic adaptation, both of which will result in inferior adaptation performance.", + "bbox": [ + 498, + 266, + 890, + 311 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To this end, we propose a holistic approach (see Fig. 1 (d)), called Dynamically Instance-Guided Adaptation (DIGA), for TTDA-Seg, which takes into account both effectiveness and efficiency. The main idea of DIGA is leveraging each instance to dynamically its own adaptation in a non-parametric manner, which is efficient and can largely avoid the error accumulation issue. In addition, our DIGA is implemented in a considerate manner by injecting with distribution adaptation module (DAM) and semantic adaptation module (SAM). Specifically, in DAM, we compute the weighed sum of the source and current statistics in BN layers to adapt target distribution, which enables the model to obtain a more robust representation. In SAM, we build a dynamic non-parametric classifier by mixing the historical prototypes with instance-level prototypes, enabling us to adjust the semantic prediction. In addition, the non-parametric classifier can be associated with the parametric one, which can further benefit the adaptation results. Our contributions can be summarized as follows:", + "bbox": [ + 498, + 313, + 892, + 599 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- Efficiency. We propose a backward-free approach for TTDA-Seg, which can be implemented within one forward propagation with a light computation cost.", + "- Effectiveness. We introduce a considerate approach to adapt the model in both distribution and semantic aspects. In addition, our method takes the mutual advantage of two types of classifiers to achieve further improvements.", + "- Usability. Our method is easy to implement and is model-agnostic, which can be readily injected into existing models (see Fig.2).", + "- Promising Results. We conduct experiments on three source domains and five target domains based on driving benchmarks and show that our method produces new state-of-the-art performance for TTDA-Seg. We also study the continual TTDA-Seg and verify the superiority of our method in this challenging task." + ], + "bbox": [ + 519, + 616, + 888, + 898 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "24091", + "bbox": [ + 478, + 945, + 517, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 76, + 89, + 218, + 104 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Test-time Domain Adaptation (TTDA) aims to adapt models on the target domain only in test time. It is firstly proposed in TTT [37] and has been applied to many fields such as instance tracking [9], object detections [16] and reinforcement learning [12]. The early works (TTT [37] and its extensions [20, 22]) require an extra training process on source data, making it inapplicable when only the source model is available. In this paper, we focus on the more practical Fully Test-time Domain Adaptation setting proposed in [41]. Current fully TTDA methods can be categorized into two main branches: backward-based adaptation and backward-free adaptation. As the pioneer of the self-supervision adaptation methods, TENT [41] proposes to minimize the entropy by updating BN affine parameters during test time. EATA [27] shows that skipping low entropy samples would achieve higher efficiency and performance. Also, an updated regularization term is utilized to alleviate the forgetting problem. [1] introduce an efficient framework by introducing contrastive learning. The problem with these methods is that they cost a long time and large GPU memory due to backpropagation, which largely limited the application for real-time inference. As for the backward-free branch, most of the approaches focus on BN statistics adaptation. IN [28] directly uses batch statistics while Momentum [33] and DUA [25] use running average to update the statistics. This branch is much more efficient while they only work on distribution, ignoring the semantic adaptation, leading to discounted adaptation power. Besides the above two branches, T3A [14] proposes to denoise the classification results in the post-processing stage, where adaptation of the model itself is not well exploited.", + "bbox": [ + 76, + 114, + 472, + 583 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Domain Adaptive for Semantic Segmentation (DASS) aims to bridge the domain gap between the training and testing data. The early works in DASS mainly focus on building adversarial training architectures to learn the domain-invariant features [24, 38, 43]. Complementary modules have been introduced to facilitate the training [24,38,40,43]. Another category exploits the self-training techniques such as entropy minimization [40] and pseudo-labeling [45, 46, 49, 51]. While these approaches require the co-existence of source-target data. Source-free DA (SFDA) is more practical and closer to our setting as they assume the source data is not available during adaptation. [40] proposes to recover source information by utilizing the BN statistics. $\\mathrm{MAS}^3$ [17] proposes to store source distribution information as prototypes and then use them during adaptation. [35] uses a multi-head structure to increase the reliability of pseudo-labeling for self-supervised training. Zhao et al. [48] present a special augmentation module to diversify samples with various patch styles at the feature level and then use them for generalization ability improvement. However, these methods can not handle TTDA well. Firstly,", + "bbox": [ + 76, + 584, + 472, + 902 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "they do not consider the efficiency problem [17, 35, 40, 48]. Moreover, they often require to visit samples repeatedly in large batch sizes [17, 35, 48].", + "bbox": [ + 496, + 90, + 890, + 137 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Methodology", + "text_level": 1, + "bbox": [ + 498, + 159, + 635, + 176 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Problem Definition. In test-time domain adaptation in semantic segmentation (TTDA-Seg), we are given a segmentation model $f_{\\theta} : \\mathbf{x} \\rightarrow y$ pretrained on a source domain $\\mathcal{D}_S$ , which will be directly deployed to unseen domains for evaluation. Due to domain shifts, the model $f_{\\theta}$ would normally produce a poor performance on unseen testing domains. The goal of TTDA-Seg is to adapt the model by utilizing continuously incoming testing data in an online fashion (see Fig. 1). For example, at each testing step $t$ , the model $f_{\\theta}$ receives an instance $\\mathbf{x}_t$ and simultaneously performs adaptation as well as produces segmentation prediction $\\hat{y}_t$ . At the next step $t + 1$ , the model $f_{\\theta}$ will perform adaptation and prediction on instance $\\mathbf{x}_{t + 1}$ without the access to previous data $\\mathbf{x}_{1 \\to t}$ .", + "bbox": [ + 496, + 186, + 893, + 402 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Overview", + "text_level": 1, + "bbox": [ + 498, + 417, + 612, + 434 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In this section, we propose a Dynamically Instance-Guided Adaptation (DIGA) method for TTDA-Seg, which is backward-free and non-parametric. As shown in Fig. 3, our DIGA includes two adaptation modules, the distribution adaptation module (DAM) and the semantic adaptation module (SAM), which are both guided by instance-aware information. Specifically, given a testing sample, we first input it into the source pretrained model and perform distribution alignment by DAM in each BN layer. The distribution alignment is implemented by weighted summing of the source statistics and instance statistics. After this, we apply semantic adaptation at the last feature level by SAM, in which we build a dynamic non-parametric classifier by weighted mixing the historical prototypes with instance-aware prototypes. This allows us to adjust the semantic prediction. Lastly, we obtain the final prediction by taking the mutual advantage between the original parametric classifier and the dynamic non-parametric classifier.", + "bbox": [ + 496, + 444, + 893, + 717 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In Fig. 3 (a-g), we show an illustration of how our DIGA helps to adapt the model with the guidance of instance-aware information. (a-d) Due to the large domain shifts (e.g., light variations), the segmentation results on the target sample might be poor. After distribution alignment by DAM, the segmentation results could be improved, especially the instances that are similar to the source (e). However, there might still exist poorly-recognized pixels that are very different from the source. Our DAM further leverages the reliable pixels to guide the predictions of other pixels in a non-parametric way (f), enabling us to achieve more accurate results (g).", + "bbox": [ + 496, + 719, + 893, + 902 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "24092", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/f73e66aaab9564c9c19f6cd691c3c7f848179fc3875558faab130195bda7d43f.jpg", + "image_caption": [ + "Figure 3. Illustration of the proposed DIGA. (a-d) The source model commonly produces poor results on unseen targets, due to significant domain shifts, such as light variation. To solve this problem, our DIGA is proposed to adapt the model in an online fashion, which consists of a distribution adaptation module (DAM) and a semantic adaptation module (SAM). Both modules are guided by instance-aware information (statistics for DAM and prototypes for SAM). The DAM is implemented in BN layers for distribution alignment (e). The SAM is implemented in the feature level for semantic alignment (f-g). The final prediction is obtained by the fusion of original classifier and non-parametric classifier built by SAM." + ], + "image_footnote": [], + "bbox": [ + 84, + 87, + 238, + 250 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/67bbf0ac011f1b3b94f45e6e7fb1685c2633913a5a8e7d95817016891504f82b.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 243, + 88, + 400, + 250 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/1a7a34d00ab664f3e0147081bdbb54850faefcf98bb0c4fc7b9f37b58596735a.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 403, + 88, + 560, + 250 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/3b494624f605214a05932aeab2b429ba0687d5a9173cd6938b0322dc3dbce088.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 562, + 88, + 728, + 250 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/0abf06c3cccf5ce04bc87852bdfe937a97480a99e98d76beca79d75ff1d9151a.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 730, + 88, + 890, + 250 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. Distribution Adaptation Module (DAM)", + "text_level": 1, + "bbox": [ + 76, + 364, + 419, + 381 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The most common way to adapt the distribution is based on adversarial training [10, 19, 23] and minimization of distribution gap metrics [4, 36]. However, these methods are not suitable for TTDA due to limited available training data and the high-cost backpropagation. Recent works [25, 28, 33] show that the static mismatch between domains in the Batch Normalization (BN) layers is a major reason that causes the performance degradation in cross-domain testing. We thus first revisit the mechanism of BN. Specifically, for each BN layer, given the input feature representation $F$ , the corresponding output is given by:", + "bbox": [ + 75, + 387, + 470, + 553 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nB N (F) = \\gamma \\frac {F - \\mathbb {E} [ F ]}{\\sqrt {\\operatorname {V a r} [ F ]}} + \\beta , \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 174, + 561, + 468, + 597 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\gamma$ and $\\beta$ are trainable parameters for scaling and shifting. $\\mathbb{E}[F]$ and $Var[F]$ are expected value and variance of input feature $F$ . In practice, due to the batch-wise training process, their values are calculated by running mean [42] during training as follows:", + "bbox": [ + 75, + 604, + 468, + 679 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\bar {u} _ {t} ^ {S} = \\left(1 - \\rho_ {B N}\\right) \\cdot \\bar {\\mu} _ {t - 1} ^ {S} + \\rho_ {B N} \\cdot \\mu_ {t - 1} ^ {S}, \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 125, + 686, + 468, + 710 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\left(\\bar {\\sigma} _ {t} ^ {S}\\right) ^ {2} = \\left(1 - \\rho_ {B N}\\right) \\cdot \\left(\\bar {\\sigma} _ {t - 1} ^ {S}\\right) ^ {2} + \\rho_ {B N} \\cdot \\left(\\sigma_ {t - 1} ^ {S}\\right) ^ {2},\n$$\n", + "text_format": "latex", + "bbox": [ + 107, + 708, + 421, + 726 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\bar{\\mu}_t^s$ and $\\bar{\\sigma}_t^s$ are serving as estimation for $\\mathbb{E}[F]$ and $Var[F]$ of source domain respectively.", + "bbox": [ + 76, + 734, + 468, + 763 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Out of the motivation that the amount of training sample is usually much larger than the testing batch and thus more stable, the last value $\\bar{\\mu}_t^s$ , $\\bar{\\sigma}_t^s$ would be frozen and serve as the estimation for $\\mathbb{E}[F]$ and $Var[F]$ for the test data during the test phase.", + "bbox": [ + 75, + 763, + 468, + 839 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "However, it has been shown that when applied to a different environment, the source statistics can hamper performance significantly. To solve this problem, DUA [42] proposes to adapt the statistics $\\gamma, \\beta$ of BN layers to the target", + "bbox": [ + 75, + 839, + 468, + 901 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "domain with a dynamic learning module. Despite the efficiency, its performance is still not satisfactory. One possible reason is that the updating rate is usually very small so that instance-level information is not fully considered during each instance evaluation.", + "bbox": [ + 496, + 364, + 890, + 439 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Different from [25, 33], instead of updating the $\\gamma, \\beta$ , the proposed Distribution Adaptation Module (DAM) dynamically merges the source and instance BN statistics to constitute the estimation $\\bar{\\mu}_t^T$ and $(\\bar{\\sigma}_t^T)^2$ for $\\mathbb{E}[F]$ , $Var[F]$ as follows:", + "bbox": [ + 496, + 441, + 890, + 515 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\bar {\\mu} _ {t} ^ {T} = \\lambda_ {B N} \\cdot \\bar {\\mu} ^ {S} + (1 - \\lambda_ {B N}) \\cdot \\mu_ {t} ^ {T},\n$$\n", + "text_format": "latex", + "bbox": [ + 566, + 525, + 803, + 542 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\left(\\bar {\\sigma} _ {t} ^ {T}\\right) ^ {2} = \\lambda_ {B N} \\cdot \\left(\\bar {\\sigma} ^ {S}\\right) ^ {2} + \\left(1 - \\lambda_ {B N}\\right) \\cdot \\left(\\sigma_ {t} ^ {T}\\right) ^ {2}, \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 550, + 541, + 890, + 565 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\mu_t^T$ and $(\\sigma_t^T)^2$ are the mean and variance calculated with the $t$ -th instance during testing.", + "bbox": [ + 500, + 577, + 890, + 609 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.3. Semantic Adaptation Module (SAM)", + "text_level": 1, + "bbox": [ + 500, + 619, + 816, + 635 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The proposed DAM is a category-agnostic since it only aligns the distribution of feature maps globally. However, category-specific is also important to segmentation adaptation because the distribution of each category varies a lot even in the same image. Hence, we argue that it is also important to implement semantic adaptation in TTDA-Seg. To achieve this, two straightforward methods are entropy maximization [41] and pseudo-labeling [22]. However, both of them require gradient-based backpropagation and thus limit the testing efficiency. Inspired by the prototype-based methods in few-shot learning [34] and domain adaptation [29,45], we introduce the semantic adaptation module (SAM) for category-specific adaptation.", + "bbox": [ + 496, + 643, + 890, + 839 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "As shown in Sec. 3.1, even though distribution alignment is implemented by DAM, the model still produces wrong predictions for pixels that are very different from the source. Fortunately, we could observe that pixels of the same ob", + "bbox": [ + 496, + 839, + 890, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "24093", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "ject share several of the same properties, e.g., the appearance within a car, the same texture color within a road, the same outfit within a person, the light intensity within an image, etc. Motivated by this, we propose to leverage the similarities between pixels to further guide the recognition of wrongly recognized pixels. To this end, we propose the semantic adaptation module (SAM) to adjust the semantic predictions by dynamic instance-aware prototypes.", + "bbox": [ + 75, + 90, + 468, + 210 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The segmentation model $f_{\\theta}$ can be separated into two learnable parts: i) an encoder $h_{\\phi}$ for dense visual feature extraction which maps each pixel $\\mathbf{x}^{(h,w)}$ to feature $\\mathbf{z}^{(h,w)} \\in \\mathbb{R}^D$ , and ii) a classifier $g_{\\psi}$ for following prediction which maps $\\mathbf{z}^{(h,w)}$ to a distribution $\\hat{p}^{(h,w)}(c|\\mathbf{x})$ over $C$ classes. Formally, it can be denoted as:", + "bbox": [ + 75, + 212, + 470, + 301 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {z} _ {t} ^ {(h, w)} = h _ {\\phi} ^ {(h, w)} \\left(\\mathbf {x} _ {t}\\right), \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 223, + 306, + 468, + 329 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {p} ^ {(h, w)} (c | \\mathbf {x} _ {t}) = g _ {\\psi} ^ {(h, w)} (\\mathbf {z} _ {t}). \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 184, + 332, + 468, + 352 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The value of logits indicates the confidence of the corresponding classes it would belong to. Thus, the largest value $\\max_c\\hat{p}_{t,c}^{(h,w)}$ of the prediction distribution can be considered as the confidence of the prediction for one pixel. For one input image $\\mathbf{x}_t$ , we select pixels whose confidences are larger than $\\mathcal{P}_0$ to calculate the centroids of each class in feature space, which are called as instance-aware prototypes $\\mathbf{q}_t$ and can be formulated as follows:", + "bbox": [ + 75, + 357, + 468, + 479 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {q} _ {t} ^ {c} = \\frac {\\sum^ {H , W} \\mathbf {z} _ {t} ^ {(h , w)} \\cdot \\mathbb {I} \\left(c _ {t} ^ {(h , w)} = c , \\max _ {c} \\hat {p} _ {t , c} ^ {(h , w)} \\geq \\mathcal {P} _ {0}\\right)}{\\sum^ {H , W} \\mathbb {I} \\left(c _ {t} ^ {(h , w)} = c , \\max _ {c} \\hat {p} _ {t , c} ^ {(h , w)} \\geq \\mathcal {P} _ {0}\\right)}. \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 88, + 482, + 468, + 539 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Using instance-aware prototypes only may produce unstable predictions due to the instance variance. To make the prediction more stable, we additionally calculate the moving average of the prototypes of different instances for each category, which are called historical prototypes.", + "bbox": [ + 75, + 546, + 468, + 622 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\bar {\\mathbf {q}} _ {t} ^ {c} = \\rho_ {P} \\cdot \\bar {\\mathbf {q}} _ {t - 1} ^ {c} + (1 - \\rho_ {P}) \\mathbf {q} _ {t} ^ {c}, \\text {w i t h} \\bar {\\mathbf {q}} _ {0} ^ {c} = \\mathbf {q} _ {0} ^ {c}. \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 114, + 628, + 468, + 646 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Since the historical prototypes are calculated by averaging prototypes from a large number of target instances, they are more stable than instance-aware prototypes.", + "bbox": [ + 75, + 650, + 468, + 696 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Given the instance-aware prototypes, we can obtain the instance-aware prediction for each class $p^{(h,w)}(c|\\mathbf{x}_t,\\mathbf{q})$ by:", + "bbox": [ + 76, + 696, + 468, + 727 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\np ^ {(h, w)} \\left(c \\mid \\mathbf {x} _ {t}, \\mathbf {q}\\right) = \\frac {\\exp \\left(- \\langle \\mathbf {z} ^ {(h , w)} , \\mathbf {q} _ {c} \\rangle\\right)}{\\sum_ {c ^ {\\prime} = 1} ^ {C} \\exp \\left(- \\langle \\mathbf {z} ^ {(h , w)}, \\mathbf {q} _ {c ^ {\\prime}} \\rangle\\right)}. \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 117, + 731, + 468, + 770 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The historical prediction $p^{(h,w)}(c|\\mathbf{x}_t,\\bar{\\mathbf{q}})$ could be obtained in a similar way.", + "bbox": [ + 75, + 775, + 468, + 805 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "By combing the predictions of the two types of prototypes, we form a dynamic non-parametric classifier and the predictions are formulated as:", + "bbox": [ + 75, + 806, + 468, + 851 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\tilde {p} ^ {(h, w)} \\left(c \\mid \\mathbf {x} _ {t}\\right) = \\lambda_ {P} \\cdot p ^ {(h, w)} \\left(c \\mid \\mathbf {x} _ {t}, \\bar {\\mathbf {q}}\\right) \\tag {9} \\\\ + (1 - \\lambda_ {P}) \\cdot p ^ {(h, w)} (c | \\mathbf {x} _ {t}, \\mathbf {q}), \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 133, + 856, + 468, + 897 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Algorithm 1 DIGA (Testing Phase)", + "text_level": 1, + "bbox": [ + 501, + 90, + 738, + 106 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Input: Model $f_{\\theta}$ , target testing sample $\\mathbf{x}_t$", + "bbox": [ + 514, + 109, + 795, + 125 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Output: Prediction of $\\mathbf{x}_t$", + "bbox": [ + 516, + 126, + 687, + 138 + ], + "page_idx": 4 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "1. Produce feature $\\mathbf{z}_t$ and prediction $\\hat{p}_t(\\mathbf{x}_t)$ with distribution alignment of DAM (Eq. 3).", + "2. Calculate instance-aware prototypes $\\mathbf{q}_t$ (Eq. 6).", + "3. Calculate historical prototypes $\\bar{\\mathbf{q}}_t$ (Eq. 7).", + "4. Calculate non-parametric predictions $\\tilde{p}_t(\\mathbf{x}_t)$ with SAM (Eq. 9).", + "5. Obtain final prediction $p(\\mathbf{x}_t)$ by weighed fusion of $\\hat{p}_t(\\mathbf{x}_t)$ and $\\tilde{p}_t(\\mathbf{x}_t)$ (Eq. 10)." + ], + "bbox": [ + 516, + 140, + 890, + 261 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Return: $p(\\mathbf{x}_t)$", + "bbox": [ + 517, + 262, + 614, + 277 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\lambda_{P}$ controls the importance of two types of prototypes.", + "bbox": [ + 498, + 306, + 890, + 338 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.4. Classifier Association", + "text_level": 1, + "bbox": [ + 500, + 347, + 700, + 362 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "To this end, we could have two types of predictions: one from the original parametric classifier $(\\hat{p})$ and one from the introduced non-parametric prototype classifier $(\\tilde{p})$ . To leverage the mutual benefit between them, we obtain the final prediction by weighted sum of them, formulated as:", + "bbox": [ + 498, + 371, + 890, + 446 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\np ^ {(h, w)} = \\lambda_ {F} \\cdot \\tilde {p} ^ {(h, w)} (c | \\mathbf {x} _ {t}) + (1 - \\lambda_ {F}) \\hat {p} ^ {(h, w)} (c | \\mathbf {x} _ {t}), \\tag {10}\n$$\n", + "text_format": "latex", + "bbox": [ + 509, + 457, + 890, + 476 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\lambda_F$ balances the importance of two classifiers. The overall process of DIGA is shown in Alg. 1.", + "bbox": [ + 498, + 487, + 890, + 517 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Experiment", + "text_level": 1, + "bbox": [ + 500, + 531, + 624, + 547 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.1. Experimental Setup", + "text_level": 1, + "bbox": [ + 500, + 556, + 689, + 571 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Datasets. Following the previous works [3, 15, 40], we evaluate our method on sim2real scenarios. Specifically, for the source model, we pretrain it with three different source domains: GTA5 [31], Synthia [31], and GTA5+Synthia. GTA5 provides 24,971 images from video games with 19 semantic classes. Synthia includes 12,000 simulated images with 16 semantic classes. GTA5+Synthia is the combination of GTA5 and Synthia datasets. Performance are evaluated on five target domains: Cityscapes [7], BDD-100K [44], Mapillary [26], IDD [39], Cross-City [5]. We test the results on the validation sets, where the number of samples is \\{500, 1,000, 2,000, 100, and 400\\} for {Cityscapes, BDD-100K, Mapillary, IDD, Cross-City} respectively.", + "bbox": [ + 498, + 579, + 890, + 776 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Evaluation. The mean intersection-over-union (mIoU) is used as the evaluation metric. As in [3,40], for source models pretrained on GTA5 and GTA5+Synthia, we report the mIoU of 19 shared semantic categories. Due to missing of annotations of some classes, we report the mIoU of 16 shared semantic classes for the model pretrained on the Synthia dataset.", + "bbox": [ + 498, + 794, + 890, + 898 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "24094", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/96b3cb343c150314fc8ec118903ce9d449f9a0a964574704c2e479aae33009b4.jpg", + "table_caption": [ + "Table 1. Comparison with state-of-the-art methods in terms of mIoU. The best score for each column is highlighted. CS: CityScapes, BDD: BDD100K, MA: Mapillary, IDD: IDD, CC: Cross-City. *: Use an extra augmented sample during adaptation. Avg.: Mean of mIoUs over five target domains." + ], + "table_footnote": [], + "table_body": "
MethodGTA5→Synthia→GTA5+Synthia→
CSBDDMAIDDCCAvg.CSBDDMAIDDCCAvg.CSBDDMAIDDCCAvg.
Source [42]35.8729.8938.6738.0530.0334.5030.8721.0131.1226.2331.9628.2437.0028.8541.5639.8832.9336.04
Backward-based Methods
TENT [41]37.3031.5338.2938.9630.5935.3334.8916.9933.4626.2331.6828.6539.3925.1937.3239.5132.8434.85
EATA [27]37.0830.6739.3538.7530.2435.2231.3120.5231.5926.4631.9128.3638.4529.3441.6340.3332.9136.53
Backward-free Methods
IN [28]34.2529.6435.0129.823.8730.5129.5319.3321.9222.0828.2424.2237.0928.8136.0230.9928.6332.31
Momentum [33]38.1232.4240.7938.7430.236.0532.8422.5131.1227.2432.2329.4539.6131.7241.7939.8833.1736.66
DUA [25]37.7931.7640.2634.7526.3234.1832.1721.5627.4224.0629.8727.0239.1730.5939.9535.3030.6535.13
SITA* [15]40.6432.9437.8035.6628.1935.2634.6322.5126.6024.6428.1827.7942.6232.2441.2038.8233.2237.62
DIGA (Ours)45.8135.7844.2542.7333.7240.4641.8529.0936.5438.3636.7836.5246.4333.8743.5142.0834.4140.06
", + "bbox": [ + 84, + 132, + 885, + 359 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Implementation Details. Following previous works [3, 15, 25, 41], we use DeepLabV2 [2] as the segmentation model. The ResNet-101 [13] pretrained on ImageNet [8] is used as the backbone. It is worth mentioning that globally consistent parameter sets are used for our DIGA, which achieves consistently good performance in all experiments. Specifically, we set the momentum updating rate $(\\rho_{P}$ and $\\rho_{BN})$ both to 0.1. The weights of DAM, SAM, and classifier association $(\\lambda_{BN},\\lambda_{P}$ and $\\lambda_F)$ are all set to 0.8. The confidence bar for prototype selection $\\mathcal{P}_0$ is 0.9. All the experiments are conducted with one RTX3090 GPU.", + "bbox": [ + 75, + 383, + 472, + 549 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.2. Comparison with State of the Art", + "text_level": 1, + "bbox": [ + 76, + 559, + 372, + 575 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We first compare our method with the state-of-the-art approaches. Generally, the compared methods can be divided into two categories: backward-based methods and backward-free methods.", + "bbox": [ + 75, + 583, + 468, + 642 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Backward-based methods: TENT [41] performs adapting by minimizing the output entropy and updating the learnable parameters of BN layers. As an extension to TENT [41], EATA [27] proposes to skip the high-entropy samples and only leverage reliable samples during model optimization, which can effectively increase testing efficiency. Both of them are initially designed for image classification. We implement them for TTDA-Seg by minimizing the entropy of pixel-level output. For EATA [27], we skip the low-entropy pixels during optimization. Backward-free methods: IN [28] uses instance statistics to replace source ones in BN at each testing step. Momentum [33] utilizes the instance statistics to update BN in a momentum-based manner. DUA [25] proposes a decaying strategy to adaptively control the momentum of BN updating. SITA [15] leverages extra augmented samples to obtain stable instance statistics, which are then mixed with the source statistics.", + "bbox": [ + 75, + 643, + 470, + 900 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "To make a fair comparison, we implement all the methods with the same source models. Note that, we report the results of the compared methods by selecting the best parameters for each source-target pair. In contrast, in our method, we only use one parameter setting for all experiments to better meet the real-world applications.", + "bbox": [ + 496, + 383, + 890, + 474 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "The following observations can be made from the results reported in Tab. 1. First, backward-based methods can consistently improve the performance when evaluating on CityScapes. However, the improvements on other target domains are limited or even negative. For example, when using Synthia as the source domain, TENT [41] increases the mIoU from $30.87\\%$ to $34.89\\%$ on CityScapes while largely reduces the mIoU from $21.01\\%$ to $16.99\\%$ for BDD100K. This indicates that using self-supervision only may not be a good choice for TTDA-Seg. Second, except for IN [28], the backward-free methods are generally effective on CityScapes and BDD100K while failing to achieve consistent improvements on other datasets, even though we have well-tuned them for each target domain. On the other hand, IN [28] largely reduces the average mIoU due to ignoring the source statistics. Third, the proposed DIGA consistently improves the mIoUs of the source models on all settings and outperforms all the compared methods by a large margin in most cases. Specifically, our DIGA is higher than the best competitor (Momentum [33]) by $4.41\\%$ , $7.07\\%$ , and $3.4\\%$ in average mIoU for GTA5, Synthia, and GTA5+Synthia settings, respectively. In Fig. 4, we provide the qualitative comparison of different methods. It is clear that our DIGA consistently improves the segmentation results of the source model and outperforms other state-of-the-art methods. The above observations demonstrate the effectiveness and universality of the proposed method for solving TTDA-Seg.", + "bbox": [ + 496, + 477, + 892, + 901 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "24095", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/b2bc63e91d61c69fe4119ef427374d706a091b2f2bc817d123a57bc44e5f4ffc.jpg", + "image_caption": [ + "Figure 4. Qualitative comparison of segmentation results." + ], + "image_footnote": [], + "bbox": [ + 129, + 88, + 841, + 297 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/76c8146c2805529a98b4725f8aadfdeb2931752063143ea2c21669c95b601635.jpg", + "table_caption": [ + "Table 2. Ablation study on DIGA. DAM: domain alignment module, SAM: semantic alignment module, Association: classifier association. For the BN branch and Semantic branch, we highlight the best and second best results, respectively. Source: GTA5." + ], + "table_footnote": [], + "table_body": "
ModulesCSBDDMAIDDCCAvg.
BNHistorical35.8729.8938.6738.0530.0334.50
Instance34.2529.6435.0129.8023.8730.51
DAM39.2633.3940.1137.2330.1236.02
SemanticHistorical38.6329.2537.6441.6732.8836.01
Instance39.1632.2638.6835.0927.9834.63
SAM42.9932.6941.3741.3033.4938.37
Association45.8135.7844.2542.7333.7240.46
", + "bbox": [ + 78, + 385, + 468, + 539 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.3. Ablation Study", + "text_level": 1, + "bbox": [ + 76, + 559, + 230, + 574 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We conduct ablative study to investigate the effectiveness of the components of the proposed DIGA, i.e., domain adaptation module, semantic adaptation module, and classifier association. Experiments are evaluated on five target domains with the source model pretrained on GTA5. Results are reported in Tab. 2.", + "bbox": [ + 75, + 582, + 468, + 672 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Effectiveness of DAM. In the BN branch of Tab. 2, \"Historical\" indicates directly using BN statistics of the source for normalization, which can be regarded as the baseline or source model. \"Instance\" represents using instance statistics for normalization. Two observations can be made. First, the \"Instance\" model produces worse performance than the \"Historical\" model on all target domains, especially on IDD and Cross-City. The average mIoU of \"Instance\" is $4.49\\%$ lower than the \"Historical\". This indicates that using instance statistics only is not suitable for TTDA-Seg. Second, DAM improves the results in most cases and obtains an improvement of $1.48\\%$ in average mIoU over the \"Historical\" model. Specifically, DAM boosts the mIoU by $3.39\\%$ and $3.5\\%$ on CityScapes and BDD100K, respectively. Even when the gap between \"Historical\" and \"Instance\" is too", + "bbox": [ + 75, + 672, + 470, + 901 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "large (e.g., $9.25\\%$ on IDD), our DAM is not deteriorated by the negative impact of \"Instance\" too much and still produces competitive results to the \"Historical\" with a marginal gap of $0.82\\%$ . These two observations suggest that our DAM can effectively merge the guidance of instance knowledge into historical statistics to achieve an effective and stable adaptation process.", + "bbox": [ + 496, + 330, + 890, + 436 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Effectiveness of SAM. In the semantic branch, \"Instance\" indicates the instance-specific prototypes calculated by reliable pixels in the current testing image. \"Historical\" represents the historical prototypes. Notice that, the semantic branch is conducted based on DAM, where the features for calculating prototypes are obtained after distribution alignment. We can make the following conclusions. First, the \"Historical\" classifier and the parametric classifier (DAM) achieve a very similar average mIoU. Second, the \"Instance\" classifier obtains lower average mIoU than the \"Historical\" classifier. However, by taking a close look at the results on five target domains, we can find that the \"Instance\" classifier outperforms the \"Historical\" classifier on three datasets (CityScapes, BDD and Mapillary). This indicates that these two non-parametric classifiers have particular merits in particular datasets. Third, SAM clearly outperforms both non-parametric classifiers in average mIoU. Specifically, our SAM surpasses the \"Historical\" classifier by $2.36\\%$ in average mIoU. Fourth, similar to the BN branch, when the gap between \"Historical\" and \"Instance\" classifiers is large, SAM may not bring improvement, e.g., the IDD case. However, our SAM still remains the high performance without influencing by the inferior classifier. The above observations verify the appropriateness of using the prototype classifiers and also the effectiveness of the proposed SAM across different target domains.", + "bbox": [ + 496, + 441, + 892, + 835 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Effectiveness of Classifier Association. With the association of the parametric classifier (outputs of DAM) and the non-parametric classifier (outputs of SAM), the results are consistently improved on all target domains. Specifi", + "bbox": [ + 496, + 839, + 893, + 902 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "24096", + "bbox": [ + 478, + 945, + 519, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/c0492f85a65b467e6e4e1a9aaceb680c5e13079d166e5635c369b0dab7ea2db4.jpg", + "image_caption": [ + "Figure 5. Experiments of continual TTDA-Seg. THe model is pretrained on Synthia [32]. The domain adaptation stream is \"BDD $\\rightarrow$ CC $\\rightarrow$ CS $\\rightarrow$ IDD $\\rightarrow$ MA\" with two rounds." + ], + "image_footnote": [], + "bbox": [ + 94, + 93, + 464, + 268 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "cally, the average mIoU is increased by $4.44\\%$ for DAM and $2.09\\%$ for SAM. This validates the effectiveness of leveraging the mutual benefit between parametric and non-parametric classifiers.", + "bbox": [ + 75, + 343, + 468, + 405 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.4. Continual TTDA-Seg", + "text_level": 1, + "bbox": [ + 76, + 416, + 277, + 431 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In real-world applications, such as autonomous driving, the environments are ever-changing and complex. To better simulate such practice scenarios, we design a continual TTDA-Seg experiment. Specifically, the dynamic environment is built by sequentially incoming target domains. The domain-stream is \"BDD $\\rightarrow$ CC $\\rightarrow$ CS $\\rightarrow$ IDD $\\rightarrow$ MA\", which is sorted by alphabetical order for simplicity and performed by two rounds. We use the Synthia-pretrained model as the source model and report the mIoU after meeting each target domain. In Fig. 5, we compare our method with TENT [41]. We implement two versions for TENT [41]. TENT-ContinualAdapt: continually adapt the model with the incoming target domains. TENT-SourceAdapt: directly adapt the source-pretrained model on the given domain.", + "bbox": [ + 75, + 440, + 468, + 651 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We can observe that \"TENT-ContinualAdapt\" suffers from significant performance degradation when compared to \"TENT-SourceAdapt\". For example, when testing on the CityScapes dataset, \"TENT-ContinualAdapt\" is $19\\%$ and $67\\%$ lower than \"TENT-SourceAdapt\" in mIoU at the first round and second round, respectively. This phenomenon can also be observed in other domains. This is mainly because that TENT will accumulate the errors during adaptation and thus leads a worse model. Instead, our DIGA does not have the error accumulation problem and consistently performs well on all domains. This further validates the effectiveness of our method in real-world TTDA-Seg.", + "bbox": [ + 75, + 652, + 470, + 834 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.5. Computational Cost", + "text_level": 1, + "bbox": [ + 76, + 845, + 269, + 862 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In TTDA-Seg, efficiency is also very important. In Tab. 3, we investigate the computational costs of", + "bbox": [ + 75, + 869, + 470, + 902 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/dbd15c8e69691836e1af9e3f5eb218fd73acfd5c665bb264e62761e7518107f1.jpg", + "table_caption": [ + "Table 3. Time and Memory Cost. Highlights indicate the Best, and Second/Third Best results." + ], + "table_footnote": [], + "table_body": "
Methods\\(T_{Avg}\\)\\(T_{Max}\\)GPU Mem.mIoU
Source-Only134ms141ms3.5GB35.87
TENT [41]411ms425ms14.5GB37.30
EATA [27]235ms490ms15.6GB37.08
Momentum [33]144ms151ms3.5GB37.33
DUA [25]145ms152ms3.6GB37.79
SITA [15]253ms256ms5.6GB40.64
Ours153ms160ms4.0GB45.51
", + "bbox": [ + 519, + 116, + 874, + 247 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "different methods. We conduct experiments on the \"GTA5 $\\rightarrow$ CityScapes\" setting. For the inference time, we report the average time $(T_{Avg} / \\mathrm{ms})$ and the maximize time $(T_{Max} / \\mathrm{ms})$ for each testing sample. In addition, the GPU memory cost is also estimated. We can find that the backward-based methods significantly improve the inference time and GPU memory cost. For example, TENT [41] increases the average time from 134ms to 411ms and the memory cost from 3.5GB to 14.5GB. Even though EATA skips the unreliable pixels during optimization and leads to a lower average inference time than TENT, it still introduces large extra computational cost over the source model. Since SITA [15] uses extra augmented image during testing, its computational cost is doubled. Our DIGA and the other two backward-free methods (Momentum [33] and DUA [25]) produce very limited extra computational cost benefiting from their lightweight designs. However, our DIGA significantly surpasses than Momentum [33] and DUA [25] in mIoU. This experiment suggests that our DIGA is an effective and efficient TTDA-Seg method.", + "bbox": [ + 496, + 273, + 890, + 577 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 592, + 617, + 608 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this paper, we propose the Dynamically Instance-Guided Adaptation (DIGA) approach for solving TTDA-Seg, which jointly enjoys the effectiveness and efficiency factors. Specifically, DIGA includes two adaptation modules, the distribution adaptation module (DAM) and the semantic adaptation module (SAM), which are both guided by instance-aware information in a non-parametric way. Experiments conducted on five target domains verify that our DIGA effectively can adapt the model at both distribution and semantic levels. We also show that the proposed DIGA achieves state-of-the-art results in TTDA-Seg. In future work, we would like to investigate (1) the learning of adaptive weights in DIGA and (2) the implementation of DIGA in other tasks, e.g., object detection.", + "bbox": [ + 496, + 619, + 890, + 829 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgement This work has been supported by the EU H2020 project AI4Media (No. 951911), the PRIN project CREATIVE (Prot. 2020ZSL9F9) and Natural Sciences and Engineering Research Council of Canada (NSERC), Discovery Grants program.", + "bbox": [ + 496, + 830, + 890, + 901 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "24097", + "bbox": [ + 478, + 944, + 517, + 957 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 118, + 171, + 132 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Dian Chen, Dequan Wang, Trevor Darrell, and Sayna Ebrahimi. Contrastive test-time adaptation. 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In ICCV, 2019. 3" + ], + "bbox": [ + 501, + 92, + 890, + 218 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "24099", + "bbox": [ + 478, + 945, + 517, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/Dynamically Instance-Guided Adaptation_ A Backward-Free Approach for Test-Time Domain Adaptive Semantic Segmentation/8fab8469-0a5d-4f13-bb47-6165f5c91b04_model.json b/2023/Dynamically Instance-Guided Adaptation_ A Backward-Free Approach for Test-Time Domain Adaptive Semantic Segmentation/8fab8469-0a5d-4f13-bb47-6165f5c91b04_model.json new file mode 100644 index 0000000000000000000000000000000000000000..a5b87b29cca229c3d085ea8adacbd45b1ad4357d --- /dev/null +++ b/2023/Dynamically Instance-Guided Adaptation_ A Backward-Free Approach for Test-Time Domain Adaptive Semantic Segmentation/8fab8469-0a5d-4f13-bb47-6165f5c91b04_model.json @@ -0,0 +1,2090 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.11, + 0.131, + 0.861, + 0.177 + ], + "angle": 0, + "content": "Dynamically Instance-Guided Adaptation: A Backward-free Approach for Test-Time Domain Adaptive Semantic Segmentation" + }, + { + "type": "text", + "bbox": [ + 0.11, + 0.203, + 0.858, + 0.24 + ], + "angle": 0, + "content": "Wei Wang\\(^{1}\\), Zhun Zhong\\(^{2}\\), Weijie Wang\\(^{2}\\), Xi Chen\\(^{3}\\), Charles Ling\\(^{1}\\), Boyu Wang\\(^{1*}\\), Nicu Sebe\\(^{2}\\) \n\\(^{1}\\)Western University \\(^{2}\\)University of Trento \\(^{3}\\)Huawei Noah's Ark Lab" + }, + { + "type": "image", + "bbox": [ + 0.091, + 0.256, + 0.891, + 0.532 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.532, + 0.894, + 0.573 + ], + "angle": 0, + "content": "Figure 1. Top: Illustration of test-time domain adaptive semantic segmentation (TTDA-Seg). Bottom: Comparison with different TTDA methods. The proposed DIGA is a holistic method that has the properties of effectiveness (distribution&semantic adaptation and avoid unstable training&error accumulation) and efficiency (backward-free)." + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.588, + 0.314, + 0.603 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.62, + 0.474, + 0.877 + ], + "angle": 0, + "content": "In this paper, we study the application of Test-time domain adaptation in semantic segmentation (TTDA-Seg) where both efficiency and effectiveness are crucial. Existing methods either have low efficiency (e.g., backward optimization) or ignore semantic adaptation (e.g., distribution alignment). Besides, they would suffer from the accumulated errors caused by unstable optimization and abnormal distributions. To solve these problems, we propose a novel backward-free approach for TTDA-Seg, called Dynamically Instance-Guided Adaptation (DIGA). Our principle is utilizing each instance to dynamically guide its own adaptation in a non-parametric way, which avoids the error accumulation issue and expensive optimizing cost. Specifically, DIGA is composed of a distribution adaptation module (DAM) and a semantic adaptation module (SAM), enabling us to jointly adapt the model in two indispensable aspects. DAM mixes the instance and source BN statistics to" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.59, + 0.895, + 0.726 + ], + "angle": 0, + "content": "encourage the model to capture robust representation. SAM combines the historical prototypes with instance-level prototypes to adjust semantic predictions, which can be associated with the parametric classifier to mutually benefit the final results. Extensive experiments evaluated on five target domains demonstrate the effectiveness and efficiency of the proposed method. Our DIGA establishes new state-of-the-art performance in TTDA-Seg. Source code is available at: https://github.com/Waybaba/DIGA." + }, + { + "type": "title", + "bbox": [ + 0.501, + 0.755, + 0.633, + 0.77 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Semantic segmentation (Seg) [3, 40, 45, 46, 49] is a fundamental task in computer vision, which is an important step in the visual-based robot, autonomous driving and etc. Modern deep-learning techniques have achieved impressive success in segmentation. However, one serious drawback of them is that the segmentation models trained on one dataset (source domain) may undergo catastrophic performance degradation when applied to another dataset sam" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.888, + 0.221, + 0.9 + ], + "angle": 0, + "content": "*Corresponding author" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "24090" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.137 + ], + "angle": 0, + "content": "pled from a different distribution. This phenomenon will be even more serious under complex and ever-changing contexts, e.g., autonomous driving." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.14, + 0.47, + 0.397 + ], + "angle": 0, + "content": "To solve this well-known problem caused by domain shifts, researchers have devoted great effort to domain generalization (DG) [6,11,18,19,21,30] and domain adaptation (DA) [23,47,47,50]. Specifically, DG aims to learn generalized models with only labeled source data. Traditional DA attempts to adapt the model on the target domain by using both labeled source data and unlabeled target data. However, both learning paradigms have their own disadvantages. The performance of DG is limited especially when evaluated on a domain with a large gap from the source since it does not leverage target data [11]. DA assumes that the unlabeled target data are available in advance and can be chronically exploited to improve target performance. This assumption, however, can not always be satisfied in real-world applications. For example, when driving in a new city, the data are incoming sequentially and we expect the system to dynamically adapt to the ever-changing scenario." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.399, + 0.471, + 0.718 + ], + "angle": 0, + "content": "To meet the real-world applications, [41] introduces the test-time domain adaptation (TTDA), which aims at adapting the model during the testing phase in an online fashion (see Fig. 1 Top). Generally, existing methods can be divided into two categories: backward-based methods [1,22,27,37, 41] and backward-free methods [15,25,28,33]. The former category (see Fig. 1 (a)) focuses on optimizing the parameters of models with self-supervision losses, such as entropy loss [27, 41]. In this way, both distribution adaptation and semantic adaptation can be achieved, which however has the following drawbacks. (1) Low-Efficiency : Due to the requirement of back-propagation, the computation cost will be multiplied, leading to low efficiency. (2) Unstable Optimization & Error Accumulation: Since the gradient is calculated with single sample by weak supervision, the randomness could be high thus leading to unstable optimization. Although this problem can be mitigated in some certain by increasing the testing batch size, it still cannot be solved well. In such cases, the accumulated errors may lead the model to forget the original well-learned knowledge and thus cause performance degradation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.72, + 0.47, + 0.901 + ], + "angle": 0, + "content": "The second category aims to adapt the model in the distribution level by updating statistics in batch normalization (BN) [25] layers, which is very efficient as it is directly implemented in forward propagation with a light computation cost. Instance normalization [28] (see Fig. 1 (b)) directly replaces the source statistics with those from each instance, which is sensitive to the target variations due to discarding the basic source knowledge and thus is unstable. Mirza et al [25] (see Fig. 1 (c)) study the impacts of updating the historical statistics by instance statistics with fixed momentum or dynamically fluctuating momentum. However, these methods also suffer from the error accumulation is" + }, + { + "type": "image", + "bbox": [ + 0.522, + 0.089, + 0.878, + 0.194 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.197, + 0.892, + 0.239 + ], + "angle": 0, + "content": "Figure 2. Illustration of the implementation of our DIGA. Given a source model, our DIGA can be readily equipped with only access to the BN layers, classifier head and feature head." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.267, + 0.892, + 0.312 + ], + "angle": 0, + "content": "sue caused by abnormal target distributions as well as the neglect of semantic adaptation, both of which will result in inferior adaptation performance." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.314, + 0.893, + 0.6 + ], + "angle": 0, + "content": "To this end, we propose a holistic approach (see Fig. 1 (d)), called Dynamically Instance-Guided Adaptation (DIGA), for TTDA-Seg, which takes into account both effectiveness and efficiency. The main idea of DIGA is leveraging each instance to dynamically its own adaptation in a non-parametric manner, which is efficient and can largely avoid the error accumulation issue. In addition, our DIGA is implemented in a considerate manner by injecting with distribution adaptation module (DAM) and semantic adaptation module (SAM). Specifically, in DAM, we compute the weighed sum of the source and current statistics in BN layers to adapt target distribution, which enables the model to obtain a more robust representation. In SAM, we build a dynamic non-parametric classifier by mixing the historical prototypes with instance-level prototypes, enabling us to adjust the semantic prediction. In addition, the non-parametric classifier can be associated with the parametric one, which can further benefit the adaptation results. Our contributions can be summarized as follows:" + }, + { + "type": "text", + "bbox": [ + 0.52, + 0.617, + 0.89, + 0.661 + ], + "angle": 0, + "content": "- Efficiency. We propose a backward-free approach for TTDA-Seg, which can be implemented within one forward propagation with a light computation cost." + }, + { + "type": "text", + "bbox": [ + 0.52, + 0.671, + 0.89, + 0.745 + ], + "angle": 0, + "content": "- Effectiveness. We introduce a considerate approach to adapt the model in both distribution and semantic aspects. In addition, our method takes the mutual advantage of two types of classifiers to achieve further improvements." + }, + { + "type": "text", + "bbox": [ + 0.52, + 0.756, + 0.89, + 0.8 + ], + "angle": 0, + "content": "- Usability. Our method is easy to implement and is model-agnostic, which can be readily injected into existing models (see Fig.2)." + }, + { + "type": "text", + "bbox": [ + 0.52, + 0.811, + 0.89, + 0.9 + ], + "angle": 0, + "content": "- Promising Results. We conduct experiments on three source domains and five target domains based on driving benchmarks and show that our method produces new state-of-the-art performance for TTDA-Seg. We also study the continual TTDA-Seg and verify the superiority of our method in this challenging task." + }, + { + "type": "list", + "bbox": [ + 0.52, + 0.617, + 0.89, + 0.9 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.946, + 0.518, + 0.957 + ], + "angle": 0, + "content": "24091" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.078, + 0.09, + 0.22, + 0.106 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.115, + 0.473, + 0.584 + ], + "angle": 0, + "content": "Test-time Domain Adaptation (TTDA) aims to adapt models on the target domain only in test time. It is firstly proposed in TTT [37] and has been applied to many fields such as instance tracking [9], object detections [16] and reinforcement learning [12]. The early works (TTT [37] and its extensions [20, 22]) require an extra training process on source data, making it inapplicable when only the source model is available. In this paper, we focus on the more practical Fully Test-time Domain Adaptation setting proposed in [41]. Current fully TTDA methods can be categorized into two main branches: backward-based adaptation and backward-free adaptation. As the pioneer of the self-supervision adaptation methods, TENT [41] proposes to minimize the entropy by updating BN affine parameters during test time. EATA [27] shows that skipping low entropy samples would achieve higher efficiency and performance. Also, an updated regularization term is utilized to alleviate the forgetting problem. [1] introduce an efficient framework by introducing contrastive learning. The problem with these methods is that they cost a long time and large GPU memory due to backpropagation, which largely limited the application for real-time inference. As for the backward-free branch, most of the approaches focus on BN statistics adaptation. IN [28] directly uses batch statistics while Momentum [33] and DUA [25] use running average to update the statistics. This branch is much more efficient while they only work on distribution, ignoring the semantic adaptation, leading to discounted adaptation power. Besides the above two branches, T3A [14] proposes to denoise the classification results in the post-processing stage, where adaptation of the model itself is not well exploited." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.585, + 0.473, + 0.904 + ], + "angle": 0, + "content": "Domain Adaptive for Semantic Segmentation (DASS) aims to bridge the domain gap between the training and testing data. The early works in DASS mainly focus on building adversarial training architectures to learn the domain-invariant features [24, 38, 43]. Complementary modules have been introduced to facilitate the training [24,38,40,43]. Another category exploits the self-training techniques such as entropy minimization [40] and pseudo-labeling [45, 46, 49, 51]. While these approaches require the co-existence of source-target data. Source-free DA (SFDA) is more practical and closer to our setting as they assume the source data is not available during adaptation. [40] proposes to recover source information by utilizing the BN statistics. \\(\\mathrm{MAS}^3\\) [17] proposes to store source distribution information as prototypes and then use them during adaptation. [35] uses a multi-head structure to increase the reliability of pseudo-labeling for self-supervised training. Zhao et al. [48] present a special augmentation module to diversify samples with various patch styles at the feature level and then use them for generalization ability improvement. However, these methods can not handle TTDA well. Firstly," + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.138 + ], + "angle": 0, + "content": "they do not consider the efficiency problem [17, 35, 40, 48]. Moreover, they often require to visit samples repeatedly in large batch sizes [17, 35, 48]." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.16, + 0.637, + 0.178 + ], + "angle": 0, + "content": "3. Methodology" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.188, + 0.895, + 0.403 + ], + "angle": 0, + "content": "Problem Definition. In test-time domain adaptation in semantic segmentation (TTDA-Seg), we are given a segmentation model \\( f_{\\theta} : \\mathbf{x} \\rightarrow y \\) pretrained on a source domain \\( \\mathcal{D}_S \\), which will be directly deployed to unseen domains for evaluation. Due to domain shifts, the model \\( f_{\\theta} \\) would normally produce a poor performance on unseen testing domains. The goal of TTDA-Seg is to adapt the model by utilizing continuously incoming testing data in an online fashion (see Fig. 1). For example, at each testing step \\( t \\), the model \\( f_{\\theta} \\) receives an instance \\( \\mathbf{x}_t \\) and simultaneously performs adaptation as well as produces segmentation prediction \\( \\hat{y}_t \\). At the next step \\( t + 1 \\), the model \\( f_{\\theta} \\) will perform adaptation and prediction on instance \\( \\mathbf{x}_{t + 1} \\) without the access to previous data \\( \\mathbf{x}_{1 \\to t} \\)." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.418, + 0.613, + 0.435 + ], + "angle": 0, + "content": "3.1. Overview" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.445, + 0.895, + 0.718 + ], + "angle": 0, + "content": "In this section, we propose a Dynamically Instance-Guided Adaptation (DIGA) method for TTDA-Seg, which is backward-free and non-parametric. As shown in Fig. 3, our DIGA includes two adaptation modules, the distribution adaptation module (DAM) and the semantic adaptation module (SAM), which are both guided by instance-aware information. Specifically, given a testing sample, we first input it into the source pretrained model and perform distribution alignment by DAM in each BN layer. The distribution alignment is implemented by weighted summing of the source statistics and instance statistics. After this, we apply semantic adaptation at the last feature level by SAM, in which we build a dynamic non-parametric classifier by weighted mixing the historical prototypes with instance-aware prototypes. This allows us to adjust the semantic prediction. Lastly, we obtain the final prediction by taking the mutual advantage between the original parametric classifier and the dynamic non-parametric classifier." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.895, + 0.903 + ], + "angle": 0, + "content": "In Fig. 3 (a-g), we show an illustration of how our DIGA helps to adapt the model with the guidance of instance-aware information. (a-d) Due to the large domain shifts (e.g., light variations), the segmentation results on the target sample might be poor. After distribution alignment by DAM, the segmentation results could be improved, especially the instances that are similar to the source (e). However, there might still exist poorly-recognized pixels that are very different from the source. Our DAM further leverages the reliable pixels to guide the predictions of other pixels in a non-parametric way (f), enabling us to achieve more accurate results (g)." + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "24092" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.086, + 0.088, + 0.239, + 0.251 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.245, + 0.089, + 0.401, + 0.251 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.405, + 0.089, + 0.562, + 0.251 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.563, + 0.089, + 0.729, + 0.251 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.731, + 0.089, + 0.891, + 0.251 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.256, + 0.894, + 0.34 + ], + "angle": 0, + "content": "Figure 3. Illustration of the proposed DIGA. (a-d) The source model commonly produces poor results on unseen targets, due to significant domain shifts, such as light variation. To solve this problem, our DIGA is proposed to adapt the model in an online fashion, which consists of a distribution adaptation module (DAM) and a semantic adaptation module (SAM). Both modules are guided by instance-aware information (statistics for DAM and prototypes for SAM). The DAM is implemented in BN layers for distribution alignment (e). The SAM is implemented in the feature level for semantic alignment (f-g). The final prediction is obtained by the fusion of original classifier and non-parametric classifier built by SAM." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.365, + 0.42, + 0.382 + ], + "angle": 0, + "content": "3.2. Distribution Adaptation Module (DAM)" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.388, + 0.471, + 0.554 + ], + "angle": 0, + "content": "The most common way to adapt the distribution is based on adversarial training [10, 19, 23] and minimization of distribution gap metrics [4, 36]. However, these methods are not suitable for TTDA due to limited available training data and the high-cost backpropagation. Recent works [25, 28, 33] show that the static mismatch between domains in the Batch Normalization (BN) layers is a major reason that causes the performance degradation in cross-domain testing. We thus first revisit the mechanism of BN. Specifically, for each BN layer, given the input feature representation \\( F \\), the corresponding output is given by:" + }, + { + "type": "equation", + "bbox": [ + 0.175, + 0.562, + 0.47, + 0.598 + ], + "angle": 0, + "content": "\\[\nB N (F) = \\gamma \\frac {F - \\mathbb {E} [ F ]}{\\sqrt {\\operatorname {V a r} [ F ]}} + \\beta , \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.605, + 0.47, + 0.68 + ], + "angle": 0, + "content": "where \\(\\gamma\\) and \\(\\beta\\) are trainable parameters for scaling and shifting. \\(\\mathbb{E}[F]\\) and \\(Var[F]\\) are expected value and variance of input feature \\(F\\). In practice, due to the batch-wise training process, their values are calculated by running mean [42] during training as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.126, + 0.687, + 0.469, + 0.712 + ], + "angle": 0, + "content": "\\[\n\\bar {u} _ {t} ^ {S} = \\left(1 - \\rho_ {B N}\\right) \\cdot \\bar {\\mu} _ {t - 1} ^ {S} + \\rho_ {B N} \\cdot \\mu_ {t - 1} ^ {S}, \\tag {2}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.108, + 0.709, + 0.422, + 0.727 + ], + "angle": 0, + "content": "\\[\n\\left(\\bar {\\sigma} _ {t} ^ {S}\\right) ^ {2} = \\left(1 - \\rho_ {B N}\\right) \\cdot \\left(\\bar {\\sigma} _ {t - 1} ^ {S}\\right) ^ {2} + \\rho_ {B N} \\cdot \\left(\\sigma_ {t - 1} ^ {S}\\right) ^ {2},\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.735, + 0.47, + 0.765 + ], + "angle": 0, + "content": "where \\(\\bar{\\mu}_t^s\\) and \\(\\bar{\\sigma}_t^s\\) are serving as estimation for \\(\\mathbb{E}[F]\\) and \\(Var[F]\\) of source domain respectively." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.765, + 0.469, + 0.84 + ], + "angle": 0, + "content": "Out of the motivation that the amount of training sample is usually much larger than the testing batch and thus more stable, the last value \\(\\bar{\\mu}_t^s\\), \\(\\bar{\\sigma}_t^s\\) would be frozen and serve as the estimation for \\(\\mathbb{E}[F]\\) and \\(Var[F]\\) for the test data during the test phase." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.47, + 0.902 + ], + "angle": 0, + "content": "However, it has been shown that when applied to a different environment, the source statistics can hamper performance significantly. To solve this problem, DUA [42] proposes to adapt the statistics \\(\\gamma, \\beta\\) of BN layers to the target" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.366, + 0.892, + 0.44 + ], + "angle": 0, + "content": "domain with a dynamic learning module. Despite the efficiency, its performance is still not satisfactory. One possible reason is that the updating rate is usually very small so that instance-level information is not fully considered during each instance evaluation." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.442, + 0.892, + 0.516 + ], + "angle": 0, + "content": "Different from [25, 33], instead of updating the \\(\\gamma, \\beta\\), the proposed Distribution Adaptation Module (DAM) dynamically merges the source and instance BN statistics to constitute the estimation \\(\\bar{\\mu}_t^T\\) and \\((\\bar{\\sigma}_t^T)^2\\) for \\(\\mathbb{E}[F]\\), \\(Var[F]\\) as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.568, + 0.526, + 0.804, + 0.544 + ], + "angle": 0, + "content": "\\[\n\\bar {\\mu} _ {t} ^ {T} = \\lambda_ {B N} \\cdot \\bar {\\mu} ^ {S} + (1 - \\lambda_ {B N}) \\cdot \\mu_ {t} ^ {T},\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.551, + 0.542, + 0.891, + 0.566 + ], + "angle": 0, + "content": "\\[\n\\left(\\bar {\\sigma} _ {t} ^ {T}\\right) ^ {2} = \\lambda_ {B N} \\cdot \\left(\\bar {\\sigma} ^ {S}\\right) ^ {2} + \\left(1 - \\lambda_ {B N}\\right) \\cdot \\left(\\sigma_ {t} ^ {T}\\right) ^ {2}, \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.578, + 0.892, + 0.61 + ], + "angle": 0, + "content": "where \\(\\mu_t^T\\) and \\((\\sigma_t^T)^2\\) are the mean and variance calculated with the \\(t\\)-th instance during testing." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.62, + 0.818, + 0.636 + ], + "angle": 0, + "content": "3.3. Semantic Adaptation Module (SAM)" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.644, + 0.892, + 0.84 + ], + "angle": 0, + "content": "The proposed DAM is a category-agnostic since it only aligns the distribution of feature maps globally. However, category-specific is also important to segmentation adaptation because the distribution of each category varies a lot even in the same image. Hence, we argue that it is also important to implement semantic adaptation in TTDA-Seg. To achieve this, two straightforward methods are entropy maximization [41] and pseudo-labeling [22]. However, both of them require gradient-based backpropagation and thus limit the testing efficiency. Inspired by the prototype-based methods in few-shot learning [34] and domain adaptation [29,45], we introduce the semantic adaptation module (SAM) for category-specific adaptation." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.892, + 0.901 + ], + "angle": 0, + "content": "As shown in Sec. 3.1, even though distribution alignment is implemented by DAM, the model still produces wrong predictions for pixels that are very different from the source. Fortunately, we could observe that pixels of the same ob" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "24093" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.212 + ], + "angle": 0, + "content": "ject share several of the same properties, e.g., the appearance within a car, the same texture color within a road, the same outfit within a person, the light intensity within an image, etc. Motivated by this, we propose to leverage the similarities between pixels to further guide the recognition of wrongly recognized pixels. To this end, we propose the semantic adaptation module (SAM) to adjust the semantic predictions by dynamic instance-aware prototypes." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.213, + 0.471, + 0.303 + ], + "angle": 0, + "content": "The segmentation model \\( f_{\\theta} \\) can be separated into two learnable parts: i) an encoder \\( h_{\\phi} \\) for dense visual feature extraction which maps each pixel \\( \\mathbf{x}^{(h,w)} \\) to feature \\( \\mathbf{z}^{(h,w)} \\in \\mathbb{R}^D \\), and ii) a classifier \\( g_{\\psi} \\) for following prediction which maps \\( \\mathbf{z}^{(h,w)} \\) to a distribution \\( \\hat{p}^{(h,w)}(c|\\mathbf{x}) \\) over \\( C \\) classes. Formally, it can be denoted as:" + }, + { + "type": "equation", + "bbox": [ + 0.224, + 0.308, + 0.469, + 0.33 + ], + "angle": 0, + "content": "\\[\n\\mathbf {z} _ {t} ^ {(h, w)} = h _ {\\phi} ^ {(h, w)} \\left(\\mathbf {x} _ {t}\\right), \\tag {4}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.186, + 0.333, + 0.469, + 0.353 + ], + "angle": 0, + "content": "\\[\n\\hat {p} ^ {(h, w)} (c | \\mathbf {x} _ {t}) = g _ {\\psi} ^ {(h, w)} (\\mathbf {z} _ {t}). \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.358, + 0.47, + 0.48 + ], + "angle": 0, + "content": "The value of logits indicates the confidence of the corresponding classes it would belong to. Thus, the largest value \\(\\max_c\\hat{p}_{t,c}^{(h,w)}\\) of the prediction distribution can be considered as the confidence of the prediction for one pixel. For one input image \\(\\mathbf{x}_t\\), we select pixels whose confidences are larger than \\(\\mathcal{P}_0\\) to calculate the centroids of each class in feature space, which are called as instance-aware prototypes \\(\\mathbf{q}_t\\) and can be formulated as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.089, + 0.483, + 0.469, + 0.54 + ], + "angle": 0, + "content": "\\[\n\\mathbf {q} _ {t} ^ {c} = \\frac {\\sum^ {H , W} \\mathbf {z} _ {t} ^ {(h , w)} \\cdot \\mathbb {I} \\left(c _ {t} ^ {(h , w)} = c , \\max _ {c} \\hat {p} _ {t , c} ^ {(h , w)} \\geq \\mathcal {P} _ {0}\\right)}{\\sum^ {H , W} \\mathbb {I} \\left(c _ {t} ^ {(h , w)} = c , \\max _ {c} \\hat {p} _ {t , c} ^ {(h , w)} \\geq \\mathcal {P} _ {0}\\right)}. \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.547, + 0.469, + 0.623 + ], + "angle": 0, + "content": "Using instance-aware prototypes only may produce unstable predictions due to the instance variance. To make the prediction more stable, we additionally calculate the moving average of the prototypes of different instances for each category, which are called historical prototypes." + }, + { + "type": "equation", + "bbox": [ + 0.116, + 0.629, + 0.469, + 0.647 + ], + "angle": 0, + "content": "\\[\n\\bar {\\mathbf {q}} _ {t} ^ {c} = \\rho_ {P} \\cdot \\bar {\\mathbf {q}} _ {t - 1} ^ {c} + (1 - \\rho_ {P}) \\mathbf {q} _ {t} ^ {c}, \\text {w i t h} \\bar {\\mathbf {q}} _ {0} ^ {c} = \\mathbf {q} _ {0} ^ {c}. \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.651, + 0.469, + 0.697 + ], + "angle": 0, + "content": "Since the historical prototypes are calculated by averaging prototypes from a large number of target instances, they are more stable than instance-aware prototypes." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.697, + 0.469, + 0.728 + ], + "angle": 0, + "content": "Given the instance-aware prototypes, we can obtain the instance-aware prediction for each class \\( p^{(h,w)}(c|\\mathbf{x}_t,\\mathbf{q}) \\) by:" + }, + { + "type": "equation", + "bbox": [ + 0.118, + 0.732, + 0.469, + 0.771 + ], + "angle": 0, + "content": "\\[\np ^ {(h, w)} \\left(c \\mid \\mathbf {x} _ {t}, \\mathbf {q}\\right) = \\frac {\\exp \\left(- \\langle \\mathbf {z} ^ {(h , w)} , \\mathbf {q} _ {c} \\rangle\\right)}{\\sum_ {c ^ {\\prime} = 1} ^ {C} \\exp \\left(- \\langle \\mathbf {z} ^ {(h , w)}, \\mathbf {q} _ {c ^ {\\prime}} \\rangle\\right)}. \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.776, + 0.469, + 0.806 + ], + "angle": 0, + "content": "The historical prediction \\( p^{(h,w)}(c|\\mathbf{x}_t,\\bar{\\mathbf{q}}) \\) could be obtained in a similar way." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.807, + 0.469, + 0.852 + ], + "angle": 0, + "content": "By combing the predictions of the two types of prototypes, we form a dynamic non-parametric classifier and the predictions are formulated as:" + }, + { + "type": "equation", + "bbox": [ + 0.135, + 0.857, + 0.469, + 0.898 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\tilde {p} ^ {(h, w)} \\left(c \\mid \\mathbf {x} _ {t}\\right) = \\lambda_ {P} \\cdot p ^ {(h, w)} \\left(c \\mid \\mathbf {x} _ {t}, \\bar {\\mathbf {q}}\\right) \\tag {9} \\\\ + (1 - \\lambda_ {P}) \\cdot p ^ {(h, w)} (c | \\mathbf {x} _ {t}, \\mathbf {q}), \\\\ \\end{array}\n\\]" + }, + { + "type": "title", + "bbox": [ + 0.502, + 0.091, + 0.74, + 0.107 + ], + "angle": 0, + "content": "Algorithm 1 DIGA (Testing Phase)" + }, + { + "type": "text", + "bbox": [ + 0.516, + 0.111, + 0.796, + 0.126 + ], + "angle": 0, + "content": "Input: Model \\(f_{\\theta}\\), target testing sample \\(\\mathbf{x}_t\\)" + }, + { + "type": "text", + "bbox": [ + 0.517, + 0.127, + 0.689, + 0.14 + ], + "angle": 0, + "content": "Output: Prediction of \\(\\mathbf{x}_t\\)" + }, + { + "type": "text", + "bbox": [ + 0.517, + 0.141, + 0.891, + 0.171 + ], + "angle": 0, + "content": "1. Produce feature \\(\\mathbf{z}_t\\) and prediction \\(\\hat{p}_t(\\mathbf{x}_t)\\) with distribution alignment of DAM (Eq. 3)." + }, + { + "type": "text", + "bbox": [ + 0.517, + 0.172, + 0.846, + 0.187 + ], + "angle": 0, + "content": "2. Calculate instance-aware prototypes \\(\\mathbf{q}_t\\) (Eq. 6)." + }, + { + "type": "text", + "bbox": [ + 0.517, + 0.187, + 0.81, + 0.202 + ], + "angle": 0, + "content": "3. Calculate historical prototypes \\(\\bar{\\mathbf{q}}_t\\) (Eq. 7)." + }, + { + "type": "text", + "bbox": [ + 0.517, + 0.202, + 0.891, + 0.231 + ], + "angle": 0, + "content": "4. Calculate non-parametric predictions \\(\\tilde{p}_t(\\mathbf{x}_t)\\) with SAM (Eq. 9)." + }, + { + "type": "text", + "bbox": [ + 0.517, + 0.232, + 0.892, + 0.262 + ], + "angle": 0, + "content": "5. Obtain final prediction \\( p(\\mathbf{x}_t) \\) by weighed fusion of \\( \\hat{p}_t(\\mathbf{x}_t) \\) and \\( \\tilde{p}_t(\\mathbf{x}_t) \\) (Eq. 10)." + }, + { + "type": "list", + "bbox": [ + 0.517, + 0.141, + 0.892, + 0.262 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.263, + 0.616, + 0.278 + ], + "angle": 0, + "content": "Return: \\( p(\\mathbf{x}_t) \\)" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.308, + 0.891, + 0.339 + ], + "angle": 0, + "content": "where \\(\\lambda_{P}\\) controls the importance of two types of prototypes." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.348, + 0.701, + 0.363 + ], + "angle": 0, + "content": "3.4. Classifier Association" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.372, + 0.892, + 0.447 + ], + "angle": 0, + "content": "To this end, we could have two types of predictions: one from the original parametric classifier \\((\\hat{p})\\) and one from the introduced non-parametric prototype classifier \\((\\tilde{p})\\). To leverage the mutual benefit between them, we obtain the final prediction by weighted sum of them, formulated as:" + }, + { + "type": "equation", + "bbox": [ + 0.51, + 0.458, + 0.891, + 0.477 + ], + "angle": 0, + "content": "\\[\np ^ {(h, w)} = \\lambda_ {F} \\cdot \\tilde {p} ^ {(h, w)} (c | \\mathbf {x} _ {t}) + (1 - \\lambda_ {F}) \\hat {p} ^ {(h, w)} (c | \\mathbf {x} _ {t}), \\tag {10}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.488, + 0.891, + 0.518 + ], + "angle": 0, + "content": "where \\(\\lambda_F\\) balances the importance of two classifiers. The overall process of DIGA is shown in Alg. 1." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.532, + 0.625, + 0.549 + ], + "angle": 0, + "content": "4. Experiment" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.557, + 0.691, + 0.573 + ], + "angle": 0, + "content": "4.1. Experimental Setup" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.58, + 0.892, + 0.777 + ], + "angle": 0, + "content": "Datasets. Following the previous works [3, 15, 40], we evaluate our method on sim2real scenarios. Specifically, for the source model, we pretrain it with three different source domains: GTA5 [31], Synthia [31], and GTA5+Synthia. GTA5 provides 24,971 images from video games with 19 semantic classes. Synthia includes 12,000 simulated images with 16 semantic classes. GTA5+Synthia is the combination of GTA5 and Synthia datasets. Performance are evaluated on five target domains: Cityscapes [7], BDD-100K [44], Mapillary [26], IDD [39], Cross-City [5]. We test the results on the validation sets, where the number of samples is \\{500, 1,000, 2,000, 100, and 400\\} for {Cityscapes, BDD-100K, Mapillary, IDD, Cross-City} respectively." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.795, + 0.892, + 0.9 + ], + "angle": 0, + "content": "Evaluation. The mean intersection-over-union (mIoU) is used as the evaluation metric. As in [3,40], for source models pretrained on GTA5 and GTA5+Synthia, we report the mIoU of 19 shared semantic categories. Due to missing of annotations of some classes, we report the mIoU of 16 shared semantic classes for the model pretrained on the Synthia dataset." + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "24094" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.089, + 0.892, + 0.131 + ], + "angle": 0, + "content": "Table 1. Comparison with state-of-the-art methods in terms of mIoU. The best score for each column is highlighted. CS: CityScapes, BDD: BDD100K, MA: Mapillary, IDD: IDD, CC: Cross-City. *: Use an extra augmented sample during adaptation. Avg.: Mean of mIoUs over five target domains." + }, + { + "type": "table", + "bbox": [ + 0.085, + 0.133, + 0.887, + 0.361 + ], + "angle": 0, + "content": "
MethodGTA5→Synthia→GTA5+Synthia→
CSBDDMAIDDCCAvg.CSBDDMAIDDCCAvg.CSBDDMAIDDCCAvg.
Source [42]35.8729.8938.6738.0530.0334.5030.8721.0131.1226.2331.9628.2437.0028.8541.5639.8832.9336.04
Backward-based Methods
TENT [41]37.3031.5338.2938.9630.5935.3334.8916.9933.4626.2331.6828.6539.3925.1937.3239.5132.8434.85
EATA [27]37.0830.6739.3538.7530.2435.2231.3120.5231.5926.4631.9128.3638.4529.3441.6340.3332.9136.53
Backward-free Methods
IN [28]34.2529.6435.0129.823.8730.5129.5319.3321.9222.0828.2424.2237.0928.8136.0230.9928.6332.31
Momentum [33]38.1232.4240.7938.7430.236.0532.8422.5131.1227.2432.2329.4539.6131.7241.7939.8833.1736.66
DUA [25]37.7931.7640.2634.7526.3234.1832.1721.5627.4224.0629.8727.0239.1730.5939.9535.3030.6535.13
SITA* [15]40.6432.9437.8035.6628.1935.2634.6322.5126.6024.6428.1827.7942.6232.2441.2038.8233.2237.62
DIGA (Ours)45.8135.7844.2542.7333.7240.4641.8529.0936.5438.3636.7836.5246.4333.8743.5142.0834.4140.06
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.384, + 0.473, + 0.55 + ], + "angle": 0, + "content": "Implementation Details. Following previous works [3, 15, 25, 41], we use DeepLabV2 [2] as the segmentation model. The ResNet-101 [13] pretrained on ImageNet [8] is used as the backbone. It is worth mentioning that globally consistent parameter sets are used for our DIGA, which achieves consistently good performance in all experiments. Specifically, we set the momentum updating rate \\((\\rho_{P}\\) and \\(\\rho_{BN})\\) both to 0.1. The weights of DAM, SAM, and classifier association \\((\\lambda_{BN},\\lambda_{P}\\) and \\(\\lambda_F)\\) are all set to 0.8. The confidence bar for prototype selection \\(\\mathcal{P}_0\\) is 0.9. All the experiments are conducted with one RTX3090 GPU." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.56, + 0.373, + 0.577 + ], + "angle": 0, + "content": "4.2. Comparison with State of the Art" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.584, + 0.47, + 0.643 + ], + "angle": 0, + "content": "We first compare our method with the state-of-the-art approaches. Generally, the compared methods can be divided into two categories: backward-based methods and backward-free methods." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.644, + 0.471, + 0.901 + ], + "angle": 0, + "content": "Backward-based methods: TENT [41] performs adapting by minimizing the output entropy and updating the learnable parameters of BN layers. As an extension to TENT [41], EATA [27] proposes to skip the high-entropy samples and only leverage reliable samples during model optimization, which can effectively increase testing efficiency. Both of them are initially designed for image classification. We implement them for TTDA-Seg by minimizing the entropy of pixel-level output. For EATA [27], we skip the low-entropy pixels during optimization. Backward-free methods: IN [28] uses instance statistics to replace source ones in BN at each testing step. Momentum [33] utilizes the instance statistics to update BN in a momentum-based manner. DUA [25] proposes a decaying strategy to adaptively control the momentum of BN updating. SITA [15] leverages extra augmented samples to obtain stable instance statistics, which are then mixed with the source statistics." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.384, + 0.892, + 0.476 + ], + "angle": 0, + "content": "To make a fair comparison, we implement all the methods with the same source models. Note that, we report the results of the compared methods by selecting the best parameters for each source-target pair. In contrast, in our method, we only use one parameter setting for all experiments to better meet the real-world applications." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.478, + 0.893, + 0.902 + ], + "angle": 0, + "content": "The following observations can be made from the results reported in Tab. 1. First, backward-based methods can consistently improve the performance when evaluating on CityScapes. However, the improvements on other target domains are limited or even negative. For example, when using Synthia as the source domain, TENT [41] increases the mIoU from \\(30.87\\%\\) to \\(34.89\\%\\) on CityScapes while largely reduces the mIoU from \\(21.01\\%\\) to \\(16.99\\%\\) for BDD100K. This indicates that using self-supervision only may not be a good choice for TTDA-Seg. Second, except for IN [28], the backward-free methods are generally effective on CityScapes and BDD100K while failing to achieve consistent improvements on other datasets, even though we have well-tuned them for each target domain. On the other hand, IN [28] largely reduces the average mIoU due to ignoring the source statistics. Third, the proposed DIGA consistently improves the mIoUs of the source models on all settings and outperforms all the compared methods by a large margin in most cases. Specifically, our DIGA is higher than the best competitor (Momentum [33]) by \\(4.41\\%\\), \\(7.07\\%\\), and \\(3.4\\%\\) in average mIoU for GTA5, Synthia, and GTA5+Synthia settings, respectively. In Fig. 4, we provide the qualitative comparison of different methods. It is clear that our DIGA consistently improves the segmentation results of the source model and outperforms other state-of-the-art methods. The above observations demonstrate the effectiveness and universality of the proposed method for solving TTDA-Seg." + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "24095" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.13, + 0.089, + 0.842, + 0.299 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.312, + 0.301, + 0.655, + 0.314 + ], + "angle": 0, + "content": "Figure 4. Qualitative comparison of segmentation results." + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.33, + 0.47, + 0.385 + ], + "angle": 0, + "content": "Table 2. Ablation study on DIGA. DAM: domain alignment module, SAM: semantic alignment module, Association: classifier association. For the BN branch and Semantic branch, we highlight the best and second best results, respectively. Source: GTA5." + }, + { + "type": "table", + "bbox": [ + 0.079, + 0.386, + 0.47, + 0.54 + ], + "angle": 0, + "content": "
ModulesCSBDDMAIDDCCAvg.
BNHistorical35.8729.8938.6738.0530.0334.50
Instance34.2529.6435.0129.8023.8730.51
DAM39.2633.3940.1137.2330.1236.02
SemanticHistorical38.6329.2537.6441.6732.8836.01
Instance39.1632.2638.6835.0927.9834.63
SAM42.9932.6941.3741.3033.4938.37
Association45.8135.7844.2542.7333.7240.46
" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.56, + 0.231, + 0.575 + ], + "angle": 0, + "content": "4.3. Ablation Study" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.583, + 0.47, + 0.673 + ], + "angle": 0, + "content": "We conduct ablative study to investigate the effectiveness of the components of the proposed DIGA, i.e., domain adaptation module, semantic adaptation module, and classifier association. Experiments are evaluated on five target domains with the source model pretrained on GTA5. Results are reported in Tab. 2." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.674, + 0.471, + 0.902 + ], + "angle": 0, + "content": "Effectiveness of DAM. In the BN branch of Tab. 2, \"Historical\" indicates directly using BN statistics of the source for normalization, which can be regarded as the baseline or source model. \"Instance\" represents using instance statistics for normalization. Two observations can be made. First, the \"Instance\" model produces worse performance than the \"Historical\" model on all target domains, especially on IDD and Cross-City. The average mIoU of \"Instance\" is \\(4.49\\%\\) lower than the \"Historical\". This indicates that using instance statistics only is not suitable for TTDA-Seg. Second, DAM improves the results in most cases and obtains an improvement of \\(1.48\\%\\) in average mIoU over the \"Historical\" model. Specifically, DAM boosts the mIoU by \\(3.39\\%\\) and \\(3.5\\%\\) on CityScapes and BDD100K, respectively. Even when the gap between \"Historical\" and \"Instance\" is too" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.332, + 0.892, + 0.438 + ], + "angle": 0, + "content": "large (e.g., \\(9.25\\%\\) on IDD), our DAM is not deteriorated by the negative impact of \"Instance\" too much and still produces competitive results to the \"Historical\" with a marginal gap of \\(0.82\\%\\). These two observations suggest that our DAM can effectively merge the guidance of instance knowledge into historical statistics to achieve an effective and stable adaptation process." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.443, + 0.893, + 0.837 + ], + "angle": 0, + "content": "Effectiveness of SAM. In the semantic branch, \"Instance\" indicates the instance-specific prototypes calculated by reliable pixels in the current testing image. \"Historical\" represents the historical prototypes. Notice that, the semantic branch is conducted based on DAM, where the features for calculating prototypes are obtained after distribution alignment. We can make the following conclusions. First, the \"Historical\" classifier and the parametric classifier (DAM) achieve a very similar average mIoU. Second, the \"Instance\" classifier obtains lower average mIoU than the \"Historical\" classifier. However, by taking a close look at the results on five target domains, we can find that the \"Instance\" classifier outperforms the \"Historical\" classifier on three datasets (CityScapes, BDD and Mapillary). This indicates that these two non-parametric classifiers have particular merits in particular datasets. Third, SAM clearly outperforms both non-parametric classifiers in average mIoU. Specifically, our SAM surpasses the \"Historical\" classifier by \\(2.36\\%\\) in average mIoU. Fourth, similar to the BN branch, when the gap between \"Historical\" and \"Instance\" classifiers is large, SAM may not bring improvement, e.g., the IDD case. However, our SAM still remains the high performance without influencing by the inferior classifier. The above observations verify the appropriateness of using the prototype classifiers and also the effectiveness of the proposed SAM across different target domains." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.894, + 0.903 + ], + "angle": 0, + "content": "Effectiveness of Classifier Association. With the association of the parametric classifier (outputs of DAM) and the non-parametric classifier (outputs of SAM), the results are consistently improved on all target domains. Specifi" + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.946, + 0.52, + 0.957 + ], + "angle": 0, + "content": "24096" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.096, + 0.094, + 0.465, + 0.27 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.274, + 0.472, + 0.318 + ], + "angle": 0, + "content": "Figure 5. Experiments of continual TTDA-Seg. THe model is pretrained on Synthia [32]. The domain adaptation stream is \"BDD \\(\\rightarrow\\) CC \\(\\rightarrow\\) CS \\(\\rightarrow\\) IDD \\(\\rightarrow\\) MA\" with two rounds." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.344, + 0.47, + 0.406 + ], + "angle": 0, + "content": "cally, the average mIoU is increased by \\(4.44\\%\\) for DAM and \\(2.09\\%\\) for SAM. This validates the effectiveness of leveraging the mutual benefit between parametric and non-parametric classifiers." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.417, + 0.279, + 0.433 + ], + "angle": 0, + "content": "4.4. Continual TTDA-Seg" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.441, + 0.47, + 0.652 + ], + "angle": 0, + "content": "In real-world applications, such as autonomous driving, the environments are ever-changing and complex. To better simulate such practice scenarios, we design a continual TTDA-Seg experiment. Specifically, the dynamic environment is built by sequentially incoming target domains. The domain-stream is \"BDD \\(\\rightarrow\\) CC \\(\\rightarrow\\) CS \\(\\rightarrow\\) IDD \\(\\rightarrow\\) MA\", which is sorted by alphabetical order for simplicity and performed by two rounds. We use the Synthia-pretrained model as the source model and report the mIoU after meeting each target domain. In Fig. 5, we compare our method with TENT [41]. We implement two versions for TENT [41]. TENT-ContinualAdapt: continually adapt the model with the incoming target domains. TENT-SourceAdapt: directly adapt the source-pretrained model on the given domain." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.653, + 0.471, + 0.835 + ], + "angle": 0, + "content": "We can observe that \"TENT-ContinualAdapt\" suffers from significant performance degradation when compared to \"TENT-SourceAdapt\". For example, when testing on the CityScapes dataset, \"TENT-ContinualAdapt\" is \\(19\\%\\) and \\(67\\%\\) lower than \"TENT-SourceAdapt\" in mIoU at the first round and second round, respectively. This phenomenon can also be observed in other domains. This is mainly because that TENT will accumulate the errors during adaptation and thus leads a worse model. Instead, our DIGA does not have the error accumulation problem and consistently performs well on all domains. This further validates the effectiveness of our method in real-world TTDA-Seg." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.847, + 0.27, + 0.863 + ], + "angle": 0, + "content": "4.5. Computational Cost" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.871, + 0.472, + 0.903 + ], + "angle": 0, + "content": "In TTDA-Seg, efficiency is also very important. In Tab. 3, we investigate the computational costs of" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.089, + 0.892, + 0.116 + ], + "angle": 0, + "content": "Table 3. Time and Memory Cost. Highlights indicate the Best, and Second/Third Best results." + }, + { + "type": "table", + "bbox": [ + 0.521, + 0.117, + 0.875, + 0.248 + ], + "angle": 0, + "content": "
Methods\\(T_{Avg}\\)\\(T_{Max}\\)GPU Mem.mIoU
Source-Only134ms141ms3.5GB35.87
TENT [41]411ms425ms14.5GB37.30
EATA [27]235ms490ms15.6GB37.08
Momentum [33]144ms151ms3.5GB37.33
DUA [25]145ms152ms3.6GB37.79
SITA [15]253ms256ms5.6GB40.64
Ours153ms160ms4.0GB45.51
" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.275, + 0.892, + 0.578 + ], + "angle": 0, + "content": "different methods. We conduct experiments on the \"GTA5 \\(\\rightarrow\\) CityScapes\" setting. For the inference time, we report the average time \\( (T_{Avg} / \\mathrm{ms}) \\) and the maximize time \\( (T_{Max} / \\mathrm{ms}) \\) for each testing sample. In addition, the GPU memory cost is also estimated. We can find that the backward-based methods significantly improve the inference time and GPU memory cost. For example, TENT [41] increases the average time from 134ms to 411ms and the memory cost from 3.5GB to 14.5GB. Even though EATA skips the unreliable pixels during optimization and leads to a lower average inference time than TENT, it still introduces large extra computational cost over the source model. Since SITA [15] uses extra augmented image during testing, its computational cost is doubled. Our DIGA and the other two backward-free methods (Momentum [33] and DUA [25]) produce very limited extra computational cost benefiting from their lightweight designs. However, our DIGA significantly surpasses than Momentum [33] and DUA [25] in mIoU. This experiment suggests that our DIGA is an effective and efficient TTDA-Seg method." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.593, + 0.619, + 0.609 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.62, + 0.892, + 0.83 + ], + "angle": 0, + "content": "In this paper, we propose the Dynamically Instance-Guided Adaptation (DIGA) approach for solving TTDA-Seg, which jointly enjoys the effectiveness and efficiency factors. Specifically, DIGA includes two adaptation modules, the distribution adaptation module (DAM) and the semantic adaptation module (SAM), which are both guided by instance-aware information in a non-parametric way. Experiments conducted on five target domains verify that our DIGA effectively can adapt the model at both distribution and semantic levels. We also show that the proposed DIGA achieves state-of-the-art results in TTDA-Seg. In future work, we would like to investigate (1) the learning of adaptive weights in DIGA and (2) the implementation of DIGA in other tasks, e.g., object detection." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.831, + 0.892, + 0.902 + ], + "angle": 0, + "content": "Acknowledgement This work has been supported by the EU H2020 project AI4Media (No. 951911), the PRIN project CREATIVE (Prot. 2020ZSL9F9) and Natural Sciences and Engineering Research Council of Canada (NSERC), Discovery Grants program." + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.519, + 0.958 + ], + "angle": 0, + "content": "24097" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.119, + 0.173, + 0.133 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.144, + 0.469, + 0.184 + ], + "angle": 0, + "content": "[1] Dian Chen, Dequan Wang, Trevor Darrell, and Sayna Ebrahimi. Contrastive test-time adaptation. 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Top: Illustration of test-time domain adaptive semantic segmentation (TTDA-Seg). Bottom: Comparison with different TTDA methods. The proposed DIGA is a holistic method that has the properties of effectiveness (distribution&semantic adaptation and avoid unstable training&error accumulation) and efficiency (backward-free). + +# Abstract + +In this paper, we study the application of Test-time domain adaptation in semantic segmentation (TTDA-Seg) where both efficiency and effectiveness are crucial. Existing methods either have low efficiency (e.g., backward optimization) or ignore semantic adaptation (e.g., distribution alignment). Besides, they would suffer from the accumulated errors caused by unstable optimization and abnormal distributions. To solve these problems, we propose a novel backward-free approach for TTDA-Seg, called Dynamically Instance-Guided Adaptation (DIGA). Our principle is utilizing each instance to dynamically guide its own adaptation in a non-parametric way, which avoids the error accumulation issue and expensive optimizing cost. Specifically, DIGA is composed of a distribution adaptation module (DAM) and a semantic adaptation module (SAM), enabling us to jointly adapt the model in two indispensable aspects. DAM mixes the instance and source BN statistics to + +encourage the model to capture robust representation. SAM combines the historical prototypes with instance-level prototypes to adjust semantic predictions, which can be associated with the parametric classifier to mutually benefit the final results. Extensive experiments evaluated on five target domains demonstrate the effectiveness and efficiency of the proposed method. Our DIGA establishes new state-of-the-art performance in TTDA-Seg. Source code is available at: https://github.com/Waybaba/DIGA. + +# 1. Introduction + +Semantic segmentation (Seg) [3, 40, 45, 46, 49] is a fundamental task in computer vision, which is an important step in the visual-based robot, autonomous driving and etc. Modern deep-learning techniques have achieved impressive success in segmentation. However, one serious drawback of them is that the segmentation models trained on one dataset (source domain) may undergo catastrophic performance degradation when applied to another dataset sam + +pled from a different distribution. This phenomenon will be even more serious under complex and ever-changing contexts, e.g., autonomous driving. + +To solve this well-known problem caused by domain shifts, researchers have devoted great effort to domain generalization (DG) [6,11,18,19,21,30] and domain adaptation (DA) [23,47,47,50]. Specifically, DG aims to learn generalized models with only labeled source data. Traditional DA attempts to adapt the model on the target domain by using both labeled source data and unlabeled target data. However, both learning paradigms have their own disadvantages. The performance of DG is limited especially when evaluated on a domain with a large gap from the source since it does not leverage target data [11]. DA assumes that the unlabeled target data are available in advance and can be chronically exploited to improve target performance. This assumption, however, can not always be satisfied in real-world applications. For example, when driving in a new city, the data are incoming sequentially and we expect the system to dynamically adapt to the ever-changing scenario. + +To meet the real-world applications, [41] introduces the test-time domain adaptation (TTDA), which aims at adapting the model during the testing phase in an online fashion (see Fig. 1 Top). Generally, existing methods can be divided into two categories: backward-based methods [1,22,27,37, 41] and backward-free methods [15,25,28,33]. The former category (see Fig. 1 (a)) focuses on optimizing the parameters of models with self-supervision losses, such as entropy loss [27, 41]. In this way, both distribution adaptation and semantic adaptation can be achieved, which however has the following drawbacks. (1) Low-Efficiency : Due to the requirement of back-propagation, the computation cost will be multiplied, leading to low efficiency. (2) Unstable Optimization & Error Accumulation: Since the gradient is calculated with single sample by weak supervision, the randomness could be high thus leading to unstable optimization. Although this problem can be mitigated in some certain by increasing the testing batch size, it still cannot be solved well. In such cases, the accumulated errors may lead the model to forget the original well-learned knowledge and thus cause performance degradation. + +The second category aims to adapt the model in the distribution level by updating statistics in batch normalization (BN) [25] layers, which is very efficient as it is directly implemented in forward propagation with a light computation cost. Instance normalization [28] (see Fig. 1 (b)) directly replaces the source statistics with those from each instance, which is sensitive to the target variations due to discarding the basic source knowledge and thus is unstable. Mirza et al [25] (see Fig. 1 (c)) study the impacts of updating the historical statistics by instance statistics with fixed momentum or dynamically fluctuating momentum. However, these methods also suffer from the error accumulation is + +![](images/5e0b116703992dc731840b17314624c7c6c6750cb4e0ec3afbcbf0be9e76675c.jpg) +Figure 2. Illustration of the implementation of our DIGA. Given a source model, our DIGA can be readily equipped with only access to the BN layers, classifier head and feature head. + +sue caused by abnormal target distributions as well as the neglect of semantic adaptation, both of which will result in inferior adaptation performance. + +To this end, we propose a holistic approach (see Fig. 1 (d)), called Dynamically Instance-Guided Adaptation (DIGA), for TTDA-Seg, which takes into account both effectiveness and efficiency. The main idea of DIGA is leveraging each instance to dynamically its own adaptation in a non-parametric manner, which is efficient and can largely avoid the error accumulation issue. In addition, our DIGA is implemented in a considerate manner by injecting with distribution adaptation module (DAM) and semantic adaptation module (SAM). Specifically, in DAM, we compute the weighed sum of the source and current statistics in BN layers to adapt target distribution, which enables the model to obtain a more robust representation. In SAM, we build a dynamic non-parametric classifier by mixing the historical prototypes with instance-level prototypes, enabling us to adjust the semantic prediction. In addition, the non-parametric classifier can be associated with the parametric one, which can further benefit the adaptation results. Our contributions can be summarized as follows: + +- Efficiency. We propose a backward-free approach for TTDA-Seg, which can be implemented within one forward propagation with a light computation cost. +- Effectiveness. We introduce a considerate approach to adapt the model in both distribution and semantic aspects. In addition, our method takes the mutual advantage of two types of classifiers to achieve further improvements. +- Usability. Our method is easy to implement and is model-agnostic, which can be readily injected into existing models (see Fig.2). +- Promising Results. We conduct experiments on three source domains and five target domains based on driving benchmarks and show that our method produces new state-of-the-art performance for TTDA-Seg. We also study the continual TTDA-Seg and verify the superiority of our method in this challenging task. + +# 2. Related Work + +Test-time Domain Adaptation (TTDA) aims to adapt models on the target domain only in test time. It is firstly proposed in TTT [37] and has been applied to many fields such as instance tracking [9], object detections [16] and reinforcement learning [12]. The early works (TTT [37] and its extensions [20, 22]) require an extra training process on source data, making it inapplicable when only the source model is available. In this paper, we focus on the more practical Fully Test-time Domain Adaptation setting proposed in [41]. Current fully TTDA methods can be categorized into two main branches: backward-based adaptation and backward-free adaptation. As the pioneer of the self-supervision adaptation methods, TENT [41] proposes to minimize the entropy by updating BN affine parameters during test time. EATA [27] shows that skipping low entropy samples would achieve higher efficiency and performance. Also, an updated regularization term is utilized to alleviate the forgetting problem. [1] introduce an efficient framework by introducing contrastive learning. The problem with these methods is that they cost a long time and large GPU memory due to backpropagation, which largely limited the application for real-time inference. As for the backward-free branch, most of the approaches focus on BN statistics adaptation. IN [28] directly uses batch statistics while Momentum [33] and DUA [25] use running average to update the statistics. This branch is much more efficient while they only work on distribution, ignoring the semantic adaptation, leading to discounted adaptation power. Besides the above two branches, T3A [14] proposes to denoise the classification results in the post-processing stage, where adaptation of the model itself is not well exploited. + +Domain Adaptive for Semantic Segmentation (DASS) aims to bridge the domain gap between the training and testing data. The early works in DASS mainly focus on building adversarial training architectures to learn the domain-invariant features [24, 38, 43]. Complementary modules have been introduced to facilitate the training [24,38,40,43]. Another category exploits the self-training techniques such as entropy minimization [40] and pseudo-labeling [45, 46, 49, 51]. While these approaches require the co-existence of source-target data. Source-free DA (SFDA) is more practical and closer to our setting as they assume the source data is not available during adaptation. [40] proposes to recover source information by utilizing the BN statistics. $\mathrm{MAS}^3$ [17] proposes to store source distribution information as prototypes and then use them during adaptation. [35] uses a multi-head structure to increase the reliability of pseudo-labeling for self-supervised training. Zhao et al. [48] present a special augmentation module to diversify samples with various patch styles at the feature level and then use them for generalization ability improvement. However, these methods can not handle TTDA well. Firstly, + +they do not consider the efficiency problem [17, 35, 40, 48]. Moreover, they often require to visit samples repeatedly in large batch sizes [17, 35, 48]. + +# 3. Methodology + +Problem Definition. In test-time domain adaptation in semantic segmentation (TTDA-Seg), we are given a segmentation model $f_{\theta} : \mathbf{x} \rightarrow y$ pretrained on a source domain $\mathcal{D}_S$ , which will be directly deployed to unseen domains for evaluation. Due to domain shifts, the model $f_{\theta}$ would normally produce a poor performance on unseen testing domains. The goal of TTDA-Seg is to adapt the model by utilizing continuously incoming testing data in an online fashion (see Fig. 1). For example, at each testing step $t$ , the model $f_{\theta}$ receives an instance $\mathbf{x}_t$ and simultaneously performs adaptation as well as produces segmentation prediction $\hat{y}_t$ . At the next step $t + 1$ , the model $f_{\theta}$ will perform adaptation and prediction on instance $\mathbf{x}_{t + 1}$ without the access to previous data $\mathbf{x}_{1 \to t}$ . + +# 3.1. Overview + +In this section, we propose a Dynamically Instance-Guided Adaptation (DIGA) method for TTDA-Seg, which is backward-free and non-parametric. As shown in Fig. 3, our DIGA includes two adaptation modules, the distribution adaptation module (DAM) and the semantic adaptation module (SAM), which are both guided by instance-aware information. Specifically, given a testing sample, we first input it into the source pretrained model and perform distribution alignment by DAM in each BN layer. The distribution alignment is implemented by weighted summing of the source statistics and instance statistics. After this, we apply semantic adaptation at the last feature level by SAM, in which we build a dynamic non-parametric classifier by weighted mixing the historical prototypes with instance-aware prototypes. This allows us to adjust the semantic prediction. Lastly, we obtain the final prediction by taking the mutual advantage between the original parametric classifier and the dynamic non-parametric classifier. + +In Fig. 3 (a-g), we show an illustration of how our DIGA helps to adapt the model with the guidance of instance-aware information. (a-d) Due to the large domain shifts (e.g., light variations), the segmentation results on the target sample might be poor. After distribution alignment by DAM, the segmentation results could be improved, especially the instances that are similar to the source (e). However, there might still exist poorly-recognized pixels that are very different from the source. Our DAM further leverages the reliable pixels to guide the predictions of other pixels in a non-parametric way (f), enabling us to achieve more accurate results (g). + +![](images/f73e66aaab9564c9c19f6cd691c3c7f848179fc3875558faab130195bda7d43f.jpg) +Figure 3. Illustration of the proposed DIGA. (a-d) The source model commonly produces poor results on unseen targets, due to significant domain shifts, such as light variation. To solve this problem, our DIGA is proposed to adapt the model in an online fashion, which consists of a distribution adaptation module (DAM) and a semantic adaptation module (SAM). Both modules are guided by instance-aware information (statistics for DAM and prototypes for SAM). The DAM is implemented in BN layers for distribution alignment (e). The SAM is implemented in the feature level for semantic alignment (f-g). The final prediction is obtained by the fusion of original classifier and non-parametric classifier built by SAM. + +![](images/67bbf0ac011f1b3b94f45e6e7fb1685c2633913a5a8e7d95817016891504f82b.jpg) + +![](images/1a7a34d00ab664f3e0147081bdbb54850faefcf98bb0c4fc7b9f37b58596735a.jpg) + +![](images/3b494624f605214a05932aeab2b429ba0687d5a9173cd6938b0322dc3dbce088.jpg) + +![](images/0abf06c3cccf5ce04bc87852bdfe937a97480a99e98d76beca79d75ff1d9151a.jpg) + +# 3.2. Distribution Adaptation Module (DAM) + +The most common way to adapt the distribution is based on adversarial training [10, 19, 23] and minimization of distribution gap metrics [4, 36]. However, these methods are not suitable for TTDA due to limited available training data and the high-cost backpropagation. Recent works [25, 28, 33] show that the static mismatch between domains in the Batch Normalization (BN) layers is a major reason that causes the performance degradation in cross-domain testing. We thus first revisit the mechanism of BN. Specifically, for each BN layer, given the input feature representation $F$ , the corresponding output is given by: + +$$ +B N (F) = \gamma \frac {F - \mathbb {E} [ F ]}{\sqrt {\operatorname {V a r} [ F ]}} + \beta , \tag {1} +$$ + +where $\gamma$ and $\beta$ are trainable parameters for scaling and shifting. $\mathbb{E}[F]$ and $Var[F]$ are expected value and variance of input feature $F$ . In practice, due to the batch-wise training process, their values are calculated by running mean [42] during training as follows: + +$$ +\bar {u} _ {t} ^ {S} = \left(1 - \rho_ {B N}\right) \cdot \bar {\mu} _ {t - 1} ^ {S} + \rho_ {B N} \cdot \mu_ {t - 1} ^ {S}, \tag {2} +$$ + +$$ +\left(\bar {\sigma} _ {t} ^ {S}\right) ^ {2} = \left(1 - \rho_ {B N}\right) \cdot \left(\bar {\sigma} _ {t - 1} ^ {S}\right) ^ {2} + \rho_ {B N} \cdot \left(\sigma_ {t - 1} ^ {S}\right) ^ {2}, +$$ + +where $\bar{\mu}_t^s$ and $\bar{\sigma}_t^s$ are serving as estimation for $\mathbb{E}[F]$ and $Var[F]$ of source domain respectively. + +Out of the motivation that the amount of training sample is usually much larger than the testing batch and thus more stable, the last value $\bar{\mu}_t^s$ , $\bar{\sigma}_t^s$ would be frozen and serve as the estimation for $\mathbb{E}[F]$ and $Var[F]$ for the test data during the test phase. + +However, it has been shown that when applied to a different environment, the source statistics can hamper performance significantly. To solve this problem, DUA [42] proposes to adapt the statistics $\gamma, \beta$ of BN layers to the target + +domain with a dynamic learning module. Despite the efficiency, its performance is still not satisfactory. One possible reason is that the updating rate is usually very small so that instance-level information is not fully considered during each instance evaluation. + +Different from [25, 33], instead of updating the $\gamma, \beta$ , the proposed Distribution Adaptation Module (DAM) dynamically merges the source and instance BN statistics to constitute the estimation $\bar{\mu}_t^T$ and $(\bar{\sigma}_t^T)^2$ for $\mathbb{E}[F]$ , $Var[F]$ as follows: + +$$ +\bar {\mu} _ {t} ^ {T} = \lambda_ {B N} \cdot \bar {\mu} ^ {S} + (1 - \lambda_ {B N}) \cdot \mu_ {t} ^ {T}, +$$ + +$$ +\left(\bar {\sigma} _ {t} ^ {T}\right) ^ {2} = \lambda_ {B N} \cdot \left(\bar {\sigma} ^ {S}\right) ^ {2} + \left(1 - \lambda_ {B N}\right) \cdot \left(\sigma_ {t} ^ {T}\right) ^ {2}, \tag {3} +$$ + +where $\mu_t^T$ and $(\sigma_t^T)^2$ are the mean and variance calculated with the $t$ -th instance during testing. + +# 3.3. Semantic Adaptation Module (SAM) + +The proposed DAM is a category-agnostic since it only aligns the distribution of feature maps globally. However, category-specific is also important to segmentation adaptation because the distribution of each category varies a lot even in the same image. Hence, we argue that it is also important to implement semantic adaptation in TTDA-Seg. To achieve this, two straightforward methods are entropy maximization [41] and pseudo-labeling [22]. However, both of them require gradient-based backpropagation and thus limit the testing efficiency. Inspired by the prototype-based methods in few-shot learning [34] and domain adaptation [29,45], we introduce the semantic adaptation module (SAM) for category-specific adaptation. + +As shown in Sec. 3.1, even though distribution alignment is implemented by DAM, the model still produces wrong predictions for pixels that are very different from the source. Fortunately, we could observe that pixels of the same ob + +ject share several of the same properties, e.g., the appearance within a car, the same texture color within a road, the same outfit within a person, the light intensity within an image, etc. Motivated by this, we propose to leverage the similarities between pixels to further guide the recognition of wrongly recognized pixels. To this end, we propose the semantic adaptation module (SAM) to adjust the semantic predictions by dynamic instance-aware prototypes. + +The segmentation model $f_{\theta}$ can be separated into two learnable parts: i) an encoder $h_{\phi}$ for dense visual feature extraction which maps each pixel $\mathbf{x}^{(h,w)}$ to feature $\mathbf{z}^{(h,w)} \in \mathbb{R}^D$ , and ii) a classifier $g_{\psi}$ for following prediction which maps $\mathbf{z}^{(h,w)}$ to a distribution $\hat{p}^{(h,w)}(c|\mathbf{x})$ over $C$ classes. Formally, it can be denoted as: + +$$ +\mathbf {z} _ {t} ^ {(h, w)} = h _ {\phi} ^ {(h, w)} \left(\mathbf {x} _ {t}\right), \tag {4} +$$ + +$$ +\hat {p} ^ {(h, w)} (c | \mathbf {x} _ {t}) = g _ {\psi} ^ {(h, w)} (\mathbf {z} _ {t}). \tag {5} +$$ + +The value of logits indicates the confidence of the corresponding classes it would belong to. Thus, the largest value $\max_c\hat{p}_{t,c}^{(h,w)}$ of the prediction distribution can be considered as the confidence of the prediction for one pixel. For one input image $\mathbf{x}_t$ , we select pixels whose confidences are larger than $\mathcal{P}_0$ to calculate the centroids of each class in feature space, which are called as instance-aware prototypes $\mathbf{q}_t$ and can be formulated as follows: + +$$ +\mathbf {q} _ {t} ^ {c} = \frac {\sum^ {H , W} \mathbf {z} _ {t} ^ {(h , w)} \cdot \mathbb {I} \left(c _ {t} ^ {(h , w)} = c , \max _ {c} \hat {p} _ {t , c} ^ {(h , w)} \geq \mathcal {P} _ {0}\right)}{\sum^ {H , W} \mathbb {I} \left(c _ {t} ^ {(h , w)} = c , \max _ {c} \hat {p} _ {t , c} ^ {(h , w)} \geq \mathcal {P} _ {0}\right)}. \tag {6} +$$ + +Using instance-aware prototypes only may produce unstable predictions due to the instance variance. To make the prediction more stable, we additionally calculate the moving average of the prototypes of different instances for each category, which are called historical prototypes. + +$$ +\bar {\mathbf {q}} _ {t} ^ {c} = \rho_ {P} \cdot \bar {\mathbf {q}} _ {t - 1} ^ {c} + (1 - \rho_ {P}) \mathbf {q} _ {t} ^ {c}, \text {w i t h} \bar {\mathbf {q}} _ {0} ^ {c} = \mathbf {q} _ {0} ^ {c}. \tag {7} +$$ + +Since the historical prototypes are calculated by averaging prototypes from a large number of target instances, they are more stable than instance-aware prototypes. + +Given the instance-aware prototypes, we can obtain the instance-aware prediction for each class $p^{(h,w)}(c|\mathbf{x}_t,\mathbf{q})$ by: + +$$ +p ^ {(h, w)} \left(c \mid \mathbf {x} _ {t}, \mathbf {q}\right) = \frac {\exp \left(- \langle \mathbf {z} ^ {(h , w)} , \mathbf {q} _ {c} \rangle\right)}{\sum_ {c ^ {\prime} = 1} ^ {C} \exp \left(- \langle \mathbf {z} ^ {(h , w)}, \mathbf {q} _ {c ^ {\prime}} \rangle\right)}. \tag {8} +$$ + +The historical prediction $p^{(h,w)}(c|\mathbf{x}_t,\bar{\mathbf{q}})$ could be obtained in a similar way. + +By combing the predictions of the two types of prototypes, we form a dynamic non-parametric classifier and the predictions are formulated as: + +$$ +\begin{array}{l} \tilde {p} ^ {(h, w)} \left(c \mid \mathbf {x} _ {t}\right) = \lambda_ {P} \cdot p ^ {(h, w)} \left(c \mid \mathbf {x} _ {t}, \bar {\mathbf {q}}\right) \tag {9} \\ + (1 - \lambda_ {P}) \cdot p ^ {(h, w)} (c | \mathbf {x} _ {t}, \mathbf {q}), \\ \end{array} +$$ + +# Algorithm 1 DIGA (Testing Phase) + +Input: Model $f_{\theta}$ , target testing sample $\mathbf{x}_t$ + +Output: Prediction of $\mathbf{x}_t$ + +1. Produce feature $\mathbf{z}_t$ and prediction $\hat{p}_t(\mathbf{x}_t)$ with distribution alignment of DAM (Eq. 3). +2. Calculate instance-aware prototypes $\mathbf{q}_t$ (Eq. 6). +3. Calculate historical prototypes $\bar{\mathbf{q}}_t$ (Eq. 7). +4. Calculate non-parametric predictions $\tilde{p}_t(\mathbf{x}_t)$ with SAM (Eq. 9). +5. Obtain final prediction $p(\mathbf{x}_t)$ by weighed fusion of $\hat{p}_t(\mathbf{x}_t)$ and $\tilde{p}_t(\mathbf{x}_t)$ (Eq. 10). + +Return: $p(\mathbf{x}_t)$ + +where $\lambda_{P}$ controls the importance of two types of prototypes. + +# 3.4. Classifier Association + +To this end, we could have two types of predictions: one from the original parametric classifier $(\hat{p})$ and one from the introduced non-parametric prototype classifier $(\tilde{p})$ . To leverage the mutual benefit between them, we obtain the final prediction by weighted sum of them, formulated as: + +$$ +p ^ {(h, w)} = \lambda_ {F} \cdot \tilde {p} ^ {(h, w)} (c | \mathbf {x} _ {t}) + (1 - \lambda_ {F}) \hat {p} ^ {(h, w)} (c | \mathbf {x} _ {t}), \tag {10} +$$ + +where $\lambda_F$ balances the importance of two classifiers. The overall process of DIGA is shown in Alg. 1. + +# 4. Experiment + +# 4.1. Experimental Setup + +Datasets. Following the previous works [3, 15, 40], we evaluate our method on sim2real scenarios. Specifically, for the source model, we pretrain it with three different source domains: GTA5 [31], Synthia [31], and GTA5+Synthia. GTA5 provides 24,971 images from video games with 19 semantic classes. Synthia includes 12,000 simulated images with 16 semantic classes. GTA5+Synthia is the combination of GTA5 and Synthia datasets. Performance are evaluated on five target domains: Cityscapes [7], BDD-100K [44], Mapillary [26], IDD [39], Cross-City [5]. We test the results on the validation sets, where the number of samples is \{500, 1,000, 2,000, 100, and 400\} for {Cityscapes, BDD-100K, Mapillary, IDD, Cross-City} respectively. + +Evaluation. The mean intersection-over-union (mIoU) is used as the evaluation metric. As in [3,40], for source models pretrained on GTA5 and GTA5+Synthia, we report the mIoU of 19 shared semantic categories. Due to missing of annotations of some classes, we report the mIoU of 16 shared semantic classes for the model pretrained on the Synthia dataset. + +Table 1. Comparison with state-of-the-art methods in terms of mIoU. The best score for each column is highlighted. CS: CityScapes, BDD: BDD100K, MA: Mapillary, IDD: IDD, CC: Cross-City. *: Use an extra augmented sample during adaptation. Avg.: Mean of mIoUs over five target domains. + +
MethodGTA5→Synthia→GTA5+Synthia→
CSBDDMAIDDCCAvg.CSBDDMAIDDCCAvg.CSBDDMAIDDCCAvg.
Source [42]35.8729.8938.6738.0530.0334.5030.8721.0131.1226.2331.9628.2437.0028.8541.5639.8832.9336.04
Backward-based Methods
TENT [41]37.3031.5338.2938.9630.5935.3334.8916.9933.4626.2331.6828.6539.3925.1937.3239.5132.8434.85
EATA [27]37.0830.6739.3538.7530.2435.2231.3120.5231.5926.4631.9128.3638.4529.3441.6340.3332.9136.53
Backward-free Methods
IN [28]34.2529.6435.0129.823.8730.5129.5319.3321.9222.0828.2424.2237.0928.8136.0230.9928.6332.31
Momentum [33]38.1232.4240.7938.7430.236.0532.8422.5131.1227.2432.2329.4539.6131.7241.7939.8833.1736.66
DUA [25]37.7931.7640.2634.7526.3234.1832.1721.5627.4224.0629.8727.0239.1730.5939.9535.3030.6535.13
SITA* [15]40.6432.9437.8035.6628.1935.2634.6322.5126.6024.6428.1827.7942.6232.2441.2038.8233.2237.62
DIGA (Ours)45.8135.7844.2542.7333.7240.4641.8529.0936.5438.3636.7836.5246.4333.8743.5142.0834.4140.06
+ +Implementation Details. Following previous works [3, 15, 25, 41], we use DeepLabV2 [2] as the segmentation model. The ResNet-101 [13] pretrained on ImageNet [8] is used as the backbone. It is worth mentioning that globally consistent parameter sets are used for our DIGA, which achieves consistently good performance in all experiments. Specifically, we set the momentum updating rate $(\rho_{P}$ and $\rho_{BN})$ both to 0.1. The weights of DAM, SAM, and classifier association $(\lambda_{BN},\lambda_{P}$ and $\lambda_F)$ are all set to 0.8. The confidence bar for prototype selection $\mathcal{P}_0$ is 0.9. All the experiments are conducted with one RTX3090 GPU. + +# 4.2. Comparison with State of the Art + +We first compare our method with the state-of-the-art approaches. Generally, the compared methods can be divided into two categories: backward-based methods and backward-free methods. + +Backward-based methods: TENT [41] performs adapting by minimizing the output entropy and updating the learnable parameters of BN layers. As an extension to TENT [41], EATA [27] proposes to skip the high-entropy samples and only leverage reliable samples during model optimization, which can effectively increase testing efficiency. Both of them are initially designed for image classification. We implement them for TTDA-Seg by minimizing the entropy of pixel-level output. For EATA [27], we skip the low-entropy pixels during optimization. Backward-free methods: IN [28] uses instance statistics to replace source ones in BN at each testing step. Momentum [33] utilizes the instance statistics to update BN in a momentum-based manner. DUA [25] proposes a decaying strategy to adaptively control the momentum of BN updating. SITA [15] leverages extra augmented samples to obtain stable instance statistics, which are then mixed with the source statistics. + +To make a fair comparison, we implement all the methods with the same source models. Note that, we report the results of the compared methods by selecting the best parameters for each source-target pair. In contrast, in our method, we only use one parameter setting for all experiments to better meet the real-world applications. + +The following observations can be made from the results reported in Tab. 1. First, backward-based methods can consistently improve the performance when evaluating on CityScapes. However, the improvements on other target domains are limited or even negative. For example, when using Synthia as the source domain, TENT [41] increases the mIoU from $30.87\%$ to $34.89\%$ on CityScapes while largely reduces the mIoU from $21.01\%$ to $16.99\%$ for BDD100K. This indicates that using self-supervision only may not be a good choice for TTDA-Seg. Second, except for IN [28], the backward-free methods are generally effective on CityScapes and BDD100K while failing to achieve consistent improvements on other datasets, even though we have well-tuned them for each target domain. On the other hand, IN [28] largely reduces the average mIoU due to ignoring the source statistics. Third, the proposed DIGA consistently improves the mIoUs of the source models on all settings and outperforms all the compared methods by a large margin in most cases. Specifically, our DIGA is higher than the best competitor (Momentum [33]) by $4.41\%$ , $7.07\%$ , and $3.4\%$ in average mIoU for GTA5, Synthia, and GTA5+Synthia settings, respectively. In Fig. 4, we provide the qualitative comparison of different methods. It is clear that our DIGA consistently improves the segmentation results of the source model and outperforms other state-of-the-art methods. The above observations demonstrate the effectiveness and universality of the proposed method for solving TTDA-Seg. + +![](images/b2bc63e91d61c69fe4119ef427374d706a091b2f2bc817d123a57bc44e5f4ffc.jpg) +Figure 4. Qualitative comparison of segmentation results. + +Table 2. Ablation study on DIGA. DAM: domain alignment module, SAM: semantic alignment module, Association: classifier association. For the BN branch and Semantic branch, we highlight the best and second best results, respectively. Source: GTA5. + +
ModulesCSBDDMAIDDCCAvg.
BNHistorical35.8729.8938.6738.0530.0334.50
Instance34.2529.6435.0129.8023.8730.51
DAM39.2633.3940.1137.2330.1236.02
SemanticHistorical38.6329.2537.6441.6732.8836.01
Instance39.1632.2638.6835.0927.9834.63
SAM42.9932.6941.3741.3033.4938.37
Association45.8135.7844.2542.7333.7240.46
+ +# 4.3. Ablation Study + +We conduct ablative study to investigate the effectiveness of the components of the proposed DIGA, i.e., domain adaptation module, semantic adaptation module, and classifier association. Experiments are evaluated on five target domains with the source model pretrained on GTA5. Results are reported in Tab. 2. + +Effectiveness of DAM. In the BN branch of Tab. 2, "Historical" indicates directly using BN statistics of the source for normalization, which can be regarded as the baseline or source model. "Instance" represents using instance statistics for normalization. Two observations can be made. First, the "Instance" model produces worse performance than the "Historical" model on all target domains, especially on IDD and Cross-City. The average mIoU of "Instance" is $4.49\%$ lower than the "Historical". This indicates that using instance statistics only is not suitable for TTDA-Seg. Second, DAM improves the results in most cases and obtains an improvement of $1.48\%$ in average mIoU over the "Historical" model. Specifically, DAM boosts the mIoU by $3.39\%$ and $3.5\%$ on CityScapes and BDD100K, respectively. Even when the gap between "Historical" and "Instance" is too + +large (e.g., $9.25\%$ on IDD), our DAM is not deteriorated by the negative impact of "Instance" too much and still produces competitive results to the "Historical" with a marginal gap of $0.82\%$ . These two observations suggest that our DAM can effectively merge the guidance of instance knowledge into historical statistics to achieve an effective and stable adaptation process. + +Effectiveness of SAM. In the semantic branch, "Instance" indicates the instance-specific prototypes calculated by reliable pixels in the current testing image. "Historical" represents the historical prototypes. Notice that, the semantic branch is conducted based on DAM, where the features for calculating prototypes are obtained after distribution alignment. We can make the following conclusions. First, the "Historical" classifier and the parametric classifier (DAM) achieve a very similar average mIoU. Second, the "Instance" classifier obtains lower average mIoU than the "Historical" classifier. However, by taking a close look at the results on five target domains, we can find that the "Instance" classifier outperforms the "Historical" classifier on three datasets (CityScapes, BDD and Mapillary). This indicates that these two non-parametric classifiers have particular merits in particular datasets. Third, SAM clearly outperforms both non-parametric classifiers in average mIoU. Specifically, our SAM surpasses the "Historical" classifier by $2.36\%$ in average mIoU. Fourth, similar to the BN branch, when the gap between "Historical" and "Instance" classifiers is large, SAM may not bring improvement, e.g., the IDD case. However, our SAM still remains the high performance without influencing by the inferior classifier. The above observations verify the appropriateness of using the prototype classifiers and also the effectiveness of the proposed SAM across different target domains. + +Effectiveness of Classifier Association. With the association of the parametric classifier (outputs of DAM) and the non-parametric classifier (outputs of SAM), the results are consistently improved on all target domains. Specifi + +![](images/c0492f85a65b467e6e4e1a9aaceb680c5e13079d166e5635c369b0dab7ea2db4.jpg) +Figure 5. Experiments of continual TTDA-Seg. THe model is pretrained on Synthia [32]. The domain adaptation stream is "BDD $\rightarrow$ CC $\rightarrow$ CS $\rightarrow$ IDD $\rightarrow$ MA" with two rounds. + +cally, the average mIoU is increased by $4.44\%$ for DAM and $2.09\%$ for SAM. This validates the effectiveness of leveraging the mutual benefit between parametric and non-parametric classifiers. + +# 4.4. Continual TTDA-Seg + +In real-world applications, such as autonomous driving, the environments are ever-changing and complex. To better simulate such practice scenarios, we design a continual TTDA-Seg experiment. Specifically, the dynamic environment is built by sequentially incoming target domains. The domain-stream is "BDD $\rightarrow$ CC $\rightarrow$ CS $\rightarrow$ IDD $\rightarrow$ MA", which is sorted by alphabetical order for simplicity and performed by two rounds. We use the Synthia-pretrained model as the source model and report the mIoU after meeting each target domain. In Fig. 5, we compare our method with TENT [41]. We implement two versions for TENT [41]. TENT-ContinualAdapt: continually adapt the model with the incoming target domains. TENT-SourceAdapt: directly adapt the source-pretrained model on the given domain. + +We can observe that "TENT-ContinualAdapt" suffers from significant performance degradation when compared to "TENT-SourceAdapt". For example, when testing on the CityScapes dataset, "TENT-ContinualAdapt" is $19\%$ and $67\%$ lower than "TENT-SourceAdapt" in mIoU at the first round and second round, respectively. This phenomenon can also be observed in other domains. This is mainly because that TENT will accumulate the errors during adaptation and thus leads a worse model. Instead, our DIGA does not have the error accumulation problem and consistently performs well on all domains. This further validates the effectiveness of our method in real-world TTDA-Seg. + +# 4.5. Computational Cost + +In TTDA-Seg, efficiency is also very important. In Tab. 3, we investigate the computational costs of + +Table 3. Time and Memory Cost. Highlights indicate the Best, and Second/Third Best results. + +
Methods\(T_{Avg}\)\(T_{Max}\)GPU Mem.mIoU
Source-Only134ms141ms3.5GB35.87
TENT [41]411ms425ms14.5GB37.30
EATA [27]235ms490ms15.6GB37.08
Momentum [33]144ms151ms3.5GB37.33
DUA [25]145ms152ms3.6GB37.79
SITA [15]253ms256ms5.6GB40.64
Ours153ms160ms4.0GB45.51
+ +different methods. We conduct experiments on the "GTA5 $\rightarrow$ CityScapes" setting. For the inference time, we report the average time $(T_{Avg} / \mathrm{ms})$ and the maximize time $(T_{Max} / \mathrm{ms})$ for each testing sample. In addition, the GPU memory cost is also estimated. We can find that the backward-based methods significantly improve the inference time and GPU memory cost. For example, TENT [41] increases the average time from 134ms to 411ms and the memory cost from 3.5GB to 14.5GB. Even though EATA skips the unreliable pixels during optimization and leads to a lower average inference time than TENT, it still introduces large extra computational cost over the source model. Since SITA [15] uses extra augmented image during testing, its computational cost is doubled. Our DIGA and the other two backward-free methods (Momentum [33] and DUA [25]) produce very limited extra computational cost benefiting from their lightweight designs. However, our DIGA significantly surpasses than Momentum [33] and DUA [25] in mIoU. This experiment suggests that our DIGA is an effective and efficient TTDA-Seg method. + +# 5. Conclusion + +In this paper, we propose the Dynamically Instance-Guided Adaptation (DIGA) approach for solving TTDA-Seg, which jointly enjoys the effectiveness and efficiency factors. Specifically, DIGA includes two adaptation modules, the distribution adaptation module (DAM) and the semantic adaptation module (SAM), which are both guided by instance-aware information in a non-parametric way. Experiments conducted on five target domains verify that our DIGA effectively can adapt the model at both distribution and semantic levels. We also show that the proposed DIGA achieves state-of-the-art results in TTDA-Seg. In future work, we would like to investigate (1) the learning of adaptive weights in DIGA and (2) the implementation of DIGA in other tasks, e.g., object detection. + +Acknowledgement This work has been supported by the EU H2020 project AI4Media (No. 951911), the PRIN project CREATIVE (Prot. 2020ZSL9F9) and Natural Sciences and Engineering Research Council of Canada (NSERC), Discovery Grants program. + +# References + +[1] Dian Chen, Dequan Wang, Trevor Darrell, and Sayna Ebrahimi. Contrastive test-time adaptation. In CVPR, 2022. 2, 3 +[2] Liang-Chieh Chen, George Papandreou, Iasonas Kokkinos, Kevin Murphy, and Alan L Yuille. Deeplab: Semantic image segmentation with deep convolutional nets, atrous convolution, and fully connected crfs. PAMI, 2017. 6 +[3] Minghao Chen, Hongyang Xue, and Deng Cai. Domain adaptation for semantic segmentation with maximum squares loss. In ICCV, 2019. 1, 5, 6 +[4] Qingchao Chen and Yang Liu. 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In ICLR, 2021. 4, 6 +[43] Haoran Wang, Tong Shen, Wei Zhang, Ling-Yu Duan, and Tao Mei. Classes matter: A fine-grained adversarial approach to cross-domain semantic segmentation. In ECCV, 2020. 3 +[44] Fisher Yu, Haofeng Chen, Xin Wang, Wenqi Xian, Yingying Chen, Fangchen Liu, Vashisht Madhavan, and Trevor Darryll. Bdd100k: A diverse driving dataset for heterogeneous multitask learning. In CVPR, 2020. 5 +[45] Pan Zhang, Bo Zhang, Ting Zhang, Dong Chen, Yong Wang, and Fang Wen. Prototypical pseudo label denoising and target structure learning for domain adaptive semantic segmentation. In CVPR, 2021. 1, 3, 4 +[46] Qiming Zhang, Jing Zhang, Wei Liu, and Dacheng Tao. Category anchor-guided unsupervised domain adaptation for semantic segmentation. NeurIPS, 2019. 1, 3 +[47] Sicheng Zhao, Bo Li, Xiangyu Yue, Yang Gu, Pengfei Xu, Runbo Hu, Hua Chai, and Kurt Keutzer. Multi-source domain adaptation for semantic segmentation. NeurIPS, 2019. 2 +[48] Yuyang Zhao, Zhun Zhong, Zhiming Luo, Gim Hee Lee, and Nicu Sebe. Source-free open compound domain adaptation in semantic segmentation. TCSVT, 2022. 3 + +[49] Zhedong Zheng and Yi Yang. Rectifying pseudo label learning via uncertainty estimation for domain adaptive semantic segmentation. IJCV, 2021. 1, 3 +[50] Yang Zou, Zhiding Yu, BVK Kumar, and Jinsong Wang. Unsupervised domain adaptation for semantic segmentation via class-balanced self-training. In ECCV, 2018. 2 +[51] Yang Zou, Zhiding Yu, Xiaofeng Liu, BVK Kumar, and Jinsong Wang. Confidence regularized self-training. In ICCV, 2019. 3 \ No newline at end of file diff --git a/2023/Dynamically Instance-Guided Adaptation_ A Backward-Free Approach for Test-Time Domain Adaptive Semantic Segmentation/images.zip b/2023/Dynamically Instance-Guided Adaptation_ A Backward-Free Approach for Test-Time Domain Adaptive Semantic Segmentation/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..94e2243503f123620092b753766afb3b9d9b266d --- /dev/null +++ b/2023/Dynamically Instance-Guided Adaptation_ A Backward-Free Approach for Test-Time Domain Adaptive Semantic Segmentation/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:8a8e5d7342e00855df692b55565e8f253822f8539e0131fa9f63aa32761c995d +size 666374 diff --git a/2023/Dynamically Instance-Guided Adaptation_ A Backward-Free Approach for Test-Time Domain Adaptive Semantic Segmentation/layout.json b/2023/Dynamically Instance-Guided Adaptation_ A Backward-Free Approach for Test-Time Domain Adaptive Semantic Segmentation/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..d436a1472dfd27b7b0aeb30d234a84cf11a8170d --- /dev/null +++ b/2023/Dynamically Instance-Guided Adaptation_ A Backward-Free Approach for Test-Time Domain Adaptive Semantic Segmentation/layout.json @@ -0,0 +1,8525 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 67, + 103, + 526, + 140 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 67, + 103, + 526, + 140 + ], + "spans": [ + { + "bbox": [ + 67, + 103, + 526, + 140 + ], + "type": "text", + "content": "Dynamically Instance-Guided Adaptation: A Backward-free Approach for Test-Time Domain Adaptive Semantic Segmentation" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 67, + 160, + 525, + 190 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 67, + 160, + 525, + 190 + ], + "spans": [ + { + "bbox": [ + 67, + 160, + 525, + 190 + ], + "type": "text", + "content": "Wei Wang" + }, + { + "bbox": [ + 67, + 160, + 525, + 190 + ], + "type": "inline_equation", + "content": "^{1}" + }, + { + "bbox": [ + 67, + 160, + 525, + 190 + ], + "type": "text", + "content": ", Zhun Zhong" + }, + { + "bbox": [ + 67, + 160, + 525, + 190 + ], + "type": "inline_equation", + "content": "^{2}" + }, + { + "bbox": [ + 67, + 160, + 525, + 190 + ], + "type": "text", + "content": ", Weijie Wang" + }, + { + "bbox": [ + 67, + 160, + 525, + 190 + ], + "type": "inline_equation", + "content": "^{2}" + }, + { + "bbox": [ + 67, + 160, + 525, + 190 + ], + "type": "text", + "content": ", Xi Chen" + }, + { + "bbox": [ + 67, + 160, + 525, + 190 + ], + "type": "inline_equation", + "content": "^{3}" + }, + { + "bbox": [ + 67, + 160, + 525, + 190 + ], + "type": "text", + "content": ", Charles Ling" + }, + { + "bbox": [ + 67, + 160, + 525, + 190 + ], + "type": "inline_equation", + "content": "^{1}" + }, + { + "bbox": [ + 67, + 160, + 525, + 190 + ], + "type": "text", + "content": ", Boyu Wang" + }, + { + "bbox": [ + 67, + 160, + 525, + 190 + ], + "type": "inline_equation", + "content": "^{1*}" + }, + { + "bbox": [ + 67, + 160, + 525, + 190 + ], + "type": "text", + "content": ", Nicu Sebe" + }, + { + "bbox": [ + 67, + 160, + 525, + 190 + ], + "type": "inline_equation", + "content": "^{2}" + }, + { + "bbox": [ + 67, + 160, + 525, + 190 + ], + "type": "inline_equation", + "content": "^{1}" + }, + { + "bbox": [ + 67, + 160, + 525, + 190 + ], + "type": "text", + "content": "Western University " + }, + { + "bbox": [ + 67, + 160, + 525, + 190 + ], + "type": "inline_equation", + "content": "^{2}" + }, + { + "bbox": [ + 67, + 160, + 525, + 190 + ], + "type": "text", + "content": "University of Trento " + }, + { + "bbox": [ + 67, + 160, + 525, + 190 + ], + "type": "inline_equation", + "content": "^{3}" + }, + { + "bbox": [ + 67, + 160, + 525, + 190 + ], + "type": "text", + "content": "Huawei Noah's Ark Lab" + } + ] + } + ], + "index": 3 + }, + { + "type": "image", + "bbox": [ + 55, + 202, + 545, + 421 + ], + "blocks": [ + { + "bbox": [ + 55, + 202, + 545, + 421 + ], + "lines": [ + { + "bbox": [ + 55, + 202, + 545, + 421 + ], + "spans": [ + { + "bbox": [ + 55, + 202, + 545, + 421 + ], + "type": "image", + "image_path": "ff8531033168e900ef0eb98e27c170abe9809915ab5b4aadcd0737d6ab6d3197.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 421, + 547, + 453 + ], + "lines": [ + { + "bbox": [ + 46, + 421, + 547, + 453 + ], + "spans": [ + { + "bbox": [ + 46, + 421, + 547, + 453 + ], + "type": "text", + "content": "Figure 1. Top: Illustration of test-time domain adaptive semantic segmentation (TTDA-Seg). Bottom: Comparison with different TTDA methods. The proposed DIGA is a holistic method that has the properties of effectiveness (distribution&semantic adaptation and avoid unstable training&error accumulation) and efficiency (backward-free)." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "bbox": [ + 143, + 465, + 192, + 477 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 465, + 192, + 477 + ], + "spans": [ + { + "bbox": [ + 143, + 465, + 192, + 477 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 491, + 290, + 694 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 491, + 290, + 694 + ], + "spans": [ + { + "bbox": [ + 46, + 491, + 290, + 694 + ], + "type": "text", + "content": "In this paper, we study the application of Test-time domain adaptation in semantic segmentation (TTDA-Seg) where both efficiency and effectiveness are crucial. Existing methods either have low efficiency (e.g., backward optimization) or ignore semantic adaptation (e.g., distribution alignment). Besides, they would suffer from the accumulated errors caused by unstable optimization and abnormal distributions. To solve these problems, we propose a novel backward-free approach for TTDA-Seg, called Dynamically Instance-Guided Adaptation (DIGA). Our principle is utilizing each instance to dynamically guide its own adaptation in a non-parametric way, which avoids the error accumulation issue and expensive optimizing cost. Specifically, DIGA is composed of a distribution adaptation module (DAM) and a semantic adaptation module (SAM), enabling us to jointly adapt the model in two indispensable aspects. DAM mixes the instance and source BN statistics to" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 467, + 547, + 574 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 467, + 547, + 574 + ], + "spans": [ + { + "bbox": [ + 304, + 467, + 547, + 574 + ], + "type": "text", + "content": "encourage the model to capture robust representation. SAM combines the historical prototypes with instance-level prototypes to adjust semantic predictions, which can be associated with the parametric classifier to mutually benefit the final results. Extensive experiments evaluated on five target domains demonstrate the effectiveness and efficiency of the proposed method. Our DIGA establishes new state-of-the-art performance in TTDA-Seg. Source code is available at: https://github.com/Waybaba/DIGA." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 597, + 387, + 609 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 597, + 387, + 609 + ], + "spans": [ + { + "bbox": [ + 306, + 597, + 387, + 609 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "type": "text", + "content": "Semantic segmentation (Seg) [3, 40, 45, 46, 49] is a fundamental task in computer vision, which is an important step in the visual-based robot, autonomous driving and etc. Modern deep-learning techniques have achieved impressive success in segmentation. However, one serious drawback of them is that the segmentation models trained on one dataset (source domain) may undergo catastrophic performance degradation when applied to another dataset sam" + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 703, + 135, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 703, + 135, + 712 + ], + "spans": [ + { + "bbox": [ + 58, + 703, + 135, + 712 + ], + "type": "text", + "content": "*Corresponding author" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "24090" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 108 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 108 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 108 + ], + "type": "text", + "content": "pled from a different distribution. This phenomenon will be even more serious under complex and ever-changing contexts, e.g., autonomous driving." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 110, + 287, + 314 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 110, + 287, + 314 + ], + "spans": [ + { + "bbox": [ + 46, + 110, + 287, + 314 + ], + "type": "text", + "content": "To solve this well-known problem caused by domain shifts, researchers have devoted great effort to domain generalization (DG) [6,11,18,19,21,30] and domain adaptation (DA) [23,47,47,50]. Specifically, DG aims to learn generalized models with only labeled source data. Traditional DA attempts to adapt the model on the target domain by using both labeled source data and unlabeled target data. However, both learning paradigms have their own disadvantages. The performance of DG is limited especially when evaluated on a domain with a large gap from the source since it does not leverage target data [11]. DA assumes that the unlabeled target data are available in advance and can be chronically exploited to improve target performance. This assumption, however, can not always be satisfied in real-world applications. For example, when driving in a new city, the data are incoming sequentially and we expect the system to dynamically adapt to the ever-changing scenario." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 316, + 288, + 568 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 316, + 288, + 568 + ], + "spans": [ + { + "bbox": [ + 46, + 316, + 288, + 568 + ], + "type": "text", + "content": "To meet the real-world applications, [41] introduces the test-time domain adaptation (TTDA), which aims at adapting the model during the testing phase in an online fashion (see Fig. 1 Top). Generally, existing methods can be divided into two categories: backward-based methods [1,22,27,37, 41] and backward-free methods [15,25,28,33]. The former category (see Fig. 1 (a)) focuses on optimizing the parameters of models with self-supervision losses, such as entropy loss [27, 41]. In this way, both distribution adaptation and semantic adaptation can be achieved, which however has the following drawbacks. (1) Low-Efficiency : Due to the requirement of back-propagation, the computation cost will be multiplied, leading to low efficiency. (2) Unstable Optimization & Error Accumulation: Since the gradient is calculated with single sample by weak supervision, the randomness could be high thus leading to unstable optimization. Although this problem can be mitigated in some certain by increasing the testing batch size, it still cannot be solved well. In such cases, the accumulated errors may lead the model to forget the original well-learned knowledge and thus cause performance degradation." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "text", + "content": "The second category aims to adapt the model in the distribution level by updating statistics in batch normalization (BN) [25] layers, which is very efficient as it is directly implemented in forward propagation with a light computation cost. Instance normalization [28] (see Fig. 1 (b)) directly replaces the source statistics with those from each instance, which is sensitive to the target variations due to discarding the basic source knowledge and thus is unstable. Mirza et al [25] (see Fig. 1 (c)) study the impacts of updating the historical statistics by instance statistics with fixed momentum or dynamically fluctuating momentum. However, these methods also suffer from the error accumulation is" + } + ] + } + ], + "index": 3 + }, + { + "type": "image", + "bbox": [ + 319, + 70, + 537, + 153 + ], + "blocks": [ + { + "bbox": [ + 319, + 70, + 537, + 153 + ], + "lines": [ + { + "bbox": [ + 319, + 70, + 537, + 153 + ], + "spans": [ + { + "bbox": [ + 319, + 70, + 537, + 153 + ], + "type": "image", + "image_path": "5e0b116703992dc731840b17314624c7c6c6750cb4e0ec3afbcbf0be9e76675c.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 156, + 545, + 189 + ], + "lines": [ + { + "bbox": [ + 305, + 156, + 545, + 189 + ], + "spans": [ + { + "bbox": [ + 305, + 156, + 545, + 189 + ], + "type": "text", + "content": "Figure 2. Illustration of the implementation of our DIGA. Given a source model, our DIGA can be readily equipped with only access to the BN layers, classifier head and feature head." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "bbox": [ + 305, + 211, + 545, + 247 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 211, + 545, + 247 + ], + "spans": [ + { + "bbox": [ + 305, + 211, + 545, + 247 + ], + "type": "text", + "content": "sue caused by abnormal target distributions as well as the neglect of semantic adaptation, both of which will result in inferior adaptation performance." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 305, + 248, + 546, + 475 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 248, + 546, + 475 + ], + "spans": [ + { + "bbox": [ + 305, + 248, + 546, + 475 + ], + "type": "text", + "content": "To this end, we propose a holistic approach (see Fig. 1 (d)), called Dynamically Instance-Guided Adaptation (DIGA), for TTDA-Seg, which takes into account both effectiveness and efficiency. The main idea of DIGA is leveraging each instance to dynamically its own adaptation in a non-parametric manner, which is efficient and can largely avoid the error accumulation issue. In addition, our DIGA is implemented in a considerate manner by injecting with distribution adaptation module (DAM) and semantic adaptation module (SAM). Specifically, in DAM, we compute the weighed sum of the source and current statistics in BN layers to adapt target distribution, which enables the model to obtain a more robust representation. In SAM, we build a dynamic non-parametric classifier by mixing the historical prototypes with instance-level prototypes, enabling us to adjust the semantic prediction. In addition, the non-parametric classifier can be associated with the parametric one, which can further benefit the adaptation results. Our contributions can be summarized as follows:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 318, + 488, + 544, + 712 + ], + "type": "list", + "angle": 0, + "index": 12, + "blocks": [ + { + "bbox": [ + 318, + 488, + 544, + 523 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 318, + 488, + 544, + 523 + ], + "spans": [ + { + "bbox": [ + 318, + 488, + 544, + 523 + ], + "type": "text", + "content": "- Efficiency. We propose a backward-free approach for TTDA-Seg, which can be implemented within one forward propagation with a light computation cost." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 318, + 531, + 544, + 590 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 318, + 531, + 544, + 590 + ], + "spans": [ + { + "bbox": [ + 318, + 531, + 544, + 590 + ], + "type": "text", + "content": "- Effectiveness. We introduce a considerate approach to adapt the model in both distribution and semantic aspects. In addition, our method takes the mutual advantage of two types of classifiers to achieve further improvements." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 318, + 598, + 544, + 633 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 318, + 598, + 544, + 633 + ], + "spans": [ + { + "bbox": [ + 318, + 598, + 544, + 633 + ], + "type": "text", + "content": "- Usability. Our method is easy to implement and is model-agnostic, which can be readily injected into existing models (see Fig.2)." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 318, + 642, + 544, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 318, + 642, + 544, + 712 + ], + "spans": [ + { + "bbox": [ + 318, + 642, + 544, + 712 + ], + "type": "text", + "content": "- Promising Results. We conduct experiments on three source domains and five target domains based on driving benchmarks and show that our method produces new state-of-the-art performance for TTDA-Seg. We also study the continual TTDA-Seg and verify the superiority of our method in this challenging task." + } + ] + } + ], + "index": 11 + } + ], + "sub_type": "text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 749, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 749, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 749, + 317, + 757 + ], + "type": "text", + "content": "24091" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 71, + 134, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 71, + 134, + 83 + ], + "spans": [ + { + "bbox": [ + 47, + 71, + 134, + 83 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 91, + 289, + 462 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 91, + 289, + 462 + ], + "spans": [ + { + "bbox": [ + 47, + 91, + 289, + 462 + ], + "type": "text", + "content": "Test-time Domain Adaptation (TTDA) aims to adapt models on the target domain only in test time. It is firstly proposed in TTT [37] and has been applied to many fields such as instance tracking [9], object detections [16] and reinforcement learning [12]. The early works (TTT [37] and its extensions [20, 22]) require an extra training process on source data, making it inapplicable when only the source model is available. In this paper, we focus on the more practical Fully Test-time Domain Adaptation setting proposed in [41]. Current fully TTDA methods can be categorized into two main branches: backward-based adaptation and backward-free adaptation. As the pioneer of the self-supervision adaptation methods, TENT [41] proposes to minimize the entropy by updating BN affine parameters during test time. EATA [27] shows that skipping low entropy samples would achieve higher efficiency and performance. Also, an updated regularization term is utilized to alleviate the forgetting problem. [1] introduce an efficient framework by introducing contrastive learning. The problem with these methods is that they cost a long time and large GPU memory due to backpropagation, which largely limited the application for real-time inference. As for the backward-free branch, most of the approaches focus on BN statistics adaptation. IN [28] directly uses batch statistics while Momentum [33] and DUA [25] use running average to update the statistics. This branch is much more efficient while they only work on distribution, ignoring the semantic adaptation, leading to discounted adaptation power. Besides the above two branches, T3A [14] proposes to denoise the classification results in the post-processing stage, where adaptation of the model itself is not well exploited." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 463, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 463, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 47, + 463, + 289, + 715 + ], + "type": "text", + "content": "Domain Adaptive for Semantic Segmentation (DASS) aims to bridge the domain gap between the training and testing data. The early works in DASS mainly focus on building adversarial training architectures to learn the domain-invariant features [24, 38, 43]. Complementary modules have been introduced to facilitate the training [24,38,40,43]. Another category exploits the self-training techniques such as entropy minimization [40] and pseudo-labeling [45, 46, 49, 51]. While these approaches require the co-existence of source-target data. Source-free DA (SFDA) is more practical and closer to our setting as they assume the source data is not available during adaptation. [40] proposes to recover source information by utilizing the BN statistics. " + }, + { + "bbox": [ + 47, + 463, + 289, + 715 + ], + "type": "inline_equation", + "content": "\\mathrm{MAS}^3" + }, + { + "bbox": [ + 47, + 463, + 289, + 715 + ], + "type": "text", + "content": " [17] proposes to store source distribution information as prototypes and then use them during adaptation. [35] uses a multi-head structure to increase the reliability of pseudo-labeling for self-supervised training. Zhao et al. [48] present a special augmentation module to diversify samples with various patch styles at the feature level and then use them for generalization ability improvement. However, these methods can not handle TTDA well. Firstly," + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 304, + 72, + 545, + 109 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 109 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 109 + ], + "type": "text", + "content": "they do not consider the efficiency problem [17, 35, 40, 48]. Moreover, they often require to visit samples repeatedly in large batch sizes [17, 35, 48]." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 305, + 126, + 389, + 140 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 126, + 389, + 140 + ], + "spans": [ + { + "bbox": [ + 305, + 126, + 389, + 140 + ], + "type": "text", + "content": "3. Methodology" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 148, + 547, + 319 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 148, + 547, + 319 + ], + "spans": [ + { + "bbox": [ + 304, + 148, + 547, + 319 + ], + "type": "text", + "content": "Problem Definition. In test-time domain adaptation in semantic segmentation (TTDA-Seg), we are given a segmentation model " + }, + { + "bbox": [ + 304, + 148, + 547, + 319 + ], + "type": "inline_equation", + "content": "f_{\\theta} : \\mathbf{x} \\rightarrow y" + }, + { + "bbox": [ + 304, + 148, + 547, + 319 + ], + "type": "text", + "content": " pretrained on a source domain " + }, + { + "bbox": [ + 304, + 148, + 547, + 319 + ], + "type": "inline_equation", + "content": "\\mathcal{D}_S" + }, + { + "bbox": [ + 304, + 148, + 547, + 319 + ], + "type": "text", + "content": ", which will be directly deployed to unseen domains for evaluation. Due to domain shifts, the model " + }, + { + "bbox": [ + 304, + 148, + 547, + 319 + ], + "type": "inline_equation", + "content": "f_{\\theta}" + }, + { + "bbox": [ + 304, + 148, + 547, + 319 + ], + "type": "text", + "content": " would normally produce a poor performance on unseen testing domains. The goal of TTDA-Seg is to adapt the model by utilizing continuously incoming testing data in an online fashion (see Fig. 1). For example, at each testing step " + }, + { + "bbox": [ + 304, + 148, + 547, + 319 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 148, + 547, + 319 + ], + "type": "text", + "content": ", the model " + }, + { + "bbox": [ + 304, + 148, + 547, + 319 + ], + "type": "inline_equation", + "content": "f_{\\theta}" + }, + { + "bbox": [ + 304, + 148, + 547, + 319 + ], + "type": "text", + "content": " receives an instance " + }, + { + "bbox": [ + 304, + 148, + 547, + 319 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_t" + }, + { + "bbox": [ + 304, + 148, + 547, + 319 + ], + "type": "text", + "content": " and simultaneously performs adaptation as well as produces segmentation prediction " + }, + { + "bbox": [ + 304, + 148, + 547, + 319 + ], + "type": "inline_equation", + "content": "\\hat{y}_t" + }, + { + "bbox": [ + 304, + 148, + 547, + 319 + ], + "type": "text", + "content": ". At the next step " + }, + { + "bbox": [ + 304, + 148, + 547, + 319 + ], + "type": "inline_equation", + "content": "t + 1" + }, + { + "bbox": [ + 304, + 148, + 547, + 319 + ], + "type": "text", + "content": ", the model " + }, + { + "bbox": [ + 304, + 148, + 547, + 319 + ], + "type": "inline_equation", + "content": "f_{\\theta}" + }, + { + "bbox": [ + 304, + 148, + 547, + 319 + ], + "type": "text", + "content": " will perform adaptation and prediction on instance " + }, + { + "bbox": [ + 304, + 148, + 547, + 319 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_{t + 1}" + }, + { + "bbox": [ + 304, + 148, + 547, + 319 + ], + "type": "text", + "content": " without the access to previous data " + }, + { + "bbox": [ + 304, + 148, + 547, + 319 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_{1 \\to t}" + }, + { + "bbox": [ + 304, + 148, + 547, + 319 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 305, + 331, + 375, + 344 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 331, + 375, + 344 + ], + "spans": [ + { + "bbox": [ + 305, + 331, + 375, + 344 + ], + "type": "text", + "content": "3.1. Overview" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 352, + 547, + 568 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 352, + 547, + 568 + ], + "spans": [ + { + "bbox": [ + 304, + 352, + 547, + 568 + ], + "type": "text", + "content": "In this section, we propose a Dynamically Instance-Guided Adaptation (DIGA) method for TTDA-Seg, which is backward-free and non-parametric. As shown in Fig. 3, our DIGA includes two adaptation modules, the distribution adaptation module (DAM) and the semantic adaptation module (SAM), which are both guided by instance-aware information. Specifically, given a testing sample, we first input it into the source pretrained model and perform distribution alignment by DAM in each BN layer. The distribution alignment is implemented by weighted summing of the source statistics and instance statistics. After this, we apply semantic adaptation at the last feature level by SAM, in which we build a dynamic non-parametric classifier by weighted mixing the historical prototypes with instance-aware prototypes. This allows us to adjust the semantic prediction. Lastly, we obtain the final prediction by taking the mutual advantage between the original parametric classifier and the dynamic non-parametric classifier." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 570, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 547, + 715 + ], + "type": "text", + "content": "In Fig. 3 (a-g), we show an illustration of how our DIGA helps to adapt the model with the guidance of instance-aware information. (a-d) Due to the large domain shifts (e.g., light variations), the segmentation results on the target sample might be poor. After distribution alignment by DAM, the segmentation results could be improved, especially the instances that are similar to the source (e). However, there might still exist poorly-recognized pixels that are very different from the source. Our DAM further leverages the reliable pixels to guide the predictions of other pixels in a non-parametric way (f), enabling us to achieve more accurate results (g)." + } + ] + } + ], + "index": 8 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "24092" + } + ] + } + ], + "index": 9 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 52, + 69, + 146, + 198 + ], + "blocks": [ + { + "bbox": [ + 52, + 69, + 146, + 198 + ], + "lines": [ + { + "bbox": [ + 52, + 69, + 146, + 198 + ], + "spans": [ + { + "bbox": [ + 52, + 69, + 146, + 198 + ], + "type": "image", + "image_path": "f73e66aaab9564c9c19f6cd691c3c7f848179fc3875558faab130195bda7d43f.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 202, + 547, + 269 + ], + "lines": [ + { + "bbox": [ + 46, + 202, + 547, + 269 + ], + "spans": [ + { + "bbox": [ + 46, + 202, + 547, + 269 + ], + "type": "text", + "content": "Figure 3. Illustration of the proposed DIGA. (a-d) The source model commonly produces poor results on unseen targets, due to significant domain shifts, such as light variation. To solve this problem, our DIGA is proposed to adapt the model in an online fashion, which consists of a distribution adaptation module (DAM) and a semantic adaptation module (SAM). Both modules are guided by instance-aware information (statistics for DAM and prototypes for SAM). The DAM is implemented in BN layers for distribution alignment (e). The SAM is implemented in the feature level for semantic alignment (f-g). The final prediction is obtained by the fusion of original classifier and non-parametric classifier built by SAM." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 149, + 70, + 245, + 198 + ], + "blocks": [ + { + "bbox": [ + 149, + 70, + 245, + 198 + ], + "lines": [ + { + "bbox": [ + 149, + 70, + 245, + 198 + ], + "spans": [ + { + "bbox": [ + 149, + 70, + 245, + 198 + ], + "type": "image", + "image_path": "67bbf0ac011f1b3b94f45e6e7fb1685c2633913a5a8e7d95817016891504f82b.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 247, + 70, + 343, + 198 + ], + "blocks": [ + { + "bbox": [ + 247, + 70, + 343, + 198 + ], + "lines": [ + { + "bbox": [ + 247, + 70, + 343, + 198 + ], + "spans": [ + { + "bbox": [ + 247, + 70, + 343, + 198 + ], + "type": "image", + "image_path": "1a7a34d00ab664f3e0147081bdbb54850faefcf98bb0c4fc7b9f37b58596735a.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 344, + 70, + 446, + 198 + ], + "blocks": [ + { + "bbox": [ + 344, + 70, + 446, + 198 + ], + "lines": [ + { + "bbox": [ + 344, + 70, + 446, + 198 + ], + "spans": [ + { + "bbox": [ + 344, + 70, + 446, + 198 + ], + "type": "image", + "image_path": "3b494624f605214a05932aeab2b429ba0687d5a9173cd6938b0322dc3dbce088.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + } + ], + "index": 3 + }, + { + "type": "image", + "bbox": [ + 447, + 70, + 545, + 198 + ], + "blocks": [ + { + "bbox": [ + 447, + 70, + 545, + 198 + ], + "lines": [ + { + "bbox": [ + 447, + 70, + 545, + 198 + ], + "spans": [ + { + "bbox": [ + 447, + 70, + 545, + 198 + ], + "type": "image", + "image_path": "0abf06c3cccf5ce04bc87852bdfe937a97480a99e98d76beca79d75ff1d9151a.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 289, + 257, + 302 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 289, + 257, + 302 + ], + "spans": [ + { + "bbox": [ + 47, + 289, + 257, + 302 + ], + "type": "text", + "content": "3.2. Distribution Adaptation Module (DAM)" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 307, + 288, + 438 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 307, + 288, + 438 + ], + "spans": [ + { + "bbox": [ + 46, + 307, + 288, + 438 + ], + "type": "text", + "content": "The most common way to adapt the distribution is based on adversarial training [10, 19, 23] and minimization of distribution gap metrics [4, 36]. However, these methods are not suitable for TTDA due to limited available training data and the high-cost backpropagation. Recent works [25, 28, 33] show that the static mismatch between domains in the Batch Normalization (BN) layers is a major reason that causes the performance degradation in cross-domain testing. We thus first revisit the mechanism of BN. Specifically, for each BN layer, given the input feature representation " + }, + { + "bbox": [ + 46, + 307, + 288, + 438 + ], + "type": "inline_equation", + "content": "F" + }, + { + "bbox": [ + 46, + 307, + 288, + 438 + ], + "type": "text", + "content": ", the corresponding output is given by:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 107, + 445, + 287, + 473 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 107, + 445, + 287, + 473 + ], + "spans": [ + { + "bbox": [ + 107, + 445, + 287, + 473 + ], + "type": "interline_equation", + "content": "B N (F) = \\gamma \\frac {F - \\mathbb {E} [ F ]}{\\sqrt {\\operatorname {V a r} [ F ]}} + \\beta , \\tag {1}", + "image_path": "aaaafa03f9ec5d14b0c6097b4dfca6e7f45a1d6df359d261973beefe27940243.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 479, + 287, + 538 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 479, + 287, + 538 + ], + "spans": [ + { + "bbox": [ + 46, + 479, + 287, + 538 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 479, + 287, + 538 + ], + "type": "inline_equation", + "content": "\\gamma" + }, + { + "bbox": [ + 46, + 479, + 287, + 538 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 479, + 287, + 538 + ], + "type": "inline_equation", + "content": "\\beta" + }, + { + "bbox": [ + 46, + 479, + 287, + 538 + ], + "type": "text", + "content": " are trainable parameters for scaling and shifting. " + }, + { + "bbox": [ + 46, + 479, + 287, + 538 + ], + "type": "inline_equation", + "content": "\\mathbb{E}[F]" + }, + { + "bbox": [ + 46, + 479, + 287, + 538 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 479, + 287, + 538 + ], + "type": "inline_equation", + "content": "Var[F]" + }, + { + "bbox": [ + 46, + 479, + 287, + 538 + ], + "type": "text", + "content": " are expected value and variance of input feature " + }, + { + "bbox": [ + 46, + 479, + 287, + 538 + ], + "type": "inline_equation", + "content": "F" + }, + { + "bbox": [ + 46, + 479, + 287, + 538 + ], + "type": "text", + "content": ". In practice, due to the batch-wise training process, their values are calculated by running mean [42] during training as follows:" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 77, + 544, + 287, + 563 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 77, + 544, + 287, + 563 + ], + "spans": [ + { + "bbox": [ + 77, + 544, + 287, + 563 + ], + "type": "interline_equation", + "content": "\\bar {u} _ {t} ^ {S} = \\left(1 - \\rho_ {B N}\\right) \\cdot \\bar {\\mu} _ {t - 1} ^ {S} + \\rho_ {B N} \\cdot \\mu_ {t - 1} ^ {S}, \\tag {2}", + "image_path": "577eeab0aaee91a2add9086c92b42d9895f985eed72012f34d6aa359e9543040.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 66, + 561, + 258, + 575 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 66, + 561, + 258, + 575 + ], + "spans": [ + { + "bbox": [ + 66, + 561, + 258, + 575 + ], + "type": "interline_equation", + "content": "\\left(\\bar {\\sigma} _ {t} ^ {S}\\right) ^ {2} = \\left(1 - \\rho_ {B N}\\right) \\cdot \\left(\\bar {\\sigma} _ {t - 1} ^ {S}\\right) ^ {2} + \\rho_ {B N} \\cdot \\left(\\sigma_ {t - 1} ^ {S}\\right) ^ {2},", + "image_path": "7b38a7d530e4fea0f010e707df81a379c08b6fb8ee01e96611e9e4823a0c19e3.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 47, + 582, + 287, + 605 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 582, + 287, + 605 + ], + "spans": [ + { + "bbox": [ + 47, + 582, + 287, + 605 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 582, + 287, + 605 + ], + "type": "inline_equation", + "content": "\\bar{\\mu}_t^s" + }, + { + "bbox": [ + 47, + 582, + 287, + 605 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 582, + 287, + 605 + ], + "type": "inline_equation", + "content": "\\bar{\\sigma}_t^s" + }, + { + "bbox": [ + 47, + 582, + 287, + 605 + ], + "type": "text", + "content": " are serving as estimation for " + }, + { + "bbox": [ + 47, + 582, + 287, + 605 + ], + "type": "inline_equation", + "content": "\\mathbb{E}[F]" + }, + { + "bbox": [ + 47, + 582, + 287, + 605 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 582, + 287, + 605 + ], + "type": "inline_equation", + "content": "Var[F]" + }, + { + "bbox": [ + 47, + 582, + 287, + 605 + ], + "type": "text", + "content": " of source domain respectively." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 46, + 605, + 287, + 665 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 605, + 287, + 665 + ], + "spans": [ + { + "bbox": [ + 46, + 605, + 287, + 665 + ], + "type": "text", + "content": "Out of the motivation that the amount of training sample is usually much larger than the testing batch and thus more stable, the last value " + }, + { + "bbox": [ + 46, + 605, + 287, + 665 + ], + "type": "inline_equation", + "content": "\\bar{\\mu}_t^s" + }, + { + "bbox": [ + 46, + 605, + 287, + 665 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 605, + 287, + 665 + ], + "type": "inline_equation", + "content": "\\bar{\\sigma}_t^s" + }, + { + "bbox": [ + 46, + 605, + 287, + 665 + ], + "type": "text", + "content": " would be frozen and serve as the estimation for " + }, + { + "bbox": [ + 46, + 605, + 287, + 665 + ], + "type": "inline_equation", + "content": "\\mathbb{E}[F]" + }, + { + "bbox": [ + 46, + 605, + 287, + 665 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 605, + 287, + 665 + ], + "type": "inline_equation", + "content": "Var[F]" + }, + { + "bbox": [ + 46, + 605, + 287, + 665 + ], + "type": "text", + "content": " for the test data during the test phase." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "text", + "content": "However, it has been shown that when applied to a different environment, the source statistics can hamper performance significantly. To solve this problem, DUA [42] proposes to adapt the statistics " + }, + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "inline_equation", + "content": "\\gamma, \\beta" + }, + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "text", + "content": " of BN layers to the target" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 289, + 545, + 348 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 289, + 545, + 348 + ], + "spans": [ + { + "bbox": [ + 304, + 289, + 545, + 348 + ], + "type": "text", + "content": "domain with a dynamic learning module. Despite the efficiency, its performance is still not satisfactory. One possible reason is that the updating rate is usually very small so that instance-level information is not fully considered during each instance evaluation." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 350, + 545, + 408 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 350, + 545, + 408 + ], + "spans": [ + { + "bbox": [ + 304, + 350, + 545, + 408 + ], + "type": "text", + "content": "Different from [25, 33], instead of updating the " + }, + { + "bbox": [ + 304, + 350, + 545, + 408 + ], + "type": "inline_equation", + "content": "\\gamma, \\beta" + }, + { + "bbox": [ + 304, + 350, + 545, + 408 + ], + "type": "text", + "content": ", the proposed Distribution Adaptation Module (DAM) dynamically merges the source and instance BN statistics to constitute the estimation " + }, + { + "bbox": [ + 304, + 350, + 545, + 408 + ], + "type": "inline_equation", + "content": "\\bar{\\mu}_t^T" + }, + { + "bbox": [ + 304, + 350, + 545, + 408 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 350, + 545, + 408 + ], + "type": "inline_equation", + "content": "(\\bar{\\sigma}_t^T)^2" + }, + { + "bbox": [ + 304, + 350, + 545, + 408 + ], + "type": "text", + "content": " for " + }, + { + "bbox": [ + 304, + 350, + 545, + 408 + ], + "type": "inline_equation", + "content": "\\mathbb{E}[F]" + }, + { + "bbox": [ + 304, + 350, + 545, + 408 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 350, + 545, + 408 + ], + "type": "inline_equation", + "content": "Var[F]" + }, + { + "bbox": [ + 304, + 350, + 545, + 408 + ], + "type": "text", + "content": " as follows:" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 347, + 416, + 492, + 430 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 347, + 416, + 492, + 430 + ], + "spans": [ + { + "bbox": [ + 347, + 416, + 492, + 430 + ], + "type": "interline_equation", + "content": "\\bar {\\mu} _ {t} ^ {T} = \\lambda_ {B N} \\cdot \\bar {\\mu} ^ {S} + (1 - \\lambda_ {B N}) \\cdot \\mu_ {t} ^ {T},", + "image_path": "f6fb9a5b578d9f80da95e5d8afc43f6e3f717c64d15cf2d01a6f616a86e1811d.jpg" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 337, + 429, + 545, + 448 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 337, + 429, + 545, + 448 + ], + "spans": [ + { + "bbox": [ + 337, + 429, + 545, + 448 + ], + "type": "interline_equation", + "content": "\\left(\\bar {\\sigma} _ {t} ^ {T}\\right) ^ {2} = \\lambda_ {B N} \\cdot \\left(\\bar {\\sigma} ^ {S}\\right) ^ {2} + \\left(1 - \\lambda_ {B N}\\right) \\cdot \\left(\\sigma_ {t} ^ {T}\\right) ^ {2}, \\tag {3}", + "image_path": "a002ff301668100d14953f4086dead670cd8f9b28e23e1e3f81ab3e1ab32bfe2.jpg" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 306, + 457, + 545, + 483 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 457, + 545, + 483 + ], + "spans": [ + { + "bbox": [ + 306, + 457, + 545, + 483 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 306, + 457, + 545, + 483 + ], + "type": "inline_equation", + "content": "\\mu_t^T" + }, + { + "bbox": [ + 306, + 457, + 545, + 483 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 306, + 457, + 545, + 483 + ], + "type": "inline_equation", + "content": "(\\sigma_t^T)^2" + }, + { + "bbox": [ + 306, + 457, + 545, + 483 + ], + "type": "text", + "content": " are the mean and variance calculated with the " + }, + { + "bbox": [ + 306, + 457, + 545, + 483 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 306, + 457, + 545, + 483 + ], + "type": "text", + "content": "-th instance during testing." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 306, + 491, + 500, + 503 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 491, + 500, + 503 + ], + "spans": [ + { + "bbox": [ + 306, + 491, + 500, + 503 + ], + "type": "text", + "content": "3.3. Semantic Adaptation Module (SAM)" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 304, + 510, + 545, + 665 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 510, + 545, + 665 + ], + "spans": [ + { + "bbox": [ + 304, + 510, + 545, + 665 + ], + "type": "text", + "content": "The proposed DAM is a category-agnostic since it only aligns the distribution of feature maps globally. However, category-specific is also important to segmentation adaptation because the distribution of each category varies a lot even in the same image. Hence, we argue that it is also important to implement semantic adaptation in TTDA-Seg. To achieve this, two straightforward methods are entropy maximization [41] and pseudo-labeling [22]. However, both of them require gradient-based backpropagation and thus limit the testing efficiency. Inspired by the prototype-based methods in few-shot learning [34] and domain adaptation [29,45], we introduce the semantic adaptation module (SAM) for category-specific adaptation." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "content": "As shown in Sec. 3.1, even though distribution alignment is implemented by DAM, the model still produces wrong predictions for pixels that are very different from the source. Fortunately, we could observe that pixels of the same ob" + } + ] + } + ], + "index": 22 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "24093" + } + ] + } + ], + "index": 23 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 167 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 167 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 167 + ], + "type": "text", + "content": "ject share several of the same properties, e.g., the appearance within a car, the same texture color within a road, the same outfit within a person, the light intensity within an image, etc. Motivated by this, we propose to leverage the similarities between pixels to further guide the recognition of wrongly recognized pixels. To this end, we propose the semantic adaptation module (SAM) to adjust the semantic predictions by dynamic instance-aware prototypes." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 168, + 288, + 239 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 168, + 288, + 239 + ], + "spans": [ + { + "bbox": [ + 46, + 168, + 288, + 239 + ], + "type": "text", + "content": "The segmentation model " + }, + { + "bbox": [ + 46, + 168, + 288, + 239 + ], + "type": "inline_equation", + "content": "f_{\\theta}" + }, + { + "bbox": [ + 46, + 168, + 288, + 239 + ], + "type": "text", + "content": " can be separated into two learnable parts: i) an encoder " + }, + { + "bbox": [ + 46, + 168, + 288, + 239 + ], + "type": "inline_equation", + "content": "h_{\\phi}" + }, + { + "bbox": [ + 46, + 168, + 288, + 239 + ], + "type": "text", + "content": " for dense visual feature extraction which maps each pixel " + }, + { + "bbox": [ + 46, + 168, + 288, + 239 + ], + "type": "inline_equation", + "content": "\\mathbf{x}^{(h,w)}" + }, + { + "bbox": [ + 46, + 168, + 288, + 239 + ], + "type": "text", + "content": " to feature " + }, + { + "bbox": [ + 46, + 168, + 288, + 239 + ], + "type": "inline_equation", + "content": "\\mathbf{z}^{(h,w)} \\in \\mathbb{R}^D" + }, + { + "bbox": [ + 46, + 168, + 288, + 239 + ], + "type": "text", + "content": ", and ii) a classifier " + }, + { + "bbox": [ + 46, + 168, + 288, + 239 + ], + "type": "inline_equation", + "content": "g_{\\psi}" + }, + { + "bbox": [ + 46, + 168, + 288, + 239 + ], + "type": "text", + "content": " for following prediction which maps " + }, + { + "bbox": [ + 46, + 168, + 288, + 239 + ], + "type": "inline_equation", + "content": "\\mathbf{z}^{(h,w)}" + }, + { + "bbox": [ + 46, + 168, + 288, + 239 + ], + "type": "text", + "content": " to a distribution " + }, + { + "bbox": [ + 46, + 168, + 288, + 239 + ], + "type": "inline_equation", + "content": "\\hat{p}^{(h,w)}(c|\\mathbf{x})" + }, + { + "bbox": [ + 46, + 168, + 288, + 239 + ], + "type": "text", + "content": " over " + }, + { + "bbox": [ + 46, + 168, + 288, + 239 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 46, + 168, + 288, + 239 + ], + "type": "text", + "content": " classes. Formally, it can be denoted as:" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 137, + 243, + 287, + 261 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 137, + 243, + 287, + 261 + ], + "spans": [ + { + "bbox": [ + 137, + 243, + 287, + 261 + ], + "type": "interline_equation", + "content": "\\mathbf {z} _ {t} ^ {(h, w)} = h _ {\\phi} ^ {(h, w)} \\left(\\mathbf {x} _ {t}\\right), \\tag {4}", + "image_path": "3ffdef0a6f3b54bbf5be8a4039d41218c728a4cad2b5518ec0a6958f22c775eb.jpg" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 113, + 263, + 287, + 279 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 113, + 263, + 287, + 279 + ], + "spans": [ + { + "bbox": [ + 113, + 263, + 287, + 279 + ], + "type": "interline_equation", + "content": "\\hat {p} ^ {(h, w)} (c | \\mathbf {x} _ {t}) = g _ {\\psi} ^ {(h, w)} (\\mathbf {z} _ {t}). \\tag {5}", + "image_path": "957f2c39fd5887e71beb9efa10268efbc992319e81b9eeef3d1b4efe5010bb8e.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 283, + 287, + 380 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 283, + 287, + 380 + ], + "spans": [ + { + "bbox": [ + 46, + 283, + 287, + 380 + ], + "type": "text", + "content": "The value of logits indicates the confidence of the corresponding classes it would belong to. Thus, the largest value " + }, + { + "bbox": [ + 46, + 283, + 287, + 380 + ], + "type": "inline_equation", + "content": "\\max_c\\hat{p}_{t,c}^{(h,w)}" + }, + { + "bbox": [ + 46, + 283, + 287, + 380 + ], + "type": "text", + "content": " of the prediction distribution can be considered as the confidence of the prediction for one pixel. For one input image " + }, + { + "bbox": [ + 46, + 283, + 287, + 380 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_t" + }, + { + "bbox": [ + 46, + 283, + 287, + 380 + ], + "type": "text", + "content": ", we select pixels whose confidences are larger than " + }, + { + "bbox": [ + 46, + 283, + 287, + 380 + ], + "type": "inline_equation", + "content": "\\mathcal{P}_0" + }, + { + "bbox": [ + 46, + 283, + 287, + 380 + ], + "type": "text", + "content": " to calculate the centroids of each class in feature space, which are called as instance-aware prototypes " + }, + { + "bbox": [ + 46, + 283, + 287, + 380 + ], + "type": "inline_equation", + "content": "\\mathbf{q}_t" + }, + { + "bbox": [ + 46, + 283, + 287, + 380 + ], + "type": "text", + "content": " and can be formulated as follows:" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 54, + 382, + 287, + 427 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 54, + 382, + 287, + 427 + ], + "spans": [ + { + "bbox": [ + 54, + 382, + 287, + 427 + ], + "type": "interline_equation", + "content": "\\mathbf {q} _ {t} ^ {c} = \\frac {\\sum^ {H , W} \\mathbf {z} _ {t} ^ {(h , w)} \\cdot \\mathbb {I} \\left(c _ {t} ^ {(h , w)} = c , \\max _ {c} \\hat {p} _ {t , c} ^ {(h , w)} \\geq \\mathcal {P} _ {0}\\right)}{\\sum^ {H , W} \\mathbb {I} \\left(c _ {t} ^ {(h , w)} = c , \\max _ {c} \\hat {p} _ {t , c} ^ {(h , w)} \\geq \\mathcal {P} _ {0}\\right)}. \\tag {6}", + "image_path": "b50c78d1e570cf7923eed3ac63957440a9ffdd2a0ae849e424804948b5b7bfe2.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 433, + 287, + 493 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 433, + 287, + 493 + ], + "spans": [ + { + "bbox": [ + 46, + 433, + 287, + 493 + ], + "type": "text", + "content": "Using instance-aware prototypes only may produce unstable predictions due to the instance variance. To make the prediction more stable, we additionally calculate the moving average of the prototypes of different instances for each category, which are called historical prototypes." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 70, + 498, + 287, + 512 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 70, + 498, + 287, + 512 + ], + "spans": [ + { + "bbox": [ + 70, + 498, + 287, + 512 + ], + "type": "interline_equation", + "content": "\\bar {\\mathbf {q}} _ {t} ^ {c} = \\rho_ {P} \\cdot \\bar {\\mathbf {q}} _ {t - 1} ^ {c} + (1 - \\rho_ {P}) \\mathbf {q} _ {t} ^ {c}, \\text {w i t h} \\bar {\\mathbf {q}} _ {0} ^ {c} = \\mathbf {q} _ {0} ^ {c}. \\tag {7}", + "image_path": "fa2745983eca0321ab6d75223cc4f134e5c5f56cf5a523367cd25e3d1f64a154.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 515, + 287, + 552 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 515, + 287, + 552 + ], + "spans": [ + { + "bbox": [ + 46, + 515, + 287, + 552 + ], + "type": "text", + "content": "Since the historical prototypes are calculated by averaging prototypes from a large number of target instances, they are more stable than instance-aware prototypes." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 552, + 287, + 576 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 552, + 287, + 576 + ], + "spans": [ + { + "bbox": [ + 47, + 552, + 287, + 576 + ], + "type": "text", + "content": "Given the instance-aware prototypes, we can obtain the instance-aware prediction for each class " + }, + { + "bbox": [ + 47, + 552, + 287, + 576 + ], + "type": "inline_equation", + "content": "p^{(h,w)}(c|\\mathbf{x}_t,\\mathbf{q})" + }, + { + "bbox": [ + 47, + 552, + 287, + 576 + ], + "type": "text", + "content": " by:" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 72, + 579, + 287, + 610 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 72, + 579, + 287, + 610 + ], + "spans": [ + { + "bbox": [ + 72, + 579, + 287, + 610 + ], + "type": "interline_equation", + "content": "p ^ {(h, w)} \\left(c \\mid \\mathbf {x} _ {t}, \\mathbf {q}\\right) = \\frac {\\exp \\left(- \\langle \\mathbf {z} ^ {(h , w)} , \\mathbf {q} _ {c} \\rangle\\right)}{\\sum_ {c ^ {\\prime} = 1} ^ {C} \\exp \\left(- \\langle \\mathbf {z} ^ {(h , w)}, \\mathbf {q} _ {c ^ {\\prime}} \\rangle\\right)}. \\tag {8}", + "image_path": "b34b23ad57bb21954171eb7c5ca46c2663014e3227d11276642a22110db1ddd0.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 614, + 287, + 638 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 614, + 287, + 638 + ], + "spans": [ + { + "bbox": [ + 46, + 614, + 287, + 638 + ], + "type": "text", + "content": "The historical prediction " + }, + { + "bbox": [ + 46, + 614, + 287, + 638 + ], + "type": "inline_equation", + "content": "p^{(h,w)}(c|\\mathbf{x}_t,\\bar{\\mathbf{q}})" + }, + { + "bbox": [ + 46, + 614, + 287, + 638 + ], + "type": "text", + "content": " could be obtained in a similar way." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 46, + 639, + 287, + 674 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 639, + 287, + 674 + ], + "spans": [ + { + "bbox": [ + 46, + 639, + 287, + 674 + ], + "type": "text", + "content": "By combing the predictions of the two types of prototypes, we form a dynamic non-parametric classifier and the predictions are formulated as:" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 82, + 678, + 287, + 711 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 82, + 678, + 287, + 711 + ], + "spans": [ + { + "bbox": [ + 82, + 678, + 287, + 711 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\tilde {p} ^ {(h, w)} \\left(c \\mid \\mathbf {x} _ {t}\\right) = \\lambda_ {P} \\cdot p ^ {(h, w)} \\left(c \\mid \\mathbf {x} _ {t}, \\bar {\\mathbf {q}}\\right) \\tag {9} \\\\ + (1 - \\lambda_ {P}) \\cdot p ^ {(h, w)} (c | \\mathbf {x} _ {t}, \\mathbf {q}), \\\\ \\end{array}", + "image_path": "3021e3df3969e77f19c621ac38dfbd13fc38aed024d66b4b3c9bc8a148e85362.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 307, + 72, + 452, + 84 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 307, + 72, + 452, + 84 + ], + "spans": [ + { + "bbox": [ + 307, + 72, + 452, + 84 + ], + "type": "text", + "content": "Algorithm 1 DIGA (Testing Phase)" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 315, + 87, + 487, + 99 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 315, + 87, + 487, + 99 + ], + "spans": [ + { + "bbox": [ + 315, + 87, + 487, + 99 + ], + "type": "text", + "content": "Input: Model " + }, + { + "bbox": [ + 315, + 87, + 487, + 99 + ], + "type": "inline_equation", + "content": "f_{\\theta}" + }, + { + "bbox": [ + 315, + 87, + 487, + 99 + ], + "type": "text", + "content": ", target testing sample " + }, + { + "bbox": [ + 315, + 87, + 487, + 99 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_t" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 316, + 100, + 421, + 110 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 316, + 100, + 421, + 110 + ], + "spans": [ + { + "bbox": [ + 316, + 100, + 421, + 110 + ], + "type": "text", + "content": "Output: Prediction of " + }, + { + "bbox": [ + 316, + 100, + 421, + 110 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_t" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 316, + 111, + 545, + 207 + ], + "type": "list", + "angle": 0, + "index": 22, + "blocks": [ + { + "bbox": [ + 316, + 111, + 545, + 135 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 316, + 111, + 545, + 135 + ], + "spans": [ + { + "bbox": [ + 316, + 111, + 545, + 135 + ], + "type": "text", + "content": "1. Produce feature " + }, + { + "bbox": [ + 316, + 111, + 545, + 135 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_t" + }, + { + "bbox": [ + 316, + 111, + 545, + 135 + ], + "type": "text", + "content": " and prediction " + }, + { + "bbox": [ + 316, + 111, + 545, + 135 + ], + "type": "inline_equation", + "content": "\\hat{p}_t(\\mathbf{x}_t)" + }, + { + "bbox": [ + 316, + 111, + 545, + 135 + ], + "type": "text", + "content": " with distribution alignment of DAM (Eq. 3)." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 316, + 136, + 517, + 148 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 316, + 136, + 517, + 148 + ], + "spans": [ + { + "bbox": [ + 316, + 136, + 517, + 148 + ], + "type": "text", + "content": "2. Calculate instance-aware prototypes " + }, + { + "bbox": [ + 316, + 136, + 517, + 148 + ], + "type": "inline_equation", + "content": "\\mathbf{q}_t" + }, + { + "bbox": [ + 316, + 136, + 517, + 148 + ], + "type": "text", + "content": " (Eq. 6)." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 316, + 148, + 495, + 159 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 316, + 148, + 495, + 159 + ], + "spans": [ + { + "bbox": [ + 316, + 148, + 495, + 159 + ], + "type": "text", + "content": "3. Calculate historical prototypes " + }, + { + "bbox": [ + 316, + 148, + 495, + 159 + ], + "type": "inline_equation", + "content": "\\bar{\\mathbf{q}}_t" + }, + { + "bbox": [ + 316, + 148, + 495, + 159 + ], + "type": "text", + "content": " (Eq. 7)." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 316, + 159, + 545, + 182 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 316, + 159, + 545, + 182 + ], + "spans": [ + { + "bbox": [ + 316, + 159, + 545, + 182 + ], + "type": "text", + "content": "4. Calculate non-parametric predictions " + }, + { + "bbox": [ + 316, + 159, + 545, + 182 + ], + "type": "inline_equation", + "content": "\\tilde{p}_t(\\mathbf{x}_t)" + }, + { + "bbox": [ + 316, + 159, + 545, + 182 + ], + "type": "text", + "content": " with SAM (Eq. 9)." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 316, + 183, + 545, + 207 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 316, + 183, + 545, + 207 + ], + "spans": [ + { + "bbox": [ + 316, + 183, + 545, + 207 + ], + "type": "text", + "content": "5. Obtain final prediction " + }, + { + "bbox": [ + 316, + 183, + 545, + 207 + ], + "type": "inline_equation", + "content": "p(\\mathbf{x}_t)" + }, + { + "bbox": [ + 316, + 183, + 545, + 207 + ], + "type": "text", + "content": " by weighed fusion of " + }, + { + "bbox": [ + 316, + 183, + 545, + 207 + ], + "type": "inline_equation", + "content": "\\hat{p}_t(\\mathbf{x}_t)" + }, + { + "bbox": [ + 316, + 183, + 545, + 207 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 316, + 183, + 545, + 207 + ], + "type": "inline_equation", + "content": "\\tilde{p}_t(\\mathbf{x}_t)" + }, + { + "bbox": [ + 316, + 183, + 545, + 207 + ], + "type": "text", + "content": " (Eq. 10)." + } + ] + } + ], + "index": 21 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 317, + 208, + 376, + 220 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 208, + 376, + 220 + ], + "spans": [ + { + "bbox": [ + 317, + 208, + 376, + 220 + ], + "type": "text", + "content": "Return: " + }, + { + "bbox": [ + 317, + 208, + 376, + 220 + ], + "type": "inline_equation", + "content": "p(\\mathbf{x}_t)" + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 305, + 243, + 545, + 268 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 243, + 545, + 268 + ], + "spans": [ + { + "bbox": [ + 305, + 243, + 545, + 268 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 243, + 545, + 268 + ], + "type": "inline_equation", + "content": "\\lambda_{P}" + }, + { + "bbox": [ + 305, + 243, + 545, + 268 + ], + "type": "text", + "content": " controls the importance of two types of prototypes." + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 306, + 275, + 429, + 287 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 275, + 429, + 287 + ], + "spans": [ + { + "bbox": [ + 306, + 275, + 429, + 287 + ], + "type": "text", + "content": "3.4. Classifier Association" + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 305, + 294, + 545, + 354 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 294, + 545, + 354 + ], + "spans": [ + { + "bbox": [ + 305, + 294, + 545, + 354 + ], + "type": "text", + "content": "To this end, we could have two types of predictions: one from the original parametric classifier " + }, + { + "bbox": [ + 305, + 294, + 545, + 354 + ], + "type": "inline_equation", + "content": "(\\hat{p})" + }, + { + "bbox": [ + 305, + 294, + 545, + 354 + ], + "type": "text", + "content": " and one from the introduced non-parametric prototype classifier " + }, + { + "bbox": [ + 305, + 294, + 545, + 354 + ], + "type": "inline_equation", + "content": "(\\tilde{p})" + }, + { + "bbox": [ + 305, + 294, + 545, + 354 + ], + "type": "text", + "content": ". To leverage the mutual benefit between them, we obtain the final prediction by weighted sum of them, formulated as:" + } + ] + } + ], + "index": 26 + }, + { + "bbox": [ + 312, + 362, + 545, + 377 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 362, + 545, + 377 + ], + "spans": [ + { + "bbox": [ + 312, + 362, + 545, + 377 + ], + "type": "interline_equation", + "content": "p ^ {(h, w)} = \\lambda_ {F} \\cdot \\tilde {p} ^ {(h, w)} (c | \\mathbf {x} _ {t}) + (1 - \\lambda_ {F}) \\hat {p} ^ {(h, w)} (c | \\mathbf {x} _ {t}), \\tag {10}", + "image_path": "4b0a34ca204e2cecdfa8f57bd60ae579945b4a6fbd32efddd526b9376f28a359.jpg" + } + ] + } + ], + "index": 27 + }, + { + "bbox": [ + 305, + 386, + 545, + 410 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 386, + 545, + 410 + ], + "spans": [ + { + "bbox": [ + 305, + 386, + 545, + 410 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 386, + 545, + 410 + ], + "type": "inline_equation", + "content": "\\lambda_F" + }, + { + "bbox": [ + 305, + 386, + 545, + 410 + ], + "type": "text", + "content": " balances the importance of two classifiers. The overall process of DIGA is shown in Alg. 1." + } + ] + } + ], + "index": 28 + }, + { + "bbox": [ + 306, + 421, + 382, + 434 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 421, + 382, + 434 + ], + "spans": [ + { + "bbox": [ + 306, + 421, + 382, + 434 + ], + "type": "text", + "content": "4. Experiment" + } + ] + } + ], + "index": 29 + }, + { + "bbox": [ + 306, + 441, + 422, + 453 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 441, + 422, + 453 + ], + "spans": [ + { + "bbox": [ + 306, + 441, + 422, + 453 + ], + "type": "text", + "content": "4.1. Experimental Setup" + } + ] + } + ], + "index": 30 + }, + { + "bbox": [ + 305, + 459, + 545, + 615 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 459, + 545, + 615 + ], + "spans": [ + { + "bbox": [ + 305, + 459, + 545, + 615 + ], + "type": "text", + "content": "Datasets. Following the previous works [3, 15, 40], we evaluate our method on sim2real scenarios. Specifically, for the source model, we pretrain it with three different source domains: GTA5 [31], Synthia [31], and GTA5+Synthia. GTA5 provides 24,971 images from video games with 19 semantic classes. Synthia includes 12,000 simulated images with 16 semantic classes. GTA5+Synthia is the combination of GTA5 and Synthia datasets. Performance are evaluated on five target domains: Cityscapes [7], BDD-100K [44], Mapillary [26], IDD [39], Cross-City [5]. We test the results on the validation sets, where the number of samples is \\{500, 1,000, 2,000, 100, and 400\\} for {Cityscapes, BDD-100K, Mapillary, IDD, Cross-City} respectively." + } + ] + } + ], + "index": 31 + }, + { + "bbox": [ + 305, + 629, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 629, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 305, + 629, + 545, + 712 + ], + "type": "text", + "content": "Evaluation. The mean intersection-over-union (mIoU) is used as the evaluation metric. As in [3,40], for source models pretrained on GTA5 and GTA5+Synthia, we report the mIoU of 19 shared semantic categories. Due to missing of annotations of some classes, we report the mIoU of 16 shared semantic classes for the model pretrained on the Synthia dataset." + } + ] + } + ], + "index": 32 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "24094" + } + ] + } + ], + "index": 33 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 52, + 105, + 542, + 285 + ], + "blocks": [ + { + "bbox": [ + 47, + 70, + 545, + 103 + ], + "lines": [ + { + "bbox": [ + 47, + 70, + 545, + 103 + ], + "spans": [ + { + "bbox": [ + 47, + 70, + 545, + 103 + ], + "type": "text", + "content": "Table 1. Comparison with state-of-the-art methods in terms of mIoU. The best score for each column is highlighted. CS: CityScapes, BDD: BDD100K, MA: Mapillary, IDD: IDD, CC: Cross-City. *: Use an extra augmented sample during adaptation. Avg.: Mean of mIoUs over five target domains." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 52, + 105, + 542, + 285 + ], + "lines": [ + { + "bbox": [ + 52, + 105, + 542, + 285 + ], + "spans": [ + { + "bbox": [ + 52, + 105, + 542, + 285 + ], + "type": "table", + "html": "
MethodGTA5→Synthia→GTA5+Synthia→
CSBDDMAIDDCCAvg.CSBDDMAIDDCCAvg.CSBDDMAIDDCCAvg.
Source [42]35.8729.8938.6738.0530.0334.5030.8721.0131.1226.2331.9628.2437.0028.8541.5639.8832.9336.04
Backward-based Methods
TENT [41]37.3031.5338.2938.9630.5935.3334.8916.9933.4626.2331.6828.6539.3925.1937.3239.5132.8434.85
EATA [27]37.0830.6739.3538.7530.2435.2231.3120.5231.5926.4631.9128.3638.4529.3441.6340.3332.9136.53
Backward-free Methods
IN [28]34.2529.6435.0129.823.8730.5129.5319.3321.9222.0828.2424.2237.0928.8136.0230.9928.6332.31
Momentum [33]38.1232.4240.7938.7430.236.0532.8422.5131.1227.2432.2329.4539.6131.7241.7939.8833.1736.66
DUA [25]37.7931.7640.2634.7526.3234.1832.1721.5627.4224.0629.8727.0239.1730.5939.9535.3030.6535.13
SITA* [15]40.6432.9437.8035.6628.1935.2634.6322.5126.6024.6428.1827.7942.6232.2441.2038.8233.2237.62
DIGA (Ours)45.8135.7844.2542.7333.7240.4641.8529.0936.5438.3636.7836.5246.4333.8743.5142.0834.4140.06
", + "image_path": "96b3cb343c150314fc8ec118903ce9d449f9a0a964574704c2e479aae33009b4.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 304, + 289, + 435 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 304, + 289, + 435 + ], + "spans": [ + { + "bbox": [ + 46, + 304, + 289, + 435 + ], + "type": "text", + "content": "Implementation Details. Following previous works [3, 15, 25, 41], we use DeepLabV2 [2] as the segmentation model. The ResNet-101 [13] pretrained on ImageNet [8] is used as the backbone. It is worth mentioning that globally consistent parameter sets are used for our DIGA, which achieves consistently good performance in all experiments. Specifically, we set the momentum updating rate " + }, + { + "bbox": [ + 46, + 304, + 289, + 435 + ], + "type": "inline_equation", + "content": "(\\rho_{P}" + }, + { + "bbox": [ + 46, + 304, + 289, + 435 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 304, + 289, + 435 + ], + "type": "inline_equation", + "content": "\\rho_{BN})" + }, + { + "bbox": [ + 46, + 304, + 289, + 435 + ], + "type": "text", + "content": " both to 0.1. The weights of DAM, SAM, and classifier association " + }, + { + "bbox": [ + 46, + 304, + 289, + 435 + ], + "type": "inline_equation", + "content": "(\\lambda_{BN},\\lambda_{P}" + }, + { + "bbox": [ + 46, + 304, + 289, + 435 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 304, + 289, + 435 + ], + "type": "inline_equation", + "content": "\\lambda_F)" + }, + { + "bbox": [ + 46, + 304, + 289, + 435 + ], + "type": "text", + "content": " are all set to 0.8. The confidence bar for prototype selection " + }, + { + "bbox": [ + 46, + 304, + 289, + 435 + ], + "type": "inline_equation", + "content": "\\mathcal{P}_0" + }, + { + "bbox": [ + 46, + 304, + 289, + 435 + ], + "type": "text", + "content": " is 0.9. All the experiments are conducted with one RTX3090 GPU." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 443, + 228, + 456 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 443, + 228, + 456 + ], + "spans": [ + { + "bbox": [ + 47, + 443, + 228, + 456 + ], + "type": "text", + "content": "4.2. Comparison with State of the Art" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 462, + 287, + 509 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 462, + 287, + 509 + ], + "spans": [ + { + "bbox": [ + 46, + 462, + 287, + 509 + ], + "type": "text", + "content": "We first compare our method with the state-of-the-art approaches. Generally, the compared methods can be divided into two categories: backward-based methods and backward-free methods." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 510, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 510, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 510, + 288, + 713 + ], + "type": "text", + "content": "Backward-based methods: TENT [41] performs adapting by minimizing the output entropy and updating the learnable parameters of BN layers. As an extension to TENT [41], EATA [27] proposes to skip the high-entropy samples and only leverage reliable samples during model optimization, which can effectively increase testing efficiency. Both of them are initially designed for image classification. We implement them for TTDA-Seg by minimizing the entropy of pixel-level output. For EATA [27], we skip the low-entropy pixels during optimization. Backward-free methods: IN [28] uses instance statistics to replace source ones in BN at each testing step. Momentum [33] utilizes the instance statistics to update BN in a momentum-based manner. DUA [25] proposes a decaying strategy to adaptively control the momentum of BN updating. SITA [15] leverages extra augmented samples to obtain stable instance statistics, which are then mixed with the source statistics." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 304, + 545, + 376 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 304, + 545, + 376 + ], + "spans": [ + { + "bbox": [ + 304, + 304, + 545, + 376 + ], + "type": "text", + "content": "To make a fair comparison, we implement all the methods with the same source models. Note that, we report the results of the compared methods by selecting the best parameters for each source-target pair. In contrast, in our method, we only use one parameter setting for all experiments to better meet the real-world applications." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 378, + 546, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 378, + 546, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 378, + 546, + 714 + ], + "type": "text", + "content": "The following observations can be made from the results reported in Tab. 1. First, backward-based methods can consistently improve the performance when evaluating on CityScapes. However, the improvements on other target domains are limited or even negative. For example, when using Synthia as the source domain, TENT [41] increases the mIoU from " + }, + { + "bbox": [ + 304, + 378, + 546, + 714 + ], + "type": "inline_equation", + "content": "30.87\\%" + }, + { + "bbox": [ + 304, + 378, + 546, + 714 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 304, + 378, + 546, + 714 + ], + "type": "inline_equation", + "content": "34.89\\%" + }, + { + "bbox": [ + 304, + 378, + 546, + 714 + ], + "type": "text", + "content": " on CityScapes while largely reduces the mIoU from " + }, + { + "bbox": [ + 304, + 378, + 546, + 714 + ], + "type": "inline_equation", + "content": "21.01\\%" + }, + { + "bbox": [ + 304, + 378, + 546, + 714 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 304, + 378, + 546, + 714 + ], + "type": "inline_equation", + "content": "16.99\\%" + }, + { + "bbox": [ + 304, + 378, + 546, + 714 + ], + "type": "text", + "content": " for BDD100K. This indicates that using self-supervision only may not be a good choice for TTDA-Seg. Second, except for IN [28], the backward-free methods are generally effective on CityScapes and BDD100K while failing to achieve consistent improvements on other datasets, even though we have well-tuned them for each target domain. On the other hand, IN [28] largely reduces the average mIoU due to ignoring the source statistics. Third, the proposed DIGA consistently improves the mIoUs of the source models on all settings and outperforms all the compared methods by a large margin in most cases. Specifically, our DIGA is higher than the best competitor (Momentum [33]) by " + }, + { + "bbox": [ + 304, + 378, + 546, + 714 + ], + "type": "inline_equation", + "content": "4.41\\%" + }, + { + "bbox": [ + 304, + 378, + 546, + 714 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 378, + 546, + 714 + ], + "type": "inline_equation", + "content": "7.07\\%" + }, + { + "bbox": [ + 304, + 378, + 546, + 714 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 304, + 378, + 546, + 714 + ], + "type": "inline_equation", + "content": "3.4\\%" + }, + { + "bbox": [ + 304, + 378, + 546, + 714 + ], + "type": "text", + "content": " in average mIoU for GTA5, Synthia, and GTA5+Synthia settings, respectively. In Fig. 4, we provide the qualitative comparison of different methods. It is clear that our DIGA consistently improves the segmentation results of the source model and outperforms other state-of-the-art methods. The above observations demonstrate the effectiveness and universality of the proposed method for solving TTDA-Seg." + } + ] + } + ], + "index": 7 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "24095" + } + ] + } + ], + "index": 8 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 79, + 70, + 515, + 236 + ], + "blocks": [ + { + "bbox": [ + 79, + 70, + 515, + 236 + ], + "lines": [ + { + "bbox": [ + 79, + 70, + 515, + 236 + ], + "spans": [ + { + "bbox": [ + 79, + 70, + 515, + 236 + ], + "type": "image", + "image_path": "b2bc63e91d61c69fe4119ef427374d706a091b2f2bc817d123a57bc44e5f4ffc.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 190, + 238, + 400, + 248 + ], + "lines": [ + { + "bbox": [ + 190, + 238, + 400, + 248 + ], + "spans": [ + { + "bbox": [ + 190, + 238, + 400, + 248 + ], + "type": "text", + "content": "Figure 4. Qualitative comparison of segmentation results." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 48, + 305, + 287, + 427 + ], + "blocks": [ + { + "bbox": [ + 46, + 261, + 287, + 304 + ], + "lines": [ + { + "bbox": [ + 46, + 261, + 287, + 304 + ], + "spans": [ + { + "bbox": [ + 46, + 261, + 287, + 304 + ], + "type": "text", + "content": "Table 2. Ablation study on DIGA. DAM: domain alignment module, SAM: semantic alignment module, Association: classifier association. For the BN branch and Semantic branch, we highlight the best and second best results, respectively. Source: GTA5." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 48, + 305, + 287, + 427 + ], + "lines": [ + { + "bbox": [ + 48, + 305, + 287, + 427 + ], + "spans": [ + { + "bbox": [ + 48, + 305, + 287, + 427 + ], + "type": "table", + "html": "
ModulesCSBDDMAIDDCCAvg.
BNHistorical35.8729.8938.6738.0530.0334.50
Instance34.2529.6435.0129.8023.8730.51
DAM39.2633.3940.1137.2330.1236.02
SemanticHistorical38.6329.2537.6441.6732.8836.01
Instance39.1632.2638.6835.0927.9834.63
SAM42.9932.6941.3741.3033.4938.37
Association45.8135.7844.2542.7333.7240.46
", + "image_path": "76c8146c2805529a98b4725f8aadfdeb2931752063143ea2c21669c95b601635.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 443, + 141, + 455 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 443, + 141, + 455 + ], + "spans": [ + { + "bbox": [ + 47, + 443, + 141, + 455 + ], + "type": "text", + "content": "4.3. Ablation Study" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 461, + 287, + 533 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 461, + 287, + 533 + ], + "spans": [ + { + "bbox": [ + 46, + 461, + 287, + 533 + ], + "type": "text", + "content": "We conduct ablative study to investigate the effectiveness of the components of the proposed DIGA, i.e., domain adaptation module, semantic adaptation module, and classifier association. Experiments are evaluated on five target domains with the source model pretrained on GTA5. Results are reported in Tab. 2." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 533, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 533, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 533, + 288, + 714 + ], + "type": "text", + "content": "Effectiveness of DAM. In the BN branch of Tab. 2, \"Historical\" indicates directly using BN statistics of the source for normalization, which can be regarded as the baseline or source model. \"Instance\" represents using instance statistics for normalization. Two observations can be made. First, the \"Instance\" model produces worse performance than the \"Historical\" model on all target domains, especially on IDD and Cross-City. The average mIoU of \"Instance\" is " + }, + { + "bbox": [ + 46, + 533, + 288, + 714 + ], + "type": "inline_equation", + "content": "4.49\\%" + }, + { + "bbox": [ + 46, + 533, + 288, + 714 + ], + "type": "text", + "content": " lower than the \"Historical\". This indicates that using instance statistics only is not suitable for TTDA-Seg. Second, DAM improves the results in most cases and obtains an improvement of " + }, + { + "bbox": [ + 46, + 533, + 288, + 714 + ], + "type": "inline_equation", + "content": "1.48\\%" + }, + { + "bbox": [ + 46, + 533, + 288, + 714 + ], + "type": "text", + "content": " in average mIoU over the \"Historical\" model. Specifically, DAM boosts the mIoU by " + }, + { + "bbox": [ + 46, + 533, + 288, + 714 + ], + "type": "inline_equation", + "content": "3.39\\%" + }, + { + "bbox": [ + 46, + 533, + 288, + 714 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 533, + 288, + 714 + ], + "type": "inline_equation", + "content": "3.5\\%" + }, + { + "bbox": [ + 46, + 533, + 288, + 714 + ], + "type": "text", + "content": " on CityScapes and BDD100K, respectively. Even when the gap between \"Historical\" and \"Instance\" is too" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 262, + 545, + 346 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 262, + 545, + 346 + ], + "spans": [ + { + "bbox": [ + 304, + 262, + 545, + 346 + ], + "type": "text", + "content": "large (e.g., " + }, + { + "bbox": [ + 304, + 262, + 545, + 346 + ], + "type": "inline_equation", + "content": "9.25\\%" + }, + { + "bbox": [ + 304, + 262, + 545, + 346 + ], + "type": "text", + "content": " on IDD), our DAM is not deteriorated by the negative impact of \"Instance\" too much and still produces competitive results to the \"Historical\" with a marginal gap of " + }, + { + "bbox": [ + 304, + 262, + 545, + 346 + ], + "type": "inline_equation", + "content": "0.82\\%" + }, + { + "bbox": [ + 304, + 262, + 545, + 346 + ], + "type": "text", + "content": ". These two observations suggest that our DAM can effectively merge the guidance of instance knowledge into historical statistics to achieve an effective and stable adaptation process." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 350, + 546, + 662 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 350, + 546, + 662 + ], + "spans": [ + { + "bbox": [ + 304, + 350, + 546, + 662 + ], + "type": "text", + "content": "Effectiveness of SAM. In the semantic branch, \"Instance\" indicates the instance-specific prototypes calculated by reliable pixels in the current testing image. \"Historical\" represents the historical prototypes. Notice that, the semantic branch is conducted based on DAM, where the features for calculating prototypes are obtained after distribution alignment. We can make the following conclusions. First, the \"Historical\" classifier and the parametric classifier (DAM) achieve a very similar average mIoU. Second, the \"Instance\" classifier obtains lower average mIoU than the \"Historical\" classifier. However, by taking a close look at the results on five target domains, we can find that the \"Instance\" classifier outperforms the \"Historical\" classifier on three datasets (CityScapes, BDD and Mapillary). This indicates that these two non-parametric classifiers have particular merits in particular datasets. Third, SAM clearly outperforms both non-parametric classifiers in average mIoU. Specifically, our SAM surpasses the \"Historical\" classifier by " + }, + { + "bbox": [ + 304, + 350, + 546, + 662 + ], + "type": "inline_equation", + "content": "2.36\\%" + }, + { + "bbox": [ + 304, + 350, + 546, + 662 + ], + "type": "text", + "content": " in average mIoU. Fourth, similar to the BN branch, when the gap between \"Historical\" and \"Instance\" classifiers is large, SAM may not bring improvement, e.g., the IDD case. However, our SAM still remains the high performance without influencing by the inferior classifier. The above observations verify the appropriateness of using the prototype classifiers and also the effectiveness of the proposed SAM across different target domains." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 665, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 547, + 715 + ], + "type": "text", + "content": "Effectiveness of Classifier Association. With the association of the parametric classifier (outputs of DAM) and the non-parametric classifier (outputs of SAM), the results are consistently improved on all target domains. Specifi" + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 749, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 749, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 749, + 318, + 757 + ], + "type": "text", + "content": "24096" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 58, + 74, + 284, + 213 + ], + "blocks": [ + { + "bbox": [ + 58, + 74, + 284, + 213 + ], + "lines": [ + { + "bbox": [ + 58, + 74, + 284, + 213 + ], + "spans": [ + { + "bbox": [ + 58, + 74, + 284, + 213 + ], + "type": "image", + "image_path": "c0492f85a65b467e6e4e1a9aaceb680c5e13079d166e5635c369b0dab7ea2db4.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 217, + 288, + 251 + ], + "lines": [ + { + "bbox": [ + 46, + 217, + 288, + 251 + ], + "spans": [ + { + "bbox": [ + 46, + 217, + 288, + 251 + ], + "type": "text", + "content": "Figure 5. Experiments of continual TTDA-Seg. THe model is pretrained on Synthia [32]. The domain adaptation stream is \"BDD " + }, + { + "bbox": [ + 46, + 217, + 288, + 251 + ], + "type": "inline_equation", + "content": "\\rightarrow" + }, + { + "bbox": [ + 46, + 217, + 288, + 251 + ], + "type": "text", + "content": " CC " + }, + { + "bbox": [ + 46, + 217, + 288, + 251 + ], + "type": "inline_equation", + "content": "\\rightarrow" + }, + { + "bbox": [ + 46, + 217, + 288, + 251 + ], + "type": "text", + "content": " CS " + }, + { + "bbox": [ + 46, + 217, + 288, + 251 + ], + "type": "inline_equation", + "content": "\\rightarrow" + }, + { + "bbox": [ + 46, + 217, + 288, + 251 + ], + "type": "text", + "content": " IDD " + }, + { + "bbox": [ + 46, + 217, + 288, + 251 + ], + "type": "inline_equation", + "content": "\\rightarrow" + }, + { + "bbox": [ + 46, + 217, + 288, + 251 + ], + "type": "text", + "content": " MA\" with two rounds." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 272, + 287, + 321 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 272, + 287, + 321 + ], + "spans": [ + { + "bbox": [ + 46, + 272, + 287, + 321 + ], + "type": "text", + "content": "cally, the average mIoU is increased by " + }, + { + "bbox": [ + 46, + 272, + 287, + 321 + ], + "type": "inline_equation", + "content": "4.44\\%" + }, + { + "bbox": [ + 46, + 272, + 287, + 321 + ], + "type": "text", + "content": " for DAM and " + }, + { + "bbox": [ + 46, + 272, + 287, + 321 + ], + "type": "inline_equation", + "content": "2.09\\%" + }, + { + "bbox": [ + 46, + 272, + 287, + 321 + ], + "type": "text", + "content": " for SAM. This validates the effectiveness of leveraging the mutual benefit between parametric and non-parametric classifiers." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 330, + 170, + 342 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 330, + 170, + 342 + ], + "spans": [ + { + "bbox": [ + 47, + 330, + 170, + 342 + ], + "type": "text", + "content": "4.4. Continual TTDA-Seg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 349, + 287, + 516 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 349, + 287, + 516 + ], + "spans": [ + { + "bbox": [ + 46, + 349, + 287, + 516 + ], + "type": "text", + "content": "In real-world applications, such as autonomous driving, the environments are ever-changing and complex. To better simulate such practice scenarios, we design a continual TTDA-Seg experiment. Specifically, the dynamic environment is built by sequentially incoming target domains. The domain-stream is \"BDD " + }, + { + "bbox": [ + 46, + 349, + 287, + 516 + ], + "type": "inline_equation", + "content": "\\rightarrow" + }, + { + "bbox": [ + 46, + 349, + 287, + 516 + ], + "type": "text", + "content": " CC " + }, + { + "bbox": [ + 46, + 349, + 287, + 516 + ], + "type": "inline_equation", + "content": "\\rightarrow" + }, + { + "bbox": [ + 46, + 349, + 287, + 516 + ], + "type": "text", + "content": " CS " + }, + { + "bbox": [ + 46, + 349, + 287, + 516 + ], + "type": "inline_equation", + "content": "\\rightarrow" + }, + { + "bbox": [ + 46, + 349, + 287, + 516 + ], + "type": "text", + "content": " IDD " + }, + { + "bbox": [ + 46, + 349, + 287, + 516 + ], + "type": "inline_equation", + "content": "\\rightarrow" + }, + { + "bbox": [ + 46, + 349, + 287, + 516 + ], + "type": "text", + "content": " MA\", which is sorted by alphabetical order for simplicity and performed by two rounds. We use the Synthia-pretrained model as the source model and report the mIoU after meeting each target domain. In Fig. 5, we compare our method with TENT [41]. We implement two versions for TENT [41]. TENT-ContinualAdapt: continually adapt the model with the incoming target domains. TENT-SourceAdapt: directly adapt the source-pretrained model on the given domain." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 517, + 288, + 661 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 517, + 288, + 661 + ], + "spans": [ + { + "bbox": [ + 46, + 517, + 288, + 661 + ], + "type": "text", + "content": "We can observe that \"TENT-ContinualAdapt\" suffers from significant performance degradation when compared to \"TENT-SourceAdapt\". For example, when testing on the CityScapes dataset, \"TENT-ContinualAdapt\" is " + }, + { + "bbox": [ + 46, + 517, + 288, + 661 + ], + "type": "inline_equation", + "content": "19\\%" + }, + { + "bbox": [ + 46, + 517, + 288, + 661 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 517, + 288, + 661 + ], + "type": "inline_equation", + "content": "67\\%" + }, + { + "bbox": [ + 46, + 517, + 288, + 661 + ], + "type": "text", + "content": " lower than \"TENT-SourceAdapt\" in mIoU at the first round and second round, respectively. This phenomenon can also be observed in other domains. This is mainly because that TENT will accumulate the errors during adaptation and thus leads a worse model. Instead, our DIGA does not have the error accumulation problem and consistently performs well on all domains. This further validates the effectiveness of our method in real-world TTDA-Seg." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 670, + 165, + 683 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 670, + 165, + 683 + ], + "spans": [ + { + "bbox": [ + 47, + 670, + 165, + 683 + ], + "type": "text", + "content": "4.5. Computational Cost" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 689, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 689, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 689, + 288, + 715 + ], + "type": "text", + "content": "In TTDA-Seg, efficiency is also very important. In Tab. 3, we investigate the computational costs of" + } + ] + } + ], + "index": 7 + }, + { + "type": "table", + "bbox": [ + 318, + 92, + 535, + 196 + ], + "blocks": [ + { + "bbox": [ + 305, + 70, + 545, + 91 + ], + "lines": [ + { + "bbox": [ + 305, + 70, + 545, + 91 + ], + "spans": [ + { + "bbox": [ + 305, + 70, + 545, + 91 + ], + "type": "text", + "content": "Table 3. Time and Memory Cost. Highlights indicate the Best, and Second/Third Best results." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 318, + 92, + 535, + 196 + ], + "lines": [ + { + "bbox": [ + 318, + 92, + 535, + 196 + ], + "spans": [ + { + "bbox": [ + 318, + 92, + 535, + 196 + ], + "type": "table", + "html": "
Methods\\(T_{Avg}\\)\\(T_{Max}\\)GPU Mem.mIoU
Source-Only134ms141ms3.5GB35.87
TENT [41]411ms425ms14.5GB37.30
EATA [27]235ms490ms15.6GB37.08
Momentum [33]144ms151ms3.5GB37.33
DUA [25]145ms152ms3.6GB37.79
SITA [15]253ms256ms5.6GB40.64
Ours153ms160ms4.0GB45.51
", + "image_path": "dbd15c8e69691836e1af9e3f5eb218fd73acfd5c665bb264e62761e7518107f1.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "table_body" + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 217, + 545, + 457 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 217, + 545, + 457 + ], + "spans": [ + { + "bbox": [ + 304, + 217, + 545, + 457 + ], + "type": "text", + "content": "different methods. We conduct experiments on the \"GTA5 " + }, + { + "bbox": [ + 304, + 217, + 545, + 457 + ], + "type": "inline_equation", + "content": "\\rightarrow" + }, + { + "bbox": [ + 304, + 217, + 545, + 457 + ], + "type": "text", + "content": " CityScapes\" setting. For the inference time, we report the average time " + }, + { + "bbox": [ + 304, + 217, + 545, + 457 + ], + "type": "inline_equation", + "content": "(T_{Avg} / \\mathrm{ms})" + }, + { + "bbox": [ + 304, + 217, + 545, + 457 + ], + "type": "text", + "content": " and the maximize time " + }, + { + "bbox": [ + 304, + 217, + 545, + 457 + ], + "type": "inline_equation", + "content": "(T_{Max} / \\mathrm{ms})" + }, + { + "bbox": [ + 304, + 217, + 545, + 457 + ], + "type": "text", + "content": " for each testing sample. In addition, the GPU memory cost is also estimated. We can find that the backward-based methods significantly improve the inference time and GPU memory cost. For example, TENT [41] increases the average time from 134ms to 411ms and the memory cost from 3.5GB to 14.5GB. Even though EATA skips the unreliable pixels during optimization and leads to a lower average inference time than TENT, it still introduces large extra computational cost over the source model. Since SITA [15] uses extra augmented image during testing, its computational cost is doubled. Our DIGA and the other two backward-free methods (Momentum [33] and DUA [25]) produce very limited extra computational cost benefiting from their lightweight designs. However, our DIGA significantly surpasses than Momentum [33] and DUA [25] in mIoU. This experiment suggests that our DIGA is an effective and efficient TTDA-Seg method." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 469, + 378, + 482 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 469, + 378, + 482 + ], + "spans": [ + { + "bbox": [ + 306, + 469, + 378, + 482 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 491, + 545, + 657 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 491, + 545, + 657 + ], + "spans": [ + { + "bbox": [ + 304, + 491, + 545, + 657 + ], + "type": "text", + "content": "In this paper, we propose the Dynamically Instance-Guided Adaptation (DIGA) approach for solving TTDA-Seg, which jointly enjoys the effectiveness and efficiency factors. Specifically, DIGA includes two adaptation modules, the distribution adaptation module (DAM) and the semantic adaptation module (SAM), which are both guided by instance-aware information in a non-parametric way. Experiments conducted on five target domains verify that our DIGA effectively can adapt the model at both distribution and semantic levels. We also show that the proposed DIGA achieves state-of-the-art results in TTDA-Seg. In future work, we would like to investigate (1) the learning of adaptive weights in DIGA and (2) the implementation of DIGA in other tasks, e.g., object detection." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 658, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 658, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 658, + 545, + 714 + ], + "type": "text", + "content": "Acknowledgement This work has been supported by the EU H2020 project AI4Media (No. 951911), the PRIN project CREATIVE (Prot. 2020ZSL9F9) and Natural Sciences and Engineering Research Council of Canada (NSERC), Discovery Grants program." + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 758 + ], + "type": "text", + "content": "24097" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 94, + 105, + 105 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 94, + 105, + 105 + ], + "spans": [ + { + "bbox": [ + 48, + 94, + 105, + 105 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 114, + 287, + 712 + ], + "type": "list", + "angle": 0, + "index": 17, + "blocks": [ + { + "bbox": [ + 53, + 114, + 287, + 145 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 114, + 287, + 145 + ], + "spans": [ + { + "bbox": [ + 53, + 114, + 287, + 145 + ], + "type": "text", + "content": "[1] Dian Chen, Dequan Wang, Trevor Darrell, and Sayna Ebrahimi. 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It can be viewed as an equivariant version of kernel point convolutions (KPCov), a widely used convolution form to process point cloud data. Compared with existing equivariant networks, our design is simple, lightweight, fast, and easy to be integrated with existing task-specific point cloud learning pipelines. We achieve these desirable properties by combining group convolutions and quotient representations. Specifically, we discretize $SO(3)$ to finite groups for their simplicity while using $SO(2)$ as the stabilizer subgroup to form spherical quotient feature fields to save computations. We also propose a permutation layer to recover $SO(3)$ features from spherical features to preserve the capacity to distinguish rotations. Experiments show that our method achieves comparable or superior performance in various tasks, including object classification, pose estimation, and keypoint-matching, while consuming much less memory and running faster than existing work. The proposed method can foster the development of equivariant models for real-world applications based on point clouds.", + "bbox": [ + 75, + 361, + 473, + 680 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 708, + 209, + 724 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Processing 3D data has become a vital task today as demands for automated robots and augmented reality technologies emerge. In the past decade, computer vision has significantly succeeded in image processing, but learning from 3D data such as point clouds is still challenging. An important reason is that 3D data presents more variations than 2D images in several aspects. For example, the rigid body transformations in 2D only have 3 degrees of freedom (DoF) with 1 for rotations. In 3D space, the DoF is 6, with 3 for rotations. The 2D translation equivariance is a key factor in the success of convolutional neural networks (CNNs)", + "bbox": [ + 75, + 734, + 468, + 900 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/82dd584913413f61d91b4829268472272c7dab067f61a940e034a69a25e9c274.jpg", + "image_caption": [ + "Figure 1. Our method achieves higher efficiency by working with smaller feature maps defined on $S^{2\\prime} \\times \\mathbb{R}^3$ rather than $SO(3)' \\times \\mathbb{R}^3$ ( $'$ denotes discretization). $\\mathbb{R}^3$ is omitted in the figure. The black arrows in each space represent elements. The top and bottom paths are equivalent, showing the relations among different representations." + ], + "image_footnote": [], + "bbox": [ + 501, + 329, + 885, + 496 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "in image processing, but it is not enough for 3D tasks.", + "bbox": [ + 500, + 595, + 856, + 609 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Generally speaking, equivariance is a property for a map such that given a transformation in the input, the output changes in a predictable way determined by the input transformation. It drastically improves generalization as the variance caused by the transformations is captured via the network by design. Take CNNs as an example, the equivariance property refers to the fact that a translation in the input image results in the same translation in the feature map output from a convolution layer. However, conventional convolutions are not equivariant to rotations, which becomes problematic, especially when we deal with 3D data where many rotational variations occur. In response, on the one hand, data augmentations with 3D rotations are frequently used. On the other hand, equivariant feature learning emerges as a research area, aiming to generalize the translational equivariance to broader transformations.", + "bbox": [ + 496, + 611, + 890, + 852 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "A lot of progress has been made in group-equivariant feature learning. The term group encompasses the 3D rotations and translations, which is called the special Euclidean", + "bbox": [ + 498, + 854, + 893, + 900 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 810, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "1223", + "bbox": [ + 483, + 924, + 514, + 936 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "group of dimension 3, denoted SE(3), and also other more general types of transformations that represent certain symmetries. While many methods have been proposed, equivariant feature learning has not yet become the default strategy for 3D deep learning tasks. From our understanding, two major reasons hinder the broader application of equivariant methods. First, networks dealing with continuous groups typically require specially designed operations not commonly used in neural networks, such as generalized Fourier transform and Monte Carlo sampling. Thus, incorporating them into general neural networks for 3D learning tasks is challenging. Second, for the strategy of working on discretized (finite) groups [6, 19], while the network structures are simpler and closer to conventional networks, they usually suffer from the high dimensionality of the feature maps and convolutions, which causes much larger memory usage and computational load, limiting their practical use.", + "bbox": [ + 75, + 90, + 472, + 347 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "This work proposes E2PN, a convolution structure for processing 3D point clouds. Our proposed approach can enable SE(3)-equivariance on any network with the KPConv [35] backbone by swapping KPCov with E2PN. The equivariance is up to a discretization on SO(3). We leverage a quotient representation to save computational and memory costs by reducing SE(3) feature maps to feature maps defined on $S^2 \\times \\mathbb{R}^3$ (where $S^2$ stands for the 2-sphere). Nevertheless, we can recover the full 6 DoF information through a final permutation layer. As a result, our proposed network is SE(3)-equivariant and computationally efficient, ready for practical point-cloud learning applications.", + "bbox": [ + 75, + 347, + 472, + 527 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Overall, this work has the following contributions:", + "bbox": [ + 96, + 529, + 429, + 544 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- We propose an efficient SE(3)-equivariant convolution structure for 3D point clouds.", + "- We design a permutation layer to recover the full SE(3) information from its quotient space.", + "- We achieve comparable or better performance with significantly reduced computational cost than existing equivariant models.", + "- Our implementation is open-sourced at https://github.com/minghanz/E2PN." + ], + "bbox": [ + 96, + 553, + 467, + 715 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Readers can find preliminary introductions to some related background concepts in the appendix.", + "bbox": [ + 76, + 726, + 468, + 757 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related work", + "text_level": 1, + "bbox": [ + 76, + 768, + 215, + 786 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Group convolutions: In 2016, Cohen and Welling proposed G-CNN [6], enabling equivariance beyond translations on 2D images with generalized G-convolutions (group convolutions) over the group of 90-degree rotations, which is one of the earliest efforts in equivariant deep learning. Group convolution is similar to conventional convolutions but has an extended domain for feature maps and kernels.", + "bbox": [ + 75, + 794, + 468, + 900 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "The idea was then applied to different networks to enable equivariance for SE(2) [6,19], SO(3) [5], SE(3) [2,42], and E(3) [41] groups up to some discretization. The idea mainly works with finite (discretized) groups, as it is convenient to parameterize feature maps and kernels on the discretized group elements just as on pixel grids. Group convolutions have a relatively simple structure, making them straightforward to apply, but a major downside is that the lifted domain of features and kernels causes higher computational and memory costs, and the problem is more prominent when the group is large. Groups convs can also work with continuous groups, for example, with the help of Monte Carlo (MC) estimation as in [13], but they suffer from a large memory burden in MC sampling when the number of layers grows [30].", + "bbox": [ + 496, + 90, + 890, + 303 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Steerable CNNs: Another line of work is steerable CNNs. Instead of augmenting the domain of feature maps, steerable CNNs generalize the space of feature values to be steerable, i.e., the feature values transform predictably as the input transforms. The way the feature transforms is called the group representation in the feature space, governed by the feature type. Features of scalar type are kept unchanged under group actions, and we call the group representation trivial. For vector or tensor feature types, the representation is not trivial, and the features will change with group actions, for example, through rotation matrix multiplication. Steerable CNNs work for both discretized and continuous groups. One may freely design the feature types based on pre-determined basic types and corresponding representations (irreducible representations, i.e., irreps) as building blocks for a given group. Group convolutions can be viewed as a special case of steerable CNNs with regular representations, i.e., channels of a feature vector undergo permutations when transformed. Examples of steerable CNNs include [4,9,36,40,43]. While the framework of steerable CNNs generalizes group convolutions with more flexibility, it requires a good understanding of representation theory and involves generalized Fourier analysis when working with a continuous group, which makes the structure complicated and challenging to apply in real-world applications broadly. The work of [21, 39] also found empirically that steerable CNNs with irreps underperform regular representations in certain tasks.", + "bbox": [ + 496, + 306, + 890, + 731 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Theoretical progress: There has been a lot of progress in the theoretical development of equivariant networks that are not group-specific. [24] developed a general formulation for steerable CNNs with scalar type features, and [7, 8] generalized it to arbitrary feature types. It is proven that all equivariant linear maps can be written as convolutions. The formulation from the perspective of Fourier analysis was presented in [46]. [39] found the general form of solution for the equivariant kernels for $E(2)$ group, later generalized to any compact group [26]. [14] proposed an algorithm to solve for the equivariance constraint for arbitrary", + "bbox": [ + 496, + 734, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "1224", + "bbox": [ + 483, + 924, + 514, + 936 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "matrix group. The formulation of group convolution based on MC estimation was proposed for any Lie group with [13] or without [30] surjective exponential maps. Equivariant non-linear layers like transformers [15, 21] and equivariant set and graph networks [14, 22, 32] are also proposed, but they are not the focus of this paper.", + "bbox": [ + 75, + 90, + 468, + 181 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Applications of equivariant learning in perception tasks: We want to highlight a few equivariant networks that gain attention in perception applications due to their simplicity and practicality. Vector Neurons [10] is a PointNet-like SO(3)-equivariant network for 3D point cloud learning, later applied to point cloud registration [49] and manipulation [34]. It can be viewed as a special case of TFN [36] with type-1 features and self-interactions only. E2CNN [39] as an SE(2)-equivariant framework was applied in several image processing tasks [27, 33], given its generality and user-friendly library. DEVIANT [25] applied scale-equivariant convolutions in monocular 3D object detection. EPN [2] is a group convolution network with SE(3)-equivariance for 3D point cloud learning based on KPCConv [35] and was used in practice, for example in place recognition task [29]. We also position this proposed work in this category, aiming to promote the application of equivariant learning with our efficient and easy-to-use design. Our work is developed based on EPN, which also serves as a major baseline in this paper.", + "bbox": [ + 75, + 183, + 470, + 484 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Methodology", + "text_level": 1, + "bbox": [ + 76, + 500, + 210, + 517 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Overview of the idea", + "text_level": 1, + "bbox": [ + 76, + 526, + 271, + 540 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We first explain why our proposed method is more efficient. Then we discuss how we gain efficiency without sacrificing expressiveness.", + "bbox": [ + 75, + 550, + 468, + 595 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1.1 Improved efficiency with quotient features", + "text_level": 1, + "bbox": [ + 76, + 618, + 426, + 633 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Following the idea of group convolutions, one needs to extend the domain of feature maps from the Euclidean space to the group space, from $\\mathbb{R}^3$ to $\\mathrm{SE}(3) \\cong \\mathrm{SO}(3) \\times \\mathbb{R}^3$ in our case, where we want $\\mathrm{SE}(3)$ -equivariant features for 3D point clouds. We then discretize $\\mathrm{SO}(3)$ to a finite group denoted as $\\mathrm{SO}(3)'$ (we use ' to denote discretization in this paper). The discretization of $\\mathbb{R}^3$ is taken care of by KPConv, which is the non-equivariant counterpart of our method, thus, not discussed here. Up to now, we can obtain a $\\mathrm{SE}(3)$ -equivariant version of KPConv [35] realized through group convolution, which is what EPN [2] presents.", + "bbox": [ + 75, + 643, + 468, + 808 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The specific form of the finite group $\\mathrm{SO}(3)'$ is introduced later in Sec. 3.2, but it can be geometrically understood as the set of all rotations that keep a Platonic solid (i.e., a convex and regular 3D polyhedron) unchanged. As illustrated at the bottom of Fig. 1, the set of rotations can be enumerated by counting the number of vertices, repre", + "bbox": [ + 75, + 810, + 468, + 900 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/3f2de0f441e64bbb7d81e4271c61cfd4141588a6d9edad368bbcd442045ccf3a.jpg", + "image_caption": [ + "Figure 2. Illustration of recovering $\\mathrm{SO}(3)'$ features from $S^{2'}$ features through permutations. The left and right subplots are from the geometric and algebraic views. See Sec. 3.1.2 for more explanation." + ], + "image_footnote": [], + "bbox": [ + 506, + 88, + 893, + 210 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "senting rotations taking a given vertex to any vertices, multiplied by the number of edges connected to a single vertex, representing the rotations that keep a vertex fixed. The same result can be achieved by counting the faces or the edges, but we stick with vertices in the following discussion.", + "bbox": [ + 496, + 282, + 890, + 357 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In comparison, we propose to define feature maps on $S^2 \\times \\mathbb{R}^3$ , where $S^2$ is the sphere space. We have $S^2 = \\mathrm{SO}(3) / \\mathrm{SO}(2)$ , meaning that it is the quotient space of SO(3) given the stabilizer subgroup SO(2). To understand the quotient space intuitively, we can see that all rotations can be grouped by the destination of a point on the sphere (e.g., the north pole) after the rotation. All rotations bringing the north pole to the same destination point form a coset. They are related by rotations around the axis passing through that point, forming a subgroup isomorphic to SO(2). Thus $S^2$ is the quotient of SO(3) and SO(2). In the discretized setup, as depicted in Fig. 1, SO(2)' is discretized by the number of edges connected to a single vertex. The quotient $S^{2'} = \\mathrm{SO}(3)' / \\mathrm{SO}(2)'$ corresponds to the vertices on the Platonic solid.", + "bbox": [ + 496, + 359, + 892, + 583 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In general, $|S^{2'}| = |\\mathrm{SO}(3)'| / |\\mathrm{SO}(2)'| < |\\mathrm{SO}(3)'|$ , thus the size of feature maps and kernels defined on $S^{2'} \\times \\mathbb{R}^3$ is much smaller than those on $\\mathrm{SO}(3)' \\times \\mathbb{R}^3$ . The convolution operation on the former space also requires smaller costs. It is the major reason our method is much more efficient than EPN. There is another design, called symmetric kernel, which further improves the efficiency of our method, but we will refer to Sec. 3.2.3 for details.", + "bbox": [ + 496, + 584, + 890, + 705 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1.2 Information recovery with permutations", + "text_level": 1, + "bbox": [ + 500, + 724, + 834, + 739 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "With the quotient feature map, all rotations moving the north pole to the same point on a sphere are represented by the same point. Thus we immediately lose the ability to distinguish among these rotations, which is a problem if our task is to learn the pose, for example, in the point cloud registration tasks.", + "bbox": [ + 496, + 750, + 890, + 839 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "However, with our proposed permutation layer, we can distinguish every element in $\\mathrm{SO}(3)^{\\prime}$ from the feature maps on $S^{2^{\\prime}}$ . The key observation is that the action of $\\mathrm{SO}(3)$ on $S^2$ is faithful, i.e., $\\forall R\\in \\mathrm{SO}(3)$ and $R\\neq I$ , $\\exists x\\in S^2$", + "bbox": [ + 496, + 840, + 890, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "1225", + "bbox": [ + 483, + 926, + 514, + 936 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "s.t. $Rx \\neq x$ . It means that an action of $\\mathrm{SO}(3)$ other than identity will always cause a change on the $S^2$ feature map when looking at all points on $S^2$ simultaneously. In the discretized setup, it means that there is an injective map $\\phi: \\mathrm{SO}(3)' \\to Sym(|S^{2'}|)$ , where $Sym(|S^{2'}|)$ stands for the symmetric group, i.e., the collection of all permutations of a set of size $|S^{2'}|$ . An element in $Sym(n)$ is a bijective map $\\{1, \\dots, n\\} \\to \\{1, \\dots, n\\}$ , permuting the indices. In other words, each rotation corresponds to a unique permutation of the $S^{2'}$ elements, from which we can distinguish each rotation from the feature map defined on $S^{2'}$ .", + "bbox": [ + 75, + 90, + 472, + 257 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Here we provide the specific form of the permutation layer. Given $\\phi$ mentioned above and a feature map $f: S^{2'} \\to \\mathbb{R}^m$ , we can build a feature map $\\tilde{f}: \\mathrm{SO}(3)' \\to \\mathbb{R}^{mn}$ defined as:", + "bbox": [ + 76, + 261, + 470, + 321 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\tilde {f} (R) = \\left[ f \\left(x \\left[ \\phi_ {R} (1) \\right]\\right), f \\left(x \\left[ \\phi_ {R} (2) \\right]\\right), \\dots , f \\left(x \\left[ \\phi_ {R} (n) \\right]\\right) \\right] \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 86, + 340, + 468, + 359 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $R \\in \\mathrm{SO}(3)'$ , $n = |S^{2'}|$ , and $x[i] \\in S^{2'}$ for $i = 1, \\dots, n$ . Given that $\\phi$ is injective, $\\tilde{f}(R_1) \\neq \\tilde{f}(R_2)$ when $R_1 \\neq R_2$ . Thus we can distinguish $\\mathrm{SO}(3)'$ rotations from $\\tilde{f}$ . See Fig. 2 for an illustration.", + "bbox": [ + 76, + 377, + 468, + 439 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. Specific form of convolution", + "text_level": 1, + "bbox": [ + 76, + 460, + 326, + 477 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2.1 Recap of KPConv", + "text_level": 1, + "bbox": [ + 76, + 488, + 254, + 503 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "A conventional 3D convolution can be written as:", + "bbox": [ + 76, + 520, + 405, + 534 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n[ \\kappa * f ] (x) = \\int_ {\\mathbb {R} ^ {3}} \\kappa (t) f (x + t) d t = \\sum_ {t \\in \\mathbb {R} ^ {3},} \\kappa (t) f (x + t), \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 84, + 551, + 468, + 589 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $x \\in \\mathbb{R}^3$ , and the right hand side is after discretization. We use correlations to implement convolutions in this paper following conventions in deep learning. For processing point clouds, Eq. (2) could be tricky in implementation because it is challenging to align $\\kappa$ with $f$ when there is no grid. The strategy of KPCov is to have a set of kernel points for $\\kappa$ and to gather features to the kernel point coordinates from the input points where $f$ is defined so that they are aligned before the convolution. It is depicted in Fig. 3 (a), and we need to replace $f$ with $\\hat{f}$ in Eq. (2) where $\\hat{f}(x) = \\sum_{y \\in \\mathcal{N}_x} w(|y - x|) f(y)$ and $w$ is a scalar weight function based on distance. $\\hat{f}$ is the features gathered from neighboring input points to align with the kernel points. In this case, the input and output feature map $f$ and $[\\kappa * f]$ are defined on $\\mathbb{R}^3$ , while the kernel $\\kappa$ is defined on $\\mathbb{R}^{3'}$ , i.e., coordinates of the set of kernel points. The gathered feature $\\hat{f}$ when calculating the convolution at $x \\in \\mathbb{R}^3$ is defined at $x + \\mathbb{R}^{3'}$ . Notice that we do not consider the deformable mode of KPCov in this paper.", + "bbox": [ + 75, + 609, + 472, + 901 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/01b7509596275b2118a6737d5ac6c05c565162b852350870d5fa669c4f0c6a17.jpg", + "image_caption": [ + "Figure 3. Illustration of different versions of KPConv. (a) original KPConv (see Sec. 3.2.1). (b) KPConv on finite group or quotient space without the symmetric kernel (see Sec. 3.2.2). (c) KPConv on group or quotient space with the symmetric kernel (see Sec. 3.2.3). (b,c) compared with (a): the convolution kernel is larger because it is defined on a higher dimension. (c) compared with (b): the feature gathering is more efficient because the kernel points are symmetric to the rotations in the rotation group." + ], + "image_footnote": [], + "bbox": [ + 500, + 90, + 895, + 428 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2.2 KPCov on group and on quotient space", + "text_level": 1, + "bbox": [ + 500, + 546, + 836, + 561 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "To extend KPConv to a group convolution [6] with finite group $G'$ , we modify Eq. (2) to", + "bbox": [ + 498, + 569, + 890, + 601 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n[ \\kappa * f ] (g) = \\sum_ {g _ {t} \\in G ^ {\\prime}} \\kappa (g _ {t}) \\hat {f} (g \\cdot g _ {t}), \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 581, + 611, + 890, + 646 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where in our case, $G' = \\mathrm{SE}(3)' = \\mathrm{SO}(3)' \\times \\mathbb{R}^{3'}$ is where $\\kappa$ is defined, $g \\in G^{\\dagger} = \\mathrm{SO}(3)' \\times \\mathbb{R}^{3}$ is where the input and output feature map is defined. $\\hat{f}$ is defined on $g \\cdot G'$ when calculating the convolution at $g$ . Denote an element $g \\in \\mathrm{SE}(3)$ as $(R,t)$ where $R \\in \\mathrm{SO}(3)$ and $t \\in \\mathbb{R}^{3}$ , the binary operation $\\cdot$ for $\\mathrm{SE}(3)$ can be specified as $(R_1,t_1) \\cdot (R_2,t_2) = (R_1R_2,t_1 + R_1t_2)$ , same for the discretized case. EPN [2] follows this form of convolution. However, as discussed in Sec. 3.1.1, the size of group $|\\mathrm{SE}(3)'| = |\\mathrm{SO}(3)'||\\mathbb{R}^{3'}|$ , making it expensive to store the feature map and compute the convolution. To alleviate this issue, EPN has to conduct convolutions in $\\mathrm{SO}(3)'$ and $\\mathbb{R}^{3'}$ separately (i.e., separable convolutions [2, 3]), so that the computational cost is reduced.", + "bbox": [ + 496, + 656, + 890, + 868 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We use quotient feature maps to address this issue. To conduct convolutions on the quotient space $X =$", + "bbox": [ + 498, + 869, + 890, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "1226", + "bbox": [ + 483, + 924, + 514, + 936 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/2a767a62d778d7279485b05fbba2413f9f322ca4a10cc66f1fb5ec41eaf4eb3b.jpg", + "image_caption": [ + "Figure 4. Visualization of the symmetric kernel $\\kappa$ used in our work, where $\\mathbb{R}^{3\\prime} = \\{rS^{2\\prime}\\cup 0\\mid r > 0\\}$" + ], + "image_footnote": [], + "bbox": [ + 109, + 90, + 297, + 224 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/520715ce54709ff811f5b358831db09955d19d3128202c7e3ac38b44b69fa6f4.jpg", + "image_caption": [ + "Figure 5. Illustration of all five types of Platonic solids and their corresponding finite rotation groups." + ], + "image_footnote": [], + "bbox": [ + 310, + 90, + 439, + 224 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "$\\mathrm{SE}(3) / \\mathrm{SO}(2) = S^2 \\times \\mathbb{R}^3$ , we cannot directly use Eq. (3), because the $\\cdot$ operation is not defined between two elements in $X$ since $X$ is not a group. It is pointed out in [7, 8] that we can write convolutions on the quotient space as", + "bbox": [ + 75, + 280, + 470, + 343 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n[ \\kappa * f ] (x) = \\sum_ {x _ {t} \\in X ^ {\\prime}} \\kappa (x _ {t}) \\hat {f} (s (x) \\cdot x _ {t}), \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 145, + 351, + 468, + 386 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $X^{\\prime} = S^{2^{\\prime}}\\times \\mathbb{R}^{3^{\\prime}}$ is the domain of $\\kappa$ , $X^{\\dagger} = S^{2^{\\prime}}\\times \\mathbb{R}^{3}$ is the domain of $f$ and $[\\kappa *f]$ , and $\\hat{f}$ is defined on $s(x)\\cdot X^{\\prime}$ . $s(x)$ is called the section map, $s:X^{\\prime}\\to G^{\\prime}$ (or $X\\rightarrow G$ in the continuous case), mapping $x\\in X^{\\prime}$ to an element of $G^{\\prime}$ in the corresponding coset. With the section map, the $\\cdot$ operation denotes the action of the group $G$ on quotient space $X$ , i.e., $\\cdot :G\\times X\\to X$ . Denote an element in $S^2\\times \\mathbb{R}^3$ as $(R\\mathbf{n},t)$ , where $R\\in \\mathrm{SO}(3)$ , $\\mathbf{n}$ is the north pole point on the unit sphere $(0,0,1)$ . Then $R\\mathbf{n}$ represents arbitrary points on the sphere $S^2$ . The action $\\cdot$ can then be written as $(R_{1},t_{1})\\cdot (R_{2}\\mathbf{n},t_{2}) = (R_{1}R_{2}\\mathbf{n},t_{1} + R_{1}t_{2})$ .", + "bbox": [ + 75, + 393, + 472, + 564 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.2.3 Symmetric kernels", + "text_level": 1, + "bbox": [ + 76, + 580, + 264, + 594 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Now we introduce the specific form of $\\mathbb{R}^{3'}$ , i.e., the location of kernel points in KPConv. In our design, $\\mathbb{R}^{3'} = \\{rS^{2'} \\cup 0 \\mid r > 0\\}$ , i.e., the set of vertices of the Platonic solid with radius $r$ and the origin point. $\\mathbb{R}^{3'}$ is very similar to $S^{2'}$ , because we want to make the kernel symmetric to $\\mathrm{SO}(3)'$ . More precisely, we desire $\\mathbb{R}^{3'}$ to be closed under the action of $\\mathrm{SO}(3)'$ . There are two reasons as follows.", + "bbox": [ + 75, + 603, + 468, + 709 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Steerability constraint To make the convolution on quotient space equivariant, defining a valid form of convolution as Eq. (4) is not the whole story. The kernel values must satisfy a condition called the steerability constraint, which is required for all steerable CNNs. More background knowledge can be found in [8]. In our case, the steerability constraint is", + "bbox": [ + 75, + 727, + 468, + 832 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\kappa (x) = \\kappa \\left(R _ {z} \\cdot x\\right), \\forall x \\in X ^ {\\prime}, \\forall R _ {z} \\in \\mathrm {S O} (2) ^ {\\prime}, \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 125, + 843, + 468, + 861 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $R_{z}$ is a $z$ -axis rotation. The derivation of Eq. (5) from the general form of steerability constraints can be found in", + "bbox": [ + 76, + 869, + 470, + 901 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/884066ac6990af7ec284f3f120286b5a422ade6392e0b3df6e260aae0e791c87.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
Rotation groupsTetrahedral TOctahedral OIcosahedral I
Platonic solidsTetrahedronCubeOctahedronDodecahedronIcosahedron
Size|SO(3)'| = 12 |S2'| = 4 |SO(2)'| = 3|SO(3)'| = 24 |S2'| = 8 |SO(2)'| = 3|SO(3)'| = 24 |S2'| = 6 |SO(2)'| = 4|SO(3)'| = 60 |S2'| = 20 |SO(2)'| = 3|SO(3)'| = 60 |S2'| = 12 |SO(2)'| = 5
", + "bbox": [ + 503, + 88, + 893, + 219 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "the appendix. Here the $\\cdot$ operation inherits from the action of $G'$ on $X'$ since $\\mathrm{SO}(2)' \\subset \\mathrm{SO}(3)' \\subset G'$ . Specifically, we have $R_z \\cdot (R\\mathbf{n}, t) = (R_z, 0) \\cdot (R\\mathbf{n}, t) = (R_z R\\mathbf{n}, R_z t)$ . Replace $x$ with $(R\\mathbf{n}, t)$ in Eq. (5), and we have", + "bbox": [ + 496, + 271, + 890, + 333 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\kappa (R \\mathbf {n}, t) = \\kappa \\left(R _ {z} R \\mathbf {n}, R _ {z} t\\right), \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 599, + 340, + 890, + 357 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "$\\forall R\\mathbf{n}\\in S^{2^{\\prime}},\\forall t\\in \\mathbb{R}^{3^{\\prime}},\\forall R_{z}\\in \\mathrm{SO}(2)^{\\prime}.$ Notice that it implies that we need $R_{z}t\\in \\mathbb{R}^{3^{\\prime}},\\forall t\\in \\mathbb{R}^{3^{\\prime}},\\forall R_{z}\\in \\mathrm{SO}(2^{\\prime})$ so that $\\kappa$ is defined on the right hand side of Eq. (6). In other words, the kernel points $\\mathbb{R}^{3^{\\prime}}$ need to be closed under $\\mathrm{SO}(2)^{\\prime}$ . Obviously, having $\\mathbb{R}^{3^{\\prime}}$ closed under $\\mathrm{SO}(3)^{\\prime}$ is a sufficient condition for this.", + "bbox": [ + 496, + 364, + 890, + 454 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "For the $S^{2'}$ dimension, since $S^{2'}$ is symmetric (closed) to $\\mathrm{SO}(3)'$ by definition and $\\mathrm{SO}(2)' \\subset \\mathrm{SO}(3)'$ , we always have $R_z R\\mathbf{n} \\in S^{2'}$ and $\\kappa$ is always defined.", + "bbox": [ + 496, + 455, + 890, + 501 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Efficient feature gathering Another important reason for the design choice of $\\mathrm{SO}(3)^{\\prime}$ -symmetric kernels is that it enables more efficient feature gathering. Consider a spatial location $t_0\\in \\mathbb{R}^3$ , the convolution feature output at this point is a stack of $[[\\kappa *f](x_i)]_i$ with $x_{i}\\in (S^{2^{\\prime}},t_{0})\\subset X^{\\dagger}$ . As shown in Eq. (4), it involves feature gathering for $\\hat{f}$ at $s(x_{i})\\cdot x_{jk}$ for every $x_{jk}\\in X' = S^{2'}\\times \\mathbb{R}^{3'}$ . Denote an instance of $s(x_{i}) = (R_{i},t_{0}),x_{jk} = (R_{j}\\mathbf{n},t_{k})$ , then $s(x_{i})\\cdot x_{jk} = (R_{i}R_{j}\\mathbf{n},t_{0} + R_{i}t_{k})$ . If $\\mathbb{R}^{3^{\\prime}}$ is closed under $\\mathrm{SO}(3)^{\\prime}$ , then we have", + "bbox": [ + 496, + 518, + 892, + 671 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\left\\{R _ {i} t _ {k} \\mid t _ {k} \\in \\mathbb {R} ^ {3 ^ {\\prime}} \\right\\} = \\mathbb {R} ^ {3 ^ {\\prime}}, \\forall R _ {i} \\in \\mathrm {S O} (3) ^ {\\prime}, \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 562, + 678, + 890, + 696 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "which implies that the feature gathering for all $S^{2'}$ channels can be done once at the same set of spatial positions specified by $\\mathbb{R}^{3'}$ . An illustration is shown in Fig. 3. Without the symmetric kernel, the KPConv on group or quotient space looks like Fig. 3 (b), where the kernel is rotated for each $\\mathrm{SO}(3)'$ (for group KPConv) or $S^{2'}$ (for quotient KPConv) channel separately to gather input features. However, with symmetric kernels, as shown in Fig. 3 (c), the rotations keep the position of kernel points unchanged up to a permutation so that the feature-gathering step is simplified. Specifically, the number of spatial positions needed for feature gathering without symmetric kernels is $|SO(3)'| \\mathbb{R}^{3'}|$ for group KPConv or $|S^{2'}| \\mathbb{R}^{3'}|$ for quotient KPConv, while the number", + "bbox": [ + 496, + 703, + 893, + 901 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "1227", + "bbox": [ + 483, + 925, + 514, + 936 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/604185e05401f76d0c39b1783d106182fa3a0b04bc4899b9e4f3768ee8dbd18b.jpg", + "table_caption": [ + "Table 1. Efficiency comparison in terms of GPU memory consumption and the computation speed between EPN [2] and our method on three tasks. Two numbers are reported for training/inference respectively. $\\downarrow$ means lower is better. $\\uparrow$ means higher is better. The best is shown in bold font." + ], + "table_footnote": [], + "table_body": "
TasksModelNet40 PoseModelNet40 Classification3DMatch Keypoint Matching
MethodsMemory (GB) ↓Speed (fps) ↑Memory (GB) ↓Speed (fps) ↑Memory (GB) ↓Speed (fps) ↑
EPN [2]22.2 / 16.91.1 / 1.613.4 / 12.71.9 / 1.537.4 / 8.50.6 / 3.1
Ours (w/o symmetric kernels)4.8 / 3.75.1 / 10.14.1 / 3.27.8 / 7.87.5 / 2.82.6 / 16.7
Ours (w/ symmetric kernels)4.3 / 2.86.7 / 11.13.9 / 2.79.1 / 10.36.5 / 2.43.7 / 23.6
", + "bbox": [ + 80, + 119, + 885, + 207 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "is $|\\mathbb{R}^{3^{\\prime}}|$ with symmetric kernels. The convolution kernels in Fig. 3 is an abstract illustration, while the actual symmetric kernel in our work is visualized in Fig. 4.", + "bbox": [ + 75, + 229, + 470, + 277 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "3.2.4 Choices of the discretization of $SO(3)$ and $S^2$", + "text_level": 1, + "bbox": [ + 76, + 297, + 444, + 314 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "In Sec. 3.1.1, we mentioned that the discretization of $\\mathrm{SO}(3)$ is the rotation group that respects the symmetry of a Platonic solid. There are five types of Platonic solids, corresponding to 3 finite rotation groups, as shown in Fig. 5. Choosing $\\mathrm{SO}(3)'$ to be any of them is valid, representing a discretization of $\\mathrm{SO}(3)$ to different resolutions. The different Platonic solids with the same rotation group $\\mathrm{SO}(3)'$ represents different discretizations of $S^{2'}$ and $\\mathrm{SO}(2)'$ .", + "bbox": [ + 75, + 321, + 467, + 444 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "If we use a small $\\mathrm{SO}(3)'$ (for example, $T$ ), the strategy of using $\\mathbb{R}^{3'} = \\{rS^{2'} \\cup 0 \\mid r > 0\\}$ could be problematic because the number of kernel points could be too few to learn representative features. In this case, we are free to design the kernel points differently, as long as they are closed under $\\mathrm{SO}(3)'$ . For example, one may add kernel points at the center of all edges and/or faces. One may even use a combination of several polyhedrons with different radii $r$ .", + "bbox": [ + 75, + 445, + 467, + 566 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "In this paper, we only choose the icosahedron as the Platonic solid to conduct experiments for three reasons. First, it has the finest discretization of SO(3). Second, it has a smaller size of $S^{2'}$ compared with the dodecahedron, maximizing the benefit of working with quotient features. Third, it is consistent with existing methods [1,2], enabling direct comparison with the baselines.", + "bbox": [ + 75, + 566, + 467, + 672 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "3.2.5 Other aspects of the network", + "text_level": 1, + "bbox": [ + 76, + 693, + 333, + 709 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We use element-wise scalar nonlinearity (ReLU and leaky ReLu) in the network. The spatial pooling is done by subsampling the input points and aggregating the features of neighboring input points to the subsampled points. Batch normalization is applied to normalize over the batch, $S^{2'}$ , and $\\mathbb{R}^3$ dimensions. All these choices follow the common practice of conventional CNNs (KPCov [35]) and group convolutions (EPN [2]). We also adopted the group attentive pooling in EPN to pool over the $S^{2'}$ dimension and generate $\\mathrm{SO}(3)'$ -invariant features.", + "bbox": [ + 75, + 718, + 467, + 868 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Depending on the specific task in the experiment, the prediction head has a slightly different design, composing", + "bbox": [ + 76, + 869, + 467, + 901 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "the last few layers of the network. The loss functions are inherited from EPN [2], including cross-entropy loss for classifications, L2 loss for residual pose regression, and batch-hard triplet loss for keypoint matching. We refer to the appendix for more details about the prediction heads and the loss functions.", + "bbox": [ + 496, + 231, + 890, + 321 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "3.3. Relation to existing work", + "text_level": 1, + "bbox": [ + 500, + 334, + 728, + 349 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "In the context of literature on group-equivariant neural networks, our method is under the theoretical framework of equivariant CNNs on homogeneous spaces [8, 24, 46]. Our work is a new form of realization when working with 3D point clouds and adapting the convolution structure of KPCov. We explore a balance of simplicity, efficiency, and expressiveness by finding the proper quotient space and discretization. Our method is an extension of group convolutions, leveraging their clean structure enabled by discretization. Our method can also be viewed as a steerable CNN with homogeneous space $S^2 \\times \\mathbb{R}^3$ and stabilizer subgroup SO(2) with scalar-type features or with homogeneous space $\\mathbb{R}^3$ and stabilizer subgroup SO(3) with $S^2$ features. The proposed work paves the way for efficiency improvement using quotient representation learning on finite groups. We also emphasize the group-variant side of equivariant models with the permutation layer to distinguish rotations, while existing work focuses on the benefit of getting group-invariant features from equivariant models.", + "bbox": [ + 496, + 358, + 890, + 645 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 500, + 660, + 633, + 678 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Our major baseline to compare with is EPN [2], a state-of-the-art group convolution network, as we are similar in several ways. Both are KPConv-style convolutions with SE(3)-equivariance. Both use the icosahedral rotation group $\\mathcal{I}$ to discretize SO(3). However, EPN has features defined on $\\mathcal{I} \\times \\mathbb{R}^3$ , compared with $S^{2'} \\times \\mathbb{R}^3$ in our method.", + "bbox": [ + 496, + 686, + 890, + 777 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Two datasets, ModelNet40 [44] and 3DMatch [47], are used in the experiments. ModelNet40 is composed of 3D CAD models of 40 categories of objects. 3DMatch is a real-scan dataset of indoor scenes. For the ModelNet40 dataset, we conduct the classification and pose estimation tasks. For the 3DMatch dataset, we conduct the keypoint matching task. These tasks are also studied in EPN [2].", + "bbox": [ + 496, + 777, + 890, + 883 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "In Tab. 1, we list the GPU memory consumption and run", + "bbox": [ + 517, + 885, + 890, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "1228", + "bbox": [ + 483, + 925, + 514, + 936 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/e1a4bd644bc676bdd2e36a2716788b948e1ce5bdbd6f436d45d9985cb48e3e35.jpg", + "table_caption": [ + "Table 2. Experimental result of object classification on ModelNet40. The best is bolded. The best in equivariant models is underlined. Noisy: test using input with random translation, scaling, jittering, and dropout. Clean: test without above processing. SO(3): random rotations. Id: no rotation. ico: random rotations in I. ESCNN works with voxelized data, thus not having Noisy results with point-wise augmentations. FLOPs are counted using fvcore, which does not support DGL used in TFN and SE(3)-T, thus left blank. The efficiency comparison uses the same batch size as in Tab. 1 (see appendix)." + ], + "table_footnote": [], + "table_body": "
TypeColumn ##1#2#3#4#5#6#7#8#9#10#11#12#13#14
MetricsModelNet40 classification performance metric: Acc (%) ↑Efficiency metricsFLOPs per training batch (G)Trainable params (M)
Train rotationSO(3)IdMemory (GB)↓ train/testSpeed (fps)↑ train/test
Test rotationSO(3)IdSO(3)Idico
Test conditionNoisyCleanNoisyCleanNoisyCleanNoisyCleanNoisyClean
Non-equivKPCov [35]75.7181.1776.8882.0212.6612.2289.4691.85--0.18/0.2517.24/18.480.741.69
PointNet++ [31]81.3184.8883.0385.7613.4413.7690.6791.55--1.03/0.57.06/7.4310.591.48
DGCNN [38]79.8684.7782.5485.6215.3617.2691.0092.18--1.96/1.6917.90/17.5032.651.81
PT [48]78.5179.6878.8379.6816.5316.7786.9888.10--4.16/5.824.80/5.03220.999.58
CurveNet [45]84.7288.3385.8288.9417.3418.0391.5392.63--1.20/0.335.61/7.544.222.14
PCT [17]86.9189.1087.6489.8316.3317.9591.6992.87--1.18/0.808.54/20.8527.412.87
EquivalentESCNN [1]-82.40-77.73-29.03-88.94--4.71/5.503.79/8.38428.610.46
TFN [36]58.2762.6458.0662.6457.5062.2859.2062.28--15.95/8.71.83/6.08-0.06
SE(3)-T [15]60.3766.2961.1866.2944.6150.5344.8150.53--19.39/9.651.54/5.13-0.11
EPN [2]84.6387.8485.3488.8330.9932.3290.0391.6190.0491.6013.40/12.721.86/1.4958.953.06
Ours (w/ GA pooling [2])85.0487.5185.4987.6341.4644.4389.7390.5090.0090.503.95/2.709.21/10.37170.682.53
Ours (w/ permutation)86.9988.6288.2189.6239.5442.7890.6691.7790.6891.773.95/2.709.09/10.28170.772.65
", + "bbox": [ + 80, + 143, + 887, + 320 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "ning speed of our method and EPN [2] in the three tasks. The comparisons are under the same input size, number of feature channels, and number of network layers. The separable convolutions on $\\mathrm{SO}(3)$ and $\\mathbb{R}^3$ in EPN are together considered as one layer. The numbers are not comparable between training and inference because the batch size could be different (see the appendix). The specific configurations in each experiment are introduced later. All experiments are run on a single NVIDIA A40 GPU. Our network with quotient space convolutions is much smaller and runs much faster in all three tasks, indicating the potential value for real applications. We boost efficiency without sacrificing performance, as is shown later.", + "bbox": [ + 75, + 344, + 468, + 540 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Ablation study: We list two rows of our results in Tab. 1 to show the effect of efficient feature gathering enabled by the symmetric kernels. The results of without symmetric kernels are generated using the same kernel points as with symmetric kernels, but ignoring the fact that they are symmetric to rotations and gathering features at $|S^{2'}| |\\mathbb{R}^{3'}|$ locations, instead of at $|\\mathbb{R}^{3'}|$ locations and permuting them. The efficient feature gathering brings further efficiency improvements, especially in terms of computational speed.", + "bbox": [ + 75, + 542, + 468, + 679 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.1. Object classification on ModelNet40", + "text_level": 1, + "bbox": [ + 76, + 691, + 390, + 709 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "For this task, given a point cloud of an object, the network predicts its category. The evaluation metric is classification accuracy (Acc). In this experiment, we show an extensive efficiency comparison with more existing networks, equivariant and non-equivariant. We also examine a wide combination of input conditions in training and testing to show the effect of equivariance and robustness against input imperfections. All models are trained with data augmentation, including random translation, scaling, jittering, and dropout.", + "bbox": [ + 75, + 717, + 468, + 868 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Our method has outstanding performance as shown in Tab. 2. In columns #1-4, all methods are trained with rota", + "bbox": [ + 76, + 869, + 468, + 898 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/197f7ddb47f0070e848db7b62fd50e69e16f7fd25fe173acec4875622d140a3b.jpg", + "table_caption": [ + "Table 3. Pose estimation on ModelNet40. Mean, median, and max angular errors are calculated over the test set. Statistics (average and standard deviation) over 10 test runs are shown to account for the randomness." + ], + "table_footnote": [], + "table_body": "
MetricsMean (°) ↓Median (°) ↓Max (°) ↓
StatsAvg μSD σAvg μSD σAvg μSD σ
KPConv [35]13.991.5310.700.81115.1957.84
EPN [2]1.100.201.360.137.062.52
Ours1.200.080.960.056.711.28
", + "bbox": [ + 503, + 385, + 885, + 452 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "tional augmentation. Our method performs the best among listed equivariant models and is on par with PCT [18] among all models. Our method is intended to work with rotational augmentations so that the equivariance gap caused by discretization can be interpolated through training. However, we still experiment with training without rotational augmentation, as shown in columns #5-10. From columns #9-10, we can verify the equivariance to the icosahedral rotation group of our model. Columns #5-6 show the effect of discretization on the continuous SO(3) if no interpolation is trained, in which case the performance lands between non-equivariant models and continuously SO(3)-equivariant models. The efficiency of our method outperforms all equivariant baselines and is similar to nonequivariant models. The FLOPs and number of trainable parameters are also listed for reference. We found that FLOPs do not strictly correlate with running speed, which could be due to different memory access costs and parallelism.", + "bbox": [ + 496, + 478, + 890, + 748 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Ablation study: Since this task requires SE(3)-invariant features, there are two options in our network: either using the group-attentive pooling (GA pooling) introduced in EPN [2] to pool over the $S^{2^{\\prime}}$ dimensions or using the permutation layer to find the canonical permutation of $S^{2^{\\prime}}$ dimensions. Either way, the canonical pose of objects in ModelNet40 can be used for supervision. Tab. 2 shows that the permutation layer yields better performance with negligible computational overhead. The reason could be that the permutation layer as in Eq. (1) stacks features from $S^{2^{\\prime}}$", + "bbox": [ + 496, + 750, + 890, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "1229", + "bbox": [ + 483, + 926, + 514, + 936 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/230273c256e1bc2745cd6cc4b37f8e456eadc8e89d5cb6a310839cfef66e2c73.jpg", + "table_caption": [ + "Table 4. Experiment result of keypoint matching on the 3DMatch dataset. The numbers are the average recall $(\\%)$ , and the higher, the better. Notation * represents the result with the given point normal information." + ], + "table_footnote": [], + "table_body": "
SHOT [37]3DM [47]CGF [23]PPFN [12]PPFF [11]3DSN [16]Li [28]Li [28]*EPN [2]Ours
Kitchen74.358.360.389.778.797.592.199.499.099.4
Home 180.172.471.155.876.396.291.098.799.498.7
Home 270.761.556.759.161.593.285.694.796.296.6
Hotel 177.454.957.158.068.197.495.199.699.699.1
Hotel 272.148.153.857.771.292.891.3100.097.198.1
Hotel 385.261.183.361.194.498.296.3100.0100.0100.0
Study64.051.737.753.462.095.091.895.596.295.2
MIT Lab62.350.745.563.662.394.184.492.293.590.9
Average73.357.358.262.371.895.691.097.597.697.3
", + "bbox": [ + 81, + 119, + 888, + 280 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "and thus preserves the information better, compared with weighted averaging over the $S^{2'}$ dimension as done in GA pooling.", + "bbox": [ + 75, + 303, + 470, + 349 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.2. Pose Estimation on ModelNet40", + "text_level": 1, + "bbox": [ + 76, + 359, + 359, + 373 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this experiment, the network takes a pair of point clouds of an object and predicts the relative rotation between them. To avoid the pose ambiguity of objects with symmetric rotational shapes, only the airplane category is used in this experiment, with 626 models in the training set and 100 models in the test set. A point cloud is generated by randomly subsampling 1,024 points on the surface, and it is randomly rotated to form a pair.", + "bbox": [ + 75, + 383, + 468, + 503 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "The experimental result is shown in Tab. 3. We achieved similar rotation estimation accuracy to EPN [2] overall. While our mean error is slightly larger, the lower median error, max error, and standard deviations show that our method delivers a more reliable registration. It could imply that representing rotations as a permutation of features is more robust than representing them as a single element in the feature map. Besides, the equivariant networks outperform the non-equivariant KPConv [35] by a large margin.", + "bbox": [ + 75, + 503, + 468, + 641 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.3. Keypoint matching on 3DMatch", + "text_level": 1, + "bbox": [ + 76, + 650, + 362, + 666 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this task, patches of point clouds extracted locally around keypoints in a large, dense scan are input to the network, and each is mapped to a feature vector of 64 dimension as the keypoint descriptor. Each patch has 1,024 points. Then we evaluate the average recall of keypoint correspondence across different scans through nearest neighbor search in the feature space, as proposed in PPFNet [12].", + "bbox": [ + 75, + 672, + 468, + 779 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "This experiment's performance in Tab. 4 indicates the capability of learning distinctive and rotation-invariant features for local patches of point clouds. Though not achieving the best in the list, our method delivers comparable performance to the top methods using only a fraction of the computational resources as EPN [2] (see Tab. 1). We use the GA pooling layer [2] in this experiment because the permutation layer requires supervision on the pose, while", + "bbox": [ + 75, + 780, + 470, + 902 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "a canonical pose is not defined for local patches of point clouds, and GA pooling works with or without the pose supervision. However, the result shows that GA pooling over the $|S^{2t}|$ features also provides distinctive features for keypoint matching. This part may be further improved by taking the information of the global scan [12] or the matching scan [20] into consideration, in which case the permutation layer may get hints on the optimal permutation from the larger context. This topic goes beyond the focus of this paper and is left for future work.", + "bbox": [ + 496, + 303, + 893, + 455 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 467, + 619, + 483 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "This paper presents a new design of SE(3)-equivariant point cloud convolution network, which is efficient, simple, and expressive simultaneously by working with feature maps defined on the quotient space $S^2 \\times \\mathbb{R}^3$ associated with the stabilizer SO(2). We further improve the efficiency of the convolutions by designing the kernel points to be symmetric to the discretized rotation group $\\mathrm{SO}(3)'$ . Moreover, we propose a permutation layer to recover $\\mathrm{SO}(3)'$ information from $S^{2/}$ dimensions of the features so that the network can detect SO(3) rotations. Experiments show that our network delivers state-of-the-art performance in multiple tasks while consuming only a fraction of memory and computation resources as a group-convolution network with similar performance. Our method can open exciting opportunities to introduce the SE(3)-equivariance property to mainstream point cloud networks for various tasks.", + "bbox": [ + 496, + 492, + 893, + 734 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "This work also has limitations. We do not outperform EPN [2] in the keypoint matching task, implying that the network, especially the permutation layer, needs improvement when dealing with inputs without a clear pose definition. Other possibilities for the network design also remain open. For example: What if we use a non-scalar type of feature on the quotient space? How to further alleviate the impact of the discretization of a continuous group? From a general perspective, extending the discretized quotient space convolution strategy to other groups is also an attractive direction for future work.", + "bbox": [ + 496, + 734, + 893, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "1230", + "bbox": [ + 483, + 925, + 517, + 936 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 174, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Gabriele Cesa, Leon Lang, and Maurice Weiler. A program to build E(N)-equivariant steerable CNNs. In International Conference on Learning Representations, 2022. 6, 7", + "[2] Haiwei Chen, Shichen Liu, Weikai Chen, Hao Li, and Randall Hill. Equivariant point network for 3D point cloud analysis. In Proceedings of the IEEE Conference on Computer Vision and Pattern Recognition, pages 14514-14523, 2021. 2, 3, 4, 6, 7, 8", + "[3] François Chollet. 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PMLR, 2022. 3" + ], + "bbox": [ + 501, + 92, + 893, + 792 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "1232", + "bbox": [ + 483, + 926, + 514, + 936 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/E2PN_ Efficient SE(3)-Equivariant Point Network/8cfd95ec-52b9-4e92-8a17-84d6d71e6730_model.json b/2023/E2PN_ Efficient SE(3)-Equivariant Point Network/8cfd95ec-52b9-4e92-8a17-84d6d71e6730_model.json new file mode 100644 index 0000000000000000000000000000000000000000..242077644eb24baff1af53be9894384679341763 --- /dev/null +++ b/2023/E2PN_ Efficient SE(3)-Equivariant Point Network/8cfd95ec-52b9-4e92-8a17-84d6d71e6730_model.json @@ -0,0 +1,2090 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.001, + 0.812, + 0.047 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.234, + 0.131, + 0.738, + 0.154 + ], + "angle": 0, + "content": "E2PN: Efficient SE(3)-Equivariant Point Network" + }, + { + "type": "text", + "bbox": [ + 0.173, + 0.182, + 0.36, + 0.234 + ], + "angle": 0, + "content": "Minghan Zhu \nUniversity of Michigan \nminghanz@umich.edu" + }, + { + "type": "text", + "bbox": [ + 0.408, + 0.182, + 0.596, + 0.234 + ], + "angle": 0, + "content": "Maani Ghaffari \nUniversity of Michigan \nmaanigj@umich.edu" + }, + { + "type": "text", + "bbox": [ + 0.644, + 0.182, + 0.798, + 0.234 + ], + "angle": 0, + "content": "William A Clark Cornell University wac76@cornell.edu" + }, + { + "type": "text", + "bbox": [ + 0.393, + 0.242, + 0.58, + 0.279 + ], + "angle": 0, + "content": "Huei Peng \nUniversity of Michigan" + }, + { + "type": "text", + "bbox": [ + 0.415, + 0.281, + 0.551, + 0.294 + ], + "angle": 0, + "content": "hpeng@umich.edu" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.329, + 0.314, + 0.345 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.362, + 0.474, + 0.681 + ], + "angle": 0, + "content": "This paper proposes a convolution structure for learning \\( SE(3) \\)-equivariant features from 3D point clouds. It can be viewed as an equivariant version of kernel point convolutions (KPCov), a widely used convolution form to process point cloud data. Compared with existing equivariant networks, our design is simple, lightweight, fast, and easy to be integrated with existing task-specific point cloud learning pipelines. We achieve these desirable properties by combining group convolutions and quotient representations. Specifically, we discretize \\( SO(3) \\) to finite groups for their simplicity while using \\( SO(2) \\) as the stabilizer subgroup to form spherical quotient feature fields to save computations. We also propose a permutation layer to recover \\( SO(3) \\) features from spherical features to preserve the capacity to distinguish rotations. Experiments show that our method achieves comparable or superior performance in various tasks, including object classification, pose estimation, and keypoint-matching, while consuming much less memory and running faster than existing work. The proposed method can foster the development of equivariant models for real-world applications based on point clouds." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.709, + 0.21, + 0.725 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.735, + 0.47, + 0.901 + ], + "angle": 0, + "content": "Processing 3D data has become a vital task today as demands for automated robots and augmented reality technologies emerge. In the past decade, computer vision has significantly succeeded in image processing, but learning from 3D data such as point clouds is still challenging. An important reason is that 3D data presents more variations than 2D images in several aspects. For example, the rigid body transformations in 2D only have 3 degrees of freedom (DoF) with 1 for rotations. In 3D space, the DoF is 6, with 3 for rotations. The 2D translation equivariance is a key factor in the success of convolutional neural networks (CNNs)" + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.33, + 0.887, + 0.497 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.505, + 0.895, + 0.567 + ], + "angle": 0, + "content": "Figure 1. Our method achieves higher efficiency by working with smaller feature maps defined on \\( S^{2\\prime} \\times \\mathbb{R}^3 \\) rather than \\( SO(3)' \\times \\mathbb{R}^3 \\) (\\( ' \\) denotes discretization). \\( \\mathbb{R}^3 \\) is omitted in the figure. The black arrows in each space represent elements. The top and bottom paths are equivalent, showing the relations among different representations." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.596, + 0.857, + 0.611 + ], + "angle": 0, + "content": "in image processing, but it is not enough for 3D tasks." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.612, + 0.892, + 0.853 + ], + "angle": 0, + "content": "Generally speaking, equivariance is a property for a map such that given a transformation in the input, the output changes in a predictable way determined by the input transformation. It drastically improves generalization as the variance caused by the transformations is captured via the network by design. Take CNNs as an example, the equivariance property refers to the fact that a translation in the input image results in the same translation in the feature map output from a convolution layer. However, conventional convolutions are not equivariant to rotations, which becomes problematic, especially when we deal with 3D data where many rotational variations occur. In response, on the one hand, data augmentations with 3D rotations are frequently used. On the other hand, equivariant feature learning emerges as a research area, aiming to generalize the translational equivariance to broader transformations." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.856, + 0.895, + 0.901 + ], + "angle": 0, + "content": "A lot of progress has been made in group-equivariant feature learning. The term group encompasses the 3D rotations and translations, which is called the special Euclidean" + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.925, + 0.516, + 0.937 + ], + "angle": 0, + "content": "1223" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.091, + 0.473, + 0.348 + ], + "angle": 0, + "content": "group of dimension 3, denoted SE(3), and also other more general types of transformations that represent certain symmetries. While many methods have been proposed, equivariant feature learning has not yet become the default strategy for 3D deep learning tasks. From our understanding, two major reasons hinder the broader application of equivariant methods. First, networks dealing with continuous groups typically require specially designed operations not commonly used in neural networks, such as generalized Fourier transform and Monte Carlo sampling. Thus, incorporating them into general neural networks for 3D learning tasks is challenging. Second, for the strategy of working on discretized (finite) groups [6, 19], while the network structures are simpler and closer to conventional networks, they usually suffer from the high dimensionality of the feature maps and convolutions, which causes much larger memory usage and computational load, limiting their practical use." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.348, + 0.473, + 0.529 + ], + "angle": 0, + "content": "This work proposes E2PN, a convolution structure for processing 3D point clouds. Our proposed approach can enable SE(3)-equivariance on any network with the KPConv [35] backbone by swapping KPCov with E2PN. The equivariance is up to a discretization on SO(3). We leverage a quotient representation to save computational and memory costs by reducing SE(3) feature maps to feature maps defined on \\( S^2 \\times \\mathbb{R}^3 \\) (where \\( S^2 \\) stands for the 2-sphere). Nevertheless, we can recover the full 6 DoF information through a final permutation layer. As a result, our proposed network is SE(3)-equivariant and computationally efficient, ready for practical point-cloud learning applications." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.53, + 0.431, + 0.545 + ], + "angle": 0, + "content": "Overall, this work has the following contributions:" + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.554, + 0.468, + 0.584 + ], + "angle": 0, + "content": "- We propose an efficient SE(3)-equivariant convolution structure for 3D point clouds." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.593, + 0.468, + 0.623 + ], + "angle": 0, + "content": "- We design a permutation layer to recover the full SE(3) information from its quotient space." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.633, + 0.468, + 0.678 + ], + "angle": 0, + "content": "- We achieve comparable or better performance with significantly reduced computational cost than existing equivariant models." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.688, + 0.468, + 0.717 + ], + "angle": 0, + "content": "- Our implementation is open-sourced at https://github.com/minghanz/E2PN." + }, + { + "type": "list", + "bbox": [ + 0.097, + 0.554, + 0.468, + 0.717 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.727, + 0.47, + 0.758 + ], + "angle": 0, + "content": "Readers can find preliminary introductions to some related background concepts in the appendix." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.77, + 0.216, + 0.787 + ], + "angle": 0, + "content": "2. Related work" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.795, + 0.47, + 0.901 + ], + "angle": 0, + "content": "Group convolutions: In 2016, Cohen and Welling proposed G-CNN [6], enabling equivariance beyond translations on 2D images with generalized G-convolutions (group convolutions) over the group of 90-degree rotations, which is one of the earliest efforts in equivariant deep learning. Group convolution is similar to conventional convolutions but has an extended domain for feature maps and kernels." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.304 + ], + "angle": 0, + "content": "The idea was then applied to different networks to enable equivariance for SE(2) [6,19], SO(3) [5], SE(3) [2,42], and E(3) [41] groups up to some discretization. The idea mainly works with finite (discretized) groups, as it is convenient to parameterize feature maps and kernels on the discretized group elements just as on pixel grids. Group convolutions have a relatively simple structure, making them straightforward to apply, but a major downside is that the lifted domain of features and kernels causes higher computational and memory costs, and the problem is more prominent when the group is large. Groups convs can also work with continuous groups, for example, with the help of Monte Carlo (MC) estimation as in [13], but they suffer from a large memory burden in MC sampling when the number of layers grows [30]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.308, + 0.892, + 0.732 + ], + "angle": 0, + "content": "Steerable CNNs: Another line of work is steerable CNNs. Instead of augmenting the domain of feature maps, steerable CNNs generalize the space of feature values to be steerable, i.e., the feature values transform predictably as the input transforms. The way the feature transforms is called the group representation in the feature space, governed by the feature type. Features of scalar type are kept unchanged under group actions, and we call the group representation trivial. For vector or tensor feature types, the representation is not trivial, and the features will change with group actions, for example, through rotation matrix multiplication. Steerable CNNs work for both discretized and continuous groups. One may freely design the feature types based on pre-determined basic types and corresponding representations (irreducible representations, i.e., irreps) as building blocks for a given group. Group convolutions can be viewed as a special case of steerable CNNs with regular representations, i.e., channels of a feature vector undergo permutations when transformed. Examples of steerable CNNs include [4,9,36,40,43]. While the framework of steerable CNNs generalizes group convolutions with more flexibility, it requires a good understanding of representation theory and involves generalized Fourier analysis when working with a continuous group, which makes the structure complicated and challenging to apply in real-world applications broadly. The work of [21, 39] also found empirically that steerable CNNs with irreps underperform regular representations in certain tasks." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.735, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Theoretical progress: There has been a lot of progress in the theoretical development of equivariant networks that are not group-specific. [24] developed a general formulation for steerable CNNs with scalar type features, and [7, 8] generalized it to arbitrary feature types. It is proven that all equivariant linear maps can be written as convolutions. The formulation from the perspective of Fourier analysis was presented in [46]. [39] found the general form of solution for the equivariant kernels for \\( E(2) \\) group, later generalized to any compact group [26]. [14] proposed an algorithm to solve for the equivariance constraint for arbitrary" + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.925, + 0.516, + 0.937 + ], + "angle": 0, + "content": "1224" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.183 + ], + "angle": 0, + "content": "matrix group. The formulation of group convolution based on MC estimation was proposed for any Lie group with [13] or without [30] surjective exponential maps. Equivariant non-linear layers like transformers [15, 21] and equivariant set and graph networks [14, 22, 32] are also proposed, but they are not the focus of this paper." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.184, + 0.471, + 0.486 + ], + "angle": 0, + "content": "Applications of equivariant learning in perception tasks: We want to highlight a few equivariant networks that gain attention in perception applications due to their simplicity and practicality. Vector Neurons [10] is a PointNet-like SO(3)-equivariant network for 3D point cloud learning, later applied to point cloud registration [49] and manipulation [34]. It can be viewed as a special case of TFN [36] with type-1 features and self-interactions only. E2CNN [39] as an SE(2)-equivariant framework was applied in several image processing tasks [27, 33], given its generality and user-friendly library. DEVIANT [25] applied scale-equivariant convolutions in monocular 3D object detection. EPN [2] is a group convolution network with SE(3)-equivariance for 3D point cloud learning based on KPCConv [35] and was used in practice, for example in place recognition task [29]. We also position this proposed work in this category, aiming to promote the application of equivariant learning with our efficient and easy-to-use design. Our work is developed based on EPN, which also serves as a major baseline in this paper." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.501, + 0.212, + 0.518 + ], + "angle": 0, + "content": "3. Methodology" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.527, + 0.272, + 0.541 + ], + "angle": 0, + "content": "3.1. Overview of the idea" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.551, + 0.47, + 0.597 + ], + "angle": 0, + "content": "We first explain why our proposed method is more efficient. Then we discuss how we gain efficiency without sacrificing expressiveness." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.619, + 0.427, + 0.634 + ], + "angle": 0, + "content": "3.1.1 Improved efficiency with quotient features" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.644, + 0.469, + 0.809 + ], + "angle": 0, + "content": "Following the idea of group convolutions, one needs to extend the domain of feature maps from the Euclidean space to the group space, from \\(\\mathbb{R}^3\\) to \\(\\mathrm{SE}(3) \\cong \\mathrm{SO}(3) \\times \\mathbb{R}^3\\) in our case, where we want \\(\\mathrm{SE}(3)\\)-equivariant features for 3D point clouds. We then discretize \\(\\mathrm{SO}(3)\\) to a finite group denoted as \\(\\mathrm{SO}(3)'\\) (we use ' to denote discretization in this paper). The discretization of \\(\\mathbb{R}^3\\) is taken care of by KPConv, which is the non-equivariant counterpart of our method, thus, not discussed here. Up to now, we can obtain a \\(\\mathrm{SE}(3)\\)-equivariant version of KPConv [35] realized through group convolution, which is what EPN [2] presents." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.811, + 0.469, + 0.901 + ], + "angle": 0, + "content": "The specific form of the finite group \\(\\mathrm{SO}(3)'\\) is introduced later in Sec. 3.2, but it can be geometrically understood as the set of all rotations that keep a Platonic solid (i.e., a convex and regular 3D polyhedron) unchanged. As illustrated at the bottom of Fig. 1, the set of rotations can be enumerated by counting the number of vertices, repre" + }, + { + "type": "image", + "bbox": [ + 0.508, + 0.089, + 0.895, + 0.212 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.219, + 0.892, + 0.257 + ], + "angle": 0, + "content": "Figure 2. Illustration of recovering \\(\\mathrm{SO}(3)'\\) features from \\(S^{2'}\\) features through permutations. The left and right subplots are from the geometric and algebraic views. See Sec. 3.1.2 for more explanation." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.283, + 0.892, + 0.358 + ], + "angle": 0, + "content": "senting rotations taking a given vertex to any vertices, multiplied by the number of edges connected to a single vertex, representing the rotations that keep a vertex fixed. The same result can be achieved by counting the faces or the edges, but we stick with vertices in the following discussion." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.36, + 0.893, + 0.584 + ], + "angle": 0, + "content": "In comparison, we propose to define feature maps on \\( S^2 \\times \\mathbb{R}^3 \\), where \\( S^2 \\) is the sphere space. We have \\( S^2 = \\mathrm{SO}(3) / \\mathrm{SO}(2) \\), meaning that it is the quotient space of SO(3) given the stabilizer subgroup SO(2). To understand the quotient space intuitively, we can see that all rotations can be grouped by the destination of a point on the sphere (e.g., the north pole) after the rotation. All rotations bringing the north pole to the same destination point form a coset. They are related by rotations around the axis passing through that point, forming a subgroup isomorphic to SO(2). Thus \\( S^2 \\) is the quotient of SO(3) and SO(2). In the discretized setup, as depicted in Fig. 1, SO(2)' is discretized by the number of edges connected to a single vertex. The quotient \\( S^{2'} = \\mathrm{SO}(3)' / \\mathrm{SO}(2)' \\) corresponds to the vertices on the Platonic solid." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.585, + 0.892, + 0.706 + ], + "angle": 0, + "content": "In general, \\( |S^{2'}| = |\\mathrm{SO}(3)'| / |\\mathrm{SO}(2)'| < |\\mathrm{SO}(3)'| \\), thus the size of feature maps and kernels defined on \\( S^{2'} \\times \\mathbb{R}^3 \\) is much smaller than those on \\( \\mathrm{SO}(3)' \\times \\mathbb{R}^3 \\). The convolution operation on the former space also requires smaller costs. It is the major reason our method is much more efficient than EPN. There is another design, called symmetric kernel, which further improves the efficiency of our method, but we will refer to Sec. 3.2.3 for details." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.726, + 0.836, + 0.741 + ], + "angle": 0, + "content": "3.1.2 Information recovery with permutations" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.75, + 0.892, + 0.84 + ], + "angle": 0, + "content": "With the quotient feature map, all rotations moving the north pole to the same point on a sphere are represented by the same point. Thus we immediately lose the ability to distinguish among these rotations, which is a problem if our task is to learn the pose, for example, in the point cloud registration tasks." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.841, + 0.892, + 0.901 + ], + "angle": 0, + "content": "However, with our proposed permutation layer, we can distinguish every element in \\(\\mathrm{SO}(3)^{\\prime}\\) from the feature maps on \\(S^{2^{\\prime}}\\). The key observation is that the action of \\(\\mathrm{SO}(3)\\) on \\(S^2\\) is faithful, i.e., \\(\\forall R\\in \\mathrm{SO}(3)\\) and \\(R\\neq I\\), \\(\\exists x\\in S^2\\)" + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.927, + 0.516, + 0.938 + ], + "angle": 0, + "content": "1225" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.258 + ], + "angle": 0, + "content": "s.t. \\(Rx \\neq x\\). It means that an action of \\(\\mathrm{SO}(3)\\) other than identity will always cause a change on the \\(S^2\\) feature map when looking at all points on \\(S^2\\) simultaneously. In the discretized setup, it means that there is an injective map \\(\\phi: \\mathrm{SO}(3)' \\to Sym(|S^{2'}|)\\), where \\(Sym(|S^{2'}|)\\) stands for the symmetric group, i.e., the collection of all permutations of a set of size \\(|S^{2'}|\\). An element in \\(Sym(n)\\) is a bijective map \\(\\{1, \\dots, n\\} \\to \\{1, \\dots, n\\}\\), permuting the indices. In other words, each rotation corresponds to a unique permutation of the \\(S^{2'}\\) elements, from which we can distinguish each rotation from the feature map defined on \\(S^{2'}\\)." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.262, + 0.472, + 0.322 + ], + "angle": 0, + "content": "Here we provide the specific form of the permutation layer. Given \\(\\phi\\) mentioned above and a feature map \\(f: S^{2'} \\to \\mathbb{R}^m\\), we can build a feature map \\(\\tilde{f}: \\mathrm{SO}(3)' \\to \\mathbb{R}^{mn}\\) defined as:" + }, + { + "type": "equation", + "bbox": [ + 0.087, + 0.341, + 0.47, + 0.361 + ], + "angle": 0, + "content": "\\[\n\\tilde {f} (R) = \\left[ f \\left(x \\left[ \\phi_ {R} (1) \\right]\\right), f \\left(x \\left[ \\phi_ {R} (2) \\right]\\right), \\dots , f \\left(x \\left[ \\phi_ {R} (n) \\right]\\right) \\right] \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.378, + 0.47, + 0.44 + ], + "angle": 0, + "content": "where \\( R \\in \\mathrm{SO}(3)' \\), \\( n = |S^{2'}| \\), and \\( x[i] \\in S^{2'} \\) for \\( i = 1, \\dots, n \\). Given that \\( \\phi \\) is injective, \\( \\tilde{f}(R_1) \\neq \\tilde{f}(R_2) \\) when \\( R_1 \\neq R_2 \\). Thus we can distinguish \\( \\mathrm{SO}(3)' \\) rotations from \\( \\tilde{f} \\). See Fig. 2 for an illustration." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.462, + 0.328, + 0.478 + ], + "angle": 0, + "content": "3.2. Specific form of convolution" + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.489, + 0.255, + 0.505 + ], + "angle": 0, + "content": "3.2.1 Recap of KPConv" + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.521, + 0.406, + 0.535 + ], + "angle": 0, + "content": "A conventional 3D convolution can be written as:" + }, + { + "type": "equation", + "bbox": [ + 0.085, + 0.553, + 0.47, + 0.59 + ], + "angle": 0, + "content": "\\[\n[ \\kappa * f ] (x) = \\int_ {\\mathbb {R} ^ {3}} \\kappa (t) f (x + t) d t = \\sum_ {t \\in \\mathbb {R} ^ {3},} \\kappa (t) f (x + t), \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.61, + 0.473, + 0.902 + ], + "angle": 0, + "content": "where \\( x \\in \\mathbb{R}^3 \\), and the right hand side is after discretization. We use correlations to implement convolutions in this paper following conventions in deep learning. For processing point clouds, Eq. (2) could be tricky in implementation because it is challenging to align \\( \\kappa \\) with \\( f \\) when there is no grid. The strategy of KPCov is to have a set of kernel points for \\( \\kappa \\) and to gather features to the kernel point coordinates from the input points where \\( f \\) is defined so that they are aligned before the convolution. It is depicted in Fig. 3 (a), and we need to replace \\( f \\) with \\( \\hat{f} \\) in Eq. (2) where \\( \\hat{f}(x) = \\sum_{y \\in \\mathcal{N}_x} w(|y - x|) f(y) \\) and \\( w \\) is a scalar weight function based on distance. \\( \\hat{f} \\) is the features gathered from neighboring input points to align with the kernel points. In this case, the input and output feature map \\( f \\) and \\( [\\kappa * f] \\) are defined on \\( \\mathbb{R}^3 \\), while the kernel \\( \\kappa \\) is defined on \\( \\mathbb{R}^{3'} \\), i.e., coordinates of the set of kernel points. The gathered feature \\( \\hat{f} \\) when calculating the convolution at \\( x \\in \\mathbb{R}^3 \\) is defined at \\( x + \\mathbb{R}^{3'} \\). Notice that we do not consider the deformable mode of KPCov in this paper." + }, + { + "type": "image", + "bbox": [ + 0.501, + 0.092, + 0.897, + 0.429 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.435, + 0.895, + 0.521 + ], + "angle": 0, + "content": "Figure 3. Illustration of different versions of KPConv. (a) original KPConv (see Sec. 3.2.1). (b) KPConv on finite group or quotient space without the symmetric kernel (see Sec. 3.2.2). (c) KPConv on group or quotient space with the symmetric kernel (see Sec. 3.2.3). (b,c) compared with (a): the convolution kernel is larger because it is defined on a higher dimension. (c) compared with (b): the feature gathering is more efficient because the kernel points are symmetric to the rotations in the rotation group." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.547, + 0.837, + 0.563 + ], + "angle": 0, + "content": "3.2.2 KPCov on group and on quotient space" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.57, + 0.892, + 0.602 + ], + "angle": 0, + "content": "To extend KPConv to a group convolution [6] with finite group \\( G' \\), we modify Eq. (2) to" + }, + { + "type": "equation", + "bbox": [ + 0.583, + 0.612, + 0.892, + 0.647 + ], + "angle": 0, + "content": "\\[\n[ \\kappa * f ] (g) = \\sum_ {g _ {t} \\in G ^ {\\prime}} \\kappa (g _ {t}) \\hat {f} (g \\cdot g _ {t}), \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.657, + 0.892, + 0.869 + ], + "angle": 0, + "content": "where in our case, \\( G' = \\mathrm{SE}(3)' = \\mathrm{SO}(3)' \\times \\mathbb{R}^{3'} \\) is where \\( \\kappa \\) is defined, \\( g \\in G^{\\dagger} = \\mathrm{SO}(3)' \\times \\mathbb{R}^{3} \\) is where the input and output feature map is defined. \\( \\hat{f} \\) is defined on \\( g \\cdot G' \\) when calculating the convolution at \\( g \\). Denote an element \\( g \\in \\mathrm{SE}(3) \\) as \\( (R,t) \\) where \\( R \\in \\mathrm{SO}(3) \\) and \\( t \\in \\mathbb{R}^{3} \\), the binary operation \\( \\cdot \\) for \\( \\mathrm{SE}(3) \\) can be specified as \\( (R_1,t_1) \\cdot (R_2,t_2) = (R_1R_2,t_1 + R_1t_2) \\), same for the discretized case. EPN [2] follows this form of convolution. However, as discussed in Sec. 3.1.1, the size of group \\( |\\mathrm{SE}(3)'| = |\\mathrm{SO}(3)'||\\mathbb{R}^{3'}| \\), making it expensive to store the feature map and compute the convolution. To alleviate this issue, EPN has to conduct convolutions in \\( \\mathrm{SO}(3)' \\) and \\( \\mathbb{R}^{3'} \\) separately (i.e., separable convolutions [2, 3]), so that the computational cost is reduced." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.871, + 0.892, + 0.901 + ], + "angle": 0, + "content": "We use quotient feature maps to address this issue. To conduct convolutions on the quotient space \\( X = \\)" + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.925, + 0.516, + 0.937 + ], + "angle": 0, + "content": "1226" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.11, + 0.091, + 0.298, + 0.226 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.312, + 0.091, + 0.44, + 0.225 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.232, + 0.47, + 0.259 + ], + "angle": 0, + "content": "Figure 4. Visualization of the symmetric kernel \\(\\kappa\\) used in our work, where \\(\\mathbb{R}^{3\\prime} = \\{rS^{2\\prime}\\cup 0\\mid r > 0\\}\\)" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.281, + 0.471, + 0.344 + ], + "angle": 0, + "content": "\\(\\mathrm{SE}(3) / \\mathrm{SO}(2) = S^2 \\times \\mathbb{R}^3\\), we cannot directly use Eq. (3), because the \\(\\cdot\\) operation is not defined between two elements in \\(X\\) since \\(X\\) is not a group. It is pointed out in [7, 8] that we can write convolutions on the quotient space as" + }, + { + "type": "equation", + "bbox": [ + 0.147, + 0.352, + 0.47, + 0.387 + ], + "angle": 0, + "content": "\\[\n[ \\kappa * f ] (x) = \\sum_ {x _ {t} \\in X ^ {\\prime}} \\kappa (x _ {t}) \\hat {f} (s (x) \\cdot x _ {t}), \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.395, + 0.473, + 0.565 + ], + "angle": 0, + "content": "where \\(X^{\\prime} = S^{2^{\\prime}}\\times \\mathbb{R}^{3^{\\prime}}\\) is the domain of \\(\\kappa\\), \\(X^{\\dagger} = S^{2^{\\prime}}\\times \\mathbb{R}^{3}\\) is the domain of \\(f\\) and \\([\\kappa *f]\\), and \\(\\hat{f}\\) is defined on \\(s(x)\\cdot X^{\\prime}\\). \\(s(x)\\) is called the section map, \\(s:X^{\\prime}\\to G^{\\prime}\\) (or \\(X\\rightarrow G\\) in the continuous case), mapping \\(x\\in X^{\\prime}\\) to an element of \\(G^{\\prime}\\) in the corresponding coset. With the section map, the \\(\\cdot\\) operation denotes the action of the group \\(G\\) on quotient space \\(X\\), i.e., \\(\\cdot :G\\times X\\to X\\). Denote an element in \\(S^2\\times \\mathbb{R}^3\\) as \\((R\\mathbf{n},t)\\), where \\(R\\in \\mathrm{SO}(3)\\), \\(\\mathbf{n}\\) is the north pole point on the unit sphere \\((0,0,1)\\). Then \\(R\\mathbf{n}\\) represents arbitrary points on the sphere \\(S^2\\). The action \\(\\cdot\\) can then be written as \\((R_{1},t_{1})\\cdot (R_{2}\\mathbf{n},t_{2}) = (R_{1}R_{2}\\mathbf{n},t_{1} + R_{1}t_{2})\\)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.581, + 0.265, + 0.595 + ], + "angle": 0, + "content": "3.2.3 Symmetric kernels" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.604, + 0.47, + 0.71 + ], + "angle": 0, + "content": "Now we introduce the specific form of \\(\\mathbb{R}^{3'}\\), i.e., the location of kernel points in KPConv. In our design, \\(\\mathbb{R}^{3'} = \\{rS^{2'} \\cup 0 \\mid r > 0\\}\\), i.e., the set of vertices of the Platonic solid with radius \\(r\\) and the origin point. \\(\\mathbb{R}^{3'}\\) is very similar to \\(S^{2'}\\), because we want to make the kernel symmetric to \\(\\mathrm{SO}(3)'\\). More precisely, we desire \\(\\mathbb{R}^{3'}\\) to be closed under the action of \\(\\mathrm{SO}(3)'\\). There are two reasons as follows." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.728, + 0.47, + 0.833 + ], + "angle": 0, + "content": "Steerability constraint To make the convolution on quotient space equivariant, defining a valid form of convolution as Eq. (4) is not the whole story. The kernel values must satisfy a condition called the steerability constraint, which is required for all steerable CNNs. More background knowledge can be found in [8]. In our case, the steerability constraint is" + }, + { + "type": "equation", + "bbox": [ + 0.126, + 0.844, + 0.469, + 0.862 + ], + "angle": 0, + "content": "\\[\n\\kappa (x) = \\kappa \\left(R _ {z} \\cdot x\\right), \\forall x \\in X ^ {\\prime}, \\forall R _ {z} \\in \\mathrm {S O} (2) ^ {\\prime}, \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.471, + 0.902 + ], + "angle": 0, + "content": "where \\( R_{z} \\) is a \\( z \\)-axis rotation. The derivation of Eq. (5) from the general form of steerability constraints can be found in" + }, + { + "type": "table", + "bbox": [ + 0.504, + 0.089, + 0.895, + 0.22 + ], + "angle": 0, + "content": "
Rotation groupsTetrahedral TOctahedral OIcosahedral I
Platonic solidsTetrahedronCubeOctahedronDodecahedronIcosahedron
Size|SO(3)'| = 12 |S2'| = 4 |SO(2)'| = 3|SO(3)'| = 24 |S2'| = 8 |SO(2)'| = 3|SO(3)'| = 24 |S2'| = 6 |SO(2)'| = 4|SO(3)'| = 60 |S2'| = 20 |SO(2)'| = 3|SO(3)'| = 60 |S2'| = 12 |SO(2)'| = 5
" + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.223, + 0.892, + 0.248 + ], + "angle": 0, + "content": "Figure 5. Illustration of all five types of Platonic solids and their corresponding finite rotation groups." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.272, + 0.892, + 0.334 + ], + "angle": 0, + "content": "the appendix. Here the \\( \\cdot \\) operation inherits from the action of \\( G' \\) on \\( X' \\) since \\( \\mathrm{SO}(2)' \\subset \\mathrm{SO}(3)' \\subset G' \\). Specifically, we have \\( R_z \\cdot (R\\mathbf{n}, t) = (R_z, 0) \\cdot (R\\mathbf{n}, t) = (R_z R\\mathbf{n}, R_z t) \\). Replace \\( x \\) with \\( (R\\mathbf{n}, t) \\) in Eq. (5), and we have" + }, + { + "type": "equation", + "bbox": [ + 0.601, + 0.341, + 0.892, + 0.358 + ], + "angle": 0, + "content": "\\[\n\\kappa (R \\mathbf {n}, t) = \\kappa \\left(R _ {z} R \\mathbf {n}, R _ {z} t\\right), \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.365, + 0.892, + 0.455 + ], + "angle": 0, + "content": "\\(\\forall R\\mathbf{n}\\in S^{2^{\\prime}},\\forall t\\in \\mathbb{R}^{3^{\\prime}},\\forall R_{z}\\in \\mathrm{SO}(2)^{\\prime}.\\) Notice that it implies that we need \\(R_{z}t\\in \\mathbb{R}^{3^{\\prime}},\\forall t\\in \\mathbb{R}^{3^{\\prime}},\\forall R_{z}\\in \\mathrm{SO}(2^{\\prime})\\) so that \\(\\kappa\\) is defined on the right hand side of Eq. (6). In other words, the kernel points \\(\\mathbb{R}^{3^{\\prime}}\\) need to be closed under \\(\\mathrm{SO}(2)^{\\prime}\\). Obviously, having \\(\\mathbb{R}^{3^{\\prime}}\\) closed under \\(\\mathrm{SO}(3)^{\\prime}\\) is a sufficient condition for this." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.456, + 0.892, + 0.502 + ], + "angle": 0, + "content": "For the \\(S^{2'}\\) dimension, since \\(S^{2'}\\) is symmetric (closed) to \\(\\mathrm{SO}(3)'\\) by definition and \\(\\mathrm{SO}(2)' \\subset \\mathrm{SO}(3)'\\), we always have \\(R_z R\\mathbf{n} \\in S^{2'}\\) and \\(\\kappa\\) is always defined." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.519, + 0.893, + 0.672 + ], + "angle": 0, + "content": "Efficient feature gathering Another important reason for the design choice of \\(\\mathrm{SO}(3)^{\\prime}\\)-symmetric kernels is that it enables more efficient feature gathering. Consider a spatial location \\(t_0\\in \\mathbb{R}^3\\), the convolution feature output at this point is a stack of \\([[\\kappa *f](x_i)]_i\\) with \\(x_{i}\\in (S^{2^{\\prime}},t_{0})\\subset X^{\\dagger}\\). As shown in Eq. (4), it involves feature gathering for \\(\\hat{f}\\) at \\(s(x_{i})\\cdot x_{jk}\\) for every \\(x_{jk}\\in X' = S^{2'}\\times \\mathbb{R}^{3'}\\). Denote an instance of \\(s(x_{i}) = (R_{i},t_{0}),x_{jk} = (R_{j}\\mathbf{n},t_{k})\\), then \\(s(x_{i})\\cdot x_{jk} = (R_{i}R_{j}\\mathbf{n},t_{0} + R_{i}t_{k})\\). If \\(\\mathbb{R}^{3^{\\prime}}\\) is closed under \\(\\mathrm{SO}(3)^{\\prime}\\), then we have" + }, + { + "type": "equation", + "bbox": [ + 0.563, + 0.679, + 0.892, + 0.698 + ], + "angle": 0, + "content": "\\[\n\\left\\{R _ {i} t _ {k} \\mid t _ {k} \\in \\mathbb {R} ^ {3 ^ {\\prime}} \\right\\} = \\mathbb {R} ^ {3 ^ {\\prime}}, \\forall R _ {i} \\in \\mathrm {S O} (3) ^ {\\prime}, \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.704, + 0.895, + 0.902 + ], + "angle": 0, + "content": "which implies that the feature gathering for all \\( S^{2'} \\) channels can be done once at the same set of spatial positions specified by \\( \\mathbb{R}^{3'} \\). An illustration is shown in Fig. 3. Without the symmetric kernel, the KPConv on group or quotient space looks like Fig. 3 (b), where the kernel is rotated for each \\( \\mathrm{SO}(3)' \\) (for group KPConv) or \\( S^{2'} \\) (for quotient KPConv) channel separately to gather input features. However, with symmetric kernels, as shown in Fig. 3 (c), the rotations keep the position of kernel points unchanged up to a permutation so that the feature-gathering step is simplified. Specifically, the number of spatial positions needed for feature gathering without symmetric kernels is \\( |SO(3)'| \\mathbb{R}^{3'}| \\) for group KPConv or \\( |S^{2'}| \\mathbb{R}^{3'}| \\) for quotient KPConv, while the number" + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.926, + 0.516, + 0.938 + ], + "angle": 0, + "content": "1227" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.095, + 0.894, + 0.12 + ], + "angle": 0, + "content": "Table 1. Efficiency comparison in terms of GPU memory consumption and the computation speed between EPN [2] and our method on three tasks. Two numbers are reported for training/inference respectively. \\( \\downarrow \\) means lower is better. \\( \\uparrow \\) means higher is better. The best is shown in bold font." + }, + { + "type": "table", + "bbox": [ + 0.081, + 0.121, + 0.887, + 0.208 + ], + "angle": 0, + "content": "
TasksModelNet40 PoseModelNet40 Classification3DMatch Keypoint Matching
MethodsMemory (GB) ↓Speed (fps) ↑Memory (GB) ↓Speed (fps) ↑Memory (GB) ↓Speed (fps) ↑
EPN [2]22.2 / 16.91.1 / 1.613.4 / 12.71.9 / 1.537.4 / 8.50.6 / 3.1
Ours (w/o symmetric kernels)4.8 / 3.75.1 / 10.14.1 / 3.27.8 / 7.87.5 / 2.82.6 / 16.7
Ours (w/ symmetric kernels)4.3 / 2.86.7 / 11.13.9 / 2.79.1 / 10.36.5 / 2.43.7 / 23.6
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.231, + 0.471, + 0.279 + ], + "angle": 0, + "content": "is \\(|\\mathbb{R}^{3^{\\prime}}|\\) with symmetric kernels. The convolution kernels in Fig. 3 is an abstract illustration, while the actual symmetric kernel in our work is visualized in Fig. 4." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.299, + 0.446, + 0.315 + ], + "angle": 0, + "content": "3.2.4 Choices of the discretization of \\(SO(3)\\) and \\(S^2\\)" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.323, + 0.468, + 0.445 + ], + "angle": 0, + "content": "In Sec. 3.1.1, we mentioned that the discretization of \\(\\mathrm{SO}(3)\\) is the rotation group that respects the symmetry of a Platonic solid. There are five types of Platonic solids, corresponding to 3 finite rotation groups, as shown in Fig. 5. Choosing \\(\\mathrm{SO}(3)'\\) to be any of them is valid, representing a discretization of \\(\\mathrm{SO}(3)\\) to different resolutions. The different Platonic solids with the same rotation group \\(\\mathrm{SO}(3)'\\) represents different discretizations of \\(S^{2'}\\) and \\(\\mathrm{SO}(2)'\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.446, + 0.468, + 0.567 + ], + "angle": 0, + "content": "If we use a small \\(\\mathrm{SO}(3)'\\) (for example, \\(T\\)), the strategy of using \\(\\mathbb{R}^{3'} = \\{rS^{2'} \\cup 0 \\mid r > 0\\}\\) could be problematic because the number of kernel points could be too few to learn representative features. In this case, we are free to design the kernel points differently, as long as they are closed under \\(\\mathrm{SO}(3)'\\). For example, one may add kernel points at the center of all edges and/or faces. One may even use a combination of several polyhedrons with different radii \\(r\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.567, + 0.468, + 0.673 + ], + "angle": 0, + "content": "In this paper, we only choose the icosahedron as the Platonic solid to conduct experiments for three reasons. First, it has the finest discretization of SO(3). Second, it has a smaller size of \\( S^{2'} \\) compared with the dodecahedron, maximizing the benefit of working with quotient features. Third, it is consistent with existing methods [1,2], enabling direct comparison with the baselines." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.694, + 0.334, + 0.71 + ], + "angle": 0, + "content": "3.2.5 Other aspects of the network" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.719, + 0.468, + 0.869 + ], + "angle": 0, + "content": "We use element-wise scalar nonlinearity (ReLU and leaky ReLu) in the network. The spatial pooling is done by subsampling the input points and aggregating the features of neighboring input points to the subsampled points. Batch normalization is applied to normalize over the batch, \\( S^{2'} \\), and \\( \\mathbb{R}^3 \\) dimensions. All these choices follow the common practice of conventional CNNs (KPCov [35]) and group convolutions (EPN [2]). We also adopted the group attentive pooling in EPN to pool over the \\( S^{2'} \\) dimension and generate \\( \\mathrm{SO}(3)' \\)-invariant features." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.468, + 0.902 + ], + "angle": 0, + "content": "Depending on the specific task in the experiment, the prediction head has a slightly different design, composing" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.232, + 0.892, + 0.323 + ], + "angle": 0, + "content": "the last few layers of the network. The loss functions are inherited from EPN [2], including cross-entropy loss for classifications, L2 loss for residual pose regression, and batch-hard triplet loss for keypoint matching. We refer to the appendix for more details about the prediction heads and the loss functions." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.335, + 0.729, + 0.351 + ], + "angle": 0, + "content": "3.3. Relation to existing work" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.359, + 0.892, + 0.646 + ], + "angle": 0, + "content": "In the context of literature on group-equivariant neural networks, our method is under the theoretical framework of equivariant CNNs on homogeneous spaces [8, 24, 46]. Our work is a new form of realization when working with 3D point clouds and adapting the convolution structure of KPCov. We explore a balance of simplicity, efficiency, and expressiveness by finding the proper quotient space and discretization. Our method is an extension of group convolutions, leveraging their clean structure enabled by discretization. Our method can also be viewed as a steerable CNN with homogeneous space \\( S^2 \\times \\mathbb{R}^3 \\) and stabilizer subgroup SO(2) with scalar-type features or with homogeneous space \\( \\mathbb{R}^3 \\) and stabilizer subgroup SO(3) with \\( S^2 \\) features. The proposed work paves the way for efficiency improvement using quotient representation learning on finite groups. We also emphasize the group-variant side of equivariant models with the permutation layer to distinguish rotations, while existing work focuses on the benefit of getting group-invariant features from equivariant models." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.661, + 0.634, + 0.679 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.688, + 0.892, + 0.779 + ], + "angle": 0, + "content": "Our major baseline to compare with is EPN [2], a state-of-the-art group convolution network, as we are similar in several ways. Both are KPConv-style convolutions with SE(3)-equivariance. Both use the icosahedral rotation group \\(\\mathcal{I}\\) to discretize SO(3). However, EPN has features defined on \\(\\mathcal{I} \\times \\mathbb{R}^3\\), compared with \\(S^{2'} \\times \\mathbb{R}^3\\) in our method." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.779, + 0.892, + 0.885 + ], + "angle": 0, + "content": "Two datasets, ModelNet40 [44] and 3DMatch [47], are used in the experiments. ModelNet40 is composed of 3D CAD models of 40 categories of objects. 3DMatch is a real-scan dataset of indoor scenes. For the ModelNet40 dataset, we conduct the classification and pose estimation tasks. For the 3DMatch dataset, we conduct the keypoint matching task. These tasks are also studied in EPN [2]." + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.886, + 0.892, + 0.901 + ], + "angle": 0, + "content": "In Tab. 1, we list the GPU memory consumption and run" + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.926, + 0.516, + 0.938 + ], + "angle": 0, + "content": "1228" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.096, + 0.892, + 0.144 + ], + "angle": 0, + "content": "Table 2. Experimental result of object classification on ModelNet40. The best is bolded. The best in equivariant models is underlined. Noisy: test using input with random translation, scaling, jittering, and dropout. Clean: test without above processing. SO(3): random rotations. Id: no rotation. ico: random rotations in I. ESCNN works with voxelized data, thus not having Noisy results with point-wise augmentations. FLOPs are counted using fvcore, which does not support DGL used in TFN and SE(3)-T, thus left blank. The efficiency comparison uses the same batch size as in Tab. 1 (see appendix)." + }, + { + "type": "table", + "bbox": [ + 0.081, + 0.145, + 0.888, + 0.321 + ], + "angle": 0, + "content": "
TypeColumn ##1#2#3#4#5#6#7#8#9#10#11#12#13#14
MetricsModelNet40 classification performance metric: Acc (%) ↑Efficiency metricsFLOPs per training batch (G)Trainable params (M)
Train rotationSO(3)IdMemory (GB)↓ train/testSpeed (fps)↑ train/test
Test rotationSO(3)IdSO(3)Idico
Test conditionNoisyCleanNoisyCleanNoisyCleanNoisyCleanNoisyClean
Non-equivKPCov [35]75.7181.1776.8882.0212.6612.2289.4691.85--0.18/0.2517.24/18.480.741.69
PointNet++ [31]81.3184.8883.0385.7613.4413.7690.6791.55--1.03/0.57.06/7.4310.591.48
DGCNN [38]79.8684.7782.5485.6215.3617.2691.0092.18--1.96/1.6917.90/17.5032.651.81
PT [48]78.5179.6878.8379.6816.5316.7786.9888.10--4.16/5.824.80/5.03220.999.58
CurveNet [45]84.7288.3385.8288.9417.3418.0391.5392.63--1.20/0.335.61/7.544.222.14
PCT [17]86.9189.1087.6489.8316.3317.9591.6992.87--1.18/0.808.54/20.8527.412.87
EquivalentESCNN [1]-82.40-77.73-29.03-88.94--4.71/5.503.79/8.38428.610.46
TFN [36]58.2762.6458.0662.6457.5062.2859.2062.28--15.95/8.71.83/6.08-0.06
SE(3)-T [15]60.3766.2961.1866.2944.6150.5344.8150.53--19.39/9.651.54/5.13-0.11
EPN [2]84.6387.8485.3488.8330.9932.3290.0391.6190.0491.6013.40/12.721.86/1.4958.953.06
Ours (w/ GA pooling [2])85.0487.5185.4987.6341.4644.4389.7390.5090.0090.503.95/2.709.21/10.37170.682.53
Ours (w/ permutation)86.9988.6288.2189.6239.5442.7890.6691.7790.6891.773.95/2.709.09/10.28170.772.65
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.345, + 0.47, + 0.541 + ], + "angle": 0, + "content": "ning speed of our method and EPN [2] in the three tasks. The comparisons are under the same input size, number of feature channels, and number of network layers. The separable convolutions on \\(\\mathrm{SO}(3)\\) and \\(\\mathbb{R}^3\\) in EPN are together considered as one layer. The numbers are not comparable between training and inference because the batch size could be different (see the appendix). The specific configurations in each experiment are introduced later. All experiments are run on a single NVIDIA A40 GPU. Our network with quotient space convolutions is much smaller and runs much faster in all three tasks, indicating the potential value for real applications. We boost efficiency without sacrificing performance, as is shown later." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.543, + 0.47, + 0.68 + ], + "angle": 0, + "content": "Ablation study: We list two rows of our results in Tab. 1 to show the effect of efficient feature gathering enabled by the symmetric kernels. The results of without symmetric kernels are generated using the same kernel points as with symmetric kernels, but ignoring the fact that they are symmetric to rotations and gathering features at \\( |S^{2'}| |\\mathbb{R}^{3'}| \\) locations, instead of at \\( |\\mathbb{R}^{3'}| \\) locations and permuting them. The efficient feature gathering brings further efficiency improvements, especially in terms of computational speed." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.693, + 0.391, + 0.71 + ], + "angle": 0, + "content": "4.1. Object classification on ModelNet40" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.718, + 0.469, + 0.869 + ], + "angle": 0, + "content": "For this task, given a point cloud of an object, the network predicts its category. The evaluation metric is classification accuracy (Acc). In this experiment, we show an extensive efficiency comparison with more existing networks, equivariant and non-equivariant. We also examine a wide combination of input conditions in training and testing to show the effect of equivariance and robustness against input imperfections. All models are trained with data augmentation, including random translation, scaling, jittering, and dropout." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.469, + 0.9 + ], + "angle": 0, + "content": "Our method has outstanding performance as shown in Tab. 2. In columns #1-4, all methods are trained with rota" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.349, + 0.892, + 0.385 + ], + "angle": 0, + "content": "Table 3. Pose estimation on ModelNet40. Mean, median, and max angular errors are calculated over the test set. Statistics (average and standard deviation) over 10 test runs are shown to account for the randomness." + }, + { + "type": "table", + "bbox": [ + 0.504, + 0.386, + 0.886, + 0.453 + ], + "angle": 0, + "content": "
MetricsMean (°) ↓Median (°) ↓Max (°) ↓
StatsAvg μSD σAvg μSD σAvg μSD σ
KPConv [35]13.991.5310.700.81115.1957.84
EPN [2]1.100.201.360.137.062.52
Ours1.200.080.960.056.711.28
" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.479, + 0.892, + 0.749 + ], + "angle": 0, + "content": "tional augmentation. Our method performs the best among listed equivariant models and is on par with PCT [18] among all models. Our method is intended to work with rotational augmentations so that the equivariance gap caused by discretization can be interpolated through training. However, we still experiment with training without rotational augmentation, as shown in columns #5-10. From columns #9-10, we can verify the equivariance to the icosahedral rotation group of our model. Columns #5-6 show the effect of discretization on the continuous SO(3) if no interpolation is trained, in which case the performance lands between non-equivariant models and continuously SO(3)-equivariant models. The efficiency of our method outperforms all equivariant baselines and is similar to nonequivariant models. The FLOPs and number of trainable parameters are also listed for reference. We found that FLOPs do not strictly correlate with running speed, which could be due to different memory access costs and parallelism." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.75, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Ablation study: Since this task requires SE(3)-invariant features, there are two options in our network: either using the group-attentive pooling (GA pooling) introduced in EPN [2] to pool over the \\( S^{2^{\\prime}} \\) dimensions or using the permutation layer to find the canonical permutation of \\( S^{2^{\\prime}} \\) dimensions. Either way, the canonical pose of objects in ModelNet40 can be used for supervision. Tab. 2 shows that the permutation layer yields better performance with negligible computational overhead. The reason could be that the permutation layer as in Eq. (1) stacks features from \\( S^{2^{\\prime}} \\)" + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.927, + 0.516, + 0.938 + ], + "angle": 0, + "content": "1229" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.095, + 0.892, + 0.12 + ], + "angle": 0, + "content": "Table 4. Experiment result of keypoint matching on the 3DMatch dataset. The numbers are the average recall \\((\\%)\\), and the higher, the better. Notation * represents the result with the given point normal information." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.121, + 0.889, + 0.281 + ], + "angle": 0, + "content": "
SHOT [37]3DM [47]CGF [23]PPFN [12]PPFF [11]3DSN [16]Li [28]Li [28]*EPN [2]Ours
Kitchen74.358.360.389.778.797.592.199.499.099.4
Home 180.172.471.155.876.396.291.098.799.498.7
Home 270.761.556.759.161.593.285.694.796.296.6
Hotel 177.454.957.158.068.197.495.199.699.699.1
Hotel 272.148.153.857.771.292.891.3100.097.198.1
Hotel 385.261.183.361.194.498.296.3100.0100.0100.0
Study64.051.737.753.462.095.091.895.596.295.2
MIT Lab62.350.745.563.662.394.184.492.293.590.9
Average73.357.358.262.371.895.691.097.597.697.3
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.304, + 0.471, + 0.351 + ], + "angle": 0, + "content": "and thus preserves the information better, compared with weighted averaging over the \\( S^{2'} \\) dimension as done in GA pooling." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.36, + 0.36, + 0.374 + ], + "angle": 0, + "content": "4.2. Pose Estimation on ModelNet40" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.384, + 0.47, + 0.504 + ], + "angle": 0, + "content": "In this experiment, the network takes a pair of point clouds of an object and predicts the relative rotation between them. To avoid the pose ambiguity of objects with symmetric rotational shapes, only the airplane category is used in this experiment, with 626 models in the training set and 100 models in the test set. A point cloud is generated by randomly subsampling 1,024 points on the surface, and it is randomly rotated to form a pair." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.505, + 0.47, + 0.642 + ], + "angle": 0, + "content": "The experimental result is shown in Tab. 3. We achieved similar rotation estimation accuracy to EPN [2] overall. While our mean error is slightly larger, the lower median error, max error, and standard deviations show that our method delivers a more reliable registration. It could imply that representing rotations as a permutation of features is more robust than representing them as a single element in the feature map. Besides, the equivariant networks outperform the non-equivariant KPConv [35] by a large margin." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.651, + 0.363, + 0.667 + ], + "angle": 0, + "content": "4.3. Keypoint matching on 3DMatch" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.674, + 0.47, + 0.78 + ], + "angle": 0, + "content": "In this task, patches of point clouds extracted locally around keypoints in a large, dense scan are input to the network, and each is mapped to a feature vector of 64 dimension as the keypoint descriptor. Each patch has 1,024 points. Then we evaluate the average recall of keypoint correspondence across different scans through nearest neighbor search in the feature space, as proposed in PPFNet [12]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.781, + 0.471, + 0.903 + ], + "angle": 0, + "content": "This experiment's performance in Tab. 4 indicates the capability of learning distinctive and rotation-invariant features for local patches of point clouds. Though not achieving the best in the list, our method delivers comparable performance to the top methods using only a fraction of the computational resources as EPN [2] (see Tab. 1). We use the GA pooling layer [2] in this experiment because the permutation layer requires supervision on the pose, while" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.304, + 0.895, + 0.457 + ], + "angle": 0, + "content": "a canonical pose is not defined for local patches of point clouds, and GA pooling works with or without the pose supervision. However, the result shows that GA pooling over the \\( |S^{2t}| \\) features also provides distinctive features for keypoint matching. This part may be further improved by taking the information of the global scan [12] or the matching scan [20] into consideration, in which case the permutation layer may get hints on the optimal permutation from the larger context. This topic goes beyond the focus of this paper and is left for future work." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.468, + 0.62, + 0.484 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.493, + 0.895, + 0.735 + ], + "angle": 0, + "content": "This paper presents a new design of SE(3)-equivariant point cloud convolution network, which is efficient, simple, and expressive simultaneously by working with feature maps defined on the quotient space \\(S^2 \\times \\mathbb{R}^3\\) associated with the stabilizer SO(2). We further improve the efficiency of the convolutions by designing the kernel points to be symmetric to the discretized rotation group \\(\\mathrm{SO}(3)'\\). Moreover, we propose a permutation layer to recover \\(\\mathrm{SO}(3)'\\) information from \\(S^{2/}\\) dimensions of the features so that the network can detect SO(3) rotations. Experiments show that our network delivers state-of-the-art performance in multiple tasks while consuming only a fraction of memory and computation resources as a group-convolution network with similar performance. Our method can open exciting opportunities to introduce the SE(3)-equivariance property to mainstream point cloud networks for various tasks." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.735, + 0.895, + 0.901 + ], + "angle": 0, + "content": "This work also has limitations. We do not outperform EPN [2] in the keypoint matching task, implying that the network, especially the permutation layer, needs improvement when dealing with inputs without a clear pose definition. Other possibilities for the network design also remain open. For example: What if we use a non-scalar type of feature on the quotient space? How to further alleviate the impact of the discretization of a continuous group? From a general perspective, extending the discretized quotient space convolution strategy to other groups is also an attractive direction for future work." + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.926, + 0.518, + 0.938 + ], + "angle": 0, + "content": "1230" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.175, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.115, + 0.47, + 0.157 + ], + "angle": 0, + "content": "[1] Gabriele Cesa, Leon Lang, and Maurice Weiler. A program to build E(N)-equivariant steerable CNNs. In International Conference on Learning Representations, 2022. 6, 7" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.157, + 0.472, + 0.225 + ], + "angle": 0, + "content": "[2] Haiwei Chen, Shichen Liu, Weikai Chen, Hao Li, and Randall Hill. Equivariant point network for 3D point cloud analysis. 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It can be viewed as an equivariant version of kernel point convolutions (KPCov), a widely used convolution form to process point cloud data. Compared with existing equivariant networks, our design is simple, lightweight, fast, and easy to be integrated with existing task-specific point cloud learning pipelines. We achieve these desirable properties by combining group convolutions and quotient representations. Specifically, we discretize $SO(3)$ to finite groups for their simplicity while using $SO(2)$ as the stabilizer subgroup to form spherical quotient feature fields to save computations. We also propose a permutation layer to recover $SO(3)$ features from spherical features to preserve the capacity to distinguish rotations. Experiments show that our method achieves comparable or superior performance in various tasks, including object classification, pose estimation, and keypoint-matching, while consuming much less memory and running faster than existing work. The proposed method can foster the development of equivariant models for real-world applications based on point clouds. + +# 1. Introduction + +Processing 3D data has become a vital task today as demands for automated robots and augmented reality technologies emerge. In the past decade, computer vision has significantly succeeded in image processing, but learning from 3D data such as point clouds is still challenging. An important reason is that 3D data presents more variations than 2D images in several aspects. For example, the rigid body transformations in 2D only have 3 degrees of freedom (DoF) with 1 for rotations. In 3D space, the DoF is 6, with 3 for rotations. The 2D translation equivariance is a key factor in the success of convolutional neural networks (CNNs) + +![](images/82dd584913413f61d91b4829268472272c7dab067f61a940e034a69a25e9c274.jpg) +Figure 1. Our method achieves higher efficiency by working with smaller feature maps defined on $S^{2\prime} \times \mathbb{R}^3$ rather than $SO(3)' \times \mathbb{R}^3$ ( $'$ denotes discretization). $\mathbb{R}^3$ is omitted in the figure. The black arrows in each space represent elements. The top and bottom paths are equivalent, showing the relations among different representations. + +in image processing, but it is not enough for 3D tasks. + +Generally speaking, equivariance is a property for a map such that given a transformation in the input, the output changes in a predictable way determined by the input transformation. It drastically improves generalization as the variance caused by the transformations is captured via the network by design. Take CNNs as an example, the equivariance property refers to the fact that a translation in the input image results in the same translation in the feature map output from a convolution layer. However, conventional convolutions are not equivariant to rotations, which becomes problematic, especially when we deal with 3D data where many rotational variations occur. In response, on the one hand, data augmentations with 3D rotations are frequently used. On the other hand, equivariant feature learning emerges as a research area, aiming to generalize the translational equivariance to broader transformations. + +A lot of progress has been made in group-equivariant feature learning. The term group encompasses the 3D rotations and translations, which is called the special Euclidean + +group of dimension 3, denoted SE(3), and also other more general types of transformations that represent certain symmetries. While many methods have been proposed, equivariant feature learning has not yet become the default strategy for 3D deep learning tasks. From our understanding, two major reasons hinder the broader application of equivariant methods. First, networks dealing with continuous groups typically require specially designed operations not commonly used in neural networks, such as generalized Fourier transform and Monte Carlo sampling. Thus, incorporating them into general neural networks for 3D learning tasks is challenging. Second, for the strategy of working on discretized (finite) groups [6, 19], while the network structures are simpler and closer to conventional networks, they usually suffer from the high dimensionality of the feature maps and convolutions, which causes much larger memory usage and computational load, limiting their practical use. + +This work proposes E2PN, a convolution structure for processing 3D point clouds. Our proposed approach can enable SE(3)-equivariance on any network with the KPConv [35] backbone by swapping KPCov with E2PN. The equivariance is up to a discretization on SO(3). We leverage a quotient representation to save computational and memory costs by reducing SE(3) feature maps to feature maps defined on $S^2 \times \mathbb{R}^3$ (where $S^2$ stands for the 2-sphere). Nevertheless, we can recover the full 6 DoF information through a final permutation layer. As a result, our proposed network is SE(3)-equivariant and computationally efficient, ready for practical point-cloud learning applications. + +Overall, this work has the following contributions: + +- We propose an efficient SE(3)-equivariant convolution structure for 3D point clouds. +- We design a permutation layer to recover the full SE(3) information from its quotient space. +- We achieve comparable or better performance with significantly reduced computational cost than existing equivariant models. +- Our implementation is open-sourced at https://github.com/minghanz/E2PN. + +Readers can find preliminary introductions to some related background concepts in the appendix. + +# 2. Related work + +Group convolutions: In 2016, Cohen and Welling proposed G-CNN [6], enabling equivariance beyond translations on 2D images with generalized G-convolutions (group convolutions) over the group of 90-degree rotations, which is one of the earliest efforts in equivariant deep learning. Group convolution is similar to conventional convolutions but has an extended domain for feature maps and kernels. + +The idea was then applied to different networks to enable equivariance for SE(2) [6,19], SO(3) [5], SE(3) [2,42], and E(3) [41] groups up to some discretization. The idea mainly works with finite (discretized) groups, as it is convenient to parameterize feature maps and kernels on the discretized group elements just as on pixel grids. Group convolutions have a relatively simple structure, making them straightforward to apply, but a major downside is that the lifted domain of features and kernels causes higher computational and memory costs, and the problem is more prominent when the group is large. Groups convs can also work with continuous groups, for example, with the help of Monte Carlo (MC) estimation as in [13], but they suffer from a large memory burden in MC sampling when the number of layers grows [30]. + +Steerable CNNs: Another line of work is steerable CNNs. Instead of augmenting the domain of feature maps, steerable CNNs generalize the space of feature values to be steerable, i.e., the feature values transform predictably as the input transforms. The way the feature transforms is called the group representation in the feature space, governed by the feature type. Features of scalar type are kept unchanged under group actions, and we call the group representation trivial. For vector or tensor feature types, the representation is not trivial, and the features will change with group actions, for example, through rotation matrix multiplication. Steerable CNNs work for both discretized and continuous groups. One may freely design the feature types based on pre-determined basic types and corresponding representations (irreducible representations, i.e., irreps) as building blocks for a given group. Group convolutions can be viewed as a special case of steerable CNNs with regular representations, i.e., channels of a feature vector undergo permutations when transformed. Examples of steerable CNNs include [4,9,36,40,43]. While the framework of steerable CNNs generalizes group convolutions with more flexibility, it requires a good understanding of representation theory and involves generalized Fourier analysis when working with a continuous group, which makes the structure complicated and challenging to apply in real-world applications broadly. The work of [21, 39] also found empirically that steerable CNNs with irreps underperform regular representations in certain tasks. + +Theoretical progress: There has been a lot of progress in the theoretical development of equivariant networks that are not group-specific. [24] developed a general formulation for steerable CNNs with scalar type features, and [7, 8] generalized it to arbitrary feature types. It is proven that all equivariant linear maps can be written as convolutions. The formulation from the perspective of Fourier analysis was presented in [46]. [39] found the general form of solution for the equivariant kernels for $E(2)$ group, later generalized to any compact group [26]. [14] proposed an algorithm to solve for the equivariance constraint for arbitrary + +matrix group. The formulation of group convolution based on MC estimation was proposed for any Lie group with [13] or without [30] surjective exponential maps. Equivariant non-linear layers like transformers [15, 21] and equivariant set and graph networks [14, 22, 32] are also proposed, but they are not the focus of this paper. + +Applications of equivariant learning in perception tasks: We want to highlight a few equivariant networks that gain attention in perception applications due to their simplicity and practicality. Vector Neurons [10] is a PointNet-like SO(3)-equivariant network for 3D point cloud learning, later applied to point cloud registration [49] and manipulation [34]. It can be viewed as a special case of TFN [36] with type-1 features and self-interactions only. E2CNN [39] as an SE(2)-equivariant framework was applied in several image processing tasks [27, 33], given its generality and user-friendly library. DEVIANT [25] applied scale-equivariant convolutions in monocular 3D object detection. EPN [2] is a group convolution network with SE(3)-equivariance for 3D point cloud learning based on KPCConv [35] and was used in practice, for example in place recognition task [29]. We also position this proposed work in this category, aiming to promote the application of equivariant learning with our efficient and easy-to-use design. Our work is developed based on EPN, which also serves as a major baseline in this paper. + +# 3. Methodology + +# 3.1. Overview of the idea + +We first explain why our proposed method is more efficient. Then we discuss how we gain efficiency without sacrificing expressiveness. + +# 3.1.1 Improved efficiency with quotient features + +Following the idea of group convolutions, one needs to extend the domain of feature maps from the Euclidean space to the group space, from $\mathbb{R}^3$ to $\mathrm{SE}(3) \cong \mathrm{SO}(3) \times \mathbb{R}^3$ in our case, where we want $\mathrm{SE}(3)$ -equivariant features for 3D point clouds. We then discretize $\mathrm{SO}(3)$ to a finite group denoted as $\mathrm{SO}(3)'$ (we use ' to denote discretization in this paper). The discretization of $\mathbb{R}^3$ is taken care of by KPConv, which is the non-equivariant counterpart of our method, thus, not discussed here. Up to now, we can obtain a $\mathrm{SE}(3)$ -equivariant version of KPConv [35] realized through group convolution, which is what EPN [2] presents. + +The specific form of the finite group $\mathrm{SO}(3)'$ is introduced later in Sec. 3.2, but it can be geometrically understood as the set of all rotations that keep a Platonic solid (i.e., a convex and regular 3D polyhedron) unchanged. As illustrated at the bottom of Fig. 1, the set of rotations can be enumerated by counting the number of vertices, repre + +![](images/3f2de0f441e64bbb7d81e4271c61cfd4141588a6d9edad368bbcd442045ccf3a.jpg) +Figure 2. Illustration of recovering $\mathrm{SO}(3)'$ features from $S^{2'}$ features through permutations. The left and right subplots are from the geometric and algebraic views. See Sec. 3.1.2 for more explanation. + +senting rotations taking a given vertex to any vertices, multiplied by the number of edges connected to a single vertex, representing the rotations that keep a vertex fixed. The same result can be achieved by counting the faces or the edges, but we stick with vertices in the following discussion. + +In comparison, we propose to define feature maps on $S^2 \times \mathbb{R}^3$ , where $S^2$ is the sphere space. We have $S^2 = \mathrm{SO}(3) / \mathrm{SO}(2)$ , meaning that it is the quotient space of SO(3) given the stabilizer subgroup SO(2). To understand the quotient space intuitively, we can see that all rotations can be grouped by the destination of a point on the sphere (e.g., the north pole) after the rotation. All rotations bringing the north pole to the same destination point form a coset. They are related by rotations around the axis passing through that point, forming a subgroup isomorphic to SO(2). Thus $S^2$ is the quotient of SO(3) and SO(2). In the discretized setup, as depicted in Fig. 1, SO(2)' is discretized by the number of edges connected to a single vertex. The quotient $S^{2'} = \mathrm{SO}(3)' / \mathrm{SO}(2)'$ corresponds to the vertices on the Platonic solid. + +In general, $|S^{2'}| = |\mathrm{SO}(3)'| / |\mathrm{SO}(2)'| < |\mathrm{SO}(3)'|$ , thus the size of feature maps and kernels defined on $S^{2'} \times \mathbb{R}^3$ is much smaller than those on $\mathrm{SO}(3)' \times \mathbb{R}^3$ . The convolution operation on the former space also requires smaller costs. It is the major reason our method is much more efficient than EPN. There is another design, called symmetric kernel, which further improves the efficiency of our method, but we will refer to Sec. 3.2.3 for details. + +# 3.1.2 Information recovery with permutations + +With the quotient feature map, all rotations moving the north pole to the same point on a sphere are represented by the same point. Thus we immediately lose the ability to distinguish among these rotations, which is a problem if our task is to learn the pose, for example, in the point cloud registration tasks. + +However, with our proposed permutation layer, we can distinguish every element in $\mathrm{SO}(3)^{\prime}$ from the feature maps on $S^{2^{\prime}}$ . The key observation is that the action of $\mathrm{SO}(3)$ on $S^2$ is faithful, i.e., $\forall R\in \mathrm{SO}(3)$ and $R\neq I$ , $\exists x\in S^2$ + +s.t. $Rx \neq x$ . It means that an action of $\mathrm{SO}(3)$ other than identity will always cause a change on the $S^2$ feature map when looking at all points on $S^2$ simultaneously. In the discretized setup, it means that there is an injective map $\phi: \mathrm{SO}(3)' \to Sym(|S^{2'}|)$ , where $Sym(|S^{2'}|)$ stands for the symmetric group, i.e., the collection of all permutations of a set of size $|S^{2'}|$ . An element in $Sym(n)$ is a bijective map $\{1, \dots, n\} \to \{1, \dots, n\}$ , permuting the indices. In other words, each rotation corresponds to a unique permutation of the $S^{2'}$ elements, from which we can distinguish each rotation from the feature map defined on $S^{2'}$ . + +Here we provide the specific form of the permutation layer. Given $\phi$ mentioned above and a feature map $f: S^{2'} \to \mathbb{R}^m$ , we can build a feature map $\tilde{f}: \mathrm{SO}(3)' \to \mathbb{R}^{mn}$ defined as: + +$$ +\tilde {f} (R) = \left[ f \left(x \left[ \phi_ {R} (1) \right]\right), f \left(x \left[ \phi_ {R} (2) \right]\right), \dots , f \left(x \left[ \phi_ {R} (n) \right]\right) \right] \tag {1} +$$ + +where $R \in \mathrm{SO}(3)'$ , $n = |S^{2'}|$ , and $x[i] \in S^{2'}$ for $i = 1, \dots, n$ . Given that $\phi$ is injective, $\tilde{f}(R_1) \neq \tilde{f}(R_2)$ when $R_1 \neq R_2$ . Thus we can distinguish $\mathrm{SO}(3)'$ rotations from $\tilde{f}$ . See Fig. 2 for an illustration. + +# 3.2. Specific form of convolution + +# 3.2.1 Recap of KPConv + +A conventional 3D convolution can be written as: + +$$ +[ \kappa * f ] (x) = \int_ {\mathbb {R} ^ {3}} \kappa (t) f (x + t) d t = \sum_ {t \in \mathbb {R} ^ {3},} \kappa (t) f (x + t), \tag {2} +$$ + +where $x \in \mathbb{R}^3$ , and the right hand side is after discretization. We use correlations to implement convolutions in this paper following conventions in deep learning. For processing point clouds, Eq. (2) could be tricky in implementation because it is challenging to align $\kappa$ with $f$ when there is no grid. The strategy of KPCov is to have a set of kernel points for $\kappa$ and to gather features to the kernel point coordinates from the input points where $f$ is defined so that they are aligned before the convolution. It is depicted in Fig. 3 (a), and we need to replace $f$ with $\hat{f}$ in Eq. (2) where $\hat{f}(x) = \sum_{y \in \mathcal{N}_x} w(|y - x|) f(y)$ and $w$ is a scalar weight function based on distance. $\hat{f}$ is the features gathered from neighboring input points to align with the kernel points. In this case, the input and output feature map $f$ and $[\kappa * f]$ are defined on $\mathbb{R}^3$ , while the kernel $\kappa$ is defined on $\mathbb{R}^{3'}$ , i.e., coordinates of the set of kernel points. The gathered feature $\hat{f}$ when calculating the convolution at $x \in \mathbb{R}^3$ is defined at $x + \mathbb{R}^{3'}$ . Notice that we do not consider the deformable mode of KPCov in this paper. + +![](images/01b7509596275b2118a6737d5ac6c05c565162b852350870d5fa669c4f0c6a17.jpg) +Figure 3. Illustration of different versions of KPConv. (a) original KPConv (see Sec. 3.2.1). (b) KPConv on finite group or quotient space without the symmetric kernel (see Sec. 3.2.2). (c) KPConv on group or quotient space with the symmetric kernel (see Sec. 3.2.3). (b,c) compared with (a): the convolution kernel is larger because it is defined on a higher dimension. (c) compared with (b): the feature gathering is more efficient because the kernel points are symmetric to the rotations in the rotation group. + +# 3.2.2 KPCov on group and on quotient space + +To extend KPConv to a group convolution [6] with finite group $G'$ , we modify Eq. (2) to + +$$ +[ \kappa * f ] (g) = \sum_ {g _ {t} \in G ^ {\prime}} \kappa (g _ {t}) \hat {f} (g \cdot g _ {t}), \tag {3} +$$ + +where in our case, $G' = \mathrm{SE}(3)' = \mathrm{SO}(3)' \times \mathbb{R}^{3'}$ is where $\kappa$ is defined, $g \in G^{\dagger} = \mathrm{SO}(3)' \times \mathbb{R}^{3}$ is where the input and output feature map is defined. $\hat{f}$ is defined on $g \cdot G'$ when calculating the convolution at $g$ . Denote an element $g \in \mathrm{SE}(3)$ as $(R,t)$ where $R \in \mathrm{SO}(3)$ and $t \in \mathbb{R}^{3}$ , the binary operation $\cdot$ for $\mathrm{SE}(3)$ can be specified as $(R_1,t_1) \cdot (R_2,t_2) = (R_1R_2,t_1 + R_1t_2)$ , same for the discretized case. EPN [2] follows this form of convolution. However, as discussed in Sec. 3.1.1, the size of group $|\mathrm{SE}(3)'| = |\mathrm{SO}(3)'||\mathbb{R}^{3'}|$ , making it expensive to store the feature map and compute the convolution. To alleviate this issue, EPN has to conduct convolutions in $\mathrm{SO}(3)'$ and $\mathbb{R}^{3'}$ separately (i.e., separable convolutions [2, 3]), so that the computational cost is reduced. + +We use quotient feature maps to address this issue. To conduct convolutions on the quotient space $X =$ + +![](images/2a767a62d778d7279485b05fbba2413f9f322ca4a10cc66f1fb5ec41eaf4eb3b.jpg) +Figure 4. Visualization of the symmetric kernel $\kappa$ used in our work, where $\mathbb{R}^{3\prime} = \{rS^{2\prime}\cup 0\mid r > 0\}$ + +![](images/520715ce54709ff811f5b358831db09955d19d3128202c7e3ac38b44b69fa6f4.jpg) +Figure 5. Illustration of all five types of Platonic solids and their corresponding finite rotation groups. + +$\mathrm{SE}(3) / \mathrm{SO}(2) = S^2 \times \mathbb{R}^3$ , we cannot directly use Eq. (3), because the $\cdot$ operation is not defined between two elements in $X$ since $X$ is not a group. It is pointed out in [7, 8] that we can write convolutions on the quotient space as + +$$ +[ \kappa * f ] (x) = \sum_ {x _ {t} \in X ^ {\prime}} \kappa (x _ {t}) \hat {f} (s (x) \cdot x _ {t}), \tag {4} +$$ + +where $X^{\prime} = S^{2^{\prime}}\times \mathbb{R}^{3^{\prime}}$ is the domain of $\kappa$ , $X^{\dagger} = S^{2^{\prime}}\times \mathbb{R}^{3}$ is the domain of $f$ and $[\kappa *f]$ , and $\hat{f}$ is defined on $s(x)\cdot X^{\prime}$ . $s(x)$ is called the section map, $s:X^{\prime}\to G^{\prime}$ (or $X\rightarrow G$ in the continuous case), mapping $x\in X^{\prime}$ to an element of $G^{\prime}$ in the corresponding coset. With the section map, the $\cdot$ operation denotes the action of the group $G$ on quotient space $X$ , i.e., $\cdot :G\times X\to X$ . Denote an element in $S^2\times \mathbb{R}^3$ as $(R\mathbf{n},t)$ , where $R\in \mathrm{SO}(3)$ , $\mathbf{n}$ is the north pole point on the unit sphere $(0,0,1)$ . Then $R\mathbf{n}$ represents arbitrary points on the sphere $S^2$ . The action $\cdot$ can then be written as $(R_{1},t_{1})\cdot (R_{2}\mathbf{n},t_{2}) = (R_{1}R_{2}\mathbf{n},t_{1} + R_{1}t_{2})$ . + +# 3.2.3 Symmetric kernels + +Now we introduce the specific form of $\mathbb{R}^{3'}$ , i.e., the location of kernel points in KPConv. In our design, $\mathbb{R}^{3'} = \{rS^{2'} \cup 0 \mid r > 0\}$ , i.e., the set of vertices of the Platonic solid with radius $r$ and the origin point. $\mathbb{R}^{3'}$ is very similar to $S^{2'}$ , because we want to make the kernel symmetric to $\mathrm{SO}(3)'$ . More precisely, we desire $\mathbb{R}^{3'}$ to be closed under the action of $\mathrm{SO}(3)'$ . There are two reasons as follows. + +Steerability constraint To make the convolution on quotient space equivariant, defining a valid form of convolution as Eq. (4) is not the whole story. The kernel values must satisfy a condition called the steerability constraint, which is required for all steerable CNNs. More background knowledge can be found in [8]. In our case, the steerability constraint is + +$$ +\kappa (x) = \kappa \left(R _ {z} \cdot x\right), \forall x \in X ^ {\prime}, \forall R _ {z} \in \mathrm {S O} (2) ^ {\prime}, \tag {5} +$$ + +where $R_{z}$ is a $z$ -axis rotation. The derivation of Eq. (5) from the general form of steerability constraints can be found in + +
Rotation groupsTetrahedral TOctahedral OIcosahedral I
Platonic solidsTetrahedronCubeOctahedronDodecahedronIcosahedron
Size|SO(3)'| = 12 |S2'| = 4 |SO(2)'| = 3|SO(3)'| = 24 |S2'| = 8 |SO(2)'| = 3|SO(3)'| = 24 |S2'| = 6 |SO(2)'| = 4|SO(3)'| = 60 |S2'| = 20 |SO(2)'| = 3|SO(3)'| = 60 |S2'| = 12 |SO(2)'| = 5
+ +the appendix. Here the $\cdot$ operation inherits from the action of $G'$ on $X'$ since $\mathrm{SO}(2)' \subset \mathrm{SO}(3)' \subset G'$ . Specifically, we have $R_z \cdot (R\mathbf{n}, t) = (R_z, 0) \cdot (R\mathbf{n}, t) = (R_z R\mathbf{n}, R_z t)$ . Replace $x$ with $(R\mathbf{n}, t)$ in Eq. (5), and we have + +$$ +\kappa (R \mathbf {n}, t) = \kappa \left(R _ {z} R \mathbf {n}, R _ {z} t\right), \tag {6} +$$ + +$\forall R\mathbf{n}\in S^{2^{\prime}},\forall t\in \mathbb{R}^{3^{\prime}},\forall R_{z}\in \mathrm{SO}(2)^{\prime}.$ Notice that it implies that we need $R_{z}t\in \mathbb{R}^{3^{\prime}},\forall t\in \mathbb{R}^{3^{\prime}},\forall R_{z}\in \mathrm{SO}(2^{\prime})$ so that $\kappa$ is defined on the right hand side of Eq. (6). In other words, the kernel points $\mathbb{R}^{3^{\prime}}$ need to be closed under $\mathrm{SO}(2)^{\prime}$ . Obviously, having $\mathbb{R}^{3^{\prime}}$ closed under $\mathrm{SO}(3)^{\prime}$ is a sufficient condition for this. + +For the $S^{2'}$ dimension, since $S^{2'}$ is symmetric (closed) to $\mathrm{SO}(3)'$ by definition and $\mathrm{SO}(2)' \subset \mathrm{SO}(3)'$ , we always have $R_z R\mathbf{n} \in S^{2'}$ and $\kappa$ is always defined. + +Efficient feature gathering Another important reason for the design choice of $\mathrm{SO}(3)^{\prime}$ -symmetric kernels is that it enables more efficient feature gathering. Consider a spatial location $t_0\in \mathbb{R}^3$ , the convolution feature output at this point is a stack of $[[\kappa *f](x_i)]_i$ with $x_{i}\in (S^{2^{\prime}},t_{0})\subset X^{\dagger}$ . As shown in Eq. (4), it involves feature gathering for $\hat{f}$ at $s(x_{i})\cdot x_{jk}$ for every $x_{jk}\in X' = S^{2'}\times \mathbb{R}^{3'}$ . Denote an instance of $s(x_{i}) = (R_{i},t_{0}),x_{jk} = (R_{j}\mathbf{n},t_{k})$ , then $s(x_{i})\cdot x_{jk} = (R_{i}R_{j}\mathbf{n},t_{0} + R_{i}t_{k})$ . If $\mathbb{R}^{3^{\prime}}$ is closed under $\mathrm{SO}(3)^{\prime}$ , then we have + +$$ +\left\{R _ {i} t _ {k} \mid t _ {k} \in \mathbb {R} ^ {3 ^ {\prime}} \right\} = \mathbb {R} ^ {3 ^ {\prime}}, \forall R _ {i} \in \mathrm {S O} (3) ^ {\prime}, \tag {7} +$$ + +which implies that the feature gathering for all $S^{2'}$ channels can be done once at the same set of spatial positions specified by $\mathbb{R}^{3'}$ . An illustration is shown in Fig. 3. Without the symmetric kernel, the KPConv on group or quotient space looks like Fig. 3 (b), where the kernel is rotated for each $\mathrm{SO}(3)'$ (for group KPConv) or $S^{2'}$ (for quotient KPConv) channel separately to gather input features. However, with symmetric kernels, as shown in Fig. 3 (c), the rotations keep the position of kernel points unchanged up to a permutation so that the feature-gathering step is simplified. Specifically, the number of spatial positions needed for feature gathering without symmetric kernels is $|SO(3)'| \mathbb{R}^{3'}|$ for group KPConv or $|S^{2'}| \mathbb{R}^{3'}|$ for quotient KPConv, while the number + +Table 1. Efficiency comparison in terms of GPU memory consumption and the computation speed between EPN [2] and our method on three tasks. Two numbers are reported for training/inference respectively. $\downarrow$ means lower is better. $\uparrow$ means higher is better. The best is shown in bold font. + +
TasksModelNet40 PoseModelNet40 Classification3DMatch Keypoint Matching
MethodsMemory (GB) ↓Speed (fps) ↑Memory (GB) ↓Speed (fps) ↑Memory (GB) ↓Speed (fps) ↑
EPN [2]22.2 / 16.91.1 / 1.613.4 / 12.71.9 / 1.537.4 / 8.50.6 / 3.1
Ours (w/o symmetric kernels)4.8 / 3.75.1 / 10.14.1 / 3.27.8 / 7.87.5 / 2.82.6 / 16.7
Ours (w/ symmetric kernels)4.3 / 2.86.7 / 11.13.9 / 2.79.1 / 10.36.5 / 2.43.7 / 23.6
+ +is $|\mathbb{R}^{3^{\prime}}|$ with symmetric kernels. The convolution kernels in Fig. 3 is an abstract illustration, while the actual symmetric kernel in our work is visualized in Fig. 4. + +# 3.2.4 Choices of the discretization of $SO(3)$ and $S^2$ + +In Sec. 3.1.1, we mentioned that the discretization of $\mathrm{SO}(3)$ is the rotation group that respects the symmetry of a Platonic solid. There are five types of Platonic solids, corresponding to 3 finite rotation groups, as shown in Fig. 5. Choosing $\mathrm{SO}(3)'$ to be any of them is valid, representing a discretization of $\mathrm{SO}(3)$ to different resolutions. The different Platonic solids with the same rotation group $\mathrm{SO}(3)'$ represents different discretizations of $S^{2'}$ and $\mathrm{SO}(2)'$ . + +If we use a small $\mathrm{SO}(3)'$ (for example, $T$ ), the strategy of using $\mathbb{R}^{3'} = \{rS^{2'} \cup 0 \mid r > 0\}$ could be problematic because the number of kernel points could be too few to learn representative features. In this case, we are free to design the kernel points differently, as long as they are closed under $\mathrm{SO}(3)'$ . For example, one may add kernel points at the center of all edges and/or faces. One may even use a combination of several polyhedrons with different radii $r$ . + +In this paper, we only choose the icosahedron as the Platonic solid to conduct experiments for three reasons. First, it has the finest discretization of SO(3). Second, it has a smaller size of $S^{2'}$ compared with the dodecahedron, maximizing the benefit of working with quotient features. Third, it is consistent with existing methods [1,2], enabling direct comparison with the baselines. + +# 3.2.5 Other aspects of the network + +We use element-wise scalar nonlinearity (ReLU and leaky ReLu) in the network. The spatial pooling is done by subsampling the input points and aggregating the features of neighboring input points to the subsampled points. Batch normalization is applied to normalize over the batch, $S^{2'}$ , and $\mathbb{R}^3$ dimensions. All these choices follow the common practice of conventional CNNs (KPCov [35]) and group convolutions (EPN [2]). We also adopted the group attentive pooling in EPN to pool over the $S^{2'}$ dimension and generate $\mathrm{SO}(3)'$ -invariant features. + +Depending on the specific task in the experiment, the prediction head has a slightly different design, composing + +the last few layers of the network. The loss functions are inherited from EPN [2], including cross-entropy loss for classifications, L2 loss for residual pose regression, and batch-hard triplet loss for keypoint matching. We refer to the appendix for more details about the prediction heads and the loss functions. + +# 3.3. Relation to existing work + +In the context of literature on group-equivariant neural networks, our method is under the theoretical framework of equivariant CNNs on homogeneous spaces [8, 24, 46]. Our work is a new form of realization when working with 3D point clouds and adapting the convolution structure of KPCov. We explore a balance of simplicity, efficiency, and expressiveness by finding the proper quotient space and discretization. Our method is an extension of group convolutions, leveraging their clean structure enabled by discretization. Our method can also be viewed as a steerable CNN with homogeneous space $S^2 \times \mathbb{R}^3$ and stabilizer subgroup SO(2) with scalar-type features or with homogeneous space $\mathbb{R}^3$ and stabilizer subgroup SO(3) with $S^2$ features. The proposed work paves the way for efficiency improvement using quotient representation learning on finite groups. We also emphasize the group-variant side of equivariant models with the permutation layer to distinguish rotations, while existing work focuses on the benefit of getting group-invariant features from equivariant models. + +# 4. Experiments + +Our major baseline to compare with is EPN [2], a state-of-the-art group convolution network, as we are similar in several ways. Both are KPConv-style convolutions with SE(3)-equivariance. Both use the icosahedral rotation group $\mathcal{I}$ to discretize SO(3). However, EPN has features defined on $\mathcal{I} \times \mathbb{R}^3$ , compared with $S^{2'} \times \mathbb{R}^3$ in our method. + +Two datasets, ModelNet40 [44] and 3DMatch [47], are used in the experiments. ModelNet40 is composed of 3D CAD models of 40 categories of objects. 3DMatch is a real-scan dataset of indoor scenes. For the ModelNet40 dataset, we conduct the classification and pose estimation tasks. For the 3DMatch dataset, we conduct the keypoint matching task. These tasks are also studied in EPN [2]. + +In Tab. 1, we list the GPU memory consumption and run + +Table 2. Experimental result of object classification on ModelNet40. The best is bolded. The best in equivariant models is underlined. Noisy: test using input with random translation, scaling, jittering, and dropout. Clean: test without above processing. SO(3): random rotations. Id: no rotation. ico: random rotations in I. ESCNN works with voxelized data, thus not having Noisy results with point-wise augmentations. FLOPs are counted using fvcore, which does not support DGL used in TFN and SE(3)-T, thus left blank. The efficiency comparison uses the same batch size as in Tab. 1 (see appendix). + +
TypeColumn ##1#2#3#4#5#6#7#8#9#10#11#12#13#14
MetricsModelNet40 classification performance metric: Acc (%) ↑Efficiency metricsFLOPs per training batch (G)Trainable params (M)
Train rotationSO(3)IdMemory (GB)↓ train/testSpeed (fps)↑ train/test
Test rotationSO(3)IdSO(3)Idico
Test conditionNoisyCleanNoisyCleanNoisyCleanNoisyCleanNoisyClean
Non-equivKPCov [35]75.7181.1776.8882.0212.6612.2289.4691.85--0.18/0.2517.24/18.480.741.69
PointNet++ [31]81.3184.8883.0385.7613.4413.7690.6791.55--1.03/0.57.06/7.4310.591.48
DGCNN [38]79.8684.7782.5485.6215.3617.2691.0092.18--1.96/1.6917.90/17.5032.651.81
PT [48]78.5179.6878.8379.6816.5316.7786.9888.10--4.16/5.824.80/5.03220.999.58
CurveNet [45]84.7288.3385.8288.9417.3418.0391.5392.63--1.20/0.335.61/7.544.222.14
PCT [17]86.9189.1087.6489.8316.3317.9591.6992.87--1.18/0.808.54/20.8527.412.87
EquivalentESCNN [1]-82.40-77.73-29.03-88.94--4.71/5.503.79/8.38428.610.46
TFN [36]58.2762.6458.0662.6457.5062.2859.2062.28--15.95/8.71.83/6.08-0.06
SE(3)-T [15]60.3766.2961.1866.2944.6150.5344.8150.53--19.39/9.651.54/5.13-0.11
EPN [2]84.6387.8485.3488.8330.9932.3290.0391.6190.0491.6013.40/12.721.86/1.4958.953.06
Ours (w/ GA pooling [2])85.0487.5185.4987.6341.4644.4389.7390.5090.0090.503.95/2.709.21/10.37170.682.53
Ours (w/ permutation)86.9988.6288.2189.6239.5442.7890.6691.7790.6891.773.95/2.709.09/10.28170.772.65
+ +ning speed of our method and EPN [2] in the three tasks. The comparisons are under the same input size, number of feature channels, and number of network layers. The separable convolutions on $\mathrm{SO}(3)$ and $\mathbb{R}^3$ in EPN are together considered as one layer. The numbers are not comparable between training and inference because the batch size could be different (see the appendix). The specific configurations in each experiment are introduced later. All experiments are run on a single NVIDIA A40 GPU. Our network with quotient space convolutions is much smaller and runs much faster in all three tasks, indicating the potential value for real applications. We boost efficiency without sacrificing performance, as is shown later. + +Ablation study: We list two rows of our results in Tab. 1 to show the effect of efficient feature gathering enabled by the symmetric kernels. The results of without symmetric kernels are generated using the same kernel points as with symmetric kernels, but ignoring the fact that they are symmetric to rotations and gathering features at $|S^{2'}| |\mathbb{R}^{3'}|$ locations, instead of at $|\mathbb{R}^{3'}|$ locations and permuting them. The efficient feature gathering brings further efficiency improvements, especially in terms of computational speed. + +# 4.1. Object classification on ModelNet40 + +For this task, given a point cloud of an object, the network predicts its category. The evaluation metric is classification accuracy (Acc). In this experiment, we show an extensive efficiency comparison with more existing networks, equivariant and non-equivariant. We also examine a wide combination of input conditions in training and testing to show the effect of equivariance and robustness against input imperfections. All models are trained with data augmentation, including random translation, scaling, jittering, and dropout. + +Our method has outstanding performance as shown in Tab. 2. In columns #1-4, all methods are trained with rota + +Table 3. Pose estimation on ModelNet40. Mean, median, and max angular errors are calculated over the test set. Statistics (average and standard deviation) over 10 test runs are shown to account for the randomness. + +
MetricsMean (°) ↓Median (°) ↓Max (°) ↓
StatsAvg μSD σAvg μSD σAvg μSD σ
KPConv [35]13.991.5310.700.81115.1957.84
EPN [2]1.100.201.360.137.062.52
Ours1.200.080.960.056.711.28
+ +tional augmentation. Our method performs the best among listed equivariant models and is on par with PCT [18] among all models. Our method is intended to work with rotational augmentations so that the equivariance gap caused by discretization can be interpolated through training. However, we still experiment with training without rotational augmentation, as shown in columns #5-10. From columns #9-10, we can verify the equivariance to the icosahedral rotation group of our model. Columns #5-6 show the effect of discretization on the continuous SO(3) if no interpolation is trained, in which case the performance lands between non-equivariant models and continuously SO(3)-equivariant models. The efficiency of our method outperforms all equivariant baselines and is similar to nonequivariant models. The FLOPs and number of trainable parameters are also listed for reference. We found that FLOPs do not strictly correlate with running speed, which could be due to different memory access costs and parallelism. + +Ablation study: Since this task requires SE(3)-invariant features, there are two options in our network: either using the group-attentive pooling (GA pooling) introduced in EPN [2] to pool over the $S^{2^{\prime}}$ dimensions or using the permutation layer to find the canonical permutation of $S^{2^{\prime}}$ dimensions. Either way, the canonical pose of objects in ModelNet40 can be used for supervision. Tab. 2 shows that the permutation layer yields better performance with negligible computational overhead. The reason could be that the permutation layer as in Eq. (1) stacks features from $S^{2^{\prime}}$ + +Table 4. Experiment result of keypoint matching on the 3DMatch dataset. The numbers are the average recall $(\%)$ , and the higher, the better. Notation * represents the result with the given point normal information. + +
SHOT [37]3DM [47]CGF [23]PPFN [12]PPFF [11]3DSN [16]Li [28]Li [28]*EPN [2]Ours
Kitchen74.358.360.389.778.797.592.199.499.099.4
Home 180.172.471.155.876.396.291.098.799.498.7
Home 270.761.556.759.161.593.285.694.796.296.6
Hotel 177.454.957.158.068.197.495.199.699.699.1
Hotel 272.148.153.857.771.292.891.3100.097.198.1
Hotel 385.261.183.361.194.498.296.3100.0100.0100.0
Study64.051.737.753.462.095.091.895.596.295.2
MIT Lab62.350.745.563.662.394.184.492.293.590.9
Average73.357.358.262.371.895.691.097.597.697.3
+ +and thus preserves the information better, compared with weighted averaging over the $S^{2'}$ dimension as done in GA pooling. + +# 4.2. Pose Estimation on ModelNet40 + +In this experiment, the network takes a pair of point clouds of an object and predicts the relative rotation between them. To avoid the pose ambiguity of objects with symmetric rotational shapes, only the airplane category is used in this experiment, with 626 models in the training set and 100 models in the test set. A point cloud is generated by randomly subsampling 1,024 points on the surface, and it is randomly rotated to form a pair. + +The experimental result is shown in Tab. 3. We achieved similar rotation estimation accuracy to EPN [2] overall. While our mean error is slightly larger, the lower median error, max error, and standard deviations show that our method delivers a more reliable registration. It could imply that representing rotations as a permutation of features is more robust than representing them as a single element in the feature map. Besides, the equivariant networks outperform the non-equivariant KPConv [35] by a large margin. + +# 4.3. Keypoint matching on 3DMatch + +In this task, patches of point clouds extracted locally around keypoints in a large, dense scan are input to the network, and each is mapped to a feature vector of 64 dimension as the keypoint descriptor. Each patch has 1,024 points. Then we evaluate the average recall of keypoint correspondence across different scans through nearest neighbor search in the feature space, as proposed in PPFNet [12]. + +This experiment's performance in Tab. 4 indicates the capability of learning distinctive and rotation-invariant features for local patches of point clouds. Though not achieving the best in the list, our method delivers comparable performance to the top methods using only a fraction of the computational resources as EPN [2] (see Tab. 1). We use the GA pooling layer [2] in this experiment because the permutation layer requires supervision on the pose, while + +a canonical pose is not defined for local patches of point clouds, and GA pooling works with or without the pose supervision. However, the result shows that GA pooling over the $|S^{2t}|$ features also provides distinctive features for keypoint matching. This part may be further improved by taking the information of the global scan [12] or the matching scan [20] into consideration, in which case the permutation layer may get hints on the optimal permutation from the larger context. This topic goes beyond the focus of this paper and is left for future work. + +# 5. Conclusion + +This paper presents a new design of SE(3)-equivariant point cloud convolution network, which is efficient, simple, and expressive simultaneously by working with feature maps defined on the quotient space $S^2 \times \mathbb{R}^3$ associated with the stabilizer SO(2). We further improve the efficiency of the convolutions by designing the kernel points to be symmetric to the discretized rotation group $\mathrm{SO}(3)'$ . Moreover, we propose a permutation layer to recover $\mathrm{SO}(3)'$ information from $S^{2/}$ dimensions of the features so that the network can detect SO(3) rotations. Experiments show that our network delivers state-of-the-art performance in multiple tasks while consuming only a fraction of memory and computation resources as a group-convolution network with similar performance. Our method can open exciting opportunities to introduce the SE(3)-equivariance property to mainstream point cloud networks for various tasks. + +This work also has limitations. We do not outperform EPN [2] in the keypoint matching task, implying that the network, especially the permutation layer, needs improvement when dealing with inputs without a clear pose definition. Other possibilities for the network design also remain open. For example: What if we use a non-scalar type of feature on the quotient space? How to further alleviate the impact of the discretization of a continuous group? From a general perspective, extending the discretized quotient space convolution strategy to other groups is also an attractive direction for future work. + +# References + +[1] Gabriele Cesa, Leon Lang, and Maurice Weiler. A program to build E(N)-equivariant steerable CNNs. In International Conference on Learning Representations, 2022. 6, 7 +[2] Haiwei Chen, Shichen Liu, Weikai Chen, Hao Li, and Randall Hill. Equivariant point network for 3D point cloud analysis. 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It can be viewed as an equivariant version of kernel point convolutions (KPCov), a widely used convolution form to process point cloud data. Compared with existing equivariant networks, our design is simple, lightweight, fast, and easy to be integrated with existing task-specific point cloud learning pipelines. We achieve these desirable properties by combining group convolutions and quotient representations. Specifically, we discretize " + }, + { + "bbox": [ + 46, + 286, + 290, + 539 + ], + "type": "inline_equation", + "content": "SO(3)" + }, + { + "bbox": [ + 46, + 286, + 290, + 539 + ], + "type": "text", + "content": " to finite groups for their simplicity while using " + }, + { + "bbox": [ + 46, + 286, + 290, + 539 + ], + "type": "inline_equation", + "content": "SO(2)" + }, + { + "bbox": [ + 46, + 286, + 290, + 539 + ], + "type": "text", + "content": " as the stabilizer subgroup to form spherical quotient feature fields to save computations. 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Introduction" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 582, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 582, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 582, + 287, + 713 + ], + "type": "text", + "content": "Processing 3D data has become a vital task today as demands for automated robots and augmented reality technologies emerge. In the past decade, computer vision has significantly succeeded in image processing, but learning from 3D data such as point clouds is still challenging. An important reason is that 3D data presents more variations than 2D images in several aspects. For example, the rigid body transformations in 2D only have 3 degrees of freedom (DoF) with 1 for rotations. In 3D space, the DoF is 6, with 3 for rotations. The 2D translation equivariance is a key factor in the success of convolutional neural networks (CNNs)" + } + ] + } + ], + "index": 11 + }, + { + "type": "image", + "bbox": [ + 307, + 261, + 542, + 393 + ], + "blocks": [ + { + "bbox": [ + 307, + 261, + 542, + 393 + ], + "lines": [ + { + "bbox": [ + 307, + 261, + 542, + 393 + ], + "spans": [ + { + "bbox": [ + 307, + 261, + 542, + 393 + ], + "type": "image", + "image_path": "82dd584913413f61d91b4829268472272c7dab067f61a940e034a69a25e9c274.jpg" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 399, + 547, + 449 + ], + "lines": [ + { + "bbox": [ + 305, + 399, + 547, + 449 + ], + "spans": [ + { + "bbox": [ + 305, + 399, + 547, + 449 + ], + "type": "text", + "content": "Figure 1. Our method achieves higher efficiency by working with smaller feature maps defined on " + }, + { + "bbox": [ + 305, + 399, + 547, + 449 + ], + "type": "inline_equation", + "content": "S^{2\\prime} \\times \\mathbb{R}^3" + }, + { + "bbox": [ + 305, + 399, + 547, + 449 + ], + "type": "text", + "content": " rather than " + }, + { + "bbox": [ + 305, + 399, + 547, + 449 + ], + "type": "inline_equation", + "content": "SO(3)' \\times \\mathbb{R}^3" + }, + { + "bbox": [ + 305, + 399, + 547, + 449 + ], + "type": "text", + "content": " (" + }, + { + "bbox": [ + 305, + 399, + 547, + 449 + ], + "type": "inline_equation", + "content": "'" + }, + { + "bbox": [ + 305, + 399, + 547, + 449 + ], + "type": "text", + "content": " denotes discretization). " + }, + { + "bbox": [ + 305, + 399, + 547, + 449 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^3" + }, + { + "bbox": [ + 305, + 399, + 547, + 449 + ], + "type": "text", + "content": " is omitted in the figure. The black arrows in each space represent elements. The top and bottom paths are equivalent, showing the relations among different representations." + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_caption" + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 472, + 524, + 483 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 472, + 524, + 483 + ], + "spans": [ + { + "bbox": [ + 306, + 472, + 524, + 483 + ], + "type": "text", + "content": "in image processing, but it is not enough for 3D tasks." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 484, + 545, + 675 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 484, + 545, + 675 + ], + "spans": [ + { + "bbox": [ + 304, + 484, + 545, + 675 + ], + "type": "text", + "content": "Generally speaking, equivariance is a property for a map such that given a transformation in the input, the output changes in a predictable way determined by the input transformation. It drastically improves generalization as the variance caused by the transformations is captured via the network by design. Take CNNs as an example, the equivariance property refers to the fact that a translation in the input image results in the same translation in the feature map output from a convolution layer. However, conventional convolutions are not equivariant to rotations, which becomes problematic, especially when we deal with 3D data where many rotational variations occur. In response, on the one hand, data augmentations with 3D rotations are frequently used. On the other hand, equivariant feature learning emerges as a research area, aiming to generalize the translational equivariance to broader transformations." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 677, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 677, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 677, + 547, + 713 + ], + "type": "text", + "content": "A lot of progress has been made in group-equivariant feature learning. The term group encompasses the 3D rotations and translations, which is called the special Euclidean" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 296, + 732, + 315, + 742 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 732, + 315, + 742 + ], + "spans": [ + { + "bbox": [ + 296, + 732, + 315, + 742 + ], + "type": "text", + "content": "1223" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 275 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 275 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 275 + ], + "type": "text", + "content": "group of dimension 3, denoted SE(3), and also other more general types of transformations that represent certain symmetries. While many methods have been proposed, equivariant feature learning has not yet become the default strategy for 3D deep learning tasks. From our understanding, two major reasons hinder the broader application of equivariant methods. First, networks dealing with continuous groups typically require specially designed operations not commonly used in neural networks, such as generalized Fourier transform and Monte Carlo sampling. Thus, incorporating them into general neural networks for 3D learning tasks is challenging. Second, for the strategy of working on discretized (finite) groups [6, 19], while the network structures are simpler and closer to conventional networks, they usually suffer from the high dimensionality of the feature maps and convolutions, which causes much larger memory usage and computational load, limiting their practical use." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 275, + 289, + 418 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 275, + 289, + 418 + ], + "spans": [ + { + "bbox": [ + 46, + 275, + 289, + 418 + ], + "type": "text", + "content": "This work proposes E2PN, a convolution structure for processing 3D point clouds. Our proposed approach can enable SE(3)-equivariance on any network with the KPConv [35] backbone by swapping KPCov with E2PN. The equivariance is up to a discretization on SO(3). We leverage a quotient representation to save computational and memory costs by reducing SE(3) feature maps to feature maps defined on " + }, + { + "bbox": [ + 46, + 275, + 289, + 418 + ], + "type": "inline_equation", + "content": "S^2 \\times \\mathbb{R}^3" + }, + { + "bbox": [ + 46, + 275, + 289, + 418 + ], + "type": "text", + "content": " (where " + }, + { + "bbox": [ + 46, + 275, + 289, + 418 + ], + "type": "inline_equation", + "content": "S^2" + }, + { + "bbox": [ + 46, + 275, + 289, + 418 + ], + "type": "text", + "content": " stands for the 2-sphere). Nevertheless, we can recover the full 6 DoF information through a final permutation layer. As a result, our proposed network is SE(3)-equivariant and computationally efficient, ready for practical point-cloud learning applications." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 59, + 419, + 263, + 431 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 419, + 263, + 431 + ], + "spans": [ + { + "bbox": [ + 59, + 419, + 263, + 431 + ], + "type": "text", + "content": "Overall, this work has the following contributions:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 59, + 438, + 286, + 567 + ], + "type": "list", + "angle": 0, + "index": 7, + "blocks": [ + { + "bbox": [ + 59, + 438, + 286, + 462 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 438, + 286, + 462 + ], + "spans": [ + { + "bbox": [ + 59, + 438, + 286, + 462 + ], + "type": "text", + "content": "- We propose an efficient SE(3)-equivariant convolution structure for 3D point clouds." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 59, + 469, + 286, + 493 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 469, + 286, + 493 + ], + "spans": [ + { + "bbox": [ + 59, + 469, + 286, + 493 + ], + "type": "text", + "content": "- We design a permutation layer to recover the full SE(3) information from its quotient space." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 59, + 501, + 286, + 536 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 501, + 286, + 536 + ], + "spans": [ + { + "bbox": [ + 59, + 501, + 286, + 536 + ], + "type": "text", + "content": "- We achieve comparable or better performance with significantly reduced computational cost than existing equivariant models." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 59, + 544, + 286, + 567 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 544, + 286, + 567 + ], + "spans": [ + { + "bbox": [ + 59, + 544, + 286, + 567 + ], + "type": "text", + "content": "- Our implementation is open-sourced at https://github.com/minghanz/E2PN." + } + ] + } + ], + "index": 6 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 47, + 575, + 287, + 600 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 575, + 287, + 600 + ], + "spans": [ + { + "bbox": [ + 47, + 575, + 287, + 600 + ], + "type": "text", + "content": "Readers can find preliminary introductions to some related background concepts in the appendix." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 609, + 132, + 623 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 609, + 132, + 623 + ], + "spans": [ + { + "bbox": [ + 47, + 609, + 132, + 623 + ], + "type": "text", + "content": "2. Related work" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 629, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 629, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 629, + 287, + 713 + ], + "type": "text", + "content": "Group convolutions: In 2016, Cohen and Welling proposed G-CNN [6], enabling equivariance beyond translations on 2D images with generalized G-convolutions (group convolutions) over the group of 90-degree rotations, which is one of the earliest efforts in equivariant deep learning. Group convolution is similar to conventional convolutions but has an extended domain for feature maps and kernels." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 72, + 545, + 240 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 240 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 240 + ], + "type": "text", + "content": "The idea was then applied to different networks to enable equivariance for SE(2) [6,19], SO(3) [5], SE(3) [2,42], and E(3) [41] groups up to some discretization. The idea mainly works with finite (discretized) groups, as it is convenient to parameterize feature maps and kernels on the discretized group elements just as on pixel grids. Group convolutions have a relatively simple structure, making them straightforward to apply, but a major downside is that the lifted domain of features and kernels causes higher computational and memory costs, and the problem is more prominent when the group is large. Groups convs can also work with continuous groups, for example, with the help of Monte Carlo (MC) estimation as in [13], but they suffer from a large memory burden in MC sampling when the number of layers grows [30]." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 243, + 545, + 579 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 243, + 545, + 579 + ], + "spans": [ + { + "bbox": [ + 304, + 243, + 545, + 579 + ], + "type": "text", + "content": "Steerable CNNs: Another line of work is steerable CNNs. Instead of augmenting the domain of feature maps, steerable CNNs generalize the space of feature values to be steerable, i.e., the feature values transform predictably as the input transforms. The way the feature transforms is called the group representation in the feature space, governed by the feature type. Features of scalar type are kept unchanged under group actions, and we call the group representation trivial. For vector or tensor feature types, the representation is not trivial, and the features will change with group actions, for example, through rotation matrix multiplication. Steerable CNNs work for both discretized and continuous groups. One may freely design the feature types based on pre-determined basic types and corresponding representations (irreducible representations, i.e., irreps) as building blocks for a given group. Group convolutions can be viewed as a special case of steerable CNNs with regular representations, i.e., channels of a feature vector undergo permutations when transformed. Examples of steerable CNNs include [4,9,36,40,43]. While the framework of steerable CNNs generalizes group convolutions with more flexibility, it requires a good understanding of representation theory and involves generalized Fourier analysis when working with a continuous group, which makes the structure complicated and challenging to apply in real-world applications broadly. The work of [21, 39] also found empirically that steerable CNNs with irreps underperform regular representations in certain tasks." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "content": "Theoretical progress: There has been a lot of progress in the theoretical development of equivariant networks that are not group-specific. [24] developed a general formulation for steerable CNNs with scalar type features, and [7, 8] generalized it to arbitrary feature types. It is proven that all equivariant linear maps can be written as convolutions. The formulation from the perspective of Fourier analysis was presented in [46]. [39] found the general form of solution for the equivariant kernels for " + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "inline_equation", + "content": "E(2)" + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "content": " group, later generalized to any compact group [26]. [14] proposed an algorithm to solve for the equivariance constraint for arbitrary" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 296, + 732, + 315, + 742 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 732, + 315, + 742 + ], + "spans": [ + { + "bbox": [ + 296, + 732, + 315, + 742 + ], + "type": "text", + "content": "1224" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "type": "text", + "content": "matrix group. The formulation of group convolution based on MC estimation was proposed for any Lie group with [13] or without [30] surjective exponential maps. Equivariant non-linear layers like transformers [15, 21] and equivariant set and graph networks [14, 22, 32] are also proposed, but they are not the focus of this paper." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 145, + 288, + 384 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 145, + 288, + 384 + ], + "spans": [ + { + "bbox": [ + 46, + 145, + 288, + 384 + ], + "type": "text", + "content": "Applications of equivariant learning in perception tasks: We want to highlight a few equivariant networks that gain attention in perception applications due to their simplicity and practicality. Vector Neurons [10] is a PointNet-like SO(3)-equivariant network for 3D point cloud learning, later applied to point cloud registration [49] and manipulation [34]. It can be viewed as a special case of TFN [36] with type-1 features and self-interactions only. E2CNN [39] as an SE(2)-equivariant framework was applied in several image processing tasks [27, 33], given its generality and user-friendly library. DEVIANT [25] applied scale-equivariant convolutions in monocular 3D object detection. EPN [2] is a group convolution network with SE(3)-equivariance for 3D point cloud learning based on KPCConv [35] and was used in practice, for example in place recognition task [29]. We also position this proposed work in this category, aiming to promote the application of equivariant learning with our efficient and easy-to-use design. Our work is developed based on EPN, which also serves as a major baseline in this paper." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 396, + 129, + 410 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 396, + 129, + 410 + ], + "spans": [ + { + "bbox": [ + 47, + 396, + 129, + 410 + ], + "type": "text", + "content": "3. Methodology" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 417, + 166, + 428 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 417, + 166, + 428 + ], + "spans": [ + { + "bbox": [ + 47, + 417, + 166, + 428 + ], + "type": "text", + "content": "3.1. Overview of the idea" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 436, + 287, + 472 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 436, + 287, + 472 + ], + "spans": [ + { + "bbox": [ + 46, + 436, + 287, + 472 + ], + "type": "text", + "content": "We first explain why our proposed method is more efficient. Then we discuss how we gain efficiency without sacrificing expressiveness." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 490, + 261, + 502 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 490, + 261, + 502 + ], + "spans": [ + { + "bbox": [ + 47, + 490, + 261, + 502 + ], + "type": "text", + "content": "3.1.1 Improved efficiency with quotient features" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 510, + 287, + 640 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 510, + 287, + 640 + ], + "spans": [ + { + "bbox": [ + 46, + 510, + 287, + 640 + ], + "type": "text", + "content": "Following the idea of group convolutions, one needs to extend the domain of feature maps from the Euclidean space to the group space, from " + }, + { + "bbox": [ + 46, + 510, + 287, + 640 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^3" + }, + { + "bbox": [ + 46, + 510, + 287, + 640 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 46, + 510, + 287, + 640 + ], + "type": "inline_equation", + "content": "\\mathrm{SE}(3) \\cong \\mathrm{SO}(3) \\times \\mathbb{R}^3" + }, + { + "bbox": [ + 46, + 510, + 287, + 640 + ], + "type": "text", + "content": " in our case, where we want " + }, + { + "bbox": [ + 46, + 510, + 287, + 640 + ], + "type": "inline_equation", + "content": "\\mathrm{SE}(3)" + }, + { + "bbox": [ + 46, + 510, + 287, + 640 + ], + "type": "text", + "content": "-equivariant features for 3D point clouds. We then discretize " + }, + { + "bbox": [ + 46, + 510, + 287, + 640 + ], + "type": "inline_equation", + "content": "\\mathrm{SO}(3)" + }, + { + "bbox": [ + 46, + 510, + 287, + 640 + ], + "type": "text", + "content": " to a finite group denoted as " + }, + { + "bbox": [ + 46, + 510, + 287, + 640 + ], + "type": "inline_equation", + "content": "\\mathrm{SO}(3)'" + }, + { + "bbox": [ + 46, + 510, + 287, + 640 + ], + "type": "text", + "content": " (we use ' to denote discretization in this paper). The discretization of " + }, + { + "bbox": [ + 46, + 510, + 287, + 640 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^3" + }, + { + "bbox": [ + 46, + 510, + 287, + 640 + ], + "type": "text", + "content": " is taken care of by KPConv, which is the non-equivariant counterpart of our method, thus, not discussed here. Up to now, we can obtain a " + }, + { + "bbox": [ + 46, + 510, + 287, + 640 + ], + "type": "inline_equation", + "content": "\\mathrm{SE}(3)" + }, + { + "bbox": [ + 46, + 510, + 287, + 640 + ], + "type": "text", + "content": "-equivariant version of KPConv [35] realized through group convolution, which is what EPN [2] presents." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 642, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 642, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 642, + 287, + 713 + ], + "type": "text", + "content": "The specific form of the finite group " + }, + { + "bbox": [ + 46, + 642, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\mathrm{SO}(3)'" + }, + { + "bbox": [ + 46, + 642, + 287, + 713 + ], + "type": "text", + "content": " is introduced later in Sec. 3.2, but it can be geometrically understood as the set of all rotations that keep a Platonic solid (i.e., a convex and regular 3D polyhedron) unchanged. As illustrated at the bottom of Fig. 1, the set of rotations can be enumerated by counting the number of vertices, repre" + } + ] + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 310, + 70, + 547, + 167 + ], + "blocks": [ + { + "bbox": [ + 310, + 70, + 547, + 167 + ], + "lines": [ + { + "bbox": [ + 310, + 70, + 547, + 167 + ], + "spans": [ + { + "bbox": [ + 310, + 70, + 547, + 167 + ], + "type": "image", + "image_path": "3f2de0f441e64bbb7d81e4271c61cfd4141588a6d9edad368bbcd442045ccf3a.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 173, + 545, + 203 + ], + "lines": [ + { + "bbox": [ + 305, + 173, + 545, + 203 + ], + "spans": [ + { + "bbox": [ + 305, + 173, + 545, + 203 + ], + "type": "text", + "content": "Figure 2. Illustration of recovering " + }, + { + "bbox": [ + 305, + 173, + 545, + 203 + ], + "type": "inline_equation", + "content": "\\mathrm{SO}(3)'" + }, + { + "bbox": [ + 305, + 173, + 545, + 203 + ], + "type": "text", + "content": " features from " + }, + { + "bbox": [ + 305, + 173, + 545, + 203 + ], + "type": "inline_equation", + "content": "S^{2'}" + }, + { + "bbox": [ + 305, + 173, + 545, + 203 + ], + "type": "text", + "content": " features through permutations. The left and right subplots are from the geometric and algebraic views. See Sec. 3.1.2 for more explanation." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 224, + 545, + 283 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 224, + 545, + 283 + ], + "spans": [ + { + "bbox": [ + 304, + 224, + 545, + 283 + ], + "type": "text", + "content": "senting rotations taking a given vertex to any vertices, multiplied by the number of edges connected to a single vertex, representing the rotations that keep a vertex fixed. The same result can be achieved by counting the faces or the edges, but we stick with vertices in the following discussion." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 285, + 546, + 462 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 285, + 546, + 462 + ], + "spans": [ + { + "bbox": [ + 304, + 285, + 546, + 462 + ], + "type": "text", + "content": "In comparison, we propose to define feature maps on " + }, + { + "bbox": [ + 304, + 285, + 546, + 462 + ], + "type": "inline_equation", + "content": "S^2 \\times \\mathbb{R}^3" + }, + { + "bbox": [ + 304, + 285, + 546, + 462 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 285, + 546, + 462 + ], + "type": "inline_equation", + "content": "S^2" + }, + { + "bbox": [ + 304, + 285, + 546, + 462 + ], + "type": "text", + "content": " is the sphere space. We have " + }, + { + "bbox": [ + 304, + 285, + 546, + 462 + ], + "type": "inline_equation", + "content": "S^2 = \\mathrm{SO}(3) / \\mathrm{SO}(2)" + }, + { + "bbox": [ + 304, + 285, + 546, + 462 + ], + "type": "text", + "content": ", meaning that it is the quotient space of SO(3) given the stabilizer subgroup SO(2). To understand the quotient space intuitively, we can see that all rotations can be grouped by the destination of a point on the sphere (e.g., the north pole) after the rotation. All rotations bringing the north pole to the same destination point form a coset. They are related by rotations around the axis passing through that point, forming a subgroup isomorphic to SO(2). Thus " + }, + { + "bbox": [ + 304, + 285, + 546, + 462 + ], + "type": "inline_equation", + "content": "S^2" + }, + { + "bbox": [ + 304, + 285, + 546, + 462 + ], + "type": "text", + "content": " is the quotient of SO(3) and SO(2). In the discretized setup, as depicted in Fig. 1, SO(2)' is discretized by the number of edges connected to a single vertex. The quotient " + }, + { + "bbox": [ + 304, + 285, + 546, + 462 + ], + "type": "inline_equation", + "content": "S^{2'} = \\mathrm{SO}(3)' / \\mathrm{SO}(2)'" + }, + { + "bbox": [ + 304, + 285, + 546, + 462 + ], + "type": "text", + "content": " corresponds to the vertices on the Platonic solid." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 463, + 545, + 559 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 463, + 545, + 559 + ], + "spans": [ + { + "bbox": [ + 304, + 463, + 545, + 559 + ], + "type": "text", + "content": "In general, " + }, + { + "bbox": [ + 304, + 463, + 545, + 559 + ], + "type": "inline_equation", + "content": "|S^{2'}| = |\\mathrm{SO}(3)'| / |\\mathrm{SO}(2)'| < |\\mathrm{SO}(3)'|" + }, + { + "bbox": [ + 304, + 463, + 545, + 559 + ], + "type": "text", + "content": ", thus the size of feature maps and kernels defined on " + }, + { + "bbox": [ + 304, + 463, + 545, + 559 + ], + "type": "inline_equation", + "content": "S^{2'} \\times \\mathbb{R}^3" + }, + { + "bbox": [ + 304, + 463, + 545, + 559 + ], + "type": "text", + "content": " is much smaller than those on " + }, + { + "bbox": [ + 304, + 463, + 545, + 559 + ], + "type": "inline_equation", + "content": "\\mathrm{SO}(3)' \\times \\mathbb{R}^3" + }, + { + "bbox": [ + 304, + 463, + 545, + 559 + ], + "type": "text", + "content": ". The convolution operation on the former space also requires smaller costs. It is the major reason our method is much more efficient than EPN. There is another design, called symmetric kernel, which further improves the efficiency of our method, but we will refer to Sec. 3.2.3 for details." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 574, + 511, + 586 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 574, + 511, + 586 + ], + "spans": [ + { + "bbox": [ + 306, + 574, + 511, + 586 + ], + "type": "text", + "content": "3.1.2 Information recovery with permutations" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 594, + 545, + 665 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 594, + 545, + 665 + ], + "spans": [ + { + "bbox": [ + 304, + 594, + 545, + 665 + ], + "type": "text", + "content": "With the quotient feature map, all rotations moving the north pole to the same point on a sphere are represented by the same point. Thus we immediately lose the ability to distinguish among these rotations, which is a problem if our task is to learn the pose, for example, in the point cloud registration tasks." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 666, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 666, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 666, + 545, + 713 + ], + "type": "text", + "content": "However, with our proposed permutation layer, we can distinguish every element in " + }, + { + "bbox": [ + 304, + 666, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathrm{SO}(3)^{\\prime}" + }, + { + "bbox": [ + 304, + 666, + 545, + 713 + ], + "type": "text", + "content": " from the feature maps on " + }, + { + "bbox": [ + 304, + 666, + 545, + 713 + ], + "type": "inline_equation", + "content": "S^{2^{\\prime}}" + }, + { + "bbox": [ + 304, + 666, + 545, + 713 + ], + "type": "text", + "content": ". The key observation is that the action of " + }, + { + "bbox": [ + 304, + 666, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathrm{SO}(3)" + }, + { + "bbox": [ + 304, + 666, + 545, + 713 + ], + "type": "text", + "content": " on " + }, + { + "bbox": [ + 304, + 666, + 545, + 713 + ], + "type": "inline_equation", + "content": "S^2" + }, + { + "bbox": [ + 304, + 666, + 545, + 713 + ], + "type": "text", + "content": " is faithful, i.e., " + }, + { + "bbox": [ + 304, + 666, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\forall R\\in \\mathrm{SO}(3)" + }, + { + "bbox": [ + 304, + 666, + 545, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 666, + 545, + 713 + ], + "type": "inline_equation", + "content": "R\\neq I" + }, + { + "bbox": [ + 304, + 666, + 545, + 713 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 666, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\exists x\\in S^2" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 296, + 734, + 315, + 742 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 734, + 315, + 742 + ], + "spans": [ + { + "bbox": [ + 296, + 734, + 315, + 742 + ], + "type": "text", + "content": "1225" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "text", + "content": "s.t. " + }, + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "inline_equation", + "content": "Rx \\neq x" + }, + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "text", + "content": ". It means that an action of " + }, + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "inline_equation", + "content": "\\mathrm{SO}(3)" + }, + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "text", + "content": " other than identity will always cause a change on the " + }, + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "inline_equation", + "content": "S^2" + }, + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "text", + "content": " feature map when looking at all points on " + }, + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "inline_equation", + "content": "S^2" + }, + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "text", + "content": " simultaneously. In the discretized setup, it means that there is an injective map " + }, + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "inline_equation", + "content": "\\phi: \\mathrm{SO}(3)' \\to Sym(|S^{2'}|)" + }, + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "inline_equation", + "content": "Sym(|S^{2'}|)" + }, + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "text", + "content": " stands for the symmetric group, i.e., the collection of all permutations of a set of size " + }, + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "inline_equation", + "content": "|S^{2'}|" + }, + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "text", + "content": ". An element in " + }, + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "inline_equation", + "content": "Sym(n)" + }, + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "text", + "content": " is a bijective map " + }, + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "inline_equation", + "content": "\\{1, \\dots, n\\} \\to \\{1, \\dots, n\\}" + }, + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "text", + "content": ", permuting the indices. In other words, each rotation corresponds to a unique permutation of the " + }, + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "inline_equation", + "content": "S^{2'}" + }, + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "text", + "content": " elements, from which we can distinguish each rotation from the feature map defined on " + }, + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "inline_equation", + "content": "S^{2'}" + }, + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 207, + 288, + 255 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 207, + 288, + 255 + ], + "spans": [ + { + "bbox": [ + 47, + 207, + 288, + 255 + ], + "type": "text", + "content": "Here we provide the specific form of the permutation layer. Given " + }, + { + "bbox": [ + 47, + 207, + 288, + 255 + ], + "type": "inline_equation", + "content": "\\phi" + }, + { + "bbox": [ + 47, + 207, + 288, + 255 + ], + "type": "text", + "content": " mentioned above and a feature map " + }, + { + "bbox": [ + 47, + 207, + 288, + 255 + ], + "type": "inline_equation", + "content": "f: S^{2'} \\to \\mathbb{R}^m" + }, + { + "bbox": [ + 47, + 207, + 288, + 255 + ], + "type": "text", + "content": ", we can build a feature map " + }, + { + "bbox": [ + 47, + 207, + 288, + 255 + ], + "type": "inline_equation", + "content": "\\tilde{f}: \\mathrm{SO}(3)' \\to \\mathbb{R}^{mn}" + }, + { + "bbox": [ + 47, + 207, + 288, + 255 + ], + "type": "text", + "content": " defined as:" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 53, + 270, + 287, + 285 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 270, + 287, + 285 + ], + "spans": [ + { + "bbox": [ + 53, + 270, + 287, + 285 + ], + "type": "interline_equation", + "content": "\\tilde {f} (R) = \\left[ f \\left(x \\left[ \\phi_ {R} (1) \\right]\\right), f \\left(x \\left[ \\phi_ {R} (2) \\right]\\right), \\dots , f \\left(x \\left[ \\phi_ {R} (n) \\right]\\right) \\right] \\tag {1}", + "image_path": "b183577aa3a97d70cbfe506bfc9c36e3d7fb04ada3598243bf6986c78c9b52b9.jpg" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 299, + 287, + 348 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 299, + 287, + 348 + ], + "spans": [ + { + "bbox": [ + 47, + 299, + 287, + 348 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 299, + 287, + 348 + ], + "type": "inline_equation", + "content": "R \\in \\mathrm{SO}(3)'" + }, + { + "bbox": [ + 47, + 299, + 287, + 348 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 299, + 287, + 348 + ], + "type": "inline_equation", + "content": "n = |S^{2'}|" + }, + { + "bbox": [ + 47, + 299, + 287, + 348 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 47, + 299, + 287, + 348 + ], + "type": "inline_equation", + "content": "x[i] \\in S^{2'}" + }, + { + "bbox": [ + 47, + 299, + 287, + 348 + ], + "type": "text", + "content": " for " + }, + { + "bbox": [ + 47, + 299, + 287, + 348 + ], + "type": "inline_equation", + "content": "i = 1, \\dots, n" + }, + { + "bbox": [ + 47, + 299, + 287, + 348 + ], + "type": "text", + "content": ". Given that " + }, + { + "bbox": [ + 47, + 299, + 287, + 348 + ], + "type": "inline_equation", + "content": "\\phi" + }, + { + "bbox": [ + 47, + 299, + 287, + 348 + ], + "type": "text", + "content": " is injective, " + }, + { + "bbox": [ + 47, + 299, + 287, + 348 + ], + "type": "inline_equation", + "content": "\\tilde{f}(R_1) \\neq \\tilde{f}(R_2)" + }, + { + "bbox": [ + 47, + 299, + 287, + 348 + ], + "type": "text", + "content": " when " + }, + { + "bbox": [ + 47, + 299, + 287, + 348 + ], + "type": "inline_equation", + "content": "R_1 \\neq R_2" + }, + { + "bbox": [ + 47, + 299, + 287, + 348 + ], + "type": "text", + "content": ". Thus we can distinguish " + }, + { + "bbox": [ + 47, + 299, + 287, + 348 + ], + "type": "inline_equation", + "content": "\\mathrm{SO}(3)'" + }, + { + "bbox": [ + 47, + 299, + 287, + 348 + ], + "type": "text", + "content": " rotations from " + }, + { + "bbox": [ + 47, + 299, + 287, + 348 + ], + "type": "inline_equation", + "content": "\\tilde{f}" + }, + { + "bbox": [ + 47, + 299, + 287, + 348 + ], + "type": "text", + "content": ". See Fig. 2 for an illustration." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 365, + 200, + 378 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 365, + 200, + 378 + ], + "spans": [ + { + "bbox": [ + 47, + 365, + 200, + 378 + ], + "type": "text", + "content": "3.2. Specific form of convolution" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 387, + 156, + 399 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 387, + 156, + 399 + ], + "spans": [ + { + "bbox": [ + 47, + 387, + 156, + 399 + ], + "type": "text", + "content": "3.2.1 Recap of KPConv" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 412, + 248, + 423 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 412, + 248, + 423 + ], + "spans": [ + { + "bbox": [ + 47, + 412, + 248, + 423 + ], + "type": "text", + "content": "A conventional 3D convolution can be written as:" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 52, + 437, + 287, + 467 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 52, + 437, + 287, + 467 + ], + "spans": [ + { + "bbox": [ + 52, + 437, + 287, + 467 + ], + "type": "interline_equation", + "content": "[ \\kappa * f ] (x) = \\int_ {\\mathbb {R} ^ {3}} \\kappa (t) f (x + t) d t = \\sum_ {t \\in \\mathbb {R} ^ {3},} \\kappa (t) f (x + t), \\tag {2}", + "image_path": "8786d5d23b92e0280026fad5babef3171b327837fd26b5c1ff735f6fce012fbd.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 483, + 289, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 483, + 289, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 483, + 289, + 714 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 483, + 289, + 714 + ], + "type": "inline_equation", + "content": "x \\in \\mathbb{R}^3" + }, + { + "bbox": [ + 46, + 483, + 289, + 714 + ], + "type": "text", + "content": ", and the right hand side is after discretization. We use correlations to implement convolutions in this paper following conventions in deep learning. For processing point clouds, Eq. (2) could be tricky in implementation because it is challenging to align " + }, + { + "bbox": [ + 46, + 483, + 289, + 714 + ], + "type": "inline_equation", + "content": "\\kappa" + }, + { + "bbox": [ + 46, + 483, + 289, + 714 + ], + "type": "text", + "content": " with " + }, + { + "bbox": [ + 46, + 483, + 289, + 714 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 46, + 483, + 289, + 714 + ], + "type": "text", + "content": " when there is no grid. The strategy of KPCov is to have a set of kernel points for " + }, + { + "bbox": [ + 46, + 483, + 289, + 714 + ], + "type": "inline_equation", + "content": "\\kappa" + }, + { + "bbox": [ + 46, + 483, + 289, + 714 + ], + "type": "text", + "content": " and to gather features to the kernel point coordinates from the input points where " + }, + { + "bbox": [ + 46, + 483, + 289, + 714 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 46, + 483, + 289, + 714 + ], + "type": "text", + "content": " is defined so that they are aligned before the convolution. It is depicted in Fig. 3 (a), and we need to replace " + }, + { + "bbox": [ + 46, + 483, + 289, + 714 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 46, + 483, + 289, + 714 + ], + "type": "text", + "content": " with " + }, + { + "bbox": [ + 46, + 483, + 289, + 714 + ], + "type": "inline_equation", + "content": "\\hat{f}" + }, + { + "bbox": [ + 46, + 483, + 289, + 714 + ], + "type": "text", + "content": " in Eq. (2) where " + }, + { + "bbox": [ + 46, + 483, + 289, + 714 + ], + "type": "inline_equation", + "content": "\\hat{f}(x) = \\sum_{y \\in \\mathcal{N}_x} w(|y - x|) f(y)" + }, + { + "bbox": [ + 46, + 483, + 289, + 714 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 483, + 289, + 714 + ], + "type": "inline_equation", + "content": "w" + }, + { + "bbox": [ + 46, + 483, + 289, + 714 + ], + "type": "text", + "content": " is a scalar weight function based on distance. " + }, + { + "bbox": [ + 46, + 483, + 289, + 714 + ], + "type": "inline_equation", + "content": "\\hat{f}" + }, + { + "bbox": [ + 46, + 483, + 289, + 714 + ], + "type": "text", + "content": " is the features gathered from neighboring input points to align with the kernel points. In this case, the input and output feature map " + }, + { + "bbox": [ + 46, + 483, + 289, + 714 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 46, + 483, + 289, + 714 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 483, + 289, + 714 + ], + "type": "inline_equation", + "content": "[\\kappa * f]" + }, + { + "bbox": [ + 46, + 483, + 289, + 714 + ], + "type": "text", + "content": " are defined on " + }, + { + "bbox": [ + 46, + 483, + 289, + 714 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^3" + }, + { + "bbox": [ + 46, + 483, + 289, + 714 + ], + "type": "text", + "content": ", while the kernel " + }, + { + "bbox": [ + 46, + 483, + 289, + 714 + ], + "type": "inline_equation", + "content": "\\kappa" + }, + { + "bbox": [ + 46, + 483, + 289, + 714 + ], + "type": "text", + "content": " is defined on " + }, + { + "bbox": [ + 46, + 483, + 289, + 714 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^{3'}" + }, + { + "bbox": [ + 46, + 483, + 289, + 714 + ], + "type": "text", + "content": ", i.e., coordinates of the set of kernel points. The gathered feature " + }, + { + "bbox": [ + 46, + 483, + 289, + 714 + ], + "type": "inline_equation", + "content": "\\hat{f}" + }, + { + "bbox": [ + 46, + 483, + 289, + 714 + ], + "type": "text", + "content": " when calculating the convolution at " + }, + { + "bbox": [ + 46, + 483, + 289, + 714 + ], + "type": "inline_equation", + "content": "x \\in \\mathbb{R}^3" + }, + { + "bbox": [ + 46, + 483, + 289, + 714 + ], + "type": "text", + "content": " is defined at " + }, + { + "bbox": [ + 46, + 483, + 289, + 714 + ], + "type": "inline_equation", + "content": "x + \\mathbb{R}^{3'}" + }, + { + "bbox": [ + 46, + 483, + 289, + 714 + ], + "type": "text", + "content": ". Notice that we do not consider the deformable mode of KPCov in this paper." + } + ] + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 306, + 72, + 548, + 339 + ], + "blocks": [ + { + "bbox": [ + 306, + 72, + 548, + 339 + ], + "lines": [ + { + "bbox": [ + 306, + 72, + 548, + 339 + ], + "spans": [ + { + "bbox": [ + 306, + 72, + 548, + 339 + ], + "type": "image", + "image_path": "01b7509596275b2118a6737d5ac6c05c565162b852350870d5fa669c4f0c6a17.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 344, + 547, + 412 + ], + "lines": [ + { + "bbox": [ + 305, + 344, + 547, + 412 + ], + "spans": [ + { + "bbox": [ + 305, + 344, + 547, + 412 + ], + "type": "text", + "content": "Figure 3. Illustration of different versions of KPConv. (a) original KPConv (see Sec. 3.2.1). (b) KPConv on finite group or quotient space without the symmetric kernel (see Sec. 3.2.2). (c) KPConv on group or quotient space with the symmetric kernel (see Sec. 3.2.3). (b,c) compared with (a): the convolution kernel is larger because it is defined on a higher dimension. (c) compared with (b): the feature gathering is more efficient because the kernel points are symmetric to the rotations in the rotation group." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 433, + 512, + 445 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 433, + 512, + 445 + ], + "spans": [ + { + "bbox": [ + 306, + 433, + 512, + 445 + ], + "type": "text", + "content": "3.2.2 KPCov on group and on quotient space" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 451, + 545, + 476 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 451, + 545, + 476 + ], + "spans": [ + { + "bbox": [ + 305, + 451, + 545, + 476 + ], + "type": "text", + "content": "To extend KPConv to a group convolution [6] with finite group " + }, + { + "bbox": [ + 305, + 451, + 545, + 476 + ], + "type": "inline_equation", + "content": "G'" + }, + { + "bbox": [ + 305, + 451, + 545, + 476 + ], + "type": "text", + "content": ", we modify Eq. (2) to" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 356, + 484, + 545, + 512 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 356, + 484, + 545, + 512 + ], + "spans": [ + { + "bbox": [ + 356, + 484, + 545, + 512 + ], + "type": "interline_equation", + "content": "[ \\kappa * f ] (g) = \\sum_ {g _ {t} \\in G ^ {\\prime}} \\kappa (g _ {t}) \\hat {f} (g \\cdot g _ {t}), \\tag {3}", + "image_path": "682c2e1f1d9dab42876ba89cfe22b66ce66225c83158a8f5450fd5ed2eeaa0db.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 520, + 545, + 688 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 520, + 545, + 688 + ], + "spans": [ + { + "bbox": [ + 304, + 520, + 545, + 688 + ], + "type": "text", + "content": "where in our case, " + }, + { + "bbox": [ + 304, + 520, + 545, + 688 + ], + "type": "inline_equation", + "content": "G' = \\mathrm{SE}(3)' = \\mathrm{SO}(3)' \\times \\mathbb{R}^{3'}" + }, + { + "bbox": [ + 304, + 520, + 545, + 688 + ], + "type": "text", + "content": " is where " + }, + { + "bbox": [ + 304, + 520, + 545, + 688 + ], + "type": "inline_equation", + "content": "\\kappa" + }, + { + "bbox": [ + 304, + 520, + 545, + 688 + ], + "type": "text", + "content": " is defined, " + }, + { + "bbox": [ + 304, + 520, + 545, + 688 + ], + "type": "inline_equation", + "content": "g \\in G^{\\dagger} = \\mathrm{SO}(3)' \\times \\mathbb{R}^{3}" + }, + { + "bbox": [ + 304, + 520, + 545, + 688 + ], + "type": "text", + "content": " is where the input and output feature map is defined. " + }, + { + "bbox": [ + 304, + 520, + 545, + 688 + ], + "type": "inline_equation", + "content": "\\hat{f}" + }, + { + "bbox": [ + 304, + 520, + 545, + 688 + ], + "type": "text", + "content": " is defined on " + }, + { + "bbox": [ + 304, + 520, + 545, + 688 + ], + "type": "inline_equation", + "content": "g \\cdot G'" + }, + { + "bbox": [ + 304, + 520, + 545, + 688 + ], + "type": "text", + "content": " when calculating the convolution at " + }, + { + "bbox": [ + 304, + 520, + 545, + 688 + ], + "type": "inline_equation", + "content": "g" + }, + { + "bbox": [ + 304, + 520, + 545, + 688 + ], + "type": "text", + "content": ". Denote an element " + }, + { + "bbox": [ + 304, + 520, + 545, + 688 + ], + "type": "inline_equation", + "content": "g \\in \\mathrm{SE}(3)" + }, + { + "bbox": [ + 304, + 520, + 545, + 688 + ], + "type": "text", + "content": " as " + }, + { + "bbox": [ + 304, + 520, + 545, + 688 + ], + "type": "inline_equation", + "content": "(R,t)" + }, + { + "bbox": [ + 304, + 520, + 545, + 688 + ], + "type": "text", + "content": " where " + }, + { + "bbox": [ + 304, + 520, + 545, + 688 + ], + "type": "inline_equation", + "content": "R \\in \\mathrm{SO}(3)" + }, + { + "bbox": [ + 304, + 520, + 545, + 688 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 520, + 545, + 688 + ], + "type": "inline_equation", + "content": "t \\in \\mathbb{R}^{3}" + }, + { + "bbox": [ + 304, + 520, + 545, + 688 + ], + "type": "text", + "content": ", the binary operation " + }, + { + "bbox": [ + 304, + 520, + 545, + 688 + ], + "type": "inline_equation", + "content": "\\cdot" + }, + { + "bbox": [ + 304, + 520, + 545, + 688 + ], + "type": "text", + "content": " for " + }, + { + "bbox": [ + 304, + 520, + 545, + 688 + ], + "type": "inline_equation", + "content": "\\mathrm{SE}(3)" + }, + { + "bbox": [ + 304, + 520, + 545, + 688 + ], + "type": "text", + "content": " can be specified as " + }, + { + "bbox": [ + 304, + 520, + 545, + 688 + ], + "type": "inline_equation", + "content": "(R_1,t_1) \\cdot (R_2,t_2) = (R_1R_2,t_1 + R_1t_2)" + }, + { + "bbox": [ + 304, + 520, + 545, + 688 + ], + "type": "text", + "content": ", same for the discretized case. EPN [2] follows this form of convolution. However, as discussed in Sec. 3.1.1, the size of group " + }, + { + "bbox": [ + 304, + 520, + 545, + 688 + ], + "type": "inline_equation", + "content": "|\\mathrm{SE}(3)'| = |\\mathrm{SO}(3)'||\\mathbb{R}^{3'}|" + }, + { + "bbox": [ + 304, + 520, + 545, + 688 + ], + "type": "text", + "content": ", making it expensive to store the feature map and compute the convolution. To alleviate this issue, EPN has to conduct convolutions in " + }, + { + "bbox": [ + 304, + 520, + 545, + 688 + ], + "type": "inline_equation", + "content": "\\mathrm{SO}(3)'" + }, + { + "bbox": [ + 304, + 520, + 545, + 688 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 520, + 545, + 688 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^{3'}" + }, + { + "bbox": [ + 304, + 520, + 545, + 688 + ], + "type": "text", + "content": " separately (i.e., separable convolutions [2, 3]), so that the computational cost is reduced." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "type": "text", + "content": "We use quotient feature maps to address this issue. To conduct convolutions on the quotient space " + }, + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "type": "inline_equation", + "content": "X =" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 296, + 732, + 315, + 742 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 732, + 315, + 742 + ], + "spans": [ + { + "bbox": [ + 296, + 732, + 315, + 742 + ], + "type": "text", + "content": "1226" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 67, + 72, + 182, + 178 + ], + "blocks": [ + { + "bbox": [ + 67, + 72, + 182, + 178 + ], + "lines": [ + { + "bbox": [ + 67, + 72, + 182, + 178 + ], + "spans": [ + { + "bbox": [ + 67, + 72, + 182, + 178 + ], + "type": "image", + "image_path": "2a767a62d778d7279485b05fbba2413f9f322ca4a10cc66f1fb5ec41eaf4eb3b.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 47, + 183, + 287, + 205 + ], + "lines": [ + { + "bbox": [ + 47, + 183, + 287, + 205 + ], + "spans": [ + { + "bbox": [ + 47, + 183, + 287, + 205 + ], + "type": "text", + "content": "Figure 4. Visualization of the symmetric kernel " + }, + { + "bbox": [ + 47, + 183, + 287, + 205 + ], + "type": "inline_equation", + "content": "\\kappa" + }, + { + "bbox": [ + 47, + 183, + 287, + 205 + ], + "type": "text", + "content": " used in our work, where " + }, + { + "bbox": [ + 47, + 183, + 287, + 205 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^{3\\prime} = \\{rS^{2\\prime}\\cup 0\\mid r > 0\\}" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 190, + 72, + 269, + 178 + ], + "blocks": [ + { + "bbox": [ + 190, + 72, + 269, + 178 + ], + "lines": [ + { + "bbox": [ + 190, + 72, + 269, + 178 + ], + "spans": [ + { + "bbox": [ + 190, + 72, + 269, + 178 + ], + "type": "image", + "image_path": "520715ce54709ff811f5b358831db09955d19d3128202c7e3ac38b44b69fa6f4.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 176, + 545, + 196 + ], + "lines": [ + { + "bbox": [ + 305, + 176, + 545, + 196 + ], + "spans": [ + { + "bbox": [ + 305, + 176, + 545, + 196 + ], + "type": "text", + "content": "Figure 5. Illustration of all five types of Platonic solids and their corresponding finite rotation groups." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 222, + 288, + 272 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 222, + 288, + 272 + ], + "spans": [ + { + "bbox": [ + 46, + 222, + 288, + 272 + ], + "type": "inline_equation", + "content": "\\mathrm{SE}(3) / \\mathrm{SO}(2) = S^2 \\times \\mathbb{R}^3" + }, + { + "bbox": [ + 46, + 222, + 288, + 272 + ], + "type": "text", + "content": ", we cannot directly use Eq. (3), because the " + }, + { + "bbox": [ + 46, + 222, + 288, + 272 + ], + "type": "inline_equation", + "content": "\\cdot" + }, + { + "bbox": [ + 46, + 222, + 288, + 272 + ], + "type": "text", + "content": " operation is not defined between two elements in " + }, + { + "bbox": [ + 46, + 222, + 288, + 272 + ], + "type": "inline_equation", + "content": "X" + }, + { + "bbox": [ + 46, + 222, + 288, + 272 + ], + "type": "text", + "content": " since " + }, + { + "bbox": [ + 46, + 222, + 288, + 272 + ], + "type": "inline_equation", + "content": "X" + }, + { + "bbox": [ + 46, + 222, + 288, + 272 + ], + "type": "text", + "content": " is not a group. It is pointed out in [7, 8] that we can write convolutions on the quotient space as" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 89, + 278, + 287, + 306 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 89, + 278, + 287, + 306 + ], + "spans": [ + { + "bbox": [ + 89, + 278, + 287, + 306 + ], + "type": "interline_equation", + "content": "[ \\kappa * f ] (x) = \\sum_ {x _ {t} \\in X ^ {\\prime}} \\kappa (x _ {t}) \\hat {f} (s (x) \\cdot x _ {t}), \\tag {4}", + "image_path": "4c1d11e1c5cf85ff18d4f1842dc604e6e45013969c98195403fa393dbdc21ba7.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "spans": [ + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "inline_equation", + "content": "X^{\\prime} = S^{2^{\\prime}}\\times \\mathbb{R}^{3^{\\prime}}" + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "text", + "content": " is the domain of " + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "inline_equation", + "content": "\\kappa" + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "inline_equation", + "content": "X^{\\dagger} = S^{2^{\\prime}}\\times \\mathbb{R}^{3}" + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "text", + "content": " is the domain of " + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "inline_equation", + "content": "[\\kappa *f]" + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "inline_equation", + "content": "\\hat{f}" + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "text", + "content": " is defined on " + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "inline_equation", + "content": "s(x)\\cdot X^{\\prime}" + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "inline_equation", + "content": "s(x)" + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "text", + "content": " is called the section map, " + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "inline_equation", + "content": "s:X^{\\prime}\\to G^{\\prime}" + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "text", + "content": " (or " + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "inline_equation", + "content": "X\\rightarrow G" + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "text", + "content": " in the continuous case), mapping " + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "inline_equation", + "content": "x\\in X^{\\prime}" + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "text", + "content": " to an element of " + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "inline_equation", + "content": "G^{\\prime}" + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "text", + "content": " in the corresponding coset. With the section map, the " + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "inline_equation", + "content": "\\cdot" + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "text", + "content": " operation denotes the action of the group " + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "inline_equation", + "content": "G" + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "text", + "content": " on quotient space " + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "inline_equation", + "content": "X" + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "text", + "content": ", i.e., " + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "inline_equation", + "content": "\\cdot :G\\times X\\to X" + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "text", + "content": ". Denote an element in " + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "inline_equation", + "content": "S^2\\times \\mathbb{R}^3" + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "text", + "content": " as " + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "inline_equation", + "content": "(R\\mathbf{n},t)" + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "inline_equation", + "content": "R\\in \\mathrm{SO}(3)" + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "inline_equation", + "content": "\\mathbf{n}" + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "text", + "content": " is the north pole point on the unit sphere " + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "inline_equation", + "content": "(0,0,1)" + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "text", + "content": ". Then " + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "inline_equation", + "content": "R\\mathbf{n}" + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "text", + "content": " represents arbitrary points on the sphere " + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "inline_equation", + "content": "S^2" + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "text", + "content": ". The action " + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "inline_equation", + "content": "\\cdot" + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "text", + "content": " can then be written as " + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "inline_equation", + "content": "(R_{1},t_{1})\\cdot (R_{2}\\mathbf{n},t_{2}) = (R_{1}R_{2}\\mathbf{n},t_{1} + R_{1}t_{2})" + }, + { + "bbox": [ + 46, + 312, + 289, + 447 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 460, + 162, + 471 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 460, + 162, + 471 + ], + "spans": [ + { + "bbox": [ + 47, + 460, + 162, + 471 + ], + "type": "text", + "content": "3.2.3 Symmetric kernels" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 478, + 287, + 562 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 478, + 287, + 562 + ], + "spans": [ + { + "bbox": [ + 46, + 478, + 287, + 562 + ], + "type": "text", + "content": "Now we introduce the specific form of " + }, + { + "bbox": [ + 46, + 478, + 287, + 562 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^{3'}" + }, + { + "bbox": [ + 46, + 478, + 287, + 562 + ], + "type": "text", + "content": ", i.e., the location of kernel points in KPConv. In our design, " + }, + { + "bbox": [ + 46, + 478, + 287, + 562 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^{3'} = \\{rS^{2'} \\cup 0 \\mid r > 0\\}" + }, + { + "bbox": [ + 46, + 478, + 287, + 562 + ], + "type": "text", + "content": ", i.e., the set of vertices of the Platonic solid with radius " + }, + { + "bbox": [ + 46, + 478, + 287, + 562 + ], + "type": "inline_equation", + "content": "r" + }, + { + "bbox": [ + 46, + 478, + 287, + 562 + ], + "type": "text", + "content": " and the origin point. " + }, + { + "bbox": [ + 46, + 478, + 287, + 562 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^{3'}" + }, + { + "bbox": [ + 46, + 478, + 287, + 562 + ], + "type": "text", + "content": " is very similar to " + }, + { + "bbox": [ + 46, + 478, + 287, + 562 + ], + "type": "inline_equation", + "content": "S^{2'}" + }, + { + "bbox": [ + 46, + 478, + 287, + 562 + ], + "type": "text", + "content": ", because we want to make the kernel symmetric to " + }, + { + "bbox": [ + 46, + 478, + 287, + 562 + ], + "type": "inline_equation", + "content": "\\mathrm{SO}(3)'" + }, + { + "bbox": [ + 46, + 478, + 287, + 562 + ], + "type": "text", + "content": ". More precisely, we desire " + }, + { + "bbox": [ + 46, + 478, + 287, + 562 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^{3'}" + }, + { + "bbox": [ + 46, + 478, + 287, + 562 + ], + "type": "text", + "content": " to be closed under the action of " + }, + { + "bbox": [ + 46, + 478, + 287, + 562 + ], + "type": "inline_equation", + "content": "\\mathrm{SO}(3)'" + }, + { + "bbox": [ + 46, + 478, + 287, + 562 + ], + "type": "text", + "content": ". There are two reasons as follows." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 576, + 287, + 659 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 576, + 287, + 659 + ], + "spans": [ + { + "bbox": [ + 46, + 576, + 287, + 659 + ], + "type": "text", + "content": "Steerability constraint To make the convolution on quotient space equivariant, defining a valid form of convolution as Eq. (4) is not the whole story. The kernel values must satisfy a condition called the steerability constraint, which is required for all steerable CNNs. More background knowledge can be found in [8]. In our case, the steerability constraint is" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 77, + 668, + 287, + 682 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 77, + 668, + 287, + 682 + ], + "spans": [ + { + "bbox": [ + 77, + 668, + 287, + 682 + ], + "type": "interline_equation", + "content": "\\kappa (x) = \\kappa \\left(R _ {z} \\cdot x\\right), \\forall x \\in X ^ {\\prime}, \\forall R _ {z} \\in \\mathrm {S O} (2) ^ {\\prime}, \\tag {5}", + "image_path": "f2b9419e25a9497ff3c83fc6621b54ea746670757049c70aa7df367f5d4fde64.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 689, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 288, + 714 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 689, + 288, + 714 + ], + "type": "inline_equation", + "content": "R_{z}" + }, + { + "bbox": [ + 47, + 689, + 288, + 714 + ], + "type": "text", + "content": " is a " + }, + { + "bbox": [ + 47, + 689, + 288, + 714 + ], + "type": "inline_equation", + "content": "z" + }, + { + "bbox": [ + 47, + 689, + 288, + 714 + ], + "type": "text", + "content": "-axis rotation. The derivation of Eq. (5) from the general form of steerability constraints can be found in" + } + ] + } + ], + "index": 10 + }, + { + "type": "table", + "bbox": [ + 308, + 70, + 547, + 174 + ], + "blocks": [ + { + "bbox": [ + 308, + 70, + 547, + 174 + ], + "lines": [ + { + "bbox": [ + 308, + 70, + 547, + 174 + ], + "spans": [ + { + "bbox": [ + 308, + 70, + 547, + 174 + ], + "type": "table", + "html": "
Rotation groupsTetrahedral TOctahedral OIcosahedral I
Platonic solidsTetrahedronCubeOctahedronDodecahedronIcosahedron
Size|SO(3)'| = 12 |S2'| = 4 |SO(2)'| = 3|SO(3)'| = 24 |S2'| = 8 |SO(2)'| = 3|SO(3)'| = 24 |S2'| = 6 |SO(2)'| = 4|SO(3)'| = 60 |S2'| = 20 |SO(2)'| = 3|SO(3)'| = 60 |S2'| = 12 |SO(2)'| = 5
", + "image_path": "884066ac6990af7ec284f3f120286b5a422ade6392e0b3df6e260aae0e791c87.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "table_body" + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 215, + 545, + 264 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 215, + 545, + 264 + ], + "spans": [ + { + "bbox": [ + 304, + 215, + 545, + 264 + ], + "type": "text", + "content": "the appendix. Here the " + }, + { + "bbox": [ + 304, + 215, + 545, + 264 + ], + "type": "inline_equation", + "content": "\\cdot" + }, + { + "bbox": [ + 304, + 215, + 545, + 264 + ], + "type": "text", + "content": " operation inherits from the action of " + }, + { + "bbox": [ + 304, + 215, + 545, + 264 + ], + "type": "inline_equation", + "content": "G'" + }, + { + "bbox": [ + 304, + 215, + 545, + 264 + ], + "type": "text", + "content": " on " + }, + { + "bbox": [ + 304, + 215, + 545, + 264 + ], + "type": "inline_equation", + "content": "X'" + }, + { + "bbox": [ + 304, + 215, + 545, + 264 + ], + "type": "text", + "content": " since " + }, + { + "bbox": [ + 304, + 215, + 545, + 264 + ], + "type": "inline_equation", + "content": "\\mathrm{SO}(2)' \\subset \\mathrm{SO}(3)' \\subset G'" + }, + { + "bbox": [ + 304, + 215, + 545, + 264 + ], + "type": "text", + "content": ". Specifically, we have " + }, + { + "bbox": [ + 304, + 215, + 545, + 264 + ], + "type": "inline_equation", + "content": "R_z \\cdot (R\\mathbf{n}, t) = (R_z, 0) \\cdot (R\\mathbf{n}, t) = (R_z R\\mathbf{n}, R_z t)" + }, + { + "bbox": [ + 304, + 215, + 545, + 264 + ], + "type": "text", + "content": ". Replace " + }, + { + "bbox": [ + 304, + 215, + 545, + 264 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 304, + 215, + 545, + 264 + ], + "type": "text", + "content": " with " + }, + { + "bbox": [ + 304, + 215, + 545, + 264 + ], + "type": "inline_equation", + "content": "(R\\mathbf{n}, t)" + }, + { + "bbox": [ + 304, + 215, + 545, + 264 + ], + "type": "text", + "content": " in Eq. (5), and we have" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 367, + 270, + 545, + 283 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 367, + 270, + 545, + 283 + ], + "spans": [ + { + "bbox": [ + 367, + 270, + 545, + 283 + ], + "type": "interline_equation", + "content": "\\kappa (R \\mathbf {n}, t) = \\kappa \\left(R _ {z} R \\mathbf {n}, R _ {z} t\\right), \\tag {6}", + "image_path": "da4186df735b7eb003e7188e1dff645c0449827c4a3f2a1b92ab8ab461863821.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 289, + 545, + 360 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 289, + 545, + 360 + ], + "spans": [ + { + "bbox": [ + 304, + 289, + 545, + 360 + ], + "type": "inline_equation", + "content": "\\forall R\\mathbf{n}\\in S^{2^{\\prime}},\\forall t\\in \\mathbb{R}^{3^{\\prime}},\\forall R_{z}\\in \\mathrm{SO}(2)^{\\prime}." + }, + { + "bbox": [ + 304, + 289, + 545, + 360 + ], + "type": "text", + "content": " Notice that it implies that we need " + }, + { + "bbox": [ + 304, + 289, + 545, + 360 + ], + "type": "inline_equation", + "content": "R_{z}t\\in \\mathbb{R}^{3^{\\prime}},\\forall t\\in \\mathbb{R}^{3^{\\prime}},\\forall R_{z}\\in \\mathrm{SO}(2^{\\prime})" + }, + { + "bbox": [ + 304, + 289, + 545, + 360 + ], + "type": "text", + "content": " so that " + }, + { + "bbox": [ + 304, + 289, + 545, + 360 + ], + "type": "inline_equation", + "content": "\\kappa" + }, + { + "bbox": [ + 304, + 289, + 545, + 360 + ], + "type": "text", + "content": " is defined on the right hand side of Eq. (6). In other words, the kernel points " + }, + { + "bbox": [ + 304, + 289, + 545, + 360 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^{3^{\\prime}}" + }, + { + "bbox": [ + 304, + 289, + 545, + 360 + ], + "type": "text", + "content": " need to be closed under " + }, + { + "bbox": [ + 304, + 289, + 545, + 360 + ], + "type": "inline_equation", + "content": "\\mathrm{SO}(2)^{\\prime}" + }, + { + "bbox": [ + 304, + 289, + 545, + 360 + ], + "type": "text", + "content": ". Obviously, having " + }, + { + "bbox": [ + 304, + 289, + 545, + 360 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^{3^{\\prime}}" + }, + { + "bbox": [ + 304, + 289, + 545, + 360 + ], + "type": "text", + "content": " closed under " + }, + { + "bbox": [ + 304, + 289, + 545, + 360 + ], + "type": "inline_equation", + "content": "\\mathrm{SO}(3)^{\\prime}" + }, + { + "bbox": [ + 304, + 289, + 545, + 360 + ], + "type": "text", + "content": " is a sufficient condition for this." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 361, + 545, + 397 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 361, + 545, + 397 + ], + "spans": [ + { + "bbox": [ + 304, + 361, + 545, + 397 + ], + "type": "text", + "content": "For the " + }, + { + "bbox": [ + 304, + 361, + 545, + 397 + ], + "type": "inline_equation", + "content": "S^{2'}" + }, + { + "bbox": [ + 304, + 361, + 545, + 397 + ], + "type": "text", + "content": " dimension, since " + }, + { + "bbox": [ + 304, + 361, + 545, + 397 + ], + "type": "inline_equation", + "content": "S^{2'}" + }, + { + "bbox": [ + 304, + 361, + 545, + 397 + ], + "type": "text", + "content": " is symmetric (closed) to " + }, + { + "bbox": [ + 304, + 361, + 545, + 397 + ], + "type": "inline_equation", + "content": "\\mathrm{SO}(3)'" + }, + { + "bbox": [ + 304, + 361, + 545, + 397 + ], + "type": "text", + "content": " by definition and " + }, + { + "bbox": [ + 304, + 361, + 545, + 397 + ], + "type": "inline_equation", + "content": "\\mathrm{SO}(2)' \\subset \\mathrm{SO}(3)'" + }, + { + "bbox": [ + 304, + 361, + 545, + 397 + ], + "type": "text", + "content": ", we always have " + }, + { + "bbox": [ + 304, + 361, + 545, + 397 + ], + "type": "inline_equation", + "content": "R_z R\\mathbf{n} \\in S^{2'}" + }, + { + "bbox": [ + 304, + 361, + 545, + 397 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 361, + 545, + 397 + ], + "type": "inline_equation", + "content": "\\kappa" + }, + { + "bbox": [ + 304, + 361, + 545, + 397 + ], + "type": "text", + "content": " is always defined." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 411, + 546, + 532 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 411, + 546, + 532 + ], + "spans": [ + { + "bbox": [ + 304, + 411, + 546, + 532 + ], + "type": "text", + "content": "Efficient feature gathering Another important reason for the design choice of " + }, + { + "bbox": [ + 304, + 411, + 546, + 532 + ], + "type": "inline_equation", + "content": "\\mathrm{SO}(3)^{\\prime}" + }, + { + "bbox": [ + 304, + 411, + 546, + 532 + ], + "type": "text", + "content": "-symmetric kernels is that it enables more efficient feature gathering. Consider a spatial location " + }, + { + "bbox": [ + 304, + 411, + 546, + 532 + ], + "type": "inline_equation", + "content": "t_0\\in \\mathbb{R}^3" + }, + { + "bbox": [ + 304, + 411, + 546, + 532 + ], + "type": "text", + "content": ", the convolution feature output at this point is a stack of " + }, + { + "bbox": [ + 304, + 411, + 546, + 532 + ], + "type": "inline_equation", + "content": "[[\\kappa *f](x_i)]_i" + }, + { + "bbox": [ + 304, + 411, + 546, + 532 + ], + "type": "text", + "content": " with " + }, + { + "bbox": [ + 304, + 411, + 546, + 532 + ], + "type": "inline_equation", + "content": "x_{i}\\in (S^{2^{\\prime}},t_{0})\\subset X^{\\dagger}" + }, + { + "bbox": [ + 304, + 411, + 546, + 532 + ], + "type": "text", + "content": ". As shown in Eq. (4), it involves feature gathering for " + }, + { + "bbox": [ + 304, + 411, + 546, + 532 + ], + "type": "inline_equation", + "content": "\\hat{f}" + }, + { + "bbox": [ + 304, + 411, + 546, + 532 + ], + "type": "text", + "content": " at " + }, + { + "bbox": [ + 304, + 411, + 546, + 532 + ], + "type": "inline_equation", + "content": "s(x_{i})\\cdot x_{jk}" + }, + { + "bbox": [ + 304, + 411, + 546, + 532 + ], + "type": "text", + "content": " for every " + }, + { + "bbox": [ + 304, + 411, + 546, + 532 + ], + "type": "inline_equation", + "content": "x_{jk}\\in X' = S^{2'}\\times \\mathbb{R}^{3'}" + }, + { + "bbox": [ + 304, + 411, + 546, + 532 + ], + "type": "text", + "content": ". Denote an instance of " + }, + { + "bbox": [ + 304, + 411, + 546, + 532 + ], + "type": "inline_equation", + "content": "s(x_{i}) = (R_{i},t_{0}),x_{jk} = (R_{j}\\mathbf{n},t_{k})" + }, + { + "bbox": [ + 304, + 411, + 546, + 532 + ], + "type": "text", + "content": ", then " + }, + { + "bbox": [ + 304, + 411, + 546, + 532 + ], + "type": "inline_equation", + "content": "s(x_{i})\\cdot x_{jk} = (R_{i}R_{j}\\mathbf{n},t_{0} + R_{i}t_{k})" + }, + { + "bbox": [ + 304, + 411, + 546, + 532 + ], + "type": "text", + "content": ". If " + }, + { + "bbox": [ + 304, + 411, + 546, + 532 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^{3^{\\prime}}" + }, + { + "bbox": [ + 304, + 411, + 546, + 532 + ], + "type": "text", + "content": " is closed under " + }, + { + "bbox": [ + 304, + 411, + 546, + 532 + ], + "type": "inline_equation", + "content": "\\mathrm{SO}(3)^{\\prime}" + }, + { + "bbox": [ + 304, + 411, + 546, + 532 + ], + "type": "text", + "content": ", then we have" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 344, + 537, + 545, + 552 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 344, + 537, + 545, + 552 + ], + "spans": [ + { + "bbox": [ + 344, + 537, + 545, + 552 + ], + "type": "interline_equation", + "content": "\\left\\{R _ {i} t _ {k} \\mid t _ {k} \\in \\mathbb {R} ^ {3 ^ {\\prime}} \\right\\} = \\mathbb {R} ^ {3 ^ {\\prime}}, \\forall R _ {i} \\in \\mathrm {S O} (3) ^ {\\prime}, \\tag {7}", + "image_path": "d168335f64a83f75e2208da201d9c18d3501b9d5b1668a483b483c4b93e22631.jpg" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 557, + 547, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 557, + 547, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 557, + 547, + 714 + ], + "type": "text", + "content": "which implies that the feature gathering for all " + }, + { + "bbox": [ + 304, + 557, + 547, + 714 + ], + "type": "inline_equation", + "content": "S^{2'}" + }, + { + "bbox": [ + 304, + 557, + 547, + 714 + ], + "type": "text", + "content": " channels can be done once at the same set of spatial positions specified by " + }, + { + "bbox": [ + 304, + 557, + 547, + 714 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^{3'}" + }, + { + "bbox": [ + 304, + 557, + 547, + 714 + ], + "type": "text", + "content": ". An illustration is shown in Fig. 3. Without the symmetric kernel, the KPConv on group or quotient space looks like Fig. 3 (b), where the kernel is rotated for each " + }, + { + "bbox": [ + 304, + 557, + 547, + 714 + ], + "type": "inline_equation", + "content": "\\mathrm{SO}(3)'" + }, + { + "bbox": [ + 304, + 557, + 547, + 714 + ], + "type": "text", + "content": " (for group KPConv) or " + }, + { + "bbox": [ + 304, + 557, + 547, + 714 + ], + "type": "inline_equation", + "content": "S^{2'}" + }, + { + "bbox": [ + 304, + 557, + 547, + 714 + ], + "type": "text", + "content": " (for quotient KPConv) channel separately to gather input features. However, with symmetric kernels, as shown in Fig. 3 (c), the rotations keep the position of kernel points unchanged up to a permutation so that the feature-gathering step is simplified. Specifically, the number of spatial positions needed for feature gathering without symmetric kernels is " + }, + { + "bbox": [ + 304, + 557, + 547, + 714 + ], + "type": "inline_equation", + "content": "|SO(3)'| \\mathbb{R}^{3'}|" + }, + { + "bbox": [ + 304, + 557, + 547, + 714 + ], + "type": "text", + "content": " for group KPConv or " + }, + { + "bbox": [ + 304, + 557, + 547, + 714 + ], + "type": "inline_equation", + "content": "|S^{2'}| \\mathbb{R}^{3'}|" + }, + { + "bbox": [ + 304, + 557, + 547, + 714 + ], + "type": "text", + "content": " for quotient KPConv, while the number" + } + ] + } + ], + "index": 19 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 296, + 733, + 315, + 742 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 733, + 315, + 742 + ], + "spans": [ + { + "bbox": [ + 296, + 733, + 315, + 742 + ], + "type": "text", + "content": "1227" + } + ] + } + ], + "index": 20 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 49, + 95, + 542, + 164 + ], + "blocks": [ + { + "bbox": [ + 47, + 75, + 547, + 95 + ], + "lines": [ + { + "bbox": [ + 47, + 75, + 547, + 95 + ], + "spans": [ + { + "bbox": [ + 47, + 75, + 547, + 95 + ], + "type": "text", + "content": "Table 1. Efficiency comparison in terms of GPU memory consumption and the computation speed between EPN [2] and our method on three tasks. Two numbers are reported for training/inference respectively. " + }, + { + "bbox": [ + 47, + 75, + 547, + 95 + ], + "type": "inline_equation", + "content": "\\downarrow" + }, + { + "bbox": [ + 47, + 75, + 547, + 95 + ], + "type": "text", + "content": " means lower is better. " + }, + { + "bbox": [ + 47, + 75, + 547, + 95 + ], + "type": "inline_equation", + "content": "\\uparrow" + }, + { + "bbox": [ + 47, + 75, + 547, + 95 + ], + "type": "text", + "content": " means higher is better. The best is shown in bold font." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 49, + 95, + 542, + 164 + ], + "lines": [ + { + "bbox": [ + 49, + 95, + 542, + 164 + ], + "spans": [ + { + "bbox": [ + 49, + 95, + 542, + 164 + ], + "type": "table", + "html": "
TasksModelNet40 PoseModelNet40 Classification3DMatch Keypoint Matching
MethodsMemory (GB) ↓Speed (fps) ↑Memory (GB) ↓Speed (fps) ↑Memory (GB) ↓Speed (fps) ↑
EPN [2]22.2 / 16.91.1 / 1.613.4 / 12.71.9 / 1.537.4 / 8.50.6 / 3.1
Ours (w/o symmetric kernels)4.8 / 3.75.1 / 10.14.1 / 3.27.8 / 7.87.5 / 2.82.6 / 16.7
Ours (w/ symmetric kernels)4.3 / 2.86.7 / 11.13.9 / 2.79.1 / 10.36.5 / 2.43.7 / 23.6
", + "image_path": "604185e05401f76d0c39b1783d106182fa3a0b04bc4899b9e4f3768ee8dbd18b.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 182, + 288, + 220 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 182, + 288, + 220 + ], + "spans": [ + { + "bbox": [ + 46, + 182, + 288, + 220 + ], + "type": "text", + "content": "is " + }, + { + "bbox": [ + 46, + 182, + 288, + 220 + ], + "type": "inline_equation", + "content": "|\\mathbb{R}^{3^{\\prime}}|" + }, + { + "bbox": [ + 46, + 182, + 288, + 220 + ], + "type": "text", + "content": " with symmetric kernels. The convolution kernels in Fig. 3 is an abstract illustration, while the actual symmetric kernel in our work is visualized in Fig. 4." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 236, + 272, + 249 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 236, + 272, + 249 + ], + "spans": [ + { + "bbox": [ + 47, + 236, + 272, + 249 + ], + "type": "text", + "content": "3.2.4 Choices of the discretization of " + }, + { + "bbox": [ + 47, + 236, + 272, + 249 + ], + "type": "inline_equation", + "content": "SO(3)" + }, + { + "bbox": [ + 47, + 236, + 272, + 249 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 236, + 272, + 249 + ], + "type": "inline_equation", + "content": "S^2" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 255, + 286, + 352 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 255, + 286, + 352 + ], + "spans": [ + { + "bbox": [ + 46, + 255, + 286, + 352 + ], + "type": "text", + "content": "In Sec. 3.1.1, we mentioned that the discretization of " + }, + { + "bbox": [ + 46, + 255, + 286, + 352 + ], + "type": "inline_equation", + "content": "\\mathrm{SO}(3)" + }, + { + "bbox": [ + 46, + 255, + 286, + 352 + ], + "type": "text", + "content": " is the rotation group that respects the symmetry of a Platonic solid. There are five types of Platonic solids, corresponding to 3 finite rotation groups, as shown in Fig. 5. Choosing " + }, + { + "bbox": [ + 46, + 255, + 286, + 352 + ], + "type": "inline_equation", + "content": "\\mathrm{SO}(3)'" + }, + { + "bbox": [ + 46, + 255, + 286, + 352 + ], + "type": "text", + "content": " to be any of them is valid, representing a discretization of " + }, + { + "bbox": [ + 46, + 255, + 286, + 352 + ], + "type": "inline_equation", + "content": "\\mathrm{SO}(3)" + }, + { + "bbox": [ + 46, + 255, + 286, + 352 + ], + "type": "text", + "content": " to different resolutions. The different Platonic solids with the same rotation group " + }, + { + "bbox": [ + 46, + 255, + 286, + 352 + ], + "type": "inline_equation", + "content": "\\mathrm{SO}(3)'" + }, + { + "bbox": [ + 46, + 255, + 286, + 352 + ], + "type": "text", + "content": " represents different discretizations of " + }, + { + "bbox": [ + 46, + 255, + 286, + 352 + ], + "type": "inline_equation", + "content": "S^{2'}" + }, + { + "bbox": [ + 46, + 255, + 286, + 352 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 255, + 286, + 352 + ], + "type": "inline_equation", + "content": "\\mathrm{SO}(2)'" + }, + { + "bbox": [ + 46, + 255, + 286, + 352 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 353, + 286, + 449 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 353, + 286, + 449 + ], + "spans": [ + { + "bbox": [ + 46, + 353, + 286, + 449 + ], + "type": "text", + "content": "If we use a small " + }, + { + "bbox": [ + 46, + 353, + 286, + 449 + ], + "type": "inline_equation", + "content": "\\mathrm{SO}(3)'" + }, + { + "bbox": [ + 46, + 353, + 286, + 449 + ], + "type": "text", + "content": " (for example, " + }, + { + "bbox": [ + 46, + 353, + 286, + 449 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 46, + 353, + 286, + 449 + ], + "type": "text", + "content": "), the strategy of using " + }, + { + "bbox": [ + 46, + 353, + 286, + 449 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^{3'} = \\{rS^{2'} \\cup 0 \\mid r > 0\\}" + }, + { + "bbox": [ + 46, + 353, + 286, + 449 + ], + "type": "text", + "content": " could be problematic because the number of kernel points could be too few to learn representative features. In this case, we are free to design the kernel points differently, as long as they are closed under " + }, + { + "bbox": [ + 46, + 353, + 286, + 449 + ], + "type": "inline_equation", + "content": "\\mathrm{SO}(3)'" + }, + { + "bbox": [ + 46, + 353, + 286, + 449 + ], + "type": "text", + "content": ". For example, one may add kernel points at the center of all edges and/or faces. One may even use a combination of several polyhedrons with different radii " + }, + { + "bbox": [ + 46, + 353, + 286, + 449 + ], + "type": "inline_equation", + "content": "r" + }, + { + "bbox": [ + 46, + 353, + 286, + 449 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 449, + 286, + 533 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 449, + 286, + 533 + ], + "spans": [ + { + "bbox": [ + 46, + 449, + 286, + 533 + ], + "type": "text", + "content": "In this paper, we only choose the icosahedron as the Platonic solid to conduct experiments for three reasons. First, it has the finest discretization of SO(3). Second, it has a smaller size of " + }, + { + "bbox": [ + 46, + 449, + 286, + 533 + ], + "type": "inline_equation", + "content": "S^{2'}" + }, + { + "bbox": [ + 46, + 449, + 286, + 533 + ], + "type": "text", + "content": " compared with the dodecahedron, maximizing the benefit of working with quotient features. Third, it is consistent with existing methods [1,2], enabling direct comparison with the baselines." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 549, + 204, + 562 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 549, + 204, + 562 + ], + "spans": [ + { + "bbox": [ + 47, + 549, + 204, + 562 + ], + "type": "text", + "content": "3.2.5 Other aspects of the network" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 569, + 286, + 688 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 569, + 286, + 688 + ], + "spans": [ + { + "bbox": [ + 46, + 569, + 286, + 688 + ], + "type": "text", + "content": "We use element-wise scalar nonlinearity (ReLU and leaky ReLu) in the network. The spatial pooling is done by subsampling the input points and aggregating the features of neighboring input points to the subsampled points. Batch normalization is applied to normalize over the batch, " + }, + { + "bbox": [ + 46, + 569, + 286, + 688 + ], + "type": "inline_equation", + "content": "S^{2'}" + }, + { + "bbox": [ + 46, + 569, + 286, + 688 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 46, + 569, + 286, + 688 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^3" + }, + { + "bbox": [ + 46, + 569, + 286, + 688 + ], + "type": "text", + "content": " dimensions. All these choices follow the common practice of conventional CNNs (KPCov [35]) and group convolutions (EPN [2]). We also adopted the group attentive pooling in EPN to pool over the " + }, + { + "bbox": [ + 46, + 569, + 286, + 688 + ], + "type": "inline_equation", + "content": "S^{2'}" + }, + { + "bbox": [ + 46, + 569, + 286, + 688 + ], + "type": "text", + "content": " dimension and generate " + }, + { + "bbox": [ + 46, + 569, + 286, + 688 + ], + "type": "inline_equation", + "content": "\\mathrm{SO}(3)'" + }, + { + "bbox": [ + 46, + 569, + 286, + 688 + ], + "type": "text", + "content": "-invariant features." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 689, + 286, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 286, + 714 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 286, + 714 + ], + "type": "text", + "content": "Depending on the specific task in the experiment, the prediction head has a slightly different design, composing" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 183, + 545, + 255 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 183, + 545, + 255 + ], + "spans": [ + { + "bbox": [ + 304, + 183, + 545, + 255 + ], + "type": "text", + "content": "the last few layers of the network. The loss functions are inherited from EPN [2], including cross-entropy loss for classifications, L2 loss for residual pose regression, and batch-hard triplet loss for keypoint matching. We refer to the appendix for more details about the prediction heads and the loss functions." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 265, + 446, + 277 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 265, + 446, + 277 + ], + "spans": [ + { + "bbox": [ + 306, + 265, + 446, + 277 + ], + "type": "text", + "content": "3.3. Relation to existing work" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 284, + 545, + 511 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 284, + 545, + 511 + ], + "spans": [ + { + "bbox": [ + 304, + 284, + 545, + 511 + ], + "type": "text", + "content": "In the context of literature on group-equivariant neural networks, our method is under the theoretical framework of equivariant CNNs on homogeneous spaces [8, 24, 46]. Our work is a new form of realization when working with 3D point clouds and adapting the convolution structure of KPCov. We explore a balance of simplicity, efficiency, and expressiveness by finding the proper quotient space and discretization. Our method is an extension of group convolutions, leveraging their clean structure enabled by discretization. Our method can also be viewed as a steerable CNN with homogeneous space " + }, + { + "bbox": [ + 304, + 284, + 545, + 511 + ], + "type": "inline_equation", + "content": "S^2 \\times \\mathbb{R}^3" + }, + { + "bbox": [ + 304, + 284, + 545, + 511 + ], + "type": "text", + "content": " and stabilizer subgroup SO(2) with scalar-type features or with homogeneous space " + }, + { + "bbox": [ + 304, + 284, + 545, + 511 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^3" + }, + { + "bbox": [ + 304, + 284, + 545, + 511 + ], + "type": "text", + "content": " and stabilizer subgroup SO(3) with " + }, + { + "bbox": [ + 304, + 284, + 545, + 511 + ], + "type": "inline_equation", + "content": "S^2" + }, + { + "bbox": [ + 304, + 284, + 545, + 511 + ], + "type": "text", + "content": " features. The proposed work paves the way for efficiency improvement using quotient representation learning on finite groups. We also emphasize the group-variant side of equivariant models with the permutation layer to distinguish rotations, while existing work focuses on the benefit of getting group-invariant features from equivariant models." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 523, + 388, + 537 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 523, + 388, + 537 + ], + "spans": [ + { + "bbox": [ + 306, + 523, + 388, + 537 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 544, + 545, + 616 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 544, + 545, + 616 + ], + "spans": [ + { + "bbox": [ + 304, + 544, + 545, + 616 + ], + "type": "text", + "content": "Our major baseline to compare with is EPN [2], a state-of-the-art group convolution network, as we are similar in several ways. Both are KPConv-style convolutions with SE(3)-equivariance. Both use the icosahedral rotation group " + }, + { + "bbox": [ + 304, + 544, + 545, + 616 + ], + "type": "inline_equation", + "content": "\\mathcal{I}" + }, + { + "bbox": [ + 304, + 544, + 545, + 616 + ], + "type": "text", + "content": " to discretize SO(3). However, EPN has features defined on " + }, + { + "bbox": [ + 304, + 544, + 545, + 616 + ], + "type": "inline_equation", + "content": "\\mathcal{I} \\times \\mathbb{R}^3" + }, + { + "bbox": [ + 304, + 544, + 545, + 616 + ], + "type": "text", + "content": ", compared with " + }, + { + "bbox": [ + 304, + 544, + 545, + 616 + ], + "type": "inline_equation", + "content": "S^{2'} \\times \\mathbb{R}^3" + }, + { + "bbox": [ + 304, + 544, + 545, + 616 + ], + "type": "text", + "content": " in our method." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 616, + 545, + 700 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 616, + 545, + 700 + ], + "spans": [ + { + "bbox": [ + 304, + 616, + 545, + 700 + ], + "type": "text", + "content": "Two datasets, ModelNet40 [44] and 3DMatch [47], are used in the experiments. ModelNet40 is composed of 3D CAD models of 40 categories of objects. 3DMatch is a real-scan dataset of indoor scenes. For the ModelNet40 dataset, we conduct the classification and pose estimation tasks. For the 3DMatch dataset, we conduct the keypoint matching task. These tasks are also studied in EPN [2]." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 317, + 701, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 701, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 317, + 701, + 545, + 713 + ], + "type": "text", + "content": "In Tab. 1, we list the GPU memory consumption and run" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 296, + 733, + 315, + 742 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 733, + 315, + 742 + ], + "spans": [ + { + "bbox": [ + 296, + 733, + 315, + 742 + ], + "type": "text", + "content": "1228" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 49, + 114, + 543, + 254 + ], + "blocks": [ + { + "bbox": [ + 47, + 76, + 545, + 114 + ], + "lines": [ + { + "bbox": [ + 47, + 76, + 545, + 114 + ], + "spans": [ + { + "bbox": [ + 47, + 76, + 545, + 114 + ], + "type": "text", + "content": "Table 2. Experimental result of object classification on ModelNet40. The best is bolded. The best in equivariant models is underlined. Noisy: test using input with random translation, scaling, jittering, and dropout. Clean: test without above processing. SO(3): random rotations. Id: no rotation. ico: random rotations in I. ESCNN works with voxelized data, thus not having Noisy results with point-wise augmentations. FLOPs are counted using fvcore, which does not support DGL used in TFN and SE(3)-T, thus left blank. The efficiency comparison uses the same batch size as in Tab. 1 (see appendix)." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 49, + 114, + 543, + 254 + ], + "lines": [ + { + "bbox": [ + 49, + 114, + 543, + 254 + ], + "spans": [ + { + "bbox": [ + 49, + 114, + 543, + 254 + ], + "type": "table", + "html": "
TypeColumn ##1#2#3#4#5#6#7#8#9#10#11#12#13#14
MetricsModelNet40 classification performance metric: Acc (%) ↑Efficiency metricsFLOPs per training batch (G)Trainable params (M)
Train rotationSO(3)IdMemory (GB)↓ train/testSpeed (fps)↑ train/test
Test rotationSO(3)IdSO(3)Idico
Test conditionNoisyCleanNoisyCleanNoisyCleanNoisyCleanNoisyClean
Non-equivKPCov [35]75.7181.1776.8882.0212.6612.2289.4691.85--0.18/0.2517.24/18.480.741.69
PointNet++ [31]81.3184.8883.0385.7613.4413.7690.6791.55--1.03/0.57.06/7.4310.591.48
DGCNN [38]79.8684.7782.5485.6215.3617.2691.0092.18--1.96/1.6917.90/17.5032.651.81
PT [48]78.5179.6878.8379.6816.5316.7786.9888.10--4.16/5.824.80/5.03220.999.58
CurveNet [45]84.7288.3385.8288.9417.3418.0391.5392.63--1.20/0.335.61/7.544.222.14
PCT [17]86.9189.1087.6489.8316.3317.9591.6992.87--1.18/0.808.54/20.8527.412.87
EquivalentESCNN [1]-82.40-77.73-29.03-88.94--4.71/5.503.79/8.38428.610.46
TFN [36]58.2762.6458.0662.6457.5062.2859.2062.28--15.95/8.71.83/6.08-0.06
SE(3)-T [15]60.3766.2961.1866.2944.6150.5344.8150.53--19.39/9.651.54/5.13-0.11
EPN [2]84.6387.8485.3488.8330.9932.3290.0391.6190.0491.6013.40/12.721.86/1.4958.953.06
Ours (w/ GA pooling [2])85.0487.5185.4987.6341.4644.4389.7390.5090.0090.503.95/2.709.21/10.37170.682.53
Ours (w/ permutation)86.9988.6288.2189.6239.5442.7890.6691.7790.6891.773.95/2.709.09/10.28170.772.65
", + "image_path": "e1a4bd644bc676bdd2e36a2716788b948e1ce5bdbd6f436d45d9985cb48e3e35.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 273, + 287, + 428 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 273, + 287, + 428 + ], + "spans": [ + { + "bbox": [ + 46, + 273, + 287, + 428 + ], + "type": "text", + "content": "ning speed of our method and EPN [2] in the three tasks. The comparisons are under the same input size, number of feature channels, and number of network layers. The separable convolutions on " + }, + { + "bbox": [ + 46, + 273, + 287, + 428 + ], + "type": "inline_equation", + "content": "\\mathrm{SO}(3)" + }, + { + "bbox": [ + 46, + 273, + 287, + 428 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 273, + 287, + 428 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^3" + }, + { + "bbox": [ + 46, + 273, + 287, + 428 + ], + "type": "text", + "content": " in EPN are together considered as one layer. The numbers are not comparable between training and inference because the batch size could be different (see the appendix). The specific configurations in each experiment are introduced later. All experiments are run on a single NVIDIA A40 GPU. Our network with quotient space convolutions is much smaller and runs much faster in all three tasks, indicating the potential value for real applications. We boost efficiency without sacrificing performance, as is shown later." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 430, + 287, + 538 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 430, + 287, + 538 + ], + "spans": [ + { + "bbox": [ + 46, + 430, + 287, + 538 + ], + "type": "text", + "content": "Ablation study: We list two rows of our results in Tab. 1 to show the effect of efficient feature gathering enabled by the symmetric kernels. The results of without symmetric kernels are generated using the same kernel points as with symmetric kernels, but ignoring the fact that they are symmetric to rotations and gathering features at " + }, + { + "bbox": [ + 46, + 430, + 287, + 538 + ], + "type": "inline_equation", + "content": "|S^{2'}| |\\mathbb{R}^{3'}|" + }, + { + "bbox": [ + 46, + 430, + 287, + 538 + ], + "type": "text", + "content": " locations, instead of at " + }, + { + "bbox": [ + 46, + 430, + 287, + 538 + ], + "type": "inline_equation", + "content": "|\\mathbb{R}^{3'}|" + }, + { + "bbox": [ + 46, + 430, + 287, + 538 + ], + "type": "text", + "content": " locations and permuting them. The efficient feature gathering brings further efficiency improvements, especially in terms of computational speed." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 548, + 239, + 562 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 548, + 239, + 562 + ], + "spans": [ + { + "bbox": [ + 47, + 548, + 239, + 562 + ], + "type": "text", + "content": "4.1. Object classification on ModelNet40" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 568, + 287, + 688 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 568, + 287, + 688 + ], + "spans": [ + { + "bbox": [ + 46, + 568, + 287, + 688 + ], + "type": "text", + "content": "For this task, given a point cloud of an object, the network predicts its category. The evaluation metric is classification accuracy (Acc). In this experiment, we show an extensive efficiency comparison with more existing networks, equivariant and non-equivariant. We also examine a wide combination of input conditions in training and testing to show the effect of equivariance and robustness against input imperfections. All models are trained with data augmentation, including random translation, scaling, jittering, and dropout." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 689, + 287, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 712 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 712 + ], + "type": "text", + "content": "Our method has outstanding performance as shown in Tab. 2. In columns #1-4, all methods are trained with rota" + } + ] + } + ], + "index": 6 + }, + { + "type": "table", + "bbox": [ + 308, + 305, + 542, + 358 + ], + "blocks": [ + { + "bbox": [ + 305, + 276, + 545, + 304 + ], + "lines": [ + { + "bbox": [ + 305, + 276, + 545, + 304 + ], + "spans": [ + { + "bbox": [ + 305, + 276, + 545, + 304 + ], + "type": "text", + "content": "Table 3. Pose estimation on ModelNet40. Mean, median, and max angular errors are calculated over the test set. Statistics (average and standard deviation) over 10 test runs are shown to account for the randomness." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 308, + 305, + 542, + 358 + ], + "lines": [ + { + "bbox": [ + 308, + 305, + 542, + 358 + ], + "spans": [ + { + "bbox": [ + 308, + 305, + 542, + 358 + ], + "type": "table", + "html": "
MetricsMean (°) ↓Median (°) ↓Max (°) ↓
StatsAvg μSD σAvg μSD σAvg μSD σ
KPConv [35]13.991.5310.700.81115.1957.84
EPN [2]1.100.201.360.137.062.52
Ours1.200.080.960.056.711.28
", + "image_path": "197f7ddb47f0070e848db7b62fd50e69e16f7fd25fe173acec4875622d140a3b.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "table_body" + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 379, + 545, + 593 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 379, + 545, + 593 + ], + "spans": [ + { + "bbox": [ + 304, + 379, + 545, + 593 + ], + "type": "text", + "content": "tional augmentation. Our method performs the best among listed equivariant models and is on par with PCT [18] among all models. Our method is intended to work with rotational augmentations so that the equivariance gap caused by discretization can be interpolated through training. However, we still experiment with training without rotational augmentation, as shown in columns #5-10. From columns #9-10, we can verify the equivariance to the icosahedral rotation group of our model. Columns #5-6 show the effect of discretization on the continuous SO(3) if no interpolation is trained, in which case the performance lands between non-equivariant models and continuously SO(3)-equivariant models. The efficiency of our method outperforms all equivariant baselines and is similar to nonequivariant models. The FLOPs and number of trainable parameters are also listed for reference. We found that FLOPs do not strictly correlate with running speed, which could be due to different memory access costs and parallelism." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 594, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 594, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 594, + 545, + 713 + ], + "type": "text", + "content": "Ablation study: Since this task requires SE(3)-invariant features, there are two options in our network: either using the group-attentive pooling (GA pooling) introduced in EPN [2] to pool over the " + }, + { + "bbox": [ + 304, + 594, + 545, + 713 + ], + "type": "inline_equation", + "content": "S^{2^{\\prime}}" + }, + { + "bbox": [ + 304, + 594, + 545, + 713 + ], + "type": "text", + "content": " dimensions or using the permutation layer to find the canonical permutation of " + }, + { + "bbox": [ + 304, + 594, + 545, + 713 + ], + "type": "inline_equation", + "content": "S^{2^{\\prime}}" + }, + { + "bbox": [ + 304, + 594, + 545, + 713 + ], + "type": "text", + "content": " dimensions. Either way, the canonical pose of objects in ModelNet40 can be used for supervision. Tab. 2 shows that the permutation layer yields better performance with negligible computational overhead. The reason could be that the permutation layer as in Eq. (1) stacks features from " + }, + { + "bbox": [ + 304, + 594, + 545, + 713 + ], + "type": "inline_equation", + "content": "S^{2^{\\prime}}" + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 296, + 734, + 315, + 742 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 734, + 315, + 742 + ], + "spans": [ + { + "bbox": [ + 296, + 734, + 315, + 742 + ], + "type": "text", + "content": "1229" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 50, + 95, + 544, + 222 + ], + "blocks": [ + { + "bbox": [ + 47, + 75, + 545, + 95 + ], + "lines": [ + { + "bbox": [ + 47, + 75, + 545, + 95 + ], + "spans": [ + { + "bbox": [ + 47, + 75, + 545, + 95 + ], + "type": "text", + "content": "Table 4. Experiment result of keypoint matching on the 3DMatch dataset. The numbers are the average recall " + }, + { + "bbox": [ + 47, + 75, + 545, + 95 + ], + "type": "inline_equation", + "content": "(\\%)" + }, + { + "bbox": [ + 47, + 75, + 545, + 95 + ], + "type": "text", + "content": ", and the higher, the better. Notation * represents the result with the given point normal information." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 50, + 95, + 544, + 222 + ], + "lines": [ + { + "bbox": [ + 50, + 95, + 544, + 222 + ], + "spans": [ + { + "bbox": [ + 50, + 95, + 544, + 222 + ], + "type": "table", + "html": "
SHOT [37]3DM [47]CGF [23]PPFN [12]PPFF [11]3DSN [16]Li [28]Li [28]*EPN [2]Ours
Kitchen74.358.360.389.778.797.592.199.499.099.4
Home 180.172.471.155.876.396.291.098.799.498.7
Home 270.761.556.759.161.593.285.694.796.296.6
Hotel 177.454.957.158.068.197.495.199.699.699.1
Hotel 272.148.153.857.771.292.891.3100.097.198.1
Hotel 385.261.183.361.194.498.296.3100.0100.0100.0
Study64.051.737.753.462.095.091.895.596.295.2
MIT Lab62.350.745.563.662.394.184.492.293.590.9
Average73.357.358.262.371.895.691.097.597.697.3
", + "image_path": "230273c256e1bc2745cd6cc4b37f8e456eadc8e89d5cb6a310839cfef66e2c73.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 240, + 288, + 277 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 240, + 288, + 277 + ], + "spans": [ + { + "bbox": [ + 46, + 240, + 288, + 277 + ], + "type": "text", + "content": "and thus preserves the information better, compared with weighted averaging over the " + }, + { + "bbox": [ + 46, + 240, + 288, + 277 + ], + "type": "inline_equation", + "content": "S^{2'}" + }, + { + "bbox": [ + 46, + 240, + 288, + 277 + ], + "type": "text", + "content": " dimension as done in GA pooling." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 285, + 220, + 296 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 285, + 220, + 296 + ], + "spans": [ + { + "bbox": [ + 47, + 285, + 220, + 296 + ], + "type": "text", + "content": "4.2. Pose Estimation on ModelNet40" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 304, + 287, + 399 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 304, + 287, + 399 + ], + "spans": [ + { + "bbox": [ + 46, + 304, + 287, + 399 + ], + "type": "text", + "content": "In this experiment, the network takes a pair of point clouds of an object and predicts the relative rotation between them. To avoid the pose ambiguity of objects with symmetric rotational shapes, only the airplane category is used in this experiment, with 626 models in the training set and 100 models in the test set. A point cloud is generated by randomly subsampling 1,024 points on the surface, and it is randomly rotated to form a pair." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 399, + 287, + 508 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 399, + 287, + 508 + ], + "spans": [ + { + "bbox": [ + 46, + 399, + 287, + 508 + ], + "type": "text", + "content": "The experimental result is shown in Tab. 3. We achieved similar rotation estimation accuracy to EPN [2] overall. While our mean error is slightly larger, the lower median error, max error, and standard deviations show that our method delivers a more reliable registration. It could imply that representing rotations as a permutation of features is more robust than representing them as a single element in the feature map. Besides, the equivariant networks outperform the non-equivariant KPConv [35] by a large margin." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 515, + 222, + 528 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 515, + 222, + 528 + ], + "spans": [ + { + "bbox": [ + 47, + 515, + 222, + 528 + ], + "type": "text", + "content": "4.3. Keypoint matching on 3DMatch" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 533, + 287, + 617 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 533, + 287, + 617 + ], + "spans": [ + { + "bbox": [ + 46, + 533, + 287, + 617 + ], + "type": "text", + "content": "In this task, patches of point clouds extracted locally around keypoints in a large, dense scan are input to the network, and each is mapped to a feature vector of 64 dimension as the keypoint descriptor. Each patch has 1,024 points. Then we evaluate the average recall of keypoint correspondence across different scans through nearest neighbor search in the feature space, as proposed in PPFNet [12]." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 618, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 618, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 618, + 288, + 715 + ], + "type": "text", + "content": "This experiment's performance in Tab. 4 indicates the capability of learning distinctive and rotation-invariant features for local patches of point clouds. Though not achieving the best in the list, our method delivers comparable performance to the top methods using only a fraction of the computational resources as EPN [2] (see Tab. 1). We use the GA pooling layer [2] in this experiment because the permutation layer requires supervision on the pose, while" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 240, + 547, + 361 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 240, + 547, + 361 + ], + "spans": [ + { + "bbox": [ + 304, + 240, + 547, + 361 + ], + "type": "text", + "content": "a canonical pose is not defined for local patches of point clouds, and GA pooling works with or without the pose supervision. However, the result shows that GA pooling over the " + }, + { + "bbox": [ + 304, + 240, + 547, + 361 + ], + "type": "inline_equation", + "content": "|S^{2t}|" + }, + { + "bbox": [ + 304, + 240, + 547, + 361 + ], + "type": "text", + "content": " features also provides distinctive features for keypoint matching. This part may be further improved by taking the information of the global scan [12] or the matching scan [20] into consideration, in which case the permutation layer may get hints on the optimal permutation from the larger context. This topic goes beyond the focus of this paper and is left for future work." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 370, + 379, + 383 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 370, + 379, + 383 + ], + "spans": [ + { + "bbox": [ + 306, + 370, + 379, + 383 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 390, + 547, + 582 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 390, + 547, + 582 + ], + "spans": [ + { + "bbox": [ + 304, + 390, + 547, + 582 + ], + "type": "text", + "content": "This paper presents a new design of SE(3)-equivariant point cloud convolution network, which is efficient, simple, and expressive simultaneously by working with feature maps defined on the quotient space " + }, + { + "bbox": [ + 304, + 390, + 547, + 582 + ], + "type": "inline_equation", + "content": "S^2 \\times \\mathbb{R}^3" + }, + { + "bbox": [ + 304, + 390, + 547, + 582 + ], + "type": "text", + "content": " associated with the stabilizer SO(2). We further improve the efficiency of the convolutions by designing the kernel points to be symmetric to the discretized rotation group " + }, + { + "bbox": [ + 304, + 390, + 547, + 582 + ], + "type": "inline_equation", + "content": "\\mathrm{SO}(3)'" + }, + { + "bbox": [ + 304, + 390, + 547, + 582 + ], + "type": "text", + "content": ". Moreover, we propose a permutation layer to recover " + }, + { + "bbox": [ + 304, + 390, + 547, + 582 + ], + "type": "inline_equation", + "content": "\\mathrm{SO}(3)'" + }, + { + "bbox": [ + 304, + 390, + 547, + 582 + ], + "type": "text", + "content": " information from " + }, + { + "bbox": [ + 304, + 390, + 547, + 582 + ], + "type": "inline_equation", + "content": "S^{2/}" + }, + { + "bbox": [ + 304, + 390, + 547, + 582 + ], + "type": "text", + "content": " dimensions of the features so that the network can detect SO(3) rotations. Experiments show that our network delivers state-of-the-art performance in multiple tasks while consuming only a fraction of memory and computation resources as a group-convolution network with similar performance. Our method can open exciting opportunities to introduce the SE(3)-equivariance property to mainstream point cloud networks for various tasks." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 582, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 547, + 713 + ], + "type": "text", + "content": "This work also has limitations. We do not outperform EPN [2] in the keypoint matching task, implying that the network, especially the permutation layer, needs improvement when dealing with inputs without a clear pose definition. Other possibilities for the network design also remain open. For example: What if we use a non-scalar type of feature on the quotient space? How to further alleviate the impact of the discretization of a continuous group? 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While recent approaches apply contrastive learning to force alignment between the two modalities, we hypothesize better modeling their complementary differences can lead to more holistic representations for downstream adaption. To this end, we propose Emergent Communication for Embodied Control $(EC^2)$ , a novel scheme to pre-train video-language representations for few-shot embodied control. The key idea is to learn an unsupervised \"language\" of videos via emergent communication, which bridges the semantics of video details and structures of natural language. We learn embodied representations of video trajectories, emergent language, and natural language using a language model, which is then used to finetune a lightweight policy network for downstream control. Through extensive experiments in Metaworld and Franka Kitchen embodied benchmarks, $EC^2$ is shown to consistently outperform previous contrastive learning methods for both videos and texts as task inputs. Further ablations confirm the importance of the emergent language, which is beneficial for both video and language learning, and significantly superior to using pre-trained video captions. We also present a quantitative and qualitative analysis of the emergent language and discuss future directions toward better understanding and leveraging emergent communication in embodied tasks.", + "bbox": [ + 75, + 300, + 473, + 753 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 782, + 209, + 799 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "We study the problem of few-shot embodied control, where an embodied agent needs to execute language instructions or follow video demonstrations given only a few examples in a new environment. Such a capability of fast adaption is key to practical robotic deployment, as it is non- scalable and expensive to collect extensive action-labeled", + "bbox": [ + 75, + 809, + 470, + 901 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/833a326db3f0d71a85550006fbbbb23324e740bab3fb6fe16521dc2884579f3b.jpg", + "image_caption": [ + "(a) Emergent language for embodied control." + ], + "image_footnote": [], + "bbox": [ + 517, + 270, + 874, + 391 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/574794532ecb74b280941005535ccbfebfa31148d70635773ddfebb47fd93c45.jpg", + "image_caption": [ + "(b) Performance comparison on overall success rate across all tasks.", + "Figure 1. Overview of $\\mathrm{EC^2}$ . The key idea of $\\mathrm{EC^2}$ is to build the link between perceptual grounding and symbolic concept via emergent communication (EC) language. We learn to extract embodied representation via language model utilizing emergent language or natural language as prompt and visual observation as input for downstream embodied control tasks. The actions are generated by a lightweight policy network containing a few MLP [51] layers that map the learned frozen embodied representation into action space. Extensive experiments show that $\\mathrm{EC^2}$ outperforms existing methods in Metaworld [60] and Franka Kitchen [17] benchmarks." + ], + "image_footnote": [], + "bbox": [ + 527, + 417, + 843, + 501 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "trajectories for each new application scenario. Instead, agents need to leverage pre-trained video and language representations to quickly learn how to act, and generalize across high-level concepts (e.g. object and verb types) as well as low-level visual features.", + "bbox": [ + 496, + 688, + 893, + 763 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "How can we pre-train multi-modal representations of videos and texts for downstream embodied control in different domains? Inspired by the success of image-text models such as CLIP [47], recent work has investigated contrastive representation learning approaches using paired video-language data, with application toward robotic manipulation and control tasks [24, 38]. However, simply aligning video and language pairs in the embedding space omits the difference between these two modalities: while", + "bbox": [ + 496, + 763, + 893, + 900 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "6704", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "videos contain more visual and motion details, language abstracts away key structures underlying the task. For example, a video of opening a door contains details of approaching the handle, pressing the handle, pulling the door open, and so on, while the corresponding language description could be as simple as \"open a door\" — more detailed language descriptions such as \"press down the handle\" is usually not available in existing datasets and very expensive to manually label. But for downstream control purposes, a video and its abstract language description could present complementary benefits — while the former is expressive in details needed for low-level control, the latter provides the structure for generalization across domains, tasks, and skills. Leveraging such modality differences presents opportunities to better incorporate language and videos for embodied representation learning, marrying their respective benefits rather than forcing them to be aligned.", + "bbox": [ + 80, + 90, + 467, + 345 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "One perspective to view the video-language difference is through the emergence of language [39, 55]: language derives meaning from its use [57]. It is a communication tool humans develop to collaboratively solve embodied tasks, thus abstracting perception experiences like videos into symbolic concepts. Emergent communication in machine learning [9, 26, 28, 30, 56] aims to similarly learn an \"emergent language\" of perception in an unsupervised and domain-adaptive way: as Figure 2(a) shows, a speaker and a listener network play a referential game, where a speaker maps some visual stimuli (e.g. image, video) into a message of discrete tokens, and a listener uses the message to choose the speaker reference out of detractors. By jointly optimizing for game success, the communication protocol emerges structural and semantic properties resembling language, yet its discrete tokens might convey more fine-grained concepts than natural language useful for distinguishing stimuli. Thus, an emergent language can act as a bridge between natural language and videos, featuring a structure similar to the former while preserving the semantics of the latter.", + "bbox": [ + 80, + 352, + 467, + 652 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Inspired by recent work that links emergent and natural language [58], we propose Emergent Communication for Embodied Control (EC²), a three-phase scheme to learn embodied representations for downstream few-shot control (Figure 1(a-c)). First, we learn an emergent language of demonstration videos without using any language labels, which could potentially capture domain-specific concepts not directly available in paired natural language captions. Second, we learn an embodied representation by using a language model to predict trajectory segments conditional on trajectory contexts and language annotations, both natural and emergent. Rather than forcing video and language representations to be aligned, such a sequence modeling approach learns to represent natural language (for compositional generalization) and emergent language (for low-level perception and control) jointly with video trajectories,", + "bbox": [ + 80, + 659, + 467, + 898 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "where the emergent language serves as a bridge between language and videos. Third, we train a lightweight policy network on top of the embodied representation to few-shot adapt to downstream embodied control.", + "bbox": [ + 503, + 90, + 890, + 150 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "We demonstrate that emergent language can help embodied control tasks and enable data-efficient few-shot downstream imitation learning via extensive experimental results across two existing benchmark simulation environments (Franka-Kitchen [18] and MetaWorld [60]). $\\mathrm{EC^2}$ outperforms existing methods and achieves state-of-the-art performance on both language and video instruction following tasks. Our study also shows that although emergent language and natural language are utilized in a parallel manner in the pre-training phase, the word embeddings of natural language can still be predicted by linear regression models from emergent language. We further investigate the impact of emergent language and natural language correlation on the performance of downstream tasks and show that the performance in downstream tasks is best when the learned EC contains more information than natural language, i.e., when the accuracy of predicting natural language from emergent language is higher than that of predicting emergent language from natural language. Overall, on the basis of these results, we believe that $\\mathrm{EC^2}$ has great potential to become a promising embodied control framework.", + "bbox": [ + 503, + 152, + 890, + 468 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To sum up, our work makes the following contributions. (1) we build an embodied representation pre-training framework with emergent communication (EC) via a language model, which incorporates both the abstract, compositional structure of language and visuals with low-level motion details. (2) we develop a few-shot embodied control system, which transfers the pre-trained language model to downstream tasks as a frozen module and quickly adapts lightweight policy networks with a few expert data to generate actions. (3) we demonstrate that the learned representation with EC can benefit few-shot embodied control tasks and extensive experiments show that $\\mathrm{EC^2}$ outperforms existing methods in Metaworld [60] and Franka Kitchen [17] benchmarks.", + "bbox": [ + 503, + 470, + 890, + 680 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 503, + 699, + 638, + 714 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.1. Emergent Communication", + "text_level": 1, + "bbox": [ + 503, + 724, + 736, + 739 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "The recent advances in NLP [7, 14, 49] benefits from huge text corpora and are striving to find statistical regularities on large amounts of data via big models like GPT [7, 48, 49] and BERT [14]. This narrow focus was leaving aside language emergence and language grounding (in some other modalities, e.g., sight, with more complex inputs than text). In contrast, human language acquisition [13] starts with a cumulative series of interactions with other people [3, 8] grounded in the physical and social world [1, 19, 54] and does not rely on passive and complex corpora like", + "bbox": [ + 503, + 750, + 890, + 898 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "6705", + "bbox": [ + 483, + 946, + 513, + 955 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/1c5139b02854949144f8f98fbba53220417dbfb0556bdc7986ede25e32e4d75e.jpg", + "image_caption": [ + "Figure 2. The overall framework of EC $^2$ . Pre-training: (a) We first pre-train a speaker (■) and listener (■) via emergent communication game for emergent language generation and a language model (■) to extract embodied representations. (b) We generate the corresponding emergent language (■) for each demonstration video in the multi-modal dataset. Predicting the cropped part of a latent trajectory is used as an auxiliary task to help pre-training the language model. The language model takes emergent language or natural language as prompt and the cropped trajectory (■) as input and aims to predict the cropped part of the trajectory (■). The loss for the prediction using emergent language as prompt and natural language as prompt is calculated separately. Few-shot downstream policy learning: In downstream imitation learning tasks, both the EC speaker and the pre-trained language model(■) are frozen. The language model extracts effective embodied features with current trajectory (■ contains current state and historical information) as input. (c) For tasks with language instruction, we use natural language as the prompt, and (d) for tasks with video instruction, we use emergent language as the prompt. The output features of the language model are mapped into actions to mimic expert behavior by a few simple MLP [51] layers (■)." + ], + "image_footnote": [], + "bbox": [ + 138, + 97, + 573, + 335 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/17289e83919e72239682c7e05010941e5c48f94e189a909f03ac4351b47576d9.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 598, + 98, + 836, + 335 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Wikipedia. Emergent Communication (EC) is one promising direction toward this motivation, where a communication protocol is shaped through multi-agent interactions with perceptual grounding like a human [43]. As a typical example, the referential image game involves a speaker creating a sequence of discrete tokens based on an input image, and a listener tasked with selecting the correct input from a group of distractors using the message. Both networks are optimized jointly using success signals from the game [58]. By studying games like this type, researchers are interested in the emergence of desirable properties resembling natural language, such as game success generalization and compositionality, which holds great promises towards more functional [56, 57] and generalizable [27] language agents.", + "bbox": [ + 75, + 496, + 472, + 709 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "2.2. Embodied Control under Instruction", + "text_level": 1, + "bbox": [ + 76, + 723, + 398, + 739 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Embodied control has achieved much success in learning grasping and pick-place tasks from low-dimensional state [2,4,10,25,36,42,52]. Deep learning makes embodied control directly learn from high dimensional observations becoming feasible [46,50,61]. Recent advances aim to build a learning-based embodied control system with deep neural networks that are flexibly conditioned on either a demonstration video [5,59] of a human or a language instruction [35, 53] via multi-modal representation learning. With the guidance of instruction, the embodied agent aims to gener", + "bbox": [ + 75, + 750, + 472, + 902 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "alize to new scenes [44], novel objects [5, 16, 22, 59, 62], novel object configurations [40], and novel goal configurations [12, 15, 20]. For instance, BC-Z [24] has developed a flexible imitation learning system that can learn from demonstrations and interventions, based on various forms of task information, such as pre-trained embeddings of natural language or human performance videos. R3M [38] pre-trains visual representations on diverse human videolanguage data by encouraging alignment between the two modalities. However, since videos often convey more detailed information than words, this framework may lose valuable teaching information that can help robots perform complex tasks. In this work, we aim to build an instruction-conditioned embodied control framework without forcing alignment on video and language and consider the video demonstrations and language instructions as \"parallel sentences\" during the pre-training process to learn useful information for downstream tasks.", + "bbox": [ + 496, + 496, + 893, + 768 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Method", + "text_level": 1, + "bbox": [ + 500, + 782, + 591, + 800 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "As shown in Figure 2, we first pre-train a speaker and listener via an emergent communication game for emergent language generation and a language model to extract embodied representations by predicting the cropped part of a latent trajectory. The language model takes the emergent language or natural language as prompt and the masked", + "bbox": [ + 496, + 810, + 893, + 902 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "6706", + "bbox": [ + 482, + 944, + 516, + 955 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "trajectory as input and aims to predict the masked part of the trajectory separately. Then, we transfer the learned speaker and language model into downstream embodied control tasks as frozen modules. The output of the language model extracts embodied representation from instruction prompt and current observations and is mapped into actions by the downstream policy network, which contains a few task-specific MLP [51] layers.", + "bbox": [ + 75, + 90, + 472, + 212 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.1. Problem Statement", + "text_level": 1, + "bbox": [ + 76, + 222, + 261, + 237 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The goal for embodied control is to learn a policy $\\pi_B$ conditioned on the instruction, either language instruction or video instruction, that reproduces the expert behavior on the desired task specified by the instruction. Usually, the demonstrations of experts are presented in the form of state-action trajectories, with each pair indicating the action to take at the state being visited. Let $\\tau_E$ denote a trajectory sampled from expert policy $\\pi_E(s|c)$ : $\\tau_E = [(s_0,a_0),(s_1,a_1),\\ldots ,(s_n,a_n)]$ . The instruction is encoded into the latent vector $c$ . To learn the behavior policy $\\pi_B(s|c)$ , the demonstrated actions are usually utilized as the target label for each state, and the mapping $a\\in \\pi_B(s|c)$ from states to actions is learned in a supervised manner with given instructions.", + "bbox": [ + 75, + 246, + 472, + 458 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. Emergent Communication Language Generation for demonstration video", + "text_level": 1, + "bbox": [ + 76, + 468, + 468, + 498 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Our idea is to automatically generate synthetic language that aligns with video demonstration through emergent communications, which connect perceptual, language, and action for pre-training. As shown in Figure 2(c), we consider a typical speaker-listener referential game [29, 30, 33] on a set of $N$ video features $\\mathcal{D}_I = \\{I_1,\\dots ,I_N\\}$ . At each training step, the speaker takes one video feature $I_{i}$ and generates a discrete message $M_{i}\\in [V]^{T}$ using the Gumbel-Softmax trick [23], where $V$ is the vocabulary size, and $T$ is the sequence length limit. For simplicity, denote $m = M_{i}$ so that $m_t = M_{i,t}$ denotes the $t$ -th token of the message $M_{i}$ . The generated discrete message is defined as \"emergent language\", and the process of emergent language generation by the speaker can be formulated as", + "bbox": [ + 75, + 507, + 472, + 719 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {h} \\mathbf {s} _ {0} = I _ {i}, \\quad \\mathbf {h} \\mathbf {s} _ {t} = \\mathrm {G P T} _ {\\mathrm {s p k}} (m _ {t - 1}, \\mathbf {h} \\mathbf {s} _ {t - 1}) (t > 0),\n$$\n", + "text_format": "latex", + "bbox": [ + 112, + 731, + 450, + 747 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nm _ {0} = \\left[ \\mathrm {C L S} \\right], \\quad m _ {t} = \\operatorname {S o f t m a x} \\left(\\mathrm {M L P} _ {\\mathrm {s p k}} \\left(\\mathbf {h s} _ {t}\\right)\\right) (t > 0). \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 86, + 750, + 468, + 779 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Here $\\mathbf{h}\\mathbf{s}_t$ denotes speaker hidden states. Next, the listener takes the message $m$ , and tries to guess the right video $I_{i}$ out of a set of $K$ confounding videos $C_i = \\{I_{j_1},\\dots ,I_{j_K}\\} \\subset \\mathcal{D}_I - \\{I_i\\}$ . Note that different from the EC games on images, in order to learn temporal information, except for irrelevant videos, we also construct several additional candidates in $C_i$ by performing temporal augmentation on the original video, such as reverse order and random disorder.", + "bbox": [ + 75, + 780, + 470, + 901 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The listener also uses a GRU [11] layer to turn the message $m$ into a hidden vector $\\mathbf{h}\\mathbf{l}_T$", + "bbox": [ + 498, + 90, + 890, + 121 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {h l} _ {0} = \\mathbf {0}, \\quad \\mathbf {h l} _ {t} = \\mathrm {G P T} _ {\\mathrm {l s n}} \\left(m _ {t}, \\mathbf {h l} _ {t - 1}\\right) (t > 0). \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 526, + 132, + 890, + 148 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Based on $\\mathbf{h}\\mathbf{l}_T$ , the listener assigns a score for each candidate video based on inverse square error [31], then selects the image by Softmax sampling across the scores. The speaker and listener are jointly optimized by minimizing the cross-entropy loss of video selection:", + "bbox": [ + 496, + 159, + 893, + 234 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\operatorname {s c o r e} (\\mathbf {I}) = \\left\\| \\mathbf {h l} _ {T} - \\operatorname {M L P} _ {\\mathrm {l s n}} (\\mathbf {I}) \\right\\| _ {2} ^ {- 2}, \\\\ p (\\text {g u e s s} = \\mathbf {I}) = \\operatorname {s o f t m a x} (\\operatorname {s c o r e} (\\mathbf {I})) \\quad (\\mathbf {I} \\in \\left\\{\\mathbf {I} _ {i} \\right\\} \\cup C _ {i}), \\\\ \\mathcal {L} _ {E C} = - \\mathbb {E} _ {\\mathbf {I} _ {i}, C _ {i}} \\mathbb {E} _ {\\mathbf {M} _ {i}} \\log p (\\text {g u e s s} = \\mathbf {I} _ {i}). \\tag {3} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 506, + 244, + 890, + 314 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The speaker can be employed to generate emergent language $\\mathcal{D}_M = \\{M_1,\\dots ,M_N\\}$ based on input videos.", + "bbox": [ + 498, + 315, + 890, + 345 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.3. Pre-training of Language Model with Emergent Language", + "text_level": 1, + "bbox": [ + 498, + 354, + 890, + 386 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We conduct a trajectory completion task to pre-train the GPT-like language model without action labels, as shown in Figure 2(a)(b). Firstly, we random sample a sequence of observations $\\hat{o} = \\{o_1,o_2,\\dots ,o_N\\}$ stored in the dataset and map it into latent trajectory $\\tau_{\\mathrm{whole}}$ by encoder $g_{\\theta}$", + "bbox": [ + 496, + 393, + 890, + 469 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\tau_ {\\text {w h o l e}} = g _ {\\theta} (\\hat {o}) \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 645, + 479, + 890, + 496 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Then we crop a random segment $\\tau_{\\mathrm{seg}}$ from the whole latent trajectory $\\tau_{\\mathrm{whole}}$ and the remained trajectory is denoted as $\\tau_{\\mathrm{rem}}$ . The language model $f_{\\phi}$ takes $\\tau_{\\mathrm{rem}}$ as input and uses either emergent language $e$ generated by the speaker or natural language $l$ as a prompt to predict the cropped segment $\\tau_{\\mathrm{seg}}$ . The language model is optimized by jointly minimizing $L_{\\mathrm{EC}}$ and $L_{\\mathrm{Lang}}$", + "bbox": [ + 496, + 507, + 890, + 614 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nL _ {\\mathrm {E C}} = \\left(\\tau_ {\\mathrm {s e g}} - f _ {\\theta} (e, \\tau_ {\\mathrm {r e m}})\\right) ^ {2} \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 602, + 623, + 890, + 642 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nL _ {\\text {L a n g}} = \\left(\\tau_ {\\text {s e g}} - f _ {\\theta} (l, \\tau_ {\\text {r e m}})\\right) ^ {2} \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 599, + 650, + 890, + 667 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The loss for the prediction using emergent language as prompt and natural language as prompt is calculated separately.", + "bbox": [ + 496, + 674, + 890, + 718 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "$\\mathrm{EC^2}$ uses the same language model for both emergent language generation and trajectory completion pretext task for framework thriftiness, and both the $L_{\\mathrm{EC - pre}}$ and $L_{\\mathrm{EC - gen}}$ are used to update the language model jointly. To ensure that the speaker's gradient is not truncated, we use an MLP [51] layer to map from the logits of the word distribution to a 512-dimensional latent vector instead of selecting a word embedding in the dictionary according to the token. For natural language, we use the Byte-Pair Encoding (BPE) tokenizer [6] to encode it into tokens, which are widely used by OpenAI for tokenization when pre-training the GPT model, including GPT [48], GPT-2 [49], RoBERTa [34],", + "bbox": [ + 496, + 719, + 890, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "6707", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "and BART [32]. We also learn a corresponding dictionary of word embedding. Although the emergent language and natural language are used separately, they can learn correlated information via the pretext trajectory completion task.", + "bbox": [ + 75, + 90, + 470, + 151 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.4. Few-shot Policy Learning for Downstream Embodied control", + "text_level": 1, + "bbox": [ + 76, + 162, + 468, + 191 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "To transfer the pre-trained language model into the downstream imitation learning tasks, the language model $f_{\\theta}(\\cdot ,\\cdot)$ take the current trajectory $\\tau_{cur} = \\{s_{t - T},\\dots ,s_{t - 1},s_t\\}$ and the emergent language $e$ or natural language instruction $l$ as prompt, then output the predicted features $m_{t}$ . Finally, the output $m_{t}$ of the language model is mapped to specific action $a_{t}$ by task-specific MLP layers $\\pi_{\\psi}$ . The language model $f_{\\theta}$ is frozen during downstream imitation learning. The action under learned behavior policy is sampled by $\\hat{a}_t\\sim \\pi_\\psi (a_t|m_t)$ and the expert demonstration action $a_{t}$ are used as the label for imitation learning. For the video instruction following task, we generate emergent language by the speaker and use it as the prompt of the language model. For language instruction following tasks, the natural language is tokenized by the BPE tokenizer, and select the corresponding word embedding in the dictionary as the prompt as language model via the inferred token. With a trajectory with length $H$ , the task-specific MLP layers are optimized by minimizing $\\mathcal{L}_{\\mathrm{IL}}(\\psi)$ .", + "bbox": [ + 75, + 200, + 470, + 488 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\mathrm {I L}} (\\psi) = E _ {\\tau \\sim \\mathcal {B}} \\left[ - \\frac {1}{H} \\sum_ {t} ^ {t + H - 1} \\log \\pi_ {\\psi} (a _ {t} | m _ {t}) \\right] \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 135, + 500, + 468, + 532 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The MLP [51] layers are implemented with hidden sizes [256, 256] with batch normalization [21] and are trained with a learning rate of 0.001 and a batch size of 32 for 20000 iterations.", + "bbox": [ + 75, + 535, + 468, + 595 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 76, + 609, + 209, + 627 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.1. Pre-training Dataset", + "text_level": 1, + "bbox": [ + 76, + 635, + 269, + 651 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We use the LOReL [37] real robot dataset, which is collected by Franka Emika Panda mounted over an IKEA desk. The LOReL dataset contains 3000 episodes (150000 frames) of reinforcement learning that trains policies for different behaviors on the IKEA desk using online RL. The language instruction is annotated by leveraging crowdsourcing, specifically Amazon Mechanical Turk. Human annotators are asked to describe the behavior if any, that the robot is doing and to phrase it as a command without any pre-specified template. The LOReL dataset contains 6000 annotations, two per episode, containing a total of 1699 unique instructions. The dataset contains different videos with the same language instruction to ensure diversity. We removed the episodes where annotators reported the robot as inactive or its actions unclear, making them incomprehensible.", + "bbox": [ + 75, + 659, + 468, + 898 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.2. Downstream Testing Environments", + "text_level": 1, + "bbox": [ + 500, + 90, + 805, + 106 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We utilize two standard robotic manipulation benchmarks, namely MetaWorld [60] and the Franka Kitchen environment [17], as our downstream testing environments. It is worth noting that these testing environments were not used during the training phase of $\\mathrm{EC^2}$ . In MetaWorld, the agent is presented with a series of tasks, including assembling a ring on a peg, picking and placing a block between bins, pushing a button, opening a drawer, and hammering a nail. In Franka Kitchen, the agent aims to learn how to slide open the right door, open the left door, turn on the light, turn the stove top knob, and open the microwave. As shown in Figure 3, both environments offer image observations to the agent, as well as proprioceptive data, which includes the end-effector pose and joint positions. These data are concatenated with the encoded vision observations for each task, providing the agent with a comprehensive understanding of the current task. All tasks involve random environment variation, either by varying the position of the target object in MetaWorld or the positioning of the desk in Franka Kitchen. Additionally, we consider three views for each environment to evaluate the robustness of representations across viewpoints. Finally, for each environment, we also consider three demo sizes used in downstream embodied control tasks: [5, 10, 25] in MetaWorld and Franka Kitchen.", + "bbox": [ + 496, + 113, + 890, + 489 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.3. Experimental Setup", + "text_level": 1, + "bbox": [ + 500, + 500, + 689, + 516 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "For embodied control tasks, we take R3M and BC-Z as the key baseline. R3M [38] learns the state-of-the-art embodied representations pre-trained on diverse paired human video-language data with time-contrastive learning, which encourages states closer in time to be closer in embedding space and video-language alignment to encourage the embeddings to capture semantically relevant features. For sufficient comparison, we implement R3M with both the language instruction-conditioned version and video instruction-conditioned version, respectively, based on their official implementation. For embodied control with natural language instruction, we use the language encoder of the pre-trained model officially released by their author team to encode the natural language. For embodied control with demonstration video instruction, we use the officially released vision encoder to extract features of every frame in the video and map them into the instruction representation by one MLP layer. BC-Z [24] jointly learns the alignment between video representation and language representation together with policy learning across multiple embodied control tasks. Our evaluation methodology is inspired by [38, 41]. We focus on evaluating the embodied representation of instruction and observation for downstream policy learning with behavior cloning. We parameterize the downstream policy $\\pi$ as a two-layer MLP preceded by a", + "bbox": [ + 496, + 523, + 890, + 902 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "6708", + "bbox": [ + 482, + 945, + 514, + 955 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/3873f4e2021a03efca2da23cea257491bf455087656ffee928a1f25c0fa324d9.jpg", + "image_caption": [ + "Slid the door of the drawer" + ], + "image_footnote": [], + "bbox": [ + 125, + 99, + 300, + 258 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/a9aa635f99da0e1010936c8306f02d2d5b66b3d1e4d97da13db4220948da5a92.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 303, + 101, + 395, + 166 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/63ec2749b1bf57c1ee089034271fadb62dbc7515649f28e33414c0db26503322.jpg", + "image_caption": [ + "Turn the light on" + ], + "image_footnote": [], + "bbox": [ + 413, + 101, + 504, + 167 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/c58f9687874883631786b53bccd6649696d9a946b1c0b6c8933dc82ff6a643da.jpg", + "image_caption": [ + "Open the door of the drawer." + ], + "image_footnote": [], + "bbox": [ + 524, + 101, + 612, + 167 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/e8dcad136afa15eec688ba1ab30a0bce3df25fe2c98711c534e47e288e3d4f48.jpg", + "image_caption": [ + "Turn the knob on the up left" + ], + "image_footnote": [], + "bbox": [ + 630, + 101, + 718, + 167 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/aa823e08bc738a13632f3c4dfb1a9ce580db6a552b2d9c53a7e12e94d797d390.jpg", + "image_caption": [ + "Open the door of the Microwave" + ], + "image_footnote": [], + "bbox": [ + 738, + 101, + 826, + 167 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/a93a0850189057f9e10827d6faed1ff097056ee627a12e51cb19317e2e1c07c2.jpg", + "image_caption": [ + "Multi-view Testing", + "Pick up the nut and place it on the nail." + ], + "image_footnote": [], + "bbox": [ + 303, + 193, + 393, + 258 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/c906bc1c7c6a0c3f0f619431015d7964a1008fff00c6dc040a965548f9dd30ed.jpg", + "image_caption": [ + "Grab the ball from the blue Press the button down bin and put it in the red one", + "Tasks with Language Instruction", + "Figure 3. Evaluation Environments: We consider a set of manipulation tasks including 5 tasks with a Sawyer from MetaWorld [60], 5 tasks from a Franka operating over a Kitchen [17]. We provide specific language instruction labels for every task and 25 demos per task for evaluation. We show an example image and corresponding language instruction for each task shown above. Evaluation Viewpoints: To robustly measure the efficacy of different visual representations, we consider three camera viewpoints per environment." + ], + "image_footnote": [], + "bbox": [ + 415, + 193, + 504, + 258 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/58e4202f636d0e6b91e61b60526bfabf65128c9ec70fe6eb999fe1f8e45f7ba9.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 526, + 193, + 614, + 258 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/0271f6430031c9f93c4b7f6d2c192659569d78b1105a3df4ced1a1a5a38c1694.jpg", + "image_caption": [ + "Open the drawer" + ], + "image_footnote": [], + "bbox": [ + 630, + 193, + 722, + 258 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/86f240df30023b545739978bf33eb43205f1cd8cb40134e91d588c85c122e8e7.jpg", + "image_caption": [ + "Pick up the hammer and hammer the wall" + ], + "image_footnote": [], + "bbox": [ + 738, + 193, + 831, + 258 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/9e53f82c2e348adc7adc0f80220e578497fd1c34e413b83d09b2b85f06806f70.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
BenchmarkNum. DemosInstructionEC2(ours)R3M [38]BC-Z [24]
MetaWorld10Lang72.4 ± 2.4%69.2 ± 2.0%63.4 ± 2.1%
Video76.0 ± 2.1% (+3.6)71.8 ± 1.8% (+2.6)64.8 ± 2.0% (+1.4)
25Lang82.6 ± 2.0%77.4 ± 2.4%74.1 ± 2.2%
Video85.0 ± 2.2% (+2.4)79.0 ± 2.1% (+1.6)75.2 ± 1.0% (+1.1)
Franka Kitchen10Lang48.4 ± 2.5%41.8 ± 2.5%34.2 ± 2.3%
Video53.6 ± 2.5%(+5.2)45.7 ± 2.4% (+3.9)37.5 ± 2.2% (+3.3)
25Lang59.8 ± 2.5%56.0 ± 2.3%38.6 ± 2.4%
Video63.2 ± 2.6% (+3.4)58.7 ± 2.0% (+2.7)40.0 ± 2.0% (+1.4)
", + "bbox": [ + 81, + 364, + 890, + 507 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 1. Performance comparison on Success rate of embodied control with language/video instruction across different demo size. We mark the performance difference between complete the task with natural language instruction and video instruction as blue.", + "bbox": [ + 75, + 510, + 892, + 539 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "BatchNorm at the input. We train the agent for 20,000 steps, evaluate it online in the environment every 1000 steps, and report the best success rate achieved. For each task, we run 5 seeds of behavior cloning. The final success rate reported for one method on one task is the average over the 5 seeds $\\times 3$ camera viewpoints $\\times 3$ demo sizes, for a total of 45 runs (see more details in Appendix).", + "bbox": [ + 75, + 546, + 468, + 652 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.4. Results", + "text_level": 1, + "bbox": [ + 76, + 664, + 169, + 679 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We aim to answer 5 questions to get insight into embodied AI community: 1) Can emergent language help embodied control tasks with natural language instruction? 2) Can emergent language help the embodied control tasks with video instruction? 3) Can the joint training of emergent language and natural language in GPT-Like network architecture help each other? 4) Can emergent language provide more detailed and effective guidelines than video captions? 5) What is the relationship between model size, control performance, and the correlation between emergent language and natural language?", + "bbox": [ + 75, + 688, + 468, + 853 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "To answer the first two questions, we study if $\\mathrm{EC^2}$ enables more data-efficient policy learning with both natural language instructions and video instructions.", + "bbox": [ + 75, + 854, + 468, + 900 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "1) Can emergent language help the embodied control tasks with natural language?", + "bbox": [ + 500, + 547, + 892, + 577 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We measure the success rate of downstream few-shot policy learning with different pre-training methods. In Franka Kitchen and MetaWorld, we only use no more than 25 demos to perform downstream few-shot policy learning and report the performance with both 10 and 25 demos separately in Table 1. Learning from scratch is struggled to perform well when working with small amounts of data since it can be challenging for the model to identify meaningful patterns or relationships with such limited data. While the methods with a pre-trained model, like $\\mathrm{EC}^2$ , R3M, and BC-Z performs better than those learning from scratch. Through our study, as shown in Table 1, $\\mathrm{EC}^2$ exceeds existing methods with natural language instruction, which indicates that emergent language can help the embodied control tasks to improve the performance with natural language instruction. Across all the evaluations, $\\mathrm{EC}^2$ is overall able to learn these embodied tasks in an extremely low data regime (only 10 demos) with $\\approx 60.4\\%$ overall success rate, despite never seeing any data from the target environments in training the representation, while R3M only achieves $\\approx 55.5\\%$ overall success rate.", + "bbox": [ + 496, + 583, + 892, + 898 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "6709", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/4bec8b23ee930a800f3c2f0379217a40c71fd1017fe08e3caf24a7678db4e87a.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
BenchmarkNum. DemosLanguage InstructionVideo Instruction
\\( EC^2 \\)\\( EC^2 (-EC) \\)\\( EC^2 \\)\\( EC^2 (-NL) \\)\\( EC^2 (+Cap,-EC) \\)
MetaWorld1072.4 ± 2.4%69.0 ± 2.0%76.0 ± 2.1%72.6 ± 2.4%73.0 ± 2.2%
2582.6 ± 2.0%78.0 ± 2.4%85.0 ± 2.5%82.0 ± 2.0%73.2 ± 2.5%
Franka Kitchen1048.4 ± 2.5%43.0 ± 3.3%53.6 ± 2.5%49.0 ± 2.5%48.6 ± 2.4%
2559.8 ± 2.5%54.0 ± 2.6%63.2 ± 2.6%61.3 ± 2.4%49.0 ± 2.3%
", + "bbox": [ + 81, + 89, + 893, + 186 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/0ef50b2a9def2b6b5488e08c3dafb82b0f86b51fa9d16f0d4b19371ea0f2530f.jpg", + "table_caption": [ + "Table 2. Ablation study on embodied control with language instruction and video instruction." + ], + "table_footnote": [], + "table_body": "
Model Size#layer#head#embedded
Base816512
Mini66192
Micro44128
", + "bbox": [ + 89, + 215, + 325, + 284 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/fcff10ea89a80a4bc3ff95c82932dd303d9ed7097fe1559e10135a18ff41bf2f.jpg", + "table_caption": [ + "Table 3. Hyper-parameters for different model sizes of ${\\mathrm{{EC}}}^{2}$ . All the models are implemented based on GPT [48]-like network architecture." + ], + "table_footnote": [], + "table_body": "
Natural LanguageEmergent language
“Open the right drawer”[262, 847, 490, 536, 108, 500, 941, 838, 749, 444]
“Grasp in the middle drawer”[356, 69, 108, 259, 72, 616, 500, 896, 623, 433]
“Reach down for stapler”[204, 897, 285, 509, 701, 545, 538, 729, 902, 195]
“Pick up the stapler in the drawer”[535, 67, 108, 661, 84, 701, 776, 500, 377, 454]
“Reach to the plug”[982, 691, 72, 538, 97, 665, 148, 369, 102, 1003]
“Reach to the left drawer”[786, 538, 601, 874, 848, 500, 315, 108, 72, 914]
", + "bbox": [ + 334, + 215, + 888, + 319 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 4. Qualitative examples of emergent language and corresponding natural language. The word and tokens that have the same semantic meaning are marked with the same color.", + "bbox": [ + 331, + 321, + 887, + 349 + ], + "page_idx": 6 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "2) Can emergent language help the embodied control tasks with video instruction?", + "As shown in Table1, $\\mathrm{EC^2}$ shows an obvious advantage over the exciting methods and achieves the best success rate ( $\\approx 64.8\\%$ with 10 demos and $\\approx 74.1\\%$ with 25 demos) with video instruction. As marked in blue in Table 1, $\\mathrm{EC^2}$ has better performance with video instruction than with language instruction, which indicates that $\\mathrm{EC^2}$ learns more effective information provided by a video demonstration. In contrast, R3M and BC-Z, which use contrast learning or regression to force the two modalities of language and video aligned, have little difference in performance under language instruction and video instruction.", + "We also investigate the task performance of $\\mathrm{EC^2}$ and baselines with different amounts of demos in policy learning. In Figure 4, we plot the average success rate of each method across each demo size. We observe that the performance improvement from $\\mathrm{EC^2}$ is consistent, outperforming the baselines across every environment and demo size.", + "Ablation Study: Also, in the data-efficient imitation learning setting, we ablate the different components of $\\mathrm{EC^2}$ training to answer question 3 and 4 and check if each module is indispensable.", + "3) Can the joint training of emergent language and natural language with GPT-Like network help each other?" + ], + "bbox": [ + 75, + 357, + 468, + 747 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We conduct ablation studies to compare $\\mathrm{EC}^2$ and $\\mathrm{EC}^2$ (-EC) in language instruction following tasks and compare $\\mathrm{EC}^2$ and $\\mathrm{EC}^2$ (-NL) in video instruction following tasks. $\\mathrm{EC}^2$ (-EC) does not use emergent language to pre-train the language model under $\\mathrm{EC}^2$ framework, which predicts the masked trajectories with only the language instruction (human-labeled caption). $\\mathrm{EC}^2$ (-NL) does not use natural language to pre-train the language model under $\\mathrm{EC}^2$ framework, which predicts the masked trajectories with only the emergent language. As shown in the left-hand column in", + "bbox": [ + 75, + 750, + 470, + 901 + ], + "page_idx": 6 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "Table 2, without the help of emergent language, the performance decreased significantly, and $\\mathrm{EC^2}$ (-EC) shows no obvious advantages to the other methods that learn pretrained models by video-language pre-training. Similarly, as shown in the right-hand column in Table 2, $\\mathrm{EC^2}$ also outperforms $\\mathrm{EC^2}$ (-NL), which demonstrates that the language pre-training helps the video instruction task with emergent language. Thus, the above ablation analysis shows that the joint training of emergent language and natural language can benefit each other.", + "4) Can emergent language provide more detailed and effective guidelines than video captions?" + ], + "bbox": [ + 496, + 357, + 890, + 542 + ], + "page_idx": 6 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "In $\\mathrm{EC^2}$ (+Cap, -EC), we replace the emergent language in $\\mathrm{EC^2}$ with the language caption given by a MARN [45] as a data augmentation, which is a pre-trained video caption model. As shown in Table 2, $\\mathrm{EC^2}$ shows an obvious advantage to $\\mathrm{EC^2}$ (+Cap, -NL), which demonstrates that emergent language provides more detailed and effective guidelines than video captions.", + "5) What is the relationship between model size, control performance, and the correlation between emergent language and natural language?" + ], + "bbox": [ + 496, + 545, + 890, + 700 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We first tested the overall average success rate of $\\mathrm{EC^2}$ with different model sizes (listed in Table 3) in the downstream tasks (Franka Kitchen and MetaWorld). As shown in Figure 5a and Figure 5b, the larger the size of the model, the more expressive it is and thus the better its performance. Then, we perform a linear correlation analysis on the word embeddings of the emergent language and the word embeddings of the matched natural language. We use the square of the coefficient of determination, denoted $R^2$ as the measure of predicting the performance of linear regression, which reflects the proportion of the variation in the dependent variable that is predictable from the independent variable. Consider a linear regression model $f(\\cdot)$ which predicts $y$ with", + "bbox": [ + 496, + 703, + 892, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "6710", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/e1c675166d9cae9f2a36e74272fe96c8a162c6992d35ea248e11595eaab3b5c2.jpg", + "image_caption": [ + "(a) MetaWorld[language instruction]" + ], + "image_footnote": [], + "bbox": [ + 80, + 99, + 263, + 205 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/4bd772172ba3c0aab7872154d602aa15871538fac270090210326801b04f0495.jpg", + "image_caption": [ + "(b) Kitchen[language instruction]" + ], + "image_footnote": [], + "bbox": [ + 282, + 99, + 467, + 205 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/e592d4735187c2f8678d03de367cc954226135ff17eb0a8c486b52e1ae3589c6.jpg", + "image_caption": [ + "(c) MetaWorld[video instruction]" + ], + "image_footnote": [], + "bbox": [ + 483, + 99, + 666, + 205 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/c37649d925918eeaf04f98e7c1930a0655a3f746233c627fdc5fac710089c438.jpg", + "image_caption": [ + "(d) Kitchen[video instruction]" + ], + "image_footnote": [], + "bbox": [ + 689, + 101, + 869, + 205 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/97d5a5ee50f1536cbdc671c9ef1675bfd10542256e6c9b469ecbb65f72f4de43.jpg", + "image_caption": [ + "Figure 4. Performance over different demo sizes used in downstream imitation learning. We report the success rate of $\\mathrm{EC^2}$ and baseline across different demo sizes. We see that the performance improvement from $\\mathrm{EC^2}$ is consistent across all demo sizes.", + "(a) Ablation on model size in MetaWorld", + "Figure 5. Ablation on model size and its relationship with the correlation of emergent language and Natural language. We show the ablation results on model size with 10 demos and 25 demos in downstream policy learning separately." + ], + "image_footnote": [], + "bbox": [ + 81, + 262, + 326, + 396 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/556d251e2aa857d811b293957b7174253612356f7e151fd5aaf16bd6f6e3d83d.jpg", + "image_caption": [ + "(b) Ablation on model size in Franka Kitchen" + ], + "image_footnote": [], + "bbox": [ + 352, + 262, + 598, + 395 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/511aa2367ec78663e5d0828678829ea61a8e5160cbfe859a9104e3359caa4f93.jpg", + "image_caption": [ + "(c) Translation score across different model sizes" + ], + "image_footnote": [], + "bbox": [ + 620, + 262, + 867, + 395 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "the input $x$ , the coefficient of determination $R$ is defined as", + "bbox": [ + 76, + 454, + 467, + 468 + ], + "page_idx": 7 + }, + { + "type": "equation", + "text": "\n$$\nR ^ {2} = 1 - \\frac {S S _ {r e s}}{S S _ {t o t}} = 1 - \\frac {\\sum_ {i} \\left(y _ {i} - f \\left(x _ {i}\\right)\\right) ^ {2}}{\\sum_ {i} \\left(y _ {i} - \\bar {y}\\right) ^ {2}} \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 129, + 478, + 468, + 513 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We evaluate the $R^2$ values of two linear regressions. One predicts natural language word embeddings from emergent language, and the other predicts emergent language word embeddings from natural language. As shown in Figure 5c, the $R^2$ of predicting natural language embeddings from the emergent language increase along with the model becoming larger, which corresponds to better performance. In contrast, the $R^2$ of predicting emergent language embeddings from the natural language is non-monotonous, along with the model size becoming larger. The reason is that emergent language captures more information that natural language does not contain when the model is large enough and has promising performance. In short, $\\mathrm{EC}^2$ has the best performance in embodied control tasks when emergent language contains more information than natural language, the performance is median when emergent language and language information are nearly equal, and the performance is worst when emergent language contains less information than language information. As shown in Table 4, we also provide qualitative examples of emergent language and its corresponding natural language to show that emergent language can capture key concepts from video. We find that the tokens \"108\" and \"500\" correspond to \"drawer\" in natural language and token \"701\" corresponds to \"stapler.\" Except for nouns, emergent language can also get the con", + "bbox": [ + 75, + 523, + 468, + 901 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "cept of verbs, for example, token “538” corresponds to the verb “reach” in natural language. The current manual check analysis of emergent language is just a preliminary attempt, and more understanding can be promising for future work.", + "bbox": [ + 498, + 454, + 890, + 513 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusions and Discussions", + "text_level": 1, + "bbox": [ + 500, + 527, + 763, + 542 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "This paper aims to build the link between perceptual grounding and symbolic concepts by emergent communication (EC) language for embodied control. To this end, we develop a novel Embodied Control framework with the help of Emergent Communication language $(\\mathrm{EC}^2)$ , which pre-trains a language model via masked trajectory complement pretext task condition on emergent language or natural language. The pre-trained language model is utilized to extract embodied representation from instructions and observations and is used as a frozen module for downstream data-efficient policy learning. Extensive experiments show that $\\mathbf{E}\\mathbf{C}^{2}$ outperforms existing methods in Metaworld and Franka kitchen benchmarks. We believe that $\\mathrm{EC^2}$ will serve as a solid step toward the general decision-making model. Limitations and future works: more understanding about emergent language, training $\\mathrm{EC}^2$ on a larger and more diverse dataset, and applications on more practical setup can be promising directions of future works.", + "bbox": [ + 496, + 551, + 890, + 824 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgement. Ping Luo is partially supported by the National Key R&D Program of China No.2022ZD0161000 and the General Research Fund of HK No.17200622. Shunyu Yao was supported in part by the National Science Foundation under Grant No. 2107048.", + "bbox": [ + 496, + 825, + 890, + 898 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "6711", + "bbox": [ + 482, + 944, + 513, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Muhammad Alomari, Paul Duckworth, David Hogg, and Anthony Cohn. Natural language acquisition and grounding for embodied robotic systems. In Proceedings of the AAAI Conference on Artificial Intelligence, volume 31, 2017. 2", + "[2] Brenna D Argall, Sonia Chernova, Manuela Veloso, and Brett Browning. A survey of robot learning from demonstration. Robotics and autonomous systems, 57(5):469-483, 2009. 3", + "[3] Michelle E Barton. Input and interaction in language acquisition. 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International Conference on Learning Representations (ICLR), 2020. 3" + ], + "bbox": [ + 78, + 92, + 467, + 345 + ], + "page_idx": 10 + }, + { + "type": "page_number", + "text": "6714", + "bbox": [ + 482, + 945, + 514, + 955 + ], + "page_idx": 10 + } +] \ No newline at end of file diff --git a/2023/EC2_ Emergent Communication for Embodied Control/1439d777-9b35-45c1-8de3-484abb88a29b_model.json b/2023/EC2_ Emergent Communication for Embodied Control/1439d777-9b35-45c1-8de3-484abb88a29b_model.json new file mode 100644 index 0000000000000000000000000000000000000000..dbec285e4385cd6a8165ca94d6ae747aa70da835 --- /dev/null +++ b/2023/EC2_ Emergent Communication for Embodied Control/1439d777-9b35-45c1-8de3-484abb88a29b_model.json @@ -0,0 +1,2455 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.205, + 0.131, + 0.766, + 0.154 + ], + "angle": 0, + "content": "\\(\\mathbf{EC}^2\\) : Emergent Communication for Embodied Control" + }, + { + "type": "text", + "bbox": [ + 0.089, + 0.18, + 0.882, + 0.236 + ], + "angle": 0, + "content": "Yao Mu\\(^{1}\\), Shunyu Yao\\(^{2}\\), Mingyu Ding\\(^{1}\\), Ping Luo\\(^{1}\\), Chuang Gan\\(^{3,4}\\) \n\\(^{1}\\)The University of Hong Kong \\(^{2}\\)Princeton University \\(^{3}\\)UMass Amherst, \\(^{4}\\)MIT-IBM Watson AI Lab ymu, myding, pluo@cs.hku.hk shunyuy@princeton.edu ganchuang@csail.mit.edu" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.269, + 0.314, + 0.285 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.301, + 0.474, + 0.755 + ], + "angle": 0, + "content": "Embodied control requires agents to leverage multimodal pre-training to quickly learn how to act in new environments, where video demonstrations contain visual and motion details needed for low-level perception and control, and language instructions support generalization with abstract, symbolic structures. While recent approaches apply contrastive learning to force alignment between the two modalities, we hypothesize better modeling their complementary differences can lead to more holistic representations for downstream adaption. To this end, we propose Emergent Communication for Embodied Control \\((EC^2)\\), a novel scheme to pre-train video-language representations for few-shot embodied control. The key idea is to learn an unsupervised \"language\" of videos via emergent communication, which bridges the semantics of video details and structures of natural language. We learn embodied representations of video trajectories, emergent language, and natural language using a language model, which is then used to finetune a lightweight policy network for downstream control. Through extensive experiments in Metaworld and Franka Kitchen embodied benchmarks, \\(EC^2\\) is shown to consistently outperform previous contrastive learning methods for both videos and texts as task inputs. Further ablations confirm the importance of the emergent language, which is beneficial for both video and language learning, and significantly superior to using pre-trained video captions. We also present a quantitative and qualitative analysis of the emergent language and discuss future directions toward better understanding and leveraging emergent communication in embodied tasks." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.784, + 0.21, + 0.8 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.81, + 0.471, + 0.902 + ], + "angle": 0, + "content": "We study the problem of few-shot embodied control, where an embodied agent needs to execute language instructions or follow video demonstrations given only a few examples in a new environment. Such a capability of fast adaption is key to practical robotic deployment, as it is non- scalable and expensive to collect extensive action-labeled" + }, + { + "type": "image", + "bbox": [ + 0.518, + 0.271, + 0.875, + 0.392 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.577, + 0.398, + 0.816, + 0.41 + ], + "angle": 0, + "content": "(a) Emergent language for embodied control." + }, + { + "type": "image", + "bbox": [ + 0.529, + 0.419, + 0.844, + 0.502 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.515, + 0.503, + 0.874, + 0.516 + ], + "angle": 0, + "content": "(b) Performance comparison on overall success rate across all tasks." + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.521, + 0.895, + 0.674 + ], + "angle": 0, + "content": "Figure 1. Overview of \\(\\mathrm{EC^2}\\). The key idea of \\(\\mathrm{EC^2}\\) is to build the link between perceptual grounding and symbolic concept via emergent communication (EC) language. We learn to extract embodied representation via language model utilizing emergent language or natural language as prompt and visual observation as input for downstream embodied control tasks. The actions are generated by a lightweight policy network containing a few MLP [51] layers that map the learned frozen embodied representation into action space. Extensive experiments show that \\(\\mathrm{EC^2}\\) outperforms existing methods in Metaworld [60] and Franka Kitchen [17] benchmarks." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.689, + 0.894, + 0.764 + ], + "angle": 0, + "content": "trajectories for each new application scenario. Instead, agents need to leverage pre-trained video and language representations to quickly learn how to act, and generalize across high-level concepts (e.g. object and verb types) as well as low-level visual features." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.895, + 0.901 + ], + "angle": 0, + "content": "How can we pre-train multi-modal representations of videos and texts for downstream embodied control in different domains? Inspired by the success of image-text models such as CLIP [47], recent work has investigated contrastive representation learning approaches using paired video-language data, with application toward robotic manipulation and control tasks [24, 38]. However, simply aligning video and language pairs in the embedding space omits the difference between these two modalities: while" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "6704" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.081, + 0.092, + 0.468, + 0.347 + ], + "angle": 0, + "content": "videos contain more visual and motion details, language abstracts away key structures underlying the task. For example, a video of opening a door contains details of approaching the handle, pressing the handle, pulling the door open, and so on, while the corresponding language description could be as simple as \"open a door\" — more detailed language descriptions such as \"press down the handle\" is usually not available in existing datasets and very expensive to manually label. But for downstream control purposes, a video and its abstract language description could present complementary benefits — while the former is expressive in details needed for low-level control, the latter provides the structure for generalization across domains, tasks, and skills. Leveraging such modality differences presents opportunities to better incorporate language and videos for embodied representation learning, marrying their respective benefits rather than forcing them to be aligned." + }, + { + "type": "text", + "bbox": [ + 0.081, + 0.353, + 0.468, + 0.654 + ], + "angle": 0, + "content": "One perspective to view the video-language difference is through the emergence of language [39, 55]: language derives meaning from its use [57]. It is a communication tool humans develop to collaboratively solve embodied tasks, thus abstracting perception experiences like videos into symbolic concepts. Emergent communication in machine learning [9, 26, 28, 30, 56] aims to similarly learn an \"emergent language\" of perception in an unsupervised and domain-adaptive way: as Figure 2(a) shows, a speaker and a listener network play a referential game, where a speaker maps some visual stimuli (e.g. image, video) into a message of discrete tokens, and a listener uses the message to choose the speaker reference out of detractors. By jointly optimizing for game success, the communication protocol emerges structural and semantic properties resembling language, yet its discrete tokens might convey more fine-grained concepts than natural language useful for distinguishing stimuli. Thus, an emergent language can act as a bridge between natural language and videos, featuring a structure similar to the former while preserving the semantics of the latter." + }, + { + "type": "text", + "bbox": [ + 0.081, + 0.66, + 0.468, + 0.9 + ], + "angle": 0, + "content": "Inspired by recent work that links emergent and natural language [58], we propose Emergent Communication for Embodied Control (EC²), a three-phase scheme to learn embodied representations for downstream few-shot control (Figure 1(a-c)). First, we learn an emergent language of demonstration videos without using any language labels, which could potentially capture domain-specific concepts not directly available in paired natural language captions. Second, we learn an embodied representation by using a language model to predict trajectory segments conditional on trajectory contexts and language annotations, both natural and emergent. Rather than forcing video and language representations to be aligned, such a sequence modeling approach learns to represent natural language (for compositional generalization) and emergent language (for low-level perception and control) jointly with video trajectories," + }, + { + "type": "text", + "bbox": [ + 0.504, + 0.092, + 0.891, + 0.151 + ], + "angle": 0, + "content": "where the emergent language serves as a bridge between language and videos. Third, we train a lightweight policy network on top of the embodied representation to few-shot adapt to downstream embodied control." + }, + { + "type": "text", + "bbox": [ + 0.504, + 0.153, + 0.891, + 0.469 + ], + "angle": 0, + "content": "We demonstrate that emergent language can help embodied control tasks and enable data-efficient few-shot downstream imitation learning via extensive experimental results across two existing benchmark simulation environments (Franka-Kitchen [18] and MetaWorld [60]). \\(\\mathrm{EC^2}\\) outperforms existing methods and achieves state-of-the-art performance on both language and video instruction following tasks. Our study also shows that although emergent language and natural language are utilized in a parallel manner in the pre-training phase, the word embeddings of natural language can still be predicted by linear regression models from emergent language. We further investigate the impact of emergent language and natural language correlation on the performance of downstream tasks and show that the performance in downstream tasks is best when the learned EC contains more information than natural language, i.e., when the accuracy of predicting natural language from emergent language is higher than that of predicting emergent language from natural language. Overall, on the basis of these results, we believe that \\(\\mathrm{EC^2}\\) has great potential to become a promising embodied control framework." + }, + { + "type": "text", + "bbox": [ + 0.504, + 0.471, + 0.891, + 0.681 + ], + "angle": 0, + "content": "To sum up, our work makes the following contributions. (1) we build an embodied representation pre-training framework with emergent communication (EC) via a language model, which incorporates both the abstract, compositional structure of language and visuals with low-level motion details. (2) we develop a few-shot embodied control system, which transfers the pre-trained language model to downstream tasks as a frozen module and quickly adapts lightweight policy networks with a few expert data to generate actions. (3) we demonstrate that the learned representation with EC can benefit few-shot embodied control tasks and extensive experiments show that \\(\\mathrm{EC^2}\\) outperforms existing methods in Metaworld [60] and Franka Kitchen [17] benchmarks." + }, + { + "type": "title", + "bbox": [ + 0.504, + 0.7, + 0.64, + 0.715 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "title", + "bbox": [ + 0.504, + 0.726, + 0.738, + 0.741 + ], + "angle": 0, + "content": "2.1. Emergent Communication" + }, + { + "type": "text", + "bbox": [ + 0.504, + 0.75, + 0.891, + 0.9 + ], + "angle": 0, + "content": "The recent advances in NLP [7, 14, 49] benefits from huge text corpora and are striving to find statistical regularities on large amounts of data via big models like GPT [7, 48, 49] and BERT [14]. This narrow focus was leaving aside language emergence and language grounding (in some other modalities, e.g., sight, with more complex inputs than text). In contrast, human language acquisition [13] starts with a cumulative series of interactions with other people [3, 8] grounded in the physical and social world [1, 19, 54] and does not rely on passive and complex corpora like" + }, + { + "type": "page_number", + "bbox": [ + 0.485, + 0.947, + 0.514, + 0.957 + ], + "angle": 0, + "content": "6705" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.139, + 0.098, + 0.574, + 0.337 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.599, + 0.099, + 0.837, + 0.337 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.344, + 0.896, + 0.485 + ], + "angle": 0, + "content": "Figure 2. The overall framework of EC\\(^2\\). Pre-training: (a) We first pre-train a speaker (■) and listener (■) via emergent communication game for emergent language generation and a language model (■) to extract embodied representations. (b) We generate the corresponding emergent language (■) for each demonstration video in the multi-modal dataset. Predicting the cropped part of a latent trajectory is used as an auxiliary task to help pre-training the language model. The language model takes emergent language or natural language as prompt and the cropped trajectory (■) as input and aims to predict the cropped part of the trajectory (■). The loss for the prediction using emergent language as prompt and natural language as prompt is calculated separately. Few-shot downstream policy learning: In downstream imitation learning tasks, both the EC speaker and the pre-trained language model(■) are frozen. The language model extracts effective embodied features with current trajectory (■ contains current state and historical information) as input. (c) For tasks with language instruction, we use natural language as the prompt, and (d) for tasks with video instruction, we use emergent language as the prompt. The output features of the language model are mapped into actions to mimic expert behavior by a few simple MLP [51] layers (■)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.497, + 0.473, + 0.71 + ], + "angle": 0, + "content": "Wikipedia. Emergent Communication (EC) is one promising direction toward this motivation, where a communication protocol is shaped through multi-agent interactions with perceptual grounding like a human [43]. As a typical example, the referential image game involves a speaker creating a sequence of discrete tokens based on an input image, and a listener tasked with selecting the correct input from a group of distractors using the message. Both networks are optimized jointly using success signals from the game [58]. By studying games like this type, researchers are interested in the emergence of desirable properties resembling natural language, such as game success generalization and compositionality, which holds great promises towards more functional [56, 57] and generalizable [27] language agents." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.724, + 0.399, + 0.74 + ], + "angle": 0, + "content": "2.2. Embodied Control under Instruction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.75, + 0.473, + 0.903 + ], + "angle": 0, + "content": "Embodied control has achieved much success in learning grasping and pick-place tasks from low-dimensional state [2,4,10,25,36,42,52]. Deep learning makes embodied control directly learn from high dimensional observations becoming feasible [46,50,61]. Recent advances aim to build a learning-based embodied control system with deep neural networks that are flexibly conditioned on either a demonstration video [5,59] of a human or a language instruction [35, 53] via multi-modal representation learning. With the guidance of instruction, the embodied agent aims to gener" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.497, + 0.895, + 0.769 + ], + "angle": 0, + "content": "alize to new scenes [44], novel objects [5, 16, 22, 59, 62], novel object configurations [40], and novel goal configurations [12, 15, 20]. For instance, BC-Z [24] has developed a flexible imitation learning system that can learn from demonstrations and interventions, based on various forms of task information, such as pre-trained embeddings of natural language or human performance videos. R3M [38] pre-trains visual representations on diverse human videolanguage data by encouraging alignment between the two modalities. However, since videos often convey more detailed information than words, this framework may lose valuable teaching information that can help robots perform complex tasks. In this work, we aim to build an instruction-conditioned embodied control framework without forcing alignment on video and language and consider the video demonstrations and language instructions as \"parallel sentences\" during the pre-training process to learn useful information for downstream tasks." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.784, + 0.593, + 0.801 + ], + "angle": 0, + "content": "3. Method" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.811, + 0.895, + 0.903 + ], + "angle": 0, + "content": "As shown in Figure 2, we first pre-train a speaker and listener via an emergent communication game for emergent language generation and a language model to extract embodied representations by predicting the cropped part of a latent trajectory. The language model takes the emergent language or natural language as prompt and the masked" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.517, + 0.957 + ], + "angle": 0, + "content": "6706" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.213 + ], + "angle": 0, + "content": "trajectory as input and aims to predict the masked part of the trajectory separately. Then, we transfer the learned speaker and language model into downstream embodied control tasks as frozen modules. The output of the language model extracts embodied representation from instruction prompt and current observations and is mapped into actions by the downstream policy network, which contains a few task-specific MLP [51] layers." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.223, + 0.262, + 0.238 + ], + "angle": 0, + "content": "3.1. Problem Statement" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.247, + 0.473, + 0.459 + ], + "angle": 0, + "content": "The goal for embodied control is to learn a policy \\(\\pi_B\\) conditioned on the instruction, either language instruction or video instruction, that reproduces the expert behavior on the desired task specified by the instruction. Usually, the demonstrations of experts are presented in the form of state-action trajectories, with each pair indicating the action to take at the state being visited. Let \\(\\tau_E\\) denote a trajectory sampled from expert policy \\(\\pi_E(s|c)\\): \\(\\tau_E = [(s_0,a_0),(s_1,a_1),\\ldots ,(s_n,a_n)]\\). The instruction is encoded into the latent vector \\(c\\). To learn the behavior policy \\(\\pi_B(s|c)\\), the demonstrated actions are usually utilized as the target label for each state, and the mapping \\(a\\in \\pi_B(s|c)\\) from states to actions is learned in a supervised manner with given instructions." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.469, + 0.47, + 0.499 + ], + "angle": 0, + "content": "3.2. Emergent Communication Language Generation for demonstration video" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.508, + 0.473, + 0.72 + ], + "angle": 0, + "content": "Our idea is to automatically generate synthetic language that aligns with video demonstration through emergent communications, which connect perceptual, language, and action for pre-training. As shown in Figure 2(c), we consider a typical speaker-listener referential game [29, 30, 33] on a set of \\(N\\) video features \\(\\mathcal{D}_I = \\{I_1,\\dots ,I_N\\}\\). At each training step, the speaker takes one video feature \\(I_{i}\\) and generates a discrete message \\(M_{i}\\in [V]^{T}\\) using the Gumbel-Softmax trick [23], where \\(V\\) is the vocabulary size, and \\(T\\) is the sequence length limit. For simplicity, denote \\(m = M_{i}\\) so that \\(m_t = M_{i,t}\\) denotes the \\(t\\)-th token of the message \\(M_{i}\\). The generated discrete message is defined as \"emergent language\", and the process of emergent language generation by the speaker can be formulated as" + }, + { + "type": "equation", + "bbox": [ + 0.113, + 0.732, + 0.451, + 0.748 + ], + "angle": 0, + "content": "\\[\n\\mathbf {h} \\mathbf {s} _ {0} = I _ {i}, \\quad \\mathbf {h} \\mathbf {s} _ {t} = \\mathrm {G P T} _ {\\mathrm {s p k}} (m _ {t - 1}, \\mathbf {h} \\mathbf {s} _ {t - 1}) (t > 0),\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.088, + 0.751, + 0.47, + 0.78 + ], + "angle": 0, + "content": "\\[\nm _ {0} = \\left[ \\mathrm {C L S} \\right], \\quad m _ {t} = \\operatorname {S o f t m a x} \\left(\\mathrm {M L P} _ {\\mathrm {s p k}} \\left(\\mathbf {h s} _ {t}\\right)\\right) (t > 0). \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.781, + 0.472, + 0.902 + ], + "angle": 0, + "content": "Here \\(\\mathbf{h}\\mathbf{s}_t\\) denotes speaker hidden states. Next, the listener takes the message \\(m\\), and tries to guess the right video \\(I_{i}\\) out of a set of \\(K\\) confounding videos \\(C_i = \\{I_{j_1},\\dots ,I_{j_K}\\} \\subset \\mathcal{D}_I - \\{I_i\\}\\). Note that different from the EC games on images, in order to learn temporal information, except for irrelevant videos, we also construct several additional candidates in \\(C_i\\) by performing temporal augmentation on the original video, such as reverse order and random disorder." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.092, + 0.892, + 0.122 + ], + "angle": 0, + "content": "The listener also uses a GRU [11] layer to turn the message \\( m \\) into a hidden vector \\( \\mathbf{h}\\mathbf{l}_T \\)" + }, + { + "type": "equation", + "bbox": [ + 0.527, + 0.133, + 0.892, + 0.15 + ], + "angle": 0, + "content": "\\[\n\\mathbf {h l} _ {0} = \\mathbf {0}, \\quad \\mathbf {h l} _ {t} = \\mathrm {G P T} _ {\\mathrm {l s n}} \\left(m _ {t}, \\mathbf {h l} _ {t - 1}\\right) (t > 0). \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.16, + 0.894, + 0.236 + ], + "angle": 0, + "content": "Based on \\(\\mathbf{h}\\mathbf{l}_T\\), the listener assigns a score for each candidate video based on inverse square error [31], then selects the image by Softmax sampling across the scores. The speaker and listener are jointly optimized by minimizing the cross-entropy loss of video selection:" + }, + { + "type": "equation", + "bbox": [ + 0.508, + 0.246, + 0.892, + 0.315 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\operatorname {s c o r e} (\\mathbf {I}) = \\left\\| \\mathbf {h l} _ {T} - \\operatorname {M L P} _ {\\mathrm {l s n}} (\\mathbf {I}) \\right\\| _ {2} ^ {- 2}, \\\\ p (\\text {g u e s s} = \\mathbf {I}) = \\operatorname {s o f t m a x} (\\operatorname {s c o r e} (\\mathbf {I})) \\quad (\\mathbf {I} \\in \\left\\{\\mathbf {I} _ {i} \\right\\} \\cup C _ {i}), \\\\ \\mathcal {L} _ {E C} = - \\mathbb {E} _ {\\mathbf {I} _ {i}, C _ {i}} \\mathbb {E} _ {\\mathbf {M} _ {i}} \\log p (\\text {g u e s s} = \\mathbf {I} _ {i}). \\tag {3} \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.316, + 0.892, + 0.347 + ], + "angle": 0, + "content": "The speaker can be employed to generate emergent language \\(\\mathcal{D}_M = \\{M_1,\\dots ,M_N\\}\\) based on input videos." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.355, + 0.892, + 0.387 + ], + "angle": 0, + "content": "3.3. Pre-training of Language Model with Emergent Language" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.394, + 0.892, + 0.47 + ], + "angle": 0, + "content": "We conduct a trajectory completion task to pre-train the GPT-like language model without action labels, as shown in Figure 2(a)(b). Firstly, we random sample a sequence of observations \\(\\hat{o} = \\{o_1,o_2,\\dots ,o_N\\}\\) stored in the dataset and map it into latent trajectory \\(\\tau_{\\mathrm{whole}}\\) by encoder \\(g_{\\theta}\\)" + }, + { + "type": "equation", + "bbox": [ + 0.647, + 0.481, + 0.892, + 0.497 + ], + "angle": 0, + "content": "\\[\n\\tau_ {\\text {w h o l e}} = g _ {\\theta} (\\hat {o}) \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.508, + 0.892, + 0.615 + ], + "angle": 0, + "content": "Then we crop a random segment \\(\\tau_{\\mathrm{seg}}\\) from the whole latent trajectory \\(\\tau_{\\mathrm{whole}}\\) and the remained trajectory is denoted as \\(\\tau_{\\mathrm{rem}}\\). The language model \\(f_{\\phi}\\) takes \\(\\tau_{\\mathrm{rem}}\\) as input and uses either emergent language \\(e\\) generated by the speaker or natural language \\(l\\) as a prompt to predict the cropped segment \\(\\tau_{\\mathrm{seg}}\\). The language model is optimized by jointly minimizing \\(L_{\\mathrm{EC}}\\) and \\(L_{\\mathrm{Lang}}\\)" + }, + { + "type": "equation", + "bbox": [ + 0.604, + 0.624, + 0.892, + 0.643 + ], + "angle": 0, + "content": "\\[\nL _ {\\mathrm {E C}} = \\left(\\tau_ {\\mathrm {s e g}} - f _ {\\theta} (e, \\tau_ {\\mathrm {r e m}})\\right) ^ {2} \\tag {5}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.601, + 0.651, + 0.892, + 0.669 + ], + "angle": 0, + "content": "\\[\nL _ {\\text {L a n g}} = \\left(\\tau_ {\\text {s e g}} - f _ {\\theta} (l, \\tau_ {\\text {r e m}})\\right) ^ {2} \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.675, + 0.892, + 0.719 + ], + "angle": 0, + "content": "The loss for the prediction using emergent language as prompt and natural language as prompt is calculated separately." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.892, + 0.901 + ], + "angle": 0, + "content": "\\(\\mathrm{EC^2}\\) uses the same language model for both emergent language generation and trajectory completion pretext task for framework thriftiness, and both the \\(L_{\\mathrm{EC - pre}}\\) and \\(L_{\\mathrm{EC - gen}}\\) are used to update the language model jointly. To ensure that the speaker's gradient is not truncated, we use an MLP [51] layer to map from the logits of the word distribution to a 512-dimensional latent vector instead of selecting a word embedding in the dictionary according to the token. For natural language, we use the Byte-Pair Encoding (BPE) tokenizer [6] to encode it into tokens, which are widely used by OpenAI for tokenization when pre-training the GPT model, including GPT [48], GPT-2 [49], RoBERTa [34]," + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "6707" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.471, + 0.152 + ], + "angle": 0, + "content": "and BART [32]. We also learn a corresponding dictionary of word embedding. Although the emergent language and natural language are used separately, they can learn correlated information via the pretext trajectory completion task." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.163, + 0.47, + 0.192 + ], + "angle": 0, + "content": "3.4. Few-shot Policy Learning for Downstream Embodied control" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.201, + 0.471, + 0.489 + ], + "angle": 0, + "content": "To transfer the pre-trained language model into the downstream imitation learning tasks, the language model \\( f_{\\theta}(\\cdot ,\\cdot) \\) take the current trajectory \\( \\tau_{cur} = \\{s_{t - T},\\dots ,s_{t - 1},s_t\\} \\) and the emergent language \\( e \\) or natural language instruction \\( l \\) as prompt, then output the predicted features \\( m_{t} \\). Finally, the output \\( m_{t} \\) of the language model is mapped to specific action \\( a_{t} \\) by task-specific MLP layers \\( \\pi_{\\psi} \\). The language model \\( f_{\\theta} \\) is frozen during downstream imitation learning. The action under learned behavior policy is sampled by \\( \\hat{a}_t\\sim \\pi_\\psi (a_t|m_t) \\) and the expert demonstration action \\( a_{t} \\) are used as the label for imitation learning. For the video instruction following task, we generate emergent language by the speaker and use it as the prompt of the language model. For language instruction following tasks, the natural language is tokenized by the BPE tokenizer, and select the corresponding word embedding in the dictionary as the prompt as language model via the inferred token. With a trajectory with length \\( H \\), the task-specific MLP layers are optimized by minimizing \\( \\mathcal{L}_{\\mathrm{IL}}(\\psi) \\)." + }, + { + "type": "equation", + "bbox": [ + 0.137, + 0.5, + 0.47, + 0.534 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\mathrm {I L}} (\\psi) = E _ {\\tau \\sim \\mathcal {B}} \\left[ - \\frac {1}{H} \\sum_ {t} ^ {t + H - 1} \\log \\pi_ {\\psi} (a _ {t} | m _ {t}) \\right] \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.536, + 0.47, + 0.596 + ], + "angle": 0, + "content": "The MLP [51] layers are implemented with hidden sizes [256, 256] with batch normalization [21] and are trained with a learning rate of 0.001 and a batch size of 32 for 20000 iterations." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.611, + 0.21, + 0.628 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.636, + 0.271, + 0.652 + ], + "angle": 0, + "content": "4.1. Pre-training Dataset" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.66, + 0.47, + 0.9 + ], + "angle": 0, + "content": "We use the LOReL [37] real robot dataset, which is collected by Franka Emika Panda mounted over an IKEA desk. The LOReL dataset contains 3000 episodes (150000 frames) of reinforcement learning that trains policies for different behaviors on the IKEA desk using online RL. The language instruction is annotated by leveraging crowdsourcing, specifically Amazon Mechanical Turk. Human annotators are asked to describe the behavior if any, that the robot is doing and to phrase it as a command without any pre-specified template. The LOReL dataset contains 6000 annotations, two per episode, containing a total of 1699 unique instructions. The dataset contains different videos with the same language instruction to ensure diversity. We removed the episodes where annotators reported the robot as inactive or its actions unclear, making them incomprehensible." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.092, + 0.807, + 0.107 + ], + "angle": 0, + "content": "4.2. Downstream Testing Environments" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.114, + 0.892, + 0.491 + ], + "angle": 0, + "content": "We utilize two standard robotic manipulation benchmarks, namely MetaWorld [60] and the Franka Kitchen environment [17], as our downstream testing environments. It is worth noting that these testing environments were not used during the training phase of \\(\\mathrm{EC^2}\\). In MetaWorld, the agent is presented with a series of tasks, including assembling a ring on a peg, picking and placing a block between bins, pushing a button, opening a drawer, and hammering a nail. In Franka Kitchen, the agent aims to learn how to slide open the right door, open the left door, turn on the light, turn the stove top knob, and open the microwave. As shown in Figure 3, both environments offer image observations to the agent, as well as proprioceptive data, which includes the end-effector pose and joint positions. These data are concatenated with the encoded vision observations for each task, providing the agent with a comprehensive understanding of the current task. All tasks involve random environment variation, either by varying the position of the target object in MetaWorld or the positioning of the desk in Franka Kitchen. Additionally, we consider three views for each environment to evaluate the robustness of representations across viewpoints. Finally, for each environment, we also consider three demo sizes used in downstream embodied control tasks: [5, 10, 25] in MetaWorld and Franka Kitchen." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.5, + 0.691, + 0.517 + ], + "angle": 0, + "content": "4.3. Experimental Setup" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.524, + 0.892, + 0.903 + ], + "angle": 0, + "content": "For embodied control tasks, we take R3M and BC-Z as the key baseline. R3M [38] learns the state-of-the-art embodied representations pre-trained on diverse paired human video-language data with time-contrastive learning, which encourages states closer in time to be closer in embedding space and video-language alignment to encourage the embeddings to capture semantically relevant features. For sufficient comparison, we implement R3M with both the language instruction-conditioned version and video instruction-conditioned version, respectively, based on their official implementation. For embodied control with natural language instruction, we use the language encoder of the pre-trained model officially released by their author team to encode the natural language. For embodied control with demonstration video instruction, we use the officially released vision encoder to extract features of every frame in the video and map them into the instruction representation by one MLP layer. BC-Z [24] jointly learns the alignment between video representation and language representation together with policy learning across multiple embodied control tasks. Our evaluation methodology is inspired by [38, 41]. We focus on evaluating the embodied representation of instruction and observation for downstream policy learning with behavior cloning. We parameterize the downstream policy \\(\\pi\\) as a two-layer MLP preceded by a" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.946, + 0.516, + 0.957 + ], + "angle": 0, + "content": "6708" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.126, + 0.101, + 0.302, + 0.26 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.305, + 0.102, + 0.396, + 0.167 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.31, + 0.17, + 0.381, + 0.188 + ], + "angle": 0, + "content": "Slid the door of the drawer" + }, + { + "type": "image", + "bbox": [ + 0.414, + 0.102, + 0.505, + 0.168 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.422, + 0.17, + 0.497, + 0.179 + ], + "angle": 0, + "content": "Turn the light on" + }, + { + "type": "image", + "bbox": [ + 0.525, + 0.102, + 0.614, + 0.168 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.535, + 0.17, + 0.602, + 0.188 + ], + "angle": 0, + "content": "Open the door of the drawer." + }, + { + "type": "image", + "bbox": [ + 0.631, + 0.102, + 0.72, + 0.168 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.64, + 0.17, + 0.716, + 0.188 + ], + "angle": 0, + "content": "Turn the knob on the up left" + }, + { + "type": "image", + "bbox": [ + 0.739, + 0.102, + 0.828, + 0.168 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.743, + 0.17, + 0.821, + 0.188 + ], + "angle": 0, + "content": "Open the door of the Microwave" + }, + { + "type": "image_caption", + "bbox": [ + 0.129, + 0.286, + 0.273, + 0.298 + ], + "angle": 0, + "content": "Multi-view Testing" + }, + { + "type": "image", + "bbox": [ + 0.304, + 0.194, + 0.395, + 0.26 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.306, + 0.265, + 0.392, + 0.283 + ], + "angle": 0, + "content": "Pick up the nut and place it on the nail." + }, + { + "type": "image", + "bbox": [ + 0.416, + 0.194, + 0.506, + 0.26 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.397, + 0.265, + 0.622, + 0.283 + ], + "angle": 0, + "content": "Grab the ball from the blue Press the button down bin and put it in the red one" + }, + { + "type": "image", + "bbox": [ + 0.527, + 0.194, + 0.615, + 0.26 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.631, + 0.194, + 0.723, + 0.26 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.645, + 0.265, + 0.72, + 0.275 + ], + "angle": 0, + "content": "Open the drawer" + }, + { + "type": "image", + "bbox": [ + 0.74, + 0.194, + 0.832, + 0.26 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.74, + 0.265, + 0.835, + 0.283 + ], + "angle": 0, + "content": "Pick up the hammer and hammer the wall" + }, + { + "type": "image_caption", + "bbox": [ + 0.497, + 0.287, + 0.638, + 0.298 + ], + "angle": 0, + "content": "Tasks with Language Instruction" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.301, + 0.894, + 0.358 + ], + "angle": 0, + "content": "Figure 3. Evaluation Environments: We consider a set of manipulation tasks including 5 tasks with a Sawyer from MetaWorld [60], 5 tasks from a Franka operating over a Kitchen [17]. We provide specific language instruction labels for every task and 25 demos per task for evaluation. We show an example image and corresponding language instruction for each task shown above. Evaluation Viewpoints: To robustly measure the efficacy of different visual representations, we consider three camera viewpoints per environment." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.365, + 0.892, + 0.508 + ], + "angle": 0, + "content": "
BenchmarkNum. DemosInstructionEC2(ours)R3M [38]BC-Z [24]
MetaWorld10Lang72.4 ± 2.4%69.2 ± 2.0%63.4 ± 2.1%
Video76.0 ± 2.1% (+3.6)71.8 ± 1.8% (+2.6)64.8 ± 2.0% (+1.4)
25Lang82.6 ± 2.0%77.4 ± 2.4%74.1 ± 2.2%
Video85.0 ± 2.2% (+2.4)79.0 ± 2.1% (+1.6)75.2 ± 1.0% (+1.1)
Franka Kitchen10Lang48.4 ± 2.5%41.8 ± 2.5%34.2 ± 2.3%
Video53.6 ± 2.5%(+5.2)45.7 ± 2.4% (+3.9)37.5 ± 2.2% (+3.3)
25Lang59.8 ± 2.5%56.0 ± 2.3%38.6 ± 2.4%
Video63.2 ± 2.6% (+3.4)58.7 ± 2.0% (+2.7)40.0 ± 2.0% (+1.4)
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.511, + 0.893, + 0.54 + ], + "angle": 0, + "content": "Table 1. Performance comparison on Success rate of embodied control with language/video instruction across different demo size. We mark the performance difference between complete the task with natural language instruction and video instruction as blue." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.547, + 0.47, + 0.653 + ], + "angle": 0, + "content": "BatchNorm at the input. We train the agent for 20,000 steps, evaluate it online in the environment every 1000 steps, and report the best success rate achieved. For each task, we run 5 seeds of behavior cloning. The final success rate reported for one method on one task is the average over the 5 seeds \\(\\times 3\\) camera viewpoints \\(\\times 3\\) demo sizes, for a total of 45 runs (see more details in Appendix)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.665, + 0.17, + 0.68 + ], + "angle": 0, + "content": "4.4. Results" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.689, + 0.47, + 0.854 + ], + "angle": 0, + "content": "We aim to answer 5 questions to get insight into embodied AI community: 1) Can emergent language help embodied control tasks with natural language instruction? 2) Can emergent language help the embodied control tasks with video instruction? 3) Can the joint training of emergent language and natural language in GPT-Like network architecture help each other? 4) Can emergent language provide more detailed and effective guidelines than video captions? 5) What is the relationship between model size, control performance, and the correlation between emergent language and natural language?" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.47, + 0.901 + ], + "angle": 0, + "content": "To answer the first two questions, we study if \\(\\mathrm{EC^2}\\) enables more data-efficient policy learning with both natural language instructions and video instructions." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.548, + 0.893, + 0.578 + ], + "angle": 0, + "content": "1) Can emergent language help the embodied control tasks with natural language?" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.584, + 0.893, + 0.9 + ], + "angle": 0, + "content": "We measure the success rate of downstream few-shot policy learning with different pre-training methods. In Franka Kitchen and MetaWorld, we only use no more than 25 demos to perform downstream few-shot policy learning and report the performance with both 10 and 25 demos separately in Table 1. Learning from scratch is struggled to perform well when working with small amounts of data since it can be challenging for the model to identify meaningful patterns or relationships with such limited data. While the methods with a pre-trained model, like \\(\\mathrm{EC}^2\\), R3M, and BC-Z performs better than those learning from scratch. Through our study, as shown in Table 1, \\(\\mathrm{EC}^2\\) exceeds existing methods with natural language instruction, which indicates that emergent language can help the embodied control tasks to improve the performance with natural language instruction. Across all the evaluations, \\(\\mathrm{EC}^2\\) is overall able to learn these embodied tasks in an extremely low data regime (only 10 demos) with \\(\\approx 60.4\\%\\) overall success rate, despite never seeing any data from the target environments in training the representation, while R3M only achieves \\(\\approx 55.5\\%\\) overall success rate." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "6709" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.082, + 0.09, + 0.894, + 0.188 + ], + "angle": 0, + "content": "
BenchmarkNum. DemosLanguage InstructionVideo Instruction
\\( EC^2 \\)\\( EC^2 (-EC) \\)\\( EC^2 \\)\\( EC^2 (-NL) \\)\\( EC^2 (+Cap,-EC) \\)
MetaWorld1072.4 ± 2.4%69.0 ± 2.0%76.0 ± 2.1%72.6 ± 2.4%73.0 ± 2.2%
2582.6 ± 2.0%78.0 ± 2.4%85.0 ± 2.5%82.0 ± 2.0%73.2 ± 2.5%
Franka Kitchen1048.4 ± 2.5%43.0 ± 3.3%53.6 ± 2.5%49.0 ± 2.5%48.6 ± 2.4%
2559.8 ± 2.5%54.0 ± 2.6%63.2 ± 2.6%61.3 ± 2.4%49.0 ± 2.3%
" + }, + { + "type": "table_caption", + "bbox": [ + 0.208, + 0.194, + 0.761, + 0.208 + ], + "angle": 0, + "content": "Table 2. Ablation study on embodied control with language instruction and video instruction." + }, + { + "type": "table", + "bbox": [ + 0.09, + 0.216, + 0.326, + 0.285 + ], + "angle": 0, + "content": "
Model Size#layer#head#embedded
Base816512
Mini66192
Micro44128
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.295, + 0.328, + 0.35 + ], + "angle": 0, + "content": "Table 3. Hyper-parameters for different model sizes of \\( {\\mathrm{{EC}}}^{2} \\) . All the models are implemented based on GPT [48]-like network architecture." + }, + { + "type": "table", + "bbox": [ + 0.336, + 0.217, + 0.889, + 0.32 + ], + "angle": 0, + "content": "
Natural LanguageEmergent language
“Open the right drawer”[262, 847, 490, 536, 108, 500, 941, 838, 749, 444]
“Grasp in the middle drawer”[356, 69, 108, 259, 72, 616, 500, 896, 623, 433]
“Reach down for stapler”[204, 897, 285, 509, 701, 545, 538, 729, 902, 195]
“Pick up the stapler in the drawer”[535, 67, 108, 661, 84, 701, 776, 500, 377, 454]
“Reach to the plug”[982, 691, 72, 538, 97, 665, 148, 369, 102, 1003]
“Reach to the left drawer”[786, 538, 601, 874, 848, 500, 315, 108, 72, 914]
" + }, + { + "type": "table_caption", + "bbox": [ + 0.332, + 0.322, + 0.888, + 0.351 + ], + "angle": 0, + "content": "Table 4. Qualitative examples of emergent language and corresponding natural language. The word and tokens that have the same semantic meaning are marked with the same color." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.358, + 0.47, + 0.388 + ], + "angle": 0, + "content": "2) Can emergent language help the embodied control tasks with video instruction?" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.391, + 0.47, + 0.557 + ], + "angle": 0, + "content": "As shown in Table1, \\(\\mathrm{EC^2}\\) shows an obvious advantage over the exciting methods and achieves the best success rate (\\(\\approx 64.8\\%\\) with 10 demos and \\(\\approx 74.1\\%\\) with 25 demos) with video instruction. As marked in blue in Table 1, \\(\\mathrm{EC^2}\\) has better performance with video instruction than with language instruction, which indicates that \\(\\mathrm{EC^2}\\) learns more effective information provided by a video demonstration. In contrast, R3M and BC-Z, which use contrast learning or regression to force the two modalities of language and video aligned, have little difference in performance under language instruction and video instruction." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.56, + 0.47, + 0.651 + ], + "angle": 0, + "content": "We also investigate the task performance of \\(\\mathrm{EC^2}\\) and baselines with different amounts of demos in policy learning. In Figure 4, we plot the average success rate of each method across each demo size. We observe that the performance improvement from \\(\\mathrm{EC^2}\\) is consistent, outperforming the baselines across every environment and demo size." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.654, + 0.47, + 0.715 + ], + "angle": 0, + "content": "Ablation Study: Also, in the data-efficient imitation learning setting, we ablate the different components of \\(\\mathrm{EC^2}\\) training to answer question 3 and 4 and check if each module is indispensable." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.717, + 0.469, + 0.748 + ], + "angle": 0, + "content": "3) Can the joint training of emergent language and natural language with GPT-Like network help each other?" + }, + { + "type": "list", + "bbox": [ + 0.076, + 0.358, + 0.47, + 0.748 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.75, + 0.471, + 0.902 + ], + "angle": 0, + "content": "We conduct ablation studies to compare \\(\\mathrm{EC}^2\\) and \\(\\mathrm{EC}^2\\) (-EC) in language instruction following tasks and compare \\(\\mathrm{EC}^2\\) and \\(\\mathrm{EC}^2\\) (-NL) in video instruction following tasks. \\(\\mathrm{EC}^2\\) (-EC) does not use emergent language to pre-train the language model under \\(\\mathrm{EC}^2\\) framework, which predicts the masked trajectories with only the language instruction (human-labeled caption). \\(\\mathrm{EC}^2\\) (-NL) does not use natural language to pre-train the language model under \\(\\mathrm{EC}^2\\) framework, which predicts the masked trajectories with only the emergent language. As shown in the left-hand column in" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.358, + 0.892, + 0.509 + ], + "angle": 0, + "content": "Table 2, without the help of emergent language, the performance decreased significantly, and \\(\\mathrm{EC^2}\\) (-EC) shows no obvious advantages to the other methods that learn pretrained models by video-language pre-training. Similarly, as shown in the right-hand column in Table 2, \\(\\mathrm{EC^2}\\) also outperforms \\(\\mathrm{EC^2}\\) (-NL), which demonstrates that the language pre-training helps the video instruction task with emergent language. Thus, the above ablation analysis shows that the joint training of emergent language and natural language can benefit each other." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.513, + 0.892, + 0.544 + ], + "angle": 0, + "content": "4) Can emergent language provide more detailed and effective guidelines than video captions?" + }, + { + "type": "list", + "bbox": [ + 0.498, + 0.358, + 0.892, + 0.544 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.546, + 0.892, + 0.652 + ], + "angle": 0, + "content": "In \\(\\mathrm{EC^2}\\) (+Cap, -EC), we replace the emergent language in \\(\\mathrm{EC^2}\\) with the language caption given by a MARN [45] as a data augmentation, which is a pre-trained video caption model. As shown in Table 2, \\(\\mathrm{EC^2}\\) shows an obvious advantage to \\(\\mathrm{EC^2}\\) (+Cap, -NL), which demonstrates that emergent language provides more detailed and effective guidelines than video captions." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.656, + 0.892, + 0.701 + ], + "angle": 0, + "content": "5) What is the relationship between model size, control performance, and the correlation between emergent language and natural language?" + }, + { + "type": "list", + "bbox": [ + 0.498, + 0.546, + 0.892, + 0.701 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.704, + 0.893, + 0.901 + ], + "angle": 0, + "content": "We first tested the overall average success rate of \\(\\mathrm{EC^2}\\) with different model sizes (listed in Table 3) in the downstream tasks (Franka Kitchen and MetaWorld). As shown in Figure 5a and Figure 5b, the larger the size of the model, the more expressive it is and thus the better its performance. Then, we perform a linear correlation analysis on the word embeddings of the emergent language and the word embeddings of the matched natural language. We use the square of the coefficient of determination, denoted \\(R^2\\) as the measure of predicting the performance of linear regression, which reflects the proportion of the variation in the dependent variable that is predictable from the independent variable. Consider a linear regression model \\(f(\\cdot)\\) which predicts \\(y\\) with" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "6710" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.081, + 0.101, + 0.264, + 0.207 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.082, + 0.209, + 0.278, + 0.221 + ], + "angle": 0, + "content": "(a) MetaWorld[language instruction]" + }, + { + "type": "image", + "bbox": [ + 0.284, + 0.101, + 0.468, + 0.207 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.294, + 0.209, + 0.471, + 0.221 + ], + "angle": 0, + "content": "(b) Kitchen[language instruction]" + }, + { + "type": "image", + "bbox": [ + 0.484, + 0.101, + 0.668, + 0.207 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.209, + 0.672, + 0.221 + ], + "angle": 0, + "content": "(c) MetaWorld[video instruction]" + }, + { + "type": "image", + "bbox": [ + 0.69, + 0.102, + 0.87, + 0.207 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.709, + 0.209, + 0.865, + 0.221 + ], + "angle": 0, + "content": "(d) Kitchen[video instruction]" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.223, + 0.892, + 0.25 + ], + "angle": 0, + "content": "Figure 4. Performance over different demo sizes used in downstream imitation learning. We report the success rate of \\(\\mathrm{EC^2}\\) and baseline across different demo sizes. We see that the performance improvement from \\(\\mathrm{EC^2}\\) is consistent across all demo sizes." + }, + { + "type": "image", + "bbox": [ + 0.083, + 0.263, + 0.327, + 0.397 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.106, + 0.402, + 0.324, + 0.414 + ], + "angle": 0, + "content": "(a) Ablation on model size in MetaWorld" + }, + { + "type": "image", + "bbox": [ + 0.354, + 0.263, + 0.599, + 0.396 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.365, + 0.402, + 0.605, + 0.413 + ], + "angle": 0, + "content": "(b) Ablation on model size in Franka Kitchen" + }, + { + "type": "image", + "bbox": [ + 0.622, + 0.263, + 0.868, + 0.396 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.627, + 0.402, + 0.886, + 0.413 + ], + "angle": 0, + "content": "(c) Translation score across different model sizes" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.419, + 0.892, + 0.447 + ], + "angle": 0, + "content": "Figure 5. Ablation on model size and its relationship with the correlation of emergent language and Natural language. We show the ablation results on model size with 10 demos and 25 demos in downstream policy learning separately." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.455, + 0.468, + 0.469 + ], + "angle": 0, + "content": "the input \\( x \\), the coefficient of determination \\( R \\) is defined as" + }, + { + "type": "equation", + "bbox": [ + 0.13, + 0.479, + 0.469, + 0.514 + ], + "angle": 0, + "content": "\\[\nR ^ {2} = 1 - \\frac {S S _ {r e s}}{S S _ {t o t}} = 1 - \\frac {\\sum_ {i} \\left(y _ {i} - f \\left(x _ {i}\\right)\\right) ^ {2}}{\\sum_ {i} \\left(y _ {i} - \\bar {y}\\right) ^ {2}} \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.524, + 0.47, + 0.902 + ], + "angle": 0, + "content": "We evaluate the \\(R^2\\) values of two linear regressions. One predicts natural language word embeddings from emergent language, and the other predicts emergent language word embeddings from natural language. As shown in Figure 5c, the \\(R^2\\) of predicting natural language embeddings from the emergent language increase along with the model becoming larger, which corresponds to better performance. In contrast, the \\(R^2\\) of predicting emergent language embeddings from the natural language is non-monotonous, along with the model size becoming larger. The reason is that emergent language captures more information that natural language does not contain when the model is large enough and has promising performance. In short, \\(\\mathrm{EC}^2\\) has the best performance in embodied control tasks when emergent language contains more information than natural language, the performance is median when emergent language and language information are nearly equal, and the performance is worst when emergent language contains less information than language information. As shown in Table 4, we also provide qualitative examples of emergent language and its corresponding natural language to show that emergent language can capture key concepts from video. We find that the tokens \"108\" and \"500\" correspond to \"drawer\" in natural language and token \"701\" corresponds to \"stapler.\" Except for nouns, emergent language can also get the con" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.455, + 0.892, + 0.515 + ], + "angle": 0, + "content": "cept of verbs, for example, token “538” corresponds to the verb “reach” in natural language. The current manual check analysis of emergent language is just a preliminary attempt, and more understanding can be promising for future work." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.529, + 0.764, + 0.544 + ], + "angle": 0, + "content": "5. Conclusions and Discussions" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.553, + 0.892, + 0.825 + ], + "angle": 0, + "content": "This paper aims to build the link between perceptual grounding and symbolic concepts by emergent communication (EC) language for embodied control. To this end, we develop a novel Embodied Control framework with the help of Emergent Communication language \\((\\mathrm{EC}^2)\\), which pre-trains a language model via masked trajectory complement pretext task condition on emergent language or natural language. The pre-trained language model is utilized to extract embodied representation from instructions and observations and is used as a frozen module for downstream data-efficient policy learning. Extensive experiments show that \\(\\mathbf{E}\\mathbf{C}^{2}\\) outperforms existing methods in Metaworld and Franka kitchen benchmarks. We believe that \\(\\mathrm{EC^2}\\) will serve as a solid step toward the general decision-making model. Limitations and future works: more understanding about emergent language, training \\(\\mathrm{EC}^2\\) on a larger and more diverse dataset, and applications on more practical setup can be promising directions of future works." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.826, + 0.892, + 0.9 + ], + "angle": 0, + "content": "Acknowledgement. Ping Luo is partially supported by the National Key R&D Program of China No.2022ZD0161000 and the General Research Fund of HK No.17200622. Shunyu Yao was supported in part by the National Science Foundation under Grant No. 2107048." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.514, + 0.957 + ], + "angle": 0, + "content": "6711" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.116, + 0.47, + 0.171 + ], + "angle": 0, + "content": "[1] Muhammad Alomari, Paul Duckworth, David Hogg, and Anthony Cohn. Natural language acquisition and grounding for embodied robotic systems. In Proceedings of the AAAI Conference on Artificial Intelligence, volume 31, 2017. 2" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.173, + 0.472, + 0.227 + ], + "angle": 0, + "content": "[2] Brenna D Argall, Sonia Chernova, Manuela Veloso, and Brett Browning. A survey of robot learning from demonstration. 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While recent approaches apply contrastive learning to force alignment between the two modalities, we hypothesize better modeling their complementary differences can lead to more holistic representations for downstream adaption. To this end, we propose Emergent Communication for Embodied Control $(EC^2)$ , a novel scheme to pre-train video-language representations for few-shot embodied control. The key idea is to learn an unsupervised "language" of videos via emergent communication, which bridges the semantics of video details and structures of natural language. We learn embodied representations of video trajectories, emergent language, and natural language using a language model, which is then used to finetune a lightweight policy network for downstream control. Through extensive experiments in Metaworld and Franka Kitchen embodied benchmarks, $EC^2$ is shown to consistently outperform previous contrastive learning methods for both videos and texts as task inputs. Further ablations confirm the importance of the emergent language, which is beneficial for both video and language learning, and significantly superior to using pre-trained video captions. We also present a quantitative and qualitative analysis of the emergent language and discuss future directions toward better understanding and leveraging emergent communication in embodied tasks. + +# 1. Introduction + +We study the problem of few-shot embodied control, where an embodied agent needs to execute language instructions or follow video demonstrations given only a few examples in a new environment. Such a capability of fast adaption is key to practical robotic deployment, as it is non- scalable and expensive to collect extensive action-labeled + +![](images/833a326db3f0d71a85550006fbbbb23324e740bab3fb6fe16521dc2884579f3b.jpg) +(a) Emergent language for embodied control. + +![](images/574794532ecb74b280941005535ccbfebfa31148d70635773ddfebb47fd93c45.jpg) +(b) Performance comparison on overall success rate across all tasks. +Figure 1. Overview of $\mathrm{EC^2}$ . The key idea of $\mathrm{EC^2}$ is to build the link between perceptual grounding and symbolic concept via emergent communication (EC) language. We learn to extract embodied representation via language model utilizing emergent language or natural language as prompt and visual observation as input for downstream embodied control tasks. The actions are generated by a lightweight policy network containing a few MLP [51] layers that map the learned frozen embodied representation into action space. Extensive experiments show that $\mathrm{EC^2}$ outperforms existing methods in Metaworld [60] and Franka Kitchen [17] benchmarks. + +trajectories for each new application scenario. Instead, agents need to leverage pre-trained video and language representations to quickly learn how to act, and generalize across high-level concepts (e.g. object and verb types) as well as low-level visual features. + +How can we pre-train multi-modal representations of videos and texts for downstream embodied control in different domains? Inspired by the success of image-text models such as CLIP [47], recent work has investigated contrastive representation learning approaches using paired video-language data, with application toward robotic manipulation and control tasks [24, 38]. However, simply aligning video and language pairs in the embedding space omits the difference between these two modalities: while + +videos contain more visual and motion details, language abstracts away key structures underlying the task. For example, a video of opening a door contains details of approaching the handle, pressing the handle, pulling the door open, and so on, while the corresponding language description could be as simple as "open a door" — more detailed language descriptions such as "press down the handle" is usually not available in existing datasets and very expensive to manually label. But for downstream control purposes, a video and its abstract language description could present complementary benefits — while the former is expressive in details needed for low-level control, the latter provides the structure for generalization across domains, tasks, and skills. Leveraging such modality differences presents opportunities to better incorporate language and videos for embodied representation learning, marrying their respective benefits rather than forcing them to be aligned. + +One perspective to view the video-language difference is through the emergence of language [39, 55]: language derives meaning from its use [57]. It is a communication tool humans develop to collaboratively solve embodied tasks, thus abstracting perception experiences like videos into symbolic concepts. Emergent communication in machine learning [9, 26, 28, 30, 56] aims to similarly learn an "emergent language" of perception in an unsupervised and domain-adaptive way: as Figure 2(a) shows, a speaker and a listener network play a referential game, where a speaker maps some visual stimuli (e.g. image, video) into a message of discrete tokens, and a listener uses the message to choose the speaker reference out of detractors. By jointly optimizing for game success, the communication protocol emerges structural and semantic properties resembling language, yet its discrete tokens might convey more fine-grained concepts than natural language useful for distinguishing stimuli. Thus, an emergent language can act as a bridge between natural language and videos, featuring a structure similar to the former while preserving the semantics of the latter. + +Inspired by recent work that links emergent and natural language [58], we propose Emergent Communication for Embodied Control (EC²), a three-phase scheme to learn embodied representations for downstream few-shot control (Figure 1(a-c)). First, we learn an emergent language of demonstration videos without using any language labels, which could potentially capture domain-specific concepts not directly available in paired natural language captions. Second, we learn an embodied representation by using a language model to predict trajectory segments conditional on trajectory contexts and language annotations, both natural and emergent. Rather than forcing video and language representations to be aligned, such a sequence modeling approach learns to represent natural language (for compositional generalization) and emergent language (for low-level perception and control) jointly with video trajectories, + +where the emergent language serves as a bridge between language and videos. Third, we train a lightweight policy network on top of the embodied representation to few-shot adapt to downstream embodied control. + +We demonstrate that emergent language can help embodied control tasks and enable data-efficient few-shot downstream imitation learning via extensive experimental results across two existing benchmark simulation environments (Franka-Kitchen [18] and MetaWorld [60]). $\mathrm{EC^2}$ outperforms existing methods and achieves state-of-the-art performance on both language and video instruction following tasks. Our study also shows that although emergent language and natural language are utilized in a parallel manner in the pre-training phase, the word embeddings of natural language can still be predicted by linear regression models from emergent language. We further investigate the impact of emergent language and natural language correlation on the performance of downstream tasks and show that the performance in downstream tasks is best when the learned EC contains more information than natural language, i.e., when the accuracy of predicting natural language from emergent language is higher than that of predicting emergent language from natural language. Overall, on the basis of these results, we believe that $\mathrm{EC^2}$ has great potential to become a promising embodied control framework. + +To sum up, our work makes the following contributions. (1) we build an embodied representation pre-training framework with emergent communication (EC) via a language model, which incorporates both the abstract, compositional structure of language and visuals with low-level motion details. (2) we develop a few-shot embodied control system, which transfers the pre-trained language model to downstream tasks as a frozen module and quickly adapts lightweight policy networks with a few expert data to generate actions. (3) we demonstrate that the learned representation with EC can benefit few-shot embodied control tasks and extensive experiments show that $\mathrm{EC^2}$ outperforms existing methods in Metaworld [60] and Franka Kitchen [17] benchmarks. + +# 2. Related Work + +# 2.1. Emergent Communication + +The recent advances in NLP [7, 14, 49] benefits from huge text corpora and are striving to find statistical regularities on large amounts of data via big models like GPT [7, 48, 49] and BERT [14]. This narrow focus was leaving aside language emergence and language grounding (in some other modalities, e.g., sight, with more complex inputs than text). In contrast, human language acquisition [13] starts with a cumulative series of interactions with other people [3, 8] grounded in the physical and social world [1, 19, 54] and does not rely on passive and complex corpora like + +![](images/1c5139b02854949144f8f98fbba53220417dbfb0556bdc7986ede25e32e4d75e.jpg) +Figure 2. The overall framework of EC $^2$ . Pre-training: (a) We first pre-train a speaker (■) and listener (■) via emergent communication game for emergent language generation and a language model (■) to extract embodied representations. (b) We generate the corresponding emergent language (■) for each demonstration video in the multi-modal dataset. Predicting the cropped part of a latent trajectory is used as an auxiliary task to help pre-training the language model. The language model takes emergent language or natural language as prompt and the cropped trajectory (■) as input and aims to predict the cropped part of the trajectory (■). The loss for the prediction using emergent language as prompt and natural language as prompt is calculated separately. Few-shot downstream policy learning: In downstream imitation learning tasks, both the EC speaker and the pre-trained language model(■) are frozen. The language model extracts effective embodied features with current trajectory (■ contains current state and historical information) as input. (c) For tasks with language instruction, we use natural language as the prompt, and (d) for tasks with video instruction, we use emergent language as the prompt. The output features of the language model are mapped into actions to mimic expert behavior by a few simple MLP [51] layers (■). + +![](images/17289e83919e72239682c7e05010941e5c48f94e189a909f03ac4351b47576d9.jpg) + +Wikipedia. Emergent Communication (EC) is one promising direction toward this motivation, where a communication protocol is shaped through multi-agent interactions with perceptual grounding like a human [43]. As a typical example, the referential image game involves a speaker creating a sequence of discrete tokens based on an input image, and a listener tasked with selecting the correct input from a group of distractors using the message. Both networks are optimized jointly using success signals from the game [58]. By studying games like this type, researchers are interested in the emergence of desirable properties resembling natural language, such as game success generalization and compositionality, which holds great promises towards more functional [56, 57] and generalizable [27] language agents. + +# 2.2. Embodied Control under Instruction + +Embodied control has achieved much success in learning grasping and pick-place tasks from low-dimensional state [2,4,10,25,36,42,52]. Deep learning makes embodied control directly learn from high dimensional observations becoming feasible [46,50,61]. Recent advances aim to build a learning-based embodied control system with deep neural networks that are flexibly conditioned on either a demonstration video [5,59] of a human or a language instruction [35, 53] via multi-modal representation learning. With the guidance of instruction, the embodied agent aims to gener + +alize to new scenes [44], novel objects [5, 16, 22, 59, 62], novel object configurations [40], and novel goal configurations [12, 15, 20]. For instance, BC-Z [24] has developed a flexible imitation learning system that can learn from demonstrations and interventions, based on various forms of task information, such as pre-trained embeddings of natural language or human performance videos. R3M [38] pre-trains visual representations on diverse human videolanguage data by encouraging alignment between the two modalities. However, since videos often convey more detailed information than words, this framework may lose valuable teaching information that can help robots perform complex tasks. In this work, we aim to build an instruction-conditioned embodied control framework without forcing alignment on video and language and consider the video demonstrations and language instructions as "parallel sentences" during the pre-training process to learn useful information for downstream tasks. + +# 3. Method + +As shown in Figure 2, we first pre-train a speaker and listener via an emergent communication game for emergent language generation and a language model to extract embodied representations by predicting the cropped part of a latent trajectory. The language model takes the emergent language or natural language as prompt and the masked + +trajectory as input and aims to predict the masked part of the trajectory separately. Then, we transfer the learned speaker and language model into downstream embodied control tasks as frozen modules. The output of the language model extracts embodied representation from instruction prompt and current observations and is mapped into actions by the downstream policy network, which contains a few task-specific MLP [51] layers. + +# 3.1. Problem Statement + +The goal for embodied control is to learn a policy $\pi_B$ conditioned on the instruction, either language instruction or video instruction, that reproduces the expert behavior on the desired task specified by the instruction. Usually, the demonstrations of experts are presented in the form of state-action trajectories, with each pair indicating the action to take at the state being visited. Let $\tau_E$ denote a trajectory sampled from expert policy $\pi_E(s|c)$ : $\tau_E = [(s_0,a_0),(s_1,a_1),\ldots ,(s_n,a_n)]$ . The instruction is encoded into the latent vector $c$ . To learn the behavior policy $\pi_B(s|c)$ , the demonstrated actions are usually utilized as the target label for each state, and the mapping $a\in \pi_B(s|c)$ from states to actions is learned in a supervised manner with given instructions. + +# 3.2. Emergent Communication Language Generation for demonstration video + +Our idea is to automatically generate synthetic language that aligns with video demonstration through emergent communications, which connect perceptual, language, and action for pre-training. As shown in Figure 2(c), we consider a typical speaker-listener referential game [29, 30, 33] on a set of $N$ video features $\mathcal{D}_I = \{I_1,\dots ,I_N\}$ . At each training step, the speaker takes one video feature $I_{i}$ and generates a discrete message $M_{i}\in [V]^{T}$ using the Gumbel-Softmax trick [23], where $V$ is the vocabulary size, and $T$ is the sequence length limit. For simplicity, denote $m = M_{i}$ so that $m_t = M_{i,t}$ denotes the $t$ -th token of the message $M_{i}$ . The generated discrete message is defined as "emergent language", and the process of emergent language generation by the speaker can be formulated as + +$$ +\mathbf {h} \mathbf {s} _ {0} = I _ {i}, \quad \mathbf {h} \mathbf {s} _ {t} = \mathrm {G P T} _ {\mathrm {s p k}} (m _ {t - 1}, \mathbf {h} \mathbf {s} _ {t - 1}) (t > 0), +$$ + +$$ +m _ {0} = \left[ \mathrm {C L S} \right], \quad m _ {t} = \operatorname {S o f t m a x} \left(\mathrm {M L P} _ {\mathrm {s p k}} \left(\mathbf {h s} _ {t}\right)\right) (t > 0). \tag {1} +$$ + +Here $\mathbf{h}\mathbf{s}_t$ denotes speaker hidden states. Next, the listener takes the message $m$ , and tries to guess the right video $I_{i}$ out of a set of $K$ confounding videos $C_i = \{I_{j_1},\dots ,I_{j_K}\} \subset \mathcal{D}_I - \{I_i\}$ . Note that different from the EC games on images, in order to learn temporal information, except for irrelevant videos, we also construct several additional candidates in $C_i$ by performing temporal augmentation on the original video, such as reverse order and random disorder. + +The listener also uses a GRU [11] layer to turn the message $m$ into a hidden vector $\mathbf{h}\mathbf{l}_T$ + +$$ +\mathbf {h l} _ {0} = \mathbf {0}, \quad \mathbf {h l} _ {t} = \mathrm {G P T} _ {\mathrm {l s n}} \left(m _ {t}, \mathbf {h l} _ {t - 1}\right) (t > 0). \tag {2} +$$ + +Based on $\mathbf{h}\mathbf{l}_T$ , the listener assigns a score for each candidate video based on inverse square error [31], then selects the image by Softmax sampling across the scores. The speaker and listener are jointly optimized by minimizing the cross-entropy loss of video selection: + +$$ +\begin{array}{l} \operatorname {s c o r e} (\mathbf {I}) = \left\| \mathbf {h l} _ {T} - \operatorname {M L P} _ {\mathrm {l s n}} (\mathbf {I}) \right\| _ {2} ^ {- 2}, \\ p (\text {g u e s s} = \mathbf {I}) = \operatorname {s o f t m a x} (\operatorname {s c o r e} (\mathbf {I})) \quad (\mathbf {I} \in \left\{\mathbf {I} _ {i} \right\} \cup C _ {i}), \\ \mathcal {L} _ {E C} = - \mathbb {E} _ {\mathbf {I} _ {i}, C _ {i}} \mathbb {E} _ {\mathbf {M} _ {i}} \log p (\text {g u e s s} = \mathbf {I} _ {i}). \tag {3} \\ \end{array} +$$ + +The speaker can be employed to generate emergent language $\mathcal{D}_M = \{M_1,\dots ,M_N\}$ based on input videos. + +# 3.3. Pre-training of Language Model with Emergent Language + +We conduct a trajectory completion task to pre-train the GPT-like language model without action labels, as shown in Figure 2(a)(b). Firstly, we random sample a sequence of observations $\hat{o} = \{o_1,o_2,\dots ,o_N\}$ stored in the dataset and map it into latent trajectory $\tau_{\mathrm{whole}}$ by encoder $g_{\theta}$ + +$$ +\tau_ {\text {w h o l e}} = g _ {\theta} (\hat {o}) \tag {4} +$$ + +Then we crop a random segment $\tau_{\mathrm{seg}}$ from the whole latent trajectory $\tau_{\mathrm{whole}}$ and the remained trajectory is denoted as $\tau_{\mathrm{rem}}$ . The language model $f_{\phi}$ takes $\tau_{\mathrm{rem}}$ as input and uses either emergent language $e$ generated by the speaker or natural language $l$ as a prompt to predict the cropped segment $\tau_{\mathrm{seg}}$ . The language model is optimized by jointly minimizing $L_{\mathrm{EC}}$ and $L_{\mathrm{Lang}}$ + +$$ +L _ {\mathrm {E C}} = \left(\tau_ {\mathrm {s e g}} - f _ {\theta} (e, \tau_ {\mathrm {r e m}})\right) ^ {2} \tag {5} +$$ + +$$ +L _ {\text {L a n g}} = \left(\tau_ {\text {s e g}} - f _ {\theta} (l, \tau_ {\text {r e m}})\right) ^ {2} \tag {6} +$$ + +The loss for the prediction using emergent language as prompt and natural language as prompt is calculated separately. + +$\mathrm{EC^2}$ uses the same language model for both emergent language generation and trajectory completion pretext task for framework thriftiness, and both the $L_{\mathrm{EC - pre}}$ and $L_{\mathrm{EC - gen}}$ are used to update the language model jointly. To ensure that the speaker's gradient is not truncated, we use an MLP [51] layer to map from the logits of the word distribution to a 512-dimensional latent vector instead of selecting a word embedding in the dictionary according to the token. For natural language, we use the Byte-Pair Encoding (BPE) tokenizer [6] to encode it into tokens, which are widely used by OpenAI for tokenization when pre-training the GPT model, including GPT [48], GPT-2 [49], RoBERTa [34], + +and BART [32]. We also learn a corresponding dictionary of word embedding. Although the emergent language and natural language are used separately, they can learn correlated information via the pretext trajectory completion task. + +# 3.4. Few-shot Policy Learning for Downstream Embodied control + +To transfer the pre-trained language model into the downstream imitation learning tasks, the language model $f_{\theta}(\cdot ,\cdot)$ take the current trajectory $\tau_{cur} = \{s_{t - T},\dots ,s_{t - 1},s_t\}$ and the emergent language $e$ or natural language instruction $l$ as prompt, then output the predicted features $m_{t}$ . Finally, the output $m_{t}$ of the language model is mapped to specific action $a_{t}$ by task-specific MLP layers $\pi_{\psi}$ . The language model $f_{\theta}$ is frozen during downstream imitation learning. The action under learned behavior policy is sampled by $\hat{a}_t\sim \pi_\psi (a_t|m_t)$ and the expert demonstration action $a_{t}$ are used as the label for imitation learning. For the video instruction following task, we generate emergent language by the speaker and use it as the prompt of the language model. For language instruction following tasks, the natural language is tokenized by the BPE tokenizer, and select the corresponding word embedding in the dictionary as the prompt as language model via the inferred token. With a trajectory with length $H$ , the task-specific MLP layers are optimized by minimizing $\mathcal{L}_{\mathrm{IL}}(\psi)$ . + +$$ +\mathcal {L} _ {\mathrm {I L}} (\psi) = E _ {\tau \sim \mathcal {B}} \left[ - \frac {1}{H} \sum_ {t} ^ {t + H - 1} \log \pi_ {\psi} (a _ {t} | m _ {t}) \right] \tag {7} +$$ + +The MLP [51] layers are implemented with hidden sizes [256, 256] with batch normalization [21] and are trained with a learning rate of 0.001 and a batch size of 32 for 20000 iterations. + +# 4. Experiments + +# 4.1. Pre-training Dataset + +We use the LOReL [37] real robot dataset, which is collected by Franka Emika Panda mounted over an IKEA desk. The LOReL dataset contains 3000 episodes (150000 frames) of reinforcement learning that trains policies for different behaviors on the IKEA desk using online RL. The language instruction is annotated by leveraging crowdsourcing, specifically Amazon Mechanical Turk. Human annotators are asked to describe the behavior if any, that the robot is doing and to phrase it as a command without any pre-specified template. The LOReL dataset contains 6000 annotations, two per episode, containing a total of 1699 unique instructions. The dataset contains different videos with the same language instruction to ensure diversity. We removed the episodes where annotators reported the robot as inactive or its actions unclear, making them incomprehensible. + +# 4.2. Downstream Testing Environments + +We utilize two standard robotic manipulation benchmarks, namely MetaWorld [60] and the Franka Kitchen environment [17], as our downstream testing environments. It is worth noting that these testing environments were not used during the training phase of $\mathrm{EC^2}$ . In MetaWorld, the agent is presented with a series of tasks, including assembling a ring on a peg, picking and placing a block between bins, pushing a button, opening a drawer, and hammering a nail. In Franka Kitchen, the agent aims to learn how to slide open the right door, open the left door, turn on the light, turn the stove top knob, and open the microwave. As shown in Figure 3, both environments offer image observations to the agent, as well as proprioceptive data, which includes the end-effector pose and joint positions. These data are concatenated with the encoded vision observations for each task, providing the agent with a comprehensive understanding of the current task. All tasks involve random environment variation, either by varying the position of the target object in MetaWorld or the positioning of the desk in Franka Kitchen. Additionally, we consider three views for each environment to evaluate the robustness of representations across viewpoints. Finally, for each environment, we also consider three demo sizes used in downstream embodied control tasks: [5, 10, 25] in MetaWorld and Franka Kitchen. + +# 4.3. Experimental Setup + +For embodied control tasks, we take R3M and BC-Z as the key baseline. R3M [38] learns the state-of-the-art embodied representations pre-trained on diverse paired human video-language data with time-contrastive learning, which encourages states closer in time to be closer in embedding space and video-language alignment to encourage the embeddings to capture semantically relevant features. For sufficient comparison, we implement R3M with both the language instruction-conditioned version and video instruction-conditioned version, respectively, based on their official implementation. For embodied control with natural language instruction, we use the language encoder of the pre-trained model officially released by their author team to encode the natural language. For embodied control with demonstration video instruction, we use the officially released vision encoder to extract features of every frame in the video and map them into the instruction representation by one MLP layer. BC-Z [24] jointly learns the alignment between video representation and language representation together with policy learning across multiple embodied control tasks. Our evaluation methodology is inspired by [38, 41]. We focus on evaluating the embodied representation of instruction and observation for downstream policy learning with behavior cloning. We parameterize the downstream policy $\pi$ as a two-layer MLP preceded by a + +![](images/3873f4e2021a03efca2da23cea257491bf455087656ffee928a1f25c0fa324d9.jpg) +Slid the door of the drawer + +![](images/a9aa635f99da0e1010936c8306f02d2d5b66b3d1e4d97da13db4220948da5a92.jpg) + +![](images/63ec2749b1bf57c1ee089034271fadb62dbc7515649f28e33414c0db26503322.jpg) +Turn the light on + +![](images/c58f9687874883631786b53bccd6649696d9a946b1c0b6c8933dc82ff6a643da.jpg) +Open the door of the drawer. + +![](images/e8dcad136afa15eec688ba1ab30a0bce3df25fe2c98711c534e47e288e3d4f48.jpg) +Turn the knob on the up left + +![](images/aa823e08bc738a13632f3c4dfb1a9ce580db6a552b2d9c53a7e12e94d797d390.jpg) +Open the door of the Microwave + +![](images/a93a0850189057f9e10827d6faed1ff097056ee627a12e51cb19317e2e1c07c2.jpg) +Multi-view Testing +Pick up the nut and place it on the nail. + +![](images/c906bc1c7c6a0c3f0f619431015d7964a1008fff00c6dc040a965548f9dd30ed.jpg) +Grab the ball from the blue Press the button down bin and put it in the red one +Tasks with Language Instruction +Figure 3. Evaluation Environments: We consider a set of manipulation tasks including 5 tasks with a Sawyer from MetaWorld [60], 5 tasks from a Franka operating over a Kitchen [17]. We provide specific language instruction labels for every task and 25 demos per task for evaluation. We show an example image and corresponding language instruction for each task shown above. Evaluation Viewpoints: To robustly measure the efficacy of different visual representations, we consider three camera viewpoints per environment. + +![](images/58e4202f636d0e6b91e61b60526bfabf65128c9ec70fe6eb999fe1f8e45f7ba9.jpg) + +![](images/0271f6430031c9f93c4b7f6d2c192659569d78b1105a3df4ced1a1a5a38c1694.jpg) +Open the drawer + +![](images/86f240df30023b545739978bf33eb43205f1cd8cb40134e91d588c85c122e8e7.jpg) +Pick up the hammer and hammer the wall + +
BenchmarkNum. DemosInstructionEC2(ours)R3M [38]BC-Z [24]
MetaWorld10Lang72.4 ± 2.4%69.2 ± 2.0%63.4 ± 2.1%
Video76.0 ± 2.1% (+3.6)71.8 ± 1.8% (+2.6)64.8 ± 2.0% (+1.4)
25Lang82.6 ± 2.0%77.4 ± 2.4%74.1 ± 2.2%
Video85.0 ± 2.2% (+2.4)79.0 ± 2.1% (+1.6)75.2 ± 1.0% (+1.1)
Franka Kitchen10Lang48.4 ± 2.5%41.8 ± 2.5%34.2 ± 2.3%
Video53.6 ± 2.5%(+5.2)45.7 ± 2.4% (+3.9)37.5 ± 2.2% (+3.3)
25Lang59.8 ± 2.5%56.0 ± 2.3%38.6 ± 2.4%
Video63.2 ± 2.6% (+3.4)58.7 ± 2.0% (+2.7)40.0 ± 2.0% (+1.4)
+ +Table 1. Performance comparison on Success rate of embodied control with language/video instruction across different demo size. We mark the performance difference between complete the task with natural language instruction and video instruction as blue. + +BatchNorm at the input. We train the agent for 20,000 steps, evaluate it online in the environment every 1000 steps, and report the best success rate achieved. For each task, we run 5 seeds of behavior cloning. The final success rate reported for one method on one task is the average over the 5 seeds $\times 3$ camera viewpoints $\times 3$ demo sizes, for a total of 45 runs (see more details in Appendix). + +# 4.4. Results + +We aim to answer 5 questions to get insight into embodied AI community: 1) Can emergent language help embodied control tasks with natural language instruction? 2) Can emergent language help the embodied control tasks with video instruction? 3) Can the joint training of emergent language and natural language in GPT-Like network architecture help each other? 4) Can emergent language provide more detailed and effective guidelines than video captions? 5) What is the relationship between model size, control performance, and the correlation between emergent language and natural language? + +To answer the first two questions, we study if $\mathrm{EC^2}$ enables more data-efficient policy learning with both natural language instructions and video instructions. + +1) Can emergent language help the embodied control tasks with natural language? + +We measure the success rate of downstream few-shot policy learning with different pre-training methods. In Franka Kitchen and MetaWorld, we only use no more than 25 demos to perform downstream few-shot policy learning and report the performance with both 10 and 25 demos separately in Table 1. Learning from scratch is struggled to perform well when working with small amounts of data since it can be challenging for the model to identify meaningful patterns or relationships with such limited data. While the methods with a pre-trained model, like $\mathrm{EC}^2$ , R3M, and BC-Z performs better than those learning from scratch. Through our study, as shown in Table 1, $\mathrm{EC}^2$ exceeds existing methods with natural language instruction, which indicates that emergent language can help the embodied control tasks to improve the performance with natural language instruction. Across all the evaluations, $\mathrm{EC}^2$ is overall able to learn these embodied tasks in an extremely low data regime (only 10 demos) with $\approx 60.4\%$ overall success rate, despite never seeing any data from the target environments in training the representation, while R3M only achieves $\approx 55.5\%$ overall success rate. + +
BenchmarkNum. DemosLanguage InstructionVideo Instruction
\( EC^2 \)\( EC^2 (-EC) \)\( EC^2 \)\( EC^2 (-NL) \)\( EC^2 (+Cap,-EC) \)
MetaWorld1072.4 ± 2.4%69.0 ± 2.0%76.0 ± 2.1%72.6 ± 2.4%73.0 ± 2.2%
2582.6 ± 2.0%78.0 ± 2.4%85.0 ± 2.5%82.0 ± 2.0%73.2 ± 2.5%
Franka Kitchen1048.4 ± 2.5%43.0 ± 3.3%53.6 ± 2.5%49.0 ± 2.5%48.6 ± 2.4%
2559.8 ± 2.5%54.0 ± 2.6%63.2 ± 2.6%61.3 ± 2.4%49.0 ± 2.3%
+ +Table 2. Ablation study on embodied control with language instruction and video instruction. + +
Model Size#layer#head#embedded
Base816512
Mini66192
Micro44128
+ +Table 3. Hyper-parameters for different model sizes of ${\mathrm{{EC}}}^{2}$ . All the models are implemented based on GPT [48]-like network architecture. + +
Natural LanguageEmergent language
“Open the right drawer”[262, 847, 490, 536, 108, 500, 941, 838, 749, 444]
“Grasp in the middle drawer”[356, 69, 108, 259, 72, 616, 500, 896, 623, 433]
“Reach down for stapler”[204, 897, 285, 509, 701, 545, 538, 729, 902, 195]
“Pick up the stapler in the drawer”[535, 67, 108, 661, 84, 701, 776, 500, 377, 454]
“Reach to the plug”[982, 691, 72, 538, 97, 665, 148, 369, 102, 1003]
“Reach to the left drawer”[786, 538, 601, 874, 848, 500, 315, 108, 72, 914]
+ +Table 4. Qualitative examples of emergent language and corresponding natural language. The word and tokens that have the same semantic meaning are marked with the same color. + +2) Can emergent language help the embodied control tasks with video instruction? +As shown in Table1, $\mathrm{EC^2}$ shows an obvious advantage over the exciting methods and achieves the best success rate ( $\approx 64.8\%$ with 10 demos and $\approx 74.1\%$ with 25 demos) with video instruction. As marked in blue in Table 1, $\mathrm{EC^2}$ has better performance with video instruction than with language instruction, which indicates that $\mathrm{EC^2}$ learns more effective information provided by a video demonstration. In contrast, R3M and BC-Z, which use contrast learning or regression to force the two modalities of language and video aligned, have little difference in performance under language instruction and video instruction. +We also investigate the task performance of $\mathrm{EC^2}$ and baselines with different amounts of demos in policy learning. In Figure 4, we plot the average success rate of each method across each demo size. We observe that the performance improvement from $\mathrm{EC^2}$ is consistent, outperforming the baselines across every environment and demo size. +Ablation Study: Also, in the data-efficient imitation learning setting, we ablate the different components of $\mathrm{EC^2}$ training to answer question 3 and 4 and check if each module is indispensable. +3) Can the joint training of emergent language and natural language with GPT-Like network help each other? + +We conduct ablation studies to compare $\mathrm{EC}^2$ and $\mathrm{EC}^2$ (-EC) in language instruction following tasks and compare $\mathrm{EC}^2$ and $\mathrm{EC}^2$ (-NL) in video instruction following tasks. $\mathrm{EC}^2$ (-EC) does not use emergent language to pre-train the language model under $\mathrm{EC}^2$ framework, which predicts the masked trajectories with only the language instruction (human-labeled caption). $\mathrm{EC}^2$ (-NL) does not use natural language to pre-train the language model under $\mathrm{EC}^2$ framework, which predicts the masked trajectories with only the emergent language. As shown in the left-hand column in + +Table 2, without the help of emergent language, the performance decreased significantly, and $\mathrm{EC^2}$ (-EC) shows no obvious advantages to the other methods that learn pretrained models by video-language pre-training. Similarly, as shown in the right-hand column in Table 2, $\mathrm{EC^2}$ also outperforms $\mathrm{EC^2}$ (-NL), which demonstrates that the language pre-training helps the video instruction task with emergent language. Thus, the above ablation analysis shows that the joint training of emergent language and natural language can benefit each other. +4) Can emergent language provide more detailed and effective guidelines than video captions? + +In $\mathrm{EC^2}$ (+Cap, -EC), we replace the emergent language in $\mathrm{EC^2}$ with the language caption given by a MARN [45] as a data augmentation, which is a pre-trained video caption model. As shown in Table 2, $\mathrm{EC^2}$ shows an obvious advantage to $\mathrm{EC^2}$ (+Cap, -NL), which demonstrates that emergent language provides more detailed and effective guidelines than video captions. +5) What is the relationship between model size, control performance, and the correlation between emergent language and natural language? + +We first tested the overall average success rate of $\mathrm{EC^2}$ with different model sizes (listed in Table 3) in the downstream tasks (Franka Kitchen and MetaWorld). As shown in Figure 5a and Figure 5b, the larger the size of the model, the more expressive it is and thus the better its performance. Then, we perform a linear correlation analysis on the word embeddings of the emergent language and the word embeddings of the matched natural language. We use the square of the coefficient of determination, denoted $R^2$ as the measure of predicting the performance of linear regression, which reflects the proportion of the variation in the dependent variable that is predictable from the independent variable. Consider a linear regression model $f(\cdot)$ which predicts $y$ with + +![](images/e1c675166d9cae9f2a36e74272fe96c8a162c6992d35ea248e11595eaab3b5c2.jpg) +(a) MetaWorld[language instruction] + +![](images/4bd772172ba3c0aab7872154d602aa15871538fac270090210326801b04f0495.jpg) +(b) Kitchen[language instruction] + +![](images/e592d4735187c2f8678d03de367cc954226135ff17eb0a8c486b52e1ae3589c6.jpg) +(c) MetaWorld[video instruction] + +![](images/c37649d925918eeaf04f98e7c1930a0655a3f746233c627fdc5fac710089c438.jpg) +(d) Kitchen[video instruction] + +![](images/97d5a5ee50f1536cbdc671c9ef1675bfd10542256e6c9b469ecbb65f72f4de43.jpg) +Figure 4. Performance over different demo sizes used in downstream imitation learning. We report the success rate of $\mathrm{EC^2}$ and baseline across different demo sizes. We see that the performance improvement from $\mathrm{EC^2}$ is consistent across all demo sizes. +(a) Ablation on model size in MetaWorld +Figure 5. Ablation on model size and its relationship with the correlation of emergent language and Natural language. We show the ablation results on model size with 10 demos and 25 demos in downstream policy learning separately. + +![](images/556d251e2aa857d811b293957b7174253612356f7e151fd5aaf16bd6f6e3d83d.jpg) +(b) Ablation on model size in Franka Kitchen + +![](images/511aa2367ec78663e5d0828678829ea61a8e5160cbfe859a9104e3359caa4f93.jpg) +(c) Translation score across different model sizes + +the input $x$ , the coefficient of determination $R$ is defined as + +$$ +R ^ {2} = 1 - \frac {S S _ {r e s}}{S S _ {t o t}} = 1 - \frac {\sum_ {i} \left(y _ {i} - f \left(x _ {i}\right)\right) ^ {2}}{\sum_ {i} \left(y _ {i} - \bar {y}\right) ^ {2}} \tag {8} +$$ + +We evaluate the $R^2$ values of two linear regressions. One predicts natural language word embeddings from emergent language, and the other predicts emergent language word embeddings from natural language. As shown in Figure 5c, the $R^2$ of predicting natural language embeddings from the emergent language increase along with the model becoming larger, which corresponds to better performance. In contrast, the $R^2$ of predicting emergent language embeddings from the natural language is non-monotonous, along with the model size becoming larger. The reason is that emergent language captures more information that natural language does not contain when the model is large enough and has promising performance. In short, $\mathrm{EC}^2$ has the best performance in embodied control tasks when emergent language contains more information than natural language, the performance is median when emergent language and language information are nearly equal, and the performance is worst when emergent language contains less information than language information. As shown in Table 4, we also provide qualitative examples of emergent language and its corresponding natural language to show that emergent language can capture key concepts from video. We find that the tokens "108" and "500" correspond to "drawer" in natural language and token "701" corresponds to "stapler." Except for nouns, emergent language can also get the con + +cept of verbs, for example, token “538” corresponds to the verb “reach” in natural language. The current manual check analysis of emergent language is just a preliminary attempt, and more understanding can be promising for future work. + +# 5. Conclusions and Discussions + +This paper aims to build the link between perceptual grounding and symbolic concepts by emergent communication (EC) language for embodied control. To this end, we develop a novel Embodied Control framework with the help of Emergent Communication language $(\mathrm{EC}^2)$ , which pre-trains a language model via masked trajectory complement pretext task condition on emergent language or natural language. The pre-trained language model is utilized to extract embodied representation from instructions and observations and is used as a frozen module for downstream data-efficient policy learning. Extensive experiments show that $\mathbf{E}\mathbf{C}^{2}$ outperforms existing methods in Metaworld and Franka kitchen benchmarks. We believe that $\mathrm{EC^2}$ will serve as a solid step toward the general decision-making model. Limitations and future works: more understanding about emergent language, training $\mathrm{EC}^2$ on a larger and more diverse dataset, and applications on more practical setup can be promising directions of future works. + +Acknowledgement. Ping Luo is partially supported by the National Key R&D Program of China No.2022ZD0161000 and the General Research Fund of HK No.17200622. Shunyu Yao was supported in part by the National Science Foundation under Grant No. 2107048. + +# References + +[1] Muhammad Alomari, Paul Duckworth, David Hogg, and Anthony Cohn. Natural language acquisition and grounding for embodied robotic systems. In Proceedings of the AAAI Conference on Artificial Intelligence, volume 31, 2017. 2 +[2] Brenna D Argall, Sonia Chernova, Manuela Veloso, and Brett Browning. A survey of robot learning from demonstration. Robotics and autonomous systems, 57(5):469-483, 2009. 3 +[3] Michelle E Barton. Input and interaction in language acquisition. Cambridge University Press, 1994. 2 +[4] Aude Billard, Yann Epars, Sylvain Calinon, Stefan Schaal, and Gordon Cheng. Discovering optimal imitation strategies. 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While recent approaches apply contrastive learning to force alignment between the two modalities, we hypothesize better modeling their complementary differences can lead to more holistic representations for downstream adaption. To this end, we propose Emergent Communication for Embodied Control " + }, + { + "bbox": [ + 46, + 238, + 290, + 597 + ], + "type": "inline_equation", + "content": "(EC^2)" + }, + { + "bbox": [ + 46, + 238, + 290, + 597 + ], + "type": "text", + "content": ", a novel scheme to pre-train video-language representations for few-shot embodied control. The key idea is to learn an unsupervised \"language\" of videos via emergent communication, which bridges the semantics of video details and structures of natural language. We learn embodied representations of video trajectories, emergent language, and natural language using a language model, which is then used to finetune a lightweight policy network for downstream control. Through extensive experiments in Metaworld and Franka Kitchen embodied benchmarks, " + }, + { + "bbox": [ + 46, + 238, + 290, + 597 + ], + "type": "inline_equation", + "content": "EC^2" + }, + { + "bbox": [ + 46, + 238, + 290, + 597 + ], + "type": "text", + "content": " is shown to consistently outperform previous contrastive learning methods for both videos and texts as task inputs. Further ablations confirm the importance of the emergent language, which is beneficial for both video and language learning, and significantly superior to using pre-trained video captions. We also present a quantitative and qualitative analysis of the emergent language and discuss future directions toward better understanding and leveraging emergent communication in embodied tasks." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 620, + 128, + 633 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 620, + 128, + 633 + ], + "spans": [ + { + "bbox": [ + 47, + 620, + 128, + 633 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 641, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 641, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 641, + 288, + 714 + ], + "type": "text", + "content": "We study the problem of few-shot embodied control, where an embodied agent needs to execute language instructions or follow video demonstrations given only a few examples in a new environment. Such a capability of fast adaption is key to practical robotic deployment, as it is non- scalable and expensive to collect extensive action-labeled" + } + ] + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 317, + 214, + 535, + 310 + ], + "blocks": [ + { + "bbox": [ + 317, + 214, + 535, + 310 + ], + "lines": [ + { + "bbox": [ + 317, + 214, + 535, + 310 + ], + "spans": [ + { + "bbox": [ + 317, + 214, + 535, + 310 + ], + "type": "image", + "image_path": "833a326db3f0d71a85550006fbbbb23324e740bab3fb6fe16521dc2884579f3b.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 353, + 315, + 499, + 324 + ], + "lines": [ + { + "bbox": [ + 353, + 315, + 499, + 324 + ], + "spans": [ + { + "bbox": [ + 353, + 315, + 499, + 324 + ], + "type": "text", + "content": "(a) Emergent language for embodied control." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 323, + 331, + 516, + 397 + ], + "blocks": [ + { + "bbox": [ + 323, + 331, + 516, + 397 + ], + "lines": [ + { + "bbox": [ + 323, + 331, + 516, + 397 + ], + "spans": [ + { + "bbox": [ + 323, + 331, + 516, + 397 + ], + "type": "image", + "image_path": "574794532ecb74b280941005535ccbfebfa31148d70635773ddfebb47fd93c45.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 315, + 398, + 534, + 408 + ], + "lines": [ + { + "bbox": [ + 315, + 398, + 534, + 408 + ], + "spans": [ + { + "bbox": [ + 315, + 398, + 534, + 408 + ], + "type": "text", + "content": "(b) Performance comparison on overall success rate across all tasks." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 304, + 412, + 547, + 533 + ], + "lines": [ + { + "bbox": [ + 304, + 412, + 547, + 533 + ], + "spans": [ + { + "bbox": [ + 304, + 412, + 547, + 533 + ], + "type": "text", + "content": "Figure 1. Overview of " + }, + { + "bbox": [ + 304, + 412, + 547, + 533 + ], + "type": "inline_equation", + "content": "\\mathrm{EC^2}" + }, + { + "bbox": [ + 304, + 412, + 547, + 533 + ], + "type": "text", + "content": ". The key idea of " + }, + { + "bbox": [ + 304, + 412, + 547, + 533 + ], + "type": "inline_equation", + "content": "\\mathrm{EC^2}" + }, + { + "bbox": [ + 304, + 412, + 547, + 533 + ], + "type": "text", + "content": " is to build the link between perceptual grounding and symbolic concept via emergent communication (EC) language. We learn to extract embodied representation via language model utilizing emergent language or natural language as prompt and visual observation as input for downstream embodied control tasks. The actions are generated by a lightweight policy network containing a few MLP [51] layers that map the learned frozen embodied representation into action space. Extensive experiments show that " + }, + { + "bbox": [ + 304, + 412, + 547, + 533 + ], + "type": "inline_equation", + "content": "\\mathrm{EC^2}" + }, + { + "bbox": [ + 304, + 412, + 547, + 533 + ], + "type": "text", + "content": " outperforms existing methods in Metaworld [60] and Franka Kitchen [17] benchmarks." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 545, + 547, + 605 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 545, + 547, + 605 + ], + "spans": [ + { + "bbox": [ + 304, + 545, + 547, + 605 + ], + "type": "text", + "content": "trajectories for each new application scenario. Instead, agents need to leverage pre-trained video and language representations to quickly learn how to act, and generalize across high-level concepts (e.g. object and verb types) as well as low-level visual features." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 605, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 547, + 713 + ], + "type": "text", + "content": "How can we pre-train multi-modal representations of videos and texts for downstream embodied control in different domains? Inspired by the success of image-text models such as CLIP [47], recent work has investigated contrastive representation learning approaches using paired video-language data, with application toward robotic manipulation and control tasks [24, 38]. However, simply aligning video and language pairs in the embedding space omits the difference between these two modalities: while" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "6704" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 49, + 72, + 286, + 274 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 72, + 286, + 274 + ], + "spans": [ + { + "bbox": [ + 49, + 72, + 286, + 274 + ], + "type": "text", + "content": "videos contain more visual and motion details, language abstracts away key structures underlying the task. For example, a video of opening a door contains details of approaching the handle, pressing the handle, pulling the door open, and so on, while the corresponding language description could be as simple as \"open a door\" — more detailed language descriptions such as \"press down the handle\" is usually not available in existing datasets and very expensive to manually label. But for downstream control purposes, a video and its abstract language description could present complementary benefits — while the former is expressive in details needed for low-level control, the latter provides the structure for generalization across domains, tasks, and skills. Leveraging such modality differences presents opportunities to better incorporate language and videos for embodied representation learning, marrying their respective benefits rather than forcing them to be aligned." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 49, + 279, + 286, + 517 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 279, + 286, + 517 + ], + "spans": [ + { + "bbox": [ + 49, + 279, + 286, + 517 + ], + "type": "text", + "content": "One perspective to view the video-language difference is through the emergence of language [39, 55]: language derives meaning from its use [57]. It is a communication tool humans develop to collaboratively solve embodied tasks, thus abstracting perception experiences like videos into symbolic concepts. Emergent communication in machine learning [9, 26, 28, 30, 56] aims to similarly learn an \"emergent language\" of perception in an unsupervised and domain-adaptive way: as Figure 2(a) shows, a speaker and a listener network play a referential game, where a speaker maps some visual stimuli (e.g. image, video) into a message of discrete tokens, and a listener uses the message to choose the speaker reference out of detractors. By jointly optimizing for game success, the communication protocol emerges structural and semantic properties resembling language, yet its discrete tokens might convey more fine-grained concepts than natural language useful for distinguishing stimuli. Thus, an emergent language can act as a bridge between natural language and videos, featuring a structure similar to the former while preserving the semantics of the latter." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 49, + 522, + 286, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 522, + 286, + 712 + ], + "spans": [ + { + "bbox": [ + 49, + 522, + 286, + 712 + ], + "type": "text", + "content": "Inspired by recent work that links emergent and natural language [58], we propose Emergent Communication for Embodied Control (EC²), a three-phase scheme to learn embodied representations for downstream few-shot control (Figure 1(a-c)). First, we learn an emergent language of demonstration videos without using any language labels, which could potentially capture domain-specific concepts not directly available in paired natural language captions. Second, we learn an embodied representation by using a language model to predict trajectory segments conditional on trajectory contexts and language annotations, both natural and emergent. Rather than forcing video and language representations to be aligned, such a sequence modeling approach learns to represent natural language (for compositional generalization) and emergent language (for low-level perception and control) jointly with video trajectories," + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 308, + 72, + 545, + 119 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 72, + 545, + 119 + ], + "spans": [ + { + "bbox": [ + 308, + 72, + 545, + 119 + ], + "type": "text", + "content": "where the emergent language serves as a bridge between language and videos. Third, we train a lightweight policy network on top of the embodied representation to few-shot adapt to downstream embodied control." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 308, + 121, + 545, + 371 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 121, + 545, + 371 + ], + "spans": [ + { + "bbox": [ + 308, + 121, + 545, + 371 + ], + "type": "text", + "content": "We demonstrate that emergent language can help embodied control tasks and enable data-efficient few-shot downstream imitation learning via extensive experimental results across two existing benchmark simulation environments (Franka-Kitchen [18] and MetaWorld [60]). " + }, + { + "bbox": [ + 308, + 121, + 545, + 371 + ], + "type": "inline_equation", + "content": "\\mathrm{EC^2}" + }, + { + "bbox": [ + 308, + 121, + 545, + 371 + ], + "type": "text", + "content": " outperforms existing methods and achieves state-of-the-art performance on both language and video instruction following tasks. Our study also shows that although emergent language and natural language are utilized in a parallel manner in the pre-training phase, the word embeddings of natural language can still be predicted by linear regression models from emergent language. We further investigate the impact of emergent language and natural language correlation on the performance of downstream tasks and show that the performance in downstream tasks is best when the learned EC contains more information than natural language, i.e., when the accuracy of predicting natural language from emergent language is higher than that of predicting emergent language from natural language. Overall, on the basis of these results, we believe that " + }, + { + "bbox": [ + 308, + 121, + 545, + 371 + ], + "type": "inline_equation", + "content": "\\mathrm{EC^2}" + }, + { + "bbox": [ + 308, + 121, + 545, + 371 + ], + "type": "text", + "content": " has great potential to become a promising embodied control framework." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 308, + 373, + 545, + 539 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 373, + 545, + 539 + ], + "spans": [ + { + "bbox": [ + 308, + 373, + 545, + 539 + ], + "type": "text", + "content": "To sum up, our work makes the following contributions. (1) we build an embodied representation pre-training framework with emergent communication (EC) via a language model, which incorporates both the abstract, compositional structure of language and visuals with low-level motion details. (2) we develop a few-shot embodied control system, which transfers the pre-trained language model to downstream tasks as a frozen module and quickly adapts lightweight policy networks with a few expert data to generate actions. (3) we demonstrate that the learned representation with EC can benefit few-shot embodied control tasks and extensive experiments show that " + }, + { + "bbox": [ + 308, + 373, + 545, + 539 + ], + "type": "inline_equation", + "content": "\\mathrm{EC^2}" + }, + { + "bbox": [ + 308, + 373, + 545, + 539 + ], + "type": "text", + "content": " outperforms existing methods in Metaworld [60] and Franka Kitchen [17] benchmarks." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 308, + 554, + 391, + 566 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 554, + 391, + 566 + ], + "spans": [ + { + "bbox": [ + 308, + 554, + 391, + 566 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 308, + 574, + 451, + 586 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 574, + 451, + 586 + ], + "spans": [ + { + "bbox": [ + 308, + 574, + 451, + 586 + ], + "type": "text", + "content": "2.1. Emergent Communication" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 308, + 594, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 594, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 308, + 594, + 545, + 712 + ], + "type": "text", + "content": "The recent advances in NLP [7, 14, 49] benefits from huge text corpora and are striving to find statistical regularities on large amounts of data via big models like GPT [7, 48, 49] and BERT [14]. This narrow focus was leaving aside language emergence and language grounding (in some other modalities, e.g., sight, with more complex inputs than text). In contrast, human language acquisition [13] starts with a cumulative series of interactions with other people [3, 8] grounded in the physical and social world [1, 19, 54] and does not rely on passive and complex corpora like" + } + ] + } + ], + "index": 8 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 296, + 750, + 314, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 750, + 314, + 757 + ], + "spans": [ + { + "bbox": [ + 296, + 750, + 314, + 757 + ], + "type": "text", + "content": "6705" + } + ] + } + ], + "index": 9 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 85, + 77, + 351, + 266 + ], + "blocks": [ + { + "bbox": [ + 85, + 77, + 351, + 266 + ], + "lines": [ + { + "bbox": [ + 85, + 77, + 351, + 266 + ], + "spans": [ + { + "bbox": [ + 85, + 77, + 351, + 266 + ], + "type": "image", + "image_path": "1c5139b02854949144f8f98fbba53220417dbfb0556bdc7986ede25e32e4d75e.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 272, + 548, + 384 + ], + "lines": [ + { + "bbox": [ + 46, + 272, + 548, + 384 + ], + "spans": [ + { + "bbox": [ + 46, + 272, + 548, + 384 + ], + "type": "text", + "content": "Figure 2. The overall framework of EC" + }, + { + "bbox": [ + 46, + 272, + 548, + 384 + ], + "type": "inline_equation", + "content": "^2" + }, + { + "bbox": [ + 46, + 272, + 548, + 384 + ], + "type": "text", + "content": ". Pre-training: (a) We first pre-train a speaker (■) and listener (■) via emergent communication game for emergent language generation and a language model (■) to extract embodied representations. (b) We generate the corresponding emergent language (■) for each demonstration video in the multi-modal dataset. Predicting the cropped part of a latent trajectory is used as an auxiliary task to help pre-training the language model. The language model takes emergent language or natural language as prompt and the cropped trajectory (■) as input and aims to predict the cropped part of the trajectory (■). The loss for the prediction using emergent language as prompt and natural language as prompt is calculated separately. Few-shot downstream policy learning: In downstream imitation learning tasks, both the EC speaker and the pre-trained language model(■) are frozen. The language model extracts effective embodied features with current trajectory (■ contains current state and historical information) as input. (c) For tasks with language instruction, we use natural language as the prompt, and (d) for tasks with video instruction, we use emergent language as the prompt. The output features of the language model are mapped into actions to mimic expert behavior by a few simple MLP [51] layers (■)." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 366, + 78, + 512, + 266 + ], + "blocks": [ + { + "bbox": [ + 366, + 78, + 512, + 266 + ], + "lines": [ + { + "bbox": [ + 366, + 78, + 512, + 266 + ], + "spans": [ + { + "bbox": [ + 366, + 78, + 512, + 266 + ], + "type": "image", + "image_path": "17289e83919e72239682c7e05010941e5c48f94e189a909f03ac4351b47576d9.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 393, + 289, + 562 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 393, + 289, + 562 + ], + "spans": [ + { + "bbox": [ + 46, + 393, + 289, + 562 + ], + "type": "text", + "content": "Wikipedia. Emergent Communication (EC) is one promising direction toward this motivation, where a communication protocol is shaped through multi-agent interactions with perceptual grounding like a human [43]. As a typical example, the referential image game involves a speaker creating a sequence of discrete tokens based on an input image, and a listener tasked with selecting the correct input from a group of distractors using the message. Both networks are optimized jointly using success signals from the game [58]. By studying games like this type, researchers are interested in the emergence of desirable properties resembling natural language, such as game success generalization and compositionality, which holds great promises towards more functional [56, 57] and generalizable [27] language agents." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 573, + 244, + 586 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 573, + 244, + 586 + ], + "spans": [ + { + "bbox": [ + 47, + 573, + 244, + 586 + ], + "type": "text", + "content": "2.2. Embodied Control under Instruction" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 594, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 594, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 289, + 715 + ], + "type": "text", + "content": "Embodied control has achieved much success in learning grasping and pick-place tasks from low-dimensional state [2,4,10,25,36,42,52]. Deep learning makes embodied control directly learn from high dimensional observations becoming feasible [46,50,61]. Recent advances aim to build a learning-based embodied control system with deep neural networks that are flexibly conditioned on either a demonstration video [5,59] of a human or a language instruction [35, 53] via multi-modal representation learning. With the guidance of instruction, the embodied agent aims to gener" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 393, + 547, + 609 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 393, + 547, + 609 + ], + "spans": [ + { + "bbox": [ + 304, + 393, + 547, + 609 + ], + "type": "text", + "content": "alize to new scenes [44], novel objects [5, 16, 22, 59, 62], novel object configurations [40], and novel goal configurations [12, 15, 20]. For instance, BC-Z [24] has developed a flexible imitation learning system that can learn from demonstrations and interventions, based on various forms of task information, such as pre-trained embeddings of natural language or human performance videos. R3M [38] pre-trains visual representations on diverse human videolanguage data by encouraging alignment between the two modalities. However, since videos often convey more detailed information than words, this framework may lose valuable teaching information that can help robots perform complex tasks. In this work, we aim to build an instruction-conditioned embodied control framework without forcing alignment on video and language and consider the video demonstrations and language instructions as \"parallel sentences\" during the pre-training process to learn useful information for downstream tasks." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 620, + 362, + 634 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 620, + 362, + 634 + ], + "spans": [ + { + "bbox": [ + 306, + 620, + 362, + 634 + ], + "type": "text", + "content": "3. Method" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 642, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 642, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 642, + 547, + 715 + ], + "type": "text", + "content": "As shown in Figure 2, we first pre-train a speaker and listener via an emergent communication game for emergent language generation and a language model to extract embodied representations by predicting the cropped part of a latent trajectory. The language model takes the emergent language or natural language as prompt and the masked" + } + ] + } + ], + "index": 8 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 316, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 316, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 316, + 757 + ], + "type": "text", + "content": "6706" + } + ] + } + ], + "index": 9 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 168 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 168 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 168 + ], + "type": "text", + "content": "trajectory as input and aims to predict the masked part of the trajectory separately. Then, we transfer the learned speaker and language model into downstream embodied control tasks as frozen modules. The output of the language model extracts embodied representation from instruction prompt and current observations and is mapped into actions by the downstream policy network, which contains a few task-specific MLP [51] layers." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 176, + 160, + 188 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 176, + 160, + 188 + ], + "spans": [ + { + "bbox": [ + 47, + 176, + 160, + 188 + ], + "type": "text", + "content": "3.1. Problem Statement" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 195, + 289, + 363 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 195, + 289, + 363 + ], + "spans": [ + { + "bbox": [ + 46, + 195, + 289, + 363 + ], + "type": "text", + "content": "The goal for embodied control is to learn a policy " + }, + { + "bbox": [ + 46, + 195, + 289, + 363 + ], + "type": "inline_equation", + "content": "\\pi_B" + }, + { + "bbox": [ + 46, + 195, + 289, + 363 + ], + "type": "text", + "content": " conditioned on the instruction, either language instruction or video instruction, that reproduces the expert behavior on the desired task specified by the instruction. Usually, the demonstrations of experts are presented in the form of state-action trajectories, with each pair indicating the action to take at the state being visited. Let " + }, + { + "bbox": [ + 46, + 195, + 289, + 363 + ], + "type": "inline_equation", + "content": "\\tau_E" + }, + { + "bbox": [ + 46, + 195, + 289, + 363 + ], + "type": "text", + "content": " denote a trajectory sampled from expert policy " + }, + { + "bbox": [ + 46, + 195, + 289, + 363 + ], + "type": "inline_equation", + "content": "\\pi_E(s|c)" + }, + { + "bbox": [ + 46, + 195, + 289, + 363 + ], + "type": "text", + "content": ": " + }, + { + "bbox": [ + 46, + 195, + 289, + 363 + ], + "type": "inline_equation", + "content": "\\tau_E = [(s_0,a_0),(s_1,a_1),\\ldots ,(s_n,a_n)]" + }, + { + "bbox": [ + 46, + 195, + 289, + 363 + ], + "type": "text", + "content": ". The instruction is encoded into the latent vector " + }, + { + "bbox": [ + 46, + 195, + 289, + 363 + ], + "type": "inline_equation", + "content": "c" + }, + { + "bbox": [ + 46, + 195, + 289, + 363 + ], + "type": "text", + "content": ". To learn the behavior policy " + }, + { + "bbox": [ + 46, + 195, + 289, + 363 + ], + "type": "inline_equation", + "content": "\\pi_B(s|c)" + }, + { + "bbox": [ + 46, + 195, + 289, + 363 + ], + "type": "text", + "content": ", the demonstrated actions are usually utilized as the target label for each state, and the mapping " + }, + { + "bbox": [ + 46, + 195, + 289, + 363 + ], + "type": "inline_equation", + "content": "a\\in \\pi_B(s|c)" + }, + { + "bbox": [ + 46, + 195, + 289, + 363 + ], + "type": "text", + "content": " from states to actions is learned in a supervised manner with given instructions." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 371, + 287, + 395 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 371, + 287, + 395 + ], + "spans": [ + { + "bbox": [ + 47, + 371, + 287, + 395 + ], + "type": "text", + "content": "3.2. Emergent Communication Language Generation for demonstration video" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 402, + 289, + 570 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 402, + 289, + 570 + ], + "spans": [ + { + "bbox": [ + 46, + 402, + 289, + 570 + ], + "type": "text", + "content": "Our idea is to automatically generate synthetic language that aligns with video demonstration through emergent communications, which connect perceptual, language, and action for pre-training. As shown in Figure 2(c), we consider a typical speaker-listener referential game [29, 30, 33] on a set of " + }, + { + "bbox": [ + 46, + 402, + 289, + 570 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 402, + 289, + 570 + ], + "type": "text", + "content": " video features " + }, + { + "bbox": [ + 46, + 402, + 289, + 570 + ], + "type": "inline_equation", + "content": "\\mathcal{D}_I = \\{I_1,\\dots ,I_N\\}" + }, + { + "bbox": [ + 46, + 402, + 289, + 570 + ], + "type": "text", + "content": ". At each training step, the speaker takes one video feature " + }, + { + "bbox": [ + 46, + 402, + 289, + 570 + ], + "type": "inline_equation", + "content": "I_{i}" + }, + { + "bbox": [ + 46, + 402, + 289, + 570 + ], + "type": "text", + "content": " and generates a discrete message " + }, + { + "bbox": [ + 46, + 402, + 289, + 570 + ], + "type": "inline_equation", + "content": "M_{i}\\in [V]^{T}" + }, + { + "bbox": [ + 46, + 402, + 289, + 570 + ], + "type": "text", + "content": " using the Gumbel-Softmax trick [23], where " + }, + { + "bbox": [ + 46, + 402, + 289, + 570 + ], + "type": "inline_equation", + "content": "V" + }, + { + "bbox": [ + 46, + 402, + 289, + 570 + ], + "type": "text", + "content": " is the vocabulary size, and " + }, + { + "bbox": [ + 46, + 402, + 289, + 570 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 46, + 402, + 289, + 570 + ], + "type": "text", + "content": " is the sequence length limit. For simplicity, denote " + }, + { + "bbox": [ + 46, + 402, + 289, + 570 + ], + "type": "inline_equation", + "content": "m = M_{i}" + }, + { + "bbox": [ + 46, + 402, + 289, + 570 + ], + "type": "text", + "content": " so that " + }, + { + "bbox": [ + 46, + 402, + 289, + 570 + ], + "type": "inline_equation", + "content": "m_t = M_{i,t}" + }, + { + "bbox": [ + 46, + 402, + 289, + 570 + ], + "type": "text", + "content": " denotes the " + }, + { + "bbox": [ + 46, + 402, + 289, + 570 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 402, + 289, + 570 + ], + "type": "text", + "content": "-th token of the message " + }, + { + "bbox": [ + 46, + 402, + 289, + 570 + ], + "type": "inline_equation", + "content": "M_{i}" + }, + { + "bbox": [ + 46, + 402, + 289, + 570 + ], + "type": "text", + "content": ". The generated discrete message is defined as \"emergent language\", and the process of emergent language generation by the speaker can be formulated as" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 69, + 579, + 276, + 592 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 69, + 579, + 276, + 592 + ], + "spans": [ + { + "bbox": [ + 69, + 579, + 276, + 592 + ], + "type": "interline_equation", + "content": "\\mathbf {h} \\mathbf {s} _ {0} = I _ {i}, \\quad \\mathbf {h} \\mathbf {s} _ {t} = \\mathrm {G P T} _ {\\mathrm {s p k}} (m _ {t - 1}, \\mathbf {h} \\mathbf {s} _ {t - 1}) (t > 0),", + "image_path": "46cbba4a67cd08def8dba8701f9ec28619e01b70b2b3650d01d333a1bd41442a.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 53, + 594, + 287, + 617 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 594, + 287, + 617 + ], + "spans": [ + { + "bbox": [ + 53, + 594, + 287, + 617 + ], + "type": "interline_equation", + "content": "m _ {0} = \\left[ \\mathrm {C L S} \\right], \\quad m _ {t} = \\operatorname {S o f t m a x} \\left(\\mathrm {M L P} _ {\\mathrm {s p k}} \\left(\\mathbf {h s} _ {t}\\right)\\right) (t > 0). \\tag {1}", + "image_path": "4ae17812b4c539ff3032dc1abeb34b3aea6200ef9b91d5a9383c9432ad324f77.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 618, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 618, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 618, + 288, + 714 + ], + "type": "text", + "content": "Here " + }, + { + "bbox": [ + 46, + 618, + 288, + 714 + ], + "type": "inline_equation", + "content": "\\mathbf{h}\\mathbf{s}_t" + }, + { + "bbox": [ + 46, + 618, + 288, + 714 + ], + "type": "text", + "content": " denotes speaker hidden states. Next, the listener takes the message " + }, + { + "bbox": [ + 46, + 618, + 288, + 714 + ], + "type": "inline_equation", + "content": "m" + }, + { + "bbox": [ + 46, + 618, + 288, + 714 + ], + "type": "text", + "content": ", and tries to guess the right video " + }, + { + "bbox": [ + 46, + 618, + 288, + 714 + ], + "type": "inline_equation", + "content": "I_{i}" + }, + { + "bbox": [ + 46, + 618, + 288, + 714 + ], + "type": "text", + "content": " out of a set of " + }, + { + "bbox": [ + 46, + 618, + 288, + 714 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 46, + 618, + 288, + 714 + ], + "type": "text", + "content": " confounding videos " + }, + { + "bbox": [ + 46, + 618, + 288, + 714 + ], + "type": "inline_equation", + "content": "C_i = \\{I_{j_1},\\dots ,I_{j_K}\\} \\subset \\mathcal{D}_I - \\{I_i\\}" + }, + { + "bbox": [ + 46, + 618, + 288, + 714 + ], + "type": "text", + "content": ". Note that different from the EC games on images, in order to learn temporal information, except for irrelevant videos, we also construct several additional candidates in " + }, + { + "bbox": [ + 46, + 618, + 288, + 714 + ], + "type": "inline_equation", + "content": "C_i" + }, + { + "bbox": [ + 46, + 618, + 288, + 714 + ], + "type": "text", + "content": " by performing temporal augmentation on the original video, such as reverse order and random disorder." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "type": "text", + "content": "The listener also uses a GRU [11] layer to turn the message " + }, + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "type": "inline_equation", + "content": "m" + }, + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "type": "text", + "content": " into a hidden vector " + }, + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "type": "inline_equation", + "content": "\\mathbf{h}\\mathbf{l}_T" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 322, + 105, + 545, + 118 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 322, + 105, + 545, + 118 + ], + "spans": [ + { + "bbox": [ + 322, + 105, + 545, + 118 + ], + "type": "interline_equation", + "content": "\\mathbf {h l} _ {0} = \\mathbf {0}, \\quad \\mathbf {h l} _ {t} = \\mathrm {G P T} _ {\\mathrm {l s n}} \\left(m _ {t}, \\mathbf {h l} _ {t - 1}\\right) (t > 0). \\tag {2}", + "image_path": "15a15f6c012f5eb9c321ef0171753a86ab9649f650ccdb1d634a3607d88149f9.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 126, + 547, + 186 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 126, + 547, + 186 + ], + "spans": [ + { + "bbox": [ + 304, + 126, + 547, + 186 + ], + "type": "text", + "content": "Based on " + }, + { + "bbox": [ + 304, + 126, + 547, + 186 + ], + "type": "inline_equation", + "content": "\\mathbf{h}\\mathbf{l}_T" + }, + { + "bbox": [ + 304, + 126, + 547, + 186 + ], + "type": "text", + "content": ", the listener assigns a score for each candidate video based on inverse square error [31], then selects the image by Softmax sampling across the scores. The speaker and listener are jointly optimized by minimizing the cross-entropy loss of video selection:" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 310, + 194, + 545, + 249 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 310, + 194, + 545, + 249 + ], + "spans": [ + { + "bbox": [ + 310, + 194, + 545, + 249 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\operatorname {s c o r e} (\\mathbf {I}) = \\left\\| \\mathbf {h l} _ {T} - \\operatorname {M L P} _ {\\mathrm {l s n}} (\\mathbf {I}) \\right\\| _ {2} ^ {- 2}, \\\\ p (\\text {g u e s s} = \\mathbf {I}) = \\operatorname {s o f t m a x} (\\operatorname {s c o r e} (\\mathbf {I})) \\quad (\\mathbf {I} \\in \\left\\{\\mathbf {I} _ {i} \\right\\} \\cup C _ {i}), \\\\ \\mathcal {L} _ {E C} = - \\mathbb {E} _ {\\mathbf {I} _ {i}, C _ {i}} \\mathbb {E} _ {\\mathbf {M} _ {i}} \\log p (\\text {g u e s s} = \\mathbf {I} _ {i}). \\tag {3} \\\\ \\end{array}", + "image_path": "48c84339c9fe339e03bc03264bb5359d9fd5b5bfd874727c4ef1f36ead17e6b0.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 250, + 545, + 274 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 250, + 545, + 274 + ], + "spans": [ + { + "bbox": [ + 305, + 250, + 545, + 274 + ], + "type": "text", + "content": "The speaker can be employed to generate emergent language " + }, + { + "bbox": [ + 305, + 250, + 545, + 274 + ], + "type": "inline_equation", + "content": "\\mathcal{D}_M = \\{M_1,\\dots ,M_N\\}" + }, + { + "bbox": [ + 305, + 250, + 545, + 274 + ], + "type": "text", + "content": " based on input videos." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 281, + 545, + 306 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 281, + 545, + 306 + ], + "spans": [ + { + "bbox": [ + 305, + 281, + 545, + 306 + ], + "type": "text", + "content": "3.3. Pre-training of Language Model with Emergent Language" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 312, + 545, + 372 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 312, + 545, + 372 + ], + "spans": [ + { + "bbox": [ + 304, + 312, + 545, + 372 + ], + "type": "text", + "content": "We conduct a trajectory completion task to pre-train the GPT-like language model without action labels, as shown in Figure 2(a)(b). Firstly, we random sample a sequence of observations " + }, + { + "bbox": [ + 304, + 312, + 545, + 372 + ], + "type": "inline_equation", + "content": "\\hat{o} = \\{o_1,o_2,\\dots ,o_N\\}" + }, + { + "bbox": [ + 304, + 312, + 545, + 372 + ], + "type": "text", + "content": " stored in the dataset and map it into latent trajectory " + }, + { + "bbox": [ + 304, + 312, + 545, + 372 + ], + "type": "inline_equation", + "content": "\\tau_{\\mathrm{whole}}" + }, + { + "bbox": [ + 304, + 312, + 545, + 372 + ], + "type": "text", + "content": " by encoder " + }, + { + "bbox": [ + 304, + 312, + 545, + 372 + ], + "type": "inline_equation", + "content": "g_{\\theta}" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 395, + 380, + 545, + 393 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 395, + 380, + 545, + 393 + ], + "spans": [ + { + "bbox": [ + 395, + 380, + 545, + 393 + ], + "type": "interline_equation", + "content": "\\tau_ {\\text {w h o l e}} = g _ {\\theta} (\\hat {o}) \\tag {4}", + "image_path": "04760888e3797e581e2d2c2cb324be344516af899b40ffd275ed5012730d12b9.jpg" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 402, + 545, + 487 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 402, + 545, + 487 + ], + "spans": [ + { + "bbox": [ + 304, + 402, + 545, + 487 + ], + "type": "text", + "content": "Then we crop a random segment " + }, + { + "bbox": [ + 304, + 402, + 545, + 487 + ], + "type": "inline_equation", + "content": "\\tau_{\\mathrm{seg}}" + }, + { + "bbox": [ + 304, + 402, + 545, + 487 + ], + "type": "text", + "content": " from the whole latent trajectory " + }, + { + "bbox": [ + 304, + 402, + 545, + 487 + ], + "type": "inline_equation", + "content": "\\tau_{\\mathrm{whole}}" + }, + { + "bbox": [ + 304, + 402, + 545, + 487 + ], + "type": "text", + "content": " and the remained trajectory is denoted as " + }, + { + "bbox": [ + 304, + 402, + 545, + 487 + ], + "type": "inline_equation", + "content": "\\tau_{\\mathrm{rem}}" + }, + { + "bbox": [ + 304, + 402, + 545, + 487 + ], + "type": "text", + "content": ". The language model " + }, + { + "bbox": [ + 304, + 402, + 545, + 487 + ], + "type": "inline_equation", + "content": "f_{\\phi}" + }, + { + "bbox": [ + 304, + 402, + 545, + 487 + ], + "type": "text", + "content": " takes " + }, + { + "bbox": [ + 304, + 402, + 545, + 487 + ], + "type": "inline_equation", + "content": "\\tau_{\\mathrm{rem}}" + }, + { + "bbox": [ + 304, + 402, + 545, + 487 + ], + "type": "text", + "content": " as input and uses either emergent language " + }, + { + "bbox": [ + 304, + 402, + 545, + 487 + ], + "type": "inline_equation", + "content": "e" + }, + { + "bbox": [ + 304, + 402, + 545, + 487 + ], + "type": "text", + "content": " generated by the speaker or natural language " + }, + { + "bbox": [ + 304, + 402, + 545, + 487 + ], + "type": "inline_equation", + "content": "l" + }, + { + "bbox": [ + 304, + 402, + 545, + 487 + ], + "type": "text", + "content": " as a prompt to predict the cropped segment " + }, + { + "bbox": [ + 304, + 402, + 545, + 487 + ], + "type": "inline_equation", + "content": "\\tau_{\\mathrm{seg}}" + }, + { + "bbox": [ + 304, + 402, + 545, + 487 + ], + "type": "text", + "content": ". The language model is optimized by jointly minimizing " + }, + { + "bbox": [ + 304, + 402, + 545, + 487 + ], + "type": "inline_equation", + "content": "L_{\\mathrm{EC}}" + }, + { + "bbox": [ + 304, + 402, + 545, + 487 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 402, + 545, + 487 + ], + "type": "inline_equation", + "content": "L_{\\mathrm{Lang}}" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 369, + 494, + 545, + 509 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 369, + 494, + 545, + 509 + ], + "spans": [ + { + "bbox": [ + 369, + 494, + 545, + 509 + ], + "type": "interline_equation", + "content": "L _ {\\mathrm {E C}} = \\left(\\tau_ {\\mathrm {s e g}} - f _ {\\theta} (e, \\tau_ {\\mathrm {r e m}})\\right) ^ {2} \\tag {5}", + "image_path": "024ae38827e8e520a48566e5b7bf8789e243a8b375b619e8ccc6aff43d33e49f.jpg" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 367, + 515, + 545, + 529 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 367, + 515, + 545, + 529 + ], + "spans": [ + { + "bbox": [ + 367, + 515, + 545, + 529 + ], + "type": "interline_equation", + "content": "L _ {\\text {L a n g}} = \\left(\\tau_ {\\text {s e g}} - f _ {\\theta} (l, \\tau_ {\\text {r e m}})\\right) ^ {2} \\tag {6}", + "image_path": "8b25575f329118591dafe1ec03f5661d0409e616b7f7d94e8dc9f86bf2b7dca8.jpg" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 534, + 545, + 569 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 534, + 545, + 569 + ], + "spans": [ + { + "bbox": [ + 304, + 534, + 545, + 569 + ], + "type": "text", + "content": "The loss for the prediction using emergent language as prompt and natural language as prompt is calculated separately." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathrm{EC^2}" + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "content": " uses the same language model for both emergent language generation and trajectory completion pretext task for framework thriftiness, and both the " + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "inline_equation", + "content": "L_{\\mathrm{EC - pre}}" + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "inline_equation", + "content": "L_{\\mathrm{EC - gen}}" + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "content": " are used to update the language model jointly. To ensure that the speaker's gradient is not truncated, we use an MLP [51] layer to map from the logits of the word distribution to a 512-dimensional latent vector instead of selecting a word embedding in the dictionary according to the token. For natural language, we use the Byte-Pair Encoding (BPE) tokenizer [6] to encode it into tokens, which are widely used by OpenAI for tokenization when pre-training the GPT model, including GPT [48], GPT-2 [49], RoBERTa [34]," + } + ] + } + ], + "index": 20 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "6707" + } + ] + } + ], + "index": 21 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 288, + 120 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 288, + 120 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 288, + 120 + ], + "type": "text", + "content": "and BART [32]. We also learn a corresponding dictionary of word embedding. Although the emergent language and natural language are used separately, they can learn correlated information via the pretext trajectory completion task." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 129, + 287, + 152 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 129, + 287, + 152 + ], + "spans": [ + { + "bbox": [ + 47, + 129, + 287, + 152 + ], + "type": "text", + "content": "3.4. Few-shot Policy Learning for Downstream Embodied control" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 159, + 288, + 387 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 159, + 288, + 387 + ], + "spans": [ + { + "bbox": [ + 46, + 159, + 288, + 387 + ], + "type": "text", + "content": "To transfer the pre-trained language model into the downstream imitation learning tasks, the language model " + }, + { + "bbox": [ + 46, + 159, + 288, + 387 + ], + "type": "inline_equation", + "content": "f_{\\theta}(\\cdot ,\\cdot)" + }, + { + "bbox": [ + 46, + 159, + 288, + 387 + ], + "type": "text", + "content": " take the current trajectory " + }, + { + "bbox": [ + 46, + 159, + 288, + 387 + ], + "type": "inline_equation", + "content": "\\tau_{cur} = \\{s_{t - T},\\dots ,s_{t - 1},s_t\\}" + }, + { + "bbox": [ + 46, + 159, + 288, + 387 + ], + "type": "text", + "content": " and the emergent language " + }, + { + "bbox": [ + 46, + 159, + 288, + 387 + ], + "type": "inline_equation", + "content": "e" + }, + { + "bbox": [ + 46, + 159, + 288, + 387 + ], + "type": "text", + "content": " or natural language instruction " + }, + { + "bbox": [ + 46, + 159, + 288, + 387 + ], + "type": "inline_equation", + "content": "l" + }, + { + "bbox": [ + 46, + 159, + 288, + 387 + ], + "type": "text", + "content": " as prompt, then output the predicted features " + }, + { + "bbox": [ + 46, + 159, + 288, + 387 + ], + "type": "inline_equation", + "content": "m_{t}" + }, + { + "bbox": [ + 46, + 159, + 288, + 387 + ], + "type": "text", + "content": ". Finally, the output " + }, + { + "bbox": [ + 46, + 159, + 288, + 387 + ], + "type": "inline_equation", + "content": "m_{t}" + }, + { + "bbox": [ + 46, + 159, + 288, + 387 + ], + "type": "text", + "content": " of the language model is mapped to specific action " + }, + { + "bbox": [ + 46, + 159, + 288, + 387 + ], + "type": "inline_equation", + "content": "a_{t}" + }, + { + "bbox": [ + 46, + 159, + 288, + 387 + ], + "type": "text", + "content": " by task-specific MLP layers " + }, + { + "bbox": [ + 46, + 159, + 288, + 387 + ], + "type": "inline_equation", + "content": "\\pi_{\\psi}" + }, + { + "bbox": [ + 46, + 159, + 288, + 387 + ], + "type": "text", + "content": ". The language model " + }, + { + "bbox": [ + 46, + 159, + 288, + 387 + ], + "type": "inline_equation", + "content": "f_{\\theta}" + }, + { + "bbox": [ + 46, + 159, + 288, + 387 + ], + "type": "text", + "content": " is frozen during downstream imitation learning. The action under learned behavior policy is sampled by " + }, + { + "bbox": [ + 46, + 159, + 288, + 387 + ], + "type": "inline_equation", + "content": "\\hat{a}_t\\sim \\pi_\\psi (a_t|m_t)" + }, + { + "bbox": [ + 46, + 159, + 288, + 387 + ], + "type": "text", + "content": " and the expert demonstration action " + }, + { + "bbox": [ + 46, + 159, + 288, + 387 + ], + "type": "inline_equation", + "content": "a_{t}" + }, + { + "bbox": [ + 46, + 159, + 288, + 387 + ], + "type": "text", + "content": " are used as the label for imitation learning. For the video instruction following task, we generate emergent language by the speaker and use it as the prompt of the language model. For language instruction following tasks, the natural language is tokenized by the BPE tokenizer, and select the corresponding word embedding in the dictionary as the prompt as language model via the inferred token. With a trajectory with length " + }, + { + "bbox": [ + 46, + 159, + 288, + 387 + ], + "type": "inline_equation", + "content": "H" + }, + { + "bbox": [ + 46, + 159, + 288, + 387 + ], + "type": "text", + "content": ", the task-specific MLP layers are optimized by minimizing " + }, + { + "bbox": [ + 46, + 159, + 288, + 387 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{IL}}(\\psi)" + }, + { + "bbox": [ + 46, + 159, + 288, + 387 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 83, + 396, + 287, + 422 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 83, + 396, + 287, + 422 + ], + "spans": [ + { + "bbox": [ + 83, + 396, + 287, + 422 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\mathrm {I L}} (\\psi) = E _ {\\tau \\sim \\mathcal {B}} \\left[ - \\frac {1}{H} \\sum_ {t} ^ {t + H - 1} \\log \\pi_ {\\psi} (a _ {t} | m _ {t}) \\right] \\tag {7}", + "image_path": "3498e96ab80d7df590e73bf0db15a1df8e98e4cc88363eaf5223a12eb4fbe7e0.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 424, + 287, + 472 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 424, + 287, + 472 + ], + "spans": [ + { + "bbox": [ + 46, + 424, + 287, + 472 + ], + "type": "text", + "content": "The MLP [51] layers are implemented with hidden sizes [256, 256] with batch normalization [21] and are trained with a learning rate of 0.001 and a batch size of 32 for 20000 iterations." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 483, + 128, + 497 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 483, + 128, + 497 + ], + "spans": [ + { + "bbox": [ + 47, + 483, + 128, + 497 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 503, + 165, + 516 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 503, + 165, + 516 + ], + "spans": [ + { + "bbox": [ + 47, + 503, + 165, + 516 + ], + "type": "text", + "content": "4.1. Pre-training Dataset" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 522, + 287, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 522, + 287, + 712 + ], + "spans": [ + { + "bbox": [ + 46, + 522, + 287, + 712 + ], + "type": "text", + "content": "We use the LOReL [37] real robot dataset, which is collected by Franka Emika Panda mounted over an IKEA desk. The LOReL dataset contains 3000 episodes (150000 frames) of reinforcement learning that trains policies for different behaviors on the IKEA desk using online RL. The language instruction is annotated by leveraging crowdsourcing, specifically Amazon Mechanical Turk. Human annotators are asked to describe the behavior if any, that the robot is doing and to phrase it as a command without any pre-specified template. The LOReL dataset contains 6000 annotations, two per episode, containing a total of 1699 unique instructions. The dataset contains different videos with the same language instruction to ensure diversity. We removed the episodes where annotators reported the robot as inactive or its actions unclear, making them incomprehensible." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 72, + 493, + 84 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 72, + 493, + 84 + ], + "spans": [ + { + "bbox": [ + 306, + 72, + 493, + 84 + ], + "type": "text", + "content": "4.2. Downstream Testing Environments" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 90, + 545, + 388 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 90, + 545, + 388 + ], + "spans": [ + { + "bbox": [ + 304, + 90, + 545, + 388 + ], + "type": "text", + "content": "We utilize two standard robotic manipulation benchmarks, namely MetaWorld [60] and the Franka Kitchen environment [17], as our downstream testing environments. It is worth noting that these testing environments were not used during the training phase of " + }, + { + "bbox": [ + 304, + 90, + 545, + 388 + ], + "type": "inline_equation", + "content": "\\mathrm{EC^2}" + }, + { + "bbox": [ + 304, + 90, + 545, + 388 + ], + "type": "text", + "content": ". In MetaWorld, the agent is presented with a series of tasks, including assembling a ring on a peg, picking and placing a block between bins, pushing a button, opening a drawer, and hammering a nail. In Franka Kitchen, the agent aims to learn how to slide open the right door, open the left door, turn on the light, turn the stove top knob, and open the microwave. As shown in Figure 3, both environments offer image observations to the agent, as well as proprioceptive data, which includes the end-effector pose and joint positions. These data are concatenated with the encoded vision observations for each task, providing the agent with a comprehensive understanding of the current task. All tasks involve random environment variation, either by varying the position of the target object in MetaWorld or the positioning of the desk in Franka Kitchen. Additionally, we consider three views for each environment to evaluate the robustness of representations across viewpoints. Finally, for each environment, we also consider three demo sizes used in downstream embodied control tasks: [5, 10, 25] in MetaWorld and Franka Kitchen." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 396, + 422, + 409 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 396, + 422, + 409 + ], + "spans": [ + { + "bbox": [ + 306, + 396, + 422, + 409 + ], + "type": "text", + "content": "4.3. Experimental Setup" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 415, + 545, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 415, + 545, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 415, + 545, + 715 + ], + "type": "text", + "content": "For embodied control tasks, we take R3M and BC-Z as the key baseline. R3M [38] learns the state-of-the-art embodied representations pre-trained on diverse paired human video-language data with time-contrastive learning, which encourages states closer in time to be closer in embedding space and video-language alignment to encourage the embeddings to capture semantically relevant features. For sufficient comparison, we implement R3M with both the language instruction-conditioned version and video instruction-conditioned version, respectively, based on their official implementation. For embodied control with natural language instruction, we use the language encoder of the pre-trained model officially released by their author team to encode the natural language. For embodied control with demonstration video instruction, we use the officially released vision encoder to extract features of every frame in the video and map them into the instruction representation by one MLP layer. BC-Z [24] jointly learns the alignment between video representation and language representation together with policy learning across multiple embodied control tasks. Our evaluation methodology is inspired by [38, 41]. We focus on evaluating the embodied representation of instruction and observation for downstream policy learning with behavior cloning. We parameterize the downstream policy " + }, + { + "bbox": [ + 304, + 415, + 545, + 715 + ], + "type": "inline_equation", + "content": "\\pi" + }, + { + "bbox": [ + 304, + 415, + 545, + 715 + ], + "type": "text", + "content": " as a two-layer MLP preceded by a" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "type": "text", + "content": "6708" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 77, + 79, + 184, + 205 + ], + "blocks": [ + { + "bbox": [ + 77, + 79, + 184, + 205 + ], + "lines": [ + { + "bbox": [ + 77, + 79, + 184, + 205 + ], + "spans": [ + { + "bbox": [ + 77, + 79, + 184, + 205 + ], + "type": "image", + "image_path": 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Evaluation Environments: We consider a set of manipulation tasks including 5 tasks with a Sawyer from MetaWorld [60], 5 tasks from a Franka operating over a Kitchen [17]. We provide specific language instruction labels for every task and 25 demos per task for evaluation. We show an example image and corresponding language instruction for each task shown above. Evaluation Viewpoints: To robustly measure the efficacy of different visual representations, we consider three camera viewpoints per environment." + } + ] + } + ], + "index": 22, + "angle": 0, + "type": "image_caption" + } + ], + "index": 14 + }, + { + "type": "image", + "bbox": [ + 322, + 153, + 376, + 205 + ], + "blocks": [ + { + "bbox": [ + 322, + 153, + 376, + 205 + ], + "lines": [ + { + "bbox": [ + 322, + 153, + 376, + 205 + ], + "spans": [ + { + "bbox": [ + 322, + 153, + 376, + 205 + ], + "type": "image", + "image_path": "58e4202f636d0e6b91e61b60526bfabf65128c9ec70fe6eb999fe1f8e45f7ba9.jpg" + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "image_body" + } + ], + "index": 16 + }, + { + "type": "image", + "bbox": [ + 386, + 153, + 442, + 205 + ], + "blocks": [ + { + "bbox": [ + 386, + 153, + 442, + 205 + ], + "lines": [ + { + "bbox": [ + 386, + 153, + 442, + 205 + ], + "spans": [ + { + "bbox": [ + 386, + 153, + 442, + 205 + ], + "type": "image", + "image_path": "0271f6430031c9f93c4b7f6d2c192659569d78b1105a3df4ced1a1a5a38c1694.jpg" + } + ] + } + ], + "index": 17, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 394, + 209, + 440, + 217 + ], + "lines": [ + { + "bbox": [ + 394, + 209, + 440, + 217 + ], + "spans": [ + { + "bbox": [ + 394, + 209, + 440, + 217 + ], + "type": "text", + "content": "Open the drawer" + } + ] + } + ], + "index": 18, + "angle": 0, + "type": "image_caption" + } + ], + "index": 17 + }, + { + "type": "image", + "bbox": [ + 452, + 153, + 509, + 205 + ], + "blocks": [ + { + "bbox": [ + 452, + 153, + 509, + 205 + ], + "lines": [ + { + "bbox": [ + 452, + 153, + 509, + 205 + ], + "spans": [ + { + "bbox": [ + 452, + 153, + 509, + 205 + ], + "type": "image", + "image_path": "86f240df30023b545739978bf33eb43205f1cd8cb40134e91d588c85c122e8e7.jpg" + } + ] + } + ], + "index": 19, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 452, + 209, + 511, + 224 + ], + "lines": [ + { + "bbox": [ + 452, + 209, + 511, + 224 + ], + "spans": [ + { + "bbox": [ + 452, + 209, + 511, + 224 + ], + "type": "text", + "content": "Pick up the hammer and hammer the wall" + } + ] + } + ], + "index": 20, + "angle": 0, + "type": "image_caption" + } + ], + "index": 19 + }, + { + "type": "table", + "bbox": [ + 50, + 289, + 545, + 402 + ], + "blocks": [ + { + "bbox": [ + 50, + 289, + 545, + 402 + ], + "lines": [ + { + "bbox": [ + 50, + 289, + 545, + 402 + ], + "spans": [ + { + "bbox": [ + 50, + 289, + 545, + 402 + ], + "type": "table", + "html": "
BenchmarkNum. DemosInstructionEC2(ours)R3M [38]BC-Z [24]
MetaWorld10Lang72.4 ± 2.4%69.2 ± 2.0%63.4 ± 2.1%
Video76.0 ± 2.1% (+3.6)71.8 ± 1.8% (+2.6)64.8 ± 2.0% (+1.4)
25Lang82.6 ± 2.0%77.4 ± 2.4%74.1 ± 2.2%
Video85.0 ± 2.2% (+2.4)79.0 ± 2.1% (+1.6)75.2 ± 1.0% (+1.1)
Franka Kitchen10Lang48.4 ± 2.5%41.8 ± 2.5%34.2 ± 2.3%
Video53.6 ± 2.5%(+5.2)45.7 ± 2.4% (+3.9)37.5 ± 2.2% (+3.3)
25Lang59.8 ± 2.5%56.0 ± 2.3%38.6 ± 2.4%
Video63.2 ± 2.6% (+3.4)58.7 ± 2.0% (+2.7)40.0 ± 2.0% (+1.4)
", + "image_path": "9e53f82c2e348adc7adc0f80220e578497fd1c34e413b83d09b2b85f06806f70.jpg" + } + ] + } + ], + "index": 23, + "angle": 0, + "type": "table_body" + } + ], + "index": 23 + }, + { + "bbox": [ + 46, + 404, + 546, + 427 + ], + "lines": [ + { + "bbox": [ + 46, + 404, + 546, + 427 + ], + "spans": [ + { + "bbox": [ + 46, + 404, + 546, + 427 + ], + "type": "text", + "content": "Table 1. Performance comparison on Success rate of embodied control with language/video instruction across different demo size. We mark the performance difference between complete the task with natural language instruction and video instruction as blue." + } + ] + } + ], + "index": 24, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 433, + 287, + 517 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 433, + 287, + 517 + ], + "spans": [ + { + "bbox": [ + 46, + 433, + 287, + 517 + ], + "type": "text", + "content": "BatchNorm at the input. We train the agent for 20,000 steps, evaluate it online in the environment every 1000 steps, and report the best success rate achieved. For each task, we run 5 seeds of behavior cloning. The final success rate reported for one method on one task is the average over the 5 seeds " + }, + { + "bbox": [ + 46, + 433, + 287, + 517 + ], + "type": "inline_equation", + "content": "\\times 3" + }, + { + "bbox": [ + 46, + 433, + 287, + 517 + ], + "type": "text", + "content": " camera viewpoints " + }, + { + "bbox": [ + 46, + 433, + 287, + 517 + ], + "type": "inline_equation", + "content": "\\times 3" + }, + { + "bbox": [ + 46, + 433, + 287, + 517 + ], + "type": "text", + "content": " demo sizes, for a total of 45 runs (see more details in Appendix)." + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 47, + 526, + 104, + 538 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 526, + 104, + 538 + ], + "spans": [ + { + "bbox": [ + 47, + 526, + 104, + 538 + ], + "type": "text", + "content": "4.4. Results" + } + ] + } + ], + "index": 26 + }, + { + "bbox": [ + 46, + 545, + 287, + 676 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 545, + 287, + 676 + ], + "spans": [ + { + "bbox": [ + 46, + 545, + 287, + 676 + ], + "type": "text", + "content": "We aim to answer 5 questions to get insight into embodied AI community: 1) Can emergent language help embodied control tasks with natural language instruction? 2) Can emergent language help the embodied control tasks with video instruction? 3) Can the joint training of emergent language and natural language in GPT-Like network architecture help each other? 4) Can emergent language provide more detailed and effective guidelines than video captions? 5) What is the relationship between model size, control performance, and the correlation between emergent language and natural language?" + } + ] + } + ], + "index": 27 + }, + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "text", + "content": "To answer the first two questions, we study if " + }, + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\mathrm{EC^2}" + }, + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "text", + "content": " enables more data-efficient policy learning with both natural language instructions and video instructions." + } + ] + } + ], + "index": 28 + }, + { + "bbox": [ + 306, + 434, + 546, + 457 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 434, + 546, + 457 + ], + "spans": [ + { + "bbox": [ + 306, + 434, + 546, + 457 + ], + "type": "text", + "content": "1) Can emergent language help the embodied control tasks with natural language?" + } + ] + } + ], + "index": 29 + }, + { + "bbox": [ + 304, + 462, + 546, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 462, + 546, + 712 + ], + "spans": [ + { + "bbox": [ + 304, + 462, + 546, + 712 + ], + "type": "text", + "content": "We measure the success rate of downstream few-shot policy learning with different pre-training methods. In Franka Kitchen and MetaWorld, we only use no more than 25 demos to perform downstream few-shot policy learning and report the performance with both 10 and 25 demos separately in Table 1. Learning from scratch is struggled to perform well when working with small amounts of data since it can be challenging for the model to identify meaningful patterns or relationships with such limited data. While the methods with a pre-trained model, like " + }, + { + "bbox": [ + 304, + 462, + 546, + 712 + ], + "type": "inline_equation", + "content": "\\mathrm{EC}^2" + }, + { + "bbox": [ + 304, + 462, + 546, + 712 + ], + "type": "text", + "content": ", R3M, and BC-Z performs better than those learning from scratch. Through our study, as shown in Table 1, " + }, + { + "bbox": [ + 304, + 462, + 546, + 712 + ], + "type": "inline_equation", + "content": "\\mathrm{EC}^2" + }, + { + "bbox": [ + 304, + 462, + 546, + 712 + ], + "type": "text", + "content": " exceeds existing methods with natural language instruction, which indicates that emergent language can help the embodied control tasks to improve the performance with natural language instruction. Across all the evaluations, " + }, + { + "bbox": [ + 304, + 462, + 546, + 712 + ], + "type": "inline_equation", + "content": "\\mathrm{EC}^2" + }, + { + "bbox": [ + 304, + 462, + 546, + 712 + ], + "type": "text", + "content": " is overall able to learn these embodied tasks in an extremely low data regime (only 10 demos) with " + }, + { + "bbox": [ + 304, + 462, + 546, + 712 + ], + "type": "inline_equation", + "content": "\\approx 60.4\\%" + }, + { + "bbox": [ + 304, + 462, + 546, + 712 + ], + "type": "text", + "content": " overall success rate, despite never seeing any data from the target environments in training the representation, while R3M only achieves " + }, + { + "bbox": [ + 304, + 462, + 546, + 712 + ], + "type": "inline_equation", + "content": "\\approx 55.5\\%" + }, + { + "bbox": [ + 304, + 462, + 546, + 712 + ], + "type": "text", + "content": " overall success rate." + } + ] + } + ], + "index": 30 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "6709" + } + ] + } + ], + "index": 31 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 50, + 71, + 547, + 148 + ], + "blocks": [ + { + "bbox": [ + 50, + 71, + 547, + 148 + ], + "lines": [ + { + "bbox": [ + 50, + 71, + 547, + 148 + ], + "spans": [ + { + "bbox": [ + 50, + 71, + 547, + 148 + ], + "type": "table", + "html": "
BenchmarkNum. DemosLanguage InstructionVideo Instruction
\\( EC^2 \\)\\( EC^2 (-EC) \\)\\( EC^2 \\)\\( EC^2 (-NL) \\)\\( EC^2 (+Cap,-EC) \\)
MetaWorld1072.4 ± 2.4%69.0 ± 2.0%76.0 ± 2.1%72.6 ± 2.4%73.0 ± 2.2%
2582.6 ± 2.0%78.0 ± 2.4%85.0 ± 2.5%82.0 ± 2.0%73.2 ± 2.5%
Franka Kitchen1048.4 ± 2.5%43.0 ± 3.3%53.6 ± 2.5%49.0 ± 2.5%48.6 ± 2.4%
2559.8 ± 2.5%54.0 ± 2.6%63.2 ± 2.6%61.3 ± 2.4%49.0 ± 2.3%
", + "image_path": "4bec8b23ee930a800f3c2f0379217a40c71fd1017fe08e3caf24a7678db4e87a.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 55, + 171, + 199, + 225 + ], + "blocks": [ + { + "bbox": [ + 127, + 153, + 465, + 164 + ], + "lines": [ + { + "bbox": [ + 127, + 153, + 465, + 164 + ], + "spans": [ + { + "bbox": [ + 127, + 153, + 465, + 164 + ], + "type": "text", + "content": "Table 2. Ablation study on embodied control with language instruction and video instruction." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 55, + 171, + 199, + 225 + ], + "lines": [ + { + "bbox": [ + 55, + 171, + 199, + 225 + ], + "spans": [ + { + "bbox": [ + 55, + 171, + 199, + 225 + ], + "type": "table", + "html": "
Model Size#layer#head#embedded
Base816512
Mini66192
Micro44128
", + "image_path": "0ef50b2a9def2b6b5488e08c3dafb82b0f86b51fa9d16f0d4b19371ea0f2530f.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "type": "table", + "bbox": [ + 205, + 171, + 544, + 253 + ], + "blocks": [ + { + "bbox": [ + 47, + 233, + 200, + 277 + ], + "lines": [ + { + "bbox": [ + 47, + 233, + 200, + 277 + ], + "spans": [ + { + "bbox": [ + 47, + 233, + 200, + 277 + ], + "type": "text", + "content": "Table 3. Hyper-parameters for different model sizes of " + }, + { + "bbox": [ + 47, + 233, + 200, + 277 + ], + "type": "inline_equation", + "content": "{\\mathrm{{EC}}}^{2}" + }, + { + "bbox": [ + 47, + 233, + 200, + 277 + ], + "type": "text", + "content": " . All the models are implemented based on GPT [48]-like network architecture." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 205, + 171, + 544, + 253 + ], + "lines": [ + { + "bbox": [ + 205, + 171, + 544, + 253 + ], + "spans": [ + { + "bbox": [ + 205, + 171, + 544, + 253 + ], + "type": "table", + "html": "
Natural LanguageEmergent language
“Open the right drawer”[262, 847, 490, 536, 108, 500, 941, 838, 749, 444]
“Grasp in the middle drawer”[356, 69, 108, 259, 72, 616, 500, 896, 623, 433]
“Reach down for stapler”[204, 897, 285, 509, 701, 545, 538, 729, 902, 195]
“Pick up the stapler in the drawer”[535, 67, 108, 661, 84, 701, 776, 500, 377, 454]
“Reach to the plug”[982, 691, 72, 538, 97, 665, 148, 369, 102, 1003]
“Reach to the left drawer”[786, 538, 601, 874, 848, 500, 315, 108, 72, 914]
", + "image_path": "fcff10ea89a80a4bc3ff95c82932dd303d9ed7097fe1559e10135a18ff41bf2f.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_body" + } + ], + "index": 4 + }, + { + "bbox": [ + 203, + 255, + 543, + 277 + ], + "lines": [ + { + "bbox": [ + 203, + 255, + 543, + 277 + ], + "spans": [ + { + "bbox": [ + 203, + 255, + 543, + 277 + ], + "type": "text", + "content": "Table 4. Qualitative examples of emergent language and corresponding natural language. The word and tokens that have the same semantic meaning are marked with the same color." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 283, + 287, + 592 + ], + "type": "list", + "angle": 0, + "index": 11, + "blocks": [ + { + "bbox": [ + 47, + 283, + 287, + 307 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 283, + 287, + 307 + ], + "spans": [ + { + "bbox": [ + 47, + 283, + 287, + 307 + ], + "type": "text", + "content": "2) Can emergent language help the embodied control tasks with video instruction?" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 309, + 287, + 441 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 309, + 287, + 441 + ], + "spans": [ + { + "bbox": [ + 46, + 309, + 287, + 441 + ], + "type": "text", + "content": "As shown in Table1, " + }, + { + "bbox": [ + 46, + 309, + 287, + 441 + ], + "type": "inline_equation", + "content": "\\mathrm{EC^2}" + }, + { + "bbox": [ + 46, + 309, + 287, + 441 + ], + "type": "text", + "content": " shows an obvious advantage over the exciting methods and achieves the best success rate (" + }, + { + "bbox": [ + 46, + 309, + 287, + 441 + ], + "type": "inline_equation", + "content": "\\approx 64.8\\%" + }, + { + "bbox": [ + 46, + 309, + 287, + 441 + ], + "type": "text", + "content": " with 10 demos and " + }, + { + "bbox": [ + 46, + 309, + 287, + 441 + ], + "type": "inline_equation", + "content": "\\approx 74.1\\%" + }, + { + "bbox": [ + 46, + 309, + 287, + 441 + ], + "type": "text", + "content": " with 25 demos) with video instruction. As marked in blue in Table 1, " + }, + { + "bbox": [ + 46, + 309, + 287, + 441 + ], + "type": "inline_equation", + "content": "\\mathrm{EC^2}" + }, + { + "bbox": [ + 46, + 309, + 287, + 441 + ], + "type": "text", + "content": " has better performance with video instruction than with language instruction, which indicates that " + }, + { + "bbox": [ + 46, + 309, + 287, + 441 + ], + "type": "inline_equation", + "content": "\\mathrm{EC^2}" + }, + { + "bbox": [ + 46, + 309, + 287, + 441 + ], + "type": "text", + "content": " learns more effective information provided by a video demonstration. In contrast, R3M and BC-Z, which use contrast learning or regression to force the two modalities of language and video aligned, have little difference in performance under language instruction and video instruction." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 443, + 287, + 515 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 443, + 287, + 515 + ], + "spans": [ + { + "bbox": [ + 46, + 443, + 287, + 515 + ], + "type": "text", + "content": "We also investigate the task performance of " + }, + { + "bbox": [ + 46, + 443, + 287, + 515 + ], + "type": "inline_equation", + "content": "\\mathrm{EC^2}" + }, + { + "bbox": [ + 46, + 443, + 287, + 515 + ], + "type": "text", + "content": " and baselines with different amounts of demos in policy learning. In Figure 4, we plot the average success rate of each method across each demo size. We observe that the performance improvement from " + }, + { + "bbox": [ + 46, + 443, + 287, + 515 + ], + "type": "inline_equation", + "content": "\\mathrm{EC^2}" + }, + { + "bbox": [ + 46, + 443, + 287, + 515 + ], + "type": "text", + "content": " is consistent, outperforming the baselines across every environment and demo size." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 517, + 287, + 566 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 517, + 287, + 566 + ], + "spans": [ + { + "bbox": [ + 46, + 517, + 287, + 566 + ], + "type": "text", + "content": "Ablation Study: Also, in the data-efficient imitation learning setting, we ablate the different components of " + }, + { + "bbox": [ + 46, + 517, + 287, + 566 + ], + "type": "inline_equation", + "content": "\\mathrm{EC^2}" + }, + { + "bbox": [ + 46, + 517, + 287, + 566 + ], + "type": "text", + "content": " training to answer question 3 and 4 and check if each module is indispensable." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 567, + 287, + 592 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 567, + 287, + 592 + ], + "spans": [ + { + "bbox": [ + 47, + 567, + 287, + 592 + ], + "type": "text", + "content": "3) Can the joint training of emergent language and natural language with GPT-Like network help each other?" + } + ] + } + ], + "index": 10 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 46, + 594, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 594, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 288, + 714 + ], + "type": "text", + "content": "We conduct ablation studies to compare " + }, + { + "bbox": [ + 46, + 594, + 288, + 714 + ], + "type": "inline_equation", + "content": "\\mathrm{EC}^2" + }, + { + "bbox": [ + 46, + 594, + 288, + 714 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 594, + 288, + 714 + ], + "type": "inline_equation", + "content": "\\mathrm{EC}^2" + }, + { + "bbox": [ + 46, + 594, + 288, + 714 + ], + "type": "text", + "content": " (-EC) in language instruction following tasks and compare " + }, + { + "bbox": [ + 46, + 594, + 288, + 714 + ], + "type": "inline_equation", + "content": "\\mathrm{EC}^2" + }, + { + "bbox": [ + 46, + 594, + 288, + 714 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 594, + 288, + 714 + ], + "type": "inline_equation", + "content": "\\mathrm{EC}^2" + }, + { + "bbox": [ + 46, + 594, + 288, + 714 + ], + "type": "text", + "content": " (-NL) in video instruction following tasks. " + }, + { + "bbox": [ + 46, + 594, + 288, + 714 + ], + "type": "inline_equation", + "content": "\\mathrm{EC}^2" + }, + { + "bbox": [ + 46, + 594, + 288, + 714 + ], + "type": "text", + "content": " (-EC) does not use emergent language to pre-train the language model under " + }, + { + "bbox": [ + 46, + 594, + 288, + 714 + ], + "type": "inline_equation", + "content": "\\mathrm{EC}^2" + }, + { + "bbox": [ + 46, + 594, + 288, + 714 + ], + "type": "text", + "content": " framework, which predicts the masked trajectories with only the language instruction (human-labeled caption). " + }, + { + "bbox": [ + 46, + 594, + 288, + 714 + ], + "type": "inline_equation", + "content": "\\mathrm{EC}^2" + }, + { + "bbox": [ + 46, + 594, + 288, + 714 + ], + "type": "text", + "content": " (-NL) does not use natural language to pre-train the language model under " + }, + { + "bbox": [ + 46, + 594, + 288, + 714 + ], + "type": "inline_equation", + "content": "\\mathrm{EC}^2" + }, + { + "bbox": [ + 46, + 594, + 288, + 714 + ], + "type": "text", + "content": " framework, which predicts the masked trajectories with only the emergent language. As shown in the left-hand column in" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 283, + 545, + 430 + ], + "type": "list", + "angle": 0, + "index": 15, + "blocks": [ + { + "bbox": [ + 304, + 283, + 545, + 403 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 283, + 545, + 403 + ], + "spans": [ + { + "bbox": [ + 304, + 283, + 545, + 403 + ], + "type": "text", + "content": "Table 2, without the help of emergent language, the performance decreased significantly, and " + }, + { + "bbox": [ + 304, + 283, + 545, + 403 + ], + "type": "inline_equation", + "content": "\\mathrm{EC^2}" + }, + { + "bbox": [ + 304, + 283, + 545, + 403 + ], + "type": "text", + "content": " (-EC) shows no obvious advantages to the other methods that learn pretrained models by video-language pre-training. Similarly, as shown in the right-hand column in Table 2, " + }, + { + "bbox": [ + 304, + 283, + 545, + 403 + ], + "type": "inline_equation", + "content": "\\mathrm{EC^2}" + }, + { + "bbox": [ + 304, + 283, + 545, + 403 + ], + "type": "text", + "content": " also outperforms " + }, + { + "bbox": [ + 304, + 283, + 545, + 403 + ], + "type": "inline_equation", + "content": "\\mathrm{EC^2}" + }, + { + "bbox": [ + 304, + 283, + 545, + 403 + ], + "type": "text", + "content": " (-NL), which demonstrates that the language pre-training helps the video instruction task with emergent language. Thus, the above ablation analysis shows that the joint training of emergent language and natural language can benefit each other." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 406, + 545, + 430 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 406, + 545, + 430 + ], + "spans": [ + { + "bbox": [ + 304, + 406, + 545, + 430 + ], + "type": "text", + "content": "4) Can emergent language provide more detailed and effective guidelines than video captions?" + } + ] + } + ], + "index": 14 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 304, + 432, + 545, + 555 + ], + "type": "list", + "angle": 0, + "index": 18, + "blocks": [ + { + "bbox": [ + 304, + 432, + 545, + 516 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 432, + 545, + 516 + ], + "spans": [ + { + "bbox": [ + 304, + 432, + 545, + 516 + ], + "type": "text", + "content": "In " + }, + { + "bbox": [ + 304, + 432, + 545, + 516 + ], + "type": "inline_equation", + "content": "\\mathrm{EC^2}" + }, + { + "bbox": [ + 304, + 432, + 545, + 516 + ], + "type": "text", + "content": " (+Cap, -EC), we replace the emergent language in " + }, + { + "bbox": [ + 304, + 432, + 545, + 516 + ], + "type": "inline_equation", + "content": "\\mathrm{EC^2}" + }, + { + "bbox": [ + 304, + 432, + 545, + 516 + ], + "type": "text", + "content": " with the language caption given by a MARN [45] as a data augmentation, which is a pre-trained video caption model. As shown in Table 2, " + }, + { + "bbox": [ + 304, + 432, + 545, + 516 + ], + "type": "inline_equation", + "content": "\\mathrm{EC^2}" + }, + { + "bbox": [ + 304, + 432, + 545, + 516 + ], + "type": "text", + "content": " shows an obvious advantage to " + }, + { + "bbox": [ + 304, + 432, + 545, + 516 + ], + "type": "inline_equation", + "content": "\\mathrm{EC^2}" + }, + { + "bbox": [ + 304, + 432, + 545, + 516 + ], + "type": "text", + "content": " (+Cap, -NL), which demonstrates that emergent language provides more detailed and effective guidelines than video captions." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 519, + 545, + 555 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 519, + 545, + 555 + ], + "spans": [ + { + "bbox": [ + 304, + 519, + 545, + 555 + ], + "type": "text", + "content": "5) What is the relationship between model size, control performance, and the correlation between emergent language and natural language?" + } + ] + } + ], + "index": 17 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 304, + 557, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 557, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 557, + 546, + 713 + ], + "type": "text", + "content": "We first tested the overall average success rate of " + }, + { + "bbox": [ + 304, + 557, + 546, + 713 + ], + "type": "inline_equation", + "content": "\\mathrm{EC^2}" + }, + { + "bbox": [ + 304, + 557, + 546, + 713 + ], + "type": "text", + "content": " with different model sizes (listed in Table 3) in the downstream tasks (Franka Kitchen and MetaWorld). As shown in Figure 5a and Figure 5b, the larger the size of the model, the more expressive it is and thus the better its performance. Then, we perform a linear correlation analysis on the word embeddings of the emergent language and the word embeddings of the matched natural language. We use the square of the coefficient of determination, denoted " + }, + { + "bbox": [ + 304, + 557, + 546, + 713 + ], + "type": "inline_equation", + "content": "R^2" + }, + { + "bbox": [ + 304, + 557, + 546, + 713 + ], + "type": "text", + "content": " as the measure of predicting the performance of linear regression, which reflects the proportion of the variation in the dependent variable that is predictable from the independent variable. Consider a linear regression model " + }, + { + "bbox": [ + 304, + 557, + 546, + 713 + ], + "type": "inline_equation", + "content": "f(\\cdot)" + }, + { + "bbox": [ + 304, + 557, + 546, + 713 + ], + "type": "text", + "content": " which predicts " + }, + { + "bbox": [ + 304, + 557, + 546, + 713 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 304, + 557, + 546, + 713 + ], + "type": "text", + "content": " with" + } + ] + } + ], + "index": 19 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "6710" + } + ] + } + ], + "index": 20 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 49, + 79, + 161, + 163 + ], + "blocks": [ + { + "bbox": [ + 49, + 79, + 161, + 163 + ], + "lines": [ + { + "bbox": [ + 49, + 79, + 161, + 163 + ], + "spans": [ + { + "bbox": [ + 49, + 79, + 161, + 163 + ], + "type": "image", + "image_path": "e1c675166d9cae9f2a36e74272fe96c8a162c6992d35ea248e11595eaab3b5c2.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 50, + 165, + 170, + 175 + ], + "lines": [ + { + "bbox": [ + 50, + 165, + 170, + 175 + ], + "spans": [ + { + "bbox": [ + 50, + 165, + 170, + 175 + ], + "type": "text", + "content": "(a) MetaWorld[language instruction]" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 173, + 79, + 286, + 163 + ], + "blocks": [ + { + "bbox": [ + 173, + 79, + 286, + 163 + ], + "lines": [ + { + "bbox": [ + 173, + 79, + 286, + 163 + ], + "spans": [ + { + "bbox": [ + 173, + 79, + 286, + 163 + ], + "type": "image", + "image_path": "4bd772172ba3c0aab7872154d602aa15871538fac270090210326801b04f0495.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 179, + 165, + 288, + 175 + ], + "lines": [ + { + "bbox": [ + 179, + 165, + 288, + 175 + ], + "spans": [ + { + "bbox": [ + 179, + 165, + 288, + 175 + ], + "type": "text", + "content": "(b) Kitchen[language instruction]" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 296, + 79, + 408, + 163 + ], + "blocks": [ + { + "bbox": [ + 296, + 79, + 408, + 163 + ], + "lines": [ + { + "bbox": [ + 296, + 79, + 408, + 163 + ], + "spans": [ + { + "bbox": [ + 296, + 79, + 408, + 163 + ], + "type": "image", + "image_path": "e592d4735187c2f8678d03de367cc954226135ff17eb0a8c486b52e1ae3589c6.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 165, + 411, + 175 + ], + "lines": [ + { + "bbox": [ + 304, + 165, + 411, + 175 + ], + "spans": [ + { + "bbox": [ + 304, + 165, + 411, + 175 + ], + "type": "text", + "content": "(c) MetaWorld[video instruction]" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "type": "image", + "bbox": [ + 422, + 80, + 532, + 163 + ], + "blocks": [ + { + "bbox": [ + 422, + 80, + 532, + 163 + ], + "lines": [ + { + "bbox": [ + 422, + 80, + 532, + 163 + ], + "spans": [ + { + "bbox": [ + 422, + 80, + 532, + 163 + ], + "type": "image", + "image_path": "c37649d925918eeaf04f98e7c1930a0655a3f746233c627fdc5fac710089c438.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 433, + 165, + 529, + 175 + ], + "lines": [ + { + "bbox": [ + 433, + 165, + 529, + 175 + ], + "spans": [ + { + "bbox": [ + 433, + 165, + 529, + 175 + ], + "type": "text", + "content": "(d) Kitchen[video instruction]" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_caption" + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 50, + 208, + 200, + 314 + ], + "blocks": [ + { + "bbox": [ + 46, + 176, + 545, + 198 + ], + "lines": [ + { + "bbox": [ + 46, + 176, + 545, + 198 + ], + "spans": [ + { + "bbox": [ + 46, + 176, + 545, + 198 + ], + "type": "text", + "content": "Figure 4. Performance over different demo sizes used in downstream imitation learning. We report the success rate of " + }, + { + "bbox": [ + 46, + 176, + 545, + 198 + ], + "type": "inline_equation", + "content": "\\mathrm{EC^2}" + }, + { + "bbox": [ + 46, + 176, + 545, + 198 + ], + "type": "text", + "content": " and baseline across different demo sizes. We see that the performance improvement from " + }, + { + "bbox": [ + 46, + 176, + 545, + 198 + ], + "type": "inline_equation", + "content": "\\mathrm{EC^2}" + }, + { + "bbox": [ + 46, + 176, + 545, + 198 + ], + "type": "text", + "content": " is consistent across all demo sizes." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 50, + 208, + 200, + 314 + ], + "lines": [ + { + "bbox": [ + 50, + 208, + 200, + 314 + ], + "spans": [ + { + "bbox": [ + 50, + 208, + 200, + 314 + ], + "type": "image", + "image_path": "97d5a5ee50f1536cbdc671c9ef1675bfd10542256e6c9b469ecbb65f72f4de43.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 64, + 318, + 198, + 327 + ], + "lines": [ + { + "bbox": [ + 64, + 318, + 198, + 327 + ], + "spans": [ + { + "bbox": [ + 64, + 318, + 198, + 327 + ], + "type": "text", + "content": "(a) Ablation on model size in MetaWorld" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 46, + 331, + 545, + 354 + ], + "lines": [ + { + "bbox": [ + 46, + 331, + 545, + 354 + ], + "spans": [ + { + "bbox": [ + 46, + 331, + 545, + 354 + ], + "type": "text", + "content": "Figure 5. Ablation on model size and its relationship with the correlation of emergent language and Natural language. We show the ablation results on model size with 10 demos and 25 demos in downstream policy learning separately." + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 216, + 208, + 366, + 313 + ], + "blocks": [ + { + "bbox": [ + 216, + 208, + 366, + 313 + ], + "lines": [ + { + "bbox": [ + 216, + 208, + 366, + 313 + ], + "spans": [ + { + "bbox": [ + 216, + 208, + 366, + 313 + ], + "type": "image", + "image_path": "556d251e2aa857d811b293957b7174253612356f7e151fd5aaf16bd6f6e3d83d.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 223, + 318, + 370, + 327 + ], + "lines": [ + { + "bbox": [ + 223, + 318, + 370, + 327 + ], + "spans": [ + { + "bbox": [ + 223, + 318, + 370, + 327 + ], + "type": "text", + "content": "(b) Ablation on model size in Franka Kitchen" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 11 + }, + { + "type": "image", + "bbox": [ + 380, + 208, + 531, + 313 + ], + "blocks": [ + { + "bbox": [ + 380, + 208, + 531, + 313 + ], + "lines": [ + { + "bbox": [ + 380, + 208, + 531, + 313 + ], + "spans": [ + { + "bbox": [ + 380, + 208, + 531, + 313 + ], + "type": "image", + "image_path": "511aa2367ec78663e5d0828678829ea61a8e5160cbfe859a9104e3359caa4f93.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 383, + 318, + 542, + 327 + ], + "lines": [ + { + "bbox": [ + 383, + 318, + 542, + 327 + ], + "spans": [ + { + "bbox": [ + 383, + 318, + 542, + 327 + ], + "type": "text", + "content": "(c) Translation score across different model sizes" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_caption" + } + ], + "index": 13 + }, + { + "bbox": [ + 47, + 360, + 286, + 371 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 360, + 286, + 371 + ], + "spans": [ + { + "bbox": [ + 47, + 360, + 286, + 371 + ], + "type": "text", + "content": "the input " + }, + { + "bbox": [ + 47, + 360, + 286, + 371 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 47, + 360, + 286, + 371 + ], + "type": "text", + "content": ", the coefficient of determination " + }, + { + "bbox": [ + 47, + 360, + 286, + 371 + ], + "type": "inline_equation", + "content": "R" + }, + { + "bbox": [ + 47, + 360, + 286, + 371 + ], + "type": "text", + "content": " is defined as" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 79, + 379, + 287, + 407 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 79, + 379, + 287, + 407 + ], + "spans": [ + { + "bbox": [ + 79, + 379, + 287, + 407 + ], + "type": "interline_equation", + "content": "R ^ {2} = 1 - \\frac {S S _ {r e s}}{S S _ {t o t}} = 1 - \\frac {\\sum_ {i} \\left(y _ {i} - f \\left(x _ {i}\\right)\\right) ^ {2}}{\\sum_ {i} \\left(y _ {i} - \\bar {y}\\right) ^ {2}} \\tag {8}", + "image_path": "51e05d6bd61d68c494596d24f4360ce854b529bb71431de5125d812b0a9411ad.jpg" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 46, + 415, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 415, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 415, + 287, + 714 + ], + "type": "text", + "content": "We evaluate the " + }, + { + "bbox": [ + 46, + 415, + 287, + 714 + ], + "type": "inline_equation", + "content": "R^2" + }, + { + "bbox": [ + 46, + 415, + 287, + 714 + ], + "type": "text", + "content": " values of two linear regressions. One predicts natural language word embeddings from emergent language, and the other predicts emergent language word embeddings from natural language. As shown in Figure 5c, the " + }, + { + "bbox": [ + 46, + 415, + 287, + 714 + ], + "type": "inline_equation", + "content": "R^2" + }, + { + "bbox": [ + 46, + 415, + 287, + 714 + ], + "type": "text", + "content": " of predicting natural language embeddings from the emergent language increase along with the model becoming larger, which corresponds to better performance. In contrast, the " + }, + { + "bbox": [ + 46, + 415, + 287, + 714 + ], + "type": "inline_equation", + "content": "R^2" + }, + { + "bbox": [ + 46, + 415, + 287, + 714 + ], + "type": "text", + "content": " of predicting emergent language embeddings from the natural language is non-monotonous, along with the model size becoming larger. The reason is that emergent language captures more information that natural language does not contain when the model is large enough and has promising performance. In short, " + }, + { + "bbox": [ + 46, + 415, + 287, + 714 + ], + "type": "inline_equation", + "content": "\\mathrm{EC}^2" + }, + { + "bbox": [ + 46, + 415, + 287, + 714 + ], + "type": "text", + "content": " has the best performance in embodied control tasks when emergent language contains more information than natural language, the performance is median when emergent language and language information are nearly equal, and the performance is worst when emergent language contains less information than language information. As shown in Table 4, we also provide qualitative examples of emergent language and its corresponding natural language to show that emergent language can capture key concepts from video. We find that the tokens \"108\" and \"500\" correspond to \"drawer\" in natural language and token \"701\" corresponds to \"stapler.\" Except for nouns, emergent language can also get the con" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 305, + 360, + 545, + 407 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 360, + 545, + 407 + ], + "spans": [ + { + "bbox": [ + 305, + 360, + 545, + 407 + ], + "type": "text", + "content": "cept of verbs, for example, token “538” corresponds to the verb “reach” in natural language. The current manual check analysis of emergent language is just a preliminary attempt, and more understanding can be promising for future work." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 306, + 418, + 467, + 430 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 418, + 467, + 430 + ], + "spans": [ + { + "bbox": [ + 306, + 418, + 467, + 430 + ], + "type": "text", + "content": "5. Conclusions and Discussions" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 304, + 437, + 545, + 653 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 437, + 545, + 653 + ], + "spans": [ + { + "bbox": [ + 304, + 437, + 545, + 653 + ], + "type": "text", + "content": "This paper aims to build the link between perceptual grounding and symbolic concepts by emergent communication (EC) language for embodied control. To this end, we develop a novel Embodied Control framework with the help of Emergent Communication language " + }, + { + "bbox": [ + 304, + 437, + 545, + 653 + ], + "type": "inline_equation", + "content": "(\\mathrm{EC}^2)" + }, + { + "bbox": [ + 304, + 437, + 545, + 653 + ], + "type": "text", + "content": ", which pre-trains a language model via masked trajectory complement pretext task condition on emergent language or natural language. The pre-trained language model is utilized to extract embodied representation from instructions and observations and is used as a frozen module for downstream data-efficient policy learning. Extensive experiments show that " + }, + { + "bbox": [ + 304, + 437, + 545, + 653 + ], + "type": "inline_equation", + "content": "\\mathbf{E}\\mathbf{C}^{2}" + }, + { + "bbox": [ + 304, + 437, + 545, + 653 + ], + "type": "text", + "content": " outperforms existing methods in Metaworld and Franka kitchen benchmarks. We believe that " + }, + { + "bbox": [ + 304, + 437, + 545, + 653 + ], + "type": "inline_equation", + "content": "\\mathrm{EC^2}" + }, + { + "bbox": [ + 304, + 437, + 545, + 653 + ], + "type": "text", + "content": " will serve as a solid step toward the general decision-making model. Limitations and future works: more understanding about emergent language, training " + }, + { + "bbox": [ + 304, + 437, + 545, + 653 + ], + "type": "inline_equation", + "content": "\\mathrm{EC}^2" + }, + { + "bbox": [ + 304, + 437, + 545, + 653 + ], + "type": "text", + "content": " on a larger and more diverse dataset, and applications on more practical setup can be promising directions of future works." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 304, + 654, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 654, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 304, + 654, + 545, + 712 + ], + "type": "text", + "content": "Acknowledgement. Ping Luo is partially supported by the National Key R&D Program of China No.2022ZD0161000 and the General Research Fund of HK No.17200622. Shunyu Yao was supported in part by the National Science Foundation under Grant No. 2107048." + } + ] + } + ], + "index": 22 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "type": "text", + "content": "6711" + } + ] + } + ], + "index": 23 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 288, + 713 + ], + "type": "list", + "angle": 0, + "index": 17, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 135 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 135 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 135 + ], + "type": "text", + "content": "[1] Muhammad Alomari, Paul Duckworth, David Hogg, and Anthony Cohn. 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Black $^{1}$", + "bbox": [ + 148, + 172, + 821, + 191 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1Max Planck Institute for Intelligent Systems, Tübingen, Germany", + "bbox": [ + 267, + 193, + 704, + 209 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "$^{2}$ Osaka University, Japan $^{3}$ University of Amsterdam, the Netherlands", + "bbox": [ + 250, + 210, + 720, + 226 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "{yuliang.xiu, jinlong.yang, black}@tue.mpg.de cao.xu@ist.osaka-u.ac.jp d.tzionas@uva.nl", + "bbox": [ + 86, + 229, + 880, + 243 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/3fbec9e0eeedc5b43664803cbdb6ad02b6c9c00139147bea260f5c8398e6717a.jpg", + "image_caption": [ + "Input Image" + ], + "image_footnote": [], + "bbox": [ + 83, + 273, + 235, + 449 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/55766b5d294a96840304ac08f167e8469683bea984c20a8707bea73366bd72e1.jpg", + "image_caption": [ + "Front & Back Normal Estimation (2D)" + ], + "image_footnote": [], + "bbox": [ + 238, + 273, + 436, + 449 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/074d4be278bec138b2570ced60a1bb462cc2c6c634d6b5bbf32a4aefdcef66d9.jpg", + "image_caption": [ + "Front & Back d-BiNI Surfaces (2.5D)", + "FullClothedHumanMesh(3D)" + ], + "image_footnote": [], + "bbox": [ + 442, + 273, + 797, + 450 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/18ba68b2d493912a5bf0162a5b63878d6d0198003f036928ae704034c0606d9c.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 803, + 273, + 890, + 409 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/2a57f24263167289a644e538bee475bb34abe0173bdff1abb80bc3b760f8ba6d.jpg", + "image_caption": [ + "Figure 1. Human digitization from a color image. ECON combines the best aspects of free-form implicit representation, and explicit anthropomorphic regularization to infer high-fidelity 3D humans, even with loose clothing or in challenging poses. It does so in three steps: (1) It infers detailed 2D normal maps for the front and back side (Sec. 3.1). (2) The normal maps are converted into detailed, yet incomplete, 2.5D front and back surfaces guided by a SMPL-X estimate (Sec. 3.2). (3) It then \"inpaints\" the missing geometry between two surfaces (Sec. 3.3). Face or hands can be optionally replaced with the cleaner ones from SMPL-X. See the video on our website for more results." + ], + "image_footnote": [], + "bbox": [ + 803, + 410, + 887, + 467 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 559, + 310, + 574 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "The combination of deep learning, artist-curated scans, and Implicit Functions (IF), is enabling the creation of detailed, clothed, 3D humans from images. However, existing methods are far from perfect. IF-based methods recover free-form geometry, but produce disembodied limbs or degenerate shapes for novel poses or clothes. To increase robustness for these cases, existing work uses an explicit parametric body model to constrain surface reconstruction, but this limits the recovery of free-form surfaces such as loose clothing that deviates from the body. What we want is a method that combines the best properties of implicit representation and explicit body regularization. To this end, we make two key observations: (1) current networks are better at inferring detailed 2D maps than full-3D surfaces, and (2) a parametric model can be seen as a \"canvas\" for stitching together detailed surface patches. Based on these, our method, ECON, has three main steps: (1) It infers detailed 2D normal maps for the front and back side of a clothed person. (2) From these, it recovers 2.5D front and back surfaces, called d-BiNI, that are equally detailed, yet incomplete, and registers these w.r.t. each other with the help of a SMPL-X", + "bbox": [ + 75, + 583, + 472, + 901 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "body mesh recovered from the image. (3) It \"inpaints\" the missing geometry between d-BiNI surfaces. If the face and hands are noisy, they can optionally be replaced with the ones of SMPL-X. As a result, ECON infers high-fidelity 3D humans even in loose clothes and challenging poses. This goes beyond previous methods, according to the quantitative evaluation on the CAPE and Renderpeople datasets. Perceptual studies also show that ECON's perceived realism is better by a large margin. Code and models are available for research purposes at econ.is.tue.mpg.de", + "bbox": [ + 496, + 560, + 893, + 712 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 500, + 739, + 630, + 753 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Human avatars will be key for future games and movies, mixed-reality, tele-presence and the \"metaverse\". To build realistic and personalized avatars at scale, we need to faithfully reconstruct detailed 3D humans from color photos taken in the wild. This is still an open problem, due to its challenges; people wear all kinds of different clothing and accessories, and they pose their bodies in many, often imaginative, ways. A good reconstruction method must accurately capture these, while also being robust to novel clothing and poses.", + "bbox": [ + 496, + 763, + 893, + 901 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "512", + "bbox": [ + 485, + 945, + 509, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Initial, promising, results have been made possible by using artist-curated scans as training data, and implicit functions (IF) [56, 59] as the 3D representation. Seminal work on PIFu(HD) [70, 71] uses \"pixel-aligned\" IF and reconstructs clothed 3D humans with unconstrained topology. However, these methods tend to overfit to the poses seen in the training data, and have no explicit knowledge about the human body's structure. Consequently, they produce disembodied limbs or degenerate shapes for images with novel poses; see the 2nd row of Fig. 2. Follow-up work [26, 82, 96] accounts for such artifacts by regularizing the IF using a shape prior provided by an explicit body model [52, 61], but regularization introduces a topological constraint, restricting generalization to novel clothing while attenuating shape details; see the 3rd and 4th rows of Fig. 2. In a nutshell, there are trade-offs between robustness, generalization and detail.", + "bbox": [ + 75, + 90, + 472, + 332 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "What we want is the best of both worlds; that is, the robustness of explicit anthropomorphic body models, and the flexibility of IF to capture arbitrary clothing topology. To that end, we make two key observations: (1) While inferring detailed 2D normal maps from color images is relatively easy [31, 71, 82], inferring 3D geometry with equally fine details is still challenging [9]. Thus, we exploit networks to infer detailed \"geometry-aware\" 2D maps that we then lift to 3D. (2) A body model can be seen as a low-frequency \"canvas\" that \"guides\" the stitching of detailed surface parts.", + "bbox": [ + 75, + 334, + 470, + 484 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "With these in mind, we develop ECON, which stands for \"Explicit Clothed humans Optimized via Normal integration\". It takes, as input, an RGB image and a SMPL-X body inferred from the image. Then, it outputs a 3D human in free-form clothing with a level of detail and robustness that goes beyond the state of the art (SOTA); see the bottom of Fig. 2. Specifically, ECON has three steps.", + "bbox": [ + 75, + 487, + 470, + 593 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Step 1: Front & back normal reconstruction. We predict front- and back-side clothed-human normal maps from the input RGB image, conditioned on the body estimate, with a standard image-to-image translation network.", + "bbox": [ + 75, + 595, + 470, + 655 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Step 2: Front & back surface reconstruction. We take the previously predicted normal maps, and the corresponding depth maps that are rendered from the SMPL-X mesh, to produce detailed and coherent front-/back-side 3D surfaces, $\\{\\mathcal{M}_{\\mathrm{F}},\\mathcal{M}_{\\mathrm{B}}\\}$ . To this end, we extend the recent BiNI method [7], and develop a novel optimization scheme that is aimed at satisfying three goals for the resulting surfaces: (1) their high-frequency components agree with clothed-human normals, (2) their low-frequency components and the discontinuities agree with the SMPL-X ones, and (3) the depth values on their silhouettes are coherent with each other and consistent with the SMPL-X-based depth maps. The two output surfaces, $\\{\\mathcal{M}_{\\mathrm{F}},\\mathcal{M}_{\\mathrm{B}}\\}$ , are detailed yet incomplete, i.e., there is missing geometry in occluded and \"profile\" regions.", + "bbox": [ + 75, + 657, + 470, + 868 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Step 3: Full 3D shape completion. This module takes two inputs: (1) the SMPL-X mesh, and (2) the two d-BiNI", + "bbox": [ + 76, + 869, + 470, + 900 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/d7622887f9cce397412347a6fa4860c177c8c531fd777bd2e2e69c2cf74de9c6.jpg", + "image_caption": [ + "Figure 2. Summary of SOTA. PIFuHD [71] recovers clothing details, but struggles with novel poses. ICON [82] and PaMIR [96] regularize shape to a body shape, but over-constrain the skirts, or over-smooth the wrinkles. ECON combines their best aspects." + ], + "image_footnote": [], + "bbox": [ + 501, + 79, + 890, + 378 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "surfaces, $\\{\\mathcal{M}_{\\mathrm{F}},\\mathcal{M}_{\\mathrm{B}}\\}$ . The goal is to \"inpaint\" the missing geometry. Existing methods struggle with this problem. On one hand, Poisson reconstruction [38] produces \"blobby\" shapes and naively \"infills\" holes without exploiting a shape distribution prior. On the other hand, data-driven approaches, such as IF-Nets [10], struggle with missing parts caused by (self-)occlusions, and fail to keep the fine details present on two d-BiNI surfaces, producing degenerate geometries.", + "bbox": [ + 496, + 444, + 893, + 565 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "We address above the limitations in two steps: (1) We extend and re-train IF-Nets to be conditioned on the SMPL-X body, so that SMPL-X regularizes shape \"infilling\". We discard the triangles that lie close to $\\{\\mathcal{M}_{\\mathrm{F}},\\mathcal{M}_{\\mathrm{B}}\\}$ , and keep the remaining ones as \"infilling patches\". (2) We stitch together the front- and back-side surfaces and infilling patches via Poisson reconstruction; note that holes between these are small enough for a general purpose method. The result is a full 3D shape of a clothed human; see Fig. 2, bottom.", + "bbox": [ + 496, + 566, + 893, + 700 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "We evaluate ECON both on established benchmarks (CAPE [55] and Renderpeople [66]) and in-the-wild images. Quantitative analysis reveals ECON's superiority. A perceptual study echos this, showing that ECON is significantly preferred over competitors on challenging poses and loose clothing, and competitive with PIFuHD on fashion images. Qualitative results show that ECON generalizes better than the SOTA to a wide variety of poses and clothing, even with extreme looseness or complex topology; see Fig. 9.", + "bbox": [ + 496, + 703, + 893, + 839 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "With both pose-robustness and topological flexibility, ECON recovers 3D clothed humans with a good level of detail and realistic pose. Code and models are available for research purposes at econ.is.tue.mpg.de", + "bbox": [ + 496, + 840, + 893, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "513", + "bbox": [ + 485, + 945, + 509, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 76, + 89, + 218, + 104 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Image-based clothed human reconstruction. Regarding geometric representation, we group the mainstream clothed human reconstruction approaches into \"implicit\" and \"explicit\". Note that with the terms implicit/explicit we mainly refer to the surface decoder rather than the feature encoder.", + "bbox": [ + 76, + 114, + 468, + 190 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "1) Explicit-shape-based approaches use either a mesh-based parametric body model [35, 52, 61, 69, 83], or a nonparametric depth map [18, 72] or point cloud [90], to reconstruct 3D humans. Many methods [15, 36, 39, 40, 42, 43, 75, 76, 87, 91, 92] estimate or regress minimally-clothed 3D body meshes from RGB pixels and ignore clothing. To account for clothed human shapes, another line of work [2-4, 41, 55, 62, 79, 100] adds 3D offsets on top of the body mesh. This is compatible with current animation pipelines, as they inherit the hierarchical skeleton and skinning weights from the underling statistical body model. However, this \"body+offset\" approach is not flexible enough to model loose clothing, which deviates significantly from the body topology, such as dresses and skirts. To increase topological flexibility, some methods [5, 33] reconstruct 3D clothed humans by identifying the type of clothing and using the appropriate model to reconstruct it. Scaling up this \"cloth-aware\" approach to many clothing styles is nontrivial, limiting generalization to in-the-wild outfit variation.", + "bbox": [ + 75, + 190, + 472, + 476 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "2) Implicit-function-based approaches are topology-agnostic and, thus, can be used to represent arbitrary 3D clothed human shapes. SMPLicit [12], ClothWild [57] and DIG [46] learn a generative clothing model with neural distance fields [11, 56, 59] from a 3D clothing dataset. Given an image, the clothed human is reconstructed by estimating a parametric body and optimizing the latent space of the clothing model. However, the results usually do not align well with the image and lack geometric detail.", + "bbox": [ + 75, + 478, + 470, + 613 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "PIFu [70] introduces pixel-aligned implicit human shape reconstruction and PIFuHD [71] significantly improves the geometric details with a multi-level architecture and normal maps predicted from the RGB image. However, these two methods do not exploit knowledge of the human body structure. Therefore, these methods overfit to the body poses in the training data, e.g. fashion poses. They fail to generalize to novel poses, producing non-human shapes with broken or disembodied limbs. To address these issues, several methods introduce different geometric priors to regularize the deep implicit representation: GeoPIFu [26] introduces a coarse shape of volumetric humans, Self-Portraits [49], PINA [14], and S3 [85] use depth or LIDAR information to regularize shape and improve robustness to pose variation.", + "bbox": [ + 75, + 613, + 470, + 824 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Another direction leverages parametric body models, which represent human body shape well, model the kinematic structure of the body, and can be reliably estimated from RGB images of clothed people. Such a representation can be viewed as a base shape upon which to model clothed", + "bbox": [ + 75, + 825, + 470, + 900 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "humans. Therefore, several methods combine parametric body models with expressive implicit representations to get the best of both worlds. PaMIR [96] and DeepMultiCap [95] condition the pixel-aligned features on a posed and voxelized SMPL mesh. JIFF Introduces a 3DMM face prior to improve the realism of the facial region. ARCH [30], $\\mathrm{ARCH} + +$ [27] and CAR [50] use SMPL to unpose the pixel-aligned query points from a posed space to a canonical space. To further generalize to unseen poses on in-the-wild photos, ICON [82] regresses shapes from locally-queried features. However, the above approaches gain robustness to unseen poses at the cost of generalization ability to various, especially loose, clothing topologies. We argue that this is because loose clothing differs greatly from human body and that conditioning on the SMPL body in 3D makes it harder for networks to make full use of 2D image features.", + "bbox": [ + 496, + 90, + 893, + 330 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Our work is also inspired by \"sandwich-like\" monocular reconstruction approaches, represented by Moduling Humans [18], FACSIMILE [72] and Any-Shot GIN [80]. Moduling Humans has two networks: a generator that estimates the visible (front) and invisible (back) depth maps from RGB images, and a discriminator that helps regularize the estimation via an adversarial loss. FACSIMILE further improves the geometric details by leveraging a normal loss, which is directly computed from depth estimates via differentiable layers. Recently, Any-Shot GIN generalizes the sandwich-like scheme to novel classes of objects. Given RGB images, it predicts front and back depth maps as well, and then exploits IF-Nets [10] for shape completion. We follow a similar path and extend it, to successfully reconstruct clothed human shapes with SOTA pose generalization, and better details from normal images.", + "bbox": [ + 496, + 332, + 895, + 575 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Method", + "text_level": 1, + "bbox": [ + 500, + 585, + 591, + 602 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Given an RGB image, ECON first estimates front and back normal maps (Sec. 3.1), then converts them into front and back partial surfaces (Sec. 3.2), and finally \"inpaints\" the missing geometry with the help of IF-Nets+ (Sec. 3.3). See ECON's overview in Fig. 3.", + "bbox": [ + 496, + 612, + 893, + 688 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Detailed normal map prediction", + "text_level": 1, + "bbox": [ + 500, + 696, + 782, + 713 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Trained on abundant pairs of RGB images and normal images, a \"front\" normal map, $\\widehat{\\mathcal{N}}_{\\mathrm{F}}^{\\mathrm{c}}$ , can be accurately estimated from an RGB image using image-to-image translation networks, as demonstrated in PIFuHD [71] or ICON [82]. Both methods also infer a \"back\" normal map, $\\widehat{\\mathcal{N}}_{\\mathrm{B}}^{\\mathrm{c}}$ , from the image. But, the absence of image cues leads to over-smooth $\\widehat{\\mathcal{N}}_{\\mathrm{B}}^{\\mathrm{c}}$ . To address this, we fine-tune ICON's backside normal predictor, $\\mathcal{G}_{\\mathrm{B}}^{\\mathrm{N}}$ , with an additional MRF loss [77] to enhance the local details by minimizing the difference between the predicted $\\widehat{\\mathcal{N}}^{\\mathrm{c}}$ and ground truth (GT) $\\mathcal{N}^{\\mathrm{c}}$ in feature space.", + "bbox": [ + 496, + 719, + 893, + 869 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "To guide the normal map prediction and make it robust to various body poses, ICON conditions the normal map", + "bbox": [ + 498, + 869, + 893, + 902 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "514", + "bbox": [ + 485, + 945, + 511, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/8cdf79210928b3e9b25205af1a11a834dd7d7a36b2f863c50ca435833101104c.jpg", + "image_caption": [ + "Figure 3. Overview. ECON takes as input an RGB image, $\\mathcal{I}$ , and a SMPL-X body, $\\mathcal{M}^{\\mathrm{b}}$ . Conditioned on the rendered front and back body normal images, $\\mathcal{N}^{\\mathrm{b}}$ , ECON first predicts front and back clothing normal maps, $\\widehat{\\mathcal{N}}^{\\mathrm{c}}$ . These two maps, along with body depth maps, $\\mathcal{Z}^{\\mathrm{b}}$ , are fed into a d-BiNI optimizer to produce front and back surfaces, $\\{\\mathcal{M}_{\\mathrm{F}}, \\mathcal{M}_{\\mathrm{B}}\\}$ . Based on such partial surfaces, and body estimate $\\mathcal{M}^{\\mathrm{b}}$ , IF-Nets+ implicitly completes $\\mathcal{R}_{\\mathrm{IF}}$ . With optional Face or hands from $\\mathcal{M}^{\\mathrm{b}}$ , screened Poisson combines everything as final watertight $\\mathcal{R}$ ." + ], + "image_footnote": [], + "bbox": [ + 78, + 85, + 723, + 354 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/e26df1a3f8f33948fdbc0d1ad14c4529af4b67c80573ce4bb637b7044d0e566b.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 751, + 95, + 885, + 349 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "prediction module on the body normal maps, $\\mathcal{N}^{\\mathrm{b}}$ , rendered from the estimated body $\\mathcal{M}^{\\mathrm{b}}$ . Thus, it is important to accurately align the estimated body and clothing silhouette. Apart from the $\\mathcal{L}_{\\mathrm{N\\_diff}}$ and $\\mathcal{L}_{\\mathrm{S\\_diff}}$ used in ICON [82], we also apply 2D body landmarks in an additional loss term, $\\mathcal{L}_{\\mathrm{J\\_diff}}$ , to further optimize the SMPL-X body, $\\mathcal{M}^{\\mathrm{b}}$ , inferred from pixie [15] or PyMAF-X [91]. Specifically, we optimize SMPL-X's shape, $\\beta$ , pose, $\\theta$ , and translation, $t$ , to minimize:", + "bbox": [ + 75, + 440, + 473, + 561 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\mathrm {S M P L - X}} = \\mathcal {L} _ {\\mathrm {N} _ {-} \\text {d i f f}} + \\mathcal {L} _ {\\mathrm {S} _ {-} \\text {d i f f}} + \\mathcal {L} _ {\\mathrm {J} _ {-} \\text {d i f f}}, \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 151, + 575, + 468, + 599 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\mathrm {J} _ {-} \\text {d i f f}} = \\lambda_ {\\mathrm {J} _ {-} \\text {d i f f}} \\left| \\mathcal {J} ^ {\\mathrm {b}} - \\widehat {\\mathcal {J} ^ {\\mathrm {c}}} \\right|,\n$$\n", + "text_format": "latex", + "bbox": [ + 187, + 594, + 357, + 613 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\mathcal{L}_{\\mathrm{N\\_diff}}$ and $\\mathcal{L}_{\\mathrm{S\\_diff}}$ are the normal-map loss and silhouette loss introduced in ICON [82], and $\\mathcal{L}_{\\mathrm{J\\_diff}}$ is the joint loss (L2) between 2D landmarks $\\widehat{\\mathcal{I}^{\\mathrm{c}}}$ , which are estimated by a 2D keypoint estimator from the RGB image $\\mathcal{I}$ , and the corresponding re-projected 2D joints $\\mathcal{I}^{\\mathrm{b}}$ from $\\mathcal{M}^{\\mathrm{b}}$ . For more implementation details, see Sec. A.1 in SupMat.", + "bbox": [ + 75, + 621, + 470, + 715 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. Front and back surface reconstruction", + "text_level": 1, + "bbox": [ + 76, + 724, + 408, + 739 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We now lift the clothed normal maps to 2.5D surfaces. We expect these 2.5D surfaces to satisfy three conditions: (1) high-frequency surface details agree with predicted clothed normal maps, (2) low-frequency surface variations, including discontinuities, agree with SMPL-X's ones, and (3) the depth of the front and back silhouettes are close to each other.", + "bbox": [ + 75, + 750, + 468, + 838 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Unlike PIFuHD [71] or ICON [82], which train a neural network to regress the implicit surface from normal maps, we explicitly model the depth-normal relationship using variational normal integration methods [7,64]. Specifi", + "bbox": [ + 75, + 839, + 470, + 901 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "cally, we tailor the recent bilateral normal integration (BiNI) method [7] to full-body mesh reconstruction by harnessing the coarse prior, depth maps, and silhouette consistency.", + "bbox": [ + 496, + 440, + 892, + 486 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "To satisfy the three conditions, we propose a depth-aware silhouette-consistent bilateral normal integration (d-BiNI) method to jointly optimize for the front and back clothed depth maps, $\\widehat{\\mathcal{Z}}_{\\mathrm{F}}^{\\mathrm{c}}$ and $\\widehat{\\mathcal{Z}}_{\\mathrm{B}}^{\\mathrm{c}}$ :", + "bbox": [ + 496, + 486, + 890, + 547 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathrm {d} - \\operatorname {B i N I} \\left(\\widehat {\\mathcal {N}} _ {\\mathrm {F}} ^ {\\mathrm {c}}, \\widehat {\\mathcal {N}} _ {\\mathrm {B}} ^ {\\mathrm {c}}, \\mathcal {Z} _ {\\mathrm {F}} ^ {\\mathrm {b}}, \\mathcal {Z} _ {\\mathrm {B}} ^ {\\mathrm {b}}\\right)\\rightarrow \\widehat {\\mathcal {Z}} _ {\\mathrm {F}} ^ {\\mathrm {c}}, \\widehat {\\mathcal {Z}} _ {\\mathrm {B}} ^ {\\mathrm {c}}. \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 571, + 556, + 892, + 579 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Here, $\\widehat{\\mathcal{N}}_{*}^{\\mathrm{c}}$ is the front or back clothed normal map predicted by $\\mathcal{G}_{\\mathrm{F,B}}^{\\mathrm{N}}$ from $\\{\\mathcal{I},\\mathcal{N}^{\\mathrm{b}}\\}$ , and $\\mathcal{Z}_{*}^{\\mathrm{b}}$ is the front or back coarse body depth image rendered from the SMPL-X mesh, $\\mathcal{M}^{\\mathrm{b}}$ .", + "bbox": [ + 496, + 590, + 890, + 638 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Specifically, our objective function consists of five terms:", + "bbox": [ + 517, + 638, + 892, + 654 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\min _ {\\widehat {\\mathcal {Z}} _ {\\mathrm {F}} ^ {\\mathrm {c}}, \\widehat {\\mathcal {Z}} _ {\\mathrm {B}} ^ {\\mathrm {c}}} \\mathcal {L} _ {\\mathrm {n}} (\\widehat {\\mathcal {Z}} _ {\\mathrm {F}} ^ {\\mathrm {c}}; \\widehat {\\mathcal {N}} _ {\\mathrm {F}} ^ {\\mathrm {c}}) + \\mathcal {L} _ {\\mathrm {n}} (\\widehat {\\mathcal {Z}} _ {\\mathrm {B}} ^ {\\mathrm {c}}; \\widehat {\\mathcal {N}} _ {\\mathrm {B}} ^ {\\mathrm {c}}) + \\\\ \\lambda_ {\\mathrm {d}} \\mathcal {L} _ {\\mathrm {d}} \\left(\\widehat {\\mathcal {Z}} _ {\\mathrm {F}} ^ {\\mathrm {c}}; \\mathcal {Z} _ {\\mathrm {F}} ^ {\\mathrm {b}}\\right) + \\lambda_ {\\mathrm {d}} \\mathcal {L} _ {\\mathrm {d}} \\left(\\widehat {\\mathcal {Z}} _ {\\mathrm {B}} ^ {\\mathrm {c}}; \\mathcal {Z} _ {\\mathrm {B}} ^ {\\mathrm {b}}\\right) + \\tag {3} \\\\ \\lambda_ {s} \\mathcal {L} _ {s} (\\widehat {\\mathcal {Z}} _ {F} ^ {c}, \\widehat {\\mathcal {Z}} _ {B} ^ {c}), \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 566, + 676, + 890, + 750 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\mathcal{L}_{\\mathrm{n}}$ is the BiNI loss term introduced by BiNI [7], $\\mathcal{L}_{\\mathrm{d}}$ is a depth prior applied to the front and back depth surfaces, and $\\mathcal{L}_{\\mathrm{s}}$ is a front-back silhouette consistency term. For a more detailed discussion on these terms, see Sec. A.2 in SupMat.", + "bbox": [ + 496, + 760, + 890, + 820 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "With Eq. (3), we make two technical contributions beyond BiNI [7]. First, we use the coarse depth prior rendered from the SMPL-X body mesh, $\\mathcal{Z}_i^{\\mathrm{b}}$ , to regularize BiNI:", + "bbox": [ + 496, + 821, + 890, + 867 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\mathrm {d}} \\left(\\widehat {\\mathcal {Z}} _ {i} ^ {\\mathrm {c}}; \\mathcal {Z} _ {i} ^ {\\mathrm {b}}\\right) = \\left| \\widehat {\\mathcal {Z}} _ {i} ^ {\\mathrm {c}} - \\mathcal {Z} _ {i} ^ {\\mathrm {b}} \\right| _ {\\Omega_ {\\mathrm {n}}} \\cap \\Omega_ {\\mathrm {z}} \\quad i \\in \\{F, B \\}. \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 540, + 877, + 892, + 898 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "515", + "bbox": [ + 485, + 944, + 509, + 955 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/e47c04f60941f1b2651a9436acf01c03110f4707a2ec6ed4b242f112a043780c.jpg", + "image_caption": [ + "Figure 4. Four inputs to d-BiNI. $\\Omega_{\\mathrm{n}}$ and $\\Omega_{\\mathrm{z}}$ are the domains of clothed and body regions, respectively. $\\partial \\Omega_{\\mathrm{n}}$ is the silhouette of $\\Omega_{\\mathrm{n}}$ ." + ], + "image_footnote": [], + "bbox": [ + 80, + 88, + 472, + 186 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "This addresses the key problem of putting the front and back surfaces together in a coherent way to form a full body. Optimizing BiNI terms $\\mathcal{L}_{\\mathrm{n}}$ leaves an arbitrary global offset between the front and back surfaces. The depth prior terms $\\mathcal{L}_{\\mathrm{d}}$ encourage the surfaces with undecided offsets to be consistent with the SMPL-X body, and is computed in the domains $\\Omega_{\\mathrm{n}} \\bigcap \\Omega_{\\mathrm{z}}$ (Fig. 4). For further intuitions on $\\mathcal{L}_{\\mathrm{n}}$ and $\\mathcal{L}_{\\mathrm{d}}$ , see Fig. S.4 and Fig. S.5 in SupMat.", + "bbox": [ + 75, + 229, + 468, + 349 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Second, we use a silhouette consistency term to encourage the front and back depth values to be the same at the silhouette boundary, which is computed in domain $\\partial \\Omega_{\\mathrm{n}}$ (Fig. 4):", + "bbox": [ + 75, + 351, + 470, + 396 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\mathrm {s}} \\left(\\widehat {\\mathcal {Z}} _ {\\mathrm {F}} ^ {\\mathrm {c}}, \\widehat {\\mathcal {Z}} _ {\\mathrm {B}} ^ {\\mathrm {c}}\\right) = \\left| \\widehat {\\mathcal {Z}} _ {\\mathrm {F}} ^ {\\mathrm {c}} - \\widehat {\\mathcal {Z}} _ {\\mathrm {B}} ^ {\\mathrm {c}} \\right| _ {\\partial \\Omega_ {\\mathrm {n}}}. \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 173, + 417, + 468, + 438 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The silhouette term improves the physical consistency of the reconstructed front and back clothed depth maps. Without this term, d-BiNI produces intersections of the front and back surfaces around the silhouette, causing \"blobby\" artifacts and hurting reconstruction quality; see Fig. S.6 in SupMat.", + "bbox": [ + 75, + 446, + 468, + 523 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.3. Human shape completion", + "text_level": 1, + "bbox": [ + 76, + 531, + 308, + 547 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "For simple body poses without self-occlusions, merging front and back d-BiNI surfaces in a straightforward way, as done in FACSIMILE [72] and Moduling Humans [18], can result in a complete 3D clothed scan. However, often poses result in self-occlusions, which cause large portions of the surfaces to be missing. In such cases, Poisson Surface Reconstruction (PSR) [37] leads to blobby artifacts.", + "bbox": [ + 75, + 554, + 470, + 660 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "PSR completion with SMPL-X $(\\mathbf{ECON_{EX}})$ . A naive way to \"infill\" the missing surface is to make use of the estimated SMPL-X body. We remove the triangles from $\\mathcal{M}^{\\mathrm{b}}$ that are visible to front or back cameras. The remaining triangle \"soup\" $\\mathcal{M}^{\\mathrm{cull}}$ contains both side-view boundaries and occluded regions. We apply PSR [37] to the union of $\\mathcal{M}^{\\mathrm{cull}}$ and d-BiNI surfaces $\\{\\mathcal{M}_{\\mathrm{F}},\\mathcal{M}_{\\mathrm{B}}\\}$ to obtain a watertight reconstruction $\\mathcal{R}$ . This approach is denoted as $\\mathrm{ECON_{EX}}$ . Although $\\mathrm{ECON_{EX}}$ avoids missing limbs or sides, it does not produce a coherent surface for the originally missing clothing and hair surfaces because of the discrepancy between SMPL-X and actual clothing or hair; see $\\mathrm{ECON_{EX}}$ in Fig. 5.", + "bbox": [ + 75, + 667, + 470, + 849 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Inpainting with IF-Nets+ $(\\mathcal{R}_{\\mathrm{IF}})$ . To improve reconstruction coherence, we use a learned implicit-function (IF) model to \"inpaint\" the missing geometry given front and back d-BiNI", + "bbox": [ + 75, + 854, + 470, + 900 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/66e611690465f64d9b77f697a90f13891919d3ac190069731b0754a9b87b9c4a.jpg", + "image_caption": [ + "Figure 5. \"Inpainting\" the missing geometry. We simulate different cases of occlusion by masking the normal images and present the intermediate and final 3D reconstruction of different design choices. While IF-Nets misses certain body parts, IF-Nets+ produces a plausible overall shape. $\\mathrm{ECON_{IF}}$ produces more consistent clothing surfaces than $\\mathrm{ECON_{EX}}$ due to a learned shape distribution." + ], + "image_footnote": [], + "bbox": [ + 506, + 87, + 893, + 300 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/3f4e4367f5d8b4b74992ae24fafa82358ff9d8880aee72ef6f83bd3554f54fdb.jpg", + "image_caption": [ + "Figure 6. Face and hand details. The face and hands of the raw reconstruction can be replaced with the ones of the SMPL-X body." + ], + "image_footnote": [], + "bbox": [ + 501, + 407, + 890, + 545 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "surfaces. Specifically, we tailor a general-purpose shape completion method, IF-Nets [10], to a SMPL-X-guided one, denoted as IF-Nets+. IF-Nets [10] completes the 3D shape from a deficient 3D input, such as an incomplete 3D human shape or a low-resolution voxel grid. Inspired by Li et al. [44], we adapt IF-Nets by conditioning it on a voxelized SMPL-X body to deal with pose variation; for details see Sec. A.3 in SupMat. IF-Nets+ is trained on voxelized front and back ground-truth clothed depth maps, $\\{\\mathcal{Z}_{\\mathrm{F}}^{\\mathrm{c}},\\mathcal{Z}_{\\mathrm{B}}^{\\mathrm{c}}\\}$ and a voxelized (estimated) body mesh, $\\mathcal{M}^{\\mathrm{b}}$ as input, and is supervised with ground-truth 3D shapes. During training, we randomly mask $\\{\\mathcal{Z}_{\\mathrm{F}}^{\\mathrm{c}},\\mathcal{Z}_{\\mathrm{B}}^{\\mathrm{c}}\\}$ for robustness to occlusions. During inference, we feed the estimated $\\widehat{\\mathcal{Z}}_{\\mathrm{F}}^{\\mathrm{c}},\\widehat{\\mathcal{Z}}_{\\mathrm{B}}^{\\mathrm{c}}$ and $\\mathcal{M}^{\\mathrm{b}}$ into IF-Nets+ to obtain an occupancy field, from which we extract the inpainted mesh, $\\mathcal{R}_{\\mathrm{IF}}$ with Marching cubes [53].", + "bbox": [ + 496, + 604, + 893, + 833 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "PSR completion with $\\mathcal{R}_{\\mathrm{IF}}$ ( $\\mathbf{ECON_{IF}}$ ). To obtain our final mesh, $\\mathcal{R}$ , we apply PSR to stitch (1) d-BiNI surfaces, (2) sided and occluded triangle soup $\\mathcal{M}^{\\mathrm{cull}}$ from $\\mathcal{R}_{\\mathrm{IF}}$ , and optionally, (3) face or hands cropped from the estimated SMPL-X", + "bbox": [ + 496, + 839, + 893, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "516", + "bbox": [ + 485, + 945, + 511, + 955 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/d74ca1518c64ce20f48994f14539737383ec83a44571337e2622f731d65b7ec3.jpg", + "image_caption": [ + "Figure 7. Datasets for numerical evaluation. We evaluate ECON on images with unseen poses (left) and unseen outfits (right) on the CAPE [55] and Renderpeople [66] datasets, respectively." + ], + "image_footnote": [], + "bbox": [ + 81, + 89, + 462, + 159 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "body $\\mathcal{M}^{\\mathrm{b}}$ . The necessity of (3) arises from the poorly reconstructed hands/face in $\\mathcal{R}_{\\mathrm{IF}}$ , see difference in Fig. 6. The approach is denoted as $\\mathrm{ECON_{IF}}$ .", + "bbox": [ + 75, + 237, + 470, + 282 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Notably, although $\\mathcal{R}_{\\mathrm{IF}}$ is already a complete human mesh, due to the lossy voxelization of inputs and limited resolution of Marching cubes algorithm, it somehow smooths out the details of $\\tilde{\\mathcal{Z}}_{\\{\\mathrm{F,B}\\}}^{\\mathrm{c}} / \\mathcal{M}_{\\{\\mathrm{F,B}\\}}$ , which are optimized via d-BiNI (see $\\mathcal{R}_{\\mathrm{IF}}$ vs ECON{IF,EX} in Fig. 5). While ECON{IF,EX} preserves d-BiNI details better, only the side-views and occluded parts of $\\mathcal{R}_{\\mathrm{IF}}$ are fused in the Poisson step. In Tabs. 1 and 4, we use ECON{IF,EX} instead of $\\mathcal{R}_{\\mathrm{IF}}$ for evaluation.", + "bbox": [ + 75, + 284, + 470, + 405 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 76, + 417, + 209, + 434 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.1. Datasets", + "text_level": 1, + "bbox": [ + 76, + 441, + 179, + 455 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Training on THuman2.0. THuman2.0 [88] contains 525 high-quality human textured scans in various poses, which are captured by a dense DSLR rig, along with their corresponding SMPL-X fits. We use THuman2.0 to train ICON, ECON $_{\\text{IF}}$ (IF-Nets+), IF-Nets, PIFu and PaMIR.", + "bbox": [ + 75, + 465, + 470, + 541 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Quantitative evaluation on CAPE & Renderpeople. We primarily evaluate on CAPE [55] and Renderpeople [66]. Specifically, we use the \"CAPE-NFP\" set (100 scans), which is used by ICON to analyze robustness to complex human poses. Moreover, we select another 100 scans from Renderpeople, containing loose clothing, such as dresses, skirts, robes, down jackets, costumes, etc. With such clothing variance, Renderpeople helps numerically evaluate the flexibility of reconstruction methods w.r.t. shape topology. Samples of the two datasets are shown in Fig. 7.", + "bbox": [ + 75, + 544, + 470, + 696 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.2. Metrics", + "text_level": 1, + "bbox": [ + 76, + 704, + 173, + 718 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Chamfer and P2S distance (cm). To capture large geometric errors, e.g. occluded parts or wrongly positioned limbs, we report the commonly used Chamfer (bi-directional point-to-surface) and P2S distance (1-directional point-to-surface) between ground-truth and reconstructed meshes.", + "bbox": [ + 75, + 727, + 470, + 801 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Normal difference (L2). To measure the fineness of reconstructed local details, as well as projection consistency from the input image, we also report the L2 error between normal images rendered from reconstructed and ground-truth surfaces, by rotating a virtual camera around these by $\\{0^{\\circ}, 90^{\\circ}, 180^{\\circ}, 270^{\\circ}\\}$ w.r.t. to a frontal view.", + "bbox": [ + 75, + 803, + 470, + 893 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/e0cc8f13ec93b7ce45d0f5f473c3caeeb3af5cec9d1bb57dcbd56dce221372c2.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodsData-drivenOOD poses (CAPE)OOD outfits (Renderpeople)
Chamfer ↓P2S ↓Normals ↓Chamfer ↓P2S ↓Normals ↓
w/o SMPL-X body prior
PIFu *✓1.7221.5480.06741.7061.6420.0709
PIFuHD†✓3.7673.5910.09941.9461.9830.0658
w/ GT SMPL-X body prior
PaMIR *✓0.9890.9920.04221.2961.4300.0518
ICON✓0.9710.9090.04091.3731.5220.0566
ECONIF✓0.9960.9670.04131.4011.4220.0516
ECONEXX0.9260.9170.03671.3421.4580.0478
", + "bbox": [ + 501, + 87, + 893, + 184 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/28f64b81f1f35a1d82df4e269da05bb60943080ac0375646cd9be13cc38716a5.jpg", + "table_caption": [ + "Table 1. Evaluation against the state of the art. All models use a resolution of 256 for marching cubes. *Methods are re-implemented in [82] for a fair comparison in terms of network settings and training data. †Official model is trained on the Renderpeople dataset. ECONEX is optimization-based, thus requires no training (X). “OOD” is short for “out-of-distribution”." + ], + "table_footnote": [], + "table_body": "
ICON [82]PIFuHD [71]PaMIR [96]
Challenging poses0.2830.1080.132
Loose clothing0.1470.3620.232
Fashion images0.1990.5510.290
", + "bbox": [ + 501, + 292, + 903, + 353 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 2. Perceptual study. Numbers denote the chance that participants prefer the reconstruction of a competing method over ECON for in-the-wild images. A value of 0.5 indicates equal preference. A value of $< 0.5$ favors ECON, while of $>0.5$ favors competitors.", + "bbox": [ + 496, + 364, + 893, + 420 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.3. Evaluation", + "text_level": 1, + "bbox": [ + 500, + 448, + 620, + 462 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Quantitative evaluation. We compare ECON with body-agnostic methods, i.e., PIFu [70] and PIFuHD [71], and body-aware methods, i.e., PaMIR [96] and ICON [82]; see in Tab. 1. For fair comparison, we use re-implementations of PIFu and PaMIR from ICON [82], because they have the same network settings and input data. $\\mathrm{ECON_{EX}}$ performs on par with ICON, and outperforms other methods on images containing out-of-distribution (OOD) poses (CAPE), with a distance error below $1\\mathrm{cm}$ . In terms of out-of-distribution outfitsits (Renderpeople), $\\mathrm{ECON_{EX/IF}}$ performs on par with PaMIR, and much better than PIFuHD. When it comes to high-frequency details measured by normals, $\\mathrm{ECON_{EX}}$ achieves SOTA performance on both datasets.", + "bbox": [ + 496, + 470, + 893, + 667 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Perceptual study. Due to the lack of ground-truth geometry (clothed scan + underneath SMPL-X), we further conduct a perceptual study to evaluate ECON on in-the-wild images. Test images are divided into three categories: \"challenging poses\", \"loose clothing\", and \"fashion images\". Examples of challenging poses and loose clothing can be seen in Fig. 9, and some of fashion images are in SupMat.'s Fig. S.2.", + "bbox": [ + 496, + 672, + 893, + 779 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Participants are asked to choose the reconstruction they perceive as more realistic, between a baseline method and ECON. We compute the chances that each baseline is preferred over ECON in Tab. 2. The results of the perceptual study confirm the quantitative evaluation in Tab. 1. For \"challenging poses\" images, ECON is significantly preferred over PIFuHD and outperforms ICON. On images of people wearing loose clothing, ECON is preferred over ICON by a large", + "bbox": [ + 496, + 780, + 893, + 901 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "517", + "bbox": [ + 485, + 944, + 509, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/a37b6e6fe5586aeb79021d082a8246de1b2ccf8a899626d9a4559a56601ab08a.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodsOOD poses (CAPE [55])OOD outfitsits (Renderpeople) [66]Speed FPS ↑
RMSE ↓MAE ↓RMSE ↓MAE ↓
BiNI [7]27.6421.1120.6116.070.52
d-BiNI13.4310.2914.4311.260.69
", + "bbox": [ + 78, + 87, + 470, + 133 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/2bbb5dff1fdb6c14a1c905c3f7172aa18b75cb6a8aabca33c63a617d51c03871.jpg", + "table_caption": [ + "Table 3. BiNI vs d-BiNI. Comparison between BiNI and d-BiNI surfaces w.r.t. reconstruction accuracy and optimization speed." + ], + "table_footnote": [], + "table_body": "
MethodsOOD poses (CAPE)OOD outfits (Renderpeople)
Chamfer ↓P2S ↓Normals ↓Chamfer ↓P2S ↓Normals ↓
IF-Nets [10]2.1161.2330.0751.8831.6220.070
IF-Nets+1.4011.3530.0561.4771.5640.055
ECONIF0.9960.9670.04131.4011.4220.0516
", + "bbox": [ + 81, + 181, + 470, + 237 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 4. Evaluation for shape completion. Same metrics as Tab. 1, and $\\mathrm{ECON_{IF}}$ is added as a reference.", + "bbox": [ + 76, + 239, + 470, + 267 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/be782cbee65257d7562303accd6e67cee66269bed332183a360618483c1d6bfb.jpg", + "image_caption": [ + "Figure 8. Failure examples of ECON. (A-B) Failures in recovering a SMPL-X body result, e.g., bent legs or wrong limb poses, cause ECON failures by extension. (C-D) Failures in normal-map estimation provide erroneous geometry to ECON to work with." + ], + "image_footnote": [], + "bbox": [ + 81, + 285, + 468, + 428 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "margin and outperforms PIFuHD. The reasons for a slight preference of PIFuHD over ECON on fashion images are discussed in Sec. 5. Figure 2 visualizes some comparisons. More examples are provided in Figs. S.7 to S.9 of the SupMat.", + "bbox": [ + 75, + 529, + 470, + 590 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.4. Ablation study", + "text_level": 1, + "bbox": [ + 76, + 603, + 225, + 618 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "d-BiNI vs BiNI. We compare d-BiNI with BiNI using 600 samples (200 scans x 3 views) from CAPE and Renderpeople where ground-truth normal maps and meshes are available. Table 3 reports the \"root mean squared error\" (RMSE) and \"mean absolute error\" (MAE) between the estimated and rendered depth maps. d-BiNI significantly improves the reconstruction accuracy by about $50\\%$ compared to BiNI. This demonstrates the efficacy of using the coarse body mesh as regularization and taking the consistency of both the front and back surface into consideration. Additionally, d-BiNI is $33\\%$ faster than BiNI.", + "bbox": [ + 75, + 627, + 470, + 792 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "IF-Nets+ vs IF-Nets. Following the metrics of Sec. 4.2, we compare IF-Nets [10] with our IF-Nets+ on $\\mathcal{R}_{\\mathrm{IF}}$ . We show the quantitative comparison in Tab. 4. The improvement for out-of-distribution (\"OOD\") poses shows that IF-Nets+ is more robust to pose variations than IF-Nets, as it is conditioned on the SMPL-X body. Figure 5 compares the geometry \" inpainting\" of both methods in the case of occlusions.", + "bbox": [ + 75, + 795, + 470, + 900 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.5. Multi-person reconstruction", + "text_level": 1, + "bbox": [ + 500, + 90, + 754, + 106 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Thanks to the shape completion module, ECON can deal with occlusions. Unlike other crowd body estimators [73-75, 86], ECON makes it possible to reconstruct multiple detailed \"clothed\" 3D humans from an image with interperson occlusions, even though ECON has not been trained for this. Figure 10 shows three examples. The occluded parts, colored in red, are successfully recovered.", + "bbox": [ + 496, + 114, + 893, + 219 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5. Discussion", + "text_level": 1, + "bbox": [ + 500, + 233, + 612, + 248 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Limitations. ECON takes as input an RGB image and an estimated SMPL-X body. However, recovering SMPL-X bodies (or similar models) from a single image is still an open problem, and not fully solved. Any failure in this could lead to ECON failures, such as in Fig. 8-A and Fig. 8-B. As the synthetic data [6,28,78] is getting sufficiently realistic, their domain gap with real data is significantly narrowed, it is predictable that such limitations will be eliminated. The reconstruction quality of ECON primarily relies on the accuracy of the predicted normal maps. Poor normal maps can result in overly close-by or even intersecting front and back surfaces, as shown in Fig. 8-C and Fig. 8-D.", + "bbox": [ + 496, + 258, + 893, + 439 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Future work. Apart from addressing the above limitations, several other directions are useful for practical applications. Currently, ECON reconstructs only 3D geometry. One could additionally recover an underlying skeleton and skinning weights [45, 84], to obtain fully-animatable avatars. Moreover, generating back-view texture [8,67,68,94] would result in fully-textured avatars. Disentangling clothing [1,63,99], hairstyle [89], or accessories [19] from the recovered geometry, would enable the simulation [23], synthesis, editing and transfer of styles [16] for these. ECON's reconstructions, together with its underneath SMPL-X body, could be useful as 3D shape prior to learn neural avatars [13,24,32].", + "bbox": [ + 496, + 443, + 893, + 625 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "In particular, ECON could be used to augment existing datasets of 2D images with 3D humans. Datasets of real clothed humans with 3D ground truth [55,60,66,88,97] are limited in size. In contrast, datasets of images without 3D ground truth are widely available in large sizes [17,21,51]. We can \"augment\" such datasets by reconstructing detailed 3D humans from their images. In SupMat., we apply ECON on SHHQ [17] and recover normal maps and 3D humans; see Fig. S.2. As ECON-like methods mature, they could produce pixel-aligned 3D humans from photos at scale, enabling the training of generative models of 3D clothed avatars with details [20,22,29,34,58,81,93].", + "bbox": [ + 496, + 625, + 893, + 805 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Possible negative impact. As the reconstruction matures, it opens the potential for low-cost realistic avatar creation. Although such a technique benefits entertainment, film production, tele-presence and future metaverse applications, it could also facilitate deep-fake avatars. Regulations must be established to clarify the appropriate use of such technology.", + "bbox": [ + 496, + 810, + 893, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "518", + "bbox": [ + 485, + 945, + 511, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/c7f125c2505c6f3dd4c10c859090ea41c66083281e346850cb76b8d96cce0b8e.jpg", + "image_caption": [ + "Figure 9. Qualitative results on in-the-wild images. We show 8 examples of reconstructing detailed clothed 3D humans from images with: (a) challenging poses and (b) loose clothing. For each example we show the input image along with two views (front and rotated) of the reconstructed 3D humans. Our approach is robust to pose variations, generalizes well to loose clothing, and contains detailed geometry." + ], + "image_footnote": [], + "bbox": [ + 76, + 61, + 890, + 416 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/98e01d57b840d8b08dcbdfa68cfe73f538fe2ba74b1b3ea51000676b0f52f97e.jpg", + "image_caption": [ + "Figure 10. Multiple humans with occlusions.. We detect multiple people and apply ECON to each separately. Although ECON is not trained on multiple people, it is robust to inter-person occlusions. We show three examples, and for each: (top) input image and the predicted front and back normal maps, (bottom) ECON's reconstruction. Red areas on the estimated mesh indicate occlusions." + ], + "image_footnote": [], + "bbox": [ + 78, + 465, + 895, + 625 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "6. Conclusion", + "text_level": 1, + "bbox": [ + 76, + 688, + 194, + 704 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We propose ECON to reconstruct detailed clothed 3D humans from a color image. It combines estimated 2.5D front and back surfaces with and underlying 3D parametric body in a highly effective way. On the one hand, it is robust to novel poses, while on the other hand, it is capable of recovering loose clothing and geometric details, since the reconstructed shape is not over-constrained to the topology of the body. ECON achieves this by using and extending recent advances in variational normal integration [7] and shape completion [10]. It effectively extends these to the task of image-based 3D human reconstruction. We believe ECON can lead to both real-world applications and useful tools for", + "bbox": [ + 75, + 719, + 472, + 901 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "the 3D vision community. The code and models are available at Econ.is.tue.mpg.de for research purposes.", + "bbox": [ + 498, + 690, + 890, + 722 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgments. We thank Lea Hering and Radek Daněček for proofreading, Yao Feng, Haven Feng and Weiyang Liu for valuable feedback, and Tsvetelina Alexiadis for perceptual study. We are especially grateful to Carlos Barreto (Blender Add-on), Teddy Huang (Docker Image), and Justin John (Windows Support). This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No.860768 (CLIPE project).", + "bbox": [ + 496, + 734, + 893, + 872 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Disclosure.is.tue.mpg.de/black/CoI_CVPR_2023.txt", + "bbox": [ + 500, + 885, + 849, + 901 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "519", + "bbox": [ + 485, + 944, + 509, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Alakh Aggarwal, Jikai Wang, Steven Hogue, Saifeng Ni, Madhukar Budagavi, and Xiaohu Guo. Layered-Garment Net: Generating Multiple Implicit Garment Layers from a Single Image. In Asian Conference on Computer Vision (ACCV), 2022. 7", + "[2] Thiemo Alldieck, Marcus A. 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Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.141, + 0.127, + 0.823, + 0.149 + ], + "angle": 0, + "content": "ECON: Explicit Clothed humans Optimized via Normal integration" + }, + { + "type": "text", + "bbox": [ + 0.15, + 0.173, + 0.822, + 0.192 + ], + "angle": 0, + "content": "Yuliang Xiu\\(^{1}\\) Jinlong Yang\\(^{1}\\) Xu Cao\\(^{2}\\) Dimitrios Tzionas\\(^{3}\\) Michael J. Black\\(^{1}\\)" + }, + { + "type": "text", + "bbox": [ + 0.268, + 0.194, + 0.705, + 0.21 + ], + "angle": 0, + "content": "1Max Planck Institute for Intelligent Systems, Tübingen, Germany" + }, + { + "type": "text", + "bbox": [ + 0.251, + 0.211, + 0.722, + 0.227 + ], + "angle": 0, + "content": "\\(^{2}\\)Osaka University, Japan \\(^{3}\\)University of Amsterdam, the Netherlands" + }, + { + "type": "text", + "bbox": [ + 0.088, + 0.23, + 0.882, + 0.244 + ], + "angle": 0, + "content": "{yuliang.xiu, jinlong.yang, black}@tue.mpg.de cao.xu@ist.osaka-u.ac.jp d.tzionas@uva.nl" + }, + { + "type": "image", + "bbox": [ + 0.084, + 0.274, + 0.236, + 0.45 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.134, + 0.453, + 0.186, + 0.462 + ], + "angle": 0, + "content": "Input Image" + }, + { + "type": "image", + "bbox": [ + 0.24, + 0.275, + 0.437, + 0.45 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.254, + 0.452, + 0.414, + 0.462 + ], + "angle": 0, + "content": "Front & Back Normal Estimation (2D)" + }, + { + "type": "image", + "bbox": [ + 0.443, + 0.274, + 0.798, + 0.452 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.448, + 0.453, + 0.606, + 0.462 + ], + "angle": 0, + "content": "Front & Back d-BiNI Surfaces (2.5D)" + }, + { + "type": "image_caption", + "bbox": [ + 0.64, + 0.452, + 0.775, + 0.462 + ], + "angle": 0, + "content": "FullClothedHumanMesh(3D)" + }, + { + "type": "image", + "bbox": [ + 0.804, + 0.275, + 0.891, + 0.41 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.805, + 0.411, + 0.888, + 0.468 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.475, + 0.893, + 0.545 + ], + "angle": 0, + "content": "Figure 1. Human digitization from a color image. ECON combines the best aspects of free-form implicit representation, and explicit anthropomorphic regularization to infer high-fidelity 3D humans, even with loose clothing or in challenging poses. It does so in three steps: (1) It infers detailed 2D normal maps for the front and back side (Sec. 3.1). (2) The normal maps are converted into detailed, yet incomplete, 2.5D front and back surfaces guided by a SMPL-X estimate (Sec. 3.2). (3) It then \"inpaints\" the missing geometry between two surfaces (Sec. 3.3). Face or hands can be optionally replaced with the cleaner ones from SMPL-X. See the video on our website for more results." + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.56, + 0.312, + 0.575 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.584, + 0.473, + 0.902 + ], + "angle": 0, + "content": "The combination of deep learning, artist-curated scans, and Implicit Functions (IF), is enabling the creation of detailed, clothed, 3D humans from images. However, existing methods are far from perfect. IF-based methods recover free-form geometry, but produce disembodied limbs or degenerate shapes for novel poses or clothes. To increase robustness for these cases, existing work uses an explicit parametric body model to constrain surface reconstruction, but this limits the recovery of free-form surfaces such as loose clothing that deviates from the body. What we want is a method that combines the best properties of implicit representation and explicit body regularization. To this end, we make two key observations: (1) current networks are better at inferring detailed 2D maps than full-3D surfaces, and (2) a parametric model can be seen as a \"canvas\" for stitching together detailed surface patches. Based on these, our method, ECON, has three main steps: (1) It infers detailed 2D normal maps for the front and back side of a clothed person. (2) From these, it recovers 2.5D front and back surfaces, called d-BiNI, that are equally detailed, yet incomplete, and registers these w.r.t. each other with the help of a SMPL-X" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.561, + 0.895, + 0.713 + ], + "angle": 0, + "content": "body mesh recovered from the image. (3) It \"inpaints\" the missing geometry between d-BiNI surfaces. If the face and hands are noisy, they can optionally be replaced with the ones of SMPL-X. As a result, ECON infers high-fidelity 3D humans even in loose clothes and challenging poses. This goes beyond previous methods, according to the quantitative evaluation on the CAPE and Renderpeople datasets. Perceptual studies also show that ECON's perceived realism is better by a large margin. Code and models are available for research purposes at econ.is.tue.mpg.de" + }, + { + "type": "title", + "bbox": [ + 0.501, + 0.74, + 0.631, + 0.755 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.895, + 0.902 + ], + "angle": 0, + "content": "Human avatars will be key for future games and movies, mixed-reality, tele-presence and the \"metaverse\". To build realistic and personalized avatars at scale, we need to faithfully reconstruct detailed 3D humans from color photos taken in the wild. This is still an open problem, due to its challenges; people wear all kinds of different clothing and accessories, and they pose their bodies in many, often imaginative, ways. A good reconstruction method must accurately capture these, while also being robust to novel clothing and poses." + }, + { + "type": "page_number", + "bbox": [ + 0.486, + 0.946, + 0.511, + 0.957 + ], + "angle": 0, + "content": "512" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.333 + ], + "angle": 0, + "content": "Initial, promising, results have been made possible by using artist-curated scans as training data, and implicit functions (IF) [56, 59] as the 3D representation. Seminal work on PIFu(HD) [70, 71] uses \"pixel-aligned\" IF and reconstructs clothed 3D humans with unconstrained topology. However, these methods tend to overfit to the poses seen in the training data, and have no explicit knowledge about the human body's structure. Consequently, they produce disembodied limbs or degenerate shapes for images with novel poses; see the 2nd row of Fig. 2. Follow-up work [26, 82, 96] accounts for such artifacts by regularizing the IF using a shape prior provided by an explicit body model [52, 61], but regularization introduces a topological constraint, restricting generalization to novel clothing while attenuating shape details; see the 3rd and 4th rows of Fig. 2. In a nutshell, there are trade-offs between robustness, generalization and detail." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.335, + 0.471, + 0.486 + ], + "angle": 0, + "content": "What we want is the best of both worlds; that is, the robustness of explicit anthropomorphic body models, and the flexibility of IF to capture arbitrary clothing topology. To that end, we make two key observations: (1) While inferring detailed 2D normal maps from color images is relatively easy [31, 71, 82], inferring 3D geometry with equally fine details is still challenging [9]. Thus, we exploit networks to infer detailed \"geometry-aware\" 2D maps that we then lift to 3D. (2) A body model can be seen as a low-frequency \"canvas\" that \"guides\" the stitching of detailed surface parts." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.488, + 0.471, + 0.594 + ], + "angle": 0, + "content": "With these in mind, we develop ECON, which stands for \"Explicit Clothed humans Optimized via Normal integration\". It takes, as input, an RGB image and a SMPL-X body inferred from the image. Then, it outputs a 3D human in free-form clothing with a level of detail and robustness that goes beyond the state of the art (SOTA); see the bottom of Fig. 2. Specifically, ECON has three steps." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.596, + 0.471, + 0.656 + ], + "angle": 0, + "content": "Step 1: Front & back normal reconstruction. We predict front- and back-side clothed-human normal maps from the input RGB image, conditioned on the body estimate, with a standard image-to-image translation network." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.658, + 0.472, + 0.869 + ], + "angle": 0, + "content": "Step 2: Front & back surface reconstruction. We take the previously predicted normal maps, and the corresponding depth maps that are rendered from the SMPL-X mesh, to produce detailed and coherent front-/back-side 3D surfaces, \\(\\{\\mathcal{M}_{\\mathrm{F}},\\mathcal{M}_{\\mathrm{B}}\\}\\). To this end, we extend the recent BiNI method [7], and develop a novel optimization scheme that is aimed at satisfying three goals for the resulting surfaces: (1) their high-frequency components agree with clothed-human normals, (2) their low-frequency components and the discontinuities agree with the SMPL-X ones, and (3) the depth values on their silhouettes are coherent with each other and consistent with the SMPL-X-based depth maps. The two output surfaces, \\(\\{\\mathcal{M}_{\\mathrm{F}},\\mathcal{M}_{\\mathrm{B}}\\}\\), are detailed yet incomplete, i.e., there is missing geometry in occluded and \"profile\" regions." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.471, + 0.901 + ], + "angle": 0, + "content": "Step 3: Full 3D shape completion. This module takes two inputs: (1) the SMPL-X mesh, and (2) the two d-BiNI" + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.08, + 0.892, + 0.379 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.38, + 0.894, + 0.436 + ], + "angle": 0, + "content": "Figure 2. Summary of SOTA. PIFuHD [71] recovers clothing details, but struggles with novel poses. ICON [82] and PaMIR [96] regularize shape to a body shape, but over-constrain the skirts, or over-smooth the wrinkles. ECON combines their best aspects." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.445, + 0.895, + 0.566 + ], + "angle": 0, + "content": "surfaces, \\(\\{\\mathcal{M}_{\\mathrm{F}},\\mathcal{M}_{\\mathrm{B}}\\}\\). The goal is to \"inpaint\" the missing geometry. Existing methods struggle with this problem. On one hand, Poisson reconstruction [38] produces \"blobby\" shapes and naively \"infills\" holes without exploiting a shape distribution prior. On the other hand, data-driven approaches, such as IF-Nets [10], struggle with missing parts caused by (self-)occlusions, and fail to keep the fine details present on two d-BiNI surfaces, producing degenerate geometries." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.567, + 0.895, + 0.702 + ], + "angle": 0, + "content": "We address above the limitations in two steps: (1) We extend and re-train IF-Nets to be conditioned on the SMPL-X body, so that SMPL-X regularizes shape \"infilling\". We discard the triangles that lie close to \\(\\{\\mathcal{M}_{\\mathrm{F}},\\mathcal{M}_{\\mathrm{B}}\\}\\), and keep the remaining ones as \"infilling patches\". (2) We stitch together the front- and back-side surfaces and infilling patches via Poisson reconstruction; note that holes between these are small enough for a general purpose method. The result is a full 3D shape of a clothed human; see Fig. 2, bottom." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.704, + 0.895, + 0.84 + ], + "angle": 0, + "content": "We evaluate ECON both on established benchmarks (CAPE [55] and Renderpeople [66]) and in-the-wild images. Quantitative analysis reveals ECON's superiority. A perceptual study echos this, showing that ECON is significantly preferred over competitors on challenging poses and loose clothing, and competitive with PIFuHD on fashion images. Qualitative results show that ECON generalizes better than the SOTA to a wide variety of poses and clothing, even with extreme looseness or complex topology; see Fig. 9." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.841, + 0.895, + 0.901 + ], + "angle": 0, + "content": "With both pose-robustness and topological flexibility, ECON recovers 3D clothed humans with a good level of detail and realistic pose. Code and models are available for research purposes at econ.is.tue.mpg.de" + }, + { + "type": "page_number", + "bbox": [ + 0.486, + 0.946, + 0.511, + 0.957 + ], + "angle": 0, + "content": "513" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.078, + 0.09, + 0.22, + 0.106 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.115, + 0.47, + 0.191 + ], + "angle": 0, + "content": "Image-based clothed human reconstruction. Regarding geometric representation, we group the mainstream clothed human reconstruction approaches into \"implicit\" and \"explicit\". Note that with the terms implicit/explicit we mainly refer to the surface decoder rather than the feature encoder." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.191, + 0.473, + 0.477 + ], + "angle": 0, + "content": "1) Explicit-shape-based approaches use either a mesh-based parametric body model [35, 52, 61, 69, 83], or a nonparametric depth map [18, 72] or point cloud [90], to reconstruct 3D humans. Many methods [15, 36, 39, 40, 42, 43, 75, 76, 87, 91, 92] estimate or regress minimally-clothed 3D body meshes from RGB pixels and ignore clothing. To account for clothed human shapes, another line of work [2-4, 41, 55, 62, 79, 100] adds 3D offsets on top of the body mesh. This is compatible with current animation pipelines, as they inherit the hierarchical skeleton and skinning weights from the underling statistical body model. However, this \"body+offset\" approach is not flexible enough to model loose clothing, which deviates significantly from the body topology, such as dresses and skirts. To increase topological flexibility, some methods [5, 33] reconstruct 3D clothed humans by identifying the type of clothing and using the appropriate model to reconstruct it. Scaling up this \"cloth-aware\" approach to many clothing styles is nontrivial, limiting generalization to in-the-wild outfit variation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.479, + 0.472, + 0.614 + ], + "angle": 0, + "content": "2) Implicit-function-based approaches are topology-agnostic and, thus, can be used to represent arbitrary 3D clothed human shapes. SMPLicit [12], ClothWild [57] and DIG [46] learn a generative clothing model with neural distance fields [11, 56, 59] from a 3D clothing dataset. Given an image, the clothed human is reconstructed by estimating a parametric body and optimizing the latent space of the clothing model. However, the results usually do not align well with the image and lack geometric detail." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.614, + 0.472, + 0.825 + ], + "angle": 0, + "content": "PIFu [70] introduces pixel-aligned implicit human shape reconstruction and PIFuHD [71] significantly improves the geometric details with a multi-level architecture and normal maps predicted from the RGB image. However, these two methods do not exploit knowledge of the human body structure. Therefore, these methods overfit to the body poses in the training data, e.g. fashion poses. They fail to generalize to novel poses, producing non-human shapes with broken or disembodied limbs. To address these issues, several methods introduce different geometric priors to regularize the deep implicit representation: GeoPIFu [26] introduces a coarse shape of volumetric humans, Self-Portraits [49], PINA [14], and S3 [85] use depth or LIDAR information to regularize shape and improve robustness to pose variation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.826, + 0.472, + 0.901 + ], + "angle": 0, + "content": "Another direction leverages parametric body models, which represent human body shape well, model the kinematic structure of the body, and can be reliably estimated from RGB images of clothed people. Such a representation can be viewed as a base shape upon which to model clothed" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.895, + 0.332 + ], + "angle": 0, + "content": "humans. Therefore, several methods combine parametric body models with expressive implicit representations to get the best of both worlds. PaMIR [96] and DeepMultiCap [95] condition the pixel-aligned features on a posed and voxelized SMPL mesh. JIFF Introduces a 3DMM face prior to improve the realism of the facial region. ARCH [30], \\(\\mathrm{ARCH} + +\\) [27] and CAR [50] use SMPL to unpose the pixel-aligned query points from a posed space to a canonical space. To further generalize to unseen poses on in-the-wild photos, ICON [82] regresses shapes from locally-queried features. However, the above approaches gain robustness to unseen poses at the cost of generalization ability to various, especially loose, clothing topologies. We argue that this is because loose clothing differs greatly from human body and that conditioning on the SMPL body in 3D makes it harder for networks to make full use of 2D image features." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.333, + 0.897, + 0.576 + ], + "angle": 0, + "content": "Our work is also inspired by \"sandwich-like\" monocular reconstruction approaches, represented by Moduling Humans [18], FACSIMILE [72] and Any-Shot GIN [80]. Moduling Humans has two networks: a generator that estimates the visible (front) and invisible (back) depth maps from RGB images, and a discriminator that helps regularize the estimation via an adversarial loss. FACSIMILE further improves the geometric details by leveraging a normal loss, which is directly computed from depth estimates via differentiable layers. Recently, Any-Shot GIN generalizes the sandwich-like scheme to novel classes of objects. Given RGB images, it predicts front and back depth maps as well, and then exploits IF-Nets [10] for shape completion. We follow a similar path and extend it, to successfully reconstruct clothed human shapes with SOTA pose generalization, and better details from normal images." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.587, + 0.593, + 0.603 + ], + "angle": 0, + "content": "3. Method" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.613, + 0.895, + 0.689 + ], + "angle": 0, + "content": "Given an RGB image, ECON first estimates front and back normal maps (Sec. 3.1), then converts them into front and back partial surfaces (Sec. 3.2), and finally \"inpaints\" the missing geometry with the help of IF-Nets+ (Sec. 3.3). See ECON's overview in Fig. 3." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.697, + 0.783, + 0.714 + ], + "angle": 0, + "content": "3.1. Detailed normal map prediction" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.895, + 0.871 + ], + "angle": 0, + "content": "Trained on abundant pairs of RGB images and normal images, a \"front\" normal map, \\(\\widehat{\\mathcal{N}}_{\\mathrm{F}}^{\\mathrm{c}}\\), can be accurately estimated from an RGB image using image-to-image translation networks, as demonstrated in PIFuHD [71] or ICON [82]. Both methods also infer a \"back\" normal map, \\(\\widehat{\\mathcal{N}}_{\\mathrm{B}}^{\\mathrm{c}}\\), from the image. But, the absence of image cues leads to over-smooth \\(\\widehat{\\mathcal{N}}_{\\mathrm{B}}^{\\mathrm{c}}\\). To address this, we fine-tune ICON's backside normal predictor, \\(\\mathcal{G}_{\\mathrm{B}}^{\\mathrm{N}}\\), with an additional MRF loss [77] to enhance the local details by minimizing the difference between the predicted \\(\\widehat{\\mathcal{N}}^{\\mathrm{c}}\\) and ground truth (GT) \\(\\mathcal{N}^{\\mathrm{c}}\\) in feature space." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.871, + 0.895, + 0.903 + ], + "angle": 0, + "content": "To guide the normal map prediction and make it robust to various body poses, ICON conditions the normal map" + }, + { + "type": "page_number", + "bbox": [ + 0.486, + 0.946, + 0.512, + 0.957 + ], + "angle": 0, + "content": "514" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.08, + 0.087, + 0.725, + 0.355 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.752, + 0.097, + 0.887, + 0.351 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.366, + 0.895, + 0.427 + ], + "angle": 0, + "content": "Figure 3. Overview. ECON takes as input an RGB image, \\(\\mathcal{I}\\), and a SMPL-X body, \\(\\mathcal{M}^{\\mathrm{b}}\\). Conditioned on the rendered front and back body normal images, \\(\\mathcal{N}^{\\mathrm{b}}\\), ECON first predicts front and back clothing normal maps, \\(\\widehat{\\mathcal{N}}^{\\mathrm{c}}\\). These two maps, along with body depth maps, \\(\\mathcal{Z}^{\\mathrm{b}}\\), are fed into a d-BiNI optimizer to produce front and back surfaces, \\(\\{\\mathcal{M}_{\\mathrm{F}}, \\mathcal{M}_{\\mathrm{B}}\\}\\). Based on such partial surfaces, and body estimate \\(\\mathcal{M}^{\\mathrm{b}}\\), IF-Nets+ implicitly completes \\(\\mathcal{R}_{\\mathrm{IF}}\\). With optional Face or hands from \\(\\mathcal{M}^{\\mathrm{b}}\\), screened Poisson combines everything as final watertight \\(\\mathcal{R}\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.441, + 0.475, + 0.562 + ], + "angle": 0, + "content": "prediction module on the body normal maps, \\(\\mathcal{N}^{\\mathrm{b}}\\), rendered from the estimated body \\(\\mathcal{M}^{\\mathrm{b}}\\). Thus, it is important to accurately align the estimated body and clothing silhouette. Apart from the \\(\\mathcal{L}_{\\mathrm{N\\_diff}}\\) and \\(\\mathcal{L}_{\\mathrm{S\\_diff}}\\) used in ICON [82], we also apply 2D body landmarks in an additional loss term, \\(\\mathcal{L}_{\\mathrm{J\\_diff}}\\), to further optimize the SMPL-X body, \\(\\mathcal{M}^{\\mathrm{b}}\\), inferred from pixie [15] or PyMAF-X [91]. Specifically, we optimize SMPL-X's shape, \\(\\beta\\), pose, \\(\\theta\\), and translation, \\(t\\), to minimize:" + }, + { + "type": "equation", + "bbox": [ + 0.152, + 0.576, + 0.47, + 0.6 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\mathrm {S M P L - X}} = \\mathcal {L} _ {\\mathrm {N} _ {-} \\text {d i f f}} + \\mathcal {L} _ {\\mathrm {S} _ {-} \\text {d i f f}} + \\mathcal {L} _ {\\mathrm {J} _ {-} \\text {d i f f}}, \\tag {1}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.188, + 0.595, + 0.359, + 0.614 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\mathrm {J} _ {-} \\text {d i f f}} = \\lambda_ {\\mathrm {J} _ {-} \\text {d i f f}} \\left| \\mathcal {J} ^ {\\mathrm {b}} - \\widehat {\\mathcal {J} ^ {\\mathrm {c}}} \\right|,\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.622, + 0.471, + 0.716 + ], + "angle": 0, + "content": "where \\(\\mathcal{L}_{\\mathrm{N\\_diff}}\\) and \\(\\mathcal{L}_{\\mathrm{S\\_diff}}\\) are the normal-map loss and silhouette loss introduced in ICON [82], and \\(\\mathcal{L}_{\\mathrm{J\\_diff}}\\) is the joint loss (L2) between 2D landmarks \\(\\widehat{\\mathcal{I}^{\\mathrm{c}}}\\), which are estimated by a 2D keypoint estimator from the RGB image \\(\\mathcal{I}\\), and the corresponding re-projected 2D joints \\(\\mathcal{I}^{\\mathrm{b}}\\) from \\(\\mathcal{M}^{\\mathrm{b}}\\). For more implementation details, see Sec. A.1 in SupMat." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.725, + 0.409, + 0.74 + ], + "angle": 0, + "content": "3.2. Front and back surface reconstruction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.75, + 0.47, + 0.839 + ], + "angle": 0, + "content": "We now lift the clothed normal maps to 2.5D surfaces. We expect these 2.5D surfaces to satisfy three conditions: (1) high-frequency surface details agree with predicted clothed normal maps, (2) low-frequency surface variations, including discontinuities, agree with SMPL-X's ones, and (3) the depth of the front and back silhouettes are close to each other." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.471, + 0.902 + ], + "angle": 0, + "content": "Unlike PIFuHD [71] or ICON [82], which train a neural network to regress the implicit surface from normal maps, we explicitly model the depth-normal relationship using variational normal integration methods [7,64]. Specifi" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.441, + 0.893, + 0.487 + ], + "angle": 0, + "content": "cally, we tailor the recent bilateral normal integration (BiNI) method [7] to full-body mesh reconstruction by harnessing the coarse prior, depth maps, and silhouette consistency." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.487, + 0.892, + 0.549 + ], + "angle": 0, + "content": "To satisfy the three conditions, we propose a depth-aware silhouette-consistent bilateral normal integration (d-BiNI) method to jointly optimize for the front and back clothed depth maps, \\(\\widehat{\\mathcal{Z}}_{\\mathrm{F}}^{\\mathrm{c}}\\) and \\(\\widehat{\\mathcal{Z}}_{\\mathrm{B}}^{\\mathrm{c}}\\):" + }, + { + "type": "equation", + "bbox": [ + 0.572, + 0.558, + 0.893, + 0.58 + ], + "angle": 0, + "content": "\\[\n\\mathrm {d} - \\operatorname {B i N I} \\left(\\widehat {\\mathcal {N}} _ {\\mathrm {F}} ^ {\\mathrm {c}}, \\widehat {\\mathcal {N}} _ {\\mathrm {B}} ^ {\\mathrm {c}}, \\mathcal {Z} _ {\\mathrm {F}} ^ {\\mathrm {b}}, \\mathcal {Z} _ {\\mathrm {B}} ^ {\\mathrm {b}}\\right)\\rightarrow \\widehat {\\mathcal {Z}} _ {\\mathrm {F}} ^ {\\mathrm {c}}, \\widehat {\\mathcal {Z}} _ {\\mathrm {B}} ^ {\\mathrm {c}}. \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.591, + 0.892, + 0.639 + ], + "angle": 0, + "content": "Here, \\(\\widehat{\\mathcal{N}}_{*}^{\\mathrm{c}}\\) is the front or back clothed normal map predicted by \\(\\mathcal{G}_{\\mathrm{F,B}}^{\\mathrm{N}}\\) from \\(\\{\\mathcal{I},\\mathcal{N}^{\\mathrm{b}}\\}\\), and \\(\\mathcal{Z}_{*}^{\\mathrm{b}}\\) is the front or back coarse body depth image rendered from the SMPL-X mesh, \\(\\mathcal{M}^{\\mathrm{b}}\\)." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.64, + 0.893, + 0.655 + ], + "angle": 0, + "content": "Specifically, our objective function consists of five terms:" + }, + { + "type": "equation", + "bbox": [ + 0.567, + 0.677, + 0.892, + 0.751 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\min _ {\\widehat {\\mathcal {Z}} _ {\\mathrm {F}} ^ {\\mathrm {c}}, \\widehat {\\mathcal {Z}} _ {\\mathrm {B}} ^ {\\mathrm {c}}} \\mathcal {L} _ {\\mathrm {n}} (\\widehat {\\mathcal {Z}} _ {\\mathrm {F}} ^ {\\mathrm {c}}; \\widehat {\\mathcal {N}} _ {\\mathrm {F}} ^ {\\mathrm {c}}) + \\mathcal {L} _ {\\mathrm {n}} (\\widehat {\\mathcal {Z}} _ {\\mathrm {B}} ^ {\\mathrm {c}}; \\widehat {\\mathcal {N}} _ {\\mathrm {B}} ^ {\\mathrm {c}}) + \\\\ \\lambda_ {\\mathrm {d}} \\mathcal {L} _ {\\mathrm {d}} \\left(\\widehat {\\mathcal {Z}} _ {\\mathrm {F}} ^ {\\mathrm {c}}; \\mathcal {Z} _ {\\mathrm {F}} ^ {\\mathrm {b}}\\right) + \\lambda_ {\\mathrm {d}} \\mathcal {L} _ {\\mathrm {d}} \\left(\\widehat {\\mathcal {Z}} _ {\\mathrm {B}} ^ {\\mathrm {c}}; \\mathcal {Z} _ {\\mathrm {B}} ^ {\\mathrm {b}}\\right) + \\tag {3} \\\\ \\lambda_ {s} \\mathcal {L} _ {s} (\\widehat {\\mathcal {Z}} _ {F} ^ {c}, \\widehat {\\mathcal {Z}} _ {B} ^ {c}), \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.761, + 0.892, + 0.821 + ], + "angle": 0, + "content": "where \\(\\mathcal{L}_{\\mathrm{n}}\\) is the BiNI loss term introduced by BiNI [7], \\(\\mathcal{L}_{\\mathrm{d}}\\) is a depth prior applied to the front and back depth surfaces, and \\(\\mathcal{L}_{\\mathrm{s}}\\) is a front-back silhouette consistency term. For a more detailed discussion on these terms, see Sec. A.2 in SupMat." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.822, + 0.892, + 0.868 + ], + "angle": 0, + "content": "With Eq. (3), we make two technical contributions beyond BiNI [7]. First, we use the coarse depth prior rendered from the SMPL-X body mesh, \\(\\mathcal{Z}_i^{\\mathrm{b}}\\), to regularize BiNI:" + }, + { + "type": "equation", + "bbox": [ + 0.541, + 0.878, + 0.893, + 0.9 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\mathrm {d}} \\left(\\widehat {\\mathcal {Z}} _ {i} ^ {\\mathrm {c}}; \\mathcal {Z} _ {i} ^ {\\mathrm {b}}\\right) = \\left| \\widehat {\\mathcal {Z}} _ {i} ^ {\\mathrm {c}} - \\mathcal {Z} _ {i} ^ {\\mathrm {b}} \\right| _ {\\Omega_ {\\mathrm {n}}} \\cap \\Omega_ {\\mathrm {z}} \\quad i \\in \\{F, B \\}. \\tag {4}\n\\]" + }, + { + "type": "page_number", + "bbox": [ + 0.486, + 0.945, + 0.511, + 0.957 + ], + "angle": 0, + "content": "515" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.081, + 0.089, + 0.473, + 0.187 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.196, + 0.471, + 0.224 + ], + "angle": 0, + "content": "Figure 4. Four inputs to d-BiNI. \\(\\Omega_{\\mathrm{n}}\\) and \\(\\Omega_{\\mathrm{z}}\\) are the domains of clothed and body regions, respectively. \\(\\partial \\Omega_{\\mathrm{n}}\\) is the silhouette of \\(\\Omega_{\\mathrm{n}}\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.23, + 0.47, + 0.351 + ], + "angle": 0, + "content": "This addresses the key problem of putting the front and back surfaces together in a coherent way to form a full body. Optimizing BiNI terms \\(\\mathcal{L}_{\\mathrm{n}}\\) leaves an arbitrary global offset between the front and back surfaces. The depth prior terms \\(\\mathcal{L}_{\\mathrm{d}}\\) encourage the surfaces with undecided offsets to be consistent with the SMPL-X body, and is computed in the domains \\(\\Omega_{\\mathrm{n}} \\bigcap \\Omega_{\\mathrm{z}}\\) (Fig. 4). For further intuitions on \\(\\mathcal{L}_{\\mathrm{n}}\\) and \\(\\mathcal{L}_{\\mathrm{d}}\\), see Fig. S.4 and Fig. S.5 in SupMat." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.352, + 0.472, + 0.397 + ], + "angle": 0, + "content": "Second, we use a silhouette consistency term to encourage the front and back depth values to be the same at the silhouette boundary, which is computed in domain \\(\\partial \\Omega_{\\mathrm{n}}\\) (Fig. 4):" + }, + { + "type": "equation", + "bbox": [ + 0.174, + 0.419, + 0.47, + 0.439 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\mathrm {s}} \\left(\\widehat {\\mathcal {Z}} _ {\\mathrm {F}} ^ {\\mathrm {c}}, \\widehat {\\mathcal {Z}} _ {\\mathrm {B}} ^ {\\mathrm {c}}\\right) = \\left| \\widehat {\\mathcal {Z}} _ {\\mathrm {F}} ^ {\\mathrm {c}} - \\widehat {\\mathcal {Z}} _ {\\mathrm {B}} ^ {\\mathrm {c}} \\right| _ {\\partial \\Omega_ {\\mathrm {n}}}. \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.448, + 0.47, + 0.524 + ], + "angle": 0, + "content": "The silhouette term improves the physical consistency of the reconstructed front and back clothed depth maps. Without this term, d-BiNI produces intersections of the front and back surfaces around the silhouette, causing \"blobby\" artifacts and hurting reconstruction quality; see Fig. S.6 in SupMat." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.532, + 0.31, + 0.549 + ], + "angle": 0, + "content": "3.3. Human shape completion" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.555, + 0.471, + 0.661 + ], + "angle": 0, + "content": "For simple body poses without self-occlusions, merging front and back d-BiNI surfaces in a straightforward way, as done in FACSIMILE [72] and Moduling Humans [18], can result in a complete 3D clothed scan. However, often poses result in self-occlusions, which cause large portions of the surfaces to be missing. In such cases, Poisson Surface Reconstruction (PSR) [37] leads to blobby artifacts." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.668, + 0.472, + 0.85 + ], + "angle": 0, + "content": "PSR completion with SMPL-X \\((\\mathbf{ECON_{EX}})\\). A naive way to \"infill\" the missing surface is to make use of the estimated SMPL-X body. We remove the triangles from \\(\\mathcal{M}^{\\mathrm{b}}\\) that are visible to front or back cameras. The remaining triangle \"soup\" \\(\\mathcal{M}^{\\mathrm{cull}}\\) contains both side-view boundaries and occluded regions. We apply PSR [37] to the union of \\(\\mathcal{M}^{\\mathrm{cull}}\\) and d-BiNI surfaces \\(\\{\\mathcal{M}_{\\mathrm{F}},\\mathcal{M}_{\\mathrm{B}}\\}\\) to obtain a watertight reconstruction \\(\\mathcal{R}\\). This approach is denoted as \\(\\mathrm{ECON_{EX}}\\). Although \\(\\mathrm{ECON_{EX}}\\) avoids missing limbs or sides, it does not produce a coherent surface for the originally missing clothing and hair surfaces because of the discrepancy between SMPL-X and actual clothing or hair; see \\(\\mathrm{ECON_{EX}}\\) in Fig. 5." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.471, + 0.901 + ], + "angle": 0, + "content": "Inpainting with IF-Nets+ \\((\\mathcal{R}_{\\mathrm{IF}})\\). To improve reconstruction coherence, we use a learned implicit-function (IF) model to \"inpaint\" the missing geometry given front and back d-BiNI" + }, + { + "type": "image", + "bbox": [ + 0.507, + 0.088, + 0.895, + 0.301 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.311, + 0.895, + 0.395 + ], + "angle": 0, + "content": "Figure 5. \"Inpainting\" the missing geometry. We simulate different cases of occlusion by masking the normal images and present the intermediate and final 3D reconstruction of different design choices. While IF-Nets misses certain body parts, IF-Nets+ produces a plausible overall shape. \\(\\mathrm{ECON_{IF}}\\) produces more consistent clothing surfaces than \\(\\mathrm{ECON_{EX}}\\) due to a learned shape distribution." + }, + { + "type": "image", + "bbox": [ + 0.502, + 0.409, + 0.892, + 0.546 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.555, + 0.894, + 0.583 + ], + "angle": 0, + "content": "Figure 6. Face and hand details. The face and hands of the raw reconstruction can be replaced with the ones of the SMPL-X body." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.605, + 0.895, + 0.834 + ], + "angle": 0, + "content": "surfaces. Specifically, we tailor a general-purpose shape completion method, IF-Nets [10], to a SMPL-X-guided one, denoted as IF-Nets+. IF-Nets [10] completes the 3D shape from a deficient 3D input, such as an incomplete 3D human shape or a low-resolution voxel grid. Inspired by Li et al. [44], we adapt IF-Nets by conditioning it on a voxelized SMPL-X body to deal with pose variation; for details see Sec. A.3 in SupMat. IF-Nets+ is trained on voxelized front and back ground-truth clothed depth maps, \\(\\{\\mathcal{Z}_{\\mathrm{F}}^{\\mathrm{c}},\\mathcal{Z}_{\\mathrm{B}}^{\\mathrm{c}}\\}\\) and a voxelized (estimated) body mesh, \\(\\mathcal{M}^{\\mathrm{b}}\\) as input, and is supervised with ground-truth 3D shapes. During training, we randomly mask \\(\\{\\mathcal{Z}_{\\mathrm{F}}^{\\mathrm{c}},\\mathcal{Z}_{\\mathrm{B}}^{\\mathrm{c}}\\}\\) for robustness to occlusions. During inference, we feed the estimated \\(\\widehat{\\mathcal{Z}}_{\\mathrm{F}}^{\\mathrm{c}},\\widehat{\\mathcal{Z}}_{\\mathrm{B}}^{\\mathrm{c}}\\) and \\(\\mathcal{M}^{\\mathrm{b}}\\) into IF-Nets+ to obtain an occupancy field, from which we extract the inpainted mesh, \\(\\mathcal{R}_{\\mathrm{IF}}\\) with Marching cubes [53]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.895, + 0.901 + ], + "angle": 0, + "content": "PSR completion with \\(\\mathcal{R}_{\\mathrm{IF}}\\) (\\(\\mathbf{ECON_{IF}}\\)). To obtain our final mesh, \\(\\mathcal{R}\\), we apply PSR to stitch (1) d-BiNI surfaces, (2) sided and occluded triangle soup \\(\\mathcal{M}^{\\mathrm{cull}}\\) from \\(\\mathcal{R}_{\\mathrm{IF}}\\), and optionally, (3) face or hands cropped from the estimated SMPL-X" + }, + { + "type": "page_number", + "bbox": [ + 0.486, + 0.946, + 0.512, + 0.957 + ], + "angle": 0, + "content": "516" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.09, + 0.464, + 0.16 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.171, + 0.47, + 0.214 + ], + "angle": 0, + "content": "Figure 7. Datasets for numerical evaluation. We evaluate ECON on images with unseen poses (left) and unseen outfits (right) on the CAPE [55] and Renderpeople [66] datasets, respectively." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.238, + 0.471, + 0.284 + ], + "angle": 0, + "content": "body \\(\\mathcal{M}^{\\mathrm{b}}\\). The necessity of (3) arises from the poorly reconstructed hands/face in \\(\\mathcal{R}_{\\mathrm{IF}}\\), see difference in Fig. 6. The approach is denoted as \\(\\mathrm{ECON_{IF}}\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.285, + 0.472, + 0.406 + ], + "angle": 0, + "content": "Notably, although \\(\\mathcal{R}_{\\mathrm{IF}}\\) is already a complete human mesh, due to the lossy voxelization of inputs and limited resolution of Marching cubes algorithm, it somehow smooths out the details of \\(\\tilde{\\mathcal{Z}}_{\\{\\mathrm{F,B}\\}}^{\\mathrm{c}} / \\mathcal{M}_{\\{\\mathrm{F,B}\\}}\\), which are optimized via d-BiNI (see \\(\\mathcal{R}_{\\mathrm{IF}}\\) vs ECON{IF,EX} in Fig. 5). While ECON{IF,EX} preserves d-BiNI details better, only the side-views and occluded parts of \\(\\mathcal{R}_{\\mathrm{IF}}\\) are fused in the Poisson step. In Tabs. 1 and 4, we use ECON{IF,EX} instead of \\(\\mathcal{R}_{\\mathrm{IF}}\\) for evaluation." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.418, + 0.21, + 0.435 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.443, + 0.18, + 0.457 + ], + "angle": 0, + "content": "4.1. Datasets" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.466, + 0.471, + 0.542 + ], + "angle": 0, + "content": "Training on THuman2.0. THuman2.0 [88] contains 525 high-quality human textured scans in various poses, which are captured by a dense DSLR rig, along with their corresponding SMPL-X fits. We use THuman2.0 to train ICON, ECON\\(_{\\text{IF}}\\) (IF-Nets+), IF-Nets, PIFu and PaMIR." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.545, + 0.472, + 0.697 + ], + "angle": 0, + "content": "Quantitative evaluation on CAPE & Renderpeople. We primarily evaluate on CAPE [55] and Renderpeople [66]. Specifically, we use the \"CAPE-NFP\" set (100 scans), which is used by ICON to analyze robustness to complex human poses. Moreover, we select another 100 scans from Renderpeople, containing loose clothing, such as dresses, skirts, robes, down jackets, costumes, etc. With such clothing variance, Renderpeople helps numerically evaluate the flexibility of reconstruction methods w.r.t. shape topology. Samples of the two datasets are shown in Fig. 7." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.705, + 0.174, + 0.719 + ], + "angle": 0, + "content": "4.2. Metrics" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.728, + 0.472, + 0.803 + ], + "angle": 0, + "content": "Chamfer and P2S distance (cm). To capture large geometric errors, e.g. occluded parts or wrongly positioned limbs, we report the commonly used Chamfer (bi-directional point-to-surface) and P2S distance (1-directional point-to-surface) between ground-truth and reconstructed meshes." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.804, + 0.472, + 0.895 + ], + "angle": 0, + "content": "Normal difference (L2). To measure the fineness of reconstructed local details, as well as projection consistency from the input image, we also report the L2 error between normal images rendered from reconstructed and ground-truth surfaces, by rotating a virtual camera around these by \\(\\{0^{\\circ}, 90^{\\circ}, 180^{\\circ}, 270^{\\circ}\\}\\) w.r.t. to a frontal view." + }, + { + "type": "table", + "bbox": [ + 0.503, + 0.088, + 0.894, + 0.185 + ], + "angle": 0, + "content": "
MethodsData-drivenOOD poses (CAPE)OOD outfits (Renderpeople)
Chamfer ↓P2S ↓Normals ↓Chamfer ↓P2S ↓Normals ↓
w/o SMPL-X body prior
PIFu *✓1.7221.5480.06741.7061.6420.0709
PIFuHD†✓3.7673.5910.09941.9461.9830.0658
w/ GT SMPL-X body prior
PaMIR *✓0.9890.9920.04221.2961.4300.0518
ICON✓0.9710.9090.04091.3731.5220.0566
ECONIF✓0.9960.9670.04131.4011.4220.0516
ECONEXX0.9260.9170.03671.3421.4580.0478
" + }, + { + "type": "table_caption", + "bbox": [ + 0.498, + 0.195, + 0.895, + 0.28 + ], + "angle": 0, + "content": "Table 1. Evaluation against the state of the art. All models use a resolution of 256 for marching cubes. *Methods are re-implemented in [82] for a fair comparison in terms of network settings and training data. †Official model is trained on the Renderpeople dataset. ECONEX is optimization-based, thus requires no training (X). “OOD” is short for “out-of-distribution”." + }, + { + "type": "table", + "bbox": [ + 0.502, + 0.293, + 0.905, + 0.354 + ], + "angle": 0, + "content": "
ICON [82]PIFuHD [71]PaMIR [96]
Challenging poses0.2830.1080.132
Loose clothing0.1470.3620.232
Fashion images0.1990.5510.290
" + }, + { + "type": "table_caption", + "bbox": [ + 0.498, + 0.365, + 0.895, + 0.421 + ], + "angle": 0, + "content": "Table 2. Perceptual study. Numbers denote the chance that participants prefer the reconstruction of a competing method over ECON for in-the-wild images. A value of 0.5 indicates equal preference. A value of \\(< 0.5\\) favors ECON, while of \\(>0.5\\) favors competitors." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.449, + 0.621, + 0.463 + ], + "angle": 0, + "content": "4.3. Evaluation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.472, + 0.895, + 0.669 + ], + "angle": 0, + "content": "Quantitative evaluation. We compare ECON with body-agnostic methods, i.e., PIFu [70] and PIFuHD [71], and body-aware methods, i.e., PaMIR [96] and ICON [82]; see in Tab. 1. For fair comparison, we use re-implementations of PIFu and PaMIR from ICON [82], because they have the same network settings and input data. \\(\\mathrm{ECON_{EX}}\\) performs on par with ICON, and outperforms other methods on images containing out-of-distribution (OOD) poses (CAPE), with a distance error below \\(1\\mathrm{cm}\\). In terms of out-of-distribution outfitsits (Renderpeople), \\(\\mathrm{ECON_{EX/IF}}\\) performs on par with PaMIR, and much better than PIFuHD. When it comes to high-frequency details measured by normals, \\(\\mathrm{ECON_{EX}}\\) achieves SOTA performance on both datasets." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.674, + 0.894, + 0.78 + ], + "angle": 0, + "content": "Perceptual study. Due to the lack of ground-truth geometry (clothed scan + underneath SMPL-X), we further conduct a perceptual study to evaluate ECON on in-the-wild images. Test images are divided into three categories: \"challenging poses\", \"loose clothing\", and \"fashion images\". Examples of challenging poses and loose clothing can be seen in Fig. 9, and some of fashion images are in SupMat.'s Fig. S.2." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.781, + 0.895, + 0.902 + ], + "angle": 0, + "content": "Participants are asked to choose the reconstruction they perceive as more realistic, between a baseline method and ECON. We compute the chances that each baseline is preferred over ECON in Tab. 2. The results of the perceptual study confirm the quantitative evaluation in Tab. 1. For \"challenging poses\" images, ECON is significantly preferred over PIFuHD and outperforms ICON. On images of people wearing loose clothing, ECON is preferred over ICON by a large" + }, + { + "type": "page_number", + "bbox": [ + 0.486, + 0.945, + 0.511, + 0.957 + ], + "angle": 0, + "content": "517" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.08, + 0.088, + 0.472, + 0.135 + ], + "angle": 0, + "content": "
MethodsOOD poses (CAPE [55])OOD outfitsits (Renderpeople) [66]Speed FPS ↑
RMSE ↓MAE ↓RMSE ↓MAE ↓
BiNI [7]27.6421.1120.6116.070.52
d-BiNI13.4310.2914.4311.260.69
" + }, + { + "type": "table_caption", + "bbox": [ + 0.078, + 0.138, + 0.47, + 0.166 + ], + "angle": 0, + "content": "Table 3. BiNI vs d-BiNI. Comparison between BiNI and d-BiNI surfaces w.r.t. reconstruction accuracy and optimization speed." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.182, + 0.472, + 0.238 + ], + "angle": 0, + "content": "
MethodsOOD poses (CAPE)OOD outfits (Renderpeople)
Chamfer ↓P2S ↓Normals ↓Chamfer ↓P2S ↓Normals ↓
IF-Nets [10]2.1161.2330.0751.8831.6220.070
IF-Nets+1.4011.3530.0561.4771.5640.055
ECONIF0.9960.9670.04131.4011.4220.0516
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.241, + 0.471, + 0.268 + ], + "angle": 0, + "content": "Table 4. Evaluation for shape completion. Same metrics as Tab. 1, and \\(\\mathrm{ECON_{IF}}\\) is added as a reference." + }, + { + "type": "image", + "bbox": [ + 0.082, + 0.286, + 0.47, + 0.429 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.445, + 0.471, + 0.501 + ], + "angle": 0, + "content": "Figure 8. Failure examples of ECON. (A-B) Failures in recovering a SMPL-X body result, e.g., bent legs or wrong limb poses, cause ECON failures by extension. (C-D) Failures in normal-map estimation provide erroneous geometry to ECON to work with." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.53, + 0.472, + 0.591 + ], + "angle": 0, + "content": "margin and outperforms PIFuHD. The reasons for a slight preference of PIFuHD over ECON on fashion images are discussed in Sec. 5. Figure 2 visualizes some comparisons. More examples are provided in Figs. S.7 to S.9 of the SupMat." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.604, + 0.227, + 0.619 + ], + "angle": 0, + "content": "4.4. Ablation study" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.628, + 0.472, + 0.794 + ], + "angle": 0, + "content": "d-BiNI vs BiNI. We compare d-BiNI with BiNI using 600 samples (200 scans x 3 views) from CAPE and Renderpeople where ground-truth normal maps and meshes are available. Table 3 reports the \"root mean squared error\" (RMSE) and \"mean absolute error\" (MAE) between the estimated and rendered depth maps. d-BiNI significantly improves the reconstruction accuracy by about \\(50\\%\\) compared to BiNI. This demonstrates the efficacy of using the coarse body mesh as regularization and taking the consistency of both the front and back surface into consideration. Additionally, d-BiNI is \\(33\\%\\) faster than BiNI." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.796, + 0.472, + 0.901 + ], + "angle": 0, + "content": "IF-Nets+ vs IF-Nets. Following the metrics of Sec. 4.2, we compare IF-Nets [10] with our IF-Nets+ on \\(\\mathcal{R}_{\\mathrm{IF}}\\). We show the quantitative comparison in Tab. 4. The improvement for out-of-distribution (\"OOD\") poses shows that IF-Nets+ is more robust to pose variations than IF-Nets, as it is conditioned on the SMPL-X body. Figure 5 compares the geometry \" inpainting\" of both methods in the case of occlusions." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.091, + 0.755, + 0.107 + ], + "angle": 0, + "content": "4.5. Multi-person reconstruction" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.115, + 0.895, + 0.22 + ], + "angle": 0, + "content": "Thanks to the shape completion module, ECON can deal with occlusions. Unlike other crowd body estimators [73-75, 86], ECON makes it possible to reconstruct multiple detailed \"clothed\" 3D humans from an image with interperson occlusions, even though ECON has not been trained for this. Figure 10 shows three examples. The occluded parts, colored in red, are successfully recovered." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.234, + 0.613, + 0.249 + ], + "angle": 0, + "content": "5. Discussion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.259, + 0.895, + 0.44 + ], + "angle": 0, + "content": "Limitations. ECON takes as input an RGB image and an estimated SMPL-X body. However, recovering SMPL-X bodies (or similar models) from a single image is still an open problem, and not fully solved. Any failure in this could lead to ECON failures, such as in Fig. 8-A and Fig. 8-B. As the synthetic data [6,28,78] is getting sufficiently realistic, their domain gap with real data is significantly narrowed, it is predictable that such limitations will be eliminated. The reconstruction quality of ECON primarily relies on the accuracy of the predicted normal maps. Poor normal maps can result in overly close-by or even intersecting front and back surfaces, as shown in Fig. 8-C and Fig. 8-D." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.444, + 0.895, + 0.626 + ], + "angle": 0, + "content": "Future work. Apart from addressing the above limitations, several other directions are useful for practical applications. Currently, ECON reconstructs only 3D geometry. One could additionally recover an underlying skeleton and skinning weights [45, 84], to obtain fully-animatable avatars. Moreover, generating back-view texture [8,67,68,94] would result in fully-textured avatars. Disentangling clothing [1,63,99], hairstyle [89], or accessories [19] from the recovered geometry, would enable the simulation [23], synthesis, editing and transfer of styles [16] for these. ECON's reconstructions, together with its underneath SMPL-X body, could be useful as 3D shape prior to learn neural avatars [13,24,32]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.626, + 0.894, + 0.806 + ], + "angle": 0, + "content": "In particular, ECON could be used to augment existing datasets of 2D images with 3D humans. Datasets of real clothed humans with 3D ground truth [55,60,66,88,97] are limited in size. In contrast, datasets of images without 3D ground truth are widely available in large sizes [17,21,51]. We can \"augment\" such datasets by reconstructing detailed 3D humans from their images. In SupMat., we apply ECON on SHHQ [17] and recover normal maps and 3D humans; see Fig. S.2. As ECON-like methods mature, they could produce pixel-aligned 3D humans from photos at scale, enabling the training of generative models of 3D clothed avatars with details [20,22,29,34,58,81,93]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.811, + 0.895, + 0.901 + ], + "angle": 0, + "content": "Possible negative impact. As the reconstruction matures, it opens the potential for low-cost realistic avatar creation. Although such a technique benefits entertainment, film production, tele-presence and future metaverse applications, it could also facilitate deep-fake avatars. Regulations must be established to clarify the appropriate use of such technology." + }, + { + "type": "page_number", + "bbox": [ + 0.486, + 0.946, + 0.512, + 0.957 + ], + "angle": 0, + "content": "518" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.078, + 0.062, + 0.891, + 0.417 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.419, + 0.897, + 0.463 + ], + "angle": 0, + "content": "Figure 9. Qualitative results on in-the-wild images. We show 8 examples of reconstructing detailed clothed 3D humans from images with: (a) challenging poses and (b) loose clothing. For each example we show the input image along with two views (front and rotated) of the reconstructed 3D humans. Our approach is robust to pose variations, generalizes well to loose clothing, and contains detailed geometry." + }, + { + "type": "image", + "bbox": [ + 0.079, + 0.467, + 0.896, + 0.626 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.635, + 0.895, + 0.679 + ], + "angle": 0, + "content": "Figure 10. Multiple humans with occlusions.. We detect multiple people and apply ECON to each separately. Although ECON is not trained on multiple people, it is robust to inter-person occlusions. We show three examples, and for each: (top) input image and the predicted front and back normal maps, (bottom) ECON's reconstruction. Red areas on the estimated mesh indicate occlusions." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.689, + 0.196, + 0.705 + ], + "angle": 0, + "content": "6. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.72, + 0.473, + 0.902 + ], + "angle": 0, + "content": "We propose ECON to reconstruct detailed clothed 3D humans from a color image. It combines estimated 2.5D front and back surfaces with and underlying 3D parametric body in a highly effective way. On the one hand, it is robust to novel poses, while on the other hand, it is capable of recovering loose clothing and geometric details, since the reconstructed shape is not over-constrained to the topology of the body. ECON achieves this by using and extending recent advances in variational normal integration [7] and shape completion [10]. It effectively extends these to the task of image-based 3D human reconstruction. We believe ECON can lead to both real-world applications and useful tools for" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.691, + 0.892, + 0.723 + ], + "angle": 0, + "content": "the 3D vision community. The code and models are available at Econ.is.tue.mpg.de for research purposes." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.736, + 0.895, + 0.873 + ], + "angle": 0, + "content": "Acknowledgments. We thank Lea Hering and Radek Daněček for proofreading, Yao Feng, Haven Feng and Weiyang Liu for valuable feedback, and Tsvetelina Alexiadis for perceptual study. We are especially grateful to Carlos Barreto (Blender Add-on), Teddy Huang (Docker Image), and Justin John (Windows Support). This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No.860768 (CLIPE project)." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.886, + 0.851, + 0.902 + ], + "angle": 0, + "content": "Disclosure.is.tue.mpg.de/black/CoI_CVPR_2023.txt" + }, + { + "type": "page_number", + "bbox": [ + 0.486, + 0.945, + 0.511, + 0.957 + ], + "angle": 0, + "content": "519" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.096, + 0.115, + 0.47, + 0.184 + ], + "angle": 0, + "content": "[1] Alakh Aggarwal, Jikai Wang, Steven Hogue, Saifeng Ni, Madhukar Budagavi, and Xiaohu Guo. Layered-Garment Net: Generating Multiple Implicit Garment Layers from a Single Image. 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Black $^{1}$ + +1Max Planck Institute for Intelligent Systems, Tübingen, Germany + +$^{2}$ Osaka University, Japan $^{3}$ University of Amsterdam, the Netherlands + +{yuliang.xiu, jinlong.yang, black}@tue.mpg.de cao.xu@ist.osaka-u.ac.jp d.tzionas@uva.nl + +![](images/3fbec9e0eeedc5b43664803cbdb6ad02b6c9c00139147bea260f5c8398e6717a.jpg) +Input Image + +![](images/55766b5d294a96840304ac08f167e8469683bea984c20a8707bea73366bd72e1.jpg) +Front & Back Normal Estimation (2D) + +![](images/074d4be278bec138b2570ced60a1bb462cc2c6c634d6b5bbf32a4aefdcef66d9.jpg) +Front & Back d-BiNI Surfaces (2.5D) +FullClothedHumanMesh(3D) + +![](images/18ba68b2d493912a5bf0162a5b63878d6d0198003f036928ae704034c0606d9c.jpg) + +![](images/2a57f24263167289a644e538bee475bb34abe0173bdff1abb80bc3b760f8ba6d.jpg) +Figure 1. Human digitization from a color image. ECON combines the best aspects of free-form implicit representation, and explicit anthropomorphic regularization to infer high-fidelity 3D humans, even with loose clothing or in challenging poses. It does so in three steps: (1) It infers detailed 2D normal maps for the front and back side (Sec. 3.1). (2) The normal maps are converted into detailed, yet incomplete, 2.5D front and back surfaces guided by a SMPL-X estimate (Sec. 3.2). (3) It then "inpaints" the missing geometry between two surfaces (Sec. 3.3). Face or hands can be optionally replaced with the cleaner ones from SMPL-X. See the video on our website for more results. + +# Abstract + +The combination of deep learning, artist-curated scans, and Implicit Functions (IF), is enabling the creation of detailed, clothed, 3D humans from images. However, existing methods are far from perfect. IF-based methods recover free-form geometry, but produce disembodied limbs or degenerate shapes for novel poses or clothes. To increase robustness for these cases, existing work uses an explicit parametric body model to constrain surface reconstruction, but this limits the recovery of free-form surfaces such as loose clothing that deviates from the body. What we want is a method that combines the best properties of implicit representation and explicit body regularization. To this end, we make two key observations: (1) current networks are better at inferring detailed 2D maps than full-3D surfaces, and (2) a parametric model can be seen as a "canvas" for stitching together detailed surface patches. Based on these, our method, ECON, has three main steps: (1) It infers detailed 2D normal maps for the front and back side of a clothed person. (2) From these, it recovers 2.5D front and back surfaces, called d-BiNI, that are equally detailed, yet incomplete, and registers these w.r.t. each other with the help of a SMPL-X + +body mesh recovered from the image. (3) It "inpaints" the missing geometry between d-BiNI surfaces. If the face and hands are noisy, they can optionally be replaced with the ones of SMPL-X. As a result, ECON infers high-fidelity 3D humans even in loose clothes and challenging poses. This goes beyond previous methods, according to the quantitative evaluation on the CAPE and Renderpeople datasets. Perceptual studies also show that ECON's perceived realism is better by a large margin. Code and models are available for research purposes at econ.is.tue.mpg.de + +# 1. Introduction + +Human avatars will be key for future games and movies, mixed-reality, tele-presence and the "metaverse". To build realistic and personalized avatars at scale, we need to faithfully reconstruct detailed 3D humans from color photos taken in the wild. This is still an open problem, due to its challenges; people wear all kinds of different clothing and accessories, and they pose their bodies in many, often imaginative, ways. A good reconstruction method must accurately capture these, while also being robust to novel clothing and poses. + +Initial, promising, results have been made possible by using artist-curated scans as training data, and implicit functions (IF) [56, 59] as the 3D representation. Seminal work on PIFu(HD) [70, 71] uses "pixel-aligned" IF and reconstructs clothed 3D humans with unconstrained topology. However, these methods tend to overfit to the poses seen in the training data, and have no explicit knowledge about the human body's structure. Consequently, they produce disembodied limbs or degenerate shapes for images with novel poses; see the 2nd row of Fig. 2. Follow-up work [26, 82, 96] accounts for such artifacts by regularizing the IF using a shape prior provided by an explicit body model [52, 61], but regularization introduces a topological constraint, restricting generalization to novel clothing while attenuating shape details; see the 3rd and 4th rows of Fig. 2. In a nutshell, there are trade-offs between robustness, generalization and detail. + +What we want is the best of both worlds; that is, the robustness of explicit anthropomorphic body models, and the flexibility of IF to capture arbitrary clothing topology. To that end, we make two key observations: (1) While inferring detailed 2D normal maps from color images is relatively easy [31, 71, 82], inferring 3D geometry with equally fine details is still challenging [9]. Thus, we exploit networks to infer detailed "geometry-aware" 2D maps that we then lift to 3D. (2) A body model can be seen as a low-frequency "canvas" that "guides" the stitching of detailed surface parts. + +With these in mind, we develop ECON, which stands for "Explicit Clothed humans Optimized via Normal integration". It takes, as input, an RGB image and a SMPL-X body inferred from the image. Then, it outputs a 3D human in free-form clothing with a level of detail and robustness that goes beyond the state of the art (SOTA); see the bottom of Fig. 2. Specifically, ECON has three steps. + +Step 1: Front & back normal reconstruction. We predict front- and back-side clothed-human normal maps from the input RGB image, conditioned on the body estimate, with a standard image-to-image translation network. + +Step 2: Front & back surface reconstruction. We take the previously predicted normal maps, and the corresponding depth maps that are rendered from the SMPL-X mesh, to produce detailed and coherent front-/back-side 3D surfaces, $\{\mathcal{M}_{\mathrm{F}},\mathcal{M}_{\mathrm{B}}\}$ . To this end, we extend the recent BiNI method [7], and develop a novel optimization scheme that is aimed at satisfying three goals for the resulting surfaces: (1) their high-frequency components agree with clothed-human normals, (2) their low-frequency components and the discontinuities agree with the SMPL-X ones, and (3) the depth values on their silhouettes are coherent with each other and consistent with the SMPL-X-based depth maps. The two output surfaces, $\{\mathcal{M}_{\mathrm{F}},\mathcal{M}_{\mathrm{B}}\}$ , are detailed yet incomplete, i.e., there is missing geometry in occluded and "profile" regions. + +Step 3: Full 3D shape completion. This module takes two inputs: (1) the SMPL-X mesh, and (2) the two d-BiNI + +![](images/d7622887f9cce397412347a6fa4860c177c8c531fd777bd2e2e69c2cf74de9c6.jpg) +Figure 2. Summary of SOTA. PIFuHD [71] recovers clothing details, but struggles with novel poses. ICON [82] and PaMIR [96] regularize shape to a body shape, but over-constrain the skirts, or over-smooth the wrinkles. ECON combines their best aspects. + +surfaces, $\{\mathcal{M}_{\mathrm{F}},\mathcal{M}_{\mathrm{B}}\}$ . The goal is to "inpaint" the missing geometry. Existing methods struggle with this problem. On one hand, Poisson reconstruction [38] produces "blobby" shapes and naively "infills" holes without exploiting a shape distribution prior. On the other hand, data-driven approaches, such as IF-Nets [10], struggle with missing parts caused by (self-)occlusions, and fail to keep the fine details present on two d-BiNI surfaces, producing degenerate geometries. + +We address above the limitations in two steps: (1) We extend and re-train IF-Nets to be conditioned on the SMPL-X body, so that SMPL-X regularizes shape "infilling". We discard the triangles that lie close to $\{\mathcal{M}_{\mathrm{F}},\mathcal{M}_{\mathrm{B}}\}$ , and keep the remaining ones as "infilling patches". (2) We stitch together the front- and back-side surfaces and infilling patches via Poisson reconstruction; note that holes between these are small enough for a general purpose method. The result is a full 3D shape of a clothed human; see Fig. 2, bottom. + +We evaluate ECON both on established benchmarks (CAPE [55] and Renderpeople [66]) and in-the-wild images. Quantitative analysis reveals ECON's superiority. A perceptual study echos this, showing that ECON is significantly preferred over competitors on challenging poses and loose clothing, and competitive with PIFuHD on fashion images. Qualitative results show that ECON generalizes better than the SOTA to a wide variety of poses and clothing, even with extreme looseness or complex topology; see Fig. 9. + +With both pose-robustness and topological flexibility, ECON recovers 3D clothed humans with a good level of detail and realistic pose. Code and models are available for research purposes at econ.is.tue.mpg.de + +# 2. Related Work + +Image-based clothed human reconstruction. Regarding geometric representation, we group the mainstream clothed human reconstruction approaches into "implicit" and "explicit". Note that with the terms implicit/explicit we mainly refer to the surface decoder rather than the feature encoder. + +1) Explicit-shape-based approaches use either a mesh-based parametric body model [35, 52, 61, 69, 83], or a nonparametric depth map [18, 72] or point cloud [90], to reconstruct 3D humans. Many methods [15, 36, 39, 40, 42, 43, 75, 76, 87, 91, 92] estimate or regress minimally-clothed 3D body meshes from RGB pixels and ignore clothing. To account for clothed human shapes, another line of work [2-4, 41, 55, 62, 79, 100] adds 3D offsets on top of the body mesh. This is compatible with current animation pipelines, as they inherit the hierarchical skeleton and skinning weights from the underling statistical body model. However, this "body+offset" approach is not flexible enough to model loose clothing, which deviates significantly from the body topology, such as dresses and skirts. To increase topological flexibility, some methods [5, 33] reconstruct 3D clothed humans by identifying the type of clothing and using the appropriate model to reconstruct it. Scaling up this "cloth-aware" approach to many clothing styles is nontrivial, limiting generalization to in-the-wild outfit variation. + +2) Implicit-function-based approaches are topology-agnostic and, thus, can be used to represent arbitrary 3D clothed human shapes. SMPLicit [12], ClothWild [57] and DIG [46] learn a generative clothing model with neural distance fields [11, 56, 59] from a 3D clothing dataset. Given an image, the clothed human is reconstructed by estimating a parametric body and optimizing the latent space of the clothing model. However, the results usually do not align well with the image and lack geometric detail. + +PIFu [70] introduces pixel-aligned implicit human shape reconstruction and PIFuHD [71] significantly improves the geometric details with a multi-level architecture and normal maps predicted from the RGB image. However, these two methods do not exploit knowledge of the human body structure. Therefore, these methods overfit to the body poses in the training data, e.g. fashion poses. They fail to generalize to novel poses, producing non-human shapes with broken or disembodied limbs. To address these issues, several methods introduce different geometric priors to regularize the deep implicit representation: GeoPIFu [26] introduces a coarse shape of volumetric humans, Self-Portraits [49], PINA [14], and S3 [85] use depth or LIDAR information to regularize shape and improve robustness to pose variation. + +Another direction leverages parametric body models, which represent human body shape well, model the kinematic structure of the body, and can be reliably estimated from RGB images of clothed people. Such a representation can be viewed as a base shape upon which to model clothed + +humans. Therefore, several methods combine parametric body models with expressive implicit representations to get the best of both worlds. PaMIR [96] and DeepMultiCap [95] condition the pixel-aligned features on a posed and voxelized SMPL mesh. JIFF Introduces a 3DMM face prior to improve the realism of the facial region. ARCH [30], $\mathrm{ARCH} + +$ [27] and CAR [50] use SMPL to unpose the pixel-aligned query points from a posed space to a canonical space. To further generalize to unseen poses on in-the-wild photos, ICON [82] regresses shapes from locally-queried features. However, the above approaches gain robustness to unseen poses at the cost of generalization ability to various, especially loose, clothing topologies. We argue that this is because loose clothing differs greatly from human body and that conditioning on the SMPL body in 3D makes it harder for networks to make full use of 2D image features. + +Our work is also inspired by "sandwich-like" monocular reconstruction approaches, represented by Moduling Humans [18], FACSIMILE [72] and Any-Shot GIN [80]. Moduling Humans has two networks: a generator that estimates the visible (front) and invisible (back) depth maps from RGB images, and a discriminator that helps regularize the estimation via an adversarial loss. FACSIMILE further improves the geometric details by leveraging a normal loss, which is directly computed from depth estimates via differentiable layers. Recently, Any-Shot GIN generalizes the sandwich-like scheme to novel classes of objects. Given RGB images, it predicts front and back depth maps as well, and then exploits IF-Nets [10] for shape completion. We follow a similar path and extend it, to successfully reconstruct clothed human shapes with SOTA pose generalization, and better details from normal images. + +# 3. Method + +Given an RGB image, ECON first estimates front and back normal maps (Sec. 3.1), then converts them into front and back partial surfaces (Sec. 3.2), and finally "inpaints" the missing geometry with the help of IF-Nets+ (Sec. 3.3). See ECON's overview in Fig. 3. + +# 3.1. Detailed normal map prediction + +Trained on abundant pairs of RGB images and normal images, a "front" normal map, $\widehat{\mathcal{N}}_{\mathrm{F}}^{\mathrm{c}}$ , can be accurately estimated from an RGB image using image-to-image translation networks, as demonstrated in PIFuHD [71] or ICON [82]. Both methods also infer a "back" normal map, $\widehat{\mathcal{N}}_{\mathrm{B}}^{\mathrm{c}}$ , from the image. But, the absence of image cues leads to over-smooth $\widehat{\mathcal{N}}_{\mathrm{B}}^{\mathrm{c}}$ . To address this, we fine-tune ICON's backside normal predictor, $\mathcal{G}_{\mathrm{B}}^{\mathrm{N}}$ , with an additional MRF loss [77] to enhance the local details by minimizing the difference between the predicted $\widehat{\mathcal{N}}^{\mathrm{c}}$ and ground truth (GT) $\mathcal{N}^{\mathrm{c}}$ in feature space. + +To guide the normal map prediction and make it robust to various body poses, ICON conditions the normal map + +![](images/8cdf79210928b3e9b25205af1a11a834dd7d7a36b2f863c50ca435833101104c.jpg) +Figure 3. Overview. ECON takes as input an RGB image, $\mathcal{I}$ , and a SMPL-X body, $\mathcal{M}^{\mathrm{b}}$ . Conditioned on the rendered front and back body normal images, $\mathcal{N}^{\mathrm{b}}$ , ECON first predicts front and back clothing normal maps, $\widehat{\mathcal{N}}^{\mathrm{c}}$ . These two maps, along with body depth maps, $\mathcal{Z}^{\mathrm{b}}$ , are fed into a d-BiNI optimizer to produce front and back surfaces, $\{\mathcal{M}_{\mathrm{F}}, \mathcal{M}_{\mathrm{B}}\}$ . Based on such partial surfaces, and body estimate $\mathcal{M}^{\mathrm{b}}$ , IF-Nets+ implicitly completes $\mathcal{R}_{\mathrm{IF}}$ . With optional Face or hands from $\mathcal{M}^{\mathrm{b}}$ , screened Poisson combines everything as final watertight $\mathcal{R}$ . + +![](images/e26df1a3f8f33948fdbc0d1ad14c4529af4b67c80573ce4bb637b7044d0e566b.jpg) + +prediction module on the body normal maps, $\mathcal{N}^{\mathrm{b}}$ , rendered from the estimated body $\mathcal{M}^{\mathrm{b}}$ . Thus, it is important to accurately align the estimated body and clothing silhouette. Apart from the $\mathcal{L}_{\mathrm{N\_diff}}$ and $\mathcal{L}_{\mathrm{S\_diff}}$ used in ICON [82], we also apply 2D body landmarks in an additional loss term, $\mathcal{L}_{\mathrm{J\_diff}}$ , to further optimize the SMPL-X body, $\mathcal{M}^{\mathrm{b}}$ , inferred from pixie [15] or PyMAF-X [91]. Specifically, we optimize SMPL-X's shape, $\beta$ , pose, $\theta$ , and translation, $t$ , to minimize: + +$$ +\mathcal {L} _ {\mathrm {S M P L - X}} = \mathcal {L} _ {\mathrm {N} _ {-} \text {d i f f}} + \mathcal {L} _ {\mathrm {S} _ {-} \text {d i f f}} + \mathcal {L} _ {\mathrm {J} _ {-} \text {d i f f}}, \tag {1} +$$ + +$$ +\mathcal {L} _ {\mathrm {J} _ {-} \text {d i f f}} = \lambda_ {\mathrm {J} _ {-} \text {d i f f}} \left| \mathcal {J} ^ {\mathrm {b}} - \widehat {\mathcal {J} ^ {\mathrm {c}}} \right|, +$$ + +where $\mathcal{L}_{\mathrm{N\_diff}}$ and $\mathcal{L}_{\mathrm{S\_diff}}$ are the normal-map loss and silhouette loss introduced in ICON [82], and $\mathcal{L}_{\mathrm{J\_diff}}$ is the joint loss (L2) between 2D landmarks $\widehat{\mathcal{I}^{\mathrm{c}}}$ , which are estimated by a 2D keypoint estimator from the RGB image $\mathcal{I}$ , and the corresponding re-projected 2D joints $\mathcal{I}^{\mathrm{b}}$ from $\mathcal{M}^{\mathrm{b}}$ . For more implementation details, see Sec. A.1 in SupMat. + +# 3.2. Front and back surface reconstruction + +We now lift the clothed normal maps to 2.5D surfaces. We expect these 2.5D surfaces to satisfy three conditions: (1) high-frequency surface details agree with predicted clothed normal maps, (2) low-frequency surface variations, including discontinuities, agree with SMPL-X's ones, and (3) the depth of the front and back silhouettes are close to each other. + +Unlike PIFuHD [71] or ICON [82], which train a neural network to regress the implicit surface from normal maps, we explicitly model the depth-normal relationship using variational normal integration methods [7,64]. Specifi + +cally, we tailor the recent bilateral normal integration (BiNI) method [7] to full-body mesh reconstruction by harnessing the coarse prior, depth maps, and silhouette consistency. + +To satisfy the three conditions, we propose a depth-aware silhouette-consistent bilateral normal integration (d-BiNI) method to jointly optimize for the front and back clothed depth maps, $\widehat{\mathcal{Z}}_{\mathrm{F}}^{\mathrm{c}}$ and $\widehat{\mathcal{Z}}_{\mathrm{B}}^{\mathrm{c}}$ : + +$$ +\mathrm {d} - \operatorname {B i N I} \left(\widehat {\mathcal {N}} _ {\mathrm {F}} ^ {\mathrm {c}}, \widehat {\mathcal {N}} _ {\mathrm {B}} ^ {\mathrm {c}}, \mathcal {Z} _ {\mathrm {F}} ^ {\mathrm {b}}, \mathcal {Z} _ {\mathrm {B}} ^ {\mathrm {b}}\right)\rightarrow \widehat {\mathcal {Z}} _ {\mathrm {F}} ^ {\mathrm {c}}, \widehat {\mathcal {Z}} _ {\mathrm {B}} ^ {\mathrm {c}}. \tag {2} +$$ + +Here, $\widehat{\mathcal{N}}_{*}^{\mathrm{c}}$ is the front or back clothed normal map predicted by $\mathcal{G}_{\mathrm{F,B}}^{\mathrm{N}}$ from $\{\mathcal{I},\mathcal{N}^{\mathrm{b}}\}$ , and $\mathcal{Z}_{*}^{\mathrm{b}}$ is the front or back coarse body depth image rendered from the SMPL-X mesh, $\mathcal{M}^{\mathrm{b}}$ . + +Specifically, our objective function consists of five terms: + +$$ +\begin{array}{l} \min _ {\widehat {\mathcal {Z}} _ {\mathrm {F}} ^ {\mathrm {c}}, \widehat {\mathcal {Z}} _ {\mathrm {B}} ^ {\mathrm {c}}} \mathcal {L} _ {\mathrm {n}} (\widehat {\mathcal {Z}} _ {\mathrm {F}} ^ {\mathrm {c}}; \widehat {\mathcal {N}} _ {\mathrm {F}} ^ {\mathrm {c}}) + \mathcal {L} _ {\mathrm {n}} (\widehat {\mathcal {Z}} _ {\mathrm {B}} ^ {\mathrm {c}}; \widehat {\mathcal {N}} _ {\mathrm {B}} ^ {\mathrm {c}}) + \\ \lambda_ {\mathrm {d}} \mathcal {L} _ {\mathrm {d}} \left(\widehat {\mathcal {Z}} _ {\mathrm {F}} ^ {\mathrm {c}}; \mathcal {Z} _ {\mathrm {F}} ^ {\mathrm {b}}\right) + \lambda_ {\mathrm {d}} \mathcal {L} _ {\mathrm {d}} \left(\widehat {\mathcal {Z}} _ {\mathrm {B}} ^ {\mathrm {c}}; \mathcal {Z} _ {\mathrm {B}} ^ {\mathrm {b}}\right) + \tag {3} \\ \lambda_ {s} \mathcal {L} _ {s} (\widehat {\mathcal {Z}} _ {F} ^ {c}, \widehat {\mathcal {Z}} _ {B} ^ {c}), \\ \end{array} +$$ + +where $\mathcal{L}_{\mathrm{n}}$ is the BiNI loss term introduced by BiNI [7], $\mathcal{L}_{\mathrm{d}}$ is a depth prior applied to the front and back depth surfaces, and $\mathcal{L}_{\mathrm{s}}$ is a front-back silhouette consistency term. For a more detailed discussion on these terms, see Sec. A.2 in SupMat. + +With Eq. (3), we make two technical contributions beyond BiNI [7]. First, we use the coarse depth prior rendered from the SMPL-X body mesh, $\mathcal{Z}_i^{\mathrm{b}}$ , to regularize BiNI: + +$$ +\mathcal {L} _ {\mathrm {d}} \left(\widehat {\mathcal {Z}} _ {i} ^ {\mathrm {c}}; \mathcal {Z} _ {i} ^ {\mathrm {b}}\right) = \left| \widehat {\mathcal {Z}} _ {i} ^ {\mathrm {c}} - \mathcal {Z} _ {i} ^ {\mathrm {b}} \right| _ {\Omega_ {\mathrm {n}}} \cap \Omega_ {\mathrm {z}} \quad i \in \{F, B \}. \tag {4} +$$ + +![](images/e47c04f60941f1b2651a9436acf01c03110f4707a2ec6ed4b242f112a043780c.jpg) +Figure 4. Four inputs to d-BiNI. $\Omega_{\mathrm{n}}$ and $\Omega_{\mathrm{z}}$ are the domains of clothed and body regions, respectively. $\partial \Omega_{\mathrm{n}}$ is the silhouette of $\Omega_{\mathrm{n}}$ . + +This addresses the key problem of putting the front and back surfaces together in a coherent way to form a full body. Optimizing BiNI terms $\mathcal{L}_{\mathrm{n}}$ leaves an arbitrary global offset between the front and back surfaces. The depth prior terms $\mathcal{L}_{\mathrm{d}}$ encourage the surfaces with undecided offsets to be consistent with the SMPL-X body, and is computed in the domains $\Omega_{\mathrm{n}} \bigcap \Omega_{\mathrm{z}}$ (Fig. 4). For further intuitions on $\mathcal{L}_{\mathrm{n}}$ and $\mathcal{L}_{\mathrm{d}}$ , see Fig. S.4 and Fig. S.5 in SupMat. + +Second, we use a silhouette consistency term to encourage the front and back depth values to be the same at the silhouette boundary, which is computed in domain $\partial \Omega_{\mathrm{n}}$ (Fig. 4): + +$$ +\mathcal {L} _ {\mathrm {s}} \left(\widehat {\mathcal {Z}} _ {\mathrm {F}} ^ {\mathrm {c}}, \widehat {\mathcal {Z}} _ {\mathrm {B}} ^ {\mathrm {c}}\right) = \left| \widehat {\mathcal {Z}} _ {\mathrm {F}} ^ {\mathrm {c}} - \widehat {\mathcal {Z}} _ {\mathrm {B}} ^ {\mathrm {c}} \right| _ {\partial \Omega_ {\mathrm {n}}}. \tag {5} +$$ + +The silhouette term improves the physical consistency of the reconstructed front and back clothed depth maps. Without this term, d-BiNI produces intersections of the front and back surfaces around the silhouette, causing "blobby" artifacts and hurting reconstruction quality; see Fig. S.6 in SupMat. + +# 3.3. Human shape completion + +For simple body poses without self-occlusions, merging front and back d-BiNI surfaces in a straightforward way, as done in FACSIMILE [72] and Moduling Humans [18], can result in a complete 3D clothed scan. However, often poses result in self-occlusions, which cause large portions of the surfaces to be missing. In such cases, Poisson Surface Reconstruction (PSR) [37] leads to blobby artifacts. + +PSR completion with SMPL-X $(\mathbf{ECON_{EX}})$ . A naive way to "infill" the missing surface is to make use of the estimated SMPL-X body. We remove the triangles from $\mathcal{M}^{\mathrm{b}}$ that are visible to front or back cameras. The remaining triangle "soup" $\mathcal{M}^{\mathrm{cull}}$ contains both side-view boundaries and occluded regions. We apply PSR [37] to the union of $\mathcal{M}^{\mathrm{cull}}$ and d-BiNI surfaces $\{\mathcal{M}_{\mathrm{F}},\mathcal{M}_{\mathrm{B}}\}$ to obtain a watertight reconstruction $\mathcal{R}$ . This approach is denoted as $\mathrm{ECON_{EX}}$ . Although $\mathrm{ECON_{EX}}$ avoids missing limbs or sides, it does not produce a coherent surface for the originally missing clothing and hair surfaces because of the discrepancy between SMPL-X and actual clothing or hair; see $\mathrm{ECON_{EX}}$ in Fig. 5. + +Inpainting with IF-Nets+ $(\mathcal{R}_{\mathrm{IF}})$ . To improve reconstruction coherence, we use a learned implicit-function (IF) model to "inpaint" the missing geometry given front and back d-BiNI + +![](images/66e611690465f64d9b77f697a90f13891919d3ac190069731b0754a9b87b9c4a.jpg) +Figure 5. "Inpainting" the missing geometry. We simulate different cases of occlusion by masking the normal images and present the intermediate and final 3D reconstruction of different design choices. While IF-Nets misses certain body parts, IF-Nets+ produces a plausible overall shape. $\mathrm{ECON_{IF}}$ produces more consistent clothing surfaces than $\mathrm{ECON_{EX}}$ due to a learned shape distribution. + +![](images/3f4e4367f5d8b4b74992ae24fafa82358ff9d8880aee72ef6f83bd3554f54fdb.jpg) +Figure 6. Face and hand details. The face and hands of the raw reconstruction can be replaced with the ones of the SMPL-X body. + +surfaces. Specifically, we tailor a general-purpose shape completion method, IF-Nets [10], to a SMPL-X-guided one, denoted as IF-Nets+. IF-Nets [10] completes the 3D shape from a deficient 3D input, such as an incomplete 3D human shape or a low-resolution voxel grid. Inspired by Li et al. [44], we adapt IF-Nets by conditioning it on a voxelized SMPL-X body to deal with pose variation; for details see Sec. A.3 in SupMat. IF-Nets+ is trained on voxelized front and back ground-truth clothed depth maps, $\{\mathcal{Z}_{\mathrm{F}}^{\mathrm{c}},\mathcal{Z}_{\mathrm{B}}^{\mathrm{c}}\}$ and a voxelized (estimated) body mesh, $\mathcal{M}^{\mathrm{b}}$ as input, and is supervised with ground-truth 3D shapes. During training, we randomly mask $\{\mathcal{Z}_{\mathrm{F}}^{\mathrm{c}},\mathcal{Z}_{\mathrm{B}}^{\mathrm{c}}\}$ for robustness to occlusions. During inference, we feed the estimated $\widehat{\mathcal{Z}}_{\mathrm{F}}^{\mathrm{c}},\widehat{\mathcal{Z}}_{\mathrm{B}}^{\mathrm{c}}$ and $\mathcal{M}^{\mathrm{b}}$ into IF-Nets+ to obtain an occupancy field, from which we extract the inpainted mesh, $\mathcal{R}_{\mathrm{IF}}$ with Marching cubes [53]. + +PSR completion with $\mathcal{R}_{\mathrm{IF}}$ ( $\mathbf{ECON_{IF}}$ ). To obtain our final mesh, $\mathcal{R}$ , we apply PSR to stitch (1) d-BiNI surfaces, (2) sided and occluded triangle soup $\mathcal{M}^{\mathrm{cull}}$ from $\mathcal{R}_{\mathrm{IF}}$ , and optionally, (3) face or hands cropped from the estimated SMPL-X + +![](images/d74ca1518c64ce20f48994f14539737383ec83a44571337e2622f731d65b7ec3.jpg) +Figure 7. Datasets for numerical evaluation. We evaluate ECON on images with unseen poses (left) and unseen outfits (right) on the CAPE [55] and Renderpeople [66] datasets, respectively. + +body $\mathcal{M}^{\mathrm{b}}$ . The necessity of (3) arises from the poorly reconstructed hands/face in $\mathcal{R}_{\mathrm{IF}}$ , see difference in Fig. 6. The approach is denoted as $\mathrm{ECON_{IF}}$ . + +Notably, although $\mathcal{R}_{\mathrm{IF}}$ is already a complete human mesh, due to the lossy voxelization of inputs and limited resolution of Marching cubes algorithm, it somehow smooths out the details of $\tilde{\mathcal{Z}}_{\{\mathrm{F,B}\}}^{\mathrm{c}} / \mathcal{M}_{\{\mathrm{F,B}\}}$ , which are optimized via d-BiNI (see $\mathcal{R}_{\mathrm{IF}}$ vs ECON{IF,EX} in Fig. 5). While ECON{IF,EX} preserves d-BiNI details better, only the side-views and occluded parts of $\mathcal{R}_{\mathrm{IF}}$ are fused in the Poisson step. In Tabs. 1 and 4, we use ECON{IF,EX} instead of $\mathcal{R}_{\mathrm{IF}}$ for evaluation. + +# 4. Experiments + +# 4.1. Datasets + +Training on THuman2.0. THuman2.0 [88] contains 525 high-quality human textured scans in various poses, which are captured by a dense DSLR rig, along with their corresponding SMPL-X fits. We use THuman2.0 to train ICON, ECON $_{\text{IF}}$ (IF-Nets+), IF-Nets, PIFu and PaMIR. + +Quantitative evaluation on CAPE & Renderpeople. We primarily evaluate on CAPE [55] and Renderpeople [66]. Specifically, we use the "CAPE-NFP" set (100 scans), which is used by ICON to analyze robustness to complex human poses. Moreover, we select another 100 scans from Renderpeople, containing loose clothing, such as dresses, skirts, robes, down jackets, costumes, etc. With such clothing variance, Renderpeople helps numerically evaluate the flexibility of reconstruction methods w.r.t. shape topology. Samples of the two datasets are shown in Fig. 7. + +# 4.2. Metrics + +Chamfer and P2S distance (cm). To capture large geometric errors, e.g. occluded parts or wrongly positioned limbs, we report the commonly used Chamfer (bi-directional point-to-surface) and P2S distance (1-directional point-to-surface) between ground-truth and reconstructed meshes. + +Normal difference (L2). To measure the fineness of reconstructed local details, as well as projection consistency from the input image, we also report the L2 error between normal images rendered from reconstructed and ground-truth surfaces, by rotating a virtual camera around these by $\{0^{\circ}, 90^{\circ}, 180^{\circ}, 270^{\circ}\}$ w.r.t. to a frontal view. + +
MethodsData-drivenOOD poses (CAPE)OOD outfits (Renderpeople)
Chamfer ↓P2S ↓Normals ↓Chamfer ↓P2S ↓Normals ↓
w/o SMPL-X body prior
PIFu *✓1.7221.5480.06741.7061.6420.0709
PIFuHD†✓3.7673.5910.09941.9461.9830.0658
w/ GT SMPL-X body prior
PaMIR *✓0.9890.9920.04221.2961.4300.0518
ICON✓0.9710.9090.04091.3731.5220.0566
ECONIF✓0.9960.9670.04131.4011.4220.0516
ECONEXX0.9260.9170.03671.3421.4580.0478
+ +Table 1. Evaluation against the state of the art. All models use a resolution of 256 for marching cubes. *Methods are re-implemented in [82] for a fair comparison in terms of network settings and training data. †Official model is trained on the Renderpeople dataset. ECONEX is optimization-based, thus requires no training (X). “OOD” is short for “out-of-distribution”. + +
ICON [82]PIFuHD [71]PaMIR [96]
Challenging poses0.2830.1080.132
Loose clothing0.1470.3620.232
Fashion images0.1990.5510.290
+ +Table 2. Perceptual study. Numbers denote the chance that participants prefer the reconstruction of a competing method over ECON for in-the-wild images. A value of 0.5 indicates equal preference. A value of $< 0.5$ favors ECON, while of $>0.5$ favors competitors. + +# 4.3. Evaluation + +Quantitative evaluation. We compare ECON with body-agnostic methods, i.e., PIFu [70] and PIFuHD [71], and body-aware methods, i.e., PaMIR [96] and ICON [82]; see in Tab. 1. For fair comparison, we use re-implementations of PIFu and PaMIR from ICON [82], because they have the same network settings and input data. $\mathrm{ECON_{EX}}$ performs on par with ICON, and outperforms other methods on images containing out-of-distribution (OOD) poses (CAPE), with a distance error below $1\mathrm{cm}$ . In terms of out-of-distribution outfitsits (Renderpeople), $\mathrm{ECON_{EX/IF}}$ performs on par with PaMIR, and much better than PIFuHD. When it comes to high-frequency details measured by normals, $\mathrm{ECON_{EX}}$ achieves SOTA performance on both datasets. + +Perceptual study. Due to the lack of ground-truth geometry (clothed scan + underneath SMPL-X), we further conduct a perceptual study to evaluate ECON on in-the-wild images. Test images are divided into three categories: "challenging poses", "loose clothing", and "fashion images". Examples of challenging poses and loose clothing can be seen in Fig. 9, and some of fashion images are in SupMat.'s Fig. S.2. + +Participants are asked to choose the reconstruction they perceive as more realistic, between a baseline method and ECON. We compute the chances that each baseline is preferred over ECON in Tab. 2. The results of the perceptual study confirm the quantitative evaluation in Tab. 1. For "challenging poses" images, ECON is significantly preferred over PIFuHD and outperforms ICON. On images of people wearing loose clothing, ECON is preferred over ICON by a large + +
MethodsOOD poses (CAPE [55])OOD outfitsits (Renderpeople) [66]Speed FPS ↑
RMSE ↓MAE ↓RMSE ↓MAE ↓
BiNI [7]27.6421.1120.6116.070.52
d-BiNI13.4310.2914.4311.260.69
+ +Table 3. BiNI vs d-BiNI. Comparison between BiNI and d-BiNI surfaces w.r.t. reconstruction accuracy and optimization speed. + +
MethodsOOD poses (CAPE)OOD outfits (Renderpeople)
Chamfer ↓P2S ↓Normals ↓Chamfer ↓P2S ↓Normals ↓
IF-Nets [10]2.1161.2330.0751.8831.6220.070
IF-Nets+1.4011.3530.0561.4771.5640.055
ECONIF0.9960.9670.04131.4011.4220.0516
+ +Table 4. Evaluation for shape completion. Same metrics as Tab. 1, and $\mathrm{ECON_{IF}}$ is added as a reference. + +![](images/be782cbee65257d7562303accd6e67cee66269bed332183a360618483c1d6bfb.jpg) +Figure 8. Failure examples of ECON. (A-B) Failures in recovering a SMPL-X body result, e.g., bent legs or wrong limb poses, cause ECON failures by extension. (C-D) Failures in normal-map estimation provide erroneous geometry to ECON to work with. + +margin and outperforms PIFuHD. The reasons for a slight preference of PIFuHD over ECON on fashion images are discussed in Sec. 5. Figure 2 visualizes some comparisons. More examples are provided in Figs. S.7 to S.9 of the SupMat. + +# 4.4. Ablation study + +d-BiNI vs BiNI. We compare d-BiNI with BiNI using 600 samples (200 scans x 3 views) from CAPE and Renderpeople where ground-truth normal maps and meshes are available. Table 3 reports the "root mean squared error" (RMSE) and "mean absolute error" (MAE) between the estimated and rendered depth maps. d-BiNI significantly improves the reconstruction accuracy by about $50\%$ compared to BiNI. This demonstrates the efficacy of using the coarse body mesh as regularization and taking the consistency of both the front and back surface into consideration. Additionally, d-BiNI is $33\%$ faster than BiNI. + +IF-Nets+ vs IF-Nets. Following the metrics of Sec. 4.2, we compare IF-Nets [10] with our IF-Nets+ on $\mathcal{R}_{\mathrm{IF}}$ . We show the quantitative comparison in Tab. 4. The improvement for out-of-distribution ("OOD") poses shows that IF-Nets+ is more robust to pose variations than IF-Nets, as it is conditioned on the SMPL-X body. Figure 5 compares the geometry " inpainting" of both methods in the case of occlusions. + +# 4.5. Multi-person reconstruction + +Thanks to the shape completion module, ECON can deal with occlusions. Unlike other crowd body estimators [73-75, 86], ECON makes it possible to reconstruct multiple detailed "clothed" 3D humans from an image with interperson occlusions, even though ECON has not been trained for this. Figure 10 shows three examples. The occluded parts, colored in red, are successfully recovered. + +# 5. Discussion + +Limitations. ECON takes as input an RGB image and an estimated SMPL-X body. However, recovering SMPL-X bodies (or similar models) from a single image is still an open problem, and not fully solved. Any failure in this could lead to ECON failures, such as in Fig. 8-A and Fig. 8-B. As the synthetic data [6,28,78] is getting sufficiently realistic, their domain gap with real data is significantly narrowed, it is predictable that such limitations will be eliminated. The reconstruction quality of ECON primarily relies on the accuracy of the predicted normal maps. Poor normal maps can result in overly close-by or even intersecting front and back surfaces, as shown in Fig. 8-C and Fig. 8-D. + +Future work. Apart from addressing the above limitations, several other directions are useful for practical applications. Currently, ECON reconstructs only 3D geometry. One could additionally recover an underlying skeleton and skinning weights [45, 84], to obtain fully-animatable avatars. Moreover, generating back-view texture [8,67,68,94] would result in fully-textured avatars. Disentangling clothing [1,63,99], hairstyle [89], or accessories [19] from the recovered geometry, would enable the simulation [23], synthesis, editing and transfer of styles [16] for these. ECON's reconstructions, together with its underneath SMPL-X body, could be useful as 3D shape prior to learn neural avatars [13,24,32]. + +In particular, ECON could be used to augment existing datasets of 2D images with 3D humans. Datasets of real clothed humans with 3D ground truth [55,60,66,88,97] are limited in size. In contrast, datasets of images without 3D ground truth are widely available in large sizes [17,21,51]. We can "augment" such datasets by reconstructing detailed 3D humans from their images. In SupMat., we apply ECON on SHHQ [17] and recover normal maps and 3D humans; see Fig. S.2. As ECON-like methods mature, they could produce pixel-aligned 3D humans from photos at scale, enabling the training of generative models of 3D clothed avatars with details [20,22,29,34,58,81,93]. + +Possible negative impact. As the reconstruction matures, it opens the potential for low-cost realistic avatar creation. Although such a technique benefits entertainment, film production, tele-presence and future metaverse applications, it could also facilitate deep-fake avatars. Regulations must be established to clarify the appropriate use of such technology. + +![](images/c7f125c2505c6f3dd4c10c859090ea41c66083281e346850cb76b8d96cce0b8e.jpg) +Figure 9. Qualitative results on in-the-wild images. We show 8 examples of reconstructing detailed clothed 3D humans from images with: (a) challenging poses and (b) loose clothing. For each example we show the input image along with two views (front and rotated) of the reconstructed 3D humans. Our approach is robust to pose variations, generalizes well to loose clothing, and contains detailed geometry. + +![](images/98e01d57b840d8b08dcbdfa68cfe73f538fe2ba74b1b3ea51000676b0f52f97e.jpg) +Figure 10. Multiple humans with occlusions.. We detect multiple people and apply ECON to each separately. Although ECON is not trained on multiple people, it is robust to inter-person occlusions. We show three examples, and for each: (top) input image and the predicted front and back normal maps, (bottom) ECON's reconstruction. Red areas on the estimated mesh indicate occlusions. + +# 6. Conclusion + +We propose ECON to reconstruct detailed clothed 3D humans from a color image. It combines estimated 2.5D front and back surfaces with and underlying 3D parametric body in a highly effective way. On the one hand, it is robust to novel poses, while on the other hand, it is capable of recovering loose clothing and geometric details, since the reconstructed shape is not over-constrained to the topology of the body. ECON achieves this by using and extending recent advances in variational normal integration [7] and shape completion [10]. It effectively extends these to the task of image-based 3D human reconstruction. We believe ECON can lead to both real-world applications and useful tools for + +the 3D vision community. The code and models are available at Econ.is.tue.mpg.de for research purposes. + +Acknowledgments. We thank Lea Hering and Radek Daněček for proofreading, Yao Feng, Haven Feng and Weiyang Liu for valuable feedback, and Tsvetelina Alexiadis for perceptual study. We are especially grateful to Carlos Barreto (Blender Add-on), Teddy Huang (Docker Image), and Justin John (Windows Support). This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No.860768 (CLIPE project). + +Disclosure.is.tue.mpg.de/black/CoI_CVPR_2023.txt + +# References + +[1] Alakh Aggarwal, Jikai Wang, Steven Hogue, Saifeng Ni, Madhukar Budagavi, and Xiaohu Guo. Layered-Garment Net: Generating Multiple Implicit Garment Layers from a Single Image. In Asian Conference on Computer Vision (ACCV), 2022. 7 +[2] Thiemo Alldieck, Marcus A. Magnor, Bharat Lal Bhatnagar, Christian Theobalt, and Gerard Pons-Moll. Learning to reconstruct people in clothing from a single RGB camera. 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+ "bbox": [ + 46, + 376, + 546, + 431 + ], + "spans": [ + { + "bbox": [ + 46, + 376, + 546, + 431 + ], + "type": "text", + "content": "Figure 1. Human digitization from a color image. ECON combines the best aspects of free-form implicit representation, and explicit anthropomorphic regularization to infer high-fidelity 3D humans, even with loose clothing or in challenging poses. It does so in three steps: (1) It infers detailed 2D normal maps for the front and back side (Sec. 3.1). (2) The normal maps are converted into detailed, yet incomplete, 2.5D front and back surfaces guided by a SMPL-X estimate (Sec. 3.2). (3) It then \"inpaints\" the missing geometry between two surfaces (Sec. 3.3). Face or hands can be optionally replaced with the cleaner ones from SMPL-X. See the video on our website for more results." + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "image_caption" + } + ], + "index": 15 + }, + { + "bbox": [ + 143, + 443, + 190, + 455 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 443, + 190, + 455 + ], + "spans": [ + { + "bbox": [ + 143, + 443, + 190, + 455 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 46, + 462, + 289, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 462, + 289, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 462, + 289, + 714 + ], + "type": "text", + "content": "The combination of deep learning, artist-curated scans, and Implicit Functions (IF), is enabling the creation of detailed, clothed, 3D humans from images. However, existing methods are far from perfect. IF-based methods recover free-form geometry, but produce disembodied limbs or degenerate shapes for novel poses or clothes. To increase robustness for these cases, existing work uses an explicit parametric body model to constrain surface reconstruction, but this limits the recovery of free-form surfaces such as loose clothing that deviates from the body. What we want is a method that combines the best properties of implicit representation and explicit body regularization. To this end, we make two key observations: (1) current networks are better at inferring detailed 2D maps than full-3D surfaces, and (2) a parametric model can be seen as a \"canvas\" for stitching together detailed surface patches. Based on these, our method, ECON, has three main steps: (1) It infers detailed 2D normal maps for the front and back side of a clothed person. (2) From these, it recovers 2.5D front and back surfaces, called d-BiNI, that are equally detailed, yet incomplete, and registers these w.r.t. each other with the help of a SMPL-X" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 444, + 547, + 564 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 444, + 547, + 564 + ], + "spans": [ + { + "bbox": [ + 304, + 444, + 547, + 564 + ], + "type": "text", + "content": "body mesh recovered from the image. (3) It \"inpaints\" the missing geometry between d-BiNI surfaces. If the face and hands are noisy, they can optionally be replaced with the ones of SMPL-X. As a result, ECON infers high-fidelity 3D humans even in loose clothes and challenging poses. This goes beyond previous methods, according to the quantitative evaluation on the CAPE and Renderpeople datasets. Perceptual studies also show that ECON's perceived realism is better by a large margin. Code and models are available for research purposes at econ.is.tue.mpg.de" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 306, + 586, + 386, + 597 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 586, + 386, + 597 + ], + "spans": [ + { + "bbox": [ + 306, + 586, + 386, + 597 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 304, + 605, + 547, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 547, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 547, + 714 + ], + "type": "text", + "content": "Human avatars will be key for future games and movies, mixed-reality, tele-presence and the \"metaverse\". To build realistic and personalized avatars at scale, we need to faithfully reconstruct detailed 3D humans from color photos taken in the wild. This is still an open problem, due to its challenges; people wear all kinds of different clothing and accessories, and they pose their bodies in many, often imaginative, ways. A good reconstruction method must accurately capture these, while also being robust to novel clothing and poses." + } + ] + } + ], + "index": 21 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 297, + 749, + 312, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 749, + 312, + 757 + ], + "spans": [ + { + "bbox": [ + 297, + 749, + 312, + 757 + ], + "type": "text", + "content": "512" + } + ] + } + ], + "index": 22 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 263 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 263 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 263 + ], + "type": "text", + "content": "Initial, promising, results have been made possible by using artist-curated scans as training data, and implicit functions (IF) [56, 59] as the 3D representation. Seminal work on PIFu(HD) [70, 71] uses \"pixel-aligned\" IF and reconstructs clothed 3D humans with unconstrained topology. However, these methods tend to overfit to the poses seen in the training data, and have no explicit knowledge about the human body's structure. Consequently, they produce disembodied limbs or degenerate shapes for images with novel poses; see the 2nd row of Fig. 2. Follow-up work [26, 82, 96] accounts for such artifacts by regularizing the IF using a shape prior provided by an explicit body model [52, 61], but regularization introduces a topological constraint, restricting generalization to novel clothing while attenuating shape details; see the 3rd and 4th rows of Fig. 2. In a nutshell, there are trade-offs between robustness, generalization and detail." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 265, + 288, + 384 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 265, + 288, + 384 + ], + "spans": [ + { + "bbox": [ + 46, + 265, + 288, + 384 + ], + "type": "text", + "content": "What we want is the best of both worlds; that is, the robustness of explicit anthropomorphic body models, and the flexibility of IF to capture arbitrary clothing topology. To that end, we make two key observations: (1) While inferring detailed 2D normal maps from color images is relatively easy [31, 71, 82], inferring 3D geometry with equally fine details is still challenging [9]. Thus, we exploit networks to infer detailed \"geometry-aware\" 2D maps that we then lift to 3D. (2) A body model can be seen as a low-frequency \"canvas\" that \"guides\" the stitching of detailed surface parts." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 386, + 288, + 470 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 386, + 288, + 470 + ], + "spans": [ + { + "bbox": [ + 46, + 386, + 288, + 470 + ], + "type": "text", + "content": "With these in mind, we develop ECON, which stands for \"Explicit Clothed humans Optimized via Normal integration\". It takes, as input, an RGB image and a SMPL-X body inferred from the image. Then, it outputs a 3D human in free-form clothing with a level of detail and robustness that goes beyond the state of the art (SOTA); see the bottom of Fig. 2. Specifically, ECON has three steps." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 472, + 288, + 519 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 472, + 288, + 519 + ], + "spans": [ + { + "bbox": [ + 46, + 472, + 288, + 519 + ], + "type": "text", + "content": "Step 1: Front & back normal reconstruction. We predict front- and back-side clothed-human normal maps from the input RGB image, conditioned on the body estimate, with a standard image-to-image translation network." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 521, + 288, + 688 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 521, + 288, + 688 + ], + "spans": [ + { + "bbox": [ + 46, + 521, + 288, + 688 + ], + "type": "text", + "content": "Step 2: Front & back surface reconstruction. We take the previously predicted normal maps, and the corresponding depth maps that are rendered from the SMPL-X mesh, to produce detailed and coherent front-/back-side 3D surfaces, " + }, + { + "bbox": [ + 46, + 521, + 288, + 688 + ], + "type": "inline_equation", + "content": "\\{\\mathcal{M}_{\\mathrm{F}},\\mathcal{M}_{\\mathrm{B}}\\}" + }, + { + "bbox": [ + 46, + 521, + 288, + 688 + ], + "type": "text", + "content": ". To this end, we extend the recent BiNI method [7], and develop a novel optimization scheme that is aimed at satisfying three goals for the resulting surfaces: (1) their high-frequency components agree with clothed-human normals, (2) their low-frequency components and the discontinuities agree with the SMPL-X ones, and (3) the depth values on their silhouettes are coherent with each other and consistent with the SMPL-X-based depth maps. The two output surfaces, " + }, + { + "bbox": [ + 46, + 521, + 288, + 688 + ], + "type": "inline_equation", + "content": "\\{\\mathcal{M}_{\\mathrm{F}},\\mathcal{M}_{\\mathrm{B}}\\}" + }, + { + "bbox": [ + 46, + 521, + 288, + 688 + ], + "type": "text", + "content": ", are detailed yet incomplete, i.e., there is missing geometry in occluded and \"profile\" regions." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 689, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 288, + 713 + ], + "type": "text", + "content": "Step 3: Full 3D shape completion. This module takes two inputs: (1) the SMPL-X mesh, and (2) the two d-BiNI" + } + ] + } + ], + "index": 5 + }, + { + "type": "image", + "bbox": [ + 307, + 63, + 545, + 300 + ], + "blocks": [ + { + "bbox": [ + 307, + 63, + 545, + 300 + ], + "lines": [ + { + "bbox": [ + 307, + 63, + 545, + 300 + ], + "spans": [ + { + "bbox": [ + 307, + 63, + 545, + 300 + ], + "type": "image", + "image_path": "d7622887f9cce397412347a6fa4860c177c8c531fd777bd2e2e69c2cf74de9c6.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 300, + 547, + 345 + ], + "lines": [ + { + "bbox": [ + 305, + 300, + 547, + 345 + ], + "spans": [ + { + "bbox": [ + 305, + 300, + 547, + 345 + ], + "type": "text", + "content": "Figure 2. Summary of SOTA. PIFuHD [71] recovers clothing details, but struggles with novel poses. ICON [82] and PaMIR [96] regularize shape to a body shape, but over-constrain the skirts, or over-smooth the wrinkles. ECON combines their best aspects." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_caption" + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 352, + 547, + 448 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 352, + 547, + 448 + ], + "spans": [ + { + "bbox": [ + 304, + 352, + 547, + 448 + ], + "type": "text", + "content": "surfaces, " + }, + { + "bbox": [ + 304, + 352, + 547, + 448 + ], + "type": "inline_equation", + "content": "\\{\\mathcal{M}_{\\mathrm{F}},\\mathcal{M}_{\\mathrm{B}}\\}" + }, + { + "bbox": [ + 304, + 352, + 547, + 448 + ], + "type": "text", + "content": ". The goal is to \"inpaint\" the missing geometry. Existing methods struggle with this problem. On one hand, Poisson reconstruction [38] produces \"blobby\" shapes and naively \"infills\" holes without exploiting a shape distribution prior. On the other hand, data-driven approaches, such as IF-Nets [10], struggle with missing parts caused by (self-)occlusions, and fail to keep the fine details present on two d-BiNI surfaces, producing degenerate geometries." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 449, + 547, + 555 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 449, + 547, + 555 + ], + "spans": [ + { + "bbox": [ + 304, + 449, + 547, + 555 + ], + "type": "text", + "content": "We address above the limitations in two steps: (1) We extend and re-train IF-Nets to be conditioned on the SMPL-X body, so that SMPL-X regularizes shape \"infilling\". We discard the triangles that lie close to " + }, + { + "bbox": [ + 304, + 449, + 547, + 555 + ], + "type": "inline_equation", + "content": "\\{\\mathcal{M}_{\\mathrm{F}},\\mathcal{M}_{\\mathrm{B}}\\}" + }, + { + "bbox": [ + 304, + 449, + 547, + 555 + ], + "type": "text", + "content": ", and keep the remaining ones as \"infilling patches\". (2) We stitch together the front- and back-side surfaces and infilling patches via Poisson reconstruction; note that holes between these are small enough for a general purpose method. The result is a full 3D shape of a clothed human; see Fig. 2, bottom." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 557, + 547, + 665 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 557, + 547, + 665 + ], + "spans": [ + { + "bbox": [ + 304, + 557, + 547, + 665 + ], + "type": "text", + "content": "We evaluate ECON both on established benchmarks (CAPE [55] and Renderpeople [66]) and in-the-wild images. Quantitative analysis reveals ECON's superiority. A perceptual study echos this, showing that ECON is significantly preferred over competitors on challenging poses and loose clothing, and competitive with PIFuHD on fashion images. Qualitative results show that ECON generalizes better than the SOTA to a wide variety of poses and clothing, even with extreme looseness or complex topology; see Fig. 9." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 666, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 666, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 666, + 547, + 713 + ], + "type": "text", + "content": "With both pose-robustness and topological flexibility, ECON recovers 3D clothed humans with a good level of detail and realistic pose. Code and models are available for research purposes at econ.is.tue.mpg.de" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 297, + 749, + 312, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 749, + 312, + 757 + ], + "spans": [ + { + "bbox": [ + 297, + 749, + 312, + 757 + ], + "type": "text", + "content": "513" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 71, + 134, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 71, + 134, + 83 + ], + "spans": [ + { + "bbox": [ + 47, + 71, + 134, + 83 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 91, + 287, + 151 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 91, + 287, + 151 + ], + "spans": [ + { + "bbox": [ + 47, + 91, + 287, + 151 + ], + "type": "text", + "content": "Image-based clothed human reconstruction. Regarding geometric representation, we group the mainstream clothed human reconstruction approaches into \"implicit\" and \"explicit\". Note that with the terms implicit/explicit we mainly refer to the surface decoder rather than the feature encoder." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 151, + 289, + 377 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 151, + 289, + 377 + ], + "spans": [ + { + "bbox": [ + 46, + 151, + 289, + 377 + ], + "type": "text", + "content": "1) Explicit-shape-based approaches use either a mesh-based parametric body model [35, 52, 61, 69, 83], or a nonparametric depth map [18, 72] or point cloud [90], to reconstruct 3D humans. Many methods [15, 36, 39, 40, 42, 43, 75, 76, 87, 91, 92] estimate or regress minimally-clothed 3D body meshes from RGB pixels and ignore clothing. To account for clothed human shapes, another line of work [2-4, 41, 55, 62, 79, 100] adds 3D offsets on top of the body mesh. This is compatible with current animation pipelines, as they inherit the hierarchical skeleton and skinning weights from the underling statistical body model. However, this \"body+offset\" approach is not flexible enough to model loose clothing, which deviates significantly from the body topology, such as dresses and skirts. To increase topological flexibility, some methods [5, 33] reconstruct 3D clothed humans by identifying the type of clothing and using the appropriate model to reconstruct it. Scaling up this \"cloth-aware\" approach to many clothing styles is nontrivial, limiting generalization to in-the-wild outfit variation." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 379, + 288, + 486 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 379, + 288, + 486 + ], + "spans": [ + { + "bbox": [ + 46, + 379, + 288, + 486 + ], + "type": "text", + "content": "2) Implicit-function-based approaches are topology-agnostic and, thus, can be used to represent arbitrary 3D clothed human shapes. SMPLicit [12], ClothWild [57] and DIG [46] learn a generative clothing model with neural distance fields [11, 56, 59] from a 3D clothing dataset. Given an image, the clothed human is reconstructed by estimating a parametric body and optimizing the latent space of the clothing model. However, the results usually do not align well with the image and lack geometric detail." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 486, + 288, + 653 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 486, + 288, + 653 + ], + "spans": [ + { + "bbox": [ + 46, + 486, + 288, + 653 + ], + "type": "text", + "content": "PIFu [70] introduces pixel-aligned implicit human shape reconstruction and PIFuHD [71] significantly improves the geometric details with a multi-level architecture and normal maps predicted from the RGB image. However, these two methods do not exploit knowledge of the human body structure. Therefore, these methods overfit to the body poses in the training data, e.g. fashion poses. They fail to generalize to novel poses, producing non-human shapes with broken or disembodied limbs. To address these issues, several methods introduce different geometric priors to regularize the deep implicit representation: GeoPIFu [26] introduces a coarse shape of volumetric humans, Self-Portraits [49], PINA [14], and S3 [85] use depth or LIDAR information to regularize shape and improve robustness to pose variation." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 654, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 654, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 654, + 288, + 713 + ], + "type": "text", + "content": "Another direction leverages parametric body models, which represent human body shape well, model the kinematic structure of the body, and can be reliably estimated from RGB images of clothed people. Such a representation can be viewed as a base shape upon which to model clothed" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 72, + 547, + 262 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 262 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 262 + ], + "type": "text", + "content": "humans. Therefore, several methods combine parametric body models with expressive implicit representations to get the best of both worlds. PaMIR [96] and DeepMultiCap [95] condition the pixel-aligned features on a posed and voxelized SMPL mesh. JIFF Introduces a 3DMM face prior to improve the realism of the facial region. ARCH [30], " + }, + { + "bbox": [ + 304, + 72, + 547, + 262 + ], + "type": "inline_equation", + "content": "\\mathrm{ARCH} + +" + }, + { + "bbox": [ + 304, + 72, + 547, + 262 + ], + "type": "text", + "content": " [27] and CAR [50] use SMPL to unpose the pixel-aligned query points from a posed space to a canonical space. To further generalize to unseen poses on in-the-wild photos, ICON [82] regresses shapes from locally-queried features. However, the above approaches gain robustness to unseen poses at the cost of generalization ability to various, especially loose, clothing topologies. We argue that this is because loose clothing differs greatly from human body and that conditioning on the SMPL body in 3D makes it harder for networks to make full use of 2D image features." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 263, + 548, + 456 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 263, + 548, + 456 + ], + "spans": [ + { + "bbox": [ + 304, + 263, + 548, + 456 + ], + "type": "text", + "content": "Our work is also inspired by \"sandwich-like\" monocular reconstruction approaches, represented by Moduling Humans [18], FACSIMILE [72] and Any-Shot GIN [80]. Moduling Humans has two networks: a generator that estimates the visible (front) and invisible (back) depth maps from RGB images, and a discriminator that helps regularize the estimation via an adversarial loss. FACSIMILE further improves the geometric details by leveraging a normal loss, which is directly computed from depth estimates via differentiable layers. Recently, Any-Shot GIN generalizes the sandwich-like scheme to novel classes of objects. Given RGB images, it predicts front and back depth maps as well, and then exploits IF-Nets [10] for shape completion. We follow a similar path and extend it, to successfully reconstruct clothed human shapes with SOTA pose generalization, and better details from normal images." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 464, + 362, + 477 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 464, + 362, + 477 + ], + "spans": [ + { + "bbox": [ + 306, + 464, + 362, + 477 + ], + "type": "text", + "content": "3. Method" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 485, + 547, + 545 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 485, + 547, + 545 + ], + "spans": [ + { + "bbox": [ + 304, + 485, + 547, + 545 + ], + "type": "text", + "content": "Given an RGB image, ECON first estimates front and back normal maps (Sec. 3.1), then converts them into front and back partial surfaces (Sec. 3.2), and finally \"inpaints\" the missing geometry with the help of IF-Nets+ (Sec. 3.3). See ECON's overview in Fig. 3." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 552, + 479, + 565 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 552, + 479, + 565 + ], + "spans": [ + { + "bbox": [ + 306, + 552, + 479, + 565 + ], + "type": "text", + "content": "3.1. Detailed normal map prediction" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 570, + 547, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 547, + 689 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 547, + 689 + ], + "type": "text", + "content": "Trained on abundant pairs of RGB images and normal images, a \"front\" normal map, " + }, + { + "bbox": [ + 304, + 570, + 547, + 689 + ], + "type": "inline_equation", + "content": "\\widehat{\\mathcal{N}}_{\\mathrm{F}}^{\\mathrm{c}}" + }, + { + "bbox": [ + 304, + 570, + 547, + 689 + ], + "type": "text", + "content": ", can be accurately estimated from an RGB image using image-to-image translation networks, as demonstrated in PIFuHD [71] or ICON [82]. Both methods also infer a \"back\" normal map, " + }, + { + "bbox": [ + 304, + 570, + 547, + 689 + ], + "type": "inline_equation", + "content": "\\widehat{\\mathcal{N}}_{\\mathrm{B}}^{\\mathrm{c}}" + }, + { + "bbox": [ + 304, + 570, + 547, + 689 + ], + "type": "text", + "content": ", from the image. But, the absence of image cues leads to over-smooth " + }, + { + "bbox": [ + 304, + 570, + 547, + 689 + ], + "type": "inline_equation", + "content": "\\widehat{\\mathcal{N}}_{\\mathrm{B}}^{\\mathrm{c}}" + }, + { + "bbox": [ + 304, + 570, + 547, + 689 + ], + "type": "text", + "content": ". To address this, we fine-tune ICON's backside normal predictor, " + }, + { + "bbox": [ + 304, + 570, + 547, + 689 + ], + "type": "inline_equation", + "content": "\\mathcal{G}_{\\mathrm{B}}^{\\mathrm{N}}" + }, + { + "bbox": [ + 304, + 570, + 547, + 689 + ], + "type": "text", + "content": ", with an additional MRF loss [77] to enhance the local details by minimizing the difference between the predicted " + }, + { + "bbox": [ + 304, + 570, + 547, + 689 + ], + "type": "inline_equation", + "content": "\\widehat{\\mathcal{N}}^{\\mathrm{c}}" + }, + { + "bbox": [ + 304, + 570, + 547, + 689 + ], + "type": "text", + "content": " and ground truth (GT) " + }, + { + "bbox": [ + 304, + 570, + 547, + 689 + ], + "type": "inline_equation", + "content": "\\mathcal{N}^{\\mathrm{c}}" + }, + { + "bbox": [ + 304, + 570, + 547, + 689 + ], + "type": "text", + "content": " in feature space." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 689, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 689, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 305, + 689, + 547, + 715 + ], + "type": "text", + "content": "To guide the normal map prediction and make it robust to various body poses, ICON conditions the normal map" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 297, + 749, + 313, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 749, + 313, + 757 + ], + "spans": [ + { + "bbox": [ + 297, + 749, + 313, + 757 + ], + "type": "text", + "content": "514" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 48, + 68, + 443, + 281 + ], + "blocks": [ + { + "bbox": [ + 48, + 68, + 443, + 281 + ], + "lines": [ + { + "bbox": [ + 48, + 68, + 443, + 281 + ], + "spans": [ + { + "bbox": [ + 48, + 68, + 443, + 281 + ], + "type": "image", + "image_path": "8cdf79210928b3e9b25205af1a11a834dd7d7a36b2f863c50ca435833101104c.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 289, + 547, + 338 + ], + "lines": [ + { + "bbox": [ + 46, + 289, + 547, + 338 + ], + "spans": [ + { + "bbox": [ + 46, + 289, + 547, + 338 + ], + "type": "text", + "content": "Figure 3. Overview. ECON takes as input an RGB image, " + }, + { + "bbox": [ + 46, + 289, + 547, + 338 + ], + "type": "inline_equation", + "content": "\\mathcal{I}" + }, + { + "bbox": [ + 46, + 289, + 547, + 338 + ], + "type": "text", + "content": ", and a SMPL-X body, " + }, + { + "bbox": [ + 46, + 289, + 547, + 338 + ], + "type": "inline_equation", + "content": "\\mathcal{M}^{\\mathrm{b}}" + }, + { + "bbox": [ + 46, + 289, + 547, + 338 + ], + "type": "text", + "content": ". Conditioned on the rendered front and back body normal images, " + }, + { + "bbox": [ + 46, + 289, + 547, + 338 + ], + "type": "inline_equation", + "content": "\\mathcal{N}^{\\mathrm{b}}" + }, + { + "bbox": [ + 46, + 289, + 547, + 338 + ], + "type": "text", + "content": ", ECON first predicts front and back clothing normal maps, " + }, + { + "bbox": [ + 46, + 289, + 547, + 338 + ], + "type": "inline_equation", + "content": "\\widehat{\\mathcal{N}}^{\\mathrm{c}}" + }, + { + "bbox": [ + 46, + 289, + 547, + 338 + ], + "type": "text", + "content": ". These two maps, along with body depth maps, " + }, + { + "bbox": [ + 46, + 289, + 547, + 338 + ], + "type": "inline_equation", + "content": "\\mathcal{Z}^{\\mathrm{b}}" + }, + { + "bbox": [ + 46, + 289, + 547, + 338 + ], + "type": "text", + "content": ", are fed into a d-BiNI optimizer to produce front and back surfaces, " + }, + { + "bbox": [ + 46, + 289, + 547, + 338 + ], + "type": "inline_equation", + "content": "\\{\\mathcal{M}_{\\mathrm{F}}, \\mathcal{M}_{\\mathrm{B}}\\}" + }, + { + "bbox": [ + 46, + 289, + 547, + 338 + ], + "type": "text", + "content": ". Based on such partial surfaces, and body estimate " + }, + { + "bbox": [ + 46, + 289, + 547, + 338 + ], + "type": "inline_equation", + "content": "\\mathcal{M}^{\\mathrm{b}}" + }, + { + "bbox": [ + 46, + 289, + 547, + 338 + ], + "type": "text", + "content": ", IF-Nets+ implicitly completes " + }, + { + "bbox": [ + 46, + 289, + 547, + 338 + ], + "type": "inline_equation", + "content": "\\mathcal{R}_{\\mathrm{IF}}" + }, + { + "bbox": [ + 46, + 289, + 547, + 338 + ], + "type": "text", + "content": ". With optional Face or hands from " + }, + { + "bbox": [ + 46, + 289, + 547, + 338 + ], + "type": "inline_equation", + "content": "\\mathcal{M}^{\\mathrm{b}}" + }, + { + "bbox": [ + 46, + 289, + 547, + 338 + ], + "type": "text", + "content": ", screened Poisson combines everything as final watertight " + }, + { + "bbox": [ + 46, + 289, + 547, + 338 + ], + "type": "inline_equation", + "content": "\\mathcal{R}" + }, + { + "bbox": [ + 46, + 289, + 547, + 338 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 460, + 76, + 542, + 277 + ], + "blocks": [ + { + "bbox": [ + 460, + 76, + 542, + 277 + ], + "lines": [ + { + "bbox": [ + 460, + 76, + 542, + 277 + ], + "spans": [ + { + "bbox": [ + 460, + 76, + 542, + 277 + ], + "type": "image", + "image_path": "e26df1a3f8f33948fdbc0d1ad14c4529af4b67c80573ce4bb637b7044d0e566b.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 349, + 290, + 445 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 349, + 290, + 445 + ], + "spans": [ + { + "bbox": [ + 46, + 349, + 290, + 445 + ], + "type": "text", + "content": "prediction module on the body normal maps, " + }, + { + "bbox": [ + 46, + 349, + 290, + 445 + ], + "type": "inline_equation", + "content": "\\mathcal{N}^{\\mathrm{b}}" + }, + { + "bbox": [ + 46, + 349, + 290, + 445 + ], + "type": "text", + "content": ", rendered from the estimated body " + }, + { + "bbox": [ + 46, + 349, + 290, + 445 + ], + "type": "inline_equation", + "content": "\\mathcal{M}^{\\mathrm{b}}" + }, + { + "bbox": [ + 46, + 349, + 290, + 445 + ], + "type": "text", + "content": ". Thus, it is important to accurately align the estimated body and clothing silhouette. Apart from the " + }, + { + "bbox": [ + 46, + 349, + 290, + 445 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{N\\_diff}}" + }, + { + "bbox": [ + 46, + 349, + 290, + 445 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 349, + 290, + 445 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{S\\_diff}}" + }, + { + "bbox": [ + 46, + 349, + 290, + 445 + ], + "type": "text", + "content": " used in ICON [82], we also apply 2D body landmarks in an additional loss term, " + }, + { + "bbox": [ + 46, + 349, + 290, + 445 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{J\\_diff}}" + }, + { + "bbox": [ + 46, + 349, + 290, + 445 + ], + "type": "text", + "content": ", to further optimize the SMPL-X body, " + }, + { + "bbox": [ + 46, + 349, + 290, + 445 + ], + "type": "inline_equation", + "content": "\\mathcal{M}^{\\mathrm{b}}" + }, + { + "bbox": [ + 46, + 349, + 290, + 445 + ], + "type": "text", + "content": ", inferred from pixie [15] or PyMAF-X [91]. Specifically, we optimize SMPL-X's shape, " + }, + { + "bbox": [ + 46, + 349, + 290, + 445 + ], + "type": "inline_equation", + "content": "\\beta" + }, + { + "bbox": [ + 46, + 349, + 290, + 445 + ], + "type": "text", + "content": ", pose, " + }, + { + "bbox": [ + 46, + 349, + 290, + 445 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 46, + 349, + 290, + 445 + ], + "type": "text", + "content": ", and translation, " + }, + { + "bbox": [ + 46, + 349, + 290, + 445 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 349, + 290, + 445 + ], + "type": "text", + "content": ", to minimize:" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 93, + 456, + 287, + 475 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 93, + 456, + 287, + 475 + ], + "spans": [ + { + "bbox": [ + 93, + 456, + 287, + 475 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\mathrm {S M P L - X}} = \\mathcal {L} _ {\\mathrm {N} _ {-} \\text {d i f f}} + \\mathcal {L} _ {\\mathrm {S} _ {-} \\text {d i f f}} + \\mathcal {L} _ {\\mathrm {J} _ {-} \\text {d i f f}}, \\tag {1}", + "image_path": "4bd33d6c5a135064255b7837a4490fa45fe681394d8a04ecb096d644a423a19e.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 115, + 471, + 219, + 486 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 115, + 471, + 219, + 486 + ], + "spans": [ + { + "bbox": [ + 115, + 471, + 219, + 486 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\mathrm {J} _ {-} \\text {d i f f}} = \\lambda_ {\\mathrm {J} _ {-} \\text {d i f f}} \\left| \\mathcal {J} ^ {\\mathrm {b}} - \\widehat {\\mathcal {J} ^ {\\mathrm {c}}} \\right|,", + "image_path": "0574e1a912fa652a8d8459dc4f16e9b5ef5423bd84a6341b86210a2c0ee1fd66.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 492, + 288, + 567 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 492, + 288, + 567 + ], + "spans": [ + { + "bbox": [ + 46, + 492, + 288, + 567 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 492, + 288, + 567 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{N\\_diff}}" + }, + { + "bbox": [ + 46, + 492, + 288, + 567 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 492, + 288, + 567 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{S\\_diff}}" + }, + { + "bbox": [ + 46, + 492, + 288, + 567 + ], + "type": "text", + "content": " are the normal-map loss and silhouette loss introduced in ICON [82], and " + }, + { + "bbox": [ + 46, + 492, + 288, + 567 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{J\\_diff}}" + }, + { + "bbox": [ + 46, + 492, + 288, + 567 + ], + "type": "text", + "content": " is the joint loss (L2) between 2D landmarks " + }, + { + "bbox": [ + 46, + 492, + 288, + 567 + ], + "type": "inline_equation", + "content": "\\widehat{\\mathcal{I}^{\\mathrm{c}}}" + }, + { + "bbox": [ + 46, + 492, + 288, + 567 + ], + "type": "text", + "content": ", which are estimated by a 2D keypoint estimator from the RGB image " + }, + { + "bbox": [ + 46, + 492, + 288, + 567 + ], + "type": "inline_equation", + "content": "\\mathcal{I}" + }, + { + "bbox": [ + 46, + 492, + 288, + 567 + ], + "type": "text", + "content": ", and the corresponding re-projected 2D joints " + }, + { + "bbox": [ + 46, + 492, + 288, + 567 + ], + "type": "inline_equation", + "content": "\\mathcal{I}^{\\mathrm{b}}" + }, + { + "bbox": [ + 46, + 492, + 288, + 567 + ], + "type": "text", + "content": " from " + }, + { + "bbox": [ + 46, + 492, + 288, + 567 + ], + "type": "inline_equation", + "content": "\\mathcal{M}^{\\mathrm{b}}" + }, + { + "bbox": [ + 46, + 492, + 288, + 567 + ], + "type": "text", + "content": ". For more implementation details, see Sec. A.1 in SupMat." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 574, + 250, + 586 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 574, + 250, + 586 + ], + "spans": [ + { + "bbox": [ + 47, + 574, + 250, + 586 + ], + "type": "text", + "content": "3.2. Front and back surface reconstruction" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 594, + 287, + 664 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 594, + 287, + 664 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 287, + 664 + ], + "type": "text", + "content": "We now lift the clothed normal maps to 2.5D surfaces. We expect these 2.5D surfaces to satisfy three conditions: (1) high-frequency surface details agree with predicted clothed normal maps, (2) low-frequency surface variations, including discontinuities, agree with SMPL-X's ones, and (3) the depth of the front and back silhouettes are close to each other." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 665, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 288, + 714 + ], + "type": "text", + "content": "Unlike PIFuHD [71] or ICON [82], which train a neural network to regress the implicit surface from normal maps, we explicitly model the depth-normal relationship using variational normal integration methods [7,64]. Specifi" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 349, + 546, + 385 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 349, + 546, + 385 + ], + "spans": [ + { + "bbox": [ + 304, + 349, + 546, + 385 + ], + "type": "text", + "content": "cally, we tailor the recent bilateral normal integration (BiNI) method [7] to full-body mesh reconstruction by harnessing the coarse prior, depth maps, and silhouette consistency." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 385, + 545, + 434 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 385, + 545, + 434 + ], + "spans": [ + { + "bbox": [ + 304, + 385, + 545, + 434 + ], + "type": "text", + "content": "To satisfy the three conditions, we propose a depth-aware silhouette-consistent bilateral normal integration (d-BiNI) method to jointly optimize for the front and back clothed depth maps, " + }, + { + "bbox": [ + 304, + 385, + 545, + 434 + ], + "type": "inline_equation", + "content": "\\widehat{\\mathcal{Z}}_{\\mathrm{F}}^{\\mathrm{c}}" + }, + { + "bbox": [ + 304, + 385, + 545, + 434 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 385, + 545, + 434 + ], + "type": "inline_equation", + "content": "\\widehat{\\mathcal{Z}}_{\\mathrm{B}}^{\\mathrm{c}}" + }, + { + "bbox": [ + 304, + 385, + 545, + 434 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 350, + 441, + 546, + 459 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 350, + 441, + 546, + 459 + ], + "spans": [ + { + "bbox": [ + 350, + 441, + 546, + 459 + ], + "type": "interline_equation", + "content": "\\mathrm {d} - \\operatorname {B i N I} \\left(\\widehat {\\mathcal {N}} _ {\\mathrm {F}} ^ {\\mathrm {c}}, \\widehat {\\mathcal {N}} _ {\\mathrm {B}} ^ {\\mathrm {c}}, \\mathcal {Z} _ {\\mathrm {F}} ^ {\\mathrm {b}}, \\mathcal {Z} _ {\\mathrm {B}} ^ {\\mathrm {b}}\\right)\\rightarrow \\widehat {\\mathcal {Z}} _ {\\mathrm {F}} ^ {\\mathrm {c}}, \\widehat {\\mathcal {Z}} _ {\\mathrm {B}} ^ {\\mathrm {c}}. \\tag {2}", + "image_path": "bd85ec4c88e1e707f5e1c449e22fbbc2d3118caf1a51e6e0e3db2848163d7829.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 468, + 545, + 506 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 468, + 545, + 506 + ], + "spans": [ + { + "bbox": [ + 304, + 468, + 545, + 506 + ], + "type": "text", + "content": "Here, " + }, + { + "bbox": [ + 304, + 468, + 545, + 506 + ], + "type": "inline_equation", + "content": "\\widehat{\\mathcal{N}}_{*}^{\\mathrm{c}}" + }, + { + "bbox": [ + 304, + 468, + 545, + 506 + ], + "type": "text", + "content": " is the front or back clothed normal map predicted by " + }, + { + "bbox": [ + 304, + 468, + 545, + 506 + ], + "type": "inline_equation", + "content": "\\mathcal{G}_{\\mathrm{F,B}}^{\\mathrm{N}}" + }, + { + "bbox": [ + 304, + 468, + 545, + 506 + ], + "type": "text", + "content": " from " + }, + { + "bbox": [ + 304, + 468, + 545, + 506 + ], + "type": "inline_equation", + "content": "\\{\\mathcal{I},\\mathcal{N}^{\\mathrm{b}}\\}" + }, + { + "bbox": [ + 304, + 468, + 545, + 506 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 304, + 468, + 545, + 506 + ], + "type": "inline_equation", + "content": "\\mathcal{Z}_{*}^{\\mathrm{b}}" + }, + { + "bbox": [ + 304, + 468, + 545, + 506 + ], + "type": "text", + "content": " is the front or back coarse body depth image rendered from the SMPL-X mesh, " + }, + { + "bbox": [ + 304, + 468, + 545, + 506 + ], + "type": "inline_equation", + "content": "\\mathcal{M}^{\\mathrm{b}}" + }, + { + "bbox": [ + 304, + 468, + 545, + 506 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 317, + 506, + 546, + 518 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 506, + 546, + 518 + ], + "spans": [ + { + "bbox": [ + 317, + 506, + 546, + 518 + ], + "type": "text", + "content": "Specifically, our objective function consists of five terms:" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 347, + 536, + 545, + 594 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 347, + 536, + 545, + 594 + ], + "spans": [ + { + "bbox": [ + 347, + 536, + 545, + 594 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\min _ {\\widehat {\\mathcal {Z}} _ {\\mathrm {F}} ^ {\\mathrm {c}}, \\widehat {\\mathcal {Z}} _ {\\mathrm {B}} ^ {\\mathrm {c}}} \\mathcal {L} _ {\\mathrm {n}} (\\widehat {\\mathcal {Z}} _ {\\mathrm {F}} ^ {\\mathrm {c}}; \\widehat {\\mathcal {N}} _ {\\mathrm {F}} ^ {\\mathrm {c}}) + \\mathcal {L} _ {\\mathrm {n}} (\\widehat {\\mathcal {Z}} _ {\\mathrm {B}} ^ {\\mathrm {c}}; \\widehat {\\mathcal {N}} _ {\\mathrm {B}} ^ {\\mathrm {c}}) + \\\\ \\lambda_ {\\mathrm {d}} \\mathcal {L} _ {\\mathrm {d}} \\left(\\widehat {\\mathcal {Z}} _ {\\mathrm {F}} ^ {\\mathrm {c}}; \\mathcal {Z} _ {\\mathrm {F}} ^ {\\mathrm {b}}\\right) + \\lambda_ {\\mathrm {d}} \\mathcal {L} _ {\\mathrm {d}} \\left(\\widehat {\\mathcal {Z}} _ {\\mathrm {B}} ^ {\\mathrm {c}}; \\mathcal {Z} _ {\\mathrm {B}} ^ {\\mathrm {b}}\\right) + \\tag {3} \\\\ \\lambda_ {s} \\mathcal {L} _ {s} (\\widehat {\\mathcal {Z}} _ {F} ^ {c}, \\widehat {\\mathcal {Z}} _ {B} ^ {c}), \\\\ \\end{array}", + "image_path": "b4ba1e71804e0a70630bfdbad2cf8d44f4e5d2f615345e801df2d486bd910067.jpg" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 602, + 545, + 650 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 602, + 545, + 650 + ], + "spans": [ + { + "bbox": [ + 304, + 602, + 545, + 650 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 602, + 545, + 650 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{n}}" + }, + { + "bbox": [ + 304, + 602, + 545, + 650 + ], + "type": "text", + "content": " is the BiNI loss term introduced by BiNI [7], " + }, + { + "bbox": [ + 304, + 602, + 545, + 650 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{d}}" + }, + { + "bbox": [ + 304, + 602, + 545, + 650 + ], + "type": "text", + "content": " is a depth prior applied to the front and back depth surfaces, and " + }, + { + "bbox": [ + 304, + 602, + 545, + 650 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{s}}" + }, + { + "bbox": [ + 304, + 602, + 545, + 650 + ], + "type": "text", + "content": " is a front-back silhouette consistency term. For a more detailed discussion on these terms, see Sec. A.2 in SupMat." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 651, + 545, + 687 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 651, + 545, + 687 + ], + "spans": [ + { + "bbox": [ + 304, + 651, + 545, + 687 + ], + "type": "text", + "content": "With Eq. (3), we make two technical contributions beyond BiNI [7]. First, we use the coarse depth prior rendered from the SMPL-X body mesh, " + }, + { + "bbox": [ + 304, + 651, + 545, + 687 + ], + "type": "inline_equation", + "content": "\\mathcal{Z}_i^{\\mathrm{b}}" + }, + { + "bbox": [ + 304, + 651, + 545, + 687 + ], + "type": "text", + "content": ", to regularize BiNI:" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 331, + 695, + 546, + 712 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 331, + 695, + 546, + 712 + ], + "spans": [ + { + "bbox": [ + 331, + 695, + 546, + 712 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\mathrm {d}} \\left(\\widehat {\\mathcal {Z}} _ {i} ^ {\\mathrm {c}}; \\mathcal {Z} _ {i} ^ {\\mathrm {b}}\\right) = \\left| \\widehat {\\mathcal {Z}} _ {i} ^ {\\mathrm {c}} - \\mathcal {Z} _ {i} ^ {\\mathrm {b}} \\right| _ {\\Omega_ {\\mathrm {n}}} \\cap \\Omega_ {\\mathrm {z}} \\quad i \\in \\{F, B \\}. \\tag {4}", + "image_path": "ce7545a4cdd5873dc71ef30b456c8d34efb2251b57b7fccf33a70f8cd38efaa0.jpg" + } + ] + } + ], + "index": 18 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 297, + 748, + 312, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 748, + 312, + 757 + ], + "spans": [ + { + "bbox": [ + 297, + 748, + 312, + 757 + ], + "type": "text", + "content": "515" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 49, + 70, + 289, + 148 + ], + "blocks": [ + { + "bbox": [ + 49, + 70, + 289, + 148 + ], + "lines": [ + { + "bbox": [ + 49, + 70, + 289, + 148 + ], + "spans": [ + { + "bbox": [ + 49, + 70, + 289, + 148 + ], + "type": "image", + "image_path": "e47c04f60941f1b2651a9436acf01c03110f4707a2ec6ed4b242f112a043780c.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 155, + 288, + 177 + ], + "lines": [ + { + "bbox": [ + 46, + 155, + 288, + 177 + ], + "spans": [ + { + "bbox": [ + 46, + 155, + 288, + 177 + ], + "type": "text", + "content": "Figure 4. Four inputs to d-BiNI. " + }, + { + "bbox": [ + 46, + 155, + 288, + 177 + ], + "type": "inline_equation", + "content": "\\Omega_{\\mathrm{n}}" + }, + { + "bbox": [ + 46, + 155, + 288, + 177 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 155, + 288, + 177 + ], + "type": "inline_equation", + "content": "\\Omega_{\\mathrm{z}}" + }, + { + "bbox": [ + 46, + 155, + 288, + 177 + ], + "type": "text", + "content": " are the domains of clothed and body regions, respectively. " + }, + { + "bbox": [ + 46, + 155, + 288, + 177 + ], + "type": "inline_equation", + "content": "\\partial \\Omega_{\\mathrm{n}}" + }, + { + "bbox": [ + 46, + 155, + 288, + 177 + ], + "type": "text", + "content": " is the silhouette of " + }, + { + "bbox": [ + 46, + 155, + 288, + 177 + ], + "type": "inline_equation", + "content": "\\Omega_{\\mathrm{n}}" + }, + { + "bbox": [ + 46, + 155, + 288, + 177 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 182, + 287, + 277 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 182, + 287, + 277 + ], + "spans": [ + { + "bbox": [ + 46, + 182, + 287, + 277 + ], + "type": "text", + "content": "This addresses the key problem of putting the front and back surfaces together in a coherent way to form a full body. Optimizing BiNI terms " + }, + { + "bbox": [ + 46, + 182, + 287, + 277 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{n}}" + }, + { + "bbox": [ + 46, + 182, + 287, + 277 + ], + "type": "text", + "content": " leaves an arbitrary global offset between the front and back surfaces. The depth prior terms " + }, + { + "bbox": [ + 46, + 182, + 287, + 277 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{d}}" + }, + { + "bbox": [ + 46, + 182, + 287, + 277 + ], + "type": "text", + "content": " encourage the surfaces with undecided offsets to be consistent with the SMPL-X body, and is computed in the domains " + }, + { + "bbox": [ + 46, + 182, + 287, + 277 + ], + "type": "inline_equation", + "content": "\\Omega_{\\mathrm{n}} \\bigcap \\Omega_{\\mathrm{z}}" + }, + { + "bbox": [ + 46, + 182, + 287, + 277 + ], + "type": "text", + "content": " (Fig. 4). For further intuitions on " + }, + { + "bbox": [ + 46, + 182, + 287, + 277 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{n}}" + }, + { + "bbox": [ + 46, + 182, + 287, + 277 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 182, + 287, + 277 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{d}}" + }, + { + "bbox": [ + 46, + 182, + 287, + 277 + ], + "type": "text", + "content": ", see Fig. S.4 and Fig. S.5 in SupMat." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 278, + 288, + 314 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 278, + 288, + 314 + ], + "spans": [ + { + "bbox": [ + 46, + 278, + 288, + 314 + ], + "type": "text", + "content": "Second, we use a silhouette consistency term to encourage the front and back depth values to be the same at the silhouette boundary, which is computed in domain " + }, + { + "bbox": [ + 46, + 278, + 288, + 314 + ], + "type": "inline_equation", + "content": "\\partial \\Omega_{\\mathrm{n}}" + }, + { + "bbox": [ + 46, + 278, + 288, + 314 + ], + "type": "text", + "content": " (Fig. 4):" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 106, + 331, + 287, + 347 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 106, + 331, + 287, + 347 + ], + "spans": [ + { + "bbox": [ + 106, + 331, + 287, + 347 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\mathrm {s}} \\left(\\widehat {\\mathcal {Z}} _ {\\mathrm {F}} ^ {\\mathrm {c}}, \\widehat {\\mathcal {Z}} _ {\\mathrm {B}} ^ {\\mathrm {c}}\\right) = \\left| \\widehat {\\mathcal {Z}} _ {\\mathrm {F}} ^ {\\mathrm {c}} - \\widehat {\\mathcal {Z}} _ {\\mathrm {B}} ^ {\\mathrm {c}} \\right| _ {\\partial \\Omega_ {\\mathrm {n}}}. \\tag {5}", + "image_path": "9f71f10c15cfb323bb88a064e012704073c3686536932859cdc982c5cb14bfaa.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 354, + 287, + 415 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 354, + 287, + 415 + ], + "spans": [ + { + "bbox": [ + 46, + 354, + 287, + 415 + ], + "type": "text", + "content": "The silhouette term improves the physical consistency of the reconstructed front and back clothed depth maps. Without this term, d-BiNI produces intersections of the front and back surfaces around the silhouette, causing \"blobby\" artifacts and hurting reconstruction quality; see Fig. S.6 in SupMat." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 421, + 189, + 434 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 421, + 189, + 434 + ], + "spans": [ + { + "bbox": [ + 47, + 421, + 189, + 434 + ], + "type": "text", + "content": "3.3. Human shape completion" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 439, + 288, + 523 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 439, + 288, + 523 + ], + "spans": [ + { + "bbox": [ + 46, + 439, + 288, + 523 + ], + "type": "text", + "content": "For simple body poses without self-occlusions, merging front and back d-BiNI surfaces in a straightforward way, as done in FACSIMILE [72] and Moduling Humans [18], can result in a complete 3D clothed scan. However, often poses result in self-occlusions, which cause large portions of the surfaces to be missing. In such cases, Poisson Surface Reconstruction (PSR) [37] leads to blobby artifacts." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 529, + 288, + 673 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 529, + 288, + 673 + ], + "spans": [ + { + "bbox": [ + 46, + 529, + 288, + 673 + ], + "type": "text", + "content": "PSR completion with SMPL-X " + }, + { + "bbox": [ + 46, + 529, + 288, + 673 + ], + "type": "inline_equation", + "content": "(\\mathbf{ECON_{EX}})" + }, + { + "bbox": [ + 46, + 529, + 288, + 673 + ], + "type": "text", + "content": ". A naive way to \"infill\" the missing surface is to make use of the estimated SMPL-X body. We remove the triangles from " + }, + { + "bbox": [ + 46, + 529, + 288, + 673 + ], + "type": "inline_equation", + "content": "\\mathcal{M}^{\\mathrm{b}}" + }, + { + "bbox": [ + 46, + 529, + 288, + 673 + ], + "type": "text", + "content": " that are visible to front or back cameras. The remaining triangle \"soup\" " + }, + { + "bbox": [ + 46, + 529, + 288, + 673 + ], + "type": "inline_equation", + "content": "\\mathcal{M}^{\\mathrm{cull}}" + }, + { + "bbox": [ + 46, + 529, + 288, + 673 + ], + "type": "text", + "content": " contains both side-view boundaries and occluded regions. We apply PSR [37] to the union of " + }, + { + "bbox": [ + 46, + 529, + 288, + 673 + ], + "type": "inline_equation", + "content": "\\mathcal{M}^{\\mathrm{cull}}" + }, + { + "bbox": [ + 46, + 529, + 288, + 673 + ], + "type": "text", + "content": " and d-BiNI surfaces " + }, + { + "bbox": [ + 46, + 529, + 288, + 673 + ], + "type": "inline_equation", + "content": "\\{\\mathcal{M}_{\\mathrm{F}},\\mathcal{M}_{\\mathrm{B}}\\}" + }, + { + "bbox": [ + 46, + 529, + 288, + 673 + ], + "type": "text", + "content": " to obtain a watertight reconstruction " + }, + { + "bbox": [ + 46, + 529, + 288, + 673 + ], + "type": "inline_equation", + "content": "\\mathcal{R}" + }, + { + "bbox": [ + 46, + 529, + 288, + 673 + ], + "type": "text", + "content": ". This approach is denoted as " + }, + { + "bbox": [ + 46, + 529, + 288, + 673 + ], + "type": "inline_equation", + "content": "\\mathrm{ECON_{EX}}" + }, + { + "bbox": [ + 46, + 529, + 288, + 673 + ], + "type": "text", + "content": ". Although " + }, + { + "bbox": [ + 46, + 529, + 288, + 673 + ], + "type": "inline_equation", + "content": "\\mathrm{ECON_{EX}}" + }, + { + "bbox": [ + 46, + 529, + 288, + 673 + ], + "type": "text", + "content": " avoids missing limbs or sides, it does not produce a coherent surface for the originally missing clothing and hair surfaces because of the discrepancy between SMPL-X and actual clothing or hair; see " + }, + { + "bbox": [ + 46, + 529, + 288, + 673 + ], + "type": "inline_equation", + "content": "\\mathrm{ECON_{EX}}" + }, + { + "bbox": [ + 46, + 529, + 288, + 673 + ], + "type": "text", + "content": " in Fig. 5." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 677, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 288, + 713 + ], + "type": "text", + "content": "Inpainting with IF-Nets+ " + }, + { + "bbox": [ + 46, + 677, + 288, + 713 + ], + "type": "inline_equation", + "content": "(\\mathcal{R}_{\\mathrm{IF}})" + }, + { + "bbox": [ + 46, + 677, + 288, + 713 + ], + "type": "text", + "content": ". To improve reconstruction coherence, we use a learned implicit-function (IF) model to \"inpaint\" the missing geometry given front and back d-BiNI" + } + ] + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 310, + 69, + 547, + 238 + ], + "blocks": [ + { + "bbox": [ + 310, + 69, + 547, + 238 + ], + "lines": [ + { + "bbox": [ + 310, + 69, + 547, + 238 + ], + "spans": [ + { + "bbox": [ + 310, + 69, + 547, + 238 + ], + "type": "image", + "image_path": "66e611690465f64d9b77f697a90f13891919d3ac190069731b0754a9b87b9c4a.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 246, + 547, + 312 + ], + "lines": [ + { + "bbox": [ + 304, + 246, + 547, + 312 + ], + "spans": [ + { + "bbox": [ + 304, + 246, + 547, + 312 + ], + "type": "text", + "content": "Figure 5. \"Inpainting\" the missing geometry. We simulate different cases of occlusion by masking the normal images and present the intermediate and final 3D reconstruction of different design choices. While IF-Nets misses certain body parts, IF-Nets+ produces a plausible overall shape. " + }, + { + "bbox": [ + 304, + 246, + 547, + 312 + ], + "type": "inline_equation", + "content": "\\mathrm{ECON_{IF}}" + }, + { + "bbox": [ + 304, + 246, + 547, + 312 + ], + "type": "text", + "content": " produces more consistent clothing surfaces than " + }, + { + "bbox": [ + 304, + 246, + 547, + 312 + ], + "type": "inline_equation", + "content": "\\mathrm{ECON_{EX}}" + }, + { + "bbox": [ + 304, + 246, + 547, + 312 + ], + "type": "text", + "content": " due to a learned shape distribution." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 307, + 323, + 545, + 432 + ], + "blocks": [ + { + "bbox": [ + 307, + 323, + 545, + 432 + ], + "lines": [ + { + "bbox": [ + 307, + 323, + 545, + 432 + ], + "spans": [ + { + "bbox": [ + 307, + 323, + 545, + 432 + ], + "type": "image", + "image_path": "3f4e4367f5d8b4b74992ae24fafa82358ff9d8880aee72ef6f83bd3554f54fdb.jpg" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 439, + 547, + 461 + ], + "lines": [ + { + "bbox": [ + 305, + 439, + 547, + 461 + ], + "spans": [ + { + "bbox": [ + 305, + 439, + 547, + 461 + ], + "type": "text", + "content": "Figure 6. Face and hand details. The face and hands of the raw reconstruction can be replaced with the ones of the SMPL-X body." + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_caption" + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 479, + 547, + 660 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 479, + 547, + 660 + ], + "spans": [ + { + "bbox": [ + 304, + 479, + 547, + 660 + ], + "type": "text", + "content": "surfaces. Specifically, we tailor a general-purpose shape completion method, IF-Nets [10], to a SMPL-X-guided one, denoted as IF-Nets+. IF-Nets [10] completes the 3D shape from a deficient 3D input, such as an incomplete 3D human shape or a low-resolution voxel grid. Inspired by Li et al. [44], we adapt IF-Nets by conditioning it on a voxelized SMPL-X body to deal with pose variation; for details see Sec. A.3 in SupMat. IF-Nets+ is trained on voxelized front and back ground-truth clothed depth maps, " + }, + { + "bbox": [ + 304, + 479, + 547, + 660 + ], + "type": "inline_equation", + "content": "\\{\\mathcal{Z}_{\\mathrm{F}}^{\\mathrm{c}},\\mathcal{Z}_{\\mathrm{B}}^{\\mathrm{c}}\\}" + }, + { + "bbox": [ + 304, + 479, + 547, + 660 + ], + "type": "text", + "content": " and a voxelized (estimated) body mesh, " + }, + { + "bbox": [ + 304, + 479, + 547, + 660 + ], + "type": "inline_equation", + "content": "\\mathcal{M}^{\\mathrm{b}}" + }, + { + "bbox": [ + 304, + 479, + 547, + 660 + ], + "type": "text", + "content": " as input, and is supervised with ground-truth 3D shapes. During training, we randomly mask " + }, + { + "bbox": [ + 304, + 479, + 547, + 660 + ], + "type": "inline_equation", + "content": "\\{\\mathcal{Z}_{\\mathrm{F}}^{\\mathrm{c}},\\mathcal{Z}_{\\mathrm{B}}^{\\mathrm{c}}\\}" + }, + { + "bbox": [ + 304, + 479, + 547, + 660 + ], + "type": "text", + "content": " for robustness to occlusions. During inference, we feed the estimated " + }, + { + "bbox": [ + 304, + 479, + 547, + 660 + ], + "type": "inline_equation", + "content": "\\widehat{\\mathcal{Z}}_{\\mathrm{F}}^{\\mathrm{c}},\\widehat{\\mathcal{Z}}_{\\mathrm{B}}^{\\mathrm{c}}" + }, + { + "bbox": [ + 304, + 479, + 547, + 660 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 479, + 547, + 660 + ], + "type": "inline_equation", + "content": "\\mathcal{M}^{\\mathrm{b}}" + }, + { + "bbox": [ + 304, + 479, + 547, + 660 + ], + "type": "text", + "content": " into IF-Nets+ to obtain an occupancy field, from which we extract the inpainted mesh, " + }, + { + "bbox": [ + 304, + 479, + 547, + 660 + ], + "type": "inline_equation", + "content": "\\mathcal{R}_{\\mathrm{IF}}" + }, + { + "bbox": [ + 304, + 479, + 547, + 660 + ], + "type": "text", + "content": " with Marching cubes [53]." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 665, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 547, + 713 + ], + "type": "text", + "content": "PSR completion with " + }, + { + "bbox": [ + 304, + 665, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{R}_{\\mathrm{IF}}" + }, + { + "bbox": [ + 304, + 665, + 547, + 713 + ], + "type": "text", + "content": " (" + }, + { + "bbox": [ + 304, + 665, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{ECON_{IF}}" + }, + { + "bbox": [ + 304, + 665, + 547, + 713 + ], + "type": "text", + "content": "). To obtain our final mesh, " + }, + { + "bbox": [ + 304, + 665, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{R}" + }, + { + "bbox": [ + 304, + 665, + 547, + 713 + ], + "type": "text", + "content": ", we apply PSR to stitch (1) d-BiNI surfaces, (2) sided and occluded triangle soup " + }, + { + "bbox": [ + 304, + 665, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{M}^{\\mathrm{cull}}" + }, + { + "bbox": [ + 304, + 665, + 547, + 713 + ], + "type": "text", + "content": " from " + }, + { + "bbox": [ + 304, + 665, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{R}_{\\mathrm{IF}}" + }, + { + "bbox": [ + 304, + 665, + 547, + 713 + ], + "type": "text", + "content": ", and optionally, (3) face or hands cropped from the estimated SMPL-X" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 297, + 749, + 313, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 749, + 313, + 757 + ], + "spans": [ + { + "bbox": [ + 297, + 749, + 313, + 757 + ], + "type": "text", + "content": "516" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 50, + 71, + 283, + 126 + ], + "blocks": [ + { + "bbox": [ + 50, + 71, + 283, + 126 + ], + "lines": [ + { + "bbox": [ + 50, + 71, + 283, + 126 + ], + "spans": [ + { + "bbox": [ + 50, + 71, + 283, + 126 + ], + "type": "image", + "image_path": "d74ca1518c64ce20f48994f14539737383ec83a44571337e2622f731d65b7ec3.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 135, + 287, + 169 + ], + "lines": [ + { + "bbox": [ + 46, + 135, + 287, + 169 + ], + "spans": [ + { + "bbox": [ + 46, + 135, + 287, + 169 + ], + "type": "text", + "content": "Figure 7. Datasets for numerical evaluation. We evaluate ECON on images with unseen poses (left) and unseen outfits (right) on the CAPE [55] and Renderpeople [66] datasets, respectively." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 188, + 288, + 224 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 188, + 288, + 224 + ], + "spans": [ + { + "bbox": [ + 46, + 188, + 288, + 224 + ], + "type": "text", + "content": "body " + }, + { + "bbox": [ + 46, + 188, + 288, + 224 + ], + "type": "inline_equation", + "content": "\\mathcal{M}^{\\mathrm{b}}" + }, + { + "bbox": [ + 46, + 188, + 288, + 224 + ], + "type": "text", + "content": ". The necessity of (3) arises from the poorly reconstructed hands/face in " + }, + { + "bbox": [ + 46, + 188, + 288, + 224 + ], + "type": "inline_equation", + "content": "\\mathcal{R}_{\\mathrm{IF}}" + }, + { + "bbox": [ + 46, + 188, + 288, + 224 + ], + "type": "text", + "content": ", see difference in Fig. 6. The approach is denoted as " + }, + { + "bbox": [ + 46, + 188, + 288, + 224 + ], + "type": "inline_equation", + "content": "\\mathrm{ECON_{IF}}" + }, + { + "bbox": [ + 46, + 188, + 288, + 224 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 225, + 288, + 321 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 225, + 288, + 321 + ], + "spans": [ + { + "bbox": [ + 46, + 225, + 288, + 321 + ], + "type": "text", + "content": "Notably, although " + }, + { + "bbox": [ + 46, + 225, + 288, + 321 + ], + "type": "inline_equation", + "content": "\\mathcal{R}_{\\mathrm{IF}}" + }, + { + "bbox": [ + 46, + 225, + 288, + 321 + ], + "type": "text", + "content": " is already a complete human mesh, due to the lossy voxelization of inputs and limited resolution of Marching cubes algorithm, it somehow smooths out the details of " + }, + { + "bbox": [ + 46, + 225, + 288, + 321 + ], + "type": "inline_equation", + "content": "\\tilde{\\mathcal{Z}}_{\\{\\mathrm{F,B}\\}}^{\\mathrm{c}} / \\mathcal{M}_{\\{\\mathrm{F,B}\\}}" + }, + { + "bbox": [ + 46, + 225, + 288, + 321 + ], + "type": "text", + "content": ", which are optimized via d-BiNI (see " + }, + { + "bbox": [ + 46, + 225, + 288, + 321 + ], + "type": "inline_equation", + "content": "\\mathcal{R}_{\\mathrm{IF}}" + }, + { + "bbox": [ + 46, + 225, + 288, + 321 + ], + "type": "text", + "content": " vs ECON{IF,EX} in Fig. 5). While ECON{IF,EX} preserves d-BiNI details better, only the side-views and occluded parts of " + }, + { + "bbox": [ + 46, + 225, + 288, + 321 + ], + "type": "inline_equation", + "content": "\\mathcal{R}_{\\mathrm{IF}}" + }, + { + "bbox": [ + 46, + 225, + 288, + 321 + ], + "type": "text", + "content": " are fused in the Poisson step. In Tabs. 1 and 4, we use ECON{IF,EX} instead of " + }, + { + "bbox": [ + 46, + 225, + 288, + 321 + ], + "type": "inline_equation", + "content": "\\mathcal{R}_{\\mathrm{IF}}" + }, + { + "bbox": [ + 46, + 225, + 288, + 321 + ], + "type": "text", + "content": " for evaluation." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 331, + 128, + 344 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 331, + 128, + 344 + ], + "spans": [ + { + "bbox": [ + 47, + 331, + 128, + 344 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 350, + 110, + 361 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 350, + 110, + 361 + ], + "spans": [ + { + "bbox": [ + 47, + 350, + 110, + 361 + ], + "type": "text", + "content": "4.1. Datasets" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 369, + 288, + 429 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 369, + 288, + 429 + ], + "spans": [ + { + "bbox": [ + 46, + 369, + 288, + 429 + ], + "type": "text", + "content": "Training on THuman2.0. THuman2.0 [88] contains 525 high-quality human textured scans in various poses, which are captured by a dense DSLR rig, along with their corresponding SMPL-X fits. We use THuman2.0 to train ICON, ECON" + }, + { + "bbox": [ + 46, + 369, + 288, + 429 + ], + "type": "inline_equation", + "content": "_{\\text{IF}}" + }, + { + "bbox": [ + 46, + 369, + 288, + 429 + ], + "type": "text", + "content": " (IF-Nets+), IF-Nets, PIFu and PaMIR." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 431, + 288, + 552 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 431, + 288, + 552 + ], + "spans": [ + { + "bbox": [ + 46, + 431, + 288, + 552 + ], + "type": "text", + "content": "Quantitative evaluation on CAPE & Renderpeople. We primarily evaluate on CAPE [55] and Renderpeople [66]. Specifically, we use the \"CAPE-NFP\" set (100 scans), which is used by ICON to analyze robustness to complex human poses. Moreover, we select another 100 scans from Renderpeople, containing loose clothing, such as dresses, skirts, robes, down jackets, costumes, etc. With such clothing variance, Renderpeople helps numerically evaluate the flexibility of reconstruction methods w.r.t. shape topology. Samples of the two datasets are shown in Fig. 7." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 558, + 106, + 569 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 558, + 106, + 569 + ], + "spans": [ + { + "bbox": [ + 47, + 558, + 106, + 569 + ], + "type": "text", + "content": "4.2. Metrics" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 576, + 288, + 635 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 576, + 288, + 635 + ], + "spans": [ + { + "bbox": [ + 46, + 576, + 288, + 635 + ], + "type": "text", + "content": "Chamfer and P2S distance (cm). To capture large geometric errors, e.g. occluded parts or wrongly positioned limbs, we report the commonly used Chamfer (bi-directional point-to-surface) and P2S distance (1-directional point-to-surface) between ground-truth and reconstructed meshes." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 636, + 288, + 708 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 636, + 288, + 708 + ], + "spans": [ + { + "bbox": [ + 46, + 636, + 288, + 708 + ], + "type": "text", + "content": "Normal difference (L2). To measure the fineness of reconstructed local details, as well as projection consistency from the input image, we also report the L2 error between normal images rendered from reconstructed and ground-truth surfaces, by rotating a virtual camera around these by " + }, + { + "bbox": [ + 46, + 636, + 288, + 708 + ], + "type": "inline_equation", + "content": "\\{0^{\\circ}, 90^{\\circ}, 180^{\\circ}, 270^{\\circ}\\}" + }, + { + "bbox": [ + 46, + 636, + 288, + 708 + ], + "type": "text", + "content": " w.r.t. to a frontal view." + } + ] + } + ], + "index": 10 + }, + { + "type": "table", + "bbox": [ + 307, + 69, + 547, + 146 + ], + "blocks": [ + { + "bbox": [ + 307, + 69, + 547, + 146 + ], + "lines": [ + { + "bbox": [ + 307, + 69, + 547, + 146 + ], + "spans": [ + { + "bbox": [ + 307, + 69, + 547, + 146 + ], + "type": "table", + "html": "
MethodsData-drivenOOD poses (CAPE)OOD outfits (Renderpeople)
Chamfer ↓P2S ↓Normals ↓Chamfer ↓P2S ↓Normals ↓
w/o SMPL-X body prior
PIFu *✓1.7221.5480.06741.7061.6420.0709
PIFuHD†✓3.7673.5910.09941.9461.9830.0658
w/ GT SMPL-X body prior
PaMIR *✓0.9890.9920.04221.2961.4300.0518
ICON✓0.9710.9090.04091.3731.5220.0566
ECONIF✓0.9960.9670.04131.4011.4220.0516
ECONEXX0.9260.9170.03671.3421.4580.0478
", + "image_path": "e0cc8f13ec93b7ce45d0f5f473c3caeeb3af5cec9d1bb57dcbd56dce221372c2.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "table_body" + } + ], + "index": 11 + }, + { + "type": "table", + "bbox": [ + 307, + 232, + 553, + 280 + ], + "blocks": [ + { + "bbox": [ + 304, + 154, + 547, + 221 + ], + "lines": [ + { + "bbox": [ + 304, + 154, + 547, + 221 + ], + "spans": [ + { + "bbox": [ + 304, + 154, + 547, + 221 + ], + "type": "text", + "content": "Table 1. Evaluation against the state of the art. All models use a resolution of 256 for marching cubes. *Methods are re-implemented in [82] for a fair comparison in terms of network settings and training data. †Official model is trained on the Renderpeople dataset. ECONEX is optimization-based, thus requires no training (X). “OOD” is short for “out-of-distribution”." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 307, + 232, + 553, + 280 + ], + "lines": [ + { + "bbox": [ + 307, + 232, + 553, + 280 + ], + "spans": [ + { + "bbox": [ + 307, + 232, + 553, + 280 + ], + "type": "table", + "html": "
ICON [82]PIFuHD [71]PaMIR [96]
Challenging poses0.2830.1080.132
Loose clothing0.1470.3620.232
Fashion images0.1990.5510.290
", + "image_path": "28f64b81f1f35a1d82df4e269da05bb60943080ac0375646cd9be13cc38716a5.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "table_body" + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 289, + 547, + 333 + ], + "lines": [ + { + "bbox": [ + 304, + 289, + 547, + 333 + ], + "spans": [ + { + "bbox": [ + 304, + 289, + 547, + 333 + ], + "type": "text", + "content": "Table 2. Perceptual study. Numbers denote the chance that participants prefer the reconstruction of a competing method over ECON for in-the-wild images. A value of 0.5 indicates equal preference. A value of " + }, + { + "bbox": [ + 304, + 289, + 547, + 333 + ], + "type": "inline_equation", + "content": "< 0.5" + }, + { + "bbox": [ + 304, + 289, + 547, + 333 + ], + "type": "text", + "content": " favors ECON, while of " + }, + { + "bbox": [ + 304, + 289, + 547, + 333 + ], + "type": "inline_equation", + "content": ">0.5" + }, + { + "bbox": [ + 304, + 289, + 547, + 333 + ], + "type": "text", + "content": " favors competitors." + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 306, + 355, + 380, + 366 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 355, + 380, + 366 + ], + "spans": [ + { + "bbox": [ + 306, + 355, + 380, + 366 + ], + "type": "text", + "content": "4.3. Evaluation" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 373, + 547, + 529 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 373, + 547, + 529 + ], + "spans": [ + { + "bbox": [ + 304, + 373, + 547, + 529 + ], + "type": "text", + "content": "Quantitative evaluation. We compare ECON with body-agnostic methods, i.e., PIFu [70] and PIFuHD [71], and body-aware methods, i.e., PaMIR [96] and ICON [82]; see in Tab. 1. For fair comparison, we use re-implementations of PIFu and PaMIR from ICON [82], because they have the same network settings and input data. " + }, + { + "bbox": [ + 304, + 373, + 547, + 529 + ], + "type": "inline_equation", + "content": "\\mathrm{ECON_{EX}}" + }, + { + "bbox": [ + 304, + 373, + 547, + 529 + ], + "type": "text", + "content": " performs on par with ICON, and outperforms other methods on images containing out-of-distribution (OOD) poses (CAPE), with a distance error below " + }, + { + "bbox": [ + 304, + 373, + 547, + 529 + ], + "type": "inline_equation", + "content": "1\\mathrm{cm}" + }, + { + "bbox": [ + 304, + 373, + 547, + 529 + ], + "type": "text", + "content": ". In terms of out-of-distribution outfitsits (Renderpeople), " + }, + { + "bbox": [ + 304, + 373, + 547, + 529 + ], + "type": "inline_equation", + "content": "\\mathrm{ECON_{EX/IF}}" + }, + { + "bbox": [ + 304, + 373, + 547, + 529 + ], + "type": "text", + "content": " performs on par with PaMIR, and much better than PIFuHD. When it comes to high-frequency details measured by normals, " + }, + { + "bbox": [ + 304, + 373, + 547, + 529 + ], + "type": "inline_equation", + "content": "\\mathrm{ECON_{EX}}" + }, + { + "bbox": [ + 304, + 373, + 547, + 529 + ], + "type": "text", + "content": " achieves SOTA performance on both datasets." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 533, + 547, + 617 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 533, + 547, + 617 + ], + "spans": [ + { + "bbox": [ + 304, + 533, + 547, + 617 + ], + "type": "text", + "content": "Perceptual study. Due to the lack of ground-truth geometry (clothed scan + underneath SMPL-X), we further conduct a perceptual study to evaluate ECON on in-the-wild images. Test images are divided into three categories: \"challenging poses\", \"loose clothing\", and \"fashion images\". Examples of challenging poses and loose clothing can be seen in Fig. 9, and some of fashion images are in SupMat.'s Fig. S.2." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 618, + 547, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 618, + 547, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 618, + 547, + 714 + ], + "type": "text", + "content": "Participants are asked to choose the reconstruction they perceive as more realistic, between a baseline method and ECON. We compute the chances that each baseline is preferred over ECON in Tab. 2. The results of the perceptual study confirm the quantitative evaluation in Tab. 1. For \"challenging poses\" images, ECON is significantly preferred over PIFuHD and outperforms ICON. On images of people wearing loose clothing, ECON is preferred over ICON by a large" + } + ] + } + ], + "index": 18 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 297, + 748, + 312, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 748, + 312, + 757 + ], + "spans": [ + { + "bbox": [ + 297, + 748, + 312, + 757 + ], + "type": "text", + "content": "517" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 48, + 69, + 288, + 106 + ], + "blocks": [ + { + "bbox": [ + 48, + 69, + 288, + 106 + ], + "lines": [ + { + "bbox": [ + 48, + 69, + 288, + 106 + ], + "spans": [ + { + "bbox": [ + 48, + 69, + 288, + 106 + ], + "type": "table", + "html": "
MethodsOOD poses (CAPE [55])OOD outfitsits (Renderpeople) [66]Speed FPS ↑
RMSE ↓MAE ↓RMSE ↓MAE ↓
BiNI [7]27.6421.1120.6116.070.52
d-BiNI13.4310.2914.4311.260.69
", + "image_path": "a37b6e6fe5586aeb79021d082a8246de1b2ccf8a899626d9a4559a56601ab08a.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 50, + 144, + 288, + 188 + ], + "blocks": [ + { + "bbox": [ + 47, + 109, + 287, + 131 + ], + "lines": [ + { + "bbox": [ + 47, + 109, + 287, + 131 + ], + "spans": [ + { + "bbox": [ + 47, + 109, + 287, + 131 + ], + "type": "text", + "content": "Table 3. BiNI vs d-BiNI. Comparison between BiNI and d-BiNI surfaces w.r.t. reconstruction accuracy and optimization speed." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 50, + 144, + 288, + 188 + ], + "lines": [ + { + "bbox": [ + 50, + 144, + 288, + 188 + ], + "spans": [ + { + "bbox": [ + 50, + 144, + 288, + 188 + ], + "type": "table", + "html": "
MethodsOOD poses (CAPE)OOD outfits (Renderpeople)
Chamfer ↓P2S ↓Normals ↓Chamfer ↓P2S ↓Normals ↓
IF-Nets [10]2.1161.2330.0751.8831.6220.070
IF-Nets+1.4011.3530.0561.4771.5640.055
ECONIF0.9960.9670.04131.4011.4220.0516
", + "image_path": "2bbb5dff1fdb6c14a1c905c3f7172aa18b75cb6a8aabca33c63a617d51c03871.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 190, + 288, + 212 + ], + "lines": [ + { + "bbox": [ + 47, + 190, + 288, + 212 + ], + "spans": [ + { + "bbox": [ + 47, + 190, + 288, + 212 + ], + "type": "text", + "content": "Table 4. Evaluation for shape completion. Same metrics as Tab. 1, and " + }, + { + "bbox": [ + 47, + 190, + 288, + 212 + ], + "type": "inline_equation", + "content": "\\mathrm{ECON_{IF}}" + }, + { + "bbox": [ + 47, + 190, + 288, + 212 + ], + "type": "text", + "content": " is added as a reference." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "text" + }, + { + "type": "image", + "bbox": [ + 50, + 226, + 287, + 339 + ], + "blocks": [ + { + "bbox": [ + 50, + 226, + 287, + 339 + ], + "lines": [ + { + "bbox": [ + 50, + 226, + 287, + 339 + ], + "spans": [ + { + "bbox": [ + 50, + 226, + 287, + 339 + ], + "type": "image", + "image_path": "be782cbee65257d7562303accd6e67cee66269bed332183a360618483c1d6bfb.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 352, + 288, + 396 + ], + "lines": [ + { + "bbox": [ + 46, + 352, + 288, + 396 + ], + "spans": [ + { + "bbox": [ + 46, + 352, + 288, + 396 + ], + "type": "text", + "content": "Figure 8. Failure examples of ECON. (A-B) Failures in recovering a SMPL-X body result, e.g., bent legs or wrong limb poses, cause ECON failures by extension. (C-D) Failures in normal-map estimation provide erroneous geometry to ECON to work with." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 419, + 288, + 468 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 419, + 288, + 468 + ], + "spans": [ + { + "bbox": [ + 46, + 419, + 288, + 468 + ], + "type": "text", + "content": "margin and outperforms PIFuHD. The reasons for a slight preference of PIFuHD over ECON on fashion images are discussed in Sec. 5. Figure 2 visualizes some comparisons. More examples are provided in Figs. S.7 to S.9 of the SupMat." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 478, + 138, + 490 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 478, + 138, + 490 + ], + "spans": [ + { + "bbox": [ + 47, + 478, + 138, + 490 + ], + "type": "text", + "content": "4.4. Ablation study" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 497, + 288, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 497, + 288, + 628 + ], + "spans": [ + { + "bbox": [ + 46, + 497, + 288, + 628 + ], + "type": "text", + "content": "d-BiNI vs BiNI. We compare d-BiNI with BiNI using 600 samples (200 scans x 3 views) from CAPE and Renderpeople where ground-truth normal maps and meshes are available. Table 3 reports the \"root mean squared error\" (RMSE) and \"mean absolute error\" (MAE) between the estimated and rendered depth maps. d-BiNI significantly improves the reconstruction accuracy by about " + }, + { + "bbox": [ + 46, + 497, + 288, + 628 + ], + "type": "inline_equation", + "content": "50\\%" + }, + { + "bbox": [ + 46, + 497, + 288, + 628 + ], + "type": "text", + "content": " compared to BiNI. This demonstrates the efficacy of using the coarse body mesh as regularization and taking the consistency of both the front and back surface into consideration. Additionally, d-BiNI is " + }, + { + "bbox": [ + 46, + 497, + 288, + 628 + ], + "type": "inline_equation", + "content": "33\\%" + }, + { + "bbox": [ + 46, + 497, + 288, + 628 + ], + "type": "text", + "content": " faster than BiNI." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 630, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 630, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 630, + 288, + 713 + ], + "type": "text", + "content": "IF-Nets+ vs IF-Nets. Following the metrics of Sec. 4.2, we compare IF-Nets [10] with our IF-Nets+ on " + }, + { + "bbox": [ + 46, + 630, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{R}_{\\mathrm{IF}}" + }, + { + "bbox": [ + 46, + 630, + 288, + 713 + ], + "type": "text", + "content": ". We show the quantitative comparison in Tab. 4. The improvement for out-of-distribution (\"OOD\") poses shows that IF-Nets+ is more robust to pose variations than IF-Nets, as it is conditioned on the SMPL-X body. Figure 5 compares the geometry \" inpainting\" of both methods in the case of occlusions." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 72, + 462, + 84 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 72, + 462, + 84 + ], + "spans": [ + { + "bbox": [ + 306, + 72, + 462, + 84 + ], + "type": "text", + "content": "4.5. Multi-person reconstruction" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 91, + 547, + 174 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 91, + 547, + 174 + ], + "spans": [ + { + "bbox": [ + 304, + 91, + 547, + 174 + ], + "type": "text", + "content": "Thanks to the shape completion module, ECON can deal with occlusions. Unlike other crowd body estimators [73-75, 86], ECON makes it possible to reconstruct multiple detailed \"clothed\" 3D humans from an image with interperson occlusions, even though ECON has not been trained for this. Figure 10 shows three examples. The occluded parts, colored in red, are successfully recovered." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 185, + 375, + 197 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 185, + 375, + 197 + ], + "spans": [ + { + "bbox": [ + 306, + 185, + 375, + 197 + ], + "type": "text", + "content": "5. Discussion" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 205, + 547, + 348 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 205, + 547, + 348 + ], + "spans": [ + { + "bbox": [ + 304, + 205, + 547, + 348 + ], + "type": "text", + "content": "Limitations. ECON takes as input an RGB image and an estimated SMPL-X body. However, recovering SMPL-X bodies (or similar models) from a single image is still an open problem, and not fully solved. Any failure in this could lead to ECON failures, such as in Fig. 8-A and Fig. 8-B. As the synthetic data [6,28,78] is getting sufficiently realistic, their domain gap with real data is significantly narrowed, it is predictable that such limitations will be eliminated. The reconstruction quality of ECON primarily relies on the accuracy of the predicted normal maps. Poor normal maps can result in overly close-by or even intersecting front and back surfaces, as shown in Fig. 8-C and Fig. 8-D." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 351, + 547, + 495 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 351, + 547, + 495 + ], + "spans": [ + { + "bbox": [ + 304, + 351, + 547, + 495 + ], + "type": "text", + "content": "Future work. Apart from addressing the above limitations, several other directions are useful for practical applications. Currently, ECON reconstructs only 3D geometry. One could additionally recover an underlying skeleton and skinning weights [45, 84], to obtain fully-animatable avatars. Moreover, generating back-view texture [8,67,68,94] would result in fully-textured avatars. Disentangling clothing [1,63,99], hairstyle [89], or accessories [19] from the recovered geometry, would enable the simulation [23], synthesis, editing and transfer of styles [16] for these. ECON's reconstructions, together with its underneath SMPL-X body, could be useful as 3D shape prior to learn neural avatars [13,24,32]." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 495, + 547, + 638 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 495, + 547, + 638 + ], + "spans": [ + { + "bbox": [ + 304, + 495, + 547, + 638 + ], + "type": "text", + "content": "In particular, ECON could be used to augment existing datasets of 2D images with 3D humans. Datasets of real clothed humans with 3D ground truth [55,60,66,88,97] are limited in size. In contrast, datasets of images without 3D ground truth are widely available in large sizes [17,21,51]. We can \"augment\" such datasets by reconstructing detailed 3D humans from their images. In SupMat., we apply ECON on SHHQ [17] and recover normal maps and 3D humans; see Fig. S.2. As ECON-like methods mature, they could produce pixel-aligned 3D humans from photos at scale, enabling the training of generative models of 3D clothed avatars with details [20,22,29,34,58,81,93]." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 642, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 642, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 642, + 547, + 713 + ], + "type": "text", + "content": "Possible negative impact. As the reconstruction matures, it opens the potential for low-cost realistic avatar creation. Although such a technique benefits entertainment, film production, tele-presence and future metaverse applications, it could also facilitate deep-fake avatars. Regulations must be established to clarify the appropriate use of such technology." + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 297, + 749, + 313, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 749, + 313, + 757 + ], + "spans": [ + { + "bbox": [ + 297, + 749, + 313, + 757 + ], + "type": "text", + "content": "518" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 47, + 49, + 545, + 330 + ], + "blocks": [ + { + "bbox": [ + 47, + 49, + 545, + 330 + ], + "lines": [ + { + "bbox": [ + 47, + 49, + 545, + 330 + ], + "spans": [ + { + "bbox": [ + 47, + 49, + 545, + 330 + ], + "type": "image", + "image_path": "c7f125c2505c6f3dd4c10c859090ea41c66083281e346850cb76b8d96cce0b8e.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 331, + 548, + 366 + ], + "lines": [ + { + "bbox": [ + 46, + 331, + 548, + 366 + ], + "spans": [ + { + "bbox": [ + 46, + 331, + 548, + 366 + ], + "type": "text", + "content": "Figure 9. Qualitative results on in-the-wild images. We show 8 examples of reconstructing detailed clothed 3D humans from images with: (a) challenging poses and (b) loose clothing. For each example we show the input image along with two views (front and rotated) of the reconstructed 3D humans. Our approach is robust to pose variations, generalizes well to loose clothing, and contains detailed geometry." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 48, + 369, + 548, + 495 + ], + "blocks": [ + { + "bbox": [ + 48, + 369, + 548, + 495 + ], + "lines": [ + { + "bbox": [ + 48, + 369, + 548, + 495 + ], + "spans": [ + { + "bbox": [ + 48, + 369, + 548, + 495 + ], + "type": "image", + "image_path": "98e01d57b840d8b08dcbdfa68cfe73f538fe2ba74b1b3ea51000676b0f52f97e.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 502, + 547, + 537 + ], + "lines": [ + { + "bbox": [ + 46, + 502, + 547, + 537 + ], + "spans": [ + { + "bbox": [ + 46, + 502, + 547, + 537 + ], + "type": "text", + "content": "Figure 10. Multiple humans with occlusions.. We detect multiple people and apply ECON to each separately. Although ECON is not trained on multiple people, it is robust to inter-person occlusions. We show three examples, and for each: (top) input image and the predicted front and back normal maps, (bottom) ECON's reconstruction. Red areas on the estimated mesh indicate occlusions." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 545, + 119, + 558 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 545, + 119, + 558 + ], + "spans": [ + { + "bbox": [ + 47, + 545, + 119, + 558 + ], + "type": "text", + "content": "6. Conclusion" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 570, + 289, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 570, + 289, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 570, + 289, + 714 + ], + "type": "text", + "content": "We propose ECON to reconstruct detailed clothed 3D humans from a color image. It combines estimated 2.5D front and back surfaces with and underlying 3D parametric body in a highly effective way. On the one hand, it is robust to novel poses, while on the other hand, it is capable of recovering loose clothing and geometric details, since the reconstructed shape is not over-constrained to the topology of the body. ECON achieves this by using and extending recent advances in variational normal integration [7] and shape completion [10]. It effectively extends these to the task of image-based 3D human reconstruction. We believe ECON can lead to both real-world applications and useful tools for" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 305, + 547, + 545, + 572 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 547, + 545, + 572 + ], + "spans": [ + { + "bbox": [ + 305, + 547, + 545, + 572 + ], + "type": "text", + "content": "the 3D vision community. The code and models are available at Econ.is.tue.mpg.de for research purposes." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 582, + 547, + 691 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 547, + 691 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 547, + 691 + ], + "type": "text", + "content": "Acknowledgments. We thank Lea Hering and Radek Daněček for proofreading, Yao Feng, Haven Feng and Weiyang Liu for valuable feedback, and Tsvetelina Alexiadis for perceptual study. We are especially grateful to Carlos Barreto (Blender Add-on), Teddy Huang (Docker Image), and Justin John (Windows Support). 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Text-decoupled, dense aligned 3D visual grounding. Different colours in the text correspond to different decoupled components. (a) Regular 3D visual grounding: locating objects requires comprehensively considering multiple semantic cues such as appearance attributes, object names, and spatial relationships. (b) Grounding without object name: not mentioning object names, avoiding short-cuts and forcing the model to predict the target based on other attributes." + ], + "image_footnote": [], + "bbox": [ + 84, + 411, + 281, + 501 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "object", + "text_level": 1, + "bbox": [ + 132, + 501, + 174, + 511 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "The door is rectangular in shape and has a small window on the upper portion.", + "bbox": [ + 104, + 513, + 269, + 544 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/4400dd0a945727ceef622bc3c5e8f0690423803330834afb82f85555e2001ac4.jpg", + "image_caption": [ + "(b2)", + "(b) Grounding without object name" + ], + "image_footnote": [], + "bbox": [ + 294, + 411, + 465, + 500 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "The white refrigerator is in front of the kitchen stove. It is to the left side of the room as one enters the kitchen.", + "bbox": [ + 305, + 510, + 460, + 550 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/ae632147d29a02f147beb464f4e3c9ef77972afa73fea37c4cd71179ee0c920e.jpg", + "image_caption": [ + "(a) Regular 3D visual grounding", + "(b3)" + ], + "image_footnote": [], + "bbox": [ + 478, + 410, + 674, + 500 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "It is a brown wooden object with a cloth seat and back. It has multicolored flower patterns on the seat, and back.", + "bbox": [ + 501, + 510, + 660, + 549 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/93a6364390e579218ec1bc03fe1b94393d594de807de3100819d811c815bd7ad.jpg", + "image_caption": [ + "(b4)" + ], + "image_footnote": [], + "bbox": [ + 683, + 412, + 880, + 501 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "This is a black object. It is located next to a tall shelf and there is a fan in front of it.", + "bbox": [ + 699, + 511, + 861, + 541 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 648, + 312, + 664 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "3D visual grounding aims to find the object within point clouds mentioned by free-form natural language descriptions with rich semantic cues. However, existing methods either extract the sentence-level features coupling all words or focus more on object names, which would lose the word-level information or neglect other attributes. To alleviate these issues, we present EDA that Explicitly Decouples the textual attributes in a sentence and conducts Dense Alignment between such fine-grained language and point cloud objects. Specifically, we first propose a text decoupling module to produce textual features for every semantic component. Then, we design two losses to supervise", + "bbox": [ + 75, + 675, + 470, + 858 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "the dense matching between two modalities: position alignment loss and semantic alignment loss. On top of that, we further introduce a new visual grounding task, locating objects without object names, which can thoroughly evaluate the model's dense alignment capacity. Through experiments, we achieve state-of-the-art performance on two widely-adopted 3D visual grounding datasets, ScanRefer and SR3D/NR3D, and obtain absolute leadership on our newly-proposed task. The source code is available at https://github.com/yanmin-wu/EDA.", + "bbox": [ + 500, + 650, + 890, + 800 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 500, + 814, + 630, + 830 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Multi-modal cues can highly benefit the 3D environment perception of an agent, including 2D images, 3D point clouds, and language. Recently, 3D visual grounding (3D VG) [8,50], also known as 3D object referencing [3], has at", + "bbox": [ + 500, + 839, + 890, + 901 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 810, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "* Corresponding author. This work was supported in part by Shenzhen Research Project under Grant JCYJ20220531093215035.", + "bbox": [ + 76, + 875, + 468, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "19231", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "tached much attention as an important 3D cross-modal task. Its objective is to find the target object in point cloud scenes by analyzing the descriptive query language, which requires understanding both 3D visual and linguistic context.", + "bbox": [ + 75, + 90, + 468, + 151 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Language utterances typically involve words describing appearance attributes, object categories, spatial relationships and other characteristics, as shown by different colours in Fig. 1(a), requiring that the model integrate multiple cues to locate the mentioned object. Compared with 2D Visual Grounding [18,19,67,71], the sparseness and incompleteness of point clouds, and the diversity of language descriptions produced by 3D multi-view, make 3D VG more challenging. Existing works made significant progress from the following perspectives: improving point cloud features extraction by sparse convolution [70] or 2D images assistance [68]; generating more discriminative object candidates through instance segmentation [33] or language modulation [46]; identifying complex spatial relationships between entities via graph convolution [23] or attention [6].", + "bbox": [ + 75, + 154, + 470, + 381 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "However, we observe two issues that remain unexplored. 1) Imbalance: The object name can exclude most candidates, and even in some cases, there is only one name-matched object, as the \"door\" and \"refrigerator\" in Fig. 1(b1, b2). This shortcut may lead to an inductive bias in the model that pays more attention to object names while weakening other properties such as appearance and relationships, resulting in imbalanced learning. 2) Ambiguity: Utterances frequently refer to multiple objects and attributes (such as \"black object, tall shelf, fan\" in Fig. 1(b4)), while the model's objective is to identify only the main object, leading to an ambiguous understanding of language descriptions. These insufficiencies of existing works stem from their characteristic of feature coupling and fusing implicitly. They input a sentence with different attribute words but output only one globally coupled sentence-level feature that subsequently matches the visual features of candidate objects. The coupled feature is ambiguous because some words may not describe the main object (green text in Fig. 1) but other auxiliary objects (red text in Fig. 1). Alternatively, using the cross-modal attention of the Transformer [21, 63] automatically and implicitly to fuse visual and text features. However, this may encourage the model to take shortcuts, such as focusing on object categories and ignoring other attributes, as previously discussed.", + "bbox": [ + 75, + 383, + 470, + 762 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Instead, we propose a more intuitive decoupled and explicit strategy. First, we parse the input text to decouple different semantic components, including the main object word, pronoun, attributes, relations, and auxiliary object words. Then, performing dense alignment between point cloud objects and multiple related decoupled components achieves fine-grained feature matching, which avoids the inductive bias resulting from imbalanced learning of different textual components. As the final grounding result, we", + "bbox": [ + 75, + 763, + 468, + 902 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "explicitly select the object with the highest similarity to the decoupled text components (instead of the entire sentence), avoiding ambiguity caused by irrelevant components. Additionally, to explore the limits of VG and examine the comprehensiveness and fine-graininess of visual-language perception of the model, we suggest a challenging new task: Grounding without object name (VG-w/o-ON), where the name is replaced by \"object\" (see Fig. 1(b)), forcing the model to locate objects based on other attributes and relationships. This setting makes sense because utterances that do not mention object names are common expressions in daily life, and in addition to testing whether the model takes shortcuts. Benefiting from our text decoupling operation and the supervision of dense aligned losses, all text components are aligned with visual features, making it possible to locate objects independent of object names.", + "bbox": [ + 496, + 90, + 890, + 332 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To sum up, the main contributions of this paper are as follows: 1) We propose a text decoupling module to parse linguistic descriptions into multiple semantic components, followed by suggesting two well-designed dense aligned losses for supervising fine-grained visual-language feature fusion and preventing imbalance and ambiguity learning. 2) The challenging new 3D VG task of grounding without object names is proposed to comprehensively examine the model's robust performance. 3) We achieve state-of-the-art performance on two datasets (ScanRefer and SR3D/NR3D) on the regular 3D VG task and absolute leadership on the new task evaluated by the same model without retraining.", + "bbox": [ + 496, + 334, + 890, + 515 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 500, + 532, + 640, + 547 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.1. 3D Vision and Language", + "text_level": 1, + "bbox": [ + 500, + 559, + 723, + 574 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "3D vision [52, 53, 75] and language are vital manners for humans to understand the environment, and they are also important research topics for the evolution of machines to be like humans. Previously, the two fields evolved independently. Due to the advance of multimodality [25, 26, 54, 56, 57, 72-74, 76], many promising works across 3D vision and language have been introduced recently. In 3D visual grounding [1, 8-10, 12], the speaker (like a human) describes an object in language. The listener (such a robot) needs to understand the language description and the 3D visual scene to grounding the target object. On the contrary, the 3D dense caption [9, 13, 14, 36, 65, 69] is analogous to an inverse process in which the input is a 3D scene, and the output is textual descriptions of each object. Language-modulated 3D detection or segmentation [7, 32, 34, 59, 78] enriches the diversity of text queries by matching visual-linguistic feature spaces rather than predicting the probability of a set number of categories. Furthermore, some studies explore the application of 3D visual language in agents such as robot perception [27, 61], vision-and-language navigation (VLN) [15, 31, 55], and embodied question answering", + "bbox": [ + 496, + 583, + 890, + 902 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "19232", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "(EQA) [4,22,30,45,47,62]. In this paper, we focus on point clouds-based 3D visual grounding, which is the fundamental technology for many embodied AI [24,38,48] tasks.", + "bbox": [ + 76, + 90, + 468, + 137 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "2.2.3D Visual Grounding", + "text_level": 1, + "bbox": [ + 76, + 148, + 277, + 166 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The majority of current mainstream techniques are two-stage. In the first stage, obtain the features of the query language and candidate point cloud objects independently by a pre-trained language model [16, 20, 49] and a pretrained 3D detector [44, 51] or segmenter [11, 35, 64]. In the second stage, the researchers focus on fusing the two modal features and then selecting the best-matched object. 1) The most straightforward solution is to concatenate the two modal features and then consider it a binary classification problem [8, 39], which provides limited performance because the two features are not sufficiently fused. 2) Taking advantage of the Transformer's attention mechanism, which is naturally suitable for multi-module feature fusion, He et al. [28] and Zhao et al. [77] achieve remarkable performance by performing self-attention and cross-attention to features. 3) In contrast, other studies view feature fusion as a matching problem rather than a classification. Yuan et al. [70] and Abdelreheem et al. [2], supervised by the contrastive loss [29], compute the cosine similarity of visual features and textual features. Inspired by [43], Feng et al. [23] parses the text to generate a text scene graph, simultaneously builds a visual scene graph, and then performs graph node matching. 4) Point clouds' sparse, noisy, incomplete, and lack of detail make learning objects' semantic information challenging. Yang et al. [68] and Cai et al. [6] use 2D images to aid visual-textual feature fusion, but at the cost of additional 2D-3D alignment and 2D feature extraction.", + "bbox": [ + 75, + 174, + 472, + 595 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "However, the two-stage method has a substantial detection bottleneck: objects overlooked in the first stage cannot be matched in the second. In contrast, object detection and feature extraction in the single-stage method is modulated by the query text, making it easier to identify the text-concerned object. Liu et al. [41] suggest fusing visual and linguistic features at the bottom level and producing text-related visual heatmaps. Similarly, Luo et al. [46] present a single-stage approach that employs textual features to guide visual keypoint selection and progressively localizes objects. BUTD-DETR [34] is also a single-stage capable framework. More importantly, inspired by the 2D image-language pre-train model (such MDETR [37], GLIP [40]), BUTD-DETR measures the similarity between each word and object and then selects the features of the word that correspond to the object's name to match the candidate object. However, there are two limitations: 1) Since multiple object names may be mentioned in a sentence, the ground truth annotation is needed to retrieve the target name, which limits its generalizability. Our text decoupling module separates", + "bbox": [ + 75, + 598, + 472, + 901 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/10e36a3a2c181dd5eb1f22ca1a614a4778f9455a969824f0fdf3054272275376.jpg", + "image_caption": [ + "Figure 2. Text component decoupling: (a) The query text. (b) Dependency tree analysis. (c) Decoupled into five components." + ], + "image_footnote": [], + "bbox": [ + 513, + 87, + 880, + 218 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "text components and determines the target object name by grammatical analysis to avoid this restriction. 2) BUTD-DETR (and MDETR and GLIP in the 2D task) only consider the sparse alignment of main object words or noun phrases to visual features. Conversely, we align all object-related decoupled textual semantic components with visual features, which we refer to dense alignment, significantly enhancing the discriminability of multimodal features.", + "bbox": [ + 496, + 271, + 890, + 393 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Proposed Method", + "text_level": 1, + "bbox": [ + 500, + 405, + 671, + 422 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The framework is illustrated in Fig. 3. First, the input text description is decoupled into multiple semantic components, and its affiliated text positions and features are obtained (Sec. 3.1). Concurrently, the Transformer-based encoder extracts and modulates features from point clouds and text, then decodes the visual features of candidate objects (Sec. 3.2). Finally, the dense aligned losses are derived between the decoupled text features and the decoded visual features (Sec. 3.3). The grounding result is the object with visual features most similar to text features (Sec. 3.4).", + "bbox": [ + 496, + 430, + 890, + 582 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Text Decoupling", + "text_level": 1, + "bbox": [ + 500, + 590, + 661, + 606 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The text features of the coupled strategy are ambiguous, where features from multiple objects and attributes are coupled, such as \"a brown wooden chair next to the black table.\" Among them, easy-to-learn clues (such as the category \"chair\" or the colour \"brown\") may predominate, weakening other attributes (such as material \"wooden\"); words of other objects (such as the \"black table\") may cause interference. To produce more discriminative text features and fine-grained cross-modal feature fusion, we decouple the query text into different semantic components, each independently aligned with visual features, avoiding the ambiguity caused by feature coupling.", + "bbox": [ + 496, + 613, + 890, + 794 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Text Component Decoupling. Analyzing grammatical dependencies between words is a fundamental task in NLP. We first use the off-the-shelf tool [60, 66] to parse the language description grammatically to generate the grammatical dependency trees, as shown in Fig. 2(b). Each sentence contains only one ROOT node, and each remaining word has a corresponding parent node. Then according to", + "bbox": [ + 496, + 795, + 890, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "19233", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/1d4faa68d8b73bd3752367807d2dc0c5a0a5ba012103c809f584a5930d2e9438.jpg", + "image_caption": [ + "Figure 3. The system framework. (a-c): Decouple the input text into several components to acquire the position label $L$ and features $t$ of the decoupled text. (d-e): Transformer-based encoders for cross-modal visual-text feature extraction. (f): Decode proposal features $\\mathcal{O}'$ and linearly project them as object position labels $L_{pred}$ and object features $o$ , in addition to a box prediction head for regression of the bounding box. (g-h): Visual-text feature dense alignment. Note that the additional 3D object detection procedure is optional." + ], + "image_footnote": [], + "bbox": [ + 78, + 88, + 893, + 364 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "the words' part-of-speech and dependencies, we decouple the long text into five semantic components (see Fig. 2(c)): Main object - the target object mentioned in the utterance; Auxiliary object - the one used to assist in locating the main object; Attributes - objects' appearance, shape, etc.; Pronoun - the word instead of the main object; Relationship - the spatial relation between the main object and the auxiliary object. Note that attributes affiliated with pronouns are equivalent to attached with the main object, thus connecting two sentences in an utterance.", + "bbox": [ + 75, + 455, + 468, + 606 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Text Position Decoupling. After decoupling each text component (Fig. 3(a)), we generate the position label (similar to a mask) $L_{\\text{main}}, L_{\\text{attr}}, L_{\\text{auxi}}, L_{\\text{pron}}, L_{\\text{rel}} \\in \\mathbb{R}^{1 \\times l}$ for the component's associated word (Fig. 3(b)). Where $l = 256$ is the maximum length of the text, each component's word position is set to 1 and the rest to 0. The label will be used to construct the position alignment loss and supervise the classification of objects. The classification result, is not one of a predetermined number of object categories but the position of the text with the highest semantic similarity.", + "bbox": [ + 75, + 609, + 468, + 761 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Text Feature Decoupling. The feature of each word (token) is produced in the backbone of multimodal feature extraction (Fig. 3(d)). The text feature of the decoupled component can be derived by dot-multiplying all words' features $\\pmb{t}$ with its position label $L$ , as shown in Fig. 3(c). The decoupled text features and visual features will be independently aligned under the supervision of the semantic alignment loss. Note that in the decoupled text features, the semantics of the corresponding components absolutely", + "bbox": [ + 75, + 763, + 470, + 902 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "predominate, but as a result of the Transformer's attention mechanism, it also implicitly contains the global sentence's information. In other words, feature decoupling produces individual features while keeping the global context.", + "bbox": [ + 498, + 455, + 892, + 517 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. Multimodal Feature Extraction", + "text_level": 1, + "bbox": [ + 500, + 527, + 777, + 542 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We employ BUTD-DETR's encoder-decoder module for feature extraction and intermodulation of cross-modal features. We strongly recommend the reader to refer to Fig. 3.", + "bbox": [ + 498, + 551, + 892, + 595 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Input Modal Tokenization. The input text and 3D point clouds are encoded by the pre-trained RoBERTa [42] and PointNet++ [53] and produce text tokens $\\mathcal{T} \\in \\mathbb{R}^{l \\times d}$ and visual tokens $\\mathcal{V} \\in \\mathbb{R}^{n \\times d}$ . Additionally, the GroupFree [44] detector is used to detect 3D boxes, which are subsequently encoded as box tokens $\\mathcal{B} \\in \\mathbb{R}^{b \\times d}$ . Note that the GroupFree is optional, the final predicted object of the network is from the prediction head (see below), and the box token is just to assist in better regression of the target object.", + "bbox": [ + 496, + 597, + 890, + 733 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Encoder-Decoder. Self-attention and cross-attention are performed in the encoder to update both visual and text features, obtaining cross-modal features $\\mathcal{V}'$ , $\\mathcal{T}'$ while keeping the dimensions. The top- $k$ ( $k = 256$ ) visual features are selected, linearly projected as query proposal features $\\mathcal{O} \\in \\mathbb{R}^{k \\times d}$ , and updated as $\\mathcal{O}'$ in the decoder.", + "bbox": [ + 496, + 734, + 890, + 824 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Prediction Head. 1) The decoded proposal features $\\mathcal{O}' \\in \\mathbb{R}^{k \\times d}$ are fed into an MLP and output the predicted position labels $L_{pred} \\in \\mathbb{R}^{k \\times l}$ , which are then utilized to calculate the position alignment loss with decoupled text position labels $L \\in \\mathbb{R}^{1 \\times l}$ . 2) Additionally, the proposal fea", + "bbox": [ + 496, + 825, + 892, + 901 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "19234", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "tures are linearly projected as object features $\\pmb{o} \\in \\mathbb{R}^{k \\times 64}$ by another MLP, which are then utilized to compute the semantic alignment loss with the similarly linearly projected text feature $\\pmb{t} \\in \\mathbb{R}^{l \\times 64}$ . 3) Lastly, a box prediction head [44] regresses the bounding box of the object.", + "bbox": [ + 75, + 89, + 468, + 167 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.3. Dense Aligned Loss", + "text_level": 1, + "bbox": [ + 76, + 174, + 264, + 189 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.3.1 Dense Position Aligned Loss", + "text_level": 1, + "bbox": [ + 76, + 196, + 326, + 212 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The objective of position alignment is to ensure that the distribution of language-modulated visual features closely matches that of the query text description, as shown in Fig. 3(g). This process is similar to standard object detection's one-hot label prediction. However, rather than being limited by the number of categories, we predict the position of text that is similar to objects.", + "bbox": [ + 75, + 220, + 468, + 325 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The constructed ground truth text distribution of the mentioned main object is obtained by element-wise summing the position labels of the associated decoupled text components:", + "bbox": [ + 75, + 325, + 468, + 387 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nP _ {\\text {m a i n}} = \\lambda_ {1} L _ {\\text {m a i n}} + \\lambda_ {2} L _ {\\text {a t t r i}} + \\lambda_ {3} L _ {\\text {p r o n}} + \\lambda_ {4} L _ {\\text {r e l}}, \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 86, + 393, + 468, + 411 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\lambda$ is the weight of different parts (refer to the parametric search in Supplementary Material.). $P_{auxi} = L_{auxi}$ represents the text distribution of the auxiliary object. The remaining candidate objects' text distribution is $P_{oth}$ , with the final bit set to 1 (see $\\varnothing$ in Fig. 3(g)). Therefore, all $k$ candidate objects' ground truth text distribution is $P_{text} = \\{P_{main}, P_{auxi}, P_{oth}\\} \\in \\mathbb{R}^{k \\times l}$ .", + "bbox": [ + 75, + 417, + 468, + 523 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The predicted visual distribution of $k$ objects is produced by applying softmax to the output $L_{pred} \\in \\mathbb{R}^{k \\times l}$ of the prediction head:", + "bbox": [ + 75, + 523, + 468, + 568 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nP _ {o b j} = \\operatorname {S o f t m a x} \\left(L _ {p r e d}\\right). \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 183, + 577, + 468, + 594 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Their KL divergence is defined as the position-aligned loss:", + "bbox": [ + 76, + 599, + 467, + 614 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {p o s} = \\sum_ {i = 1} ^ {k} \\left[ P _ {t e x t} ^ {i} \\log \\left(P _ {t e x t} ^ {i}\\right) - P _ {t e x t} ^ {i} \\log \\left(P _ {o b j} ^ {i}\\right) \\right]. \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 102, + 633, + 468, + 674 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We highlight that \"dense alignment\" indicates that the target object is aligned with the positions of multiple components (Eq. (1)), significantly different from BUTD-DETR (and MDETR for 2D tasks), which only sparsely aligns with the object name's position $L_{main}$ .", + "bbox": [ + 75, + 681, + 468, + 757 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.3.2 Dense Semantic Aligned Loss", + "text_level": 1, + "bbox": [ + 76, + 773, + 334, + 789 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Semantic alignment aims to learn the similarity of visual-text multimodal features through contrastive learning. The object loss of semantic alignment is defined as follows:", + "bbox": [ + 75, + 796, + 468, + 839 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\text {s e m - o}} = \\sum_ {i = 1} ^ {k} \\frac {1}{| \\mathbf {T} _ {i} ^ {+} |} \\sum_ {\\boldsymbol {t} _ {i} \\in \\mathbf {T} _ {i} ^ {+}} - \\log \\left(\\frac {\\exp \\left(w _ {+} * \\left(\\boldsymbol {o} _ {i} ^ {\\top} \\boldsymbol {t} _ {i} / \\tau\\right)\\right)}{\\sum_ {j = 1} ^ {l} \\exp \\left(w _ {-} * \\left(\\boldsymbol {o} _ {i} ^ {\\top} \\boldsymbol {t} _ {j} / \\tau\\right)\\right)}\\right), \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 76, + 845, + 468, + 900 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\pmb{o}$ and $\\pmb{t}$ are the object and text features after linear projection, and $o^\\top t / \\tau$ is their similarity, as shown in Fig. 3 (h). $k$ and $l$ are the number of objects and words. $\\pmb{t}_i$ is the positive text feature of the $i_{th}$ candidate object. Taking the main object as an example, the positive text feature $\\mathbf{T}_i^+$ corresponding to it is:", + "bbox": [ + 498, + 90, + 890, + 181 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {t} _ {i} \\in \\mathbf {T} _ {i} ^ {+} = \\left\\{\\boldsymbol {t} _ {\\text {m a i n}}, \\boldsymbol {t} _ {\\text {a t t r i}}, \\boldsymbol {t} _ {\\text {p r o n}}, \\boldsymbol {t} _ {\\text {r e l}} \\right\\}, \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 563, + 196, + 890, + 215 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "and $w_{+}$ is the weight of each positive term. $t_j$ is the feature of the $i_{th}$ text, but note that the negative similarity weight $w_{-}$ for auxiliary object term $t_{auxi}$ is 2, while the rest weight 1. The text loss of semantic alignment defined similarly:", + "bbox": [ + 498, + 228, + 890, + 285 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {s e m - t} = \\sum_ {i = 1} ^ {l} \\frac {w _ {+}}{\\left| \\mathbf {O} _ {i} ^ {+} \\right|} \\sum_ {\\boldsymbol {o} _ {i} \\in \\mathbf {O} _ {i} ^ {+}} - \\log \\left(\\frac {\\exp \\left(\\boldsymbol {t} _ {i} ^ {\\top} \\boldsymbol {o} _ {i} / \\tau\\right)}{\\sum_ {j = 1} ^ {k} \\exp \\left(\\boldsymbol {t} _ {i} ^ {\\top} \\boldsymbol {o} _ {j} / \\tau\\right)}\\right), \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 509, + 299, + 890, + 354 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $o_i \\in \\mathbf{O}_i^+$ is the positive object feature of the $i_{th}$ text, and $o_j$ is the feature of the $j_{th}$ object. The final semantic alignment loss is the mean of the two: $\\mathcal{L}_{sem} = (\\mathcal{L}_{sem\\_o} + \\mathcal{L}_{sem\\_t}) / 2$ .", + "bbox": [ + 498, + 354, + 890, + 416 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Similarly, the semantic alignment of multiple text components (Eq. (5)) with visual features also illustrates our insight of \"dense.\" This is intuitive, such as \"It is a brown chair with legs under a blackboard,\" where the main object's visual features should be not only similar to \"chair\" but also similar to \"brown, legs\" and distinct to \"blackboard\" as possible.", + "bbox": [ + 496, + 417, + 890, + 523 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The total loss for training also includes the box regression loss. Refer to Supplementary Material for details.", + "bbox": [ + 498, + 525, + 890, + 555 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.4. Explicit Inference", + "text_level": 1, + "bbox": [ + 500, + 570, + 671, + 585 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Because of our text decoupling and dense alignment operations, object features fused multiple related text component features, allowing for the computation of the similarity between individual text components and candidate objects. For instance, $S_{main} = \\text{Softmax}(\\boldsymbol{o}^{\\top}\\boldsymbol{t}_{main} / \\tau)$ indicates the similarity between objects $\\boldsymbol{o}$ and the main text component $\\boldsymbol{t}_{main}$ . Therefore, the similarity of objects and related components can be explicitly combined to obtain the total score and select the candidate with the highest score:", + "bbox": [ + 496, + 595, + 890, + 731 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nS _ {a l l} = S _ {\\text {m a i n}} + S _ {\\text {a t t r i}} + S _ {\\text {p r o n}} + S _ {\\text {r e l}} - S _ {\\text {a u x i}}, \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 524, + 747, + 890, + 763 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where the definition of $S_{attri}$ , $S_{pron}$ , $S_{rel}$ , and $S_{auxi}$ is similar to $S_{main}$ . If providing supervision of auxiliary objects during training, and the auxiliary object can be identified by solely computing the similarity between the object features and the auxiliary component's text features: $S_{all} = S_{attri}$ . Being able to infer the object based on the part of the text is a significant sign that the network has learned well-aligned and fine-grained visual-text feature space.", + "bbox": [ + 496, + 779, + 890, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "19235", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 76, + 90, + 209, + 107 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "First, we conduct comprehensive and fair comparisons with SOTA methods in the Regular 3D Visual Grounding setting in Sec. 4.1. Then, in Sec. 4.2, we introduce our proposed new task, Grounding without Object Name, and perform comparison and analysis. Implementation details, additional experiments and more qualitative results are detailed in the supplementary material.", + "bbox": [ + 75, + 114, + 470, + 220 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.1. Regular 3D Visual Grounding", + "text_level": 1, + "bbox": [ + 76, + 229, + 344, + 244 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.1.1 Experiment settings", + "text_level": 1, + "bbox": [ + 76, + 253, + 269, + 268 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We keep the same settings as existing works, with ScanRefer [8] and SR3D/NR3D [3] as datasets and Acc@0.25IoU and Acc@0.5IoU as metrics. Based on the visual data of ScanNet [17], ScanRefer adds 51,583 manually annotated text descriptions about objects. These complex and free-form descriptions involve object categories and attributes such as colour, shape, size, and spatial relationships. SR3D/NR3D is also proposed based on ScanNet, with SR3D including 83,572 simple machine-generated descriptions and NR3D containing 41,503 descriptions similar to ScanRefer's human annotation. The difference is that in the ScanRefer configuration, detecting and matching objects are required, while SR3D/NR3D is simpler. It supplies GT boxes for all candidate objects and only needs to classify the classes of the boxes and choose the target object.", + "bbox": [ + 75, + 276, + 468, + 503 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.1.2 Comparison to the state of the art", + "text_level": 1, + "bbox": [ + 76, + 513, + 366, + 529 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "ScanRefer. Table 1 reports the results on the ScanRefer dataset. i) Our method achieves state-of-the-art performance by a substantial margin, with an overall improvement of $4.2\\%$ and $3.7\\%$ to $54.59\\%$ and $42.26\\%$ . ii) Some studies [6,8,9,46,68,77] proved that supplemented 2D images with detailed and dense semantics could learn better point cloud features. Surprisingly, we only use sparse 3D point cloud features and even outperformed 2D assistance methods. This superiority illustrates that our decoupling and dense alignment strategies mine more efficient and meaningful visual-text co-representations. iii) Another finding is that the accuracy of most existing techniques is less than $40\\%$ and $30\\%$ in the \"multiple\" setting because multiple means that the category of the target object mentioned in the language is not unique, with more interference candidates with the same category. However, we reached a remarkable $49.13\\%$ and $37.64\\%$ . To identify similar objects, a finer-grained understanding of the text and vision is required in this complex setting. iv) The last three rows in Table 1 compare single-stage methods, where our method's single-stage implementation is without the object detection step ( $\\mathcal{B}$ in Fig. 3) in training and inference. The result illustrates that while not requiring an additional pre-trained 3D object detector, our approach also can achieve SOTA performance.", + "bbox": [ + 75, + 537, + 470, + 902 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "v) The qualitative results are depicted in Fig. 4(a-c), which reveals that our method with an excellent perception of appearance attributes, spatial relationships, and even ordinal numbers.", + "bbox": [ + 496, + 90, + 890, + 150 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "SR3D/NR3D. Table 2 shows the accuracy on the SR3D/NR3D dataset, where we achieve the best performance of $68.1\\%$ and $52.1\\%$ . In SR3D, since the language descriptions are concise and the object is easy to identify, our method and [34, 46] reach an accuracy of over $60\\%$ . Conversely, in NR3D, descriptions are too detailed and complex, causing additional challenges for text decoupling. However, we still achieve SOTA accuracy with the 3D-only data, while other comparable methods [46, 68] rely on additional 2D images for training. Some methods [6, 8, 9] compared in Table 1 are not discussed here because they are not evaluated on the SR3D/NR3D dataset. In addition, because GT boxes of candidate objects are provided in this setting, the single-stage methods are not applicable and discussed.", + "bbox": [ + 496, + 151, + 892, + 364 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.1.3 Ablation studies", + "text_level": 1, + "bbox": [ + 498, + 377, + 666, + 391 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Loss ablation. The ablation of the position-aligned loss and the semantic-aligned loss is shown in Table 3. The performance of the semantic-aligned loss is marginally better because its contrastive loss not only shortens the distance between similar text-visual features but also enlarges the distance between dis-matched features (such as $t_{auxi}$ is a negative term in Eq. (4)). Whereas position-aligned loss only considers object-related components (as in Eq. (1)). When both losses supervise together, the best accuracy is achieved, demonstrating that they can produce complementary performance.", + "bbox": [ + 496, + 401, + 890, + 568 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Dense components ablation. To demonstrate our insight into dense alignment, we perform ablation analysis on the different decoupled text components, and the results are displayed in the \"Regular VG\" column in Table 4. Analysis: i) (a) is our baseline implementation of the sparse concept, using only the \"Main object\" component decoupled from the text. In contrast to BUTD-DETR, the text decoupling module (Sec. 3.1) is used to obtain text labels and features during training and inference instead of employing ground truth labels. ii) Dense-aligned sub-methods (b)-(h) outperform the sparse alignment (a) because of the finer-grained visual-linguistic feature fusion. iii) (b)-(e) indicate that adding any other component on top of the \"Main object\" improves performance, demonstrating the validity of each text component. The \"Attribute\" component aids in identifying characteristics such as colour, and shape, frequently mentioned in language descriptions. Unexpectedly, the \"Pronoun\" component such as \"it, that, and which\" have little meaning when used alone but also function in our method, indicating that the pronoun learned contextual information from the sentence. The \"Relationship\" component facilitates comprehension of spatial relationships be", + "bbox": [ + 496, + 569, + 892, + 901 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "19236", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/4a7d0252ba4a904c57efb7a7a01fb2bd7b1fc13f1ecd17425b8eadf01bce5caf.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodVenueModalityUnique (~19%)Multiple (~81%)Overall
0.250.50.250.50.250.5
ScanRefer [8]ECCV20203D67.6446.1932.0621.2638.9726.10
3D+2D76.3353.5132.7321.1141.1927.40
ReferIt3D [3]ECCV20203D53.837.521.012.826.416.9
TGNN [33]AAAI20213D68.6156.8029.8423.1837.3729.70
InstanceRefer [70]ICCV20213D77.4566.8331.2724.7740.2332.93
SAT [68]ICCV20213D+2D73.2150.8337.6425.1644.5430.14
FFL-3DOG [23]ICCV20213D78.8067.9435.1925.7041.3334.01
3DVG-Transformer [77]ICCV20213D77.1658.4738.3828.7045.9034.47
3D+2D81.9360.6439.3028.4247.5734.67
3D-SPS [46]CVPR20223D+2D84.1266.7240.3229.8248.8236.98
3DJCG [6]CVPR20223D78.7561.3040.1330.0847.6236.14
3D+2D83.4764.3441.3930.8249.5637.33
BUTD-DETR [34] †ECCV20223D82.8864.9844.7333.9750.4238.60
D3Net [9]ECCV20223D+2D-70.35-30.50-37.87
EDA-3D85.7668.5749.1337.6454.59 (+4.2%)42.26 (+3.7%)
3D-SPS(single-stage) [46]CVPR20223D81.6364.7739.4829.6147.6536.43
BUTD-DETR (single-stage) [34]‡ECCV20223D81.4761.2444.2032.8149.7637.05
EDA (single-stage) §-3D86.4069.4248.1136.8253.8341.70
", + "bbox": [ + 86, + 89, + 883, + 398 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/9037d79ceea271416f13156088e030025640ea32efcc36b7ac0b667a171ed3b5.jpg", + "table_caption": [ + "Table 1. The 3D visual grounding results on ScanRefer, accuracy evaluated by IoU 0.25 and IoU 0.5. † The accuracy is reevaluated using our parsed text labels because the performance reported by BUTD-DETR used ground truth text labels and ignored some challenging samples (see supplementary materials for more details). § Our single-stage implementation without the assistance of the additional 3D object detection step (dotted arrows in Fig. 3). ‡ BUTD-DETR did not provide single-stage results and we retrained the model." + ], + "table_footnote": [], + "table_body": "
MethodVenueModalitySR3DNR3D
ReferIt3D [3]ECCV203D39.835.6
TGNN [33]AAAI213D45.037.3
TransRefer3D [28]MM213D57.442.1
InstanceRefer [70]ICCV213D48.038.8
3DVG-Transfor. [77]ICCV213D51.440.8
FFL-3DOG [23]ICCV213D-41.7
SAT [68]ICCV213D+2D57.949.2
3DReferTrans. [2]WACV223D47.039.0
LanguageRefer [58]CoRL223D56.043.9
3D-SPS [46]CVPR223D+2D62.651.5
BUTD-DETR † [34]ECCV223D65.649.1
LAR [5]NeurIPS223D59.648.9
EDA (Ours)-3D68.152.1
", + "bbox": [ + 78, + 465, + 470, + 683 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "tween objects. The component \"Auxiliary object\" is a negative term in the loss (Eq. (4)). During inference (Eq. (7)), its similarity is subtracted in the hopes that the predicted main object is as dissimilar to it as possible. iv) (f)-(h) integrate different components to make performance gains and reach the peak when all are involved, demonstrating that the functions of each component can be complementary, and there may be no overlap between the features of each one. The result reveals that our method effectively decouples and matches fine-grained multimodal features.", + "bbox": [ + 75, + 750, + 472, + 902 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/e635ca81cbb771f28d3d0a5c883cf6fc41d0f396bb938cb95e11b99667f40934.jpg", + "table_caption": [ + "Table 2. Performance on SR3D/NR3D datasets by Acc@0.25IoU as the metric. The detailed results of EDA in four subsets are provided in the Supplementary Material. $\\dagger$ Reevaluated by parsed text labels (see supp. for more details)." + ], + "table_footnote": [], + "table_body": "
+Lpos+LsemAcc@0.25Acc@0.5
(a)✓51.239.6
(b)✓52.239.9
(c)✓✓54.642.3
", + "bbox": [ + 517, + 465, + 875, + 537 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/f995be33ee9bbf441e798c74561f14faf81f4df74b106a60e77b141640c1c233.jpg", + "table_caption": [ + "Table 3. Loss ablation on the ScanRefer dataset." + ], + "table_footnote": [], + "table_body": "
Dense componentsRegular VGVG-w/o-ON
MainAttri.Pron.Auxi.Rel.@0.25@0.5@0.25@0.5
(a)✓51.538.821.816.7
(b)✓✓53.141.323.217.8
(c)✓✓52.940.823.718.6
(d)✓✓52.941.023.218.4
(e)✓✓52.840.725.719.6
(f)✓✓✓53.841.824.218.5
(g)✓✓✓✓54.242.324.018.8
(h)✓✓✓✓✓54.642.326.521.2
", + "bbox": [ + 506, + 556, + 887, + 703 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 4. Ablation studies of different text components on Regular VG and VG-w/o-ON tasks. Evaluated on the ScanRefer dataset.", + "bbox": [ + 500, + 704, + 890, + 731 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.2. Grounding without Object Name (VG-w/o-ON)", + "text_level": 1, + "bbox": [ + 500, + 746, + 890, + 763 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.2.1 Experiment settings", + "text_level": 1, + "bbox": [ + 500, + 770, + 694, + 787 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "To evaluate the comprehensive reasoning ability of the model and avoid inductive biases about object names, we propose a new and more challenging task: grounding objects without mentioning object names (VG-w/o-ON). Specifically, we manually replace the object's name with \"object\" in the ScanRefer validation set. For instance: \"This is a brown wooden chair\" becomes \"this is a brown", + "bbox": [ + 498, + 794, + 893, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "19237", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/bf70433eed626fc245fe49f339213e576052f800121603c1926c7651d816c5a7.jpg", + "image_caption": [ + "Figure 4. Qualitative results with ScanRefer texts. (a-c): Regular 3D visual grounding. (d-e): Grounding without object name." + ], + "image_footnote": [], + "bbox": [ + 76, + 88, + 890, + 361 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "wooden object\". A total of 9253 samples were annotated and discarded another 255 ambiguous samples. We divide this language set into four subsets: only mentioning object attributes ( $\\sim 15\\%$ ), only mentioning spatial relationships ( $\\sim 20\\%$ ), mentioning both attributes and relationships ( $\\sim 63\\%$ ), and others ( $\\sim 2\\%$ ), as the first row in Table 5. Note that, without retraining, we perform comparisons using our best model and comparative approaches' best models trained for the regular VG task (Sec. 4.1).", + "bbox": [ + 75, + 391, + 468, + 526 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.2.2 Result and analysis", + "text_level": 1, + "bbox": [ + 76, + 542, + 264, + 556 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 5 reports the experimental results. i) The performance of all methods on this challenging task is significantly lower than that of regular VG (see Table. 1), indicating that object categories provide rich semantic information, which is also conducive to classifying features. It's accessible to produce the category's inductive bias, especially in the \"unique\" setting. ii) Our method achieves absolute lead with the overall performance of $26.5\\%$ and $21.2\\%$ , which is over $10\\%$ higher than other methods. This preponderance demonstrates that our proposed text decoupling and dense alignment enable fine-grained visual-linguistic feature matching, where the model identifies the visual features most similar to other text components (e.g. attributes, relations, etc.). iii) Notably, in subset \"Attri+Rel\", our method performs better than in the other subsets because additional cues can be exploited for fine-grained localization. However, the performance of the comparison approaches on this subset drops, revealing that more clues make them suffer from ambiguity. iv) Column \"VG-w/o-ON\" in Table 4 shows ablation studies of text components for this new task. The performance increase offered by the additional components is more remarkable than during the regular VG task. Among them, the", + "bbox": [ + 75, + 568, + 470, + 900 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/b6c948cf966536f6d5df527b205f55c7110a174aa41e1ae3a98c5426413a27f6.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodSubsetsOverall
Attri onlyRel onlyAttri+Rel@0.25@0.5
ScanRefer [8]11.1710.5310.2910.516.20
TGNN [33]10.5213.3211.3511.649.51
InstanceRefer [70]14.7413.7113.8113.9211.47
BUTD-DETR [34]12.3012.1111.8611.998.95
EDA (Ours)25.4025.8226.9626.5021.20
", + "bbox": [ + 501, + 388, + 890, + 498 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 5. Performance of grounding without object name. The accuracy of subsets is measured by acc@0.25IoU, where the \"other\" subset is not reported due to its small proportion.", + "bbox": [ + 498, + 500, + 890, + 542 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "\"Relationship\" component plays the most significant role because the spatial relationship with other objects may provide more obvious indications in this setting. v) Fig. 4(d-e) shows qualitative examples. Even without knowing the target's name, our method can infer it by other cues, while BUTD-DETR's performance drops catastrophically.", + "bbox": [ + 496, + 556, + 890, + 647 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 660, + 617, + 674 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We present EDA, an explicit, dense-aligned method for 3D Visual Grounding tasks. By decoupling text into multiple semantic components and densely aligning it with visual features under the supervision of position-aligned and semantic-aligned loss, we enable fine-grained visual-text feature fusion, avoiding the imbalance and ambiguity of existing methods. Extensive experiments and ablation demonstrate the superiority of our method. In addition, we propose a new challenging 3D VG subtask of grounding without the object name to evaluate model robustness comprehensively. However, our limitations are the performance bottlenecks of multiple modules, such as PointNet++, RoBERTa, and text parsing modules. 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Pointclip v2: Adapting clip for powerful 3d open-world learning. arXiv preprint arXiv:2211.11682, 2022. 2" + ], + "bbox": [ + 78, + 90, + 468, + 527 + ], + "page_idx": 11 + }, + { + "type": "page_number", + "text": "19242", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 11 + } +] \ No newline at end of file diff --git a/2023/EDA_ Explicit Text-Decoupling and Dense Alignment for 3D Visual Grounding/3140b022-de45-49be-b6c5-fb6d9f5aae53_model.json b/2023/EDA_ Explicit Text-Decoupling and Dense Alignment for 3D Visual Grounding/3140b022-de45-49be-b6c5-fb6d9f5aae53_model.json new file mode 100644 index 0000000000000000000000000000000000000000..689cc41d48b0086a362a1fdfa067c8617e84f375 --- /dev/null +++ b/2023/EDA_ Explicit Text-Decoupling and Dense Alignment for 3D Visual Grounding/3140b022-de45-49be-b6c5-fb6d9f5aae53_model.json @@ -0,0 +1,2578 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.001, + 0.812, + 0.047 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. 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It is under the left side of the counter, to the left of the door when you enter." + }, + { + "type": "image", + "bbox": [ + 0.365, + 0.282, + 0.614, + 0.373 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.379, + 0.373, + 0.582, + 0.392 + ], + "angle": 0, + "content": "This is a black trash can. It is under a bathroom counter." + }, + { + "type": "image", + "bbox": [ + 0.629, + 0.282, + 0.876, + 0.373 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.646, + 0.377, + 0.874, + 0.398 + ], + "angle": 0, + "content": "The trash can is white and plastic. It is attached to the wall to the left of the toilet." + }, + { + "type": "image_caption", + "bbox": [ + 0.382, + 0.394, + 0.604, + 0.408 + ], + "angle": 0, + "content": "(a) Regular 3D visual grounding" + }, + { + "type": "image", + "bbox": [ + 0.086, + 0.412, + 0.282, + 0.502 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.092, + 0.502, + 0.114, + 0.512 + ], + "angle": 0, + "content": "(b1)" + }, + { + "type": "title", + "bbox": [ + 0.133, + 0.502, + 0.175, + 0.512 + ], + "angle": 0, + "content": "object" + }, + { + "type": "text", + "bbox": [ + 0.106, + 0.514, + 0.271, + 0.545 + ], + "angle": 0, + "content": "The door is rectangular in shape and has a small window on the upper portion." + }, + { + "type": "image", + "bbox": [ + 0.295, + 0.412, + 0.467, + 0.5 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.294, + 0.5, + 0.316, + 0.511 + ], + "angle": 0, + "content": "(b2)" + }, + { + "type": "text", + "bbox": [ + 0.306, + 0.511, + 0.461, + 0.551 + ], + "angle": 0, + "content": "The white refrigerator is in front of the kitchen stove. It is to the left side of the room as one enters the kitchen." + }, + { + "type": "image", + "bbox": [ + 0.479, + 0.411, + 0.676, + 0.5 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.479, + 0.501, + 0.502, + 0.511 + ], + "angle": 0, + "content": "(b3)" + }, + { + "type": "text", + "bbox": [ + 0.502, + 0.511, + 0.661, + 0.55 + ], + "angle": 0, + "content": "It is a brown wooden object with a cloth seat and back. It has multicolored flower patterns on the seat, and back." + }, + { + "type": "image", + "bbox": [ + 0.684, + 0.414, + 0.882, + 0.502 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.686, + 0.501, + 0.708, + 0.511 + ], + "angle": 0, + "content": "(b4)" + }, + { + "type": "text", + "bbox": [ + 0.7, + 0.512, + 0.862, + 0.542 + ], + "angle": 0, + "content": "This is a black object. It is located next to a tall shelf and there is a fan in front of it." + }, + { + "type": "image_caption", + "bbox": [ + 0.373, + 0.552, + 0.618, + 0.566 + ], + "angle": 0, + "content": "(b) Grounding without object name" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.58, + 0.892, + 0.636 + ], + "angle": 0, + "content": "Figure 1. Text-decoupled, dense aligned 3D visual grounding. Different colours in the text correspond to different decoupled components. (a) Regular 3D visual grounding: locating objects requires comprehensively considering multiple semantic cues such as appearance attributes, object names, and spatial relationships. (b) Grounding without object name: not mentioning object names, avoiding short-cuts and forcing the model to predict the target based on other attributes." + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.649, + 0.313, + 0.665 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.676, + 0.471, + 0.859 + ], + "angle": 0, + "content": "3D visual grounding aims to find the object within point clouds mentioned by free-form natural language descriptions with rich semantic cues. However, existing methods either extract the sentence-level features coupling all words or focus more on object names, which would lose the word-level information or neglect other attributes. To alleviate these issues, we present EDA that Explicitly Decouples the textual attributes in a sentence and conducts Dense Alignment between such fine-grained language and point cloud objects. Specifically, we first propose a text decoupling module to produce textual features for every semantic component. Then, we design two losses to supervise" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.651, + 0.892, + 0.801 + ], + "angle": 0, + "content": "the dense matching between two modalities: position alignment loss and semantic alignment loss. On top of that, we further introduce a new visual grounding task, locating objects without object names, which can thoroughly evaluate the model's dense alignment capacity. Through experiments, we achieve state-of-the-art performance on two widely-adopted 3D visual grounding datasets, ScanRefer and SR3D/NR3D, and obtain absolute leadership on our newly-proposed task. The source code is available at https://github.com/yanmin-wu/EDA." + }, + { + "type": "title", + "bbox": [ + 0.501, + 0.815, + 0.631, + 0.831 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.84, + 0.892, + 0.902 + ], + "angle": 0, + "content": "Multi-modal cues can highly benefit the 3D environment perception of an agent, including 2D images, 3D point clouds, and language. Recently, 3D visual grounding (3D VG) [8,50], also known as 3D object referencing [3], has at" + }, + { + "type": "page_footnote", + "bbox": [ + 0.077, + 0.875, + 0.469, + 0.9 + ], + "angle": 0, + "content": "* Corresponding author. This work was supported in part by Shenzhen Research Project under Grant JCYJ20220531093215035." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "19231" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.152 + ], + "angle": 0, + "content": "tached much attention as an important 3D cross-modal task. Its objective is to find the target object in point cloud scenes by analyzing the descriptive query language, which requires understanding both 3D visual and linguistic context." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.155, + 0.471, + 0.382 + ], + "angle": 0, + "content": "Language utterances typically involve words describing appearance attributes, object categories, spatial relationships and other characteristics, as shown by different colours in Fig. 1(a), requiring that the model integrate multiple cues to locate the mentioned object. Compared with 2D Visual Grounding [18,19,67,71], the sparseness and incompleteness of point clouds, and the diversity of language descriptions produced by 3D multi-view, make 3D VG more challenging. Existing works made significant progress from the following perspectives: improving point cloud features extraction by sparse convolution [70] or 2D images assistance [68]; generating more discriminative object candidates through instance segmentation [33] or language modulation [46]; identifying complex spatial relationships between entities via graph convolution [23] or attention [6]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.385, + 0.471, + 0.763 + ], + "angle": 0, + "content": "However, we observe two issues that remain unexplored. 1) Imbalance: The object name can exclude most candidates, and even in some cases, there is only one name-matched object, as the \"door\" and \"refrigerator\" in Fig. 1(b1, b2). This shortcut may lead to an inductive bias in the model that pays more attention to object names while weakening other properties such as appearance and relationships, resulting in imbalanced learning. 2) Ambiguity: Utterances frequently refer to multiple objects and attributes (such as \"black object, tall shelf, fan\" in Fig. 1(b4)), while the model's objective is to identify only the main object, leading to an ambiguous understanding of language descriptions. These insufficiencies of existing works stem from their characteristic of feature coupling and fusing implicitly. They input a sentence with different attribute words but output only one globally coupled sentence-level feature that subsequently matches the visual features of candidate objects. The coupled feature is ambiguous because some words may not describe the main object (green text in Fig. 1) but other auxiliary objects (red text in Fig. 1). Alternatively, using the cross-modal attention of the Transformer [21, 63] automatically and implicitly to fuse visual and text features. However, this may encourage the model to take shortcuts, such as focusing on object categories and ignoring other attributes, as previously discussed." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.765, + 0.47, + 0.903 + ], + "angle": 0, + "content": "Instead, we propose a more intuitive decoupled and explicit strategy. First, we parse the input text to decouple different semantic components, including the main object word, pronoun, attributes, relations, and auxiliary object words. Then, performing dense alignment between point cloud objects and multiple related decoupled components achieves fine-grained feature matching, which avoids the inductive bias resulting from imbalanced learning of different textual components. As the final grounding result, we" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.333 + ], + "angle": 0, + "content": "explicitly select the object with the highest similarity to the decoupled text components (instead of the entire sentence), avoiding ambiguity caused by irrelevant components. Additionally, to explore the limits of VG and examine the comprehensiveness and fine-graininess of visual-language perception of the model, we suggest a challenging new task: Grounding without object name (VG-w/o-ON), where the name is replaced by \"object\" (see Fig. 1(b)), forcing the model to locate objects based on other attributes and relationships. This setting makes sense because utterances that do not mention object names are common expressions in daily life, and in addition to testing whether the model takes shortcuts. Benefiting from our text decoupling operation and the supervision of dense aligned losses, all text components are aligned with visual features, making it possible to locate objects independent of object names." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.335, + 0.892, + 0.516 + ], + "angle": 0, + "content": "To sum up, the main contributions of this paper are as follows: 1) We propose a text decoupling module to parse linguistic descriptions into multiple semantic components, followed by suggesting two well-designed dense aligned losses for supervising fine-grained visual-language feature fusion and preventing imbalance and ambiguity learning. 2) The challenging new 3D VG task of grounding without object names is proposed to comprehensively examine the model's robust performance. 3) We achieve state-of-the-art performance on two datasets (ScanRefer and SR3D/NR3D) on the regular 3D VG task and absolute leadership on the new task evaluated by the same model without retraining." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.534, + 0.642, + 0.549 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.56, + 0.725, + 0.575 + ], + "angle": 0, + "content": "2.1. 3D Vision and Language" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.584, + 0.892, + 0.903 + ], + "angle": 0, + "content": "3D vision [52, 53, 75] and language are vital manners for humans to understand the environment, and they are also important research topics for the evolution of machines to be like humans. Previously, the two fields evolved independently. Due to the advance of multimodality [25, 26, 54, 56, 57, 72-74, 76], many promising works across 3D vision and language have been introduced recently. In 3D visual grounding [1, 8-10, 12], the speaker (like a human) describes an object in language. The listener (such a robot) needs to understand the language description and the 3D visual scene to grounding the target object. On the contrary, the 3D dense caption [9, 13, 14, 36, 65, 69] is analogous to an inverse process in which the input is a 3D scene, and the output is textual descriptions of each object. Language-modulated 3D detection or segmentation [7, 32, 34, 59, 78] enriches the diversity of text queries by matching visual-linguistic feature spaces rather than predicting the probability of a set number of categories. Furthermore, some studies explore the application of 3D visual language in agents such as robot perception [27, 61], vision-and-language navigation (VLN) [15, 31, 55], and embodied question answering" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "19232" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.091, + 0.47, + 0.138 + ], + "angle": 0, + "content": "(EQA) [4,22,30,45,47,62]. In this paper, we focus on point clouds-based 3D visual grounding, which is the fundamental technology for many embodied AI [24,38,48] tasks." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.15, + 0.279, + 0.167 + ], + "angle": 0, + "content": "2.2.3D Visual Grounding" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.175, + 0.473, + 0.597 + ], + "angle": 0, + "content": "The majority of current mainstream techniques are two-stage. In the first stage, obtain the features of the query language and candidate point cloud objects independently by a pre-trained language model [16, 20, 49] and a pretrained 3D detector [44, 51] or segmenter [11, 35, 64]. In the second stage, the researchers focus on fusing the two modal features and then selecting the best-matched object. 1) The most straightforward solution is to concatenate the two modal features and then consider it a binary classification problem [8, 39], which provides limited performance because the two features are not sufficiently fused. 2) Taking advantage of the Transformer's attention mechanism, which is naturally suitable for multi-module feature fusion, He et al. [28] and Zhao et al. [77] achieve remarkable performance by performing self-attention and cross-attention to features. 3) In contrast, other studies view feature fusion as a matching problem rather than a classification. Yuan et al. [70] and Abdelreheem et al. [2], supervised by the contrastive loss [29], compute the cosine similarity of visual features and textual features. Inspired by [43], Feng et al. [23] parses the text to generate a text scene graph, simultaneously builds a visual scene graph, and then performs graph node matching. 4) Point clouds' sparse, noisy, incomplete, and lack of detail make learning objects' semantic information challenging. Yang et al. [68] and Cai et al. [6] use 2D images to aid visual-textual feature fusion, but at the cost of additional 2D-3D alignment and 2D feature extraction." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.599, + 0.473, + 0.902 + ], + "angle": 0, + "content": "However, the two-stage method has a substantial detection bottleneck: objects overlooked in the first stage cannot be matched in the second. In contrast, object detection and feature extraction in the single-stage method is modulated by the query text, making it easier to identify the text-concerned object. Liu et al. [41] suggest fusing visual and linguistic features at the bottom level and producing text-related visual heatmaps. Similarly, Luo et al. [46] present a single-stage approach that employs textual features to guide visual keypoint selection and progressively localizes objects. BUTD-DETR [34] is also a single-stage capable framework. More importantly, inspired by the 2D image-language pre-train model (such MDETR [37], GLIP [40]), BUTD-DETR measures the similarity between each word and object and then selects the features of the word that correspond to the object's name to match the candidate object. However, there are two limitations: 1) Since multiple object names may be mentioned in a sentence, the ground truth annotation is needed to retrieve the target name, which limits its generalizability. Our text decoupling module separates" + }, + { + "type": "image", + "bbox": [ + 0.514, + 0.088, + 0.882, + 0.219 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.228, + 0.892, + 0.258 + ], + "angle": 0, + "content": "Figure 2. Text component decoupling: (a) The query text. (b) Dependency tree analysis. (c) Decoupled into five components." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.272, + 0.892, + 0.394 + ], + "angle": 0, + "content": "text components and determines the target object name by grammatical analysis to avoid this restriction. 2) BUTD-DETR (and MDETR and GLIP in the 2D task) only consider the sparse alignment of main object words or noun phrases to visual features. Conversely, we align all object-related decoupled textual semantic components with visual features, which we refer to dense alignment, significantly enhancing the discriminability of multimodal features." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.406, + 0.673, + 0.423 + ], + "angle": 0, + "content": "3. Proposed Method" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.431, + 0.892, + 0.583 + ], + "angle": 0, + "content": "The framework is illustrated in Fig. 3. First, the input text description is decoupled into multiple semantic components, and its affiliated text positions and features are obtained (Sec. 3.1). Concurrently, the Transformer-based encoder extracts and modulates features from point clouds and text, then decodes the visual features of candidate objects (Sec. 3.2). Finally, the dense aligned losses are derived between the decoupled text features and the decoded visual features (Sec. 3.3). The grounding result is the object with visual features most similar to text features (Sec. 3.4)." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.591, + 0.663, + 0.607 + ], + "angle": 0, + "content": "3.1. Text Decoupling" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.614, + 0.892, + 0.795 + ], + "angle": 0, + "content": "The text features of the coupled strategy are ambiguous, where features from multiple objects and attributes are coupled, such as \"a brown wooden chair next to the black table.\" Among them, easy-to-learn clues (such as the category \"chair\" or the colour \"brown\") may predominate, weakening other attributes (such as material \"wooden\"); words of other objects (such as the \"black table\") may cause interference. To produce more discriminative text features and fine-grained cross-modal feature fusion, we decouple the query text into different semantic components, each independently aligned with visual features, avoiding the ambiguity caused by feature coupling." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.796, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Text Component Decoupling. Analyzing grammatical dependencies between words is a fundamental task in NLP. We first use the off-the-shelf tool [60, 66] to parse the language description grammatically to generate the grammatical dependency trees, as shown in Fig. 2(b). Each sentence contains only one ROOT node, and each remaining word has a corresponding parent node. Then according to" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "19233" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.08, + 0.089, + 0.895, + 0.365 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.373, + 0.895, + 0.43 + ], + "angle": 0, + "content": "Figure 3. The system framework. (a-c): Decouple the input text into several components to acquire the position label \\( L \\) and features \\( t \\) of the decoupled text. (d-e): Transformer-based encoders for cross-modal visual-text feature extraction. (f): Decode proposal features \\( \\mathcal{O}' \\) and linearly project them as object position labels \\( L_{pred} \\) and object features \\( o \\), in addition to a box prediction head for regression of the bounding box. (g-h): Visual-text feature dense alignment. Note that the additional 3D object detection procedure is optional." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.456, + 0.47, + 0.607 + ], + "angle": 0, + "content": "the words' part-of-speech and dependencies, we decouple the long text into five semantic components (see Fig. 2(c)): Main object - the target object mentioned in the utterance; Auxiliary object - the one used to assist in locating the main object; Attributes - objects' appearance, shape, etc.; Pronoun - the word instead of the main object; Relationship - the spatial relation between the main object and the auxiliary object. Note that attributes affiliated with pronouns are equivalent to attached with the main object, thus connecting two sentences in an utterance." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.611, + 0.47, + 0.762 + ], + "angle": 0, + "content": "Text Position Decoupling. After decoupling each text component (Fig. 3(a)), we generate the position label (similar to a mask) \\( L_{\\text{main}}, L_{\\text{attr}}, L_{\\text{auxi}}, L_{\\text{pron}}, L_{\\text{rel}} \\in \\mathbb{R}^{1 \\times l} \\) for the component's associated word (Fig. 3(b)). Where \\( l = 256 \\) is the maximum length of the text, each component's word position is set to 1 and the rest to 0. The label will be used to construct the position alignment loss and supervise the classification of objects. The classification result, is not one of a predetermined number of object categories but the position of the text with the highest semantic similarity." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.765, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Text Feature Decoupling. The feature of each word (token) is produced in the backbone of multimodal feature extraction (Fig. 3(d)). The text feature of the decoupled component can be derived by dot-multiplying all words' features \\( \\pmb{t} \\) with its position label \\( L \\), as shown in Fig. 3(c). The decoupled text features and visual features will be independently aligned under the supervision of the semantic alignment loss. Note that in the decoupled text features, the semantics of the corresponding components absolutely" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.456, + 0.893, + 0.518 + ], + "angle": 0, + "content": "predominate, but as a result of the Transformer's attention mechanism, it also implicitly contains the global sentence's information. In other words, feature decoupling produces individual features while keeping the global context." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.528, + 0.779, + 0.543 + ], + "angle": 0, + "content": "3.2. Multimodal Feature Extraction" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.552, + 0.893, + 0.597 + ], + "angle": 0, + "content": "We employ BUTD-DETR's encoder-decoder module for feature extraction and intermodulation of cross-modal features. We strongly recommend the reader to refer to Fig. 3." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.598, + 0.892, + 0.734 + ], + "angle": 0, + "content": "Input Modal Tokenization. The input text and 3D point clouds are encoded by the pre-trained RoBERTa [42] and PointNet++ [53] and produce text tokens \\(\\mathcal{T} \\in \\mathbb{R}^{l \\times d}\\) and visual tokens \\(\\mathcal{V} \\in \\mathbb{R}^{n \\times d}\\). Additionally, the GroupFree [44] detector is used to detect 3D boxes, which are subsequently encoded as box tokens \\(\\mathcal{B} \\in \\mathbb{R}^{b \\times d}\\). Note that the GroupFree is optional, the final predicted object of the network is from the prediction head (see below), and the box token is just to assist in better regression of the target object." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.735, + 0.892, + 0.825 + ], + "angle": 0, + "content": "Encoder-Decoder. Self-attention and cross-attention are performed in the encoder to update both visual and text features, obtaining cross-modal features \\(\\mathcal{V}'\\), \\(\\mathcal{T}'\\) while keeping the dimensions. The top-\\(k\\) (\\(k = 256\\)) visual features are selected, linearly projected as query proposal features \\(\\mathcal{O} \\in \\mathbb{R}^{k \\times d}\\), and updated as \\(\\mathcal{O}'\\) in the decoder." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.826, + 0.893, + 0.902 + ], + "angle": 0, + "content": "Prediction Head. 1) The decoded proposal features \\(\\mathcal{O}' \\in \\mathbb{R}^{k \\times d}\\) are fed into an MLP and output the predicted position labels \\(L_{pred} \\in \\mathbb{R}^{k \\times l}\\), which are then utilized to calculate the position alignment loss with decoupled text position labels \\(L \\in \\mathbb{R}^{1 \\times l}\\). 2) Additionally, the proposal fea" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "19234" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.09, + 0.47, + 0.168 + ], + "angle": 0, + "content": "tures are linearly projected as object features \\(\\pmb{o} \\in \\mathbb{R}^{k \\times 64}\\) by another MLP, which are then utilized to compute the semantic alignment loss with the similarly linearly projected text feature \\(\\pmb{t} \\in \\mathbb{R}^{l \\times 64}\\). 3) Lastly, a box prediction head [44] regresses the bounding box of the object." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.175, + 0.265, + 0.19 + ], + "angle": 0, + "content": "3.3. Dense Aligned Loss" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.198, + 0.327, + 0.213 + ], + "angle": 0, + "content": "3.3.1 Dense Position Aligned Loss" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.221, + 0.469, + 0.326 + ], + "angle": 0, + "content": "The objective of position alignment is to ensure that the distribution of language-modulated visual features closely matches that of the query text description, as shown in Fig. 3(g). This process is similar to standard object detection's one-hot label prediction. However, rather than being limited by the number of categories, we predict the position of text that is similar to objects." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.327, + 0.469, + 0.388 + ], + "angle": 0, + "content": "The constructed ground truth text distribution of the mentioned main object is obtained by element-wise summing the position labels of the associated decoupled text components:" + }, + { + "type": "equation", + "bbox": [ + 0.088, + 0.395, + 0.469, + 0.412 + ], + "angle": 0, + "content": "\\[\nP _ {\\text {m a i n}} = \\lambda_ {1} L _ {\\text {m a i n}} + \\lambda_ {2} L _ {\\text {a t t r i}} + \\lambda_ {3} L _ {\\text {p r o n}} + \\lambda_ {4} L _ {\\text {r e l}}, \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.418, + 0.469, + 0.524 + ], + "angle": 0, + "content": "where \\(\\lambda\\) is the weight of different parts (refer to the parametric search in Supplementary Material.). \\(P_{auxi} = L_{auxi}\\) represents the text distribution of the auxiliary object. The remaining candidate objects' text distribution is \\(P_{oth}\\), with the final bit set to 1 (see \\(\\varnothing\\) in Fig. 3(g)). Therefore, all \\(k\\) candidate objects' ground truth text distribution is \\(P_{text} = \\{P_{main}, P_{auxi}, P_{oth}\\} \\in \\mathbb{R}^{k \\times l}\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.524, + 0.469, + 0.569 + ], + "angle": 0, + "content": "The predicted visual distribution of \\(k\\) objects is produced by applying softmax to the output \\(L_{pred} \\in \\mathbb{R}^{k \\times l}\\) of the prediction head:" + }, + { + "type": "equation", + "bbox": [ + 0.184, + 0.578, + 0.469, + 0.595 + ], + "angle": 0, + "content": "\\[\nP _ {o b j} = \\operatorname {S o f t m a x} \\left(L _ {p r e d}\\right). \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.6, + 0.468, + 0.616 + ], + "angle": 0, + "content": "Their KL divergence is defined as the position-aligned loss:" + }, + { + "type": "equation", + "bbox": [ + 0.103, + 0.635, + 0.469, + 0.675 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {p o s} = \\sum_ {i = 1} ^ {k} \\left[ P _ {t e x t} ^ {i} \\log \\left(P _ {t e x t} ^ {i}\\right) - P _ {t e x t} ^ {i} \\log \\left(P _ {o b j} ^ {i}\\right) \\right]. \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.682, + 0.469, + 0.758 + ], + "angle": 0, + "content": "We highlight that \"dense alignment\" indicates that the target object is aligned with the positions of multiple components (Eq. (1)), significantly different from BUTD-DETR (and MDETR for 2D tasks), which only sparsely aligns with the object name's position \\( L_{main} \\)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.775, + 0.336, + 0.79 + ], + "angle": 0, + "content": "3.3.2 Dense Semantic Aligned Loss" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.797, + 0.469, + 0.84 + ], + "angle": 0, + "content": "Semantic alignment aims to learn the similarity of visual-text multimodal features through contrastive learning. The object loss of semantic alignment is defined as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.078, + 0.846, + 0.469, + 0.901 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\text {s e m - o}} = \\sum_ {i = 1} ^ {k} \\frac {1}{| \\mathbf {T} _ {i} ^ {+} |} \\sum_ {\\boldsymbol {t} _ {i} \\in \\mathbf {T} _ {i} ^ {+}} - \\log \\left(\\frac {\\exp \\left(w _ {+} * \\left(\\boldsymbol {o} _ {i} ^ {\\top} \\boldsymbol {t} _ {i} / \\tau\\right)\\right)}{\\sum_ {j = 1} ^ {l} \\exp \\left(w _ {-} * \\left(\\boldsymbol {o} _ {i} ^ {\\top} \\boldsymbol {t} _ {j} / \\tau\\right)\\right)}\\right), \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.092, + 0.892, + 0.182 + ], + "angle": 0, + "content": "where \\( \\pmb{o} \\) and \\( \\pmb{t} \\) are the object and text features after linear projection, and \\( o^\\top t / \\tau \\) is their similarity, as shown in Fig. 3 (h). \\( k \\) and \\( l \\) are the number of objects and words. \\( \\pmb{t}_i \\) is the positive text feature of the \\( i_{th} \\) candidate object. Taking the main object as an example, the positive text feature \\( \\mathbf{T}_i^+ \\) corresponding to it is:" + }, + { + "type": "equation", + "bbox": [ + 0.564, + 0.198, + 0.892, + 0.216 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {t} _ {i} \\in \\mathbf {T} _ {i} ^ {+} = \\left\\{\\boldsymbol {t} _ {\\text {m a i n}}, \\boldsymbol {t} _ {\\text {a t t r i}}, \\boldsymbol {t} _ {\\text {p r o n}}, \\boldsymbol {t} _ {\\text {r e l}} \\right\\}, \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.229, + 0.892, + 0.286 + ], + "angle": 0, + "content": "and \\( w_{+} \\) is the weight of each positive term. \\( t_j \\) is the feature of the \\( i_{th} \\) text, but note that the negative similarity weight \\( w_{-} \\) for auxiliary object term \\( t_{auxi} \\) is 2, while the rest weight 1. The text loss of semantic alignment defined similarly:" + }, + { + "type": "equation", + "bbox": [ + 0.51, + 0.3, + 0.892, + 0.355 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {s e m - t} = \\sum_ {i = 1} ^ {l} \\frac {w _ {+}}{\\left| \\mathbf {O} _ {i} ^ {+} \\right|} \\sum_ {\\boldsymbol {o} _ {i} \\in \\mathbf {O} _ {i} ^ {+}} - \\log \\left(\\frac {\\exp \\left(\\boldsymbol {t} _ {i} ^ {\\top} \\boldsymbol {o} _ {i} / \\tau\\right)}{\\sum_ {j = 1} ^ {k} \\exp \\left(\\boldsymbol {t} _ {i} ^ {\\top} \\boldsymbol {o} _ {j} / \\tau\\right)}\\right), \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.356, + 0.892, + 0.417 + ], + "angle": 0, + "content": "where \\(o_i \\in \\mathbf{O}_i^+\\) is the positive object feature of the \\(i_{th}\\) text, and \\(o_j\\) is the feature of the \\(j_{th}\\) object. The final semantic alignment loss is the mean of the two: \\(\\mathcal{L}_{sem} = (\\mathcal{L}_{sem\\_o} + \\mathcal{L}_{sem\\_t}) / 2\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.418, + 0.892, + 0.524 + ], + "angle": 0, + "content": "Similarly, the semantic alignment of multiple text components (Eq. (5)) with visual features also illustrates our insight of \"dense.\" This is intuitive, such as \"It is a brown chair with legs under a blackboard,\" where the main object's visual features should be not only similar to \"chair\" but also similar to \"brown, legs\" and distinct to \"blackboard\" as possible." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.526, + 0.892, + 0.556 + ], + "angle": 0, + "content": "The total loss for training also includes the box regression loss. Refer to Supplementary Material for details." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.571, + 0.673, + 0.587 + ], + "angle": 0, + "content": "3.4. Explicit Inference" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.597, + 0.892, + 0.732 + ], + "angle": 0, + "content": "Because of our text decoupling and dense alignment operations, object features fused multiple related text component features, allowing for the computation of the similarity between individual text components and candidate objects. For instance, \\( S_{main} = \\text{Softmax}(\\boldsymbol{o}^{\\top}\\boldsymbol{t}_{main} / \\tau) \\) indicates the similarity between objects \\( \\boldsymbol{o} \\) and the main text component \\( \\boldsymbol{t}_{main} \\). Therefore, the similarity of objects and related components can be explicitly combined to obtain the total score and select the candidate with the highest score:" + }, + { + "type": "equation", + "bbox": [ + 0.525, + 0.748, + 0.892, + 0.765 + ], + "angle": 0, + "content": "\\[\nS _ {a l l} = S _ {\\text {m a i n}} + S _ {\\text {a t t r i}} + S _ {\\text {p r o n}} + S _ {\\text {r e l}} - S _ {\\text {a u x i}}, \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.892, + 0.901 + ], + "angle": 0, + "content": "where the definition of \\( S_{attri} \\), \\( S_{pron} \\), \\( S_{rel} \\), and \\( S_{auxi} \\) is similar to \\( S_{main} \\). If providing supervision of auxiliary objects during training, and the auxiliary object can be identified by solely computing the similarity between the object features and the auxiliary component's text features: \\( S_{all} = S_{attri} \\). Being able to infer the object based on the part of the text is a significant sign that the network has learned well-aligned and fine-grained visual-text feature space." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "19235" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.077, + 0.091, + 0.21, + 0.108 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.115, + 0.471, + 0.222 + ], + "angle": 0, + "content": "First, we conduct comprehensive and fair comparisons with SOTA methods in the Regular 3D Visual Grounding setting in Sec. 4.1. Then, in Sec. 4.2, we introduce our proposed new task, Grounding without Object Name, and perform comparison and analysis. Implementation details, additional experiments and more qualitative results are detailed in the supplementary material." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.23, + 0.345, + 0.246 + ], + "angle": 0, + "content": "4.1. Regular 3D Visual Grounding" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.254, + 0.271, + 0.269 + ], + "angle": 0, + "content": "4.1.1 Experiment settings" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.277, + 0.47, + 0.504 + ], + "angle": 0, + "content": "We keep the same settings as existing works, with ScanRefer [8] and SR3D/NR3D [3] as datasets and Acc@0.25IoU and Acc@0.5IoU as metrics. Based on the visual data of ScanNet [17], ScanRefer adds 51,583 manually annotated text descriptions about objects. These complex and free-form descriptions involve object categories and attributes such as colour, shape, size, and spatial relationships. SR3D/NR3D is also proposed based on ScanNet, with SR3D including 83,572 simple machine-generated descriptions and NR3D containing 41,503 descriptions similar to ScanRefer's human annotation. The difference is that in the ScanRefer configuration, detecting and matching objects are required, while SR3D/NR3D is simpler. It supplies GT boxes for all candidate objects and only needs to classify the classes of the boxes and choose the target object." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.515, + 0.367, + 0.53 + ], + "angle": 0, + "content": "4.1.2 Comparison to the state of the art" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.539, + 0.471, + 0.903 + ], + "angle": 0, + "content": "ScanRefer. Table 1 reports the results on the ScanRefer dataset. i) Our method achieves state-of-the-art performance by a substantial margin, with an overall improvement of \\(4.2\\%\\) and \\(3.7\\%\\) to \\(54.59\\%\\) and \\(42.26\\%\\). ii) Some studies [6,8,9,46,68,77] proved that supplemented 2D images with detailed and dense semantics could learn better point cloud features. Surprisingly, we only use sparse 3D point cloud features and even outperformed 2D assistance methods. This superiority illustrates that our decoupling and dense alignment strategies mine more efficient and meaningful visual-text co-representations. iii) Another finding is that the accuracy of most existing techniques is less than \\(40\\%\\) and \\(30\\%\\) in the \"multiple\" setting because multiple means that the category of the target object mentioned in the language is not unique, with more interference candidates with the same category. However, we reached a remarkable \\(49.13\\%\\) and \\(37.64\\%\\). To identify similar objects, a finer-grained understanding of the text and vision is required in this complex setting. iv) The last three rows in Table 1 compare single-stage methods, where our method's single-stage implementation is without the object detection step (\\(\\mathcal{B}\\) in Fig. 3) in training and inference. The result illustrates that while not requiring an additional pre-trained 3D object detector, our approach also can achieve SOTA performance." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.151 + ], + "angle": 0, + "content": "v) The qualitative results are depicted in Fig. 4(a-c), which reveals that our method with an excellent perception of appearance attributes, spatial relationships, and even ordinal numbers." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.152, + 0.893, + 0.365 + ], + "angle": 0, + "content": "SR3D/NR3D. Table 2 shows the accuracy on the SR3D/NR3D dataset, where we achieve the best performance of \\(68.1\\%\\) and \\(52.1\\%\\). In SR3D, since the language descriptions are concise and the object is easy to identify, our method and [34, 46] reach an accuracy of over \\(60\\%\\). Conversely, in NR3D, descriptions are too detailed and complex, causing additional challenges for text decoupling. However, we still achieve SOTA accuracy with the 3D-only data, while other comparable methods [46, 68] rely on additional 2D images for training. Some methods [6, 8, 9] compared in Table 1 are not discussed here because they are not evaluated on the SR3D/NR3D dataset. In addition, because GT boxes of candidate objects are provided in this setting, the single-stage methods are not applicable and discussed." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.378, + 0.668, + 0.392 + ], + "angle": 0, + "content": "4.1.3 Ablation studies" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.402, + 0.892, + 0.569 + ], + "angle": 0, + "content": "Loss ablation. The ablation of the position-aligned loss and the semantic-aligned loss is shown in Table 3. The performance of the semantic-aligned loss is marginally better because its contrastive loss not only shortens the distance between similar text-visual features but also enlarges the distance between dis-matched features (such as \\( t_{auxi} \\) is a negative term in Eq. (4)). Whereas position-aligned loss only considers object-related components (as in Eq. (1)). When both losses supervise together, the best accuracy is achieved, demonstrating that they can produce complementary performance." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.57, + 0.893, + 0.902 + ], + "angle": 0, + "content": "Dense components ablation. To demonstrate our insight into dense alignment, we perform ablation analysis on the different decoupled text components, and the results are displayed in the \"Regular VG\" column in Table 4. Analysis: i) (a) is our baseline implementation of the sparse concept, using only the \"Main object\" component decoupled from the text. In contrast to BUTD-DETR, the text decoupling module (Sec. 3.1) is used to obtain text labels and features during training and inference instead of employing ground truth labels. ii) Dense-aligned sub-methods (b)-(h) outperform the sparse alignment (a) because of the finer-grained visual-linguistic feature fusion. iii) (b)-(e) indicate that adding any other component on top of the \"Main object\" improves performance, demonstrating the validity of each text component. The \"Attribute\" component aids in identifying characteristics such as colour, and shape, frequently mentioned in language descriptions. Unexpectedly, the \"Pronoun\" component such as \"it, that, and which\" have little meaning when used alone but also function in our method, indicating that the pronoun learned contextual information from the sentence. The \"Relationship\" component facilitates comprehension of spatial relationships be" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "19236" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.087, + 0.09, + 0.885, + 0.399 + ], + "angle": 0, + "content": "
MethodVenueModalityUnique (~19%)Multiple (~81%)Overall
0.250.50.250.50.250.5
ScanRefer [8]ECCV20203D67.6446.1932.0621.2638.9726.10
3D+2D76.3353.5132.7321.1141.1927.40
ReferIt3D [3]ECCV20203D53.837.521.012.826.416.9
TGNN [33]AAAI20213D68.6156.8029.8423.1837.3729.70
InstanceRefer [70]ICCV20213D77.4566.8331.2724.7740.2332.93
SAT [68]ICCV20213D+2D73.2150.8337.6425.1644.5430.14
FFL-3DOG [23]ICCV20213D78.8067.9435.1925.7041.3334.01
3DVG-Transformer [77]ICCV20213D77.1658.4738.3828.7045.9034.47
3D+2D81.9360.6439.3028.4247.5734.67
3D-SPS [46]CVPR20223D+2D84.1266.7240.3229.8248.8236.98
3DJCG [6]CVPR20223D78.7561.3040.1330.0847.6236.14
3D+2D83.4764.3441.3930.8249.5637.33
BUTD-DETR [34] †ECCV20223D82.8864.9844.7333.9750.4238.60
D3Net [9]ECCV20223D+2D-70.35-30.50-37.87
EDA-3D85.7668.5749.1337.6454.59 (+4.2%)42.26 (+3.7%)
3D-SPS(single-stage) [46]CVPR20223D81.6364.7739.4829.6147.6536.43
BUTD-DETR (single-stage) [34]‡ECCV20223D81.4761.2444.2032.8149.7637.05
EDA (single-stage) §-3D86.4069.4248.1136.8253.8341.70
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.401, + 0.895, + 0.459 + ], + "angle": 0, + "content": "Table 1. The 3D visual grounding results on ScanRefer, accuracy evaluated by IoU 0.25 and IoU 0.5. † The accuracy is reevaluated using our parsed text labels because the performance reported by BUTD-DETR used ground truth text labels and ignored some challenging samples (see supplementary materials for more details). § Our single-stage implementation without the assistance of the additional 3D object detection step (dotted arrows in Fig. 3). ‡ BUTD-DETR did not provide single-stage results and we retrained the model." + }, + { + "type": "table", + "bbox": [ + 0.08, + 0.467, + 0.472, + 0.684 + ], + "angle": 0, + "content": "
MethodVenueModalitySR3DNR3D
ReferIt3D [3]ECCV203D39.835.6
TGNN [33]AAAI213D45.037.3
TransRefer3D [28]MM213D57.442.1
InstanceRefer [70]ICCV213D48.038.8
3DVG-Transfor. [77]ICCV213D51.440.8
FFL-3DOG [23]ICCV213D-41.7
SAT [68]ICCV213D+2D57.949.2
3DReferTrans. [2]WACV223D47.039.0
LanguageRefer [58]CoRL223D56.043.9
3D-SPS [46]CVPR223D+2D62.651.5
BUTD-DETR † [34]ECCV223D65.649.1
LAR [5]NeurIPS223D59.648.9
EDA (Ours)-3D68.152.1
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.685, + 0.472, + 0.743 + ], + "angle": 0, + "content": "Table 2. Performance on SR3D/NR3D datasets by Acc@0.25IoU as the metric. The detailed results of EDA in four subsets are provided in the Supplementary Material. \\(\\dagger\\) Reevaluated by parsed text labels (see supp. for more details)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.75, + 0.473, + 0.903 + ], + "angle": 0, + "content": "tween objects. The component \"Auxiliary object\" is a negative term in the loss (Eq. (4)). During inference (Eq. (7)), its similarity is subtracted in the hopes that the predicted main object is as dissimilar to it as possible. iv) (f)-(h) integrate different components to make performance gains and reach the peak when all are involved, demonstrating that the functions of each component can be complementary, and there may be no overlap between the features of each one. The result reveals that our method effectively decouples and matches fine-grained multimodal features." + }, + { + "type": "table", + "bbox": [ + 0.518, + 0.467, + 0.876, + 0.538 + ], + "angle": 0, + "content": "
+Lpos+LsemAcc@0.25Acc@0.5
(a)✓51.239.6
(b)✓52.239.9
(c)✓✓54.642.3
" + }, + { + "type": "table_caption", + "bbox": [ + 0.551, + 0.54, + 0.84, + 0.553 + ], + "angle": 0, + "content": "Table 3. Loss ablation on the ScanRefer dataset." + }, + { + "type": "table", + "bbox": [ + 0.508, + 0.558, + 0.888, + 0.704 + ], + "angle": 0, + "content": "
Dense componentsRegular VGVG-w/o-ON
MainAttri.Pron.Auxi.Rel.@0.25@0.5@0.25@0.5
(a)✓51.538.821.816.7
(b)✓✓53.141.323.217.8
(c)✓✓52.940.823.718.6
(d)✓✓52.941.023.218.4
(e)✓✓52.840.725.719.6
(f)✓✓✓53.841.824.218.5
(g)✓✓✓✓54.242.324.018.8
(h)✓✓✓✓✓54.642.326.521.2
" + }, + { + "type": "table_caption", + "bbox": [ + 0.5, + 0.705, + 0.892, + 0.732 + ], + "angle": 0, + "content": "Table 4. Ablation studies of different text components on Regular VG and VG-w/o-ON tasks. Evaluated on the ScanRefer dataset." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.747, + 0.892, + 0.765 + ], + "angle": 0, + "content": "4.2. Grounding without Object Name (VG-w/o-ON)" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.771, + 0.695, + 0.788 + ], + "angle": 0, + "content": "4.2.1 Experiment settings" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.795, + 0.895, + 0.901 + ], + "angle": 0, + "content": "To evaluate the comprehensive reasoning ability of the model and avoid inductive biases about object names, we propose a new and more challenging task: grounding objects without mentioning object names (VG-w/o-ON). Specifically, we manually replace the object's name with \"object\" in the ScanRefer validation set. For instance: \"This is a brown wooden chair\" becomes \"this is a brown" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "19237" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.078, + 0.089, + 0.891, + 0.362 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.111, + 0.364, + 0.856, + 0.377 + ], + "angle": 0, + "content": "Figure 4. Qualitative results with ScanRefer texts. (a-c): Regular 3D visual grounding. (d-e): Grounding without object name." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.392, + 0.47, + 0.527 + ], + "angle": 0, + "content": "wooden object\". A total of 9253 samples were annotated and discarded another 255 ambiguous samples. We divide this language set into four subsets: only mentioning object attributes (\\(\\sim 15\\%\\)), only mentioning spatial relationships (\\(\\sim 20\\%\\)), mentioning both attributes and relationships (\\(\\sim 63\\%\\)), and others (\\(\\sim 2\\%\\)), as the first row in Table 5. Note that, without retraining, we perform comparisons using our best model and comparative approaches' best models trained for the regular VG task (Sec. 4.1)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.544, + 0.266, + 0.558 + ], + "angle": 0, + "content": "4.2.2 Result and analysis" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.569, + 0.471, + 0.901 + ], + "angle": 0, + "content": "Table 5 reports the experimental results. i) The performance of all methods on this challenging task is significantly lower than that of regular VG (see Table. 1), indicating that object categories provide rich semantic information, which is also conducive to classifying features. It's accessible to produce the category's inductive bias, especially in the \"unique\" setting. ii) Our method achieves absolute lead with the overall performance of \\(26.5\\%\\) and \\(21.2\\%\\), which is over \\(10\\%\\) higher than other methods. This preponderance demonstrates that our proposed text decoupling and dense alignment enable fine-grained visual-linguistic feature matching, where the model identifies the visual features most similar to other text components (e.g. attributes, relations, etc.). iii) Notably, in subset \"Attri+Rel\", our method performs better than in the other subsets because additional cues can be exploited for fine-grained localization. However, the performance of the comparison approaches on this subset drops, revealing that more clues make them suffer from ambiguity. iv) Column \"VG-w/o-ON\" in Table 4 shows ablation studies of text components for this new task. The performance increase offered by the additional components is more remarkable than during the regular VG task. Among them, the" + }, + { + "type": "table", + "bbox": [ + 0.503, + 0.39, + 0.891, + 0.499 + ], + "angle": 0, + "content": "
MethodSubsetsOverall
Attri onlyRel onlyAttri+Rel@0.25@0.5
ScanRefer [8]11.1710.5310.2910.516.20
TGNN [33]10.5213.3211.3511.649.51
InstanceRefer [70]14.7413.7113.8113.9211.47
BUTD-DETR [34]12.3012.1111.8611.998.95
EDA (Ours)25.4025.8226.9626.5021.20
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.501, + 0.892, + 0.543 + ], + "angle": 0, + "content": "Table 5. Performance of grounding without object name. The accuracy of subsets is measured by acc@0.25IoU, where the \"other\" subset is not reported due to its small proportion." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.557, + 0.892, + 0.648 + ], + "angle": 0, + "content": "\"Relationship\" component plays the most significant role because the spatial relationship with other objects may provide more obvious indications in this setting. v) Fig. 4(d-e) shows qualitative examples. Even without knowing the target's name, our method can infer it by other cues, while BUTD-DETR's performance drops catastrophically." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.661, + 0.619, + 0.675 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.686, + 0.892, + 0.898 + ], + "angle": 0, + "content": "We present EDA, an explicit, dense-aligned method for 3D Visual Grounding tasks. By decoupling text into multiple semantic components and densely aligning it with visual features under the supervision of position-aligned and semantic-aligned loss, we enable fine-grained visual-text feature fusion, avoiding the imbalance and ambiguity of existing methods. Extensive experiments and ablation demonstrate the superiority of our method. In addition, we propose a new challenging 3D VG subtask of grounding without the object name to evaluate model robustness comprehensively. However, our limitations are the performance bottlenecks of multiple modules, such as PointNet++, RoBERTa, and text parsing modules. 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It is under the left side of the counter, to the left of the door when you enter. + +![](images/546e38ab085f4a1273eedc52494b4a9d7bf7df1a82f021e5d1fb576664f51da6.jpg) +This is a black trash can. It is under a bathroom counter. + +![](images/c5e4102129e36b8422a5c9dd9a3836cd74b557cf47ccd92f1c0ac9c47a6fc1c4.jpg) +The trash can is white and plastic. It is attached to the wall to the left of the toilet. + +![](images/b755417f201743bcb2a283006afdba0654b488f71ecc698d35c5c3db2708eb4c.jpg) +(b1) +Figure 1. Text-decoupled, dense aligned 3D visual grounding. Different colours in the text correspond to different decoupled components. (a) Regular 3D visual grounding: locating objects requires comprehensively considering multiple semantic cues such as appearance attributes, object names, and spatial relationships. (b) Grounding without object name: not mentioning object names, avoiding short-cuts and forcing the model to predict the target based on other attributes. + +# object + +The door is rectangular in shape and has a small window on the upper portion. + +![](images/4400dd0a945727ceef622bc3c5e8f0690423803330834afb82f85555e2001ac4.jpg) +(b2) +(b) Grounding without object name + +The white refrigerator is in front of the kitchen stove. It is to the left side of the room as one enters the kitchen. + +![](images/ae632147d29a02f147beb464f4e3c9ef77972afa73fea37c4cd71179ee0c920e.jpg) +(a) Regular 3D visual grounding +(b3) + +It is a brown wooden object with a cloth seat and back. It has multicolored flower patterns on the seat, and back. + +![](images/93a6364390e579218ec1bc03fe1b94393d594de807de3100819d811c815bd7ad.jpg) +(b4) + +This is a black object. It is located next to a tall shelf and there is a fan in front of it. + +# Abstract + +3D visual grounding aims to find the object within point clouds mentioned by free-form natural language descriptions with rich semantic cues. However, existing methods either extract the sentence-level features coupling all words or focus more on object names, which would lose the word-level information or neglect other attributes. To alleviate these issues, we present EDA that Explicitly Decouples the textual attributes in a sentence and conducts Dense Alignment between such fine-grained language and point cloud objects. Specifically, we first propose a text decoupling module to produce textual features for every semantic component. Then, we design two losses to supervise + +the dense matching between two modalities: position alignment loss and semantic alignment loss. On top of that, we further introduce a new visual grounding task, locating objects without object names, which can thoroughly evaluate the model's dense alignment capacity. Through experiments, we achieve state-of-the-art performance on two widely-adopted 3D visual grounding datasets, ScanRefer and SR3D/NR3D, and obtain absolute leadership on our newly-proposed task. The source code is available at https://github.com/yanmin-wu/EDA. + +# 1. Introduction + +Multi-modal cues can highly benefit the 3D environment perception of an agent, including 2D images, 3D point clouds, and language. Recently, 3D visual grounding (3D VG) [8,50], also known as 3D object referencing [3], has at + +tached much attention as an important 3D cross-modal task. Its objective is to find the target object in point cloud scenes by analyzing the descriptive query language, which requires understanding both 3D visual and linguistic context. + +Language utterances typically involve words describing appearance attributes, object categories, spatial relationships and other characteristics, as shown by different colours in Fig. 1(a), requiring that the model integrate multiple cues to locate the mentioned object. Compared with 2D Visual Grounding [18,19,67,71], the sparseness and incompleteness of point clouds, and the diversity of language descriptions produced by 3D multi-view, make 3D VG more challenging. Existing works made significant progress from the following perspectives: improving point cloud features extraction by sparse convolution [70] or 2D images assistance [68]; generating more discriminative object candidates through instance segmentation [33] or language modulation [46]; identifying complex spatial relationships between entities via graph convolution [23] or attention [6]. + +However, we observe two issues that remain unexplored. 1) Imbalance: The object name can exclude most candidates, and even in some cases, there is only one name-matched object, as the "door" and "refrigerator" in Fig. 1(b1, b2). This shortcut may lead to an inductive bias in the model that pays more attention to object names while weakening other properties such as appearance and relationships, resulting in imbalanced learning. 2) Ambiguity: Utterances frequently refer to multiple objects and attributes (such as "black object, tall shelf, fan" in Fig. 1(b4)), while the model's objective is to identify only the main object, leading to an ambiguous understanding of language descriptions. These insufficiencies of existing works stem from their characteristic of feature coupling and fusing implicitly. They input a sentence with different attribute words but output only one globally coupled sentence-level feature that subsequently matches the visual features of candidate objects. The coupled feature is ambiguous because some words may not describe the main object (green text in Fig. 1) but other auxiliary objects (red text in Fig. 1). Alternatively, using the cross-modal attention of the Transformer [21, 63] automatically and implicitly to fuse visual and text features. However, this may encourage the model to take shortcuts, such as focusing on object categories and ignoring other attributes, as previously discussed. + +Instead, we propose a more intuitive decoupled and explicit strategy. First, we parse the input text to decouple different semantic components, including the main object word, pronoun, attributes, relations, and auxiliary object words. Then, performing dense alignment between point cloud objects and multiple related decoupled components achieves fine-grained feature matching, which avoids the inductive bias resulting from imbalanced learning of different textual components. As the final grounding result, we + +explicitly select the object with the highest similarity to the decoupled text components (instead of the entire sentence), avoiding ambiguity caused by irrelevant components. Additionally, to explore the limits of VG and examine the comprehensiveness and fine-graininess of visual-language perception of the model, we suggest a challenging new task: Grounding without object name (VG-w/o-ON), where the name is replaced by "object" (see Fig. 1(b)), forcing the model to locate objects based on other attributes and relationships. This setting makes sense because utterances that do not mention object names are common expressions in daily life, and in addition to testing whether the model takes shortcuts. Benefiting from our text decoupling operation and the supervision of dense aligned losses, all text components are aligned with visual features, making it possible to locate objects independent of object names. + +To sum up, the main contributions of this paper are as follows: 1) We propose a text decoupling module to parse linguistic descriptions into multiple semantic components, followed by suggesting two well-designed dense aligned losses for supervising fine-grained visual-language feature fusion and preventing imbalance and ambiguity learning. 2) The challenging new 3D VG task of grounding without object names is proposed to comprehensively examine the model's robust performance. 3) We achieve state-of-the-art performance on two datasets (ScanRefer and SR3D/NR3D) on the regular 3D VG task and absolute leadership on the new task evaluated by the same model without retraining. + +# 2. Related Work + +# 2.1. 3D Vision and Language + +3D vision [52, 53, 75] and language are vital manners for humans to understand the environment, and they are also important research topics for the evolution of machines to be like humans. Previously, the two fields evolved independently. Due to the advance of multimodality [25, 26, 54, 56, 57, 72-74, 76], many promising works across 3D vision and language have been introduced recently. In 3D visual grounding [1, 8-10, 12], the speaker (like a human) describes an object in language. The listener (such a robot) needs to understand the language description and the 3D visual scene to grounding the target object. On the contrary, the 3D dense caption [9, 13, 14, 36, 65, 69] is analogous to an inverse process in which the input is a 3D scene, and the output is textual descriptions of each object. Language-modulated 3D detection or segmentation [7, 32, 34, 59, 78] enriches the diversity of text queries by matching visual-linguistic feature spaces rather than predicting the probability of a set number of categories. Furthermore, some studies explore the application of 3D visual language in agents such as robot perception [27, 61], vision-and-language navigation (VLN) [15, 31, 55], and embodied question answering + +(EQA) [4,22,30,45,47,62]. In this paper, we focus on point clouds-based 3D visual grounding, which is the fundamental technology for many embodied AI [24,38,48] tasks. + +# 2.2.3D Visual Grounding + +The majority of current mainstream techniques are two-stage. In the first stage, obtain the features of the query language and candidate point cloud objects independently by a pre-trained language model [16, 20, 49] and a pretrained 3D detector [44, 51] or segmenter [11, 35, 64]. In the second stage, the researchers focus on fusing the two modal features and then selecting the best-matched object. 1) The most straightforward solution is to concatenate the two modal features and then consider it a binary classification problem [8, 39], which provides limited performance because the two features are not sufficiently fused. 2) Taking advantage of the Transformer's attention mechanism, which is naturally suitable for multi-module feature fusion, He et al. [28] and Zhao et al. [77] achieve remarkable performance by performing self-attention and cross-attention to features. 3) In contrast, other studies view feature fusion as a matching problem rather than a classification. Yuan et al. [70] and Abdelreheem et al. [2], supervised by the contrastive loss [29], compute the cosine similarity of visual features and textual features. Inspired by [43], Feng et al. [23] parses the text to generate a text scene graph, simultaneously builds a visual scene graph, and then performs graph node matching. 4) Point clouds' sparse, noisy, incomplete, and lack of detail make learning objects' semantic information challenging. Yang et al. [68] and Cai et al. [6] use 2D images to aid visual-textual feature fusion, but at the cost of additional 2D-3D alignment and 2D feature extraction. + +However, the two-stage method has a substantial detection bottleneck: objects overlooked in the first stage cannot be matched in the second. In contrast, object detection and feature extraction in the single-stage method is modulated by the query text, making it easier to identify the text-concerned object. Liu et al. [41] suggest fusing visual and linguistic features at the bottom level and producing text-related visual heatmaps. Similarly, Luo et al. [46] present a single-stage approach that employs textual features to guide visual keypoint selection and progressively localizes objects. BUTD-DETR [34] is also a single-stage capable framework. More importantly, inspired by the 2D image-language pre-train model (such MDETR [37], GLIP [40]), BUTD-DETR measures the similarity between each word and object and then selects the features of the word that correspond to the object's name to match the candidate object. However, there are two limitations: 1) Since multiple object names may be mentioned in a sentence, the ground truth annotation is needed to retrieve the target name, which limits its generalizability. Our text decoupling module separates + +![](images/10e36a3a2c181dd5eb1f22ca1a614a4778f9455a969824f0fdf3054272275376.jpg) +Figure 2. Text component decoupling: (a) The query text. (b) Dependency tree analysis. (c) Decoupled into five components. + +text components and determines the target object name by grammatical analysis to avoid this restriction. 2) BUTD-DETR (and MDETR and GLIP in the 2D task) only consider the sparse alignment of main object words or noun phrases to visual features. Conversely, we align all object-related decoupled textual semantic components with visual features, which we refer to dense alignment, significantly enhancing the discriminability of multimodal features. + +# 3. Proposed Method + +The framework is illustrated in Fig. 3. First, the input text description is decoupled into multiple semantic components, and its affiliated text positions and features are obtained (Sec. 3.1). Concurrently, the Transformer-based encoder extracts and modulates features from point clouds and text, then decodes the visual features of candidate objects (Sec. 3.2). Finally, the dense aligned losses are derived between the decoupled text features and the decoded visual features (Sec. 3.3). The grounding result is the object with visual features most similar to text features (Sec. 3.4). + +# 3.1. Text Decoupling + +The text features of the coupled strategy are ambiguous, where features from multiple objects and attributes are coupled, such as "a brown wooden chair next to the black table." Among them, easy-to-learn clues (such as the category "chair" or the colour "brown") may predominate, weakening other attributes (such as material "wooden"); words of other objects (such as the "black table") may cause interference. To produce more discriminative text features and fine-grained cross-modal feature fusion, we decouple the query text into different semantic components, each independently aligned with visual features, avoiding the ambiguity caused by feature coupling. + +Text Component Decoupling. Analyzing grammatical dependencies between words is a fundamental task in NLP. We first use the off-the-shelf tool [60, 66] to parse the language description grammatically to generate the grammatical dependency trees, as shown in Fig. 2(b). Each sentence contains only one ROOT node, and each remaining word has a corresponding parent node. Then according to + +![](images/1d4faa68d8b73bd3752367807d2dc0c5a0a5ba012103c809f584a5930d2e9438.jpg) +Figure 3. The system framework. (a-c): Decouple the input text into several components to acquire the position label $L$ and features $t$ of the decoupled text. (d-e): Transformer-based encoders for cross-modal visual-text feature extraction. (f): Decode proposal features $\mathcal{O}'$ and linearly project them as object position labels $L_{pred}$ and object features $o$ , in addition to a box prediction head for regression of the bounding box. (g-h): Visual-text feature dense alignment. Note that the additional 3D object detection procedure is optional. + +the words' part-of-speech and dependencies, we decouple the long text into five semantic components (see Fig. 2(c)): Main object - the target object mentioned in the utterance; Auxiliary object - the one used to assist in locating the main object; Attributes - objects' appearance, shape, etc.; Pronoun - the word instead of the main object; Relationship - the spatial relation between the main object and the auxiliary object. Note that attributes affiliated with pronouns are equivalent to attached with the main object, thus connecting two sentences in an utterance. + +Text Position Decoupling. After decoupling each text component (Fig. 3(a)), we generate the position label (similar to a mask) $L_{\text{main}}, L_{\text{attr}}, L_{\text{auxi}}, L_{\text{pron}}, L_{\text{rel}} \in \mathbb{R}^{1 \times l}$ for the component's associated word (Fig. 3(b)). Where $l = 256$ is the maximum length of the text, each component's word position is set to 1 and the rest to 0. The label will be used to construct the position alignment loss and supervise the classification of objects. The classification result, is not one of a predetermined number of object categories but the position of the text with the highest semantic similarity. + +Text Feature Decoupling. The feature of each word (token) is produced in the backbone of multimodal feature extraction (Fig. 3(d)). The text feature of the decoupled component can be derived by dot-multiplying all words' features $\pmb{t}$ with its position label $L$ , as shown in Fig. 3(c). The decoupled text features and visual features will be independently aligned under the supervision of the semantic alignment loss. Note that in the decoupled text features, the semantics of the corresponding components absolutely + +predominate, but as a result of the Transformer's attention mechanism, it also implicitly contains the global sentence's information. In other words, feature decoupling produces individual features while keeping the global context. + +# 3.2. Multimodal Feature Extraction + +We employ BUTD-DETR's encoder-decoder module for feature extraction and intermodulation of cross-modal features. We strongly recommend the reader to refer to Fig. 3. + +Input Modal Tokenization. The input text and 3D point clouds are encoded by the pre-trained RoBERTa [42] and PointNet++ [53] and produce text tokens $\mathcal{T} \in \mathbb{R}^{l \times d}$ and visual tokens $\mathcal{V} \in \mathbb{R}^{n \times d}$ . Additionally, the GroupFree [44] detector is used to detect 3D boxes, which are subsequently encoded as box tokens $\mathcal{B} \in \mathbb{R}^{b \times d}$ . Note that the GroupFree is optional, the final predicted object of the network is from the prediction head (see below), and the box token is just to assist in better regression of the target object. + +Encoder-Decoder. Self-attention and cross-attention are performed in the encoder to update both visual and text features, obtaining cross-modal features $\mathcal{V}'$ , $\mathcal{T}'$ while keeping the dimensions. The top- $k$ ( $k = 256$ ) visual features are selected, linearly projected as query proposal features $\mathcal{O} \in \mathbb{R}^{k \times d}$ , and updated as $\mathcal{O}'$ in the decoder. + +Prediction Head. 1) The decoded proposal features $\mathcal{O}' \in \mathbb{R}^{k \times d}$ are fed into an MLP and output the predicted position labels $L_{pred} \in \mathbb{R}^{k \times l}$ , which are then utilized to calculate the position alignment loss with decoupled text position labels $L \in \mathbb{R}^{1 \times l}$ . 2) Additionally, the proposal fea + +tures are linearly projected as object features $\pmb{o} \in \mathbb{R}^{k \times 64}$ by another MLP, which are then utilized to compute the semantic alignment loss with the similarly linearly projected text feature $\pmb{t} \in \mathbb{R}^{l \times 64}$ . 3) Lastly, a box prediction head [44] regresses the bounding box of the object. + +# 3.3. Dense Aligned Loss + +# 3.3.1 Dense Position Aligned Loss + +The objective of position alignment is to ensure that the distribution of language-modulated visual features closely matches that of the query text description, as shown in Fig. 3(g). This process is similar to standard object detection's one-hot label prediction. However, rather than being limited by the number of categories, we predict the position of text that is similar to objects. + +The constructed ground truth text distribution of the mentioned main object is obtained by element-wise summing the position labels of the associated decoupled text components: + +$$ +P _ {\text {m a i n}} = \lambda_ {1} L _ {\text {m a i n}} + \lambda_ {2} L _ {\text {a t t r i}} + \lambda_ {3} L _ {\text {p r o n}} + \lambda_ {4} L _ {\text {r e l}}, \tag {1} +$$ + +where $\lambda$ is the weight of different parts (refer to the parametric search in Supplementary Material.). $P_{auxi} = L_{auxi}$ represents the text distribution of the auxiliary object. The remaining candidate objects' text distribution is $P_{oth}$ , with the final bit set to 1 (see $\varnothing$ in Fig. 3(g)). Therefore, all $k$ candidate objects' ground truth text distribution is $P_{text} = \{P_{main}, P_{auxi}, P_{oth}\} \in \mathbb{R}^{k \times l}$ . + +The predicted visual distribution of $k$ objects is produced by applying softmax to the output $L_{pred} \in \mathbb{R}^{k \times l}$ of the prediction head: + +$$ +P _ {o b j} = \operatorname {S o f t m a x} \left(L _ {p r e d}\right). \tag {2} +$$ + +Their KL divergence is defined as the position-aligned loss: + +$$ +\mathcal {L} _ {p o s} = \sum_ {i = 1} ^ {k} \left[ P _ {t e x t} ^ {i} \log \left(P _ {t e x t} ^ {i}\right) - P _ {t e x t} ^ {i} \log \left(P _ {o b j} ^ {i}\right) \right]. \tag {3} +$$ + +We highlight that "dense alignment" indicates that the target object is aligned with the positions of multiple components (Eq. (1)), significantly different from BUTD-DETR (and MDETR for 2D tasks), which only sparsely aligns with the object name's position $L_{main}$ . + +# 3.3.2 Dense Semantic Aligned Loss + +Semantic alignment aims to learn the similarity of visual-text multimodal features through contrastive learning. The object loss of semantic alignment is defined as follows: + +$$ +\mathcal {L} _ {\text {s e m - o}} = \sum_ {i = 1} ^ {k} \frac {1}{| \mathbf {T} _ {i} ^ {+} |} \sum_ {\boldsymbol {t} _ {i} \in \mathbf {T} _ {i} ^ {+}} - \log \left(\frac {\exp \left(w _ {+} * \left(\boldsymbol {o} _ {i} ^ {\top} \boldsymbol {t} _ {i} / \tau\right)\right)}{\sum_ {j = 1} ^ {l} \exp \left(w _ {-} * \left(\boldsymbol {o} _ {i} ^ {\top} \boldsymbol {t} _ {j} / \tau\right)\right)}\right), \tag {4} +$$ + +where $\pmb{o}$ and $\pmb{t}$ are the object and text features after linear projection, and $o^\top t / \tau$ is their similarity, as shown in Fig. 3 (h). $k$ and $l$ are the number of objects and words. $\pmb{t}_i$ is the positive text feature of the $i_{th}$ candidate object. Taking the main object as an example, the positive text feature $\mathbf{T}_i^+$ corresponding to it is: + +$$ +\boldsymbol {t} _ {i} \in \mathbf {T} _ {i} ^ {+} = \left\{\boldsymbol {t} _ {\text {m a i n}}, \boldsymbol {t} _ {\text {a t t r i}}, \boldsymbol {t} _ {\text {p r o n}}, \boldsymbol {t} _ {\text {r e l}} \right\}, \tag {5} +$$ + +and $w_{+}$ is the weight of each positive term. $t_j$ is the feature of the $i_{th}$ text, but note that the negative similarity weight $w_{-}$ for auxiliary object term $t_{auxi}$ is 2, while the rest weight 1. The text loss of semantic alignment defined similarly: + +$$ +\mathcal {L} _ {s e m - t} = \sum_ {i = 1} ^ {l} \frac {w _ {+}}{\left| \mathbf {O} _ {i} ^ {+} \right|} \sum_ {\boldsymbol {o} _ {i} \in \mathbf {O} _ {i} ^ {+}} - \log \left(\frac {\exp \left(\boldsymbol {t} _ {i} ^ {\top} \boldsymbol {o} _ {i} / \tau\right)}{\sum_ {j = 1} ^ {k} \exp \left(\boldsymbol {t} _ {i} ^ {\top} \boldsymbol {o} _ {j} / \tau\right)}\right), \tag {6} +$$ + +where $o_i \in \mathbf{O}_i^+$ is the positive object feature of the $i_{th}$ text, and $o_j$ is the feature of the $j_{th}$ object. The final semantic alignment loss is the mean of the two: $\mathcal{L}_{sem} = (\mathcal{L}_{sem\_o} + \mathcal{L}_{sem\_t}) / 2$ . + +Similarly, the semantic alignment of multiple text components (Eq. (5)) with visual features also illustrates our insight of "dense." This is intuitive, such as "It is a brown chair with legs under a blackboard," where the main object's visual features should be not only similar to "chair" but also similar to "brown, legs" and distinct to "blackboard" as possible. + +The total loss for training also includes the box regression loss. Refer to Supplementary Material for details. + +# 3.4. Explicit Inference + +Because of our text decoupling and dense alignment operations, object features fused multiple related text component features, allowing for the computation of the similarity between individual text components and candidate objects. For instance, $S_{main} = \text{Softmax}(\boldsymbol{o}^{\top}\boldsymbol{t}_{main} / \tau)$ indicates the similarity between objects $\boldsymbol{o}$ and the main text component $\boldsymbol{t}_{main}$ . Therefore, the similarity of objects and related components can be explicitly combined to obtain the total score and select the candidate with the highest score: + +$$ +S _ {a l l} = S _ {\text {m a i n}} + S _ {\text {a t t r i}} + S _ {\text {p r o n}} + S _ {\text {r e l}} - S _ {\text {a u x i}}, \tag {7} +$$ + +where the definition of $S_{attri}$ , $S_{pron}$ , $S_{rel}$ , and $S_{auxi}$ is similar to $S_{main}$ . If providing supervision of auxiliary objects during training, and the auxiliary object can be identified by solely computing the similarity between the object features and the auxiliary component's text features: $S_{all} = S_{attri}$ . Being able to infer the object based on the part of the text is a significant sign that the network has learned well-aligned and fine-grained visual-text feature space. + +# 4. Experiments + +First, we conduct comprehensive and fair comparisons with SOTA methods in the Regular 3D Visual Grounding setting in Sec. 4.1. Then, in Sec. 4.2, we introduce our proposed new task, Grounding without Object Name, and perform comparison and analysis. Implementation details, additional experiments and more qualitative results are detailed in the supplementary material. + +# 4.1. Regular 3D Visual Grounding + +# 4.1.1 Experiment settings + +We keep the same settings as existing works, with ScanRefer [8] and SR3D/NR3D [3] as datasets and Acc@0.25IoU and Acc@0.5IoU as metrics. Based on the visual data of ScanNet [17], ScanRefer adds 51,583 manually annotated text descriptions about objects. These complex and free-form descriptions involve object categories and attributes such as colour, shape, size, and spatial relationships. SR3D/NR3D is also proposed based on ScanNet, with SR3D including 83,572 simple machine-generated descriptions and NR3D containing 41,503 descriptions similar to ScanRefer's human annotation. The difference is that in the ScanRefer configuration, detecting and matching objects are required, while SR3D/NR3D is simpler. It supplies GT boxes for all candidate objects and only needs to classify the classes of the boxes and choose the target object. + +# 4.1.2 Comparison to the state of the art + +ScanRefer. Table 1 reports the results on the ScanRefer dataset. i) Our method achieves state-of-the-art performance by a substantial margin, with an overall improvement of $4.2\%$ and $3.7\%$ to $54.59\%$ and $42.26\%$ . ii) Some studies [6,8,9,46,68,77] proved that supplemented 2D images with detailed and dense semantics could learn better point cloud features. Surprisingly, we only use sparse 3D point cloud features and even outperformed 2D assistance methods. This superiority illustrates that our decoupling and dense alignment strategies mine more efficient and meaningful visual-text co-representations. iii) Another finding is that the accuracy of most existing techniques is less than $40\%$ and $30\%$ in the "multiple" setting because multiple means that the category of the target object mentioned in the language is not unique, with more interference candidates with the same category. However, we reached a remarkable $49.13\%$ and $37.64\%$ . To identify similar objects, a finer-grained understanding of the text and vision is required in this complex setting. iv) The last three rows in Table 1 compare single-stage methods, where our method's single-stage implementation is without the object detection step ( $\mathcal{B}$ in Fig. 3) in training and inference. The result illustrates that while not requiring an additional pre-trained 3D object detector, our approach also can achieve SOTA performance. + +v) The qualitative results are depicted in Fig. 4(a-c), which reveals that our method with an excellent perception of appearance attributes, spatial relationships, and even ordinal numbers. + +SR3D/NR3D. Table 2 shows the accuracy on the SR3D/NR3D dataset, where we achieve the best performance of $68.1\%$ and $52.1\%$ . In SR3D, since the language descriptions are concise and the object is easy to identify, our method and [34, 46] reach an accuracy of over $60\%$ . Conversely, in NR3D, descriptions are too detailed and complex, causing additional challenges for text decoupling. However, we still achieve SOTA accuracy with the 3D-only data, while other comparable methods [46, 68] rely on additional 2D images for training. Some methods [6, 8, 9] compared in Table 1 are not discussed here because they are not evaluated on the SR3D/NR3D dataset. In addition, because GT boxes of candidate objects are provided in this setting, the single-stage methods are not applicable and discussed. + +# 4.1.3 Ablation studies + +Loss ablation. The ablation of the position-aligned loss and the semantic-aligned loss is shown in Table 3. The performance of the semantic-aligned loss is marginally better because its contrastive loss not only shortens the distance between similar text-visual features but also enlarges the distance between dis-matched features (such as $t_{auxi}$ is a negative term in Eq. (4)). Whereas position-aligned loss only considers object-related components (as in Eq. (1)). When both losses supervise together, the best accuracy is achieved, demonstrating that they can produce complementary performance. + +Dense components ablation. To demonstrate our insight into dense alignment, we perform ablation analysis on the different decoupled text components, and the results are displayed in the "Regular VG" column in Table 4. Analysis: i) (a) is our baseline implementation of the sparse concept, using only the "Main object" component decoupled from the text. In contrast to BUTD-DETR, the text decoupling module (Sec. 3.1) is used to obtain text labels and features during training and inference instead of employing ground truth labels. ii) Dense-aligned sub-methods (b)-(h) outperform the sparse alignment (a) because of the finer-grained visual-linguistic feature fusion. iii) (b)-(e) indicate that adding any other component on top of the "Main object" improves performance, demonstrating the validity of each text component. The "Attribute" component aids in identifying characteristics such as colour, and shape, frequently mentioned in language descriptions. Unexpectedly, the "Pronoun" component such as "it, that, and which" have little meaning when used alone but also function in our method, indicating that the pronoun learned contextual information from the sentence. The "Relationship" component facilitates comprehension of spatial relationships be + +
MethodVenueModalityUnique (~19%)Multiple (~81%)Overall
0.250.50.250.50.250.5
ScanRefer [8]ECCV20203D67.6446.1932.0621.2638.9726.10
3D+2D76.3353.5132.7321.1141.1927.40
ReferIt3D [3]ECCV20203D53.837.521.012.826.416.9
TGNN [33]AAAI20213D68.6156.8029.8423.1837.3729.70
InstanceRefer [70]ICCV20213D77.4566.8331.2724.7740.2332.93
SAT [68]ICCV20213D+2D73.2150.8337.6425.1644.5430.14
FFL-3DOG [23]ICCV20213D78.8067.9435.1925.7041.3334.01
3DVG-Transformer [77]ICCV20213D77.1658.4738.3828.7045.9034.47
3D+2D81.9360.6439.3028.4247.5734.67
3D-SPS [46]CVPR20223D+2D84.1266.7240.3229.8248.8236.98
3DJCG [6]CVPR20223D78.7561.3040.1330.0847.6236.14
3D+2D83.4764.3441.3930.8249.5637.33
BUTD-DETR [34] †ECCV20223D82.8864.9844.7333.9750.4238.60
D3Net [9]ECCV20223D+2D-70.35-30.50-37.87
EDA-3D85.7668.5749.1337.6454.59 (+4.2%)42.26 (+3.7%)
3D-SPS(single-stage) [46]CVPR20223D81.6364.7739.4829.6147.6536.43
BUTD-DETR (single-stage) [34]‡ECCV20223D81.4761.2444.2032.8149.7637.05
EDA (single-stage) §-3D86.4069.4248.1136.8253.8341.70
+ +Table 1. The 3D visual grounding results on ScanRefer, accuracy evaluated by IoU 0.25 and IoU 0.5. † The accuracy is reevaluated using our parsed text labels because the performance reported by BUTD-DETR used ground truth text labels and ignored some challenging samples (see supplementary materials for more details). § Our single-stage implementation without the assistance of the additional 3D object detection step (dotted arrows in Fig. 3). ‡ BUTD-DETR did not provide single-stage results and we retrained the model. + +
MethodVenueModalitySR3DNR3D
ReferIt3D [3]ECCV203D39.835.6
TGNN [33]AAAI213D45.037.3
TransRefer3D [28]MM213D57.442.1
InstanceRefer [70]ICCV213D48.038.8
3DVG-Transfor. [77]ICCV213D51.440.8
FFL-3DOG [23]ICCV213D-41.7
SAT [68]ICCV213D+2D57.949.2
3DReferTrans. [2]WACV223D47.039.0
LanguageRefer [58]CoRL223D56.043.9
3D-SPS [46]CVPR223D+2D62.651.5
BUTD-DETR † [34]ECCV223D65.649.1
LAR [5]NeurIPS223D59.648.9
EDA (Ours)-3D68.152.1
+ +tween objects. The component "Auxiliary object" is a negative term in the loss (Eq. (4)). During inference (Eq. (7)), its similarity is subtracted in the hopes that the predicted main object is as dissimilar to it as possible. iv) (f)-(h) integrate different components to make performance gains and reach the peak when all are involved, demonstrating that the functions of each component can be complementary, and there may be no overlap between the features of each one. The result reveals that our method effectively decouples and matches fine-grained multimodal features. + +Table 2. Performance on SR3D/NR3D datasets by Acc@0.25IoU as the metric. The detailed results of EDA in four subsets are provided in the Supplementary Material. $\dagger$ Reevaluated by parsed text labels (see supp. for more details). + +
+Lpos+LsemAcc@0.25Acc@0.5
(a)✓51.239.6
(b)✓52.239.9
(c)✓✓54.642.3
+ +Table 3. Loss ablation on the ScanRefer dataset. + +
Dense componentsRegular VGVG-w/o-ON
MainAttri.Pron.Auxi.Rel.@0.25@0.5@0.25@0.5
(a)✓51.538.821.816.7
(b)✓✓53.141.323.217.8
(c)✓✓52.940.823.718.6
(d)✓✓52.941.023.218.4
(e)✓✓52.840.725.719.6
(f)✓✓✓53.841.824.218.5
(g)✓✓✓✓54.242.324.018.8
(h)✓✓✓✓✓54.642.326.521.2
+ +Table 4. Ablation studies of different text components on Regular VG and VG-w/o-ON tasks. Evaluated on the ScanRefer dataset. + +# 4.2. Grounding without Object Name (VG-w/o-ON) + +# 4.2.1 Experiment settings + +To evaluate the comprehensive reasoning ability of the model and avoid inductive biases about object names, we propose a new and more challenging task: grounding objects without mentioning object names (VG-w/o-ON). Specifically, we manually replace the object's name with "object" in the ScanRefer validation set. For instance: "This is a brown wooden chair" becomes "this is a brown + +![](images/bf70433eed626fc245fe49f339213e576052f800121603c1926c7651d816c5a7.jpg) +Figure 4. Qualitative results with ScanRefer texts. (a-c): Regular 3D visual grounding. (d-e): Grounding without object name. + +wooden object". A total of 9253 samples were annotated and discarded another 255 ambiguous samples. We divide this language set into four subsets: only mentioning object attributes ( $\sim 15\%$ ), only mentioning spatial relationships ( $\sim 20\%$ ), mentioning both attributes and relationships ( $\sim 63\%$ ), and others ( $\sim 2\%$ ), as the first row in Table 5. Note that, without retraining, we perform comparisons using our best model and comparative approaches' best models trained for the regular VG task (Sec. 4.1). + +# 4.2.2 Result and analysis + +Table 5 reports the experimental results. i) The performance of all methods on this challenging task is significantly lower than that of regular VG (see Table. 1), indicating that object categories provide rich semantic information, which is also conducive to classifying features. It's accessible to produce the category's inductive bias, especially in the "unique" setting. ii) Our method achieves absolute lead with the overall performance of $26.5\%$ and $21.2\%$ , which is over $10\%$ higher than other methods. This preponderance demonstrates that our proposed text decoupling and dense alignment enable fine-grained visual-linguistic feature matching, where the model identifies the visual features most similar to other text components (e.g. attributes, relations, etc.). iii) Notably, in subset "Attri+Rel", our method performs better than in the other subsets because additional cues can be exploited for fine-grained localization. However, the performance of the comparison approaches on this subset drops, revealing that more clues make them suffer from ambiguity. iv) Column "VG-w/o-ON" in Table 4 shows ablation studies of text components for this new task. The performance increase offered by the additional components is more remarkable than during the regular VG task. Among them, the + +
MethodSubsetsOverall
Attri onlyRel onlyAttri+Rel@0.25@0.5
ScanRefer [8]11.1710.5310.2910.516.20
TGNN [33]10.5213.3211.3511.649.51
InstanceRefer [70]14.7413.7113.8113.9211.47
BUTD-DETR [34]12.3012.1111.8611.998.95
EDA (Ours)25.4025.8226.9626.5021.20
+ +Table 5. Performance of grounding without object name. The accuracy of subsets is measured by acc@0.25IoU, where the "other" subset is not reported due to its small proportion. + +"Relationship" component plays the most significant role because the spatial relationship with other objects may provide more obvious indications in this setting. v) Fig. 4(d-e) shows qualitative examples. Even without knowing the target's name, our method can infer it by other cues, while BUTD-DETR's performance drops catastrophically. + +# 5. Conclusion + +We present EDA, an explicit, dense-aligned method for 3D Visual Grounding tasks. By decoupling text into multiple semantic components and densely aligning it with visual features under the supervision of position-aligned and semantic-aligned loss, we enable fine-grained visual-text feature fusion, avoiding the imbalance and ambiguity of existing methods. Extensive experiments and ablation demonstrate the superiority of our method. In addition, we propose a new challenging 3D VG subtask of grounding without the object name to evaluate model robustness comprehensively. However, our limitations are the performance bottlenecks of multiple modules, such as PointNet++, RoBERTa, and text parsing modules. Especially when the text is lengthy, text decoupling may fail, resulting in performance degradation. + +# References + +[1] Ahmed Abdelreheem, Kyle Olszewski, Hsin-Ying Lee, Peter Wonka, and Panos Achlioptas. Scanents3d: Exploiting phrase-to-3d-object correspondences for improved visio-linguistic models in 3d scenes. arXiv preprint arXiv:2212.06250, 2022. 2 +[2] Ahmed Abdelreheem, Ujjwal Upadhyay, Ivan Skorokhodov, Rawan Al Yahya, Jun Chen, and Mohamed Elhoseiny. 3dreftransformer: Fine-grained object identification in real-world scenes using natural language. 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Text-decoupled, dense aligned 3D visual grounding. Different colours in the text correspond to different decoupled components. (a) Regular 3D visual grounding: locating objects requires comprehensively considering multiple semantic cues such as appearance attributes, object names, and spatial relationships. (b) Grounding without object name: not mentioning object names, avoiding short-cuts and forcing the model to predict the target based on other attributes." + } + ] + } + ], + "index": 33, + "angle": 0, + "type": "image_caption" + } + ], + "index": 19 + }, + { + "bbox": [ + 81, + 397, + 107, + 405 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 81, + 397, + 107, + 405 + ], + "spans": [ + { + "bbox": [ + 81, + 397, + 107, + 405 + ], + "type": "text", + "content": "object" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 64, + 407, + 165, + 431 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 64, + 407, + 165, + 431 + ], + "spans": [ + { + "bbox": [ + 64, + 407, + 165, + 431 + ], + "type": "text", + "content": "The door is rectangular in shape and has a small window on the upper portion." + } + ] + } + ], + "index": 22 + }, + { + "type": "image", + "bbox": [ + 180, + 326, + 285, + 396 + ], + "blocks": [ + { + "bbox": [ + 180, + 326, + 285, + 396 + ], + "lines": [ + { + "bbox": [ + 180, + 326, + 285, + 396 + ], + "spans": [ + { + "bbox": [ + 180, + 326, + 285, + 396 + ], + "type": "image", + "image_path": "4400dd0a945727ceef622bc3c5e8f0690423803330834afb82f85555e2001ac4.jpg" + } + ] + } + ], + "index": 23, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 179, + 396, + 193, + 404 + ], + "lines": [ + { + "bbox": [ + 179, + 396, + 193, + 404 + ], + "spans": [ + { + "bbox": [ + 179, + 396, + 193, + 404 + ], + "type": "text", + "content": "(b2)" + } + ] + } + ], + "index": 24, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 228, + 437, + 378, + 448 + ], + "lines": [ + { + "bbox": [ + 228, + 437, + 378, + 448 + ], + "spans": [ + { + "bbox": [ + 228, + 437, + 378, + 448 + ], + "type": "text", + "content": "(b) Grounding without object name" + } + ] + } + ], + "index": 32, + "angle": 0, + "type": "image_caption" + } + ], + "index": 23 + }, + { + "bbox": [ + 187, + 404, + 282, + 436 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 187, + 404, + 282, + 436 + ], + "spans": [ + { + "bbox": [ + 187, + 404, + 282, + 436 + ], + "type": "text", + "content": "The white refrigerator is in front of the kitchen stove. It is to the left side of the room as one enters the kitchen." + } + ] + } + ], + "index": 25 + }, + { + "type": "image", + "bbox": [ + 293, + 325, + 413, + 396 + ], + "blocks": [ + { + "bbox": [ + 233, + 312, + 369, + 323 + ], + "lines": [ + { + "bbox": [ + 233, + 312, + 369, + 323 + ], + "spans": [ + { + "bbox": [ + 233, + 312, + 369, + 323 + ], + "type": "text", + "content": "(a) Regular 3D visual grounding" + } + ] + } + ], + "index": 18, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 293, + 325, + 413, + 396 + ], + "lines": [ + { + "bbox": [ + 293, + 325, + 413, + 396 + ], + "spans": [ + { + "bbox": [ + 293, + 325, + 413, + 396 + ], + "type": "image", + "image_path": "ae632147d29a02f147beb464f4e3c9ef77972afa73fea37c4cd71179ee0c920e.jpg" + } + ] + } + ], + "index": 26, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 293, + 396, + 307, + 404 + ], + "lines": [ + { + "bbox": [ + 293, + 396, + 307, + 404 + ], + "spans": [ + { + "bbox": [ + 293, + 396, + 307, + 404 + ], + "type": "text", + "content": "(b3)" + } + ] + } + ], + "index": 27, + "angle": 0, + "type": "image_caption" + } + ], + "index": 26 + }, + { + "bbox": [ + 307, + 404, + 404, + 435 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 307, + 404, + 404, + 435 + ], + "spans": [ + { + "bbox": [ + 307, + 404, + 404, + 435 + ], + "type": "text", + "content": "It is a brown wooden object with a cloth seat and back. It has multicolored flower patterns on the seat, and back." + } + ] + } + ], + "index": 28 + }, + { + "type": "image", + "bbox": [ + 418, + 327, + 539, + 397 + ], + "blocks": [ + { + "bbox": [ + 418, + 327, + 539, + 397 + ], + "lines": [ + { + "bbox": [ + 418, + 327, + 539, + 397 + ], + "spans": [ + { + "bbox": [ + 418, + 327, + 539, + 397 + ], + "type": "image", + "image_path": "93a6364390e579218ec1bc03fe1b94393d594de807de3100819d811c815bd7ad.jpg" + } + ] + } + ], + "index": 29, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 419, + 396, + 433, + 404 + ], + "lines": [ + { + "bbox": [ + 419, + 396, + 433, + 404 + ], + "spans": [ + { + "bbox": [ + 419, + 396, + 433, + 404 + ], + "type": "text", + "content": "(b4)" + } + ] + } + ], + "index": 30, + "angle": 0, + "type": "image_caption" + } + ], + "index": 29 + }, + { + "bbox": [ + 428, + 405, + 527, + 429 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 428, + 405, + 527, + 429 + ], + "spans": [ + { + "bbox": [ + 428, + 405, + 527, + 429 + ], + "type": "text", + "content": "This is a black object. It is located next to a tall shelf and there is a fan in front of it." + } + ] + } + ], + "index": 31 + }, + { + "bbox": [ + 143, + 514, + 191, + 526 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 514, + 191, + 526 + ], + "spans": [ + { + "bbox": [ + 143, + 514, + 191, + 526 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 34 + }, + { + "bbox": [ + 46, + 535, + 288, + 680 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 535, + 288, + 680 + ], + "spans": [ + { + "bbox": [ + 46, + 535, + 288, + 680 + ], + "type": "text", + "content": "3D visual grounding aims to find the object within point clouds mentioned by free-form natural language descriptions with rich semantic cues. However, existing methods either extract the sentence-level features coupling all words or focus more on object names, which would lose the word-level information or neglect other attributes. To alleviate these issues, we present EDA that Explicitly Decouples the textual attributes in a sentence and conducts Dense Alignment between such fine-grained language and point cloud objects. Specifically, we first propose a text decoupling module to produce textual features for every semantic component. Then, we design two losses to supervise" + } + ] + } + ], + "index": 35 + }, + { + "bbox": [ + 306, + 515, + 545, + 634 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 515, + 545, + 634 + ], + "spans": [ + { + "bbox": [ + 306, + 515, + 545, + 634 + ], + "type": "text", + "content": "the dense matching between two modalities: position alignment loss and semantic alignment loss. On top of that, we further introduce a new visual grounding task, locating objects without object names, which can thoroughly evaluate the model's dense alignment capacity. Through experiments, we achieve state-of-the-art performance on two widely-adopted 3D visual grounding datasets, ScanRefer and SR3D/NR3D, and obtain absolute leadership on our newly-proposed task. The source code is available at https://github.com/yanmin-wu/EDA." + } + ] + } + ], + "index": 36 + }, + { + "bbox": [ + 306, + 645, + 386, + 658 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 645, + 386, + 658 + ], + "spans": [ + { + "bbox": [ + 306, + 645, + 386, + 658 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 37 + }, + { + "bbox": [ + 306, + 665, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 665, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 306, + 665, + 545, + 714 + ], + "type": "text", + "content": "Multi-modal cues can highly benefit the 3D environment perception of an agent, including 2D images, 3D point clouds, and language. Recently, 3D visual grounding (3D VG) [8,50], also known as 3D object referencing [3], has at" + } + ] + } + ], + "index": 38 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 693, + 287, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 693, + 287, + 712 + ], + "spans": [ + { + "bbox": [ + 47, + 693, + 287, + 712 + ], + "type": "text", + "content": "* Corresponding author. This work was supported in part by Shenzhen Research Project under Grant JCYJ20220531093215035." + } + ] + } + ], + "index": 39 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "19231" + } + ] + } + ], + "index": 40 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 120 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 120 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 120 + ], + "type": "text", + "content": "tached much attention as an important 3D cross-modal task. Its objective is to find the target object in point cloud scenes by analyzing the descriptive query language, which requires understanding both 3D visual and linguistic context." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 122, + 288, + 302 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 122, + 288, + 302 + ], + "spans": [ + { + "bbox": [ + 46, + 122, + 288, + 302 + ], + "type": "text", + "content": "Language utterances typically involve words describing appearance attributes, object categories, spatial relationships and other characteristics, as shown by different colours in Fig. 1(a), requiring that the model integrate multiple cues to locate the mentioned object. Compared with 2D Visual Grounding [18,19,67,71], the sparseness and incompleteness of point clouds, and the diversity of language descriptions produced by 3D multi-view, make 3D VG more challenging. Existing works made significant progress from the following perspectives: improving point cloud features extraction by sparse convolution [70] or 2D images assistance [68]; generating more discriminative object candidates through instance segmentation [33] or language modulation [46]; identifying complex spatial relationships between entities via graph convolution [23] or attention [6]." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 304, + 288, + 604 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 304, + 288, + 604 + ], + "spans": [ + { + "bbox": [ + 46, + 304, + 288, + 604 + ], + "type": "text", + "content": "However, we observe two issues that remain unexplored. 1) Imbalance: The object name can exclude most candidates, and even in some cases, there is only one name-matched object, as the \"door\" and \"refrigerator\" in Fig. 1(b1, b2). This shortcut may lead to an inductive bias in the model that pays more attention to object names while weakening other properties such as appearance and relationships, resulting in imbalanced learning. 2) Ambiguity: Utterances frequently refer to multiple objects and attributes (such as \"black object, tall shelf, fan\" in Fig. 1(b4)), while the model's objective is to identify only the main object, leading to an ambiguous understanding of language descriptions. These insufficiencies of existing works stem from their characteristic of feature coupling and fusing implicitly. They input a sentence with different attribute words but output only one globally coupled sentence-level feature that subsequently matches the visual features of candidate objects. The coupled feature is ambiguous because some words may not describe the main object (green text in Fig. 1) but other auxiliary objects (red text in Fig. 1). Alternatively, using the cross-modal attention of the Transformer [21, 63] automatically and implicitly to fuse visual and text features. However, this may encourage the model to take shortcuts, such as focusing on object categories and ignoring other attributes, as previously discussed." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 605, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 605, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 605, + 287, + 715 + ], + "type": "text", + "content": "Instead, we propose a more intuitive decoupled and explicit strategy. First, we parse the input text to decouple different semantic components, including the main object word, pronoun, attributes, relations, and auxiliary object words. Then, performing dense alignment between point cloud objects and multiple related decoupled components achieves fine-grained feature matching, which avoids the inductive bias resulting from imbalanced learning of different textual components. As the final grounding result, we" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 304, + 72, + 545, + 263 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 263 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 263 + ], + "type": "text", + "content": "explicitly select the object with the highest similarity to the decoupled text components (instead of the entire sentence), avoiding ambiguity caused by irrelevant components. Additionally, to explore the limits of VG and examine the comprehensiveness and fine-graininess of visual-language perception of the model, we suggest a challenging new task: Grounding without object name (VG-w/o-ON), where the name is replaced by \"object\" (see Fig. 1(b)), forcing the model to locate objects based on other attributes and relationships. This setting makes sense because utterances that do not mention object names are common expressions in daily life, and in addition to testing whether the model takes shortcuts. Benefiting from our text decoupling operation and the supervision of dense aligned losses, all text components are aligned with visual features, making it possible to locate objects independent of object names." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 265, + 545, + 408 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 265, + 545, + 408 + ], + "spans": [ + { + "bbox": [ + 304, + 265, + 545, + 408 + ], + "type": "text", + "content": "To sum up, the main contributions of this paper are as follows: 1) We propose a text decoupling module to parse linguistic descriptions into multiple semantic components, followed by suggesting two well-designed dense aligned losses for supervising fine-grained visual-language feature fusion and preventing imbalance and ambiguity learning. 2) The challenging new 3D VG task of grounding without object names is proposed to comprehensively examine the model's robust performance. 3) We achieve state-of-the-art performance on two datasets (ScanRefer and SR3D/NR3D) on the regular 3D VG task and absolute leadership on the new task evaluated by the same model without retraining." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 306, + 422, + 392, + 434 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 422, + 392, + 434 + ], + "spans": [ + { + "bbox": [ + 306, + 422, + 392, + 434 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 443, + 443, + 455 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 443, + 443, + 455 + ], + "spans": [ + { + "bbox": [ + 306, + 443, + 443, + 455 + ], + "type": "text", + "content": "2.1. 3D Vision and Language" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 462, + 545, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 462, + 545, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 462, + 545, + 715 + ], + "type": "text", + "content": "3D vision [52, 53, 75] and language are vital manners for humans to understand the environment, and they are also important research topics for the evolution of machines to be like humans. Previously, the two fields evolved independently. Due to the advance of multimodality [25, 26, 54, 56, 57, 72-74, 76], many promising works across 3D vision and language have been introduced recently. In 3D visual grounding [1, 8-10, 12], the speaker (like a human) describes an object in language. The listener (such a robot) needs to understand the language description and the 3D visual scene to grounding the target object. On the contrary, the 3D dense caption [9, 13, 14, 36, 65, 69] is analogous to an inverse process in which the input is a 3D scene, and the output is textual descriptions of each object. Language-modulated 3D detection or segmentation [7, 32, 34, 59, 78] enriches the diversity of text queries by matching visual-linguistic feature spaces rather than predicting the probability of a set number of categories. Furthermore, some studies explore the application of 3D visual language in agents such as robot perception [27, 61], vision-and-language navigation (VLN) [15, 31, 55], and embodied question answering" + } + ] + } + ], + "index": 8 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "19232" + } + ] + } + ], + "index": 9 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 287, + 109 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 287, + 109 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 287, + 109 + ], + "type": "text", + "content": "(EQA) [4,22,30,45,47,62]. In this paper, we focus on point clouds-based 3D visual grounding, which is the fundamental technology for many embodied AI [24,38,48] tasks." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 118, + 170, + 132 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 118, + 170, + 132 + ], + "spans": [ + { + "bbox": [ + 47, + 118, + 170, + 132 + ], + "type": "text", + "content": "2.2.3D Visual Grounding" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 138, + 289, + 472 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 138, + 289, + 472 + ], + "spans": [ + { + "bbox": [ + 46, + 138, + 289, + 472 + ], + "type": "text", + "content": "The majority of current mainstream techniques are two-stage. In the first stage, obtain the features of the query language and candidate point cloud objects independently by a pre-trained language model [16, 20, 49] and a pretrained 3D detector [44, 51] or segmenter [11, 35, 64]. In the second stage, the researchers focus on fusing the two modal features and then selecting the best-matched object. 1) The most straightforward solution is to concatenate the two modal features and then consider it a binary classification problem [8, 39], which provides limited performance because the two features are not sufficiently fused. 2) Taking advantage of the Transformer's attention mechanism, which is naturally suitable for multi-module feature fusion, He et al. [28] and Zhao et al. [77] achieve remarkable performance by performing self-attention and cross-attention to features. 3) In contrast, other studies view feature fusion as a matching problem rather than a classification. Yuan et al. [70] and Abdelreheem et al. [2], supervised by the contrastive loss [29], compute the cosine similarity of visual features and textual features. Inspired by [43], Feng et al. [23] parses the text to generate a text scene graph, simultaneously builds a visual scene graph, and then performs graph node matching. 4) Point clouds' sparse, noisy, incomplete, and lack of detail make learning objects' semantic information challenging. Yang et al. [68] and Cai et al. [6] use 2D images to aid visual-textual feature fusion, but at the cost of additional 2D-3D alignment and 2D feature extraction." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 474, + 289, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 474, + 289, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 474, + 289, + 714 + ], + "type": "text", + "content": "However, the two-stage method has a substantial detection bottleneck: objects overlooked in the first stage cannot be matched in the second. In contrast, object detection and feature extraction in the single-stage method is modulated by the query text, making it easier to identify the text-concerned object. Liu et al. [41] suggest fusing visual and linguistic features at the bottom level and producing text-related visual heatmaps. Similarly, Luo et al. [46] present a single-stage approach that employs textual features to guide visual keypoint selection and progressively localizes objects. BUTD-DETR [34] is also a single-stage capable framework. More importantly, inspired by the 2D image-language pre-train model (such MDETR [37], GLIP [40]), BUTD-DETR measures the similarity between each word and object and then selects the features of the word that correspond to the object's name to match the candidate object. However, there are two limitations: 1) Since multiple object names may be mentioned in a sentence, the ground truth annotation is needed to retrieve the target name, which limits its generalizability. Our text decoupling module separates" + } + ] + } + ], + "index": 3 + }, + { + "type": "image", + "bbox": [ + 314, + 69, + 539, + 173 + ], + "blocks": [ + { + "bbox": [ + 314, + 69, + 539, + 173 + ], + "lines": [ + { + "bbox": [ + 314, + 69, + 539, + 173 + ], + "spans": [ + { + "bbox": [ + 314, + 69, + 539, + 173 + ], + "type": "image", + "image_path": "10e36a3a2c181dd5eb1f22ca1a614a4778f9455a969824f0fdf3054272275376.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 180, + 545, + 204 + ], + "lines": [ + { + "bbox": [ + 305, + 180, + 545, + 204 + ], + "spans": [ + { + "bbox": [ + 305, + 180, + 545, + 204 + ], + "type": "text", + "content": "Figure 2. Text component decoupling: (a) The query text. (b) Dependency tree analysis. (c) Decoupled into five components." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 215, + 545, + 312 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 215, + 545, + 312 + ], + "spans": [ + { + "bbox": [ + 304, + 215, + 545, + 312 + ], + "type": "text", + "content": "text components and determines the target object name by grammatical analysis to avoid this restriction. 2) BUTD-DETR (and MDETR and GLIP in the 2D task) only consider the sparse alignment of main object words or noun phrases to visual features. Conversely, we align all object-related decoupled textual semantic components with visual features, which we refer to dense alignment, significantly enhancing the discriminability of multimodal features." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 321, + 411, + 335 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 321, + 411, + 335 + ], + "spans": [ + { + "bbox": [ + 306, + 321, + 411, + 335 + ], + "type": "text", + "content": "3. Proposed Method" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 341, + 545, + 461 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 341, + 545, + 461 + ], + "spans": [ + { + "bbox": [ + 304, + 341, + 545, + 461 + ], + "type": "text", + "content": "The framework is illustrated in Fig. 3. First, the input text description is decoupled into multiple semantic components, and its affiliated text positions and features are obtained (Sec. 3.1). Concurrently, the Transformer-based encoder extracts and modulates features from point clouds and text, then decodes the visual features of candidate objects (Sec. 3.2). Finally, the dense aligned losses are derived between the decoupled text features and the decoded visual features (Sec. 3.3). The grounding result is the object with visual features most similar to text features (Sec. 3.4)." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 468, + 405, + 480 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 468, + 405, + 480 + ], + "spans": [ + { + "bbox": [ + 306, + 468, + 405, + 480 + ], + "type": "text", + "content": "3.1. Text Decoupling" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 486, + 545, + 629 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 486, + 545, + 629 + ], + "spans": [ + { + "bbox": [ + 304, + 486, + 545, + 629 + ], + "type": "text", + "content": "The text features of the coupled strategy are ambiguous, where features from multiple objects and attributes are coupled, such as \"a brown wooden chair next to the black table.\" Among them, easy-to-learn clues (such as the category \"chair\" or the colour \"brown\") may predominate, weakening other attributes (such as material \"wooden\"); words of other objects (such as the \"black table\") may cause interference. To produce more discriminative text features and fine-grained cross-modal feature fusion, we decouple the query text into different semantic components, each independently aligned with visual features, avoiding the ambiguity caused by feature coupling." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "content": "Text Component Decoupling. Analyzing grammatical dependencies between words is a fundamental task in NLP. We first use the off-the-shelf tool [60, 66] to parse the language description grammatically to generate the grammatical dependency trees, as shown in Fig. 2(b). Each sentence contains only one ROOT node, and each remaining word has a corresponding parent node. Then according to" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "19233" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 48, + 70, + 547, + 289 + ], + "blocks": [ + { + "bbox": [ + 48, + 70, + 547, + 289 + ], + "lines": [ + { + "bbox": [ + 48, + 70, + 547, + 289 + ], + "spans": [ + { + "bbox": [ + 48, + 70, + 547, + 289 + ], + "type": "image", + "image_path": "1d4faa68d8b73bd3752367807d2dc0c5a0a5ba012103c809f584a5930d2e9438.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 295, + 547, + 340 + ], + "lines": [ + { + "bbox": [ + 46, + 295, + 547, + 340 + ], + "spans": [ + { + "bbox": [ + 46, + 295, + 547, + 340 + ], + "type": "text", + "content": "Figure 3. The system framework. (a-c): Decouple the input text into several components to acquire the position label " + }, + { + "bbox": [ + 46, + 295, + 547, + 340 + ], + "type": "inline_equation", + "content": "L" + }, + { + "bbox": [ + 46, + 295, + 547, + 340 + ], + "type": "text", + "content": " and features " + }, + { + "bbox": [ + 46, + 295, + 547, + 340 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 295, + 547, + 340 + ], + "type": "text", + "content": " of the decoupled text. (d-e): Transformer-based encoders for cross-modal visual-text feature extraction. (f): Decode proposal features " + }, + { + "bbox": [ + 46, + 295, + 547, + 340 + ], + "type": "inline_equation", + "content": "\\mathcal{O}'" + }, + { + "bbox": [ + 46, + 295, + 547, + 340 + ], + "type": "text", + "content": " and linearly project them as object position labels " + }, + { + "bbox": [ + 46, + 295, + 547, + 340 + ], + "type": "inline_equation", + "content": "L_{pred}" + }, + { + "bbox": [ + 46, + 295, + 547, + 340 + ], + "type": "text", + "content": " and object features " + }, + { + "bbox": [ + 46, + 295, + 547, + 340 + ], + "type": "inline_equation", + "content": "o" + }, + { + "bbox": [ + 46, + 295, + 547, + 340 + ], + "type": "text", + "content": ", in addition to a box prediction head for regression of the bounding box. (g-h): Visual-text feature dense alignment. Note that the additional 3D object detection procedure is optional." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 361, + 287, + 480 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 361, + 287, + 480 + ], + "spans": [ + { + "bbox": [ + 46, + 361, + 287, + 480 + ], + "type": "text", + "content": "the words' part-of-speech and dependencies, we decouple the long text into five semantic components (see Fig. 2(c)): Main object - the target object mentioned in the utterance; Auxiliary object - the one used to assist in locating the main object; Attributes - objects' appearance, shape, etc.; Pronoun - the word instead of the main object; Relationship - the spatial relation between the main object and the auxiliary object. Note that attributes affiliated with pronouns are equivalent to attached with the main object, thus connecting two sentences in an utterance." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 483, + 287, + 603 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 483, + 287, + 603 + ], + "spans": [ + { + "bbox": [ + 46, + 483, + 287, + 603 + ], + "type": "text", + "content": "Text Position Decoupling. After decoupling each text component (Fig. 3(a)), we generate the position label (similar to a mask) " + }, + { + "bbox": [ + 46, + 483, + 287, + 603 + ], + "type": "inline_equation", + "content": "L_{\\text{main}}, L_{\\text{attr}}, L_{\\text{auxi}}, L_{\\text{pron}}, L_{\\text{rel}} \\in \\mathbb{R}^{1 \\times l}" + }, + { + "bbox": [ + 46, + 483, + 287, + 603 + ], + "type": "text", + "content": " for the component's associated word (Fig. 3(b)). Where " + }, + { + "bbox": [ + 46, + 483, + 287, + 603 + ], + "type": "inline_equation", + "content": "l = 256" + }, + { + "bbox": [ + 46, + 483, + 287, + 603 + ], + "type": "text", + "content": " is the maximum length of the text, each component's word position is set to 1 and the rest to 0. The label will be used to construct the position alignment loss and supervise the classification of objects. The classification result, is not one of a predetermined number of object categories but the position of the text with the highest semantic similarity." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "text", + "content": "Text Feature Decoupling. The feature of each word (token) is produced in the backbone of multimodal feature extraction (Fig. 3(d)). The text feature of the decoupled component can be derived by dot-multiplying all words' features " + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\pmb{t}" + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "text", + "content": " with its position label " + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "inline_equation", + "content": "L" + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "text", + "content": ", as shown in Fig. 3(c). The decoupled text features and visual features will be independently aligned under the supervision of the semantic alignment loss. Note that in the decoupled text features, the semantics of the corresponding components absolutely" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 305, + 361, + 546, + 410 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 361, + 546, + 410 + ], + "spans": [ + { + "bbox": [ + 305, + 361, + 546, + 410 + ], + "type": "text", + "content": "predominate, but as a result of the Transformer's attention mechanism, it also implicitly contains the global sentence's information. In other words, feature decoupling produces individual features while keeping the global context." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 306, + 418, + 476, + 430 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 418, + 476, + 430 + ], + "spans": [ + { + "bbox": [ + 306, + 418, + 476, + 430 + ], + "type": "text", + "content": "3.2. Multimodal Feature Extraction" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 305, + 437, + 546, + 472 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 437, + 546, + 472 + ], + "spans": [ + { + "bbox": [ + 305, + 437, + 546, + 472 + ], + "type": "text", + "content": "We employ BUTD-DETR's encoder-decoder module for feature extraction and intermodulation of cross-modal features. We strongly recommend the reader to refer to Fig. 3." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 473, + 545, + 581 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 473, + 545, + 581 + ], + "spans": [ + { + "bbox": [ + 304, + 473, + 545, + 581 + ], + "type": "text", + "content": "Input Modal Tokenization. The input text and 3D point clouds are encoded by the pre-trained RoBERTa [42] and PointNet++ [53] and produce text tokens " + }, + { + "bbox": [ + 304, + 473, + 545, + 581 + ], + "type": "inline_equation", + "content": "\\mathcal{T} \\in \\mathbb{R}^{l \\times d}" + }, + { + "bbox": [ + 304, + 473, + 545, + 581 + ], + "type": "text", + "content": " and visual tokens " + }, + { + "bbox": [ + 304, + 473, + 545, + 581 + ], + "type": "inline_equation", + "content": "\\mathcal{V} \\in \\mathbb{R}^{n \\times d}" + }, + { + "bbox": [ + 304, + 473, + 545, + 581 + ], + "type": "text", + "content": ". Additionally, the GroupFree [44] detector is used to detect 3D boxes, which are subsequently encoded as box tokens " + }, + { + "bbox": [ + 304, + 473, + 545, + 581 + ], + "type": "inline_equation", + "content": "\\mathcal{B} \\in \\mathbb{R}^{b \\times d}" + }, + { + "bbox": [ + 304, + 473, + 545, + 581 + ], + "type": "text", + "content": ". Note that the GroupFree is optional, the final predicted object of the network is from the prediction head (see below), and the box token is just to assist in better regression of the target object." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 582, + 545, + 653 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 545, + 653 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 545, + 653 + ], + "type": "text", + "content": "Encoder-Decoder. Self-attention and cross-attention are performed in the encoder to update both visual and text features, obtaining cross-modal features " + }, + { + "bbox": [ + 304, + 582, + 545, + 653 + ], + "type": "inline_equation", + "content": "\\mathcal{V}'" + }, + { + "bbox": [ + 304, + 582, + 545, + 653 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 582, + 545, + 653 + ], + "type": "inline_equation", + "content": "\\mathcal{T}'" + }, + { + "bbox": [ + 304, + 582, + 545, + 653 + ], + "type": "text", + "content": " while keeping the dimensions. The top-" + }, + { + "bbox": [ + 304, + 582, + 545, + 653 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 304, + 582, + 545, + 653 + ], + "type": "text", + "content": " (" + }, + { + "bbox": [ + 304, + 582, + 545, + 653 + ], + "type": "inline_equation", + "content": "k = 256" + }, + { + "bbox": [ + 304, + 582, + 545, + 653 + ], + "type": "text", + "content": ") visual features are selected, linearly projected as query proposal features " + }, + { + "bbox": [ + 304, + 582, + 545, + 653 + ], + "type": "inline_equation", + "content": "\\mathcal{O} \\in \\mathbb{R}^{k \\times d}" + }, + { + "bbox": [ + 304, + 582, + 545, + 653 + ], + "type": "text", + "content": ", and updated as " + }, + { + "bbox": [ + 304, + 582, + 545, + 653 + ], + "type": "inline_equation", + "content": "\\mathcal{O}'" + }, + { + "bbox": [ + 304, + 582, + 545, + 653 + ], + "type": "text", + "content": " in the decoder." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 654, + 546, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 654, + 546, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 654, + 546, + 714 + ], + "type": "text", + "content": "Prediction Head. 1) The decoded proposal features " + }, + { + "bbox": [ + 304, + 654, + 546, + 714 + ], + "type": "inline_equation", + "content": "\\mathcal{O}' \\in \\mathbb{R}^{k \\times d}" + }, + { + "bbox": [ + 304, + 654, + 546, + 714 + ], + "type": "text", + "content": " are fed into an MLP and output the predicted position labels " + }, + { + "bbox": [ + 304, + 654, + 546, + 714 + ], + "type": "inline_equation", + "content": "L_{pred} \\in \\mathbb{R}^{k \\times l}" + }, + { + "bbox": [ + 304, + 654, + 546, + 714 + ], + "type": "text", + "content": ", which are then utilized to calculate the position alignment loss with decoupled text position labels " + }, + { + "bbox": [ + 304, + 654, + 546, + 714 + ], + "type": "inline_equation", + "content": "L \\in \\mathbb{R}^{1 \\times l}" + }, + { + "bbox": [ + 304, + 654, + 546, + 714 + ], + "type": "text", + "content": ". 2) Additionally, the proposal fea" + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "19234" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 71, + 287, + 133 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 71, + 287, + 133 + ], + "spans": [ + { + "bbox": [ + 46, + 71, + 287, + 133 + ], + "type": "text", + "content": "tures are linearly projected as object features " + }, + { + "bbox": [ + 46, + 71, + 287, + 133 + ], + "type": "inline_equation", + "content": "\\pmb{o} \\in \\mathbb{R}^{k \\times 64}" + }, + { + "bbox": [ + 46, + 71, + 287, + 133 + ], + "type": "text", + "content": " by another MLP, which are then utilized to compute the semantic alignment loss with the similarly linearly projected text feature " + }, + { + "bbox": [ + 46, + 71, + 287, + 133 + ], + "type": "inline_equation", + "content": "\\pmb{t} \\in \\mathbb{R}^{l \\times 64}" + }, + { + "bbox": [ + 46, + 71, + 287, + 133 + ], + "type": "text", + "content": ". 3) Lastly, a box prediction head [44] regresses the bounding box of the object." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 138, + 162, + 150 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 138, + 162, + 150 + ], + "spans": [ + { + "bbox": [ + 47, + 138, + 162, + 150 + ], + "type": "text", + "content": "3.3. Dense Aligned Loss" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 156, + 200, + 168 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 156, + 200, + 168 + ], + "spans": [ + { + "bbox": [ + 47, + 156, + 200, + 168 + ], + "type": "text", + "content": "3.3.1 Dense Position Aligned Loss" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 175, + 287, + 258 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 175, + 287, + 258 + ], + "spans": [ + { + "bbox": [ + 46, + 175, + 287, + 258 + ], + "type": "text", + "content": "The objective of position alignment is to ensure that the distribution of language-modulated visual features closely matches that of the query text description, as shown in Fig. 3(g). This process is similar to standard object detection's one-hot label prediction. However, rather than being limited by the number of categories, we predict the position of text that is similar to objects." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 258, + 287, + 307 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 258, + 287, + 307 + ], + "spans": [ + { + "bbox": [ + 46, + 258, + 287, + 307 + ], + "type": "text", + "content": "The constructed ground truth text distribution of the mentioned main object is obtained by element-wise summing the position labels of the associated decoupled text components:" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 53, + 312, + 287, + 326 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 312, + 287, + 326 + ], + "spans": [ + { + "bbox": [ + 53, + 312, + 287, + 326 + ], + "type": "interline_equation", + "content": "P _ {\\text {m a i n}} = \\lambda_ {1} L _ {\\text {m a i n}} + \\lambda_ {2} L _ {\\text {a t t r i}} + \\lambda_ {3} L _ {\\text {p r o n}} + \\lambda_ {4} L _ {\\text {r e l}}, \\tag {1}", + "image_path": "56d9d27e480aaaf92ebe47830529f1a5dedb50a4618f506e3da3ec883f62ad6c.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 331, + 287, + 415 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 331, + 287, + 415 + ], + "spans": [ + { + "bbox": [ + 46, + 331, + 287, + 415 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 331, + 287, + 415 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 46, + 331, + 287, + 415 + ], + "type": "text", + "content": " is the weight of different parts (refer to the parametric search in Supplementary Material.). " + }, + { + "bbox": [ + 46, + 331, + 287, + 415 + ], + "type": "inline_equation", + "content": "P_{auxi} = L_{auxi}" + }, + { + "bbox": [ + 46, + 331, + 287, + 415 + ], + "type": "text", + "content": " represents the text distribution of the auxiliary object. The remaining candidate objects' text distribution is " + }, + { + "bbox": [ + 46, + 331, + 287, + 415 + ], + "type": "inline_equation", + "content": "P_{oth}" + }, + { + "bbox": [ + 46, + 331, + 287, + 415 + ], + "type": "text", + "content": ", with the final bit set to 1 (see " + }, + { + "bbox": [ + 46, + 331, + 287, + 415 + ], + "type": "inline_equation", + "content": "\\varnothing" + }, + { + "bbox": [ + 46, + 331, + 287, + 415 + ], + "type": "text", + "content": " in Fig. 3(g)). Therefore, all " + }, + { + "bbox": [ + 46, + 331, + 287, + 415 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 331, + 287, + 415 + ], + "type": "text", + "content": " candidate objects' ground truth text distribution is " + }, + { + "bbox": [ + 46, + 331, + 287, + 415 + ], + "type": "inline_equation", + "content": "P_{text} = \\{P_{main}, P_{auxi}, P_{oth}\\} \\in \\mathbb{R}^{k \\times l}" + }, + { + "bbox": [ + 46, + 331, + 287, + 415 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 415, + 287, + 450 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 415, + 287, + 450 + ], + "spans": [ + { + "bbox": [ + 46, + 415, + 287, + 450 + ], + "type": "text", + "content": "The predicted visual distribution of " + }, + { + "bbox": [ + 46, + 415, + 287, + 450 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 415, + 287, + 450 + ], + "type": "text", + "content": " objects is produced by applying softmax to the output " + }, + { + "bbox": [ + 46, + 415, + 287, + 450 + ], + "type": "inline_equation", + "content": "L_{pred} \\in \\mathbb{R}^{k \\times l}" + }, + { + "bbox": [ + 46, + 415, + 287, + 450 + ], + "type": "text", + "content": " of the prediction head:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 112, + 457, + 287, + 471 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 112, + 457, + 287, + 471 + ], + "spans": [ + { + "bbox": [ + 112, + 457, + 287, + 471 + ], + "type": "interline_equation", + "content": "P _ {o b j} = \\operatorname {S o f t m a x} \\left(L _ {p r e d}\\right). \\tag {2}", + "image_path": "dd25a623f89dc552aab1be92479345462880d615162321c6f548e3d832de9937.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 475, + 286, + 487 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 475, + 286, + 487 + ], + "spans": [ + { + "bbox": [ + 47, + 475, + 286, + 487 + ], + "type": "text", + "content": "Their KL divergence is defined as the position-aligned loss:" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 63, + 502, + 287, + 534 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 63, + 502, + 287, + 534 + ], + "spans": [ + { + "bbox": [ + 63, + 502, + 287, + 534 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {p o s} = \\sum_ {i = 1} ^ {k} \\left[ P _ {t e x t} ^ {i} \\log \\left(P _ {t e x t} ^ {i}\\right) - P _ {t e x t} ^ {i} \\log \\left(P _ {o b j} ^ {i}\\right) \\right]. \\tag {3}", + "image_path": "8925ae91ba45dcadcde8190adf74bae6e196968d6f2f0c7e5d14008aae5324a2.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 540, + 287, + 600 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 540, + 287, + 600 + ], + "spans": [ + { + "bbox": [ + 46, + 540, + 287, + 600 + ], + "type": "text", + "content": "We highlight that \"dense alignment\" indicates that the target object is aligned with the positions of multiple components (Eq. (1)), significantly different from BUTD-DETR (and MDETR for 2D tasks), which only sparsely aligns with the object name's position " + }, + { + "bbox": [ + 46, + 540, + 287, + 600 + ], + "type": "inline_equation", + "content": "L_{main}" + }, + { + "bbox": [ + 46, + 540, + 287, + 600 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 47, + 613, + 205, + 625 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 613, + 205, + 625 + ], + "spans": [ + { + "bbox": [ + 47, + 613, + 205, + 625 + ], + "type": "text", + "content": "3.3.2 Dense Semantic Aligned Loss" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 46, + 631, + 287, + 665 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 631, + 287, + 665 + ], + "spans": [ + { + "bbox": [ + 46, + 631, + 287, + 665 + ], + "type": "text", + "content": "Semantic alignment aims to learn the similarity of visual-text multimodal features through contrastive learning. The object loss of semantic alignment is defined as follows:" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 47, + 670, + 287, + 713 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 670, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 670, + 287, + 713 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\text {s e m - o}} = \\sum_ {i = 1} ^ {k} \\frac {1}{| \\mathbf {T} _ {i} ^ {+} |} \\sum_ {\\boldsymbol {t} _ {i} \\in \\mathbf {T} _ {i} ^ {+}} - \\log \\left(\\frac {\\exp \\left(w _ {+} * \\left(\\boldsymbol {o} _ {i} ^ {\\top} \\boldsymbol {t} _ {i} / \\tau\\right)\\right)}{\\sum_ {j = 1} ^ {l} \\exp \\left(w _ {-} * \\left(\\boldsymbol {o} _ {i} ^ {\\top} \\boldsymbol {t} _ {j} / \\tau\\right)\\right)}\\right), \\tag {4}", + "image_path": "48034bbb192e543003754be0f7c0bd77f13d8482c43ea6a991b6103adf5ab50c.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 72, + 545, + 144 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 545, + 144 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 545, + 144 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 72, + 545, + 144 + ], + "type": "inline_equation", + "content": "\\pmb{o}" + }, + { + "bbox": [ + 305, + 72, + 545, + 144 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 72, + 545, + 144 + ], + "type": "inline_equation", + "content": "\\pmb{t}" + }, + { + "bbox": [ + 305, + 72, + 545, + 144 + ], + "type": "text", + "content": " are the object and text features after linear projection, and " + }, + { + "bbox": [ + 305, + 72, + 545, + 144 + ], + "type": "inline_equation", + "content": "o^\\top t / \\tau" + }, + { + "bbox": [ + 305, + 72, + 545, + 144 + ], + "type": "text", + "content": " is their similarity, as shown in Fig. 3 (h). " + }, + { + "bbox": [ + 305, + 72, + 545, + 144 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 305, + 72, + 545, + 144 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 72, + 545, + 144 + ], + "type": "inline_equation", + "content": "l" + }, + { + "bbox": [ + 305, + 72, + 545, + 144 + ], + "type": "text", + "content": " are the number of objects and words. " + }, + { + "bbox": [ + 305, + 72, + 545, + 144 + ], + "type": "inline_equation", + "content": "\\pmb{t}_i" + }, + { + "bbox": [ + 305, + 72, + 545, + 144 + ], + "type": "text", + "content": " is the positive text feature of the " + }, + { + "bbox": [ + 305, + 72, + 545, + 144 + ], + "type": "inline_equation", + "content": "i_{th}" + }, + { + "bbox": [ + 305, + 72, + 545, + 144 + ], + "type": "text", + "content": " candidate object. Taking the main object as an example, the positive text feature " + }, + { + "bbox": [ + 305, + 72, + 545, + 144 + ], + "type": "inline_equation", + "content": "\\mathbf{T}_i^+" + }, + { + "bbox": [ + 305, + 72, + 545, + 144 + ], + "type": "text", + "content": " corresponding to it is:" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 345, + 156, + 545, + 171 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 345, + 156, + 545, + 171 + ], + "spans": [ + { + "bbox": [ + 345, + 156, + 545, + 171 + ], + "type": "interline_equation", + "content": "\\boldsymbol {t} _ {i} \\in \\mathbf {T} _ {i} ^ {+} = \\left\\{\\boldsymbol {t} _ {\\text {m a i n}}, \\boldsymbol {t} _ {\\text {a t t r i}}, \\boldsymbol {t} _ {\\text {p r o n}}, \\boldsymbol {t} _ {\\text {r e l}} \\right\\}, \\tag {5}", + "image_path": "feee9b5e9e46a1a44f405d1d3aca76e70ddfdda1b6c687c0259e42dc5db62a27.jpg" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 305, + 181, + 545, + 226 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 181, + 545, + 226 + ], + "spans": [ + { + "bbox": [ + 305, + 181, + 545, + 226 + ], + "type": "text", + "content": "and " + }, + { + "bbox": [ + 305, + 181, + 545, + 226 + ], + "type": "inline_equation", + "content": "w_{+}" + }, + { + "bbox": [ + 305, + 181, + 545, + 226 + ], + "type": "text", + "content": " is the weight of each positive term. " + }, + { + "bbox": [ + 305, + 181, + 545, + 226 + ], + "type": "inline_equation", + "content": "t_j" + }, + { + "bbox": [ + 305, + 181, + 545, + 226 + ], + "type": "text", + "content": " is the feature of the " + }, + { + "bbox": [ + 305, + 181, + 545, + 226 + ], + "type": "inline_equation", + "content": "i_{th}" + }, + { + "bbox": [ + 305, + 181, + 545, + 226 + ], + "type": "text", + "content": " text, but note that the negative similarity weight " + }, + { + "bbox": [ + 305, + 181, + 545, + 226 + ], + "type": "inline_equation", + "content": "w_{-}" + }, + { + "bbox": [ + 305, + 181, + 545, + 226 + ], + "type": "text", + "content": " for auxiliary object term " + }, + { + "bbox": [ + 305, + 181, + 545, + 226 + ], + "type": "inline_equation", + "content": "t_{auxi}" + }, + { + "bbox": [ + 305, + 181, + 545, + 226 + ], + "type": "text", + "content": " is 2, while the rest weight 1. The text loss of semantic alignment defined similarly:" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 312, + 237, + 545, + 281 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 237, + 545, + 281 + ], + "spans": [ + { + "bbox": [ + 312, + 237, + 545, + 281 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {s e m - t} = \\sum_ {i = 1} ^ {l} \\frac {w _ {+}}{\\left| \\mathbf {O} _ {i} ^ {+} \\right|} \\sum_ {\\boldsymbol {o} _ {i} \\in \\mathbf {O} _ {i} ^ {+}} - \\log \\left(\\frac {\\exp \\left(\\boldsymbol {t} _ {i} ^ {\\top} \\boldsymbol {o} _ {i} / \\tau\\right)}{\\sum_ {j = 1} ^ {k} \\exp \\left(\\boldsymbol {t} _ {i} ^ {\\top} \\boldsymbol {o} _ {j} / \\tau\\right)}\\right), \\tag {6}", + "image_path": "a630f653ea487f053ff3ea75e2f8c2ca41b9a16182943b6d7a8047ff5cc9887d.jpg" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 305, + 281, + 545, + 330 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 281, + 545, + 330 + ], + "spans": [ + { + "bbox": [ + 305, + 281, + 545, + 330 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 281, + 545, + 330 + ], + "type": "inline_equation", + "content": "o_i \\in \\mathbf{O}_i^+" + }, + { + "bbox": [ + 305, + 281, + 545, + 330 + ], + "type": "text", + "content": " is the positive object feature of the " + }, + { + "bbox": [ + 305, + 281, + 545, + 330 + ], + "type": "inline_equation", + "content": "i_{th}" + }, + { + "bbox": [ + 305, + 281, + 545, + 330 + ], + "type": "text", + "content": " text, and " + }, + { + "bbox": [ + 305, + 281, + 545, + 330 + ], + "type": "inline_equation", + "content": "o_j" + }, + { + "bbox": [ + 305, + 281, + 545, + 330 + ], + "type": "text", + "content": " is the feature of the " + }, + { + "bbox": [ + 305, + 281, + 545, + 330 + ], + "type": "inline_equation", + "content": "j_{th}" + }, + { + "bbox": [ + 305, + 281, + 545, + 330 + ], + "type": "text", + "content": " object. The final semantic alignment loss is the mean of the two: " + }, + { + "bbox": [ + 305, + 281, + 545, + 330 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{sem} = (\\mathcal{L}_{sem\\_o} + \\mathcal{L}_{sem\\_t}) / 2" + }, + { + "bbox": [ + 305, + 281, + 545, + 330 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 331, + 545, + 415 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 331, + 545, + 415 + ], + "spans": [ + { + "bbox": [ + 304, + 331, + 545, + 415 + ], + "type": "text", + "content": "Similarly, the semantic alignment of multiple text components (Eq. (5)) with visual features also illustrates our insight of \"dense.\" This is intuitive, such as \"It is a brown chair with legs under a blackboard,\" where the main object's visual features should be not only similar to \"chair\" but also similar to \"brown, legs\" and distinct to \"blackboard\" as possible." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 305, + 416, + 545, + 440 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 416, + 545, + 440 + ], + "spans": [ + { + "bbox": [ + 305, + 416, + 545, + 440 + ], + "type": "text", + "content": "The total loss for training also includes the box regression loss. Refer to Supplementary Material for details." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 306, + 452, + 411, + 464 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 452, + 411, + 464 + ], + "spans": [ + { + "bbox": [ + 306, + 452, + 411, + 464 + ], + "type": "text", + "content": "3.4. Explicit Inference" + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 304, + 472, + 545, + 579 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 472, + 545, + 579 + ], + "spans": [ + { + "bbox": [ + 304, + 472, + 545, + 579 + ], + "type": "text", + "content": "Because of our text decoupling and dense alignment operations, object features fused multiple related text component features, allowing for the computation of the similarity between individual text components and candidate objects. For instance, " + }, + { + "bbox": [ + 304, + 472, + 545, + 579 + ], + "type": "inline_equation", + "content": "S_{main} = \\text{Softmax}(\\boldsymbol{o}^{\\top}\\boldsymbol{t}_{main} / \\tau)" + }, + { + "bbox": [ + 304, + 472, + 545, + 579 + ], + "type": "text", + "content": " indicates the similarity between objects " + }, + { + "bbox": [ + 304, + 472, + 545, + 579 + ], + "type": "inline_equation", + "content": "\\boldsymbol{o}" + }, + { + "bbox": [ + 304, + 472, + 545, + 579 + ], + "type": "text", + "content": " and the main text component " + }, + { + "bbox": [ + 304, + 472, + 545, + 579 + ], + "type": "inline_equation", + "content": "\\boldsymbol{t}_{main}" + }, + { + "bbox": [ + 304, + 472, + 545, + 579 + ], + "type": "text", + "content": ". Therefore, the similarity of objects and related components can be explicitly combined to obtain the total score and select the candidate with the highest score:" + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 321, + 592, + 545, + 605 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 321, + 592, + 545, + 605 + ], + "spans": [ + { + "bbox": [ + 321, + 592, + 545, + 605 + ], + "type": "interline_equation", + "content": "S _ {a l l} = S _ {\\text {m a i n}} + S _ {\\text {a t t r i}} + S _ {\\text {p r o n}} + S _ {\\text {r e l}} - S _ {\\text {a u x i}}, \\tag {7}", + "image_path": "1167068da2b248802457f565e8411f893f3e70abec3cbc09546b1064781937d4.jpg" + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "type": "text", + "content": "where the definition of " + }, + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "type": "inline_equation", + "content": "S_{attri}" + }, + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "type": "inline_equation", + "content": "S_{pron}" + }, + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "type": "inline_equation", + "content": "S_{rel}" + }, + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "type": "inline_equation", + "content": "S_{auxi}" + }, + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "type": "text", + "content": " is similar to " + }, + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "type": "inline_equation", + "content": "S_{main}" + }, + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "type": "text", + "content": ". If providing supervision of auxiliary objects during training, and the auxiliary object can be identified by solely computing the similarity between the object features and the auxiliary component's text features: " + }, + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "type": "inline_equation", + "content": "S_{all} = S_{attri}" + }, + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "type": "text", + "content": ". Being able to infer the object based on the part of the text is a significant sign that the network has learned well-aligned and fine-grained visual-text feature space." + } + ] + } + ], + "index": 25 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "19235" + } + ] + } + ], + "index": 26 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 128, + 85 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 128, + 85 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 128, + 85 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 91, + 288, + 175 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 91, + 288, + 175 + ], + "spans": [ + { + "bbox": [ + 46, + 91, + 288, + 175 + ], + "type": "text", + "content": "First, we conduct comprehensive and fair comparisons with SOTA methods in the Regular 3D Visual Grounding setting in Sec. 4.1. Then, in Sec. 4.2, we introduce our proposed new task, Grounding without Object Name, and perform comparison and analysis. Implementation details, additional experiments and more qualitative results are detailed in the supplementary material." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 182, + 211, + 194 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 182, + 211, + 194 + ], + "spans": [ + { + "bbox": [ + 47, + 182, + 211, + 194 + ], + "type": "text", + "content": "4.1. Regular 3D Visual Grounding" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 201, + 165, + 213 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 201, + 165, + 213 + ], + "spans": [ + { + "bbox": [ + 47, + 201, + 165, + 213 + ], + "type": "text", + "content": "4.1.1 Experiment settings" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 219, + 287, + 399 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 219, + 287, + 399 + ], + "spans": [ + { + "bbox": [ + 46, + 219, + 287, + 399 + ], + "type": "text", + "content": "We keep the same settings as existing works, with ScanRefer [8] and SR3D/NR3D [3] as datasets and Acc@0.25IoU and Acc@0.5IoU as metrics. Based on the visual data of ScanNet [17], ScanRefer adds 51,583 manually annotated text descriptions about objects. These complex and free-form descriptions involve object categories and attributes such as colour, shape, size, and spatial relationships. SR3D/NR3D is also proposed based on ScanNet, with SR3D including 83,572 simple machine-generated descriptions and NR3D containing 41,503 descriptions similar to ScanRefer's human annotation. The difference is that in the ScanRefer configuration, detecting and matching objects are required, while SR3D/NR3D is simpler. It supplies GT boxes for all candidate objects and only needs to classify the classes of the boxes and choose the target object." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 407, + 224, + 419 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 407, + 224, + 419 + ], + "spans": [ + { + "bbox": [ + 47, + 407, + 224, + 419 + ], + "type": "text", + "content": "4.1.2 Comparison to the state of the art" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 426, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 426, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 426, + 288, + 715 + ], + "type": "text", + "content": "ScanRefer. Table 1 reports the results on the ScanRefer dataset. i) Our method achieves state-of-the-art performance by a substantial margin, with an overall improvement of " + }, + { + "bbox": [ + 46, + 426, + 288, + 715 + ], + "type": "inline_equation", + "content": "4.2\\%" + }, + { + "bbox": [ + 46, + 426, + 288, + 715 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 426, + 288, + 715 + ], + "type": "inline_equation", + "content": "3.7\\%" + }, + { + "bbox": [ + 46, + 426, + 288, + 715 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 46, + 426, + 288, + 715 + ], + "type": "inline_equation", + "content": "54.59\\%" + }, + { + "bbox": [ + 46, + 426, + 288, + 715 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 426, + 288, + 715 + ], + "type": "inline_equation", + "content": "42.26\\%" + }, + { + "bbox": [ + 46, + 426, + 288, + 715 + ], + "type": "text", + "content": ". ii) Some studies [6,8,9,46,68,77] proved that supplemented 2D images with detailed and dense semantics could learn better point cloud features. Surprisingly, we only use sparse 3D point cloud features and even outperformed 2D assistance methods. This superiority illustrates that our decoupling and dense alignment strategies mine more efficient and meaningful visual-text co-representations. iii) Another finding is that the accuracy of most existing techniques is less than " + }, + { + "bbox": [ + 46, + 426, + 288, + 715 + ], + "type": "inline_equation", + "content": "40\\%" + }, + { + "bbox": [ + 46, + 426, + 288, + 715 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 426, + 288, + 715 + ], + "type": "inline_equation", + "content": "30\\%" + }, + { + "bbox": [ + 46, + 426, + 288, + 715 + ], + "type": "text", + "content": " in the \"multiple\" setting because multiple means that the category of the target object mentioned in the language is not unique, with more interference candidates with the same category. However, we reached a remarkable " + }, + { + "bbox": [ + 46, + 426, + 288, + 715 + ], + "type": "inline_equation", + "content": "49.13\\%" + }, + { + "bbox": [ + 46, + 426, + 288, + 715 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 426, + 288, + 715 + ], + "type": "inline_equation", + "content": "37.64\\%" + }, + { + "bbox": [ + 46, + 426, + 288, + 715 + ], + "type": "text", + "content": ". To identify similar objects, a finer-grained understanding of the text and vision is required in this complex setting. iv) The last three rows in Table 1 compare single-stage methods, where our method's single-stage implementation is without the object detection step (" + }, + { + "bbox": [ + 46, + 426, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\mathcal{B}" + }, + { + "bbox": [ + 46, + 426, + 288, + 715 + ], + "type": "text", + "content": " in Fig. 3) in training and inference. The result illustrates that while not requiring an additional pre-trained 3D object detector, our approach also can achieve SOTA performance." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 72, + 545, + 119 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 119 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 119 + ], + "type": "text", + "content": "v) The qualitative results are depicted in Fig. 4(a-c), which reveals that our method with an excellent perception of appearance attributes, spatial relationships, and even ordinal numbers." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 120, + 546, + 289 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 120, + 546, + 289 + ], + "spans": [ + { + "bbox": [ + 304, + 120, + 546, + 289 + ], + "type": "text", + "content": "SR3D/NR3D. Table 2 shows the accuracy on the SR3D/NR3D dataset, where we achieve the best performance of " + }, + { + "bbox": [ + 304, + 120, + 546, + 289 + ], + "type": "inline_equation", + "content": "68.1\\%" + }, + { + "bbox": [ + 304, + 120, + 546, + 289 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 120, + 546, + 289 + ], + "type": "inline_equation", + "content": "52.1\\%" + }, + { + "bbox": [ + 304, + 120, + 546, + 289 + ], + "type": "text", + "content": ". In SR3D, since the language descriptions are concise and the object is easy to identify, our method and [34, 46] reach an accuracy of over " + }, + { + "bbox": [ + 304, + 120, + 546, + 289 + ], + "type": "inline_equation", + "content": "60\\%" + }, + { + "bbox": [ + 304, + 120, + 546, + 289 + ], + "type": "text", + "content": ". Conversely, in NR3D, descriptions are too detailed and complex, causing additional challenges for text decoupling. However, we still achieve SOTA accuracy with the 3D-only data, while other comparable methods [46, 68] rely on additional 2D images for training. Some methods [6, 8, 9] compared in Table 1 are not discussed here because they are not evaluated on the SR3D/NR3D dataset. In addition, because GT boxes of candidate objects are provided in this setting, the single-stage methods are not applicable and discussed." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 299, + 408, + 310 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 299, + 408, + 310 + ], + "spans": [ + { + "bbox": [ + 305, + 299, + 408, + 310 + ], + "type": "text", + "content": "4.1.3 Ablation studies" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 318, + 545, + 450 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 318, + 545, + 450 + ], + "spans": [ + { + "bbox": [ + 304, + 318, + 545, + 450 + ], + "type": "text", + "content": "Loss ablation. The ablation of the position-aligned loss and the semantic-aligned loss is shown in Table 3. The performance of the semantic-aligned loss is marginally better because its contrastive loss not only shortens the distance between similar text-visual features but also enlarges the distance between dis-matched features (such as " + }, + { + "bbox": [ + 304, + 318, + 545, + 450 + ], + "type": "inline_equation", + "content": "t_{auxi}" + }, + { + "bbox": [ + 304, + 318, + 545, + 450 + ], + "type": "text", + "content": " is a negative term in Eq. (4)). Whereas position-aligned loss only considers object-related components (as in Eq. (1)). When both losses supervise together, the best accuracy is achieved, demonstrating that they can produce complementary performance." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 451, + 546, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 451, + 546, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 451, + 546, + 714 + ], + "type": "text", + "content": "Dense components ablation. To demonstrate our insight into dense alignment, we perform ablation analysis on the different decoupled text components, and the results are displayed in the \"Regular VG\" column in Table 4. Analysis: i) (a) is our baseline implementation of the sparse concept, using only the \"Main object\" component decoupled from the text. In contrast to BUTD-DETR, the text decoupling module (Sec. 3.1) is used to obtain text labels and features during training and inference instead of employing ground truth labels. ii) Dense-aligned sub-methods (b)-(h) outperform the sparse alignment (a) because of the finer-grained visual-linguistic feature fusion. iii) (b)-(e) indicate that adding any other component on top of the \"Main object\" improves performance, demonstrating the validity of each text component. The \"Attribute\" component aids in identifying characteristics such as colour, and shape, frequently mentioned in language descriptions. Unexpectedly, the \"Pronoun\" component such as \"it, that, and which\" have little meaning when used alone but also function in our method, indicating that the pronoun learned contextual information from the sentence. The \"Relationship\" component facilitates comprehension of spatial relationships be" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "19236" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 53, + 71, + 541, + 316 + ], + "blocks": [ + { + "bbox": [ + 53, + 71, + 541, + 316 + ], + "lines": [ + { + "bbox": [ + 53, + 71, + 541, + 316 + ], + "spans": [ + { + "bbox": [ + 53, + 71, + 541, + 316 + ], + "type": "table", + "html": "
MethodVenueModalityUnique (~19%)Multiple (~81%)Overall
0.250.50.250.50.250.5
ScanRefer [8]ECCV20203D67.6446.1932.0621.2638.9726.10
3D+2D76.3353.5132.7321.1141.1927.40
ReferIt3D [3]ECCV20203D53.837.521.012.826.416.9
TGNN [33]AAAI20213D68.6156.8029.8423.1837.3729.70
InstanceRefer [70]ICCV20213D77.4566.8331.2724.7740.2332.93
SAT [68]ICCV20213D+2D73.2150.8337.6425.1644.5430.14
FFL-3DOG [23]ICCV20213D78.8067.9435.1925.7041.3334.01
3DVG-Transformer [77]ICCV20213D77.1658.4738.3828.7045.9034.47
3D+2D81.9360.6439.3028.4247.5734.67
3D-SPS [46]CVPR20223D+2D84.1266.7240.3229.8248.8236.98
3DJCG [6]CVPR20223D78.7561.3040.1330.0847.6236.14
3D+2D83.4764.3441.3930.8249.5637.33
BUTD-DETR [34] †ECCV20223D82.8864.9844.7333.9750.4238.60
D3Net [9]ECCV20223D+2D-70.35-30.50-37.87
EDA-3D85.7668.5749.1337.6454.59 (+4.2%)42.26 (+3.7%)
3D-SPS(single-stage) [46]CVPR20223D81.6364.7739.4829.6147.6536.43
BUTD-DETR (single-stage) [34]‡ECCV20223D81.4761.2444.2032.8149.7637.05
EDA (single-stage) §-3D86.4069.4248.1136.8253.8341.70
", + "image_path": "4a7d0252ba4a904c57efb7a7a01fb2bd7b1fc13f1ecd17425b8eadf01bce5caf.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 48, + 369, + 288, + 541 + ], + "blocks": [ + { + "bbox": [ + 46, + 317, + 547, + 363 + ], + "lines": [ + { + "bbox": [ + 46, + 317, + 547, + 363 + ], + "spans": [ + { + "bbox": [ + 46, + 317, + 547, + 363 + ], + "type": "text", + "content": "Table 1. The 3D visual grounding results on ScanRefer, accuracy evaluated by IoU 0.25 and IoU 0.5. † The accuracy is reevaluated using our parsed text labels because the performance reported by BUTD-DETR used ground truth text labels and ignored some challenging samples (see supplementary materials for more details). § Our single-stage implementation without the assistance of the additional 3D object detection step (dotted arrows in Fig. 3). ‡ BUTD-DETR did not provide single-stage results and we retrained the model." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 48, + 369, + 288, + 541 + ], + "lines": [ + { + "bbox": [ + 48, + 369, + 288, + 541 + ], + "spans": [ + { + "bbox": [ + 48, + 369, + 288, + 541 + ], + "type": "table", + "html": "
MethodVenueModalitySR3DNR3D
ReferIt3D [3]ECCV203D39.835.6
TGNN [33]AAAI213D45.037.3
TransRefer3D [28]MM213D57.442.1
InstanceRefer [70]ICCV213D48.038.8
3DVG-Transfor. [77]ICCV213D51.440.8
FFL-3DOG [23]ICCV213D-41.7
SAT [68]ICCV213D+2D57.949.2
3DReferTrans. [2]WACV223D47.039.0
LanguageRefer [58]CoRL223D56.043.9
3D-SPS [46]CVPR223D+2D62.651.5
BUTD-DETR † [34]ECCV223D65.649.1
LAR [5]NeurIPS223D59.648.9
EDA (Ours)-3D68.152.1
", + "image_path": "9037d79ceea271416f13156088e030025640ea32efcc36b7ac0b667a171ed3b5.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 594, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 594, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 289, + 715 + ], + "type": "text", + "content": "tween objects. The component \"Auxiliary object\" is a negative term in the loss (Eq. (4)). During inference (Eq. (7)), its similarity is subtracted in the hopes that the predicted main object is as dissimilar to it as possible. iv) (f)-(h) integrate different components to make performance gains and reach the peak when all are involved, demonstrating that the functions of each component can be complementary, and there may be no overlap between the features of each one. The result reveals that our method effectively decouples and matches fine-grained multimodal features." + } + ] + } + ], + "index": 4 + }, + { + "type": "table", + "bbox": [ + 317, + 369, + 536, + 426 + ], + "blocks": [ + { + "bbox": [ + 46, + 542, + 288, + 588 + ], + "lines": [ + { + "bbox": [ + 46, + 542, + 288, + 588 + ], + "spans": [ + { + "bbox": [ + 46, + 542, + 288, + 588 + ], + "type": "text", + "content": "Table 2. Performance on SR3D/NR3D datasets by Acc@0.25IoU as the metric. The detailed results of EDA in four subsets are provided in the Supplementary Material. " + }, + { + "bbox": [ + 46, + 542, + 288, + 588 + ], + "type": "inline_equation", + "content": "\\dagger" + }, + { + "bbox": [ + 46, + 542, + 288, + 588 + ], + "type": "text", + "content": " Reevaluated by parsed text labels (see supp. for more details)." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 317, + 369, + 536, + 426 + ], + "lines": [ + { + "bbox": [ + 317, + 369, + 536, + 426 + ], + "spans": [ + { + "bbox": [ + 317, + 369, + 536, + 426 + ], + "type": "table", + "html": "
+Lpos+LsemAcc@0.25Acc@0.5
(a)✓51.239.6
(b)✓52.239.9
(c)✓✓54.642.3
", + "image_path": "e635ca81cbb771f28d3d0a5c883cf6fc41d0f396bb938cb95e11b99667f40934.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "table_body" + } + ], + "index": 5 + }, + { + "type": "table", + "bbox": [ + 310, + 441, + 543, + 557 + ], + "blocks": [ + { + "bbox": [ + 337, + 427, + 514, + 437 + ], + "lines": [ + { + "bbox": [ + 337, + 427, + 514, + 437 + ], + "spans": [ + { + "bbox": [ + 337, + 427, + 514, + 437 + ], + "type": "text", + "content": "Table 3. Loss ablation on the ScanRefer dataset." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 310, + 441, + 543, + 557 + ], + "lines": [ + { + "bbox": [ + 310, + 441, + 543, + 557 + ], + "spans": [ + { + "bbox": [ + 310, + 441, + 543, + 557 + ], + "type": "table", + "html": "
Dense componentsRegular VGVG-w/o-ON
MainAttri.Pron.Auxi.Rel.@0.25@0.5@0.25@0.5
(a)✓51.538.821.816.7
(b)✓✓53.141.323.217.8
(c)✓✓52.940.823.718.6
(d)✓✓52.941.023.218.4
(e)✓✓52.840.725.719.6
(f)✓✓✓53.841.824.218.5
(g)✓✓✓✓54.242.324.018.8
(h)✓✓✓✓✓54.642.326.521.2
", + "image_path": "f995be33ee9bbf441e798c74561f14faf81f4df74b106a60e77b141640c1c233.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "table_body" + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 558, + 545, + 579 + ], + "lines": [ + { + "bbox": [ + 306, + 558, + 545, + 579 + ], + "spans": [ + { + "bbox": [ + 306, + 558, + 545, + 579 + ], + "type": "text", + "content": "Table 4. Ablation studies of different text components on Regular VG and VG-w/o-ON tasks. Evaluated on the ScanRefer dataset." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 306, + 591, + 545, + 605 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 591, + 545, + 605 + ], + "spans": [ + { + "bbox": [ + 306, + 591, + 545, + 605 + ], + "type": "text", + "content": "4.2. Grounding without Object Name (VG-w/o-ON)" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 610, + 425, + 624 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 610, + 425, + 624 + ], + "spans": [ + { + "bbox": [ + 306, + 610, + 425, + 624 + ], + "type": "text", + "content": "4.2.1 Experiment settings" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 629, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 629, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 629, + 547, + 713 + ], + "type": "text", + "content": "To evaluate the comprehensive reasoning ability of the model and avoid inductive biases about object names, we propose a new and more challenging task: grounding objects without mentioning object names (VG-w/o-ON). Specifically, we manually replace the object's name with \"object\" in the ScanRefer validation set. For instance: \"This is a brown wooden chair\" becomes \"this is a brown" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "19237" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 47, + 70, + 545, + 286 + ], + "blocks": [ + { + "bbox": [ + 47, + 70, + 545, + 286 + ], + "lines": [ + { + "bbox": [ + 47, + 70, + 545, + 286 + ], + "spans": [ + { + "bbox": [ + 47, + 70, + 545, + 286 + ], + "type": "image", + "image_path": "bf70433eed626fc245fe49f339213e576052f800121603c1926c7651d816c5a7.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 67, + 288, + 523, + 298 + ], + "lines": [ + { + "bbox": [ + 67, + 288, + 523, + 298 + ], + "spans": [ + { + "bbox": [ + 67, + 288, + 523, + 298 + ], + "type": "text", + "content": "Figure 4. Qualitative results with ScanRefer texts. (a-c): Regular 3D visual grounding. (d-e): Grounding without object name." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 310, + 287, + 417 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 310, + 287, + 417 + ], + "spans": [ + { + "bbox": [ + 46, + 310, + 287, + 417 + ], + "type": "text", + "content": "wooden object\". A total of 9253 samples were annotated and discarded another 255 ambiguous samples. We divide this language set into four subsets: only mentioning object attributes (" + }, + { + "bbox": [ + 46, + 310, + 287, + 417 + ], + "type": "inline_equation", + "content": "\\sim 15\\%" + }, + { + "bbox": [ + 46, + 310, + 287, + 417 + ], + "type": "text", + "content": "), only mentioning spatial relationships (" + }, + { + "bbox": [ + 46, + 310, + 287, + 417 + ], + "type": "inline_equation", + "content": "\\sim 20\\%" + }, + { + "bbox": [ + 46, + 310, + 287, + 417 + ], + "type": "text", + "content": "), mentioning both attributes and relationships (" + }, + { + "bbox": [ + 46, + 310, + 287, + 417 + ], + "type": "inline_equation", + "content": "\\sim 63\\%" + }, + { + "bbox": [ + 46, + 310, + 287, + 417 + ], + "type": "text", + "content": "), and others (" + }, + { + "bbox": [ + 46, + 310, + 287, + 417 + ], + "type": "inline_equation", + "content": "\\sim 2\\%" + }, + { + "bbox": [ + 46, + 310, + 287, + 417 + ], + "type": "text", + "content": "), as the first row in Table 5. Note that, without retraining, we perform comparisons using our best model and comparative approaches' best models trained for the regular VG task (Sec. 4.1)." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 430, + 162, + 441 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 430, + 162, + 441 + ], + "spans": [ + { + "bbox": [ + 47, + 430, + 162, + 441 + ], + "type": "text", + "content": "4.2.2 Result and analysis" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 450, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 450, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 450, + 288, + 713 + ], + "type": "text", + "content": "Table 5 reports the experimental results. i) The performance of all methods on this challenging task is significantly lower than that of regular VG (see Table. 1), indicating that object categories provide rich semantic information, which is also conducive to classifying features. It's accessible to produce the category's inductive bias, especially in the \"unique\" setting. ii) Our method achieves absolute lead with the overall performance of " + }, + { + "bbox": [ + 46, + 450, + 288, + 713 + ], + "type": "inline_equation", + "content": "26.5\\%" + }, + { + "bbox": [ + 46, + 450, + 288, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 450, + 288, + 713 + ], + "type": "inline_equation", + "content": "21.2\\%" + }, + { + "bbox": [ + 46, + 450, + 288, + 713 + ], + "type": "text", + "content": ", which is over " + }, + { + "bbox": [ + 46, + 450, + 288, + 713 + ], + "type": "inline_equation", + "content": "10\\%" + }, + { + "bbox": [ + 46, + 450, + 288, + 713 + ], + "type": "text", + "content": " higher than other methods. This preponderance demonstrates that our proposed text decoupling and dense alignment enable fine-grained visual-linguistic feature matching, where the model identifies the visual features most similar to other text components (e.g. attributes, relations, etc.). iii) Notably, in subset \"Attri+Rel\", our method performs better than in the other subsets because additional cues can be exploited for fine-grained localization. However, the performance of the comparison approaches on this subset drops, revealing that more clues make them suffer from ambiguity. iv) Column \"VG-w/o-ON\" in Table 4 shows ablation studies of text components for this new task. The performance increase offered by the additional components is more remarkable than during the regular VG task. Among them, the" + } + ] + } + ], + "index": 4 + }, + { + "type": "table", + "bbox": [ + 307, + 308, + 545, + 395 + ], + "blocks": [ + { + "bbox": [ + 307, + 308, + 545, + 395 + ], + "lines": [ + { + "bbox": [ + 307, + 308, + 545, + 395 + ], + "spans": [ + { + "bbox": [ + 307, + 308, + 545, + 395 + ], + "type": "table", + "html": "
MethodSubsetsOverall
Attri onlyRel onlyAttri+Rel@0.25@0.5
ScanRefer [8]11.1710.5310.2910.516.20
TGNN [33]10.5213.3211.3511.649.51
InstanceRefer [70]14.7413.7113.8113.9211.47
BUTD-DETR [34]12.3012.1111.8611.998.95
EDA (Ours)25.4025.8226.9626.5021.20
", + "image_path": "b6c948cf966536f6d5df527b205f55c7110a174aa41e1ae3a98c5426413a27f6.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "table_body" + } + ], + "index": 5 + }, + { + "bbox": [ + 305, + 396, + 545, + 430 + ], + "lines": [ + { + "bbox": [ + 305, + 396, + 545, + 430 + ], + "spans": [ + { + "bbox": [ + 305, + 396, + 545, + 430 + ], + "type": "text", + "content": "Table 5. Performance of grounding without object name. The accuracy of subsets is measured by acc@0.25IoU, where the \"other\" subset is not reported due to its small proportion." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 304, + 441, + 545, + 513 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 441, + 545, + 513 + ], + "spans": [ + { + "bbox": [ + 304, + 441, + 545, + 513 + ], + "type": "text", + "content": "\"Relationship\" component plays the most significant role because the spatial relationship with other objects may provide more obvious indications in this setting. v) Fig. 4(d-e) shows qualitative examples. Even without knowing the target's name, our method can infer it by other cues, while BUTD-DETR's performance drops catastrophically." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 523, + 378, + 534 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 523, + 378, + 534 + ], + "spans": [ + { + "bbox": [ + 306, + 523, + 378, + 534 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 543, + 545, + 711 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 543, + 545, + 711 + ], + "spans": [ + { + "bbox": [ + 304, + 543, + 545, + 711 + ], + "type": "text", + "content": "We present EDA, an explicit, dense-aligned method for 3D Visual Grounding tasks. By decoupling text into multiple semantic components and densely aligning it with visual features under the supervision of position-aligned and semantic-aligned loss, we enable fine-grained visual-text feature fusion, avoiding the imbalance and ambiguity of existing methods. Extensive experiments and ablation demonstrate the superiority of our method. In addition, we propose a new challenging 3D VG subtask of grounding without the object name to evaluate model robustness comprehensively. However, our limitations are the performance bottlenecks of multiple modules, such as PointNet++, RoBERTa, and text parsing modules. Especially when the text is lengthy, text decoupling may fail, resulting in performance degradation." + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "19238" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 288, + 712 + ], + "type": "list", + "angle": 0, + "index": 12, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 145 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 145 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 145 + ], + "type": "text", + "content": "[1] Ahmed Abdelreheem, Kyle Olszewski, Hsin-Ying Lee, Peter Wonka, and Panos Achlioptas. 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Karen Liu \nStanford University", + "bbox": [ + 287, + 180, + 679, + 217 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "{jtseng20, rjcaste, karenliu}@cs.stanford.edu", + "bbox": [ + 294, + 219, + 673, + 233 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/3a3f8e50d0c37e8e065f7c76d957915f7fa2d3424005923f12cab50a4674fc0f.jpg", + "image_caption": [ + "Figure 1. EDGE generates diverse, physically plausible dance choreographies conditioned on music." + ], + "image_footnote": [], + "bbox": [ + 80, + 237, + 893, + 407 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 453, + 313, + 468 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Dance is an important human art form, but creating new dances can be difficult and time-consuming. In this work, we introduce Editable Dance Generation (EDGE), a state-of-the-art method for editable dance generation that is capable of creating realistic, physically-plausible dances while remaining faithful to the input music. EDGE uses a transformer-based diffusion model paired with Jukebox, a strong music feature extractor, and confers powerful editing capabilities well-suited to dance, including joint-wise conditioning, and in-betweening. We introduce a new metric for physical plausibility, and evaluate dance quality generated by our method extensively through (1) multiple quantitative metrics on physical plausibility, beat alignment, and diversity benchmarks, and more importantly, (2) a large-scale user study, demonstrating a significant improvement over previous state-of-the-art methods. Qualitative samples from our model can be found at our website.", + "bbox": [ + 73, + 484, + 473, + 742 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 770, + 209, + 786 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Dance is an important part of many cultures around the world: it is a form of expression, communication, and social interaction [29]. However, creating new dances or dance animations is uniquely difficult because dance movements are expressive and freeform, yet precisely structured by music. In practice, this requires tedious hand animation or motion capture solutions, which can be expensive and impractical.", + "bbox": [ + 75, + 796, + 468, + 902 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "On the other hand, using computational methods to generate dances automatically can alleviate the burden of the creation process, leading to many applications: such methods can help animators create new dances or provide interactive characters in video games or virtual reality with realistic and varied movements based on user-provided music. In addition, dance generation can provide insights into the relationship between music and movement, which is an important area of research in neuroscience [2].", + "bbox": [ + 496, + 454, + 890, + 590 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Previous work has made significant progress using machine learning-based methods, but has achieved limited success in generating dances from music that satisfy user constraints. Furthermore, the evaluation of generated dances is subjective and complex, and existing papers often use quantitative metrics that we show to be flawed.", + "bbox": [ + 496, + 595, + 890, + 685 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "In this work, we propose Editable Dance GEneration (EDGE), a state-of-the-art method for dance generation that creates realistic, physically-plausible dance motions based on input music. Our method uses a transformer-based diffusion model paired with Jukebox, a strong music feature extractor. This unique diffusion-based approach confers powerful editing capabilities well-suited to dance, including joint-wise conditioning and in-betweening. In addition to the advantages immediately conferred by the modeling choices, we observe flaws with previous metrics and propose a new metric that captures the physical accuracy of ground contact behaviors without explicit physical modeling. In summary, our contributions are the following:", + "bbox": [ + 496, + 690, + 892, + 887 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 810, + 44 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "448", + "bbox": [ + 485, + 945, + 511, + 955 + ], + "page_idx": 0 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "1. We introduce EDGE, a diffusion-based approach for dance generation that combines state-of-the-art performance with powerful editing capabilities and is able to generate arbitrarily long sequences. EDGE improves on previous hand-crafted audio feature extraction strategies by leveraging music audio representations from Jukebox [5], a pre-trained generative model for music that has previously demonstrated strong performance on music-specific prediction tasks [3, 7].", + "2. We analyze the metrics proposed in previous works and show that they do not accurately represent human-evaluated quality as reported by a large user study.", + "3. We propose a new approach to eliminating foot-sliding physical implausibilities in generated motions using a novel Contact Consistency Loss, and introduce Physical Foot Contact Score, a simple new acceleration-based quantitative metric for scoring physical plausibility of generated kinematic motions that requires no explicit physical modeling." + ], + "bbox": [ + 88, + 90, + 468, + 390 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "This work is best enjoyed when accompanied by our demo samples. Please see the samples at our website.", + "bbox": [ + 76, + 395, + 468, + 426 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 76, + 440, + 218, + 455 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.1. Human motion generation", + "text_level": 1, + "bbox": [ + 76, + 465, + 316, + 481 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Human motion generation, the problem of automatically generating realistic human motions, is well-studied in computer vision, graphics, and robotics. Despite its importance and recent progress, it remains a challenging problem, with existing methods often struggling to capture the complexities of physically and stylistically realistic human motion.", + "bbox": [ + 76, + 488, + 468, + 579 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Many early approaches fall under the category of motion matching, which operates by interpolating between sequences retrieved from a database [21]. While these approaches generate outputs that are physically plausible, their application has been primarily restricted to simple domains such as locomotion.", + "bbox": [ + 76, + 580, + 468, + 669 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In recent years, deep neural networks have emerged as a promising alternative method for human motion generation. These approaches are often capable of generating diverse motions, but often fall short in capturing the physical laws governing human movement or rely on difficult-to-train reinforcement learning solutions [34, 60]. Generating human motion conditioned on various inputs—e.g., joystick control [34], class-conditioning [15, 43], text-to-motion [44, 63], seed motions [8, 22, 46, 62]—is also an active area of study.", + "bbox": [ + 75, + 670, + 468, + 821 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.2. Dance Generation", + "text_level": 1, + "bbox": [ + 76, + 830, + 253, + 845 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "The uniquely challenging task of generating dances stylistically faithful to input music has been tackled by many researchers. Many early approaches follow a motion", + "bbox": [ + 76, + 854, + 468, + 900 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "retrieval paradigm [11, 30, 40], but tend to create unrealistic choreographies that lack the complexity of human dances. Later works instead synthesize motion from scratch by training on large datasets [1, 10, 23, 27, 31, 33, 45, 47, 53, 59] and propose many modeling approaches, including adversarial learning, recurrent neural networks, and transformers. Despite achieving impressive performance, many such systems are complex [1, 4, 31, 53], often involving many layers of conditioning and sub-networks. In contrast, our proposed method contains a single model trained with a simple objective, yet offers both strong generative and editing capabilities without significant hand-crafted design.", + "bbox": [ + 496, + 90, + 890, + 272 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.3. Generative Diffusion Models", + "text_level": 1, + "bbox": [ + 500, + 279, + 756, + 294 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Diffusion models [19, 54] are a class of deep generative models which learn a data distribution by reversing a scheduled noising process. In the past few years, diffusion models have been shown to be a promising avenue for generative modeling, exceeding the state-of-the-art in generative tasks [18, 24, 50]. Much like previous generative approaches like VAE [28] and GAN [12], diffusion models are also capable of conditional generation. Dhariwal et al. [6] introduced classifier guidance for image generation, where the output of a diffusion model may be \"steered\" towards a target, such as a class label, using the gradients of a differentiable auxiliary model. Sahara et al. [49] proposed to use direct concatenation of conditions for Pix2Pix-like tasks, akin to Conditional GAN and CVAE [38, 55], and Ho et al. [20] demonstrated that classifier-free guidance can achieve state-of-the-art results while allowing more explicit control over the diversity-fidelity tradeoff.", + "bbox": [ + 496, + 301, + 890, + 559 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Most recently, diffusion-based methods have demonstrated strong performance in generating motions conditioned on text [26,58,63]. While the tasks of text-to-motion and music-conditioned dance generation share high-level similarities, the dance generation task suffers more challenging computational scaling (see Sec. 3) and, due to its specialized nature, much lower data availability.", + "bbox": [ + 496, + 560, + 890, + 666 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "3. Method", + "text_level": 1, + "bbox": [ + 500, + 676, + 589, + 691 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Pose Representation We represent dances as sequences of poses in the 24-joint SMPL format [35], using the 6-DOF rotation representation [64] for every joint and a single root translation: $\\pmb{w} \\in \\mathbb{R}^{24 \\cdot 6 + 3 = 147}$ . For the heel and toe of each foot, we also include a binary contact label: $\\pmb{b} \\in \\{0,1\\}^{2 \\cdot 2 = 4}$ . The total pose representation is therefore $\\pmb{x} = \\{\\pmb{b}, \\pmb{w}\\} \\in \\mathbb{R}^{4 + 147 = 151}$ . EDGE uses a diffusion-based framework to learn to synthesize sequences of $N$ frames, $\\pmb{x} \\in \\mathbb{R}^{N \\times 151}$ , given arbitrary music conditioning $\\pmb{c}$ .", + "bbox": [ + 496, + 702, + 890, + 839 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Diffusion Framework We follow the DDPM [19] definition of diffusion as a Markov noising process with latents $\\{z_t\\}_{t=0}^T$ that follow a forward noising process $q(z_t | x)$ ,", + "bbox": [ + 496, + 854, + 890, + 902 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "449", + "bbox": [ + 485, + 945, + 509, + 955 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/5a0a20fa10228603122e197d2a3f50a4ff9e7ae0f11c30240c38f5c01ed60df3.jpg", + "image_caption": [ + "Figure 2. EDGE Pipeline Overview: EDGE learns to denoise dance sequences from time $t = T$ to $t = 0$ , conditioned on music. Music embedding information is provided by a frozen Jukebox model [5] and acts as cross-attention context. EDGE takes a noisy sequence $\\mathbf{z}_T \\sim \\mathcal{N}(0, I)$ and produces the estimated final sequence $\\hat{\\mathbf{x}}$ , noising it back to $\\hat{\\mathbf{z}}_{T - 1}$ and repeating until $t = 0$ ." + ], + "image_footnote": [], + "bbox": [ + 81, + 87, + 467, + 318 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/7e4fdd3f3feae443dffef04a6b0511a4bc8e211de5f09b07edb4b627d611ec5a.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 475, + 85, + 893, + 316 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\pmb{x} \\sim p(\\pmb{x})$ is drawn from the data distribution. The forward noising process is defined as", + "bbox": [ + 76, + 397, + 470, + 428 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nq \\left(\\boldsymbol {z} _ {t} | \\boldsymbol {x}\\right) \\sim \\mathcal {N} \\left(\\sqrt {\\bar {\\alpha} _ {t}} \\boldsymbol {x}, \\left(1 - \\bar {\\alpha} _ {t}\\right) \\boldsymbol {I}\\right), \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 158, + 434, + 468, + 453 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\bar{\\alpha}_t\\in (0,1)$ are constants which follow a monotonically decreasing schedule such that when $\\bar{\\alpha}_t$ approaches 0, we can approximate $z_{T}\\sim \\mathcal{N}(0,I)$ . We chose to use $T = 1000$ timesteps.", + "bbox": [ + 76, + 457, + 468, + 518 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In our setting with paired music conditioning $\\pmb{c}$ , we reverse the forward diffusion process by learning to estimate $\\hat{\\pmb{x}}_{\\theta}(z_t,t,\\pmb {c})\\approx \\pmb {x}$ with model parameters $\\theta$ for all $t$ . We optimize $\\theta$ with the \"simple\" objective introduced in Ho et al. [19]:", + "bbox": [ + 76, + 518, + 468, + 594 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\text {s i m p l e}} = \\mathbb {E} _ {\\boldsymbol {x}, t} \\left[ \\| \\boldsymbol {x} - \\hat {\\boldsymbol {x}} _ {\\theta} (\\boldsymbol {z} _ {t}, t, \\boldsymbol {c}) \\| _ {2} ^ {2} \\right]. \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 147, + 599, + 468, + 619 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "From now on, we refer to $\\hat{\\pmb{x}}_{\\theta}(\\pmb{z}_t,t,\\pmb {c})$ as $\\hat{\\pmb{x}} (\\pmb {z}_t,\\pmb {c})$ for ease of notation.", + "bbox": [ + 76, + 623, + 468, + 654 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Auxiliary losses Auxiliary losses are commonly used in kinematic motion generation settings to improve physical realism in the absence of true simulation [43, 52, 57]. In addition to the reconstruction loss $\\mathcal{L}_{\\mathrm{simple}}$ , we adopt auxiliary losses similar to those in Tevet et al. [58], which encourage matching three aspects of physical realism: joint positions (Eq. (3)), velocities (Eq. (4)), and foot velocities via our Contact Consistency Loss (Eq. (5)).", + "bbox": [ + 76, + 671, + 470, + 792 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\text {j o i n t}} = \\frac {1}{N} \\sum_ {i = 1} ^ {N} \\| F K (\\boldsymbol {x} ^ {(i)}) - F K (\\hat {\\boldsymbol {x}} ^ {(i)}) \\| _ {2} ^ {2} \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 130, + 797, + 468, + 840 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\mathrm {v e l}} = \\frac {1}{N - 1} \\sum_ {i = 1} ^ {N - 1} \\| \\left(\\boldsymbol {x} ^ {(i + 1)} - \\boldsymbol {x} ^ {(i)}\\right) - \\left(\\hat {\\boldsymbol {x}} ^ {(i + 1)} - \\hat {\\boldsymbol {x}} ^ {(i)}\\right) \\| _ {2} ^ {2} \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 81, + 845, + 468, + 901 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\text {c o n t a c t}} = \\frac {1}{N - 1} \\sum_ {i = 1} ^ {N - 1} \\| \\left(F K \\left(\\hat {\\boldsymbol {x}} ^ {(i + 1)}\\right) - F K \\left(\\hat {\\boldsymbol {x}} ^ {(i)}\\right)\\right) \\cdot \\hat {\\boldsymbol {b}} ^ {(i)} \\| _ {2} ^ {2}, \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 500, + 415, + 895, + 468 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $FK(\\cdot)$ denotes the forward kinematic function that converts joint angles into joint positions (though it only applies to the foot joints in Eq. (5)) and the $(i)$ superscript denotes the frame index. In the Contact Consistency Loss, $\\hat{\\pmb{b}}^{(i)}$ is the model's own prediction of the binary foot contact label's portion of the pose at each frame $i$ . While this formulation is similar to the foot skate loss terms in previous works [57, 58], where foot velocity is penalized in frames where the ground truth motion exhibits a static foot contact, our Contact Consistency Loss formulation differs in that it encourages the model to (1) predict foot contact, and (2) maintain consistency with its own predictions. We find that this formulation significantly improves the realism of generated motions (see Sec. 4.1).", + "bbox": [ + 496, + 469, + 892, + 679 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Our overall training loss is the weighted sum of the simple objective and the auxiliary losses, where the weights $\\lambda$ were chosen to balance the magnitudes of the losses at the start of training.:", + "bbox": [ + 496, + 680, + 893, + 742 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} = \\mathcal {L} _ {\\text {s i m p l e}} + \\lambda_ {\\text {p o s}} \\mathcal {L} _ {\\text {p o s}} + \\lambda_ {\\text {v e l}} \\mathcal {L} _ {\\text {v e l}} + \\lambda_ {\\text {c o n t a c t}} \\mathcal {L} _ {\\text {c o n t a c t}}. \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 517, + 747, + 890, + 763 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Sampling and Guidance At each of the denoising timesteps $t$ , EDGE predicts the denoised sample and noises it back to timestep $t - 1: \\hat{\\pmb{z}}_{t - 1} \\sim q(\\hat{\\pmb{x}}_{\\theta}(\\hat{\\pmb{z}}_t, \\pmb{c}), t - 1)$ , terminating when it reaches $t = 0$ (Fig. 2, right). We train our model using classifier-free guidance [20], which is commonly used in diffusion-based models [26, 48, 50, 58, 63]. Following Ho et al. [20], we implement classifier-free guidance by randomly replacing the conditioning with $\\pmb{c} = \\emptyset$", + "bbox": [ + 496, + 779, + 893, + 902 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "450", + "bbox": [ + 485, + 944, + 511, + 957 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "during training with low probability (e.g., $25\\%$ ). Guided inference is then expressed as the weighted sum of unconditionally and conditionally generated samples:", + "bbox": [ + 75, + 90, + 468, + 137 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\tilde {\\boldsymbol {x}} (\\hat {\\boldsymbol {z}} _ {t}, \\boldsymbol {c}) = w \\cdot \\hat {\\boldsymbol {x}} (\\hat {\\boldsymbol {z}} _ {t}, \\boldsymbol {c}) + (1 - w) \\cdot \\hat {\\boldsymbol {x}} (\\hat {\\boldsymbol {z}} _ {t}, \\emptyset). \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 120, + 147, + 468, + 164 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "At sampling time, we can amplify the conditioning $c$ by choosing a guidance weight $w > 1$ .", + "bbox": [ + 75, + 174, + 468, + 205 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Editing To enable editing for dances generated by EDGE, we use the standard masked denoising technique from diffusion image inpainting [36], and more recently text-to-motion models [26,58]. EDGE supports any combination of temporal and joint-wise constraints, shown in Fig. 4. Given a joint-wise and/or temporal constraint $\\pmb{x}^{\\mathrm{known}}$ with positions indicated by a binary mask $m$ , we perform the following at every denoising timestep:", + "bbox": [ + 75, + 222, + 468, + 344 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {z} _ {t - 1} := \\boldsymbol {m} \\odot q \\left(\\boldsymbol {x} ^ {\\text {k n o w n}}, t - 1\\right) + (1 - \\boldsymbol {m}) \\odot \\hat {z} _ {t - 1}, \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 94, + 353, + 468, + 369 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\odot$ is the Hadamard (element-wise) product, replacing the known regions with forward-diffused samples of the constraint. This technique allows editability at inference time with no special training processes necessary.", + "bbox": [ + 75, + 381, + 468, + 441 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "For example, a user can perform motion in-between by providing a reference motion $\\pmb{x}^{\\mathrm{known}} \\in \\mathbb{R}^{N \\times 151}$ and a mask $m \\in \\{0,1\\}^{N \\times 151}$ , where $m$ is all 1's in the first and last $n$ frames and 0 everywhere else. This would result in a sequence $N$ frames long, where the first and last $n$ frames are provided by the reference motion and the rest is filled in with a plausible \"in-between\" dance that smoothly connects the constraint frames, for arbitrary $2n < N$ . This editing framework provides a powerful tool for downstream applications, enabling the generation of dances that precisely conform to arbitrary constraints.", + "bbox": [ + 75, + 441, + 468, + 608 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Long-form sampling The ability to synthesize sequences of arbitrary length, often many minutes long, is critical to the task of dance generation. However, since EDGE generates every frame of a dance sequence at once, naively increasing the maximum sequence length incurs a linear increase in computational cost. Moreover, dance generation requires that the conditioning $c$ match the motion sequence in length, causing further scaling of memory demands, which is especially severe in the case of embeddings from large models like Jukebox [5]. To approach the challenge of long-form generation, EDGE leverages its editability to enforce temporal consistency between multiple sequences such that they can be concatenated into a single longer sequence. Refer to Fig. 3 for a depiction of this process.", + "bbox": [ + 75, + 626, + 468, + 851 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Model Our model architecture is illustrated in Fig. 2. We adopt a transformer decoder architecture, which processes", + "bbox": [ + 75, + 869, + 468, + 901 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/192319357babfb8b2670021f030e318542871678ea13571d671abd928cde5501.jpg", + "image_caption": [ + "Figure 3. Although EDGE is trained on 5-second clips, it can generate choreographies of any length by imposing temporal constraints on batches of sequences. In this example, EDGE constrains the first 2.5 seconds of each sequence to match the last 2.5 seconds of the previous one to generate a 12.5-second clip, as represented by the temporal regions of distinct clips in the batch that share the same color." + ], + "image_footnote": [], + "bbox": [ + 540, + 90, + 854, + 250 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "music conditioning projected to the transformer dimension with a cross-attention mechanism following Sahara et al. [50]. Timestep information, which is represented as a sinusoidal embedding [19], is incorporated both through a token concatenated with the music conditioning and feature-wise linear modulation (FiLM) layers [42]. In our model, FiLM layers are given an output from a previous layer $\\mathbf{Y}$ and a timestep embedding $\\boldsymbol{e}_t$ , and process the embeddings as:", + "bbox": [ + 496, + 368, + 890, + 502 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {W} = \\psi_ {w} (\\phi (\\boldsymbol {e} _ {t})), \\quad \\boldsymbol {B} = \\psi_ {b} (\\phi (\\boldsymbol {e} _ {t})) \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 573, + 523, + 890, + 541 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\operatorname {F i L M} (\\boldsymbol {Y}) = \\boldsymbol {W} \\odot \\boldsymbol {Y} + \\boldsymbol {B} \\tag {10}\n$$\n", + "text_format": "latex", + "bbox": [ + 602, + 556, + 890, + 573 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": ", where $\\psi_w,\\psi_w$ , and $\\phi$ are separate linear projections.", + "bbox": [ + 500, + 585, + 854, + 599 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Music Audio Features Past work [1, 10, 23, 27, 31, 33, 45, 53, 59] has largely focused on advancing the generative modeling approach for the dance generation problem, with little focus on the representation of the music signal itself, which we argue is equally important. Indeed, state-of-the-art results in the text-to-image domain have found that scaling the text encoder is more important for performance than scaling the diffusion model [50].", + "bbox": [ + 496, + 627, + 890, + 747 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In this vein, recent work [3, 7] in music information retrieval has demonstrated that Jukebox [5], a large GPT-style model trained on 1M songs to generate raw music audio, contains representations that serve as strong features for music audio prediction tasks. We take inspiration from these advances and extract Jukebox features as the conditioning input for our diffusion model, and develop a new memory-efficient implementation that enables near real-time extraction on a single commodity GPU (see Appendix I for details).", + "bbox": [ + 496, + 750, + 890, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "451", + "bbox": [ + 485, + 945, + 509, + 955 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/a5295bd63756b00733529aee1d74ef9ccbb2a17f8074f15d35ea283502d7c1c6.jpg", + "image_caption": [ + "Figure 4. EDGE allows the user to specify both temporal and joint-wise constraints. Constraint joints / frames are highlighted in green and tan, generated joints / frames are in blue and gray. Pictured, top to bottom: dance completion from seed motion, dance that hits a specified keyframe mid-choreography, completion from specified upper-body joint angles, completion from specified lower-body joint angles and root trajectory." + ], + "image_footnote": [], + "bbox": [ + 84, + 99, + 464, + 375 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 76, + 523, + 209, + 540 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Dataset In this work, we use AIST++ [33], a dataset consisting of 1,408 high-quality dance motions paired to music from a diverse set of genres. We re-use the train/test splits provided by the original dataset. All training examples are split into clips of 5 seconds at 30 FPS.", + "bbox": [ + 75, + 547, + 468, + 625 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Baselines Among recent state-of-the-art dance generation methods [1, 10, 23, 27, 31, 33, 45, 53, 59], we select the following baselines:", + "bbox": [ + 76, + 630, + 468, + 674 + ], + "page_idx": 4 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- FACT [33], an autoregressive model introduced together with the AIST++ dataset, and", + "- Bailando [53], a follow-up approach that achieves the strongest qualitative performance to date." + ], + "bbox": [ + 94, + 681, + 467, + 751 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Implementation details Our final model has 49M total parameters, and was trained on 4 NVIDIA A100 GPUs for 16 hours with a batch size of 512.", + "bbox": [ + 76, + 763, + 468, + 808 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "For long-form generation, we use 5-second slices and choose to enforce consistency for overlapping 2.5-second slices by interpolating between the two slices with linearly decaying weight. We find that this simple approach is sufficient to result in smooth, consistent generation, as demonstrated throughout our website. In our results, we perform", + "bbox": [ + 75, + 810, + 468, + 898 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "no post-processing to correct foot contacts or physical plausibility, and show the model outputs directly.", + "bbox": [ + 498, + 92, + 888, + 119 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We evaluate two separate feature extraction strategies. The \"baseline\" strategy uses the popular audio package librosa [37] to extract beats and accompanying audio features using the same code as in Li et al. [33] (when the ground truth BPM is not known, we estimate it with librosa). The \"Jukebox\" [5] extraction strategy follows Castellon et al. [3], extracting representations from Jukebox and downsampling to 30 FPS to match our frame rates for motion data.", + "bbox": [ + 496, + 122, + 890, + 255 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.1. Comparison to Existing Methods", + "text_level": 1, + "bbox": [ + 498, + 267, + 790, + 282 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In this section, we compare our proposed model to several past works on (1) human evaluations, (2) our proposed physical plausibility metric, (3) beat alignment scores, (4) diversity, and (5) performance on in-the-wild music.", + "bbox": [ + 496, + 291, + 890, + 351 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Human Evaluations To obtain the results in Tab. 1, we recruited 147 human raters who evaluated a total of 11,610 pairs of clips randomly sampled from our models, ground truth, baseline models, or a checkpoint from our model training (as seen in Sec. 4.3).", + "bbox": [ + 496, + 359, + 890, + 434 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The study reveals that human raters overwhelmingly prefer the dances generated by EDGE over previous methods, and even favor EDGE dances over real dances. For more information on the exact details of our study, see Appendix A.", + "bbox": [ + 496, + 435, + 890, + 494 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Physical Plausibility Any generated dance should be physically plausible; otherwise, its downstream applicability is dramatically limited. Previous works evaluate plausibility of foot-ground contact by measuring foot sliding [17,56]; however, dance is unique in that sliding is not only common but integral to many choreographies. This reflects a need for a metric that can measure the realism of foot-ground contact that does not assume that feet should exhibit static contact at all times. In this work, we propose a new metric to evaluate physical plausibility, Physical Foot Contact score (PFC), that we believe captures this concept well.", + "bbox": [ + 496, + 515, + 890, + 681 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "PFC is a physically-inspired metric that requires no explicit physical modeling. Our metric arises from two simple, related observations:", + "bbox": [ + 496, + 681, + 888, + 726 + ], + "page_idx": 4 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "1. On the horizontal (xy) plane, any center of mass (COM) acceleration must be due to static contact between the feet and the ground. Therefore, either at least one foot is stationary on the ground or the COM is not accelerating.", + "2. On the vertical (z) axis, any positive COM acceleration must be due to static foot contact." + ], + "bbox": [ + 511, + 738, + 890, + 842 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Therefore, we can represent adherence to these conditions as an average over time of the below expression, scaled to normalize acceleration:", + "bbox": [ + 496, + 854, + 890, + 898 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "452", + "bbox": [ + 485, + 945, + 509, + 955 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/caea73879f3950000e0f165593b76072a688b617f950ff3c382d2eb36fc01d73.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodElo ↑EDGE Win RatePFC ↓Beat Align. ↑Distk →Distg →Fixed BonesEditing
EDGE (w = 2)1751N/A1.53630.269.485.72✓✓
EDGE (w = 1)160158.0% ± 3.8%1.65450.2710.587.62✓✓
Bailando139791.1% ± 5.9%1.7540.237.927.72✗✗
FACT132590.0% ± 7.0%2.25430.2210.856.14✓✗
Ground Truth165365.7% ± 11.1%1.3320.2410.617.48✓N/A
", + "bbox": [ + 84, + 88, + 885, + 209 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/f64cb7d2f1ecc2beb2a034d16cc28c446f9da7f95b0a8a08e0e3a8cd375c4371.jpg", + "table_caption": [ + "Table 1. We compare our method against FACT [33] and Bailando [53]. In the table, $w$ refers to the guidance weight at inference time. We evaluate all methods qualitatively via human raters to obtain Elo [9] and Win Rate, and compute the rest of the metrics automatically. For reference, the Elo rating system is designed such that a 400 point gap corresponds to a $\\sim {90}\\%$ head-to-head win rate,which is reflected in our empirical results (the \"EDGE Win Rate\" column). Refer to the Wikipedia page for the mathematical details. Error bars for \"EDGE Win Rate\" correspond to a 95% confidence interval (see Appendix A for details). $\\uparrow$ means higher is better, $\\downarrow$ means lower is better,and $\\rightarrow$ means closer to ground truth is better." + ], + "table_footnote": [], + "table_body": "
Method (In-the-Wild)Elo ↑EDGE Win Rate
EDGE174753.8% ± 11.1%
w/o Jukebox160383.3% ± 8.3%
Bailando122282.4% ± 5.5%
FACT136789.3% ± 4.4%
", + "bbox": [ + 99, + 325, + 447, + 417 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\ns ^ {i} = \\left\\| \\bar {\\mathbf {a}} _ {\\mathrm {C O M}} ^ {i} \\right\\| \\cdot \\left\\| \\mathbf {v} _ {\\text {L e f t F o o t}} ^ {i} \\right\\| \\cdot \\left\\| \\mathbf {v} _ {\\text {R i g h t F o o t}} ^ {i} \\right\\|, \\tag {11}\n$$\n", + "text_format": "latex", + "bbox": [ + 135, + 513, + 468, + 532 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\nP F C = \\frac {1}{N \\cdot \\max _ {1 \\leq j \\leq N} \\left\\| \\bar {a} _ {\\mathrm {C O M}} ^ {j} \\right\\|} \\sum_ {i = 1} ^ {N} s ^ {i}, \\tag {12}\n$$\n", + "text_format": "latex", + "bbox": [ + 150, + 542, + 468, + 588 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where", + "bbox": [ + 76, + 595, + 122, + 609 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\overline {{\\boldsymbol {a}}} _ {\\mathrm {C O M}} ^ {i} = \\left( \\begin{array}{c} a _ {\\mathrm {C O M}, x} ^ {i} \\\\ a _ {\\mathrm {C O M}, y} ^ {i} \\\\ \\max (a _ {\\mathrm {C O M}, z} ^ {i}, 0) \\end{array} \\right)\n$$\n", + "text_format": "latex", + "bbox": [ + 173, + 607, + 369, + 657 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "and the $i$ superscript denotes the frame index.", + "bbox": [ + 96, + 664, + 398, + 679 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "In our results (Tab. 1), we find that our method attains a greater level of physical plausibility than previous methods, and approaches the plausibility of ground truth motion capture data.", + "bbox": [ + 75, + 680, + 468, + 739 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Maintaining fixed bone length is another important aspect of physical plausibility. Our method operates in the reduced coordinate (joint angle) space, which guarantees fixed bone length. However, methods that operate in the joint Cartesian space, such as Bailando, can produce significantly varying bone lengths. For example, on average, bone lengths change up to $\\pm 20\\%$ over the course of dance sequences generated by Bailando.", + "bbox": [ + 75, + 741, + 468, + 862 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Beat Alignment Scores Our experiments evaluate the tendency of our generated dances to follow the beat of the", + "bbox": [ + 75, + 869, + 470, + 902 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/d01ba117741ec8e34d31afaf1ab9d43ab5f885d26136dc8cc12980be9e99c6d6.jpg", + "table_caption": [ + "Table 2. We test our model on in-the-wild music and ablate Jukebox features in this setting, showing that Jukebox features are critical for generalization." + ], + "table_footnote": [], + "table_body": "
MethodEDGE Win RatePFC ↓
EDGEN/A1.5363
w/o CCL61.8% ± 7.3%3.0806
Ground Truth40.6% ± 7.4%1.332
", + "bbox": [ + 542, + 325, + 849, + 404 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 3. We ablate our contact consistency loss (CCL) and study its impact on qualitative and quantitative physical plausibility. While EDGE wins more on average against ground truth on overall quality evaluation (Tab. 1), the user study for this table specifically asks about physical plausibility, and we find that ground truth still performs favorably compared to EDGE.", + "bbox": [ + 496, + 412, + 893, + 498 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "music, following previous work [53] for the precise implementation of this metric. The results demonstrate that EDGE outperforms past work, including Bailando, which includes a reinforcement learning module that explicitly optimizes beat alignment. We further examine the robustness of this metric in Sec. 5.", + "bbox": [ + 496, + 526, + 890, + 617 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Diversity Diversity metrics are computed following the methods of previous work [33, 53], which measure the distributional spread of generated dances in the \"kinetic\" $(\\mathrm{Dist}_k)$ and \"geometric\" $(\\mathrm{Dist}_g)$ feature spaces, as implemented by fairmotion [13, 39, 41]. We compute these metrics on 5-second dance clips produced by each approach. Given that the ultimate goal of dance generation is to automatically produce dances that emulate the ground truth distribution, we argue that models should aim to match the scores of the ground truth distribution rather than maximize their absolute values. Indeed, past work has found that jittery dances result in high diversity scores, in some cases exceeding the ground truth [32, 33].", + "bbox": [ + 496, + 627, + 892, + 824 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "At low guidance weight $(w = 1)$ , EDGE achieves a level of diversity that closely matches that of the ground truth distribution while attaining state-of-the-art qualitative performance. At high guidance weight $(w = 2)$ , EDGE produces dances of markedly higher fidelity, reflected by a signifi", + "bbox": [ + 496, + 825, + 893, + 902 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "453", + "bbox": [ + 485, + 945, + 509, + 955 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/e40c9eeda1b196ab29d9f3dce74241fc34528584185c31c90d6a3a804b9a82b5.jpg", + "image_caption": [ + "Figure 5. Temporal Conditioning: In-Betweening Given start (green) and end (red) poses, EDGE can generate in-between dance sequences." + ], + "image_footnote": [], + "bbox": [ + 80, + 88, + 465, + 257 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "cantly higher Elo rating, while trading off diversity. These results reflect those of past studies, which show that sampling using guidance weights $w > 1$ significantly increases fidelity at the cost of diversity [20, 50]. This simple control over the diversity-fidelity tradeoff via the modulation of a single scalar parameter provides a powerful tool for downstream applications.", + "bbox": [ + 75, + 327, + 467, + 434 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.2. Additional Evaluation", + "text_level": 1, + "bbox": [ + 76, + 444, + 282, + 459 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "In-the-Wild Music While past approaches achieve strong results on AIST++, these results are not necessarily indicative of the models' ability to generalize to in-the-wild music inputs. In order to evaluate generalization, we tested our proposed method and the baseline approaches on a diverse selection of popular songs from YouTube.", + "bbox": [ + 75, + 468, + 467, + 559 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "The results, as shown in Tab. 2, demonstrate that our proposed method continues to perform well on in-the-wild music. We find through ablation that Jukebox features are critical for performance in this setting, bringing human-rated quality almost to par with in-distribution music; furthermore, we find that our approach continues to beat baselines in human evaluations for dance quality. We note that Bailando has an additional fine-tuning procedure available to improve performance on in-the-wild samples by training its actor-critic component. While we evaluated Bailando directly without additional fine-tuning, we found that human raters significantly preferred in-the-wild EDGE samples over in-distribution Bailando samples. We interpret these results as evidence that our proposed method is able to successfully generalize to in-the-wild music inputs.", + "bbox": [ + 75, + 561, + 467, + 787 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Editing We find through an additional human evaluation that our model is capable of in-betweening, motion continuation, joint-conditioned generation, and long-form generation with quality on par with unconstrained samples. Please see our website for demo examples, and Appendix H for more details.", + "bbox": [ + 75, + 809, + 467, + 900 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Contact Consistency Ablation We test the soundness of our PFC metric and ablate our Contact Consistency Loss (CCL) term (see Eq. (5)) using a human evaluation study. Raters were shown pairs of dances from the ground truth distribution, EDGE with CCL, and EDGE without CCL, and asked which dance looked more physically plausible. The results (Tab. 3) show that CCL noticeably improves both the PFC metric and qualitative physical plausibility user evaluations, winning $61.8\\%$ of matchups against the version without CCL, and coming close to parity with ground truth samples. The results also indicate that PFC tracks well with human perception of physical plausibility.", + "bbox": [ + 496, + 90, + 890, + 272 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "For a discussion of limitations and implementation details of PFC, please see Sec. 5 and Appendix D, respectively.", + "bbox": [ + 496, + 273, + 890, + 319 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.3. Analysis of FID Metrics for Dance", + "text_level": 1, + "bbox": [ + 498, + 332, + 797, + 348 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "A reasonable solution to the problem of overall evaluation is to compute the difference between an empirical distribution of generated dances and a ground truth distribution. Several past works follow this intuition and automatically evaluate dance quality with Frechet Distance metrics [32, 33, 53]. As part of our experiments, we conduct a two-pronged analysis into the prevailing metrics, \"FID $_k$ \" and \"FID $_g$ \" [33], which compute the difference between distributions of heuristically extracted motion features, and show them to be unsound for the AIST++ dataset.", + "bbox": [ + 496, + 357, + 890, + 508 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "“ $\\mathrm{FID}_g$ ” We compute $\\mathrm{FID}_g$ on the ground truth AIST++ dataset following the implementation in Li et al. [33]. Specifically, we compute metrics on the test set against the training set and obtain a score of 41.4, a stark increase from metrics obtained from generated outputs: running on FACT outputs gives 12.75, running on Bailando outputs gives 24.82, and running on our final model's outputs gives 23.08. Given that FACT performs the best in “ $\\mathrm{FID}_g$ ” but performs the worst according to user studies and that all three models perform significantly better than ground truth, we conclude that the “ $\\mathrm{FID}_g$ ” values are unreliable as a measure of quality on this dataset.", + "bbox": [ + 496, + 522, + 890, + 704 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "\" $\\mathbf{FID}_k$ \" We take 10 checkpoints throughout the training process for our model and poll raters on the overall quality of dances sampled from each checkpoint in a round-robin tournament. Intuitively, this should result in a consistent-to-monotonic improvement in both qualitative performance and in the quantitative quality metrics. However, we observe that this is not the case. In Fig. 6, we show the results of this experiment with our proposed model's $\\mathrm{FID}_k$ .", + "bbox": [ + 496, + 717, + 890, + 838 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "While the qualitative performance of the generated motion improves considerably as we train the model, the $\\mathrm{FID}_k$ does not improve, and actually significantly worsens during the latter half of training.", + "bbox": [ + 496, + 839, + 890, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "454", + "bbox": [ + 485, + 944, + 509, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/c3fc18ef65019a4cf216bead516406222c06ea52e6290821838f568e9cd3781c.jpg", + "image_caption": [ + "Figure 6. We plot $\\mathrm{FID}_k$ over the course of model training and find that it is inconsistent with overall quality evaluations." + ], + "image_footnote": [], + "bbox": [ + 81, + 89, + 464, + 215 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Limitations of Existing Metrics", + "text_level": 1, + "bbox": [ + 76, + 271, + 362, + 289 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Developing automated metrics for the quality of generated dances is a fundamentally challenging undertaking, since the practice of dance is complex, subjective, and even culturally specific. In this section, we discuss our findings on the limitations in automated metrics for dance evaluation, including our proposed PFC metric.", + "bbox": [ + 75, + 297, + 468, + 388 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Overall Quality Evaluation Our results suggest that despite the current standardized use of FIDs for evaluating dance generation models on the AIST++ dataset, these FID metrics, as they currently stand, are unreliable for measuring quality. One potential explanation may be that the AIST++ test set does not thoroughly cover the train distribution given its very small size. Additionally, due to data scarcity, both $\\mathrm{FID}_k$ and $\\mathrm{FID}_g$ depend on heuristic feature extractors that only compute superficial features of the data. By contrast, FID-based metrics in data-rich domains such as image generation (where FID originated) enjoy the use of learned feature extractors (e.g., pre-trained ImageNet models), which are known to directly extract semantically meaningful features [51]. Indeed, in the text-to-motion domain, where significantly more paired data is available [14], the standard feature extractors for FID-style metrics depend on deep contrastively learned models [58, 63].", + "bbox": [ + 75, + 409, + 468, + 666 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Our experiments suggest that the current FID metrics can be further improved for evaluating motion sequences. We believe that the idea of evaluating the difference between two featurized distributions of dance motions is not necessarily fundamentally flawed, but that more representative features could result in reliable automatic quality evaluations.", + "bbox": [ + 75, + 667, + 468, + 772 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Beat Alignment Scoring Some automated metrics aim to capture one of the core aspects of a dance performance: its ability to \"follow the beat\" of the song. Previous work [33, 53] has proposed using a beat alignment metric that rewards kinematic beats (local minima of joint speed) which line up with music beats.", + "bbox": [ + 75, + 792, + 467, + 883 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "However, dance is not strictly about matching local min", + "bbox": [ + 96, + 885, + 467, + 900 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "ima in joint speed to beats: instead, the beats of the music are a loose guide for timing, rhythm, and transitions between movements and dance steps. This discrepancy is reflected in our results: empirically, we observe that in addition to exceeding scores of competing baselines, our beat alignment scores exceed those of ground truth samples. This seems to suggest that while the metric has served to drive progress on this problem in the past, the metric loses its meaning when candidate examples reach quality on par with ground truth.", + "bbox": [ + 496, + 90, + 890, + 242 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Physical Foot Contact In this work, we introduce PFC, Eq. (12), a physically-inspired metric that specifically targets the challenging issue of foot sliding. While PFC is intuitive, it is not without its limitations. In its current form, PFC assumes that the feet are the only joints that experience static contact. This means that PFC cannot be applied without modification to motions such as gymnastics routines, where a variable number of non-foot (e.g., hand) contacts are integral to their execution. We believe that a careful analysis of other contact points (e.g., hands in gymnastics) could provide an extension of PFC that is more widely applicable. Another issue is the assumption that the COM can be accelerated only by static contact: though rare, it is possible to decelerate the COM using friction during extended sliding (which is not present in AIST++.). For more analysis and discussion of PFC, see Appendix D.", + "bbox": [ + 496, + 258, + 890, + 501 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "6. Conclusion and Future Work", + "text_level": 1, + "bbox": [ + 500, + 512, + 769, + 529 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this work, we propose a diffusion-based model that generates realistic and long-form dance sequences conditioned on music. We evaluate our model on multiple automated metrics (including our proposed PFC) and a large user study, and find that it achieves state-of-the-art results on the AIST++ dataset and generalizes well to in-the-wild music inputs. Importantly, we demonstrate that our model admits powerful editing capabilities, allowing users to freely specify both temporal and joint-wise constraints. The introduction of editable dance generation provides multiple promising avenues for future work. Whereas our method is able to create arbitrarily long dance sequences via the chaining of locally consistent, shorter clips, it cannot generate choreographies with very-long-term dependencies. Future work may explore the use of non-uniform sampling patterns such as those implemented in Harvey et al. [16], or a variation of the frame in-between scheme used in Ho et al. [18]. Editability also opens the door to the generation of more complex choreographies, including multi-person and scene-aware dance forms. Joint-wise conditioning may also potentially be used to address the issue of self-penetrating motions, which are sometimes present in our results. We are excited to see the future that this new direction of editable dance generation will enable.", + "bbox": [ + 496, + 537, + 890, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "455", + "bbox": [ + 485, + 945, + 509, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 174, + 106 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Ho Yin Au, Jie Chen, Junkun Jiang, and Yike Guo. Choreograph: Music-conditioned automatic dance choreography over a style and tempo consistent dynamic graph. In Proceedings of the 30th ACM International Conference on Multimedia, pages 3917-3925, 2022. 2, 4, 5", + "[2] Steven Brown and Lawrence M Parsons. The neuroscience of dance. Scientific American, 299(1):78-83, 2008. 1", + "[3] Rodrigo Castellon, Chris Donahue, and Percy Liang. 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In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 5745-5753, 2019. 2" + ], + "bbox": [ + 78, + 90, + 468, + 513 + ], + "page_idx": 10 + }, + { + "type": "page_number", + "text": "458", + "bbox": [ + 486, + 945, + 509, + 955 + ], + "page_idx": 10 + } +] \ No newline at end of file diff --git a/2023/EDGE_ Editable Dance Generation From Music/97e29d71-2a36-4f04-a26f-23105d30e787_model.json b/2023/EDGE_ Editable Dance Generation From Music/97e29d71-2a36-4f04-a26f-23105d30e787_model.json new file mode 100644 index 0000000000000000000000000000000000000000..cd85f0f29796af0a8cebdf62d1f6b16ba6aefc2a --- /dev/null +++ b/2023/EDGE_ Editable Dance Generation From Music/97e29d71-2a36-4f04-a26f-23105d30e787_model.json @@ -0,0 +1,2389 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.0, + 0.812, + 0.045 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.243, + 0.131, + 0.73, + 0.151 + ], + "angle": 0, + "content": "EDGE: Editable Dance Generation From Music" + }, + { + "type": "text", + "bbox": [ + 0.289, + 0.181, + 0.681, + 0.218 + ], + "angle": 0, + "content": "Jonathan Tseng, Rodrigo Castellon, C. Karen Liu \nStanford University" + }, + { + "type": "text", + "bbox": [ + 0.295, + 0.22, + 0.674, + 0.234 + ], + "angle": 0, + "content": "{jtseng20, rjcaste, karenliu}@cs.stanford.edu" + }, + { + "type": "image", + "bbox": [ + 0.081, + 0.238, + 0.894, + 0.409 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.186, + 0.419, + 0.782, + 0.433 + ], + "angle": 0, + "content": "Figure 1. EDGE generates diverse, physically plausible dance choreographies conditioned on music." + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.454, + 0.314, + 0.469 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.075, + 0.486, + 0.474, + 0.743 + ], + "angle": 0, + "content": "Dance is an important human art form, but creating new dances can be difficult and time-consuming. In this work, we introduce Editable Dance Generation (EDGE), a state-of-the-art method for editable dance generation that is capable of creating realistic, physically-plausible dances while remaining faithful to the input music. EDGE uses a transformer-based diffusion model paired with Jukebox, a strong music feature extractor, and confers powerful editing capabilities well-suited to dance, including joint-wise conditioning, and in-betweening. We introduce a new metric for physical plausibility, and evaluate dance quality generated by our method extensively through (1) multiple quantitative metrics on physical plausibility, beat alignment, and diversity benchmarks, and more importantly, (2) a large-scale user study, demonstrating a significant improvement over previous state-of-the-art methods. Qualitative samples from our model can be found at our website." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.771, + 0.21, + 0.787 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.797, + 0.47, + 0.904 + ], + "angle": 0, + "content": "Dance is an important part of many cultures around the world: it is a form of expression, communication, and social interaction [29]. However, creating new dances or dance animations is uniquely difficult because dance movements are expressive and freeform, yet precisely structured by music. In practice, this requires tedious hand animation or motion capture solutions, which can be expensive and impractical." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.455, + 0.892, + 0.592 + ], + "angle": 0, + "content": "On the other hand, using computational methods to generate dances automatically can alleviate the burden of the creation process, leading to many applications: such methods can help animators create new dances or provide interactive characters in video games or virtual reality with realistic and varied movements based on user-provided music. In addition, dance generation can provide insights into the relationship between music and movement, which is an important area of research in neuroscience [2]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.596, + 0.892, + 0.686 + ], + "angle": 0, + "content": "Previous work has made significant progress using machine learning-based methods, but has achieved limited success in generating dances from music that satisfy user constraints. Furthermore, the evaluation of generated dances is subjective and complex, and existing papers often use quantitative metrics that we show to be flawed." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.691, + 0.893, + 0.888 + ], + "angle": 0, + "content": "In this work, we propose Editable Dance GEneration (EDGE), a state-of-the-art method for dance generation that creates realistic, physically-plausible dance motions based on input music. Our method uses a transformer-based diffusion model paired with Jukebox, a strong music feature extractor. This unique diffusion-based approach confers powerful editing capabilities well-suited to dance, including joint-wise conditioning and in-betweening. In addition to the advantages immediately conferred by the modeling choices, we observe flaws with previous metrics and propose a new metric that captures the physical accuracy of ground contact behaviors without explicit physical modeling. In summary, our contributions are the following:" + }, + { + "type": "page_number", + "bbox": [ + 0.486, + 0.946, + 0.512, + 0.957 + ], + "angle": 0, + "content": "448" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.09, + 0.092, + 0.47, + 0.228 + ], + "angle": 0, + "content": "1. We introduce EDGE, a diffusion-based approach for dance generation that combines state-of-the-art performance with powerful editing capabilities and is able to generate arbitrarily long sequences. EDGE improves on previous hand-crafted audio feature extraction strategies by leveraging music audio representations from Jukebox [5], a pre-trained generative model for music that has previously demonstrated strong performance on music-specific prediction tasks [3, 7]." + }, + { + "type": "text", + "bbox": [ + 0.089, + 0.233, + 0.47, + 0.279 + ], + "angle": 0, + "content": "2. We analyze the metrics proposed in previous works and show that they do not accurately represent human-evaluated quality as reported by a large user study." + }, + { + "type": "text", + "bbox": [ + 0.089, + 0.284, + 0.47, + 0.391 + ], + "angle": 0, + "content": "3. We propose a new approach to eliminating foot-sliding physical implausibilities in generated motions using a novel Contact Consistency Loss, and introduce Physical Foot Contact Score, a simple new acceleration-based quantitative metric for scoring physical plausibility of generated kinematic motions that requires no explicit physical modeling." + }, + { + "type": "list", + "bbox": [ + 0.089, + 0.092, + 0.47, + 0.391 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.396, + 0.47, + 0.427 + ], + "angle": 0, + "content": "This work is best enjoyed when accompanied by our demo samples. Please see the samples at our website." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.441, + 0.22, + 0.456 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.466, + 0.317, + 0.482 + ], + "angle": 0, + "content": "2.1. Human motion generation" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.489, + 0.469, + 0.58 + ], + "angle": 0, + "content": "Human motion generation, the problem of automatically generating realistic human motions, is well-studied in computer vision, graphics, and robotics. Despite its importance and recent progress, it remains a challenging problem, with existing methods often struggling to capture the complexities of physically and stylistically realistic human motion." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.581, + 0.469, + 0.67 + ], + "angle": 0, + "content": "Many early approaches fall under the category of motion matching, which operates by interpolating between sequences retrieved from a database [21]. While these approaches generate outputs that are physically plausible, their application has been primarily restricted to simple domains such as locomotion." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.671, + 0.469, + 0.822 + ], + "angle": 0, + "content": "In recent years, deep neural networks have emerged as a promising alternative method for human motion generation. These approaches are often capable of generating diverse motions, but often fall short in capturing the physical laws governing human movement or rely on difficult-to-train reinforcement learning solutions [34, 60]. Generating human motion conditioned on various inputs—e.g., joystick control [34], class-conditioning [15, 43], text-to-motion [44, 63], seed motions [8, 22, 46, 62]—is also an active area of study." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.832, + 0.254, + 0.847 + ], + "angle": 0, + "content": "2.2. Dance Generation" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.856, + 0.469, + 0.901 + ], + "angle": 0, + "content": "The uniquely challenging task of generating dances stylistically faithful to input music has been tackled by many researchers. Many early approaches follow a motion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.273 + ], + "angle": 0, + "content": "retrieval paradigm [11, 30, 40], but tend to create unrealistic choreographies that lack the complexity of human dances. Later works instead synthesize motion from scratch by training on large datasets [1, 10, 23, 27, 31, 33, 45, 47, 53, 59] and propose many modeling approaches, including adversarial learning, recurrent neural networks, and transformers. Despite achieving impressive performance, many such systems are complex [1, 4, 31, 53], often involving many layers of conditioning and sub-networks. In contrast, our proposed method contains a single model trained with a simple objective, yet offers both strong generative and editing capabilities without significant hand-crafted design." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.28, + 0.757, + 0.295 + ], + "angle": 0, + "content": "2.3. Generative Diffusion Models" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.303, + 0.892, + 0.56 + ], + "angle": 0, + "content": "Diffusion models [19, 54] are a class of deep generative models which learn a data distribution by reversing a scheduled noising process. In the past few years, diffusion models have been shown to be a promising avenue for generative modeling, exceeding the state-of-the-art in generative tasks [18, 24, 50]. Much like previous generative approaches like VAE [28] and GAN [12], diffusion models are also capable of conditional generation. Dhariwal et al. [6] introduced classifier guidance for image generation, where the output of a diffusion model may be \"steered\" towards a target, such as a class label, using the gradients of a differentiable auxiliary model. Sahara et al. [49] proposed to use direct concatenation of conditions for Pix2Pix-like tasks, akin to Conditional GAN and CVAE [38, 55], and Ho et al. [20] demonstrated that classifier-free guidance can achieve state-of-the-art results while allowing more explicit control over the diversity-fidelity tradeoff." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.561, + 0.892, + 0.667 + ], + "angle": 0, + "content": "Most recently, diffusion-based methods have demonstrated strong performance in generating motions conditioned on text [26,58,63]. While the tasks of text-to-motion and music-conditioned dance generation share high-level similarities, the dance generation task suffers more challenging computational scaling (see Sec. 3) and, due to its specialized nature, much lower data availability." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.677, + 0.591, + 0.692 + ], + "angle": 0, + "content": "3. Method" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.703, + 0.892, + 0.84 + ], + "angle": 0, + "content": "Pose Representation We represent dances as sequences of poses in the 24-joint SMPL format [35], using the 6-DOF rotation representation [64] for every joint and a single root translation: \\(\\pmb{w} \\in \\mathbb{R}^{24 \\cdot 6 + 3 = 147}\\). For the heel and toe of each foot, we also include a binary contact label: \\(\\pmb{b} \\in \\{0,1\\}^{2 \\cdot 2 = 4}\\). The total pose representation is therefore \\(\\pmb{x} = \\{\\pmb{b}, \\pmb{w}\\} \\in \\mathbb{R}^{4 + 147 = 151}\\). EDGE uses a diffusion-based framework to learn to synthesize sequences of \\(N\\) frames, \\(\\pmb{x} \\in \\mathbb{R}^{N \\times 151}\\), given arbitrary music conditioning \\(\\pmb{c}\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.856, + 0.892, + 0.903 + ], + "angle": 0, + "content": "Diffusion Framework We follow the DDPM [19] definition of diffusion as a Markov noising process with latents \\(\\{z_t\\}_{t=0}^T\\) that follow a forward noising process \\(q(z_t | x)\\)," + }, + { + "type": "page_number", + "bbox": [ + 0.486, + 0.946, + 0.511, + 0.957 + ], + "angle": 0, + "content": "449" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.088, + 0.468, + 0.319 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.476, + 0.087, + 0.895, + 0.317 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.329, + 0.895, + 0.375 + ], + "angle": 0, + "content": "Figure 2. EDGE Pipeline Overview: EDGE learns to denoise dance sequences from time \\( t = T \\) to \\( t = 0 \\), conditioned on music. Music embedding information is provided by a frozen Jukebox model [5] and acts as cross-attention context. EDGE takes a noisy sequence \\( \\mathbf{z}_T \\sim \\mathcal{N}(0, I) \\) and produces the estimated final sequence \\( \\hat{\\mathbf{x}} \\), noising it back to \\( \\hat{\\mathbf{z}}_{T - 1} \\) and repeating until \\( t = 0 \\)." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.398, + 0.471, + 0.429 + ], + "angle": 0, + "content": "where \\( \\pmb{x} \\sim p(\\pmb{x}) \\) is drawn from the data distribution. The forward noising process is defined as" + }, + { + "type": "equation", + "bbox": [ + 0.16, + 0.435, + 0.47, + 0.454 + ], + "angle": 0, + "content": "\\[\nq \\left(\\boldsymbol {z} _ {t} | \\boldsymbol {x}\\right) \\sim \\mathcal {N} \\left(\\sqrt {\\bar {\\alpha} _ {t}} \\boldsymbol {x}, \\left(1 - \\bar {\\alpha} _ {t}\\right) \\boldsymbol {I}\\right), \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.458, + 0.47, + 0.519 + ], + "angle": 0, + "content": "where \\(\\bar{\\alpha}_t\\in (0,1)\\) are constants which follow a monotonically decreasing schedule such that when \\(\\bar{\\alpha}_t\\) approaches 0, we can approximate \\(z_{T}\\sim \\mathcal{N}(0,I)\\). We chose to use \\(T = 1000\\) timesteps." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.519, + 0.47, + 0.595 + ], + "angle": 0, + "content": "In our setting with paired music conditioning \\( \\pmb{c} \\), we reverse the forward diffusion process by learning to estimate \\( \\hat{\\pmb{x}}_{\\theta}(z_t,t,\\pmb {c})\\approx \\pmb {x} \\) with model parameters \\( \\theta \\) for all \\( t \\). We optimize \\( \\theta \\) with the \"simple\" objective introduced in Ho et al. [19]:" + }, + { + "type": "equation", + "bbox": [ + 0.148, + 0.6, + 0.47, + 0.62 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\text {s i m p l e}} = \\mathbb {E} _ {\\boldsymbol {x}, t} \\left[ \\| \\boldsymbol {x} - \\hat {\\boldsymbol {x}} _ {\\theta} (\\boldsymbol {z} _ {t}, t, \\boldsymbol {c}) \\| _ {2} ^ {2} \\right]. \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.624, + 0.47, + 0.655 + ], + "angle": 0, + "content": "From now on, we refer to \\(\\hat{\\pmb{x}}_{\\theta}(\\pmb{z}_t,t,\\pmb {c})\\) as \\(\\hat{\\pmb{x}} (\\pmb {z}_t,\\pmb {c})\\) for ease of notation." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.672, + 0.471, + 0.794 + ], + "angle": 0, + "content": "Auxiliary losses Auxiliary losses are commonly used in kinematic motion generation settings to improve physical realism in the absence of true simulation [43, 52, 57]. In addition to the reconstruction loss \\(\\mathcal{L}_{\\mathrm{simple}}\\), we adopt auxiliary losses similar to those in Tevet et al. [58], which encourage matching three aspects of physical realism: joint positions (Eq. (3)), velocities (Eq. (4)), and foot velocities via our Contact Consistency Loss (Eq. (5))." + }, + { + "type": "equation", + "bbox": [ + 0.131, + 0.799, + 0.47, + 0.842 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\text {j o i n t}} = \\frac {1}{N} \\sum_ {i = 1} ^ {N} \\| F K (\\boldsymbol {x} ^ {(i)}) - F K (\\hat {\\boldsymbol {x}} ^ {(i)}) \\| _ {2} ^ {2} \\tag {3}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.082, + 0.846, + 0.469, + 0.902 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\mathrm {v e l}} = \\frac {1}{N - 1} \\sum_ {i = 1} ^ {N - 1} \\| \\left(\\boldsymbol {x} ^ {(i + 1)} - \\boldsymbol {x} ^ {(i)}\\right) - \\left(\\hat {\\boldsymbol {x}} ^ {(i + 1)} - \\hat {\\boldsymbol {x}} ^ {(i)}\\right) \\| _ {2} ^ {2} \\tag {4}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.5, + 0.416, + 0.897, + 0.469 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\text {c o n t a c t}} = \\frac {1}{N - 1} \\sum_ {i = 1} ^ {N - 1} \\| \\left(F K \\left(\\hat {\\boldsymbol {x}} ^ {(i + 1)}\\right) - F K \\left(\\hat {\\boldsymbol {x}} ^ {(i)}\\right)\\right) \\cdot \\hat {\\boldsymbol {b}} ^ {(i)} \\| _ {2} ^ {2}, \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.47, + 0.893, + 0.68 + ], + "angle": 0, + "content": "where \\( FK(\\cdot) \\) denotes the forward kinematic function that converts joint angles into joint positions (though it only applies to the foot joints in Eq. (5)) and the \\((i)\\) superscript denotes the frame index. In the Contact Consistency Loss, \\(\\hat{\\pmb{b}}^{(i)}\\) is the model's own prediction of the binary foot contact label's portion of the pose at each frame \\( i \\). While this formulation is similar to the foot skate loss terms in previous works [57, 58], where foot velocity is penalized in frames where the ground truth motion exhibits a static foot contact, our Contact Consistency Loss formulation differs in that it encourages the model to (1) predict foot contact, and (2) maintain consistency with its own predictions. We find that this formulation significantly improves the realism of generated motions (see Sec. 4.1)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.681, + 0.894, + 0.743 + ], + "angle": 0, + "content": "Our overall training loss is the weighted sum of the simple objective and the auxiliary losses, where the weights \\(\\lambda\\) were chosen to balance the magnitudes of the losses at the start of training.:" + }, + { + "type": "equation", + "bbox": [ + 0.518, + 0.748, + 0.892, + 0.765 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} = \\mathcal {L} _ {\\text {s i m p l e}} + \\lambda_ {\\text {p o s}} \\mathcal {L} _ {\\text {p o s}} + \\lambda_ {\\text {v e l}} \\mathcal {L} _ {\\text {v e l}} + \\lambda_ {\\text {c o n t a c t}} \\mathcal {L} _ {\\text {c o n t a c t}}. \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Sampling and Guidance At each of the denoising timesteps \\(t\\), EDGE predicts the denoised sample and noises it back to timestep \\(t - 1: \\hat{\\pmb{z}}_{t - 1} \\sim q(\\hat{\\pmb{x}}_{\\theta}(\\hat{\\pmb{z}}_t, \\pmb{c}), t - 1)\\), terminating when it reaches \\(t = 0\\) (Fig. 2, right). We train our model using classifier-free guidance [20], which is commonly used in diffusion-based models [26, 48, 50, 58, 63]. Following Ho et al. [20], we implement classifier-free guidance by randomly replacing the conditioning with \\(\\pmb{c} = \\emptyset\\)" + }, + { + "type": "page_number", + "bbox": [ + 0.486, + 0.945, + 0.512, + 0.958 + ], + "angle": 0, + "content": "450" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.138 + ], + "angle": 0, + "content": "during training with low probability (e.g., \\(25\\%\\)). Guided inference is then expressed as the weighted sum of unconditionally and conditionally generated samples:" + }, + { + "type": "equation", + "bbox": [ + 0.122, + 0.148, + 0.469, + 0.165 + ], + "angle": 0, + "content": "\\[\n\\tilde {\\boldsymbol {x}} (\\hat {\\boldsymbol {z}} _ {t}, \\boldsymbol {c}) = w \\cdot \\hat {\\boldsymbol {x}} (\\hat {\\boldsymbol {z}} _ {t}, \\boldsymbol {c}) + (1 - w) \\cdot \\hat {\\boldsymbol {x}} (\\hat {\\boldsymbol {z}} _ {t}, \\emptyset). \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.175, + 0.469, + 0.207 + ], + "angle": 0, + "content": "At sampling time, we can amplify the conditioning \\( c \\) by choosing a guidance weight \\( w > 1 \\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.223, + 0.469, + 0.345 + ], + "angle": 0, + "content": "Editing To enable editing for dances generated by EDGE, we use the standard masked denoising technique from diffusion image inpainting [36], and more recently text-to-motion models [26,58]. EDGE supports any combination of temporal and joint-wise constraints, shown in Fig. 4. Given a joint-wise and/or temporal constraint \\( \\pmb{x}^{\\mathrm{known}} \\) with positions indicated by a binary mask \\( m \\), we perform the following at every denoising timestep:" + }, + { + "type": "equation", + "bbox": [ + 0.096, + 0.354, + 0.469, + 0.371 + ], + "angle": 0, + "content": "\\[\n\\hat {z} _ {t - 1} := \\boldsymbol {m} \\odot q \\left(\\boldsymbol {x} ^ {\\text {k n o w n}}, t - 1\\right) + (1 - \\boldsymbol {m}) \\odot \\hat {z} _ {t - 1}, \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.382, + 0.469, + 0.442 + ], + "angle": 0, + "content": "where \\(\\odot\\) is the Hadamard (element-wise) product, replacing the known regions with forward-diffused samples of the constraint. This technique allows editability at inference time with no special training processes necessary." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.442, + 0.469, + 0.609 + ], + "angle": 0, + "content": "For example, a user can perform motion in-between by providing a reference motion \\( \\pmb{x}^{\\mathrm{known}} \\in \\mathbb{R}^{N \\times 151} \\) and a mask \\( m \\in \\{0,1\\}^{N \\times 151} \\), where \\( m \\) is all 1's in the first and last \\( n \\) frames and 0 everywhere else. This would result in a sequence \\( N \\) frames long, where the first and last \\( n \\) frames are provided by the reference motion and the rest is filled in with a plausible \"in-between\" dance that smoothly connects the constraint frames, for arbitrary \\( 2n < N \\). This editing framework provides a powerful tool for downstream applications, enabling the generation of dances that precisely conform to arbitrary constraints." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.627, + 0.469, + 0.852 + ], + "angle": 0, + "content": "Long-form sampling The ability to synthesize sequences of arbitrary length, often many minutes long, is critical to the task of dance generation. However, since EDGE generates every frame of a dance sequence at once, naively increasing the maximum sequence length incurs a linear increase in computational cost. Moreover, dance generation requires that the conditioning \\( c \\) match the motion sequence in length, causing further scaling of memory demands, which is especially severe in the case of embeddings from large models like Jukebox [5]. To approach the challenge of long-form generation, EDGE leverages its editability to enforce temporal consistency between multiple sequences such that they can be concatenated into a single longer sequence. Refer to Fig. 3 for a depiction of this process." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.871, + 0.469, + 0.902 + ], + "angle": 0, + "content": "Model Our model architecture is illustrated in Fig. 2. We adopt a transformer decoder architecture, which processes" + }, + { + "type": "image", + "bbox": [ + 0.541, + 0.092, + 0.856, + 0.25 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.26, + 0.892, + 0.356 + ], + "angle": 0, + "content": "Figure 3. Although EDGE is trained on 5-second clips, it can generate choreographies of any length by imposing temporal constraints on batches of sequences. In this example, EDGE constrains the first 2.5 seconds of each sequence to match the last 2.5 seconds of the previous one to generate a 12.5-second clip, as represented by the temporal regions of distinct clips in the batch that share the same color." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.369, + 0.892, + 0.503 + ], + "angle": 0, + "content": "music conditioning projected to the transformer dimension with a cross-attention mechanism following Sahara et al. [50]. Timestep information, which is represented as a sinusoidal embedding [19], is incorporated both through a token concatenated with the music conditioning and feature-wise linear modulation (FiLM) layers [42]. In our model, FiLM layers are given an output from a previous layer \\( \\mathbf{Y} \\) and a timestep embedding \\( \\boldsymbol{e}_t \\), and process the embeddings as:" + }, + { + "type": "equation", + "bbox": [ + 0.575, + 0.525, + 0.891, + 0.542 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {W} = \\psi_ {w} (\\phi (\\boldsymbol {e} _ {t})), \\quad \\boldsymbol {B} = \\psi_ {b} (\\phi (\\boldsymbol {e} _ {t})) \\tag {9}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.604, + 0.558, + 0.891, + 0.574 + ], + "angle": 0, + "content": "\\[\n\\operatorname {F i L M} (\\boldsymbol {Y}) = \\boldsymbol {W} \\odot \\boldsymbol {Y} + \\boldsymbol {B} \\tag {10}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.586, + 0.856, + 0.601 + ], + "angle": 0, + "content": ", where \\(\\psi_w,\\psi_w\\) , and \\(\\phi\\) are separate linear projections." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.628, + 0.892, + 0.748 + ], + "angle": 0, + "content": "Music Audio Features Past work [1, 10, 23, 27, 31, 33, 45, 53, 59] has largely focused on advancing the generative modeling approach for the dance generation problem, with little focus on the representation of the music signal itself, which we argue is equally important. Indeed, state-of-the-art results in the text-to-image domain have found that scaling the text encoder is more important for performance than scaling the diffusion model [50]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.75, + 0.892, + 0.901 + ], + "angle": 0, + "content": "In this vein, recent work [3, 7] in music information retrieval has demonstrated that Jukebox [5], a large GPT-style model trained on 1M songs to generate raw music audio, contains representations that serve as strong features for music audio prediction tasks. We take inspiration from these advances and extract Jukebox features as the conditioning input for our diffusion model, and develop a new memory-efficient implementation that enables near real-time extraction on a single commodity GPU (see Appendix I for details)." + }, + { + "type": "page_number", + "bbox": [ + 0.486, + 0.946, + 0.51, + 0.957 + ], + "angle": 0, + "content": "451" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.086, + 0.101, + 0.465, + 0.375 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.404, + 0.47, + 0.502 + ], + "angle": 0, + "content": "Figure 4. EDGE allows the user to specify both temporal and joint-wise constraints. Constraint joints / frames are highlighted in green and tan, generated joints / frames are in blue and gray. Pictured, top to bottom: dance completion from seed motion, dance that hits a specified keyframe mid-choreography, completion from specified upper-body joint angles, completion from specified lower-body joint angles and root trajectory." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.524, + 0.21, + 0.541 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.549, + 0.469, + 0.625 + ], + "angle": 0, + "content": "Dataset In this work, we use AIST++ [33], a dataset consisting of 1,408 high-quality dance motions paired to music from a diverse set of genres. We re-use the train/test splits provided by the original dataset. All training examples are split into clips of 5 seconds at 30 FPS." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.631, + 0.469, + 0.675 + ], + "angle": 0, + "content": "Baselines Among recent state-of-the-art dance generation methods [1, 10, 23, 27, 31, 33, 45, 53, 59], we select the following baselines:" + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.683, + 0.468, + 0.713 + ], + "angle": 0, + "content": "- FACT [33], an autoregressive model introduced together with the AIST++ dataset, and" + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.722, + 0.468, + 0.752 + ], + "angle": 0, + "content": "- Bailando [53], a follow-up approach that achieves the strongest qualitative performance to date." + }, + { + "type": "list", + "bbox": [ + 0.096, + 0.683, + 0.468, + 0.752 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.765, + 0.469, + 0.809 + ], + "angle": 0, + "content": "Implementation details Our final model has 49M total parameters, and was trained on 4 NVIDIA A100 GPUs for 16 hours with a batch size of 512." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.811, + 0.469, + 0.9 + ], + "angle": 0, + "content": "For long-form generation, we use 5-second slices and choose to enforce consistency for overlapping 2.5-second slices by interpolating between the two slices with linearly decaying weight. We find that this simple approach is sufficient to result in smooth, consistent generation, as demonstrated throughout our website. In our results, we perform" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.093, + 0.89, + 0.121 + ], + "angle": 0, + "content": "no post-processing to correct foot contacts or physical plausibility, and show the model outputs directly." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.123, + 0.892, + 0.256 + ], + "angle": 0, + "content": "We evaluate two separate feature extraction strategies. The \"baseline\" strategy uses the popular audio package librosa [37] to extract beats and accompanying audio features using the same code as in Li et al. [33] (when the ground truth BPM is not known, we estimate it with librosa). The \"Jukebox\" [5] extraction strategy follows Castellon et al. [3], extracting representations from Jukebox and downsampling to 30 FPS to match our frame rates for motion data." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.268, + 0.791, + 0.284 + ], + "angle": 0, + "content": "4.1. Comparison to Existing Methods" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.292, + 0.892, + 0.352 + ], + "angle": 0, + "content": "In this section, we compare our proposed model to several past works on (1) human evaluations, (2) our proposed physical plausibility metric, (3) beat alignment scores, (4) diversity, and (5) performance on in-the-wild music." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.36, + 0.892, + 0.435 + ], + "angle": 0, + "content": "Human Evaluations To obtain the results in Tab. 1, we recruited 147 human raters who evaluated a total of 11,610 pairs of clips randomly sampled from our models, ground truth, baseline models, or a checkpoint from our model training (as seen in Sec. 4.3)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.436, + 0.892, + 0.495 + ], + "angle": 0, + "content": "The study reveals that human raters overwhelmingly prefer the dances generated by EDGE over previous methods, and even favor EDGE dances over real dances. For more information on the exact details of our study, see Appendix A." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.516, + 0.892, + 0.682 + ], + "angle": 0, + "content": "Physical Plausibility Any generated dance should be physically plausible; otherwise, its downstream applicability is dramatically limited. Previous works evaluate plausibility of foot-ground contact by measuring foot sliding [17,56]; however, dance is unique in that sliding is not only common but integral to many choreographies. This reflects a need for a metric that can measure the realism of foot-ground contact that does not assume that feet should exhibit static contact at all times. In this work, we propose a new metric to evaluate physical plausibility, Physical Foot Contact score (PFC), that we believe captures this concept well." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.683, + 0.89, + 0.727 + ], + "angle": 0, + "content": "PFC is a physically-inspired metric that requires no explicit physical modeling. Our metric arises from two simple, related observations:" + }, + { + "type": "text", + "bbox": [ + 0.513, + 0.739, + 0.892, + 0.814 + ], + "angle": 0, + "content": "1. On the horizontal (xy) plane, any center of mass (COM) acceleration must be due to static contact between the feet and the ground. Therefore, either at least one foot is stationary on the ground or the COM is not accelerating." + }, + { + "type": "text", + "bbox": [ + 0.512, + 0.815, + 0.891, + 0.843 + ], + "angle": 0, + "content": "2. On the vertical (z) axis, any positive COM acceleration must be due to static foot contact." + }, + { + "type": "list", + "bbox": [ + 0.512, + 0.739, + 0.892, + 0.843 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.856, + 0.892, + 0.899 + ], + "angle": 0, + "content": "Therefore, we can represent adherence to these conditions as an average over time of the below expression, scaled to normalize acceleration:" + }, + { + "type": "page_number", + "bbox": [ + 0.486, + 0.946, + 0.511, + 0.957 + ], + "angle": 0, + "content": "452" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.086, + 0.089, + 0.887, + 0.21 + ], + "angle": 0, + "content": "
MethodElo ↑EDGE Win RatePFC ↓Beat Align. ↑Distk →Distg →Fixed BonesEditing
EDGE (w = 2)1751N/A1.53630.269.485.72✓✓
EDGE (w = 1)160158.0% ± 3.8%1.65450.2710.587.62✓✓
Bailando139791.1% ± 5.9%1.7540.237.927.72✗✗
FACT132590.0% ± 7.0%2.25430.2210.856.14✓✗
Ground Truth165365.7% ± 11.1%1.3320.2410.617.48✓N/A
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.219, + 0.895, + 0.304 + ], + "angle": 0, + "content": "Table 1. We compare our method against FACT [33] and Bailando [53]. In the table, \\( w \\) refers to the guidance weight at inference time. We evaluate all methods qualitatively via human raters to obtain Elo [9] and Win Rate, and compute the rest of the metrics automatically. For reference, the Elo rating system is designed such that a 400 point gap corresponds to a \\( \\sim {90}\\% \\) head-to-head win rate,which is reflected in our empirical results (the \"EDGE Win Rate\" column). Refer to the Wikipedia page for the mathematical details. Error bars for \"EDGE Win Rate\" correspond to a 95% confidence interval (see Appendix A for details). \\( \\uparrow \\) means higher is better, \\( \\downarrow \\) means lower is better,and \\( \\rightarrow \\) means closer to ground truth is better." + }, + { + "type": "table", + "bbox": [ + 0.1, + 0.326, + 0.449, + 0.419 + ], + "angle": 0, + "content": "
Method (In-the-Wild)Elo ↑EDGE Win Rate
EDGE174753.8% ± 11.1%
w/o Jukebox160383.3% ± 8.3%
Bailando122282.4% ± 5.5%
FACT136789.3% ± 4.4%
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.429, + 0.471, + 0.471 + ], + "angle": 0, + "content": "Table 2. We test our model on in-the-wild music and ablate Jukebox features in this setting, showing that Jukebox features are critical for generalization." + }, + { + "type": "equation", + "bbox": [ + 0.137, + 0.514, + 0.47, + 0.534 + ], + "angle": 0, + "content": "\\[\ns ^ {i} = \\left\\| \\bar {\\mathbf {a}} _ {\\mathrm {C O M}} ^ {i} \\right\\| \\cdot \\left\\| \\mathbf {v} _ {\\text {L e f t F o o t}} ^ {i} \\right\\| \\cdot \\left\\| \\mathbf {v} _ {\\text {R i g h t F o o t}} ^ {i} \\right\\|, \\tag {11}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.151, + 0.543, + 0.469, + 0.589 + ], + "angle": 0, + "content": "\\[\nP F C = \\frac {1}{N \\cdot \\max _ {1 \\leq j \\leq N} \\left\\| \\bar {a} _ {\\mathrm {C O M}} ^ {j} \\right\\|} \\sum_ {i = 1} ^ {N} s ^ {i}, \\tag {12}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.597, + 0.124, + 0.61 + ], + "angle": 0, + "content": "where" + }, + { + "type": "equation", + "bbox": [ + 0.174, + 0.608, + 0.37, + 0.658 + ], + "angle": 0, + "content": "\\[\n\\overline {{\\boldsymbol {a}}} _ {\\mathrm {C O M}} ^ {i} = \\left( \\begin{array}{c} a _ {\\mathrm {C O M}, x} ^ {i} \\\\ a _ {\\mathrm {C O M}, y} ^ {i} \\\\ \\max (a _ {\\mathrm {C O M}, z} ^ {i}, 0) \\end{array} \\right)\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.665, + 0.399, + 0.68 + ], + "angle": 0, + "content": "and the \\(i\\) superscript denotes the frame index." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.681, + 0.47, + 0.741 + ], + "angle": 0, + "content": "In our results (Tab. 1), we find that our method attains a greater level of physical plausibility than previous methods, and approaches the plausibility of ground truth motion capture data." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.742, + 0.469, + 0.863 + ], + "angle": 0, + "content": "Maintaining fixed bone length is another important aspect of physical plausibility. Our method operates in the reduced coordinate (joint angle) space, which guarantees fixed bone length. However, methods that operate in the joint Cartesian space, such as Bailando, can produce significantly varying bone lengths. For example, on average, bone lengths change up to \\(\\pm 20\\%\\) over the course of dance sequences generated by Bailando." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.871, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Beat Alignment Scores Our experiments evaluate the tendency of our generated dances to follow the beat of the" + }, + { + "type": "table", + "bbox": [ + 0.543, + 0.326, + 0.851, + 0.405 + ], + "angle": 0, + "content": "
MethodEDGE Win RatePFC ↓
EDGEN/A1.5363
w/o CCL61.8% ± 7.3%3.0806
Ground Truth40.6% ± 7.4%1.332
" + }, + { + "type": "table_caption", + "bbox": [ + 0.498, + 0.414, + 0.895, + 0.499 + ], + "angle": 0, + "content": "Table 3. We ablate our contact consistency loss (CCL) and study its impact on qualitative and quantitative physical plausibility. While EDGE wins more on average against ground truth on overall quality evaluation (Tab. 1), the user study for this table specifically asks about physical plausibility, and we find that ground truth still performs favorably compared to EDGE." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.527, + 0.892, + 0.618 + ], + "angle": 0, + "content": "music, following previous work [53] for the precise implementation of this metric. The results demonstrate that EDGE outperforms past work, including Bailando, which includes a reinforcement learning module that explicitly optimizes beat alignment. We further examine the robustness of this metric in Sec. 5." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.628, + 0.893, + 0.825 + ], + "angle": 0, + "content": "Diversity Diversity metrics are computed following the methods of previous work [33, 53], which measure the distributional spread of generated dances in the \"kinetic\" \\((\\mathrm{Dist}_k)\\) and \"geometric\" \\((\\mathrm{Dist}_g)\\) feature spaces, as implemented by fairmotion [13, 39, 41]. We compute these metrics on 5-second dance clips produced by each approach. Given that the ultimate goal of dance generation is to automatically produce dances that emulate the ground truth distribution, we argue that models should aim to match the scores of the ground truth distribution rather than maximize their absolute values. Indeed, past work has found that jittery dances result in high diversity scores, in some cases exceeding the ground truth [32, 33]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.826, + 0.894, + 0.903 + ], + "angle": 0, + "content": "At low guidance weight \\((w = 1)\\), EDGE achieves a level of diversity that closely matches that of the ground truth distribution while attaining state-of-the-art qualitative performance. At high guidance weight \\((w = 2)\\), EDGE produces dances of markedly higher fidelity, reflected by a signifi" + }, + { + "type": "page_number", + "bbox": [ + 0.486, + 0.946, + 0.511, + 0.957 + ], + "angle": 0, + "content": "453" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.081, + 0.089, + 0.467, + 0.258 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.269, + 0.47, + 0.312 + ], + "angle": 0, + "content": "Figure 5. Temporal Conditioning: In-Betweening Given start (green) and end (red) poses, EDGE can generate in-between dance sequences." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.328, + 0.468, + 0.435 + ], + "angle": 0, + "content": "cantly higher Elo rating, while trading off diversity. These results reflect those of past studies, which show that sampling using guidance weights \\( w > 1 \\) significantly increases fidelity at the cost of diversity [20, 50]. This simple control over the diversity-fidelity tradeoff via the modulation of a single scalar parameter provides a powerful tool for downstream applications." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.445, + 0.284, + 0.46 + ], + "angle": 0, + "content": "4.2. Additional Evaluation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.469, + 0.468, + 0.56 + ], + "angle": 0, + "content": "In-the-Wild Music While past approaches achieve strong results on AIST++, these results are not necessarily indicative of the models' ability to generalize to in-the-wild music inputs. In order to evaluate generalization, we tested our proposed method and the baseline approaches on a diverse selection of popular songs from YouTube." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.562, + 0.468, + 0.789 + ], + "angle": 0, + "content": "The results, as shown in Tab. 2, demonstrate that our proposed method continues to perform well on in-the-wild music. We find through ablation that Jukebox features are critical for performance in this setting, bringing human-rated quality almost to par with in-distribution music; furthermore, we find that our approach continues to beat baselines in human evaluations for dance quality. We note that Bailando has an additional fine-tuning procedure available to improve performance on in-the-wild samples by training its actor-critic component. While we evaluated Bailando directly without additional fine-tuning, we found that human raters significantly preferred in-the-wild EDGE samples over in-distribution Bailando samples. We interpret these results as evidence that our proposed method is able to successfully generalize to in-the-wild music inputs." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.81, + 0.468, + 0.901 + ], + "angle": 0, + "content": "Editing We find through an additional human evaluation that our model is capable of in-betweening, motion continuation, joint-conditioned generation, and long-form generation with quality on par with unconstrained samples. Please see our website for demo examples, and Appendix H for more details." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.273 + ], + "angle": 0, + "content": "Contact Consistency Ablation We test the soundness of our PFC metric and ablate our Contact Consistency Loss (CCL) term (see Eq. (5)) using a human evaluation study. Raters were shown pairs of dances from the ground truth distribution, EDGE with CCL, and EDGE without CCL, and asked which dance looked more physically plausible. The results (Tab. 3) show that CCL noticeably improves both the PFC metric and qualitative physical plausibility user evaluations, winning \\(61.8\\%\\) of matchups against the version without CCL, and coming close to parity with ground truth samples. The results also indicate that PFC tracks well with human perception of physical plausibility." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.274, + 0.892, + 0.32 + ], + "angle": 0, + "content": "For a discussion of limitations and implementation details of PFC, please see Sec. 5 and Appendix D, respectively." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.333, + 0.799, + 0.349 + ], + "angle": 0, + "content": "4.3. Analysis of FID Metrics for Dance" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.358, + 0.892, + 0.509 + ], + "angle": 0, + "content": "A reasonable solution to the problem of overall evaluation is to compute the difference between an empirical distribution of generated dances and a ground truth distribution. Several past works follow this intuition and automatically evaluate dance quality with Frechet Distance metrics [32, 33, 53]. As part of our experiments, we conduct a two-pronged analysis into the prevailing metrics, \"FID\\(_k\\) \" and \"FID\\(_g\\) \" [33], which compute the difference between distributions of heuristically extracted motion features, and show them to be unsound for the AIST++ dataset." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.523, + 0.892, + 0.705 + ], + "angle": 0, + "content": "“\\(\\mathrm{FID}_g\\)” We compute \\(\\mathrm{FID}_g\\) on the ground truth AIST++ dataset following the implementation in Li et al. [33]. Specifically, we compute metrics on the test set against the training set and obtain a score of 41.4, a stark increase from metrics obtained from generated outputs: running on FACT outputs gives 12.75, running on Bailando outputs gives 24.82, and running on our final model's outputs gives 23.08. Given that FACT performs the best in “\\(\\mathrm{FID}_g\\)” but performs the worst according to user studies and that all three models perform significantly better than ground truth, we conclude that the “\\(\\mathrm{FID}_g\\)” values are unreliable as a measure of quality on this dataset." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.718, + 0.892, + 0.839 + ], + "angle": 0, + "content": "\" \\(\\mathbf{FID}_k\\) \" We take 10 checkpoints throughout the training process for our model and poll raters on the overall quality of dances sampled from each checkpoint in a round-robin tournament. Intuitively, this should result in a consistent-to-monotonic improvement in both qualitative performance and in the quantitative quality metrics. However, we observe that this is not the case. In Fig. 6, we show the results of this experiment with our proposed model's \\(\\mathrm{FID}_k\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.892, + 0.901 + ], + "angle": 0, + "content": "While the qualitative performance of the generated motion improves considerably as we train the model, the \\(\\mathrm{FID}_k\\) does not improve, and actually significantly worsens during the latter half of training." + }, + { + "type": "page_number", + "bbox": [ + 0.486, + 0.945, + 0.511, + 0.956 + ], + "angle": 0, + "content": "454" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.09, + 0.465, + 0.216 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.23, + 0.47, + 0.259 + ], + "angle": 0, + "content": "Figure 6. We plot \\(\\mathrm{FID}_k\\) over the course of model training and find that it is inconsistent with overall quality evaluations." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.272, + 0.363, + 0.29 + ], + "angle": 0, + "content": "5. Limitations of Existing Metrics" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.298, + 0.47, + 0.389 + ], + "angle": 0, + "content": "Developing automated metrics for the quality of generated dances is a fundamentally challenging undertaking, since the practice of dance is complex, subjective, and even culturally specific. In this section, we discuss our findings on the limitations in automated metrics for dance evaluation, including our proposed PFC metric." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.41, + 0.47, + 0.667 + ], + "angle": 0, + "content": "Overall Quality Evaluation Our results suggest that despite the current standardized use of FIDs for evaluating dance generation models on the AIST++ dataset, these FID metrics, as they currently stand, are unreliable for measuring quality. One potential explanation may be that the AIST++ test set does not thoroughly cover the train distribution given its very small size. Additionally, due to data scarcity, both \\(\\mathrm{FID}_k\\) and \\(\\mathrm{FID}_g\\) depend on heuristic feature extractors that only compute superficial features of the data. By contrast, FID-based metrics in data-rich domains such as image generation (where FID originated) enjoy the use of learned feature extractors (e.g., pre-trained ImageNet models), which are known to directly extract semantically meaningful features [51]. Indeed, in the text-to-motion domain, where significantly more paired data is available [14], the standard feature extractors for FID-style metrics depend on deep contrastively learned models [58, 63]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.668, + 0.47, + 0.773 + ], + "angle": 0, + "content": "Our experiments suggest that the current FID metrics can be further improved for evaluating motion sequences. We believe that the idea of evaluating the difference between two featurized distributions of dance motions is not necessarily fundamentally flawed, but that more representative features could result in reliable automatic quality evaluations." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.794, + 0.468, + 0.884 + ], + "angle": 0, + "content": "Beat Alignment Scoring Some automated metrics aim to capture one of the core aspects of a dance performance: its ability to \"follow the beat\" of the song. Previous work [33, 53] has proposed using a beat alignment metric that rewards kinematic beats (local minima of joint speed) which line up with music beats." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.886, + 0.468, + 0.901 + ], + "angle": 0, + "content": "However, dance is not strictly about matching local min" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.243 + ], + "angle": 0, + "content": "ima in joint speed to beats: instead, the beats of the music are a loose guide for timing, rhythm, and transitions between movements and dance steps. This discrepancy is reflected in our results: empirically, we observe that in addition to exceeding scores of competing baselines, our beat alignment scores exceed those of ground truth samples. This seems to suggest that while the metric has served to drive progress on this problem in the past, the metric loses its meaning when candidate examples reach quality on par with ground truth." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.26, + 0.892, + 0.502 + ], + "angle": 0, + "content": "Physical Foot Contact In this work, we introduce PFC, Eq. (12), a physically-inspired metric that specifically targets the challenging issue of foot sliding. While PFC is intuitive, it is not without its limitations. In its current form, PFC assumes that the feet are the only joints that experience static contact. This means that PFC cannot be applied without modification to motions such as gymnastics routines, where a variable number of non-foot (e.g., hand) contacts are integral to their execution. We believe that a careful analysis of other contact points (e.g., hands in gymnastics) could provide an extension of PFC that is more widely applicable. Another issue is the assumption that the COM can be accelerated only by static contact: though rare, it is possible to decelerate the COM using friction during extended sliding (which is not present in AIST++.). For more analysis and discussion of PFC, see Appendix D." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.513, + 0.771, + 0.53 + ], + "angle": 0, + "content": "6. Conclusion and Future Work" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.539, + 0.892, + 0.901 + ], + "angle": 0, + "content": "In this work, we propose a diffusion-based model that generates realistic and long-form dance sequences conditioned on music. We evaluate our model on multiple automated metrics (including our proposed PFC) and a large user study, and find that it achieves state-of-the-art results on the AIST++ dataset and generalizes well to in-the-wild music inputs. Importantly, we demonstrate that our model admits powerful editing capabilities, allowing users to freely specify both temporal and joint-wise constraints. The introduction of editable dance generation provides multiple promising avenues for future work. Whereas our method is able to create arbitrarily long dance sequences via the chaining of locally consistent, shorter clips, it cannot generate choreographies with very-long-term dependencies. Future work may explore the use of non-uniform sampling patterns such as those implemented in Harvey et al. [16], or a variation of the frame in-between scheme used in Ho et al. [18]. Editability also opens the door to the generation of more complex choreographies, including multi-person and scene-aware dance forms. Joint-wise conditioning may also potentially be used to address the issue of self-penetrating motions, which are sometimes present in our results. 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In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 5745-5753, 2019. 2" + }, + { + "type": "list", + "bbox": [ + 0.08, + 0.092, + 0.469, + 0.515 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.487, + 0.946, + 0.511, + 0.956 + ], + "angle": 0, + "content": "458" + } + ] +] \ No newline at end of file diff --git a/2023/EDGE_ Editable Dance Generation From Music/97e29d71-2a36-4f04-a26f-23105d30e787_origin.pdf b/2023/EDGE_ Editable Dance Generation From Music/97e29d71-2a36-4f04-a26f-23105d30e787_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..cdf79d2c7951d1d473763bd5489498689da49994 --- /dev/null +++ b/2023/EDGE_ Editable Dance Generation From Music/97e29d71-2a36-4f04-a26f-23105d30e787_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:59a37ab5c9861fb9821704b40f7a9b7223e03865e613e69231af3367099ff996 +size 4672941 diff --git a/2023/EDGE_ Editable Dance Generation From Music/full.md b/2023/EDGE_ Editable Dance Generation From Music/full.md new file mode 100644 index 0000000000000000000000000000000000000000..235487559d9b998f133c190f35fd7be6e7888ff3 --- /dev/null +++ b/2023/EDGE_ Editable Dance Generation From Music/full.md @@ -0,0 +1,343 @@ +# EDGE: Editable Dance Generation From Music + +Jonathan Tseng, Rodrigo Castellon, C. Karen Liu +Stanford University + +{jtseng20, rjcaste, karenliu}@cs.stanford.edu + +![](images/3a3f8e50d0c37e8e065f7c76d957915f7fa2d3424005923f12cab50a4674fc0f.jpg) +Figure 1. EDGE generates diverse, physically plausible dance choreographies conditioned on music. + +# Abstract + +Dance is an important human art form, but creating new dances can be difficult and time-consuming. In this work, we introduce Editable Dance Generation (EDGE), a state-of-the-art method for editable dance generation that is capable of creating realistic, physically-plausible dances while remaining faithful to the input music. EDGE uses a transformer-based diffusion model paired with Jukebox, a strong music feature extractor, and confers powerful editing capabilities well-suited to dance, including joint-wise conditioning, and in-betweening. We introduce a new metric for physical plausibility, and evaluate dance quality generated by our method extensively through (1) multiple quantitative metrics on physical plausibility, beat alignment, and diversity benchmarks, and more importantly, (2) a large-scale user study, demonstrating a significant improvement over previous state-of-the-art methods. Qualitative samples from our model can be found at our website. + +# 1. Introduction + +Dance is an important part of many cultures around the world: it is a form of expression, communication, and social interaction [29]. However, creating new dances or dance animations is uniquely difficult because dance movements are expressive and freeform, yet precisely structured by music. In practice, this requires tedious hand animation or motion capture solutions, which can be expensive and impractical. + +On the other hand, using computational methods to generate dances automatically can alleviate the burden of the creation process, leading to many applications: such methods can help animators create new dances or provide interactive characters in video games or virtual reality with realistic and varied movements based on user-provided music. In addition, dance generation can provide insights into the relationship between music and movement, which is an important area of research in neuroscience [2]. + +Previous work has made significant progress using machine learning-based methods, but has achieved limited success in generating dances from music that satisfy user constraints. Furthermore, the evaluation of generated dances is subjective and complex, and existing papers often use quantitative metrics that we show to be flawed. + +In this work, we propose Editable Dance GEneration (EDGE), a state-of-the-art method for dance generation that creates realistic, physically-plausible dance motions based on input music. Our method uses a transformer-based diffusion model paired with Jukebox, a strong music feature extractor. This unique diffusion-based approach confers powerful editing capabilities well-suited to dance, including joint-wise conditioning and in-betweening. In addition to the advantages immediately conferred by the modeling choices, we observe flaws with previous metrics and propose a new metric that captures the physical accuracy of ground contact behaviors without explicit physical modeling. In summary, our contributions are the following: + +1. We introduce EDGE, a diffusion-based approach for dance generation that combines state-of-the-art performance with powerful editing capabilities and is able to generate arbitrarily long sequences. EDGE improves on previous hand-crafted audio feature extraction strategies by leveraging music audio representations from Jukebox [5], a pre-trained generative model for music that has previously demonstrated strong performance on music-specific prediction tasks [3, 7]. +2. We analyze the metrics proposed in previous works and show that they do not accurately represent human-evaluated quality as reported by a large user study. +3. We propose a new approach to eliminating foot-sliding physical implausibilities in generated motions using a novel Contact Consistency Loss, and introduce Physical Foot Contact Score, a simple new acceleration-based quantitative metric for scoring physical plausibility of generated kinematic motions that requires no explicit physical modeling. + +This work is best enjoyed when accompanied by our demo samples. Please see the samples at our website. + +# 2. Related Work + +# 2.1. Human motion generation + +Human motion generation, the problem of automatically generating realistic human motions, is well-studied in computer vision, graphics, and robotics. Despite its importance and recent progress, it remains a challenging problem, with existing methods often struggling to capture the complexities of physically and stylistically realistic human motion. + +Many early approaches fall under the category of motion matching, which operates by interpolating between sequences retrieved from a database [21]. While these approaches generate outputs that are physically plausible, their application has been primarily restricted to simple domains such as locomotion. + +In recent years, deep neural networks have emerged as a promising alternative method for human motion generation. These approaches are often capable of generating diverse motions, but often fall short in capturing the physical laws governing human movement or rely on difficult-to-train reinforcement learning solutions [34, 60]. Generating human motion conditioned on various inputs—e.g., joystick control [34], class-conditioning [15, 43], text-to-motion [44, 63], seed motions [8, 22, 46, 62]—is also an active area of study. + +# 2.2. Dance Generation + +The uniquely challenging task of generating dances stylistically faithful to input music has been tackled by many researchers. Many early approaches follow a motion + +retrieval paradigm [11, 30, 40], but tend to create unrealistic choreographies that lack the complexity of human dances. Later works instead synthesize motion from scratch by training on large datasets [1, 10, 23, 27, 31, 33, 45, 47, 53, 59] and propose many modeling approaches, including adversarial learning, recurrent neural networks, and transformers. Despite achieving impressive performance, many such systems are complex [1, 4, 31, 53], often involving many layers of conditioning and sub-networks. In contrast, our proposed method contains a single model trained with a simple objective, yet offers both strong generative and editing capabilities without significant hand-crafted design. + +# 2.3. Generative Diffusion Models + +Diffusion models [19, 54] are a class of deep generative models which learn a data distribution by reversing a scheduled noising process. In the past few years, diffusion models have been shown to be a promising avenue for generative modeling, exceeding the state-of-the-art in generative tasks [18, 24, 50]. Much like previous generative approaches like VAE [28] and GAN [12], diffusion models are also capable of conditional generation. Dhariwal et al. [6] introduced classifier guidance for image generation, where the output of a diffusion model may be "steered" towards a target, such as a class label, using the gradients of a differentiable auxiliary model. Sahara et al. [49] proposed to use direct concatenation of conditions for Pix2Pix-like tasks, akin to Conditional GAN and CVAE [38, 55], and Ho et al. [20] demonstrated that classifier-free guidance can achieve state-of-the-art results while allowing more explicit control over the diversity-fidelity tradeoff. + +Most recently, diffusion-based methods have demonstrated strong performance in generating motions conditioned on text [26,58,63]. While the tasks of text-to-motion and music-conditioned dance generation share high-level similarities, the dance generation task suffers more challenging computational scaling (see Sec. 3) and, due to its specialized nature, much lower data availability. + +# 3. Method + +Pose Representation We represent dances as sequences of poses in the 24-joint SMPL format [35], using the 6-DOF rotation representation [64] for every joint and a single root translation: $\pmb{w} \in \mathbb{R}^{24 \cdot 6 + 3 = 147}$ . For the heel and toe of each foot, we also include a binary contact label: $\pmb{b} \in \{0,1\}^{2 \cdot 2 = 4}$ . The total pose representation is therefore $\pmb{x} = \{\pmb{b}, \pmb{w}\} \in \mathbb{R}^{4 + 147 = 151}$ . EDGE uses a diffusion-based framework to learn to synthesize sequences of $N$ frames, $\pmb{x} \in \mathbb{R}^{N \times 151}$ , given arbitrary music conditioning $\pmb{c}$ . + +Diffusion Framework We follow the DDPM [19] definition of diffusion as a Markov noising process with latents $\{z_t\}_{t=0}^T$ that follow a forward noising process $q(z_t | x)$ , + +![](images/5a0a20fa10228603122e197d2a3f50a4ff9e7ae0f11c30240c38f5c01ed60df3.jpg) +Figure 2. EDGE Pipeline Overview: EDGE learns to denoise dance sequences from time $t = T$ to $t = 0$ , conditioned on music. Music embedding information is provided by a frozen Jukebox model [5] and acts as cross-attention context. EDGE takes a noisy sequence $\mathbf{z}_T \sim \mathcal{N}(0, I)$ and produces the estimated final sequence $\hat{\mathbf{x}}$ , noising it back to $\hat{\mathbf{z}}_{T - 1}$ and repeating until $t = 0$ . + +![](images/7e4fdd3f3feae443dffef04a6b0511a4bc8e211de5f09b07edb4b627d611ec5a.jpg) + +where $\pmb{x} \sim p(\pmb{x})$ is drawn from the data distribution. The forward noising process is defined as + +$$ +q \left(\boldsymbol {z} _ {t} | \boldsymbol {x}\right) \sim \mathcal {N} \left(\sqrt {\bar {\alpha} _ {t}} \boldsymbol {x}, \left(1 - \bar {\alpha} _ {t}\right) \boldsymbol {I}\right), \tag {1} +$$ + +where $\bar{\alpha}_t\in (0,1)$ are constants which follow a monotonically decreasing schedule such that when $\bar{\alpha}_t$ approaches 0, we can approximate $z_{T}\sim \mathcal{N}(0,I)$ . We chose to use $T = 1000$ timesteps. + +In our setting with paired music conditioning $\pmb{c}$ , we reverse the forward diffusion process by learning to estimate $\hat{\pmb{x}}_{\theta}(z_t,t,\pmb {c})\approx \pmb {x}$ with model parameters $\theta$ for all $t$ . We optimize $\theta$ with the "simple" objective introduced in Ho et al. [19]: + +$$ +\mathcal {L} _ {\text {s i m p l e}} = \mathbb {E} _ {\boldsymbol {x}, t} \left[ \| \boldsymbol {x} - \hat {\boldsymbol {x}} _ {\theta} (\boldsymbol {z} _ {t}, t, \boldsymbol {c}) \| _ {2} ^ {2} \right]. \tag {2} +$$ + +From now on, we refer to $\hat{\pmb{x}}_{\theta}(\pmb{z}_t,t,\pmb {c})$ as $\hat{\pmb{x}} (\pmb {z}_t,\pmb {c})$ for ease of notation. + +Auxiliary losses Auxiliary losses are commonly used in kinematic motion generation settings to improve physical realism in the absence of true simulation [43, 52, 57]. In addition to the reconstruction loss $\mathcal{L}_{\mathrm{simple}}$ , we adopt auxiliary losses similar to those in Tevet et al. [58], which encourage matching three aspects of physical realism: joint positions (Eq. (3)), velocities (Eq. (4)), and foot velocities via our Contact Consistency Loss (Eq. (5)). + +$$ +\mathcal {L} _ {\text {j o i n t}} = \frac {1}{N} \sum_ {i = 1} ^ {N} \| F K (\boldsymbol {x} ^ {(i)}) - F K (\hat {\boldsymbol {x}} ^ {(i)}) \| _ {2} ^ {2} \tag {3} +$$ + +$$ +\mathcal {L} _ {\mathrm {v e l}} = \frac {1}{N - 1} \sum_ {i = 1} ^ {N - 1} \| \left(\boldsymbol {x} ^ {(i + 1)} - \boldsymbol {x} ^ {(i)}\right) - \left(\hat {\boldsymbol {x}} ^ {(i + 1)} - \hat {\boldsymbol {x}} ^ {(i)}\right) \| _ {2} ^ {2} \tag {4} +$$ + +$$ +\mathcal {L} _ {\text {c o n t a c t}} = \frac {1}{N - 1} \sum_ {i = 1} ^ {N - 1} \| \left(F K \left(\hat {\boldsymbol {x}} ^ {(i + 1)}\right) - F K \left(\hat {\boldsymbol {x}} ^ {(i)}\right)\right) \cdot \hat {\boldsymbol {b}} ^ {(i)} \| _ {2} ^ {2}, \tag {5} +$$ + +where $FK(\cdot)$ denotes the forward kinematic function that converts joint angles into joint positions (though it only applies to the foot joints in Eq. (5)) and the $(i)$ superscript denotes the frame index. In the Contact Consistency Loss, $\hat{\pmb{b}}^{(i)}$ is the model's own prediction of the binary foot contact label's portion of the pose at each frame $i$ . While this formulation is similar to the foot skate loss terms in previous works [57, 58], where foot velocity is penalized in frames where the ground truth motion exhibits a static foot contact, our Contact Consistency Loss formulation differs in that it encourages the model to (1) predict foot contact, and (2) maintain consistency with its own predictions. We find that this formulation significantly improves the realism of generated motions (see Sec. 4.1). + +Our overall training loss is the weighted sum of the simple objective and the auxiliary losses, where the weights $\lambda$ were chosen to balance the magnitudes of the losses at the start of training.: + +$$ +\mathcal {L} = \mathcal {L} _ {\text {s i m p l e}} + \lambda_ {\text {p o s}} \mathcal {L} _ {\text {p o s}} + \lambda_ {\text {v e l}} \mathcal {L} _ {\text {v e l}} + \lambda_ {\text {c o n t a c t}} \mathcal {L} _ {\text {c o n t a c t}}. \tag {6} +$$ + +Sampling and Guidance At each of the denoising timesteps $t$ , EDGE predicts the denoised sample and noises it back to timestep $t - 1: \hat{\pmb{z}}_{t - 1} \sim q(\hat{\pmb{x}}_{\theta}(\hat{\pmb{z}}_t, \pmb{c}), t - 1)$ , terminating when it reaches $t = 0$ (Fig. 2, right). We train our model using classifier-free guidance [20], which is commonly used in diffusion-based models [26, 48, 50, 58, 63]. Following Ho et al. [20], we implement classifier-free guidance by randomly replacing the conditioning with $\pmb{c} = \emptyset$ + +during training with low probability (e.g., $25\%$ ). Guided inference is then expressed as the weighted sum of unconditionally and conditionally generated samples: + +$$ +\tilde {\boldsymbol {x}} (\hat {\boldsymbol {z}} _ {t}, \boldsymbol {c}) = w \cdot \hat {\boldsymbol {x}} (\hat {\boldsymbol {z}} _ {t}, \boldsymbol {c}) + (1 - w) \cdot \hat {\boldsymbol {x}} (\hat {\boldsymbol {z}} _ {t}, \emptyset). \tag {7} +$$ + +At sampling time, we can amplify the conditioning $c$ by choosing a guidance weight $w > 1$ . + +Editing To enable editing for dances generated by EDGE, we use the standard masked denoising technique from diffusion image inpainting [36], and more recently text-to-motion models [26,58]. EDGE supports any combination of temporal and joint-wise constraints, shown in Fig. 4. Given a joint-wise and/or temporal constraint $\pmb{x}^{\mathrm{known}}$ with positions indicated by a binary mask $m$ , we perform the following at every denoising timestep: + +$$ +\hat {z} _ {t - 1} := \boldsymbol {m} \odot q \left(\boldsymbol {x} ^ {\text {k n o w n}}, t - 1\right) + (1 - \boldsymbol {m}) \odot \hat {z} _ {t - 1}, \tag {8} +$$ + +where $\odot$ is the Hadamard (element-wise) product, replacing the known regions with forward-diffused samples of the constraint. This technique allows editability at inference time with no special training processes necessary. + +For example, a user can perform motion in-between by providing a reference motion $\pmb{x}^{\mathrm{known}} \in \mathbb{R}^{N \times 151}$ and a mask $m \in \{0,1\}^{N \times 151}$ , where $m$ is all 1's in the first and last $n$ frames and 0 everywhere else. This would result in a sequence $N$ frames long, where the first and last $n$ frames are provided by the reference motion and the rest is filled in with a plausible "in-between" dance that smoothly connects the constraint frames, for arbitrary $2n < N$ . This editing framework provides a powerful tool for downstream applications, enabling the generation of dances that precisely conform to arbitrary constraints. + +Long-form sampling The ability to synthesize sequences of arbitrary length, often many minutes long, is critical to the task of dance generation. However, since EDGE generates every frame of a dance sequence at once, naively increasing the maximum sequence length incurs a linear increase in computational cost. Moreover, dance generation requires that the conditioning $c$ match the motion sequence in length, causing further scaling of memory demands, which is especially severe in the case of embeddings from large models like Jukebox [5]. To approach the challenge of long-form generation, EDGE leverages its editability to enforce temporal consistency between multiple sequences such that they can be concatenated into a single longer sequence. Refer to Fig. 3 for a depiction of this process. + +Model Our model architecture is illustrated in Fig. 2. We adopt a transformer decoder architecture, which processes + +![](images/192319357babfb8b2670021f030e318542871678ea13571d671abd928cde5501.jpg) +Figure 3. Although EDGE is trained on 5-second clips, it can generate choreographies of any length by imposing temporal constraints on batches of sequences. In this example, EDGE constrains the first 2.5 seconds of each sequence to match the last 2.5 seconds of the previous one to generate a 12.5-second clip, as represented by the temporal regions of distinct clips in the batch that share the same color. + +music conditioning projected to the transformer dimension with a cross-attention mechanism following Sahara et al. [50]. Timestep information, which is represented as a sinusoidal embedding [19], is incorporated both through a token concatenated with the music conditioning and feature-wise linear modulation (FiLM) layers [42]. In our model, FiLM layers are given an output from a previous layer $\mathbf{Y}$ and a timestep embedding $\boldsymbol{e}_t$ , and process the embeddings as: + +$$ +\boldsymbol {W} = \psi_ {w} (\phi (\boldsymbol {e} _ {t})), \quad \boldsymbol {B} = \psi_ {b} (\phi (\boldsymbol {e} _ {t})) \tag {9} +$$ + +$$ +\operatorname {F i L M} (\boldsymbol {Y}) = \boldsymbol {W} \odot \boldsymbol {Y} + \boldsymbol {B} \tag {10} +$$ + +, where $\psi_w,\psi_w$ , and $\phi$ are separate linear projections. + +Music Audio Features Past work [1, 10, 23, 27, 31, 33, 45, 53, 59] has largely focused on advancing the generative modeling approach for the dance generation problem, with little focus on the representation of the music signal itself, which we argue is equally important. Indeed, state-of-the-art results in the text-to-image domain have found that scaling the text encoder is more important for performance than scaling the diffusion model [50]. + +In this vein, recent work [3, 7] in music information retrieval has demonstrated that Jukebox [5], a large GPT-style model trained on 1M songs to generate raw music audio, contains representations that serve as strong features for music audio prediction tasks. We take inspiration from these advances and extract Jukebox features as the conditioning input for our diffusion model, and develop a new memory-efficient implementation that enables near real-time extraction on a single commodity GPU (see Appendix I for details). + +![](images/a5295bd63756b00733529aee1d74ef9ccbb2a17f8074f15d35ea283502d7c1c6.jpg) +Figure 4. EDGE allows the user to specify both temporal and joint-wise constraints. Constraint joints / frames are highlighted in green and tan, generated joints / frames are in blue and gray. Pictured, top to bottom: dance completion from seed motion, dance that hits a specified keyframe mid-choreography, completion from specified upper-body joint angles, completion from specified lower-body joint angles and root trajectory. + +# 4. Experiments + +Dataset In this work, we use AIST++ [33], a dataset consisting of 1,408 high-quality dance motions paired to music from a diverse set of genres. We re-use the train/test splits provided by the original dataset. All training examples are split into clips of 5 seconds at 30 FPS. + +Baselines Among recent state-of-the-art dance generation methods [1, 10, 23, 27, 31, 33, 45, 53, 59], we select the following baselines: + +- FACT [33], an autoregressive model introduced together with the AIST++ dataset, and +- Bailando [53], a follow-up approach that achieves the strongest qualitative performance to date. + +Implementation details Our final model has 49M total parameters, and was trained on 4 NVIDIA A100 GPUs for 16 hours with a batch size of 512. + +For long-form generation, we use 5-second slices and choose to enforce consistency for overlapping 2.5-second slices by interpolating between the two slices with linearly decaying weight. We find that this simple approach is sufficient to result in smooth, consistent generation, as demonstrated throughout our website. In our results, we perform + +no post-processing to correct foot contacts or physical plausibility, and show the model outputs directly. + +We evaluate two separate feature extraction strategies. The "baseline" strategy uses the popular audio package librosa [37] to extract beats and accompanying audio features using the same code as in Li et al. [33] (when the ground truth BPM is not known, we estimate it with librosa). The "Jukebox" [5] extraction strategy follows Castellon et al. [3], extracting representations from Jukebox and downsampling to 30 FPS to match our frame rates for motion data. + +# 4.1. Comparison to Existing Methods + +In this section, we compare our proposed model to several past works on (1) human evaluations, (2) our proposed physical plausibility metric, (3) beat alignment scores, (4) diversity, and (5) performance on in-the-wild music. + +Human Evaluations To obtain the results in Tab. 1, we recruited 147 human raters who evaluated a total of 11,610 pairs of clips randomly sampled from our models, ground truth, baseline models, or a checkpoint from our model training (as seen in Sec. 4.3). + +The study reveals that human raters overwhelmingly prefer the dances generated by EDGE over previous methods, and even favor EDGE dances over real dances. For more information on the exact details of our study, see Appendix A. + +Physical Plausibility Any generated dance should be physically plausible; otherwise, its downstream applicability is dramatically limited. Previous works evaluate plausibility of foot-ground contact by measuring foot sliding [17,56]; however, dance is unique in that sliding is not only common but integral to many choreographies. This reflects a need for a metric that can measure the realism of foot-ground contact that does not assume that feet should exhibit static contact at all times. In this work, we propose a new metric to evaluate physical plausibility, Physical Foot Contact score (PFC), that we believe captures this concept well. + +PFC is a physically-inspired metric that requires no explicit physical modeling. Our metric arises from two simple, related observations: + +1. On the horizontal (xy) plane, any center of mass (COM) acceleration must be due to static contact between the feet and the ground. Therefore, either at least one foot is stationary on the ground or the COM is not accelerating. +2. On the vertical (z) axis, any positive COM acceleration must be due to static foot contact. + +Therefore, we can represent adherence to these conditions as an average over time of the below expression, scaled to normalize acceleration: + +
MethodElo ↑EDGE Win RatePFC ↓Beat Align. ↑Distk →Distg →Fixed BonesEditing
EDGE (w = 2)1751N/A1.53630.269.485.72✓✓
EDGE (w = 1)160158.0% ± 3.8%1.65450.2710.587.62✓✓
Bailando139791.1% ± 5.9%1.7540.237.927.72✗✗
FACT132590.0% ± 7.0%2.25430.2210.856.14✓✗
Ground Truth165365.7% ± 11.1%1.3320.2410.617.48✓N/A
+ +Table 1. We compare our method against FACT [33] and Bailando [53]. In the table, $w$ refers to the guidance weight at inference time. We evaluate all methods qualitatively via human raters to obtain Elo [9] and Win Rate, and compute the rest of the metrics automatically. For reference, the Elo rating system is designed such that a 400 point gap corresponds to a $\sim {90}\%$ head-to-head win rate,which is reflected in our empirical results (the "EDGE Win Rate" column). Refer to the Wikipedia page for the mathematical details. Error bars for "EDGE Win Rate" correspond to a 95% confidence interval (see Appendix A for details). $\uparrow$ means higher is better, $\downarrow$ means lower is better,and $\rightarrow$ means closer to ground truth is better. + +
Method (In-the-Wild)Elo ↑EDGE Win Rate
EDGE174753.8% ± 11.1%
w/o Jukebox160383.3% ± 8.3%
Bailando122282.4% ± 5.5%
FACT136789.3% ± 4.4%
+ +$$ +s ^ {i} = \left\| \bar {\mathbf {a}} _ {\mathrm {C O M}} ^ {i} \right\| \cdot \left\| \mathbf {v} _ {\text {L e f t F o o t}} ^ {i} \right\| \cdot \left\| \mathbf {v} _ {\text {R i g h t F o o t}} ^ {i} \right\|, \tag {11} +$$ + +$$ +P F C = \frac {1}{N \cdot \max _ {1 \leq j \leq N} \left\| \bar {a} _ {\mathrm {C O M}} ^ {j} \right\|} \sum_ {i = 1} ^ {N} s ^ {i}, \tag {12} +$$ + +where + +$$ +\overline {{\boldsymbol {a}}} _ {\mathrm {C O M}} ^ {i} = \left( \begin{array}{c} a _ {\mathrm {C O M}, x} ^ {i} \\ a _ {\mathrm {C O M}, y} ^ {i} \\ \max (a _ {\mathrm {C O M}, z} ^ {i}, 0) \end{array} \right) +$$ + +and the $i$ superscript denotes the frame index. + +In our results (Tab. 1), we find that our method attains a greater level of physical plausibility than previous methods, and approaches the plausibility of ground truth motion capture data. + +Maintaining fixed bone length is another important aspect of physical plausibility. Our method operates in the reduced coordinate (joint angle) space, which guarantees fixed bone length. However, methods that operate in the joint Cartesian space, such as Bailando, can produce significantly varying bone lengths. For example, on average, bone lengths change up to $\pm 20\%$ over the course of dance sequences generated by Bailando. + +Beat Alignment Scores Our experiments evaluate the tendency of our generated dances to follow the beat of the + +Table 2. We test our model on in-the-wild music and ablate Jukebox features in this setting, showing that Jukebox features are critical for generalization. + +
MethodEDGE Win RatePFC ↓
EDGEN/A1.5363
w/o CCL61.8% ± 7.3%3.0806
Ground Truth40.6% ± 7.4%1.332
+ +Table 3. We ablate our contact consistency loss (CCL) and study its impact on qualitative and quantitative physical plausibility. While EDGE wins more on average against ground truth on overall quality evaluation (Tab. 1), the user study for this table specifically asks about physical plausibility, and we find that ground truth still performs favorably compared to EDGE. + +music, following previous work [53] for the precise implementation of this metric. The results demonstrate that EDGE outperforms past work, including Bailando, which includes a reinforcement learning module that explicitly optimizes beat alignment. We further examine the robustness of this metric in Sec. 5. + +Diversity Diversity metrics are computed following the methods of previous work [33, 53], which measure the distributional spread of generated dances in the "kinetic" $(\mathrm{Dist}_k)$ and "geometric" $(\mathrm{Dist}_g)$ feature spaces, as implemented by fairmotion [13, 39, 41]. We compute these metrics on 5-second dance clips produced by each approach. Given that the ultimate goal of dance generation is to automatically produce dances that emulate the ground truth distribution, we argue that models should aim to match the scores of the ground truth distribution rather than maximize their absolute values. Indeed, past work has found that jittery dances result in high diversity scores, in some cases exceeding the ground truth [32, 33]. + +At low guidance weight $(w = 1)$ , EDGE achieves a level of diversity that closely matches that of the ground truth distribution while attaining state-of-the-art qualitative performance. At high guidance weight $(w = 2)$ , EDGE produces dances of markedly higher fidelity, reflected by a signifi + +![](images/e40c9eeda1b196ab29d9f3dce74241fc34528584185c31c90d6a3a804b9a82b5.jpg) +Figure 5. Temporal Conditioning: In-Betweening Given start (green) and end (red) poses, EDGE can generate in-between dance sequences. + +cantly higher Elo rating, while trading off diversity. These results reflect those of past studies, which show that sampling using guidance weights $w > 1$ significantly increases fidelity at the cost of diversity [20, 50]. This simple control over the diversity-fidelity tradeoff via the modulation of a single scalar parameter provides a powerful tool for downstream applications. + +# 4.2. Additional Evaluation + +In-the-Wild Music While past approaches achieve strong results on AIST++, these results are not necessarily indicative of the models' ability to generalize to in-the-wild music inputs. In order to evaluate generalization, we tested our proposed method and the baseline approaches on a diverse selection of popular songs from YouTube. + +The results, as shown in Tab. 2, demonstrate that our proposed method continues to perform well on in-the-wild music. We find through ablation that Jukebox features are critical for performance in this setting, bringing human-rated quality almost to par with in-distribution music; furthermore, we find that our approach continues to beat baselines in human evaluations for dance quality. We note that Bailando has an additional fine-tuning procedure available to improve performance on in-the-wild samples by training its actor-critic component. While we evaluated Bailando directly without additional fine-tuning, we found that human raters significantly preferred in-the-wild EDGE samples over in-distribution Bailando samples. We interpret these results as evidence that our proposed method is able to successfully generalize to in-the-wild music inputs. + +Editing We find through an additional human evaluation that our model is capable of in-betweening, motion continuation, joint-conditioned generation, and long-form generation with quality on par with unconstrained samples. Please see our website for demo examples, and Appendix H for more details. + +Contact Consistency Ablation We test the soundness of our PFC metric and ablate our Contact Consistency Loss (CCL) term (see Eq. (5)) using a human evaluation study. Raters were shown pairs of dances from the ground truth distribution, EDGE with CCL, and EDGE without CCL, and asked which dance looked more physically plausible. The results (Tab. 3) show that CCL noticeably improves both the PFC metric and qualitative physical plausibility user evaluations, winning $61.8\%$ of matchups against the version without CCL, and coming close to parity with ground truth samples. The results also indicate that PFC tracks well with human perception of physical plausibility. + +For a discussion of limitations and implementation details of PFC, please see Sec. 5 and Appendix D, respectively. + +# 4.3. Analysis of FID Metrics for Dance + +A reasonable solution to the problem of overall evaluation is to compute the difference between an empirical distribution of generated dances and a ground truth distribution. Several past works follow this intuition and automatically evaluate dance quality with Frechet Distance metrics [32, 33, 53]. As part of our experiments, we conduct a two-pronged analysis into the prevailing metrics, "FID $_k$ " and "FID $_g$ " [33], which compute the difference between distributions of heuristically extracted motion features, and show them to be unsound for the AIST++ dataset. + +“ $\mathrm{FID}_g$ ” We compute $\mathrm{FID}_g$ on the ground truth AIST++ dataset following the implementation in Li et al. [33]. Specifically, we compute metrics on the test set against the training set and obtain a score of 41.4, a stark increase from metrics obtained from generated outputs: running on FACT outputs gives 12.75, running on Bailando outputs gives 24.82, and running on our final model's outputs gives 23.08. Given that FACT performs the best in “ $\mathrm{FID}_g$ ” but performs the worst according to user studies and that all three models perform significantly better than ground truth, we conclude that the “ $\mathrm{FID}_g$ ” values are unreliable as a measure of quality on this dataset. + +" $\mathbf{FID}_k$ " We take 10 checkpoints throughout the training process for our model and poll raters on the overall quality of dances sampled from each checkpoint in a round-robin tournament. Intuitively, this should result in a consistent-to-monotonic improvement in both qualitative performance and in the quantitative quality metrics. However, we observe that this is not the case. In Fig. 6, we show the results of this experiment with our proposed model's $\mathrm{FID}_k$ . + +While the qualitative performance of the generated motion improves considerably as we train the model, the $\mathrm{FID}_k$ does not improve, and actually significantly worsens during the latter half of training. + +![](images/c3fc18ef65019a4cf216bead516406222c06ea52e6290821838f568e9cd3781c.jpg) +Figure 6. We plot $\mathrm{FID}_k$ over the course of model training and find that it is inconsistent with overall quality evaluations. + +# 5. Limitations of Existing Metrics + +Developing automated metrics for the quality of generated dances is a fundamentally challenging undertaking, since the practice of dance is complex, subjective, and even culturally specific. In this section, we discuss our findings on the limitations in automated metrics for dance evaluation, including our proposed PFC metric. + +Overall Quality Evaluation Our results suggest that despite the current standardized use of FIDs for evaluating dance generation models on the AIST++ dataset, these FID metrics, as they currently stand, are unreliable for measuring quality. One potential explanation may be that the AIST++ test set does not thoroughly cover the train distribution given its very small size. Additionally, due to data scarcity, both $\mathrm{FID}_k$ and $\mathrm{FID}_g$ depend on heuristic feature extractors that only compute superficial features of the data. By contrast, FID-based metrics in data-rich domains such as image generation (where FID originated) enjoy the use of learned feature extractors (e.g., pre-trained ImageNet models), which are known to directly extract semantically meaningful features [51]. Indeed, in the text-to-motion domain, where significantly more paired data is available [14], the standard feature extractors for FID-style metrics depend on deep contrastively learned models [58, 63]. + +Our experiments suggest that the current FID metrics can be further improved for evaluating motion sequences. We believe that the idea of evaluating the difference between two featurized distributions of dance motions is not necessarily fundamentally flawed, but that more representative features could result in reliable automatic quality evaluations. + +Beat Alignment Scoring Some automated metrics aim to capture one of the core aspects of a dance performance: its ability to "follow the beat" of the song. Previous work [33, 53] has proposed using a beat alignment metric that rewards kinematic beats (local minima of joint speed) which line up with music beats. + +However, dance is not strictly about matching local min + +ima in joint speed to beats: instead, the beats of the music are a loose guide for timing, rhythm, and transitions between movements and dance steps. This discrepancy is reflected in our results: empirically, we observe that in addition to exceeding scores of competing baselines, our beat alignment scores exceed those of ground truth samples. This seems to suggest that while the metric has served to drive progress on this problem in the past, the metric loses its meaning when candidate examples reach quality on par with ground truth. + +Physical Foot Contact In this work, we introduce PFC, Eq. (12), a physically-inspired metric that specifically targets the challenging issue of foot sliding. While PFC is intuitive, it is not without its limitations. In its current form, PFC assumes that the feet are the only joints that experience static contact. This means that PFC cannot be applied without modification to motions such as gymnastics routines, where a variable number of non-foot (e.g., hand) contacts are integral to their execution. We believe that a careful analysis of other contact points (e.g., hands in gymnastics) could provide an extension of PFC that is more widely applicable. Another issue is the assumption that the COM can be accelerated only by static contact: though rare, it is possible to decelerate the COM using friction during extended sliding (which is not present in AIST++.). For more analysis and discussion of PFC, see Appendix D. + +# 6. Conclusion and Future Work + +In this work, we propose a diffusion-based model that generates realistic and long-form dance sequences conditioned on music. We evaluate our model on multiple automated metrics (including our proposed PFC) and a large user study, and find that it achieves state-of-the-art results on the AIST++ dataset and generalizes well to in-the-wild music inputs. Importantly, we demonstrate that our model admits powerful editing capabilities, allowing users to freely specify both temporal and joint-wise constraints. The introduction of editable dance generation provides multiple promising avenues for future work. Whereas our method is able to create arbitrarily long dance sequences via the chaining of locally consistent, shorter clips, it cannot generate choreographies with very-long-term dependencies. Future work may explore the use of non-uniform sampling patterns such as those implemented in Harvey et al. [16], or a variation of the frame in-between scheme used in Ho et al. [18]. Editability also opens the door to the generation of more complex choreographies, including multi-person and scene-aware dance forms. 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High-resolution image synthesis with latent diffusion models. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 10684-10695, 2022. 3 +[49] Chitwan Sahara, William Chan, Huiwen Chang, Chris Lee, Jonathan Ho, Tim Salimans, David Fleet, and Mohammad Norouzi. Palette: Image-to-image diffusion models. In ACM SIGGRAPH 2022 Conference Proceedings, pages 1-10, 2022. 2 +[50] Chitwan Sahara, William Chan, Saurabh Saxena, Lala Li, Jay Whang, Emily Denton, Seyed Kamyar Seyed Ghasemipour, Burcu Karagol Ayan, S Sara Mahdavi, Rapha Gontijo Lopes, et al. Photorealistic text-to-image diffusion models with deep language understanding. arXiv preprint arXiv:2205.11487, 2022. 2, 3, 4, 7 +[51] Ali Sharif Razavian, Hossein Azizpour, Josephine Sullivan, and Stefan Carlsson. Cnn features off-the-shelf: an astounding baseline for recognition. In Proceedings of the IEEE conference on computer vision and pattern recognition workshops, pages 806-813, 2014. 8 +[52] Mingyi Shi, Kfir Aberman, Andreas Aristidou, Taku Komura, Dani Lischinski, Daniel Cohen-Or, and Baoquan Chen. Motionet: 3d human motion reconstruction from monocular video with skeleton consistency. ACM Transactions on Graphics (TOG), 40(1):1-15, 2020. 3 +[53] Li Siyao, Weijiang Yu, Tianpei Gu, Chunze Lin, Quan Wang, Chen Qian, Chen Change Loy, and Ziwei Liu. Bailando: 3d dance generation by actor-critic gpt with choreographic memory. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 11050-11059, 2022. 2, 4, 5, 6, 7, 8 +[54] Jascha Sohl-Dickstein, Eric Weiss, Niru Maheswaranathan, and Surya Ganguli. Deep unsupervised learning using nonequilibrium thermodynamics. In International Conference on Machine Learning, pages 2256-2265. PMLR, 2015. 2 +[55] Kihyuk Sohn, Honglak Lee, and Xinchen Yan. Learning structured output representation using deep conditional generative models. Advances in neural information processing systems, 28, 2015. 2 +[56] Omid Taheri, Vasileios Choutas, Michael J Black, and Dimitrios Tzionas. Goal: Generating 4d whole-body motion for hand-object grasping. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 13263-13273, 2022. 5 +[57] Xiangjun Tang, He Wang, Bo Hu, Xu Gong, Ruifan Yi, Qilong Kou, and Xiaogang Jin. Real-time controllable motion + +transition for characters. arXiv preprint arXiv:2205.02540, 2022.3 +[58] Guy Tevet, Sigal Raab, Brian Gordon, Yonatan Shafir, Daniel Cohen-Or, and Amit H Bermano. Human motion diffusion model. arXiv preprint arXiv:2209.14916, 2022. 2, 3, 4, 8 +[59] Guillermo Valle-Pérez, Gustav Eje Henter, Jonas Beskow, Andre Holzapfel, Pierre-Yves Oudeyer, and Simon Alexanderson. Transflower: probabilistic autoregressive dance generation with multimodal attention. ACM Transactions on Graphics (TOG), 40(6):1-14, 2021. 2, 4, 5 +[60] Jungdam Won, Deepak Gopinath, and Jessica Hodgins. Physics-based character controllers using conditional vaes. ACM Transactions on Graphics (TOG), 41(4):1-12, 2022. 2 +[61] Xingyu Xie, Pan Zhou, Huan Li, Zhouchen Lin, and Shuicheng Yan. Adan: Adaptive nesterov momentum algorithm for faster optimizing deep models. arXiv preprint arXiv:2208.06677, 2022. 14 +[62] Wenjie Yin, Hang Yin, Kim Baraka, Danica Kragic, and Marten Björkman. Dance style transfer with cross-modal transformer. arXiv preprint arXiv:2208.09406, 2022. 2 +[63] Mingyuan Zhang, Zhongang Cai, Liang Pan, Fangzhou Hong, Xinying Guo, Lei Yang, and Ziwei Liu. Motiondiffuse: Text-driven human motion generation with diffusion model. arXiv preprint arXiv:2208.15001, 2022. 2, 3, 8 +[64] Yi Zhou, Connelly Barnes, Jingwan Lu, Jimei Yang, and Hao Li. On the continuity of rotation representations in neural networks. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 5745-5753, 2019. 2 \ No newline at end of file diff --git a/2023/EDGE_ Editable Dance Generation From Music/images.zip b/2023/EDGE_ Editable Dance Generation From Music/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..99fb81446b4d0f7538930e9c94a5c79e2a4e1ad7 --- /dev/null +++ b/2023/EDGE_ Editable Dance Generation From Music/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:0725b8280beb2d1e2614e8d564e9f3850a791d6e18bf0281735b9209503fb9e9 +size 361055 diff --git a/2023/EDGE_ Editable Dance Generation From Music/layout.json b/2023/EDGE_ Editable Dance Generation From Music/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..ef27848121fae0a60209b7cd53af0eca75ab6d76 --- /dev/null +++ b/2023/EDGE_ Editable Dance Generation From Music/layout.json @@ -0,0 +1,8776 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 148, + 103, + 446, + 119 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 148, + 103, + 446, + 119 + ], + "spans": [ + { + "bbox": [ + 148, + 103, + 446, + 119 + ], + "type": "text", + "content": "EDGE: Editable Dance Generation From Music" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 176, + 143, + 416, + 172 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 176, + 143, + 416, + 172 + ], + "spans": [ + { + "bbox": [ + 176, + 143, + 416, + 172 + ], + "type": "text", + "content": "Jonathan Tseng, Rodrigo Castellon, C. 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EDGE generates diverse, physically plausible dance choreographies conditioned on music." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_caption" + } + ], + "index": 5 + }, + { + "bbox": [ + 143, + 359, + 192, + 371 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 359, + 192, + 371 + ], + "spans": [ + { + "bbox": [ + 143, + 359, + 192, + 371 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 45, + 384, + 290, + 588 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 384, + 290, + 588 + ], + "spans": [ + { + "bbox": [ + 45, + 384, + 290, + 588 + ], + "type": "text", + "content": "Dance is an important human art form, but creating new dances can be difficult and time-consuming. In this work, we introduce Editable Dance Generation (EDGE), a state-of-the-art method for editable dance generation that is capable of creating realistic, physically-plausible dances while remaining faithful to the input music. EDGE uses a transformer-based diffusion model paired with Jukebox, a strong music feature extractor, and confers powerful editing capabilities well-suited to dance, including joint-wise conditioning, and in-betweening. We introduce a new metric for physical plausibility, and evaluate dance quality generated by our method extensively through (1) multiple quantitative metrics on physical plausibility, beat alignment, and diversity benchmarks, and more importantly, (2) a large-scale user study, demonstrating a significant improvement over previous state-of-the-art methods. Qualitative samples from our model can be found at our website." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 610, + 128, + 623 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 610, + 128, + 623 + ], + "spans": [ + { + "bbox": [ + 47, + 610, + 128, + 623 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 631, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 631, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 631, + 287, + 715 + ], + "type": "text", + "content": "Dance is an important part of many cultures around the world: it is a form of expression, communication, and social interaction [29]. However, creating new dances or dance animations is uniquely difficult because dance movements are expressive and freeform, yet precisely structured by music. In practice, this requires tedious hand animation or motion capture solutions, which can be expensive and impractical." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 360, + 545, + 468 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 360, + 545, + 468 + ], + "spans": [ + { + "bbox": [ + 304, + 360, + 545, + 468 + ], + "type": "text", + "content": "On the other hand, using computational methods to generate dances automatically can alleviate the burden of the creation process, leading to many applications: such methods can help animators create new dances or provide interactive characters in video games or virtual reality with realistic and varied movements based on user-provided music. In addition, dance generation can provide insights into the relationship between music and movement, which is an important area of research in neuroscience [2]." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 472, + 545, + 543 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 472, + 545, + 543 + ], + "spans": [ + { + "bbox": [ + 304, + 472, + 545, + 543 + ], + "type": "text", + "content": "Previous work has made significant progress using machine learning-based methods, but has achieved limited success in generating dances from music that satisfy user constraints. Furthermore, the evaluation of generated dances is subjective and complex, and existing papers often use quantitative metrics that we show to be flawed." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 547, + 546, + 703 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 547, + 546, + 703 + ], + "spans": [ + { + "bbox": [ + 304, + 547, + 546, + 703 + ], + "type": "text", + "content": "In this work, we propose Editable Dance GEneration (EDGE), a state-of-the-art method for dance generation that creates realistic, physically-plausible dance motions based on input music. Our method uses a transformer-based diffusion model paired with Jukebox, a strong music feature extractor. This unique diffusion-based approach confers powerful editing capabilities well-suited to dance, including joint-wise conditioning and in-betweening. In addition to the advantages immediately conferred by the modeling choices, we observe flaws with previous metrics and propose a new metric that captures the physical accuracy of ground contact behaviors without explicit physical modeling. In summary, our contributions are the following:" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 496, + 35 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 496, + 35 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 496, + 35 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 297, + 749, + 313, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 749, + 313, + 757 + ], + "spans": [ + { + "bbox": [ + 297, + 749, + 313, + 757 + ], + "type": "text", + "content": "448" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 54, + 72, + 287, + 309 + ], + "type": "list", + "angle": 0, + "index": 3, + "blocks": [ + { + "bbox": [ + 55, + 72, + 287, + 180 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 55, + 72, + 287, + 180 + ], + "spans": [ + { + "bbox": [ + 55, + 72, + 287, + 180 + ], + "type": "text", + "content": "1. We introduce EDGE, a diffusion-based approach for dance generation that combines state-of-the-art performance with powerful editing capabilities and is able to generate arbitrarily long sequences. EDGE improves on previous hand-crafted audio feature extraction strategies by leveraging music audio representations from Jukebox [5], a pre-trained generative model for music that has previously demonstrated strong performance on music-specific prediction tasks [3, 7]." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 54, + 184, + 287, + 220 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 54, + 184, + 287, + 220 + ], + "spans": [ + { + "bbox": [ + 54, + 184, + 287, + 220 + ], + "type": "text", + "content": "2. We analyze the metrics proposed in previous works and show that they do not accurately represent human-evaluated quality as reported by a large user study." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 54, + 224, + 287, + 309 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 54, + 224, + 287, + 309 + ], + "spans": [ + { + "bbox": [ + 54, + 224, + 287, + 309 + ], + "type": "text", + "content": "3. We propose a new approach to eliminating foot-sliding physical implausibilities in generated motions using a novel Contact Consistency Loss, and introduce Physical Foot Contact Score, a simple new acceleration-based quantitative metric for scoring physical plausibility of generated kinematic motions that requires no explicit physical modeling." + } + ] + } + ], + "index": 2 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 47, + 313, + 287, + 338 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 313, + 287, + 338 + ], + "spans": [ + { + "bbox": [ + 47, + 313, + 287, + 338 + ], + "type": "text", + "content": "This work is best enjoyed when accompanied by our demo samples. Please see the samples at our website." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 349, + 134, + 361 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 349, + 134, + 361 + ], + "spans": [ + { + "bbox": [ + 47, + 349, + 134, + 361 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 369, + 194, + 381 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 369, + 194, + 381 + ], + "spans": [ + { + "bbox": [ + 47, + 369, + 194, + 381 + ], + "type": "text", + "content": "2.1. Human motion generation" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 387, + 287, + 459 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 387, + 287, + 459 + ], + "spans": [ + { + "bbox": [ + 47, + 387, + 287, + 459 + ], + "type": "text", + "content": "Human motion generation, the problem of automatically generating realistic human motions, is well-studied in computer vision, graphics, and robotics. Despite its importance and recent progress, it remains a challenging problem, with existing methods often struggling to capture the complexities of physically and stylistically realistic human motion." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 460, + 287, + 530 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 460, + 287, + 530 + ], + "spans": [ + { + "bbox": [ + 47, + 460, + 287, + 530 + ], + "type": "text", + "content": "Many early approaches fall under the category of motion matching, which operates by interpolating between sequences retrieved from a database [21]. While these approaches generate outputs that are physically plausible, their application has been primarily restricted to simple domains such as locomotion." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 531, + 287, + 651 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 531, + 287, + 651 + ], + "spans": [ + { + "bbox": [ + 46, + 531, + 287, + 651 + ], + "type": "text", + "content": "In recent years, deep neural networks have emerged as a promising alternative method for human motion generation. These approaches are often capable of generating diverse motions, but often fall short in capturing the physical laws governing human movement or rely on difficult-to-train reinforcement learning solutions [34, 60]. Generating human motion conditioned on various inputs—e.g., joystick control [34], class-conditioning [15, 43], text-to-motion [44, 63], seed motions [8, 22, 46, 62]—is also an active area of study." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 658, + 155, + 670 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 658, + 155, + 670 + ], + "spans": [ + { + "bbox": [ + 47, + 658, + 155, + 670 + ], + "type": "text", + "content": "2.2. Dance Generation" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 47, + 677, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 677, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 677, + 287, + 713 + ], + "type": "text", + "content": "The uniquely challenging task of generating dances stylistically faithful to input music has been tackled by many researchers. Many early approaches follow a motion" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 72, + 545, + 216 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 216 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 216 + ], + "type": "text", + "content": "retrieval paradigm [11, 30, 40], but tend to create unrealistic choreographies that lack the complexity of human dances. Later works instead synthesize motion from scratch by training on large datasets [1, 10, 23, 27, 31, 33, 45, 47, 53, 59] and propose many modeling approaches, including adversarial learning, recurrent neural networks, and transformers. Despite achieving impressive performance, many such systems are complex [1, 4, 31, 53], often involving many layers of conditioning and sub-networks. In contrast, our proposed method contains a single model trained with a simple objective, yet offers both strong generative and editing capabilities without significant hand-crafted design." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 221, + 463, + 233 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 221, + 463, + 233 + ], + "spans": [ + { + "bbox": [ + 306, + 221, + 463, + 233 + ], + "type": "text", + "content": "2.3. Generative Diffusion Models" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 239, + 545, + 443 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 239, + 545, + 443 + ], + "spans": [ + { + "bbox": [ + 304, + 239, + 545, + 443 + ], + "type": "text", + "content": "Diffusion models [19, 54] are a class of deep generative models which learn a data distribution by reversing a scheduled noising process. In the past few years, diffusion models have been shown to be a promising avenue for generative modeling, exceeding the state-of-the-art in generative tasks [18, 24, 50]. Much like previous generative approaches like VAE [28] and GAN [12], diffusion models are also capable of conditional generation. Dhariwal et al. [6] introduced classifier guidance for image generation, where the output of a diffusion model may be \"steered\" towards a target, such as a class label, using the gradients of a differentiable auxiliary model. Sahara et al. [49] proposed to use direct concatenation of conditions for Pix2Pix-like tasks, akin to Conditional GAN and CVAE [38, 55], and Ho et al. [20] demonstrated that classifier-free guidance can achieve state-of-the-art results while allowing more explicit control over the diversity-fidelity tradeoff." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 444, + 545, + 528 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 444, + 545, + 528 + ], + "spans": [ + { + "bbox": [ + 304, + 444, + 545, + 528 + ], + "type": "text", + "content": "Most recently, diffusion-based methods have demonstrated strong performance in generating motions conditioned on text [26,58,63]. While the tasks of text-to-motion and music-conditioned dance generation share high-level similarities, the dance generation task suffers more challenging computational scaling (see Sec. 3) and, due to its specialized nature, much lower data availability." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 306, + 536, + 361, + 548 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 536, + 361, + 548 + ], + "spans": [ + { + "bbox": [ + 306, + 536, + 361, + 548 + ], + "type": "text", + "content": "3. Method" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 556, + 545, + 665 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 556, + 545, + 665 + ], + "spans": [ + { + "bbox": [ + 304, + 556, + 545, + 665 + ], + "type": "text", + "content": "Pose Representation We represent dances as sequences of poses in the 24-joint SMPL format [35], using the 6-DOF rotation representation [64] for every joint and a single root translation: " + }, + { + "bbox": [ + 304, + 556, + 545, + 665 + ], + "type": "inline_equation", + "content": "\\pmb{w} \\in \\mathbb{R}^{24 \\cdot 6 + 3 = 147}" + }, + { + "bbox": [ + 304, + 556, + 545, + 665 + ], + "type": "text", + "content": ". For the heel and toe of each foot, we also include a binary contact label: " + }, + { + "bbox": [ + 304, + 556, + 545, + 665 + ], + "type": "inline_equation", + "content": "\\pmb{b} \\in \\{0,1\\}^{2 \\cdot 2 = 4}" + }, + { + "bbox": [ + 304, + 556, + 545, + 665 + ], + "type": "text", + "content": ". The total pose representation is therefore " + }, + { + "bbox": [ + 304, + 556, + 545, + 665 + ], + "type": "inline_equation", + "content": "\\pmb{x} = \\{\\pmb{b}, \\pmb{w}\\} \\in \\mathbb{R}^{4 + 147 = 151}" + }, + { + "bbox": [ + 304, + 556, + 545, + 665 + ], + "type": "text", + "content": ". EDGE uses a diffusion-based framework to learn to synthesize sequences of " + }, + { + "bbox": [ + 304, + 556, + 545, + 665 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 304, + 556, + 545, + 665 + ], + "type": "text", + "content": " frames, " + }, + { + "bbox": [ + 304, + 556, + 545, + 665 + ], + "type": "inline_equation", + "content": "\\pmb{x} \\in \\mathbb{R}^{N \\times 151}" + }, + { + "bbox": [ + 304, + 556, + 545, + 665 + ], + "type": "text", + "content": ", given arbitrary music conditioning " + }, + { + "bbox": [ + 304, + 556, + 545, + 665 + ], + "type": "inline_equation", + "content": "\\pmb{c}" + }, + { + "bbox": [ + 304, + 556, + 545, + 665 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 677, + 545, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 545, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 545, + 715 + ], + "type": "text", + "content": "Diffusion Framework We follow the DDPM [19] definition of diffusion as a Markov noising process with latents " + }, + { + "bbox": [ + 304, + 677, + 545, + 715 + ], + "type": "inline_equation", + "content": "\\{z_t\\}_{t=0}^T" + }, + { + "bbox": [ + 304, + 677, + 545, + 715 + ], + "type": "text", + "content": " that follow a forward noising process " + }, + { + "bbox": [ + 304, + 677, + 545, + 715 + ], + "type": "inline_equation", + "content": "q(z_t | x)" + }, + { + "bbox": [ + 304, + 677, + 545, + 715 + ], + "type": "text", + "content": "," + } + ] + } + ], + "index": 18 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 297, + 749, + 312, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 749, + 312, + 757 + ], + "spans": [ + { + "bbox": [ + 297, + 749, + 312, + 757 + ], + "type": "text", + "content": "449" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 50, + 69, + 286, + 252 + ], + "blocks": [ + { + "bbox": [ + 50, + 69, + 286, + 252 + ], + "lines": [ + { + "bbox": [ + 50, + 69, + 286, + 252 + ], + "spans": [ + { + "bbox": [ + 50, + 69, + 286, + 252 + ], + "type": "image", + "image_path": "5a0a20fa10228603122e197d2a3f50a4ff9e7ae0f11c30240c38f5c01ed60df3.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 260, + 547, + 297 + ], + "lines": [ + { + "bbox": [ + 46, + 260, + 547, + 297 + ], + "spans": [ + { + "bbox": [ + 46, + 260, + 547, + 297 + ], + "type": "text", + "content": "Figure 2. EDGE Pipeline Overview: EDGE learns to denoise dance sequences from time " + }, + { + "bbox": [ + 46, + 260, + 547, + 297 + ], + "type": "inline_equation", + "content": "t = T" + }, + { + "bbox": [ + 46, + 260, + 547, + 297 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 46, + 260, + 547, + 297 + ], + "type": "inline_equation", + "content": "t = 0" + }, + { + "bbox": [ + 46, + 260, + 547, + 297 + ], + "type": "text", + "content": ", conditioned on music. Music embedding information is provided by a frozen Jukebox model [5] and acts as cross-attention context. EDGE takes a noisy sequence " + }, + { + "bbox": [ + 46, + 260, + 547, + 297 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_T \\sim \\mathcal{N}(0, I)" + }, + { + "bbox": [ + 46, + 260, + 547, + 297 + ], + "type": "text", + "content": " and produces the estimated final sequence " + }, + { + "bbox": [ + 46, + 260, + 547, + 297 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{x}}" + }, + { + "bbox": [ + 46, + 260, + 547, + 297 + ], + "type": "text", + "content": ", noising it back to " + }, + { + "bbox": [ + 46, + 260, + 547, + 297 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{z}}_{T - 1}" + }, + { + "bbox": [ + 46, + 260, + 547, + 297 + ], + "type": "text", + "content": " and repeating until " + }, + { + "bbox": [ + 46, + 260, + 547, + 297 + ], + "type": "inline_equation", + "content": "t = 0" + }, + { + "bbox": [ + 46, + 260, + 547, + 297 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 291, + 68, + 547, + 251 + ], + "blocks": [ + { + "bbox": [ + 291, + 68, + 547, + 251 + ], + "lines": [ + { + "bbox": [ + 291, + 68, + 547, + 251 + ], + "spans": [ + { + "bbox": [ + 291, + 68, + 547, + 251 + ], + "type": "image", + "image_path": "7e4fdd3f3feae443dffef04a6b0511a4bc8e211de5f09b07edb4b627d611ec5a.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 315, + 288, + 339 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 315, + 288, + 339 + ], + "spans": [ + { + "bbox": [ + 47, + 315, + 288, + 339 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 315, + 288, + 339 + ], + "type": "inline_equation", + "content": "\\pmb{x} \\sim p(\\pmb{x})" + }, + { + "bbox": [ + 47, + 315, + 288, + 339 + ], + "type": "text", + "content": " is drawn from the data distribution. The forward noising process is defined as" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 97, + 344, + 287, + 359 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 97, + 344, + 287, + 359 + ], + "spans": [ + { + "bbox": [ + 97, + 344, + 287, + 359 + ], + "type": "interline_equation", + "content": "q \\left(\\boldsymbol {z} _ {t} | \\boldsymbol {x}\\right) \\sim \\mathcal {N} \\left(\\sqrt {\\bar {\\alpha} _ {t}} \\boldsymbol {x}, \\left(1 - \\bar {\\alpha} _ {t}\\right) \\boldsymbol {I}\\right), \\tag {1}", + "image_path": "7fda5fb74d2cf039ffed92442c3158dad1bc8940a8000552f89b8c5aeb50f3a8.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 362, + 287, + 411 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 362, + 287, + 411 + ], + "spans": [ + { + "bbox": [ + 47, + 362, + 287, + 411 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 362, + 287, + 411 + ], + "type": "inline_equation", + "content": "\\bar{\\alpha}_t\\in (0,1)" + }, + { + "bbox": [ + 47, + 362, + 287, + 411 + ], + "type": "text", + "content": " are constants which follow a monotonically decreasing schedule such that when " + }, + { + "bbox": [ + 47, + 362, + 287, + 411 + ], + "type": "inline_equation", + "content": "\\bar{\\alpha}_t" + }, + { + "bbox": [ + 47, + 362, + 287, + 411 + ], + "type": "text", + "content": " approaches 0, we can approximate " + }, + { + "bbox": [ + 47, + 362, + 287, + 411 + ], + "type": "inline_equation", + "content": "z_{T}\\sim \\mathcal{N}(0,I)" + }, + { + "bbox": [ + 47, + 362, + 287, + 411 + ], + "type": "text", + "content": ". We chose to use " + }, + { + "bbox": [ + 47, + 362, + 287, + 411 + ], + "type": "inline_equation", + "content": "T = 1000" + }, + { + "bbox": [ + 47, + 362, + 287, + 411 + ], + "type": "text", + "content": " timesteps." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 411, + 287, + 471 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 411, + 287, + 471 + ], + "spans": [ + { + "bbox": [ + 47, + 411, + 287, + 471 + ], + "type": "text", + "content": "In our setting with paired music conditioning " + }, + { + "bbox": [ + 47, + 411, + 287, + 471 + ], + "type": "inline_equation", + "content": "\\pmb{c}" + }, + { + "bbox": [ + 47, + 411, + 287, + 471 + ], + "type": "text", + "content": ", we reverse the forward diffusion process by learning to estimate " + }, + { + "bbox": [ + 47, + 411, + 287, + 471 + ], + "type": "inline_equation", + "content": "\\hat{\\pmb{x}}_{\\theta}(z_t,t,\\pmb {c})\\approx \\pmb {x}" + }, + { + "bbox": [ + 47, + 411, + 287, + 471 + ], + "type": "text", + "content": " with model parameters " + }, + { + "bbox": [ + 47, + 411, + 287, + 471 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 47, + 411, + 287, + 471 + ], + "type": "text", + "content": " for all " + }, + { + "bbox": [ + 47, + 411, + 287, + 471 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 47, + 411, + 287, + 471 + ], + "type": "text", + "content": ". We optimize " + }, + { + "bbox": [ + 47, + 411, + 287, + 471 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 47, + 411, + 287, + 471 + ], + "type": "text", + "content": " with the \"simple\" objective introduced in Ho et al. [19]:" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 90, + 475, + 287, + 491 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 90, + 475, + 287, + 491 + ], + "spans": [ + { + "bbox": [ + 90, + 475, + 287, + 491 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\text {s i m p l e}} = \\mathbb {E} _ {\\boldsymbol {x}, t} \\left[ \\| \\boldsymbol {x} - \\hat {\\boldsymbol {x}} _ {\\theta} (\\boldsymbol {z} _ {t}, t, \\boldsymbol {c}) \\| _ {2} ^ {2} \\right]. \\tag {2}", + "image_path": "428f24f4cd4f72796c84591f6e0caa99b1238a1c59b8de1af983eb760f1f98f4.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 494, + 287, + 518 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 494, + 287, + 518 + ], + "spans": [ + { + "bbox": [ + 47, + 494, + 287, + 518 + ], + "type": "text", + "content": "From now on, we refer to " + }, + { + "bbox": [ + 47, + 494, + 287, + 518 + ], + "type": "inline_equation", + "content": "\\hat{\\pmb{x}}_{\\theta}(\\pmb{z}_t,t,\\pmb {c})" + }, + { + "bbox": [ + 47, + 494, + 287, + 518 + ], + "type": "text", + "content": " as " + }, + { + "bbox": [ + 47, + 494, + 287, + 518 + ], + "type": "inline_equation", + "content": "\\hat{\\pmb{x}} (\\pmb {z}_t,\\pmb {c})" + }, + { + "bbox": [ + 47, + 494, + 287, + 518 + ], + "type": "text", + "content": " for ease of notation." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 532, + 288, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 532, + 288, + 628 + ], + "spans": [ + { + "bbox": [ + 47, + 532, + 288, + 628 + ], + "type": "text", + "content": "Auxiliary losses Auxiliary losses are commonly used in kinematic motion generation settings to improve physical realism in the absence of true simulation [43, 52, 57]. In addition to the reconstruction loss " + }, + { + "bbox": [ + 47, + 532, + 288, + 628 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{simple}}" + }, + { + "bbox": [ + 47, + 532, + 288, + 628 + ], + "type": "text", + "content": ", we adopt auxiliary losses similar to those in Tevet et al. [58], which encourage matching three aspects of physical realism: joint positions (Eq. (3)), velocities (Eq. (4)), and foot velocities via our Contact Consistency Loss (Eq. (5))." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 80, + 632, + 287, + 666 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 80, + 632, + 287, + 666 + ], + "spans": [ + { + "bbox": [ + 80, + 632, + 287, + 666 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\text {j o i n t}} = \\frac {1}{N} \\sum_ {i = 1} ^ {N} \\| F K (\\boldsymbol {x} ^ {(i)}) - F K (\\hat {\\boldsymbol {x}} ^ {(i)}) \\| _ {2} ^ {2} \\tag {3}", + "image_path": "9a11fa5a60a08b0ca7db6b222839505e38a0bb540be81f9005bcd9f959639950.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 50, + 670, + 287, + 714 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 50, + 670, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 50, + 670, + 287, + 714 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\mathrm {v e l}} = \\frac {1}{N - 1} \\sum_ {i = 1} ^ {N - 1} \\| \\left(\\boldsymbol {x} ^ {(i + 1)} - \\boldsymbol {x} ^ {(i)}\\right) - \\left(\\hat {\\boldsymbol {x}} ^ {(i + 1)} - \\hat {\\boldsymbol {x}} ^ {(i)}\\right) \\| _ {2} ^ {2} \\tag {4}", + "image_path": "9d6dd8a3e88e8ad0c9e5d93b77fe1a9c3f70e7e868a126e8c0094bd2df480be8.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 329, + 548, + 371 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 329, + 548, + 371 + ], + "spans": [ + { + "bbox": [ + 306, + 329, + 548, + 371 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\text {c o n t a c t}} = \\frac {1}{N - 1} \\sum_ {i = 1} ^ {N - 1} \\| \\left(F K \\left(\\hat {\\boldsymbol {x}} ^ {(i + 1)}\\right) - F K \\left(\\hat {\\boldsymbol {x}} ^ {(i)}\\right)\\right) \\cdot \\hat {\\boldsymbol {b}} ^ {(i)} \\| _ {2} ^ {2}, \\tag {5}", + "image_path": "2dc237b9e2aefc42c40a35534894f7ddeae39e2b177396a81848e0f192fc795f.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 372, + 546, + 538 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 372, + 546, + 538 + ], + "spans": [ + { + "bbox": [ + 304, + 372, + 546, + 538 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 372, + 546, + 538 + ], + "type": "inline_equation", + "content": "FK(\\cdot)" + }, + { + "bbox": [ + 304, + 372, + 546, + 538 + ], + "type": "text", + "content": " denotes the forward kinematic function that converts joint angles into joint positions (though it only applies to the foot joints in Eq. (5)) and the " + }, + { + "bbox": [ + 304, + 372, + 546, + 538 + ], + "type": "inline_equation", + "content": "(i)" + }, + { + "bbox": [ + 304, + 372, + 546, + 538 + ], + "type": "text", + "content": " superscript denotes the frame index. In the Contact Consistency Loss, " + }, + { + "bbox": [ + 304, + 372, + 546, + 538 + ], + "type": "inline_equation", + "content": "\\hat{\\pmb{b}}^{(i)}" + }, + { + "bbox": [ + 304, + 372, + 546, + 538 + ], + "type": "text", + "content": " is the model's own prediction of the binary foot contact label's portion of the pose at each frame " + }, + { + "bbox": [ + 304, + 372, + 546, + 538 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 304, + 372, + 546, + 538 + ], + "type": "text", + "content": ". While this formulation is similar to the foot skate loss terms in previous works [57, 58], where foot velocity is penalized in frames where the ground truth motion exhibits a static foot contact, our Contact Consistency Loss formulation differs in that it encourages the model to (1) predict foot contact, and (2) maintain consistency with its own predictions. We find that this formulation significantly improves the realism of generated motions (see Sec. 4.1)." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 539, + 547, + 588 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 539, + 547, + 588 + ], + "spans": [ + { + "bbox": [ + 304, + 539, + 547, + 588 + ], + "type": "text", + "content": "Our overall training loss is the weighted sum of the simple objective and the auxiliary losses, where the weights " + }, + { + "bbox": [ + 304, + 539, + 547, + 588 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 304, + 539, + 547, + 588 + ], + "type": "text", + "content": " were chosen to balance the magnitudes of the losses at the start of training.:" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 317, + 592, + 545, + 605 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 592, + 545, + 605 + ], + "spans": [ + { + "bbox": [ + 317, + 592, + 545, + 605 + ], + "type": "interline_equation", + "content": "\\mathcal {L} = \\mathcal {L} _ {\\text {s i m p l e}} + \\lambda_ {\\text {p o s}} \\mathcal {L} _ {\\text {p o s}} + \\lambda_ {\\text {v e l}} \\mathcal {L} _ {\\text {v e l}} + \\lambda_ {\\text {c o n t a c t}} \\mathcal {L} _ {\\text {c o n t a c t}}. \\tag {6}", + "image_path": "bc1e713f2790f1a591da417f4855019e6781efdff4187a2f393329ebfe8b2856.jpg" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "type": "text", + "content": "Sampling and Guidance At each of the denoising timesteps " + }, + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "type": "text", + "content": ", EDGE predicts the denoised sample and noises it back to timestep " + }, + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "type": "inline_equation", + "content": "t - 1: \\hat{\\pmb{z}}_{t - 1} \\sim q(\\hat{\\pmb{x}}_{\\theta}(\\hat{\\pmb{z}}_t, \\pmb{c}), t - 1)" + }, + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "type": "text", + "content": ", terminating when it reaches " + }, + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "type": "inline_equation", + "content": "t = 0" + }, + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "type": "text", + "content": " (Fig. 2, right). We train our model using classifier-free guidance [20], which is commonly used in diffusion-based models [26, 48, 50, 58, 63]. Following Ho et al. [20], we implement classifier-free guidance by randomly replacing the conditioning with " + }, + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "type": "inline_equation", + "content": "\\pmb{c} = \\emptyset" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 297, + 748, + 313, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 748, + 313, + 758 + ], + "spans": [ + { + "bbox": [ + 297, + 748, + 313, + 758 + ], + "type": "text", + "content": "450" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 109 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 109 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 109 + ], + "type": "text", + "content": "during training with low probability (e.g., " + }, + { + "bbox": [ + 46, + 72, + 287, + 109 + ], + "type": "inline_equation", + "content": "25\\%" + }, + { + "bbox": [ + 46, + 72, + 287, + 109 + ], + "type": "text", + "content": "). Guided inference is then expressed as the weighted sum of unconditionally and conditionally generated samples:" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 74, + 117, + 287, + 130 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 74, + 117, + 287, + 130 + ], + "spans": [ + { + "bbox": [ + 74, + 117, + 287, + 130 + ], + "type": "interline_equation", + "content": "\\tilde {\\boldsymbol {x}} (\\hat {\\boldsymbol {z}} _ {t}, \\boldsymbol {c}) = w \\cdot \\hat {\\boldsymbol {x}} (\\hat {\\boldsymbol {z}} _ {t}, \\boldsymbol {c}) + (1 - w) \\cdot \\hat {\\boldsymbol {x}} (\\hat {\\boldsymbol {z}} _ {t}, \\emptyset). \\tag {7}", + "image_path": "18a7b8a5d77bfe73c42050be855cd6d6cffc94966d75599754d54cc43717d43e.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 138, + 287, + 163 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 138, + 287, + 163 + ], + "spans": [ + { + "bbox": [ + 46, + 138, + 287, + 163 + ], + "type": "text", + "content": "At sampling time, we can amplify the conditioning " + }, + { + "bbox": [ + 46, + 138, + 287, + 163 + ], + "type": "inline_equation", + "content": "c" + }, + { + "bbox": [ + 46, + 138, + 287, + 163 + ], + "type": "text", + "content": " by choosing a guidance weight " + }, + { + "bbox": [ + 46, + 138, + 287, + 163 + ], + "type": "inline_equation", + "content": "w > 1" + }, + { + "bbox": [ + 46, + 138, + 287, + 163 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 176, + 287, + 273 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 176, + 287, + 273 + ], + "spans": [ + { + "bbox": [ + 46, + 176, + 287, + 273 + ], + "type": "text", + "content": "Editing To enable editing for dances generated by EDGE, we use the standard masked denoising technique from diffusion image inpainting [36], and more recently text-to-motion models [26,58]. EDGE supports any combination of temporal and joint-wise constraints, shown in Fig. 4. Given a joint-wise and/or temporal constraint " + }, + { + "bbox": [ + 46, + 176, + 287, + 273 + ], + "type": "inline_equation", + "content": "\\pmb{x}^{\\mathrm{known}}" + }, + { + "bbox": [ + 46, + 176, + 287, + 273 + ], + "type": "text", + "content": " with positions indicated by a binary mask " + }, + { + "bbox": [ + 46, + 176, + 287, + 273 + ], + "type": "inline_equation", + "content": "m" + }, + { + "bbox": [ + 46, + 176, + 287, + 273 + ], + "type": "text", + "content": ", we perform the following at every denoising timestep:" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 58, + 280, + 287, + 293 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 280, + 287, + 293 + ], + "spans": [ + { + "bbox": [ + 58, + 280, + 287, + 293 + ], + "type": "interline_equation", + "content": "\\hat {z} _ {t - 1} := \\boldsymbol {m} \\odot q \\left(\\boldsymbol {x} ^ {\\text {k n o w n}}, t - 1\\right) + (1 - \\boldsymbol {m}) \\odot \\hat {z} _ {t - 1}, \\tag {8}", + "image_path": "b9f86ca175771a0877cec437652dba6020a510d84686285091c2a81004da493b.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 302, + 287, + 350 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 302, + 287, + 350 + ], + "spans": [ + { + "bbox": [ + 46, + 302, + 287, + 350 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 302, + 287, + 350 + ], + "type": "inline_equation", + "content": "\\odot" + }, + { + "bbox": [ + 46, + 302, + 287, + 350 + ], + "type": "text", + "content": " is the Hadamard (element-wise) product, replacing the known regions with forward-diffused samples of the constraint. This technique allows editability at inference time with no special training processes necessary." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 350, + 287, + 482 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 350, + 287, + 482 + ], + "spans": [ + { + "bbox": [ + 46, + 350, + 287, + 482 + ], + "type": "text", + "content": "For example, a user can perform motion in-between by providing a reference motion " + }, + { + "bbox": [ + 46, + 350, + 287, + 482 + ], + "type": "inline_equation", + "content": "\\pmb{x}^{\\mathrm{known}} \\in \\mathbb{R}^{N \\times 151}" + }, + { + "bbox": [ + 46, + 350, + 287, + 482 + ], + "type": "text", + "content": " and a mask " + }, + { + "bbox": [ + 46, + 350, + 287, + 482 + ], + "type": "inline_equation", + "content": "m \\in \\{0,1\\}^{N \\times 151}" + }, + { + "bbox": [ + 46, + 350, + 287, + 482 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 350, + 287, + 482 + ], + "type": "inline_equation", + "content": "m" + }, + { + "bbox": [ + 46, + 350, + 287, + 482 + ], + "type": "text", + "content": " is all 1's in the first and last " + }, + { + "bbox": [ + 46, + 350, + 287, + 482 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 46, + 350, + 287, + 482 + ], + "type": "text", + "content": " frames and 0 everywhere else. This would result in a sequence " + }, + { + "bbox": [ + 46, + 350, + 287, + 482 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 350, + 287, + 482 + ], + "type": "text", + "content": " frames long, where the first and last " + }, + { + "bbox": [ + 46, + 350, + 287, + 482 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 46, + 350, + 287, + 482 + ], + "type": "text", + "content": " frames are provided by the reference motion and the rest is filled in with a plausible \"in-between\" dance that smoothly connects the constraint frames, for arbitrary " + }, + { + "bbox": [ + 46, + 350, + 287, + 482 + ], + "type": "inline_equation", + "content": "2n < N" + }, + { + "bbox": [ + 46, + 350, + 287, + 482 + ], + "type": "text", + "content": ". This editing framework provides a powerful tool for downstream applications, enabling the generation of dances that precisely conform to arbitrary constraints." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 496, + 287, + 674 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 496, + 287, + 674 + ], + "spans": [ + { + "bbox": [ + 46, + 496, + 287, + 674 + ], + "type": "text", + "content": "Long-form sampling The ability to synthesize sequences of arbitrary length, often many minutes long, is critical to the task of dance generation. However, since EDGE generates every frame of a dance sequence at once, naively increasing the maximum sequence length incurs a linear increase in computational cost. Moreover, dance generation requires that the conditioning " + }, + { + "bbox": [ + 46, + 496, + 287, + 674 + ], + "type": "inline_equation", + "content": "c" + }, + { + "bbox": [ + 46, + 496, + 287, + 674 + ], + "type": "text", + "content": " match the motion sequence in length, causing further scaling of memory demands, which is especially severe in the case of embeddings from large models like Jukebox [5]. To approach the challenge of long-form generation, EDGE leverages its editability to enforce temporal consistency between multiple sequences such that they can be concatenated into a single longer sequence. Refer to Fig. 3 for a depiction of this process." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 689, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 689, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 689, + 287, + 714 + ], + "type": "text", + "content": "Model Our model architecture is illustrated in Fig. 2. We adopt a transformer decoder architecture, which processes" + } + ] + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 331, + 72, + 523, + 198 + ], + "blocks": [ + { + "bbox": [ + 331, + 72, + 523, + 198 + ], + "lines": [ + { + "bbox": [ + 331, + 72, + 523, + 198 + ], + "spans": [ + { + "bbox": [ + 331, + 72, + 523, + 198 + ], + "type": "image", + "image_path": "192319357babfb8b2670021f030e318542871678ea13571d671abd928cde5501.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 205, + 545, + 281 + ], + "lines": [ + { + "bbox": [ + 304, + 205, + 545, + 281 + ], + "spans": [ + { + "bbox": [ + 304, + 205, + 545, + 281 + ], + "type": "text", + "content": "Figure 3. Although EDGE is trained on 5-second clips, it can generate choreographies of any length by imposing temporal constraints on batches of sequences. In this example, EDGE constrains the first 2.5 seconds of each sequence to match the last 2.5 seconds of the previous one to generate a 12.5-second clip, as represented by the temporal regions of distinct clips in the batch that share the same color." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 292, + 545, + 398 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 292, + 545, + 398 + ], + "spans": [ + { + "bbox": [ + 304, + 292, + 545, + 398 + ], + "type": "text", + "content": "music conditioning projected to the transformer dimension with a cross-attention mechanism following Sahara et al. [50]. Timestep information, which is represented as a sinusoidal embedding [19], is incorporated both through a token concatenated with the music conditioning and feature-wise linear modulation (FiLM) layers [42]. In our model, FiLM layers are given an output from a previous layer " + }, + { + "bbox": [ + 304, + 292, + 545, + 398 + ], + "type": "inline_equation", + "content": "\\mathbf{Y}" + }, + { + "bbox": [ + 304, + 292, + 545, + 398 + ], + "type": "text", + "content": " and a timestep embedding " + }, + { + "bbox": [ + 304, + 292, + 545, + 398 + ], + "type": "inline_equation", + "content": "\\boldsymbol{e}_t" + }, + { + "bbox": [ + 304, + 292, + 545, + 398 + ], + "type": "text", + "content": ", and process the embeddings as:" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 351, + 415, + 545, + 429 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 351, + 415, + 545, + 429 + ], + "spans": [ + { + "bbox": [ + 351, + 415, + 545, + 429 + ], + "type": "interline_equation", + "content": "\\boldsymbol {W} = \\psi_ {w} (\\phi (\\boldsymbol {e} _ {t})), \\quad \\boldsymbol {B} = \\psi_ {b} (\\phi (\\boldsymbol {e} _ {t})) \\tag {9}", + "image_path": "31a995a8f9d7ceffa668066c0bb413e44589c00e26b31f45722c89e1d494e2a0.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 369, + 441, + 545, + 454 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 369, + 441, + 545, + 454 + ], + "spans": [ + { + "bbox": [ + 369, + 441, + 545, + 454 + ], + "type": "interline_equation", + "content": "\\operatorname {F i L M} (\\boldsymbol {Y}) = \\boldsymbol {W} \\odot \\boldsymbol {Y} + \\boldsymbol {B} \\tag {10}", + "image_path": "17ae3308d91c80181fff3692b8afdf956b5b0d1864714add4db7002e6eff633e.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 464, + 523, + 475 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 464, + 523, + 475 + ], + "spans": [ + { + "bbox": [ + 306, + 464, + 523, + 475 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 306, + 464, + 523, + 475 + ], + "type": "inline_equation", + "content": "\\psi_w,\\psi_w" + }, + { + "bbox": [ + 306, + 464, + 523, + 475 + ], + "type": "text", + "content": " , and " + }, + { + "bbox": [ + 306, + 464, + 523, + 475 + ], + "type": "inline_equation", + "content": "\\phi" + }, + { + "bbox": [ + 306, + 464, + 523, + 475 + ], + "type": "text", + "content": " are separate linear projections." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 497, + 545, + 592 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 497, + 545, + 592 + ], + "spans": [ + { + "bbox": [ + 304, + 497, + 545, + 592 + ], + "type": "text", + "content": "Music Audio Features Past work [1, 10, 23, 27, 31, 33, 45, 53, 59] has largely focused on advancing the generative modeling approach for the dance generation problem, with little focus on the representation of the music signal itself, which we argue is equally important. Indeed, state-of-the-art results in the text-to-image domain have found that scaling the text encoder is more important for performance than scaling the diffusion model [50]." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 594, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 594, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 594, + 545, + 713 + ], + "type": "text", + "content": "In this vein, recent work [3, 7] in music information retrieval has demonstrated that Jukebox [5], a large GPT-style model trained on 1M songs to generate raw music audio, contains representations that serve as strong features for music audio prediction tasks. We take inspiration from these advances and extract Jukebox features as the conditioning input for our diffusion model, and develop a new memory-efficient implementation that enables near real-time extraction on a single commodity GPU (see Appendix I for details)." + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 297, + 749, + 312, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 749, + 312, + 757 + ], + "spans": [ + { + "bbox": [ + 297, + 749, + 312, + 757 + ], + "type": "text", + "content": "451" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 52, + 79, + 284, + 297 + ], + "blocks": [ + { + "bbox": [ + 52, + 79, + 284, + 297 + ], + "lines": [ + { + "bbox": [ + 52, + 79, + 284, + 297 + ], + "spans": [ + { + "bbox": [ + 52, + 79, + 284, + 297 + ], + "type": "image", + "image_path": "a5295bd63756b00733529aee1d74ef9ccbb2a17f8074f15d35ea283502d7c1c6.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 319, + 287, + 397 + ], + "lines": [ + { + "bbox": [ + 46, + 319, + 287, + 397 + ], + "spans": [ + { + "bbox": [ + 46, + 319, + 287, + 397 + ], + "type": "text", + "content": "Figure 4. EDGE allows the user to specify both temporal and joint-wise constraints. Constraint joints / frames are highlighted in green and tan, generated joints / frames are in blue and gray. Pictured, top to bottom: dance completion from seed motion, dance that hits a specified keyframe mid-choreography, completion from specified upper-body joint angles, completion from specified lower-body joint angles and root trajectory." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 415, + 128, + 428 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 415, + 128, + 428 + ], + "spans": [ + { + "bbox": [ + 47, + 415, + 128, + 428 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 434, + 287, + 495 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 434, + 287, + 495 + ], + "spans": [ + { + "bbox": [ + 46, + 434, + 287, + 495 + ], + "type": "text", + "content": "Dataset In this work, we use AIST++ [33], a dataset consisting of 1,408 high-quality dance motions paired to music from a diverse set of genres. We re-use the train/test splits provided by the original dataset. All training examples are split into clips of 5 seconds at 30 FPS." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 499, + 287, + 534 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 499, + 287, + 534 + ], + "spans": [ + { + "bbox": [ + 47, + 499, + 287, + 534 + ], + "type": "text", + "content": "Baselines Among recent state-of-the-art dance generation methods [1, 10, 23, 27, 31, 33, 45, 53, 59], we select the following baselines:" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 58, + 540, + 286, + 595 + ], + "type": "list", + "angle": 0, + "index": 7, + "blocks": [ + { + "bbox": [ + 58, + 540, + 286, + 564 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 540, + 286, + 564 + ], + "spans": [ + { + "bbox": [ + 58, + 540, + 286, + 564 + ], + "type": "text", + "content": "- FACT [33], an autoregressive model introduced together with the AIST++ dataset, and" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 58, + 571, + 286, + 595 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 571, + 286, + 595 + ], + "spans": [ + { + "bbox": [ + 58, + 571, + 286, + 595 + ], + "type": "text", + "content": "- Bailando [53], a follow-up approach that achieves the strongest qualitative performance to date." + } + ] + } + ], + "index": 6 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 47, + 605, + 287, + 640 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 605, + 287, + 640 + ], + "spans": [ + { + "bbox": [ + 47, + 605, + 287, + 640 + ], + "type": "text", + "content": "Implementation details Our final model has 49M total parameters, and was trained on 4 NVIDIA A100 GPUs for 16 hours with a batch size of 512." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 642, + 287, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 642, + 287, + 712 + ], + "spans": [ + { + "bbox": [ + 46, + 642, + 287, + 712 + ], + "type": "text", + "content": "For long-form generation, we use 5-second slices and choose to enforce consistency for overlapping 2.5-second slices by interpolating between the two slices with linearly decaying weight. We find that this simple approach is sufficient to result in smooth, consistent generation, as demonstrated throughout our website. In our results, we perform" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 73, + 544, + 95 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 73, + 544, + 95 + ], + "spans": [ + { + "bbox": [ + 305, + 73, + 544, + 95 + ], + "type": "text", + "content": "no post-processing to correct foot contacts or physical plausibility, and show the model outputs directly." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 97, + 545, + 202 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 97, + 545, + 202 + ], + "spans": [ + { + "bbox": [ + 304, + 97, + 545, + 202 + ], + "type": "text", + "content": "We evaluate two separate feature extraction strategies. The \"baseline\" strategy uses the popular audio package librosa [37] to extract beats and accompanying audio features using the same code as in Li et al. [33] (when the ground truth BPM is not known, we estimate it with librosa). The \"Jukebox\" [5] extraction strategy follows Castellon et al. [3], extracting representations from Jukebox and downsampling to 30 FPS to match our frame rates for motion data." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 212, + 484, + 224 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 212, + 484, + 224 + ], + "spans": [ + { + "bbox": [ + 305, + 212, + 484, + 224 + ], + "type": "text", + "content": "4.1. Comparison to Existing Methods" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 231, + 545, + 278 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 231, + 545, + 278 + ], + "spans": [ + { + "bbox": [ + 304, + 231, + 545, + 278 + ], + "type": "text", + "content": "In this section, we compare our proposed model to several past works on (1) human evaluations, (2) our proposed physical plausibility metric, (3) beat alignment scores, (4) diversity, and (5) performance on in-the-wild music." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 285, + 545, + 344 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 285, + 545, + 344 + ], + "spans": [ + { + "bbox": [ + 304, + 285, + 545, + 344 + ], + "type": "text", + "content": "Human Evaluations To obtain the results in Tab. 1, we recruited 147 human raters who evaluated a total of 11,610 pairs of clips randomly sampled from our models, ground truth, baseline models, or a checkpoint from our model training (as seen in Sec. 4.3)." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 345, + 545, + 392 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 345, + 545, + 392 + ], + "spans": [ + { + "bbox": [ + 304, + 345, + 545, + 392 + ], + "type": "text", + "content": "The study reveals that human raters overwhelmingly prefer the dances generated by EDGE over previous methods, and even favor EDGE dances over real dances. For more information on the exact details of our study, see Appendix A." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 408, + 545, + 540 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 408, + 545, + 540 + ], + "spans": [ + { + "bbox": [ + 304, + 408, + 545, + 540 + ], + "type": "text", + "content": "Physical Plausibility Any generated dance should be physically plausible; otherwise, its downstream applicability is dramatically limited. Previous works evaluate plausibility of foot-ground contact by measuring foot sliding [17,56]; however, dance is unique in that sliding is not only common but integral to many choreographies. This reflects a need for a metric that can measure the realism of foot-ground contact that does not assume that feet should exhibit static contact at all times. In this work, we propose a new metric to evaluate physical plausibility, Physical Foot Contact score (PFC), that we believe captures this concept well." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 540, + 544, + 575 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 540, + 544, + 575 + ], + "spans": [ + { + "bbox": [ + 304, + 540, + 544, + 575 + ], + "type": "text", + "content": "PFC is a physically-inspired metric that requires no explicit physical modeling. Our metric arises from two simple, related observations:" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 313, + 585, + 545, + 667 + ], + "type": "list", + "angle": 0, + "index": 20, + "blocks": [ + { + "bbox": [ + 313, + 585, + 545, + 644 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 313, + 585, + 545, + 644 + ], + "spans": [ + { + "bbox": [ + 313, + 585, + 545, + 644 + ], + "type": "text", + "content": "1. On the horizontal (xy) plane, any center of mass (COM) acceleration must be due to static contact between the feet and the ground. Therefore, either at least one foot is stationary on the ground or the COM is not accelerating." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 313, + 645, + 545, + 667 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 313, + 645, + 545, + 667 + ], + "spans": [ + { + "bbox": [ + 313, + 645, + 545, + 667 + ], + "type": "text", + "content": "2. On the vertical (z) axis, any positive COM acceleration must be due to static foot contact." + } + ] + } + ], + "index": 19 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 304, + 677, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 545, + 712 + ], + "type": "text", + "content": "Therefore, we can represent adherence to these conditions as an average over time of the below expression, scaled to normalize acceleration:" + } + ] + } + ], + "index": 21 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 297, + 749, + 312, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 749, + 312, + 757 + ], + "spans": [ + { + "bbox": [ + 297, + 749, + 312, + 757 + ], + "type": "text", + "content": "452" + } + ] + } + ], + "index": 22 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 52, + 70, + 542, + 166 + ], + "blocks": [ + { + "bbox": [ + 52, + 70, + 542, + 166 + ], + "lines": [ + { + "bbox": [ + 52, + 70, + 542, + 166 + ], + "spans": [ + { + "bbox": [ + 52, + 70, + 542, + 166 + ], + "type": "table", + "html": "
MethodElo ↑EDGE Win RatePFC ↓Beat Align. ↑Distk →Distg →Fixed BonesEditing
EDGE (w = 2)1751N/A1.53630.269.485.72✓✓
EDGE (w = 1)160158.0% ± 3.8%1.65450.2710.587.62✓✓
Bailando139791.1% ± 5.9%1.7540.237.927.72✗✗
FACT132590.0% ± 7.0%2.25430.2210.856.14✓✗
Ground Truth165365.7% ± 11.1%1.3320.2410.617.48✓N/A
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Method (In-the-Wild)Elo ↑EDGE Win Rate
EDGE174753.8% ± 11.1%
w/o Jukebox160383.3% ± 8.3%
Bailando122282.4% ± 5.5%
FACT136789.3% ± 4.4%
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Our method operates in the reduced coordinate (joint angle) space, which guarantees fixed bone length. However, methods that operate in the joint Cartesian space, such as Bailando, can produce significantly varying bone lengths. For example, on average, bone lengths change up to " + }, + { + "bbox": [ + 46, + 587, + 287, + 683 + ], + "type": "inline_equation", + "content": "\\pm 20\\%" + }, + { + "bbox": [ + 46, + 587, + 287, + 683 + ], + "type": "text", + "content": " over the course of dance sequences generated by Bailando." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 689, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 689, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 689, + 288, + 715 + ], + "type": "text", + "content": "Beat Alignment Scores Our experiments evaluate the tendency of our generated dances to follow the beat of the" + } + ] + } + ], + "index": 11 + }, + { + "type": "table", + "bbox": [ + 332, + 258, + 520, + 320 + ], + "blocks": [ + { + "bbox": [ + 46, + 339, + 288, + 373 + ], + "lines": [ + { + "bbox": [ + 46, + 339, + 288, + 373 + ], + "spans": [ + { + "bbox": [ + 46, + 339, + 288, + 373 + ], + "type": "text", + "content": "Table 2. We test our model on in-the-wild music and ablate Jukebox features in this setting, showing that Jukebox features are critical for generalization." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 332, + 258, + 520, + 320 + ], + "lines": [ + { + "bbox": [ + 332, + 258, + 520, + 320 + ], + "spans": [ + { + "bbox": [ + 332, + 258, + 520, + 320 + ], + "type": "table", + "html": "
MethodEDGE Win RatePFC ↓
EDGEN/A1.5363
w/o CCL61.8% ± 7.3%3.0806
Ground Truth40.6% ± 7.4%1.332
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While EDGE wins more on average against ground truth on overall quality evaluation (Tab. 1), the user study for this table specifically asks about physical plausibility, and we find that ground truth still performs favorably compared to EDGE." + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 304, + 417, + 545, + 489 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 417, + 545, + 489 + ], + "spans": [ + { + "bbox": [ + 304, + 417, + 545, + 489 + ], + "type": "text", + "content": "music, following previous work [53] for the precise implementation of this metric. The results demonstrate that EDGE outperforms past work, including Bailando, which includes a reinforcement learning module that explicitly optimizes beat alignment. We further examine the robustness of this metric in Sec. 5." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 497, + 546, + 653 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 497, + 546, + 653 + ], + "spans": [ + { + "bbox": [ + 304, + 497, + 546, + 653 + ], + "type": "text", + "content": "Diversity Diversity metrics are computed following the methods of previous work [33, 53], which measure the distributional spread of generated dances in the \"kinetic\" " + }, + { + "bbox": [ + 304, + 497, + 546, + 653 + ], + "type": "inline_equation", + "content": "(\\mathrm{Dist}_k)" + }, + { + "bbox": [ + 304, + 497, + 546, + 653 + ], + "type": "text", + "content": " and \"geometric\" " + }, + { + "bbox": [ + 304, + 497, + 546, + 653 + ], + "type": "inline_equation", + "content": "(\\mathrm{Dist}_g)" + }, + { + "bbox": [ + 304, + 497, + 546, + 653 + ], + "type": "text", + "content": " feature spaces, as implemented by fairmotion [13, 39, 41]. We compute these metrics on 5-second dance clips produced by each approach. Given that the ultimate goal of dance generation is to automatically produce dances that emulate the ground truth distribution, we argue that models should aim to match the scores of the ground truth distribution rather than maximize their absolute values. Indeed, past work has found that jittery dances result in high diversity scores, in some cases exceeding the ground truth [32, 33]." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 654, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 654, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 654, + 547, + 715 + ], + "type": "text", + "content": "At low guidance weight " + }, + { + "bbox": [ + 304, + 654, + 547, + 715 + ], + "type": "inline_equation", + "content": "(w = 1)" + }, + { + "bbox": [ + 304, + 654, + 547, + 715 + ], + "type": "text", + "content": ", EDGE achieves a level of diversity that closely matches that of the ground truth distribution while attaining state-of-the-art qualitative performance. At high guidance weight " + }, + { + "bbox": [ + 304, + 654, + 547, + 715 + ], + "type": "inline_equation", + "content": "(w = 2)" + }, + { + "bbox": [ + 304, + 654, + 547, + 715 + ], + "type": "text", + "content": ", EDGE produces dances of markedly higher fidelity, reflected by a signifi" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 297, + 749, + 312, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 749, + 312, + 757 + ], + "spans": [ + { + "bbox": [ + 297, + 749, + 312, + 757 + ], + "type": "text", + "content": "453" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 49, + 70, + 285, + 204 + ], + "blocks": [ + { + "bbox": [ + 49, + 70, + 285, + 204 + ], + "lines": [ + { + "bbox": [ + 49, + 70, + 285, + 204 + ], + "spans": [ + { + "bbox": [ + 49, + 70, + 285, + 204 + ], + "type": "image", + "image_path": "e40c9eeda1b196ab29d9f3dce74241fc34528584185c31c90d6a3a804b9a82b5.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 213, + 287, + 247 + ], + "lines": [ + { + "bbox": [ + 46, + 213, + 287, + 247 + ], + "spans": [ + { + "bbox": [ + 46, + 213, + 287, + 247 + ], + "type": "text", + "content": "Figure 5. Temporal Conditioning: In-Betweening Given start (green) and end (red) poses, EDGE can generate in-between dance sequences." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 259, + 286, + 344 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 259, + 286, + 344 + ], + "spans": [ + { + "bbox": [ + 46, + 259, + 286, + 344 + ], + "type": "text", + "content": "cantly higher Elo rating, while trading off diversity. These results reflect those of past studies, which show that sampling using guidance weights " + }, + { + "bbox": [ + 46, + 259, + 286, + 344 + ], + "type": "inline_equation", + "content": "w > 1" + }, + { + "bbox": [ + 46, + 259, + 286, + 344 + ], + "type": "text", + "content": " significantly increases fidelity at the cost of diversity [20, 50]. This simple control over the diversity-fidelity tradeoff via the modulation of a single scalar parameter provides a powerful tool for downstream applications." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 352, + 173, + 364 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 352, + 173, + 364 + ], + "spans": [ + { + "bbox": [ + 47, + 352, + 173, + 364 + ], + "type": "text", + "content": "4.2. Additional Evaluation" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 371, + 286, + 443 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 371, + 286, + 443 + ], + "spans": [ + { + "bbox": [ + 46, + 371, + 286, + 443 + ], + "type": "text", + "content": "In-the-Wild Music While past approaches achieve strong results on AIST++, these results are not necessarily indicative of the models' ability to generalize to in-the-wild music inputs. In order to evaluate generalization, we tested our proposed method and the baseline approaches on a diverse selection of popular songs from YouTube." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 445, + 286, + 624 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 445, + 286, + 624 + ], + "spans": [ + { + "bbox": [ + 46, + 445, + 286, + 624 + ], + "type": "text", + "content": "The results, as shown in Tab. 2, demonstrate that our proposed method continues to perform well on in-the-wild music. We find through ablation that Jukebox features are critical for performance in this setting, bringing human-rated quality almost to par with in-distribution music; furthermore, we find that our approach continues to beat baselines in human evaluations for dance quality. We note that Bailando has an additional fine-tuning procedure available to improve performance on in-the-wild samples by training its actor-critic component. While we evaluated Bailando directly without additional fine-tuning, we found that human raters significantly preferred in-the-wild EDGE samples over in-distribution Bailando samples. We interpret these results as evidence that our proposed method is able to successfully generalize to in-the-wild music inputs." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 641, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 641, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 641, + 286, + 713 + ], + "type": "text", + "content": "Editing We find through an additional human evaluation that our model is capable of in-betweening, motion continuation, joint-conditioned generation, and long-form generation with quality on par with unconstrained samples. Please see our website for demo examples, and Appendix H for more details." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 72, + 545, + 216 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 216 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 216 + ], + "type": "text", + "content": "Contact Consistency Ablation We test the soundness of our PFC metric and ablate our Contact Consistency Loss (CCL) term (see Eq. (5)) using a human evaluation study. Raters were shown pairs of dances from the ground truth distribution, EDGE with CCL, and EDGE without CCL, and asked which dance looked more physically plausible. The results (Tab. 3) show that CCL noticeably improves both the PFC metric and qualitative physical plausibility user evaluations, winning " + }, + { + "bbox": [ + 304, + 72, + 545, + 216 + ], + "type": "inline_equation", + "content": "61.8\\%" + }, + { + "bbox": [ + 304, + 72, + 545, + 216 + ], + "type": "text", + "content": " of matchups against the version without CCL, and coming close to parity with ground truth samples. The results also indicate that PFC tracks well with human perception of physical plausibility." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 217, + 545, + 253 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 217, + 545, + 253 + ], + "spans": [ + { + "bbox": [ + 304, + 217, + 545, + 253 + ], + "type": "text", + "content": "For a discussion of limitations and implementation details of PFC, please see Sec. 5 and Appendix D, respectively." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 263, + 488, + 276 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 263, + 488, + 276 + ], + "spans": [ + { + "bbox": [ + 305, + 263, + 488, + 276 + ], + "type": "text", + "content": "4.3. Analysis of FID Metrics for Dance" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 283, + 545, + 403 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 283, + 545, + 403 + ], + "spans": [ + { + "bbox": [ + 304, + 283, + 545, + 403 + ], + "type": "text", + "content": "A reasonable solution to the problem of overall evaluation is to compute the difference between an empirical distribution of generated dances and a ground truth distribution. Several past works follow this intuition and automatically evaluate dance quality with Frechet Distance metrics [32, 33, 53]. As part of our experiments, we conduct a two-pronged analysis into the prevailing metrics, \"FID" + }, + { + "bbox": [ + 304, + 283, + 545, + 403 + ], + "type": "inline_equation", + "content": "_k" + }, + { + "bbox": [ + 304, + 283, + 545, + 403 + ], + "type": "text", + "content": " \" and \"FID" + }, + { + "bbox": [ + 304, + 283, + 545, + 403 + ], + "type": "inline_equation", + "content": "_g" + }, + { + "bbox": [ + 304, + 283, + 545, + 403 + ], + "type": "text", + "content": " \" [33], which compute the difference between distributions of heuristically extracted motion features, and show them to be unsound for the AIST++ dataset." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 414, + 545, + 558 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 414, + 545, + 558 + ], + "spans": [ + { + "bbox": [ + 304, + 414, + 545, + 558 + ], + "type": "text", + "content": "“" + }, + { + "bbox": [ + 304, + 414, + 545, + 558 + ], + "type": "inline_equation", + "content": "\\mathrm{FID}_g" + }, + { + "bbox": [ + 304, + 414, + 545, + 558 + ], + "type": "text", + "content": "” We compute " + }, + { + "bbox": [ + 304, + 414, + 545, + 558 + ], + "type": "inline_equation", + "content": "\\mathrm{FID}_g" + }, + { + "bbox": [ + 304, + 414, + 545, + 558 + ], + "type": "text", + "content": " on the ground truth AIST++ dataset following the implementation in Li et al. [33]. Specifically, we compute metrics on the test set against the training set and obtain a score of 41.4, a stark increase from metrics obtained from generated outputs: running on FACT outputs gives 12.75, running on Bailando outputs gives 24.82, and running on our final model's outputs gives 23.08. Given that FACT performs the best in “" + }, + { + "bbox": [ + 304, + 414, + 545, + 558 + ], + "type": "inline_equation", + "content": "\\mathrm{FID}_g" + }, + { + "bbox": [ + 304, + 414, + 545, + 558 + ], + "type": "text", + "content": "” but performs the worst according to user studies and that all three models perform significantly better than ground truth, we conclude that the “" + }, + { + "bbox": [ + 304, + 414, + 545, + 558 + ], + "type": "inline_equation", + "content": "\\mathrm{FID}_g" + }, + { + "bbox": [ + 304, + 414, + 545, + 558 + ], + "type": "text", + "content": "” values are unreliable as a measure of quality on this dataset." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 568, + 545, + 664 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 568, + 545, + 664 + ], + "spans": [ + { + "bbox": [ + 304, + 568, + 545, + 664 + ], + "type": "text", + "content": "\" " + }, + { + "bbox": [ + 304, + 568, + 545, + 664 + ], + "type": "inline_equation", + "content": "\\mathbf{FID}_k" + }, + { + "bbox": [ + 304, + 568, + 545, + 664 + ], + "type": "text", + "content": " \" We take 10 checkpoints throughout the training process for our model and poll raters on the overall quality of dances sampled from each checkpoint in a round-robin tournament. Intuitively, this should result in a consistent-to-monotonic improvement in both qualitative performance and in the quantitative quality metrics. However, we observe that this is not the case. In Fig. 6, we show the results of this experiment with our proposed model's " + }, + { + "bbox": [ + 304, + 568, + 545, + 664 + ], + "type": "inline_equation", + "content": "\\mathrm{FID}_k" + }, + { + "bbox": [ + 304, + 568, + 545, + 664 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "content": "While the qualitative performance of the generated motion improves considerably as we train the model, the " + }, + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathrm{FID}_k" + }, + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "content": " does not improve, and actually significantly worsens during the latter half of training." + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 297, + 748, + 312, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 748, + 312, + 757 + ], + "spans": [ + { + "bbox": [ + 297, + 748, + 312, + 757 + ], + "type": "text", + "content": "454" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 50, + 71, + 284, + 171 + ], + "blocks": [ + { + "bbox": [ + 50, + 71, + 284, + 171 + ], + "lines": [ + { + "bbox": [ + 50, + 71, + 284, + 171 + ], + "spans": [ + { + "bbox": [ + 50, + 71, + 284, + 171 + ], + "type": "image", + "image_path": "c3fc18ef65019a4cf216bead516406222c06ea52e6290821838f568e9cd3781c.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 182, + 287, + 205 + ], + "lines": [ + { + "bbox": [ + 46, + 182, + 287, + 205 + ], + "spans": [ + { + "bbox": [ + 46, + 182, + 287, + 205 + ], + "type": "text", + "content": "Figure 6. We plot " + }, + { + "bbox": [ + 46, + 182, + 287, + 205 + ], + "type": "inline_equation", + "content": "\\mathrm{FID}_k" + }, + { + "bbox": [ + 46, + 182, + 287, + 205 + ], + "type": "text", + "content": " over the course of model training and find that it is inconsistent with overall quality evaluations." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 215, + 222, + 229 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 215, + 222, + 229 + ], + "spans": [ + { + "bbox": [ + 47, + 215, + 222, + 229 + ], + "type": "text", + "content": "5. Limitations of Existing Metrics" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 236, + 287, + 308 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 236, + 287, + 308 + ], + "spans": [ + { + "bbox": [ + 46, + 236, + 287, + 308 + ], + "type": "text", + "content": "Developing automated metrics for the quality of generated dances is a fundamentally challenging undertaking, since the practice of dance is complex, subjective, and even culturally specific. In this section, we discuss our findings on the limitations in automated metrics for dance evaluation, including our proposed PFC metric." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 324, + 287, + 528 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 324, + 287, + 528 + ], + "spans": [ + { + "bbox": [ + 46, + 324, + 287, + 528 + ], + "type": "text", + "content": "Overall Quality Evaluation Our results suggest that despite the current standardized use of FIDs for evaluating dance generation models on the AIST++ dataset, these FID metrics, as they currently stand, are unreliable for measuring quality. One potential explanation may be that the AIST++ test set does not thoroughly cover the train distribution given its very small size. Additionally, due to data scarcity, both " + }, + { + "bbox": [ + 46, + 324, + 287, + 528 + ], + "type": "inline_equation", + "content": "\\mathrm{FID}_k" + }, + { + "bbox": [ + 46, + 324, + 287, + 528 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 324, + 287, + 528 + ], + "type": "inline_equation", + "content": "\\mathrm{FID}_g" + }, + { + "bbox": [ + 46, + 324, + 287, + 528 + ], + "type": "text", + "content": " depend on heuristic feature extractors that only compute superficial features of the data. By contrast, FID-based metrics in data-rich domains such as image generation (where FID originated) enjoy the use of learned feature extractors (e.g., pre-trained ImageNet models), which are known to directly extract semantically meaningful features [51]. Indeed, in the text-to-motion domain, where significantly more paired data is available [14], the standard feature extractors for FID-style metrics depend on deep contrastively learned models [58, 63]." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 529, + 287, + 612 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 529, + 287, + 612 + ], + "spans": [ + { + "bbox": [ + 46, + 529, + 287, + 612 + ], + "type": "text", + "content": "Our experiments suggest that the current FID metrics can be further improved for evaluating motion sequences. We believe that the idea of evaluating the difference between two featurized distributions of dance motions is not necessarily fundamentally flawed, but that more representative features could result in reliable automatic quality evaluations." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 628, + 286, + 700 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 628, + 286, + 700 + ], + "spans": [ + { + "bbox": [ + 46, + 628, + 286, + 700 + ], + "type": "text", + "content": "Beat Alignment Scoring Some automated metrics aim to capture one of the core aspects of a dance performance: its ability to \"follow the beat\" of the song. Previous work [33, 53] has proposed using a beat alignment metric that rewards kinematic beats (local minima of joint speed) which line up with music beats." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 59, + 701, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 701, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 59, + 701, + 286, + 713 + ], + "type": "text", + "content": "However, dance is not strictly about matching local min" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 72, + 545, + 192 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 192 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 192 + ], + "type": "text", + "content": "ima in joint speed to beats: instead, the beats of the music are a loose guide for timing, rhythm, and transitions between movements and dance steps. This discrepancy is reflected in our results: empirically, we observe that in addition to exceeding scores of competing baselines, our beat alignment scores exceed those of ground truth samples. This seems to suggest that while the metric has served to drive progress on this problem in the past, the metric loses its meaning when candidate examples reach quality on par with ground truth." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 205, + 545, + 397 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 205, + 545, + 397 + ], + "spans": [ + { + "bbox": [ + 304, + 205, + 545, + 397 + ], + "type": "text", + "content": "Physical Foot Contact In this work, we introduce PFC, Eq. (12), a physically-inspired metric that specifically targets the challenging issue of foot sliding. While PFC is intuitive, it is not without its limitations. In its current form, PFC assumes that the feet are the only joints that experience static contact. This means that PFC cannot be applied without modification to motions such as gymnastics routines, where a variable number of non-foot (e.g., hand) contacts are integral to their execution. We believe that a careful analysis of other contact points (e.g., hands in gymnastics) could provide an extension of PFC that is more widely applicable. Another issue is the assumption that the COM can be accelerated only by static contact: though rare, it is possible to decelerate the COM using friction during extended sliding (which is not present in AIST++.). For more analysis and discussion of PFC, see Appendix D." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 406, + 471, + 419 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 406, + 471, + 419 + ], + "spans": [ + { + "bbox": [ + 306, + 406, + 471, + 419 + ], + "type": "text", + "content": "6. Conclusion and Future Work" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 426, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 426, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 426, + 545, + 713 + ], + "type": "text", + "content": "In this work, we propose a diffusion-based model that generates realistic and long-form dance sequences conditioned on music. We evaluate our model on multiple automated metrics (including our proposed PFC) and a large user study, and find that it achieves state-of-the-art results on the AIST++ dataset and generalizes well to in-the-wild music inputs. Importantly, we demonstrate that our model admits powerful editing capabilities, allowing users to freely specify both temporal and joint-wise constraints. The introduction of editable dance generation provides multiple promising avenues for future work. Whereas our method is able to create arbitrarily long dance sequences via the chaining of locally consistent, shorter clips, it cannot generate choreographies with very-long-term dependencies. Future work may explore the use of non-uniform sampling patterns such as those implemented in Harvey et al. [16], or a variation of the frame in-between scheme used in Ho et al. [18]. Editability also opens the door to the generation of more complex choreographies, including multi-person and scene-aware dance forms. Joint-wise conditioning may also potentially be used to address the issue of self-penetrating motions, which are sometimes present in our results. We are excited to see the future that this new direction of editable dance generation will enable." + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 297, + 749, + 312, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 749, + 312, + 757 + ], + "spans": [ + { + "bbox": [ + 297, + 749, + 312, + 757 + ], + "type": "text", + "content": "455" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 107, + 84 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 107, + 84 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 107, + 84 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 92, + 288, + 714 + ], + "type": "list", + "angle": 0, + "index": 16, + "blocks": [ + { + "bbox": [ + 53, + 92, + 287, + 147 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 92, + 287, + 147 + ], + "spans": [ + { + "bbox": [ + 53, + 92, + 287, + 147 + ], + "type": "text", + "content": "[1] Ho Yin Au, Jie Chen, Junkun Jiang, and Yike Guo. 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In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 5745-5753, 2019. 2" + } + ] + } + ], + "index": 7 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 298, + 749, + 312, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 298, + 749, + 312, + 757 + ], + "spans": [ + { + "bbox": [ + 298, + 749, + 312, + 757 + ], + "type": "text", + "content": "458" + } + ] + } + ], + "index": 9 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 10 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/EDICT_ Exact Diffusion Inversion via Coupled Transformations/5ac781e1-0cfa-4238-8cf2-ceb66647f068_content_list.json b/2023/EDICT_ Exact Diffusion Inversion via Coupled Transformations/5ac781e1-0cfa-4238-8cf2-ceb66647f068_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..579e12619bc58b1af153db280d5600ad660a5a07 --- /dev/null +++ b/2023/EDICT_ Exact Diffusion Inversion via Coupled Transformations/5ac781e1-0cfa-4238-8cf2-ceb66647f068_content_list.json @@ -0,0 +1,1727 @@ +[ + { + "type": "text", + "text": "EDICT: Exact Diffusion Inversion via Coupled Transformations", + "text_level": 1, + "bbox": [ + 161, + 130, + 808, + 151 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Bram Wallace", + "bbox": [ + 215, + 181, + 330, + 196 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Salesforce Research", + "bbox": [ + 191, + 199, + 352, + 214 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "b.wallace@salesforce.com", + "bbox": [ + 181, + 219, + 361, + 232 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "AkashGokul", + "bbox": [ + 439, + 181, + 547, + 196 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Salesforce Research", + "bbox": [ + 413, + 199, + 573, + 214 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "agokul@salesforce.com", + "bbox": [ + 415, + 219, + 571, + 233 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Nikhil Naik", + "bbox": [ + 656, + 181, + 754, + 196 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Salesforce Research", + "bbox": [ + 625, + 199, + 787, + 214 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "nnaik@salesforce.com", + "bbox": [ + 627, + 219, + 779, + 232 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 268, + 313, + 284 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Finding an initial noise vector that produces an input image when fed into the diffusion process (known as inversion) is an important problem in denoising diffusion models (DDMs), with applications for real image editing. The standard approach for real image editing with inversion uses denoising diffusion implicit models (DDIMs [29]) to deterministically noise the image to the intermediate state along the path that the denoising would follow given the original conditioning. However, DDIM inversion for real images is unstable as it relies on local linearization assumptions, which result in the propagation of errors, leading to incorrect image reconstruction and loss of content. To alleviate these problems, we propose Exact Diffusion Inversion via Coupled Transformations (EDICT), an inversion method that draws inspiration from affine coupling layers. EDICT enables mathematically exact inversion of real and model-generated images by maintaining two coupled noise vectors which are used to invert each other in an alternating fashion. Using Stable Diffusion [25], a state-of-the-art latent diffusion model, we demonstrate that EDICT successfully reconstructs real images with high fidelity. On complex image datasets like MS-COCO, EDICT reconstruction significantly outperforms DDIM, improving the mean square error of reconstruction by a factor of two. Using noise vectors inverted from real images, EDICT enables a wide range of image edits—from local and global semantic edits to image stylization—while maintaining fidelity to the original image structure. EDICT requires no model training/finetuning, prompt tuning, or extra data and can be combined with any pretrained DDM.", + "bbox": [ + 76, + 300, + 472, + 753 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 782, + 209, + 799 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Using the iterative denoising diffusion principle, denoising diffusion models (DDMs) trained with web-scale data can generate highly realistic images conditioned on input text, layouts, and scene graphs [24, 25, 27]. After image generation, the next important application of DDMs being explored by the research community is that of im", + "bbox": [ + 75, + 809, + 470, + 901 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "age editing. Models such as DALL-E-2 [24] and Stable Diffusion [25] can perform inpainting, allowing users to edit images through manual annotation. Methods such as SDEdit [20] have demonstrated that both synthetic and real images can be edited using stroke or composite guidance via DDMs. However, the goal of holistic image editing tools that can edit any real/artificial image using purely text is still a field of active research.", + "bbox": [ + 496, + 268, + 893, + 390 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "The generative process of DDMs starts with an initial noise vector $(x_{T})$ and performs iterative denoising (typically with a guidance signal e.g. in the form of text-conditional denoising), ending with a realistic image sample $(x_0)$ . Reversing this generative process is key in solving this image editing problem for one family of approaches. Formally, this problem is known as \"inversion\" i.e., finding the initial noise vector that produces the input image when passed through the diffusion process.", + "bbox": [ + 496, + 393, + 893, + 531 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "A naive approach for inversion is to add Gaussian noise to the input image and perform a predefined number of diffusion steps, which typically results in significant distortions [7]. A more robust method is adapting Denoising Diffusion Implicit Models (DDIMs) [29]. Unlike the commonly used Denoising Diffusion Probabilistic Models (DDPMs) [9], the generative process in DDIMs is defined in a non-Markovian manner, which results in a deterministic denoising process. DDIM can also be used for inversion, deterministically noising an image to obtain the initial noise vector $(x_0 \\to x_T)$ .", + "bbox": [ + 496, + 534, + 895, + 700 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "DDIM inversion has been used for editing real images through text methods such as DDIBs [30] and Prompt-to-Prompt (P2P) image editing [7]. After DDIM inversion, P2P edits the original image by running the generative process from the noise vector and injecting conditioning information from a new text prompt through the cross-attention layers in the diffusion model, thus generating an edited image that maintains faithfulness to the original content while incorporating the edit. However, as noted in the original P2P work [7], the DDIM inversion is unstable in many cases—encoding from $x_0$ to $x_T$ and back often results in inexact reconstructions of the original image as in Fig. 2. These distortions limit the ability to perform significant ma", + "bbox": [ + 496, + 703, + 895, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "22532", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/059ae3ec808c9023739ec4f379fbccd17656068e96a090dd6aba6202bd853bf0.jpg", + "image_caption": [ + "Figure 1. EDICT enables complex real image edits, such as editing dog breeds. We highlight the fine-grain text preservation in the bottom row of examples, with the message remaining even as the dog undergoes dramatic transformations. More examples, including baseline comparisons for all image-breed pairs, are included in the Supplementary. All original images from the ImageNet 2012 validation set." + ], + "image_footnote": [], + "bbox": [ + 98, + 97, + 880, + 559 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "nipulations through text as increase in the corruption is correlated with the strength of the conditioning.", + "bbox": [ + 75, + 643, + 470, + 676 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To improve the inversion ability of DDMs and enable robust real image editing, we diagnose the problems in DDIM inversion, and offer a solution: Exact Diffusion Inversion via Coupled Transformations (EDICT). EDICT is a re-formulation of the DDIM process inspired by coupling layers in normalizing flow models [4, 5, 12] that allows for mathematically exact inversion. By maintaining two coupled noise vectors in the diffusion process, EDICT enables recovery of the original noise vector in the case of model-generated images; and for real imagery, initial noise vectors that are guaranteed to map to the original image when the EDICT generative process is run. While EDICT doubles the computation time of the diffusion process, it can be combined with any pretrained DDM model and does", + "bbox": [ + 75, + 688, + 472, + 902 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "not require any computationally-expensive model finetuning, prompt tuning, or multiple images.", + "bbox": [ + 498, + 643, + 890, + 676 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "For the standard generative process, EDICT approximates DDIM well, resulting in nearly identical generations given equal initial conditions. For real images, EDICT can recover a noise vector which yields an exact reconstruction when used as input to the generative process. Experiments with the COCO dataset [16] show that EDICT can recover complex image features such as detailed textures, thin objects, subtle reflections, faces, and text, while DDIM fails to do so consistently. Finally, using the initial noise vectors derived from a real image with EDICT, we can sample from a DDM and perform complex edits or transformations to real images using textual guidance. We show editing capabilities including local and global modifications of objects and background and object transformations (Fig. 1).", + "bbox": [ + 496, + 688, + 893, + 902 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "22533", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/9340c0f66c4c7d5c585f6eff50f62ece6b4153becc99d60ba8b226f539fa76ef.jpg", + "image_caption": [ + "Figure 2. While both unconditional and conditional DDIM [29] often fail to accurately reconstruct real images, leading to loss of global image structure and/or finer details, EDICT is able to almost perfectly reconstruct even complex scenes. Examples from ImageNet and COCO with 50 DDIM steps. Captions used only in DDIM Conditional reconstruction with a guidance scale of 3." + ], + "image_footnote": [], + "bbox": [ + 80, + 89, + 468, + 375 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 76, + 494, + 218, + 511 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Diffusion Models and Normalizing Flows: Denoising diffusion models (DDMs), drawing on nonequilibrium thermodynamics [28], have emerged at the forefront of image generation. Models such as GLIDE [22], DALLE-2 [24], Imagen (Video) [8, 27], Latent/Stable Diffusion [25], and eDiffi [1] all utilize concepts borrowed from thermodynamics to hallucinate an image from pure noise by training on intermediately noised images. While a commonly used sampling process in DDMs is the stochastic Denoising Diffusion Probabilistic Models (DDPMs) method [9], a deterministic sampling method was introduced in Denoising Diffusion Implicit Models (DDIM) [29]. Multi-step or higher-order methods that parallel DDIM have also been proposed [17, 19], including methods that aim to reducing the computational time for generation [13, 18]. Another class of generative models relevant to our work are normalizing flow models [4, 5, 12]. In these models, an invertible mapping is learned between a latent gaussian distribution and image space. The methods of invertibility, specifically coupling layers, are used as an inspiration for our method. Invertible neural networks have been studied in areas outside of normalizing flows as well. Neural ODEs [2] have many parallels with the diffusion process and can be inverted using a variety of ODE solvers.", + "bbox": [ + 75, + 521, + 468, + 883 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Editing in Diffusion Models: The seminal work in apply", + "bbox": [ + 76, + 885, + 468, + 901 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "ing DDMs to image editing is SDEdit [20] where coarse layouts are used to guide the generative process by nois-ing the layout to resemble an intermediately noised image. Prompt-to-Prompt [7] combines query-key pairs from one prompt with values from another in the attention layers of a DDM to enable prompt-guided image editing from intermediate latents obtained by sampler inversion [29, 31]. DiffEdit [3] edits real/synthetic images using automatically generated masks for regions of an input image that should be edited given a text query. Kwon et al. [14] introduce style and structure losses to guide the sampling process to enable text-guided image translation. CycleDiffusion [32] uses a deterministic DPM encoder to enable zero-shot image-to-image translation. Concurrent work [21] also stabilizes text-conditioned inversion, optimizing the null embedding $\\emptyset$ for consistency. While highly effective, the algorithmic exactness is not guaranteed and per-case optimization is required. Another set of methods [6, 11, 26] finetune the model with the target image and/or learn a new conditioning prompt to enable indirect image editing via sampling. EDICT, our proposed approach, does not require any specialized training/finetuning, and can be paired with any pretrained DDM.", + "bbox": [ + 496, + 90, + 890, + 424 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Background", + "text_level": 1, + "bbox": [ + 500, + 435, + 627, + 452 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Denoising Diffusion Models", + "text_level": 1, + "bbox": [ + 500, + 459, + 746, + 476 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "DDMs are trained on a simple denoising objective. A set of timesteps index a monotonic strictly increasing noisingschedule $\\{\\alpha_{t}\\}_{t = 0}^{T},\\alpha_{T} = 0,\\alpha_{0} = 1$ . Images (or autoencoded latents) $x\\in X$ are noised with draws $\\epsilon \\sim N(0,I)$ according to the noising schedule following the formula", + "bbox": [ + 496, + 483, + 890, + 559 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nx _ {t} = \\sqrt {\\alpha_ {t}} x + \\sqrt {1 - \\alpha_ {t}} \\epsilon \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 612, + 566, + 890, + 583 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The time-aware DDM $\\Theta$ is trained on the objective $MSE(\\Theta(x_{t}, t, C), \\epsilon)$ to predict the noise added to the original image where $C$ is a conditioning signal (typically in the form of a text embedding) with some probability of random assignment to the null conditioning $\\emptyset$ . To generate a novel image from a gaussian draw $\\epsilon_{T} \\sim N(0, I)$ , partial denoising is applied at each $t$ . The most common sampling scheme is that of DDIM [29] where intermediate steps are calculated as", + "bbox": [ + 496, + 590, + 890, + 727 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} x _ {t - 1} = \\sqrt {\\alpha_ {t - 1}} \\frac {x _ {t} - \\sqrt {1 - \\alpha_ {t}} \\Theta \\left(x _ {t} , t , C\\right)}{\\sqrt {\\alpha_ {t}}} \\tag {2} \\\\ + \\sqrt {1 - \\alpha_ {t - 1}} \\Theta (x _ {t}, t, C) \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 558, + 732, + 890, + 787 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In practice, for text-to-image models to hallucinate from random noise an $x_0$ that matches conditioning $C$ to desired levels, the model has to be biased more heavily towards generations aligned with $C$ . To do so, a pseudo-gradient $G \\cdot (\\Theta(x_t, t, C) - \\Theta(x_t, t, \\emptyset))$ is added to the unconditional prediction $\\Theta(x_t, t, \\emptyset)$ to up-weight the effect of conditioning, where $G$ is a weighting parameter, Substituting", + "bbox": [ + 496, + 794, + 890, + 901 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "22534", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "$\\Phi (x_{t},t,C,G) = \\Theta (x_{t},t,\\emptyset) + G\\cdot (\\Theta (x_{t},t,C) - \\Theta (x_{t},t,\\emptyset))$ into the prior equation for the $\\Theta$ term, we simplify the notation $\\Phi (x_{t},t,C,G)\\rightarrow \\epsilon (x_{t},t)$ and rewrite the previous equation as $x_{t - 1} = a_tx_t + b_t\\epsilon (x_t,t)$ where", + "bbox": [ + 76, + 90, + 468, + 151 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\na _ {t} = \\sqrt {\\alpha_ {t - 1} / \\alpha_ {t}} \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 132, + 160, + 468, + 179 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nb _ {t} = - \\sqrt {\\alpha_ {t - 1} \\left(1 - \\alpha_ {t}\\right) / \\alpha_ {t}} + \\sqrt {1 - \\alpha_ {t - 1}} \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 133, + 181, + 468, + 202 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. Denoising Diffusion Implicit Model (DDIM)", + "text_level": 1, + "bbox": [ + 76, + 209, + 449, + 224 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "As noted in DDIM [29], the above denoising process is approximately invertible; that is $x_{t}$ is approximately recoverable from $x_{t - 1}$", + "bbox": [ + 76, + 233, + 468, + 277 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nx _ {t} = \\frac {x _ {t - 1} - b _ {t} \\epsilon (x _ {t} , t)}{a _ {t}} \\approx \\frac {x _ {t - 1} - b _ {t} \\epsilon (x _ {t - 1} , t)}{a _ {t}} \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 116, + 286, + 468, + 319 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where the approximation is a linearization assumption that $\\epsilon(x_{t}, t) \\approx \\epsilon(x_{t-1}, t)$ (necessary due to the discrete nature of both computation and the underlying noise schedule). This corresponds with reversing the Euler integration which is a first-order ODE solver. More sophisticated solvers such as multi-step Euler [17] have been shown to stabilize the generative process, and correspondingly the deterministic inversion process, with fewer time steps. However, such methods are also approximations where the inversion accuracy ultimately relies on the strength of the linearization assumption and the reconstruction is not exactly equal. This assumption is largely accurate for unconditional DDIM generation, but the pseudo-gradient of classifier-free guidance $G \\cdot (\\Theta(x_{t}, t, C) - \\Theta(x_{t}, t, \\emptyset))$ is inconsistent across time steps as shown in the Supplementary.", + "bbox": [ + 75, + 325, + 468, + 551 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "While unconditional reconstructions have relatively insignificant errors (Fig. 2), conditional reconstructions are extremely distorted when noised to high levels. This phenomenon was noted in [7], where the guidance scale must be heavily downweighted in order for inversions on real-world images to be stable, thus limiting the strength of edits. Obtaining an $x_{t}$ from $x_{0}$ allows for the generative process to be run with novel conditioning. In SDEdit [20], this process is done stochastically to obtain broad sample diversity, at the cost of controllability and faithfulness to the original image contents. In contrast, the inverse DDIM process produces a unique $x_{t}$ from a single $x_{0}$ in a deterministic manner, yielding only one sample but enabling higher strength edits while preserving finer-grain structure and content.", + "bbox": [ + 75, + 551, + 468, + 763 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.3. Affine Coupling Layers", + "text_level": 1, + "bbox": [ + 76, + 772, + 292, + 787 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Affine Coupling Layers (ACL) are invertible neural network layers introduced in [4, 5] and used in other normalizing flow models such as Glow [12]. The layer input $z$ , is split into two equal-dimensional halves $z_{a}$ and $z_{b}$ . A modified version of $z_{a}$ is then calculated, according to:", + "bbox": [ + 76, + 795, + 468, + 871 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nz _ {a} ^ {\\prime} = \\Psi (z _ {b}) z _ {a} + \\psi (z _ {b}) \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 194, + 880, + 468, + 897 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/bb054b1b36b60322f620e1c82f637bdd28a47a010a6bf6d2281469fec8337a1c.jpg", + "image_caption": [ + "Figure 3. Information flow of EDICT. Denoising process (sampling) follows the arrows forwards, sampler inversion backwards. From $(x_{t},y_{t})$ , $(x_{t - 1},y_{t - 1})$ can be calculated while holding a single member of each sequence in memory at a time. All steps are invertible, so $(x_{t},y_{t})$ can be exactly recovered from $(x_{t - 1},y_{t - 1})$ , as opposed to current methods which compute an approximation." + ], + "image_footnote": [], + "bbox": [ + 549, + 87, + 807, + 152 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\Psi$ and $\\psi$ are neural networks. The layer output $z^{\\prime}$ is the concatenation of $z_{a}^{\\prime}$ and $z_{b}$ in accordance with the original splitting function. ACL can parameterize complex functions and $z$ can be exactly recovered given $z^{\\prime}$ :", + "bbox": [ + 498, + 273, + 890, + 334 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nz _ {a} = \\left(z _ {a} ^ {\\prime} - \\psi \\left(z _ {b}\\right)\\right) / \\Psi \\left(z _ {b}\\right) \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 607, + 340, + 890, + 358 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Noting the similarity of equations 6 and 7 to the simplified form of Eq. (2), we parallel this construction in our method (described next) where two separate quantities are tracked and alternately modified by transformations that are affine with respect to the original modified quantity and a nonlinear transformation of its counterpart.", + "bbox": [ + 498, + 364, + 890, + 455 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4. Exact Diffusion Inversion via Coupled Transformations (EDICT)", + "text_level": 1, + "bbox": [ + 500, + 468, + 890, + 502 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4.1. Making an Invertible Diffusion Process", + "text_level": 1, + "bbox": [ + 500, + 510, + 834, + 526 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "As summarized in Sec. 3.3, affine coupling layers track two quantities which can then be used to invert each other. These two quantities are partitions of a latent representation with a network specifically designed to operate in a fitting alternating manner. Without training of a new DDM, this method can not be applied out-of-the-box to the forward diffusion process. We consider the simplified form of the forward step equation from Sec. 3.1 below", + "bbox": [ + 498, + 534, + 890, + 655 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nx _ {t - 1} := a _ {t} x _ {t} + b _ {t} \\epsilon \\left(x _ {t}, t\\right) \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 607, + 664, + 890, + 679 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "If the noise prediction term, $\\epsilon (x_{t},t) = \\varepsilon$ was independent of $x_{t}$ , this would be an affine function in both $x_{t}$ , and $\\varepsilon$ . Paralleling Eq. (6), by creating a new variable $y_{t} = x_{t}$ the stepping equation fits the desired form. Consider performing this computation, so we have the variables $x_{t}$ , $y_{t} = x_{t}$ , $x_{t - 1} = a_{t}x_{t} + b_{t}\\epsilon (y_{t},t)$ . $x_{t}$ can be recovered exactly from $x_{t - 1}$ in the non-trivial form:", + "bbox": [ + 498, + 686, + 890, + 792 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nx _ {t} = \\left(x _ {t - 1} - b _ {t} \\cdot \\epsilon \\left(y _ {t}, t\\right)\\right) / a _ {t} \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 594, + 801, + 890, + 816 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "$y_{t} = x_{t}$ is trivial and will not be true in the general case. Now consider the initialization of the reverse (denoising) diffusion process, where $x_{T} \\sim \\mathcal{N}(0,1)$ , we similarly initialize $y_{T} = x_{T}$ . Following the above process, we define the update rule", + "bbox": [ + 498, + 825, + 890, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "22535", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/90b3298bfd76d45f2823ab8e44b5b7d233eded607230e45731119768d302ef7f.jpg", + "image_caption": [ + "Figure 4. Images generated from the same text prompt and random seed. EDICT $x / y$ (No mixing) employs coupling layers but not intermediate mixing layers, resulting in distorted and inconsistent images as $x$ and $y$ diverge. EDICT is our full method with the sequences explicitly contracted together, resulting in identical images that match DDIM (Baseline) in quality and composition. Top row prompt: A white horse galloping through a forest Bottom row prompt: A couple of glasses are sitting on a table" + ], + "image_footnote": [], + "bbox": [ + 81, + 87, + 467, + 227 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nx _ {t - 1} = a _ {t} x _ {t} + b _ {t} \\cdot \\epsilon \\left(y _ {t}, t\\right) \\tag {10}\n$$\n", + "text_format": "latex", + "bbox": [ + 189, + 366, + 468, + 388 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\ny _ {t - 1} = a _ {t} y _ {t} + b _ {t} \\cdot \\epsilon \\left(x _ {t - 1}, t\\right)\n$$\n", + "text_format": "latex", + "bbox": [ + 176, + 386, + 369, + 401 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Note that the noise prediction term in the second line is a function of the other sequence value at the next timestep. Only one member of each sequence $(x_{t},y_{t(\\pm 1)})$ must be held in memory at any given time. The sequences can be recovered exactly according to", + "bbox": [ + 75, + 406, + 468, + 481 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\ny _ {t} = \\left(y _ {t - 1} - b _ {t} \\cdot \\epsilon \\left(x _ {t - 1}, t\\right)\\right) / a _ {t} \\tag {11}\n$$\n", + "text_format": "latex", + "bbox": [ + 163, + 482, + 468, + 506 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nx _ {t} = \\left(x _ {t - 1} - b _ {t} \\cdot \\epsilon \\left(y _ {t}, t\\right)\\right) / a _ {t}\n$$\n", + "text_format": "latex", + "bbox": [ + 181, + 502, + 380, + 517 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "As illustrated in Fig. 3, the entire sequence can be reconstructed from any two adjacent $x_{i}$ and $y_{i}$ . In sum, our method reuses the linearization assumption of Euler DDIM inversion, that $\\epsilon(x_{t}, t) \\approx \\epsilon(x_{t-1}, t)$ , but crucially does not rely on it for invertibility, guaranteeing recovery up to machine precision. We note that the functional form of our approach bears similarities to the ODE solver Heun's method where derivative values at initial predictions are used to refine predictions, but due to the need for invertibility we cannot exploit this for more accurate/faster sampling.", + "bbox": [ + 75, + 523, + 468, + 675 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.2. Stabilization", + "text_level": 1, + "bbox": [ + 76, + 681, + 210, + 696 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "While our method assures invertibility by design, realism and faithfulness to the original diffusion process are not automatic. When naively applied for a typical, low number of DDIM steps (e.g., $T = 50$ ), the sequences $x_{t}$ and $y_{t}$ can diverge (Fig. 4). This is a result of the strong linearization assumption not holding in practice. To alleviate this problem, we introduce intermediate mixing layers after each diffusion step computing weighted averages of the form", + "bbox": [ + 75, + 704, + 468, + 825 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nx ^ {\\prime} = p x + (1 - p) y, 0 \\leq p \\leq 1 \\tag {12}\n$$\n", + "text_format": "latex", + "bbox": [ + 163, + 832, + 468, + 849 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "which are invertible affine transformations. Note that this averaging layer becomes a dilating layer during deterministic noising; the inversion being", + "bbox": [ + 75, + 854, + 468, + 901 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/5f3652f90e3e40046e8328cdd26066256f89842732702c5d7a098b7362d2e236.jpg", + "image_caption": [ + "Figure 5. We visualize the effect of the mixing coefficient $p$ . Top row: an EDICT-generated image with $p = 0.93$ , for each listed $p$ a generation is computed from $T = 50$ to $T = 0$ followed by reconstructing initial latents $(T = 50)$ . Cosine similarity between $(x_{t}, y_{t})$ is computed at each step. $p = 0.97$ suffices for generative convergence, but the inverse process diverges when $p$ is too small. Repeated dilation can exponentially exaggerate small floating-point differences, annulling the theoretical guarantee. These trends hold in the bottom row for a non-generated image put through the EDICT inversion/generation process. While all reconstructions ultimately are aligned, a sufficiently large $p$ is needed for the latents to maintain alignment throughout." + ], + "image_footnote": [], + "bbox": [ + 501, + 88, + 885, + 333 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nx = \\frac {x ^ {\\prime} - (1 - p) y}{p} \\tag {13}\n$$\n", + "text_format": "latex", + "bbox": [ + 629, + 530, + 890, + 564 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "A high (near 1) value of $p$ results in the averaging layer not being strong enough to prevent divergence of the $x$ and $y$ series during denoising, while a low value of $p$ results in a numerically unstable exponential dilation in the backwards pass (Fig. 5). Note that in both cases that our generative process remains exactly mathematically invertible with no further assumptions, but there is a degradation in utility of the results. Typically we employ $p = 0.93$ , with values in the interval [0.9, 0.97] generally being effective for 50 steps.", + "bbox": [ + 496, + 568, + 890, + 705 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.3. Complete Summary of the Method", + "text_level": 1, + "bbox": [ + 500, + 710, + 803, + 728 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We dub our presented process EDICT: Exact Diffusion Inversion via Coupled Transformations. In sum, EDICT uses a combination of \"coupling\" and \"averaging/dilating\" steps for exact inversion of the diffusion process. Given $x_{t}$ and $y_{t}$ , we calculate the denoising process by", + "bbox": [ + 496, + 734, + 890, + 811 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nx _ {t} ^ {\\text {i n t e r}} = a _ {t} \\cdot x _ {t} + b _ {t} \\cdot \\epsilon (y _ {t}, t)\n$$\n", + "text_format": "latex", + "bbox": [ + 570, + 816, + 769, + 835 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\ny _ {t} ^ {\\text {i n t e r}} = a _ {t} \\cdot y _ {t} + b _ {t} \\cdot \\epsilon \\left(x _ {t} ^ {\\text {i n t e r}}, t\\right) \\tag {14}\n$$\n", + "text_format": "latex", + "bbox": [ + 571, + 838, + 890, + 863 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nx _ {t - 1} = p \\cdot x _ {t} ^ {\\text {i n t e r}} + (1 - p) \\cdot y _ {t} ^ {\\text {i n t e r}}\n$$\n", + "text_format": "latex", + "bbox": [ + 581, + 859, + 820, + 877 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\ny _ {t - 1} = p \\cdot y _ {t} ^ {\\text {i n t e r}} + (1 - p) \\cdot x _ {t - 1}\n$$\n", + "text_format": "latex", + "bbox": [ + 581, + 880, + 810, + 897 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "22536", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/16499592b34a18af3a3a6ce514b8300f45648af186de8d96ae8f483555e23997.jpg", + "table_caption": [ + "COCO Reconstruction Error (MSE)" + ], + "table_footnote": [], + "table_body": "
MethodLDM AEEDICT (UC)EDICT (C)DDIM (UC)DDIM (C)
50 Steps0.0150.0150.0150.0300.420
100 Steps0.0150.0150.0150.0270.471
200 Steps0.0150.0150.0150.0230.497
", + "bbox": [ + 81, + 102, + 465, + 184 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 1. Mean-square reconstruction error for COCO-val using the first listed prompt as conditioning with $G = 7$ . The latent diffusion model autoencoder (LDM AE) is the lower bound on reconstruction error. Using half precision increases 50-step EDICT (C) MSE by $6\\%$ . More step values are in the Supplementary.", + "bbox": [ + 75, + 194, + 468, + 265 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "and the deterministic noising inversion process by:", + "bbox": [ + 76, + 287, + 413, + 303 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\ny _ {t + 1} ^ {i n t e r} = \\left(y _ {t} - (1 - p) \\cdot x _ {t}\\right) / p\n$$\n", + "text_format": "latex", + "bbox": [ + 99, + 309, + 305, + 327 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\nx _ {t + 1} ^ {\\text {i n t e r}} = \\left(x _ {t} - (1 - p) \\cdot y _ {t + 1} ^ {\\text {i n t e r}}\\right) / p \\tag {15}\n$$\n", + "text_format": "latex", + "bbox": [ + 99, + 329, + 468, + 354 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\ny _ {t + 1} = \\left(y _ {t + 1} ^ {\\text {i n t e r}} - b _ {t + 1} \\cdot \\epsilon \\left(x _ {t + 1} ^ {\\text {i n t e r}}, t + 1\\right)\\right) / a _ {t + 1}\n$$\n", + "text_format": "latex", + "bbox": [ + 109, + 349, + 418, + 368 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\nx _ {t + 1} = \\left(x _ {t + 1} ^ {\\text {i n t e r}} - b _ {t + 1} \\cdot \\epsilon \\left(y _ {t + 1}, t + 1\\right)\\right) / a _ {t + 1}\n$$\n", + "text_format": "latex", + "bbox": [ + 109, + 371, + 408, + 388 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Recall that the conditioning $C$ is implicitly included in the $\\epsilon$ terms. In practice, we alternate the order in which the $x$ and $y$ series are calculated at each step in order to symmetrize the process with respect to both sequences. We cast all operations to double floating point precision (from the native half precision) to mitigate roundoff floating point errors.", + "bbox": [ + 75, + 393, + 468, + 484 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.4. Image Editing", + "text_level": 1, + "bbox": [ + 76, + 493, + 225, + 508 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "While EDICT can theoretically operate on either pixel-based or latent-diffusion models we present the latter case in this work. Given an image $I$ , we edit the semantic contents to match text conditioning $C_{target}$ . We describe the current content by text $C_{base}$ in a parallel manner to $C_{target}$ . We compute an autoencoder latent $x_0 = VAE_{enc}(I)$ , initializing $y_0 = x_0$ . We run the deterministic noising process of Eq. (15) on $(x_0, y_0)$ using text conditioning $C_{base}$ for $s \\cdot S$ steps, where $S$ is the number of global timesteps and $s$ is a chosen editing strength. This yields partially \"noised\" latents $(x_t, y_t)$ which are not necessarily equal and, in practice, tend to diverge by a small amount due to linearization error and the dilation of the mixing layers. These intermediate representations are then used as input to Eq. (14) using text condition $C_{target}$ , and identical step parameters, $(s, S)$ . The resulting image outputs $(VAE_{dec}(x_0^{edit}), VAE_{dec}(y_0^{edit}))$ are empirically nearly identical as seen in Fig. 4, this is by design of the method and in particular, the mixing layers. For all methods we find that a guidance scale of 3 performs well (as opposed to the standard 7.5 for generation).", + "bbox": [ + 75, + 516, + 472, + 834 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5. Experiments", + "text_level": 1, + "bbox": [ + 76, + 845, + 209, + 862 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We now describe results using the Stable Diffusion 1.4 latent diffusion model [25].", + "bbox": [ + 76, + 869, + 468, + 901 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5.1. Image Reconstruction", + "text_level": 1, + "bbox": [ + 500, + 90, + 705, + 106 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We demonstrate the exact invertibility of EDICT using the MS-COCO-2017 validation set $(n = 5,000)$ , which contains both simple object-centric images and complex scene images [16]. Given an image-caption pair, inverted latents are calculated and used to reconstruct the image. Mean-square error is calculated on pixels normalized to $[-1,1]$ and averaged across all images in the dataset. This process is performed both with and without the text as conditioning (C vs. UC). For COCO, we use the first listed prompt as conditioning. The LDM autoencoder reconstruction error serves as a lower bound. EDICT maintains complete latent recovery in all examples for both 50 and 200 steps, with error $50 - 75\\%$ that of DDIM (UC) (Tab. 1). DDIM (C) is unstable for inversions (also noted in [7]), which results in an error an order of magnitude greater than any other, with failure to reconstruct as shown in Fig. 2.", + "bbox": [ + 496, + 113, + 893, + 354 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5.2. Image Editing", + "text_level": 1, + "bbox": [ + 500, + 363, + 648, + 380 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We show EDICT's ability to perform complex editing tasks on real images in Fig. 6. In the first row, a diverse set of objects are added to a lake scene, demonstrating object addition. In the giraffe and car examples, we see interaction between introduced and original objects. Additionally, both the giraffe and castle examples capture reflections of the added objects, while the pattern of the water is maintained. Throughout all edits, details such as the cloud patterns and patches of tree color are preserved. The second row shows object-preserving global changes. A chair is placed into a variety of settings while keeping near-perfect identity and detail, even when occlusions are generated (grass and snow). In all examples the chair keeps a realistic footing, despite ground changes.", + "bbox": [ + 496, + 387, + 890, + 598 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "In the third row, we demonstrate that EDICT is able to perform object deformations, a challenging class of edits for DDM methods, as many broad compositional components are determined very early in the generation [7]. The previously most successful method for these types of edits, Imagic [11] requires model finetuning. EDICT makes the sculpture assume a broad set of poses, spatially changing the semantic map in a refined way. Novel views, such as \"A statue from behind\" are able to be plausibly rendered Across these large-scale edits, fine-grained details such as the face and dress of the statue -as well as the foliage and path- are preserved. In the fourth row, we show that EDICT is able to perform global style changes while maintaining layout and details where appropriate. The layout is nearly identical across images (note the preserved cloud pattern), but can be changed when needed (e.g., the lack of trees in the Mars example). Specific art-styles are capable of being generated, including challenging concepts such as cubism.", + "bbox": [ + 496, + 598, + 892, + 869 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "In Fig. 1, EDICT makes semantic entity edits to and from a variety of dog breeds. It proves adept at holding the", + "bbox": [ + 498, + 869, + 890, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "22537", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/b2409047b8de2f4cb1ec6918e40e59eb8fe51be5553ccc7fdb526fb2be9b1884.jpg", + "image_caption": [ + "Real Image" + ], + "image_footnote": [], + "bbox": [ + 80, + 103, + 232, + 222 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/d6d8dbc9d8a262a0c5812b885f9f4abe6ecb53d229430c244e441a1f5287b7bd.jpg", + "image_caption": [ + "Edited Images", + "\"A giraffe in .." + ], + "image_footnote": [], + "bbox": [ + 245, + 104, + 397, + 222 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/ea1716688dc97f43dfaaff378a2c6f8445ba4441c6d4b260518ceac0a204e393.jpg", + "image_caption": [ + "\"A car stuck in...\"" + ], + "image_footnote": [], + "bbox": [ + 408, + 104, + 562, + 222 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/6a0fc9d130bda7624ae74d33de851f59601f914daaca643a1b2933a304ebe81e.jpg", + "image_caption": [ + "\"A castle overlooking .." + ], + "image_footnote": [], + "bbox": [ + 573, + 104, + 727, + 222 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/61abb83360787d974e7c87ef3f177970f85c41158c82b1e78a487b2eeb231639.jpg", + "image_caption": [ + "\"A fountain in...\"" + ], + "image_footnote": [], + "bbox": [ + 738, + 104, + 890, + 222 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/75d6fd8c098299e82e2818da9bd0443f1ea3ae710ed49da83bb38bcf45e0b003.jpg", + "image_caption": [ + "\"A lake\"", + "\"A red chair\"" + ], + "image_footnote": [], + "bbox": [ + 81, + 238, + 232, + 357 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/80bab42ac80fdca000489be65dc54ccb6dc55fa8e58260463a8ee38fd8cbb6e2.jpg", + "image_caption": [ + "\"at the Grand Canyon\"" + ], + "image_footnote": [], + "bbox": [ + 245, + 238, + 397, + 358 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/33acbf351fcd47b4a8c08add040c67c01e4b85be6824235e0f7ed45c0785fd9e.jpg", + "image_caption": [ + "\".. on a field of grass\"" + ], + "image_footnote": [], + "bbox": [ + 408, + 238, + 562, + 358 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/ea5b3e74d3fe94ed0d7911e260b372ffd5263261d43e3dd0adb285764e2928f6.jpg", + "image_caption": [ + ".. covered in snow in the mountains" + ], + "image_footnote": [], + "bbox": [ + 573, + 238, + 727, + 358 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/da476fa9f80cc9c9bb6ffbea16fa0611676d1073cad2adb4e8046d8b0d5ccd25.jpg", + "image_caption": [ + "..after a flood" + ], + "image_footnote": [], + "bbox": [ + 738, + 239, + 890, + 358 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/e85b879fd1e6a6050c200b9be662879acdbeb8710c74815594948272fa26aa13.jpg", + "image_caption": [ + "\"A statue\"" + ], + "image_footnote": [], + "bbox": [ + 80, + 383, + 232, + 501 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/44b48845a1fa1f3232ac38876cb8fcbcdd25d82e3050fc3dc99a7314e10c88aa.jpg", + "image_caption": [ + "..with raised arms" + ], + "image_footnote": [], + "bbox": [ + 245, + 383, + 397, + 501 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/9871c42437f0c2c1a9b591147fa3067d712c88bd21c9a35a4ed81386bfd4000f.jpg", + "image_caption": [ + "walking" + ], + "image_footnote": [], + "bbox": [ + 410, + 383, + 562, + 501 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/367b3d1d0387c6e4414787034b1680a806895ec9dec6eee540bb58824627ff91.jpg", + "image_caption": [ + "\".. from behind" + ], + "image_footnote": [], + "bbox": [ + 575, + 383, + 727, + 501 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/af38b4d0c7173e07cad29f19391cec846b59971bd4fac87d6ad21be2f4a0ff43.jpg", + "image_caption": [ + "\".. standing alone giving a thumbs-up\"" + ], + "image_footnote": [], + "bbox": [ + 738, + 383, + 890, + 501 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/cd015e724d6ce017c72aa73ff47fc70bf25e645f89c19e10f50d6d9ab1531e64.jpg", + "image_caption": [ + "\"A waterfall in the mountains\"", + "Figure 6. Examples of the strength and varied editing ability of EDICT. From top to bottom: object additions, global context changes with object preservation, deformations while preserving identity, and global style changes. The bidirectional reversibility of EDICT's process allows for large-scale changes to the image while maintaining auxiliary details." + ], + "image_footnote": [], + "bbox": [ + 80, + 527, + 232, + 648 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/1825ecf54775b7a8e0d5cd11512d7dbbbf77b52e90fc44a5db67446469c843ac.jpg", + "image_caption": [ + "\"A cubist painting of .." + ], + "image_footnote": [], + "bbox": [ + 245, + 527, + 397, + 648 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/e66e95a17b3b1382d613daf794810ca14bbc12fa5667462591db7fdfa96c8634.jpg", + "image_caption": [ + "\"An impressionistic painting of .." + ], + "image_footnote": [], + "bbox": [ + 410, + 527, + 562, + 648 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/5081d8e63440fe7b2d89eb4d6eaf19b043ea6fda6a26019f9de8cd909404a5e0.jpg", + "image_caption": [ + "\".. in the fall" + ], + "image_footnote": [], + "bbox": [ + 575, + 527, + 727, + 648 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/b027898018a085a89edc982bf76e94f5d1f0a1db0b0afb9a2c44ae5ed275bd95.jpg", + "image_caption": [ + "\".. on Mars\"" + ], + "image_footnote": [], + "bbox": [ + 738, + 527, + 890, + 648 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "original subject pose, including in the third row where the dog is viewed in a very atypical position. The realism in the Chihuahua examples is particularly interesting, due to the relatively small size of the breed. We again highlight the preservation of details such as the background foliage or ground in the upper three rows. The fourth row is of specific interest as small text is preserved across examples (a typical failure case for DDIM).", + "bbox": [ + 75, + 750, + 472, + 872 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Baseline Comparison: In Fig. 7, we demonstrate EDICT's superior performance to other DDM sampling-based methods for image editing: conditional and unconditional DDIM inversion, prompt-to-prompt image editing, and SDEdit (as a stochastic baseline). All methods are run with 50 steps (we do not observe improvement of baselines when the number of steps are increased, see Supplementary). Since methods that require model finetuning or prompt tuning [6, 11, 26] can be combined with EDICT, we view them", + "bbox": [ + 496, + 750, + 893, + 887 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "22538", + "bbox": [ + 478, + 945, + 517, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/c95eb20135da6785b55fe2325f18089f68ed3c50aea15ba8e59e01d7ef42250c.jpg", + "image_caption": [ + "Figure 7. EDICT compared to baseline editing methods. EDICT demonstrates superior preservation of unedited components while still performing the edit edit. Further comparison between EDICT and baselines (including concurrent work ([14,32]) is in the Supplementary." + ], + "image_footnote": [], + "bbox": [ + 80, + 88, + 866, + 415 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "as complementary to, rather than competitive with, EDICT, and do not perform a direct comparison with them. We quantitatively compare visual metrics of edits in Fig. 8.", + "bbox": [ + 75, + 481, + 470, + 527 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "6. Discussion", + "text_level": 1, + "bbox": [ + 76, + 542, + 191, + 556 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Limitations and Future Work: EDICT is deterministic, only outputs one generation per image-prompt pair (vs. SDEdit). Also, the computational time is approximately twice that of baseline DDIM. As with all editing methods, performance can vary across inputs in a hard-to-predict manner and sometimes requires careful prompt selection. For future work, we note that the induced latent space constructed by the inversion process admits operations such as latent interpolation [10] which has not been widely applied to real images. As in prompt tuning [15], formalizing the process of prompt selection could further improve EDICT. Adding a controllable degree of randomness to EDICT could yield multiple candidate generations per input.", + "bbox": [ + 75, + 568, + 468, + 763 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Ethics: Like other image generation and editing models, EDICT will produce images that may reflect the socioeconomic biases of the training data or images that could be considered inappropriate. Image editing methods can also utilized for malicious purposes, including harassment and misinformation spread. Practitioners utilizing EDICT or its methodologies in a production setting should consider these limitations. An in-depth discussion on the ethics of image generation can be found in Imagen [27].", + "bbox": [ + 75, + 763, + 470, + 902 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/40d2877efabc602fe0fe62095caf8e99ed47caf750a546fd8b2e642244b6ecc5.jpg", + "image_caption": [ + "Figure 8. We quantitatively benchmark all methods on image editing using images from five ImageNet mammal classes (African Elephant, Ram, Egyptian Cat, Brown Bear, and Norfolk Terrier). Four experiments are performed, one swapping the pictured animal's species to each of the other classes (20 species editing pairs in total), two contextual changes (A [animal] in the snow and A [animal] in a parking lot), and one stylistic (An impressionistic painting of a [animal]). The LPIPS [33] (visual similarity) score to the original image and a CLIP score [23] (semantic similarity) to a set of five related text queries is computed per edit. Metrics are averaged across images and experiments. Details and human evaluation are provided in the Supplementary. We sweep across the fraction of inverted steps (overlaid in black on top of gray EDICT bubbles), observing that EDICT forms a Pareto frontier." + ], + "image_footnote": [], + "bbox": [ + 526, + 484, + 867, + 642 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "22539", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Yogesh Balaji, Seungjun Nah, Xun Huang, Arash Vahdat, Jiaming Song, Karsten Kreis, Miika Aittala, Timo Aila, Samuli Laine, Bryan Catanzaro, et al. edifi: Text-to-image diffusion models with an ensemble of expert denoisers. arXiv preprint arXiv:2211.01324, 2022. 3", + "[2] Ricky TQ Chen, Yulia Rubanova, Jesse Bettencourt, and David K Duvenaud. Neural ordinary differential equations. 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In CVPR, 2018. 8" + ], + "bbox": [ + 78, + 90, + 468, + 318 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "22541", + "bbox": [ + 478, + 945, + 517, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/EDICT_ Exact Diffusion Inversion via Coupled Transformations/5ac781e1-0cfa-4238-8cf2-ceb66647f068_model.json b/2023/EDICT_ Exact Diffusion Inversion via Coupled Transformations/5ac781e1-0cfa-4238-8cf2-ceb66647f068_model.json new file mode 100644 index 0000000000000000000000000000000000000000..446cf6cbe4e6ed85c4aadfeb4aa274bf1b438dbd --- /dev/null +++ b/2023/EDICT_ Exact Diffusion Inversion via Coupled Transformations/5ac781e1-0cfa-4238-8cf2-ceb66647f068_model.json @@ -0,0 +1,2255 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.163, + 0.131, + 0.809, + 0.152 + ], + "angle": 0, + "content": "EDICT: Exact Diffusion Inversion via Coupled Transformations" + }, + { + "type": "text", + "bbox": [ + 0.216, + 0.182, + 0.331, + 0.198 + ], + "angle": 0, + "content": "Bram Wallace" + }, + { + "type": "text", + "bbox": [ + 0.192, + 0.2, + 0.353, + 0.215 + ], + "angle": 0, + "content": "Salesforce Research" + }, + { + "type": "text", + "bbox": [ + 0.183, + 0.22, + 0.362, + 0.233 + ], + "angle": 0, + "content": "b.wallace@salesforce.com" + }, + { + "type": "text", + "bbox": [ + 0.441, + 0.182, + 0.548, + 0.198 + ], + "angle": 0, + "content": "AkashGokul" + }, + { + "type": "text", + "bbox": [ + 0.414, + 0.2, + 0.575, + 0.215 + ], + "angle": 0, + "content": "Salesforce Research" + }, + { + "type": "text", + "bbox": [ + 0.416, + 0.22, + 0.573, + 0.234 + ], + "angle": 0, + "content": "agokul@salesforce.com" + }, + { + "type": "text", + "bbox": [ + 0.658, + 0.182, + 0.756, + 0.198 + ], + "angle": 0, + "content": "Nikhil Naik" + }, + { + "type": "text", + "bbox": [ + 0.627, + 0.2, + 0.788, + 0.215 + ], + "angle": 0, + "content": "Salesforce Research" + }, + { + "type": "text", + "bbox": [ + 0.629, + 0.22, + 0.781, + 0.233 + ], + "angle": 0, + "content": "nnaik@salesforce.com" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.269, + 0.314, + 0.285 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.301, + 0.473, + 0.755 + ], + "angle": 0, + "content": "Finding an initial noise vector that produces an input image when fed into the diffusion process (known as inversion) is an important problem in denoising diffusion models (DDMs), with applications for real image editing. The standard approach for real image editing with inversion uses denoising diffusion implicit models (DDIMs [29]) to deterministically noise the image to the intermediate state along the path that the denoising would follow given the original conditioning. However, DDIM inversion for real images is unstable as it relies on local linearization assumptions, which result in the propagation of errors, leading to incorrect image reconstruction and loss of content. To alleviate these problems, we propose Exact Diffusion Inversion via Coupled Transformations (EDICT), an inversion method that draws inspiration from affine coupling layers. EDICT enables mathematically exact inversion of real and model-generated images by maintaining two coupled noise vectors which are used to invert each other in an alternating fashion. Using Stable Diffusion [25], a state-of-the-art latent diffusion model, we demonstrate that EDICT successfully reconstructs real images with high fidelity. On complex image datasets like MS-COCO, EDICT reconstruction significantly outperforms DDIM, improving the mean square error of reconstruction by a factor of two. Using noise vectors inverted from real images, EDICT enables a wide range of image edits—from local and global semantic edits to image stylization—while maintaining fidelity to the original image structure. EDICT requires no model training/finetuning, prompt tuning, or extra data and can be combined with any pretrained DDM." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.784, + 0.21, + 0.8 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.81, + 0.471, + 0.902 + ], + "angle": 0, + "content": "Using the iterative denoising diffusion principle, denoising diffusion models (DDMs) trained with web-scale data can generate highly realistic images conditioned on input text, layouts, and scene graphs [24, 25, 27]. After image generation, the next important application of DDMs being explored by the research community is that of im" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.27, + 0.895, + 0.391 + ], + "angle": 0, + "content": "age editing. Models such as DALL-E-2 [24] and Stable Diffusion [25] can perform inpainting, allowing users to edit images through manual annotation. Methods such as SDEdit [20] have demonstrated that both synthetic and real images can be edited using stroke or composite guidance via DDMs. However, the goal of holistic image editing tools that can edit any real/artificial image using purely text is still a field of active research." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.395, + 0.895, + 0.532 + ], + "angle": 0, + "content": "The generative process of DDMs starts with an initial noise vector \\((x_{T})\\) and performs iterative denoising (typically with a guidance signal e.g. in the form of text-conditional denoising), ending with a realistic image sample \\((x_0)\\). Reversing this generative process is key in solving this image editing problem for one family of approaches. Formally, this problem is known as \"inversion\" i.e., finding the initial noise vector that produces the input image when passed through the diffusion process." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.535, + 0.896, + 0.702 + ], + "angle": 0, + "content": "A naive approach for inversion is to add Gaussian noise to the input image and perform a predefined number of diffusion steps, which typically results in significant distortions [7]. A more robust method is adapting Denoising Diffusion Implicit Models (DDIMs) [29]. Unlike the commonly used Denoising Diffusion Probabilistic Models (DDPMs) [9], the generative process in DDIMs is defined in a non-Markovian manner, which results in a deterministic denoising process. DDIM can also be used for inversion, deterministically noising an image to obtain the initial noise vector \\((x_0 \\to x_T)\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.704, + 0.896, + 0.903 + ], + "angle": 0, + "content": "DDIM inversion has been used for editing real images through text methods such as DDIBs [30] and Prompt-to-Prompt (P2P) image editing [7]. After DDIM inversion, P2P edits the original image by running the generative process from the noise vector and injecting conditioning information from a new text prompt through the cross-attention layers in the diffusion model, thus generating an edited image that maintains faithfulness to the original content while incorporating the edit. However, as noted in the original P2P work [7], the DDIM inversion is unstable in many cases—encoding from \\( x_0 \\) to \\( x_T \\) and back often results in inexact reconstructions of the original image as in Fig. 2. These distortions limit the ability to perform significant ma" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "22532" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.099, + 0.098, + 0.881, + 0.56 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.576, + 0.893, + 0.62 + ], + "angle": 0, + "content": "Figure 1. EDICT enables complex real image edits, such as editing dog breeds. We highlight the fine-grain text preservation in the bottom row of examples, with the message remaining even as the dog undergoes dramatic transformations. More examples, including baseline comparisons for all image-breed pairs, are included in the Supplementary. All original images from the ImageNet 2012 validation set." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.645, + 0.471, + 0.677 + ], + "angle": 0, + "content": "nipulations through text as increase in the corruption is correlated with the strength of the conditioning." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.689, + 0.473, + 0.903 + ], + "angle": 0, + "content": "To improve the inversion ability of DDMs and enable robust real image editing, we diagnose the problems in DDIM inversion, and offer a solution: Exact Diffusion Inversion via Coupled Transformations (EDICT). EDICT is a re-formulation of the DDIM process inspired by coupling layers in normalizing flow models [4, 5, 12] that allows for mathematically exact inversion. By maintaining two coupled noise vectors in the diffusion process, EDICT enables recovery of the original noise vector in the case of model-generated images; and for real imagery, initial noise vectors that are guaranteed to map to the original image when the EDICT generative process is run. While EDICT doubles the computation time of the diffusion process, it can be combined with any pretrained DDM model and does" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.645, + 0.892, + 0.677 + ], + "angle": 0, + "content": "not require any computationally-expensive model finetuning, prompt tuning, or multiple images." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.689, + 0.895, + 0.903 + ], + "angle": 0, + "content": "For the standard generative process, EDICT approximates DDIM well, resulting in nearly identical generations given equal initial conditions. For real images, EDICT can recover a noise vector which yields an exact reconstruction when used as input to the generative process. Experiments with the COCO dataset [16] show that EDICT can recover complex image features such as detailed textures, thin objects, subtle reflections, faces, and text, while DDIM fails to do so consistently. Finally, using the initial noise vectors derived from a real image with EDICT, we can sample from a DDM and perform complex edits or transformations to real images using textual guidance. We show editing capabilities including local and global modifications of objects and background and object transformations (Fig. 1)." + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "22533" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.081, + 0.09, + 0.47, + 0.376 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.386, + 0.471, + 0.471 + ], + "angle": 0, + "content": "Figure 2. While both unconditional and conditional DDIM [29] often fail to accurately reconstruct real images, leading to loss of global image structure and/or finer details, EDICT is able to almost perfectly reconstruct even complex scenes. Examples from ImageNet and COCO with 50 DDIM steps. Captions used only in DDIM Conditional reconstruction with a guidance scale of 3." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.496, + 0.22, + 0.512 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.522, + 0.47, + 0.884 + ], + "angle": 0, + "content": "Diffusion Models and Normalizing Flows: Denoising diffusion models (DDMs), drawing on nonequilibrium thermodynamics [28], have emerged at the forefront of image generation. Models such as GLIDE [22], DALLE-2 [24], Imagen (Video) [8, 27], Latent/Stable Diffusion [25], and eDiffi [1] all utilize concepts borrowed from thermodynamics to hallucinate an image from pure noise by training on intermediately noised images. While a commonly used sampling process in DDMs is the stochastic Denoising Diffusion Probabilistic Models (DDPMs) method [9], a deterministic sampling method was introduced in Denoising Diffusion Implicit Models (DDIM) [29]. Multi-step or higher-order methods that parallel DDIM have also been proposed [17, 19], including methods that aim to reducing the computational time for generation [13, 18]. Another class of generative models relevant to our work are normalizing flow models [4, 5, 12]. In these models, an invertible mapping is learned between a latent gaussian distribution and image space. The methods of invertibility, specifically coupling layers, are used as an inspiration for our method. Invertible neural networks have been studied in areas outside of normalizing flows as well. Neural ODEs [2] have many parallels with the diffusion process and can be inverted using a variety of ODE solvers." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.886, + 0.469, + 0.902 + ], + "angle": 0, + "content": "Editing in Diffusion Models: The seminal work in apply" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.425 + ], + "angle": 0, + "content": "ing DDMs to image editing is SDEdit [20] where coarse layouts are used to guide the generative process by nois-ing the layout to resemble an intermediately noised image. Prompt-to-Prompt [7] combines query-key pairs from one prompt with values from another in the attention layers of a DDM to enable prompt-guided image editing from intermediate latents obtained by sampler inversion [29, 31]. DiffEdit [3] edits real/synthetic images using automatically generated masks for regions of an input image that should be edited given a text query. Kwon et al. [14] introduce style and structure losses to guide the sampling process to enable text-guided image translation. CycleDiffusion [32] uses a deterministic DPM encoder to enable zero-shot image-to-image translation. Concurrent work [21] also stabilizes text-conditioned inversion, optimizing the null embedding \\(\\emptyset\\) for consistency. While highly effective, the algorithmic exactness is not guaranteed and per-case optimization is required. Another set of methods [6, 11, 26] finetune the model with the target image and/or learn a new conditioning prompt to enable indirect image editing via sampling. EDICT, our proposed approach, does not require any specialized training/finetuning, and can be paired with any pretrained DDM." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.436, + 0.628, + 0.453 + ], + "angle": 0, + "content": "3. Background" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.46, + 0.748, + 0.477 + ], + "angle": 0, + "content": "3.1. Denoising Diffusion Models" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.484, + 0.892, + 0.56 + ], + "angle": 0, + "content": "DDMs are trained on a simple denoising objective. A set of timesteps index a monotonic strictly increasing noisingschedule \\(\\{\\alpha_{t}\\}_{t = 0}^{T},\\alpha_{T} = 0,\\alpha_{0} = 1\\) . Images (or autoencoded latents) \\(x\\in X\\) are noised with draws \\(\\epsilon \\sim N(0,I)\\) according to the noising schedule following the formula" + }, + { + "type": "equation", + "bbox": [ + 0.613, + 0.567, + 0.891, + 0.584 + ], + "angle": 0, + "content": "\\[\nx _ {t} = \\sqrt {\\alpha_ {t}} x + \\sqrt {1 - \\alpha_ {t}} \\epsilon \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.592, + 0.892, + 0.728 + ], + "angle": 0, + "content": "The time-aware DDM \\(\\Theta\\) is trained on the objective \\(MSE(\\Theta(x_{t}, t, C), \\epsilon)\\) to predict the noise added to the original image where \\(C\\) is a conditioning signal (typically in the form of a text embedding) with some probability of random assignment to the null conditioning \\(\\emptyset\\). To generate a novel image from a gaussian draw \\(\\epsilon_{T} \\sim N(0, I)\\), partial denoising is applied at each \\(t\\). The most common sampling scheme is that of DDIM [29] where intermediate steps are calculated as" + }, + { + "type": "equation", + "bbox": [ + 0.56, + 0.733, + 0.891, + 0.789 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} x _ {t - 1} = \\sqrt {\\alpha_ {t - 1}} \\frac {x _ {t} - \\sqrt {1 - \\alpha_ {t}} \\Theta \\left(x _ {t} , t , C\\right)}{\\sqrt {\\alpha_ {t}}} \\tag {2} \\\\ + \\sqrt {1 - \\alpha_ {t - 1}} \\Theta (x _ {t}, t, C) \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.795, + 0.892, + 0.902 + ], + "angle": 0, + "content": "In practice, for text-to-image models to hallucinate from random noise an \\( x_0 \\) that matches conditioning \\( C \\) to desired levels, the model has to be biased more heavily towards generations aligned with \\( C \\). To do so, a pseudo-gradient \\( G \\cdot (\\Theta(x_t, t, C) - \\Theta(x_t, t, \\emptyset)) \\) is added to the unconditional prediction \\( \\Theta(x_t, t, \\emptyset) \\) to up-weight the effect of conditioning, where \\( G \\) is a weighting parameter, Substituting" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "22534" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.091, + 0.47, + 0.152 + ], + "angle": 0, + "content": "\\(\\Phi (x_{t},t,C,G) = \\Theta (x_{t},t,\\emptyset) + G\\cdot (\\Theta (x_{t},t,C) - \\Theta (x_{t},t,\\emptyset))\\) into the prior equation for the \\(\\Theta\\) term, we simplify the notation \\(\\Phi (x_{t},t,C,G)\\rightarrow \\epsilon (x_{t},t)\\) and rewrite the previous equation as \\(x_{t - 1} = a_tx_t + b_t\\epsilon (x_t,t)\\) where" + }, + { + "type": "equation", + "bbox": [ + 0.133, + 0.161, + 0.469, + 0.18 + ], + "angle": 0, + "content": "\\[\na _ {t} = \\sqrt {\\alpha_ {t - 1} / \\alpha_ {t}} \\tag {3}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.134, + 0.183, + 0.469, + 0.203 + ], + "angle": 0, + "content": "\\[\nb _ {t} = - \\sqrt {\\alpha_ {t - 1} \\left(1 - \\alpha_ {t}\\right) / \\alpha_ {t}} + \\sqrt {1 - \\alpha_ {t - 1}} \\tag {4}\n\\]" + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.21, + 0.45, + 0.226 + ], + "angle": 0, + "content": "3.2. Denoising Diffusion Implicit Model (DDIM)" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.234, + 0.469, + 0.279 + ], + "angle": 0, + "content": "As noted in DDIM [29], the above denoising process is approximately invertible; that is \\( x_{t} \\) is approximately recoverable from \\( x_{t - 1} \\)" + }, + { + "type": "equation", + "bbox": [ + 0.117, + 0.287, + 0.469, + 0.32 + ], + "angle": 0, + "content": "\\[\nx _ {t} = \\frac {x _ {t - 1} - b _ {t} \\epsilon (x _ {t} , t)}{a _ {t}} \\approx \\frac {x _ {t - 1} - b _ {t} \\epsilon (x _ {t - 1} , t)}{a _ {t}} \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.327, + 0.469, + 0.552 + ], + "angle": 0, + "content": "where the approximation is a linearization assumption that \\(\\epsilon(x_{t}, t) \\approx \\epsilon(x_{t-1}, t)\\) (necessary due to the discrete nature of both computation and the underlying noise schedule). This corresponds with reversing the Euler integration which is a first-order ODE solver. More sophisticated solvers such as multi-step Euler [17] have been shown to stabilize the generative process, and correspondingly the deterministic inversion process, with fewer time steps. However, such methods are also approximations where the inversion accuracy ultimately relies on the strength of the linearization assumption and the reconstruction is not exactly equal. This assumption is largely accurate for unconditional DDIM generation, but the pseudo-gradient of classifier-free guidance \\(G \\cdot (\\Theta(x_{t}, t, C) - \\Theta(x_{t}, t, \\emptyset))\\) is inconsistent across time steps as shown in the Supplementary." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.553, + 0.469, + 0.765 + ], + "angle": 0, + "content": "While unconditional reconstructions have relatively insignificant errors (Fig. 2), conditional reconstructions are extremely distorted when noised to high levels. This phenomenon was noted in [7], where the guidance scale must be heavily downweighted in order for inversions on real-world images to be stable, thus limiting the strength of edits. Obtaining an \\( x_{t} \\) from \\( x_{0} \\) allows for the generative process to be run with novel conditioning. In SDEdit [20], this process is done stochastically to obtain broad sample diversity, at the cost of controllability and faithfulness to the original image contents. In contrast, the inverse DDIM process produces a unique \\( x_{t} \\) from a single \\( x_{0} \\) in a deterministic manner, yielding only one sample but enabling higher strength edits while preserving finer-grain structure and content." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.773, + 0.294, + 0.789 + ], + "angle": 0, + "content": "3.3. Affine Coupling Layers" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.796, + 0.469, + 0.872 + ], + "angle": 0, + "content": "Affine Coupling Layers (ACL) are invertible neural network layers introduced in [4, 5] and used in other normalizing flow models such as Glow [12]. The layer input \\(z\\), is split into two equal-dimensional halves \\(z_{a}\\) and \\(z_{b}\\). A modified version of \\(z_{a}\\) is then calculated, according to:" + }, + { + "type": "equation", + "bbox": [ + 0.196, + 0.881, + 0.469, + 0.898 + ], + "angle": 0, + "content": "\\[\nz _ {a} ^ {\\prime} = \\Psi (z _ {b}) z _ {a} + \\psi (z _ {b}) \\tag {6}\n\\]" + }, + { + "type": "image", + "bbox": [ + 0.55, + 0.088, + 0.808, + 0.154 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.167, + 0.892, + 0.251 + ], + "angle": 0, + "content": "Figure 3. Information flow of EDICT. Denoising process (sampling) follows the arrows forwards, sampler inversion backwards. From \\((x_{t},y_{t})\\), \\((x_{t - 1},y_{t - 1})\\) can be calculated while holding a single member of each sequence in memory at a time. All steps are invertible, so \\((x_{t},y_{t})\\) can be exactly recovered from \\((x_{t - 1},y_{t - 1})\\), as opposed to current methods which compute an approximation." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.274, + 0.892, + 0.335 + ], + "angle": 0, + "content": "where \\(\\Psi\\) and \\(\\psi\\) are neural networks. The layer output \\(z^{\\prime}\\) is the concatenation of \\(z_{a}^{\\prime}\\) and \\(z_{b}\\) in accordance with the original splitting function. ACL can parameterize complex functions and \\(z\\) can be exactly recovered given \\(z^{\\prime}\\):" + }, + { + "type": "equation", + "bbox": [ + 0.608, + 0.342, + 0.891, + 0.359 + ], + "angle": 0, + "content": "\\[\nz _ {a} = \\left(z _ {a} ^ {\\prime} - \\psi \\left(z _ {b}\\right)\\right) / \\Psi \\left(z _ {b}\\right) \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.366, + 0.892, + 0.457 + ], + "angle": 0, + "content": "Noting the similarity of equations 6 and 7 to the simplified form of Eq. (2), we parallel this construction in our method (described next) where two separate quantities are tracked and alternately modified by transformations that are affine with respect to the original modified quantity and a nonlinear transformation of its counterpart." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.469, + 0.892, + 0.503 + ], + "angle": 0, + "content": "4. Exact Diffusion Inversion via Coupled Transformations (EDICT)" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.511, + 0.836, + 0.527 + ], + "angle": 0, + "content": "4.1. Making an Invertible Diffusion Process" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.535, + 0.892, + 0.656 + ], + "angle": 0, + "content": "As summarized in Sec. 3.3, affine coupling layers track two quantities which can then be used to invert each other. These two quantities are partitions of a latent representation with a network specifically designed to operate in a fitting alternating manner. Without training of a new DDM, this method can not be applied out-of-the-box to the forward diffusion process. We consider the simplified form of the forward step equation from Sec. 3.1 below" + }, + { + "type": "equation", + "bbox": [ + 0.609, + 0.665, + 0.891, + 0.68 + ], + "angle": 0, + "content": "\\[\nx _ {t - 1} := a _ {t} x _ {t} + b _ {t} \\epsilon \\left(x _ {t}, t\\right) \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.688, + 0.892, + 0.793 + ], + "angle": 0, + "content": "If the noise prediction term, \\(\\epsilon (x_{t},t) = \\varepsilon\\) was independent of \\(x_{t}\\), this would be an affine function in both \\(x_{t}\\), and \\(\\varepsilon\\). Paralleling Eq. (6), by creating a new variable \\(y_{t} = x_{t}\\) the stepping equation fits the desired form. Consider performing this computation, so we have the variables \\(x_{t}\\), \\(y_{t} = x_{t}\\), \\(x_{t - 1} = a_{t}x_{t} + b_{t}\\epsilon (y_{t},t)\\). \\(x_{t}\\) can be recovered exactly from \\(x_{t - 1}\\) in the non-trivial form:" + }, + { + "type": "equation", + "bbox": [ + 0.596, + 0.802, + 0.891, + 0.817 + ], + "angle": 0, + "content": "\\[\nx _ {t} = \\left(x _ {t - 1} - b _ {t} \\cdot \\epsilon \\left(y _ {t}, t\\right)\\right) / a _ {t} \\tag {9}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.826, + 0.892, + 0.901 + ], + "angle": 0, + "content": "\\(y_{t} = x_{t}\\) is trivial and will not be true in the general case. Now consider the initialization of the reverse (denoising) diffusion process, where \\(x_{T} \\sim \\mathcal{N}(0,1)\\), we similarly initialize \\(y_{T} = x_{T}\\). Following the above process, we define the update rule" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "22535" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.088, + 0.468, + 0.228 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.239, + 0.473, + 0.351 + ], + "angle": 0, + "content": "Figure 4. Images generated from the same text prompt and random seed. EDICT \\( x / y \\) (No mixing) employs coupling layers but not intermediate mixing layers, resulting in distorted and inconsistent images as \\( x \\) and \\( y \\) diverge. EDICT is our full method with the sequences explicitly contracted together, resulting in identical images that match DDIM (Baseline) in quality and composition. Top row prompt: A white horse galloping through a forest Bottom row prompt: A couple of glasses are sitting on a table" + }, + { + "type": "equation", + "bbox": [ + 0.19, + 0.367, + 0.469, + 0.39 + ], + "angle": 0, + "content": "\\[\nx _ {t - 1} = a _ {t} x _ {t} + b _ {t} \\cdot \\epsilon \\left(y _ {t}, t\\right) \\tag {10}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.177, + 0.387, + 0.37, + 0.402 + ], + "angle": 0, + "content": "\\[\ny _ {t - 1} = a _ {t} y _ {t} + b _ {t} \\cdot \\epsilon \\left(x _ {t - 1}, t\\right)\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.407, + 0.47, + 0.482 + ], + "angle": 0, + "content": "Note that the noise prediction term in the second line is a function of the other sequence value at the next timestep. Only one member of each sequence \\((x_{t},y_{t(\\pm 1)})\\) must be held in memory at any given time. The sequences can be recovered exactly according to" + }, + { + "type": "equation", + "bbox": [ + 0.165, + 0.483, + 0.47, + 0.507 + ], + "angle": 0, + "content": "\\[\ny _ {t} = \\left(y _ {t - 1} - b _ {t} \\cdot \\epsilon \\left(x _ {t - 1}, t\\right)\\right) / a _ {t} \\tag {11}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.182, + 0.503, + 0.381, + 0.518 + ], + "angle": 0, + "content": "\\[\nx _ {t} = \\left(x _ {t - 1} - b _ {t} \\cdot \\epsilon \\left(y _ {t}, t\\right)\\right) / a _ {t}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.524, + 0.47, + 0.676 + ], + "angle": 0, + "content": "As illustrated in Fig. 3, the entire sequence can be reconstructed from any two adjacent \\( x_{i} \\) and \\( y_{i} \\). In sum, our method reuses the linearization assumption of Euler DDIM inversion, that \\( \\epsilon(x_{t}, t) \\approx \\epsilon(x_{t-1}, t) \\), but crucially does not rely on it for invertibility, guaranteeing recovery up to machine precision. We note that the functional form of our approach bears similarities to the ODE solver Heun's method where derivative values at initial predictions are used to refine predictions, but due to the need for invertibility we cannot exploit this for more accurate/faster sampling." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.682, + 0.212, + 0.697 + ], + "angle": 0, + "content": "4.2. Stabilization" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.705, + 0.47, + 0.827 + ], + "angle": 0, + "content": "While our method assures invertibility by design, realism and faithfulness to the original diffusion process are not automatic. When naively applied for a typical, low number of DDIM steps (e.g., \\( T = 50 \\)), the sequences \\( x_{t} \\) and \\( y_{t} \\) can diverge (Fig. 4). This is a result of the strong linearization assumption not holding in practice. To alleviate this problem, we introduce intermediate mixing layers after each diffusion step computing weighted averages of the form" + }, + { + "type": "equation", + "bbox": [ + 0.165, + 0.833, + 0.469, + 0.85 + ], + "angle": 0, + "content": "\\[\nx ^ {\\prime} = p x + (1 - p) y, 0 \\leq p \\leq 1 \\tag {12}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.47, + 0.902 + ], + "angle": 0, + "content": "which are invertible affine transformations. Note that this averaging layer becomes a dilating layer during deterministic noising; the inversion being" + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.089, + 0.886, + 0.334 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.345, + 0.895, + 0.513 + ], + "angle": 0, + "content": "Figure 5. We visualize the effect of the mixing coefficient \\( p \\). Top row: an EDICT-generated image with \\( p = 0.93 \\), for each listed \\( p \\) a generation is computed from \\( T = 50 \\) to \\( T = 0 \\) followed by reconstructing initial latents \\( (T = 50) \\). Cosine similarity between \\( (x_{t}, y_{t}) \\) is computed at each step. \\( p = 0.97 \\) suffices for generative convergence, but the inverse process diverges when \\( p \\) is too small. Repeated dilation can exponentially exaggerate small floating-point differences, annulling the theoretical guarantee. These trends hold in the bottom row for a non-generated image put through the EDICT inversion/generation process. While all reconstructions ultimately are aligned, a sufficiently large \\( p \\) is needed for the latents to maintain alignment throughout." + }, + { + "type": "equation", + "bbox": [ + 0.63, + 0.531, + 0.892, + 0.565 + ], + "angle": 0, + "content": "\\[\nx = \\frac {x ^ {\\prime} - (1 - p) y}{p} \\tag {13}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.569, + 0.892, + 0.707 + ], + "angle": 0, + "content": "A high (near 1) value of \\( p \\) results in the averaging layer not being strong enough to prevent divergence of the \\( x \\) and \\( y \\) series during denoising, while a low value of \\( p \\) results in a numerically unstable exponential dilation in the backwards pass (Fig. 5). Note that in both cases that our generative process remains exactly mathematically invertible with no further assumptions, but there is a degradation in utility of the results. Typically we employ \\( p = 0.93 \\), with values in the interval [0.9, 0.97] generally being effective for 50 steps." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.712, + 0.805, + 0.729 + ], + "angle": 0, + "content": "4.3. Complete Summary of the Method" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.736, + 0.892, + 0.813 + ], + "angle": 0, + "content": "We dub our presented process EDICT: Exact Diffusion Inversion via Coupled Transformations. In sum, EDICT uses a combination of \"coupling\" and \"averaging/dilating\" steps for exact inversion of the diffusion process. Given \\( x_{t} \\) and \\( y_{t} \\), we calculate the denoising process by" + }, + { + "type": "equation", + "bbox": [ + 0.571, + 0.818, + 0.771, + 0.837 + ], + "angle": 0, + "content": "\\[\nx _ {t} ^ {\\text {i n t e r}} = a _ {t} \\cdot x _ {t} + b _ {t} \\cdot \\epsilon (y _ {t}, t)\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.573, + 0.839, + 0.892, + 0.864 + ], + "angle": 0, + "content": "\\[\ny _ {t} ^ {\\text {i n t e r}} = a _ {t} \\cdot y _ {t} + b _ {t} \\cdot \\epsilon \\left(x _ {t} ^ {\\text {i n t e r}}, t\\right) \\tag {14}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.582, + 0.86, + 0.821, + 0.878 + ], + "angle": 0, + "content": "\\[\nx _ {t - 1} = p \\cdot x _ {t} ^ {\\text {i n t e r}} + (1 - p) \\cdot y _ {t} ^ {\\text {i n t e r}}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.582, + 0.881, + 0.812, + 0.898 + ], + "angle": 0, + "content": "\\[\ny _ {t - 1} = p \\cdot y _ {t} ^ {\\text {i n t e r}} + (1 - p) \\cdot x _ {t - 1}\n\\]" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "22536" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.168, + 0.09, + 0.38, + 0.102 + ], + "angle": 0, + "content": "COCO Reconstruction Error (MSE)" + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.103, + 0.467, + 0.185 + ], + "angle": 0, + "content": "
MethodLDM AEEDICT (UC)EDICT (C)DDIM (UC)DDIM (C)
50 Steps0.0150.0150.0150.0300.420
100 Steps0.0150.0150.0150.0270.471
200 Steps0.0150.0150.0150.0230.497
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.195, + 0.47, + 0.266 + ], + "angle": 0, + "content": "Table 1. Mean-square reconstruction error for COCO-val using the first listed prompt as conditioning with \\( G = 7 \\). The latent diffusion model autoencoder (LDM AE) is the lower bound on reconstruction error. Using half precision increases 50-step EDICT (C) MSE by \\( 6\\% \\). More step values are in the Supplementary." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.288, + 0.414, + 0.304 + ], + "angle": 0, + "content": "and the deterministic noising inversion process by:" + }, + { + "type": "equation", + "bbox": [ + 0.1, + 0.31, + 0.306, + 0.328 + ], + "angle": 0, + "content": "\\[\ny _ {t + 1} ^ {i n t e r} = \\left(y _ {t} - (1 - p) \\cdot x _ {t}\\right) / p\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.1, + 0.33, + 0.469, + 0.356 + ], + "angle": 0, + "content": "\\[\nx _ {t + 1} ^ {\\text {i n t e r}} = \\left(x _ {t} - (1 - p) \\cdot y _ {t + 1} ^ {\\text {i n t e r}}\\right) / p \\tag {15}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.11, + 0.351, + 0.419, + 0.369 + ], + "angle": 0, + "content": "\\[\ny _ {t + 1} = \\left(y _ {t + 1} ^ {\\text {i n t e r}} - b _ {t + 1} \\cdot \\epsilon \\left(x _ {t + 1} ^ {\\text {i n t e r}}, t + 1\\right)\\right) / a _ {t + 1}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.11, + 0.372, + 0.41, + 0.389 + ], + "angle": 0, + "content": "\\[\nx _ {t + 1} = \\left(x _ {t + 1} ^ {\\text {i n t e r}} - b _ {t + 1} \\cdot \\epsilon \\left(y _ {t + 1}, t + 1\\right)\\right) / a _ {t + 1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.395, + 0.47, + 0.486 + ], + "angle": 0, + "content": "Recall that the conditioning \\( C \\) is implicitly included in the \\( \\epsilon \\) terms. In practice, we alternate the order in which the \\( x \\) and \\( y \\) series are calculated at each step in order to symmetrize the process with respect to both sequences. We cast all operations to double floating point precision (from the native half precision) to mitigate roundoff floating point errors." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.494, + 0.226, + 0.51 + ], + "angle": 0, + "content": "4.4. Image Editing" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.517, + 0.473, + 0.835 + ], + "angle": 0, + "content": "While EDICT can theoretically operate on either pixel-based or latent-diffusion models we present the latter case in this work. Given an image \\(I\\), we edit the semantic contents to match text conditioning \\(C_{target}\\). We describe the current content by text \\(C_{base}\\) in a parallel manner to \\(C_{target}\\). We compute an autoencoder latent \\(x_0 = VAE_{enc}(I)\\), initializing \\(y_0 = x_0\\). We run the deterministic noising process of Eq. (15) on \\((x_0, y_0)\\) using text conditioning \\(C_{base}\\) for \\(s \\cdot S\\) steps, where \\(S\\) is the number of global timesteps and \\(s\\) is a chosen editing strength. This yields partially \"noised\" latents \\((x_t, y_t)\\) which are not necessarily equal and, in practice, tend to diverge by a small amount due to linearization error and the dilation of the mixing layers. These intermediate representations are then used as input to Eq. (14) using text condition \\(C_{target}\\), and identical step parameters, \\((s, S)\\). The resulting image outputs \\((VAE_{dec}(x_0^{edit}), VAE_{dec}(y_0^{edit}))\\) are empirically nearly identical as seen in Fig. 4, this is by design of the method and in particular, the mixing layers. For all methods we find that a guidance scale of 3 performs well (as opposed to the standard 7.5 for generation)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.846, + 0.21, + 0.863 + ], + "angle": 0, + "content": "5. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.469, + 0.902 + ], + "angle": 0, + "content": "We now describe results using the Stable Diffusion 1.4 latent diffusion model [25]." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.091, + 0.707, + 0.107 + ], + "angle": 0, + "content": "5.1. Image Reconstruction" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.114, + 0.895, + 0.356 + ], + "angle": 0, + "content": "We demonstrate the exact invertibility of EDICT using the MS-COCO-2017 validation set \\((n = 5,000)\\), which contains both simple object-centric images and complex scene images [16]. Given an image-caption pair, inverted latents are calculated and used to reconstruct the image. Mean-square error is calculated on pixels normalized to \\([-1,1]\\) and averaged across all images in the dataset. This process is performed both with and without the text as conditioning (C vs. UC). For COCO, we use the first listed prompt as conditioning. The LDM autoencoder reconstruction error serves as a lower bound. EDICT maintains complete latent recovery in all examples for both 50 and 200 steps, with error \\(50 - 75\\%\\) that of DDIM (UC) (Tab. 1). DDIM (C) is unstable for inversions (also noted in [7]), which results in an error an order of magnitude greater than any other, with failure to reconstruct as shown in Fig. 2." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.364, + 0.649, + 0.381 + ], + "angle": 0, + "content": "5.2. Image Editing" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.388, + 0.892, + 0.599 + ], + "angle": 0, + "content": "We show EDICT's ability to perform complex editing tasks on real images in Fig. 6. In the first row, a diverse set of objects are added to a lake scene, demonstrating object addition. In the giraffe and car examples, we see interaction between introduced and original objects. Additionally, both the giraffe and castle examples capture reflections of the added objects, while the pattern of the water is maintained. Throughout all edits, details such as the cloud patterns and patches of tree color are preserved. The second row shows object-preserving global changes. A chair is placed into a variety of settings while keeping near-perfect identity and detail, even when occlusions are generated (grass and snow). In all examples the chair keeps a realistic footing, despite ground changes." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.599, + 0.893, + 0.87 + ], + "angle": 0, + "content": "In the third row, we demonstrate that EDICT is able to perform object deformations, a challenging class of edits for DDM methods, as many broad compositional components are determined very early in the generation [7]. The previously most successful method for these types of edits, Imagic [11] requires model finetuning. EDICT makes the sculpture assume a broad set of poses, spatially changing the semantic map in a refined way. Novel views, such as \"A statue from behind\" are able to be plausibly rendered Across these large-scale edits, fine-grained details such as the face and dress of the statue -as well as the foliage and path- are preserved. In the fourth row, we show that EDICT is able to perform global style changes while maintaining layout and details where appropriate. The layout is nearly identical across images (note the preserved cloud pattern), but can be changed when needed (e.g., the lack of trees in the Mars example). Specific art-styles are capable of being generated, including challenging concepts such as cubism." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.871, + 0.892, + 0.901 + ], + "angle": 0, + "content": "In Fig. 1, EDICT makes semantic entity edits to and from a variety of dog breeds. It proves adept at holding the" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "22537" + } + ], + [ + { + "type": "image_caption", + "bbox": [ + 0.124, + 0.09, + 0.19, + 0.102 + ], + "angle": 0, + "content": "Real Image" + }, + { + "type": "image", + "bbox": [ + 0.081, + 0.104, + 0.233, + 0.223 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.135, + 0.226, + 0.179, + 0.236 + ], + "angle": 0, + "content": "\"A lake\"" + }, + { + "type": "image_caption", + "bbox": [ + 0.26, + 0.09, + 0.342, + 0.102 + ], + "angle": 0, + "content": "Edited Images" + }, + { + "type": "image", + "bbox": [ + 0.246, + 0.105, + 0.398, + 0.223 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.282, + 0.224, + 0.361, + 0.236 + ], + "angle": 0, + "content": "\"A giraffe in .." + }, + { + "type": "image", + "bbox": [ + 0.41, + 0.105, + 0.563, + 0.223 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.443, + 0.224, + 0.534, + 0.235 + ], + "angle": 0, + "content": "\"A car stuck in...\"" + }, + { + "type": "image", + "bbox": [ + 0.575, + 0.105, + 0.728, + 0.223 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.585, + 0.224, + 0.716, + 0.236 + ], + "angle": 0, + "content": "\"A castle overlooking .." + }, + { + "type": "image", + "bbox": [ + 0.74, + 0.105, + 0.892, + 0.223 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.776, + 0.224, + 0.862, + 0.235 + ], + "angle": 0, + "content": "\"A fountain in...\"" + }, + { + "type": "image", + "bbox": [ + 0.082, + 0.239, + 0.233, + 0.358 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.126, + 0.36, + 0.194, + 0.371 + ], + "angle": 0, + "content": "\"A red chair\"" + }, + { + "type": "image", + "bbox": [ + 0.246, + 0.239, + 0.398, + 0.359 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.26, + 0.36, + 0.395, + 0.372 + ], + "angle": 0, + "content": "\"at the Grand Canyon\"" + }, + { + "type": "image", + "bbox": [ + 0.41, + 0.239, + 0.563, + 0.359 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.435, + 0.36, + 0.553, + 0.372 + ], + "angle": 0, + "content": "\".. on a field of grass\"" + }, + { + "type": "image", + "bbox": [ + 0.575, + 0.239, + 0.728, + 0.359 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.599, + 0.36, + 0.718, + 0.382 + ], + "angle": 0, + "content": ".. covered in snow in the mountains" + }, + { + "type": "image", + "bbox": [ + 0.74, + 0.24, + 0.892, + 0.359 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.771, + 0.36, + 0.858, + 0.371 + ], + "angle": 0, + "content": "..after a flood" + }, + { + "type": "image", + "bbox": [ + 0.081, + 0.384, + 0.233, + 0.502 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.13, + 0.502, + 0.184, + 0.512 + ], + "angle": 0, + "content": "\"A statue\"" + }, + { + "type": "image", + "bbox": [ + 0.246, + 0.384, + 0.398, + 0.502 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.267, + 0.502, + 0.374, + 0.512 + ], + "angle": 0, + "content": "..with raised arms" + }, + { + "type": "image", + "bbox": [ + 0.411, + 0.384, + 0.563, + 0.502 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.457, + 0.502, + 0.516, + 0.513 + ], + "angle": 0, + "content": "walking" + }, + { + "type": "image", + "bbox": [ + 0.576, + 0.384, + 0.728, + 0.502 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.611, + 0.502, + 0.695, + 0.512 + ], + "angle": 0, + "content": "\".. from behind" + }, + { + "type": "image", + "bbox": [ + 0.74, + 0.384, + 0.892, + 0.502 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.748, + 0.502, + 0.881, + 0.523 + ], + "angle": 0, + "content": "\".. standing alone giving a thumbs-up\"" + }, + { + "type": "image", + "bbox": [ + 0.081, + 0.528, + 0.233, + 0.649 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.111, + 0.649, + 0.205, + 0.67 + ], + "angle": 0, + "content": "\"A waterfall in the mountains\"" + }, + { + "type": "image", + "bbox": [ + 0.246, + 0.528, + 0.398, + 0.649 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.285, + 0.649, + 0.359, + 0.671 + ], + "angle": 0, + "content": "\"A cubist painting of .." + }, + { + "type": "image", + "bbox": [ + 0.411, + 0.528, + 0.563, + 0.649 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.435, + 0.649, + 0.54, + 0.671 + ], + "angle": 0, + "content": "\"An impressionistic painting of .." + }, + { + "type": "image", + "bbox": [ + 0.576, + 0.528, + 0.728, + 0.649 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.611, + 0.649, + 0.68, + 0.658 + ], + "angle": 0, + "content": "\".. in the fall" + }, + { + "type": "image", + "bbox": [ + 0.74, + 0.528, + 0.892, + 0.649 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.776, + 0.649, + 0.84, + 0.658 + ], + "angle": 0, + "content": "\".. on Mars\"" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.683, + 0.893, + 0.725 + ], + "angle": 0, + "content": "Figure 6. Examples of the strength and varied editing ability of EDICT. From top to bottom: object additions, global context changes with object preservation, deformations while preserving identity, and global style changes. The bidirectional reversibility of EDICT's process allows for large-scale changes to the image while maintaining auxiliary details." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.751, + 0.473, + 0.873 + ], + "angle": 0, + "content": "original subject pose, including in the third row where the dog is viewed in a very atypical position. The realism in the Chihuahua examples is particularly interesting, due to the relatively small size of the breed. We again highlight the preservation of details such as the background foliage or ground in the upper three rows. The fourth row is of specific interest as small text is preserved across examples (a typical failure case for DDIM)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.751, + 0.895, + 0.888 + ], + "angle": 0, + "content": "Baseline Comparison: In Fig. 7, we demonstrate EDICT's superior performance to other DDM sampling-based methods for image editing: conditional and unconditional DDIM inversion, prompt-to-prompt image editing, and SDEdit (as a stochastic baseline). All methods are run with 50 steps (we do not observe improvement of baselines when the number of steps are increased, see Supplementary). Since methods that require model finetuning or prompt tuning [6, 11, 26] can be combined with EDICT, we view them" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.946, + 0.519, + 0.957 + ], + "angle": 0, + "content": "22538" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.081, + 0.089, + 0.867, + 0.416 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.427, + 0.895, + 0.457 + ], + "angle": 0, + "content": "Figure 7. EDICT compared to baseline editing methods. EDICT demonstrates superior preservation of unedited components while still performing the edit edit. Further comparison between EDICT and baselines (including concurrent work ([14,32]) is in the Supplementary." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.482, + 0.471, + 0.529 + ], + "angle": 0, + "content": "as complementary to, rather than competitive with, EDICT, and do not perform a direct comparison with them. We quantitatively compare visual metrics of edits in Fig. 8." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.543, + 0.192, + 0.558 + ], + "angle": 0, + "content": "6. Discussion" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.569, + 0.47, + 0.765 + ], + "angle": 0, + "content": "Limitations and Future Work: EDICT is deterministic, only outputs one generation per image-prompt pair (vs. SDEdit). Also, the computational time is approximately twice that of baseline DDIM. As with all editing methods, performance can vary across inputs in a hard-to-predict manner and sometimes requires careful prompt selection. For future work, we note that the induced latent space constructed by the inversion process admits operations such as latent interpolation [10] which has not been widely applied to real images. As in prompt tuning [15], formalizing the process of prompt selection could further improve EDICT. Adding a controllable degree of randomness to EDICT could yield multiple candidate generations per input." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.765, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Ethics: Like other image generation and editing models, EDICT will produce images that may reflect the socioeconomic biases of the training data or images that could be considered inappropriate. Image editing methods can also utilized for malicious purposes, including harassment and misinformation spread. Practitioners utilizing EDICT or its methodologies in a production setting should consider these limitations. An in-depth discussion on the ethics of image generation can be found in Imagen [27]." + }, + { + "type": "image", + "bbox": [ + 0.527, + 0.486, + 0.868, + 0.643 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.659, + 0.892, + 0.852 + ], + "angle": 0, + "content": "Figure 8. We quantitatively benchmark all methods on image editing using images from five ImageNet mammal classes (African Elephant, Ram, Egyptian Cat, Brown Bear, and Norfolk Terrier). Four experiments are performed, one swapping the pictured animal's species to each of the other classes (20 species editing pairs in total), two contextual changes (A [animal] in the snow and A [animal] in a parking lot), and one stylistic (An impressionistic painting of a [animal]). The LPIPS [33] (visual similarity) score to the original image and a CLIP score [23] (semantic similarity) to a set of five related text queries is computed per edit. Metrics are averaged across images and experiments. Details and human evaluation are provided in the Supplementary. We sweep across the fraction of inverted steps (overlaid in black on top of gray EDICT bubbles), observing that EDICT forms a Pareto frontier." + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "22539" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.115, + 0.47, + 0.184 + ], + "angle": 0, + "content": "[1] Yogesh Balaji, Seungjun Nah, Xun Huang, Arash Vahdat, Jiaming Song, Karsten Kreis, Miika Aittala, Timo Aila, Samuli Laine, Bryan Catanzaro, et al. edifi: Text-to-image diffusion models with an ensemble of expert denoisers. arXiv preprint arXiv:2211.01324, 2022. 3" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.185, + 0.472, + 0.24 + ], + "angle": 0, + "content": "[2] Ricky TQ Chen, Yulia Rubanova, Jesse Bettencourt, and David K Duvenaud. Neural ordinary differential equations. 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In CVPR, 2018. 8" + }, + { + "type": "list", + "bbox": [ + 0.08, + 0.092, + 0.47, + 0.319 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.946, + 0.518, + 0.957 + ], + "angle": 0, + "content": "22541" + } + ] +] \ No newline at end of file diff --git a/2023/EDICT_ Exact Diffusion Inversion via Coupled Transformations/5ac781e1-0cfa-4238-8cf2-ceb66647f068_origin.pdf b/2023/EDICT_ Exact Diffusion Inversion via Coupled Transformations/5ac781e1-0cfa-4238-8cf2-ceb66647f068_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..d1849f0a4f9e5251c35b25dbb685c2d11db0e7e6 --- /dev/null +++ b/2023/EDICT_ Exact Diffusion Inversion via Coupled Transformations/5ac781e1-0cfa-4238-8cf2-ceb66647f068_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:10c44b2acaaa0daace01740d44b19ab70e17713a3b8b337cb72aa4c3321fa3ec +size 9364183 diff --git a/2023/EDICT_ Exact Diffusion Inversion via Coupled Transformations/full.md b/2023/EDICT_ Exact Diffusion Inversion via Coupled Transformations/full.md new file mode 100644 index 0000000000000000000000000000000000000000..88dd6fcd3025d3e9e3393a6824c3ac3c8e47ce67 --- /dev/null +++ b/2023/EDICT_ Exact Diffusion Inversion via Coupled Transformations/full.md @@ -0,0 +1,361 @@ +# EDICT: Exact Diffusion Inversion via Coupled Transformations + +Bram Wallace + +Salesforce Research + +b.wallace@salesforce.com + +AkashGokul + +Salesforce Research + +agokul@salesforce.com + +Nikhil Naik + +Salesforce Research + +nnaik@salesforce.com + +# Abstract + +Finding an initial noise vector that produces an input image when fed into the diffusion process (known as inversion) is an important problem in denoising diffusion models (DDMs), with applications for real image editing. The standard approach for real image editing with inversion uses denoising diffusion implicit models (DDIMs [29]) to deterministically noise the image to the intermediate state along the path that the denoising would follow given the original conditioning. However, DDIM inversion for real images is unstable as it relies on local linearization assumptions, which result in the propagation of errors, leading to incorrect image reconstruction and loss of content. To alleviate these problems, we propose Exact Diffusion Inversion via Coupled Transformations (EDICT), an inversion method that draws inspiration from affine coupling layers. EDICT enables mathematically exact inversion of real and model-generated images by maintaining two coupled noise vectors which are used to invert each other in an alternating fashion. Using Stable Diffusion [25], a state-of-the-art latent diffusion model, we demonstrate that EDICT successfully reconstructs real images with high fidelity. On complex image datasets like MS-COCO, EDICT reconstruction significantly outperforms DDIM, improving the mean square error of reconstruction by a factor of two. Using noise vectors inverted from real images, EDICT enables a wide range of image edits—from local and global semantic edits to image stylization—while maintaining fidelity to the original image structure. EDICT requires no model training/finetuning, prompt tuning, or extra data and can be combined with any pretrained DDM. + +# 1. Introduction + +Using the iterative denoising diffusion principle, denoising diffusion models (DDMs) trained with web-scale data can generate highly realistic images conditioned on input text, layouts, and scene graphs [24, 25, 27]. After image generation, the next important application of DDMs being explored by the research community is that of im + +age editing. Models such as DALL-E-2 [24] and Stable Diffusion [25] can perform inpainting, allowing users to edit images through manual annotation. Methods such as SDEdit [20] have demonstrated that both synthetic and real images can be edited using stroke or composite guidance via DDMs. However, the goal of holistic image editing tools that can edit any real/artificial image using purely text is still a field of active research. + +The generative process of DDMs starts with an initial noise vector $(x_{T})$ and performs iterative denoising (typically with a guidance signal e.g. in the form of text-conditional denoising), ending with a realistic image sample $(x_0)$ . Reversing this generative process is key in solving this image editing problem for one family of approaches. Formally, this problem is known as "inversion" i.e., finding the initial noise vector that produces the input image when passed through the diffusion process. + +A naive approach for inversion is to add Gaussian noise to the input image and perform a predefined number of diffusion steps, which typically results in significant distortions [7]. A more robust method is adapting Denoising Diffusion Implicit Models (DDIMs) [29]. Unlike the commonly used Denoising Diffusion Probabilistic Models (DDPMs) [9], the generative process in DDIMs is defined in a non-Markovian manner, which results in a deterministic denoising process. DDIM can also be used for inversion, deterministically noising an image to obtain the initial noise vector $(x_0 \to x_T)$ . + +DDIM inversion has been used for editing real images through text methods such as DDIBs [30] and Prompt-to-Prompt (P2P) image editing [7]. After DDIM inversion, P2P edits the original image by running the generative process from the noise vector and injecting conditioning information from a new text prompt through the cross-attention layers in the diffusion model, thus generating an edited image that maintains faithfulness to the original content while incorporating the edit. However, as noted in the original P2P work [7], the DDIM inversion is unstable in many cases—encoding from $x_0$ to $x_T$ and back often results in inexact reconstructions of the original image as in Fig. 2. These distortions limit the ability to perform significant ma + +![](images/059ae3ec808c9023739ec4f379fbccd17656068e96a090dd6aba6202bd853bf0.jpg) +Figure 1. EDICT enables complex real image edits, such as editing dog breeds. We highlight the fine-grain text preservation in the bottom row of examples, with the message remaining even as the dog undergoes dramatic transformations. More examples, including baseline comparisons for all image-breed pairs, are included in the Supplementary. All original images from the ImageNet 2012 validation set. + +nipulations through text as increase in the corruption is correlated with the strength of the conditioning. + +To improve the inversion ability of DDMs and enable robust real image editing, we diagnose the problems in DDIM inversion, and offer a solution: Exact Diffusion Inversion via Coupled Transformations (EDICT). EDICT is a re-formulation of the DDIM process inspired by coupling layers in normalizing flow models [4, 5, 12] that allows for mathematically exact inversion. By maintaining two coupled noise vectors in the diffusion process, EDICT enables recovery of the original noise vector in the case of model-generated images; and for real imagery, initial noise vectors that are guaranteed to map to the original image when the EDICT generative process is run. While EDICT doubles the computation time of the diffusion process, it can be combined with any pretrained DDM model and does + +not require any computationally-expensive model finetuning, prompt tuning, or multiple images. + +For the standard generative process, EDICT approximates DDIM well, resulting in nearly identical generations given equal initial conditions. For real images, EDICT can recover a noise vector which yields an exact reconstruction when used as input to the generative process. Experiments with the COCO dataset [16] show that EDICT can recover complex image features such as detailed textures, thin objects, subtle reflections, faces, and text, while DDIM fails to do so consistently. Finally, using the initial noise vectors derived from a real image with EDICT, we can sample from a DDM and perform complex edits or transformations to real images using textual guidance. We show editing capabilities including local and global modifications of objects and background and object transformations (Fig. 1). + +![](images/9340c0f66c4c7d5c585f6eff50f62ece6b4153becc99d60ba8b226f539fa76ef.jpg) +Figure 2. While both unconditional and conditional DDIM [29] often fail to accurately reconstruct real images, leading to loss of global image structure and/or finer details, EDICT is able to almost perfectly reconstruct even complex scenes. Examples from ImageNet and COCO with 50 DDIM steps. Captions used only in DDIM Conditional reconstruction with a guidance scale of 3. + +# 2. Related Work + +Diffusion Models and Normalizing Flows: Denoising diffusion models (DDMs), drawing on nonequilibrium thermodynamics [28], have emerged at the forefront of image generation. Models such as GLIDE [22], DALLE-2 [24], Imagen (Video) [8, 27], Latent/Stable Diffusion [25], and eDiffi [1] all utilize concepts borrowed from thermodynamics to hallucinate an image from pure noise by training on intermediately noised images. While a commonly used sampling process in DDMs is the stochastic Denoising Diffusion Probabilistic Models (DDPMs) method [9], a deterministic sampling method was introduced in Denoising Diffusion Implicit Models (DDIM) [29]. Multi-step or higher-order methods that parallel DDIM have also been proposed [17, 19], including methods that aim to reducing the computational time for generation [13, 18]. Another class of generative models relevant to our work are normalizing flow models [4, 5, 12]. In these models, an invertible mapping is learned between a latent gaussian distribution and image space. The methods of invertibility, specifically coupling layers, are used as an inspiration for our method. Invertible neural networks have been studied in areas outside of normalizing flows as well. Neural ODEs [2] have many parallels with the diffusion process and can be inverted using a variety of ODE solvers. + +Editing in Diffusion Models: The seminal work in apply + +ing DDMs to image editing is SDEdit [20] where coarse layouts are used to guide the generative process by nois-ing the layout to resemble an intermediately noised image. Prompt-to-Prompt [7] combines query-key pairs from one prompt with values from another in the attention layers of a DDM to enable prompt-guided image editing from intermediate latents obtained by sampler inversion [29, 31]. DiffEdit [3] edits real/synthetic images using automatically generated masks for regions of an input image that should be edited given a text query. Kwon et al. [14] introduce style and structure losses to guide the sampling process to enable text-guided image translation. CycleDiffusion [32] uses a deterministic DPM encoder to enable zero-shot image-to-image translation. Concurrent work [21] also stabilizes text-conditioned inversion, optimizing the null embedding $\emptyset$ for consistency. While highly effective, the algorithmic exactness is not guaranteed and per-case optimization is required. Another set of methods [6, 11, 26] finetune the model with the target image and/or learn a new conditioning prompt to enable indirect image editing via sampling. EDICT, our proposed approach, does not require any specialized training/finetuning, and can be paired with any pretrained DDM. + +# 3. Background + +# 3.1. Denoising Diffusion Models + +DDMs are trained on a simple denoising objective. A set of timesteps index a monotonic strictly increasing noisingschedule $\{\alpha_{t}\}_{t = 0}^{T},\alpha_{T} = 0,\alpha_{0} = 1$ . Images (or autoencoded latents) $x\in X$ are noised with draws $\epsilon \sim N(0,I)$ according to the noising schedule following the formula + +$$ +x _ {t} = \sqrt {\alpha_ {t}} x + \sqrt {1 - \alpha_ {t}} \epsilon \tag {1} +$$ + +The time-aware DDM $\Theta$ is trained on the objective $MSE(\Theta(x_{t}, t, C), \epsilon)$ to predict the noise added to the original image where $C$ is a conditioning signal (typically in the form of a text embedding) with some probability of random assignment to the null conditioning $\emptyset$ . To generate a novel image from a gaussian draw $\epsilon_{T} \sim N(0, I)$ , partial denoising is applied at each $t$ . The most common sampling scheme is that of DDIM [29] where intermediate steps are calculated as + +$$ +\begin{array}{l} x _ {t - 1} = \sqrt {\alpha_ {t - 1}} \frac {x _ {t} - \sqrt {1 - \alpha_ {t}} \Theta \left(x _ {t} , t , C\right)}{\sqrt {\alpha_ {t}}} \tag {2} \\ + \sqrt {1 - \alpha_ {t - 1}} \Theta (x _ {t}, t, C) \\ \end{array} +$$ + +In practice, for text-to-image models to hallucinate from random noise an $x_0$ that matches conditioning $C$ to desired levels, the model has to be biased more heavily towards generations aligned with $C$ . To do so, a pseudo-gradient $G \cdot (\Theta(x_t, t, C) - \Theta(x_t, t, \emptyset))$ is added to the unconditional prediction $\Theta(x_t, t, \emptyset)$ to up-weight the effect of conditioning, where $G$ is a weighting parameter, Substituting + +$\Phi (x_{t},t,C,G) = \Theta (x_{t},t,\emptyset) + G\cdot (\Theta (x_{t},t,C) - \Theta (x_{t},t,\emptyset))$ into the prior equation for the $\Theta$ term, we simplify the notation $\Phi (x_{t},t,C,G)\rightarrow \epsilon (x_{t},t)$ and rewrite the previous equation as $x_{t - 1} = a_tx_t + b_t\epsilon (x_t,t)$ where + +$$ +a _ {t} = \sqrt {\alpha_ {t - 1} / \alpha_ {t}} \tag {3} +$$ + +$$ +b _ {t} = - \sqrt {\alpha_ {t - 1} \left(1 - \alpha_ {t}\right) / \alpha_ {t}} + \sqrt {1 - \alpha_ {t - 1}} \tag {4} +$$ + +# 3.2. Denoising Diffusion Implicit Model (DDIM) + +As noted in DDIM [29], the above denoising process is approximately invertible; that is $x_{t}$ is approximately recoverable from $x_{t - 1}$ + +$$ +x _ {t} = \frac {x _ {t - 1} - b _ {t} \epsilon (x _ {t} , t)}{a _ {t}} \approx \frac {x _ {t - 1} - b _ {t} \epsilon (x _ {t - 1} , t)}{a _ {t}} \tag {5} +$$ + +where the approximation is a linearization assumption that $\epsilon(x_{t}, t) \approx \epsilon(x_{t-1}, t)$ (necessary due to the discrete nature of both computation and the underlying noise schedule). This corresponds with reversing the Euler integration which is a first-order ODE solver. More sophisticated solvers such as multi-step Euler [17] have been shown to stabilize the generative process, and correspondingly the deterministic inversion process, with fewer time steps. However, such methods are also approximations where the inversion accuracy ultimately relies on the strength of the linearization assumption and the reconstruction is not exactly equal. This assumption is largely accurate for unconditional DDIM generation, but the pseudo-gradient of classifier-free guidance $G \cdot (\Theta(x_{t}, t, C) - \Theta(x_{t}, t, \emptyset))$ is inconsistent across time steps as shown in the Supplementary. + +While unconditional reconstructions have relatively insignificant errors (Fig. 2), conditional reconstructions are extremely distorted when noised to high levels. This phenomenon was noted in [7], where the guidance scale must be heavily downweighted in order for inversions on real-world images to be stable, thus limiting the strength of edits. Obtaining an $x_{t}$ from $x_{0}$ allows for the generative process to be run with novel conditioning. In SDEdit [20], this process is done stochastically to obtain broad sample diversity, at the cost of controllability and faithfulness to the original image contents. In contrast, the inverse DDIM process produces a unique $x_{t}$ from a single $x_{0}$ in a deterministic manner, yielding only one sample but enabling higher strength edits while preserving finer-grain structure and content. + +# 3.3. Affine Coupling Layers + +Affine Coupling Layers (ACL) are invertible neural network layers introduced in [4, 5] and used in other normalizing flow models such as Glow [12]. The layer input $z$ , is split into two equal-dimensional halves $z_{a}$ and $z_{b}$ . A modified version of $z_{a}$ is then calculated, according to: + +$$ +z _ {a} ^ {\prime} = \Psi (z _ {b}) z _ {a} + \psi (z _ {b}) \tag {6} +$$ + +![](images/bb054b1b36b60322f620e1c82f637bdd28a47a010a6bf6d2281469fec8337a1c.jpg) +Figure 3. Information flow of EDICT. Denoising process (sampling) follows the arrows forwards, sampler inversion backwards. From $(x_{t},y_{t})$ , $(x_{t - 1},y_{t - 1})$ can be calculated while holding a single member of each sequence in memory at a time. All steps are invertible, so $(x_{t},y_{t})$ can be exactly recovered from $(x_{t - 1},y_{t - 1})$ , as opposed to current methods which compute an approximation. + +where $\Psi$ and $\psi$ are neural networks. The layer output $z^{\prime}$ is the concatenation of $z_{a}^{\prime}$ and $z_{b}$ in accordance with the original splitting function. ACL can parameterize complex functions and $z$ can be exactly recovered given $z^{\prime}$ : + +$$ +z _ {a} = \left(z _ {a} ^ {\prime} - \psi \left(z _ {b}\right)\right) / \Psi \left(z _ {b}\right) \tag {7} +$$ + +Noting the similarity of equations 6 and 7 to the simplified form of Eq. (2), we parallel this construction in our method (described next) where two separate quantities are tracked and alternately modified by transformations that are affine with respect to the original modified quantity and a nonlinear transformation of its counterpart. + +# 4. Exact Diffusion Inversion via Coupled Transformations (EDICT) + +# 4.1. Making an Invertible Diffusion Process + +As summarized in Sec. 3.3, affine coupling layers track two quantities which can then be used to invert each other. These two quantities are partitions of a latent representation with a network specifically designed to operate in a fitting alternating manner. Without training of a new DDM, this method can not be applied out-of-the-box to the forward diffusion process. We consider the simplified form of the forward step equation from Sec. 3.1 below + +$$ +x _ {t - 1} := a _ {t} x _ {t} + b _ {t} \epsilon \left(x _ {t}, t\right) \tag {8} +$$ + +If the noise prediction term, $\epsilon (x_{t},t) = \varepsilon$ was independent of $x_{t}$ , this would be an affine function in both $x_{t}$ , and $\varepsilon$ . Paralleling Eq. (6), by creating a new variable $y_{t} = x_{t}$ the stepping equation fits the desired form. Consider performing this computation, so we have the variables $x_{t}$ , $y_{t} = x_{t}$ , $x_{t - 1} = a_{t}x_{t} + b_{t}\epsilon (y_{t},t)$ . $x_{t}$ can be recovered exactly from $x_{t - 1}$ in the non-trivial form: + +$$ +x _ {t} = \left(x _ {t - 1} - b _ {t} \cdot \epsilon \left(y _ {t}, t\right)\right) / a _ {t} \tag {9} +$$ + +$y_{t} = x_{t}$ is trivial and will not be true in the general case. Now consider the initialization of the reverse (denoising) diffusion process, where $x_{T} \sim \mathcal{N}(0,1)$ , we similarly initialize $y_{T} = x_{T}$ . Following the above process, we define the update rule + +![](images/90b3298bfd76d45f2823ab8e44b5b7d233eded607230e45731119768d302ef7f.jpg) +Figure 4. Images generated from the same text prompt and random seed. EDICT $x / y$ (No mixing) employs coupling layers but not intermediate mixing layers, resulting in distorted and inconsistent images as $x$ and $y$ diverge. EDICT is our full method with the sequences explicitly contracted together, resulting in identical images that match DDIM (Baseline) in quality and composition. Top row prompt: A white horse galloping through a forest Bottom row prompt: A couple of glasses are sitting on a table + +$$ +x _ {t - 1} = a _ {t} x _ {t} + b _ {t} \cdot \epsilon \left(y _ {t}, t\right) \tag {10} +$$ + +$$ +y _ {t - 1} = a _ {t} y _ {t} + b _ {t} \cdot \epsilon \left(x _ {t - 1}, t\right) +$$ + +Note that the noise prediction term in the second line is a function of the other sequence value at the next timestep. Only one member of each sequence $(x_{t},y_{t(\pm 1)})$ must be held in memory at any given time. The sequences can be recovered exactly according to + +$$ +y _ {t} = \left(y _ {t - 1} - b _ {t} \cdot \epsilon \left(x _ {t - 1}, t\right)\right) / a _ {t} \tag {11} +$$ + +$$ +x _ {t} = \left(x _ {t - 1} - b _ {t} \cdot \epsilon \left(y _ {t}, t\right)\right) / a _ {t} +$$ + +As illustrated in Fig. 3, the entire sequence can be reconstructed from any two adjacent $x_{i}$ and $y_{i}$ . In sum, our method reuses the linearization assumption of Euler DDIM inversion, that $\epsilon(x_{t}, t) \approx \epsilon(x_{t-1}, t)$ , but crucially does not rely on it for invertibility, guaranteeing recovery up to machine precision. We note that the functional form of our approach bears similarities to the ODE solver Heun's method where derivative values at initial predictions are used to refine predictions, but due to the need for invertibility we cannot exploit this for more accurate/faster sampling. + +# 4.2. Stabilization + +While our method assures invertibility by design, realism and faithfulness to the original diffusion process are not automatic. When naively applied for a typical, low number of DDIM steps (e.g., $T = 50$ ), the sequences $x_{t}$ and $y_{t}$ can diverge (Fig. 4). This is a result of the strong linearization assumption not holding in practice. To alleviate this problem, we introduce intermediate mixing layers after each diffusion step computing weighted averages of the form + +$$ +x ^ {\prime} = p x + (1 - p) y, 0 \leq p \leq 1 \tag {12} +$$ + +which are invertible affine transformations. Note that this averaging layer becomes a dilating layer during deterministic noising; the inversion being + +![](images/5f3652f90e3e40046e8328cdd26066256f89842732702c5d7a098b7362d2e236.jpg) +Figure 5. We visualize the effect of the mixing coefficient $p$ . Top row: an EDICT-generated image with $p = 0.93$ , for each listed $p$ a generation is computed from $T = 50$ to $T = 0$ followed by reconstructing initial latents $(T = 50)$ . Cosine similarity between $(x_{t}, y_{t})$ is computed at each step. $p = 0.97$ suffices for generative convergence, but the inverse process diverges when $p$ is too small. Repeated dilation can exponentially exaggerate small floating-point differences, annulling the theoretical guarantee. These trends hold in the bottom row for a non-generated image put through the EDICT inversion/generation process. While all reconstructions ultimately are aligned, a sufficiently large $p$ is needed for the latents to maintain alignment throughout. + +$$ +x = \frac {x ^ {\prime} - (1 - p) y}{p} \tag {13} +$$ + +A high (near 1) value of $p$ results in the averaging layer not being strong enough to prevent divergence of the $x$ and $y$ series during denoising, while a low value of $p$ results in a numerically unstable exponential dilation in the backwards pass (Fig. 5). Note that in both cases that our generative process remains exactly mathematically invertible with no further assumptions, but there is a degradation in utility of the results. Typically we employ $p = 0.93$ , with values in the interval [0.9, 0.97] generally being effective for 50 steps. + +# 4.3. Complete Summary of the Method + +We dub our presented process EDICT: Exact Diffusion Inversion via Coupled Transformations. In sum, EDICT uses a combination of "coupling" and "averaging/dilating" steps for exact inversion of the diffusion process. Given $x_{t}$ and $y_{t}$ , we calculate the denoising process by + +$$ +x _ {t} ^ {\text {i n t e r}} = a _ {t} \cdot x _ {t} + b _ {t} \cdot \epsilon (y _ {t}, t) +$$ + +$$ +y _ {t} ^ {\text {i n t e r}} = a _ {t} \cdot y _ {t} + b _ {t} \cdot \epsilon \left(x _ {t} ^ {\text {i n t e r}}, t\right) \tag {14} +$$ + +$$ +x _ {t - 1} = p \cdot x _ {t} ^ {\text {i n t e r}} + (1 - p) \cdot y _ {t} ^ {\text {i n t e r}} +$$ + +$$ +y _ {t - 1} = p \cdot y _ {t} ^ {\text {i n t e r}} + (1 - p) \cdot x _ {t - 1} +$$ + +COCO Reconstruction Error (MSE) + +
MethodLDM AEEDICT (UC)EDICT (C)DDIM (UC)DDIM (C)
50 Steps0.0150.0150.0150.0300.420
100 Steps0.0150.0150.0150.0270.471
200 Steps0.0150.0150.0150.0230.497
+ +Table 1. Mean-square reconstruction error for COCO-val using the first listed prompt as conditioning with $G = 7$ . The latent diffusion model autoencoder (LDM AE) is the lower bound on reconstruction error. Using half precision increases 50-step EDICT (C) MSE by $6\%$ . More step values are in the Supplementary. + +and the deterministic noising inversion process by: + +$$ +y _ {t + 1} ^ {i n t e r} = \left(y _ {t} - (1 - p) \cdot x _ {t}\right) / p +$$ + +$$ +x _ {t + 1} ^ {\text {i n t e r}} = \left(x _ {t} - (1 - p) \cdot y _ {t + 1} ^ {\text {i n t e r}}\right) / p \tag {15} +$$ + +$$ +y _ {t + 1} = \left(y _ {t + 1} ^ {\text {i n t e r}} - b _ {t + 1} \cdot \epsilon \left(x _ {t + 1} ^ {\text {i n t e r}}, t + 1\right)\right) / a _ {t + 1} +$$ + +$$ +x _ {t + 1} = \left(x _ {t + 1} ^ {\text {i n t e r}} - b _ {t + 1} \cdot \epsilon \left(y _ {t + 1}, t + 1\right)\right) / a _ {t + 1} +$$ + +Recall that the conditioning $C$ is implicitly included in the $\epsilon$ terms. In practice, we alternate the order in which the $x$ and $y$ series are calculated at each step in order to symmetrize the process with respect to both sequences. We cast all operations to double floating point precision (from the native half precision) to mitigate roundoff floating point errors. + +# 4.4. Image Editing + +While EDICT can theoretically operate on either pixel-based or latent-diffusion models we present the latter case in this work. Given an image $I$ , we edit the semantic contents to match text conditioning $C_{target}$ . We describe the current content by text $C_{base}$ in a parallel manner to $C_{target}$ . We compute an autoencoder latent $x_0 = VAE_{enc}(I)$ , initializing $y_0 = x_0$ . We run the deterministic noising process of Eq. (15) on $(x_0, y_0)$ using text conditioning $C_{base}$ for $s \cdot S$ steps, where $S$ is the number of global timesteps and $s$ is a chosen editing strength. This yields partially "noised" latents $(x_t, y_t)$ which are not necessarily equal and, in practice, tend to diverge by a small amount due to linearization error and the dilation of the mixing layers. These intermediate representations are then used as input to Eq. (14) using text condition $C_{target}$ , and identical step parameters, $(s, S)$ . The resulting image outputs $(VAE_{dec}(x_0^{edit}), VAE_{dec}(y_0^{edit}))$ are empirically nearly identical as seen in Fig. 4, this is by design of the method and in particular, the mixing layers. For all methods we find that a guidance scale of 3 performs well (as opposed to the standard 7.5 for generation). + +# 5. Experiments + +We now describe results using the Stable Diffusion 1.4 latent diffusion model [25]. + +# 5.1. Image Reconstruction + +We demonstrate the exact invertibility of EDICT using the MS-COCO-2017 validation set $(n = 5,000)$ , which contains both simple object-centric images and complex scene images [16]. Given an image-caption pair, inverted latents are calculated and used to reconstruct the image. Mean-square error is calculated on pixels normalized to $[-1,1]$ and averaged across all images in the dataset. This process is performed both with and without the text as conditioning (C vs. UC). For COCO, we use the first listed prompt as conditioning. The LDM autoencoder reconstruction error serves as a lower bound. EDICT maintains complete latent recovery in all examples for both 50 and 200 steps, with error $50 - 75\%$ that of DDIM (UC) (Tab. 1). DDIM (C) is unstable for inversions (also noted in [7]), which results in an error an order of magnitude greater than any other, with failure to reconstruct as shown in Fig. 2. + +# 5.2. Image Editing + +We show EDICT's ability to perform complex editing tasks on real images in Fig. 6. In the first row, a diverse set of objects are added to a lake scene, demonstrating object addition. In the giraffe and car examples, we see interaction between introduced and original objects. Additionally, both the giraffe and castle examples capture reflections of the added objects, while the pattern of the water is maintained. Throughout all edits, details such as the cloud patterns and patches of tree color are preserved. The second row shows object-preserving global changes. A chair is placed into a variety of settings while keeping near-perfect identity and detail, even when occlusions are generated (grass and snow). In all examples the chair keeps a realistic footing, despite ground changes. + +In the third row, we demonstrate that EDICT is able to perform object deformations, a challenging class of edits for DDM methods, as many broad compositional components are determined very early in the generation [7]. The previously most successful method for these types of edits, Imagic [11] requires model finetuning. EDICT makes the sculpture assume a broad set of poses, spatially changing the semantic map in a refined way. Novel views, such as "A statue from behind" are able to be plausibly rendered Across these large-scale edits, fine-grained details such as the face and dress of the statue -as well as the foliage and path- are preserved. In the fourth row, we show that EDICT is able to perform global style changes while maintaining layout and details where appropriate. The layout is nearly identical across images (note the preserved cloud pattern), but can be changed when needed (e.g., the lack of trees in the Mars example). Specific art-styles are capable of being generated, including challenging concepts such as cubism. + +In Fig. 1, EDICT makes semantic entity edits to and from a variety of dog breeds. It proves adept at holding the + +![](images/b2409047b8de2f4cb1ec6918e40e59eb8fe51be5553ccc7fdb526fb2be9b1884.jpg) +Real Image + +![](images/d6d8dbc9d8a262a0c5812b885f9f4abe6ecb53d229430c244e441a1f5287b7bd.jpg) +Edited Images +"A giraffe in .. + +![](images/ea1716688dc97f43dfaaff378a2c6f8445ba4441c6d4b260518ceac0a204e393.jpg) +"A car stuck in..." + +![](images/6a0fc9d130bda7624ae74d33de851f59601f914daaca643a1b2933a304ebe81e.jpg) +"A castle overlooking .. + +![](images/61abb83360787d974e7c87ef3f177970f85c41158c82b1e78a487b2eeb231639.jpg) +"A fountain in..." + +![](images/75d6fd8c098299e82e2818da9bd0443f1ea3ae710ed49da83bb38bcf45e0b003.jpg) +"A lake" +"A red chair" + +![](images/80bab42ac80fdca000489be65dc54ccb6dc55fa8e58260463a8ee38fd8cbb6e2.jpg) +"at the Grand Canyon" + +![](images/33acbf351fcd47b4a8c08add040c67c01e4b85be6824235e0f7ed45c0785fd9e.jpg) +".. on a field of grass" + +![](images/ea5b3e74d3fe94ed0d7911e260b372ffd5263261d43e3dd0adb285764e2928f6.jpg) +.. covered in snow in the mountains + +![](images/da476fa9f80cc9c9bb6ffbea16fa0611676d1073cad2adb4e8046d8b0d5ccd25.jpg) +..after a flood + +![](images/e85b879fd1e6a6050c200b9be662879acdbeb8710c74815594948272fa26aa13.jpg) +"A statue" + +![](images/44b48845a1fa1f3232ac38876cb8fcbcdd25d82e3050fc3dc99a7314e10c88aa.jpg) +..with raised arms + +![](images/9871c42437f0c2c1a9b591147fa3067d712c88bd21c9a35a4ed81386bfd4000f.jpg) +walking + +![](images/367b3d1d0387c6e4414787034b1680a806895ec9dec6eee540bb58824627ff91.jpg) +".. from behind + +![](images/af38b4d0c7173e07cad29f19391cec846b59971bd4fac87d6ad21be2f4a0ff43.jpg) +".. standing alone giving a thumbs-up" + +![](images/cd015e724d6ce017c72aa73ff47fc70bf25e645f89c19e10f50d6d9ab1531e64.jpg) +"A waterfall in the mountains" +Figure 6. Examples of the strength and varied editing ability of EDICT. From top to bottom: object additions, global context changes with object preservation, deformations while preserving identity, and global style changes. The bidirectional reversibility of EDICT's process allows for large-scale changes to the image while maintaining auxiliary details. + +![](images/1825ecf54775b7a8e0d5cd11512d7dbbbf77b52e90fc44a5db67446469c843ac.jpg) +"A cubist painting of .. + +![](images/e66e95a17b3b1382d613daf794810ca14bbc12fa5667462591db7fdfa96c8634.jpg) +"An impressionistic painting of .. + +![](images/5081d8e63440fe7b2d89eb4d6eaf19b043ea6fda6a26019f9de8cd909404a5e0.jpg) +".. in the fall + +![](images/b027898018a085a89edc982bf76e94f5d1f0a1db0b0afb9a2c44ae5ed275bd95.jpg) +".. on Mars" + +original subject pose, including in the third row where the dog is viewed in a very atypical position. The realism in the Chihuahua examples is particularly interesting, due to the relatively small size of the breed. We again highlight the preservation of details such as the background foliage or ground in the upper three rows. The fourth row is of specific interest as small text is preserved across examples (a typical failure case for DDIM). + +Baseline Comparison: In Fig. 7, we demonstrate EDICT's superior performance to other DDM sampling-based methods for image editing: conditional and unconditional DDIM inversion, prompt-to-prompt image editing, and SDEdit (as a stochastic baseline). All methods are run with 50 steps (we do not observe improvement of baselines when the number of steps are increased, see Supplementary). Since methods that require model finetuning or prompt tuning [6, 11, 26] can be combined with EDICT, we view them + +![](images/c95eb20135da6785b55fe2325f18089f68ed3c50aea15ba8e59e01d7ef42250c.jpg) +Figure 7. EDICT compared to baseline editing methods. EDICT demonstrates superior preservation of unedited components while still performing the edit edit. Further comparison between EDICT and baselines (including concurrent work ([14,32]) is in the Supplementary. + +as complementary to, rather than competitive with, EDICT, and do not perform a direct comparison with them. We quantitatively compare visual metrics of edits in Fig. 8. + +# 6. Discussion + +Limitations and Future Work: EDICT is deterministic, only outputs one generation per image-prompt pair (vs. SDEdit). Also, the computational time is approximately twice that of baseline DDIM. As with all editing methods, performance can vary across inputs in a hard-to-predict manner and sometimes requires careful prompt selection. For future work, we note that the induced latent space constructed by the inversion process admits operations such as latent interpolation [10] which has not been widely applied to real images. As in prompt tuning [15], formalizing the process of prompt selection could further improve EDICT. Adding a controllable degree of randomness to EDICT could yield multiple candidate generations per input. + +Ethics: Like other image generation and editing models, EDICT will produce images that may reflect the socioeconomic biases of the training data or images that could be considered inappropriate. Image editing methods can also utilized for malicious purposes, including harassment and misinformation spread. Practitioners utilizing EDICT or its methodologies in a production setting should consider these limitations. An in-depth discussion on the ethics of image generation can be found in Imagen [27]. + +![](images/40d2877efabc602fe0fe62095caf8e99ed47caf750a546fd8b2e642244b6ecc5.jpg) +Figure 8. We quantitatively benchmark all methods on image editing using images from five ImageNet mammal classes (African Elephant, Ram, Egyptian Cat, Brown Bear, and Norfolk Terrier). Four experiments are performed, one swapping the pictured animal's species to each of the other classes (20 species editing pairs in total), two contextual changes (A [animal] in the snow and A [animal] in a parking lot), and one stylistic (An impressionistic painting of a [animal]). The LPIPS [33] (visual similarity) score to the original image and a CLIP score [23] (semantic similarity) to a set of five related text queries is computed per edit. Metrics are averaged across images and experiments. Details and human evaluation are provided in the Supplementary. 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The standard approach for real image editing with inversion uses denoising diffusion implicit models (DDIMs [29]) to deterministically noise the image to the intermediate state along the path that the denoising would follow given the original conditioning. However, DDIM inversion for real images is unstable as it relies on local linearization assumptions, which result in the propagation of errors, leading to incorrect image reconstruction and loss of content. To alleviate these problems, we propose Exact Diffusion Inversion via Coupled Transformations (EDICT), an inversion method that draws inspiration from affine coupling layers. EDICT enables mathematically exact inversion of real and model-generated images by maintaining two coupled noise vectors which are used to invert each other in an alternating fashion. Using Stable Diffusion [25], a state-of-the-art latent diffusion model, we demonstrate that EDICT successfully reconstructs real images with high fidelity. On complex image datasets like MS-COCO, EDICT reconstruction significantly outperforms DDIM, improving the mean square error of reconstruction by a factor of two. Using noise vectors inverted from real images, EDICT enables a wide range of image edits—from local and global semantic edits to image stylization—while maintaining fidelity to the original image structure. EDICT requires no model training/finetuning, prompt tuning, or extra data and can be combined with any pretrained DDM." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 47, + 620, + 128, + 633 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 620, + 128, + 633 + ], + "spans": [ + { + "bbox": [ + 47, + 620, + 128, + 633 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 46, + 641, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 641, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 641, + 288, + 714 + ], + "type": "text", + "content": "Using the iterative denoising diffusion principle, denoising diffusion models (DDMs) trained with web-scale data can generate highly realistic images conditioned on input text, layouts, and scene graphs [24, 25, 27]. After image generation, the next important application of DDMs being explored by the research community is that of im" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 213, + 547, + 309 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 213, + 547, + 309 + ], + "spans": [ + { + "bbox": [ + 304, + 213, + 547, + 309 + ], + "type": "text", + "content": "age editing. Models such as DALL-E-2 [24] and Stable Diffusion [25] can perform inpainting, allowing users to edit images through manual annotation. Methods such as SDEdit [20] have demonstrated that both synthetic and real images can be edited using stroke or composite guidance via DDMs. However, the goal of holistic image editing tools that can edit any real/artificial image using purely text is still a field of active research." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 312, + 547, + 421 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 312, + 547, + 421 + ], + "spans": [ + { + "bbox": [ + 304, + 312, + 547, + 421 + ], + "type": "text", + "content": "The generative process of DDMs starts with an initial noise vector " + }, + { + "bbox": [ + 304, + 312, + 547, + 421 + ], + "type": "inline_equation", + "content": "(x_{T})" + }, + { + "bbox": [ + 304, + 312, + 547, + 421 + ], + "type": "text", + "content": " and performs iterative denoising (typically with a guidance signal e.g. in the form of text-conditional denoising), ending with a realistic image sample " + }, + { + "bbox": [ + 304, + 312, + 547, + 421 + ], + "type": "inline_equation", + "content": "(x_0)" + }, + { + "bbox": [ + 304, + 312, + 547, + 421 + ], + "type": "text", + "content": ". Reversing this generative process is key in solving this image editing problem for one family of approaches. Formally, this problem is known as \"inversion\" i.e., finding the initial noise vector that produces the input image when passed through the diffusion process." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 423, + 548, + 555 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 423, + 548, + 555 + ], + "spans": [ + { + "bbox": [ + 304, + 423, + 548, + 555 + ], + "type": "text", + "content": "A naive approach for inversion is to add Gaussian noise to the input image and perform a predefined number of diffusion steps, which typically results in significant distortions [7]. A more robust method is adapting Denoising Diffusion Implicit Models (DDIMs) [29]. Unlike the commonly used Denoising Diffusion Probabilistic Models (DDPMs) [9], the generative process in DDIMs is defined in a non-Markovian manner, which results in a deterministic denoising process. DDIM can also be used for inversion, deterministically noising an image to obtain the initial noise vector " + }, + { + "bbox": [ + 304, + 423, + 548, + 555 + ], + "type": "inline_equation", + "content": "(x_0 \\to x_T)" + }, + { + "bbox": [ + 304, + 423, + 548, + 555 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 557, + 548, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 557, + 548, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 557, + 548, + 715 + ], + "type": "text", + "content": "DDIM inversion has been used for editing real images through text methods such as DDIBs [30] and Prompt-to-Prompt (P2P) image editing [7]. After DDIM inversion, P2P edits the original image by running the generative process from the noise vector and injecting conditioning information from a new text prompt through the cross-attention layers in the diffusion model, thus generating an edited image that maintains faithfulness to the original content while incorporating the edit. However, as noted in the original P2P work [7], the DDIM inversion is unstable in many cases—encoding from " + }, + { + "bbox": [ + 304, + 557, + 548, + 715 + ], + "type": "inline_equation", + "content": "x_0" + }, + { + "bbox": [ + 304, + 557, + 548, + 715 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 304, + 557, + 548, + 715 + ], + "type": "inline_equation", + "content": "x_T" + }, + { + "bbox": [ + 304, + 557, + 548, + 715 + ], + "type": "text", + "content": " and back often results in inexact reconstructions of the original image as in Fig. 2. These distortions limit the ability to perform significant ma" + } + ] + } + ], + "index": 19 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "22532" + } + ] + } + ], + "index": 20 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 60, + 77, + 539, + 443 + ], + "blocks": [ + { + "bbox": [ + 60, + 77, + 539, + 443 + ], + "lines": [ + { + "bbox": [ + 60, + 77, + 539, + 443 + ], + "spans": [ + { + "bbox": [ + 60, + 77, + 539, + 443 + ], + "type": "image", + "image_path": "059ae3ec808c9023739ec4f379fbccd17656068e96a090dd6aba6202bd853bf0.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 456, + 546, + 491 + ], + "lines": [ + { + "bbox": [ + 46, + 456, + 546, + 491 + ], + "spans": [ + { + "bbox": [ + 46, + 456, + 546, + 491 + ], + "type": "text", + "content": "Figure 1. EDICT enables complex real image edits, such as editing dog breeds. We highlight the fine-grain text preservation in the bottom row of examples, with the message remaining even as the dog undergoes dramatic transformations. More examples, including baseline comparisons for all image-breed pairs, are included in the Supplementary. All original images from the ImageNet 2012 validation set." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 510, + 288, + 536 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 510, + 288, + 536 + ], + "spans": [ + { + "bbox": [ + 46, + 510, + 288, + 536 + ], + "type": "text", + "content": "nipulations through text as increase in the corruption is correlated with the strength of the conditioning." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 545, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 545, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 545, + 289, + 715 + ], + "type": "text", + "content": "To improve the inversion ability of DDMs and enable robust real image editing, we diagnose the problems in DDIM inversion, and offer a solution: Exact Diffusion Inversion via Coupled Transformations (EDICT). EDICT is a re-formulation of the DDIM process inspired by coupling layers in normalizing flow models [4, 5, 12] that allows for mathematically exact inversion. By maintaining two coupled noise vectors in the diffusion process, EDICT enables recovery of the original noise vector in the case of model-generated images; and for real imagery, initial noise vectors that are guaranteed to map to the original image when the EDICT generative process is run. While EDICT doubles the computation time of the diffusion process, it can be combined with any pretrained DDM model and does" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 305, + 510, + 545, + 536 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 510, + 545, + 536 + ], + "spans": [ + { + "bbox": [ + 305, + 510, + 545, + 536 + ], + "type": "text", + "content": "not require any computationally-expensive model finetuning, prompt tuning, or multiple images." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 545, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 545, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 545, + 547, + 715 + ], + "type": "text", + "content": "For the standard generative process, EDICT approximates DDIM well, resulting in nearly identical generations given equal initial conditions. For real images, EDICT can recover a noise vector which yields an exact reconstruction when used as input to the generative process. Experiments with the COCO dataset [16] show that EDICT can recover complex image features such as detailed textures, thin objects, subtle reflections, faces, and text, while DDIM fails to do so consistently. Finally, using the initial noise vectors derived from a real image with EDICT, we can sample from a DDM and perform complex edits or transformations to real images using textual guidance. We show editing capabilities including local and global modifications of objects and background and object transformations (Fig. 1)." + } + ] + } + ], + "index": 5 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "22533" + } + ] + } + ], + "index": 6 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 49, + 71, + 287, + 297 + ], + "blocks": [ + { + "bbox": [ + 49, + 71, + 287, + 297 + ], + "lines": [ + { + "bbox": [ + 49, + 71, + 287, + 297 + ], + "spans": [ + { + "bbox": [ + 49, + 71, + 287, + 297 + ], + "type": "image", + "image_path": "9340c0f66c4c7d5c585f6eff50f62ece6b4153becc99d60ba8b226f539fa76ef.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 305, + 288, + 373 + ], + "lines": [ + { + "bbox": [ + 46, + 305, + 288, + 373 + ], + "spans": [ + { + "bbox": [ + 46, + 305, + 288, + 373 + ], + "type": "text", + "content": "Figure 2. While both unconditional and conditional DDIM [29] often fail to accurately reconstruct real images, leading to loss of global image structure and/or finer details, EDICT is able to almost perfectly reconstruct even complex scenes. Examples from ImageNet and COCO with 50 DDIM steps. Captions used only in DDIM Conditional reconstruction with a guidance scale of 3." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 392, + 134, + 405 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 392, + 134, + 405 + ], + "spans": [ + { + "bbox": [ + 47, + 392, + 134, + 405 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 413, + 287, + 700 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 413, + 287, + 700 + ], + "spans": [ + { + "bbox": [ + 46, + 413, + 287, + 700 + ], + "type": "text", + "content": "Diffusion Models and Normalizing Flows: Denoising diffusion models (DDMs), drawing on nonequilibrium thermodynamics [28], have emerged at the forefront of image generation. Models such as GLIDE [22], DALLE-2 [24], Imagen (Video) [8, 27], Latent/Stable Diffusion [25], and eDiffi [1] all utilize concepts borrowed from thermodynamics to hallucinate an image from pure noise by training on intermediately noised images. While a commonly used sampling process in DDMs is the stochastic Denoising Diffusion Probabilistic Models (DDPMs) method [9], a deterministic sampling method was introduced in Denoising Diffusion Implicit Models (DDIM) [29]. Multi-step or higher-order methods that parallel DDIM have also been proposed [17, 19], including methods that aim to reducing the computational time for generation [13, 18]. Another class of generative models relevant to our work are normalizing flow models [4, 5, 12]. In these models, an invertible mapping is learned between a latent gaussian distribution and image space. The methods of invertibility, specifically coupling layers, are used as an inspiration for our method. Invertible neural networks have been studied in areas outside of normalizing flows as well. Neural ODEs [2] have many parallels with the diffusion process and can be inverted using a variety of ODE solvers." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 701, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 701, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 47, + 701, + 287, + 714 + ], + "type": "text", + "content": "Editing in Diffusion Models: The seminal work in apply" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 72, + 545, + 336 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 336 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 336 + ], + "type": "text", + "content": "ing DDMs to image editing is SDEdit [20] where coarse layouts are used to guide the generative process by nois-ing the layout to resemble an intermediately noised image. Prompt-to-Prompt [7] combines query-key pairs from one prompt with values from another in the attention layers of a DDM to enable prompt-guided image editing from intermediate latents obtained by sampler inversion [29, 31]. DiffEdit [3] edits real/synthetic images using automatically generated masks for regions of an input image that should be edited given a text query. Kwon et al. [14] introduce style and structure losses to guide the sampling process to enable text-guided image translation. CycleDiffusion [32] uses a deterministic DPM encoder to enable zero-shot image-to-image translation. Concurrent work [21] also stabilizes text-conditioned inversion, optimizing the null embedding " + }, + { + "bbox": [ + 304, + 72, + 545, + 336 + ], + "type": "inline_equation", + "content": "\\emptyset" + }, + { + "bbox": [ + 304, + 72, + 545, + 336 + ], + "type": "text", + "content": " for consistency. While highly effective, the algorithmic exactness is not guaranteed and per-case optimization is required. Another set of methods [6, 11, 26] finetune the model with the target image and/or learn a new conditioning prompt to enable indirect image editing via sampling. EDICT, our proposed approach, does not require any specialized training/finetuning, and can be paired with any pretrained DDM." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 306, + 345, + 384, + 358 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 345, + 384, + 358 + ], + "spans": [ + { + "bbox": [ + 306, + 345, + 384, + 358 + ], + "type": "text", + "content": "3. Background" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 364, + 457, + 377 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 364, + 457, + 377 + ], + "spans": [ + { + "bbox": [ + 306, + 364, + 457, + 377 + ], + "type": "text", + "content": "3.1. Denoising Diffusion Models" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 383, + 545, + 443 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 383, + 545, + 443 + ], + "spans": [ + { + "bbox": [ + 304, + 383, + 545, + 443 + ], + "type": "text", + "content": "DDMs are trained on a simple denoising objective. A set of timesteps index a monotonic strictly increasing noisingschedule " + }, + { + "bbox": [ + 304, + 383, + 545, + 443 + ], + "type": "inline_equation", + "content": "\\{\\alpha_{t}\\}_{t = 0}^{T},\\alpha_{T} = 0,\\alpha_{0} = 1" + }, + { + "bbox": [ + 304, + 383, + 545, + 443 + ], + "type": "text", + "content": " . Images (or autoencoded latents) " + }, + { + "bbox": [ + 304, + 383, + 545, + 443 + ], + "type": "inline_equation", + "content": "x\\in X" + }, + { + "bbox": [ + 304, + 383, + 545, + 443 + ], + "type": "text", + "content": " are noised with draws " + }, + { + "bbox": [ + 304, + 383, + 545, + 443 + ], + "type": "inline_equation", + "content": "\\epsilon \\sim N(0,I)" + }, + { + "bbox": [ + 304, + 383, + 545, + 443 + ], + "type": "text", + "content": " according to the noising schedule following the formula" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 375, + 449, + 545, + 462 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 375, + 449, + 545, + 462 + ], + "spans": [ + { + "bbox": [ + 375, + 449, + 545, + 462 + ], + "type": "interline_equation", + "content": "x _ {t} = \\sqrt {\\alpha_ {t}} x + \\sqrt {1 - \\alpha_ {t}} \\epsilon \\tag {1}", + "image_path": "2bcfd554791a5d0460b7f54ac9c1e4099705d6eaf5b653c22a809cf5927cdae8.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 468, + 545, + 576 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 468, + 545, + 576 + ], + "spans": [ + { + "bbox": [ + 304, + 468, + 545, + 576 + ], + "type": "text", + "content": "The time-aware DDM " + }, + { + "bbox": [ + 304, + 468, + 545, + 576 + ], + "type": "inline_equation", + "content": "\\Theta" + }, + { + "bbox": [ + 304, + 468, + 545, + 576 + ], + "type": "text", + "content": " is trained on the objective " + }, + { + "bbox": [ + 304, + 468, + 545, + 576 + ], + "type": "inline_equation", + "content": "MSE(\\Theta(x_{t}, t, C), \\epsilon)" + }, + { + "bbox": [ + 304, + 468, + 545, + 576 + ], + "type": "text", + "content": " to predict the noise added to the original image where " + }, + { + "bbox": [ + 304, + 468, + 545, + 576 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 304, + 468, + 545, + 576 + ], + "type": "text", + "content": " is a conditioning signal (typically in the form of a text embedding) with some probability of random assignment to the null conditioning " + }, + { + "bbox": [ + 304, + 468, + 545, + 576 + ], + "type": "inline_equation", + "content": "\\emptyset" + }, + { + "bbox": [ + 304, + 468, + 545, + 576 + ], + "type": "text", + "content": ". To generate a novel image from a gaussian draw " + }, + { + "bbox": [ + 304, + 468, + 545, + 576 + ], + "type": "inline_equation", + "content": "\\epsilon_{T} \\sim N(0, I)" + }, + { + "bbox": [ + 304, + 468, + 545, + 576 + ], + "type": "text", + "content": ", partial denoising is applied at each " + }, + { + "bbox": [ + 304, + 468, + 545, + 576 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 468, + 545, + 576 + ], + "type": "text", + "content": ". The most common sampling scheme is that of DDIM [29] where intermediate steps are calculated as" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 342, + 580, + 545, + 624 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 342, + 580, + 545, + 624 + ], + "spans": [ + { + "bbox": [ + 342, + 580, + 545, + 624 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} x _ {t - 1} = \\sqrt {\\alpha_ {t - 1}} \\frac {x _ {t} - \\sqrt {1 - \\alpha_ {t}} \\Theta \\left(x _ {t} , t , C\\right)}{\\sqrt {\\alpha_ {t}}} \\tag {2} \\\\ + \\sqrt {1 - \\alpha_ {t - 1}} \\Theta (x _ {t}, t, C) \\\\ \\end{array}", + "image_path": "d0c6730ff248c4b20cc8feb333f0ea03b00a20e346e85d82b68570fe83e20079.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 629, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 629, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 629, + 545, + 714 + ], + "type": "text", + "content": "In practice, for text-to-image models to hallucinate from random noise an " + }, + { + "bbox": [ + 304, + 629, + 545, + 714 + ], + "type": "inline_equation", + "content": "x_0" + }, + { + "bbox": [ + 304, + 629, + 545, + 714 + ], + "type": "text", + "content": " that matches conditioning " + }, + { + "bbox": [ + 304, + 629, + 545, + 714 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 304, + 629, + 545, + 714 + ], + "type": "text", + "content": " to desired levels, the model has to be biased more heavily towards generations aligned with " + }, + { + "bbox": [ + 304, + 629, + 545, + 714 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 304, + 629, + 545, + 714 + ], + "type": "text", + "content": ". To do so, a pseudo-gradient " + }, + { + "bbox": [ + 304, + 629, + 545, + 714 + ], + "type": "inline_equation", + "content": "G \\cdot (\\Theta(x_t, t, C) - \\Theta(x_t, t, \\emptyset))" + }, + { + "bbox": [ + 304, + 629, + 545, + 714 + ], + "type": "text", + "content": " is added to the unconditional prediction " + }, + { + "bbox": [ + 304, + 629, + 545, + 714 + ], + "type": "inline_equation", + "content": "\\Theta(x_t, t, \\emptyset)" + }, + { + "bbox": [ + 304, + 629, + 545, + 714 + ], + "type": "text", + "content": " to up-weight the effect of conditioning, where " + }, + { + "bbox": [ + 304, + 629, + 545, + 714 + ], + "type": "inline_equation", + "content": "G" + }, + { + "bbox": [ + 304, + 629, + 545, + 714 + ], + "type": "text", + "content": " is a weighting parameter, Substituting" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "22534" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 287, + 120 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 287, + 120 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 287, + 120 + ], + "type": "inline_equation", + "content": "\\Phi (x_{t},t,C,G) = \\Theta (x_{t},t,\\emptyset) + G\\cdot (\\Theta (x_{t},t,C) - \\Theta (x_{t},t,\\emptyset))" + }, + { + "bbox": [ + 47, + 72, + 287, + 120 + ], + "type": "text", + "content": " into the prior equation for the " + }, + { + "bbox": [ + 47, + 72, + 287, + 120 + ], + "type": "inline_equation", + "content": "\\Theta" + }, + { + "bbox": [ + 47, + 72, + 287, + 120 + ], + "type": "text", + "content": " term, we simplify the notation " + }, + { + "bbox": [ + 47, + 72, + 287, + 120 + ], + "type": "inline_equation", + "content": "\\Phi (x_{t},t,C,G)\\rightarrow \\epsilon (x_{t},t)" + }, + { + "bbox": [ + 47, + 72, + 287, + 120 + ], + "type": "text", + "content": " and rewrite the previous equation as " + }, + { + "bbox": [ + 47, + 72, + 287, + 120 + ], + "type": "inline_equation", + "content": "x_{t - 1} = a_tx_t + b_t\\epsilon (x_t,t)" + }, + { + "bbox": [ + 47, + 72, + 287, + 120 + ], + "type": "text", + "content": " where" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 81, + 127, + 287, + 142 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 81, + 127, + 287, + 142 + ], + "spans": [ + { + "bbox": [ + 81, + 127, + 287, + 142 + ], + "type": "interline_equation", + "content": "a _ {t} = \\sqrt {\\alpha_ {t - 1} / \\alpha_ {t}} \\tag {3}", + "image_path": "f54cc7352079e6808c9a34da725fe5905f784427a45c3f7c5848298c09104313.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 82, + 144, + 287, + 160 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 82, + 144, + 287, + 160 + ], + "spans": [ + { + "bbox": [ + 82, + 144, + 287, + 160 + ], + "type": "interline_equation", + "content": "b _ {t} = - \\sqrt {\\alpha_ {t - 1} \\left(1 - \\alpha_ {t}\\right) / \\alpha_ {t}} + \\sqrt {1 - \\alpha_ {t - 1}} \\tag {4}", + "image_path": "50e2210834bd3ce521a478995a419d6763a5d85183039445d8cc3986b769343b.jpg" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 166, + 275, + 178 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 166, + 275, + 178 + ], + "spans": [ + { + "bbox": [ + 47, + 166, + 275, + 178 + ], + "type": "text", + "content": "3.2. Denoising Diffusion Implicit Model (DDIM)" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 185, + 287, + 220 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 185, + 287, + 220 + ], + "spans": [ + { + "bbox": [ + 47, + 185, + 287, + 220 + ], + "type": "text", + "content": "As noted in DDIM [29], the above denoising process is approximately invertible; that is " + }, + { + "bbox": [ + 47, + 185, + 287, + 220 + ], + "type": "inline_equation", + "content": "x_{t}" + }, + { + "bbox": [ + 47, + 185, + 287, + 220 + ], + "type": "text", + "content": " is approximately recoverable from " + }, + { + "bbox": [ + 47, + 185, + 287, + 220 + ], + "type": "inline_equation", + "content": "x_{t - 1}" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 71, + 227, + 287, + 253 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 71, + 227, + 287, + 253 + ], + "spans": [ + { + "bbox": [ + 71, + 227, + 287, + 253 + ], + "type": "interline_equation", + "content": "x _ {t} = \\frac {x _ {t - 1} - b _ {t} \\epsilon (x _ {t} , t)}{a _ {t}} \\approx \\frac {x _ {t - 1} - b _ {t} \\epsilon (x _ {t - 1} , t)}{a _ {t}} \\tag {5}", + "image_path": "687fb9261e64e531812dc57b7c0bf95887a87c743dcb7aeecf0f372b293ec6ef.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 258, + 287, + 437 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 258, + 287, + 437 + ], + "spans": [ + { + "bbox": [ + 46, + 258, + 287, + 437 + ], + "type": "text", + "content": "where the approximation is a linearization assumption that " + }, + { + "bbox": [ + 46, + 258, + 287, + 437 + ], + "type": "inline_equation", + "content": "\\epsilon(x_{t}, t) \\approx \\epsilon(x_{t-1}, t)" + }, + { + "bbox": [ + 46, + 258, + 287, + 437 + ], + "type": "text", + "content": " (necessary due to the discrete nature of both computation and the underlying noise schedule). This corresponds with reversing the Euler integration which is a first-order ODE solver. More sophisticated solvers such as multi-step Euler [17] have been shown to stabilize the generative process, and correspondingly the deterministic inversion process, with fewer time steps. However, such methods are also approximations where the inversion accuracy ultimately relies on the strength of the linearization assumption and the reconstruction is not exactly equal. This assumption is largely accurate for unconditional DDIM generation, but the pseudo-gradient of classifier-free guidance " + }, + { + "bbox": [ + 46, + 258, + 287, + 437 + ], + "type": "inline_equation", + "content": "G \\cdot (\\Theta(x_{t}, t, C) - \\Theta(x_{t}, t, \\emptyset))" + }, + { + "bbox": [ + 46, + 258, + 287, + 437 + ], + "type": "text", + "content": " is inconsistent across time steps as shown in the Supplementary." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 437, + 287, + 605 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 437, + 287, + 605 + ], + "spans": [ + { + "bbox": [ + 46, + 437, + 287, + 605 + ], + "type": "text", + "content": "While unconditional reconstructions have relatively insignificant errors (Fig. 2), conditional reconstructions are extremely distorted when noised to high levels. This phenomenon was noted in [7], where the guidance scale must be heavily downweighted in order for inversions on real-world images to be stable, thus limiting the strength of edits. Obtaining an " + }, + { + "bbox": [ + 46, + 437, + 287, + 605 + ], + "type": "inline_equation", + "content": "x_{t}" + }, + { + "bbox": [ + 46, + 437, + 287, + 605 + ], + "type": "text", + "content": " from " + }, + { + "bbox": [ + 46, + 437, + 287, + 605 + ], + "type": "inline_equation", + "content": "x_{0}" + }, + { + "bbox": [ + 46, + 437, + 287, + 605 + ], + "type": "text", + "content": " allows for the generative process to be run with novel conditioning. In SDEdit [20], this process is done stochastically to obtain broad sample diversity, at the cost of controllability and faithfulness to the original image contents. In contrast, the inverse DDIM process produces a unique " + }, + { + "bbox": [ + 46, + 437, + 287, + 605 + ], + "type": "inline_equation", + "content": "x_{t}" + }, + { + "bbox": [ + 46, + 437, + 287, + 605 + ], + "type": "text", + "content": " from a single " + }, + { + "bbox": [ + 46, + 437, + 287, + 605 + ], + "type": "inline_equation", + "content": "x_{0}" + }, + { + "bbox": [ + 46, + 437, + 287, + 605 + ], + "type": "text", + "content": " in a deterministic manner, yielding only one sample but enabling higher strength edits while preserving finer-grain structure and content." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 612, + 179, + 624 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 612, + 179, + 624 + ], + "spans": [ + { + "bbox": [ + 47, + 612, + 179, + 624 + ], + "type": "text", + "content": "3.3. Affine Coupling Layers" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 630, + 287, + 690 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 630, + 287, + 690 + ], + "spans": [ + { + "bbox": [ + 47, + 630, + 287, + 690 + ], + "type": "text", + "content": "Affine Coupling Layers (ACL) are invertible neural network layers introduced in [4, 5] and used in other normalizing flow models such as Glow [12]. The layer input " + }, + { + "bbox": [ + 47, + 630, + 287, + 690 + ], + "type": "inline_equation", + "content": "z" + }, + { + "bbox": [ + 47, + 630, + 287, + 690 + ], + "type": "text", + "content": ", is split into two equal-dimensional halves " + }, + { + "bbox": [ + 47, + 630, + 287, + 690 + ], + "type": "inline_equation", + "content": "z_{a}" + }, + { + "bbox": [ + 47, + 630, + 287, + 690 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 630, + 287, + 690 + ], + "type": "inline_equation", + "content": "z_{b}" + }, + { + "bbox": [ + 47, + 630, + 287, + 690 + ], + "type": "text", + "content": ". A modified version of " + }, + { + "bbox": [ + 47, + 630, + 287, + 690 + ], + "type": "inline_equation", + "content": "z_{a}" + }, + { + "bbox": [ + 47, + 630, + 287, + 690 + ], + "type": "text", + "content": " is then calculated, according to:" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 119, + 697, + 287, + 711 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 119, + 697, + 287, + 711 + ], + "spans": [ + { + "bbox": [ + 119, + 697, + 287, + 711 + ], + "type": "interline_equation", + "content": "z _ {a} ^ {\\prime} = \\Psi (z _ {b}) z _ {a} + \\psi (z _ {b}) \\tag {6}", + "image_path": "9328185aad1108f6c98b16f0866ed225c781b2b19049b7fc3b4364f1106b6440.jpg" + } + ] + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 336, + 69, + 494, + 121 + ], + "blocks": [ + { + "bbox": [ + 336, + 69, + 494, + 121 + ], + "lines": [ + { + "bbox": [ + 336, + 69, + 494, + 121 + ], + "spans": [ + { + "bbox": [ + 336, + 69, + 494, + 121 + ], + "type": "image", + "image_path": "bb054b1b36b60322f620e1c82f637bdd28a47a010a6bf6d2281469fec8337a1c.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 132, + 545, + 198 + ], + "lines": [ + { + "bbox": [ + 305, + 132, + 545, + 198 + ], + "spans": [ + { + "bbox": [ + 305, + 132, + 545, + 198 + ], + "type": "text", + "content": "Figure 3. Information flow of EDICT. Denoising process (sampling) follows the arrows forwards, sampler inversion backwards. From " + }, + { + "bbox": [ + 305, + 132, + 545, + 198 + ], + "type": "inline_equation", + "content": "(x_{t},y_{t})" + }, + { + "bbox": [ + 305, + 132, + 545, + 198 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 305, + 132, + 545, + 198 + ], + "type": "inline_equation", + "content": "(x_{t - 1},y_{t - 1})" + }, + { + "bbox": [ + 305, + 132, + 545, + 198 + ], + "type": "text", + "content": " can be calculated while holding a single member of each sequence in memory at a time. All steps are invertible, so " + }, + { + "bbox": [ + 305, + 132, + 545, + 198 + ], + "type": "inline_equation", + "content": "(x_{t},y_{t})" + }, + { + "bbox": [ + 305, + 132, + 545, + 198 + ], + "type": "text", + "content": " can be exactly recovered from " + }, + { + "bbox": [ + 305, + 132, + 545, + 198 + ], + "type": "inline_equation", + "content": "(x_{t - 1},y_{t - 1})" + }, + { + "bbox": [ + 305, + 132, + 545, + 198 + ], + "type": "text", + "content": ", as opposed to current methods which compute an approximation." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 217, + 545, + 265 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 217, + 545, + 265 + ], + "spans": [ + { + "bbox": [ + 305, + 217, + 545, + 265 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 217, + 545, + 265 + ], + "type": "inline_equation", + "content": "\\Psi" + }, + { + "bbox": [ + 305, + 217, + 545, + 265 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 217, + 545, + 265 + ], + "type": "inline_equation", + "content": "\\psi" + }, + { + "bbox": [ + 305, + 217, + 545, + 265 + ], + "type": "text", + "content": " are neural networks. The layer output " + }, + { + "bbox": [ + 305, + 217, + 545, + 265 + ], + "type": "inline_equation", + "content": "z^{\\prime}" + }, + { + "bbox": [ + 305, + 217, + 545, + 265 + ], + "type": "text", + "content": " is the concatenation of " + }, + { + "bbox": [ + 305, + 217, + 545, + 265 + ], + "type": "inline_equation", + "content": "z_{a}^{\\prime}" + }, + { + "bbox": [ + 305, + 217, + 545, + 265 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 217, + 545, + 265 + ], + "type": "inline_equation", + "content": "z_{b}" + }, + { + "bbox": [ + 305, + 217, + 545, + 265 + ], + "type": "text", + "content": " in accordance with the original splitting function. ACL can parameterize complex functions and " + }, + { + "bbox": [ + 305, + 217, + 545, + 265 + ], + "type": "inline_equation", + "content": "z" + }, + { + "bbox": [ + 305, + 217, + 545, + 265 + ], + "type": "text", + "content": " can be exactly recovered given " + }, + { + "bbox": [ + 305, + 217, + 545, + 265 + ], + "type": "inline_equation", + "content": "z^{\\prime}" + }, + { + "bbox": [ + 305, + 217, + 545, + 265 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 372, + 270, + 545, + 284 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 372, + 270, + 545, + 284 + ], + "spans": [ + { + "bbox": [ + 372, + 270, + 545, + 284 + ], + "type": "interline_equation", + "content": "z _ {a} = \\left(z _ {a} ^ {\\prime} - \\psi \\left(z _ {b}\\right)\\right) / \\Psi \\left(z _ {b}\\right) \\tag {7}", + "image_path": "aff8b7eb60bb0cb61e24f0a14839f4acc32e58c07a5d2e5b7ba3743ab1c94dd9.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 289, + 545, + 361 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 289, + 545, + 361 + ], + "spans": [ + { + "bbox": [ + 305, + 289, + 545, + 361 + ], + "type": "text", + "content": "Noting the similarity of equations 6 and 7 to the simplified form of Eq. (2), we parallel this construction in our method (described next) where two separate quantities are tracked and alternately modified by transformations that are affine with respect to the original modified quantity and a nonlinear transformation of its counterpart." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 306, + 371, + 545, + 398 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 371, + 545, + 398 + ], + "spans": [ + { + "bbox": [ + 306, + 371, + 545, + 398 + ], + "type": "text", + "content": "4. Exact Diffusion Inversion via Coupled Transformations (EDICT)" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 404, + 511, + 417 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 404, + 511, + 417 + ], + "spans": [ + { + "bbox": [ + 306, + 404, + 511, + 417 + ], + "type": "text", + "content": "4.1. Making an Invertible Diffusion Process" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 305, + 423, + 545, + 519 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 423, + 545, + 519 + ], + "spans": [ + { + "bbox": [ + 305, + 423, + 545, + 519 + ], + "type": "text", + "content": "As summarized in Sec. 3.3, affine coupling layers track two quantities which can then be used to invert each other. These two quantities are partitions of a latent representation with a network specifically designed to operate in a fitting alternating manner. Without training of a new DDM, this method can not be applied out-of-the-box to the forward diffusion process. We consider the simplified form of the forward step equation from Sec. 3.1 below" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 372, + 526, + 545, + 538 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 372, + 526, + 545, + 538 + ], + "spans": [ + { + "bbox": [ + 372, + 526, + 545, + 538 + ], + "type": "interline_equation", + "content": "x _ {t - 1} := a _ {t} x _ {t} + b _ {t} \\epsilon \\left(x _ {t}, t\\right) \\tag {8}", + "image_path": "c9a82970bb7c8a7e5dd70aaf95488af40aa5dce6a57beb369060a2b649f33b60.jpg" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 305, + 544, + 545, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 544, + 545, + 628 + ], + "spans": [ + { + "bbox": [ + 305, + 544, + 545, + 628 + ], + "type": "text", + "content": "If the noise prediction term, " + }, + { + "bbox": [ + 305, + 544, + 545, + 628 + ], + "type": "inline_equation", + "content": "\\epsilon (x_{t},t) = \\varepsilon" + }, + { + "bbox": [ + 305, + 544, + 545, + 628 + ], + "type": "text", + "content": " was independent of " + }, + { + "bbox": [ + 305, + 544, + 545, + 628 + ], + "type": "inline_equation", + "content": "x_{t}" + }, + { + "bbox": [ + 305, + 544, + 545, + 628 + ], + "type": "text", + "content": ", this would be an affine function in both " + }, + { + "bbox": [ + 305, + 544, + 545, + 628 + ], + "type": "inline_equation", + "content": "x_{t}" + }, + { + "bbox": [ + 305, + 544, + 545, + 628 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 305, + 544, + 545, + 628 + ], + "type": "inline_equation", + "content": "\\varepsilon" + }, + { + "bbox": [ + 305, + 544, + 545, + 628 + ], + "type": "text", + "content": ". Paralleling Eq. (6), by creating a new variable " + }, + { + "bbox": [ + 305, + 544, + 545, + 628 + ], + "type": "inline_equation", + "content": "y_{t} = x_{t}" + }, + { + "bbox": [ + 305, + 544, + 545, + 628 + ], + "type": "text", + "content": " the stepping equation fits the desired form. Consider performing this computation, so we have the variables " + }, + { + "bbox": [ + 305, + 544, + 545, + 628 + ], + "type": "inline_equation", + "content": "x_{t}" + }, + { + "bbox": [ + 305, + 544, + 545, + 628 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 305, + 544, + 545, + 628 + ], + "type": "inline_equation", + "content": "y_{t} = x_{t}" + }, + { + "bbox": [ + 305, + 544, + 545, + 628 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 305, + 544, + 545, + 628 + ], + "type": "inline_equation", + "content": "x_{t - 1} = a_{t}x_{t} + b_{t}\\epsilon (y_{t},t)" + }, + { + "bbox": [ + 305, + 544, + 545, + 628 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 305, + 544, + 545, + 628 + ], + "type": "inline_equation", + "content": "x_{t}" + }, + { + "bbox": [ + 305, + 544, + 545, + 628 + ], + "type": "text", + "content": " can be recovered exactly from " + }, + { + "bbox": [ + 305, + 544, + 545, + 628 + ], + "type": "inline_equation", + "content": "x_{t - 1}" + }, + { + "bbox": [ + 305, + 544, + 545, + 628 + ], + "type": "text", + "content": " in the non-trivial form:" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 364, + 635, + 545, + 647 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 364, + 635, + 545, + 647 + ], + "spans": [ + { + "bbox": [ + 364, + 635, + 545, + 647 + ], + "type": "interline_equation", + "content": "x _ {t} = \\left(x _ {t - 1} - b _ {t} \\cdot \\epsilon \\left(y _ {t}, t\\right)\\right) / a _ {t} \\tag {9}", + "image_path": "ca0b032624ccfd0f36cfcca932a57f7454caa9bf29f37a67417db6132b762c5c.jpg" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 305, + 654, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 654, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 654, + 545, + 713 + ], + "type": "inline_equation", + "content": "y_{t} = x_{t}" + }, + { + "bbox": [ + 305, + 654, + 545, + 713 + ], + "type": "text", + "content": " is trivial and will not be true in the general case. Now consider the initialization of the reverse (denoising) diffusion process, where " + }, + { + "bbox": [ + 305, + 654, + 545, + 713 + ], + "type": "inline_equation", + "content": "x_{T} \\sim \\mathcal{N}(0,1)" + }, + { + "bbox": [ + 305, + 654, + 545, + 713 + ], + "type": "text", + "content": ", we similarly initialize " + }, + { + "bbox": [ + 305, + 654, + 545, + 713 + ], + "type": "inline_equation", + "content": "y_{T} = x_{T}" + }, + { + "bbox": [ + 305, + 654, + 545, + 713 + ], + "type": "text", + "content": ". Following the above process, we define the update rule" + } + ] + } + ], + "index": 22 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "22535" + } + ] + } + ], + "index": 23 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 50, + 69, + 286, + 180 + ], + "blocks": [ + { + "bbox": [ + 50, + 69, + 286, + 180 + ], + "lines": [ + { + "bbox": [ + 50, + 69, + 286, + 180 + ], + "spans": [ + { + "bbox": [ + 50, + 69, + 286, + 180 + ], + "type": "image", + "image_path": "90b3298bfd76d45f2823ab8e44b5b7d233eded607230e45731119768d302ef7f.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 189, + 289, + 277 + ], + "lines": [ + { + "bbox": [ + 46, + 189, + 289, + 277 + ], + "spans": [ + { + "bbox": [ + 46, + 189, + 289, + 277 + ], + "type": "text", + "content": "Figure 4. Images generated from the same text prompt and random seed. EDICT " + }, + { + "bbox": [ + 46, + 189, + 289, + 277 + ], + "type": "inline_equation", + "content": "x / y" + }, + { + "bbox": [ + 46, + 189, + 289, + 277 + ], + "type": "text", + "content": " (No mixing) employs coupling layers but not intermediate mixing layers, resulting in distorted and inconsistent images as " + }, + { + "bbox": [ + 46, + 189, + 289, + 277 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 46, + 189, + 289, + 277 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 189, + 289, + 277 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 46, + 189, + 289, + 277 + ], + "type": "text", + "content": " diverge. EDICT is our full method with the sequences explicitly contracted together, resulting in identical images that match DDIM (Baseline) in quality and composition. Top row prompt: A white horse galloping through a forest Bottom row prompt: A couple of glasses are sitting on a table" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 116, + 290, + 287, + 308 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 116, + 290, + 287, + 308 + ], + "spans": [ + { + "bbox": [ + 116, + 290, + 287, + 308 + ], + "type": "interline_equation", + "content": "x _ {t - 1} = a _ {t} x _ {t} + b _ {t} \\cdot \\epsilon \\left(y _ {t}, t\\right) \\tag {10}", + "image_path": "2f0506afa21428462fc09e1788206c06e6f477ab01f6ea885a77350ada3d1641.jpg" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 108, + 306, + 226, + 318 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 108, + 306, + 226, + 318 + ], + "spans": [ + { + "bbox": [ + 108, + 306, + 226, + 318 + ], + "type": "interline_equation", + "content": "y _ {t - 1} = a _ {t} y _ {t} + b _ {t} \\cdot \\epsilon \\left(x _ {t - 1}, t\\right)", + "image_path": "f2859754f983390722400730536c7a58b7aaac2aa00760590d04614d926c35b7.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 322, + 287, + 381 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 322, + 287, + 381 + ], + "spans": [ + { + "bbox": [ + 46, + 322, + 287, + 381 + ], + "type": "text", + "content": "Note that the noise prediction term in the second line is a function of the other sequence value at the next timestep. Only one member of each sequence " + }, + { + "bbox": [ + 46, + 322, + 287, + 381 + ], + "type": "inline_equation", + "content": "(x_{t},y_{t(\\pm 1)})" + }, + { + "bbox": [ + 46, + 322, + 287, + 381 + ], + "type": "text", + "content": " must be held in memory at any given time. The sequences can be recovered exactly according to" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 100, + 382, + 287, + 401 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 100, + 382, + 287, + 401 + ], + "spans": [ + { + "bbox": [ + 100, + 382, + 287, + 401 + ], + "type": "interline_equation", + "content": "y _ {t} = \\left(y _ {t - 1} - b _ {t} \\cdot \\epsilon \\left(x _ {t - 1}, t\\right)\\right) / a _ {t} \\tag {11}", + "image_path": "af8eeadbd8d0eb32558f9ac54923c107508507683dda5f4b64d87d0b331c787d.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 111, + 398, + 233, + 410 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 111, + 398, + 233, + 410 + ], + "spans": [ + { + "bbox": [ + 111, + 398, + 233, + 410 + ], + "type": "interline_equation", + "content": "x _ {t} = \\left(x _ {t - 1} - b _ {t} \\cdot \\epsilon \\left(y _ {t}, t\\right)\\right) / a _ {t}", + "image_path": "bec4909163719b6ca33c0a623b4d2cbec0e9f0b379066e5251f1f0a53f991d66.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 415, + 287, + 535 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 415, + 287, + 535 + ], + "spans": [ + { + "bbox": [ + 46, + 415, + 287, + 535 + ], + "type": "text", + "content": "As illustrated in Fig. 3, the entire sequence can be reconstructed from any two adjacent " + }, + { + "bbox": [ + 46, + 415, + 287, + 535 + ], + "type": "inline_equation", + "content": "x_{i}" + }, + { + "bbox": [ + 46, + 415, + 287, + 535 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 415, + 287, + 535 + ], + "type": "inline_equation", + "content": "y_{i}" + }, + { + "bbox": [ + 46, + 415, + 287, + 535 + ], + "type": "text", + "content": ". In sum, our method reuses the linearization assumption of Euler DDIM inversion, that " + }, + { + "bbox": [ + 46, + 415, + 287, + 535 + ], + "type": "inline_equation", + "content": "\\epsilon(x_{t}, t) \\approx \\epsilon(x_{t-1}, t)" + }, + { + "bbox": [ + 46, + 415, + 287, + 535 + ], + "type": "text", + "content": ", but crucially does not rely on it for invertibility, guaranteeing recovery up to machine precision. We note that the functional form of our approach bears similarities to the ODE solver Heun's method where derivative values at initial predictions are used to refine predictions, but due to the need for invertibility we cannot exploit this for more accurate/faster sampling." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 540, + 129, + 552 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 540, + 129, + 552 + ], + "spans": [ + { + "bbox": [ + 47, + 540, + 129, + 552 + ], + "type": "text", + "content": "4.2. Stabilization" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 558, + 287, + 654 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 558, + 287, + 654 + ], + "spans": [ + { + "bbox": [ + 46, + 558, + 287, + 654 + ], + "type": "text", + "content": "While our method assures invertibility by design, realism and faithfulness to the original diffusion process are not automatic. When naively applied for a typical, low number of DDIM steps (e.g., " + }, + { + "bbox": [ + 46, + 558, + 287, + 654 + ], + "type": "inline_equation", + "content": "T = 50" + }, + { + "bbox": [ + 46, + 558, + 287, + 654 + ], + "type": "text", + "content": "), the sequences " + }, + { + "bbox": [ + 46, + 558, + 287, + 654 + ], + "type": "inline_equation", + "content": "x_{t}" + }, + { + "bbox": [ + 46, + 558, + 287, + 654 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 558, + 287, + 654 + ], + "type": "inline_equation", + "content": "y_{t}" + }, + { + "bbox": [ + 46, + 558, + 287, + 654 + ], + "type": "text", + "content": " can diverge (Fig. 4). This is a result of the strong linearization assumption not holding in practice. To alleviate this problem, we introduce intermediate mixing layers after each diffusion step computing weighted averages of the form" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 100, + 659, + 287, + 673 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 100, + 659, + 287, + 673 + ], + "spans": [ + { + "bbox": [ + 100, + 659, + 287, + 673 + ], + "type": "interline_equation", + "content": "x ^ {\\prime} = p x + (1 - p) y, 0 \\leq p \\leq 1 \\tag {12}", + "image_path": "fbd6ef2b2923ee6fbadc18f87c93215e2513275102506441f4d43642e3ac8bde.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 677, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 287, + 714 + ], + "type": "text", + "content": "which are invertible affine transformations. Note that this averaging layer becomes a dilating layer during deterministic noising; the inversion being" + } + ] + } + ], + "index": 11 + }, + { + "type": "image", + "bbox": [ + 307, + 70, + 542, + 264 + ], + "blocks": [ + { + "bbox": [ + 307, + 70, + 542, + 264 + ], + "lines": [ + { + "bbox": [ + 307, + 70, + 542, + 264 + ], + "spans": [ + { + "bbox": [ + 307, + 70, + 542, + 264 + ], + "type": "image", + "image_path": "5f3652f90e3e40046e8328cdd26066256f89842732702c5d7a098b7362d2e236.jpg" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 273, + 547, + 406 + ], + "lines": [ + { + "bbox": [ + 304, + 273, + 547, + 406 + ], + "spans": [ + { + "bbox": [ + 304, + 273, + 547, + 406 + ], + "type": "text", + "content": "Figure 5. We visualize the effect of the mixing coefficient " + }, + { + "bbox": [ + 304, + 273, + 547, + 406 + ], + "type": "inline_equation", + "content": "p" + }, + { + "bbox": [ + 304, + 273, + 547, + 406 + ], + "type": "text", + "content": ". Top row: an EDICT-generated image with " + }, + { + "bbox": [ + 304, + 273, + 547, + 406 + ], + "type": "inline_equation", + "content": "p = 0.93" + }, + { + "bbox": [ + 304, + 273, + 547, + 406 + ], + "type": "text", + "content": ", for each listed " + }, + { + "bbox": [ + 304, + 273, + 547, + 406 + ], + "type": "inline_equation", + "content": "p" + }, + { + "bbox": [ + 304, + 273, + 547, + 406 + ], + "type": "text", + "content": " a generation is computed from " + }, + { + "bbox": [ + 304, + 273, + 547, + 406 + ], + "type": "inline_equation", + "content": "T = 50" + }, + { + "bbox": [ + 304, + 273, + 547, + 406 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 304, + 273, + 547, + 406 + ], + "type": "inline_equation", + "content": "T = 0" + }, + { + "bbox": [ + 304, + 273, + 547, + 406 + ], + "type": "text", + "content": " followed by reconstructing initial latents " + }, + { + "bbox": [ + 304, + 273, + 547, + 406 + ], + "type": "inline_equation", + "content": "(T = 50)" + }, + { + "bbox": [ + 304, + 273, + 547, + 406 + ], + "type": "text", + "content": ". Cosine similarity between " + }, + { + "bbox": [ + 304, + 273, + 547, + 406 + ], + "type": "inline_equation", + "content": "(x_{t}, y_{t})" + }, + { + "bbox": [ + 304, + 273, + 547, + 406 + ], + "type": "text", + "content": " is computed at each step. " + }, + { + "bbox": [ + 304, + 273, + 547, + 406 + ], + "type": "inline_equation", + "content": "p = 0.97" + }, + { + "bbox": [ + 304, + 273, + 547, + 406 + ], + "type": "text", + "content": " suffices for generative convergence, but the inverse process diverges when " + }, + { + "bbox": [ + 304, + 273, + 547, + 406 + ], + "type": "inline_equation", + "content": "p" + }, + { + "bbox": [ + 304, + 273, + 547, + 406 + ], + "type": "text", + "content": " is too small. Repeated dilation can exponentially exaggerate small floating-point differences, annulling the theoretical guarantee. These trends hold in the bottom row for a non-generated image put through the EDICT inversion/generation process. While all reconstructions ultimately are aligned, a sufficiently large " + }, + { + "bbox": [ + 304, + 273, + 547, + 406 + ], + "type": "inline_equation", + "content": "p" + }, + { + "bbox": [ + 304, + 273, + 547, + 406 + ], + "type": "text", + "content": " is needed for the latents to maintain alignment throughout." + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_caption" + } + ], + "index": 12 + }, + { + "bbox": [ + 385, + 420, + 545, + 447 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 385, + 420, + 545, + 447 + ], + "spans": [ + { + "bbox": [ + 385, + 420, + 545, + 447 + ], + "type": "interline_equation", + "content": "x = \\frac {x ^ {\\prime} - (1 - p) y}{p} \\tag {13}", + "image_path": "6b55f2cb6811d68650960be8d2db43df814d158319fa79ef9878377dd29e1ccc.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 450, + 545, + 559 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 450, + 545, + 559 + ], + "spans": [ + { + "bbox": [ + 304, + 450, + 545, + 559 + ], + "type": "text", + "content": "A high (near 1) value of " + }, + { + "bbox": [ + 304, + 450, + 545, + 559 + ], + "type": "inline_equation", + "content": "p" + }, + { + "bbox": [ + 304, + 450, + 545, + 559 + ], + "type": "text", + "content": " results in the averaging layer not being strong enough to prevent divergence of the " + }, + { + "bbox": [ + 304, + 450, + 545, + 559 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 304, + 450, + 545, + 559 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 450, + 545, + 559 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 304, + 450, + 545, + 559 + ], + "type": "text", + "content": " series during denoising, while a low value of " + }, + { + "bbox": [ + 304, + 450, + 545, + 559 + ], + "type": "inline_equation", + "content": "p" + }, + { + "bbox": [ + 304, + 450, + 545, + 559 + ], + "type": "text", + "content": " results in a numerically unstable exponential dilation in the backwards pass (Fig. 5). Note that in both cases that our generative process remains exactly mathematically invertible with no further assumptions, but there is a degradation in utility of the results. Typically we employ " + }, + { + "bbox": [ + 304, + 450, + 545, + 559 + ], + "type": "inline_equation", + "content": "p = 0.93" + }, + { + "bbox": [ + 304, + 450, + 545, + 559 + ], + "type": "text", + "content": ", with values in the interval [0.9, 0.97] generally being effective for 50 steps." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 306, + 563, + 492, + 577 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 563, + 492, + 577 + ], + "spans": [ + { + "bbox": [ + 306, + 563, + 492, + 577 + ], + "type": "text", + "content": "4.3. Complete Summary of the Method" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 582, + 545, + 643 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 545, + 643 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 545, + 643 + ], + "type": "text", + "content": "We dub our presented process EDICT: Exact Diffusion Inversion via Coupled Transformations. In sum, EDICT uses a combination of \"coupling\" and \"averaging/dilating\" steps for exact inversion of the diffusion process. Given " + }, + { + "bbox": [ + 304, + 582, + 545, + 643 + ], + "type": "inline_equation", + "content": "x_{t}" + }, + { + "bbox": [ + 304, + 582, + 545, + 643 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 582, + 545, + 643 + ], + "type": "inline_equation", + "content": "y_{t}" + }, + { + "bbox": [ + 304, + 582, + 545, + 643 + ], + "type": "text", + "content": ", we calculate the denoising process by" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 349, + 647, + 471, + 662 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 349, + 647, + 471, + 662 + ], + "spans": [ + { + "bbox": [ + 349, + 647, + 471, + 662 + ], + "type": "interline_equation", + "content": "x _ {t} ^ {\\text {i n t e r}} = a _ {t} \\cdot x _ {t} + b _ {t} \\cdot \\epsilon (y _ {t}, t)", + "image_path": "814ecab9e8c5b1737c4bce6d7b7e77dce96f22a16658beef175d0c56132e86cf.jpg" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 350, + 664, + 545, + 684 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 350, + 664, + 545, + 684 + ], + "spans": [ + { + "bbox": [ + 350, + 664, + 545, + 684 + ], + "type": "interline_equation", + "content": "y _ {t} ^ {\\text {i n t e r}} = a _ {t} \\cdot y _ {t} + b _ {t} \\cdot \\epsilon \\left(x _ {t} ^ {\\text {i n t e r}}, t\\right) \\tag {14}", + "image_path": "45cee00059b30540a2735cf6a97672ba3b86ddd822d7c834f8adc45305d3881f.jpg" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 356, + 681, + 502, + 695 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 356, + 681, + 502, + 695 + ], + "spans": [ + { + "bbox": [ + 356, + 681, + 502, + 695 + ], + "type": "interline_equation", + "content": "x _ {t - 1} = p \\cdot x _ {t} ^ {\\text {i n t e r}} + (1 - p) \\cdot y _ {t} ^ {\\text {i n t e r}}", + "image_path": "55897dcadbcd89cb4242b27e7b06c82484ed5ae077817bdc075f67c322e15ff1.jpg" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 356, + 697, + 496, + 711 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 356, + 697, + 496, + 711 + ], + "spans": [ + { + "bbox": [ + 356, + 697, + 496, + 711 + ], + "type": "interline_equation", + "content": "y _ {t - 1} = p \\cdot y _ {t} ^ {\\text {i n t e r}} + (1 - p) \\cdot x _ {t - 1}", + "image_path": "b6260b77cd721cad853dc8e46934972a49cfaed4b1ce947cd93d1b4289ab0a7f.jpg" + } + ] + } + ], + "index": 21 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "22536" + } + ] + } + ], + "index": 22 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 50, + 81, + 285, + 146 + ], + "blocks": [ + { + "bbox": [ + 102, + 71, + 232, + 80 + ], + "lines": [ + { + "bbox": [ + 102, + 71, + 232, + 80 + ], + "spans": [ + { + "bbox": [ + 102, + 71, + 232, + 80 + ], + "type": "text", + "content": "COCO Reconstruction Error (MSE)" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 50, + 81, + 285, + 146 + ], + "lines": [ + { + "bbox": [ + 50, + 81, + 285, + 146 + ], + "spans": [ + { + "bbox": [ + 50, + 81, + 285, + 146 + ], + "type": "table", + "html": "
MethodLDM AEEDICT (UC)EDICT (C)DDIM (UC)DDIM (C)
50 Steps0.0150.0150.0150.0300.420
100 Steps0.0150.0150.0150.0270.471
200 Steps0.0150.0150.0150.0230.497
", + "image_path": "16499592b34a18af3a3a6ce514b8300f45648af186de8d96ae8f483555e23997.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 154, + 287, + 210 + ], + "lines": [ + { + "bbox": [ + 46, + 154, + 287, + 210 + ], + "spans": [ + { + "bbox": [ + 46, + 154, + 287, + 210 + ], + "type": "text", + "content": "Table 1. Mean-square reconstruction error for COCO-val using the first listed prompt as conditioning with " + }, + { + "bbox": [ + 46, + 154, + 287, + 210 + ], + "type": "inline_equation", + "content": "G = 7" + }, + { + "bbox": [ + 46, + 154, + 287, + 210 + ], + "type": "text", + "content": ". The latent diffusion model autoencoder (LDM AE) is the lower bound on reconstruction error. Using half precision increases 50-step EDICT (C) MSE by " + }, + { + "bbox": [ + 46, + 154, + 287, + 210 + ], + "type": "inline_equation", + "content": "6\\%" + }, + { + "bbox": [ + 46, + 154, + 287, + 210 + ], + "type": "text", + "content": ". More step values are in the Supplementary." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 47, + 228, + 253, + 240 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 228, + 253, + 240 + ], + "spans": [ + { + "bbox": [ + 47, + 228, + 253, + 240 + ], + "type": "text", + "content": "and the deterministic noising inversion process by:" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 61, + 245, + 187, + 259 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 61, + 245, + 187, + 259 + ], + "spans": [ + { + "bbox": [ + 61, + 245, + 187, + 259 + ], + "type": "interline_equation", + "content": "y _ {t + 1} ^ {i n t e r} = \\left(y _ {t} - (1 - p) \\cdot x _ {t}\\right) / p", + "image_path": "79675ed505982d54f2550cd5c4e8d713644791f6dfe75e024417f79184070ffe.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 61, + 261, + 287, + 281 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 61, + 261, + 287, + 281 + ], + "spans": [ + { + "bbox": [ + 61, + 261, + 287, + 281 + ], + "type": "interline_equation", + "content": "x _ {t + 1} ^ {\\text {i n t e r}} = \\left(x _ {t} - (1 - p) \\cdot y _ {t + 1} ^ {\\text {i n t e r}}\\right) / p \\tag {15}", + "image_path": "347671d1c4b6d340c5408c57cc9c02cef6f557231d7f84c5584d29256c7024b7.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 67, + 277, + 256, + 292 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 67, + 277, + 256, + 292 + ], + "spans": [ + { + "bbox": [ + 67, + 277, + 256, + 292 + ], + "type": "interline_equation", + "content": "y _ {t + 1} = \\left(y _ {t + 1} ^ {\\text {i n t e r}} - b _ {t + 1} \\cdot \\epsilon \\left(x _ {t + 1} ^ {\\text {i n t e r}}, t + 1\\right)\\right) / a _ {t + 1}", + "image_path": "8937a7dbf4d459452e3880a69b0def1b52fd646158e4975b1a796cccb98608bf.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 67, + 294, + 250, + 308 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 67, + 294, + 250, + 308 + ], + "spans": [ + { + "bbox": [ + 67, + 294, + 250, + 308 + ], + "type": "interline_equation", + "content": "x _ {t + 1} = \\left(x _ {t + 1} ^ {\\text {i n t e r}} - b _ {t + 1} \\cdot \\epsilon \\left(y _ {t + 1}, t + 1\\right)\\right) / a _ {t + 1}", + "image_path": "2200d1767681a6950a72a9c59f1d65c89c5b2708776670f2d5fee2d930e50a94.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 312, + 287, + 384 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 312, + 287, + 384 + ], + "spans": [ + { + "bbox": [ + 46, + 312, + 287, + 384 + ], + "type": "text", + "content": "Recall that the conditioning " + }, + { + "bbox": [ + 46, + 312, + 287, + 384 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 46, + 312, + 287, + 384 + ], + "type": "text", + "content": " is implicitly included in the " + }, + { + "bbox": [ + 46, + 312, + 287, + 384 + ], + "type": "inline_equation", + "content": "\\epsilon" + }, + { + "bbox": [ + 46, + 312, + 287, + 384 + ], + "type": "text", + "content": " terms. In practice, we alternate the order in which the " + }, + { + "bbox": [ + 46, + 312, + 287, + 384 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 46, + 312, + 287, + 384 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 312, + 287, + 384 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 46, + 312, + 287, + 384 + ], + "type": "text", + "content": " series are calculated at each step in order to symmetrize the process with respect to both sequences. We cast all operations to double floating point precision (from the native half precision) to mitigate roundoff floating point errors." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 391, + 138, + 403 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 391, + 138, + 403 + ], + "spans": [ + { + "bbox": [ + 47, + 391, + 138, + 403 + ], + "type": "text", + "content": "4.4. Image Editing" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 409, + 289, + 661 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 409, + 289, + 661 + ], + "spans": [ + { + "bbox": [ + 46, + 409, + 289, + 661 + ], + "type": "text", + "content": "While EDICT can theoretically operate on either pixel-based or latent-diffusion models we present the latter case in this work. Given an image " + }, + { + "bbox": [ + 46, + 409, + 289, + 661 + ], + "type": "inline_equation", + "content": "I" + }, + { + "bbox": [ + 46, + 409, + 289, + 661 + ], + "type": "text", + "content": ", we edit the semantic contents to match text conditioning " + }, + { + "bbox": [ + 46, + 409, + 289, + 661 + ], + "type": "inline_equation", + "content": "C_{target}" + }, + { + "bbox": [ + 46, + 409, + 289, + 661 + ], + "type": "text", + "content": ". We describe the current content by text " + }, + { + "bbox": [ + 46, + 409, + 289, + 661 + ], + "type": "inline_equation", + "content": "C_{base}" + }, + { + "bbox": [ + 46, + 409, + 289, + 661 + ], + "type": "text", + "content": " in a parallel manner to " + }, + { + "bbox": [ + 46, + 409, + 289, + 661 + ], + "type": "inline_equation", + "content": "C_{target}" + }, + { + "bbox": [ + 46, + 409, + 289, + 661 + ], + "type": "text", + "content": ". We compute an autoencoder latent " + }, + { + "bbox": [ + 46, + 409, + 289, + 661 + ], + "type": "inline_equation", + "content": "x_0 = VAE_{enc}(I)" + }, + { + "bbox": [ + 46, + 409, + 289, + 661 + ], + "type": "text", + "content": ", initializing " + }, + { + "bbox": [ + 46, + 409, + 289, + 661 + ], + "type": "inline_equation", + "content": "y_0 = x_0" + }, + { + "bbox": [ + 46, + 409, + 289, + 661 + ], + "type": "text", + "content": ". We run the deterministic noising process of Eq. (15) on " + }, + { + "bbox": [ + 46, + 409, + 289, + 661 + ], + "type": "inline_equation", + "content": "(x_0, y_0)" + }, + { + "bbox": [ + 46, + 409, + 289, + 661 + ], + "type": "text", + "content": " using text conditioning " + }, + { + "bbox": [ + 46, + 409, + 289, + 661 + ], + "type": "inline_equation", + "content": "C_{base}" + }, + { + "bbox": [ + 46, + 409, + 289, + 661 + ], + "type": "text", + "content": " for " + }, + { + "bbox": [ + 46, + 409, + 289, + 661 + ], + "type": "inline_equation", + "content": "s \\cdot S" + }, + { + "bbox": [ + 46, + 409, + 289, + 661 + ], + "type": "text", + "content": " steps, where " + }, + { + "bbox": [ + 46, + 409, + 289, + 661 + ], + "type": "inline_equation", + "content": "S" + }, + { + "bbox": [ + 46, + 409, + 289, + 661 + ], + "type": "text", + "content": " is the number of global timesteps and " + }, + { + "bbox": [ + 46, + 409, + 289, + 661 + ], + "type": "inline_equation", + "content": "s" + }, + { + "bbox": [ + 46, + 409, + 289, + 661 + ], + "type": "text", + "content": " is a chosen editing strength. This yields partially \"noised\" latents " + }, + { + "bbox": [ + 46, + 409, + 289, + 661 + ], + "type": "inline_equation", + "content": "(x_t, y_t)" + }, + { + "bbox": [ + 46, + 409, + 289, + 661 + ], + "type": "text", + "content": " which are not necessarily equal and, in practice, tend to diverge by a small amount due to linearization error and the dilation of the mixing layers. These intermediate representations are then used as input to Eq. (14) using text condition " + }, + { + "bbox": [ + 46, + 409, + 289, + 661 + ], + "type": "inline_equation", + "content": "C_{target}" + }, + { + "bbox": [ + 46, + 409, + 289, + 661 + ], + "type": "text", + "content": ", and identical step parameters, " + }, + { + "bbox": [ + 46, + 409, + 289, + 661 + ], + "type": "inline_equation", + "content": "(s, S)" + }, + { + "bbox": [ + 46, + 409, + 289, + 661 + ], + "type": "text", + "content": ". The resulting image outputs " + }, + { + "bbox": [ + 46, + 409, + 289, + 661 + ], + "type": "inline_equation", + "content": "(VAE_{dec}(x_0^{edit}), VAE_{dec}(y_0^{edit}))" + }, + { + "bbox": [ + 46, + 409, + 289, + 661 + ], + "type": "text", + "content": " are empirically nearly identical as seen in Fig. 4, this is by design of the method and in particular, the mixing layers. For all methods we find that a guidance scale of 3 performs well (as opposed to the standard 7.5 for generation)." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 47, + 670, + 128, + 683 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 670, + 128, + 683 + ], + "spans": [ + { + "bbox": [ + 47, + 670, + 128, + 683 + ], + "type": "text", + "content": "5. Experiments" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "text", + "content": "We now describe results using the Stable Diffusion 1.4 latent diffusion model [25]." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 72, + 432, + 84 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 72, + 432, + 84 + ], + "spans": [ + { + "bbox": [ + 306, + 72, + 432, + 84 + ], + "type": "text", + "content": "5.1. Image Reconstruction" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 90, + 547, + 281 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 90, + 547, + 281 + ], + "spans": [ + { + "bbox": [ + 304, + 90, + 547, + 281 + ], + "type": "text", + "content": "We demonstrate the exact invertibility of EDICT using the MS-COCO-2017 validation set " + }, + { + "bbox": [ + 304, + 90, + 547, + 281 + ], + "type": "inline_equation", + "content": "(n = 5,000)" + }, + { + "bbox": [ + 304, + 90, + 547, + 281 + ], + "type": "text", + "content": ", which contains both simple object-centric images and complex scene images [16]. Given an image-caption pair, inverted latents are calculated and used to reconstruct the image. Mean-square error is calculated on pixels normalized to " + }, + { + "bbox": [ + 304, + 90, + 547, + 281 + ], + "type": "inline_equation", + "content": "[-1,1]" + }, + { + "bbox": [ + 304, + 90, + 547, + 281 + ], + "type": "text", + "content": " and averaged across all images in the dataset. This process is performed both with and without the text as conditioning (C vs. UC). For COCO, we use the first listed prompt as conditioning. The LDM autoencoder reconstruction error serves as a lower bound. EDICT maintains complete latent recovery in all examples for both 50 and 200 steps, with error " + }, + { + "bbox": [ + 304, + 90, + 547, + 281 + ], + "type": "inline_equation", + "content": "50 - 75\\%" + }, + { + "bbox": [ + 304, + 90, + 547, + 281 + ], + "type": "text", + "content": " that of DDIM (UC) (Tab. 1). DDIM (C) is unstable for inversions (also noted in [7]), which results in an error an order of magnitude greater than any other, with failure to reconstruct as shown in Fig. 2." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 288, + 397, + 301 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 288, + 397, + 301 + ], + "spans": [ + { + "bbox": [ + 306, + 288, + 397, + 301 + ], + "type": "text", + "content": "5.2. Image Editing" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 307, + 545, + 474 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 307, + 545, + 474 + ], + "spans": [ + { + "bbox": [ + 304, + 307, + 545, + 474 + ], + "type": "text", + "content": "We show EDICT's ability to perform complex editing tasks on real images in Fig. 6. In the first row, a diverse set of objects are added to a lake scene, demonstrating object addition. In the giraffe and car examples, we see interaction between introduced and original objects. Additionally, both the giraffe and castle examples capture reflections of the added objects, while the pattern of the water is maintained. Throughout all edits, details such as the cloud patterns and patches of tree color are preserved. The second row shows object-preserving global changes. A chair is placed into a variety of settings while keeping near-perfect identity and detail, even when occlusions are generated (grass and snow). In all examples the chair keeps a realistic footing, despite ground changes." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 474, + 546, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 474, + 546, + 689 + ], + "spans": [ + { + "bbox": [ + 304, + 474, + 546, + 689 + ], + "type": "text", + "content": "In the third row, we demonstrate that EDICT is able to perform object deformations, a challenging class of edits for DDM methods, as many broad compositional components are determined very early in the generation [7]. The previously most successful method for these types of edits, Imagic [11] requires model finetuning. EDICT makes the sculpture assume a broad set of poses, spatially changing the semantic map in a refined way. Novel views, such as \"A statue from behind\" are able to be plausibly rendered Across these large-scale edits, fine-grained details such as the face and dress of the statue -as well as the foliage and path- are preserved. In the fourth row, we show that EDICT is able to perform global style changes while maintaining layout and details where appropriate. The layout is nearly identical across images (note the preserved cloud pattern), but can be changed when needed (e.g., the lack of trees in the Mars example). Specific art-styles are capable of being generated, including challenging concepts such as cubism." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "type": "text", + "content": "In Fig. 1, EDICT makes semantic entity edits to and from a variety of dog breeds. 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} + ] + } + ], + "index": 33, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 46, + 540, + 546, + 574 + ], + "lines": [ + { + "bbox": [ + 46, + 540, + 546, + 574 + ], + "spans": [ + { + "bbox": [ + 46, + 540, + 546, + 574 + ], + "type": "text", + "content": "Figure 6. Examples of the strength and varied editing ability of EDICT. From top to bottom: object additions, global context changes with object preservation, deformations while preserving identity, and global style changes. The bidirectional reversibility of EDICT's process allows for large-scale changes to the image while maintaining auxiliary details." + } + ] + } + ], + "index": 42, + "angle": 0, + "type": "image_caption" + } + ], + "index": 32 + }, + { + "type": "image", + "bbox": [ + 150, + 418, + 243, + 514 + ], + "blocks": [ + { + "bbox": [ + 150, + 418, + 243, + 514 + ], + "lines": [ + { + "bbox": [ + 150, + 418, + 243, + 514 + ], + "spans": [ + { + "bbox": [ + 150, + 418, + 243, + 514 + ], + "type": "image", + "image_path": "1825ecf54775b7a8e0d5cd11512d7dbbbf77b52e90fc44a5db67446469c843ac.jpg" + } + ] + } + ], + "index": 34, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 174, + 514, + 219, + 531 + ], + "lines": [ + { + "bbox": [ + 174, + 514, + 219, + 531 + ], + "spans": [ + { + "bbox": [ + 174, + 514, + 219, + 531 + ], + "type": "text", + "content": "\"A cubist painting of .." + } + ] + } + ], + "index": 35, + "angle": 0, + "type": "image_caption" + } + ], + "index": 34 + }, + { + "type": "image", + "bbox": [ + 251, + 418, + 344, + 514 + ], + "blocks": [ + { + "bbox": [ + 251, + 418, + 344, + 514 + ], + "lines": [ + { + "bbox": [ + 251, + 418, + 344, + 514 + ], + "spans": [ + { + "bbox": [ + 251, + 418, + 344, + 514 + ], + "type": "image", + "image_path": "e66e95a17b3b1382d613daf794810ca14bbc12fa5667462591db7fdfa96c8634.jpg" + } + ] + } + ], + "index": 36, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 266, + 514, + 330, + 531 + ], + "lines": [ + { + "bbox": [ + 266, + 514, + 330, + 531 + ], + "spans": [ + { + "bbox": [ + 266, + 514, + 330, + 531 + ], + "type": "text", + "content": "\"An impressionistic painting of .." + } + ] + } + ], + "index": 37, + "angle": 0, + "type": "image_caption" + } + ], + "index": 36 + }, + { + "type": "image", + "bbox": [ + 352, + 418, + 445, + 514 + ], + "blocks": [ + { + "bbox": [ + 352, + 418, + 445, + 514 + ], + "lines": [ + { + "bbox": [ + 352, + 418, + 445, + 514 + ], + "spans": [ + { + "bbox": [ + 352, + 418, + 445, + 514 + ], + "type": "image", + "image_path": "5081d8e63440fe7b2d89eb4d6eaf19b043ea6fda6a26019f9de8cd909404a5e0.jpg" + } + ] + } + ], + "index": 38, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 373, + 514, + 416, + 521 + ], + "lines": [ + { + "bbox": [ + 373, + 514, + 416, + 521 + ], + "spans": [ + { + "bbox": [ + 373, + 514, + 416, + 521 + ], + "type": "text", + "content": "\".. in the fall" + } + ] + } + ], + "index": 39, + "angle": 0, + "type": "image_caption" + } + ], + "index": 38 + }, + { + "type": "image", + "bbox": [ + 452, + 418, + 545, + 514 + ], + "blocks": [ + { + "bbox": [ + 452, + 418, + 545, + 514 + ], + "lines": [ + { + "bbox": [ + 452, + 418, + 545, + 514 + ], + "spans": [ + { + "bbox": [ + 452, + 418, + 545, + 514 + ], + "type": "image", + "image_path": "b027898018a085a89edc982bf76e94f5d1f0a1db0b0afb9a2c44ae5ed275bd95.jpg" + } + ] + } + ], + "index": 40, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 474, + 514, + 514, + 521 + ], + "lines": [ + { + "bbox": [ + 474, + 514, + 514, + 521 + ], + "spans": [ + { + "bbox": [ + 474, + 514, + 514, + 521 + ], + "type": "text", + "content": "\".. on Mars\"" + } + ] + } + ], + "index": 41, + "angle": 0, + "type": "image_caption" + } + ], + "index": 40 + }, + { + "bbox": [ + 46, + 594, + 289, + 691 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 594, + 289, + 691 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 289, + 691 + ], + "type": "text", + "content": "original subject pose, including in the third row where the dog is viewed in a very atypical position. The realism in the Chihuahua examples is particularly interesting, due to the relatively small size of the breed. We again highlight the preservation of details such as the background foliage or ground in the upper three rows. The fourth row is of specific interest as small text is preserved across examples (a typical failure case for DDIM)." + } + ] + } + ], + "index": 43 + }, + { + "bbox": [ + 304, + 594, + 547, + 703 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 594, + 547, + 703 + ], + "spans": [ + { + "bbox": [ + 304, + 594, + 547, + 703 + ], + "type": "text", + "content": "Baseline Comparison: In Fig. 7, we demonstrate EDICT's superior performance to other DDM sampling-based methods for image editing: conditional and unconditional DDIM inversion, prompt-to-prompt image editing, and SDEdit (as a stochastic baseline). All methods are run with 50 steps (we do not observe improvement of baselines when the number of steps are increased, see Supplementary). Since methods that require model finetuning or prompt tuning [6, 11, 26] can be combined with EDICT, we view them" + } + ] + } + ], + "index": 44 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 749, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 749, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 749, + 317, + 757 + ], + "type": "text", + "content": "22538" + } + ] + } + ], + "index": 45 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 49, + 70, + 530, + 329 + ], + "blocks": [ + { + "bbox": [ + 49, + 70, + 530, + 329 + ], + "lines": [ + { + "bbox": [ + 49, + 70, + 530, + 329 + ], + "spans": [ + { + "bbox": [ + 49, + 70, + 530, + 329 + ], + "type": "image", + "image_path": "c95eb20135da6785b55fe2325f18089f68ed3c50aea15ba8e59e01d7ef42250c.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 338, + 547, + 361 + ], + "lines": [ + { + "bbox": [ + 46, + 338, + 547, + 361 + ], + "spans": [ + { + "bbox": [ + 46, + 338, + 547, + 361 + ], + "type": "text", + "content": "Figure 7. EDICT compared to baseline editing methods. EDICT demonstrates superior preservation of unedited components while still performing the edit edit. Further comparison between EDICT and baselines (including concurrent work ([14,32]) is in the Supplementary." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 381, + 288, + 418 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 381, + 288, + 418 + ], + "spans": [ + { + "bbox": [ + 46, + 381, + 288, + 418 + ], + "type": "text", + "content": "as complementary to, rather than competitive with, EDICT, and do not perform a direct comparison with them. We quantitatively compare visual metrics of edits in Fig. 8." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 430, + 117, + 441 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 430, + 117, + 441 + ], + "spans": [ + { + "bbox": [ + 47, + 430, + 117, + 441 + ], + "type": "text", + "content": "6. Discussion" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 450, + 287, + 605 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 450, + 287, + 605 + ], + "spans": [ + { + "bbox": [ + 46, + 450, + 287, + 605 + ], + "type": "text", + "content": "Limitations and Future Work: EDICT is deterministic, only outputs one generation per image-prompt pair (vs. SDEdit). Also, the computational time is approximately twice that of baseline DDIM. As with all editing methods, performance can vary across inputs in a hard-to-predict manner and sometimes requires careful prompt selection. For future work, we note that the induced latent space constructed by the inversion process admits operations such as latent interpolation [10] which has not been widely applied to real images. As in prompt tuning [15], formalizing the process of prompt selection could further improve EDICT. Adding a controllable degree of randomness to EDICT could yield multiple candidate generations per input." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "text", + "content": "Ethics: Like other image generation and editing models, EDICT will produce images that may reflect the socioeconomic biases of the training data or images that could be considered inappropriate. Image editing methods can also utilized for malicious purposes, including harassment and misinformation spread. Practitioners utilizing EDICT or its methodologies in a production setting should consider these limitations. An in-depth discussion on the ethics of image generation can be found in Imagen [27]." + } + ] + } + ], + "index": 5 + }, + { + "type": "image", + "bbox": [ + 322, + 384, + 531, + 509 + ], + "blocks": [ + { + "bbox": [ + 322, + 384, + 531, + 509 + ], + "lines": [ + { + "bbox": [ + 322, + 384, + 531, + 509 + ], + "spans": [ + { + "bbox": [ + 322, + 384, + 531, + 509 + ], + "type": "image", + "image_path": "40d2877efabc602fe0fe62095caf8e99ed47caf750a546fd8b2e642244b6ecc5.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 521, + 545, + 674 + ], + "lines": [ + { + "bbox": [ + 304, + 521, + 545, + 674 + ], + "spans": [ + { + "bbox": [ + 304, + 521, + 545, + 674 + ], + "type": "text", + "content": "Figure 8. We quantitatively benchmark all methods on image editing using images from five ImageNet mammal classes (African Elephant, Ram, Egyptian Cat, Brown Bear, and Norfolk Terrier). Four experiments are performed, one swapping the pictured animal's species to each of the other classes (20 species editing pairs in total), two contextual changes (A [animal] in the snow and A [animal] in a parking lot), and one stylistic (An impressionistic painting of a [animal]). The LPIPS [33] (visual similarity) score to the original image and a CLIP score [23] (semantic similarity) to a set of five related text queries is computed per edit. Metrics are averaged across images and experiments. Details and human evaluation are provided in the Supplementary. We sweep across the fraction of inverted steps (overlaid in black on top of gray EDICT bubbles), observing that EDICT forms a Pareto frontier." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_caption" + } + ], + "index": 6 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "22539" + } + ] + } + ], + "index": 8 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 288, + 712 + ], + "type": "list", + "angle": 0, + "index": 16, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 145 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 145 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 145 + ], + "type": "text", + "content": "[1] Yogesh Balaji, Seungjun Nah, Xun Huang, Arash Vahdat, Jiaming Song, Karsten Kreis, Miika Aittala, Timo Aila, Samuli Laine, Bryan Catanzaro, et al. edifi: Text-to-image diffusion models with an ensemble of expert denoisers. arXiv preprint arXiv:2211.01324, 2022. 3" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 53, + 146, + 288, + 190 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 146, + 288, + 190 + ], + "spans": [ + { + "bbox": [ + 53, + 146, + 288, + 190 + ], + "type": "text", + "content": "[2] Ricky TQ Chen, Yulia Rubanova, Jesse Bettencourt, and David K Duvenaud. 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In CVPR, 2018. 8" + } + ] + } + ], + "index": 4 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 749, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 749, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 749, + 317, + 757 + ], + "type": "text", + "content": "22541" + } + ] + } + ], + "index": 6 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 9 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/EFEM_ Equivariant Neural Field Expectation Maximization for 3D Object Segmentation Without Scene Supervision/3d7e3a10-9770-4e87-8f5a-9ec61b4fbebc_content_list.json b/2023/EFEM_ Equivariant Neural Field Expectation Maximization for 3D Object Segmentation Without Scene Supervision/3d7e3a10-9770-4e87-8f5a-9ec61b4fbebc_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..3ab176692716024caf744a0530ce2eed5fa55306 --- /dev/null +++ b/2023/EFEM_ Equivariant Neural Field Expectation Maximization for 3D Object Segmentation Without Scene Supervision/3d7e3a10-9770-4e87-8f5a-9ec61b4fbebc_content_list.json @@ -0,0 +1,1660 @@ +[ + { + "type": "text", + "text": "EFEM: Equivariant Neural Field Expectation Maximization for 3D Object Segmentation Without Scene Supervision", + "text_level": 1, + "bbox": [ + 179, + 130, + 789, + 176 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Jiahui Lei1 Congyue Deng2 Karl Schmeckpeper1 Leonidas Guibas2 Kostas Daniilidis1 \n1 University of Pennsylvania \n2 Stanford University", + "bbox": [ + 104, + 202, + 859, + 239 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "{leijh, karls, kostas}@cis.upenn.edu, {congyue, guibas}@cs.stanford.edu", + "bbox": [ + 169, + 241, + 792, + 255 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 291, + 312, + 306 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "We introduce Equivariant Neural Field Expectation Maximization (EFEM), a simple, effective, and robust geometric algorithm that can segment objects in 3D scenes without annotations or training on scenes. We achieve such unsupervised segmentation by exploiting single object shape priors. We make two novel steps in that direction. First, we introduce equivariant shape representations to this problem to eliminate the complexity induced by the variation in object configuration. Second, we propose a novel EM algorithm that can iteratively refine segmentation masks using the equivariant shape prior. We collect a novel real dataset Chairs and Mugs that contains various object configurations and novel scenes in order to verify the effectiveness and robustness of our method. Experimental results demonstrate that our method achieves consistent and robust performance across different scenes where the (weakly) supervised methods may fail. Code and data available at https://www.cis.upenn.edu/~leijh/projects/efem", + "bbox": [ + 75, + 324, + 473, + 609 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 623, + 209, + 638 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Learning how to decompose 3D scenes into object instances is a fundamental problem in visual perception systems. Past developments in 3D computer vision have made huge strides on this problem by training neural networks on 3D scene datasets with segmentation masks [55, 63, 67]. However, these works heavily rely on large labeled datasets [3, 15] that require laborious 3D annotation based on special expertise. Few recent papers alleviate this problem by reducing the need to either sparse point labeling [24, 60] or bounding boxes [12].", + "bbox": [ + 75, + 642, + 468, + 794 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "In this work, we follow an object-centric approach inspired by the Gestalt school of perception that captures an object as a whole shape [32, 47] invariant to its pose and scale [31]. A holistic approach builds up a prior for each object category, that then enables object recognition in different complex scenes with varying configurations. Directly learning object-centric priors instead of analyzing each 3D", + "bbox": [ + 75, + 795, + 468, + 901 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/e2ea2c2d876e3ddf0b1411ade2b4dd5a83fbce1f4c13a5c71bea5ca478dc6aa3.jpg", + "image_caption": [ + "Figure 1. We present EFEM, an unsupervised 3D object segmentation method applicable to real-world scenes (results on the right) by only training on ShapeNet single object reconstruction." + ], + "image_footnote": [], + "bbox": [ + 501, + 290, + 658, + 380 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/ef70092ac0cccd9970d68b76d3c66663e7ddc1f3fd4c3d95fb0f6389692a2dad.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 663, + 290, + 890, + 380 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "scene inspires a more efficient way of learning instance segmentation: both a mug on the table and a mug in the dishwasher are mugs, and one does not have to learn to segment out a mug in all possible environmental contexts if we have a unified shape concept for mugs. Such object-centric recognition facilitates a robust scene analysis for autonomous systems in many interactive real-world environments with a diversity of object configurations: Imagine a scenario where a robot is doing the dishes in the kitchen. Dirty bowls are piled in the sink and the robot is cleaning them and placing them into a cabinet. Objects of the same category appear in the scene repeatedly under different configurations (piles, neat lines in the cabinet). What is even more challenging is that even within this one single task (doing dishes) the scene configuration can drastically change when objects are moved. We show that such scenarios cannot be addressed by the state-of-the-art strongly or weakly supervised methods that struggle under such scene configuration variations.", + "bbox": [ + 496, + 443, + 892, + 731 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "In this paper, we introduce a method that can segment 3D object instances from 3D static scenes by learning priors of single object shapes (ShapeNet [4]) without using any scene-level labels. Two main challenges arise when we remove the scene-level annotation. First, objects in the scene can have a different position, rotation, and scale than the canonical poses where the single object shapes were trained. Second, the shape encoder which is trained on object-level input cannot be directly applied to the scene observations unless the object masks are known. We address the first challenge by introducing equivariance to this problem. By", + "bbox": [ + 496, + 734, + 893, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "4902", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "learning a shape prior that is equivariant to the similitude group SIM(3), the composition of a rotation, a translation, and a uniform scaling in 3D (Sec. 3.1), we address the complexity induced by the SIM(3) composition of objects. For the second challenge, we introduce a simple and effective iterative algorithm, Equivariant neural Field Expectation Maximization (EFEM), that refines the object segmentation mask, by alternately iterating between mask updating and shape reconstruction (Sec. 3.2). The above two steps enable us to directly exploit the learned single instance shape prior to perform segmentation in real-world scenes. We collected and annotated a novel real-world test set (240 scenes) (Sec. 4.4) that contains diverse object configurations and novel scenes to evaluate the generalizability and robustness to novel object instances and object configuration changes. Experiments on both synthetic data (Sec. 4.3) and our novel real dataset (Sec. 4.4) give us an insight to the effectiveness of the method. Compared to weakly supervised methods, when the testing scene setup is similar to the training setup, our method has a small performance gap to the (weakly) supervised baselines. However, when the testing scenes are drawn from novel object configurations, our method consistently outperforms the (weakly) supervised baselines.", + "bbox": [ + 80, + 90, + 467, + 436 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Our paper makes the following novel contributions to the 3D scene segmentation problem: (1) a simple and effective iterative EM algorithm that can segment objects from the scenes using only single object shape priors. (2) addressing the diversity of object composition in 3D scenes by combining representations equivariant to rotation, translation, and scaling of the objects. (3) an unsupervised pipeline for 3D instance segmentation that works in real-world data and can generalize to novel setups. (4) a novel real-world test set Chairs and Mugs that contains diverse object configurations and scenes.", + "bbox": [ + 80, + 439, + 467, + 604 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 80, + 614, + 215, + 631 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "3D Instance segmentation. Point cloud instance segmentation has been a long-existing challenge in 3D vision even before the existence of deep learning. Early interests have been focusing on 3D object retrieval in scenes where RANSAC and generalized Hough voting were the most prominent paradigms [54]. In recent years, with the proliferation of large synthetic [17, 68] or real [3, 15, 22, 25] datasets with rich annotations, learning-based methods have shown great success on this task.", + "bbox": [ + 80, + 635, + 467, + 770 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Supervised methods. Most supervised methods fall into two categories: top-down methods that locate objects first and then predict the refined segmentation mask [23, 76], and bottom-up methods learning to group points into object proposals. Regarding the grouping approach, a variety of algorithms have been explored, such as point-pair similarity matrices [64, 80], mean-shift clustering [35], graph-based grouping [20], cluster growing [29], hierarchical ag", + "bbox": [ + 80, + 779, + 467, + 900 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "gregation [7, 40], or adversarial methods [78]. Later works [62, 63] combine top-down and bottom-up approaches and achieve impressive results. Recently, transformers and attention mechanisms have also been introduced to this problem [55]. [46] also incorporates neural implicit representations and simultaneously performs segmentation and shape reconstruction. Despite their requirements for laborious data annotation, we will also show that supervised methods heavily rely on the correlation between training and test scenes, and even the state-of-the-art supervised methods struggle to generalize to novel scene configurations or to changes in background patterns.", + "bbox": [ + 503, + 90, + 888, + 271 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Unsupervised or weakly supervised methods. Many attempts have been made to learn instance segmentation with limited annotations. A number of works leverage preextracted features from scenes via representation learning such as graph attentions [36] or contrastive learning [13, 24, 70, 77] to facilitate weakly-supervised training with fewer point labels. Other approaches directly propagate sparse annotations to dense point labels by learning point affinity graphs [60] or by bounding box voting [12]. These methods are usually the most scalable to large scenes, but their point features are scene-dependent, and we will show that similarly to fully-supervised learning methods, weakly-supervised methods have difficulties in generalizing to scenes with different configurations. When confronting dynamic scenes, one can exploit temporal self-consistency [58] or scene pair constraints [26, 77] but such constraints introduce additional assumptions about the scenes. Most related to our work are the retrieval-based methods leveraging object priors [39, 72]. Traditional retrieval methods are either limited to one given object template [72] or need to solve a discrete combinatorial optimization problem searching for the target template in the object category [39]. We resolve these issues by learning an implicit shape prior which can be optimized continuously in the feature space.", + "bbox": [ + 503, + 275, + 888, + 636 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Implicit object priors. First introduced in [10, 45, 49], neural implicit representations (also known as neural fields [71]) parameterize 3D shapes as level sets of neural networks. They not only show strong capabilities of capturing geometric details within limited capacity [28, 50, 57, 59] but also avoid shape discretization that introduces sampling noises. When representing a collection of objects with a shared implicit network, its bottleneck layer naturally forms a latent embedding of the objects, which can serve as a shape prior for many downstream tasks such as shape generation [10, 27, 44], reconstruction [41], completion [11, 45, 49], computing correspondences [33, 37, 43, 56], and part decomposition [9]. We refer the readers to [71] for a comprehensive review. Our method takes advantage of the recent work in neural fields to learn a deep shape prior.", + "bbox": [ + 503, + 640, + 888, + 867 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Equivariant point cloud networks. Equivariant networks are designed to preserve transformation coherence", + "bbox": [ + 503, + 869, + 888, + 898 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "4903", + "bbox": [ + 483, + 946, + 513, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "between the input and latent representations. With well-developed theories [1, 14, 34, 65, 74], equivariant networks have a variety of designs on point clouds [2, 16, 19, 30, 51, 61], which benefits many downstream tasks such as robotic applications [18, 21, 52, 56, 66, 75], 3D reconstruction [5, 6], and object pose estimation/canonicalization [38, 42, 48, 53, 81]. Unlike these object-level works, we focus on leveraging equivariance object features in scene understandings. Most related to us is [79] which also applies object equivariance to scenes. But they perform supervised 3D object bounding box detection while we predict dense instance masks. In this work, we employ the vector neurons [2, 6, 16] to build our equivariant shape prior.", + "bbox": [ + 75, + 90, + 472, + 287 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Method", + "text_level": 1, + "bbox": [ + 76, + 295, + 169, + 310 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Now we introduce our method for unsupervised object segmentation in 3D scenes. At the training stage, we learn an object-level shape prior (Sec. 3.1, Fig. 2 top left) utilizing a collection of synthetic models from an object category (e.g. all chairs in ShapeNet [4]). At inference time, we are given a scene point cloud $X_{N \\times 6}$ of $N$ points with coordinates as well as normal vectors with an unknown number of novel instances from the object category, and our task is to predict their instance segmentation masks. We will introduce a simple and novel iterative algorithm for predicting instance segmentation masks, starting from a single-object proposal phase (Sec. 3.2, Fig. 2 top right) and followed by a multiple-object joint proposal phase (Sec. 3.3, Fig. 2 bottom). As by-products, our model also outputs implicit surface reconstructions, poses, and bounding boxes.", + "bbox": [ + 75, + 314, + 472, + 541 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. SIM(3) Equivariant Shape Priors", + "text_level": 1, + "bbox": [ + 76, + 545, + 370, + 560 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Most synthetic datasets have their objects manually aligned to canonical poses and unit scales, yet the SIM(3) transformations (translations, rotations, and scales) must be considered when applying the shape priors to real-world scenes. To this end, we constructed a SIM(3)-equivariant SDF encoder-decoder following the paradigms of prior work [16, 45] (Fig. 2 left top).", + "bbox": [ + 75, + 561, + 468, + 667 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Point cloud encoder. Given an object point cloud $P_{N_O \\times 3}$ with $N_O$ points, it is first encoded by a SIM(3)-equivariant encoder $\\Phi$ (yellow block Fig. 2 left) constructed with Vector Neurons (VN) [2, 8, 16] into a latent embedding $\\Theta = \\Phi(P)$ (orange block Fig. 2 middle). More concretely, the input point cloud $P$ is first subtracted by its centroid $\\bar{P}$ for translation equivariance, followed by a backbone network providing a global vector-channeled embedding $F$ , which is scale- and rotation-equivariant and translation invariant. $F$ is then mapped to the shape implicit code $\\Theta$ comprising four components $(\\Theta_{\\mathrm{R}}, \\Theta_{\\mathrm{inv}}, \\Theta_{\\mathrm{c}}, \\Theta_{\\mathrm{s}})$ . The backbone network is a rotation-equivariant VN Point-Transformer [2] with additional scale equivariance enforced by channel-wise normalizations as in [8]. We denote the modified linear layer with scale invariance [8] as $\\widehat{\\mathrm{VN}}$ . The four components of $\\Theta$ are", + "bbox": [ + 75, + 672, + 472, + 901 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "computed from $F$ with four heads separately:", + "bbox": [ + 498, + 90, + 803, + 106 + ], + "page_idx": 2 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "1. A vector-channeled rotation equivariant latent code $\\Theta_{\\mathrm{R}} = \\widehat{\\mathrm{VN}}_R(F)$", + "2. A scalar-channeled invariant latent code $\\Theta_{\\mathrm{inv}} = \\langle \\widehat{\\nabla}\\mathbf{N}_I(F),\\Theta_{\\mathrm{R}}\\rangle$ computed with inner product.", + "3. A scalar $\\Theta_{\\mathrm{s}}$ by taking the average of $F$ 's per-channel norm which explicitly encodes the object scale.", + "4. A centroid correction vector predicting the offset between the centroid of points and the actual object center, which could be different due to the partiality and noises of the point could: $\\Theta_{\\mathrm{c}} = \\mathrm{VN}_{C}(F) + \\bar{P}$ , where $\\mathrm{VN}_C$ has 1 output vector channel." + ], + "bbox": [ + 511, + 106, + 890, + 273 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Network architecture details can be found in the supplementary. For any transformation $g = (s, R, t) \\in \\mathrm{SIM}(3)$ with scale $s$ , rotation $R$ , and translation $t$ , its action on $\\Theta$ and the equivariance of the encoder $\\Phi$ can be written as:", + "bbox": [ + 496, + 273, + 890, + 334 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\ng \\circ \\Theta = \\left(\\Theta_ {\\mathrm {R}} R, \\Theta_ {\\text {i n v}}, s \\Theta_ {\\mathrm {c}} R + t, s \\Theta_ {\\mathrm {s}}\\right) = \\Phi (s P R + t). \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 504, + 345, + 890, + 363 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "SDF decoder. Give a query position $x \\in \\mathbb{R}^3$ , its SDF value $\\hat{v}(x)$ is predicted as", + "bbox": [ + 496, + 368, + 890, + 398 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {v} (x) = \\Psi (x; \\Theta) = \\Psi \\left(\\Theta_ {\\text {i n v}}, \\langle \\Theta_ {\\mathrm {R}}, \\tilde {x} \\rangle\\right), \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 570, + 411, + 890, + 428 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\tilde{x} = (x - \\Theta_{\\mathrm{c}}) / \\Theta_{\\mathrm{s}}$ is the canonicalized coordinate of $x$ with center $\\Theta_{\\mathrm{c}}$ and scale $\\Theta_{\\mathrm{s}}$ , and $\\Psi$ is an MLP as in [16] that decodes the concatenation of the invariant feature $\\Theta_{\\mathrm{inv}}$ and the channel-wise inner product between $\\Theta_{\\mathrm{R}}$ and $\\tilde{x}$ .", + "bbox": [ + 496, + 433, + 890, + 494 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Training. The implicit shape prior is trained with the standard L2 loss for the query points sampled around each object. To avoid arbitrary prediction of $\\Theta_{\\mathrm{c}}$ and $\\Theta_{\\mathrm{s}}$ that may make training unstable in early epochs, we regularize $\\Theta_{\\mathrm{c}}$ to stay around zero and $\\Theta_{\\mathrm{s}}$ to stay around one. To help the network's generalization to real-world scenarios with partial observations, clutters, and sensor noises, we further augment the input object point clouds with partial depths and content-wise augmentations. Additional details of these augmentations are provided in the supplementary. We will next introduce how to exploit this learned shape-prior network which only takes instance-level inputs in scene-level point cloud segmentation.", + "bbox": [ + 496, + 497, + 892, + 694 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. Iterative Algorithm for Single Proposal", + "text_level": 1, + "bbox": [ + 500, + 703, + 834, + 719 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Algorithm 1 Single Proposal Estimation", + "bbox": [ + 500, + 728, + 772, + 744 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Data: Scene Point Cloud $X_{N\\times 6}$ ; trained encoder $\\Phi$ and decoder $\\Psi$ with frozen weight", + "bbox": [ + 500, + 746, + 890, + 776 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Initialize $W_0$", + "bbox": [ + 500, + 777, + 589, + 790 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "while not reach max step do", + "bbox": [ + 500, + 792, + 689, + 806 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "M-step: Sample $P_{t}$ by Eq. 3 from $W_{t - 1}$ and forward encoder $\\Phi$ to update $\\Theta_t$ .", + "bbox": [ + 524, + 806, + 890, + 834 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "E-step: Evaluate decoder $\\Psi$ and update $W_{t}$ by Eq. 7.", + "bbox": [ + 524, + 835, + 874, + 849 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "end", + "bbox": [ + 500, + 851, + 529, + 862 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Extract mesh and compute absolute pose as a byproduct.", + "bbox": [ + 500, + 864, + 872, + 878 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Compute confidence $C$ in Eq. 10 and output mask.", + "bbox": [ + 500, + 878, + 834, + 893 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "4904", + "bbox": [ + 480, + 944, + 514, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/58ef2952e7877ba2c842704d870dfb534b921e5af30bc291c28c682f3626dc85.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 78, + 89, + 277, + 188 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/02e0c628537808f4e98041ad17105a959177167fc550d485afc74677cc70f53a.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 279, + 90, + 890, + 188 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/6397ff26fd4d09cbc00c5e8050eb194e781317bf200380f68a8c67c1c773ebf8.jpg", + "image_caption": [ + "Figure 2. Overview: Left top: the single object SDF Encoder-Decoder (Sec. 3.1) is trained on the shape collection. Once trained, the network's weights are frozen.Top right Single EM step on scene observations (Sec. 3.2): given the last estimation of the object mask $W_{t - 1}$ , a set of points is sampled from the full scene point cloud and then passed to the shape encoder $\\Phi$ to produce the current estimation of the shape embedding $\\Theta$ . Based on the $\\Theta$ , all the scene points are queried again through the decoder $\\Psi$ to generate a new assignment mask $W_{t}$ . Bottom Object segmentation pipeline: starting from random crop initializations from the left, the above EM step is applied to each proposal (each row) in parallel to refine their masks. In the early steps (Phase-1 Sec. 3.2), all the proposals run independently but in the second phase, multiple proposals can be jointly optimized (Sec. 3.3). Note that we eliminate the duplicated (the second) or unreasonably sized (the fourth) proposals during optimization. Finally, the remaining proposals and their confidences are output." + ], + "image_footnote": [], + "bbox": [ + 81, + 195, + 890, + 375 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "As shown in Fig 2, the key component of our full algorithm is the single proposal processing (right top) since the full algorithm is constructed by many single proposals being processed in parallel. Each proposal is represented by a soft assignment mask $W$ over all scene points, where the continuous value on each point $W[i] \\in [0,1]$ indicates how likely this point belongs to the object that the proposal is representing. In the early single proposal iteration steps (Phase-1), each proposal aims to fit its $W$ to one object independently. In later iterations, we optimize the proposals jointly, as discussed in Section 3.3.", + "bbox": [ + 75, + 503, + 470, + 672 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Initialization. The single proposal algorithm starts from the initial assignment $W_{0}$ which is drawn from a random ball or cylinder cropping of the scene. The radius of the crop is set to be similar to the average size of the target class. All points inside the crop are set to have $W[i] = 1.0$ while all other points are set to have $W[i] = 0.0$ .", + "bbox": [ + 75, + 679, + 468, + 772 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "M-Step: Estimating shape embeddings. We treat the learned decoder with fixed weight as a parametric model of shape categories driven by the parameter $\\Theta$ . In each iteration of our algorithm, a new $\\Theta_{t}$ is estimated from the last assignment $W_{t - 1}$ . Note that the learned shape prior encoder $\\Phi$ only accepts a fixed number $N_O$ of points as input, which is always far less than the number of points in the scene observation. Therefore at each iteration, we first sam", + "bbox": [ + 75, + 779, + 470, + 900 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "ple a fixed number $N_{O}$ of points from the scene point cloud $X_{N\\times 6}$ based on the last assignment estimation $W_{t - 1}$", + "bbox": [ + 498, + 503, + 892, + 535 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nP _ {t} = \\mathcal {M} \\left(W _ {t - 1}, X _ {N \\times 6}\\right), \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 612, + 547, + 890, + 564 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where the sampling operations $\\mathcal{M}$ contain two steps. First, a sample is drawn from a Bernoulli distribution with positive probability $W_{t - 1}[i]$ to determine if the point $X[i]$ belongs to the object's foreground. Second, for all points that are marked as foreground, we globally apply multinomial sampling based on their $W[i]$ to find $N_O$ sampled points. Finally, we produce the new shape estimation by passing the sampled point cloud through $\\Phi$ so $\\Theta_t = \\Phi (P_t)$ . This method of updating the shape parameter can be interpreted as the M-step of an EM algorithm, which computes better distribution parameters based on the last assignment via weighted maximum likelihood.", + "bbox": [ + 496, + 571, + 892, + 752 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Fitting error. Given the $\\Theta$ estimation, the fitting error of one observed point $\\mathbf{x} = [x_{\\mathrm{obs}}, n_{\\mathrm{obs}}]$ ( $x_{\\mathrm{obs}}$ denotes position and $n_{\\mathrm{obs}}$ denotes normal) in the scene point cloud $X_{N \\times 6}$ is:", + "bbox": [ + 496, + 758, + 893, + 805 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\ne _ {D} (\\mathbf {x}, \\Theta) = | \\Psi (x _ {\\mathrm {o b s}}; \\Theta) | \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 609, + 820, + 890, + 837 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\ne _ {N} (\\mathbf {x}, \\Theta) = \\operatorname {a c o s} \\left(\\frac {n _ {\\mathrm {o b s}} ^ {T} \\nabla_ {x} \\Psi \\left(x _ {\\mathrm {o b s}} ; \\Theta\\right)}{\\| \\nabla_ {x} \\Psi \\left(x _ {\\mathrm {o b s}} ; \\Theta\\right) \\|}\\right) \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 560, + 839, + 890, + 875 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nE (\\mathbf {x}, \\Theta) = \\alpha_ {D} e _ {D} (\\mathbf {x}, \\Theta) + \\alpha_ {N} e _ {N} (\\mathbf {x}, \\Theta) \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 560, + 883, + 890, + 901 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "4905", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "which measures the observed point distance to the zero level set of the SDF and the normal consistency between the observed point and the decoded SDF gradient. The hyperparameters $\\alpha_{D}$ and $\\alpha_{N}$ control the importance of the distance and angle terms respectively.", + "bbox": [ + 75, + 90, + 468, + 167 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "E-Step: Updating point assignments. After updating the shape parameters $\\Theta_t$ , we update the assignment weight $W_t$ by querying the decoder $\\Psi$ for all the points in the scene point cloud $X$ and computing the error in Eq. 6. The new assignment is designed to be updated as:", + "bbox": [ + 76, + 169, + 467, + 244 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nW _ {t} [ i ] = \\frac {e ^ {- E (X [ i ] , \\Theta_ {t})}}{e ^ {- E (X [ i ] , \\Theta_ {t})} + \\Omega}, \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 179, + 252, + 468, + 286 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\Omega$ is a constant hyperparameter that gives every point some probability to be in the background. This step can be interpreted as the E-step in an EM algorithm.", + "bbox": [ + 75, + 287, + 468, + 333 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Termination and confidence score. When the initialization is not near an object instance of the target class, the shape prior tends to never fit the input observations, so that the error $E$ is large everywhere and the weight $W$ is always small. We terminate the proposals that have less than a predefined threshold of small-error points at each iteration. After the last iteration, we use Marching Cubes to extract a mesh $(\\mathcal{V}, \\mathcal{E})$ for each proposal and the mesh serves as the byproduct of our method. Our algorithm also produces a pose estimation with respect to the training shape collection via Procrustes registration [81] on $\\Theta_{SO3}$ between the observed objects and the member of the training set with the most similar $\\Theta$ (see Supp.). We also remove proposals with meshes outside a predefined reasonable range of scales.", + "bbox": [ + 75, + 335, + 468, + 547 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "One advantage of utilizing our shape prior is that we can explicitly compute the confidence score from the shape reconstruction. Specifically, we compute two scores by measuring the fitting errors: (1.) Observation fitting score: a good fitting should have all the encoder input points located on the decoded SDF zero level set. We measure the proportion of the encoder input point cloud which has a small distance and angle error:", + "bbox": [ + 75, + 547, + 468, + 667 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nS _ {1} = \\frac {1}{N _ {O}} \\left| \\left\\{\\mathbf {x} \\in P _ {T} \\left| \\begin{array}{l} e _ {D} (\\mathbf {x}, \\Theta) < \\delta_ {D}, \\\\ e _ {N} (\\mathbf {x}, \\Theta) < \\delta_ {N} \\end{array} \\right. \\right\\} \\right|, \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 120, + 676, + 468, + 710 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where the $\\delta_D, \\delta_N$ are the thresholds. (2.) Reconstruction coverage score: Since we recognize objects by their shapes, we should be less confident in detections where the observed points only cover a small portion of the extracted mesh. For every vertex $\\mathbf{v} = [x_{\\mathrm{recon}}, n_{\\mathrm{recon}}]$ from the extracted mesh, we find its nearest neighbour $\\mathbf{x} = [x_{\\mathrm{obs}}, n_{\\mathrm{obs}}]$ in the observed scene point cloud $X_{N \\times 6}$ and measure their distance error as $e_D'(\\mathbf{v}) = \\| x_{\\mathrm{obs}} - x_{\\mathrm{recon}}\\|_2$ and their orientation error as $e_N'(\\mathbf{v}) = \\cos(n_{\\mathrm{obs}}^T n_{\\mathrm{recon}})$ . This gives a combined coverage score of:", + "bbox": [ + 75, + 713, + 468, + 863 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nS _ {2} = \\frac {1}{| \\mathcal {V} |} | \\left\\{\\mathbf {v} \\in \\mathcal {V} \\mid e _ {D} ^ {\\prime} (\\mathbf {v}) < \\delta_ {D}, e _ {N} ^ {\\prime} (\\mathbf {v}) < \\delta_ {N} \\right\\} |. \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 101, + 872, + 468, + 902 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We use $S_{1}$ as the main confidence measurement and $S_{2}$ for avoiding poorly observed cases, so the final confidence score $C$ is:", + "bbox": [ + 498, + 90, + 890, + 135 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nC = S _ {1} * \\max \\left(1. 0, S _ {2} / \\delta_ {C}\\right), \\tag {10}\n$$\n", + "text_format": "latex", + "bbox": [ + 598, + 147, + 890, + 162 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\delta_C \\in [0.0, 1.0]$ is a threshold controlling the importance of the coverage score. Note how the above confidence values evaluate the quality of the output shown on the right in Fig. 2, which enables the user to select the balance between recall and precision during inference.", + "bbox": [ + 496, + 167, + 890, + 243 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Finally, for each point in the scene point cloud $X_{N \\times 6}$ , we check whether the distance error in Eq. 4 and Eq. 5 is smaller than the output threshold and mark points with small errors as in the foreground. Note that since the observation is noisy and the learned shape prior is not perfect, the output error thresholds can be larger than the ones used in Eq. 8 and Eq.9.", + "bbox": [ + 496, + 244, + 890, + 349 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.3. Multiple Proposals", + "text_level": 1, + "bbox": [ + 500, + 359, + 681, + 375 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Since the EM algorithm outputs can be affected by its initialization and we do not know the number of objects in the scene, we initialize a large number of proposals randomly spread across the entire scene to cover all possible objects. We observe that many proposals will quickly converge to similar positions during the early iterations. Therefore, at each iteration, we remove duplicated proposals and only keep the one with the highest fitting score $S_{1}$ defined in Eq. 8. Duplication is determined by computing the overlap of $W$ between different proposals (see Supp. for details).", + "bbox": [ + 496, + 381, + 890, + 532 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "As shown in Fig. 2, we further divide the iterations into two phases. In the first phase, since the early shape estimation is not converged to a reasonable place, we let each proposal run fully independently. When we enter the second phase, mesh extraction and pose estimation will be first applied to remove proposals with unreasonable scales. Then, we optimize all proposals globally by updating the joint assignment weight with:", + "bbox": [ + 496, + 532, + 890, + 654 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nW _ {t} ^ {(k)} [ i ] = \\frac {S _ {1} ^ {(k)} e ^ {- E (X [ i ] , \\Theta_ {t} ^ {(k)})}}{\\sum_ {j} S _ {1} ^ {(j)} e ^ {- E (X [ i ] , \\Theta_ {t} ^ {(j)})} + \\Omega}, \\tag {11}\n$$\n", + "text_format": "latex", + "bbox": [ + 563, + 662, + 890, + 705 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $k$ is the index of current active proposals and $S_1^{(k)}$ is the current fitting score in Eq. 8, which increases the assignment weight for more confident proposals. During the last iterations in Phase-2, we also remove the proposals that are largely contained by other proposals to simplify the decomposition of the scene, following a similar methodology to duplication removal. Additional details of this process are available in the supplemental.", + "bbox": [ + 496, + 707, + 890, + 829 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 500, + 835, + 632, + 852 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We focus our experiments on answering four main questions: First, can our method successfully segment the objects of interest from the scene? Second, how does our", + "bbox": [ + 496, + 854, + 890, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "4906", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/3d2b9b9199912bb86cbe8a5ef397dee4a4ac5e332210b1a903e7f76d9a5cf483.jpg", + "image_caption": [ + "Figure 3. Synthetic scenes: Top: the mesh reconstruction as input, note how our data has a realistic simulated depth pattern; Middle: visualization of the estimated shapes, poses and bounding boxes as the byproducts of our method. Bottom: Our segmentation prediction." + ], + "image_footnote": [], + "bbox": [ + 78, + 85, + 890, + 208 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/0ddd746a1fb5f79589820024ef3365e05087e797bde8138af7efc70c5936ae9d.jpg", + "image_caption": [ + "Figure 4. Chairs and Mugs real testset: the three rows are in the same format as Fig. 3." + ], + "image_footnote": [], + "bbox": [ + 78, + 250, + 890, + 383 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "method compare to existing baselines when different training data distributions are accessible? Third, how does each approach generalize to the different testing environments, including the real-world scenes and the out-of-distribution configurations? And fourth, how do the different components of our model contribute to its performance? To answer these questions, we perform a series of baseline comparisons as well as ablation studies both on synthetic and real-world scenes.", + "bbox": [ + 75, + 426, + 472, + 561 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.1. Baselines", + "text_level": 1, + "bbox": [ + 76, + 564, + 184, + 578 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "To the best of the authors' knowledge, fully unsupervised instance segmentation (not foreground-background segmentation) in static scenes remains unexplored in the deep learning literature. Therefore, we compare our method with supervised and weakly supervised methods. SoftGroup (CVPR22) [63] is the current SoTA for 3D instance segmentation methods that are trained with ground truth instance masks. Box2Mask (ECCV22) [12] is a recent weakly supervised method, which only needs ground truth instance bounding boxes as supervision while retaining competitive performance. The closest weakly supervised method to ours is ContrastiveSceneContext (CVPR21) [24], which can be trained with only a few point labels. To conduct fair comparisons and reduce the sim2real gap, all baselines are fully trained on the corresponding training set with positions and normals as input while not using colors.", + "bbox": [ + 75, + 580, + 468, + 821 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.2. Experimental Setup", + "text_level": 1, + "bbox": [ + 76, + 823, + 266, + 839 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We focus our experiments on scenes that contain objects humans or robots can interact with. These objects are more interesting targets for segmentation as their configurations can change dramatically in real-world applications, such as", + "bbox": [ + 75, + 840, + 470, + 902 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "robotics or AR/VR. We experiment with three object categories that frequently appear in the presence of clutter and in diverse configurations in real-world data: Mugs, Kitchen containers, and Chairs. Since there is no available dataset that contains these objects with rich configuration changes (not just sitting upright on a flat surface), and all baselines need to be trained with ground truth, we gather simulated data to train the baselines, then evaluate on simulated and real test scenes containing completely unseen object instances.", + "bbox": [ + 496, + 426, + 892, + 575 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Three types of scenes are used for training baselines on each of the object classes. Take the mugs scene as an example (Fig. 3 Left top): In the Z scenes, all instances are upright and not in contact with each other. In SO(3), the objects can have a random orientation but are still not in contact with each other. Pile is a much more challenging setting where the objects can touch each other, can take any orientation, and can form piles. We simulate 500 scenes for training, 50 scenes for validation and 100 scenes for testing in each of the setups. For each baseline we train three models, one on the data from each of the three scene types.", + "bbox": [ + 496, + 580, + 892, + 747 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We train our equivariant shape prior (Sec. 3.1) on the corresponding categories from ShapeNet [4] and freeze their weights once trained. Note that all the following results are generated from the same trained shape prior for each category, and all the objects in our testing scenes never appear in the training set of the shape prior. We evaluate each model on all of the scenes and report results in Tab. 1, Tab. 2 and Tab. 3. The gray cells indicate results from models that were trained on less difficult datasets than they were evaluated on, with the underlined number indicating the best", + "bbox": [ + 496, + 750, + 893, + 901 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "4907", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/da285a444d65549fe902139a7c098fff527c04e25236490b0f52469349355609.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MugsTestingZSO3PileTreeBoxShelf(R) Z(R) SO3(R) Pile(R) Tree(R) Others(R) Wild
TrainingMetricsAPA50APA50APA50APA50APA50APA50APA50APA50APA50APA50APA50APA50
Scene ZCSC (100)6.022.01.97.60.10.50.00.00.00.20.00.00.00.00.00.00.00.00.00.00.00.00.20.9
CSC (200)78.798.162.783.38.917.40.62.02.05.00.83.172.199.89.521.40.31.60.62.86.716.02.06.1
Box2Mask96.910092.199.336.727.612.345.310.024.08.614.698.110093.11005.619.18.428.818.439.518.127.9
SoftGroup10010096.598.521.927.60.41.81.63.79.217.293.797.697.31000.00.00.93.44.39.118.332.9
Scene SO3CSC (100)1.78.61.46.50.10.60.00.00.00.10.10.60.00.00.00.00.00.00.00.00.00.00.71.9
CSC (200)70.099.372.795.722.342.210.224.65.412.35.220.068.410059.81001.03.74.820.16.919.73.911.8
Box2Mask95.810094.710053.780.130.280.626.540.113.433.010010095.310012.734.319.649.227.150.650.374.8
SoftGroup10010099.699.843.951.910.018.715.321.320.830.999.210098.21002.84.810.421.76.513.318.330.7
Scene PileCSC (100)0.00.30.00.30.00.10.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.71.8
CSC (200)53.388.450.277.729.561.329.466.27.619.810.334.113.045.022.765.25.330.11.58.03.515.42.88.5
Box2Mask96.010094.710078.799.655.294.842.752.926.354.610010095.810072.398.055.898.156.079.245.171.4
SoftGroup99.510099.710089.093.242.372.823.425.528.839.599.610099.710074.786.353.483.050.966.548.165.9
ShapeNetEFEM78.499.879.399.868.296.868.899.059.977.048.772.487.210087.310063.194.069.695.469.789.454.182.3
", + "bbox": [ + 81, + 89, + 893, + 250 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/032c7ea023985b7761207c7bc98317f867e7fa20fc1037f6ae467b84e1265458.jpg", + "table_caption": [ + "Table 1. Results (%) on SynMugs (left) and RealMugs (right with label R). A50 corresponds to mAP50. The full table including mAP25 is available in the supplemental. The grey cells highlight that the testing scenes are out of the training distribution and the bold number means the best among all methods while the underlined number means the best within grey cells." + ], + "table_footnote": [], + "table_body": "
Testing(C) Z(C) SO3(C) Pile(K) Z(K) SO3(K) Pile
TrainingMetricsAPA50APA50APA50APA50APA50APA50
Scene ZCSC (100)66.283.156.680.26.115.212.729.97.514.52.35.9
CSC (200)77.791.063.785.110.522.763.080.937.949.212.223.2
Box2Mask99.910095.898.919.341.289.797.369.687.041.468.9
SoftGroup99.810094.898.524.136.593.696.894.099.352.363.5
Scene SO3CSC (100)74.981.477.382.417.731.08.521.711.323.82.05.4
CSC (200)84.386.685.488.520.635.327.848.953.977.518.138.9
Box2Mask99.710099.199.550.580.385.396.291.898.552.976.5
SoftGroup99.610099.110055.168.289.393.996.999.356.267.2
Scene PileCSC (100)67.074.174.682.147.263.83.411.22.67.11.44.5
CSC (200)71.776.388.492.467.481.626.553.844.873.628.860.4
Box2Mask99.699.799.599.778.696.987.297.992.198.674.894.6
SoftGroup99.410098.910095.097.093.797.396.098.884.691.3
ShapeNetEFEM93.199.286.197.475.388.069.483.467.683.160.178.9
", + "bbox": [ + 81, + 319, + 465, + 454 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/b3acb0c6ccdc03888c5376ac8a0ec68bc814281c2aa868e089254ad76edb967b.jpg", + "table_caption": [ + "Table 2. SynChairs (left) and SynKit (right), same format as Tab. 1" + ], + "table_footnote": [], + "table_body": "
RealChairsTestingR(Z)R(SO3)R(Pile)
TrainingMetricsAPAP50AP25APAP50AP25APAP50AP25
Scene ZCSC (100)0.51.49.41.32.810.80.00.07.2
CSC (200)0.81.211.00.30.69.80.00.23.1
Box2Mask0.00.320.20.31.927.20.00.111.8
SoftGroup5.17.727.02.86.721.90.00.03.7
Scene SO3CSC (100)3.65.318.21.42.513.30.00.14.5
CSC (200)1.22.610.41.84.920.20.10.59.1
Box2Mask1.55.948.45.119.956.70.41.828.2
SoftGroup13.817.227.47.916.230.30.10.16.1
Scene PileCSC (100)5.27.19.63.27.412.30.10.32.9
CSC (200)8.311.723.113.923.233.61.02.613.1
Box2Mask1.66.537.89.422.065.31.34.846.6
SoftGroup20.627.836.114.424.442.10.41.58.0
ScannetCSC (100)36.849.862.05.313.118.83.910.818.1
CSC (200)50.074.377.86.213.118.65.513.427.1
Box2Mask84.199.499.416.233.741.214.329.850.7
SoftGroup74.081.187.522.339.648.611.518.036.1
ShapeNetEFEM51.078.385.051.275.787.934.455.374.8
", + "bbox": [ + 84, + 474, + 457, + 657 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 3. Results on RealChairs, same format as Tab. 1", + "bbox": [ + 109, + 662, + 431, + 674 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "performing inside gray cells. The metric for evaluating the segmentation is the commonly used mAP [15].", + "bbox": [ + 75, + 681, + 467, + 710 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.3. Results on synthetic data", + "text_level": 1, + "bbox": [ + 76, + 715, + 305, + 732 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We first evaluate the performance on simulated data, and we found that existing baselines work very well inside the training distribution if trained with enough supervisory signals. However, the weakly supervised method CSC [24] has a significant performance drop when the number of supervision points decreases from 200 to 100. This performance drop becomes increasingly severe when the training set distribution becomes more complex, demonstrating the difficulty of unsupervised segmentation. With zero scene-level supervision, our method performs well with a small gap in performance to the (weakly) supervised methods.", + "bbox": [ + 75, + 734, + 467, + 900 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "When the baselines are trained on $\\mathbf{Z}$ but tested on SO3, the baselines do not show a large drop in performance, potentially because both $\\mathbf{Z}$ and SO3 scenes have no objects in contact with each other. However, when tested on Pile, we see that baselines trained on $\\mathbf{Z}$ or SO3 perform differently, and are both worse than the ones trained on Pile, indicating a failure to generalize to clutter. Our method outperforms all the baselines that are not trained on Pile configurations.", + "bbox": [ + 498, + 321, + 890, + 443 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We additionally generate 50 scenes each from three new and more difficult scene setups for testing on Mugs as shown in Fig. 3. In the Tree scenes mugs are hanging on a holder tree and distributed vertically. The Box scenes include cubes to simulate objects that have not been seen during training. In the Shelf scenes, the mugs are put on a shelf that is only visible from one side. In all three of these scene setups, our method is able to outperform all baselines as the baselines are unable to generalize to configurations of mugs that are significantly outside of the training distribution.", + "bbox": [ + 496, + 443, + 890, + 595 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.4. Results on real data", + "text_level": 1, + "bbox": [ + 500, + 606, + 687, + 619 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We additionally evaluate the performance of our model on real data. To the best of the authors' knowledge, there is no existing real dataset that contains interactable objects in diverse configurations for 3D instance segmentation. Therefore we collect a test set Chairs and Mugs that contains the reconstruction of 240 real scenes with object instance mask annotations to test our method in the real world.", + "bbox": [ + 496, + 623, + 890, + 728 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "RealMugs: As shown in Fig. 4 we replicate the Z, SO3, Pile and Tree setups in the real world. The scene is captured by 4 calibrated realsense D455 cameras mounted on the corners of the table. We further introduce two new setups that cover hard-to-simulate scenes. The Others setup contains random objects that a manipulator may encounter, including cloth, toys, paper bags, wires and tools. These objects are added into the tabletop scene, contacting and occluding the mugs. The Wild setup contains crops of real-world indoor scans from labs, kitchens, and teaching buildings. Unlike [73], our scenes are not restricted to only showing the", + "bbox": [ + 496, + 734, + 890, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "4908", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/130b828df894e63e4f49711608be9d5072d3580cee6c84503ec3278c323e4e94.jpg", + "image_caption": [ + "Figure 5. ScanNet qualitative results, the same format as Fig. 3" + ], + "image_footnote": [], + "bbox": [ + 81, + 87, + 467, + 207 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "table and upright mugs, but include diverse configurations, backgrounds, and distractors. These scans are captured by an iPad with a lidar scanner. Since the Z, SO3 and Pile setups are easy to simulate realistically, we only collect 10 scenes per setup. We collect 50 scenes for each of the Tree, Others and Wild setups.", + "bbox": [ + 75, + 238, + 468, + 329 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We test all the baselines trained on the synthetic dataset and our method trained on ShapeNet directly on these real scenes. Quantitative results are shown in Tab. 1. Since our simulator includes advanced techniques of active light simulation in the physical engine [69] and we do not use the colours as input, the sim2real gap for the baseline methods is minimal in these controlled setups. We can draw similar conclusions for Z, SO3, Pile and Tree setups as with the synthetic experiments. Our method retains reasonable performance on Others scenes due to its awareness of the object shape. When tested on the Wild real-world scenes, our method also performs the best, which demonstrates the strong generalizability of our method.", + "bbox": [ + 75, + 330, + 472, + 526 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "RealChairs: We also collect data of chairs in the real world following the Z, SO3 and Pile setups. Although we have plenty of real-world scan datasets like [15], none of them include diverse configuration changes of chairs. Therefore we collected and annotated a small test set with 20 scenes per setup as shown in Fig. 4. We train the baselines in simulation and test them in the real world. Additionally, we take all the baselines' official model weights from being trained on the real world ScanNet dataset [15] to evaluate on our test set. The results are shown in Tab. 3. There is a larger sim2real gap for the baselines with the chairs data than with the mugs data because of less realistic depth simulation and difficulties aligning the scale between Shapenet chairs and real-world chairs. In contrast, the baselines trained on ScanNet work very well on the Z setup, which aligns best with the ScanNet dataset. However, they have a significant drop in performance when the testing distribution shifts to the SO3 and Pile setups. In contrast, our method retains reasonable performance on real world chairs across different setups. We will release our Chairs and Mugs dataset to provide more opportunities to study robustness, generalizability and equivariance for scene and object understanding in the real world.", + "bbox": [ + 75, + 537, + 472, + 883 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We also show our effectiveness on ScanNet [15], where", + "bbox": [ + 96, + 885, + 468, + 900 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "the indoor scene scan can span the whole room. Qualitative results are shown in Fig. 5 and the AP metrics for the chairs category of our method on the validation/test set are $AP = 24.6 / 20.2$ , $AP50 = 50.8 / 39.0$ and $AP25 = 61.3 / 48.3$ where in comparison the weakly supervised method CSC [24] trained on 200 points labels achieves $AP50 = 62.9 / 61.1$ (See Suppl. for a table). One main reason for our performance drop on ScanNet is that ScanNet has many partially observed chairs, which are hard to be recognized via shape. We leave future explorations to fill this gap between our unsupervised method and the (weakly) supervised ones.", + "bbox": [ + 496, + 90, + 893, + 272 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.5. Ablations", + "text_level": 1, + "bbox": [ + 500, + 275, + 609, + 289 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We verify the effectiveness of our design by removing the phase-2 joint iterations and removing the usage of the normals. When not", + "bbox": [ + 496, + 292, + 658, + 382 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/4b229b541bae7f5e54a41b6fa4999d1c2629519d9843b01f2e587cb5e35efa83.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
AblationAPAP50AP25
Full0.6010.7890.807
No Phase 20.5480.7400.756
No Normal0.2030.3020.337
", + "bbox": [ + 668, + 292, + 885, + 354 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 4. Ablations", + "bbox": [ + 718, + 364, + 833, + 378 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "using phase-2 (Sec. 3.3), we let the phase-1 independent iterations run more steps to keep the total number of iterations constant. When removing the normals, all error computing, assignment weight updating, and confidence scoring will only take the distance error term in to account while ignoring the normal term. We compare our full model with the ablated models on SynKit Pile setups. The quantitative results are shown in Tab. 4, which illustrates that both components contribute to our model's overall performance. More ablation studies can be found in our supplementary.", + "bbox": [ + 496, + 383, + 890, + 535 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusions", + "text_level": 1, + "bbox": [ + 500, + 541, + 627, + 556 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We present EFEM, a method for 3D instance segmentation that is trained only on shape datasets. Without requiring any real or simulated scene data, our method can generalize to complex, real world scenes better than existing methods that also require more supervision.", + "bbox": [ + 496, + 560, + 890, + 635 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Limitations and future work. Although we show an encouraging step towards unsupervised 3D instance segmentation by generalizing knowledge directly from a shape collection to a scene, several weaknesses remain. First, our method has a performance drop when the object is significantly occluded. This is due to our method recognizing objects only via their shape, rather than also reasoning about color or other features. Second our current running speed is slow ( $\\sim$ 1min per scene) due to the large number of proposals the initialization requires.", + "bbox": [ + 496, + 638, + 893, + 789 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgements. The authors appreciate the support of the following grants: NSF FRR 2220868, NSF IISRI 2212433, NSF TRIPODS 1934960, ARL DCIST CRA W911NF-17-2-0181, ARO MURI W911NF-20-1-0080, ONR N00014-22-1-2677 awarded to UPenn; Toyota University 2.0 program and Vannevar Bush Faculty Fellowship awarded to Stanford University.", + "bbox": [ + 496, + 792, + 893, + 898 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "4909", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 90, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Jimmy Aronsson. 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PMLR, 2022. 3, 5" + ], + "bbox": [ + 501, + 92, + 890, + 891 + ], + "page_idx": 10 + }, + { + "type": "page_number", + "text": "4912", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 10 + } +] \ No newline at end of file diff --git a/2023/EFEM_ Equivariant Neural Field Expectation Maximization for 3D Object Segmentation Without Scene Supervision/3d7e3a10-9770-4e87-8f5a-9ec61b4fbebc_model.json b/2023/EFEM_ Equivariant Neural Field Expectation Maximization for 3D Object Segmentation Without Scene Supervision/3d7e3a10-9770-4e87-8f5a-9ec61b4fbebc_model.json new file mode 100644 index 0000000000000000000000000000000000000000..d577ff9cf6ba9763798892bea219b6ec35829664 --- /dev/null +++ b/2023/EFEM_ Equivariant Neural Field Expectation Maximization for 3D Object Segmentation Without Scene Supervision/3d7e3a10-9770-4e87-8f5a-9ec61b4fbebc_model.json @@ -0,0 +1,2576 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.18, + 0.131, + 0.79, + 0.177 + ], + "angle": 0, + "content": "EFEM: Equivariant Neural Field Expectation Maximization for 3D Object Segmentation Without Scene Supervision" + }, + { + "type": "text", + "bbox": [ + 0.106, + 0.203, + 0.861, + 0.24 + ], + "angle": 0, + "content": "Jiahui Lei1 Congyue Deng2 Karl Schmeckpeper1 Leonidas Guibas2 Kostas Daniilidis1 \n1 University of Pennsylvania \n2 Stanford University" + }, + { + "type": "text", + "bbox": [ + 0.17, + 0.242, + 0.794, + 0.256 + ], + "angle": 0, + "content": "{leijh, karls, kostas}@cis.upenn.edu, {congyue, guibas}@cs.stanford.edu" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.292, + 0.313, + 0.308 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.325, + 0.474, + 0.611 + ], + "angle": 0, + "content": "We introduce Equivariant Neural Field Expectation Maximization (EFEM), a simple, effective, and robust geometric algorithm that can segment objects in 3D scenes without annotations or training on scenes. We achieve such unsupervised segmentation by exploiting single object shape priors. We make two novel steps in that direction. First, we introduce equivariant shape representations to this problem to eliminate the complexity induced by the variation in object configuration. Second, we propose a novel EM algorithm that can iteratively refine segmentation masks using the equivariant shape prior. We collect a novel real dataset Chairs and Mugs that contains various object configurations and novel scenes in order to verify the effectiveness and robustness of our method. Experimental results demonstrate that our method achieves consistent and robust performance across different scenes where the (weakly) supervised methods may fail. Code and data available at https://www.cis.upenn.edu/~leijh/projects/efem" + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.624, + 0.21, + 0.639 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.643, + 0.47, + 0.795 + ], + "angle": 0, + "content": "Learning how to decompose 3D scenes into object instances is a fundamental problem in visual perception systems. Past developments in 3D computer vision have made huge strides on this problem by training neural networks on 3D scene datasets with segmentation masks [55, 63, 67]. However, these works heavily rely on large labeled datasets [3, 15] that require laborious 3D annotation based on special expertise. Few recent papers alleviate this problem by reducing the need to either sparse point labeling [24, 60] or bounding boxes [12]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.796, + 0.47, + 0.902 + ], + "angle": 0, + "content": "In this work, we follow an object-centric approach inspired by the Gestalt school of perception that captures an object as a whole shape [32, 47] invariant to its pose and scale [31]. A holistic approach builds up a prior for each object category, that then enables object recognition in different complex scenes with varying configurations. Directly learning object-centric priors instead of analyzing each 3D" + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.291, + 0.66, + 0.381 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.664, + 0.291, + 0.891, + 0.381 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.392, + 0.893, + 0.435 + ], + "angle": 0, + "content": "Figure 1. We present EFEM, an unsupervised 3D object segmentation method applicable to real-world scenes (results on the right) by only training on ShapeNet single object reconstruction." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.444, + 0.893, + 0.732 + ], + "angle": 0, + "content": "scene inspires a more efficient way of learning instance segmentation: both a mug on the table and a mug in the dishwasher are mugs, and one does not have to learn to segment out a mug in all possible environmental contexts if we have a unified shape concept for mugs. Such object-centric recognition facilitates a robust scene analysis for autonomous systems in many interactive real-world environments with a diversity of object configurations: Imagine a scenario where a robot is doing the dishes in the kitchen. Dirty bowls are piled in the sink and the robot is cleaning them and placing them into a cabinet. Objects of the same category appear in the scene repeatedly under different configurations (piles, neat lines in the cabinet). What is even more challenging is that even within this one single task (doing dishes) the scene configuration can drastically change when objects are moved. We show that such scenarios cannot be addressed by the state-of-the-art strongly or weakly supervised methods that struggle under such scene configuration variations." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.735, + 0.895, + 0.903 + ], + "angle": 0, + "content": "In this paper, we introduce a method that can segment 3D object instances from 3D static scenes by learning priors of single object shapes (ShapeNet [4]) without using any scene-level labels. Two main challenges arise when we remove the scene-level annotation. First, objects in the scene can have a different position, rotation, and scale than the canonical poses where the single object shapes were trained. Second, the shape encoder which is trained on object-level input cannot be directly applied to the scene observations unless the object masks are known. We address the first challenge by introducing equivariance to this problem. By" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "4902" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.081, + 0.092, + 0.468, + 0.438 + ], + "angle": 0, + "content": "learning a shape prior that is equivariant to the similitude group SIM(3), the composition of a rotation, a translation, and a uniform scaling in 3D (Sec. 3.1), we address the complexity induced by the SIM(3) composition of objects. For the second challenge, we introduce a simple and effective iterative algorithm, Equivariant neural Field Expectation Maximization (EFEM), that refines the object segmentation mask, by alternately iterating between mask updating and shape reconstruction (Sec. 3.2). The above two steps enable us to directly exploit the learned single instance shape prior to perform segmentation in real-world scenes. We collected and annotated a novel real-world test set (240 scenes) (Sec. 4.4) that contains diverse object configurations and novel scenes to evaluate the generalizability and robustness to novel object instances and object configuration changes. Experiments on both synthetic data (Sec. 4.3) and our novel real dataset (Sec. 4.4) give us an insight to the effectiveness of the method. Compared to weakly supervised methods, when the testing scene setup is similar to the training setup, our method has a small performance gap to the (weakly) supervised baselines. However, when the testing scenes are drawn from novel object configurations, our method consistently outperforms the (weakly) supervised baselines." + }, + { + "type": "text", + "bbox": [ + 0.081, + 0.44, + 0.468, + 0.605 + ], + "angle": 0, + "content": "Our paper makes the following novel contributions to the 3D scene segmentation problem: (1) a simple and effective iterative EM algorithm that can segment objects from the scenes using only single object shape priors. (2) addressing the diversity of object composition in 3D scenes by combining representations equivariant to rotation, translation, and scaling of the objects. (3) an unsupervised pipeline for 3D instance segmentation that works in real-world data and can generalize to novel setups. (4) a novel real-world test set Chairs and Mugs that contains diverse object configurations and scenes." + }, + { + "type": "title", + "bbox": [ + 0.081, + 0.616, + 0.217, + 0.632 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.081, + 0.636, + 0.468, + 0.771 + ], + "angle": 0, + "content": "3D Instance segmentation. Point cloud instance segmentation has been a long-existing challenge in 3D vision even before the existence of deep learning. Early interests have been focusing on 3D object retrieval in scenes where RANSAC and generalized Hough voting were the most prominent paradigms [54]. In recent years, with the proliferation of large synthetic [17, 68] or real [3, 15, 22, 25] datasets with rich annotations, learning-based methods have shown great success on this task." + }, + { + "type": "text", + "bbox": [ + 0.081, + 0.78, + 0.468, + 0.901 + ], + "angle": 0, + "content": "Supervised methods. Most supervised methods fall into two categories: top-down methods that locate objects first and then predict the refined segmentation mask [23, 76], and bottom-up methods learning to group points into object proposals. Regarding the grouping approach, a variety of algorithms have been explored, such as point-pair similarity matrices [64, 80], mean-shift clustering [35], graph-based grouping [20], cluster growing [29], hierarchical ag" + }, + { + "type": "text", + "bbox": [ + 0.504, + 0.092, + 0.89, + 0.272 + ], + "angle": 0, + "content": "gregation [7, 40], or adversarial methods [78]. Later works [62, 63] combine top-down and bottom-up approaches and achieve impressive results. Recently, transformers and attention mechanisms have also been introduced to this problem [55]. [46] also incorporates neural implicit representations and simultaneously performs segmentation and shape reconstruction. Despite their requirements for laborious data annotation, we will also show that supervised methods heavily rely on the correlation between training and test scenes, and even the state-of-the-art supervised methods struggle to generalize to novel scene configurations or to changes in background patterns." + }, + { + "type": "text", + "bbox": [ + 0.504, + 0.276, + 0.89, + 0.637 + ], + "angle": 0, + "content": "Unsupervised or weakly supervised methods. Many attempts have been made to learn instance segmentation with limited annotations. A number of works leverage preextracted features from scenes via representation learning such as graph attentions [36] or contrastive learning [13, 24, 70, 77] to facilitate weakly-supervised training with fewer point labels. Other approaches directly propagate sparse annotations to dense point labels by learning point affinity graphs [60] or by bounding box voting [12]. These methods are usually the most scalable to large scenes, but their point features are scene-dependent, and we will show that similarly to fully-supervised learning methods, weakly-supervised methods have difficulties in generalizing to scenes with different configurations. When confronting dynamic scenes, one can exploit temporal self-consistency [58] or scene pair constraints [26, 77] but such constraints introduce additional assumptions about the scenes. Most related to our work are the retrieval-based methods leveraging object priors [39, 72]. Traditional retrieval methods are either limited to one given object template [72] or need to solve a discrete combinatorial optimization problem searching for the target template in the object category [39]. We resolve these issues by learning an implicit shape prior which can be optimized continuously in the feature space." + }, + { + "type": "text", + "bbox": [ + 0.504, + 0.641, + 0.89, + 0.868 + ], + "angle": 0, + "content": "Implicit object priors. First introduced in [10, 45, 49], neural implicit representations (also known as neural fields [71]) parameterize 3D shapes as level sets of neural networks. They not only show strong capabilities of capturing geometric details within limited capacity [28, 50, 57, 59] but also avoid shape discretization that introduces sampling noises. When representing a collection of objects with a shared implicit network, its bottleneck layer naturally forms a latent embedding of the objects, which can serve as a shape prior for many downstream tasks such as shape generation [10, 27, 44], reconstruction [41], completion [11, 45, 49], computing correspondences [33, 37, 43, 56], and part decomposition [9]. We refer the readers to [71] for a comprehensive review. Our method takes advantage of the recent work in neural fields to learn a deep shape prior." + }, + { + "type": "text", + "bbox": [ + 0.504, + 0.871, + 0.89, + 0.9 + ], + "angle": 0, + "content": "Equivariant point cloud networks. Equivariant networks are designed to preserve transformation coherence" + }, + { + "type": "page_number", + "bbox": [ + 0.485, + 0.947, + 0.514, + 0.957 + ], + "angle": 0, + "content": "4903" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.289 + ], + "angle": 0, + "content": "between the input and latent representations. With well-developed theories [1, 14, 34, 65, 74], equivariant networks have a variety of designs on point clouds [2, 16, 19, 30, 51, 61], which benefits many downstream tasks such as robotic applications [18, 21, 52, 56, 66, 75], 3D reconstruction [5, 6], and object pose estimation/canonicalization [38, 42, 48, 53, 81]. Unlike these object-level works, we focus on leveraging equivariance object features in scene understandings. Most related to us is [79] which also applies object equivariance to scenes. But they perform supervised 3D object bounding box detection while we predict dense instance masks. In this work, we employ the vector neurons [2, 6, 16] to build our equivariant shape prior." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.296, + 0.17, + 0.311 + ], + "angle": 0, + "content": "3. Method" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.315, + 0.473, + 0.542 + ], + "angle": 0, + "content": "Now we introduce our method for unsupervised object segmentation in 3D scenes. At the training stage, we learn an object-level shape prior (Sec. 3.1, Fig. 2 top left) utilizing a collection of synthetic models from an object category (e.g. all chairs in ShapeNet [4]). At inference time, we are given a scene point cloud \\( X_{N \\times 6} \\) of \\( N \\) points with coordinates as well as normal vectors with an unknown number of novel instances from the object category, and our task is to predict their instance segmentation masks. We will introduce a simple and novel iterative algorithm for predicting instance segmentation masks, starting from a single-object proposal phase (Sec. 3.2, Fig. 2 top right) and followed by a multiple-object joint proposal phase (Sec. 3.3, Fig. 2 bottom). As by-products, our model also outputs implicit surface reconstructions, poses, and bounding boxes." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.546, + 0.371, + 0.561 + ], + "angle": 0, + "content": "3.1. SIM(3) Equivariant Shape Priors" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.563, + 0.47, + 0.669 + ], + "angle": 0, + "content": "Most synthetic datasets have their objects manually aligned to canonical poses and unit scales, yet the SIM(3) transformations (translations, rotations, and scales) must be considered when applying the shape priors to real-world scenes. To this end, we constructed a SIM(3)-equivariant SDF encoder-decoder following the paradigms of prior work [16, 45] (Fig. 2 left top)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.673, + 0.473, + 0.902 + ], + "angle": 0, + "content": "Point cloud encoder. Given an object point cloud \\( P_{N_O \\times 3} \\) with \\( N_O \\) points, it is first encoded by a SIM(3)-equivariant encoder \\( \\Phi \\) (yellow block Fig. 2 left) constructed with Vector Neurons (VN) [2, 8, 16] into a latent embedding \\( \\Theta = \\Phi(P) \\) (orange block Fig. 2 middle). More concretely, the input point cloud \\( P \\) is first subtracted by its centroid \\( \\bar{P} \\) for translation equivariance, followed by a backbone network providing a global vector-channeled embedding \\( F \\), which is scale- and rotation-equivariant and translation invariant. \\( F \\) is then mapped to the shape implicit code \\( \\Theta \\) comprising four components \\( (\\Theta_{\\mathrm{R}}, \\Theta_{\\mathrm{inv}}, \\Theta_{\\mathrm{c}}, \\Theta_{\\mathrm{s}}) \\). The backbone network is a rotation-equivariant VN Point-Transformer [2] with additional scale equivariance enforced by channel-wise normalizations as in [8]. We denote the modified linear layer with scale invariance [8] as \\( \\widehat{\\mathrm{VN}} \\). The four components of \\( \\Theta \\) are" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.092, + 0.804, + 0.107 + ], + "angle": 0, + "content": "computed from \\(F\\) with four heads separately:" + }, + { + "type": "text", + "bbox": [ + 0.512, + 0.107, + 0.892, + 0.138 + ], + "angle": 0, + "content": "1. A vector-channeled rotation equivariant latent code \\(\\Theta_{\\mathrm{R}} = \\widehat{\\mathrm{VN}}_R(F)\\)" + }, + { + "type": "text", + "bbox": [ + 0.512, + 0.138, + 0.892, + 0.169 + ], + "angle": 0, + "content": "2. A scalar-channeled invariant latent code \\(\\Theta_{\\mathrm{inv}} = \\langle \\widehat{\\nabla}\\mathbf{N}_I(F),\\Theta_{\\mathrm{R}}\\rangle\\) computed with inner product." + }, + { + "type": "text", + "bbox": [ + 0.512, + 0.169, + 0.892, + 0.199 + ], + "angle": 0, + "content": "3. A scalar \\(\\Theta_{\\mathrm{s}}\\) by taking the average of \\(F\\)'s per-channel norm which explicitly encodes the object scale." + }, + { + "type": "text", + "bbox": [ + 0.512, + 0.199, + 0.892, + 0.274 + ], + "angle": 0, + "content": "4. A centroid correction vector predicting the offset between the centroid of points and the actual object center, which could be different due to the partiality and noises of the point could: \\(\\Theta_{\\mathrm{c}} = \\mathrm{VN}_{C}(F) + \\bar{P}\\), where \\(\\mathrm{VN}_C\\) has 1 output vector channel." + }, + { + "type": "list", + "bbox": [ + 0.512, + 0.107, + 0.892, + 0.274 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.275, + 0.892, + 0.335 + ], + "angle": 0, + "content": "Network architecture details can be found in the supplementary. For any transformation \\( g = (s, R, t) \\in \\mathrm{SIM}(3) \\) with scale \\( s \\), rotation \\( R \\), and translation \\( t \\), its action on \\( \\Theta \\) and the equivariance of the encoder \\( \\Phi \\) can be written as:" + }, + { + "type": "equation", + "bbox": [ + 0.506, + 0.347, + 0.892, + 0.364 + ], + "angle": 0, + "content": "\\[\ng \\circ \\Theta = \\left(\\Theta_ {\\mathrm {R}} R, \\Theta_ {\\text {i n v}}, s \\Theta_ {\\mathrm {c}} R + t, s \\Theta_ {\\mathrm {s}}\\right) = \\Phi (s P R + t). \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.369, + 0.892, + 0.4 + ], + "angle": 0, + "content": "SDF decoder. Give a query position \\( x \\in \\mathbb{R}^3 \\), its SDF value \\( \\hat{v}(x) \\) is predicted as" + }, + { + "type": "equation", + "bbox": [ + 0.571, + 0.412, + 0.892, + 0.429 + ], + "angle": 0, + "content": "\\[\n\\hat {v} (x) = \\Psi (x; \\Theta) = \\Psi \\left(\\Theta_ {\\text {i n v}}, \\langle \\Theta_ {\\mathrm {R}}, \\tilde {x} \\rangle\\right), \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.434, + 0.892, + 0.495 + ], + "angle": 0, + "content": "where \\(\\tilde{x} = (x - \\Theta_{\\mathrm{c}}) / \\Theta_{\\mathrm{s}}\\) is the canonicalized coordinate of \\(x\\) with center \\(\\Theta_{\\mathrm{c}}\\) and scale \\(\\Theta_{\\mathrm{s}}\\), and \\(\\Psi\\) is an MLP as in [16] that decodes the concatenation of the invariant feature \\(\\Theta_{\\mathrm{inv}}\\) and the channel-wise inner product between \\(\\Theta_{\\mathrm{R}}\\) and \\(\\tilde{x}\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.498, + 0.893, + 0.695 + ], + "angle": 0, + "content": "Training. The implicit shape prior is trained with the standard L2 loss for the query points sampled around each object. To avoid arbitrary prediction of \\(\\Theta_{\\mathrm{c}}\\) and \\(\\Theta_{\\mathrm{s}}\\) that may make training unstable in early epochs, we regularize \\(\\Theta_{\\mathrm{c}}\\) to stay around zero and \\(\\Theta_{\\mathrm{s}}\\) to stay around one. To help the network's generalization to real-world scenarios with partial observations, clutters, and sensor noises, we further augment the input object point clouds with partial depths and content-wise augmentations. Additional details of these augmentations are provided in the supplementary. We will next introduce how to exploit this learned shape-prior network which only takes instance-level inputs in scene-level point cloud segmentation." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.704, + 0.836, + 0.72 + ], + "angle": 0, + "content": "3.2. Iterative Algorithm for Single Proposal" + }, + { + "type": "text", + "bbox": [ + 0.501, + 0.729, + 0.773, + 0.746 + ], + "angle": 0, + "content": "Algorithm 1 Single Proposal Estimation" + }, + { + "type": "text", + "bbox": [ + 0.501, + 0.747, + 0.892, + 0.777 + ], + "angle": 0, + "content": "Data: Scene Point Cloud \\(X_{N\\times 6}\\); trained encoder \\(\\Phi\\) and decoder \\(\\Psi\\) with frozen weight" + }, + { + "type": "text", + "bbox": [ + 0.501, + 0.778, + 0.59, + 0.791 + ], + "angle": 0, + "content": "Initialize \\(W_0\\)" + }, + { + "type": "text", + "bbox": [ + 0.501, + 0.793, + 0.691, + 0.807 + ], + "angle": 0, + "content": "while not reach max step do" + }, + { + "type": "text", + "bbox": [ + 0.526, + 0.807, + 0.892, + 0.835 + ], + "angle": 0, + "content": "M-step: Sample \\(P_{t}\\) by Eq. 3 from \\(W_{t - 1}\\) and forward encoder \\(\\Phi\\) to update \\(\\Theta_t\\)." + }, + { + "type": "text", + "bbox": [ + 0.526, + 0.836, + 0.875, + 0.851 + ], + "angle": 0, + "content": "E-step: Evaluate decoder \\(\\Psi\\) and update \\(W_{t}\\) by Eq. 7." + }, + { + "type": "text", + "bbox": [ + 0.501, + 0.852, + 0.531, + 0.863 + ], + "angle": 0, + "content": "end" + }, + { + "type": "text", + "bbox": [ + 0.501, + 0.865, + 0.873, + 0.88 + ], + "angle": 0, + "content": "Extract mesh and compute absolute pose as a byproduct." + }, + { + "type": "text", + "bbox": [ + 0.501, + 0.88, + 0.836, + 0.895 + ], + "angle": 0, + "content": "Compute confidence \\(C\\) in Eq. 10 and output mask." + }, + { + "type": "page_number", + "bbox": [ + 0.482, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "4904" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.08, + 0.09, + 0.278, + 0.189 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.28, + 0.091, + 0.891, + 0.189 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.082, + 0.196, + 0.891, + 0.375 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.378, + 0.893, + 0.49 + ], + "angle": 0, + "content": "Figure 2. Overview: Left top: the single object SDF Encoder-Decoder (Sec. 3.1) is trained on the shape collection. Once trained, the network's weights are frozen.Top right Single EM step on scene observations (Sec. 3.2): given the last estimation of the object mask \\(W_{t - 1}\\), a set of points is sampled from the full scene point cloud and then passed to the shape encoder \\(\\Phi\\) to produce the current estimation of the shape embedding \\(\\Theta\\). Based on the \\(\\Theta\\), all the scene points are queried again through the decoder \\(\\Psi\\) to generate a new assignment mask \\(W_{t}\\). Bottom Object segmentation pipeline: starting from random crop initializations from the left, the above EM step is applied to each proposal (each row) in parallel to refine their masks. In the early steps (Phase-1 Sec. 3.2), all the proposals run independently but in the second phase, multiple proposals can be jointly optimized (Sec. 3.3). Note that we eliminate the duplicated (the second) or unreasonably sized (the fourth) proposals during optimization. Finally, the remaining proposals and their confidences are output." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.504, + 0.471, + 0.673 + ], + "angle": 0, + "content": "As shown in Fig 2, the key component of our full algorithm is the single proposal processing (right top) since the full algorithm is constructed by many single proposals being processed in parallel. Each proposal is represented by a soft assignment mask \\( W \\) over all scene points, where the continuous value on each point \\( W[i] \\in [0,1] \\) indicates how likely this point belongs to the object that the proposal is representing. In the early single proposal iteration steps (Phase-1), each proposal aims to fit its \\( W \\) to one object independently. In later iterations, we optimize the proposals jointly, as discussed in Section 3.3." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.68, + 0.47, + 0.773 + ], + "angle": 0, + "content": "Initialization. The single proposal algorithm starts from the initial assignment \\( W_{0} \\) which is drawn from a random ball or cylinder cropping of the scene. The radius of the crop is set to be similar to the average size of the target class. All points inside the crop are set to have \\( W[i] = 1.0 \\) while all other points are set to have \\( W[i] = 0.0 \\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.78, + 0.471, + 0.901 + ], + "angle": 0, + "content": "M-Step: Estimating shape embeddings. We treat the learned decoder with fixed weight as a parametric model of shape categories driven by the parameter \\(\\Theta\\). In each iteration of our algorithm, a new \\(\\Theta_{t}\\) is estimated from the last assignment \\(W_{t - 1}\\). Note that the learned shape prior encoder \\(\\Phi\\) only accepts a fixed number \\(N_O\\) of points as input, which is always far less than the number of points in the scene observation. Therefore at each iteration, we first sam" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.504, + 0.893, + 0.536 + ], + "angle": 0, + "content": "ple a fixed number \\(N_{O}\\) of points from the scene point cloud \\(X_{N\\times 6}\\) based on the last assignment estimation \\(W_{t - 1}\\)" + }, + { + "type": "equation", + "bbox": [ + 0.613, + 0.548, + 0.892, + 0.565 + ], + "angle": 0, + "content": "\\[\nP _ {t} = \\mathcal {M} \\left(W _ {t - 1}, X _ {N \\times 6}\\right), \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.572, + 0.893, + 0.753 + ], + "angle": 0, + "content": "where the sampling operations \\(\\mathcal{M}\\) contain two steps. First, a sample is drawn from a Bernoulli distribution with positive probability \\(W_{t - 1}[i]\\) to determine if the point \\(X[i]\\) belongs to the object's foreground. Second, for all points that are marked as foreground, we globally apply multinomial sampling based on their \\(W[i]\\) to find \\(N_O\\) sampled points. Finally, we produce the new shape estimation by passing the sampled point cloud through \\(\\Phi\\) so \\(\\Theta_t = \\Phi (P_t)\\). This method of updating the shape parameter can be interpreted as the M-step of an EM algorithm, which computes better distribution parameters based on the last assignment via weighted maximum likelihood." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.759, + 0.894, + 0.806 + ], + "angle": 0, + "content": "Fitting error. Given the \\(\\Theta\\) estimation, the fitting error of one observed point \\(\\mathbf{x} = [x_{\\mathrm{obs}}, n_{\\mathrm{obs}}]\\) (\\(x_{\\mathrm{obs}}\\) denotes position and \\(n_{\\mathrm{obs}}\\) denotes normal) in the scene point cloud \\(X_{N \\times 6}\\) is:" + }, + { + "type": "equation", + "bbox": [ + 0.611, + 0.821, + 0.891, + 0.838 + ], + "angle": 0, + "content": "\\[\ne _ {D} (\\mathbf {x}, \\Theta) = | \\Psi (x _ {\\mathrm {o b s}}; \\Theta) | \\tag {4}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.561, + 0.84, + 0.892, + 0.875 + ], + "angle": 0, + "content": "\\[\ne _ {N} (\\mathbf {x}, \\Theta) = \\operatorname {a c o s} \\left(\\frac {n _ {\\mathrm {o b s}} ^ {T} \\nabla_ {x} \\Psi \\left(x _ {\\mathrm {o b s}} ; \\Theta\\right)}{\\| \\nabla_ {x} \\Psi \\left(x _ {\\mathrm {o b s}} ; \\Theta\\right) \\|}\\right) \\tag {5}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.561, + 0.885, + 0.891, + 0.902 + ], + "angle": 0, + "content": "\\[\nE (\\mathbf {x}, \\Theta) = \\alpha_ {D} e _ {D} (\\mathbf {x}, \\Theta) + \\alpha_ {N} e _ {N} (\\mathbf {x}, \\Theta) \\tag {6}\n\\]" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "4905" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.168 + ], + "angle": 0, + "content": "which measures the observed point distance to the zero level set of the SDF and the normal consistency between the observed point and the decoded SDF gradient. The hyperparameters \\(\\alpha_{D}\\) and \\(\\alpha_{N}\\) control the importance of the distance and angle terms respectively." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.17, + 0.468, + 0.246 + ], + "angle": 0, + "content": "E-Step: Updating point assignments. After updating the shape parameters \\(\\Theta_t\\), we update the assignment weight \\(W_t\\) by querying the decoder \\(\\Psi\\) for all the points in the scene point cloud \\(X\\) and computing the error in Eq. 6. The new assignment is designed to be updated as:" + }, + { + "type": "equation", + "bbox": [ + 0.18, + 0.253, + 0.469, + 0.287 + ], + "angle": 0, + "content": "\\[\nW _ {t} [ i ] = \\frac {e ^ {- E (X [ i ] , \\Theta_ {t})}}{e ^ {- E (X [ i ] , \\Theta_ {t})} + \\Omega}, \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.289, + 0.469, + 0.334 + ], + "angle": 0, + "content": "where \\(\\Omega\\) is a constant hyperparameter that gives every point some probability to be in the background. This step can be interpreted as the E-step in an EM algorithm." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.337, + 0.469, + 0.548 + ], + "angle": 0, + "content": "Termination and confidence score. When the initialization is not near an object instance of the target class, the shape prior tends to never fit the input observations, so that the error \\( E \\) is large everywhere and the weight \\( W \\) is always small. We terminate the proposals that have less than a predefined threshold of small-error points at each iteration. After the last iteration, we use Marching Cubes to extract a mesh \\( (\\mathcal{V}, \\mathcal{E}) \\) for each proposal and the mesh serves as the byproduct of our method. Our algorithm also produces a pose estimation with respect to the training shape collection via Procrustes registration [81] on \\( \\Theta_{SO3} \\) between the observed objects and the member of the training set with the most similar \\( \\Theta \\) (see Supp.). We also remove proposals with meshes outside a predefined reasonable range of scales." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.549, + 0.469, + 0.669 + ], + "angle": 0, + "content": "One advantage of utilizing our shape prior is that we can explicitly compute the confidence score from the shape reconstruction. Specifically, we compute two scores by measuring the fitting errors: (1.) Observation fitting score: a good fitting should have all the encoder input points located on the decoded SDF zero level set. We measure the proportion of the encoder input point cloud which has a small distance and angle error:" + }, + { + "type": "equation", + "bbox": [ + 0.122, + 0.678, + 0.469, + 0.711 + ], + "angle": 0, + "content": "\\[\nS _ {1} = \\frac {1}{N _ {O}} \\left| \\left\\{\\mathbf {x} \\in P _ {T} \\left| \\begin{array}{l} e _ {D} (\\mathbf {x}, \\Theta) < \\delta_ {D}, \\\\ e _ {N} (\\mathbf {x}, \\Theta) < \\delta_ {N} \\end{array} \\right. \\right\\} \\right|, \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.714, + 0.469, + 0.864 + ], + "angle": 0, + "content": "where the \\(\\delta_D, \\delta_N\\) are the thresholds. (2.) Reconstruction coverage score: Since we recognize objects by their shapes, we should be less confident in detections where the observed points only cover a small portion of the extracted mesh. For every vertex \\(\\mathbf{v} = [x_{\\mathrm{recon}}, n_{\\mathrm{recon}}]\\) from the extracted mesh, we find its nearest neighbour \\(\\mathbf{x} = [x_{\\mathrm{obs}}, n_{\\mathrm{obs}}]\\) in the observed scene point cloud \\(X_{N \\times 6}\\) and measure their distance error as \\(e_D'(\\mathbf{v}) = \\| x_{\\mathrm{obs}} - x_{\\mathrm{recon}}\\|_2\\) and their orientation error as \\(e_N'(\\mathbf{v}) = \\cos(n_{\\mathrm{obs}}^T n_{\\mathrm{recon}})\\). This gives a combined coverage score of:" + }, + { + "type": "equation", + "bbox": [ + 0.102, + 0.873, + 0.469, + 0.904 + ], + "angle": 0, + "content": "\\[\nS _ {2} = \\frac {1}{| \\mathcal {V} |} | \\left\\{\\mathbf {v} \\in \\mathcal {V} \\mid e _ {D} ^ {\\prime} (\\mathbf {v}) < \\delta_ {D}, e _ {N} ^ {\\prime} (\\mathbf {v}) < \\delta_ {N} \\right\\} |. \\tag {9}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.092, + 0.892, + 0.136 + ], + "angle": 0, + "content": "We use \\( S_{1} \\) as the main confidence measurement and \\( S_{2} \\) for avoiding poorly observed cases, so the final confidence score \\( C \\) is:" + }, + { + "type": "equation", + "bbox": [ + 0.599, + 0.148, + 0.892, + 0.164 + ], + "angle": 0, + "content": "\\[\nC = S _ {1} * \\max \\left(1. 0, S _ {2} / \\delta_ {C}\\right), \\tag {10}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.169, + 0.892, + 0.244 + ], + "angle": 0, + "content": "where \\(\\delta_C \\in [0.0, 1.0]\\) is a threshold controlling the importance of the coverage score. Note how the above confidence values evaluate the quality of the output shown on the right in Fig. 2, which enables the user to select the balance between recall and precision during inference." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.245, + 0.892, + 0.351 + ], + "angle": 0, + "content": "Finally, for each point in the scene point cloud \\( X_{N \\times 6} \\), we check whether the distance error in Eq. 4 and Eq. 5 is smaller than the output threshold and mark points with small errors as in the foreground. Note that since the observation is noisy and the learned shape prior is not perfect, the output error thresholds can be larger than the ones used in Eq. 8 and Eq.9." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.36, + 0.682, + 0.376 + ], + "angle": 0, + "content": "3.3. Multiple Proposals" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.382, + 0.892, + 0.534 + ], + "angle": 0, + "content": "Since the EM algorithm outputs can be affected by its initialization and we do not know the number of objects in the scene, we initialize a large number of proposals randomly spread across the entire scene to cover all possible objects. We observe that many proposals will quickly converge to similar positions during the early iterations. Therefore, at each iteration, we remove duplicated proposals and only keep the one with the highest fitting score \\( S_{1} \\) defined in Eq. 8. Duplication is determined by computing the overlap of \\( W \\) between different proposals (see Supp. for details)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.534, + 0.892, + 0.655 + ], + "angle": 0, + "content": "As shown in Fig. 2, we further divide the iterations into two phases. In the first phase, since the early shape estimation is not converged to a reasonable place, we let each proposal run fully independently. When we enter the second phase, mesh extraction and pose estimation will be first applied to remove proposals with unreasonable scales. Then, we optimize all proposals globally by updating the joint assignment weight with:" + }, + { + "type": "equation", + "bbox": [ + 0.564, + 0.664, + 0.891, + 0.707 + ], + "angle": 0, + "content": "\\[\nW _ {t} ^ {(k)} [ i ] = \\frac {S _ {1} ^ {(k)} e ^ {- E (X [ i ] , \\Theta_ {t} ^ {(k)})}}{\\sum_ {j} S _ {1} ^ {(j)} e ^ {- E (X [ i ] , \\Theta_ {t} ^ {(j)})} + \\Omega}, \\tag {11}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.708, + 0.892, + 0.83 + ], + "angle": 0, + "content": "where \\( k \\) is the index of current active proposals and \\( S_1^{(k)} \\) is the current fitting score in Eq. 8, which increases the assignment weight for more confident proposals. During the last iterations in Phase-2, we also remove the proposals that are largely contained by other proposals to simplify the decomposition of the scene, following a similar methodology to duplication removal. Additional details of this process are available in the supplemental." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.837, + 0.633, + 0.853 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.856, + 0.892, + 0.901 + ], + "angle": 0, + "content": "We focus our experiments on answering four main questions: First, can our method successfully segment the objects of interest from the scene? Second, how does our" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "4906" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.08, + 0.087, + 0.891, + 0.209 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.212, + 0.893, + 0.242 + ], + "angle": 0, + "content": "Figure 3. Synthetic scenes: Top: the mesh reconstruction as input, note how our data has a realistic simulated depth pattern; Middle: visualization of the estimated shapes, poses and bounding boxes as the byproducts of our method. Bottom: Our segmentation prediction." + }, + { + "type": "image", + "bbox": [ + 0.079, + 0.251, + 0.891, + 0.384 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.223, + 0.386, + 0.746, + 0.401 + ], + "angle": 0, + "content": "Figure 4. Chairs and Mugs real testset: the three rows are in the same format as Fig. 3." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.427, + 0.473, + 0.562 + ], + "angle": 0, + "content": "method compare to existing baselines when different training data distributions are accessible? Third, how does each approach generalize to the different testing environments, including the real-world scenes and the out-of-distribution configurations? And fourth, how do the different components of our model contribute to its performance? To answer these questions, we perform a series of baseline comparisons as well as ablation studies both on synthetic and real-world scenes." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.565, + 0.186, + 0.579 + ], + "angle": 0, + "content": "4.1. Baselines" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.581, + 0.47, + 0.822 + ], + "angle": 0, + "content": "To the best of the authors' knowledge, fully unsupervised instance segmentation (not foreground-background segmentation) in static scenes remains unexplored in the deep learning literature. Therefore, we compare our method with supervised and weakly supervised methods. SoftGroup (CVPR22) [63] is the current SoTA for 3D instance segmentation methods that are trained with ground truth instance masks. Box2Mask (ECCV22) [12] is a recent weakly supervised method, which only needs ground truth instance bounding boxes as supervision while retaining competitive performance. The closest weakly supervised method to ours is ContrastiveSceneContext (CVPR21) [24], which can be trained with only a few point labels. To conduct fair comparisons and reduce the sim2real gap, all baselines are fully trained on the corresponding training set with positions and normals as input while not using colors." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.824, + 0.267, + 0.84 + ], + "angle": 0, + "content": "4.2. Experimental Setup" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.841, + 0.471, + 0.903 + ], + "angle": 0, + "content": "We focus our experiments on scenes that contain objects humans or robots can interact with. These objects are more interesting targets for segmentation as their configurations can change dramatically in real-world applications, such as" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.427, + 0.893, + 0.577 + ], + "angle": 0, + "content": "robotics or AR/VR. We experiment with three object categories that frequently appear in the presence of clutter and in diverse configurations in real-world data: Mugs, Kitchen containers, and Chairs. Since there is no available dataset that contains these objects with rich configuration changes (not just sitting upright on a flat surface), and all baselines need to be trained with ground truth, we gather simulated data to train the baselines, then evaluate on simulated and real test scenes containing completely unseen object instances." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.581, + 0.893, + 0.748 + ], + "angle": 0, + "content": "Three types of scenes are used for training baselines on each of the object classes. Take the mugs scene as an example (Fig. 3 Left top): In the Z scenes, all instances are upright and not in contact with each other. In SO(3), the objects can have a random orientation but are still not in contact with each other. Pile is a much more challenging setting where the objects can touch each other, can take any orientation, and can form piles. We simulate 500 scenes for training, 50 scenes for validation and 100 scenes for testing in each of the setups. For each baseline we train three models, one on the data from each of the three scene types." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.75, + 0.895, + 0.902 + ], + "angle": 0, + "content": "We train our equivariant shape prior (Sec. 3.1) on the corresponding categories from ShapeNet [4] and freeze their weights once trained. Note that all the following results are generated from the same trained shape prior for each category, and all the objects in our testing scenes never appear in the training set of the shape prior. We evaluate each model on all of the scenes and report results in Tab. 1, Tab. 2 and Tab. 3. The gray cells indicate results from models that were trained on less difficult datasets than they were evaluated on, with the underlined number indicating the best" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "4907" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.082, + 0.09, + 0.894, + 0.25 + ], + "angle": 0, + "content": "
MugsTestingZSO3PileTreeBoxShelf(R) Z(R) SO3(R) Pile(R) Tree(R) Others(R) Wild
TrainingMetricsAPA50APA50APA50APA50APA50APA50APA50APA50APA50APA50APA50APA50
Scene ZCSC (100)6.022.01.97.60.10.50.00.00.00.20.00.00.00.00.00.00.00.00.00.00.00.00.20.9
CSC (200)78.798.162.783.38.917.40.62.02.05.00.83.172.199.89.521.40.31.60.62.86.716.02.06.1
Box2Mask96.910092.199.336.727.612.345.310.024.08.614.698.110093.11005.619.18.428.818.439.518.127.9
SoftGroup10010096.598.521.927.60.41.81.63.79.217.293.797.697.31000.00.00.93.44.39.118.332.9
Scene SO3CSC (100)1.78.61.46.50.10.60.00.00.00.10.10.60.00.00.00.00.00.00.00.00.00.00.71.9
CSC (200)70.099.372.795.722.342.210.224.65.412.35.220.068.410059.81001.03.74.820.16.919.73.911.8
Box2Mask95.810094.710053.780.130.280.626.540.113.433.010010095.310012.734.319.649.227.150.650.374.8
SoftGroup10010099.699.843.951.910.018.715.321.320.830.999.210098.21002.84.810.421.76.513.318.330.7
Scene PileCSC (100)0.00.30.00.30.00.10.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.71.8
CSC (200)53.388.450.277.729.561.329.466.27.619.810.334.113.045.022.765.25.330.11.58.03.515.42.88.5
Box2Mask96.010094.710078.799.655.294.842.752.926.354.610010095.810072.398.055.898.156.079.245.171.4
SoftGroup99.510099.710089.093.242.372.823.425.528.839.599.610099.710074.786.353.483.050.966.548.165.9
ShapeNetEFEM78.499.879.399.868.296.868.899.059.977.048.772.487.210087.310063.194.069.695.469.789.454.182.3
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.254, + 0.893, + 0.296 + ], + "angle": 0, + "content": "Table 1. Results (%) on SynMugs (left) and RealMugs (right with label R). A50 corresponds to mAP50. The full table including mAP25 is available in the supplemental. The grey cells highlight that the testing scenes are out of the training distribution and the bold number means the best among all methods while the underlined number means the best within grey cells." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.32, + 0.466, + 0.455 + ], + "angle": 0, + "content": "
Testing(C) Z(C) SO3(C) Pile(K) Z(K) SO3(K) Pile
TrainingMetricsAPA50APA50APA50APA50APA50APA50
Scene ZCSC (100)66.283.156.680.26.115.212.729.97.514.52.35.9
CSC (200)77.791.063.785.110.522.763.080.937.949.212.223.2
Box2Mask99.910095.898.919.341.289.797.369.687.041.468.9
SoftGroup99.810094.898.524.136.593.696.894.099.352.363.5
Scene SO3CSC (100)74.981.477.382.417.731.08.521.711.323.82.05.4
CSC (200)84.386.685.488.520.635.327.848.953.977.518.138.9
Box2Mask99.710099.199.550.580.385.396.291.898.552.976.5
SoftGroup99.610099.110055.168.289.393.996.999.356.267.2
Scene PileCSC (100)67.074.174.682.147.263.83.411.22.67.11.44.5
CSC (200)71.776.388.492.467.481.626.553.844.873.628.860.4
Box2Mask99.699.799.599.778.696.987.297.992.198.674.894.6
SoftGroup99.410098.910095.097.093.797.396.098.884.691.3
ShapeNetEFEM93.199.286.197.475.388.069.483.467.683.160.178.9
" + }, + { + "type": "table_caption", + "bbox": [ + 0.08, + 0.459, + 0.468, + 0.472 + ], + "angle": 0, + "content": "Table 2. SynChairs (left) and SynKit (right), same format as Tab. 1" + }, + { + "type": "table", + "bbox": [ + 0.085, + 0.476, + 0.458, + 0.659 + ], + "angle": 0, + "content": "
RealChairsTestingR(Z)R(SO3)R(Pile)
TrainingMetricsAPAP50AP25APAP50AP25APAP50AP25
Scene ZCSC (100)0.51.49.41.32.810.80.00.07.2
CSC (200)0.81.211.00.30.69.80.00.23.1
Box2Mask0.00.320.20.31.927.20.00.111.8
SoftGroup5.17.727.02.86.721.90.00.03.7
Scene SO3CSC (100)3.65.318.21.42.513.30.00.14.5
CSC (200)1.22.610.41.84.920.20.10.59.1
Box2Mask1.55.948.45.119.956.70.41.828.2
SoftGroup13.817.227.47.916.230.30.10.16.1
Scene PileCSC (100)5.27.19.63.27.412.30.10.32.9
CSC (200)8.311.723.113.923.233.61.02.613.1
Box2Mask1.66.537.89.422.065.31.34.846.6
SoftGroup20.627.836.114.424.442.10.41.58.0
ScannetCSC (100)36.849.862.05.313.118.83.910.818.1
CSC (200)50.074.377.86.213.118.65.513.427.1
Box2Mask84.199.499.416.233.741.214.329.850.7
SoftGroup74.081.187.522.339.648.611.518.036.1
ShapeNetEFEM51.078.385.051.275.787.934.455.374.8
" + }, + { + "type": "table_caption", + "bbox": [ + 0.111, + 0.663, + 0.433, + 0.675 + ], + "angle": 0, + "content": "Table 3. Results on RealChairs, same format as Tab. 1" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.682, + 0.468, + 0.711 + ], + "angle": 0, + "content": "performing inside gray cells. The metric for evaluating the segmentation is the commonly used mAP [15]." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.717, + 0.306, + 0.733 + ], + "angle": 0, + "content": "4.3. Results on synthetic data" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.735, + 0.468, + 0.901 + ], + "angle": 0, + "content": "We first evaluate the performance on simulated data, and we found that existing baselines work very well inside the training distribution if trained with enough supervisory signals. However, the weakly supervised method CSC [24] has a significant performance drop when the number of supervision points decreases from 200 to 100. This performance drop becomes increasingly severe when the training set distribution becomes more complex, demonstrating the difficulty of unsupervised segmentation. With zero scene-level supervision, our method performs well with a small gap in performance to the (weakly) supervised methods." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.322, + 0.892, + 0.444 + ], + "angle": 0, + "content": "When the baselines are trained on \\(\\mathbf{Z}\\) but tested on SO3, the baselines do not show a large drop in performance, potentially because both \\(\\mathbf{Z}\\) and SO3 scenes have no objects in contact with each other. However, when tested on Pile, we see that baselines trained on \\(\\mathbf{Z}\\) or SO3 perform differently, and are both worse than the ones trained on Pile, indicating a failure to generalize to clutter. Our method outperforms all the baselines that are not trained on Pile configurations." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.444, + 0.892, + 0.596 + ], + "angle": 0, + "content": "We additionally generate 50 scenes each from three new and more difficult scene setups for testing on Mugs as shown in Fig. 3. In the Tree scenes mugs are hanging on a holder tree and distributed vertically. The Box scenes include cubes to simulate objects that have not been seen during training. In the Shelf scenes, the mugs are put on a shelf that is only visible from one side. In all three of these scene setups, our method is able to outperform all baselines as the baselines are unable to generalize to configurations of mugs that are significantly outside of the training distribution." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.607, + 0.689, + 0.62 + ], + "angle": 0, + "content": "4.4. Results on real data" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.624, + 0.892, + 0.729 + ], + "angle": 0, + "content": "We additionally evaluate the performance of our model on real data. To the best of the authors' knowledge, there is no existing real dataset that contains interactable objects in diverse configurations for 3D instance segmentation. Therefore we collect a test set Chairs and Mugs that contains the reconstruction of 240 real scenes with object instance mask annotations to test our method in the real world." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.735, + 0.892, + 0.901 + ], + "angle": 0, + "content": "RealMugs: As shown in Fig. 4 we replicate the Z, SO3, Pile and Tree setups in the real world. The scene is captured by 4 calibrated realsense D455 cameras mounted on the corners of the table. We further introduce two new setups that cover hard-to-simulate scenes. The Others setup contains random objects that a manipulator may encounter, including cloth, toys, paper bags, wires and tools. These objects are added into the tabletop scene, contacting and occluding the mugs. The Wild setup contains crops of real-world indoor scans from labs, kitchens, and teaching buildings. Unlike [73], our scenes are not restricted to only showing the" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "4908" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.088, + 0.468, + 0.208 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.086, + 0.209, + 0.462, + 0.223 + ], + "angle": 0, + "content": "Figure 5. ScanNet qualitative results, the same format as Fig. 3" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.239, + 0.47, + 0.33 + ], + "angle": 0, + "content": "table and upright mugs, but include diverse configurations, backgrounds, and distractors. These scans are captured by an iPad with a lidar scanner. Since the Z, SO3 and Pile setups are easy to simulate realistically, we only collect 10 scenes per setup. We collect 50 scenes for each of the Tree, Others and Wild setups." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.331, + 0.473, + 0.527 + ], + "angle": 0, + "content": "We test all the baselines trained on the synthetic dataset and our method trained on ShapeNet directly on these real scenes. Quantitative results are shown in Tab. 1. Since our simulator includes advanced techniques of active light simulation in the physical engine [69] and we do not use the colours as input, the sim2real gap for the baseline methods is minimal in these controlled setups. We can draw similar conclusions for Z, SO3, Pile and Tree setups as with the synthetic experiments. Our method retains reasonable performance on Others scenes due to its awareness of the object shape. When tested on the Wild real-world scenes, our method also performs the best, which demonstrates the strong generalizability of our method." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.538, + 0.473, + 0.884 + ], + "angle": 0, + "content": "RealChairs: We also collect data of chairs in the real world following the Z, SO3 and Pile setups. Although we have plenty of real-world scan datasets like [15], none of them include diverse configuration changes of chairs. Therefore we collected and annotated a small test set with 20 scenes per setup as shown in Fig. 4. We train the baselines in simulation and test them in the real world. Additionally, we take all the baselines' official model weights from being trained on the real world ScanNet dataset [15] to evaluate on our test set. The results are shown in Tab. 3. There is a larger sim2real gap for the baselines with the chairs data than with the mugs data because of less realistic depth simulation and difficulties aligning the scale between Shapenet chairs and real-world chairs. In contrast, the baselines trained on ScanNet work very well on the Z setup, which aligns best with the ScanNet dataset. However, they have a significant drop in performance when the testing distribution shifts to the SO3 and Pile setups. In contrast, our method retains reasonable performance on real world chairs across different setups. We will release our Chairs and Mugs dataset to provide more opportunities to study robustness, generalizability and equivariance for scene and object understanding in the real world." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.886, + 0.47, + 0.901 + ], + "angle": 0, + "content": "We also show our effectiveness on ScanNet [15], where" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.895, + 0.273 + ], + "angle": 0, + "content": "the indoor scene scan can span the whole room. Qualitative results are shown in Fig. 5 and the AP metrics for the chairs category of our method on the validation/test set are \\(AP = 24.6 / 20.2\\), \\(AP50 = 50.8 / 39.0\\) and \\(AP25 = 61.3 / 48.3\\) where in comparison the weakly supervised method CSC [24] trained on 200 points labels achieves \\(AP50 = 62.9 / 61.1\\) (See Suppl. for a table). One main reason for our performance drop on ScanNet is that ScanNet has many partially observed chairs, which are hard to be recognized via shape. We leave future explorations to fill this gap between our unsupervised method and the (weakly) supervised ones." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.276, + 0.611, + 0.29 + ], + "angle": 0, + "content": "4.5. Ablations" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.293, + 0.66, + 0.383 + ], + "angle": 0, + "content": "We verify the effectiveness of our design by removing the phase-2 joint iterations and removing the usage of the normals. When not" + }, + { + "type": "table", + "bbox": [ + 0.669, + 0.293, + 0.887, + 0.356 + ], + "angle": 0, + "content": "
AblationAPAP50AP25
Full0.6010.7890.807
No Phase 20.5480.7400.756
No Normal0.2030.3020.337
" + }, + { + "type": "table_caption", + "bbox": [ + 0.72, + 0.366, + 0.834, + 0.379 + ], + "angle": 0, + "content": "Table 4. Ablations" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.384, + 0.892, + 0.536 + ], + "angle": 0, + "content": "using phase-2 (Sec. 3.3), we let the phase-1 independent iterations run more steps to keep the total number of iterations constant. When removing the normals, all error computing, assignment weight updating, and confidence scoring will only take the distance error term in to account while ignoring the normal term. We compare our full model with the ablated models on SynKit Pile setups. The quantitative results are shown in Tab. 4, which illustrates that both components contribute to our model's overall performance. More ablation studies can be found in our supplementary." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.542, + 0.628, + 0.557 + ], + "angle": 0, + "content": "5. Conclusions" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.561, + 0.892, + 0.636 + ], + "angle": 0, + "content": "We present EFEM, a method for 3D instance segmentation that is trained only on shape datasets. Without requiring any real or simulated scene data, our method can generalize to complex, real world scenes better than existing methods that also require more supervision." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.639, + 0.895, + 0.79 + ], + "angle": 0, + "content": "Limitations and future work. Although we show an encouraging step towards unsupervised 3D instance segmentation by generalizing knowledge directly from a shape collection to a scene, several weaknesses remain. First, our method has a performance drop when the object is significantly occluded. This is due to our method recognizing objects only via their shape, rather than also reasoning about color or other features. 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We achieve such unsupervised segmentation by exploiting single object shape priors. We make two novel steps in that direction. First, we introduce equivariant shape representations to this problem to eliminate the complexity induced by the variation in object configuration. Second, we propose a novel EM algorithm that can iteratively refine segmentation masks using the equivariant shape prior. We collect a novel real dataset Chairs and Mugs that contains various object configurations and novel scenes in order to verify the effectiveness and robustness of our method. Experimental results demonstrate that our method achieves consistent and robust performance across different scenes where the (weakly) supervised methods may fail. Code and data available at https://www.cis.upenn.edu/~leijh/projects/efem + +# 1. Introduction + +Learning how to decompose 3D scenes into object instances is a fundamental problem in visual perception systems. Past developments in 3D computer vision have made huge strides on this problem by training neural networks on 3D scene datasets with segmentation masks [55, 63, 67]. However, these works heavily rely on large labeled datasets [3, 15] that require laborious 3D annotation based on special expertise. Few recent papers alleviate this problem by reducing the need to either sparse point labeling [24, 60] or bounding boxes [12]. + +In this work, we follow an object-centric approach inspired by the Gestalt school of perception that captures an object as a whole shape [32, 47] invariant to its pose and scale [31]. A holistic approach builds up a prior for each object category, that then enables object recognition in different complex scenes with varying configurations. Directly learning object-centric priors instead of analyzing each 3D + +![](images/e2ea2c2d876e3ddf0b1411ade2b4dd5a83fbce1f4c13a5c71bea5ca478dc6aa3.jpg) +Figure 1. We present EFEM, an unsupervised 3D object segmentation method applicable to real-world scenes (results on the right) by only training on ShapeNet single object reconstruction. + +![](images/ef70092ac0cccd9970d68b76d3c66663e7ddc1f3fd4c3d95fb0f6389692a2dad.jpg) + +scene inspires a more efficient way of learning instance segmentation: both a mug on the table and a mug in the dishwasher are mugs, and one does not have to learn to segment out a mug in all possible environmental contexts if we have a unified shape concept for mugs. Such object-centric recognition facilitates a robust scene analysis for autonomous systems in many interactive real-world environments with a diversity of object configurations: Imagine a scenario where a robot is doing the dishes in the kitchen. Dirty bowls are piled in the sink and the robot is cleaning them and placing them into a cabinet. Objects of the same category appear in the scene repeatedly under different configurations (piles, neat lines in the cabinet). What is even more challenging is that even within this one single task (doing dishes) the scene configuration can drastically change when objects are moved. We show that such scenarios cannot be addressed by the state-of-the-art strongly or weakly supervised methods that struggle under such scene configuration variations. + +In this paper, we introduce a method that can segment 3D object instances from 3D static scenes by learning priors of single object shapes (ShapeNet [4]) without using any scene-level labels. Two main challenges arise when we remove the scene-level annotation. First, objects in the scene can have a different position, rotation, and scale than the canonical poses where the single object shapes were trained. Second, the shape encoder which is trained on object-level input cannot be directly applied to the scene observations unless the object masks are known. We address the first challenge by introducing equivariance to this problem. By + +learning a shape prior that is equivariant to the similitude group SIM(3), the composition of a rotation, a translation, and a uniform scaling in 3D (Sec. 3.1), we address the complexity induced by the SIM(3) composition of objects. For the second challenge, we introduce a simple and effective iterative algorithm, Equivariant neural Field Expectation Maximization (EFEM), that refines the object segmentation mask, by alternately iterating between mask updating and shape reconstruction (Sec. 3.2). The above two steps enable us to directly exploit the learned single instance shape prior to perform segmentation in real-world scenes. We collected and annotated a novel real-world test set (240 scenes) (Sec. 4.4) that contains diverse object configurations and novel scenes to evaluate the generalizability and robustness to novel object instances and object configuration changes. Experiments on both synthetic data (Sec. 4.3) and our novel real dataset (Sec. 4.4) give us an insight to the effectiveness of the method. Compared to weakly supervised methods, when the testing scene setup is similar to the training setup, our method has a small performance gap to the (weakly) supervised baselines. However, when the testing scenes are drawn from novel object configurations, our method consistently outperforms the (weakly) supervised baselines. + +Our paper makes the following novel contributions to the 3D scene segmentation problem: (1) a simple and effective iterative EM algorithm that can segment objects from the scenes using only single object shape priors. (2) addressing the diversity of object composition in 3D scenes by combining representations equivariant to rotation, translation, and scaling of the objects. (3) an unsupervised pipeline for 3D instance segmentation that works in real-world data and can generalize to novel setups. (4) a novel real-world test set Chairs and Mugs that contains diverse object configurations and scenes. + +# 2. Related Work + +3D Instance segmentation. Point cloud instance segmentation has been a long-existing challenge in 3D vision even before the existence of deep learning. Early interests have been focusing on 3D object retrieval in scenes where RANSAC and generalized Hough voting were the most prominent paradigms [54]. In recent years, with the proliferation of large synthetic [17, 68] or real [3, 15, 22, 25] datasets with rich annotations, learning-based methods have shown great success on this task. + +Supervised methods. Most supervised methods fall into two categories: top-down methods that locate objects first and then predict the refined segmentation mask [23, 76], and bottom-up methods learning to group points into object proposals. Regarding the grouping approach, a variety of algorithms have been explored, such as point-pair similarity matrices [64, 80], mean-shift clustering [35], graph-based grouping [20], cluster growing [29], hierarchical ag + +gregation [7, 40], or adversarial methods [78]. Later works [62, 63] combine top-down and bottom-up approaches and achieve impressive results. Recently, transformers and attention mechanisms have also been introduced to this problem [55]. [46] also incorporates neural implicit representations and simultaneously performs segmentation and shape reconstruction. Despite their requirements for laborious data annotation, we will also show that supervised methods heavily rely on the correlation between training and test scenes, and even the state-of-the-art supervised methods struggle to generalize to novel scene configurations or to changes in background patterns. + +Unsupervised or weakly supervised methods. Many attempts have been made to learn instance segmentation with limited annotations. A number of works leverage preextracted features from scenes via representation learning such as graph attentions [36] or contrastive learning [13, 24, 70, 77] to facilitate weakly-supervised training with fewer point labels. Other approaches directly propagate sparse annotations to dense point labels by learning point affinity graphs [60] or by bounding box voting [12]. These methods are usually the most scalable to large scenes, but their point features are scene-dependent, and we will show that similarly to fully-supervised learning methods, weakly-supervised methods have difficulties in generalizing to scenes with different configurations. When confronting dynamic scenes, one can exploit temporal self-consistency [58] or scene pair constraints [26, 77] but such constraints introduce additional assumptions about the scenes. Most related to our work are the retrieval-based methods leveraging object priors [39, 72]. Traditional retrieval methods are either limited to one given object template [72] or need to solve a discrete combinatorial optimization problem searching for the target template in the object category [39]. We resolve these issues by learning an implicit shape prior which can be optimized continuously in the feature space. + +Implicit object priors. First introduced in [10, 45, 49], neural implicit representations (also known as neural fields [71]) parameterize 3D shapes as level sets of neural networks. They not only show strong capabilities of capturing geometric details within limited capacity [28, 50, 57, 59] but also avoid shape discretization that introduces sampling noises. When representing a collection of objects with a shared implicit network, its bottleneck layer naturally forms a latent embedding of the objects, which can serve as a shape prior for many downstream tasks such as shape generation [10, 27, 44], reconstruction [41], completion [11, 45, 49], computing correspondences [33, 37, 43, 56], and part decomposition [9]. We refer the readers to [71] for a comprehensive review. Our method takes advantage of the recent work in neural fields to learn a deep shape prior. + +Equivariant point cloud networks. Equivariant networks are designed to preserve transformation coherence + +between the input and latent representations. With well-developed theories [1, 14, 34, 65, 74], equivariant networks have a variety of designs on point clouds [2, 16, 19, 30, 51, 61], which benefits many downstream tasks such as robotic applications [18, 21, 52, 56, 66, 75], 3D reconstruction [5, 6], and object pose estimation/canonicalization [38, 42, 48, 53, 81]. Unlike these object-level works, we focus on leveraging equivariance object features in scene understandings. Most related to us is [79] which also applies object equivariance to scenes. But they perform supervised 3D object bounding box detection while we predict dense instance masks. In this work, we employ the vector neurons [2, 6, 16] to build our equivariant shape prior. + +# 3. Method + +Now we introduce our method for unsupervised object segmentation in 3D scenes. At the training stage, we learn an object-level shape prior (Sec. 3.1, Fig. 2 top left) utilizing a collection of synthetic models from an object category (e.g. all chairs in ShapeNet [4]). At inference time, we are given a scene point cloud $X_{N \times 6}$ of $N$ points with coordinates as well as normal vectors with an unknown number of novel instances from the object category, and our task is to predict their instance segmentation masks. We will introduce a simple and novel iterative algorithm for predicting instance segmentation masks, starting from a single-object proposal phase (Sec. 3.2, Fig. 2 top right) and followed by a multiple-object joint proposal phase (Sec. 3.3, Fig. 2 bottom). As by-products, our model also outputs implicit surface reconstructions, poses, and bounding boxes. + +# 3.1. SIM(3) Equivariant Shape Priors + +Most synthetic datasets have their objects manually aligned to canonical poses and unit scales, yet the SIM(3) transformations (translations, rotations, and scales) must be considered when applying the shape priors to real-world scenes. To this end, we constructed a SIM(3)-equivariant SDF encoder-decoder following the paradigms of prior work [16, 45] (Fig. 2 left top). + +Point cloud encoder. Given an object point cloud $P_{N_O \times 3}$ with $N_O$ points, it is first encoded by a SIM(3)-equivariant encoder $\Phi$ (yellow block Fig. 2 left) constructed with Vector Neurons (VN) [2, 8, 16] into a latent embedding $\Theta = \Phi(P)$ (orange block Fig. 2 middle). More concretely, the input point cloud $P$ is first subtracted by its centroid $\bar{P}$ for translation equivariance, followed by a backbone network providing a global vector-channeled embedding $F$ , which is scale- and rotation-equivariant and translation invariant. $F$ is then mapped to the shape implicit code $\Theta$ comprising four components $(\Theta_{\mathrm{R}}, \Theta_{\mathrm{inv}}, \Theta_{\mathrm{c}}, \Theta_{\mathrm{s}})$ . The backbone network is a rotation-equivariant VN Point-Transformer [2] with additional scale equivariance enforced by channel-wise normalizations as in [8]. We denote the modified linear layer with scale invariance [8] as $\widehat{\mathrm{VN}}$ . The four components of $\Theta$ are + +computed from $F$ with four heads separately: + +1. A vector-channeled rotation equivariant latent code $\Theta_{\mathrm{R}} = \widehat{\mathrm{VN}}_R(F)$ +2. A scalar-channeled invariant latent code $\Theta_{\mathrm{inv}} = \langle \widehat{\nabla}\mathbf{N}_I(F),\Theta_{\mathrm{R}}\rangle$ computed with inner product. +3. A scalar $\Theta_{\mathrm{s}}$ by taking the average of $F$ 's per-channel norm which explicitly encodes the object scale. +4. A centroid correction vector predicting the offset between the centroid of points and the actual object center, which could be different due to the partiality and noises of the point could: $\Theta_{\mathrm{c}} = \mathrm{VN}_{C}(F) + \bar{P}$ , where $\mathrm{VN}_C$ has 1 output vector channel. + +Network architecture details can be found in the supplementary. For any transformation $g = (s, R, t) \in \mathrm{SIM}(3)$ with scale $s$ , rotation $R$ , and translation $t$ , its action on $\Theta$ and the equivariance of the encoder $\Phi$ can be written as: + +$$ +g \circ \Theta = \left(\Theta_ {\mathrm {R}} R, \Theta_ {\text {i n v}}, s \Theta_ {\mathrm {c}} R + t, s \Theta_ {\mathrm {s}}\right) = \Phi (s P R + t). \tag {1} +$$ + +SDF decoder. Give a query position $x \in \mathbb{R}^3$ , its SDF value $\hat{v}(x)$ is predicted as + +$$ +\hat {v} (x) = \Psi (x; \Theta) = \Psi \left(\Theta_ {\text {i n v}}, \langle \Theta_ {\mathrm {R}}, \tilde {x} \rangle\right), \tag {2} +$$ + +where $\tilde{x} = (x - \Theta_{\mathrm{c}}) / \Theta_{\mathrm{s}}$ is the canonicalized coordinate of $x$ with center $\Theta_{\mathrm{c}}$ and scale $\Theta_{\mathrm{s}}$ , and $\Psi$ is an MLP as in [16] that decodes the concatenation of the invariant feature $\Theta_{\mathrm{inv}}$ and the channel-wise inner product between $\Theta_{\mathrm{R}}$ and $\tilde{x}$ . + +Training. The implicit shape prior is trained with the standard L2 loss for the query points sampled around each object. To avoid arbitrary prediction of $\Theta_{\mathrm{c}}$ and $\Theta_{\mathrm{s}}$ that may make training unstable in early epochs, we regularize $\Theta_{\mathrm{c}}$ to stay around zero and $\Theta_{\mathrm{s}}$ to stay around one. To help the network's generalization to real-world scenarios with partial observations, clutters, and sensor noises, we further augment the input object point clouds with partial depths and content-wise augmentations. Additional details of these augmentations are provided in the supplementary. We will next introduce how to exploit this learned shape-prior network which only takes instance-level inputs in scene-level point cloud segmentation. + +# 3.2. Iterative Algorithm for Single Proposal + +Algorithm 1 Single Proposal Estimation + +Data: Scene Point Cloud $X_{N\times 6}$ ; trained encoder $\Phi$ and decoder $\Psi$ with frozen weight + +Initialize $W_0$ + +while not reach max step do + +M-step: Sample $P_{t}$ by Eq. 3 from $W_{t - 1}$ and forward encoder $\Phi$ to update $\Theta_t$ . + +E-step: Evaluate decoder $\Psi$ and update $W_{t}$ by Eq. 7. + +end + +Extract mesh and compute absolute pose as a byproduct. + +Compute confidence $C$ in Eq. 10 and output mask. + +![](images/58ef2952e7877ba2c842704d870dfb534b921e5af30bc291c28c682f3626dc85.jpg) + +![](images/02e0c628537808f4e98041ad17105a959177167fc550d485afc74677cc70f53a.jpg) + +![](images/6397ff26fd4d09cbc00c5e8050eb194e781317bf200380f68a8c67c1c773ebf8.jpg) +Figure 2. Overview: Left top: the single object SDF Encoder-Decoder (Sec. 3.1) is trained on the shape collection. Once trained, the network's weights are frozen.Top right Single EM step on scene observations (Sec. 3.2): given the last estimation of the object mask $W_{t - 1}$ , a set of points is sampled from the full scene point cloud and then passed to the shape encoder $\Phi$ to produce the current estimation of the shape embedding $\Theta$ . Based on the $\Theta$ , all the scene points are queried again through the decoder $\Psi$ to generate a new assignment mask $W_{t}$ . Bottom Object segmentation pipeline: starting from random crop initializations from the left, the above EM step is applied to each proposal (each row) in parallel to refine their masks. In the early steps (Phase-1 Sec. 3.2), all the proposals run independently but in the second phase, multiple proposals can be jointly optimized (Sec. 3.3). Note that we eliminate the duplicated (the second) or unreasonably sized (the fourth) proposals during optimization. Finally, the remaining proposals and their confidences are output. + +As shown in Fig 2, the key component of our full algorithm is the single proposal processing (right top) since the full algorithm is constructed by many single proposals being processed in parallel. Each proposal is represented by a soft assignment mask $W$ over all scene points, where the continuous value on each point $W[i] \in [0,1]$ indicates how likely this point belongs to the object that the proposal is representing. In the early single proposal iteration steps (Phase-1), each proposal aims to fit its $W$ to one object independently. In later iterations, we optimize the proposals jointly, as discussed in Section 3.3. + +Initialization. The single proposal algorithm starts from the initial assignment $W_{0}$ which is drawn from a random ball or cylinder cropping of the scene. The radius of the crop is set to be similar to the average size of the target class. All points inside the crop are set to have $W[i] = 1.0$ while all other points are set to have $W[i] = 0.0$ . + +M-Step: Estimating shape embeddings. We treat the learned decoder with fixed weight as a parametric model of shape categories driven by the parameter $\Theta$ . In each iteration of our algorithm, a new $\Theta_{t}$ is estimated from the last assignment $W_{t - 1}$ . Note that the learned shape prior encoder $\Phi$ only accepts a fixed number $N_O$ of points as input, which is always far less than the number of points in the scene observation. Therefore at each iteration, we first sam + +ple a fixed number $N_{O}$ of points from the scene point cloud $X_{N\times 6}$ based on the last assignment estimation $W_{t - 1}$ + +$$ +P _ {t} = \mathcal {M} \left(W _ {t - 1}, X _ {N \times 6}\right), \tag {3} +$$ + +where the sampling operations $\mathcal{M}$ contain two steps. First, a sample is drawn from a Bernoulli distribution with positive probability $W_{t - 1}[i]$ to determine if the point $X[i]$ belongs to the object's foreground. Second, for all points that are marked as foreground, we globally apply multinomial sampling based on their $W[i]$ to find $N_O$ sampled points. Finally, we produce the new shape estimation by passing the sampled point cloud through $\Phi$ so $\Theta_t = \Phi (P_t)$ . This method of updating the shape parameter can be interpreted as the M-step of an EM algorithm, which computes better distribution parameters based on the last assignment via weighted maximum likelihood. + +Fitting error. Given the $\Theta$ estimation, the fitting error of one observed point $\mathbf{x} = [x_{\mathrm{obs}}, n_{\mathrm{obs}}]$ ( $x_{\mathrm{obs}}$ denotes position and $n_{\mathrm{obs}}$ denotes normal) in the scene point cloud $X_{N \times 6}$ is: + +$$ +e _ {D} (\mathbf {x}, \Theta) = | \Psi (x _ {\mathrm {o b s}}; \Theta) | \tag {4} +$$ + +$$ +e _ {N} (\mathbf {x}, \Theta) = \operatorname {a c o s} \left(\frac {n _ {\mathrm {o b s}} ^ {T} \nabla_ {x} \Psi \left(x _ {\mathrm {o b s}} ; \Theta\right)}{\| \nabla_ {x} \Psi \left(x _ {\mathrm {o b s}} ; \Theta\right) \|}\right) \tag {5} +$$ + +$$ +E (\mathbf {x}, \Theta) = \alpha_ {D} e _ {D} (\mathbf {x}, \Theta) + \alpha_ {N} e _ {N} (\mathbf {x}, \Theta) \tag {6} +$$ + +which measures the observed point distance to the zero level set of the SDF and the normal consistency between the observed point and the decoded SDF gradient. The hyperparameters $\alpha_{D}$ and $\alpha_{N}$ control the importance of the distance and angle terms respectively. + +E-Step: Updating point assignments. After updating the shape parameters $\Theta_t$ , we update the assignment weight $W_t$ by querying the decoder $\Psi$ for all the points in the scene point cloud $X$ and computing the error in Eq. 6. The new assignment is designed to be updated as: + +$$ +W _ {t} [ i ] = \frac {e ^ {- E (X [ i ] , \Theta_ {t})}}{e ^ {- E (X [ i ] , \Theta_ {t})} + \Omega}, \tag {7} +$$ + +where $\Omega$ is a constant hyperparameter that gives every point some probability to be in the background. This step can be interpreted as the E-step in an EM algorithm. + +Termination and confidence score. When the initialization is not near an object instance of the target class, the shape prior tends to never fit the input observations, so that the error $E$ is large everywhere and the weight $W$ is always small. We terminate the proposals that have less than a predefined threshold of small-error points at each iteration. After the last iteration, we use Marching Cubes to extract a mesh $(\mathcal{V}, \mathcal{E})$ for each proposal and the mesh serves as the byproduct of our method. Our algorithm also produces a pose estimation with respect to the training shape collection via Procrustes registration [81] on $\Theta_{SO3}$ between the observed objects and the member of the training set with the most similar $\Theta$ (see Supp.). We also remove proposals with meshes outside a predefined reasonable range of scales. + +One advantage of utilizing our shape prior is that we can explicitly compute the confidence score from the shape reconstruction. Specifically, we compute two scores by measuring the fitting errors: (1.) Observation fitting score: a good fitting should have all the encoder input points located on the decoded SDF zero level set. We measure the proportion of the encoder input point cloud which has a small distance and angle error: + +$$ +S _ {1} = \frac {1}{N _ {O}} \left| \left\{\mathbf {x} \in P _ {T} \left| \begin{array}{l} e _ {D} (\mathbf {x}, \Theta) < \delta_ {D}, \\ e _ {N} (\mathbf {x}, \Theta) < \delta_ {N} \end{array} \right. \right\} \right|, \tag {8} +$$ + +where the $\delta_D, \delta_N$ are the thresholds. (2.) Reconstruction coverage score: Since we recognize objects by their shapes, we should be less confident in detections where the observed points only cover a small portion of the extracted mesh. For every vertex $\mathbf{v} = [x_{\mathrm{recon}}, n_{\mathrm{recon}}]$ from the extracted mesh, we find its nearest neighbour $\mathbf{x} = [x_{\mathrm{obs}}, n_{\mathrm{obs}}]$ in the observed scene point cloud $X_{N \times 6}$ and measure their distance error as $e_D'(\mathbf{v}) = \| x_{\mathrm{obs}} - x_{\mathrm{recon}}\|_2$ and their orientation error as $e_N'(\mathbf{v}) = \cos(n_{\mathrm{obs}}^T n_{\mathrm{recon}})$ . This gives a combined coverage score of: + +$$ +S _ {2} = \frac {1}{| \mathcal {V} |} | \left\{\mathbf {v} \in \mathcal {V} \mid e _ {D} ^ {\prime} (\mathbf {v}) < \delta_ {D}, e _ {N} ^ {\prime} (\mathbf {v}) < \delta_ {N} \right\} |. \tag {9} +$$ + +We use $S_{1}$ as the main confidence measurement and $S_{2}$ for avoiding poorly observed cases, so the final confidence score $C$ is: + +$$ +C = S _ {1} * \max \left(1. 0, S _ {2} / \delta_ {C}\right), \tag {10} +$$ + +where $\delta_C \in [0.0, 1.0]$ is a threshold controlling the importance of the coverage score. Note how the above confidence values evaluate the quality of the output shown on the right in Fig. 2, which enables the user to select the balance between recall and precision during inference. + +Finally, for each point in the scene point cloud $X_{N \times 6}$ , we check whether the distance error in Eq. 4 and Eq. 5 is smaller than the output threshold and mark points with small errors as in the foreground. Note that since the observation is noisy and the learned shape prior is not perfect, the output error thresholds can be larger than the ones used in Eq. 8 and Eq.9. + +# 3.3. Multiple Proposals + +Since the EM algorithm outputs can be affected by its initialization and we do not know the number of objects in the scene, we initialize a large number of proposals randomly spread across the entire scene to cover all possible objects. We observe that many proposals will quickly converge to similar positions during the early iterations. Therefore, at each iteration, we remove duplicated proposals and only keep the one with the highest fitting score $S_{1}$ defined in Eq. 8. Duplication is determined by computing the overlap of $W$ between different proposals (see Supp. for details). + +As shown in Fig. 2, we further divide the iterations into two phases. In the first phase, since the early shape estimation is not converged to a reasonable place, we let each proposal run fully independently. When we enter the second phase, mesh extraction and pose estimation will be first applied to remove proposals with unreasonable scales. Then, we optimize all proposals globally by updating the joint assignment weight with: + +$$ +W _ {t} ^ {(k)} [ i ] = \frac {S _ {1} ^ {(k)} e ^ {- E (X [ i ] , \Theta_ {t} ^ {(k)})}}{\sum_ {j} S _ {1} ^ {(j)} e ^ {- E (X [ i ] , \Theta_ {t} ^ {(j)})} + \Omega}, \tag {11} +$$ + +where $k$ is the index of current active proposals and $S_1^{(k)}$ is the current fitting score in Eq. 8, which increases the assignment weight for more confident proposals. During the last iterations in Phase-2, we also remove the proposals that are largely contained by other proposals to simplify the decomposition of the scene, following a similar methodology to duplication removal. Additional details of this process are available in the supplemental. + +# 4. Experiments + +We focus our experiments on answering four main questions: First, can our method successfully segment the objects of interest from the scene? Second, how does our + +![](images/3d2b9b9199912bb86cbe8a5ef397dee4a4ac5e332210b1a903e7f76d9a5cf483.jpg) +Figure 3. Synthetic scenes: Top: the mesh reconstruction as input, note how our data has a realistic simulated depth pattern; Middle: visualization of the estimated shapes, poses and bounding boxes as the byproducts of our method. Bottom: Our segmentation prediction. + +![](images/0ddd746a1fb5f79589820024ef3365e05087e797bde8138af7efc70c5936ae9d.jpg) +Figure 4. Chairs and Mugs real testset: the three rows are in the same format as Fig. 3. + +method compare to existing baselines when different training data distributions are accessible? Third, how does each approach generalize to the different testing environments, including the real-world scenes and the out-of-distribution configurations? And fourth, how do the different components of our model contribute to its performance? To answer these questions, we perform a series of baseline comparisons as well as ablation studies both on synthetic and real-world scenes. + +# 4.1. Baselines + +To the best of the authors' knowledge, fully unsupervised instance segmentation (not foreground-background segmentation) in static scenes remains unexplored in the deep learning literature. Therefore, we compare our method with supervised and weakly supervised methods. SoftGroup (CVPR22) [63] is the current SoTA for 3D instance segmentation methods that are trained with ground truth instance masks. Box2Mask (ECCV22) [12] is a recent weakly supervised method, which only needs ground truth instance bounding boxes as supervision while retaining competitive performance. The closest weakly supervised method to ours is ContrastiveSceneContext (CVPR21) [24], which can be trained with only a few point labels. To conduct fair comparisons and reduce the sim2real gap, all baselines are fully trained on the corresponding training set with positions and normals as input while not using colors. + +# 4.2. Experimental Setup + +We focus our experiments on scenes that contain objects humans or robots can interact with. These objects are more interesting targets for segmentation as their configurations can change dramatically in real-world applications, such as + +robotics or AR/VR. We experiment with three object categories that frequently appear in the presence of clutter and in diverse configurations in real-world data: Mugs, Kitchen containers, and Chairs. Since there is no available dataset that contains these objects with rich configuration changes (not just sitting upright on a flat surface), and all baselines need to be trained with ground truth, we gather simulated data to train the baselines, then evaluate on simulated and real test scenes containing completely unseen object instances. + +Three types of scenes are used for training baselines on each of the object classes. Take the mugs scene as an example (Fig. 3 Left top): In the Z scenes, all instances are upright and not in contact with each other. In SO(3), the objects can have a random orientation but are still not in contact with each other. Pile is a much more challenging setting where the objects can touch each other, can take any orientation, and can form piles. We simulate 500 scenes for training, 50 scenes for validation and 100 scenes for testing in each of the setups. For each baseline we train three models, one on the data from each of the three scene types. + +We train our equivariant shape prior (Sec. 3.1) on the corresponding categories from ShapeNet [4] and freeze their weights once trained. Note that all the following results are generated from the same trained shape prior for each category, and all the objects in our testing scenes never appear in the training set of the shape prior. We evaluate each model on all of the scenes and report results in Tab. 1, Tab. 2 and Tab. 3. The gray cells indicate results from models that were trained on less difficult datasets than they were evaluated on, with the underlined number indicating the best + +
MugsTestingZSO3PileTreeBoxShelf(R) Z(R) SO3(R) Pile(R) Tree(R) Others(R) Wild
TrainingMetricsAPA50APA50APA50APA50APA50APA50APA50APA50APA50APA50APA50APA50
Scene ZCSC (100)6.022.01.97.60.10.50.00.00.00.20.00.00.00.00.00.00.00.00.00.00.00.00.20.9
CSC (200)78.798.162.783.38.917.40.62.02.05.00.83.172.199.89.521.40.31.60.62.86.716.02.06.1
Box2Mask96.910092.199.336.727.612.345.310.024.08.614.698.110093.11005.619.18.428.818.439.518.127.9
SoftGroup10010096.598.521.927.60.41.81.63.79.217.293.797.697.31000.00.00.93.44.39.118.332.9
Scene SO3CSC (100)1.78.61.46.50.10.60.00.00.00.10.10.60.00.00.00.00.00.00.00.00.00.00.71.9
CSC (200)70.099.372.795.722.342.210.224.65.412.35.220.068.410059.81001.03.74.820.16.919.73.911.8
Box2Mask95.810094.710053.780.130.280.626.540.113.433.010010095.310012.734.319.649.227.150.650.374.8
SoftGroup10010099.699.843.951.910.018.715.321.320.830.999.210098.21002.84.810.421.76.513.318.330.7
Scene PileCSC (100)0.00.30.00.30.00.10.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.71.8
CSC (200)53.388.450.277.729.561.329.466.27.619.810.334.113.045.022.765.25.330.11.58.03.515.42.88.5
Box2Mask96.010094.710078.799.655.294.842.752.926.354.610010095.810072.398.055.898.156.079.245.171.4
SoftGroup99.510099.710089.093.242.372.823.425.528.839.599.610099.710074.786.353.483.050.966.548.165.9
ShapeNetEFEM78.499.879.399.868.296.868.899.059.977.048.772.487.210087.310063.194.069.695.469.789.454.182.3
+ +Table 1. Results (%) on SynMugs (left) and RealMugs (right with label R). A50 corresponds to mAP50. The full table including mAP25 is available in the supplemental. The grey cells highlight that the testing scenes are out of the training distribution and the bold number means the best among all methods while the underlined number means the best within grey cells. + +
Testing(C) Z(C) SO3(C) Pile(K) Z(K) SO3(K) Pile
TrainingMetricsAPA50APA50APA50APA50APA50APA50
Scene ZCSC (100)66.283.156.680.26.115.212.729.97.514.52.35.9
CSC (200)77.791.063.785.110.522.763.080.937.949.212.223.2
Box2Mask99.910095.898.919.341.289.797.369.687.041.468.9
SoftGroup99.810094.898.524.136.593.696.894.099.352.363.5
Scene SO3CSC (100)74.981.477.382.417.731.08.521.711.323.82.05.4
CSC (200)84.386.685.488.520.635.327.848.953.977.518.138.9
Box2Mask99.710099.199.550.580.385.396.291.898.552.976.5
SoftGroup99.610099.110055.168.289.393.996.999.356.267.2
Scene PileCSC (100)67.074.174.682.147.263.83.411.22.67.11.44.5
CSC (200)71.776.388.492.467.481.626.553.844.873.628.860.4
Box2Mask99.699.799.599.778.696.987.297.992.198.674.894.6
SoftGroup99.410098.910095.097.093.797.396.098.884.691.3
ShapeNetEFEM93.199.286.197.475.388.069.483.467.683.160.178.9
+ +Table 2. SynChairs (left) and SynKit (right), same format as Tab. 1 + +
RealChairsTestingR(Z)R(SO3)R(Pile)
TrainingMetricsAPAP50AP25APAP50AP25APAP50AP25
Scene ZCSC (100)0.51.49.41.32.810.80.00.07.2
CSC (200)0.81.211.00.30.69.80.00.23.1
Box2Mask0.00.320.20.31.927.20.00.111.8
SoftGroup5.17.727.02.86.721.90.00.03.7
Scene SO3CSC (100)3.65.318.21.42.513.30.00.14.5
CSC (200)1.22.610.41.84.920.20.10.59.1
Box2Mask1.55.948.45.119.956.70.41.828.2
SoftGroup13.817.227.47.916.230.30.10.16.1
Scene PileCSC (100)5.27.19.63.27.412.30.10.32.9
CSC (200)8.311.723.113.923.233.61.02.613.1
Box2Mask1.66.537.89.422.065.31.34.846.6
SoftGroup20.627.836.114.424.442.10.41.58.0
ScannetCSC (100)36.849.862.05.313.118.83.910.818.1
CSC (200)50.074.377.86.213.118.65.513.427.1
Box2Mask84.199.499.416.233.741.214.329.850.7
SoftGroup74.081.187.522.339.648.611.518.036.1
ShapeNetEFEM51.078.385.051.275.787.934.455.374.8
+ +Table 3. Results on RealChairs, same format as Tab. 1 + +performing inside gray cells. The metric for evaluating the segmentation is the commonly used mAP [15]. + +# 4.3. Results on synthetic data + +We first evaluate the performance on simulated data, and we found that existing baselines work very well inside the training distribution if trained with enough supervisory signals. However, the weakly supervised method CSC [24] has a significant performance drop when the number of supervision points decreases from 200 to 100. This performance drop becomes increasingly severe when the training set distribution becomes more complex, demonstrating the difficulty of unsupervised segmentation. With zero scene-level supervision, our method performs well with a small gap in performance to the (weakly) supervised methods. + +When the baselines are trained on $\mathbf{Z}$ but tested on SO3, the baselines do not show a large drop in performance, potentially because both $\mathbf{Z}$ and SO3 scenes have no objects in contact with each other. However, when tested on Pile, we see that baselines trained on $\mathbf{Z}$ or SO3 perform differently, and are both worse than the ones trained on Pile, indicating a failure to generalize to clutter. Our method outperforms all the baselines that are not trained on Pile configurations. + +We additionally generate 50 scenes each from three new and more difficult scene setups for testing on Mugs as shown in Fig. 3. In the Tree scenes mugs are hanging on a holder tree and distributed vertically. The Box scenes include cubes to simulate objects that have not been seen during training. In the Shelf scenes, the mugs are put on a shelf that is only visible from one side. In all three of these scene setups, our method is able to outperform all baselines as the baselines are unable to generalize to configurations of mugs that are significantly outside of the training distribution. + +# 4.4. Results on real data + +We additionally evaluate the performance of our model on real data. To the best of the authors' knowledge, there is no existing real dataset that contains interactable objects in diverse configurations for 3D instance segmentation. Therefore we collect a test set Chairs and Mugs that contains the reconstruction of 240 real scenes with object instance mask annotations to test our method in the real world. + +RealMugs: As shown in Fig. 4 we replicate the Z, SO3, Pile and Tree setups in the real world. The scene is captured by 4 calibrated realsense D455 cameras mounted on the corners of the table. We further introduce two new setups that cover hard-to-simulate scenes. The Others setup contains random objects that a manipulator may encounter, including cloth, toys, paper bags, wires and tools. These objects are added into the tabletop scene, contacting and occluding the mugs. The Wild setup contains crops of real-world indoor scans from labs, kitchens, and teaching buildings. Unlike [73], our scenes are not restricted to only showing the + +![](images/130b828df894e63e4f49711608be9d5072d3580cee6c84503ec3278c323e4e94.jpg) +Figure 5. ScanNet qualitative results, the same format as Fig. 3 + +table and upright mugs, but include diverse configurations, backgrounds, and distractors. These scans are captured by an iPad with a lidar scanner. Since the Z, SO3 and Pile setups are easy to simulate realistically, we only collect 10 scenes per setup. We collect 50 scenes for each of the Tree, Others and Wild setups. + +We test all the baselines trained on the synthetic dataset and our method trained on ShapeNet directly on these real scenes. Quantitative results are shown in Tab. 1. Since our simulator includes advanced techniques of active light simulation in the physical engine [69] and we do not use the colours as input, the sim2real gap for the baseline methods is minimal in these controlled setups. We can draw similar conclusions for Z, SO3, Pile and Tree setups as with the synthetic experiments. Our method retains reasonable performance on Others scenes due to its awareness of the object shape. When tested on the Wild real-world scenes, our method also performs the best, which demonstrates the strong generalizability of our method. + +RealChairs: We also collect data of chairs in the real world following the Z, SO3 and Pile setups. Although we have plenty of real-world scan datasets like [15], none of them include diverse configuration changes of chairs. Therefore we collected and annotated a small test set with 20 scenes per setup as shown in Fig. 4. We train the baselines in simulation and test them in the real world. Additionally, we take all the baselines' official model weights from being trained on the real world ScanNet dataset [15] to evaluate on our test set. The results are shown in Tab. 3. There is a larger sim2real gap for the baselines with the chairs data than with the mugs data because of less realistic depth simulation and difficulties aligning the scale between Shapenet chairs and real-world chairs. In contrast, the baselines trained on ScanNet work very well on the Z setup, which aligns best with the ScanNet dataset. However, they have a significant drop in performance when the testing distribution shifts to the SO3 and Pile setups. In contrast, our method retains reasonable performance on real world chairs across different setups. We will release our Chairs and Mugs dataset to provide more opportunities to study robustness, generalizability and equivariance for scene and object understanding in the real world. + +We also show our effectiveness on ScanNet [15], where + +the indoor scene scan can span the whole room. Qualitative results are shown in Fig. 5 and the AP metrics for the chairs category of our method on the validation/test set are $AP = 24.6 / 20.2$ , $AP50 = 50.8 / 39.0$ and $AP25 = 61.3 / 48.3$ where in comparison the weakly supervised method CSC [24] trained on 200 points labels achieves $AP50 = 62.9 / 61.1$ (See Suppl. for a table). One main reason for our performance drop on ScanNet is that ScanNet has many partially observed chairs, which are hard to be recognized via shape. We leave future explorations to fill this gap between our unsupervised method and the (weakly) supervised ones. + +# 4.5. Ablations + +We verify the effectiveness of our design by removing the phase-2 joint iterations and removing the usage of the normals. When not + +
AblationAPAP50AP25
Full0.6010.7890.807
No Phase 20.5480.7400.756
No Normal0.2030.3020.337
+ +Table 4. Ablations + +using phase-2 (Sec. 3.3), we let the phase-1 independent iterations run more steps to keep the total number of iterations constant. When removing the normals, all error computing, assignment weight updating, and confidence scoring will only take the distance error term in to account while ignoring the normal term. We compare our full model with the ablated models on SynKit Pile setups. The quantitative results are shown in Tab. 4, which illustrates that both components contribute to our model's overall performance. More ablation studies can be found in our supplementary. + +# 5. Conclusions + +We present EFEM, a method for 3D instance segmentation that is trained only on shape datasets. Without requiring any real or simulated scene data, our method can generalize to complex, real world scenes better than existing methods that also require more supervision. + +Limitations and future work. Although we show an encouraging step towards unsupervised 3D instance segmentation by generalizing knowledge directly from a shape collection to a scene, several weaknesses remain. First, our method has a performance drop when the object is significantly occluded. This is due to our method recognizing objects only via their shape, rather than also reasoning about color or other features. Second our current running speed is slow ( $\sim$ 1min per scene) due to the large number of proposals the initialization requires. + +Acknowledgements. The authors appreciate the support of the following grants: NSF FRR 2220868, NSF IISRI 2212433, NSF TRIPODS 1934960, ARL DCIST CRA W911NF-17-2-0181, ARO MURI W911NF-20-1-0080, ONR N00014-22-1-2677 awarded to UPenn; Toyota University 2.0 program and Vannevar Bush Faculty Fellowship awarded to Stanford University. + +# References + +[1] Jimmy Aronsson. Homogeneous vector bundles and g-equivariant convolutional neural networks. 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PMLR, 2022. 3, 5 \ No newline at end of file diff --git a/2023/EFEM_ Equivariant Neural Field Expectation Maximization for 3D Object Segmentation Without Scene Supervision/images.zip b/2023/EFEM_ Equivariant Neural Field Expectation Maximization for 3D Object Segmentation Without Scene Supervision/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..3fc94cbc06f5dd5b5924776ecdadb17c7a705e03 --- /dev/null +++ b/2023/EFEM_ Equivariant Neural Field Expectation Maximization for 3D Object Segmentation Without Scene Supervision/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:05f73fdca3040dab612efa6531b558555d94cc8bab442c37166b22d1135b06e4 +size 616628 diff --git a/2023/EFEM_ Equivariant Neural Field Expectation Maximization for 3D Object Segmentation Without Scene Supervision/layout.json b/2023/EFEM_ Equivariant Neural Field Expectation Maximization for 3D Object Segmentation Without Scene Supervision/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..87c82340d365caad3a6e6395df796089100efdde --- /dev/null +++ b/2023/EFEM_ Equivariant Neural Field Expectation Maximization for 3D Object Segmentation Without Scene Supervision/layout.json @@ -0,0 +1,10159 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 110, + 103, + 483, + 140 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 110, + 103, + 483, + 140 + ], + "spans": [ + { + "bbox": [ + 110, + 103, + 483, + 140 + ], + "type": "text", + "content": "EFEM: Equivariant Neural Field Expectation Maximization for 3D Object Segmentation Without Scene Supervision" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 64, + 160, + 526, + 190 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 64, + 160, + 526, + 190 + ], + "spans": [ + { + "bbox": [ + 64, + 160, + 526, + 190 + ], + "type": "text", + "content": "Jiahui Lei1 Congyue Deng2 Karl Schmeckpeper1 Leonidas Guibas2 Kostas Daniilidis1 \n1 University of Pennsylvania \n2 Stanford University" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 104, + 191, + 485, + 202 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 104, + 191, + 485, + 202 + ], + "spans": [ + { + "bbox": [ + 104, + 191, + 485, + 202 + ], + "type": "text", + "content": "{leijh, karls, kostas}@cis.upenn.edu, {congyue, guibas}@cs.stanford.edu" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 143, + 231, + 191, + 243 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 231, + 191, + 243 + ], + "spans": [ + { + "bbox": [ + 143, + 231, + 191, + 243 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 257, + 290, + 483 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 257, + 290, + 483 + ], + "spans": [ + { + "bbox": [ + 46, + 257, + 290, + 483 + ], + "type": "text", + "content": "We introduce Equivariant Neural Field Expectation Maximization (EFEM), a simple, effective, and robust geometric algorithm that can segment objects in 3D scenes without annotations or training on scenes. We achieve such unsupervised segmentation by exploiting single object shape priors. We make two novel steps in that direction. First, we introduce equivariant shape representations to this problem to eliminate the complexity induced by the variation in object configuration. Second, we propose a novel EM algorithm that can iteratively refine segmentation masks using the equivariant shape prior. We collect a novel real dataset Chairs and Mugs that contains various object configurations and novel scenes in order to verify the effectiveness and robustness of our method. Experimental results demonstrate that our method achieves consistent and robust performance across different scenes where the (weakly) supervised methods may fail. Code and data available at https://www.cis.upenn.edu/~leijh/projects/efem" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 494, + 128, + 506 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 494, + 128, + 506 + ], + "spans": [ + { + "bbox": [ + 47, + 494, + 128, + 506 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 509, + 287, + 629 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 509, + 287, + 629 + ], + "spans": [ + { + "bbox": [ + 46, + 509, + 287, + 629 + ], + "type": "text", + "content": "Learning how to decompose 3D scenes into object instances is a fundamental problem in visual perception systems. Past developments in 3D computer vision have made huge strides on this problem by training neural networks on 3D scene datasets with segmentation masks [55, 63, 67]. However, these works heavily rely on large labeled datasets [3, 15] that require laborious 3D annotation based on special expertise. Few recent papers alleviate this problem by reducing the need to either sparse point labeling [24, 60] or bounding boxes [12]." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 630, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 630, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 630, + 287, + 714 + ], + "type": "text", + "content": "In this work, we follow an object-centric approach inspired by the Gestalt school of perception that captures an object as a whole shape [32, 47] invariant to its pose and scale [31]. A holistic approach builds up a prior for each object category, that then enables object recognition in different complex scenes with varying configurations. Directly learning object-centric priors instead of analyzing each 3D" + } + ] + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 307, + 230, + 403, + 301 + ], + "blocks": [ + { + "bbox": [ + 307, + 230, + 403, + 301 + ], + "lines": [ + { + "bbox": [ + 307, + 230, + 403, + 301 + ], + "spans": [ + { + "bbox": [ + 307, + 230, + 403, + 301 + ], + "type": "image", + "image_path": "e2ea2c2d876e3ddf0b1411ade2b4dd5a83fbce1f4c13a5c71bea5ca478dc6aa3.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 310, + 546, + 344 + ], + "lines": [ + { + "bbox": [ + 305, + 310, + 546, + 344 + ], + "spans": [ + { + "bbox": [ + 305, + 310, + 546, + 344 + ], + "type": "text", + "content": "Figure 1. We present EFEM, an unsupervised 3D object segmentation method applicable to real-world scenes (results on the right) by only training on ShapeNet single object reconstruction." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 406, + 230, + 545, + 301 + ], + "blocks": [ + { + "bbox": [ + 406, + 230, + 545, + 301 + ], + "lines": [ + { + "bbox": [ + 406, + 230, + 545, + 301 + ], + "spans": [ + { + "bbox": [ + 406, + 230, + 545, + 301 + ], + "type": "image", + "image_path": "ef70092ac0cccd9970d68b76d3c66663e7ddc1f3fd4c3d95fb0f6389692a2dad.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 351, + 546, + 579 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 351, + 546, + 579 + ], + "spans": [ + { + "bbox": [ + 304, + 351, + 546, + 579 + ], + "type": "text", + "content": "scene inspires a more efficient way of learning instance segmentation: both a mug on the table and a mug in the dishwasher are mugs, and one does not have to learn to segment out a mug in all possible environmental contexts if we have a unified shape concept for mugs. Such object-centric recognition facilitates a robust scene analysis for autonomous systems in many interactive real-world environments with a diversity of object configurations: Imagine a scenario where a robot is doing the dishes in the kitchen. Dirty bowls are piled in the sink and the robot is cleaning them and placing them into a cabinet. Objects of the same category appear in the scene repeatedly under different configurations (piles, neat lines in the cabinet). What is even more challenging is that even within this one single task (doing dishes) the scene configuration can drastically change when objects are moved. We show that such scenarios cannot be addressed by the state-of-the-art strongly or weakly supervised methods that struggle under such scene configuration variations." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 582, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 547, + 715 + ], + "type": "text", + "content": "In this paper, we introduce a method that can segment 3D object instances from 3D static scenes by learning priors of single object shapes (ShapeNet [4]) without using any scene-level labels. Two main challenges arise when we remove the scene-level annotation. First, objects in the scene can have a different position, rotation, and scale than the canonical poses where the single object shapes were trained. Second, the shape encoder which is trained on object-level input cannot be directly applied to the scene observations unless the object masks are known. We address the first challenge by introducing equivariance to this problem. By" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "4902" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 49, + 72, + 286, + 346 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 72, + 286, + 346 + ], + "spans": [ + { + "bbox": [ + 49, + 72, + 286, + 346 + ], + "type": "text", + "content": "learning a shape prior that is equivariant to the similitude group SIM(3), the composition of a rotation, a translation, and a uniform scaling in 3D (Sec. 3.1), we address the complexity induced by the SIM(3) composition of objects. For the second challenge, we introduce a simple and effective iterative algorithm, Equivariant neural Field Expectation Maximization (EFEM), that refines the object segmentation mask, by alternately iterating between mask updating and shape reconstruction (Sec. 3.2). The above two steps enable us to directly exploit the learned single instance shape prior to perform segmentation in real-world scenes. We collected and annotated a novel real-world test set (240 scenes) (Sec. 4.4) that contains diverse object configurations and novel scenes to evaluate the generalizability and robustness to novel object instances and object configuration changes. Experiments on both synthetic data (Sec. 4.3) and our novel real dataset (Sec. 4.4) give us an insight to the effectiveness of the method. Compared to weakly supervised methods, when the testing scene setup is similar to the training setup, our method has a small performance gap to the (weakly) supervised baselines. However, when the testing scenes are drawn from novel object configurations, our method consistently outperforms the (weakly) supervised baselines." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 49, + 348, + 286, + 479 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 348, + 286, + 479 + ], + "spans": [ + { + "bbox": [ + 49, + 348, + 286, + 479 + ], + "type": "text", + "content": "Our paper makes the following novel contributions to the 3D scene segmentation problem: (1) a simple and effective iterative EM algorithm that can segment objects from the scenes using only single object shape priors. (2) addressing the diversity of object composition in 3D scenes by combining representations equivariant to rotation, translation, and scaling of the objects. (3) an unsupervised pipeline for 3D instance segmentation that works in real-world data and can generalize to novel setups. (4) a novel real-world test set Chairs and Mugs that contains diverse object configurations and scenes." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 49, + 487, + 132, + 500 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 487, + 132, + 500 + ], + "spans": [ + { + "bbox": [ + 49, + 487, + 132, + 500 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 49, + 503, + 286, + 610 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 503, + 286, + 610 + ], + "spans": [ + { + "bbox": [ + 49, + 503, + 286, + 610 + ], + "type": "text", + "content": "3D Instance segmentation. Point cloud instance segmentation has been a long-existing challenge in 3D vision even before the existence of deep learning. Early interests have been focusing on 3D object retrieval in scenes where RANSAC and generalized Hough voting were the most prominent paradigms [54]. In recent years, with the proliferation of large synthetic [17, 68] or real [3, 15, 22, 25] datasets with rich annotations, learning-based methods have shown great success on this task." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 49, + 617, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 617, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 49, + 617, + 286, + 713 + ], + "type": "text", + "content": "Supervised methods. Most supervised methods fall into two categories: top-down methods that locate objects first and then predict the refined segmentation mask [23, 76], and bottom-up methods learning to group points into object proposals. Regarding the grouping approach, a variety of algorithms have been explored, such as point-pair similarity matrices [64, 80], mean-shift clustering [35], graph-based grouping [20], cluster growing [29], hierarchical ag" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 308, + 72, + 544, + 215 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 72, + 544, + 215 + ], + "spans": [ + { + "bbox": [ + 308, + 72, + 544, + 215 + ], + "type": "text", + "content": "gregation [7, 40], or adversarial methods [78]. Later works [62, 63] combine top-down and bottom-up approaches and achieve impressive results. Recently, transformers and attention mechanisms have also been introduced to this problem [55]. [46] also incorporates neural implicit representations and simultaneously performs segmentation and shape reconstruction. Despite their requirements for laborious data annotation, we will also show that supervised methods heavily rely on the correlation between training and test scenes, and even the state-of-the-art supervised methods struggle to generalize to novel scene configurations or to changes in background patterns." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 308, + 218, + 544, + 504 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 218, + 544, + 504 + ], + "spans": [ + { + "bbox": [ + 308, + 218, + 544, + 504 + ], + "type": "text", + "content": "Unsupervised or weakly supervised methods. Many attempts have been made to learn instance segmentation with limited annotations. A number of works leverage preextracted features from scenes via representation learning such as graph attentions [36] or contrastive learning [13, 24, 70, 77] to facilitate weakly-supervised training with fewer point labels. Other approaches directly propagate sparse annotations to dense point labels by learning point affinity graphs [60] or by bounding box voting [12]. These methods are usually the most scalable to large scenes, but their point features are scene-dependent, and we will show that similarly to fully-supervised learning methods, weakly-supervised methods have difficulties in generalizing to scenes with different configurations. When confronting dynamic scenes, one can exploit temporal self-consistency [58] or scene pair constraints [26, 77] but such constraints introduce additional assumptions about the scenes. Most related to our work are the retrieval-based methods leveraging object priors [39, 72]. Traditional retrieval methods are either limited to one given object template [72] or need to solve a discrete combinatorial optimization problem searching for the target template in the object category [39]. We resolve these issues by learning an implicit shape prior which can be optimized continuously in the feature space." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 308, + 507, + 544, + 687 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 507, + 544, + 687 + ], + "spans": [ + { + "bbox": [ + 308, + 507, + 544, + 687 + ], + "type": "text", + "content": "Implicit object priors. First introduced in [10, 45, 49], neural implicit representations (also known as neural fields [71]) parameterize 3D shapes as level sets of neural networks. They not only show strong capabilities of capturing geometric details within limited capacity [28, 50, 57, 59] but also avoid shape discretization that introduces sampling noises. When representing a collection of objects with a shared implicit network, its bottleneck layer naturally forms a latent embedding of the objects, which can serve as a shape prior for many downstream tasks such as shape generation [10, 27, 44], reconstruction [41], completion [11, 45, 49], computing correspondences [33, 37, 43, 56], and part decomposition [9]. We refer the readers to [71] for a comprehensive review. Our method takes advantage of the recent work in neural fields to learn a deep shape prior." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 308, + 689, + 544, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 689, + 544, + 712 + ], + "spans": [ + { + "bbox": [ + 308, + 689, + 544, + 712 + ], + "type": "text", + "content": "Equivariant point cloud networks. Equivariant networks are designed to preserve transformation coherence" + } + ] + } + ], + "index": 8 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 296, + 750, + 314, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 750, + 314, + 757 + ], + "spans": [ + { + "bbox": [ + 296, + 750, + 314, + 757 + ], + "type": "text", + "content": "4903" + } + ] + } + ], + "index": 9 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 228 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 228 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 228 + ], + "type": "text", + "content": "between the input and latent representations. With well-developed theories [1, 14, 34, 65, 74], equivariant networks have a variety of designs on point clouds [2, 16, 19, 30, 51, 61], which benefits many downstream tasks such as robotic applications [18, 21, 52, 56, 66, 75], 3D reconstruction [5, 6], and object pose estimation/canonicalization [38, 42, 48, 53, 81]. Unlike these object-level works, we focus on leveraging equivariance object features in scene understandings. Most related to us is [79] which also applies object equivariance to scenes. But they perform supervised 3D object bounding box detection while we predict dense instance masks. In this work, we employ the vector neurons [2, 6, 16] to build our equivariant shape prior." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 234, + 104, + 246 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 234, + 104, + 246 + ], + "spans": [ + { + "bbox": [ + 47, + 234, + 104, + 246 + ], + "type": "text", + "content": "3. Method" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 249, + 289, + 429 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 249, + 289, + 429 + ], + "spans": [ + { + "bbox": [ + 46, + 249, + 289, + 429 + ], + "type": "text", + "content": "Now we introduce our method for unsupervised object segmentation in 3D scenes. At the training stage, we learn an object-level shape prior (Sec. 3.1, Fig. 2 top left) utilizing a collection of synthetic models from an object category (e.g. all chairs in ShapeNet [4]). At inference time, we are given a scene point cloud " + }, + { + "bbox": [ + 46, + 249, + 289, + 429 + ], + "type": "inline_equation", + "content": "X_{N \\times 6}" + }, + { + "bbox": [ + 46, + 249, + 289, + 429 + ], + "type": "text", + "content": " of " + }, + { + "bbox": [ + 46, + 249, + 289, + 429 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 249, + 289, + 429 + ], + "type": "text", + "content": " points with coordinates as well as normal vectors with an unknown number of novel instances from the object category, and our task is to predict their instance segmentation masks. We will introduce a simple and novel iterative algorithm for predicting instance segmentation masks, starting from a single-object proposal phase (Sec. 3.2, Fig. 2 top right) and followed by a multiple-object joint proposal phase (Sec. 3.3, Fig. 2 bottom). As by-products, our model also outputs implicit surface reconstructions, poses, and bounding boxes." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 432, + 227, + 444 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 432, + 227, + 444 + ], + "spans": [ + { + "bbox": [ + 47, + 432, + 227, + 444 + ], + "type": "text", + "content": "3.1. SIM(3) Equivariant Shape Priors" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 445, + 287, + 529 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 445, + 287, + 529 + ], + "spans": [ + { + "bbox": [ + 46, + 445, + 287, + 529 + ], + "type": "text", + "content": "Most synthetic datasets have their objects manually aligned to canonical poses and unit scales, yet the SIM(3) transformations (translations, rotations, and scales) must be considered when applying the shape priors to real-world scenes. To this end, we constructed a SIM(3)-equivariant SDF encoder-decoder following the paradigms of prior work [16, 45] (Fig. 2 left top)." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 533, + 289, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 533, + 289, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 533, + 289, + 714 + ], + "type": "text", + "content": "Point cloud encoder. Given an object point cloud " + }, + { + "bbox": [ + 46, + 533, + 289, + 714 + ], + "type": "inline_equation", + "content": "P_{N_O \\times 3}" + }, + { + "bbox": [ + 46, + 533, + 289, + 714 + ], + "type": "text", + "content": " with " + }, + { + "bbox": [ + 46, + 533, + 289, + 714 + ], + "type": "inline_equation", + "content": "N_O" + }, + { + "bbox": [ + 46, + 533, + 289, + 714 + ], + "type": "text", + "content": " points, it is first encoded by a SIM(3)-equivariant encoder " + }, + { + "bbox": [ + 46, + 533, + 289, + 714 + ], + "type": "inline_equation", + "content": "\\Phi" + }, + { + "bbox": [ + 46, + 533, + 289, + 714 + ], + "type": "text", + "content": " (yellow block Fig. 2 left) constructed with Vector Neurons (VN) [2, 8, 16] into a latent embedding " + }, + { + "bbox": [ + 46, + 533, + 289, + 714 + ], + "type": "inline_equation", + "content": "\\Theta = \\Phi(P)" + }, + { + "bbox": [ + 46, + 533, + 289, + 714 + ], + "type": "text", + "content": " (orange block Fig. 2 middle). More concretely, the input point cloud " + }, + { + "bbox": [ + 46, + 533, + 289, + 714 + ], + "type": "inline_equation", + "content": "P" + }, + { + "bbox": [ + 46, + 533, + 289, + 714 + ], + "type": "text", + "content": " is first subtracted by its centroid " + }, + { + "bbox": [ + 46, + 533, + 289, + 714 + ], + "type": "inline_equation", + "content": "\\bar{P}" + }, + { + "bbox": [ + 46, + 533, + 289, + 714 + ], + "type": "text", + "content": " for translation equivariance, followed by a backbone network providing a global vector-channeled embedding " + }, + { + "bbox": [ + 46, + 533, + 289, + 714 + ], + "type": "inline_equation", + "content": "F" + }, + { + "bbox": [ + 46, + 533, + 289, + 714 + ], + "type": "text", + "content": ", which is scale- and rotation-equivariant and translation invariant. " + }, + { + "bbox": [ + 46, + 533, + 289, + 714 + ], + "type": "inline_equation", + "content": "F" + }, + { + "bbox": [ + 46, + 533, + 289, + 714 + ], + "type": "text", + "content": " is then mapped to the shape implicit code " + }, + { + "bbox": [ + 46, + 533, + 289, + 714 + ], + "type": "inline_equation", + "content": "\\Theta" + }, + { + "bbox": [ + 46, + 533, + 289, + 714 + ], + "type": "text", + "content": " comprising four components " + }, + { + "bbox": [ + 46, + 533, + 289, + 714 + ], + "type": "inline_equation", + "content": "(\\Theta_{\\mathrm{R}}, \\Theta_{\\mathrm{inv}}, \\Theta_{\\mathrm{c}}, \\Theta_{\\mathrm{s}})" + }, + { + "bbox": [ + 46, + 533, + 289, + 714 + ], + "type": "text", + "content": ". The backbone network is a rotation-equivariant VN Point-Transformer [2] with additional scale equivariance enforced by channel-wise normalizations as in [8]. We denote the modified linear layer with scale invariance [8] as " + }, + { + "bbox": [ + 46, + 533, + 289, + 714 + ], + "type": "inline_equation", + "content": "\\widehat{\\mathrm{VN}}" + }, + { + "bbox": [ + 46, + 533, + 289, + 714 + ], + "type": "text", + "content": ". The four components of " + }, + { + "bbox": [ + 46, + 533, + 289, + 714 + ], + "type": "inline_equation", + "content": "\\Theta" + }, + { + "bbox": [ + 46, + 533, + 289, + 714 + ], + "type": "text", + "content": " are" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 305, + 72, + 492, + 84 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 492, + 84 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 492, + 84 + ], + "type": "text", + "content": "computed from " + }, + { + "bbox": [ + 305, + 72, + 492, + 84 + ], + "type": "inline_equation", + "content": "F" + }, + { + "bbox": [ + 305, + 72, + 492, + 84 + ], + "type": "text", + "content": " with four heads separately:" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 313, + 84, + 545, + 217 + ], + "type": "list", + "angle": 0, + "index": 11, + "blocks": [ + { + "bbox": [ + 313, + 84, + 545, + 109 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 313, + 84, + 545, + 109 + ], + "spans": [ + { + "bbox": [ + 313, + 84, + 545, + 109 + ], + "type": "text", + "content": "1. 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A scalar-channeled invariant latent code " + }, + { + "bbox": [ + 313, + 109, + 545, + 133 + ], + "type": "inline_equation", + "content": "\\Theta_{\\mathrm{inv}} = \\langle \\widehat{\\nabla}\\mathbf{N}_I(F),\\Theta_{\\mathrm{R}}\\rangle" + }, + { + "bbox": [ + 313, + 109, + 545, + 133 + ], + "type": "text", + "content": " computed with inner product." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 313, + 133, + 545, + 157 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 313, + 133, + 545, + 157 + ], + "spans": [ + { + "bbox": [ + 313, + 133, + 545, + 157 + ], + "type": "text", + "content": "3. 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A centroid correction vector predicting the offset between the centroid of points and the actual object center, which could be different due to the partiality and noises of the point could: " + }, + { + "bbox": [ + 313, + 157, + 545, + 217 + ], + "type": "inline_equation", + "content": "\\Theta_{\\mathrm{c}} = \\mathrm{VN}_{C}(F) + \\bar{P}" + }, + { + "bbox": [ + 313, + 157, + 545, + 217 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 313, + 157, + 545, + 217 + ], + "type": "inline_equation", + "content": "\\mathrm{VN}_C" + }, + { + "bbox": [ + 313, + 157, + 545, + 217 + ], + "type": "text", + "content": " has 1 output vector channel." + } + ] + } + ], + "index": 10 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 304, + 217, + 545, + 265 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 217, + 545, + 265 + ], + "spans": [ + { + "bbox": [ + 304, + 217, + 545, + 265 + ], + "type": "text", + "content": "Network architecture details can be found in the supplementary. For any transformation " + }, + { + "bbox": [ + 304, + 217, + 545, + 265 + ], + "type": "inline_equation", + "content": "g = (s, R, t) \\in \\mathrm{SIM}(3)" + }, + { + "bbox": [ + 304, + 217, + 545, + 265 + ], + "type": "text", + "content": " with scale " + }, + { + "bbox": [ + 304, + 217, + 545, + 265 + ], + "type": "inline_equation", + "content": "s" + }, + { + "bbox": [ + 304, + 217, + 545, + 265 + ], + "type": "text", + "content": ", rotation " + }, + { + "bbox": [ + 304, + 217, + 545, + 265 + ], + "type": "inline_equation", + "content": "R" + }, + { + "bbox": [ + 304, + 217, + 545, + 265 + ], + "type": "text", + "content": ", and translation " + }, + { + "bbox": [ + 304, + 217, + 545, + 265 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 217, + 545, + 265 + ], + "type": "text", + "content": ", its action on " + }, + { + "bbox": [ + 304, + 217, + 545, + 265 + ], + "type": "inline_equation", + "content": "\\Theta" + }, + { + "bbox": [ + 304, + 217, + 545, + 265 + ], + "type": "text", + "content": " and the equivariance of the encoder " + }, + { + "bbox": [ + 304, + 217, + 545, + 265 + ], + "type": "inline_equation", + "content": "\\Phi" + }, + { + "bbox": [ + 304, + 217, + 545, + 265 + ], + "type": "text", + "content": " can be written as:" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 309, + 274, + 545, + 288 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 309, + 274, + 545, + 288 + ], + "spans": [ + { + "bbox": [ + 309, + 274, + 545, + 288 + ], + "type": "interline_equation", + "content": "g \\circ \\Theta = \\left(\\Theta_ {\\mathrm {R}} R, \\Theta_ {\\text {i n v}}, s \\Theta_ {\\mathrm {c}} R + t, s \\Theta_ {\\mathrm {s}}\\right) = \\Phi (s P R + t). \\tag {1}", + "image_path": "935bf8d7884117102876e2bf735bf54e2e11d675c52be1e4fefc9657e9321921.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 292, + 545, + 316 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 292, + 545, + 316 + ], + "spans": [ + { + "bbox": [ + 304, + 292, + 545, + 316 + ], + "type": "text", + "content": "SDF decoder. Give a query position " + }, + { + "bbox": [ + 304, + 292, + 545, + 316 + ], + "type": "inline_equation", + "content": "x \\in \\mathbb{R}^3" + }, + { + "bbox": [ + 304, + 292, + 545, + 316 + ], + "type": "text", + "content": ", its SDF value " + }, + { + "bbox": [ + 304, + 292, + 545, + 316 + ], + "type": "inline_equation", + "content": "\\hat{v}(x)" + }, + { + "bbox": [ + 304, + 292, + 545, + 316 + ], + "type": "text", + "content": " is predicted as" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 349, + 326, + 545, + 339 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 349, + 326, + 545, + 339 + ], + "spans": [ + { + "bbox": [ + 349, + 326, + 545, + 339 + ], + "type": "interline_equation", + "content": "\\hat {v} (x) = \\Psi (x; \\Theta) = \\Psi \\left(\\Theta_ {\\text {i n v}}, \\langle \\Theta_ {\\mathrm {R}}, \\tilde {x} \\rangle\\right), \\tag {2}", + "image_path": "58ad2692d002c265f19f15609c9526b1ae6adb14cd915482cea934338173357f.jpg" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 343, + 545, + 392 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 343, + 545, + 392 + ], + "spans": [ + { + "bbox": [ + 304, + 343, + 545, + 392 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 343, + 545, + 392 + ], + "type": "inline_equation", + "content": "\\tilde{x} = (x - \\Theta_{\\mathrm{c}}) / \\Theta_{\\mathrm{s}}" + }, + { + "bbox": [ + 304, + 343, + 545, + 392 + ], + "type": "text", + "content": " is the canonicalized coordinate of " + }, + { + "bbox": [ + 304, + 343, + 545, + 392 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 304, + 343, + 545, + 392 + ], + "type": "text", + "content": " with center " + }, + { + "bbox": [ + 304, + 343, + 545, + 392 + ], + "type": "inline_equation", + "content": "\\Theta_{\\mathrm{c}}" + }, + { + "bbox": [ + 304, + 343, + 545, + 392 + ], + "type": "text", + "content": " and scale " + }, + { + "bbox": [ + 304, + 343, + 545, + 392 + ], + "type": "inline_equation", + "content": "\\Theta_{\\mathrm{s}}" + }, + { + "bbox": [ + 304, + 343, + 545, + 392 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 304, + 343, + 545, + 392 + ], + "type": "inline_equation", + "content": "\\Psi" + }, + { + "bbox": [ + 304, + 343, + 545, + 392 + ], + "type": "text", + "content": " is an MLP as in [16] that decodes the concatenation of the invariant feature " + }, + { + "bbox": [ + 304, + 343, + 545, + 392 + ], + "type": "inline_equation", + "content": "\\Theta_{\\mathrm{inv}}" + }, + { + "bbox": [ + 304, + 343, + 545, + 392 + ], + "type": "text", + "content": " and the channel-wise inner product between " + }, + { + "bbox": [ + 304, + 343, + 545, + 392 + ], + "type": "inline_equation", + "content": "\\Theta_{\\mathrm{R}}" + }, + { + "bbox": [ + 304, + 343, + 545, + 392 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 343, + 545, + 392 + ], + "type": "inline_equation", + "content": "\\tilde{x}" + }, + { + "bbox": [ + 304, + 343, + 545, + 392 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 394, + 546, + 550 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 394, + 546, + 550 + ], + "spans": [ + { + "bbox": [ + 304, + 394, + 546, + 550 + ], + "type": "text", + "content": "Training. The implicit shape prior is trained with the standard L2 loss for the query points sampled around each object. To avoid arbitrary prediction of " + }, + { + "bbox": [ + 304, + 394, + 546, + 550 + ], + "type": "inline_equation", + "content": "\\Theta_{\\mathrm{c}}" + }, + { + "bbox": [ + 304, + 394, + 546, + 550 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 394, + 546, + 550 + ], + "type": "inline_equation", + "content": "\\Theta_{\\mathrm{s}}" + }, + { + "bbox": [ + 304, + 394, + 546, + 550 + ], + "type": "text", + "content": " that may make training unstable in early epochs, we regularize " + }, + { + "bbox": [ + 304, + 394, + 546, + 550 + ], + "type": "inline_equation", + "content": "\\Theta_{\\mathrm{c}}" + }, + { + "bbox": [ + 304, + 394, + 546, + 550 + ], + "type": "text", + "content": " to stay around zero and " + }, + { + "bbox": [ + 304, + 394, + 546, + 550 + ], + "type": "inline_equation", + "content": "\\Theta_{\\mathrm{s}}" + }, + { + "bbox": [ + 304, + 394, + 546, + 550 + ], + "type": "text", + "content": " to stay around one. To help the network's generalization to real-world scenarios with partial observations, clutters, and sensor noises, we further augment the input object point clouds with partial depths and content-wise augmentations. Additional details of these augmentations are provided in the supplementary. We will next introduce how to exploit this learned shape-prior network which only takes instance-level inputs in scene-level point cloud segmentation." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 306, + 557, + 511, + 570 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 557, + 511, + 570 + ], + "spans": [ + { + "bbox": [ + 306, + 557, + 511, + 570 + ], + "type": "text", + "content": "3.2. Iterative Algorithm for Single Proposal" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 306, + 577, + 473, + 590 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 577, + 473, + 590 + ], + "spans": [ + { + "bbox": [ + 306, + 577, + 473, + 590 + ], + "type": "text", + "content": "Algorithm 1 Single Proposal Estimation" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 306, + 591, + 545, + 615 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 591, + 545, + 615 + ], + "spans": [ + { + "bbox": [ + 306, + 591, + 545, + 615 + ], + "type": "text", + "content": "Data: Scene Point Cloud " + }, + { + "bbox": [ + 306, + 591, + 545, + 615 + ], + "type": "inline_equation", + "content": "X_{N\\times 6}" + }, + { + "bbox": [ + 306, + 591, + 545, + 615 + ], + "type": "text", + "content": "; trained encoder " + }, + { + "bbox": [ + 306, + 591, + 545, + 615 + ], + "type": "inline_equation", + "content": "\\Phi" + }, + { + "bbox": [ + 306, + 591, + 545, + 615 + ], + "type": "text", + "content": " and decoder " + }, + { + "bbox": [ + 306, + 591, + 545, + 615 + ], + "type": "inline_equation", + "content": "\\Psi" + }, + { + "bbox": [ + 306, + 591, + 545, + 615 + ], + "type": "text", + "content": " with frozen weight" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 306, + 616, + 361, + 626 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 616, + 361, + 626 + ], + "spans": [ + { + "bbox": [ + 306, + 616, + 361, + 626 + ], + "type": "text", + "content": "Initialize " + }, + { + "bbox": [ + 306, + 616, + 361, + 626 + ], + "type": "inline_equation", + "content": "W_0" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 306, + 628, + 422, + 639 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 628, + 422, + 639 + ], + "spans": [ + { + "bbox": [ + 306, + 628, + 422, + 639 + ], + "type": "text", + "content": "while not reach max step do" + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 321, + 639, + 545, + 661 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 321, + 639, + 545, + 661 + ], + "spans": [ + { + "bbox": [ + 321, + 639, + 545, + 661 + ], + "type": "text", + "content": "M-step: Sample " + }, + { + "bbox": [ + 321, + 639, + 545, + 661 + ], + "type": "inline_equation", + "content": "P_{t}" + }, + { + "bbox": [ + 321, + 639, + 545, + 661 + ], + "type": "text", + "content": " by Eq. 3 from " + }, + { + "bbox": [ + 321, + 639, + 545, + 661 + ], + "type": "inline_equation", + "content": "W_{t - 1}" + }, + { + "bbox": [ + 321, + 639, + 545, + 661 + ], + "type": "text", + "content": " and forward encoder " + }, + { + "bbox": [ + 321, + 639, + 545, + 661 + ], + "type": "inline_equation", + "content": "\\Phi" + }, + { + "bbox": [ + 321, + 639, + 545, + 661 + ], + "type": "text", + "content": " to update " + }, + { + "bbox": [ + 321, + 639, + 545, + 661 + ], + "type": "inline_equation", + "content": "\\Theta_t" + }, + { + "bbox": [ + 321, + 639, + 545, + 661 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 321, + 662, + 535, + 673 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 321, + 662, + 535, + 673 + ], + "spans": [ + { + "bbox": [ + 321, + 662, + 535, + 673 + ], + "type": "text", + "content": "E-step: Evaluate decoder " + }, + { + "bbox": [ + 321, + 662, + 535, + 673 + ], + "type": "inline_equation", + "content": "\\Psi" + }, + { + "bbox": [ + 321, + 662, + 535, + 673 + ], + "type": "text", + "content": " and update " + }, + { + "bbox": [ + 321, + 662, + 535, + 673 + ], + "type": "inline_equation", + "content": "W_{t}" + }, + { + "bbox": [ + 321, + 662, + 535, + 673 + ], + "type": "text", + "content": " by Eq. 7." + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 306, + 674, + 324, + 683 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 674, + 324, + 683 + ], + "spans": [ + { + "bbox": [ + 306, + 674, + 324, + 683 + ], + "type": "text", + "content": "end" + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 306, + 685, + 534, + 696 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 685, + 534, + 696 + ], + "spans": [ + { + "bbox": [ + 306, + 685, + 534, + 696 + ], + "type": "text", + "content": "Extract mesh and compute absolute pose as a byproduct." + } + ] + } + ], + "index": 26 + }, + { + "bbox": [ + 306, + 696, + 511, + 708 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 696, + 511, + 708 + ], + "spans": [ + { + "bbox": [ + 306, + 696, + 511, + 708 + ], + "type": "text", + "content": "Compute confidence " + }, + { + "bbox": [ + 306, + 696, + 511, + 708 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 306, + 696, + 511, + 708 + ], + "type": "text", + "content": " in Eq. 10 and output mask." + } + ] + } + ], + "index": 27 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "text", + "content": "4904" + } + ] + } + ], + "index": 28 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 48, + 71, + 170, + 149 + ], + "blocks": [ + { + "bbox": [ + 48, + 71, + 170, + 149 + ], + "lines": [ + { + "bbox": [ + 48, + 71, + 170, + 149 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 170, + 149 + ], + "type": "image", + "image_path": "58ef2952e7877ba2c842704d870dfb534b921e5af30bc291c28c682f3626dc85.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 171, + 72, + 545, + 149 + ], + "blocks": [ + { + "bbox": [ + 171, + 72, + 545, + 149 + ], + "lines": [ + { + "bbox": [ + 171, + 72, + 545, + 149 + ], + "spans": [ + { + "bbox": [ + 171, + 72, + 545, + 149 + ], + "type": "image", + "image_path": "02e0c628537808f4e98041ad17105a959177167fc550d485afc74677cc70f53a.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 50, + 155, + 545, + 297 + ], + "blocks": [ + { + "bbox": [ + 50, + 155, + 545, + 297 + ], + "lines": [ + { + "bbox": [ + 50, + 155, + 545, + 297 + ], + "spans": [ + { + "bbox": [ + 50, + 155, + 545, + 297 + ], + "type": "image", + "image_path": "6397ff26fd4d09cbc00c5e8050eb194e781317bf200380f68a8c67c1c773ebf8.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 299, + 546, + 388 + ], + "lines": [ + { + "bbox": [ + 46, + 299, + 546, + 388 + ], + "spans": [ + { + "bbox": [ + 46, + 299, + 546, + 388 + ], + "type": "text", + "content": "Figure 2. Overview: Left top: the single object SDF Encoder-Decoder (Sec. 3.1) is trained on the shape collection. Once trained, the network's weights are frozen.Top right Single EM step on scene observations (Sec. 3.2): given the last estimation of the object mask " + }, + { + "bbox": [ + 46, + 299, + 546, + 388 + ], + "type": "inline_equation", + "content": "W_{t - 1}" + }, + { + "bbox": [ + 46, + 299, + 546, + 388 + ], + "type": "text", + "content": ", a set of points is sampled from the full scene point cloud and then passed to the shape encoder " + }, + { + "bbox": [ + 46, + 299, + 546, + 388 + ], + "type": "inline_equation", + "content": "\\Phi" + }, + { + "bbox": [ + 46, + 299, + 546, + 388 + ], + "type": "text", + "content": " to produce the current estimation of the shape embedding " + }, + { + "bbox": [ + 46, + 299, + 546, + 388 + ], + "type": "inline_equation", + "content": "\\Theta" + }, + { + "bbox": [ + 46, + 299, + 546, + 388 + ], + "type": "text", + "content": ". Based on the " + }, + { + "bbox": [ + 46, + 299, + 546, + 388 + ], + "type": "inline_equation", + "content": "\\Theta" + }, + { + "bbox": [ + 46, + 299, + 546, + 388 + ], + "type": "text", + "content": ", all the scene points are queried again through the decoder " + }, + { + "bbox": [ + 46, + 299, + 546, + 388 + ], + "type": "inline_equation", + "content": "\\Psi" + }, + { + "bbox": [ + 46, + 299, + 546, + 388 + ], + "type": "text", + "content": " to generate a new assignment mask " + }, + { + "bbox": [ + 46, + 299, + 546, + 388 + ], + "type": "inline_equation", + "content": "W_{t}" + }, + { + "bbox": [ + 46, + 299, + 546, + 388 + ], + "type": "text", + "content": ". Bottom Object segmentation pipeline: starting from random crop initializations from the left, the above EM step is applied to each proposal (each row) in parallel to refine their masks. In the early steps (Phase-1 Sec. 3.2), all the proposals run independently but in the second phase, multiple proposals can be jointly optimized (Sec. 3.3). Note that we eliminate the duplicated (the second) or unreasonably sized (the fourth) proposals during optimization. Finally, the remaining proposals and their confidences are output." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 399, + 288, + 533 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 399, + 288, + 533 + ], + "spans": [ + { + "bbox": [ + 46, + 399, + 288, + 533 + ], + "type": "text", + "content": "As shown in Fig 2, the key component of our full algorithm is the single proposal processing (right top) since the full algorithm is constructed by many single proposals being processed in parallel. Each proposal is represented by a soft assignment mask " + }, + { + "bbox": [ + 46, + 399, + 288, + 533 + ], + "type": "inline_equation", + "content": "W" + }, + { + "bbox": [ + 46, + 399, + 288, + 533 + ], + "type": "text", + "content": " over all scene points, where the continuous value on each point " + }, + { + "bbox": [ + 46, + 399, + 288, + 533 + ], + "type": "inline_equation", + "content": "W[i] \\in [0,1]" + }, + { + "bbox": [ + 46, + 399, + 288, + 533 + ], + "type": "text", + "content": " indicates how likely this point belongs to the object that the proposal is representing. In the early single proposal iteration steps (Phase-1), each proposal aims to fit its " + }, + { + "bbox": [ + 46, + 399, + 288, + 533 + ], + "type": "inline_equation", + "content": "W" + }, + { + "bbox": [ + 46, + 399, + 288, + 533 + ], + "type": "text", + "content": " to one object independently. In later iterations, we optimize the proposals jointly, as discussed in Section 3.3." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 538, + 287, + 612 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 538, + 287, + 612 + ], + "spans": [ + { + "bbox": [ + 46, + 538, + 287, + 612 + ], + "type": "text", + "content": "Initialization. The single proposal algorithm starts from the initial assignment " + }, + { + "bbox": [ + 46, + 538, + 287, + 612 + ], + "type": "inline_equation", + "content": "W_{0}" + }, + { + "bbox": [ + 46, + 538, + 287, + 612 + ], + "type": "text", + "content": " which is drawn from a random ball or cylinder cropping of the scene. The radius of the crop is set to be similar to the average size of the target class. All points inside the crop are set to have " + }, + { + "bbox": [ + 46, + 538, + 287, + 612 + ], + "type": "inline_equation", + "content": "W[i] = 1.0" + }, + { + "bbox": [ + 46, + 538, + 287, + 612 + ], + "type": "text", + "content": " while all other points are set to have " + }, + { + "bbox": [ + 46, + 538, + 287, + 612 + ], + "type": "inline_equation", + "content": "W[i] = 0.0" + }, + { + "bbox": [ + 46, + 538, + 287, + 612 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 617, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 617, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 617, + 288, + 713 + ], + "type": "text", + "content": "M-Step: Estimating shape embeddings. We treat the learned decoder with fixed weight as a parametric model of shape categories driven by the parameter " + }, + { + "bbox": [ + 46, + 617, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\Theta" + }, + { + "bbox": [ + 46, + 617, + 288, + 713 + ], + "type": "text", + "content": ". In each iteration of our algorithm, a new " + }, + { + "bbox": [ + 46, + 617, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\Theta_{t}" + }, + { + "bbox": [ + 46, + 617, + 288, + 713 + ], + "type": "text", + "content": " is estimated from the last assignment " + }, + { + "bbox": [ + 46, + 617, + 288, + 713 + ], + "type": "inline_equation", + "content": "W_{t - 1}" + }, + { + "bbox": [ + 46, + 617, + 288, + 713 + ], + "type": "text", + "content": ". Note that the learned shape prior encoder " + }, + { + "bbox": [ + 46, + 617, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\Phi" + }, + { + "bbox": [ + 46, + 617, + 288, + 713 + ], + "type": "text", + "content": " only accepts a fixed number " + }, + { + "bbox": [ + 46, + 617, + 288, + 713 + ], + "type": "inline_equation", + "content": "N_O" + }, + { + "bbox": [ + 46, + 617, + 288, + 713 + ], + "type": "text", + "content": " of points as input, which is always far less than the number of points in the scene observation. Therefore at each iteration, we first sam" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 305, + 399, + 546, + 424 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 399, + 546, + 424 + ], + "spans": [ + { + "bbox": [ + 305, + 399, + 546, + 424 + ], + "type": "text", + "content": "ple a fixed number " + }, + { + "bbox": [ + 305, + 399, + 546, + 424 + ], + "type": "inline_equation", + "content": "N_{O}" + }, + { + "bbox": [ + 305, + 399, + 546, + 424 + ], + "type": "text", + "content": " of points from the scene point cloud " + }, + { + "bbox": [ + 305, + 399, + 546, + 424 + ], + "type": "inline_equation", + "content": "X_{N\\times 6}" + }, + { + "bbox": [ + 305, + 399, + 546, + 424 + ], + "type": "text", + "content": " based on the last assignment estimation " + }, + { + "bbox": [ + 305, + 399, + 546, + 424 + ], + "type": "inline_equation", + "content": "W_{t - 1}" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 375, + 434, + 545, + 447 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 375, + 434, + 545, + 447 + ], + "spans": [ + { + "bbox": [ + 375, + 434, + 545, + 447 + ], + "type": "interline_equation", + "content": "P _ {t} = \\mathcal {M} \\left(W _ {t - 1}, X _ {N \\times 6}\\right), \\tag {3}", + "image_path": "0ed259a7a8796c4c0ae2afe8501ef1c7489ff69302c99f6b457431785010eda1.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 453, + 546, + 596 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 453, + 546, + 596 + ], + "spans": [ + { + "bbox": [ + 304, + 453, + 546, + 596 + ], + "type": "text", + "content": "where the sampling operations " + }, + { + "bbox": [ + 304, + 453, + 546, + 596 + ], + "type": "inline_equation", + "content": "\\mathcal{M}" + }, + { + "bbox": [ + 304, + 453, + 546, + 596 + ], + "type": "text", + "content": " contain two steps. First, a sample is drawn from a Bernoulli distribution with positive probability " + }, + { + "bbox": [ + 304, + 453, + 546, + 596 + ], + "type": "inline_equation", + "content": "W_{t - 1}[i]" + }, + { + "bbox": [ + 304, + 453, + 546, + 596 + ], + "type": "text", + "content": " to determine if the point " + }, + { + "bbox": [ + 304, + 453, + 546, + 596 + ], + "type": "inline_equation", + "content": "X[i]" + }, + { + "bbox": [ + 304, + 453, + 546, + 596 + ], + "type": "text", + "content": " belongs to the object's foreground. Second, for all points that are marked as foreground, we globally apply multinomial sampling based on their " + }, + { + "bbox": [ + 304, + 453, + 546, + 596 + ], + "type": "inline_equation", + "content": "W[i]" + }, + { + "bbox": [ + 304, + 453, + 546, + 596 + ], + "type": "text", + "content": " to find " + }, + { + "bbox": [ + 304, + 453, + 546, + 596 + ], + "type": "inline_equation", + "content": "N_O" + }, + { + "bbox": [ + 304, + 453, + 546, + 596 + ], + "type": "text", + "content": " sampled points. Finally, we produce the new shape estimation by passing the sampled point cloud through " + }, + { + "bbox": [ + 304, + 453, + 546, + 596 + ], + "type": "inline_equation", + "content": "\\Phi" + }, + { + "bbox": [ + 304, + 453, + 546, + 596 + ], + "type": "text", + "content": " so " + }, + { + "bbox": [ + 304, + 453, + 546, + 596 + ], + "type": "inline_equation", + "content": "\\Theta_t = \\Phi (P_t)" + }, + { + "bbox": [ + 304, + 453, + 546, + 596 + ], + "type": "text", + "content": ". This method of updating the shape parameter can be interpreted as the M-step of an EM algorithm, which computes better distribution parameters based on the last assignment via weighted maximum likelihood." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 601, + 547, + 638 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 601, + 547, + 638 + ], + "spans": [ + { + "bbox": [ + 304, + 601, + 547, + 638 + ], + "type": "text", + "content": "Fitting error. Given the " + }, + { + "bbox": [ + 304, + 601, + 547, + 638 + ], + "type": "inline_equation", + "content": "\\Theta" + }, + { + "bbox": [ + 304, + 601, + 547, + 638 + ], + "type": "text", + "content": " estimation, the fitting error of one observed point " + }, + { + "bbox": [ + 304, + 601, + 547, + 638 + ], + "type": "inline_equation", + "content": "\\mathbf{x} = [x_{\\mathrm{obs}}, n_{\\mathrm{obs}}]" + }, + { + "bbox": [ + 304, + 601, + 547, + 638 + ], + "type": "text", + "content": " (" + }, + { + "bbox": [ + 304, + 601, + 547, + 638 + ], + "type": "inline_equation", + "content": "x_{\\mathrm{obs}}" + }, + { + "bbox": [ + 304, + 601, + 547, + 638 + ], + "type": "text", + "content": " denotes position and " + }, + { + "bbox": [ + 304, + 601, + 547, + 638 + ], + "type": "inline_equation", + "content": "n_{\\mathrm{obs}}" + }, + { + "bbox": [ + 304, + 601, + 547, + 638 + ], + "type": "text", + "content": " denotes normal) in the scene point cloud " + }, + { + "bbox": [ + 304, + 601, + 547, + 638 + ], + "type": "inline_equation", + "content": "X_{N \\times 6}" + }, + { + "bbox": [ + 304, + 601, + 547, + 638 + ], + "type": "text", + "content": " is:" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 373, + 650, + 545, + 663 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 373, + 650, + 545, + 663 + ], + "spans": [ + { + "bbox": [ + 373, + 650, + 545, + 663 + ], + "type": "interline_equation", + "content": "e _ {D} (\\mathbf {x}, \\Theta) = | \\Psi (x _ {\\mathrm {o b s}}; \\Theta) | \\tag {4}", + "image_path": "320605a8cb54fd0b10a87c2d946b2a7bbabf745d1995a329d88875973a072309.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 343, + 665, + 545, + 693 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 343, + 665, + 545, + 693 + ], + "spans": [ + { + "bbox": [ + 343, + 665, + 545, + 693 + ], + "type": "interline_equation", + "content": "e _ {N} (\\mathbf {x}, \\Theta) = \\operatorname {a c o s} \\left(\\frac {n _ {\\mathrm {o b s}} ^ {T} \\nabla_ {x} \\Psi \\left(x _ {\\mathrm {o b s}} ; \\Theta\\right)}{\\| \\nabla_ {x} \\Psi \\left(x _ {\\mathrm {o b s}} ; \\Theta\\right) \\|}\\right) \\tag {5}", + "image_path": "9fe6e0b48f01b79227478dcb9ff6ecc7b8cb142d90b4442d2468f953e4eccf4b.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 343, + 700, + 545, + 714 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 343, + 700, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 343, + 700, + 545, + 714 + ], + "type": "interline_equation", + "content": "E (\\mathbf {x}, \\Theta) = \\alpha_ {D} e _ {D} (\\mathbf {x}, \\Theta) + \\alpha_ {N} e _ {N} (\\mathbf {x}, \\Theta) \\tag {6}", + "image_path": "d8553cb6f8ccafde915ae708df1b8803cc9770716d13f2de84293846eb1223a5.jpg" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "4905" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 133 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 133 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 133 + ], + "type": "text", + "content": "which measures the observed point distance to the zero level set of the SDF and the normal consistency between the observed point and the decoded SDF gradient. The hyperparameters " + }, + { + "bbox": [ + 46, + 72, + 287, + 133 + ], + "type": "inline_equation", + "content": "\\alpha_{D}" + }, + { + "bbox": [ + 46, + 72, + 287, + 133 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 72, + 287, + 133 + ], + "type": "inline_equation", + "content": "\\alpha_{N}" + }, + { + "bbox": [ + 46, + 72, + 287, + 133 + ], + "type": "text", + "content": " control the importance of the distance and angle terms respectively." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 134, + 286, + 194 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 134, + 286, + 194 + ], + "spans": [ + { + "bbox": [ + 47, + 134, + 286, + 194 + ], + "type": "text", + "content": "E-Step: Updating point assignments. After updating the shape parameters " + }, + { + "bbox": [ + 47, + 134, + 286, + 194 + ], + "type": "inline_equation", + "content": "\\Theta_t" + }, + { + "bbox": [ + 47, + 134, + 286, + 194 + ], + "type": "text", + "content": ", we update the assignment weight " + }, + { + "bbox": [ + 47, + 134, + 286, + 194 + ], + "type": "inline_equation", + "content": "W_t" + }, + { + "bbox": [ + 47, + 134, + 286, + 194 + ], + "type": "text", + "content": " by querying the decoder " + }, + { + "bbox": [ + 47, + 134, + 286, + 194 + ], + "type": "inline_equation", + "content": "\\Psi" + }, + { + "bbox": [ + 47, + 134, + 286, + 194 + ], + "type": "text", + "content": " for all the points in the scene point cloud " + }, + { + "bbox": [ + 47, + 134, + 286, + 194 + ], + "type": "inline_equation", + "content": "X" + }, + { + "bbox": [ + 47, + 134, + 286, + 194 + ], + "type": "text", + "content": " and computing the error in Eq. 6. The new assignment is designed to be updated as:" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 110, + 200, + 287, + 227 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 110, + 200, + 287, + 227 + ], + "spans": [ + { + "bbox": [ + 110, + 200, + 287, + 227 + ], + "type": "interline_equation", + "content": "W _ {t} [ i ] = \\frac {e ^ {- E (X [ i ] , \\Theta_ {t})}}{e ^ {- E (X [ i ] , \\Theta_ {t})} + \\Omega}, \\tag {7}", + "image_path": "bed9c519aa6cb284f16d557c486088f4e241f475f8bc3406c79a5366cc7ef1c5.jpg" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 228, + 287, + 264 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 228, + 287, + 264 + ], + "spans": [ + { + "bbox": [ + 46, + 228, + 287, + 264 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 228, + 287, + 264 + ], + "type": "inline_equation", + "content": "\\Omega" + }, + { + "bbox": [ + 46, + 228, + 287, + 264 + ], + "type": "text", + "content": " is a constant hyperparameter that gives every point some probability to be in the background. This step can be interpreted as the E-step in an EM algorithm." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 266, + 287, + 434 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 266, + 287, + 434 + ], + "spans": [ + { + "bbox": [ + 46, + 266, + 287, + 434 + ], + "type": "text", + "content": "Termination and confidence score. When the initialization is not near an object instance of the target class, the shape prior tends to never fit the input observations, so that the error " + }, + { + "bbox": [ + 46, + 266, + 287, + 434 + ], + "type": "inline_equation", + "content": "E" + }, + { + "bbox": [ + 46, + 266, + 287, + 434 + ], + "type": "text", + "content": " is large everywhere and the weight " + }, + { + "bbox": [ + 46, + 266, + 287, + 434 + ], + "type": "inline_equation", + "content": "W" + }, + { + "bbox": [ + 46, + 266, + 287, + 434 + ], + "type": "text", + "content": " is always small. We terminate the proposals that have less than a predefined threshold of small-error points at each iteration. After the last iteration, we use Marching Cubes to extract a mesh " + }, + { + "bbox": [ + 46, + 266, + 287, + 434 + ], + "type": "inline_equation", + "content": "(\\mathcal{V}, \\mathcal{E})" + }, + { + "bbox": [ + 46, + 266, + 287, + 434 + ], + "type": "text", + "content": " for each proposal and the mesh serves as the byproduct of our method. Our algorithm also produces a pose estimation with respect to the training shape collection via Procrustes registration [81] on " + }, + { + "bbox": [ + 46, + 266, + 287, + 434 + ], + "type": "inline_equation", + "content": "\\Theta_{SO3}" + }, + { + "bbox": [ + 46, + 266, + 287, + 434 + ], + "type": "text", + "content": " between the observed objects and the member of the training set with the most similar " + }, + { + "bbox": [ + 46, + 266, + 287, + 434 + ], + "type": "inline_equation", + "content": "\\Theta" + }, + { + "bbox": [ + 46, + 266, + 287, + 434 + ], + "type": "text", + "content": " (see Supp.). We also remove proposals with meshes outside a predefined reasonable range of scales." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 434, + 287, + 529 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 434, + 287, + 529 + ], + "spans": [ + { + "bbox": [ + 46, + 434, + 287, + 529 + ], + "type": "text", + "content": "One advantage of utilizing our shape prior is that we can explicitly compute the confidence score from the shape reconstruction. Specifically, we compute two scores by measuring the fitting errors: (1.) Observation fitting score: a good fitting should have all the encoder input points located on the decoded SDF zero level set. We measure the proportion of the encoder input point cloud which has a small distance and angle error:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 74, + 536, + 287, + 563 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 74, + 536, + 287, + 563 + ], + "spans": [ + { + "bbox": [ + 74, + 536, + 287, + 563 + ], + "type": "interline_equation", + "content": "S _ {1} = \\frac {1}{N _ {O}} \\left| \\left\\{\\mathbf {x} \\in P _ {T} \\left| \\begin{array}{l} e _ {D} (\\mathbf {x}, \\Theta) < \\delta_ {D}, \\\\ e _ {N} (\\mathbf {x}, \\Theta) < \\delta_ {N} \\end{array} \\right. \\right\\} \\right|, \\tag {8}", + "image_path": "bc58878c4af50cfc52f4797e36f4f74b21adca55a327cd49ec524f6f1633bda0.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 565, + 287, + 684 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 565, + 287, + 684 + ], + "spans": [ + { + "bbox": [ + 46, + 565, + 287, + 684 + ], + "type": "text", + "content": "where the " + }, + { + "bbox": [ + 46, + 565, + 287, + 684 + ], + "type": "inline_equation", + "content": "\\delta_D, \\delta_N" + }, + { + "bbox": [ + 46, + 565, + 287, + 684 + ], + "type": "text", + "content": " are the thresholds. (2.) Reconstruction coverage score: Since we recognize objects by their shapes, we should be less confident in detections where the observed points only cover a small portion of the extracted mesh. For every vertex " + }, + { + "bbox": [ + 46, + 565, + 287, + 684 + ], + "type": "inline_equation", + "content": "\\mathbf{v} = [x_{\\mathrm{recon}}, n_{\\mathrm{recon}}]" + }, + { + "bbox": [ + 46, + 565, + 287, + 684 + ], + "type": "text", + "content": " from the extracted mesh, we find its nearest neighbour " + }, + { + "bbox": [ + 46, + 565, + 287, + 684 + ], + "type": "inline_equation", + "content": "\\mathbf{x} = [x_{\\mathrm{obs}}, n_{\\mathrm{obs}}]" + }, + { + "bbox": [ + 46, + 565, + 287, + 684 + ], + "type": "text", + "content": " in the observed scene point cloud " + }, + { + "bbox": [ + 46, + 565, + 287, + 684 + ], + "type": "inline_equation", + "content": "X_{N \\times 6}" + }, + { + "bbox": [ + 46, + 565, + 287, + 684 + ], + "type": "text", + "content": " and measure their distance error as " + }, + { + "bbox": [ + 46, + 565, + 287, + 684 + ], + "type": "inline_equation", + "content": "e_D'(\\mathbf{v}) = \\| x_{\\mathrm{obs}} - x_{\\mathrm{recon}}\\|_2" + }, + { + "bbox": [ + 46, + 565, + 287, + 684 + ], + "type": "text", + "content": " and their orientation error as " + }, + { + "bbox": [ + 46, + 565, + 287, + 684 + ], + "type": "inline_equation", + "content": "e_N'(\\mathbf{v}) = \\cos(n_{\\mathrm{obs}}^T n_{\\mathrm{recon}})" + }, + { + "bbox": [ + 46, + 565, + 287, + 684 + ], + "type": "text", + "content": ". This gives a combined coverage score of:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 62, + 691, + 287, + 715 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 62, + 691, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 62, + 691, + 287, + 715 + ], + "type": "interline_equation", + "content": "S _ {2} = \\frac {1}{| \\mathcal {V} |} | \\left\\{\\mathbf {v} \\in \\mathcal {V} \\mid e _ {D} ^ {\\prime} (\\mathbf {v}) < \\delta_ {D}, e _ {N} ^ {\\prime} (\\mathbf {v}) < \\delta_ {N} \\right\\} |. \\tag {9}", + "image_path": "d29250258c0f496f690037f7d8e366656fd19f25642420031e815afa889d037a.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 72, + 545, + 107 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 545, + 107 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 545, + 107 + ], + "type": "text", + "content": "We use " + }, + { + "bbox": [ + 305, + 72, + 545, + 107 + ], + "type": "inline_equation", + "content": "S_{1}" + }, + { + "bbox": [ + 305, + 72, + 545, + 107 + ], + "type": "text", + "content": " as the main confidence measurement and " + }, + { + "bbox": [ + 305, + 72, + 545, + 107 + ], + "type": "inline_equation", + "content": "S_{2}" + }, + { + "bbox": [ + 305, + 72, + 545, + 107 + ], + "type": "text", + "content": " for avoiding poorly observed cases, so the final confidence score " + }, + { + "bbox": [ + 305, + 72, + 545, + 107 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 305, + 72, + 545, + 107 + ], + "type": "text", + "content": " is:" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 366, + 117, + 545, + 129 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 366, + 117, + 545, + 129 + ], + "spans": [ + { + "bbox": [ + 366, + 117, + 545, + 129 + ], + "type": "interline_equation", + "content": "C = S _ {1} * \\max \\left(1. 0, S _ {2} / \\delta_ {C}\\right), \\tag {10}", + "image_path": "8578ac86d34e2eb7a513342b9daa2b9e48ce8763d9e40fb05b105c57c250f953.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 133, + 545, + 193 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 133, + 545, + 193 + ], + "spans": [ + { + "bbox": [ + 304, + 133, + 545, + 193 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 133, + 545, + 193 + ], + "type": "inline_equation", + "content": "\\delta_C \\in [0.0, 1.0]" + }, + { + "bbox": [ + 304, + 133, + 545, + 193 + ], + "type": "text", + "content": " is a threshold controlling the importance of the coverage score. Note how the above confidence values evaluate the quality of the output shown on the right in Fig. 2, which enables the user to select the balance between recall and precision during inference." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 194, + 545, + 277 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 194, + 545, + 277 + ], + "spans": [ + { + "bbox": [ + 304, + 194, + 545, + 277 + ], + "type": "text", + "content": "Finally, for each point in the scene point cloud " + }, + { + "bbox": [ + 304, + 194, + 545, + 277 + ], + "type": "inline_equation", + "content": "X_{N \\times 6}" + }, + { + "bbox": [ + 304, + 194, + 545, + 277 + ], + "type": "text", + "content": ", we check whether the distance error in Eq. 4 and Eq. 5 is smaller than the output threshold and mark points with small errors as in the foreground. Note that since the observation is noisy and the learned shape prior is not perfect, the output error thresholds can be larger than the ones used in Eq. 8 and Eq.9." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 285, + 417, + 297 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 285, + 417, + 297 + ], + "spans": [ + { + "bbox": [ + 306, + 285, + 417, + 297 + ], + "type": "text", + "content": "3.3. Multiple Proposals" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 302, + 545, + 422 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 302, + 545, + 422 + ], + "spans": [ + { + "bbox": [ + 304, + 302, + 545, + 422 + ], + "type": "text", + "content": "Since the EM algorithm outputs can be affected by its initialization and we do not know the number of objects in the scene, we initialize a large number of proposals randomly spread across the entire scene to cover all possible objects. We observe that many proposals will quickly converge to similar positions during the early iterations. Therefore, at each iteration, we remove duplicated proposals and only keep the one with the highest fitting score " + }, + { + "bbox": [ + 304, + 302, + 545, + 422 + ], + "type": "inline_equation", + "content": "S_{1}" + }, + { + "bbox": [ + 304, + 302, + 545, + 422 + ], + "type": "text", + "content": " defined in Eq. 8. Duplication is determined by computing the overlap of " + }, + { + "bbox": [ + 304, + 302, + 545, + 422 + ], + "type": "inline_equation", + "content": "W" + }, + { + "bbox": [ + 304, + 302, + 545, + 422 + ], + "type": "text", + "content": " between different proposals (see Supp. for details)." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 422, + 545, + 518 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 422, + 545, + 518 + ], + "spans": [ + { + "bbox": [ + 304, + 422, + 545, + 518 + ], + "type": "text", + "content": "As shown in Fig. 2, we further divide the iterations into two phases. In the first phase, since the early shape estimation is not converged to a reasonable place, we let each proposal run fully independently. When we enter the second phase, mesh extraction and pose estimation will be first applied to remove proposals with unreasonable scales. Then, we optimize all proposals globally by updating the joint assignment weight with:" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 345, + 525, + 545, + 559 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 345, + 525, + 545, + 559 + ], + "spans": [ + { + "bbox": [ + 345, + 525, + 545, + 559 + ], + "type": "interline_equation", + "content": "W _ {t} ^ {(k)} [ i ] = \\frac {S _ {1} ^ {(k)} e ^ {- E (X [ i ] , \\Theta_ {t} ^ {(k)})}}{\\sum_ {j} S _ {1} ^ {(j)} e ^ {- E (X [ i ] , \\Theta_ {t} ^ {(j)})} + \\Omega}, \\tag {11}", + "image_path": "491126c7f1a168af3e463ed1705795200d35f4dfc3ad44a1dcb52f0846277075.jpg" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 560, + 545, + 657 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 560, + 545, + 657 + ], + "spans": [ + { + "bbox": [ + 304, + 560, + 545, + 657 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 560, + 545, + 657 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 304, + 560, + 545, + 657 + ], + "type": "text", + "content": " is the index of current active proposals and " + }, + { + "bbox": [ + 304, + 560, + 545, + 657 + ], + "type": "inline_equation", + "content": "S_1^{(k)}" + }, + { + "bbox": [ + 304, + 560, + 545, + 657 + ], + "type": "text", + "content": " is the current fitting score in Eq. 8, which increases the assignment weight for more confident proposals. During the last iterations in Phase-2, we also remove the proposals that are largely contained by other proposals to simplify the decomposition of the scene, following a similar methodology to duplication removal. Additional details of this process are available in the supplemental." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 306, + 662, + 387, + 675 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 662, + 387, + 675 + ], + "spans": [ + { + "bbox": [ + 306, + 662, + 387, + 675 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "text", + "content": "We focus our experiments on answering four main questions: First, can our method successfully segment the objects of interest from the scene? Second, how does our" + } + ] + } + ], + "index": 19 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "4906" + } + ] + } + ], + "index": 20 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 48, + 68, + 545, + 165 + ], + "blocks": [ + { + "bbox": [ + 48, + 68, + 545, + 165 + ], + "lines": [ + { + "bbox": [ + 48, + 68, + 545, + 165 + ], + "spans": [ + { + "bbox": [ + 48, + 68, + 545, + 165 + ], + "type": "image", + "image_path": "3d2b9b9199912bb86cbe8a5ef397dee4a4ac5e332210b1a903e7f76d9a5cf483.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 167, + 546, + 191 + ], + "lines": [ + { + "bbox": [ + 46, + 167, + 546, + 191 + ], + "spans": [ + { + "bbox": [ + 46, + 167, + 546, + 191 + ], + "type": "text", + "content": "Figure 3. Synthetic scenes: Top: the mesh reconstruction as input, note how our data has a realistic simulated depth pattern; Middle: visualization of the estimated shapes, poses and bounding boxes as the byproducts of our method. Bottom: Our segmentation prediction." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 48, + 198, + 545, + 304 + ], + "blocks": [ + { + "bbox": [ + 48, + 198, + 545, + 304 + ], + "lines": [ + { + "bbox": [ + 48, + 198, + 545, + 304 + ], + "spans": [ + { + "bbox": [ + 48, + 198, + 545, + 304 + ], + "type": "image", + "image_path": "0ddd746a1fb5f79589820024ef3365e05087e797bde8138af7efc70c5936ae9d.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 136, + 305, + 456, + 317 + ], + "lines": [ + { + "bbox": [ + 136, + 305, + 456, + 317 + ], + "spans": [ + { + "bbox": [ + 136, + 305, + 456, + 317 + ], + "type": "text", + "content": "Figure 4. Chairs and Mugs real testset: the three rows are in the same format as Fig. 3." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 338, + 289, + 445 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 338, + 289, + 445 + ], + "spans": [ + { + "bbox": [ + 46, + 338, + 289, + 445 + ], + "type": "text", + "content": "method compare to existing baselines when different training data distributions are accessible? Third, how does each approach generalize to the different testing environments, including the real-world scenes and the out-of-distribution configurations? And fourth, how do the different components of our model contribute to its performance? To answer these questions, we perform a series of baseline comparisons as well as ablation studies both on synthetic and real-world scenes." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 447, + 113, + 458 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 447, + 113, + 458 + ], + "spans": [ + { + "bbox": [ + 47, + 447, + 113, + 458 + ], + "type": "text", + "content": "4.1. Baselines" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 460, + 287, + 651 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 460, + 287, + 651 + ], + "spans": [ + { + "bbox": [ + 46, + 460, + 287, + 651 + ], + "type": "text", + "content": "To the best of the authors' knowledge, fully unsupervised instance segmentation (not foreground-background segmentation) in static scenes remains unexplored in the deep learning literature. Therefore, we compare our method with supervised and weakly supervised methods. SoftGroup (CVPR22) [63] is the current SoTA for 3D instance segmentation methods that are trained with ground truth instance masks. Box2Mask (ECCV22) [12] is a recent weakly supervised method, which only needs ground truth instance bounding boxes as supervision while retaining competitive performance. The closest weakly supervised method to ours is ContrastiveSceneContext (CVPR21) [24], which can be trained with only a few point labels. To conduct fair comparisons and reduce the sim2real gap, all baselines are fully trained on the corresponding training set with positions and normals as input while not using colors." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 652, + 163, + 665 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 652, + 163, + 665 + ], + "spans": [ + { + "bbox": [ + 47, + 652, + 163, + 665 + ], + "type": "text", + "content": "4.2. Experimental Setup" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 666, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 666, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 666, + 288, + 715 + ], + "type": "text", + "content": "We focus our experiments on scenes that contain objects humans or robots can interact with. These objects are more interesting targets for segmentation as their configurations can change dramatically in real-world applications, such as" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 338, + 546, + 456 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 338, + 546, + 456 + ], + "spans": [ + { + "bbox": [ + 304, + 338, + 546, + 456 + ], + "type": "text", + "content": "robotics or AR/VR. We experiment with three object categories that frequently appear in the presence of clutter and in diverse configurations in real-world data: Mugs, Kitchen containers, and Chairs. Since there is no available dataset that contains these objects with rich configuration changes (not just sitting upright on a flat surface), and all baselines need to be trained with ground truth, we gather simulated data to train the baselines, then evaluate on simulated and real test scenes containing completely unseen object instances." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 460, + 546, + 592 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 460, + 546, + 592 + ], + "spans": [ + { + "bbox": [ + 304, + 460, + 546, + 592 + ], + "type": "text", + "content": "Three types of scenes are used for training baselines on each of the object classes. Take the mugs scene as an example (Fig. 3 Left top): In the Z scenes, all instances are upright and not in contact with each other. In SO(3), the objects can have a random orientation but are still not in contact with each other. Pile is a much more challenging setting where the objects can touch each other, can take any orientation, and can form piles. We simulate 500 scenes for training, 50 scenes for validation and 100 scenes for testing in each of the setups. For each baseline we train three models, one on the data from each of the three scene types." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 594, + 547, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 594, + 547, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 594, + 547, + 714 + ], + "type": "text", + "content": "We train our equivariant shape prior (Sec. 3.1) on the corresponding categories from ShapeNet [4] and freeze their weights once trained. Note that all the following results are generated from the same trained shape prior for each category, and all the objects in our testing scenes never appear in the training set of the shape prior. We evaluate each model on all of the scenes and report results in Tab. 1, Tab. 2 and Tab. 3. The gray cells indicate results from models that were trained on less difficult datasets than they were evaluated on, with the underlined number indicating the best" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "4907" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 50, + 71, + 547, + 198 + ], + "blocks": [ + { + "bbox": [ + 50, + 71, + 547, + 198 + ], + "lines": [ + { + "bbox": [ + 50, + 71, + 547, + 198 + ], + "spans": [ + { + "bbox": [ + 50, + 71, + 547, + 198 + ], + "type": "table", + "html": "
MugsTestingZSO3PileTreeBoxShelf(R) Z(R) SO3(R) Pile(R) Tree(R) Others(R) Wild
TrainingMetricsAPA50APA50APA50APA50APA50APA50APA50APA50APA50APA50APA50APA50
Scene ZCSC (100)6.022.01.97.60.10.50.00.00.00.20.00.00.00.00.00.00.00.00.00.00.00.00.20.9
CSC (200)78.798.162.783.38.917.40.62.02.05.00.83.172.199.89.521.40.31.60.62.86.716.02.06.1
Box2Mask96.910092.199.336.727.612.345.310.024.08.614.698.110093.11005.619.18.428.818.439.518.127.9
SoftGroup10010096.598.521.927.60.41.81.63.79.217.293.797.697.31000.00.00.93.44.39.118.332.9
Scene SO3CSC (100)1.78.61.46.50.10.60.00.00.00.10.10.60.00.00.00.00.00.00.00.00.00.00.71.9
CSC (200)70.099.372.795.722.342.210.224.65.412.35.220.068.410059.81001.03.74.820.16.919.73.911.8
Box2Mask95.810094.710053.780.130.280.626.540.113.433.010010095.310012.734.319.649.227.150.650.374.8
SoftGroup10010099.699.843.951.910.018.715.321.320.830.999.210098.21002.84.810.421.76.513.318.330.7
Scene PileCSC (100)0.00.30.00.30.00.10.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.71.8
CSC (200)53.388.450.277.729.561.329.466.27.619.810.334.113.045.022.765.25.330.11.58.03.515.42.88.5
Box2Mask96.010094.710078.799.655.294.842.752.926.354.610010095.810072.398.055.898.156.079.245.171.4
SoftGroup99.510099.710089.093.242.372.823.425.528.839.599.610099.710074.786.353.483.050.966.548.165.9
ShapeNetEFEM78.499.879.399.868.296.868.899.059.977.048.772.487.210087.310063.194.069.695.469.789.454.182.3
", + "image_path": "da285a444d65549fe902139a7c098fff527c04e25236490b0f52469349355609.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 50, + 253, + 285, + 360 + ], + "blocks": [ + { + "bbox": [ + 46, + 201, + 546, + 234 + ], + "lines": [ + { + "bbox": [ + 46, + 201, + 546, + 234 + ], + "spans": [ + { + "bbox": [ + 46, + 201, + 546, + 234 + ], + "type": "text", + "content": "Table 1. Results (%) on SynMugs (left) and RealMugs (right with label R). A50 corresponds to mAP50. The full table including mAP25 is available in the supplemental. The grey cells highlight that the testing scenes are out of the training distribution and the bold number means the best among all methods while the underlined number means the best within grey cells." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 50, + 253, + 285, + 360 + ], + "lines": [ + { + "bbox": [ + 50, + 253, + 285, + 360 + ], + "spans": [ + { + "bbox": [ + 50, + 253, + 285, + 360 + ], + "type": "table", + "html": "
Testing(C) Z(C) SO3(C) Pile(K) Z(K) SO3(K) Pile
TrainingMetricsAPA50APA50APA50APA50APA50APA50
Scene ZCSC (100)66.283.156.680.26.115.212.729.97.514.52.35.9
CSC (200)77.791.063.785.110.522.763.080.937.949.212.223.2
Box2Mask99.910095.898.919.341.289.797.369.687.041.468.9
SoftGroup99.810094.898.524.136.593.696.894.099.352.363.5
Scene SO3CSC (100)74.981.477.382.417.731.08.521.711.323.82.05.4
CSC (200)84.386.685.488.520.635.327.848.953.977.518.138.9
Box2Mask99.710099.199.550.580.385.396.291.898.552.976.5
SoftGroup99.610099.110055.168.289.393.996.999.356.267.2
Scene PileCSC (100)67.074.174.682.147.263.83.411.22.67.11.44.5
CSC (200)71.776.388.492.467.481.626.553.844.873.628.860.4
Box2Mask99.699.799.599.778.696.987.297.992.198.674.894.6
SoftGroup99.410098.910095.097.093.797.396.098.884.691.3
ShapeNetEFEM93.199.286.197.475.388.069.483.467.683.160.178.9
", + "image_path": "032c7ea023985b7761207c7bc98317f867e7fa20fc1037f6ae467b84e1265458.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "type": "table", + "bbox": [ + 52, + 376, + 280, + 521 + ], + "blocks": [ + { + "bbox": [ + 48, + 363, + 286, + 373 + ], + "lines": [ + { + "bbox": [ + 48, + 363, + 286, + 373 + ], + "spans": [ + { + "bbox": [ + 48, + 363, + 286, + 373 + ], + "type": "text", + "content": "Table 2. SynChairs (left) and SynKit (right), same format as Tab. 1" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 52, + 376, + 280, + 521 + ], + "lines": [ + { + "bbox": [ + 52, + 376, + 280, + 521 + ], + "spans": [ + { + "bbox": [ + 52, + 376, + 280, + 521 + ], + "type": "table", + "html": "
RealChairsTestingR(Z)R(SO3)R(Pile)
TrainingMetricsAPAP50AP25APAP50AP25APAP50AP25
Scene ZCSC (100)0.51.49.41.32.810.80.00.07.2
CSC (200)0.81.211.00.30.69.80.00.23.1
Box2Mask0.00.320.20.31.927.20.00.111.8
SoftGroup5.17.727.02.86.721.90.00.03.7
Scene SO3CSC (100)3.65.318.21.42.513.30.00.14.5
CSC (200)1.22.610.41.84.920.20.10.59.1
Box2Mask1.55.948.45.119.956.70.41.828.2
SoftGroup13.817.227.47.916.230.30.10.16.1
Scene PileCSC (100)5.27.19.63.27.412.30.10.32.9
CSC (200)8.311.723.113.923.233.61.02.613.1
Box2Mask1.66.537.89.422.065.31.34.846.6
SoftGroup20.627.836.114.424.442.10.41.58.0
ScannetCSC (100)36.849.862.05.313.118.83.910.818.1
CSC (200)50.074.377.86.213.118.65.513.427.1
Box2Mask84.199.499.416.233.741.214.329.850.7
SoftGroup74.081.187.522.339.648.611.518.036.1
ShapeNetEFEM51.078.385.051.275.787.934.455.374.8
", + "image_path": "b3acb0c6ccdc03888c5376ac8a0ec68bc814281c2aa868e089254ad76edb967b.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_body" + } + ], + "index": 4 + }, + { + "bbox": [ + 67, + 525, + 264, + 534 + ], + "lines": [ + { + "bbox": [ + 67, + 525, + 264, + 534 + ], + "spans": [ + { + "bbox": [ + 67, + 525, + 264, + 534 + ], + "type": "text", + "content": "Table 3. Results on RealChairs, same format as Tab. 1" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 540, + 286, + 563 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 540, + 286, + 563 + ], + "spans": [ + { + "bbox": [ + 46, + 540, + 286, + 563 + ], + "type": "text", + "content": "performing inside gray cells. The metric for evaluating the segmentation is the commonly used mAP [15]." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 567, + 187, + 580 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 567, + 187, + 580 + ], + "spans": [ + { + "bbox": [ + 47, + 567, + 187, + 580 + ], + "type": "text", + "content": "4.3. Results on synthetic data" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 582, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 582, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 582, + 286, + 713 + ], + "type": "text", + "content": "We first evaluate the performance on simulated data, and we found that existing baselines work very well inside the training distribution if trained with enough supervisory signals. However, the weakly supervised method CSC [24] has a significant performance drop when the number of supervision points decreases from 200 to 100. This performance drop becomes increasingly severe when the training set distribution becomes more complex, demonstrating the difficulty of unsupervised segmentation. With zero scene-level supervision, our method performs well with a small gap in performance to the (weakly) supervised methods." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 255, + 545, + 351 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 255, + 545, + 351 + ], + "spans": [ + { + "bbox": [ + 305, + 255, + 545, + 351 + ], + "type": "text", + "content": "When the baselines are trained on " + }, + { + "bbox": [ + 305, + 255, + 545, + 351 + ], + "type": "inline_equation", + "content": "\\mathbf{Z}" + }, + { + "bbox": [ + 305, + 255, + 545, + 351 + ], + "type": "text", + "content": " but tested on SO3, the baselines do not show a large drop in performance, potentially because both " + }, + { + "bbox": [ + 305, + 255, + 545, + 351 + ], + "type": "inline_equation", + "content": "\\mathbf{Z}" + }, + { + "bbox": [ + 305, + 255, + 545, + 351 + ], + "type": "text", + "content": " and SO3 scenes have no objects in contact with each other. However, when tested on Pile, we see that baselines trained on " + }, + { + "bbox": [ + 305, + 255, + 545, + 351 + ], + "type": "inline_equation", + "content": "\\mathbf{Z}" + }, + { + "bbox": [ + 305, + 255, + 545, + 351 + ], + "type": "text", + "content": " or SO3 perform differently, and are both worse than the ones trained on Pile, indicating a failure to generalize to clutter. Our method outperforms all the baselines that are not trained on Pile configurations." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 351, + 545, + 472 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 351, + 545, + 472 + ], + "spans": [ + { + "bbox": [ + 304, + 351, + 545, + 472 + ], + "type": "text", + "content": "We additionally generate 50 scenes each from three new and more difficult scene setups for testing on Mugs as shown in Fig. 3. In the Tree scenes mugs are hanging on a holder tree and distributed vertically. The Box scenes include cubes to simulate objects that have not been seen during training. In the Shelf scenes, the mugs are put on a shelf that is only visible from one side. In all three of these scene setups, our method is able to outperform all baselines as the baselines are unable to generalize to configurations of mugs that are significantly outside of the training distribution." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 480, + 421, + 491 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 480, + 421, + 491 + ], + "spans": [ + { + "bbox": [ + 306, + 480, + 421, + 491 + ], + "type": "text", + "content": "4.4. Results on real data" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 494, + 545, + 577 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 494, + 545, + 577 + ], + "spans": [ + { + "bbox": [ + 304, + 494, + 545, + 577 + ], + "type": "text", + "content": "We additionally evaluate the performance of our model on real data. To the best of the authors' knowledge, there is no existing real dataset that contains interactable objects in diverse configurations for 3D instance segmentation. Therefore we collect a test set Chairs and Mugs that contains the reconstruction of 240 real scenes with object instance mask annotations to test our method in the real world." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "content": "RealMugs: As shown in Fig. 4 we replicate the Z, SO3, Pile and Tree setups in the real world. The scene is captured by 4 calibrated realsense D455 cameras mounted on the corners of the table. We further introduce two new setups that cover hard-to-simulate scenes. The Others setup contains random objects that a manipulator may encounter, including cloth, toys, paper bags, wires and tools. These objects are added into the tabletop scene, contacting and occluding the mugs. The Wild setup contains crops of real-world indoor scans from labs, kitchens, and teaching buildings. Unlike [73], our scenes are not restricted to only showing the" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "4908" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 50, + 69, + 286, + 164 + ], + "blocks": [ + { + "bbox": [ + 50, + 69, + 286, + 164 + ], + "lines": [ + { + "bbox": [ + 50, + 69, + 286, + 164 + ], + "spans": [ + { + "bbox": [ + 50, + 69, + 286, + 164 + ], + "type": "image", + "image_path": "130b828df894e63e4f49711608be9d5072d3580cee6c84503ec3278c323e4e94.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 52, + 165, + 282, + 176 + ], + "lines": [ + { + "bbox": [ + 52, + 165, + 282, + 176 + ], + "spans": [ + { + "bbox": [ + 52, + 165, + 282, + 176 + ], + "type": "text", + "content": "Figure 5. ScanNet qualitative results, the same format as Fig. 3" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 189, + 287, + 261 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 189, + 287, + 261 + ], + "spans": [ + { + "bbox": [ + 46, + 189, + 287, + 261 + ], + "type": "text", + "content": "table and upright mugs, but include diverse configurations, backgrounds, and distractors. These scans are captured by an iPad with a lidar scanner. Since the Z, SO3 and Pile setups are easy to simulate realistically, we only collect 10 scenes per setup. We collect 50 scenes for each of the Tree, Others and Wild setups." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 262, + 289, + 417 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 262, + 289, + 417 + ], + "spans": [ + { + "bbox": [ + 46, + 262, + 289, + 417 + ], + "type": "text", + "content": "We test all the baselines trained on the synthetic dataset and our method trained on ShapeNet directly on these real scenes. Quantitative results are shown in Tab. 1. Since our simulator includes advanced techniques of active light simulation in the physical engine [69] and we do not use the colours as input, the sim2real gap for the baseline methods is minimal in these controlled setups. We can draw similar conclusions for Z, SO3, Pile and Tree setups as with the synthetic experiments. Our method retains reasonable performance on Others scenes due to its awareness of the object shape. When tested on the Wild real-world scenes, our method also performs the best, which demonstrates the strong generalizability of our method." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 426, + 289, + 700 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 426, + 289, + 700 + ], + "spans": [ + { + "bbox": [ + 46, + 426, + 289, + 700 + ], + "type": "text", + "content": "RealChairs: We also collect data of chairs in the real world following the Z, SO3 and Pile setups. Although we have plenty of real-world scan datasets like [15], none of them include diverse configuration changes of chairs. Therefore we collected and annotated a small test set with 20 scenes per setup as shown in Fig. 4. We train the baselines in simulation and test them in the real world. Additionally, we take all the baselines' official model weights from being trained on the real world ScanNet dataset [15] to evaluate on our test set. The results are shown in Tab. 3. There is a larger sim2real gap for the baselines with the chairs data than with the mugs data because of less realistic depth simulation and difficulties aligning the scale between Shapenet chairs and real-world chairs. In contrast, the baselines trained on ScanNet work very well on the Z setup, which aligns best with the ScanNet dataset. However, they have a significant drop in performance when the testing distribution shifts to the SO3 and Pile setups. In contrast, our method retains reasonable performance on real world chairs across different setups. We will release our Chairs and Mugs dataset to provide more opportunities to study robustness, generalizability and equivariance for scene and object understanding in the real world." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 59, + 701, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 701, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 59, + 701, + 287, + 713 + ], + "type": "text", + "content": "We also show our effectiveness on ScanNet [15], where" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 72, + 547, + 216 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 216 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 216 + ], + "type": "text", + "content": "the indoor scene scan can span the whole room. Qualitative results are shown in Fig. 5 and the AP metrics for the chairs category of our method on the validation/test set are " + }, + { + "bbox": [ + 304, + 72, + 547, + 216 + ], + "type": "inline_equation", + "content": "AP = 24.6 / 20.2" + }, + { + "bbox": [ + 304, + 72, + 547, + 216 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 72, + 547, + 216 + ], + "type": "inline_equation", + "content": "AP50 = 50.8 / 39.0" + }, + { + "bbox": [ + 304, + 72, + 547, + 216 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 72, + 547, + 216 + ], + "type": "inline_equation", + "content": "AP25 = 61.3 / 48.3" + }, + { + "bbox": [ + 304, + 72, + 547, + 216 + ], + "type": "text", + "content": " where in comparison the weakly supervised method CSC [24] trained on 200 points labels achieves " + }, + { + "bbox": [ + 304, + 72, + 547, + 216 + ], + "type": "inline_equation", + "content": "AP50 = 62.9 / 61.1" + }, + { + "bbox": [ + 304, + 72, + 547, + 216 + ], + "type": "text", + "content": " (See Suppl. for a table). One main reason for our performance drop on ScanNet is that ScanNet has many partially observed chairs, which are hard to be recognized via shape. We leave future explorations to fill this gap between our unsupervised method and the (weakly) supervised ones." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 218, + 373, + 229 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 218, + 373, + 229 + ], + "spans": [ + { + "bbox": [ + 306, + 218, + 373, + 229 + ], + "type": "text", + "content": "4.5. Ablations" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 232, + 403, + 303 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 232, + 403, + 303 + ], + "spans": [ + { + "bbox": [ + 304, + 232, + 403, + 303 + ], + "type": "text", + "content": "We verify the effectiveness of our design by removing the phase-2 joint iterations and removing the usage of the normals. When not" + } + ] + } + ], + "index": 8 + }, + { + "type": "table", + "bbox": [ + 409, + 232, + 542, + 281 + ], + "blocks": [ + { + "bbox": [ + 409, + 232, + 542, + 281 + ], + "lines": [ + { + "bbox": [ + 409, + 232, + 542, + 281 + ], + "spans": [ + { + "bbox": [ + 409, + 232, + 542, + 281 + ], + "type": "table", + "html": "
AblationAPAP50AP25
Full0.6010.7890.807
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", + "image_path": "4b229b541bae7f5e54a41b6fa4999d1c2629519d9843b01f2e587cb5e35efa83.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "table_body" + } + ], + "index": 9 + }, + { + "bbox": [ + 440, + 289, + 510, + 300 + ], + "lines": [ + { + "bbox": [ + 440, + 289, + 510, + 300 + ], + "spans": [ + { + "bbox": [ + 440, + 289, + 510, + 300 + ], + "type": "text", + "content": "Table 4. Ablations" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 304, + 304, + 545, + 424 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 304, + 545, + 424 + ], + "spans": [ + { + "bbox": [ + 304, + 304, + 545, + 424 + ], + "type": "text", + "content": "using phase-2 (Sec. 3.3), we let the phase-1 independent iterations run more steps to keep the total number of iterations constant. When removing the normals, all error computing, assignment weight updating, and confidence scoring will only take the distance error term in to account while ignoring the normal term. We compare our full model with the ablated models on SynKit Pile setups. The quantitative results are shown in Tab. 4, which illustrates that both components contribute to our model's overall performance. More ablation studies can be found in our supplementary." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 429, + 384, + 441 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 429, + 384, + 441 + ], + "spans": [ + { + "bbox": [ + 306, + 429, + 384, + 441 + ], + "type": "text", + "content": "5. Conclusions" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 444, + 545, + 503 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 444, + 545, + 503 + ], + "spans": [ + { + "bbox": [ + 304, + 444, + 545, + 503 + ], + "type": "text", + "content": "We present EFEM, a method for 3D instance segmentation that is trained only on shape datasets. Without requiring any real or simulated scene data, our method can generalize to complex, real world scenes better than existing methods that also require more supervision." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 506, + 547, + 625 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 506, + 547, + 625 + ], + "spans": [ + { + "bbox": [ + 304, + 506, + 547, + 625 + ], + "type": "text", + "content": "Limitations and future work. Although we show an encouraging step towards unsupervised 3D instance segmentation by generalizing knowledge directly from a shape collection to a scene, several weaknesses remain. First, our method has a performance drop when the object is significantly occluded. This is due to our method recognizing objects only via their shape, rather than also reasoning about color or other features. Second our current running speed is slow (" + }, + { + "bbox": [ + 304, + 506, + 547, + 625 + ], + "type": "inline_equation", + "content": "\\sim" + }, + { + "bbox": [ + 304, + 506, + 547, + 625 + ], + "type": "text", + "content": "1min per scene) due to the large number of proposals the initialization requires." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 628, + 547, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 628, + 547, + 712 + ], + "spans": [ + { + "bbox": [ + 304, + 628, + 547, + 712 + ], + "type": "text", + "content": "Acknowledgements. The authors appreciate the support of the following grants: NSF FRR 2220868, NSF IISRI 2212433, NSF TRIPODS 1934960, ARL DCIST CRA W911NF-17-2-0181, ARO MURI W911NF-20-1-0080, ONR N00014-22-1-2677 awarded to UPenn; Toyota University 2.0 program and Vannevar Bush Faculty Fellowship awarded to Stanford University." + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "4909" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 72, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 72, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 72, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 287, + 704 + ], + "type": "list", + "angle": 0, + "index": 14, + "blocks": [ + { + "bbox": [ + 53, + 91, + 286, + 123 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 286, + 123 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 286, + 123 + ], + "type": "text", + "content": "[1] Jimmy Aronsson. 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PMLR, 2022. 3, 5" + } + ] + } + ], + "index": 28 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "4912" + } + ] + } + ], + "index": 30 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 10 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/EMT-NAS_Transferring Architectural Knowledge Between Tasks From Different Datasets/f54bf63e-2702-4fdf-815c-53bb8912c6fe_content_list.json b/2023/EMT-NAS_Transferring Architectural Knowledge Between Tasks From Different Datasets/f54bf63e-2702-4fdf-815c-53bb8912c6fe_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..ed7debb0fd76c976114760b9174e5ebdce3076c7 --- /dev/null +++ b/2023/EMT-NAS_Transferring Architectural Knowledge Between Tasks From Different Datasets/f54bf63e-2702-4fdf-815c-53bb8912c6fe_content_list.json @@ -0,0 +1,1436 @@ +[ + { + "type": "text", + "text": "EMT-NAS:Transferring architectural knowledge between tasks from different datasets", + "text_level": 1, + "bbox": [ + 91, + 128, + 879, + 174 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Peng Liao $^{1}$ , Yaochu Jin $^{1,2*}$ , Wenli Du $^{1*}$", + "bbox": [ + 367, + 202, + 673, + 220 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1 Key Laboratory of Smart Manufacturing in Energy Chemical Process, Ministry of Education, ECUST, China \n2 Faculty of Technology, Bielefeld University, Germany", + "bbox": [ + 88, + 220, + 955, + 257 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "pengliao@mail.ecust.edu.cn, yaochu.jin@uni-bielefeld.de, wldu@ecust.edu.cn", + "bbox": [ + 192, + 258, + 849, + 273 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 308, + 313, + 325 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "The success of multi-task learning (MTL) can largely be attributed to the shared representation of related tasks, allowing the models to better generalise. In deep learning, this is usually achieved by sharing a common neural network architecture and jointly training the weights. However, the joint training of weighting parameters on multiple related tasks may lead to performance degradation, known as negative transfer. To address this issue, this work proposes an evolutionary multi-tasking neural architecture search (EMT-NAS) algorithm to accelerate the search process by transferring architectural knowledge across multiple related tasks. In EMT-NAS, unlike the traditional MTL, the model for each task has a personalised network architecture and its own weights, thus offering the capability of effectively alleviating negative transfer. A fitness re-evaluation method is suggested to alleviate fluctuations in performance evaluations resulting from parameter sharing and the mini-batch gradient descent training method, thereby avoiding losing promising solutions during the search process. To rigorously verify the performance of EMT-NAS, the classification tasks used in the empirical assessments are derived from different datasets, including the CIFAR-10 and CIFAR-100, and four MedMNIST datasets. Extensive comparative experiments on different numbers of tasks demonstrate that EMT-NAS takes $8\\%$ and up to $40\\%$ on CIFAR and MedMNIST, respectively, less time to find competitive neural architectures than its single-task counterparts.", + "bbox": [ + 76, + 340, + 473, + 765 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 78, + 792, + 209, + 809 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Many neural architecture search (NAS) algorithms [8, 16, 23, 56] have shown better performance on a specific task than manually designed deep neural networks [11, 14,", + "bbox": [ + 76, + 819, + 468, + 864 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/b3ce56e560da4fcca584f7153b50060f14d548c8c9671ccfe1779804cf380263.jpg", + "image_caption": [ + "Figure 1. Conceptual differences between our work and two main existing methodologies for two-task learning. (a) Existing multi-task NAS typically handles multiple tasks such as semantic segmentation and surface normal prediction on the same dataset, where the loss function contains losses for multiple tasks, resulting in a network architecture that shares a common set of weight parameters. (b) Model-based transfer learning trains a network architecture on a source dataset and then transfers it to a target dataset by fine-tuning the weights using a separate loss function. (c) EMT-NAS simultaneously optimises multiple classification tasks from different datasets using a separate loss function for each task, resulting in an individual network architecture and corresponding weights for each task. EMT-NAS aims to optimise each task separately while sharing the knowledge of good network architectures to facilitate the optimisation of each task. Best viewed in colour." + ], + "image_footnote": [], + "bbox": [ + 500, + 308, + 715, + 532 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/bcb99c75970b3ce6347b53239ce83467d937638191aee0bea7a29835b6491807.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 718, + 308, + 887, + 532 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "35, 51]. However, when the task (or dataset) changes, the NAS algorithm needs to be run again to find a new optimal network architecture for the new task, which is typical for single-task learning (STL).", + "bbox": [ + 496, + 761, + 892, + 821 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "By contrast, it has been shown that simultaneously learning multiple related tasks, known as multi-task learning (MTL) is beneficial [3, 52]. One class of MTL focuses on designing or training a single network to jointly solve multiple tasks formed by scene understanding (the same", + "bbox": [ + 496, + 825, + 893, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Corresponding author.", + "bbox": [ + 94, + 875, + 222, + 887 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "Code: https://github.com/PengLiao12/EMT-NAS", + "bbox": [ + 102, + 888, + 429, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "3643", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "dataset) [38, 46], such as the NYU v2 dataset [37], the CityScapes dataset [4], and the Taskonomy dataset [48]. These tasks consist of semantic segmentation, surface normal prediction, depth prediction, keypoint detection and edge detection, which are known as multiple tasks that arise naturally [3]. Another typical scenario of MTL is inspired from human learning, where humans often transfer knowledge from one task to another related task, for example, the skills of playing squash and tennis could help each other to improve [52]. In this case, tasks may come from different datasets. More often than not, a pair of tasks from different datasets have a lower relatedness score than those from the same dataset [18]. This can be clearly shown if we analyse the task relatedness [1] between classification tasks from four medical datasets using the representation similarity analysis (RSA) [7]. The results of our analysis are presented in Fig. 2, from which we can see that the relatedness score becomes especially low when the datasets are from different data modalities, implying that MTL on tasks from different datasets is more challenging.", + "bbox": [ + 76, + 90, + 472, + 393 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "MTL is able to improve the performance of learning multiple related tasks by means of sharing common knowledge between tasks, including the network architecture and the weights of the model. Existing MTL designs one architecture for multiple tasks, although only a subset of that network architecture is practically used for each task. In other words, there are shares and differences between these subsets of model architectures [33]. In sharing the weights, if one or more tasks have a dominating influence in training the network weights, the performance of MTL may deteriorate on some of the dominated tasks, which is called negative transfer [40]. Therefore, this work aims to improve the performance of each task by finding a personalised network architecture for each task, thereby alleviating negative transfer resulting from the jointly trained weights.", + "bbox": [ + 76, + 396, + 472, + 625 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Inspired by the successful research on multi-factorial evolutionary algorithms (MFEAs) [9], a recently proposed approach to knowledge transfer in evolutionary optimisation, this work designs an algorithm to separately search for a personalised network architecture and corresponding weight parameters for each task in the same search space. This way, knowledge transfer across different tasks can be achieved through crossover between these architectures to accelerate the search process on each task, provided that there are similarities between the multiple learning tasks.", + "bbox": [ + 76, + 625, + 472, + 777 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Contributions: First, we propose an evolutionary multitasking NAS algorithm (EMT-NAS) for finding personalised network architectures for different tasks (datasets) in the same search space. Architectural knowledge transfer is achieved by optimising the supernet parameters of each task separately and recommending neural network architectures with good performance on their own task. Second, block-based crossover and bit-based mutation opera", + "bbox": [ + 76, + 779, + 472, + 902 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/0df761503b86f8f7b1693b413eb7b7b581864523e92e0a1b81b0413960b53d46.jpg", + "image_caption": [ + "Figure 2. Task similarity matrix. The relatedness scores between four medical tasks are computed using ResNet-50 as a feature extractor. PathMNIST [44] is the tissue classification based on colorectal cancer histology slides, while OrganMNIST-{Axial,Coronal,Sagittal} [44] are organ classifications based on 3 types of 2D images formed by 3D computed tomography (CT) images. We observe that the relatedness between PathMNIST and OrganMNIST-{Axial,Coronal,Sagittal}, respectively, are all smaller than that between OrganMNIST-{Axial,Coronal,Sagittal}." + ], + "image_footnote": [], + "bbox": [ + 540, + 90, + 844, + 258 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "tors are designed to accommodate the transformation from a continuous space to a discrete space. Finally, a fitness re-evaluation method is introduced to alleviate fitness fluctuations over the generations resulting from parameter sharing and the mini-batch gradient descent based training to keep promising solutions. We present thorough experimental evaluations on different datasets, including medical classification benchmarks (PathMNIST, OrganMNIST-{Axial,Coronal,Sagittal}) and popular image classification benchmarks (CIFAR-10, CIFAR-100, ImageNet), demonstrating the efficacy and the value of each component of EMT-NAS. Our results demonstrate that, unlike traditional MTL, it is feasible to search for personalised network architectures for multiple tasks through architectural knowledge transfer, obtaining better performance and requiring less search time compared with single-task learning.", + "bbox": [ + 496, + 407, + 893, + 652 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 500, + 664, + 640, + 680 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Below we summarise the similarities and differences with our work in the following themes.", + "bbox": [ + 496, + 688, + 890, + 718 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Multi-Task Learning is designed to learn a network with shared representation from multiple tasks in deep learning. A major challenge in MTL is to balance the joint learning of all tasks to avoid negative transfer [40], motivated by [17] to balance the gradient magnitudes by setting the task-specific weights in the loss. The back-propagation loss function consists of a linear weighting of the losses for each task [18], as shown in Fig. 1a, which may additionally include purpose-specific losses, e.g., the sparsity and sharing of the architecture [38], or loss of generators [32]. Both the coefficients in the loss function and the complexity of the losses affect the final performance of the MTL. In [36],", + "bbox": [ + 496, + 719, + 893, + 901 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "3644", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "MTL is considered as multi-objective optimisation, searching for the Pareto optimal solutions to avoid a linear weighting of different losses.", + "bbox": [ + 76, + 90, + 468, + 135 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "However, all above mentioned algorithms deal with tasks from the same dataset. In this work, updating of the weight parameters of the supernet for each task is independent, i.e., each task has an independent loss function. Rather than solving multiple tasks that arise naturally, the tasks in our MTL setting come from different datasets, or even have from different data modalities.", + "bbox": [ + 76, + 138, + 467, + 243 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Transfer Learning establishes a mapping from the source domain to the target domain [15]. Model-based transfer learning is shown in Fig. 1b, where the first step pretrains the model on the source dataset and the second step tunes the parameters of the pre-trained model on the target dataset. During the transfer, the model structure is also adjusted to adapt it to the target task [22]. Note that in the proposed framework, the architectural, rather than the weights parameters, is shared.", + "bbox": [ + 75, + 246, + 467, + 381 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Neural Architecture Search has been shown to be effective in the search for network architectures for specific tasks. Three main search strategies have been adopted in NAS, namely reinforcement learning (RL) [6, 53, 57], evolutionary algorithms (EAs) [20, 24, 26, 30, 39], and gradient descent (GD) [25, 41, 43, 45]. With the help of parameter sharing [28], the performance of new neural architectures can be evaluated without training from scratch [31]. It should be pointed out that while parameter sharing can greatly reduce the computation time, it may lead to inaccurate performance assessments of candidate submodels [42] and so-called multi-model forgetting, when multiple models are subsequently trained [2]. Although parameter sharing combined with the mini-batch gradient descent method can further reduce the computation time, promising candidate neural architectures may get lost in evolutionary NAS due to strong fluctuations in performance caused by the mini-batch gradient descent method [50]. Therefore, in our work, a fitness re-evaluation method is proposed to alleviate fitness fluctuations in population iterations.", + "bbox": [ + 75, + 383, + 467, + 686 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Evolutionary Multi-Tasking is proposed for solving numerical optimisation problems. When the function landscapes or optimal solutions of two tasks have a certain degree of similarity, promising candidate solutions belonging to one task may be helpful for the other task. Evolutionary multi-tasking has been extended to multi-objective [27], constrained multi-objective [29], and surrogate-assisted for expensive problems [21], and has been shown to be effective for practical problems such as hyperspectral band selection [10] and multi-scene scheduling [49]. In this work, we use evolutionary multi-tasking for the first time to transfer architectural knowledge across multiple tasks from different datasets, and block-based crossover and bit-based mutation are designed to accommodate the transformation from", + "bbox": [ + 75, + 688, + 467, + 898 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "a continuous space to a discrete space.", + "bbox": [ + 500, + 90, + 753, + 106 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Proposed Work", + "text_level": 1, + "bbox": [ + 500, + 118, + 653, + 135 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Evolutionary Multi-Tasking Optimization", + "text_level": 1, + "bbox": [ + 500, + 143, + 856, + 159 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In an MFEA, each individual in the population belongs to only one of the tasks to be optimized, and knowledge transfer between tasks is realized with crossover at a probability between individuals belonging to different tasks. A multi-tasking optimization problem consisting of $K$ single-objective minimization tasks can be formulated as follows:", + "bbox": [ + 496, + 166, + 890, + 257 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\left\\{ \\begin{array}{l} \\mathbf {x} _ {1} ^ {*}, \\mathbf {x} _ {2} ^ {*}, \\dots , \\mathbf {x} _ {K} ^ {*} \\end{array} \\right\\} = \\left\\{\\operatorname {a r g m i n} f _ {1} (\\mathbf {x} _ {1}), \\operatorname {a r g m i n} f _ {2} (\\mathbf {x} _ {2}), \\dots , \\operatorname {a r g m i n} f _ {K} (\\mathbf {x} _ {K}) \\right\\} \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 532, + 265, + 888, + 301 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $f_{k}(\\mathbf{x}_{k}), k = 1,2,\\ldots ,K$ is the $k$ -th task. $\\mathbf{x}_k^* = (x_{k,1}^*,x_{k,2}^*,\\dots,x_{k,D_M}^*)$ , $k = 1,2,\\ldots ,K$ is the optimal solution of the $k$ -th task, $D_{M}$ is the dimension of the $k$ -th task.", + "bbox": [ + 498, + 309, + 890, + 368 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. Search Space and Architecture Encoding", + "text_level": 1, + "bbox": [ + 500, + 377, + 849, + 393 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "To facilitate the transfer of architectural knowledge between multiple tasks, the same search space is used for multiple tasks, i.e., the candidate architectures are consistent for each task. Similar to [57], the search space is based on normal and reduced cells. And the optional operations in each block include depthwise-separable convolution, dilated convolution, max pooling, average pooling and identity. The chromosome of each individual encodes the structure of the block, i.e., four integer bits (the first two encoding the inputs, and the last two the operation) represent a block. The coding of the five blocks constitutes a cell coding. Since two types of cells are used, 40 integers in total are used to represent each neural architecture. More details can be found in Supplementary Material A.", + "bbox": [ + 496, + 401, + 890, + 612 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.3. EMT-NAS", + "text_level": 1, + "bbox": [ + 500, + 619, + 616, + 633 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The overall framework of the proposed EMT-NAS is presented in Fig. 3, where an evolutionary algorithm searches for optimal neural architectures for two different tasks at the same time. The main components of EMT-NAS are in the upper panel of Fig. 3, which is composed of randomly generated initial population, offspring generation by means of crossover and mutation according to the parents' skill factor $\\tau$ (see Section 3.4), and a top $K$ selection for each task as the environmental selection. The full pseudo code and a detailed description of EMT-NAS can be found in Supplementary Material B.", + "bbox": [ + 496, + 643, + 890, + 809 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Each task has a set of supernet weights that do not affect each other. Sampled training is a method for continuous updating of the supernet weights on the training set based on weight sharing. For each mini-batch of the training data of each task at one epoch, one individual (representing one candidate architecture) belonging to this task will", + "bbox": [ + 496, + 810, + 890, + 898 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "3645", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/96534d886ebf24e08b2a18ee706a51030d6c7bfbf5756d38a4844655490b53f1.jpg", + "image_caption": [ + "Figure 3. The flow chart of EMT-NAS, where two tasks are used as an example. The difference with the single-tasking evolutionary algorithm is that each individual in the population may belong to the same or different tasks. In addition, each task has a separate set of weights for the supernet. The lower panel shows the sampled training based on a weight sharing method on the training set and the sampled evaluation based on a fitness re-evaluation method on the validation set. Best viewed in colour." + ], + "image_footnote": [], + "bbox": [ + 80, + 89, + 890, + 325 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/6eb7b4623c8652793aa6b1a368c0be052fcfe62e58f0ddfead2c17441629e594.jpg", + "image_caption": [ + "Figure 4. Block-based crossover and bit-based mutation." + ], + "image_footnote": [], + "bbox": [ + 78, + 390, + 472, + 511 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "be randomly sampled and trained on the mini-batch using the gradient based method. After training, sampled evaluating computes the fitness of the individual by calculating the classification accuracy on the validation data of the same task. Each individual is evaluated once on a random minibatch of the corresponding task validation dataset. Hence, the computational cost of training the weighting parameters and evaluating the fitness can be significantly reduced.", + "bbox": [ + 75, + 542, + 468, + 664 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.4. Offspring Generation", + "text_level": 1, + "bbox": [ + 76, + 676, + 279, + 694 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Transfer of useful knowledge between tasks is the key reason for EMT-NAS to enhance its performance. As in MFEAs, knowledge transfer in EMT-NAS is realised through simultaneously evolving neural architectures for multiple related tasks in one population. More specifically, knowledge exchange across the tasks is achieved by performing crossover on individuals optimizing architectures on different tasks.", + "bbox": [ + 75, + 702, + 468, + 821 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In reproduction, two parents will be selected each time at a probability proportional to the individuals' fitness value. That is, the greater the fitness of an individual, the larger chance it will have to produce offspring. If the two selected parents belong to the same task, then crossover will be car", + "bbox": [ + 75, + 825, + 470, + 902 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "ried out to generate two offspring, both inheriting the same skill factor $\\tau$ of their parents. In addition, mutation will also be applied to the two offspring to promote exploration.", + "bbox": [ + 496, + 393, + 890, + 441 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "When the pair of the selected parent individuals belong to different tasks, two different procedures will be carried out according to a predefined probability, called random mating probability (RMP). If a randomly generated number between 0 and 1 is less than $RMP$ , a crossover operator will be applied to the two parents to generate two offsprings, which are then mutated. The two tasks of the parents will be randomly assigned to one of the offsprings at an equal probability. At a probability of 1- $RMP$ , only mutations will be performed on each of the two parents to generate two offsprings. Consequently, the skill factor $\\tau$ of each offspring is the same as that of its parent. The probability threshold $RMP$ is a parameter to be specified by the user and a sensitivity analysis of $RMP$ will be provided in the experimental Section 4.6.", + "bbox": [ + 496, + 450, + 892, + 676 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Illustrative examples of the crossover and mutation are given in Fig. 4. For clarity, we only show a segment of the parent chromosome consisting of three blocks. There is a strong correlation between the input source and the operation of the connection, which has a great impact on the performance of the network structure [50]. In block-based crossover, the parent chromosomes $p_1$ and $p_2$ , in blocks, are swapped at less than the crossover probability $CP$ to generate offspring $q_1$ and $q_2$ . In bit-based mutation, the parent chromosome $q_i$ , in bits, is randomly replaced from the candidate space at less than the mutation probability $MP$ , generating offspring $o_i$ . This is done by changing the input source or operation to improve the performance of the network architecture.", + "bbox": [ + 496, + 689, + 892, + 898 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "3646", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/486aa3e56a443a1e8e1fdc35b68998a25f0d6ec700e8ae48d647d93ca84a8a0f.jpg", + "image_caption": [ + "(a)" + ], + "image_footnote": [], + "bbox": [ + 81, + 88, + 279, + 215 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/5c1060720207f624fe4f6a3922124bd663df40bf790a301d1edef562caaf400f.jpg", + "image_caption": [ + "(b)" + ], + "image_footnote": [], + "bbox": [ + 282, + 88, + 480, + 215 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/0b1d377c5c34b72f55e1e08a4cc4763f32b7c062c9e5374bb8e6714b5da0918f.jpg", + "image_caption": [ + "(c)" + ], + "image_footnote": [], + "bbox": [ + 80, + 234, + 279, + 359 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/d5c62122fac71a25ab75d7025ec0ba0fdf5d8dbd5019cb5f3938b1a9f5cc6697.jpg", + "image_caption": [ + "(d)", + "Figure 5. Empirical evaluations of the proposed fitness re-evaluation method on CIFAR-10 and CIFAR-100. In the figures, the red dashed lines denote the estimated fitness based on the sampled evaluation without re-evaluation ((a) and (b)) and with the proposed re-evaluation ((c) and (d)), while the blue solid lines denote the true fitness based on an accurate evaluation using all validation data. From these results, we can see that strong fluctuations in the true fitness of the network have been reduced when the proposed fitness re-evaluation is adopted." + ], + "image_footnote": [], + "bbox": [ + 282, + 234, + 480, + 359 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.5. Fitness Re-evaluation", + "text_level": 1, + "bbox": [ + 76, + 513, + 277, + 529 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "There are two important reasons why the fitness re-evaluation method was proposed. First, when using the mini-batch gradient descent training, the sign of the gradient resulting from each mini-batch data may be inconsistent. Consequently, the performance of a network estimated using the sampled evaluating may fluctuate strongly over the generations. Second, such fluctuations are made even more serious because of parameter sharing adopted in training.", + "bbox": [ + 75, + 537, + 468, + 659 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "To examine this issue more closely, we plot the fitness (the validation accuracy) of the best individual from a typical run of evolutionary NAS on CIFAR-10 and CIFAR-100 simultaneously in Figs. 5a and 5b. We can observe that there is a big difference between the estimated and true validation accuracies and the true performance fluctuates strongly over the generations. As a result, promising individual may get lost because of the strong fitness fluctuations and inaccurate sampled evaluations.", + "bbox": [ + 75, + 660, + 468, + 796 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "To alleviate strong fluctuations in the fitness, we propose to use the fitness of the corresponding parent individual to modify the fitness of the offspring so that the increase or decrease will become less dramatic. Thus, the fitness of an offspring is modified as follows:", + "bbox": [ + 75, + 796, + 468, + 872 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nF = F _ {p} + \\left(F _ {o} - F _ {p}\\right) \\times \\log_ {T} t \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 169, + 883, + 468, + 902 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where, $F_{o}, F_{p}, F$ are the fitness value of the offspring, the fitness of the parent that generates the offspring, and the modified fitness of the offspring; $t = 2,\\dots ,T$ is the current generation, and $T$ is the maximum number of generations. We call the modification of the offspring fitness according to Equation (2) fitness re-evaluation.", + "bbox": [ + 496, + 90, + 890, + 180 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The logarithmic function in Eq. 2 is based on $T$ , which increases to 1.0 as $t$ increases. Thus, $F_{o} - F_{p}$ will be penalised by the logarithm function. Now we re-run the evolutionary NAS on the two tasks (CIFAR-10 and CIFAR-100) by applying the fitness re-evaluation method, and the true fitness as well as the re-evaluated fitness using the sampled validation of the best individual are plotted in Figs. 5c and 5d. From these results, we can see that the individual's true fitness value improves more steadily when the proposed fitness re-evaluation method is adopted, indicating that the modified fitness evaluated based on the sampled evaluating can better reflect the true fitness of the individuals.", + "bbox": [ + 496, + 181, + 892, + 363 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Experimental Results", + "text_level": 1, + "bbox": [ + 498, + 378, + 705, + 395 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.1. Experimental Settings", + "text_level": 1, + "bbox": [ + 500, + 402, + 705, + 420 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "To validate the effectiveness of our approach, we set single-tasking (evolutionary single-tasking based NAS) as the baseline. Most of the experiments are conducted on MedMNIST [44], which is a collection of 10 preprocessed medical datasets. We selected the PathMNIST dataset of colon pathology, OrganMNIST_Axial, OragnMNIST_Coronal, and OrganMNIST_Sagittal through different processing methods in abdominal CT along three axes. We use these four tasks to construct multitasks with task numbers of 2, 3 and 4, respectively. We also conduct experiments on CIFAR-10 and CIFAR-100 [19], and then transfer the searched best network architecture to ImageNet [34] to explore its effectiveness. For the sake of simplicity, we denote PathMNIST, OrganMNIST_Axial, OragnMNIST_Coronal, OrganMNIST_Sagittal, CIFAR-10, and CIFAR-100 as Path, Organ_A, Organ_C, Organ_S, C-10, and C-100. Similar to [57], the cross-entropy loss function is used for the six tasks and the parameter settings are presented in Table 1 for the search phase. For fair comparisons, the same parameters as in EMT-NAS are maintained for single tasks during the search phase and retraining phase. All experiments are statistical results of five independent runs with an exception to the results on ImageNet, where all experiments were run once only on 1 Nvidia GeForce RTX 2080Ti due to limited computational resources. More details are given in Supplementary Material C.", + "bbox": [ + 496, + 428, + 892, + 820 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.2. Medical Multi-Tasking", + "text_level": 1, + "bbox": [ + 500, + 830, + 712, + 848 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Here, we evaluate the network architectures searched by Single-Tasking and EMT-NAS on the medical multitasking. The results when the number of tasks varies from two to", + "bbox": [ + 500, + 854, + 890, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "3647", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/31d8ac57486bd4844225057e3d71e2734215582af68b40d5338ac3b676f18436.jpg", + "table_caption": [ + "Table 1. A summary of hyper-parameter settings." + ], + "table_footnote": [], + "table_body": "
CategoriesParametersSettings (MedMNIST/CIFAR)
Search spaceInitial channels48/20
Repetitions of cells1
Gradient descentBatch size for training128
Batch size for validation1000
Weight decay1.00E-04
Dropout0.1
Momentum0.9
Initial learning rate0.1
Learning rate scheduleCosine Annealing
Search strategyPopulation size20
Generations100/300
Random mating probability0.3
Crossover probability1.00
Mutation probability0.02
", + "bbox": [ + 83, + 104, + 460, + 263 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/131db406ea04dd3de8a63ce8e61f6907ec440ddd986d9c87e92cc00c04c4a386.jpg", + "table_caption": [ + "Table 2. Comparison on MedMNIST." + ], + "table_footnote": [], + "table_body": "
Index# TasksModelPath (%)Organ_A (%)Organ_C (%)Organ_S (%)GPU Days (%) ↓
1ResNet-18 [11]84.492.188.976.2
1ResNet-50 [11]86.491.689.374.6
1Auto-skearn [8]18.656.367.660.1
1AutoKeras [16]86.492.991.580.3
1AutoML [56]81.181.886.170.6
1SI-EvoNAS [50]90.5±0.793.0±0.391.8±0.480.1±0.3
1Single-Tasking (Baseline)87.4±2.994.0±0.791.5±0.880.7±0.5+00.0
①2EMT-NAS (Ours)91.6±0.595.1±0.2-11.0
②2EMT-NAS (Ours)91.2±0.792.3±0.3-18.4
③2EMT-NAS (Ours)90.5±0.981.5±0.2-12.8
④2EMT-NAS (Ours)94.8±0.592.2±0.5-28.4
⑤2EMT-NAS (Ours)95.0±0.381.3±0.5-23.2
⑥2EMT-NAS (Ours)92.2±0.381.5±0.2-40.1
⑦3EMT-NAS (Ours)95.3±0.392.3±0.281.7±0.4-36.0
⑧3EMT-NAS (Ours)91.4±0.392.3±0.381.8±0.3-29.9
⑨3EMT-NAS (Ours)91.9±0.295.0±0.281.4±0.3-23.3
⑩3EMT-NAS (Ours)91.7±0.695.0±0.492.5±0.2-25.1
⑪4EMT-NAS (Ours)91.2±0.694.9±0.392.2±0.381.4±0.5-31.4
", + "bbox": [ + 78, + 285, + 467, + 479 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "four in comparison to the corresponding single tasks are given in Table 2. In the top rows of the table, the results of the first five results on the four medical datasets taken from [44] are listed. SI-EvoNAS [50] is a state-of-the-art evolutionary NAS algorithm. Single-Tasking is an evolutionary single-tasking algorithm that we have implemented as the baseline. In column GPU Days (\\%), the reduction in the runtime of EMT-NAS relative to the corresponding Single-Tasking are listed as a percentage.", + "bbox": [ + 75, + 491, + 467, + 627 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "From Table 2, it is clear that the classification accuracy of the neural architectures found by EMT-NAS is higher than the networks found by all single-tasking NAS on the corresponding tasks, and the search time is reduced by $11\\% - 40\\%$ compared to the baseline. This demonstrates that it is possible to improve the performance of each task through architectural knowledge transfer only. In addition, the best classification accuracy of the network architecture has been obtained when the number of tasks is three. This shows that which tasks and how many tasks are formulated as a multi-tasking problem will influence the performance of algorithm in solving each of the individual tasks.", + "bbox": [ + 75, + 628, + 467, + 808 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Multi-tasking with the same data modality: EMT-NAS (numbered ④, ⑤, ⑥, ⑦) searched for network architectures with a higher classification accuracy than those found by Single-Tasking. As described in [44], crop 2D images from the center slices of the 3D CT bounding boxes in axial/coronal/sagittal views (planes) are obtained in datasets", + "bbox": [ + 75, + 809, + 467, + 900 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Organ_A, Organ_C, and Organ_S. Therefore, these datasets are correlated, and it is reasonable to make use of the common knowledge of these datasets to improve classification accuracy. In addition, ⑦ VS ④, ⑤ and ⑥, respectively, have the best performance on Organ_A, Organ_C, and Organ_S. This demonstrates that the three tasks enhance each other to a greater extent than two by two. Therefore, architectural knowledge transfer works well for different datasets of the same data modality.", + "bbox": [ + 496, + 90, + 890, + 226 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Multi-tasking with different data modalities: The classification accuracy of EMT-NAS (numbered ①, ②, ③, ⑧, ⑨ and ⑩) are slightly higher than that of EMT-NAS (numbered ④, ⑤ and ⑥) on Organ_A, Organ_C, and Organ_S datasets, respectively. From [44], we know that Path is for predicting survival from colorectal cancer histology slides, which means that Organt_A, Organ_C, and Organ_S can benefit more from Path. By contrast, EMT-NAS has transferred different degrees of useful knowledge from Organ_A, Organ_C, and Organ_S, respectively, to Path. From the table, we can observe that the classification accuracy of EMT-NAS (numbered ①, ② and ③) decreases sequentially on PATH. Organ_A, Organ_C, and Organ_S are obtained by different processing methods in abdominal CT along three axes, so their data characteristics are different. Clearly, Path and Organ_A are most beneficial to each other. This also corroborates with the task relational analysis in Fig. 2. Therefore, although these datasets are from different data modalities and are weakly correlated, they can still improve their respective performance through architectural knowledge transfer.", + "bbox": [ + 496, + 227, + 890, + 545 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.3. CIFAR-10 and CIFAR-100", + "text_level": 1, + "bbox": [ + 500, + 556, + 741, + 571 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We again used RSA in Fig. 2 to analyse the task relatedness between C-10 and C-100, with a task relatedness score of 0.38. C-100 is made up of 20 classes (each containing five subclasses), while C-10 is 10 classes. The results show that ResNet-50, trained on C-100, extracts many different features from the same image compared to those trained on C-10. Therefore, C-10 and C-100 are differentiated.", + "bbox": [ + 496, + 580, + 890, + 686 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "The representative algorithms can be roughly divided into four categories, namely manually designed, RL-based, GD-based, and EAs-based. The comparative results on C-10 and C-100 are listed in Table 3. Note that all algorithms are meant for single-tasking search, i.e., they either search for an optimal network architecture on C-10 and C-100, respectively, or search on C-10 and then the found architectures are transferred to C-100. By contrast, EMT-NAS searches for optimal neural architectures simultaneously on C-10 and C-100, and therefore, the GPU days of EMT-NAS is the total time for searching for both architectures.", + "bbox": [ + 496, + 688, + 890, + 853 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "In Table 3, EMT-NAS stacks normal blocks twice, while EMT-NAS† stacks three times. EMT-NAS searched the network architecture's on C-10 and C-100 with a higher clas", + "bbox": [ + 496, + 854, + 890, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "3648", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/45916bf790a6b5caaf4496d5f29b739cb758921f3086323c28dc405ab4984f4b.jpg", + "table_caption": [ + "Table 3. Comparison on C-10 and C-100. * indicates that the same network architecture is used on both C-10 and C-100, so their GPU days for searching are the same. † indicates normal cell stacking three times for better performance." + ], + "table_footnote": [], + "table_body": "
ModelSearch MethodGPU DaysParams (M)C-10 (%)Params (M)C-100 (%)
Wide ResNet [47]manual-36.595.83*79.50
DenseNet [14]manual-27.296.26*80.75
MobileNetV2 [35]manual-2.194.56*77.09
PNAS [23]SMBO1503.296.59±0.09*80.47
ENAS [28]RL0.454.697.11*80.57
NASNet-A [57]RL20003.397.35--
Block-QNN-Faster [53]RL0.83.996.43*81.79
DARTS [25]GD1.53.397.00±0.14*79.48±0.31
SNAS [41]GD1.52.997.02--
large-scale Evo [31]EA27505.494.640.477
Hier-EA [24]EA3006496.25±0.12--
Amoebanet-A [30]EA31503.296.66±0.06*81.07
AE-CNN [39]EA27/36295.75.479.15
SHEDA-CNN [20]EA0.58/0.9710.8896.3618.6478.84
Single-Tasking (Baseline)EA0.461.8396.24±0.201.6879.70±0.44
Single-Tasking† (Baseline)EA0.462.4196.64±0.182.1980.82±0.71
EMT-NAS (Ours)EA0.422.1796.73±0.152.2381.86±0.10
EMT-NAS† (Ours)EA0.422.9197.04±0.042.9782.60±0.38
", + "bbox": [ + 76, + 146, + 480, + 354 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "sification accuracy than Single-Tasking (baseline), demonstrating that architecture knowledge transfer can effectively improve performance on C-10 and C-100. Compared to other NAS algorithms, our approach achieves better performance and more compact network architectures searched on C-10 and C-100 through architectural knowledge transfer, except for ENAS and NASNet-A on C-10. However, the models found by EMT-NAS have only two-thirds the number of parameters of models found by ENAS. On the other hand, NASNet-A consumes about 4,700 times more GPU days than EMT-NAS. These indicate that our approach can achieve a good performance-complexity trade-off. We also analysed two baselines for joint training (shared or unshared network architectures) in Supplementary Material D. The performance of the algorithms has degraded as data from different tasks are used to update the same supernet.", + "bbox": [ + 75, + 367, + 473, + 609 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.4. Transferability to ImageNet", + "text_level": 1, + "bbox": [ + 76, + 619, + 328, + 636 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "As done in [25], we transferred the best network architectures found on C-10 and C-100 to ImageNet for training from scratch, to further validate the transferability of the architectures searched by EMT-NAS. The results comparing EMT-NAS with 15 models (or their variants) on ImageNet are given in Table 4. EMT-NAS-4-C-100 has a lower number of model parameters (2.49M) than all compared algorithms, while it has a higher top-1 accuracy (74.25%) except for MoblieNet-V3, MobileNetV2-1.0+CA, RepVGG-A1, AutoSpace, PC-DARTS and MUXNet-m. For better performance, we change the number of normal cells stacked from two to three to get EMT-NAS-C-100†. The top-1 accuracy of EMT-NAS-C-100† is 75.44%, which again surpasses the accuracy of the rest of the algorithms, and the number of model parameters is 3.25M. This demonstrates that EMT-NAS has good transferability between the network architectures searched on C-10 and C-100.", + "bbox": [ + 75, + 643, + 470, + 900 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/514331c98e3ddf95a47f8bea10accc2c4d657983d5582bbfda96c0e25075061d.jpg", + "table_caption": [ + "Table 4. Comparisons on ImageNet. $\\dagger$ indicates normal cell stacking three times for better performance." + ], + "table_footnote": [], + "table_body": "
ModelTop-1 (%)Top-5 (%)Params (M)GPU DaysSearch Method
ShuffleNet 2.0 [51]73.7-5.4-manual
MobileNet-V3 [13]75.2-5.1-manual
MobileNeXt-0.75 [54]72.6-2.5-manual
MobileNetV2-1.0+CA [12]74.3-3.95-manual
RepVGG-A1 [5]74.46-12.78-manual
PNAS [23]74.291.95.1225SMBO
NASNet-A [57]74.091.65.32000RL
DPP-Net-Panacea [6]74.291.794.88RL
AutoSpace [55]75.3-4.38.33RL
DARTS [25]73.391.34.74GD
SNAS [41]72.791.84.31.5GD
PC-DARTS [43]74.992.25.30.1GD
HourNAS-C [45]74.191.64.80.1GD
Amoebanet-A [30]74.592.05.13150EA
MUXNet-m [26]75.392.53.4176EA
Single-Tasking-C-10 (Baseline)73.1891.222.410.23EA
Single-Tasking-C-100 (Baseline)72.8891.062.250.22EA
Single-Tasking-C-10† (Baseline)74.5992.093.150.23EA
Single-Tasking-C-100† (Baseline)74.1191.862.970.22EA
EMT-NAS-C-10 (Ours)73.8391.632.380.42EA
EMT-NAS-C-100 (Ours)74.2591.802.49
EMT-NAS-C-10† (Ours)75.1192.393.130.42EA
EMT-NAS-C-100† (Ours)75.4492.553.25
", + "bbox": [ + 511, + 119, + 879, + 376 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.5. Ablation Studies", + "text_level": 1, + "bbox": [ + 500, + 388, + 663, + 402 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "To verify the effectiveness of the evolutionary multitasking NAS algorithm and the fitness re-evaluation method, four algorithms are compared, namely evolutionary single-Tasking NAS, which serves as the baseline (denoted as Single-tasking in Table 5), evolutionary single-tasking NAS with the fitness re-evaluation method, called Single-Tasking+Reeval, evolutionary multi-tasking NAS without fitness re-evaluation, called Multi-Tasking, and evolutionary multi-tasking NAS with the fitness re-evaluation method, denoted as Multi-Tasking+Reeval.", + "bbox": [ + 496, + 412, + 890, + 564 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Evolutionary Multi-Tasking: By comparing the results of Single-tasking and Multi-Tasking (③ vs ① and ④ vs ②), evolutionary multi-tasking NAS can improve the performance on both C-10 and C-100, confirming the effectiveness of knowledge transfer when simultaneously searching for the optimal neural architectures on similar tasks.", + "bbox": [ + 496, + 565, + 890, + 655 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Fitness Re-Evaluation: By comparing the results with and without fitness re-evaluation (④ vs ③ and ② vs ①), we can see that the proposed fitness re-evaluation method improves the performance on both C-10 and C-100. This confirms that the fitness re-evaluation method is effective in enhancing the performance by alleviating fitness fluctuations in the search based on sampled evaluations.", + "bbox": [ + 496, + 657, + 890, + 762 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Search Efficiency: We take the total runtime of Single-Tasking, and count the percentage increase or decrease of the other three algorithms relative to it. We also calculate three parts of the runtime, including time for training model parameters on the training dataset, time for evaluating model performance on the validation dataset, and time for searching. First, we note that the time taken by the evolutionary multi-tasking is reduced by $50\\%$ compared to single-tasking(③ vs ① and ④ vs ②). Because the compu", + "bbox": [ + 496, + 763, + 890, + 901 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "3649", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/25002e73628439e61748e584c81f806c605ef4f2ef6f3f9e1645dfae13726e66.jpg", + "table_caption": [ + "Table 5. Comparison of evolutionary single- and multi-tasking optimisation with/without fitness re-evaluation on CIFAR-10 and -100." + ], + "table_footnote": [], + "table_body": "
IndexAlgorithmTask 1Task 2Total Time (%) ↓Training Time (%) ↓Evaluation Time (%) ↓Search Time (%) ↓Average Params (M)Average FLOPs (M)
C-10 (%)Params (M)Transfer (%)C-100 (%)Params (M)Transfer (%)
①Single-Tasking96.23±0.201.8396.07±0.2579.70±0.441.6878.95±0.60+0.0+0.0+0.0+0.01.83334
②Single-Tasking+Reeval96.29±0.251.7496.26±0.1880.48±0.281.9078.77±0.65-5.1-4.1-15.1-1.41.81323
③Multi-Tasking96.49±0.162.02-80.68±0.432.03--2.1+3.8-37.4-49.42.06382
④Multi-Tasking+Reeval96.73±0.152.17-81.86±0.102.23--8.7-4.0-35.9-51.61.97355
", + "bbox": [ + 96, + 104, + 870, + 181 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "tational complexity of the Evolutionary Multi-Tasking and Single-Tasking algorithms is almost the same, except for the time spent on training and evaluation. Second, $③$ vs $①$ and $④$ vs $②$ , the time spent on the evaluation is reduced by about $36\\%$ . The population size and the number of generations are the same for single and multi-tasking, i.e., the number of fitness evaluations is the same, so that the total time to optimise multiple tasks simultaneously will be less than the sum of the runtimes when the tasks are optimised one by one. Finally, $④$ vs $③$ and $②$ vs $①$ with a small percentage reduction in the training time. To investigate this further, we reproduce the sampled training process and chose two model metrics, namely the number of parameters and the number of floating point operations (FLOPs). Specifically, when each network architecture was trained once, two metrics were recorded until five runs of the algorithm have stopped, and then averaged and listed in the column Average Params $(M)$ and Average FLOPs $(M)$ of Table 5, respectively. The results show a small reduction in the average number of parameters and the average FLOPs for both $④$ vs $③$ and $②$ vs $①$ . It is assumed that the fitness re-evaluation method allows the algorithm to favour network architectures consisting of operations with a small number of parameters or a low computational complexity in the search process. This may explain the fact that introducing the fitness re-evaluation method can reduce the time spent by the model on the training set by a small amount. Overall, EMT-NAS consumes less runtime than its single-task counterparts.", + "bbox": [ + 76, + 191, + 472, + 628 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Model Transferability: We transferred the network architectures that Single-tasking and Single-tasking+Reeval searched on C-10 and C-100, respectively, to C-100 and C-10 for retraining. The results are presented in column Transfer $(\\%)$ , which show that through transfer learning, the performance of the network architectures on the new dataset is much lower than that of the network architectures obtained by evolutionary multi-tasking NAS (Multi-Tasking and Multi-Tasking+Reeval) search. Therefore, evolutionary multi-tasking NAS is more competitive than evolutionary single-tasking NAS with transfer learning.", + "bbox": [ + 75, + 631, + 470, + 799 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.6. Sensitivity Analysis", + "text_level": 1, + "bbox": [ + 76, + 814, + 264, + 830 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In EMT-NAS, $RMP$ is a key parameter that controls the degree of knowledge transfer between tasks. Here, we set the random mating probability $RMP = 0, 0.1, 0.2, 0.3, 0.4, 0.5$ and note that when $RMP = 0$ , two", + "bbox": [ + 75, + 839, + 470, + 900 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/e85998df59d8d6303f4f1571bf0eaf6290ddccebbcf3f498b588845c5eee44df.jpg", + "table_caption": [ + "Table 6. Comparison of EMT-NAS when random mating probability is set to 0, 0.1, 0.2, 0.3, 0.4, and 0.5." + ], + "table_footnote": [], + "table_body": "
RMPTask 1Validation ACC (%)Test ACC (%)Task 2Validation ACC (%)Test ACC (%)
0C-1088.36±0.6996.28±0.09C-10061.48±1.6580.31±0.40
0.1C-1087.36±1.6096.48±0.18C-10058.85±4.1080.46±0.71
0.2C-1088.32±1.0296.52±0.18C-10059.67±0.4781.11±0.54
0.3C-1088.76±1.0596.73±0.15C-10061.69±2.1581.86±0.10
0.4C-1088.09±1.2596.49±0.18C-10061.27±3.0981.26±0.27
0.5C-1088.52±1.1696.52±0.17C-10061.42±2.5781.15±0.31
", + "bbox": [ + 522, + 219, + 867, + 305 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "single tasks run in the same population without any knowledge transfer between the tasks. Table 6 shows that the validation and test accuracies increase as $RMP$ increases in the beginning, and then decrease as $RMP$ becomes larger, indicating that too much or too little knowledge transfer between tasks can degrade the performance of EMT-NAS. The best performance was achieved on the validation set and test set when $RMP = 0.3$ .", + "bbox": [ + 496, + 320, + 890, + 439 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We also analysed the influence of the population size, crossover and mutation probabilities, and the number of generations on the performance. The results are presented in Supplementary Material E.", + "bbox": [ + 496, + 441, + 893, + 503 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 523, + 619, + 539 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this work, evolutionary multi-tasking is applied to NAS for the first time. Extensive experiments have demonstrated that for multiple classification tasks from different datasets (data modalities), architectural knowledge transfer and fitness re-evaluation method allow EMT-NAS to outperform each task obtained simultaneously over a single task, and that the runtime of EMT-NAS is less than the sum of the runtimes of solving multiple single tasks independently. Although this work achieves implicit architectural knowledge transfer, more precise, explicit knowledge transfer between tasks in evolutionary multi-tasking NAS is desirable and will be investigated in the future.", + "bbox": [ + 496, + 550, + 890, + 731 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgment", + "text_level": 1, + "bbox": [ + 500, + 752, + 651, + 768 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "This work is supported by National Natural Science Foundation of China (62136003, 61988101), the Programme of Introducing Talents of Discipline to Universities (the 111 Project) under Grant B17017, Fundamental Research Funds for the Central Universities (222202317006) and Shanghai AI Lab. Y. Jin is supported by an Alexander von Humboldt Professorship for AI endowed by the German Federal Ministry of Education and Research.", + "bbox": [ + 496, + 779, + 890, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "3650", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Shai Ben-David and Reba Schuller Borbely. A notion of task relatedness yielding provable multiple-task learning guarantees. Machine learning, 73(3):273-287, 2008. 2", + "[2] Yassine Benyahia, Kaicheng Yu, Kamil Bennani Smires, Martin Jaggi, Anthony C Davison, Mathieu Salzmann, and Claudiu Musat. Overcoming multi-model forgetting. In International Conference on Machine Learning, pages 594-603. PMLR, 2019. 3", + "[3] Rich Caruana. Multitask learning. 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In Proceedings of the IEEE Conference on Computer Vision and Pattern Recognition (CVPR), pages 8697-8710, 2018. 3, 5, 7" + ], + "bbox": [ + 78, + 90, + 468, + 373 + ], + "page_idx": 10 + }, + { + "type": "page_number", + "text": "3653", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 10 + } +] \ No newline at end of file diff --git a/2023/EMT-NAS_Transferring Architectural Knowledge Between Tasks From Different Datasets/f54bf63e-2702-4fdf-815c-53bb8912c6fe_model.json b/2023/EMT-NAS_Transferring Architectural Knowledge Between Tasks From Different Datasets/f54bf63e-2702-4fdf-815c-53bb8912c6fe_model.json new file mode 100644 index 0000000000000000000000000000000000000000..349f2ee1a12d5a5db9d1893817618cc36a29ed0b --- /dev/null +++ b/2023/EMT-NAS_Transferring Architectural Knowledge Between Tasks From Different Datasets/f54bf63e-2702-4fdf-815c-53bb8912c6fe_model.json @@ -0,0 +1,2147 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.092, + 0.13, + 0.88, + 0.175 + ], + "angle": 0, + "content": "EMT-NAS:Transferring architectural knowledge between tasks from different datasets" + }, + { + "type": "text", + "bbox": [ + 0.368, + 0.203, + 0.674, + 0.221 + ], + "angle": 0, + "content": "Peng Liao\\(^{1}\\), Yaochu Jin\\(^{1,2*}\\), Wenli Du\\(^{1*}\\)" + }, + { + "type": "text", + "bbox": [ + 0.089, + 0.222, + 0.956, + 0.258 + ], + "angle": 0, + "content": "1 Key Laboratory of Smart Manufacturing in Energy Chemical Process, Ministry of Education, ECUST, China \n2 Faculty of Technology, Bielefeld University, Germany" + }, + { + "type": "text", + "bbox": [ + 0.193, + 0.26, + 0.851, + 0.275 + ], + "angle": 0, + "content": "pengliao@mail.ecust.edu.cn, yaochu.jin@uni-bielefeld.de, wldu@ecust.edu.cn" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.309, + 0.314, + 0.327 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.341, + 0.474, + 0.766 + ], + "angle": 0, + "content": "The success of multi-task learning (MTL) can largely be attributed to the shared representation of related tasks, allowing the models to better generalise. In deep learning, this is usually achieved by sharing a common neural network architecture and jointly training the weights. However, the joint training of weighting parameters on multiple related tasks may lead to performance degradation, known as negative transfer. To address this issue, this work proposes an evolutionary multi-tasking neural architecture search (EMT-NAS) algorithm to accelerate the search process by transferring architectural knowledge across multiple related tasks. In EMT-NAS, unlike the traditional MTL, the model for each task has a personalised network architecture and its own weights, thus offering the capability of effectively alleviating negative transfer. A fitness re-evaluation method is suggested to alleviate fluctuations in performance evaluations resulting from parameter sharing and the mini-batch gradient descent training method, thereby avoiding losing promising solutions during the search process. To rigorously verify the performance of EMT-NAS, the classification tasks used in the empirical assessments are derived from different datasets, including the CIFAR-10 and CIFAR-100, and four MedMNIST datasets. Extensive comparative experiments on different numbers of tasks demonstrate that EMT-NAS takes \\(8\\%\\) and up to \\(40\\%\\) on CIFAR and MedMNIST, respectively, less time to find competitive neural architectures than its single-task counterparts." + }, + { + "type": "title", + "bbox": [ + 0.079, + 0.794, + 0.21, + 0.81 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.82, + 0.47, + 0.866 + ], + "angle": 0, + "content": "Many neural architecture search (NAS) algorithms [8, 16, 23, 56] have shown better performance on a specific task than manually designed deep neural networks [11, 14," + }, + { + "type": "image", + "bbox": [ + 0.501, + 0.309, + 0.716, + 0.534 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.719, + 0.309, + 0.888, + 0.534 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.536, + 0.895, + 0.744 + ], + "angle": 0, + "content": "Figure 1. Conceptual differences between our work and two main existing methodologies for two-task learning. (a) Existing multi-task NAS typically handles multiple tasks such as semantic segmentation and surface normal prediction on the same dataset, where the loss function contains losses for multiple tasks, resulting in a network architecture that shares a common set of weight parameters. (b) Model-based transfer learning trains a network architecture on a source dataset and then transfers it to a target dataset by fine-tuning the weights using a separate loss function. (c) EMT-NAS simultaneously optimises multiple classification tasks from different datasets using a separate loss function for each task, resulting in an individual network architecture and corresponding weights for each task. EMT-NAS aims to optimise each task separately while sharing the knowledge of good network architectures to facilitate the optimisation of each task. Best viewed in colour." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.762, + 0.893, + 0.823 + ], + "angle": 0, + "content": "35, 51]. However, when the task (or dataset) changes, the NAS algorithm needs to be run again to find a new optimal network architecture for the new task, which is typical for single-task learning (STL)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.826, + 0.894, + 0.903 + ], + "angle": 0, + "content": "By contrast, it has been shown that simultaneously learning multiple related tasks, known as multi-task learning (MTL) is beneficial [3, 52]. One class of MTL focuses on designing or training a single network to jointly solve multiple tasks formed by scene understanding (the same" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.876, + 0.223, + 0.888 + ], + "angle": 0, + "content": "*Corresponding author." + }, + { + "type": "page_footnote", + "bbox": [ + 0.103, + 0.889, + 0.431, + 0.9 + ], + "angle": 0, + "content": "Code: https://github.com/PengLiao12/EMT-NAS" + }, + { + "type": "list", + "bbox": [ + 0.096, + 0.876, + 0.431, + 0.9 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "3643" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.091, + 0.473, + 0.395 + ], + "angle": 0, + "content": "dataset) [38, 46], such as the NYU v2 dataset [37], the CityScapes dataset [4], and the Taskonomy dataset [48]. These tasks consist of semantic segmentation, surface normal prediction, depth prediction, keypoint detection and edge detection, which are known as multiple tasks that arise naturally [3]. Another typical scenario of MTL is inspired from human learning, where humans often transfer knowledge from one task to another related task, for example, the skills of playing squash and tennis could help each other to improve [52]. In this case, tasks may come from different datasets. More often than not, a pair of tasks from different datasets have a lower relatedness score than those from the same dataset [18]. This can be clearly shown if we analyse the task relatedness [1] between classification tasks from four medical datasets using the representation similarity analysis (RSA) [7]. The results of our analysis are presented in Fig. 2, from which we can see that the relatedness score becomes especially low when the datasets are from different data modalities, implying that MTL on tasks from different datasets is more challenging." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.397, + 0.473, + 0.625 + ], + "angle": 0, + "content": "MTL is able to improve the performance of learning multiple related tasks by means of sharing common knowledge between tasks, including the network architecture and the weights of the model. Existing MTL designs one architecture for multiple tasks, although only a subset of that network architecture is practically used for each task. In other words, there are shares and differences between these subsets of model architectures [33]. In sharing the weights, if one or more tasks have a dominating influence in training the network weights, the performance of MTL may deteriorate on some of the dominated tasks, which is called negative transfer [40]. Therefore, this work aims to improve the performance of each task by finding a personalised network architecture for each task, thereby alleviating negative transfer resulting from the jointly trained weights." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.626, + 0.473, + 0.779 + ], + "angle": 0, + "content": "Inspired by the successful research on multi-factorial evolutionary algorithms (MFEAs) [9], a recently proposed approach to knowledge transfer in evolutionary optimisation, this work designs an algorithm to separately search for a personalised network architecture and corresponding weight parameters for each task in the same search space. This way, knowledge transfer across different tasks can be achieved through crossover between these architectures to accelerate the search process on each task, provided that there are similarities between the multiple learning tasks." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.78, + 0.473, + 0.903 + ], + "angle": 0, + "content": "Contributions: First, we propose an evolutionary multitasking NAS algorithm (EMT-NAS) for finding personalised network architectures for different tasks (datasets) in the same search space. Architectural knowledge transfer is achieved by optimising the supernet parameters of each task separately and recommending neural network architectures with good performance on their own task. Second, block-based crossover and bit-based mutation opera" + }, + { + "type": "image", + "bbox": [ + 0.541, + 0.092, + 0.845, + 0.26 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.261, + 0.895, + 0.402 + ], + "angle": 0, + "content": "Figure 2. Task similarity matrix. The relatedness scores between four medical tasks are computed using ResNet-50 as a feature extractor. PathMNIST [44] is the tissue classification based on colorectal cancer histology slides, while OrganMNIST-{Axial,Coronal,Sagittal} [44] are organ classifications based on 3 types of 2D images formed by 3D computed tomography (CT) images. We observe that the relatedness between PathMNIST and OrganMNIST-{Axial,Coronal,Sagittal}, respectively, are all smaller than that between OrganMNIST-{Axial,Coronal,Sagittal}." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.409, + 0.895, + 0.653 + ], + "angle": 0, + "content": "tors are designed to accommodate the transformation from a continuous space to a discrete space. Finally, a fitness re-evaluation method is introduced to alleviate fitness fluctuations over the generations resulting from parameter sharing and the mini-batch gradient descent based training to keep promising solutions. We present thorough experimental evaluations on different datasets, including medical classification benchmarks (PathMNIST, OrganMNIST-{Axial,Coronal,Sagittal}) and popular image classification benchmarks (CIFAR-10, CIFAR-100, ImageNet), demonstrating the efficacy and the value of each component of EMT-NAS. Our results demonstrate that, unlike traditional MTL, it is feasible to search for personalised network architectures for multiple tasks through architectural knowledge transfer, obtaining better performance and requiring less search time compared with single-task learning." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.665, + 0.642, + 0.681 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.689, + 0.892, + 0.719 + ], + "angle": 0, + "content": "Below we summarise the similarities and differences with our work in the following themes." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.895, + 0.902 + ], + "angle": 0, + "content": "Multi-Task Learning is designed to learn a network with shared representation from multiple tasks in deep learning. A major challenge in MTL is to balance the joint learning of all tasks to avoid negative transfer [40], motivated by [17] to balance the gradient magnitudes by setting the task-specific weights in the loss. The back-propagation loss function consists of a linear weighting of the losses for each task [18], as shown in Fig. 1a, which may additionally include purpose-specific losses, e.g., the sparsity and sharing of the architecture [38], or loss of generators [32]. Both the coefficients in the loss function and the complexity of the losses affect the final performance of the MTL. In [36]," + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "3644" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.47, + 0.136 + ], + "angle": 0, + "content": "MTL is considered as multi-objective optimisation, searching for the Pareto optimal solutions to avoid a linear weighting of different losses." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.139, + 0.468, + 0.244 + ], + "angle": 0, + "content": "However, all above mentioned algorithms deal with tasks from the same dataset. In this work, updating of the weight parameters of the supernet for each task is independent, i.e., each task has an independent loss function. Rather than solving multiple tasks that arise naturally, the tasks in our MTL setting come from different datasets, or even have from different data modalities." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.247, + 0.468, + 0.382 + ], + "angle": 0, + "content": "Transfer Learning establishes a mapping from the source domain to the target domain [15]. Model-based transfer learning is shown in Fig. 1b, where the first step pretrains the model on the source dataset and the second step tunes the parameters of the pre-trained model on the target dataset. During the transfer, the model structure is also adjusted to adapt it to the target task [22]. Note that in the proposed framework, the architectural, rather than the weights parameters, is shared." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.385, + 0.468, + 0.687 + ], + "angle": 0, + "content": "Neural Architecture Search has been shown to be effective in the search for network architectures for specific tasks. Three main search strategies have been adopted in NAS, namely reinforcement learning (RL) [6, 53, 57], evolutionary algorithms (EAs) [20, 24, 26, 30, 39], and gradient descent (GD) [25, 41, 43, 45]. With the help of parameter sharing [28], the performance of new neural architectures can be evaluated without training from scratch [31]. It should be pointed out that while parameter sharing can greatly reduce the computation time, it may lead to inaccurate performance assessments of candidate submodels [42] and so-called multi-model forgetting, when multiple models are subsequently trained [2]. Although parameter sharing combined with the mini-batch gradient descent method can further reduce the computation time, promising candidate neural architectures may get lost in evolutionary NAS due to strong fluctuations in performance caused by the mini-batch gradient descent method [50]. Therefore, in our work, a fitness re-evaluation method is proposed to alleviate fitness fluctuations in population iterations." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.689, + 0.468, + 0.9 + ], + "angle": 0, + "content": "Evolutionary Multi-Tasking is proposed for solving numerical optimisation problems. When the function landscapes or optimal solutions of two tasks have a certain degree of similarity, promising candidate solutions belonging to one task may be helpful for the other task. Evolutionary multi-tasking has been extended to multi-objective [27], constrained multi-objective [29], and surrogate-assisted for expensive problems [21], and has been shown to be effective for practical problems such as hyperspectral band selection [10] and multi-scene scheduling [49]. In this work, we use evolutionary multi-tasking for the first time to transfer architectural knowledge across multiple tasks from different datasets, and block-based crossover and bit-based mutation are designed to accommodate the transformation from" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.092, + 0.754, + 0.107 + ], + "angle": 0, + "content": "a continuous space to a discrete space." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.119, + 0.655, + 0.136 + ], + "angle": 0, + "content": "3. Proposed Work" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.144, + 0.857, + 0.16 + ], + "angle": 0, + "content": "3.1. Evolutionary Multi-Tasking Optimization" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.167, + 0.892, + 0.258 + ], + "angle": 0, + "content": "In an MFEA, each individual in the population belongs to only one of the tasks to be optimized, and knowledge transfer between tasks is realized with crossover at a probability between individuals belonging to different tasks. A multi-tasking optimization problem consisting of \\( K \\) single-objective minimization tasks can be formulated as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.534, + 0.266, + 0.89, + 0.302 + ], + "angle": 0, + "content": "\\[\n\\left\\{ \\begin{array}{l} \\mathbf {x} _ {1} ^ {*}, \\mathbf {x} _ {2} ^ {*}, \\dots , \\mathbf {x} _ {K} ^ {*} \\end{array} \\right\\} = \\left\\{\\operatorname {a r g m i n} f _ {1} (\\mathbf {x} _ {1}), \\operatorname {a r g m i n} f _ {2} (\\mathbf {x} _ {2}), \\dots , \\operatorname {a r g m i n} f _ {K} (\\mathbf {x} _ {K}) \\right\\} \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.31, + 0.892, + 0.369 + ], + "angle": 0, + "content": "where \\( f_{k}(\\mathbf{x}_{k}), k = 1,2,\\ldots ,K \\) is the \\( k \\)-th task. \\( \\mathbf{x}_k^* = (x_{k,1}^*,x_{k,2}^*,\\dots,x_{k,D_M}^*) \\), \\( k = 1,2,\\ldots ,K \\) is the optimal solution of the \\( k \\)-th task, \\( D_{M} \\) is the dimension of the \\( k \\)-th task." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.378, + 0.851, + 0.394 + ], + "angle": 0, + "content": "3.2. Search Space and Architecture Encoding" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.402, + 0.892, + 0.613 + ], + "angle": 0, + "content": "To facilitate the transfer of architectural knowledge between multiple tasks, the same search space is used for multiple tasks, i.e., the candidate architectures are consistent for each task. Similar to [57], the search space is based on normal and reduced cells. And the optional operations in each block include depthwise-separable convolution, dilated convolution, max pooling, average pooling and identity. The chromosome of each individual encodes the structure of the block, i.e., four integer bits (the first two encoding the inputs, and the last two the operation) represent a block. The coding of the five blocks constitutes a cell coding. Since two types of cells are used, 40 integers in total are used to represent each neural architecture. More details can be found in Supplementary Material A." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.621, + 0.617, + 0.635 + ], + "angle": 0, + "content": "3.3. EMT-NAS" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.644, + 0.892, + 0.81 + ], + "angle": 0, + "content": "The overall framework of the proposed EMT-NAS is presented in Fig. 3, where an evolutionary algorithm searches for optimal neural architectures for two different tasks at the same time. The main components of EMT-NAS are in the upper panel of Fig. 3, which is composed of randomly generated initial population, offspring generation by means of crossover and mutation according to the parents' skill factor \\(\\tau\\) (see Section 3.4), and a top \\(K\\) selection for each task as the environmental selection. The full pseudo code and a detailed description of EMT-NAS can be found in Supplementary Material B." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.811, + 0.892, + 0.9 + ], + "angle": 0, + "content": "Each task has a set of supernet weights that do not affect each other. Sampled training is a method for continuous updating of the supernet weights on the training set based on weight sharing. For each mini-batch of the training data of each task at one epoch, one individual (representing one candidate architecture) belonging to this task will" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "3645" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.081, + 0.09, + 0.891, + 0.326 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.327, + 0.895, + 0.385 + ], + "angle": 0, + "content": "Figure 3. The flow chart of EMT-NAS, where two tasks are used as an example. The difference with the single-tasking evolutionary algorithm is that each individual in the population may belong to the same or different tasks. In addition, each task has a separate set of weights for the supernet. The lower panel shows the sampled training based on a weight sharing method on the training set and the sampled evaluation based on a fitness re-evaluation method on the validation set. Best viewed in colour." + }, + { + "type": "image", + "bbox": [ + 0.08, + 0.391, + 0.473, + 0.512 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.104, + 0.514, + 0.442, + 0.528 + ], + "angle": 0, + "content": "Figure 4. Block-based crossover and bit-based mutation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.544, + 0.47, + 0.665 + ], + "angle": 0, + "content": "be randomly sampled and trained on the mini-batch using the gradient based method. After training, sampled evaluating computes the fitness of the individual by calculating the classification accuracy on the validation data of the same task. Each individual is evaluated once on a random minibatch of the corresponding task validation dataset. Hence, the computational cost of training the weighting parameters and evaluating the fitness can be significantly reduced." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.678, + 0.281, + 0.695 + ], + "angle": 0, + "content": "3.4. Offspring Generation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.703, + 0.47, + 0.822 + ], + "angle": 0, + "content": "Transfer of useful knowledge between tasks is the key reason for EMT-NAS to enhance its performance. As in MFEAs, knowledge transfer in EMT-NAS is realised through simultaneously evolving neural architectures for multiple related tasks in one population. More specifically, knowledge exchange across the tasks is achieved by performing crossover on individuals optimizing architectures on different tasks." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.826, + 0.471, + 0.903 + ], + "angle": 0, + "content": "In reproduction, two parents will be selected each time at a probability proportional to the individuals' fitness value. That is, the greater the fitness of an individual, the larger chance it will have to produce offspring. If the two selected parents belong to the same task, then crossover will be car" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.395, + 0.892, + 0.442 + ], + "angle": 0, + "content": "ried out to generate two offspring, both inheriting the same skill factor \\(\\tau\\) of their parents. In addition, mutation will also be applied to the two offspring to promote exploration." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.452, + 0.893, + 0.678 + ], + "angle": 0, + "content": "When the pair of the selected parent individuals belong to different tasks, two different procedures will be carried out according to a predefined probability, called random mating probability (RMP). If a randomly generated number between 0 and 1 is less than \\( RMP \\), a crossover operator will be applied to the two parents to generate two offsprings, which are then mutated. The two tasks of the parents will be randomly assigned to one of the offsprings at an equal probability. At a probability of 1-\\( RMP \\), only mutations will be performed on each of the two parents to generate two offsprings. Consequently, the skill factor \\( \\tau \\) of each offspring is the same as that of its parent. The probability threshold \\( RMP \\) is a parameter to be specified by the user and a sensitivity analysis of \\( RMP \\) will be provided in the experimental Section 4.6." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.69, + 0.893, + 0.9 + ], + "angle": 0, + "content": "Illustrative examples of the crossover and mutation are given in Fig. 4. For clarity, we only show a segment of the parent chromosome consisting of three blocks. There is a strong correlation between the input source and the operation of the connection, which has a great impact on the performance of the network structure [50]. In block-based crossover, the parent chromosomes \\( p_1 \\) and \\( p_2 \\), in blocks, are swapped at less than the crossover probability \\( CP \\) to generate offspring \\( q_1 \\) and \\( q_2 \\). In bit-based mutation, the parent chromosome \\( q_i \\), in bits, is randomly replaced from the candidate space at less than the mutation probability \\( MP \\), generating offspring \\( o_i \\). This is done by changing the input source or operation to improve the performance of the network architecture." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "3646" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.089, + 0.28, + 0.216 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.171, + 0.222, + 0.188, + 0.232 + ], + "angle": 0, + "content": "(a)" + }, + { + "type": "image", + "bbox": [ + 0.284, + 0.089, + 0.482, + 0.216 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.371, + 0.222, + 0.388, + 0.232 + ], + "angle": 0, + "content": "(b)" + }, + { + "type": "image", + "bbox": [ + 0.081, + 0.236, + 0.28, + 0.361 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.171, + 0.367, + 0.188, + 0.377 + ], + "angle": 0, + "content": "(c)" + }, + { + "type": "image", + "bbox": [ + 0.284, + 0.235, + 0.481, + 0.361 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.371, + 0.367, + 0.388, + 0.377 + ], + "angle": 0, + "content": "(d)" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.378, + 0.47, + 0.504 + ], + "angle": 0, + "content": "Figure 5. Empirical evaluations of the proposed fitness re-evaluation method on CIFAR-10 and CIFAR-100. In the figures, the red dashed lines denote the estimated fitness based on the sampled evaluation without re-evaluation ((a) and (b)) and with the proposed re-evaluation ((c) and (d)), while the blue solid lines denote the true fitness based on an accurate evaluation using all validation data. From these results, we can see that strong fluctuations in the true fitness of the network have been reduced when the proposed fitness re-evaluation is adopted." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.515, + 0.279, + 0.53 + ], + "angle": 0, + "content": "3.5. Fitness Re-evaluation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.539, + 0.47, + 0.66 + ], + "angle": 0, + "content": "There are two important reasons why the fitness re-evaluation method was proposed. First, when using the mini-batch gradient descent training, the sign of the gradient resulting from each mini-batch data may be inconsistent. Consequently, the performance of a network estimated using the sampled evaluating may fluctuate strongly over the generations. Second, such fluctuations are made even more serious because of parameter sharing adopted in training." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.661, + 0.47, + 0.797 + ], + "angle": 0, + "content": "To examine this issue more closely, we plot the fitness (the validation accuracy) of the best individual from a typical run of evolutionary NAS on CIFAR-10 and CIFAR-100 simultaneously in Figs. 5a and 5b. We can observe that there is a big difference between the estimated and true validation accuracies and the true performance fluctuates strongly over the generations. As a result, promising individual may get lost because of the strong fitness fluctuations and inaccurate sampled evaluations." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.797, + 0.47, + 0.873 + ], + "angle": 0, + "content": "To alleviate strong fluctuations in the fitness, we propose to use the fitness of the corresponding parent individual to modify the fitness of the offspring so that the increase or decrease will become less dramatic. Thus, the fitness of an offspring is modified as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.17, + 0.885, + 0.469, + 0.903 + ], + "angle": 0, + "content": "\\[\nF = F _ {p} + \\left(F _ {o} - F _ {p}\\right) \\times \\log_ {T} t \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.181 + ], + "angle": 0, + "content": "where, \\( F_{o}, F_{p}, F \\) are the fitness value of the offspring, the fitness of the parent that generates the offspring, and the modified fitness of the offspring; \\( t = 2,\\dots ,T \\) is the current generation, and \\( T \\) is the maximum number of generations. We call the modification of the offspring fitness according to Equation (2) fitness re-evaluation." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.183, + 0.893, + 0.364 + ], + "angle": 0, + "content": "The logarithmic function in Eq. 2 is based on \\( T \\), which increases to 1.0 as \\( t \\) increases. Thus, \\( F_{o} - F_{p} \\) will be penalised by the logarithm function. Now we re-run the evolutionary NAS on the two tasks (CIFAR-10 and CIFAR-100) by applying the fitness re-evaluation method, and the true fitness as well as the re-evaluated fitness using the sampled validation of the best individual are plotted in Figs. 5c and 5d. From these results, we can see that the individual's true fitness value improves more steadily when the proposed fitness re-evaluation method is adopted, indicating that the modified fitness evaluated based on the sampled evaluating can better reflect the true fitness of the individuals." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.38, + 0.706, + 0.396 + ], + "angle": 0, + "content": "4. Experimental Results" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.404, + 0.707, + 0.421 + ], + "angle": 0, + "content": "4.1. Experimental Settings" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.429, + 0.893, + 0.821 + ], + "angle": 0, + "content": "To validate the effectiveness of our approach, we set single-tasking (evolutionary single-tasking based NAS) as the baseline. Most of the experiments are conducted on MedMNIST [44], which is a collection of 10 preprocessed medical datasets. We selected the PathMNIST dataset of colon pathology, OrganMNIST_Axial, OragnMNIST_Coronal, and OrganMNIST_Sagittal through different processing methods in abdominal CT along three axes. We use these four tasks to construct multitasks with task numbers of 2, 3 and 4, respectively. We also conduct experiments on CIFAR-10 and CIFAR-100 [19], and then transfer the searched best network architecture to ImageNet [34] to explore its effectiveness. For the sake of simplicity, we denote PathMNIST, OrganMNIST_Axial, OragnMNIST_Coronal, OrganMNIST_Sagittal, CIFAR-10, and CIFAR-100 as Path, Organ_A, Organ_C, Organ_S, C-10, and C-100. Similar to [57], the cross-entropy loss function is used for the six tasks and the parameter settings are presented in Table 1 for the search phase. For fair comparisons, the same parameters as in EMT-NAS are maintained for single tasks during the search phase and retraining phase. All experiments are statistical results of five independent runs with an exception to the results on ImageNet, where all experiments were run once only on 1 Nvidia GeForce RTX 2080Ti due to limited computational resources. More details are given in Supplementary Material C." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.832, + 0.714, + 0.849 + ], + "angle": 0, + "content": "4.2. Medical Multi-Tasking" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.856, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Here, we evaluate the network architectures searched by Single-Tasking and EMT-NAS on the medical multitasking. The results when the number of tasks varies from two to" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "3647" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.127, + 0.09, + 0.419, + 0.104 + ], + "angle": 0, + "content": "Table 1. A summary of hyper-parameter settings." + }, + { + "type": "table", + "bbox": [ + 0.084, + 0.106, + 0.462, + 0.264 + ], + "angle": 0, + "content": "
CategoriesParametersSettings (MedMNIST/CIFAR)
Search spaceInitial channels48/20
Repetitions of cells1
Gradient descentBatch size for training128
Batch size for validation1000
Weight decay1.00E-04
Dropout0.1
Momentum0.9
Initial learning rate0.1
Learning rate scheduleCosine Annealing
Search strategyPopulation size20
Generations100/300
Random mating probability0.3
Crossover probability1.00
Mutation probability0.02
" + }, + { + "type": "table_caption", + "bbox": [ + 0.16, + 0.269, + 0.385, + 0.283 + ], + "angle": 0, + "content": "Table 2. Comparison on MedMNIST." + }, + { + "type": "table", + "bbox": [ + 0.079, + 0.286, + 0.468, + 0.48 + ], + "angle": 0, + "content": "
Index# TasksModelPath (%)Organ_A (%)Organ_C (%)Organ_S (%)GPU Days (%) ↓
1ResNet-18 [11]84.492.188.976.2
1ResNet-50 [11]86.491.689.374.6
1Auto-skearn [8]18.656.367.660.1
1AutoKeras [16]86.492.991.580.3
1AutoML [56]81.181.886.170.6
1SI-EvoNAS [50]90.5±0.793.0±0.391.8±0.480.1±0.3
1Single-Tasking (Baseline)87.4±2.994.0±0.791.5±0.880.7±0.5+00.0
①2EMT-NAS (Ours)91.6±0.595.1±0.2-11.0
②2EMT-NAS (Ours)91.2±0.792.3±0.3-18.4
③2EMT-NAS (Ours)90.5±0.981.5±0.2-12.8
④2EMT-NAS (Ours)94.8±0.592.2±0.5-28.4
⑤2EMT-NAS (Ours)95.0±0.381.3±0.5-23.2
⑥2EMT-NAS (Ours)92.2±0.381.5±0.2-40.1
⑦3EMT-NAS (Ours)95.3±0.392.3±0.281.7±0.4-36.0
⑧3EMT-NAS (Ours)91.4±0.392.3±0.381.8±0.3-29.9
⑨3EMT-NAS (Ours)91.9±0.295.0±0.281.4±0.3-23.3
⑩3EMT-NAS (Ours)91.7±0.695.0±0.492.5±0.2-25.1
⑪4EMT-NAS (Ours)91.2±0.694.9±0.392.2±0.381.4±0.5-31.4
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.492, + 0.468, + 0.628 + ], + "angle": 0, + "content": "four in comparison to the corresponding single tasks are given in Table 2. In the top rows of the table, the results of the first five results on the four medical datasets taken from [44] are listed. SI-EvoNAS [50] is a state-of-the-art evolutionary NAS algorithm. Single-Tasking is an evolutionary single-tasking algorithm that we have implemented as the baseline. In column GPU Days (\\%), the reduction in the runtime of EMT-NAS relative to the corresponding Single-Tasking are listed as a percentage." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.629, + 0.468, + 0.809 + ], + "angle": 0, + "content": "From Table 2, it is clear that the classification accuracy of the neural architectures found by EMT-NAS is higher than the networks found by all single-tasking NAS on the corresponding tasks, and the search time is reduced by \\(11\\% - 40\\%\\) compared to the baseline. This demonstrates that it is possible to improve the performance of each task through architectural knowledge transfer only. In addition, the best classification accuracy of the network architecture has been obtained when the number of tasks is three. This shows that which tasks and how many tasks are formulated as a multi-tasking problem will influence the performance of algorithm in solving each of the individual tasks." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.81, + 0.468, + 0.901 + ], + "angle": 0, + "content": "Multi-tasking with the same data modality: EMT-NAS (numbered ④, ⑤, ⑥, ⑦) searched for network architectures with a higher classification accuracy than those found by Single-Tasking. As described in [44], crop 2D images from the center slices of the 3D CT bounding boxes in axial/coronal/sagittal views (planes) are obtained in datasets" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.227 + ], + "angle": 0, + "content": "Organ_A, Organ_C, and Organ_S. Therefore, these datasets are correlated, and it is reasonable to make use of the common knowledge of these datasets to improve classification accuracy. In addition, ⑦ VS ④, ⑤ and ⑥, respectively, have the best performance on Organ_A, Organ_C, and Organ_S. This demonstrates that the three tasks enhance each other to a greater extent than two by two. Therefore, architectural knowledge transfer works well for different datasets of the same data modality." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.228, + 0.892, + 0.546 + ], + "angle": 0, + "content": "Multi-tasking with different data modalities: The classification accuracy of EMT-NAS (numbered ①, ②, ③, ⑧, ⑨ and ⑩) are slightly higher than that of EMT-NAS (numbered ④, ⑤ and ⑥) on Organ_A, Organ_C, and Organ_S datasets, respectively. From [44], we know that Path is for predicting survival from colorectal cancer histology slides, which means that Organt_A, Organ_C, and Organ_S can benefit more from Path. By contrast, EMT-NAS has transferred different degrees of useful knowledge from Organ_A, Organ_C, and Organ_S, respectively, to Path. From the table, we can observe that the classification accuracy of EMT-NAS (numbered ①, ② and ③) decreases sequentially on PATH. Organ_A, Organ_C, and Organ_S are obtained by different processing methods in abdominal CT along three axes, so their data characteristics are different. Clearly, Path and Organ_A are most beneficial to each other. This also corroborates with the task relational analysis in Fig. 2. Therefore, although these datasets are from different data modalities and are weakly correlated, they can still improve their respective performance through architectural knowledge transfer." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.558, + 0.742, + 0.573 + ], + "angle": 0, + "content": "4.3. CIFAR-10 and CIFAR-100" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.582, + 0.892, + 0.687 + ], + "angle": 0, + "content": "We again used RSA in Fig. 2 to analyse the task relatedness between C-10 and C-100, with a task relatedness score of 0.38. C-100 is made up of 20 classes (each containing five subclasses), while C-10 is 10 classes. The results show that ResNet-50, trained on C-100, extracts many different features from the same image compared to those trained on C-10. Therefore, C-10 and C-100 are differentiated." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.689, + 0.892, + 0.854 + ], + "angle": 0, + "content": "The representative algorithms can be roughly divided into four categories, namely manually designed, RL-based, GD-based, and EAs-based. The comparative results on C-10 and C-100 are listed in Table 3. Note that all algorithms are meant for single-tasking search, i.e., they either search for an optimal network architecture on C-10 and C-100, respectively, or search on C-10 and then the found architectures are transferred to C-100. By contrast, EMT-NAS searches for optimal neural architectures simultaneously on C-10 and C-100, and therefore, the GPU days of EMT-NAS is the total time for searching for both architectures." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.856, + 0.892, + 0.901 + ], + "angle": 0, + "content": "In Table 3, EMT-NAS stacks normal blocks twice, while EMT-NAS† stacks three times. EMT-NAS searched the network architecture's on C-10 and C-100 with a higher clas" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.956 + ], + "angle": 0, + "content": "3648" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.089, + 0.472, + 0.146 + ], + "angle": 0, + "content": "Table 3. Comparison on C-10 and C-100. * indicates that the same network architecture is used on both C-10 and C-100, so their GPU days for searching are the same. † indicates normal cell stacking three times for better performance." + }, + { + "type": "table", + "bbox": [ + 0.078, + 0.147, + 0.481, + 0.355 + ], + "angle": 0, + "content": "
ModelSearch MethodGPU DaysParams (M)C-10 (%)Params (M)C-100 (%)
Wide ResNet [47]manual-36.595.83*79.50
DenseNet [14]manual-27.296.26*80.75
MobileNetV2 [35]manual-2.194.56*77.09
PNAS [23]SMBO1503.296.59±0.09*80.47
ENAS [28]RL0.454.697.11*80.57
NASNet-A [57]RL20003.397.35--
Block-QNN-Faster [53]RL0.83.996.43*81.79
DARTS [25]GD1.53.397.00±0.14*79.48±0.31
SNAS [41]GD1.52.997.02--
large-scale Evo [31]EA27505.494.640.477
Hier-EA [24]EA3006496.25±0.12--
Amoebanet-A [30]EA31503.296.66±0.06*81.07
AE-CNN [39]EA27/36295.75.479.15
SHEDA-CNN [20]EA0.58/0.9710.8896.3618.6478.84
Single-Tasking (Baseline)EA0.461.8396.24±0.201.6879.70±0.44
Single-Tasking† (Baseline)EA0.462.4196.64±0.182.1980.82±0.71
EMT-NAS (Ours)EA0.422.1796.73±0.152.2381.86±0.10
EMT-NAS† (Ours)EA0.422.9197.04±0.042.9782.60±0.38
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.368, + 0.474, + 0.611 + ], + "angle": 0, + "content": "sification accuracy than Single-Tasking (baseline), demonstrating that architecture knowledge transfer can effectively improve performance on C-10 and C-100. Compared to other NAS algorithms, our approach achieves better performance and more compact network architectures searched on C-10 and C-100 through architectural knowledge transfer, except for ENAS and NASNet-A on C-10. However, the models found by EMT-NAS have only two-thirds the number of parameters of models found by ENAS. On the other hand, NASNet-A consumes about 4,700 times more GPU days than EMT-NAS. These indicate that our approach can achieve a good performance-complexity trade-off. We also analysed two baselines for joint training (shared or unshared network architectures) in Supplementary Material D. The performance of the algorithms has degraded as data from different tasks are used to update the same supernet." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.62, + 0.33, + 0.637 + ], + "angle": 0, + "content": "4.4. Transferability to ImageNet" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.644, + 0.472, + 0.901 + ], + "angle": 0, + "content": "As done in [25], we transferred the best network architectures found on C-10 and C-100 to ImageNet for training from scratch, to further validate the transferability of the architectures searched by EMT-NAS. The results comparing EMT-NAS with 15 models (or their variants) on ImageNet are given in Table 4. EMT-NAS-4-C-100 has a lower number of model parameters (2.49M) than all compared algorithms, while it has a higher top-1 accuracy (74.25%) except for MoblieNet-V3, MobileNetV2-1.0+CA, RepVGG-A1, AutoSpace, PC-DARTS and MUXNet-m. For better performance, we change the number of normal cells stacked from two to three to get EMT-NAS-C-100†. The top-1 accuracy of EMT-NAS-C-100† is 75.44%, which again surpasses the accuracy of the rest of the algorithms, and the number of model parameters is 3.25M. This demonstrates that EMT-NAS has good transferability between the network architectures searched on C-10 and C-100." + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.089, + 0.892, + 0.118 + ], + "angle": 0, + "content": "Table 4. Comparisons on ImageNet. \\(\\dagger\\) indicates normal cell stacking three times for better performance." + }, + { + "type": "table", + "bbox": [ + 0.513, + 0.12, + 0.88, + 0.377 + ], + "angle": 0, + "content": "
ModelTop-1 (%)Top-5 (%)Params (M)GPU DaysSearch Method
ShuffleNet 2.0 [51]73.7-5.4-manual
MobileNet-V3 [13]75.2-5.1-manual
MobileNeXt-0.75 [54]72.6-2.5-manual
MobileNetV2-1.0+CA [12]74.3-3.95-manual
RepVGG-A1 [5]74.46-12.78-manual
PNAS [23]74.291.95.1225SMBO
NASNet-A [57]74.091.65.32000RL
DPP-Net-Panacea [6]74.291.794.88RL
AutoSpace [55]75.3-4.38.33RL
DARTS [25]73.391.34.74GD
SNAS [41]72.791.84.31.5GD
PC-DARTS [43]74.992.25.30.1GD
HourNAS-C [45]74.191.64.80.1GD
Amoebanet-A [30]74.592.05.13150EA
MUXNet-m [26]75.392.53.4176EA
Single-Tasking-C-10 (Baseline)73.1891.222.410.23EA
Single-Tasking-C-100 (Baseline)72.8891.062.250.22EA
Single-Tasking-C-10† (Baseline)74.5992.093.150.23EA
Single-Tasking-C-100† (Baseline)74.1191.862.970.22EA
EMT-NAS-C-10 (Ours)73.8391.632.380.42EA
EMT-NAS-C-100 (Ours)74.2591.802.49
EMT-NAS-C-10† (Ours)75.1192.393.130.42EA
EMT-NAS-C-100† (Ours)75.4492.553.25
" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.39, + 0.665, + 0.404 + ], + "angle": 0, + "content": "4.5. Ablation Studies" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.414, + 0.892, + 0.565 + ], + "angle": 0, + "content": "To verify the effectiveness of the evolutionary multitasking NAS algorithm and the fitness re-evaluation method, four algorithms are compared, namely evolutionary single-Tasking NAS, which serves as the baseline (denoted as Single-tasking in Table 5), evolutionary single-tasking NAS with the fitness re-evaluation method, called Single-Tasking+Reeval, evolutionary multi-tasking NAS without fitness re-evaluation, called Multi-Tasking, and evolutionary multi-tasking NAS with the fitness re-evaluation method, denoted as Multi-Tasking+Reeval." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.566, + 0.892, + 0.656 + ], + "angle": 0, + "content": "Evolutionary Multi-Tasking: By comparing the results of Single-tasking and Multi-Tasking (③ vs ① and ④ vs ②), evolutionary multi-tasking NAS can improve the performance on both C-10 and C-100, confirming the effectiveness of knowledge transfer when simultaneously searching for the optimal neural architectures on similar tasks." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.658, + 0.892, + 0.763 + ], + "angle": 0, + "content": "Fitness Re-Evaluation: By comparing the results with and without fitness re-evaluation (④ vs ③ and ② vs ①), we can see that the proposed fitness re-evaluation method improves the performance on both C-10 and C-100. This confirms that the fitness re-evaluation method is effective in enhancing the performance by alleviating fitness fluctuations in the search based on sampled evaluations." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.892, + 0.902 + ], + "angle": 0, + "content": "Search Efficiency: We take the total runtime of Single-Tasking, and count the percentage increase or decrease of the other three algorithms relative to it. We also calculate three parts of the runtime, including time for training model parameters on the training dataset, time for evaluating model performance on the validation dataset, and time for searching. First, we note that the time taken by the evolutionary multi-tasking is reduced by \\(50\\%\\) compared to single-tasking(③ vs ① and ④ vs ②). Because the compu" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.956 + ], + "angle": 0, + "content": "3649" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.09, + 0.09, + 0.88, + 0.104 + ], + "angle": 0, + "content": "Table 5. Comparison of evolutionary single- and multi-tasking optimisation with/without fitness re-evaluation on CIFAR-10 and -100." + }, + { + "type": "table", + "bbox": [ + 0.097, + 0.106, + 0.872, + 0.182 + ], + "angle": 0, + "content": "
IndexAlgorithmTask 1Task 2Total Time (%) ↓Training Time (%) ↓Evaluation Time (%) ↓Search Time (%) ↓Average Params (M)Average FLOPs (M)
C-10 (%)Params (M)Transfer (%)C-100 (%)Params (M)Transfer (%)
①Single-Tasking96.23±0.201.8396.07±0.2579.70±0.441.6878.95±0.60+0.0+0.0+0.0+0.01.83334
②Single-Tasking+Reeval96.29±0.251.7496.26±0.1880.48±0.281.9078.77±0.65-5.1-4.1-15.1-1.41.81323
③Multi-Tasking96.49±0.162.02-80.68±0.432.03--2.1+3.8-37.4-49.42.06382
④Multi-Tasking+Reeval96.73±0.152.17-81.86±0.102.23--8.7-4.0-35.9-51.61.97355
" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.192, + 0.473, + 0.63 + ], + "angle": 0, + "content": "tational complexity of the Evolutionary Multi-Tasking and Single-Tasking algorithms is almost the same, except for the time spent on training and evaluation. Second, \\(③\\) vs \\(①\\) and \\(④\\) vs \\(②\\), the time spent on the evaluation is reduced by about \\(36\\%\\). The population size and the number of generations are the same for single and multi-tasking, i.e., the number of fitness evaluations is the same, so that the total time to optimise multiple tasks simultaneously will be less than the sum of the runtimes when the tasks are optimised one by one. Finally, \\(④\\) vs \\(③\\) and \\(②\\) vs \\(①\\) with a small percentage reduction in the training time. To investigate this further, we reproduce the sampled training process and chose two model metrics, namely the number of parameters and the number of floating point operations (FLOPs). Specifically, when each network architecture was trained once, two metrics were recorded until five runs of the algorithm have stopped, and then averaged and listed in the column Average Params \\((M)\\) and Average FLOPs \\((M)\\) of Table 5, respectively. The results show a small reduction in the average number of parameters and the average FLOPs for both \\(④\\) vs \\(③\\) and \\(②\\) vs \\(①\\). It is assumed that the fitness re-evaluation method allows the algorithm to favour network architectures consisting of operations with a small number of parameters or a low computational complexity in the search process. This may explain the fact that introducing the fitness re-evaluation method can reduce the time spent by the model on the training set by a small amount. Overall, EMT-NAS consumes less runtime than its single-task counterparts." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.632, + 0.471, + 0.8 + ], + "angle": 0, + "content": "Model Transferability: We transferred the network architectures that Single-tasking and Single-tasking+Reeval searched on C-10 and C-100, respectively, to C-100 and C-10 for retraining. The results are presented in column Transfer \\((\\%)\\), which show that through transfer learning, the performance of the network architectures on the new dataset is much lower than that of the network architectures obtained by evolutionary multi-tasking NAS (Multi-Tasking and Multi-Tasking+Reeval) search. Therefore, evolutionary multi-tasking NAS is more competitive than evolutionary single-tasking NAS with transfer learning." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.815, + 0.265, + 0.831 + ], + "angle": 0, + "content": "4.6. Sensitivity Analysis" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.471, + 0.901 + ], + "angle": 0, + "content": "In EMT-NAS, \\( RMP \\) is a key parameter that controls the degree of knowledge transfer between tasks. Here, we set the random mating probability \\( RMP = 0, 0.1, 0.2, 0.3, 0.4, 0.5 \\) and note that when \\( RMP = 0 \\), two" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.19, + 0.892, + 0.217 + ], + "angle": 0, + "content": "Table 6. Comparison of EMT-NAS when random mating probability is set to 0, 0.1, 0.2, 0.3, 0.4, and 0.5." + }, + { + "type": "table", + "bbox": [ + 0.524, + 0.22, + 0.868, + 0.306 + ], + "angle": 0, + "content": "
RMPTask 1Validation ACC (%)Test ACC (%)Task 2Validation ACC (%)Test ACC (%)
0C-1088.36±0.6996.28±0.09C-10061.48±1.6580.31±0.40
0.1C-1087.36±1.6096.48±0.18C-10058.85±4.1080.46±0.71
0.2C-1088.32±1.0296.52±0.18C-10059.67±0.4781.11±0.54
0.3C-1088.76±1.0596.73±0.15C-10061.69±2.1581.86±0.10
0.4C-1088.09±1.2596.49±0.18C-10061.27±3.0981.26±0.27
0.5C-1088.52±1.1696.52±0.17C-10061.42±2.5781.15±0.31
" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.321, + 0.892, + 0.44 + ], + "angle": 0, + "content": "single tasks run in the same population without any knowledge transfer between the tasks. Table 6 shows that the validation and test accuracies increase as \\( RMP \\) increases in the beginning, and then decrease as \\( RMP \\) becomes larger, indicating that too much or too little knowledge transfer between tasks can degrade the performance of EMT-NAS. The best performance was achieved on the validation set and test set when \\( RMP = 0.3 \\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.443, + 0.894, + 0.504 + ], + "angle": 0, + "content": "We also analysed the influence of the population size, crossover and mutation probabilities, and the number of generations on the performance. The results are presented in Supplementary Material E." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.524, + 0.62, + 0.54 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.551, + 0.892, + 0.732 + ], + "angle": 0, + "content": "In this work, evolutionary multi-tasking is applied to NAS for the first time. Extensive experiments have demonstrated that for multiple classification tasks from different datasets (data modalities), architectural knowledge transfer and fitness re-evaluation method allow EMT-NAS to outperform each task obtained simultaneously over a single task, and that the runtime of EMT-NAS is less than the sum of the runtimes of solving multiple single tasks independently. Although this work achieves implicit architectural knowledge transfer, more precise, explicit knowledge transfer between tasks in evolutionary multi-tasking NAS is desirable and will be investigated in the future." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.753, + 0.652, + 0.77 + ], + "angle": 0, + "content": "Acknowledgment" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.892, + 0.901 + ], + "angle": 0, + "content": "This work is supported by National Natural Science Foundation of China (62136003, 61988101), the Programme of Introducing Talents of Discipline to Universities (the 111 Project) under Grant B17017, Fundamental Research Funds for the Central Universities (222202317006) and Shanghai AI Lab. Y. Jin is supported by an Alexander von Humboldt Professorship for AI endowed by the German Federal Ministry of Education and Research." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "3650" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.105 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.115, + 0.469, + 0.156 + ], + "angle": 0, + "content": "[1] Shai Ben-David and Reba Schuller Borbely. A notion of task relatedness yielding provable multiple-task learning guarantees. Machine learning, 73(3):273-287, 2008. 2" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.159, + 0.469, + 0.225 + ], + "angle": 0, + "content": "[2] Yassine Benyahia, Kaicheng Yu, Kamil Bennani Smires, Martin Jaggi, Anthony C Davison, Mathieu Salzmann, and Claudiu Musat. Overcoming multi-model forgetting. In International Conference on Machine Learning, pages 594-603. 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In deep learning, this is usually achieved by sharing a common neural network architecture and jointly training the weights. However, the joint training of weighting parameters on multiple related tasks may lead to performance degradation, known as negative transfer. To address this issue, this work proposes an evolutionary multi-tasking neural architecture search (EMT-NAS) algorithm to accelerate the search process by transferring architectural knowledge across multiple related tasks. In EMT-NAS, unlike the traditional MTL, the model for each task has a personalised network architecture and its own weights, thus offering the capability of effectively alleviating negative transfer. A fitness re-evaluation method is suggested to alleviate fluctuations in performance evaluations resulting from parameter sharing and the mini-batch gradient descent training method, thereby avoiding losing promising solutions during the search process. To rigorously verify the performance of EMT-NAS, the classification tasks used in the empirical assessments are derived from different datasets, including the CIFAR-10 and CIFAR-100, and four MedMNIST datasets. Extensive comparative experiments on different numbers of tasks demonstrate that EMT-NAS takes $8\%$ and up to $40\%$ on CIFAR and MedMNIST, respectively, less time to find competitive neural architectures than its single-task counterparts. + +# 1. Introduction + +Many neural architecture search (NAS) algorithms [8, 16, 23, 56] have shown better performance on a specific task than manually designed deep neural networks [11, 14, + +![](images/b3ce56e560da4fcca584f7153b50060f14d548c8c9671ccfe1779804cf380263.jpg) +Figure 1. Conceptual differences between our work and two main existing methodologies for two-task learning. (a) Existing multi-task NAS typically handles multiple tasks such as semantic segmentation and surface normal prediction on the same dataset, where the loss function contains losses for multiple tasks, resulting in a network architecture that shares a common set of weight parameters. (b) Model-based transfer learning trains a network architecture on a source dataset and then transfers it to a target dataset by fine-tuning the weights using a separate loss function. (c) EMT-NAS simultaneously optimises multiple classification tasks from different datasets using a separate loss function for each task, resulting in an individual network architecture and corresponding weights for each task. EMT-NAS aims to optimise each task separately while sharing the knowledge of good network architectures to facilitate the optimisation of each task. Best viewed in colour. + +![](images/bcb99c75970b3ce6347b53239ce83467d937638191aee0bea7a29835b6491807.jpg) + +35, 51]. However, when the task (or dataset) changes, the NAS algorithm needs to be run again to find a new optimal network architecture for the new task, which is typical for single-task learning (STL). + +By contrast, it has been shown that simultaneously learning multiple related tasks, known as multi-task learning (MTL) is beneficial [3, 52]. One class of MTL focuses on designing or training a single network to jointly solve multiple tasks formed by scene understanding (the same + +dataset) [38, 46], such as the NYU v2 dataset [37], the CityScapes dataset [4], and the Taskonomy dataset [48]. These tasks consist of semantic segmentation, surface normal prediction, depth prediction, keypoint detection and edge detection, which are known as multiple tasks that arise naturally [3]. Another typical scenario of MTL is inspired from human learning, where humans often transfer knowledge from one task to another related task, for example, the skills of playing squash and tennis could help each other to improve [52]. In this case, tasks may come from different datasets. More often than not, a pair of tasks from different datasets have a lower relatedness score than those from the same dataset [18]. This can be clearly shown if we analyse the task relatedness [1] between classification tasks from four medical datasets using the representation similarity analysis (RSA) [7]. The results of our analysis are presented in Fig. 2, from which we can see that the relatedness score becomes especially low when the datasets are from different data modalities, implying that MTL on tasks from different datasets is more challenging. + +MTL is able to improve the performance of learning multiple related tasks by means of sharing common knowledge between tasks, including the network architecture and the weights of the model. Existing MTL designs one architecture for multiple tasks, although only a subset of that network architecture is practically used for each task. In other words, there are shares and differences between these subsets of model architectures [33]. In sharing the weights, if one or more tasks have a dominating influence in training the network weights, the performance of MTL may deteriorate on some of the dominated tasks, which is called negative transfer [40]. Therefore, this work aims to improve the performance of each task by finding a personalised network architecture for each task, thereby alleviating negative transfer resulting from the jointly trained weights. + +Inspired by the successful research on multi-factorial evolutionary algorithms (MFEAs) [9], a recently proposed approach to knowledge transfer in evolutionary optimisation, this work designs an algorithm to separately search for a personalised network architecture and corresponding weight parameters for each task in the same search space. This way, knowledge transfer across different tasks can be achieved through crossover between these architectures to accelerate the search process on each task, provided that there are similarities between the multiple learning tasks. + +Contributions: First, we propose an evolutionary multitasking NAS algorithm (EMT-NAS) for finding personalised network architectures for different tasks (datasets) in the same search space. Architectural knowledge transfer is achieved by optimising the supernet parameters of each task separately and recommending neural network architectures with good performance on their own task. Second, block-based crossover and bit-based mutation opera + +![](images/0df761503b86f8f7b1693b413eb7b7b581864523e92e0a1b81b0413960b53d46.jpg) +Figure 2. Task similarity matrix. The relatedness scores between four medical tasks are computed using ResNet-50 as a feature extractor. PathMNIST [44] is the tissue classification based on colorectal cancer histology slides, while OrganMNIST-{Axial,Coronal,Sagittal} [44] are organ classifications based on 3 types of 2D images formed by 3D computed tomography (CT) images. We observe that the relatedness between PathMNIST and OrganMNIST-{Axial,Coronal,Sagittal}, respectively, are all smaller than that between OrganMNIST-{Axial,Coronal,Sagittal}. + +tors are designed to accommodate the transformation from a continuous space to a discrete space. Finally, a fitness re-evaluation method is introduced to alleviate fitness fluctuations over the generations resulting from parameter sharing and the mini-batch gradient descent based training to keep promising solutions. We present thorough experimental evaluations on different datasets, including medical classification benchmarks (PathMNIST, OrganMNIST-{Axial,Coronal,Sagittal}) and popular image classification benchmarks (CIFAR-10, CIFAR-100, ImageNet), demonstrating the efficacy and the value of each component of EMT-NAS. Our results demonstrate that, unlike traditional MTL, it is feasible to search for personalised network architectures for multiple tasks through architectural knowledge transfer, obtaining better performance and requiring less search time compared with single-task learning. + +# 2. Related Work + +Below we summarise the similarities and differences with our work in the following themes. + +Multi-Task Learning is designed to learn a network with shared representation from multiple tasks in deep learning. A major challenge in MTL is to balance the joint learning of all tasks to avoid negative transfer [40], motivated by [17] to balance the gradient magnitudes by setting the task-specific weights in the loss. The back-propagation loss function consists of a linear weighting of the losses for each task [18], as shown in Fig. 1a, which may additionally include purpose-specific losses, e.g., the sparsity and sharing of the architecture [38], or loss of generators [32]. Both the coefficients in the loss function and the complexity of the losses affect the final performance of the MTL. In [36], + +MTL is considered as multi-objective optimisation, searching for the Pareto optimal solutions to avoid a linear weighting of different losses. + +However, all above mentioned algorithms deal with tasks from the same dataset. In this work, updating of the weight parameters of the supernet for each task is independent, i.e., each task has an independent loss function. Rather than solving multiple tasks that arise naturally, the tasks in our MTL setting come from different datasets, or even have from different data modalities. + +Transfer Learning establishes a mapping from the source domain to the target domain [15]. Model-based transfer learning is shown in Fig. 1b, where the first step pretrains the model on the source dataset and the second step tunes the parameters of the pre-trained model on the target dataset. During the transfer, the model structure is also adjusted to adapt it to the target task [22]. Note that in the proposed framework, the architectural, rather than the weights parameters, is shared. + +Neural Architecture Search has been shown to be effective in the search for network architectures for specific tasks. Three main search strategies have been adopted in NAS, namely reinforcement learning (RL) [6, 53, 57], evolutionary algorithms (EAs) [20, 24, 26, 30, 39], and gradient descent (GD) [25, 41, 43, 45]. With the help of parameter sharing [28], the performance of new neural architectures can be evaluated without training from scratch [31]. It should be pointed out that while parameter sharing can greatly reduce the computation time, it may lead to inaccurate performance assessments of candidate submodels [42] and so-called multi-model forgetting, when multiple models are subsequently trained [2]. Although parameter sharing combined with the mini-batch gradient descent method can further reduce the computation time, promising candidate neural architectures may get lost in evolutionary NAS due to strong fluctuations in performance caused by the mini-batch gradient descent method [50]. Therefore, in our work, a fitness re-evaluation method is proposed to alleviate fitness fluctuations in population iterations. + +Evolutionary Multi-Tasking is proposed for solving numerical optimisation problems. When the function landscapes or optimal solutions of two tasks have a certain degree of similarity, promising candidate solutions belonging to one task may be helpful for the other task. Evolutionary multi-tasking has been extended to multi-objective [27], constrained multi-objective [29], and surrogate-assisted for expensive problems [21], and has been shown to be effective for practical problems such as hyperspectral band selection [10] and multi-scene scheduling [49]. In this work, we use evolutionary multi-tasking for the first time to transfer architectural knowledge across multiple tasks from different datasets, and block-based crossover and bit-based mutation are designed to accommodate the transformation from + +a continuous space to a discrete space. + +# 3. Proposed Work + +# 3.1. Evolutionary Multi-Tasking Optimization + +In an MFEA, each individual in the population belongs to only one of the tasks to be optimized, and knowledge transfer between tasks is realized with crossover at a probability between individuals belonging to different tasks. A multi-tasking optimization problem consisting of $K$ single-objective minimization tasks can be formulated as follows: + +$$ +\left\{ \begin{array}{l} \mathbf {x} _ {1} ^ {*}, \mathbf {x} _ {2} ^ {*}, \dots , \mathbf {x} _ {K} ^ {*} \end{array} \right\} = \left\{\operatorname {a r g m i n} f _ {1} (\mathbf {x} _ {1}), \operatorname {a r g m i n} f _ {2} (\mathbf {x} _ {2}), \dots , \operatorname {a r g m i n} f _ {K} (\mathbf {x} _ {K}) \right\} \tag {1} +$$ + +where $f_{k}(\mathbf{x}_{k}), k = 1,2,\ldots ,K$ is the $k$ -th task. $\mathbf{x}_k^* = (x_{k,1}^*,x_{k,2}^*,\dots,x_{k,D_M}^*)$ , $k = 1,2,\ldots ,K$ is the optimal solution of the $k$ -th task, $D_{M}$ is the dimension of the $k$ -th task. + +# 3.2. Search Space and Architecture Encoding + +To facilitate the transfer of architectural knowledge between multiple tasks, the same search space is used for multiple tasks, i.e., the candidate architectures are consistent for each task. Similar to [57], the search space is based on normal and reduced cells. And the optional operations in each block include depthwise-separable convolution, dilated convolution, max pooling, average pooling and identity. The chromosome of each individual encodes the structure of the block, i.e., four integer bits (the first two encoding the inputs, and the last two the operation) represent a block. The coding of the five blocks constitutes a cell coding. Since two types of cells are used, 40 integers in total are used to represent each neural architecture. More details can be found in Supplementary Material A. + +# 3.3. EMT-NAS + +The overall framework of the proposed EMT-NAS is presented in Fig. 3, where an evolutionary algorithm searches for optimal neural architectures for two different tasks at the same time. The main components of EMT-NAS are in the upper panel of Fig. 3, which is composed of randomly generated initial population, offspring generation by means of crossover and mutation according to the parents' skill factor $\tau$ (see Section 3.4), and a top $K$ selection for each task as the environmental selection. The full pseudo code and a detailed description of EMT-NAS can be found in Supplementary Material B. + +Each task has a set of supernet weights that do not affect each other. Sampled training is a method for continuous updating of the supernet weights on the training set based on weight sharing. For each mini-batch of the training data of each task at one epoch, one individual (representing one candidate architecture) belonging to this task will + +![](images/96534d886ebf24e08b2a18ee706a51030d6c7bfbf5756d38a4844655490b53f1.jpg) +Figure 3. The flow chart of EMT-NAS, where two tasks are used as an example. The difference with the single-tasking evolutionary algorithm is that each individual in the population may belong to the same or different tasks. In addition, each task has a separate set of weights for the supernet. The lower panel shows the sampled training based on a weight sharing method on the training set and the sampled evaluation based on a fitness re-evaluation method on the validation set. Best viewed in colour. + +![](images/6eb7b4623c8652793aa6b1a368c0be052fcfe62e58f0ddfead2c17441629e594.jpg) +Figure 4. Block-based crossover and bit-based mutation. + +be randomly sampled and trained on the mini-batch using the gradient based method. After training, sampled evaluating computes the fitness of the individual by calculating the classification accuracy on the validation data of the same task. Each individual is evaluated once on a random minibatch of the corresponding task validation dataset. Hence, the computational cost of training the weighting parameters and evaluating the fitness can be significantly reduced. + +# 3.4. Offspring Generation + +Transfer of useful knowledge between tasks is the key reason for EMT-NAS to enhance its performance. As in MFEAs, knowledge transfer in EMT-NAS is realised through simultaneously evolving neural architectures for multiple related tasks in one population. More specifically, knowledge exchange across the tasks is achieved by performing crossover on individuals optimizing architectures on different tasks. + +In reproduction, two parents will be selected each time at a probability proportional to the individuals' fitness value. That is, the greater the fitness of an individual, the larger chance it will have to produce offspring. If the two selected parents belong to the same task, then crossover will be car + +ried out to generate two offspring, both inheriting the same skill factor $\tau$ of their parents. In addition, mutation will also be applied to the two offspring to promote exploration. + +When the pair of the selected parent individuals belong to different tasks, two different procedures will be carried out according to a predefined probability, called random mating probability (RMP). If a randomly generated number between 0 and 1 is less than $RMP$ , a crossover operator will be applied to the two parents to generate two offsprings, which are then mutated. The two tasks of the parents will be randomly assigned to one of the offsprings at an equal probability. At a probability of 1- $RMP$ , only mutations will be performed on each of the two parents to generate two offsprings. Consequently, the skill factor $\tau$ of each offspring is the same as that of its parent. The probability threshold $RMP$ is a parameter to be specified by the user and a sensitivity analysis of $RMP$ will be provided in the experimental Section 4.6. + +Illustrative examples of the crossover and mutation are given in Fig. 4. For clarity, we only show a segment of the parent chromosome consisting of three blocks. There is a strong correlation between the input source and the operation of the connection, which has a great impact on the performance of the network structure [50]. In block-based crossover, the parent chromosomes $p_1$ and $p_2$ , in blocks, are swapped at less than the crossover probability $CP$ to generate offspring $q_1$ and $q_2$ . In bit-based mutation, the parent chromosome $q_i$ , in bits, is randomly replaced from the candidate space at less than the mutation probability $MP$ , generating offspring $o_i$ . This is done by changing the input source or operation to improve the performance of the network architecture. + +![](images/486aa3e56a443a1e8e1fdc35b68998a25f0d6ec700e8ae48d647d93ca84a8a0f.jpg) +(a) + +![](images/5c1060720207f624fe4f6a3922124bd663df40bf790a301d1edef562caaf400f.jpg) +(b) + +![](images/0b1d377c5c34b72f55e1e08a4cc4763f32b7c062c9e5374bb8e6714b5da0918f.jpg) +(c) + +![](images/d5c62122fac71a25ab75d7025ec0ba0fdf5d8dbd5019cb5f3938b1a9f5cc6697.jpg) +(d) +Figure 5. Empirical evaluations of the proposed fitness re-evaluation method on CIFAR-10 and CIFAR-100. In the figures, the red dashed lines denote the estimated fitness based on the sampled evaluation without re-evaluation ((a) and (b)) and with the proposed re-evaluation ((c) and (d)), while the blue solid lines denote the true fitness based on an accurate evaluation using all validation data. From these results, we can see that strong fluctuations in the true fitness of the network have been reduced when the proposed fitness re-evaluation is adopted. + +# 3.5. Fitness Re-evaluation + +There are two important reasons why the fitness re-evaluation method was proposed. First, when using the mini-batch gradient descent training, the sign of the gradient resulting from each mini-batch data may be inconsistent. Consequently, the performance of a network estimated using the sampled evaluating may fluctuate strongly over the generations. Second, such fluctuations are made even more serious because of parameter sharing adopted in training. + +To examine this issue more closely, we plot the fitness (the validation accuracy) of the best individual from a typical run of evolutionary NAS on CIFAR-10 and CIFAR-100 simultaneously in Figs. 5a and 5b. We can observe that there is a big difference between the estimated and true validation accuracies and the true performance fluctuates strongly over the generations. As a result, promising individual may get lost because of the strong fitness fluctuations and inaccurate sampled evaluations. + +To alleviate strong fluctuations in the fitness, we propose to use the fitness of the corresponding parent individual to modify the fitness of the offspring so that the increase or decrease will become less dramatic. Thus, the fitness of an offspring is modified as follows: + +$$ +F = F _ {p} + \left(F _ {o} - F _ {p}\right) \times \log_ {T} t \tag {2} +$$ + +where, $F_{o}, F_{p}, F$ are the fitness value of the offspring, the fitness of the parent that generates the offspring, and the modified fitness of the offspring; $t = 2,\dots ,T$ is the current generation, and $T$ is the maximum number of generations. We call the modification of the offspring fitness according to Equation (2) fitness re-evaluation. + +The logarithmic function in Eq. 2 is based on $T$ , which increases to 1.0 as $t$ increases. Thus, $F_{o} - F_{p}$ will be penalised by the logarithm function. Now we re-run the evolutionary NAS on the two tasks (CIFAR-10 and CIFAR-100) by applying the fitness re-evaluation method, and the true fitness as well as the re-evaluated fitness using the sampled validation of the best individual are plotted in Figs. 5c and 5d. From these results, we can see that the individual's true fitness value improves more steadily when the proposed fitness re-evaluation method is adopted, indicating that the modified fitness evaluated based on the sampled evaluating can better reflect the true fitness of the individuals. + +# 4. Experimental Results + +# 4.1. Experimental Settings + +To validate the effectiveness of our approach, we set single-tasking (evolutionary single-tasking based NAS) as the baseline. Most of the experiments are conducted on MedMNIST [44], which is a collection of 10 preprocessed medical datasets. We selected the PathMNIST dataset of colon pathology, OrganMNIST_Axial, OragnMNIST_Coronal, and OrganMNIST_Sagittal through different processing methods in abdominal CT along three axes. We use these four tasks to construct multitasks with task numbers of 2, 3 and 4, respectively. We also conduct experiments on CIFAR-10 and CIFAR-100 [19], and then transfer the searched best network architecture to ImageNet [34] to explore its effectiveness. For the sake of simplicity, we denote PathMNIST, OrganMNIST_Axial, OragnMNIST_Coronal, OrganMNIST_Sagittal, CIFAR-10, and CIFAR-100 as Path, Organ_A, Organ_C, Organ_S, C-10, and C-100. Similar to [57], the cross-entropy loss function is used for the six tasks and the parameter settings are presented in Table 1 for the search phase. For fair comparisons, the same parameters as in EMT-NAS are maintained for single tasks during the search phase and retraining phase. All experiments are statistical results of five independent runs with an exception to the results on ImageNet, where all experiments were run once only on 1 Nvidia GeForce RTX 2080Ti due to limited computational resources. More details are given in Supplementary Material C. + +# 4.2. Medical Multi-Tasking + +Here, we evaluate the network architectures searched by Single-Tasking and EMT-NAS on the medical multitasking. The results when the number of tasks varies from two to + +Table 1. A summary of hyper-parameter settings. + +
CategoriesParametersSettings (MedMNIST/CIFAR)
Search spaceInitial channels48/20
Repetitions of cells1
Gradient descentBatch size for training128
Batch size for validation1000
Weight decay1.00E-04
Dropout0.1
Momentum0.9
Initial learning rate0.1
Learning rate scheduleCosine Annealing
Search strategyPopulation size20
Generations100/300
Random mating probability0.3
Crossover probability1.00
Mutation probability0.02
+ +Table 2. Comparison on MedMNIST. + +
Index# TasksModelPath (%)Organ_A (%)Organ_C (%)Organ_S (%)GPU Days (%) ↓
1ResNet-18 [11]84.492.188.976.2
1ResNet-50 [11]86.491.689.374.6
1Auto-skearn [8]18.656.367.660.1
1AutoKeras [16]86.492.991.580.3
1AutoML [56]81.181.886.170.6
1SI-EvoNAS [50]90.5±0.793.0±0.391.8±0.480.1±0.3
1Single-Tasking (Baseline)87.4±2.994.0±0.791.5±0.880.7±0.5+00.0
①2EMT-NAS (Ours)91.6±0.595.1±0.2-11.0
②2EMT-NAS (Ours)91.2±0.792.3±0.3-18.4
③2EMT-NAS (Ours)90.5±0.981.5±0.2-12.8
④2EMT-NAS (Ours)94.8±0.592.2±0.5-28.4
⑤2EMT-NAS (Ours)95.0±0.381.3±0.5-23.2
⑥2EMT-NAS (Ours)92.2±0.381.5±0.2-40.1
⑦3EMT-NAS (Ours)95.3±0.392.3±0.281.7±0.4-36.0
⑧3EMT-NAS (Ours)91.4±0.392.3±0.381.8±0.3-29.9
⑨3EMT-NAS (Ours)91.9±0.295.0±0.281.4±0.3-23.3
⑩3EMT-NAS (Ours)91.7±0.695.0±0.492.5±0.2-25.1
⑪4EMT-NAS (Ours)91.2±0.694.9±0.392.2±0.381.4±0.5-31.4
+ +four in comparison to the corresponding single tasks are given in Table 2. In the top rows of the table, the results of the first five results on the four medical datasets taken from [44] are listed. SI-EvoNAS [50] is a state-of-the-art evolutionary NAS algorithm. Single-Tasking is an evolutionary single-tasking algorithm that we have implemented as the baseline. In column GPU Days (\%), the reduction in the runtime of EMT-NAS relative to the corresponding Single-Tasking are listed as a percentage. + +From Table 2, it is clear that the classification accuracy of the neural architectures found by EMT-NAS is higher than the networks found by all single-tasking NAS on the corresponding tasks, and the search time is reduced by $11\% - 40\%$ compared to the baseline. This demonstrates that it is possible to improve the performance of each task through architectural knowledge transfer only. In addition, the best classification accuracy of the network architecture has been obtained when the number of tasks is three. This shows that which tasks and how many tasks are formulated as a multi-tasking problem will influence the performance of algorithm in solving each of the individual tasks. + +Multi-tasking with the same data modality: EMT-NAS (numbered ④, ⑤, ⑥, ⑦) searched for network architectures with a higher classification accuracy than those found by Single-Tasking. As described in [44], crop 2D images from the center slices of the 3D CT bounding boxes in axial/coronal/sagittal views (planes) are obtained in datasets + +Organ_A, Organ_C, and Organ_S. Therefore, these datasets are correlated, and it is reasonable to make use of the common knowledge of these datasets to improve classification accuracy. In addition, ⑦ VS ④, ⑤ and ⑥, respectively, have the best performance on Organ_A, Organ_C, and Organ_S. This demonstrates that the three tasks enhance each other to a greater extent than two by two. Therefore, architectural knowledge transfer works well for different datasets of the same data modality. + +Multi-tasking with different data modalities: The classification accuracy of EMT-NAS (numbered ①, ②, ③, ⑧, ⑨ and ⑩) are slightly higher than that of EMT-NAS (numbered ④, ⑤ and ⑥) on Organ_A, Organ_C, and Organ_S datasets, respectively. From [44], we know that Path is for predicting survival from colorectal cancer histology slides, which means that Organt_A, Organ_C, and Organ_S can benefit more from Path. By contrast, EMT-NAS has transferred different degrees of useful knowledge from Organ_A, Organ_C, and Organ_S, respectively, to Path. From the table, we can observe that the classification accuracy of EMT-NAS (numbered ①, ② and ③) decreases sequentially on PATH. Organ_A, Organ_C, and Organ_S are obtained by different processing methods in abdominal CT along three axes, so their data characteristics are different. Clearly, Path and Organ_A are most beneficial to each other. This also corroborates with the task relational analysis in Fig. 2. Therefore, although these datasets are from different data modalities and are weakly correlated, they can still improve their respective performance through architectural knowledge transfer. + +# 4.3. CIFAR-10 and CIFAR-100 + +We again used RSA in Fig. 2 to analyse the task relatedness between C-10 and C-100, with a task relatedness score of 0.38. C-100 is made up of 20 classes (each containing five subclasses), while C-10 is 10 classes. The results show that ResNet-50, trained on C-100, extracts many different features from the same image compared to those trained on C-10. Therefore, C-10 and C-100 are differentiated. + +The representative algorithms can be roughly divided into four categories, namely manually designed, RL-based, GD-based, and EAs-based. The comparative results on C-10 and C-100 are listed in Table 3. Note that all algorithms are meant for single-tasking search, i.e., they either search for an optimal network architecture on C-10 and C-100, respectively, or search on C-10 and then the found architectures are transferred to C-100. By contrast, EMT-NAS searches for optimal neural architectures simultaneously on C-10 and C-100, and therefore, the GPU days of EMT-NAS is the total time for searching for both architectures. + +In Table 3, EMT-NAS stacks normal blocks twice, while EMT-NAS† stacks three times. EMT-NAS searched the network architecture's on C-10 and C-100 with a higher clas + +Table 3. Comparison on C-10 and C-100. * indicates that the same network architecture is used on both C-10 and C-100, so their GPU days for searching are the same. † indicates normal cell stacking three times for better performance. + +
ModelSearch MethodGPU DaysParams (M)C-10 (%)Params (M)C-100 (%)
Wide ResNet [47]manual-36.595.83*79.50
DenseNet [14]manual-27.296.26*80.75
MobileNetV2 [35]manual-2.194.56*77.09
PNAS [23]SMBO1503.296.59±0.09*80.47
ENAS [28]RL0.454.697.11*80.57
NASNet-A [57]RL20003.397.35--
Block-QNN-Faster [53]RL0.83.996.43*81.79
DARTS [25]GD1.53.397.00±0.14*79.48±0.31
SNAS [41]GD1.52.997.02--
large-scale Evo [31]EA27505.494.640.477
Hier-EA [24]EA3006496.25±0.12--
Amoebanet-A [30]EA31503.296.66±0.06*81.07
AE-CNN [39]EA27/36295.75.479.15
SHEDA-CNN [20]EA0.58/0.9710.8896.3618.6478.84
Single-Tasking (Baseline)EA0.461.8396.24±0.201.6879.70±0.44
Single-Tasking† (Baseline)EA0.462.4196.64±0.182.1980.82±0.71
EMT-NAS (Ours)EA0.422.1796.73±0.152.2381.86±0.10
EMT-NAS† (Ours)EA0.422.9197.04±0.042.9782.60±0.38
+ +sification accuracy than Single-Tasking (baseline), demonstrating that architecture knowledge transfer can effectively improve performance on C-10 and C-100. Compared to other NAS algorithms, our approach achieves better performance and more compact network architectures searched on C-10 and C-100 through architectural knowledge transfer, except for ENAS and NASNet-A on C-10. However, the models found by EMT-NAS have only two-thirds the number of parameters of models found by ENAS. On the other hand, NASNet-A consumes about 4,700 times more GPU days than EMT-NAS. These indicate that our approach can achieve a good performance-complexity trade-off. We also analysed two baselines for joint training (shared or unshared network architectures) in Supplementary Material D. The performance of the algorithms has degraded as data from different tasks are used to update the same supernet. + +# 4.4. Transferability to ImageNet + +As done in [25], we transferred the best network architectures found on C-10 and C-100 to ImageNet for training from scratch, to further validate the transferability of the architectures searched by EMT-NAS. The results comparing EMT-NAS with 15 models (or their variants) on ImageNet are given in Table 4. EMT-NAS-4-C-100 has a lower number of model parameters (2.49M) than all compared algorithms, while it has a higher top-1 accuracy (74.25%) except for MoblieNet-V3, MobileNetV2-1.0+CA, RepVGG-A1, AutoSpace, PC-DARTS and MUXNet-m. For better performance, we change the number of normal cells stacked from two to three to get EMT-NAS-C-100†. The top-1 accuracy of EMT-NAS-C-100† is 75.44%, which again surpasses the accuracy of the rest of the algorithms, and the number of model parameters is 3.25M. This demonstrates that EMT-NAS has good transferability between the network architectures searched on C-10 and C-100. + +Table 4. Comparisons on ImageNet. $\dagger$ indicates normal cell stacking three times for better performance. + +
ModelTop-1 (%)Top-5 (%)Params (M)GPU DaysSearch Method
ShuffleNet 2.0 [51]73.7-5.4-manual
MobileNet-V3 [13]75.2-5.1-manual
MobileNeXt-0.75 [54]72.6-2.5-manual
MobileNetV2-1.0+CA [12]74.3-3.95-manual
RepVGG-A1 [5]74.46-12.78-manual
PNAS [23]74.291.95.1225SMBO
NASNet-A [57]74.091.65.32000RL
DPP-Net-Panacea [6]74.291.794.88RL
AutoSpace [55]75.3-4.38.33RL
DARTS [25]73.391.34.74GD
SNAS [41]72.791.84.31.5GD
PC-DARTS [43]74.992.25.30.1GD
HourNAS-C [45]74.191.64.80.1GD
Amoebanet-A [30]74.592.05.13150EA
MUXNet-m [26]75.392.53.4176EA
Single-Tasking-C-10 (Baseline)73.1891.222.410.23EA
Single-Tasking-C-100 (Baseline)72.8891.062.250.22EA
Single-Tasking-C-10† (Baseline)74.5992.093.150.23EA
Single-Tasking-C-100† (Baseline)74.1191.862.970.22EA
EMT-NAS-C-10 (Ours)73.8391.632.380.42EA
EMT-NAS-C-100 (Ours)74.2591.802.49
EMT-NAS-C-10† (Ours)75.1192.393.130.42EA
EMT-NAS-C-100† (Ours)75.4492.553.25
+ +# 4.5. Ablation Studies + +To verify the effectiveness of the evolutionary multitasking NAS algorithm and the fitness re-evaluation method, four algorithms are compared, namely evolutionary single-Tasking NAS, which serves as the baseline (denoted as Single-tasking in Table 5), evolutionary single-tasking NAS with the fitness re-evaluation method, called Single-Tasking+Reeval, evolutionary multi-tasking NAS without fitness re-evaluation, called Multi-Tasking, and evolutionary multi-tasking NAS with the fitness re-evaluation method, denoted as Multi-Tasking+Reeval. + +Evolutionary Multi-Tasking: By comparing the results of Single-tasking and Multi-Tasking (③ vs ① and ④ vs ②), evolutionary multi-tasking NAS can improve the performance on both C-10 and C-100, confirming the effectiveness of knowledge transfer when simultaneously searching for the optimal neural architectures on similar tasks. + +Fitness Re-Evaluation: By comparing the results with and without fitness re-evaluation (④ vs ③ and ② vs ①), we can see that the proposed fitness re-evaluation method improves the performance on both C-10 and C-100. This confirms that the fitness re-evaluation method is effective in enhancing the performance by alleviating fitness fluctuations in the search based on sampled evaluations. + +Search Efficiency: We take the total runtime of Single-Tasking, and count the percentage increase or decrease of the other three algorithms relative to it. We also calculate three parts of the runtime, including time for training model parameters on the training dataset, time for evaluating model performance on the validation dataset, and time for searching. First, we note that the time taken by the evolutionary multi-tasking is reduced by $50\%$ compared to single-tasking(③ vs ① and ④ vs ②). Because the compu + +Table 5. Comparison of evolutionary single- and multi-tasking optimisation with/without fitness re-evaluation on CIFAR-10 and -100. + +
IndexAlgorithmTask 1Task 2Total Time (%) ↓Training Time (%) ↓Evaluation Time (%) ↓Search Time (%) ↓Average Params (M)Average FLOPs (M)
C-10 (%)Params (M)Transfer (%)C-100 (%)Params (M)Transfer (%)
①Single-Tasking96.23±0.201.8396.07±0.2579.70±0.441.6878.95±0.60+0.0+0.0+0.0+0.01.83334
②Single-Tasking+Reeval96.29±0.251.7496.26±0.1880.48±0.281.9078.77±0.65-5.1-4.1-15.1-1.41.81323
③Multi-Tasking96.49±0.162.02-80.68±0.432.03--2.1+3.8-37.4-49.42.06382
④Multi-Tasking+Reeval96.73±0.152.17-81.86±0.102.23--8.7-4.0-35.9-51.61.97355
+ +tational complexity of the Evolutionary Multi-Tasking and Single-Tasking algorithms is almost the same, except for the time spent on training and evaluation. Second, $③$ vs $①$ and $④$ vs $②$ , the time spent on the evaluation is reduced by about $36\%$ . The population size and the number of generations are the same for single and multi-tasking, i.e., the number of fitness evaluations is the same, so that the total time to optimise multiple tasks simultaneously will be less than the sum of the runtimes when the tasks are optimised one by one. Finally, $④$ vs $③$ and $②$ vs $①$ with a small percentage reduction in the training time. To investigate this further, we reproduce the sampled training process and chose two model metrics, namely the number of parameters and the number of floating point operations (FLOPs). Specifically, when each network architecture was trained once, two metrics were recorded until five runs of the algorithm have stopped, and then averaged and listed in the column Average Params $(M)$ and Average FLOPs $(M)$ of Table 5, respectively. The results show a small reduction in the average number of parameters and the average FLOPs for both $④$ vs $③$ and $②$ vs $①$ . It is assumed that the fitness re-evaluation method allows the algorithm to favour network architectures consisting of operations with a small number of parameters or a low computational complexity in the search process. This may explain the fact that introducing the fitness re-evaluation method can reduce the time spent by the model on the training set by a small amount. Overall, EMT-NAS consumes less runtime than its single-task counterparts. + +Model Transferability: We transferred the network architectures that Single-tasking and Single-tasking+Reeval searched on C-10 and C-100, respectively, to C-100 and C-10 for retraining. The results are presented in column Transfer $(\%)$ , which show that through transfer learning, the performance of the network architectures on the new dataset is much lower than that of the network architectures obtained by evolutionary multi-tasking NAS (Multi-Tasking and Multi-Tasking+Reeval) search. Therefore, evolutionary multi-tasking NAS is more competitive than evolutionary single-tasking NAS with transfer learning. + +# 4.6. Sensitivity Analysis + +In EMT-NAS, $RMP$ is a key parameter that controls the degree of knowledge transfer between tasks. Here, we set the random mating probability $RMP = 0, 0.1, 0.2, 0.3, 0.4, 0.5$ and note that when $RMP = 0$ , two + +Table 6. Comparison of EMT-NAS when random mating probability is set to 0, 0.1, 0.2, 0.3, 0.4, and 0.5. + +
RMPTask 1Validation ACC (%)Test ACC (%)Task 2Validation ACC (%)Test ACC (%)
0C-1088.36±0.6996.28±0.09C-10061.48±1.6580.31±0.40
0.1C-1087.36±1.6096.48±0.18C-10058.85±4.1080.46±0.71
0.2C-1088.32±1.0296.52±0.18C-10059.67±0.4781.11±0.54
0.3C-1088.76±1.0596.73±0.15C-10061.69±2.1581.86±0.10
0.4C-1088.09±1.2596.49±0.18C-10061.27±3.0981.26±0.27
0.5C-1088.52±1.1696.52±0.17C-10061.42±2.5781.15±0.31
+ +single tasks run in the same population without any knowledge transfer between the tasks. Table 6 shows that the validation and test accuracies increase as $RMP$ increases in the beginning, and then decrease as $RMP$ becomes larger, indicating that too much or too little knowledge transfer between tasks can degrade the performance of EMT-NAS. The best performance was achieved on the validation set and test set when $RMP = 0.3$ . + +We also analysed the influence of the population size, crossover and mutation probabilities, and the number of generations on the performance. The results are presented in Supplementary Material E. + +# 5. Conclusion + +In this work, evolutionary multi-tasking is applied to NAS for the first time. Extensive experiments have demonstrated that for multiple classification tasks from different datasets (data modalities), architectural knowledge transfer and fitness re-evaluation method allow EMT-NAS to outperform each task obtained simultaneously over a single task, and that the runtime of EMT-NAS is less than the sum of the runtimes of solving multiple single tasks independently. Although this work achieves implicit architectural knowledge transfer, more precise, explicit knowledge transfer between tasks in evolutionary multi-tasking NAS is desirable and will be investigated in the future. + +# Acknowledgment + +This work is supported by National Natural Science Foundation of China (62136003, 61988101), the Programme of Introducing Talents of Discipline to Universities (the 111 Project) under Grant B17017, Fundamental Research Funds for the Central Universities (222202317006) and Shanghai AI Lab. Y. 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In deep learning, this is usually achieved by sharing a common neural network architecture and jointly training the weights. However, the joint training of weighting parameters on multiple related tasks may lead to performance degradation, known as negative transfer. To address this issue, this work proposes an evolutionary multi-tasking neural architecture search (EMT-NAS) algorithm to accelerate the search process by transferring architectural knowledge across multiple related tasks. In EMT-NAS, unlike the traditional MTL, the model for each task has a personalised network architecture and its own weights, thus offering the capability of effectively alleviating negative transfer. A fitness re-evaluation method is suggested to alleviate fluctuations in performance evaluations resulting from parameter sharing and the mini-batch gradient descent training method, thereby avoiding losing promising solutions during the search process. To rigorously verify the performance of EMT-NAS, the classification tasks used in the empirical assessments are derived from different datasets, including the CIFAR-10 and CIFAR-100, and four MedMNIST datasets. 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Introduction" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 649, + 287, + 685 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 649, + 287, + 685 + ], + "spans": [ + { + "bbox": [ + 47, + 649, + 287, + 685 + ], + "type": "text", + "content": "Many neural architecture search (NAS) algorithms [8, 16, 23, 56] have shown better performance on a specific task than manually designed deep neural networks [11, 14," + } + ] + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 306, + 244, + 438, + 422 + ], + "blocks": [ + { + "bbox": [ + 306, + 244, + 438, + 422 + ], + "lines": [ + { + "bbox": [ + 306, + 244, + 438, + 422 + ], + "spans": [ + { + "bbox": [ + 306, + 244, + 438, + 422 + ], + "type": "image", + "image_path": "b3ce56e560da4fcca584f7153b50060f14d548c8c9671ccfe1779804cf380263.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 424, + 547, + 589 + ], + "lines": [ + { + "bbox": [ + 304, + 424, + 547, + 589 + ], + "spans": [ + { + "bbox": [ + 304, + 424, + 547, + 589 + ], + "type": "text", + "content": "Figure 1. Conceptual differences between our work and two main existing methodologies for two-task learning. (a) Existing multi-task NAS typically handles multiple tasks such as semantic segmentation and surface normal prediction on the same dataset, where the loss function contains losses for multiple tasks, resulting in a network architecture that shares a common set of weight parameters. (b) Model-based transfer learning trains a network architecture on a source dataset and then transfers it to a target dataset by fine-tuning the weights using a separate loss function. (c) EMT-NAS simultaneously optimises multiple classification tasks from different datasets using a separate loss function for each task, resulting in an individual network architecture and corresponding weights for each task. EMT-NAS aims to optimise each task separately while sharing the knowledge of good network architectures to facilitate the optimisation of each task. Best viewed in colour." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 440, + 244, + 543, + 422 + ], + "blocks": [ + { + "bbox": [ + 440, + 244, + 543, + 422 + ], + "lines": [ + { + "bbox": [ + 440, + 244, + 543, + 422 + ], + "spans": [ + { + "bbox": [ + 440, + 244, + 543, + 422 + ], + "type": "image", + "image_path": "bcb99c75970b3ce6347b53239ce83467d937638191aee0bea7a29835b6491807.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 603, + 546, + 651 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 603, + 546, + 651 + ], + "spans": [ + { + "bbox": [ + 304, + 603, + 546, + 651 + ], + "type": "text", + "content": "35, 51]. However, when the task (or dataset) changes, the NAS algorithm needs to be run again to find a new optimal network architecture for the new task, which is typical for single-task learning (STL)." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 654, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 654, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 654, + 547, + 715 + ], + "type": "text", + "content": "By contrast, it has been shown that simultaneously learning multiple related tasks, known as multi-task learning (MTL) is beneficial [3, 52]. One class of MTL focuses on designing or training a single network to jointly solve multiple tasks formed by scene understanding (the same" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 693, + 136, + 703 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 693, + 136, + 703 + ], + "spans": [ + { + "bbox": [ + 58, + 693, + 136, + 703 + ], + "type": "text", + "content": "*Corresponding author." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 63, + 704, + 263, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 63, + 704, + 263, + 712 + ], + "spans": [ + { + "bbox": [ + 63, + 704, + 263, + 712 + ], + "type": "text", + "content": "Code: https://github.com/PengLiao12/EMT-NAS" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "3643" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 289, + 312 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 289, + 312 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 289, + 312 + ], + "type": "text", + "content": "dataset) [38, 46], such as the NYU v2 dataset [37], the CityScapes dataset [4], and the Taskonomy dataset [48]. These tasks consist of semantic segmentation, surface normal prediction, depth prediction, keypoint detection and edge detection, which are known as multiple tasks that arise naturally [3]. Another typical scenario of MTL is inspired from human learning, where humans often transfer knowledge from one task to another related task, for example, the skills of playing squash and tennis could help each other to improve [52]. In this case, tasks may come from different datasets. More often than not, a pair of tasks from different datasets have a lower relatedness score than those from the same dataset [18]. This can be clearly shown if we analyse the task relatedness [1] between classification tasks from four medical datasets using the representation similarity analysis (RSA) [7]. The results of our analysis are presented in Fig. 2, from which we can see that the relatedness score becomes especially low when the datasets are from different data modalities, implying that MTL on tasks from different datasets is more challenging." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 314, + 289, + 495 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 314, + 289, + 495 + ], + "spans": [ + { + "bbox": [ + 47, + 314, + 289, + 495 + ], + "type": "text", + "content": "MTL is able to improve the performance of learning multiple related tasks by means of sharing common knowledge between tasks, including the network architecture and the weights of the model. Existing MTL designs one architecture for multiple tasks, although only a subset of that network architecture is practically used for each task. In other words, there are shares and differences between these subsets of model architectures [33]. In sharing the weights, if one or more tasks have a dominating influence in training the network weights, the performance of MTL may deteriorate on some of the dominated tasks, which is called negative transfer [40]. Therefore, this work aims to improve the performance of each task by finding a personalised network architecture for each task, thereby alleviating negative transfer resulting from the jointly trained weights." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 495, + 289, + 616 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 495, + 289, + 616 + ], + "spans": [ + { + "bbox": [ + 47, + 495, + 289, + 616 + ], + "type": "text", + "content": "Inspired by the successful research on multi-factorial evolutionary algorithms (MFEAs) [9], a recently proposed approach to knowledge transfer in evolutionary optimisation, this work designs an algorithm to separately search for a personalised network architecture and corresponding weight parameters for each task in the same search space. This way, knowledge transfer across different tasks can be achieved through crossover between these architectures to accelerate the search process on each task, provided that there are similarities between the multiple learning tasks." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 617, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 617, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 47, + 617, + 289, + 715 + ], + "type": "text", + "content": "Contributions: First, we propose an evolutionary multitasking NAS algorithm (EMT-NAS) for finding personalised network architectures for different tasks (datasets) in the same search space. Architectural knowledge transfer is achieved by optimising the supernet parameters of each task separately and recommending neural network architectures with good performance on their own task. Second, block-based crossover and bit-based mutation opera" + } + ] + } + ], + "index": 3 + }, + { + "type": "image", + "bbox": [ + 331, + 72, + 517, + 205 + ], + "blocks": [ + { + "bbox": [ + 331, + 72, + 517, + 205 + ], + "lines": [ + { + "bbox": [ + 331, + 72, + 517, + 205 + ], + "spans": [ + { + "bbox": [ + 331, + 72, + 517, + 205 + ], + "type": "image", + "image_path": "0df761503b86f8f7b1693b413eb7b7b581864523e92e0a1b81b0413960b53d46.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 206, + 547, + 318 + ], + "lines": [ + { + "bbox": [ + 304, + 206, + 547, + 318 + ], + "spans": [ + { + "bbox": [ + 304, + 206, + 547, + 318 + ], + "type": "text", + "content": "Figure 2. Task similarity matrix. The relatedness scores between four medical tasks are computed using ResNet-50 as a feature extractor. PathMNIST [44] is the tissue classification based on colorectal cancer histology slides, while OrganMNIST-{Axial,Coronal,Sagittal} [44] are organ classifications based on 3 types of 2D images formed by 3D computed tomography (CT) images. We observe that the relatedness between PathMNIST and OrganMNIST-{Axial,Coronal,Sagittal}, respectively, are all smaller than that between OrganMNIST-{Axial,Coronal,Sagittal}." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 323, + 547, + 517 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 323, + 547, + 517 + ], + "spans": [ + { + "bbox": [ + 304, + 323, + 547, + 517 + ], + "type": "text", + "content": "tors are designed to accommodate the transformation from a continuous space to a discrete space. Finally, a fitness re-evaluation method is introduced to alleviate fitness fluctuations over the generations resulting from parameter sharing and the mini-batch gradient descent based training to keep promising solutions. We present thorough experimental evaluations on different datasets, including medical classification benchmarks (PathMNIST, OrganMNIST-{Axial,Coronal,Sagittal}) and popular image classification benchmarks (CIFAR-10, CIFAR-100, ImageNet), demonstrating the efficacy and the value of each component of EMT-NAS. Our results demonstrate that, unlike traditional MTL, it is feasible to search for personalised network architectures for multiple tasks through architectural knowledge transfer, obtaining better performance and requiring less search time compared with single-task learning." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 526, + 392, + 539 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 526, + 392, + 539 + ], + "spans": [ + { + "bbox": [ + 306, + 526, + 392, + 539 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 545, + 545, + 569 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 545, + 545, + 569 + ], + "spans": [ + { + "bbox": [ + 304, + 545, + 545, + 569 + ], + "type": "text", + "content": "Below we summarise the similarities and differences with our work in the following themes." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "type": "text", + "content": "Multi-Task Learning is designed to learn a network with shared representation from multiple tasks in deep learning. A major challenge in MTL is to balance the joint learning of all tasks to avoid negative transfer [40], motivated by [17] to balance the gradient magnitudes by setting the task-specific weights in the loss. The back-propagation loss function consists of a linear weighting of the losses for each task [18], as shown in Fig. 1a, which may additionally include purpose-specific losses, e.g., the sparsity and sharing of the architecture [38], or loss of generators [32]. Both the coefficients in the loss function and the complexity of the losses affect the final performance of the MTL. In [36]," + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "3644" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 287, + 107 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 287, + 107 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 287, + 107 + ], + "type": "text", + "content": "MTL is considered as multi-objective optimisation, searching for the Pareto optimal solutions to avoid a linear weighting of different losses." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 110, + 286, + 193 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 110, + 286, + 193 + ], + "spans": [ + { + "bbox": [ + 47, + 110, + 286, + 193 + ], + "type": "text", + "content": "However, all above mentioned algorithms deal with tasks from the same dataset. In this work, updating of the weight parameters of the supernet for each task is independent, i.e., each task has an independent loss function. Rather than solving multiple tasks that arise naturally, the tasks in our MTL setting come from different datasets, or even have from different data modalities." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 195, + 286, + 302 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 195, + 286, + 302 + ], + "spans": [ + { + "bbox": [ + 46, + 195, + 286, + 302 + ], + "type": "text", + "content": "Transfer Learning establishes a mapping from the source domain to the target domain [15]. Model-based transfer learning is shown in Fig. 1b, where the first step pretrains the model on the source dataset and the second step tunes the parameters of the pre-trained model on the target dataset. During the transfer, the model structure is also adjusted to adapt it to the target task [22]. Note that in the proposed framework, the architectural, rather than the weights parameters, is shared." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 304, + 286, + 544 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 304, + 286, + 544 + ], + "spans": [ + { + "bbox": [ + 46, + 304, + 286, + 544 + ], + "type": "text", + "content": "Neural Architecture Search has been shown to be effective in the search for network architectures for specific tasks. Three main search strategies have been adopted in NAS, namely reinforcement learning (RL) [6, 53, 57], evolutionary algorithms (EAs) [20, 24, 26, 30, 39], and gradient descent (GD) [25, 41, 43, 45]. With the help of parameter sharing [28], the performance of new neural architectures can be evaluated without training from scratch [31]. It should be pointed out that while parameter sharing can greatly reduce the computation time, it may lead to inaccurate performance assessments of candidate submodels [42] and so-called multi-model forgetting, when multiple models are subsequently trained [2]. Although parameter sharing combined with the mini-batch gradient descent method can further reduce the computation time, promising candidate neural architectures may get lost in evolutionary NAS due to strong fluctuations in performance caused by the mini-batch gradient descent method [50]. Therefore, in our work, a fitness re-evaluation method is proposed to alleviate fitness fluctuations in population iterations." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 545, + 286, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 545, + 286, + 712 + ], + "spans": [ + { + "bbox": [ + 46, + 545, + 286, + 712 + ], + "type": "text", + "content": "Evolutionary Multi-Tasking is proposed for solving numerical optimisation problems. When the function landscapes or optimal solutions of two tasks have a certain degree of similarity, promising candidate solutions belonging to one task may be helpful for the other task. Evolutionary multi-tasking has been extended to multi-objective [27], constrained multi-objective [29], and surrogate-assisted for expensive problems [21], and has been shown to be effective for practical problems such as hyperspectral band selection [10] and multi-scene scheduling [49]. In this work, we use evolutionary multi-tasking for the first time to transfer architectural knowledge across multiple tasks from different datasets, and block-based crossover and bit-based mutation are designed to accommodate the transformation from" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 306, + 72, + 461, + 84 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 72, + 461, + 84 + ], + "spans": [ + { + "bbox": [ + 306, + 72, + 461, + 84 + ], + "type": "text", + "content": "a continuous space to a discrete space." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 306, + 94, + 400, + 107 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 94, + 400, + 107 + ], + "spans": [ + { + "bbox": [ + 306, + 94, + 400, + 107 + ], + "type": "text", + "content": "3. Proposed Work" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 114, + 524, + 126 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 114, + 524, + 126 + ], + "spans": [ + { + "bbox": [ + 306, + 114, + 524, + 126 + ], + "type": "text", + "content": "3.1. Evolutionary Multi-Tasking Optimization" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 132, + 545, + 204 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 132, + 545, + 204 + ], + "spans": [ + { + "bbox": [ + 304, + 132, + 545, + 204 + ], + "type": "text", + "content": "In an MFEA, each individual in the population belongs to only one of the tasks to be optimized, and knowledge transfer between tasks is realized with crossover at a probability between individuals belonging to different tasks. A multi-tasking optimization problem consisting of " + }, + { + "bbox": [ + 304, + 132, + 545, + 204 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 304, + 132, + 545, + 204 + ], + "type": "text", + "content": " single-objective minimization tasks can be formulated as follows:" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 326, + 210, + 544, + 239 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 326, + 210, + 544, + 239 + ], + "spans": [ + { + "bbox": [ + 326, + 210, + 544, + 239 + ], + "type": "interline_equation", + "content": "\\left\\{ \\begin{array}{l} \\mathbf {x} _ {1} ^ {*}, \\mathbf {x} _ {2} ^ {*}, \\dots , \\mathbf {x} _ {K} ^ {*} \\end{array} \\right\\} = \\left\\{\\operatorname {a r g m i n} f _ {1} (\\mathbf {x} _ {1}), \\operatorname {a r g m i n} f _ {2} (\\mathbf {x} _ {2}), \\dots , \\operatorname {a r g m i n} f _ {K} (\\mathbf {x} _ {K}) \\right\\} \\tag {1}", + "image_path": "d533b495704d97957274bd5e3c7d4ffc89d5fef0be59fc95624d71b864ffb0e5.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 245, + 545, + 292 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 245, + 545, + 292 + ], + "spans": [ + { + "bbox": [ + 305, + 245, + 545, + 292 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 245, + 545, + 292 + ], + "type": "inline_equation", + "content": "f_{k}(\\mathbf{x}_{k}), k = 1,2,\\ldots ,K" + }, + { + "bbox": [ + 305, + 245, + 545, + 292 + ], + "type": "text", + "content": " is the " + }, + { + "bbox": [ + 305, + 245, + 545, + 292 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 305, + 245, + 545, + 292 + ], + "type": "text", + "content": "-th task. " + }, + { + "bbox": [ + 305, + 245, + 545, + 292 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_k^* = (x_{k,1}^*,x_{k,2}^*,\\dots,x_{k,D_M}^*)" + }, + { + "bbox": [ + 305, + 245, + 545, + 292 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 305, + 245, + 545, + 292 + ], + "type": "inline_equation", + "content": "k = 1,2,\\ldots ,K" + }, + { + "bbox": [ + 305, + 245, + 545, + 292 + ], + "type": "text", + "content": " is the optimal solution of the " + }, + { + "bbox": [ + 305, + 245, + 545, + 292 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 305, + 245, + 545, + 292 + ], + "type": "text", + "content": "-th task, " + }, + { + "bbox": [ + 305, + 245, + 545, + 292 + ], + "type": "inline_equation", + "content": "D_{M}" + }, + { + "bbox": [ + 305, + 245, + 545, + 292 + ], + "type": "text", + "content": " is the dimension of the " + }, + { + "bbox": [ + 305, + 245, + 545, + 292 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 305, + 245, + 545, + 292 + ], + "type": "text", + "content": "-th task." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 299, + 520, + 312 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 299, + 520, + 312 + ], + "spans": [ + { + "bbox": [ + 306, + 299, + 520, + 312 + ], + "type": "text", + "content": "3.2. Search Space and Architecture Encoding" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 318, + 545, + 485 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 318, + 545, + 485 + ], + "spans": [ + { + "bbox": [ + 304, + 318, + 545, + 485 + ], + "type": "text", + "content": "To facilitate the transfer of architectural knowledge between multiple tasks, the same search space is used for multiple tasks, i.e., the candidate architectures are consistent for each task. Similar to [57], the search space is based on normal and reduced cells. And the optional operations in each block include depthwise-separable convolution, dilated convolution, max pooling, average pooling and identity. The chromosome of each individual encodes the structure of the block, i.e., four integer bits (the first two encoding the inputs, and the last two the operation) represent a block. The coding of the five blocks constitutes a cell coding. Since two types of cells are used, 40 integers in total are used to represent each neural architecture. More details can be found in Supplementary Material A." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 491, + 377, + 502 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 491, + 377, + 502 + ], + "spans": [ + { + "bbox": [ + 306, + 491, + 377, + 502 + ], + "type": "text", + "content": "3.3. EMT-NAS" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 510, + 545, + 641 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 510, + 545, + 641 + ], + "spans": [ + { + "bbox": [ + 304, + 510, + 545, + 641 + ], + "type": "text", + "content": "The overall framework of the proposed EMT-NAS is presented in Fig. 3, where an evolutionary algorithm searches for optimal neural architectures for two different tasks at the same time. The main components of EMT-NAS are in the upper panel of Fig. 3, which is composed of randomly generated initial population, offspring generation by means of crossover and mutation according to the parents' skill factor " + }, + { + "bbox": [ + 304, + 510, + 545, + 641 + ], + "type": "inline_equation", + "content": "\\tau" + }, + { + "bbox": [ + 304, + 510, + 545, + 641 + ], + "type": "text", + "content": " (see Section 3.4), and a top " + }, + { + "bbox": [ + 304, + 510, + 545, + 641 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 304, + 510, + 545, + 641 + ], + "type": "text", + "content": " selection for each task as the environmental selection. The full pseudo code and a detailed description of EMT-NAS can be found in Supplementary Material B." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 642, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 642, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 304, + 642, + 545, + 712 + ], + "type": "text", + "content": "Each task has a set of supernet weights that do not affect each other. Sampled training is a method for continuous updating of the supernet weights on the training set based on weight sharing. For each mini-batch of the training data of each task at one epoch, one individual (representing one candidate architecture) belonging to this task will" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "3645" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 49, + 71, + 545, + 258 + ], + "blocks": [ + { + "bbox": [ + 49, + 71, + 545, + 258 + ], + "lines": [ + { + "bbox": [ + 49, + 71, + 545, + 258 + ], + "spans": [ + { + "bbox": [ + 49, + 71, + 545, + 258 + ], + "type": "image", + "image_path": "96534d886ebf24e08b2a18ee706a51030d6c7bfbf5756d38a4844655490b53f1.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 258, + 547, + 304 + ], + "lines": [ + { + "bbox": [ + 46, + 258, + 547, + 304 + ], + "spans": [ + { + "bbox": [ + 46, + 258, + 547, + 304 + ], + "type": "text", + "content": "Figure 3. The flow chart of EMT-NAS, where two tasks are used as an example. The difference with the single-tasking evolutionary algorithm is that each individual in the population may belong to the same or different tasks. In addition, each task has a separate set of weights for the supernet. The lower panel shows the sampled training based on a weight sharing method on the training set and the sampled evaluation based on a fitness re-evaluation method on the validation set. Best viewed in colour." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 48, + 309, + 289, + 405 + ], + "blocks": [ + { + "bbox": [ + 48, + 309, + 289, + 405 + ], + "lines": [ + { + "bbox": [ + 48, + 309, + 289, + 405 + ], + "spans": [ + { + "bbox": [ + 48, + 309, + 289, + 405 + ], + "type": "image", + "image_path": "6eb7b4623c8652793aa6b1a368c0be052fcfe62e58f0ddfead2c17441629e594.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 63, + 407, + 270, + 418 + ], + "lines": [ + { + "bbox": [ + 63, + 407, + 270, + 418 + ], + "spans": [ + { + "bbox": [ + 63, + 407, + 270, + 418 + ], + "type": "text", + "content": "Figure 4. Block-based crossover and bit-based mutation." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 430, + 287, + 526 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 430, + 287, + 526 + ], + "spans": [ + { + "bbox": [ + 46, + 430, + 287, + 526 + ], + "type": "text", + "content": "be randomly sampled and trained on the mini-batch using the gradient based method. After training, sampled evaluating computes the fitness of the individual by calculating the classification accuracy on the validation data of the same task. Each individual is evaluated once on a random minibatch of the corresponding task validation dataset. Hence, the computational cost of training the weighting parameters and evaluating the fitness can be significantly reduced." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 536, + 171, + 550 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 536, + 171, + 550 + ], + "spans": [ + { + "bbox": [ + 47, + 536, + 171, + 550 + ], + "type": "text", + "content": "3.4. Offspring Generation" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 556, + 287, + 651 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 556, + 287, + 651 + ], + "spans": [ + { + "bbox": [ + 46, + 556, + 287, + 651 + ], + "type": "text", + "content": "Transfer of useful knowledge between tasks is the key reason for EMT-NAS to enhance its performance. As in MFEAs, knowledge transfer in EMT-NAS is realised through simultaneously evolving neural architectures for multiple related tasks in one population. More specifically, knowledge exchange across the tasks is achieved by performing crossover on individuals optimizing architectures on different tasks." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 654, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 654, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 654, + 288, + 715 + ], + "type": "text", + "content": "In reproduction, two parents will be selected each time at a probability proportional to the individuals' fitness value. That is, the greater the fitness of an individual, the larger chance it will have to produce offspring. If the two selected parents belong to the same task, then crossover will be car" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 312, + 545, + 350 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 312, + 545, + 350 + ], + "spans": [ + { + "bbox": [ + 304, + 312, + 545, + 350 + ], + "type": "text", + "content": "ried out to generate two offspring, both inheriting the same skill factor " + }, + { + "bbox": [ + 304, + 312, + 545, + 350 + ], + "type": "inline_equation", + "content": "\\tau" + }, + { + "bbox": [ + 304, + 312, + 545, + 350 + ], + "type": "text", + "content": " of their parents. In addition, mutation will also be applied to the two offspring to promote exploration." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 357, + 546, + 536 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 357, + 546, + 536 + ], + "spans": [ + { + "bbox": [ + 304, + 357, + 546, + 536 + ], + "type": "text", + "content": "When the pair of the selected parent individuals belong to different tasks, two different procedures will be carried out according to a predefined probability, called random mating probability (RMP). If a randomly generated number between 0 and 1 is less than " + }, + { + "bbox": [ + 304, + 357, + 546, + 536 + ], + "type": "inline_equation", + "content": "RMP" + }, + { + "bbox": [ + 304, + 357, + 546, + 536 + ], + "type": "text", + "content": ", a crossover operator will be applied to the two parents to generate two offsprings, which are then mutated. The two tasks of the parents will be randomly assigned to one of the offsprings at an equal probability. At a probability of 1-" + }, + { + "bbox": [ + 304, + 357, + 546, + 536 + ], + "type": "inline_equation", + "content": "RMP" + }, + { + "bbox": [ + 304, + 357, + 546, + 536 + ], + "type": "text", + "content": ", only mutations will be performed on each of the two parents to generate two offsprings. Consequently, the skill factor " + }, + { + "bbox": [ + 304, + 357, + 546, + 536 + ], + "type": "inline_equation", + "content": "\\tau" + }, + { + "bbox": [ + 304, + 357, + 546, + 536 + ], + "type": "text", + "content": " of each offspring is the same as that of its parent. The probability threshold " + }, + { + "bbox": [ + 304, + 357, + 546, + 536 + ], + "type": "inline_equation", + "content": "RMP" + }, + { + "bbox": [ + 304, + 357, + 546, + 536 + ], + "type": "text", + "content": " is a parameter to be specified by the user and a sensitivity analysis of " + }, + { + "bbox": [ + 304, + 357, + 546, + 536 + ], + "type": "inline_equation", + "content": "RMP" + }, + { + "bbox": [ + 304, + 357, + 546, + 536 + ], + "type": "text", + "content": " will be provided in the experimental Section 4.6." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 546, + 546, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 546, + 546, + 712 + ], + "spans": [ + { + "bbox": [ + 304, + 546, + 546, + 712 + ], + "type": "text", + "content": "Illustrative examples of the crossover and mutation are given in Fig. 4. For clarity, we only show a segment of the parent chromosome consisting of three blocks. There is a strong correlation between the input source and the operation of the connection, which has a great impact on the performance of the network structure [50]. In block-based crossover, the parent chromosomes " + }, + { + "bbox": [ + 304, + 546, + 546, + 712 + ], + "type": "inline_equation", + "content": "p_1" + }, + { + "bbox": [ + 304, + 546, + 546, + 712 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 546, + 546, + 712 + ], + "type": "inline_equation", + "content": "p_2" + }, + { + "bbox": [ + 304, + 546, + 546, + 712 + ], + "type": "text", + "content": ", in blocks, are swapped at less than the crossover probability " + }, + { + "bbox": [ + 304, + 546, + 546, + 712 + ], + "type": "inline_equation", + "content": "CP" + }, + { + "bbox": [ + 304, + 546, + 546, + 712 + ], + "type": "text", + "content": " to generate offspring " + }, + { + "bbox": [ + 304, + 546, + 546, + 712 + ], + "type": "inline_equation", + "content": "q_1" + }, + { + "bbox": [ + 304, + 546, + 546, + 712 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 546, + 546, + 712 + ], + "type": "inline_equation", + "content": "q_2" + }, + { + "bbox": [ + 304, + 546, + 546, + 712 + ], + "type": "text", + "content": ". In bit-based mutation, the parent chromosome " + }, + { + "bbox": [ + 304, + 546, + 546, + 712 + ], + "type": "inline_equation", + "content": "q_i" + }, + { + "bbox": [ + 304, + 546, + 546, + 712 + ], + "type": "text", + "content": ", in bits, is randomly replaced from the candidate space at less than the mutation probability " + }, + { + "bbox": [ + 304, + 546, + 546, + 712 + ], + "type": "inline_equation", + "content": "MP" + }, + { + "bbox": [ + 304, + 546, + 546, + 712 + ], + "type": "text", + "content": ", generating offspring " + }, + { + "bbox": [ + 304, + 546, + 546, + 712 + ], + "type": "inline_equation", + "content": "o_i" + }, + { + "bbox": [ + 304, + 546, + 546, + 712 + ], + "type": "text", + "content": ". This is done by changing the input source or operation to improve the performance of the network architecture." + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "3646" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 50, + 70, + 171, + 171 + ], + "blocks": [ + { + "bbox": [ + 50, + 70, + 171, + 171 + ], + "lines": [ + { + "bbox": [ + 50, + 70, + 171, + 171 + ], + "spans": [ + { + "bbox": [ + 50, + 70, + 171, + 171 + ], + "type": "image", + "image_path": "486aa3e56a443a1e8e1fdc35b68998a25f0d6ec700e8ae48d647d93ca84a8a0f.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 104, + 175, + 115, + 183 + ], + "lines": [ + { + "bbox": [ + 104, + 175, + 115, + 183 + ], + "spans": [ + { + "bbox": [ + 104, + 175, + 115, + 183 + ], + "type": "text", + "content": "(a)" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 173, + 70, + 294, + 171 + ], + "blocks": [ + { + "bbox": [ + 173, + 70, + 294, + 171 + ], + "lines": [ + { + "bbox": [ + 173, + 70, + 294, + 171 + ], + "spans": [ + { + "bbox": [ + 173, + 70, + 294, + 171 + ], + "type": "image", + "image_path": "5c1060720207f624fe4f6a3922124bd663df40bf790a301d1edef562caaf400f.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 227, + 175, + 237, + 183 + ], + "lines": [ + { + "bbox": [ + 227, + 175, + 237, + 183 + ], + "spans": [ + { + "bbox": [ + 227, + 175, + 237, + 183 + ], + "type": "text", + "content": "(b)" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 49, + 186, + 171, + 285 + ], + "blocks": [ + { + "bbox": [ + 49, + 186, + 171, + 285 + ], + "lines": [ + { + "bbox": [ + 49, + 186, + 171, + 285 + ], + "spans": [ + { + "bbox": [ + 49, + 186, + 171, + 285 + ], + "type": "image", + "image_path": "0b1d377c5c34b72f55e1e08a4cc4763f32b7c062c9e5374bb8e6714b5da0918f.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 104, + 290, + 115, + 298 + ], + "lines": [ + { + "bbox": [ + 104, + 290, + 115, + 298 + ], + "spans": [ + { + "bbox": [ + 104, + 290, + 115, + 298 + ], + "type": "text", + "content": "(c)" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "type": "image", + "bbox": [ + 173, + 186, + 294, + 285 + ], + "blocks": [ + { + "bbox": [ + 173, + 186, + 294, + 285 + ], + "lines": [ + { + "bbox": [ + 173, + 186, + 294, + 285 + ], + "spans": [ + { + "bbox": [ + 173, + 186, + 294, + 285 + ], + "type": "image", + "image_path": "d5c62122fac71a25ab75d7025ec0ba0fdf5d8dbd5019cb5f3938b1a9f5cc6697.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 227, + 290, + 237, + 298 + ], + "lines": [ + { + "bbox": [ + 227, + 290, + 237, + 298 + ], + "spans": [ + { + "bbox": [ + 227, + 290, + 237, + 298 + ], + "type": "text", + "content": "(d)" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 46, + 299, + 287, + 399 + ], + "lines": [ + { + "bbox": [ + 46, + 299, + 287, + 399 + ], + "spans": [ + { + "bbox": [ + 46, + 299, + 287, + 399 + ], + "type": "text", + "content": "Figure 5. Empirical evaluations of the proposed fitness re-evaluation method on CIFAR-10 and CIFAR-100. In the figures, the red dashed lines denote the estimated fitness based on the sampled evaluation without re-evaluation ((a) and (b)) and with the proposed re-evaluation ((c) and (d)), while the blue solid lines denote the true fitness based on an accurate evaluation using all validation data. From these results, we can see that strong fluctuations in the true fitness of the network have been reduced when the proposed fitness re-evaluation is adopted." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_caption" + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 407, + 170, + 419 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 407, + 170, + 419 + ], + "spans": [ + { + "bbox": [ + 47, + 407, + 170, + 419 + ], + "type": "text", + "content": "3.5. Fitness Re-evaluation" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 426, + 287, + 522 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 426, + 287, + 522 + ], + "spans": [ + { + "bbox": [ + 46, + 426, + 287, + 522 + ], + "type": "text", + "content": "There are two important reasons why the fitness re-evaluation method was proposed. First, when using the mini-batch gradient descent training, the sign of the gradient resulting from each mini-batch data may be inconsistent. Consequently, the performance of a network estimated using the sampled evaluating may fluctuate strongly over the generations. Second, such fluctuations are made even more serious because of parameter sharing adopted in training." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 523, + 287, + 631 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 523, + 287, + 631 + ], + "spans": [ + { + "bbox": [ + 46, + 523, + 287, + 631 + ], + "type": "text", + "content": "To examine this issue more closely, we plot the fitness (the validation accuracy) of the best individual from a typical run of evolutionary NAS on CIFAR-10 and CIFAR-100 simultaneously in Figs. 5a and 5b. We can observe that there is a big difference between the estimated and true validation accuracies and the true performance fluctuates strongly over the generations. As a result, promising individual may get lost because of the strong fitness fluctuations and inaccurate sampled evaluations." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 46, + 631, + 287, + 691 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 631, + 287, + 691 + ], + "spans": [ + { + "bbox": [ + 46, + 631, + 287, + 691 + ], + "type": "text", + "content": "To alleviate strong fluctuations in the fitness, we propose to use the fitness of the corresponding parent individual to modify the fitness of the offspring so that the increase or decrease will become less dramatic. Thus, the fitness of an offspring is modified as follows:" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 104, + 700, + 287, + 715 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 104, + 700, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 104, + 700, + 287, + 715 + ], + "type": "interline_equation", + "content": "F = F _ {p} + \\left(F _ {o} - F _ {p}\\right) \\times \\log_ {T} t \\tag {2}", + "image_path": "4c182f5913d083e5abfdf037cf2e2002f1d9f8bcb8831a531c551f267db8762c.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 72, + 545, + 143 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 143 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 143 + ], + "type": "text", + "content": "where, " + }, + { + "bbox": [ + 304, + 72, + 545, + 143 + ], + "type": "inline_equation", + "content": "F_{o}, F_{p}, F" + }, + { + "bbox": [ + 304, + 72, + 545, + 143 + ], + "type": "text", + "content": " are the fitness value of the offspring, the fitness of the parent that generates the offspring, and the modified fitness of the offspring; " + }, + { + "bbox": [ + 304, + 72, + 545, + 143 + ], + "type": "inline_equation", + "content": "t = 2,\\dots ,T" + }, + { + "bbox": [ + 304, + 72, + 545, + 143 + ], + "type": "text", + "content": " is the current generation, and " + }, + { + "bbox": [ + 304, + 72, + 545, + 143 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 304, + 72, + 545, + 143 + ], + "type": "text", + "content": " is the maximum number of generations. We call the modification of the offspring fitness according to Equation (2) fitness re-evaluation." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 144, + 546, + 288 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 144, + 546, + 288 + ], + "spans": [ + { + "bbox": [ + 304, + 144, + 546, + 288 + ], + "type": "text", + "content": "The logarithmic function in Eq. 2 is based on " + }, + { + "bbox": [ + 304, + 144, + 546, + 288 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 304, + 144, + 546, + 288 + ], + "type": "text", + "content": ", which increases to 1.0 as " + }, + { + "bbox": [ + 304, + 144, + 546, + 288 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 144, + 546, + 288 + ], + "type": "text", + "content": " increases. Thus, " + }, + { + "bbox": [ + 304, + 144, + 546, + 288 + ], + "type": "inline_equation", + "content": "F_{o} - F_{p}" + }, + { + "bbox": [ + 304, + 144, + 546, + 288 + ], + "type": "text", + "content": " will be penalised by the logarithm function. Now we re-run the evolutionary NAS on the two tasks (CIFAR-10 and CIFAR-100) by applying the fitness re-evaluation method, and the true fitness as well as the re-evaluated fitness using the sampled validation of the best individual are plotted in Figs. 5c and 5d. From these results, we can see that the individual's true fitness value improves more steadily when the proposed fitness re-evaluation method is adopted, indicating that the modified fitness evaluated based on the sampled evaluating can better reflect the true fitness of the individuals." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 300, + 432, + 313 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 300, + 432, + 313 + ], + "spans": [ + { + "bbox": [ + 305, + 300, + 432, + 313 + ], + "type": "text", + "content": "4. Experimental Results" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 319, + 432, + 333 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 319, + 432, + 333 + ], + "spans": [ + { + "bbox": [ + 306, + 319, + 432, + 333 + ], + "type": "text", + "content": "4.1. Experimental Settings" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 339, + 546, + 650 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 339, + 546, + 650 + ], + "spans": [ + { + "bbox": [ + 304, + 339, + 546, + 650 + ], + "type": "text", + "content": "To validate the effectiveness of our approach, we set single-tasking (evolutionary single-tasking based NAS) as the baseline. Most of the experiments are conducted on MedMNIST [44], which is a collection of 10 preprocessed medical datasets. We selected the PathMNIST dataset of colon pathology, OrganMNIST_Axial, OragnMNIST_Coronal, and OrganMNIST_Sagittal through different processing methods in abdominal CT along three axes. We use these four tasks to construct multitasks with task numbers of 2, 3 and 4, respectively. We also conduct experiments on CIFAR-10 and CIFAR-100 [19], and then transfer the searched best network architecture to ImageNet [34] to explore its effectiveness. For the sake of simplicity, we denote PathMNIST, OrganMNIST_Axial, OragnMNIST_Coronal, OrganMNIST_Sagittal, CIFAR-10, and CIFAR-100 as Path, Organ_A, Organ_C, Organ_S, C-10, and C-100. Similar to [57], the cross-entropy loss function is used for the six tasks and the parameter settings are presented in Table 1 for the search phase. For fair comparisons, the same parameters as in EMT-NAS are maintained for single tasks during the search phase and retraining phase. All experiments are statistical results of five independent runs with an exception to the results on ImageNet, where all experiments were run once only on 1 Nvidia GeForce RTX 2080Ti due to limited computational resources. More details are given in Supplementary Material C." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 306, + 658, + 436, + 672 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 658, + 436, + 672 + ], + "spans": [ + { + "bbox": [ + 306, + 658, + 436, + 672 + ], + "type": "text", + "content": "4.2. Medical Multi-Tasking" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 306, + 677, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 677, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 306, + 677, + 545, + 713 + ], + "type": "text", + "content": "Here, we evaluate the network architectures searched by Single-Tasking and EMT-NAS on the medical multitasking. The results when the number of tasks varies from two to" + } + ] + } + ], + "index": 20 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "3647" + } + ] + } + ], + "index": 21 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 51, + 83, + 282, + 209 + ], + "blocks": [ + { + "bbox": [ + 77, + 71, + 256, + 82 + ], + "lines": [ + { + "bbox": [ + 77, + 71, + 256, + 82 + ], + "spans": [ + { + "bbox": [ + 77, + 71, + 256, + 82 + ], + "type": "text", + "content": "Table 1. A summary of hyper-parameter settings." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 51, + 83, + 282, + 209 + ], + "lines": [ + { + "bbox": [ + 51, + 83, + 282, + 209 + ], + "spans": [ + { + "bbox": [ + 51, + 83, + 282, + 209 + ], + "type": "table", + "html": "
CategoriesParametersSettings (MedMNIST/CIFAR)
Search spaceInitial channels48/20
Repetitions of cells1
Gradient descentBatch size for training128
Batch size for validation1000
Weight decay1.00E-04
Dropout0.1
Momentum0.9
Initial learning rate0.1
Learning rate scheduleCosine Annealing
Search strategyPopulation size20
Generations100/300
Random mating probability0.3
Crossover probability1.00
Mutation probability0.02
", + "image_path": "31d8ac57486bd4844225057e3d71e2734215582af68b40d5338ac3b676f18436.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "type": "table", + "bbox": [ + 48, + 226, + 286, + 380 + ], + "blocks": [ + { + "bbox": [ + 97, + 213, + 235, + 224 + ], + "lines": [ + { + "bbox": [ + 97, + 213, + 235, + 224 + ], + "spans": [ + { + "bbox": [ + 97, + 213, + 235, + 224 + ], + "type": "text", + "content": "Table 2. Comparison on MedMNIST." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 48, + 226, + 286, + 380 + ], + "lines": [ + { + "bbox": [ + 48, + 226, + 286, + 380 + ], + "spans": [ + { + "bbox": [ + 48, + 226, + 286, + 380 + ], + "type": "table", + "html": "
Index# TasksModelPath (%)Organ_A (%)Organ_C (%)Organ_S (%)GPU Days (%) ↓
1ResNet-18 [11]84.492.188.976.2
1ResNet-50 [11]86.491.689.374.6
1Auto-skearn [8]18.656.367.660.1
1AutoKeras [16]86.492.991.580.3
1AutoML [56]81.181.886.170.6
1SI-EvoNAS [50]90.5±0.793.0±0.391.8±0.480.1±0.3
1Single-Tasking (Baseline)87.4±2.994.0±0.791.5±0.880.7±0.5+00.0
①2EMT-NAS (Ours)91.6±0.595.1±0.2-11.0
②2EMT-NAS (Ours)91.2±0.792.3±0.3-18.4
③2EMT-NAS (Ours)90.5±0.981.5±0.2-12.8
④2EMT-NAS (Ours)94.8±0.592.2±0.5-28.4
⑤2EMT-NAS (Ours)95.0±0.381.3±0.5-23.2
⑥2EMT-NAS (Ours)92.2±0.381.5±0.2-40.1
⑦3EMT-NAS (Ours)95.3±0.392.3±0.281.7±0.4-36.0
⑧3EMT-NAS (Ours)91.4±0.392.3±0.381.8±0.3-29.9
⑨3EMT-NAS (Ours)91.9±0.295.0±0.281.4±0.3-23.3
⑩3EMT-NAS (Ours)91.7±0.695.0±0.492.5±0.2-25.1
⑪4EMT-NAS (Ours)91.2±0.694.9±0.392.2±0.381.4±0.5-31.4
", + "image_path": "131db406ea04dd3de8a63ce8e61f6907ec440ddd986d9c87e92cc00c04c4a386.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 389, + 286, + 497 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 389, + 286, + 497 + ], + "spans": [ + { + "bbox": [ + 46, + 389, + 286, + 497 + ], + "type": "text", + "content": "four in comparison to the corresponding single tasks are given in Table 2. In the top rows of the table, the results of the first five results on the four medical datasets taken from [44] are listed. SI-EvoNAS [50] is a state-of-the-art evolutionary NAS algorithm. Single-Tasking is an evolutionary single-tasking algorithm that we have implemented as the baseline. In column GPU Days (\\%), the reduction in the runtime of EMT-NAS relative to the corresponding Single-Tasking are listed as a percentage." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 498, + 286, + 640 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 498, + 286, + 640 + ], + "spans": [ + { + "bbox": [ + 46, + 498, + 286, + 640 + ], + "type": "text", + "content": "From Table 2, it is clear that the classification accuracy of the neural architectures found by EMT-NAS is higher than the networks found by all single-tasking NAS on the corresponding tasks, and the search time is reduced by " + }, + { + "bbox": [ + 46, + 498, + 286, + 640 + ], + "type": "inline_equation", + "content": "11\\% - 40\\%" + }, + { + "bbox": [ + 46, + 498, + 286, + 640 + ], + "type": "text", + "content": " compared to the baseline. This demonstrates that it is possible to improve the performance of each task through architectural knowledge transfer only. In addition, the best classification accuracy of the network architecture has been obtained when the number of tasks is three. This shows that which tasks and how many tasks are formulated as a multi-tasking problem will influence the performance of algorithm in solving each of the individual tasks." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 641, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 641, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 641, + 286, + 713 + ], + "type": "text", + "content": "Multi-tasking with the same data modality: EMT-NAS (numbered ④, ⑤, ⑥, ⑦) searched for network architectures with a higher classification accuracy than those found by Single-Tasking. As described in [44], crop 2D images from the center slices of the 3D CT bounding boxes in axial/coronal/sagittal views (planes) are obtained in datasets" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 72, + 545, + 179 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 179 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 179 + ], + "type": "text", + "content": "Organ_A, Organ_C, and Organ_S. Therefore, these datasets are correlated, and it is reasonable to make use of the common knowledge of these datasets to improve classification accuracy. In addition, ⑦ VS ④, ⑤ and ⑥, respectively, have the best performance on Organ_A, Organ_C, and Organ_S. This demonstrates that the three tasks enhance each other to a greater extent than two by two. Therefore, architectural knowledge transfer works well for different datasets of the same data modality." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 180, + 545, + 432 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 180, + 545, + 432 + ], + "spans": [ + { + "bbox": [ + 304, + 180, + 545, + 432 + ], + "type": "text", + "content": "Multi-tasking with different data modalities: The classification accuracy of EMT-NAS (numbered ①, ②, ③, ⑧, ⑨ and ⑩) are slightly higher than that of EMT-NAS (numbered ④, ⑤ and ⑥) on Organ_A, Organ_C, and Organ_S datasets, respectively. From [44], we know that Path is for predicting survival from colorectal cancer histology slides, which means that Organt_A, Organ_C, and Organ_S can benefit more from Path. By contrast, EMT-NAS has transferred different degrees of useful knowledge from Organ_A, Organ_C, and Organ_S, respectively, to Path. From the table, we can observe that the classification accuracy of EMT-NAS (numbered ①, ② and ③) decreases sequentially on PATH. Organ_A, Organ_C, and Organ_S are obtained by different processing methods in abdominal CT along three axes, so their data characteristics are different. Clearly, Path and Organ_A are most beneficial to each other. This also corroborates with the task relational analysis in Fig. 2. Therefore, although these datasets are from different data modalities and are weakly correlated, they can still improve their respective performance through architectural knowledge transfer." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 441, + 454, + 453 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 441, + 454, + 453 + ], + "spans": [ + { + "bbox": [ + 306, + 441, + 454, + 453 + ], + "type": "text", + "content": "4.3. CIFAR-10 and CIFAR-100" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 460, + 545, + 544 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 460, + 545, + 544 + ], + "spans": [ + { + "bbox": [ + 304, + 460, + 545, + 544 + ], + "type": "text", + "content": "We again used RSA in Fig. 2 to analyse the task relatedness between C-10 and C-100, with a task relatedness score of 0.38. C-100 is made up of 20 classes (each containing five subclasses), while C-10 is 10 classes. The results show that ResNet-50, trained on C-100, extracts many different features from the same image compared to those trained on C-10. Therefore, C-10 and C-100 are differentiated." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 545, + 545, + 676 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 545, + 545, + 676 + ], + "spans": [ + { + "bbox": [ + 304, + 545, + 545, + 676 + ], + "type": "text", + "content": "The representative algorithms can be roughly divided into four categories, namely manually designed, RL-based, GD-based, and EAs-based. The comparative results on C-10 and C-100 are listed in Table 3. Note that all algorithms are meant for single-tasking search, i.e., they either search for an optimal network architecture on C-10 and C-100, respectively, or search on C-10 and then the found architectures are transferred to C-100. By contrast, EMT-NAS searches for optimal neural architectures simultaneously on C-10 and C-100, and therefore, the GPU days of EMT-NAS is the total time for searching for both architectures." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "text", + "content": "In Table 3, EMT-NAS stacks normal blocks twice, while EMT-NAS† stacks three times. EMT-NAS searched the network architecture's on C-10 and C-100 with a higher clas" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "3648" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 47, + 116, + 294, + 281 + ], + "blocks": [ + { + "bbox": [ + 47, + 70, + 288, + 115 + ], + "lines": [ + { + "bbox": [ + 47, + 70, + 288, + 115 + ], + "spans": [ + { + "bbox": [ + 47, + 70, + 288, + 115 + ], + "type": "text", + "content": "Table 3. Comparison on C-10 and C-100. * indicates that the same network architecture is used on both C-10 and C-100, so their GPU days for searching are the same. † indicates normal cell stacking three times for better performance." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 47, + 116, + 294, + 281 + ], + "lines": [ + { + "bbox": [ + 47, + 116, + 294, + 281 + ], + "spans": [ + { + "bbox": [ + 47, + 116, + 294, + 281 + ], + "type": "table", + "html": "
ModelSearch MethodGPU DaysParams (M)C-10 (%)Params (M)C-100 (%)
Wide ResNet [47]manual-36.595.83*79.50
DenseNet [14]manual-27.296.26*80.75
MobileNetV2 [35]manual-2.194.56*77.09
PNAS [23]SMBO1503.296.59±0.09*80.47
ENAS [28]RL0.454.697.11*80.57
NASNet-A [57]RL20003.397.35--
Block-QNN-Faster [53]RL0.83.996.43*81.79
DARTS [25]GD1.53.397.00±0.14*79.48±0.31
SNAS [41]GD1.52.997.02--
large-scale Evo [31]EA27505.494.640.477
Hier-EA [24]EA3006496.25±0.12--
Amoebanet-A [30]EA31503.296.66±0.06*81.07
AE-CNN [39]EA27/36295.75.479.15
SHEDA-CNN [20]EA0.58/0.9710.8896.3618.6478.84
Single-Tasking (Baseline)EA0.461.8396.24±0.201.6879.70±0.44
Single-Tasking† (Baseline)EA0.462.4196.64±0.182.1980.82±0.71
EMT-NAS (Ours)EA0.422.1796.73±0.152.2381.86±0.10
EMT-NAS† (Ours)EA0.422.9197.04±0.042.9782.60±0.38
", + "image_path": "45916bf790a6b5caaf4496d5f29b739cb758921f3086323c28dc405ab4984f4b.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 291, + 290, + 483 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 291, + 290, + 483 + ], + "spans": [ + { + "bbox": [ + 46, + 291, + 290, + 483 + ], + "type": "text", + "content": "sification accuracy than Single-Tasking (baseline), demonstrating that architecture knowledge transfer can effectively improve performance on C-10 and C-100. Compared to other NAS algorithms, our approach achieves better performance and more compact network architectures searched on C-10 and C-100 through architectural knowledge transfer, except for ENAS and NASNet-A on C-10. However, the models found by EMT-NAS have only two-thirds the number of parameters of models found by ENAS. On the other hand, NASNet-A consumes about 4,700 times more GPU days than EMT-NAS. These indicate that our approach can achieve a good performance-complexity trade-off. We also analysed two baselines for joint training (shared or unshared network architectures) in Supplementary Material D. The performance of the algorithms has degraded as data from different tasks are used to update the same supernet." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 491, + 201, + 504 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 491, + 201, + 504 + ], + "spans": [ + { + "bbox": [ + 47, + 491, + 201, + 504 + ], + "type": "text", + "content": "4.4. Transferability to ImageNet" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 510, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 510, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 510, + 288, + 713 + ], + "type": "text", + "content": "As done in [25], we transferred the best network architectures found on C-10 and C-100 to ImageNet for training from scratch, to further validate the transferability of the architectures searched by EMT-NAS. The results comparing EMT-NAS with 15 models (or their variants) on ImageNet are given in Table 4. EMT-NAS-4-C-100 has a lower number of model parameters (2.49M) than all compared algorithms, while it has a higher top-1 accuracy (74.25%) except for MoblieNet-V3, MobileNetV2-1.0+CA, RepVGG-A1, AutoSpace, PC-DARTS and MUXNet-m. For better performance, we change the number of normal cells stacked from two to three to get EMT-NAS-C-100†. The top-1 accuracy of EMT-NAS-C-100† is 75.44%, which again surpasses the accuracy of the rest of the algorithms, and the number of model parameters is 3.25M. This demonstrates that EMT-NAS has good transferability between the network architectures searched on C-10 and C-100." + } + ] + } + ], + "index": 4 + }, + { + "type": "table", + "bbox": [ + 313, + 95, + 538, + 298 + ], + "blocks": [ + { + "bbox": [ + 305, + 70, + 545, + 93 + ], + "lines": [ + { + "bbox": [ + 305, + 70, + 545, + 93 + ], + "spans": [ + { + "bbox": [ + 305, + 70, + 545, + 93 + ], + "type": "text", + "content": "Table 4. Comparisons on ImageNet. " + }, + { + "bbox": [ + 305, + 70, + 545, + 93 + ], + "type": "inline_equation", + "content": "\\dagger" + }, + { + "bbox": [ + 305, + 70, + 545, + 93 + ], + "type": "text", + "content": " indicates normal cell stacking three times for better performance." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 313, + 95, + 538, + 298 + ], + "lines": [ + { + "bbox": [ + 313, + 95, + 538, + 298 + ], + "spans": [ + { + "bbox": [ + 313, + 95, + 538, + 298 + ], + "type": "table", + "html": "
ModelTop-1 (%)Top-5 (%)Params (M)GPU DaysSearch Method
ShuffleNet 2.0 [51]73.7-5.4-manual
MobileNet-V3 [13]75.2-5.1-manual
MobileNeXt-0.75 [54]72.6-2.5-manual
MobileNetV2-1.0+CA [12]74.3-3.95-manual
RepVGG-A1 [5]74.46-12.78-manual
PNAS [23]74.291.95.1225SMBO
NASNet-A [57]74.091.65.32000RL
DPP-Net-Panacea [6]74.291.794.88RL
AutoSpace [55]75.3-4.38.33RL
DARTS [25]73.391.34.74GD
SNAS [41]72.791.84.31.5GD
PC-DARTS [43]74.992.25.30.1GD
HourNAS-C [45]74.191.64.80.1GD
Amoebanet-A [30]74.592.05.13150EA
MUXNet-m [26]75.392.53.4176EA
Single-Tasking-C-10 (Baseline)73.1891.222.410.23EA
Single-Tasking-C-100 (Baseline)72.8891.062.250.22EA
Single-Tasking-C-10† (Baseline)74.5992.093.150.23EA
Single-Tasking-C-100† (Baseline)74.1191.862.970.22EA
EMT-NAS-C-10 (Ours)73.8391.632.380.42EA
EMT-NAS-C-100 (Ours)74.2591.802.49
EMT-NAS-C-10† (Ours)75.1192.393.130.42EA
EMT-NAS-C-100† (Ours)75.4492.553.25
", + "image_path": "514331c98e3ddf95a47f8bea10accc2c4d657983d5582bbfda96c0e25075061d.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "table_body" + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 308, + 406, + 319 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 308, + 406, + 319 + ], + "spans": [ + { + "bbox": [ + 306, + 308, + 406, + 319 + ], + "type": "text", + "content": "4.5. Ablation Studies" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 327, + 545, + 447 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 327, + 545, + 447 + ], + "spans": [ + { + "bbox": [ + 304, + 327, + 545, + 447 + ], + "type": "text", + "content": "To verify the effectiveness of the evolutionary multitasking NAS algorithm and the fitness re-evaluation method, four algorithms are compared, namely evolutionary single-Tasking NAS, which serves as the baseline (denoted as Single-tasking in Table 5), evolutionary single-tasking NAS with the fitness re-evaluation method, called Single-Tasking+Reeval, evolutionary multi-tasking NAS without fitness re-evaluation, called Multi-Tasking, and evolutionary multi-tasking NAS with the fitness re-evaluation method, denoted as Multi-Tasking+Reeval." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 448, + 545, + 519 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 448, + 545, + 519 + ], + "spans": [ + { + "bbox": [ + 304, + 448, + 545, + 519 + ], + "type": "text", + "content": "Evolutionary Multi-Tasking: By comparing the results of Single-tasking and Multi-Tasking (③ vs ① and ④ vs ②), evolutionary multi-tasking NAS can improve the performance on both C-10 and C-100, confirming the effectiveness of knowledge transfer when simultaneously searching for the optimal neural architectures on similar tasks." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 521, + 545, + 604 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 521, + 545, + 604 + ], + "spans": [ + { + "bbox": [ + 304, + 521, + 545, + 604 + ], + "type": "text", + "content": "Fitness Re-Evaluation: By comparing the results with and without fitness re-evaluation (④ vs ③ and ② vs ①), we can see that the proposed fitness re-evaluation method improves the performance on both C-10 and C-100. This confirms that the fitness re-evaluation method is effective in enhancing the performance by alleviating fitness fluctuations in the search based on sampled evaluations." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 605, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 545, + 714 + ], + "type": "text", + "content": "Search Efficiency: We take the total runtime of Single-Tasking, and count the percentage increase or decrease of the other three algorithms relative to it. We also calculate three parts of the runtime, including time for training model parameters on the training dataset, time for evaluating model performance on the validation dataset, and time for searching. First, we note that the time taken by the evolutionary multi-tasking is reduced by " + }, + { + "bbox": [ + 304, + 605, + 545, + 714 + ], + "type": "inline_equation", + "content": "50\\%" + }, + { + "bbox": [ + 304, + 605, + 545, + 714 + ], + "type": "text", + "content": " compared to single-tasking(③ vs ① and ④ vs ②). Because the compu" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "3649" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 59, + 83, + 533, + 144 + ], + "blocks": [ + { + "bbox": [ + 55, + 71, + 538, + 82 + ], + "lines": [ + { + "bbox": [ + 55, + 71, + 538, + 82 + ], + "spans": [ + { + "bbox": [ + 55, + 71, + 538, + 82 + ], + "type": "text", + "content": "Table 5. Comparison of evolutionary single- and multi-tasking optimisation with/without fitness re-evaluation on CIFAR-10 and -100." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 59, + 83, + 533, + 144 + ], + "lines": [ + { + "bbox": [ + 59, + 83, + 533, + 144 + ], + "spans": [ + { + "bbox": [ + 59, + 83, + 533, + 144 + ], + "type": "table", + "html": "
IndexAlgorithmTask 1Task 2Total Time (%) ↓Training Time (%) ↓Evaluation Time (%) ↓Search Time (%) ↓Average Params (M)Average FLOPs (M)
C-10 (%)Params (M)Transfer (%)C-100 (%)Params (M)Transfer (%)
①Single-Tasking96.23±0.201.8396.07±0.2579.70±0.441.6878.95±0.60+0.0+0.0+0.0+0.01.83334
②Single-Tasking+Reeval96.29±0.251.7496.26±0.1880.48±0.281.9078.77±0.65-5.1-4.1-15.1-1.41.81323
③Multi-Tasking96.49±0.162.02-80.68±0.432.03--2.1+3.8-37.4-49.42.06382
④Multi-Tasking+Reeval96.73±0.152.17-81.86±0.102.23--8.7-4.0-35.9-51.61.97355
", + "image_path": "25002e73628439e61748e584c81f806c605ef4f2ef6f3f9e1645dfae13726e66.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 152, + 289, + 498 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 152, + 289, + 498 + ], + "spans": [ + { + "bbox": [ + 47, + 152, + 289, + 498 + ], + "type": "text", + "content": "tational complexity of the Evolutionary Multi-Tasking and Single-Tasking algorithms is almost the same, except for the time spent on training and evaluation. Second, " + }, + { + "bbox": [ + 47, + 152, + 289, + 498 + ], + "type": "inline_equation", + "content": "③" + }, + { + "bbox": [ + 47, + 152, + 289, + 498 + ], + "type": "text", + "content": " vs " + }, + { + "bbox": [ + 47, + 152, + 289, + 498 + ], + "type": "inline_equation", + "content": "①" + }, + { + "bbox": [ + 47, + 152, + 289, + 498 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 152, + 289, + 498 + ], + "type": "inline_equation", + "content": "④" + }, + { + "bbox": [ + 47, + 152, + 289, + 498 + ], + "type": "text", + "content": " vs " + }, + { + "bbox": [ + 47, + 152, + 289, + 498 + ], + "type": "inline_equation", + "content": "②" + }, + { + "bbox": [ + 47, + 152, + 289, + 498 + ], + "type": "text", + "content": ", the time spent on the evaluation is reduced by about " + }, + { + "bbox": [ + 47, + 152, + 289, + 498 + ], + "type": "inline_equation", + "content": "36\\%" + }, + { + "bbox": [ + 47, + 152, + 289, + 498 + ], + "type": "text", + "content": ". The population size and the number of generations are the same for single and multi-tasking, i.e., the number of fitness evaluations is the same, so that the total time to optimise multiple tasks simultaneously will be less than the sum of the runtimes when the tasks are optimised one by one. Finally, " + }, + { + "bbox": [ + 47, + 152, + 289, + 498 + ], + "type": "inline_equation", + "content": "④" + }, + { + "bbox": [ + 47, + 152, + 289, + 498 + ], + "type": "text", + "content": " vs " + }, + { + "bbox": [ + 47, + 152, + 289, + 498 + ], + "type": "inline_equation", + "content": "③" + }, + { + "bbox": [ + 47, + 152, + 289, + 498 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 152, + 289, + 498 + ], + "type": "inline_equation", + "content": "②" + }, + { + "bbox": [ + 47, + 152, + 289, + 498 + ], + "type": "text", + "content": " vs " + }, + { + "bbox": [ + 47, + 152, + 289, + 498 + ], + "type": "inline_equation", + "content": "①" + }, + { + "bbox": [ + 47, + 152, + 289, + 498 + ], + "type": "text", + "content": " with a small percentage reduction in the training time. To investigate this further, we reproduce the sampled training process and chose two model metrics, namely the number of parameters and the number of floating point operations (FLOPs). Specifically, when each network architecture was trained once, two metrics were recorded until five runs of the algorithm have stopped, and then averaged and listed in the column Average Params " + }, + { + "bbox": [ + 47, + 152, + 289, + 498 + ], + "type": "inline_equation", + "content": "(M)" + }, + { + "bbox": [ + 47, + 152, + 289, + 498 + ], + "type": "text", + "content": " and Average FLOPs " + }, + { + "bbox": [ + 47, + 152, + 289, + 498 + ], + "type": "inline_equation", + "content": "(M)" + }, + { + "bbox": [ + 47, + 152, + 289, + 498 + ], + "type": "text", + "content": " of Table 5, respectively. The results show a small reduction in the average number of parameters and the average FLOPs for both " + }, + { + "bbox": [ + 47, + 152, + 289, + 498 + ], + "type": "inline_equation", + "content": "④" + }, + { + "bbox": [ + 47, + 152, + 289, + 498 + ], + "type": "text", + "content": " vs " + }, + { + "bbox": [ + 47, + 152, + 289, + 498 + ], + "type": "inline_equation", + "content": "③" + }, + { + "bbox": [ + 47, + 152, + 289, + 498 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 152, + 289, + 498 + ], + "type": "inline_equation", + "content": "②" + }, + { + "bbox": [ + 47, + 152, + 289, + 498 + ], + "type": "text", + "content": " vs " + }, + { + "bbox": [ + 47, + 152, + 289, + 498 + ], + "type": "inline_equation", + "content": "①" + }, + { + "bbox": [ + 47, + 152, + 289, + 498 + ], + "type": "text", + "content": ". It is assumed that the fitness re-evaluation method allows the algorithm to favour network architectures consisting of operations with a small number of parameters or a low computational complexity in the search process. This may explain the fact that introducing the fitness re-evaluation method can reduce the time spent by the model on the training set by a small amount. Overall, EMT-NAS consumes less runtime than its single-task counterparts." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 500, + 288, + 633 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 500, + 288, + 633 + ], + "spans": [ + { + "bbox": [ + 46, + 500, + 288, + 633 + ], + "type": "text", + "content": "Model Transferability: We transferred the network architectures that Single-tasking and Single-tasking+Reeval searched on C-10 and C-100, respectively, to C-100 and C-10 for retraining. The results are presented in column Transfer " + }, + { + "bbox": [ + 46, + 500, + 288, + 633 + ], + "type": "inline_equation", + "content": "(\\%)" + }, + { + "bbox": [ + 46, + 500, + 288, + 633 + ], + "type": "text", + "content": ", which show that through transfer learning, the performance of the network architectures on the new dataset is much lower than that of the network architectures obtained by evolutionary multi-tasking NAS (Multi-Tasking and Multi-Tasking+Reeval) search. Therefore, evolutionary multi-tasking NAS is more competitive than evolutionary single-tasking NAS with transfer learning." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 645, + 162, + 658 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 645, + 162, + 658 + ], + "spans": [ + { + "bbox": [ + 47, + 645, + 162, + 658 + ], + "type": "text", + "content": "4.6. Sensitivity Analysis" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 665, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 288, + 713 + ], + "type": "text", + "content": "In EMT-NAS, " + }, + { + "bbox": [ + 46, + 665, + 288, + 713 + ], + "type": "inline_equation", + "content": "RMP" + }, + { + "bbox": [ + 46, + 665, + 288, + 713 + ], + "type": "text", + "content": " is a key parameter that controls the degree of knowledge transfer between tasks. Here, we set the random mating probability " + }, + { + "bbox": [ + 46, + 665, + 288, + 713 + ], + "type": "inline_equation", + "content": "RMP = 0, 0.1, 0.2, 0.3, 0.4, 0.5" + }, + { + "bbox": [ + 46, + 665, + 288, + 713 + ], + "type": "text", + "content": " and note that when " + }, + { + "bbox": [ + 46, + 665, + 288, + 713 + ], + "type": "inline_equation", + "content": "RMP = 0" + }, + { + "bbox": [ + 46, + 665, + 288, + 713 + ], + "type": "text", + "content": ", two" + } + ] + } + ], + "index": 5 + }, + { + "type": "table", + "bbox": [ + 320, + 174, + 531, + 242 + ], + "blocks": [ + { + "bbox": [ + 305, + 150, + 545, + 171 + ], + "lines": [ + { + "bbox": [ + 305, + 150, + 545, + 171 + ], + "spans": [ + { + "bbox": [ + 305, + 150, + 545, + 171 + ], + "type": "text", + "content": "Table 6. Comparison of EMT-NAS when random mating probability is set to 0, 0.1, 0.2, 0.3, 0.4, and 0.5." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 320, + 174, + 531, + 242 + ], + "lines": [ + { + "bbox": [ + 320, + 174, + 531, + 242 + ], + "spans": [ + { + "bbox": [ + 320, + 174, + 531, + 242 + ], + "type": "table", + "html": "
RMPTask 1Validation ACC (%)Test ACC (%)Task 2Validation ACC (%)Test ACC (%)
0C-1088.36±0.6996.28±0.09C-10061.48±1.6580.31±0.40
0.1C-1087.36±1.6096.48±0.18C-10058.85±4.1080.46±0.71
0.2C-1088.32±1.0296.52±0.18C-10059.67±0.4781.11±0.54
0.3C-1088.76±1.0596.73±0.15C-10061.69±2.1581.86±0.10
0.4C-1088.09±1.2596.49±0.18C-10061.27±3.0981.26±0.27
0.5C-1088.52±1.1696.52±0.17C-10061.42±2.5781.15±0.31
", + "image_path": "e85998df59d8d6303f4f1571bf0eaf6290ddccebbcf3f498b588845c5eee44df.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "table_body" + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 254, + 545, + 348 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 254, + 545, + 348 + ], + "spans": [ + { + "bbox": [ + 304, + 254, + 545, + 348 + ], + "type": "text", + "content": "single tasks run in the same population without any knowledge transfer between the tasks. Table 6 shows that the validation and test accuracies increase as " + }, + { + "bbox": [ + 304, + 254, + 545, + 348 + ], + "type": "inline_equation", + "content": "RMP" + }, + { + "bbox": [ + 304, + 254, + 545, + 348 + ], + "type": "text", + "content": " increases in the beginning, and then decrease as " + }, + { + "bbox": [ + 304, + 254, + 545, + 348 + ], + "type": "inline_equation", + "content": "RMP" + }, + { + "bbox": [ + 304, + 254, + 545, + 348 + ], + "type": "text", + "content": " becomes larger, indicating that too much or too little knowledge transfer between tasks can degrade the performance of EMT-NAS. The best performance was achieved on the validation set and test set when " + }, + { + "bbox": [ + 304, + 254, + 545, + 348 + ], + "type": "inline_equation", + "content": "RMP = 0.3" + }, + { + "bbox": [ + 304, + 254, + 545, + 348 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 350, + 547, + 399 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 350, + 547, + 399 + ], + "spans": [ + { + "bbox": [ + 304, + 350, + 547, + 399 + ], + "type": "text", + "content": "We also analysed the influence of the population size, crossover and mutation probabilities, and the number of generations on the performance. The results are presented in Supplementary Material E." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 415, + 379, + 427 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 415, + 379, + 427 + ], + "spans": [ + { + "bbox": [ + 306, + 415, + 379, + 427 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 436, + 545, + 579 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 436, + 545, + 579 + ], + "spans": [ + { + "bbox": [ + 304, + 436, + 545, + 579 + ], + "type": "text", + "content": "In this work, evolutionary multi-tasking is applied to NAS for the first time. Extensive experiments have demonstrated that for multiple classification tasks from different datasets (data modalities), architectural knowledge transfer and fitness re-evaluation method allow EMT-NAS to outperform each task obtained simultaneously over a single task, and that the runtime of EMT-NAS is less than the sum of the runtimes of solving multiple single tasks independently. Although this work achieves implicit architectural knowledge transfer, more precise, explicit knowledge transfer between tasks in evolutionary multi-tasking NAS is desirable and will be investigated in the future." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 596, + 399, + 609 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 596, + 399, + 609 + ], + "spans": [ + { + "bbox": [ + 306, + 596, + 399, + 609 + ], + "type": "text", + "content": "Acknowledgment" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "type": "text", + "content": "This work is supported by National Natural Science Foundation of China (62136003, 61988101), the Programme of Introducing Talents of Discipline to Universities (the 111 Project) under Grant B17017, Fundamental Research Funds for the Central Universities (222202317006) and Shanghai AI Lab. Y. Jin is supported by an Alexander von Humboldt Professorship for AI endowed by the German Federal Ministry of Education and Research." + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "3650" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 287, + 712 + ], + "type": "list", + "angle": 0, + "index": 14, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 123 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 123 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 123 + ], + "type": "text", + "content": "[1] Shai Ben-David and Reba Schuller Borbely. 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Unfortunately, the exact unlearning approaches are inefficient, and the approximate unlearning approaches are unsuitable for complicated CNNs. Moreover, the approximate approaches have serious security flaws because even unlearning completely different data points can produce the same contribution estimation as unlearning the target data points. To address the above problems, we try to define machine unlearning from the knowledge perspective, and we propose a knowledge-level machine unlearning method, namely ERM-KTP. Specifically, we propose an entanglement-reduced mask (ERM) structure to reduce the knowledge entanglement among classes during the training phase. When receiving the unlearning requests, we transfer the knowledge of the nontarget data points from the original model to the unlearned model and meanwhile prohibit the knowledge of the target data points via our proposed knowledge transfer and prohibition (KTP) method. Finally, we will get the unlearned model as the result and delete the original model to accomplish the unlearning process. Especially, our proposed ERM-KTP is an interpretable unlearning method because the ERM structure and the crafted masks in KTP can explicitly explain the operation and the effect of unlearning data points. Extensive experiments demonstrate the effectiveness, efficiency, high fidelity, and scalability of the ERM-KTP unlearning method. Code is available at https://github.com/RUIYUN-ML/ERM-KTP", + "bbox": [ + 76, + 327, + 473, + 750 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 779, + 209, + 794 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "In recent years, many countries have raised concerns about protecting personal privacy. The privacy legislation, e.g., the well-known European Union's GDPR [19], have been promulgated to oblige information service providers", + "bbox": [ + 75, + 805, + 468, + 866 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "to remove personal data when receiving a request from the data owner, i.e., the right-to-be-forgotten. Besides, the GDPR stipulates that the service providers should remove the corresponding impact of the data requested by the data owner, in which the machine learning models are the most representative. Many kinds of research demonstrate that the machine learning models can memorize knowledge of the data points, e.g., the membership inference attack [7, 14, 15] can infer whether a data point is in the training set or not.", + "bbox": [ + 500, + 297, + 892, + 434 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "A naive approach is retraining the model after removing the target data points from the training set, but the human resources and materials consumed are costly. Thus, aiming to efficiently remove data as well as their generated contribution to the model, a new ML privacy protection research direction emerged, called machine unlearning. A good deal of related work attempted to solve the data-removing challenge of inefficient retraining, and there are two representative research fields, including exact unlearning [1] and approximate unlearning [3-5]. Unfortunately, these approaches usually require huge computational, storage overhead, and memory requirements for class-specific machine unlearning tasks on the complicated convolutional neural networks (CNNs). Furthermore, they may compromise the model's performance and even cause disastrous forgetting. Most significantly, Thudi et al. [18] believed that such approximate unlearning approaches have serious security flaws because they usually define machine unlearning as the distribution difference between the unlearned model and the retrained model. According to this definition, even unlearning completely different data points can produce the same contribution estimation as unlearning the target data points.", + "bbox": [ + 496, + 439, + 893, + 787 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Unlearning algorithms are difficult to implement on deep learning models because these models are often seen as a black box and lack interpretability, which makes data points' contributions challenging to estimate. Though many related works [2, 10, 16, 21] attempted to improve the interpretability of deep learning models, they can not apply to machine unlearning directly. For example, Zhou et al. [22]", + "bbox": [ + 496, + 794, + 893, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 810, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "* Both authors contributed equally", + "bbox": [ + 94, + 875, + 277, + 887 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "† Corresponding author", + "bbox": [ + 96, + 887, + 220, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "20147", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "leveraged the global average pooling (GAP) in CNNs to generate a class activation mapping (CAM) to indicate the discriminative image regions used by the CNNs to identify the class. Liang et al. [12] proposed class-specific filters to transform the complex representations in convolutional layers into interpretable graphs.", + "bbox": [ + 75, + 90, + 468, + 181 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To address the above problems, for the first time, we consider the need for subsequent unlearning tasks during the model training phase. We define machine unlearning in the knowledge perspective, i.e., a reliable machine unlearning approach should satisfy that the knowledge of the unlearned model should be identical to the retrained model. Furthermore, we propose an interpretable unlearning method, i.e., ERM-KTP. The ERM structure can interpret the relation between data points and channels in the activation maps. Such a relationship can describe which filters the data points contribute to the convolutional layer. Then, KTP utilizes the relation to transfer the knowledge from corresponding filters to the unlearned model. Furthermore, the crafted masks in KTP interpret the operation of the knowledge transfer. With these interpretable methods, we can precisely unlearn data points and enhance the reliability of our proposed unlearning approach. We summarize our contributions of this paper as follows:", + "bbox": [ + 75, + 181, + 470, + 454 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- We give a novel definition of machine unlearning from the knowledge perspective, and we further propose an interpretable knowledge-level machine unlearning method, i.e., ERM-KTP. Especially, the interpretability of ERM-KTP enhances the reliability of the unlearning operation.", + "- We introduce an ERM structure that reduces the knowledge entanglement among classes to get a pretrained model. When receiving the unlearning requests, we use the proposed KTP method to transfer the knowledge of the remaining set from the original model to the unlearned model and, meanwhile, prohibit the knowledge of the unlearning set. Finally, we will get the unlearned model as the result and delete the original model to complete the unlearning process.", + "- We conduct experiments on three different scales of image classification datasets and three complicated CNNs. Extensive experimental results demonstrate the effectiveness, efficiency, high fidelity, and scalability of ERM-KTP." + ], + "bbox": [ + 96, + 463, + 468, + 785 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Problem Formulation", + "text_level": 1, + "bbox": [ + 76, + 800, + 284, + 816 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In this paper, we primarily consider a class-specific machine unlearning scenario. We assume a sample space $\\mathcal{X} \\subseteq \\mathbb{R}^d$ and corresponding labels $\\mathcal{Y} = \\{1,2,\\dots,C\\}$ , where $d$ is the number of dimensions and $C$ is the number of classes. The training set can be represented as", + "bbox": [ + 75, + 825, + 468, + 902 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "$\\mathcal{D} = \\{\\mathcal{D}_1,\\mathcal{D}_2,\\dots ,\\mathcal{D}_C\\}$ . To unlearn the target class's data points $\\mathcal{D}_u\\subseteq \\mathcal{D}$ exactly, we need to apply a removal method, which should be equivalent to applying the training algorithm to the dataset without target data points.", + "bbox": [ + 498, + 90, + 890, + 151 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Definition 1. We define a learning algorithm, $\\mathcal{A}:\\mathcal{D}\\to \\mathcal{W}$ as a function from a dataset to a model in hypothesis space $\\mathcal{W}$ . A removal method, $\\mathcal{R}:\\mathcal{A}(\\mathcal{D})\\times \\mathcal{D}\\times \\mathcal{D}_u\\rightarrow \\mathcal{W}$ , is a function from an original model $\\mathcal{A}(D)$ , training dataset $\\mathcal{D}$ , an unlearning dataset $\\mathcal{D}_u$ to remove from the training dataset $\\mathcal{D}$ to an unlearned model in $\\mathcal{W}$ , and a remaining dataset $\\mathcal{D}_r = \\mathcal{D}\\backslash \\mathcal{D}_u$ . We define equivalence as having identical knowledge for each model in $\\mathcal{W}$ :", + "bbox": [ + 498, + 154, + 893, + 275 + ], + "page_idx": 1 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbb {K} (\\mathcal {A} \\left(\\mathcal {D} _ {r}\\right)) = \\mathbb {K} \\left(\\mathcal {R} \\left(\\mathcal {A} (\\mathcal {D}), \\mathcal {D}, \\mathcal {D} _ {u}\\right)\\right), \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 573, + 290, + 890, + 306 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "in which $\\mathbb{K}(\\cdot)$ is a knowledge measuring function. If an exact unlearning method satisfy the above definition, it can be defined as a knowledge-level unlearning method.", + "bbox": [ + 496, + 311, + 890, + 357 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "3. Related Work", + "text_level": 1, + "bbox": [ + 500, + 369, + 640, + 386 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Exact unlearning. The exact unlearning approaches can provide algorithmic unlearning proof. The most representative exact unlearning approach is retrain-from-scratch (RfS), i.e., remove the target data points from the training set and retrain the model. Bourtoule et al. proposed SISA to improve efficiency by retraining the sub-model instead of retrain-from-scratch. These exact unlearning approaches are knowledge-level because they remove all target data points in the input phase so that the model can not learn any knowledge of them. However, their computational overhead is still significant because they need to relearn the remaining set's knowledge through retraining.", + "bbox": [ + 496, + 398, + 890, + 580 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Approximate unlearning. The main idea of approximate unlearning approaches is to estimate the target data points' contribution to the model and update the parameters for unlearning. For example, Graves et al. [4] leveraged gradients to estimate the contributions. They stored gradients of batches consisting of target data points and then subtracted the target gradients to update the model's parameters. For class-specific unlearning tasks or large-scale unlearning requests, it needs to store gradients of almost every batch, and the model will degenerate to the initialization state. Guo et al. [5] utilized the Influence Theory [8], and Golatkar et al. [3] used the Fisher Information [13] to estimate the contributions. However, the above two methods need to calculate the hessian matrix, which is very expensive in deep learning models. Besides, they may compromise the model's performance due to imprecise estimates of contributions on CNNs and even cause disastrous forgetting. Most significantly, Thudi et al. [18] pointed out that different data points can also generate the same network, making approximate unlearning approaches unable to provide an algorithmic unlearning proof.", + "bbox": [ + 496, + 583, + 890, + 901 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "20148", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "4. Proposed Method", + "text_level": 1, + "bbox": [ + 76, + 89, + 250, + 107 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In this section, we will explain the ERM-KTP unlearning method in detail. We will describe how the proposed ERM structure reduces the entanglement of knowledge in Section 4.1. Then, we will explain how the proposed KTP method transfers knowledge in Section 4.2. Finally, we will explain how we combine the ERM and the KTP method to construct the ERM-KTP unlearning method in Section 4.3.", + "bbox": [ + 75, + 114, + 468, + 220 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "4.1. Entanglement-Reduced Mask (ERM) Structure", + "text_level": 1, + "bbox": [ + 76, + 227, + 468, + 258 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The most representative knowledge the ML models learn is the features extracted by the convolutional layers. However, the features of different classes are entangled, so the key features of different classes are always highly overlapping. As a result, it is difficult to transfer the knowledge of target classes without affecting others.", + "bbox": [ + 75, + 266, + 470, + 356 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/bc41ffd1e350d572b7a7ad647f093149dd2ccfa05cabe94bf737b9c8cf1bf7a4.jpg", + "image_caption": [ + "Figure 1. An overview of our proposed ERM structure." + ], + "image_footnote": [], + "bbox": [ + 89, + 366, + 455, + 541 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In order to reduce the entanglement of knowledge, we propose an Entanglement-Reduced Mask (ERM) structure as a learnable layer of the CNNs inspired by the model interpretability work [12]. The learnable ERM structure can be represented as a matrix $G \\in \\mathbb{R}^{C \\times K}$ , where $C$ is the number of classes and $K$ is the number of filters. Each element $G_{c}^{k} \\in [0,1]$ represents the relevance between the $k$ -th filter and the $c$ -th class, and a higher value of $G_{c}^{k}$ denotes a closer correlation. Given a data point $(x \\in \\mathcal{X}, y \\in \\mathcal{Y})$ as an input, we use the $y$ -th row $G_{y} \\in \\mathbb{R}^{1 \\times K}$ as a mask vector multiplied to the activation maps $\\mathcal{M} = (\\mathcal{M}_1, \\dots, \\mathcal{M}_K)$ of the last convolution layer (before the fully connected layer) to shut down irrelevant channels. Formally, we can define the above multiply operation as", + "bbox": [ + 75, + 584, + 468, + 796 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nA \\circ B = \\left(A _ {1} B ^ {1}, \\dots , A _ {d _ {1}} B ^ {d _ {1}}\\right), \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 163, + 801, + 468, + 819 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "in which $A\\in \\mathbb{R}^{d_1\\times d_2\\times d_3}$ $B\\in \\mathbb{R}^{1\\times d_1}$ $A_{i}\\in \\mathbb{R}^{d_{2}\\times d_{3}}$ , and $B^{i}\\in \\mathbb{R}$", + "bbox": [ + 76, + 823, + 468, + 854 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "For a CNN with an ERM structure (ERM-CNN), we set two forward propagation paths of an ERM-CNN with parameters $\\theta$ : (1) the STD path with the predicting probability", + "bbox": [ + 76, + 854, + 468, + 901 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "vector $\\tilde{y}_{\\theta}$ ; (2) the ERM path with mask matrix $G$ predicting $\\tilde{y}_{\\theta}^{G}$ , as shown in Fig. 1. In the training phase, we train the network alternately through the STD and ERM paths, while only the STD path is used in the validation phase.", + "bbox": [ + 496, + 90, + 890, + 151 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Then, we will discuss the details of training an ERM-CNN. We first define an ideal ERM structure in which each row of the matrix $G$ is at least one element equal to 1, and each row is orthogonal. In this ideal state, the knowledge of each class learned by the model is not entangled and independent of each other. Thus, the training objectives are to train an ERM-CNN with an ideal ERM structure, and its classification performance is comparable to the STD-CNNs. To train a model with the ideal ERM, we first consider its validation accuracy through two paths and ensure that at least one element of each row of $G$ equals 1, i.e., $\\| G_{c}\\|_{\\infty} = 1$ . We can get the following formulation:", + "bbox": [ + 496, + 151, + 892, + 333 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\min _ {\\theta , G} L _ {0} (\\theta) = \\mathrm {C E} (y | | \\tilde {y} _ {\\theta}) + \\lambda_ {1} \\mathrm {C E} (y | | \\tilde {y} _ {\\theta} ^ {G}) \\quad s. t. G \\in V _ {G}, \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 509, + 340, + 890, + 378 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where CE denotes the cross entropy loss and $V_{G} = \\{G\\in$ $\\mathbb{R}^{C\\times K}: \\| G_c\\|_{\\infty} = 1\\}$ . Furthermore, we introduce a regulation term to encourage the sparsity of the matrix $G$ , and encourage the $L_{1}$ -norm of $G$ not to exceed the preset upper bound $\\alpha$ and has no effect when $\\| G\\| _1 < \\alpha$ . Apparently, we should set $\\alpha \\geqslant K$ because $\\| G_c\\|_{\\infty} = 1$ ensures $\\| G\\| _1\\geqslant K$ As described above, we can formulate the regulation term as", + "bbox": [ + 498, + 378, + 890, + 484 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\min _ {G} L _ {1} (\\theta) = \\| \\operatorname {R e L U} (\\| G \\| _ {1} - \\alpha) \\| _ {p} \\quad s. t. G \\in V _ {G}, \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 514, + 494, + 890, + 517 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "in which $\\| \\cdot \\| _p$ indicates $p$ -norm. Moreover, we introduce the inner product regulation to encourage each row of $G$ to be orthogonal to the other as", + "bbox": [ + 496, + 525, + 890, + 571 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\operatorname {I n P} = \\sum_ {c _ {1} = 0} ^ {C} \\sum_ {c _ {2} = 0, \\atop c _ {1} < c _ {2}} ^ {C} \\left(G _ {c _ {1}} \\cdot G _ {c _ {2}}\\right). \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 596, + 579, + 890, + 630 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "To facilitate the solution in practice, we replace Eq. (5) with the following equivalent form as our inner product regulation term:", + "bbox": [ + 496, + 638, + 890, + 681 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\min _ {G} L _ {2} (\\theta) = \\sum_ {c _ {1} = 0} ^ {C} \\sum_ {c _ {2} = 0, \\atop c _ {1} < c _ {2}} ^ {C} (G G ^ {T}) _ {c _ {1}} ^ {c _ {2}} \\quad s. t. G \\in V _ {G}, \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 522, + 688, + 890, + 739 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "in which $(GG^{T})_{c_{1}}^{c_{2}}$ denotes the $c_{1}$ -th row and the $c_{2}$ -th column of the matrix $(GG^{T})$ . When we minimize $L_{2}(\\theta)$ , it will tend to 0 if $G_{c}^{k} \\in [0,1]$ , i.e., each row of $\\mathbf{G}$ will be orthogonal to the other. Essentially, the inner product describes the similarity between two vectors as $\\vec{a} \\cdot \\vec{b} = \\|\\vec{a}\\| \\|\\vec{b}\\| \\cos \\langle \\vec{a}, \\vec{b} \\rangle$ . When we minimize $L_{2}(\\theta)$ , the cosine value and their $L_{2}$ -norm are minimized simultaneously.", + "bbox": [ + 496, + 750, + 890, + 854 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "To sum up, we formulate an optimization problem to train an ERM-CNN by combining Eq. (3), (4), and (6):", + "bbox": [ + 498, + 854, + 890, + 886 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "20149", + "bbox": [ + 478, + 944, + 519, + 955 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\min _ {\\theta , G} L (\\theta) = \\mathrm {C E} (y | | \\tilde {y} _ {\\theta}) + \\lambda_ {1} \\mathrm {C E} (y | | \\tilde {y} _ {\\theta} ^ {G}) \\\\ + \\lambda_ {2} \\| \\operatorname {R e L U} (\\| G \\| _ {1} - \\alpha) \\| _ {p} \\\\ + \\lambda_ {3} \\sum_ {c _ {1} = 0} ^ {C} \\sum_ {\\substack {c _ {2} = 0, \\\\ c _ {1} < c _ {2}}} ^ {C} (G G ^ {T}) _ {c _ {1}} ^ {c _ {2}} \\quad s. t. G \\in V _ {G}, \\tag{7} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 94, + 84, + 468, + 184 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "in which the first and the second term ensure the classification performance, the third term ensures the sparsity of the matrix $G$ , and the last term imposes a rigorous constraint on each row of $G$ .", + "bbox": [ + 75, + 193, + 468, + 252 + ], + "page_idx": 3 + }, + { + "type": "code", + "sub_type": "algorithm", + "code_caption": [ + "Algorithm 1: Alternate Training (AT)" + ], + "code_body": "1 for e in epochs do \n2 if $e \\in ERM's$ epoch then \n3 $\\tilde{y}_{\\theta}^{G} \\gets$ prediction through the ERM path \n4 $\\mathcal{L} \\gets \\lambda_{1}CE(y||\\tilde{y}_{\\theta}^{G}) + \\lambda_{2}L_{1} + \\lambda_{3}L_{2}$ \n5 $G \\gets G - \\eta \\frac{\\partial\\mathcal{L}}{\\partial G}$ \n6 $G_{c} \\gets G_{c} / \\| G_{c}\\|_{\\infty}$ \n7 $G \\gets G.\\mathrm{clip}(0,1)$ \n8 else \n9 $\\tilde{y}_{\\theta} \\gets$ prediction through the STD path \n10 $\\mathcal{L} \\gets \\mathrm{CE}(y||\\tilde{y}_{\\theta})$ \n11 end \n12 $\\theta \\gets \\theta - \\eta \\frac{\\partial\\mathcal{L}}{\\partial\\theta}$ \n13 end", + "bbox": [ + 78, + 287, + 413, + 494 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "To solve the above optimization problem in Eq. (7), we apply an approximate projected gradient descent (PGD) algorithm. After the matrix $G$ is updated, $G_{c}$ will be normalized by $G_{c} / \\| G_{c}\\|_{\\infty}$ to ensure $\\| G_c\\|_{\\infty} = 1$ , and then each element of $G_{c}$ will be clipped into the range [0, 1]. However, the joint training scheme may have some difficulties due to poor convergence. The forward propagation through the ERM path can make most features block, leading to a much poorer convergence than the STD path because of the weaker gradient. Therefore, we propose an alternate training (AT) scheme instead of the normal joint training scheme in that the forward propagation uses the STD path and ERM path alternately in different epochs. Specifically, we update $G$ and $\\theta$ by descend the gradient of $\\lambda_1\\mathrm{CE}(y||\\tilde{y}_\\theta^G) + \\lambda_2L_1 + \\lambda_3L_2$ in the epoch for ERM path, and we update $\\theta$ with the gradient of $\\mathrm{CE}(y||\\tilde{y}_{\\theta})$ in the STD path, as shown in Algorithm 1.", + "bbox": [ + 75, + 520, + 472, + 777 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4.2. Knowledge Transfer and Prohibition (KTP)", + "text_level": 1, + "bbox": [ + 76, + 786, + 449, + 801 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "After training an ERM-CNN as a pre-trained model, different classes' knowledge (features and parameters) is independent. When receiving the unlearning requests, we can transfer the knowledge of a single class separately via our proposed knowledge transfer and prohibition (KTP) method. Specifically, KTP transfers the knowledge of the", + "bbox": [ + 75, + 809, + 468, + 900 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "non-target class of data in the origin model $\\theta_T$ to the unlearned model $\\theta_S$ while prohibiting the knowledge of the target data points. We can describe the KTP method as the following three processes: (1) convolution layers $(\\theta_S^{cv}$ and $\\theta_T^{cv})$ knowledge transfer (CKT); (2) fully connected layers $(\\theta_S^{fc}$ and $\\theta_T^{fc})$ knowledge transfer (FKT); (3) matrix $G$ ( $G_S$ and $G_T$ ) knowledge transfer (GKT). Formally, we can define the KTP method as", + "bbox": [ + 496, + 90, + 893, + 213 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\operatorname {C K T}: \\theta_ {S} ^ {c v} \\stackrel {{t r a n s}} {{\\longleftarrow}} \\theta_ {T} ^ {c v},\n$$\n", + "text_format": "latex", + "bbox": [ + 625, + 224, + 764, + 244 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\operatorname {F K T}: \\theta_ {S} ^ {f c} \\xleftarrow {\\text {t r a n s}} \\theta_ {T} ^ {f c}, \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 629, + 247, + 890, + 267 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\operatorname {G K T}: G _ {S} \\stackrel {{t r a n s}} {{\\longleftarrow}} G _ {T}.\n$$\n", + "text_format": "latex", + "bbox": [ + 625, + 271, + 764, + 290 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In the CKT process, we transfer the knowledge of features extracted by the convolutional layers by a crafted channel mask $\\bar{G}_{\\mathbf{c}} \\in \\mathbb{R}^{1 \\times K}$ . For the single target class $\\mathbf{c}$ unlearning task, the mask can be defined as", + "bbox": [ + 496, + 301, + 893, + 362 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\bar {G} _ {\\mathbf {c}, i} = \\left\\{ \\begin{array}{l l} 0, & G _ {\\mathbf {c}, i} = 1 \\\\ 1, & G _ {\\mathbf {c}, i} = 0 \\end{array} . \\right. \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 611, + 375, + 890, + 415 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "For the multiple target classes $\\mathbf{c} = \\{\\mathbf{c}_0,\\dots ,\\mathbf{c}_{|c|}\\}$ unlearning task, we calculate $\\bar{G}_{\\mathbf{c}_j}$ for each class $j$ and then aggregate them as", + "bbox": [ + 496, + 426, + 892, + 472 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\bar {G} _ {\\mathbf {c}, i} = \\left\\{ \\begin{array}{l l} 1, & \\left(\\sum_ {j} ^ {| c |} \\bar {G} _ {\\mathbf {c} _ {j}}\\right) _ {i} = | c | \\\\ 0, & \\left(\\sum_ {j} ^ {| c |} \\bar {G} _ {\\mathbf {c} _ {j}}\\right) _ {i} < | c | \\end{array} . \\right. \\tag {10}\n$$\n", + "text_format": "latex", + "bbox": [ + 584, + 484, + 890, + 579 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Formally, the CKT process can be formulated as an optimization problem:", + "bbox": [ + 496, + 589, + 890, + 619 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\min _ {\\theta_ {S} ^ {c v}} L _ {3} \\left(\\theta_ {S} ^ {c v}\\right) = \\operatorname {M S E} \\left(f \\left(x; \\theta_ {T} ^ {c v}\\right), g \\left(x; \\theta_ {S} ^ {c v}\\right) \\circ \\bar {G} _ {\\mathbf {c}}\\right), \\tag {11}\n$$\n", + "text_format": "latex", + "bbox": [ + 519, + 632, + 890, + 657 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\mathrm{MSE}(\\cdot)$ is Mean Square Error, $x$ is data points, $\\circ$ is the multiply operation (Eq. (2)), and $f(\\theta_S^{cv})$ and $g(\\theta_S^{cv})$ denote the output of the origin model's last convolution layer with parameters $\\theta_S^{cv}$ and the output from unlearned model's last convolution layer with parameters $\\theta_S^{cv}$ , respectively. Note that the knowledge of the corresponding channels in the feature maps multiplied by the matrix $G$ where the value equals one has been transferred. In contrast, the knowledge associated with values equal to 0 has been prohibited.", + "bbox": [ + 496, + 669, + 893, + 818 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "For the FKT process, we transfer the knowledge of parameters in fully connected (FC) layer $\\theta^{fc} = \\{\\theta_{\\beta}^{fc},\\theta_{\\gamma}^{fc}\\}$ , in which $\\theta_{\\beta}^{fc}\\in \\mathbb{R}^{K\\times C}$ denotes the weight, and $\\theta_{\\gamma}^{fc}\\in \\mathbb{R}^{1\\times C}$ denotes the bias. The FKT process can be executed by directly modifying the original model's parameters of fully", + "bbox": [ + 496, + 821, + 893, + 901 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "20150", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "connected layers as", + "bbox": [ + 76, + 90, + 209, + 104 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\theta_ {S, \\beta} ^ {f c} = \\theta_ {T, \\beta} ^ {f c} * \\mathcal {A} _ {\\beta}, \\quad \\mathcal {A} _ {\\beta} = (\\underbrace {(\\bar {G} _ {c}) ^ {T} , \\cdots , (\\bar {G} _ {c}) ^ {T}} _ {C}), \\tag {12} \\\\ \\theta_ {S, \\gamma} ^ {f c} = \\theta_ {T, \\gamma} ^ {f c} * \\mathcal {A} _ {\\gamma}, \\quad \\mathcal {A} _ {\\gamma} \\in [ 0, 1 ] ^ {1 \\times C}, \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 94, + 114, + 468, + 176 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where all elements of $\\mathcal{A}_{\\gamma}$ are equal to 1 except the c-th column, $(\\cdot)^T$ denotes the matrix transpose operation, and $*$ denotes the hardamad product operation. Similar to the channel mask $\\bar{G}_c$ , the FC mask $\\mathcal{A} = \\{\\mathcal{A}_{\\beta}, \\mathcal{A}_{\\gamma}\\}$ prohibits the knowledge of the FC layer related to the target class of data points.", + "bbox": [ + 76, + 185, + 468, + 275 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Finally, we update the matrix $G_{S}$ of the unlearned model through the GKT process by the following equation:", + "bbox": [ + 76, + 276, + 468, + 306 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nG _ {S} = G _ {T} * \\mathcal {A} _ {G}, \\quad \\mathcal {A} _ {G} \\in [ 0, 1 ] ^ {C \\times K}, \\tag {13}\n$$\n", + "text_format": "latex", + "bbox": [ + 147, + 316, + 468, + 334 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where only the c-th row of the mask matrix $\\mathcal{A}_G$ is equal to 0, and the others are equal to 1. The updated matrix $G_{S}$ can visualize which classes of data points have been removed by checking which rows are equal to 0. We summarize the KTP method in Algorithm 2.", + "bbox": [ + 76, + 345, + 468, + 420 + ], + "page_idx": 4 + }, + { + "type": "code", + "sub_type": "algorithm", + "code_caption": [ + "Algorithm 2: Knowledge Transfer and Prohibition (KTP)" + ], + "code_body": "// CKT \n1 for e in epochs do \n2 $f(x;\\theta_T^{cv})\\gets$ forward propagation through $\\theta_T$ \n3 $g(x;\\theta_S^{cv})\\gets$ forward propagation through $\\theta_S$ \n4 $\\mathcal{L}\\gets \\mathrm{MSE}(f(x;\\theta_T^{cv})\\circ \\bar{G}_c,g(x;\\theta_S^{cv}))$ \n5 $\\theta_S^{cv}\\gets \\theta_S^{cv} - \\eta \\frac{\\partial\\mathcal{L}}{\\partial\\theta_S^{cv}}$ \n6 end \n// FKT \n7 $\\theta_{S,\\beta}^{fc} = \\theta_{T,\\beta}^{fc}*\\mathcal{A}_{\\beta}$ \n8 $\\theta_{S,\\gamma}^{fc} = \\theta_{T,\\gamma}^{fc}*\\mathcal{A}_{\\gamma}$ \n9 $\\theta_S^{fc} = \\{\\theta_{S,\\beta}^{fc},\\theta_{S,\\gamma}^{fc}\\}$ \n// GKT \n10 $G_{S} = G_{T}*\\mathcal{A}_{G}$ \n// Unlearned Model \n11 $\\theta_S = \\{\\theta_S^{cv},G_S,\\theta_S^{fc}\\}$", + "bbox": [ + 80, + 473, + 447, + 723 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.3. Machine Unlearning via ERM-KTP", + "text_level": 1, + "bbox": [ + 76, + 741, + 387, + 757 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Here, we will explain how we combine the ERM structure and KTP method to construct a class-specific knowledge-level machine unlearning approach. We first train the original ERM-CNNs by Algorithm 1. When receiving unlearning requests, we then transfer the remaining dataset's knowledge to the unlearned model by Algorithm 2. Finally, we complete the unlearning process by deleting the original model. The detailed ERM-KTP unlearning algorithm is shown in Algorithm 3.", + "bbox": [ + 76, + 763, + 468, + 900 + ], + "page_idx": 4 + }, + { + "type": "code", + "sub_type": "algorithm", + "code_caption": [ + "Algorithm 3: ERM-KTP Unlearning" + ], + "code_body": "1 $\\theta_T\\gets \\mathrm{AT}(\\theta)$ \n2 while receiving unlearning requests do \n3 $\\theta_S\\gets \\mathrm{KTP}(\\theta_T)$ \n4 Delete $\\theta_T$ \n5 $\\theta_T = \\theta_S$ \n6 end", + "bbox": [ + 506, + 112, + 781, + 205 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "5. Experiments", + "text_level": 1, + "bbox": [ + 500, + 239, + 630, + 255 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In this section, we empirically evaluate the performance of the proposed unlearning method on three popular image classification benchmarks. All experiments are implemented with Python 3.8 and PyTorch 1.10.1 on a machine with Intel(R) Core(TM) i9-10980XE CPU, 32GB RAM, and a Nvidia 3090 GPU.", + "bbox": [ + 496, + 263, + 890, + 353 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "5.1. Datasets & Models", + "text_level": 1, + "bbox": [ + 500, + 364, + 679, + 378 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We evaluate the proposed unlearning method in three public image classification datasets, i.e., CIFAR10, CIFAR100 [9], and Tiny-ImageNet [11]. The input size of CIFAR-10 and CIFAR-100 is $32 \\times 32$ , and they both contain 50,000 training images and 10,000 for validation. For Tiny-ImageNet, the size of image samples is $224 \\times 224$ . It contains 200 classes of samples, and each class has 500 samples for training, 50 for validation, and 50 for testing.", + "bbox": [ + 496, + 388, + 890, + 508 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Moreover, the model structure is three common image classification deep neural networks, ResNet-20, ResNet-50 [6], and ResNeXt-50 [20]. The original models are trained for 200 epochs using Stochastic Gradient Descent (SGD) optimizer with a momentum of 0.9, weight decay of 5e-4, and an initial learning rate of 0.1, divided by 10 after 100 and 150 epochs, respectively.", + "bbox": [ + 496, + 510, + 890, + 614 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "5.2. Effectiveness of the ERM Structure", + "text_level": 1, + "bbox": [ + 500, + 625, + 805, + 638 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In order to evaluate the effectiveness of ERM structure, we propose the following metrics:", + "bbox": [ + 500, + 648, + 888, + 679 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "- Cosine similarity (CSI) to analyze the orthogonality of each row of the matrix $G$ as follows,", + "bbox": [ + 517, + 689, + 888, + 718 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathrm {C S I} = \\sum_ {c _ {1} = 0} ^ {C} \\sum_ {\\substack {c _ {2} = 0, \\\\ c _ {1} \\neq c _ {2}}} ^ {C} \\left(\\frac {G _ {c _ {1}} \\cdot G _ {c _ {2}}}{\\| G _ {c _ {1}} \\| \\| G _ {c _ {2}} \\|\\right). \\tag{14}\n$$\n", + "text_format": "latex", + "bbox": [ + 599, + 729, + 888, + 781 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "- $L_{1}$ -density to evaluate the sparsity of the matrix $G$ as", + "bbox": [ + 517, + 799, + 885, + 813 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nL _ {1} \\text {- d e n s i t y} = \\frac {\\| G \\| _ {1}}{C K}. \\tag {15}\n$$\n", + "text_format": "latex", + "bbox": [ + 640, + 824, + 888, + 854 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Table 1 shows that the CNNs with the ERM structure have slightly better classification performance than the STD", + "bbox": [ + 498, + 869, + 890, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "20151", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "CNNs. Moreover, the $L_{1}$ -density convergences to $\\alpha$ , and CSI convergences close to 0, meaning each class of data is independent to the other. These metrics quantitatively demonstrate ERM's effectiveness in learning a sparse mask matrix to reduce the entanglement for the following unlearning task without sacrificing classification accuracy.", + "bbox": [ + 75, + 90, + 470, + 183 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/0942aa2ac749b782605c3b5da0c2d196800649fdb7af5dff0dd60f98dd34a143.jpg", + "table_caption": [ + "Table 1. Metrics of the STD-CNNs and ERM-CNNs. The first row of each two stand for STD-CNNs and the second one stand for ERM-CNNs. $Acc_{val}$ is the original model's classification accuracy on the validation dataset." + ], + "table_footnote": [], + "table_body": "
DatasetModelCKCSIL1-densityAccval
CIFAR10ResNet-20----89.6%
10640.00.192.6%
CIFAR100ResNeXt-50----76.2%
1002,0480.00.0177.6%
Tiny-ImageNetResNet-50----49.3%
2002,0480.00.00553.4%
", + "bbox": [ + 78, + 256, + 468, + 366 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Moreover, we evaluate if the ERM structure can reduce or eliminate the knowledge entanglement across classes by prohibiting each class's knowledge successively during the ERM path's forward propagation. As shown in Table 2, the classification accuracy will degrade into $0.0\\%$ for the knowledge-prohibited classes, while the accuracy will remain the same for the knowledge-permitted classes.", + "bbox": [ + 75, + 378, + 468, + 486 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/280d3f433bb2e205f41869519b36e8bd05ccd5f289880b17cb09b3bb02736ef4.jpg", + "table_caption": [ + "Table 2. Accuracy of the data points with prohibited or permitted Knowledge. $Acc_{(\\cdot)}^{pro}$ and $Acc_{(\\cdot)}^{per}$ denote the accuracy of the knowledge-prohibited classes and the knowledge-permitted classes, respectively." + ], + "table_footnote": [], + "table_body": "
DatasetModelAccprotrainAccpertrainAccprovalAccperval
CIFAR10ResNet-200.0%97.1%0.0%91.8%
CIFAR100ResNeXt-500.0%99.9%0.0%78.1%
Tiny-ImageNetResNet-500.0%99.9%0.0%53.4%
", + "bbox": [ + 78, + 563, + 468, + 633 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We also evaluate the time overhead and memory requirements of the ERM CNNs in the training phase. The computation overhead is the activation map multiplied by the corresponding $y$ -th row of the matrix $G$ and computing the regulation terms $L_{1}$ and $L_{2}$ . As shown in Table 3, the time overhead of the ERM structure is comparable to the standard (STD) CNNs, and the additional memory requirements are negligible, which demonstrates that ERM structure has great scalability and can be applied to any CNN structures.", + "bbox": [ + 75, + 650, + 468, + 787 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5.3. Effectiveness of the ERM-KTP Unlearning Method", + "text_level": 1, + "bbox": [ + 76, + 794, + 468, + 824 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We utilize some common metrics to evaluate the effectiveness of the ERM-KTP unlearning method as follows.", + "bbox": [ + 76, + 833, + 468, + 863 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "- $Acc_{D_r}$ is the original model's classification accuracy on the training set of the remaining classes.", + "bbox": [ + 94, + 869, + 468, + 901 + ], + "page_idx": 5 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- $Acc_{val}$ is the original model's classification accuracy on the validation dataset of the remaining classes.", + "- $Acc_{D_r}'$ measures the unlearned model's performance on the training set of the remaining classes.", + "- $\\Delta Acc_{D_r} = Acc_{D_r}' - Acc_{D_r}$ indicates the difference between the accuracy of the remaining set before and after the unlearning operation.", + "- $\\Delta Acc_{val} = Acc_{val}' - Acc_{val}$ indicates the difference between the accuracy of the validation set before and after the unlearning operation." + ], + "bbox": [ + 517, + 90, + 890, + 268 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/64be2b569eec93131f32ba1179444ae18a832421b1e2ac1c25513209f9fadb9a.jpg", + "table_caption": [ + "Table 3. Time overhead and memory requirements of the ERM-CNNs and the STD-CNNs in the training phase." + ], + "table_footnote": [], + "table_body": "
DatasetModelStructureTimeMemory
CIFAR10ResNet-20STD1206s2867MiB
ERM1541s2867MiB
CIFAR100ResNeXt-50STD9447s19223MiB
ERM9983s19275MiB
Tiny-ImageNetResNet-50STD5025s6769MiB
ERM6164s6803MiB
", + "bbox": [ + 501, + 316, + 890, + 428 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Then, we conduct experiments in the case of unlearning $10\\%$ , $40\\%$ , and $80\\%$ of classes, respectively. Table 4 shows that $Acc_{D_u}$ equals $0.0\\%$ in all cases, demonstrating that ERM-KTP can effectively unlearn target data points. Furthermore, $\\Delta Acc_{D_r}$ are close to $0.0\\%$ and $\\Delta Acc_{D_r}$ is greater than $0.0\\%$ in most cases. These show that ERM-KTP can unlearn target data without affecting the model classification performance, demonstrating the high fidelity of ERM-KTP. In summary, ERM-KTP performs well on all these datasets and model structures, demonstrating the scalability of ERM-KTP.", + "bbox": [ + 496, + 446, + 890, + 612 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5.4. Comparison with Baselines", + "text_level": 1, + "bbox": [ + 500, + 621, + 745, + 636 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "To further prove the advantage of ERM-KTP, we compare ERM-KTP with the following baseline approaches:", + "bbox": [ + 498, + 643, + 890, + 675 + ], + "page_idx": 5 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- Retrain from scratch (RfS): Retrain model from scratch with remaining data points $\\mathcal{D}_r$ .", + "- SISA: Retrain the sub-model whose training set contains the target data points [1].", + "- Fine-tune: Fine-tune the model on the remaining data $\\mathcal{D}_r$ using a slightly larger learning rate.", + "- Random Labels (RL): Fine-tune the model on $\\mathcal{D}$ by randomly resampling labels corresponding to images belonging to the remaining data points $\\mathcal{D}_r$ .", + "- Amnesiac Unlearning: Track gradient in every training batch. Then, update the model by subtracting the gradients when the batch is marked for removal [4]." + ], + "bbox": [ + 517, + 681, + 890, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "20152", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/769f325b52956e016bac1ba668e28b6f0f27d527c0fff8b22d905be79a1f7d80.jpg", + "table_caption": [ + "Table 4. Performance evaluation of ERM-KTP unlearning method. #Classes denotes the number of the unlearned classes of data points" + ], + "table_footnote": [], + "table_body": "
DatasetModel#ClassesAccDrAccvalAccDuAcc'DrΔAccDrΔAccval
CIFAR10ResNet-20096.8%92.6%----
196.6%91.3%0.0%95.3%-1.3%-1.3%
497.4%96.1%0.0%97.3%-0.1%+3.5%
898.4%97.8%0.0%98.5%+0.1%+3.1%
CIFAR100ResNeXt-50099.9%77.6%----
1099.9%76.1%0.0%98.1%-1.8%-0.6%
4099.9%79.4%0.0%98.4%-1.5%+1.1%
8099.9%86.4%0.0%99.8%-0.1%+7.6%
Tiny-ImageNetResNet-50099.9%53.4%----
2099.9%52.6%0.0%97.6%-2.3%-0.3%
8099.9%53.8%0.0%98.3%-1.6%+1.5%
16099.9%59.3%0.0%97.6%-2.3%+4.4%
", + "bbox": [ + 147, + 114, + 820, + 309 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "- Fisher Unlearning: Perform a corrective Newton step using the Fisher Information Matrix. Add fisher noises sampled from Gaussian distribution to the weight to scrub the information [3].", + "bbox": [ + 96, + 338, + 470, + 398 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/28fe54ce2793837aa561a985f0ccf63fb283bf6f37c669a1c18edad3a1530e55.jpg", + "image_caption": [ + "Figure 2. Train the unlearned model with the training datasets, and $\\Delta Acc_{D_u}$ denotes the difference between the accuracy of the unlearning dataset on the relearned model and the accuracy on the original model on CIFAR10 and ResNet-20." + ], + "image_footnote": [], + "bbox": [ + 135, + 417, + 411, + 585 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Then, we conduct the comparison experiments for $40\\%$ classes of data points removed. As shown in Table 5, the Amenesiac method [4] stores the gradients of almost every batch, and the model's performance degrades to random guess because it makes the model return to its initial state. For SISA [1], we need to retrain all shards to unlearn target classes of data points because every shard contains the target data points. Also, SISA's validation accuracy is lower by about $6\\%$ than STD CNNs due to the aggregation operation. Though the literature [3] reports that the Fisher method performs well on All-CNN [17] and CIFAR-10, our experimental results show that it is not suitable for complicated CNNs, e.g., ResNet-20, ResNet-50 [6], and ResNeXt-50 [20].", + "bbox": [ + 75, + 659, + 468, + 869 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Note that fine-tune and random labels (RL) methods show great performance on $\\Delta Acc_{D_r}$ and $\\Delta Acc_{val}$ . How-", + "bbox": [ + 76, + 869, + 470, + 902 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "ever, these two methods are only an output-level unlearning, i.e., they only change the model's output of the target data points but not remove the corresponding knowledge. To prove that, we fine-tune the unlearned model to observe how long the model can relearn the forget knowledge. As shown in Fig. 2, the Fine-tune and RL method restore the performance on the unlearning dataset at about the 50th epoch, while the relearn time of ERM-KTP method is similar to the RfS method, i.e., they both recover the performance around the 100th epoch. It demonstrates that ERM-KTP can completely remove the target data points like the RfS method, i.e., ERM-KTP is a knowledge-level unlearning method.", + "bbox": [ + 496, + 338, + 890, + 534 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/db80f615976325037f7e707c893af6c32fe1fe8d376d06f846b52c4a1a2b6e9d.jpg", + "image_caption": [ + "(a) CSI" + ], + "image_footnote": [], + "bbox": [ + 516, + 550, + 687, + 652 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/dbb7aeca50952eb07ba9718e148ff7b399e7b4ad4bb6224313af388c9cb9c572.jpg", + "image_caption": [ + "(b) $L_{1}$ -density", + "Figure 3. Ablation experiments of our proposed regulation terms on CIFAR100 and ResNet-50." + ], + "image_footnote": [], + "bbox": [ + 707, + 550, + 880, + 654 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "For the efficiency comparison, we conduct the experiments on CIFAR10 and ResNet-20 because some methods can not be implemented on the other two settings, e.g., Fisher method needs more than 200 hours in TinyImageNet. As shown in Table 6, ERM-KTP improves by $5 \\times$ compared to RfS, $5.4 \\times$ compared to SISA, and $42 \\times$ compared to Fisher. Though the time overhead of Finetune is less than ERM-KTP, Fine-tune method is only an output-level unlearning method, as mentioned above. In summary, compared with these baseline approaches, ERM-KTP is more effective, more efficient, and has better scalability.", + "bbox": [ + 496, + 719, + 890, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "20153", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/7969e00a82257e2fe4bf0e745575ac14378a2754d69de68f770aa1b945dd0459.jpg", + "table_caption": [ + "Table 5. Unlearning performance comparison with baseline approaches when unlearning ${40}\\%$ classes of data points." + ], + "table_footnote": [], + "table_body": "
DatasetModelApproachAccDrAccvalAccDuAcc'DrΔAccDrΔAccval
CIFAR10ResNet-20STD99.9%93.7%----
RfS99.9%96.3%0.0%99.8%-0.1%+2.6%
Fine-tune99.9%97.0%0.0%99.8%-0.1%+3.3%
RL99.9%97.0%0.0%99.8%-0.1%+3.3%
SISA92.4%91.0%0.0%92.8%+0.4%+0.2%
Fisher99.9%54.0%48.4%53.0%-46.9%-25.1%
Amnesiac99.9%9.0%0.0%15.4%-84.5%-84.7%
ERM-KTP (ours)97.4%96.1%0.0%97.3%-0.1%+3.5%
CIFAR100ResNeXt-50STD99.9%78.9%----
RfS99.9%79.6%0.0%99.9%0.0%+0.7%
RL99.9%78.1%0.0%99.7%0.0%-0.8%
Fisher99.9%1.0%0.0%1.0%-98.9%-77.9%
Fine-tune99.9%83.4%0.0%99.9%0.0%+4.5%
Amnesiac99.9%0.89%0.0%1.0%-98.9%-77.8%
ERM-KTP (ours)99.9%79.4%0.0%98.4%-1.5%+1.1%
Tiny-ImageNetResNet-50STD99.9%48.3%----
RfS99.9%45.1%0.0%99.9%0.0%-3.2%
RL99.9%43.4%0.0%96.7%-3.2%-4.9%
SISA67.6%52.8%0.0%68.0%+0.4%-1.3%
Fine-tune99.9%50.0%0.0%99.9%0.0%+1.7%
Amnesiac99.9%0.3%0.8%0.7%-99.2%-48.0%
ERM-KTP (ours)99.9%53.8%0.0%98.3%-1.6%+1.5%
", + "bbox": [ + 120, + 114, + 846, + 448 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/266a357959021df3edf05b04f0ab721952a33e8bc04326016756fae056e8bdb0.jpg", + "table_caption": [ + "Table 6. Unlearn time comparison with baselines on CIFAR10 and ResNet-20." + ], + "table_footnote": [], + "table_body": "
ApproachTimeΔAccDrΔAccval
RfS668s-1.7%+1.7%
SISA672s+0.4%+0.2%
Fine-tune492s-0.2%+2.4%
RL68s-1.5%+1.4%
Fisher5162s-46.9%-25.1%
ERM-KTP (ours)124s-1.6%+2.0%
", + "bbox": [ + 107, + 513, + 436, + 625 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5.5. Ablation Experiments", + "text_level": 1, + "bbox": [ + 76, + 660, + 282, + 678 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "To further demonstrate that our proposed regulation terms are effective, we conduct an ablation experiment on CIFAR100 and ResNet-50 by setting the hyper-parameters as: (1) $\\lambda_{1} = 1$ , $\\lambda_{2} = 1 \\times 10^{-3}$ , and $\\lambda_{3} = 0$ ; (2) $\\lambda_{1} = 1$ , $\\lambda_{2} = 0$ , and $\\lambda_{3} = 5 \\times 10^{-4}$ ; (3) $\\lambda_{1} = 1$ , $\\lambda_{2} = 1 \\times 10^{-3}$ , and $\\lambda_{3} = 5 \\times 10^{-4}$ . Fig. 3 demonstrates that applying both $L_{2}$ and $L_{3}$ achieves the best performance and convergence to the optimal value. Only using the $L_{2}$ regulation term (Eq. (4)), the $L_{1}$ -density tends to 0.01, but the CSI convergences to around 3,500. It illustrates that the $L_{1}$ -norm regulation term can find the spars solution, but the $L_{1}$ -norm does not constrain the relative position, which leads to the high value of CSI. However, the $L_{1}$ -norm can make both CSI and $L_{1}$ -density convergence to a lower value when the", + "bbox": [ + 75, + 688, + 470, + 900 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "inner-product regulation term (Eq. (6)) is used. Furthermore, the inner-product can make both two values descend more quickly.", + "bbox": [ + 498, + 476, + 890, + 521 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "6. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 535, + 617, + 550 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this paper, we propose an interpretable knowledge-level unlearning method, ERM-KTP, for the class-specific unlearning task. We propose the ERM structure to tackle the challenge of high knowledge entanglement. Then, we transfer the knowledge of the remaining set from the original model to the unlearned model via our proposed KTP method. Finally, we delete the original model to accomplish the unlearning task. The interpretability brought by the EMR structure and the crafted masks in KTP enhances the reliability of the unlearning. Extensive experiments demonstrate the effectiveness, fidelity, efficiency, and scalability of our proposed ERM-KTP unlearning method. For future work, we attempt to solve the entanglement of each single data point to tackle the sample-specific unlearning task.", + "bbox": [ + 496, + 560, + 890, + 772 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgments. This work was supported in part by the National Natural Science Foundation of China under Grant 61960206014, 62102300, and 62121001, in part by the China 111 Project under Grant B16037, in part by the Fundamental Research Funds for the Central Universities under Grant XJS211510.", + "bbox": [ + 496, + 775, + 890, + 866 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "20154", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Lucas Bourtoule, Varun Chandrasekaran, Christopher A Choquette-Choo, Hengrui Jia, Adelin Travers, Baiwu Zhang, David Lie, and Nicolas Papernot. Machine unlearning. In 2021 IEEE Symposium on Security and Privacy (SP), pages 141-159. IEEE, 2021. 1, 6, 7", + "[2] Amirata Ghorbani, Abubakar Abid, and James Zou. 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In Proceedings of the IEEE conference on computer vision and pattern recognition, pages 2921-2929, 2016. 1" + ], + "bbox": [ + 501, + 92, + 893, + 570 + ], + "page_idx": 8 + }, + { + "type": "page_number", + "text": "20155", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 8 + } +] \ No newline at end of file diff --git a/2023/ERM-KTP_ Knowledge-Level Machine Unlearning via Knowledge Transfer/ab5287df-b899-4bb9-ae6b-5d2f41d1b6fe_model.json b/2023/ERM-KTP_ Knowledge-Level Machine Unlearning via Knowledge Transfer/ab5287df-b899-4bb9-ae6b-5d2f41d1b6fe_model.json new file mode 100644 index 0000000000000000000000000000000000000000..b6276be6650cbcce0515011c9d444fa68b46e3f8 --- /dev/null +++ b/2023/ERM-KTP_ Knowledge-Level Machine Unlearning via Knowledge Transfer/ab5287df-b899-4bb9-ae6b-5d2f41d1b6fe_model.json @@ -0,0 +1,1978 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.001, + 0.812, + 0.047 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.11, + 0.13, + 0.862, + 0.154 + ], + "angle": 0, + "content": "ERM-KTP: Knowledge-level Machine Unlearning via Knowledge Transfer" + }, + { + "type": "text", + "bbox": [ + 0.17, + 0.18, + 0.794, + 0.2 + ], + "angle": 0, + "content": "Shen Lin\\(^{1*}\\), Xiaoyu Zhang\\(^{1*}\\), Chenyang Chen\\(^{1}\\), Xiaofeng Chen\\(^{1\\dagger}\\), Willy Susilo\\(^{2}\\)" + }, + { + "type": "text", + "bbox": [ + 0.144, + 0.208, + 0.825, + 0.261 + ], + "angle": 0, + "content": "\\(^{1}\\)Xidian University, \\(^{2}\\)University of Wollongong linshen@stu.xidian.edu.cn, xiaoyuzhang@xidian.edu.cn, cychen_1@stu.xidian.edu.cn, xfchen@xidian.edu.cn, wsusilo@uow.edu.au" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.296, + 0.314, + 0.312 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.328, + 0.474, + 0.751 + ], + "angle": 0, + "content": "Machine unlearning can fortify the privacy and security of machine learning applications. Unfortunately, the exact unlearning approaches are inefficient, and the approximate unlearning approaches are unsuitable for complicated CNNs. Moreover, the approximate approaches have serious security flaws because even unlearning completely different data points can produce the same contribution estimation as unlearning the target data points. To address the above problems, we try to define machine unlearning from the knowledge perspective, and we propose a knowledge-level machine unlearning method, namely ERM-KTP. Specifically, we propose an entanglement-reduced mask (ERM) structure to reduce the knowledge entanglement among classes during the training phase. When receiving the unlearning requests, we transfer the knowledge of the nontarget data points from the original model to the unlearned model and meanwhile prohibit the knowledge of the target data points via our proposed knowledge transfer and prohibition (KTP) method. Finally, we will get the unlearned model as the result and delete the original model to accomplish the unlearning process. Especially, our proposed ERM-KTP is an interpretable unlearning method because the ERM structure and the crafted masks in KTP can explicitly explain the operation and the effect of unlearning data points. Extensive experiments demonstrate the effectiveness, efficiency, high fidelity, and scalability of the ERM-KTP unlearning method. Code is available at https://github.com/RUIYUN-ML/ERM-KTP" + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.78, + 0.21, + 0.795 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.806, + 0.47, + 0.867 + ], + "angle": 0, + "content": "In recent years, many countries have raised concerns about protecting personal privacy. The privacy legislation, e.g., the well-known European Union's GDPR [19], have been promulgated to oblige information service providers" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.298, + 0.893, + 0.435 + ], + "angle": 0, + "content": "to remove personal data when receiving a request from the data owner, i.e., the right-to-be-forgotten. Besides, the GDPR stipulates that the service providers should remove the corresponding impact of the data requested by the data owner, in which the machine learning models are the most representative. Many kinds of research demonstrate that the machine learning models can memorize knowledge of the data points, e.g., the membership inference attack [7, 14, 15] can infer whether a data point is in the training set or not." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.44, + 0.895, + 0.789 + ], + "angle": 0, + "content": "A naive approach is retraining the model after removing the target data points from the training set, but the human resources and materials consumed are costly. Thus, aiming to efficiently remove data as well as their generated contribution to the model, a new ML privacy protection research direction emerged, called machine unlearning. A good deal of related work attempted to solve the data-removing challenge of inefficient retraining, and there are two representative research fields, including exact unlearning [1] and approximate unlearning [3-5]. Unfortunately, these approaches usually require huge computational, storage overhead, and memory requirements for class-specific machine unlearning tasks on the complicated convolutional neural networks (CNNs). Furthermore, they may compromise the model's performance and even cause disastrous forgetting. Most significantly, Thudi et al. [18] believed that such approximate unlearning approaches have serious security flaws because they usually define machine unlearning as the distribution difference between the unlearned model and the retrained model. According to this definition, even unlearning completely different data points can produce the same contribution estimation as unlearning the target data points." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.795, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Unlearning algorithms are difficult to implement on deep learning models because these models are often seen as a black box and lack interpretability, which makes data points' contributions challenging to estimate. Though many related works [2, 10, 16, 21] attempted to improve the interpretability of deep learning models, they can not apply to machine unlearning directly. For example, Zhou et al. [22]" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.875, + 0.278, + 0.888 + ], + "angle": 0, + "content": "* Both authors contributed equally" + }, + { + "type": "page_footnote", + "bbox": [ + 0.098, + 0.888, + 0.221, + 0.9 + ], + "angle": 0, + "content": "† Corresponding author" + }, + { + "type": "list", + "bbox": [ + 0.096, + 0.875, + 0.278, + 0.9 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "20147" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.182 + ], + "angle": 0, + "content": "leveraged the global average pooling (GAP) in CNNs to generate a class activation mapping (CAM) to indicate the discriminative image regions used by the CNNs to identify the class. Liang et al. [12] proposed class-specific filters to transform the complex representations in convolutional layers into interpretable graphs." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.183, + 0.471, + 0.455 + ], + "angle": 0, + "content": "To address the above problems, for the first time, we consider the need for subsequent unlearning tasks during the model training phase. We define machine unlearning in the knowledge perspective, i.e., a reliable machine unlearning approach should satisfy that the knowledge of the unlearned model should be identical to the retrained model. Furthermore, we propose an interpretable unlearning method, i.e., ERM-KTP. The ERM structure can interpret the relation between data points and channels in the activation maps. Such a relationship can describe which filters the data points contribute to the convolutional layer. Then, KTP utilizes the relation to transfer the knowledge from corresponding filters to the unlearned model. Furthermore, the crafted masks in KTP interpret the operation of the knowledge transfer. With these interpretable methods, we can precisely unlearn data points and enhance the reliability of our proposed unlearning approach. We summarize our contributions of this paper as follows:" + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.464, + 0.47, + 0.554 + ], + "angle": 0, + "content": "- We give a novel definition of machine unlearning from the knowledge perspective, and we further propose an interpretable knowledge-level machine unlearning method, i.e., ERM-KTP. Especially, the interpretability of ERM-KTP enhances the reliability of the unlearning operation." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.565, + 0.47, + 0.702 + ], + "angle": 0, + "content": "- We introduce an ERM structure that reduces the knowledge entanglement among classes to get a pretrained model. When receiving the unlearning requests, we use the proposed KTP method to transfer the knowledge of the remaining set from the original model to the unlearned model and, meanwhile, prohibit the knowledge of the unlearning set. Finally, we will get the unlearned model as the result and delete the original model to complete the unlearning process." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.711, + 0.47, + 0.786 + ], + "angle": 0, + "content": "- We conduct experiments on three different scales of image classification datasets and three complicated CNNs. Extensive experimental results demonstrate the effectiveness, efficiency, high fidelity, and scalability of ERM-KTP." + }, + { + "type": "list", + "bbox": [ + 0.097, + 0.464, + 0.47, + 0.786 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.801, + 0.285, + 0.817 + ], + "angle": 0, + "content": "2. Problem Formulation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.826, + 0.47, + 0.903 + ], + "angle": 0, + "content": "In this paper, we primarily consider a class-specific machine unlearning scenario. We assume a sample space \\(\\mathcal{X} \\subseteq \\mathbb{R}^d\\) and corresponding labels \\(\\mathcal{Y} = \\{1,2,\\dots,C\\}\\), where \\(d\\) is the number of dimensions and \\(C\\) is the number of classes. The training set can be represented as" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.092, + 0.892, + 0.152 + ], + "angle": 0, + "content": "\\(\\mathcal{D} = \\{\\mathcal{D}_1,\\mathcal{D}_2,\\dots ,\\mathcal{D}_C\\}\\) . To unlearn the target class's data points \\(\\mathcal{D}_u\\subseteq \\mathcal{D}\\) exactly, we need to apply a removal method, which should be equivalent to applying the training algorithm to the dataset without target data points." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.155, + 0.894, + 0.276 + ], + "angle": 0, + "content": "Definition 1. We define a learning algorithm, \\(\\mathcal{A}:\\mathcal{D}\\to \\mathcal{W}\\) as a function from a dataset to a model in hypothesis space \\(\\mathcal{W}\\). A removal method, \\(\\mathcal{R}:\\mathcal{A}(\\mathcal{D})\\times \\mathcal{D}\\times \\mathcal{D}_u\\rightarrow \\mathcal{W}\\), is a function from an original model \\(\\mathcal{A}(D)\\), training dataset \\(\\mathcal{D}\\), an unlearning dataset \\(\\mathcal{D}_u\\) to remove from the training dataset \\(\\mathcal{D}\\) to an unlearned model in \\(\\mathcal{W}\\), and a remaining dataset \\(\\mathcal{D}_r = \\mathcal{D}\\backslash \\mathcal{D}_u\\). We define equivalence as having identical knowledge for each model in \\(\\mathcal{W}\\):" + }, + { + "type": "equation", + "bbox": [ + 0.574, + 0.291, + 0.892, + 0.308 + ], + "angle": 0, + "content": "\\[\n\\mathbb {K} (\\mathcal {A} \\left(\\mathcal {D} _ {r}\\right)) = \\mathbb {K} \\left(\\mathcal {R} \\left(\\mathcal {A} (\\mathcal {D}), \\mathcal {D}, \\mathcal {D} _ {u}\\right)\\right), \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.313, + 0.892, + 0.358 + ], + "angle": 0, + "content": "in which \\(\\mathbb{K}(\\cdot)\\) is a knowledge measuring function. If an exact unlearning method satisfy the above definition, it can be defined as a knowledge-level unlearning method." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.371, + 0.642, + 0.387 + ], + "angle": 0, + "content": "3. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.4, + 0.892, + 0.581 + ], + "angle": 0, + "content": "Exact unlearning. The exact unlearning approaches can provide algorithmic unlearning proof. The most representative exact unlearning approach is retrain-from-scratch (RfS), i.e., remove the target data points from the training set and retrain the model. Bourtoule et al. proposed SISA to improve efficiency by retraining the sub-model instead of retrain-from-scratch. These exact unlearning approaches are knowledge-level because they remove all target data points in the input phase so that the model can not learn any knowledge of them. However, their computational overhead is still significant because they need to relearn the remaining set's knowledge through retraining." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.584, + 0.892, + 0.902 + ], + "angle": 0, + "content": "Approximate unlearning. The main idea of approximate unlearning approaches is to estimate the target data points' contribution to the model and update the parameters for unlearning. For example, Graves et al. [4] leveraged gradients to estimate the contributions. They stored gradients of batches consisting of target data points and then subtracted the target gradients to update the model's parameters. For class-specific unlearning tasks or large-scale unlearning requests, it needs to store gradients of almost every batch, and the model will degenerate to the initialization state. Guo et al. [5] utilized the Influence Theory [8], and Golatkar et al. [3] used the Fisher Information [13] to estimate the contributions. However, the above two methods need to calculate the hessian matrix, which is very expensive in deep learning models. Besides, they may compromise the model's performance due to imprecise estimates of contributions on CNNs and even cause disastrous forgetting. Most significantly, Thudi et al. [18] pointed out that different data points can also generate the same network, making approximate unlearning approaches unable to provide an algorithmic unlearning proof." + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "20148" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.077, + 0.09, + 0.251, + 0.108 + ], + "angle": 0, + "content": "4. Proposed Method" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.115, + 0.47, + 0.221 + ], + "angle": 0, + "content": "In this section, we will explain the ERM-KTP unlearning method in detail. We will describe how the proposed ERM structure reduces the entanglement of knowledge in Section 4.1. Then, we will explain how the proposed KTP method transfers knowledge in Section 4.2. Finally, we will explain how we combine the ERM and the KTP method to construct the ERM-KTP unlearning method in Section 4.3." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.228, + 0.47, + 0.259 + ], + "angle": 0, + "content": "4.1. Entanglement-Reduced Mask (ERM) Structure" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.267, + 0.471, + 0.357 + ], + "angle": 0, + "content": "The most representative knowledge the ML models learn is the features extracted by the convolutional layers. However, the features of different classes are entangled, so the key features of different classes are always highly overlapping. As a result, it is difficult to transfer the knowledge of target classes without affecting others." + }, + { + "type": "image", + "bbox": [ + 0.09, + 0.367, + 0.457, + 0.542 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.108, + 0.556, + 0.438, + 0.571 + ], + "angle": 0, + "content": "Figure 1. An overview of our proposed ERM structure." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.585, + 0.47, + 0.797 + ], + "angle": 0, + "content": "In order to reduce the entanglement of knowledge, we propose an Entanglement-Reduced Mask (ERM) structure as a learnable layer of the CNNs inspired by the model interpretability work [12]. The learnable ERM structure can be represented as a matrix \\( G \\in \\mathbb{R}^{C \\times K} \\), where \\( C \\) is the number of classes and \\( K \\) is the number of filters. Each element \\( G_{c}^{k} \\in [0,1] \\) represents the relevance between the \\( k \\)-th filter and the \\( c \\)-th class, and a higher value of \\( G_{c}^{k} \\) denotes a closer correlation. Given a data point \\( (x \\in \\mathcal{X}, y \\in \\mathcal{Y}) \\) as an input, we use the \\( y \\)-th row \\( G_{y} \\in \\mathbb{R}^{1 \\times K} \\) as a mask vector multiplied to the activation maps \\( \\mathcal{M} = (\\mathcal{M}_1, \\dots, \\mathcal{M}_K) \\) of the last convolution layer (before the fully connected layer) to shut down irrelevant channels. Formally, we can define the above multiply operation as" + }, + { + "type": "equation", + "bbox": [ + 0.165, + 0.802, + 0.469, + 0.82 + ], + "angle": 0, + "content": "\\[\nA \\circ B = \\left(A _ {1} B ^ {1}, \\dots , A _ {d _ {1}} B ^ {d _ {1}}\\right), \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.824, + 0.47, + 0.855 + ], + "angle": 0, + "content": "in which \\(A\\in \\mathbb{R}^{d_1\\times d_2\\times d_3}\\) \\(B\\in \\mathbb{R}^{1\\times d_1}\\) \\(A_{i}\\in \\mathbb{R}^{d_{2}\\times d_{3}}\\) , and \\(B^{i}\\in \\mathbb{R}\\)" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.856, + 0.469, + 0.902 + ], + "angle": 0, + "content": "For a CNN with an ERM structure (ERM-CNN), we set two forward propagation paths of an ERM-CNN with parameters \\(\\theta\\): (1) the STD path with the predicting probability" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.152 + ], + "angle": 0, + "content": "vector \\(\\tilde{y}_{\\theta}\\); (2) the ERM path with mask matrix \\(G\\) predicting \\(\\tilde{y}_{\\theta}^{G}\\), as shown in Fig. 1. In the training phase, we train the network alternately through the STD and ERM paths, while only the STD path is used in the validation phase." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.152, + 0.893, + 0.334 + ], + "angle": 0, + "content": "Then, we will discuss the details of training an ERM-CNN. We first define an ideal ERM structure in which each row of the matrix \\( G \\) is at least one element equal to 1, and each row is orthogonal. In this ideal state, the knowledge of each class learned by the model is not entangled and independent of each other. Thus, the training objectives are to train an ERM-CNN with an ideal ERM structure, and its classification performance is comparable to the STD-CNNs. To train a model with the ideal ERM, we first consider its validation accuracy through two paths and ensure that at least one element of each row of \\( G \\) equals 1, i.e., \\( \\| G_{c}\\|_{\\infty} = 1 \\). We can get the following formulation:" + }, + { + "type": "equation", + "bbox": [ + 0.51, + 0.342, + 0.892, + 0.379 + ], + "angle": 0, + "content": "\\[\n\\min _ {\\theta , G} L _ {0} (\\theta) = \\mathrm {C E} (y | | \\tilde {y} _ {\\theta}) + \\lambda_ {1} \\mathrm {C E} (y | | \\tilde {y} _ {\\theta} ^ {G}) \\quad s. t. G \\in V _ {G}, \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.379, + 0.892, + 0.485 + ], + "angle": 0, + "content": "where CE denotes the cross entropy loss and \\(V_{G} = \\{G\\in\\) \\(\\mathbb{R}^{C\\times K}: \\| G_c\\|_{\\infty} = 1\\}\\) . Furthermore, we introduce a regulation term to encourage the sparsity of the matrix \\(G\\) , and encourage the \\(L_{1}\\) -norm of \\(G\\) not to exceed the preset upper bound \\(\\alpha\\) and has no effect when \\(\\| G\\| _1 < \\alpha\\) . Apparently, we should set \\(\\alpha \\geqslant K\\) because \\(\\| G_c\\|_{\\infty} = 1\\) ensures \\(\\| G\\| _1\\geqslant K\\) As described above, we can formulate the regulation term as" + }, + { + "type": "equation", + "bbox": [ + 0.516, + 0.496, + 0.892, + 0.518 + ], + "angle": 0, + "content": "\\[\n\\min _ {G} L _ {1} (\\theta) = \\| \\operatorname {R e L U} (\\| G \\| _ {1} - \\alpha) \\| _ {p} \\quad s. t. G \\in V _ {G}, \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.526, + 0.892, + 0.572 + ], + "angle": 0, + "content": "in which \\(\\| \\cdot \\| _p\\) indicates \\(p\\)-norm. Moreover, we introduce the inner product regulation to encourage each row of \\(G\\) to be orthogonal to the other as" + }, + { + "type": "equation", + "bbox": [ + 0.597, + 0.58, + 0.892, + 0.631 + ], + "angle": 0, + "content": "\\[\n\\operatorname {I n P} = \\sum_ {c _ {1} = 0} ^ {C} \\sum_ {c _ {2} = 0, \\atop c _ {1} < c _ {2}} ^ {C} \\left(G _ {c _ {1}} \\cdot G _ {c _ {2}}\\right). \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.639, + 0.892, + 0.682 + ], + "angle": 0, + "content": "To facilitate the solution in practice, we replace Eq. (5) with the following equivalent form as our inner product regulation term:" + }, + { + "type": "equation", + "bbox": [ + 0.523, + 0.689, + 0.892, + 0.741 + ], + "angle": 0, + "content": "\\[\n\\min _ {G} L _ {2} (\\theta) = \\sum_ {c _ {1} = 0} ^ {C} \\sum_ {c _ {2} = 0, \\atop c _ {1} < c _ {2}} ^ {C} (G G ^ {T}) _ {c _ {1}} ^ {c _ {2}} \\quad s. t. G \\in V _ {G}, \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.75, + 0.892, + 0.855 + ], + "angle": 0, + "content": "in which \\((GG^{T})_{c_{1}}^{c_{2}}\\) denotes the \\(c_{1}\\)-th row and the \\(c_{2}\\)-th column of the matrix \\((GG^{T})\\). When we minimize \\(L_{2}(\\theta)\\), it will tend to 0 if \\(G_{c}^{k} \\in [0,1]\\), i.e., each row of \\(\\mathbf{G}\\) will be orthogonal to the other. Essentially, the inner product describes the similarity between two vectors as \\(\\vec{a} \\cdot \\vec{b} = \\|\\vec{a}\\| \\|\\vec{b}\\| \\cos \\langle \\vec{a}, \\vec{b} \\rangle\\). When we minimize \\(L_{2}(\\theta)\\), the cosine value and their \\(L_{2}\\)-norm are minimized simultaneously." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.856, + 0.892, + 0.887 + ], + "angle": 0, + "content": "To sum up, we formulate an optimization problem to train an ERM-CNN by combining Eq. (3), (4), and (6):" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.957 + ], + "angle": 0, + "content": "20149" + } + ], + [ + { + "type": "equation", + "bbox": [ + 0.096, + 0.085, + 0.469, + 0.185 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\min _ {\\theta , G} L (\\theta) = \\mathrm {C E} (y | | \\tilde {y} _ {\\theta}) + \\lambda_ {1} \\mathrm {C E} (y | | \\tilde {y} _ {\\theta} ^ {G}) \\\\ + \\lambda_ {2} \\| \\operatorname {R e L U} (\\| G \\| _ {1} - \\alpha) \\| _ {p} \\\\ + \\lambda_ {3} \\sum_ {c _ {1} = 0} ^ {C} \\sum_ {\\substack {c _ {2} = 0, \\\\ c _ {1} < c _ {2}}} ^ {C} (G G ^ {T}) _ {c _ {1}} ^ {c _ {2}} \\quad s. t. G \\in V _ {G}, \\tag{7} \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.194, + 0.47, + 0.253 + ], + "angle": 0, + "content": "in which the first and the second term ensure the classification performance, the third term ensures the sparsity of the matrix \\( G \\), and the last term imposes a rigorous constraint on each row of \\( G \\)." + }, + { + "type": "code_caption", + "bbox": [ + 0.088, + 0.271, + 0.342, + 0.285 + ], + "angle": 0, + "content": "Algorithm 1: Alternate Training (AT)" + }, + { + "type": "algorithm", + "bbox": [ + 0.08, + 0.289, + 0.415, + 0.495 + ], + "angle": 0, + "content": "1 for e in epochs do \n2 if \\(e \\in ERM's\\) epoch then \n3 \\(\\tilde{y}_{\\theta}^{G} \\gets\\) prediction through the ERM path \n4 \\(\\mathcal{L} \\gets \\lambda_{1}CE(y||\\tilde{y}_{\\theta}^{G}) + \\lambda_{2}L_{1} + \\lambda_{3}L_{2}\\) \n5 \\(G \\gets G - \\eta \\frac{\\partial\\mathcal{L}}{\\partial G}\\) \n6 \\(G_{c} \\gets G_{c} / \\| G_{c}\\|_{\\infty}\\) \n7 \\(G \\gets G.\\mathrm{clip}(0,1)\\) \n8 else \n9 \\(\\tilde{y}_{\\theta} \\gets\\) prediction through the STD path \n10 \\(\\mathcal{L} \\gets \\mathrm{CE}(y||\\tilde{y}_{\\theta})\\) \n11 end \n12 \\(\\theta \\gets \\theta - \\eta \\frac{\\partial\\mathcal{L}}{\\partial\\theta}\\) \n13 end" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.521, + 0.473, + 0.779 + ], + "angle": 0, + "content": "To solve the above optimization problem in Eq. (7), we apply an approximate projected gradient descent (PGD) algorithm. After the matrix \\(G\\) is updated, \\(G_{c}\\) will be normalized by \\(G_{c} / \\| G_{c}\\|_{\\infty}\\) to ensure \\(\\| G_c\\|_{\\infty} = 1\\), and then each element of \\(G_{c}\\) will be clipped into the range [0, 1]. However, the joint training scheme may have some difficulties due to poor convergence. The forward propagation through the ERM path can make most features block, leading to a much poorer convergence than the STD path because of the weaker gradient. Therefore, we propose an alternate training (AT) scheme instead of the normal joint training scheme in that the forward propagation uses the STD path and ERM path alternately in different epochs. Specifically, we update \\(G\\) and \\(\\theta\\) by descend the gradient of \\(\\lambda_1\\mathrm{CE}(y||\\tilde{y}_\\theta^G) + \\lambda_2L_1 + \\lambda_3L_2\\) in the epoch for ERM path, and we update \\(\\theta\\) with the gradient of \\(\\mathrm{CE}(y||\\tilde{y}_{\\theta})\\) in the STD path, as shown in Algorithm 1." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.787, + 0.45, + 0.803 + ], + "angle": 0, + "content": "4.2. Knowledge Transfer and Prohibition (KTP)" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.81, + 0.47, + 0.901 + ], + "angle": 0, + "content": "After training an ERM-CNN as a pre-trained model, different classes' knowledge (features and parameters) is independent. When receiving the unlearning requests, we can transfer the knowledge of a single class separately via our proposed knowledge transfer and prohibition (KTP) method. Specifically, KTP transfers the knowledge of the" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.895, + 0.214 + ], + "angle": 0, + "content": "non-target class of data in the origin model \\(\\theta_T\\) to the unlearned model \\(\\theta_S\\) while prohibiting the knowledge of the target data points. We can describe the KTP method as the following three processes: (1) convolution layers \\((\\theta_S^{cv}\\) and \\(\\theta_T^{cv})\\) knowledge transfer (CKT); (2) fully connected layers \\((\\theta_S^{fc}\\) and \\(\\theta_T^{fc})\\) knowledge transfer (FKT); (3) matrix \\(G\\) (\\(G_S\\) and \\(G_T\\)) knowledge transfer (GKT). Formally, we can define the KTP method as" + }, + { + "type": "equation", + "bbox": [ + 0.627, + 0.225, + 0.765, + 0.246 + ], + "angle": 0, + "content": "\\[\n\\operatorname {C K T}: \\theta_ {S} ^ {c v} \\stackrel {{t r a n s}} {{\\longleftarrow}} \\theta_ {T} ^ {c v},\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.63, + 0.248, + 0.892, + 0.268 + ], + "angle": 0, + "content": "\\[\n\\operatorname {F K T}: \\theta_ {S} ^ {f c} \\xleftarrow {\\text {t r a n s}} \\theta_ {T} ^ {f c}, \\tag {8}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.627, + 0.272, + 0.766, + 0.291 + ], + "angle": 0, + "content": "\\[\n\\operatorname {G K T}: G _ {S} \\stackrel {{t r a n s}} {{\\longleftarrow}} G _ {T}.\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.303, + 0.894, + 0.363 + ], + "angle": 0, + "content": "In the CKT process, we transfer the knowledge of features extracted by the convolutional layers by a crafted channel mask \\(\\bar{G}_{\\mathbf{c}} \\in \\mathbb{R}^{1 \\times K}\\). For the single target class \\(\\mathbf{c}\\) unlearning task, the mask can be defined as" + }, + { + "type": "equation", + "bbox": [ + 0.612, + 0.375, + 0.892, + 0.416 + ], + "angle": 0, + "content": "\\[\n\\bar {G} _ {\\mathbf {c}, i} = \\left\\{ \\begin{array}{l l} 0, & G _ {\\mathbf {c}, i} = 1 \\\\ 1, & G _ {\\mathbf {c}, i} = 0 \\end{array} . \\right. \\tag {9}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.428, + 0.893, + 0.473 + ], + "angle": 0, + "content": "For the multiple target classes \\(\\mathbf{c} = \\{\\mathbf{c}_0,\\dots ,\\mathbf{c}_{|c|}\\}\\) unlearning task, we calculate \\(\\bar{G}_{\\mathbf{c}_j}\\) for each class \\(j\\) and then aggregate them as" + }, + { + "type": "equation", + "bbox": [ + 0.585, + 0.485, + 0.892, + 0.58 + ], + "angle": 0, + "content": "\\[\n\\bar {G} _ {\\mathbf {c}, i} = \\left\\{ \\begin{array}{l l} 1, & \\left(\\sum_ {j} ^ {| c |} \\bar {G} _ {\\mathbf {c} _ {j}}\\right) _ {i} = | c | \\\\ 0, & \\left(\\sum_ {j} ^ {| c |} \\bar {G} _ {\\mathbf {c} _ {j}}\\right) _ {i} < | c | \\end{array} . \\right. \\tag {10}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.59, + 0.892, + 0.62 + ], + "angle": 0, + "content": "Formally, the CKT process can be formulated as an optimization problem:" + }, + { + "type": "equation", + "bbox": [ + 0.52, + 0.633, + 0.892, + 0.658 + ], + "angle": 0, + "content": "\\[\n\\min _ {\\theta_ {S} ^ {c v}} L _ {3} \\left(\\theta_ {S} ^ {c v}\\right) = \\operatorname {M S E} \\left(f \\left(x; \\theta_ {T} ^ {c v}\\right), g \\left(x; \\theta_ {S} ^ {c v}\\right) \\circ \\bar {G} _ {\\mathbf {c}}\\right), \\tag {11}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.67, + 0.895, + 0.819 + ], + "angle": 0, + "content": "where \\(\\mathrm{MSE}(\\cdot)\\) is Mean Square Error, \\(x\\) is data points, \\(\\circ\\) is the multiply operation (Eq. (2)), and \\(f(\\theta_S^{cv})\\) and \\(g(\\theta_S^{cv})\\) denote the output of the origin model's last convolution layer with parameters \\(\\theta_S^{cv}\\) and the output from unlearned model's last convolution layer with parameters \\(\\theta_S^{cv}\\), respectively. Note that the knowledge of the corresponding channels in the feature maps multiplied by the matrix \\(G\\) where the value equals one has been transferred. In contrast, the knowledge associated with values equal to 0 has been prohibited." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.822, + 0.894, + 0.902 + ], + "angle": 0, + "content": "For the FKT process, we transfer the knowledge of parameters in fully connected (FC) layer \\(\\theta^{fc} = \\{\\theta_{\\beta}^{fc},\\theta_{\\gamma}^{fc}\\}\\), in which \\(\\theta_{\\beta}^{fc}\\in \\mathbb{R}^{K\\times C}\\) denotes the weight, and \\(\\theta_{\\gamma}^{fc}\\in \\mathbb{R}^{1\\times C}\\) denotes the bias. The FKT process can be executed by directly modifying the original model's parameters of fully" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "20150" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.078, + 0.092, + 0.21, + 0.106 + ], + "angle": 0, + "content": "connected layers as" + }, + { + "type": "equation", + "bbox": [ + 0.095, + 0.116, + 0.469, + 0.177 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\theta_ {S, \\beta} ^ {f c} = \\theta_ {T, \\beta} ^ {f c} * \\mathcal {A} _ {\\beta}, \\quad \\mathcal {A} _ {\\beta} = (\\underbrace {(\\bar {G} _ {c}) ^ {T} , \\cdots , (\\bar {G} _ {c}) ^ {T}} _ {C}), \\tag {12} \\\\ \\theta_ {S, \\gamma} ^ {f c} = \\theta_ {T, \\gamma} ^ {f c} * \\mathcal {A} _ {\\gamma}, \\quad \\mathcal {A} _ {\\gamma} \\in [ 0, 1 ] ^ {1 \\times C}, \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.186, + 0.47, + 0.276 + ], + "angle": 0, + "content": "where all elements of \\(\\mathcal{A}_{\\gamma}\\) are equal to 1 except the c-th column, \\((\\cdot)^T\\) denotes the matrix transpose operation, and \\(*\\) denotes the hardamad product operation. Similar to the channel mask \\(\\bar{G}_c\\), the FC mask \\(\\mathcal{A} = \\{\\mathcal{A}_{\\beta}, \\mathcal{A}_{\\gamma}\\}\\) prohibits the knowledge of the FC layer related to the target class of data points." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.277, + 0.469, + 0.307 + ], + "angle": 0, + "content": "Finally, we update the matrix \\( G_{S} \\) of the unlearned model through the GKT process by the following equation:" + }, + { + "type": "equation", + "bbox": [ + 0.148, + 0.317, + 0.469, + 0.335 + ], + "angle": 0, + "content": "\\[\nG _ {S} = G _ {T} * \\mathcal {A} _ {G}, \\quad \\mathcal {A} _ {G} \\in [ 0, 1 ] ^ {C \\times K}, \\tag {13}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.346, + 0.469, + 0.421 + ], + "angle": 0, + "content": "where only the c-th row of the mask matrix \\(\\mathcal{A}_G\\) is equal to 0, and the others are equal to 1. The updated matrix \\(G_{S}\\) can visualize which classes of data points have been removed by checking which rows are equal to 0. We summarize the KTP method in Algorithm 2." + }, + { + "type": "code_caption", + "bbox": [ + 0.088, + 0.44, + 0.425, + 0.469 + ], + "angle": 0, + "content": "Algorithm 2: Knowledge Transfer and Prohibition (KTP)" + }, + { + "type": "algorithm", + "bbox": [ + 0.081, + 0.474, + 0.449, + 0.724 + ], + "angle": 0, + "content": "// CKT \n1 for e in epochs do \n2 \\(f(x;\\theta_T^{cv})\\gets\\) forward propagation through \\(\\theta_T\\) \n3 \\(g(x;\\theta_S^{cv})\\gets\\) forward propagation through \\(\\theta_S\\) \n4 \\(\\mathcal{L}\\gets \\mathrm{MSE}(f(x;\\theta_T^{cv})\\circ \\bar{G}_c,g(x;\\theta_S^{cv}))\\) \n5 \\(\\theta_S^{cv}\\gets \\theta_S^{cv} - \\eta \\frac{\\partial\\mathcal{L}}{\\partial\\theta_S^{cv}}\\) \n6 end \n// FKT \n7 \\(\\theta_{S,\\beta}^{fc} = \\theta_{T,\\beta}^{fc}*\\mathcal{A}_{\\beta}\\) \n8 \\(\\theta_{S,\\gamma}^{fc} = \\theta_{T,\\gamma}^{fc}*\\mathcal{A}_{\\gamma}\\) \n9 \\(\\theta_S^{fc} = \\{\\theta_{S,\\beta}^{fc},\\theta_{S,\\gamma}^{fc}\\}\\) \n// GKT \n10 \\(G_{S} = G_{T}*\\mathcal{A}_{G}\\) \n// Unlearned Model \n11 \\(\\theta_S = \\{\\theta_S^{cv},G_S,\\theta_S^{fc}\\}\\)" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.742, + 0.388, + 0.758 + ], + "angle": 0, + "content": "4.3. Machine Unlearning via ERM-KTP" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.765, + 0.469, + 0.901 + ], + "angle": 0, + "content": "Here, we will explain how we combine the ERM structure and KTP method to construct a class-specific knowledge-level machine unlearning approach. We first train the original ERM-CNNs by Algorithm 1. When receiving unlearning requests, we then transfer the remaining dataset's knowledge to the unlearned model by Algorithm 2. Finally, we complete the unlearning process by deleting the original model. The detailed ERM-KTP unlearning algorithm is shown in Algorithm 3." + }, + { + "type": "code_caption", + "bbox": [ + 0.51, + 0.095, + 0.758, + 0.11 + ], + "angle": 0, + "content": "Algorithm 3: ERM-KTP Unlearning" + }, + { + "type": "algorithm", + "bbox": [ + 0.507, + 0.113, + 0.782, + 0.207 + ], + "angle": 0, + "content": "1 \\(\\theta_T\\gets \\mathrm{AT}(\\theta)\\) \n2 while receiving unlearning requests do \n3 \\(\\theta_S\\gets \\mathrm{KTP}(\\theta_T)\\) \n4 Delete \\(\\theta_T\\) \n5 \\(\\theta_T = \\theta_S\\) \n6 end" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.24, + 0.632, + 0.256 + ], + "angle": 0, + "content": "5. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.265, + 0.892, + 0.354 + ], + "angle": 0, + "content": "In this section, we empirically evaluate the performance of the proposed unlearning method on three popular image classification benchmarks. All experiments are implemented with Python 3.8 and PyTorch 1.10.1 on a machine with Intel(R) Core(TM) i9-10980XE CPU, 32GB RAM, and a Nvidia 3090 GPU." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.366, + 0.681, + 0.38 + ], + "angle": 0, + "content": "5.1. Datasets & Models" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.389, + 0.892, + 0.51 + ], + "angle": 0, + "content": "We evaluate the proposed unlearning method in three public image classification datasets, i.e., CIFAR10, CIFAR100 [9], and Tiny-ImageNet [11]. The input size of CIFAR-10 and CIFAR-100 is \\(32 \\times 32\\), and they both contain 50,000 training images and 10,000 for validation. For Tiny-ImageNet, the size of image samples is \\(224 \\times 224\\). It contains 200 classes of samples, and each class has 500 samples for training, 50 for validation, and 50 for testing." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.511, + 0.892, + 0.616 + ], + "angle": 0, + "content": "Moreover, the model structure is three common image classification deep neural networks, ResNet-20, ResNet-50 [6], and ResNeXt-50 [20]. The original models are trained for 200 epochs using Stochastic Gradient Descent (SGD) optimizer with a momentum of 0.9, weight decay of 5e-4, and an initial learning rate of 0.1, divided by 10 after 100 and 150 epochs, respectively." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.626, + 0.807, + 0.64 + ], + "angle": 0, + "content": "5.2. Effectiveness of the ERM Structure" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.65, + 0.89, + 0.68 + ], + "angle": 0, + "content": "In order to evaluate the effectiveness of ERM structure, we propose the following metrics:" + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.69, + 0.89, + 0.719 + ], + "angle": 0, + "content": "- Cosine similarity (CSI) to analyze the orthogonality of each row of the matrix \\(G\\) as follows," + }, + { + "type": "equation", + "bbox": [ + 0.6, + 0.731, + 0.89, + 0.782 + ], + "angle": 0, + "content": "\\[\n\\mathrm {C S I} = \\sum_ {c _ {1} = 0} ^ {C} \\sum_ {\\substack {c _ {2} = 0, \\\\ c _ {1} \\neq c _ {2}}} ^ {C} \\left(\\frac {G _ {c _ {1}} \\cdot G _ {c _ {2}}}{\\| G _ {c _ {1}} \\| \\| G _ {c _ {2}} \\|\\right). \\tag{14}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.8, + 0.887, + 0.814 + ], + "angle": 0, + "content": "- \\( L_{1} \\)-density to evaluate the sparsity of the matrix \\( G \\) as" + }, + { + "type": "equation", + "bbox": [ + 0.642, + 0.825, + 0.89, + 0.856 + ], + "angle": 0, + "content": "\\[\nL _ {1} \\text {- d e n s i t y} = \\frac {\\| G \\| _ {1}}{C K}. \\tag {15}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.871, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Table 1 shows that the CNNs with the ERM structure have slightly better classification performance than the STD" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "20151" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.471, + 0.184 + ], + "angle": 0, + "content": "CNNs. Moreover, the \\(L_{1}\\)-density convergences to \\(\\alpha\\), and CSI convergences close to 0, meaning each class of data is independent to the other. These metrics quantitatively demonstrate ERM's effectiveness in learning a sparse mask matrix to reduce the entanglement for the following unlearning task without sacrificing classification accuracy." + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.188, + 0.471, + 0.245 + ], + "angle": 0, + "content": "Table 1. Metrics of the STD-CNNs and ERM-CNNs. The first row of each two stand for STD-CNNs and the second one stand for ERM-CNNs. \\( Acc_{val} \\) is the original model's classification accuracy on the validation dataset." + }, + { + "type": "table", + "bbox": [ + 0.08, + 0.257, + 0.47, + 0.367 + ], + "angle": 0, + "content": "
DatasetModelCKCSIL1-densityAccval
CIFAR10ResNet-20----89.6%
10640.00.192.6%
CIFAR100ResNeXt-50----76.2%
1002,0480.00.0177.6%
Tiny-ImageNetResNet-50----49.3%
2002,0480.00.00553.4%
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.38, + 0.47, + 0.487 + ], + "angle": 0, + "content": "Moreover, we evaluate if the ERM structure can reduce or eliminate the knowledge entanglement across classes by prohibiting each class's knowledge successively during the ERM path's forward propagation. As shown in Table 2, the classification accuracy will degrade into \\(0.0\\%\\) for the knowledge-prohibited classes, while the accuracy will remain the same for the knowledge-permitted classes." + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.497, + 0.471, + 0.553 + ], + "angle": 0, + "content": "Table 2. Accuracy of the data points with prohibited or permitted Knowledge. \\( Acc_{(\\cdot)}^{pro} \\) and \\( Acc_{(\\cdot)}^{per} \\) denote the accuracy of the knowledge-prohibited classes and the knowledge-permitted classes, respectively." + }, + { + "type": "table", + "bbox": [ + 0.079, + 0.564, + 0.469, + 0.634 + ], + "angle": 0, + "content": "
DatasetModelAccprotrainAccpertrainAccprovalAccperval
CIFAR10ResNet-200.0%97.1%0.0%91.8%
CIFAR100ResNeXt-500.0%99.9%0.0%78.1%
Tiny-ImageNetResNet-500.0%99.9%0.0%53.4%
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.651, + 0.47, + 0.789 + ], + "angle": 0, + "content": "We also evaluate the time overhead and memory requirements of the ERM CNNs in the training phase. The computation overhead is the activation map multiplied by the corresponding \\(y\\)-th row of the matrix \\(G\\) and computing the regulation terms \\(L_{1}\\) and \\(L_{2}\\). As shown in Table 3, the time overhead of the ERM structure is comparable to the standard (STD) CNNs, and the additional memory requirements are negligible, which demonstrates that ERM structure has great scalability and can be applied to any CNN structures." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.795, + 0.47, + 0.825 + ], + "angle": 0, + "content": "5.3. Effectiveness of the ERM-KTP Unlearning Method" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.834, + 0.469, + 0.864 + ], + "angle": 0, + "content": "We utilize some common metrics to evaluate the effectiveness of the ERM-KTP unlearning method as follows." + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.871, + 0.469, + 0.902 + ], + "angle": 0, + "content": "- \\( Acc_{D_r} \\) is the original model's classification accuracy on the training set of the remaining classes." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.092, + 0.891, + 0.122 + ], + "angle": 0, + "content": "- \\( Acc_{val} \\) is the original model's classification accuracy on the validation dataset of the remaining classes." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.131, + 0.892, + 0.161 + ], + "angle": 0, + "content": "- \\( Acc_{D_r}' \\) measures the unlearned model's performance on the training set of the remaining classes." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.17, + 0.892, + 0.216 + ], + "angle": 0, + "content": "- \\(\\Delta Acc_{D_r} = Acc_{D_r}' - Acc_{D_r}\\) indicates the difference between the accuracy of the remaining set before and after the unlearning operation." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.225, + 0.892, + 0.27 + ], + "angle": 0, + "content": "- \\(\\Delta Acc_{val} = Acc_{val}' - Acc_{val}\\) indicates the difference between the accuracy of the validation set before and after the unlearning operation." + }, + { + "type": "list", + "bbox": [ + 0.518, + 0.092, + 0.892, + 0.27 + ], + "angle": 0, + "content": null + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.278, + 0.891, + 0.307 + ], + "angle": 0, + "content": "Table 3. Time overhead and memory requirements of the ERM-CNNs and the STD-CNNs in the training phase." + }, + { + "type": "table", + "bbox": [ + 0.502, + 0.318, + 0.891, + 0.429 + ], + "angle": 0, + "content": "
DatasetModelStructureTimeMemory
CIFAR10ResNet-20STD1206s2867MiB
ERM1541s2867MiB
CIFAR100ResNeXt-50STD9447s19223MiB
ERM9983s19275MiB
Tiny-ImageNetResNet-50STD5025s6769MiB
ERM6164s6803MiB
" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.447, + 0.892, + 0.613 + ], + "angle": 0, + "content": "Then, we conduct experiments in the case of unlearning \\(10\\%\\), \\(40\\%\\), and \\(80\\%\\) of classes, respectively. Table 4 shows that \\(Acc_{D_u}\\) equals \\(0.0\\%\\) in all cases, demonstrating that ERM-KTP can effectively unlearn target data points. Furthermore, \\(\\Delta Acc_{D_r}\\) are close to \\(0.0\\%\\) and \\(\\Delta Acc_{D_r}\\) is greater than \\(0.0\\%\\) in most cases. These show that ERM-KTP can unlearn target data without affecting the model classification performance, demonstrating the high fidelity of ERM-KTP. In summary, ERM-KTP performs well on all these datasets and model structures, demonstrating the scalability of ERM-KTP." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.622, + 0.746, + 0.637 + ], + "angle": 0, + "content": "5.4. Comparison with Baselines" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.645, + 0.891, + 0.676 + ], + "angle": 0, + "content": "To further prove the advantage of ERM-KTP, we compare ERM-KTP with the following baseline approaches:" + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.683, + 0.891, + 0.713 + ], + "angle": 0, + "content": "- Retrain from scratch (RfS): Retrain model from scratch with remaining data points \\(\\mathcal{D}_r\\)." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.722, + 0.89, + 0.753 + ], + "angle": 0, + "content": "- SISA: Retrain the sub-model whose training set contains the target data points [1]." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.762, + 0.89, + 0.792 + ], + "angle": 0, + "content": "- Fine-tune: Fine-tune the model on the remaining data \\(\\mathcal{D}_r\\) using a slightly larger learning rate." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.801, + 0.891, + 0.846 + ], + "angle": 0, + "content": "- Random Labels (RL): Fine-tune the model on \\(\\mathcal{D}\\) by randomly resampling labels corresponding to images belonging to the remaining data points \\(\\mathcal{D}_r\\)." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.856, + 0.891, + 0.901 + ], + "angle": 0, + "content": "- Amnesiac Unlearning: Track gradient in every training batch. Then, update the model by subtracting the gradients when the batch is marked for removal [4]." + }, + { + "type": "list", + "bbox": [ + 0.518, + 0.683, + 0.891, + 0.901 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "20152" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.086, + 0.09, + 0.885, + 0.105 + ], + "angle": 0, + "content": "Table 4. Performance evaluation of ERM-KTP unlearning method. #Classes denotes the number of the unlearned classes of data points" + }, + { + "type": "table", + "bbox": [ + 0.148, + 0.115, + 0.821, + 0.31 + ], + "angle": 0, + "content": "
DatasetModel#ClassesAccDrAccvalAccDuAcc'DrΔAccDrΔAccval
CIFAR10ResNet-20096.8%92.6%----
196.6%91.3%0.0%95.3%-1.3%-1.3%
497.4%96.1%0.0%97.3%-0.1%+3.5%
898.4%97.8%0.0%98.5%+0.1%+3.1%
CIFAR100ResNeXt-50099.9%77.6%----
1099.9%76.1%0.0%98.1%-1.8%-0.6%
4099.9%79.4%0.0%98.4%-1.5%+1.1%
8099.9%86.4%0.0%99.8%-0.1%+7.6%
Tiny-ImageNetResNet-50099.9%53.4%----
2099.9%52.6%0.0%97.6%-2.3%-0.3%
8099.9%53.8%0.0%98.3%-1.6%+1.5%
16099.9%59.3%0.0%97.6%-2.3%+4.4%
" + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.339, + 0.471, + 0.399 + ], + "angle": 0, + "content": "- Fisher Unlearning: Perform a corrective Newton step using the Fisher Information Matrix. Add fisher noises sampled from Gaussian distribution to the weight to scrub the information [3]." + }, + { + "type": "image", + "bbox": [ + 0.136, + 0.419, + 0.413, + 0.587 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.598, + 0.47, + 0.655 + ], + "angle": 0, + "content": "Figure 2. Train the unlearned model with the training datasets, and \\(\\Delta Acc_{D_u}\\) denotes the difference between the accuracy of the unlearning dataset on the relearned model and the accuracy on the original model on CIFAR10 and ResNet-20." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.66, + 0.47, + 0.87 + ], + "angle": 0, + "content": "Then, we conduct the comparison experiments for \\(40\\%\\) classes of data points removed. As shown in Table 5, the Amenesiac method [4] stores the gradients of almost every batch, and the model's performance degrades to random guess because it makes the model return to its initial state. For SISA [1], we need to retrain all shards to unlearn target classes of data points because every shard contains the target data points. Also, SISA's validation accuracy is lower by about \\(6\\%\\) than STD CNNs due to the aggregation operation. Though the literature [3] reports that the Fisher method performs well on All-CNN [17] and CIFAR-10, our experimental results show that it is not suitable for complicated CNNs, e.g., ResNet-20, ResNet-50 [6], and ResNeXt-50 [20]." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Note that fine-tune and random labels (RL) methods show great performance on \\(\\Delta Acc_{D_r}\\) and \\(\\Delta Acc_{val}\\). How-" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.339, + 0.892, + 0.535 + ], + "angle": 0, + "content": "ever, these two methods are only an output-level unlearning, i.e., they only change the model's output of the target data points but not remove the corresponding knowledge. To prove that, we fine-tune the unlearned model to observe how long the model can relearn the forget knowledge. As shown in Fig. 2, the Fine-tune and RL method restore the performance on the unlearning dataset at about the 50th epoch, while the relearn time of ERM-KTP method is similar to the RfS method, i.e., they both recover the performance around the 100th epoch. It demonstrates that ERM-KTP can completely remove the target data points like the RfS method, i.e., ERM-KTP is a knowledge-level unlearning method." + }, + { + "type": "image", + "bbox": [ + 0.517, + 0.551, + 0.688, + 0.654 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.579, + 0.658, + 0.621, + 0.669 + ], + "angle": 0, + "content": "(a) CSI" + }, + { + "type": "image", + "bbox": [ + 0.709, + 0.551, + 0.882, + 0.655 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.754, + 0.657, + 0.834, + 0.67 + ], + "angle": 0, + "content": "(b) \\(L_{1}\\)-density" + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.682, + 0.892, + 0.71 + ], + "angle": 0, + "content": "Figure 3. Ablation experiments of our proposed regulation terms on CIFAR100 and ResNet-50." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.892, + 0.901 + ], + "angle": 0, + "content": "For the efficiency comparison, we conduct the experiments on CIFAR10 and ResNet-20 because some methods can not be implemented on the other two settings, e.g., Fisher method needs more than 200 hours in TinyImageNet. As shown in Table 6, ERM-KTP improves by \\(5 \\times\\) compared to RfS, \\(5.4 \\times\\) compared to SISA, and \\(42 \\times\\) compared to Fisher. Though the time overhead of Finetune is less than ERM-KTP, Fine-tune method is only an output-level unlearning method, as mentioned above. In summary, compared with these baseline approaches, ERM-KTP is more effective, more efficient, and has better scalability." + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "20153" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.141, + 0.09, + 0.827, + 0.105 + ], + "angle": 0, + "content": "Table 5. Unlearning performance comparison with baseline approaches when unlearning \\( {40}\\% \\) classes of data points." + }, + { + "type": "table", + "bbox": [ + 0.122, + 0.115, + 0.847, + 0.449 + ], + "angle": 0, + "content": "
DatasetModelApproachAccDrAccvalAccDuAcc'DrΔAccDrΔAccval
CIFAR10ResNet-20STD99.9%93.7%----
RfS99.9%96.3%0.0%99.8%-0.1%+2.6%
Fine-tune99.9%97.0%0.0%99.8%-0.1%+3.3%
RL99.9%97.0%0.0%99.8%-0.1%+3.3%
SISA92.4%91.0%0.0%92.8%+0.4%+0.2%
Fisher99.9%54.0%48.4%53.0%-46.9%-25.1%
Amnesiac99.9%9.0%0.0%15.4%-84.5%-84.7%
ERM-KTP (ours)97.4%96.1%0.0%97.3%-0.1%+3.5%
CIFAR100ResNeXt-50STD99.9%78.9%----
RfS99.9%79.6%0.0%99.9%0.0%+0.7%
RL99.9%78.1%0.0%99.7%0.0%-0.8%
Fisher99.9%1.0%0.0%1.0%-98.9%-77.9%
Fine-tune99.9%83.4%0.0%99.9%0.0%+4.5%
Amnesiac99.9%0.89%0.0%1.0%-98.9%-77.8%
ERM-KTP (ours)99.9%79.4%0.0%98.4%-1.5%+1.1%
Tiny-ImageNetResNet-50STD99.9%48.3%----
RfS99.9%45.1%0.0%99.9%0.0%-3.2%
RL99.9%43.4%0.0%96.7%-3.2%-4.9%
SISA67.6%52.8%0.0%68.0%+0.4%-1.3%
Fine-tune99.9%50.0%0.0%99.9%0.0%+1.7%
Amnesiac99.9%0.3%0.8%0.7%-99.2%-48.0%
ERM-KTP (ours)99.9%53.8%0.0%98.3%-1.6%+1.5%
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.475, + 0.47, + 0.501 + ], + "angle": 0, + "content": "Table 6. Unlearn time comparison with baselines on CIFAR10 and ResNet-20." + }, + { + "type": "table", + "bbox": [ + 0.108, + 0.514, + 0.437, + 0.626 + ], + "angle": 0, + "content": "
ApproachTimeΔAccDrΔAccval
RfS668s-1.7%+1.7%
SISA672s+0.4%+0.2%
Fine-tune492s-0.2%+2.4%
RL68s-1.5%+1.4%
Fisher5162s-46.9%-25.1%
ERM-KTP (ours)124s-1.6%+2.0%
" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.661, + 0.283, + 0.679 + ], + "angle": 0, + "content": "5.5. Ablation Experiments" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.689, + 0.471, + 0.901 + ], + "angle": 0, + "content": "To further demonstrate that our proposed regulation terms are effective, we conduct an ablation experiment on CIFAR100 and ResNet-50 by setting the hyper-parameters as: (1) \\(\\lambda_{1} = 1\\), \\(\\lambda_{2} = 1 \\times 10^{-3}\\), and \\(\\lambda_{3} = 0\\); (2) \\(\\lambda_{1} = 1\\), \\(\\lambda_{2} = 0\\), and \\(\\lambda_{3} = 5 \\times 10^{-4}\\); (3) \\(\\lambda_{1} = 1\\), \\(\\lambda_{2} = 1 \\times 10^{-3}\\), and \\(\\lambda_{3} = 5 \\times 10^{-4}\\). Fig. 3 demonstrates that applying both \\(L_{2}\\) and \\(L_{3}\\) achieves the best performance and convergence to the optimal value. Only using the \\(L_{2}\\) regulation term (Eq. (4)), the \\(L_{1}\\)-density tends to 0.01, but the CSI convergences to around 3,500. It illustrates that the \\(L_{1}\\)-norm regulation term can find the spars solution, but the \\(L_{1}\\)-norm does not constrain the relative position, which leads to the high value of CSI. However, the \\(L_{1}\\)-norm can make both CSI and \\(L_{1}\\)-density convergence to a lower value when the" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.477, + 0.892, + 0.522 + ], + "angle": 0, + "content": "inner-product regulation term (Eq. (6)) is used. Furthermore, the inner-product can make both two values descend more quickly." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.536, + 0.619, + 0.551 + ], + "angle": 0, + "content": "6. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.561, + 0.892, + 0.773 + ], + "angle": 0, + "content": "In this paper, we propose an interpretable knowledge-level unlearning method, ERM-KTP, for the class-specific unlearning task. We propose the ERM structure to tackle the challenge of high knowledge entanglement. Then, we transfer the knowledge of the remaining set from the original model to the unlearned model via our proposed KTP method. Finally, we delete the original model to accomplish the unlearning task. The interpretability brought by the EMR structure and the crafted masks in KTP enhances the reliability of the unlearning. Extensive experiments demonstrate the effectiveness, fidelity, efficiency, and scalability of our proposed ERM-KTP unlearning method. For future work, we attempt to solve the entanglement of each single data point to tackle the sample-specific unlearning task." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.776, + 0.892, + 0.867 + ], + "angle": 0, + "content": "Acknowledgments. This work was supported in part by the National Natural Science Foundation of China under Grant 61960206014, 62102300, and 62121001, in part by the China 111 Project under Grant B16037, in part by the Fundamental Research Funds for the Central Universities under Grant XJS211510." + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "20154" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.116, + 0.47, + 0.185 + ], + "angle": 0, + "content": "[1] Lucas Bourtoule, Varun Chandrasekaran, Christopher A Choquette-Choo, Hengrui Jia, Adelin Travers, Baiwu Zhang, David Lie, and Nicolas Papernot. Machine unlearning. In 2021 IEEE Symposium on Security and Privacy (SP), pages 141-159. 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In Proceedings of the IEEE conference on computer vision and pattern recognition, pages 2921-2929, 2016. 1" + }, + { + "type": "list", + "bbox": [ + 0.503, + 0.093, + 0.895, + 0.571 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "20155" + } + ] +] \ No newline at end of file diff --git a/2023/ERM-KTP_ Knowledge-Level Machine Unlearning via Knowledge Transfer/ab5287df-b899-4bb9-ae6b-5d2f41d1b6fe_origin.pdf b/2023/ERM-KTP_ Knowledge-Level Machine Unlearning via Knowledge Transfer/ab5287df-b899-4bb9-ae6b-5d2f41d1b6fe_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..3eee0c7803569c822d27973e31b47e43c07a5fb8 --- /dev/null +++ b/2023/ERM-KTP_ Knowledge-Level Machine Unlearning via Knowledge Transfer/ab5287df-b899-4bb9-ae6b-5d2f41d1b6fe_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:012ad5266fe8a57e2f14f344cb9b97c7404d411968064830b3984b74c8523885 +size 839785 diff --git a/2023/ERM-KTP_ Knowledge-Level Machine Unlearning via Knowledge Transfer/full.md b/2023/ERM-KTP_ Knowledge-Level Machine Unlearning via Knowledge Transfer/full.md new file mode 100644 index 0000000000000000000000000000000000000000..efa60c81d959cd0ff5809ade43689d59923ddb47 --- /dev/null +++ b/2023/ERM-KTP_ Knowledge-Level Machine Unlearning via Knowledge Transfer/full.md @@ -0,0 +1,345 @@ +# ERM-KTP: Knowledge-level Machine Unlearning via Knowledge Transfer + +Shen Lin $^{1*}$ , Xiaoyu Zhang $^{1*}$ , Chenyang Chen $^{1}$ , Xiaofeng Chen $^{1\dagger}$ , Willy Susilo $^{2}$ + +$^{1}$ Xidian University, $^{2}$ University of Wollongong linshen@stu.xidian.edu.cn, xiaoyuzhang@xidian.edu.cn, cychen_1@stu.xidian.edu.cn, xfchen@xidian.edu.cn, wsusilo@uow.edu.au + +# Abstract + +Machine unlearning can fortify the privacy and security of machine learning applications. Unfortunately, the exact unlearning approaches are inefficient, and the approximate unlearning approaches are unsuitable for complicated CNNs. Moreover, the approximate approaches have serious security flaws because even unlearning completely different data points can produce the same contribution estimation as unlearning the target data points. To address the above problems, we try to define machine unlearning from the knowledge perspective, and we propose a knowledge-level machine unlearning method, namely ERM-KTP. Specifically, we propose an entanglement-reduced mask (ERM) structure to reduce the knowledge entanglement among classes during the training phase. When receiving the unlearning requests, we transfer the knowledge of the nontarget data points from the original model to the unlearned model and meanwhile prohibit the knowledge of the target data points via our proposed knowledge transfer and prohibition (KTP) method. Finally, we will get the unlearned model as the result and delete the original model to accomplish the unlearning process. Especially, our proposed ERM-KTP is an interpretable unlearning method because the ERM structure and the crafted masks in KTP can explicitly explain the operation and the effect of unlearning data points. Extensive experiments demonstrate the effectiveness, efficiency, high fidelity, and scalability of the ERM-KTP unlearning method. Code is available at https://github.com/RUIYUN-ML/ERM-KTP + +# 1. Introduction + +In recent years, many countries have raised concerns about protecting personal privacy. The privacy legislation, e.g., the well-known European Union's GDPR [19], have been promulgated to oblige information service providers + +to remove personal data when receiving a request from the data owner, i.e., the right-to-be-forgotten. Besides, the GDPR stipulates that the service providers should remove the corresponding impact of the data requested by the data owner, in which the machine learning models are the most representative. Many kinds of research demonstrate that the machine learning models can memorize knowledge of the data points, e.g., the membership inference attack [7, 14, 15] can infer whether a data point is in the training set or not. + +A naive approach is retraining the model after removing the target data points from the training set, but the human resources and materials consumed are costly. Thus, aiming to efficiently remove data as well as their generated contribution to the model, a new ML privacy protection research direction emerged, called machine unlearning. A good deal of related work attempted to solve the data-removing challenge of inefficient retraining, and there are two representative research fields, including exact unlearning [1] and approximate unlearning [3-5]. Unfortunately, these approaches usually require huge computational, storage overhead, and memory requirements for class-specific machine unlearning tasks on the complicated convolutional neural networks (CNNs). Furthermore, they may compromise the model's performance and even cause disastrous forgetting. Most significantly, Thudi et al. [18] believed that such approximate unlearning approaches have serious security flaws because they usually define machine unlearning as the distribution difference between the unlearned model and the retrained model. According to this definition, even unlearning completely different data points can produce the same contribution estimation as unlearning the target data points. + +Unlearning algorithms are difficult to implement on deep learning models because these models are often seen as a black box and lack interpretability, which makes data points' contributions challenging to estimate. Though many related works [2, 10, 16, 21] attempted to improve the interpretability of deep learning models, they can not apply to machine unlearning directly. For example, Zhou et al. [22] + +leveraged the global average pooling (GAP) in CNNs to generate a class activation mapping (CAM) to indicate the discriminative image regions used by the CNNs to identify the class. Liang et al. [12] proposed class-specific filters to transform the complex representations in convolutional layers into interpretable graphs. + +To address the above problems, for the first time, we consider the need for subsequent unlearning tasks during the model training phase. We define machine unlearning in the knowledge perspective, i.e., a reliable machine unlearning approach should satisfy that the knowledge of the unlearned model should be identical to the retrained model. Furthermore, we propose an interpretable unlearning method, i.e., ERM-KTP. The ERM structure can interpret the relation between data points and channels in the activation maps. Such a relationship can describe which filters the data points contribute to the convolutional layer. Then, KTP utilizes the relation to transfer the knowledge from corresponding filters to the unlearned model. Furthermore, the crafted masks in KTP interpret the operation of the knowledge transfer. With these interpretable methods, we can precisely unlearn data points and enhance the reliability of our proposed unlearning approach. We summarize our contributions of this paper as follows: + +- We give a novel definition of machine unlearning from the knowledge perspective, and we further propose an interpretable knowledge-level machine unlearning method, i.e., ERM-KTP. Especially, the interpretability of ERM-KTP enhances the reliability of the unlearning operation. +- We introduce an ERM structure that reduces the knowledge entanglement among classes to get a pretrained model. When receiving the unlearning requests, we use the proposed KTP method to transfer the knowledge of the remaining set from the original model to the unlearned model and, meanwhile, prohibit the knowledge of the unlearning set. Finally, we will get the unlearned model as the result and delete the original model to complete the unlearning process. +- We conduct experiments on three different scales of image classification datasets and three complicated CNNs. Extensive experimental results demonstrate the effectiveness, efficiency, high fidelity, and scalability of ERM-KTP. + +# 2. Problem Formulation + +In this paper, we primarily consider a class-specific machine unlearning scenario. We assume a sample space $\mathcal{X} \subseteq \mathbb{R}^d$ and corresponding labels $\mathcal{Y} = \{1,2,\dots,C\}$ , where $d$ is the number of dimensions and $C$ is the number of classes. The training set can be represented as + +$\mathcal{D} = \{\mathcal{D}_1,\mathcal{D}_2,\dots ,\mathcal{D}_C\}$ . To unlearn the target class's data points $\mathcal{D}_u\subseteq \mathcal{D}$ exactly, we need to apply a removal method, which should be equivalent to applying the training algorithm to the dataset without target data points. + +Definition 1. We define a learning algorithm, $\mathcal{A}:\mathcal{D}\to \mathcal{W}$ as a function from a dataset to a model in hypothesis space $\mathcal{W}$ . A removal method, $\mathcal{R}:\mathcal{A}(\mathcal{D})\times \mathcal{D}\times \mathcal{D}_u\rightarrow \mathcal{W}$ , is a function from an original model $\mathcal{A}(D)$ , training dataset $\mathcal{D}$ , an unlearning dataset $\mathcal{D}_u$ to remove from the training dataset $\mathcal{D}$ to an unlearned model in $\mathcal{W}$ , and a remaining dataset $\mathcal{D}_r = \mathcal{D}\backslash \mathcal{D}_u$ . We define equivalence as having identical knowledge for each model in $\mathcal{W}$ : + +$$ +\mathbb {K} (\mathcal {A} \left(\mathcal {D} _ {r}\right)) = \mathbb {K} \left(\mathcal {R} \left(\mathcal {A} (\mathcal {D}), \mathcal {D}, \mathcal {D} _ {u}\right)\right), \tag {1} +$$ + +in which $\mathbb{K}(\cdot)$ is a knowledge measuring function. If an exact unlearning method satisfy the above definition, it can be defined as a knowledge-level unlearning method. + +# 3. Related Work + +Exact unlearning. The exact unlearning approaches can provide algorithmic unlearning proof. The most representative exact unlearning approach is retrain-from-scratch (RfS), i.e., remove the target data points from the training set and retrain the model. Bourtoule et al. proposed SISA to improve efficiency by retraining the sub-model instead of retrain-from-scratch. These exact unlearning approaches are knowledge-level because they remove all target data points in the input phase so that the model can not learn any knowledge of them. However, their computational overhead is still significant because they need to relearn the remaining set's knowledge through retraining. + +Approximate unlearning. The main idea of approximate unlearning approaches is to estimate the target data points' contribution to the model and update the parameters for unlearning. For example, Graves et al. [4] leveraged gradients to estimate the contributions. They stored gradients of batches consisting of target data points and then subtracted the target gradients to update the model's parameters. For class-specific unlearning tasks or large-scale unlearning requests, it needs to store gradients of almost every batch, and the model will degenerate to the initialization state. Guo et al. [5] utilized the Influence Theory [8], and Golatkar et al. [3] used the Fisher Information [13] to estimate the contributions. However, the above two methods need to calculate the hessian matrix, which is very expensive in deep learning models. Besides, they may compromise the model's performance due to imprecise estimates of contributions on CNNs and even cause disastrous forgetting. Most significantly, Thudi et al. [18] pointed out that different data points can also generate the same network, making approximate unlearning approaches unable to provide an algorithmic unlearning proof. + +# 4. Proposed Method + +In this section, we will explain the ERM-KTP unlearning method in detail. We will describe how the proposed ERM structure reduces the entanglement of knowledge in Section 4.1. Then, we will explain how the proposed KTP method transfers knowledge in Section 4.2. Finally, we will explain how we combine the ERM and the KTP method to construct the ERM-KTP unlearning method in Section 4.3. + +# 4.1. Entanglement-Reduced Mask (ERM) Structure + +The most representative knowledge the ML models learn is the features extracted by the convolutional layers. However, the features of different classes are entangled, so the key features of different classes are always highly overlapping. As a result, it is difficult to transfer the knowledge of target classes without affecting others. + +![](images/bc41ffd1e350d572b7a7ad647f093149dd2ccfa05cabe94bf737b9c8cf1bf7a4.jpg) +Figure 1. An overview of our proposed ERM structure. + +In order to reduce the entanglement of knowledge, we propose an Entanglement-Reduced Mask (ERM) structure as a learnable layer of the CNNs inspired by the model interpretability work [12]. The learnable ERM structure can be represented as a matrix $G \in \mathbb{R}^{C \times K}$ , where $C$ is the number of classes and $K$ is the number of filters. Each element $G_{c}^{k} \in [0,1]$ represents the relevance between the $k$ -th filter and the $c$ -th class, and a higher value of $G_{c}^{k}$ denotes a closer correlation. Given a data point $(x \in \mathcal{X}, y \in \mathcal{Y})$ as an input, we use the $y$ -th row $G_{y} \in \mathbb{R}^{1 \times K}$ as a mask vector multiplied to the activation maps $\mathcal{M} = (\mathcal{M}_1, \dots, \mathcal{M}_K)$ of the last convolution layer (before the fully connected layer) to shut down irrelevant channels. Formally, we can define the above multiply operation as + +$$ +A \circ B = \left(A _ {1} B ^ {1}, \dots , A _ {d _ {1}} B ^ {d _ {1}}\right), \tag {2} +$$ + +in which $A\in \mathbb{R}^{d_1\times d_2\times d_3}$ $B\in \mathbb{R}^{1\times d_1}$ $A_{i}\in \mathbb{R}^{d_{2}\times d_{3}}$ , and $B^{i}\in \mathbb{R}$ + +For a CNN with an ERM structure (ERM-CNN), we set two forward propagation paths of an ERM-CNN with parameters $\theta$ : (1) the STD path with the predicting probability + +vector $\tilde{y}_{\theta}$ ; (2) the ERM path with mask matrix $G$ predicting $\tilde{y}_{\theta}^{G}$ , as shown in Fig. 1. In the training phase, we train the network alternately through the STD and ERM paths, while only the STD path is used in the validation phase. + +Then, we will discuss the details of training an ERM-CNN. We first define an ideal ERM structure in which each row of the matrix $G$ is at least one element equal to 1, and each row is orthogonal. In this ideal state, the knowledge of each class learned by the model is not entangled and independent of each other. Thus, the training objectives are to train an ERM-CNN with an ideal ERM structure, and its classification performance is comparable to the STD-CNNs. To train a model with the ideal ERM, we first consider its validation accuracy through two paths and ensure that at least one element of each row of $G$ equals 1, i.e., $\| G_{c}\|_{\infty} = 1$ . We can get the following formulation: + +$$ +\min _ {\theta , G} L _ {0} (\theta) = \mathrm {C E} (y | | \tilde {y} _ {\theta}) + \lambda_ {1} \mathrm {C E} (y | | \tilde {y} _ {\theta} ^ {G}) \quad s. t. G \in V _ {G}, \tag {3} +$$ + +where CE denotes the cross entropy loss and $V_{G} = \{G\in$ $\mathbb{R}^{C\times K}: \| G_c\|_{\infty} = 1\}$ . Furthermore, we introduce a regulation term to encourage the sparsity of the matrix $G$ , and encourage the $L_{1}$ -norm of $G$ not to exceed the preset upper bound $\alpha$ and has no effect when $\| G\| _1 < \alpha$ . Apparently, we should set $\alpha \geqslant K$ because $\| G_c\|_{\infty} = 1$ ensures $\| G\| _1\geqslant K$ As described above, we can formulate the regulation term as + +$$ +\min _ {G} L _ {1} (\theta) = \| \operatorname {R e L U} (\| G \| _ {1} - \alpha) \| _ {p} \quad s. t. G \in V _ {G}, \tag {4} +$$ + +in which $\| \cdot \| _p$ indicates $p$ -norm. Moreover, we introduce the inner product regulation to encourage each row of $G$ to be orthogonal to the other as + +$$ +\operatorname {I n P} = \sum_ {c _ {1} = 0} ^ {C} \sum_ {c _ {2} = 0, \atop c _ {1} < c _ {2}} ^ {C} \left(G _ {c _ {1}} \cdot G _ {c _ {2}}\right). \tag {5} +$$ + +To facilitate the solution in practice, we replace Eq. (5) with the following equivalent form as our inner product regulation term: + +$$ +\min _ {G} L _ {2} (\theta) = \sum_ {c _ {1} = 0} ^ {C} \sum_ {c _ {2} = 0, \atop c _ {1} < c _ {2}} ^ {C} (G G ^ {T}) _ {c _ {1}} ^ {c _ {2}} \quad s. t. G \in V _ {G}, \tag {6} +$$ + +in which $(GG^{T})_{c_{1}}^{c_{2}}$ denotes the $c_{1}$ -th row and the $c_{2}$ -th column of the matrix $(GG^{T})$ . When we minimize $L_{2}(\theta)$ , it will tend to 0 if $G_{c}^{k} \in [0,1]$ , i.e., each row of $\mathbf{G}$ will be orthogonal to the other. Essentially, the inner product describes the similarity between two vectors as $\vec{a} \cdot \vec{b} = \|\vec{a}\| \|\vec{b}\| \cos \langle \vec{a}, \vec{b} \rangle$ . When we minimize $L_{2}(\theta)$ , the cosine value and their $L_{2}$ -norm are minimized simultaneously. + +To sum up, we formulate an optimization problem to train an ERM-CNN by combining Eq. (3), (4), and (6): + +$$ +\begin{array}{l} \min _ {\theta , G} L (\theta) = \mathrm {C E} (y | | \tilde {y} _ {\theta}) + \lambda_ {1} \mathrm {C E} (y | | \tilde {y} _ {\theta} ^ {G}) \\ + \lambda_ {2} \| \operatorname {R e L U} (\| G \| _ {1} - \alpha) \| _ {p} \\ + \lambda_ {3} \sum_ {c _ {1} = 0} ^ {C} \sum_ {\substack {c _ {2} = 0, \\ c _ {1} < c _ {2}}} ^ {C} (G G ^ {T}) _ {c _ {1}} ^ {c _ {2}} \quad s. t. G \in V _ {G}, \tag{7} \\ \end{array} +$$ + +in which the first and the second term ensure the classification performance, the third term ensures the sparsity of the matrix $G$ , and the last term imposes a rigorous constraint on each row of $G$ . + +Algorithm 1: Alternate Training (AT) +1 for e in epochs do +2 if $e \in ERM's$ epoch then +3 $\tilde{y}_{\theta}^{G} \gets$ prediction through the ERM path +4 $\mathcal{L} \gets \lambda_{1}CE(y||\tilde{y}_{\theta}^{G}) + \lambda_{2}L_{1} + \lambda_{3}L_{2}$ +5 $G \gets G - \eta \frac{\partial\mathcal{L}}{\partial G}$ +6 $G_{c} \gets G_{c} / \| G_{c}\|_{\infty}$ +7 $G \gets G.\mathrm{clip}(0,1)$ +8 else +9 $\tilde{y}_{\theta} \gets$ prediction through the STD path +10 $\mathcal{L} \gets \mathrm{CE}(y||\tilde{y}_{\theta})$ +11 end +12 $\theta \gets \theta - \eta \frac{\partial\mathcal{L}}{\partial\theta}$ +13 end + +To solve the above optimization problem in Eq. (7), we apply an approximate projected gradient descent (PGD) algorithm. After the matrix $G$ is updated, $G_{c}$ will be normalized by $G_{c} / \| G_{c}\|_{\infty}$ to ensure $\| G_c\|_{\infty} = 1$ , and then each element of $G_{c}$ will be clipped into the range [0, 1]. However, the joint training scheme may have some difficulties due to poor convergence. The forward propagation through the ERM path can make most features block, leading to a much poorer convergence than the STD path because of the weaker gradient. Therefore, we propose an alternate training (AT) scheme instead of the normal joint training scheme in that the forward propagation uses the STD path and ERM path alternately in different epochs. Specifically, we update $G$ and $\theta$ by descend the gradient of $\lambda_1\mathrm{CE}(y||\tilde{y}_\theta^G) + \lambda_2L_1 + \lambda_3L_2$ in the epoch for ERM path, and we update $\theta$ with the gradient of $\mathrm{CE}(y||\tilde{y}_{\theta})$ in the STD path, as shown in Algorithm 1. + +# 4.2. Knowledge Transfer and Prohibition (KTP) + +After training an ERM-CNN as a pre-trained model, different classes' knowledge (features and parameters) is independent. When receiving the unlearning requests, we can transfer the knowledge of a single class separately via our proposed knowledge transfer and prohibition (KTP) method. Specifically, KTP transfers the knowledge of the + +non-target class of data in the origin model $\theta_T$ to the unlearned model $\theta_S$ while prohibiting the knowledge of the target data points. We can describe the KTP method as the following three processes: (1) convolution layers $(\theta_S^{cv}$ and $\theta_T^{cv})$ knowledge transfer (CKT); (2) fully connected layers $(\theta_S^{fc}$ and $\theta_T^{fc})$ knowledge transfer (FKT); (3) matrix $G$ ( $G_S$ and $G_T$ ) knowledge transfer (GKT). Formally, we can define the KTP method as + +$$ +\operatorname {C K T}: \theta_ {S} ^ {c v} \stackrel {{t r a n s}} {{\longleftarrow}} \theta_ {T} ^ {c v}, +$$ + +$$ +\operatorname {F K T}: \theta_ {S} ^ {f c} \xleftarrow {\text {t r a n s}} \theta_ {T} ^ {f c}, \tag {8} +$$ + +$$ +\operatorname {G K T}: G _ {S} \stackrel {{t r a n s}} {{\longleftarrow}} G _ {T}. +$$ + +In the CKT process, we transfer the knowledge of features extracted by the convolutional layers by a crafted channel mask $\bar{G}_{\mathbf{c}} \in \mathbb{R}^{1 \times K}$ . For the single target class $\mathbf{c}$ unlearning task, the mask can be defined as + +$$ +\bar {G} _ {\mathbf {c}, i} = \left\{ \begin{array}{l l} 0, & G _ {\mathbf {c}, i} = 1 \\ 1, & G _ {\mathbf {c}, i} = 0 \end{array} . \right. \tag {9} +$$ + +For the multiple target classes $\mathbf{c} = \{\mathbf{c}_0,\dots ,\mathbf{c}_{|c|}\}$ unlearning task, we calculate $\bar{G}_{\mathbf{c}_j}$ for each class $j$ and then aggregate them as + +$$ +\bar {G} _ {\mathbf {c}, i} = \left\{ \begin{array}{l l} 1, & \left(\sum_ {j} ^ {| c |} \bar {G} _ {\mathbf {c} _ {j}}\right) _ {i} = | c | \\ 0, & \left(\sum_ {j} ^ {| c |} \bar {G} _ {\mathbf {c} _ {j}}\right) _ {i} < | c | \end{array} . \right. \tag {10} +$$ + +Formally, the CKT process can be formulated as an optimization problem: + +$$ +\min _ {\theta_ {S} ^ {c v}} L _ {3} \left(\theta_ {S} ^ {c v}\right) = \operatorname {M S E} \left(f \left(x; \theta_ {T} ^ {c v}\right), g \left(x; \theta_ {S} ^ {c v}\right) \circ \bar {G} _ {\mathbf {c}}\right), \tag {11} +$$ + +where $\mathrm{MSE}(\cdot)$ is Mean Square Error, $x$ is data points, $\circ$ is the multiply operation (Eq. (2)), and $f(\theta_S^{cv})$ and $g(\theta_S^{cv})$ denote the output of the origin model's last convolution layer with parameters $\theta_S^{cv}$ and the output from unlearned model's last convolution layer with parameters $\theta_S^{cv}$ , respectively. Note that the knowledge of the corresponding channels in the feature maps multiplied by the matrix $G$ where the value equals one has been transferred. In contrast, the knowledge associated with values equal to 0 has been prohibited. + +For the FKT process, we transfer the knowledge of parameters in fully connected (FC) layer $\theta^{fc} = \{\theta_{\beta}^{fc},\theta_{\gamma}^{fc}\}$ , in which $\theta_{\beta}^{fc}\in \mathbb{R}^{K\times C}$ denotes the weight, and $\theta_{\gamma}^{fc}\in \mathbb{R}^{1\times C}$ denotes the bias. The FKT process can be executed by directly modifying the original model's parameters of fully + +connected layers as + +$$ +\begin{array}{l} \theta_ {S, \beta} ^ {f c} = \theta_ {T, \beta} ^ {f c} * \mathcal {A} _ {\beta}, \quad \mathcal {A} _ {\beta} = (\underbrace {(\bar {G} _ {c}) ^ {T} , \cdots , (\bar {G} _ {c}) ^ {T}} _ {C}), \tag {12} \\ \theta_ {S, \gamma} ^ {f c} = \theta_ {T, \gamma} ^ {f c} * \mathcal {A} _ {\gamma}, \quad \mathcal {A} _ {\gamma} \in [ 0, 1 ] ^ {1 \times C}, \\ \end{array} +$$ + +where all elements of $\mathcal{A}_{\gamma}$ are equal to 1 except the c-th column, $(\cdot)^T$ denotes the matrix transpose operation, and $*$ denotes the hardamad product operation. Similar to the channel mask $\bar{G}_c$ , the FC mask $\mathcal{A} = \{\mathcal{A}_{\beta}, \mathcal{A}_{\gamma}\}$ prohibits the knowledge of the FC layer related to the target class of data points. + +Finally, we update the matrix $G_{S}$ of the unlearned model through the GKT process by the following equation: + +$$ +G _ {S} = G _ {T} * \mathcal {A} _ {G}, \quad \mathcal {A} _ {G} \in [ 0, 1 ] ^ {C \times K}, \tag {13} +$$ + +where only the c-th row of the mask matrix $\mathcal{A}_G$ is equal to 0, and the others are equal to 1. The updated matrix $G_{S}$ can visualize which classes of data points have been removed by checking which rows are equal to 0. We summarize the KTP method in Algorithm 2. + +Algorithm 2: Knowledge Transfer and Prohibition (KTP) +// CKT +1 for e in epochs do +2 $f(x;\theta_T^{cv})\gets$ forward propagation through $\theta_T$ +3 $g(x;\theta_S^{cv})\gets$ forward propagation through $\theta_S$ +4 $\mathcal{L}\gets \mathrm{MSE}(f(x;\theta_T^{cv})\circ \bar{G}_c,g(x;\theta_S^{cv}))$ +5 $\theta_S^{cv}\gets \theta_S^{cv} - \eta \frac{\partial\mathcal{L}}{\partial\theta_S^{cv}}$ +6 end +// FKT +7 $\theta_{S,\beta}^{fc} = \theta_{T,\beta}^{fc}*\mathcal{A}_{\beta}$ +8 $\theta_{S,\gamma}^{fc} = \theta_{T,\gamma}^{fc}*\mathcal{A}_{\gamma}$ +9 $\theta_S^{fc} = \{\theta_{S,\beta}^{fc},\theta_{S,\gamma}^{fc}\}$ +// GKT +10 $G_{S} = G_{T}*\mathcal{A}_{G}$ +// Unlearned Model +11 $\theta_S = \{\theta_S^{cv},G_S,\theta_S^{fc}\}$ + +# 4.3. Machine Unlearning via ERM-KTP + +Here, we will explain how we combine the ERM structure and KTP method to construct a class-specific knowledge-level machine unlearning approach. We first train the original ERM-CNNs by Algorithm 1. When receiving unlearning requests, we then transfer the remaining dataset's knowledge to the unlearned model by Algorithm 2. Finally, we complete the unlearning process by deleting the original model. The detailed ERM-KTP unlearning algorithm is shown in Algorithm 3. + +Algorithm 3: ERM-KTP Unlearning +1 $\theta_T\gets \mathrm{AT}(\theta)$ +2 while receiving unlearning requests do +3 $\theta_S\gets \mathrm{KTP}(\theta_T)$ +4 Delete $\theta_T$ +5 $\theta_T = \theta_S$ +6 end + +# 5. Experiments + +In this section, we empirically evaluate the performance of the proposed unlearning method on three popular image classification benchmarks. All experiments are implemented with Python 3.8 and PyTorch 1.10.1 on a machine with Intel(R) Core(TM) i9-10980XE CPU, 32GB RAM, and a Nvidia 3090 GPU. + +# 5.1. Datasets & Models + +We evaluate the proposed unlearning method in three public image classification datasets, i.e., CIFAR10, CIFAR100 [9], and Tiny-ImageNet [11]. The input size of CIFAR-10 and CIFAR-100 is $32 \times 32$ , and they both contain 50,000 training images and 10,000 for validation. For Tiny-ImageNet, the size of image samples is $224 \times 224$ . It contains 200 classes of samples, and each class has 500 samples for training, 50 for validation, and 50 for testing. + +Moreover, the model structure is three common image classification deep neural networks, ResNet-20, ResNet-50 [6], and ResNeXt-50 [20]. The original models are trained for 200 epochs using Stochastic Gradient Descent (SGD) optimizer with a momentum of 0.9, weight decay of 5e-4, and an initial learning rate of 0.1, divided by 10 after 100 and 150 epochs, respectively. + +# 5.2. Effectiveness of the ERM Structure + +In order to evaluate the effectiveness of ERM structure, we propose the following metrics: + +- Cosine similarity (CSI) to analyze the orthogonality of each row of the matrix $G$ as follows, + +$$ +\mathrm {C S I} = \sum_ {c _ {1} = 0} ^ {C} \sum_ {\substack {c _ {2} = 0, \\ c _ {1} \neq c _ {2}}} ^ {C} \left(\frac {G _ {c _ {1}} \cdot G _ {c _ {2}}}{\| G _ {c _ {1}} \| \| G _ {c _ {2}} \|\right). \tag{14} +$$ + +- $L_{1}$ -density to evaluate the sparsity of the matrix $G$ as + +$$ +L _ {1} \text {- d e n s i t y} = \frac {\| G \| _ {1}}{C K}. \tag {15} +$$ + +Table 1 shows that the CNNs with the ERM structure have slightly better classification performance than the STD + +CNNs. Moreover, the $L_{1}$ -density convergences to $\alpha$ , and CSI convergences close to 0, meaning each class of data is independent to the other. These metrics quantitatively demonstrate ERM's effectiveness in learning a sparse mask matrix to reduce the entanglement for the following unlearning task without sacrificing classification accuracy. + +Table 1. Metrics of the STD-CNNs and ERM-CNNs. The first row of each two stand for STD-CNNs and the second one stand for ERM-CNNs. $Acc_{val}$ is the original model's classification accuracy on the validation dataset. + +
DatasetModelCKCSIL1-densityAccval
CIFAR10ResNet-20----89.6%
10640.00.192.6%
CIFAR100ResNeXt-50----76.2%
1002,0480.00.0177.6%
Tiny-ImageNetResNet-50----49.3%
2002,0480.00.00553.4%
+ +Moreover, we evaluate if the ERM structure can reduce or eliminate the knowledge entanglement across classes by prohibiting each class's knowledge successively during the ERM path's forward propagation. As shown in Table 2, the classification accuracy will degrade into $0.0\%$ for the knowledge-prohibited classes, while the accuracy will remain the same for the knowledge-permitted classes. + +Table 2. Accuracy of the data points with prohibited or permitted Knowledge. $Acc_{(\cdot)}^{pro}$ and $Acc_{(\cdot)}^{per}$ denote the accuracy of the knowledge-prohibited classes and the knowledge-permitted classes, respectively. + +
DatasetModelAccprotrainAccpertrainAccprovalAccperval
CIFAR10ResNet-200.0%97.1%0.0%91.8%
CIFAR100ResNeXt-500.0%99.9%0.0%78.1%
Tiny-ImageNetResNet-500.0%99.9%0.0%53.4%
+ +We also evaluate the time overhead and memory requirements of the ERM CNNs in the training phase. The computation overhead is the activation map multiplied by the corresponding $y$ -th row of the matrix $G$ and computing the regulation terms $L_{1}$ and $L_{2}$ . As shown in Table 3, the time overhead of the ERM structure is comparable to the standard (STD) CNNs, and the additional memory requirements are negligible, which demonstrates that ERM structure has great scalability and can be applied to any CNN structures. + +# 5.3. Effectiveness of the ERM-KTP Unlearning Method + +We utilize some common metrics to evaluate the effectiveness of the ERM-KTP unlearning method as follows. + +- $Acc_{D_r}$ is the original model's classification accuracy on the training set of the remaining classes. + +- $Acc_{val}$ is the original model's classification accuracy on the validation dataset of the remaining classes. +- $Acc_{D_r}'$ measures the unlearned model's performance on the training set of the remaining classes. +- $\Delta Acc_{D_r} = Acc_{D_r}' - Acc_{D_r}$ indicates the difference between the accuracy of the remaining set before and after the unlearning operation. +- $\Delta Acc_{val} = Acc_{val}' - Acc_{val}$ indicates the difference between the accuracy of the validation set before and after the unlearning operation. + +Table 3. Time overhead and memory requirements of the ERM-CNNs and the STD-CNNs in the training phase. + +
DatasetModelStructureTimeMemory
CIFAR10ResNet-20STD1206s2867MiB
ERM1541s2867MiB
CIFAR100ResNeXt-50STD9447s19223MiB
ERM9983s19275MiB
Tiny-ImageNetResNet-50STD5025s6769MiB
ERM6164s6803MiB
+ +Then, we conduct experiments in the case of unlearning $10\%$ , $40\%$ , and $80\%$ of classes, respectively. Table 4 shows that $Acc_{D_u}$ equals $0.0\%$ in all cases, demonstrating that ERM-KTP can effectively unlearn target data points. Furthermore, $\Delta Acc_{D_r}$ are close to $0.0\%$ and $\Delta Acc_{D_r}$ is greater than $0.0\%$ in most cases. These show that ERM-KTP can unlearn target data without affecting the model classification performance, demonstrating the high fidelity of ERM-KTP. In summary, ERM-KTP performs well on all these datasets and model structures, demonstrating the scalability of ERM-KTP. + +# 5.4. Comparison with Baselines + +To further prove the advantage of ERM-KTP, we compare ERM-KTP with the following baseline approaches: + +- Retrain from scratch (RfS): Retrain model from scratch with remaining data points $\mathcal{D}_r$ . +- SISA: Retrain the sub-model whose training set contains the target data points [1]. +- Fine-tune: Fine-tune the model on the remaining data $\mathcal{D}_r$ using a slightly larger learning rate. +- Random Labels (RL): Fine-tune the model on $\mathcal{D}$ by randomly resampling labels corresponding to images belonging to the remaining data points $\mathcal{D}_r$ . +- Amnesiac Unlearning: Track gradient in every training batch. Then, update the model by subtracting the gradients when the batch is marked for removal [4]. + +Table 4. Performance evaluation of ERM-KTP unlearning method. #Classes denotes the number of the unlearned classes of data points + +
DatasetModel#ClassesAccDrAccvalAccDuAcc'DrΔAccDrΔAccval
CIFAR10ResNet-20096.8%92.6%----
196.6%91.3%0.0%95.3%-1.3%-1.3%
497.4%96.1%0.0%97.3%-0.1%+3.5%
898.4%97.8%0.0%98.5%+0.1%+3.1%
CIFAR100ResNeXt-50099.9%77.6%----
1099.9%76.1%0.0%98.1%-1.8%-0.6%
4099.9%79.4%0.0%98.4%-1.5%+1.1%
8099.9%86.4%0.0%99.8%-0.1%+7.6%
Tiny-ImageNetResNet-50099.9%53.4%----
2099.9%52.6%0.0%97.6%-2.3%-0.3%
8099.9%53.8%0.0%98.3%-1.6%+1.5%
16099.9%59.3%0.0%97.6%-2.3%+4.4%
+ +- Fisher Unlearning: Perform a corrective Newton step using the Fisher Information Matrix. Add fisher noises sampled from Gaussian distribution to the weight to scrub the information [3]. + +![](images/28fe54ce2793837aa561a985f0ccf63fb283bf6f37c669a1c18edad3a1530e55.jpg) +Figure 2. Train the unlearned model with the training datasets, and $\Delta Acc_{D_u}$ denotes the difference between the accuracy of the unlearning dataset on the relearned model and the accuracy on the original model on CIFAR10 and ResNet-20. + +Then, we conduct the comparison experiments for $40\%$ classes of data points removed. As shown in Table 5, the Amenesiac method [4] stores the gradients of almost every batch, and the model's performance degrades to random guess because it makes the model return to its initial state. For SISA [1], we need to retrain all shards to unlearn target classes of data points because every shard contains the target data points. Also, SISA's validation accuracy is lower by about $6\%$ than STD CNNs due to the aggregation operation. Though the literature [3] reports that the Fisher method performs well on All-CNN [17] and CIFAR-10, our experimental results show that it is not suitable for complicated CNNs, e.g., ResNet-20, ResNet-50 [6], and ResNeXt-50 [20]. + +Note that fine-tune and random labels (RL) methods show great performance on $\Delta Acc_{D_r}$ and $\Delta Acc_{val}$ . How- + +ever, these two methods are only an output-level unlearning, i.e., they only change the model's output of the target data points but not remove the corresponding knowledge. To prove that, we fine-tune the unlearned model to observe how long the model can relearn the forget knowledge. As shown in Fig. 2, the Fine-tune and RL method restore the performance on the unlearning dataset at about the 50th epoch, while the relearn time of ERM-KTP method is similar to the RfS method, i.e., they both recover the performance around the 100th epoch. It demonstrates that ERM-KTP can completely remove the target data points like the RfS method, i.e., ERM-KTP is a knowledge-level unlearning method. + +![](images/db80f615976325037f7e707c893af6c32fe1fe8d376d06f846b52c4a1a2b6e9d.jpg) +(a) CSI + +![](images/dbb7aeca50952eb07ba9718e148ff7b399e7b4ad4bb6224313af388c9cb9c572.jpg) +(b) $L_{1}$ -density +Figure 3. Ablation experiments of our proposed regulation terms on CIFAR100 and ResNet-50. + +For the efficiency comparison, we conduct the experiments on CIFAR10 and ResNet-20 because some methods can not be implemented on the other two settings, e.g., Fisher method needs more than 200 hours in TinyImageNet. As shown in Table 6, ERM-KTP improves by $5 \times$ compared to RfS, $5.4 \times$ compared to SISA, and $42 \times$ compared to Fisher. Though the time overhead of Finetune is less than ERM-KTP, Fine-tune method is only an output-level unlearning method, as mentioned above. In summary, compared with these baseline approaches, ERM-KTP is more effective, more efficient, and has better scalability. + +Table 5. Unlearning performance comparison with baseline approaches when unlearning ${40}\%$ classes of data points. + +
DatasetModelApproachAccDrAccvalAccDuAcc'DrΔAccDrΔAccval
CIFAR10ResNet-20STD99.9%93.7%----
RfS99.9%96.3%0.0%99.8%-0.1%+2.6%
Fine-tune99.9%97.0%0.0%99.8%-0.1%+3.3%
RL99.9%97.0%0.0%99.8%-0.1%+3.3%
SISA92.4%91.0%0.0%92.8%+0.4%+0.2%
Fisher99.9%54.0%48.4%53.0%-46.9%-25.1%
Amnesiac99.9%9.0%0.0%15.4%-84.5%-84.7%
ERM-KTP (ours)97.4%96.1%0.0%97.3%-0.1%+3.5%
CIFAR100ResNeXt-50STD99.9%78.9%----
RfS99.9%79.6%0.0%99.9%0.0%+0.7%
RL99.9%78.1%0.0%99.7%0.0%-0.8%
Fisher99.9%1.0%0.0%1.0%-98.9%-77.9%
Fine-tune99.9%83.4%0.0%99.9%0.0%+4.5%
Amnesiac99.9%0.89%0.0%1.0%-98.9%-77.8%
ERM-KTP (ours)99.9%79.4%0.0%98.4%-1.5%+1.1%
Tiny-ImageNetResNet-50STD99.9%48.3%----
RfS99.9%45.1%0.0%99.9%0.0%-3.2%
RL99.9%43.4%0.0%96.7%-3.2%-4.9%
SISA67.6%52.8%0.0%68.0%+0.4%-1.3%
Fine-tune99.9%50.0%0.0%99.9%0.0%+1.7%
Amnesiac99.9%0.3%0.8%0.7%-99.2%-48.0%
ERM-KTP (ours)99.9%53.8%0.0%98.3%-1.6%+1.5%
+ +Table 6. Unlearn time comparison with baselines on CIFAR10 and ResNet-20. + +
ApproachTimeΔAccDrΔAccval
RfS668s-1.7%+1.7%
SISA672s+0.4%+0.2%
Fine-tune492s-0.2%+2.4%
RL68s-1.5%+1.4%
Fisher5162s-46.9%-25.1%
ERM-KTP (ours)124s-1.6%+2.0%
+ +# 5.5. Ablation Experiments + +To further demonstrate that our proposed regulation terms are effective, we conduct an ablation experiment on CIFAR100 and ResNet-50 by setting the hyper-parameters as: (1) $\lambda_{1} = 1$ , $\lambda_{2} = 1 \times 10^{-3}$ , and $\lambda_{3} = 0$ ; (2) $\lambda_{1} = 1$ , $\lambda_{2} = 0$ , and $\lambda_{3} = 5 \times 10^{-4}$ ; (3) $\lambda_{1} = 1$ , $\lambda_{2} = 1 \times 10^{-3}$ , and $\lambda_{3} = 5 \times 10^{-4}$ . Fig. 3 demonstrates that applying both $L_{2}$ and $L_{3}$ achieves the best performance and convergence to the optimal value. Only using the $L_{2}$ regulation term (Eq. (4)), the $L_{1}$ -density tends to 0.01, but the CSI convergences to around 3,500. It illustrates that the $L_{1}$ -norm regulation term can find the spars solution, but the $L_{1}$ -norm does not constrain the relative position, which leads to the high value of CSI. However, the $L_{1}$ -norm can make both CSI and $L_{1}$ -density convergence to a lower value when the + +inner-product regulation term (Eq. (6)) is used. Furthermore, the inner-product can make both two values descend more quickly. + +# 6. Conclusion + +In this paper, we propose an interpretable knowledge-level unlearning method, ERM-KTP, for the class-specific unlearning task. We propose the ERM structure to tackle the challenge of high knowledge entanglement. Then, we transfer the knowledge of the remaining set from the original model to the unlearned model via our proposed KTP method. Finally, we delete the original model to accomplish the unlearning task. The interpretability brought by the EMR structure and the crafted masks in KTP enhances the reliability of the unlearning. Extensive experiments demonstrate the effectiveness, fidelity, efficiency, and scalability of our proposed ERM-KTP unlearning method. For future work, we attempt to solve the entanglement of each single data point to tackle the sample-specific unlearning task. + +Acknowledgments. This work was supported in part by the National Natural Science Foundation of China under Grant 61960206014, 62102300, and 62121001, in part by the China 111 Project under Grant B16037, in part by the Fundamental Research Funds for the Central Universities under Grant XJS211510. + +# References + +[1] Lucas Bourtoule, Varun Chandrasekaran, Christopher A Choquette-Choo, Hengrui Jia, Adelin Travers, Baiwu Zhang, David Lie, and Nicolas Papernot. Machine unlearning. In 2021 IEEE Symposium on Security and Privacy (SP), pages 141-159. IEEE, 2021. 1, 6, 7 +[2] Amirata Ghorbani, Abubakar Abid, and James Zou. Interpretation of neural networks is fragile. In Proceedings of the AAAI conference on artificial intelligence, volume 33, pages 3681-3688, 2019. 1 +[3] Aditya Golatkar, Alessandro Achille, and Stefano Soatto. Eternal sunshine of the spotless net: Selective forgetting in deep networks. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 9304-9312, 2020. 1, 2, 7 +[4] Laura Graves, Vineel Nagisetty, and Vijay Ganesh. Amnesiac machine learning. In Proceedings of the AAAI Conference on Artificial Intelligence, volume 35, pages 11516-11524, 2021. 1, 2, 6, 7 +[5] Chuan Guo, Tom Goldstein, Awni Hannun, and Laurens Van Der Maaten. Certified data removal from machine learning models. In Proceedings of the 37th International Conference on Machine Learning, pages 3832-3842, 2020. 1, 2 +[6] Kaiming He, Xiangyu Zhang, Shaoqing Ren, and Jian Sun. Deep residual learning for image recognition. In Proceedings of the IEEE conference on computer vision and pattern recognition, pages 770-778, 2016. 5, 7 +[7] Hongsheng Hu, Zoran Salcic, Lichao Sun, Gillian Dobbie, Philip S Yu, and Xuyun Zhang. Membership inference attacks on machine learning: A survey. ACM Computing Surveys (CSUR), 54(11s):1-37, 2022. 1 +[8] Pang Wei Koh and Percy Liang. Understanding black-box predictions via influence functions. In International conference on machine learning, pages 1885-1894. PMLR, 2017. 2 +[9] A Krizhevsky. Learning multiple layers of features from tiny images. Master's thesis, University of Tront, 2009. 5 +[10] Himabindu Lakkaraju, Nino Arsov, and Osbert Bastani. Robust and stable black box explanations. In International Conference on Machine Learning, pages 5628-5638. PMLR, 2020. 1 +[11] Ya Le and Xuan Yang. Tiny imagenet visual recognition challenge. CS 231N, 7(7):3, 2015. 5 +[12] Haoyu Liang, Zhihao Ouyang, Yuyuan Zeng, Hang Su, Zihao He, Shu-Tao Xia, Jun Zhu, and Bo Zhang. Training interpretable convolutional neural networks by differentiating class-specific filters. In European Conference on Computer Vision, pages 622-638. Springer, 2020. 2, 3 +[13] James Martens. New insights and perspectives on the natural gradient method. The Journal of Machine Learning Research, 21(1):5776-5851, 2020. 2 +[14] Ahmed Salem, Yang Zhang, Mathias Humbert, Pascal Berrang, Mario Fritz, and Michael Backes. Ml-leaks: Model and data independent membership inference attacks and defenses on machine learning models. arXiv preprint arXiv:1806.01246, 2018. 1 + +[15] Reza Shokri, Marco Stronati, Congzheng Song, and Vitaly Shmatikov. Membership inference attacks against machine learning models. In 2017 IEEE symposium on security and privacy (SP), pages 3-18. IEEE, 2017. 1 +[16] Karen Simonyan, Andrea Vedaldi, and Andrew Zisserman. Deep inside convolutional networks: Visualising image classification models and saliency maps. arXiv preprint arXiv:1312.6034, 2013. 1 +[17] Jost Tobias Springenberg, Alexey Dosovitskiy, Thomas Brox, and Martin Riedmiller. Striving for simplicity: The all convolutional net. arXiv preprint arXiv:1412.6806, 2014. 7 +[18] Anvith Thudi, Hengrui Jia, Ilia Shumailov, and Nicolas Papernot. On the necessity of auditable algorithmic definitions for machine unlearning. In 31st USENIX Security Symposium (USENIX Security 22), pages 4007-4022, 2022. 1, 2 +[19] Paul Voigt and Axel Von dem Bussche. The eu general data protection regulation (gdpr). A Practical Guide, 1st Ed., Cham: Springer International Publishing, 10(3152676):10-5555, 2017. 1 +[20] Saining Xie, Ross Girshick, Piotr Dólár, Zhuowen Tu, and Kaiming He. Aggregated residual transformations for deep neural networks. In Proceedings of the IEEE conference on computer vision and pattern recognition, pages 1492-1500, 2017. 5, 7 +[21] Quanshi Zhang, Ying Nian Wu, and Song-Chun Zhu. Interpretable convolutional neural networks. In Proceedings of the IEEE conference on computer vision and pattern recognition, pages 8827-8836, 2018. 1 +[22] Bolei Zhou, Aditya Khosla, Agata Lapedriza, Aude Oliva, and Antonio Torralba. Learning deep features for discriminative localization. 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Unfortunately, the exact unlearning approaches are inefficient, and the approximate unlearning approaches are unsuitable for complicated CNNs. Moreover, the approximate approaches have serious security flaws because even unlearning completely different data points can produce the same contribution estimation as unlearning the target data points. To address the above problems, we try to define machine unlearning from the knowledge perspective, and we propose a knowledge-level machine unlearning method, namely ERM-KTP. Specifically, we propose an entanglement-reduced mask (ERM) structure to reduce the knowledge entanglement among classes during the training phase. When receiving the unlearning requests, we transfer the knowledge of the nontarget data points from the original model to the unlearned model and meanwhile prohibit the knowledge of the target data points via our proposed knowledge transfer and prohibition (KTP) method. Finally, we will get the unlearned model as the result and delete the original model to accomplish the unlearning process. Especially, our proposed ERM-KTP is an interpretable unlearning method because the ERM structure and the crafted masks in KTP can explicitly explain the operation and the effect of unlearning data points. Extensive experiments demonstrate the effectiveness, efficiency, high fidelity, and scalability of the ERM-KTP unlearning method. Code is available at https://github.com/RUIYUN-ML/ERM-KTP" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 617, + 128, + 629 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 617, + 128, + 629 + ], + "spans": [ + { + "bbox": [ + 47, + 617, + 128, + 629 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 638, + 287, + 686 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 638, + 287, + 686 + ], + "spans": [ + { + "bbox": [ + 46, + 638, + 287, + 686 + ], + "type": "text", + "content": "In recent years, many countries have raised concerns about protecting personal privacy. The privacy legislation, e.g., the well-known European Union's GDPR [19], have been promulgated to oblige information service providers" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 236, + 546, + 344 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 236, + 546, + 344 + ], + "spans": [ + { + "bbox": [ + 306, + 236, + 546, + 344 + ], + "type": "text", + "content": "to remove personal data when receiving a request from the data owner, i.e., the right-to-be-forgotten. Besides, the GDPR stipulates that the service providers should remove the corresponding impact of the data requested by the data owner, in which the machine learning models are the most representative. Many kinds of research demonstrate that the machine learning models can memorize knowledge of the data points, e.g., the membership inference attack [7, 14, 15] can infer whether a data point is in the training set or not." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 348, + 547, + 624 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 348, + 547, + 624 + ], + "spans": [ + { + "bbox": [ + 304, + 348, + 547, + 624 + ], + "type": "text", + "content": "A naive approach is retraining the model after removing the target data points from the training set, but the human resources and materials consumed are costly. Thus, aiming to efficiently remove data as well as their generated contribution to the model, a new ML privacy protection research direction emerged, called machine unlearning. A good deal of related work attempted to solve the data-removing challenge of inefficient retraining, and there are two representative research fields, including exact unlearning [1] and approximate unlearning [3-5]. Unfortunately, these approaches usually require huge computational, storage overhead, and memory requirements for class-specific machine unlearning tasks on the complicated convolutional neural networks (CNNs). Furthermore, they may compromise the model's performance and even cause disastrous forgetting. Most significantly, Thudi et al. [18] believed that such approximate unlearning approaches have serious security flaws because they usually define machine unlearning as the distribution difference between the unlearned model and the retrained model. According to this definition, even unlearning completely different data points can produce the same contribution estimation as unlearning the target data points." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 629, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 629, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 629, + 547, + 715 + ], + "type": "text", + "content": "Unlearning algorithms are difficult to implement on deep learning models because these models are often seen as a black box and lack interpretability, which makes data points' contributions challenging to estimate. Though many related works [2, 10, 16, 21] attempted to improve the interpretability of deep learning models, they can not apply to machine unlearning directly. For example, Zhou et al. [22]" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 693, + 170, + 703 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 693, + 170, + 703 + ], + "spans": [ + { + "bbox": [ + 58, + 693, + 170, + 703 + ], + "type": "text", + "content": "* Both authors contributed equally" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 59, + 703, + 135, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 703, + 135, + 712 + ], + "spans": [ + { + "bbox": [ + 59, + 703, + 135, + 712 + ], + "type": "text", + "content": "† Corresponding author" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "20147" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "type": "text", + "content": "leveraged the global average pooling (GAP) in CNNs to generate a class activation mapping (CAM) to indicate the discriminative image regions used by the CNNs to identify the class. Liang et al. [12] proposed class-specific filters to transform the complex representations in convolutional layers into interpretable graphs." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 144, + 288, + 360 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 144, + 288, + 360 + ], + "spans": [ + { + "bbox": [ + 46, + 144, + 288, + 360 + ], + "type": "text", + "content": "To address the above problems, for the first time, we consider the need for subsequent unlearning tasks during the model training phase. We define machine unlearning in the knowledge perspective, i.e., a reliable machine unlearning approach should satisfy that the knowledge of the unlearned model should be identical to the retrained model. Furthermore, we propose an interpretable unlearning method, i.e., ERM-KTP. The ERM structure can interpret the relation between data points and channels in the activation maps. Such a relationship can describe which filters the data points contribute to the convolutional layer. Then, KTP utilizes the relation to transfer the knowledge from corresponding filters to the unlearned model. Furthermore, the crafted masks in KTP interpret the operation of the knowledge transfer. With these interpretable methods, we can precisely unlearn data points and enhance the reliability of our proposed unlearning approach. We summarize our contributions of this paper as follows:" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 59, + 367, + 287, + 622 + ], + "type": "list", + "angle": 0, + "index": 5, + "blocks": [ + { + "bbox": [ + 59, + 367, + 287, + 438 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 367, + 287, + 438 + ], + "spans": [ + { + "bbox": [ + 59, + 367, + 287, + 438 + ], + "type": "text", + "content": "- We give a novel definition of machine unlearning from the knowledge perspective, and we further propose an interpretable knowledge-level machine unlearning method, i.e., ERM-KTP. Especially, the interpretability of ERM-KTP enhances the reliability of the unlearning operation." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 59, + 447, + 287, + 555 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 447, + 287, + 555 + ], + "spans": [ + { + "bbox": [ + 59, + 447, + 287, + 555 + ], + "type": "text", + "content": "- We introduce an ERM structure that reduces the knowledge entanglement among classes to get a pretrained model. When receiving the unlearning requests, we use the proposed KTP method to transfer the knowledge of the remaining set from the original model to the unlearned model and, meanwhile, prohibit the knowledge of the unlearning set. Finally, we will get the unlearned model as the result and delete the original model to complete the unlearning process." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 59, + 563, + 287, + 622 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 563, + 287, + 622 + ], + "spans": [ + { + "bbox": [ + 59, + 563, + 287, + 622 + ], + "type": "text", + "content": "- We conduct experiments on three different scales of image classification datasets and three complicated CNNs. Extensive experimental results demonstrate the effectiveness, efficiency, high fidelity, and scalability of ERM-KTP." + } + ] + } + ], + "index": 4 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 47, + 634, + 174, + 647 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 634, + 174, + 647 + ], + "spans": [ + { + "bbox": [ + 47, + 634, + 174, + 647 + ], + "type": "text", + "content": "2. Problem Formulation" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 654, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 654, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 654, + 287, + 715 + ], + "type": "text", + "content": "In this paper, we primarily consider a class-specific machine unlearning scenario. We assume a sample space " + }, + { + "bbox": [ + 46, + 654, + 287, + 715 + ], + "type": "inline_equation", + "content": "\\mathcal{X} \\subseteq \\mathbb{R}^d" + }, + { + "bbox": [ + 46, + 654, + 287, + 715 + ], + "type": "text", + "content": " and corresponding labels " + }, + { + "bbox": [ + 46, + 654, + 287, + 715 + ], + "type": "inline_equation", + "content": "\\mathcal{Y} = \\{1,2,\\dots,C\\}" + }, + { + "bbox": [ + 46, + 654, + 287, + 715 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 654, + 287, + 715 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 46, + 654, + 287, + 715 + ], + "type": "text", + "content": " is the number of dimensions and " + }, + { + "bbox": [ + 46, + 654, + 287, + 715 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 46, + 654, + 287, + 715 + ], + "type": "text", + "content": " is the number of classes. The training set can be represented as" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 305, + 72, + 545, + 120 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 545, + 120 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 545, + 120 + ], + "type": "inline_equation", + "content": "\\mathcal{D} = \\{\\mathcal{D}_1,\\mathcal{D}_2,\\dots ,\\mathcal{D}_C\\}" + }, + { + "bbox": [ + 305, + 72, + 545, + 120 + ], + "type": "text", + "content": " . To unlearn the target class's data points " + }, + { + "bbox": [ + 305, + 72, + 545, + 120 + ], + "type": "inline_equation", + "content": "\\mathcal{D}_u\\subseteq \\mathcal{D}" + }, + { + "bbox": [ + 305, + 72, + 545, + 120 + ], + "type": "text", + "content": " exactly, we need to apply a removal method, which should be equivalent to applying the training algorithm to the dataset without target data points." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 122, + 547, + 218 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 122, + 547, + 218 + ], + "spans": [ + { + "bbox": [ + 305, + 122, + 547, + 218 + ], + "type": "text", + "content": "Definition 1. We define a learning algorithm, " + }, + { + "bbox": [ + 305, + 122, + 547, + 218 + ], + "type": "inline_equation", + "content": "\\mathcal{A}:\\mathcal{D}\\to \\mathcal{W}" + }, + { + "bbox": [ + 305, + 122, + 547, + 218 + ], + "type": "text", + "content": " as a function from a dataset to a model in hypothesis space " + }, + { + "bbox": [ + 305, + 122, + 547, + 218 + ], + "type": "inline_equation", + "content": "\\mathcal{W}" + }, + { + "bbox": [ + 305, + 122, + 547, + 218 + ], + "type": "text", + "content": ". A removal method, " + }, + { + "bbox": [ + 305, + 122, + 547, + 218 + ], + "type": "inline_equation", + "content": "\\mathcal{R}:\\mathcal{A}(\\mathcal{D})\\times \\mathcal{D}\\times \\mathcal{D}_u\\rightarrow \\mathcal{W}" + }, + { + "bbox": [ + 305, + 122, + 547, + 218 + ], + "type": "text", + "content": ", is a function from an original model " + }, + { + "bbox": [ + 305, + 122, + 547, + 218 + ], + "type": "inline_equation", + "content": "\\mathcal{A}(D)" + }, + { + "bbox": [ + 305, + 122, + 547, + 218 + ], + "type": "text", + "content": ", training dataset " + }, + { + "bbox": [ + 305, + 122, + 547, + 218 + ], + "type": "inline_equation", + "content": "\\mathcal{D}" + }, + { + "bbox": [ + 305, + 122, + 547, + 218 + ], + "type": "text", + "content": ", an unlearning dataset " + }, + { + "bbox": [ + 305, + 122, + 547, + 218 + ], + "type": "inline_equation", + "content": "\\mathcal{D}_u" + }, + { + "bbox": [ + 305, + 122, + 547, + 218 + ], + "type": "text", + "content": " to remove from the training dataset " + }, + { + "bbox": [ + 305, + 122, + 547, + 218 + ], + "type": "inline_equation", + "content": "\\mathcal{D}" + }, + { + "bbox": [ + 305, + 122, + 547, + 218 + ], + "type": "text", + "content": " to an unlearned model in " + }, + { + "bbox": [ + 305, + 122, + 547, + 218 + ], + "type": "inline_equation", + "content": "\\mathcal{W}" + }, + { + "bbox": [ + 305, + 122, + 547, + 218 + ], + "type": "text", + "content": ", and a remaining dataset " + }, + { + "bbox": [ + 305, + 122, + 547, + 218 + ], + "type": "inline_equation", + "content": "\\mathcal{D}_r = \\mathcal{D}\\backslash \\mathcal{D}_u" + }, + { + "bbox": [ + 305, + 122, + 547, + 218 + ], + "type": "text", + "content": ". We define equivalence as having identical knowledge for each model in " + }, + { + "bbox": [ + 305, + 122, + 547, + 218 + ], + "type": "inline_equation", + "content": "\\mathcal{W}" + }, + { + "bbox": [ + 305, + 122, + 547, + 218 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 351, + 230, + 545, + 243 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 351, + 230, + 545, + 243 + ], + "spans": [ + { + "bbox": [ + 351, + 230, + 545, + 243 + ], + "type": "interline_equation", + "content": "\\mathbb {K} (\\mathcal {A} \\left(\\mathcal {D} _ {r}\\right)) = \\mathbb {K} \\left(\\mathcal {R} \\left(\\mathcal {A} (\\mathcal {D}), \\mathcal {D}, \\mathcal {D} _ {u}\\right)\\right), \\tag {1}", + "image_path": "4b778faa64355a225d2f52cc9b95bc9472b657328f08c7f025c53d2f0414c171.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 247, + 545, + 283 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 247, + 545, + 283 + ], + "spans": [ + { + "bbox": [ + 304, + 247, + 545, + 283 + ], + "type": "text", + "content": "in which " + }, + { + "bbox": [ + 304, + 247, + 545, + 283 + ], + "type": "inline_equation", + "content": "\\mathbb{K}(\\cdot)" + }, + { + "bbox": [ + 304, + 247, + 545, + 283 + ], + "type": "text", + "content": " is a knowledge measuring function. If an exact unlearning method satisfy the above definition, it can be defined as a knowledge-level unlearning method." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 293, + 392, + 306 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 293, + 392, + 306 + ], + "spans": [ + { + "bbox": [ + 306, + 293, + 392, + 306 + ], + "type": "text", + "content": "3. Related Work" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 316, + 545, + 460 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 316, + 545, + 460 + ], + "spans": [ + { + "bbox": [ + 304, + 316, + 545, + 460 + ], + "type": "text", + "content": "Exact unlearning. The exact unlearning approaches can provide algorithmic unlearning proof. The most representative exact unlearning approach is retrain-from-scratch (RfS), i.e., remove the target data points from the training set and retrain the model. Bourtoule et al. proposed SISA to improve efficiency by retraining the sub-model instead of retrain-from-scratch. These exact unlearning approaches are knowledge-level because they remove all target data points in the input phase so that the model can not learn any knowledge of them. However, their computational overhead is still significant because they need to relearn the remaining set's knowledge through retraining." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 462, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 462, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 462, + 545, + 714 + ], + "type": "text", + "content": "Approximate unlearning. The main idea of approximate unlearning approaches is to estimate the target data points' contribution to the model and update the parameters for unlearning. For example, Graves et al. [4] leveraged gradients to estimate the contributions. They stored gradients of batches consisting of target data points and then subtracted the target gradients to update the model's parameters. For class-specific unlearning tasks or large-scale unlearning requests, it needs to store gradients of almost every batch, and the model will degenerate to the initialization state. Guo et al. [5] utilized the Influence Theory [8], and Golatkar et al. [3] used the Fisher Information [13] to estimate the contributions. However, the above two methods need to calculate the hessian matrix, which is very expensive in deep learning models. Besides, they may compromise the model's performance due to imprecise estimates of contributions on CNNs and even cause disastrous forgetting. Most significantly, Thudi et al. [18] pointed out that different data points can also generate the same network, making approximate unlearning approaches unable to provide an algorithmic unlearning proof." + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "20148" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 71, + 153, + 85 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 71, + 153, + 85 + ], + "spans": [ + { + "bbox": [ + 47, + 71, + 153, + 85 + ], + "type": "text", + "content": "4. Proposed Method" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 91, + 287, + 175 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 91, + 287, + 175 + ], + "spans": [ + { + "bbox": [ + 46, + 91, + 287, + 175 + ], + "type": "text", + "content": "In this section, we will explain the ERM-KTP unlearning method in detail. We will describe how the proposed ERM structure reduces the entanglement of knowledge in Section 4.1. Then, we will explain how the proposed KTP method transfers knowledge in Section 4.2. Finally, we will explain how we combine the ERM and the KTP method to construct the ERM-KTP unlearning method in Section 4.3." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 180, + 287, + 205 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 180, + 287, + 205 + ], + "spans": [ + { + "bbox": [ + 47, + 180, + 287, + 205 + ], + "type": "text", + "content": "4.1. Entanglement-Reduced Mask (ERM) Structure" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 211, + 288, + 282 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 211, + 288, + 282 + ], + "spans": [ + { + "bbox": [ + 46, + 211, + 288, + 282 + ], + "type": "text", + "content": "The most representative knowledge the ML models learn is the features extracted by the convolutional layers. However, the features of different classes are entangled, so the key features of different classes are always highly overlapping. As a result, it is difficult to transfer the knowledge of target classes without affecting others." + } + ] + } + ], + "index": 3 + }, + { + "type": "image", + "bbox": [ + 55, + 290, + 279, + 429 + ], + "blocks": [ + { + "bbox": [ + 55, + 290, + 279, + 429 + ], + "lines": [ + { + "bbox": [ + 55, + 290, + 279, + 429 + ], + "spans": [ + { + "bbox": [ + 55, + 290, + 279, + 429 + ], + "type": "image", + "image_path": "bc41ffd1e350d572b7a7ad647f093149dd2ccfa05cabe94bf737b9c8cf1bf7a4.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 66, + 440, + 268, + 452 + ], + "lines": [ + { + "bbox": [ + 66, + 440, + 268, + 452 + ], + "spans": [ + { + "bbox": [ + 66, + 440, + 268, + 452 + ], + "type": "text", + "content": "Figure 1. An overview of our proposed ERM structure." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 463, + 287, + 631 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 463, + 287, + 631 + ], + "spans": [ + { + "bbox": [ + 46, + 463, + 287, + 631 + ], + "type": "text", + "content": "In order to reduce the entanglement of knowledge, we propose an Entanglement-Reduced Mask (ERM) structure as a learnable layer of the CNNs inspired by the model interpretability work [12]. The learnable ERM structure can be represented as a matrix " + }, + { + "bbox": [ + 46, + 463, + 287, + 631 + ], + "type": "inline_equation", + "content": "G \\in \\mathbb{R}^{C \\times K}" + }, + { + "bbox": [ + 46, + 463, + 287, + 631 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 463, + 287, + 631 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 46, + 463, + 287, + 631 + ], + "type": "text", + "content": " is the number of classes and " + }, + { + "bbox": [ + 46, + 463, + 287, + 631 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 46, + 463, + 287, + 631 + ], + "type": "text", + "content": " is the number of filters. Each element " + }, + { + "bbox": [ + 46, + 463, + 287, + 631 + ], + "type": "inline_equation", + "content": "G_{c}^{k} \\in [0,1]" + }, + { + "bbox": [ + 46, + 463, + 287, + 631 + ], + "type": "text", + "content": " represents the relevance between the " + }, + { + "bbox": [ + 46, + 463, + 287, + 631 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 463, + 287, + 631 + ], + "type": "text", + "content": "-th filter and the " + }, + { + "bbox": [ + 46, + 463, + 287, + 631 + ], + "type": "inline_equation", + "content": "c" + }, + { + "bbox": [ + 46, + 463, + 287, + 631 + ], + "type": "text", + "content": "-th class, and a higher value of " + }, + { + "bbox": [ + 46, + 463, + 287, + 631 + ], + "type": "inline_equation", + "content": "G_{c}^{k}" + }, + { + "bbox": [ + 46, + 463, + 287, + 631 + ], + "type": "text", + "content": " denotes a closer correlation. Given a data point " + }, + { + "bbox": [ + 46, + 463, + 287, + 631 + ], + "type": "inline_equation", + "content": "(x \\in \\mathcal{X}, y \\in \\mathcal{Y})" + }, + { + "bbox": [ + 46, + 463, + 287, + 631 + ], + "type": "text", + "content": " as an input, we use the " + }, + { + "bbox": [ + 46, + 463, + 287, + 631 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 46, + 463, + 287, + 631 + ], + "type": "text", + "content": "-th row " + }, + { + "bbox": [ + 46, + 463, + 287, + 631 + ], + "type": "inline_equation", + "content": "G_{y} \\in \\mathbb{R}^{1 \\times K}" + }, + { + "bbox": [ + 46, + 463, + 287, + 631 + ], + "type": "text", + "content": " as a mask vector multiplied to the activation maps " + }, + { + "bbox": [ + 46, + 463, + 287, + 631 + ], + "type": "inline_equation", + "content": "\\mathcal{M} = (\\mathcal{M}_1, \\dots, \\mathcal{M}_K)" + }, + { + "bbox": [ + 46, + 463, + 287, + 631 + ], + "type": "text", + "content": " of the last convolution layer (before the fully connected layer) to shut down irrelevant channels. Formally, we can define the above multiply operation as" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 100, + 635, + 287, + 649 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 100, + 635, + 287, + 649 + ], + "spans": [ + { + "bbox": [ + 100, + 635, + 287, + 649 + ], + "type": "interline_equation", + "content": "A \\circ B = \\left(A _ {1} B ^ {1}, \\dots , A _ {d _ {1}} B ^ {d _ {1}}\\right), \\tag {2}", + "image_path": "4b2c768a65b72e733d0208066bf014b085abce46b740c60343d9da22694f5919.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 652, + 287, + 677 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 652, + 287, + 677 + ], + "spans": [ + { + "bbox": [ + 47, + 652, + 287, + 677 + ], + "type": "text", + "content": "in which " + }, + { + "bbox": [ + 47, + 652, + 287, + 677 + ], + "type": "inline_equation", + "content": "A\\in \\mathbb{R}^{d_1\\times d_2\\times d_3}" + }, + { + "bbox": [ + 47, + 652, + 287, + 677 + ], + "type": "inline_equation", + "content": "B\\in \\mathbb{R}^{1\\times d_1}" + }, + { + "bbox": [ + 47, + 652, + 287, + 677 + ], + "type": "inline_equation", + "content": "A_{i}\\in \\mathbb{R}^{d_{2}\\times d_{3}}" + }, + { + "bbox": [ + 47, + 652, + 287, + 677 + ], + "type": "text", + "content": " , and " + }, + { + "bbox": [ + 47, + 652, + 287, + 677 + ], + "type": "inline_equation", + "content": "B^{i}\\in \\mathbb{R}" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 677, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 677, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 47, + 677, + 287, + 714 + ], + "type": "text", + "content": "For a CNN with an ERM structure (ERM-CNN), we set two forward propagation paths of an ERM-CNN with parameters " + }, + { + "bbox": [ + 47, + 677, + 287, + 714 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 47, + 677, + 287, + 714 + ], + "type": "text", + "content": ": (1) the STD path with the predicting probability" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "text", + "content": "vector " + }, + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "inline_equation", + "content": "\\tilde{y}_{\\theta}" + }, + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "text", + "content": "; (2) the ERM path with mask matrix " + }, + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "inline_equation", + "content": "G" + }, + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "text", + "content": " predicting " + }, + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "inline_equation", + "content": "\\tilde{y}_{\\theta}^{G}" + }, + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "text", + "content": ", as shown in Fig. 1. In the training phase, we train the network alternately through the STD and ERM paths, while only the STD path is used in the validation phase." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 120, + 546, + 264 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 120, + 546, + 264 + ], + "spans": [ + { + "bbox": [ + 304, + 120, + 546, + 264 + ], + "type": "text", + "content": "Then, we will discuss the details of training an ERM-CNN. We first define an ideal ERM structure in which each row of the matrix " + }, + { + "bbox": [ + 304, + 120, + 546, + 264 + ], + "type": "inline_equation", + "content": "G" + }, + { + "bbox": [ + 304, + 120, + 546, + 264 + ], + "type": "text", + "content": " is at least one element equal to 1, and each row is orthogonal. In this ideal state, the knowledge of each class learned by the model is not entangled and independent of each other. Thus, the training objectives are to train an ERM-CNN with an ideal ERM structure, and its classification performance is comparable to the STD-CNNs. To train a model with the ideal ERM, we first consider its validation accuracy through two paths and ensure that at least one element of each row of " + }, + { + "bbox": [ + 304, + 120, + 546, + 264 + ], + "type": "inline_equation", + "content": "G" + }, + { + "bbox": [ + 304, + 120, + 546, + 264 + ], + "type": "text", + "content": " equals 1, i.e., " + }, + { + "bbox": [ + 304, + 120, + 546, + 264 + ], + "type": "inline_equation", + "content": "\\| G_{c}\\|_{\\infty} = 1" + }, + { + "bbox": [ + 304, + 120, + 546, + 264 + ], + "type": "text", + "content": ". We can get the following formulation:" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 312, + 270, + 545, + 300 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 270, + 545, + 300 + ], + "spans": [ + { + "bbox": [ + 312, + 270, + 545, + 300 + ], + "type": "interline_equation", + "content": "\\min _ {\\theta , G} L _ {0} (\\theta) = \\mathrm {C E} (y | | \\tilde {y} _ {\\theta}) + \\lambda_ {1} \\mathrm {C E} (y | | \\tilde {y} _ {\\theta} ^ {G}) \\quad s. t. G \\in V _ {G}, \\tag {3}", + "image_path": "12174bd9eb4d842c8befa96c5734b6443655772b2e9ca01b2bcb57445aedd183.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 300, + 545, + 384 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 300, + 545, + 384 + ], + "spans": [ + { + "bbox": [ + 305, + 300, + 545, + 384 + ], + "type": "text", + "content": "where CE denotes the cross entropy loss and " + }, + { + "bbox": [ + 305, + 300, + 545, + 384 + ], + "type": "inline_equation", + "content": "V_{G} = \\{G\\in" + }, + { + "bbox": [ + 305, + 300, + 545, + 384 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^{C\\times K}: \\| G_c\\|_{\\infty} = 1\\}" + }, + { + "bbox": [ + 305, + 300, + 545, + 384 + ], + "type": "text", + "content": " . Furthermore, we introduce a regulation term to encourage the sparsity of the matrix " + }, + { + "bbox": [ + 305, + 300, + 545, + 384 + ], + "type": "inline_equation", + "content": "G" + }, + { + "bbox": [ + 305, + 300, + 545, + 384 + ], + "type": "text", + "content": " , and encourage the " + }, + { + "bbox": [ + 305, + 300, + 545, + 384 + ], + "type": "inline_equation", + "content": "L_{1}" + }, + { + "bbox": [ + 305, + 300, + 545, + 384 + ], + "type": "text", + "content": " -norm of " + }, + { + "bbox": [ + 305, + 300, + 545, + 384 + ], + "type": "inline_equation", + "content": "G" + }, + { + "bbox": [ + 305, + 300, + 545, + 384 + ], + "type": "text", + "content": " not to exceed the preset upper bound " + }, + { + "bbox": [ + 305, + 300, + 545, + 384 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 305, + 300, + 545, + 384 + ], + "type": "text", + "content": " and has no effect when " + }, + { + "bbox": [ + 305, + 300, + 545, + 384 + ], + "type": "inline_equation", + "content": "\\| G\\| _1 < \\alpha" + }, + { + "bbox": [ + 305, + 300, + 545, + 384 + ], + "type": "text", + "content": " . Apparently, we should set " + }, + { + "bbox": [ + 305, + 300, + 545, + 384 + ], + "type": "inline_equation", + "content": "\\alpha \\geqslant K" + }, + { + "bbox": [ + 305, + 300, + 545, + 384 + ], + "type": "text", + "content": " because " + }, + { + "bbox": [ + 305, + 300, + 545, + 384 + ], + "type": "inline_equation", + "content": "\\| G_c\\|_{\\infty} = 1" + }, + { + "bbox": [ + 305, + 300, + 545, + 384 + ], + "type": "text", + "content": " ensures " + }, + { + "bbox": [ + 305, + 300, + 545, + 384 + ], + "type": "inline_equation", + "content": "\\| G\\| _1\\geqslant K" + }, + { + "bbox": [ + 305, + 300, + 545, + 384 + ], + "type": "text", + "content": " As described above, we can formulate the regulation term as" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 315, + 392, + 545, + 410 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 315, + 392, + 545, + 410 + ], + "spans": [ + { + "bbox": [ + 315, + 392, + 545, + 410 + ], + "type": "interline_equation", + "content": "\\min _ {G} L _ {1} (\\theta) = \\| \\operatorname {R e L U} (\\| G \\| _ {1} - \\alpha) \\| _ {p} \\quad s. t. G \\in V _ {G}, \\tag {4}", + "image_path": "6e739bf5fca45cd225ae5efe5178218cb96cb12a832c062cfbff33ee0d6d43b0.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 416, + 545, + 453 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 416, + 545, + 453 + ], + "spans": [ + { + "bbox": [ + 304, + 416, + 545, + 453 + ], + "type": "text", + "content": "in which " + }, + { + "bbox": [ + 304, + 416, + 545, + 453 + ], + "type": "inline_equation", + "content": "\\| \\cdot \\| _p" + }, + { + "bbox": [ + 304, + 416, + 545, + 453 + ], + "type": "text", + "content": " indicates " + }, + { + "bbox": [ + 304, + 416, + 545, + 453 + ], + "type": "inline_equation", + "content": "p" + }, + { + "bbox": [ + 304, + 416, + 545, + 453 + ], + "type": "text", + "content": "-norm. Moreover, we introduce the inner product regulation to encourage each row of " + }, + { + "bbox": [ + 304, + 416, + 545, + 453 + ], + "type": "inline_equation", + "content": "G" + }, + { + "bbox": [ + 304, + 416, + 545, + 453 + ], + "type": "text", + "content": " to be orthogonal to the other as" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 365, + 459, + 545, + 499 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 365, + 459, + 545, + 499 + ], + "spans": [ + { + "bbox": [ + 365, + 459, + 545, + 499 + ], + "type": "interline_equation", + "content": "\\operatorname {I n P} = \\sum_ {c _ {1} = 0} ^ {C} \\sum_ {c _ {2} = 0, \\atop c _ {1} < c _ {2}} ^ {C} \\left(G _ {c _ {1}} \\cdot G _ {c _ {2}}\\right). \\tag {5}", + "image_path": "a9e4c627e179401c7063ff2b0ba6265569e2502c64167c1439c7d1a4f5adb97c.jpg" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 506, + 545, + 540 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 506, + 545, + 540 + ], + "spans": [ + { + "bbox": [ + 304, + 506, + 545, + 540 + ], + "type": "text", + "content": "To facilitate the solution in practice, we replace Eq. (5) with the following equivalent form as our inner product regulation term:" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 320, + 545, + 545, + 586 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 320, + 545, + 545, + 586 + ], + "spans": [ + { + "bbox": [ + 320, + 545, + 545, + 586 + ], + "type": "interline_equation", + "content": "\\min _ {G} L _ {2} (\\theta) = \\sum_ {c _ {1} = 0} ^ {C} \\sum_ {c _ {2} = 0, \\atop c _ {1} < c _ {2}} ^ {C} (G G ^ {T}) _ {c _ {1}} ^ {c _ {2}} \\quad s. t. G \\in V _ {G}, \\tag {6}", + "image_path": "80ad42284d228881ac359684596852760caa168e8cc201c2ade519a43a460458.jpg" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 594, + 545, + 677 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 594, + 545, + 677 + ], + "spans": [ + { + "bbox": [ + 304, + 594, + 545, + 677 + ], + "type": "text", + "content": "in which " + }, + { + "bbox": [ + 304, + 594, + 545, + 677 + ], + "type": "inline_equation", + "content": "(GG^{T})_{c_{1}}^{c_{2}}" + }, + { + "bbox": [ + 304, + 594, + 545, + 677 + ], + "type": "text", + "content": " denotes the " + }, + { + "bbox": [ + 304, + 594, + 545, + 677 + ], + "type": "inline_equation", + "content": "c_{1}" + }, + { + "bbox": [ + 304, + 594, + 545, + 677 + ], + "type": "text", + "content": "-th row and the " + }, + { + "bbox": [ + 304, + 594, + 545, + 677 + ], + "type": "inline_equation", + "content": "c_{2}" + }, + { + "bbox": [ + 304, + 594, + 545, + 677 + ], + "type": "text", + "content": "-th column of the matrix " + }, + { + "bbox": [ + 304, + 594, + 545, + 677 + ], + "type": "inline_equation", + "content": "(GG^{T})" + }, + { + "bbox": [ + 304, + 594, + 545, + 677 + ], + "type": "text", + "content": ". When we minimize " + }, + { + "bbox": [ + 304, + 594, + 545, + 677 + ], + "type": "inline_equation", + "content": "L_{2}(\\theta)" + }, + { + "bbox": [ + 304, + 594, + 545, + 677 + ], + "type": "text", + "content": ", it will tend to 0 if " + }, + { + "bbox": [ + 304, + 594, + 545, + 677 + ], + "type": "inline_equation", + "content": "G_{c}^{k} \\in [0,1]" + }, + { + "bbox": [ + 304, + 594, + 545, + 677 + ], + "type": "text", + "content": ", i.e., each row of " + }, + { + "bbox": [ + 304, + 594, + 545, + 677 + ], + "type": "inline_equation", + "content": "\\mathbf{G}" + }, + { + "bbox": [ + 304, + 594, + 545, + 677 + ], + "type": "text", + "content": " will be orthogonal to the other. Essentially, the inner product describes the similarity between two vectors as " + }, + { + "bbox": [ + 304, + 594, + 545, + 677 + ], + "type": "inline_equation", + "content": "\\vec{a} \\cdot \\vec{b} = \\|\\vec{a}\\| \\|\\vec{b}\\| \\cos \\langle \\vec{a}, \\vec{b} \\rangle" + }, + { + "bbox": [ + 304, + 594, + 545, + 677 + ], + "type": "text", + "content": ". When we minimize " + }, + { + "bbox": [ + 304, + 594, + 545, + 677 + ], + "type": "inline_equation", + "content": "L_{2}(\\theta)" + }, + { + "bbox": [ + 304, + 594, + 545, + 677 + ], + "type": "text", + "content": ", the cosine value and their " + }, + { + "bbox": [ + 304, + 594, + 545, + 677 + ], + "type": "inline_equation", + "content": "L_{2}" + }, + { + "bbox": [ + 304, + 594, + 545, + 677 + ], + "type": "text", + "content": "-norm are minimized simultaneously." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 305, + 677, + 545, + 702 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 677, + 545, + 702 + ], + "spans": [ + { + "bbox": [ + 305, + 677, + 545, + 702 + ], + "type": "text", + "content": "To sum up, we formulate an optimization problem to train an ERM-CNN by combining Eq. (3), (4), and (6):" + } + ] + } + ], + "index": 20 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "type": "text", + "content": "20149" + } + ] + } + ], + "index": 21 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 58, + 67, + 287, + 146 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 67, + 287, + 146 + ], + "spans": [ + { + "bbox": [ + 58, + 67, + 287, + 146 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\min _ {\\theta , G} L (\\theta) = \\mathrm {C E} (y | | \\tilde {y} _ {\\theta}) + \\lambda_ {1} \\mathrm {C E} (y | | \\tilde {y} _ {\\theta} ^ {G}) \\\\ + \\lambda_ {2} \\| \\operatorname {R e L U} (\\| G \\| _ {1} - \\alpha) \\| _ {p} \\\\ + \\lambda_ {3} \\sum_ {c _ {1} = 0} ^ {C} \\sum_ {\\substack {c _ {2} = 0, \\\\ c _ {1} < c _ {2}}} ^ {C} (G G ^ {T}) _ {c _ {1}} ^ {c _ {2}} \\quad s. t. G \\in V _ {G}, \\tag{7} \\\\ \\end{array}", + "image_path": "c476be45d4f8efc84dfda1479b6a58a9d0e3b7371701547e38a8659d05e0c2d2.jpg" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 153, + 287, + 200 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 153, + 287, + 200 + ], + "spans": [ + { + "bbox": [ + 46, + 153, + 287, + 200 + ], + "type": "text", + "content": "in which the first and the second term ensure the classification performance, the third term ensures the sparsity of the matrix " + }, + { + "bbox": [ + 46, + 153, + 287, + 200 + ], + "type": "inline_equation", + "content": "G" + }, + { + "bbox": [ + 46, + 153, + 287, + 200 + ], + "type": "text", + "content": ", and the last term imposes a rigorous constraint on each row of " + }, + { + "bbox": [ + 46, + 153, + 287, + 200 + ], + "type": "inline_equation", + "content": "G" + }, + { + "bbox": [ + 46, + 153, + 287, + 200 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 1 + }, + { + "type": "code", + "bbox": [ + 48, + 228, + 253, + 392 + ], + "blocks": [ + { + "bbox": [ + 53, + 214, + 209, + 225 + ], + "lines": [ + { + "bbox": [ + 53, + 214, + 209, + 225 + ], + "spans": [ + { + "bbox": [ + 53, + 214, + 209, + 225 + ], + "type": "text", + "content": "Algorithm 1: Alternate Training (AT)" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "code_caption" + }, + { + "bbox": [ + 48, + 228, + 253, + 392 + ], + "lines": [ + { + "bbox": [ + 48, + 228, + 253, + 392 + ], + "spans": [ + { + "bbox": [ + 48, + 228, + 253, + 392 + ], + "type": "text", + "content": "1 for e in epochs do \n2 if " + }, + { + "bbox": [ + 48, + 228, + 253, + 392 + ], + "type": "inline_equation", + "content": "e \\in ERM's" + }, + { + "bbox": [ + 48, + 228, + 253, + 392 + ], + "type": "text", + "content": " epoch then \n3 " + }, + { + "bbox": [ + 48, + 228, + 253, + 392 + ], + "type": "inline_equation", + "content": "\\tilde{y}_{\\theta}^{G} \\gets" + }, + { + "bbox": [ + 48, + 228, + 253, + 392 + ], + "type": "text", + "content": " prediction through the ERM path \n4 " + }, + { + "bbox": [ + 48, + 228, + 253, + 392 + ], + "type": "inline_equation", + "content": "\\mathcal{L} \\gets \\lambda_{1}CE(y||\\tilde{y}_{\\theta}^{G}) + \\lambda_{2}L_{1} + \\lambda_{3}L_{2}" + }, + { + "bbox": [ + 48, + 228, + 253, + 392 + ], + "type": "text", + "content": " \n5 " + }, + { + "bbox": [ + 48, + 228, + 253, + 392 + ], + "type": "inline_equation", + "content": "G \\gets G - \\eta \\frac{\\partial\\mathcal{L}}{\\partial G}" + }, + { + "bbox": [ + 48, + 228, + 253, + 392 + ], + "type": "text", + "content": " \n6 " + }, + { + "bbox": [ + 48, + 228, + 253, + 392 + ], + "type": "inline_equation", + "content": "G_{c} \\gets G_{c} / \\| G_{c}\\|_{\\infty}" + }, + { + "bbox": [ + 48, + 228, + 253, + 392 + ], + "type": "text", + "content": " \n7 " + }, + { + "bbox": [ + 48, + 228, + 253, + 392 + ], + "type": "inline_equation", + "content": "G \\gets G.\\mathrm{clip}(0,1)" + }, + { + "bbox": [ + 48, + 228, + 253, + 392 + ], + "type": "text", + "content": " \n8 else \n9 " + }, + { + "bbox": [ + 48, + 228, + 253, + 392 + ], + "type": "inline_equation", + "content": "\\tilde{y}_{\\theta} \\gets" + }, + { + "bbox": [ + 48, + 228, + 253, + 392 + ], + "type": "text", + "content": " prediction through the STD path \n10 " + }, + { + "bbox": [ + 48, + 228, + 253, + 392 + ], + "type": "inline_equation", + "content": "\\mathcal{L} \\gets \\mathrm{CE}(y||\\tilde{y}_{\\theta})" + }, + { + "bbox": [ + 48, + 228, + 253, + 392 + ], + "type": "text", + "content": " \n11 end \n12 " + }, + { + "bbox": [ + 48, + 228, + 253, + 392 + ], + "type": "inline_equation", + "content": "\\theta \\gets \\theta - \\eta \\frac{\\partial\\mathcal{L}}{\\partial\\theta}" + }, + { + "bbox": [ + 48, + 228, + 253, + 392 + ], + "type": "text", + "content": " \n13 end" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "code_body" + } + ], + "index": 3, + "sub_type": "algorithm" + }, + { + "bbox": [ + 46, + 412, + 289, + 616 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 412, + 289, + 616 + ], + "spans": [ + { + "bbox": [ + 46, + 412, + 289, + 616 + ], + "type": "text", + "content": "To solve the above optimization problem in Eq. (7), we apply an approximate projected gradient descent (PGD) algorithm. After the matrix " + }, + { + "bbox": [ + 46, + 412, + 289, + 616 + ], + "type": "inline_equation", + "content": "G" + }, + { + "bbox": [ + 46, + 412, + 289, + 616 + ], + "type": "text", + "content": " is updated, " + }, + { + "bbox": [ + 46, + 412, + 289, + 616 + ], + "type": "inline_equation", + "content": "G_{c}" + }, + { + "bbox": [ + 46, + 412, + 289, + 616 + ], + "type": "text", + "content": " will be normalized by " + }, + { + "bbox": [ + 46, + 412, + 289, + 616 + ], + "type": "inline_equation", + "content": "G_{c} / \\| G_{c}\\|_{\\infty}" + }, + { + "bbox": [ + 46, + 412, + 289, + 616 + ], + "type": "text", + "content": " to ensure " + }, + { + "bbox": [ + 46, + 412, + 289, + 616 + ], + "type": "inline_equation", + "content": "\\| G_c\\|_{\\infty} = 1" + }, + { + "bbox": [ + 46, + 412, + 289, + 616 + ], + "type": "text", + "content": ", and then each element of " + }, + { + "bbox": [ + 46, + 412, + 289, + 616 + ], + "type": "inline_equation", + "content": "G_{c}" + }, + { + "bbox": [ + 46, + 412, + 289, + 616 + ], + "type": "text", + "content": " will be clipped into the range [0, 1]. However, the joint training scheme may have some difficulties due to poor convergence. The forward propagation through the ERM path can make most features block, leading to a much poorer convergence than the STD path because of the weaker gradient. Therefore, we propose an alternate training (AT) scheme instead of the normal joint training scheme in that the forward propagation uses the STD path and ERM path alternately in different epochs. Specifically, we update " + }, + { + "bbox": [ + 46, + 412, + 289, + 616 + ], + "type": "inline_equation", + "content": "G" + }, + { + "bbox": [ + 46, + 412, + 289, + 616 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 412, + 289, + 616 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 46, + 412, + 289, + 616 + ], + "type": "text", + "content": " by descend the gradient of " + }, + { + "bbox": [ + 46, + 412, + 289, + 616 + ], + "type": "inline_equation", + "content": "\\lambda_1\\mathrm{CE}(y||\\tilde{y}_\\theta^G) + \\lambda_2L_1 + \\lambda_3L_2" + }, + { + "bbox": [ + 46, + 412, + 289, + 616 + ], + "type": "text", + "content": " in the epoch for ERM path, and we update " + }, + { + "bbox": [ + 46, + 412, + 289, + 616 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 46, + 412, + 289, + 616 + ], + "type": "text", + "content": " with the gradient of " + }, + { + "bbox": [ + 46, + 412, + 289, + 616 + ], + "type": "inline_equation", + "content": "\\mathrm{CE}(y||\\tilde{y}_{\\theta})" + }, + { + "bbox": [ + 46, + 412, + 289, + 616 + ], + "type": "text", + "content": " in the STD path, as shown in Algorithm 1." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 623, + 275, + 635 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 623, + 275, + 635 + ], + "spans": [ + { + "bbox": [ + 47, + 623, + 275, + 635 + ], + "type": "text", + "content": "4.2. Knowledge Transfer and Prohibition (KTP)" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 641, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 641, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 641, + 287, + 713 + ], + "type": "text", + "content": "After training an ERM-CNN as a pre-trained model, different classes' knowledge (features and parameters) is independent. When receiving the unlearning requests, we can transfer the knowledge of a single class separately via our proposed knowledge transfer and prohibition (KTP) method. Specifically, KTP transfers the knowledge of the" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 72, + 547, + 169 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 169 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 169 + ], + "type": "text", + "content": "non-target class of data in the origin model " + }, + { + "bbox": [ + 304, + 72, + 547, + 169 + ], + "type": "inline_equation", + "content": "\\theta_T" + }, + { + "bbox": [ + 304, + 72, + 547, + 169 + ], + "type": "text", + "content": " to the unlearned model " + }, + { + "bbox": [ + 304, + 72, + 547, + 169 + ], + "type": "inline_equation", + "content": "\\theta_S" + }, + { + "bbox": [ + 304, + 72, + 547, + 169 + ], + "type": "text", + "content": " while prohibiting the knowledge of the target data points. We can describe the KTP method as the following three processes: (1) convolution layers " + }, + { + "bbox": [ + 304, + 72, + 547, + 169 + ], + "type": "inline_equation", + "content": "(\\theta_S^{cv}" + }, + { + "bbox": [ + 304, + 72, + 547, + 169 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 72, + 547, + 169 + ], + "type": "inline_equation", + "content": "\\theta_T^{cv})" + }, + { + "bbox": [ + 304, + 72, + 547, + 169 + ], + "type": "text", + "content": " knowledge transfer (CKT); (2) fully connected layers " + }, + { + "bbox": [ + 304, + 72, + 547, + 169 + ], + "type": "inline_equation", + "content": "(\\theta_S^{fc}" + }, + { + "bbox": [ + 304, + 72, + 547, + 169 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 72, + 547, + 169 + ], + "type": "inline_equation", + "content": "\\theta_T^{fc})" + }, + { + "bbox": [ + 304, + 72, + 547, + 169 + ], + "type": "text", + "content": " knowledge transfer (FKT); (3) matrix " + }, + { + "bbox": [ + 304, + 72, + 547, + 169 + ], + "type": "inline_equation", + "content": "G" + }, + { + "bbox": [ + 304, + 72, + 547, + 169 + ], + "type": "text", + "content": " (" + }, + { + "bbox": [ + 304, + 72, + 547, + 169 + ], + "type": "inline_equation", + "content": "G_S" + }, + { + "bbox": [ + 304, + 72, + 547, + 169 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 72, + 547, + 169 + ], + "type": "inline_equation", + "content": "G_T" + }, + { + "bbox": [ + 304, + 72, + 547, + 169 + ], + "type": "text", + "content": ") knowledge transfer (GKT). Formally, we can define the KTP method as" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 383, + 178, + 468, + 194 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 383, + 178, + 468, + 194 + ], + "spans": [ + { + "bbox": [ + 383, + 178, + 468, + 194 + ], + "type": "interline_equation", + "content": "\\operatorname {C K T}: \\theta_ {S} ^ {c v} \\stackrel {{t r a n s}} {{\\longleftarrow}} \\theta_ {T} ^ {c v},", + "image_path": "b7409c2420e3bf044b036aa51b42a6b0ac3a65c2806230a0e7df4e1e6d838f27.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 385, + 196, + 545, + 212 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 385, + 196, + 545, + 212 + ], + "spans": [ + { + "bbox": [ + 385, + 196, + 545, + 212 + ], + "type": "interline_equation", + "content": "\\operatorname {F K T}: \\theta_ {S} ^ {f c} \\xleftarrow {\\text {t r a n s}} \\theta_ {T} ^ {f c}, \\tag {8}", + "image_path": "8b4e520238a352daf9942a5a8bad315d84fef8f3e749efadc0770f34d873d06f.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 383, + 215, + 468, + 230 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 383, + 215, + 468, + 230 + ], + "spans": [ + { + "bbox": [ + 383, + 215, + 468, + 230 + ], + "type": "interline_equation", + "content": "\\operatorname {G K T}: G _ {S} \\stackrel {{t r a n s}} {{\\longleftarrow}} G _ {T}.", + "image_path": "d4b70f6f19aef3c9e57ed0dddefe68fda5f83c8bf02e6c8e2e273b601fe22f21.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 239, + 547, + 287 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 239, + 547, + 287 + ], + "spans": [ + { + "bbox": [ + 304, + 239, + 547, + 287 + ], + "type": "text", + "content": "In the CKT process, we transfer the knowledge of features extracted by the convolutional layers by a crafted channel mask " + }, + { + "bbox": [ + 304, + 239, + 547, + 287 + ], + "type": "inline_equation", + "content": "\\bar{G}_{\\mathbf{c}} \\in \\mathbb{R}^{1 \\times K}" + }, + { + "bbox": [ + 304, + 239, + 547, + 287 + ], + "type": "text", + "content": ". For the single target class " + }, + { + "bbox": [ + 304, + 239, + 547, + 287 + ], + "type": "inline_equation", + "content": "\\mathbf{c}" + }, + { + "bbox": [ + 304, + 239, + 547, + 287 + ], + "type": "text", + "content": " unlearning task, the mask can be defined as" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 374, + 297, + 545, + 329 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 374, + 297, + 545, + 329 + ], + "spans": [ + { + "bbox": [ + 374, + 297, + 545, + 329 + ], + "type": "interline_equation", + "content": "\\bar {G} _ {\\mathbf {c}, i} = \\left\\{ \\begin{array}{l l} 0, & G _ {\\mathbf {c}, i} = 1 \\\\ 1, & G _ {\\mathbf {c}, i} = 0 \\end{array} . \\right. \\tag {9}", + "image_path": "feb61b72323fdba7ba317f3d107a1bce00f57f8ddb39978baa8bfa18bb92d3bd.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 338, + 546, + 374 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 338, + 546, + 374 + ], + "spans": [ + { + "bbox": [ + 304, + 338, + 546, + 374 + ], + "type": "text", + "content": "For the multiple target classes " + }, + { + "bbox": [ + 304, + 338, + 546, + 374 + ], + "type": "inline_equation", + "content": "\\mathbf{c} = \\{\\mathbf{c}_0,\\dots ,\\mathbf{c}_{|c|}\\}" + }, + { + "bbox": [ + 304, + 338, + 546, + 374 + ], + "type": "text", + "content": " unlearning task, we calculate " + }, + { + "bbox": [ + 304, + 338, + 546, + 374 + ], + "type": "inline_equation", + "content": "\\bar{G}_{\\mathbf{c}_j}" + }, + { + "bbox": [ + 304, + 338, + 546, + 374 + ], + "type": "text", + "content": " for each class " + }, + { + "bbox": [ + 304, + 338, + 546, + 374 + ], + "type": "inline_equation", + "content": "j" + }, + { + "bbox": [ + 304, + 338, + 546, + 374 + ], + "type": "text", + "content": " and then aggregate them as" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 358, + 384, + 545, + 459 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 358, + 384, + 545, + 459 + ], + "spans": [ + { + "bbox": [ + 358, + 384, + 545, + 459 + ], + "type": "interline_equation", + "content": "\\bar {G} _ {\\mathbf {c}, i} = \\left\\{ \\begin{array}{l l} 1, & \\left(\\sum_ {j} ^ {| c |} \\bar {G} _ {\\mathbf {c} _ {j}}\\right) _ {i} = | c | \\\\ 0, & \\left(\\sum_ {j} ^ {| c |} \\bar {G} _ {\\mathbf {c} _ {j}}\\right) _ {i} < | c | \\end{array} . \\right. \\tag {10}", + "image_path": "b4baa9aa03ad5dc76432dff9ed0656bcc675e1350201ddb5d586759aec7d8715.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 467, + 545, + 491 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 467, + 545, + 491 + ], + "spans": [ + { + "bbox": [ + 304, + 467, + 545, + 491 + ], + "type": "text", + "content": "Formally, the CKT process can be formulated as an optimization problem:" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 318, + 501, + 545, + 521 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 318, + 501, + 545, + 521 + ], + "spans": [ + { + "bbox": [ + 318, + 501, + 545, + 521 + ], + "type": "interline_equation", + "content": "\\min _ {\\theta_ {S} ^ {c v}} L _ {3} \\left(\\theta_ {S} ^ {c v}\\right) = \\operatorname {M S E} \\left(f \\left(x; \\theta_ {T} ^ {c v}\\right), g \\left(x; \\theta_ {S} ^ {c v}\\right) \\circ \\bar {G} _ {\\mathbf {c}}\\right), \\tag {11}", + "image_path": "fb24a0365e8de0280be4d52b71703fb2cf5bf1149f74c06431b7a02389e6ea98.jpg" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 530, + 547, + 648 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 530, + 547, + 648 + ], + "spans": [ + { + "bbox": [ + 304, + 530, + 547, + 648 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 530, + 547, + 648 + ], + "type": "inline_equation", + "content": "\\mathrm{MSE}(\\cdot)" + }, + { + "bbox": [ + 304, + 530, + 547, + 648 + ], + "type": "text", + "content": " is Mean Square Error, " + }, + { + "bbox": [ + 304, + 530, + 547, + 648 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 304, + 530, + 547, + 648 + ], + "type": "text", + "content": " is data points, " + }, + { + "bbox": [ + 304, + 530, + 547, + 648 + ], + "type": "inline_equation", + "content": "\\circ" + }, + { + "bbox": [ + 304, + 530, + 547, + 648 + ], + "type": "text", + "content": " is the multiply operation (Eq. (2)), and " + }, + { + "bbox": [ + 304, + 530, + 547, + 648 + ], + "type": "inline_equation", + "content": "f(\\theta_S^{cv})" + }, + { + "bbox": [ + 304, + 530, + 547, + 648 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 530, + 547, + 648 + ], + "type": "inline_equation", + "content": "g(\\theta_S^{cv})" + }, + { + "bbox": [ + 304, + 530, + 547, + 648 + ], + "type": "text", + "content": " denote the output of the origin model's last convolution layer with parameters " + }, + { + "bbox": [ + 304, + 530, + 547, + 648 + ], + "type": "inline_equation", + "content": "\\theta_S^{cv}" + }, + { + "bbox": [ + 304, + 530, + 547, + 648 + ], + "type": "text", + "content": " and the output from unlearned model's last convolution layer with parameters " + }, + { + "bbox": [ + 304, + 530, + 547, + 648 + ], + "type": "inline_equation", + "content": "\\theta_S^{cv}" + }, + { + "bbox": [ + 304, + 530, + 547, + 648 + ], + "type": "text", + "content": ", respectively. Note that the knowledge of the corresponding channels in the feature maps multiplied by the matrix " + }, + { + "bbox": [ + 304, + 530, + 547, + 648 + ], + "type": "inline_equation", + "content": "G" + }, + { + "bbox": [ + 304, + 530, + 547, + 648 + ], + "type": "text", + "content": " where the value equals one has been transferred. In contrast, the knowledge associated with values equal to 0 has been prohibited." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 651, + 547, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 651, + 547, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 651, + 547, + 714 + ], + "type": "text", + "content": "For the FKT process, we transfer the knowledge of parameters in fully connected (FC) layer " + }, + { + "bbox": [ + 304, + 651, + 547, + 714 + ], + "type": "inline_equation", + "content": "\\theta^{fc} = \\{\\theta_{\\beta}^{fc},\\theta_{\\gamma}^{fc}\\}" + }, + { + "bbox": [ + 304, + 651, + 547, + 714 + ], + "type": "text", + "content": ", in which " + }, + { + "bbox": [ + 304, + 651, + 547, + 714 + ], + "type": "inline_equation", + "content": "\\theta_{\\beta}^{fc}\\in \\mathbb{R}^{K\\times C}" + }, + { + "bbox": [ + 304, + 651, + 547, + 714 + ], + "type": "text", + "content": " denotes the weight, and " + }, + { + "bbox": [ + 304, + 651, + 547, + 714 + ], + "type": "inline_equation", + "content": "\\theta_{\\gamma}^{fc}\\in \\mathbb{R}^{1\\times C}" + }, + { + "bbox": [ + 304, + 651, + 547, + 714 + ], + "type": "text", + "content": " denotes the bias. The FKT process can be executed by directly modifying the original model's parameters of fully" + } + ] + } + ], + "index": 18 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "20150" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 128, + 83 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 128, + 83 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 128, + 83 + ], + "type": "text", + "content": "connected layers as" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 58, + 91, + 287, + 140 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 91, + 287, + 140 + ], + "spans": [ + { + "bbox": [ + 58, + 91, + 287, + 140 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\theta_ {S, \\beta} ^ {f c} = \\theta_ {T, \\beta} ^ {f c} * \\mathcal {A} _ {\\beta}, \\quad \\mathcal {A} _ {\\beta} = (\\underbrace {(\\bar {G} _ {c}) ^ {T} , \\cdots , (\\bar {G} _ {c}) ^ {T}} _ {C}), \\tag {12} \\\\ \\theta_ {S, \\gamma} ^ {f c} = \\theta_ {T, \\gamma} ^ {f c} * \\mathcal {A} _ {\\gamma}, \\quad \\mathcal {A} _ {\\gamma} \\in [ 0, 1 ] ^ {1 \\times C}, \\\\ \\end{array}", + "image_path": "69e6ef2754e129a7221e181ed9cce2b4f8e304c74feab8886e76f82a2077e3f4.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 147, + 287, + 218 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 147, + 287, + 218 + ], + "spans": [ + { + "bbox": [ + 47, + 147, + 287, + 218 + ], + "type": "text", + "content": "where all elements of " + }, + { + "bbox": [ + 47, + 147, + 287, + 218 + ], + "type": "inline_equation", + "content": "\\mathcal{A}_{\\gamma}" + }, + { + "bbox": [ + 47, + 147, + 287, + 218 + ], + "type": "text", + "content": " are equal to 1 except the c-th column, " + }, + { + "bbox": [ + 47, + 147, + 287, + 218 + ], + "type": "inline_equation", + "content": "(\\cdot)^T" + }, + { + "bbox": [ + 47, + 147, + 287, + 218 + ], + "type": "text", + "content": " denotes the matrix transpose operation, and " + }, + { + "bbox": [ + 47, + 147, + 287, + 218 + ], + "type": "inline_equation", + "content": "*" + }, + { + "bbox": [ + 47, + 147, + 287, + 218 + ], + "type": "text", + "content": " denotes the hardamad product operation. Similar to the channel mask " + }, + { + "bbox": [ + 47, + 147, + 287, + 218 + ], + "type": "inline_equation", + "content": "\\bar{G}_c" + }, + { + "bbox": [ + 47, + 147, + 287, + 218 + ], + "type": "text", + "content": ", the FC mask " + }, + { + "bbox": [ + 47, + 147, + 287, + 218 + ], + "type": "inline_equation", + "content": "\\mathcal{A} = \\{\\mathcal{A}_{\\beta}, \\mathcal{A}_{\\gamma}\\}" + }, + { + "bbox": [ + 47, + 147, + 287, + 218 + ], + "type": "text", + "content": " prohibits the knowledge of the FC layer related to the target class of data points." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 219, + 287, + 243 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 219, + 287, + 243 + ], + "spans": [ + { + "bbox": [ + 47, + 219, + 287, + 243 + ], + "type": "text", + "content": "Finally, we update the matrix " + }, + { + "bbox": [ + 47, + 219, + 287, + 243 + ], + "type": "inline_equation", + "content": "G_{S}" + }, + { + "bbox": [ + 47, + 219, + 287, + 243 + ], + "type": "text", + "content": " of the unlearned model through the GKT process by the following equation:" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 90, + 251, + 287, + 265 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 90, + 251, + 287, + 265 + ], + "spans": [ + { + "bbox": [ + 90, + 251, + 287, + 265 + ], + "type": "interline_equation", + "content": "G _ {S} = G _ {T} * \\mathcal {A} _ {G}, \\quad \\mathcal {A} _ {G} \\in [ 0, 1 ] ^ {C \\times K}, \\tag {13}", + "image_path": "bca4426c164d8b2005cd0cdf1a6d5f5c615db288cd499d69c9fdb511ac2e3397.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 274, + 287, + 333 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 274, + 287, + 333 + ], + "spans": [ + { + "bbox": [ + 47, + 274, + 287, + 333 + ], + "type": "text", + "content": "where only the c-th row of the mask matrix " + }, + { + "bbox": [ + 47, + 274, + 287, + 333 + ], + "type": "inline_equation", + "content": "\\mathcal{A}_G" + }, + { + "bbox": [ + 47, + 274, + 287, + 333 + ], + "type": "text", + "content": " is equal to 0, and the others are equal to 1. The updated matrix " + }, + { + "bbox": [ + 47, + 274, + 287, + 333 + ], + "type": "inline_equation", + "content": "G_{S}" + }, + { + "bbox": [ + 47, + 274, + 287, + 333 + ], + "type": "text", + "content": " can visualize which classes of data points have been removed by checking which rows are equal to 0. We summarize the KTP method in Algorithm 2." + } + ] + } + ], + "index": 5 + }, + { + "type": "code", + "bbox": [ + 49, + 375, + 274, + 573 + ], + "blocks": [ + { + "bbox": [ + 53, + 348, + 260, + 371 + ], + "lines": [ + { + "bbox": [ + 53, + 348, + 260, + 371 + ], + "spans": [ + { + "bbox": [ + 53, + 348, + 260, + 371 + ], + "type": "text", + "content": "Algorithm 2: Knowledge Transfer and Prohibition (KTP)" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "code_caption" + }, + { + "bbox": [ + 49, + 375, + 274, + 573 + ], + "lines": [ + { + "bbox": [ + 49, + 375, + 274, + 573 + ], + "spans": [ + { + "bbox": [ + 49, + 375, + 274, + 573 + ], + "type": "text", + "content": "// CKT \n1 for e in epochs do \n2 " + }, + { + "bbox": [ + 49, + 375, + 274, + 573 + ], + "type": "inline_equation", + "content": "f(x;\\theta_T^{cv})\\gets" + }, + { + "bbox": [ + 49, + 375, + 274, + 573 + ], + "type": "text", + "content": " forward propagation through " + }, + { + "bbox": [ + 49, + 375, + 274, + 573 + ], + "type": "inline_equation", + "content": "\\theta_T" + }, + { + "bbox": [ + 49, + 375, + 274, + 573 + ], + "type": "text", + "content": " \n3 " + }, + { + "bbox": [ + 49, + 375, + 274, + 573 + ], + "type": "inline_equation", + "content": "g(x;\\theta_S^{cv})\\gets" + }, + { + "bbox": [ + 49, + 375, + 274, + 573 + ], + "type": "text", + "content": " forward propagation through " + }, + { + "bbox": [ + 49, + 375, + 274, + 573 + ], + "type": "inline_equation", + "content": "\\theta_S" + }, + { + "bbox": [ + 49, + 375, + 274, + 573 + ], + "type": "text", + "content": " \n4 " + }, + { + "bbox": [ + 49, + 375, + 274, + 573 + ], + "type": "inline_equation", + "content": "\\mathcal{L}\\gets \\mathrm{MSE}(f(x;\\theta_T^{cv})\\circ \\bar{G}_c,g(x;\\theta_S^{cv}))" + }, + { + "bbox": [ + 49, + 375, + 274, + 573 + ], + "type": "text", + "content": " \n5 " + }, + { + "bbox": [ + 49, + 375, + 274, + 573 + ], + "type": "inline_equation", + "content": "\\theta_S^{cv}\\gets \\theta_S^{cv} - \\eta \\frac{\\partial\\mathcal{L}}{\\partial\\theta_S^{cv}}" + }, + { + "bbox": [ + 49, + 375, + 274, + 573 + ], + "type": "text", + "content": " \n6 end \n// FKT \n7 " + }, + { + "bbox": [ + 49, + 375, + 274, + 573 + ], + "type": "inline_equation", + "content": "\\theta_{S,\\beta}^{fc} = \\theta_{T,\\beta}^{fc}*\\mathcal{A}_{\\beta}" + }, + { + "bbox": [ + 49, + 375, + 274, + 573 + ], + "type": "text", + "content": " \n8 " + }, + { + "bbox": [ + 49, + 375, + 274, + 573 + ], + "type": "inline_equation", + "content": "\\theta_{S,\\gamma}^{fc} = \\theta_{T,\\gamma}^{fc}*\\mathcal{A}_{\\gamma}" + }, + { + "bbox": [ + 49, + 375, + 274, + 573 + ], + "type": "text", + "content": " \n9 " + }, + { + "bbox": [ + 49, + 375, + 274, + 573 + ], + "type": "inline_equation", + "content": "\\theta_S^{fc} = \\{\\theta_{S,\\beta}^{fc},\\theta_{S,\\gamma}^{fc}\\}" + }, + { + "bbox": [ + 49, + 375, + 274, + 573 + ], + "type": "text", + "content": " \n// GKT \n10 " + }, + { + "bbox": [ + 49, + 375, + 274, + 573 + ], + "type": "inline_equation", + "content": "G_{S} = G_{T}*\\mathcal{A}_{G}" + }, + { + "bbox": [ + 49, + 375, + 274, + 573 + ], + "type": "text", + "content": " \n// Unlearned Model \n11 " + }, + { + "bbox": [ + 49, + 375, + 274, + 573 + ], + "type": "inline_equation", + "content": "\\theta_S = \\{\\theta_S^{cv},G_S,\\theta_S^{fc}\\}" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "code_body" + } + ], + "index": 7, + "sub_type": "algorithm" + }, + { + "bbox": [ + 47, + 587, + 237, + 600 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 587, + 237, + 600 + ], + "spans": [ + { + "bbox": [ + 47, + 587, + 237, + 600 + ], + "type": "text", + "content": "4.3. Machine Unlearning via ERM-KTP" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 605, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 605, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 605, + 287, + 713 + ], + "type": "text", + "content": "Here, we will explain how we combine the ERM structure and KTP method to construct a class-specific knowledge-level machine unlearning approach. We first train the original ERM-CNNs by Algorithm 1. When receiving unlearning requests, we then transfer the remaining dataset's knowledge to the unlearned model by Algorithm 2. Finally, we complete the unlearning process by deleting the original model. The detailed ERM-KTP unlearning algorithm is shown in Algorithm 3." + } + ] + } + ], + "index": 9 + }, + { + "type": "code", + "bbox": [ + 310, + 89, + 478, + 163 + ], + "blocks": [ + { + "bbox": [ + 312, + 75, + 463, + 87 + ], + "lines": [ + { + "bbox": [ + 312, + 75, + 463, + 87 + ], + "spans": [ + { + "bbox": [ + 312, + 75, + 463, + 87 + ], + "type": "text", + "content": "Algorithm 3: ERM-KTP Unlearning" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "code_caption" + }, + { + "bbox": [ + 310, + 89, + 478, + 163 + ], + "lines": [ + { + "bbox": [ + 310, + 89, + 478, + 163 + ], + "spans": [ + { + "bbox": [ + 310, + 89, + 478, + 163 + ], + "type": "text", + "content": "1 " + }, + { + "bbox": [ + 310, + 89, + 478, + 163 + ], + "type": "inline_equation", + "content": "\\theta_T\\gets \\mathrm{AT}(\\theta)" + }, + { + "bbox": [ + 310, + 89, + 478, + 163 + ], + "type": "text", + "content": " \n2 while receiving unlearning requests do \n3 " + }, + { + "bbox": [ + 310, + 89, + 478, + 163 + ], + "type": "inline_equation", + "content": "\\theta_S\\gets \\mathrm{KTP}(\\theta_T)" + }, + { + "bbox": [ + 310, + 89, + 478, + 163 + ], + "type": "text", + "content": " \n4 Delete " + }, + { + "bbox": [ + 310, + 89, + 478, + 163 + ], + "type": "inline_equation", + "content": "\\theta_T" + }, + { + "bbox": [ + 310, + 89, + 478, + 163 + ], + "type": "text", + "content": " \n5 " + }, + { + "bbox": [ + 310, + 89, + 478, + 163 + ], + "type": "inline_equation", + "content": "\\theta_T = \\theta_S" + }, + { + "bbox": [ + 310, + 89, + 478, + 163 + ], + "type": "text", + "content": " \n6 end" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "code_body" + } + ], + "index": 11, + "sub_type": "algorithm" + }, + { + "bbox": [ + 306, + 190, + 386, + 202 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 190, + 386, + 202 + ], + "spans": [ + { + "bbox": [ + 306, + 190, + 386, + 202 + ], + "type": "text", + "content": "5. Experiments" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 209, + 545, + 280 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 209, + 545, + 280 + ], + "spans": [ + { + "bbox": [ + 304, + 209, + 545, + 280 + ], + "type": "text", + "content": "In this section, we empirically evaluate the performance of the proposed unlearning method on three popular image classification benchmarks. All experiments are implemented with Python 3.8 and PyTorch 1.10.1 on a machine with Intel(R) Core(TM) i9-10980XE CPU, 32GB RAM, and a Nvidia 3090 GPU." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 289, + 416, + 300 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 289, + 416, + 300 + ], + "spans": [ + { + "bbox": [ + 306, + 289, + 416, + 300 + ], + "type": "text", + "content": "5.1. Datasets & Models" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 308, + 545, + 403 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 308, + 545, + 403 + ], + "spans": [ + { + "bbox": [ + 304, + 308, + 545, + 403 + ], + "type": "text", + "content": "We evaluate the proposed unlearning method in three public image classification datasets, i.e., CIFAR10, CIFAR100 [9], and Tiny-ImageNet [11]. The input size of CIFAR-10 and CIFAR-100 is " + }, + { + "bbox": [ + 304, + 308, + 545, + 403 + ], + "type": "inline_equation", + "content": "32 \\times 32" + }, + { + "bbox": [ + 304, + 308, + 545, + 403 + ], + "type": "text", + "content": ", and they both contain 50,000 training images and 10,000 for validation. For Tiny-ImageNet, the size of image samples is " + }, + { + "bbox": [ + 304, + 308, + 545, + 403 + ], + "type": "inline_equation", + "content": "224 \\times 224" + }, + { + "bbox": [ + 304, + 308, + 545, + 403 + ], + "type": "text", + "content": ". It contains 200 classes of samples, and each class has 500 samples for training, 50 for validation, and 50 for testing." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 404, + 545, + 487 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 404, + 545, + 487 + ], + "spans": [ + { + "bbox": [ + 304, + 404, + 545, + 487 + ], + "type": "text", + "content": "Moreover, the model structure is three common image classification deep neural networks, ResNet-20, ResNet-50 [6], and ResNeXt-50 [20]. The original models are trained for 200 epochs using Stochastic Gradient Descent (SGD) optimizer with a momentum of 0.9, weight decay of 5e-4, and an initial learning rate of 0.1, divided by 10 after 100 and 150 epochs, respectively." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 495, + 493, + 506 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 495, + 493, + 506 + ], + "spans": [ + { + "bbox": [ + 306, + 495, + 493, + 506 + ], + "type": "text", + "content": "5.2. Effectiveness of the ERM Structure" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 306, + 514, + 544, + 538 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 514, + 544, + 538 + ], + "spans": [ + { + "bbox": [ + 306, + 514, + 544, + 538 + ], + "type": "text", + "content": "In order to evaluate the effectiveness of ERM structure, we propose the following metrics:" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 317, + 546, + 544, + 569 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 546, + 544, + 569 + ], + "spans": [ + { + "bbox": [ + 317, + 546, + 544, + 569 + ], + "type": "text", + "content": "- Cosine similarity (CSI) to analyze the orthogonality of each row of the matrix " + }, + { + "bbox": [ + 317, + 546, + 544, + 569 + ], + "type": "inline_equation", + "content": "G" + }, + { + "bbox": [ + 317, + 546, + 544, + 569 + ], + "type": "text", + "content": " as follows," + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 367, + 578, + 544, + 619 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 367, + 578, + 544, + 619 + ], + "spans": [ + { + "bbox": [ + 367, + 578, + 544, + 619 + ], + "type": "interline_equation", + "content": "\\mathrm {C S I} = \\sum_ {c _ {1} = 0} ^ {C} \\sum_ {\\substack {c _ {2} = 0, \\\\ c _ {1} \\neq c _ {2}}} ^ {C} \\left(\\frac {G _ {c _ {1}} \\cdot G _ {c _ {2}}}{\\| G _ {c _ {1}} \\| \\| G _ {c _ {2}} \\|\\right). \\tag{14}", + "image_path": "44bbcd70e2629f034e3a07a02df3e07264d7416f5d5c8c87621f635e130b7875.jpg" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 317, + 633, + 542, + 644 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 633, + 542, + 644 + ], + "spans": [ + { + "bbox": [ + 317, + 633, + 542, + 644 + ], + "type": "text", + "content": "- " + }, + { + "bbox": [ + 317, + 633, + 542, + 644 + ], + "type": "inline_equation", + "content": "L_{1}" + }, + { + "bbox": [ + 317, + 633, + 542, + 644 + ], + "type": "text", + "content": "-density to evaluate the sparsity of the matrix " + }, + { + "bbox": [ + 317, + 633, + 542, + 644 + ], + "type": "inline_equation", + "content": "G" + }, + { + "bbox": [ + 317, + 633, + 542, + 644 + ], + "type": "text", + "content": " as" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 392, + 653, + 544, + 677 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 392, + 653, + 544, + 677 + ], + "spans": [ + { + "bbox": [ + 392, + 653, + 544, + 677 + ], + "type": "interline_equation", + "content": "L _ {1} \\text {- d e n s i t y} = \\frac {\\| G \\| _ {1}}{C K}. \\tag {15}", + "image_path": "e85365fec91d8dafd44ebc3a771556e6f2d6bb2dd40ae6912ad0aab212fdf911.jpg" + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "type": "text", + "content": "Table 1 shows that the CNNs with the ERM structure have slightly better classification performance than the STD" + } + ] + } + ], + "index": 23 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "20151" + } + ] + } + ], + "index": 24 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 288, + 145 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 288, + 145 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 288, + 145 + ], + "type": "text", + "content": "CNNs. Moreover, the " + }, + { + "bbox": [ + 46, + 72, + 288, + 145 + ], + "type": "inline_equation", + "content": "L_{1}" + }, + { + "bbox": [ + 46, + 72, + 288, + 145 + ], + "type": "text", + "content": "-density convergences to " + }, + { + "bbox": [ + 46, + 72, + 288, + 145 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 46, + 72, + 288, + 145 + ], + "type": "text", + "content": ", and CSI convergences close to 0, meaning each class of data is independent to the other. These metrics quantitatively demonstrate ERM's effectiveness in learning a sparse mask matrix to reduce the entanglement for the following unlearning task without sacrificing classification accuracy." + } + ] + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 48, + 203, + 287, + 290 + ], + "blocks": [ + { + "bbox": [ + 46, + 148, + 288, + 194 + ], + "lines": [ + { + "bbox": [ + 46, + 148, + 288, + 194 + ], + "spans": [ + { + "bbox": [ + 46, + 148, + 288, + 194 + ], + "type": "text", + "content": "Table 1. Metrics of the STD-CNNs and ERM-CNNs. The first row of each two stand for STD-CNNs and the second one stand for ERM-CNNs. " + }, + { + "bbox": [ + 46, + 148, + 288, + 194 + ], + "type": "inline_equation", + "content": "Acc_{val}" + }, + { + "bbox": [ + 46, + 148, + 288, + 194 + ], + "type": "text", + "content": " is the original model's classification accuracy on the validation dataset." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 48, + 203, + 287, + 290 + ], + "lines": [ + { + "bbox": [ + 48, + 203, + 287, + 290 + ], + "spans": [ + { + "bbox": [ + 48, + 203, + 287, + 290 + ], + "type": "table", + "html": "
DatasetModelCKCSIL1-densityAccval
CIFAR10ResNet-20----89.6%
10640.00.192.6%
CIFAR100ResNeXt-50----76.2%
1002,0480.00.0177.6%
Tiny-ImageNetResNet-50----49.3%
2002,0480.00.00553.4%
", + "image_path": "0942aa2ac749b782605c3b5da0c2d196800649fdb7af5dff0dd60f98dd34a143.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 300, + 287, + 385 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 300, + 287, + 385 + ], + "spans": [ + { + "bbox": [ + 46, + 300, + 287, + 385 + ], + "type": "text", + "content": "Moreover, we evaluate if the ERM structure can reduce or eliminate the knowledge entanglement across classes by prohibiting each class's knowledge successively during the ERM path's forward propagation. As shown in Table 2, the classification accuracy will degrade into " + }, + { + "bbox": [ + 46, + 300, + 287, + 385 + ], + "type": "inline_equation", + "content": "0.0\\%" + }, + { + "bbox": [ + 46, + 300, + 287, + 385 + ], + "type": "text", + "content": " for the knowledge-prohibited classes, while the accuracy will remain the same for the knowledge-permitted classes." + } + ] + } + ], + "index": 3 + }, + { + "type": "table", + "bbox": [ + 48, + 446, + 287, + 502 + ], + "blocks": [ + { + "bbox": [ + 46, + 393, + 288, + 437 + ], + "lines": [ + { + "bbox": [ + 46, + 393, + 288, + 437 + ], + "spans": [ + { + "bbox": [ + 46, + 393, + 288, + 437 + ], + "type": "text", + "content": "Table 2. Accuracy of the data points with prohibited or permitted Knowledge. " + }, + { + "bbox": [ + 46, + 393, + 288, + 437 + ], + "type": "inline_equation", + "content": "Acc_{(\\cdot)}^{pro}" + }, + { + "bbox": [ + 46, + 393, + 288, + 437 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 393, + 288, + 437 + ], + "type": "inline_equation", + "content": "Acc_{(\\cdot)}^{per}" + }, + { + "bbox": [ + 46, + 393, + 288, + 437 + ], + "type": "text", + "content": " denote the accuracy of the knowledge-prohibited classes and the knowledge-permitted classes, respectively." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 48, + 446, + 287, + 502 + ], + "lines": [ + { + "bbox": [ + 48, + 446, + 287, + 502 + ], + "spans": [ + { + "bbox": [ + 48, + 446, + 287, + 502 + ], + "type": "table", + "html": "
DatasetModelAccprotrainAccpertrainAccprovalAccperval
CIFAR10ResNet-200.0%97.1%0.0%91.8%
CIFAR100ResNeXt-500.0%99.9%0.0%78.1%
Tiny-ImageNetResNet-500.0%99.9%0.0%53.4%
", + "image_path": "280d3f433bb2e205f41869519b36e8bd05ccd5f289880b17cb09b3bb02736ef4.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "table_body" + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 515, + 287, + 624 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 515, + 287, + 624 + ], + "spans": [ + { + "bbox": [ + 46, + 515, + 287, + 624 + ], + "type": "text", + "content": "We also evaluate the time overhead and memory requirements of the ERM CNNs in the training phase. The computation overhead is the activation map multiplied by the corresponding " + }, + { + "bbox": [ + 46, + 515, + 287, + 624 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 46, + 515, + 287, + 624 + ], + "type": "text", + "content": "-th row of the matrix " + }, + { + "bbox": [ + 46, + 515, + 287, + 624 + ], + "type": "inline_equation", + "content": "G" + }, + { + "bbox": [ + 46, + 515, + 287, + 624 + ], + "type": "text", + "content": " and computing the regulation terms " + }, + { + "bbox": [ + 46, + 515, + 287, + 624 + ], + "type": "inline_equation", + "content": "L_{1}" + }, + { + "bbox": [ + 46, + 515, + 287, + 624 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 515, + 287, + 624 + ], + "type": "inline_equation", + "content": "L_{2}" + }, + { + "bbox": [ + 46, + 515, + 287, + 624 + ], + "type": "text", + "content": ". As shown in Table 3, the time overhead of the ERM structure is comparable to the standard (STD) CNNs, and the additional memory requirements are negligible, which demonstrates that ERM structure has great scalability and can be applied to any CNN structures." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 629, + 287, + 653 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 629, + 287, + 653 + ], + "spans": [ + { + "bbox": [ + 47, + 629, + 287, + 653 + ], + "type": "text", + "content": "5.3. Effectiveness of the ERM-KTP Unlearning Method" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 660, + 287, + 684 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 660, + 287, + 684 + ], + "spans": [ + { + "bbox": [ + 47, + 660, + 287, + 684 + ], + "type": "text", + "content": "We utilize some common metrics to evaluate the effectiveness of the ERM-KTP unlearning method as follows." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 58, + 689, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 689, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 58, + 689, + 287, + 714 + ], + "type": "text", + "content": "- " + }, + { + "bbox": [ + 58, + 689, + 287, + 714 + ], + "type": "inline_equation", + "content": "Acc_{D_r}" + }, + { + "bbox": [ + 58, + 689, + 287, + 714 + ], + "type": "text", + "content": " is the original model's classification accuracy on the training set of the remaining classes." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 317, + 72, + 545, + 213 + ], + "type": "list", + "angle": 0, + "index": 14, + "blocks": [ + { + "bbox": [ + 317, + 72, + 545, + 96 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 72, + 545, + 96 + ], + "spans": [ + { + "bbox": [ + 317, + 72, + 545, + 96 + ], + "type": "text", + "content": "- " + }, + { + "bbox": [ + 317, + 72, + 545, + 96 + ], + "type": "inline_equation", + "content": "Acc_{val}" + }, + { + "bbox": [ + 317, + 72, + 545, + 96 + ], + "type": "text", + "content": " is the original model's classification accuracy on the validation dataset of the remaining classes." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 317, + 103, + 545, + 127 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 103, + 545, + 127 + ], + "spans": [ + { + "bbox": [ + 317, + 103, + 545, + 127 + ], + "type": "text", + "content": "- " + }, + { + "bbox": [ + 317, + 103, + 545, + 127 + ], + "type": "inline_equation", + "content": "Acc_{D_r}'" + }, + { + "bbox": [ + 317, + 103, + 545, + 127 + ], + "type": "text", + "content": " measures the unlearned model's performance on the training set of the remaining classes." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 317, + 134, + 545, + 171 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 134, + 545, + 171 + ], + "spans": [ + { + "bbox": [ + 317, + 134, + 545, + 171 + ], + "type": "text", + "content": "- " + }, + { + "bbox": [ + 317, + 134, + 545, + 171 + ], + "type": "inline_equation", + "content": "\\Delta Acc_{D_r} = Acc_{D_r}' - Acc_{D_r}" + }, + { + "bbox": [ + 317, + 134, + 545, + 171 + ], + "type": "text", + "content": " indicates the difference between the accuracy of the remaining set before and after the unlearning operation." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 317, + 178, + 545, + 213 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 178, + 545, + 213 + ], + "spans": [ + { + "bbox": [ + 317, + 178, + 545, + 213 + ], + "type": "text", + "content": "- " + }, + { + "bbox": [ + 317, + 178, + 545, + 213 + ], + "type": "inline_equation", + "content": "\\Delta Acc_{val} = Acc_{val}' - Acc_{val}" + }, + { + "bbox": [ + 317, + 178, + 545, + 213 + ], + "type": "text", + "content": " indicates the difference between the accuracy of the validation set before and after the unlearning operation." + } + ] + } + ], + "index": 13 + } + ], + "sub_type": "text" + }, + { + "type": "table", + "bbox": [ + 307, + 251, + 545, + 339 + ], + "blocks": [ + { + "bbox": [ + 305, + 220, + 545, + 243 + ], + "lines": [ + { + "bbox": [ + 305, + 220, + 545, + 243 + ], + "spans": [ + { + "bbox": [ + 305, + 220, + 545, + 243 + ], + "type": "text", + "content": "Table 3. Time overhead and memory requirements of the ERM-CNNs and the STD-CNNs in the training phase." + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 307, + 251, + 545, + 339 + ], + "lines": [ + { + "bbox": [ + 307, + 251, + 545, + 339 + ], + "spans": [ + { + "bbox": [ + 307, + 251, + 545, + 339 + ], + "type": "table", + "html": "
DatasetModelStructureTimeMemory
CIFAR10ResNet-20STD1206s2867MiB
ERM1541s2867MiB
CIFAR100ResNeXt-50STD9447s19223MiB
ERM9983s19275MiB
Tiny-ImageNetResNet-50STD5025s6769MiB
ERM6164s6803MiB
", + "image_path": "64be2b569eec93131f32ba1179444ae18a832421b1e2ac1c25513209f9fadb9a.jpg" + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "table_body" + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 354, + 545, + 485 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 354, + 545, + 485 + ], + "spans": [ + { + "bbox": [ + 304, + 354, + 545, + 485 + ], + "type": "text", + "content": "Then, we conduct experiments in the case of unlearning " + }, + { + "bbox": [ + 304, + 354, + 545, + 485 + ], + "type": "inline_equation", + "content": "10\\%" + }, + { + "bbox": [ + 304, + 354, + 545, + 485 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 354, + 545, + 485 + ], + "type": "inline_equation", + "content": "40\\%" + }, + { + "bbox": [ + 304, + 354, + 545, + 485 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 304, + 354, + 545, + 485 + ], + "type": "inline_equation", + "content": "80\\%" + }, + { + "bbox": [ + 304, + 354, + 545, + 485 + ], + "type": "text", + "content": " of classes, respectively. Table 4 shows that " + }, + { + "bbox": [ + 304, + 354, + 545, + 485 + ], + "type": "inline_equation", + "content": "Acc_{D_u}" + }, + { + "bbox": [ + 304, + 354, + 545, + 485 + ], + "type": "text", + "content": " equals " + }, + { + "bbox": [ + 304, + 354, + 545, + 485 + ], + "type": "inline_equation", + "content": "0.0\\%" + }, + { + "bbox": [ + 304, + 354, + 545, + 485 + ], + "type": "text", + "content": " in all cases, demonstrating that ERM-KTP can effectively unlearn target data points. Furthermore, " + }, + { + "bbox": [ + 304, + 354, + 545, + 485 + ], + "type": "inline_equation", + "content": "\\Delta Acc_{D_r}" + }, + { + "bbox": [ + 304, + 354, + 545, + 485 + ], + "type": "text", + "content": " are close to " + }, + { + "bbox": [ + 304, + 354, + 545, + 485 + ], + "type": "inline_equation", + "content": "0.0\\%" + }, + { + "bbox": [ + 304, + 354, + 545, + 485 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 354, + 545, + 485 + ], + "type": "inline_equation", + "content": "\\Delta Acc_{D_r}" + }, + { + "bbox": [ + 304, + 354, + 545, + 485 + ], + "type": "text", + "content": " is greater than " + }, + { + "bbox": [ + 304, + 354, + 545, + 485 + ], + "type": "inline_equation", + "content": "0.0\\%" + }, + { + "bbox": [ + 304, + 354, + 545, + 485 + ], + "type": "text", + "content": " in most cases. These show that ERM-KTP can unlearn target data without affecting the model classification performance, demonstrating the high fidelity of ERM-KTP. In summary, ERM-KTP performs well on all these datasets and model structures, demonstrating the scalability of ERM-KTP." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 306, + 492, + 456, + 504 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 492, + 456, + 504 + ], + "spans": [ + { + "bbox": [ + 306, + 492, + 456, + 504 + ], + "type": "text", + "content": "5.4. Comparison with Baselines" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 305, + 510, + 545, + 535 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 510, + 545, + 535 + ], + "spans": [ + { + "bbox": [ + 305, + 510, + 545, + 535 + ], + "type": "text", + "content": "To further prove the advantage of ERM-KTP, we compare ERM-KTP with the following baseline approaches:" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 317, + 540, + 545, + 713 + ], + "type": "list", + "angle": 0, + "index": 25, + "blocks": [ + { + "bbox": [ + 317, + 540, + 545, + 564 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 540, + 545, + 564 + ], + "spans": [ + { + "bbox": [ + 317, + 540, + 545, + 564 + ], + "type": "text", + "content": "- Retrain from scratch (RfS): Retrain model from scratch with remaining data points " + }, + { + "bbox": [ + 317, + 540, + 545, + 564 + ], + "type": "inline_equation", + "content": "\\mathcal{D}_r" + }, + { + "bbox": [ + 317, + 540, + 545, + 564 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 317, + 571, + 544, + 596 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 571, + 544, + 596 + ], + "spans": [ + { + "bbox": [ + 317, + 571, + 544, + 596 + ], + "type": "text", + "content": "- SISA: Retrain the sub-model whose training set contains the target data points [1]." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 317, + 603, + 544, + 627 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 603, + 544, + 627 + ], + "spans": [ + { + "bbox": [ + 317, + 603, + 544, + 627 + ], + "type": "text", + "content": "- Fine-tune: Fine-tune the model on the remaining data " + }, + { + "bbox": [ + 317, + 603, + 544, + 627 + ], + "type": "inline_equation", + "content": "\\mathcal{D}_r" + }, + { + "bbox": [ + 317, + 603, + 544, + 627 + ], + "type": "text", + "content": " using a slightly larger learning rate." + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 317, + 634, + 545, + 670 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 634, + 545, + 670 + ], + "spans": [ + { + "bbox": [ + 317, + 634, + 545, + 670 + ], + "type": "text", + "content": "- Random Labels (RL): Fine-tune the model on " + }, + { + "bbox": [ + 317, + 634, + 545, + 670 + ], + "type": "inline_equation", + "content": "\\mathcal{D}" + }, + { + "bbox": [ + 317, + 634, + 545, + 670 + ], + "type": "text", + "content": " by randomly resampling labels corresponding to images belonging to the remaining data points " + }, + { + "bbox": [ + 317, + 634, + 545, + 670 + ], + "type": "inline_equation", + "content": "\\mathcal{D}_r" + }, + { + "bbox": [ + 317, + 634, + 545, + 670 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 317, + 677, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 677, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 317, + 677, + 545, + 713 + ], + "type": "text", + "content": "- Amnesiac Unlearning: Track gradient in every training batch. Then, update the model by subtracting the gradients when the batch is marked for removal [4]." + } + ] + } + ], + "index": 24 + } + ], + "sub_type": "text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "20152" + } + ] + } + ], + "index": 26 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 90, + 91, + 502, + 245 + ], + "blocks": [ + { + "bbox": [ + 52, + 71, + 541, + 83 + ], + "lines": [ + { + "bbox": [ + 52, + 71, + 541, + 83 + ], + "spans": [ + { + "bbox": [ + 52, + 71, + 541, + 83 + ], + "type": "text", + "content": "Table 4. Performance evaluation of ERM-KTP unlearning method. #Classes denotes the number of the unlearned classes of data points" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 90, + 91, + 502, + 245 + ], + "lines": [ + { + "bbox": [ + 90, + 91, + 502, + 245 + ], + "spans": [ + { + "bbox": [ + 90, + 91, + 502, + 245 + ], + "type": "table", + "html": "
DatasetModel#ClassesAccDrAccvalAccDuAcc'DrΔAccDrΔAccval
CIFAR10ResNet-20096.8%92.6%----
196.6%91.3%0.0%95.3%-1.3%-1.3%
497.4%96.1%0.0%97.3%-0.1%+3.5%
898.4%97.8%0.0%98.5%+0.1%+3.1%
CIFAR100ResNeXt-50099.9%77.6%----
1099.9%76.1%0.0%98.1%-1.8%-0.6%
4099.9%79.4%0.0%98.4%-1.5%+1.1%
8099.9%86.4%0.0%99.8%-0.1%+7.6%
Tiny-ImageNetResNet-50099.9%53.4%----
2099.9%52.6%0.0%97.6%-2.3%-0.3%
8099.9%53.8%0.0%98.3%-1.6%+1.5%
16099.9%59.3%0.0%97.6%-2.3%+4.4%
", + "image_path": "769f325b52956e016bac1ba668e28b6f0f27d527c0fff8b22d905be79a1f7d80.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 59, + 268, + 288, + 316 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 268, + 288, + 316 + ], + "spans": [ + { + "bbox": [ + 59, + 268, + 288, + 316 + ], + "type": "text", + "content": "- Fisher Unlearning: Perform a corrective Newton step using the Fisher Information Matrix. Add fisher noises sampled from Gaussian distribution to the weight to scrub the information [3]." + } + ] + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 83, + 331, + 252, + 464 + ], + "blocks": [ + { + "bbox": [ + 83, + 331, + 252, + 464 + ], + "lines": [ + { + "bbox": [ + 83, + 331, + 252, + 464 + ], + "spans": [ + { + "bbox": [ + 83, + 331, + 252, + 464 + ], + "type": "image", + "image_path": "28fe54ce2793837aa561a985f0ccf63fb283bf6f37c669a1c18edad3a1530e55.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 473, + 287, + 518 + ], + "lines": [ + { + "bbox": [ + 46, + 473, + 287, + 518 + ], + "spans": [ + { + "bbox": [ + 46, + 473, + 287, + 518 + ], + "type": "text", + "content": "Figure 2. Train the unlearned model with the training datasets, and " + }, + { + "bbox": [ + 46, + 473, + 287, + 518 + ], + "type": "inline_equation", + "content": "\\Delta Acc_{D_u}" + }, + { + "bbox": [ + 46, + 473, + 287, + 518 + ], + "type": "text", + "content": " denotes the difference between the accuracy of the unlearning dataset on the relearned model and the accuracy on the original model on CIFAR10 and ResNet-20." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_caption" + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 522, + 287, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 522, + 287, + 689 + ], + "spans": [ + { + "bbox": [ + 46, + 522, + 287, + 689 + ], + "type": "text", + "content": "Then, we conduct the comparison experiments for " + }, + { + "bbox": [ + 46, + 522, + 287, + 689 + ], + "type": "inline_equation", + "content": "40\\%" + }, + { + "bbox": [ + 46, + 522, + 287, + 689 + ], + "type": "text", + "content": " classes of data points removed. As shown in Table 5, the Amenesiac method [4] stores the gradients of almost every batch, and the model's performance degrades to random guess because it makes the model return to its initial state. For SISA [1], we need to retrain all shards to unlearn target classes of data points because every shard contains the target data points. Also, SISA's validation accuracy is lower by about " + }, + { + "bbox": [ + 46, + 522, + 287, + 689 + ], + "type": "inline_equation", + "content": "6\\%" + }, + { + "bbox": [ + 46, + 522, + 287, + 689 + ], + "type": "text", + "content": " than STD CNNs due to the aggregation operation. Though the literature [3] reports that the Fisher method performs well on All-CNN [17] and CIFAR-10, our experimental results show that it is not suitable for complicated CNNs, e.g., ResNet-20, ResNet-50 [6], and ResNeXt-50 [20]." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 689, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 288, + 715 + ], + "type": "text", + "content": "Note that fine-tune and random labels (RL) methods show great performance on " + }, + { + "bbox": [ + 47, + 689, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\Delta Acc_{D_r}" + }, + { + "bbox": [ + 47, + 689, + 288, + 715 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 689, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\Delta Acc_{val}" + }, + { + "bbox": [ + 47, + 689, + 288, + 715 + ], + "type": "text", + "content": ". How-" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 268, + 545, + 423 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 268, + 545, + 423 + ], + "spans": [ + { + "bbox": [ + 304, + 268, + 545, + 423 + ], + "type": "text", + "content": "ever, these two methods are only an output-level unlearning, i.e., they only change the model's output of the target data points but not remove the corresponding knowledge. To prove that, we fine-tune the unlearned model to observe how long the model can relearn the forget knowledge. As shown in Fig. 2, the Fine-tune and RL method restore the performance on the unlearning dataset at about the 50th epoch, while the relearn time of ERM-KTP method is similar to the RfS method, i.e., they both recover the performance around the 100th epoch. It demonstrates that ERM-KTP can completely remove the target data points like the RfS method, i.e., ERM-KTP is a knowledge-level unlearning method." + } + ] + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 316, + 436, + 421, + 517 + ], + "blocks": [ + { + "bbox": [ + 316, + 436, + 421, + 517 + ], + "lines": [ + { + "bbox": [ + 316, + 436, + 421, + 517 + ], + "spans": [ + { + "bbox": [ + 316, + 436, + 421, + 517 + ], + "type": "image", + "image_path": "db80f615976325037f7e707c893af6c32fe1fe8d376d06f846b52c4a1a2b6e9d.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 354, + 521, + 380, + 529 + ], + "lines": [ + { + "bbox": [ + 354, + 521, + 380, + 529 + ], + "spans": [ + { + "bbox": [ + 354, + 521, + 380, + 529 + ], + "type": "text", + "content": "(a) CSI" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 433, + 436, + 539, + 518 + ], + "blocks": [ + { + "bbox": [ + 433, + 436, + 539, + 518 + ], + "lines": [ + { + "bbox": [ + 433, + 436, + 539, + 518 + ], + "spans": [ + { + "bbox": [ + 433, + 436, + 539, + 518 + ], + "type": "image", + "image_path": "dbb7aeca50952eb07ba9718e148ff7b399e7b4ad4bb6224313af388c9cb9c572.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 461, + 520, + 510, + 530 + ], + "lines": [ + { + "bbox": [ + 461, + 520, + 510, + 530 + ], + "spans": [ + { + "bbox": [ + 461, + 520, + 510, + 530 + ], + "type": "text", + "content": "(b) " + }, + { + "bbox": [ + 461, + 520, + 510, + 530 + ], + "type": "inline_equation", + "content": "L_{1}" + }, + { + "bbox": [ + 461, + 520, + 510, + 530 + ], + "type": "text", + "content": "-density" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 304, + 540, + 545, + 562 + ], + "lines": [ + { + "bbox": [ + 304, + 540, + 545, + 562 + ], + "spans": [ + { + "bbox": [ + 304, + 540, + 545, + 562 + ], + "type": "text", + "content": "Figure 3. Ablation experiments of our proposed regulation terms on CIFAR100 and ResNet-50." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "content": "For the efficiency comparison, we conduct the experiments on CIFAR10 and ResNet-20 because some methods can not be implemented on the other two settings, e.g., Fisher method needs more than 200 hours in TinyImageNet. As shown in Table 6, ERM-KTP improves by " + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "inline_equation", + "content": "5 \\times" + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "content": " compared to RfS, " + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "inline_equation", + "content": "5.4 \\times" + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "content": " compared to SISA, and " + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "inline_equation", + "content": "42 \\times" + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "content": " compared to Fisher. Though the time overhead of Finetune is less than ERM-KTP, Fine-tune method is only an output-level unlearning method, as mentioned above. In summary, compared with these baseline approaches, ERM-KTP is more effective, more efficient, and has better scalability." + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "20153" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 74, + 91, + 518, + 355 + ], + "blocks": [ + { + "bbox": [ + 86, + 71, + 506, + 83 + ], + "lines": [ + { + "bbox": [ + 86, + 71, + 506, + 83 + ], + "spans": [ + { + "bbox": [ + 86, + 71, + 506, + 83 + ], + "type": "text", + "content": "Table 5. Unlearning performance comparison with baseline approaches when unlearning " + }, + { + "bbox": [ + 86, + 71, + 506, + 83 + ], + "type": "inline_equation", + "content": "{40}\\%" + }, + { + "bbox": [ + 86, + 71, + 506, + 83 + ], + "type": "text", + "content": " classes of data points." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 74, + 91, + 518, + 355 + ], + "lines": [ + { + "bbox": [ + 74, + 91, + 518, + 355 + ], + "spans": [ + { + "bbox": [ + 74, + 91, + 518, + 355 + ], + "type": "table", + "html": "
DatasetModelApproachAccDrAccvalAccDuAcc'DrΔAccDrΔAccval
CIFAR10ResNet-20STD99.9%93.7%----
RfS99.9%96.3%0.0%99.8%-0.1%+2.6%
Fine-tune99.9%97.0%0.0%99.8%-0.1%+3.3%
RL99.9%97.0%0.0%99.8%-0.1%+3.3%
SISA92.4%91.0%0.0%92.8%+0.4%+0.2%
Fisher99.9%54.0%48.4%53.0%-46.9%-25.1%
Amnesiac99.9%9.0%0.0%15.4%-84.5%-84.7%
ERM-KTP (ours)97.4%96.1%0.0%97.3%-0.1%+3.5%
CIFAR100ResNeXt-50STD99.9%78.9%----
RfS99.9%79.6%0.0%99.9%0.0%+0.7%
RL99.9%78.1%0.0%99.7%0.0%-0.8%
Fisher99.9%1.0%0.0%1.0%-98.9%-77.9%
Fine-tune99.9%83.4%0.0%99.9%0.0%+4.5%
Amnesiac99.9%0.89%0.0%1.0%-98.9%-77.8%
ERM-KTP (ours)99.9%79.4%0.0%98.4%-1.5%+1.1%
Tiny-ImageNetResNet-50STD99.9%48.3%----
RfS99.9%45.1%0.0%99.9%0.0%-3.2%
RL99.9%43.4%0.0%96.7%-3.2%-4.9%
SISA67.6%52.8%0.0%68.0%+0.4%-1.3%
Fine-tune99.9%50.0%0.0%99.9%0.0%+1.7%
Amnesiac99.9%0.3%0.8%0.7%-99.2%-48.0%
ERM-KTP (ours)99.9%53.8%0.0%98.3%-1.6%+1.5%
", + "image_path": "7969e00a82257e2fe4bf0e745575ac14378a2754d69de68f770aa1b945dd0459.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "type": "table", + "bbox": [ + 66, + 407, + 267, + 495 + ], + "blocks": [ + { + "bbox": [ + 47, + 376, + 287, + 396 + ], + "lines": [ + { + "bbox": [ + 47, + 376, + 287, + 396 + ], + "spans": [ + { + "bbox": [ + 47, + 376, + 287, + 396 + ], + "type": "text", + "content": "Table 6. Unlearn time comparison with baselines on CIFAR10 and ResNet-20." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 66, + 407, + 267, + 495 + ], + "lines": [ + { + "bbox": [ + 66, + 407, + 267, + 495 + ], + "spans": [ + { + "bbox": [ + 66, + 407, + 267, + 495 + ], + "type": "table", + "html": "
ApproachTimeΔAccDrΔAccval
RfS668s-1.7%+1.7%
SISA672s+0.4%+0.2%
Fine-tune492s-0.2%+2.4%
RL68s-1.5%+1.4%
Fisher5162s-46.9%-25.1%
ERM-KTP (ours)124s-1.6%+2.0%
", + "image_path": "266a357959021df3edf05b04f0ab721952a33e8bc04326016756fae056e8bdb0.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 523, + 173, + 537 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 523, + 173, + 537 + ], + "spans": [ + { + "bbox": [ + 47, + 523, + 173, + 537 + ], + "type": "text", + "content": "5.5. Ablation Experiments" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "content": "To further demonstrate that our proposed regulation terms are effective, we conduct an ablation experiment on CIFAR100 and ResNet-50 by setting the hyper-parameters as: (1) " + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\lambda_{1} = 1" + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\lambda_{2} = 1 \\times 10^{-3}" + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\lambda_{3} = 0" + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "content": "; (2) " + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\lambda_{1} = 1" + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\lambda_{2} = 0" + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\lambda_{3} = 5 \\times 10^{-4}" + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "content": "; (3) " + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\lambda_{1} = 1" + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\lambda_{2} = 1 \\times 10^{-3}" + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\lambda_{3} = 5 \\times 10^{-4}" + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "content": ". Fig. 3 demonstrates that applying both " + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "inline_equation", + "content": "L_{2}" + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "inline_equation", + "content": "L_{3}" + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "content": " achieves the best performance and convergence to the optimal value. Only using the " + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "inline_equation", + "content": "L_{2}" + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "content": " regulation term (Eq. (4)), the " + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "inline_equation", + "content": "L_{1}" + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "content": "-density tends to 0.01, but the CSI convergences to around 3,500. It illustrates that the " + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "inline_equation", + "content": "L_{1}" + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "content": "-norm regulation term can find the spars solution, but the " + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "inline_equation", + "content": "L_{1}" + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "content": "-norm does not constrain the relative position, which leads to the high value of CSI. However, the " + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "inline_equation", + "content": "L_{1}" + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "content": "-norm can make both CSI and " + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "inline_equation", + "content": "L_{1}" + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "content": "-density convergence to a lower value when the" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 305, + 377, + 545, + 413 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 377, + 545, + 413 + ], + "spans": [ + { + "bbox": [ + 305, + 377, + 545, + 413 + ], + "type": "text", + "content": "inner-product regulation term (Eq. (6)) is used. Furthermore, the inner-product can make both two values descend more quickly." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 424, + 378, + 436 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 424, + 378, + 436 + ], + "spans": [ + { + "bbox": [ + 306, + 424, + 378, + 436 + ], + "type": "text", + "content": "6. Conclusion" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 444, + 545, + 612 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 444, + 545, + 612 + ], + "spans": [ + { + "bbox": [ + 304, + 444, + 545, + 612 + ], + "type": "text", + "content": "In this paper, we propose an interpretable knowledge-level unlearning method, ERM-KTP, for the class-specific unlearning task. We propose the ERM structure to tackle the challenge of high knowledge entanglement. Then, we transfer the knowledge of the remaining set from the original model to the unlearned model via our proposed KTP method. Finally, we delete the original model to accomplish the unlearning task. The interpretability brought by the EMR structure and the crafted masks in KTP enhances the reliability of the unlearning. Extensive experiments demonstrate the effectiveness, fidelity, efficiency, and scalability of our proposed ERM-KTP unlearning method. For future work, we attempt to solve the entanglement of each single data point to tackle the sample-specific unlearning task." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 614, + 545, + 686 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 614, + 545, + 686 + ], + "spans": [ + { + "bbox": [ + 304, + 614, + 545, + 686 + ], + "type": "text", + "content": "Acknowledgments. This work was supported in part by the National Natural Science Foundation of China under Grant 61960206014, 62102300, and 62121001, in part by the China 111 Project under Grant B16037, in part by the Fundamental Research Funds for the Central Universities under Grant XJS211510." + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "20154" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 288, + 712 + ], + "type": "list", + "angle": 0, + "index": 15, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 146 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 146 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 146 + ], + "type": "text", + "content": "[1] Lucas Bourtoule, Varun Chandrasekaran, Christopher A Choquette-Choo, Hengrui Jia, Adelin Travers, Baiwu Zhang, David Lie, and Nicolas Papernot. 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In Proceedings of the IEEE conference on computer vision and pattern recognition, pages 2921-2929, 2016. 1" + } + ] + } + ], + "index": 23 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "20155" + } + ] + } + ], + "index": 25 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 8 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/ERNIE-ViLG 2.0_ Improving Text-to-Image Diffusion Model With Knowledge-Enhanced Mixture-of-Denoising-Experts/4f139481-82b6-4525-8567-38b399fee431_content_list.json b/2023/ERNIE-ViLG 2.0_ Improving Text-to-Image Diffusion Model With Knowledge-Enhanced Mixture-of-Denoising-Experts/4f139481-82b6-4525-8567-38b399fee431_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..1c947a6fc9e98d242f6fdf85e9c9201494fe00ae --- /dev/null +++ b/2023/ERNIE-ViLG 2.0_ Improving Text-to-Image Diffusion Model With Knowledge-Enhanced Mixture-of-Denoising-Experts/4f139481-82b6-4525-8567-38b399fee431_content_list.json @@ -0,0 +1,1692 @@ +[ + { + "type": "text", + "text": "ERNIE-ViLG 2.0: Improving Text-to-Image Diffusion Model with Knowledge-Enhanced Mixture-of-Denoising-Experts", + "text_level": 1, + "bbox": [ + 151, + 130, + 818, + 176 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Zhida Feng $^{1,2,*}$ , Zhenyu Zhang $^{1,*}$ , Xintong Yu $^{1,*}$ , Yewei Fang $^{1}$ , Lanxin Li $^{1}$ , Xuyi Chen $^{1}$ , Yuxiang Lu $^{1}$ , Jiaxiang Liu $^{1}$ , Weichong Yin $^{1}$ , Shikun Feng $^{1}$ , Yu Sun $^{1}$ , Li Chen $^{2}$ , Hao Tian $^{1}$ , Hua Wu $^{1}$ , Haifeng Wang $^{1}$ , Baidu Inc.", + "bbox": [ + 86, + 202, + 898, + 253 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "$^{2}$ School of Computer Science and Technology, Wuhan University of Science and Technology", + "bbox": [ + 125, + 256, + 861, + 273 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "{fengzhida, zhangzhenyu07, yuxintong}@baidu.com", + "bbox": [ + 281, + 277, + 699, + 291 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "{liujiaxiang,yinweichong,fengshikun01,sunyu02}@baidu.com", + "bbox": [ + 228, + 295, + 751, + 309 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/707fa99cdcc4d576d9c2f8e907d41f88327e0247bc04e674602eac832e69f6b9.jpg", + "image_caption": [ + "一艘青花瓷质感的战舰" + ], + "image_footnote": [], + "bbox": [ + 91, + 344, + 287, + 494 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/caf4242fde8f54d392ae440aae6920c49b8f7569d7f5b51db9ff487d130d61ee.jpg", + "image_caption": [ + "精致面容的古风少女,头戴百鸟鲜花头冠" + ], + "image_footnote": [], + "bbox": [ + 287, + 344, + 483, + 496 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/606c314d25146c80a24afedda1f27ec7e77e4c99bdd64b4baedef3a13c972b61.jpg", + "image_caption": [ + "一只仙鹤站在平静的湖面上,后面有一轮云雾缭绕的明月" + ], + "image_footnote": [], + "bbox": [ + 485, + 344, + 681, + 496 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/4193d9300ead1c0f5d0bd6bb2579c863c9ff672a8e62108272dda1d2975e3bc8.jpg", + "image_caption": [ + "穿西装的孙悟空的特写镜头" + ], + "image_footnote": [], + "bbox": [ + 683, + 344, + 879, + 496 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/9bb256365f25edfba25eadf053308d71b75bd0623ff891b114db0f73609c7d70.jpg", + "image_caption": [ + "A warship with blue and white porcelain texture", + "狮子王身穿紫色皇家大衣,身披红色皇家斗篷,正在发表史诗级的演说The Lion King, wearing a purple royal coat and a red royal cloak, is delivering an epic speech", + "Figure 1. Selected $1024\\times 1024$ samples with various text inputs, which shows that ERNIE-ViLG 2.0 has powerful capabilities of fine-grained semantic control and high-resolution image synthesis, as well as to produce high-quality creative images of different styles." + ], + "image_footnote": [], + "bbox": [ + 89, + 550, + 287, + 703 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/6c3b2885bb300e83563407d9874d9791909c60ce26bb8c2161052bd10fa6a175.jpg", + "image_caption": [ + "An ancient style girl with delicate face, wearing a crown of birds and flowers", + "雪地里的熊猫宝宝戴着红帽子、黄手套,穿着绿毛衣和蓝裤子A baby panda in the snow, wearing red hat, yellow gloves, green sweater and blue pants" + ], + "image_footnote": [], + "bbox": [ + 287, + 550, + 483, + 703 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/3548b0143b12c917cf618a0c012c8a4da2463d74d8ee210ef928cb157eefe40f.jpg", + "image_caption": [ + "A crane is standing on the calm lake, with a bright moon surrounded by clouds in the background", + "一只欢快的柯基行走在夕阳里, \n光从右边打来铺成一地金黄 \nA cheerful Koji is walking in the sunset, \nthe golden light comes from the right side and spreads all over the ground", + "泰迪熊穿着戏服,站在太和殿前唱京剧" + ], + "image_footnote": [], + "bbox": [ + 485, + 550, + 681, + 703 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/a99d53906ab3815a43560babcd6bb768a61b7bec54dbfacff9298ab1b6244fa2.jpg", + "image_caption": [ + "The close up of Sun Wukong in a suit", + "A teddy bear, wearing a costume, is standing in front of the Hall of Supreme Harmony and singing Beijing opera" + ], + "image_footnote": [], + "bbox": [ + 683, + 550, + 879, + 703 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 809, + 313, + 825 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Recent progress in diffusion models has revolutionized the popular technology of text-to-image generation. While exist-", + "bbox": [ + 75, + 843, + 470, + 873 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "ing approaches could produce photorealistic high-resolution images with text conditions, there are still several open problems to be solved, which limits the further improvement of image fidelity and text relevancy. In this paper, we propose ERNIE-ViLG 2.0, a large-scale Chinese text-to-image", + "bbox": [ + 500, + 811, + 893, + 888 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 810, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "* denotes equal contribution. Work done during Feng's internship at Baidu.", + "bbox": [ + 73, + 886, + 467, + 900 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "10135", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "diffusion model, to progressively upgrade the quality of generated images by: (1) incorporating fine-grained textual and visual knowledge of key elements in the scene, and (2) utilizing different denoising experts at different denoising stages. With the proposed mechanisms, ERNIE-ViLG $2.0^{1}$ not only achieves a new state-of-the-art on MS-COCO with zero-shot FID-30k score of 6.75, but also significantly outperforms recent models in terms of image fidelity and image-text alignment, with side-by-side human evaluation on the bilingual prompt set ViLG-300.", + "bbox": [ + 75, + 90, + 472, + 243 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 273, + 209, + 289 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Recent years have witnessed incredible progress in text-to-image generation. With large-scale training data and model parameters, kinds of text-to-image generation models are now able to vividly depict the visual scene described by a text prompt, and enable anyone to create exquisite images without sophisticated drawing skills. Among all types of image generation approaches, diffusion models [9] are attracting increasing attention due to their ability to produce highly photorealistic images conditioned on text prompts. Given a text prompt, the models transform a Gaussian noise into an image that conforms to the prompt through iterative denoising steps. In the past years, text-to-image diffusion models such as LDM [25], GLIDE [18], DALL-E 2 [22], and Imagen [26] have achieved impressive performance in both text relevancy and image fidelity. Despite these advances, the exploration of diffusion models by existing methods is still at the initial stage. When we go deep into the principle and implementation of text-to-image diffusion models, there are still many opportunities to improve the quality of generated images further.", + "bbox": [ + 75, + 299, + 472, + 601 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "First, during the learning process of each denoising step, all text tokens interact with image regions and all the image regions contribute equally to the final loss function. However, a visual scene of text and image contains many elements (i.e., textual words and visual objects), and different elements usually hold different importance for the expression of the scene semantics [42]. The indiscriminate learning process may cause the model to miss some key elements and interactions in the scene, thus facing the risk of text-image misalignment, such as the attribute confusion problem, especially for text prompts containing multiple objects with specific attributes [22]. Second, when opening the horizon from individual step to the whole denoising process, we can found that the requirements of different denoising stages are also not identical. In the early stages, the input images are highly noised, and the model is required to outline the semantic layout and skeleton out of almost pure noise. By contrast, in the later steps close to the image output, denois", + "bbox": [ + 75, + 602, + 472, + 875 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "ing mainly means improving the details based on an almost completed image [25]. In practice, existing models usually use one U-Net for all steps, which means that the same set of parameters has to learn different denoising capabilities.", + "bbox": [ + 496, + 90, + 890, + 151 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In this paper, we propose ERNIE-ViLG 2.0, an improved text-to-image diffusion model with knowledge-enhanced mixture-of-denoising-experts, to incorporate extra knowledge about the visual scene and decouple the denoising capabilities in different steps. Specifically, we employ a text parser and an object detector to extract key elements of the scene in the input text-image pair, and then guide the model to pay more attention to their alignment in the learning process, so as to hope the model could handle the relationships among various objects and attributes. Moreover, we divide the denoising steps into several stages and employ specific denoising \"experts\" for each stage. With the mixture of multiple experts, the model can involve more parameters and learn the data distribution of each denoising stage better, without increasing the inference time, as only one expert is activated in each denoising step.", + "bbox": [ + 496, + 152, + 893, + 393 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "With the extra knowledge from the visual scene and the mixture-of-denoising-experts mechanism, we train ERNIE-ViLG 2.0 and scale up the model size to 24B parameters. Experiments on MS-COCO show that our model exceeds previous text-to-image models by setting a new state-of-the-art of 6.75 zeros-shot FID-30k score, and detailed ablation studies confirm the contributions of each proposed strategy. Apart from automatic metrics, we also collect 300 bilingual text prompts that could assess the quality of generated images from different aspects and enable a fair comparison between English and Chinese text-to-image models. The human evaluation results again indicate that ERNIE-ViLG 2.0 outperforms other recent methods, including DALL-E 2 [22] and Stable Diffusion [25], by a significant margin both in terms of image-text alignment and image fidelity.", + "bbox": [ + 496, + 393, + 893, + 619 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To sum up, the main contributions of this work are: (1) We incorporate textual and visual knowledge into the text-to-image diffusion model, which effectively improves the ability of fine-grained semantic control and alleviates the problem of object-attribute mismatching in generated images. (2) We propose the mixture-of-denoising-experts mechanism to refine the denoising process, which can adapt to the characteristics of different denoising steps and scale up the model to 24B parameters, making it the largest text-to-image model at present. (3) ERNIE-ViLG 2.0 achieves the state-of-the-art zero-shot FID-30k score of 6.75 on MS-COCO, surpasses DALL-E 2 and Stable Diffusion in human evaluation on the Chinese-English bilingual prompt set ViLG-300.", + "bbox": [ + 496, + 619, + 893, + 816 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Method", + "text_level": 1, + "bbox": [ + 500, + 829, + 591, + 845 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "During the training process, the text-to-image diffusion model receives paired inputs $(x,y)$ consisting of an image $x$ with its text description $y$ , and the ultimate goal is to gener", + "bbox": [ + 496, + 854, + 893, + 902 + ], + "page_idx": 1 + }, + { + "type": "page_footnote", + "text": "1https://wenxin.baidu.com/ernie-vilg", + "bbox": [ + 94, + 886, + 380, + 898 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "10136", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/98703e8653de4112f825824710d507010fa1422127f54a65a0bdf648e7351202.jpg", + "image_caption": [ + "Figure 2. The architecture of ERNIE-ViLG 2.0, which incorporates fine-grained textual and visual knowledge of key elements in the scene and utilizes different denoising experts at different denoising stages." + ], + "image_footnote": [], + "bbox": [ + 117, + 88, + 441, + 265 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/aabd235a83b03c753b6aca05d13216b85403057063e044f0a025e03c7b8b3695.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 446, + 88, + 851, + 263 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "ate $x$ based on $y$ . To achieve this, a text encoder $f_{\\theta}(\\cdot)$ first encodes $y$ as $f_{\\theta}(y)$ , then a denoising network $\\epsilon_{\\theta}(\\cdot)$ conditioned on $f_{\\theta}(y)$ learns to generate $x$ from a Gaussian noise. To help the model generate high-quality images that accurately match the text description (i.e., text prompt), ERNIE-ViLG 2.0 enhances text encoder $f_{\\theta}(\\cdot)$ and denoising network $\\epsilon_{\\theta}(\\cdot)$ with textual and visual knowledge of key elements in the scene. Furthermore, ERNIE-ViLG 2.0 employs mixture-of-denoising-experts to refine the image generation process, where different experts are responsible for different generation steps in the denoising process. The overall architecture of ERNIE-ViLG 2.0 is shown in Figure 2 and the details are described in the following subsections.", + "bbox": [ + 75, + 330, + 473, + 527 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "2.1. Preliminary", + "text_level": 1, + "bbox": [ + 76, + 536, + 207, + 553 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Denoising diffusion probabilistic models (DDPM) are a class of score-based generative models that have recently shown delightful talents in the field of text-to-image generation [9]. The diffusion process of DDPM aims to iteratively add diagonal Gaussian noise to the initial data sample $x$ and turn it into an isotropic Gaussian distribution after $T$ steps:", + "bbox": [ + 75, + 559, + 470, + 650 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nx _ {t} = \\sqrt {\\alpha_ {t}} x _ {t - 1} + \\sqrt {1 - \\alpha_ {t}} \\epsilon_ {t}, \\quad t \\in \\{1, \\dots , T \\} \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 125, + 657, + 468, + 674 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where the sequence $\\{x_{t}\\}$ starts with $x_0 = x$ and ends with $x_{T} \\sim \\mathcal{N}(0, I)$ , the added noise at each step is $\\epsilon_{t} \\sim \\mathcal{N}(0, I)$ , and $\\{\\alpha_{t}\\}_{1 \\ldots T}$ is a pre-defined schedule [30, 32]. The denoising process is the reverse of diffusion, which converts the Gaussian noise $x_{T} \\sim \\mathcal{N}(0, I)$ back into the data distribution $x_{0}$ through iterative denoising steps $t = T, \\ldots, 1$ . During training, for a given image $x$ , the model calculates $x_{t}$ by sampling a Gaussian noise $\\epsilon \\sim \\mathcal{N}(0, I)$ :", + "bbox": [ + 75, + 680, + 470, + 801 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nx _ {t} = \\sqrt {\\bar {\\alpha} _ {t}} x _ {0} + \\sqrt {1 - \\bar {\\alpha} _ {t}} \\epsilon , \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 189, + 808, + 468, + 825 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\bar{\\alpha}_t = \\prod_{s=1}^t \\alpha_s$ . Given $x_t$ , the target of the denoising network $\\epsilon_\\theta(\\cdot)$ is to restore $x_0$ by predicting the noise $\\epsilon$ . It is learned via the loss function", + "bbox": [ + 75, + 830, + 468, + 878 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} = \\mathbb {E} _ {x, \\epsilon \\sim \\mathcal {N} (0, I), t} \\left[ | | \\epsilon - \\epsilon_ {\\theta} (x _ {t}, t) | | _ {2} ^ {2} \\right]. \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 153, + 883, + 468, + 902 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "With the predicted $\\epsilon_{\\theta}(x_t,t)$ , we can have the prediction of $x_0$ at step $t$ by converting Equation (2):", + "bbox": [ + 498, + 330, + 890, + 362 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {x} _ {0, t} = \\frac {1}{\\sqrt {\\bar {\\alpha} _ {t}}} \\left(x _ {t} - \\sqrt {1 - \\bar {\\alpha} _ {t}} \\epsilon_ {\\theta} \\left(x _ {t}, t\\right)\\right). \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 576, + 366, + 890, + 396 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In Figure 2, we visualize the sampled $x_{t}$ and the predicted $\\hat{x}_{0,t}$ for several timesteps during training. In the inference process of DDPM, $x_{0}$ is unknown, so the model iteratively generates $x_{t-1}$ based on $x_{t}$ and $\\hat{x}_{0,t}$ :", + "bbox": [ + 498, + 398, + 892, + 460 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} x _ {t - 1} = \\frac {1 - \\bar {\\alpha} _ {t - 1}}{1 - \\bar {\\alpha} _ {t}} \\sqrt {\\alpha_ {t}} x _ {t} + \\frac {1 - \\alpha_ {t}}{1 - \\bar {\\alpha} _ {t}} \\sqrt {\\bar {\\alpha} _ {t - 1}} \\hat {x} _ {0, t} \\tag {5} \\\\ + \\sqrt {\\frac {(1 - \\bar {\\alpha} _ {t - 1}) (1 - \\alpha_ {t})}{1 - \\bar {\\alpha} _ {t}}} \\epsilon_ {t} ^ {\\prime}, \\quad t \\in \\{T, \\dots , 1 \\}, \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 517, + 465, + 890, + 526 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\epsilon_t^\\prime \\sim \\mathcal{N}(0,I)$ is a sampled Gaussian noise.", + "bbox": [ + 498, + 530, + 823, + 546 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The denoising network $\\epsilon_{\\theta}(\\cdot)$ is typically implemented by U-Net [9]. To allow $\\epsilon_{\\theta}(\\cdot)$ to condition on text prompts, a text encoder $f_{\\theta}(\\cdot)$ first extracts the text representation $f_{\\theta}(y) \\in \\mathbb{R}^{n_y \\times d_y}$ , which is then fed into $\\epsilon_{\\theta}(\\cdot)$ via a cross-modal attention layer [18]. Formally, the U-Net representation $\\varphi_i(x_t) \\in \\mathbb{R}^{n_x \\times d}$ is concatenated with the text representation $f_{\\theta}(y)$ after projection, and then goes through an attention layer to achieve cross-modal interaction,", + "bbox": [ + 498, + 547, + 893, + 667 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} Q = \\varphi_ {i} (x _ {t}) W _ {Q} ^ {(i)}, \\\\ K = \\left[ \\varphi_ {i} \\left(x _ {t}\\right) W _ {K _ {x}} ^ {(i)}; f _ {\\theta} (y) W _ {K _ {y}} ^ {(i)} \\right], (6) \\\\ V = \\left[ \\varphi_ {i} \\left(x _ {t}\\right) W _ {V _ {x}} ^ {(i)}; f _ {\\theta} (y) W _ {V _ {y}} ^ {(i)} \\right], \\\\ \\operatorname {A t t e n t i o n} (Q, K, V) = \\operatorname {s o f t m a x} \\left(\\frac {Q K ^ {\\top}}{\\sqrt {d}}\\right) V, (7) \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 553, + 672, + 890, + 772 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $i$ is the index for U-Net layers, $[;]$ is the concatenation operator, $W_{Q}^{(i)}, W_{K_{x}}^{(i)}, W_{V_{x}}^{(i)} \\in \\mathbb{R}^{d \\times d}$ and $W_{K_{y}}^{(i)}, W_{V_{y}}^{(i)} \\in \\mathbb{R}^{d_{y} \\times d}$ are learnable projection layers, $n_{x}$ and $n_{y}$ are the length of encoded image and text, respectively.", + "bbox": [ + 498, + 773, + 893, + 840 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "During inference, given a text prompt $y$ , the denoising U-Net $\\epsilon_{\\theta}(\\cdot)$ predicts the image sample $x$ conditioned on the text $y$ with classifier-free guidance [10] and Denoising Diffusion Implicit Models (DDIM) sampling [31].", + "bbox": [ + 498, + 840, + 890, + 901 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "10137", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "2.2. Knowledge-Enhanced Diffusion Model", + "text_level": 1, + "bbox": [ + 76, + 90, + 410, + 106 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The text-to-image model receives a text prompt that describes the scene of an image, then depicts it with crucial objects and corresponding attribute details. In other words, both text and image are intended to express a visual scene, in which key elements have different expressions, such as keywords in text or salient regions in image. However, naive diffusion model does not distinguish the importance of elements and indiscriminately iterates the denoising process. ERNIE-ViLG 2.0 incorporates extra text and visual knowledge into the learning stage, hoping to enhance the fine-grained semantic perception of diffusion model.", + "bbox": [ + 75, + 113, + 470, + 279 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Textual Knowledge. An ideal text-to-image model is expected to focus on all the critical semantics mentioned in the text prompt. To distinguish function words and words describing key semantics, we adopt an off-the-shelf part-of-speech toolkit to extract lexical knowledge of the input prompt, and then improve the learning process by (1) inserting special tokens into the input sequence and (2) increasing the weight of tokens with specific part-of-speech tags in the attention layer. Specifically, we selected $50\\%$ of samples and inserted special tokens at the beginning of each word, in which each part-of-speech tag corresponds to a special token. For the selected samples, we also strengthen the attention weight of keywords based on the lexical analysis results. In this way, Equation (7) is modified to,", + "bbox": [ + 75, + 279, + 473, + 491 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\operatorname {A t t e n t i o n} (Q, K, V) ^ {\\prime} = \\operatorname {s o f t m a x} \\left(\\frac {W _ {a} \\cdot \\left(Q K ^ {\\top}\\right)}{\\sqrt {d}}\\right) V, \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 99, + 498, + 470, + 530 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $W_{a} \\in \\mathbb{R}^{n_{x} \\times (n_{x} + n_{y})}$ is an auxiliary weight matrix that used to scale the vanilla attention, and", + "bbox": [ + 75, + 537, + 468, + 570 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nW _ {a} ^ {i j} = \\left\\{ \\begin{array}{c c} 1 + w _ {a} & t o k _ {i} \\in \\{x \\}, t o k _ {j} \\in \\{x, y _ {k e y} \\} \\\\ 1 & \\text {o t h e r w i s e .} \\end{array} \\right. \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 112, + 575, + 468, + 606 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Here $w_{a}^{ij}$ is the scaling factor of the attention weight between token $tok_{i}$ and $tok_{j}$ , $w_{a}$ is a hyper-parameter, $x$ refers to all the image tokens, and $y_{key}$ denotes the keywords in $text^{2}$ . Figure 2 gives an example, where special tokens “[a]” and “[n)” are inserted for adjectives and nouns, respectively.", + "bbox": [ + 75, + 614, + 468, + 691 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Visual Knowledge. Similar to notional words in the text prompt, there are also salient regions in an image, such as people, trees, buildings, and objects mentioned in the input. To extract such visual knowledge, we apply an object detector [1] to $50\\%$ of training samples, and then select eye-catching objects from the results with heuristic strategies. Since the loss function of the diffusion model directly acts on the image space, we can assign higher weights to corresponding regions by modifying Equation (3), thus promoting the model to focus on the generation of these objects:", + "bbox": [ + 75, + 691, + 470, + 843 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} ^ {\\prime} = \\mathbb {E} _ {z, \\epsilon \\sim \\mathcal {N} (0, I), t} \\left[ W _ {l} \\cdot | | \\epsilon - \\epsilon_ {\\theta} (z _ {t}, t) | | _ {2} ^ {2} \\right], \\tag {10}\n$$\n", + "text_format": "latex", + "bbox": [ + 137, + 849, + 468, + 867 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nW _ {l} ^ {i j} = \\left\\{ \\begin{array}{c c} 1 + w _ {l} & \\operatorname {l o s} _ {i j} \\in \\left\\{x _ {\\text {k e y}} \\right\\} \\\\ 1 & \\text {o t h e r w i s e .} \\end{array} \\right. \\tag {11}\n$$\n", + "text_format": "latex", + "bbox": [ + 578, + 88, + 890, + 118 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Here $W_{l} \\in \\mathbb{R}^{n_{h} \\times n_{w}}$ is the weight matrix, $n_{h}$ and $n_{w}$ are the height and weight of image space, $w_{l}$ is a hyper-parameter, $los_{ij}$ is the loss item in $i$ -th row and $j$ -th column of image space, $x_{key}$ is the regions that corresponding to key objects. As Figure 2 illustrates, the regions of \"dog\" and \"cat\" are assigned with larger weights in the calculation of $\\mathcal{L}'$ .", + "bbox": [ + 496, + 123, + 893, + 214 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Now a new problem arises: as a kind of fine-grained knowledge, the selected objects may not appear in the text prompt, thus perplexing the model in learning the alignment between words and objects. An intuitive idea is first to obtain the object and attribute category of each region, then combine corresponding class labels with the original text prompt to achieve fine-grained description, thus ensuring the input contains both coarse and fine granularity information. For instance, as shown in Figure 2, the detected object \"bowl\" is not included in the caption, so we append it to the original description. Besides, we also employ an image captioning model [38] to generate text for images, and randomly replace the original prompt with generated captions, because the generated captions of many images are more concise and reveal more accurate semantics than original prompts.", + "bbox": [ + 496, + 214, + 893, + 441 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Most notably, the above strategies are only limited to the training stage. By randomly selecting a part of samples to equip these additional enhancement strategies, the model is supposed to sense the hints of knowledge from various perspectives, and generate higher quality images for the given text in the inference stage, even without special tokens, attention strengthening, or text refinement.", + "bbox": [ + 496, + 441, + 893, + 547 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "2.3. Mixture-of-Denoising-Experts", + "text_level": 1, + "bbox": [ + 500, + 559, + 767, + 574 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Recall that the diffusion process is to iteratively corrupt the image with Gaussian noises by a series of diffusion steps $t = 1, \\dots, T$ , and DDPM [9] are trained to revert the diffusion process by denoising steps $t = T, \\dots, 1$ . During the denoising process, all steps aim to denoise a noised input, and they together convert a completely random noise into a meaningful image gradually. Although sharing the same goal, the difficulty of these denoising steps varies according to the noise ratio of input. Figure 2 illustrates such difference by presenting some examples of $x_{t}$ and the denoising prediction $\\hat{x}_{0,t}$ during training. For timesteps $t$ near $T$ , such as $t = T, t_{k}, t_{j}$ in the figure, the input of the denoising network $x_{t}$ is highly noised, and the network of these steps mainly tackles a generation task, i.e., generating an image from a noise. On the contrary, for timesteps $t$ near 1, such as $t = t_{i}, 1$ , the input $x_{t}$ is close to the original image, and the network of these steps needs to refine the image details.", + "bbox": [ + 496, + 582, + 893, + 839 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "DDPM makes no specific assumption on the implementation of denoising network, that is, the denoising process does not require the same denoising network for all steps in theory. However, most of the previous text-to-image diffusion ap", + "bbox": [ + 496, + 839, + 893, + 901 + ], + "page_idx": 3 + }, + { + "type": "page_footnote", + "text": "2The keywords is defined as notional words in modern Chinese (i.e., nouns, verbs, adjectives, numerals, quantifiers, and pronouns).", + "bbox": [ + 76, + 875, + 470, + 901 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "10138", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "proaches [18,22,25,26] follow the vanilla implementation to adopt a denoising network for the whole denoising process. Considering that tasks of different timesteps are different, we conjecture that using the same set of parameters to learn different tasks might lead to suboptimal performance.", + "bbox": [ + 75, + 90, + 468, + 167 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In view of this, we further propose Mixture-of-Denoising-Experts (MoDE), where the primary motivation is to employ multiple specialized expert networks to fit different tasks at different timesteps. Since the inputs of adjacent timesteps are similar and so are the denoising tasks, we divide all the timesteps uniformly into $n$ blocks $(S_{1},\\dots ,S_{i},\\dots ,S_{n})$ in which each block consists of consecutive timesteps and is assigned to one denoising expert. In other words, the timesteps in the same block are denoised by the same group of network parameters. In practice, we share the same text encoder for all denoising experts, and utilize different U-Net experts for different timestep blocks:", + "bbox": [ + 75, + 167, + 473, + 349 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\epsilon_ {\\theta} \\left(x _ {t}, t\\right) = \\left\\{\\epsilon_ {\\theta , i} \\left(x _ {t}, t\\right) \\right\\}, \\quad t \\in S _ {i}, \\tag {12}\n$$\n", + "text_format": "latex", + "bbox": [ + 165, + 359, + 468, + 376 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\epsilon_{\\theta ,i}(x_t,t)$ is the $i$ -th expert network. Herein, MoDE improves the model performance by adopting expert networks to specially deal with different denoising stages.", + "bbox": [ + 75, + 385, + 468, + 431 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Intuitively, when using more experts, each block contains fewer timesteps, so each expert could better focus on learning the characteristics of specific denoising steps assigned to it. Meanwhile, as only one expert network is activated at each step, increasing the number of experts does not affect the computation overhead during inference. Therefore, ERNIE-ViLG 2.0 can flexibly scale up the parameters of diffusion model, allowing the experts to fit the data distribution better without increasing inference time.", + "bbox": [ + 75, + 431, + 473, + 568 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3. Experiments", + "text_level": 1, + "bbox": [ + 76, + 582, + 209, + 599 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In this section, we first introduce the implementation details of ERNIE-ViLG 2.0. Then we present the comparison of models with automatic metrics and human evaluation. Last, we further analyze the results with quantitative ablation studies and qualitative showcases.", + "bbox": [ + 75, + 607, + 468, + 683 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.1. Implementation Details", + "text_level": 1, + "bbox": [ + 76, + 693, + 294, + 709 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "To reduce learning complexity, we use diffusion models to generate the representations of images in latent space of an image auto-encoder following Latent Diffusion Models [25]. We first pre-train an image encoder to transform an image $x \\in \\mathbb{R}^{n_h \\times n_w \\times 3}$ from pixel space into latent space $\\hat{x} \\in \\mathbb{R}^{n_h^l \\times n_w^l \\times 4}$ and an image decoder to convert it back. Here $n_h / n_h^l$ and $n_w / n_w^l$ denote the image's original/latent height and width, and we collectively refer to pixel space and hidden space as image space in this paper. Then we fix the auto-encoder and train the diffusion model to generate $\\hat{x}$ from text prompt $y$ . During inference, we adopt the pre-trained image decoder to turn $\\hat{x}$ into pixel-level image output.", + "bbox": [ + 75, + 717, + 473, + 902 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/3c99dfdd509beb7985cb4747f408bd66dd92e5eb9b4167326d2a1c948c82533e.jpg", + "table_caption": [ + "Table 1. Comparison of ERNIE-ViLG 2.0 and representative text-to-image generation models on MS-COCO $256 \\times 256$ with zero-shot FID-30k. We use classifier-free guidance scale 2.1 for our diffusion model and achieve the best performance." + ], + "table_footnote": [], + "table_body": "
ModelZero-Shot FID-30k ↓
DALL-E [23]27.50
CogView [2]27.10
LAFITE [46]26.94
LDM [25]12.61
ERNIE-ViLG [45]14.70
GLIDE [18]12.24
Make-A-Scene [6]11.84
DALL-E 2 [22]10.39
CogView2 [3]24.00
Imagen [26]7.27
Parti [43]7.23
ERNIE-ViLG 2.06.75
", + "bbox": [ + 557, + 156, + 836, + 361 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "ERNIE-ViLG 2.0 contains a transformer-based text encoder with 1.3B parameters and 10 denoising U-Net experts with 2.2B parameters each, which totally add up to about 24B parameters. For hyper-parameters to incorporate knowledge, the attention weight scale $w_{a}$ is set to 0.01 and the loss weight scale $w_{l}$ is set to 0.1 (both chosen from [0.01, 0.1, 0.5, 1]). For the MoDE strategy, all timesteps are divided into 10 blocks. The model is optimized by AdamW [15], with a fixed learning rate $0.9 \\times 10^{-4}$ , $\\beta_{1} = 0.9$ , $\\beta_{2} = 0.999$ , and weight decay of 0.01. We train ERNIE-ViLG 2.0 on 320 Tesla A100 GPUs for 18 days.", + "bbox": [ + 496, + 386, + 893, + 551 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The training data consists of 170M image-text pairs, including publicly available English datasets like LAION [28] and a series of internal Chinese datasets. The image autoencoder is trained on the same set. For images with English captions, we translate them with Baidu Translate API3 to get the Chinese version.", + "bbox": [ + 496, + 553, + 893, + 643 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.2. Results", + "text_level": 1, + "bbox": [ + 500, + 654, + 591, + 669 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Automatic Evaluation on MS-COCO. Following previous work [22, 25, 26], we evaluate ERNIE-ViLG 2.0 on MS-COCO $256 \\times 256$ with zero-shot FID-30k, where 30,000 images from the validation set are randomly selected and the English captions are automatically translated to Chinese.", + "bbox": [ + 496, + 678, + 893, + 753 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Table 1 shows that ERNIE-ViLG 2.0 achieves new state-of-the-art performance of text-to-image generation, with 6.75 zero-shot FID-30k on MS-COCO. Inspired by DALL-E [23] and Parti [43], we rerank the batch-sampled images (with only 4 images per text prompt, comparing with 512 images used in DALL-E and 16 images used in Parti) based on the image-text alignment score, calculated by a pre-trained CLIP model [21], in which the text is the initial English", + "bbox": [ + 496, + 753, + 893, + 876 + ], + "page_idx": 4 + }, + { + "type": "page_footnote", + "text": "3https://fanyi.baidu.com", + "bbox": [ + 514, + 886, + 709, + 898 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "10139", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/7e71d91cd4297fd38746c6412c13349d89479d497c5ec14c1b5b64613668dd21.jpg", + "image_caption": [ + "(a) v.s. DALL-E 2." + ], + "image_footnote": [], + "bbox": [ + 83, + 94, + 271, + 172 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/c200b365a9c7dbf5c7cdfa01ca6752e50e7fc0e275975856cd976839467f8e58.jpg", + "image_caption": [ + "(b) v.s. Stable Diffusion." + ], + "image_footnote": [], + "bbox": [ + 276, + 94, + 464, + 172 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/651ac096b4c4cfe97e804d7d1ccd0605c7ac6e8cc6dd6e2f044f89e552f1135a.jpg", + "image_caption": [ + "Figure 3. Comparison of ERNIE-ViLG 2.0 and DALL-E 2/Stable Diffusion on ViLG-300 with human evaluation. We report the user preference rates with $95\\%$ confidence intervals.", + "Figure 4. Qualitative Comparison of ERNIE-ViLG 2.0 and DALL-E 2/Stable Diffusion on ViLG-300." + ], + "image_footnote": [ + "(1) A green cup and a blue cell phone (2) A wine glass on top of a dog \n(3) Zongzi and corn boiled in the pot (4) Cherry blossom, digital oil painting" + ], + "bbox": [ + 83, + 258, + 452, + 452 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "caption in MS-COCO and the image is generated from the auto-translated Chinese caption. Besides, even without the reranking strategy, we find that ERNIE-ViLG 2.0 can also beat the latest diffusion-based models like DALL-E 2 [22] and Imagen [26], with the zero-shot FID-30k of 7.23.", + "bbox": [ + 75, + 542, + 468, + 618 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Human Evaluation on ViLG-300. ERNIE-ViLG 2.0 takes Chinese prompts as input and generates high-resolution images, unlike recent English-oriented text-to-image models. Herein, we introduce ViLG-3004, a bilingual prompt set that supports the systematic evaluation and comparison of Chinese and English text-to-image models. ViLG-300 contains 300 prompts from 16 categories, composed of Draw-Bench [26] (in English) and the prompt set used in ERNIE-ViLG [45] (in Chinese).", + "bbox": [ + 75, + 619, + 468, + 755 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "With ViLG-300, we can make convincing comparisons between ERNIE-ViLG 2.0 and DALL-E $2^{5}$ , Stable Diffusion $^{67}$ . For evaluation, five raters are presented with two sets", + "bbox": [ + 75, + 756, + 468, + 801 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/11d548238597a109c14f4d0bb66136530abf393ee35e9fdbd9a05531481cfe33.jpg", + "image_caption": [ + "(a) Knowledge enhancement." + ], + "image_footnote": [], + "bbox": [ + 514, + 95, + 679, + 172 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/0ed21de18038d5d08c8ff3b22e790c5399e6863d6dc48e6d00b92f48a8f5444b.jpg", + "image_caption": [ + "(b) Mixture-of-denoising-experts." + ], + "image_footnote": [], + "bbox": [ + 702, + 95, + 875, + 172 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/bd405357ab018fbe892aa23985a9177836dea1af05bd7e00f52a6cb11164cad4.jpg", + "image_caption": [ + "Figure 5. Performance with various strategies in ERNIE-ViLG 2.0. Here we draw pareto curves with guidance scale [2,3,4,5,6,7,8,9].", + "Figure 6. Samples from ViLG-300 with different knowledge enhancement strategies (left) and different number of experts (right)." + ], + "image_footnote": [], + "bbox": [ + 503, + 244, + 888, + 431 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "of images generated by ERNIE-ViLG 2.0 and the compared model. Next, they are asked to compare these images from two dimensions of image-text alignment and image fidelity, and then select the model they prefer, or respond that there is no measurable difference between two models. Throughout the process, raters are unaware of which model the image is generated from, and we do not apply any filtering strategy to the rating results. Figure 3 shows that human raters prefer ERNIE-ViLG 2.0 over all other models in both imagedtext alignment (56.5%±3.8% and 68.2%±3.8% when compared to DALL-E 2 and Stable Diffusion, respectively) and image fidelity (58.8%±3.6% to DALL-E 2, 66.5%±3.5% to Stable Diffusion, respectively), which again proves that ERNIE-ViLG 2.0 can generate high-quality images that conform to the text, with the help of knowledge enhancement and mixture-of-denoising-experts strategies. Beyond text relevancy and image fidelity, we also observe that ERNIE-ViLG 2.0 can generate images with better sharpness and textures than baseline models.", + "bbox": [ + 496, + 500, + 893, + 786 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "3.3. Analysis", + "text_level": 1, + "bbox": [ + 500, + 800, + 601, + 816 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "To examine the effectiveness of our design philosophy, we conduct two groups of ablation studies. Similar to the main experiment, we also provide both automatic metrics and intuitive showcases to demonstrate the advantages of each strategy in ERNIE-ViLG 2.0 here.", + "bbox": [ + 496, + 825, + 893, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_footnote", + "text": "4https://github.com/PaddlePaddle/ERNIE/tree/ernie-kit-open-v1.0/Research/ERNIE-ViLG2/data/ViLG-300.csv", + "bbox": [ + 75, + 813, + 468, + 849 + ], + "page_idx": 5 + }, + { + "type": "page_footnote", + "text": "5 https://openai.com/dall-e-2/", + "bbox": [ + 96, + 849, + 325, + 863 + ], + "page_idx": 5 + }, + { + "type": "page_footnote", + "text": "$^{6}$ https://beta.dreamstudio.ai/dream", + "bbox": [ + 96, + 863, + 364, + 875 + ], + "page_idx": 5 + }, + { + "type": "page_footnote", + "text": "7We use DALL-E 2 and Stable Diffusion interfaces to generate images on October 25, 2022, before the CVPR 2023 submission deadline.", + "bbox": [ + 78, + 875, + 468, + 898 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "10140", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/6abde2dc5018772b695b8234b609d73aaceea3c7f700cfdcfc7647e0baf61952.jpg", + "image_caption": [ + "Figure 7. The visualization of cross-attention maps in different denoising timesteps, where each value in the image space is the average of attention from this image token to all text tokens." + ], + "image_footnote": [], + "bbox": [ + 80, + 90, + 467, + 141 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Knowledge Enhancement Strategies. In this part, we focus on the impact of various knowledge enhancement strategies by training a series of lightweight models, with 500M text encoders, 870M U-Nets, and 500M training samples. The pareto curves in Figure 5a demonstrate that incorporating knowledge in the learning process brings significant performance gains in image fidelity and image-text alignment. Specifically, (1) the benefits of textual knowledge are mainly reflected in precise fine-grained semantic control (w/ textual), (2) only utilizing object knowledge may not be able to steadily promote the performance (w/ object), while taking synthetic descriptions into consideration is an effective solution to make full use of visual knowledge (w/ visual). Figure 6 provides more visual comparisons to intuitively demonstrate the changes brought by each strategy. When handling complex prompts, baseline model faces problems such as the absence of key objects or incorrect assignment of attributes. At this point, textual knowledge helps the model accurately understand the attributes of each object, but the generated images sometimes fall into a new problem of distortion. Complementarily, visual knowledge promotes the generation of high-fidelity images, but it cannot well understand specific entities in text. Eventually, the combination of two kinds of knowledge harmoniously promotes the model from single- and multi-modal views, which ensures high fidelity and boost the image-text alignment in fine-grained visual scene.", + "bbox": [ + 76, + 232, + 472, + 640 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Mixture-of-Denoising-Experts Strategies. Based on the above lightweight settings, we further train the baseline model with 500M samples, and then train 200M samples for each denoising expert. Figure 5b shows that with the increasing number of denoising experts, the overall performance is gradually improved, proving that scaling the size of U-Net is also an effective solution to achieve better image quality. More showcases are provided in Figure 6. When the number of experts increases from 1 to 10, the model can not only better handle the coupling between different elements but also generate images with more natural textures. For instance, the numbers on clocks become clearer, the proportion of wolf and suit becomes more harmonious, and the model can generate more photorealistic pictures instead of cartoon drawings. We also tried to analyze the impact of the amount of denoising experts and training samples, and found that using more expert networks has better performance than", + "bbox": [ + 76, + 643, + 472, + 901 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "using a network to train more samples.", + "bbox": [ + 498, + 92, + 758, + 106 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Figure 7 further visualizes the cross-attention maps from image features to text representations in denoising experts during 1,000-step denoising process, where these steps shown are denoised by different experts. As shown in the illustration, attentions of different denoising timesteps vary. Specifically, the attention maps of timesteps $t$ near 1,000 are almost evenly distributed over the whole image, which is because the input of these steps is close to Gaussian noise and the image layout is unclear, so all the image tokens have to attend to the text prompt to generate image skeleton. When the timesteps are close to 1, attention maps concentrate more on foreground objects. For these timesteps, the input to denoising network is close to the final image and the layout is clear, and only a few parts of the image need to focus on the text to fill in the details of object. These observations again illustrate the difference among denoising timesteps and demonstrate the need to disentangle different timesteps with multiple experts.", + "bbox": [ + 496, + 106, + 893, + 378 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4. Related Work", + "text_level": 1, + "bbox": [ + 498, + 392, + 640, + 407 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Text-to-Image Generation. Text-to-image generation is the task of synthesizing images according to natural language descriptions. Early works adopted generative adversarial networks [7] to produce images based on text [36,41,44,47]. Inspired by the success of transformers in various generation tasks [37], models such as ERNIE-ViLG [45], DALL-E [23], Cogview [2], Make-A-Scene [6], and Parti [43] have also explored text-to-image generation as a sequence-to-sequence problem, with auto-regressive transformers as generators and text/image tokens as input/output sequences. Recently, another line of works have applied diffusion models [30], shaping it as an iterative denoising task [9, 27, 31]. By adding text condition in the denoising steps, practices such as LDM [25], DALL-E 2 [22], and Imagen [26] constantly set new records in text-to-image generation. Based on diffusion models as the backbone, ERNIE-ViLG 2.0 proposes incorporating knowledge of scene and mixture-of-denoising-experts mechanism into the denoising process.", + "bbox": [ + 496, + 417, + 893, + 688 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Knowledge-Enhanced Pre-trained Models. While transformers benefit from pre-training on large-scale data, many attempts have been adding knowledge to guide them to focus on key elements during learning. For language-based tasks, knowledge-enhanced models used knowledge masking strategy [11, 34] or knowledge-aware pre-training tasks [33, 35] to understand the language data distribution. As for vision-language multi-modal discrimination models, OSCAR [14], ERNIE-ViL [42] and ERNIE-Layout [19] leveraged object tags, scene graphs, and document layouts as extra knowledge to help the models better align language and vision modalities. Among multi-modal generation models, Make-A-Scene [6] emphasized the importance of object and face regions by integrating domain-specific perceptual knowledge.", + "bbox": [ + 496, + 689, + 895, + 901 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "10141", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "While current text-to-image diffusion models suffer from attribute misalignment problems [22], they have not employed any specific knowledge of objects. Herein, ERNIE-ViLG 2.0 utilizes the knowledge of key elements in images and text to enhance diffusion models, leading to better fine-grained image-text alignment in generated pictures.", + "bbox": [ + 75, + 90, + 472, + 181 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Mixture-of-Expert. Mixture-of-Experts (MoE) in neural networks means dividing specific parts of the parameters into subsets, each of which is called an expert [4, 29]. During the forward pass, a router assigns experts to different input, and each input only interacts with the experts assigned to. The router is a critical part of MoE. In language tasks, the most common strategy is a matching algorithm that assigns each text token to several experts in the linear feed-forward layer [5, 8, 12, 24]. While most practices formulate multiple experts in only the linear layers, some works also use an entire language model as an expert [13]. Beyond the natural language processing tasks, the idea of MoE have also been applied to vision models [20] and Mixture-of-Modality-Expert in multi-modal transformers [17, 39, 40]. In ERNIE-ViLG 2.0, the MoDE mechanism takes multiple denoising U-Nets as experts. It uses the denoising step index as the fixed router to determine which expert to use.", + "bbox": [ + 75, + 181, + 472, + 439 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Risks, Limitations, and Future Work", + "text_level": 1, + "bbox": [ + 76, + 452, + 410, + 468 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Model Usage and Data Bias. Text-to-image generation models trained by large-scale image-text data have all faced similar risks regarding to inappropriate usage of generation and data bias [22, 25, 26]. Considering that text-to-image models help people realize their imagination with less effort, the malicious use of models may result in unexpected deceptive or harmful outcomes. Moreover, since the models are trained on datasets consisting of images and their alt-text crawled from websites, the generated images may exhibit social and cultural bias in the datasets and websites.", + "bbox": [ + 75, + 477, + 470, + 628 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Character Rendering. Figure 8 shows two successful character rendering cases (a, b) and one failure case (c). Character rendering is a challenging task for ERNIE-ViLG 2.0 for two reasons. First, the training data contains both Chinese text-image pairs and English text-image pairs translated into Chinese. When a text prompt mentions characters, the characters in the image could be in Chinese or English, and it is hard for the model to learn corresponding characters in both languages simultaneously. In the cases of successful character rendering that we observed, the characters could be words that are common in Chinese and do not have an exact match in English, such as “福” (“blessing, happiness, good luck” in English) in Figure 8a, or numbers which are the same in English and Chinese images, such as “20” in Figure 8b. The second reason that makes character rendering difficult is probably that Chinese characters are complex combinations of strokes without basic components like English letters. In Figure 8c, the model does learn that it should write some", + "bbox": [ + 75, + 628, + 473, + 901 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/b97a5f692b3780d04e0e32031357ab30ec5464f7290f70a8442c416ee5c9bfa1.jpg", + "image_caption": [ + "(a)国风福字挂饰", + "A hanging ornament with \"福\" in Chinese fashion", + "(b) 生日蛋糕上有蜡烛“20”", + "Figure 8. Examples of character rendering. The model successfully renders simple characters specified in the prompt, while for more difficult cases, the model only learns the position for now." + ], + "image_footnote": [], + "bbox": [ + 506, + 88, + 625, + 180 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/713143af1965d7c0112976ad94198564fe85c634f050019293a96141e9c8d472.jpg", + "image_caption": [ + "A birthday cake with candles of \"20\" on it" + ], + "image_footnote": [], + "bbox": [ + 633, + 88, + 754, + 180 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/8a821fd422a15738138005f0abb2d82f6d515c43120bdde1abe7cf5d0caf6791.jpg", + "image_caption": [ + "(c)国画葡萄", + "Chinese painting of grapes" + ], + "image_footnote": [], + "bbox": [ + 763, + 88, + 882, + 180 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Chinese characters in the top right corner, but it only paints meaningless strokes there.", + "bbox": [ + 498, + 300, + 890, + 329 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Variation of Mixture-of-Denoising-Experts. Section 3.3 shows that using more denoising experts leads to better model performance. It indicates that using parallel U-Net experts is an effective way to augment the denoising network. Due to the computation limitation, we only try using up to 10 experts in this work, while we believe that exploring more denoising experts and multiple text encoders as experts is a meaningful future direction. Herein, we can further scale up the model and allow it to learn data distribution better with similar inference time.", + "bbox": [ + 498, + 330, + 892, + 479 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "6. Conclusions", + "text_level": 1, + "bbox": [ + 500, + 494, + 625, + 508 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We present ERNIE-ViLG 2.0, the first Chinese large-scale text-to-image generation model based on diffusion models. To improve the fine-grained control of scene semantics, we incorporate visual and textual knowledge of the scene into diffusion models. To disentangle the model parameters for different denoising timesteps, we introduce MoDE and scale up the model parameters to 24B with a relatively short inference time. Experiments show that ERNIE-ViLG 2.0 achieves state-of-the-art on MS-COCO and each proposed mechanism contributes to the final results. To allow fair comparisons between Chinese and English text-to-image models, we collect a bilingual prompt set ViLG-300, and human evaluation indicates that ERNIE-ViLG 2.0 is preferred over strong baselines in both text relevancy and image fidelity. Further analysis suggests that different knowledge sources improve the generation in different aspects, and using more experts results in better image quality. In the future, we intend to enrich external image-text alignment knowledge and expand the usage of multiple experts to advance the generation. See also Appendix for more details on training and evaluation.", + "bbox": [ + 498, + 518, + 893, + 821 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgement This work was partly supported by National Natural Science Foundation of China (62271359). We thank Yehan Zheng for help on dataset collection; Weixin Liu and Bin Shan for discussions on paper.", + "bbox": [ + 498, + 839, + 893, + 902 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "10142", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Peter Anderson, Xiaodong He, Chris Buehler, Damien Teney, Mark Johnson, Stephen Gould, and Lei Zhang. Bottom-up and top-down attention for image captioning and visual question answering. 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In IEEE Conference on Computer Vision and Pattern Recognition, CVPR 2019, Long Beach, CA," + ], + "bbox": [ + 78, + 90, + 470, + 900 + ], + "page_idx": 10 + }, + { + "type": "text", + "text": "USA, June 16-20, 2019, pages 5802-5810. 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Selected \\(1024\\times 1024\\) samples with various text inputs, which shows that ERNIE-ViLG 2.0 has powerful capabilities of fine-grained semantic control and high-resolution image synthesis, as well as to produce high-quality creative images of different styles." + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.81, + 0.314, + 0.827 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.844, + 0.471, + 0.874 + ], + "angle": 0, + "content": "Recent progress in diffusion models has revolutionized the popular technology of text-to-image generation. While exist-" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.812, + 0.895, + 0.889 + ], + "angle": 0, + "content": "ing approaches could produce photorealistic high-resolution images with text conditions, there are still several open problems to be solved, which limits the further improvement of image fidelity and text relevancy. In this paper, we propose ERNIE-ViLG 2.0, a large-scale Chinese text-to-image" + }, + { + "type": "page_footnote", + "bbox": [ + 0.075, + 0.887, + 0.468, + 0.901 + ], + "angle": 0, + "content": "* denotes equal contribution. Work done during Feng's internship at Baidu." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "10135" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.244 + ], + "angle": 0, + "content": "diffusion model, to progressively upgrade the quality of generated images by: (1) incorporating fine-grained textual and visual knowledge of key elements in the scene, and (2) utilizing different denoising experts at different denoising stages. With the proposed mechanisms, ERNIE-ViLG \\(2.0^{1}\\) not only achieves a new state-of-the-art on MS-COCO with zero-shot FID-30k score of 6.75, but also significantly outperforms recent models in terms of image fidelity and image-text alignment, with side-by-side human evaluation on the bilingual prompt set ViLG-300." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.274, + 0.21, + 0.29 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.3, + 0.473, + 0.602 + ], + "angle": 0, + "content": "Recent years have witnessed incredible progress in text-to-image generation. With large-scale training data and model parameters, kinds of text-to-image generation models are now able to vividly depict the visual scene described by a text prompt, and enable anyone to create exquisite images without sophisticated drawing skills. Among all types of image generation approaches, diffusion models [9] are attracting increasing attention due to their ability to produce highly photorealistic images conditioned on text prompts. Given a text prompt, the models transform a Gaussian noise into an image that conforms to the prompt through iterative denoising steps. In the past years, text-to-image diffusion models such as LDM [25], GLIDE [18], DALL-E 2 [22], and Imagen [26] have achieved impressive performance in both text relevancy and image fidelity. Despite these advances, the exploration of diffusion models by existing methods is still at the initial stage. When we go deep into the principle and implementation of text-to-image diffusion models, there are still many opportunities to improve the quality of generated images further." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.603, + 0.473, + 0.875 + ], + "angle": 0, + "content": "First, during the learning process of each denoising step, all text tokens interact with image regions and all the image regions contribute equally to the final loss function. However, a visual scene of text and image contains many elements (i.e., textual words and visual objects), and different elements usually hold different importance for the expression of the scene semantics [42]. The indiscriminate learning process may cause the model to miss some key elements and interactions in the scene, thus facing the risk of text-image misalignment, such as the attribute confusion problem, especially for text prompts containing multiple objects with specific attributes [22]. Second, when opening the horizon from individual step to the whole denoising process, we can found that the requirements of different denoising stages are also not identical. In the early stages, the input images are highly noised, and the model is required to outline the semantic layout and skeleton out of almost pure noise. By contrast, in the later steps close to the image output, denois" + }, + { + "type": "text", + "bbox": [ + 0.497, + 0.092, + 0.892, + 0.152 + ], + "angle": 0, + "content": "ing mainly means improving the details based on an almost completed image [25]. In practice, existing models usually use one U-Net for all steps, which means that the same set of parameters has to learn different denoising capabilities." + }, + { + "type": "text", + "bbox": [ + 0.497, + 0.153, + 0.895, + 0.394 + ], + "angle": 0, + "content": "In this paper, we propose ERNIE-ViLG 2.0, an improved text-to-image diffusion model with knowledge-enhanced mixture-of-denoising-experts, to incorporate extra knowledge about the visual scene and decouple the denoising capabilities in different steps. Specifically, we employ a text parser and an object detector to extract key elements of the scene in the input text-image pair, and then guide the model to pay more attention to their alignment in the learning process, so as to hope the model could handle the relationships among various objects and attributes. Moreover, we divide the denoising steps into several stages and employ specific denoising \"experts\" for each stage. With the mixture of multiple experts, the model can involve more parameters and learn the data distribution of each denoising stage better, without increasing the inference time, as only one expert is activated in each denoising step." + }, + { + "type": "text", + "bbox": [ + 0.497, + 0.394, + 0.895, + 0.621 + ], + "angle": 0, + "content": "With the extra knowledge from the visual scene and the mixture-of-denoising-experts mechanism, we train ERNIE-ViLG 2.0 and scale up the model size to 24B parameters. Experiments on MS-COCO show that our model exceeds previous text-to-image models by setting a new state-of-the-art of 6.75 zeros-shot FID-30k score, and detailed ablation studies confirm the contributions of each proposed strategy. Apart from automatic metrics, we also collect 300 bilingual text prompts that could assess the quality of generated images from different aspects and enable a fair comparison between English and Chinese text-to-image models. The human evaluation results again indicate that ERNIE-ViLG 2.0 outperforms other recent methods, including DALL-E 2 [22] and Stable Diffusion [25], by a significant margin both in terms of image-text alignment and image fidelity." + }, + { + "type": "text", + "bbox": [ + 0.497, + 0.621, + 0.895, + 0.817 + ], + "angle": 0, + "content": "To sum up, the main contributions of this work are: (1) We incorporate textual and visual knowledge into the text-to-image diffusion model, which effectively improves the ability of fine-grained semantic control and alleviates the problem of object-attribute mismatching in generated images. (2) We propose the mixture-of-denoising-experts mechanism to refine the denoising process, which can adapt to the characteristics of different denoising steps and scale up the model to 24B parameters, making it the largest text-to-image model at present. (3) ERNIE-ViLG 2.0 achieves the state-of-the-art zero-shot FID-30k score of 6.75 on MS-COCO, surpasses DALL-E 2 and Stable Diffusion in human evaluation on the Chinese-English bilingual prompt set ViLG-300." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.83, + 0.593, + 0.846 + ], + "angle": 0, + "content": "2. Method" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.856, + 0.895, + 0.903 + ], + "angle": 0, + "content": "During the training process, the text-to-image diffusion model receives paired inputs \\((x,y)\\) consisting of an image \\(x\\) with its text description \\(y\\), and the ultimate goal is to gener" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.887, + 0.381, + 0.9 + ], + "angle": 0, + "content": "1https://wenxin.baidu.com/ernie-vilg" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "10136" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.119, + 0.089, + 0.442, + 0.266 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.447, + 0.089, + 0.852, + 0.265 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.277, + 0.895, + 0.308 + ], + "angle": 0, + "content": "Figure 2. The architecture of ERNIE-ViLG 2.0, which incorporates fine-grained textual and visual knowledge of key elements in the scene and utilizes different denoising experts at different denoising stages." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.332, + 0.474, + 0.529 + ], + "angle": 0, + "content": "ate \\(x\\) based on \\(y\\). To achieve this, a text encoder \\(f_{\\theta}(\\cdot)\\) first encodes \\(y\\) as \\(f_{\\theta}(y)\\), then a denoising network \\(\\epsilon_{\\theta}(\\cdot)\\) conditioned on \\(f_{\\theta}(y)\\) learns to generate \\(x\\) from a Gaussian noise. To help the model generate high-quality images that accurately match the text description (i.e., text prompt), ERNIE-ViLG 2.0 enhances text encoder \\(f_{\\theta}(\\cdot)\\) and denoising network \\(\\epsilon_{\\theta}(\\cdot)\\) with textual and visual knowledge of key elements in the scene. Furthermore, ERNIE-ViLG 2.0 employs mixture-of-denoising-experts to refine the image generation process, where different experts are responsible for different generation steps in the denoising process. The overall architecture of ERNIE-ViLG 2.0 is shown in Figure 2 and the details are described in the following subsections." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.537, + 0.208, + 0.554 + ], + "angle": 0, + "content": "2.1. Preliminary" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.56, + 0.471, + 0.651 + ], + "angle": 0, + "content": "Denoising diffusion probabilistic models (DDPM) are a class of score-based generative models that have recently shown delightful talents in the field of text-to-image generation [9]. The diffusion process of DDPM aims to iteratively add diagonal Gaussian noise to the initial data sample \\( x \\) and turn it into an isotropic Gaussian distribution after \\( T \\) steps:" + }, + { + "type": "equation", + "bbox": [ + 0.127, + 0.658, + 0.47, + 0.675 + ], + "angle": 0, + "content": "\\[\nx _ {t} = \\sqrt {\\alpha_ {t}} x _ {t - 1} + \\sqrt {1 - \\alpha_ {t}} \\epsilon_ {t}, \\quad t \\in \\{1, \\dots , T \\} \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.681, + 0.472, + 0.803 + ], + "angle": 0, + "content": "where the sequence \\(\\{x_{t}\\}\\) starts with \\(x_0 = x\\) and ends with \\(x_{T} \\sim \\mathcal{N}(0, I)\\), the added noise at each step is \\(\\epsilon_{t} \\sim \\mathcal{N}(0, I)\\), and \\(\\{\\alpha_{t}\\}_{1 \\ldots T}\\) is a pre-defined schedule [30, 32]. The denoising process is the reverse of diffusion, which converts the Gaussian noise \\(x_{T} \\sim \\mathcal{N}(0, I)\\) back into the data distribution \\(x_{0}\\) through iterative denoising steps \\(t = T, \\ldots, 1\\). During training, for a given image \\(x\\), the model calculates \\(x_{t}\\) by sampling a Gaussian noise \\(\\epsilon \\sim \\mathcal{N}(0, I)\\):" + }, + { + "type": "equation", + "bbox": [ + 0.19, + 0.809, + 0.47, + 0.827 + ], + "angle": 0, + "content": "\\[\nx _ {t} = \\sqrt {\\bar {\\alpha} _ {t}} x _ {0} + \\sqrt {1 - \\bar {\\alpha} _ {t}} \\epsilon , \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.832, + 0.47, + 0.879 + ], + "angle": 0, + "content": "where \\(\\bar{\\alpha}_t = \\prod_{s=1}^t \\alpha_s\\). Given \\(x_t\\), the target of the denoising network \\(\\epsilon_\\theta(\\cdot)\\) is to restore \\(x_0\\) by predicting the noise \\(\\epsilon\\). It is learned via the loss function" + }, + { + "type": "equation", + "bbox": [ + 0.154, + 0.885, + 0.47, + 0.903 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} = \\mathbb {E} _ {x, \\epsilon \\sim \\mathcal {N} (0, I), t} \\left[ | | \\epsilon - \\epsilon_ {\\theta} (x _ {t}, t) | | _ {2} ^ {2} \\right]. \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.332, + 0.892, + 0.363 + ], + "angle": 0, + "content": "With the predicted \\(\\epsilon_{\\theta}(x_t,t)\\), we can have the prediction of \\(x_0\\) at step \\(t\\) by converting Equation (2):" + }, + { + "type": "equation", + "bbox": [ + 0.578, + 0.367, + 0.892, + 0.397 + ], + "angle": 0, + "content": "\\[\n\\hat {x} _ {0, t} = \\frac {1}{\\sqrt {\\bar {\\alpha} _ {t}}} \\left(x _ {t} - \\sqrt {1 - \\bar {\\alpha} _ {t}} \\epsilon_ {\\theta} \\left(x _ {t}, t\\right)\\right). \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.4, + 0.893, + 0.462 + ], + "angle": 0, + "content": "In Figure 2, we visualize the sampled \\( x_{t} \\) and the predicted \\( \\hat{x}_{0,t} \\) for several timesteps during training. In the inference process of DDPM, \\( x_{0} \\) is unknown, so the model iteratively generates \\( x_{t-1} \\) based on \\( x_{t} \\) and \\( \\hat{x}_{0,t} \\):" + }, + { + "type": "equation", + "bbox": [ + 0.519, + 0.466, + 0.892, + 0.527 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} x _ {t - 1} = \\frac {1 - \\bar {\\alpha} _ {t - 1}}{1 - \\bar {\\alpha} _ {t}} \\sqrt {\\alpha_ {t}} x _ {t} + \\frac {1 - \\alpha_ {t}}{1 - \\bar {\\alpha} _ {t}} \\sqrt {\\bar {\\alpha} _ {t - 1}} \\hat {x} _ {0, t} \\tag {5} \\\\ + \\sqrt {\\frac {(1 - \\bar {\\alpha} _ {t - 1}) (1 - \\alpha_ {t})}{1 - \\bar {\\alpha} _ {t}}} \\epsilon_ {t} ^ {\\prime}, \\quad t \\in \\{T, \\dots , 1 \\}, \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.531, + 0.825, + 0.547 + ], + "angle": 0, + "content": "where \\(\\epsilon_t^\\prime \\sim \\mathcal{N}(0,I)\\) is a sampled Gaussian noise." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.548, + 0.894, + 0.668 + ], + "angle": 0, + "content": "The denoising network \\(\\epsilon_{\\theta}(\\cdot)\\) is typically implemented by U-Net [9]. To allow \\(\\epsilon_{\\theta}(\\cdot)\\) to condition on text prompts, a text encoder \\(f_{\\theta}(\\cdot)\\) first extracts the text representation \\(f_{\\theta}(y) \\in \\mathbb{R}^{n_y \\times d_y}\\), which is then fed into \\(\\epsilon_{\\theta}(\\cdot)\\) via a cross-modal attention layer [18]. Formally, the U-Net representation \\(\\varphi_i(x_t) \\in \\mathbb{R}^{n_x \\times d}\\) is concatenated with the text representation \\(f_{\\theta}(y)\\) after projection, and then goes through an attention layer to achieve cross-modal interaction," + }, + { + "type": "equation", + "bbox": [ + 0.555, + 0.673, + 0.892, + 0.773 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} Q = \\varphi_ {i} (x _ {t}) W _ {Q} ^ {(i)}, \\\\ K = \\left[ \\varphi_ {i} \\left(x _ {t}\\right) W _ {K _ {x}} ^ {(i)}; f _ {\\theta} (y) W _ {K _ {y}} ^ {(i)} \\right], (6) \\\\ V = \\left[ \\varphi_ {i} \\left(x _ {t}\\right) W _ {V _ {x}} ^ {(i)}; f _ {\\theta} (y) W _ {V _ {y}} ^ {(i)} \\right], \\\\ \\operatorname {A t t e n t i o n} (Q, K, V) = \\operatorname {s o f t m a x} \\left(\\frac {Q K ^ {\\top}}{\\sqrt {d}}\\right) V, (7) \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.775, + 0.894, + 0.841 + ], + "angle": 0, + "content": "where \\(i\\) is the index for U-Net layers, \\([;]\\) is the concatenation operator, \\(W_{Q}^{(i)}, W_{K_{x}}^{(i)}, W_{V_{x}}^{(i)} \\in \\mathbb{R}^{d \\times d}\\) and \\(W_{K_{y}}^{(i)}, W_{V_{y}}^{(i)} \\in \\mathbb{R}^{d_{y} \\times d}\\) are learnable projection layers, \\(n_{x}\\) and \\(n_{y}\\) are the length of encoded image and text, respectively." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.841, + 0.892, + 0.902 + ], + "angle": 0, + "content": "During inference, given a text prompt \\(y\\), the denoising U-Net \\(\\epsilon_{\\theta}(\\cdot)\\) predicts the image sample \\(x\\) conditioned on the text \\(y\\) with classifier-free guidance [10] and Denoising Diffusion Implicit Models (DDIM) sampling [31]." + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "10137" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.077, + 0.091, + 0.411, + 0.107 + ], + "angle": 0, + "content": "2.2. Knowledge-Enhanced Diffusion Model" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.114, + 0.471, + 0.28 + ], + "angle": 0, + "content": "The text-to-image model receives a text prompt that describes the scene of an image, then depicts it with crucial objects and corresponding attribute details. In other words, both text and image are intended to express a visual scene, in which key elements have different expressions, such as keywords in text or salient regions in image. However, naive diffusion model does not distinguish the importance of elements and indiscriminately iterates the denoising process. ERNIE-ViLG 2.0 incorporates extra text and visual knowledge into the learning stage, hoping to enhance the fine-grained semantic perception of diffusion model." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.28, + 0.474, + 0.492 + ], + "angle": 0, + "content": "Textual Knowledge. An ideal text-to-image model is expected to focus on all the critical semantics mentioned in the text prompt. To distinguish function words and words describing key semantics, we adopt an off-the-shelf part-of-speech toolkit to extract lexical knowledge of the input prompt, and then improve the learning process by (1) inserting special tokens into the input sequence and (2) increasing the weight of tokens with specific part-of-speech tags in the attention layer. Specifically, we selected \\(50\\%\\) of samples and inserted special tokens at the beginning of each word, in which each part-of-speech tag corresponds to a special token. For the selected samples, we also strengthen the attention weight of keywords based on the lexical analysis results. In this way, Equation (7) is modified to," + }, + { + "type": "equation", + "bbox": [ + 0.1, + 0.499, + 0.471, + 0.531 + ], + "angle": 0, + "content": "\\[\n\\operatorname {A t t e n t i o n} (Q, K, V) ^ {\\prime} = \\operatorname {s o f t m a x} \\left(\\frac {W _ {a} \\cdot \\left(Q K ^ {\\top}\\right)}{\\sqrt {d}}\\right) V, \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.539, + 0.47, + 0.571 + ], + "angle": 0, + "content": "where \\( W_{a} \\in \\mathbb{R}^{n_{x} \\times (n_{x} + n_{y})} \\) is an auxiliary weight matrix that used to scale the vanilla attention, and" + }, + { + "type": "equation", + "bbox": [ + 0.113, + 0.577, + 0.47, + 0.607 + ], + "angle": 0, + "content": "\\[\nW _ {a} ^ {i j} = \\left\\{ \\begin{array}{c c} 1 + w _ {a} & t o k _ {i} \\in \\{x \\}, t o k _ {j} \\in \\{x, y _ {k e y} \\} \\\\ 1 & \\text {o t h e r w i s e .} \\end{array} \\right. \\tag {9}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.615, + 0.47, + 0.692 + ], + "angle": 0, + "content": "Here \\( w_{a}^{ij} \\) is the scaling factor of the attention weight between token \\( tok_{i} \\) and \\( tok_{j} \\), \\( w_{a} \\) is a hyper-parameter, \\( x \\) refers to all the image tokens, and \\( y_{key} \\) denotes the keywords in \\( text^{2} \\). Figure 2 gives an example, where special tokens “[a]” and “[n)” are inserted for adjectives and nouns, respectively." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.692, + 0.471, + 0.844 + ], + "angle": 0, + "content": "Visual Knowledge. Similar to notional words in the text prompt, there are also salient regions in an image, such as people, trees, buildings, and objects mentioned in the input. To extract such visual knowledge, we apply an object detector [1] to \\(50\\%\\) of training samples, and then select eye-catching objects from the results with heuristic strategies. Since the loss function of the diffusion model directly acts on the image space, we can assign higher weights to corresponding regions by modifying Equation (3), thus promoting the model to focus on the generation of these objects:" + }, + { + "type": "equation", + "bbox": [ + 0.138, + 0.85, + 0.47, + 0.868 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} ^ {\\prime} = \\mathbb {E} _ {z, \\epsilon \\sim \\mathcal {N} (0, I), t} \\left[ W _ {l} \\cdot | | \\epsilon - \\epsilon_ {\\theta} (z _ {t}, t) | | _ {2} ^ {2} \\right], \\tag {10}\n\\]" + }, + { + "type": "page_footnote", + "bbox": [ + 0.077, + 0.875, + 0.471, + 0.902 + ], + "angle": 0, + "content": "2The keywords is defined as notional words in modern Chinese (i.e., nouns, verbs, adjectives, numerals, quantifiers, and pronouns)." + }, + { + "type": "equation", + "bbox": [ + 0.58, + 0.089, + 0.892, + 0.119 + ], + "angle": 0, + "content": "\\[\nW _ {l} ^ {i j} = \\left\\{ \\begin{array}{c c} 1 + w _ {l} & \\operatorname {l o s} _ {i j} \\in \\left\\{x _ {\\text {k e y}} \\right\\} \\\\ 1 & \\text {o t h e r w i s e .} \\end{array} \\right. \\tag {11}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.124, + 0.894, + 0.215 + ], + "angle": 0, + "content": "Here \\( W_{l} \\in \\mathbb{R}^{n_{h} \\times n_{w}} \\) is the weight matrix, \\( n_{h} \\) and \\( n_{w} \\) are the height and weight of image space, \\( w_{l} \\) is a hyper-parameter, \\( los_{ij} \\) is the loss item in \\( i \\)-th row and \\( j \\)-th column of image space, \\( x_{key} \\) is the regions that corresponding to key objects. As Figure 2 illustrates, the regions of \"dog\" and \"cat\" are assigned with larger weights in the calculation of \\( \\mathcal{L}' \\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.215, + 0.895, + 0.442 + ], + "angle": 0, + "content": "Now a new problem arises: as a kind of fine-grained knowledge, the selected objects may not appear in the text prompt, thus perplexing the model in learning the alignment between words and objects. An intuitive idea is first to obtain the object and attribute category of each region, then combine corresponding class labels with the original text prompt to achieve fine-grained description, thus ensuring the input contains both coarse and fine granularity information. For instance, as shown in Figure 2, the detected object \"bowl\" is not included in the caption, so we append it to the original description. Besides, we also employ an image captioning model [38] to generate text for images, and randomly replace the original prompt with generated captions, because the generated captions of many images are more concise and reveal more accurate semantics than original prompts." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.443, + 0.894, + 0.549 + ], + "angle": 0, + "content": "Most notably, the above strategies are only limited to the training stage. By randomly selecting a part of samples to equip these additional enhancement strategies, the model is supposed to sense the hints of knowledge from various perspectives, and generate higher quality images for the given text in the inference stage, even without special tokens, attention strengthening, or text refinement." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.56, + 0.768, + 0.575 + ], + "angle": 0, + "content": "2.3. Mixture-of-Denoising-Experts" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.583, + 0.895, + 0.84 + ], + "angle": 0, + "content": "Recall that the diffusion process is to iteratively corrupt the image with Gaussian noises by a series of diffusion steps \\( t = 1, \\dots, T \\), and DDPM [9] are trained to revert the diffusion process by denoising steps \\( t = T, \\dots, 1 \\). During the denoising process, all steps aim to denoise a noised input, and they together convert a completely random noise into a meaningful image gradually. Although sharing the same goal, the difficulty of these denoising steps varies according to the noise ratio of input. Figure 2 illustrates such difference by presenting some examples of \\( x_{t} \\) and the denoising prediction \\( \\hat{x}_{0,t} \\) during training. For timesteps \\( t \\) near \\( T \\), such as \\( t = T, t_{k}, t_{j} \\) in the figure, the input of the denoising network \\( x_{t} \\) is highly noised, and the network of these steps mainly tackles a generation task, i.e., generating an image from a noise. On the contrary, for timesteps \\( t \\) near 1, such as \\( t = t_{i}, 1 \\), the input \\( x_{t} \\) is close to the original image, and the network of these steps needs to refine the image details." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.895, + 0.902 + ], + "angle": 0, + "content": "DDPM makes no specific assumption on the implementation of denoising network, that is, the denoising process does not require the same denoising network for all steps in theory. However, most of the previous text-to-image diffusion ap" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "10138" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.091, + 0.47, + 0.168 + ], + "angle": 0, + "content": "proaches [18,22,25,26] follow the vanilla implementation to adopt a denoising network for the whole denoising process. Considering that tasks of different timesteps are different, we conjecture that using the same set of parameters to learn different tasks might lead to suboptimal performance." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.168, + 0.474, + 0.351 + ], + "angle": 0, + "content": "In view of this, we further propose Mixture-of-Denoising-Experts (MoDE), where the primary motivation is to employ multiple specialized expert networks to fit different tasks at different timesteps. Since the inputs of adjacent timesteps are similar and so are the denoising tasks, we divide all the timesteps uniformly into \\( n \\) blocks \\( (S_{1},\\dots ,S_{i},\\dots ,S_{n}) \\) in which each block consists of consecutive timesteps and is assigned to one denoising expert. In other words, the timesteps in the same block are denoised by the same group of network parameters. In practice, we share the same text encoder for all denoising experts, and utilize different U-Net experts for different timestep blocks:" + }, + { + "type": "equation", + "bbox": [ + 0.166, + 0.36, + 0.47, + 0.377 + ], + "angle": 0, + "content": "\\[\n\\epsilon_ {\\theta} \\left(x _ {t}, t\\right) = \\left\\{\\epsilon_ {\\theta , i} \\left(x _ {t}, t\\right) \\right\\}, \\quad t \\in S _ {i}, \\tag {12}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.386, + 0.47, + 0.432 + ], + "angle": 0, + "content": "where \\(\\epsilon_{\\theta ,i}(x_t,t)\\) is the \\(i\\) -th expert network. Herein, MoDE improves the model performance by adopting expert networks to specially deal with different denoising stages." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.432, + 0.474, + 0.569 + ], + "angle": 0, + "content": "Intuitively, when using more experts, each block contains fewer timesteps, so each expert could better focus on learning the characteristics of specific denoising steps assigned to it. Meanwhile, as only one expert network is activated at each step, increasing the number of experts does not affect the computation overhead during inference. Therefore, ERNIE-ViLG 2.0 can flexibly scale up the parameters of diffusion model, allowing the experts to fit the data distribution better without increasing inference time." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.583, + 0.21, + 0.601 + ], + "angle": 0, + "content": "3. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.608, + 0.47, + 0.684 + ], + "angle": 0, + "content": "In this section, we first introduce the implementation details of ERNIE-ViLG 2.0. Then we present the comparison of models with automatic metrics and human evaluation. Last, we further analyze the results with quantitative ablation studies and qualitative showcases." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.694, + 0.295, + 0.71 + ], + "angle": 0, + "content": "3.1. Implementation Details" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.718, + 0.474, + 0.903 + ], + "angle": 0, + "content": "To reduce learning complexity, we use diffusion models to generate the representations of images in latent space of an image auto-encoder following Latent Diffusion Models [25]. We first pre-train an image encoder to transform an image \\( x \\in \\mathbb{R}^{n_h \\times n_w \\times 3} \\) from pixel space into latent space \\( \\hat{x} \\in \\mathbb{R}^{n_h^l \\times n_w^l \\times 4} \\) and an image decoder to convert it back. Here \\( n_h / n_h^l \\) and \\( n_w / n_w^l \\) denote the image's original/latent height and width, and we collectively refer to pixel space and hidden space as image space in this paper. Then we fix the auto-encoder and train the diffusion model to generate \\( \\hat{x} \\) from text prompt \\( y \\). During inference, we adopt the pre-trained image decoder to turn \\( \\hat{x} \\) into pixel-level image output." + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.089, + 0.895, + 0.146 + ], + "angle": 0, + "content": "Table 1. Comparison of ERNIE-ViLG 2.0 and representative text-to-image generation models on MS-COCO \\(256 \\times 256\\) with zero-shot FID-30k. We use classifier-free guidance scale 2.1 for our diffusion model and achieve the best performance." + }, + { + "type": "table", + "bbox": [ + 0.558, + 0.157, + 0.837, + 0.362 + ], + "angle": 0, + "content": "
ModelZero-Shot FID-30k ↓
DALL-E [23]27.50
CogView [2]27.10
LAFITE [46]26.94
LDM [25]12.61
ERNIE-ViLG [45]14.70
GLIDE [18]12.24
Make-A-Scene [6]11.84
DALL-E 2 [22]10.39
CogView2 [3]24.00
Imagen [26]7.27
Parti [43]7.23
ERNIE-ViLG 2.06.75
" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.387, + 0.895, + 0.553 + ], + "angle": 0, + "content": "ERNIE-ViLG 2.0 contains a transformer-based text encoder with 1.3B parameters and 10 denoising U-Net experts with 2.2B parameters each, which totally add up to about 24B parameters. For hyper-parameters to incorporate knowledge, the attention weight scale \\( w_{a} \\) is set to 0.01 and the loss weight scale \\( w_{l} \\) is set to 0.1 (both chosen from [0.01, 0.1, 0.5, 1]). For the MoDE strategy, all timesteps are divided into 10 blocks. The model is optimized by AdamW [15], with a fixed learning rate \\( 0.9 \\times 10^{-4} \\), \\( \\beta_{1} = 0.9 \\), \\( \\beta_{2} = 0.999 \\), and weight decay of 0.01. We train ERNIE-ViLG 2.0 on 320 Tesla A100 GPUs for 18 days." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.554, + 0.895, + 0.645 + ], + "angle": 0, + "content": "The training data consists of 170M image-text pairs, including publicly available English datasets like LAION [28] and a series of internal Chinese datasets. The image autoencoder is trained on the same set. For images with English captions, we translate them with Baidu Translate API3 to get the Chinese version." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.655, + 0.593, + 0.67 + ], + "angle": 0, + "content": "3.2. Results" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.679, + 0.894, + 0.755 + ], + "angle": 0, + "content": "Automatic Evaluation on MS-COCO. Following previous work [22, 25, 26], we evaluate ERNIE-ViLG 2.0 on MS-COCO \\(256 \\times 256\\) with zero-shot FID-30k, where 30,000 images from the validation set are randomly selected and the English captions are automatically translated to Chinese." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.755, + 0.895, + 0.877 + ], + "angle": 0, + "content": "Table 1 shows that ERNIE-ViLG 2.0 achieves new state-of-the-art performance of text-to-image generation, with 6.75 zero-shot FID-30k on MS-COCO. Inspired by DALL-E [23] and Parti [43], we rerank the batch-sampled images (with only 4 images per text prompt, comparing with 512 images used in DALL-E and 16 images used in Parti) based on the image-text alignment score, calculated by a pre-trained CLIP model [21], in which the text is the initial English" + }, + { + "type": "page_footnote", + "bbox": [ + 0.516, + 0.887, + 0.71, + 0.9 + ], + "angle": 0, + "content": "3https://fanyi.baidu.com" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "10139" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.084, + 0.095, + 0.272, + 0.173 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.127, + 0.179, + 0.227, + 0.191 + ], + "angle": 0, + "content": "(a) v.s. DALL-E 2." + }, + { + "type": "image", + "bbox": [ + 0.277, + 0.095, + 0.465, + 0.173 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.305, + 0.178, + 0.435, + 0.19 + ], + "angle": 0, + "content": "(b) v.s. Stable Diffusion." + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.203, + 0.47, + 0.245 + ], + "angle": 0, + "content": "Figure 3. Comparison of ERNIE-ViLG 2.0 and DALL-E 2/Stable Diffusion on ViLG-300 with human evaluation. We report the user preference rates with \\(95\\%\\) confidence intervals." + }, + { + "type": "image", + "bbox": [ + 0.084, + 0.259, + 0.453, + 0.453 + ], + "angle": 0, + "content": null + }, + { + "type": "image_footnote", + "bbox": [ + 0.102, + 0.454, + 0.461, + 0.476 + ], + "angle": 0, + "content": "(1) A green cup and a blue cell phone (2) A wine glass on top of a dog \n(3) Zongzi and corn boiled in the pot (4) Cherry blossom, digital oil painting" + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.487, + 0.471, + 0.515 + ], + "angle": 0, + "content": "Figure 4. Qualitative Comparison of ERNIE-ViLG 2.0 and DALL-E 2/Stable Diffusion on ViLG-300." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.544, + 0.469, + 0.619 + ], + "angle": 0, + "content": "caption in MS-COCO and the image is generated from the auto-translated Chinese caption. Besides, even without the reranking strategy, we find that ERNIE-ViLG 2.0 can also beat the latest diffusion-based models like DALL-E 2 [22] and Imagen [26], with the zero-shot FID-30k of 7.23." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.62, + 0.47, + 0.756 + ], + "angle": 0, + "content": "Human Evaluation on ViLG-300. ERNIE-ViLG 2.0 takes Chinese prompts as input and generates high-resolution images, unlike recent English-oriented text-to-image models. Herein, we introduce ViLG-3004, a bilingual prompt set that supports the systematic evaluation and comparison of Chinese and English text-to-image models. ViLG-300 contains 300 prompts from 16 categories, composed of Draw-Bench [26] (in English) and the prompt set used in ERNIE-ViLG [45] (in Chinese)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.757, + 0.47, + 0.802 + ], + "angle": 0, + "content": "With ViLG-300, we can make convincing comparisons between ERNIE-ViLG 2.0 and DALL-E \\(2^{5}\\), Stable Diffusion\\(^{67}\\). For evaluation, five raters are presented with two sets" + }, + { + "type": "image", + "bbox": [ + 0.516, + 0.096, + 0.681, + 0.174 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.525, + 0.177, + 0.679, + 0.189 + ], + "angle": 0, + "content": "(a) Knowledge enhancement." + }, + { + "type": "image", + "bbox": [ + 0.704, + 0.096, + 0.877, + 0.174 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.703, + 0.177, + 0.88, + 0.19 + ], + "angle": 0, + "content": "(b) Mixture-of-denoising-experts." + }, + { + "type": "image_caption", + "bbox": [ + 0.5, + 0.201, + 0.894, + 0.23 + ], + "angle": 0, + "content": "Figure 5. Performance with various strategies in ERNIE-ViLG 2.0. Here we draw pareto curves with guidance scale [2,3,4,5,6,7,8,9]." + }, + { + "type": "image", + "bbox": [ + 0.504, + 0.245, + 0.89, + 0.432 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.443, + 0.894, + 0.471 + ], + "angle": 0, + "content": "Figure 6. Samples from ViLG-300 with different knowledge enhancement strategies (left) and different number of experts (right)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.5, + 0.895, + 0.787 + ], + "angle": 0, + "content": "of images generated by ERNIE-ViLG 2.0 and the compared model. Next, they are asked to compare these images from two dimensions of image-text alignment and image fidelity, and then select the model they prefer, or respond that there is no measurable difference between two models. Throughout the process, raters are unaware of which model the image is generated from, and we do not apply any filtering strategy to the rating results. Figure 3 shows that human raters prefer ERNIE-ViLG 2.0 over all other models in both imagedtext alignment (56.5%±3.8% and 68.2%±3.8% when compared to DALL-E 2 and Stable Diffusion, respectively) and image fidelity (58.8%±3.6% to DALL-E 2, 66.5%±3.5% to Stable Diffusion, respectively), which again proves that ERNIE-ViLG 2.0 can generate high-quality images that conform to the text, with the help of knowledge enhancement and mixture-of-denoising-experts strategies. Beyond text relevancy and image fidelity, we also observe that ERNIE-ViLG 2.0 can generate images with better sharpness and textures than baseline models." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.801, + 0.602, + 0.817 + ], + "angle": 0, + "content": "3.3. Analysis" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.826, + 0.894, + 0.901 + ], + "angle": 0, + "content": "To examine the effectiveness of our design philosophy, we conduct two groups of ablation studies. Similar to the main experiment, we also provide both automatic metrics and intuitive showcases to demonstrate the advantages of each strategy in ERNIE-ViLG 2.0 here." + }, + { + "type": "page_footnote", + "bbox": [ + 0.076, + 0.814, + 0.47, + 0.851 + ], + "angle": 0, + "content": "4https://github.com/PaddlePaddle/ERNIE/tree/ernie-kit-open-v1.0/Research/ERNIE-ViLG2/data/ViLG-300.csv" + }, + { + "type": "page_footnote", + "bbox": [ + 0.098, + 0.851, + 0.326, + 0.864 + ], + "angle": 0, + "content": "5 https://openai.com/dall-e-2/" + }, + { + "type": "page_footnote", + "bbox": [ + 0.098, + 0.864, + 0.365, + 0.876 + ], + "angle": 0, + "content": "\\(^{6}\\)https://beta.dreamstudio.ai/dream" + }, + { + "type": "page_footnote", + "bbox": [ + 0.08, + 0.876, + 0.469, + 0.9 + ], + "angle": 0, + "content": "7We use DALL-E 2 and Stable Diffusion interfaces to generate images on October 25, 2022, before the CVPR 2023 submission deadline." + }, + { + "type": "list", + "bbox": [ + 0.076, + 0.814, + 0.47, + 0.9 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "10140" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.081, + 0.092, + 0.468, + 0.142 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.156, + 0.471, + 0.199 + ], + "angle": 0, + "content": "Figure 7. The visualization of cross-attention maps in different denoising timesteps, where each value in the image space is the average of attention from this image token to all text tokens." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.233, + 0.473, + 0.641 + ], + "angle": 0, + "content": "Knowledge Enhancement Strategies. In this part, we focus on the impact of various knowledge enhancement strategies by training a series of lightweight models, with 500M text encoders, 870M U-Nets, and 500M training samples. The pareto curves in Figure 5a demonstrate that incorporating knowledge in the learning process brings significant performance gains in image fidelity and image-text alignment. Specifically, (1) the benefits of textual knowledge are mainly reflected in precise fine-grained semantic control (w/ textual), (2) only utilizing object knowledge may not be able to steadily promote the performance (w/ object), while taking synthetic descriptions into consideration is an effective solution to make full use of visual knowledge (w/ visual). Figure 6 provides more visual comparisons to intuitively demonstrate the changes brought by each strategy. When handling complex prompts, baseline model faces problems such as the absence of key objects or incorrect assignment of attributes. At this point, textual knowledge helps the model accurately understand the attributes of each object, but the generated images sometimes fall into a new problem of distortion. Complementarily, visual knowledge promotes the generation of high-fidelity images, but it cannot well understand specific entities in text. Eventually, the combination of two kinds of knowledge harmoniously promotes the model from single- and multi-modal views, which ensures high fidelity and boost the image-text alignment in fine-grained visual scene." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.645, + 0.473, + 0.902 + ], + "angle": 0, + "content": "Mixture-of-Denoising-Experts Strategies. Based on the above lightweight settings, we further train the baseline model with 500M samples, and then train 200M samples for each denoising expert. Figure 5b shows that with the increasing number of denoising experts, the overall performance is gradually improved, proving that scaling the size of U-Net is also an effective solution to achieve better image quality. More showcases are provided in Figure 6. When the number of experts increases from 1 to 10, the model can not only better handle the coupling between different elements but also generate images with more natural textures. For instance, the numbers on clocks become clearer, the proportion of wolf and suit becomes more harmonious, and the model can generate more photorealistic pictures instead of cartoon drawings. We also tried to analyze the impact of the amount of denoising experts and training samples, and found that using more expert networks has better performance than" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.093, + 0.759, + 0.107 + ], + "angle": 0, + "content": "using a network to train more samples." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.107, + 0.895, + 0.379 + ], + "angle": 0, + "content": "Figure 7 further visualizes the cross-attention maps from image features to text representations in denoising experts during 1,000-step denoising process, where these steps shown are denoised by different experts. As shown in the illustration, attentions of different denoising timesteps vary. Specifically, the attention maps of timesteps \\(t\\) near 1,000 are almost evenly distributed over the whole image, which is because the input of these steps is close to Gaussian noise and the image layout is unclear, so all the image tokens have to attend to the text prompt to generate image skeleton. When the timesteps are close to 1, attention maps concentrate more on foreground objects. For these timesteps, the input to denoising network is close to the final image and the layout is clear, and only a few parts of the image need to focus on the text to fill in the details of object. These observations again illustrate the difference among denoising timesteps and demonstrate the need to disentangle different timesteps with multiple experts." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.393, + 0.642, + 0.408 + ], + "angle": 0, + "content": "4. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.418, + 0.895, + 0.689 + ], + "angle": 0, + "content": "Text-to-Image Generation. Text-to-image generation is the task of synthesizing images according to natural language descriptions. Early works adopted generative adversarial networks [7] to produce images based on text [36,41,44,47]. Inspired by the success of transformers in various generation tasks [37], models such as ERNIE-ViLG [45], DALL-E [23], Cogview [2], Make-A-Scene [6], and Parti [43] have also explored text-to-image generation as a sequence-to-sequence problem, with auto-regressive transformers as generators and text/image tokens as input/output sequences. Recently, another line of works have applied diffusion models [30], shaping it as an iterative denoising task [9, 27, 31]. By adding text condition in the denoising steps, practices such as LDM [25], DALL-E 2 [22], and Imagen [26] constantly set new records in text-to-image generation. Based on diffusion models as the backbone, ERNIE-ViLG 2.0 proposes incorporating knowledge of scene and mixture-of-denoising-experts mechanism into the denoising process." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.69, + 0.897, + 0.902 + ], + "angle": 0, + "content": "Knowledge-Enhanced Pre-trained Models. While transformers benefit from pre-training on large-scale data, many attempts have been adding knowledge to guide them to focus on key elements during learning. For language-based tasks, knowledge-enhanced models used knowledge masking strategy [11, 34] or knowledge-aware pre-training tasks [33, 35] to understand the language data distribution. As for vision-language multi-modal discrimination models, OSCAR [14], ERNIE-ViL [42] and ERNIE-Layout [19] leveraged object tags, scene graphs, and document layouts as extra knowledge to help the models better align language and vision modalities. Among multi-modal generation models, Make-A-Scene [6] emphasized the importance of object and face regions by integrating domain-specific perceptual knowledge." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "10141" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.182 + ], + "angle": 0, + "content": "While current text-to-image diffusion models suffer from attribute misalignment problems [22], they have not employed any specific knowledge of objects. Herein, ERNIE-ViLG 2.0 utilizes the knowledge of key elements in images and text to enhance diffusion models, leading to better fine-grained image-text alignment in generated pictures." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.182, + 0.473, + 0.44 + ], + "angle": 0, + "content": "Mixture-of-Expert. Mixture-of-Experts (MoE) in neural networks means dividing specific parts of the parameters into subsets, each of which is called an expert [4, 29]. During the forward pass, a router assigns experts to different input, and each input only interacts with the experts assigned to. The router is a critical part of MoE. In language tasks, the most common strategy is a matching algorithm that assigns each text token to several experts in the linear feed-forward layer [5, 8, 12, 24]. While most practices formulate multiple experts in only the linear layers, some works also use an entire language model as an expert [13]. Beyond the natural language processing tasks, the idea of MoE have also been applied to vision models [20] and Mixture-of-Modality-Expert in multi-modal transformers [17, 39, 40]. In ERNIE-ViLG 2.0, the MoDE mechanism takes multiple denoising U-Nets as experts. It uses the denoising step index as the fixed router to determine which expert to use." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.453, + 0.411, + 0.469 + ], + "angle": 0, + "content": "5. Risks, Limitations, and Future Work" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.478, + 0.472, + 0.629 + ], + "angle": 0, + "content": "Model Usage and Data Bias. Text-to-image generation models trained by large-scale image-text data have all faced similar risks regarding to inappropriate usage of generation and data bias [22, 25, 26]. Considering that text-to-image models help people realize their imagination with less effort, the malicious use of models may result in unexpected deceptive or harmful outcomes. Moreover, since the models are trained on datasets consisting of images and their alt-text crawled from websites, the generated images may exhibit social and cultural bias in the datasets and websites." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.63, + 0.474, + 0.902 + ], + "angle": 0, + "content": "Character Rendering. Figure 8 shows two successful character rendering cases (a, b) and one failure case (c). Character rendering is a challenging task for ERNIE-ViLG 2.0 for two reasons. First, the training data contains both Chinese text-image pairs and English text-image pairs translated into Chinese. When a text prompt mentions characters, the characters in the image could be in Chinese or English, and it is hard for the model to learn corresponding characters in both languages simultaneously. In the cases of successful character rendering that we observed, the characters could be words that are common in Chinese and do not have an exact match in English, such as “福” (“blessing, happiness, good luck” in English) in Figure 8a, or numbers which are the same in English and Chinese images, such as “20” in Figure 8b. The second reason that makes character rendering difficult is probably that Chinese characters are complex combinations of strokes without basic components like English letters. In Figure 8c, the model does learn that it should write some" + }, + { + "type": "image", + "bbox": [ + 0.508, + 0.089, + 0.627, + 0.181 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.525, + 0.186, + 0.612, + 0.197 + ], + "angle": 0, + "content": "(a)国风福字挂饰" + }, + { + "type": "image_caption", + "bbox": [ + 0.508, + 0.199, + 0.627, + 0.219 + ], + "angle": 0, + "content": "A hanging ornament with \"福\" in Chinese fashion" + }, + { + "type": "image", + "bbox": [ + 0.635, + 0.089, + 0.755, + 0.181 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.629, + 0.185, + 0.759, + 0.197 + ], + "angle": 0, + "content": "(b) 生日蛋糕上有蜡烛“20”" + }, + { + "type": "image_caption", + "bbox": [ + 0.645, + 0.199, + 0.744, + 0.219 + ], + "angle": 0, + "content": "A birthday cake with candles of \"20\" on it" + }, + { + "type": "image", + "bbox": [ + 0.764, + 0.089, + 0.883, + 0.181 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.791, + 0.186, + 0.855, + 0.198 + ], + "angle": 0, + "content": "(c)国画葡萄" + }, + { + "type": "image_caption", + "bbox": [ + 0.76, + 0.204, + 0.886, + 0.215 + ], + "angle": 0, + "content": "Chinese painting of grapes" + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.232, + 0.892, + 0.274 + ], + "angle": 0, + "content": "Figure 8. Examples of character rendering. The model successfully renders simple characters specified in the prompt, while for more difficult cases, the model only learns the position for now." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.301, + 0.891, + 0.33 + ], + "angle": 0, + "content": "Chinese characters in the top right corner, but it only paints meaningless strokes there." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.331, + 0.893, + 0.481 + ], + "angle": 0, + "content": "Variation of Mixture-of-Denoising-Experts. Section 3.3 shows that using more denoising experts leads to better model performance. It indicates that using parallel U-Net experts is an effective way to augment the denoising network. Due to the computation limitation, we only try using up to 10 experts in this work, while we believe that exploring more denoising experts and multiple text encoders as experts is a meaningful future direction. Herein, we can further scale up the model and allow it to learn data distribution better with similar inference time." + }, + { + "type": "title", + "bbox": [ + 0.501, + 0.495, + 0.627, + 0.51 + ], + "angle": 0, + "content": "6. Conclusions" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.52, + 0.895, + 0.823 + ], + "angle": 0, + "content": "We present ERNIE-ViLG 2.0, the first Chinese large-scale text-to-image generation model based on diffusion models. To improve the fine-grained control of scene semantics, we incorporate visual and textual knowledge of the scene into diffusion models. To disentangle the model parameters for different denoising timesteps, we introduce MoDE and scale up the model parameters to 24B with a relatively short inference time. Experiments show that ERNIE-ViLG 2.0 achieves state-of-the-art on MS-COCO and each proposed mechanism contributes to the final results. To allow fair comparisons between Chinese and English text-to-image models, we collect a bilingual prompt set ViLG-300, and human evaluation indicates that ERNIE-ViLG 2.0 is preferred over strong baselines in both text relevancy and image fidelity. Further analysis suggests that different knowledge sources improve the generation in different aspects, and using more experts results in better image quality. In the future, we intend to enrich external image-text alignment knowledge and expand the usage of multiple experts to advance the generation. See also Appendix for more details on training and evaluation." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.84, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Acknowledgement This work was partly supported by National Natural Science Foundation of China (62271359). We thank Yehan Zheng for help on dataset collection; Weixin Liu and Bin Shan for discussions on paper." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "10142" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.117, + 0.473, + 0.215 + ], + "angle": 0, + "content": "[1] Peter Anderson, Xiaodong He, Chris Buehler, Damien Teney, Mark Johnson, Stephen Gould, and Lei Zhang. Bottom-up and top-down attention for image captioning and visual question answering. In 2018 IEEE Conference on Computer Vision and Pattern Recognition, CVPR 2018, Salt Lake City, UT, USA, June 18-22, 2018, pages 6077-6086. 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Selected $1024\times 1024$ samples with various text inputs, which shows that ERNIE-ViLG 2.0 has powerful capabilities of fine-grained semantic control and high-resolution image synthesis, as well as to produce high-quality creative images of different styles. + +![](images/6c3b2885bb300e83563407d9874d9791909c60ce26bb8c2161052bd10fa6a175.jpg) +An ancient style girl with delicate face, wearing a crown of birds and flowers +雪地里的熊猫宝宝戴着红帽子、黄手套,穿着绿毛衣和蓝裤子A baby panda in the snow, wearing red hat, yellow gloves, green sweater and blue pants + +![](images/3548b0143b12c917cf618a0c012c8a4da2463d74d8ee210ef928cb157eefe40f.jpg) +A crane is standing on the calm lake, with a bright moon surrounded by clouds in the background +一只欢快的柯基行走在夕阳里, +光从右边打来铺成一地金黄 +A cheerful Koji is walking in the sunset, +the golden light comes from the right side and spreads all over the ground +泰迪熊穿着戏服,站在太和殿前唱京剧 + +![](images/a99d53906ab3815a43560babcd6bb768a61b7bec54dbfacff9298ab1b6244fa2.jpg) +The close up of Sun Wukong in a suit +A teddy bear, wearing a costume, is standing in front of the Hall of Supreme Harmony and singing Beijing opera + +# Abstract + +Recent progress in diffusion models has revolutionized the popular technology of text-to-image generation. While exist- + +ing approaches could produce photorealistic high-resolution images with text conditions, there are still several open problems to be solved, which limits the further improvement of image fidelity and text relevancy. In this paper, we propose ERNIE-ViLG 2.0, a large-scale Chinese text-to-image + +diffusion model, to progressively upgrade the quality of generated images by: (1) incorporating fine-grained textual and visual knowledge of key elements in the scene, and (2) utilizing different denoising experts at different denoising stages. With the proposed mechanisms, ERNIE-ViLG $2.0^{1}$ not only achieves a new state-of-the-art on MS-COCO with zero-shot FID-30k score of 6.75, but also significantly outperforms recent models in terms of image fidelity and image-text alignment, with side-by-side human evaluation on the bilingual prompt set ViLG-300. + +# 1. Introduction + +Recent years have witnessed incredible progress in text-to-image generation. With large-scale training data and model parameters, kinds of text-to-image generation models are now able to vividly depict the visual scene described by a text prompt, and enable anyone to create exquisite images without sophisticated drawing skills. Among all types of image generation approaches, diffusion models [9] are attracting increasing attention due to their ability to produce highly photorealistic images conditioned on text prompts. Given a text prompt, the models transform a Gaussian noise into an image that conforms to the prompt through iterative denoising steps. In the past years, text-to-image diffusion models such as LDM [25], GLIDE [18], DALL-E 2 [22], and Imagen [26] have achieved impressive performance in both text relevancy and image fidelity. Despite these advances, the exploration of diffusion models by existing methods is still at the initial stage. When we go deep into the principle and implementation of text-to-image diffusion models, there are still many opportunities to improve the quality of generated images further. + +First, during the learning process of each denoising step, all text tokens interact with image regions and all the image regions contribute equally to the final loss function. However, a visual scene of text and image contains many elements (i.e., textual words and visual objects), and different elements usually hold different importance for the expression of the scene semantics [42]. The indiscriminate learning process may cause the model to miss some key elements and interactions in the scene, thus facing the risk of text-image misalignment, such as the attribute confusion problem, especially for text prompts containing multiple objects with specific attributes [22]. Second, when opening the horizon from individual step to the whole denoising process, we can found that the requirements of different denoising stages are also not identical. In the early stages, the input images are highly noised, and the model is required to outline the semantic layout and skeleton out of almost pure noise. By contrast, in the later steps close to the image output, denois + +ing mainly means improving the details based on an almost completed image [25]. In practice, existing models usually use one U-Net for all steps, which means that the same set of parameters has to learn different denoising capabilities. + +In this paper, we propose ERNIE-ViLG 2.0, an improved text-to-image diffusion model with knowledge-enhanced mixture-of-denoising-experts, to incorporate extra knowledge about the visual scene and decouple the denoising capabilities in different steps. Specifically, we employ a text parser and an object detector to extract key elements of the scene in the input text-image pair, and then guide the model to pay more attention to their alignment in the learning process, so as to hope the model could handle the relationships among various objects and attributes. Moreover, we divide the denoising steps into several stages and employ specific denoising "experts" for each stage. With the mixture of multiple experts, the model can involve more parameters and learn the data distribution of each denoising stage better, without increasing the inference time, as only one expert is activated in each denoising step. + +With the extra knowledge from the visual scene and the mixture-of-denoising-experts mechanism, we train ERNIE-ViLG 2.0 and scale up the model size to 24B parameters. Experiments on MS-COCO show that our model exceeds previous text-to-image models by setting a new state-of-the-art of 6.75 zeros-shot FID-30k score, and detailed ablation studies confirm the contributions of each proposed strategy. Apart from automatic metrics, we also collect 300 bilingual text prompts that could assess the quality of generated images from different aspects and enable a fair comparison between English and Chinese text-to-image models. The human evaluation results again indicate that ERNIE-ViLG 2.0 outperforms other recent methods, including DALL-E 2 [22] and Stable Diffusion [25], by a significant margin both in terms of image-text alignment and image fidelity. + +To sum up, the main contributions of this work are: (1) We incorporate textual and visual knowledge into the text-to-image diffusion model, which effectively improves the ability of fine-grained semantic control and alleviates the problem of object-attribute mismatching in generated images. (2) We propose the mixture-of-denoising-experts mechanism to refine the denoising process, which can adapt to the characteristics of different denoising steps and scale up the model to 24B parameters, making it the largest text-to-image model at present. (3) ERNIE-ViLG 2.0 achieves the state-of-the-art zero-shot FID-30k score of 6.75 on MS-COCO, surpasses DALL-E 2 and Stable Diffusion in human evaluation on the Chinese-English bilingual prompt set ViLG-300. + +# 2. Method + +During the training process, the text-to-image diffusion model receives paired inputs $(x,y)$ consisting of an image $x$ with its text description $y$ , and the ultimate goal is to gener + +![](images/98703e8653de4112f825824710d507010fa1422127f54a65a0bdf648e7351202.jpg) +Figure 2. The architecture of ERNIE-ViLG 2.0, which incorporates fine-grained textual and visual knowledge of key elements in the scene and utilizes different denoising experts at different denoising stages. + +![](images/aabd235a83b03c753b6aca05d13216b85403057063e044f0a025e03c7b8b3695.jpg) + +ate $x$ based on $y$ . To achieve this, a text encoder $f_{\theta}(\cdot)$ first encodes $y$ as $f_{\theta}(y)$ , then a denoising network $\epsilon_{\theta}(\cdot)$ conditioned on $f_{\theta}(y)$ learns to generate $x$ from a Gaussian noise. To help the model generate high-quality images that accurately match the text description (i.e., text prompt), ERNIE-ViLG 2.0 enhances text encoder $f_{\theta}(\cdot)$ and denoising network $\epsilon_{\theta}(\cdot)$ with textual and visual knowledge of key elements in the scene. Furthermore, ERNIE-ViLG 2.0 employs mixture-of-denoising-experts to refine the image generation process, where different experts are responsible for different generation steps in the denoising process. The overall architecture of ERNIE-ViLG 2.0 is shown in Figure 2 and the details are described in the following subsections. + +# 2.1. Preliminary + +Denoising diffusion probabilistic models (DDPM) are a class of score-based generative models that have recently shown delightful talents in the field of text-to-image generation [9]. The diffusion process of DDPM aims to iteratively add diagonal Gaussian noise to the initial data sample $x$ and turn it into an isotropic Gaussian distribution after $T$ steps: + +$$ +x _ {t} = \sqrt {\alpha_ {t}} x _ {t - 1} + \sqrt {1 - \alpha_ {t}} \epsilon_ {t}, \quad t \in \{1, \dots , T \} \tag {1} +$$ + +where the sequence $\{x_{t}\}$ starts with $x_0 = x$ and ends with $x_{T} \sim \mathcal{N}(0, I)$ , the added noise at each step is $\epsilon_{t} \sim \mathcal{N}(0, I)$ , and $\{\alpha_{t}\}_{1 \ldots T}$ is a pre-defined schedule [30, 32]. The denoising process is the reverse of diffusion, which converts the Gaussian noise $x_{T} \sim \mathcal{N}(0, I)$ back into the data distribution $x_{0}$ through iterative denoising steps $t = T, \ldots, 1$ . During training, for a given image $x$ , the model calculates $x_{t}$ by sampling a Gaussian noise $\epsilon \sim \mathcal{N}(0, I)$ : + +$$ +x _ {t} = \sqrt {\bar {\alpha} _ {t}} x _ {0} + \sqrt {1 - \bar {\alpha} _ {t}} \epsilon , \tag {2} +$$ + +where $\bar{\alpha}_t = \prod_{s=1}^t \alpha_s$ . Given $x_t$ , the target of the denoising network $\epsilon_\theta(\cdot)$ is to restore $x_0$ by predicting the noise $\epsilon$ . It is learned via the loss function + +$$ +\mathcal {L} = \mathbb {E} _ {x, \epsilon \sim \mathcal {N} (0, I), t} \left[ | | \epsilon - \epsilon_ {\theta} (x _ {t}, t) | | _ {2} ^ {2} \right]. \tag {3} +$$ + +With the predicted $\epsilon_{\theta}(x_t,t)$ , we can have the prediction of $x_0$ at step $t$ by converting Equation (2): + +$$ +\hat {x} _ {0, t} = \frac {1}{\sqrt {\bar {\alpha} _ {t}}} \left(x _ {t} - \sqrt {1 - \bar {\alpha} _ {t}} \epsilon_ {\theta} \left(x _ {t}, t\right)\right). \tag {4} +$$ + +In Figure 2, we visualize the sampled $x_{t}$ and the predicted $\hat{x}_{0,t}$ for several timesteps during training. In the inference process of DDPM, $x_{0}$ is unknown, so the model iteratively generates $x_{t-1}$ based on $x_{t}$ and $\hat{x}_{0,t}$ : + +$$ +\begin{array}{l} x _ {t - 1} = \frac {1 - \bar {\alpha} _ {t - 1}}{1 - \bar {\alpha} _ {t}} \sqrt {\alpha_ {t}} x _ {t} + \frac {1 - \alpha_ {t}}{1 - \bar {\alpha} _ {t}} \sqrt {\bar {\alpha} _ {t - 1}} \hat {x} _ {0, t} \tag {5} \\ + \sqrt {\frac {(1 - \bar {\alpha} _ {t - 1}) (1 - \alpha_ {t})}{1 - \bar {\alpha} _ {t}}} \epsilon_ {t} ^ {\prime}, \quad t \in \{T, \dots , 1 \}, \\ \end{array} +$$ + +where $\epsilon_t^\prime \sim \mathcal{N}(0,I)$ is a sampled Gaussian noise. + +The denoising network $\epsilon_{\theta}(\cdot)$ is typically implemented by U-Net [9]. To allow $\epsilon_{\theta}(\cdot)$ to condition on text prompts, a text encoder $f_{\theta}(\cdot)$ first extracts the text representation $f_{\theta}(y) \in \mathbb{R}^{n_y \times d_y}$ , which is then fed into $\epsilon_{\theta}(\cdot)$ via a cross-modal attention layer [18]. Formally, the U-Net representation $\varphi_i(x_t) \in \mathbb{R}^{n_x \times d}$ is concatenated with the text representation $f_{\theta}(y)$ after projection, and then goes through an attention layer to achieve cross-modal interaction, + +$$ +\begin{array}{l} Q = \varphi_ {i} (x _ {t}) W _ {Q} ^ {(i)}, \\ K = \left[ \varphi_ {i} \left(x _ {t}\right) W _ {K _ {x}} ^ {(i)}; f _ {\theta} (y) W _ {K _ {y}} ^ {(i)} \right], (6) \\ V = \left[ \varphi_ {i} \left(x _ {t}\right) W _ {V _ {x}} ^ {(i)}; f _ {\theta} (y) W _ {V _ {y}} ^ {(i)} \right], \\ \operatorname {A t t e n t i o n} (Q, K, V) = \operatorname {s o f t m a x} \left(\frac {Q K ^ {\top}}{\sqrt {d}}\right) V, (7) \\ \end{array} +$$ + +where $i$ is the index for U-Net layers, $[;]$ is the concatenation operator, $W_{Q}^{(i)}, W_{K_{x}}^{(i)}, W_{V_{x}}^{(i)} \in \mathbb{R}^{d \times d}$ and $W_{K_{y}}^{(i)}, W_{V_{y}}^{(i)} \in \mathbb{R}^{d_{y} \times d}$ are learnable projection layers, $n_{x}$ and $n_{y}$ are the length of encoded image and text, respectively. + +During inference, given a text prompt $y$ , the denoising U-Net $\epsilon_{\theta}(\cdot)$ predicts the image sample $x$ conditioned on the text $y$ with classifier-free guidance [10] and Denoising Diffusion Implicit Models (DDIM) sampling [31]. + +# 2.2. Knowledge-Enhanced Diffusion Model + +The text-to-image model receives a text prompt that describes the scene of an image, then depicts it with crucial objects and corresponding attribute details. In other words, both text and image are intended to express a visual scene, in which key elements have different expressions, such as keywords in text or salient regions in image. However, naive diffusion model does not distinguish the importance of elements and indiscriminately iterates the denoising process. ERNIE-ViLG 2.0 incorporates extra text and visual knowledge into the learning stage, hoping to enhance the fine-grained semantic perception of diffusion model. + +Textual Knowledge. An ideal text-to-image model is expected to focus on all the critical semantics mentioned in the text prompt. To distinguish function words and words describing key semantics, we adopt an off-the-shelf part-of-speech toolkit to extract lexical knowledge of the input prompt, and then improve the learning process by (1) inserting special tokens into the input sequence and (2) increasing the weight of tokens with specific part-of-speech tags in the attention layer. Specifically, we selected $50\%$ of samples and inserted special tokens at the beginning of each word, in which each part-of-speech tag corresponds to a special token. For the selected samples, we also strengthen the attention weight of keywords based on the lexical analysis results. In this way, Equation (7) is modified to, + +$$ +\operatorname {A t t e n t i o n} (Q, K, V) ^ {\prime} = \operatorname {s o f t m a x} \left(\frac {W _ {a} \cdot \left(Q K ^ {\top}\right)}{\sqrt {d}}\right) V, \tag {8} +$$ + +where $W_{a} \in \mathbb{R}^{n_{x} \times (n_{x} + n_{y})}$ is an auxiliary weight matrix that used to scale the vanilla attention, and + +$$ +W _ {a} ^ {i j} = \left\{ \begin{array}{c c} 1 + w _ {a} & t o k _ {i} \in \{x \}, t o k _ {j} \in \{x, y _ {k e y} \} \\ 1 & \text {o t h e r w i s e .} \end{array} \right. \tag {9} +$$ + +Here $w_{a}^{ij}$ is the scaling factor of the attention weight between token $tok_{i}$ and $tok_{j}$ , $w_{a}$ is a hyper-parameter, $x$ refers to all the image tokens, and $y_{key}$ denotes the keywords in $text^{2}$ . Figure 2 gives an example, where special tokens “[a]” and “[n)” are inserted for adjectives and nouns, respectively. + +Visual Knowledge. Similar to notional words in the text prompt, there are also salient regions in an image, such as people, trees, buildings, and objects mentioned in the input. To extract such visual knowledge, we apply an object detector [1] to $50\%$ of training samples, and then select eye-catching objects from the results with heuristic strategies. Since the loss function of the diffusion model directly acts on the image space, we can assign higher weights to corresponding regions by modifying Equation (3), thus promoting the model to focus on the generation of these objects: + +$$ +\mathcal {L} ^ {\prime} = \mathbb {E} _ {z, \epsilon \sim \mathcal {N} (0, I), t} \left[ W _ {l} \cdot | | \epsilon - \epsilon_ {\theta} (z _ {t}, t) | | _ {2} ^ {2} \right], \tag {10} +$$ + +$$ +W _ {l} ^ {i j} = \left\{ \begin{array}{c c} 1 + w _ {l} & \operatorname {l o s} _ {i j} \in \left\{x _ {\text {k e y}} \right\} \\ 1 & \text {o t h e r w i s e .} \end{array} \right. \tag {11} +$$ + +Here $W_{l} \in \mathbb{R}^{n_{h} \times n_{w}}$ is the weight matrix, $n_{h}$ and $n_{w}$ are the height and weight of image space, $w_{l}$ is a hyper-parameter, $los_{ij}$ is the loss item in $i$ -th row and $j$ -th column of image space, $x_{key}$ is the regions that corresponding to key objects. As Figure 2 illustrates, the regions of "dog" and "cat" are assigned with larger weights in the calculation of $\mathcal{L}'$ . + +Now a new problem arises: as a kind of fine-grained knowledge, the selected objects may not appear in the text prompt, thus perplexing the model in learning the alignment between words and objects. An intuitive idea is first to obtain the object and attribute category of each region, then combine corresponding class labels with the original text prompt to achieve fine-grained description, thus ensuring the input contains both coarse and fine granularity information. For instance, as shown in Figure 2, the detected object "bowl" is not included in the caption, so we append it to the original description. Besides, we also employ an image captioning model [38] to generate text for images, and randomly replace the original prompt with generated captions, because the generated captions of many images are more concise and reveal more accurate semantics than original prompts. + +Most notably, the above strategies are only limited to the training stage. By randomly selecting a part of samples to equip these additional enhancement strategies, the model is supposed to sense the hints of knowledge from various perspectives, and generate higher quality images for the given text in the inference stage, even without special tokens, attention strengthening, or text refinement. + +# 2.3. Mixture-of-Denoising-Experts + +Recall that the diffusion process is to iteratively corrupt the image with Gaussian noises by a series of diffusion steps $t = 1, \dots, T$ , and DDPM [9] are trained to revert the diffusion process by denoising steps $t = T, \dots, 1$ . During the denoising process, all steps aim to denoise a noised input, and they together convert a completely random noise into a meaningful image gradually. Although sharing the same goal, the difficulty of these denoising steps varies according to the noise ratio of input. Figure 2 illustrates such difference by presenting some examples of $x_{t}$ and the denoising prediction $\hat{x}_{0,t}$ during training. For timesteps $t$ near $T$ , such as $t = T, t_{k}, t_{j}$ in the figure, the input of the denoising network $x_{t}$ is highly noised, and the network of these steps mainly tackles a generation task, i.e., generating an image from a noise. On the contrary, for timesteps $t$ near 1, such as $t = t_{i}, 1$ , the input $x_{t}$ is close to the original image, and the network of these steps needs to refine the image details. + +DDPM makes no specific assumption on the implementation of denoising network, that is, the denoising process does not require the same denoising network for all steps in theory. However, most of the previous text-to-image diffusion ap + +proaches [18,22,25,26] follow the vanilla implementation to adopt a denoising network for the whole denoising process. Considering that tasks of different timesteps are different, we conjecture that using the same set of parameters to learn different tasks might lead to suboptimal performance. + +In view of this, we further propose Mixture-of-Denoising-Experts (MoDE), where the primary motivation is to employ multiple specialized expert networks to fit different tasks at different timesteps. Since the inputs of adjacent timesteps are similar and so are the denoising tasks, we divide all the timesteps uniformly into $n$ blocks $(S_{1},\dots ,S_{i},\dots ,S_{n})$ in which each block consists of consecutive timesteps and is assigned to one denoising expert. In other words, the timesteps in the same block are denoised by the same group of network parameters. In practice, we share the same text encoder for all denoising experts, and utilize different U-Net experts for different timestep blocks: + +$$ +\epsilon_ {\theta} \left(x _ {t}, t\right) = \left\{\epsilon_ {\theta , i} \left(x _ {t}, t\right) \right\}, \quad t \in S _ {i}, \tag {12} +$$ + +where $\epsilon_{\theta ,i}(x_t,t)$ is the $i$ -th expert network. Herein, MoDE improves the model performance by adopting expert networks to specially deal with different denoising stages. + +Intuitively, when using more experts, each block contains fewer timesteps, so each expert could better focus on learning the characteristics of specific denoising steps assigned to it. Meanwhile, as only one expert network is activated at each step, increasing the number of experts does not affect the computation overhead during inference. Therefore, ERNIE-ViLG 2.0 can flexibly scale up the parameters of diffusion model, allowing the experts to fit the data distribution better without increasing inference time. + +# 3. Experiments + +In this section, we first introduce the implementation details of ERNIE-ViLG 2.0. Then we present the comparison of models with automatic metrics and human evaluation. Last, we further analyze the results with quantitative ablation studies and qualitative showcases. + +# 3.1. Implementation Details + +To reduce learning complexity, we use diffusion models to generate the representations of images in latent space of an image auto-encoder following Latent Diffusion Models [25]. We first pre-train an image encoder to transform an image $x \in \mathbb{R}^{n_h \times n_w \times 3}$ from pixel space into latent space $\hat{x} \in \mathbb{R}^{n_h^l \times n_w^l \times 4}$ and an image decoder to convert it back. Here $n_h / n_h^l$ and $n_w / n_w^l$ denote the image's original/latent height and width, and we collectively refer to pixel space and hidden space as image space in this paper. Then we fix the auto-encoder and train the diffusion model to generate $\hat{x}$ from text prompt $y$ . During inference, we adopt the pre-trained image decoder to turn $\hat{x}$ into pixel-level image output. + +Table 1. Comparison of ERNIE-ViLG 2.0 and representative text-to-image generation models on MS-COCO $256 \times 256$ with zero-shot FID-30k. We use classifier-free guidance scale 2.1 for our diffusion model and achieve the best performance. + +
ModelZero-Shot FID-30k ↓
DALL-E [23]27.50
CogView [2]27.10
LAFITE [46]26.94
LDM [25]12.61
ERNIE-ViLG [45]14.70
GLIDE [18]12.24
Make-A-Scene [6]11.84
DALL-E 2 [22]10.39
CogView2 [3]24.00
Imagen [26]7.27
Parti [43]7.23
ERNIE-ViLG 2.06.75
+ +ERNIE-ViLG 2.0 contains a transformer-based text encoder with 1.3B parameters and 10 denoising U-Net experts with 2.2B parameters each, which totally add up to about 24B parameters. For hyper-parameters to incorporate knowledge, the attention weight scale $w_{a}$ is set to 0.01 and the loss weight scale $w_{l}$ is set to 0.1 (both chosen from [0.01, 0.1, 0.5, 1]). For the MoDE strategy, all timesteps are divided into 10 blocks. The model is optimized by AdamW [15], with a fixed learning rate $0.9 \times 10^{-4}$ , $\beta_{1} = 0.9$ , $\beta_{2} = 0.999$ , and weight decay of 0.01. We train ERNIE-ViLG 2.0 on 320 Tesla A100 GPUs for 18 days. + +The training data consists of 170M image-text pairs, including publicly available English datasets like LAION [28] and a series of internal Chinese datasets. The image autoencoder is trained on the same set. For images with English captions, we translate them with Baidu Translate API3 to get the Chinese version. + +# 3.2. Results + +Automatic Evaluation on MS-COCO. Following previous work [22, 25, 26], we evaluate ERNIE-ViLG 2.0 on MS-COCO $256 \times 256$ with zero-shot FID-30k, where 30,000 images from the validation set are randomly selected and the English captions are automatically translated to Chinese. + +Table 1 shows that ERNIE-ViLG 2.0 achieves new state-of-the-art performance of text-to-image generation, with 6.75 zero-shot FID-30k on MS-COCO. Inspired by DALL-E [23] and Parti [43], we rerank the batch-sampled images (with only 4 images per text prompt, comparing with 512 images used in DALL-E and 16 images used in Parti) based on the image-text alignment score, calculated by a pre-trained CLIP model [21], in which the text is the initial English + +![](images/7e71d91cd4297fd38746c6412c13349d89479d497c5ec14c1b5b64613668dd21.jpg) +(a) v.s. DALL-E 2. + +![](images/c200b365a9c7dbf5c7cdfa01ca6752e50e7fc0e275975856cd976839467f8e58.jpg) +(b) v.s. Stable Diffusion. + +Figure 3. Comparison of ERNIE-ViLG 2.0 and DALL-E 2/Stable Diffusion on ViLG-300 with human evaluation. We report the user preference rates with $95\%$ confidence intervals. +Figure 4. Qualitative Comparison of ERNIE-ViLG 2.0 and DALL-E 2/Stable Diffusion on ViLG-300. +![](images/651ac096b4c4cfe97e804d7d1ccd0605c7ac6e8cc6dd6e2f044f89e552f1135a.jpg) +(1) A green cup and a blue cell phone (2) A wine glass on top of a dog +(3) Zongzi and corn boiled in the pot (4) Cherry blossom, digital oil painting + +caption in MS-COCO and the image is generated from the auto-translated Chinese caption. Besides, even without the reranking strategy, we find that ERNIE-ViLG 2.0 can also beat the latest diffusion-based models like DALL-E 2 [22] and Imagen [26], with the zero-shot FID-30k of 7.23. + +Human Evaluation on ViLG-300. ERNIE-ViLG 2.0 takes Chinese prompts as input and generates high-resolution images, unlike recent English-oriented text-to-image models. Herein, we introduce ViLG-3004, a bilingual prompt set that supports the systematic evaluation and comparison of Chinese and English text-to-image models. ViLG-300 contains 300 prompts from 16 categories, composed of Draw-Bench [26] (in English) and the prompt set used in ERNIE-ViLG [45] (in Chinese). + +With ViLG-300, we can make convincing comparisons between ERNIE-ViLG 2.0 and DALL-E $2^{5}$ , Stable Diffusion $^{67}$ . For evaluation, five raters are presented with two sets + +![](images/11d548238597a109c14f4d0bb66136530abf393ee35e9fdbd9a05531481cfe33.jpg) +(a) Knowledge enhancement. + +![](images/0ed21de18038d5d08c8ff3b22e790c5399e6863d6dc48e6d00b92f48a8f5444b.jpg) +(b) Mixture-of-denoising-experts. + +![](images/bd405357ab018fbe892aa23985a9177836dea1af05bd7e00f52a6cb11164cad4.jpg) +Figure 5. Performance with various strategies in ERNIE-ViLG 2.0. Here we draw pareto curves with guidance scale [2,3,4,5,6,7,8,9]. +Figure 6. Samples from ViLG-300 with different knowledge enhancement strategies (left) and different number of experts (right). + +of images generated by ERNIE-ViLG 2.0 and the compared model. Next, they are asked to compare these images from two dimensions of image-text alignment and image fidelity, and then select the model they prefer, or respond that there is no measurable difference between two models. Throughout the process, raters are unaware of which model the image is generated from, and we do not apply any filtering strategy to the rating results. Figure 3 shows that human raters prefer ERNIE-ViLG 2.0 over all other models in both imagedtext alignment (56.5%±3.8% and 68.2%±3.8% when compared to DALL-E 2 and Stable Diffusion, respectively) and image fidelity (58.8%±3.6% to DALL-E 2, 66.5%±3.5% to Stable Diffusion, respectively), which again proves that ERNIE-ViLG 2.0 can generate high-quality images that conform to the text, with the help of knowledge enhancement and mixture-of-denoising-experts strategies. Beyond text relevancy and image fidelity, we also observe that ERNIE-ViLG 2.0 can generate images with better sharpness and textures than baseline models. + +# 3.3. Analysis + +To examine the effectiveness of our design philosophy, we conduct two groups of ablation studies. Similar to the main experiment, we also provide both automatic metrics and intuitive showcases to demonstrate the advantages of each strategy in ERNIE-ViLG 2.0 here. + +![](images/6abde2dc5018772b695b8234b609d73aaceea3c7f700cfdcfc7647e0baf61952.jpg) +Figure 7. The visualization of cross-attention maps in different denoising timesteps, where each value in the image space is the average of attention from this image token to all text tokens. + +Knowledge Enhancement Strategies. In this part, we focus on the impact of various knowledge enhancement strategies by training a series of lightweight models, with 500M text encoders, 870M U-Nets, and 500M training samples. The pareto curves in Figure 5a demonstrate that incorporating knowledge in the learning process brings significant performance gains in image fidelity and image-text alignment. Specifically, (1) the benefits of textual knowledge are mainly reflected in precise fine-grained semantic control (w/ textual), (2) only utilizing object knowledge may not be able to steadily promote the performance (w/ object), while taking synthetic descriptions into consideration is an effective solution to make full use of visual knowledge (w/ visual). Figure 6 provides more visual comparisons to intuitively demonstrate the changes brought by each strategy. When handling complex prompts, baseline model faces problems such as the absence of key objects or incorrect assignment of attributes. At this point, textual knowledge helps the model accurately understand the attributes of each object, but the generated images sometimes fall into a new problem of distortion. Complementarily, visual knowledge promotes the generation of high-fidelity images, but it cannot well understand specific entities in text. Eventually, the combination of two kinds of knowledge harmoniously promotes the model from single- and multi-modal views, which ensures high fidelity and boost the image-text alignment in fine-grained visual scene. + +Mixture-of-Denoising-Experts Strategies. Based on the above lightweight settings, we further train the baseline model with 500M samples, and then train 200M samples for each denoising expert. Figure 5b shows that with the increasing number of denoising experts, the overall performance is gradually improved, proving that scaling the size of U-Net is also an effective solution to achieve better image quality. More showcases are provided in Figure 6. When the number of experts increases from 1 to 10, the model can not only better handle the coupling between different elements but also generate images with more natural textures. For instance, the numbers on clocks become clearer, the proportion of wolf and suit becomes more harmonious, and the model can generate more photorealistic pictures instead of cartoon drawings. We also tried to analyze the impact of the amount of denoising experts and training samples, and found that using more expert networks has better performance than + +using a network to train more samples. + +Figure 7 further visualizes the cross-attention maps from image features to text representations in denoising experts during 1,000-step denoising process, where these steps shown are denoised by different experts. As shown in the illustration, attentions of different denoising timesteps vary. Specifically, the attention maps of timesteps $t$ near 1,000 are almost evenly distributed over the whole image, which is because the input of these steps is close to Gaussian noise and the image layout is unclear, so all the image tokens have to attend to the text prompt to generate image skeleton. When the timesteps are close to 1, attention maps concentrate more on foreground objects. For these timesteps, the input to denoising network is close to the final image and the layout is clear, and only a few parts of the image need to focus on the text to fill in the details of object. These observations again illustrate the difference among denoising timesteps and demonstrate the need to disentangle different timesteps with multiple experts. + +# 4. Related Work + +Text-to-Image Generation. Text-to-image generation is the task of synthesizing images according to natural language descriptions. Early works adopted generative adversarial networks [7] to produce images based on text [36,41,44,47]. Inspired by the success of transformers in various generation tasks [37], models such as ERNIE-ViLG [45], DALL-E [23], Cogview [2], Make-A-Scene [6], and Parti [43] have also explored text-to-image generation as a sequence-to-sequence problem, with auto-regressive transformers as generators and text/image tokens as input/output sequences. Recently, another line of works have applied diffusion models [30], shaping it as an iterative denoising task [9, 27, 31]. By adding text condition in the denoising steps, practices such as LDM [25], DALL-E 2 [22], and Imagen [26] constantly set new records in text-to-image generation. Based on diffusion models as the backbone, ERNIE-ViLG 2.0 proposes incorporating knowledge of scene and mixture-of-denoising-experts mechanism into the denoising process. + +Knowledge-Enhanced Pre-trained Models. While transformers benefit from pre-training on large-scale data, many attempts have been adding knowledge to guide them to focus on key elements during learning. For language-based tasks, knowledge-enhanced models used knowledge masking strategy [11, 34] or knowledge-aware pre-training tasks [33, 35] to understand the language data distribution. As for vision-language multi-modal discrimination models, OSCAR [14], ERNIE-ViL [42] and ERNIE-Layout [19] leveraged object tags, scene graphs, and document layouts as extra knowledge to help the models better align language and vision modalities. Among multi-modal generation models, Make-A-Scene [6] emphasized the importance of object and face regions by integrating domain-specific perceptual knowledge. + +While current text-to-image diffusion models suffer from attribute misalignment problems [22], they have not employed any specific knowledge of objects. Herein, ERNIE-ViLG 2.0 utilizes the knowledge of key elements in images and text to enhance diffusion models, leading to better fine-grained image-text alignment in generated pictures. + +Mixture-of-Expert. Mixture-of-Experts (MoE) in neural networks means dividing specific parts of the parameters into subsets, each of which is called an expert [4, 29]. During the forward pass, a router assigns experts to different input, and each input only interacts with the experts assigned to. The router is a critical part of MoE. In language tasks, the most common strategy is a matching algorithm that assigns each text token to several experts in the linear feed-forward layer [5, 8, 12, 24]. While most practices formulate multiple experts in only the linear layers, some works also use an entire language model as an expert [13]. Beyond the natural language processing tasks, the idea of MoE have also been applied to vision models [20] and Mixture-of-Modality-Expert in multi-modal transformers [17, 39, 40]. In ERNIE-ViLG 2.0, the MoDE mechanism takes multiple denoising U-Nets as experts. It uses the denoising step index as the fixed router to determine which expert to use. + +# 5. Risks, Limitations, and Future Work + +Model Usage and Data Bias. Text-to-image generation models trained by large-scale image-text data have all faced similar risks regarding to inappropriate usage of generation and data bias [22, 25, 26]. Considering that text-to-image models help people realize their imagination with less effort, the malicious use of models may result in unexpected deceptive or harmful outcomes. Moreover, since the models are trained on datasets consisting of images and their alt-text crawled from websites, the generated images may exhibit social and cultural bias in the datasets and websites. + +Character Rendering. Figure 8 shows two successful character rendering cases (a, b) and one failure case (c). Character rendering is a challenging task for ERNIE-ViLG 2.0 for two reasons. First, the training data contains both Chinese text-image pairs and English text-image pairs translated into Chinese. When a text prompt mentions characters, the characters in the image could be in Chinese or English, and it is hard for the model to learn corresponding characters in both languages simultaneously. In the cases of successful character rendering that we observed, the characters could be words that are common in Chinese and do not have an exact match in English, such as “福” (“blessing, happiness, good luck” in English) in Figure 8a, or numbers which are the same in English and Chinese images, such as “20” in Figure 8b. The second reason that makes character rendering difficult is probably that Chinese characters are complex combinations of strokes without basic components like English letters. In Figure 8c, the model does learn that it should write some + +![](images/b97a5f692b3780d04e0e32031357ab30ec5464f7290f70a8442c416ee5c9bfa1.jpg) +(a)国风福字挂饰 +A hanging ornament with "福" in Chinese fashion +(b) 生日蛋糕上有蜡烛“20” +Figure 8. Examples of character rendering. The model successfully renders simple characters specified in the prompt, while for more difficult cases, the model only learns the position for now. + +![](images/713143af1965d7c0112976ad94198564fe85c634f050019293a96141e9c8d472.jpg) +A birthday cake with candles of "20" on it + +![](images/8a821fd422a15738138005f0abb2d82f6d515c43120bdde1abe7cf5d0caf6791.jpg) +(c)国画葡萄 +Chinese painting of grapes + +Chinese characters in the top right corner, but it only paints meaningless strokes there. + +Variation of Mixture-of-Denoising-Experts. Section 3.3 shows that using more denoising experts leads to better model performance. It indicates that using parallel U-Net experts is an effective way to augment the denoising network. Due to the computation limitation, we only try using up to 10 experts in this work, while we believe that exploring more denoising experts and multiple text encoders as experts is a meaningful future direction. Herein, we can further scale up the model and allow it to learn data distribution better with similar inference time. + +# 6. Conclusions + +We present ERNIE-ViLG 2.0, the first Chinese large-scale text-to-image generation model based on diffusion models. To improve the fine-grained control of scene semantics, we incorporate visual and textual knowledge of the scene into diffusion models. To disentangle the model parameters for different denoising timesteps, we introduce MoDE and scale up the model parameters to 24B with a relatively short inference time. Experiments show that ERNIE-ViLG 2.0 achieves state-of-the-art on MS-COCO and each proposed mechanism contributes to the final results. To allow fair comparisons between Chinese and English text-to-image models, we collect a bilingual prompt set ViLG-300, and human evaluation indicates that ERNIE-ViLG 2.0 is preferred over strong baselines in both text relevancy and image fidelity. Further analysis suggests that different knowledge sources improve the generation in different aspects, and using more experts results in better image quality. In the future, we intend to enrich external image-text alignment knowledge and expand the usage of multiple experts to advance the generation. See also Appendix for more details on training and evaluation. + +Acknowledgement This work was partly supported by National Natural Science Foundation of China (62271359). We thank Yehan Zheng for help on dataset collection; Weixin Liu and Bin Shan for discussions on paper. + +# References + +[1] Peter Anderson, Xiaodong He, Chris Buehler, Damien Teney, Mark Johnson, Stephen Gould, and Lei Zhang. Bottom-up and top-down attention for image captioning and visual question answering. In 2018 IEEE Conference on Computer Vision and Pattern Recognition, CVPR 2018, Salt Lake City, UT, USA, June 18-22, 2018, pages 6077-6086. 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progress in diffusion models has revolutionized the popular technology of text-to-image generation. While exist-" + } + ] + } + ], + "index": 30 + }, + { + "bbox": [ + 306, + 643, + 547, + 704 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 643, + 547, + 704 + ], + "spans": [ + { + "bbox": [ + 306, + 643, + 547, + 704 + ], + "type": "text", + "content": "ing approaches could produce photorealistic high-resolution images with text conditions, there are still several open problems to be solved, which limits the further improvement of image fidelity and text relevancy. In this paper, we propose ERNIE-ViLG 2.0, a large-scale Chinese text-to-image" + } + ] + } + ], + "index": 31 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 45, + 702, + 286, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 702, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 45, + 702, + 286, + 713 + ], + "type": "text", + "content": "* denotes equal contribution. Work done during Feng's internship at Baidu." + } + ] + } + ], + "index": 32 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "10135" + } + ] + } + ], + "index": 33 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 193 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 193 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 193 + ], + "type": "text", + "content": "diffusion model, to progressively upgrade the quality of generated images by: (1) incorporating fine-grained textual and visual knowledge of key elements in the scene, and (2) utilizing different denoising experts at different denoising stages. With the proposed mechanisms, ERNIE-ViLG " + }, + { + "bbox": [ + 46, + 72, + 289, + 193 + ], + "type": "inline_equation", + "content": "2.0^{1}" + }, + { + "bbox": [ + 46, + 72, + 289, + 193 + ], + "type": "text", + "content": " not only achieves a new state-of-the-art on MS-COCO with zero-shot FID-30k score of 6.75, but also significantly outperforms recent models in terms of image fidelity and image-text alignment, with side-by-side human evaluation on the bilingual prompt set ViLG-300." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 217, + 128, + 229 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 217, + 128, + 229 + ], + "spans": [ + { + "bbox": [ + 47, + 217, + 128, + 229 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 237, + 289, + 476 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 237, + 289, + 476 + ], + "spans": [ + { + "bbox": [ + 46, + 237, + 289, + 476 + ], + "type": "text", + "content": "Recent years have witnessed incredible progress in text-to-image generation. With large-scale training data and model parameters, kinds of text-to-image generation models are now able to vividly depict the visual scene described by a text prompt, and enable anyone to create exquisite images without sophisticated drawing skills. Among all types of image generation approaches, diffusion models [9] are attracting increasing attention due to their ability to produce highly photorealistic images conditioned on text prompts. Given a text prompt, the models transform a Gaussian noise into an image that conforms to the prompt through iterative denoising steps. In the past years, text-to-image diffusion models such as LDM [25], GLIDE [18], DALL-E 2 [22], and Imagen [26] have achieved impressive performance in both text relevancy and image fidelity. Despite these advances, the exploration of diffusion models by existing methods is still at the initial stage. When we go deep into the principle and implementation of text-to-image diffusion models, there are still many opportunities to improve the quality of generated images further." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 477, + 289, + 693 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 477, + 289, + 693 + ], + "spans": [ + { + "bbox": [ + 46, + 477, + 289, + 693 + ], + "type": "text", + "content": "First, during the learning process of each denoising step, all text tokens interact with image regions and all the image regions contribute equally to the final loss function. However, a visual scene of text and image contains many elements (i.e., textual words and visual objects), and different elements usually hold different importance for the expression of the scene semantics [42]. The indiscriminate learning process may cause the model to miss some key elements and interactions in the scene, thus facing the risk of text-image misalignment, such as the attribute confusion problem, especially for text prompts containing multiple objects with specific attributes [22]. Second, when opening the horizon from individual step to the whole denoising process, we can found that the requirements of different denoising stages are also not identical. In the early stages, the input images are highly noised, and the model is required to outline the semantic layout and skeleton out of almost pure noise. By contrast, in the later steps close to the image output, denois" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "text", + "content": "ing mainly means improving the details based on an almost completed image [25]. In practice, existing models usually use one U-Net for all steps, which means that the same set of parameters has to learn different denoising capabilities." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 121, + 547, + 312 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 121, + 547, + 312 + ], + "spans": [ + { + "bbox": [ + 304, + 121, + 547, + 312 + ], + "type": "text", + "content": "In this paper, we propose ERNIE-ViLG 2.0, an improved text-to-image diffusion model with knowledge-enhanced mixture-of-denoising-experts, to incorporate extra knowledge about the visual scene and decouple the denoising capabilities in different steps. Specifically, we employ a text parser and an object detector to extract key elements of the scene in the input text-image pair, and then guide the model to pay more attention to their alignment in the learning process, so as to hope the model could handle the relationships among various objects and attributes. Moreover, we divide the denoising steps into several stages and employ specific denoising \"experts\" for each stage. With the mixture of multiple experts, the model can involve more parameters and learn the data distribution of each denoising stage better, without increasing the inference time, as only one expert is activated in each denoising step." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 312, + 547, + 491 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 312, + 547, + 491 + ], + "spans": [ + { + "bbox": [ + 304, + 312, + 547, + 491 + ], + "type": "text", + "content": "With the extra knowledge from the visual scene and the mixture-of-denoising-experts mechanism, we train ERNIE-ViLG 2.0 and scale up the model size to 24B parameters. Experiments on MS-COCO show that our model exceeds previous text-to-image models by setting a new state-of-the-art of 6.75 zeros-shot FID-30k score, and detailed ablation studies confirm the contributions of each proposed strategy. Apart from automatic metrics, we also collect 300 bilingual text prompts that could assess the quality of generated images from different aspects and enable a fair comparison between English and Chinese text-to-image models. The human evaluation results again indicate that ERNIE-ViLG 2.0 outperforms other recent methods, including DALL-E 2 [22] and Stable Diffusion [25], by a significant margin both in terms of image-text alignment and image fidelity." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 491, + 547, + 647 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 491, + 547, + 647 + ], + "spans": [ + { + "bbox": [ + 304, + 491, + 547, + 647 + ], + "type": "text", + "content": "To sum up, the main contributions of this work are: (1) We incorporate textual and visual knowledge into the text-to-image diffusion model, which effectively improves the ability of fine-grained semantic control and alleviates the problem of object-attribute mismatching in generated images. (2) We propose the mixture-of-denoising-experts mechanism to refine the denoising process, which can adapt to the characteristics of different denoising steps and scale up the model to 24B parameters, making it the largest text-to-image model at present. (3) ERNIE-ViLG 2.0 achieves the state-of-the-art zero-shot FID-30k score of 6.75 on MS-COCO, surpasses DALL-E 2 and Stable Diffusion in human evaluation on the Chinese-English bilingual prompt set ViLG-300." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 657, + 362, + 670 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 657, + 362, + 670 + ], + "spans": [ + { + "bbox": [ + 306, + 657, + 362, + 670 + ], + "type": "text", + "content": "2. Method" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 677, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 547, + 715 + ], + "type": "text", + "content": "During the training process, the text-to-image diffusion model receives paired inputs " + }, + { + "bbox": [ + 304, + 677, + 547, + 715 + ], + "type": "inline_equation", + "content": "(x,y)" + }, + { + "bbox": [ + 304, + 677, + 547, + 715 + ], + "type": "text", + "content": " consisting of an image " + }, + { + "bbox": [ + 304, + 677, + 547, + 715 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 304, + 677, + 547, + 715 + ], + "type": "text", + "content": " with its text description " + }, + { + "bbox": [ + 304, + 677, + 547, + 715 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 304, + 677, + 547, + 715 + ], + "type": "text", + "content": ", and the ultimate goal is to gener" + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 58, + 702, + 233, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 702, + 233, + 712 + ], + "spans": [ + { + "bbox": [ + 58, + 702, + 233, + 712 + ], + "type": "text", + "content": "1https://wenxin.baidu.com/ernie-vilg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "10136" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 72, + 70, + 270, + 210 + ], + "blocks": [ + { + "bbox": [ + 72, + 70, + 270, + 210 + ], + "lines": [ + { + "bbox": [ + 72, + 70, + 270, + 210 + ], + "spans": [ + { + "bbox": [ + 72, + 70, + 270, + 210 + ], + "type": "image", + "image_path": "98703e8653de4112f825824710d507010fa1422127f54a65a0bdf648e7351202.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 219, + 547, + 243 + ], + "lines": [ + { + "bbox": [ + 46, + 219, + 547, + 243 + ], + "spans": [ + { + "bbox": [ + 46, + 219, + 547, + 243 + ], + "type": "text", + "content": "Figure 2. The architecture of ERNIE-ViLG 2.0, which incorporates fine-grained textual and visual knowledge of key elements in the scene and utilizes different denoising experts at different denoising stages." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 273, + 70, + 521, + 209 + ], + "blocks": [ + { + "bbox": [ + 273, + 70, + 521, + 209 + ], + "lines": [ + { + "bbox": [ + 273, + 70, + 521, + 209 + ], + "spans": [ + { + "bbox": [ + 273, + 70, + 521, + 209 + ], + "type": "image", + "image_path": "aabd235a83b03c753b6aca05d13216b85403057063e044f0a025e03c7b8b3695.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 262, + 290, + 418 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 262, + 290, + 418 + ], + "spans": [ + { + "bbox": [ + 46, + 262, + 290, + 418 + ], + "type": "text", + "content": "ate " + }, + { + "bbox": [ + 46, + 262, + 290, + 418 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 46, + 262, + 290, + 418 + ], + "type": "text", + "content": " based on " + }, + { + "bbox": [ + 46, + 262, + 290, + 418 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 46, + 262, + 290, + 418 + ], + "type": "text", + "content": ". 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To help the model generate high-quality images that accurately match the text description (i.e., text prompt), ERNIE-ViLG 2.0 enhances text encoder " + }, + { + "bbox": [ + 46, + 262, + 290, + 418 + ], + "type": "inline_equation", + "content": "f_{\\theta}(\\cdot)" + }, + { + "bbox": [ + 46, + 262, + 290, + 418 + ], + "type": "text", + "content": " and denoising network " + }, + { + "bbox": [ + 46, + 262, + 290, + 418 + ], + "type": "inline_equation", + "content": "\\epsilon_{\\theta}(\\cdot)" + }, + { + "bbox": [ + 46, + 262, + 290, + 418 + ], + "type": "text", + "content": " with textual and visual knowledge of key elements in the scene. Furthermore, ERNIE-ViLG 2.0 employs mixture-of-denoising-experts to refine the image generation process, where different experts are responsible for different generation steps in the denoising process. The overall architecture of ERNIE-ViLG 2.0 is shown in Figure 2 and the details are described in the following subsections." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 425, + 127, + 438 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 425, + 127, + 438 + ], + "spans": [ + { + "bbox": [ + 47, + 425, + 127, + 438 + ], + "type": "text", + "content": "2.1. Preliminary" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 443, + 288, + 515 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 443, + 288, + 515 + ], + "spans": [ + { + "bbox": [ + 46, + 443, + 288, + 515 + ], + "type": "text", + "content": "Denoising diffusion probabilistic models (DDPM) are a class of score-based generative models that have recently shown delightful talents in the field of text-to-image generation [9]. The diffusion process of DDPM aims to iteratively add diagonal Gaussian noise to the initial data sample " + }, + { + "bbox": [ + 46, + 443, + 288, + 515 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 46, + 443, + 288, + 515 + ], + "type": "text", + "content": " and turn it into an isotropic Gaussian distribution after " + }, + { + "bbox": [ + 46, + 443, + 288, + 515 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 46, + 443, + 288, + 515 + ], + "type": "text", + "content": " steps:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 77, + 521, + 287, + 534 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 77, + 521, + 287, + 534 + ], + "spans": [ + { + "bbox": [ + 77, + 521, + 287, + 534 + ], + "type": "interline_equation", + "content": "x _ {t} = \\sqrt {\\alpha_ {t}} x _ {t - 1} + \\sqrt {1 - \\alpha_ {t}} \\epsilon_ {t}, \\quad t \\in \\{1, \\dots , T \\} \\tag {1}", + "image_path": "3dd368802ed1d3a59bdd12f751baae428069ff409c33b94477bc8222325238d7.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 539, + 288, + 635 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 539, + 288, + 635 + ], + "spans": [ + { + "bbox": [ + 46, + 539, + 288, + 635 + ], + "type": "text", + "content": "where the sequence " + }, + { + "bbox": [ + 46, + 539, + 288, + 635 + ], + "type": "inline_equation", + "content": "\\{x_{t}\\}" + }, + { + "bbox": [ + 46, + 539, + 288, + 635 + ], + "type": "text", + "content": " starts with " + }, + { + "bbox": [ + 46, + 539, + 288, + 635 + ], + "type": "inline_equation", + "content": "x_0 = x" + }, + { + "bbox": [ + 46, + 539, + 288, + 635 + ], + "type": "text", + "content": " and ends with " + }, + { + "bbox": [ + 46, + 539, + 288, + 635 + ], + "type": "inline_equation", + "content": "x_{T} \\sim \\mathcal{N}(0, I)" + }, + { + "bbox": [ + 46, + 539, + 288, + 635 + ], + "type": "text", + "content": ", the added noise at each step is " + }, + { + "bbox": [ + 46, + 539, + 288, + 635 + ], + "type": "inline_equation", + "content": "\\epsilon_{t} \\sim \\mathcal{N}(0, I)" + }, + { + "bbox": [ + 46, + 539, + 288, + 635 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 46, + 539, + 288, + 635 + ], + "type": "inline_equation", + "content": "\\{\\alpha_{t}\\}_{1 \\ldots T}" + }, + { + "bbox": [ + 46, + 539, + 288, + 635 + ], + "type": "text", + "content": " is a pre-defined schedule [30, 32]. 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During training, for a given image " + }, + { + "bbox": [ + 46, + 539, + 288, + 635 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 46, + 539, + 288, + 635 + ], + "type": "text", + "content": ", the model calculates " + }, + { + "bbox": [ + 46, + 539, + 288, + 635 + ], + "type": "inline_equation", + "content": "x_{t}" + }, + { + "bbox": [ + 46, + 539, + 288, + 635 + ], + "type": "text", + "content": " by sampling a Gaussian noise " + }, + { + "bbox": [ + 46, + 539, + 288, + 635 + ], + "type": "inline_equation", + "content": "\\epsilon \\sim \\mathcal{N}(0, I)" + }, + { + "bbox": [ + 46, + 539, + 288, + 635 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 116, + 640, + 287, + 654 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 116, + 640, + 287, + 654 + ], + "spans": [ + { + "bbox": [ + 116, + 640, + 287, + 654 + ], + "type": "interline_equation", + "content": "x _ {t} = \\sqrt {\\bar {\\alpha} _ {t}} x _ {0} + \\sqrt {1 - \\bar {\\alpha} _ {t}} \\epsilon , \\tag {2}", + "image_path": "0aa2fc0a0442a8b68f0f3e25fe008580c05fef7113d87b40f7910a9d0fe3a7d0.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 658, + 287, + 696 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 658, + 287, + 696 + ], + "spans": [ + { + "bbox": [ + 46, + 658, + 287, + 696 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 658, + 287, + 696 + ], + "type": "inline_equation", + "content": "\\bar{\\alpha}_t = \\prod_{s=1}^t \\alpha_s" + }, + { + "bbox": [ + 46, + 658, + 287, + 696 + ], + "type": "text", + "content": ". Given " + }, + { + "bbox": [ + 46, + 658, + 287, + 696 + ], + "type": "inline_equation", + "content": "x_t" + }, + { + "bbox": [ + 46, + 658, + 287, + 696 + ], + "type": "text", + "content": ", the target of the denoising network " + }, + { + "bbox": [ + 46, + 658, + 287, + 696 + ], + "type": "inline_equation", + "content": "\\epsilon_\\theta(\\cdot)" + }, + { + "bbox": [ + 46, + 658, + 287, + 696 + ], + "type": "text", + "content": " is to restore " + }, + { + "bbox": [ + 46, + 658, + 287, + 696 + ], + "type": "inline_equation", + "content": "x_0" + }, + { + "bbox": [ + 46, + 658, + 287, + 696 + ], + "type": "text", + "content": " by predicting the noise " + }, + { + "bbox": [ + 46, + 658, + 287, + 696 + ], + "type": "inline_equation", + "content": "\\epsilon" + }, + { + "bbox": [ + 46, + 658, + 287, + 696 + ], + "type": "text", + "content": ". It is learned via the loss function" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 94, + 700, + 287, + 715 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 94, + 700, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 94, + 700, + 287, + 715 + ], + "type": "interline_equation", + "content": "\\mathcal {L} = \\mathbb {E} _ {x, \\epsilon \\sim \\mathcal {N} (0, I), t} \\left[ | | \\epsilon - \\epsilon_ {\\theta} (x _ {t}, t) | | _ {2} ^ {2} \\right]. \\tag {3}", + "image_path": "f3bd2f2f009fe8f9fd05891a3c5826895ef96049ecb811e22e0a8fd3319e1783.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 262, + 545, + 287 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 262, + 545, + 287 + ], + "spans": [ + { + "bbox": [ + 305, + 262, + 545, + 287 + ], + "type": "text", + "content": "With the predicted " + }, + { + "bbox": [ + 305, + 262, + 545, + 287 + ], + "type": "inline_equation", + "content": "\\epsilon_{\\theta}(x_t,t)" + }, + { + "bbox": [ + 305, + 262, + 545, + 287 + ], + "type": "text", + "content": ", we can have the prediction of " + }, + { + "bbox": [ + 305, + 262, + 545, + 287 + ], + "type": "inline_equation", + "content": "x_0" + }, + { + "bbox": [ + 305, + 262, + 545, + 287 + ], + "type": "text", + "content": " at step " + }, + { + "bbox": [ + 305, + 262, + 545, + 287 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 305, + 262, + 545, + 287 + ], + "type": "text", + "content": " by converting Equation (2):" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 353, + 290, + 545, + 314 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 353, + 290, + 545, + 314 + ], + "spans": [ + { + "bbox": [ + 353, + 290, + 545, + 314 + ], + "type": "interline_equation", + "content": "\\hat {x} _ {0, t} = \\frac {1}{\\sqrt {\\bar {\\alpha} _ {t}}} \\left(x _ {t} - \\sqrt {1 - \\bar {\\alpha} _ {t}} \\epsilon_ {\\theta} \\left(x _ {t}, t\\right)\\right). \\tag {4}", + "image_path": "0d35afaff26f871af64cae94cb5f8aacf5c9b7405fc97d875f348f9bbd76d8e1.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 316, + 546, + 365 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 316, + 546, + 365 + ], + "spans": [ + { + "bbox": [ + 305, + 316, + 546, + 365 + ], + "type": "text", + "content": "In Figure 2, we visualize the sampled " + }, + { + "bbox": [ + 305, + 316, + 546, + 365 + ], + "type": "inline_equation", + "content": "x_{t}" + }, + { + "bbox": [ + 305, + 316, + 546, + 365 + ], + "type": "text", + "content": " and the predicted " + }, + { + "bbox": [ + 305, + 316, + 546, + 365 + ], + "type": "inline_equation", + "content": "\\hat{x}_{0,t}" + }, + { + "bbox": [ + 305, + 316, + 546, + 365 + ], + "type": "text", + "content": " for several timesteps during training. In the inference process of DDPM, " + }, + { + "bbox": [ + 305, + 316, + 546, + 365 + ], + "type": "inline_equation", + "content": "x_{0}" + }, + { + "bbox": [ + 305, + 316, + 546, + 365 + ], + "type": "text", + "content": " is unknown, so the model iteratively generates " + }, + { + "bbox": [ + 305, + 316, + 546, + 365 + ], + "type": "inline_equation", + "content": "x_{t-1}" + }, + { + "bbox": [ + 305, + 316, + 546, + 365 + ], + "type": "text", + "content": " based on " + }, + { + "bbox": [ + 305, + 316, + 546, + 365 + ], + "type": "inline_equation", + "content": "x_{t}" + }, + { + "bbox": [ + 305, + 316, + 546, + 365 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 316, + 546, + 365 + ], + "type": "inline_equation", + "content": "\\hat{x}_{0,t}" + }, + { + "bbox": [ + 305, + 316, + 546, + 365 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 317, + 369, + 545, + 417 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 369, + 545, + 417 + ], + "spans": [ + { + "bbox": [ + 317, + 369, + 545, + 417 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} x _ {t - 1} = \\frac {1 - \\bar {\\alpha} _ {t - 1}}{1 - \\bar {\\alpha} _ {t}} \\sqrt {\\alpha_ {t}} x _ {t} + \\frac {1 - \\alpha_ {t}}{1 - \\bar {\\alpha} _ {t}} \\sqrt {\\bar {\\alpha} _ {t - 1}} \\hat {x} _ {0, t} \\tag {5} \\\\ + \\sqrt {\\frac {(1 - \\bar {\\alpha} _ {t - 1}) (1 - \\alpha_ {t})}{1 - \\bar {\\alpha} _ {t}}} \\epsilon_ {t} ^ {\\prime}, \\quad t \\in \\{T, \\dots , 1 \\}, \\\\ \\end{array}", + "image_path": "88f28d08df4c403d72c5ef7c38326f4a7ae8c100a491a76912deb499d976fb1b.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 420, + 504, + 433 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 420, + 504, + 433 + ], + "spans": [ + { + "bbox": [ + 305, + 420, + 504, + 433 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 420, + 504, + 433 + ], + "type": "inline_equation", + "content": "\\epsilon_t^\\prime \\sim \\mathcal{N}(0,I)" + }, + { + "bbox": [ + 305, + 420, + 504, + 433 + ], + "type": "text", + "content": " is a sampled Gaussian noise." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 434, + 547, + 529 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 434, + 547, + 529 + ], + "spans": [ + { + "bbox": [ + 305, + 434, + 547, + 529 + ], + "type": "text", + "content": "The denoising network " + }, + { + "bbox": [ + 305, + 434, + 547, + 529 + ], + "type": "inline_equation", + "content": "\\epsilon_{\\theta}(\\cdot)" + }, + { + "bbox": [ + 305, + 434, + 547, + 529 + ], + "type": "text", + "content": " is typically implemented by U-Net [9]. To allow " + }, + { + "bbox": [ + 305, + 434, + 547, + 529 + ], + "type": "inline_equation", + "content": "\\epsilon_{\\theta}(\\cdot)" + }, + { + "bbox": [ + 305, + 434, + 547, + 529 + ], + "type": "text", + "content": " to condition on text prompts, a text encoder " + }, + { + "bbox": [ + 305, + 434, + 547, + 529 + ], + "type": "inline_equation", + "content": "f_{\\theta}(\\cdot)" + }, + { + "bbox": [ + 305, + 434, + 547, + 529 + ], + "type": "text", + "content": " first extracts the text representation " + }, + { + "bbox": [ + 305, + 434, + 547, + 529 + ], + "type": "inline_equation", + "content": "f_{\\theta}(y) \\in \\mathbb{R}^{n_y \\times d_y}" + }, + { + "bbox": [ + 305, + 434, + 547, + 529 + ], + "type": "text", + "content": ", which is then fed into " + }, + { + "bbox": [ + 305, + 434, + 547, + 529 + ], + "type": "inline_equation", + "content": "\\epsilon_{\\theta}(\\cdot)" + }, + { + "bbox": [ + 305, + 434, + 547, + 529 + ], + "type": "text", + "content": " via a cross-modal attention layer [18]. Formally, the U-Net representation " + }, + { + "bbox": [ + 305, + 434, + 547, + 529 + ], + "type": "inline_equation", + "content": "\\varphi_i(x_t) \\in \\mathbb{R}^{n_x \\times d}" + }, + { + "bbox": [ + 305, + 434, + 547, + 529 + ], + "type": "text", + "content": " is concatenated with the text representation " + }, + { + "bbox": [ + 305, + 434, + 547, + 529 + ], + "type": "inline_equation", + "content": "f_{\\theta}(y)" + }, + { + "bbox": [ + 305, + 434, + 547, + 529 + ], + "type": "text", + "content": " after projection, and then goes through an attention layer to achieve cross-modal interaction," + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 339, + 533, + 545, + 612 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 339, + 533, + 545, + 612 + ], + "spans": [ + { + "bbox": [ + 339, + 533, + 545, + 612 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} Q = \\varphi_ {i} (x _ {t}) W _ {Q} ^ {(i)}, \\\\ K = \\left[ \\varphi_ {i} \\left(x _ {t}\\right) W _ {K _ {x}} ^ {(i)}; f _ {\\theta} (y) W _ {K _ {y}} ^ {(i)} \\right], (6) \\\\ V = \\left[ \\varphi_ {i} \\left(x _ {t}\\right) W _ {V _ {x}} ^ {(i)}; f _ {\\theta} (y) W _ {V _ {y}} ^ {(i)} \\right], \\\\ \\operatorname {A t t e n t i o n} (Q, K, V) = \\operatorname {s o f t m a x} \\left(\\frac {Q K ^ {\\top}}{\\sqrt {d}}\\right) V, (7) \\\\ \\end{array}", + "image_path": "f9bc3219462e8bd84c5286ee95ae9698cdcf71a893a91623577d4284c994e9a0.jpg" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 305, + 613, + 547, + 666 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 613, + 547, + 666 + ], + "spans": [ + { + "bbox": [ + 305, + 613, + 547, + 666 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 613, + 547, + 666 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 305, + 613, + 547, + 666 + ], + "type": "text", + "content": " is the index for U-Net layers, " + }, + { + "bbox": [ + 305, + 613, + 547, + 666 + ], + "type": "inline_equation", + "content": "[;]" + }, + { + "bbox": [ + 305, + 613, + 547, + 666 + ], + "type": "text", + "content": " is the concatenation operator, " + }, + { + "bbox": [ + 305, + 613, + 547, + 666 + ], + "type": "inline_equation", + "content": "W_{Q}^{(i)}, W_{K_{x}}^{(i)}, W_{V_{x}}^{(i)} \\in \\mathbb{R}^{d \\times d}" + }, + { + "bbox": [ + 305, + 613, + 547, + 666 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 613, + 547, + 666 + ], + "type": "inline_equation", + "content": "W_{K_{y}}^{(i)}, W_{V_{y}}^{(i)} \\in \\mathbb{R}^{d_{y} \\times d}" + }, + { + "bbox": [ + 305, + 613, + 547, + 666 + ], + "type": "text", + "content": " are learnable projection layers, " + }, + { + "bbox": [ + 305, + 613, + 547, + 666 + ], + "type": "inline_equation", + "content": "n_{x}" + }, + { + "bbox": [ + 305, + 613, + 547, + 666 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 613, + 547, + 666 + ], + "type": "inline_equation", + "content": "n_{y}" + }, + { + "bbox": [ + 305, + 613, + 547, + 666 + ], + "type": "text", + "content": " are the length of encoded image and text, respectively." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 305, + 666, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 666, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 305, + 666, + 545, + 714 + ], + "type": "text", + "content": "During inference, given a text prompt " + }, + { + "bbox": [ + 305, + 666, + 545, + 714 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 305, + 666, + 545, + 714 + ], + "type": "text", + "content": ", the denoising U-Net " + }, + { + "bbox": [ + 305, + 666, + 545, + 714 + ], + "type": "inline_equation", + "content": "\\epsilon_{\\theta}(\\cdot)" + }, + { + "bbox": [ + 305, + 666, + 545, + 714 + ], + "type": "text", + "content": " predicts the image sample " + }, + { + "bbox": [ + 305, + 666, + 545, + 714 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 305, + 666, + 545, + 714 + ], + "type": "text", + "content": " conditioned on the text " + }, + { + "bbox": [ + 305, + 666, + 545, + 714 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 305, + 666, + 545, + 714 + ], + "type": "text", + "content": " with classifier-free guidance [10] and Denoising Diffusion Implicit Models (DDIM) sampling [31]." + } + ] + } + ], + "index": 19 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "10137" + } + ] + } + ], + "index": 20 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 251, + 84 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 251, + 84 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 251, + 84 + ], + "type": "text", + "content": "2.2. Knowledge-Enhanced Diffusion Model" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 90, + 288, + 221 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 90, + 288, + 221 + ], + "spans": [ + { + "bbox": [ + 46, + 90, + 288, + 221 + ], + "type": "text", + "content": "The text-to-image model receives a text prompt that describes the scene of an image, then depicts it with crucial objects and corresponding attribute details. In other words, both text and image are intended to express a visual scene, in which key elements have different expressions, such as keywords in text or salient regions in image. However, naive diffusion model does not distinguish the importance of elements and indiscriminately iterates the denoising process. ERNIE-ViLG 2.0 incorporates extra text and visual knowledge into the learning stage, hoping to enhance the fine-grained semantic perception of diffusion model." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 221, + 290, + 389 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 221, + 290, + 389 + ], + "spans": [ + { + "bbox": [ + 46, + 221, + 290, + 389 + ], + "type": "text", + "content": "Textual Knowledge. An ideal text-to-image model is expected to focus on all the critical semantics mentioned in the text prompt. To distinguish function words and words describing key semantics, we adopt an off-the-shelf part-of-speech toolkit to extract lexical knowledge of the input prompt, and then improve the learning process by (1) inserting special tokens into the input sequence and (2) increasing the weight of tokens with specific part-of-speech tags in the attention layer. Specifically, we selected " + }, + { + "bbox": [ + 46, + 221, + 290, + 389 + ], + "type": "inline_equation", + "content": "50\\%" + }, + { + "bbox": [ + 46, + 221, + 290, + 389 + ], + "type": "text", + "content": " of samples and inserted special tokens at the beginning of each word, in which each part-of-speech tag corresponds to a special token. For the selected samples, we also strengthen the attention weight of keywords based on the lexical analysis results. In this way, Equation (7) is modified to," + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 61, + 395, + 288, + 420 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 61, + 395, + 288, + 420 + ], + "spans": [ + { + "bbox": [ + 61, + 395, + 288, + 420 + ], + "type": "interline_equation", + "content": "\\operatorname {A t t e n t i o n} (Q, K, V) ^ {\\prime} = \\operatorname {s o f t m a x} \\left(\\frac {W _ {a} \\cdot \\left(Q K ^ {\\top}\\right)}{\\sqrt {d}}\\right) V, \\tag {8}", + "image_path": "96a0b769efae2971f164a39fcfc901d2c8778aa753ec74655383f3f3155cc518.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 426, + 287, + 452 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 426, + 287, + 452 + ], + "spans": [ + { + "bbox": [ + 46, + 426, + 287, + 452 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 426, + 287, + 452 + ], + "type": "inline_equation", + "content": "W_{a} \\in \\mathbb{R}^{n_{x} \\times (n_{x} + n_{y})}" + }, + { + "bbox": [ + 46, + 426, + 287, + 452 + ], + "type": "text", + "content": " is an auxiliary weight matrix that used to scale the vanilla attention, and" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 69, + 456, + 287, + 480 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 69, + 456, + 287, + 480 + ], + "spans": [ + { + "bbox": [ + 69, + 456, + 287, + 480 + ], + "type": "interline_equation", + "content": "W _ {a} ^ {i j} = \\left\\{ \\begin{array}{c c} 1 + w _ {a} & t o k _ {i} \\in \\{x \\}, t o k _ {j} \\in \\{x, y _ {k e y} \\} \\\\ 1 & \\text {o t h e r w i s e .} \\end{array} \\right. \\tag {9}", + "image_path": "e7085569ebc5f30610d895f350256df69a6bc5a8c299772b4555ff3ebb344ae9.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 487, + 287, + 548 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 487, + 287, + 548 + ], + "spans": [ + { + "bbox": [ + 46, + 487, + 287, + 548 + ], + "type": "text", + "content": "Here " + }, + { + "bbox": [ + 46, + 487, + 287, + 548 + ], + "type": "inline_equation", + "content": "w_{a}^{ij}" + }, + { + "bbox": [ + 46, + 487, + 287, + 548 + ], + "type": "text", + "content": " is the scaling factor of the attention weight between token " + }, + { + "bbox": [ + 46, + 487, + 287, + 548 + ], + "type": "inline_equation", + "content": "tok_{i}" + }, + { + "bbox": [ + 46, + 487, + 287, + 548 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 487, + 287, + 548 + ], + "type": "inline_equation", + "content": "tok_{j}" + }, + { + "bbox": [ + 46, + 487, + 287, + 548 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 487, + 287, + 548 + ], + "type": "inline_equation", + "content": "w_{a}" + }, + { + "bbox": [ + 46, + 487, + 287, + 548 + ], + "type": "text", + "content": " is a hyper-parameter, " + }, + { + "bbox": [ + 46, + 487, + 287, + 548 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 46, + 487, + 287, + 548 + ], + "type": "text", + "content": " refers to all the image tokens, and " + }, + { + "bbox": [ + 46, + 487, + 287, + 548 + ], + "type": "inline_equation", + "content": "y_{key}" + }, + { + "bbox": [ + 46, + 487, + 287, + 548 + ], + "type": "text", + "content": " denotes the keywords in " + }, + { + "bbox": [ + 46, + 487, + 287, + 548 + ], + "type": "inline_equation", + "content": "text^{2}" + }, + { + "bbox": [ + 46, + 487, + 287, + 548 + ], + "type": "text", + "content": ". Figure 2 gives an example, where special tokens “[a]” and “[n)” are inserted for adjectives and nouns, respectively." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 548, + 288, + 668 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 548, + 288, + 668 + ], + "spans": [ + { + "bbox": [ + 46, + 548, + 288, + 668 + ], + "type": "text", + "content": "Visual Knowledge. Similar to notional words in the text prompt, there are also salient regions in an image, such as people, trees, buildings, and objects mentioned in the input. To extract such visual knowledge, we apply an object detector [1] to " + }, + { + "bbox": [ + 46, + 548, + 288, + 668 + ], + "type": "inline_equation", + "content": "50\\%" + }, + { + "bbox": [ + 46, + 548, + 288, + 668 + ], + "type": "text", + "content": " of training samples, and then select eye-catching objects from the results with heuristic strategies. Since the loss function of the diffusion model directly acts on the image space, we can assign higher weights to corresponding regions by modifying Equation (3), thus promoting the model to focus on the generation of these objects:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 84, + 673, + 287, + 687 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 84, + 673, + 287, + 687 + ], + "spans": [ + { + "bbox": [ + 84, + 673, + 287, + 687 + ], + "type": "interline_equation", + "content": "\\mathcal {L} ^ {\\prime} = \\mathbb {E} _ {z, \\epsilon \\sim \\mathcal {N} (0, I), t} \\left[ W _ {l} \\cdot | | \\epsilon - \\epsilon_ {\\theta} (z _ {t}, t) | | _ {2} ^ {2} \\right], \\tag {10}", + "image_path": "e6b06052f970cdb928f3b09131f4cb7ae14785ccf2fba02abb8fbce74cc44426.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 354, + 70, + 545, + 94 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 354, + 70, + 545, + 94 + ], + "spans": [ + { + "bbox": [ + 354, + 70, + 545, + 94 + ], + "type": "interline_equation", + "content": "W _ {l} ^ {i j} = \\left\\{ \\begin{array}{c c} 1 + w _ {l} & \\operatorname {l o s} _ {i j} \\in \\left\\{x _ {\\text {k e y}} \\right\\} \\\\ 1 & \\text {o t h e r w i s e .} \\end{array} \\right. \\tag {11}", + "image_path": "2ad6f3b5c95321f6aad1e44505eaef1fd205c8020d9e643f9888b43227d5c3cb.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 98, + 547, + 170 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 98, + 547, + 170 + ], + "spans": [ + { + "bbox": [ + 304, + 98, + 547, + 170 + ], + "type": "text", + "content": "Here " + }, + { + "bbox": [ + 304, + 98, + 547, + 170 + ], + "type": "inline_equation", + "content": "W_{l} \\in \\mathbb{R}^{n_{h} \\times n_{w}}" + }, + { + "bbox": [ + 304, + 98, + 547, + 170 + ], + "type": "text", + "content": " is the weight matrix, " + }, + { + "bbox": [ + 304, + 98, + 547, + 170 + ], + "type": "inline_equation", + "content": "n_{h}" + }, + { + "bbox": [ + 304, + 98, + 547, + 170 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 98, + 547, + 170 + ], + "type": "inline_equation", + "content": "n_{w}" + }, + { + "bbox": [ + 304, + 98, + 547, + 170 + ], + "type": "text", + "content": " are the height and weight of image space, " + }, + { + "bbox": [ + 304, + 98, + 547, + 170 + ], + "type": "inline_equation", + "content": "w_{l}" + }, + { + "bbox": [ + 304, + 98, + 547, + 170 + ], + "type": "text", + "content": " is a hyper-parameter, " + }, + { + "bbox": [ + 304, + 98, + 547, + 170 + ], + "type": "inline_equation", + "content": "los_{ij}" + }, + { + "bbox": [ + 304, + 98, + 547, + 170 + ], + "type": "text", + "content": " is the loss item in " + }, + { + "bbox": [ + 304, + 98, + 547, + 170 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 304, + 98, + 547, + 170 + ], + "type": "text", + "content": "-th row and " + }, + { + "bbox": [ + 304, + 98, + 547, + 170 + ], + "type": "inline_equation", + "content": "j" + }, + { + "bbox": [ + 304, + 98, + 547, + 170 + ], + "type": "text", + "content": "-th column of image space, " + }, + { + "bbox": [ + 304, + 98, + 547, + 170 + ], + "type": "inline_equation", + "content": "x_{key}" + }, + { + "bbox": [ + 304, + 98, + 547, + 170 + ], + "type": "text", + "content": " is the regions that corresponding to key objects. As Figure 2 illustrates, the regions of \"dog\" and \"cat\" are assigned with larger weights in the calculation of " + }, + { + "bbox": [ + 304, + 98, + 547, + 170 + ], + "type": "inline_equation", + "content": "\\mathcal{L}'" + }, + { + "bbox": [ + 304, + 98, + 547, + 170 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 170, + 547, + 350 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 170, + 547, + 350 + ], + "spans": [ + { + "bbox": [ + 304, + 170, + 547, + 350 + ], + "type": "text", + "content": "Now a new problem arises: as a kind of fine-grained knowledge, the selected objects may not appear in the text prompt, thus perplexing the model in learning the alignment between words and objects. An intuitive idea is first to obtain the object and attribute category of each region, then combine corresponding class labels with the original text prompt to achieve fine-grained description, thus ensuring the input contains both coarse and fine granularity information. For instance, as shown in Figure 2, the detected object \"bowl\" is not included in the caption, so we append it to the original description. Besides, we also employ an image captioning model [38] to generate text for images, and randomly replace the original prompt with generated captions, because the generated captions of many images are more concise and reveal more accurate semantics than original prompts." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 350, + 547, + 434 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 350, + 547, + 434 + ], + "spans": [ + { + "bbox": [ + 304, + 350, + 547, + 434 + ], + "type": "text", + "content": "Most notably, the above strategies are only limited to the training stage. By randomly selecting a part of samples to equip these additional enhancement strategies, the model is supposed to sense the hints of knowledge from various perspectives, and generate higher quality images for the given text in the inference stage, even without special tokens, attention strengthening, or text refinement." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 443, + 470, + 455 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 443, + 470, + 455 + ], + "spans": [ + { + "bbox": [ + 306, + 443, + 470, + 455 + ], + "type": "text", + "content": "2.3. Mixture-of-Denoising-Experts" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 461, + 547, + 665 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 461, + 547, + 665 + ], + "spans": [ + { + "bbox": [ + 304, + 461, + 547, + 665 + ], + "type": "text", + "content": "Recall that the diffusion process is to iteratively corrupt the image with Gaussian noises by a series of diffusion steps " + }, + { + "bbox": [ + 304, + 461, + 547, + 665 + ], + "type": "inline_equation", + "content": "t = 1, \\dots, T" + }, + { + "bbox": [ + 304, + 461, + 547, + 665 + ], + "type": "text", + "content": ", and DDPM [9] are trained to revert the diffusion process by denoising steps " + }, + { + "bbox": [ + 304, + 461, + 547, + 665 + ], + "type": "inline_equation", + "content": "t = T, \\dots, 1" + }, + { + "bbox": [ + 304, + 461, + 547, + 665 + ], + "type": "text", + "content": ". During the denoising process, all steps aim to denoise a noised input, and they together convert a completely random noise into a meaningful image gradually. Although sharing the same goal, the difficulty of these denoising steps varies according to the noise ratio of input. Figure 2 illustrates such difference by presenting some examples of " + }, + { + "bbox": [ + 304, + 461, + 547, + 665 + ], + "type": "inline_equation", + "content": "x_{t}" + }, + { + "bbox": [ + 304, + 461, + 547, + 665 + ], + "type": "text", + "content": " and the denoising prediction " + }, + { + "bbox": [ + 304, + 461, + 547, + 665 + ], + "type": "inline_equation", + "content": "\\hat{x}_{0,t}" + }, + { + "bbox": [ + 304, + 461, + 547, + 665 + ], + "type": "text", + "content": " during training. For timesteps " + }, + { + "bbox": [ + 304, + 461, + 547, + 665 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 461, + 547, + 665 + ], + "type": "text", + "content": " near " + }, + { + "bbox": [ + 304, + 461, + 547, + 665 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 304, + 461, + 547, + 665 + ], + "type": "text", + "content": ", such as " + }, + { + "bbox": [ + 304, + 461, + 547, + 665 + ], + "type": "inline_equation", + "content": "t = T, t_{k}, t_{j}" + }, + { + "bbox": [ + 304, + 461, + 547, + 665 + ], + "type": "text", + "content": " in the figure, the input of the denoising network " + }, + { + "bbox": [ + 304, + 461, + 547, + 665 + ], + "type": "inline_equation", + "content": "x_{t}" + }, + { + "bbox": [ + 304, + 461, + 547, + 665 + ], + "type": "text", + "content": " is highly noised, and the network of these steps mainly tackles a generation task, i.e., generating an image from a noise. On the contrary, for timesteps " + }, + { + "bbox": [ + 304, + 461, + 547, + 665 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 461, + 547, + 665 + ], + "type": "text", + "content": " near 1, such as " + }, + { + "bbox": [ + 304, + 461, + 547, + 665 + ], + "type": "inline_equation", + "content": "t = t_{i}, 1" + }, + { + "bbox": [ + 304, + 461, + 547, + 665 + ], + "type": "text", + "content": ", the input " + }, + { + "bbox": [ + 304, + 461, + 547, + 665 + ], + "type": "inline_equation", + "content": "x_{t}" + }, + { + "bbox": [ + 304, + 461, + 547, + 665 + ], + "type": "text", + "content": " is close to the original image, and the network of these steps needs to refine the image details." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 665, + 547, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 547, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 547, + 714 + ], + "type": "text", + "content": "DDPM makes no specific assumption on the implementation of denoising network, that is, the denoising process does not require the same denoising network for all steps in theory. However, most of the previous text-to-image diffusion ap" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 47, + 693, + 288, + 714 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 693, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 47, + 693, + 288, + 714 + ], + "type": "text", + "content": "2The keywords is defined as notional words in modern Chinese (i.e., nouns, verbs, adjectives, numerals, quantifiers, and pronouns)." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "10138" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 133 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 133 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 133 + ], + "type": "text", + "content": "proaches [18,22,25,26] follow the vanilla implementation to adopt a denoising network for the whole denoising process. Considering that tasks of different timesteps are different, we conjecture that using the same set of parameters to learn different tasks might lead to suboptimal performance." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 133, + 290, + 277 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 133, + 290, + 277 + ], + "spans": [ + { + "bbox": [ + 46, + 133, + 290, + 277 + ], + "type": "text", + "content": "In view of this, we further propose Mixture-of-Denoising-Experts (MoDE), where the primary motivation is to employ multiple specialized expert networks to fit different tasks at different timesteps. Since the inputs of adjacent timesteps are similar and so are the denoising tasks, we divide all the timesteps uniformly into " + }, + { + "bbox": [ + 46, + 133, + 290, + 277 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 46, + 133, + 290, + 277 + ], + "type": "text", + "content": " blocks " + }, + { + "bbox": [ + 46, + 133, + 290, + 277 + ], + "type": "inline_equation", + "content": "(S_{1},\\dots ,S_{i},\\dots ,S_{n})" + }, + { + "bbox": [ + 46, + 133, + 290, + 277 + ], + "type": "text", + "content": " in which each block consists of consecutive timesteps and is assigned to one denoising expert. In other words, the timesteps in the same block are denoised by the same group of network parameters. In practice, we share the same text encoder for all denoising experts, and utilize different U-Net experts for different timestep blocks:" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 101, + 285, + 287, + 298 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 101, + 285, + 287, + 298 + ], + "spans": [ + { + "bbox": [ + 101, + 285, + 287, + 298 + ], + "type": "interline_equation", + "content": "\\epsilon_ {\\theta} \\left(x _ {t}, t\\right) = \\left\\{\\epsilon_ {\\theta , i} \\left(x _ {t}, t\\right) \\right\\}, \\quad t \\in S _ {i}, \\tag {12}", + "image_path": "f92227ca46c5625735ae2f1db601095fad3d14be74b8cc0754d0be12d02d2888.jpg" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 305, + 287, + 342 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 305, + 287, + 342 + ], + "spans": [ + { + "bbox": [ + 46, + 305, + 287, + 342 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 305, + 287, + 342 + ], + "type": "inline_equation", + "content": "\\epsilon_{\\theta ,i}(x_t,t)" + }, + { + "bbox": [ + 46, + 305, + 287, + 342 + ], + "type": "text", + "content": " is the " + }, + { + "bbox": [ + 46, + 305, + 287, + 342 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 305, + 287, + 342 + ], + "type": "text", + "content": " -th expert network. Herein, MoDE improves the model performance by adopting expert networks to specially deal with different denoising stages." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 342, + 290, + 450 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 342, + 290, + 450 + ], + "spans": [ + { + "bbox": [ + 46, + 342, + 290, + 450 + ], + "type": "text", + "content": "Intuitively, when using more experts, each block contains fewer timesteps, so each expert could better focus on learning the characteristics of specific denoising steps assigned to it. Meanwhile, as only one expert network is activated at each step, increasing the number of experts does not affect the computation overhead during inference. Therefore, ERNIE-ViLG 2.0 can flexibly scale up the parameters of diffusion model, allowing the experts to fit the data distribution better without increasing inference time." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 461, + 128, + 475 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 461, + 128, + 475 + ], + "spans": [ + { + "bbox": [ + 47, + 461, + 128, + 475 + ], + "type": "text", + "content": "3. Experiments" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 481, + 287, + 541 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 481, + 287, + 541 + ], + "spans": [ + { + "bbox": [ + 46, + 481, + 287, + 541 + ], + "type": "text", + "content": "In this section, we first introduce the implementation details of ERNIE-ViLG 2.0. Then we present the comparison of models with automatic metrics and human evaluation. Last, we further analyze the results with quantitative ablation studies and qualitative showcases." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 549, + 180, + 562 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 549, + 180, + 562 + ], + "spans": [ + { + "bbox": [ + 47, + 549, + 180, + 562 + ], + "type": "text", + "content": "3.1. Implementation Details" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 568, + 290, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 568, + 290, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 568, + 290, + 715 + ], + "type": "text", + "content": "To reduce learning complexity, we use diffusion models to generate the representations of images in latent space of an image auto-encoder following Latent Diffusion Models [25]. We first pre-train an image encoder to transform an image " + }, + { + "bbox": [ + 46, + 568, + 290, + 715 + ], + "type": "inline_equation", + "content": "x \\in \\mathbb{R}^{n_h \\times n_w \\times 3}" + }, + { + "bbox": [ + 46, + 568, + 290, + 715 + ], + "type": "text", + "content": " from pixel space into latent space " + }, + { + "bbox": [ + 46, + 568, + 290, + 715 + ], + "type": "inline_equation", + "content": "\\hat{x} \\in \\mathbb{R}^{n_h^l \\times n_w^l \\times 4}" + }, + { + "bbox": [ + 46, + 568, + 290, + 715 + ], + "type": "text", + "content": " and an image decoder to convert it back. Here " + }, + { + "bbox": [ + 46, + 568, + 290, + 715 + ], + "type": "inline_equation", + "content": "n_h / n_h^l" + }, + { + "bbox": [ + 46, + 568, + 290, + 715 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 568, + 290, + 715 + ], + "type": "inline_equation", + "content": "n_w / n_w^l" + }, + { + "bbox": [ + 46, + 568, + 290, + 715 + ], + "type": "text", + "content": " denote the image's original/latent height and width, and we collectively refer to pixel space and hidden space as image space in this paper. Then we fix the auto-encoder and train the diffusion model to generate " + }, + { + "bbox": [ + 46, + 568, + 290, + 715 + ], + "type": "inline_equation", + "content": "\\hat{x}" + }, + { + "bbox": [ + 46, + 568, + 290, + 715 + ], + "type": "text", + "content": " from text prompt " + }, + { + "bbox": [ + 46, + 568, + 290, + 715 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 46, + 568, + 290, + 715 + ], + "type": "text", + "content": ". During inference, we adopt the pre-trained image decoder to turn " + }, + { + "bbox": [ + 46, + 568, + 290, + 715 + ], + "type": "inline_equation", + "content": "\\hat{x}" + }, + { + "bbox": [ + 46, + 568, + 290, + 715 + ], + "type": "text", + "content": " into pixel-level image output." + } + ] + } + ], + "index": 8 + }, + { + "type": "table", + "bbox": [ + 341, + 124, + 512, + 286 + ], + "blocks": [ + { + "bbox": [ + 305, + 70, + 547, + 115 + ], + "lines": [ + { + "bbox": [ + 305, + 70, + 547, + 115 + ], + "spans": [ + { + "bbox": [ + 305, + 70, + 547, + 115 + ], + "type": "text", + "content": "Table 1. Comparison of ERNIE-ViLG 2.0 and representative text-to-image generation models on MS-COCO " + }, + { + "bbox": [ + 305, + 70, + 547, + 115 + ], + "type": "inline_equation", + "content": "256 \\times 256" + }, + { + "bbox": [ + 305, + 70, + 547, + 115 + ], + "type": "text", + "content": " with zero-shot FID-30k. We use classifier-free guidance scale 2.1 for our diffusion model and achieve the best performance." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 341, + 124, + 512, + 286 + ], + "lines": [ + { + "bbox": [ + 341, + 124, + 512, + 286 + ], + "spans": [ + { + "bbox": [ + 341, + 124, + 512, + 286 + ], + "type": "table", + "html": "
ModelZero-Shot FID-30k ↓
DALL-E [23]27.50
CogView [2]27.10
LAFITE [46]26.94
LDM [25]12.61
ERNIE-ViLG [45]14.70
GLIDE [18]12.24
Make-A-Scene [6]11.84
DALL-E 2 [22]10.39
CogView2 [3]24.00
Imagen [26]7.27
Parti [43]7.23
ERNIE-ViLG 2.06.75
", + "image_path": "3c99dfdd509beb7985cb4747f408bd66dd92e5eb9b4167326d2a1c948c82533e.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "table_body" + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 306, + 547, + 437 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 306, + 547, + 437 + ], + "spans": [ + { + "bbox": [ + 304, + 306, + 547, + 437 + ], + "type": "text", + "content": "ERNIE-ViLG 2.0 contains a transformer-based text encoder with 1.3B parameters and 10 denoising U-Net experts with 2.2B parameters each, which totally add up to about 24B parameters. For hyper-parameters to incorporate knowledge, the attention weight scale " + }, + { + "bbox": [ + 304, + 306, + 547, + 437 + ], + "type": "inline_equation", + "content": "w_{a}" + }, + { + "bbox": [ + 304, + 306, + 547, + 437 + ], + "type": "text", + "content": " is set to 0.01 and the loss weight scale " + }, + { + "bbox": [ + 304, + 306, + 547, + 437 + ], + "type": "inline_equation", + "content": "w_{l}" + }, + { + "bbox": [ + 304, + 306, + 547, + 437 + ], + "type": "text", + "content": " is set to 0.1 (both chosen from [0.01, 0.1, 0.5, 1]). For the MoDE strategy, all timesteps are divided into 10 blocks. The model is optimized by AdamW [15], with a fixed learning rate " + }, + { + "bbox": [ + 304, + 306, + 547, + 437 + ], + "type": "inline_equation", + "content": "0.9 \\times 10^{-4}" + }, + { + "bbox": [ + 304, + 306, + 547, + 437 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 306, + 547, + 437 + ], + "type": "inline_equation", + "content": "\\beta_{1} = 0.9" + }, + { + "bbox": [ + 304, + 306, + 547, + 437 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 306, + 547, + 437 + ], + "type": "inline_equation", + "content": "\\beta_{2} = 0.999" + }, + { + "bbox": [ + 304, + 306, + 547, + 437 + ], + "type": "text", + "content": ", and weight decay of 0.01. We train ERNIE-ViLG 2.0 on 320 Tesla A100 GPUs for 18 days." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 438, + 547, + 510 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 438, + 547, + 510 + ], + "spans": [ + { + "bbox": [ + 304, + 438, + 547, + 510 + ], + "type": "text", + "content": "The training data consists of 170M image-text pairs, including publicly available English datasets like LAION [28] and a series of internal Chinese datasets. The image autoencoder is trained on the same set. For images with English captions, we translate them with Baidu Translate API3 to get the Chinese version." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 518, + 362, + 530 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 518, + 362, + 530 + ], + "spans": [ + { + "bbox": [ + 306, + 518, + 362, + 530 + ], + "type": "text", + "content": "3.2. Results" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 537, + 547, + 597 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 537, + 547, + 597 + ], + "spans": [ + { + "bbox": [ + 304, + 537, + 547, + 597 + ], + "type": "text", + "content": "Automatic Evaluation on MS-COCO. Following previous work [22, 25, 26], we evaluate ERNIE-ViLG 2.0 on MS-COCO " + }, + { + "bbox": [ + 304, + 537, + 547, + 597 + ], + "type": "inline_equation", + "content": "256 \\times 256" + }, + { + "bbox": [ + 304, + 537, + 547, + 597 + ], + "type": "text", + "content": " with zero-shot FID-30k, where 30,000 images from the validation set are randomly selected and the English captions are automatically translated to Chinese." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 597, + 547, + 694 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 597, + 547, + 694 + ], + "spans": [ + { + "bbox": [ + 304, + 597, + 547, + 694 + ], + "type": "text", + "content": "Table 1 shows that ERNIE-ViLG 2.0 achieves new state-of-the-art performance of text-to-image generation, with 6.75 zero-shot FID-30k on MS-COCO. Inspired by DALL-E [23] and Parti [43], we rerank the batch-sampled images (with only 4 images per text prompt, comparing with 512 images used in DALL-E and 16 images used in Parti) based on the image-text alignment score, calculated by a pre-trained CLIP model [21], in which the text is the initial English" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 315, + 702, + 434, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 315, + 702, + 434, + 712 + ], + "spans": [ + { + "bbox": [ + 315, + 702, + 434, + 712 + ], + "type": "text", + "content": "3https://fanyi.baidu.com" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "10139" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 51, + 75, + 166, + 137 + ], + "blocks": [ + { + "bbox": [ + 51, + 75, + 166, + 137 + ], + "lines": [ + { + "bbox": [ + 51, + 75, + 166, + 137 + ], + "spans": [ + { + "bbox": [ + 51, + 75, + 166, + 137 + ], + "type": "image", + "image_path": "7e71d91cd4297fd38746c6412c13349d89479d497c5ec14c1b5b64613668dd21.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 77, + 141, + 138, + 151 + ], + "lines": [ + { + "bbox": [ + 77, + 141, + 138, + 151 + ], + "spans": [ + { + "bbox": [ + 77, + 141, + 138, + 151 + ], + "type": "text", + "content": "(a) v.s. DALL-E 2." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 169, + 75, + 284, + 137 + ], + "blocks": [ + { + "bbox": [ + 169, + 75, + 284, + 137 + ], + "lines": [ + { + "bbox": [ + 169, + 75, + 284, + 137 + ], + "spans": [ + { + "bbox": [ + 169, + 75, + 284, + 137 + ], + "type": "image", + "image_path": "c200b365a9c7dbf5c7cdfa01ca6752e50e7fc0e275975856cd976839467f8e58.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 186, + 140, + 266, + 150 + ], + "lines": [ + { + "bbox": [ + 186, + 140, + 266, + 150 + ], + "spans": [ + { + "bbox": [ + 186, + 140, + 266, + 150 + ], + "type": "text", + "content": "(b) v.s. Stable Diffusion." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 51, + 205, + 277, + 358 + ], + "blocks": [ + { + "bbox": [ + 47, + 160, + 287, + 194 + ], + "lines": [ + { + "bbox": [ + 47, + 160, + 287, + 194 + ], + "spans": [ + { + "bbox": [ + 47, + 160, + 287, + 194 + ], + "type": "text", + "content": "Figure 3. Comparison of ERNIE-ViLG 2.0 and DALL-E 2/Stable Diffusion on ViLG-300 with human evaluation. We report the user preference rates with " + }, + { + "bbox": [ + 47, + 160, + 287, + 194 + ], + "type": "inline_equation", + "content": "95\\%" + }, + { + "bbox": [ + 47, + 160, + 287, + 194 + ], + "type": "text", + "content": " confidence intervals." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 51, + 205, + 277, + 358 + ], + "lines": [ + { + "bbox": [ + 51, + 205, + 277, + 358 + ], + "spans": [ + { + "bbox": [ + 51, + 205, + 277, + 358 + ], + "type": "image", + "image_path": "651ac096b4c4cfe97e804d7d1ccd0605c7ac6e8cc6dd6e2f044f89e552f1135a.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 62, + 359, + 282, + 376 + ], + "lines": [ + { + "bbox": [ + 62, + 359, + 282, + 376 + ], + "spans": [ + { + "bbox": [ + 62, + 359, + 282, + 376 + ], + "type": "text", + "content": "(1) A green cup and a blue cell phone (2) A wine glass on top of a dog \n(3) Zongzi and corn boiled in the pot (4) Cherry blossom, digital oil painting" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_footnote" + }, + { + "bbox": [ + 47, + 385, + 288, + 407 + ], + "lines": [ + { + "bbox": [ + 47, + 385, + 288, + 407 + ], + "spans": [ + { + "bbox": [ + 47, + 385, + 288, + 407 + ], + "type": "text", + "content": "Figure 4. Qualitative Comparison of ERNIE-ViLG 2.0 and DALL-E 2/Stable Diffusion on ViLG-300." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_caption" + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 430, + 287, + 490 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 430, + 287, + 490 + ], + "spans": [ + { + "bbox": [ + 46, + 430, + 287, + 490 + ], + "type": "text", + "content": "caption in MS-COCO and the image is generated from the auto-translated Chinese caption. Besides, even without the reranking strategy, we find that ERNIE-ViLG 2.0 can also beat the latest diffusion-based models like DALL-E 2 [22] and Imagen [26], with the zero-shot FID-30k of 7.23." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 491, + 287, + 598 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 491, + 287, + 598 + ], + "spans": [ + { + "bbox": [ + 46, + 491, + 287, + 598 + ], + "type": "text", + "content": "Human Evaluation on ViLG-300. ERNIE-ViLG 2.0 takes Chinese prompts as input and generates high-resolution images, unlike recent English-oriented text-to-image models. Herein, we introduce ViLG-3004, a bilingual prompt set that supports the systematic evaluation and comparison of Chinese and English text-to-image models. ViLG-300 contains 300 prompts from 16 categories, composed of Draw-Bench [26] (in English) and the prompt set used in ERNIE-ViLG [45] (in Chinese)." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 599, + 287, + 635 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 599, + 287, + 635 + ], + "spans": [ + { + "bbox": [ + 46, + 599, + 287, + 635 + ], + "type": "text", + "content": "With ViLG-300, we can make convincing comparisons between ERNIE-ViLG 2.0 and DALL-E " + }, + { + "bbox": [ + 46, + 599, + 287, + 635 + ], + "type": "inline_equation", + "content": "2^{5}" + }, + { + "bbox": [ + 46, + 599, + 287, + 635 + ], + "type": "text", + "content": ", Stable Diffusion" + }, + { + "bbox": [ + 46, + 599, + 287, + 635 + ], + "type": "inline_equation", + "content": "^{67}" + }, + { + "bbox": [ + 46, + 599, + 287, + 635 + ], + "type": "text", + "content": ". For evaluation, five raters are presented with two sets" + } + ] + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 315, + 76, + 416, + 137 + ], + "blocks": [ + { + "bbox": [ + 315, + 76, + 416, + 137 + ], + "lines": [ + { + "bbox": [ + 315, + 76, + 416, + 137 + ], + "spans": [ + { + "bbox": [ + 315, + 76, + 416, + 137 + ], + "type": "image", + "image_path": "11d548238597a109c14f4d0bb66136530abf393ee35e9fdbd9a05531481cfe33.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 321, + 140, + 415, + 149 + ], + "lines": [ + { + "bbox": [ + 321, + 140, + 415, + 149 + ], + "spans": [ + { + "bbox": [ + 321, + 140, + 415, + 149 + ], + "type": "text", + "content": "(a) Knowledge enhancement." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 11 + }, + { + "type": "image", + "bbox": [ + 430, + 76, + 536, + 137 + ], + "blocks": [ + { + "bbox": [ + 430, + 76, + 536, + 137 + ], + "lines": [ + { + "bbox": [ + 430, + 76, + 536, + 137 + ], + "spans": [ + { + "bbox": [ + 430, + 76, + 536, + 137 + ], + "type": "image", + "image_path": "0ed21de18038d5d08c8ff3b22e790c5399e6863d6dc48e6d00b92f48a8f5444b.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 430, + 140, + 538, + 150 + ], + "lines": [ + { + "bbox": [ + 430, + 140, + 538, + 150 + ], + "spans": [ + { + "bbox": [ + 430, + 140, + 538, + 150 + ], + "type": "text", + "content": "(b) Mixture-of-denoising-experts." + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_caption" + } + ], + "index": 13 + }, + { + "type": "image", + "bbox": [ + 308, + 194, + 544, + 342 + ], + "blocks": [ + { + "bbox": [ + 306, + 159, + 547, + 182 + ], + "lines": [ + { + "bbox": [ + 306, + 159, + 547, + 182 + ], + "spans": [ + { + "bbox": [ + 306, + 159, + 547, + 182 + ], + "type": "text", + "content": "Figure 5. Performance with various strategies in ERNIE-ViLG 2.0. Here we draw pareto curves with guidance scale [2,3,4,5,6,7,8,9]." + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 308, + 194, + 544, + 342 + ], + "lines": [ + { + "bbox": [ + 308, + 194, + 544, + 342 + ], + "spans": [ + { + "bbox": [ + 308, + 194, + 544, + 342 + ], + "type": "image", + "image_path": "bd405357ab018fbe892aa23985a9177836dea1af05bd7e00f52a6cb11164cad4.jpg" + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 350, + 547, + 373 + ], + "lines": [ + { + "bbox": [ + 305, + 350, + 547, + 373 + ], + "spans": [ + { + "bbox": [ + 305, + 350, + 547, + 373 + ], + "type": "text", + "content": "Figure 6. Samples from ViLG-300 with different knowledge enhancement strategies (left) and different number of experts (right)." + } + ] + } + ], + "index": 17, + "angle": 0, + "type": "image_caption" + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 396, + 547, + 623 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 396, + 547, + 623 + ], + "spans": [ + { + "bbox": [ + 304, + 396, + 547, + 623 + ], + "type": "text", + "content": "of images generated by ERNIE-ViLG 2.0 and the compared model. Next, they are asked to compare these images from two dimensions of image-text alignment and image fidelity, and then select the model they prefer, or respond that there is no measurable difference between two models. Throughout the process, raters are unaware of which model the image is generated from, and we do not apply any filtering strategy to the rating results. Figure 3 shows that human raters prefer ERNIE-ViLG 2.0 over all other models in both imagedtext alignment (56.5%±3.8% and 68.2%±3.8% when compared to DALL-E 2 and Stable Diffusion, respectively) and image fidelity (58.8%±3.6% to DALL-E 2, 66.5%±3.5% to Stable Diffusion, respectively), which again proves that ERNIE-ViLG 2.0 can generate high-quality images that conform to the text, with the help of knowledge enhancement and mixture-of-denoising-experts strategies. Beyond text relevancy and image fidelity, we also observe that ERNIE-ViLG 2.0 can generate images with better sharpness and textures than baseline models." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 306, + 634, + 368, + 647 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 634, + 368, + 647 + ], + "spans": [ + { + "bbox": [ + 306, + 634, + 368, + 647 + ], + "type": "text", + "content": "3.3. Analysis" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 654, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 654, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 654, + 547, + 713 + ], + "type": "text", + "content": "To examine the effectiveness of our design philosophy, we conduct two groups of ablation studies. Similar to the main experiment, we also provide both automatic metrics and intuitive showcases to demonstrate the advantages of each strategy in ERNIE-ViLG 2.0 here." + } + ] + } + ], + "index": 20 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 46, + 644, + 287, + 673 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 644, + 287, + 673 + ], + "spans": [ + { + "bbox": [ + 46, + 644, + 287, + 673 + ], + "type": "text", + "content": "4https://github.com/PaddlePaddle/ERNIE/tree/ernie-kit-open-v1.0/Research/ERNIE-ViLG2/data/ViLG-300.csv" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 59, + 673, + 199, + 684 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 673, + 199, + 684 + ], + "spans": [ + { + "bbox": [ + 59, + 673, + 199, + 684 + ], + "type": "text", + "content": "5 https://openai.com/dall-e-2/" + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 59, + 684, + 223, + 693 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 684, + 223, + 693 + ], + "spans": [ + { + "bbox": [ + 59, + 684, + 223, + 693 + ], + "type": "inline_equation", + "content": "^{6}" + }, + { + "bbox": [ + 59, + 684, + 223, + 693 + ], + "type": "text", + "content": "https://beta.dreamstudio.ai/dream" + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 48, + 693, + 287, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 693, + 287, + 712 + ], + "spans": [ + { + "bbox": [ + 48, + 693, + 287, + 712 + ], + "type": "text", + "content": "7We use DALL-E 2 and Stable Diffusion interfaces to generate images on October 25, 2022, before the CVPR 2023 submission deadline." + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "10140" + } + ] + } + ], + "index": 26 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 49, + 72, + 286, + 112 + ], + "blocks": [ + { + "bbox": [ + 49, + 72, + 286, + 112 + ], + "lines": [ + { + "bbox": [ + 49, + 72, + 286, + 112 + ], + "spans": [ + { + "bbox": [ + 49, + 72, + 286, + 112 + ], + "type": "image", + "image_path": "6abde2dc5018772b695b8234b609d73aaceea3c7f700cfdcfc7647e0baf61952.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 123, + 288, + 157 + ], + "lines": [ + { + "bbox": [ + 46, + 123, + 288, + 157 + ], + "spans": [ + { + "bbox": [ + 46, + 123, + 288, + 157 + ], + "type": "text", + "content": "Figure 7. The visualization of cross-attention maps in different denoising timesteps, where each value in the image space is the average of attention from this image token to all text tokens." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 184, + 289, + 507 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 184, + 289, + 507 + ], + "spans": [ + { + "bbox": [ + 47, + 184, + 289, + 507 + ], + "type": "text", + "content": "Knowledge Enhancement Strategies. In this part, we focus on the impact of various knowledge enhancement strategies by training a series of lightweight models, with 500M text encoders, 870M U-Nets, and 500M training samples. The pareto curves in Figure 5a demonstrate that incorporating knowledge in the learning process brings significant performance gains in image fidelity and image-text alignment. Specifically, (1) the benefits of textual knowledge are mainly reflected in precise fine-grained semantic control (w/ textual), (2) only utilizing object knowledge may not be able to steadily promote the performance (w/ object), while taking synthetic descriptions into consideration is an effective solution to make full use of visual knowledge (w/ visual). Figure 6 provides more visual comparisons to intuitively demonstrate the changes brought by each strategy. When handling complex prompts, baseline model faces problems such as the absence of key objects or incorrect assignment of attributes. At this point, textual knowledge helps the model accurately understand the attributes of each object, but the generated images sometimes fall into a new problem of distortion. Complementarily, visual knowledge promotes the generation of high-fidelity images, but it cannot well understand specific entities in text. Eventually, the combination of two kinds of knowledge harmoniously promotes the model from single- and multi-modal views, which ensures high fidelity and boost the image-text alignment in fine-grained visual scene." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 510, + 289, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 510, + 289, + 714 + ], + "spans": [ + { + "bbox": [ + 47, + 510, + 289, + 714 + ], + "type": "text", + "content": "Mixture-of-Denoising-Experts Strategies. Based on the above lightweight settings, we further train the baseline model with 500M samples, and then train 200M samples for each denoising expert. Figure 5b shows that with the increasing number of denoising experts, the overall performance is gradually improved, proving that scaling the size of U-Net is also an effective solution to achieve better image quality. More showcases are provided in Figure 6. When the number of experts increases from 1 to 10, the model can not only better handle the coupling between different elements but also generate images with more natural textures. For instance, the numbers on clocks become clearer, the proportion of wolf and suit becomes more harmonious, and the model can generate more photorealistic pictures instead of cartoon drawings. We also tried to analyze the impact of the amount of denoising experts and training samples, and found that using more expert networks has better performance than" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 305, + 73, + 464, + 84 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 73, + 464, + 84 + ], + "spans": [ + { + "bbox": [ + 305, + 73, + 464, + 84 + ], + "type": "text", + "content": "using a network to train more samples." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 84, + 547, + 300 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 84, + 547, + 300 + ], + "spans": [ + { + "bbox": [ + 304, + 84, + 547, + 300 + ], + "type": "text", + "content": "Figure 7 further visualizes the cross-attention maps from image features to text representations in denoising experts during 1,000-step denoising process, where these steps shown are denoised by different experts. As shown in the illustration, attentions of different denoising timesteps vary. Specifically, the attention maps of timesteps " + }, + { + "bbox": [ + 304, + 84, + 547, + 300 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 84, + 547, + 300 + ], + "type": "text", + "content": " near 1,000 are almost evenly distributed over the whole image, which is because the input of these steps is close to Gaussian noise and the image layout is unclear, so all the image tokens have to attend to the text prompt to generate image skeleton. When the timesteps are close to 1, attention maps concentrate more on foreground objects. For these timesteps, the input to denoising network is close to the final image and the layout is clear, and only a few parts of the image need to focus on the text to fill in the details of object. These observations again illustrate the difference among denoising timesteps and demonstrate the need to disentangle different timesteps with multiple experts." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 305, + 311, + 392, + 323 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 311, + 392, + 323 + ], + "spans": [ + { + "bbox": [ + 305, + 311, + 392, + 323 + ], + "type": "text", + "content": "4. Related Work" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 331, + 547, + 545 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 331, + 547, + 545 + ], + "spans": [ + { + "bbox": [ + 304, + 331, + 547, + 545 + ], + "type": "text", + "content": "Text-to-Image Generation. Text-to-image generation is the task of synthesizing images according to natural language descriptions. Early works adopted generative adversarial networks [7] to produce images based on text [36,41,44,47]. Inspired by the success of transformers in various generation tasks [37], models such as ERNIE-ViLG [45], DALL-E [23], Cogview [2], Make-A-Scene [6], and Parti [43] have also explored text-to-image generation as a sequence-to-sequence problem, with auto-regressive transformers as generators and text/image tokens as input/output sequences. Recently, another line of works have applied diffusion models [30], shaping it as an iterative denoising task [9, 27, 31]. By adding text condition in the denoising steps, practices such as LDM [25], DALL-E 2 [22], and Imagen [26] constantly set new records in text-to-image generation. Based on diffusion models as the backbone, ERNIE-ViLG 2.0 proposes incorporating knowledge of scene and mixture-of-denoising-experts mechanism into the denoising process." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 546, + 548, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 546, + 548, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 546, + 548, + 714 + ], + "type": "text", + "content": "Knowledge-Enhanced Pre-trained Models. While transformers benefit from pre-training on large-scale data, many attempts have been adding knowledge to guide them to focus on key elements during learning. For language-based tasks, knowledge-enhanced models used knowledge masking strategy [11, 34] or knowledge-aware pre-training tasks [33, 35] to understand the language data distribution. As for vision-language multi-modal discrimination models, OSCAR [14], ERNIE-ViL [42] and ERNIE-Layout [19] leveraged object tags, scene graphs, and document layouts as extra knowledge to help the models better align language and vision modalities. Among multi-modal generation models, Make-A-Scene [6] emphasized the importance of object and face regions by integrating domain-specific perceptual knowledge." + } + ] + } + ], + "index": 8 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "10141" + } + ] + } + ], + "index": 9 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 144 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 144 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 144 + ], + "type": "text", + "content": "While current text-to-image diffusion models suffer from attribute misalignment problems [22], they have not employed any specific knowledge of objects. Herein, ERNIE-ViLG 2.0 utilizes the knowledge of key elements in images and text to enhance diffusion models, leading to better fine-grained image-text alignment in generated pictures." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 144, + 289, + 348 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 144, + 289, + 348 + ], + "spans": [ + { + "bbox": [ + 46, + 144, + 289, + 348 + ], + "type": "text", + "content": "Mixture-of-Expert. Mixture-of-Experts (MoE) in neural networks means dividing specific parts of the parameters into subsets, each of which is called an expert [4, 29]. During the forward pass, a router assigns experts to different input, and each input only interacts with the experts assigned to. The router is a critical part of MoE. In language tasks, the most common strategy is a matching algorithm that assigns each text token to several experts in the linear feed-forward layer [5, 8, 12, 24]. While most practices formulate multiple experts in only the linear layers, some works also use an entire language model as an expert [13]. Beyond the natural language processing tasks, the idea of MoE have also been applied to vision models [20] and Mixture-of-Modality-Expert in multi-modal transformers [17, 39, 40]. In ERNIE-ViLG 2.0, the MoDE mechanism takes multiple denoising U-Nets as experts. It uses the denoising step index as the fixed router to determine which expert to use." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 358, + 251, + 371 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 358, + 251, + 371 + ], + "spans": [ + { + "bbox": [ + 47, + 358, + 251, + 371 + ], + "type": "text", + "content": "5. Risks, Limitations, and Future Work" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 378, + 288, + 498 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 378, + 288, + 498 + ], + "spans": [ + { + "bbox": [ + 46, + 378, + 288, + 498 + ], + "type": "text", + "content": "Model Usage and Data Bias. Text-to-image generation models trained by large-scale image-text data have all faced similar risks regarding to inappropriate usage of generation and data bias [22, 25, 26]. Considering that text-to-image models help people realize their imagination with less effort, the malicious use of models may result in unexpected deceptive or harmful outcomes. Moreover, since the models are trained on datasets consisting of images and their alt-text crawled from websites, the generated images may exhibit social and cultural bias in the datasets and websites." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 498, + 290, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 498, + 290, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 498, + 290, + 714 + ], + "type": "text", + "content": "Character Rendering. Figure 8 shows two successful character rendering cases (a, b) and one failure case (c). Character rendering is a challenging task for ERNIE-ViLG 2.0 for two reasons. First, the training data contains both Chinese text-image pairs and English text-image pairs translated into Chinese. When a text prompt mentions characters, the characters in the image could be in Chinese or English, and it is hard for the model to learn corresponding characters in both languages simultaneously. In the cases of successful character rendering that we observed, the characters could be words that are common in Chinese and do not have an exact match in English, such as “福” (“blessing, happiness, good luck” in English) in Figure 8a, or numbers which are the same in English and Chinese images, such as “20” in Figure 8b. The second reason that makes character rendering difficult is probably that Chinese characters are complex combinations of strokes without basic components like English letters. In Figure 8c, the model does learn that it should write some" + } + ] + } + ], + "index": 4 + }, + { + "type": "image", + "bbox": [ + 310, + 70, + 383, + 143 + ], + "blocks": [ + { + "bbox": [ + 310, + 70, + 383, + 143 + ], + "lines": [ + { + "bbox": [ + 310, + 70, + 383, + 143 + ], + "spans": [ + { + "bbox": [ + 310, + 70, + 383, + 143 + ], + "type": "image", + "image_path": "b97a5f692b3780d04e0e32031357ab30ec5464f7290f70a8442c416ee5c9bfa1.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 321, + 147, + 374, + 156 + ], + "lines": [ + { + "bbox": [ + 321, + 147, + 374, + 156 + ], + "spans": [ + { + "bbox": [ + 321, + 147, + 374, + 156 + ], + "type": "text", + "content": "(a)国风福字挂饰" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 310, + 157, + 383, + 173 + ], + "lines": [ + { + "bbox": [ + 310, + 157, + 383, + 173 + ], + "spans": [ + { + "bbox": [ + 310, + 157, + 383, + 173 + ], + "type": "text", + "content": "A hanging ornament with \"福\" in Chinese fashion" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 384, + 146, + 464, + 156 + ], + "lines": [ + { + "bbox": [ + 384, + 146, + 464, + 156 + ], + "spans": [ + { + "bbox": [ + 384, + 146, + 464, + 156 + ], + "type": "text", + "content": "(b) 生日蛋糕上有蜡烛“20”" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 305, + 183, + 545, + 217 + ], + "lines": [ + { + "bbox": [ + 305, + 183, + 545, + 217 + ], + "spans": [ + { + "bbox": [ + 305, + 183, + 545, + 217 + ], + "type": "text", + "content": "Figure 8. Examples of character rendering. The model successfully renders simple characters specified in the prompt, while for more difficult cases, the model only learns the position for now." + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_caption" + } + ], + "index": 5 + }, + { + "type": "image", + "bbox": [ + 388, + 70, + 462, + 143 + ], + "blocks": [ + { + "bbox": [ + 388, + 70, + 462, + 143 + ], + "lines": [ + { + "bbox": [ + 388, + 70, + 462, + 143 + ], + "spans": [ + { + "bbox": [ + 388, + 70, + 462, + 143 + ], + "type": "image", + "image_path": "713143af1965d7c0112976ad94198564fe85c634f050019293a96141e9c8d472.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 394, + 157, + 455, + 173 + ], + "lines": [ + { + "bbox": [ + 394, + 157, + 455, + 173 + ], + "spans": [ + { + "bbox": [ + 394, + 157, + 455, + 173 + ], + "type": "text", + "content": "A birthday cake with candles of \"20\" on it" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 467, + 70, + 540, + 143 + ], + "blocks": [ + { + "bbox": [ + 467, + 70, + 540, + 143 + ], + "lines": [ + { + "bbox": [ + 467, + 70, + 540, + 143 + ], + "spans": [ + { + "bbox": [ + 467, + 70, + 540, + 143 + ], + "type": "image", + "image_path": "8a821fd422a15738138005f0abb2d82f6d515c43120bdde1abe7cf5d0caf6791.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 484, + 147, + 523, + 156 + ], + "lines": [ + { + "bbox": [ + 484, + 147, + 523, + 156 + ], + "spans": [ + { + "bbox": [ + 484, + 147, + 523, + 156 + ], + "type": "text", + "content": "(c)国画葡萄" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 465, + 161, + 542, + 170 + ], + "lines": [ + { + "bbox": [ + 465, + 161, + 542, + 170 + ], + "spans": [ + { + "bbox": [ + 465, + 161, + 542, + 170 + ], + "type": "text", + "content": "Chinese painting of grapes" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_caption" + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 238, + 545, + 261 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 238, + 545, + 261 + ], + "spans": [ + { + "bbox": [ + 305, + 238, + 545, + 261 + ], + "type": "text", + "content": "Chinese characters in the top right corner, but it only paints meaningless strokes there." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 262, + 546, + 380 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 262, + 546, + 380 + ], + "spans": [ + { + "bbox": [ + 305, + 262, + 546, + 380 + ], + "type": "text", + "content": "Variation of Mixture-of-Denoising-Experts. Section 3.3 shows that using more denoising experts leads to better model performance. It indicates that using parallel U-Net experts is an effective way to augment the denoising network. Due to the computation limitation, we only try using up to 10 experts in this work, while we believe that exploring more denoising experts and multiple text encoders as experts is a meaningful future direction. Herein, we can further scale up the model and allow it to learn data distribution better with similar inference time." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 392, + 383, + 403 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 392, + 383, + 403 + ], + "spans": [ + { + "bbox": [ + 306, + 392, + 383, + 403 + ], + "type": "text", + "content": "6. Conclusions" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 305, + 411, + 547, + 651 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 411, + 547, + 651 + ], + "spans": [ + { + "bbox": [ + 305, + 411, + 547, + 651 + ], + "type": "text", + "content": "We present ERNIE-ViLG 2.0, the first Chinese large-scale text-to-image generation model based on diffusion models. To improve the fine-grained control of scene semantics, we incorporate visual and textual knowledge of the scene into diffusion models. To disentangle the model parameters for different denoising timesteps, we introduce MoDE and scale up the model parameters to 24B with a relatively short inference time. Experiments show that ERNIE-ViLG 2.0 achieves state-of-the-art on MS-COCO and each proposed mechanism contributes to the final results. To allow fair comparisons between Chinese and English text-to-image models, we collect a bilingual prompt set ViLG-300, and human evaluation indicates that ERNIE-ViLG 2.0 is preferred over strong baselines in both text relevancy and image fidelity. Further analysis suggests that different knowledge sources improve the generation in different aspects, and using more experts results in better image quality. In the future, we intend to enrich external image-text alignment knowledge and expand the usage of multiple experts to advance the generation. See also Appendix for more details on training and evaluation." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 305, + 665, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 665, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 305, + 665, + 547, + 715 + ], + "type": "text", + "content": "Acknowledgement This work was partly supported by National Natural Science Foundation of China (62271359). We thank Yehan Zheng for help on dataset collection; Weixin Liu and Bin Shan for discussions on paper." + } + ] + } + ], + "index": 19 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "10142" + } + ] + } + ], + "index": 20 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 53, + 92, + 289, + 713 + ], + "type": "list", + "angle": 0, + "index": 10, + "blocks": [ + { + "bbox": [ + 53, + 92, + 289, + 170 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 92, + 289, + 170 + ], + "spans": [ + { + "bbox": [ + 53, + 92, + 289, + 170 + ], + "type": "text", + "content": "[1] Peter Anderson, Xiaodong He, Chris Buehler, Damien Teney, Mark Johnson, Stephen Gould, and Lei Zhang. 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Our pre-train-free ESLAM model reconstructs scene details more accurately than existing works: iMAP* [59] and NICE-SLAM [87], while it runs up to $\\times 10$ faster (see Sec. 4.2 for runtime analysis). The ground truth image is rendered with ReplicaViewer [57]." + ], + "image_footnote": [], + "bbox": [ + 282, + 273, + 483, + 364 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/51ddac899f9cb8262d233931a44e73d1f49c9078fd410fe79fd3d706737b3c73.jpg", + "image_caption": [ + "ESLAM (ours)" + ], + "image_footnote": [], + "bbox": [ + 486, + 273, + 687, + 364 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/0a17d4523d025d700ad7c877f6805e8cb9614a7418722ac1a33e16326bc6afe0.jpg", + "image_caption": [ + "Ground Truth" + ], + "image_footnote": [], + "bbox": [ + 689, + 273, + 890, + 364 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 424, + 313, + 439 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "We present ESLAM, an efficient implicit neural representation method for Simultaneous Localization and Mapping (SLAM). ESLAM reads RGB-D frames with unknown camera poses in a sequential manner and incrementally reconstructs the scene representation while estimating the current camera position in the scene. We incorporate the latest advances in Neural Radiance Fields (NeRF) into a SLAM system, resulting in an efficient and accurate dense visual SLAM method. Our scene representation consists of multiscale axis-aligned perpendicular feature planes and shallow decoders that, for each point in the continuous space, decode the interpolated features into Truncated Signed Distance Field (TSDF) and RGB values. Our extensive experiments on three standard datasets, Replica, ScanNet, and TUM RGB-D show that ESLAM improves the accuracy of 3D reconstruction and camera localization of state-of-the-art dense visual SLAM methods by more than $50\\%$ , while it runs up to $\\times 10$ faster and does not require any pre-training. Project page: https://www.idiap.ch/paper/eslam", + "bbox": [ + 75, + 455, + 473, + 743 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 768, + 209, + 784 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Dense visual Simultaneous Localization and Mapping (SLAM) is a fundamental challenge in 3D computer vision with several applications such as autonomous driving, robotics, and virtual/augmented reality. It is defined as constructing a 3D map of an unknown environment while simultaneously approximating the camera pose.", + "bbox": [ + 75, + 794, + 468, + 885 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "While traditional SLAM systems [16, 41, 45, 55, 76, 77]", + "bbox": [ + 96, + 885, + 468, + 901 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "mostly focus on localization accuracy, recent learning-based dense visual SLAM methods [2, 11, 25, 35, 60, 64, 65, 67, 81, 86] provide meaningful global 3D maps and show reasonable but limited reconstruction accuracy.", + "bbox": [ + 496, + 425, + 890, + 484 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Following the advent of Neural Radiance Fields (NeRF) [37] and the demonstration of their capacity to reason about the geometry of a large-scale scene [8, 13, 20, 22, 26, 75, 78] and reconstruct 3D surfaces [1, 29, 47, 48, 62, 71, 72, 82, 85], novel NeRF-based dense SLAM methods have been developed. In particular, iMAP [59] and NICE-SLAM [87] utilize neural implicit networks to achieve a consistent geometry representation.", + "bbox": [ + 496, + 484, + 892, + 606 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "IMAP [59] represents the geometry with a single huge MLP, similar to NeRF [37], and optimizes the camera poses during the rendering process. NICE-SLAM [87] improves iMAP by storing the representation locally on voxel grids to prevent the forgetting problem. Despite promising reconstruction quality, these methods are computationally demanding for real-time applications, and their ability to capture geometry details is limited. In addition, NICE-SLAM [87] uses frozen pre-trained MLPs, which limits its generalizability to novel scenes. We take NICE-SLAM [87] as a baseline and provide the following contributions:", + "bbox": [ + 496, + 607, + 893, + 773 + ], + "page_idx": 0 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- We leverage implicit Truncated Signed Distance Field (TSDF) [1] to represent geometry, which converges noticeably faster than the common rendering-based representations like volume density [59] or occupancy [87] and results in higher quality reconstruction.", + "Instead of storing features on voxel grids, we propose employing multi-scale axis-aligned feature planes [6]" + ], + "bbox": [ + 517, + 782, + 890, + 901 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 810, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "17408", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "which leads to reducing the memory footprint growth rate w.r.t. scene side-length from cubic to quadratic.", + "bbox": [ + 107, + 90, + 467, + 121 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "- We benchmark our method on three challenging datasets, Replica [57], ScanNet [12], and TUM RGB-D [58], to demonstrate the performance of our method in comparison to existing ones and provide an extensive ablation study to validate our design choices.", + "bbox": [ + 96, + 132, + 467, + 208 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Thanks to the inherent smoothness of representing the scene with feature planes, our method produces higher-quality smooth surfaces without employing explicit smoothness loss functions like [70].", + "bbox": [ + 76, + 219, + 467, + 279 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Concurrent with our work, the followings also propose Radiance Fields-based SLAM systems: iDF-SLAM [38] also uses TSDF, but it is substantially slower and less accurate than NICE-SLAM [87]. Orbeez-SLAM [10] operates in real-time at the cost of poor 3D reconstruction. Compromising accuracy and quality, MeSLAM [27] introduces a memory-efficient SLAM. MonoNeuralFusion [88] proposes an incremental 3D reconstruction model, assuming that ground truth camera postures are available. Lastly, NeRF-SLAM [54] presents a monocular SLAM system with hierarchical volumetric Neural Radiance Fields optimized using an uncertainty-based depth loss.", + "bbox": [ + 75, + 280, + 467, + 460 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 76, + 476, + 217, + 491 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Dense Visual SLAM. The ubiquity of cameras has made visual SLAM a field of major interest in the last decades. Traditional visual SLAM employs pixel-wise optimization of geometric and/or photometric constraints from image information. Depending on the information source, visual SLAM divides into three main categories: visual-only [15-17,41,45,66], visual-inertial [3,28,39,42,53,69] and RGB-D [5, 14, 23, 44] SLAM. Visual-only SLAM uses single or multi-camera setups but presents higher technical challenges compared to others. Visual-inertial information can improve accuracy, but complexifies the system and requires an extra calibration step. The advent of the Kinect brought popularity to RGB-D setups with improved performance but had drawbacks such as larger memory and power requirements, and limitation to indoor settings. Recently, learning-based approaches [2,11,30,31,67] have made great advances in the field, improving both accuracy and robustness compared to traditional methods.", + "bbox": [ + 75, + 501, + 467, + 773 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Neural Implicit 3D Reconstruction. Neural Radiance Fields (NeRF) have impacted 3D Computer Vision applications, such as novel view synthesis [34, 36, 37, 68], surface reconstruction [46, 49, 71, 72, 82, 83, 85], dynamic scene representation [19, 50-52], and camera pose estimation [21, 32, 73, 79, 84]. The exploitation of neural implicit representations for 3D reconstruction at real-world scale is studied in [1, 4, 9, 29, 43, 63, 70, 74, 80]. The most related works", + "bbox": [ + 75, + 779, + 467, + 900 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "to ours are iMAP [59] and NICE-SLAM [87]. IMAP [59] presents a NeRF-style dense SLAM system. NICE-SLAM [87] extends iMAP [59] by modeling the scene with voxel grid features and decoding them into occupancies using pre-trained MLPs. However, the generalizability of NICE-SLAM [87] to novel scenes is limited because of the frozen pre-trained MLPs. Another issue is the cubic memory growth rate of their model, which results in using low-resolution voxel grids and losing fine geometry details. In contrast, we employ compact plane-based features [6] which are directly decoded to TSDF, improving both efficiency and accuracy of localization and reconstruction.", + "bbox": [ + 496, + 90, + 890, + 272 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "3. Method", + "text_level": 1, + "bbox": [ + 500, + 289, + 589, + 304 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "The overview of our method is shown in Fig. 2. Given a set of sequential RGB-D frames $\\{I_i, D_i\\}_{i=1}^M$ , our model predicts camera poses $\\{R_i|t_i\\}_{i=1}^M$ and an implicit TSDF $\\phi_g$ representation that can be used in marching cubes algorithm [33] to extract 3D meshes. We expect TSDF to denote the distance to the closest surface with a positive sign in the free space and a negative sign inside the surfaces. We employ normalized TSDF, such that it is zero on the surfaces and has a magnitude of one at the truncation distance $T$ , which is a hyper-parameter. Sec. 3.1 describes how we represent a scene with axis-aligned feature planes. Sec. 3.2 walks through the rendering process, which converts raw representations into pixel depths and colors. Sec. 3.3 introduces our loss functions. And Sec. 3.4 provides the details of localization and reconstruction in our SLAM system.", + "bbox": [ + 496, + 315, + 890, + 542 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "3.1. Axis-Aligned Feature Planes", + "text_level": 1, + "bbox": [ + 500, + 554, + 754, + 570 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Although voxel grid-based NeRF architectures [18, 61, 70] exhibit rapid convergence, they struggle with cubical memory growing. Different solutions have been proposed to mitigate the memory growth issue [6, 7, 40]. Inspired by [6], we employ a tri-plane architecture (see Fig. 2), in which we store and optimize features on perpendicular axis-aligned planes. Mimicking the trend in voxel-based methods [7, 40, 61], we propose using feature planes at two scales, i.e. coarse and fine. Coarse-level representation allows efficient reconstruction of free space with fewer sample points and optimization iterations. Moreover, we suggest employing separate feature planes for representing geometry and appearance, which mitigates the forgetting problem for geometry reconstruction since appearance fluctuates more frequently in a scene than geometry.", + "bbox": [ + 496, + 579, + 890, + 805 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Specifically, we use three coarse feature planes $\\{F_{g - xy}^{c}, F_{g - xz}^{c}, F_{g - yz}^{c}\\}$ and three fine ones $\\{F_{g - xy}^{f}, F_{g - xz}^{f}, F_{g - yz}^{f}\\}$ for representing the geometry. Similarly, three coarse $\\{F_{a - xy}^{c}, F_{a - xz}^{c}, F_{a - yz}^{c}\\}$ and three fine $\\{F_{a - xy}^{f}, F_{a - xz}^{f}, F_{a - yz}^{f}\\}$ planes are used for representing appearance of a scene. This architecture prevents model size from growing cubically with the", + "bbox": [ + 496, + 806, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "17409", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/9e46bfe5df6bfcce88422ca3957594a179c55ad87ed66096bec5bcbc49db5738.jpg", + "image_caption": [ + "Figure 2. The overview of ESLAM. Given the symmetry of our processes for geometry and appearance, we exhibit both processes on the same pipeline for simplicity. The symbol $*$ represents both geometry $g$ and appearance $a$ , e.g., $f_{*}(p_{n})$ can be either $f_{g}(p_{n})$ or $f_{a}(p_{n})$ . At an estimated camera pose $\\{R, t\\}$ , we cast a ray for each pixel and sample $N$ points $\\{p_n\\}_{n=1}^N$ along it (Sec. 3.2). Each point $p_n$ is projected onto the coarse and fine feature planes and bilinearly interpolates the four nearest neighbor features on each plane (Sec. 3.1). The interpolated features at each level are added together, and the results from both levels are concatenated together to form the inputs $\\{\\pmb{f}_{g}(p_{n}), \\pmb{f}_{a}(p_{n})\\}$ of the decoders $\\{h_g, h_a\\}$ (Sec. 3.1). The geometry decoder $h_g$ estimates TSDF $\\phi_{g}(p_{n})$ based on $f_{g}(p_{n})$ , and the appearance decoder $h_a$ estimates the raw color $\\phi_{a}(p_{n})$ based on $f_{a}(p_{n})$ for each point $p_n$ (Sec. 3.1). Once TSDFs and raw colors of all points on a ray are generated, our SDF-based rendering process estimates the depth $\\hat{\\pmb{d}}$ and the color $\\hat{\\pmb{c}}$ for each pixel (Sec. 3.2)." + ], + "image_footnote": [], + "bbox": [ + 96, + 93, + 890, + 421 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "scene side-length as is the case for voxel-based models.", + "bbox": [ + 75, + 556, + 442, + 570 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "To reason about the geometry of a point $p$ in the continuous space, we first project it onto all the geometry planes. The geometry feature $f_{g}(p)$ for point $p$ is then formed by 1) bilinearly interpolating the four nearest neighbors on each feature plane, 2) summing the interpolated coarse features and the fine ones respectively into the coarse output $f_{g}^{c}(p)$ and fine output $f_{g}^{f}(p)$ , and 3) concatenating the outputs together. Formally:", + "bbox": [ + 75, + 571, + 468, + 693 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nf _ {g} ^ {c} (p) = F _ {g - x y} ^ {c} (p) + F _ {g - x z} ^ {c} (p) + F _ {g - y z} ^ {c} (p)\n$$\n", + "text_format": "latex", + "bbox": [ + 135, + 704, + 408, + 722 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nf _ {g} ^ {f} (p) = F _ {g - x y} ^ {f} (p) + F _ {g - x z} ^ {f} (p) + F _ {g - y z} ^ {f} (p)\n$$\n", + "text_format": "latex", + "bbox": [ + 135, + 724, + 408, + 743 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {f} _ {\\boldsymbol {g}} (p) = \\left[ f _ {g} ^ {c} (p); f _ {g} ^ {f} (p) \\right] \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 135, + 744, + 468, + 763 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The appearance feature $f_{a}(p)$ is obtained similarly:", + "bbox": [ + 96, + 773, + 434, + 789 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nf _ {a} ^ {c} (p) = F _ {a - x y} ^ {c} (p) + F _ {a - x z} ^ {c} (p) + F _ {a - y z} ^ {c} (p)\n$$\n", + "text_format": "latex", + "bbox": [ + 135, + 799, + 410, + 818 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nf _ {a} ^ {f} (p) = F _ {a - x y} ^ {f} (p) + F _ {a - x z} ^ {f} (p) + F _ {a - y z} ^ {f} (p)\n$$\n", + "text_format": "latex", + "bbox": [ + 135, + 820, + 410, + 839 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {f} _ {\\boldsymbol {a}} (p) = \\left[ f _ {a} ^ {c} (p); f _ {a} ^ {f} (p) \\right] \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 135, + 840, + 468, + 859 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "These features are decoded into TSDF $\\phi_g(p)$ and raw color $\\phi_{a}(p)$ values via shallow two-layer MLPs $\\{h_g,h_a\\}$ :", + "bbox": [ + 76, + 869, + 468, + 902 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\phi_ {\\boldsymbol {g}} (p) = h _ {g} \\left(\\boldsymbol {f} _ {\\boldsymbol {g}} (p)\\right) \\text {a n d} \\phi_ {\\boldsymbol {a}} (p) = h _ {a} \\left(\\boldsymbol {f} _ {\\boldsymbol {a}} (p)\\right) \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 527, + 583, + 890, + 599 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "These raw TSDF and color outputs can be utilized for depth/color rendering as well as mesh extraction.", + "bbox": [ + 498, + 611, + 890, + 641 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. SDF-Based Volume Rendering", + "text_level": 1, + "bbox": [ + 500, + 650, + 769, + 667 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "When processing input frame $i$ , emulating the ray casting in NeRF [37], we select random pixels and calculate their corresponding rays using the current estimate of the camera pose $\\{R_i|t_i\\}$ . For rendering the depths and colors of the rays, we first sample $N_{strat}$ samples on each ray by stratified sampling and then sample additional $N_{imp}$ points near surfaces. For pixels with ground truth depths, the $N_{imp}$ additional points are sampled uniformly inside the truncation distance $T$ w.r.t. the depth measurement, whereas for other pixels, $N_{imp}$ points are sampled with the importance sampling technique [34, 37, 59, 70] based on the weights computed for the stratified samples.", + "bbox": [ + 496, + 674, + 890, + 853 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "For all $N = N_{strat} + N_{imp}$ points on a ray $\\{p_n\\}_{n=1}^N$ , we query TSDF $\\phi_g(p_n)$ and raw color $\\phi_a(p_n)$ from our networks and use the SDF-Based rendering approach in", + "bbox": [ + 496, + 854, + 890, + 901 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "17410", + "bbox": [ + 478, + 944, + 519, + 955 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "StyleSDF [47] to convert SDF values to volume densities:", + "bbox": [ + 76, + 90, + 468, + 106 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {\\sigma} \\left(p _ {n}\\right) = \\beta \\cdot \\text {S i g m o i d} \\left(- \\beta \\cdot \\phi_ {\\boldsymbol {g}} \\left(p _ {n}\\right)\\right) \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 148, + 130, + 468, + 148 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\beta$ is a learnable parameter that controls the sharpness of the surface boundary. Negative values of SDF push Sigmoid toward one, resulting in volume density inside the surface. The volume density then is used for rendering the color and depth of each ray:", + "bbox": [ + 76, + 155, + 468, + 231 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nw _ {n} = \\exp \\left(- \\sum_ {k = 1} ^ {n - 1} \\boldsymbol {\\sigma} (p _ {k})\\right) (1 - \\exp (- \\boldsymbol {\\sigma} (p _ {n})))\n$$\n", + "text_format": "latex", + "bbox": [ + 109, + 238, + 436, + 280 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {\\boldsymbol {c}} = \\sum_ {n = 1} ^ {N} w _ {n} \\phi_ {\\boldsymbol {a}} \\left(p _ {n}\\right) \\quad \\text {a n d} \\quad \\hat {\\boldsymbol {d}} = \\sum_ {n = 1} ^ {N} w _ {n} z _ {n} \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 122, + 282, + 468, + 324 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $z_{n}$ is the depth of point $p_n$ w.r.t. the camera pose.", + "bbox": [ + 76, + 330, + 446, + 345 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.3. Loss Functions", + "text_level": 1, + "bbox": [ + 76, + 354, + 228, + 369 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "One advantage of TSDF over other representations, such as occupancy, is that it allows us to use per-point losses, along with rendering ones. These losses account for the rapid convergence of our model. Following the practice in [1], assuming a batch of rays $R$ with ground truth depths are selected, we define the free space loss as:", + "bbox": [ + 76, + 377, + 468, + 467 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {f s} = \\frac {1}{| R |} \\sum_ {r \\in R} \\frac {1}{| P _ {r} ^ {f s} |} \\sum_ {p \\in P _ {r} ^ {f s}} (\\phi_ {\\boldsymbol {g}} (p) - 1) ^ {2} \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 132, + 474, + 468, + 513 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $P_r^{fs}$ is a set of points on the ray $r$ that lie between the camera center and the truncation region of the surface measured by the depth sensor. This loss function encourages TSDF $\\phi_g$ to have a value of one in the free space.", + "bbox": [ + 76, + 523, + 468, + 585 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "For sample points close to the surface and within the truncation region, we use the signed distance objective, which leverages the depth sensor measurement to approximate the signed distance field:", + "bbox": [ + 76, + 585, + 468, + 645 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {T} (P _ {r} ^ {T}) =\n$$\n", + "text_format": "latex", + "bbox": [ + 99, + 652, + 181, + 672 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\frac {1}{| R |} \\sum_ {r \\in R} \\frac {1}{| P _ {r} ^ {T} |} \\sum_ {p \\in P _ {r} ^ {T}} (z (p) + \\phi_ {\\mathbf {g}} (p) \\cdot T - D (r)) ^ {2} \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 102, + 674, + 468, + 712 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $z(p)$ is the planar depth of point $p$ w.r.t. camera, $T$ is the truncation distance, $D(r)$ is the ray depth measured by the sensor, and $P_r^T$ is a set of points on the ray $r$ that lie in the truncation region, i.e. $|z(p) - D(r)| < T$ . We apply the same loss to all points in the truncation region, but we differentiate the importance of points that are closer to the surface in the middle of the truncation region $P_r^{T - m}$ from those that are at the tail of the truncation region $P_r^{T - t}$ . Formally, we define $P_r^{T - m}$ as a set of points that $|z(p) - D(r)| < 0.4T$ , and define $P_r^{T - t} = P_r^T - P_r^{T - m}$ , then:", + "bbox": [ + 76, + 720, + 468, + 872 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {T - m} = \\mathcal {L} _ {T} \\left(P _ {r} ^ {T - m}\\right) \\quad \\text {a n d} \\quad \\mathcal {L} _ {T - t} = \\mathcal {L} _ {T} \\left(P _ {r} ^ {T - t}\\right) \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 104, + 878, + 468, + 897 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "This enables us to decrease the importance of $\\mathcal{L}_{T - t}$ in mapping, which leads to having a smaller effective truncation distance, reducing artifacts in occluded areas, and reconstructing with higher accuracy while leveraging the entire truncation distance in camera tracking.", + "bbox": [ + 498, + 90, + 890, + 166 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In addition to these two per-point loss functions, we also employ reconstruction losses. For pixels with ground truth depths, we impose consistency between the rendered depth and the depth measured by the sensor:", + "bbox": [ + 498, + 167, + 890, + 227 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {d} = \\frac {1}{| R |} \\sum_ {r \\in R} (\\hat {\\boldsymbol {d}} (r) - D (r)) ^ {2} \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 588, + 237, + 890, + 273 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Similarly, we impose consistency between the pixel colors and rendered colors:", + "bbox": [ + 498, + 284, + 890, + 313 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {c} = \\frac {1}{| R |} \\sum_ {r \\in R} (\\hat {\\boldsymbol {c}} (r) - I (r)) ^ {2} \\tag {10}\n$$\n", + "text_format": "latex", + "bbox": [ + 596, + 321, + 890, + 357 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $I(r)$ is the pixel color of ray $r$ .", + "bbox": [ + 500, + 369, + 748, + 383 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The global loss function of our method is defined as:", + "bbox": [ + 517, + 383, + 859, + 400 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} = \\lambda_ {f s} \\mathcal {L} _ {f s} + \\lambda_ {T - m} \\mathcal {L} _ {T - m} + \\lambda_ {T - t} \\mathcal {L} _ {T - t} + \\lambda_ {d} \\mathcal {L} _ {d} + \\lambda_ {c} \\mathcal {L} _ {c} \\tag {11}\n$$\n", + "text_format": "latex", + "bbox": [ + 504, + 411, + 888, + 441 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\{\\lambda_{fs},\\lambda_{T - m},\\lambda_{T - t},\\lambda_d,\\lambda_c\\}$ are the weighting coefficients. Note that $\\mathcal{L}_c$ is defined on all rays in a training batch, while other losses are only imposed on rays with ground truth measured depths. The global objective is the same for both mapping and tracking in our method, but the weighting coefficients are different.", + "bbox": [ + 498, + 454, + 890, + 544 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.4. Mapping and Tracking", + "text_level": 1, + "bbox": [ + 500, + 554, + 714, + 570 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Mapping. Our scene representation, i.e. the feature planes and MLP decoders, are randomly initialized at the beginning. With the first input frame $\\{I_0, D_0\\}$ , we fix the camera pose and optimize the feature planes and MLP decoders to best represent the first frame. For subsequent inputs, we update the scene representation iteratively every $k$ frames, and add the latest frame to the global keyframe list, following the practice in iMAP [59] and NICE-SLAM [87]. For mapping, we first choose $|R|$ pixels randomly from $W$ frames, which include the current frame, the previous two keyframes, and $W - 3$ frames randomly selected from the keyframe list. Then, we jointly optimize the feature planes, MLP decoders, and camera poses of the $W$ selected frames using the loss functions introduced in Sec. 3.3. Unlike NICE-SLAM [87], our method does not require a staged-optimization policy, and we simply optimize all scene parameters and camera poses simultaneously.", + "bbox": [ + 498, + 577, + 890, + 835 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Tracking. The localization process of our method is initiated for each input frame. The current estimate of the camera parameters, represented by translation vectors and quaternion rotations [56] $\\{R|t\\}$ , are optimized solely based", + "bbox": [ + 498, + 839, + 890, + 901 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "17411", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 3 + }, + { + "type": "table", + "img_path": "images/6da1aa0c91307e0420ab29371ba7260053f60e2bc05e2b6f3182e30cde255d39.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodReconstruction (cm)Localization (cm)
Depth L1↓Acc.↓Comp.↓Comp. Ratio (%)↑ATE Mean↓ATE RMSE↓
iMAP* [59]8.23 ± 0.887.16 ± 0.265.83 ± 0.2767.17 ± 2.702.59 ± 0.583.42 ± 0.87
NICE-SLAM [87]3.29 ± 0.331.66 ± 0.071.63 ± 0.0596.74 ± 0.361.56 ± 0.292.05 ± 0.45
ESLAM (ours)1.18 ± 0.050.97 ± 0.021.05 ± 0.0198.60 ± 0.070.52 ± 0.030.63 ± 0.05
", + "bbox": [ + 104, + 88, + 866, + 170 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Table 1. Quantitative comparison of our proposed ESLAM with existing NeRF-based dense visual SLAM models on the Replica dataset [57] for both reconstruction and localization accuracy. The results are the average and standard deviation of five runs on eight scenes of the Replica dataset [57]. Our method outperforms previous works by a high margin and has lower variances, indicating it is also more stable from run to run. The evaluation metrics for reconstruction are L1 loss (cm) between rendered and ground truth depth maps of 1000 random camera poses, reconstruction accuracy (cm), reconstruction completion (cm), and completion ratio (\\%). The evaluation metrics for localization are mean and RMSE of ATE (cm) [58]. For the details of the evaluations for each scene, refer to the supplementary. It should also be noted that our method runs up to $\\times 10$ faster on this dataset (see Sec. 4.2 for runtime analysis).", + "bbox": [ + 75, + 175, + 893, + 273 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/df6f19a7a5dcf0d5634fe30d8b88f5c6c966b6203fcbfe0bc20f69d1f6f40600.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 81, + 286, + 279, + 380 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/52334a27e92b9f6bd8a78c96d7e175bd8cba297d27a932a0a8ff8998b72adc7f.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 83, + 382, + 279, + 476 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/99e1511332064f946574ea150828fb085edc7f779b2bf4935cbf48603615287b.jpg", + "image_caption": [ + "iMAP*" + ], + "image_footnote": [], + "bbox": [ + 83, + 477, + 279, + 571 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/bd2de7132c5c8517c09971644492b7335324a19b3400a1881881b4425cf0595b.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 285, + 286, + 482, + 380 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/cbd65baef018ec4ed400a4a842a3a265fe2f3917c7fa40221837cda5383c6e8a.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 285, + 382, + 480, + 476 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/db7140467f172a23fb17fc3e755d62b60fd69056f18fd2e7bde42ccea384556d.jpg", + "image_caption": [ + "NICE-SLAM" + ], + "image_footnote": [], + "bbox": [ + 285, + 477, + 480, + 571 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/c46a87aacac28d4ebaf353ca610fe3ef1b3a11133b41b5dd1e8e762ce72a3a81.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 486, + 286, + 684, + 380 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/3c1f49bcefca8d3f50da9a3aafca1210f32538447b96dd865154a48f4a0bf857.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 488, + 382, + 684, + 476 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/89623a0a2ffd3f3dce57c2dd20b40fcf240842170c50a5f35585c814d968d0d9.jpg", + "image_caption": [ + "ESLAM (ours)", + "Figure 3. Qualitative comparison of our proposed ESLAM method's geometry reconstruction with existing NeRF-based dense visual SLAM models, iMAP* [59] and NICE-SLAM [87], on the Replica dataset [57]. Our method produces more accurate detailed geometry as well as higher-quality textures. The ground truth images are rendered with the ReplicaViewer software [57]. It should also be noted that our method runs up to $\\times 10$ faster on this dataset (see Sec. 4.2 for runtime analysis). For further qualitative analysis on this dataset, as well as videos demonstrating the localization and reconstruction process, refer to the supplementary." + ], + "image_footnote": [], + "bbox": [ + 488, + 477, + 684, + 571 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/496ef5241a9cfd25b5a9f6bb1fa859d4d550485618f7ff02e6fb50daf827e458.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 689, + 286, + 885, + 380 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/41e36306c11e615c1cc9d7e86a8b22896e8ba5f1758a9814a77975bdd788e73e.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 691, + 382, + 885, + 476 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/006983f2c589ec40d783cb3ca6840e6b9087d2231831e4019e51b5720d673012.jpg", + "image_caption": [ + "Ground Truth" + ], + "image_footnote": [], + "bbox": [ + 691, + 477, + 885, + 571 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "on our global loss function (see Sec. 3.3) with the gradient-based Adam optimizer [24]. No second-order optimizers or manifold operations are employed for camera tracking in our method. We exclude rays with no ground truth depths and outlier pixels from each optimization step. A pixel is considered an outlier if the difference between its measured depth and rendered depth is ten times greater than the batch's median rendered depth error.", + "bbox": [ + 75, + 680, + 470, + 801 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 76, + 815, + 209, + 832 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In this section, we validate that our method outperforms existing implicit representation-based methods in both localization and reconstruction accuracy on three standard benchmarks while running up to $\\times 10$ faster.", + "bbox": [ + 75, + 839, + 470, + 902 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Baselines. We compare our method to two existing state-of-the-art NeRF-based dense visual SLAM methods: iMAP [59] and NICE-SLAM [87]. Because iMAP is not open source, we use the iMAP* model in our experiment, which is the reimplementation of iMAP in [87].", + "bbox": [ + 496, + 680, + 892, + 756 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Datasets. We evaluate our method on three standard 3D benchmarks: Replica [57], ScanNet [12], and TUM RGB-D [58] datasets. We select the same scenes for evaluation as NICE-SLAM [87].", + "bbox": [ + 496, + 767, + 893, + 829 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Metrics. We borrow our evaluation metrics from NICE-SLAM [87]. For evaluating scene geometry, we use both 2D and 3D metrics. For the 2D metric, we render depth maps from 1000 random camera poses in each scene and calculate", + "bbox": [ + 496, + 839, + 893, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "17412", + "bbox": [ + 478, + 944, + 519, + 955 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/7e243b4f0c75fb9fc3c606c8600948e2095863db80463f725d0c21ce8d666724.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodATESc. 0000Sc. 0059Sc. 0106Sc. 0169Sc. 0181Sc. 0207Ave.
iMAP* [59]Mean34.2 ± 12.813.0 ± 2.412.9 ± 1.733.6 ± 15.320.8 ± 3.818.6 ± 6.022.2 ± 7.0
RMSE42.7 ± 16.617.8 ± 7.415.0 ± 1.739.1 ± 18.224.7 ± 5.820.1 ± 6.826.6 ± 9.4
NICE-SLAM [87]Mean9.9 ± 0.411.9 ± 1.87.0 ± 0.29.2 ± 1.012.2 ± 0.35.5 ± 0.39.3 ± 0.7
RMSE12.0 ± 0.514.0 ± 1.87.9 ± 0.210.9 ± 1.113.4 ± 0.36.2 ± 0.410.7 ± 0.7
ESLAM (ours)Mean6.5 ± 0.16.4 ± 0.46.7 ± 0.15.9 ± 0.18.3 ± 0.25.4 ± 0.16.5 ± 0.2
RMSE7.3 ± 0.28.5 ± 0.57.5 ± 0.16.5 ± 0.19.0 ± 0.25.7 ± 0.17.4 ± 0.2
", + "bbox": [ + 83, + 87, + 885, + 200 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 2. Quantitative comparison of our proposed ESLAM method's localization accuracy with existing NeRF-based dense visual SLAM models on the ScanNet dataset [12]. The results are the average and standard deviation of five runs on each scene of ScanNet [12]. Our method outperforms previous works and has lower variances, indicating it is also more stable from run to run. The evaluation metrics for localization are mean and RMSE of ATE (cm) [58]. It should also be noted that our method runs up to $\\times 6$ faster on this dataset (see Sec. 4.2 for runtime analysis).", + "bbox": [ + 75, + 205, + 893, + 275 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/ff31a36899570c251739a91b580fd61a4f970b1a4aabdce8e44cf304259eda09.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 81, + 290, + 344, + 405 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/0a317639eb62dce83b139f1397c2392da4bacd2e321f21e2f78f2942f356e1e5.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 352, + 289, + 616, + 406 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/a52246afbe81751d25ef1065531323ed6aad9e6765228ada1bd325d423770e61.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 624, + 290, + 885, + 406 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/5f99eb7df57d29b48b1e9a07aae863093d25a08c363c52124f4677b88da34e78.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 83, + 415, + 344, + 532 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/857423e71723c247bd6f6d2e4c8dd57139ed925e077f945bfa8b60326114cb1f.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 354, + 415, + 616, + 531 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/dda558e6a037d0b11ca21867dea1c662e11282396a017a1993e249c58f4b71df.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 624, + 415, + 885, + 532 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/553c0add2540cf2c226fd97e4bdffbf89ca05e0605e23ff7a5a841eb7edd2614.jpg", + "image_caption": [ + "iMAP*" + ], + "image_footnote": [], + "bbox": [ + 83, + 539, + 344, + 656 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/1f79952e3d5146a4c68b6d7be276b8ce5eb879b66234f345d3f210fe82f8c5b0.jpg", + "image_caption": [ + "NICE-SLAM" + ], + "image_footnote": [], + "bbox": [ + 352, + 539, + 614, + 656 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/d6afad49e2030248db35091d13133ec995cd2ab303ab08bc2ba326d5dd9248c8.jpg", + "image_caption": [ + "ESLAM (ours)", + "Figure 4. Qualitative comparison of our proposed ESLAM method's localization accuracy with existing NeRF-based dense visual SLAM models, iMAP* [59] and NICE-SLAM [87], on the ScanNet dataset [12]. The ground truth camera trajectory is shown in green, and the estimated trajectory is shown in red. Our method predicts more accurate camera trajectories and does not suffer from drifting issues. It should also be noted that our method runs up to $\\times 6$ faster on this dataset (see Sec. 4.2 for runtime analysis)." + ], + "image_footnote": [], + "bbox": [ + 624, + 540, + 885, + 656 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "the L1 difference between depths from ground truth meshes and the reconstructed ones. For the 3D metrics, we consider reconstruction accuracy [cm], reconstruction completion [cm], and completion ratio $[< 5\\mathrm{cm}\\%]$ . For evaluating these metrics, we build a TSDF volume for a scene with a resolution of $1\\mathrm{cm}$ and use the marching cubes algorithm [33] to obtain scene meshes. Before evaluating the 3D metrics for our method and for the baselines, we perform mesh culling as recommended in [1, 70]. For this purpose, we remove faces from a mesh that are not inside any", + "bbox": [ + 75, + 748, + 472, + 900 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "camera frustum or are occluded in all RGB-D frames. For evaluating camera localization, we use ATE [58].", + "bbox": [ + 498, + 748, + 890, + 779 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Implementation Details. The truncation distance $T$ is set to $6\\mathrm{cm}$ in our method. We employ coarse feature planes with a resolution of $24\\mathrm{cm}$ for both geometry and appearance. For fine feature planes, we use a resolution of $6\\mathrm{cm}$ for geometry and $3\\mathrm{cm}$ for appearance. All feature planes have 32 channels, resulting in a 64-channel concatenated feature input for the decoders. The decoders are two-layer MLPs", + "bbox": [ + 496, + 794, + 893, + 902 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "17413", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/3f1e3fdabf330312f732c32494fd45dd69522d5eda47312a1e8ee326957dcf9b.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 81, + 87, + 282, + 180 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/aa857cdc9a01f378bb08359b44d337bab7e4abd63d662d8a76d09b73844990c5.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 282, + 88, + 483, + 180 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/116cd37d850f88ae7199ed99a71c6319a1c41de1bc4d59626c202217b68a3566.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 483, + 88, + 684, + 180 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/f3da189632d3717f70520e1850adba07a8179da3132e5279cb1434615f8a911c.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 687, + 88, + 887, + 180 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/bb87ac1c0e4525ee039f9a3fc635675ec6d1522f298daa99a094a27b565f492d.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 80, + 181, + 282, + 273 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/f7b566926e75ae4b848797086fda2dc90c7b8adc2a7efa9c92d39368cd6ffa6a.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 282, + 181, + 483, + 273 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/b59d02cc78a36650838969c3d69b0cb4389d2549183e91c2bc01e0baa72b4f3f.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 485, + 181, + 684, + 273 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/7b72e65f3b74b285a5b3203fbb26b1f86b32acfa401c39fbf12abb245fae2321.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 687, + 181, + 887, + 273 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/f391a2abe1755b941c501299d6ff487cee01cfed01a94f1a6f1b6cf68f688f1b.jpg", + "image_caption": [ + "iMAP*" + ], + "image_footnote": [], + "bbox": [ + 81, + 275, + 282, + 371 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/c78412b6fe891b7152bedd7a01cc76657b15ef597ce6fcf7185f07b14d32a0bf.jpg", + "image_caption": [ + "NICE-SLAM" + ], + "image_footnote": [], + "bbox": [ + 282, + 275, + 483, + 371 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/b62632ea3d38af7582e4c02e77d622fe1e7a203544d3ea07ccb59003eef3dde8.jpg", + "image_caption": [ + "ESLAM (ours)", + "Figure 5. Qualitative comparison of our proposed ESLAM method's geometry reconstruction with existing NeRF-based dense visual SLAM models, iMAP* [59] and NICE-SLAM [87], on the ScanNet dataset [12]. Our method produces more accurate detailed geometry as well as higher-quality textures. The appearance of white backgrounds in ground truth meshes is due to the fact that the ground truth meshes of the ScanNet dataset [12] are incomplete. It should also be noted that our method runs up to $\\times 6$ faster on this dataset (see Sec. 4.2 for runtime analysis)." + ], + "image_footnote": [], + "bbox": [ + 485, + 275, + 684, + 371 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/1b66c7eb0b4cbaa159cf96288e81ce6477dbeefef4b6c615c5e6fe8a4cd10917.jpg", + "image_caption": [ + "Ground Truth" + ], + "image_footnote": [], + "bbox": [ + 687, + 275, + 887, + 371 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "with 32 channels in the hidden layer. For the Replica [57] dataset, we sample $N_{strat} = 32$ points for stratified sampling and $N_{imp} = 8$ points for importance sampling on each ray. And for the ScanNet [12] and TUM RGB-D [58] datasets, we set $N_{strat} = 48$ and $N_{imp} = 8$ .", + "bbox": [ + 75, + 470, + 468, + 547 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We use different set of loss coefficients for mapping and tracking. During mapping we set $\\lambda_{fs} = 5$ , $\\lambda_{T - m} = 200$ , $\\lambda_{T - t} = 10$ , $\\lambda_d = 0.1$ , and $\\lambda_c = 5$ . And during tracking, we set $\\lambda_{fs} = 10$ , $\\lambda_{T - m} = 200$ , $\\lambda_{T - t} = 50$ , $\\lambda_d = 1$ , and $\\lambda_c = 5$ . These coefficients are obtained by performing grid search in our experiments. For further details of our implementation, refer to the supplementary.", + "bbox": [ + 75, + 547, + 468, + 652 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.1. Experimental Results", + "text_level": 1, + "bbox": [ + 76, + 664, + 277, + 680 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Evaluation on Replica [57]. We provide the quantitative analysis of our experimental results on eight scenes of the Replica dataset [57] in Tab. 1. The numbers represent the average and standard deviation of the metrics for five independent runs. As shown in Tab. 1, our method outperforms the baselines for both reconstruction and localization accuracy. Our method also has lower variances, indicating that it is more stable and more robust than existing methods.", + "bbox": [ + 75, + 688, + 468, + 808 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Qualitative analysis on the Replica dataset [57] is provided in Fig. 3. The results show that our method reconstructs the details of the scenes more accurately and produces fewer artifacts. Although it is not the focus of this paper, our method also produces higher-quality colors for the reconstructed meshes.", + "bbox": [ + 75, + 810, + 468, + 898 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Evaluation on ScanNet [12]. We also benchmark ours and existing methods on multiple large scenes from ScanNet [12] to evaluate and compare their scalability. For evaluating camera localization, we conduct five independent experiments on each scene and report the average and standard deviation of the mean and RMSE of ATE [58] in Tab. 2. As demonstrated in the table, our method's localization is more accurate than existing methods. Our method is also considerably more stable from run to run as it has much lower standard deviations. We provide qualitative analysis of camera localization, along with geometry reconstruction, in Fig. 4. The results show that our method does not suffer from any large drifting and is more robust than existing methods.", + "bbox": [ + 496, + 470, + 890, + 667 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Since the ground truth meshes of the ScanNet dataset [12] are incomplete, we only provide qualitative analysis for geometry reconstruction, similar to previous works. The qualitative comparison in Fig. 5 validates that our model reconstructs more precise geometry and detailed textures compared to existing approaches.", + "bbox": [ + 496, + 683, + 890, + 773 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Evaluation on TUM RGB-D [58]. To further contrast the robustness of our method with the existing ones, we conduct an evaluation study on the real-world TUM RGB-D dataset [58]. Since there are no ground truth meshes for the scenes in this dataset, we only present the localization results in Tab. 3 and the qualitative analysis of rendered meshes in Fig. 6.", + "bbox": [ + 496, + 794, + 890, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "17414", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/69f676ea7ba4850e123bcd996e44f45b845e61cdaaaef558f5db28cbce5c88b5.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 83, + 87, + 277, + 193 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/b0102e0387427e255e011e38ab43e70e71826d611a57812baae7221bd7c75cbf.jpg", + "image_caption": [ + "Sample Image" + ], + "image_footnote": [], + "bbox": [ + 83, + 195, + 277, + 305 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/90fe874fd558e115abb596b689bbe270467eaaec92c9028b9c5a9f373ec91ec7.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 285, + 87, + 480, + 195 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/797290ddc05a8bda71cd0338f50cfb0868702f6979e13293ebf6dd7a738ee9f5.jpg", + "image_caption": [ + "iMAP*" + ], + "image_footnote": [], + "bbox": [ + 285, + 196, + 480, + 305 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/8f00e5b90af071416630a75cd714c858dbc1a087be0b3480b7a2eb185ca3ce67.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 488, + 87, + 684, + 196 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/1c1f84bc3bf4e40528ec8deadad14070a4d3f2cfbe406e8dc130b0c8fcaf3916.jpg", + "image_caption": [ + "NICE-SLAM", + "Figure 6. Qualitative comparison of our proposed ESLAM method's geometry reconstruction with existing NeRF-based dense visual SLAM models, iMAP* [59] and NICE-SLAM [87], on the TUM RGB-D dataset [58]. Our method produces more accurate detailed geometry as well as higher-quality textures. Since there are no ground truth meshes for this dataset, we depict a sample input image." + ], + "image_footnote": [], + "bbox": [ + 488, + 196, + 683, + 305 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/cad4003aa79b54cf2f3d8265f6a050724d61e03642833e1eadfaeabb220e6e71.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 692, + 95, + 885, + 196 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/5ec7f20951817b8bc5d70abc352f10762af60ec8891b1ac56f1497fc6af3b9b6.jpg", + "image_caption": [ + "ESLAM (ours)" + ], + "image_footnote": [], + "bbox": [ + 692, + 196, + 885, + 305 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/9bd60a116cb08e6b571a3107fe32225455ea66654f22371c672d8b4e0ec5b4f7.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
fr1/deskfr2/xyzfr3/office
iMAP* [59]4.902.055.80
NICE-SLAM [87]2.852.393.02
ESLAM (ours)2.471.112.42
", + "bbox": [ + 91, + 381, + 455, + 446 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/9a926a465fc0a27cb7ce3091b8157d342706ca71bf6ae9dfd3abbd05ca6f6df8.jpg", + "table_caption": [ + "Table 3. Quantitative comparison of our proposed ESLAM method's localization accuracy with existing NeRF-based dense visual SLAM models on the TUM RGB-D dataset [58]. The evaluation metric is ATE RMSE $\\downarrow$ (cm) [58]." + ], + "table_footnote": [], + "table_body": "
MethodSpeed FPT (s)Memory
# Param.Grow. R.
ReplicaiMAP* [59]5.200.22 M?
NICE-SLAM [87]2.1012.18 MO(L3)
ESLAM (ours)0.186.79 MO(L2)
ScanNetiMAP* [59]5.200.22 M?
NICE-SLAM [87]3.3522.04 MO(L3)
ESLAM (ours)0.5517.63 MO(L2)
", + "bbox": [ + 83, + 518, + 464, + 645 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 4. Runtime analysis of our method in comparison with existing ones in terms of average frame processing time (FPT), number of parameters, and model size growth rate w.r.t. scene side-length $L$ . All methods are benchmarked with an NVIDIA GeForce RTX 3090 GPU on room0 of Replica [57] and scene0000 of ScanNet [12]. Our method is significantly faster and does not grow cubically in size w.r.t. scene side-length $L$ . Note that iMAP [59] represents a whole scene in a single MLP, hence its small number of parameters. Accordingly, the scalability and growth rate of iMAP [59] w.r.t. the scene side-length $L$ are also unclear.", + "bbox": [ + 75, + 651, + 468, + 789 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.2. Runtime Analysis", + "text_level": 1, + "bbox": [ + 76, + 801, + 250, + 816 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We evaluate the speed and size of our method in comparison with existing approaches in Tab. 4. We report the average frame processing time (FPT), the number of parameters of the model, and memory growth rate w.r.t. scene side-length for the scenes room0 of Replica [57] and", + "bbox": [ + 75, + 824, + 468, + 902 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "scene0000 of ScanNet [12] datasets. All methods are benchmarked with an NVIDIA GeForce RTX 3090 GPU. The results indicate that our method is significantly faster than previous works on both datasets. Furthermore, in contrast to NICE-SLAM [87], our model size is smaller and does not grow cubically with the scene side-length.", + "bbox": [ + 496, + 383, + 890, + 476 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 487, + 617, + 502 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We presented ESLAM, a dense visual SLAM approach that leverages the latest advances in the Neural Radiance Fields study to improve both the speed and accuracy of neural implicit-based SLAM systems. We proposed replacing the voxel grid representation with axis-aligned feature planes to prevent the model size from growing cubically with respect to the scene side-length. We also demonstrated that modeling the scene geometry with Truncated Signed Distance Field (TSDF) leads to efficient and high-quality surface reconstruction. We verified through extensive experiments that our approach outperforms existing methods significantly in both reconstruction and localization accuracy while running up to one order of magnitude faster.", + "bbox": [ + 496, + 512, + 890, + 708 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "ESLAM accepts and deals with the forgetting problem in exchange for memory preservation. Due to the structure of our feature plane representation, updating features to adapt to new geometry may affect previously reconstructed geometries. To address this issue, we keep track of previous keyframes and allocate a large portion of computation resources to retain and remember previously reconstructed regions. Although ESLAM is substantially faster than competing approaches, handling the forgetting problem more efficiently could further reduce frame processing time.", + "bbox": [ + 496, + 709, + 890, + 859 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgement", + "text_level": 1, + "bbox": [ + 500, + 869, + 633, + 883 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "This research was supported by ams OSRAM.", + "bbox": [ + 500, + 885, + 805, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "17415", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 174, + 106 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Dejan Azinović, Ricardo Martin-Brualla, Dan B Goldman, Matthias Nießner, and Justus Thies. Neural rgb-d surface reconstruction. 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Mononeuralfusion: Online monocular neural 3d reconstruction with geometric priors. arXiv preprint arXiv:2209.15153, 2022. 2" + ], + "bbox": [ + 78, + 90, + 468, + 893 + ], + "page_idx": 11 + }, + { + "type": "page_number", + "text": "17419", + "bbox": [ + 478, + 944, + 519, + 955 + ], + "page_idx": 11 + } +] \ No newline at end of file diff --git a/2023/ESLAM_ Efficient Dense SLAM System Based on Hybrid Representation of Signed Distance Fields/d4f0d86a-9d2c-4b36-b0b6-8aa8c847e904_model.json b/2023/ESLAM_ Efficient Dense SLAM System Based on Hybrid Representation of Signed Distance Fields/d4f0d86a-9d2c-4b36-b0b6-8aa8c847e904_model.json new file mode 100644 index 0000000000000000000000000000000000000000..bdc4852e85fe2d9a767890b6d6007936c52a1b92 --- /dev/null +++ b/2023/ESLAM_ Efficient Dense SLAM System Based on Hybrid Representation of Signed Distance Fields/d4f0d86a-9d2c-4b36-b0b6-8aa8c847e904_model.json @@ -0,0 +1,3227 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.0, + 0.812, + 0.047 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.105, + 0.13, + 0.87, + 0.175 + ], + "angle": 0, + "content": "ESLAM: Efficient Dense SLAM System Based on Hybrid Representation of Signed Distance Fields" + }, + { + "type": "text", + "bbox": [ + 0.092, + 0.204, + 0.338, + 0.24 + ], + "angle": 0, + "content": "Mohammad Mahdi Johari Idiap Research Institute, EPFL" + }, + { + "type": "text", + "bbox": [ + 0.106, + 0.243, + 0.321, + 0.256 + ], + "angle": 0, + "content": "mohammad.johari@idiap.ch" + }, + { + "type": "text", + "bbox": [ + 0.437, + 0.205, + 0.55, + 0.238 + ], + "angle": 0, + "content": "Camilla Cartaams OSRAM" + }, + { + "type": "text", + "bbox": [ + 0.373, + 0.243, + 0.614, + 0.256 + ], + "angle": 0, + "content": "camilla-carta@ams-osram.com" + }, + { + "type": "text", + "bbox": [ + 0.651, + 0.205, + 0.877, + 0.256 + ], + "angle": 0, + "content": "François Fleuret \nUniversity of Geneva, EPFL \nfrancois.fleuret@unige.ch" + }, + { + "type": "image", + "bbox": [ + 0.08, + 0.275, + 0.282, + 0.366 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.165, + 0.369, + 0.2, + 0.379 + ], + "angle": 0, + "content": "iMAP*" + }, + { + "type": "image", + "bbox": [ + 0.284, + 0.275, + 0.485, + 0.365 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.351, + 0.369, + 0.416, + 0.379 + ], + "angle": 0, + "content": "NICE-SLAM" + }, + { + "type": "image", + "bbox": [ + 0.487, + 0.275, + 0.688, + 0.365 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.561, + 0.369, + 0.631, + 0.38 + ], + "angle": 0, + "content": "ESLAM (ours)" + }, + { + "type": "image", + "bbox": [ + 0.69, + 0.275, + 0.892, + 0.366 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.765, + 0.369, + 0.838, + 0.379 + ], + "angle": 0, + "content": "Ground Truth" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.383, + 0.893, + 0.412 + ], + "angle": 0, + "content": "Figure 1. Our pre-train-free ESLAM model reconstructs scene details more accurately than existing works: iMAP* [59] and NICE-SLAM [87], while it runs up to \\(\\times 10\\) faster (see Sec. 4.2 for runtime analysis). The ground truth image is rendered with ReplicaViewer [57]." + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.425, + 0.314, + 0.44 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.456, + 0.474, + 0.744 + ], + "angle": 0, + "content": "We present ESLAM, an efficient implicit neural representation method for Simultaneous Localization and Mapping (SLAM). ESLAM reads RGB-D frames with unknown camera poses in a sequential manner and incrementally reconstructs the scene representation while estimating the current camera position in the scene. We incorporate the latest advances in Neural Radiance Fields (NeRF) into a SLAM system, resulting in an efficient and accurate dense visual SLAM method. Our scene representation consists of multiscale axis-aligned perpendicular feature planes and shallow decoders that, for each point in the continuous space, decode the interpolated features into Truncated Signed Distance Field (TSDF) and RGB values. Our extensive experiments on three standard datasets, Replica, ScanNet, and TUM RGB-D show that ESLAM improves the accuracy of 3D reconstruction and camera localization of state-of-the-art dense visual SLAM methods by more than \\(50\\%\\), while it runs up to \\(\\times 10\\) faster and does not require any pre-training. Project page: https://www.idiap.ch/paper/eslam" + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.77, + 0.21, + 0.785 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.795, + 0.469, + 0.886 + ], + "angle": 0, + "content": "Dense visual Simultaneous Localization and Mapping (SLAM) is a fundamental challenge in 3D computer vision with several applications such as autonomous driving, robotics, and virtual/augmented reality. It is defined as constructing a 3D map of an unknown environment while simultaneously approximating the camera pose." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.886, + 0.469, + 0.902 + ], + "angle": 0, + "content": "While traditional SLAM systems [16, 41, 45, 55, 76, 77]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.426, + 0.892, + 0.486 + ], + "angle": 0, + "content": "mostly focus on localization accuracy, recent learning-based dense visual SLAM methods [2, 11, 25, 35, 60, 64, 65, 67, 81, 86] provide meaningful global 3D maps and show reasonable but limited reconstruction accuracy." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.486, + 0.893, + 0.607 + ], + "angle": 0, + "content": "Following the advent of Neural Radiance Fields (NeRF) [37] and the demonstration of their capacity to reason about the geometry of a large-scale scene [8, 13, 20, 22, 26, 75, 78] and reconstruct 3D surfaces [1, 29, 47, 48, 62, 71, 72, 82, 85], novel NeRF-based dense SLAM methods have been developed. In particular, iMAP [59] and NICE-SLAM [87] utilize neural implicit networks to achieve a consistent geometry representation." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.608, + 0.894, + 0.774 + ], + "angle": 0, + "content": "IMAP [59] represents the geometry with a single huge MLP, similar to NeRF [37], and optimizes the camera poses during the rendering process. NICE-SLAM [87] improves iMAP by storing the representation locally on voxel grids to prevent the forgetting problem. Despite promising reconstruction quality, these methods are computationally demanding for real-time applications, and their ability to capture geometry details is limited. In addition, NICE-SLAM [87] uses frozen pre-trained MLPs, which limits its generalizability to novel scenes. We take NICE-SLAM [87] as a baseline and provide the following contributions:" + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.784, + 0.892, + 0.86 + ], + "angle": 0, + "content": "- We leverage implicit Truncated Signed Distance Field (TSDF) [1] to represent geometry, which converges noticeably faster than the common rendering-based representations like volume density [59] or occupancy [87] and results in higher quality reconstruction." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.871, + 0.892, + 0.902 + ], + "angle": 0, + "content": "Instead of storing features on voxel grids, we propose employing multi-scale axis-aligned feature planes [6]" + }, + { + "type": "list", + "bbox": [ + 0.518, + 0.784, + 0.892, + 0.902 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "17408" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.109, + 0.092, + 0.468, + 0.122 + ], + "angle": 0, + "content": "which leads to reducing the memory footprint growth rate w.r.t. scene side-length from cubic to quadratic." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.133, + 0.468, + 0.209 + ], + "angle": 0, + "content": "- We benchmark our method on three challenging datasets, Replica [57], ScanNet [12], and TUM RGB-D [58], to demonstrate the performance of our method in comparison to existing ones and provide an extensive ablation study to validate our design choices." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.22, + 0.468, + 0.28 + ], + "angle": 0, + "content": "Thanks to the inherent smoothness of representing the scene with feature planes, our method produces higher-quality smooth surfaces without employing explicit smoothness loss functions like [70]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.281, + 0.468, + 0.462 + ], + "angle": 0, + "content": "Concurrent with our work, the followings also propose Radiance Fields-based SLAM systems: iDF-SLAM [38] also uses TSDF, but it is substantially slower and less accurate than NICE-SLAM [87]. Orbeez-SLAM [10] operates in real-time at the cost of poor 3D reconstruction. Compromising accuracy and quality, MeSLAM [27] introduces a memory-efficient SLAM. MonoNeuralFusion [88] proposes an incremental 3D reconstruction model, assuming that ground truth camera postures are available. Lastly, NeRF-SLAM [54] presents a monocular SLAM system with hierarchical volumetric Neural Radiance Fields optimized using an uncertainty-based depth loss." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.477, + 0.218, + 0.492 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.502, + 0.468, + 0.775 + ], + "angle": 0, + "content": "Dense Visual SLAM. The ubiquity of cameras has made visual SLAM a field of major interest in the last decades. Traditional visual SLAM employs pixel-wise optimization of geometric and/or photometric constraints from image information. Depending on the information source, visual SLAM divides into three main categories: visual-only [15-17,41,45,66], visual-inertial [3,28,39,42,53,69] and RGB-D [5, 14, 23, 44] SLAM. Visual-only SLAM uses single or multi-camera setups but presents higher technical challenges compared to others. Visual-inertial information can improve accuracy, but complexifies the system and requires an extra calibration step. The advent of the Kinect brought popularity to RGB-D setups with improved performance but had drawbacks such as larger memory and power requirements, and limitation to indoor settings. Recently, learning-based approaches [2,11,30,31,67] have made great advances in the field, improving both accuracy and robustness compared to traditional methods." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.78, + 0.468, + 0.901 + ], + "angle": 0, + "content": "Neural Implicit 3D Reconstruction. Neural Radiance Fields (NeRF) have impacted 3D Computer Vision applications, such as novel view synthesis [34, 36, 37, 68], surface reconstruction [46, 49, 71, 72, 82, 83, 85], dynamic scene representation [19, 50-52], and camera pose estimation [21, 32, 73, 79, 84]. The exploitation of neural implicit representations for 3D reconstruction at real-world scale is studied in [1, 4, 9, 29, 43, 63, 70, 74, 80]. The most related works" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.273 + ], + "angle": 0, + "content": "to ours are iMAP [59] and NICE-SLAM [87]. IMAP [59] presents a NeRF-style dense SLAM system. NICE-SLAM [87] extends iMAP [59] by modeling the scene with voxel grid features and decoding them into occupancies using pre-trained MLPs. However, the generalizability of NICE-SLAM [87] to novel scenes is limited because of the frozen pre-trained MLPs. Another issue is the cubic memory growth rate of their model, which results in using low-resolution voxel grids and losing fine geometry details. In contrast, we employ compact plane-based features [6] which are directly decoded to TSDF, improving both efficiency and accuracy of localization and reconstruction." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.29, + 0.59, + 0.305 + ], + "angle": 0, + "content": "3. Method" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.316, + 0.892, + 0.543 + ], + "angle": 0, + "content": "The overview of our method is shown in Fig. 2. Given a set of sequential RGB-D frames \\(\\{I_i, D_i\\}_{i=1}^M\\), our model predicts camera poses \\(\\{R_i|t_i\\}_{i=1}^M\\) and an implicit TSDF \\(\\phi_g\\) representation that can be used in marching cubes algorithm [33] to extract 3D meshes. We expect TSDF to denote the distance to the closest surface with a positive sign in the free space and a negative sign inside the surfaces. We employ normalized TSDF, such that it is zero on the surfaces and has a magnitude of one at the truncation distance \\(T\\), which is a hyper-parameter. Sec. 3.1 describes how we represent a scene with axis-aligned feature planes. Sec. 3.2 walks through the rendering process, which converts raw representations into pixel depths and colors. Sec. 3.3 introduces our loss functions. And Sec. 3.4 provides the details of localization and reconstruction in our SLAM system." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.555, + 0.755, + 0.571 + ], + "angle": 0, + "content": "3.1. Axis-Aligned Feature Planes" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.58, + 0.892, + 0.806 + ], + "angle": 0, + "content": "Although voxel grid-based NeRF architectures [18, 61, 70] exhibit rapid convergence, they struggle with cubical memory growing. Different solutions have been proposed to mitigate the memory growth issue [6, 7, 40]. Inspired by [6], we employ a tri-plane architecture (see Fig. 2), in which we store and optimize features on perpendicular axis-aligned planes. Mimicking the trend in voxel-based methods [7, 40, 61], we propose using feature planes at two scales, i.e. coarse and fine. Coarse-level representation allows efficient reconstruction of free space with fewer sample points and optimization iterations. Moreover, we suggest employing separate feature planes for representing geometry and appearance, which mitigates the forgetting problem for geometry reconstruction since appearance fluctuates more frequently in a scene than geometry." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.807, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Specifically, we use three coarse feature planes \\(\\{F_{g - xy}^{c}, F_{g - xz}^{c}, F_{g - yz}^{c}\\}\\) and three fine ones \\(\\{F_{g - xy}^{f}, F_{g - xz}^{f}, F_{g - yz}^{f}\\}\\) for representing the geometry. Similarly, three coarse \\(\\{F_{a - xy}^{c}, F_{a - xz}^{c}, F_{a - yz}^{c}\\}\\) and three fine \\(\\{F_{a - xy}^{f}, F_{a - xz}^{f}, F_{a - yz}^{f}\\}\\) planes are used for representing appearance of a scene. This architecture prevents model size from growing cubically with the" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "17409" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.098, + 0.094, + 0.891, + 0.422 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.43, + 0.895, + 0.542 + ], + "angle": 0, + "content": "Figure 2. The overview of ESLAM. Given the symmetry of our processes for geometry and appearance, we exhibit both processes on the same pipeline for simplicity. The symbol \\(*\\) represents both geometry \\(g\\) and appearance \\(a\\), e.g., \\(f_{*}(p_{n})\\) can be either \\(f_{g}(p_{n})\\) or \\(f_{a}(p_{n})\\). At an estimated camera pose \\(\\{R, t\\}\\), we cast a ray for each pixel and sample \\(N\\) points \\(\\{p_n\\}_{n=1}^N\\) along it (Sec. 3.2). Each point \\(p_n\\) is projected onto the coarse and fine feature planes and bilinearly interpolates the four nearest neighbor features on each plane (Sec. 3.1). The interpolated features at each level are added together, and the results from both levels are concatenated together to form the inputs \\(\\{\\pmb{f}_{g}(p_{n}), \\pmb{f}_{a}(p_{n})\\}\\) of the decoders \\(\\{h_g, h_a\\}\\) (Sec. 3.1). The geometry decoder \\(h_g\\) estimates TSDF \\(\\phi_{g}(p_{n})\\) based on \\(f_{g}(p_{n})\\), and the appearance decoder \\(h_a\\) estimates the raw color \\(\\phi_{a}(p_{n})\\) based on \\(f_{a}(p_{n})\\) for each point \\(p_n\\) (Sec. 3.1). Once TSDFs and raw colors of all points on a ray are generated, our SDF-based rendering process estimates the depth \\(\\hat{\\pmb{d}}\\) and the color \\(\\hat{\\pmb{c}}\\) for each pixel (Sec. 3.2)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.557, + 0.444, + 0.571 + ], + "angle": 0, + "content": "scene side-length as is the case for voxel-based models." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.572, + 0.47, + 0.694 + ], + "angle": 0, + "content": "To reason about the geometry of a point \\( p \\) in the continuous space, we first project it onto all the geometry planes. The geometry feature \\( f_{g}(p) \\) for point \\( p \\) is then formed by 1) bilinearly interpolating the four nearest neighbors on each feature plane, 2) summing the interpolated coarse features and the fine ones respectively into the coarse output \\( f_{g}^{c}(p) \\) and fine output \\( f_{g}^{f}(p) \\), and 3) concatenating the outputs together. Formally:" + }, + { + "type": "equation", + "bbox": [ + 0.136, + 0.705, + 0.41, + 0.723 + ], + "angle": 0, + "content": "\\[\nf _ {g} ^ {c} (p) = F _ {g - x y} ^ {c} (p) + F _ {g - x z} ^ {c} (p) + F _ {g - y z} ^ {c} (p)\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.136, + 0.725, + 0.41, + 0.744 + ], + "angle": 0, + "content": "\\[\nf _ {g} ^ {f} (p) = F _ {g - x y} ^ {f} (p) + F _ {g - x z} ^ {f} (p) + F _ {g - y z} ^ {f} (p)\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.137, + 0.746, + 0.469, + 0.765 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {f} _ {\\boldsymbol {g}} (p) = \\left[ f _ {g} ^ {c} (p); f _ {g} ^ {f} (p) \\right] \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.775, + 0.436, + 0.79 + ], + "angle": 0, + "content": "The appearance feature \\( f_{a}(p) \\) is obtained similarly:" + }, + { + "type": "equation", + "bbox": [ + 0.136, + 0.8, + 0.411, + 0.819 + ], + "angle": 0, + "content": "\\[\nf _ {a} ^ {c} (p) = F _ {a - x y} ^ {c} (p) + F _ {a - x z} ^ {c} (p) + F _ {a - y z} ^ {c} (p)\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.137, + 0.821, + 0.411, + 0.84 + ], + "angle": 0, + "content": "\\[\nf _ {a} ^ {f} (p) = F _ {a - x y} ^ {f} (p) + F _ {a - x z} ^ {f} (p) + F _ {a - y z} ^ {f} (p)\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.136, + 0.842, + 0.469, + 0.861 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {f} _ {\\boldsymbol {a}} (p) = \\left[ f _ {a} ^ {c} (p); f _ {a} ^ {f} (p) \\right] \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.47, + 0.903 + ], + "angle": 0, + "content": "These features are decoded into TSDF \\(\\phi_g(p)\\) and raw color \\(\\phi_{a}(p)\\) values via shallow two-layer MLPs \\(\\{h_g,h_a\\}\\):" + }, + { + "type": "equation", + "bbox": [ + 0.528, + 0.584, + 0.892, + 0.601 + ], + "angle": 0, + "content": "\\[\n\\phi_ {\\boldsymbol {g}} (p) = h _ {g} \\left(\\boldsymbol {f} _ {\\boldsymbol {g}} (p)\\right) \\text {a n d} \\phi_ {\\boldsymbol {a}} (p) = h _ {a} \\left(\\boldsymbol {f} _ {\\boldsymbol {a}} (p)\\right) \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.612, + 0.892, + 0.642 + ], + "angle": 0, + "content": "These raw TSDF and color outputs can be utilized for depth/color rendering as well as mesh extraction." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.651, + 0.771, + 0.668 + ], + "angle": 0, + "content": "3.2. SDF-Based Volume Rendering" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.675, + 0.892, + 0.854 + ], + "angle": 0, + "content": "When processing input frame \\(i\\), emulating the ray casting in NeRF [37], we select random pixels and calculate their corresponding rays using the current estimate of the camera pose \\(\\{R_i|t_i\\}\\). For rendering the depths and colors of the rays, we first sample \\(N_{strat}\\) samples on each ray by stratified sampling and then sample additional \\(N_{imp}\\) points near surfaces. For pixels with ground truth depths, the \\(N_{imp}\\) additional points are sampled uniformly inside the truncation distance \\(T\\) w.r.t. the depth measurement, whereas for other pixels, \\(N_{imp}\\) points are sampled with the importance sampling technique [34, 37, 59, 70] based on the weights computed for the stratified samples." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.855, + 0.892, + 0.902 + ], + "angle": 0, + "content": "For all \\(N = N_{strat} + N_{imp}\\) points on a ray \\(\\{p_n\\}_{n=1}^N\\), we query TSDF \\(\\phi_g(p_n)\\) and raw color \\(\\phi_a(p_n)\\) from our networks and use the SDF-Based rendering approach in" + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "17410" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.078, + 0.092, + 0.47, + 0.107 + ], + "angle": 0, + "content": "StyleSDF [47] to convert SDF values to volume densities:" + }, + { + "type": "equation", + "bbox": [ + 0.15, + 0.131, + 0.47, + 0.149 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {\\sigma} \\left(p _ {n}\\right) = \\beta \\cdot \\text {S i g m o i d} \\left(- \\beta \\cdot \\phi_ {\\boldsymbol {g}} \\left(p _ {n}\\right)\\right) \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.156, + 0.469, + 0.232 + ], + "angle": 0, + "content": "where \\(\\beta\\) is a learnable parameter that controls the sharpness of the surface boundary. Negative values of SDF push Sigmoid toward one, resulting in volume density inside the surface. The volume density then is used for rendering the color and depth of each ray:" + }, + { + "type": "equation", + "bbox": [ + 0.11, + 0.239, + 0.437, + 0.281 + ], + "angle": 0, + "content": "\\[\nw _ {n} = \\exp \\left(- \\sum_ {k = 1} ^ {n - 1} \\boldsymbol {\\sigma} (p _ {k})\\right) (1 - \\exp (- \\boldsymbol {\\sigma} (p _ {n})))\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.123, + 0.283, + 0.469, + 0.325 + ], + "angle": 0, + "content": "\\[\n\\hat {\\boldsymbol {c}} = \\sum_ {n = 1} ^ {N} w _ {n} \\phi_ {\\boldsymbol {a}} \\left(p _ {n}\\right) \\quad \\text {a n d} \\quad \\hat {\\boldsymbol {d}} = \\sum_ {n = 1} ^ {N} w _ {n} z _ {n} \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.332, + 0.447, + 0.347 + ], + "angle": 0, + "content": "where \\( z_{n} \\) is the depth of point \\( p_n \\) w.r.t. the camera pose." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.355, + 0.23, + 0.37 + ], + "angle": 0, + "content": "3.3. Loss Functions" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.378, + 0.469, + 0.468 + ], + "angle": 0, + "content": "One advantage of TSDF over other representations, such as occupancy, is that it allows us to use per-point losses, along with rendering ones. These losses account for the rapid convergence of our model. Following the practice in [1], assuming a batch of rays \\( R \\) with ground truth depths are selected, we define the free space loss as:" + }, + { + "type": "equation", + "bbox": [ + 0.133, + 0.476, + 0.469, + 0.515 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {f s} = \\frac {1}{| R |} \\sum_ {r \\in R} \\frac {1}{| P _ {r} ^ {f s} |} \\sum_ {p \\in P _ {r} ^ {f s}} (\\phi_ {\\boldsymbol {g}} (p) - 1) ^ {2} \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.525, + 0.469, + 0.586 + ], + "angle": 0, + "content": "where \\( P_r^{fs} \\) is a set of points on the ray \\( r \\) that lie between the camera center and the truncation region of the surface measured by the depth sensor. This loss function encourages TSDF \\( \\phi_g \\) to have a value of one in the free space." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.586, + 0.469, + 0.646 + ], + "angle": 0, + "content": "For sample points close to the surface and within the truncation region, we use the signed distance objective, which leverages the depth sensor measurement to approximate the signed distance field:" + }, + { + "type": "equation", + "bbox": [ + 0.101, + 0.653, + 0.182, + 0.673 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {T} (P _ {r} ^ {T}) =\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.104, + 0.675, + 0.469, + 0.713 + ], + "angle": 0, + "content": "\\[\n\\frac {1}{| R |} \\sum_ {r \\in R} \\frac {1}{| P _ {r} ^ {T} |} \\sum_ {p \\in P _ {r} ^ {T}} (z (p) + \\phi_ {\\mathbf {g}} (p) \\cdot T - D (r)) ^ {2} \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.721, + 0.469, + 0.873 + ], + "angle": 0, + "content": "where \\(z(p)\\) is the planar depth of point \\(p\\) w.r.t. camera, \\(T\\) is the truncation distance, \\(D(r)\\) is the ray depth measured by the sensor, and \\(P_r^T\\) is a set of points on the ray \\(r\\) that lie in the truncation region, i.e. \\(|z(p) - D(r)| < T\\). We apply the same loss to all points in the truncation region, but we differentiate the importance of points that are closer to the surface in the middle of the truncation region \\(P_r^{T - m}\\) from those that are at the tail of the truncation region \\(P_r^{T - t}\\). Formally, we define \\(P_r^{T - m}\\) as a set of points that \\(|z(p) - D(r)| < 0.4T\\), and define \\(P_r^{T - t} = P_r^T - P_r^{T - m}\\), then:" + }, + { + "type": "equation", + "bbox": [ + 0.105, + 0.88, + 0.469, + 0.898 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {T - m} = \\mathcal {L} _ {T} \\left(P _ {r} ^ {T - m}\\right) \\quad \\text {a n d} \\quad \\mathcal {L} _ {T - t} = \\mathcal {L} _ {T} \\left(P _ {r} ^ {T - t}\\right) \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.092, + 0.892, + 0.167 + ], + "angle": 0, + "content": "This enables us to decrease the importance of \\(\\mathcal{L}_{T - t}\\) in mapping, which leads to having a smaller effective truncation distance, reducing artifacts in occluded areas, and reconstructing with higher accuracy while leveraging the entire truncation distance in camera tracking." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.168, + 0.892, + 0.228 + ], + "angle": 0, + "content": "In addition to these two per-point loss functions, we also employ reconstruction losses. For pixels with ground truth depths, we impose consistency between the rendered depth and the depth measured by the sensor:" + }, + { + "type": "equation", + "bbox": [ + 0.589, + 0.238, + 0.892, + 0.275 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {d} = \\frac {1}{| R |} \\sum_ {r \\in R} (\\hat {\\boldsymbol {d}} (r) - D (r)) ^ {2} \\tag {9}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.285, + 0.891, + 0.314 + ], + "angle": 0, + "content": "Similarly, we impose consistency between the pixel colors and rendered colors:" + }, + { + "type": "equation", + "bbox": [ + 0.597, + 0.323, + 0.892, + 0.358 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {c} = \\frac {1}{| R |} \\sum_ {r \\in R} (\\hat {\\boldsymbol {c}} (r) - I (r)) ^ {2} \\tag {10}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.37, + 0.749, + 0.385 + ], + "angle": 0, + "content": "where \\(I(r)\\) is the pixel color of ray \\(r\\)." + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.385, + 0.86, + 0.401 + ], + "angle": 0, + "content": "The global loss function of our method is defined as:" + }, + { + "type": "equation", + "bbox": [ + 0.505, + 0.412, + 0.89, + 0.443 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} = \\lambda_ {f s} \\mathcal {L} _ {f s} + \\lambda_ {T - m} \\mathcal {L} _ {T - m} + \\lambda_ {T - t} \\mathcal {L} _ {T - t} + \\lambda_ {d} \\mathcal {L} _ {d} + \\lambda_ {c} \\mathcal {L} _ {c} \\tag {11}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.455, + 0.892, + 0.545 + ], + "angle": 0, + "content": "where \\(\\{\\lambda_{fs},\\lambda_{T - m},\\lambda_{T - t},\\lambda_d,\\lambda_c\\}\\) are the weighting coefficients. Note that \\(\\mathcal{L}_c\\) is defined on all rays in a training batch, while other losses are only imposed on rays with ground truth measured depths. The global objective is the same for both mapping and tracking in our method, but the weighting coefficients are different." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.555, + 0.715, + 0.571 + ], + "angle": 0, + "content": "3.4. Mapping and Tracking" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.578, + 0.892, + 0.836 + ], + "angle": 0, + "content": "Mapping. Our scene representation, i.e. the feature planes and MLP decoders, are randomly initialized at the beginning. With the first input frame \\(\\{I_0, D_0\\}\\), we fix the camera pose and optimize the feature planes and MLP decoders to best represent the first frame. For subsequent inputs, we update the scene representation iteratively every \\(k\\) frames, and add the latest frame to the global keyframe list, following the practice in iMAP [59] and NICE-SLAM [87]. For mapping, we first choose \\(|R|\\) pixels randomly from \\(W\\) frames, which include the current frame, the previous two keyframes, and \\(W - 3\\) frames randomly selected from the keyframe list. Then, we jointly optimize the feature planes, MLP decoders, and camera poses of the \\(W\\) selected frames using the loss functions introduced in Sec. 3.3. Unlike NICE-SLAM [87], our method does not require a staged-optimization policy, and we simply optimize all scene parameters and camera poses simultaneously." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.84, + 0.892, + 0.902 + ], + "angle": 0, + "content": "Tracking. The localization process of our method is initiated for each input frame. The current estimate of the camera parameters, represented by translation vectors and quaternion rotations [56] \\(\\{R|t\\}\\), are optimized solely based" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "17411" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.105, + 0.089, + 0.867, + 0.171 + ], + "angle": 0, + "content": "
MethodReconstruction (cm)Localization (cm)
Depth L1↓Acc.↓Comp.↓Comp. Ratio (%)↑ATE Mean↓ATE RMSE↓
iMAP* [59]8.23 ± 0.887.16 ± 0.265.83 ± 0.2767.17 ± 2.702.59 ± 0.583.42 ± 0.87
NICE-SLAM [87]3.29 ± 0.331.66 ± 0.071.63 ± 0.0596.74 ± 0.361.56 ± 0.292.05 ± 0.45
ESLAM (ours)1.18 ± 0.050.97 ± 0.021.05 ± 0.0198.60 ± 0.070.52 ± 0.030.63 ± 0.05
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.176, + 0.895, + 0.274 + ], + "angle": 0, + "content": "Table 1. Quantitative comparison of our proposed ESLAM with existing NeRF-based dense visual SLAM models on the Replica dataset [57] for both reconstruction and localization accuracy. The results are the average and standard deviation of five runs on eight scenes of the Replica dataset [57]. Our method outperforms previous works by a high margin and has lower variances, indicating it is also more stable from run to run. The evaluation metrics for reconstruction are L1 loss (cm) between rendered and ground truth depth maps of 1000 random camera poses, reconstruction accuracy (cm), reconstruction completion (cm), and completion ratio (\\%). The evaluation metrics for localization are mean and RMSE of ATE (cm) [58]. For the details of the evaluations for each scene, refer to the supplementary. It should also be noted that our method runs up to \\(\\times 10\\) faster on this dataset (see Sec. 4.2 for runtime analysis)." + }, + { + "type": "image", + "bbox": [ + 0.083, + 0.287, + 0.281, + 0.381 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.084, + 0.383, + 0.28, + 0.477 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.084, + 0.478, + 0.28, + 0.572 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.165, + 0.578, + 0.2, + 0.588 + ], + "angle": 0, + "content": "iMAP*" + }, + { + "type": "image", + "bbox": [ + 0.286, + 0.287, + 0.483, + 0.381 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.287, + 0.383, + 0.482, + 0.477 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.287, + 0.478, + 0.482, + 0.572 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.346, + 0.578, + 0.411, + 0.588 + ], + "angle": 0, + "content": "NICE-SLAM" + }, + { + "type": "image", + "bbox": [ + 0.488, + 0.287, + 0.685, + 0.381 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.489, + 0.383, + 0.685, + 0.477 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.489, + 0.478, + 0.685, + 0.572 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.553, + 0.578, + 0.621, + 0.589 + ], + "angle": 0, + "content": "ESLAM (ours)" + }, + { + "type": "image", + "bbox": [ + 0.691, + 0.287, + 0.887, + 0.381 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.692, + 0.383, + 0.887, + 0.477 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.692, + 0.478, + 0.887, + 0.572 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.758, + 0.578, + 0.83, + 0.588 + ], + "angle": 0, + "content": "Ground Truth" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.596, + 0.895, + 0.667 + ], + "angle": 0, + "content": "Figure 3. Qualitative comparison of our proposed ESLAM method's geometry reconstruction with existing NeRF-based dense visual SLAM models, iMAP* [59] and NICE-SLAM [87], on the Replica dataset [57]. Our method produces more accurate detailed geometry as well as higher-quality textures. The ground truth images are rendered with the ReplicaViewer software [57]. It should also be noted that our method runs up to \\(\\times 10\\) faster on this dataset (see Sec. 4.2 for runtime analysis). For further qualitative analysis on this dataset, as well as videos demonstrating the localization and reconstruction process, refer to the supplementary." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.681, + 0.471, + 0.803 + ], + "angle": 0, + "content": "on our global loss function (see Sec. 3.3) with the gradient-based Adam optimizer [24]. No second-order optimizers or manifold operations are employed for camera tracking in our method. We exclude rays with no ground truth depths and outlier pixels from each optimization step. A pixel is considered an outlier if the difference between its measured depth and rendered depth is ten times greater than the batch's median rendered depth error." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.816, + 0.21, + 0.833 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.471, + 0.903 + ], + "angle": 0, + "content": "In this section, we validate that our method outperforms existing implicit representation-based methods in both localization and reconstruction accuracy on three standard benchmarks while running up to \\(\\times 10\\) faster." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.681, + 0.893, + 0.757 + ], + "angle": 0, + "content": "Baselines. We compare our method to two existing state-of-the-art NeRF-based dense visual SLAM methods: iMAP [59] and NICE-SLAM [87]. Because iMAP is not open source, we use the iMAP* model in our experiment, which is the reimplementation of iMAP in [87]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.768, + 0.894, + 0.83 + ], + "angle": 0, + "content": "Datasets. We evaluate our method on three standard 3D benchmarks: Replica [57], ScanNet [12], and TUM RGB-D [58] datasets. We select the same scenes for evaluation as NICE-SLAM [87]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.894, + 0.901 + ], + "angle": 0, + "content": "Metrics. We borrow our evaluation metrics from NICE-SLAM [87]. For evaluating scene geometry, we use both 2D and 3D metrics. For the 2D metric, we render depth maps from 1000 random camera poses in each scene and calculate" + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "17412" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.084, + 0.088, + 0.887, + 0.201 + ], + "angle": 0, + "content": "
MethodATESc. 0000Sc. 0059Sc. 0106Sc. 0169Sc. 0181Sc. 0207Ave.
iMAP* [59]Mean34.2 ± 12.813.0 ± 2.412.9 ± 1.733.6 ± 15.320.8 ± 3.818.6 ± 6.022.2 ± 7.0
RMSE42.7 ± 16.617.8 ± 7.415.0 ± 1.739.1 ± 18.224.7 ± 5.820.1 ± 6.826.6 ± 9.4
NICE-SLAM [87]Mean9.9 ± 0.411.9 ± 1.87.0 ± 0.29.2 ± 1.012.2 ± 0.35.5 ± 0.39.3 ± 0.7
RMSE12.0 ± 0.514.0 ± 1.87.9 ± 0.210.9 ± 1.113.4 ± 0.36.2 ± 0.410.7 ± 0.7
ESLAM (ours)Mean6.5 ± 0.16.4 ± 0.46.7 ± 0.15.9 ± 0.18.3 ± 0.25.4 ± 0.16.5 ± 0.2
RMSE7.3 ± 0.28.5 ± 0.57.5 ± 0.16.5 ± 0.19.0 ± 0.25.7 ± 0.17.4 ± 0.2
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.207, + 0.894, + 0.276 + ], + "angle": 0, + "content": "Table 2. Quantitative comparison of our proposed ESLAM method's localization accuracy with existing NeRF-based dense visual SLAM models on the ScanNet dataset [12]. The results are the average and standard deviation of five runs on each scene of ScanNet [12]. Our method outperforms previous works and has lower variances, indicating it is also more stable from run to run. The evaluation metrics for localization are mean and RMSE of ATE (cm) [58]. It should also be noted that our method runs up to \\(\\times 6\\) faster on this dataset (see Sec. 4.2 for runtime analysis)." + }, + { + "type": "image", + "bbox": [ + 0.083, + 0.291, + 0.346, + 0.406 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.354, + 0.29, + 0.617, + 0.407 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.625, + 0.291, + 0.887, + 0.407 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.084, + 0.416, + 0.346, + 0.533 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.355, + 0.416, + 0.617, + 0.532 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.625, + 0.416, + 0.887, + 0.533 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.084, + 0.54, + 0.346, + 0.657 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.198, + 0.663, + 0.237, + 0.674 + ], + "angle": 0, + "content": "iMAP*" + }, + { + "type": "image", + "bbox": [ + 0.354, + 0.54, + 0.616, + 0.657 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.457, + 0.662, + 0.528, + 0.673 + ], + "angle": 0, + "content": "NICE-SLAM" + }, + { + "type": "image", + "bbox": [ + 0.625, + 0.541, + 0.887, + 0.657 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.726, + 0.662, + 0.806, + 0.674 + ], + "angle": 0, + "content": "ESLAM (ours)" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.681, + 0.895, + 0.737 + ], + "angle": 0, + "content": "Figure 4. Qualitative comparison of our proposed ESLAM method's localization accuracy with existing NeRF-based dense visual SLAM models, iMAP* [59] and NICE-SLAM [87], on the ScanNet dataset [12]. The ground truth camera trajectory is shown in green, and the estimated trajectory is shown in red. Our method predicts more accurate camera trajectories and does not suffer from drifting issues. It should also be noted that our method runs up to \\(\\times 6\\) faster on this dataset (see Sec. 4.2 for runtime analysis)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.749, + 0.473, + 0.901 + ], + "angle": 0, + "content": "the L1 difference between depths from ground truth meshes and the reconstructed ones. For the 3D metrics, we consider reconstruction accuracy [cm], reconstruction completion [cm], and completion ratio \\([< 5\\mathrm{cm}\\%]\\). For evaluating these metrics, we build a TSDF volume for a scene with a resolution of \\(1\\mathrm{cm}\\) and use the marching cubes algorithm [33] to obtain scene meshes. Before evaluating the 3D metrics for our method and for the baselines, we perform mesh culling as recommended in [1, 70]. For this purpose, we remove faces from a mesh that are not inside any" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.749, + 0.892, + 0.78 + ], + "angle": 0, + "content": "camera frustum or are occluded in all RGB-D frames. For evaluating camera localization, we use ATE [58]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.795, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Implementation Details. The truncation distance \\( T \\) is set to \\( 6\\mathrm{cm} \\) in our method. We employ coarse feature planes with a resolution of \\( 24\\mathrm{cm} \\) for both geometry and appearance. For fine feature planes, we use a resolution of \\( 6\\mathrm{cm} \\) for geometry and \\( 3\\mathrm{cm} \\) for appearance. All feature planes have 32 channels, resulting in a 64-channel concatenated feature input for the decoders. The decoders are two-layer MLPs" + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "17413" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.083, + 0.088, + 0.283, + 0.181 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.284, + 0.089, + 0.484, + 0.181 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.485, + 0.089, + 0.686, + 0.181 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.688, + 0.089, + 0.888, + 0.181 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.081, + 0.183, + 0.283, + 0.275 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.284, + 0.183, + 0.484, + 0.274 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.486, + 0.183, + 0.686, + 0.274 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.688, + 0.183, + 0.888, + 0.274 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.082, + 0.276, + 0.283, + 0.372 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.157, + 0.374, + 0.198, + 0.386 + ], + "angle": 0, + "content": "iMAP*" + }, + { + "type": "image", + "bbox": [ + 0.284, + 0.276, + 0.484, + 0.372 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.341, + 0.374, + 0.422, + 0.386 + ], + "angle": 0, + "content": "NICE-SLAM" + }, + { + "type": "image", + "bbox": [ + 0.486, + 0.276, + 0.686, + 0.372 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.549, + 0.374, + 0.633, + 0.386 + ], + "angle": 0, + "content": "ESLAM (ours)" + }, + { + "type": "image", + "bbox": [ + 0.688, + 0.276, + 0.888, + 0.372 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.744, + 0.374, + 0.833, + 0.386 + ], + "angle": 0, + "content": "Ground Truth" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.393, + 0.892, + 0.462 + ], + "angle": 0, + "content": "Figure 5. Qualitative comparison of our proposed ESLAM method's geometry reconstruction with existing NeRF-based dense visual SLAM models, iMAP* [59] and NICE-SLAM [87], on the ScanNet dataset [12]. Our method produces more accurate detailed geometry as well as higher-quality textures. The appearance of white backgrounds in ground truth meshes is due to the fact that the ground truth meshes of the ScanNet dataset [12] are incomplete. It should also be noted that our method runs up to \\(\\times 6\\) faster on this dataset (see Sec. 4.2 for runtime analysis)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.472, + 0.469, + 0.548 + ], + "angle": 0, + "content": "with 32 channels in the hidden layer. For the Replica [57] dataset, we sample \\( N_{strat} = 32 \\) points for stratified sampling and \\( N_{imp} = 8 \\) points for importance sampling on each ray. And for the ScanNet [12] and TUM RGB-D [58] datasets, we set \\( N_{strat} = 48 \\) and \\( N_{imp} = 8 \\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.549, + 0.469, + 0.654 + ], + "angle": 0, + "content": "We use different set of loss coefficients for mapping and tracking. During mapping we set \\(\\lambda_{fs} = 5\\), \\(\\lambda_{T - m} = 200\\), \\(\\lambda_{T - t} = 10\\), \\(\\lambda_d = 0.1\\), and \\(\\lambda_c = 5\\). And during tracking, we set \\(\\lambda_{fs} = 10\\), \\(\\lambda_{T - m} = 200\\), \\(\\lambda_{T - t} = 50\\), \\(\\lambda_d = 1\\), and \\(\\lambda_c = 5\\). These coefficients are obtained by performing grid search in our experiments. For further details of our implementation, refer to the supplementary." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.665, + 0.279, + 0.681 + ], + "angle": 0, + "content": "4.1. Experimental Results" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.689, + 0.469, + 0.809 + ], + "angle": 0, + "content": "Evaluation on Replica [57]. We provide the quantitative analysis of our experimental results on eight scenes of the Replica dataset [57] in Tab. 1. The numbers represent the average and standard deviation of the metrics for five independent runs. As shown in Tab. 1, our method outperforms the baselines for both reconstruction and localization accuracy. Our method also has lower variances, indicating that it is more stable and more robust than existing methods." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.811, + 0.469, + 0.899 + ], + "angle": 0, + "content": "Qualitative analysis on the Replica dataset [57] is provided in Fig. 3. The results show that our method reconstructs the details of the scenes more accurately and produces fewer artifacts. Although it is not the focus of this paper, our method also produces higher-quality colors for the reconstructed meshes." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.472, + 0.892, + 0.669 + ], + "angle": 0, + "content": "Evaluation on ScanNet [12]. We also benchmark ours and existing methods on multiple large scenes from ScanNet [12] to evaluate and compare their scalability. For evaluating camera localization, we conduct five independent experiments on each scene and report the average and standard deviation of the mean and RMSE of ATE [58] in Tab. 2. As demonstrated in the table, our method's localization is more accurate than existing methods. Our method is also considerably more stable from run to run as it has much lower standard deviations. We provide qualitative analysis of camera localization, along with geometry reconstruction, in Fig. 4. The results show that our method does not suffer from any large drifting and is more robust than existing methods." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.684, + 0.892, + 0.775 + ], + "angle": 0, + "content": "Since the ground truth meshes of the ScanNet dataset [12] are incomplete, we only provide qualitative analysis for geometry reconstruction, similar to previous works. The qualitative comparison in Fig. 5 validates that our model reconstructs more precise geometry and detailed textures compared to existing approaches." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.795, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Evaluation on TUM RGB-D [58]. To further contrast the robustness of our method with the existing ones, we conduct an evaluation study on the real-world TUM RGB-D dataset [58]. Since there are no ground truth meshes for the scenes in this dataset, we only present the localization results in Tab. 3 and the qualitative analysis of rendered meshes in Fig. 6." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.956 + ], + "angle": 0, + "content": "17414" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.084, + 0.088, + 0.278, + 0.194 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.084, + 0.196, + 0.278, + 0.306 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.139, + 0.309, + 0.223, + 0.322 + ], + "angle": 0, + "content": "Sample Image" + }, + { + "type": "image", + "bbox": [ + 0.286, + 0.088, + 0.481, + 0.196 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.287, + 0.197, + 0.481, + 0.306 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.369, + 0.309, + 0.411, + 0.32 + ], + "angle": 0, + "content": "iMAP*" + }, + { + "type": "image", + "bbox": [ + 0.49, + 0.088, + 0.685, + 0.197 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.49, + 0.198, + 0.684, + 0.306 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.557, + 0.309, + 0.632, + 0.32 + ], + "angle": 0, + "content": "NICE-SLAM" + }, + { + "type": "image", + "bbox": [ + 0.693, + 0.097, + 0.887, + 0.197 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.693, + 0.198, + 0.887, + 0.306 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.76, + 0.309, + 0.84, + 0.32 + ], + "angle": 0, + "content": "ESLAM (ours)" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.328, + 0.892, + 0.371 + ], + "angle": 0, + "content": "Figure 6. Qualitative comparison of our proposed ESLAM method's geometry reconstruction with existing NeRF-based dense visual SLAM models, iMAP* [59] and NICE-SLAM [87], on the TUM RGB-D dataset [58]. Our method produces more accurate detailed geometry as well as higher-quality textures. Since there are no ground truth meshes for this dataset, we depict a sample input image." + }, + { + "type": "table", + "bbox": [ + 0.093, + 0.382, + 0.456, + 0.448 + ], + "angle": 0, + "content": "
fr1/deskfr2/xyzfr3/office
iMAP* [59]4.902.055.80
NICE-SLAM [87]2.852.393.02
ESLAM (ours)2.471.112.42
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.454, + 0.47, + 0.51 + ], + "angle": 0, + "content": "Table 3. Quantitative comparison of our proposed ESLAM method's localization accuracy with existing NeRF-based dense visual SLAM models on the TUM RGB-D dataset [58]. The evaluation metric is ATE RMSE\\(\\downarrow\\) (cm) [58]." + }, + { + "type": "table", + "bbox": [ + 0.084, + 0.52, + 0.465, + 0.646 + ], + "angle": 0, + "content": "
MethodSpeed FPT (s)Memory
# Param.Grow. R.
ReplicaiMAP* [59]5.200.22 M?
NICE-SLAM [87]2.1012.18 MO(L3)
ESLAM (ours)0.186.79 MO(L2)
ScanNetiMAP* [59]5.200.22 M?
NICE-SLAM [87]3.3522.04 MO(L3)
ESLAM (ours)0.5517.63 MO(L2)
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.652, + 0.47, + 0.79 + ], + "angle": 0, + "content": "Table 4. Runtime analysis of our method in comparison with existing ones in terms of average frame processing time (FPT), number of parameters, and model size growth rate w.r.t. scene side-length \\( L \\). All methods are benchmarked with an NVIDIA GeForce RTX 3090 GPU on room0 of Replica [57] and scene0000 of ScanNet [12]. Our method is significantly faster and does not grow cubically in size w.r.t. scene side-length \\( L \\). Note that iMAP [59] represents a whole scene in a single MLP, hence its small number of parameters. Accordingly, the scalability and growth rate of iMAP [59] w.r.t. the scene side-length \\( L \\) are also unclear." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.802, + 0.251, + 0.817 + ], + "angle": 0, + "content": "4.2. Runtime Analysis" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.825, + 0.47, + 0.903 + ], + "angle": 0, + "content": "We evaluate the speed and size of our method in comparison with existing approaches in Tab. 4. We report the average frame processing time (FPT), the number of parameters of the model, and memory growth rate w.r.t. scene side-length for the scenes room0 of Replica [57] and" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.385, + 0.892, + 0.477 + ], + "angle": 0, + "content": "scene0000 of ScanNet [12] datasets. All methods are benchmarked with an NVIDIA GeForce RTX 3090 GPU. The results indicate that our method is significantly faster than previous works on both datasets. Furthermore, in contrast to NICE-SLAM [87], our model size is smaller and does not grow cubically with the scene side-length." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.488, + 0.619, + 0.503 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.513, + 0.892, + 0.709 + ], + "angle": 0, + "content": "We presented ESLAM, a dense visual SLAM approach that leverages the latest advances in the Neural Radiance Fields study to improve both the speed and accuracy of neural implicit-based SLAM systems. We proposed replacing the voxel grid representation with axis-aligned feature planes to prevent the model size from growing cubically with respect to the scene side-length. We also demonstrated that modeling the scene geometry with Truncated Signed Distance Field (TSDF) leads to efficient and high-quality surface reconstruction. We verified through extensive experiments that our approach outperforms existing methods significantly in both reconstruction and localization accuracy while running up to one order of magnitude faster." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.71, + 0.892, + 0.86 + ], + "angle": 0, + "content": "ESLAM accepts and deals with the forgetting problem in exchange for memory preservation. Due to the structure of our feature plane representation, updating features to adapt to new geometry may affect previously reconstructed geometries. To address this issue, we keep track of previous keyframes and allocate a large portion of computation resources to retain and remember previously reconstructed regions. Although ESLAM is substantially faster than competing approaches, handling the forgetting problem more efficiently could further reduce frame processing time." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.871, + 0.635, + 0.885 + ], + "angle": 0, + "content": "Acknowledgement" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.886, + 0.806, + 0.901 + ], + "angle": 0, + "content": "This research was supported by ams OSRAM." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "17415" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.079, + 0.09, + 0.176, + 0.107 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.115, + 0.47, + 0.184 + ], + "angle": 0, + "content": "[1] Dejan Azinović, Ricardo Martin-Brualla, Dan B Goldman, Matthias Nießner, and Justus Thies. Neural rgb-d surface reconstruction. 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Mononeuralfusion: Online monocular neural 3d reconstruction with geometric priors. arXiv preprint arXiv:2209.15153, 2022. 2" + }, + { + "type": "list", + "bbox": [ + 0.08, + 0.092, + 0.469, + 0.894 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "17419" + } + ] +] \ No newline at end of file diff --git a/2023/ESLAM_ Efficient Dense SLAM System Based on Hybrid Representation of Signed Distance Fields/d4f0d86a-9d2c-4b36-b0b6-8aa8c847e904_origin.pdf b/2023/ESLAM_ Efficient Dense SLAM System Based on Hybrid Representation of Signed Distance Fields/d4f0d86a-9d2c-4b36-b0b6-8aa8c847e904_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..18b4b4f73f793e43124f7b77190ac52de9adfcf6 --- /dev/null +++ b/2023/ESLAM_ Efficient Dense SLAM System Based on Hybrid Representation of Signed Distance Fields/d4f0d86a-9d2c-4b36-b0b6-8aa8c847e904_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:4138618c5f5d636c718e26885df625d28cd64ff6140cbd4c130e313ba7ea776a +size 10309227 diff --git a/2023/ESLAM_ Efficient Dense SLAM System Based on Hybrid Representation of Signed Distance Fields/full.md b/2023/ESLAM_ Efficient Dense SLAM System Based on Hybrid Representation of Signed Distance Fields/full.md new file mode 100644 index 0000000000000000000000000000000000000000..a546ea446ba608dd833030dfd73cbe45ea1ad1dc --- /dev/null +++ b/2023/ESLAM_ Efficient Dense SLAM System Based on Hybrid Representation of Signed Distance Fields/full.md @@ -0,0 +1,461 @@ +# ESLAM: Efficient Dense SLAM System Based on Hybrid Representation of Signed Distance Fields + +Mohammad Mahdi Johari Idiap Research Institute, EPFL + +mohammad.johari@idiap.ch + +Camilla Cartaams OSRAM + +camilla-carta@ams-osram.com + +François Fleuret +University of Geneva, EPFL +francois.fleuret@unige.ch + +![](images/31231cdd34ae6a3a584ccb4b2bf62c9256e9473774750f08f2f00d563a6ae4df.jpg) +iMAP* + +![](images/6b93ebde8c629cb5f75ab0a9f5bf41d305dbfd1a12e4c9fa40ea594cca4eb706.jpg) +NICE-SLAM +Figure 1. Our pre-train-free ESLAM model reconstructs scene details more accurately than existing works: iMAP* [59] and NICE-SLAM [87], while it runs up to $\times 10$ faster (see Sec. 4.2 for runtime analysis). The ground truth image is rendered with ReplicaViewer [57]. + +![](images/51ddac899f9cb8262d233931a44e73d1f49c9078fd410fe79fd3d706737b3c73.jpg) +ESLAM (ours) + +![](images/0a17d4523d025d700ad7c877f6805e8cb9614a7418722ac1a33e16326bc6afe0.jpg) +Ground Truth + +# Abstract + +We present ESLAM, an efficient implicit neural representation method for Simultaneous Localization and Mapping (SLAM). ESLAM reads RGB-D frames with unknown camera poses in a sequential manner and incrementally reconstructs the scene representation while estimating the current camera position in the scene. We incorporate the latest advances in Neural Radiance Fields (NeRF) into a SLAM system, resulting in an efficient and accurate dense visual SLAM method. Our scene representation consists of multiscale axis-aligned perpendicular feature planes and shallow decoders that, for each point in the continuous space, decode the interpolated features into Truncated Signed Distance Field (TSDF) and RGB values. Our extensive experiments on three standard datasets, Replica, ScanNet, and TUM RGB-D show that ESLAM improves the accuracy of 3D reconstruction and camera localization of state-of-the-art dense visual SLAM methods by more than $50\%$ , while it runs up to $\times 10$ faster and does not require any pre-training. Project page: https://www.idiap.ch/paper/eslam + +# 1. Introduction + +Dense visual Simultaneous Localization and Mapping (SLAM) is a fundamental challenge in 3D computer vision with several applications such as autonomous driving, robotics, and virtual/augmented reality. It is defined as constructing a 3D map of an unknown environment while simultaneously approximating the camera pose. + +While traditional SLAM systems [16, 41, 45, 55, 76, 77] + +mostly focus on localization accuracy, recent learning-based dense visual SLAM methods [2, 11, 25, 35, 60, 64, 65, 67, 81, 86] provide meaningful global 3D maps and show reasonable but limited reconstruction accuracy. + +Following the advent of Neural Radiance Fields (NeRF) [37] and the demonstration of their capacity to reason about the geometry of a large-scale scene [8, 13, 20, 22, 26, 75, 78] and reconstruct 3D surfaces [1, 29, 47, 48, 62, 71, 72, 82, 85], novel NeRF-based dense SLAM methods have been developed. In particular, iMAP [59] and NICE-SLAM [87] utilize neural implicit networks to achieve a consistent geometry representation. + +IMAP [59] represents the geometry with a single huge MLP, similar to NeRF [37], and optimizes the camera poses during the rendering process. NICE-SLAM [87] improves iMAP by storing the representation locally on voxel grids to prevent the forgetting problem. Despite promising reconstruction quality, these methods are computationally demanding for real-time applications, and their ability to capture geometry details is limited. In addition, NICE-SLAM [87] uses frozen pre-trained MLPs, which limits its generalizability to novel scenes. We take NICE-SLAM [87] as a baseline and provide the following contributions: + +- We leverage implicit Truncated Signed Distance Field (TSDF) [1] to represent geometry, which converges noticeably faster than the common rendering-based representations like volume density [59] or occupancy [87] and results in higher quality reconstruction. +Instead of storing features on voxel grids, we propose employing multi-scale axis-aligned feature planes [6] + +which leads to reducing the memory footprint growth rate w.r.t. scene side-length from cubic to quadratic. + +- We benchmark our method on three challenging datasets, Replica [57], ScanNet [12], and TUM RGB-D [58], to demonstrate the performance of our method in comparison to existing ones and provide an extensive ablation study to validate our design choices. + +Thanks to the inherent smoothness of representing the scene with feature planes, our method produces higher-quality smooth surfaces without employing explicit smoothness loss functions like [70]. + +Concurrent with our work, the followings also propose Radiance Fields-based SLAM systems: iDF-SLAM [38] also uses TSDF, but it is substantially slower and less accurate than NICE-SLAM [87]. Orbeez-SLAM [10] operates in real-time at the cost of poor 3D reconstruction. Compromising accuracy and quality, MeSLAM [27] introduces a memory-efficient SLAM. MonoNeuralFusion [88] proposes an incremental 3D reconstruction model, assuming that ground truth camera postures are available. Lastly, NeRF-SLAM [54] presents a monocular SLAM system with hierarchical volumetric Neural Radiance Fields optimized using an uncertainty-based depth loss. + +# 2. Related Work + +Dense Visual SLAM. The ubiquity of cameras has made visual SLAM a field of major interest in the last decades. Traditional visual SLAM employs pixel-wise optimization of geometric and/or photometric constraints from image information. Depending on the information source, visual SLAM divides into three main categories: visual-only [15-17,41,45,66], visual-inertial [3,28,39,42,53,69] and RGB-D [5, 14, 23, 44] SLAM. Visual-only SLAM uses single or multi-camera setups but presents higher technical challenges compared to others. Visual-inertial information can improve accuracy, but complexifies the system and requires an extra calibration step. The advent of the Kinect brought popularity to RGB-D setups with improved performance but had drawbacks such as larger memory and power requirements, and limitation to indoor settings. Recently, learning-based approaches [2,11,30,31,67] have made great advances in the field, improving both accuracy and robustness compared to traditional methods. + +Neural Implicit 3D Reconstruction. Neural Radiance Fields (NeRF) have impacted 3D Computer Vision applications, such as novel view synthesis [34, 36, 37, 68], surface reconstruction [46, 49, 71, 72, 82, 83, 85], dynamic scene representation [19, 50-52], and camera pose estimation [21, 32, 73, 79, 84]. The exploitation of neural implicit representations for 3D reconstruction at real-world scale is studied in [1, 4, 9, 29, 43, 63, 70, 74, 80]. The most related works + +to ours are iMAP [59] and NICE-SLAM [87]. IMAP [59] presents a NeRF-style dense SLAM system. NICE-SLAM [87] extends iMAP [59] by modeling the scene with voxel grid features and decoding them into occupancies using pre-trained MLPs. However, the generalizability of NICE-SLAM [87] to novel scenes is limited because of the frozen pre-trained MLPs. Another issue is the cubic memory growth rate of their model, which results in using low-resolution voxel grids and losing fine geometry details. In contrast, we employ compact plane-based features [6] which are directly decoded to TSDF, improving both efficiency and accuracy of localization and reconstruction. + +# 3. Method + +The overview of our method is shown in Fig. 2. Given a set of sequential RGB-D frames $\{I_i, D_i\}_{i=1}^M$ , our model predicts camera poses $\{R_i|t_i\}_{i=1}^M$ and an implicit TSDF $\phi_g$ representation that can be used in marching cubes algorithm [33] to extract 3D meshes. We expect TSDF to denote the distance to the closest surface with a positive sign in the free space and a negative sign inside the surfaces. We employ normalized TSDF, such that it is zero on the surfaces and has a magnitude of one at the truncation distance $T$ , which is a hyper-parameter. Sec. 3.1 describes how we represent a scene with axis-aligned feature planes. Sec. 3.2 walks through the rendering process, which converts raw representations into pixel depths and colors. Sec. 3.3 introduces our loss functions. And Sec. 3.4 provides the details of localization and reconstruction in our SLAM system. + +# 3.1. Axis-Aligned Feature Planes + +Although voxel grid-based NeRF architectures [18, 61, 70] exhibit rapid convergence, they struggle with cubical memory growing. Different solutions have been proposed to mitigate the memory growth issue [6, 7, 40]. Inspired by [6], we employ a tri-plane architecture (see Fig. 2), in which we store and optimize features on perpendicular axis-aligned planes. Mimicking the trend in voxel-based methods [7, 40, 61], we propose using feature planes at two scales, i.e. coarse and fine. Coarse-level representation allows efficient reconstruction of free space with fewer sample points and optimization iterations. Moreover, we suggest employing separate feature planes for representing geometry and appearance, which mitigates the forgetting problem for geometry reconstruction since appearance fluctuates more frequently in a scene than geometry. + +Specifically, we use three coarse feature planes $\{F_{g - xy}^{c}, F_{g - xz}^{c}, F_{g - yz}^{c}\}$ and three fine ones $\{F_{g - xy}^{f}, F_{g - xz}^{f}, F_{g - yz}^{f}\}$ for representing the geometry. Similarly, three coarse $\{F_{a - xy}^{c}, F_{a - xz}^{c}, F_{a - yz}^{c}\}$ and three fine $\{F_{a - xy}^{f}, F_{a - xz}^{f}, F_{a - yz}^{f}\}$ planes are used for representing appearance of a scene. This architecture prevents model size from growing cubically with the + +![](images/9e46bfe5df6bfcce88422ca3957594a179c55ad87ed66096bec5bcbc49db5738.jpg) +Figure 2. The overview of ESLAM. Given the symmetry of our processes for geometry and appearance, we exhibit both processes on the same pipeline for simplicity. The symbol $*$ represents both geometry $g$ and appearance $a$ , e.g., $f_{*}(p_{n})$ can be either $f_{g}(p_{n})$ or $f_{a}(p_{n})$ . At an estimated camera pose $\{R, t\}$ , we cast a ray for each pixel and sample $N$ points $\{p_n\}_{n=1}^N$ along it (Sec. 3.2). Each point $p_n$ is projected onto the coarse and fine feature planes and bilinearly interpolates the four nearest neighbor features on each plane (Sec. 3.1). The interpolated features at each level are added together, and the results from both levels are concatenated together to form the inputs $\{\pmb{f}_{g}(p_{n}), \pmb{f}_{a}(p_{n})\}$ of the decoders $\{h_g, h_a\}$ (Sec. 3.1). The geometry decoder $h_g$ estimates TSDF $\phi_{g}(p_{n})$ based on $f_{g}(p_{n})$ , and the appearance decoder $h_a$ estimates the raw color $\phi_{a}(p_{n})$ based on $f_{a}(p_{n})$ for each point $p_n$ (Sec. 3.1). Once TSDFs and raw colors of all points on a ray are generated, our SDF-based rendering process estimates the depth $\hat{\pmb{d}}$ and the color $\hat{\pmb{c}}$ for each pixel (Sec. 3.2). + +scene side-length as is the case for voxel-based models. + +To reason about the geometry of a point $p$ in the continuous space, we first project it onto all the geometry planes. The geometry feature $f_{g}(p)$ for point $p$ is then formed by 1) bilinearly interpolating the four nearest neighbors on each feature plane, 2) summing the interpolated coarse features and the fine ones respectively into the coarse output $f_{g}^{c}(p)$ and fine output $f_{g}^{f}(p)$ , and 3) concatenating the outputs together. Formally: + +$$ +f _ {g} ^ {c} (p) = F _ {g - x y} ^ {c} (p) + F _ {g - x z} ^ {c} (p) + F _ {g - y z} ^ {c} (p) +$$ + +$$ +f _ {g} ^ {f} (p) = F _ {g - x y} ^ {f} (p) + F _ {g - x z} ^ {f} (p) + F _ {g - y z} ^ {f} (p) +$$ + +$$ +\boldsymbol {f} _ {\boldsymbol {g}} (p) = \left[ f _ {g} ^ {c} (p); f _ {g} ^ {f} (p) \right] \tag {1} +$$ + +The appearance feature $f_{a}(p)$ is obtained similarly: + +$$ +f _ {a} ^ {c} (p) = F _ {a - x y} ^ {c} (p) + F _ {a - x z} ^ {c} (p) + F _ {a - y z} ^ {c} (p) +$$ + +$$ +f _ {a} ^ {f} (p) = F _ {a - x y} ^ {f} (p) + F _ {a - x z} ^ {f} (p) + F _ {a - y z} ^ {f} (p) +$$ + +$$ +\boldsymbol {f} _ {\boldsymbol {a}} (p) = \left[ f _ {a} ^ {c} (p); f _ {a} ^ {f} (p) \right] \tag {2} +$$ + +These features are decoded into TSDF $\phi_g(p)$ and raw color $\phi_{a}(p)$ values via shallow two-layer MLPs $\{h_g,h_a\}$ : + +$$ +\phi_ {\boldsymbol {g}} (p) = h _ {g} \left(\boldsymbol {f} _ {\boldsymbol {g}} (p)\right) \text {a n d} \phi_ {\boldsymbol {a}} (p) = h _ {a} \left(\boldsymbol {f} _ {\boldsymbol {a}} (p)\right) \tag {3} +$$ + +These raw TSDF and color outputs can be utilized for depth/color rendering as well as mesh extraction. + +# 3.2. SDF-Based Volume Rendering + +When processing input frame $i$ , emulating the ray casting in NeRF [37], we select random pixels and calculate their corresponding rays using the current estimate of the camera pose $\{R_i|t_i\}$ . For rendering the depths and colors of the rays, we first sample $N_{strat}$ samples on each ray by stratified sampling and then sample additional $N_{imp}$ points near surfaces. For pixels with ground truth depths, the $N_{imp}$ additional points are sampled uniformly inside the truncation distance $T$ w.r.t. the depth measurement, whereas for other pixels, $N_{imp}$ points are sampled with the importance sampling technique [34, 37, 59, 70] based on the weights computed for the stratified samples. + +For all $N = N_{strat} + N_{imp}$ points on a ray $\{p_n\}_{n=1}^N$ , we query TSDF $\phi_g(p_n)$ and raw color $\phi_a(p_n)$ from our networks and use the SDF-Based rendering approach in + +StyleSDF [47] to convert SDF values to volume densities: + +$$ +\boldsymbol {\sigma} \left(p _ {n}\right) = \beta \cdot \text {S i g m o i d} \left(- \beta \cdot \phi_ {\boldsymbol {g}} \left(p _ {n}\right)\right) \tag {4} +$$ + +where $\beta$ is a learnable parameter that controls the sharpness of the surface boundary. Negative values of SDF push Sigmoid toward one, resulting in volume density inside the surface. The volume density then is used for rendering the color and depth of each ray: + +$$ +w _ {n} = \exp \left(- \sum_ {k = 1} ^ {n - 1} \boldsymbol {\sigma} (p _ {k})\right) (1 - \exp (- \boldsymbol {\sigma} (p _ {n}))) +$$ + +$$ +\hat {\boldsymbol {c}} = \sum_ {n = 1} ^ {N} w _ {n} \phi_ {\boldsymbol {a}} \left(p _ {n}\right) \quad \text {a n d} \quad \hat {\boldsymbol {d}} = \sum_ {n = 1} ^ {N} w _ {n} z _ {n} \tag {5} +$$ + +where $z_{n}$ is the depth of point $p_n$ w.r.t. the camera pose. + +# 3.3. Loss Functions + +One advantage of TSDF over other representations, such as occupancy, is that it allows us to use per-point losses, along with rendering ones. These losses account for the rapid convergence of our model. Following the practice in [1], assuming a batch of rays $R$ with ground truth depths are selected, we define the free space loss as: + +$$ +\mathcal {L} _ {f s} = \frac {1}{| R |} \sum_ {r \in R} \frac {1}{| P _ {r} ^ {f s} |} \sum_ {p \in P _ {r} ^ {f s}} (\phi_ {\boldsymbol {g}} (p) - 1) ^ {2} \tag {6} +$$ + +where $P_r^{fs}$ is a set of points on the ray $r$ that lie between the camera center and the truncation region of the surface measured by the depth sensor. This loss function encourages TSDF $\phi_g$ to have a value of one in the free space. + +For sample points close to the surface and within the truncation region, we use the signed distance objective, which leverages the depth sensor measurement to approximate the signed distance field: + +$$ +\mathcal {L} _ {T} (P _ {r} ^ {T}) = +$$ + +$$ +\frac {1}{| R |} \sum_ {r \in R} \frac {1}{| P _ {r} ^ {T} |} \sum_ {p \in P _ {r} ^ {T}} (z (p) + \phi_ {\mathbf {g}} (p) \cdot T - D (r)) ^ {2} \tag {7} +$$ + +where $z(p)$ is the planar depth of point $p$ w.r.t. camera, $T$ is the truncation distance, $D(r)$ is the ray depth measured by the sensor, and $P_r^T$ is a set of points on the ray $r$ that lie in the truncation region, i.e. $|z(p) - D(r)| < T$ . We apply the same loss to all points in the truncation region, but we differentiate the importance of points that are closer to the surface in the middle of the truncation region $P_r^{T - m}$ from those that are at the tail of the truncation region $P_r^{T - t}$ . Formally, we define $P_r^{T - m}$ as a set of points that $|z(p) - D(r)| < 0.4T$ , and define $P_r^{T - t} = P_r^T - P_r^{T - m}$ , then: + +$$ +\mathcal {L} _ {T - m} = \mathcal {L} _ {T} \left(P _ {r} ^ {T - m}\right) \quad \text {a n d} \quad \mathcal {L} _ {T - t} = \mathcal {L} _ {T} \left(P _ {r} ^ {T - t}\right) \tag {8} +$$ + +This enables us to decrease the importance of $\mathcal{L}_{T - t}$ in mapping, which leads to having a smaller effective truncation distance, reducing artifacts in occluded areas, and reconstructing with higher accuracy while leveraging the entire truncation distance in camera tracking. + +In addition to these two per-point loss functions, we also employ reconstruction losses. For pixels with ground truth depths, we impose consistency between the rendered depth and the depth measured by the sensor: + +$$ +\mathcal {L} _ {d} = \frac {1}{| R |} \sum_ {r \in R} (\hat {\boldsymbol {d}} (r) - D (r)) ^ {2} \tag {9} +$$ + +Similarly, we impose consistency between the pixel colors and rendered colors: + +$$ +\mathcal {L} _ {c} = \frac {1}{| R |} \sum_ {r \in R} (\hat {\boldsymbol {c}} (r) - I (r)) ^ {2} \tag {10} +$$ + +where $I(r)$ is the pixel color of ray $r$ . + +The global loss function of our method is defined as: + +$$ +\mathcal {L} = \lambda_ {f s} \mathcal {L} _ {f s} + \lambda_ {T - m} \mathcal {L} _ {T - m} + \lambda_ {T - t} \mathcal {L} _ {T - t} + \lambda_ {d} \mathcal {L} _ {d} + \lambda_ {c} \mathcal {L} _ {c} \tag {11} +$$ + +where $\{\lambda_{fs},\lambda_{T - m},\lambda_{T - t},\lambda_d,\lambda_c\}$ are the weighting coefficients. Note that $\mathcal{L}_c$ is defined on all rays in a training batch, while other losses are only imposed on rays with ground truth measured depths. The global objective is the same for both mapping and tracking in our method, but the weighting coefficients are different. + +# 3.4. Mapping and Tracking + +Mapping. Our scene representation, i.e. the feature planes and MLP decoders, are randomly initialized at the beginning. With the first input frame $\{I_0, D_0\}$ , we fix the camera pose and optimize the feature planes and MLP decoders to best represent the first frame. For subsequent inputs, we update the scene representation iteratively every $k$ frames, and add the latest frame to the global keyframe list, following the practice in iMAP [59] and NICE-SLAM [87]. For mapping, we first choose $|R|$ pixels randomly from $W$ frames, which include the current frame, the previous two keyframes, and $W - 3$ frames randomly selected from the keyframe list. Then, we jointly optimize the feature planes, MLP decoders, and camera poses of the $W$ selected frames using the loss functions introduced in Sec. 3.3. Unlike NICE-SLAM [87], our method does not require a staged-optimization policy, and we simply optimize all scene parameters and camera poses simultaneously. + +Tracking. The localization process of our method is initiated for each input frame. The current estimate of the camera parameters, represented by translation vectors and quaternion rotations [56] $\{R|t\}$ , are optimized solely based + +
MethodReconstruction (cm)Localization (cm)
Depth L1↓Acc.↓Comp.↓Comp. Ratio (%)↑ATE Mean↓ATE RMSE↓
iMAP* [59]8.23 ± 0.887.16 ± 0.265.83 ± 0.2767.17 ± 2.702.59 ± 0.583.42 ± 0.87
NICE-SLAM [87]3.29 ± 0.331.66 ± 0.071.63 ± 0.0596.74 ± 0.361.56 ± 0.292.05 ± 0.45
ESLAM (ours)1.18 ± 0.050.97 ± 0.021.05 ± 0.0198.60 ± 0.070.52 ± 0.030.63 ± 0.05
+ +Table 1. Quantitative comparison of our proposed ESLAM with existing NeRF-based dense visual SLAM models on the Replica dataset [57] for both reconstruction and localization accuracy. The results are the average and standard deviation of five runs on eight scenes of the Replica dataset [57]. Our method outperforms previous works by a high margin and has lower variances, indicating it is also more stable from run to run. The evaluation metrics for reconstruction are L1 loss (cm) between rendered and ground truth depth maps of 1000 random camera poses, reconstruction accuracy (cm), reconstruction completion (cm), and completion ratio (\%). The evaluation metrics for localization are mean and RMSE of ATE (cm) [58]. For the details of the evaluations for each scene, refer to the supplementary. It should also be noted that our method runs up to $\times 10$ faster on this dataset (see Sec. 4.2 for runtime analysis). + +![](images/df6f19a7a5dcf0d5634fe30d8b88f5c6c966b6203fcbfe0bc20f69d1f6f40600.jpg) + +![](images/52334a27e92b9f6bd8a78c96d7e175bd8cba297d27a932a0a8ff8998b72adc7f.jpg) + +![](images/99e1511332064f946574ea150828fb085edc7f779b2bf4935cbf48603615287b.jpg) +iMAP* + +![](images/bd2de7132c5c8517c09971644492b7335324a19b3400a1881881b4425cf0595b.jpg) + +![](images/cbd65baef018ec4ed400a4a842a3a265fe2f3917c7fa40221837cda5383c6e8a.jpg) + +![](images/db7140467f172a23fb17fc3e755d62b60fd69056f18fd2e7bde42ccea384556d.jpg) +NICE-SLAM + +![](images/c46a87aacac28d4ebaf353ca610fe3ef1b3a11133b41b5dd1e8e762ce72a3a81.jpg) + +![](images/3c1f49bcefca8d3f50da9a3aafca1210f32538447b96dd865154a48f4a0bf857.jpg) + +![](images/89623a0a2ffd3f3dce57c2dd20b40fcf240842170c50a5f35585c814d968d0d9.jpg) +ESLAM (ours) +Figure 3. Qualitative comparison of our proposed ESLAM method's geometry reconstruction with existing NeRF-based dense visual SLAM models, iMAP* [59] and NICE-SLAM [87], on the Replica dataset [57]. Our method produces more accurate detailed geometry as well as higher-quality textures. The ground truth images are rendered with the ReplicaViewer software [57]. It should also be noted that our method runs up to $\times 10$ faster on this dataset (see Sec. 4.2 for runtime analysis). For further qualitative analysis on this dataset, as well as videos demonstrating the localization and reconstruction process, refer to the supplementary. + +![](images/496ef5241a9cfd25b5a9f6bb1fa859d4d550485618f7ff02e6fb50daf827e458.jpg) + +![](images/41e36306c11e615c1cc9d7e86a8b22896e8ba5f1758a9814a77975bdd788e73e.jpg) + +![](images/006983f2c589ec40d783cb3ca6840e6b9087d2231831e4019e51b5720d673012.jpg) +Ground Truth + +on our global loss function (see Sec. 3.3) with the gradient-based Adam optimizer [24]. No second-order optimizers or manifold operations are employed for camera tracking in our method. We exclude rays with no ground truth depths and outlier pixels from each optimization step. A pixel is considered an outlier if the difference between its measured depth and rendered depth is ten times greater than the batch's median rendered depth error. + +# 4. Experiments + +In this section, we validate that our method outperforms existing implicit representation-based methods in both localization and reconstruction accuracy on three standard benchmarks while running up to $\times 10$ faster. + +Baselines. We compare our method to two existing state-of-the-art NeRF-based dense visual SLAM methods: iMAP [59] and NICE-SLAM [87]. Because iMAP is not open source, we use the iMAP* model in our experiment, which is the reimplementation of iMAP in [87]. + +Datasets. We evaluate our method on three standard 3D benchmarks: Replica [57], ScanNet [12], and TUM RGB-D [58] datasets. We select the same scenes for evaluation as NICE-SLAM [87]. + +Metrics. We borrow our evaluation metrics from NICE-SLAM [87]. For evaluating scene geometry, we use both 2D and 3D metrics. For the 2D metric, we render depth maps from 1000 random camera poses in each scene and calculate + +
MethodATESc. 0000Sc. 0059Sc. 0106Sc. 0169Sc. 0181Sc. 0207Ave.
iMAP* [59]Mean34.2 ± 12.813.0 ± 2.412.9 ± 1.733.6 ± 15.320.8 ± 3.818.6 ± 6.022.2 ± 7.0
RMSE42.7 ± 16.617.8 ± 7.415.0 ± 1.739.1 ± 18.224.7 ± 5.820.1 ± 6.826.6 ± 9.4
NICE-SLAM [87]Mean9.9 ± 0.411.9 ± 1.87.0 ± 0.29.2 ± 1.012.2 ± 0.35.5 ± 0.39.3 ± 0.7
RMSE12.0 ± 0.514.0 ± 1.87.9 ± 0.210.9 ± 1.113.4 ± 0.36.2 ± 0.410.7 ± 0.7
ESLAM (ours)Mean6.5 ± 0.16.4 ± 0.46.7 ± 0.15.9 ± 0.18.3 ± 0.25.4 ± 0.16.5 ± 0.2
RMSE7.3 ± 0.28.5 ± 0.57.5 ± 0.16.5 ± 0.19.0 ± 0.25.7 ± 0.17.4 ± 0.2
+ +Table 2. Quantitative comparison of our proposed ESLAM method's localization accuracy with existing NeRF-based dense visual SLAM models on the ScanNet dataset [12]. The results are the average and standard deviation of five runs on each scene of ScanNet [12]. Our method outperforms previous works and has lower variances, indicating it is also more stable from run to run. The evaluation metrics for localization are mean and RMSE of ATE (cm) [58]. It should also be noted that our method runs up to $\times 6$ faster on this dataset (see Sec. 4.2 for runtime analysis). + +![](images/ff31a36899570c251739a91b580fd61a4f970b1a4aabdce8e44cf304259eda09.jpg) + +![](images/0a317639eb62dce83b139f1397c2392da4bacd2e321f21e2f78f2942f356e1e5.jpg) + +![](images/a52246afbe81751d25ef1065531323ed6aad9e6765228ada1bd325d423770e61.jpg) + +![](images/5f99eb7df57d29b48b1e9a07aae863093d25a08c363c52124f4677b88da34e78.jpg) + +![](images/857423e71723c247bd6f6d2e4c8dd57139ed925e077f945bfa8b60326114cb1f.jpg) + +![](images/dda558e6a037d0b11ca21867dea1c662e11282396a017a1993e249c58f4b71df.jpg) + +![](images/553c0add2540cf2c226fd97e4bdffbf89ca05e0605e23ff7a5a841eb7edd2614.jpg) +iMAP* + +![](images/1f79952e3d5146a4c68b6d7be276b8ce5eb879b66234f345d3f210fe82f8c5b0.jpg) +NICE-SLAM + +![](images/d6afad49e2030248db35091d13133ec995cd2ab303ab08bc2ba326d5dd9248c8.jpg) +ESLAM (ours) +Figure 4. Qualitative comparison of our proposed ESLAM method's localization accuracy with existing NeRF-based dense visual SLAM models, iMAP* [59] and NICE-SLAM [87], on the ScanNet dataset [12]. The ground truth camera trajectory is shown in green, and the estimated trajectory is shown in red. Our method predicts more accurate camera trajectories and does not suffer from drifting issues. It should also be noted that our method runs up to $\times 6$ faster on this dataset (see Sec. 4.2 for runtime analysis). + +the L1 difference between depths from ground truth meshes and the reconstructed ones. For the 3D metrics, we consider reconstruction accuracy [cm], reconstruction completion [cm], and completion ratio $[< 5\mathrm{cm}\%]$ . For evaluating these metrics, we build a TSDF volume for a scene with a resolution of $1\mathrm{cm}$ and use the marching cubes algorithm [33] to obtain scene meshes. Before evaluating the 3D metrics for our method and for the baselines, we perform mesh culling as recommended in [1, 70]. For this purpose, we remove faces from a mesh that are not inside any + +camera frustum or are occluded in all RGB-D frames. For evaluating camera localization, we use ATE [58]. + +Implementation Details. The truncation distance $T$ is set to $6\mathrm{cm}$ in our method. We employ coarse feature planes with a resolution of $24\mathrm{cm}$ for both geometry and appearance. For fine feature planes, we use a resolution of $6\mathrm{cm}$ for geometry and $3\mathrm{cm}$ for appearance. All feature planes have 32 channels, resulting in a 64-channel concatenated feature input for the decoders. The decoders are two-layer MLPs + +![](images/3f1e3fdabf330312f732c32494fd45dd69522d5eda47312a1e8ee326957dcf9b.jpg) + +![](images/aa857cdc9a01f378bb08359b44d337bab7e4abd63d662d8a76d09b73844990c5.jpg) + +![](images/116cd37d850f88ae7199ed99a71c6319a1c41de1bc4d59626c202217b68a3566.jpg) + +![](images/f3da189632d3717f70520e1850adba07a8179da3132e5279cb1434615f8a911c.jpg) + +![](images/bb87ac1c0e4525ee039f9a3fc635675ec6d1522f298daa99a094a27b565f492d.jpg) + +![](images/f7b566926e75ae4b848797086fda2dc90c7b8adc2a7efa9c92d39368cd6ffa6a.jpg) + +![](images/b59d02cc78a36650838969c3d69b0cb4389d2549183e91c2bc01e0baa72b4f3f.jpg) + +![](images/7b72e65f3b74b285a5b3203fbb26b1f86b32acfa401c39fbf12abb245fae2321.jpg) + +![](images/f391a2abe1755b941c501299d6ff487cee01cfed01a94f1a6f1b6cf68f688f1b.jpg) +iMAP* + +![](images/c78412b6fe891b7152bedd7a01cc76657b15ef597ce6fcf7185f07b14d32a0bf.jpg) +NICE-SLAM + +![](images/b62632ea3d38af7582e4c02e77d622fe1e7a203544d3ea07ccb59003eef3dde8.jpg) +ESLAM (ours) +Figure 5. Qualitative comparison of our proposed ESLAM method's geometry reconstruction with existing NeRF-based dense visual SLAM models, iMAP* [59] and NICE-SLAM [87], on the ScanNet dataset [12]. Our method produces more accurate detailed geometry as well as higher-quality textures. The appearance of white backgrounds in ground truth meshes is due to the fact that the ground truth meshes of the ScanNet dataset [12] are incomplete. It should also be noted that our method runs up to $\times 6$ faster on this dataset (see Sec. 4.2 for runtime analysis). + +![](images/1b66c7eb0b4cbaa159cf96288e81ce6477dbeefef4b6c615c5e6fe8a4cd10917.jpg) +Ground Truth + +with 32 channels in the hidden layer. For the Replica [57] dataset, we sample $N_{strat} = 32$ points for stratified sampling and $N_{imp} = 8$ points for importance sampling on each ray. And for the ScanNet [12] and TUM RGB-D [58] datasets, we set $N_{strat} = 48$ and $N_{imp} = 8$ . + +We use different set of loss coefficients for mapping and tracking. During mapping we set $\lambda_{fs} = 5$ , $\lambda_{T - m} = 200$ , $\lambda_{T - t} = 10$ , $\lambda_d = 0.1$ , and $\lambda_c = 5$ . And during tracking, we set $\lambda_{fs} = 10$ , $\lambda_{T - m} = 200$ , $\lambda_{T - t} = 50$ , $\lambda_d = 1$ , and $\lambda_c = 5$ . These coefficients are obtained by performing grid search in our experiments. For further details of our implementation, refer to the supplementary. + +# 4.1. Experimental Results + +Evaluation on Replica [57]. We provide the quantitative analysis of our experimental results on eight scenes of the Replica dataset [57] in Tab. 1. The numbers represent the average and standard deviation of the metrics for five independent runs. As shown in Tab. 1, our method outperforms the baselines for both reconstruction and localization accuracy. Our method also has lower variances, indicating that it is more stable and more robust than existing methods. + +Qualitative analysis on the Replica dataset [57] is provided in Fig. 3. The results show that our method reconstructs the details of the scenes more accurately and produces fewer artifacts. Although it is not the focus of this paper, our method also produces higher-quality colors for the reconstructed meshes. + +Evaluation on ScanNet [12]. We also benchmark ours and existing methods on multiple large scenes from ScanNet [12] to evaluate and compare their scalability. For evaluating camera localization, we conduct five independent experiments on each scene and report the average and standard deviation of the mean and RMSE of ATE [58] in Tab. 2. As demonstrated in the table, our method's localization is more accurate than existing methods. Our method is also considerably more stable from run to run as it has much lower standard deviations. We provide qualitative analysis of camera localization, along with geometry reconstruction, in Fig. 4. The results show that our method does not suffer from any large drifting and is more robust than existing methods. + +Since the ground truth meshes of the ScanNet dataset [12] are incomplete, we only provide qualitative analysis for geometry reconstruction, similar to previous works. The qualitative comparison in Fig. 5 validates that our model reconstructs more precise geometry and detailed textures compared to existing approaches. + +Evaluation on TUM RGB-D [58]. To further contrast the robustness of our method with the existing ones, we conduct an evaluation study on the real-world TUM RGB-D dataset [58]. Since there are no ground truth meshes for the scenes in this dataset, we only present the localization results in Tab. 3 and the qualitative analysis of rendered meshes in Fig. 6. + +![](images/69f676ea7ba4850e123bcd996e44f45b845e61cdaaaef558f5db28cbce5c88b5.jpg) + +![](images/b0102e0387427e255e011e38ab43e70e71826d611a57812baae7221bd7c75cbf.jpg) +Sample Image + +![](images/90fe874fd558e115abb596b689bbe270467eaaec92c9028b9c5a9f373ec91ec7.jpg) + +![](images/797290ddc05a8bda71cd0338f50cfb0868702f6979e13293ebf6dd7a738ee9f5.jpg) +iMAP* + +![](images/8f00e5b90af071416630a75cd714c858dbc1a087be0b3480b7a2eb185ca3ce67.jpg) + +![](images/1c1f84bc3bf4e40528ec8deadad14070a4d3f2cfbe406e8dc130b0c8fcaf3916.jpg) +NICE-SLAM +Figure 6. Qualitative comparison of our proposed ESLAM method's geometry reconstruction with existing NeRF-based dense visual SLAM models, iMAP* [59] and NICE-SLAM [87], on the TUM RGB-D dataset [58]. Our method produces more accurate detailed geometry as well as higher-quality textures. Since there are no ground truth meshes for this dataset, we depict a sample input image. + +![](images/cad4003aa79b54cf2f3d8265f6a050724d61e03642833e1eadfaeabb220e6e71.jpg) + +![](images/5ec7f20951817b8bc5d70abc352f10762af60ec8891b1ac56f1497fc6af3b9b6.jpg) +ESLAM (ours) + +
fr1/deskfr2/xyzfr3/office
iMAP* [59]4.902.055.80
NICE-SLAM [87]2.852.393.02
ESLAM (ours)2.471.112.42
+ +Table 3. Quantitative comparison of our proposed ESLAM method's localization accuracy with existing NeRF-based dense visual SLAM models on the TUM RGB-D dataset [58]. The evaluation metric is ATE RMSE $\downarrow$ (cm) [58]. + +
MethodSpeed FPT (s)Memory
# Param.Grow. R.
ReplicaiMAP* [59]5.200.22 M?
NICE-SLAM [87]2.1012.18 MO(L3)
ESLAM (ours)0.186.79 MO(L2)
ScanNetiMAP* [59]5.200.22 M?
NICE-SLAM [87]3.3522.04 MO(L3)
ESLAM (ours)0.5517.63 MO(L2)
+ +Table 4. Runtime analysis of our method in comparison with existing ones in terms of average frame processing time (FPT), number of parameters, and model size growth rate w.r.t. scene side-length $L$ . All methods are benchmarked with an NVIDIA GeForce RTX 3090 GPU on room0 of Replica [57] and scene0000 of ScanNet [12]. Our method is significantly faster and does not grow cubically in size w.r.t. scene side-length $L$ . Note that iMAP [59] represents a whole scene in a single MLP, hence its small number of parameters. Accordingly, the scalability and growth rate of iMAP [59] w.r.t. the scene side-length $L$ are also unclear. + +# 4.2. Runtime Analysis + +We evaluate the speed and size of our method in comparison with existing approaches in Tab. 4. We report the average frame processing time (FPT), the number of parameters of the model, and memory growth rate w.r.t. scene side-length for the scenes room0 of Replica [57] and + +scene0000 of ScanNet [12] datasets. All methods are benchmarked with an NVIDIA GeForce RTX 3090 GPU. The results indicate that our method is significantly faster than previous works on both datasets. Furthermore, in contrast to NICE-SLAM [87], our model size is smaller and does not grow cubically with the scene side-length. + +# 5. Conclusion + +We presented ESLAM, a dense visual SLAM approach that leverages the latest advances in the Neural Radiance Fields study to improve both the speed and accuracy of neural implicit-based SLAM systems. We proposed replacing the voxel grid representation with axis-aligned feature planes to prevent the model size from growing cubically with respect to the scene side-length. We also demonstrated that modeling the scene geometry with Truncated Signed Distance Field (TSDF) leads to efficient and high-quality surface reconstruction. We verified through extensive experiments that our approach outperforms existing methods significantly in both reconstruction and localization accuracy while running up to one order of magnitude faster. + +ESLAM accepts and deals with the forgetting problem in exchange for memory preservation. Due to the structure of our feature plane representation, updating features to adapt to new geometry may affect previously reconstructed geometries. To address this issue, we keep track of previous keyframes and allocate a large portion of computation resources to retain and remember previously reconstructed regions. Although ESLAM is substantially faster than competing approaches, handling the forgetting problem more efficiently could further reduce frame processing time. + +# Acknowledgement + +This research was supported by ams OSRAM. + +# References + +[1] Dejan Azinović, Ricardo Martin-Brualla, Dan B Goldman, Matthias Nießner, and Justus Thies. Neural rgb-d surface reconstruction. 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ESLAM reads RGB-D frames with unknown camera poses in a sequential manner and incrementally reconstructs the scene representation while estimating the current camera position in the scene. We incorporate the latest advances in Neural Radiance Fields (NeRF) into a SLAM system, resulting in an efficient and accurate dense visual SLAM method. Our scene representation consists of multiscale axis-aligned perpendicular feature planes and shallow decoders that, for each point in the continuous space, decode the interpolated features into Truncated Signed Distance Field (TSDF) and RGB values. Our extensive experiments on three standard datasets, Replica, ScanNet, and TUM RGB-D show that ESLAM improves the accuracy of 3D reconstruction and camera localization of state-of-the-art dense visual SLAM methods by more than " + }, + { + "bbox": [ + 46, + 361, + 290, + 589 + ], + "type": "inline_equation", + "content": "50\\%" + }, + { + "bbox": [ + 46, + 361, + 290, + 589 + ], + "type": "text", + "content": ", while it runs up to " + }, + { + "bbox": [ + 46, + 361, + 290, + 589 + ], + "type": "inline_equation", + "content": "\\times 10" + }, + { + "bbox": [ + 46, + 361, + 290, + 589 + ], + "type": "text", + "content": " faster and does not require any pre-training. Project page: https://www.idiap.ch/paper/eslam" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 47, + 609, + 128, + 621 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 609, + 128, + 621 + ], + "spans": [ + { + "bbox": [ + 47, + 609, + 128, + 621 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 46, + 629, + 287, + 701 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 629, + 287, + 701 + ], + "spans": [ + { + "bbox": [ + 46, + 629, + 287, + 701 + ], + "type": "text", + "content": "Dense visual Simultaneous Localization and Mapping (SLAM) is a fundamental challenge in 3D computer vision with several applications such as autonomous driving, robotics, and virtual/augmented reality. It is defined as constructing a 3D map of an unknown environment while simultaneously approximating the camera pose." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 59, + 701, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 701, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 59, + 701, + 287, + 714 + ], + "type": "text", + "content": "While traditional SLAM systems [16, 41, 45, 55, 76, 77]" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 304, + 337, + 545, + 384 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 337, + 545, + 384 + ], + "spans": [ + { + "bbox": [ + 304, + 337, + 545, + 384 + ], + "type": "text", + "content": "mostly focus on localization accuracy, recent learning-based dense visual SLAM methods [2, 11, 25, 35, 60, 64, 65, 67, 81, 86] provide meaningful global 3D maps and show reasonable but limited reconstruction accuracy." + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 304, + 384, + 546, + 480 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 384, + 546, + 480 + ], + "spans": [ + { + "bbox": [ + 304, + 384, + 546, + 480 + ], + "type": "text", + "content": "Following the advent of Neural Radiance Fields (NeRF) [37] and the demonstration of their capacity to reason about the geometry of a large-scale scene [8, 13, 20, 22, 26, 75, 78] and reconstruct 3D surfaces [1, 29, 47, 48, 62, 71, 72, 82, 85], novel NeRF-based dense SLAM methods have been developed. In particular, iMAP [59] and NICE-SLAM [87] utilize neural implicit networks to achieve a consistent geometry representation." + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 304, + 481, + 547, + 613 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 481, + 547, + 613 + ], + "spans": [ + { + "bbox": [ + 304, + 481, + 547, + 613 + ], + "type": "text", + "content": "IMAP [59] represents the geometry with a single huge MLP, similar to NeRF [37], and optimizes the camera poses during the rendering process. NICE-SLAM [87] improves iMAP by storing the representation locally on voxel grids to prevent the forgetting problem. Despite promising reconstruction quality, these methods are computationally demanding for real-time applications, and their ability to capture geometry details is limited. In addition, NICE-SLAM [87] uses frozen pre-trained MLPs, which limits its generalizability to novel scenes. We take NICE-SLAM [87] as a baseline and provide the following contributions:" + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 317, + 620, + 545, + 714 + ], + "type": "list", + "angle": 0, + "index": 27, + "blocks": [ + { + "bbox": [ + 317, + 620, + 545, + 681 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 620, + 545, + 681 + ], + "spans": [ + { + "bbox": [ + 317, + 620, + 545, + 681 + ], + "type": "text", + "content": "- We leverage implicit Truncated Signed Distance Field (TSDF) [1] to represent geometry, which converges noticeably faster than the common rendering-based representations like volume density [59] or occupancy [87] and results in higher quality reconstruction." + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 317, + 689, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 689, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 317, + 689, + 545, + 714 + ], + "type": "text", + "content": "Instead of storing features on voxel grids, we propose employing multi-scale axis-aligned feature planes [6]" + } + ] + } + ], + "index": 26 + } + ], + "sub_type": "text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "17408" + } + ] + } + ], + "index": 28 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 66, + 72, + 286, + 96 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 66, + 72, + 286, + 96 + ], + "spans": [ + { + "bbox": [ + 66, + 72, + 286, + 96 + ], + "type": "text", + "content": "which leads to reducing the memory footprint growth rate w.r.t. scene side-length from cubic to quadratic." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 59, + 105, + 286, + 165 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 105, + 286, + 165 + ], + "spans": [ + { + "bbox": [ + 59, + 105, + 286, + 165 + ], + "type": "text", + "content": "- We benchmark our method on three challenging datasets, Replica [57], ScanNet [12], and TUM RGB-D [58], to demonstrate the performance of our method in comparison to existing ones and provide an extensive ablation study to validate our design choices." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 174, + 286, + 221 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 174, + 286, + 221 + ], + "spans": [ + { + "bbox": [ + 47, + 174, + 286, + 221 + ], + "type": "text", + "content": "Thanks to the inherent smoothness of representing the scene with feature planes, our method produces higher-quality smooth surfaces without employing explicit smoothness loss functions like [70]." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 222, + 286, + 365 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 222, + 286, + 365 + ], + "spans": [ + { + "bbox": [ + 46, + 222, + 286, + 365 + ], + "type": "text", + "content": "Concurrent with our work, the followings also propose Radiance Fields-based SLAM systems: iDF-SLAM [38] also uses TSDF, but it is substantially slower and less accurate than NICE-SLAM [87]. Orbeez-SLAM [10] operates in real-time at the cost of poor 3D reconstruction. Compromising accuracy and quality, MeSLAM [27] introduces a memory-efficient SLAM. MonoNeuralFusion [88] proposes an incremental 3D reconstruction model, assuming that ground truth camera postures are available. Lastly, NeRF-SLAM [54] presents a monocular SLAM system with hierarchical volumetric Neural Radiance Fields optimized using an uncertainty-based depth loss." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 377, + 133, + 389 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 377, + 133, + 389 + ], + "spans": [ + { + "bbox": [ + 47, + 377, + 133, + 389 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 397, + 286, + 613 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 397, + 286, + 613 + ], + "spans": [ + { + "bbox": [ + 46, + 397, + 286, + 613 + ], + "type": "text", + "content": "Dense Visual SLAM. The ubiquity of cameras has made visual SLAM a field of major interest in the last decades. Traditional visual SLAM employs pixel-wise optimization of geometric and/or photometric constraints from image information. Depending on the information source, visual SLAM divides into three main categories: visual-only [15-17,41,45,66], visual-inertial [3,28,39,42,53,69] and RGB-D [5, 14, 23, 44] SLAM. Visual-only SLAM uses single or multi-camera setups but presents higher technical challenges compared to others. Visual-inertial information can improve accuracy, but complexifies the system and requires an extra calibration step. The advent of the Kinect brought popularity to RGB-D setups with improved performance but had drawbacks such as larger memory and power requirements, and limitation to indoor settings. Recently, learning-based approaches [2,11,30,31,67] have made great advances in the field, improving both accuracy and robustness compared to traditional methods." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 617, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 617, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 617, + 286, + 713 + ], + "type": "text", + "content": "Neural Implicit 3D Reconstruction. Neural Radiance Fields (NeRF) have impacted 3D Computer Vision applications, such as novel view synthesis [34, 36, 37, 68], surface reconstruction [46, 49, 71, 72, 82, 83, 85], dynamic scene representation [19, 50-52], and camera pose estimation [21, 32, 73, 79, 84]. The exploitation of neural implicit representations for 3D reconstruction at real-world scale is studied in [1, 4, 9, 29, 43, 63, 70, 74, 80]. The most related works" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 72, + 545, + 216 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 216 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 216 + ], + "type": "text", + "content": "to ours are iMAP [59] and NICE-SLAM [87]. IMAP [59] presents a NeRF-style dense SLAM system. NICE-SLAM [87] extends iMAP [59] by modeling the scene with voxel grid features and decoding them into occupancies using pre-trained MLPs. However, the generalizability of NICE-SLAM [87] to novel scenes is limited because of the frozen pre-trained MLPs. Another issue is the cubic memory growth rate of their model, which results in using low-resolution voxel grids and losing fine geometry details. In contrast, we employ compact plane-based features [6] which are directly decoded to TSDF, improving both efficiency and accuracy of localization and reconstruction." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 229, + 361, + 241 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 229, + 361, + 241 + ], + "spans": [ + { + "bbox": [ + 306, + 229, + 361, + 241 + ], + "type": "text", + "content": "3. Method" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 250, + 545, + 430 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 250, + 545, + 430 + ], + "spans": [ + { + "bbox": [ + 304, + 250, + 545, + 430 + ], + "type": "text", + "content": "The overview of our method is shown in Fig. 2. Given a set of sequential RGB-D frames " + }, + { + "bbox": [ + 304, + 250, + 545, + 430 + ], + "type": "inline_equation", + "content": "\\{I_i, D_i\\}_{i=1}^M" + }, + { + "bbox": [ + 304, + 250, + 545, + 430 + ], + "type": "text", + "content": ", our model predicts camera poses " + }, + { + "bbox": [ + 304, + 250, + 545, + 430 + ], + "type": "inline_equation", + "content": "\\{R_i|t_i\\}_{i=1}^M" + }, + { + "bbox": [ + 304, + 250, + 545, + 430 + ], + "type": "text", + "content": " and an implicit TSDF " + }, + { + "bbox": [ + 304, + 250, + 545, + 430 + ], + "type": "inline_equation", + "content": "\\phi_g" + }, + { + "bbox": [ + 304, + 250, + 545, + 430 + ], + "type": "text", + "content": " representation that can be used in marching cubes algorithm [33] to extract 3D meshes. We expect TSDF to denote the distance to the closest surface with a positive sign in the free space and a negative sign inside the surfaces. We employ normalized TSDF, such that it is zero on the surfaces and has a magnitude of one at the truncation distance " + }, + { + "bbox": [ + 304, + 250, + 545, + 430 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 304, + 250, + 545, + 430 + ], + "type": "text", + "content": ", which is a hyper-parameter. Sec. 3.1 describes how we represent a scene with axis-aligned feature planes. Sec. 3.2 walks through the rendering process, which converts raw representations into pixel depths and colors. Sec. 3.3 introduces our loss functions. And Sec. 3.4 provides the details of localization and reconstruction in our SLAM system." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 439, + 462, + 452 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 439, + 462, + 452 + ], + "spans": [ + { + "bbox": [ + 306, + 439, + 462, + 452 + ], + "type": "text", + "content": "3.1. Axis-Aligned Feature Planes" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 459, + 545, + 638 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 459, + 545, + 638 + ], + "spans": [ + { + "bbox": [ + 304, + 459, + 545, + 638 + ], + "type": "text", + "content": "Although voxel grid-based NeRF architectures [18, 61, 70] exhibit rapid convergence, they struggle with cubical memory growing. Different solutions have been proposed to mitigate the memory growth issue [6, 7, 40]. Inspired by [6], we employ a tri-plane architecture (see Fig. 2), in which we store and optimize features on perpendicular axis-aligned planes. Mimicking the trend in voxel-based methods [7, 40, 61], we propose using feature planes at two scales, i.e. coarse and fine. Coarse-level representation allows efficient reconstruction of free space with fewer sample points and optimization iterations. Moreover, we suggest employing separate feature planes for representing geometry and appearance, which mitigates the forgetting problem for geometry reconstruction since appearance fluctuates more frequently in a scene than geometry." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 639, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 639, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 639, + 545, + 713 + ], + "type": "text", + "content": "Specifically, we use three coarse feature planes " + }, + { + "bbox": [ + 304, + 639, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\{F_{g - xy}^{c}, F_{g - xz}^{c}, F_{g - yz}^{c}\\}" + }, + { + "bbox": [ + 304, + 639, + 545, + 713 + ], + "type": "text", + "content": " and three fine ones " + }, + { + "bbox": [ + 304, + 639, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\{F_{g - xy}^{f}, F_{g - xz}^{f}, F_{g - yz}^{f}\\}" + }, + { + "bbox": [ + 304, + 639, + 545, + 713 + ], + "type": "text", + "content": " for representing the geometry. Similarly, three coarse " + }, + { + "bbox": [ + 304, + 639, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\{F_{a - xy}^{c}, F_{a - xz}^{c}, F_{a - yz}^{c}\\}" + }, + { + "bbox": [ + 304, + 639, + 545, + 713 + ], + "type": "text", + "content": " and three fine " + }, + { + "bbox": [ + 304, + 639, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\{F_{a - xy}^{f}, F_{a - xz}^{f}, F_{a - yz}^{f}\\}" + }, + { + "bbox": [ + 304, + 639, + 545, + 713 + ], + "type": "text", + "content": " planes are used for representing appearance of a scene. This architecture prevents model size from growing cubically with the" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "17409" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 59, + 74, + 545, + 334 + ], + "blocks": [ + { + "bbox": [ + 59, + 74, + 545, + 334 + ], + "lines": [ + { + "bbox": [ + 59, + 74, + 545, + 334 + ], + "spans": [ + { + "bbox": [ + 59, + 74, + 545, + 334 + ], + "type": "image", + "image_path": "9e46bfe5df6bfcce88422ca3957594a179c55ad87ed66096bec5bcbc49db5738.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 340, + 547, + 429 + ], + "lines": [ + { + "bbox": [ + 46, + 340, + 547, + 429 + ], + "spans": [ + { + "bbox": [ + 46, + 340, + 547, + 429 + ], + "type": "text", + "content": "Figure 2. The overview of ESLAM. Given the symmetry of our processes for geometry and appearance, we exhibit both processes on the same pipeline for simplicity. The symbol " + }, + { + "bbox": [ + 46, + 340, + 547, + 429 + ], + "type": "inline_equation", + "content": "*" + }, + { + "bbox": [ + 46, + 340, + 547, + 429 + ], + "type": "text", + "content": " represents both geometry " + }, + { + "bbox": [ + 46, + 340, + 547, + 429 + ], + "type": "inline_equation", + "content": "g" + }, + { + "bbox": [ + 46, + 340, + 547, + 429 + ], + "type": "text", + "content": " and appearance " + }, + { + "bbox": [ + 46, + 340, + 547, + 429 + ], + "type": "inline_equation", + "content": "a" + }, + { + "bbox": [ + 46, + 340, + 547, + 429 + ], + "type": "text", + "content": ", e.g., " + }, + { + "bbox": [ + 46, + 340, + 547, + 429 + ], + "type": "inline_equation", + "content": "f_{*}(p_{n})" + }, + { + "bbox": [ + 46, + 340, + 547, + 429 + ], + "type": "text", + "content": " can be either " + }, + { + "bbox": [ + 46, + 340, + 547, + 429 + ], + "type": "inline_equation", + "content": "f_{g}(p_{n})" + }, + { + "bbox": [ + 46, + 340, + 547, + 429 + ], + "type": "text", + "content": " or " + }, + { + "bbox": [ + 46, + 340, + 547, + 429 + ], + "type": "inline_equation", + "content": "f_{a}(p_{n})" + }, + { + "bbox": [ + 46, + 340, + 547, + 429 + ], + "type": "text", + "content": ". At an estimated camera pose " + }, + { + "bbox": [ + 46, + 340, + 547, + 429 + ], + "type": "inline_equation", + "content": "\\{R, t\\}" + }, + { + "bbox": [ + 46, + 340, + 547, + 429 + ], + "type": "text", + "content": ", we cast a ray for each pixel and sample " + }, + { + "bbox": [ + 46, + 340, + 547, + 429 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 340, + 547, + 429 + ], + "type": "text", + "content": " points " + }, + { + "bbox": [ + 46, + 340, + 547, + 429 + ], + "type": "inline_equation", + "content": "\\{p_n\\}_{n=1}^N" + }, + { + "bbox": [ + 46, + 340, + 547, + 429 + ], + "type": "text", + "content": " along it (Sec. 3.2). Each point " + }, + { + "bbox": [ + 46, + 340, + 547, + 429 + ], + "type": "inline_equation", + "content": "p_n" + }, + { + "bbox": [ + 46, + 340, + 547, + 429 + ], + "type": "text", + "content": " is projected onto the coarse and fine feature planes and bilinearly interpolates the four nearest neighbor features on each plane (Sec. 3.1). The interpolated features at each level are added together, and the results from both levels are concatenated together to form the inputs " + }, + { + "bbox": [ + 46, + 340, + 547, + 429 + ], + "type": "inline_equation", + "content": "\\{\\pmb{f}_{g}(p_{n}), \\pmb{f}_{a}(p_{n})\\}" + }, + { + "bbox": [ + 46, + 340, + 547, + 429 + ], + "type": "text", + "content": " of the decoders " + }, + { + "bbox": [ + 46, + 340, + 547, + 429 + ], + "type": "inline_equation", + "content": "\\{h_g, h_a\\}" + }, + { + "bbox": [ + 46, + 340, + 547, + 429 + ], + "type": "text", + "content": " (Sec. 3.1). The geometry decoder " + }, + { + "bbox": [ + 46, + 340, + 547, + 429 + ], + "type": "inline_equation", + "content": "h_g" + }, + { + "bbox": [ + 46, + 340, + 547, + 429 + ], + "type": "text", + "content": " estimates TSDF " + }, + { + "bbox": [ + 46, + 340, + 547, + 429 + ], + "type": "inline_equation", + "content": "\\phi_{g}(p_{n})" + }, + { + "bbox": [ + 46, + 340, + 547, + 429 + ], + "type": "text", + "content": " based on " + }, + { + "bbox": [ + 46, + 340, + 547, + 429 + ], + "type": "inline_equation", + "content": "f_{g}(p_{n})" + }, + { + "bbox": [ + 46, + 340, + 547, + 429 + ], + "type": "text", + "content": ", and the appearance decoder " + }, + { + "bbox": [ + 46, + 340, + 547, + 429 + ], + "type": "inline_equation", + "content": "h_a" + }, + { + "bbox": [ + 46, + 340, + 547, + 429 + ], + "type": "text", + "content": " estimates the raw color " + }, + { + "bbox": [ + 46, + 340, + 547, + 429 + ], + "type": "inline_equation", + "content": "\\phi_{a}(p_{n})" + }, + { + "bbox": [ + 46, + 340, + 547, + 429 + ], + "type": "text", + "content": " based on " + }, + { + "bbox": [ + 46, + 340, + 547, + 429 + ], + "type": "inline_equation", + "content": "f_{a}(p_{n})" + }, + { + "bbox": [ + 46, + 340, + 547, + 429 + ], + "type": "text", + "content": " for each point " + }, + { + "bbox": [ + 46, + 340, + 547, + 429 + ], + "type": "inline_equation", + "content": "p_n" + }, + { + "bbox": [ + 46, + 340, + 547, + 429 + ], + "type": "text", + "content": " (Sec. 3.1). Once TSDFs and raw colors of all points on a ray are generated, our SDF-based rendering process estimates the depth " + }, + { + "bbox": [ + 46, + 340, + 547, + 429 + ], + "type": "inline_equation", + "content": "\\hat{\\pmb{d}}" + }, + { + "bbox": [ + 46, + 340, + 547, + 429 + ], + "type": "text", + "content": " and the color " + }, + { + "bbox": [ + 46, + 340, + 547, + 429 + ], + "type": "inline_equation", + "content": "\\hat{\\pmb{c}}" + }, + { + "bbox": [ + 46, + 340, + 547, + 429 + ], + "type": "text", + "content": " for each pixel (Sec. 3.2)." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 441, + 271, + 452 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 441, + 271, + 452 + ], + "spans": [ + { + "bbox": [ + 46, + 441, + 271, + 452 + ], + "type": "text", + "content": "scene side-length as is the case for voxel-based models." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 453, + 287, + 549 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 453, + 287, + 549 + ], + "spans": [ + { + "bbox": [ + 46, + 453, + 287, + 549 + ], + "type": "text", + "content": "To reason about the geometry of a point " + }, + { + "bbox": [ + 46, + 453, + 287, + 549 + ], + "type": "inline_equation", + "content": "p" + }, + { + "bbox": [ + 46, + 453, + 287, + 549 + ], + "type": "text", + "content": " in the continuous space, we first project it onto all the geometry planes. The geometry feature " + }, + { + "bbox": [ + 46, + 453, + 287, + 549 + ], + "type": "inline_equation", + "content": "f_{g}(p)" + }, + { + "bbox": [ + 46, + 453, + 287, + 549 + ], + "type": "text", + "content": " for point " + }, + { + "bbox": [ + 46, + 453, + 287, + 549 + ], + "type": "inline_equation", + "content": "p" + }, + { + "bbox": [ + 46, + 453, + 287, + 549 + ], + "type": "text", + "content": " is then formed by 1) bilinearly interpolating the four nearest neighbors on each feature plane, 2) summing the interpolated coarse features and the fine ones respectively into the coarse output " + }, + { + "bbox": [ + 46, + 453, + 287, + 549 + ], + "type": "inline_equation", + "content": "f_{g}^{c}(p)" + }, + { + "bbox": [ + 46, + 453, + 287, + 549 + ], + "type": "text", + "content": " and fine output " + }, + { + "bbox": [ + 46, + 453, + 287, + 549 + ], + "type": "inline_equation", + "content": "f_{g}^{f}(p)" + }, + { + "bbox": [ + 46, + 453, + 287, + 549 + ], + "type": "text", + "content": ", and 3) concatenating the outputs together. Formally:" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 83, + 558, + 250, + 572 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 83, + 558, + 250, + 572 + ], + "spans": [ + { + "bbox": [ + 83, + 558, + 250, + 572 + ], + "type": "interline_equation", + "content": "f _ {g} ^ {c} (p) = F _ {g - x y} ^ {c} (p) + F _ {g - x z} ^ {c} (p) + F _ {g - y z} ^ {c} (p)", + "image_path": "0054267552aca609d7bc9cabcce3e37cf5d00db542ad017d9112049f34550eff.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 83, + 574, + 250, + 589 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 83, + 574, + 250, + 589 + ], + "spans": [ + { + "bbox": [ + 83, + 574, + 250, + 589 + ], + "type": "interline_equation", + "content": "f _ {g} ^ {f} (p) = F _ {g - x y} ^ {f} (p) + F _ {g - x z} ^ {f} (p) + F _ {g - y z} ^ {f} (p)", + "image_path": "34ad5d9441507613d6e7fd18e95314fe52e2395a36e82e6838ec88bb4c127f36.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 83, + 590, + 287, + 605 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 83, + 590, + 287, + 605 + ], + "spans": [ + { + "bbox": [ + 83, + 590, + 287, + 605 + ], + "type": "interline_equation", + "content": "\\boldsymbol {f} _ {\\boldsymbol {g}} (p) = \\left[ f _ {g} ^ {c} (p); f _ {g} ^ {f} (p) \\right] \\tag {1}", + "image_path": "7a103c3c57b27508cc2d3abff3d1716b5e7f17ae1eea4ce5dec5ff7c3b002bb6.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 59, + 613, + 266, + 625 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 613, + 266, + 625 + ], + "spans": [ + { + "bbox": [ + 59, + 613, + 266, + 625 + ], + "type": "text", + "content": "The appearance feature " + }, + { + "bbox": [ + 59, + 613, + 266, + 625 + ], + "type": "inline_equation", + "content": "f_{a}(p)" + }, + { + "bbox": [ + 59, + 613, + 266, + 625 + ], + "type": "text", + "content": " is obtained similarly:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 83, + 633, + 251, + 648 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 83, + 633, + 251, + 648 + ], + "spans": [ + { + "bbox": [ + 83, + 633, + 251, + 648 + ], + "type": "interline_equation", + "content": "f _ {a} ^ {c} (p) = F _ {a - x y} ^ {c} (p) + F _ {a - x z} ^ {c} (p) + F _ {a - y z} ^ {c} (p)", + "image_path": "75d7bc424734fd152908961abb5d753cb910bdf2caba1658fe20e232e4d9b173.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 83, + 650, + 251, + 665 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 83, + 650, + 251, + 665 + ], + "spans": [ + { + "bbox": [ + 83, + 650, + 251, + 665 + ], + "type": "interline_equation", + "content": "f _ {a} ^ {f} (p) = F _ {a - x y} ^ {f} (p) + F _ {a - x z} ^ {f} (p) + F _ {a - y z} ^ {f} (p)", + "image_path": "c3f86e342e835ceabd3b46d6189cb4bd7ad084e2557c67dfd6f859133a7d6494.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 83, + 666, + 287, + 681 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 83, + 666, + 287, + 681 + ], + "spans": [ + { + "bbox": [ + 83, + 666, + 287, + 681 + ], + "type": "interline_equation", + "content": "\\boldsymbol {f} _ {\\boldsymbol {a}} (p) = \\left[ f _ {a} ^ {c} (p); f _ {a} ^ {f} (p) \\right] \\tag {2}", + "image_path": "bed2f78d3aed8baa9358175b539ac413668907e72767c238309844e0907447d9.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 47, + 689, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 715 + ], + "type": "text", + "content": "These features are decoded into TSDF " + }, + { + "bbox": [ + 47, + 689, + 287, + 715 + ], + "type": "inline_equation", + "content": "\\phi_g(p)" + }, + { + "bbox": [ + 47, + 689, + 287, + 715 + ], + "type": "text", + "content": " and raw color " + }, + { + "bbox": [ + 47, + 689, + 287, + 715 + ], + "type": "inline_equation", + "content": "\\phi_{a}(p)" + }, + { + "bbox": [ + 47, + 689, + 287, + 715 + ], + "type": "text", + "content": " values via shallow two-layer MLPs " + }, + { + "bbox": [ + 47, + 689, + 287, + 715 + ], + "type": "inline_equation", + "content": "\\{h_g,h_a\\}" + }, + { + "bbox": [ + 47, + 689, + 287, + 715 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 323, + 462, + 545, + 475 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 323, + 462, + 545, + 475 + ], + "spans": [ + { + "bbox": [ + 323, + 462, + 545, + 475 + ], + "type": "interline_equation", + "content": "\\phi_ {\\boldsymbol {g}} (p) = h _ {g} \\left(\\boldsymbol {f} _ {\\boldsymbol {g}} (p)\\right) \\text {a n d} \\phi_ {\\boldsymbol {a}} (p) = h _ {a} \\left(\\boldsymbol {f} _ {\\boldsymbol {a}} (p)\\right) \\tag {3}", + "image_path": "143672e8205c71012faf3cd21725a18ed57601e11e0038a4f4d4ed8acc6cc51b.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 484, + 545, + 508 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 484, + 545, + 508 + ], + "spans": [ + { + "bbox": [ + 305, + 484, + 545, + 508 + ], + "type": "text", + "content": "These raw TSDF and color outputs can be utilized for depth/color rendering as well as mesh extraction." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 515, + 471, + 529 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 515, + 471, + 529 + ], + "spans": [ + { + "bbox": [ + 306, + 515, + 471, + 529 + ], + "type": "text", + "content": "3.2. SDF-Based Volume Rendering" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 534, + 545, + 676 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 534, + 545, + 676 + ], + "spans": [ + { + "bbox": [ + 304, + 534, + 545, + 676 + ], + "type": "text", + "content": "When processing input frame " + }, + { + "bbox": [ + 304, + 534, + 545, + 676 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 304, + 534, + 545, + 676 + ], + "type": "text", + "content": ", emulating the ray casting in NeRF [37], we select random pixels and calculate their corresponding rays using the current estimate of the camera pose " + }, + { + "bbox": [ + 304, + 534, + 545, + 676 + ], + "type": "inline_equation", + "content": "\\{R_i|t_i\\}" + }, + { + "bbox": [ + 304, + 534, + 545, + 676 + ], + "type": "text", + "content": ". For rendering the depths and colors of the rays, we first sample " + }, + { + "bbox": [ + 304, + 534, + 545, + 676 + ], + "type": "inline_equation", + "content": "N_{strat}" + }, + { + "bbox": [ + 304, + 534, + 545, + 676 + ], + "type": "text", + "content": " samples on each ray by stratified sampling and then sample additional " + }, + { + "bbox": [ + 304, + 534, + 545, + 676 + ], + "type": "inline_equation", + "content": "N_{imp}" + }, + { + "bbox": [ + 304, + 534, + 545, + 676 + ], + "type": "text", + "content": " points near surfaces. For pixels with ground truth depths, the " + }, + { + "bbox": [ + 304, + 534, + 545, + 676 + ], + "type": "inline_equation", + "content": "N_{imp}" + }, + { + "bbox": [ + 304, + 534, + 545, + 676 + ], + "type": "text", + "content": " additional points are sampled uniformly inside the truncation distance " + }, + { + "bbox": [ + 304, + 534, + 545, + 676 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 304, + 534, + 545, + 676 + ], + "type": "text", + "content": " w.r.t. the depth measurement, whereas for other pixels, " + }, + { + "bbox": [ + 304, + 534, + 545, + 676 + ], + "type": "inline_equation", + "content": "N_{imp}" + }, + { + "bbox": [ + 304, + 534, + 545, + 676 + ], + "type": "text", + "content": " points are sampled with the importance sampling technique [34, 37, 59, 70] based on the weights computed for the stratified samples." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 677, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 545, + 714 + ], + "type": "text", + "content": "For all " + }, + { + "bbox": [ + 304, + 677, + 545, + 714 + ], + "type": "inline_equation", + "content": "N = N_{strat} + N_{imp}" + }, + { + "bbox": [ + 304, + 677, + 545, + 714 + ], + "type": "text", + "content": " points on a ray " + }, + { + "bbox": [ + 304, + 677, + 545, + 714 + ], + "type": "inline_equation", + "content": "\\{p_n\\}_{n=1}^N" + }, + { + "bbox": [ + 304, + 677, + 545, + 714 + ], + "type": "text", + "content": ", we query TSDF " + }, + { + "bbox": [ + 304, + 677, + 545, + 714 + ], + "type": "inline_equation", + "content": "\\phi_g(p_n)" + }, + { + "bbox": [ + 304, + 677, + 545, + 714 + ], + "type": "text", + "content": " and raw color " + }, + { + "bbox": [ + 304, + 677, + 545, + 714 + ], + "type": "inline_equation", + "content": "\\phi_a(p_n)" + }, + { + "bbox": [ + 304, + 677, + 545, + 714 + ], + "type": "text", + "content": " from our networks and use the SDF-Based rendering approach in" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "type": "text", + "content": "17410" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 287, + 84 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 287, + 84 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 287, + 84 + ], + "type": "text", + "content": "StyleSDF [47] to convert SDF values to volume densities:" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 91, + 103, + 287, + 118 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 91, + 103, + 287, + 118 + ], + "spans": [ + { + "bbox": [ + 91, + 103, + 287, + 118 + ], + "type": "interline_equation", + "content": "\\boldsymbol {\\sigma} \\left(p _ {n}\\right) = \\beta \\cdot \\text {S i g m o i d} \\left(- \\beta \\cdot \\phi_ {\\boldsymbol {g}} \\left(p _ {n}\\right)\\right) \\tag {4}", + "image_path": "5ec0a8be2cc3cd5f6def965cf399580c84ae0d311e5b35a544599a840e2f5d6b.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 123, + 287, + 183 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 123, + 287, + 183 + ], + "spans": [ + { + "bbox": [ + 47, + 123, + 287, + 183 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 123, + 287, + 183 + ], + "type": "inline_equation", + "content": "\\beta" + }, + { + "bbox": [ + 47, + 123, + 287, + 183 + ], + "type": "text", + "content": " is a learnable parameter that controls the sharpness of the surface boundary. Negative values of SDF push Sigmoid toward one, resulting in volume density inside the surface. The volume density then is used for rendering the color and depth of each ray:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 67, + 189, + 267, + 222 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 67, + 189, + 267, + 222 + ], + "spans": [ + { + "bbox": [ + 67, + 189, + 267, + 222 + ], + "type": "interline_equation", + "content": "w _ {n} = \\exp \\left(- \\sum_ {k = 1} ^ {n - 1} \\boldsymbol {\\sigma} (p _ {k})\\right) (1 - \\exp (- \\boldsymbol {\\sigma} (p _ {n})))", + "image_path": "18bb7ef459a1a071d96b98e707aac54347fcc578dfb9930ba1e7199660ee1aab.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 75, + 224, + 287, + 257 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 75, + 224, + 287, + 257 + ], + "spans": [ + { + "bbox": [ + 75, + 224, + 287, + 257 + ], + "type": "interline_equation", + "content": "\\hat {\\boldsymbol {c}} = \\sum_ {n = 1} ^ {N} w _ {n} \\phi_ {\\boldsymbol {a}} \\left(p _ {n}\\right) \\quad \\text {a n d} \\quad \\hat {\\boldsymbol {d}} = \\sum_ {n = 1} ^ {N} w _ {n} z _ {n} \\tag {5}", + "image_path": "0b78f30c1b9eda311cc1104f79062ff31da3360f27ea542b3cb3ce10f1d23692.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 262, + 273, + 274 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 262, + 273, + 274 + ], + "spans": [ + { + "bbox": [ + 47, + 262, + 273, + 274 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 262, + 273, + 274 + ], + "type": "inline_equation", + "content": "z_{n}" + }, + { + "bbox": [ + 47, + 262, + 273, + 274 + ], + "type": "text", + "content": " is the depth of point " + }, + { + "bbox": [ + 47, + 262, + 273, + 274 + ], + "type": "inline_equation", + "content": "p_n" + }, + { + "bbox": [ + 47, + 262, + 273, + 274 + ], + "type": "text", + "content": " w.r.t. the camera pose." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 281, + 140, + 293 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 281, + 140, + 293 + ], + "spans": [ + { + "bbox": [ + 47, + 281, + 140, + 293 + ], + "type": "text", + "content": "3.3. Loss Functions" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 299, + 287, + 370 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 299, + 287, + 370 + ], + "spans": [ + { + "bbox": [ + 47, + 299, + 287, + 370 + ], + "type": "text", + "content": "One advantage of TSDF over other representations, such as occupancy, is that it allows us to use per-point losses, along with rendering ones. These losses account for the rapid convergence of our model. Following the practice in [1], assuming a batch of rays " + }, + { + "bbox": [ + 47, + 299, + 287, + 370 + ], + "type": "inline_equation", + "content": "R" + }, + { + "bbox": [ + 47, + 299, + 287, + 370 + ], + "type": "text", + "content": " with ground truth depths are selected, we define the free space loss as:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 81, + 376, + 287, + 407 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 81, + 376, + 287, + 407 + ], + "spans": [ + { + "bbox": [ + 81, + 376, + 287, + 407 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {f s} = \\frac {1}{| R |} \\sum_ {r \\in R} \\frac {1}{| P _ {r} ^ {f s} |} \\sum_ {p \\in P _ {r} ^ {f s}} (\\phi_ {\\boldsymbol {g}} (p) - 1) ^ {2} \\tag {6}", + "image_path": "0c92adafb3aef545657d6757a3fee4bbafcc0413fa6343bd028d033cf4b57b92.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 415, + 287, + 464 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 415, + 287, + 464 + ], + "spans": [ + { + "bbox": [ + 47, + 415, + 287, + 464 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 415, + 287, + 464 + ], + "type": "inline_equation", + "content": "P_r^{fs}" + }, + { + "bbox": [ + 47, + 415, + 287, + 464 + ], + "type": "text", + "content": " is a set of points on the ray " + }, + { + "bbox": [ + 47, + 415, + 287, + 464 + ], + "type": "inline_equation", + "content": "r" + }, + { + "bbox": [ + 47, + 415, + 287, + 464 + ], + "type": "text", + "content": " that lie between the camera center and the truncation region of the surface measured by the depth sensor. This loss function encourages TSDF " + }, + { + "bbox": [ + 47, + 415, + 287, + 464 + ], + "type": "inline_equation", + "content": "\\phi_g" + }, + { + "bbox": [ + 47, + 415, + 287, + 464 + ], + "type": "text", + "content": " to have a value of one in the free space." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 464, + 287, + 511 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 464, + 287, + 511 + ], + "spans": [ + { + "bbox": [ + 47, + 464, + 287, + 511 + ], + "type": "text", + "content": "For sample points close to the surface and within the truncation region, we use the signed distance objective, which leverages the depth sensor measurement to approximate the signed distance field:" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 61, + 517, + 111, + 533 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 61, + 517, + 111, + 533 + ], + "spans": [ + { + "bbox": [ + 61, + 517, + 111, + 533 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {T} (P _ {r} ^ {T}) =", + "image_path": "af327b65a7f13bbed9fc8fa6aae164f26c7041f2db616739b66a9fa5d1e48391.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 63, + 534, + 287, + 564 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 63, + 534, + 287, + 564 + ], + "spans": [ + { + "bbox": [ + 63, + 534, + 287, + 564 + ], + "type": "interline_equation", + "content": "\\frac {1}{| R |} \\sum_ {r \\in R} \\frac {1}{| P _ {r} ^ {T} |} \\sum_ {p \\in P _ {r} ^ {T}} (z (p) + \\phi_ {\\mathbf {g}} (p) \\cdot T - D (r)) ^ {2} \\tag {7}", + "image_path": "109c440ea47c799a062949a3377c27a17789461755c627d91b905b626916a9a4.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 47, + 571, + 287, + 691 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 571, + 287, + 691 + ], + "spans": [ + { + "bbox": [ + 47, + 571, + 287, + 691 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 571, + 287, + 691 + ], + "type": "inline_equation", + "content": "z(p)" + }, + { + "bbox": [ + 47, + 571, + 287, + 691 + ], + "type": "text", + "content": " is the planar depth of point " + }, + { + "bbox": [ + 47, + 571, + 287, + 691 + ], + "type": "inline_equation", + "content": "p" + }, + { + "bbox": [ + 47, + 571, + 287, + 691 + ], + "type": "text", + "content": " w.r.t. camera, " + }, + { + "bbox": [ + 47, + 571, + 287, + 691 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 47, + 571, + 287, + 691 + ], + "type": "text", + "content": " is the truncation distance, " + }, + { + "bbox": [ + 47, + 571, + 287, + 691 + ], + "type": "inline_equation", + "content": "D(r)" + }, + { + "bbox": [ + 47, + 571, + 287, + 691 + ], + "type": "text", + "content": " is the ray depth measured by the sensor, and " + }, + { + "bbox": [ + 47, + 571, + 287, + 691 + ], + "type": "inline_equation", + "content": "P_r^T" + }, + { + "bbox": [ + 47, + 571, + 287, + 691 + ], + "type": "text", + "content": " is a set of points on the ray " + }, + { + "bbox": [ + 47, + 571, + 287, + 691 + ], + "type": "inline_equation", + "content": "r" + }, + { + "bbox": [ + 47, + 571, + 287, + 691 + ], + "type": "text", + "content": " that lie in the truncation region, i.e. " + }, + { + "bbox": [ + 47, + 571, + 287, + 691 + ], + "type": "inline_equation", + "content": "|z(p) - D(r)| < T" + }, + { + "bbox": [ + 47, + 571, + 287, + 691 + ], + "type": "text", + "content": ". We apply the same loss to all points in the truncation region, but we differentiate the importance of points that are closer to the surface in the middle of the truncation region " + }, + { + "bbox": [ + 47, + 571, + 287, + 691 + ], + "type": "inline_equation", + "content": "P_r^{T - m}" + }, + { + "bbox": [ + 47, + 571, + 287, + 691 + ], + "type": "text", + "content": " from those that are at the tail of the truncation region " + }, + { + "bbox": [ + 47, + 571, + 287, + 691 + ], + "type": "inline_equation", + "content": "P_r^{T - t}" + }, + { + "bbox": [ + 47, + 571, + 287, + 691 + ], + "type": "text", + "content": ". Formally, we define " + }, + { + "bbox": [ + 47, + 571, + 287, + 691 + ], + "type": "inline_equation", + "content": "P_r^{T - m}" + }, + { + "bbox": [ + 47, + 571, + 287, + 691 + ], + "type": "text", + "content": " as a set of points that " + }, + { + "bbox": [ + 47, + 571, + 287, + 691 + ], + "type": "inline_equation", + "content": "|z(p) - D(r)| < 0.4T" + }, + { + "bbox": [ + 47, + 571, + 287, + 691 + ], + "type": "text", + "content": ", and define " + }, + { + "bbox": [ + 47, + 571, + 287, + 691 + ], + "type": "inline_equation", + "content": "P_r^{T - t} = P_r^T - P_r^{T - m}" + }, + { + "bbox": [ + 47, + 571, + 287, + 691 + ], + "type": "text", + "content": ", then:" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 64, + 696, + 287, + 711 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 64, + 696, + 287, + 711 + ], + "spans": [ + { + "bbox": [ + 64, + 696, + 287, + 711 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {T - m} = \\mathcal {L} _ {T} \\left(P _ {r} ^ {T - m}\\right) \\quad \\text {a n d} \\quad \\mathcal {L} _ {T - t} = \\mathcal {L} _ {T} \\left(P _ {r} ^ {T - t}\\right) \\tag {8}", + "image_path": "9320c019a245e2d20e40d5b2a324aa16545106258dfcc7e582fd42d9d620c3af.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 72, + 545, + 132 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 545, + 132 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 545, + 132 + ], + "type": "text", + "content": "This enables us to decrease the importance of " + }, + { + "bbox": [ + 305, + 72, + 545, + 132 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{T - t}" + }, + { + "bbox": [ + 305, + 72, + 545, + 132 + ], + "type": "text", + "content": " in mapping, which leads to having a smaller effective truncation distance, reducing artifacts in occluded areas, and reconstructing with higher accuracy while leveraging the entire truncation distance in camera tracking." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 133, + 545, + 180 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 133, + 545, + 180 + ], + "spans": [ + { + "bbox": [ + 305, + 133, + 545, + 180 + ], + "type": "text", + "content": "In addition to these two per-point loss functions, we also employ reconstruction losses. For pixels with ground truth depths, we impose consistency between the rendered depth and the depth measured by the sensor:" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 360, + 188, + 545, + 217 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 360, + 188, + 545, + 217 + ], + "spans": [ + { + "bbox": [ + 360, + 188, + 545, + 217 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {d} = \\frac {1}{| R |} \\sum_ {r \\in R} (\\hat {\\boldsymbol {d}} (r) - D (r)) ^ {2} \\tag {9}", + "image_path": "9297c9186d142e0725f44ae881c1a71710e4aa23b7a72c3d6c14374574e1457d.jpg" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 305, + 225, + 545, + 248 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 225, + 545, + 248 + ], + "spans": [ + { + "bbox": [ + 305, + 225, + 545, + 248 + ], + "type": "text", + "content": "Similarly, we impose consistency between the pixel colors and rendered colors:" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 365, + 255, + 545, + 283 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 365, + 255, + 545, + 283 + ], + "spans": [ + { + "bbox": [ + 365, + 255, + 545, + 283 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {c} = \\frac {1}{| R |} \\sum_ {r \\in R} (\\hat {\\boldsymbol {c}} (r) - I (r)) ^ {2} \\tag {10}", + "image_path": "597f73ff8ff454e5245dd54cd28f69b5a9ad1463540055899bc8cf2fbd5178b4.jpg" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 306, + 293, + 458, + 304 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 293, + 458, + 304 + ], + "spans": [ + { + "bbox": [ + 306, + 293, + 458, + 304 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 306, + 293, + 458, + 304 + ], + "type": "inline_equation", + "content": "I(r)" + }, + { + "bbox": [ + 306, + 293, + 458, + 304 + ], + "type": "text", + "content": " is the pixel color of ray " + }, + { + "bbox": [ + 306, + 293, + 458, + 304 + ], + "type": "inline_equation", + "content": "r" + }, + { + "bbox": [ + 306, + 293, + 458, + 304 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 317, + 304, + 526, + 317 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 304, + 526, + 317 + ], + "spans": [ + { + "bbox": [ + 317, + 304, + 526, + 317 + ], + "type": "text", + "content": "The global loss function of our method is defined as:" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 309, + 326, + 544, + 350 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 309, + 326, + 544, + 350 + ], + "spans": [ + { + "bbox": [ + 309, + 326, + 544, + 350 + ], + "type": "interline_equation", + "content": "\\mathcal {L} = \\lambda_ {f s} \\mathcal {L} _ {f s} + \\lambda_ {T - m} \\mathcal {L} _ {T - m} + \\lambda_ {T - t} \\mathcal {L} _ {T - t} + \\lambda_ {d} \\mathcal {L} _ {d} + \\lambda_ {c} \\mathcal {L} _ {c} \\tag {11}", + "image_path": "101ca7848a009dfa0dbe29ec3e7823de604f1ec1f94eae1d270e38feda6132ee.jpg" + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 305, + 360, + 545, + 431 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 360, + 545, + 431 + ], + "spans": [ + { + "bbox": [ + 305, + 360, + 545, + 431 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 360, + 545, + 431 + ], + "type": "inline_equation", + "content": "\\{\\lambda_{fs},\\lambda_{T - m},\\lambda_{T - t},\\lambda_d,\\lambda_c\\}" + }, + { + "bbox": [ + 305, + 360, + 545, + 431 + ], + "type": "text", + "content": " are the weighting coefficients. Note that " + }, + { + "bbox": [ + 305, + 360, + 545, + 431 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_c" + }, + { + "bbox": [ + 305, + 360, + 545, + 431 + ], + "type": "text", + "content": " is defined on all rays in a training batch, while other losses are only imposed on rays with ground truth measured depths. The global objective is the same for both mapping and tracking in our method, but the weighting coefficients are different." + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 306, + 439, + 437, + 452 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 439, + 437, + 452 + ], + "spans": [ + { + "bbox": [ + 306, + 439, + 437, + 452 + ], + "type": "text", + "content": "3.4. Mapping and Tracking" + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 305, + 457, + 545, + 662 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 457, + 545, + 662 + ], + "spans": [ + { + "bbox": [ + 305, + 457, + 545, + 662 + ], + "type": "text", + "content": "Mapping. Our scene representation, i.e. the feature planes and MLP decoders, are randomly initialized at the beginning. With the first input frame " + }, + { + "bbox": [ + 305, + 457, + 545, + 662 + ], + "type": "inline_equation", + "content": "\\{I_0, D_0\\}" + }, + { + "bbox": [ + 305, + 457, + 545, + 662 + ], + "type": "text", + "content": ", we fix the camera pose and optimize the feature planes and MLP decoders to best represent the first frame. For subsequent inputs, we update the scene representation iteratively every " + }, + { + "bbox": [ + 305, + 457, + 545, + 662 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 305, + 457, + 545, + 662 + ], + "type": "text", + "content": " frames, and add the latest frame to the global keyframe list, following the practice in iMAP [59] and NICE-SLAM [87]. For mapping, we first choose " + }, + { + "bbox": [ + 305, + 457, + 545, + 662 + ], + "type": "inline_equation", + "content": "|R|" + }, + { + "bbox": [ + 305, + 457, + 545, + 662 + ], + "type": "text", + "content": " pixels randomly from " + }, + { + "bbox": [ + 305, + 457, + 545, + 662 + ], + "type": "inline_equation", + "content": "W" + }, + { + "bbox": [ + 305, + 457, + 545, + 662 + ], + "type": "text", + "content": " frames, which include the current frame, the previous two keyframes, and " + }, + { + "bbox": [ + 305, + 457, + 545, + 662 + ], + "type": "inline_equation", + "content": "W - 3" + }, + { + "bbox": [ + 305, + 457, + 545, + 662 + ], + "type": "text", + "content": " frames randomly selected from the keyframe list. Then, we jointly optimize the feature planes, MLP decoders, and camera poses of the " + }, + { + "bbox": [ + 305, + 457, + 545, + 662 + ], + "type": "inline_equation", + "content": "W" + }, + { + "bbox": [ + 305, + 457, + 545, + 662 + ], + "type": "text", + "content": " selected frames using the loss functions introduced in Sec. 3.3. Unlike NICE-SLAM [87], our method does not require a staged-optimization policy, and we simply optimize all scene parameters and camera poses simultaneously." + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 305, + 665, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 665, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 305, + 665, + 545, + 714 + ], + "type": "text", + "content": "Tracking. The localization process of our method is initiated for each input frame. The current estimate of the camera parameters, represented by translation vectors and quaternion rotations [56] " + }, + { + "bbox": [ + 305, + 665, + 545, + 714 + ], + "type": "inline_equation", + "content": "\\{R|t\\}" + }, + { + "bbox": [ + 305, + 665, + 545, + 714 + ], + "type": "text", + "content": ", are optimized solely based" + } + ] + } + ], + "index": 26 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "17411" + } + ] + } + ], + "index": 27 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 64, + 70, + 530, + 135 + ], + "blocks": [ + { + "bbox": [ + 64, + 70, + 530, + 135 + ], + "lines": [ + { + "bbox": [ + 64, + 70, + 530, + 135 + ], + "spans": [ + { + "bbox": [ + 64, + 70, + 530, + 135 + ], + "type": "table", + "html": "
MethodReconstruction (cm)Localization (cm)
Depth L1↓Acc.↓Comp.↓Comp. Ratio (%)↑ATE Mean↓ATE RMSE↓
iMAP* [59]8.23 ± 0.887.16 ± 0.265.83 ± 0.2767.17 ± 2.702.59 ± 0.583.42 ± 0.87
NICE-SLAM [87]3.29 ± 0.331.66 ± 0.071.63 ± 0.0596.74 ± 0.361.56 ± 0.292.05 ± 0.45
ESLAM (ours)1.18 ± 0.050.97 ± 0.021.05 ± 0.0198.60 ± 0.070.52 ± 0.030.63 ± 0.05
", + "image_path": "6da1aa0c91307e0420ab29371ba7260053f60e2bc05e2b6f3182e30cde255d39.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 139, + 547, + 217 + ], + "lines": [ + { + "bbox": [ + 46, + 139, + 547, + 217 + ], + "spans": [ + { + "bbox": [ + 46, + 139, + 547, + 217 + ], + "type": "text", + "content": "Table 1. Quantitative comparison of our proposed ESLAM with existing NeRF-based dense visual SLAM models on the Replica dataset [57] for both reconstruction and localization accuracy. The results are the average and standard deviation of five runs on eight scenes of the Replica dataset [57]. Our method outperforms previous works by a high margin and has lower variances, indicating it is also more stable from run to run. The evaluation metrics for reconstruction are L1 loss (cm) between rendered and ground truth depth maps of 1000 random camera poses, reconstruction accuracy (cm), reconstruction completion (cm), and completion ratio (\\%). The evaluation metrics for localization are mean and RMSE of ATE (cm) [58]. For the details of the evaluations for each scene, refer to the supplementary. 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Qualitative comparison of our proposed ESLAM method's geometry reconstruction with existing NeRF-based dense visual SLAM models, iMAP* [59] and NICE-SLAM [87], on the Replica dataset [57]. Our method produces more accurate detailed geometry as well as higher-quality textures. The ground truth images are rendered with the ReplicaViewer software [57]. It should also be noted that our method runs up to " + }, + { + "bbox": [ + 46, + 472, + 547, + 528 + ], + "type": "inline_equation", + "content": "\\times 10" + }, + { + "bbox": [ + 46, + 472, + 547, + 528 + ], + "type": "text", + "content": " faster on this dataset (see Sec. 4.2 for runtime analysis). 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No second-order optimizers or manifold operations are employed for camera tracking in our method. We exclude rays with no ground truth depths and outlier pixels from each optimization step. A pixel is considered an outlier if the difference between its measured depth and rendered depth is ten times greater than the batch's median rendered depth error." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 47, + 646, + 128, + 659 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 646, + 128, + 659 + ], + "spans": [ + { + "bbox": [ + 47, + 646, + 128, + 659 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "text", + "content": "In this section, we validate that our method outperforms existing implicit representation-based methods in both localization and reconstruction accuracy on three standard benchmarks while running up to " + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\times 10" + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "text", + "content": " faster." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 304, + 539, + 546, + 599 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 539, + 546, + 599 + ], + "spans": [ + { + "bbox": [ + 304, + 539, + 546, + 599 + ], + "type": "text", + "content": "Baselines. We compare our method to two existing state-of-the-art NeRF-based dense visual SLAM methods: iMAP [59] and NICE-SLAM [87]. Because iMAP is not open source, we use the iMAP* model in our experiment, which is the reimplementation of iMAP in [87]." + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 304, + 608, + 547, + 657 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 608, + 547, + 657 + ], + "spans": [ + { + "bbox": [ + 304, + 608, + 547, + 657 + ], + "type": "text", + "content": "Datasets. We evaluate our method on three standard 3D benchmarks: Replica [57], ScanNet [12], and TUM RGB-D [58] datasets. We select the same scenes for evaluation as NICE-SLAM [87]." + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 304, + 665, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 547, + 713 + ], + "type": "text", + "content": "Metrics. We borrow our evaluation metrics from NICE-SLAM [87]. For evaluating scene geometry, we use both 2D and 3D metrics. For the 2D metric, we render depth maps from 1000 random camera poses in each scene and calculate" + } + ] + } + ], + "index": 24 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "type": "text", + "content": "17412" + } + ] + } + ], + "index": 25 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 51, + 69, + 542, + 159 + ], + "blocks": [ + { + "bbox": [ + 51, + 69, + 542, + 159 + ], + "lines": [ + { + "bbox": [ + 51, + 69, + 542, + 159 + ], + "spans": [ + { + "bbox": [ + 51, + 69, + 542, + 159 + ], + "type": "table", + "html": "
MethodATESc. 0000Sc. 0059Sc. 0106Sc. 0169Sc. 0181Sc. 0207Ave.
iMAP* [59]Mean34.2 ± 12.813.0 ± 2.412.9 ± 1.733.6 ± 15.320.8 ± 3.818.6 ± 6.022.2 ± 7.0
RMSE42.7 ± 16.617.8 ± 7.415.0 ± 1.739.1 ± 18.224.7 ± 5.820.1 ± 6.826.6 ± 9.4
NICE-SLAM [87]Mean9.9 ± 0.411.9 ± 1.87.0 ± 0.29.2 ± 1.012.2 ± 0.35.5 ± 0.39.3 ± 0.7
RMSE12.0 ± 0.514.0 ± 1.87.9 ± 0.210.9 ± 1.113.4 ± 0.36.2 ± 0.410.7 ± 0.7
ESLAM (ours)Mean6.5 ± 0.16.4 ± 0.46.7 ± 0.15.9 ± 0.18.3 ± 0.25.4 ± 0.16.5 ± 0.2
RMSE7.3 ± 0.28.5 ± 0.57.5 ± 0.16.5 ± 0.19.0 ± 0.25.7 ± 0.17.4 ± 0.2
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Qualitative comparison of our proposed ESLAM method's localization accuracy with existing NeRF-based dense visual SLAM models, iMAP* [59] and NICE-SLAM [87], on the ScanNet dataset [12]. The ground truth camera trajectory is shown in green, and the estimated trajectory is shown in red. Our method predicts more accurate camera trajectories and does not suffer from drifting issues. It should also be noted that our method runs up to " + }, + { + "bbox": [ + 46, + 539, + 547, + 583 + ], + "type": "inline_equation", + "content": "\\times 6" + }, + { + "bbox": [ + 46, + 539, + 547, + 583 + ], + "type": "text", + "content": " faster on this dataset (see Sec. 4.2 for runtime analysis)." + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_caption" + } + ], + "index": 12 + }, + { + "bbox": [ + 46, + 593, + 289, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 593, + 289, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 593, + 289, + 713 + ], + "type": "text", + "content": "the L1 difference between depths from ground truth meshes and the reconstructed ones. For the 3D metrics, we consider reconstruction accuracy [cm], reconstruction completion [cm], and completion ratio " + }, + { + "bbox": [ + 46, + 593, + 289, + 713 + ], + "type": "inline_equation", + "content": "[< 5\\mathrm{cm}\\%]" + }, + { + "bbox": [ + 46, + 593, + 289, + 713 + ], + "type": "text", + "content": ". For evaluating these metrics, we build a TSDF volume for a scene with a resolution of " + }, + { + "bbox": [ + 46, + 593, + 289, + 713 + ], + "type": "inline_equation", + "content": "1\\mathrm{cm}" + }, + { + "bbox": [ + 46, + 593, + 289, + 713 + ], + "type": "text", + "content": " and use the marching cubes algorithm [33] to obtain scene meshes. Before evaluating the 3D metrics for our method and for the baselines, we perform mesh culling as recommended in [1, 70]. For this purpose, we remove faces from a mesh that are not inside any" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 593, + 545, + 617 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 593, + 545, + 617 + ], + "spans": [ + { + "bbox": [ + 305, + 593, + 545, + 617 + ], + "type": "text", + "content": "camera frustum or are occluded in all RGB-D frames. For evaluating camera localization, we use ATE [58]." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 629, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 629, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 629, + 547, + 715 + ], + "type": "text", + "content": "Implementation Details. The truncation distance " + }, + { + "bbox": [ + 304, + 629, + 547, + 715 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 304, + 629, + 547, + 715 + ], + "type": "text", + "content": " is set to " + }, + { + "bbox": [ + 304, + 629, + 547, + 715 + ], + "type": "inline_equation", + "content": "6\\mathrm{cm}" + }, + { + "bbox": [ + 304, + 629, + 547, + 715 + ], + "type": "text", + "content": " in our method. We employ coarse feature planes with a resolution of " + }, + { + "bbox": [ + 304, + 629, + 547, + 715 + ], + "type": "inline_equation", + "content": "24\\mathrm{cm}" + }, + { + "bbox": [ + 304, + 629, + 547, + 715 + ], + "type": "text", + "content": " for both geometry and appearance. For fine feature planes, we use a resolution of " + }, + { + "bbox": [ + 304, + 629, + 547, + 715 + ], + "type": "inline_equation", + "content": "6\\mathrm{cm}" + }, + { + "bbox": [ + 304, + 629, + 547, + 715 + ], + "type": "text", + "content": " for geometry and " + }, + { + "bbox": [ + 304, + 629, + 547, + 715 + ], + "type": "inline_equation", + "content": "3\\mathrm{cm}" + }, + { + "bbox": [ + 304, + 629, + 547, + 715 + ], + "type": "text", + "content": " for appearance. All feature planes have 32 channels, resulting in a 64-channel concatenated feature input for the decoders. 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Qualitative comparison of our proposed ESLAM method's geometry reconstruction with existing NeRF-based dense visual SLAM models, iMAP* [59] and NICE-SLAM [87], on the ScanNet dataset [12]. Our method produces more accurate detailed geometry as well as higher-quality textures. The appearance of white backgrounds in ground truth meshes is due to the fact that the ground truth meshes of the ScanNet dataset [12] are incomplete. It should also be noted that our method runs up to " + }, + { + "bbox": [ + 46, + 311, + 545, + 365 + ], + "type": "inline_equation", + "content": "\\times 6" + }, + { + "bbox": [ + 46, + 311, + 545, + 365 + ], + "type": "text", + "content": " faster on this dataset (see Sec. 4.2 for runtime analysis)." + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "image_caption" + } + ], + "index": 12 + }, + { + "type": "image", + "bbox": [ + 421, + 218, + 543, + 294 + ], + "blocks": [ + { + "bbox": [ + 421, + 218, + 543, + 294 + ], + "lines": [ + { + "bbox": [ + 421, + 218, + 543, + 294 + ], + "spans": [ + { + "bbox": [ + 421, + 218, + 543, + 294 + ], + "type": "image", + "image_path": "1b66c7eb0b4cbaa159cf96288e81ce6477dbeefef4b6c615c5e6fe8a4cd10917.jpg" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 455, + 296, + 509, + 305 + ], + "lines": [ + { + "bbox": [ + 455, + 296, + 509, + 305 + ], + "spans": [ + { + "bbox": [ + 455, + 296, + 509, + 305 + ], + "type": "text", + "content": "Ground Truth" + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_caption" + } + ], + "index": 14 + }, + { + "bbox": [ + 46, + 373, + 287, + 434 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 373, + 287, + 434 + ], + "spans": [ + { + "bbox": [ + 46, + 373, + 287, + 434 + ], + "type": "text", + "content": "with 32 channels in the hidden layer. For the Replica [57] dataset, we sample " + }, + { + "bbox": [ + 46, + 373, + 287, + 434 + ], + "type": "inline_equation", + "content": "N_{strat} = 32" + }, + { + "bbox": [ + 46, + 373, + 287, + 434 + ], + "type": "text", + "content": " points for stratified sampling and " + }, + { + "bbox": [ + 46, + 373, + 287, + 434 + ], + "type": "inline_equation", + "content": "N_{imp} = 8" + }, + { + "bbox": [ + 46, + 373, + 287, + 434 + ], + "type": "text", + "content": " points for importance sampling on each ray. And for the ScanNet [12] and TUM RGB-D [58] datasets, we set " + }, + { + "bbox": [ + 46, + 373, + 287, + 434 + ], + "type": "inline_equation", + "content": "N_{strat} = 48" + }, + { + "bbox": [ + 46, + 373, + 287, + 434 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 373, + 287, + 434 + ], + "type": "inline_equation", + "content": "N_{imp} = 8" + }, + { + "bbox": [ + 46, + 373, + 287, + 434 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 46, + 434, + 287, + 517 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 434, + 287, + 517 + ], + "spans": [ + { + "bbox": [ + 46, + 434, + 287, + 517 + ], + "type": "text", + "content": "We use different set of loss coefficients for mapping and tracking. During mapping we set " + }, + { + "bbox": [ + 46, + 434, + 287, + 517 + ], + "type": "inline_equation", + "content": "\\lambda_{fs} = 5" + }, + { + "bbox": [ + 46, + 434, + 287, + 517 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 434, + 287, + 517 + ], + "type": "inline_equation", + "content": "\\lambda_{T - m} = 200" + }, + { + "bbox": [ + 46, + 434, + 287, + 517 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 434, + 287, + 517 + ], + "type": "inline_equation", + "content": "\\lambda_{T - t} = 10" + }, + { + "bbox": [ + 46, + 434, + 287, + 517 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 434, + 287, + 517 + ], + "type": "inline_equation", + "content": "\\lambda_d = 0.1" + }, + { + "bbox": [ + 46, + 434, + 287, + 517 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 46, + 434, + 287, + 517 + ], + "type": "inline_equation", + "content": "\\lambda_c = 5" + }, + { + "bbox": [ + 46, + 434, + 287, + 517 + ], + "type": "text", + "content": ". And during tracking, we set " + }, + { + "bbox": [ + 46, + 434, + 287, + 517 + ], + "type": "inline_equation", + "content": "\\lambda_{fs} = 10" + }, + { + "bbox": [ + 46, + 434, + 287, + 517 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 434, + 287, + 517 + ], + "type": "inline_equation", + "content": "\\lambda_{T - m} = 200" + }, + { + "bbox": [ + 46, + 434, + 287, + 517 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 434, + 287, + 517 + ], + "type": "inline_equation", + "content": "\\lambda_{T - t} = 50" + }, + { + "bbox": [ + 46, + 434, + 287, + 517 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 434, + 287, + 517 + ], + "type": "inline_equation", + "content": "\\lambda_d = 1" + }, + { + "bbox": [ + 46, + 434, + 287, + 517 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 46, + 434, + 287, + 517 + ], + "type": "inline_equation", + "content": "\\lambda_c = 5" + }, + { + "bbox": [ + 46, + 434, + 287, + 517 + ], + "type": "text", + "content": ". These coefficients are obtained by performing grid search in our experiments. For further details of our implementation, refer to the supplementary." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 47, + 526, + 170, + 539 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 526, + 170, + 539 + ], + "spans": [ + { + "bbox": [ + 47, + 526, + 170, + 539 + ], + "type": "text", + "content": "4.1. Experimental Results" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 46, + 545, + 287, + 640 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 545, + 287, + 640 + ], + "spans": [ + { + "bbox": [ + 46, + 545, + 287, + 640 + ], + "type": "text", + "content": "Evaluation on Replica [57]. We provide the quantitative analysis of our experimental results on eight scenes of the Replica dataset [57] in Tab. 1. The numbers represent the average and standard deviation of the metrics for five independent runs. As shown in Tab. 1, our method outperforms the baselines for both reconstruction and localization accuracy. Our method also has lower variances, indicating that it is more stable and more robust than existing methods." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 46, + 642, + 287, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 642, + 287, + 712 + ], + "spans": [ + { + "bbox": [ + 46, + 642, + 287, + 712 + ], + "type": "text", + "content": "Qualitative analysis on the Replica dataset [57] is provided in Fig. 3. The results show that our method reconstructs the details of the scenes more accurately and produces fewer artifacts. Although it is not the focus of this paper, our method also produces higher-quality colors for the reconstructed meshes." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 304, + 373, + 545, + 529 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 373, + 545, + 529 + ], + "spans": [ + { + "bbox": [ + 304, + 373, + 545, + 529 + ], + "type": "text", + "content": "Evaluation on ScanNet [12]. We also benchmark ours and existing methods on multiple large scenes from ScanNet [12] to evaluate and compare their scalability. For evaluating camera localization, we conduct five independent experiments on each scene and report the average and standard deviation of the mean and RMSE of ATE [58] in Tab. 2. As demonstrated in the table, our method's localization is more accurate than existing methods. Our method is also considerably more stable from run to run as it has much lower standard deviations. We provide qualitative analysis of camera localization, along with geometry reconstruction, in Fig. 4. The results show that our method does not suffer from any large drifting and is more robust than existing methods." + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 304, + 541, + 545, + 613 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 541, + 545, + 613 + ], + "spans": [ + { + "bbox": [ + 304, + 541, + 545, + 613 + ], + "type": "text", + "content": "Since the ground truth meshes of the ScanNet dataset [12] are incomplete, we only provide qualitative analysis for geometry reconstruction, similar to previous works. The qualitative comparison in Fig. 5 validates that our model reconstructs more precise geometry and detailed textures compared to existing approaches." + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 304, + 629, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 629, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 629, + 545, + 713 + ], + "type": "text", + "content": "Evaluation on TUM RGB-D [58]. To further contrast the robustness of our method with the existing ones, we conduct an evaluation study on the real-world TUM RGB-D dataset [58]. Since there are no ground truth meshes for the scenes in this dataset, we only present the localization results in Tab. 3 and the qualitative analysis of rendered meshes in Fig. 6." + } + ] + } + ], + "index": 24 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "17414" + } + ] + } + ], + "index": 25 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 51, + 69, + 170, + 153 + ], + "blocks": [ + { + "bbox": [ + 51, + 69, + 170, + 153 + ], + "lines": [ + { + "bbox": [ + 51, + 69, + 170, + 153 + ], + "spans": [ + { + "bbox": [ + 51, + 69, + 170, + 153 + ], + "type": "image", + "image_path": "69f676ea7ba4850e123bcd996e44f45b845e61cdaaaef558f5db28cbce5c88b5.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 51, + 155, + 170, + 242 + ], + "blocks": [ + { + "bbox": [ + 51, + 155, + 170, + 242 + ], + "lines": [ + { + "bbox": [ + 51, + 155, + 170, + 242 + ], + "spans": [ + { + "bbox": [ + 51, + 155, + 170, + 242 + ], + "type": "image", + "image_path": "b0102e0387427e255e011e38ab43e70e71826d611a57812baae7221bd7c75cbf.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 85, + 244, + 136, + 255 + ], + "lines": [ + { + "bbox": [ + 85, + 244, + 136, + 255 + ], + "spans": [ + { + "bbox": [ + 85, + 244, + 136, + 255 + ], + "type": "text", + "content": "Sample Image" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_caption" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 175, + 69, + 294, + 155 + ], + "blocks": [ + { + "bbox": [ + 175, + 69, + 294, + 155 + ], + "lines": [ + { + "bbox": [ + 175, + 69, + 294, + 155 + ], + "spans": [ + { + "bbox": [ + 175, + 69, + 294, + 155 + ], + "type": "image", + "image_path": "90fe874fd558e115abb596b689bbe270467eaaec92c9028b9c5a9f373ec91ec7.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + } + ], + "index": 3 + }, + { + "type": "image", + "bbox": [ + 175, + 156, + 294, + 242 + ], + "blocks": [ + { + "bbox": [ + 175, + 156, + 294, + 242 + ], + "lines": [ + { + "bbox": [ + 175, + 156, + 294, + 242 + ], + "spans": [ + { + "bbox": [ + 175, + 156, + 294, + 242 + ], + "type": "image", + "image_path": "797290ddc05a8bda71cd0338f50cfb0868702f6979e13293ebf6dd7a738ee9f5.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 225, + 244, + 251, + 253 + ], + "lines": [ + { + "bbox": [ + 225, + 244, + 251, + 253 + ], + "spans": [ + { + "bbox": [ + 225, + 244, + 251, + 253 + ], + "type": "text", + "content": "iMAP*" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "type": "image", + "bbox": [ + 299, + 69, + 419, + 156 + ], + "blocks": [ + { + "bbox": [ + 299, + 69, + 419, + 156 + ], + "lines": [ + { + "bbox": [ + 299, + 69, + 419, + 156 + ], + "spans": [ + { + "bbox": [ + 299, + 69, + 419, + 156 + ], + "type": "image", + "image_path": "8f00e5b90af071416630a75cd714c858dbc1a087be0b3480b7a2eb185ca3ce67.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_body" + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 299, + 156, + 418, + 242 + ], + "blocks": [ + { + "bbox": [ + 299, + 156, + 418, + 242 + ], + "lines": [ + { + "bbox": [ + 299, + 156, + 418, + 242 + ], + "spans": [ + { + "bbox": [ + 299, + 156, + 418, + 242 + ], + "type": "image", + "image_path": "1c1f84bc3bf4e40528ec8deadad14070a4d3f2cfbe406e8dc130b0c8fcaf3916.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 340, + 244, + 386, + 253 + ], + "lines": [ + { + "bbox": [ + 340, + 244, + 386, + 253 + ], + "spans": [ + { + "bbox": [ + 340, + 244, + 386, + 253 + ], + "type": "text", + "content": "NICE-SLAM" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 46, + 259, + 545, + 293 + ], + "lines": [ + { + "bbox": [ + 46, + 259, + 545, + 293 + ], + "spans": [ + { + "bbox": [ + 46, + 259, + 545, + 293 + ], + "type": "text", + "content": "Figure 6. Qualitative comparison of our proposed ESLAM method's geometry reconstruction with existing NeRF-based dense visual SLAM models, iMAP* [59] and NICE-SLAM [87], on the TUM RGB-D dataset [58]. Our method produces more accurate detailed geometry as well as higher-quality textures. Since there are no ground truth meshes for this dataset, we depict a sample input image." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 424, + 76, + 542, + 156 + ], + "blocks": [ + { + "bbox": [ + 424, + 76, + 542, + 156 + ], + "lines": [ + { + "bbox": [ + 424, + 76, + 542, + 156 + ], + "spans": [ + { + "bbox": [ + 424, + 76, + 542, + 156 + ], + "type": "image", + "image_path": "cad4003aa79b54cf2f3d8265f6a050724d61e03642833e1eadfaeabb220e6e71.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 424, + 156, + 542, + 242 + ], + "blocks": [ + { + "bbox": [ + 424, + 156, + 542, + 242 + ], + "lines": [ + { + "bbox": [ + 424, + 156, + 542, + 242 + ], + "spans": [ + { + "bbox": [ + 424, + 156, + 542, + 242 + ], + "type": "image", + "image_path": "5ec7f20951817b8bc5d70abc352f10762af60ec8891b1ac56f1497fc6af3b9b6.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 465, + 244, + 514, + 253 + ], + "lines": [ + { + "bbox": [ + 465, + 244, + 514, + 253 + ], + "spans": [ + { + "bbox": [ + 465, + 244, + 514, + 253 + ], + "type": "text", + "content": "ESLAM (ours)" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "type": "table", + "bbox": [ + 56, + 302, + 279, + 354 + ], + "blocks": [ + { + "bbox": [ + 56, + 302, + 279, + 354 + ], + "lines": [ + { + "bbox": [ + 56, + 302, + 279, + 354 + ], + "spans": [ + { + "bbox": [ + 56, + 302, + 279, + 354 + ], + "type": "table", + "html": "
fr1/deskfr2/xyzfr3/office
iMAP* [59]4.902.055.80
NICE-SLAM [87]2.852.393.02
ESLAM (ours)2.471.112.42
", + "image_path": "9bd60a116cb08e6b571a3107fe32225455ea66654f22371c672d8b4e0ec5b4f7.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "table_body" + } + ], + "index": 13 + }, + { + "type": "table", + "bbox": [ + 51, + 411, + 284, + 511 + ], + "blocks": [ + { + "bbox": [ + 46, + 359, + 287, + 403 + ], + "lines": [ + { + "bbox": [ + 46, + 359, + 287, + 403 + ], + "spans": [ + { + "bbox": [ + 46, + 359, + 287, + 403 + ], + "type": "text", + "content": "Table 3. Quantitative comparison of our proposed ESLAM method's localization accuracy with existing NeRF-based dense visual SLAM models on the TUM RGB-D dataset [58]. The evaluation metric is ATE RMSE" + }, + { + "bbox": [ + 46, + 359, + 287, + 403 + ], + "type": "inline_equation", + "content": "\\downarrow" + }, + { + "bbox": [ + 46, + 359, + 287, + 403 + ], + "type": "text", + "content": " (cm) [58]." + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 51, + 411, + 284, + 511 + ], + "lines": [ + { + "bbox": [ + 51, + 411, + 284, + 511 + ], + "spans": [ + { + "bbox": [ + 51, + 411, + 284, + 511 + ], + "type": "table", + "html": "
MethodSpeed FPT (s)Memory
# Param.Grow. R.
ReplicaiMAP* [59]5.200.22 M?
NICE-SLAM [87]2.1012.18 MO(L3)
ESLAM (ours)0.186.79 MO(L2)
ScanNetiMAP* [59]5.200.22 M?
NICE-SLAM [87]3.3522.04 MO(L3)
ESLAM (ours)0.5517.63 MO(L2)
", + "image_path": "9a926a465fc0a27cb7ce3091b8157d342706ca71bf6ae9dfd3abbd05ca6f6df8.jpg" + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "table_body" + } + ], + "index": 15 + }, + { + "bbox": [ + 46, + 516, + 287, + 625 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 516, + 287, + 625 + ], + "spans": [ + { + "bbox": [ + 46, + 516, + 287, + 625 + ], + "type": "text", + "content": "Table 4. Runtime analysis of our method in comparison with existing ones in terms of average frame processing time (FPT), number of parameters, and model size growth rate w.r.t. scene side-length " + }, + { + "bbox": [ + 46, + 516, + 287, + 625 + ], + "type": "inline_equation", + "content": "L" + }, + { + "bbox": [ + 46, + 516, + 287, + 625 + ], + "type": "text", + "content": ". All methods are benchmarked with an NVIDIA GeForce RTX 3090 GPU on room0 of Replica [57] and scene0000 of ScanNet [12]. Our method is significantly faster and does not grow cubically in size w.r.t. scene side-length " + }, + { + "bbox": [ + 46, + 516, + 287, + 625 + ], + "type": "inline_equation", + "content": "L" + }, + { + "bbox": [ + 46, + 516, + 287, + 625 + ], + "type": "text", + "content": ". Note that iMAP [59] represents a whole scene in a single MLP, hence its small number of parameters. Accordingly, the scalability and growth rate of iMAP [59] w.r.t. the scene side-length " + }, + { + "bbox": [ + 46, + 516, + 287, + 625 + ], + "type": "inline_equation", + "content": "L" + }, + { + "bbox": [ + 46, + 516, + 287, + 625 + ], + "type": "text", + "content": " are also unclear." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 47, + 635, + 153, + 647 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 635, + 153, + 647 + ], + "spans": [ + { + "bbox": [ + 47, + 635, + 153, + 647 + ], + "type": "text", + "content": "4.2. Runtime Analysis" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "type": "text", + "content": "We evaluate the speed and size of our method in comparison with existing approaches in Tab. 4. We report the average frame processing time (FPT), the number of parameters of the model, and memory growth rate w.r.t. scene side-length for the scenes room0 of Replica [57] and" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 304, + 545, + 377 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 304, + 545, + 377 + ], + "spans": [ + { + "bbox": [ + 304, + 304, + 545, + 377 + ], + "type": "text", + "content": "scene0000 of ScanNet [12] datasets. All methods are benchmarked with an NVIDIA GeForce RTX 3090 GPU. The results indicate that our method is significantly faster than previous works on both datasets. Furthermore, in contrast to NICE-SLAM [87], our model size is smaller and does not grow cubically with the scene side-length." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 306, + 386, + 378, + 398 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 386, + 378, + 398 + ], + "spans": [ + { + "bbox": [ + 306, + 386, + 378, + 398 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 304, + 406, + 545, + 561 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 406, + 545, + 561 + ], + "spans": [ + { + "bbox": [ + 304, + 406, + 545, + 561 + ], + "type": "text", + "content": "We presented ESLAM, a dense visual SLAM approach that leverages the latest advances in the Neural Radiance Fields study to improve both the speed and accuracy of neural implicit-based SLAM systems. We proposed replacing the voxel grid representation with axis-aligned feature planes to prevent the model size from growing cubically with respect to the scene side-length. We also demonstrated that modeling the scene geometry with Truncated Signed Distance Field (TSDF) leads to efficient and high-quality surface reconstruction. We verified through extensive experiments that our approach outperforms existing methods significantly in both reconstruction and localization accuracy while running up to one order of magnitude faster." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 304, + 562, + 545, + 681 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 562, + 545, + 681 + ], + "spans": [ + { + "bbox": [ + 304, + 562, + 545, + 681 + ], + "type": "text", + "content": "ESLAM accepts and deals with the forgetting problem in exchange for memory preservation. Due to the structure of our feature plane representation, updating features to adapt to new geometry may affect previously reconstructed geometries. To address this issue, we keep track of previous keyframes and allocate a large portion of computation resources to retain and remember previously reconstructed regions. Although ESLAM is substantially faster than competing approaches, handling the forgetting problem more efficiently could further reduce frame processing time." + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 306, + 689, + 388, + 700 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 689, + 388, + 700 + ], + "spans": [ + { + "bbox": [ + 306, + 689, + 388, + 700 + ], + "type": "text", + "content": "Acknowledgement" + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 306, + 701, + 493, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 701, + 493, + 713 + ], + "spans": [ + { + "bbox": [ + 306, + 701, + 493, + 713 + ], + "type": "text", + "content": "This research was supported by ams OSRAM." + } + ] + } + ], + "index": 24 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "17415" + } + ] + } + ], + "index": 25 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 107, + 84 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 107, + 84 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 107, + 84 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 288, + 713 + ], + "type": "list", + "angle": 0, + "index": 13, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 145 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 145 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 145 + ], + "type": "text", + "content": "[1] Dejan Azinović, Ricardo Martin-Brualla, Dan B Goldman, Matthias Nießner, and Justus Thies. 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In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 12786-12796, 2022. 1, 2, 4, 5, 6, 7, 8" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 48, + 664, + 287, + 708 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 664, + 287, + 708 + ], + "spans": [ + { + "bbox": [ + 48, + 664, + 287, + 708 + ], + "type": "text", + "content": "[88] Zi-Xin Zou, Shi-Sheng Huang, Yan-Pei Cao, Tai-Jiang Mu, Ying Shan, and Hongbo Fu. Mononeuralfusion: Online monocular neural 3d reconstruction with geometric priors. arXiv preprint arXiv:2209.15153, 2022. 2" + } + ] + } + ], + "index": 12 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "type": "text", + "content": "17419" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 11 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/EVAL_ Explainable Video Anomaly Localization/396d953c-501f-406c-be61-8e06127066d0_content_list.json b/2023/EVAL_ Explainable Video Anomaly Localization/396d953c-501f-406c-be61-8e06127066d0_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..e6abddfad58401b4d49ec4f3d1ee7fa6c53a7fb5 --- /dev/null +++ b/2023/EVAL_ Explainable Video Anomaly Localization/396d953c-501f-406c-be61-8e06127066d0_content_list.json @@ -0,0 +1,1580 @@ +[ + { + "type": "text", + "text": "EVAL: Explainable Video Anomaly Localization", + "text_level": 1, + "bbox": [ + 238, + 130, + 732, + 152 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Ashish Singh $^{1,2*}$", + "bbox": [ + 207, + 179, + 344, + 196 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Michael J. Jones $^{2*}$", + "bbox": [ + 374, + 180, + 524, + 196 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Erik G. Learned-Miller1,2", + "bbox": [ + 557, + 180, + 761, + 196 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "$^{1}$ CICS, University of Massachusetts Amherst", + "bbox": [ + 145, + 198, + 504, + 215 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "$^{2}$ Mitsubishi Electric Research Labs", + "bbox": [ + 542, + 198, + 823, + 215 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "ashishsingh@cs.umass.edu", + "bbox": [ + 200, + 219, + 418, + 233 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "mjones@merl.com", + "bbox": [ + 441, + 219, + 578, + 233 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "elm@cs.umass.edu", + "bbox": [ + 617, + 219, + 761, + 232 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 268, + 313, + 284 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "We develop a novel framework for single-scene video anomaly localization that allows for human-understandable reasons for the decisions the system makes. We first learn general representations of objects and their motions (using deep networks) and then use these representations to build a high-level, location-dependent model of any particular scene. This model can be used to detect anomalies in new videos of the same scene. Importantly, our approach is explainable – our high-level appearance and motion features can provide human-understandable reasons for why any part of a video is classified as normal or anomalous. We conduct experiments on standard video anomaly detection datasets (Street Scene, CUHK Avenue, ShanghaiTech and UCSD Ped1, Ped2) and show significant improvements over the previous state-of-the-art. All of our code and extra datasets will be made publicly available.", + "bbox": [ + 75, + 301, + 473, + 544 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 575, + 209, + 590 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "We are interested in the problem of spatio-temporal localization of anomalous activities in videos of a given scene. Informally, anomalous activities are events that differ from those typically observed in a scene, such as a cyclist riding through an indoor shopping mall [35]. Like many other papers on anomaly detection, this work addresses the setting in which we have access to an initial set of videos that are used to define the typical, or 'nominal' activities in a particular scene. Such a situation naturally arises in surveillance and monitoring tasks [41], where it is easy to collect nominal data, but it is not practical to collect a representative set of possible anomalies for a scene. Thus, the problem setup is as follows: provided with a set of videos of a scene which do not contain any anomalies, (called the nominal set), the goal is to detect any events in a test video from the same scene that differ substantially from all events in the nominal set [29, 35]. In defining anomaly detection, it is important to consider the role of location. In real-world", + "bbox": [ + 75, + 601, + 470, + 875 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "surveillance scenarios, an event may be normal in one location but anomalous in another. For example, a car driving on a road is typically not anomalous, while one driving on a sidewalk typically is. In view of this, we adopt the following definition [35].", + "bbox": [ + 496, + 268, + 893, + 345 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Definition 1 An anomaly is any spatio-temporal region of test video that is significantly different from all of the nominal video in the same spatial region.", + "bbox": [ + 496, + 345, + 893, + 388 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Unlike most recent work in anomaly detection, a key goal of our work is to produce not only a set of anomalies, but a simple and clear explanation for what makes them anomalous. We are motivated by how people tasked with watching video from a stationary surveillance camera would detect an unusual incident. While monitoring a scene, we expect a person to note the types of objects seen (people, buildings, cars) and the motions of those objects (walking east or west on a sidewalk, driving northwest on the street) to characterize the given scene. The person could then notice an anomaly when the objects or motions do not match what has been seen before. The person could also explain why something was anomalous.", + "bbox": [ + 496, + 388, + 895, + 583 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "We design our video anomaly detection system using this sketch of how a human would solve the problem as motivation. We want to use deep networks to give a high-level understanding of the objects and motions occurring in a scene. By 'high-level', we mean at the level of whole objects and not at the level of pixels or edges. To do this, we train deep networks that take a spatio-temporal region of video (which we call a video volume) as input and output attribute vectors representing the object classes, the directions and speeds of motion and the fraction of stationary pixels (which gives information on the sizes of moving objects) occurring in a spatio-temporal region. The feature vectors from the penultimate layers of these deep networks yield high-level representations, or embeddings, of the appearance and motion content of each video volume. Ten frames are used for video volumes in our experiments.", + "bbox": [ + 496, + 584, + 895, + 824 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Unlike many other recent works, we do not learn new embedding functions (i.e. networks) for new scenes. We use the same embedding networks for every environment. Instead, to characterize the nominal video for a new scene, we store a representative set of all the embeddings found in", + "bbox": [ + 496, + 825, + 893, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 810, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*equal contribution", + "bbox": [ + 94, + 887, + 200, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "18717", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "the nominal video. That is, for every video volume in the nominal video of a new scene, we calculate our representations of appearance, motion direction, speed, and background fraction. We then reduce this set of embeddings to a smaller set which we call exemplars by removing redundant embeddings. We select a separate set of exemplars for each spatial region. This results in a compact, accurate, and location-dependent model of the nominal data in a new scene. Since there is no training of deep networks for each new environment, modeling a new environment is 'lightweight' compared to many other methods, making it efficient to model new scenes. Our exemplar model also allows very efficient updating if new nominal video is introduced. This is a crucial property for video anomaly detection methods because, in practice, it is unrealistic to assume that the initial nominal video covers every possible normal change. New nominal video will occasionally need to be added, making it critical that models are easy to extend.", + "bbox": [ + 75, + 90, + 472, + 363 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Given test video of the same scene, we compute our high-level features for each video volume. We then compare these to the exemplars stored in the nominal model at the corresponding spatial region. Any test feature with a high distance to every nominal exemplar for that region is considered anomalous. Because the feature vectors map to human-interpretable attributes, these attributes can be used to give human-understandable explanations for why our system labeled video volumes as normal or anomalous. We define a method as 'explainable' if it can give human-understandable reasons for its decisions. Details of how our system provides explanations are given in Section 4.4.", + "bbox": [ + 75, + 363, + 472, + 542 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In summary, we make the following key contributions: 1) We show that modeling scenes using high-level attributes leads to robust anomaly detection. 2) We introduce the idea of directly estimating high-level motion attributes from raw video volumes using deep networks. 3) We show how these high-level attributes also allow human-interpretable explanations. 4) Finally, we demonstrate an alternative to much of the previous work that is based on learning to reconstruct the nominal data. Our alternative approach is practical since it does not require training deep networks for each new scene and allows for simple and efficient updates to a scene model given new nominal training data.", + "bbox": [ + 75, + 545, + 472, + 726 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 76, + 739, + 218, + 753 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Most Video Anomaly Detection (VAD) methods can be analyzed in terms of their representation learning or their detection method.", + "bbox": [ + 75, + 763, + 468, + 808 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Representation of Nominal Data: Early approaches to VAD [2, 3, 7, 20, 30, 40, 47] primarily relied on the usage of handcrafted features. This included features like spatiotemporal gradients [17, 24], histogram of gradients [28, 40], flow fields [2, 3, 30, 47], histogram of flows [7, 40, 41], dense trajectories [28, 43] and foreground masks [3]. Re", + "bbox": [ + 75, + 810, + 468, + 901 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "cently, most authors have used deep learning for this task [1,9,10,14-16,21,26,34,36,37,39,42,45]. These methods either use a pretrained model [15, 17, 26, 36, 39, 42] for feature extraction or train a model to specifically optimize for a particular task related to anomaly detection. These tasks can generally be categorized as either a variant of training an auto-encoder architecture to minimize the reconstruction error of nominal frames [6, 14, 16, 22, 25, 31], a generative adversarial network (GAN) to model nominal frames [21,25], or future frame prediction given a sequence of nominal frames [21,44]. To further improve their performance, recent works have tried specialized architectures and training methodologies. Particularly [8,22,32] transform their respective generative model by memory-based modules to memorize the normal prototypes in the training data. Most recently [38] proposed a module based on masked convolution and channel attention to reconstruct a masked part of the convolutional receptive field. A key drawback of reconstruction and future frame prediction methods is that they do not generate interpretable features. It is not clear what aspects of the video make it difficult to reconstruct since there is no mapping to higher-level features as in our work. Our work mostly aligns with methods utilizing pretrained models. However, unlike most of these approaches, we incorporate the output of our pretrained models to interpret model decisions. We additionally make sure that the predictions of our model generalize to a wide variety of scenes through our data generation and training procedures. One high-level motion attribute that our method learns is similar to the histogram of flow feature used in some early work [7,40,41]. However, instead of computing the histogram of flow from an optical flow field, our method learns a deep network to predict these features directly from RGB video volumes and then uses the network's learned feature embedding as the representation.", + "bbox": [ + 496, + 90, + 893, + 619 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Detection Methods: Most methods use either standard outlier detection methods [5] as an external module or utilize the reconstruction strategy to predict anomalies. General methods of detection that most authors have used in the past include one-class SVM [17, 28, 42, 49], nearest neighbour approaches [9, 11, 15, 33, 34], and Probabilistic Graphical Models [3]. In [4, 13], pseudo-anomalous samples are used during training to improve discriminative learning. In [12], an object detector is used to focus on regions around objects and then networks are trained for various 'proxy' tasks (such as predicting the arrow of time) on the nominal data. Thus, unlike our work, they require training deep nework models for each different scene. Our work has some similarity to the work of [33, 34] in that we also use an overlapping grid of spatial regions, build exemplar-based models and use nearest neighbors distances as anomaly scores. The high-level features that we use are the biggest difference as compared to the pixel-based features used in their", + "bbox": [ + 496, + 619, + 895, + 891 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "18718", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/a4b7bed804a7344578c2dde4a82da114f4cf052661f729bec81fda0a764d12fa.jpg", + "image_caption": [ + "Figure 1. Our pipeline for building a location-dependent model of nominal video and detecting anomalies in test video. During the model building phase, we extract a high-level representation of each video volume using our appearance and motion networks. Using the exemplar selection method, we select a representative subset of video volumes for a given spatial region. By comparing video volumes in test video to the exemplar set we can detect anomalies." + ], + "image_footnote": [], + "bbox": [ + 174, + 99, + 769, + 349 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "work. Our high-level features allow for explainable models as well as much smaller models than theirs.", + "bbox": [ + 75, + 433, + 468, + 462 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Explainable VAD: Our work is similar in spirit to the work of [15,46] with respect to providing explanations for detecting anomalies. In [15], the authors pre-train their feature extractor on public image datasets (MS-COCO and Visual Genome) to detect objects and predict their attributes and actions. They further use these predictions for 'event recounting' on VAD benchmarks. In [46], the authors utilize models pretrained for semantic segmentation, object classification, and multi-object tracking and use the output of these models directly as their feature representation.", + "bbox": [ + 75, + 463, + 468, + 613 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Despite these coarse similarities, virtually all of the details of our methods are different. Specifically, in [15], they rely on object proposals to find candidate anomalous regions which can lead to missed detections for objects not represented in their training data. Our action/motion classes are also very different - ours being more generic (direction distributions and speed of motion) while in [15] are much more specific (bending, riding) and hence not applicable to a wide variety of scenarios. The method of [46] is specific to detecting and tracking pedestrians and is not a general video anomaly detection method. Furthermore, unlike ours, their method does not spatially localize anomalies.", + "bbox": [ + 75, + 614, + 470, + 797 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Our Approach", + "text_level": 1, + "bbox": [ + 76, + 813, + 225, + 830 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Our method consists of three distinct stages: high-level attribute learning, model building, and anomaly localization. The high-level attribute learning stage is done only once and uses training samples that are independent of any", + "bbox": [ + 75, + 839, + 470, + 902 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "video anomaly detection dataset. The resulting deep networks learn general representations of object appearances and object motions which can then be used in the subsequent two stages to build a model of a specific scene and to localize anomalies in that scene, for a wide variety of surveillance scenarios. The outside data used to train our high-level attribute models are equivalent to the outside data used in various prior works on VAD; for example, the M-OCOCO and Visual Genome data used to train the models of Hinami et al. [15], the outside data used to train object detectors in [11, 12, 17, 42], as well as the many deep models pretrained on ImageNet and applied to VAD. Our outside data is not used to build models of a scene.", + "bbox": [ + 496, + 433, + 893, + 628 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. High-Level Attribute Learning", + "text_level": 1, + "bbox": [ + 498, + 636, + 751, + 652 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "For this stage, our main objective is to learn features that are (a) transferable across scenes and (b) interpretable. Given this motivation, we learn an object recognizer for our appearance model as well as regression networks for estimating the following motion attributes for a given video volume: the fraction of stationary pixels, the distribution of motion directions and the average speed of movement in each direction. We also learn a classifier to indicate whether a video volume is stationary or not. We will describe each of these deep networks in the following subsections.", + "bbox": [ + 496, + 659, + 890, + 809 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "To clarify our terminology, we use the term 'high-level attribute' to denote the object classes, histogram of motion directions, vector of motion speeds or fraction of stationary pixels which are the final outputs of the various deep networks that are learned. The term 'high-level feature' denotes the feature vector from the penultimate layer of one of", + "bbox": [ + 496, + 810, + 893, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "18719", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "the deep networks. A high-level feature can be mapped to a high-level attribute using the final layer of that network.", + "bbox": [ + 76, + 90, + 468, + 121 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.1.1 Appearance model", + "text_level": 1, + "bbox": [ + 76, + 128, + 261, + 143 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We formulate the task of object recognition as a multi-label image classification problem as any given input image patch may contain more than one object class (or none).", + "bbox": [ + 76, + 152, + 468, + 196 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Training Data: We are particularly interested in learning to recognize objects that have high likelihood of being present in outdoor scenes. To this end, we select the following 8 categories as our primary set of object classes : [Person, Car, Cyclist, Dog, Tree, House, Skyscraper, and Bridge]. For our formulation, we want the learned features to generalize across different domains. To achieve this, we construct our training dataset of images from multiple sources. We use labeled examples of each class (as well as background images containing none of the classes) taken from the CIFAR-10 [19], CIFAR-100 [19], and MIO-TCD [27] datasets as well as a set of publicly available surveillance videos from static webcams that we collected and annotated. More details about the data collection is given in the supplemental material. In total we used 187,793 RGB training examples, resized to 64x64 pixels.", + "bbox": [ + 75, + 198, + 468, + 439 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Neural Architecture: We use a modified ResNext-50 network [48] as our backbone architecture. We modified the original model by adding an extra fully connected layer that maps the 2048-dimensional feature vector after the average pooling layer to a 128-dimensional layer. The 128-dimensional layer is then mapped by a final fully connected layer to an 8-dimensional output layer with sigmoid activations that represent the categories. The extra fully connected layer gives us a 128-dimensional feature vector to represent appearance instead of the 2048-dimensional feature vector after RexNext-50's usual penultimate layer thus greatly reducing feature size. To train our model, we utilize the Binary Cross Entropy as our loss function.", + "bbox": [ + 75, + 439, + 468, + 636 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Note that high-level features are usually distinctive even for unseen object classes despite the corresponding high-level attribute having low probabilities for all of the known object classes. This allows our appearance model to have unique representations for object classes other than the eight that we train on. See supplemental material for experiments on this.", + "bbox": [ + 75, + 636, + 468, + 742 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.1.2 Motion Model", + "text_level": 1, + "bbox": [ + 76, + 755, + 230, + 768 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "To characterize the motion information for a given video volume, we train deep networks to estimate the following attributes directly from an RGB video volume: (a) histogram of optical flow $(Y_{ang})$ , (b) a vector of the average speed of pixels in each direction of motion $(Y_{speed})$ , (c) background classifier $(Y_{bkg.cls})$ and (d) percentage of stationary pixels $(Y_{bkgpix})$ . The histogram of optical flow consists of 12 bins each of which stores the fraction of pixels", + "bbox": [ + 75, + 780, + 468, + 900 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "in the video volume that are estimated to be moving in one of the 30 degree directions of motion. The average speed vector consists of the average speed (in pixels per frame) of all pixels falling in each of the 12 histogram of flow bins. The background classifier classifies whether the video volume contains motion or not. The percentage of stationary pixels in a video volume gives the rough size of the moving objects in a video volume.", + "bbox": [ + 496, + 90, + 890, + 210 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Motion Training Data: We use the set of surveillance videos mentioned above to learn motion attributes in a self-supervised way. For each video, we sample video volumes from regions with significant 'motion' as well as very little motion ('background'). We identify these regions by computing their pixelwise optical flow fields using the TV-L1 method [50], which is also used to automatically generate ground-truth motion attributes. (Note that optical flow is only used to create ground truth for training our motion models. It is not used in later stages.) In total we obtain 283,486 'background' video volumes and 2,551,376 'motion' video volumes. We use $90\\%$ of these for training our models and the remainder for validation.", + "bbox": [ + 496, + 213, + 890, + 409 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The ground truth motion attributes for each training video volume are computed from the corresponding pixelwise flow fields as follows: We represent the $Y_{bkg.cls}$ attribute as a single binary variable denoting if a video volume is 'background' ( $Y_{bkg.cls} = 1$ ) or not ( $Y_{bkg.cls} = 0$ ). The ground truth for $Y_{ang}$ and $Y_{bkg}$ are computed by first computing a 13-bin normalized histogram, wherein the first 12 bins represent the number of pixels with flow orientation in the ranges $[i * \\pi / 6 : (i + 1) * \\pi / 6)$ with $i \\in [0, 11]$ , while the last bin denotes the number of pixels with flow magnitude below threshold. The histogram is then normalized by the total number of pixels. The first 12 bins of this histogram are used as the ground truth for $Y_{ang}$ and the $13^{th}$ bin is the ground truth for $Y_{bkg}$ . Finally, we represent $Y_{mag}$ as a 12-dimensional vector denoting the average flow magnitude for pixels in each of the 12 flow orientation ranges.", + "bbox": [ + 496, + 412, + 890, + 654 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Learning Task and Neural Architecture: We treat each motion attribute independently and train separate models respectively. For each attribute prediction task, we use the same backbone architecture design, but train each model using different objective functions. Our model is a stack of 3D convolutions (3DConv) with batch normalization (BN) and ReLU. In total we have 3 layers of [3Dconv-BN-ReLU] followed by a fully connected layer. We provide additional details in the supplemental material.", + "bbox": [ + 496, + 656, + 890, + 792 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We formulate $Y_{bkg,cls}$ attribute prediction as a standard binary classification task and train the model using cross-entropy loss function. For $Y_{bkg}$ and $Y_{mag}$ attribute prediction, we treat the learning task as a regression problem and train the model using mean squared error loss. And finally, for training the model to predict $Y_{ang}$ attribute, we utilize KL Divergence loss. For all the tasks, we construct a sim", + "bbox": [ + 496, + 795, + 890, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "18720", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "ple light-weight CNN. The detailed configuration of our 3D CNN architecture is presented in the supplemental material.", + "bbox": [ + 75, + 90, + 468, + 121 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.2. Model Building", + "text_level": 1, + "bbox": [ + 76, + 130, + 235, + 146 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Once trained, the attribute deep nets are used to build a model of any scene given the nominal video. As illustrated in Figure 1, to process each nominal video, we slide a spatio-temporal window of dimension $[h\\times w\\times t]$ with spatial stride $(h / 2,w / 2)$ and temporal stride of $t$ to construct video volumes. In the experiments, we select $h = w$ and choose $h$ to be roughly the height in pixels of a person in a particular dataset. For each RGB video volume, we extract its features using the previously trained appearance net and four motion nets. To get a single appearance feature vector for a video volume, the feature vectors computed by the appearance network for each frame of the video volume are averaged. We concatenate the feature vectors from the penultimate layers of the appearance, angle, speed and background pixel nets along with the binary output of the background classifier net to create a combined feature vector. We use $F$ to denote a combined feature vector and app, ang, mag, and bkg to denote the appearance, angle, magnitude and background pixel fraction feature vectors, each of size $1\\times 128$ . Finally, cls denotes the binary background classification of size $1\\times 1$ . $F$ is of size $1\\times 513$ .", + "bbox": [ + 75, + 152, + 472, + 470 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "After computing features, we use the exemplar selection approach of [18, 34] to create a region-specific compact model of the nominal data. For each region, we use the following greedy exemplar selection algorithm:", + "bbox": [ + 75, + 470, + 468, + 531 + ], + "page_idx": 4 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "1. Add the first feature vector to the exemplar set.", + "2. For each subsequent feature vector, compute its distance to each feature vector in the exemplar set and add it to the exemplar set only if all distances are above a threshold, $th$ ." + ], + "bbox": [ + 88, + 536, + 468, + 614 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "To be clear, a separate set of exemplars is selected for each different spatial region in a scene. This allows our model to represent the fact that different object and motions occur in different regions of a scene. To compute the distance between two feature vectors $F_{1} = [app_{1}; ang_{1}; mag_{1}; bkg_{1}; cls_{1}]$ and $F_{2} = [app_{2}; ang_{2}; mag_{2}; bkg_{2}; cls_{2}]$ we use $L_{2}$ distances between corresponding components normalized by a constant to make the maximum distance for each component approximately 1. When a video volume does not contain motion (as determined by the background classification, $cls$ ), the motion component vectors are set to 0. The distance function can be written as follows:", + "bbox": [ + 75, + 622, + 472, + 818 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nd _ {A} \\left(F _ {1}, F _ {2}\\right) = \\left\\| A _ {1} - A _ {2} \\right\\| _ {2} \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 179, + 828, + 468, + 845 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $A\\in \\{app,ang,mag,bkg\\}$", + "bbox": [ + 76, + 854, + 308, + 871 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nd (F _ {1}, F _ {2}) = \\frac {d _ {a p p}}{Z _ {a p p}} + \\frac {d _ {a n g}}{Z _ {a n g}} + \\frac {d _ {b k g}}{Z _ {b k g}} + \\frac {d _ {m a g}}{Z _ {m a g}}. (2)\n$$\n", + "text_format": "latex", + "bbox": [ + 102, + 878, + 468, + 906 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The normalization factors, $Z_{app}$ , $Z_{ang}$ , $Z_{mag}$ and $Z_{bkg}$ are computed once by finding the max $L_{2}$ distances between a large set of feature vector components computed from a validation set (UCSD Ped1 and Ped2 in our experiments).", + "bbox": [ + 496, + 90, + 890, + 151 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "One big advantage of the exemplar learning approach is that updating the exemplar set in a streaming fashion is possible. This makes the approach scalable and adaptable to environmental changes over time.", + "bbox": [ + 496, + 152, + 893, + 212 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.3. Anomaly Detection", + "text_level": 1, + "bbox": [ + 500, + 222, + 684, + 237 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "At test time, we process each test video in the same way (by sliding a $[h\\times w\\times t]$ spatio-temporal window with spatial stride $(h / 2,w / 2)$ and temporal stride of $t$ ) to generate video volumes. For each video volume, we compute the combined feature vector as before using the pre-trained nets. Each combined feature vector is compared with every exemplar for the corresponding region using the distance function in Equation 2. The anomaly score for the given test video volume is the minimum distance over the set of all exemplars from the same spatial region. A pixelwise anomaly score map is maintained by assigning the anomaly score to all pixels corresponding to every frame of the video volume. If a pixel has already been assigned an anomaly score (because of partially overlapping video volumes), then the maximum of the previous score and the current score is assigned. Figure 1 shows our anomaly detection pipeline.", + "bbox": [ + 496, + 246, + 893, + 488 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.4. A Note on Computational Efficiency", + "text_level": 1, + "bbox": [ + 500, + 497, + 815, + 513 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "For both model building and anomaly detection, most of the time is spent computing feature vectors (forward passes of 5 networks). This is greatly sped up by testing whether a video volume is the same as the previous video volume in time. If there is no change then the anomaly score for the new video volume should be the same as the one before it and no computation of feature vectors is needed. This allows our method to run at 20 to 100 fps (dataset dependent). Details are in the supplemental material.", + "bbox": [ + 496, + 520, + 893, + 657 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 500, + 670, + 633, + 688 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.1. Datasets and Evaluation Criteria", + "text_level": 1, + "bbox": [ + 500, + 696, + 790, + 710 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We experiment on five benchmark datasets: UCSD Ped1 and Ped2 [29], CUHK Avenue [24], Street Scene [33] and ShanghaiTech [26]. We use UCSD Ped1 and Ped2 with modified ground truth for parameter tuning and CUHK Avenue, Street Scene and ShanghaiTech for evaluation.", + "bbox": [ + 496, + 719, + 890, + 794 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "UCSD Ped1 & Ped2: UCSD Ped1 dataset contains 34 training videos and 36 test videos while UCSD Ped2 dataset contains 16 training videos and 12 test videos. Anomalies consists of bikers, skaters and cars in a pedestrian area.", + "bbox": [ + 496, + 794, + 890, + 854 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "CUHK Avenue: The Avenue [24] dataset contains 16 training videos with normal activity and 21 test videos. Examples of abnormal events in Avenue are related to people run", + "bbox": [ + 496, + 854, + 890, + 901 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "18721", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "ning, throwing objects or walking in wrong direction.", + "bbox": [ + 75, + 90, + 431, + 104 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Street Scene: The Street Scene [33] dataset contains 46 training videos defining the normal events and 35 test videos. Prominent examples of anomalies include jaywalking, loitering and bikes or cars driving outside their lanes.", + "bbox": [ + 75, + 106, + 467, + 166 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "ShanghaiTech: The ShanghaiTech [26] dataset is a multiscene benchmark for video anomaly detection. It consists of 330 training and 107 test videos. Major categories of anomalies include people fighting, stealing, chasing, jumping, and riding bikes or skating in pedestrian zones.", + "bbox": [ + 75, + 167, + 467, + 242 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "While our primary focus is on single scene video anomaly detection task, we consider the ShanghaiTech dataset only to highlight the ease of usability and robustness of our method to multi-scene benchmarks. Our method is applied to ShanghaiTech without modification even though the location-dependent aspect of our model is not necessary for a multi-scene dataset. Improvements in accuracy are likely if we specialize our model to multi-scene datasets.", + "bbox": [ + 75, + 243, + 467, + 362 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Evaluation Criteria. We use the Region-Based Detection Criterion (RBDC) and the Track-Based Detection Criterion (TBDC) as proposed in [33] for quantitative evaluation of our framework. These criteria correctly measure the accuracy of spatially and temporally localizing anomalous regions (RBDC) and anomalous tracks (TBDC) versus false positive detections per frame. We report the area under the curve (AUC) for false positive rates per frame from 0 to 1 for each of these criteria. As pointed out in [33], frame-AUC [29] is not an appropriate evaluation metric for video anomaly detection methods that spatially localize anomalies. However, we report frame-AUC scores of our method for completeness and comparison with other older methods. We also do not use the pixel-level criterion [29] because of its serious flaws as mentioned in [33].", + "bbox": [ + 75, + 364, + 467, + 590 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.2. Implementation", + "text_level": 1, + "bbox": [ + 76, + 603, + 235, + 618 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Feature Learning. To train our appearance model, we use SGD with a 0.001 learning rate and 0.9 momentum and train for 50 epochs. The model with lowest classification error on the validation set is selected. For motion models we optimize with AdamW [23] with a 0.001 learning rate and train for 30 epochs. We select the best model for each attribute using the validation set.", + "bbox": [ + 75, + 627, + 467, + 733 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Video volume parameters. We define the dimensions $(w, h)$ of a video volume for each dataset so that $h$ is roughly the height of a person in pixels and $w = h$ . Specifically, for Ped1, Ped2, Avenue, Street Scene and ShanghaiTech, our region dimensions are (32, 32), (32, 32), (128, 128), (64, 64) and (100, 100) respectively. Zeropadding was used for edge regions as needed. The number of frames in a video volume, $t$ , is 10 for all datasets.", + "bbox": [ + 75, + 734, + 467, + 852 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Parameter Tuning. To set a threshold $th$ for exemplar selection without fitting to test data, a validation data set is needed. We chose Ped1 and Ped2 for this purpose, both", + "bbox": [ + 75, + 854, + 467, + 900 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/af3568db28c388b991ea1b62cc62e20ffb7302eb42939130ba1c31624374e5af.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
ThUCSD Ped1UCSD Ped2
RBDCTBDCNUMRBDCTBDCNUM
336.86677.8328864.80889.13350
2.549.3689.4342478.81393.716761
257.52489.694484.6695.971339
1.561.6588.9420187.4495.084470
161.49687.541992687.40895.77619138
0.561.43587.724911387.19595.1234862
0.2561.4987.815763687.19995.12745795
", + "bbox": [ + 506, + 88, + 887, + 204 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 1. RBDC and TBDC scores (in %) of our method for different thresholds (th) on UCSD Ped1 and Ped2. NUM denotes the total number of exemplars across all regions.", + "bbox": [ + 498, + 214, + 890, + 257 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "because these data sets are performance-saturated, and because previous works [34] have identified inconsistencies in their ground truth. Specifically, ground-truth annotations of Ped1 and Ped2 do not label every location-specific anomaly. To rectify this, we augment the existing ground truth annotations to include all anomalies consistent with Definition 1. This is justified because we are using Ped1 and Ped2 to set our hyperparameters and not to compare against previous methods. Table 1 shows region-based and track-based AUC for different values of the threshold $th$ used for exemplar selection for both Ped1 and Ped2. We see that the accuracy of our method is robust to large variations of $th$ . However, larger values of $th$ lead to smaller numbers of exemplars and thus smaller models of the nominal video which is desirable. We select $th = 1.5$ as a good trade-off between accuracy and model-size. We use this value on all datasets in our experiments. For Ped2, the average number of exemplars selected per region is about 13 ( $\\approx 0.5\\%$ of the total number of video volumes in the nominal video). Exemplar selection typically finds tens to sometimes low hundreds of exemplars (for Street Scene) for regions with lots of activity. Regions with very little activity typically have only 1 or 2 exemplars. This leads to very compact models of the nominal video.", + "bbox": [ + 496, + 273, + 890, + 633 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.3. Quantitative Results", + "text_level": 1, + "bbox": [ + 500, + 648, + 692, + 665 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Tables 2 and 3 compare our method to other top methods on Avenue, ShanghaiTech and Street Scene. On Avenue, we improve over all previous methods for the region-based detection criterion (RBDC) and are second best for the track-based detection criterion (TBDC). On ShanghaiTech, we improve over the next best method for both RBDC and TBDC by significant margins. For the frame-level criterion which does not measure spatial localization we are in the middle of the pack compared to other recent methods for both Avenue and ShanghaiTech. On the difficult Street Scene dataset (Table 3), we improve the previous state of the art for both RBDC and TBDC, the latter by more than $11\\%$ . The good results across five different datasets (including Ped1 and Ped2) show the generality of the high-level features that we use in our models.", + "bbox": [ + 496, + 674, + 890, + 898 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "18722", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/a3296f53f2064b1442b9cadfef3315d7c864fc6b47008e576d8387f84a7e9676.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodAvenueShanghaiTech
RBDCTBDCFrameRBDCTBDCFrame
Ionescu et al. [16]15.7727.0787.420.6544.5478.7
Ramachandra et al. [33]35.8080.9072.0---
Ramachandra et al. [34]41.2078.6087.2---
Georgescu et al. [12]57.0058.3091.542.8083.9090.02
Liu et al. [21]19.5956.0185.117.0354.2372.8
Liu et al. [22]41.0586.1889.944.4183.8674.2
Georgescu et al. [13]65.0566.8592.341.3478.7982.7
Liu et al. [21] + Ristea et al. [38]20.1362.3087.318.5160.2274.5
Liu et al. [22] + Ristea et al. [38]62.2789.2890.945.4584.5075.5
Georgescu et al. [13] + Ristea et al. [38]65.9964.9192.940.5583.4683.6
Our Method68.287.5686.0259.2189.4476.63
", + "bbox": [ + 84, + 88, + 464, + 270 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/5a42d6256e701badc4a6d63688f06c603a5d4f8bc4427a1beffbb3938cedd66b.jpg", + "table_caption": [ + "Table 2. RRBDC, TBDC and Frame AUC scores (in %) of various state-of-the-art methods on Avenue and ShanghaiTech datasets. The top score for each metric is highlighted in red, while the second best score is in blue." + ], + "table_footnote": [], + "table_body": "
MethodsRBDCTBDC
Auto-encoder [14]0.292.0
Dictionary method [24]1.610.0
Flow baseline [33]11.052.0
FG Baseline [33]21.053.0
Our Method24.364.5
", + "bbox": [ + 140, + 340, + 406, + 421 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 3. RBDC and TBDC AUC scores (in %) of various baseline methods on Street Scene dataset. The top score for each metric is highlighted in red, while the second best score is highlighted in blue.", + "bbox": [ + 75, + 431, + 468, + 487 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.4. Qualitative Results: Explainability", + "text_level": 1, + "bbox": [ + 76, + 511, + 379, + 527 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "One of the big advantages of our method in addition to its accuracy is that it allows intuitive explanations of what the model has learned and why it labels a particular test video volume as anomalous or not. To visualize the feature vector representing a video volume, the appearance and motion components of the combined feature vector are mapped using the last fully connected layer of the respective network to the high-level appearance and motion attributes. We can then visualize these attributes as illustrated in Figure 2.", + "bbox": [ + 75, + 536, + 468, + 672 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "As an illustration of our model's explainability, the top of Figure 3 visualizes the exemplars learned from the nominal video for a spatial region in the middle of the street. Cars travel down and to the right in this lane of the street. The top six exemplars learned show mainly cars (or unknown objects, since video volumes containing only parts of cars are often not classified as cars) traveling down and to the right, as expected. There are also exemplars for stationary background, as well as stationary cars (since occasionally traffic stops on this part of the street). Thus, our learned model is understandable and consistent with what one expects. Furthermore, for a video volume containing a person jaywalking, the visualization in the bottom, left of the figure shows that our networks correctly identify it as containing a person walking mainly to the right at moderate speed. The", + "bbox": [ + 75, + 674, + 470, + 902 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "closest exemplar to this test volume is an unknown object moving down and to the right which yields a high anomaly score of 2.08. (A threshold of 1.8 yields high detection rates with low false positive rates across all the datasets.) Thus, the explanation of this anomaly is that there is an unusual object (person) walking in an unusual direction.", + "bbox": [ + 496, + 90, + 890, + 181 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Another example is shown for Ped2 in Figure 4. Here we analyze a region on the sidewalk. The exemplars learned for this region (shown at the top of Figure 4) are mainly background with very little movement or people moving mainly left or right at slow speeds. Some video volumes containing only parts of people are not classified as people which leads to exemplars of unknown objects moving left or right. Overall, these exemplars are again what we would expect for this region. For the test frame shown, a cyclist is riding on the sidewalk. The visualization of the video volume centered on that frame at that spatial region shows that it was classified as a cyclist traveling down and right at a high speed. These high-level attributes differs from the nearest exemplar in terms of its object class and speed and therefore leads to a high anomaly score.", + "bbox": [ + 496, + 183, + 892, + 409 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "As a final illustration (we show more in the supplemental material), we look at an example from CUHK Avenue in Figure 5. The top six exemplars for the region highlighted at the left of the figure show that the model has learned that this region contains either background with very little movement or else people or unknown objects moving mainly left or right slowly. For the anomalous test video volume shown containing a person running to the left, the high-level features estimate an unknown object moving left at high speed. Even though the object recognizer did not correctly predict that the video volume contains a person, the person class is the most likely out of the eight classes. The nearest exemplar is an unknown object (closest to a person class) moving slowly to the left. The main difference between the test video volume and the closest exemplar is the unusual speed which correctly explains this anomaly.", + "bbox": [ + 496, + 410, + 892, + 652 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.5. Ablation Study", + "text_level": 1, + "bbox": [ + 500, + 664, + 653, + 681 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We perform an ablation study on all the benchmarks to evaluate the benefit of each attribute in detecting anomalies. We consider features from each model separately, combining features from only motion models and finally our full model which uses all features. We accordingly change the distance function to compare features of two video volumes so that it only uses the provided features. We present our results in Table 4. We see that different attributes can be important for different types of scenarios. However, we get best results across all the benchmarks only when we combine all the motion and appearance features. This highlights the importance of modeling both appearance and different components of motion, especially to be able to predict anomalies under wide variety of scenarios.", + "bbox": [ + 496, + 688, + 890, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "18723", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Bar graphs of sigmoid outputs for the 8 object classes in the appearance network. $[0 =$ person, $1 =$ car, $2 =$ cyclist, $3 =$ dog, $4 =$ tree, $5 =$ house, $6 =$ skyscraper, $7 =$ bridge.] Length of each bar is proportional to the distance of the sigmoid value from 0.5.Values above 0.5 (green) indicate the likely presence of that object class, while values below 0.5 (red) indicate otherwise.", + "bbox": [ + 125, + 93, + 393, + 145 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Visualization of the direction of motion histogram. For each of the 12 angles estimated by the direction network, the length of the ray in that direction is proportional to the number of pixels (in that video volume) estimated to be moving in that direction.", + "bbox": [ + 125, + 155, + 390, + 190 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/b6d30256665e11b68ff1be4b87be6af328f9771e77eafef96adb99490e25c395.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 398, + 93, + 539, + 181 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Bar graph of the output of the network estimating the fraction of stationary pixels. If the bar is all white then it indicates that there was no motion in the video volume. If the bar is all black then every pixel was predicted to be moving.", + "bbox": [ + 539, + 95, + 841, + 132 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Visualization of the average speed of pixels moving in a particular direction which are estimated by the directional speed network. Each ray is proportional to the speed in a particular direction. It is not proportional to the number of pixels moving in a particular direction as in the case of the angle histogram.", + "bbox": [ + 539, + 140, + 836, + 184 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/f6773b2dab33d298809686d909c8f010d87b79d12990edf423f223a6dc2d3b1d.jpg", + "image_caption": [ + "Figure 2. Explanation of our \"instrument panel\" showing the estimated attributes for a video volume. The interpretation of this visualization would be (roughly) a car (class 1) taking up most of the video volume, moving right at a high speed.", + "Frame 1719 of Street Scene Test005. The bounding box indicates a particular spatial region containing a ground truth anomaly (jawwalking)." + ], + "image_footnote": [], + "bbox": [ + 81, + 244, + 209, + 328 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/06a052f87bc65bef1cd3269436f880d023b9058f79b16871036f12d851eb1262.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 210, + 244, + 470, + 400 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/d546ba1a42ab5b043b287836e081e4819b36f67e86beb86ecc6cc8aa08cab94d.jpg", + "image_caption": [ + "Figure 3. Visualization of the learned exemplars for a region of Street Scene and visualization of a test video volume explaining why it was detected as an anomaly.", + "Frame 119 of UCSD Ped2 Test001. The bounding box indicates a particular spatial region containing a ground truth anomaly (cyclist on sidewalk)." + ], + "image_footnote": [], + "bbox": [ + 81, + 460, + 205, + 527 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/7907fd9fe77160be63a2cd16f0c3fcb82afc16764f0f94ba0f8ef400236173e5.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 205, + 460, + 470, + 532 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/7db7751ff3424ef39d554282c61f95622a50d789939f2ce0021e0bf1b6a5bc14.jpg", + "image_caption": [ + "Attributes for the test video volume centered around the cyclist shown at left." + ], + "image_footnote": [], + "bbox": [ + 339, + 536, + 467, + 614 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/151ba021317951f04c1d4eb150e0c2a8184751ee5166e5db332d8e05c94a8a97.jpg", + "image_caption": [ + "Figure 4. Visualization example for a region of UCSD Ped2 showing an explanation of the anomaly.", + "Frame 400 of Avenue Test004. The bounding box indicates a particular spatial region containing a ground truth anomaly (running)." + ], + "image_footnote": [], + "bbox": [ + 81, + 659, + 210, + 720 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/7edeaa65695e5e5a288935036b7f50c892168f9754ed07aa3d6bb2d3852918d4.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 210, + 659, + 470, + 729 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/1ba8a742beaa4c69385c929fdb41e5b270655e7a9599bc58892d4225cbe97d53.jpg", + "image_caption": [ + "Figure 5. Visualization example for a region of CUHK Avenue showing an explanation of the anomaly." + ], + "image_footnote": [], + "bbox": [ + 210, + 732, + 460, + 816 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/fe04e6387b217efa308f869e700f6be3432a73d063a764e978a317dbb4fed8d8.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
AttributesPed1Ped2AvenueStreet Scene
App29.6 / 64.877.7 / 92.575.6 / 67.41.1 / 4.8
Motion59.2 / 83.781.6 / 93.369.0 / 89.022.6 / 64.1
Angle40.9 / 70.670.8 / 88.166.4 / 89.324.5 / 65.9
Mag60.6 / 90.170.1 / 88.559.5 / 91.116.6 / 50.8
Bkg45.5 / 86.471.7 / 95.249.9 / 81.511.9 / 49.8
App+Mot61.7 / 88.987.4 / 97.169.6 / 86.723.9 / 65.3
", + "bbox": [ + 504, + 243, + 888, + 358 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/961f64a01cb72e35e2b984be5dc40d4a0a8151a6e2a397c6ed6e47828ad2ea2c.jpg", + "table_caption": [ + "Table 4. RBDC / TBDC AUC scores (in %) of our method when using only appearance, only motion (using angle, magnitude and background pixel predictions combined), each motion component separately and all the features" + ], + "table_footnote": [], + "table_body": "
AttributesPed1Ped2
ImageNet25.148 / 44.6364.67 / 83.17
Ours29.6 / 64.877.7 / 92.5
", + "bbox": [ + 513, + 438, + 879, + 491 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 5. RBDC / TBDC AUC scores (in %) of our method when using our pre-trained model versus ImageNet pe-trained model as appearance feature extractor.", + "bbox": [ + 498, + 501, + 890, + 542 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We further perform an ablation study on UCSD Ped1 and Ped2 datasets to empirically evaluate the benefit of our appearance model to represent object features versus using ImageNet pre-trained features. For the ImageNet pretrained model, we use the pre-classification layer output of ResNext-50 as features. We present our results in Table 5. The superiority of our model is most likely due to the loss function used (binary cross-entropy) which allows an image patch to contain zero or multiple object classes.", + "bbox": [ + 498, + 551, + 890, + 688 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Discussion and Conclusions", + "text_level": 1, + "bbox": [ + 500, + 700, + 754, + 717 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We have presented a novel method for explainable video anomaly localization that has a number of desired properties. Foremost, the method is accurate and general. We have shown that it works very well on five different datasets and, in particular, achieves state-of-the-art results on CUHK Avenue, Street Scene and ShanghaiTech. Setting it apart from almost all previous work, our model is understandable by humans and the decisions that our method makes are explainable. Finally, because our method does not require an expensive training phase on the nominal data, it is easy to expand our model when new nominal data is available.", + "bbox": [ + 496, + 727, + 890, + 892 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "18724", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Detecting anomalous events in videos by learning deep representations of appearance and motion. Comput. Vis. Image Underst., 156(C):117-127, mar 2017. 2", + "[2] Amit Adam, Ehud Rivlin, Ilan Shimshoni, and Daviv Reinitz. Robust real-time unusual event detection using multiple fixed-location monitors. IEEE transactions on pattern analysis and machine intelligence, 30(3):555-560, 2008. 2", + "[3] Borislav Antić and Björn Ommer. 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Springer, 2007. 4" + ], + "bbox": [ + 501, + 92, + 890, + 710 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "18726", + "bbox": [ + 480, + 945, + 519, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/EVAL_ Explainable Video Anomaly Localization/396d953c-501f-406c-be61-8e06127066d0_model.json b/2023/EVAL_ Explainable Video Anomaly Localization/396d953c-501f-406c-be61-8e06127066d0_model.json new file mode 100644 index 0000000000000000000000000000000000000000..2572cc264a792c9ba6bf9550836ce92e156149e6 --- /dev/null +++ b/2023/EVAL_ Explainable Video Anomaly Localization/396d953c-501f-406c-be61-8e06127066d0_model.json @@ -0,0 +1,2156 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.001, + 0.812, + 0.047 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.24, + 0.131, + 0.733, + 0.154 + ], + "angle": 0, + "content": "EVAL: Explainable Video Anomaly Localization" + }, + { + "type": "text", + "bbox": [ + 0.208, + 0.18, + 0.345, + 0.198 + ], + "angle": 0, + "content": "Ashish Singh\\(^{1,2*}\\)" + }, + { + "type": "text", + "bbox": [ + 0.375, + 0.181, + 0.525, + 0.198 + ], + "angle": 0, + "content": "Michael J. Jones\\(^{2*}\\)" + }, + { + "type": "text", + "bbox": [ + 0.558, + 0.181, + 0.762, + 0.198 + ], + "angle": 0, + "content": "Erik G. Learned-Miller1,2" + }, + { + "type": "text", + "bbox": [ + 0.146, + 0.199, + 0.506, + 0.216 + ], + "angle": 0, + "content": "\\(^{1}\\)CICS, University of Massachusetts Amherst" + }, + { + "type": "text", + "bbox": [ + 0.544, + 0.199, + 0.824, + 0.216 + ], + "angle": 0, + "content": "\\(^{2}\\)Mitsubishi Electric Research Labs" + }, + { + "type": "text", + "bbox": [ + 0.202, + 0.22, + 0.419, + 0.234 + ], + "angle": 0, + "content": "ashishsingh@cs.umass.edu" + }, + { + "type": "text", + "bbox": [ + 0.442, + 0.22, + 0.58, + 0.234 + ], + "angle": 0, + "content": "mjones@merl.com" + }, + { + "type": "text", + "bbox": [ + 0.618, + 0.22, + 0.763, + 0.233 + ], + "angle": 0, + "content": "elm@cs.umass.edu" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.269, + 0.314, + 0.285 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.302, + 0.474, + 0.545 + ], + "angle": 0, + "content": "We develop a novel framework for single-scene video anomaly localization that allows for human-understandable reasons for the decisions the system makes. We first learn general representations of objects and their motions (using deep networks) and then use these representations to build a high-level, location-dependent model of any particular scene. This model can be used to detect anomalies in new videos of the same scene. Importantly, our approach is explainable – our high-level appearance and motion features can provide human-understandable reasons for why any part of a video is classified as normal or anomalous. We conduct experiments on standard video anomaly detection datasets (Street Scene, CUHK Avenue, ShanghaiTech and UCSD Ped1, Ped2) and show significant improvements over the previous state-of-the-art. All of our code and extra datasets will be made publicly available." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.576, + 0.21, + 0.592 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.602, + 0.471, + 0.875 + ], + "angle": 0, + "content": "We are interested in the problem of spatio-temporal localization of anomalous activities in videos of a given scene. Informally, anomalous activities are events that differ from those typically observed in a scene, such as a cyclist riding through an indoor shopping mall [35]. Like many other papers on anomaly detection, this work addresses the setting in which we have access to an initial set of videos that are used to define the typical, or 'nominal' activities in a particular scene. Such a situation naturally arises in surveillance and monitoring tasks [41], where it is easy to collect nominal data, but it is not practical to collect a representative set of possible anomalies for a scene. Thus, the problem setup is as follows: provided with a set of videos of a scene which do not contain any anomalies, (called the nominal set), the goal is to detect any events in a test video from the same scene that differ substantially from all events in the nominal set [29, 35]. In defining anomaly detection, it is important to consider the role of location. In real-world" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.27, + 0.895, + 0.346 + ], + "angle": 0, + "content": "surveillance scenarios, an event may be normal in one location but anomalous in another. For example, a car driving on a road is typically not anomalous, while one driving on a sidewalk typically is. In view of this, we adopt the following definition [35]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.346, + 0.895, + 0.39 + ], + "angle": 0, + "content": "Definition 1 An anomaly is any spatio-temporal region of test video that is significantly different from all of the nominal video in the same spatial region." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.389, + 0.896, + 0.584 + ], + "angle": 0, + "content": "Unlike most recent work in anomaly detection, a key goal of our work is to produce not only a set of anomalies, but a simple and clear explanation for what makes them anomalous. We are motivated by how people tasked with watching video from a stationary surveillance camera would detect an unusual incident. While monitoring a scene, we expect a person to note the types of objects seen (people, buildings, cars) and the motions of those objects (walking east or west on a sidewalk, driving northwest on the street) to characterize the given scene. The person could then notice an anomaly when the objects or motions do not match what has been seen before. The person could also explain why something was anomalous." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.585, + 0.896, + 0.825 + ], + "angle": 0, + "content": "We design our video anomaly detection system using this sketch of how a human would solve the problem as motivation. We want to use deep networks to give a high-level understanding of the objects and motions occurring in a scene. By 'high-level', we mean at the level of whole objects and not at the level of pixels or edges. To do this, we train deep networks that take a spatio-temporal region of video (which we call a video volume) as input and output attribute vectors representing the object classes, the directions and speeds of motion and the fraction of stationary pixels (which gives information on the sizes of moving objects) occurring in a spatio-temporal region. The feature vectors from the penultimate layers of these deep networks yield high-level representations, or embeddings, of the appearance and motion content of each video volume. Ten frames are used for video volumes in our experiments." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.826, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Unlike many other recent works, we do not learn new embedding functions (i.e. networks) for new scenes. We use the same embedding networks for every environment. Instead, to characterize the nominal video for a new scene, we store a representative set of all the embeddings found in" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.888, + 0.202, + 0.9 + ], + "angle": 0, + "content": "*equal contribution" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "18717" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.364 + ], + "angle": 0, + "content": "the nominal video. That is, for every video volume in the nominal video of a new scene, we calculate our representations of appearance, motion direction, speed, and background fraction. We then reduce this set of embeddings to a smaller set which we call exemplars by removing redundant embeddings. We select a separate set of exemplars for each spatial region. This results in a compact, accurate, and location-dependent model of the nominal data in a new scene. Since there is no training of deep networks for each new environment, modeling a new environment is 'lightweight' compared to many other methods, making it efficient to model new scenes. Our exemplar model also allows very efficient updating if new nominal video is introduced. This is a crucial property for video anomaly detection methods because, in practice, it is unrealistic to assume that the initial nominal video covers every possible normal change. New nominal video will occasionally need to be added, making it critical that models are easy to extend." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.364, + 0.473, + 0.544 + ], + "angle": 0, + "content": "Given test video of the same scene, we compute our high-level features for each video volume. We then compare these to the exemplars stored in the nominal model at the corresponding spatial region. Any test feature with a high distance to every nominal exemplar for that region is considered anomalous. Because the feature vectors map to human-interpretable attributes, these attributes can be used to give human-understandable explanations for why our system labeled video volumes as normal or anomalous. We define a method as 'explainable' if it can give human-understandable reasons for its decisions. Details of how our system provides explanations are given in Section 4.4." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.546, + 0.473, + 0.727 + ], + "angle": 0, + "content": "In summary, we make the following key contributions: 1) We show that modeling scenes using high-level attributes leads to robust anomaly detection. 2) We introduce the idea of directly estimating high-level motion attributes from raw video volumes using deep networks. 3) We show how these high-level attributes also allow human-interpretable explanations. 4) Finally, we demonstrate an alternative to much of the previous work that is based on learning to reconstruct the nominal data. Our alternative approach is practical since it does not require training deep networks for each new scene and allows for simple and efficient updates to a scene model given new nominal training data." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.74, + 0.22, + 0.755 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.765, + 0.47, + 0.809 + ], + "angle": 0, + "content": "Most Video Anomaly Detection (VAD) methods can be analyzed in terms of their representation learning or their detection method." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.811, + 0.47, + 0.902 + ], + "angle": 0, + "content": "Representation of Nominal Data: Early approaches to VAD [2, 3, 7, 20, 30, 40, 47] primarily relied on the usage of handcrafted features. This included features like spatiotemporal gradients [17, 24], histogram of gradients [28, 40], flow fields [2, 3, 30, 47], histogram of flows [7, 40, 41], dense trajectories [28, 43] and foreground masks [3]. Re" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.895, + 0.62 + ], + "angle": 0, + "content": "cently, most authors have used deep learning for this task [1,9,10,14-16,21,26,34,36,37,39,42,45]. These methods either use a pretrained model [15, 17, 26, 36, 39, 42] for feature extraction or train a model to specifically optimize for a particular task related to anomaly detection. These tasks can generally be categorized as either a variant of training an auto-encoder architecture to minimize the reconstruction error of nominal frames [6, 14, 16, 22, 25, 31], a generative adversarial network (GAN) to model nominal frames [21,25], or future frame prediction given a sequence of nominal frames [21,44]. To further improve their performance, recent works have tried specialized architectures and training methodologies. Particularly [8,22,32] transform their respective generative model by memory-based modules to memorize the normal prototypes in the training data. Most recently [38] proposed a module based on masked convolution and channel attention to reconstruct a masked part of the convolutional receptive field. A key drawback of reconstruction and future frame prediction methods is that they do not generate interpretable features. It is not clear what aspects of the video make it difficult to reconstruct since there is no mapping to higher-level features as in our work. Our work mostly aligns with methods utilizing pretrained models. However, unlike most of these approaches, we incorporate the output of our pretrained models to interpret model decisions. We additionally make sure that the predictions of our model generalize to a wide variety of scenes through our data generation and training procedures. One high-level motion attribute that our method learns is similar to the histogram of flow feature used in some early work [7,40,41]. However, instead of computing the histogram of flow from an optical flow field, our method learns a deep network to predict these features directly from RGB video volumes and then uses the network's learned feature embedding as the representation." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.62, + 0.897, + 0.892 + ], + "angle": 0, + "content": "Detection Methods: Most methods use either standard outlier detection methods [5] as an external module or utilize the reconstruction strategy to predict anomalies. General methods of detection that most authors have used in the past include one-class SVM [17, 28, 42, 49], nearest neighbour approaches [9, 11, 15, 33, 34], and Probabilistic Graphical Models [3]. In [4, 13], pseudo-anomalous samples are used during training to improve discriminative learning. In [12], an object detector is used to focus on regions around objects and then networks are trained for various 'proxy' tasks (such as predicting the arrow of time) on the nominal data. Thus, unlike our work, they require training deep nework models for each different scene. Our work has some similarity to the work of [33, 34] in that we also use an overlapping grid of spatial regions, build exemplar-based models and use nearest neighbors distances as anomaly scores. The high-level features that we use are the biggest difference as compared to the pixel-based features used in their" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "18718" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.176, + 0.1, + 0.77, + 0.351 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.364, + 0.895, + 0.42 + ], + "angle": 0, + "content": "Figure 1. Our pipeline for building a location-dependent model of nominal video and detecting anomalies in test video. During the model building phase, we extract a high-level representation of each video volume using our appearance and motion networks. Using the exemplar selection method, we select a representative subset of video volumes for a given spatial region. By comparing video volumes in test video to the exemplar set we can detect anomalies." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.434, + 0.47, + 0.463 + ], + "angle": 0, + "content": "work. Our high-level features allow for explainable models as well as much smaller models than theirs." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.464, + 0.47, + 0.614 + ], + "angle": 0, + "content": "Explainable VAD: Our work is similar in spirit to the work of [15,46] with respect to providing explanations for detecting anomalies. In [15], the authors pre-train their feature extractor on public image datasets (MS-COCO and Visual Genome) to detect objects and predict their attributes and actions. They further use these predictions for 'event recounting' on VAD benchmarks. In [46], the authors utilize models pretrained for semantic segmentation, object classification, and multi-object tracking and use the output of these models directly as their feature representation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.616, + 0.471, + 0.798 + ], + "angle": 0, + "content": "Despite these coarse similarities, virtually all of the details of our methods are different. Specifically, in [15], they rely on object proposals to find candidate anomalous regions which can lead to missed detections for objects not represented in their training data. Our action/motion classes are also very different - ours being more generic (direction distributions and speed of motion) while in [15] are much more specific (bending, riding) and hence not applicable to a wide variety of scenarios. The method of [46] is specific to detecting and tracking pedestrians and is not a general video anomaly detection method. Furthermore, unlike ours, their method does not spatially localize anomalies." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.814, + 0.226, + 0.832 + ], + "angle": 0, + "content": "3. Our Approach" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Our method consists of three distinct stages: high-level attribute learning, model building, and anomaly localization. The high-level attribute learning stage is done only once and uses training samples that are independent of any" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.434, + 0.895, + 0.63 + ], + "angle": 0, + "content": "video anomaly detection dataset. The resulting deep networks learn general representations of object appearances and object motions which can then be used in the subsequent two stages to build a model of a specific scene and to localize anomalies in that scene, for a wide variety of surveillance scenarios. The outside data used to train our high-level attribute models are equivalent to the outside data used in various prior works on VAD; for example, the M-OCOCO and Visual Genome data used to train the models of Hinami et al. [15], the outside data used to train object detectors in [11, 12, 17, 42], as well as the many deep models pretrained on ImageNet and applied to VAD. Our outside data is not used to build models of a scene." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.637, + 0.753, + 0.653 + ], + "angle": 0, + "content": "3.1. High-Level Attribute Learning" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.66, + 0.892, + 0.81 + ], + "angle": 0, + "content": "For this stage, our main objective is to learn features that are (a) transferable across scenes and (b) interpretable. Given this motivation, we learn an object recognizer for our appearance model as well as regression networks for estimating the following motion attributes for a given video volume: the fraction of stationary pixels, the distribution of motion directions and the average speed of movement in each direction. We also learn a classifier to indicate whether a video volume is stationary or not. We will describe each of these deep networks in the following subsections." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.811, + 0.895, + 0.901 + ], + "angle": 0, + "content": "To clarify our terminology, we use the term 'high-level attribute' to denote the object classes, histogram of motion directions, vector of motion speeds or fraction of stationary pixels which are the final outputs of the various deep networks that are learned. The term 'high-level feature' denotes the feature vector from the penultimate layer of one of" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "18719" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.47, + 0.122 + ], + "angle": 0, + "content": "the deep networks. A high-level feature can be mapped to a high-level attribute using the final layer of that network." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.129, + 0.263, + 0.144 + ], + "angle": 0, + "content": "3.1.1 Appearance model" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.153, + 0.469, + 0.198 + ], + "angle": 0, + "content": "We formulate the task of object recognition as a multi-label image classification problem as any given input image patch may contain more than one object class (or none)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.199, + 0.469, + 0.44 + ], + "angle": 0, + "content": "Training Data: We are particularly interested in learning to recognize objects that have high likelihood of being present in outdoor scenes. To this end, we select the following 8 categories as our primary set of object classes : [Person, Car, Cyclist, Dog, Tree, House, Skyscraper, and Bridge]. For our formulation, we want the learned features to generalize across different domains. To achieve this, we construct our training dataset of images from multiple sources. We use labeled examples of each class (as well as background images containing none of the classes) taken from the CIFAR-10 [19], CIFAR-100 [19], and MIO-TCD [27] datasets as well as a set of publicly available surveillance videos from static webcams that we collected and annotated. More details about the data collection is given in the supplemental material. In total we used 187,793 RGB training examples, resized to 64x64 pixels." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.44, + 0.469, + 0.637 + ], + "angle": 0, + "content": "Neural Architecture: We use a modified ResNext-50 network [48] as our backbone architecture. We modified the original model by adding an extra fully connected layer that maps the 2048-dimensional feature vector after the average pooling layer to a 128-dimensional layer. The 128-dimensional layer is then mapped by a final fully connected layer to an 8-dimensional output layer with sigmoid activations that represent the categories. The extra fully connected layer gives us a 128-dimensional feature vector to represent appearance instead of the 2048-dimensional feature vector after RexNext-50's usual penultimate layer thus greatly reducing feature size. To train our model, we utilize the Binary Cross Entropy as our loss function." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.637, + 0.469, + 0.743 + ], + "angle": 0, + "content": "Note that high-level features are usually distinctive even for unseen object classes despite the corresponding high-level attribute having low probabilities for all of the known object classes. This allows our appearance model to have unique representations for object classes other than the eight that we train on. See supplemental material for experiments on this." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.756, + 0.231, + 0.77 + ], + "angle": 0, + "content": "3.1.2 Motion Model" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.781, + 0.469, + 0.901 + ], + "angle": 0, + "content": "To characterize the motion information for a given video volume, we train deep networks to estimate the following attributes directly from an RGB video volume: (a) histogram of optical flow \\((Y_{ang})\\), (b) a vector of the average speed of pixels in each direction of motion \\((Y_{speed})\\), (c) background classifier \\((Y_{bkg.cls})\\) and (d) percentage of stationary pixels \\((Y_{bkgpix})\\). The histogram of optical flow consists of 12 bins each of which stores the fraction of pixels" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.212 + ], + "angle": 0, + "content": "in the video volume that are estimated to be moving in one of the 30 degree directions of motion. The average speed vector consists of the average speed (in pixels per frame) of all pixels falling in each of the 12 histogram of flow bins. The background classifier classifies whether the video volume contains motion or not. The percentage of stationary pixels in a video volume gives the rough size of the moving objects in a video volume." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.214, + 0.892, + 0.41 + ], + "angle": 0, + "content": "Motion Training Data: We use the set of surveillance videos mentioned above to learn motion attributes in a self-supervised way. For each video, we sample video volumes from regions with significant 'motion' as well as very little motion ('background'). We identify these regions by computing their pixelwise optical flow fields using the TV-L1 method [50], which is also used to automatically generate ground-truth motion attributes. (Note that optical flow is only used to create ground truth for training our motion models. It is not used in later stages.) In total we obtain 283,486 'background' video volumes and 2,551,376 'motion' video volumes. We use \\(90\\%\\) of these for training our models and the remainder for validation." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.413, + 0.892, + 0.655 + ], + "angle": 0, + "content": "The ground truth motion attributes for each training video volume are computed from the corresponding pixelwise flow fields as follows: We represent the \\( Y_{bkg.cls} \\) attribute as a single binary variable denoting if a video volume is 'background' (\\( Y_{bkg.cls} = 1 \\)) or not (\\( Y_{bkg.cls} = 0 \\)). The ground truth for \\( Y_{ang} \\) and \\( Y_{bkg} \\) are computed by first computing a 13-bin normalized histogram, wherein the first 12 bins represent the number of pixels with flow orientation in the ranges \\( [i * \\pi / 6 : (i + 1) * \\pi / 6) \\) with \\( i \\in [0, 11] \\), while the last bin denotes the number of pixels with flow magnitude below threshold. The histogram is then normalized by the total number of pixels. The first 12 bins of this histogram are used as the ground truth for \\( Y_{ang} \\) and the \\( 13^{th} \\) bin is the ground truth for \\( Y_{bkg} \\). Finally, we represent \\( Y_{mag} \\) as a 12-dimensional vector denoting the average flow magnitude for pixels in each of the 12 flow orientation ranges." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.657, + 0.892, + 0.793 + ], + "angle": 0, + "content": "Learning Task and Neural Architecture: We treat each motion attribute independently and train separate models respectively. For each attribute prediction task, we use the same backbone architecture design, but train each model using different objective functions. Our model is a stack of 3D convolutions (3DConv) with batch normalization (BN) and ReLU. In total we have 3 layers of [3Dconv-BN-ReLU] followed by a fully connected layer. We provide additional details in the supplemental material." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.796, + 0.892, + 0.901 + ], + "angle": 0, + "content": "We formulate \\( Y_{bkg,cls} \\) attribute prediction as a standard binary classification task and train the model using cross-entropy loss function. For \\( Y_{bkg} \\) and \\( Y_{mag} \\) attribute prediction, we treat the learning task as a regression problem and train the model using mean squared error loss. And finally, for training the model to predict \\( Y_{ang} \\) attribute, we utilize KL Divergence loss. For all the tasks, we construct a sim" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "18720" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.122 + ], + "angle": 0, + "content": "ple light-weight CNN. The detailed configuration of our 3D CNN architecture is presented in the supplemental material." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.131, + 0.236, + 0.147 + ], + "angle": 0, + "content": "3.2. Model Building" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.154, + 0.473, + 0.472 + ], + "angle": 0, + "content": "Once trained, the attribute deep nets are used to build a model of any scene given the nominal video. As illustrated in Figure 1, to process each nominal video, we slide a spatio-temporal window of dimension \\([h\\times w\\times t]\\) with spatial stride \\((h / 2,w / 2)\\) and temporal stride of \\(t\\) to construct video volumes. In the experiments, we select \\(h = w\\) and choose \\(h\\) to be roughly the height in pixels of a person in a particular dataset. For each RGB video volume, we extract its features using the previously trained appearance net and four motion nets. To get a single appearance feature vector for a video volume, the feature vectors computed by the appearance network for each frame of the video volume are averaged. We concatenate the feature vectors from the penultimate layers of the appearance, angle, speed and background pixel nets along with the binary output of the background classifier net to create a combined feature vector. We use \\(F\\) to denote a combined feature vector and app, ang, mag, and bkg to denote the appearance, angle, magnitude and background pixel fraction feature vectors, each of size \\(1\\times 128\\). Finally, cls denotes the binary background classification of size \\(1\\times 1\\). \\(F\\) is of size \\(1\\times 513\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.472, + 0.47, + 0.532 + ], + "angle": 0, + "content": "After computing features, we use the exemplar selection approach of [18, 34] to create a region-specific compact model of the nominal data. For each region, we use the following greedy exemplar selection algorithm:" + }, + { + "type": "text", + "bbox": [ + 0.09, + 0.537, + 0.422, + 0.552 + ], + "angle": 0, + "content": "1. Add the first feature vector to the exemplar set." + }, + { + "type": "text", + "bbox": [ + 0.089, + 0.557, + 0.47, + 0.616 + ], + "angle": 0, + "content": "2. For each subsequent feature vector, compute its distance to each feature vector in the exemplar set and add it to the exemplar set only if all distances are above a threshold, \\( th \\)." + }, + { + "type": "list", + "bbox": [ + 0.089, + 0.537, + 0.47, + 0.616 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.623, + 0.473, + 0.819 + ], + "angle": 0, + "content": "To be clear, a separate set of exemplars is selected for each different spatial region in a scene. This allows our model to represent the fact that different object and motions occur in different regions of a scene. To compute the distance between two feature vectors \\( F_{1} = [app_{1}; ang_{1}; mag_{1}; bkg_{1}; cls_{1}] \\) and \\( F_{2} = [app_{2}; ang_{2}; mag_{2}; bkg_{2}; cls_{2}] \\) we use \\( L_{2} \\) distances between corresponding components normalized by a constant to make the maximum distance for each component approximately 1. When a video volume does not contain motion (as determined by the background classification, \\( cls \\)), the motion component vectors are set to 0. The distance function can be written as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.18, + 0.829, + 0.47, + 0.847 + ], + "angle": 0, + "content": "\\[\nd _ {A} \\left(F _ {1}, F _ {2}\\right) = \\left\\| A _ {1} - A _ {2} \\right\\| _ {2} \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.856, + 0.31, + 0.872 + ], + "angle": 0, + "content": "where \\(A\\in \\{app,ang,mag,bkg\\}\\)" + }, + { + "type": "equation", + "bbox": [ + 0.104, + 0.88, + 0.47, + 0.907 + ], + "angle": 0, + "content": "\\[\nd (F _ {1}, F _ {2}) = \\frac {d _ {a p p}}{Z _ {a p p}} + \\frac {d _ {a n g}}{Z _ {a n g}} + \\frac {d _ {b k g}}{Z _ {b k g}} + \\frac {d _ {m a g}}{Z _ {m a g}}. (2)\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.152 + ], + "angle": 0, + "content": "The normalization factors, \\( Z_{app} \\), \\( Z_{ang} \\), \\( Z_{mag} \\) and \\( Z_{bkg} \\) are computed once by finding the max \\( L_{2} \\) distances between a large set of feature vector components computed from a validation set (UCSD Ped1 and Ped2 in our experiments)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.153, + 0.894, + 0.213 + ], + "angle": 0, + "content": "One big advantage of the exemplar learning approach is that updating the exemplar set in a streaming fashion is possible. This makes the approach scalable and adaptable to environmental changes over time." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.223, + 0.686, + 0.238 + ], + "angle": 0, + "content": "3.3. Anomaly Detection" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.247, + 0.895, + 0.489 + ], + "angle": 0, + "content": "At test time, we process each test video in the same way (by sliding a \\([h\\times w\\times t]\\) spatio-temporal window with spatial stride \\((h / 2,w / 2)\\) and temporal stride of \\(t\\)) to generate video volumes. For each video volume, we compute the combined feature vector as before using the pre-trained nets. Each combined feature vector is compared with every exemplar for the corresponding region using the distance function in Equation 2. The anomaly score for the given test video volume is the minimum distance over the set of all exemplars from the same spatial region. A pixelwise anomaly score map is maintained by assigning the anomaly score to all pixels corresponding to every frame of the video volume. If a pixel has already been assigned an anomaly score (because of partially overlapping video volumes), then the maximum of the previous score and the current score is assigned. Figure 1 shows our anomaly detection pipeline." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.498, + 0.816, + 0.515 + ], + "angle": 0, + "content": "3.4. A Note on Computational Efficiency" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.521, + 0.894, + 0.658 + ], + "angle": 0, + "content": "For both model building and anomaly detection, most of the time is spent computing feature vectors (forward passes of 5 networks). This is greatly sped up by testing whether a video volume is the same as the previous video volume in time. If there is no change then the anomaly score for the new video volume should be the same as the one before it and no computation of feature vectors is needed. This allows our method to run at 20 to 100 fps (dataset dependent). Details are in the supplemental material." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.671, + 0.634, + 0.689 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.697, + 0.791, + 0.712 + ], + "angle": 0, + "content": "4.1. Datasets and Evaluation Criteria" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.892, + 0.795 + ], + "angle": 0, + "content": "We experiment on five benchmark datasets: UCSD Ped1 and Ped2 [29], CUHK Avenue [24], Street Scene [33] and ShanghaiTech [26]. We use UCSD Ped1 and Ped2 with modified ground truth for parameter tuning and CUHK Avenue, Street Scene and ShanghaiTech for evaluation." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.795, + 0.892, + 0.856 + ], + "angle": 0, + "content": "UCSD Ped1 & Ped2: UCSD Ped1 dataset contains 34 training videos and 36 test videos while UCSD Ped2 dataset contains 16 training videos and 12 test videos. Anomalies consists of bikers, skaters and cars in a pedestrian area." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.856, + 0.892, + 0.902 + ], + "angle": 0, + "content": "CUHK Avenue: The Avenue [24] dataset contains 16 training videos with normal activity and 21 test videos. Examples of abnormal events in Avenue are related to people run" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "18721" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.432, + 0.106 + ], + "angle": 0, + "content": "ning, throwing objects or walking in wrong direction." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.107, + 0.468, + 0.167 + ], + "angle": 0, + "content": "Street Scene: The Street Scene [33] dataset contains 46 training videos defining the normal events and 35 test videos. Prominent examples of anomalies include jaywalking, loitering and bikes or cars driving outside their lanes." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.168, + 0.468, + 0.243 + ], + "angle": 0, + "content": "ShanghaiTech: The ShanghaiTech [26] dataset is a multiscene benchmark for video anomaly detection. It consists of 330 training and 107 test videos. Major categories of anomalies include people fighting, stealing, chasing, jumping, and riding bikes or skating in pedestrian zones." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.244, + 0.468, + 0.363 + ], + "angle": 0, + "content": "While our primary focus is on single scene video anomaly detection task, we consider the ShanghaiTech dataset only to highlight the ease of usability and robustness of our method to multi-scene benchmarks. Our method is applied to ShanghaiTech without modification even though the location-dependent aspect of our model is not necessary for a multi-scene dataset. Improvements in accuracy are likely if we specialize our model to multi-scene datasets." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.366, + 0.468, + 0.591 + ], + "angle": 0, + "content": "Evaluation Criteria. We use the Region-Based Detection Criterion (RBDC) and the Track-Based Detection Criterion (TBDC) as proposed in [33] for quantitative evaluation of our framework. These criteria correctly measure the accuracy of spatially and temporally localizing anomalous regions (RBDC) and anomalous tracks (TBDC) versus false positive detections per frame. We report the area under the curve (AUC) for false positive rates per frame from 0 to 1 for each of these criteria. As pointed out in [33], frame-AUC [29] is not an appropriate evaluation metric for video anomaly detection methods that spatially localize anomalies. However, we report frame-AUC scores of our method for completeness and comparison with other older methods. We also do not use the pixel-level criterion [29] because of its serious flaws as mentioned in [33]." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.604, + 0.236, + 0.619 + ], + "angle": 0, + "content": "4.2. Implementation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.628, + 0.468, + 0.734 + ], + "angle": 0, + "content": "Feature Learning. To train our appearance model, we use SGD with a 0.001 learning rate and 0.9 momentum and train for 50 epochs. The model with lowest classification error on the validation set is selected. For motion models we optimize with AdamW [23] with a 0.001 learning rate and train for 30 epochs. We select the best model for each attribute using the validation set." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.735, + 0.468, + 0.853 + ], + "angle": 0, + "content": "Video volume parameters. We define the dimensions \\((w, h)\\) of a video volume for each dataset so that \\(h\\) is roughly the height of a person in pixels and \\(w = h\\). Specifically, for Ped1, Ped2, Avenue, Street Scene and ShanghaiTech, our region dimensions are (32, 32), (32, 32), (128, 128), (64, 64) and (100, 100) respectively. Zeropadding was used for edge regions as needed. The number of frames in a video volume, \\(t\\), is 10 for all datasets." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.468, + 0.901 + ], + "angle": 0, + "content": "Parameter Tuning. To set a threshold \\( th \\) for exemplar selection without fitting to test data, a validation data set is needed. We chose Ped1 and Ped2 for this purpose, both" + }, + { + "type": "table", + "bbox": [ + 0.508, + 0.089, + 0.888, + 0.205 + ], + "angle": 0, + "content": "
ThUCSD Ped1UCSD Ped2
RBDCTBDCNUMRBDCTBDCNUM
336.86677.8328864.80889.13350
2.549.3689.4342478.81393.716761
257.52489.694484.6695.971339
1.561.6588.9420187.4495.084470
161.49687.541992687.40895.77619138
0.561.43587.724911387.19595.1234862
0.2561.4987.815763687.19995.12745795
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.215, + 0.892, + 0.258 + ], + "angle": 0, + "content": "Table 1. RBDC and TBDC scores (in %) of our method for different thresholds (th) on UCSD Ped1 and Ped2. NUM denotes the total number of exemplars across all regions." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.274, + 0.892, + 0.635 + ], + "angle": 0, + "content": "because these data sets are performance-saturated, and because previous works [34] have identified inconsistencies in their ground truth. Specifically, ground-truth annotations of Ped1 and Ped2 do not label every location-specific anomaly. To rectify this, we augment the existing ground truth annotations to include all anomalies consistent with Definition 1. This is justified because we are using Ped1 and Ped2 to set our hyperparameters and not to compare against previous methods. Table 1 shows region-based and track-based AUC for different values of the threshold \\( th \\) used for exemplar selection for both Ped1 and Ped2. We see that the accuracy of our method is robust to large variations of \\( th \\). However, larger values of \\( th \\) lead to smaller numbers of exemplars and thus smaller models of the nominal video which is desirable. We select \\( th = 1.5 \\) as a good trade-off between accuracy and model-size. We use this value on all datasets in our experiments. For Ped2, the average number of exemplars selected per region is about 13 (\\( \\approx 0.5\\% \\) of the total number of video volumes in the nominal video). Exemplar selection typically finds tens to sometimes low hundreds of exemplars (for Street Scene) for regions with lots of activity. Regions with very little activity typically have only 1 or 2 exemplars. This leads to very compact models of the nominal video." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.65, + 0.694, + 0.666 + ], + "angle": 0, + "content": "4.3. Quantitative Results" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.675, + 0.892, + 0.9 + ], + "angle": 0, + "content": "Tables 2 and 3 compare our method to other top methods on Avenue, ShanghaiTech and Street Scene. On Avenue, we improve over all previous methods for the region-based detection criterion (RBDC) and are second best for the track-based detection criterion (TBDC). On ShanghaiTech, we improve over the next best method for both RBDC and TBDC by significant margins. For the frame-level criterion which does not measure spatial localization we are in the middle of the pack compared to other recent methods for both Avenue and ShanghaiTech. On the difficult Street Scene dataset (Table 3), we improve the previous state of the art for both RBDC and TBDC, the latter by more than \\(11\\%\\). The good results across five different datasets (including Ped1 and Ped2) show the generality of the high-level features that we use in our models." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "18722" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.085, + 0.089, + 0.465, + 0.271 + ], + "angle": 0, + "content": "
MethodAvenueShanghaiTech
RBDCTBDCFrameRBDCTBDCFrame
Ionescu et al. [16]15.7727.0787.420.6544.5478.7
Ramachandra et al. [33]35.8080.9072.0---
Ramachandra et al. [34]41.2078.6087.2---
Georgescu et al. [12]57.0058.3091.542.8083.9090.02
Liu et al. [21]19.5956.0185.117.0354.2372.8
Liu et al. [22]41.0586.1889.944.4183.8674.2
Georgescu et al. [13]65.0566.8592.341.3478.7982.7
Liu et al. [21] + Ristea et al. [38]20.1362.3087.318.5160.2274.5
Liu et al. [22] + Ristea et al. [38]62.2789.2890.945.4584.5075.5
Georgescu et al. [13] + Ristea et al. [38]65.9964.9192.940.5583.4683.6
Our Method68.287.5686.0259.2189.4476.63
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.281, + 0.47, + 0.337 + ], + "angle": 0, + "content": "Table 2. RRBDC, TBDC and Frame AUC scores (in %) of various state-of-the-art methods on Avenue and ShanghaiTech datasets. The top score for each metric is highlighted in red, while the second best score is in blue." + }, + { + "type": "table", + "bbox": [ + 0.141, + 0.342, + 0.407, + 0.422 + ], + "angle": 0, + "content": "
MethodsRBDCTBDC
Auto-encoder [14]0.292.0
Dictionary method [24]1.610.0
Flow baseline [33]11.052.0
FG Baseline [33]21.053.0
Our Method24.364.5
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.433, + 0.47, + 0.488 + ], + "angle": 0, + "content": "Table 3. RBDC and TBDC AUC scores (in %) of various baseline methods on Street Scene dataset. The top score for each metric is highlighted in red, while the second best score is highlighted in blue." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.512, + 0.38, + 0.529 + ], + "angle": 0, + "content": "4.4. Qualitative Results: Explainability" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.537, + 0.47, + 0.673 + ], + "angle": 0, + "content": "One of the big advantages of our method in addition to its accuracy is that it allows intuitive explanations of what the model has learned and why it labels a particular test video volume as anomalous or not. To visualize the feature vector representing a video volume, the appearance and motion components of the combined feature vector are mapped using the last fully connected layer of the respective network to the high-level appearance and motion attributes. We can then visualize these attributes as illustrated in Figure 2." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.675, + 0.471, + 0.903 + ], + "angle": 0, + "content": "As an illustration of our model's explainability, the top of Figure 3 visualizes the exemplars learned from the nominal video for a spatial region in the middle of the street. Cars travel down and to the right in this lane of the street. The top six exemplars learned show mainly cars (or unknown objects, since video volumes containing only parts of cars are often not classified as cars) traveling down and to the right, as expected. There are also exemplars for stationary background, as well as stationary cars (since occasionally traffic stops on this part of the street). Thus, our learned model is understandable and consistent with what one expects. Furthermore, for a video volume containing a person jaywalking, the visualization in the bottom, left of the figure shows that our networks correctly identify it as containing a person walking mainly to the right at moderate speed. The" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.182 + ], + "angle": 0, + "content": "closest exemplar to this test volume is an unknown object moving down and to the right which yields a high anomaly score of 2.08. (A threshold of 1.8 yields high detection rates with low false positive rates across all the datasets.) Thus, the explanation of this anomaly is that there is an unusual object (person) walking in an unusual direction." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.184, + 0.893, + 0.41 + ], + "angle": 0, + "content": "Another example is shown for Ped2 in Figure 4. Here we analyze a region on the sidewalk. The exemplars learned for this region (shown at the top of Figure 4) are mainly background with very little movement or people moving mainly left or right at slow speeds. Some video volumes containing only parts of people are not classified as people which leads to exemplars of unknown objects moving left or right. Overall, these exemplars are again what we would expect for this region. For the test frame shown, a cyclist is riding on the sidewalk. The visualization of the video volume centered on that frame at that spatial region shows that it was classified as a cyclist traveling down and right at a high speed. These high-level attributes differs from the nearest exemplar in terms of its object class and speed and therefore leads to a high anomaly score." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.411, + 0.893, + 0.653 + ], + "angle": 0, + "content": "As a final illustration (we show more in the supplemental material), we look at an example from CUHK Avenue in Figure 5. The top six exemplars for the region highlighted at the left of the figure show that the model has learned that this region contains either background with very little movement or else people or unknown objects moving mainly left or right slowly. For the anomalous test video volume shown containing a person running to the left, the high-level features estimate an unknown object moving left at high speed. Even though the object recognizer did not correctly predict that the video volume contains a person, the person class is the most likely out of the eight classes. The nearest exemplar is an unknown object (closest to a person class) moving slowly to the left. The main difference between the test video volume and the closest exemplar is the unusual speed which correctly explains this anomaly." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.665, + 0.655, + 0.682 + ], + "angle": 0, + "content": "4.5. Ablation Study" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.689, + 0.892, + 0.901 + ], + "angle": 0, + "content": "We perform an ablation study on all the benchmarks to evaluate the benefit of each attribute in detecting anomalies. We consider features from each model separately, combining features from only motion models and finally our full model which uses all features. We accordingly change the distance function to compare features of two video volumes so that it only uses the provided features. We present our results in Table 4. We see that different attributes can be important for different types of scenarios. However, we get best results across all the benchmarks only when we combine all the motion and appearance features. This highlights the importance of modeling both appearance and different components of motion, especially to be able to predict anomalies under wide variety of scenarios." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "18723" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.127, + 0.094, + 0.395, + 0.146 + ], + "angle": 0, + "content": "Bar graphs of sigmoid outputs for the 8 object classes in the appearance network. \\([0 =\\) person, \\(1 =\\) car, \\(2 =\\) cyclist, \\(3 =\\) dog, \\(4 =\\) tree, \\(5 =\\) house, \\(6 =\\) skyscraper, \\(7 =\\) bridge.] Length of each bar is proportional to the distance of the sigmoid value from 0.5.Values above 0.5 (green) indicate the likely presence of that object class, while values below 0.5 (red) indicate otherwise." + }, + { + "type": "text", + "bbox": [ + 0.127, + 0.156, + 0.391, + 0.191 + ], + "angle": 0, + "content": "Visualization of the direction of motion histogram. For each of the 12 angles estimated by the direction network, the length of the ray in that direction is proportional to the number of pixels (in that video volume) estimated to be moving in that direction." + }, + { + "type": "image", + "bbox": [ + 0.4, + 0.094, + 0.54, + 0.182 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.54, + 0.097, + 0.842, + 0.133 + ], + "angle": 0, + "content": "Bar graph of the output of the network estimating the fraction of stationary pixels. If the bar is all white then it indicates that there was no motion in the video volume. If the bar is all black then every pixel was predicted to be moving." + }, + { + "type": "text", + "bbox": [ + 0.54, + 0.141, + 0.837, + 0.185 + ], + "angle": 0, + "content": "Visualization of the average speed of pixels moving in a particular direction which are estimated by the directional speed network. Each ray is proportional to the speed in a particular direction. It is not proportional to the number of pixels moving in a particular direction as in the case of the angle histogram." + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.205, + 0.892, + 0.233 + ], + "angle": 0, + "content": "Figure 2. Explanation of our \"instrument panel\" showing the estimated attributes for a video volume. The interpretation of this visualization would be (roughly) a car (class 1) taking up most of the video volume, moving right at a high speed." + }, + { + "type": "image", + "bbox": [ + 0.082, + 0.245, + 0.21, + 0.329 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.084, + 0.33, + 0.205, + 0.368 + ], + "angle": 0, + "content": "Frame 1719 of Street Scene Test005. The bounding box indicates a particular spatial region containing a ground truth anomaly (jawwalking)." + }, + { + "type": "image", + "bbox": [ + 0.211, + 0.245, + 0.471, + 0.401 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.413, + 0.47, + 0.456 + ], + "angle": 0, + "content": "Figure 3. Visualization of the learned exemplars for a region of Street Scene and visualization of a test video volume explaining why it was detected as an anomaly." + }, + { + "type": "image", + "bbox": [ + 0.082, + 0.461, + 0.206, + 0.528 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.082, + 0.529, + 0.203, + 0.566 + ], + "angle": 0, + "content": "Frame 119 of UCSD Ped2 Test001. The bounding box indicates a particular spatial region containing a ground truth anomaly (cyclist on sidewalk)." + }, + { + "type": "image", + "bbox": [ + 0.206, + 0.461, + 0.471, + 0.534 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.211, + 0.537, + 0.338, + 0.564 + ], + "angle": 0, + "content": "Attributes for the test video volume centered around the cyclist shown at left." + }, + { + "type": "image", + "bbox": [ + 0.34, + 0.537, + 0.468, + 0.615 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.628, + 0.469, + 0.656 + ], + "angle": 0, + "content": "Figure 4. Visualization example for a region of UCSD Ped2 showing an explanation of the anomaly." + }, + { + "type": "image", + "bbox": [ + 0.082, + 0.66, + 0.212, + 0.721 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.084, + 0.723, + 0.205, + 0.755 + ], + "angle": 0, + "content": "Frame 400 of Avenue Test004. The bounding box indicates a particular spatial region containing a ground truth anomaly (running)." + }, + { + "type": "image", + "bbox": [ + 0.212, + 0.66, + 0.471, + 0.731 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.212, + 0.733, + 0.461, + 0.818 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.831, + 0.47, + 0.859 + ], + "angle": 0, + "content": "Figure 5. Visualization example for a region of CUHK Avenue showing an explanation of the anomaly." + }, + { + "type": "table", + "bbox": [ + 0.505, + 0.244, + 0.89, + 0.359 + ], + "angle": 0, + "content": "
AttributesPed1Ped2AvenueStreet Scene
App29.6 / 64.877.7 / 92.575.6 / 67.41.1 / 4.8
Motion59.2 / 83.781.6 / 93.369.0 / 89.022.6 / 64.1
Angle40.9 / 70.670.8 / 88.166.4 / 89.324.5 / 65.9
Mag60.6 / 90.170.1 / 88.559.5 / 91.116.6 / 50.8
Bkg45.5 / 86.471.7 / 95.249.9 / 81.511.9 / 49.8
App+Mot61.7 / 88.987.4 / 97.169.6 / 86.723.9 / 65.3
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.37, + 0.892, + 0.425 + ], + "angle": 0, + "content": "Table 4. RBDC / TBDC AUC scores (in %) of our method when using only appearance, only motion (using angle, magnitude and background pixel predictions combined), each motion component separately and all the features" + }, + { + "type": "table", + "bbox": [ + 0.514, + 0.439, + 0.88, + 0.492 + ], + "angle": 0, + "content": "
AttributesPed1Ped2
ImageNet25.148 / 44.6364.67 / 83.17
Ours29.6 / 64.877.7 / 92.5
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.502, + 0.892, + 0.544 + ], + "angle": 0, + "content": "Table 5. RBDC / TBDC AUC scores (in %) of our method when using our pre-trained model versus ImageNet pe-trained model as appearance feature extractor." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.552, + 0.892, + 0.689 + ], + "angle": 0, + "content": "We further perform an ablation study on UCSD Ped1 and Ped2 datasets to empirically evaluate the benefit of our appearance model to represent object features versus using ImageNet pre-trained features. For the ImageNet pretrained model, we use the pre-classification layer output of ResNext-50 as features. We present our results in Table 5. The superiority of our model is most likely due to the loss function used (binary cross-entropy) which allows an image patch to contain zero or multiple object classes." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.702, + 0.756, + 0.718 + ], + "angle": 0, + "content": "5. Discussion and Conclusions" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.728, + 0.892, + 0.893 + ], + "angle": 0, + "content": "We have presented a novel method for explainable video anomaly localization that has a number of desired properties. Foremost, the method is accurate and general. We have shown that it works very well on five different datasets and, in particular, achieves state-of-the-art results on CUHK Avenue, Street Scene and ShanghaiTech. Setting it apart from almost all previous work, our model is understandable by humans and the decisions that our method makes are explainable. Finally, because our method does not require an expensive training phase on the nominal data, it is easy to expand our model when new nominal data is available." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "18724" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.115, + 0.47, + 0.156 + ], + "angle": 0, + "content": "[1] Detecting anomalous events in videos by learning deep representations of appearance and motion. Comput. Vis. Image Underst., 156(C):117-127, mar 2017. 2" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.158, + 0.471, + 0.212 + ], + "angle": 0, + "content": "[2] Amit Adam, Ehud Rivlin, Ilan Shimshoni, and Daviv Reinitz. Robust real-time unusual event detection using multiple fixed-location monitors. 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Springer, 2007. 4" + }, + { + "type": "list", + "bbox": [ + 0.503, + 0.093, + 0.892, + 0.711 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.946, + 0.52, + 0.957 + ], + "angle": 0, + "content": "18726" + } + ] +] \ No newline at end of file diff --git a/2023/EVAL_ Explainable Video Anomaly Localization/396d953c-501f-406c-be61-8e06127066d0_origin.pdf b/2023/EVAL_ Explainable Video Anomaly Localization/396d953c-501f-406c-be61-8e06127066d0_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..5ada66a9bdb6cae1a65574eebcb06756b506741f --- /dev/null +++ b/2023/EVAL_ Explainable Video Anomaly Localization/396d953c-501f-406c-be61-8e06127066d0_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:52e836acd5f66b0410c28aa26c05918273685efcb1e223e6cbd7f38cf93e4bc5 +size 1585555 diff --git a/2023/EVAL_ Explainable Video Anomaly Localization/full.md b/2023/EVAL_ Explainable Video Anomaly Localization/full.md new file mode 100644 index 0000000000000000000000000000000000000000..824e578b0d3997386a1fecc501f7de7061033342 --- /dev/null +++ b/2023/EVAL_ Explainable Video Anomaly Localization/full.md @@ -0,0 +1,299 @@ +# EVAL: Explainable Video Anomaly Localization + +Ashish Singh $^{1,2*}$ + +Michael J. Jones $^{2*}$ + +Erik G. Learned-Miller1,2 + +$^{1}$ CICS, University of Massachusetts Amherst + +$^{2}$ Mitsubishi Electric Research Labs + +ashishsingh@cs.umass.edu + +mjones@merl.com + +elm@cs.umass.edu + +# Abstract + +We develop a novel framework for single-scene video anomaly localization that allows for human-understandable reasons for the decisions the system makes. We first learn general representations of objects and their motions (using deep networks) and then use these representations to build a high-level, location-dependent model of any particular scene. This model can be used to detect anomalies in new videos of the same scene. Importantly, our approach is explainable – our high-level appearance and motion features can provide human-understandable reasons for why any part of a video is classified as normal or anomalous. We conduct experiments on standard video anomaly detection datasets (Street Scene, CUHK Avenue, ShanghaiTech and UCSD Ped1, Ped2) and show significant improvements over the previous state-of-the-art. All of our code and extra datasets will be made publicly available. + +# 1. Introduction + +We are interested in the problem of spatio-temporal localization of anomalous activities in videos of a given scene. Informally, anomalous activities are events that differ from those typically observed in a scene, such as a cyclist riding through an indoor shopping mall [35]. Like many other papers on anomaly detection, this work addresses the setting in which we have access to an initial set of videos that are used to define the typical, or 'nominal' activities in a particular scene. Such a situation naturally arises in surveillance and monitoring tasks [41], where it is easy to collect nominal data, but it is not practical to collect a representative set of possible anomalies for a scene. Thus, the problem setup is as follows: provided with a set of videos of a scene which do not contain any anomalies, (called the nominal set), the goal is to detect any events in a test video from the same scene that differ substantially from all events in the nominal set [29, 35]. In defining anomaly detection, it is important to consider the role of location. In real-world + +surveillance scenarios, an event may be normal in one location but anomalous in another. For example, a car driving on a road is typically not anomalous, while one driving on a sidewalk typically is. In view of this, we adopt the following definition [35]. + +Definition 1 An anomaly is any spatio-temporal region of test video that is significantly different from all of the nominal video in the same spatial region. + +Unlike most recent work in anomaly detection, a key goal of our work is to produce not only a set of anomalies, but a simple and clear explanation for what makes them anomalous. We are motivated by how people tasked with watching video from a stationary surveillance camera would detect an unusual incident. While monitoring a scene, we expect a person to note the types of objects seen (people, buildings, cars) and the motions of those objects (walking east or west on a sidewalk, driving northwest on the street) to characterize the given scene. The person could then notice an anomaly when the objects or motions do not match what has been seen before. The person could also explain why something was anomalous. + +We design our video anomaly detection system using this sketch of how a human would solve the problem as motivation. We want to use deep networks to give a high-level understanding of the objects and motions occurring in a scene. By 'high-level', we mean at the level of whole objects and not at the level of pixels or edges. To do this, we train deep networks that take a spatio-temporal region of video (which we call a video volume) as input and output attribute vectors representing the object classes, the directions and speeds of motion and the fraction of stationary pixels (which gives information on the sizes of moving objects) occurring in a spatio-temporal region. The feature vectors from the penultimate layers of these deep networks yield high-level representations, or embeddings, of the appearance and motion content of each video volume. Ten frames are used for video volumes in our experiments. + +Unlike many other recent works, we do not learn new embedding functions (i.e. networks) for new scenes. We use the same embedding networks for every environment. Instead, to characterize the nominal video for a new scene, we store a representative set of all the embeddings found in + +the nominal video. That is, for every video volume in the nominal video of a new scene, we calculate our representations of appearance, motion direction, speed, and background fraction. We then reduce this set of embeddings to a smaller set which we call exemplars by removing redundant embeddings. We select a separate set of exemplars for each spatial region. This results in a compact, accurate, and location-dependent model of the nominal data in a new scene. Since there is no training of deep networks for each new environment, modeling a new environment is 'lightweight' compared to many other methods, making it efficient to model new scenes. Our exemplar model also allows very efficient updating if new nominal video is introduced. This is a crucial property for video anomaly detection methods because, in practice, it is unrealistic to assume that the initial nominal video covers every possible normal change. New nominal video will occasionally need to be added, making it critical that models are easy to extend. + +Given test video of the same scene, we compute our high-level features for each video volume. We then compare these to the exemplars stored in the nominal model at the corresponding spatial region. Any test feature with a high distance to every nominal exemplar for that region is considered anomalous. Because the feature vectors map to human-interpretable attributes, these attributes can be used to give human-understandable explanations for why our system labeled video volumes as normal or anomalous. We define a method as 'explainable' if it can give human-understandable reasons for its decisions. Details of how our system provides explanations are given in Section 4.4. + +In summary, we make the following key contributions: 1) We show that modeling scenes using high-level attributes leads to robust anomaly detection. 2) We introduce the idea of directly estimating high-level motion attributes from raw video volumes using deep networks. 3) We show how these high-level attributes also allow human-interpretable explanations. 4) Finally, we demonstrate an alternative to much of the previous work that is based on learning to reconstruct the nominal data. Our alternative approach is practical since it does not require training deep networks for each new scene and allows for simple and efficient updates to a scene model given new nominal training data. + +# 2. Related Work + +Most Video Anomaly Detection (VAD) methods can be analyzed in terms of their representation learning or their detection method. + +Representation of Nominal Data: Early approaches to VAD [2, 3, 7, 20, 30, 40, 47] primarily relied on the usage of handcrafted features. This included features like spatiotemporal gradients [17, 24], histogram of gradients [28, 40], flow fields [2, 3, 30, 47], histogram of flows [7, 40, 41], dense trajectories [28, 43] and foreground masks [3]. Re + +cently, most authors have used deep learning for this task [1,9,10,14-16,21,26,34,36,37,39,42,45]. These methods either use a pretrained model [15, 17, 26, 36, 39, 42] for feature extraction or train a model to specifically optimize for a particular task related to anomaly detection. These tasks can generally be categorized as either a variant of training an auto-encoder architecture to minimize the reconstruction error of nominal frames [6, 14, 16, 22, 25, 31], a generative adversarial network (GAN) to model nominal frames [21,25], or future frame prediction given a sequence of nominal frames [21,44]. To further improve their performance, recent works have tried specialized architectures and training methodologies. Particularly [8,22,32] transform their respective generative model by memory-based modules to memorize the normal prototypes in the training data. Most recently [38] proposed a module based on masked convolution and channel attention to reconstruct a masked part of the convolutional receptive field. A key drawback of reconstruction and future frame prediction methods is that they do not generate interpretable features. It is not clear what aspects of the video make it difficult to reconstruct since there is no mapping to higher-level features as in our work. Our work mostly aligns with methods utilizing pretrained models. However, unlike most of these approaches, we incorporate the output of our pretrained models to interpret model decisions. We additionally make sure that the predictions of our model generalize to a wide variety of scenes through our data generation and training procedures. One high-level motion attribute that our method learns is similar to the histogram of flow feature used in some early work [7,40,41]. However, instead of computing the histogram of flow from an optical flow field, our method learns a deep network to predict these features directly from RGB video volumes and then uses the network's learned feature embedding as the representation. + +Detection Methods: Most methods use either standard outlier detection methods [5] as an external module or utilize the reconstruction strategy to predict anomalies. General methods of detection that most authors have used in the past include one-class SVM [17, 28, 42, 49], nearest neighbour approaches [9, 11, 15, 33, 34], and Probabilistic Graphical Models [3]. In [4, 13], pseudo-anomalous samples are used during training to improve discriminative learning. In [12], an object detector is used to focus on regions around objects and then networks are trained for various 'proxy' tasks (such as predicting the arrow of time) on the nominal data. Thus, unlike our work, they require training deep nework models for each different scene. Our work has some similarity to the work of [33, 34] in that we also use an overlapping grid of spatial regions, build exemplar-based models and use nearest neighbors distances as anomaly scores. The high-level features that we use are the biggest difference as compared to the pixel-based features used in their + +![](images/a4b7bed804a7344578c2dde4a82da114f4cf052661f729bec81fda0a764d12fa.jpg) +Figure 1. Our pipeline for building a location-dependent model of nominal video and detecting anomalies in test video. During the model building phase, we extract a high-level representation of each video volume using our appearance and motion networks. Using the exemplar selection method, we select a representative subset of video volumes for a given spatial region. By comparing video volumes in test video to the exemplar set we can detect anomalies. + +work. Our high-level features allow for explainable models as well as much smaller models than theirs. + +Explainable VAD: Our work is similar in spirit to the work of [15,46] with respect to providing explanations for detecting anomalies. In [15], the authors pre-train their feature extractor on public image datasets (MS-COCO and Visual Genome) to detect objects and predict their attributes and actions. They further use these predictions for 'event recounting' on VAD benchmarks. In [46], the authors utilize models pretrained for semantic segmentation, object classification, and multi-object tracking and use the output of these models directly as their feature representation. + +Despite these coarse similarities, virtually all of the details of our methods are different. Specifically, in [15], they rely on object proposals to find candidate anomalous regions which can lead to missed detections for objects not represented in their training data. Our action/motion classes are also very different - ours being more generic (direction distributions and speed of motion) while in [15] are much more specific (bending, riding) and hence not applicable to a wide variety of scenarios. The method of [46] is specific to detecting and tracking pedestrians and is not a general video anomaly detection method. Furthermore, unlike ours, their method does not spatially localize anomalies. + +# 3. Our Approach + +Our method consists of three distinct stages: high-level attribute learning, model building, and anomaly localization. The high-level attribute learning stage is done only once and uses training samples that are independent of any + +video anomaly detection dataset. The resulting deep networks learn general representations of object appearances and object motions which can then be used in the subsequent two stages to build a model of a specific scene and to localize anomalies in that scene, for a wide variety of surveillance scenarios. The outside data used to train our high-level attribute models are equivalent to the outside data used in various prior works on VAD; for example, the M-OCOCO and Visual Genome data used to train the models of Hinami et al. [15], the outside data used to train object detectors in [11, 12, 17, 42], as well as the many deep models pretrained on ImageNet and applied to VAD. Our outside data is not used to build models of a scene. + +# 3.1. High-Level Attribute Learning + +For this stage, our main objective is to learn features that are (a) transferable across scenes and (b) interpretable. Given this motivation, we learn an object recognizer for our appearance model as well as regression networks for estimating the following motion attributes for a given video volume: the fraction of stationary pixels, the distribution of motion directions and the average speed of movement in each direction. We also learn a classifier to indicate whether a video volume is stationary or not. We will describe each of these deep networks in the following subsections. + +To clarify our terminology, we use the term 'high-level attribute' to denote the object classes, histogram of motion directions, vector of motion speeds or fraction of stationary pixels which are the final outputs of the various deep networks that are learned. The term 'high-level feature' denotes the feature vector from the penultimate layer of one of + +the deep networks. A high-level feature can be mapped to a high-level attribute using the final layer of that network. + +# 3.1.1 Appearance model + +We formulate the task of object recognition as a multi-label image classification problem as any given input image patch may contain more than one object class (or none). + +Training Data: We are particularly interested in learning to recognize objects that have high likelihood of being present in outdoor scenes. To this end, we select the following 8 categories as our primary set of object classes : [Person, Car, Cyclist, Dog, Tree, House, Skyscraper, and Bridge]. For our formulation, we want the learned features to generalize across different domains. To achieve this, we construct our training dataset of images from multiple sources. We use labeled examples of each class (as well as background images containing none of the classes) taken from the CIFAR-10 [19], CIFAR-100 [19], and MIO-TCD [27] datasets as well as a set of publicly available surveillance videos from static webcams that we collected and annotated. More details about the data collection is given in the supplemental material. In total we used 187,793 RGB training examples, resized to 64x64 pixels. + +Neural Architecture: We use a modified ResNext-50 network [48] as our backbone architecture. We modified the original model by adding an extra fully connected layer that maps the 2048-dimensional feature vector after the average pooling layer to a 128-dimensional layer. The 128-dimensional layer is then mapped by a final fully connected layer to an 8-dimensional output layer with sigmoid activations that represent the categories. The extra fully connected layer gives us a 128-dimensional feature vector to represent appearance instead of the 2048-dimensional feature vector after RexNext-50's usual penultimate layer thus greatly reducing feature size. To train our model, we utilize the Binary Cross Entropy as our loss function. + +Note that high-level features are usually distinctive even for unseen object classes despite the corresponding high-level attribute having low probabilities for all of the known object classes. This allows our appearance model to have unique representations for object classes other than the eight that we train on. See supplemental material for experiments on this. + +# 3.1.2 Motion Model + +To characterize the motion information for a given video volume, we train deep networks to estimate the following attributes directly from an RGB video volume: (a) histogram of optical flow $(Y_{ang})$ , (b) a vector of the average speed of pixels in each direction of motion $(Y_{speed})$ , (c) background classifier $(Y_{bkg.cls})$ and (d) percentage of stationary pixels $(Y_{bkgpix})$ . The histogram of optical flow consists of 12 bins each of which stores the fraction of pixels + +in the video volume that are estimated to be moving in one of the 30 degree directions of motion. The average speed vector consists of the average speed (in pixels per frame) of all pixels falling in each of the 12 histogram of flow bins. The background classifier classifies whether the video volume contains motion or not. The percentage of stationary pixels in a video volume gives the rough size of the moving objects in a video volume. + +Motion Training Data: We use the set of surveillance videos mentioned above to learn motion attributes in a self-supervised way. For each video, we sample video volumes from regions with significant 'motion' as well as very little motion ('background'). We identify these regions by computing their pixelwise optical flow fields using the TV-L1 method [50], which is also used to automatically generate ground-truth motion attributes. (Note that optical flow is only used to create ground truth for training our motion models. It is not used in later stages.) In total we obtain 283,486 'background' video volumes and 2,551,376 'motion' video volumes. We use $90\%$ of these for training our models and the remainder for validation. + +The ground truth motion attributes for each training video volume are computed from the corresponding pixelwise flow fields as follows: We represent the $Y_{bkg.cls}$ attribute as a single binary variable denoting if a video volume is 'background' ( $Y_{bkg.cls} = 1$ ) or not ( $Y_{bkg.cls} = 0$ ). The ground truth for $Y_{ang}$ and $Y_{bkg}$ are computed by first computing a 13-bin normalized histogram, wherein the first 12 bins represent the number of pixels with flow orientation in the ranges $[i * \pi / 6 : (i + 1) * \pi / 6)$ with $i \in [0, 11]$ , while the last bin denotes the number of pixels with flow magnitude below threshold. The histogram is then normalized by the total number of pixels. The first 12 bins of this histogram are used as the ground truth for $Y_{ang}$ and the $13^{th}$ bin is the ground truth for $Y_{bkg}$ . Finally, we represent $Y_{mag}$ as a 12-dimensional vector denoting the average flow magnitude for pixels in each of the 12 flow orientation ranges. + +Learning Task and Neural Architecture: We treat each motion attribute independently and train separate models respectively. For each attribute prediction task, we use the same backbone architecture design, but train each model using different objective functions. Our model is a stack of 3D convolutions (3DConv) with batch normalization (BN) and ReLU. In total we have 3 layers of [3Dconv-BN-ReLU] followed by a fully connected layer. We provide additional details in the supplemental material. + +We formulate $Y_{bkg,cls}$ attribute prediction as a standard binary classification task and train the model using cross-entropy loss function. For $Y_{bkg}$ and $Y_{mag}$ attribute prediction, we treat the learning task as a regression problem and train the model using mean squared error loss. And finally, for training the model to predict $Y_{ang}$ attribute, we utilize KL Divergence loss. For all the tasks, we construct a sim + +ple light-weight CNN. The detailed configuration of our 3D CNN architecture is presented in the supplemental material. + +# 3.2. Model Building + +Once trained, the attribute deep nets are used to build a model of any scene given the nominal video. As illustrated in Figure 1, to process each nominal video, we slide a spatio-temporal window of dimension $[h\times w\times t]$ with spatial stride $(h / 2,w / 2)$ and temporal stride of $t$ to construct video volumes. In the experiments, we select $h = w$ and choose $h$ to be roughly the height in pixels of a person in a particular dataset. For each RGB video volume, we extract its features using the previously trained appearance net and four motion nets. To get a single appearance feature vector for a video volume, the feature vectors computed by the appearance network for each frame of the video volume are averaged. We concatenate the feature vectors from the penultimate layers of the appearance, angle, speed and background pixel nets along with the binary output of the background classifier net to create a combined feature vector. We use $F$ to denote a combined feature vector and app, ang, mag, and bkg to denote the appearance, angle, magnitude and background pixel fraction feature vectors, each of size $1\times 128$ . Finally, cls denotes the binary background classification of size $1\times 1$ . $F$ is of size $1\times 513$ . + +After computing features, we use the exemplar selection approach of [18, 34] to create a region-specific compact model of the nominal data. For each region, we use the following greedy exemplar selection algorithm: + +1. Add the first feature vector to the exemplar set. +2. For each subsequent feature vector, compute its distance to each feature vector in the exemplar set and add it to the exemplar set only if all distances are above a threshold, $th$ . + +To be clear, a separate set of exemplars is selected for each different spatial region in a scene. This allows our model to represent the fact that different object and motions occur in different regions of a scene. To compute the distance between two feature vectors $F_{1} = [app_{1}; ang_{1}; mag_{1}; bkg_{1}; cls_{1}]$ and $F_{2} = [app_{2}; ang_{2}; mag_{2}; bkg_{2}; cls_{2}]$ we use $L_{2}$ distances between corresponding components normalized by a constant to make the maximum distance for each component approximately 1. When a video volume does not contain motion (as determined by the background classification, $cls$ ), the motion component vectors are set to 0. The distance function can be written as follows: + +$$ +d _ {A} \left(F _ {1}, F _ {2}\right) = \left\| A _ {1} - A _ {2} \right\| _ {2} \tag {1} +$$ + +where $A\in \{app,ang,mag,bkg\}$ + +$$ +d (F _ {1}, F _ {2}) = \frac {d _ {a p p}}{Z _ {a p p}} + \frac {d _ {a n g}}{Z _ {a n g}} + \frac {d _ {b k g}}{Z _ {b k g}} + \frac {d _ {m a g}}{Z _ {m a g}}. (2) +$$ + +The normalization factors, $Z_{app}$ , $Z_{ang}$ , $Z_{mag}$ and $Z_{bkg}$ are computed once by finding the max $L_{2}$ distances between a large set of feature vector components computed from a validation set (UCSD Ped1 and Ped2 in our experiments). + +One big advantage of the exemplar learning approach is that updating the exemplar set in a streaming fashion is possible. This makes the approach scalable and adaptable to environmental changes over time. + +# 3.3. Anomaly Detection + +At test time, we process each test video in the same way (by sliding a $[h\times w\times t]$ spatio-temporal window with spatial stride $(h / 2,w / 2)$ and temporal stride of $t$ ) to generate video volumes. For each video volume, we compute the combined feature vector as before using the pre-trained nets. Each combined feature vector is compared with every exemplar for the corresponding region using the distance function in Equation 2. The anomaly score for the given test video volume is the minimum distance over the set of all exemplars from the same spatial region. A pixelwise anomaly score map is maintained by assigning the anomaly score to all pixels corresponding to every frame of the video volume. If a pixel has already been assigned an anomaly score (because of partially overlapping video volumes), then the maximum of the previous score and the current score is assigned. Figure 1 shows our anomaly detection pipeline. + +# 3.4. A Note on Computational Efficiency + +For both model building and anomaly detection, most of the time is spent computing feature vectors (forward passes of 5 networks). This is greatly sped up by testing whether a video volume is the same as the previous video volume in time. If there is no change then the anomaly score for the new video volume should be the same as the one before it and no computation of feature vectors is needed. This allows our method to run at 20 to 100 fps (dataset dependent). Details are in the supplemental material. + +# 4. Experiments + +# 4.1. Datasets and Evaluation Criteria + +We experiment on five benchmark datasets: UCSD Ped1 and Ped2 [29], CUHK Avenue [24], Street Scene [33] and ShanghaiTech [26]. We use UCSD Ped1 and Ped2 with modified ground truth for parameter tuning and CUHK Avenue, Street Scene and ShanghaiTech for evaluation. + +UCSD Ped1 & Ped2: UCSD Ped1 dataset contains 34 training videos and 36 test videos while UCSD Ped2 dataset contains 16 training videos and 12 test videos. Anomalies consists of bikers, skaters and cars in a pedestrian area. + +CUHK Avenue: The Avenue [24] dataset contains 16 training videos with normal activity and 21 test videos. Examples of abnormal events in Avenue are related to people run + +ning, throwing objects or walking in wrong direction. + +Street Scene: The Street Scene [33] dataset contains 46 training videos defining the normal events and 35 test videos. Prominent examples of anomalies include jaywalking, loitering and bikes or cars driving outside their lanes. + +ShanghaiTech: The ShanghaiTech [26] dataset is a multiscene benchmark for video anomaly detection. It consists of 330 training and 107 test videos. Major categories of anomalies include people fighting, stealing, chasing, jumping, and riding bikes or skating in pedestrian zones. + +While our primary focus is on single scene video anomaly detection task, we consider the ShanghaiTech dataset only to highlight the ease of usability and robustness of our method to multi-scene benchmarks. Our method is applied to ShanghaiTech without modification even though the location-dependent aspect of our model is not necessary for a multi-scene dataset. Improvements in accuracy are likely if we specialize our model to multi-scene datasets. + +Evaluation Criteria. We use the Region-Based Detection Criterion (RBDC) and the Track-Based Detection Criterion (TBDC) as proposed in [33] for quantitative evaluation of our framework. These criteria correctly measure the accuracy of spatially and temporally localizing anomalous regions (RBDC) and anomalous tracks (TBDC) versus false positive detections per frame. We report the area under the curve (AUC) for false positive rates per frame from 0 to 1 for each of these criteria. As pointed out in [33], frame-AUC [29] is not an appropriate evaluation metric for video anomaly detection methods that spatially localize anomalies. However, we report frame-AUC scores of our method for completeness and comparison with other older methods. We also do not use the pixel-level criterion [29] because of its serious flaws as mentioned in [33]. + +# 4.2. Implementation + +Feature Learning. To train our appearance model, we use SGD with a 0.001 learning rate and 0.9 momentum and train for 50 epochs. The model with lowest classification error on the validation set is selected. For motion models we optimize with AdamW [23] with a 0.001 learning rate and train for 30 epochs. We select the best model for each attribute using the validation set. + +Video volume parameters. We define the dimensions $(w, h)$ of a video volume for each dataset so that $h$ is roughly the height of a person in pixels and $w = h$ . Specifically, for Ped1, Ped2, Avenue, Street Scene and ShanghaiTech, our region dimensions are (32, 32), (32, 32), (128, 128), (64, 64) and (100, 100) respectively. Zeropadding was used for edge regions as needed. The number of frames in a video volume, $t$ , is 10 for all datasets. + +Parameter Tuning. To set a threshold $th$ for exemplar selection without fitting to test data, a validation data set is needed. We chose Ped1 and Ped2 for this purpose, both + +
ThUCSD Ped1UCSD Ped2
RBDCTBDCNUMRBDCTBDCNUM
336.86677.8328864.80889.13350
2.549.3689.4342478.81393.716761
257.52489.694484.6695.971339
1.561.6588.9420187.4495.084470
161.49687.541992687.40895.77619138
0.561.43587.724911387.19595.1234862
0.2561.4987.815763687.19995.12745795
+ +Table 1. RBDC and TBDC scores (in %) of our method for different thresholds (th) on UCSD Ped1 and Ped2. NUM denotes the total number of exemplars across all regions. + +because these data sets are performance-saturated, and because previous works [34] have identified inconsistencies in their ground truth. Specifically, ground-truth annotations of Ped1 and Ped2 do not label every location-specific anomaly. To rectify this, we augment the existing ground truth annotations to include all anomalies consistent with Definition 1. This is justified because we are using Ped1 and Ped2 to set our hyperparameters and not to compare against previous methods. Table 1 shows region-based and track-based AUC for different values of the threshold $th$ used for exemplar selection for both Ped1 and Ped2. We see that the accuracy of our method is robust to large variations of $th$ . However, larger values of $th$ lead to smaller numbers of exemplars and thus smaller models of the nominal video which is desirable. We select $th = 1.5$ as a good trade-off between accuracy and model-size. We use this value on all datasets in our experiments. For Ped2, the average number of exemplars selected per region is about 13 ( $\approx 0.5\%$ of the total number of video volumes in the nominal video). Exemplar selection typically finds tens to sometimes low hundreds of exemplars (for Street Scene) for regions with lots of activity. Regions with very little activity typically have only 1 or 2 exemplars. This leads to very compact models of the nominal video. + +# 4.3. Quantitative Results + +Tables 2 and 3 compare our method to other top methods on Avenue, ShanghaiTech and Street Scene. On Avenue, we improve over all previous methods for the region-based detection criterion (RBDC) and are second best for the track-based detection criterion (TBDC). On ShanghaiTech, we improve over the next best method for both RBDC and TBDC by significant margins. For the frame-level criterion which does not measure spatial localization we are in the middle of the pack compared to other recent methods for both Avenue and ShanghaiTech. On the difficult Street Scene dataset (Table 3), we improve the previous state of the art for both RBDC and TBDC, the latter by more than $11\%$ . The good results across five different datasets (including Ped1 and Ped2) show the generality of the high-level features that we use in our models. + +
MethodAvenueShanghaiTech
RBDCTBDCFrameRBDCTBDCFrame
Ionescu et al. [16]15.7727.0787.420.6544.5478.7
Ramachandra et al. [33]35.8080.9072.0---
Ramachandra et al. [34]41.2078.6087.2---
Georgescu et al. [12]57.0058.3091.542.8083.9090.02
Liu et al. [21]19.5956.0185.117.0354.2372.8
Liu et al. [22]41.0586.1889.944.4183.8674.2
Georgescu et al. [13]65.0566.8592.341.3478.7982.7
Liu et al. [21] + Ristea et al. [38]20.1362.3087.318.5160.2274.5
Liu et al. [22] + Ristea et al. [38]62.2789.2890.945.4584.5075.5
Georgescu et al. [13] + Ristea et al. [38]65.9964.9192.940.5583.4683.6
Our Method68.287.5686.0259.2189.4476.63
+ +Table 2. RRBDC, TBDC and Frame AUC scores (in %) of various state-of-the-art methods on Avenue and ShanghaiTech datasets. The top score for each metric is highlighted in red, while the second best score is in blue. + +
MethodsRBDCTBDC
Auto-encoder [14]0.292.0
Dictionary method [24]1.610.0
Flow baseline [33]11.052.0
FG Baseline [33]21.053.0
Our Method24.364.5
+ +Table 3. RBDC and TBDC AUC scores (in %) of various baseline methods on Street Scene dataset. The top score for each metric is highlighted in red, while the second best score is highlighted in blue. + +# 4.4. Qualitative Results: Explainability + +One of the big advantages of our method in addition to its accuracy is that it allows intuitive explanations of what the model has learned and why it labels a particular test video volume as anomalous or not. To visualize the feature vector representing a video volume, the appearance and motion components of the combined feature vector are mapped using the last fully connected layer of the respective network to the high-level appearance and motion attributes. We can then visualize these attributes as illustrated in Figure 2. + +As an illustration of our model's explainability, the top of Figure 3 visualizes the exemplars learned from the nominal video for a spatial region in the middle of the street. Cars travel down and to the right in this lane of the street. The top six exemplars learned show mainly cars (or unknown objects, since video volumes containing only parts of cars are often not classified as cars) traveling down and to the right, as expected. There are also exemplars for stationary background, as well as stationary cars (since occasionally traffic stops on this part of the street). Thus, our learned model is understandable and consistent with what one expects. Furthermore, for a video volume containing a person jaywalking, the visualization in the bottom, left of the figure shows that our networks correctly identify it as containing a person walking mainly to the right at moderate speed. The + +closest exemplar to this test volume is an unknown object moving down and to the right which yields a high anomaly score of 2.08. (A threshold of 1.8 yields high detection rates with low false positive rates across all the datasets.) Thus, the explanation of this anomaly is that there is an unusual object (person) walking in an unusual direction. + +Another example is shown for Ped2 in Figure 4. Here we analyze a region on the sidewalk. The exemplars learned for this region (shown at the top of Figure 4) are mainly background with very little movement or people moving mainly left or right at slow speeds. Some video volumes containing only parts of people are not classified as people which leads to exemplars of unknown objects moving left or right. Overall, these exemplars are again what we would expect for this region. For the test frame shown, a cyclist is riding on the sidewalk. The visualization of the video volume centered on that frame at that spatial region shows that it was classified as a cyclist traveling down and right at a high speed. These high-level attributes differs from the nearest exemplar in terms of its object class and speed and therefore leads to a high anomaly score. + +As a final illustration (we show more in the supplemental material), we look at an example from CUHK Avenue in Figure 5. The top six exemplars for the region highlighted at the left of the figure show that the model has learned that this region contains either background with very little movement or else people or unknown objects moving mainly left or right slowly. For the anomalous test video volume shown containing a person running to the left, the high-level features estimate an unknown object moving left at high speed. Even though the object recognizer did not correctly predict that the video volume contains a person, the person class is the most likely out of the eight classes. The nearest exemplar is an unknown object (closest to a person class) moving slowly to the left. The main difference between the test video volume and the closest exemplar is the unusual speed which correctly explains this anomaly. + +# 4.5. Ablation Study + +We perform an ablation study on all the benchmarks to evaluate the benefit of each attribute in detecting anomalies. We consider features from each model separately, combining features from only motion models and finally our full model which uses all features. We accordingly change the distance function to compare features of two video volumes so that it only uses the provided features. We present our results in Table 4. We see that different attributes can be important for different types of scenarios. However, we get best results across all the benchmarks only when we combine all the motion and appearance features. This highlights the importance of modeling both appearance and different components of motion, especially to be able to predict anomalies under wide variety of scenarios. + +Bar graphs of sigmoid outputs for the 8 object classes in the appearance network. $[0 =$ person, $1 =$ car, $2 =$ cyclist, $3 =$ dog, $4 =$ tree, $5 =$ house, $6 =$ skyscraper, $7 =$ bridge.] Length of each bar is proportional to the distance of the sigmoid value from 0.5.Values above 0.5 (green) indicate the likely presence of that object class, while values below 0.5 (red) indicate otherwise. + +Visualization of the direction of motion histogram. For each of the 12 angles estimated by the direction network, the length of the ray in that direction is proportional to the number of pixels (in that video volume) estimated to be moving in that direction. + +![](images/b6d30256665e11b68ff1be4b87be6af328f9771e77eafef96adb99490e25c395.jpg) + +Bar graph of the output of the network estimating the fraction of stationary pixels. If the bar is all white then it indicates that there was no motion in the video volume. If the bar is all black then every pixel was predicted to be moving. + +Visualization of the average speed of pixels moving in a particular direction which are estimated by the directional speed network. Each ray is proportional to the speed in a particular direction. It is not proportional to the number of pixels moving in a particular direction as in the case of the angle histogram. + +![](images/f6773b2dab33d298809686d909c8f010d87b79d12990edf423f223a6dc2d3b1d.jpg) +Figure 2. Explanation of our "instrument panel" showing the estimated attributes for a video volume. The interpretation of this visualization would be (roughly) a car (class 1) taking up most of the video volume, moving right at a high speed. +Frame 1719 of Street Scene Test005. The bounding box indicates a particular spatial region containing a ground truth anomaly (jawwalking). + +![](images/06a052f87bc65bef1cd3269436f880d023b9058f79b16871036f12d851eb1262.jpg) + +![](images/d546ba1a42ab5b043b287836e081e4819b36f67e86beb86ecc6cc8aa08cab94d.jpg) +Figure 3. Visualization of the learned exemplars for a region of Street Scene and visualization of a test video volume explaining why it was detected as an anomaly. +Frame 119 of UCSD Ped2 Test001. The bounding box indicates a particular spatial region containing a ground truth anomaly (cyclist on sidewalk). + +![](images/7907fd9fe77160be63a2cd16f0c3fcb82afc16764f0f94ba0f8ef400236173e5.jpg) + +![](images/7db7751ff3424ef39d554282c61f95622a50d789939f2ce0021e0bf1b6a5bc14.jpg) +Attributes for the test video volume centered around the cyclist shown at left. + +![](images/151ba021317951f04c1d4eb150e0c2a8184751ee5166e5db332d8e05c94a8a97.jpg) +Figure 4. Visualization example for a region of UCSD Ped2 showing an explanation of the anomaly. +Frame 400 of Avenue Test004. The bounding box indicates a particular spatial region containing a ground truth anomaly (running). + +![](images/7edeaa65695e5e5a288935036b7f50c892168f9754ed07aa3d6bb2d3852918d4.jpg) + +![](images/1ba8a742beaa4c69385c929fdb41e5b270655e7a9599bc58892d4225cbe97d53.jpg) +Figure 5. Visualization example for a region of CUHK Avenue showing an explanation of the anomaly. + +
AttributesPed1Ped2AvenueStreet Scene
App29.6 / 64.877.7 / 92.575.6 / 67.41.1 / 4.8
Motion59.2 / 83.781.6 / 93.369.0 / 89.022.6 / 64.1
Angle40.9 / 70.670.8 / 88.166.4 / 89.324.5 / 65.9
Mag60.6 / 90.170.1 / 88.559.5 / 91.116.6 / 50.8
Bkg45.5 / 86.471.7 / 95.249.9 / 81.511.9 / 49.8
App+Mot61.7 / 88.987.4 / 97.169.6 / 86.723.9 / 65.3
+ +Table 4. RBDC / TBDC AUC scores (in %) of our method when using only appearance, only motion (using angle, magnitude and background pixel predictions combined), each motion component separately and all the features + +
AttributesPed1Ped2
ImageNet25.148 / 44.6364.67 / 83.17
Ours29.6 / 64.877.7 / 92.5
+ +Table 5. RBDC / TBDC AUC scores (in %) of our method when using our pre-trained model versus ImageNet pe-trained model as appearance feature extractor. + +We further perform an ablation study on UCSD Ped1 and Ped2 datasets to empirically evaluate the benefit of our appearance model to represent object features versus using ImageNet pre-trained features. For the ImageNet pretrained model, we use the pre-classification layer output of ResNext-50 as features. We present our results in Table 5. The superiority of our model is most likely due to the loss function used (binary cross-entropy) which allows an image patch to contain zero or multiple object classes. + +# 5. Discussion and Conclusions + +We have presented a novel method for explainable video anomaly localization that has a number of desired properties. Foremost, the method is accurate and general. We have shown that it works very well on five different datasets and, in particular, achieves state-of-the-art results on CUHK Avenue, Street Scene and ShanghaiTech. Setting it apart from almost all previous work, our model is understandable by humans and the decisions that our method makes are explainable. Finally, because our method does not require an expensive training phase on the nominal data, it is easy to expand our model when new nominal data is available. + +# References + +[1] Detecting anomalous events in videos by learning deep representations of appearance and motion. Comput. Vis. Image Underst., 156(C):117-127, mar 2017. 2 +[2] Amit Adam, Ehud Rivlin, Ilan Shimshoni, and Daviv Reinitz. Robust real-time unusual event detection using multiple fixed-location monitors. IEEE transactions on pattern analysis and machine intelligence, 30(3):555-560, 2008. 2 +[3] Borislav Antić and Björn Ommer. Video parsing for abnormality detection. 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We first learn general representations of objects and their motions (using deep networks) and then use these representations to build a high-level, location-dependent model of any particular scene. This model can be used to detect anomalies in new videos of the same scene. Importantly, our approach is explainable – our high-level appearance and motion features can provide human-understandable reasons for why any part of a video is classified as normal or anomalous. We conduct experiments on standard video anomaly detection datasets (Street Scene, CUHK Avenue, ShanghaiTech and UCSD Ped1, Ped2) and show significant improvements over the previous state-of-the-art. All of our code and extra datasets will be made publicly available." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 47, + 456, + 128, + 468 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 456, + 128, + 468 + ], + "spans": [ + { + "bbox": [ + 47, + 456, + 128, + 468 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 46, + 476, + 288, + 693 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 476, + 288, + 693 + ], + "spans": [ + { + "bbox": [ + 46, + 476, + 288, + 693 + ], + "type": "text", + "content": "We are interested in the problem of spatio-temporal localization of anomalous activities in videos of a given scene. Informally, anomalous activities are events that differ from those typically observed in a scene, such as a cyclist riding through an indoor shopping mall [35]. Like many other papers on anomaly detection, this work addresses the setting in which we have access to an initial set of videos that are used to define the typical, or 'nominal' activities in a particular scene. Such a situation naturally arises in surveillance and monitoring tasks [41], where it is easy to collect nominal data, but it is not practical to collect a representative set of possible anomalies for a scene. Thus, the problem setup is as follows: provided with a set of videos of a scene which do not contain any anomalies, (called the nominal set), the goal is to detect any events in a test video from the same scene that differ substantially from all events in the nominal set [29, 35]. In defining anomaly detection, it is important to consider the role of location. In real-world" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 213, + 547, + 274 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 213, + 547, + 274 + ], + "spans": [ + { + "bbox": [ + 304, + 213, + 547, + 274 + ], + "type": "text", + "content": "surveillance scenarios, an event may be normal in one location but anomalous in another. For example, a car driving on a road is typically not anomalous, while one driving on a sidewalk typically is. In view of this, we adopt the following definition [35]." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 274, + 547, + 308 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 274, + 547, + 308 + ], + "spans": [ + { + "bbox": [ + 304, + 274, + 547, + 308 + ], + "type": "text", + "content": "Definition 1 An anomaly is any spatio-temporal region of test video that is significantly different from all of the nominal video in the same spatial region." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 308, + 548, + 462 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 308, + 548, + 462 + ], + "spans": [ + { + "bbox": [ + 304, + 308, + 548, + 462 + ], + "type": "text", + "content": "Unlike most recent work in anomaly detection, a key goal of our work is to produce not only a set of anomalies, but a simple and clear explanation for what makes them anomalous. We are motivated by how people tasked with watching video from a stationary surveillance camera would detect an unusual incident. While monitoring a scene, we expect a person to note the types of objects seen (people, buildings, cars) and the motions of those objects (walking east or west on a sidewalk, driving northwest on the street) to characterize the given scene. The person could then notice an anomaly when the objects or motions do not match what has been seen before. The person could also explain why something was anomalous." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 463, + 548, + 653 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 463, + 548, + 653 + ], + "spans": [ + { + "bbox": [ + 304, + 463, + 548, + 653 + ], + "type": "text", + "content": "We design our video anomaly detection system using this sketch of how a human would solve the problem as motivation. We want to use deep networks to give a high-level understanding of the objects and motions occurring in a scene. By 'high-level', we mean at the level of whole objects and not at the level of pixels or edges. To do this, we train deep networks that take a spatio-temporal region of video (which we call a video volume) as input and output attribute vectors representing the object classes, the directions and speeds of motion and the fraction of stationary pixels (which gives information on the sizes of moving objects) occurring in a spatio-temporal region. The feature vectors from the penultimate layers of these deep networks yield high-level representations, or embeddings, of the appearance and motion content of each video volume. Ten frames are used for video volumes in our experiments." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 654, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 654, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 654, + 547, + 715 + ], + "type": "text", + "content": "Unlike many other recent works, we do not learn new embedding functions (i.e. networks) for new scenes. We use the same embedding networks for every environment. Instead, to characterize the nominal video for a new scene, we store a representative set of all the embeddings found in" + } + ] + } + ], + "index": 19 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 703, + 123, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 703, + 123, + 712 + ], + "spans": [ + { + "bbox": [ + 58, + 703, + 123, + 712 + ], + "type": "text", + "content": "*equal contribution" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "18717" + } + ] + } + ], + "index": 21 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 288 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 288 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 288 + ], + "type": "text", + "content": "the nominal video. That is, for every video volume in the nominal video of a new scene, we calculate our representations of appearance, motion direction, speed, and background fraction. We then reduce this set of embeddings to a smaller set which we call exemplars by removing redundant embeddings. We select a separate set of exemplars for each spatial region. This results in a compact, accurate, and location-dependent model of the nominal data in a new scene. Since there is no training of deep networks for each new environment, modeling a new environment is 'lightweight' compared to many other methods, making it efficient to model new scenes. Our exemplar model also allows very efficient updating if new nominal video is introduced. This is a crucial property for video anomaly detection methods because, in practice, it is unrealistic to assume that the initial nominal video covers every possible normal change. New nominal video will occasionally need to be added, making it critical that models are easy to extend." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 288, + 289, + 430 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 288, + 289, + 430 + ], + "spans": [ + { + "bbox": [ + 46, + 288, + 289, + 430 + ], + "type": "text", + "content": "Given test video of the same scene, we compute our high-level features for each video volume. We then compare these to the exemplars stored in the nominal model at the corresponding spatial region. Any test feature with a high distance to every nominal exemplar for that region is considered anomalous. Because the feature vectors map to human-interpretable attributes, these attributes can be used to give human-understandable explanations for why our system labeled video volumes as normal or anomalous. We define a method as 'explainable' if it can give human-understandable reasons for its decisions. Details of how our system provides explanations are given in Section 4.4." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 432, + 289, + 575 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 432, + 289, + 575 + ], + "spans": [ + { + "bbox": [ + 46, + 432, + 289, + 575 + ], + "type": "text", + "content": "In summary, we make the following key contributions: 1) We show that modeling scenes using high-level attributes leads to robust anomaly detection. 2) We introduce the idea of directly estimating high-level motion attributes from raw video volumes using deep networks. 3) We show how these high-level attributes also allow human-interpretable explanations. 4) Finally, we demonstrate an alternative to much of the previous work that is based on learning to reconstruct the nominal data. Our alternative approach is practical since it does not require training deep networks for each new scene and allows for simple and efficient updates to a scene model given new nominal training data." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 586, + 134, + 597 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 586, + 134, + 597 + ], + "spans": [ + { + "bbox": [ + 47, + 586, + 134, + 597 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 605, + 287, + 640 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 605, + 287, + 640 + ], + "spans": [ + { + "bbox": [ + 46, + 605, + 287, + 640 + ], + "type": "text", + "content": "Most Video Anomaly Detection (VAD) methods can be analyzed in terms of their representation learning or their detection method." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 642, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 642, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 642, + 287, + 714 + ], + "type": "text", + "content": "Representation of Nominal Data: Early approaches to VAD [2, 3, 7, 20, 30, 40, 47] primarily relied on the usage of handcrafted features. This included features like spatiotemporal gradients [17, 24], histogram of gradients [28, 40], flow fields [2, 3, 30, 47], histogram of flows [7, 40, 41], dense trajectories [28, 43] and foreground masks [3]. Re" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 72, + 547, + 491 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 491 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 491 + ], + "type": "text", + "content": "cently, most authors have used deep learning for this task [1,9,10,14-16,21,26,34,36,37,39,42,45]. These methods either use a pretrained model [15, 17, 26, 36, 39, 42] for feature extraction or train a model to specifically optimize for a particular task related to anomaly detection. These tasks can generally be categorized as either a variant of training an auto-encoder architecture to minimize the reconstruction error of nominal frames [6, 14, 16, 22, 25, 31], a generative adversarial network (GAN) to model nominal frames [21,25], or future frame prediction given a sequence of nominal frames [21,44]. To further improve their performance, recent works have tried specialized architectures and training methodologies. Particularly [8,22,32] transform their respective generative model by memory-based modules to memorize the normal prototypes in the training data. Most recently [38] proposed a module based on masked convolution and channel attention to reconstruct a masked part of the convolutional receptive field. A key drawback of reconstruction and future frame prediction methods is that they do not generate interpretable features. It is not clear what aspects of the video make it difficult to reconstruct since there is no mapping to higher-level features as in our work. Our work mostly aligns with methods utilizing pretrained models. However, unlike most of these approaches, we incorporate the output of our pretrained models to interpret model decisions. We additionally make sure that the predictions of our model generalize to a wide variety of scenes through our data generation and training procedures. One high-level motion attribute that our method learns is similar to the histogram of flow feature used in some early work [7,40,41]. However, instead of computing the histogram of flow from an optical flow field, our method learns a deep network to predict these features directly from RGB video volumes and then uses the network's learned feature embedding as the representation." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 491, + 548, + 706 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 491, + 548, + 706 + ], + "spans": [ + { + "bbox": [ + 304, + 491, + 548, + 706 + ], + "type": "text", + "content": "Detection Methods: Most methods use either standard outlier detection methods [5] as an external module or utilize the reconstruction strategy to predict anomalies. General methods of detection that most authors have used in the past include one-class SVM [17, 28, 42, 49], nearest neighbour approaches [9, 11, 15, 33, 34], and Probabilistic Graphical Models [3]. In [4, 13], pseudo-anomalous samples are used during training to improve discriminative learning. In [12], an object detector is used to focus on regions around objects and then networks are trained for various 'proxy' tasks (such as predicting the arrow of time) on the nominal data. Thus, unlike our work, they require training deep nework models for each different scene. Our work has some similarity to the work of [33, 34] in that we also use an overlapping grid of spatial regions, build exemplar-based models and use nearest neighbors distances as anomaly scores. The high-level features that we use are the biggest difference as compared to the pixel-based features used in their" + } + ] + } + ], + "index": 7 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "18718" + } + ] + } + ], + "index": 8 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 107, + 79, + 471, + 277 + ], + "blocks": [ + { + "bbox": [ + 107, + 79, + 471, + 277 + ], + "lines": [ + { + "bbox": [ + 107, + 79, + 471, + 277 + ], + "spans": [ + { + "bbox": [ + 107, + 79, + 471, + 277 + ], + "type": "image", + "image_path": "a4b7bed804a7344578c2dde4a82da114f4cf052661f729bec81fda0a764d12fa.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 288, + 547, + 332 + ], + "lines": [ + { + "bbox": [ + 46, + 288, + 547, + 332 + ], + "spans": [ + { + "bbox": [ + 46, + 288, + 547, + 332 + ], + "type": "text", + "content": "Figure 1. Our pipeline for building a location-dependent model of nominal video and detecting anomalies in test video. During the model building phase, we extract a high-level representation of each video volume using our appearance and motion networks. Using the exemplar selection method, we select a representative subset of video volumes for a given spatial region. By comparing video volumes in test video to the exemplar set we can detect anomalies." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 343, + 287, + 366 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 343, + 287, + 366 + ], + "spans": [ + { + "bbox": [ + 46, + 343, + 287, + 366 + ], + "type": "text", + "content": "work. Our high-level features allow for explainable models as well as much smaller models than theirs." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 367, + 287, + 486 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 367, + 287, + 486 + ], + "spans": [ + { + "bbox": [ + 46, + 367, + 287, + 486 + ], + "type": "text", + "content": "Explainable VAD: Our work is similar in spirit to the work of [15,46] with respect to providing explanations for detecting anomalies. In [15], the authors pre-train their feature extractor on public image datasets (MS-COCO and Visual Genome) to detect objects and predict their attributes and actions. They further use these predictions for 'event recounting' on VAD benchmarks. In [46], the authors utilize models pretrained for semantic segmentation, object classification, and multi-object tracking and use the output of these models directly as their feature representation." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 487, + 288, + 632 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 487, + 288, + 632 + ], + "spans": [ + { + "bbox": [ + 46, + 487, + 288, + 632 + ], + "type": "text", + "content": "Despite these coarse similarities, virtually all of the details of our methods are different. Specifically, in [15], they rely on object proposals to find candidate anomalous regions which can lead to missed detections for objects not represented in their training data. Our action/motion classes are also very different - ours being more generic (direction distributions and speed of motion) while in [15] are much more specific (bending, riding) and hence not applicable to a wide variety of scenarios. The method of [46] is specific to detecting and tracking pedestrians and is not a general video anomaly detection method. Furthermore, unlike ours, their method does not spatially localize anomalies." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 644, + 138, + 658 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 644, + 138, + 658 + ], + "spans": [ + { + "bbox": [ + 47, + 644, + 138, + 658 + ], + "type": "text", + "content": "3. Our Approach" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "text", + "content": "Our method consists of three distinct stages: high-level attribute learning, model building, and anomaly localization. The high-level attribute learning stage is done only once and uses training samples that are independent of any" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 343, + 547, + 498 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 343, + 547, + 498 + ], + "spans": [ + { + "bbox": [ + 304, + 343, + 547, + 498 + ], + "type": "text", + "content": "video anomaly detection dataset. The resulting deep networks learn general representations of object appearances and object motions which can then be used in the subsequent two stages to build a model of a specific scene and to localize anomalies in that scene, for a wide variety of surveillance scenarios. The outside data used to train our high-level attribute models are equivalent to the outside data used in various prior works on VAD; for example, the M-OCOCO and Visual Genome data used to train the models of Hinami et al. [15], the outside data used to train object detectors in [11, 12, 17, 42], as well as the many deep models pretrained on ImageNet and applied to VAD. Our outside data is not used to build models of a scene." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 305, + 504, + 460, + 517 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 504, + 460, + 517 + ], + "spans": [ + { + "bbox": [ + 305, + 504, + 460, + 517 + ], + "type": "text", + "content": "3.1. High-Level Attribute Learning" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 522, + 545, + 641 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 522, + 545, + 641 + ], + "spans": [ + { + "bbox": [ + 304, + 522, + 545, + 641 + ], + "type": "text", + "content": "For this stage, our main objective is to learn features that are (a) transferable across scenes and (b) interpretable. Given this motivation, we learn an object recognizer for our appearance model as well as regression networks for estimating the following motion attributes for a given video volume: the fraction of stationary pixels, the distribution of motion directions and the average speed of movement in each direction. We also learn a classifier to indicate whether a video volume is stationary or not. We will describe each of these deep networks in the following subsections." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 642, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 642, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 642, + 547, + 713 + ], + "type": "text", + "content": "To clarify our terminology, we use the term 'high-level attribute' to denote the object classes, histogram of motion directions, vector of motion speeds or fraction of stationary pixels which are the final outputs of the various deep networks that are learned. The term 'high-level feature' denotes the feature vector from the penultimate layer of one of" + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "18719" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 287, + 96 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 287, + 96 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 287, + 96 + ], + "type": "text", + "content": "the deep networks. A high-level feature can be mapped to a high-level attribute using the final layer of that network." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 102, + 160, + 114 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 102, + 160, + 114 + ], + "spans": [ + { + "bbox": [ + 47, + 102, + 160, + 114 + ], + "type": "text", + "content": "3.1.1 Appearance model" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 121, + 287, + 156 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 121, + 287, + 156 + ], + "spans": [ + { + "bbox": [ + 47, + 121, + 287, + 156 + ], + "type": "text", + "content": "We formulate the task of object recognition as a multi-label image classification problem as any given input image patch may contain more than one object class (or none)." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 157, + 287, + 348 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 157, + 287, + 348 + ], + "spans": [ + { + "bbox": [ + 46, + 157, + 287, + 348 + ], + "type": "text", + "content": "Training Data: We are particularly interested in learning to recognize objects that have high likelihood of being present in outdoor scenes. To this end, we select the following 8 categories as our primary set of object classes : [Person, Car, Cyclist, Dog, Tree, House, Skyscraper, and Bridge]. For our formulation, we want the learned features to generalize across different domains. To achieve this, we construct our training dataset of images from multiple sources. We use labeled examples of each class (as well as background images containing none of the classes) taken from the CIFAR-10 [19], CIFAR-100 [19], and MIO-TCD [27] datasets as well as a set of publicly available surveillance videos from static webcams that we collected and annotated. More details about the data collection is given in the supplemental material. In total we used 187,793 RGB training examples, resized to 64x64 pixels." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 348, + 287, + 504 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 348, + 287, + 504 + ], + "spans": [ + { + "bbox": [ + 46, + 348, + 287, + 504 + ], + "type": "text", + "content": "Neural Architecture: We use a modified ResNext-50 network [48] as our backbone architecture. We modified the original model by adding an extra fully connected layer that maps the 2048-dimensional feature vector after the average pooling layer to a 128-dimensional layer. The 128-dimensional layer is then mapped by a final fully connected layer to an 8-dimensional output layer with sigmoid activations that represent the categories. The extra fully connected layer gives us a 128-dimensional feature vector to represent appearance instead of the 2048-dimensional feature vector after RexNext-50's usual penultimate layer thus greatly reducing feature size. To train our model, we utilize the Binary Cross Entropy as our loss function." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 504, + 287, + 588 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 504, + 287, + 588 + ], + "spans": [ + { + "bbox": [ + 46, + 504, + 287, + 588 + ], + "type": "text", + "content": "Note that high-level features are usually distinctive even for unseen object classes despite the corresponding high-level attribute having low probabilities for all of the known object classes. This allows our appearance model to have unique representations for object classes other than the eight that we train on. See supplemental material for experiments on this." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 598, + 141, + 609 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 598, + 141, + 609 + ], + "spans": [ + { + "bbox": [ + 47, + 598, + 141, + 609 + ], + "type": "text", + "content": "3.1.2 Motion Model" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 618, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 618, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 618, + 287, + 713 + ], + "type": "text", + "content": "To characterize the motion information for a given video volume, we train deep networks to estimate the following attributes directly from an RGB video volume: (a) histogram of optical flow " + }, + { + "bbox": [ + 46, + 618, + 287, + 713 + ], + "type": "inline_equation", + "content": "(Y_{ang})" + }, + { + "bbox": [ + 46, + 618, + 287, + 713 + ], + "type": "text", + "content": ", (b) a vector of the average speed of pixels in each direction of motion " + }, + { + "bbox": [ + 46, + 618, + 287, + 713 + ], + "type": "inline_equation", + "content": "(Y_{speed})" + }, + { + "bbox": [ + 46, + 618, + 287, + 713 + ], + "type": "text", + "content": ", (c) background classifier " + }, + { + "bbox": [ + 46, + 618, + 287, + 713 + ], + "type": "inline_equation", + "content": "(Y_{bkg.cls})" + }, + { + "bbox": [ + 46, + 618, + 287, + 713 + ], + "type": "text", + "content": " and (d) percentage of stationary pixels " + }, + { + "bbox": [ + 46, + 618, + 287, + 713 + ], + "type": "inline_equation", + "content": "(Y_{bkgpix})" + }, + { + "bbox": [ + 46, + 618, + 287, + 713 + ], + "type": "text", + "content": ". The histogram of optical flow consists of 12 bins each of which stores the fraction of pixels" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 72, + 545, + 167 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 167 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 167 + ], + "type": "text", + "content": "in the video volume that are estimated to be moving in one of the 30 degree directions of motion. The average speed vector consists of the average speed (in pixels per frame) of all pixels falling in each of the 12 histogram of flow bins. The background classifier classifies whether the video volume contains motion or not. The percentage of stationary pixels in a video volume gives the rough size of the moving objects in a video volume." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 169, + 545, + 324 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 169, + 545, + 324 + ], + "spans": [ + { + "bbox": [ + 304, + 169, + 545, + 324 + ], + "type": "text", + "content": "Motion Training Data: We use the set of surveillance videos mentioned above to learn motion attributes in a self-supervised way. For each video, we sample video volumes from regions with significant 'motion' as well as very little motion ('background'). We identify these regions by computing their pixelwise optical flow fields using the TV-L1 method [50], which is also used to automatically generate ground-truth motion attributes. (Note that optical flow is only used to create ground truth for training our motion models. It is not used in later stages.) In total we obtain 283,486 'background' video volumes and 2,551,376 'motion' video volumes. We use " + }, + { + "bbox": [ + 304, + 169, + 545, + 324 + ], + "type": "inline_equation", + "content": "90\\%" + }, + { + "bbox": [ + 304, + 169, + 545, + 324 + ], + "type": "text", + "content": " of these for training our models and the remainder for validation." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 327, + 545, + 518 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 327, + 545, + 518 + ], + "spans": [ + { + "bbox": [ + 304, + 327, + 545, + 518 + ], + "type": "text", + "content": "The ground truth motion attributes for each training video volume are computed from the corresponding pixelwise flow fields as follows: We represent the " + }, + { + "bbox": [ + 304, + 327, + 545, + 518 + ], + "type": "inline_equation", + "content": "Y_{bkg.cls}" + }, + { + "bbox": [ + 304, + 327, + 545, + 518 + ], + "type": "text", + "content": " attribute as a single binary variable denoting if a video volume is 'background' (" + }, + { + "bbox": [ + 304, + 327, + 545, + 518 + ], + "type": "inline_equation", + "content": "Y_{bkg.cls} = 1" + }, + { + "bbox": [ + 304, + 327, + 545, + 518 + ], + "type": "text", + "content": ") or not (" + }, + { + "bbox": [ + 304, + 327, + 545, + 518 + ], + "type": "inline_equation", + "content": "Y_{bkg.cls} = 0" + }, + { + "bbox": [ + 304, + 327, + 545, + 518 + ], + "type": "text", + "content": "). The ground truth for " + }, + { + "bbox": [ + 304, + 327, + 545, + 518 + ], + "type": "inline_equation", + "content": "Y_{ang}" + }, + { + "bbox": [ + 304, + 327, + 545, + 518 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 327, + 545, + 518 + ], + "type": "inline_equation", + "content": "Y_{bkg}" + }, + { + "bbox": [ + 304, + 327, + 545, + 518 + ], + "type": "text", + "content": " are computed by first computing a 13-bin normalized histogram, wherein the first 12 bins represent the number of pixels with flow orientation in the ranges " + }, + { + "bbox": [ + 304, + 327, + 545, + 518 + ], + "type": "inline_equation", + "content": "[i * \\pi / 6 : (i + 1) * \\pi / 6)" + }, + { + "bbox": [ + 304, + 327, + 545, + 518 + ], + "type": "text", + "content": " with " + }, + { + "bbox": [ + 304, + 327, + 545, + 518 + ], + "type": "inline_equation", + "content": "i \\in [0, 11]" + }, + { + "bbox": [ + 304, + 327, + 545, + 518 + ], + "type": "text", + "content": ", while the last bin denotes the number of pixels with flow magnitude below threshold. The histogram is then normalized by the total number of pixels. The first 12 bins of this histogram are used as the ground truth for " + }, + { + "bbox": [ + 304, + 327, + 545, + 518 + ], + "type": "inline_equation", + "content": "Y_{ang}" + }, + { + "bbox": [ + 304, + 327, + 545, + 518 + ], + "type": "text", + "content": " and the " + }, + { + "bbox": [ + 304, + 327, + 545, + 518 + ], + "type": "inline_equation", + "content": "13^{th}" + }, + { + "bbox": [ + 304, + 327, + 545, + 518 + ], + "type": "text", + "content": " bin is the ground truth for " + }, + { + "bbox": [ + 304, + 327, + 545, + 518 + ], + "type": "inline_equation", + "content": "Y_{bkg}" + }, + { + "bbox": [ + 304, + 327, + 545, + 518 + ], + "type": "text", + "content": ". Finally, we represent " + }, + { + "bbox": [ + 304, + 327, + 545, + 518 + ], + "type": "inline_equation", + "content": "Y_{mag}" + }, + { + "bbox": [ + 304, + 327, + 545, + 518 + ], + "type": "text", + "content": " as a 12-dimensional vector denoting the average flow magnitude for pixels in each of the 12 flow orientation ranges." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 520, + 545, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 520, + 545, + 628 + ], + "spans": [ + { + "bbox": [ + 304, + 520, + 545, + 628 + ], + "type": "text", + "content": "Learning Task and Neural Architecture: We treat each motion attribute independently and train separate models respectively. For each attribute prediction task, we use the same backbone architecture design, but train each model using different objective functions. Our model is a stack of 3D convolutions (3DConv) with batch normalization (BN) and ReLU. In total we have 3 layers of [3Dconv-BN-ReLU] followed by a fully connected layer. We provide additional details in the supplemental material." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "content": "We formulate " + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "inline_equation", + "content": "Y_{bkg,cls}" + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "content": " attribute prediction as a standard binary classification task and train the model using cross-entropy loss function. For " + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "inline_equation", + "content": "Y_{bkg}" + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "inline_equation", + "content": "Y_{mag}" + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "content": " attribute prediction, we treat the learning task as a regression problem and train the model using mean squared error loss. And finally, for training the model to predict " + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "inline_equation", + "content": "Y_{ang}" + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "content": " attribute, we utilize KL Divergence loss. For all the tasks, we construct a sim" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "18720" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 96 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 96 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 96 + ], + "type": "text", + "content": "ple light-weight CNN. The detailed configuration of our 3D CNN architecture is presented in the supplemental material." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 103, + 144, + 116 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 103, + 144, + 116 + ], + "spans": [ + { + "bbox": [ + 47, + 103, + 144, + 116 + ], + "type": "text", + "content": "3.2. Model Building" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 121, + 289, + 373 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 121, + 289, + 373 + ], + "spans": [ + { + "bbox": [ + 46, + 121, + 289, + 373 + ], + "type": "text", + "content": "Once trained, the attribute deep nets are used to build a model of any scene given the nominal video. As illustrated in Figure 1, to process each nominal video, we slide a spatio-temporal window of dimension " + }, + { + "bbox": [ + 46, + 121, + 289, + 373 + ], + "type": "inline_equation", + "content": "[h\\times w\\times t]" + }, + { + "bbox": [ + 46, + 121, + 289, + 373 + ], + "type": "text", + "content": " with spatial stride " + }, + { + "bbox": [ + 46, + 121, + 289, + 373 + ], + "type": "inline_equation", + "content": "(h / 2,w / 2)" + }, + { + "bbox": [ + 46, + 121, + 289, + 373 + ], + "type": "text", + "content": " and temporal stride of " + }, + { + "bbox": [ + 46, + 121, + 289, + 373 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 121, + 289, + 373 + ], + "type": "text", + "content": " to construct video volumes. In the experiments, we select " + }, + { + "bbox": [ + 46, + 121, + 289, + 373 + ], + "type": "inline_equation", + "content": "h = w" + }, + { + "bbox": [ + 46, + 121, + 289, + 373 + ], + "type": "text", + "content": " and choose " + }, + { + "bbox": [ + 46, + 121, + 289, + 373 + ], + "type": "inline_equation", + "content": "h" + }, + { + "bbox": [ + 46, + 121, + 289, + 373 + ], + "type": "text", + "content": " to be roughly the height in pixels of a person in a particular dataset. For each RGB video volume, we extract its features using the previously trained appearance net and four motion nets. To get a single appearance feature vector for a video volume, the feature vectors computed by the appearance network for each frame of the video volume are averaged. We concatenate the feature vectors from the penultimate layers of the appearance, angle, speed and background pixel nets along with the binary output of the background classifier net to create a combined feature vector. We use " + }, + { + "bbox": [ + 46, + 121, + 289, + 373 + ], + "type": "inline_equation", + "content": "F" + }, + { + "bbox": [ + 46, + 121, + 289, + 373 + ], + "type": "text", + "content": " to denote a combined feature vector and app, ang, mag, and bkg to denote the appearance, angle, magnitude and background pixel fraction feature vectors, each of size " + }, + { + "bbox": [ + 46, + 121, + 289, + 373 + ], + "type": "inline_equation", + "content": "1\\times 128" + }, + { + "bbox": [ + 46, + 121, + 289, + 373 + ], + "type": "text", + "content": ". Finally, cls denotes the binary background classification of size " + }, + { + "bbox": [ + 46, + 121, + 289, + 373 + ], + "type": "inline_equation", + "content": "1\\times 1" + }, + { + "bbox": [ + 46, + 121, + 289, + 373 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 46, + 121, + 289, + 373 + ], + "type": "inline_equation", + "content": "F" + }, + { + "bbox": [ + 46, + 121, + 289, + 373 + ], + "type": "text", + "content": " is of size " + }, + { + "bbox": [ + 46, + 121, + 289, + 373 + ], + "type": "inline_equation", + "content": "1\\times 513" + }, + { + "bbox": [ + 46, + 121, + 289, + 373 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 373, + 287, + 421 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 373, + 287, + 421 + ], + "spans": [ + { + "bbox": [ + 46, + 373, + 287, + 421 + ], + "type": "text", + "content": "After computing features, we use the exemplar selection approach of [18, 34] to create a region-specific compact model of the nominal data. For each region, we use the following greedy exemplar selection algorithm:" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 54, + 425, + 287, + 487 + ], + "type": "list", + "angle": 0, + "index": 6, + "blocks": [ + { + "bbox": [ + 55, + 425, + 258, + 437 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 55, + 425, + 258, + 437 + ], + "spans": [ + { + "bbox": [ + 55, + 425, + 258, + 437 + ], + "type": "text", + "content": "1. Add the first feature vector to the exemplar set." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 54, + 441, + 287, + 487 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 54, + 441, + 287, + 487 + ], + "spans": [ + { + "bbox": [ + 54, + 441, + 287, + 487 + ], + "type": "text", + "content": "2. For each subsequent feature vector, compute its distance to each feature vector in the exemplar set and add it to the exemplar set only if all distances are above a threshold, " + }, + { + "bbox": [ + 54, + 441, + 287, + 487 + ], + "type": "inline_equation", + "content": "th" + }, + { + "bbox": [ + 54, + 441, + 287, + 487 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 5 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 46, + 493, + 289, + 648 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 493, + 289, + 648 + ], + "spans": [ + { + "bbox": [ + 46, + 493, + 289, + 648 + ], + "type": "text", + "content": "To be clear, a separate set of exemplars is selected for each different spatial region in a scene. This allows our model to represent the fact that different object and motions occur in different regions of a scene. To compute the distance between two feature vectors " + }, + { + "bbox": [ + 46, + 493, + 289, + 648 + ], + "type": "inline_equation", + "content": "F_{1} = [app_{1}; ang_{1}; mag_{1}; bkg_{1}; cls_{1}]" + }, + { + "bbox": [ + 46, + 493, + 289, + 648 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 493, + 289, + 648 + ], + "type": "inline_equation", + "content": "F_{2} = [app_{2}; ang_{2}; mag_{2}; bkg_{2}; cls_{2}]" + }, + { + "bbox": [ + 46, + 493, + 289, + 648 + ], + "type": "text", + "content": " we use " + }, + { + "bbox": [ + 46, + 493, + 289, + 648 + ], + "type": "inline_equation", + "content": "L_{2}" + }, + { + "bbox": [ + 46, + 493, + 289, + 648 + ], + "type": "text", + "content": " distances between corresponding components normalized by a constant to make the maximum distance for each component approximately 1. When a video volume does not contain motion (as determined by the background classification, " + }, + { + "bbox": [ + 46, + 493, + 289, + 648 + ], + "type": "inline_equation", + "content": "cls" + }, + { + "bbox": [ + 46, + 493, + 289, + 648 + ], + "type": "text", + "content": "), the motion component vectors are set to 0. The distance function can be written as follows:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 110, + 656, + 287, + 670 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 110, + 656, + 287, + 670 + ], + "spans": [ + { + "bbox": [ + 110, + 656, + 287, + 670 + ], + "type": "interline_equation", + "content": "d _ {A} \\left(F _ {1}, F _ {2}\\right) = \\left\\| A _ {1} - A _ {2} \\right\\| _ {2} \\tag {1}", + "image_path": "12a0f2d389b2f8e63b5e2dda82008561595d65829972da315af762f56a5dfb20.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 677, + 189, + 690 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 677, + 189, + 690 + ], + "spans": [ + { + "bbox": [ + 47, + 677, + 189, + 690 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 677, + 189, + 690 + ], + "type": "inline_equation", + "content": "A\\in \\{app,ang,mag,bkg\\}" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 63, + 696, + 287, + 718 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 63, + 696, + 287, + 718 + ], + "spans": [ + { + "bbox": [ + 63, + 696, + 287, + 718 + ], + "type": "interline_equation", + "content": "d (F _ {1}, F _ {2}) = \\frac {d _ {a p p}}{Z _ {a p p}} + \\frac {d _ {a n g}}{Z _ {a n g}} + \\frac {d _ {b k g}}{Z _ {b k g}} + \\frac {d _ {m a g}}{Z _ {m a g}}. (2)", + "image_path": "baa73ad4d3d3b3819f01db694433f9fbf1298093b47905de1d2ceca7cd77743a.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "text", + "content": "The normalization factors, " + }, + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "inline_equation", + "content": "Z_{app}" + }, + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "inline_equation", + "content": "Z_{ang}" + }, + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "inline_equation", + "content": "Z_{mag}" + }, + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "inline_equation", + "content": "Z_{bkg}" + }, + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "text", + "content": " are computed once by finding the max " + }, + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "inline_equation", + "content": "L_{2}" + }, + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "text", + "content": " distances between a large set of feature vector components computed from a validation set (UCSD Ped1 and Ped2 in our experiments)." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 121, + 547, + 168 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 121, + 547, + 168 + ], + "spans": [ + { + "bbox": [ + 304, + 121, + 547, + 168 + ], + "type": "text", + "content": "One big advantage of the exemplar learning approach is that updating the exemplar set in a streaming fashion is possible. This makes the approach scalable and adaptable to environmental changes over time." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 176, + 419, + 188 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 176, + 419, + 188 + ], + "spans": [ + { + "bbox": [ + 306, + 176, + 419, + 188 + ], + "type": "text", + "content": "3.3. Anomaly Detection" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 195, + 547, + 387 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 195, + 547, + 387 + ], + "spans": [ + { + "bbox": [ + 304, + 195, + 547, + 387 + ], + "type": "text", + "content": "At test time, we process each test video in the same way (by sliding a " + }, + { + "bbox": [ + 304, + 195, + 547, + 387 + ], + "type": "inline_equation", + "content": "[h\\times w\\times t]" + }, + { + "bbox": [ + 304, + 195, + 547, + 387 + ], + "type": "text", + "content": " spatio-temporal window with spatial stride " + }, + { + "bbox": [ + 304, + 195, + 547, + 387 + ], + "type": "inline_equation", + "content": "(h / 2,w / 2)" + }, + { + "bbox": [ + 304, + 195, + 547, + 387 + ], + "type": "text", + "content": " and temporal stride of " + }, + { + "bbox": [ + 304, + 195, + 547, + 387 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 195, + 547, + 387 + ], + "type": "text", + "content": ") to generate video volumes. For each video volume, we compute the combined feature vector as before using the pre-trained nets. Each combined feature vector is compared with every exemplar for the corresponding region using the distance function in Equation 2. The anomaly score for the given test video volume is the minimum distance over the set of all exemplars from the same spatial region. A pixelwise anomaly score map is maintained by assigning the anomaly score to all pixels corresponding to every frame of the video volume. If a pixel has already been assigned an anomaly score (because of partially overlapping video volumes), then the maximum of the previous score and the current score is assigned. Figure 1 shows our anomaly detection pipeline." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 394, + 499, + 407 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 394, + 499, + 407 + ], + "spans": [ + { + "bbox": [ + 306, + 394, + 499, + 407 + ], + "type": "text", + "content": "3.4. A Note on Computational Efficiency" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 412, + 547, + 521 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 412, + 547, + 521 + ], + "spans": [ + { + "bbox": [ + 304, + 412, + 547, + 521 + ], + "type": "text", + "content": "For both model building and anomaly detection, most of the time is spent computing feature vectors (forward passes of 5 networks). This is greatly sped up by testing whether a video volume is the same as the previous video volume in time. If there is no change then the anomaly score for the new video volume should be the same as the one before it and no computation of feature vectors is needed. This allows our method to run at 20 to 100 fps (dataset dependent). Details are in the supplemental material." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 531, + 388, + 545 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 531, + 388, + 545 + ], + "spans": [ + { + "bbox": [ + 306, + 531, + 388, + 545 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 306, + 552, + 484, + 563 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 552, + 484, + 563 + ], + "spans": [ + { + "bbox": [ + 306, + 552, + 484, + 563 + ], + "type": "text", + "content": "4.1. Datasets and Evaluation Criteria" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 570, + 545, + 629 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 545, + 629 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 545, + 629 + ], + "type": "text", + "content": "We experiment on five benchmark datasets: UCSD Ped1 and Ped2 [29], CUHK Avenue [24], Street Scene [33] and ShanghaiTech [26]. We use UCSD Ped1 and Ped2 with modified ground truth for parameter tuning and CUHK Avenue, Street Scene and ShanghaiTech for evaluation." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 629, + 545, + 677 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 629, + 545, + 677 + ], + "spans": [ + { + "bbox": [ + 304, + 629, + 545, + 677 + ], + "type": "text", + "content": "UCSD Ped1 & Ped2: UCSD Ped1 dataset contains 34 training videos and 36 test videos while UCSD Ped2 dataset contains 16 training videos and 12 test videos. Anomalies consists of bikers, skaters and cars in a pedestrian area." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 304, + 677, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 545, + 714 + ], + "type": "text", + "content": "CUHK Avenue: The Avenue [24] dataset contains 16 training videos with normal activity and 21 test videos. Examples of abnormal events in Avenue are related to people run" + } + ] + } + ], + "index": 21 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "18721" + } + ] + } + ], + "index": 22 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 264, + 83 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 264, + 83 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 264, + 83 + ], + "type": "text", + "content": "ning, throwing objects or walking in wrong direction." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 84, + 286, + 132 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 84, + 286, + 132 + ], + "spans": [ + { + "bbox": [ + 46, + 84, + 286, + 132 + ], + "type": "text", + "content": "Street Scene: The Street Scene [33] dataset contains 46 training videos defining the normal events and 35 test videos. Prominent examples of anomalies include jaywalking, loitering and bikes or cars driving outside their lanes." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 133, + 286, + 192 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 133, + 286, + 192 + ], + "spans": [ + { + "bbox": [ + 46, + 133, + 286, + 192 + ], + "type": "text", + "content": "ShanghaiTech: The ShanghaiTech [26] dataset is a multiscene benchmark for video anomaly detection. It consists of 330 training and 107 test videos. Major categories of anomalies include people fighting, stealing, chasing, jumping, and riding bikes or skating in pedestrian zones." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 193, + 286, + 287 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 193, + 286, + 287 + ], + "spans": [ + { + "bbox": [ + 46, + 193, + 286, + 287 + ], + "type": "text", + "content": "While our primary focus is on single scene video anomaly detection task, we consider the ShanghaiTech dataset only to highlight the ease of usability and robustness of our method to multi-scene benchmarks. Our method is applied to ShanghaiTech without modification even though the location-dependent aspect of our model is not necessary for a multi-scene dataset. Improvements in accuracy are likely if we specialize our model to multi-scene datasets." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 289, + 286, + 468 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 289, + 286, + 468 + ], + "spans": [ + { + "bbox": [ + 46, + 289, + 286, + 468 + ], + "type": "text", + "content": "Evaluation Criteria. We use the Region-Based Detection Criterion (RBDC) and the Track-Based Detection Criterion (TBDC) as proposed in [33] for quantitative evaluation of our framework. These criteria correctly measure the accuracy of spatially and temporally localizing anomalous regions (RBDC) and anomalous tracks (TBDC) versus false positive detections per frame. We report the area under the curve (AUC) for false positive rates per frame from 0 to 1 for each of these criteria. As pointed out in [33], frame-AUC [29] is not an appropriate evaluation metric for video anomaly detection methods that spatially localize anomalies. However, we report frame-AUC scores of our method for completeness and comparison with other older methods. We also do not use the pixel-level criterion [29] because of its serious flaws as mentioned in [33]." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 478, + 144, + 490 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 478, + 144, + 490 + ], + "spans": [ + { + "bbox": [ + 47, + 478, + 144, + 490 + ], + "type": "text", + "content": "4.2. Implementation" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 497, + 286, + 581 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 497, + 286, + 581 + ], + "spans": [ + { + "bbox": [ + 46, + 497, + 286, + 581 + ], + "type": "text", + "content": "Feature Learning. To train our appearance model, we use SGD with a 0.001 learning rate and 0.9 momentum and train for 50 epochs. The model with lowest classification error on the validation set is selected. For motion models we optimize with AdamW [23] with a 0.001 learning rate and train for 30 epochs. We select the best model for each attribute using the validation set." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 582, + 286, + 675 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 582, + 286, + 675 + ], + "spans": [ + { + "bbox": [ + 46, + 582, + 286, + 675 + ], + "type": "text", + "content": "Video volume parameters. We define the dimensions " + }, + { + "bbox": [ + 46, + 582, + 286, + 675 + ], + "type": "inline_equation", + "content": "(w, h)" + }, + { + "bbox": [ + 46, + 582, + 286, + 675 + ], + "type": "text", + "content": " of a video volume for each dataset so that " + }, + { + "bbox": [ + 46, + 582, + 286, + 675 + ], + "type": "inline_equation", + "content": "h" + }, + { + "bbox": [ + 46, + 582, + 286, + 675 + ], + "type": "text", + "content": " is roughly the height of a person in pixels and " + }, + { + "bbox": [ + 46, + 582, + 286, + 675 + ], + "type": "inline_equation", + "content": "w = h" + }, + { + "bbox": [ + 46, + 582, + 286, + 675 + ], + "type": "text", + "content": ". Specifically, for Ped1, Ped2, Avenue, Street Scene and ShanghaiTech, our region dimensions are (32, 32), (32, 32), (128, 128), (64, 64) and (100, 100) respectively. Zeropadding was used for edge regions as needed. The number of frames in a video volume, " + }, + { + "bbox": [ + 46, + 582, + 286, + 675 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 582, + 286, + 675 + ], + "type": "text", + "content": ", is 10 for all datasets." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 677, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 286, + 713 + ], + "type": "text", + "content": "Parameter Tuning. To set a threshold " + }, + { + "bbox": [ + 46, + 677, + 286, + 713 + ], + "type": "inline_equation", + "content": "th" + }, + { + "bbox": [ + 46, + 677, + 286, + 713 + ], + "type": "text", + "content": " for exemplar selection without fitting to test data, a validation data set is needed. We chose Ped1 and Ped2 for this purpose, both" + } + ] + } + ], + "index": 8 + }, + { + "type": "table", + "bbox": [ + 310, + 70, + 543, + 162 + ], + "blocks": [ + { + "bbox": [ + 310, + 70, + 543, + 162 + ], + "lines": [ + { + "bbox": [ + 310, + 70, + 543, + 162 + ], + "spans": [ + { + "bbox": [ + 310, + 70, + 543, + 162 + ], + "type": "table", + "html": "
ThUCSD Ped1UCSD Ped2
RBDCTBDCNUMRBDCTBDCNUM
336.86677.8328864.80889.13350
2.549.3689.4342478.81393.716761
257.52489.694484.6695.971339
1.561.6588.9420187.4495.084470
161.49687.541992687.40895.77619138
0.561.43587.724911387.19595.1234862
0.2561.4987.815763687.19995.12745795
", + "image_path": "af3568db28c388b991ea1b62cc62e20ffb7302eb42939130ba1c31624374e5af.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "table_body" + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 170, + 545, + 204 + ], + "lines": [ + { + "bbox": [ + 305, + 170, + 545, + 204 + ], + "spans": [ + { + "bbox": [ + 305, + 170, + 545, + 204 + ], + "type": "text", + "content": "Table 1. RBDC and TBDC scores (in %) of our method for different thresholds (th) on UCSD Ped1 and Ped2. NUM denotes the total number of exemplars across all regions." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 304, + 217, + 545, + 502 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 217, + 545, + 502 + ], + "spans": [ + { + "bbox": [ + 304, + 217, + 545, + 502 + ], + "type": "text", + "content": "because these data sets are performance-saturated, and because previous works [34] have identified inconsistencies in their ground truth. Specifically, ground-truth annotations of Ped1 and Ped2 do not label every location-specific anomaly. To rectify this, we augment the existing ground truth annotations to include all anomalies consistent with Definition 1. This is justified because we are using Ped1 and Ped2 to set our hyperparameters and not to compare against previous methods. Table 1 shows region-based and track-based AUC for different values of the threshold " + }, + { + "bbox": [ + 304, + 217, + 545, + 502 + ], + "type": "inline_equation", + "content": "th" + }, + { + "bbox": [ + 304, + 217, + 545, + 502 + ], + "type": "text", + "content": " used for exemplar selection for both Ped1 and Ped2. We see that the accuracy of our method is robust to large variations of " + }, + { + "bbox": [ + 304, + 217, + 545, + 502 + ], + "type": "inline_equation", + "content": "th" + }, + { + "bbox": [ + 304, + 217, + 545, + 502 + ], + "type": "text", + "content": ". However, larger values of " + }, + { + "bbox": [ + 304, + 217, + 545, + 502 + ], + "type": "inline_equation", + "content": "th" + }, + { + "bbox": [ + 304, + 217, + 545, + 502 + ], + "type": "text", + "content": " lead to smaller numbers of exemplars and thus smaller models of the nominal video which is desirable. We select " + }, + { + "bbox": [ + 304, + 217, + 545, + 502 + ], + "type": "inline_equation", + "content": "th = 1.5" + }, + { + "bbox": [ + 304, + 217, + 545, + 502 + ], + "type": "text", + "content": " as a good trade-off between accuracy and model-size. We use this value on all datasets in our experiments. For Ped2, the average number of exemplars selected per region is about 13 (" + }, + { + "bbox": [ + 304, + 217, + 545, + 502 + ], + "type": "inline_equation", + "content": "\\approx 0.5\\%" + }, + { + "bbox": [ + 304, + 217, + 545, + 502 + ], + "type": "text", + "content": " of the total number of video volumes in the nominal video). Exemplar selection typically finds tens to sometimes low hundreds of exemplars (for Street Scene) for regions with lots of activity. Regions with very little activity typically have only 1 or 2 exemplars. This leads to very compact models of the nominal video." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 514, + 424, + 527 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 514, + 424, + 527 + ], + "spans": [ + { + "bbox": [ + 306, + 514, + 424, + 527 + ], + "type": "text", + "content": "4.3. Quantitative Results" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 534, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 534, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 304, + 534, + 545, + 712 + ], + "type": "text", + "content": "Tables 2 and 3 compare our method to other top methods on Avenue, ShanghaiTech and Street Scene. On Avenue, we improve over all previous methods for the region-based detection criterion (RBDC) and are second best for the track-based detection criterion (TBDC). On ShanghaiTech, we improve over the next best method for both RBDC and TBDC by significant margins. For the frame-level criterion which does not measure spatial localization we are in the middle of the pack compared to other recent methods for both Avenue and ShanghaiTech. On the difficult Street Scene dataset (Table 3), we improve the previous state of the art for both RBDC and TBDC, the latter by more than " + }, + { + "bbox": [ + 304, + 534, + 545, + 712 + ], + "type": "inline_equation", + "content": "11\\%" + }, + { + "bbox": [ + 304, + 534, + 545, + 712 + ], + "type": "text", + "content": ". The good results across five different datasets (including Ped1 and Ped2) show the generality of the high-level features that we use in our models." + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "18722" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 52, + 70, + 284, + 214 + ], + "blocks": [ + { + "bbox": [ + 52, + 70, + 284, + 214 + ], + "lines": [ + { + "bbox": [ + 52, + 70, + 284, + 214 + ], + "spans": [ + { + "bbox": [ + 52, + 70, + 284, + 214 + ], + "type": "table", + "html": "
MethodAvenueShanghaiTech
RBDCTBDCFrameRBDCTBDCFrame
Ionescu et al. [16]15.7727.0787.420.6544.5478.7
Ramachandra et al. [33]35.8080.9072.0---
Ramachandra et al. [34]41.2078.6087.2---
Georgescu et al. [12]57.0058.3091.542.8083.9090.02
Liu et al. [21]19.5956.0185.117.0354.2372.8
Liu et al. [22]41.0586.1889.944.4183.8674.2
Georgescu et al. [13]65.0566.8592.341.3478.7982.7
Liu et al. [21] + Ristea et al. [38]20.1362.3087.318.5160.2274.5
Liu et al. [22] + Ristea et al. [38]62.2789.2890.945.4584.5075.5
Georgescu et al. [13] + Ristea et al. [38]65.9964.9192.940.5583.4683.6
Our Method68.287.5686.0259.2189.4476.63
", + "image_path": "a3296f53f2064b1442b9cadfef3315d7c864fc6b47008e576d8387f84a7e9676.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 86, + 270, + 249, + 334 + ], + "blocks": [ + { + "bbox": [ + 46, + 222, + 287, + 266 + ], + "lines": [ + { + "bbox": [ + 46, + 222, + 287, + 266 + ], + "spans": [ + { + "bbox": [ + 46, + 222, + 287, + 266 + ], + "type": "text", + "content": "Table 2. RRBDC, TBDC and Frame AUC scores (in %) of various state-of-the-art methods on Avenue and ShanghaiTech datasets. The top score for each metric is highlighted in red, while the second best score is in blue." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 86, + 270, + 249, + 334 + ], + "lines": [ + { + "bbox": [ + 86, + 270, + 249, + 334 + ], + "spans": [ + { + "bbox": [ + 86, + 270, + 249, + 334 + ], + "type": "table", + "html": "
MethodsRBDCTBDC
Auto-encoder [14]0.292.0
Dictionary method [24]1.610.0
Flow baseline [33]11.052.0
FG Baseline [33]21.053.0
Our Method24.364.5
", + "image_path": "5a42d6256e701badc4a6d63688f06c603a5d4f8bc4427a1beffbb3938cedd66b.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 342, + 287, + 386 + ], + "lines": [ + { + "bbox": [ + 46, + 342, + 287, + 386 + ], + "spans": [ + { + "bbox": [ + 46, + 342, + 287, + 386 + ], + "type": "text", + "content": "Table 3. RBDC and TBDC AUC scores (in %) of various baseline methods on Street Scene dataset. The top score for each metric is highlighted in red, while the second best score is highlighted in blue." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 47, + 405, + 232, + 418 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 405, + 232, + 418 + ], + "spans": [ + { + "bbox": [ + 47, + 405, + 232, + 418 + ], + "type": "text", + "content": "4.4. Qualitative Results: Explainability" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 425, + 287, + 533 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 425, + 287, + 533 + ], + "spans": [ + { + "bbox": [ + 46, + 425, + 287, + 533 + ], + "type": "text", + "content": "One of the big advantages of our method in addition to its accuracy is that it allows intuitive explanations of what the model has learned and why it labels a particular test video volume as anomalous or not. To visualize the feature vector representing a video volume, the appearance and motion components of the combined feature vector are mapped using the last fully connected layer of the respective network to the high-level appearance and motion attributes. We can then visualize these attributes as illustrated in Figure 2." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 534, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 534, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 534, + 288, + 715 + ], + "type": "text", + "content": "As an illustration of our model's explainability, the top of Figure 3 visualizes the exemplars learned from the nominal video for a spatial region in the middle of the street. Cars travel down and to the right in this lane of the street. The top six exemplars learned show mainly cars (or unknown objects, since video volumes containing only parts of cars are often not classified as cars) traveling down and to the right, as expected. There are also exemplars for stationary background, as well as stationary cars (since occasionally traffic stops on this part of the street). Thus, our learned model is understandable and consistent with what one expects. Furthermore, for a video volume containing a person jaywalking, the visualization in the bottom, left of the figure shows that our networks correctly identify it as containing a person walking mainly to the right at moderate speed. The" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "text", + "content": "closest exemplar to this test volume is an unknown object moving down and to the right which yields a high anomaly score of 2.08. (A threshold of 1.8 yields high detection rates with low false positive rates across all the datasets.) Thus, the explanation of this anomaly is that there is an unusual object (person) walking in an unusual direction." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 145, + 546, + 324 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 145, + 546, + 324 + ], + "spans": [ + { + "bbox": [ + 304, + 145, + 546, + 324 + ], + "type": "text", + "content": "Another example is shown for Ped2 in Figure 4. Here we analyze a region on the sidewalk. The exemplars learned for this region (shown at the top of Figure 4) are mainly background with very little movement or people moving mainly left or right at slow speeds. Some video volumes containing only parts of people are not classified as people which leads to exemplars of unknown objects moving left or right. Overall, these exemplars are again what we would expect for this region. For the test frame shown, a cyclist is riding on the sidewalk. The visualization of the video volume centered on that frame at that spatial region shows that it was classified as a cyclist traveling down and right at a high speed. These high-level attributes differs from the nearest exemplar in terms of its object class and speed and therefore leads to a high anomaly score." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 325, + 546, + 517 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 325, + 546, + 517 + ], + "spans": [ + { + "bbox": [ + 304, + 325, + 546, + 517 + ], + "type": "text", + "content": "As a final illustration (we show more in the supplemental material), we look at an example from CUHK Avenue in Figure 5. The top six exemplars for the region highlighted at the left of the figure show that the model has learned that this region contains either background with very little movement or else people or unknown objects moving mainly left or right slowly. For the anomalous test video volume shown containing a person running to the left, the high-level features estimate an unknown object moving left at high speed. Even though the object recognizer did not correctly predict that the video volume contains a person, the person class is the most likely out of the eight classes. The nearest exemplar is an unknown object (closest to a person class) moving slowly to the left. The main difference between the test video volume and the closest exemplar is the unusual speed which correctly explains this anomaly." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 526, + 400, + 540 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 526, + 400, + 540 + ], + "spans": [ + { + "bbox": [ + 306, + 526, + 400, + 540 + ], + "type": "text", + "content": "4.5. Ablation Study" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 545, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 545, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 545, + 545, + 713 + ], + "type": "text", + "content": "We perform an ablation study on all the benchmarks to evaluate the benefit of each attribute in detecting anomalies. We consider features from each model separately, combining features from only motion models and finally our full model which uses all features. We accordingly change the distance function to compare features of two video volumes so that it only uses the provided features. We present our results in Table 4. We see that different attributes can be important for different types of scenarios. However, we get best results across all the benchmarks only when we combine all the motion and appearance features. This highlights the importance of modeling both appearance and different components of motion, especially to be able to predict anomalies under wide variety of scenarios." + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "18723" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "bbox": [ + 77, + 74, + 241, + 115 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 77, + 74, + 241, + 115 + ], + "spans": [ + { + "bbox": [ + 77, + 74, + 241, + 115 + ], + "type": "text", + "content": "Bar graphs of sigmoid outputs for the 8 object classes in the appearance network. " + }, + { + "bbox": [ + 77, + 74, + 241, + 115 + ], + "type": "inline_equation", + "content": "[0 =" + }, + { + "bbox": [ + 77, + 74, + 241, + 115 + ], + "type": "text", + "content": " person, " + }, + { + "bbox": [ + 77, + 74, + 241, + 115 + ], + "type": "inline_equation", + "content": "1 =" + }, + { + "bbox": [ + 77, + 74, + 241, + 115 + ], + "type": "text", + "content": " car, " + }, + { + "bbox": [ + 77, + 74, + 241, + 115 + ], + "type": "inline_equation", + "content": "2 =" + }, + { + "bbox": [ + 77, + 74, + 241, + 115 + ], + "type": "text", + "content": " cyclist, " + }, + { + "bbox": [ + 77, + 74, + 241, + 115 + ], + "type": "inline_equation", + "content": "3 =" + }, + { + "bbox": [ + 77, + 74, + 241, + 115 + ], + "type": "text", + "content": " dog, " + }, + { + "bbox": [ + 77, + 74, + 241, + 115 + ], + "type": "inline_equation", + "content": "4 =" + }, + { + "bbox": [ + 77, + 74, + 241, + 115 + ], + "type": "text", + "content": " tree, " + }, + { + "bbox": [ + 77, + 74, + 241, + 115 + ], + "type": "inline_equation", + "content": "5 =" + }, + { + "bbox": [ + 77, + 74, + 241, + 115 + ], + "type": "text", + "content": " house, " + }, + { + "bbox": [ + 77, + 74, + 241, + 115 + ], + "type": "inline_equation", + "content": "6 =" + }, + { + "bbox": [ + 77, + 74, + 241, + 115 + ], + "type": "text", + "content": " skyscraper, " + }, + { + "bbox": [ + 77, + 74, + 241, + 115 + ], + "type": "inline_equation", + "content": "7 =" + }, + { + "bbox": [ + 77, + 74, + 241, + 115 + ], + "type": "text", + "content": " bridge.] Length of each bar is proportional to the distance of the sigmoid value from 0.5.Values above 0.5 (green) indicate the likely presence of that object class, while values below 0.5 (red) indicate otherwise." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 77, + 123, + 239, + 151 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 77, + 123, + 239, + 151 + ], + "spans": [ + { + "bbox": [ + 77, + 123, + 239, + 151 + ], + "type": "text", + "content": "Visualization of the direction of motion histogram. For each of the 12 angles estimated by the direction network, the length of the ray in that direction is proportional to the number of pixels (in that video volume) estimated to be moving in that direction." + } + ] + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 244, + 74, + 330, + 144 + ], + "blocks": [ + { + "bbox": [ + 244, + 74, + 330, + 144 + ], + "lines": [ + { + "bbox": [ + 244, + 74, + 330, + 144 + ], + "spans": [ + { + "bbox": [ + 244, + 74, + 330, + 144 + ], + "type": "image", + "image_path": "b6d30256665e11b68ff1be4b87be6af328f9771e77eafef96adb99490e25c395.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 330, + 76, + 515, + 105 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 330, + 76, + 515, + 105 + ], + "spans": [ + { + "bbox": [ + 330, + 76, + 515, + 105 + ], + "type": "text", + "content": "Bar graph of the output of the network estimating the fraction of stationary pixels. If the bar is all white then it indicates that there was no motion in the video volume. If the bar is all black then every pixel was predicted to be moving." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 330, + 111, + 512, + 146 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 330, + 111, + 512, + 146 + ], + "spans": [ + { + "bbox": [ + 330, + 111, + 512, + 146 + ], + "type": "text", + "content": "Visualization of the average speed of pixels moving in a particular direction which are estimated by the directional speed network. Each ray is proportional to the speed in a particular direction. It is not proportional to the number of pixels moving in a particular direction as in the case of the angle histogram." + } + ] + } + ], + "index": 4 + }, + { + "type": "image", + "bbox": [ + 50, + 194, + 128, + 260 + ], + "blocks": [ + { + "bbox": [ + 47, + 162, + 545, + 184 + ], + "lines": [ + { + "bbox": [ + 47, + 162, + 545, + 184 + ], + "spans": [ + { + "bbox": [ + 47, + 162, + 545, + 184 + ], + "type": "text", + "content": "Figure 2. Explanation of our \"instrument panel\" showing the estimated attributes for a video volume. The interpretation of this visualization would be (roughly) a car (class 1) taking up most of the video volume, moving right at a high speed." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 50, + 194, + 128, + 260 + ], + "lines": [ + { + "bbox": [ + 50, + 194, + 128, + 260 + ], + "spans": [ + { + "bbox": [ + 50, + 194, + 128, + 260 + ], + "type": "image", + "image_path": "f6773b2dab33d298809686d909c8f010d87b79d12990edf423f223a6dc2d3b1d.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 51, + 261, + 125, + 291 + ], + "lines": [ + { + "bbox": [ + 51, + 261, + 125, + 291 + ], + "spans": [ + { + "bbox": [ + 51, + 261, + 125, + 291 + ], + "type": "text", + "content": "Frame 1719 of Street Scene Test005. The bounding box indicates a particular spatial region containing a ground truth anomaly (jawwalking)." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_caption" + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 129, + 194, + 288, + 317 + ], + "blocks": [ + { + "bbox": [ + 129, + 194, + 288, + 317 + ], + "lines": [ + { + "bbox": [ + 129, + 194, + 288, + 317 + ], + "spans": [ + { + "bbox": [ + 129, + 194, + 288, + 317 + ], + "type": "image", + "image_path": "06a052f87bc65bef1cd3269436f880d023b9058f79b16871036f12d851eb1262.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 50, + 365, + 126, + 418 + ], + "blocks": [ + { + "bbox": [ + 47, + 327, + 287, + 361 + ], + "lines": [ + { + "bbox": [ + 47, + 327, + 287, + 361 + ], + "spans": [ + { + "bbox": [ + 47, + 327, + 287, + 361 + ], + "type": "text", + "content": "Figure 3. Visualization of the learned exemplars for a region of Street Scene and visualization of a test video volume explaining why it was detected as an anomaly." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 50, + 365, + 126, + 418 + ], + "lines": [ + { + "bbox": [ + 50, + 365, + 126, + 418 + ], + "spans": [ + { + "bbox": [ + 50, + 365, + 126, + 418 + ], + "type": "image", + "image_path": "d546ba1a42ab5b043b287836e081e4819b36f67e86beb86ecc6cc8aa08cab94d.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 50, + 418, + 124, + 448 + ], + "lines": [ + { + "bbox": [ + 50, + 418, + 124, + 448 + ], + "spans": [ + { + "bbox": [ + 50, + 418, + 124, + 448 + ], + "type": "text", + "content": "Frame 119 of UCSD Ped2 Test001. The bounding box indicates a particular spatial region containing a ground truth anomaly (cyclist on sidewalk)." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 126, + 365, + 288, + 422 + ], + "blocks": [ + { + "bbox": [ + 126, + 365, + 288, + 422 + ], + "lines": [ + { + "bbox": [ + 126, + 365, + 288, + 422 + ], + "spans": [ + { + "bbox": [ + 126, + 365, + 288, + 422 + ], + "type": "image", + "image_path": "7907fd9fe77160be63a2cd16f0c3fcb82afc16764f0f94ba0f8ef400236173e5.jpg" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_body" + } + ], + "index": 12 + }, + { + "type": "image", + "bbox": [ + 208, + 425, + 286, + 487 + ], + "blocks": [ + { + "bbox": [ + 129, + 425, + 206, + 446 + ], + "lines": [ + { + "bbox": [ + 129, + 425, + 206, + 446 + ], + "spans": [ + { + "bbox": [ + 129, + 425, + 206, + 446 + ], + "type": "text", + "content": "Attributes for the test video volume centered around the cyclist shown at left." + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 208, + 425, + 286, + 487 + ], + "lines": [ + { + "bbox": [ + 208, + 425, + 286, + 487 + ], + "spans": [ + { + "bbox": [ + 208, + 425, + 286, + 487 + ], + "type": "image", + "image_path": "7db7751ff3424ef39d554282c61f95622a50d789939f2ce0021e0bf1b6a5bc14.jpg" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_body" + } + ], + "index": 14 + }, + { + "type": "image", + "bbox": [ + 50, + 522, + 129, + 571 + ], + "blocks": [ + { + "bbox": [ + 47, + 497, + 287, + 519 + ], + "lines": [ + { + "bbox": [ + 47, + 497, + 287, + 519 + ], + "spans": [ + { + "bbox": [ + 47, + 497, + 287, + 519 + ], + "type": "text", + "content": "Figure 4. Visualization example for a region of UCSD Ped2 showing an explanation of the anomaly." + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 50, + 522, + 129, + 571 + ], + "lines": [ + { + "bbox": [ + 50, + 522, + 129, + 571 + ], + "spans": [ + { + "bbox": [ + 50, + 522, + 129, + 571 + ], + "type": "image", + "image_path": "151ba021317951f04c1d4eb150e0c2a8184751ee5166e5db332d8e05c94a8a97.jpg" + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 51, + 572, + 125, + 597 + ], + "lines": [ + { + "bbox": [ + 51, + 572, + 125, + 597 + ], + "spans": [ + { + "bbox": [ + 51, + 572, + 125, + 597 + ], + "type": "text", + "content": "Frame 400 of Avenue Test004. The bounding box indicates a particular spatial region containing a ground truth anomaly (running)." + } + ] + } + ], + "index": 17, + "angle": 0, + "type": "image_caption" + } + ], + "index": 16 + }, + { + "type": "image", + "bbox": [ + 129, + 522, + 288, + 578 + ], + "blocks": [ + { + "bbox": [ + 129, + 522, + 288, + 578 + ], + "lines": [ + { + "bbox": [ + 129, + 522, + 288, + 578 + ], + "spans": [ + { + "bbox": [ + 129, + 522, + 288, + 578 + ], + "type": "image", + "image_path": "7edeaa65695e5e5a288935036b7f50c892168f9754ed07aa3d6bb2d3852918d4.jpg" + } + ] + } + ], + "index": 18, + "angle": 0, + "type": "image_body" + } + ], + "index": 18 + }, + { + "type": "image", + "bbox": [ + 129, + 580, + 282, + 647 + ], + "blocks": [ + { + "bbox": [ + 129, + 580, + 282, + 647 + ], + "lines": [ + { + "bbox": [ + 129, + 580, + 282, + 647 + ], + "spans": [ + { + "bbox": [ + 129, + 580, + 282, + 647 + ], + "type": "image", + "image_path": "1ba8a742beaa4c69385c929fdb41e5b270655e7a9599bc58892d4225cbe97d53.jpg" + } + ] + } + ], + "index": 19, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 47, + 658, + 287, + 680 + ], + "lines": [ + { + "bbox": [ + 47, + 658, + 287, + 680 + ], + "spans": [ + { + "bbox": [ + 47, + 658, + 287, + 680 + ], + "type": "text", + "content": "Figure 5. Visualization example for a region of CUHK Avenue showing an explanation of the anomaly." + } + ] + } + ], + "index": 20, + "angle": 0, + "type": "image_caption" + } + ], + "index": 19 + }, + { + "type": "table", + "bbox": [ + 309, + 193, + 544, + 284 + ], + "blocks": [ + { + "bbox": [ + 309, + 193, + 544, + 284 + ], + "lines": [ + { + "bbox": [ + 309, + 193, + 544, + 284 + ], + "spans": [ + { + "bbox": [ + 309, + 193, + 544, + 284 + ], + "type": "table", + "html": "
AttributesPed1Ped2AvenueStreet Scene
App29.6 / 64.877.7 / 92.575.6 / 67.41.1 / 4.8
Motion59.2 / 83.781.6 / 93.369.0 / 89.022.6 / 64.1
Angle40.9 / 70.670.8 / 88.166.4 / 89.324.5 / 65.9
Mag60.6 / 90.170.1 / 88.559.5 / 91.116.6 / 50.8
Bkg45.5 / 86.471.7 / 95.249.9 / 81.511.9 / 49.8
App+Mot61.7 / 88.987.4 / 97.169.6 / 86.723.9 / 65.3
", + "image_path": "fe04e6387b217efa308f869e700f6be3432a73d063a764e978a317dbb4fed8d8.jpg" + } + ] + } + ], + "index": 21, + "angle": 0, + "type": "table_body" + } + ], + "index": 21 + }, + { + "type": "table", + "bbox": [ + 314, + 347, + 538, + 389 + ], + "blocks": [ + { + "bbox": [ + 305, + 293, + 545, + 336 + ], + "lines": [ + { + "bbox": [ + 305, + 293, + 545, + 336 + ], + "spans": [ + { + "bbox": [ + 305, + 293, + 545, + 336 + ], + "type": "text", + "content": "Table 4. RBDC / TBDC AUC scores (in %) of our method when using only appearance, only motion (using angle, magnitude and background pixel predictions combined), each motion component separately and all the features" + } + ] + } + ], + "index": 22, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 314, + 347, + 538, + 389 + ], + "lines": [ + { + "bbox": [ + 314, + 347, + 538, + 389 + ], + "spans": [ + { + "bbox": [ + 314, + 347, + 538, + 389 + ], + "type": "table", + "html": "
AttributesPed1Ped2
ImageNet25.148 / 44.6364.67 / 83.17
Ours29.6 / 64.877.7 / 92.5
", + "image_path": "961f64a01cb72e35e2b984be5dc40d4a0a8151a6e2a397c6ed6e47828ad2ea2c.jpg" + } + ] + } + ], + "index": 23, + "angle": 0, + "type": "table_body" + } + ], + "index": 23 + }, + { + "bbox": [ + 305, + 397, + 545, + 430 + ], + "lines": [ + { + "bbox": [ + 305, + 397, + 545, + 430 + ], + "spans": [ + { + "bbox": [ + 305, + 397, + 545, + 430 + ], + "type": "text", + "content": "Table 5. RBDC / TBDC AUC scores (in %) of our method when using our pre-trained model versus ImageNet pe-trained model as appearance feature extractor." + } + ] + } + ], + "index": 24, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 305, + 437, + 545, + 545 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 437, + 545, + 545 + ], + "spans": [ + { + "bbox": [ + 305, + 437, + 545, + 545 + ], + "type": "text", + "content": "We further perform an ablation study on UCSD Ped1 and Ped2 datasets to empirically evaluate the benefit of our appearance model to represent object features versus using ImageNet pre-trained features. For the ImageNet pretrained model, we use the pre-classification layer output of ResNext-50 as features. We present our results in Table 5. The superiority of our model is most likely due to the loss function used (binary cross-entropy) which allows an image patch to contain zero or multiple object classes." + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 306, + 555, + 462, + 568 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 555, + 462, + 568 + ], + "spans": [ + { + "bbox": [ + 306, + 555, + 462, + 568 + ], + "type": "text", + "content": "5. Discussion and Conclusions" + } + ] + } + ], + "index": 26 + }, + { + "bbox": [ + 304, + 576, + 545, + 707 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 576, + 545, + 707 + ], + "spans": [ + { + "bbox": [ + 304, + 576, + 545, + 707 + ], + "type": "text", + "content": "We have presented a novel method for explainable video anomaly localization that has a number of desired properties. Foremost, the method is accurate and general. We have shown that it works very well on five different datasets and, in particular, achieves state-of-the-art results on CUHK Avenue, Street Scene and ShanghaiTech. Setting it apart from almost all previous work, our model is understandable by humans and the decisions that our method makes are explainable. Finally, because our method does not require an expensive training phase on the nominal data, it is easy to expand our model when new nominal data is available." + } + ] + } + ], + "index": 27 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "18724" + } + ] + } + ], + "index": 28 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 288, + 712 + ], + "type": "list", + "angle": 0, + "index": 15, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 123 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 123 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 123 + ], + "type": "text", + "content": "[1] Detecting anomalous events in videos by learning deep representations of appearance and motion. 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Springer, 2007. 4" + } + ] + } + ], + "index": 23 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 749, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 749, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 749, + 318, + 757 + ], + "type": "text", + "content": "18726" + } + ] + } + ], + "index": 25 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 9 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/EVA_ Exploring the Limits of Masked Visual Representation Learning at Scale/c4046a48-182c-4cee-86a4-65a7035e3e1d_content_list.json b/2023/EVA_ Exploring the Limits of Masked Visual Representation Learning at Scale/c4046a48-182c-4cee-86a4-65a7035e3e1d_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..a43fa06ed8dea73387288cdbc5c484d86d5f34b5 --- /dev/null +++ b/2023/EVA_ Exploring the Limits of Masked Visual Representation Learning at Scale/c4046a48-182c-4cee-86a4-65a7035e3e1d_content_list.json @@ -0,0 +1,1714 @@ +[ + { + "type": "text", + "text": "EVA: Exploring the Limits of Masked Visual Representation Learning at Scale", + "text_level": 1, + "bbox": [ + 88, + 130, + 880, + 152 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Yuxin Fang $^{1,2\\dagger}$ Wen Wang $^{3,2\\dagger}$ Binhui Xie $^{4,2\\dagger}$ Quan Sun $^{2}$ Ledell Wu $^{2}$ Xinggang Wang $^{1\\dagger}$ Tiejun Huang $^{2}$ Xinlong Wang $^{2\\dagger}$ Yue Cao $^{2\\dagger}$", + "bbox": [ + 169, + 178, + 799, + 220 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1Huazhong University of Science and Technology \n2Beijing Academy of Artificial Intelligence \n3Zhejiang University \n4Beijing Institute of Technology", + "bbox": [ + 125, + 224, + 797, + 261 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Code & Models: baaivision/EVA/01", + "bbox": [ + 346, + 272, + 614, + 285 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 321, + 313, + 338 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "We launch EVA, a vision-centric foundation model to Explore the limits of Visual representation at scAle using only publicly accessible data. EVA is a vanilla ViT pretrained to reconstruct the masked out image-text aligned vision features conditioned on visible image patches. Via this pretext task, we can efficiently scale up EVA to one billion parameters, and sets new records on a broad range of representative vision downstream tasks, such as image recognition, video action recognition, object detection, instance segmentation and semantic segmentation without heavy supervised training. Moreover, we observe quantitative changes in scaling EVA result in qualitative changes in transfer learning performance that are not present in other models. For instance, EVA takes a great leap in the challenging large vocabulary instance segmentation task: our model achieves almost the same state-of-the-art performance on LVIS dataset with over a thousand categories and COCO dataset with only eighty categories. Beyond a pure vision encoder, EVA can also serve as a vision-centric, multi-modal pivot to connect images and text. We find initializing the vision tower of a giant CLIP from EVA can greatly stabilize the training and outperform the training from scratch counterpart with much fewer samples and less compute, providing a new direction for scaling up and accelerating the costly training of multi-modal foundation models.", + "bbox": [ + 76, + 353, + 473, + 731 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 758, + 209, + 773 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Scaling up pre-trained language models (PLMs) [9,64,76] has revolutionized natural language processing (NLP) in the past few years. The key to this success lies in the simple and scalable self-supervised learning task of masked signal", + "bbox": [ + 75, + 782, + 468, + 844 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "prediction [29, 74], with which Transformer models [99] could be scaled up to billions of parameters using nearly unlimited unlabelled data, and generalize well to a wide range of downstream tasks with little tuning. With further scaling on compute, data, and model sizes, PLMs have led to not only continuous performance improvements [50, 75, 76], but also a surprising emergence of in-context learning capability [9, 25, 104, 105].", + "bbox": [ + 500, + 323, + 893, + 444 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Motivated by the success of model scaling in NLP, it is appealing that we can also translate this success from language to vision, i.e., to scale up a vision-centric foundation model that is beneficial for both vision & multi-modal downstream tasks. Recently, masked image modeling (MIM) [5, 39, 113] has boomed as a viable approach for vision model pretraining and scaling. However, the most competitive billion-sized vision pre-trained models [31, 65, 71, 119] still heavily rely on supervised or weakly-supervised training with hundreds of millions of (often publicly inaccessible) labeled data. MIM is somewhat only adopted as an initialization stage before the heavily supervised pre-training [65], or a pure MIM pre-trained model could not achieve favorable performance at billion-scale model sizes [114]. We regard this gap stems from the fact that natural images are raw and information-sparse. Meanwhile, an ideal vision pretext task needs the abstraction of not only the low-level geometry & structure information, but also high-level semantics, which is hardly captured by pixel-level recovery tasks [112].", + "bbox": [ + 496, + 445, + 895, + 733 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "In this work, we seek a suitable MIM pretext task for large scale vision representation learning and explore its limits at the scale of one billion parameters with tens of millions of unlabeled data. Recently, there are a few trials leveraging the semantic information from image-image or image-text contrastive learning [13, 22, 73] for MIM pretraining [43, 106, 124], which perform fairly well in vision downstream tasks. However, there remains a debate that (i) tokenized semantic features could provide better supervision signal for masked modeling in vision [5, 70, 101], and (ii) good performances could be also achieved via a simple post", + "bbox": [ + 496, + 734, + 895, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 810, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "†Interns at Beijing Academy of Artificial Intelligence (BAAI). ‡Corresponding authors: Yue Cao (caoyue10@gmail.com), Xinlong Wang (xinlong.wang96@gmail.com) and Xinggang Wang (xgwang@hust.edu.cn).", + "bbox": [ + 75, + 849, + 472, + 900 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "19358", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 0 + }, + { + "type": "table", + "img_path": "images/82a953b2c1e1c5fd24326288c52724d9881d9da00319f680323000afdbdbe23c.jpg", + "table_caption": [], + "table_footnote": [ + "Table 1. Summary of EVA performance on various mainstream vision benchmarks. EVA is performant compared with previous best / leading approaches. “”: methods / results that only exploit publicly accessible data / academic resources. “ft”: end-to-end fine-tuning. “lin”: linear probing. “zs”: zero-shot classification. “avg. zs”: averaged zero-shot classification performance on 8 image and 4 video datasets with contrastive language-image pre-training. (timestamp: Nov 10, 2022)", + "methods / results reference. a: BEiT-3 [101], b: iBOT [124], c: Open CLIP-H [47], d: Text4Vis [109], e: MaskFeat [103], f: Group DETRv2 [19], g: FocalNet [116], h: FD-SwinV2-G [107], i: Mask DINO [57], j: LVIS 2021 competition $1^{\\text{st}}$ [35], k: ViT-Adapter [23]." + ], + "table_body": "
modelimage & video classification (G)object detection (det) & instance segmentation (seg)semantic segmentation
IN-1K ftIN-1K linIN-1K zsavg. zsK400K600K700COCO det (test/val)COCO seg (test/val)LVIS segCOCO-StuffADE20K
Florence----86.587.8-62.4 / 62.0----
SwinV2-G----86.8--63.1 / 62.554.4 / 53.7--59.9
prev. best89.6a82.3b78.0c73.1c87.8d88.3e80.4e64.5f / 64.2g55.4h / 54.5i49.2j52.3k62.8a
EVA89.7(+0.1)86.5(+4.2)78.5(+0.5)75.7(+2.6)89.7(+1.9)89.8(+1.5)82.9(+2.5)64.7 / 64.5(+0.2/+0.3)55.5 / 55.0(+0.1/+0.5)55.0(+5.8)53.4(+1.1)62.3(-0.5)
", + "bbox": [ + 76, + 50, + 895, + 135 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "distillation process without masked prediction tasks [107]. Through a pilot empirical study, we find that simply using image-text aligned (i.e., CLIP [73]) vision features as the prediction targets in MIM scales up well and achieves satisfactory performances on a broad range of downstream benchmarks. This pre-training task draws the benefits from both the high-level semantic abstraction of image-text contrastive learning as well as the good capture of geometry & structure in masked image modeling, which typically covers the information needed for most visual perception tasks.", + "bbox": [ + 75, + 242, + 472, + 393 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Via this MIM pretext task, we can efficiently scale up a vanilla ViT encoder [31], dubbed EVA, to one billion parameters with strong visual representations that transfers well to a wide range of downstream tasks. Using 29.6 million public accessible unlabeled images for pre-training, EVA sets new records on several representative vision benchmarks, such as image classification on ImageNet-1K [28] (89.7% top-1 accuracy), object detection and instance segmentation on LVIS [38] (62.2 AP $^{\\text{box}}$ & 55.0 AP $^{\\text{mask}}$ on val) and COCO [62] (64.5 AP $^{\\text{box}}$ & 55.0 AP $^{\\text{mask}}$ on val, 64.7 AP $^{\\text{box}}$ & 55.5 AP $^{\\text{mask}}$ on test-dev),", + "bbox": [ + 75, + 396, + 473, + 547 + ], + "page_idx": 1 + }, + { + "type": "table", + "img_path": "images/c0a8edfdc0e7f49372919217f15d4c61583566b0a3849b7dcb29ff19b9cfd8e3.jpg", + "table_caption": [], + "table_footnote": [ + "(a) (Additional) semantic feature tokenization is not required for achieving good downstream performance." + ], + "table_body": "
tokenizer? [70]pt epochsImageNet-1K top-1 acc.ADE20K mIoUss
X-85.052.6
✓30085.052.7
✓160085.553.1
X80085.553.3
", + "bbox": [ + 106, + 553, + 449, + 631 + ], + "page_idx": 1 + }, + { + "type": "table", + "img_path": "images/dcec287983f48fca359b2a408746b62c37030ee9fac4798b0dae3380c8c3544f.jpg", + "table_caption": [], + "table_footnote": [ + "(b) Feature distillation fails to achieve consistent performance gain as the pre-training becomes longer." + ], + "table_body": "
distill.?[107]pt epochsImageNet-1K top-1 acc.ADE20K mIoUss
X-85.052.6
✓30085.152.5
✓80085.152.7
X80085.553.3
", + "bbox": [ + 106, + 666, + 447, + 744 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Table 2. Pilot experiment. We evaluate different pre-training approaches using ViT-B and report their performance on ImageNet-1K image classification (top-1 accuracy) and ADE20K semantic segmentation (single-scale mIoU). Numbers in grey refer to the results of directly fine-tuning CLIP vision encoder on corresponding downstream tasks. Default settings for EVA pre-training are marked in purple, i.e., directly regressing the masked out CLIP vision features conditioned on visible image patches.", + "bbox": [ + 75, + 782, + 472, + 896 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "semantic segmentation on COCO-stuff [11] (53.4 mIoU $^{\\mathrm{ss}}$ ) and ADE20K [123] (62.3 mIoU $^{\\mathrm{ms}}$ ), and video action recognition on Kinetics-400 [51] (89.7% top-1 accuracy), Kinetics-600 [14] (89.8% top-1 accuracy), Kinetics-700 [15] (82.9% top-1 accuracy). Notably, different from other state-of-the-art billion-scale vision foundation models that demand tens of millions of or even billions of labeled images, such as SwinV2-G using ImageNet-21K-ext-70M [65] and ViT-g/G using JFT3B [119], EVA does not need a costly supervised training stage and only leverage images from open-sourced datasets for academic reproducibility.", + "bbox": [ + 496, + 242, + 893, + 409 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Moreover, we observe quantitative changes in scaling EVA result in qualitative changes in transfer learning performance that are not observed in other smaller-scale models, e.g., EVA makes a significant breakthrough in the challenging large vocabulary object-level recognition task: our model achieves almost the same performance on LVIS [38], an instance segmentation benchmark with more than 1,200 categories, as COCO [62], which almost shares the same image set as LVIS but with only 80 categories annotated. This emergent ability well matches the expectation of model scaling [105], that larger capability of model results in not only predictable performance improvements on standard benchmarks, but also unpredictable phenomena and capabilities for resolving more challenging tasks.", + "bbox": [ + 496, + 411, + 895, + 625 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Going beyond a pure vision encoder, EVA can also serve as a vision-centric, multi-modal pivot that builds a bridge between vision and language. We show that initializing the image encoder via pre-trained EVA in a 1.1 billion parameters CLIP model can outperform the training from scratch counterpart on a broad range of zero-shot image / video classification benchmarks with much fewer samples and less compute. Moreover, EVA can greatly stabilize the giant CLIP's training & optimization process. Since large CLIP models usually suffer from training instability and inefficiency issues [2,47], we hope our solution opens up a new direction for scaling up and accelerating the costly training of multi-modal foundation models.", + "bbox": [ + 496, + 626, + 895, + 821 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "By scaling up vision-centric foundation models with MIM pre-training to achieve strong performance on broad downstream tasks, we hope EVA would bridge the gap between vision and language with masked signal modeling, and contributes to the big convergence across different modalities.", + "bbox": [ + 496, + 824, + 893, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "19359", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 1 + }, + { + "type": "table", + "img_path": "images/b5580e9164c9c64e077ee38af74c73be0fee35b01fd07a22c1d4944d64ab418f.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
patch size#layershidden dimmlp dimattn heads#param.
14×144014086144161011M
", + "bbox": [ + 107, + 44, + 467, + 77 + ], + "page_idx": 2 + }, + { + "type": "table", + "img_path": "images/02202355881f2015355298116ec8289fa144492f37a3f4884602485ccf9243d5.jpg", + "table_caption": [ + "(a) EVA architecture configurations." + ], + "table_footnote": [ + "(c) some pre-training settings and hyper-parameters." + ], + "table_body": "
image sizebatch sizeoptimizerpeak lr(β1, β2)pt epochs
22424096AdamW1e-3(0.9, 0.98)150
", + "bbox": [ + 106, + 99, + 464, + 128 + ], + "page_idx": 2 + }, + { + "type": "table", + "img_path": "images/7d9e8d5dbb1938fdde8dbaf10db4ec537b6242ff6375dd8f06d63ba7bbabcade.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
datasettotal size
ImageNet-21K, CC12M, CC3M, Object365, COCO, ADE29.6M images
", + "bbox": [ + 496, + 44, + 875, + 77 + ], + "page_idx": 2 + }, + { + "type": "table", + "img_path": "images/f8b53c1d5fc01d79cb31b513157724825e11067db902b46d2b63d38a2a0612a7.jpg", + "table_caption": [ + "(b) datasets for pre-training EVA." + ], + "table_footnote": [], + "table_body": "
precisionZeRO#gpusamples / sec.max mem.pt days
fp16stage-1128~3150~26.5GB~14.5
", + "bbox": [ + 501, + 99, + 875, + 128 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "(d) basic statistics of EVA pre-training.", + "bbox": [ + 581, + 132, + 787, + 143 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Table 3. A brief summary of pre-training settings and configurations for EVA.", + "bbox": [ + 238, + 150, + 730, + 164 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "2. Fly EVA to the Moon", + "text_level": 1, + "bbox": [ + 76, + 183, + 279, + 200 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We first conduct a series of pilot experiments for choosing an ideal vision pretext task in §2.1, then we scale up EVA pre-training via the chosen pre-training objective in §2.2. Finally, we evaluate the pre-trained representation on various downstream tasks in §2.3. Detailed experimental settings and configurations are in Appendix.", + "bbox": [ + 75, + 209, + 470, + 299 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "2.1. The Feature Instrumentality Project", + "text_level": 1, + "bbox": [ + 76, + 306, + 392, + 324 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In this section, we seek a MIM vision pretext task with compelling transfer performance. Based on previous literature on vision pre-training, we study two promising candidates: (i) recovering the masked out tokenized semantic vision features [5, 70, 101], and (ii) feature distillation from strong pre-trained representation as in [107]. Both of them exploit pre-trained image-text aligned vision features (i.e., CLIP [73] vision features). Via a series of pilot experiments shown in Table 2, we find that: (i) the (additional) CLIP feature tokenization process is unnecessary for achieving good downstream performance (ii) feature distillation fails to provide consistent performance gain as the pre-training becomes longer. Instead, we find that simply reconstructing the masked out CLIP vision features conditioned on visible image patches is highly performant, which is chosen for scaling up EVA.", + "bbox": [ + 75, + 330, + 470, + 571 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We clarify that this MIM pretext task is not originally proposed by us. Regressing the masked out image-text aligned vision features for MIM pre-training has been studied in MVP [106] and recently has been revisited by MILAN [43]. In this work, we show that this pretext task can scale up to billion-scale parameters and tens of millions of unlabeled images for vision-centric representation learning without (i) semantic feature quantization / tokenization [5, 70], and (ii) explicitly using image-text paired pre-training data and large corpora as in BEiT-3 [101].", + "bbox": [ + 75, + 571, + 470, + 723 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "2.2. Pre-training", + "text_level": 1, + "bbox": [ + 76, + 732, + 209, + 748 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Architecture. The architecture configurations of EVA are in Table 3a. EVA is a vanilla ViT [31] with 1.0B parameters. The shape of her follows ViT giant [119] and the vision encoder of BEiT-3 [101]. We do not use relative positional embeddings [89] and layer-scale [97] during pre-training.", + "bbox": [ + 75, + 758, + 468, + 835 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Pre-training objective. EVA is pre-trained to reconstruct the masked out image-text aligned vision features conditioned on visible image patches. We corrupt the input patches with [MASK] tokens, and we use block-wise masking with", + "bbox": [ + 75, + 839, + 470, + 901 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "a masking ratio of $40\\%$ following [5, 70, 101]. The target for MIM pre-training is from the publicly available OpenAI CLIP-L/14 vision tower trained on $224\\times 224$ pixel images [73]. The output feature of EVA is first normalized [3] and then projected to the same dimension as the CLIP feature via a linear layer. We use negative cosine similarity as the loss function.", + "bbox": [ + 496, + 184, + 893, + 289 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Pre-training data. The data we used for pre-training EVA are summarized in Table 3b. For CC12M [16] and CC3M [88] datasets, we only use the image data without captions. For COCO [62] and ADE20K [123] datasets, we only use the train set data. ImageNet-21K [28] and Object365 [87] image data are also used. All these data are publicly accessible. The merged dataset for pre-training has 29.6 million images in total.", + "bbox": [ + 496, + 304, + 893, + 425 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Pre-training settings & hyper-parameters. As shown in Table 3c, EVA is optimized via Adam [52] with decoupled weight decay [67] of 0.05. The peak learning rate is 1e-3 and decays according to a cosine learning rate schedule. We employed stochastic depth [45] with a rate of 0.1 for regularization and RandResizeCrop (0.2, 1) for data augmentation. Color jitter is not used.", + "bbox": [ + 496, + 438, + 893, + 544 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Pre-training infrastructure and statistics. Some basic pre-training statistics are available in Table 3d. The GPU we use is NVIDIA A100-SXM4-40GB. Pre-training code is based on BEiT [5] written in PyTorch [69]. We also adopt DeepSpeed optimization library [80] with ZeRO stage-1 optimizer [77] to save memory. We find using fp16 format with dynamic loss scaling is stable enough during the whole course of pre-training while using bf1oat16 format is unnecessary. Since we use fp16 precision, EVA can also be pre-trained using $16 \\times$ NVIDIA 24GB (32GB) GPUs with (without) gradient checkpointing [20].", + "bbox": [ + 496, + 558, + 893, + 724 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "2.3. Evaluation on Downstream Tasks", + "text_level": 1, + "bbox": [ + 500, + 761, + 792, + 777 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In this section, we extensively evaluate pre-trained EVA on several representative benchmarks, such as image classification (§2.3.1), video action recognition (§2.3.2), object detection & instance segmentation (§2.3.3), semantic segmentation (§2.3.4), and contrastive image-text pre-training with zero-shot evaluation (§2.3.5). EVA achieves state-of-the-art performance on a broad range of downstream tasks.", + "bbox": [ + 496, + 794, + 893, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "19360", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 2 + }, + { + "type": "table", + "img_path": "images/8b488b1a745fda83165ec8c1fdedc051e89ff3bf4c3871b80c253dc8407b599f.jpg", + "table_caption": [ + "model #param. extra labeled data image size top-1 acc." + ], + "table_footnote": [], + "table_body": "
using private labeled data
SwinV2-G [65]3.0BIN-21K-ext-70M640290.2
ViT-G [119]1.8BJFT-3B518290.5
ViT-g (CoCa) [117]1.0BJFT-3B+ALIGN576291.0
using public labeled data
CoAtNet-4 [27]275MIN-21K (14M)512288.6
MaxViT-XL [98]475MIN-21K (14M)512288.7
MViTv2-H [61]667MIN-21K (14M)512288.8
FD-CLIP-L [107]304MIN-21K (14M)336289.0
BEiT-3 [101]2.0B35M img-text pairs336289.6
EVA1.0BIN-21K (14M)336289.6
EVA1.0BIN-21K (14M)560289.7
", + "bbox": [ + 78, + 66, + 468, + 234 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "2.3.1 Image Classification", + "text_level": 1, + "bbox": [ + 76, + 309, + 272, + 324 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Datasets. For image classification task, we evaluate EVA on ImageNet-1K (IN-1K) [28] validation set. We also evaluate the robustness & generalization capability of EVA along with our training settings & hyper-parameters using ImageNet-V2 matched frequency (IN-V2) [81], ImageNet-ReaL (IN-ReaL) [7], ImageNet-Adversarial (IN-Adv.) [42], ImageNet-Rendition (IN-Ren.) [41], ImageNet-Sketch (IN-Ske.) [100].", + "bbox": [ + 75, + 339, + 470, + 445 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Training Settings. Following the conventional setting [5, 70, 101], we first perform intermediate fine-tuning on ImageNet-21K [28] for 60 epochs with an image resolution of $224^2$ , then EVA is further fine-tuned on ImageNet-1K training set for 10 epochs. Different from [117, 119] that use multi-head attention pooling and BEiT-3 that exploits an additional pretrained giant language tower as the image classification task layer, we simply adopt a linear layer as the classifier [31]. Notice that the supervised intermediate fine-tuning consumes only $\\sim 1/5$ of the time & compute of the MIM pre-training stage. While for other billion-scale vision models such as SwinV2-G-3B, the supervised training phase costs $\\sim 1.5 \\times$ resources than the MIM pre-training.", + "bbox": [ + 75, + 450, + 470, + 648 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Results. Table 4 compares EVA with some state-of-the-art models on ImageNet-1K validation set. EVA achieves $89.6\\%$ top-1 accuracy with $336^{2}$ inputs, comparable to BEiT-3. Using a larger image resolution of $560^{2}$ can further boost the top-1 accuracy to $89.7\\%$ . Notice that BEiT-3 treats image classification as an image-to-text retrieval task. Therefore they leverage an additional one billion parameters pre-trained language encoder along with 35 million image-text data (21M pairs from CC12M, CC3M, SBU, COCO, VG and 14M pairs from ImageNet-21K) as well as 160GB text data in total. Meanwhile, we simply use a linear classifier on top of EVA with only ImageNet-21K image-tag data used for additional finetuning. With only publicly available data, EVA creates a new state-of-the-art image classification result on ImageNet-1K with a much neater architecture.", + "bbox": [ + 75, + 652, + 470, + 878 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Robustness & generalization ability evaluation. We eval", + "bbox": [ + 76, + 885, + 470, + 900 + ], + "page_idx": 3 + }, + { + "type": "table", + "img_path": "images/3b38f2848db87ab1fd77242281c8b946170222af8e36179b3cee879649970651.jpg", + "table_caption": [ + "Table 4. Comparisons of image classification performance on ImageNet-1K validation set. With only publicly available data, EVA creates a new state-of-the-art ImageNet-1K image classification result with a canonical linear classifier." + ], + "table_footnote": [], + "table_body": "
modelIN-1KIN-V2IN-ReALIN-Adv.IN-Ren.IN-Ske.avg.Δ↓
ConvNeXt87.577.790.570.867.053.774.513.0
SwinV287.577.390.273.967.752.374.812.7
MAE87.879.290.376.766.550.975.212.6
DeiT387.779.190.279.270.654.977.010.7
Eff-L2-NS88.480.590.684.874.747.677.810.6
BEiTv288.480.190.376.276.458.378.310.1
BEiT88.679.990.781.773.256.878.510.1
EVA89.681.690.886.288.367.784.05.6
", + "bbox": [ + 501, + 50, + 893, + 176 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Table 5. Robustness & generalization capability evaluation on ImageNet-1K variants. We test each model on different ImageNet-1K validation sets, without any specialized fine-tuning. \"avg.\": the averaged top-1 accuracy on 6 different ImageNet-1K validation set variants. \"Δ↓\": The gap between the averaged top-1 accuracy on 6 variants (i.e., IN-{1K, V2, Real, Adv., Ren., Ske.}) and the original ImageNet-1K validation set top-1 accuracy (the lower the better).", + "bbox": [ + 496, + 180, + 893, + 277 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "uate the robustness and generalization capability of EVA trained with an image size of $336^{2}$ on 6 different ImageNet1K validation set variants. In Table 5, we compare EVA with some top open-sourced models collected by the timm library [108]. Following the evaluation procedure in [39], all these models are first fine-tuned on the original ImageNet1K training set and then evaluated on different validation sets using the same fine-tuned model without further hyperparameter selection and specialized fine-tuning.", + "bbox": [ + 496, + 297, + 893, + 434 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "As shown in Table 5, EVA is the most competitive one in terms of absolute top-1 accuracies. However, these model various in pre-train data (from ImageNet-1K, ImageNet-21K to JFT-300M), input resolutions (from $224^2$ to $800^2$ ), model sizes (from hundreds of millions to one billion parameters) as well as architectures (ConvNets, vanilla & hierarchical ViTs), etc. Therefore their absolute accuracies are not directly comparable. Instead, we are more interested in the gap between the averaged top-1 accuracy on 6 validation set variants and the original ImageNet-1K validation set top-1 accuracy (the lower the better), i.e., we care about whether a model along with its training settings biases towards the original validation set and generalize well on other variants. From this perspective, EVA not only achieves the highest averaged accuracy, but also has the smallest performance gap, which reflects the excellent robustness and generalization ability of EVA.", + "bbox": [ + 496, + 435, + 893, + 676 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "2.3.2 Video Action Recognition", + "text_level": 1, + "bbox": [ + 500, + 695, + 732, + 709 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Datasets. For video action recognition, we evaluate EVA on Kinetics-400 (K-400) [51], Kinetics-600 (K-600) [14] and Kinetics-700 (K-700) [15] benchmarks. We first conduct intermediate fine-tuning on a merged dataset coined Kinetics-722 (K-722) that integrates videos from K-400, K-600 and K-700. We remove leaked as well as repeated videos in both training and validation sets. After this data de-duplicating", + "bbox": [ + 496, + 723, + 893, + 830 + ], + "page_idx": 3 + }, + { + "type": "page_footnote", + "text": "Source: link (timestamp: Nov 10, 2022). The detailed model configurations are (arch-model_size-Img_resolution-data): ConvNeXt-XL-384px-21K [66], SwinV2-L-384px-21K [65], MAE-H-448px-1K [39], DeiT3-L-384px-21K [96], EfficientNet-L2&NS-800px-JFT300M [110], BEiTv2-L-224px-21K [70], BEiT-L-512px-21K [5], EVA-g-336px-merged30M&21K.", + "bbox": [ + 496, + 839, + 893, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "19361", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 3 + }, + { + "type": "table", + "img_path": "images/83a46e8246b5294dd9a4570aa2bd4f3d28dbe35c6bd5725ca18255a60eb6a4a3.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
modeltop-1 accuracy
Kinetics-400Kinetics-600Kinetics-700
MAE [34]86.8--
SwinV2-G [65]86.8--
Florence [118]86.888.0-
MaskFeat [103]87.088.380.4
VideoMAE [95]87.4--
X-CLIP [68]87.788.3-
CoVeR [120]87.287.978.5
CoCa [117] (frozen)88.088.581.1
CoCa [117] (finetuned)88.989.482.7
EVA89.789.882.9
", + "bbox": [ + 81, + 89, + 460, + 250 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Table 6. Video action recognition. With only publicly available K-400, K-600 and K-700 as video pre-training data, EVA is also quite performant in video action recognition tasks.", + "bbox": [ + 75, + 250, + 468, + 292 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "process, K-722 has 0.63M training videos in total with 722 action classes. A similar approach is also used in [58].", + "bbox": [ + 75, + 309, + 468, + 340 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Training & evaluation settings. EVA processes video data simply via spatial-temporal attention as [34, 95] with no specific architectural adaptation for video related tasks. We first train EVA using K-722 training set for 40 epochs with 8 frames and $224^2$ resolution, then we fine-tune EVA on each dataset for only 1 or 2 epochs. We set frame $\\times$ crop $\\times$ clip to $16 \\times 3 \\times 4$ for fine-tuning and evaluation for all datasets. The frame resolution is $224^2$ .", + "bbox": [ + 75, + 344, + 468, + 465 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Results. As shown in Table 6, EVA achieves better performance compared with some recent video-specific or large foundation models in video recognition. For reference, directly adapting image-only pre-trained EVA to K-400 without K-722 intermediate fine-tuning can also achieve a very competitive top-1 accuracy of $88.4\\%$ .", + "bbox": [ + 75, + 469, + 468, + 561 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "2.3.3 Object Detection & Instance Segmentation", + "text_level": 1, + "bbox": [ + 76, + 580, + 428, + 595 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Datasets. We evaluate the object detection and instance segmentation performance of EVA on both COCO [62] and LVIS [38]. COCO is a widely used object-level recognition benchmark with 80 common object categories. LVIS is an emerging large-vocabulary object-level recognition benchmark, which has more than 1,200 object categories as well as more than 2 million high quality instance segmentation masks (nearly $2 \\times$ of COCO). Notably, COCO and LVIS almost use the same set of images, and both train and val split of LVIS have a huge overlap with COCO train and val split. Meanwhile, COCO has much fewer object categories than LVIS (i.e., $80 \\text{ v.s. } 1,200+$ ). Therefore it is meaningful to evaluate models' performance on both COCO and LVIS.", + "bbox": [ + 75, + 609, + 468, + 805 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Training & evaluation settings. EVA uses Cascade Mask R-CNN [12] as the detector and adopts the training settings (e.g., LSJ data augmentation [36]) & architecture configurations (e.g., interleaved window & global attention) of ViTDet [60]. Following the common practice [65, 101, 121], we first conduct intermediate fine-tuning for the whole detec", + "bbox": [ + 75, + 809, + 470, + 901 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "tor using Objects365 [87] dataset with a resolution of $1024^2$ , then we fine-tune the detector on COCO and LVIS train split respectively with $1280^2$ inputs.", + "bbox": [ + 496, + 90, + 890, + 136 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We report single-scale evaluation and multi-scale evaluation / test-time augmentation (tta) results of EVA for comparison. For COCO, Soft-NMS [8] is also applied. For instance segmentation task, the classification score is calibrated [46] via maskness [102].", + "bbox": [ + 496, + 136, + 893, + 210 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The model architecture as well as the hyper-parameters for COCO and LVIS are almost the same (i.e., the hyperparameters are nearly \"zero-shot\" transferred from COCO to LVIS), expect we use federated loss [125] and repeat factor sampling [38] following ViTDet on LVIS.", + "bbox": [ + 496, + 212, + 893, + 287 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Results. Perhaps COCO is the most fierce vision benchmark. Table 7 compares EVA with some leading approaches on COCO. Our model creates new state-of-the-art results on both object detection and instance segmentation tasks.", + "bbox": [ + 496, + 291, + 890, + 351 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Compared with ViTDet-H [60] that uses Cascade Mask R-CNN [12] as well, EVA shows that with a larger model and better encoder & detector pre-training, the performance can be greatly improved with the same detector.", + "bbox": [ + 496, + 352, + 890, + 412 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Compared with FocalNet [116] and Group DETRv2 [19] that choose better-established and highly-optimized DINO detector [121], EVA demonstrates that with sufficient model size, data and pre-training, better performance can be also achieved via the classic R-CNN framework [37]. On the other hand, FocalNet and Group DETRv2 are incapable of instance segmentation due to using DINO.", + "bbox": [ + 496, + 412, + 890, + 518 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Compared with SwinV2-Giant [65] and FD-SwinV2-Giant [107] that also adopt a (stronger $\\mathrm{HTC}++$ [17]) detector from the R-CNN family but with $\\sim 3\\times$ model size of EVA, our approach streamlines the pre-training processes and pulls off a \"Giant-killing\" act via better representations.", + "bbox": [ + 496, + 518, + 893, + 593 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Compared with BEiT-3, EVA shows that it is possible to build a state-of-the-art object-level recognition system without exploiting (i) semantic feature quantization / tokenization [5, 70], and (ii) image-text paired pre-training data and large corpora during pre-training.", + "bbox": [ + 496, + 594, + 893, + 670 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Analyzing the performance gap between LVIS and COCO. Evaluating models on both COCO and LVIS benchmarks is essential, as they share nearly the same image set but differ in the number of annotated object categories. COCO has only 80 annotated categories, while LVIS annotates over 1,200 object categories, resulting in a long-tail distribution that more closely resembles challenging real-world scenarios [38]. In general, LVIS is considered a much more difficult benchmark than COCO for object-level recognition, with conventional methods typically experiencing a significant performance drop on LVIS.", + "bbox": [ + 496, + 674, + 893, + 839 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In Table 8a, we analyze the performance gap between the LVIS and COCO benchmarks for EVA and other state-of-the-art approaches. For previous leading methods, such as ViTDet, the performance gap for $\\mathrm{AP^{box}}$ is around 8, and", + "bbox": [ + 496, + 840, + 893, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "19362", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/f0e16c581dfb7abaaae9a76fae682250aff9c8fd2f73df5fd34c69b1ccbb9cbb.jpg", + "table_caption": [], + "table_footnote": [ + "\"merged data\": FourODs + INBoxes + GoldG + CC15M + SBU, \"merged data\": IN-21K (14M) + Image-Text (35M) + Text (160GB)." + ], + "table_body": "
model / methoddetector#param.pre-training datatta?COCO valCOCO test-dev
encoderdetectorAPboxAPmaskAPboxAPmask
Soft-Teacher [115]HTC++ [17]284MIN-21K (14M)COCO(unlabeled)+O365✓60.752.561.353.0
GLIP [59]DyHead [26]≥ 284MIN-21K (14M)4ODs+GoldG+Cap12M✓60.8-61.5-
GLIPv2 [122]DyHead [26]≥ 637MFLD-900M\\( merged\\ data^a \\)✓--62.4-
ViTDet-H [60]CMask R-CNN [12]692MIN-1K (1M)-✓61.353.1--
Florence [118]DyHead [26]≥ 637MFLD-900M\\( merged\\ data^a \\)✓62.0-62.4-
SwinV2-G [65]HTC++ [17]≥ 3000MIN-21K-ext-70MO365✓62.553.763.154.4
DINO [121]-218MIN-21K (14M)O365✓63.2-63.3-
Mask DINO [57]-223MIN-21K (14M)O365✓-54.5-54.7
BEiT-3 [101]CMask R-CNN [12]1074M\\( merged\\ data^b \\)O365✓--63.754.8
FD-SwinV2-G [107]HTC++ [17]≥ 3000MIN-21K-ext-70MO365✓--64.255.4
FocalNet [116]DINO [121]746MIN-21K (14M)O365✓64.2-64.4-
Group DETRv2 [19]DINO [121]629MIN-1K (1M)O365✓--64.5-
EVACMask R-CNN [12]1074Mmerged-30MO365✘64.255.064.455.5
EVACMask R-CNN [12]1074Mmerged-30MO365✓64.5-64.7-
", + "bbox": [ + 78, + 50, + 890, + 275 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/95397cdcec0ebadc1b78ae228fdc5eaae6b01dc3d5da65b5661f9d85bd0b4f5d.jpg", + "table_caption": [ + "Table 7. Object detection & instance segmentation on results COCO dataset. EVA establishes new state-of-the-art results in object detection and instance segmentation tasks on both COCO val and test-dev splits with the canonical R-CNN [37] object detection & segmentation framework. \"tta\" refers to test-time augmentation. (timestamp: Nov 10, 2022)" + ], + "table_footnote": [], + "table_body": "
modelAPboxAPmask
COCOLVISΔ↓COCOLVISΔ↓
(a) evaluation using COCO & LVIS official annotations respectively
Copy-Paste [36]57.041.615.448.938.110.8
ViTDet-H [60]61.353.47.953.148.15.0
prev. best63.2a53.4b9.854.5c49.2d5.3
EVA (single-scale test)64.162.21.955.055.00.0
(b) evaluation using LVIS val1-5K annotations
EVA (single-scale test)69.668.31.359.659.8-0.2
", + "bbox": [ + 84, + 348, + 459, + 474 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "for $\\mathrm{AP^{mask}}$ , it is around 5. However, when using the same detector (Cascade Mask R-CNN) and nearly identical settings as those in ViTDet pre-trained via MAE-Huge (ViTDet-H), EVA not only achieves state-of-the-art results on both LVIS and COCO benchmarks simultaneously but also significantly reduces the performance gap between them, particularly for the instance segmentation task. EVA attains the same performance on LVIS and COCO using single-scale evaluation. In comparison with ViTDet-H, we demonstrate that a slightly larger model with stronger representations can greatly improve performance on the challenging large vocabulary instance segmentation benchmark, with one caveat described below.", + "bbox": [ + 75, + 566, + 468, + 763 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Note that the Merged-30M unlabeled images include 15K out of 20K LVIS val set images (the Merged-30M images contain all the COCO training images, and the LVIS validation split also includes 15k images from the COCO training set). Although a recent study [33] shows that including unlabeled images from the development / test set for MIM pre-training has minimal impact on the final performance, we conduct a more rigorous analysis of the LVIS and COCO performance gap to eliminate potential data contamination issues: We evaluate both", + "bbox": [ + 75, + 763, + 470, + 900 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/c0ab57f9ba9e68deb5702c75f8d5f6ceaa7e807d45579e0aca5bcabbe41365cf.jpg", + "table_caption": [ + "Table 8. LVIS & COCO performance gap on val set. “prev. best” refers to the best individual model / result in each benchmark (a: DINO [121], b: ViTDet-H [60], c: Mask DINO [57], d: 2021 competition $1^{\\text{st}}$ [35]) “ $\\Delta \\downarrow$ ”: the performance gap between LVIS and COCO (the lower the better)." + ], + "table_footnote": [], + "table_body": "
modelcrop sizeADE20KCOCO-Stuff
mIoUssmIoUmsmIoUss
HorNet [79]640257.557.9-
SeMask [48]640257.058.3-
SwinV2-G [65]896259.359.9-
Mask DINO [57]896259.560.8-
FD-SwinV2-G [107]8962-61.4-
ViT-Adapter [23]896261.261.552.3
BEiT-3 [101]896262.062.8-
EVA896261.562.353.4
", + "bbox": [ + 501, + 348, + 893, + 489 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 9. Semantic segmentation performance on ADE20K and COCO-Stuff-164K dataset. \"mIoUss\": mIoU of single-scale evaluation, \"mIoUms\": mIoU using multi-scale evaluation.", + "bbox": [ + 496, + 494, + 892, + 537 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "COCO and LVIS models using the 5K images present in both the COCO and LVIS val sets, denoted as LVIS val-5K. The COCO results are measured using the 80-category COCO subset of LVIS with the higher-quality LVIS annotations (a similar approach also employed in [53], but for a different purpose). The results are shown in Table 8b, and we find that the conclusion remains unchanged.", + "bbox": [ + 496, + 551, + 893, + 657 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "2.3.4 Semantic Segmentation", + "text_level": 1, + "bbox": [ + 500, + 683, + 718, + 698 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Dataset. We evaluate EVA on ADE20K [123] and COCO-Stuff-164K [11] datasets for semantic segmentation task. ADE20K includes 150 semantic categories, and has 20k images for training & 2k images for validation. COCO-Stuff-164K augments 164K complex images from COCO with pixel-level annotations that span over 172 categories including 80 things, 91 stuff, and 1 unlabeled class. Compared with ADE20K, COCO-Stuff is a more challenging but under-explored semantic segmentation benchmark.", + "bbox": [ + 496, + 713, + 893, + 849 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Training & evaluation settings. We follow the task transfer pipelines of ViT-Adapter [23] + mask2former [24] but with a weakened model adaptation processes due to GPU memory", + "bbox": [ + 496, + 854, + 893, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "19363", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/fa19bbee91632c961d2317ff84c963a5dd861e6fc591ecc324d6d1c9d61c5765.jpg", + "table_caption": [], + "table_footnote": [ + "(a) CLIP model configurations. EVA CLIP-g can be stably trained via fp16 precision with fewer image-text pairs (7B v.s. 12B / 32B) sampled from a smaller data pool (LAION-400M v.s. LAION-2B) on $\\sim 1/3 \\times$ GPUs compared with other open-sourced billion-scale competitors." + ], + "table_body": "
modelprecisiontotal #param.image #param.text #param.clip training datasamples seenimage sizepatch sizebatch sizegpu for training
OpenAI CLIP-Lfloat16430M304M124MCLIP-400M [73]12B\\( 224^2 \\)\\( 14 \\times 14 \\)32k\\( 256 \\times V100 (32GB) \\)
ALIGNbfloat16834M480M354MALIGN-1.8B [73]22B\\( 289^2 \\)-16k\\( 1024 \\times TPUv3 \\)
Open CLIP-Hbfloat161.0B632M354MLAION-2B [85]32B\\( 224^2 \\)\\( 14 \\times 14 \\)79k\\( 824 \\times A100 (40GB) \\)
Open CLIP-gbfloat161.3B1.0B354MLAION-2B [85]12B\\( 224^2 \\)\\( 14 \\times 14 \\)64k\\( 800 \\times A100 (40GB) \\)
EVA CLIP-gfloat161.1B1.0B124MLAION-400M [86]11B\\( 224^2 \\)\\( 14 \\times 14 \\)41k\\( 256 \\times A100 (40GB) \\)
", + "bbox": [ + 83, + 50, + 898, + 155 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/d1ac2c9e16100ddc10d95bb5aa9bda82a0facfd2a3186b6de656d8b782ede1a3.jpg", + "table_caption": [], + "table_footnote": [ + "(b) Summary of zero-shot image / video classification performance. “ $\\Delta \\downarrow$ ”: The gap between the averaged performance of ImageNet-{1K, V2, Adv., Ren., Ske.} & ObjectNet that with natural distribution shifts and the original ImageNet-1K validation accuracy. Our model suffers from the smallest performance drop (only $2.5\\%$ top-1 accuracy gap) while maintaining the highest zero-shot classification accuracy averaged on all 12 benchmarks ( $72.7\\%$ top-1 accuracy).", + "Table 10. EVA as a vision-centric, multi-modal pivot. We evaluate a billion-scale contrastive language-image pre-trained (CLIP) model with the vision tower initialized from pre-trained EVA, which largely accelerates the contrastive training efficiency and shows promising zero-shot classification performance across a wide range of image / video benchmarks. The statistics & performance of EVA's MIM teacher (OpenAI CLIP-L) are also presented for reference." + ], + "table_body": "
datasetsImageNet-1K [28]ImageNet-V2 [82]ImageNet-Adv. [42]ImageNet-Ren. [41]ImageNet-Ske. [100]ObjectNet [6]CIFAR-10 [54]CIFAR-100 [54]UCF-101 [92]Video classificationAvg. all
modelimage classificationΔ↓Kinetics-400 [51]Kinetics-600 [14]Kinetics-700 [15]
OpenAI CLIP-L75.569.970.887.859.669.095.675.93.476.464.564.257.772.2
ALIGN76.470.175.892.264.872.2--------
Open CLIP-H78.070.959.389.366.669.797.584.75.778.263.163.656.173.1
Open CLIP-g76.669.657.288.765.267.597.183.95.877.761.762.255.071.9
EVA CLIP-g78.5(+1.9)71.5(+1.9)73.6(+16.4)92.5(+3.8)67.3(+2.1)72.3(+4.8)98.3(+1.2)88.7(+4.8)2.576.1(-1.6)65.2(+3.5)64.4(+2.2)58.4(+3.4)75.7(+3.8)
", + "bbox": [ + 84, + 191, + 897, + 364 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "limitation (40GB of VRAM): (i) relative position biases [90] are not applied. (ii) We use $8 \\times$ decoders in mask2former segmentation head instead of $9 \\times$ . (iii) The feature dimension in mask2former head is $\\sim 0.6 \\times$ of EVA encoder.", + "bbox": [ + 75, + 481, + 468, + 541 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Results. We compare EVA with other leading semantic segmentation methods in Table 9. EVA achieves strong results in both ADE20K and COCO-Stuff-164K datasets. On the other hand, the segmentation performance of EVA is slightly lower compared with BEiT-3 on ADE20K, we suspect this is partially due to our weakened architectural configurations.", + "bbox": [ + 75, + 547, + 468, + 652 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "2.3.5 Contrastive Language-Image Pre-training with Zero-shot Classification Evaluation", + "text_level": 1, + "bbox": [ + 76, + 676, + 423, + 705 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "CLIP (Contrastive Language-Image Pre-training) [47, 49, 72, 73] is a type of multi-modal foundation model that connects vision and language via contrastive image-text pre-training. CLIP can be applied to any image classification benchmark by simply providing the names of the visual categories to be recognized [1]. Thus the introduction of CLIP essentially reshapes the landscape of visual recognition. Meanwhile, CLIP features also play a central role in representation leaning [70, 101], AI generated content [78, 83, 84] and large dataset filtering [10, 85, 86], etc.", + "bbox": [ + 75, + 717, + 470, + 868 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "In this section and Table 10, we show that EVA is not only a strong encoder for a wide range of vision downstream", + "bbox": [ + 76, + 869, + 470, + 900 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "tasks, but also a multi-modal pivot that builds a bridge between vision and language. To demonstrate that, we train & evaluate EVA as a billion-scale CLIP's vision tower in various zero-shot image / video classification benchmarks.", + "bbox": [ + 496, + 481, + 893, + 542 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Baselines and major challenges in CLIP model scaling. We compare our CLIP (dubbed EVA CLIP) with other open-sourced strong CLIP competitors that exploit publicly accessible data / academic resources only. Model configurations and statistics are detailed in Table 10a.", + "bbox": [ + 496, + 546, + 893, + 621 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "There are two well-known major challenges of CLIP model training and scaling: (i) Large-scale Open CLIP models (e.g., Open CLIP-H & Open CLIP-g [2, 47]) usually suffer from severe training instability issues [2] and have to use bfloat16 format for optimization. (ii) The training efficiency is low, which may hinder model scaling and downstream performance. For instance, Open CLIP-g is heavily under-trained due to its large compute requirement, and its performance is even worse than the sufficiently-trained Open CLIP-H with a smaller model size.", + "bbox": [ + 496, + 623, + 893, + 772 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Compared with our CLIP model, Open CLIP-H & -g are trained from scratch with much more image-text pairs ( $\\sim 2.9 \\times$ and $\\sim 1.1 \\times$ of ours) sampled from a much larger dataset ( $\\sim 5 \\times$ of ours) on $\\sim 3 \\times$ of GPUs. While by leveraging EVA, billion-scale CLIP model training can be accelerated with improved zero-shot classification performance, described next.", + "bbox": [ + 496, + 773, + 893, + 864 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Training settings. For our CLIP model, we initialize the vision encoder via pre-trained EVA and the language encoder", + "bbox": [ + 496, + 869, + 893, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "19364", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/7023f939fc56fc7993efb4d1a2c410d6dea21f22a4822dfa82d2798a1a8b7626.jpg", + "table_caption": [], + "table_footnote": [ + "Table 11. Zero-shot, linear probing and fine-tuning performance of EVA-CLIP on ImageNet-1K. Notice that the linear probing and fine-tuning results are from the vision encoder of EVA-CLIP. Our approach establishes the new state-of-the-art results among all existing self-supervised learning (SSL) methods. (timestamp: Nov 10, 2022) results reference. a: Open CLIP-H [47], b: iBOT [124], c: dBOT [63]." + ], + "table_body": "
model (SSL)zero-shotlinear probingfine-tuning
prev. best78.0a82.3b89.1c
EVA78.586.589.4
", + "bbox": [ + 78, + 89, + 470, + 133 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "from OpenAI CLIP-L. The pre-training implementation is based on Open CLIP [47]. We also adopt DeepSpeed optimization library [80] with ZeRO stage-1 optimizer [77] to save memory. We find using fp16 format with dynamic loss scaling is stable enough during the whole course of training while using bf1oat16 format is unnecessary. These modifications allow us to train a 1.1B CLIP with a batch size of 41k on $256 \\times$ NVIDIA A100 40GB GPUs.", + "bbox": [ + 75, + 233, + 470, + 353 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Evaluation settings. We evaluate zero-shot image / video classification performance of each CLIP model on 12 benchmarks and report top-1 accuracy for comparisons.", + "bbox": [ + 76, + 359, + 470, + 405 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "For zero-shot image classification task, we choose 8 benchmarks, i.e., ImageNet-1K [28], ImageNet-V2 [81], ImageNet-Adversarial (ImageNet-Adv.) [42], ImageNet-Rendition (ImageNet-Adv.) [41], ImageNet-Sketch (ImageNet-Ske.) [100], ObjectNet [6], CIFAR-10 and CIFAR-100 [54]. We are also interested in the robustness of CLIP models, evaluated via the performance gap between the averaged performance of ImageNet-{1K, V2, Adv., Ren., Ske.} & ObjectNet that with natural distribution shifts and the original ImageNet-1K validation accuracy.", + "bbox": [ + 75, + 407, + 470, + 556 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "For zero-shot video classification task, we choose 4 benchmarks, namely UCF-101 [92], Kinetics-400 [51], Kinetics-600 [14], and Kinetics-700 [15].", + "bbox": [ + 76, + 559, + 470, + 604 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Results. Table 10b shows the comparison. Our EVA CLIP achieves the highest averaged accuracy, and performs the best in 10 out of 12 zero-shot classification benchmarks. Notably, the ImageNet-1K validation zero-shot top-1 accuracy is $78.2\\%$ without using any of its training set labels, matching the original ResNet-101 [40]. Moreover, our model is quite robust and suffers from the smallest performance drop when facing natural distribution shifts in ImageNet.", + "bbox": [ + 75, + 609, + 470, + 731 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "At last, in Table 11 we provide zero-shot, linear probing & end-to-end fine-tuning top-1 accuracy of EVA-CLIP on ImageNet-1K validation set for reference. Our approach creates the new state-of-the-art results among all existing self-supervised learning methods.", + "bbox": [ + 75, + 733, + 468, + 808 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Notice that EVA CLIP's vision branch learns from OpenAI CLIP-L, while language branch initialized from the same CLIP-L model. Therefore, starting from a CLIP-L with only 430M parameters, we progressively scale up a 1.1B EVA CLIP-g with large performance improvements. This implies that interleaved MIM & image-text contrastive", + "bbox": [ + 75, + 809, + 470, + 901 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "pre-training could be an efficient and scalable CLIP training approach. To our knowledge, EVA CLIP-g is the largest performant CLIP model trained via publicly accessible data and resources. We hope our practice on scaling and improving CLIP can also inspire and transfer to the study of other large scale multi-modal foundation models.", + "bbox": [ + 496, + 90, + 893, + 181 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "3. Related Work", + "text_level": 1, + "bbox": [ + 500, + 196, + 640, + 212 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Masked image modeling (MIM) learns rich visual representations via predicting masked visual contents conditioned on visible context. ViT [31] and iGPT [18] report the first meaningful MIM pre-training results. The BEiT family [5,70,101] greatly improves MIM's performance via masked visual token prediction. Recent work [4,21,30,32,39,103,113,124] (re-)explore pixel / feature regression in MIM, but only in a relatively small model and data scales. In this work, we explore the limits of large scale MIM pre-training via masked image-text aligned feature prediction [43, 106].", + "bbox": [ + 496, + 226, + 893, + 378 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Vision foundation models. ConvNets [56] have long been the de-facto standard visual architecture ab initio. Since AlexNet [55], ConvNets have rapidly evolved and become deeper, wider and larger [40, 44, 66, 91, 93, 94, 111]. However, at sufficient model and data scales, ConvNets lag behind ViTs [31] due to a lack of scalable pre-training tasks and the built-in inductive biases. Entering the 2020s, large pretrained ViTs [31, 119] such as SwinV2-G [65] with hierarchical architectures as well as BEiT-3 [101] with multi-modal representations started to demonstrate various vision benchmarks. In this work, we show by leveraging unlabeled images, vanilla ViT can be efficiently scaled up to billion-scale parameters, and stands out in various downstream tasks.", + "bbox": [ + 496, + 382, + 893, + 579 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 593, + 617, + 608 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this work, we launch EVA, a one billion parameters vanilla ViT encoder to explore the limits of masked visual representation learning. We show simple masked feature modeling as a visual learning pretext task scales well on an architecture with minimal vision priors, and attains excellent results in a representative & diverse set of downstream tasks. We hope EVA would bridge the gap between vision and language study via masked modeling, and contributes to the Neon Genesis of vision research.", + "bbox": [ + 496, + 618, + 893, + 753 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgement", + "text_level": 1, + "bbox": [ + 500, + 768, + 660, + 786 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "This work is supported by the National Key R&D Program of China (2020AAA0105200) and NSFC (No. 617333007). We would like to thank Hanxiao Qu, Yan Tian, Yemin Shi and Xigang Cao for their help on GPU resources. Zhao Xue, Quanyue Ma and Bowen Zhang for their help on datasets and benchmarks, and other colleagues at BAAI for support throughout this project.", + "bbox": [ + 496, + 794, + 893, + 902 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "19365", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 90, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Clip: Connecting text and images. https://openai.com/blog/clip/.7", + "[2] Large scale openclip: L/14, h/14 and g/14 trained on laion-2b. https://laion.ai/blog/large-openclip.2,7", + "[3] Jimmy Lei Ba, Jamie Ryan Kiros, and Geoffrey E Hinton. Layer normalization. arXiv preprint arXiv:1607.06450, 2016. 3", + "[4] Alexei Baevski, Wei-Ning Hsu, Qiantong Xu, Arun Babu, Jiatao Gu, and Michael Auli. 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Probabilistic two-stage detection. arXiv preprint arXiv:2103.07461, 2021. 5" + ], + "bbox": [ + 501, + 93, + 893, + 210 + ], + "page_idx": 11 + }, + { + "type": "page_number", + "text": "19369", + "bbox": [ + 480, + 945, + 519, + 955 + ], + "page_idx": 11 + } +] \ No newline at end of file diff --git a/2023/EVA_ Exploring the Limits of Masked Visual Representation Learning at Scale/c4046a48-182c-4cee-86a4-65a7035e3e1d_model.json b/2023/EVA_ Exploring the Limits of Masked Visual Representation Learning at Scale/c4046a48-182c-4cee-86a4-65a7035e3e1d_model.json new file mode 100644 index 0000000000000000000000000000000000000000..2c3af6a3c1aeebd8bb54c8a5d59f9821d54de2ca --- /dev/null +++ b/2023/EVA_ Exploring the Limits of Masked Visual Representation Learning at Scale/c4046a48-182c-4cee-86a4-65a7035e3e1d_model.json @@ -0,0 +1,3106 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.001, + 0.812, + 0.047 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.089, + 0.131, + 0.882, + 0.154 + ], + "angle": 0, + "content": "EVA: Exploring the Limits of Masked Visual Representation Learning at Scale" + }, + { + "type": "text", + "bbox": [ + 0.171, + 0.179, + 0.8, + 0.221 + ], + "angle": 0, + "content": "Yuxin Fang\\(^{1,2\\dagger}\\) Wen Wang\\(^{3,2\\dagger}\\) Binhui Xie\\(^{4,2\\dagger}\\) Quan Sun\\(^{2}\\) Ledell Wu\\(^{2}\\) Xinggang Wang\\(^{1\\dagger}\\) Tiejun Huang\\(^{2}\\) Xinlong Wang\\(^{2\\dagger}\\) Yue Cao\\(^{2\\dagger}\\)" + }, + { + "type": "text", + "bbox": [ + 0.127, + 0.226, + 0.799, + 0.262 + ], + "angle": 0, + "content": "1Huazhong University of Science and Technology \n2Beijing Academy of Artificial Intelligence \n3Zhejiang University \n4Beijing Institute of Technology" + }, + { + "type": "text", + "bbox": [ + 0.348, + 0.273, + 0.616, + 0.286 + ], + "angle": 0, + "content": "Code & Models: baaivision/EVA/01" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.323, + 0.314, + 0.339 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.354, + 0.474, + 0.732 + ], + "angle": 0, + "content": "We launch EVA, a vision-centric foundation model to Explore the limits of Visual representation at scAle using only publicly accessible data. EVA is a vanilla ViT pretrained to reconstruct the masked out image-text aligned vision features conditioned on visible image patches. Via this pretext task, we can efficiently scale up EVA to one billion parameters, and sets new records on a broad range of representative vision downstream tasks, such as image recognition, video action recognition, object detection, instance segmentation and semantic segmentation without heavy supervised training. Moreover, we observe quantitative changes in scaling EVA result in qualitative changes in transfer learning performance that are not present in other models. For instance, EVA takes a great leap in the challenging large vocabulary instance segmentation task: our model achieves almost the same state-of-the-art performance on LVIS dataset with over a thousand categories and COCO dataset with only eighty categories. Beyond a pure vision encoder, EVA can also serve as a vision-centric, multi-modal pivot to connect images and text. We find initializing the vision tower of a giant CLIP from EVA can greatly stabilize the training and outperform the training from scratch counterpart with much fewer samples and less compute, providing a new direction for scaling up and accelerating the costly training of multi-modal foundation models." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.759, + 0.21, + 0.774 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.784, + 0.47, + 0.845 + ], + "angle": 0, + "content": "Scaling up pre-trained language models (PLMs) [9,64,76] has revolutionized natural language processing (NLP) in the past few years. The key to this success lies in the simple and scalable self-supervised learning task of masked signal" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.324, + 0.895, + 0.445 + ], + "angle": 0, + "content": "prediction [29, 74], with which Transformer models [99] could be scaled up to billions of parameters using nearly unlimited unlabelled data, and generalize well to a wide range of downstream tasks with little tuning. With further scaling on compute, data, and model sizes, PLMs have led to not only continuous performance improvements [50, 75, 76], but also a surprising emergence of in-context learning capability [9, 25, 104, 105]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.446, + 0.896, + 0.734 + ], + "angle": 0, + "content": "Motivated by the success of model scaling in NLP, it is appealing that we can also translate this success from language to vision, i.e., to scale up a vision-centric foundation model that is beneficial for both vision & multi-modal downstream tasks. Recently, masked image modeling (MIM) [5, 39, 113] has boomed as a viable approach for vision model pretraining and scaling. However, the most competitive billion-sized vision pre-trained models [31, 65, 71, 119] still heavily rely on supervised or weakly-supervised training with hundreds of millions of (often publicly inaccessible) labeled data. MIM is somewhat only adopted as an initialization stage before the heavily supervised pre-training [65], or a pure MIM pre-trained model could not achieve favorable performance at billion-scale model sizes [114]. We regard this gap stems from the fact that natural images are raw and information-sparse. Meanwhile, an ideal vision pretext task needs the abstraction of not only the low-level geometry & structure information, but also high-level semantics, which is hardly captured by pixel-level recovery tasks [112]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.735, + 0.897, + 0.903 + ], + "angle": 0, + "content": "In this work, we seek a suitable MIM pretext task for large scale vision representation learning and explore its limits at the scale of one billion parameters with tens of millions of unlabeled data. Recently, there are a few trials leveraging the semantic information from image-image or image-text contrastive learning [13, 22, 73] for MIM pretraining [43, 106, 124], which perform fairly well in vision downstream tasks. However, there remains a debate that (i) tokenized semantic features could provide better supervision signal for masked modeling in vision [5, 70, 101], and (ii) good performances could be also achieved via a simple post" + }, + { + "type": "page_footnote", + "bbox": [ + 0.076, + 0.851, + 0.473, + 0.901 + ], + "angle": 0, + "content": "†Interns at Beijing Academy of Artificial Intelligence (BAAI). ‡Corresponding authors: Yue Cao (caoyue10@gmail.com), Xinlong Wang (xinlong.wang96@gmail.com) and Xinggang Wang (xgwang@hust.edu.cn)." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "19358" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.078, + 0.051, + 0.897, + 0.136 + ], + "angle": 0, + "content": "
modelimage & video classification (G)object detection (det) & instance segmentation (seg)semantic segmentation
IN-1K ftIN-1K linIN-1K zsavg. zsK400K600K700COCO det (test/val)COCO seg (test/val)LVIS segCOCO-StuffADE20K
Florence----86.587.8-62.4 / 62.0----
SwinV2-G----86.8--63.1 / 62.554.4 / 53.7--59.9
prev. best89.6a82.3b78.0c73.1c87.8d88.3e80.4e64.5f / 64.2g55.4h / 54.5i49.2j52.3k62.8a
EVA89.7(+0.1)86.5(+4.2)78.5(+0.5)75.7(+2.6)89.7(+1.9)89.8(+1.5)82.9(+2.5)64.7 / 64.5(+0.2/+0.3)55.5 / 55.0(+0.1/+0.5)55.0(+5.8)53.4(+1.1)62.3(-0.5)
" + }, + { + "type": "table_footnote", + "bbox": [ + 0.075, + 0.14, + 0.895, + 0.194 + ], + "angle": 0, + "content": "Table 1. Summary of EVA performance on various mainstream vision benchmarks. EVA is performant compared with previous best / leading approaches. “”: methods / results that only exploit publicly accessible data / academic resources. “ft”: end-to-end fine-tuning. “lin”: linear probing. “zs”: zero-shot classification. “avg. zs”: averaged zero-shot classification performance on 8 image and 4 video datasets with contrastive language-image pre-training. (timestamp: Nov 10, 2022)" + }, + { + "type": "table_footnote", + "bbox": [ + 0.075, + 0.196, + 0.895, + 0.223 + ], + "angle": 0, + "content": "methods / results reference. a: BEiT-3 [101], b: iBOT [124], c: Open CLIP-H [47], d: Text4Vis [109], e: MaskFeat [103], f: Group DETRv2 [19], g: FocalNet [116], h: FD-SwinV2-G [107], i: Mask DINO [57], j: LVIS 2021 competition \\(1^{\\text{st}}\\) [35], k: ViT-Adapter [23]." + }, + { + "type": "list", + "bbox": [ + 0.075, + 0.14, + 0.895, + 0.223 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.243, + 0.473, + 0.395 + ], + "angle": 0, + "content": "distillation process without masked prediction tasks [107]. Through a pilot empirical study, we find that simply using image-text aligned (i.e., CLIP [73]) vision features as the prediction targets in MIM scales up well and achieves satisfactory performances on a broad range of downstream benchmarks. This pre-training task draws the benefits from both the high-level semantic abstraction of image-text contrastive learning as well as the good capture of geometry & structure in masked image modeling, which typically covers the information needed for most visual perception tasks." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.397, + 0.474, + 0.548 + ], + "angle": 0, + "content": "Via this MIM pretext task, we can efficiently scale up a vanilla ViT encoder [31], dubbed EVA, to one billion parameters with strong visual representations that transfers well to a wide range of downstream tasks. Using 29.6 million public accessible unlabeled images for pre-training, EVA sets new records on several representative vision benchmarks, such as image classification on ImageNet-1K [28] (89.7% top-1 accuracy), object detection and instance segmentation on LVIS [38] (62.2 AP\\(^{\\text{box}}\\) & 55.0 AP\\(^{\\text{mask}}\\) on val) and COCO [62] (64.5 AP\\(^{\\text{box}}\\) & 55.0 AP\\(^{\\text{mask}}\\) on val, 64.7 AP\\(^{\\text{box}}\\) & 55.5 AP\\(^{\\text{mask}}\\) on test-dev)," + }, + { + "type": "table", + "bbox": [ + 0.107, + 0.554, + 0.45, + 0.632 + ], + "angle": 0, + "content": "
tokenizer? [70]pt epochsImageNet-1K top-1 acc.ADE20K mIoUss
X-85.052.6
✓30085.052.7
✓160085.553.1
X80085.553.3
" + }, + { + "type": "table_footnote", + "bbox": [ + 0.095, + 0.635, + 0.452, + 0.66 + ], + "angle": 0, + "content": "(a) (Additional) semantic feature tokenization is not required for achieving good downstream performance." + }, + { + "type": "table", + "bbox": [ + 0.107, + 0.667, + 0.449, + 0.745 + ], + "angle": 0, + "content": "
distill.?[107]pt epochsImageNet-1K top-1 acc.ADE20K mIoUss
X-85.052.6
✓30085.152.5
✓80085.152.7
X80085.553.3
" + }, + { + "type": "table_footnote", + "bbox": [ + 0.095, + 0.747, + 0.452, + 0.771 + ], + "angle": 0, + "content": "(b) Feature distillation fails to achieve consistent performance gain as the pre-training becomes longer." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.783, + 0.473, + 0.897 + ], + "angle": 0, + "content": "Table 2. Pilot experiment. We evaluate different pre-training approaches using ViT-B and report their performance on ImageNet-1K image classification (top-1 accuracy) and ADE20K semantic segmentation (single-scale mIoU). Numbers in grey refer to the results of directly fine-tuning CLIP vision encoder on corresponding downstream tasks. Default settings for EVA pre-training are marked in purple, i.e., directly regressing the masked out CLIP vision features conditioned on visible image patches." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.243, + 0.895, + 0.41 + ], + "angle": 0, + "content": "semantic segmentation on COCO-stuff [11] (53.4 mIoU\\(^{\\mathrm{ss}}\\)) and ADE20K [123] (62.3 mIoU\\(^{\\mathrm{ms}}\\)), and video action recognition on Kinetics-400 [51] (89.7% top-1 accuracy), Kinetics-600 [14] (89.8% top-1 accuracy), Kinetics-700 [15] (82.9% top-1 accuracy). Notably, different from other state-of-the-art billion-scale vision foundation models that demand tens of millions of or even billions of labeled images, such as SwinV2-G using ImageNet-21K-ext-70M [65] and ViT-g/G using JFT3B [119], EVA does not need a costly supervised training stage and only leverage images from open-sourced datasets for academic reproducibility." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.412, + 0.897, + 0.625 + ], + "angle": 0, + "content": "Moreover, we observe quantitative changes in scaling EVA result in qualitative changes in transfer learning performance that are not observed in other smaller-scale models, e.g., EVA makes a significant breakthrough in the challenging large vocabulary object-level recognition task: our model achieves almost the same performance on LVIS [38], an instance segmentation benchmark with more than 1,200 categories, as COCO [62], which almost shares the same image set as LVIS but with only 80 categories annotated. This emergent ability well matches the expectation of model scaling [105], that larger capability of model results in not only predictable performance improvements on standard benchmarks, but also unpredictable phenomena and capabilities for resolving more challenging tasks." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.627, + 0.896, + 0.822 + ], + "angle": 0, + "content": "Going beyond a pure vision encoder, EVA can also serve as a vision-centric, multi-modal pivot that builds a bridge between vision and language. We show that initializing the image encoder via pre-trained EVA in a 1.1 billion parameters CLIP model can outperform the training from scratch counterpart on a broad range of zero-shot image / video classification benchmarks with much fewer samples and less compute. Moreover, EVA can greatly stabilize the giant CLIP's training & optimization process. Since large CLIP models usually suffer from training instability and inefficiency issues [2,47], we hope our solution opens up a new direction for scaling up and accelerating the costly training of multi-modal foundation models." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.825, + 0.895, + 0.901 + ], + "angle": 0, + "content": "By scaling up vision-centric foundation models with MIM pre-training to achieve strong performance on broad downstream tasks, we hope EVA would bridge the gap between vision and language with masked signal modeling, and contributes to the big convergence across different modalities." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "19359" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.109, + 0.045, + 0.468, + 0.078 + ], + "angle": 0, + "content": "
patch size#layershidden dimmlp dimattn heads#param.
14×144014086144161011M
" + }, + { + "type": "table_caption", + "bbox": [ + 0.188, + 0.08, + 0.381, + 0.092 + ], + "angle": 0, + "content": "(a) EVA architecture configurations." + }, + { + "type": "table", + "bbox": [ + 0.107, + 0.1, + 0.465, + 0.129 + ], + "angle": 0, + "content": "
image sizebatch sizeoptimizerpeak lr(β1, β2)pt epochs
22424096AdamW1e-3(0.9, 0.98)150
" + }, + { + "type": "table_footnote", + "bbox": [ + 0.143, + 0.133, + 0.419, + 0.145 + ], + "angle": 0, + "content": "(c) some pre-training settings and hyper-parameters." + }, + { + "type": "table", + "bbox": [ + 0.498, + 0.045, + 0.877, + 0.078 + ], + "angle": 0, + "content": "
datasettotal size
ImageNet-21K, CC12M, CC3M, Object365, COCO, ADE29.6M images
" + }, + { + "type": "table_caption", + "bbox": [ + 0.592, + 0.08, + 0.771, + 0.092 + ], + "angle": 0, + "content": "(b) datasets for pre-training EVA." + }, + { + "type": "table", + "bbox": [ + 0.503, + 0.1, + 0.877, + 0.13 + ], + "angle": 0, + "content": "
precisionZeRO#gpusamples / sec.max mem.pt days
fp16stage-1128~3150~26.5GB~14.5
" + }, + { + "type": "table_caption", + "bbox": [ + 0.582, + 0.133, + 0.789, + 0.145 + ], + "angle": 0, + "content": "(d) basic statistics of EVA pre-training." + }, + { + "type": "table_caption", + "bbox": [ + 0.239, + 0.151, + 0.731, + 0.165 + ], + "angle": 0, + "content": "Table 3. A brief summary of pre-training settings and configurations for EVA." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.184, + 0.281, + 0.202 + ], + "angle": 0, + "content": "2. Fly EVA to the Moon" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.21, + 0.471, + 0.3 + ], + "angle": 0, + "content": "We first conduct a series of pilot experiments for choosing an ideal vision pretext task in §2.1, then we scale up EVA pre-training via the chosen pre-training objective in §2.2. Finally, we evaluate the pre-trained representation on various downstream tasks in §2.3. Detailed experimental settings and configurations are in Appendix." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.308, + 0.393, + 0.325 + ], + "angle": 0, + "content": "2.1. The Feature Instrumentality Project" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.332, + 0.471, + 0.573 + ], + "angle": 0, + "content": "In this section, we seek a MIM vision pretext task with compelling transfer performance. Based on previous literature on vision pre-training, we study two promising candidates: (i) recovering the masked out tokenized semantic vision features [5, 70, 101], and (ii) feature distillation from strong pre-trained representation as in [107]. Both of them exploit pre-trained image-text aligned vision features (i.e., CLIP [73] vision features). Via a series of pilot experiments shown in Table 2, we find that: (i) the (additional) CLIP feature tokenization process is unnecessary for achieving good downstream performance (ii) feature distillation fails to provide consistent performance gain as the pre-training becomes longer. Instead, we find that simply reconstructing the masked out CLIP vision features conditioned on visible image patches is highly performant, which is chosen for scaling up EVA." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.573, + 0.471, + 0.724 + ], + "angle": 0, + "content": "We clarify that this MIM pretext task is not originally proposed by us. Regressing the masked out image-text aligned vision features for MIM pre-training has been studied in MVP [106] and recently has been revisited by MILAN [43]. In this work, we show that this pretext task can scale up to billion-scale parameters and tens of millions of unlabeled images for vision-centric representation learning without (i) semantic feature quantization / tokenization [5, 70], and (ii) explicitly using image-text paired pre-training data and large corpora as in BEiT-3 [101]." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.733, + 0.21, + 0.749 + ], + "angle": 0, + "content": "2.2. Pre-training" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.76, + 0.47, + 0.837 + ], + "angle": 0, + "content": "Architecture. The architecture configurations of EVA are in Table 3a. EVA is a vanilla ViT [31] with 1.0B parameters. The shape of her follows ViT giant [119] and the vision encoder of BEiT-3 [101]. We do not use relative positional embeddings [89] and layer-scale [97] during pre-training." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.471, + 0.902 + ], + "angle": 0, + "content": "Pre-training objective. EVA is pre-trained to reconstruct the masked out image-text aligned vision features conditioned on visible image patches. We corrupt the input patches with [MASK] tokens, and we use block-wise masking with" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.185, + 0.895, + 0.29 + ], + "angle": 0, + "content": "a masking ratio of \\(40\\%\\) following [5, 70, 101]. The target for MIM pre-training is from the publicly available OpenAI CLIP-L/14 vision tower trained on \\(224\\times 224\\) pixel images [73]. The output feature of EVA is first normalized [3] and then projected to the same dimension as the CLIP feature via a linear layer. We use negative cosine similarity as the loss function." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.305, + 0.895, + 0.426 + ], + "angle": 0, + "content": "Pre-training data. The data we used for pre-training EVA are summarized in Table 3b. For CC12M [16] and CC3M [88] datasets, we only use the image data without captions. For COCO [62] and ADE20K [123] datasets, we only use the train set data. ImageNet-21K [28] and Object365 [87] image data are also used. All these data are publicly accessible. The merged dataset for pre-training has 29.6 million images in total." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.439, + 0.895, + 0.545 + ], + "angle": 0, + "content": "Pre-training settings & hyper-parameters. As shown in Table 3c, EVA is optimized via Adam [52] with decoupled weight decay [67] of 0.05. The peak learning rate is 1e-3 and decays according to a cosine learning rate schedule. We employed stochastic depth [45] with a rate of 0.1 for regularization and RandResizeCrop (0.2, 1) for data augmentation. Color jitter is not used." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.559, + 0.895, + 0.726 + ], + "angle": 0, + "content": "Pre-training infrastructure and statistics. Some basic pre-training statistics are available in Table 3d. The GPU we use is NVIDIA A100-SXM4-40GB. Pre-training code is based on BEiT [5] written in PyTorch [69]. We also adopt DeepSpeed optimization library [80] with ZeRO stage-1 optimizer [77] to save memory. We find using fp16 format with dynamic loss scaling is stable enough during the whole course of pre-training while using bf1oat16 format is unnecessary. Since we use fp16 precision, EVA can also be pre-trained using \\(16 \\times\\) NVIDIA 24GB (32GB) GPUs with (without) gradient checkpointing [20]." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.762, + 0.794, + 0.778 + ], + "angle": 0, + "content": "2.3. Evaluation on Downstream Tasks" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.795, + 0.895, + 0.901 + ], + "angle": 0, + "content": "In this section, we extensively evaluate pre-trained EVA on several representative benchmarks, such as image classification (§2.3.1), video action recognition (§2.3.2), object detection & instance segmentation (§2.3.3), semantic segmentation (§2.3.4), and contrastive image-text pre-training with zero-shot evaluation (§2.3.5). EVA achieves state-of-the-art performance on a broad range of downstream tasks." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "19360" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.082, + 0.053, + 0.466, + 0.066 + ], + "angle": 0, + "content": "model #param. extra labeled data image size top-1 acc." + }, + { + "type": "table", + "bbox": [ + 0.08, + 0.067, + 0.469, + 0.236 + ], + "angle": 0, + "content": "
using private labeled data
SwinV2-G [65]3.0BIN-21K-ext-70M640290.2
ViT-G [119]1.8BJFT-3B518290.5
ViT-g (CoCa) [117]1.0BJFT-3B+ALIGN576291.0
using public labeled data
CoAtNet-4 [27]275MIN-21K (14M)512288.6
MaxViT-XL [98]475MIN-21K (14M)512288.7
MViTv2-H [61]667MIN-21K (14M)512288.8
FD-CLIP-L [107]304MIN-21K (14M)336289.0
BEiT-3 [101]2.0B35M img-text pairs336289.6
EVA1.0BIN-21K (14M)336289.6
EVA1.0BIN-21K (14M)560289.7
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.238, + 0.471, + 0.293 + ], + "angle": 0, + "content": "Table 4. Comparisons of image classification performance on ImageNet-1K validation set. With only publicly available data, EVA creates a new state-of-the-art ImageNet-1K image classification result with a canonical linear classifier." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.31, + 0.273, + 0.325 + ], + "angle": 0, + "content": "2.3.1 Image Classification" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.34, + 0.471, + 0.446 + ], + "angle": 0, + "content": "Datasets. For image classification task, we evaluate EVA on ImageNet-1K (IN-1K) [28] validation set. We also evaluate the robustness & generalization capability of EVA along with our training settings & hyper-parameters using ImageNet-V2 matched frequency (IN-V2) [81], ImageNet-ReaL (IN-ReaL) [7], ImageNet-Adversarial (IN-Adv.) [42], ImageNet-Rendition (IN-Ren.) [41], ImageNet-Sketch (IN-Ske.) [100]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.452, + 0.471, + 0.649 + ], + "angle": 0, + "content": "Training Settings. Following the conventional setting [5, 70, 101], we first perform intermediate fine-tuning on ImageNet-21K [28] for 60 epochs with an image resolution of \\(224^2\\), then EVA is further fine-tuned on ImageNet-1K training set for 10 epochs. Different from [117, 119] that use multi-head attention pooling and BEiT-3 that exploits an additional pretrained giant language tower as the image classification task layer, we simply adopt a linear layer as the classifier [31]. Notice that the supervised intermediate fine-tuning consumes only \\(\\sim 1/5\\) of the time & compute of the MIM pre-training stage. While for other billion-scale vision models such as SwinV2-G-3B, the supervised training phase costs \\(\\sim 1.5 \\times\\) resources than the MIM pre-training." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.654, + 0.471, + 0.879 + ], + "angle": 0, + "content": "Results. Table 4 compares EVA with some state-of-the-art models on ImageNet-1K validation set. EVA achieves \\(89.6\\%\\) top-1 accuracy with \\(336^{2}\\) inputs, comparable to BEiT-3. Using a larger image resolution of \\(560^{2}\\) can further boost the top-1 accuracy to \\(89.7\\%\\). Notice that BEiT-3 treats image classification as an image-to-text retrieval task. Therefore they leverage an additional one billion parameters pre-trained language encoder along with 35 million image-text data (21M pairs from CC12M, CC3M, SBU, COCO, VG and 14M pairs from ImageNet-21K) as well as 160GB text data in total. Meanwhile, we simply use a linear classifier on top of EVA with only ImageNet-21K image-tag data used for additional finetuning. With only publicly available data, EVA creates a new state-of-the-art image classification result on ImageNet-1K with a much neater architecture." + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.886, + 0.471, + 0.901 + ], + "angle": 0, + "content": "Robustness & generalization ability evaluation. We eval" + }, + { + "type": "table", + "bbox": [ + 0.503, + 0.051, + 0.894, + 0.178 + ], + "angle": 0, + "content": "
modelIN-1KIN-V2IN-ReALIN-Adv.IN-Ren.IN-Ske.avg.Δ↓
ConvNeXt87.577.790.570.867.053.774.513.0
SwinV287.577.390.273.967.752.374.812.7
MAE87.879.290.376.766.550.975.212.6
DeiT387.779.190.279.270.654.977.010.7
Eff-L2-NS88.480.590.684.874.747.677.810.6
BEiTv288.480.190.376.276.458.378.310.1
BEiT88.679.990.781.773.256.878.510.1
EVA89.681.690.886.288.367.784.05.6
" + }, + { + "type": "table_caption", + "bbox": [ + 0.498, + 0.181, + 0.894, + 0.278 + ], + "angle": 0, + "content": "Table 5. Robustness & generalization capability evaluation on ImageNet-1K variants. We test each model on different ImageNet-1K validation sets, without any specialized fine-tuning. \"avg.\": the averaged top-1 accuracy on 6 different ImageNet-1K validation set variants. \"Δ↓\": The gap between the averaged top-1 accuracy on 6 variants (i.e., IN-{1K, V2, Real, Adv., Ren., Ske.}) and the original ImageNet-1K validation set top-1 accuracy (the lower the better)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.299, + 0.895, + 0.435 + ], + "angle": 0, + "content": "uate the robustness and generalization capability of EVA trained with an image size of \\(336^{2}\\) on 6 different ImageNet1K validation set variants. In Table 5, we compare EVA with some top open-sourced models collected by the timm library [108]. Following the evaluation procedure in [39], all these models are first fine-tuned on the original ImageNet1K training set and then evaluated on different validation sets using the same fine-tuned model without further hyperparameter selection and specialized fine-tuning." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.436, + 0.895, + 0.678 + ], + "angle": 0, + "content": "As shown in Table 5, EVA is the most competitive one in terms of absolute top-1 accuracies. However, these model various in pre-train data (from ImageNet-1K, ImageNet-21K to JFT-300M), input resolutions (from \\(224^2\\) to \\(800^2\\)), model sizes (from hundreds of millions to one billion parameters) as well as architectures (ConvNets, vanilla & hierarchical ViTs), etc. Therefore their absolute accuracies are not directly comparable. Instead, we are more interested in the gap between the averaged top-1 accuracy on 6 validation set variants and the original ImageNet-1K validation set top-1 accuracy (the lower the better), i.e., we care about whether a model along with its training settings biases towards the original validation set and generalize well on other variants. From this perspective, EVA not only achieves the highest averaged accuracy, but also has the smallest performance gap, which reflects the excellent robustness and generalization ability of EVA." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.696, + 0.733, + 0.71 + ], + "angle": 0, + "content": "2.3.2 Video Action Recognition" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.724, + 0.894, + 0.831 + ], + "angle": 0, + "content": "Datasets. For video action recognition, we evaluate EVA on Kinetics-400 (K-400) [51], Kinetics-600 (K-600) [14] and Kinetics-700 (K-700) [15] benchmarks. We first conduct intermediate fine-tuning on a merged dataset coined Kinetics-722 (K-722) that integrates videos from K-400, K-600 and K-700. We remove leaked as well as repeated videos in both training and validation sets. After this data de-duplicating" + }, + { + "type": "page_footnote", + "bbox": [ + 0.498, + 0.84, + 0.894, + 0.901 + ], + "angle": 0, + "content": "Source: link (timestamp: Nov 10, 2022). The detailed model configurations are (arch-model_size-Img_resolution-data): ConvNeXt-XL-384px-21K [66], SwinV2-L-384px-21K [65], MAE-H-448px-1K [39], DeiT3-L-384px-21K [96], EfficientNet-L2&NS-800px-JFT300M [110], BEiTv2-L-224px-21K [70], BEiT-L-512px-21K [5], EVA-g-336px-merged30M&21K." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "19361" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.082, + 0.09, + 0.462, + 0.25 + ], + "angle": 0, + "content": "
modeltop-1 accuracy
Kinetics-400Kinetics-600Kinetics-700
MAE [34]86.8--
SwinV2-G [65]86.8--
Florence [118]86.888.0-
MaskFeat [103]87.088.380.4
VideoMAE [95]87.4--
X-CLIP [68]87.788.3-
CoVeR [120]87.287.978.5
CoCa [117] (frozen)88.088.581.1
CoCa [117] (finetuned)88.989.482.7
EVA89.789.882.9
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.251, + 0.47, + 0.294 + ], + "angle": 0, + "content": "Table 6. Video action recognition. With only publicly available K-400, K-600 and K-700 as video pre-training data, EVA is also quite performant in video action recognition tasks." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.31, + 0.469, + 0.342 + ], + "angle": 0, + "content": "process, K-722 has 0.63M training videos in total with 722 action classes. A similar approach is also used in [58]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.345, + 0.469, + 0.466 + ], + "angle": 0, + "content": "Training & evaluation settings. EVA processes video data simply via spatial-temporal attention as [34, 95] with no specific architectural adaptation for video related tasks. We first train EVA using K-722 training set for 40 epochs with 8 frames and \\(224^2\\) resolution, then we fine-tune EVA on each dataset for only 1 or 2 epochs. We set frame \\(\\times\\) crop \\(\\times\\) clip to \\(16 \\times 3 \\times 4\\) for fine-tuning and evaluation for all datasets. The frame resolution is \\(224^2\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.47, + 0.47, + 0.562 + ], + "angle": 0, + "content": "Results. As shown in Table 6, EVA achieves better performance compared with some recent video-specific or large foundation models in video recognition. For reference, directly adapting image-only pre-trained EVA to K-400 without K-722 intermediate fine-tuning can also achieve a very competitive top-1 accuracy of \\(88.4\\%\\)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.581, + 0.429, + 0.596 + ], + "angle": 0, + "content": "2.3.3 Object Detection & Instance Segmentation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.61, + 0.47, + 0.806 + ], + "angle": 0, + "content": "Datasets. We evaluate the object detection and instance segmentation performance of EVA on both COCO [62] and LVIS [38]. COCO is a widely used object-level recognition benchmark with 80 common object categories. LVIS is an emerging large-vocabulary object-level recognition benchmark, which has more than 1,200 object categories as well as more than 2 million high quality instance segmentation masks (nearly \\(2 \\times\\) of COCO). Notably, COCO and LVIS almost use the same set of images, and both train and val split of LVIS have a huge overlap with COCO train and val split. Meanwhile, COCO has much fewer object categories than LVIS (i.e., \\(80 \\text{ v.s. } 1,200+\\)). Therefore it is meaningful to evaluate models' performance on both COCO and LVIS." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.81, + 0.471, + 0.902 + ], + "angle": 0, + "content": "Training & evaluation settings. EVA uses Cascade Mask R-CNN [12] as the detector and adopts the training settings (e.g., LSJ data augmentation [36]) & architecture configurations (e.g., interleaved window & global attention) of ViTDet [60]. Following the common practice [65, 101, 121], we first conduct intermediate fine-tuning for the whole detec" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.091, + 0.892, + 0.137 + ], + "angle": 0, + "content": "tor using Objects365 [87] dataset with a resolution of \\(1024^2\\), then we fine-tune the detector on COCO and LVIS train split respectively with \\(1280^2\\) inputs." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.137, + 0.894, + 0.212 + ], + "angle": 0, + "content": "We report single-scale evaluation and multi-scale evaluation / test-time augmentation (tta) results of EVA for comparison. For COCO, Soft-NMS [8] is also applied. For instance segmentation task, the classification score is calibrated [46] via maskness [102]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.213, + 0.894, + 0.288 + ], + "angle": 0, + "content": "The model architecture as well as the hyper-parameters for COCO and LVIS are almost the same (i.e., the hyperparameters are nearly \"zero-shot\" transferred from COCO to LVIS), expect we use federated loss [125] and repeat factor sampling [38] following ViTDet on LVIS." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.292, + 0.892, + 0.352 + ], + "angle": 0, + "content": "Results. Perhaps COCO is the most fierce vision benchmark. Table 7 compares EVA with some leading approaches on COCO. Our model creates new state-of-the-art results on both object detection and instance segmentation tasks." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.353, + 0.892, + 0.413 + ], + "angle": 0, + "content": "Compared with ViTDet-H [60] that uses Cascade Mask R-CNN [12] as well, EVA shows that with a larger model and better encoder & detector pre-training, the performance can be greatly improved with the same detector." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.413, + 0.892, + 0.519 + ], + "angle": 0, + "content": "Compared with FocalNet [116] and Group DETRv2 [19] that choose better-established and highly-optimized DINO detector [121], EVA demonstrates that with sufficient model size, data and pre-training, better performance can be also achieved via the classic R-CNN framework [37]. On the other hand, FocalNet and Group DETRv2 are incapable of instance segmentation due to using DINO." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.519, + 0.894, + 0.594 + ], + "angle": 0, + "content": "Compared with SwinV2-Giant [65] and FD-SwinV2-Giant [107] that also adopt a (stronger \\(\\mathrm{HTC}++\\) [17]) detector from the R-CNN family but with \\(\\sim 3\\times\\) model size of EVA, our approach streamlines the pre-training processes and pulls off a \"Giant-killing\" act via better representations." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.595, + 0.894, + 0.671 + ], + "angle": 0, + "content": "Compared with BEiT-3, EVA shows that it is possible to build a state-of-the-art object-level recognition system without exploiting (i) semantic feature quantization / tokenization [5, 70], and (ii) image-text paired pre-training data and large corpora during pre-training." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.675, + 0.894, + 0.84 + ], + "angle": 0, + "content": "Analyzing the performance gap between LVIS and COCO. Evaluating models on both COCO and LVIS benchmarks is essential, as they share nearly the same image set but differ in the number of annotated object categories. COCO has only 80 annotated categories, while LVIS annotates over 1,200 object categories, resulting in a long-tail distribution that more closely resembles challenging real-world scenarios [38]. In general, LVIS is considered a much more difficult benchmark than COCO for object-level recognition, with conventional methods typically experiencing a significant performance drop on LVIS." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.841, + 0.894, + 0.901 + ], + "angle": 0, + "content": "In Table 8a, we analyze the performance gap between the LVIS and COCO benchmarks for EVA and other state-of-the-art approaches. For previous leading methods, such as ViTDet, the performance gap for \\(\\mathrm{AP^{box}}\\) is around 8, and" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "19362" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.08, + 0.051, + 0.891, + 0.276 + ], + "angle": 0, + "content": "
model / methoddetector#param.pre-training datatta?COCO valCOCO test-dev
encoderdetectorAPboxAPmaskAPboxAPmask
Soft-Teacher [115]HTC++ [17]284MIN-21K (14M)COCO(unlabeled)+O365✓60.752.561.353.0
GLIP [59]DyHead [26]≥ 284MIN-21K (14M)4ODs+GoldG+Cap12M✓60.8-61.5-
GLIPv2 [122]DyHead [26]≥ 637MFLD-900M\\( merged\\ data^a \\)✓--62.4-
ViTDet-H [60]CMask R-CNN [12]692MIN-1K (1M)-✓61.353.1--
Florence [118]DyHead [26]≥ 637MFLD-900M\\( merged\\ data^a \\)✓62.0-62.4-
SwinV2-G [65]HTC++ [17]≥ 3000MIN-21K-ext-70MO365✓62.553.763.154.4
DINO [121]-218MIN-21K (14M)O365✓63.2-63.3-
Mask DINO [57]-223MIN-21K (14M)O365✓-54.5-54.7
BEiT-3 [101]CMask R-CNN [12]1074M\\( merged\\ data^b \\)O365✓--63.754.8
FD-SwinV2-G [107]HTC++ [17]≥ 3000MIN-21K-ext-70MO365✓--64.255.4
FocalNet [116]DINO [121]746MIN-21K (14M)O365✓64.2-64.4-
Group DETRv2 [19]DINO [121]629MIN-1K (1M)O365✓--64.5-
EVACMask R-CNN [12]1074Mmerged-30MO365✘64.255.064.455.5
EVACMask R-CNN [12]1074Mmerged-30MO365✓64.5-64.7-
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.28, + 0.893, + 0.322 + ], + "angle": 0, + "content": "Table 7. Object detection & instance segmentation on results COCO dataset. EVA establishes new state-of-the-art results in object detection and instance segmentation tasks on both COCO val and test-dev splits with the canonical R-CNN [37] object detection & segmentation framework. \"tta\" refers to test-time augmentation. (timestamp: Nov 10, 2022)" + }, + { + "type": "table_footnote", + "bbox": [ + 0.086, + 0.324, + 0.722, + 0.336 + ], + "angle": 0, + "content": "\"merged data\": FourODs + INBoxes + GoldG + CC15M + SBU, \"merged data\": IN-21K (14M) + Image-Text (35M) + Text (160GB)." + }, + { + "type": "table", + "bbox": [ + 0.086, + 0.349, + 0.46, + 0.476 + ], + "angle": 0, + "content": "
modelAPboxAPmask
COCOLVISΔ↓COCOLVISΔ↓
(a) evaluation using COCO & LVIS official annotations respectively
Copy-Paste [36]57.041.615.448.938.110.8
ViTDet-H [60]61.353.47.953.148.15.0
prev. best63.2a53.4b9.854.5c49.2d5.3
EVA (single-scale test)64.162.21.955.055.00.0
(b) evaluation using LVIS val1-5K annotations
EVA (single-scale test)69.668.31.359.659.8-0.2
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.482, + 0.471, + 0.552 + ], + "angle": 0, + "content": "Table 8. LVIS & COCO performance gap on val set. “prev. best” refers to the best individual model / result in each benchmark (a: DINO [121], b: ViTDet-H [60], c: Mask DINO [57], d: 2021 competition \\(1^{\\text{st}}\\) [35]) “\\(\\Delta \\downarrow\\)”: the performance gap between LVIS and COCO (the lower the better)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.568, + 0.47, + 0.764 + ], + "angle": 0, + "content": "for \\(\\mathrm{AP^{mask}}\\), it is around 5. However, when using the same detector (Cascade Mask R-CNN) and nearly identical settings as those in ViTDet pre-trained via MAE-Huge (ViTDet-H), EVA not only achieves state-of-the-art results on both LVIS and COCO benchmarks simultaneously but also significantly reduces the performance gap between them, particularly for the instance segmentation task. EVA attains the same performance on LVIS and COCO using single-scale evaluation. In comparison with ViTDet-H, we demonstrate that a slightly larger model with stronger representations can greatly improve performance on the challenging large vocabulary instance segmentation benchmark, with one caveat described below." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.765, + 0.471, + 0.901 + ], + "angle": 0, + "content": "Note that the Merged-30M unlabeled images include 15K out of 20K LVIS val set images (the Merged-30M images contain all the COCO training images, and the LVIS validation split also includes 15k images from the COCO training set). Although a recent study [33] shows that including unlabeled images from the development / test set for MIM pre-training has minimal impact on the final performance, we conduct a more rigorous analysis of the LVIS and COCO performance gap to eliminate potential data contamination issues: We evaluate both" + }, + { + "type": "table", + "bbox": [ + 0.503, + 0.349, + 0.895, + 0.491 + ], + "angle": 0, + "content": "
modelcrop sizeADE20KCOCO-Stuff
mIoUssmIoUmsmIoUss
HorNet [79]640257.557.9-
SeMask [48]640257.058.3-
SwinV2-G [65]896259.359.9-
Mask DINO [57]896259.560.8-
FD-SwinV2-G [107]8962-61.4-
ViT-Adapter [23]896261.261.552.3
BEiT-3 [101]896262.062.8-
EVA896261.562.353.4
" + }, + { + "type": "table_caption", + "bbox": [ + 0.498, + 0.496, + 0.893, + 0.538 + ], + "angle": 0, + "content": "Table 9. Semantic segmentation performance on ADE20K and COCO-Stuff-164K dataset. \"mIoUss\": mIoU of single-scale evaluation, \"mIoUms\": mIoU using multi-scale evaluation." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.552, + 0.894, + 0.658 + ], + "angle": 0, + "content": "COCO and LVIS models using the 5K images present in both the COCO and LVIS val sets, denoted as LVIS val-5K. The COCO results are measured using the 80-category COCO subset of LVIS with the higher-quality LVIS annotations (a similar approach also employed in [53], but for a different purpose). The results are shown in Table 8b, and we find that the conclusion remains unchanged." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.684, + 0.719, + 0.699 + ], + "angle": 0, + "content": "2.3.4 Semantic Segmentation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.714, + 0.895, + 0.85 + ], + "angle": 0, + "content": "Dataset. We evaluate EVA on ADE20K [123] and COCO-Stuff-164K [11] datasets for semantic segmentation task. ADE20K includes 150 semantic categories, and has 20k images for training & 2k images for validation. COCO-Stuff-164K augments 164K complex images from COCO with pixel-level annotations that span over 172 categories including 80 things, 91 stuff, and 1 unlabeled class. Compared with ADE20K, COCO-Stuff is a more challenging but under-explored semantic segmentation benchmark." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.856, + 0.894, + 0.901 + ], + "angle": 0, + "content": "Training & evaluation settings. We follow the task transfer pipelines of ViT-Adapter [23] + mask2former [24] but with a weakened model adaptation processes due to GPU memory" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "19363" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.084, + 0.051, + 0.899, + 0.156 + ], + "angle": 0, + "content": "
modelprecisiontotal #param.image #param.text #param.clip training datasamples seenimage sizepatch sizebatch sizegpu for training
OpenAI CLIP-Lfloat16430M304M124MCLIP-400M [73]12B\\( 224^2 \\)\\( 14 \\times 14 \\)32k\\( 256 \\times V100 (32GB) \\)
ALIGNbfloat16834M480M354MALIGN-1.8B [73]22B\\( 289^2 \\)-16k\\( 1024 \\times TPUv3 \\)
Open CLIP-Hbfloat161.0B632M354MLAION-2B [85]32B\\( 224^2 \\)\\( 14 \\times 14 \\)79k\\( 824 \\times A100 (40GB) \\)
Open CLIP-gbfloat161.3B1.0B354MLAION-2B [85]12B\\( 224^2 \\)\\( 14 \\times 14 \\)64k\\( 800 \\times A100 (40GB) \\)
EVA CLIP-gfloat161.1B1.0B124MLAION-400M [86]11B\\( 224^2 \\)\\( 14 \\times 14 \\)41k\\( 256 \\times A100 (40GB) \\)
" + }, + { + "type": "table_footnote", + "bbox": [ + 0.077, + 0.157, + 0.9, + 0.182 + ], + "angle": 0, + "content": "(a) CLIP model configurations. EVA CLIP-g can be stably trained via fp16 precision with fewer image-text pairs (7B v.s. 12B / 32B) sampled from a smaller data pool (LAION-400M v.s. LAION-2B) on \\(\\sim 1/3 \\times\\) GPUs compared with other open-sourced billion-scale competitors." + }, + { + "type": "table", + "bbox": [ + 0.085, + 0.193, + 0.898, + 0.365 + ], + "angle": 0, + "content": "
datasetsImageNet-1K [28]ImageNet-V2 [82]ImageNet-Adv. [42]ImageNet-Ren. [41]ImageNet-Ske. [100]ObjectNet [6]CIFAR-10 [54]CIFAR-100 [54]UCF-101 [92]Video classificationAvg. all
modelimage classificationΔ↓Kinetics-400 [51]Kinetics-600 [14]Kinetics-700 [15]
OpenAI CLIP-L75.569.970.887.859.669.095.675.93.476.464.564.257.772.2
ALIGN76.470.175.892.264.872.2--------
Open CLIP-H78.070.959.389.366.669.797.584.75.778.263.163.656.173.1
Open CLIP-g76.669.657.288.765.267.597.183.95.877.761.762.255.071.9
EVA CLIP-g78.5(+1.9)71.5(+1.9)73.6(+16.4)92.5(+3.8)67.3(+2.1)72.3(+4.8)98.3(+1.2)88.7(+4.8)2.576.1(-1.6)65.2(+3.5)64.4(+2.2)58.4(+3.4)75.7(+3.8)
" + }, + { + "type": "table_footnote", + "bbox": [ + 0.076, + 0.367, + 0.9, + 0.406 + ], + "angle": 0, + "content": "(b) Summary of zero-shot image / video classification performance. “\\(\\Delta \\downarrow\\)”: The gap between the averaged performance of ImageNet-{1K, V2, Adv., Ren., Ske.} & ObjectNet that with natural distribution shifts and the original ImageNet-1K validation accuracy. Our model suffers from the smallest performance drop (only \\(2.5\\%\\) top-1 accuracy gap) while maintaining the highest zero-shot classification accuracy averaged on all 12 benchmarks (\\(72.7\\%\\) top-1 accuracy)." + }, + { + "type": "table_footnote", + "bbox": [ + 0.076, + 0.412, + 0.895, + 0.468 + ], + "angle": 0, + "content": "Table 10. EVA as a vision-centric, multi-modal pivot. We evaluate a billion-scale contrastive language-image pre-trained (CLIP) model with the vision tower initialized from pre-trained EVA, which largely accelerates the contrastive training efficiency and shows promising zero-shot classification performance across a wide range of image / video benchmarks. The statistics & performance of EVA's MIM teacher (OpenAI CLIP-L) are also presented for reference." + }, + { + "type": "list", + "bbox": [ + 0.076, + 0.367, + 0.9, + 0.468 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.482, + 0.47, + 0.542 + ], + "angle": 0, + "content": "limitation (40GB of VRAM): (i) relative position biases [90] are not applied. (ii) We use \\(8 \\times\\) decoders in mask2former segmentation head instead of \\(9 \\times\\). (iii) The feature dimension in mask2former head is \\(\\sim 0.6 \\times\\) of EVA encoder." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.548, + 0.47, + 0.653 + ], + "angle": 0, + "content": "Results. We compare EVA with other leading semantic segmentation methods in Table 9. EVA achieves strong results in both ADE20K and COCO-Stuff-164K datasets. On the other hand, the segmentation performance of EVA is slightly lower compared with BEiT-3 on ADE20K, we suspect this is partially due to our weakened architectural configurations." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.678, + 0.424, + 0.707 + ], + "angle": 0, + "content": "2.3.5 Contrastive Language-Image Pre-training with Zero-shot Classification Evaluation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.718, + 0.471, + 0.869 + ], + "angle": 0, + "content": "CLIP (Contrastive Language-Image Pre-training) [47, 49, 72, 73] is a type of multi-modal foundation model that connects vision and language via contrastive image-text pre-training. CLIP can be applied to any image classification benchmark by simply providing the names of the visual categories to be recognized [1]. Thus the introduction of CLIP essentially reshapes the landscape of visual recognition. Meanwhile, CLIP features also play a central role in representation leaning [70, 101], AI generated content [78, 83, 84] and large dataset filtering [10, 85, 86], etc." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.471, + 0.901 + ], + "angle": 0, + "content": "In this section and Table 10, we show that EVA is not only a strong encoder for a wide range of vision downstream" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.482, + 0.895, + 0.543 + ], + "angle": 0, + "content": "tasks, but also a multi-modal pivot that builds a bridge between vision and language. To demonstrate that, we train & evaluate EVA as a billion-scale CLIP's vision tower in various zero-shot image / video classification benchmarks." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.547, + 0.895, + 0.622 + ], + "angle": 0, + "content": "Baselines and major challenges in CLIP model scaling. We compare our CLIP (dubbed EVA CLIP) with other open-sourced strong CLIP competitors that exploit publicly accessible data / academic resources only. Model configurations and statistics are detailed in Table 10a." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.624, + 0.895, + 0.773 + ], + "angle": 0, + "content": "There are two well-known major challenges of CLIP model training and scaling: (i) Large-scale Open CLIP models (e.g., Open CLIP-H & Open CLIP-g [2, 47]) usually suffer from severe training instability issues [2] and have to use bfloat16 format for optimization. (ii) The training efficiency is low, which may hinder model scaling and downstream performance. For instance, Open CLIP-g is heavily under-trained due to its large compute requirement, and its performance is even worse than the sufficiently-trained Open CLIP-H with a smaller model size." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.775, + 0.895, + 0.866 + ], + "angle": 0, + "content": "Compared with our CLIP model, Open CLIP-H & -g are trained from scratch with much more image-text pairs (\\(\\sim 2.9 \\times\\) and \\(\\sim 1.1 \\times\\) of ours) sampled from a much larger dataset (\\(\\sim 5 \\times\\) of ours) on \\(\\sim 3 \\times\\) of GPUs. While by leveraging EVA, billion-scale CLIP model training can be accelerated with improved zero-shot classification performance, described next." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.871, + 0.895, + 0.901 + ], + "angle": 0, + "content": "Training settings. For our CLIP model, we initialize the vision encoder via pre-trained EVA and the language encoder" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "19364" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.08, + 0.09, + 0.472, + 0.134 + ], + "angle": 0, + "content": "
model (SSL)zero-shotlinear probingfine-tuning
prev. best78.0a82.3b89.1c
EVA78.586.589.4
" + }, + { + "type": "table_footnote", + "bbox": [ + 0.076, + 0.136, + 0.47, + 0.22 + ], + "angle": 0, + "content": "Table 11. Zero-shot, linear probing and fine-tuning performance of EVA-CLIP on ImageNet-1K. Notice that the linear probing and fine-tuning results are from the vision encoder of EVA-CLIP. Our approach establishes the new state-of-the-art results among all existing self-supervised learning (SSL) methods. (timestamp: Nov 10, 2022) results reference. a: Open CLIP-H [47], b: iBOT [124], c: dBOT [63]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.234, + 0.471, + 0.354 + ], + "angle": 0, + "content": "from OpenAI CLIP-L. The pre-training implementation is based on Open CLIP [47]. We also adopt DeepSpeed optimization library [80] with ZeRO stage-1 optimizer [77] to save memory. We find using fp16 format with dynamic loss scaling is stable enough during the whole course of training while using bf1oat16 format is unnecessary. These modifications allow us to train a 1.1B CLIP with a batch size of 41k on \\(256 \\times\\) NVIDIA A100 40GB GPUs." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.361, + 0.471, + 0.406 + ], + "angle": 0, + "content": "Evaluation settings. We evaluate zero-shot image / video classification performance of each CLIP model on 12 benchmarks and report top-1 accuracy for comparisons." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.408, + 0.472, + 0.558 + ], + "angle": 0, + "content": "For zero-shot image classification task, we choose 8 benchmarks, i.e., ImageNet-1K [28], ImageNet-V2 [81], ImageNet-Adversarial (ImageNet-Adv.) [42], ImageNet-Rendition (ImageNet-Adv.) [41], ImageNet-Sketch (ImageNet-Ske.) [100], ObjectNet [6], CIFAR-10 and CIFAR-100 [54]. We are also interested in the robustness of CLIP models, evaluated via the performance gap between the averaged performance of ImageNet-{1K, V2, Adv., Ren., Ske.} & ObjectNet that with natural distribution shifts and the original ImageNet-1K validation accuracy." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.56, + 0.472, + 0.606 + ], + "angle": 0, + "content": "For zero-shot video classification task, we choose 4 benchmarks, namely UCF-101 [92], Kinetics-400 [51], Kinetics-600 [14], and Kinetics-700 [15]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.611, + 0.471, + 0.732 + ], + "angle": 0, + "content": "Results. Table 10b shows the comparison. Our EVA CLIP achieves the highest averaged accuracy, and performs the best in 10 out of 12 zero-shot classification benchmarks. Notably, the ImageNet-1K validation zero-shot top-1 accuracy is \\(78.2\\%\\) without using any of its training set labels, matching the original ResNet-101 [40]. Moreover, our model is quite robust and suffers from the smallest performance drop when facing natural distribution shifts in ImageNet." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.734, + 0.47, + 0.809 + ], + "angle": 0, + "content": "At last, in Table 11 we provide zero-shot, linear probing & end-to-end fine-tuning top-1 accuracy of EVA-CLIP on ImageNet-1K validation set for reference. Our approach creates the new state-of-the-art results among all existing self-supervised learning methods." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.81, + 0.472, + 0.902 + ], + "angle": 0, + "content": "Notice that EVA CLIP's vision branch learns from OpenAI CLIP-L, while language branch initialized from the same CLIP-L model. Therefore, starting from a CLIP-L with only 430M parameters, we progressively scale up a 1.1B EVA CLIP-g with large performance improvements. This implies that interleaved MIM & image-text contrastive" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.894, + 0.182 + ], + "angle": 0, + "content": "pre-training could be an efficient and scalable CLIP training approach. To our knowledge, EVA CLIP-g is the largest performant CLIP model trained via publicly accessible data and resources. We hope our practice on scaling and improving CLIP can also inspire and transfer to the study of other large scale multi-modal foundation models." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.197, + 0.642, + 0.213 + ], + "angle": 0, + "content": "3. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.227, + 0.895, + 0.379 + ], + "angle": 0, + "content": "Masked image modeling (MIM) learns rich visual representations via predicting masked visual contents conditioned on visible context. ViT [31] and iGPT [18] report the first meaningful MIM pre-training results. The BEiT family [5,70,101] greatly improves MIM's performance via masked visual token prediction. Recent work [4,21,30,32,39,103,113,124] (re-)explore pixel / feature regression in MIM, but only in a relatively small model and data scales. In this work, we explore the limits of large scale MIM pre-training via masked image-text aligned feature prediction [43, 106]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.383, + 0.895, + 0.58 + ], + "angle": 0, + "content": "Vision foundation models. ConvNets [56] have long been the de-facto standard visual architecture ab initio. Since AlexNet [55], ConvNets have rapidly evolved and become deeper, wider and larger [40, 44, 66, 91, 93, 94, 111]. However, at sufficient model and data scales, ConvNets lag behind ViTs [31] due to a lack of scalable pre-training tasks and the built-in inductive biases. Entering the 2020s, large pretrained ViTs [31, 119] such as SwinV2-G [65] with hierarchical architectures as well as BEiT-3 [101] with multi-modal representations started to demonstrate various vision benchmarks. In this work, we show by leveraging unlabeled images, vanilla ViT can be efficiently scaled up to billion-scale parameters, and stands out in various downstream tasks." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.594, + 0.619, + 0.609 + ], + "angle": 0, + "content": "4. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.619, + 0.894, + 0.755 + ], + "angle": 0, + "content": "In this work, we launch EVA, a one billion parameters vanilla ViT encoder to explore the limits of masked visual representation learning. We show simple masked feature modeling as a visual learning pretext task scales well on an architecture with minimal vision priors, and attains excellent results in a representative & diverse set of downstream tasks. We hope EVA would bridge the gap between vision and language study via masked modeling, and contributes to the Neon Genesis of vision research." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.77, + 0.661, + 0.787 + ], + "angle": 0, + "content": "Acknowledgement" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.795, + 0.895, + 0.903 + ], + "angle": 0, + "content": "This work is supported by the National Key R&D Program of China (2020AAA0105200) and NSFC (No. 617333007). We would like to thank Hanxiao Qu, Yan Tian, Yemin Shi and Xigang Cao for their help on GPU resources. 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IJCV, 2018. 2, 3, 6" + }, + { + "type": "ref_text", + "bbox": [ + 0.504, + 0.135, + 0.893, + 0.171 + ], + "angle": 0, + "content": "[124] Jinghao Zhou, Chen Wei, Huiyu Wang, Wei Shen, Cihang Xie, Alan Yuille, and Tao Kong. ibot: Image bert pre-training with online tokenizer. arXiv preprint arXiv:2111.07832, 2021. 1, 2, 8" + }, + { + "type": "ref_text", + "bbox": [ + 0.504, + 0.176, + 0.894, + 0.211 + ], + "angle": 0, + "content": "[125] Xingyi Zhou, Vladlen Koltun, and Philipp Krahenbuhl. Probabilistic two-stage detection. arXiv preprint arXiv:2103.07461, 2021. 5" + }, + { + "type": "list", + "bbox": [ + 0.503, + 0.094, + 0.894, + 0.211 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.946, + 0.52, + 0.957 + ], + "angle": 0, + "content": "19369" + } + ] +] \ No newline at end of file diff --git a/2023/EVA_ Exploring the Limits of Masked Visual Representation Learning at Scale/c4046a48-182c-4cee-86a4-65a7035e3e1d_origin.pdf b/2023/EVA_ Exploring the Limits of Masked Visual Representation Learning at Scale/c4046a48-182c-4cee-86a4-65a7035e3e1d_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..5377c60f464c592e082b69e7fc85f85904a2ae5a --- /dev/null +++ b/2023/EVA_ Exploring the Limits of Masked Visual Representation Learning at Scale/c4046a48-182c-4cee-86a4-65a7035e3e1d_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:27287e710f23c28006149185a33eba37dbb4706752fcdd1b4b7ea456d0df7bcd +size 416631 diff --git a/2023/EVA_ Exploring the Limits of Masked Visual Representation Learning at Scale/full.md b/2023/EVA_ Exploring the Limits of Masked Visual Representation Learning at Scale/full.md new file mode 100644 index 0000000000000000000000000000000000000000..879f5b1bfdac8a62cdb20126bfb409002c2f49e7 --- /dev/null +++ b/2023/EVA_ Exploring the Limits of Masked Visual Representation Learning at Scale/full.md @@ -0,0 +1,388 @@ +# EVA: Exploring the Limits of Masked Visual Representation Learning at Scale + +Yuxin Fang $^{1,2\dagger}$ Wen Wang $^{3,2\dagger}$ Binhui Xie $^{4,2\dagger}$ Quan Sun $^{2}$ Ledell Wu $^{2}$ Xinggang Wang $^{1\dagger}$ Tiejun Huang $^{2}$ Xinlong Wang $^{2\dagger}$ Yue Cao $^{2\dagger}$ + +1Huazhong University of Science and Technology +2Beijing Academy of Artificial Intelligence +3Zhejiang University +4Beijing Institute of Technology + +Code & Models: baaivision/EVA/01 + +# Abstract + +We launch EVA, a vision-centric foundation model to Explore the limits of Visual representation at scAle using only publicly accessible data. EVA is a vanilla ViT pretrained to reconstruct the masked out image-text aligned vision features conditioned on visible image patches. Via this pretext task, we can efficiently scale up EVA to one billion parameters, and sets new records on a broad range of representative vision downstream tasks, such as image recognition, video action recognition, object detection, instance segmentation and semantic segmentation without heavy supervised training. Moreover, we observe quantitative changes in scaling EVA result in qualitative changes in transfer learning performance that are not present in other models. For instance, EVA takes a great leap in the challenging large vocabulary instance segmentation task: our model achieves almost the same state-of-the-art performance on LVIS dataset with over a thousand categories and COCO dataset with only eighty categories. Beyond a pure vision encoder, EVA can also serve as a vision-centric, multi-modal pivot to connect images and text. We find initializing the vision tower of a giant CLIP from EVA can greatly stabilize the training and outperform the training from scratch counterpart with much fewer samples and less compute, providing a new direction for scaling up and accelerating the costly training of multi-modal foundation models. + +# 1. Introduction + +Scaling up pre-trained language models (PLMs) [9,64,76] has revolutionized natural language processing (NLP) in the past few years. The key to this success lies in the simple and scalable self-supervised learning task of masked signal + +prediction [29, 74], with which Transformer models [99] could be scaled up to billions of parameters using nearly unlimited unlabelled data, and generalize well to a wide range of downstream tasks with little tuning. With further scaling on compute, data, and model sizes, PLMs have led to not only continuous performance improvements [50, 75, 76], but also a surprising emergence of in-context learning capability [9, 25, 104, 105]. + +Motivated by the success of model scaling in NLP, it is appealing that we can also translate this success from language to vision, i.e., to scale up a vision-centric foundation model that is beneficial for both vision & multi-modal downstream tasks. Recently, masked image modeling (MIM) [5, 39, 113] has boomed as a viable approach for vision model pretraining and scaling. However, the most competitive billion-sized vision pre-trained models [31, 65, 71, 119] still heavily rely on supervised or weakly-supervised training with hundreds of millions of (often publicly inaccessible) labeled data. MIM is somewhat only adopted as an initialization stage before the heavily supervised pre-training [65], or a pure MIM pre-trained model could not achieve favorable performance at billion-scale model sizes [114]. We regard this gap stems from the fact that natural images are raw and information-sparse. Meanwhile, an ideal vision pretext task needs the abstraction of not only the low-level geometry & structure information, but also high-level semantics, which is hardly captured by pixel-level recovery tasks [112]. + +In this work, we seek a suitable MIM pretext task for large scale vision representation learning and explore its limits at the scale of one billion parameters with tens of millions of unlabeled data. Recently, there are a few trials leveraging the semantic information from image-image or image-text contrastive learning [13, 22, 73] for MIM pretraining [43, 106, 124], which perform fairly well in vision downstream tasks. However, there remains a debate that (i) tokenized semantic features could provide better supervision signal for masked modeling in vision [5, 70, 101], and (ii) good performances could be also achieved via a simple post + +
modelimage & video classification (G)object detection (det) & instance segmentation (seg)semantic segmentation
IN-1K ftIN-1K linIN-1K zsavg. zsK400K600K700COCO det (test/val)COCO seg (test/val)LVIS segCOCO-StuffADE20K
Florence----86.587.8-62.4 / 62.0----
SwinV2-G----86.8--63.1 / 62.554.4 / 53.7--59.9
prev. best89.6a82.3b78.0c73.1c87.8d88.3e80.4e64.5f / 64.2g55.4h / 54.5i49.2j52.3k62.8a
EVA89.7(+0.1)86.5(+4.2)78.5(+0.5)75.7(+2.6)89.7(+1.9)89.8(+1.5)82.9(+2.5)64.7 / 64.5(+0.2/+0.3)55.5 / 55.0(+0.1/+0.5)55.0(+5.8)53.4(+1.1)62.3(-0.5)
+ +Table 1. Summary of EVA performance on various mainstream vision benchmarks. EVA is performant compared with previous best / leading approaches. “”: methods / results that only exploit publicly accessible data / academic resources. “ft”: end-to-end fine-tuning. “lin”: linear probing. “zs”: zero-shot classification. “avg. zs”: averaged zero-shot classification performance on 8 image and 4 video datasets with contrastive language-image pre-training. (timestamp: Nov 10, 2022) +methods / results reference. a: BEiT-3 [101], b: iBOT [124], c: Open CLIP-H [47], d: Text4Vis [109], e: MaskFeat [103], f: Group DETRv2 [19], g: FocalNet [116], h: FD-SwinV2-G [107], i: Mask DINO [57], j: LVIS 2021 competition $1^{\text{st}}$ [35], k: ViT-Adapter [23]. + +distillation process without masked prediction tasks [107]. Through a pilot empirical study, we find that simply using image-text aligned (i.e., CLIP [73]) vision features as the prediction targets in MIM scales up well and achieves satisfactory performances on a broad range of downstream benchmarks. This pre-training task draws the benefits from both the high-level semantic abstraction of image-text contrastive learning as well as the good capture of geometry & structure in masked image modeling, which typically covers the information needed for most visual perception tasks. + +Via this MIM pretext task, we can efficiently scale up a vanilla ViT encoder [31], dubbed EVA, to one billion parameters with strong visual representations that transfers well to a wide range of downstream tasks. Using 29.6 million public accessible unlabeled images for pre-training, EVA sets new records on several representative vision benchmarks, such as image classification on ImageNet-1K [28] (89.7% top-1 accuracy), object detection and instance segmentation on LVIS [38] (62.2 AP $^{\text{box}}$ & 55.0 AP $^{\text{mask}}$ on val) and COCO [62] (64.5 AP $^{\text{box}}$ & 55.0 AP $^{\text{mask}}$ on val, 64.7 AP $^{\text{box}}$ & 55.5 AP $^{\text{mask}}$ on test-dev), + +
tokenizer? [70]pt epochsImageNet-1K top-1 acc.ADE20K mIoUss
X-85.052.6
✓30085.052.7
✓160085.553.1
X80085.553.3
+ +(a) (Additional) semantic feature tokenization is not required for achieving good downstream performance. + +
distill.?[107]pt epochsImageNet-1K top-1 acc.ADE20K mIoUss
X-85.052.6
✓30085.152.5
✓80085.152.7
X80085.553.3
+ +(b) Feature distillation fails to achieve consistent performance gain as the pre-training becomes longer. + +Table 2. Pilot experiment. We evaluate different pre-training approaches using ViT-B and report their performance on ImageNet-1K image classification (top-1 accuracy) and ADE20K semantic segmentation (single-scale mIoU). Numbers in grey refer to the results of directly fine-tuning CLIP vision encoder on corresponding downstream tasks. Default settings for EVA pre-training are marked in purple, i.e., directly regressing the masked out CLIP vision features conditioned on visible image patches. + +semantic segmentation on COCO-stuff [11] (53.4 mIoU $^{\mathrm{ss}}$ ) and ADE20K [123] (62.3 mIoU $^{\mathrm{ms}}$ ), and video action recognition on Kinetics-400 [51] (89.7% top-1 accuracy), Kinetics-600 [14] (89.8% top-1 accuracy), Kinetics-700 [15] (82.9% top-1 accuracy). Notably, different from other state-of-the-art billion-scale vision foundation models that demand tens of millions of or even billions of labeled images, such as SwinV2-G using ImageNet-21K-ext-70M [65] and ViT-g/G using JFT3B [119], EVA does not need a costly supervised training stage and only leverage images from open-sourced datasets for academic reproducibility. + +Moreover, we observe quantitative changes in scaling EVA result in qualitative changes in transfer learning performance that are not observed in other smaller-scale models, e.g., EVA makes a significant breakthrough in the challenging large vocabulary object-level recognition task: our model achieves almost the same performance on LVIS [38], an instance segmentation benchmark with more than 1,200 categories, as COCO [62], which almost shares the same image set as LVIS but with only 80 categories annotated. This emergent ability well matches the expectation of model scaling [105], that larger capability of model results in not only predictable performance improvements on standard benchmarks, but also unpredictable phenomena and capabilities for resolving more challenging tasks. + +Going beyond a pure vision encoder, EVA can also serve as a vision-centric, multi-modal pivot that builds a bridge between vision and language. We show that initializing the image encoder via pre-trained EVA in a 1.1 billion parameters CLIP model can outperform the training from scratch counterpart on a broad range of zero-shot image / video classification benchmarks with much fewer samples and less compute. Moreover, EVA can greatly stabilize the giant CLIP's training & optimization process. Since large CLIP models usually suffer from training instability and inefficiency issues [2,47], we hope our solution opens up a new direction for scaling up and accelerating the costly training of multi-modal foundation models. + +By scaling up vision-centric foundation models with MIM pre-training to achieve strong performance on broad downstream tasks, we hope EVA would bridge the gap between vision and language with masked signal modeling, and contributes to the big convergence across different modalities. + +
patch size#layershidden dimmlp dimattn heads#param.
14×144014086144161011M
+ +(a) EVA architecture configurations. + +
image sizebatch sizeoptimizerpeak lr(β1, β2)pt epochs
22424096AdamW1e-3(0.9, 0.98)150
+ +(c) some pre-training settings and hyper-parameters. + +
datasettotal size
ImageNet-21K, CC12M, CC3M, Object365, COCO, ADE29.6M images
+ +(b) datasets for pre-training EVA. + +
precisionZeRO#gpusamples / sec.max mem.pt days
fp16stage-1128~3150~26.5GB~14.5
+ +(d) basic statistics of EVA pre-training. + +Table 3. A brief summary of pre-training settings and configurations for EVA. + +# 2. Fly EVA to the Moon + +We first conduct a series of pilot experiments for choosing an ideal vision pretext task in §2.1, then we scale up EVA pre-training via the chosen pre-training objective in §2.2. Finally, we evaluate the pre-trained representation on various downstream tasks in §2.3. Detailed experimental settings and configurations are in Appendix. + +# 2.1. The Feature Instrumentality Project + +In this section, we seek a MIM vision pretext task with compelling transfer performance. Based on previous literature on vision pre-training, we study two promising candidates: (i) recovering the masked out tokenized semantic vision features [5, 70, 101], and (ii) feature distillation from strong pre-trained representation as in [107]. Both of them exploit pre-trained image-text aligned vision features (i.e., CLIP [73] vision features). Via a series of pilot experiments shown in Table 2, we find that: (i) the (additional) CLIP feature tokenization process is unnecessary for achieving good downstream performance (ii) feature distillation fails to provide consistent performance gain as the pre-training becomes longer. Instead, we find that simply reconstructing the masked out CLIP vision features conditioned on visible image patches is highly performant, which is chosen for scaling up EVA. + +We clarify that this MIM pretext task is not originally proposed by us. Regressing the masked out image-text aligned vision features for MIM pre-training has been studied in MVP [106] and recently has been revisited by MILAN [43]. In this work, we show that this pretext task can scale up to billion-scale parameters and tens of millions of unlabeled images for vision-centric representation learning without (i) semantic feature quantization / tokenization [5, 70], and (ii) explicitly using image-text paired pre-training data and large corpora as in BEiT-3 [101]. + +# 2.2. Pre-training + +Architecture. The architecture configurations of EVA are in Table 3a. EVA is a vanilla ViT [31] with 1.0B parameters. The shape of her follows ViT giant [119] and the vision encoder of BEiT-3 [101]. We do not use relative positional embeddings [89] and layer-scale [97] during pre-training. + +Pre-training objective. EVA is pre-trained to reconstruct the masked out image-text aligned vision features conditioned on visible image patches. We corrupt the input patches with [MASK] tokens, and we use block-wise masking with + +a masking ratio of $40\%$ following [5, 70, 101]. The target for MIM pre-training is from the publicly available OpenAI CLIP-L/14 vision tower trained on $224\times 224$ pixel images [73]. The output feature of EVA is first normalized [3] and then projected to the same dimension as the CLIP feature via a linear layer. We use negative cosine similarity as the loss function. + +Pre-training data. The data we used for pre-training EVA are summarized in Table 3b. For CC12M [16] and CC3M [88] datasets, we only use the image data without captions. For COCO [62] and ADE20K [123] datasets, we only use the train set data. ImageNet-21K [28] and Object365 [87] image data are also used. All these data are publicly accessible. The merged dataset for pre-training has 29.6 million images in total. + +Pre-training settings & hyper-parameters. As shown in Table 3c, EVA is optimized via Adam [52] with decoupled weight decay [67] of 0.05. The peak learning rate is 1e-3 and decays according to a cosine learning rate schedule. We employed stochastic depth [45] with a rate of 0.1 for regularization and RandResizeCrop (0.2, 1) for data augmentation. Color jitter is not used. + +Pre-training infrastructure and statistics. Some basic pre-training statistics are available in Table 3d. The GPU we use is NVIDIA A100-SXM4-40GB. Pre-training code is based on BEiT [5] written in PyTorch [69]. We also adopt DeepSpeed optimization library [80] with ZeRO stage-1 optimizer [77] to save memory. We find using fp16 format with dynamic loss scaling is stable enough during the whole course of pre-training while using bf1oat16 format is unnecessary. Since we use fp16 precision, EVA can also be pre-trained using $16 \times$ NVIDIA 24GB (32GB) GPUs with (without) gradient checkpointing [20]. + +# 2.3. Evaluation on Downstream Tasks + +In this section, we extensively evaluate pre-trained EVA on several representative benchmarks, such as image classification (§2.3.1), video action recognition (§2.3.2), object detection & instance segmentation (§2.3.3), semantic segmentation (§2.3.4), and contrastive image-text pre-training with zero-shot evaluation (§2.3.5). EVA achieves state-of-the-art performance on a broad range of downstream tasks. + +model #param. extra labeled data image size top-1 acc. + +
using private labeled data
SwinV2-G [65]3.0BIN-21K-ext-70M640290.2
ViT-G [119]1.8BJFT-3B518290.5
ViT-g (CoCa) [117]1.0BJFT-3B+ALIGN576291.0
using public labeled data
CoAtNet-4 [27]275MIN-21K (14M)512288.6
MaxViT-XL [98]475MIN-21K (14M)512288.7
MViTv2-H [61]667MIN-21K (14M)512288.8
FD-CLIP-L [107]304MIN-21K (14M)336289.0
BEiT-3 [101]2.0B35M img-text pairs336289.6
EVA1.0BIN-21K (14M)336289.6
EVA1.0BIN-21K (14M)560289.7
+ +# 2.3.1 Image Classification + +Datasets. For image classification task, we evaluate EVA on ImageNet-1K (IN-1K) [28] validation set. We also evaluate the robustness & generalization capability of EVA along with our training settings & hyper-parameters using ImageNet-V2 matched frequency (IN-V2) [81], ImageNet-ReaL (IN-ReaL) [7], ImageNet-Adversarial (IN-Adv.) [42], ImageNet-Rendition (IN-Ren.) [41], ImageNet-Sketch (IN-Ske.) [100]. + +Training Settings. Following the conventional setting [5, 70, 101], we first perform intermediate fine-tuning on ImageNet-21K [28] for 60 epochs with an image resolution of $224^2$ , then EVA is further fine-tuned on ImageNet-1K training set for 10 epochs. Different from [117, 119] that use multi-head attention pooling and BEiT-3 that exploits an additional pretrained giant language tower as the image classification task layer, we simply adopt a linear layer as the classifier [31]. Notice that the supervised intermediate fine-tuning consumes only $\sim 1/5$ of the time & compute of the MIM pre-training stage. While for other billion-scale vision models such as SwinV2-G-3B, the supervised training phase costs $\sim 1.5 \times$ resources than the MIM pre-training. + +Results. Table 4 compares EVA with some state-of-the-art models on ImageNet-1K validation set. EVA achieves $89.6\%$ top-1 accuracy with $336^{2}$ inputs, comparable to BEiT-3. Using a larger image resolution of $560^{2}$ can further boost the top-1 accuracy to $89.7\%$ . Notice that BEiT-3 treats image classification as an image-to-text retrieval task. Therefore they leverage an additional one billion parameters pre-trained language encoder along with 35 million image-text data (21M pairs from CC12M, CC3M, SBU, COCO, VG and 14M pairs from ImageNet-21K) as well as 160GB text data in total. Meanwhile, we simply use a linear classifier on top of EVA with only ImageNet-21K image-tag data used for additional finetuning. With only publicly available data, EVA creates a new state-of-the-art image classification result on ImageNet-1K with a much neater architecture. + +Robustness & generalization ability evaluation. We eval + +Table 4. Comparisons of image classification performance on ImageNet-1K validation set. With only publicly available data, EVA creates a new state-of-the-art ImageNet-1K image classification result with a canonical linear classifier. + +
modelIN-1KIN-V2IN-ReALIN-Adv.IN-Ren.IN-Ske.avg.Δ↓
ConvNeXt87.577.790.570.867.053.774.513.0
SwinV287.577.390.273.967.752.374.812.7
MAE87.879.290.376.766.550.975.212.6
DeiT387.779.190.279.270.654.977.010.7
Eff-L2-NS88.480.590.684.874.747.677.810.6
BEiTv288.480.190.376.276.458.378.310.1
BEiT88.679.990.781.773.256.878.510.1
EVA89.681.690.886.288.367.784.05.6
+ +Table 5. Robustness & generalization capability evaluation on ImageNet-1K variants. We test each model on different ImageNet-1K validation sets, without any specialized fine-tuning. "avg.": the averaged top-1 accuracy on 6 different ImageNet-1K validation set variants. "Δ↓": The gap between the averaged top-1 accuracy on 6 variants (i.e., IN-{1K, V2, Real, Adv., Ren., Ske.}) and the original ImageNet-1K validation set top-1 accuracy (the lower the better). + +uate the robustness and generalization capability of EVA trained with an image size of $336^{2}$ on 6 different ImageNet1K validation set variants. In Table 5, we compare EVA with some top open-sourced models collected by the timm library [108]. Following the evaluation procedure in [39], all these models are first fine-tuned on the original ImageNet1K training set and then evaluated on different validation sets using the same fine-tuned model without further hyperparameter selection and specialized fine-tuning. + +As shown in Table 5, EVA is the most competitive one in terms of absolute top-1 accuracies. However, these model various in pre-train data (from ImageNet-1K, ImageNet-21K to JFT-300M), input resolutions (from $224^2$ to $800^2$ ), model sizes (from hundreds of millions to one billion parameters) as well as architectures (ConvNets, vanilla & hierarchical ViTs), etc. Therefore their absolute accuracies are not directly comparable. Instead, we are more interested in the gap between the averaged top-1 accuracy on 6 validation set variants and the original ImageNet-1K validation set top-1 accuracy (the lower the better), i.e., we care about whether a model along with its training settings biases towards the original validation set and generalize well on other variants. From this perspective, EVA not only achieves the highest averaged accuracy, but also has the smallest performance gap, which reflects the excellent robustness and generalization ability of EVA. + +# 2.3.2 Video Action Recognition + +Datasets. For video action recognition, we evaluate EVA on Kinetics-400 (K-400) [51], Kinetics-600 (K-600) [14] and Kinetics-700 (K-700) [15] benchmarks. We first conduct intermediate fine-tuning on a merged dataset coined Kinetics-722 (K-722) that integrates videos from K-400, K-600 and K-700. We remove leaked as well as repeated videos in both training and validation sets. After this data de-duplicating + +
modeltop-1 accuracy
Kinetics-400Kinetics-600Kinetics-700
MAE [34]86.8--
SwinV2-G [65]86.8--
Florence [118]86.888.0-
MaskFeat [103]87.088.380.4
VideoMAE [95]87.4--
X-CLIP [68]87.788.3-
CoVeR [120]87.287.978.5
CoCa [117] (frozen)88.088.581.1
CoCa [117] (finetuned)88.989.482.7
EVA89.789.882.9
+ +Table 6. Video action recognition. With only publicly available K-400, K-600 and K-700 as video pre-training data, EVA is also quite performant in video action recognition tasks. + +process, K-722 has 0.63M training videos in total with 722 action classes. A similar approach is also used in [58]. + +Training & evaluation settings. EVA processes video data simply via spatial-temporal attention as [34, 95] with no specific architectural adaptation for video related tasks. We first train EVA using K-722 training set for 40 epochs with 8 frames and $224^2$ resolution, then we fine-tune EVA on each dataset for only 1 or 2 epochs. We set frame $\times$ crop $\times$ clip to $16 \times 3 \times 4$ for fine-tuning and evaluation for all datasets. The frame resolution is $224^2$ . + +Results. As shown in Table 6, EVA achieves better performance compared with some recent video-specific or large foundation models in video recognition. For reference, directly adapting image-only pre-trained EVA to K-400 without K-722 intermediate fine-tuning can also achieve a very competitive top-1 accuracy of $88.4\%$ . + +# 2.3.3 Object Detection & Instance Segmentation + +Datasets. We evaluate the object detection and instance segmentation performance of EVA on both COCO [62] and LVIS [38]. COCO is a widely used object-level recognition benchmark with 80 common object categories. LVIS is an emerging large-vocabulary object-level recognition benchmark, which has more than 1,200 object categories as well as more than 2 million high quality instance segmentation masks (nearly $2 \times$ of COCO). Notably, COCO and LVIS almost use the same set of images, and both train and val split of LVIS have a huge overlap with COCO train and val split. Meanwhile, COCO has much fewer object categories than LVIS (i.e., $80 \text{ v.s. } 1,200+$ ). Therefore it is meaningful to evaluate models' performance on both COCO and LVIS. + +Training & evaluation settings. EVA uses Cascade Mask R-CNN [12] as the detector and adopts the training settings (e.g., LSJ data augmentation [36]) & architecture configurations (e.g., interleaved window & global attention) of ViTDet [60]. Following the common practice [65, 101, 121], we first conduct intermediate fine-tuning for the whole detec + +tor using Objects365 [87] dataset with a resolution of $1024^2$ , then we fine-tune the detector on COCO and LVIS train split respectively with $1280^2$ inputs. + +We report single-scale evaluation and multi-scale evaluation / test-time augmentation (tta) results of EVA for comparison. For COCO, Soft-NMS [8] is also applied. For instance segmentation task, the classification score is calibrated [46] via maskness [102]. + +The model architecture as well as the hyper-parameters for COCO and LVIS are almost the same (i.e., the hyperparameters are nearly "zero-shot" transferred from COCO to LVIS), expect we use federated loss [125] and repeat factor sampling [38] following ViTDet on LVIS. + +Results. Perhaps COCO is the most fierce vision benchmark. Table 7 compares EVA with some leading approaches on COCO. Our model creates new state-of-the-art results on both object detection and instance segmentation tasks. + +Compared with ViTDet-H [60] that uses Cascade Mask R-CNN [12] as well, EVA shows that with a larger model and better encoder & detector pre-training, the performance can be greatly improved with the same detector. + +Compared with FocalNet [116] and Group DETRv2 [19] that choose better-established and highly-optimized DINO detector [121], EVA demonstrates that with sufficient model size, data and pre-training, better performance can be also achieved via the classic R-CNN framework [37]. On the other hand, FocalNet and Group DETRv2 are incapable of instance segmentation due to using DINO. + +Compared with SwinV2-Giant [65] and FD-SwinV2-Giant [107] that also adopt a (stronger $\mathrm{HTC}++$ [17]) detector from the R-CNN family but with $\sim 3\times$ model size of EVA, our approach streamlines the pre-training processes and pulls off a "Giant-killing" act via better representations. + +Compared with BEiT-3, EVA shows that it is possible to build a state-of-the-art object-level recognition system without exploiting (i) semantic feature quantization / tokenization [5, 70], and (ii) image-text paired pre-training data and large corpora during pre-training. + +Analyzing the performance gap between LVIS and COCO. Evaluating models on both COCO and LVIS benchmarks is essential, as they share nearly the same image set but differ in the number of annotated object categories. COCO has only 80 annotated categories, while LVIS annotates over 1,200 object categories, resulting in a long-tail distribution that more closely resembles challenging real-world scenarios [38]. In general, LVIS is considered a much more difficult benchmark than COCO for object-level recognition, with conventional methods typically experiencing a significant performance drop on LVIS. + +In Table 8a, we analyze the performance gap between the LVIS and COCO benchmarks for EVA and other state-of-the-art approaches. For previous leading methods, such as ViTDet, the performance gap for $\mathrm{AP^{box}}$ is around 8, and + +
model / methoddetector#param.pre-training datatta?COCO valCOCO test-dev
encoderdetectorAPboxAPmaskAPboxAPmask
Soft-Teacher [115]HTC++ [17]284MIN-21K (14M)COCO(unlabeled)+O365✓60.752.561.353.0
GLIP [59]DyHead [26]≥ 284MIN-21K (14M)4ODs+GoldG+Cap12M✓60.8-61.5-
GLIPv2 [122]DyHead [26]≥ 637MFLD-900M\( merged\ data^a \)✓--62.4-
ViTDet-H [60]CMask R-CNN [12]692MIN-1K (1M)-✓61.353.1--
Florence [118]DyHead [26]≥ 637MFLD-900M\( merged\ data^a \)✓62.0-62.4-
SwinV2-G [65]HTC++ [17]≥ 3000MIN-21K-ext-70MO365✓62.553.763.154.4
DINO [121]-218MIN-21K (14M)O365✓63.2-63.3-
Mask DINO [57]-223MIN-21K (14M)O365✓-54.5-54.7
BEiT-3 [101]CMask R-CNN [12]1074M\( merged\ data^b \)O365✓--63.754.8
FD-SwinV2-G [107]HTC++ [17]≥ 3000MIN-21K-ext-70MO365✓--64.255.4
FocalNet [116]DINO [121]746MIN-21K (14M)O365✓64.2-64.4-
Group DETRv2 [19]DINO [121]629MIN-1K (1M)O365✓--64.5-
EVACMask R-CNN [12]1074Mmerged-30MO365✘64.255.064.455.5
EVACMask R-CNN [12]1074Mmerged-30MO365✓64.5-64.7-
+ +"merged data": FourODs + INBoxes + GoldG + CC15M + SBU, "merged data": IN-21K (14M) + Image-Text (35M) + Text (160GB). + +Table 7. Object detection & instance segmentation on results COCO dataset. EVA establishes new state-of-the-art results in object detection and instance segmentation tasks on both COCO val and test-dev splits with the canonical R-CNN [37] object detection & segmentation framework. "tta" refers to test-time augmentation. (timestamp: Nov 10, 2022) + +
modelAPboxAPmask
COCOLVISΔ↓COCOLVISΔ↓
(a) evaluation using COCO & LVIS official annotations respectively
Copy-Paste [36]57.041.615.448.938.110.8
ViTDet-H [60]61.353.47.953.148.15.0
prev. best63.2a53.4b9.854.5c49.2d5.3
EVA (single-scale test)64.162.21.955.055.00.0
(b) evaluation using LVIS val1-5K annotations
EVA (single-scale test)69.668.31.359.659.8-0.2
+ +for $\mathrm{AP^{mask}}$ , it is around 5. However, when using the same detector (Cascade Mask R-CNN) and nearly identical settings as those in ViTDet pre-trained via MAE-Huge (ViTDet-H), EVA not only achieves state-of-the-art results on both LVIS and COCO benchmarks simultaneously but also significantly reduces the performance gap between them, particularly for the instance segmentation task. EVA attains the same performance on LVIS and COCO using single-scale evaluation. In comparison with ViTDet-H, we demonstrate that a slightly larger model with stronger representations can greatly improve performance on the challenging large vocabulary instance segmentation benchmark, with one caveat described below. + +Note that the Merged-30M unlabeled images include 15K out of 20K LVIS val set images (the Merged-30M images contain all the COCO training images, and the LVIS validation split also includes 15k images from the COCO training set). Although a recent study [33] shows that including unlabeled images from the development / test set for MIM pre-training has minimal impact on the final performance, we conduct a more rigorous analysis of the LVIS and COCO performance gap to eliminate potential data contamination issues: We evaluate both + +Table 8. LVIS & COCO performance gap on val set. “prev. best” refers to the best individual model / result in each benchmark (a: DINO [121], b: ViTDet-H [60], c: Mask DINO [57], d: 2021 competition $1^{\text{st}}$ [35]) “ $\Delta \downarrow$ ”: the performance gap between LVIS and COCO (the lower the better). + +
modelcrop sizeADE20KCOCO-Stuff
mIoUssmIoUmsmIoUss
HorNet [79]640257.557.9-
SeMask [48]640257.058.3-
SwinV2-G [65]896259.359.9-
Mask DINO [57]896259.560.8-
FD-SwinV2-G [107]8962-61.4-
ViT-Adapter [23]896261.261.552.3
BEiT-3 [101]896262.062.8-
EVA896261.562.353.4
+ +Table 9. Semantic segmentation performance on ADE20K and COCO-Stuff-164K dataset. "mIoUss": mIoU of single-scale evaluation, "mIoUms": mIoU using multi-scale evaluation. + +COCO and LVIS models using the 5K images present in both the COCO and LVIS val sets, denoted as LVIS val-5K. The COCO results are measured using the 80-category COCO subset of LVIS with the higher-quality LVIS annotations (a similar approach also employed in [53], but for a different purpose). The results are shown in Table 8b, and we find that the conclusion remains unchanged. + +# 2.3.4 Semantic Segmentation + +Dataset. We evaluate EVA on ADE20K [123] and COCO-Stuff-164K [11] datasets for semantic segmentation task. ADE20K includes 150 semantic categories, and has 20k images for training & 2k images for validation. COCO-Stuff-164K augments 164K complex images from COCO with pixel-level annotations that span over 172 categories including 80 things, 91 stuff, and 1 unlabeled class. Compared with ADE20K, COCO-Stuff is a more challenging but under-explored semantic segmentation benchmark. + +Training & evaluation settings. We follow the task transfer pipelines of ViT-Adapter [23] + mask2former [24] but with a weakened model adaptation processes due to GPU memory + +
modelprecisiontotal #param.image #param.text #param.clip training datasamples seenimage sizepatch sizebatch sizegpu for training
OpenAI CLIP-Lfloat16430M304M124MCLIP-400M [73]12B\( 224^2 \)\( 14 \times 14 \)32k\( 256 \times V100 (32GB) \)
ALIGNbfloat16834M480M354MALIGN-1.8B [73]22B\( 289^2 \)-16k\( 1024 \times TPUv3 \)
Open CLIP-Hbfloat161.0B632M354MLAION-2B [85]32B\( 224^2 \)\( 14 \times 14 \)79k\( 824 \times A100 (40GB) \)
Open CLIP-gbfloat161.3B1.0B354MLAION-2B [85]12B\( 224^2 \)\( 14 \times 14 \)64k\( 800 \times A100 (40GB) \)
EVA CLIP-gfloat161.1B1.0B124MLAION-400M [86]11B\( 224^2 \)\( 14 \times 14 \)41k\( 256 \times A100 (40GB) \)
+ +(a) CLIP model configurations. EVA CLIP-g can be stably trained via fp16 precision with fewer image-text pairs (7B v.s. 12B / 32B) sampled from a smaller data pool (LAION-400M v.s. LAION-2B) on $\sim 1/3 \times$ GPUs compared with other open-sourced billion-scale competitors. + +
datasetsImageNet-1K [28]ImageNet-V2 [82]ImageNet-Adv. [42]ImageNet-Ren. [41]ImageNet-Ske. [100]ObjectNet [6]CIFAR-10 [54]CIFAR-100 [54]UCF-101 [92]Video classificationAvg. all
modelimage classificationΔ↓Kinetics-400 [51]Kinetics-600 [14]Kinetics-700 [15]
OpenAI CLIP-L75.569.970.887.859.669.095.675.93.476.464.564.257.772.2
ALIGN76.470.175.892.264.872.2--------
Open CLIP-H78.070.959.389.366.669.797.584.75.778.263.163.656.173.1
Open CLIP-g76.669.657.288.765.267.597.183.95.877.761.762.255.071.9
EVA CLIP-g78.5(+1.9)71.5(+1.9)73.6(+16.4)92.5(+3.8)67.3(+2.1)72.3(+4.8)98.3(+1.2)88.7(+4.8)2.576.1(-1.6)65.2(+3.5)64.4(+2.2)58.4(+3.4)75.7(+3.8)
+ +(b) Summary of zero-shot image / video classification performance. “ $\Delta \downarrow$ ”: The gap between the averaged performance of ImageNet-{1K, V2, Adv., Ren., Ske.} & ObjectNet that with natural distribution shifts and the original ImageNet-1K validation accuracy. Our model suffers from the smallest performance drop (only $2.5\%$ top-1 accuracy gap) while maintaining the highest zero-shot classification accuracy averaged on all 12 benchmarks ( $72.7\%$ top-1 accuracy). +Table 10. EVA as a vision-centric, multi-modal pivot. We evaluate a billion-scale contrastive language-image pre-trained (CLIP) model with the vision tower initialized from pre-trained EVA, which largely accelerates the contrastive training efficiency and shows promising zero-shot classification performance across a wide range of image / video benchmarks. The statistics & performance of EVA's MIM teacher (OpenAI CLIP-L) are also presented for reference. + +limitation (40GB of VRAM): (i) relative position biases [90] are not applied. (ii) We use $8 \times$ decoders in mask2former segmentation head instead of $9 \times$ . (iii) The feature dimension in mask2former head is $\sim 0.6 \times$ of EVA encoder. + +Results. We compare EVA with other leading semantic segmentation methods in Table 9. EVA achieves strong results in both ADE20K and COCO-Stuff-164K datasets. On the other hand, the segmentation performance of EVA is slightly lower compared with BEiT-3 on ADE20K, we suspect this is partially due to our weakened architectural configurations. + +# 2.3.5 Contrastive Language-Image Pre-training with Zero-shot Classification Evaluation + +CLIP (Contrastive Language-Image Pre-training) [47, 49, 72, 73] is a type of multi-modal foundation model that connects vision and language via contrastive image-text pre-training. CLIP can be applied to any image classification benchmark by simply providing the names of the visual categories to be recognized [1]. Thus the introduction of CLIP essentially reshapes the landscape of visual recognition. Meanwhile, CLIP features also play a central role in representation leaning [70, 101], AI generated content [78, 83, 84] and large dataset filtering [10, 85, 86], etc. + +In this section and Table 10, we show that EVA is not only a strong encoder for a wide range of vision downstream + +tasks, but also a multi-modal pivot that builds a bridge between vision and language. To demonstrate that, we train & evaluate EVA as a billion-scale CLIP's vision tower in various zero-shot image / video classification benchmarks. + +Baselines and major challenges in CLIP model scaling. We compare our CLIP (dubbed EVA CLIP) with other open-sourced strong CLIP competitors that exploit publicly accessible data / academic resources only. Model configurations and statistics are detailed in Table 10a. + +There are two well-known major challenges of CLIP model training and scaling: (i) Large-scale Open CLIP models (e.g., Open CLIP-H & Open CLIP-g [2, 47]) usually suffer from severe training instability issues [2] and have to use bfloat16 format for optimization. (ii) The training efficiency is low, which may hinder model scaling and downstream performance. For instance, Open CLIP-g is heavily under-trained due to its large compute requirement, and its performance is even worse than the sufficiently-trained Open CLIP-H with a smaller model size. + +Compared with our CLIP model, Open CLIP-H & -g are trained from scratch with much more image-text pairs ( $\sim 2.9 \times$ and $\sim 1.1 \times$ of ours) sampled from a much larger dataset ( $\sim 5 \times$ of ours) on $\sim 3 \times$ of GPUs. While by leveraging EVA, billion-scale CLIP model training can be accelerated with improved zero-shot classification performance, described next. + +Training settings. For our CLIP model, we initialize the vision encoder via pre-trained EVA and the language encoder + +
model (SSL)zero-shotlinear probingfine-tuning
prev. best78.0a82.3b89.1c
EVA78.586.589.4
+ +Table 11. Zero-shot, linear probing and fine-tuning performance of EVA-CLIP on ImageNet-1K. Notice that the linear probing and fine-tuning results are from the vision encoder of EVA-CLIP. Our approach establishes the new state-of-the-art results among all existing self-supervised learning (SSL) methods. (timestamp: Nov 10, 2022) results reference. a: Open CLIP-H [47], b: iBOT [124], c: dBOT [63]. + +from OpenAI CLIP-L. The pre-training implementation is based on Open CLIP [47]. We also adopt DeepSpeed optimization library [80] with ZeRO stage-1 optimizer [77] to save memory. We find using fp16 format with dynamic loss scaling is stable enough during the whole course of training while using bf1oat16 format is unnecessary. These modifications allow us to train a 1.1B CLIP with a batch size of 41k on $256 \times$ NVIDIA A100 40GB GPUs. + +Evaluation settings. We evaluate zero-shot image / video classification performance of each CLIP model on 12 benchmarks and report top-1 accuracy for comparisons. + +For zero-shot image classification task, we choose 8 benchmarks, i.e., ImageNet-1K [28], ImageNet-V2 [81], ImageNet-Adversarial (ImageNet-Adv.) [42], ImageNet-Rendition (ImageNet-Adv.) [41], ImageNet-Sketch (ImageNet-Ske.) [100], ObjectNet [6], CIFAR-10 and CIFAR-100 [54]. We are also interested in the robustness of CLIP models, evaluated via the performance gap between the averaged performance of ImageNet-{1K, V2, Adv., Ren., Ske.} & ObjectNet that with natural distribution shifts and the original ImageNet-1K validation accuracy. + +For zero-shot video classification task, we choose 4 benchmarks, namely UCF-101 [92], Kinetics-400 [51], Kinetics-600 [14], and Kinetics-700 [15]. + +Results. Table 10b shows the comparison. Our EVA CLIP achieves the highest averaged accuracy, and performs the best in 10 out of 12 zero-shot classification benchmarks. Notably, the ImageNet-1K validation zero-shot top-1 accuracy is $78.2\%$ without using any of its training set labels, matching the original ResNet-101 [40]. Moreover, our model is quite robust and suffers from the smallest performance drop when facing natural distribution shifts in ImageNet. + +At last, in Table 11 we provide zero-shot, linear probing & end-to-end fine-tuning top-1 accuracy of EVA-CLIP on ImageNet-1K validation set for reference. Our approach creates the new state-of-the-art results among all existing self-supervised learning methods. + +Notice that EVA CLIP's vision branch learns from OpenAI CLIP-L, while language branch initialized from the same CLIP-L model. Therefore, starting from a CLIP-L with only 430M parameters, we progressively scale up a 1.1B EVA CLIP-g with large performance improvements. This implies that interleaved MIM & image-text contrastive + +pre-training could be an efficient and scalable CLIP training approach. To our knowledge, EVA CLIP-g is the largest performant CLIP model trained via publicly accessible data and resources. We hope our practice on scaling and improving CLIP can also inspire and transfer to the study of other large scale multi-modal foundation models. + +# 3. Related Work + +Masked image modeling (MIM) learns rich visual representations via predicting masked visual contents conditioned on visible context. ViT [31] and iGPT [18] report the first meaningful MIM pre-training results. The BEiT family [5,70,101] greatly improves MIM's performance via masked visual token prediction. Recent work [4,21,30,32,39,103,113,124] (re-)explore pixel / feature regression in MIM, but only in a relatively small model and data scales. In this work, we explore the limits of large scale MIM pre-training via masked image-text aligned feature prediction [43, 106]. + +Vision foundation models. ConvNets [56] have long been the de-facto standard visual architecture ab initio. Since AlexNet [55], ConvNets have rapidly evolved and become deeper, wider and larger [40, 44, 66, 91, 93, 94, 111]. However, at sufficient model and data scales, ConvNets lag behind ViTs [31] due to a lack of scalable pre-training tasks and the built-in inductive biases. Entering the 2020s, large pretrained ViTs [31, 119] such as SwinV2-G [65] with hierarchical architectures as well as BEiT-3 [101] with multi-modal representations started to demonstrate various vision benchmarks. In this work, we show by leveraging unlabeled images, vanilla ViT can be efficiently scaled up to billion-scale parameters, and stands out in various downstream tasks. + +# 4. Conclusion + +In this work, we launch EVA, a one billion parameters vanilla ViT encoder to explore the limits of masked visual representation learning. We show simple masked feature modeling as a visual learning pretext task scales well on an architecture with minimal vision priors, and attains excellent results in a representative & diverse set of downstream tasks. We hope EVA would bridge the gap between vision and language study via masked modeling, and contributes to the Neon Genesis of vision research. + +# Acknowledgement + +This work is supported by the National Key R&D Program of China (2020AAA0105200) and NSFC (No. 617333007). We would like to thank Hanxiao Qu, Yan Tian, Yemin Shi and Xigang Cao for their help on GPU resources. 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EVA is a vanilla ViT pretrained to reconstruct the masked out image-text aligned vision features conditioned on visible image patches. Via this pretext task, we can efficiently scale up EVA to one billion parameters, and sets new records on a broad range of representative vision downstream tasks, such as image recognition, video action recognition, object detection, instance segmentation and semantic segmentation without heavy supervised training. Moreover, we observe quantitative changes in scaling EVA result in qualitative changes in transfer learning performance that are not present in other models. For instance, EVA takes a great leap in the challenging large vocabulary instance segmentation task: our model achieves almost the same state-of-the-art performance on LVIS dataset with over a thousand categories and COCO dataset with only eighty categories. Beyond a pure vision encoder, EVA can also serve as a vision-centric, multi-modal pivot to connect images and text. We find initializing the vision tower of a giant CLIP from EVA can greatly stabilize the training and outperform the training from scratch counterpart with much fewer samples and less compute, providing a new direction for scaling up and accelerating the costly training of multi-modal foundation models." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 601, + 128, + 613 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 601, + 128, + 613 + ], + "spans": [ + { + "bbox": [ + 47, + 601, + 128, + 613 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 620, + 287, + 669 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 620, + 287, + 669 + ], + "spans": [ + { + "bbox": [ + 46, + 620, + 287, + 669 + ], + "type": "text", + "content": "Scaling up pre-trained language models (PLMs) [9,64,76] has revolutionized natural language processing (NLP) in the past few years. The key to this success lies in the simple and scalable self-supervised learning task of masked signal" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 256, + 547, + 352 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 256, + 547, + 352 + ], + "spans": [ + { + "bbox": [ + 306, + 256, + 547, + 352 + ], + "type": "text", + "content": "prediction [29, 74], with which Transformer models [99] could be scaled up to billions of parameters using nearly unlimited unlabelled data, and generalize well to a wide range of downstream tasks with little tuning. With further scaling on compute, data, and model sizes, PLMs have led to not only continuous performance improvements [50, 75, 76], but also a surprising emergence of in-context learning capability [9, 25, 104, 105]." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 353, + 548, + 581 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 353, + 548, + 581 + ], + "spans": [ + { + "bbox": [ + 304, + 353, + 548, + 581 + ], + "type": "text", + "content": "Motivated by the success of model scaling in NLP, it is appealing that we can also translate this success from language to vision, i.e., to scale up a vision-centric foundation model that is beneficial for both vision & multi-modal downstream tasks. Recently, masked image modeling (MIM) [5, 39, 113] has boomed as a viable approach for vision model pretraining and scaling. However, the most competitive billion-sized vision pre-trained models [31, 65, 71, 119] still heavily rely on supervised or weakly-supervised training with hundreds of millions of (often publicly inaccessible) labeled data. MIM is somewhat only adopted as an initialization stage before the heavily supervised pre-training [65], or a pure MIM pre-trained model could not achieve favorable performance at billion-scale model sizes [114]. We regard this gap stems from the fact that natural images are raw and information-sparse. Meanwhile, an ideal vision pretext task needs the abstraction of not only the low-level geometry & structure information, but also high-level semantics, which is hardly captured by pixel-level recovery tasks [112]." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 582, + 548, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 548, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 548, + 715 + ], + "type": "text", + "content": "In this work, we seek a suitable MIM pretext task for large scale vision representation learning and explore its limits at the scale of one billion parameters with tens of millions of unlabeled data. Recently, there are a few trials leveraging the semantic information from image-image or image-text contrastive learning [13, 22, 73] for MIM pretraining [43, 106, 124], which perform fairly well in vision downstream tasks. However, there remains a debate that (i) tokenized semantic features could provide better supervision signal for masked modeling in vision [5, 70, 101], and (ii) good performances could be also achieved via a simple post" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 673, + 289, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 673, + 289, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 673, + 289, + 713 + ], + "type": "text", + "content": "†Interns at Beijing Academy of Artificial Intelligence (BAAI). ‡Corresponding authors: Yue Cao (caoyue10@gmail.com), Xinlong Wang (xinlong.wang96@gmail.com) and Xinggang Wang (xgwang@hust.edu.cn)." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "19358" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 47, + 40, + 548, + 107 + ], + "blocks": [ + { + "bbox": [ + 47, + 40, + 548, + 107 + ], + "lines": [ + { + "bbox": [ + 47, + 40, + 548, + 107 + ], + "spans": [ + { + "bbox": [ + 47, + 40, + 548, + 107 + ], + "type": "table", + "html": "
modelimage & video classification (G)object detection (det) & instance segmentation (seg)semantic segmentation
IN-1K ftIN-1K linIN-1K zsavg. zsK400K600K700COCO det (test/val)COCO seg (test/val)LVIS segCOCO-StuffADE20K
Florence----86.587.8-62.4 / 62.0----
SwinV2-G----86.8--63.1 / 62.554.4 / 53.7--59.9
prev. best89.6a82.3b78.0c73.1c87.8d88.3e80.4e64.5f / 64.2g55.4h / 54.5i49.2j52.3k62.8a
EVA89.7(+0.1)86.5(+4.2)78.5(+0.5)75.7(+2.6)89.7(+1.9)89.8(+1.5)82.9(+2.5)64.7 / 64.5(+0.2/+0.3)55.5 / 55.0(+0.1/+0.5)55.0(+5.8)53.4(+1.1)62.3(-0.5)
", + "image_path": "82a953b2c1e1c5fd24326288c52724d9881d9da00319f680323000afdbdbe23c.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + }, + { + "bbox": [ + 45, + 110, + 547, + 153 + ], + "lines": [ + { + "bbox": [ + 45, + 110, + 547, + 153 + ], + "spans": [ + { + "bbox": [ + 45, + 110, + 547, + 153 + ], + "type": "text", + "content": "Table 1. Summary of EVA performance on various mainstream vision benchmarks. EVA is performant compared with previous best / leading approaches. “”: methods / results that only exploit publicly accessible data / academic resources. “ft”: end-to-end fine-tuning. “lin”: linear probing. “zs”: zero-shot classification. “avg. zs”: averaged zero-shot classification performance on 8 image and 4 video datasets with contrastive language-image pre-training. (timestamp: Nov 10, 2022)" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_footnote" + }, + { + "bbox": [ + 45, + 155, + 547, + 176 + ], + "lines": [ + { + "bbox": [ + 45, + 155, + 547, + 176 + ], + "spans": [ + { + "bbox": [ + 45, + 155, + 547, + 176 + ], + "type": "text", + "content": "methods / results reference. a: BEiT-3 [101], b: iBOT [124], c: Open CLIP-H [47], d: Text4Vis [109], e: MaskFeat [103], f: Group DETRv2 [19], g: FocalNet [116], h: FD-SwinV2-G [107], i: Mask DINO [57], j: LVIS 2021 competition " + }, + { + "bbox": [ + 45, + 155, + 547, + 176 + ], + "type": "inline_equation", + "content": "1^{\\text{st}}" + }, + { + "bbox": [ + 45, + 155, + 547, + 176 + ], + "type": "text", + "content": " [35], k: ViT-Adapter [23]." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_footnote" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 192, + 289, + 312 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 192, + 289, + 312 + ], + "spans": [ + { + "bbox": [ + 46, + 192, + 289, + 312 + ], + "type": "text", + "content": "distillation process without masked prediction tasks [107]. Through a pilot empirical study, we find that simply using image-text aligned (i.e., CLIP [73]) vision features as the prediction targets in MIM scales up well and achieves satisfactory performances on a broad range of downstream benchmarks. This pre-training task draws the benefits from both the high-level semantic abstraction of image-text contrastive learning as well as the good capture of geometry & structure in masked image modeling, which typically covers the information needed for most visual perception tasks." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 314, + 290, + 434 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 314, + 290, + 434 + ], + "spans": [ + { + "bbox": [ + 46, + 314, + 290, + 434 + ], + "type": "text", + "content": "Via this MIM pretext task, we can efficiently scale up a vanilla ViT encoder [31], dubbed EVA, to one billion parameters with strong visual representations that transfers well to a wide range of downstream tasks. Using 29.6 million public accessible unlabeled images for pre-training, EVA sets new records on several representative vision benchmarks, such as image classification on ImageNet-1K [28] (89.7% top-1 accuracy), object detection and instance segmentation on LVIS [38] (62.2 AP" + }, + { + "bbox": [ + 46, + 314, + 290, + 434 + ], + "type": "inline_equation", + "content": "^{\\text{box}}" + }, + { + "bbox": [ + 46, + 314, + 290, + 434 + ], + "type": "text", + "content": " & 55.0 AP" + }, + { + "bbox": [ + 46, + 314, + 290, + 434 + ], + "type": "inline_equation", + "content": "^{\\text{mask}}" + }, + { + "bbox": [ + 46, + 314, + 290, + 434 + ], + "type": "text", + "content": " on val) and COCO [62] (64.5 AP" + }, + { + "bbox": [ + 46, + 314, + 290, + 434 + ], + "type": "inline_equation", + "content": "^{\\text{box}}" + }, + { + "bbox": [ + 46, + 314, + 290, + 434 + ], + "type": "text", + "content": " & 55.0 AP" + }, + { + "bbox": [ + 46, + 314, + 290, + 434 + ], + "type": "inline_equation", + "content": "^{\\text{mask}}" + }, + { + "bbox": [ + 46, + 314, + 290, + 434 + ], + "type": "text", + "content": " on val, 64.7 AP" + }, + { + "bbox": [ + 46, + 314, + 290, + 434 + ], + "type": "inline_equation", + "content": "^{\\text{box}}" + }, + { + "bbox": [ + 46, + 314, + 290, + 434 + ], + "type": "text", + "content": " & 55.5 AP" + }, + { + "bbox": [ + 46, + 314, + 290, + 434 + ], + "type": "inline_equation", + "content": "^{\\text{mask}}" + }, + { + "bbox": [ + 46, + 314, + 290, + 434 + ], + "type": "text", + "content": " on test-dev)," + } + ] + } + ], + "index": 5 + }, + { + "type": "table", + "bbox": [ + 65, + 438, + 275, + 500 + ], + "blocks": [ + { + "bbox": [ + 65, + 438, + 275, + 500 + ], + "lines": [ + { + "bbox": [ + 65, + 438, + 275, + 500 + ], + "spans": [ + { + "bbox": [ + 65, + 438, + 275, + 500 + ], + "type": "table", + "html": "
tokenizer? [70]pt epochsImageNet-1K top-1 acc.ADE20K mIoUss
X-85.052.6
✓30085.052.7
✓160085.553.1
X80085.553.3
", + "image_path": "c0a8edfdc0e7f49372919217f15d4c61583566b0a3849b7dcb29ff19b9cfd8e3.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "table_body" + }, + { + "bbox": [ + 58, + 502, + 276, + 522 + ], + "lines": [ + { + "bbox": [ + 58, + 502, + 276, + 522 + ], + "spans": [ + { + "bbox": [ + 58, + 502, + 276, + 522 + ], + "type": "text", + "content": "(a) (Additional) semantic feature tokenization is not required for achieving good downstream performance." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "table_footnote" + } + ], + "index": 6 + }, + { + "type": "table", + "bbox": [ + 65, + 528, + 274, + 590 + ], + "blocks": [ + { + "bbox": [ + 65, + 528, + 274, + 590 + ], + "lines": [ + { + "bbox": [ + 65, + 528, + 274, + 590 + ], + "spans": [ + { + "bbox": [ + 65, + 528, + 274, + 590 + ], + "type": "table", + "html": "
distill.?[107]pt epochsImageNet-1K top-1 acc.ADE20K mIoUss
X-85.052.6
✓30085.152.5
✓80085.152.7
X80085.553.3
", + "image_path": "dcec287983f48fca359b2a408746b62c37030ee9fac4798b0dae3380c8c3544f.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "table_body" + }, + { + "bbox": [ + 58, + 591, + 276, + 610 + ], + "lines": [ + { + "bbox": [ + 58, + 591, + 276, + 610 + ], + "spans": [ + { + "bbox": [ + 58, + 591, + 276, + 610 + ], + "type": "text", + "content": "(b) Feature distillation fails to achieve consistent performance gain as the pre-training becomes longer." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "table_footnote" + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 620, + 289, + 710 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 620, + 289, + 710 + ], + "spans": [ + { + "bbox": [ + 46, + 620, + 289, + 710 + ], + "type": "text", + "content": "Table 2. Pilot experiment. We evaluate different pre-training approaches using ViT-B and report their performance on ImageNet-1K image classification (top-1 accuracy) and ADE20K semantic segmentation (single-scale mIoU). Numbers in grey refer to the results of directly fine-tuning CLIP vision encoder on corresponding downstream tasks. Default settings for EVA pre-training are marked in purple, i.e., directly regressing the masked out CLIP vision features conditioned on visible image patches." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 192, + 547, + 324 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 192, + 547, + 324 + ], + "spans": [ + { + "bbox": [ + 304, + 192, + 547, + 324 + ], + "type": "text", + "content": "semantic segmentation on COCO-stuff [11] (53.4 mIoU" + }, + { + "bbox": [ + 304, + 192, + 547, + 324 + ], + "type": "inline_equation", + "content": "^{\\mathrm{ss}}" + }, + { + "bbox": [ + 304, + 192, + 547, + 324 + ], + "type": "text", + "content": ") and ADE20K [123] (62.3 mIoU" + }, + { + "bbox": [ + 304, + 192, + 547, + 324 + ], + "type": "inline_equation", + "content": "^{\\mathrm{ms}}" + }, + { + "bbox": [ + 304, + 192, + 547, + 324 + ], + "type": "text", + "content": "), and video action recognition on Kinetics-400 [51] (89.7% top-1 accuracy), Kinetics-600 [14] (89.8% top-1 accuracy), Kinetics-700 [15] (82.9% top-1 accuracy). Notably, different from other state-of-the-art billion-scale vision foundation models that demand tens of millions of or even billions of labeled images, such as SwinV2-G using ImageNet-21K-ext-70M [65] and ViT-g/G using JFT3B [119], EVA does not need a costly supervised training stage and only leverage images from open-sourced datasets for academic reproducibility." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 326, + 548, + 495 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 326, + 548, + 495 + ], + "spans": [ + { + "bbox": [ + 304, + 326, + 548, + 495 + ], + "type": "text", + "content": "Moreover, we observe quantitative changes in scaling EVA result in qualitative changes in transfer learning performance that are not observed in other smaller-scale models, e.g., EVA makes a significant breakthrough in the challenging large vocabulary object-level recognition task: our model achieves almost the same performance on LVIS [38], an instance segmentation benchmark with more than 1,200 categories, as COCO [62], which almost shares the same image set as LVIS but with only 80 categories annotated. This emergent ability well matches the expectation of model scaling [105], that larger capability of model results in not only predictable performance improvements on standard benchmarks, but also unpredictable phenomena and capabilities for resolving more challenging tasks." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 496, + 548, + 651 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 496, + 548, + 651 + ], + "spans": [ + { + "bbox": [ + 304, + 496, + 548, + 651 + ], + "type": "text", + "content": "Going beyond a pure vision encoder, EVA can also serve as a vision-centric, multi-modal pivot that builds a bridge between vision and language. We show that initializing the image encoder via pre-trained EVA in a 1.1 billion parameters CLIP model can outperform the training from scratch counterpart on a broad range of zero-shot image / video classification benchmarks with much fewer samples and less compute. Moreover, EVA can greatly stabilize the giant CLIP's training & optimization process. Since large CLIP models usually suffer from training instability and inefficiency issues [2,47], we hope our solution opens up a new direction for scaling up and accelerating the costly training of multi-modal foundation models." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 653, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 653, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 653, + 547, + 713 + ], + "type": "text", + "content": "By scaling up vision-centric foundation models with MIM pre-training to achieve strong performance on broad downstream tasks, we hope EVA would bridge the gap between vision and language with masked signal modeling, and contributes to the big convergence across different modalities." + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "19359" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 66, + 35, + 286, + 61 + ], + "blocks": [ + { + "bbox": [ + 66, + 35, + 286, + 61 + ], + "lines": [ + { + "bbox": [ + 66, + 35, + 286, + 61 + ], + "spans": [ + { + "bbox": [ + 66, + 35, + 286, + 61 + ], + "type": "table", + "html": "
patch size#layershidden dimmlp dimattn heads#param.
14×144014086144161011M
", + "image_path": "b5580e9164c9c64e077ee38af74c73be0fee35b01fd07a22c1d4944d64ab418f.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 65, + 79, + 284, + 102 + ], + "blocks": [ + { + "bbox": [ + 115, + 63, + 233, + 72 + ], + "lines": [ + { + "bbox": [ + 115, + 63, + 233, + 72 + ], + "spans": [ + { + "bbox": [ + 115, + 63, + 233, + 72 + ], + "type": "text", + "content": "(a) EVA architecture configurations." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 65, + 79, + 284, + 102 + ], + "lines": [ + { + "bbox": [ + 65, + 79, + 284, + 102 + ], + "spans": [ + { + "bbox": [ + 65, + 79, + 284, + 102 + ], + "type": "table", + "html": "
image sizebatch sizeoptimizerpeak lr(β1, β2)pt epochs
22424096AdamW1e-3(0.9, 0.98)150
", + "image_path": "02202355881f2015355298116ec8289fa144492f37a3f4884602485ccf9243d5.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + }, + { + "bbox": [ + 87, + 105, + 256, + 114 + ], + "lines": [ + { + "bbox": [ + 87, + 105, + 256, + 114 + ], + "spans": [ + { + "bbox": [ + 87, + 105, + 256, + 114 + ], + "type": "text", + "content": "(c) some pre-training settings and hyper-parameters." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_footnote" + } + ], + "index": 2 + }, + { + "type": "table", + "bbox": [ + 304, + 35, + 536, + 61 + ], + "blocks": [ + { + "bbox": [ + 304, + 35, + 536, + 61 + ], + "lines": [ + { + "bbox": [ + 304, + 35, + 536, + 61 + ], + "spans": [ + { + "bbox": [ + 304, + 35, + 536, + 61 + ], + "type": "table", + "html": "
datasettotal size
ImageNet-21K, CC12M, CC3M, Object365, COCO, ADE29.6M images
", + "image_path": "7d9e8d5dbb1938fdde8dbaf10db4ec537b6242ff6375dd8f06d63ba7bbabcade.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_body" + } + ], + "index": 4 + }, + { + "type": "table", + "bbox": [ + 307, + 79, + 536, + 102 + ], + "blocks": [ + { + "bbox": [ + 362, + 63, + 471, + 72 + ], + "lines": [ + { + "bbox": [ + 362, + 63, + 471, + 72 + ], + "spans": [ + { + "bbox": [ + 362, + 63, + 471, + 72 + ], + "type": "text", + "content": "(b) datasets for pre-training EVA." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 307, + 79, + 536, + 102 + ], + "lines": [ + { + "bbox": [ + 307, + 79, + 536, + 102 + ], + "spans": [ + { + "bbox": [ + 307, + 79, + 536, + 102 + ], + "type": "table", + "html": "
precisionZeRO#gpusamples / sec.max mem.pt days
fp16stage-1128~3150~26.5GB~14.5
", + "image_path": "f8b53c1d5fc01d79cb31b513157724825e11067db902b46d2b63d38a2a0612a7.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "table_body" + } + ], + "index": 6 + }, + { + "bbox": [ + 356, + 105, + 482, + 114 + ], + "lines": [ + { + "bbox": [ + 356, + 105, + 482, + 114 + ], + "spans": [ + { + "bbox": [ + 356, + 105, + 482, + 114 + ], + "type": "text", + "content": "(d) basic statistics of EVA pre-training." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 146, + 119, + 447, + 130 + ], + "lines": [ + { + "bbox": [ + 146, + 119, + 447, + 130 + ], + "spans": [ + { + "bbox": [ + 146, + 119, + 447, + 130 + ], + "type": "text", + "content": "Table 3. A brief summary of pre-training settings and configurations for EVA." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 47, + 145, + 171, + 159 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 145, + 171, + 159 + ], + "spans": [ + { + "bbox": [ + 47, + 145, + 171, + 159 + ], + "type": "text", + "content": "2. Fly EVA to the Moon" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 166, + 288, + 237 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 166, + 288, + 237 + ], + "spans": [ + { + "bbox": [ + 46, + 166, + 288, + 237 + ], + "type": "text", + "content": "We first conduct a series of pilot experiments for choosing an ideal vision pretext task in §2.1, then we scale up EVA pre-training via the chosen pre-training objective in §2.2. Finally, we evaluate the pre-trained representation on various downstream tasks in §2.3. Detailed experimental settings and configurations are in Appendix." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 47, + 243, + 240, + 257 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 243, + 240, + 257 + ], + "spans": [ + { + "bbox": [ + 47, + 243, + 240, + 257 + ], + "type": "text", + "content": "2.1. The Feature Instrumentality Project" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 46, + 262, + 288, + 453 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 262, + 288, + 453 + ], + "spans": [ + { + "bbox": [ + 46, + 262, + 288, + 453 + ], + "type": "text", + "content": "In this section, we seek a MIM vision pretext task with compelling transfer performance. Based on previous literature on vision pre-training, we study two promising candidates: (i) recovering the masked out tokenized semantic vision features [5, 70, 101], and (ii) feature distillation from strong pre-trained representation as in [107]. Both of them exploit pre-trained image-text aligned vision features (i.e., CLIP [73] vision features). Via a series of pilot experiments shown in Table 2, we find that: (i) the (additional) CLIP feature tokenization process is unnecessary for achieving good downstream performance (ii) feature distillation fails to provide consistent performance gain as the pre-training becomes longer. Instead, we find that simply reconstructing the masked out CLIP vision features conditioned on visible image patches is highly performant, which is chosen for scaling up EVA." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 46, + 453, + 288, + 573 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 453, + 288, + 573 + ], + "spans": [ + { + "bbox": [ + 46, + 453, + 288, + 573 + ], + "type": "text", + "content": "We clarify that this MIM pretext task is not originally proposed by us. Regressing the masked out image-text aligned vision features for MIM pre-training has been studied in MVP [106] and recently has been revisited by MILAN [43]. In this work, we show that this pretext task can scale up to billion-scale parameters and tens of millions of unlabeled images for vision-centric representation learning without (i) semantic feature quantization / tokenization [5, 70], and (ii) explicitly using image-text paired pre-training data and large corpora as in BEiT-3 [101]." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 47, + 580, + 128, + 593 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 580, + 128, + 593 + ], + "spans": [ + { + "bbox": [ + 47, + 580, + 128, + 593 + ], + "type": "text", + "content": "2.2. Pre-training" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 46, + 601, + 287, + 662 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 601, + 287, + 662 + ], + "spans": [ + { + "bbox": [ + 46, + 601, + 287, + 662 + ], + "type": "text", + "content": "Architecture. The architecture configurations of EVA are in Table 3a. EVA is a vanilla ViT [31] with 1.0B parameters. The shape of her follows ViT giant [119] and the vision encoder of BEiT-3 [101]. We do not use relative positional embeddings [89] and layer-scale [97] during pre-training." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 46, + 665, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 288, + 714 + ], + "type": "text", + "content": "Pre-training objective. EVA is pre-trained to reconstruct the masked out image-text aligned vision features conditioned on visible image patches. We corrupt the input patches with [MASK] tokens, and we use block-wise masking with" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 146, + 547, + 229 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 146, + 547, + 229 + ], + "spans": [ + { + "bbox": [ + 304, + 146, + 547, + 229 + ], + "type": "text", + "content": "a masking ratio of " + }, + { + "bbox": [ + 304, + 146, + 547, + 229 + ], + "type": "inline_equation", + "content": "40\\%" + }, + { + "bbox": [ + 304, + 146, + 547, + 229 + ], + "type": "text", + "content": " following [5, 70, 101]. The target for MIM pre-training is from the publicly available OpenAI CLIP-L/14 vision tower trained on " + }, + { + "bbox": [ + 304, + 146, + 547, + 229 + ], + "type": "inline_equation", + "content": "224\\times 224" + }, + { + "bbox": [ + 304, + 146, + 547, + 229 + ], + "type": "text", + "content": " pixel images [73]. The output feature of EVA is first normalized [3] and then projected to the same dimension as the CLIP feature via a linear layer. We use negative cosine similarity as the loss function." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 241, + 547, + 337 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 241, + 547, + 337 + ], + "spans": [ + { + "bbox": [ + 304, + 241, + 547, + 337 + ], + "type": "text", + "content": "Pre-training data. The data we used for pre-training EVA are summarized in Table 3b. For CC12M [16] and CC3M [88] datasets, we only use the image data without captions. For COCO [62] and ADE20K [123] datasets, we only use the train set data. ImageNet-21K [28] and Object365 [87] image data are also used. All these data are publicly accessible. The merged dataset for pre-training has 29.6 million images in total." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 347, + 547, + 431 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 347, + 547, + 431 + ], + "spans": [ + { + "bbox": [ + 304, + 347, + 547, + 431 + ], + "type": "text", + "content": "Pre-training settings & hyper-parameters. As shown in Table 3c, EVA is optimized via Adam [52] with decoupled weight decay [67] of 0.05. The peak learning rate is 1e-3 and decays according to a cosine learning rate schedule. We employed stochastic depth [45] with a rate of 0.1 for regularization and RandResizeCrop (0.2, 1) for data augmentation. Color jitter is not used." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 442, + 547, + 574 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 442, + 547, + 574 + ], + "spans": [ + { + "bbox": [ + 304, + 442, + 547, + 574 + ], + "type": "text", + "content": "Pre-training infrastructure and statistics. Some basic pre-training statistics are available in Table 3d. The GPU we use is NVIDIA A100-SXM4-40GB. Pre-training code is based on BEiT [5] written in PyTorch [69]. We also adopt DeepSpeed optimization library [80] with ZeRO stage-1 optimizer [77] to save memory. We find using fp16 format with dynamic loss scaling is stable enough during the whole course of pre-training while using bf1oat16 format is unnecessary. Since we use fp16 precision, EVA can also be pre-trained using " + }, + { + "bbox": [ + 304, + 442, + 547, + 574 + ], + "type": "inline_equation", + "content": "16 \\times" + }, + { + "bbox": [ + 304, + 442, + 547, + 574 + ], + "type": "text", + "content": " NVIDIA 24GB (32GB) GPUs with (without) gradient checkpointing [20]." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 306, + 603, + 485, + 616 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 603, + 485, + 616 + ], + "spans": [ + { + "bbox": [ + 306, + 603, + 485, + 616 + ], + "type": "text", + "content": "2.3. Evaluation on Downstream Tasks" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 304, + 629, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 629, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 629, + 547, + 713 + ], + "type": "text", + "content": "In this section, we extensively evaluate pre-trained EVA on several representative benchmarks, such as image classification (§2.3.1), video action recognition (§2.3.2), object detection & instance segmentation (§2.3.3), semantic segmentation (§2.3.4), and contrastive image-text pre-training with zero-shot evaluation (§2.3.5). EVA achieves state-of-the-art performance on a broad range of downstream tasks." + } + ] + } + ], + "index": 22 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "19360" + } + ] + } + ], + "index": 23 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 48, + 53, + 287, + 186 + ], + "blocks": [ + { + "bbox": [ + 50, + 41, + 285, + 52 + ], + "lines": [ + { + "bbox": [ + 50, + 41, + 285, + 52 + ], + "spans": [ + { + "bbox": [ + 50, + 41, + 285, + 52 + ], + "type": "text", + "content": "model #param. extra labeled data image size top-1 acc." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 48, + 53, + 287, + 186 + ], + "lines": [ + { + "bbox": [ + 48, + 53, + 287, + 186 + ], + "spans": [ + { + "bbox": [ + 48, + 53, + 287, + 186 + ], + "type": "table", + "html": "
using private labeled data
SwinV2-G [65]3.0BIN-21K-ext-70M640290.2
ViT-G [119]1.8BJFT-3B518290.5
ViT-g (CoCa) [117]1.0BJFT-3B+ALIGN576291.0
using public labeled data
CoAtNet-4 [27]275MIN-21K (14M)512288.6
MaxViT-XL [98]475MIN-21K (14M)512288.7
MViTv2-H [61]667MIN-21K (14M)512288.8
FD-CLIP-L [107]304MIN-21K (14M)336289.0
BEiT-3 [101]2.0B35M img-text pairs336289.6
EVA1.0BIN-21K (14M)336289.6
EVA1.0BIN-21K (14M)560289.7
", + "image_path": "8b488b1a745fda83165ec8c1fdedc051e89ff3bf4c3871b80c253dc8407b599f.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 245, + 167, + 257 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 245, + 167, + 257 + ], + "spans": [ + { + "bbox": [ + 47, + 245, + 167, + 257 + ], + "type": "text", + "content": "2.3.1 Image Classification" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 269, + 288, + 353 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 269, + 288, + 353 + ], + "spans": [ + { + "bbox": [ + 46, + 269, + 288, + 353 + ], + "type": "text", + "content": "Datasets. For image classification task, we evaluate EVA on ImageNet-1K (IN-1K) [28] validation set. We also evaluate the robustness & generalization capability of EVA along with our training settings & hyper-parameters using ImageNet-V2 matched frequency (IN-V2) [81], ImageNet-ReaL (IN-ReaL) [7], ImageNet-Adversarial (IN-Adv.) [42], ImageNet-Rendition (IN-Ren.) [41], ImageNet-Sketch (IN-Ske.) [100]." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 357, + 288, + 514 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 357, + 288, + 514 + ], + "spans": [ + { + "bbox": [ + 46, + 357, + 288, + 514 + ], + "type": "text", + "content": "Training Settings. Following the conventional setting [5, 70, 101], we first perform intermediate fine-tuning on ImageNet-21K [28] for 60 epochs with an image resolution of " + }, + { + "bbox": [ + 46, + 357, + 288, + 514 + ], + "type": "inline_equation", + "content": "224^2" + }, + { + "bbox": [ + 46, + 357, + 288, + 514 + ], + "type": "text", + "content": ", then EVA is further fine-tuned on ImageNet-1K training set for 10 epochs. Different from [117, 119] that use multi-head attention pooling and BEiT-3 that exploits an additional pretrained giant language tower as the image classification task layer, we simply adopt a linear layer as the classifier [31]. Notice that the supervised intermediate fine-tuning consumes only " + }, + { + "bbox": [ + 46, + 357, + 288, + 514 + ], + "type": "inline_equation", + "content": "\\sim 1/5" + }, + { + "bbox": [ + 46, + 357, + 288, + 514 + ], + "type": "text", + "content": " of the time & compute of the MIM pre-training stage. While for other billion-scale vision models such as SwinV2-G-3B, the supervised training phase costs " + }, + { + "bbox": [ + 46, + 357, + 288, + 514 + ], + "type": "inline_equation", + "content": "\\sim 1.5 \\times" + }, + { + "bbox": [ + 46, + 357, + 288, + 514 + ], + "type": "text", + "content": " resources than the MIM pre-training." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 517, + 288, + 696 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 517, + 288, + 696 + ], + "spans": [ + { + "bbox": [ + 46, + 517, + 288, + 696 + ], + "type": "text", + "content": "Results. Table 4 compares EVA with some state-of-the-art models on ImageNet-1K validation set. EVA achieves " + }, + { + "bbox": [ + 46, + 517, + 288, + 696 + ], + "type": "inline_equation", + "content": "89.6\\%" + }, + { + "bbox": [ + 46, + 517, + 288, + 696 + ], + "type": "text", + "content": " top-1 accuracy with " + }, + { + "bbox": [ + 46, + 517, + 288, + 696 + ], + "type": "inline_equation", + "content": "336^{2}" + }, + { + "bbox": [ + 46, + 517, + 288, + 696 + ], + "type": "text", + "content": " inputs, comparable to BEiT-3. Using a larger image resolution of " + }, + { + "bbox": [ + 46, + 517, + 288, + 696 + ], + "type": "inline_equation", + "content": "560^{2}" + }, + { + "bbox": [ + 46, + 517, + 288, + 696 + ], + "type": "text", + "content": " can further boost the top-1 accuracy to " + }, + { + "bbox": [ + 46, + 517, + 288, + 696 + ], + "type": "inline_equation", + "content": "89.7\\%" + }, + { + "bbox": [ + 46, + 517, + 288, + 696 + ], + "type": "text", + "content": ". Notice that BEiT-3 treats image classification as an image-to-text retrieval task. Therefore they leverage an additional one billion parameters pre-trained language encoder along with 35 million image-text data (21M pairs from CC12M, CC3M, SBU, COCO, VG and 14M pairs from ImageNet-21K) as well as 160GB text data in total. Meanwhile, we simply use a linear classifier on top of EVA with only ImageNet-21K image-tag data used for additional finetuning. With only publicly available data, EVA creates a new state-of-the-art image classification result on ImageNet-1K with a much neater architecture." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 701, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 701, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 701, + 288, + 713 + ], + "type": "text", + "content": "Robustness & generalization ability evaluation. We eval" + } + ] + } + ], + "index": 7 + }, + { + "type": "table", + "bbox": [ + 307, + 40, + 547, + 140 + ], + "blocks": [ + { + "bbox": [ + 47, + 188, + 288, + 232 + ], + "lines": [ + { + "bbox": [ + 47, + 188, + 288, + 232 + ], + "spans": [ + { + "bbox": [ + 47, + 188, + 288, + 232 + ], + "type": "text", + "content": "Table 4. Comparisons of image classification performance on ImageNet-1K validation set. With only publicly available data, EVA creates a new state-of-the-art ImageNet-1K image classification result with a canonical linear classifier." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 307, + 40, + 547, + 140 + ], + "lines": [ + { + "bbox": [ + 307, + 40, + 547, + 140 + ], + "spans": [ + { + "bbox": [ + 307, + 40, + 547, + 140 + ], + "type": "table", + "html": "
modelIN-1KIN-V2IN-ReALIN-Adv.IN-Ren.IN-Ske.avg.Δ↓
ConvNeXt87.577.790.570.867.053.774.513.0
SwinV287.577.390.273.967.752.374.812.7
MAE87.879.290.376.766.550.975.212.6
DeiT387.779.190.279.270.654.977.010.7
Eff-L2-NS88.480.590.684.874.747.677.810.6
BEiTv288.480.190.376.276.458.378.310.1
BEiT88.679.990.781.773.256.878.510.1
EVA89.681.690.886.288.367.784.05.6
", + "image_path": "3b38f2848db87ab1fd77242281c8b946170222af8e36179b3cee879649970651.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "table_body" + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 143, + 547, + 220 + ], + "lines": [ + { + "bbox": [ + 304, + 143, + 547, + 220 + ], + "spans": [ + { + "bbox": [ + 304, + 143, + 547, + 220 + ], + "type": "text", + "content": "Table 5. Robustness & generalization capability evaluation on ImageNet-1K variants. We test each model on different ImageNet-1K validation sets, without any specialized fine-tuning. \"avg.\": the averaged top-1 accuracy on 6 different ImageNet-1K validation set variants. \"Δ↓\": The gap between the averaged top-1 accuracy on 6 variants (i.e., IN-{1K, V2, Real, Adv., Ren., Ske.}) and the original ImageNet-1K validation set top-1 accuracy (the lower the better)." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 304, + 236, + 547, + 344 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 236, + 547, + 344 + ], + "spans": [ + { + "bbox": [ + 304, + 236, + 547, + 344 + ], + "type": "text", + "content": "uate the robustness and generalization capability of EVA trained with an image size of " + }, + { + "bbox": [ + 304, + 236, + 547, + 344 + ], + "type": "inline_equation", + "content": "336^{2}" + }, + { + "bbox": [ + 304, + 236, + 547, + 344 + ], + "type": "text", + "content": " on 6 different ImageNet1K validation set variants. In Table 5, we compare EVA with some top open-sourced models collected by the timm library [108]. Following the evaluation procedure in [39], all these models are first fine-tuned on the original ImageNet1K training set and then evaluated on different validation sets using the same fine-tuned model without further hyperparameter selection and specialized fine-tuning." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 345, + 547, + 536 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 345, + 547, + 536 + ], + "spans": [ + { + "bbox": [ + 304, + 345, + 547, + 536 + ], + "type": "text", + "content": "As shown in Table 5, EVA is the most competitive one in terms of absolute top-1 accuracies. However, these model various in pre-train data (from ImageNet-1K, ImageNet-21K to JFT-300M), input resolutions (from " + }, + { + "bbox": [ + 304, + 345, + 547, + 536 + ], + "type": "inline_equation", + "content": "224^2" + }, + { + "bbox": [ + 304, + 345, + 547, + 536 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 304, + 345, + 547, + 536 + ], + "type": "inline_equation", + "content": "800^2" + }, + { + "bbox": [ + 304, + 345, + 547, + 536 + ], + "type": "text", + "content": "), model sizes (from hundreds of millions to one billion parameters) as well as architectures (ConvNets, vanilla & hierarchical ViTs), etc. Therefore their absolute accuracies are not directly comparable. Instead, we are more interested in the gap between the averaged top-1 accuracy on 6 validation set variants and the original ImageNet-1K validation set top-1 accuracy (the lower the better), i.e., we care about whether a model along with its training settings biases towards the original validation set and generalize well on other variants. From this perspective, EVA not only achieves the highest averaged accuracy, but also has the smallest performance gap, which reflects the excellent robustness and generalization ability of EVA." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 551, + 448, + 562 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 551, + 448, + 562 + ], + "spans": [ + { + "bbox": [ + 306, + 551, + 448, + 562 + ], + "type": "text", + "content": "2.3.2 Video Action Recognition" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 573, + 547, + 658 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 573, + 547, + 658 + ], + "spans": [ + { + "bbox": [ + 304, + 573, + 547, + 658 + ], + "type": "text", + "content": "Datasets. For video action recognition, we evaluate EVA on Kinetics-400 (K-400) [51], Kinetics-600 (K-600) [14] and Kinetics-700 (K-700) [15] benchmarks. We first conduct intermediate fine-tuning on a merged dataset coined Kinetics-722 (K-722) that integrates videos from K-400, K-600 and K-700. We remove leaked as well as repeated videos in both training and validation sets. After this data de-duplicating" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 304, + 665, + 547, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 547, + 713 + ], + "type": "text", + "content": "Source: link (timestamp: Nov 10, 2022). The detailed model configurations are (arch-model_size-Img_resolution-data): ConvNeXt-XL-384px-21K [66], SwinV2-L-384px-21K [65], MAE-H-448px-1K [39], DeiT3-L-384px-21K [96], EfficientNet-L2&NS-800px-JFT300M [110], BEiTv2-L-224px-21K [70], BEiT-L-512px-21K [5], EVA-g-336px-merged30M&21K." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "19361" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 50, + 71, + 282, + 198 + ], + "blocks": [ + { + "bbox": [ + 50, + 71, + 282, + 198 + ], + "lines": [ + { + "bbox": [ + 50, + 71, + 282, + 198 + ], + "spans": [ + { + "bbox": [ + 50, + 71, + 282, + 198 + ], + "type": "table", + "html": "
modeltop-1 accuracy
Kinetics-400Kinetics-600Kinetics-700
MAE [34]86.8--
SwinV2-G [65]86.8--
Florence [118]86.888.0-
MaskFeat [103]87.088.380.4
VideoMAE [95]87.4--
X-CLIP [68]87.788.3-
CoVeR [120]87.287.978.5
CoCa [117] (frozen)88.088.581.1
CoCa [117] (finetuned)88.989.482.7
EVA89.789.882.9
", + "image_path": "83a46e8246b5294dd9a4570aa2bd4f3d28dbe35c6bd5725ca18255a60eb6a4a3.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 198, + 287, + 232 + ], + "lines": [ + { + "bbox": [ + 46, + 198, + 287, + 232 + ], + "spans": [ + { + "bbox": [ + 46, + 198, + 287, + 232 + ], + "type": "text", + "content": "Table 6. Video action recognition. With only publicly available K-400, K-600 and K-700 as video pre-training data, EVA is also quite performant in video action recognition tasks." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 245, + 287, + 270 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 245, + 287, + 270 + ], + "spans": [ + { + "bbox": [ + 46, + 245, + 287, + 270 + ], + "type": "text", + "content": "process, K-722 has 0.63M training videos in total with 722 action classes. A similar approach is also used in [58]." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 273, + 287, + 369 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 273, + 287, + 369 + ], + "spans": [ + { + "bbox": [ + 46, + 273, + 287, + 369 + ], + "type": "text", + "content": "Training & evaluation settings. EVA processes video data simply via spatial-temporal attention as [34, 95] with no specific architectural adaptation for video related tasks. We first train EVA using K-722 training set for 40 epochs with 8 frames and " + }, + { + "bbox": [ + 46, + 273, + 287, + 369 + ], + "type": "inline_equation", + "content": "224^2" + }, + { + "bbox": [ + 46, + 273, + 287, + 369 + ], + "type": "text", + "content": " resolution, then we fine-tune EVA on each dataset for only 1 or 2 epochs. We set frame " + }, + { + "bbox": [ + 46, + 273, + 287, + 369 + ], + "type": "inline_equation", + "content": "\\times" + }, + { + "bbox": [ + 46, + 273, + 287, + 369 + ], + "type": "text", + "content": " crop " + }, + { + "bbox": [ + 46, + 273, + 287, + 369 + ], + "type": "inline_equation", + "content": "\\times" + }, + { + "bbox": [ + 46, + 273, + 287, + 369 + ], + "type": "text", + "content": " clip to " + }, + { + "bbox": [ + 46, + 273, + 287, + 369 + ], + "type": "inline_equation", + "content": "16 \\times 3 \\times 4" + }, + { + "bbox": [ + 46, + 273, + 287, + 369 + ], + "type": "text", + "content": " for fine-tuning and evaluation for all datasets. The frame resolution is " + }, + { + "bbox": [ + 46, + 273, + 287, + 369 + ], + "type": "inline_equation", + "content": "224^2" + }, + { + "bbox": [ + 46, + 273, + 287, + 369 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 372, + 287, + 445 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 372, + 287, + 445 + ], + "spans": [ + { + "bbox": [ + 46, + 372, + 287, + 445 + ], + "type": "text", + "content": "Results. As shown in Table 6, EVA achieves better performance compared with some recent video-specific or large foundation models in video recognition. For reference, directly adapting image-only pre-trained EVA to K-400 without K-722 intermediate fine-tuning can also achieve a very competitive top-1 accuracy of " + }, + { + "bbox": [ + 46, + 372, + 287, + 445 + ], + "type": "inline_equation", + "content": "88.4\\%" + }, + { + "bbox": [ + 46, + 372, + 287, + 445 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 460, + 262, + 472 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 460, + 262, + 472 + ], + "spans": [ + { + "bbox": [ + 47, + 460, + 262, + 472 + ], + "type": "text", + "content": "2.3.3 Object Detection & Instance Segmentation" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 483, + 287, + 638 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 483, + 287, + 638 + ], + "spans": [ + { + "bbox": [ + 46, + 483, + 287, + 638 + ], + "type": "text", + "content": "Datasets. We evaluate the object detection and instance segmentation performance of EVA on both COCO [62] and LVIS [38]. COCO is a widely used object-level recognition benchmark with 80 common object categories. LVIS is an emerging large-vocabulary object-level recognition benchmark, which has more than 1,200 object categories as well as more than 2 million high quality instance segmentation masks (nearly " + }, + { + "bbox": [ + 46, + 483, + 287, + 638 + ], + "type": "inline_equation", + "content": "2 \\times" + }, + { + "bbox": [ + 46, + 483, + 287, + 638 + ], + "type": "text", + "content": " of COCO). Notably, COCO and LVIS almost use the same set of images, and both train and val split of LVIS have a huge overlap with COCO train and val split. Meanwhile, COCO has much fewer object categories than LVIS (i.e., " + }, + { + "bbox": [ + 46, + 483, + 287, + 638 + ], + "type": "inline_equation", + "content": "80 \\text{ v.s. } 1,200+" + }, + { + "bbox": [ + 46, + 483, + 287, + 638 + ], + "type": "text", + "content": "). Therefore it is meaningful to evaluate models' performance on both COCO and LVIS." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 641, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 641, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 641, + 288, + 714 + ], + "type": "text", + "content": "Training & evaluation settings. EVA uses Cascade Mask R-CNN [12] as the detector and adopts the training settings (e.g., LSJ data augmentation [36]) & architecture configurations (e.g., interleaved window & global attention) of ViTDet [60]. Following the common practice [65, 101, 121], we first conduct intermediate fine-tuning for the whole detec" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 72, + 545, + 108 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 108 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 108 + ], + "type": "text", + "content": "tor using Objects365 [87] dataset with a resolution of " + }, + { + "bbox": [ + 304, + 72, + 545, + 108 + ], + "type": "inline_equation", + "content": "1024^2" + }, + { + "bbox": [ + 304, + 72, + 545, + 108 + ], + "type": "text", + "content": ", then we fine-tune the detector on COCO and LVIS train split respectively with " + }, + { + "bbox": [ + 304, + 72, + 545, + 108 + ], + "type": "inline_equation", + "content": "1280^2" + }, + { + "bbox": [ + 304, + 72, + 545, + 108 + ], + "type": "text", + "content": " inputs." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 108, + 547, + 167 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 108, + 547, + 167 + ], + "spans": [ + { + "bbox": [ + 304, + 108, + 547, + 167 + ], + "type": "text", + "content": "We report single-scale evaluation and multi-scale evaluation / test-time augmentation (tta) results of EVA for comparison. For COCO, Soft-NMS [8] is also applied. For instance segmentation task, the classification score is calibrated [46] via maskness [102]." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 168, + 547, + 228 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 168, + 547, + 228 + ], + "spans": [ + { + "bbox": [ + 304, + 168, + 547, + 228 + ], + "type": "text", + "content": "The model architecture as well as the hyper-parameters for COCO and LVIS are almost the same (i.e., the hyperparameters are nearly \"zero-shot\" transferred from COCO to LVIS), expect we use federated loss [125] and repeat factor sampling [38] following ViTDet on LVIS." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 231, + 545, + 278 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 231, + 545, + 278 + ], + "spans": [ + { + "bbox": [ + 304, + 231, + 545, + 278 + ], + "type": "text", + "content": "Results. Perhaps COCO is the most fierce vision benchmark. Table 7 compares EVA with some leading approaches on COCO. Our model creates new state-of-the-art results on both object detection and instance segmentation tasks." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 279, + 545, + 327 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 279, + 545, + 327 + ], + "spans": [ + { + "bbox": [ + 304, + 279, + 545, + 327 + ], + "type": "text", + "content": "Compared with ViTDet-H [60] that uses Cascade Mask R-CNN [12] as well, EVA shows that with a larger model and better encoder & detector pre-training, the performance can be greatly improved with the same detector." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 327, + 545, + 411 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 327, + 545, + 411 + ], + "spans": [ + { + "bbox": [ + 304, + 327, + 545, + 411 + ], + "type": "text", + "content": "Compared with FocalNet [116] and Group DETRv2 [19] that choose better-established and highly-optimized DINO detector [121], EVA demonstrates that with sufficient model size, data and pre-training, better performance can be also achieved via the classic R-CNN framework [37]. On the other hand, FocalNet and Group DETRv2 are incapable of instance segmentation due to using DINO." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 411, + 547, + 470 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 411, + 547, + 470 + ], + "spans": [ + { + "bbox": [ + 304, + 411, + 547, + 470 + ], + "type": "text", + "content": "Compared with SwinV2-Giant [65] and FD-SwinV2-Giant [107] that also adopt a (stronger " + }, + { + "bbox": [ + 304, + 411, + 547, + 470 + ], + "type": "inline_equation", + "content": "\\mathrm{HTC}++" + }, + { + "bbox": [ + 304, + 411, + 547, + 470 + ], + "type": "text", + "content": " [17]) detector from the R-CNN family but with " + }, + { + "bbox": [ + 304, + 411, + 547, + 470 + ], + "type": "inline_equation", + "content": "\\sim 3\\times" + }, + { + "bbox": [ + 304, + 411, + 547, + 470 + ], + "type": "text", + "content": " model size of EVA, our approach streamlines the pre-training processes and pulls off a \"Giant-killing\" act via better representations." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 471, + 547, + 531 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 471, + 547, + 531 + ], + "spans": [ + { + "bbox": [ + 304, + 471, + 547, + 531 + ], + "type": "text", + "content": "Compared with BEiT-3, EVA shows that it is possible to build a state-of-the-art object-level recognition system without exploiting (i) semantic feature quantization / tokenization [5, 70], and (ii) image-text paired pre-training data and large corpora during pre-training." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 534, + 547, + 665 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 534, + 547, + 665 + ], + "spans": [ + { + "bbox": [ + 304, + 534, + 547, + 665 + ], + "type": "text", + "content": "Analyzing the performance gap between LVIS and COCO. Evaluating models on both COCO and LVIS benchmarks is essential, as they share nearly the same image set but differ in the number of annotated object categories. COCO has only 80 annotated categories, while LVIS annotates over 1,200 object categories, resulting in a long-tail distribution that more closely resembles challenging real-world scenarios [38]. In general, LVIS is considered a much more difficult benchmark than COCO for object-level recognition, with conventional methods typically experiencing a significant performance drop on LVIS." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 666, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 666, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 666, + 547, + 713 + ], + "type": "text", + "content": "In Table 8a, we analyze the performance gap between the LVIS and COCO benchmarks for EVA and other state-of-the-art approaches. For previous leading methods, such as ViTDet, the performance gap for " + }, + { + "bbox": [ + 304, + 666, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\mathrm{AP^{box}}" + }, + { + "bbox": [ + 304, + 666, + 547, + 713 + ], + "type": "text", + "content": " is around 8, and" + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "19362" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 48, + 40, + 545, + 218 + ], + "blocks": [ + { + "bbox": [ + 48, + 40, + 545, + 218 + ], + "lines": [ + { + "bbox": [ + 48, + 40, + 545, + 218 + ], + "spans": [ + { + "bbox": [ + 48, + 40, + 545, + 218 + ], + "type": "table", + "html": "
model / methoddetector#param.pre-training datatta?COCO valCOCO test-dev
encoderdetectorAPboxAPmaskAPboxAPmask
Soft-Teacher [115]HTC++ [17]284MIN-21K (14M)COCO(unlabeled)+O365✓60.752.561.353.0
GLIP [59]DyHead [26]≥ 284MIN-21K (14M)4ODs+GoldG+Cap12M✓60.8-61.5-
GLIPv2 [122]DyHead [26]≥ 637MFLD-900M\\( merged\\ data^a \\)✓--62.4-
ViTDet-H [60]CMask R-CNN [12]692MIN-1K (1M)-✓61.353.1--
Florence [118]DyHead [26]≥ 637MFLD-900M\\( merged\\ data^a \\)✓62.0-62.4-
SwinV2-G [65]HTC++ [17]≥ 3000MIN-21K-ext-70MO365✓62.553.763.154.4
DINO [121]-218MIN-21K (14M)O365✓63.2-63.3-
Mask DINO [57]-223MIN-21K (14M)O365✓-54.5-54.7
BEiT-3 [101]CMask R-CNN [12]1074M\\( merged\\ data^b \\)O365✓--63.754.8
FD-SwinV2-G [107]HTC++ [17]≥ 3000MIN-21K-ext-70MO365✓--64.255.4
FocalNet [116]DINO [121]746MIN-21K (14M)O365✓64.2-64.4-
Group DETRv2 [19]DINO [121]629MIN-1K (1M)O365✓--64.5-
EVACMask R-CNN [12]1074Mmerged-30MO365✘64.255.064.455.5
EVACMask R-CNN [12]1074Mmerged-30MO365✓64.5-64.7-
", + "image_path": "f0e16c581dfb7abaaae9a76fae682250aff9c8fd2f73df5fd34c69b1ccbb9cbb.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + }, + { + "bbox": [ + 52, + 256, + 441, + 266 + ], + "lines": [ + { + "bbox": [ + 52, + 256, + 441, + 266 + ], + "spans": [ + { + "bbox": [ + 52, + 256, + 441, + 266 + ], + "type": "text", + "content": "\"merged data\": FourODs + INBoxes + GoldG + CC15M + SBU, \"merged data\": IN-21K (14M) + Image-Text (35M) + Text (160GB)." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_footnote" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 52, + 276, + 281, + 376 + ], + "blocks": [ + { + "bbox": [ + 46, + 221, + 546, + 255 + ], + "lines": [ + { + "bbox": [ + 46, + 221, + 546, + 255 + ], + "spans": [ + { + "bbox": [ + 46, + 221, + 546, + 255 + ], + "type": "text", + "content": "Table 7. Object detection & instance segmentation on results COCO dataset. EVA establishes new state-of-the-art results in object detection and instance segmentation tasks on both COCO val and test-dev splits with the canonical R-CNN [37] object detection & segmentation framework. \"tta\" refers to test-time augmentation. (timestamp: Nov 10, 2022)" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 52, + 276, + 281, + 376 + ], + "lines": [ + { + "bbox": [ + 52, + 276, + 281, + 376 + ], + "spans": [ + { + "bbox": [ + 52, + 276, + 281, + 376 + ], + "type": "table", + "html": "
modelAPboxAPmask
COCOLVISΔ↓COCOLVISΔ↓
(a) evaluation using COCO & LVIS official annotations respectively
Copy-Paste [36]57.041.615.448.938.110.8
ViTDet-H [60]61.353.47.953.148.15.0
prev. best63.2a53.4b9.854.5c49.2d5.3
EVA (single-scale test)64.162.21.955.055.00.0
(b) evaluation using LVIS val1-5K annotations
EVA (single-scale test)69.668.31.359.659.8-0.2
", + "image_path": "95397cdcec0ebadc1b78ae228fdc5eaae6b01dc3d5da65b5661f9d85bd0b4f5d.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 449, + 287, + 605 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 449, + 287, + 605 + ], + "spans": [ + { + "bbox": [ + 46, + 449, + 287, + 605 + ], + "type": "text", + "content": "for " + }, + { + "bbox": [ + 46, + 449, + 287, + 605 + ], + "type": "inline_equation", + "content": "\\mathrm{AP^{mask}}" + }, + { + "bbox": [ + 46, + 449, + 287, + 605 + ], + "type": "text", + "content": ", it is around 5. However, when using the same detector (Cascade Mask R-CNN) and nearly identical settings as those in ViTDet pre-trained via MAE-Huge (ViTDet-H), EVA not only achieves state-of-the-art results on both LVIS and COCO benchmarks simultaneously but also significantly reduces the performance gap between them, particularly for the instance segmentation task. EVA attains the same performance on LVIS and COCO using single-scale evaluation. In comparison with ViTDet-H, we demonstrate that a slightly larger model with stronger representations can greatly improve performance on the challenging large vocabulary instance segmentation benchmark, with one caveat described below." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 605, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 605, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 605, + 288, + 713 + ], + "type": "text", + "content": "Note that the Merged-30M unlabeled images include 15K out of 20K LVIS val set images (the Merged-30M images contain all the COCO training images, and the LVIS validation split also includes 15k images from the COCO training set). Although a recent study [33] shows that including unlabeled images from the development / test set for MIM pre-training has minimal impact on the final performance, we conduct a more rigorous analysis of the LVIS and COCO performance gap to eliminate potential data contamination issues: We evaluate both" + } + ] + } + ], + "index": 6 + }, + { + "type": "table", + "bbox": [ + 307, + 276, + 547, + 388 + ], + "blocks": [ + { + "bbox": [ + 46, + 381, + 288, + 437 + ], + "lines": [ + { + "bbox": [ + 46, + 381, + 288, + 437 + ], + "spans": [ + { + "bbox": [ + 46, + 381, + 288, + 437 + ], + "type": "text", + "content": "Table 8. LVIS & COCO performance gap on val set. “prev. best” refers to the best individual model / result in each benchmark (a: DINO [121], b: ViTDet-H [60], c: Mask DINO [57], d: 2021 competition " + }, + { + "bbox": [ + 46, + 381, + 288, + 437 + ], + "type": "inline_equation", + "content": "1^{\\text{st}}" + }, + { + "bbox": [ + 46, + 381, + 288, + 437 + ], + "type": "text", + "content": " [35]) “" + }, + { + "bbox": [ + 46, + 381, + 288, + 437 + ], + "type": "inline_equation", + "content": "\\Delta \\downarrow" + }, + { + "bbox": [ + 46, + 381, + 288, + 437 + ], + "type": "text", + "content": "”: the performance gap between LVIS and COCO (the lower the better)." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 307, + 276, + 547, + 388 + ], + "lines": [ + { + "bbox": [ + 307, + 276, + 547, + 388 + ], + "spans": [ + { + "bbox": [ + 307, + 276, + 547, + 388 + ], + "type": "table", + "html": "
modelcrop sizeADE20KCOCO-Stuff
mIoUssmIoUmsmIoUss
HorNet [79]640257.557.9-
SeMask [48]640257.058.3-
SwinV2-G [65]896259.359.9-
Mask DINO [57]896259.560.8-
FD-SwinV2-G [107]8962-61.4-
ViT-Adapter [23]896261.261.552.3
BEiT-3 [101]896262.062.8-
EVA896261.562.353.4
", + "image_path": "c0ab57f9ba9e68deb5702c75f8d5f6ceaa7e807d45579e0aca5bcabbe41365cf.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "table_body" + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 392, + 546, + 426 + ], + "lines": [ + { + "bbox": [ + 304, + 392, + 546, + 426 + ], + "spans": [ + { + "bbox": [ + 304, + 392, + 546, + 426 + ], + "type": "text", + "content": "Table 9. Semantic segmentation performance on ADE20K and COCO-Stuff-164K dataset. \"mIoUss\": mIoU of single-scale evaluation, \"mIoUms\": mIoU using multi-scale evaluation." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 304, + 437, + 547, + 521 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 437, + 547, + 521 + ], + "spans": [ + { + "bbox": [ + 304, + 437, + 547, + 521 + ], + "type": "text", + "content": "COCO and LVIS models using the 5K images present in both the COCO and LVIS val sets, denoted as LVIS val-5K. The COCO results are measured using the 80-category COCO subset of LVIS with the higher-quality LVIS annotations (a similar approach also employed in [53], but for a different purpose). The results are shown in Table 8b, and we find that the conclusion remains unchanged." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 541, + 440, + 553 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 541, + 440, + 553 + ], + "spans": [ + { + "bbox": [ + 306, + 541, + 440, + 553 + ], + "type": "text", + "content": "2.3.4 Semantic Segmentation" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 565, + 547, + 673 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 565, + 547, + 673 + ], + "spans": [ + { + "bbox": [ + 304, + 565, + 547, + 673 + ], + "type": "text", + "content": "Dataset. We evaluate EVA on ADE20K [123] and COCO-Stuff-164K [11] datasets for semantic segmentation task. ADE20K includes 150 semantic categories, and has 20k images for training & 2k images for validation. COCO-Stuff-164K augments 164K complex images from COCO with pixel-level annotations that span over 172 categories including 80 things, 91 stuff, and 1 unlabeled class. Compared with ADE20K, COCO-Stuff is a more challenging but under-explored semantic segmentation benchmark." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 677, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 547, + 713 + ], + "type": "text", + "content": "Training & evaluation settings. We follow the task transfer pipelines of ViT-Adapter [23] + mask2former [24] but with a weakened model adaptation processes due to GPU memory" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "19363" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 51, + 40, + 550, + 123 + ], + "blocks": [ + { + "bbox": [ + 51, + 40, + 550, + 123 + ], + "lines": [ + { + "bbox": [ + 51, + 40, + 550, + 123 + ], + "spans": [ + { + "bbox": [ + 51, + 40, + 550, + 123 + ], + "type": "table", + "html": "
modelprecisiontotal #param.image #param.text #param.clip training datasamples seenimage sizepatch sizebatch sizegpu for training
OpenAI CLIP-Lfloat16430M304M124MCLIP-400M [73]12B\\( 224^2 \\)\\( 14 \\times 14 \\)32k\\( 256 \\times V100 (32GB) \\)
ALIGNbfloat16834M480M354MALIGN-1.8B [73]22B\\( 289^2 \\)-16k\\( 1024 \\times TPUv3 \\)
Open CLIP-Hbfloat161.0B632M354MLAION-2B [85]32B\\( 224^2 \\)\\( 14 \\times 14 \\)79k\\( 824 \\times A100 (40GB) \\)
Open CLIP-gbfloat161.3B1.0B354MLAION-2B [85]12B\\( 224^2 \\)\\( 14 \\times 14 \\)64k\\( 800 \\times A100 (40GB) \\)
EVA CLIP-gfloat161.1B1.0B124MLAION-400M [86]11B\\( 224^2 \\)\\( 14 \\times 14 \\)41k\\( 256 \\times A100 (40GB) \\)
", + "image_path": "fa19bbee91632c961d2317ff84c963a5dd861e6fc591ecc324d6d1c9d61c5765.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + }, + { + "bbox": [ + 47, + 124, + 550, + 144 + ], + "lines": [ + { + "bbox": [ + 47, + 124, + 550, + 144 + ], + "spans": [ + { + "bbox": [ + 47, + 124, + 550, + 144 + ], + "type": "text", + "content": "(a) CLIP model configurations. EVA CLIP-g can be stably trained via fp16 precision with fewer image-text pairs (7B v.s. 12B / 32B) sampled from a smaller data pool (LAION-400M v.s. LAION-2B) on " + }, + { + "bbox": [ + 47, + 124, + 550, + 144 + ], + "type": "inline_equation", + "content": "\\sim 1/3 \\times" + }, + { + "bbox": [ + 47, + 124, + 550, + 144 + ], + "type": "text", + "content": " GPUs compared with other open-sourced billion-scale competitors." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_footnote" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 52, + 152, + 549, + 289 + ], + "blocks": [ + { + "bbox": [ + 52, + 152, + 549, + 289 + ], + "lines": [ + { + "bbox": [ + 52, + 152, + 549, + 289 + ], + "spans": [ + { + "bbox": [ + 52, + 152, + 549, + 289 + ], + "type": "table", + "html": "
datasetsImageNet-1K [28]ImageNet-V2 [82]ImageNet-Adv. [42]ImageNet-Ren. [41]ImageNet-Ske. [100]ObjectNet [6]CIFAR-10 [54]CIFAR-100 [54]UCF-101 [92]Video classificationAvg. all
modelimage classificationΔ↓Kinetics-400 [51]Kinetics-600 [14]Kinetics-700 [15]
OpenAI CLIP-L75.569.970.887.859.669.095.675.93.476.464.564.257.772.2
ALIGN76.470.175.892.264.872.2--------
Open CLIP-H78.070.959.389.366.669.797.584.75.778.263.163.656.173.1
Open CLIP-g76.669.657.288.765.267.597.183.95.877.761.762.255.071.9
EVA CLIP-g78.5(+1.9)71.5(+1.9)73.6(+16.4)92.5(+3.8)67.3(+2.1)72.3(+4.8)98.3(+1.2)88.7(+4.8)2.576.1(-1.6)65.2(+3.5)64.4(+2.2)58.4(+3.4)75.7(+3.8)
", + "image_path": "d1ac2c9e16100ddc10d95bb5aa9bda82a0facfd2a3186b6de656d8b782ede1a3.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + }, + { + "bbox": [ + 46, + 290, + 550, + 321 + ], + "lines": [ + { + "bbox": [ + 46, + 290, + 550, + 321 + ], + "spans": [ + { + "bbox": [ + 46, + 290, + 550, + 321 + ], + "type": "text", + "content": "(b) Summary of zero-shot image / video classification performance. “" + }, + { + "bbox": [ + 46, + 290, + 550, + 321 + ], + "type": "inline_equation", + "content": "\\Delta \\downarrow" + }, + { + "bbox": [ + 46, + 290, + 550, + 321 + ], + "type": "text", + "content": "”: The gap between the averaged performance of ImageNet-{1K, V2, Adv., Ren., Ske.} & ObjectNet that with natural distribution shifts and the original ImageNet-1K validation accuracy. Our model suffers from the smallest performance drop (only " + }, + { + "bbox": [ + 46, + 290, + 550, + 321 + ], + "type": "inline_equation", + "content": "2.5\\%" + }, + { + "bbox": [ + 46, + 290, + 550, + 321 + ], + "type": "text", + "content": " top-1 accuracy gap) while maintaining the highest zero-shot classification accuracy averaged on all 12 benchmarks (" + }, + { + "bbox": [ + 46, + 290, + 550, + 321 + ], + "type": "inline_equation", + "content": "72.7\\%" + }, + { + "bbox": [ + 46, + 290, + 550, + 321 + ], + "type": "text", + "content": " top-1 accuracy)." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_footnote" + }, + { + "bbox": [ + 46, + 326, + 547, + 370 + ], + "lines": [ + { + "bbox": [ + 46, + 326, + 547, + 370 + ], + "spans": [ + { + "bbox": [ + 46, + 326, + 547, + 370 + ], + "type": "text", + "content": "Table 10. EVA as a vision-centric, multi-modal pivot. We evaluate a billion-scale contrastive language-image pre-trained (CLIP) model with the vision tower initialized from pre-trained EVA, which largely accelerates the contrastive training efficiency and shows promising zero-shot classification performance across a wide range of image / video benchmarks. The statistics & performance of EVA's MIM teacher (OpenAI CLIP-L) are also presented for reference." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_footnote" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 381, + 287, + 429 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 381, + 287, + 429 + ], + "spans": [ + { + "bbox": [ + 46, + 381, + 287, + 429 + ], + "type": "text", + "content": "limitation (40GB of VRAM): (i) relative position biases [90] are not applied. (ii) We use " + }, + { + "bbox": [ + 46, + 381, + 287, + 429 + ], + "type": "inline_equation", + "content": "8 \\times" + }, + { + "bbox": [ + 46, + 381, + 287, + 429 + ], + "type": "text", + "content": " decoders in mask2former segmentation head instead of " + }, + { + "bbox": [ + 46, + 381, + 287, + 429 + ], + "type": "inline_equation", + "content": "9 \\times" + }, + { + "bbox": [ + 46, + 381, + 287, + 429 + ], + "type": "text", + "content": ". (iii) The feature dimension in mask2former head is " + }, + { + "bbox": [ + 46, + 381, + 287, + 429 + ], + "type": "inline_equation", + "content": "\\sim 0.6 \\times" + }, + { + "bbox": [ + 46, + 381, + 287, + 429 + ], + "type": "text", + "content": " of EVA encoder." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 434, + 287, + 517 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 434, + 287, + 517 + ], + "spans": [ + { + "bbox": [ + 46, + 434, + 287, + 517 + ], + "type": "text", + "content": "Results. We compare EVA with other leading semantic segmentation methods in Table 9. EVA achieves strong results in both ADE20K and COCO-Stuff-164K datasets. On the other hand, the segmentation performance of EVA is slightly lower compared with BEiT-3 on ADE20K, we suspect this is partially due to our weakened architectural configurations." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 536, + 259, + 559 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 536, + 259, + 559 + ], + "spans": [ + { + "bbox": [ + 47, + 536, + 259, + 559 + ], + "type": "text", + "content": "2.3.5 Contrastive Language-Image Pre-training with Zero-shot Classification Evaluation" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 568, + 288, + 688 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 568, + 288, + 688 + ], + "spans": [ + { + "bbox": [ + 46, + 568, + 288, + 688 + ], + "type": "text", + "content": "CLIP (Contrastive Language-Image Pre-training) [47, 49, 72, 73] is a type of multi-modal foundation model that connects vision and language via contrastive image-text pre-training. CLIP can be applied to any image classification benchmark by simply providing the names of the visual categories to be recognized [1]. Thus the introduction of CLIP essentially reshapes the landscape of visual recognition. Meanwhile, CLIP features also play a central role in representation leaning [70, 101], AI generated content [78, 83, 84] and large dataset filtering [10, 85, 86], etc." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 689, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 288, + 713 + ], + "type": "text", + "content": "In this section and Table 10, we show that EVA is not only a strong encoder for a wide range of vision downstream" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 381, + 547, + 430 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 381, + 547, + 430 + ], + "spans": [ + { + "bbox": [ + 304, + 381, + 547, + 430 + ], + "type": "text", + "content": "tasks, but also a multi-modal pivot that builds a bridge between vision and language. To demonstrate that, we train & evaluate EVA as a billion-scale CLIP's vision tower in various zero-shot image / video classification benchmarks." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 433, + 547, + 492 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 433, + 547, + 492 + ], + "spans": [ + { + "bbox": [ + 304, + 433, + 547, + 492 + ], + "type": "text", + "content": "Baselines and major challenges in CLIP model scaling. We compare our CLIP (dubbed EVA CLIP) with other open-sourced strong CLIP competitors that exploit publicly accessible data / academic resources only. Model configurations and statistics are detailed in Table 10a." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 494, + 547, + 612 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 494, + 547, + 612 + ], + "spans": [ + { + "bbox": [ + 304, + 494, + 547, + 612 + ], + "type": "text", + "content": "There are two well-known major challenges of CLIP model training and scaling: (i) Large-scale Open CLIP models (e.g., Open CLIP-H & Open CLIP-g [2, 47]) usually suffer from severe training instability issues [2] and have to use bfloat16 format for optimization. (ii) The training efficiency is low, which may hinder model scaling and downstream performance. For instance, Open CLIP-g is heavily under-trained due to its large compute requirement, and its performance is even worse than the sufficiently-trained Open CLIP-H with a smaller model size." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 613, + 547, + 685 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 613, + 547, + 685 + ], + "spans": [ + { + "bbox": [ + 304, + 613, + 547, + 685 + ], + "type": "text", + "content": "Compared with our CLIP model, Open CLIP-H & -g are trained from scratch with much more image-text pairs (" + }, + { + "bbox": [ + 304, + 613, + 547, + 685 + ], + "type": "inline_equation", + "content": "\\sim 2.9 \\times" + }, + { + "bbox": [ + 304, + 613, + 547, + 685 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 613, + 547, + 685 + ], + "type": "inline_equation", + "content": "\\sim 1.1 \\times" + }, + { + "bbox": [ + 304, + 613, + 547, + 685 + ], + "type": "text", + "content": " of ours) sampled from a much larger dataset (" + }, + { + "bbox": [ + 304, + 613, + 547, + 685 + ], + "type": "inline_equation", + "content": "\\sim 5 \\times" + }, + { + "bbox": [ + 304, + 613, + 547, + 685 + ], + "type": "text", + "content": " of ours) on " + }, + { + "bbox": [ + 304, + 613, + 547, + 685 + ], + "type": "inline_equation", + "content": "\\sim 3 \\times" + }, + { + "bbox": [ + 304, + 613, + 547, + 685 + ], + "type": "text", + "content": " of GPUs. While by leveraging EVA, billion-scale CLIP model training can be accelerated with improved zero-shot classification performance, described next." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 689, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 689, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 689, + 547, + 713 + ], + "type": "text", + "content": "Training settings. For our CLIP model, we initialize the vision encoder via pre-trained EVA and the language encoder" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "19364" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 48, + 71, + 288, + 106 + ], + "blocks": [ + { + "bbox": [ + 48, + 71, + 288, + 106 + ], + "lines": [ + { + "bbox": [ + 48, + 71, + 288, + 106 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 288, + 106 + ], + "type": "table", + "html": "
model (SSL)zero-shotlinear probingfine-tuning
prev. best78.0a82.3b89.1c
EVA78.586.589.4
", + "image_path": "7023f939fc56fc7993efb4d1a2c410d6dea21f22a4822dfa82d2798a1a8b7626.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + }, + { + "bbox": [ + 46, + 107, + 287, + 174 + ], + "lines": [ + { + "bbox": [ + 46, + 107, + 287, + 174 + ], + "spans": [ + { + "bbox": [ + 46, + 107, + 287, + 174 + ], + "type": "text", + "content": "Table 11. Zero-shot, linear probing and fine-tuning performance of EVA-CLIP on ImageNet-1K. Notice that the linear probing and fine-tuning results are from the vision encoder of EVA-CLIP. Our approach establishes the new state-of-the-art results among all existing self-supervised learning (SSL) methods. (timestamp: Nov 10, 2022) results reference. a: Open CLIP-H [47], b: iBOT [124], c: dBOT [63]." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_footnote" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 185, + 288, + 280 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 185, + 288, + 280 + ], + "spans": [ + { + "bbox": [ + 46, + 185, + 288, + 280 + ], + "type": "text", + "content": "from OpenAI CLIP-L. The pre-training implementation is based on Open CLIP [47]. We also adopt DeepSpeed optimization library [80] with ZeRO stage-1 optimizer [77] to save memory. We find using fp16 format with dynamic loss scaling is stable enough during the whole course of training while using bf1oat16 format is unnecessary. These modifications allow us to train a 1.1B CLIP with a batch size of 41k on " + }, + { + "bbox": [ + 46, + 185, + 288, + 280 + ], + "type": "inline_equation", + "content": "256 \\times" + }, + { + "bbox": [ + 46, + 185, + 288, + 280 + ], + "type": "text", + "content": " NVIDIA A100 40GB GPUs." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 285, + 288, + 321 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 285, + 288, + 321 + ], + "spans": [ + { + "bbox": [ + 47, + 285, + 288, + 321 + ], + "type": "text", + "content": "Evaluation settings. We evaluate zero-shot image / video classification performance of each CLIP model on 12 benchmarks and report top-1 accuracy for comparisons." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 323, + 288, + 441 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 323, + 288, + 441 + ], + "spans": [ + { + "bbox": [ + 46, + 323, + 288, + 441 + ], + "type": "text", + "content": "For zero-shot image classification task, we choose 8 benchmarks, i.e., ImageNet-1K [28], ImageNet-V2 [81], ImageNet-Adversarial (ImageNet-Adv.) [42], ImageNet-Rendition (ImageNet-Adv.) [41], ImageNet-Sketch (ImageNet-Ske.) [100], ObjectNet [6], CIFAR-10 and CIFAR-100 [54]. We are also interested in the robustness of CLIP models, evaluated via the performance gap between the averaged performance of ImageNet-{1K, V2, Adv., Ren., Ske.} & ObjectNet that with natural distribution shifts and the original ImageNet-1K validation accuracy." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 443, + 288, + 479 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 443, + 288, + 479 + ], + "spans": [ + { + "bbox": [ + 47, + 443, + 288, + 479 + ], + "type": "text", + "content": "For zero-shot video classification task, we choose 4 benchmarks, namely UCF-101 [92], Kinetics-400 [51], Kinetics-600 [14], and Kinetics-700 [15]." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 483, + 288, + 579 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 483, + 288, + 579 + ], + "spans": [ + { + "bbox": [ + 46, + 483, + 288, + 579 + ], + "type": "text", + "content": "Results. Table 10b shows the comparison. Our EVA CLIP achieves the highest averaged accuracy, and performs the best in 10 out of 12 zero-shot classification benchmarks. Notably, the ImageNet-1K validation zero-shot top-1 accuracy is " + }, + { + "bbox": [ + 46, + 483, + 288, + 579 + ], + "type": "inline_equation", + "content": "78.2\\%" + }, + { + "bbox": [ + 46, + 483, + 288, + 579 + ], + "type": "text", + "content": " without using any of its training set labels, matching the original ResNet-101 [40]. Moreover, our model is quite robust and suffers from the smallest performance drop when facing natural distribution shifts in ImageNet." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 581, + 287, + 640 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 581, + 287, + 640 + ], + "spans": [ + { + "bbox": [ + 46, + 581, + 287, + 640 + ], + "type": "text", + "content": "At last, in Table 11 we provide zero-shot, linear probing & end-to-end fine-tuning top-1 accuracy of EVA-CLIP on ImageNet-1K validation set for reference. Our approach creates the new state-of-the-art results among all existing self-supervised learning methods." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 641, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 641, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 641, + 288, + 714 + ], + "type": "text", + "content": "Notice that EVA CLIP's vision branch learns from OpenAI CLIP-L, while language branch initialized from the same CLIP-L model. Therefore, starting from a CLIP-L with only 430M parameters, we progressively scale up a 1.1B EVA CLIP-g with large performance improvements. This implies that interleaved MIM & image-text contrastive" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 72, + 547, + 144 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 144 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 144 + ], + "type": "text", + "content": "pre-training could be an efficient and scalable CLIP training approach. To our knowledge, EVA CLIP-g is the largest performant CLIP model trained via publicly accessible data and resources. We hope our practice on scaling and improving CLIP can also inspire and transfer to the study of other large scale multi-modal foundation models." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 156, + 392, + 168 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 156, + 392, + 168 + ], + "spans": [ + { + "bbox": [ + 306, + 156, + 392, + 168 + ], + "type": "text", + "content": "3. Related Work" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 179, + 547, + 300 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 179, + 547, + 300 + ], + "spans": [ + { + "bbox": [ + 304, + 179, + 547, + 300 + ], + "type": "text", + "content": "Masked image modeling (MIM) learns rich visual representations via predicting masked visual contents conditioned on visible context. ViT [31] and iGPT [18] report the first meaningful MIM pre-training results. The BEiT family [5,70,101] greatly improves MIM's performance via masked visual token prediction. Recent work [4,21,30,32,39,103,113,124] (re-)explore pixel / feature regression in MIM, but only in a relatively small model and data scales. In this work, we explore the limits of large scale MIM pre-training via masked image-text aligned feature prediction [43, 106]." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 303, + 547, + 459 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 303, + 547, + 459 + ], + "spans": [ + { + "bbox": [ + 304, + 303, + 547, + 459 + ], + "type": "text", + "content": "Vision foundation models. ConvNets [56] have long been the de-facto standard visual architecture ab initio. Since AlexNet [55], ConvNets have rapidly evolved and become deeper, wider and larger [40, 44, 66, 91, 93, 94, 111]. However, at sufficient model and data scales, ConvNets lag behind ViTs [31] due to a lack of scalable pre-training tasks and the built-in inductive biases. Entering the 2020s, large pretrained ViTs [31, 119] such as SwinV2-G [65] with hierarchical architectures as well as BEiT-3 [101] with multi-modal representations started to demonstrate various vision benchmarks. In this work, we show by leveraging unlabeled images, vanilla ViT can be efficiently scaled up to billion-scale parameters, and stands out in various downstream tasks." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 470, + 378, + 482 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 470, + 378, + 482 + ], + "spans": [ + { + "bbox": [ + 306, + 470, + 378, + 482 + ], + "type": "text", + "content": "4. Conclusion" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 490, + 547, + 597 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 490, + 547, + 597 + ], + "spans": [ + { + "bbox": [ + 304, + 490, + 547, + 597 + ], + "type": "text", + "content": "In this work, we launch EVA, a one billion parameters vanilla ViT encoder to explore the limits of masked visual representation learning. We show simple masked feature modeling as a visual learning pretext task scales well on an architecture with minimal vision priors, and attains excellent results in a representative & diverse set of downstream tasks. We hope EVA would bridge the gap between vision and language study via masked modeling, and contributes to the Neon Genesis of vision research." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 609, + 404, + 623 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 609, + 404, + 623 + ], + "spans": [ + { + "bbox": [ + 306, + 609, + 404, + 623 + ], + "type": "text", + "content": "Acknowledgement" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 629, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 629, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 629, + 547, + 715 + ], + "type": "text", + "content": "This work is supported by the National Key R&D Program of China (2020AAA0105200) and NSFC (No. 617333007). We would like to thank Hanxiao Qu, Yan Tian, Yemin Shi and Xigang Cao for their help on GPU resources. 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Episode in EXCALIBUR played by a human annotator. An episode is divided into four sequential phases: in Phase I, the agent explores the house for 2,500 steps (each action takes a step); in Phase II the agent needs to answer 20 questions (5 shown) about the explored environment; in Phase III the agent is given a second chance to reenter the house, now with knowledge of the questions; in Phase IV the agent answers the questions again. Performance is evaluated with the answer accuracy in Phases II&IV and the time spent in Phase III. The observation space is egocentric (see left and right panels). The action space includes navigation and manipulation actions (Fig. 2)." + ], + "image_footnote": [], + "bbox": [ + 681, + 330, + 841, + 648 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 734, + 313, + 750 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Experience precedes understanding. Humans constantly explore and learn about their environment out of curiosity, gather information, and update their models of the world. On the other hand, machines are either trained to learn passively from static and fixed datasets, or taught to complete specific goal-conditioned tasks. To encourage the development of exploratory interactive agents, we present the EXCALIBUR benchmark. EXCALIBUR allows agents to explore their environment for long durations and then query", + "bbox": [ + 75, + 763, + 470, + 902 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "their understanding of the physical world via inquiries like: \"is the small heavy red bowl made from glass?\" or \"is there a silver spoon heavier than the egg?\". This design encourages agents to perform free-form home exploration without myopia induced by goal conditioning. Once the agents have answered a series of questions, they can renter the scene to refine their knowledge, update their beliefs, and improve their performance on the questions. Our experiments demonstrate the challenges posed by this dataset for the present-day state-of-the-art embodied systems and", + "bbox": [ + 496, + 734, + 893, + 888 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 810, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "14931", + "bbox": [ + 480, + 945, + 517, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "the headroom afforded to develop new innovative methods. Finally, we present a virtual reality interface that enables humans to seamlessly interact within the simulated world and use it to gather human performance measures. EXCALIBUR affords unique challenges in comparison to present-day benchmarks and represents the next frontier for embodied AI research.", + "bbox": [ + 75, + 90, + 472, + 196 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 215, + 209, + 231 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Humans are active learners, acquiring knowledge of the physical world through intentional experiments with their bodies and senses. Children as young as a few months old learn about objects and their environment through observation and interaction [6, 24]. This sensorimotor experience, as pointed out by Piaget [47], is critical in forming a fundamental understanding of reality. This is the cognitive motivation for the creation of EXCALIBUR.", + "bbox": [ + 75, + 241, + 468, + 361 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In contrast, machine learning models typically obtain knowledge by passively observing web-crawled, encyclopedic, or crowd-sourced static datasets [67]. This passive approach has clear limitations. For instance, grounding physical concepts like heavy, large, and long requires moving beyond passive observation. To weigh an object, humans will often try to use different forces to move it. To compare the sizes of objects, they move around and perceive the objects from different angles and distances. Although large pre-trained models have made progress in aligning with the grounded world [41, 45], they still lack an embodied understanding of physical concepts [59].", + "bbox": [ + 75, + 363, + 468, + 542 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Todays popular active, embodied-learning benchmarks in the Embodied AI community focus on directed task completion. These include navigating to specified GPS coordinates [3], locating an object of a specified category [7], translating commands into low-level actions [5, 56], and inspecting a scene to answer a question about the presence or count of an object category [15, 25]. A more recent benchmark, Room Rearrangement [62] requires agents to explore the scene, but the focus there is on navigation, observation, and memorization. Progress on these benchmarks has been promising. We can now train agents that can comprehend goal instructions reasonably well and complete simple tasks, particularly navigation heavy tasks. None of these benchmarks, however, explicitly probe how these models have learned to represent their environments, nor do they encourage the type of free-form, undirected, experimental, exploration performed by humans.", + "bbox": [ + 75, + 545, + 468, + 801 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To encourage and evaluate the capacity of embodied agents to openly explore their environment and interact with objects within it, we present the EXCALIBUR benchmark. EXCALIBUR is built using large procedurally generated", + "bbox": [ + 76, + 801, + 468, + 863 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "houses via ProcTHOR [18]. Each episode in EXCALIBUR consists of four phases as shown in Fig. 1. Phase I Exploration – The agent must navigate to and interact with objects in the environment. Importantly, the agent isn't seeded with a goal and must instead perform open-ended exploration. Interacting with objects takes place via physics-enabled arm manipulation. Phase II Question Answering – We probe the agent's understanding of the physical world through natural language inquiries. Our questions go beyond simple primitive queries, e.g. regarding object existence, and include physical attributes (e.g. masses and materials) and visual attributes (e.g. colors and shapes). Phase III Reentering – This is a goal-directed phase, since the agent must interact with the environment to refine its understanding of the world in response to questions asked in the previous stage. Phase IV Refined Question Answering – This phase repeats the inquiries made in Phase II to query if the agent was able to successfully acquire the required knowledge about its world after being provided the goal question set.", + "bbox": [ + 500, + 90, + 890, + 378 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Our use of question-answering in this benchmark which focuses on interaction and exploration has several benefits. Natural language inquiries allow us to probe the agent's understanding of the world. They also provide a clear and objective metric for EXCALIBUR. Further, they can serve as supervisory signals to encourage agents to interact with objects and explore the world. Finally, the introduction of language opens the door to using pre-trained language models in future work, given the recent rise of their use for planning for embodied agents [2].", + "bbox": [ + 496, + 380, + 892, + 532 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "EXCALIBUR is the first benchmark that offers the following new avenues and challenges for Embodied AI research: (1) It encourages open-ended exploration. (2) Agents in EXCALIBUR have access to a rich interactive action space that covers navigation, arm-based manipulation, and grasping with different degrees of force. (3) The questions in this benchmark move beyond existence and counting. They probe the agent on its abilities to learn physical and visual attributes of the world. (4) Our task requires long-horizon planning and reasoning. Most embodied benchmarks today have maximum episode lengths of up to 250 steps. Our task has four phases that include an exploration phase of 2500 steps. (5) Our task also evaluates the ability of an agent to refine and improve the existing knowledge of its environment. This is an ability that humans commonly showcase in their everyday experiences.", + "bbox": [ + 496, + 534, + 892, + 777 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "We present baselines using state-of-the-art Embodied AI neural models and learning methods. We also design a Virtual Reality interface to enable humans to navigate and interact with objects in ProcTHOR scenes in an immersive way. This allows for a more accurate human baseline measurement, which demonstrates that there remains substantial room for model improvement. Finally, in Sec. 5, we show that the failure patterns of models are distinct from", + "bbox": [ + 496, + 779, + 893, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_footnote", + "text": "1 Exploratory Curious Agents with Language Induced Embodied World Understanding", + "bbox": [ + 76, + 875, + 468, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "14932", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/d90b346429fe0d257f4b204d53a6d030cd61c338b3341770d43f599bc08bd58f.jpg", + "image_caption": [ + "Figure 2. The action space of EXCALIBUR. The whole action space consists of two sets of actions: Navigation (left) and Manipulation (right). Navigation actions are used to move the agent (bottom left) and look at different angles (top left). Manipulation actions are used to move the arm (top right), grasp with force and open and close closets, drawers and fridges (which are implemented as high action which can be triggered when the gripper is close to the handles), and signal finishing the task (bottom right). All of the actions are discretized: angler motion are discretized into 15 degrees, linear motion are discretized into 0.05 meter for joints and 0.25 meter for base and force is discretized into 0.05 kilogram-force." + ], + "image_footnote": [], + "bbox": [ + 184, + 89, + 787, + 354 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "those of humans. Humans are great at exploration, but fall short at memorization, while agents tend to succeed at answering questions that depend on memory but are poor explorers - even when trained with popular exploration rewards. Altogether, we find that EXCALIBUR serves as a powerful and flexible framework and environment for evaluating and building Exploratory Curious Agents with Language Induced Embodied World Understanding.", + "bbox": [ + 75, + 455, + 470, + 578 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "2. EXCALIBUR", + "text_level": 1, + "bbox": [ + 76, + 599, + 207, + 616 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Consider the example depicted in Fig. 1: the embodied agent is spawned in the bedroom of a random house at a random position. It traverses the bedroom, living room, kitchen, and bathroom, opens closets, fridges, and drawers, and picks up various objects. After 2,500 steps, the agent is asked 20 questions and answers some questions correctly and some incorrectly, e.g. \"How many silver objects are heavier than the white egg in the kitchen?\" The agent then returns to the house and explores the scene again. This time it starts lifting silver objects in the room to estimate their weight. As the example reveals, EXCALIBUR encourages agents to openly explore their world in the first phase but also evaluates their ability to perform goal-directed exploration once the questions become known. Natural language inquiries are used to ascertain what the agent has learned about its environment. We now present details about the EXCALIBUR task, and contrast it to previous Embodied AI benchmarks in Sec. 6 and Tab. 3.", + "bbox": [ + 75, + 628, + 468, + 898 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "2.1. Task.", + "text_level": 1, + "bbox": [ + 500, + 455, + 576, + 469 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "An EXCALIBUR task is defined as a triple $\\langle \\mathcal{H}, \\mathcal{Q}, \\mathcal{P} \\rangle$ , where a House consists of a floor plan and objects in it, a Question set is a list of English question-answer pairs, and a Position is a 2D location on the floor of $\\mathcal{H}$ that is empty (i.e. at which the agent can be placed) along with an initial agent camera orientation. Each object in the house is defined by its type, colors, materials (full list of object types, colors, and materials is in Appendix B), meshes (3D shape of the objects), location, size (width, depth, height), and weight (under $5\\mathrm{kg}$ ). At the start of each episode, the floor plan, objects (including colors, materials, sizes, and weights), questions, and agent spawn position are randomly sampled with the distribution specified in Appendix C.", + "bbox": [ + 496, + 484, + 890, + 681 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Phases. The EXCALIBUR task consists of four phases: (I) exploration, (II) question answering, (III) reentering, and (IV) refined question answering. In both (I) and (III), the agent may navigate throughout the house and manipulate objects. One difference between (I) and (III) is that the time steps in (I) are limited to 2,500, while the steps in (III) $T_{3}$ are unlimited but used to discount the accuracy improvement in Eq. 1. In (II) the agent is asked 20 questions. This brings up another notable difference between (I) and (III). In (I), an agent must perform open-ended exploration, learning about objects and their relationships. In (III), its exploration is conditioned on its experience in (I), the goal questions and its own answers in (II), and it attempts to improve its answers in (IV). We denote the accuracy in Phase (II) and", + "bbox": [ + 496, + 688, + 892, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "14933", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/bd29bcbce27ac5ded5628090190f9edcbc4017ede084b6182cd7583bf98ce0a1.jpg", + "image_caption": [ + "Figure 3. Dataset construction procedure. We generate the dataset in four steps (each in a pane). (1) We consider the procedurally generated floor plans and houses generated with PROCTHOR. (2) We then randomize the sizes and weights of objects in the scene. (3) We then extract the scene graphs of objects and relations in the scenes. (4) Based on hand-crafted templates, we generate questions and filter out questions that can be answered without exploring the scenes." + ], + "image_footnote": [], + "bbox": [ + 181, + 88, + 488, + 385 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/e47e911233b19ef0e5117ee16c98e9f9d141e675569909c7afff80311ae2ee81.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 491, + 89, + 635, + 383 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/b41cd86b3ac957c11b30efa4c5987682581efbe879fcaca00b976ef5f429b0b5.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 637, + 90, + 790, + 383 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Phase (IV) as $\\mathrm{Acc}_{\\mathrm{exp}}$ and $\\mathrm{Acc}_{\\mathrm{ref}}$", + "bbox": [ + 76, + 458, + 294, + 473 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Agents. The breadth of embodied experience results from the versatility of human bodies. With this in mind, the agent used in EXCALIBUR is the MANIPULATHOR arm agent of Ehsani et al. [21]. This agent has a dexterous 6 DOF Kinova-inspired robotic arm, see Fig. 2. We extend their design by adding a force argument to grasping action. This is one step further towards more realistic manipulation and also empowers the agents to \"feel\" the weights of objects through interaction. Fig. 2 shows the available actions of the armed agent in Phase (I) and (III). The \"Done\" action signals that the agent wishes to end Phase (III), the number of time steps spent before which are counted as $T_{3}$ . At every timestep, the agent acts given egocentric RGB images (of size $800 \\times 600$ ) as its observation.", + "bbox": [ + 75, + 473, + 470, + 683 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Evaluation. We wish to evaluate two facets of exploration: (1) \"how many questions can be answered with the knowledge acquired in Phase (I)?\", and (2) \"how efficient is the agent in refining its answers in Phase (IV)?\". To define a unified metric measuring both facets, we propose the following exploration score (ExQA):", + "bbox": [ + 75, + 685, + 468, + 776 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\operatorname {E x Q A} \\triangleq \\operatorname {A c c} _ {\\exp} + \\left(\\operatorname {A c c} _ {\\text {r e f}} - \\operatorname {A c c} _ {\\exp}\\right) \\exp (- k T _ {3}), \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 96, + 787, + 468, + 808 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where we call $k > 0$ the energy coefficient. ExQA reduces to $\\mathrm{Acc}_{\\mathrm{ref}}$ when $k = 0$ and reduces to $\\mathrm{Acc}_{\\mathrm{exp}}$ as $k \\to \\infty$ . Our choice of $k$ thus determines how we prioritize accuracy after exploration versus after answer refinement. We choose", + "bbox": [ + 75, + 816, + 470, + 878 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "a value for $k$ that maximizes human performance, biasing models to uncover strategies of similar efficiency and efficacy as we see in human demonstrations.", + "bbox": [ + 500, + 458, + 890, + 503 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "2.2. Dataset Construction", + "text_level": 1, + "bbox": [ + 500, + 513, + 699, + 527 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The EXCALIBUR dataset is built upon PROCTHOR-10k, a dataset of 10,000 procedurally generated home environments, each containing between 1-10 rooms [18]. For each PROCTHOR-10k home, we apply a variety of scene augmentations (e.g. randomizing object weight and sizes) and generate sets of challenging questions. We break our dataset generation process into four stages: randomization, scene graph generation, question generation, and filtering. We detail each stage below, see Fig. 3 for a visual overview. Randomization. The diversity across PROCTHOR-10k houses is very large: objects placements, floor plans, materials, ||are all randomized while respecting sensible constraints common across real homes. Despite this diversity, we found that, without applying additional scene augmentations, many questions of interest become either trivial or answerable via commonsense. For instance, the weights of many objects in AI2-THOR (and thus in PROCTHOR-10k) are set uniformly across object categories. This means that a question such as \"is the cup in the kitchen heavier than the bowl?\", may have a constant answer across all cups and bowls. Thus, without applying weight randomization,", + "bbox": [ + 496, + 536, + 890, + 854 + ], + "page_idx": 3 + }, + { + "type": "page_footnote", + "text": "3Empirically, we find $k$ which maximizes ExQA likelihood under a gaussian prior. The procedure for choosing an optimal value of $k$ is described in App. F.", + "bbox": [ + 500, + 862, + 893, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_footnote", + "text": "2Force feedback mechanisms are common in physical manipulators.", + "bbox": [ + 76, + 886, + 437, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "14934", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "the agent may answer accurately without any exploration or object interaction. In EXCALIBUR, we apply two types of supplemental randomization to PROCTHOR-10k: object weight and size randomization. In particular, within each house, we uniformly sample the weights of pickupable (i.e. excluding large objects that cannot be held by the agent, e.g. a fridge) objects to be between $0.5 \\times$ and $1.5 \\times$ their starting values. Similarly, the size of pickupable objects (i.e. their scale) is randomized to be with $0.8 \\times$ and $1.0 \\times$ of their starting values. Note that we only downscale objects as this prevents potential collisions between nearby objects.", + "bbox": [ + 75, + 90, + 472, + 257 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Scene Graph. Before moving to question generation, we first preprocess each house to produce a scene graph representation of the environment. This scene graph provides a compact summary of the objects in the house along with their relationships and attributes. In our formulation, rooms, objects, and agent are represented as nodes with edges between nodes representing their relationships. These relationships include, for example, CONTAINEDBY, ADJACENTTO, ONTOPOF. A full listing of object relationships and node attributes can be found in the appendix.", + "bbox": [ + 75, + 257, + 472, + 409 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Question Generation. To generate our question sets, we follow the process used to generate the single-image visual question answering (VQA) dataset CLEVR [31]. In particular, we represent questions using functional programs whose answer values can be found by evaluating these programs upon the above described scene graph. As for CLEVR, we design a collection of (11) question families, which can be composed and chained to generate questions. This question generation process may produce degenerate or tautological questions, we prune these using the depth-first approach employed when constructing CLEVR. Details of question generation procedure is in App. E.", + "bbox": [ + 75, + 409, + 472, + 592 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/265ad915bea8f14fe3344ecd5a1e6f5184da9d37b5a61c6d7779b66ed178b98c.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
Type%
QuestionYes-no78.8
Count12.3
Query8.9
RelationColor26.7
Material66.2
CONTAINEDBY8.2
ADJACENTTO39.5
ONTOPOF0.8
HEAVIERTHAN430.6
LARGER THAN18.9
", + "bbox": [ + 84, + 594, + 267, + 748 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Table 1. Dataset Distribution.", + "bbox": [ + 83, + 758, + 261, + 771 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Filtering. In order to create questions that are challenging and whose answers are not overly biased to certain answers, we use extensive question filtering to remove easy questions. In particular, for each candidate question $q$ , we compute the answer of $q$ across all scenes, which produces a distribution", + "bbox": [ + 297, + 590, + 468, + 787 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "over answers. We filter questions to only include those whose answer distribution is sufficiently balanced. For more details see, App. D.", + "bbox": [ + 75, + 787, + 468, + 832 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The result of such a process is an underlying dataset with a range of difficult questions of 3 different types and 7 kinds", + "bbox": [ + 75, + 833, + 468, + 863 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "of physical properties and relations (Fig. 1) Different types of questions are evaluated in slightly different ways: Yes-no questions are evaluated by exact matching, count questions are answered correctly when the prediction is only different than the standard answer by $5\\%$ , and query questions match prediction and the standard answer order-agnostically. In this way, we use accuracy as an umbrella metric for all of the questions. There are four splits in EXCALIBUR: (1) a training set with 10k PROCTHOR scenes, (2) a validation and a test set with 1k PROCTHOR scenes each, and (3) another test set with 9 hand-crafted ARCHITECTHOR scenes5 for comparison between agents and humans.", + "bbox": [ + 496, + 90, + 893, + 273 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3. Human Baseline with VR Interface", + "text_level": 1, + "bbox": [ + 498, + 287, + 818, + 304 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "One challenge of comparing human performance fairly with that of our agents is that our agents are extensively trained on houses from our dataset while human annotators, on the other hand, are only exposed to a small handful of training episodes. It is therefore important to create a realistic environment where real-life experience and knowledge can be easily transferred to the simulated environment. For this, we create a VR interface to EXCALIBUR and ask human annotators to complete tasks while virtually embodied as the agent. In our experiments, human participants used the Meta Quest 2 VR headset6 and were evaluated using the same metric as our agents. Concretely, to make the experience interactive and immersive, we ensured that our VR experience satisfied the following requirements.", + "bbox": [ + 496, + 314, + 890, + 526 + ], + "page_idx": 4 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- Flexible Head Movement: The head movement of the human annotators is smoothly reflected as camera movement in the VR environment, so that the information-seeking behavior of the human annotators can be easily transferred to the simulated environment.", + "- Intuitive Arm Movement: Human annotators should be able to intuitively manipulate the robotic, 6 DOF Knovalike, the arm of the MANIPULATHOR agent used in EX-CALIBUR. As the robotic arm has greater degrees of freedom than a human arm (ignoring human fingers) this means that special attention must be paid to ensure that humans need not worry about the rotation of joints of the arm, but only the position and orientation of the gripper.", + "- Gripping With Force: We leveraged the pressure on the grip button of the Meta Quest 2 controller to map it to the grasp force in the environment so annotators can use different magnitudes of forces to grip objects.", + "- Open/Close: We also facilitated the user to open and close various objects in the VR environment, to make the experience more immersive and allow the user to explore the house in greater depth." + ], + "bbox": [ + 496, + 527, + 890, + 845 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "For more details on VR interface, training and evaluating", + "bbox": [ + 500, + 847, + 890, + 863 + ], + "page_idx": 4 + }, + { + "type": "page_footnote", + "text": "HEAVIERTHAN includes LIGHTERTHAN, and LARGERTHAN includes SMALLERTHAN, LONGERTHAN, and SHORTERTHAN", + "bbox": [ + 76, + 875, + 467, + 898 + ], + "page_idx": 4 + }, + { + "type": "page_footnote", + "text": "One ARCHITECTHOR scene is used for training human annotators.", + "bbox": [ + 500, + 875, + 862, + 886 + ], + "page_idx": 4 + }, + { + "type": "page_footnote", + "text": "$^{6}$ https://www.meta.com/quest/products/quest-2/", + "bbox": [ + 500, + 887, + 854, + 898 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "14935", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "human annotators, see App. A.", + "bbox": [ + 76, + 90, + 282, + 106 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4. Reinforcement Learning Baselines", + "text_level": 1, + "bbox": [ + 76, + 116, + 388, + 133 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "EXCALIBUR requires a model to actively plan, explore the houses, manipulate objects, memorize its history, and answer questions. In this work, and as is common across modern embodied benchmarks, we train reinforcement learning models as our baselines. Recurrent neural networks (RNNs) are frequently used as generic models for encoding language instructions, historical observations, and actions, into belief states for embodied agents [18, 21, 32, 62-64]. Following this prior work, we use a GRU [13] to encode the history of observations seen and actions taken by the agent to produce, at every time step $t \\geq 0$ , a vector belief state $b_{t}$ corresponding to the output of the RNN at that timestep. We extend this practice by feeding the belief states as input to an actor-critic policy head as well as to a question answering module. To understand whether questions answering serves as a good stimulation for encouraging exploration, we consider three training signals: a (1) coverage-based reward, (2) QA reward, and (3) QA cross-entropy loss. Our goal in the following experiments is to show that modern Embodied AI models and training techniques can achieve some level of success on EXCALIBUR with the goal of inspiring future work to build upon these results.", + "bbox": [ + 75, + 142, + 472, + 489 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Actor-critic policy The belief state is fed into an MLP with one hidden layer, which we call the actor-head, and decoded into logits, one logit for each discrete action available to the agent (recall Sec. 2.1). By passing these logits through a softmax we produce the agent's policy (i.e. a distribution over agent actions). To enable training with PPO [52,63], we also must produce an estimate of the value of the agent's current state. To do this, we feed the belief state through another similar MLP, the critic-head, which returns a 1-dimensional output.", + "bbox": [ + 75, + 489, + 472, + 642 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Question answering To make full use of existing large, pretrained, language models, we follow [60] and propose to convert belief states into continuous prefix tokens using a prefix generator MLP with two hidden layers $f_{\\theta}^{\\text{prefix}}$ . These prefix tokens are prepended to with the question tokens and fed into the encoder of pre-trained T5 [49]. We then use the, pretrained, T5 decoder module to produce a (distribution over) natural-language answers to the given question. Note that the T5 model has its parameters frozen and so is not trained in our experiments.", + "bbox": [ + 75, + 643, + 472, + 792 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Featurizing agent observations We experiment with two different visual feature extractors for the agent's egocentric RGB observations: (1) a pre-trained CLIP ResNet50 model [32, 48] and (2) a MaskRCNN [29] model finetuned on our training scenes. Visual features and an embedding of the agent's last action are concatenated and passed as input to the above RNN. After Phase II, the agent additionally", + "bbox": [ + 75, + 795, + 472, + 902 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/2dcf3778f31c9ddf84b388a0c2be5e10928be388d56e00fb964e8cf6a5ecae7a.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
ProcTHOR Test SetArchitecTHOR Test Set
AccexpAccrefT3ExQAAccexpAccrefT3ExQA
Random41.741.7-41.739.139.1-39.1
Language53.553.5-53.549.249.2-49.2
QA58.560.2131.260.052.456.0159.155.7
Novelty54.256.599.656.449.954.5125.754.1
Novelty+QA58.763.1203.262.453.556.3211.755.9
Human w/o replay----63.687.1759.479.4
Human w/ replay----81.394.3782.190.1
", + "bbox": [ + 501, + 88, + 893, + 195 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 2. Human and baseline performance across two test sets. We bold best metric values among AI systems.", + "bbox": [ + 498, + 205, + 893, + 234 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "conditions the question embeddings from the T5 encoder as input to the RNN, which is also concatenated to observation and question embeddings.", + "bbox": [ + 498, + 261, + 893, + 306 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Training Our training loss equals the unweighted sum of the standard PPO RL loss [52] and $\\mathcal{L}_{\\mathrm{QA}}$ , a cross-entropy loss for question answering defined as", + "bbox": [ + 498, + 306, + 893, + 354 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\mathrm {Q A}} = \\sum_ {t = 1} ^ {T} \\sum_ {(q, a) \\in \\mathcal {Q}} - \\log p _ {\\mathrm {T} 5} (a \\mid [ f _ {\\theta} ^ {\\text {p r e f i x}} (h _ {t}), f ^ {\\text {e m b}} (q) ]), \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 513, + 363, + 890, + 421 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $p_{\\mathrm{T5}}$ is the probability of answer $a$ produced by a T5 encoder-decoder, and $f^{\\mathrm{emb}}$ is the embedding layer of the T5 encoder, and $\\mathcal{Q}$ is the set of question-answer pairs associated with an episode.", + "bbox": [ + 498, + 421, + 890, + 479 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Rewards We consider two kinds of rewards in this paper: (1) a QA reward and (2) a novelty-based reward. The QA reward is calculated by comparing the answers generated through beam search from T5 and the ground truth answers:", + "bbox": [ + 498, + 481, + 893, + 542 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\nr _ {t} ^ {\\mathrm {Q A}} = \\frac {1}{| \\mathcal {Q} |} \\sum_ {(q, a) \\in \\mathcal {Q}} \\left(\\mathbb {I} (a = \\mathrm {T} 5 _ {t} (q)) - \\mathbb {I} (a = \\mathrm {T} 5 _ {t - 1} (q))\\right), \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 504, + 565, + 890, + 617 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $\\mathrm{T}5_{t}(q) = \\mathrm{T}5(f_{\\theta}^{\\mathrm{decoder}}(h_{t}),f^{\\mathrm{emb}}(q))$ denotes the output of the T5 model when using beam search decoding. Note that $r_t^{\\mathrm{QA}}$ can only be non-zero when the agent's answer to a question changes between time steps $t - 1$ and $t$ . Our novelty reward encourages the agent to exhaustively navigate and observe novel objects, in particular, we let", + "bbox": [ + 498, + 616, + 893, + 708 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\nr _ {t} ^ {\\text {n o v e l t y}} = \\frac {O _ {t} ^ {\\text {s e e n}} - O _ {t - 1} ^ {\\text {s e e n}}}{O _ {\\text {a l l}}} + \\frac {A _ {t} - A _ {t - 1}}{A _ {\\text {r e a c h a b l e}}}, \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 562, + 717, + 890, + 752 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $O_{t}^{\\mathrm{seen}}$ denotes the number of objects seen till time step $t$ , $O_{\\mathrm{all}}$ denotes number of objects in $\\mathcal{H}$ , $A_{t}$ denotes the area covered by time step $t$ , and $A_{\\mathrm{reachable}}$ denotes the total reachable area in $\\mathcal{H}$ .", + "bbox": [ + 498, + 761, + 893, + 821 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5. EXCALIBUR Human and Agent Evaluation", + "text_level": 1, + "bbox": [ + 498, + 829, + 885, + 847 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "To gain insight into the gap between humans' and state-of-the-art embodied AI models' performance on EXCALIBUR we first must train such embodied models. To this", + "bbox": [ + 498, + 854, + 893, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "14936", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "end, we train several variants of the reinforcement learning baseline described in Sec. 4 on the training split of EXCALIBUR. In particular, we train three variants denoted $QA$ , Novelty, and $Novelty + QA$ ; as suggested by their names, the $QA$ agent is only given the QA reward signal, the Novelty agent has access to the novelty reward, and the $Novelty + QA$ is given the sum of both rewards at every timestep. For all of these agents, cross entropy loss is used for optimizing the prefix generator. Beyond these RL baselines, we also include non-interactive Random and Language baselines; the Random baseline simply chooses answers at random from among plausible answers when conditioned on the question type while the Language model is trained to answer questions given only question text, which helps indentifying artifacts in question generation.", + "bbox": [ + 75, + 90, + 472, + 316 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "To make cross-model and human-agent comparisons we evaluate our embodied models on two test sets: (1) the procedurally generally PROCTHOR-10k testing scenes and (2) the set of, human-designed, ARCHITECTHOR test houses [18]. We evaluate humans only in the ARCHITECTHOR houses as the ARCHITECTHOR test houses were meticulously crafted to closely imitate real-world houses and represent a smaller domain shift for human participants.", + "bbox": [ + 75, + 318, + 472, + 439 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "The results of these evaluations can be found in Table 2. Among AI systems, we see that the Novelty $+QA$ agent performs best across the $\\mathrm{Acc}_{\\mathrm{exp}}$ , $\\mathrm{Acc}_{\\mathrm{ref}}$ , and ExQA metrics with the $QA$ model close behind. This suggests that the novelty reward may provide only marginal benefits and, indeed, the Novelty agent obtains results only slightly above those of the Language model which, at best, simply reproduces the biases in our question-answer pairs.", + "bbox": [ + 75, + 439, + 472, + 561 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "For our human evaluations, we consider two experimental conditions Human w/o replay and Human w/ replay. In the Human w/ replay trials, unlike in Human w/o replay, humans are allowed to view a video of their behavior in Phase I and Phase III when answering questions in Phase II and IV, respectively. Hence participants in the Human w/ replay trials are relieved of the burden of needing to remember all of the details of their exploration. While humans outperform the AI systems in both experimental conditions, the gap between AI and human performance is far narrower (gap of $+10.1\\mathrm{Acc}_{\\mathrm{exp}}$ for Human w/o replay v.s. a gap of $+27.8$ for $\\mathrm{Acc}_{\\mathrm{exp}}$ Human w/o replay). This suggests that memorization is a significant bottleneck for humans. Note that, in the Human w/ replay condition, humans achieve an extremely high $\\mathrm{Acc}_{\\mathrm{ref}}$ value (94.3) showing clearly that EXCALIBUR is, in principle, solvable by intelligent systems.", + "bbox": [ + 75, + 561, + 472, + 803 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Further analysis of our results as well as descriptive metrics of agent exploration behavior can be found in App. H.", + "bbox": [ + 76, + 804, + 470, + 835 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "6. Related Work", + "text_level": 1, + "bbox": [ + 76, + 844, + 218, + 859 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "The domain of embodied AI has seen an explosion of attention in recent years [17, 19]. Here, we review three", + "bbox": [ + 76, + 869, + 470, + 902 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "sub-areas of this community most relevant to this work.", + "bbox": [ + 500, + 90, + 867, + 106 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "6.1. Exploration, Execution and Manipulation", + "text_level": 1, + "bbox": [ + 500, + 117, + 856, + 133 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Tab. 3 summarizes recent embodied AI benchmarks and evaluation frameworks comparing our EXCALIBUR benchmark with those including those designed for question answering, instruction following, rearrangement, and visual navigation. We say that an embodied benchmark or framework requires: open-ended exploration if the agent must act before being given fully specified goal information, goal-driven execution if the agent must act after being given the task definition, and manipulation if the agent must directly interact with objects, either with a physically simulated arm (e.g., [21,36,58]) to complete its goal or with a higher-level abstraction (e.g., in [62], the agent picks up objects by specifying their semantic category). We can see that most benchmarks emphasize either exploration or execution and manipulation. Most similar to EXCALIBUR are the BEHAVIOR [57] and AI2-THOR Rearrangement [62] benchmarks. BEHAVIOR requires agents to complete activities, defined using predicate logic, using rich interaction and object manipulation but, unlike EXCALIBUR, does not emphasize open-ended exploration and experimentation. AI2-THOR rearrangement, on the other hand, includes an exploration component but this exploration requires only memorizing object states, unlike EXCALIBUR which rewards agents who directly interact with objects. In total, EXCALIBUR is the first benchmark that explicitly evaluates agents' understanding of the physical world after agents explore, and manipulate objects within, virtual homes. As argued previously, EXCALIBUR requires that agents understand scenes with their body, form a representation that can be used to answer symbolic questions, and apply the knowledge acquired from exploration to execution.", + "bbox": [ + 496, + 141, + 893, + 611 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "6.2. Visual Exploration", + "text_level": 1, + "bbox": [ + 500, + 619, + 681, + 636 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "The task of visual exploration in embodied and robotics contexts has a long history of study with a rich diversity in perspectives. This diversity exists, in part, as the meaning of \"exploration\" is ambiguous: is an agent successful in exploration if it visits many locations, if it interacts with many objects, or something else entirely? The excellent survey of Ramakrishnan, et al. [51] divides space of existing exploration strategies into four groups: curiosity (seeking unexpected states), novelty (seeking unseen states), coverage (looking to visual reveal large areas), and reconstruction (seeking states that aid in predicting other unseen states). Some recent works that have touched on these areas include, curiosity [38,42,46,54], novelty [8,9,20,43], coverage [11, 12, 64], and reconstruction [30, 33, 50]. Of course not all work falls cleanly into these categories, for instance Eysenbach et al. perform skill discovery (i.e. exploration) by maximizing information theoretic quantities [22] and", + "bbox": [ + 496, + 643, + 893, + 902 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "14937", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/937e5f653dcb93d0cf6012456b82a2f5215578b99478ce02d0f4c3548d0a6116.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
WorkExplorationExecutionManipulationHuman Perf.Language
QAEQA [15]NoYesNoNoQA
IQA [25]NoYesAbstractKeyboardQA
QA Probing [14]YesNoNoNoQA
EMQA [16]NoNoNoNoQA
Instr.RxR Habitat [34]NoYesNoKeyboardInstruction
ALFRED [56]NoYesAbstractKeyboardInstruction
TEACH [44]NoYesAbstractKeyboardDialog
Rear.AI2THOR [62]YesYesAbstractNoNo
Habitat [58]YesNoArmNoNo
Nav.PointNav [3]NoYesNoNoNo
ObjectNav [3]NoYesNoNoNo
ArmPointNav [21]NoYesArmNoNo
BEHAVIOR [57]NoYesArmImmersiveDescriptive
EXCALIBURYesYesArmImmersiveQA
", + "bbox": [ + 215, + 88, + 751, + 316 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 3. Comparison between Embodied AI agents and human evaluation frameworks.", + "bbox": [ + 225, + 325, + 740, + 340 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Chaplot et al. perform a type of heuristic semantic-goal-guided exploration using learned priors [10].", + "bbox": [ + 75, + 354, + 468, + 383 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We argue that question answering rewards act as highly versatile and symbolic training signal for embodied agents. While clearly a non-traditional exploration training signal, our work can be seen as a type of reconstruction-based exploration. While existing reconstruction-based exploration generally uses a pixel-based objective (e.g. ability to predict how an environment would look from an unseen camera location), our natural language queries require the agent the agent to \"reconstruct\" a general semantic understanding of the environment.", + "bbox": [ + 75, + 385, + 468, + 535 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "6.3. Question Answering for Vision", + "text_level": 1, + "bbox": [ + 76, + 545, + 349, + 561 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "The work of Agrawal et al. [1] introduced the task of large-scale free-form open-ended Visual Question Answering (VQA) where, given a static image and natural language question about the image, a model is expected to return a natural language answer to this question. This seminal work began a new subdomain of computer vision with hundreds of publications and dozens of related datasets, see [55] for a recent review. These VQA benchmarks probe model's ability to reason about, for example, common sense [68], spatial relationships [31], potential agent actions [37], and diverse world knowledge [53]. Fundamentally, VQA focuses on single-image-understanding while our work requires interaction-driven agent exploration of an entire environment; for instance, questions about an object's weight in our dataset are unanswerable without interaction.", + "bbox": [ + 75, + 568, + 468, + 792 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "More recently, several video question answering datasets have been introduced, e.g. [23, 26, 28, 35, 65, 66]. Among these datasets, perhaps most related to our work, as it requires answering questions from an egocentric perspective, is the episodic memory task from the Ego4D benchmark suite [26]; in this a task a model must answer natural language questions about a video by returning the segment of", + "bbox": [ + 75, + 795, + 468, + 902 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "the video including the question's answer. While moving from single-images to videos requires utilizing long-term memory and building a holistic representation of the environment, the lack of agent-driven interaction in these tasks means that agent learning is constrained to the prefixed trajectories taken when filming the videos. This makes it challenging to train agents who run their own experiments and are able to flexibly correct their mistakes.", + "bbox": [ + 496, + 354, + 890, + 474 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "The vision and language research community has produced a vast array of models for VQA ranging from the earliest vanilla architectures [1], to using explicit object detectors [4], to pre-training with transformers [39] to general purpose unified architectures [27, 40, 61]. In this work we use a T5 language decoder to answer questions that conditions on the belief state of the agent which forms a representation of its current and past observations.", + "bbox": [ + 496, + 477, + 890, + 598 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "7. Conclusion and Future Directions", + "text_level": 1, + "bbox": [ + 500, + 602, + 807, + 618 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this paper, we present a novel benchmark EXCALIBUR for encouraging and evaluating the exploration ability of embodied agents. We build strong baseline models trained with both question answering reward and novelty based exploration-encouraging reward. We compared them with human performance in immersive environment. Human's great exploration ability not only leads to much higher accuracy after exploration but also leads to faster answer finding in reentering phase. Putting it all together, EXCALIBUR is still a challenging task and improvements on this benchmark could be made in various directions, including but not limit to fine-grained semantic map building, adversarial question generation, better features from observation, and leveraging large language models. A successful agent on EXCALIBUR will lead to embodied agents with the ability to actively understanding environments in a symbolic way and being able to ground and articulate embodied concepts in language.", + "bbox": [ + 496, + 628, + 890, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "14938", + "bbox": [ + 480, + 945, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Aishwarya Agrawal, Jiasen Lu, Stanislaw Antol, Margaret Mitchell, C. Lawrence Zitnick, Devi Parikh, and Dhruv Bartra. VQA: visual question answering - www.visualqa.org. Int. J. Comput. 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Computer Vision Foundation / IEEE, 2019. 8" + ], + "bbox": [ + 78, + 90, + 468, + 709 + ], + "page_idx": 11 + }, + { + "type": "page_number", + "text": "14942", + "bbox": [ + 480, + 945, + 519, + 955 + ], + "page_idx": 11 + } +] \ No newline at end of file diff --git a/2023/EXCALIBUR_ Encouraging and Evaluating Embodied Exploration/c84853fe-e5d3-4737-8cec-5e8fb595ae84_model.json b/2023/EXCALIBUR_ Encouraging and Evaluating Embodied Exploration/c84853fe-e5d3-4737-8cec-5e8fb595ae84_model.json new file mode 100644 index 0000000000000000000000000000000000000000..d5f37ec57bbc1bddb4d0fb4e92df1117d9518056 --- /dev/null +++ b/2023/EXCALIBUR_ Encouraging and Evaluating Embodied Exploration/c84853fe-e5d3-4737-8cec-5e8fb595ae84_model.json @@ -0,0 +1,2435 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.0, + 0.812, + 0.047 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.41, + 0.138, + 0.54, + 0.156 + ], + "angle": 0, + "content": "EXCALIBUR" + }, + { + "type": "image", + "bbox": [ + 0.54, + 0.124, + 0.561, + 0.155 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.221, + 0.16, + 0.75, + 0.183 + ], + "angle": 0, + "content": "Encouraging and Evaluating Embodied Exploration" + }, + { + "type": "text", + "bbox": [ + 0.194, + 0.216, + 0.774, + 0.314 + ], + "angle": 0, + "content": "Hao Zhu\\*, Raghav Kapoor\\*, So Yeon Min\\*, Winson Han\\*, Jiatai Li\\*, Kaiwen Geng\\*, Graham Neubig\\*, Yonatan Bisk\\*, Aniruddha Kembhavi\\*, Luca Weihs\\* Carnegie Mellon University, Allen Institute for Artificial Intelligence zhuhao@cmu.edu" + }, + { + "type": "image", + "bbox": [ + 0.116, + 0.331, + 0.273, + 0.649 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.281, + 0.331, + 0.653, + 0.5 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.277, + 0.508, + 0.501, + 0.521 + ], + "angle": 0, + "content": "QUESTIONS AVAILABLE SINCE PHASE II" + }, + { + "type": "text", + "bbox": [ + 0.277, + 0.532, + 0.499, + 0.554 + ], + "angle": 0, + "content": "Q1: How many eggs are there in the glass bowl in the fridge?" + }, + { + "type": "text", + "bbox": [ + 0.277, + 0.562, + 0.498, + 0.583 + ], + "angle": 0, + "content": "Q2: What is the sculpture on the bedroom table made of?" + }, + { + "type": "text", + "bbox": [ + 0.277, + 0.591, + 0.493, + 0.613 + ], + "angle": 0, + "content": "Q3: What is the color of the scrub in the larger bathroom?" + }, + { + "type": "text", + "bbox": [ + 0.277, + 0.623, + 0.492, + 0.646 + ], + "angle": 0, + "content": "Q4: Is there a pot lighter than the laptop in the living room?" + }, + { + "type": "list", + "bbox": [ + 0.277, + 0.532, + 0.499, + 0.646 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.519, + 0.508, + 0.574, + 0.52 + ], + "angle": 0, + "content": "PHASE II" + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.532, + 0.561, + 0.544 + ], + "angle": 0, + "content": "A1:3 X" + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.565, + 0.584, + 0.577 + ], + "angle": 0, + "content": "A2: Plastic X" + }, + { + "type": "text", + "bbox": [ + 0.517, + 0.592, + 0.574, + 0.604 + ], + "angle": 0, + "content": "A3: Blue X" + }, + { + "type": "text", + "bbox": [ + 0.517, + 0.624, + 0.569, + 0.636 + ], + "angle": 0, + "content": "A4: Yes" + }, + { + "type": "list", + "bbox": [ + 0.517, + 0.532, + 0.584, + 0.636 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.607, + 0.508, + 0.663, + 0.52 + ], + "angle": 0, + "content": "PHASE IV" + }, + { + "type": "text", + "bbox": [ + 0.606, + 0.532, + 0.648, + 0.543 + ], + "angle": 0, + "content": "A1: 1" + }, + { + "type": "text", + "bbox": [ + 0.605, + 0.565, + 0.666, + 0.576 + ], + "angle": 0, + "content": "A2: Metal" + }, + { + "type": "text", + "bbox": [ + 0.604, + 0.591, + 0.673, + 0.614 + ], + "angle": 0, + "content": "A3:Green and yellow" + }, + { + "type": "text", + "bbox": [ + 0.604, + 0.626, + 0.655, + 0.637 + ], + "angle": 0, + "content": "A4: Yes" + }, + { + "type": "list", + "bbox": [ + 0.604, + 0.532, + 0.673, + 0.637 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.683, + 0.331, + 0.843, + 0.649 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.075, + 0.655, + 0.892, + 0.725 + ], + "angle": 0, + "content": "Figure 1. Episode in EXCALIBUR played by a human annotator. An episode is divided into four sequential phases: in Phase I, the agent explores the house for 2,500 steps (each action takes a step); in Phase II the agent needs to answer 20 questions (5 shown) about the explored environment; in Phase III the agent is given a second chance to reenter the house, now with knowledge of the questions; in Phase IV the agent answers the questions again. Performance is evaluated with the answer accuracy in Phases II&IV and the time spent in Phase III. The observation space is egocentric (see left and right panels). The action space includes navigation and manipulation actions (Fig. 2)." + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.735, + 0.314, + 0.751 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.765, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Experience precedes understanding. Humans constantly explore and learn about their environment out of curiosity, gather information, and update their models of the world. On the other hand, machines are either trained to learn passively from static and fixed datasets, or taught to complete specific goal-conditioned tasks. To encourage the development of exploratory interactive agents, we present the EXCALIBUR benchmark. EXCALIBUR allows agents to explore their environment for long durations and then query" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.736, + 0.895, + 0.89 + ], + "angle": 0, + "content": "their understanding of the physical world via inquiries like: \"is the small heavy red bowl made from glass?\" or \"is there a silver spoon heavier than the egg?\". This design encourages agents to perform free-form home exploration without myopia induced by goal conditioning. Once the agents have answered a series of questions, they can renter the scene to refine their knowledge, update their beliefs, and improve their performance on the questions. Our experiments demonstrate the challenges posed by this dataset for the present-day state-of-the-art embodied systems and" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.946, + 0.518, + 0.957 + ], + "angle": 0, + "content": "14931" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.198 + ], + "angle": 0, + "content": "the headroom afforded to develop new innovative methods. Finally, we present a virtual reality interface that enables humans to seamlessly interact within the simulated world and use it to gather human performance measures. EXCALIBUR affords unique challenges in comparison to present-day benchmarks and represents the next frontier for embodied AI research." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.216, + 0.21, + 0.232 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.242, + 0.47, + 0.362 + ], + "angle": 0, + "content": "Humans are active learners, acquiring knowledge of the physical world through intentional experiments with their bodies and senses. Children as young as a few months old learn about objects and their environment through observation and interaction [6, 24]. This sensorimotor experience, as pointed out by Piaget [47], is critical in forming a fundamental understanding of reality. This is the cognitive motivation for the creation of EXCALIBUR." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.364, + 0.47, + 0.544 + ], + "angle": 0, + "content": "In contrast, machine learning models typically obtain knowledge by passively observing web-crawled, encyclopedic, or crowd-sourced static datasets [67]. This passive approach has clear limitations. For instance, grounding physical concepts like heavy, large, and long requires moving beyond passive observation. To weigh an object, humans will often try to use different forces to move it. To compare the sizes of objects, they move around and perceive the objects from different angles and distances. Although large pre-trained models have made progress in aligning with the grounded world [41, 45], they still lack an embodied understanding of physical concepts [59]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.546, + 0.47, + 0.802 + ], + "angle": 0, + "content": "Todays popular active, embodied-learning benchmarks in the Embodied AI community focus on directed task completion. These include navigating to specified GPS coordinates [3], locating an object of a specified category [7], translating commands into low-level actions [5, 56], and inspecting a scene to answer a question about the presence or count of an object category [15, 25]. A more recent benchmark, Room Rearrangement [62] requires agents to explore the scene, but the focus there is on navigation, observation, and memorization. Progress on these benchmarks has been promising. We can now train agents that can comprehend goal instructions reasonably well and complete simple tasks, particularly navigation heavy tasks. None of these benchmarks, however, explicitly probe how these models have learned to represent their environments, nor do they encourage the type of free-form, undirected, experimental, exploration performed by humans." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.803, + 0.47, + 0.864 + ], + "angle": 0, + "content": "To encourage and evaluate the capacity of embodied agents to openly explore their environment and interact with objects within it, we present the EXCALIBUR benchmark. EXCALIBUR is built using large procedurally generated" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.092, + 0.892, + 0.379 + ], + "angle": 0, + "content": "houses via ProcTHOR [18]. Each episode in EXCALIBUR consists of four phases as shown in Fig. 1. Phase I Exploration – The agent must navigate to and interact with objects in the environment. Importantly, the agent isn't seeded with a goal and must instead perform open-ended exploration. Interacting with objects takes place via physics-enabled arm manipulation. Phase II Question Answering – We probe the agent's understanding of the physical world through natural language inquiries. Our questions go beyond simple primitive queries, e.g. regarding object existence, and include physical attributes (e.g. masses and materials) and visual attributes (e.g. colors and shapes). Phase III Reentering – This is a goal-directed phase, since the agent must interact with the environment to refine its understanding of the world in response to questions asked in the previous stage. Phase IV Refined Question Answering – This phase repeats the inquiries made in Phase II to query if the agent was able to successfully acquire the required knowledge about its world after being provided the goal question set." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.381, + 0.893, + 0.533 + ], + "angle": 0, + "content": "Our use of question-answering in this benchmark which focuses on interaction and exploration has several benefits. Natural language inquiries allow us to probe the agent's understanding of the world. They also provide a clear and objective metric for EXCALIBUR. Further, they can serve as supervisory signals to encourage agents to interact with objects and explore the world. Finally, the introduction of language opens the door to using pre-trained language models in future work, given the recent rise of their use for planning for embodied agents [2]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.535, + 0.893, + 0.778 + ], + "angle": 0, + "content": "EXCALIBUR is the first benchmark that offers the following new avenues and challenges for Embodied AI research: (1) It encourages open-ended exploration. (2) Agents in EXCALIBUR have access to a rich interactive action space that covers navigation, arm-based manipulation, and grasping with different degrees of force. (3) The questions in this benchmark move beyond existence and counting. They probe the agent on its abilities to learn physical and visual attributes of the world. (4) Our task requires long-horizon planning and reasoning. Most embodied benchmarks today have maximum episode lengths of up to 250 steps. Our task has four phases that include an exploration phase of 2500 steps. (5) Our task also evaluates the ability of an agent to refine and improve the existing knowledge of its environment. This is an ability that humans commonly showcase in their everyday experiences." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.894, + 0.901 + ], + "angle": 0, + "content": "We present baselines using state-of-the-art Embodied AI neural models and learning methods. We also design a Virtual Reality interface to enable humans to navigate and interact with objects in ProcTHOR scenes in an immersive way. This allows for a more accurate human baseline measurement, which demonstrates that there remains substantial room for model improvement. Finally, in Sec. 5, we show that the failure patterns of models are distinct from" + }, + { + "type": "page_footnote", + "bbox": [ + 0.078, + 0.875, + 0.47, + 0.901 + ], + "angle": 0, + "content": "1 Exploratory Curious Agents with Language Induced Embodied World Understanding" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "14932" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.186, + 0.09, + 0.788, + 0.355 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.366, + 0.892, + 0.449 + ], + "angle": 0, + "content": "Figure 2. The action space of EXCALIBUR. The whole action space consists of two sets of actions: Navigation (left) and Manipulation (right). Navigation actions are used to move the agent (bottom left) and look at different angles (top left). Manipulation actions are used to move the arm (top right), grasp with force and open and close closets, drawers and fridges (which are implemented as high action which can be triggered when the gripper is close to the handles), and signal finishing the task (bottom right). All of the actions are discretized: angler motion are discretized into 15 degrees, linear motion are discretized into 0.05 meter for joints and 0.25 meter for base and force is discretized into 0.05 kilogram-force." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.457, + 0.471, + 0.579 + ], + "angle": 0, + "content": "those of humans. Humans are great at exploration, but fall short at memorization, while agents tend to succeed at answering questions that depend on memory but are poor explorers - even when trained with popular exploration rewards. Altogether, we find that EXCALIBUR serves as a powerful and flexible framework and environment for evaluating and building Exploratory Curious Agents with Language Induced Embodied World Understanding." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.601, + 0.208, + 0.617 + ], + "angle": 0, + "content": "2. EXCALIBUR" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.629, + 0.47, + 0.9 + ], + "angle": 0, + "content": "Consider the example depicted in Fig. 1: the embodied agent is spawned in the bedroom of a random house at a random position. It traverses the bedroom, living room, kitchen, and bathroom, opens closets, fridges, and drawers, and picks up various objects. After 2,500 steps, the agent is asked 20 questions and answers some questions correctly and some incorrectly, e.g. \"How many silver objects are heavier than the white egg in the kitchen?\" The agent then returns to the house and explores the scene again. This time it starts lifting silver objects in the room to estimate their weight. As the example reveals, EXCALIBUR encourages agents to openly explore their world in the first phase but also evaluates their ability to perform goal-directed exploration once the questions become known. Natural language inquiries are used to ascertain what the agent has learned about its environment. We now present details about the EXCALIBUR task, and contrast it to previous Embodied AI benchmarks in Sec. 6 and Tab. 3." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.457, + 0.577, + 0.47 + ], + "angle": 0, + "content": "2.1. Task." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.486, + 0.892, + 0.683 + ], + "angle": 0, + "content": "An EXCALIBUR task is defined as a triple \\(\\langle \\mathcal{H}, \\mathcal{Q}, \\mathcal{P} \\rangle\\), where a House consists of a floor plan and objects in it, a Question set is a list of English question-answer pairs, and a Position is a 2D location on the floor of \\(\\mathcal{H}\\) that is empty (i.e. at which the agent can be placed) along with an initial agent camera orientation. Each object in the house is defined by its type, colors, materials (full list of object types, colors, and materials is in Appendix B), meshes (3D shape of the objects), location, size (width, depth, height), and weight (under \\(5\\mathrm{kg}\\)). At the start of each episode, the floor plan, objects (including colors, materials, sizes, and weights), questions, and agent spawn position are randomly sampled with the distribution specified in Appendix C." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.689, + 0.893, + 0.901 + ], + "angle": 0, + "content": "Phases. The EXCALIBUR task consists of four phases: (I) exploration, (II) question answering, (III) reentering, and (IV) refined question answering. In both (I) and (III), the agent may navigate throughout the house and manipulate objects. One difference between (I) and (III) is that the time steps in (I) are limited to 2,500, while the steps in (III) \\( T_{3} \\) are unlimited but used to discount the accuracy improvement in Eq. 1. In (II) the agent is asked 20 questions. This brings up another notable difference between (I) and (III). In (I), an agent must perform open-ended exploration, learning about objects and their relationships. In (III), its exploration is conditioned on its experience in (I), the goal questions and its own answers in (II), and it attempts to improve its answers in (IV). We denote the accuracy in Phase (II) and" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.956 + ], + "angle": 0, + "content": "14933" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.182, + 0.089, + 0.49, + 0.386 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.493, + 0.09, + 0.637, + 0.385 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.638, + 0.091, + 0.792, + 0.385 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.395, + 0.895, + 0.452 + ], + "angle": 0, + "content": "Figure 3. Dataset construction procedure. We generate the dataset in four steps (each in a pane). (1) We consider the procedurally generated floor plans and houses generated with PROCTHOR. (2) We then randomize the sizes and weights of objects in the scene. (3) We then extract the scene graphs of objects and relations in the scenes. (4) Based on hand-crafted templates, we generate questions and filter out questions that can be answered without exploring the scenes." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.459, + 0.295, + 0.474 + ], + "angle": 0, + "content": "Phase (IV) as \\(\\mathrm{Acc}_{\\mathrm{exp}}\\) and \\(\\mathrm{Acc}_{\\mathrm{ref}}\\)" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.474, + 0.471, + 0.684 + ], + "angle": 0, + "content": "Agents. The breadth of embodied experience results from the versatility of human bodies. With this in mind, the agent used in EXCALIBUR is the MANIPULATHOR arm agent of Ehsani et al. [21]. This agent has a dexterous 6 DOF Kinova-inspired robotic arm, see Fig. 2. We extend their design by adding a force argument to grasping action. This is one step further towards more realistic manipulation and also empowers the agents to \"feel\" the weights of objects through interaction. Fig. 2 shows the available actions of the armed agent in Phase (I) and (III). The \"Done\" action signals that the agent wishes to end Phase (III), the number of time steps spent before which are counted as \\( T_{3} \\). At every timestep, the agent acts given egocentric RGB images (of size \\( 800 \\times 600 \\)) as its observation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.686, + 0.47, + 0.777 + ], + "angle": 0, + "content": "Evaluation. We wish to evaluate two facets of exploration: (1) \"how many questions can be answered with the knowledge acquired in Phase (I)?\", and (2) \"how efficient is the agent in refining its answers in Phase (IV)?\". To define a unified metric measuring both facets, we propose the following exploration score (ExQA):" + }, + { + "type": "equation", + "bbox": [ + 0.097, + 0.788, + 0.47, + 0.809 + ], + "angle": 0, + "content": "\\[\n\\operatorname {E x Q A} \\triangleq \\operatorname {A c c} _ {\\exp} + \\left(\\operatorname {A c c} _ {\\text {r e f}} - \\operatorname {A c c} _ {\\exp}\\right) \\exp (- k T _ {3}), \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.818, + 0.471, + 0.879 + ], + "angle": 0, + "content": "where we call \\( k > 0 \\) the energy coefficient. ExQA reduces to \\( \\mathrm{Acc}_{\\mathrm{ref}} \\) when \\( k = 0 \\) and reduces to \\( \\mathrm{Acc}_{\\mathrm{exp}} \\) as \\( k \\to \\infty \\). Our choice of \\( k \\) thus determines how we prioritize accuracy after exploration versus after answer refinement. We choose" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.459, + 0.892, + 0.504 + ], + "angle": 0, + "content": "a value for \\( k \\) that maximizes human performance, biasing models to uncover strategies of similar efficiency and efficacy as we see in human demonstrations." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.514, + 0.7, + 0.529 + ], + "angle": 0, + "content": "2.2. Dataset Construction" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.537, + 0.892, + 0.856 + ], + "angle": 0, + "content": "The EXCALIBUR dataset is built upon PROCTHOR-10k, a dataset of 10,000 procedurally generated home environments, each containing between 1-10 rooms [18]. For each PROCTHOR-10k home, we apply a variety of scene augmentations (e.g. randomizing object weight and sizes) and generate sets of challenging questions. We break our dataset generation process into four stages: randomization, scene graph generation, question generation, and filtering. We detail each stage below, see Fig. 3 for a visual overview. Randomization. The diversity across PROCTHOR-10k houses is very large: objects placements, floor plans, materials, ||are all randomized while respecting sensible constraints common across real homes. Despite this diversity, we found that, without applying additional scene augmentations, many questions of interest become either trivial or answerable via commonsense. For instance, the weights of many objects in AI2-THOR (and thus in PROCTHOR-10k) are set uniformly across object categories. This means that a question such as \"is the cup in the kitchen heavier than the bowl?\", may have a constant answer across all cups and bowls. Thus, without applying weight randomization," + }, + { + "type": "page_footnote", + "bbox": [ + 0.501, + 0.863, + 0.894, + 0.901 + ], + "angle": 0, + "content": "3Empirically, we find \\( k \\) which maximizes ExQA likelihood under a gaussian prior. The procedure for choosing an optimal value of \\( k \\) is described in App. F." + }, + { + "type": "page_footnote", + "bbox": [ + 0.078, + 0.887, + 0.438, + 0.901 + ], + "angle": 0, + "content": "2Force feedback mechanisms are common in physical manipulators." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "14934" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.258 + ], + "angle": 0, + "content": "the agent may answer accurately without any exploration or object interaction. In EXCALIBUR, we apply two types of supplemental randomization to PROCTHOR-10k: object weight and size randomization. In particular, within each house, we uniformly sample the weights of pickupable (i.e. excluding large objects that cannot be held by the agent, e.g. a fridge) objects to be between \\( 0.5 \\times \\) and \\( 1.5 \\times \\) their starting values. Similarly, the size of pickupable objects (i.e. their scale) is randomized to be with \\( 0.8 \\times \\) and \\( 1.0 \\times \\) of their starting values. Note that we only downscale objects as this prevents potential collisions between nearby objects." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.258, + 0.473, + 0.41 + ], + "angle": 0, + "content": "Scene Graph. Before moving to question generation, we first preprocess each house to produce a scene graph representation of the environment. This scene graph provides a compact summary of the objects in the house along with their relationships and attributes. In our formulation, rooms, objects, and agent are represented as nodes with edges between nodes representing their relationships. These relationships include, for example, CONTAINEDBY, ADJACENTTO, ONTOPOF. A full listing of object relationships and node attributes can be found in the appendix." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.41, + 0.473, + 0.593 + ], + "angle": 0, + "content": "Question Generation. To generate our question sets, we follow the process used to generate the single-image visual question answering (VQA) dataset CLEVR [31]. In particular, we represent questions using functional programs whose answer values can be found by evaluating these programs upon the above described scene graph. As for CLEVR, we design a collection of (11) question families, which can be composed and chained to generate questions. This question generation process may produce degenerate or tautological questions, we prune these using the depth-first approach employed when constructing CLEVR. Details of question generation procedure is in App. E." + }, + { + "type": "table", + "bbox": [ + 0.086, + 0.595, + 0.268, + 0.749 + ], + "angle": 0, + "content": "
Type%
QuestionYes-no78.8
Count12.3
Query8.9
RelationColor26.7
Material66.2
CONTAINEDBY8.2
ADJACENTTO39.5
ONTOPOF0.8
HEAVIERTHAN430.6
LARGER THAN18.9
" + }, + { + "type": "table_caption", + "bbox": [ + 0.084, + 0.759, + 0.262, + 0.772 + ], + "angle": 0, + "content": "Table 1. Dataset Distribution." + }, + { + "type": "text", + "bbox": [ + 0.299, + 0.592, + 0.47, + 0.788 + ], + "angle": 0, + "content": "Filtering. In order to create questions that are challenging and whose answers are not overly biased to certain answers, we use extensive question filtering to remove easy questions. In particular, for each candidate question \\( q \\), we compute the answer of \\( q \\) across all scenes, which produces a distribution" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.788, + 0.47, + 0.833 + ], + "angle": 0, + "content": "over answers. We filter questions to only include those whose answer distribution is sufficiently balanced. For more details see, App. D." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.834, + 0.47, + 0.864 + ], + "angle": 0, + "content": "The result of such a process is an underlying dataset with a range of difficult questions of 3 different types and 7 kinds" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.895, + 0.274 + ], + "angle": 0, + "content": "of physical properties and relations (Fig. 1) Different types of questions are evaluated in slightly different ways: Yes-no questions are evaluated by exact matching, count questions are answered correctly when the prediction is only different than the standard answer by \\(5\\%\\), and query questions match prediction and the standard answer order-agnostically. In this way, we use accuracy as an umbrella metric for all of the questions. There are four splits in EXCALIBUR: (1) a training set with 10k PROCTHOR scenes, (2) a validation and a test set with 1k PROCTHOR scenes each, and (3) another test set with 9 hand-crafted ARCHITECTHOR scenes5 for comparison between agents and humans." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.289, + 0.82, + 0.305 + ], + "angle": 0, + "content": "3. Human Baseline with VR Interface" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.315, + 0.892, + 0.527 + ], + "angle": 0, + "content": "One challenge of comparing human performance fairly with that of our agents is that our agents are extensively trained on houses from our dataset while human annotators, on the other hand, are only exposed to a small handful of training episodes. It is therefore important to create a realistic environment where real-life experience and knowledge can be easily transferred to the simulated environment. For this, we create a VR interface to EXCALIBUR and ask human annotators to complete tasks while virtually embodied as the agent. In our experiments, human participants used the Meta Quest 2 VR headset6 and were evaluated using the same metric as our agents. Concretely, to make the experience interactive and immersive, we ensured that our VR experience satisfied the following requirements." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.528, + 0.892, + 0.602 + ], + "angle": 0, + "content": "- Flexible Head Movement: The head movement of the human annotators is smoothly reflected as camera movement in the VR environment, so that the information-seeking behavior of the human annotators can be easily transferred to the simulated environment." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.604, + 0.892, + 0.725 + ], + "angle": 0, + "content": "- Intuitive Arm Movement: Human annotators should be able to intuitively manipulate the robotic, 6 DOF Knovalike, the arm of the MANIPULATHOR agent used in EX-CALIBUR. As the robotic arm has greater degrees of freedom than a human arm (ignoring human fingers) this means that special attention must be paid to ensure that humans need not worry about the rotation of joints of the arm, but only the position and orientation of the gripper." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.725, + 0.892, + 0.786 + ], + "angle": 0, + "content": "- Gripping With Force: We leveraged the pressure on the grip button of the Meta Quest 2 controller to map it to the grasp force in the environment so annotators can use different magnitudes of forces to grip objects." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.787, + 0.892, + 0.847 + ], + "angle": 0, + "content": "- Open/Close: We also facilitated the user to open and close various objects in the VR environment, to make the experience more immersive and allow the user to explore the house in greater depth." + }, + { + "type": "list", + "bbox": [ + 0.498, + 0.528, + 0.892, + 0.847 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.848, + 0.892, + 0.864 + ], + "angle": 0, + "content": "For more details on VR interface, training and evaluating" + }, + { + "type": "page_footnote", + "bbox": [ + 0.078, + 0.875, + 0.468, + 0.9 + ], + "angle": 0, + "content": "HEAVIERTHAN includes LIGHTERTHAN, and LARGERTHAN includes SMALLERTHAN, LONGERTHAN, and SHORTERTHAN" + }, + { + "type": "page_footnote", + "bbox": [ + 0.5, + 0.875, + 0.863, + 0.887 + ], + "angle": 0, + "content": "One ARCHITECTHOR scene is used for training human annotators." + }, + { + "type": "page_footnote", + "bbox": [ + 0.501, + 0.888, + 0.855, + 0.9 + ], + "angle": 0, + "content": "\\(^{6}\\)https://www.meta.com/quest/products/quest-2/" + }, + { + "type": "list", + "bbox": [ + 0.5, + 0.875, + 0.863, + 0.9 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "14935" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.078, + 0.092, + 0.284, + 0.107 + ], + "angle": 0, + "content": "human annotators, see App. A." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.117, + 0.39, + 0.135 + ], + "angle": 0, + "content": "4. Reinforcement Learning Baselines" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.143, + 0.473, + 0.49 + ], + "angle": 0, + "content": "EXCALIBUR requires a model to actively plan, explore the houses, manipulate objects, memorize its history, and answer questions. In this work, and as is common across modern embodied benchmarks, we train reinforcement learning models as our baselines. Recurrent neural networks (RNNs) are frequently used as generic models for encoding language instructions, historical observations, and actions, into belief states for embodied agents [18, 21, 32, 62-64]. Following this prior work, we use a GRU [13] to encode the history of observations seen and actions taken by the agent to produce, at every time step \\( t \\geq 0 \\), a vector belief state \\( b_{t} \\) corresponding to the output of the RNN at that timestep. We extend this practice by feeding the belief states as input to an actor-critic policy head as well as to a question answering module. To understand whether questions answering serves as a good stimulation for encouraging exploration, we consider three training signals: a (1) coverage-based reward, (2) QA reward, and (3) QA cross-entropy loss. Our goal in the following experiments is to show that modern Embodied AI models and training techniques can achieve some level of success on EXCALIBUR with the goal of inspiring future work to build upon these results." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.491, + 0.473, + 0.643 + ], + "angle": 0, + "content": "Actor-critic policy The belief state is fed into an MLP with one hidden layer, which we call the actor-head, and decoded into logits, one logit for each discrete action available to the agent (recall Sec. 2.1). By passing these logits through a softmax we produce the agent's policy (i.e. a distribution over agent actions). To enable training with PPO [52,63], we also must produce an estimate of the value of the agent's current state. To do this, we feed the belief state through another similar MLP, the critic-head, which returns a 1-dimensional output." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.644, + 0.473, + 0.794 + ], + "angle": 0, + "content": "Question answering To make full use of existing large, pretrained, language models, we follow [60] and propose to convert belief states into continuous prefix tokens using a prefix generator MLP with two hidden layers \\( f_{\\theta}^{\\text{prefix}} \\). These prefix tokens are prepended to with the question tokens and fed into the encoder of pre-trained T5 [49]. We then use the, pretrained, T5 decoder module to produce a (distribution over) natural-language answers to the given question. Note that the T5 model has its parameters frozen and so is not trained in our experiments." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.796, + 0.473, + 0.904 + ], + "angle": 0, + "content": "Featurizing agent observations We experiment with two different visual feature extractors for the agent's egocentric RGB observations: (1) a pre-trained CLIP ResNet50 model [32, 48] and (2) a MaskRCNN [29] model finetuned on our training scenes. Visual features and an embedding of the agent's last action are concatenated and passed as input to the above RNN. After Phase II, the agent additionally" + }, + { + "type": "table", + "bbox": [ + 0.503, + 0.089, + 0.895, + 0.196 + ], + "angle": 0, + "content": "
ProcTHOR Test SetArchitecTHOR Test Set
AccexpAccrefT3ExQAAccexpAccrefT3ExQA
Random41.741.7-41.739.139.1-39.1
Language53.553.5-53.549.249.2-49.2
QA58.560.2131.260.052.456.0159.155.7
Novelty54.256.599.656.449.954.5125.754.1
Novelty+QA58.763.1203.262.453.556.3211.755.9
Human w/o replay----63.687.1759.479.4
Human w/ replay----81.394.3782.190.1
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.206, + 0.895, + 0.235 + ], + "angle": 0, + "content": "Table 2. Human and baseline performance across two test sets. We bold best metric values among AI systems." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.262, + 0.894, + 0.307 + ], + "angle": 0, + "content": "conditions the question embeddings from the T5 encoder as input to the RNN, which is also concatenated to observation and question embeddings." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.308, + 0.894, + 0.355 + ], + "angle": 0, + "content": "Training Our training loss equals the unweighted sum of the standard PPO RL loss [52] and \\(\\mathcal{L}_{\\mathrm{QA}}\\), a cross-entropy loss for question answering defined as" + }, + { + "type": "equation", + "bbox": [ + 0.514, + 0.364, + 0.892, + 0.422 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\mathrm {Q A}} = \\sum_ {t = 1} ^ {T} \\sum_ {(q, a) \\in \\mathcal {Q}} - \\log p _ {\\mathrm {T} 5} (a \\mid [ f _ {\\theta} ^ {\\text {p r e f i x}} (h _ {t}), f ^ {\\text {e m b}} (q) ]), \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.422, + 0.892, + 0.481 + ], + "angle": 0, + "content": "where \\( p_{\\mathrm{T5}} \\) is the probability of answer \\( a \\) produced by a T5 encoder-decoder, and \\( f^{\\mathrm{emb}} \\) is the embedding layer of the T5 encoder, and \\( \\mathcal{Q} \\) is the set of question-answer pairs associated with an episode." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.482, + 0.894, + 0.544 + ], + "angle": 0, + "content": "Rewards We consider two kinds of rewards in this paper: (1) a QA reward and (2) a novelty-based reward. The QA reward is calculated by comparing the answers generated through beam search from T5 and the ground truth answers:" + }, + { + "type": "equation", + "bbox": [ + 0.505, + 0.566, + 0.892, + 0.618 + ], + "angle": 0, + "content": "\\[\nr _ {t} ^ {\\mathrm {Q A}} = \\frac {1}{| \\mathcal {Q} |} \\sum_ {(q, a) \\in \\mathcal {Q}} \\left(\\mathbb {I} (a = \\mathrm {T} 5 _ {t} (q)) - \\mathbb {I} (a = \\mathrm {T} 5 _ {t - 1} (q))\\right), \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.617, + 0.894, + 0.709 + ], + "angle": 0, + "content": "where \\(\\mathrm{T}5_{t}(q) = \\mathrm{T}5(f_{\\theta}^{\\mathrm{decoder}}(h_{t}),f^{\\mathrm{emb}}(q))\\) denotes the output of the T5 model when using beam search decoding. Note that \\(r_t^{\\mathrm{QA}}\\) can only be non-zero when the agent's answer to a question changes between time steps \\(t - 1\\) and \\(t\\). Our novelty reward encourages the agent to exhaustively navigate and observe novel objects, in particular, we let" + }, + { + "type": "equation", + "bbox": [ + 0.563, + 0.718, + 0.892, + 0.753 + ], + "angle": 0, + "content": "\\[\nr _ {t} ^ {\\text {n o v e l t y}} = \\frac {O _ {t} ^ {\\text {s e e n}} - O _ {t - 1} ^ {\\text {s e e n}}}{O _ {\\text {a l l}}} + \\frac {A _ {t} - A _ {t - 1}}{A _ {\\text {r e a c h a b l e}}}, \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.762, + 0.894, + 0.822 + ], + "angle": 0, + "content": "where \\( O_{t}^{\\mathrm{seen}} \\) denotes the number of objects seen till time step \\( t \\), \\( O_{\\mathrm{all}} \\) denotes number of objects in \\( \\mathcal{H} \\), \\( A_{t} \\) denotes the area covered by time step \\( t \\), and \\( A_{\\mathrm{reachable}} \\) denotes the total reachable area in \\( \\mathcal{H} \\)." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.83, + 0.887, + 0.848 + ], + "angle": 0, + "content": "5. EXCALIBUR Human and Agent Evaluation" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.856, + 0.894, + 0.901 + ], + "angle": 0, + "content": "To gain insight into the gap between humans' and state-of-the-art embodied AI models' performance on EXCALIBUR we first must train such embodied models. To this" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "14936" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.318 + ], + "angle": 0, + "content": "end, we train several variants of the reinforcement learning baseline described in Sec. 4 on the training split of EXCALIBUR. In particular, we train three variants denoted \\(QA\\), Novelty, and \\(Novelty + QA\\); as suggested by their names, the \\(QA\\) agent is only given the QA reward signal, the Novelty agent has access to the novelty reward, and the \\(Novelty + QA\\) is given the sum of both rewards at every timestep. For all of these agents, cross entropy loss is used for optimizing the prefix generator. Beyond these RL baselines, we also include non-interactive Random and Language baselines; the Random baseline simply chooses answers at random from among plausible answers when conditioned on the question type while the Language model is trained to answer questions given only question text, which helps indentifying artifacts in question generation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.319, + 0.473, + 0.44 + ], + "angle": 0, + "content": "To make cross-model and human-agent comparisons we evaluate our embodied models on two test sets: (1) the procedurally generally PROCTHOR-10k testing scenes and (2) the set of, human-designed, ARCHITECTHOR test houses [18]. We evaluate humans only in the ARCHITECTHOR houses as the ARCHITECTHOR test houses were meticulously crafted to closely imitate real-world houses and represent a smaller domain shift for human participants." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.44, + 0.473, + 0.562 + ], + "angle": 0, + "content": "The results of these evaluations can be found in Table 2. Among AI systems, we see that the Novelty \\(+QA\\) agent performs best across the \\(\\mathrm{Acc}_{\\mathrm{exp}}\\), \\(\\mathrm{Acc}_{\\mathrm{ref}}\\), and ExQA metrics with the \\(QA\\) model close behind. This suggests that the novelty reward may provide only marginal benefits and, indeed, the Novelty agent obtains results only slightly above those of the Language model which, at best, simply reproduces the biases in our question-answer pairs." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.563, + 0.473, + 0.804 + ], + "angle": 0, + "content": "For our human evaluations, we consider two experimental conditions Human w/o replay and Human w/ replay. In the Human w/ replay trials, unlike in Human w/o replay, humans are allowed to view a video of their behavior in Phase I and Phase III when answering questions in Phase II and IV, respectively. Hence participants in the Human w/ replay trials are relieved of the burden of needing to remember all of the details of their exploration. While humans outperform the AI systems in both experimental conditions, the gap between AI and human performance is far narrower (gap of \\(+10.1\\mathrm{Acc}_{\\mathrm{exp}}\\) for Human w/o replay v.s. a gap of \\(+27.8\\) for \\(\\mathrm{Acc}_{\\mathrm{exp}}\\) Human w/o replay). This suggests that memorization is a significant bottleneck for humans. Note that, in the Human w/ replay condition, humans achieve an extremely high \\(\\mathrm{Acc}_{\\mathrm{ref}}\\) value (94.3) showing clearly that EXCALIBUR is, in principle, solvable by intelligent systems." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.805, + 0.472, + 0.837 + ], + "angle": 0, + "content": "Further analysis of our results as well as descriptive metrics of agent exploration behavior can be found in App. H." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.845, + 0.22, + 0.86 + ], + "angle": 0, + "content": "6. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.472, + 0.903 + ], + "angle": 0, + "content": "The domain of embodied AI has seen an explosion of attention in recent years [17, 19]. Here, we review three" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.092, + 0.868, + 0.107 + ], + "angle": 0, + "content": "sub-areas of this community most relevant to this work." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.118, + 0.857, + 0.135 + ], + "angle": 0, + "content": "6.1. Exploration, Execution and Manipulation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.142, + 0.895, + 0.612 + ], + "angle": 0, + "content": "Tab. 3 summarizes recent embodied AI benchmarks and evaluation frameworks comparing our EXCALIBUR benchmark with those including those designed for question answering, instruction following, rearrangement, and visual navigation. We say that an embodied benchmark or framework requires: open-ended exploration if the agent must act before being given fully specified goal information, goal-driven execution if the agent must act after being given the task definition, and manipulation if the agent must directly interact with objects, either with a physically simulated arm (e.g., [21,36,58]) to complete its goal or with a higher-level abstraction (e.g., in [62], the agent picks up objects by specifying their semantic category). We can see that most benchmarks emphasize either exploration or execution and manipulation. Most similar to EXCALIBUR are the BEHAVIOR [57] and AI2-THOR Rearrangement [62] benchmarks. BEHAVIOR requires agents to complete activities, defined using predicate logic, using rich interaction and object manipulation but, unlike EXCALIBUR, does not emphasize open-ended exploration and experimentation. AI2-THOR rearrangement, on the other hand, includes an exploration component but this exploration requires only memorizing object states, unlike EXCALIBUR which rewards agents who directly interact with objects. In total, EXCALIBUR is the first benchmark that explicitly evaluates agents' understanding of the physical world after agents explore, and manipulate objects within, virtual homes. As argued previously, EXCALIBUR requires that agents understand scenes with their body, form a representation that can be used to answer symbolic questions, and apply the knowledge acquired from exploration to execution." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.621, + 0.682, + 0.637 + ], + "angle": 0, + "content": "6.2. Visual Exploration" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.644, + 0.895, + 0.903 + ], + "angle": 0, + "content": "The task of visual exploration in embodied and robotics contexts has a long history of study with a rich diversity in perspectives. This diversity exists, in part, as the meaning of \"exploration\" is ambiguous: is an agent successful in exploration if it visits many locations, if it interacts with many objects, or something else entirely? The excellent survey of Ramakrishnan, et al. [51] divides space of existing exploration strategies into four groups: curiosity (seeking unexpected states), novelty (seeking unseen states), coverage (looking to visual reveal large areas), and reconstruction (seeking states that aid in predicting other unseen states). Some recent works that have touched on these areas include, curiosity [38,42,46,54], novelty [8,9,20,43], coverage [11, 12, 64], and reconstruction [30, 33, 50]. Of course not all work falls cleanly into these categories, for instance Eysenbach et al. perform skill discovery (i.e. exploration) by maximizing information theoretic quantities [22] and" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "14937" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.217, + 0.089, + 0.753, + 0.317 + ], + "angle": 0, + "content": "
WorkExplorationExecutionManipulationHuman Perf.Language
QAEQA [15]NoYesNoNoQA
IQA [25]NoYesAbstractKeyboardQA
QA Probing [14]YesNoNoNoQA
EMQA [16]NoNoNoNoQA
Instr.RxR Habitat [34]NoYesNoKeyboardInstruction
ALFRED [56]NoYesAbstractKeyboardInstruction
TEACH [44]NoYesAbstractKeyboardDialog
Rear.AI2THOR [62]YesYesAbstractNoNo
Habitat [58]YesNoArmNoNo
Nav.PointNav [3]NoYesNoNoNo
ObjectNav [3]NoYesNoNoNo
ArmPointNav [21]NoYesArmNoNo
BEHAVIOR [57]NoYesArmImmersiveDescriptive
EXCALIBURYesYesArmImmersiveQA
" + }, + { + "type": "table_caption", + "bbox": [ + 0.227, + 0.327, + 0.741, + 0.341 + ], + "angle": 0, + "content": "Table 3. Comparison between Embodied AI agents and human evaluation frameworks." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.355, + 0.469, + 0.385 + ], + "angle": 0, + "content": "Chaplot et al. perform a type of heuristic semantic-goal-guided exploration using learned priors [10]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.386, + 0.469, + 0.536 + ], + "angle": 0, + "content": "We argue that question answering rewards act as highly versatile and symbolic training signal for embodied agents. While clearly a non-traditional exploration training signal, our work can be seen as a type of reconstruction-based exploration. While existing reconstruction-based exploration generally uses a pixel-based objective (e.g. ability to predict how an environment would look from an unseen camera location), our natural language queries require the agent the agent to \"reconstruct\" a general semantic understanding of the environment." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.546, + 0.35, + 0.563 + ], + "angle": 0, + "content": "6.3. Question Answering for Vision" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.569, + 0.47, + 0.794 + ], + "angle": 0, + "content": "The work of Agrawal et al. [1] introduced the task of large-scale free-form open-ended Visual Question Answering (VQA) where, given a static image and natural language question about the image, a model is expected to return a natural language answer to this question. This seminal work began a new subdomain of computer vision with hundreds of publications and dozens of related datasets, see [55] for a recent review. These VQA benchmarks probe model's ability to reason about, for example, common sense [68], spatial relationships [31], potential agent actions [37], and diverse world knowledge [53]. Fundamentally, VQA focuses on single-image-understanding while our work requires interaction-driven agent exploration of an entire environment; for instance, questions about an object's weight in our dataset are unanswerable without interaction." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.796, + 0.47, + 0.903 + ], + "angle": 0, + "content": "More recently, several video question answering datasets have been introduced, e.g. [23, 26, 28, 35, 65, 66]. Among these datasets, perhaps most related to our work, as it requires answering questions from an egocentric perspective, is the episodic memory task from the Ego4D benchmark suite [26]; in this a task a model must answer natural language questions about a video by returning the segment of" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.355, + 0.892, + 0.476 + ], + "angle": 0, + "content": "the video including the question's answer. While moving from single-images to videos requires utilizing long-term memory and building a holistic representation of the environment, the lack of agent-driven interaction in these tasks means that agent learning is constrained to the prefixed trajectories taken when filming the videos. This makes it challenging to train agents who run their own experiments and are able to flexibly correct their mistakes." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.478, + 0.892, + 0.599 + ], + "angle": 0, + "content": "The vision and language research community has produced a vast array of models for VQA ranging from the earliest vanilla architectures [1], to using explicit object detectors [4], to pre-training with transformers [39] to general purpose unified architectures [27, 40, 61]. In this work we use a T5 language decoder to answer questions that conditions on the belief state of the agent which forms a representation of its current and past observations." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.603, + 0.808, + 0.619 + ], + "angle": 0, + "content": "7. Conclusion and Future Directions" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.629, + 0.892, + 0.901 + ], + "angle": 0, + "content": "In this paper, we present a novel benchmark EXCALIBUR for encouraging and evaluating the exploration ability of embodied agents. We build strong baseline models trained with both question answering reward and novelty based exploration-encouraging reward. We compared them with human performance in immersive environment. Human's great exploration ability not only leads to much higher accuracy after exploration but also leads to faster answer finding in reentering phase. Putting it all together, EXCALIBUR is still a challenging task and improvements on this benchmark could be made in various directions, including but not limit to fine-grained semantic map building, adversarial question generation, better features from observation, and leveraging large language models. A successful agent on EXCALIBUR will lead to embodied agents with the ability to actively understanding environments in a symbolic way and being able to ground and articulate embodied concepts in language." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.946, + 0.519, + 0.956 + ], + "angle": 0, + "content": "14938" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.115, + 0.47, + 0.17 + ], + "angle": 0, + "content": "[1] Aishwarya Agrawal, Jiasen Lu, Stanislaw Antol, Margaret Mitchell, C. Lawrence Zitnick, Devi Parikh, and Dhruv Bartra. VQA: visual question answering - www.visualqa.org. Int. J. Comput. 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Episode in EXCALIBUR played by a human annotator. An episode is divided into four sequential phases: in Phase I, the agent explores the house for 2,500 steps (each action takes a step); in Phase II the agent needs to answer 20 questions (5 shown) about the explored environment; in Phase III the agent is given a second chance to reenter the house, now with knowledge of the questions; in Phase IV the agent answers the questions again. Performance is evaluated with the answer accuracy in Phases II&IV and the time spent in Phase III. The observation space is egocentric (see left and right panels). The action space includes navigation and manipulation actions (Fig. 2). + +# Abstract + +Experience precedes understanding. Humans constantly explore and learn about their environment out of curiosity, gather information, and update their models of the world. On the other hand, machines are either trained to learn passively from static and fixed datasets, or taught to complete specific goal-conditioned tasks. To encourage the development of exploratory interactive agents, we present the EXCALIBUR benchmark. EXCALIBUR allows agents to explore their environment for long durations and then query + +their understanding of the physical world via inquiries like: "is the small heavy red bowl made from glass?" or "is there a silver spoon heavier than the egg?". This design encourages agents to perform free-form home exploration without myopia induced by goal conditioning. Once the agents have answered a series of questions, they can renter the scene to refine their knowledge, update their beliefs, and improve their performance on the questions. Our experiments demonstrate the challenges posed by this dataset for the present-day state-of-the-art embodied systems and + +the headroom afforded to develop new innovative methods. Finally, we present a virtual reality interface that enables humans to seamlessly interact within the simulated world and use it to gather human performance measures. EXCALIBUR affords unique challenges in comparison to present-day benchmarks and represents the next frontier for embodied AI research. + +# 1. Introduction + +Humans are active learners, acquiring knowledge of the physical world through intentional experiments with their bodies and senses. Children as young as a few months old learn about objects and their environment through observation and interaction [6, 24]. This sensorimotor experience, as pointed out by Piaget [47], is critical in forming a fundamental understanding of reality. This is the cognitive motivation for the creation of EXCALIBUR. + +In contrast, machine learning models typically obtain knowledge by passively observing web-crawled, encyclopedic, or crowd-sourced static datasets [67]. This passive approach has clear limitations. For instance, grounding physical concepts like heavy, large, and long requires moving beyond passive observation. To weigh an object, humans will often try to use different forces to move it. To compare the sizes of objects, they move around and perceive the objects from different angles and distances. Although large pre-trained models have made progress in aligning with the grounded world [41, 45], they still lack an embodied understanding of physical concepts [59]. + +Todays popular active, embodied-learning benchmarks in the Embodied AI community focus on directed task completion. These include navigating to specified GPS coordinates [3], locating an object of a specified category [7], translating commands into low-level actions [5, 56], and inspecting a scene to answer a question about the presence or count of an object category [15, 25]. A more recent benchmark, Room Rearrangement [62] requires agents to explore the scene, but the focus there is on navigation, observation, and memorization. Progress on these benchmarks has been promising. We can now train agents that can comprehend goal instructions reasonably well and complete simple tasks, particularly navigation heavy tasks. None of these benchmarks, however, explicitly probe how these models have learned to represent their environments, nor do they encourage the type of free-form, undirected, experimental, exploration performed by humans. + +To encourage and evaluate the capacity of embodied agents to openly explore their environment and interact with objects within it, we present the EXCALIBUR benchmark. EXCALIBUR is built using large procedurally generated + +houses via ProcTHOR [18]. Each episode in EXCALIBUR consists of four phases as shown in Fig. 1. Phase I Exploration – The agent must navigate to and interact with objects in the environment. Importantly, the agent isn't seeded with a goal and must instead perform open-ended exploration. Interacting with objects takes place via physics-enabled arm manipulation. Phase II Question Answering – We probe the agent's understanding of the physical world through natural language inquiries. Our questions go beyond simple primitive queries, e.g. regarding object existence, and include physical attributes (e.g. masses and materials) and visual attributes (e.g. colors and shapes). Phase III Reentering – This is a goal-directed phase, since the agent must interact with the environment to refine its understanding of the world in response to questions asked in the previous stage. Phase IV Refined Question Answering – This phase repeats the inquiries made in Phase II to query if the agent was able to successfully acquire the required knowledge about its world after being provided the goal question set. + +Our use of question-answering in this benchmark which focuses on interaction and exploration has several benefits. Natural language inquiries allow us to probe the agent's understanding of the world. They also provide a clear and objective metric for EXCALIBUR. Further, they can serve as supervisory signals to encourage agents to interact with objects and explore the world. Finally, the introduction of language opens the door to using pre-trained language models in future work, given the recent rise of their use for planning for embodied agents [2]. + +EXCALIBUR is the first benchmark that offers the following new avenues and challenges for Embodied AI research: (1) It encourages open-ended exploration. (2) Agents in EXCALIBUR have access to a rich interactive action space that covers navigation, arm-based manipulation, and grasping with different degrees of force. (3) The questions in this benchmark move beyond existence and counting. They probe the agent on its abilities to learn physical and visual attributes of the world. (4) Our task requires long-horizon planning and reasoning. Most embodied benchmarks today have maximum episode lengths of up to 250 steps. Our task has four phases that include an exploration phase of 2500 steps. (5) Our task also evaluates the ability of an agent to refine and improve the existing knowledge of its environment. This is an ability that humans commonly showcase in their everyday experiences. + +We present baselines using state-of-the-art Embodied AI neural models and learning methods. We also design a Virtual Reality interface to enable humans to navigate and interact with objects in ProcTHOR scenes in an immersive way. This allows for a more accurate human baseline measurement, which demonstrates that there remains substantial room for model improvement. Finally, in Sec. 5, we show that the failure patterns of models are distinct from + +![](images/d90b346429fe0d257f4b204d53a6d030cd61c338b3341770d43f599bc08bd58f.jpg) +Figure 2. The action space of EXCALIBUR. The whole action space consists of two sets of actions: Navigation (left) and Manipulation (right). Navigation actions are used to move the agent (bottom left) and look at different angles (top left). Manipulation actions are used to move the arm (top right), grasp with force and open and close closets, drawers and fridges (which are implemented as high action which can be triggered when the gripper is close to the handles), and signal finishing the task (bottom right). All of the actions are discretized: angler motion are discretized into 15 degrees, linear motion are discretized into 0.05 meter for joints and 0.25 meter for base and force is discretized into 0.05 kilogram-force. + +those of humans. Humans are great at exploration, but fall short at memorization, while agents tend to succeed at answering questions that depend on memory but are poor explorers - even when trained with popular exploration rewards. Altogether, we find that EXCALIBUR serves as a powerful and flexible framework and environment for evaluating and building Exploratory Curious Agents with Language Induced Embodied World Understanding. + +# 2. EXCALIBUR + +Consider the example depicted in Fig. 1: the embodied agent is spawned in the bedroom of a random house at a random position. It traverses the bedroom, living room, kitchen, and bathroom, opens closets, fridges, and drawers, and picks up various objects. After 2,500 steps, the agent is asked 20 questions and answers some questions correctly and some incorrectly, e.g. "How many silver objects are heavier than the white egg in the kitchen?" The agent then returns to the house and explores the scene again. This time it starts lifting silver objects in the room to estimate their weight. As the example reveals, EXCALIBUR encourages agents to openly explore their world in the first phase but also evaluates their ability to perform goal-directed exploration once the questions become known. Natural language inquiries are used to ascertain what the agent has learned about its environment. We now present details about the EXCALIBUR task, and contrast it to previous Embodied AI benchmarks in Sec. 6 and Tab. 3. + +# 2.1. Task. + +An EXCALIBUR task is defined as a triple $\langle \mathcal{H}, \mathcal{Q}, \mathcal{P} \rangle$ , where a House consists of a floor plan and objects in it, a Question set is a list of English question-answer pairs, and a Position is a 2D location on the floor of $\mathcal{H}$ that is empty (i.e. at which the agent can be placed) along with an initial agent camera orientation. Each object in the house is defined by its type, colors, materials (full list of object types, colors, and materials is in Appendix B), meshes (3D shape of the objects), location, size (width, depth, height), and weight (under $5\mathrm{kg}$ ). At the start of each episode, the floor plan, objects (including colors, materials, sizes, and weights), questions, and agent spawn position are randomly sampled with the distribution specified in Appendix C. + +Phases. The EXCALIBUR task consists of four phases: (I) exploration, (II) question answering, (III) reentering, and (IV) refined question answering. In both (I) and (III), the agent may navigate throughout the house and manipulate objects. One difference between (I) and (III) is that the time steps in (I) are limited to 2,500, while the steps in (III) $T_{3}$ are unlimited but used to discount the accuracy improvement in Eq. 1. In (II) the agent is asked 20 questions. This brings up another notable difference between (I) and (III). In (I), an agent must perform open-ended exploration, learning about objects and their relationships. In (III), its exploration is conditioned on its experience in (I), the goal questions and its own answers in (II), and it attempts to improve its answers in (IV). We denote the accuracy in Phase (II) and + +![](images/bd29bcbce27ac5ded5628090190f9edcbc4017ede084b6182cd7583bf98ce0a1.jpg) +Figure 3. Dataset construction procedure. We generate the dataset in four steps (each in a pane). (1) We consider the procedurally generated floor plans and houses generated with PROCTHOR. (2) We then randomize the sizes and weights of objects in the scene. (3) We then extract the scene graphs of objects and relations in the scenes. (4) Based on hand-crafted templates, we generate questions and filter out questions that can be answered without exploring the scenes. + +![](images/e47e911233b19ef0e5117ee16c98e9f9d141e675569909c7afff80311ae2ee81.jpg) + +![](images/b41cd86b3ac957c11b30efa4c5987682581efbe879fcaca00b976ef5f429b0b5.jpg) + +Phase (IV) as $\mathrm{Acc}_{\mathrm{exp}}$ and $\mathrm{Acc}_{\mathrm{ref}}$ + +Agents. The breadth of embodied experience results from the versatility of human bodies. With this in mind, the agent used in EXCALIBUR is the MANIPULATHOR arm agent of Ehsani et al. [21]. This agent has a dexterous 6 DOF Kinova-inspired robotic arm, see Fig. 2. We extend their design by adding a force argument to grasping action. This is one step further towards more realistic manipulation and also empowers the agents to "feel" the weights of objects through interaction. Fig. 2 shows the available actions of the armed agent in Phase (I) and (III). The "Done" action signals that the agent wishes to end Phase (III), the number of time steps spent before which are counted as $T_{3}$ . At every timestep, the agent acts given egocentric RGB images (of size $800 \times 600$ ) as its observation. + +Evaluation. We wish to evaluate two facets of exploration: (1) "how many questions can be answered with the knowledge acquired in Phase (I)?", and (2) "how efficient is the agent in refining its answers in Phase (IV)?". To define a unified metric measuring both facets, we propose the following exploration score (ExQA): + +$$ +\operatorname {E x Q A} \triangleq \operatorname {A c c} _ {\exp} + \left(\operatorname {A c c} _ {\text {r e f}} - \operatorname {A c c} _ {\exp}\right) \exp (- k T _ {3}), \tag {1} +$$ + +where we call $k > 0$ the energy coefficient. ExQA reduces to $\mathrm{Acc}_{\mathrm{ref}}$ when $k = 0$ and reduces to $\mathrm{Acc}_{\mathrm{exp}}$ as $k \to \infty$ . Our choice of $k$ thus determines how we prioritize accuracy after exploration versus after answer refinement. We choose + +a value for $k$ that maximizes human performance, biasing models to uncover strategies of similar efficiency and efficacy as we see in human demonstrations. + +# 2.2. Dataset Construction + +The EXCALIBUR dataset is built upon PROCTHOR-10k, a dataset of 10,000 procedurally generated home environments, each containing between 1-10 rooms [18]. For each PROCTHOR-10k home, we apply a variety of scene augmentations (e.g. randomizing object weight and sizes) and generate sets of challenging questions. We break our dataset generation process into four stages: randomization, scene graph generation, question generation, and filtering. We detail each stage below, see Fig. 3 for a visual overview. Randomization. The diversity across PROCTHOR-10k houses is very large: objects placements, floor plans, materials, ||are all randomized while respecting sensible constraints common across real homes. Despite this diversity, we found that, without applying additional scene augmentations, many questions of interest become either trivial or answerable via commonsense. For instance, the weights of many objects in AI2-THOR (and thus in PROCTHOR-10k) are set uniformly across object categories. This means that a question such as "is the cup in the kitchen heavier than the bowl?", may have a constant answer across all cups and bowls. Thus, without applying weight randomization, + +the agent may answer accurately without any exploration or object interaction. In EXCALIBUR, we apply two types of supplemental randomization to PROCTHOR-10k: object weight and size randomization. In particular, within each house, we uniformly sample the weights of pickupable (i.e. excluding large objects that cannot be held by the agent, e.g. a fridge) objects to be between $0.5 \times$ and $1.5 \times$ their starting values. Similarly, the size of pickupable objects (i.e. their scale) is randomized to be with $0.8 \times$ and $1.0 \times$ of their starting values. Note that we only downscale objects as this prevents potential collisions between nearby objects. + +Scene Graph. Before moving to question generation, we first preprocess each house to produce a scene graph representation of the environment. This scene graph provides a compact summary of the objects in the house along with their relationships and attributes. In our formulation, rooms, objects, and agent are represented as nodes with edges between nodes representing their relationships. These relationships include, for example, CONTAINEDBY, ADJACENTTO, ONTOPOF. A full listing of object relationships and node attributes can be found in the appendix. + +Question Generation. To generate our question sets, we follow the process used to generate the single-image visual question answering (VQA) dataset CLEVR [31]. In particular, we represent questions using functional programs whose answer values can be found by evaluating these programs upon the above described scene graph. As for CLEVR, we design a collection of (11) question families, which can be composed and chained to generate questions. This question generation process may produce degenerate or tautological questions, we prune these using the depth-first approach employed when constructing CLEVR. Details of question generation procedure is in App. E. + +
Type%
QuestionYes-no78.8
Count12.3
Query8.9
RelationColor26.7
Material66.2
CONTAINEDBY8.2
ADJACENTTO39.5
ONTOPOF0.8
HEAVIERTHAN430.6
LARGER THAN18.9
+ +Table 1. Dataset Distribution. + +Filtering. In order to create questions that are challenging and whose answers are not overly biased to certain answers, we use extensive question filtering to remove easy questions. In particular, for each candidate question $q$ , we compute the answer of $q$ across all scenes, which produces a distribution + +over answers. We filter questions to only include those whose answer distribution is sufficiently balanced. For more details see, App. D. + +The result of such a process is an underlying dataset with a range of difficult questions of 3 different types and 7 kinds + +of physical properties and relations (Fig. 1) Different types of questions are evaluated in slightly different ways: Yes-no questions are evaluated by exact matching, count questions are answered correctly when the prediction is only different than the standard answer by $5\%$ , and query questions match prediction and the standard answer order-agnostically. In this way, we use accuracy as an umbrella metric for all of the questions. There are four splits in EXCALIBUR: (1) a training set with 10k PROCTHOR scenes, (2) a validation and a test set with 1k PROCTHOR scenes each, and (3) another test set with 9 hand-crafted ARCHITECTHOR scenes5 for comparison between agents and humans. + +# 3. Human Baseline with VR Interface + +One challenge of comparing human performance fairly with that of our agents is that our agents are extensively trained on houses from our dataset while human annotators, on the other hand, are only exposed to a small handful of training episodes. It is therefore important to create a realistic environment where real-life experience and knowledge can be easily transferred to the simulated environment. For this, we create a VR interface to EXCALIBUR and ask human annotators to complete tasks while virtually embodied as the agent. In our experiments, human participants used the Meta Quest 2 VR headset6 and were evaluated using the same metric as our agents. Concretely, to make the experience interactive and immersive, we ensured that our VR experience satisfied the following requirements. + +- Flexible Head Movement: The head movement of the human annotators is smoothly reflected as camera movement in the VR environment, so that the information-seeking behavior of the human annotators can be easily transferred to the simulated environment. +- Intuitive Arm Movement: Human annotators should be able to intuitively manipulate the robotic, 6 DOF Knovalike, the arm of the MANIPULATHOR agent used in EX-CALIBUR. As the robotic arm has greater degrees of freedom than a human arm (ignoring human fingers) this means that special attention must be paid to ensure that humans need not worry about the rotation of joints of the arm, but only the position and orientation of the gripper. +- Gripping With Force: We leveraged the pressure on the grip button of the Meta Quest 2 controller to map it to the grasp force in the environment so annotators can use different magnitudes of forces to grip objects. +- Open/Close: We also facilitated the user to open and close various objects in the VR environment, to make the experience more immersive and allow the user to explore the house in greater depth. + +For more details on VR interface, training and evaluating + +human annotators, see App. A. + +# 4. Reinforcement Learning Baselines + +EXCALIBUR requires a model to actively plan, explore the houses, manipulate objects, memorize its history, and answer questions. In this work, and as is common across modern embodied benchmarks, we train reinforcement learning models as our baselines. Recurrent neural networks (RNNs) are frequently used as generic models for encoding language instructions, historical observations, and actions, into belief states for embodied agents [18, 21, 32, 62-64]. Following this prior work, we use a GRU [13] to encode the history of observations seen and actions taken by the agent to produce, at every time step $t \geq 0$ , a vector belief state $b_{t}$ corresponding to the output of the RNN at that timestep. We extend this practice by feeding the belief states as input to an actor-critic policy head as well as to a question answering module. To understand whether questions answering serves as a good stimulation for encouraging exploration, we consider three training signals: a (1) coverage-based reward, (2) QA reward, and (3) QA cross-entropy loss. Our goal in the following experiments is to show that modern Embodied AI models and training techniques can achieve some level of success on EXCALIBUR with the goal of inspiring future work to build upon these results. + +Actor-critic policy The belief state is fed into an MLP with one hidden layer, which we call the actor-head, and decoded into logits, one logit for each discrete action available to the agent (recall Sec. 2.1). By passing these logits through a softmax we produce the agent's policy (i.e. a distribution over agent actions). To enable training with PPO [52,63], we also must produce an estimate of the value of the agent's current state. To do this, we feed the belief state through another similar MLP, the critic-head, which returns a 1-dimensional output. + +Question answering To make full use of existing large, pretrained, language models, we follow [60] and propose to convert belief states into continuous prefix tokens using a prefix generator MLP with two hidden layers $f_{\theta}^{\text{prefix}}$ . These prefix tokens are prepended to with the question tokens and fed into the encoder of pre-trained T5 [49]. We then use the, pretrained, T5 decoder module to produce a (distribution over) natural-language answers to the given question. Note that the T5 model has its parameters frozen and so is not trained in our experiments. + +Featurizing agent observations We experiment with two different visual feature extractors for the agent's egocentric RGB observations: (1) a pre-trained CLIP ResNet50 model [32, 48] and (2) a MaskRCNN [29] model finetuned on our training scenes. Visual features and an embedding of the agent's last action are concatenated and passed as input to the above RNN. After Phase II, the agent additionally + +
ProcTHOR Test SetArchitecTHOR Test Set
AccexpAccrefT3ExQAAccexpAccrefT3ExQA
Random41.741.7-41.739.139.1-39.1
Language53.553.5-53.549.249.2-49.2
QA58.560.2131.260.052.456.0159.155.7
Novelty54.256.599.656.449.954.5125.754.1
Novelty+QA58.763.1203.262.453.556.3211.755.9
Human w/o replay----63.687.1759.479.4
Human w/ replay----81.394.3782.190.1
+ +Table 2. Human and baseline performance across two test sets. We bold best metric values among AI systems. + +conditions the question embeddings from the T5 encoder as input to the RNN, which is also concatenated to observation and question embeddings. + +Training Our training loss equals the unweighted sum of the standard PPO RL loss [52] and $\mathcal{L}_{\mathrm{QA}}$ , a cross-entropy loss for question answering defined as + +$$ +\mathcal {L} _ {\mathrm {Q A}} = \sum_ {t = 1} ^ {T} \sum_ {(q, a) \in \mathcal {Q}} - \log p _ {\mathrm {T} 5} (a \mid [ f _ {\theta} ^ {\text {p r e f i x}} (h _ {t}), f ^ {\text {e m b}} (q) ]), \tag {2} +$$ + +where $p_{\mathrm{T5}}$ is the probability of answer $a$ produced by a T5 encoder-decoder, and $f^{\mathrm{emb}}$ is the embedding layer of the T5 encoder, and $\mathcal{Q}$ is the set of question-answer pairs associated with an episode. + +Rewards We consider two kinds of rewards in this paper: (1) a QA reward and (2) a novelty-based reward. The QA reward is calculated by comparing the answers generated through beam search from T5 and the ground truth answers: + +$$ +r _ {t} ^ {\mathrm {Q A}} = \frac {1}{| \mathcal {Q} |} \sum_ {(q, a) \in \mathcal {Q}} \left(\mathbb {I} (a = \mathrm {T} 5 _ {t} (q)) - \mathbb {I} (a = \mathrm {T} 5 _ {t - 1} (q))\right), \tag {3} +$$ + +where $\mathrm{T}5_{t}(q) = \mathrm{T}5(f_{\theta}^{\mathrm{decoder}}(h_{t}),f^{\mathrm{emb}}(q))$ denotes the output of the T5 model when using beam search decoding. Note that $r_t^{\mathrm{QA}}$ can only be non-zero when the agent's answer to a question changes between time steps $t - 1$ and $t$ . Our novelty reward encourages the agent to exhaustively navigate and observe novel objects, in particular, we let + +$$ +r _ {t} ^ {\text {n o v e l t y}} = \frac {O _ {t} ^ {\text {s e e n}} - O _ {t - 1} ^ {\text {s e e n}}}{O _ {\text {a l l}}} + \frac {A _ {t} - A _ {t - 1}}{A _ {\text {r e a c h a b l e}}}, \tag {4} +$$ + +where $O_{t}^{\mathrm{seen}}$ denotes the number of objects seen till time step $t$ , $O_{\mathrm{all}}$ denotes number of objects in $\mathcal{H}$ , $A_{t}$ denotes the area covered by time step $t$ , and $A_{\mathrm{reachable}}$ denotes the total reachable area in $\mathcal{H}$ . + +# 5. EXCALIBUR Human and Agent Evaluation + +To gain insight into the gap between humans' and state-of-the-art embodied AI models' performance on EXCALIBUR we first must train such embodied models. To this + +end, we train several variants of the reinforcement learning baseline described in Sec. 4 on the training split of EXCALIBUR. In particular, we train three variants denoted $QA$ , Novelty, and $Novelty + QA$ ; as suggested by their names, the $QA$ agent is only given the QA reward signal, the Novelty agent has access to the novelty reward, and the $Novelty + QA$ is given the sum of both rewards at every timestep. For all of these agents, cross entropy loss is used for optimizing the prefix generator. Beyond these RL baselines, we also include non-interactive Random and Language baselines; the Random baseline simply chooses answers at random from among plausible answers when conditioned on the question type while the Language model is trained to answer questions given only question text, which helps indentifying artifacts in question generation. + +To make cross-model and human-agent comparisons we evaluate our embodied models on two test sets: (1) the procedurally generally PROCTHOR-10k testing scenes and (2) the set of, human-designed, ARCHITECTHOR test houses [18]. We evaluate humans only in the ARCHITECTHOR houses as the ARCHITECTHOR test houses were meticulously crafted to closely imitate real-world houses and represent a smaller domain shift for human participants. + +The results of these evaluations can be found in Table 2. Among AI systems, we see that the Novelty $+QA$ agent performs best across the $\mathrm{Acc}_{\mathrm{exp}}$ , $\mathrm{Acc}_{\mathrm{ref}}$ , and ExQA metrics with the $QA$ model close behind. This suggests that the novelty reward may provide only marginal benefits and, indeed, the Novelty agent obtains results only slightly above those of the Language model which, at best, simply reproduces the biases in our question-answer pairs. + +For our human evaluations, we consider two experimental conditions Human w/o replay and Human w/ replay. In the Human w/ replay trials, unlike in Human w/o replay, humans are allowed to view a video of their behavior in Phase I and Phase III when answering questions in Phase II and IV, respectively. Hence participants in the Human w/ replay trials are relieved of the burden of needing to remember all of the details of their exploration. While humans outperform the AI systems in both experimental conditions, the gap between AI and human performance is far narrower (gap of $+10.1\mathrm{Acc}_{\mathrm{exp}}$ for Human w/o replay v.s. a gap of $+27.8$ for $\mathrm{Acc}_{\mathrm{exp}}$ Human w/o replay). This suggests that memorization is a significant bottleneck for humans. Note that, in the Human w/ replay condition, humans achieve an extremely high $\mathrm{Acc}_{\mathrm{ref}}$ value (94.3) showing clearly that EXCALIBUR is, in principle, solvable by intelligent systems. + +Further analysis of our results as well as descriptive metrics of agent exploration behavior can be found in App. H. + +# 6. Related Work + +The domain of embodied AI has seen an explosion of attention in recent years [17, 19]. Here, we review three + +sub-areas of this community most relevant to this work. + +# 6.1. Exploration, Execution and Manipulation + +Tab. 3 summarizes recent embodied AI benchmarks and evaluation frameworks comparing our EXCALIBUR benchmark with those including those designed for question answering, instruction following, rearrangement, and visual navigation. We say that an embodied benchmark or framework requires: open-ended exploration if the agent must act before being given fully specified goal information, goal-driven execution if the agent must act after being given the task definition, and manipulation if the agent must directly interact with objects, either with a physically simulated arm (e.g., [21,36,58]) to complete its goal or with a higher-level abstraction (e.g., in [62], the agent picks up objects by specifying their semantic category). We can see that most benchmarks emphasize either exploration or execution and manipulation. Most similar to EXCALIBUR are the BEHAVIOR [57] and AI2-THOR Rearrangement [62] benchmarks. BEHAVIOR requires agents to complete activities, defined using predicate logic, using rich interaction and object manipulation but, unlike EXCALIBUR, does not emphasize open-ended exploration and experimentation. AI2-THOR rearrangement, on the other hand, includes an exploration component but this exploration requires only memorizing object states, unlike EXCALIBUR which rewards agents who directly interact with objects. In total, EXCALIBUR is the first benchmark that explicitly evaluates agents' understanding of the physical world after agents explore, and manipulate objects within, virtual homes. As argued previously, EXCALIBUR requires that agents understand scenes with their body, form a representation that can be used to answer symbolic questions, and apply the knowledge acquired from exploration to execution. + +# 6.2. Visual Exploration + +The task of visual exploration in embodied and robotics contexts has a long history of study with a rich diversity in perspectives. This diversity exists, in part, as the meaning of "exploration" is ambiguous: is an agent successful in exploration if it visits many locations, if it interacts with many objects, or something else entirely? The excellent survey of Ramakrishnan, et al. [51] divides space of existing exploration strategies into four groups: curiosity (seeking unexpected states), novelty (seeking unseen states), coverage (looking to visual reveal large areas), and reconstruction (seeking states that aid in predicting other unseen states). Some recent works that have touched on these areas include, curiosity [38,42,46,54], novelty [8,9,20,43], coverage [11, 12, 64], and reconstruction [30, 33, 50]. Of course not all work falls cleanly into these categories, for instance Eysenbach et al. perform skill discovery (i.e. exploration) by maximizing information theoretic quantities [22] and + +
WorkExplorationExecutionManipulationHuman Perf.Language
QAEQA [15]NoYesNoNoQA
IQA [25]NoYesAbstractKeyboardQA
QA Probing [14]YesNoNoNoQA
EMQA [16]NoNoNoNoQA
Instr.RxR Habitat [34]NoYesNoKeyboardInstruction
ALFRED [56]NoYesAbstractKeyboardInstruction
TEACH [44]NoYesAbstractKeyboardDialog
Rear.AI2THOR [62]YesYesAbstractNoNo
Habitat [58]YesNoArmNoNo
Nav.PointNav [3]NoYesNoNoNo
ObjectNav [3]NoYesNoNoNo
ArmPointNav [21]NoYesArmNoNo
BEHAVIOR [57]NoYesArmImmersiveDescriptive
EXCALIBURYesYesArmImmersiveQA
+ +Table 3. Comparison between Embodied AI agents and human evaluation frameworks. + +Chaplot et al. perform a type of heuristic semantic-goal-guided exploration using learned priors [10]. + +We argue that question answering rewards act as highly versatile and symbolic training signal for embodied agents. While clearly a non-traditional exploration training signal, our work can be seen as a type of reconstruction-based exploration. While existing reconstruction-based exploration generally uses a pixel-based objective (e.g. ability to predict how an environment would look from an unseen camera location), our natural language queries require the agent the agent to "reconstruct" a general semantic understanding of the environment. + +# 6.3. Question Answering for Vision + +The work of Agrawal et al. [1] introduced the task of large-scale free-form open-ended Visual Question Answering (VQA) where, given a static image and natural language question about the image, a model is expected to return a natural language answer to this question. This seminal work began a new subdomain of computer vision with hundreds of publications and dozens of related datasets, see [55] for a recent review. These VQA benchmarks probe model's ability to reason about, for example, common sense [68], spatial relationships [31], potential agent actions [37], and diverse world knowledge [53]. Fundamentally, VQA focuses on single-image-understanding while our work requires interaction-driven agent exploration of an entire environment; for instance, questions about an object's weight in our dataset are unanswerable without interaction. + +More recently, several video question answering datasets have been introduced, e.g. [23, 26, 28, 35, 65, 66]. Among these datasets, perhaps most related to our work, as it requires answering questions from an egocentric perspective, is the episodic memory task from the Ego4D benchmark suite [26]; in this a task a model must answer natural language questions about a video by returning the segment of + +the video including the question's answer. While moving from single-images to videos requires utilizing long-term memory and building a holistic representation of the environment, the lack of agent-driven interaction in these tasks means that agent learning is constrained to the prefixed trajectories taken when filming the videos. This makes it challenging to train agents who run their own experiments and are able to flexibly correct their mistakes. + +The vision and language research community has produced a vast array of models for VQA ranging from the earliest vanilla architectures [1], to using explicit object detectors [4], to pre-training with transformers [39] to general purpose unified architectures [27, 40, 61]. In this work we use a T5 language decoder to answer questions that conditions on the belief state of the agent which forms a representation of its current and past observations. + +# 7. Conclusion and Future Directions + +In this paper, we present a novel benchmark EXCALIBUR for encouraging and evaluating the exploration ability of embodied agents. We build strong baseline models trained with both question answering reward and novelty based exploration-encouraging reward. We compared them with human performance in immersive environment. Human's great exploration ability not only leads to much higher accuracy after exploration but also leads to faster answer finding in reentering phase. Putting it all together, EXCALIBUR is still a challenging task and improvements on this benchmark could be made in various directions, including but not limit to fine-grained semantic map building, adversarial question generation, better features from observation, and leveraging large language models. A successful agent on EXCALIBUR will lead to embodied agents with the ability to actively understanding environments in a symbolic way and being able to ground and articulate embodied concepts in language. + +# References + +[1] Aishwarya Agrawal, Jiasen Lu, Stanislaw Antol, Margaret Mitchell, C. Lawrence Zitnick, Devi Parikh, and Dhruv Bartra. VQA: visual question answering - www.visualqa.org. Int. J. Comput. 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"Figure 1. Episode in EXCALIBUR played by a human annotator. An episode is divided into four sequential phases: in Phase I, the agent explores the house for 2,500 steps (each action takes a step); in Phase II the agent needs to answer 20 questions (5 shown) about the explored environment; in Phase III the agent is given a second chance to reenter the house, now with knowledge of the questions; in Phase IV the agent answers the questions again. Performance is evaluated with the answer accuracy in Phases II&IV and the time spent in Phase III. The observation space is egocentric (see left and right panels). The action space includes navigation and manipulation actions (Fig. 2)." + } + ] + } + ], + "index": 27, + "angle": 0, + "type": "image_caption" + } + ], + "index": 26 + }, + { + "bbox": [ + 143, + 582, + 192, + 594 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 582, + 192, + 594 + ], + "spans": [ + { + "bbox": [ + 143, + 582, + 192, + 594 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 28 + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "text", + "content": "Experience precedes understanding. Humans constantly explore and learn about their environment out of curiosity, gather information, and update their models of the world. On the other hand, machines are either trained to learn passively from static and fixed datasets, or taught to complete specific goal-conditioned tasks. To encourage the development of exploratory interactive agents, we present the EXCALIBUR benchmark. EXCALIBUR allows agents to explore their environment for long durations and then query" + } + ] + } + ], + "index": 29 + }, + { + "bbox": [ + 304, + 582, + 547, + 704 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 547, + 704 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 547, + 704 + ], + "type": "text", + "content": "their understanding of the physical world via inquiries like: \"is the small heavy red bowl made from glass?\" or \"is there a silver spoon heavier than the egg?\". This design encourages agents to perform free-form home exploration without myopia induced by goal conditioning. Once the agents have answered a series of questions, they can renter the scene to refine their knowledge, update their beliefs, and improve their performance on the questions. Our experiments demonstrate the challenges posed by this dataset for the present-day state-of-the-art embodied systems and" + } + ] + } + ], + "index": 30 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "type": "text", + "content": "14931" + } + ] + } + ], + "index": 31 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 156 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 156 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 156 + ], + "type": "text", + "content": "the headroom afforded to develop new innovative methods. Finally, we present a virtual reality interface that enables humans to seamlessly interact within the simulated world and use it to gather human performance measures. EXCALIBUR affords unique challenges in comparison to present-day benchmarks and represents the next frontier for embodied AI research." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 171, + 128, + 183 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 171, + 128, + 183 + ], + "spans": [ + { + "bbox": [ + 47, + 171, + 128, + 183 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 191, + 287, + 286 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 191, + 287, + 286 + ], + "spans": [ + { + "bbox": [ + 46, + 191, + 287, + 286 + ], + "type": "text", + "content": "Humans are active learners, acquiring knowledge of the physical world through intentional experiments with their bodies and senses. Children as young as a few months old learn about objects and their environment through observation and interaction [6, 24]. This sensorimotor experience, as pointed out by Piaget [47], is critical in forming a fundamental understanding of reality. This is the cognitive motivation for the creation of EXCALIBUR." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 288, + 287, + 430 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 288, + 287, + 430 + ], + "spans": [ + { + "bbox": [ + 46, + 288, + 287, + 430 + ], + "type": "text", + "content": "In contrast, machine learning models typically obtain knowledge by passively observing web-crawled, encyclopedic, or crowd-sourced static datasets [67]. This passive approach has clear limitations. For instance, grounding physical concepts like heavy, large, and long requires moving beyond passive observation. To weigh an object, humans will often try to use different forces to move it. To compare the sizes of objects, they move around and perceive the objects from different angles and distances. Although large pre-trained models have made progress in aligning with the grounded world [41, 45], they still lack an embodied understanding of physical concepts [59]." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 432, + 287, + 635 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 432, + 287, + 635 + ], + "spans": [ + { + "bbox": [ + 46, + 432, + 287, + 635 + ], + "type": "text", + "content": "Todays popular active, embodied-learning benchmarks in the Embodied AI community focus on directed task completion. These include navigating to specified GPS coordinates [3], locating an object of a specified category [7], translating commands into low-level actions [5, 56], and inspecting a scene to answer a question about the presence or count of an object category [15, 25]. A more recent benchmark, Room Rearrangement [62] requires agents to explore the scene, but the focus there is on navigation, observation, and memorization. Progress on these benchmarks has been promising. We can now train agents that can comprehend goal instructions reasonably well and complete simple tasks, particularly navigation heavy tasks. None of these benchmarks, however, explicitly probe how these models have learned to represent their environments, nor do they encourage the type of free-form, undirected, experimental, exploration performed by humans." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 635, + 287, + 684 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 635, + 287, + 684 + ], + "spans": [ + { + "bbox": [ + 47, + 635, + 287, + 684 + ], + "type": "text", + "content": "To encourage and evaluate the capacity of embodied agents to openly explore their environment and interact with objects within it, we present the EXCALIBUR benchmark. EXCALIBUR is built using large procedurally generated" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 306, + 72, + 545, + 300 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 72, + 545, + 300 + ], + "spans": [ + { + "bbox": [ + 306, + 72, + 545, + 300 + ], + "type": "text", + "content": "houses via ProcTHOR [18]. Each episode in EXCALIBUR consists of four phases as shown in Fig. 1. Phase I Exploration – The agent must navigate to and interact with objects in the environment. Importantly, the agent isn't seeded with a goal and must instead perform open-ended exploration. Interacting with objects takes place via physics-enabled arm manipulation. Phase II Question Answering – We probe the agent's understanding of the physical world through natural language inquiries. Our questions go beyond simple primitive queries, e.g. regarding object existence, and include physical attributes (e.g. masses and materials) and visual attributes (e.g. colors and shapes). Phase III Reentering – This is a goal-directed phase, since the agent must interact with the environment to refine its understanding of the world in response to questions asked in the previous stage. Phase IV Refined Question Answering – This phase repeats the inquiries made in Phase II to query if the agent was able to successfully acquire the required knowledge about its world after being provided the goal question set." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 301, + 546, + 422 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 301, + 546, + 422 + ], + "spans": [ + { + "bbox": [ + 304, + 301, + 546, + 422 + ], + "type": "text", + "content": "Our use of question-answering in this benchmark which focuses on interaction and exploration has several benefits. Natural language inquiries allow us to probe the agent's understanding of the world. They also provide a clear and objective metric for EXCALIBUR. Further, they can serve as supervisory signals to encourage agents to interact with objects and explore the world. Finally, the introduction of language opens the door to using pre-trained language models in future work, given the recent rise of their use for planning for embodied agents [2]." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 423, + 546, + 616 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 423, + 546, + 616 + ], + "spans": [ + { + "bbox": [ + 304, + 423, + 546, + 616 + ], + "type": "text", + "content": "EXCALIBUR is the first benchmark that offers the following new avenues and challenges for Embodied AI research: (1) It encourages open-ended exploration. (2) Agents in EXCALIBUR have access to a rich interactive action space that covers navigation, arm-based manipulation, and grasping with different degrees of force. (3) The questions in this benchmark move beyond existence and counting. They probe the agent on its abilities to learn physical and visual attributes of the world. (4) Our task requires long-horizon planning and reasoning. Most embodied benchmarks today have maximum episode lengths of up to 250 steps. Our task has four phases that include an exploration phase of 2500 steps. (5) Our task also evaluates the ability of an agent to refine and improve the existing knowledge of its environment. This is an ability that humans commonly showcase in their everyday experiences." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 617, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 547, + 713 + ], + "type": "text", + "content": "We present baselines using state-of-the-art Embodied AI neural models and learning methods. We also design a Virtual Reality interface to enable humans to navigate and interact with objects in ProcTHOR scenes in an immersive way. This allows for a more accurate human baseline measurement, which demonstrates that there remains substantial room for model improvement. Finally, in Sec. 5, we show that the failure patterns of models are distinct from" + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 47, + 693, + 287, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 693, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 693, + 287, + 713 + ], + "type": "text", + "content": "1 Exploratory Curious Agents with Language Induced Embodied World Understanding" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "14932" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 113, + 71, + 482, + 281 + ], + "blocks": [ + { + "bbox": [ + 113, + 71, + 482, + 281 + ], + "lines": [ + { + "bbox": [ + 113, + 71, + 482, + 281 + ], + "spans": [ + { + "bbox": [ + 113, + 71, + 482, + 281 + ], + "type": "image", + "image_path": "d90b346429fe0d257f4b204d53a6d030cd61c338b3341770d43f599bc08bd58f.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 289, + 545, + 355 + ], + "lines": [ + { + "bbox": [ + 46, + 289, + 545, + 355 + ], + "spans": [ + { + "bbox": [ + 46, + 289, + 545, + 355 + ], + "type": "text", + "content": "Figure 2. The action space of EXCALIBUR. The whole action space consists of two sets of actions: Navigation (left) and Manipulation (right). Navigation actions are used to move the agent (bottom left) and look at different angles (top left). Manipulation actions are used to move the arm (top right), grasp with force and open and close closets, drawers and fridges (which are implemented as high action which can be triggered when the gripper is close to the handles), and signal finishing the task (bottom right). All of the actions are discretized: angler motion are discretized into 15 degrees, linear motion are discretized into 0.05 meter for joints and 0.25 meter for base and force is discretized into 0.05 kilogram-force." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 361, + 288, + 458 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 361, + 288, + 458 + ], + "spans": [ + { + "bbox": [ + 46, + 361, + 288, + 458 + ], + "type": "text", + "content": "those of humans. Humans are great at exploration, but fall short at memorization, while agents tend to succeed at answering questions that depend on memory but are poor explorers - even when trained with popular exploration rewards. Altogether, we find that EXCALIBUR serves as a powerful and flexible framework and environment for evaluating and building Exploratory Curious Agents with Language Induced Embodied World Understanding." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 475, + 127, + 488 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 475, + 127, + 488 + ], + "spans": [ + { + "bbox": [ + 47, + 475, + 127, + 488 + ], + "type": "text", + "content": "2. EXCALIBUR" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 498, + 287, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 498, + 287, + 712 + ], + "spans": [ + { + "bbox": [ + 46, + 498, + 287, + 712 + ], + "type": "text", + "content": "Consider the example depicted in Fig. 1: the embodied agent is spawned in the bedroom of a random house at a random position. It traverses the bedroom, living room, kitchen, and bathroom, opens closets, fridges, and drawers, and picks up various objects. After 2,500 steps, the agent is asked 20 questions and answers some questions correctly and some incorrectly, e.g. \"How many silver objects are heavier than the white egg in the kitchen?\" The agent then returns to the house and explores the scene again. This time it starts lifting silver objects in the room to estimate their weight. As the example reveals, EXCALIBUR encourages agents to openly explore their world in the first phase but also evaluates their ability to perform goal-directed exploration once the questions become known. Natural language inquiries are used to ascertain what the agent has learned about its environment. We now present details about the EXCALIBUR task, and contrast it to previous Embodied AI benchmarks in Sec. 6 and Tab. 3." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 306, + 361, + 353, + 372 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 361, + 353, + 372 + ], + "spans": [ + { + "bbox": [ + 306, + 361, + 353, + 372 + ], + "type": "text", + "content": "2.1. Task." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 384, + 545, + 540 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 384, + 545, + 540 + ], + "spans": [ + { + "bbox": [ + 304, + 384, + 545, + 540 + ], + "type": "text", + "content": "An EXCALIBUR task is defined as a triple " + }, + { + "bbox": [ + 304, + 384, + 545, + 540 + ], + "type": "inline_equation", + "content": "\\langle \\mathcal{H}, \\mathcal{Q}, \\mathcal{P} \\rangle" + }, + { + "bbox": [ + 304, + 384, + 545, + 540 + ], + "type": "text", + "content": ", where a House consists of a floor plan and objects in it, a Question set is a list of English question-answer pairs, and a Position is a 2D location on the floor of " + }, + { + "bbox": [ + 304, + 384, + 545, + 540 + ], + "type": "inline_equation", + "content": "\\mathcal{H}" + }, + { + "bbox": [ + 304, + 384, + 545, + 540 + ], + "type": "text", + "content": " that is empty (i.e. at which the agent can be placed) along with an initial agent camera orientation. Each object in the house is defined by its type, colors, materials (full list of object types, colors, and materials is in Appendix B), meshes (3D shape of the objects), location, size (width, depth, height), and weight (under " + }, + { + "bbox": [ + 304, + 384, + 545, + 540 + ], + "type": "inline_equation", + "content": "5\\mathrm{kg}" + }, + { + "bbox": [ + 304, + 384, + 545, + 540 + ], + "type": "text", + "content": "). At the start of each episode, the floor plan, objects (including colors, materials, sizes, and weights), questions, and agent spawn position are randomly sampled with the distribution specified in Appendix C." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "text", + "content": "Phases. The EXCALIBUR task consists of four phases: (I) exploration, (II) question answering, (III) reentering, and (IV) refined question answering. In both (I) and (III), the agent may navigate throughout the house and manipulate objects. One difference between (I) and (III) is that the time steps in (I) are limited to 2,500, while the steps in (III) " + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "inline_equation", + "content": "T_{3}" + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "text", + "content": " are unlimited but used to discount the accuracy improvement in Eq. 1. In (II) the agent is asked 20 questions. This brings up another notable difference between (I) and (III). In (I), an agent must perform open-ended exploration, learning about objects and their relationships. In (III), its exploration is conditioned on its experience in (I), the goal questions and its own answers in (II), and it attempts to improve its answers in (IV). We denote the accuracy in Phase (II) and" + } + ] + } + ], + "index": 7 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "14933" + } + ] + } + ], + "index": 8 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 111, + 70, + 299, + 305 + ], + "blocks": [ + { + "bbox": [ + 111, + 70, + 299, + 305 + ], + "lines": [ + { + "bbox": [ + 111, + 70, + 299, + 305 + ], + "spans": [ + { + "bbox": [ + 111, + 70, + 299, + 305 + ], + "type": "image", + "image_path": "bd29bcbce27ac5ded5628090190f9edcbc4017ede084b6182cd7583bf98ce0a1.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 312, + 547, + 357 + ], + "lines": [ + { + "bbox": [ + 46, + 312, + 547, + 357 + ], + "spans": [ + { + "bbox": [ + 46, + 312, + 547, + 357 + ], + "type": "text", + "content": "Figure 3. Dataset construction procedure. We generate the dataset in four steps (each in a pane). (1) We consider the procedurally generated floor plans and houses generated with PROCTHOR. (2) We then randomize the sizes and weights of objects in the scene. (3) We then extract the scene graphs of objects and relations in the scenes. (4) Based on hand-crafted templates, we generate questions and filter out questions that can be answered without exploring the scenes." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 301, + 71, + 389, + 304 + ], + "blocks": [ + { + "bbox": [ + 301, + 71, + 389, + 304 + ], + "lines": [ + { + "bbox": [ + 301, + 71, + 389, + 304 + ], + "spans": [ + { + "bbox": [ + 301, + 71, + 389, + 304 + ], + "type": "image", + "image_path": "e47e911233b19ef0e5117ee16c98e9f9d141e675569909c7afff80311ae2ee81.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 390, + 72, + 484, + 304 + ], + "blocks": [ + { + "bbox": [ + 390, + 72, + 484, + 304 + ], + "lines": [ + { + "bbox": [ + 390, + 72, + 484, + 304 + ], + "spans": [ + { + "bbox": [ + 390, + 72, + 484, + 304 + ], + "type": "image", + "image_path": "b41cd86b3ac957c11b30efa4c5987682581efbe879fcaca00b976ef5f429b0b5.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 363, + 180, + 375 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 363, + 180, + 375 + ], + "spans": [ + { + "bbox": [ + 47, + 363, + 180, + 375 + ], + "type": "text", + "content": "Phase (IV) as " + }, + { + "bbox": [ + 47, + 363, + 180, + 375 + ], + "type": "inline_equation", + "content": "\\mathrm{Acc}_{\\mathrm{exp}}" + }, + { + "bbox": [ + 47, + 363, + 180, + 375 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 363, + 180, + 375 + ], + "type": "inline_equation", + "content": "\\mathrm{Acc}_{\\mathrm{ref}}" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 375, + 288, + 541 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 375, + 288, + 541 + ], + "spans": [ + { + "bbox": [ + 46, + 375, + 288, + 541 + ], + "type": "text", + "content": "Agents. The breadth of embodied experience results from the versatility of human bodies. With this in mind, the agent used in EXCALIBUR is the MANIPULATHOR arm agent of Ehsani et al. [21]. This agent has a dexterous 6 DOF Kinova-inspired robotic arm, see Fig. 2. We extend their design by adding a force argument to grasping action. This is one step further towards more realistic manipulation and also empowers the agents to \"feel\" the weights of objects through interaction. Fig. 2 shows the available actions of the armed agent in Phase (I) and (III). The \"Done\" action signals that the agent wishes to end Phase (III), the number of time steps spent before which are counted as " + }, + { + "bbox": [ + 46, + 375, + 288, + 541 + ], + "type": "inline_equation", + "content": "T_{3}" + }, + { + "bbox": [ + 46, + 375, + 288, + 541 + ], + "type": "text", + "content": ". At every timestep, the agent acts given egocentric RGB images (of size " + }, + { + "bbox": [ + 46, + 375, + 288, + 541 + ], + "type": "inline_equation", + "content": "800 \\times 600" + }, + { + "bbox": [ + 46, + 375, + 288, + 541 + ], + "type": "text", + "content": ") as its observation." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 543, + 287, + 615 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 543, + 287, + 615 + ], + "spans": [ + { + "bbox": [ + 46, + 543, + 287, + 615 + ], + "type": "text", + "content": "Evaluation. We wish to evaluate two facets of exploration: (1) \"how many questions can be answered with the knowledge acquired in Phase (I)?\", and (2) \"how efficient is the agent in refining its answers in Phase (IV)?\". To define a unified metric measuring both facets, we propose the following exploration score (ExQA):" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 59, + 624, + 287, + 640 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 624, + 287, + 640 + ], + "spans": [ + { + "bbox": [ + 59, + 624, + 287, + 640 + ], + "type": "interline_equation", + "content": "\\operatorname {E x Q A} \\triangleq \\operatorname {A c c} _ {\\exp} + \\left(\\operatorname {A c c} _ {\\text {r e f}} - \\operatorname {A c c} _ {\\exp}\\right) \\exp (- k T _ {3}), \\tag {1}", + "image_path": "3738c2f72910c0a49f0facca8ced697631f67243588063db80efa58a6f7e4ccd.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 647, + 288, + 696 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 647, + 288, + 696 + ], + "spans": [ + { + "bbox": [ + 46, + 647, + 288, + 696 + ], + "type": "text", + "content": "where we call " + }, + { + "bbox": [ + 46, + 647, + 288, + 696 + ], + "type": "inline_equation", + "content": "k > 0" + }, + { + "bbox": [ + 46, + 647, + 288, + 696 + ], + "type": "text", + "content": " the energy coefficient. ExQA reduces to " + }, + { + "bbox": [ + 46, + 647, + 288, + 696 + ], + "type": "inline_equation", + "content": "\\mathrm{Acc}_{\\mathrm{ref}}" + }, + { + "bbox": [ + 46, + 647, + 288, + 696 + ], + "type": "text", + "content": " when " + }, + { + "bbox": [ + 46, + 647, + 288, + 696 + ], + "type": "inline_equation", + "content": "k = 0" + }, + { + "bbox": [ + 46, + 647, + 288, + 696 + ], + "type": "text", + "content": " and reduces to " + }, + { + "bbox": [ + 46, + 647, + 288, + 696 + ], + "type": "inline_equation", + "content": "\\mathrm{Acc}_{\\mathrm{exp}}" + }, + { + "bbox": [ + 46, + 647, + 288, + 696 + ], + "type": "text", + "content": " as " + }, + { + "bbox": [ + 46, + 647, + 288, + 696 + ], + "type": "inline_equation", + "content": "k \\to \\infty" + }, + { + "bbox": [ + 46, + 647, + 288, + 696 + ], + "type": "text", + "content": ". Our choice of " + }, + { + "bbox": [ + 46, + 647, + 288, + 696 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 647, + 288, + 696 + ], + "type": "text", + "content": " thus determines how we prioritize accuracy after exploration versus after answer refinement. We choose" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 363, + 545, + 399 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 363, + 545, + 399 + ], + "spans": [ + { + "bbox": [ + 306, + 363, + 545, + 399 + ], + "type": "text", + "content": "a value for " + }, + { + "bbox": [ + 306, + 363, + 545, + 399 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 306, + 363, + 545, + 399 + ], + "type": "text", + "content": " that maximizes human performance, biasing models to uncover strategies of similar efficiency and efficacy as we see in human demonstrations." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 407, + 428, + 418 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 407, + 428, + 418 + ], + "spans": [ + { + "bbox": [ + 306, + 407, + 428, + 418 + ], + "type": "text", + "content": "2.2. Dataset Construction" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 425, + 545, + 677 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 425, + 545, + 677 + ], + "spans": [ + { + "bbox": [ + 304, + 425, + 545, + 677 + ], + "type": "text", + "content": "The EXCALIBUR dataset is built upon PROCTHOR-10k, a dataset of 10,000 procedurally generated home environments, each containing between 1-10 rooms [18]. For each PROCTHOR-10k home, we apply a variety of scene augmentations (e.g. randomizing object weight and sizes) and generate sets of challenging questions. We break our dataset generation process into four stages: randomization, scene graph generation, question generation, and filtering. We detail each stage below, see Fig. 3 for a visual overview. Randomization. The diversity across PROCTHOR-10k houses is very large: objects placements, floor plans, materials, ||are all randomized while respecting sensible constraints common across real homes. Despite this diversity, we found that, without applying additional scene augmentations, many questions of interest become either trivial or answerable via commonsense. For instance, the weights of many objects in AI2-THOR (and thus in PROCTHOR-10k) are set uniformly across object categories. This means that a question such as \"is the cup in the kitchen heavier than the bowl?\", may have a constant answer across all cups and bowls. Thus, without applying weight randomization," + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 306, + 683, + 547, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 683, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 306, + 683, + 547, + 713 + ], + "type": "text", + "content": "3Empirically, we find " + }, + { + "bbox": [ + 306, + 683, + 547, + 713 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 306, + 683, + 547, + 713 + ], + "type": "text", + "content": " which maximizes ExQA likelihood under a gaussian prior. The procedure for choosing an optimal value of " + }, + { + "bbox": [ + 306, + 683, + 547, + 713 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 306, + 683, + 547, + 713 + ], + "type": "text", + "content": " is described in App. F." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 47, + 702, + 268, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 702, + 268, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 702, + 268, + 713 + ], + "type": "text", + "content": "2Force feedback mechanisms are common in physical manipulators." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "14934" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "text", + "content": "the agent may answer accurately without any exploration or object interaction. In EXCALIBUR, we apply two types of supplemental randomization to PROCTHOR-10k: object weight and size randomization. In particular, within each house, we uniformly sample the weights of pickupable (i.e. excluding large objects that cannot be held by the agent, e.g. a fridge) objects to be between " + }, + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "inline_equation", + "content": "0.5 \\times" + }, + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "inline_equation", + "content": "1.5 \\times" + }, + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "text", + "content": " their starting values. Similarly, the size of pickupable objects (i.e. their scale) is randomized to be with " + }, + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "inline_equation", + "content": "0.8 \\times" + }, + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "inline_equation", + "content": "1.0 \\times" + }, + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "text", + "content": " of their starting values. Note that we only downscale objects as this prevents potential collisions between nearby objects." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 204, + 289, + 324 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 204, + 289, + 324 + ], + "spans": [ + { + "bbox": [ + 46, + 204, + 289, + 324 + ], + "type": "text", + "content": "Scene Graph. Before moving to question generation, we first preprocess each house to produce a scene graph representation of the environment. This scene graph provides a compact summary of the objects in the house along with their relationships and attributes. In our formulation, rooms, objects, and agent are represented as nodes with edges between nodes representing their relationships. These relationships include, for example, CONTAINEDBY, ADJACENTTO, ONTOPOF. A full listing of object relationships and node attributes can be found in the appendix." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 324, + 289, + 469 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 324, + 289, + 469 + ], + "spans": [ + { + "bbox": [ + 46, + 324, + 289, + 469 + ], + "type": "text", + "content": "Question Generation. To generate our question sets, we follow the process used to generate the single-image visual question answering (VQA) dataset CLEVR [31]. In particular, we represent questions using functional programs whose answer values can be found by evaluating these programs upon the above described scene graph. As for CLEVR, we design a collection of (11) question families, which can be composed and chained to generate questions. This question generation process may produce degenerate or tautological questions, we prune these using the depth-first approach employed when constructing CLEVR. Details of question generation procedure is in App. E." + } + ] + } + ], + "index": 2 + }, + { + "type": "table", + "bbox": [ + 52, + 471, + 164, + 593 + ], + "blocks": [ + { + "bbox": [ + 52, + 471, + 164, + 593 + ], + "lines": [ + { + "bbox": [ + 52, + 471, + 164, + 593 + ], + "spans": [ + { + "bbox": [ + 52, + 471, + 164, + 593 + ], + "type": "table", + "html": "
Type%
QuestionYes-no78.8
Count12.3
Query8.9
RelationColor26.7
Material66.2
CONTAINEDBY8.2
ADJACENTTO39.5
ONTOPOF0.8
HEAVIERTHAN430.6
LARGER THAN18.9
", + "image_path": "265ad915bea8f14fe3344ecd5a1e6f5184da9d37b5a61c6d7779b66ed178b98c.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 51, + 601, + 160, + 611 + ], + "lines": [ + { + "bbox": [ + 51, + 601, + 160, + 611 + ], + "spans": [ + { + "bbox": [ + 51, + 601, + 160, + 611 + ], + "type": "text", + "content": "Table 1. Dataset Distribution." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 182, + 468, + 287, + 624 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 182, + 468, + 287, + 624 + ], + "spans": [ + { + "bbox": [ + 182, + 468, + 287, + 624 + ], + "type": "text", + "content": "Filtering. In order to create questions that are challenging and whose answers are not overly biased to certain answers, we use extensive question filtering to remove easy questions. In particular, for each candidate question " + }, + { + "bbox": [ + 182, + 468, + 287, + 624 + ], + "type": "inline_equation", + "content": "q" + }, + { + "bbox": [ + 182, + 468, + 287, + 624 + ], + "type": "text", + "content": ", we compute the answer of " + }, + { + "bbox": [ + 182, + 468, + 287, + 624 + ], + "type": "inline_equation", + "content": "q" + }, + { + "bbox": [ + 182, + 468, + 287, + 624 + ], + "type": "text", + "content": " across all scenes, which produces a distribution" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 624, + 287, + 659 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 624, + 287, + 659 + ], + "spans": [ + { + "bbox": [ + 46, + 624, + 287, + 659 + ], + "type": "text", + "content": "over answers. We filter questions to only include those whose answer distribution is sufficiently balanced. For more details see, App. D." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 660, + 287, + 684 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 660, + 287, + 684 + ], + "spans": [ + { + "bbox": [ + 46, + 660, + 287, + 684 + ], + "type": "text", + "content": "The result of such a process is an underlying dataset with a range of difficult questions of 3 different types and 7 kinds" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 72, + 547, + 217 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 217 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 217 + ], + "type": "text", + "content": "of physical properties and relations (Fig. 1) Different types of questions are evaluated in slightly different ways: Yes-no questions are evaluated by exact matching, count questions are answered correctly when the prediction is only different than the standard answer by " + }, + { + "bbox": [ + 304, + 72, + 547, + 217 + ], + "type": "inline_equation", + "content": "5\\%" + }, + { + "bbox": [ + 304, + 72, + 547, + 217 + ], + "type": "text", + "content": ", and query questions match prediction and the standard answer order-agnostically. In this way, we use accuracy as an umbrella metric for all of the questions. There are four splits in EXCALIBUR: (1) a training set with 10k PROCTHOR scenes, (2) a validation and a test set with 1k PROCTHOR scenes each, and (3) another test set with 9 hand-crafted ARCHITECTHOR scenes5 for comparison between agents and humans." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 228, + 501, + 241 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 228, + 501, + 241 + ], + "spans": [ + { + "bbox": [ + 305, + 228, + 501, + 241 + ], + "type": "text", + "content": "3. Human Baseline with VR Interface" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 249, + 545, + 417 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 249, + 545, + 417 + ], + "spans": [ + { + "bbox": [ + 304, + 249, + 545, + 417 + ], + "type": "text", + "content": "One challenge of comparing human performance fairly with that of our agents is that our agents are extensively trained on houses from our dataset while human annotators, on the other hand, are only exposed to a small handful of training episodes. It is therefore important to create a realistic environment where real-life experience and knowledge can be easily transferred to the simulated environment. For this, we create a VR interface to EXCALIBUR and ask human annotators to complete tasks while virtually embodied as the agent. In our experiments, human participants used the Meta Quest 2 VR headset6 and were evaluated using the same metric as our agents. Concretely, to make the experience interactive and immersive, we ensured that our VR experience satisfied the following requirements." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 418, + 545, + 670 + ], + "type": "list", + "angle": 0, + "index": 15, + "blocks": [ + { + "bbox": [ + 304, + 418, + 545, + 476 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 418, + 545, + 476 + ], + "spans": [ + { + "bbox": [ + 304, + 418, + 545, + 476 + ], + "type": "text", + "content": "- Flexible Head Movement: The head movement of the human annotators is smoothly reflected as camera movement in the VR environment, so that the information-seeking behavior of the human annotators can be easily transferred to the simulated environment." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 478, + 545, + 574 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 478, + 545, + 574 + ], + "spans": [ + { + "bbox": [ + 304, + 478, + 545, + 574 + ], + "type": "text", + "content": "- Intuitive Arm Movement: Human annotators should be able to intuitively manipulate the robotic, 6 DOF Knovalike, the arm of the MANIPULATHOR agent used in EX-CALIBUR. As the robotic arm has greater degrees of freedom than a human arm (ignoring human fingers) this means that special attention must be paid to ensure that humans need not worry about the rotation of joints of the arm, but only the position and orientation of the gripper." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 574, + 545, + 622 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 574, + 545, + 622 + ], + "spans": [ + { + "bbox": [ + 304, + 574, + 545, + 622 + ], + "type": "text", + "content": "- Gripping With Force: We leveraged the pressure on the grip button of the Meta Quest 2 controller to map it to the grasp force in the environment so annotators can use different magnitudes of forces to grip objects." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 623, + 545, + 670 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 623, + 545, + 670 + ], + "spans": [ + { + "bbox": [ + 304, + 623, + 545, + 670 + ], + "type": "text", + "content": "- Open/Close: We also facilitated the user to open and close various objects in the VR environment, to make the experience more immersive and allow the user to explore the house in greater depth." + } + ] + } + ], + "index": 14 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 306, + 671, + 545, + 684 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 671, + 545, + 684 + ], + "spans": [ + { + "bbox": [ + 306, + 671, + 545, + 684 + ], + "type": "text", + "content": "For more details on VR interface, training and evaluating" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 47, + 693, + 286, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 693, + 286, + 712 + ], + "spans": [ + { + "bbox": [ + 47, + 693, + 286, + 712 + ], + "type": "text", + "content": "HEAVIERTHAN includes LIGHTERTHAN, and LARGERTHAN includes SMALLERTHAN, LONGERTHAN, and SHORTERTHAN" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 306, + 693, + 528, + 702 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 693, + 528, + 702 + ], + "spans": [ + { + "bbox": [ + 306, + 693, + 528, + 702 + ], + "type": "text", + "content": "One ARCHITECTHOR scene is used for training human annotators." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 306, + 703, + 523, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 703, + 523, + 712 + ], + "spans": [ + { + "bbox": [ + 306, + 703, + 523, + 712 + ], + "type": "inline_equation", + "content": "^{6}" + }, + { + "bbox": [ + 306, + 703, + 523, + 712 + ], + "type": "text", + "content": "https://www.meta.com/quest/products/quest-2/" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "14935" + } + ] + } + ], + "index": 21 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 173, + 84 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 173, + 84 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 173, + 84 + ], + "type": "text", + "content": "human annotators, see App. A." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 92, + 238, + 106 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 92, + 238, + 106 + ], + "spans": [ + { + "bbox": [ + 47, + 92, + 238, + 106 + ], + "type": "text", + "content": "4. Reinforcement Learning Baselines" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 113, + 289, + 388 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 113, + 289, + 388 + ], + "spans": [ + { + "bbox": [ + 46, + 113, + 289, + 388 + ], + "type": "text", + "content": "EXCALIBUR requires a model to actively plan, explore the houses, manipulate objects, memorize its history, and answer questions. In this work, and as is common across modern embodied benchmarks, we train reinforcement learning models as our baselines. Recurrent neural networks (RNNs) are frequently used as generic models for encoding language instructions, historical observations, and actions, into belief states for embodied agents [18, 21, 32, 62-64]. Following this prior work, we use a GRU [13] to encode the history of observations seen and actions taken by the agent to produce, at every time step " + }, + { + "bbox": [ + 46, + 113, + 289, + 388 + ], + "type": "inline_equation", + "content": "t \\geq 0" + }, + { + "bbox": [ + 46, + 113, + 289, + 388 + ], + "type": "text", + "content": ", a vector belief state " + }, + { + "bbox": [ + 46, + 113, + 289, + 388 + ], + "type": "inline_equation", + "content": "b_{t}" + }, + { + "bbox": [ + 46, + 113, + 289, + 388 + ], + "type": "text", + "content": " corresponding to the output of the RNN at that timestep. We extend this practice by feeding the belief states as input to an actor-critic policy head as well as to a question answering module. To understand whether questions answering serves as a good stimulation for encouraging exploration, we consider three training signals: a (1) coverage-based reward, (2) QA reward, and (3) QA cross-entropy loss. Our goal in the following experiments is to show that modern Embodied AI models and training techniques can achieve some level of success on EXCALIBUR with the goal of inspiring future work to build upon these results." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 388, + 289, + 509 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 388, + 289, + 509 + ], + "spans": [ + { + "bbox": [ + 46, + 388, + 289, + 509 + ], + "type": "text", + "content": "Actor-critic policy The belief state is fed into an MLP with one hidden layer, which we call the actor-head, and decoded into logits, one logit for each discrete action available to the agent (recall Sec. 2.1). By passing these logits through a softmax we produce the agent's policy (i.e. a distribution over agent actions). To enable training with PPO [52,63], we also must produce an estimate of the value of the agent's current state. To do this, we feed the belief state through another similar MLP, the critic-head, which returns a 1-dimensional output." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 510, + 289, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 510, + 289, + 628 + ], + "spans": [ + { + "bbox": [ + 46, + 510, + 289, + 628 + ], + "type": "text", + "content": "Question answering To make full use of existing large, pretrained, language models, we follow [60] and propose to convert belief states into continuous prefix tokens using a prefix generator MLP with two hidden layers " + }, + { + "bbox": [ + 46, + 510, + 289, + 628 + ], + "type": "inline_equation", + "content": "f_{\\theta}^{\\text{prefix}}" + }, + { + "bbox": [ + 46, + 510, + 289, + 628 + ], + "type": "text", + "content": ". These prefix tokens are prepended to with the question tokens and fed into the encoder of pre-trained T5 [49]. We then use the, pretrained, T5 decoder module to produce a (distribution over) natural-language answers to the given question. Note that the T5 model has its parameters frozen and so is not trained in our experiments." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 630, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 630, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 630, + 289, + 715 + ], + "type": "text", + "content": "Featurizing agent observations We experiment with two different visual feature extractors for the agent's egocentric RGB observations: (1) a pre-trained CLIP ResNet50 model [32, 48] and (2) a MaskRCNN [29] model finetuned on our training scenes. Visual features and an embedding of the agent's last action are concatenated and passed as input to the above RNN. After Phase II, the agent additionally" + } + ] + } + ], + "index": 5 + }, + { + "type": "table", + "bbox": [ + 307, + 70, + 547, + 155 + ], + "blocks": [ + { + "bbox": [ + 307, + 70, + 547, + 155 + ], + "lines": [ + { + "bbox": [ + 307, + 70, + 547, + 155 + ], + "spans": [ + { + "bbox": [ + 307, + 70, + 547, + 155 + ], + "type": "table", + "html": "
ProcTHOR Test SetArchitecTHOR Test Set
AccexpAccrefT3ExQAAccexpAccrefT3ExQA
Random41.741.7-41.739.139.1-39.1
Language53.553.5-53.549.249.2-49.2
QA58.560.2131.260.052.456.0159.155.7
Novelty54.256.599.656.449.954.5125.754.1
Novelty+QA58.763.1203.262.453.556.3211.755.9
Human w/o replay----63.687.1759.479.4
Human w/ replay----81.394.3782.190.1
", + "image_path": "2dcf3778f31c9ddf84b388a0c2be5e10928be388d56e00fb964e8cf6a5ecae7a.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "table_body" + } + ], + "index": 6 + }, + { + "bbox": [ + 305, + 163, + 547, + 186 + ], + "lines": [ + { + "bbox": [ + 305, + 163, + 547, + 186 + ], + "spans": [ + { + "bbox": [ + 305, + 163, + 547, + 186 + ], + "type": "text", + "content": "Table 2. Human and baseline performance across two test sets. We bold best metric values among AI systems." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 305, + 207, + 547, + 243 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 207, + 547, + 243 + ], + "spans": [ + { + "bbox": [ + 305, + 207, + 547, + 243 + ], + "type": "text", + "content": "conditions the question embeddings from the T5 encoder as input to the RNN, which is also concatenated to observation and question embeddings." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 243, + 547, + 281 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 243, + 547, + 281 + ], + "spans": [ + { + "bbox": [ + 305, + 243, + 547, + 281 + ], + "type": "text", + "content": "Training Our training loss equals the unweighted sum of the standard PPO RL loss [52] and " + }, + { + "bbox": [ + 305, + 243, + 547, + 281 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{QA}}" + }, + { + "bbox": [ + 305, + 243, + 547, + 281 + ], + "type": "text", + "content": ", a cross-entropy loss for question answering defined as" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 314, + 288, + 545, + 334 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 314, + 288, + 545, + 334 + ], + "spans": [ + { + "bbox": [ + 314, + 288, + 545, + 334 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\mathrm {Q A}} = \\sum_ {t = 1} ^ {T} \\sum_ {(q, a) \\in \\mathcal {Q}} - \\log p _ {\\mathrm {T} 5} (a \\mid [ f _ {\\theta} ^ {\\text {p r e f i x}} (h _ {t}), f ^ {\\text {e m b}} (q) ]), \\tag {2}", + "image_path": "b288e59dea7fdc519bbef6cfc8b09eb88af6eede07242e0646cbb617a3a5b23f.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 334, + 545, + 380 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 334, + 545, + 380 + ], + "spans": [ + { + "bbox": [ + 305, + 334, + 545, + 380 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 334, + 545, + 380 + ], + "type": "inline_equation", + "content": "p_{\\mathrm{T5}}" + }, + { + "bbox": [ + 305, + 334, + 545, + 380 + ], + "type": "text", + "content": " is the probability of answer " + }, + { + "bbox": [ + 305, + 334, + 545, + 380 + ], + "type": "inline_equation", + "content": "a" + }, + { + "bbox": [ + 305, + 334, + 545, + 380 + ], + "type": "text", + "content": " produced by a T5 encoder-decoder, and " + }, + { + "bbox": [ + 305, + 334, + 545, + 380 + ], + "type": "inline_equation", + "content": "f^{\\mathrm{emb}}" + }, + { + "bbox": [ + 305, + 334, + 545, + 380 + ], + "type": "text", + "content": " is the embedding layer of the T5 encoder, and " + }, + { + "bbox": [ + 305, + 334, + 545, + 380 + ], + "type": "inline_equation", + "content": "\\mathcal{Q}" + }, + { + "bbox": [ + 305, + 334, + 545, + 380 + ], + "type": "text", + "content": " is the set of question-answer pairs associated with an episode." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 381, + 547, + 430 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 381, + 547, + 430 + ], + "spans": [ + { + "bbox": [ + 305, + 381, + 547, + 430 + ], + "type": "text", + "content": "Rewards We consider two kinds of rewards in this paper: (1) a QA reward and (2) a novelty-based reward. The QA reward is calculated by comparing the answers generated through beam search from T5 and the ground truth answers:" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 309, + 448, + 545, + 489 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 309, + 448, + 545, + 489 + ], + "spans": [ + { + "bbox": [ + 309, + 448, + 545, + 489 + ], + "type": "interline_equation", + "content": "r _ {t} ^ {\\mathrm {Q A}} = \\frac {1}{| \\mathcal {Q} |} \\sum_ {(q, a) \\in \\mathcal {Q}} \\left(\\mathbb {I} (a = \\mathrm {T} 5 _ {t} (q)) - \\mathbb {I} (a = \\mathrm {T} 5 _ {t - 1} (q))\\right), \\tag {3}", + "image_path": "33232850c6bd21cb88a9139a920806bc4ba2a7d3e12e8a7aa1ae4b03015a5893.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 488, + 547, + 561 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 488, + 547, + 561 + ], + "spans": [ + { + "bbox": [ + 305, + 488, + 547, + 561 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 488, + 547, + 561 + ], + "type": "inline_equation", + "content": "\\mathrm{T}5_{t}(q) = \\mathrm{T}5(f_{\\theta}^{\\mathrm{decoder}}(h_{t}),f^{\\mathrm{emb}}(q))" + }, + { + "bbox": [ + 305, + 488, + 547, + 561 + ], + "type": "text", + "content": " denotes the output of the T5 model when using beam search decoding. Note that " + }, + { + "bbox": [ + 305, + 488, + 547, + 561 + ], + "type": "inline_equation", + "content": "r_t^{\\mathrm{QA}}" + }, + { + "bbox": [ + 305, + 488, + 547, + 561 + ], + "type": "text", + "content": " can only be non-zero when the agent's answer to a question changes between time steps " + }, + { + "bbox": [ + 305, + 488, + 547, + 561 + ], + "type": "inline_equation", + "content": "t - 1" + }, + { + "bbox": [ + 305, + 488, + 547, + 561 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 488, + 547, + 561 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 305, + 488, + 547, + 561 + ], + "type": "text", + "content": ". Our novelty reward encourages the agent to exhaustively navigate and observe novel objects, in particular, we let" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 344, + 568, + 545, + 596 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 344, + 568, + 545, + 596 + ], + "spans": [ + { + "bbox": [ + 344, + 568, + 545, + 596 + ], + "type": "interline_equation", + "content": "r _ {t} ^ {\\text {n o v e l t y}} = \\frac {O _ {t} ^ {\\text {s e e n}} - O _ {t - 1} ^ {\\text {s e e n}}}{O _ {\\text {a l l}}} + \\frac {A _ {t} - A _ {t - 1}}{A _ {\\text {r e a c h a b l e}}}, \\tag {4}", + "image_path": "28c978ae42931f88f7c9d4354c52b368285f6d63e23c9a29761301a9e7ae1cd2.jpg" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 603, + 547, + 651 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 603, + 547, + 651 + ], + "spans": [ + { + "bbox": [ + 305, + 603, + 547, + 651 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 603, + 547, + 651 + ], + "type": "inline_equation", + "content": "O_{t}^{\\mathrm{seen}}" + }, + { + "bbox": [ + 305, + 603, + 547, + 651 + ], + "type": "text", + "content": " denotes the number of objects seen till time step " + }, + { + "bbox": [ + 305, + 603, + 547, + 651 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 305, + 603, + 547, + 651 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 305, + 603, + 547, + 651 + ], + "type": "inline_equation", + "content": "O_{\\mathrm{all}}" + }, + { + "bbox": [ + 305, + 603, + 547, + 651 + ], + "type": "text", + "content": " denotes number of objects in " + }, + { + "bbox": [ + 305, + 603, + 547, + 651 + ], + "type": "inline_equation", + "content": "\\mathcal{H}" + }, + { + "bbox": [ + 305, + 603, + 547, + 651 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 305, + 603, + 547, + 651 + ], + "type": "inline_equation", + "content": "A_{t}" + }, + { + "bbox": [ + 305, + 603, + 547, + 651 + ], + "type": "text", + "content": " denotes the area covered by time step " + }, + { + "bbox": [ + 305, + 603, + 547, + 651 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 305, + 603, + 547, + 651 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 305, + 603, + 547, + 651 + ], + "type": "inline_equation", + "content": "A_{\\mathrm{reachable}}" + }, + { + "bbox": [ + 305, + 603, + 547, + 651 + ], + "type": "text", + "content": " denotes the total reachable area in " + }, + { + "bbox": [ + 305, + 603, + 547, + 651 + ], + "type": "inline_equation", + "content": "\\mathcal{H}" + }, + { + "bbox": [ + 305, + 603, + 547, + 651 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 305, + 657, + 542, + 671 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 657, + 542, + 671 + ], + "spans": [ + { + "bbox": [ + 305, + 657, + 542, + 671 + ], + "type": "text", + "content": "5. EXCALIBUR Human and Agent Evaluation" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 305, + 677, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 677, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 677, + 547, + 713 + ], + "type": "text", + "content": "To gain insight into the gap between humans' and state-of-the-art embodied AI models' performance on EXCALIBUR we first must train such embodied models. To this" + } + ] + } + ], + "index": 18 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "14936" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "text", + "content": "end, we train several variants of the reinforcement learning baseline described in Sec. 4 on the training split of EXCALIBUR. In particular, we train three variants denoted " + }, + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "inline_equation", + "content": "QA" + }, + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "text", + "content": ", Novelty, and " + }, + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "inline_equation", + "content": "Novelty + QA" + }, + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "text", + "content": "; as suggested by their names, the " + }, + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "inline_equation", + "content": "QA" + }, + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "text", + "content": " agent is only given the QA reward signal, the Novelty agent has access to the novelty reward, and the " + }, + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "inline_equation", + "content": "Novelty + QA" + }, + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "text", + "content": " is given the sum of both rewards at every timestep. For all of these agents, cross entropy loss is used for optimizing the prefix generator. Beyond these RL baselines, we also include non-interactive Random and Language baselines; the Random baseline simply chooses answers at random from among plausible answers when conditioned on the question type while the Language model is trained to answer questions given only question text, which helps indentifying artifacts in question generation." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 252, + 289, + 348 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 252, + 289, + 348 + ], + "spans": [ + { + "bbox": [ + 46, + 252, + 289, + 348 + ], + "type": "text", + "content": "To make cross-model and human-agent comparisons we evaluate our embodied models on two test sets: (1) the procedurally generally PROCTHOR-10k testing scenes and (2) the set of, human-designed, ARCHITECTHOR test houses [18]. We evaluate humans only in the ARCHITECTHOR houses as the ARCHITECTHOR test houses were meticulously crafted to closely imitate real-world houses and represent a smaller domain shift for human participants." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 348, + 289, + 445 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 348, + 289, + 445 + ], + "spans": [ + { + "bbox": [ + 46, + 348, + 289, + 445 + ], + "type": "text", + "content": "The results of these evaluations can be found in Table 2. Among AI systems, we see that the Novelty " + }, + { + "bbox": [ + 46, + 348, + 289, + 445 + ], + "type": "inline_equation", + "content": "+QA" + }, + { + "bbox": [ + 46, + 348, + 289, + 445 + ], + "type": "text", + "content": " agent performs best across the " + }, + { + "bbox": [ + 46, + 348, + 289, + 445 + ], + "type": "inline_equation", + "content": "\\mathrm{Acc}_{\\mathrm{exp}}" + }, + { + "bbox": [ + 46, + 348, + 289, + 445 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 348, + 289, + 445 + ], + "type": "inline_equation", + "content": "\\mathrm{Acc}_{\\mathrm{ref}}" + }, + { + "bbox": [ + 46, + 348, + 289, + 445 + ], + "type": "text", + "content": ", and ExQA metrics with the " + }, + { + "bbox": [ + 46, + 348, + 289, + 445 + ], + "type": "inline_equation", + "content": "QA" + }, + { + "bbox": [ + 46, + 348, + 289, + 445 + ], + "type": "text", + "content": " model close behind. This suggests that the novelty reward may provide only marginal benefits and, indeed, the Novelty agent obtains results only slightly above those of the Language model which, at best, simply reproduces the biases in our question-answer pairs." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 445, + 289, + 636 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 445, + 289, + 636 + ], + "spans": [ + { + "bbox": [ + 46, + 445, + 289, + 636 + ], + "type": "text", + "content": "For our human evaluations, we consider two experimental conditions Human w/o replay and Human w/ replay. In the Human w/ replay trials, unlike in Human w/o replay, humans are allowed to view a video of their behavior in Phase I and Phase III when answering questions in Phase II and IV, respectively. Hence participants in the Human w/ replay trials are relieved of the burden of needing to remember all of the details of their exploration. While humans outperform the AI systems in both experimental conditions, the gap between AI and human performance is far narrower (gap of " + }, + { + "bbox": [ + 46, + 445, + 289, + 636 + ], + "type": "inline_equation", + "content": "+10.1\\mathrm{Acc}_{\\mathrm{exp}}" + }, + { + "bbox": [ + 46, + 445, + 289, + 636 + ], + "type": "text", + "content": " for Human w/o replay v.s. a gap of " + }, + { + "bbox": [ + 46, + 445, + 289, + 636 + ], + "type": "inline_equation", + "content": "+27.8" + }, + { + "bbox": [ + 46, + 445, + 289, + 636 + ], + "type": "text", + "content": " for " + }, + { + "bbox": [ + 46, + 445, + 289, + 636 + ], + "type": "inline_equation", + "content": "\\mathrm{Acc}_{\\mathrm{exp}}" + }, + { + "bbox": [ + 46, + 445, + 289, + 636 + ], + "type": "text", + "content": " Human w/o replay). This suggests that memorization is a significant bottleneck for humans. Note that, in the Human w/ replay condition, humans achieve an extremely high " + }, + { + "bbox": [ + 46, + 445, + 289, + 636 + ], + "type": "inline_equation", + "content": "\\mathrm{Acc}_{\\mathrm{ref}}" + }, + { + "bbox": [ + 46, + 445, + 289, + 636 + ], + "type": "text", + "content": " value (94.3) showing clearly that EXCALIBUR is, in principle, solvable by intelligent systems." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 637, + 288, + 662 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 637, + 288, + 662 + ], + "spans": [ + { + "bbox": [ + 47, + 637, + 288, + 662 + ], + "type": "text", + "content": "Further analysis of our results as well as descriptive metrics of agent exploration behavior can be found in App. H." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 669, + 134, + 681 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 669, + 134, + 681 + ], + "spans": [ + { + "bbox": [ + 47, + 669, + 134, + 681 + ], + "type": "text", + "content": "6. Related Work" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 689, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 288, + 715 + ], + "type": "text", + "content": "The domain of embodied AI has seen an explosion of attention in recent years [17, 19]. Here, we review three" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 72, + 531, + 84 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 72, + 531, + 84 + ], + "spans": [ + { + "bbox": [ + 306, + 72, + 531, + 84 + ], + "type": "text", + "content": "sub-areas of this community most relevant to this work." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 93, + 524, + 106 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 93, + 524, + 106 + ], + "spans": [ + { + "bbox": [ + 306, + 93, + 524, + 106 + ], + "type": "text", + "content": "6.1. Exploration, Execution and Manipulation" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 112, + 547, + 484 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 112, + 547, + 484 + ], + "spans": [ + { + "bbox": [ + 304, + 112, + 547, + 484 + ], + "type": "text", + "content": "Tab. 3 summarizes recent embodied AI benchmarks and evaluation frameworks comparing our EXCALIBUR benchmark with those including those designed for question answering, instruction following, rearrangement, and visual navigation. We say that an embodied benchmark or framework requires: open-ended exploration if the agent must act before being given fully specified goal information, goal-driven execution if the agent must act after being given the task definition, and manipulation if the agent must directly interact with objects, either with a physically simulated arm (e.g., [21,36,58]) to complete its goal or with a higher-level abstraction (e.g., in [62], the agent picks up objects by specifying their semantic category). We can see that most benchmarks emphasize either exploration or execution and manipulation. Most similar to EXCALIBUR are the BEHAVIOR [57] and AI2-THOR Rearrangement [62] benchmarks. BEHAVIOR requires agents to complete activities, defined using predicate logic, using rich interaction and object manipulation but, unlike EXCALIBUR, does not emphasize open-ended exploration and experimentation. AI2-THOR rearrangement, on the other hand, includes an exploration component but this exploration requires only memorizing object states, unlike EXCALIBUR which rewards agents who directly interact with objects. In total, EXCALIBUR is the first benchmark that explicitly evaluates agents' understanding of the physical world after agents explore, and manipulate objects within, virtual homes. As argued previously, EXCALIBUR requires that agents understand scenes with their body, form a representation that can be used to answer symbolic questions, and apply the knowledge acquired from exploration to execution." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 491, + 417, + 504 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 491, + 417, + 504 + ], + "spans": [ + { + "bbox": [ + 306, + 491, + 417, + 504 + ], + "type": "text", + "content": "6.2. Visual Exploration" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 510, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 510, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 510, + 547, + 715 + ], + "type": "text", + "content": "The task of visual exploration in embodied and robotics contexts has a long history of study with a rich diversity in perspectives. This diversity exists, in part, as the meaning of \"exploration\" is ambiguous: is an agent successful in exploration if it visits many locations, if it interacts with many objects, or something else entirely? The excellent survey of Ramakrishnan, et al. [51] divides space of existing exploration strategies into four groups: curiosity (seeking unexpected states), novelty (seeking unseen states), coverage (looking to visual reveal large areas), and reconstruction (seeking states that aid in predicting other unseen states). Some recent works that have touched on these areas include, curiosity [38,42,46,54], novelty [8,9,20,43], coverage [11, 12, 64], and reconstruction [30, 33, 50]. Of course not all work falls cleanly into these categories, for instance Eysenbach et al. perform skill discovery (i.e. exploration) by maximizing information theoretic quantities [22] and" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "14937" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 132, + 70, + 460, + 251 + ], + "blocks": [ + { + "bbox": [ + 132, + 70, + 460, + 251 + ], + "lines": [ + { + "bbox": [ + 132, + 70, + 460, + 251 + ], + "spans": [ + { + "bbox": [ + 132, + 70, + 460, + 251 + ], + "type": "table", + "html": "
WorkExplorationExecutionManipulationHuman Perf.Language
QAEQA [15]NoYesNoNoQA
IQA [25]NoYesAbstractKeyboardQA
QA Probing [14]YesNoNoNoQA
EMQA [16]NoNoNoNoQA
Instr.RxR Habitat [34]NoYesNoKeyboardInstruction
ALFRED [56]NoYesAbstractKeyboardInstruction
TEACH [44]NoYesAbstractKeyboardDialog
Rear.AI2THOR [62]YesYesAbstractNoNo
Habitat [58]YesNoArmNoNo
Nav.PointNav [3]NoYesNoNoNo
ObjectNav [3]NoYesNoNoNo
ArmPointNav [21]NoYesArmNoNo
BEHAVIOR [57]NoYesArmImmersiveDescriptive
EXCALIBURYesYesArmImmersiveQA
", + "image_path": "937e5f653dcb93d0cf6012456b82a2f5215578b99478ce02d0f4c3548d0a6116.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 138, + 258, + 453, + 270 + ], + "lines": [ + { + "bbox": [ + 138, + 258, + 453, + 270 + ], + "spans": [ + { + "bbox": [ + 138, + 258, + 453, + 270 + ], + "type": "text", + "content": "Table 3. Comparison between Embodied AI agents and human evaluation frameworks." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 281, + 287, + 304 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 281, + 287, + 304 + ], + "spans": [ + { + "bbox": [ + 46, + 281, + 287, + 304 + ], + "type": "text", + "content": "Chaplot et al. perform a type of heuristic semantic-goal-guided exploration using learned priors [10]." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 305, + 287, + 424 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 305, + 287, + 424 + ], + "spans": [ + { + "bbox": [ + 46, + 305, + 287, + 424 + ], + "type": "text", + "content": "We argue that question answering rewards act as highly versatile and symbolic training signal for embodied agents. While clearly a non-traditional exploration training signal, our work can be seen as a type of reconstruction-based exploration. While existing reconstruction-based exploration generally uses a pixel-based objective (e.g. ability to predict how an environment would look from an unseen camera location), our natural language queries require the agent the agent to \"reconstruct\" a general semantic understanding of the environment." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 432, + 214, + 445 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 432, + 214, + 445 + ], + "spans": [ + { + "bbox": [ + 47, + 432, + 214, + 445 + ], + "type": "text", + "content": "6.3. Question Answering for Vision" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 450, + 287, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 450, + 287, + 628 + ], + "spans": [ + { + "bbox": [ + 46, + 450, + 287, + 628 + ], + "type": "text", + "content": "The work of Agrawal et al. [1] introduced the task of large-scale free-form open-ended Visual Question Answering (VQA) where, given a static image and natural language question about the image, a model is expected to return a natural language answer to this question. This seminal work began a new subdomain of computer vision with hundreds of publications and dozens of related datasets, see [55] for a recent review. These VQA benchmarks probe model's ability to reason about, for example, common sense [68], spatial relationships [31], potential agent actions [37], and diverse world knowledge [53]. Fundamentally, VQA focuses on single-image-understanding while our work requires interaction-driven agent exploration of an entire environment; for instance, questions about an object's weight in our dataset are unanswerable without interaction." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 630, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 630, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 630, + 287, + 715 + ], + "type": "text", + "content": "More recently, several video question answering datasets have been introduced, e.g. [23, 26, 28, 35, 65, 66]. Among these datasets, perhaps most related to our work, as it requires answering questions from an egocentric perspective, is the episodic memory task from the Ego4D benchmark suite [26]; in this a task a model must answer natural language questions about a video by returning the segment of" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 281, + 545, + 376 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 281, + 545, + 376 + ], + "spans": [ + { + "bbox": [ + 304, + 281, + 545, + 376 + ], + "type": "text", + "content": "the video including the question's answer. While moving from single-images to videos requires utilizing long-term memory and building a holistic representation of the environment, the lack of agent-driven interaction in these tasks means that agent learning is constrained to the prefixed trajectories taken when filming the videos. This makes it challenging to train agents who run their own experiments and are able to flexibly correct their mistakes." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 378, + 545, + 474 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 378, + 545, + 474 + ], + "spans": [ + { + "bbox": [ + 304, + 378, + 545, + 474 + ], + "type": "text", + "content": "The vision and language research community has produced a vast array of models for VQA ranging from the earliest vanilla architectures [1], to using explicit object detectors [4], to pre-training with transformers [39] to general purpose unified architectures [27, 40, 61]. In this work we use a T5 language decoder to answer questions that conditions on the belief state of the agent which forms a representation of its current and past observations." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 477, + 494, + 490 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 477, + 494, + 490 + ], + "spans": [ + { + "bbox": [ + 306, + 477, + 494, + 490 + ], + "type": "text", + "content": "7. Conclusion and Future Directions" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 498, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 498, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 498, + 545, + 713 + ], + "type": "text", + "content": "In this paper, we present a novel benchmark EXCALIBUR for encouraging and evaluating the exploration ability of embodied agents. We build strong baseline models trained with both question answering reward and novelty based exploration-encouraging reward. We compared them with human performance in immersive environment. Human's great exploration ability not only leads to much higher accuracy after exploration but also leads to faster answer finding in reentering phase. Putting it all together, EXCALIBUR is still a challenging task and improvements on this benchmark could be made in various directions, including but not limit to fine-grained semantic map building, adversarial question generation, better features from observation, and leveraging large language models. A successful agent on EXCALIBUR will lead to embodied agents with the ability to actively understanding environments in a symbolic way and being able to ground and articulate embodied concepts in language." + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "type": "text", + "content": "14938" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 288, + 714 + ], + "type": "list", + "angle": 0, + "index": 11, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 134 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 134 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 134 + ], + "type": "text", + "content": "[1] Aishwarya Agrawal, Jiasen Lu, Stanislaw Antol, Margaret Mitchell, C. 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Computer Vision Foundation / IEEE, 2019. 8" + } + ] + } + ], + "index": 7 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 749, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 749, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 749, + 318, + 757 + ], + "type": "text", + "content": "14942" + } + ] + } + ], + "index": 9 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 11 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/EXIF As Language_ Learning Cross-Modal Associations Between Images and Camera Metadata/dfc40f9a-79af-47cc-ac0b-335308cd3774_content_list.json b/2023/EXIF As Language_ Learning Cross-Modal Associations Between Images and Camera Metadata/dfc40f9a-79af-47cc-ac0b-335308cd3774_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..482415b071248b207f824b239cb2d29a66b202b2 --- /dev/null +++ b/2023/EXIF As Language_ Learning Cross-Modal Associations Between Images and Camera Metadata/dfc40f9a-79af-47cc-ac0b-335308cd3774_content_list.json @@ -0,0 +1,1492 @@ +[ + { + "type": "text", + "text": "EXIF as Language: Learning Cross-Modal Associations Between Images and Camera Metadata", + "text_level": 1, + "bbox": [ + 220, + 130, + 750, + 174 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Chenhao Zheng", + "bbox": [ + 240, + 203, + 370, + 220 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Ayush Shrivastava", + "bbox": [ + 410, + 204, + 557, + 220 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "University of Michigan", + "bbox": [ + 390, + 224, + 575, + 242 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "https://hellomuffin.github.io/exif-as-language", + "bbox": [ + 346, + 250, + 617, + 263 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/a17b7c3c4b4f0f67f778a72abc66db20f513e2004c75ecac18f19e931bb6803f.jpg", + "image_caption": [ + "(a) Multimodal image-metadata embeddings", + "(b) Detecting spliced images by spotting inconsistent patch embeddings" + ], + "image_footnote": [], + "bbox": [ + 84, + 301, + 377, + 429 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/4713c221b7d18df1b160a60779165e07f4da8bdff0c2ecd3db83817558b0813b.jpg", + "image_caption": [ + "Manipulated image", + "Figure 1. (a) We learn a joint embedding between image patches and the EXIF metadata that cameras automatically insert into image files. Our model treats this metadata as a language-like modality: we convert the EXIF tags to text, concatenate them together, and then processes the result with a transformer. (b) We apply our representation to tasks that require understanding camera properties. For example, we can detect image splicing \"zero shot\" (and without metadata at test time) by finding inconsistent embeddings within an image. We show a manipulated image that contains content from two source photos. Since these photos were captured with different cameras, the two regions have dissimilar embeddings (visualized by PCA). We localize the splice by clustering the image's patch embeddings." + ], + "image_footnote": [], + "bbox": [ + 395, + 301, + 498, + 409 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/ce5e683e3ffb1d50f9ccbac1261ad00d9adfadb0a4038ce02a7cd4e84148e92c.jpg", + "image_caption": [ + "Patch embeddings" + ], + "image_footnote": [], + "bbox": [ + 500, + 303, + 601, + 409 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/94dcea636089c61a35addffb94f89c231e103c1ef8b43f81b6147292fe09e32f.jpg", + "image_caption": [ + "Detected splice" + ], + "image_footnote": [], + "bbox": [ + 602, + 303, + 705, + 409 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/c7ab03850a618e033c7aa01b66bad2b73ca07cea7d06f61e485bb1ffd89bc8ef.jpg", + "image_caption": [ + "Ground truth" + ], + "image_footnote": [], + "bbox": [ + 707, + 303, + 810, + 409 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 564, + 313, + 579 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "We learn a visual representation that captures information about the camera that recorded a given photo. To do this, we train a multimodal embedding between image patches and the EXIF metadata that cameras automatically insert into image files. Our model represents this metadata by simply converting it to text and then processing it with a transformer. The features that we learn significantly outperform other self-supervised and supervised features on downstream image forensics and calibration tasks. In particular, we successfully localize spliced image regions \"zero shot\" by clustering the visual embeddings for all of the patches within an image.", + "bbox": [ + 75, + 597, + 470, + 779 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 814, + 207, + 829 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "A major goal of the computer vision community has been to use cross-modal associations to learn concepts that would be hard to glean from images alone [2]. A particular focus has been on learning high level semantics, such as", + "bbox": [ + 75, + 840, + 468, + 902 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "objects, from other rich sensory signals, like language and sound [58, 62]. By design, the representations learned by these approaches typically discard imaging properties, such as the type of camera that shot the photo, its lens, and the exposure settings, which are not useful for their cross-modal prediction tasks [17].", + "bbox": [ + 496, + 565, + 890, + 655 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "We argue that obtaining a complete understanding of an image requires both capabilities — for our models to perceive not only the semantic content of a scene, but also the properties of the camera that captured it. This type of low level understanding has proven crucial for a variety of tasks, from image forensics [33, 52, 80] to 3D reconstruction [34, 35], yet it has not typically been a focus of representation learning. It is also widely used in image generation, such as when users of text-to-image tools specify camera properties with phrases like \"DSLR photo\" [59, 63].", + "bbox": [ + 496, + 657, + 892, + 809 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "We propose to learn low level imaging properties from the abundantly available (but often neglected) camera metadata that is added to the image file at the moment of capture. This metadata is typically represented as dozens of Exchangeable Image File Format (EXIF) tags that describe the camera, its settings, and postprocessing operations that", + "bbox": [ + 496, + 811, + 893, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 810, + 44 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "6945", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "were applied to the image: e.g., Model: \"iPhone 4s\" or Focal Length: $35.0 \\, \\text{mm}$ . We train a joint embedding through contrastive learning that puts image patches into correspondence with camera metadata (Fig. 1a). Our model processes the metadata with a transformer [75] after converting it to a language-like representation. To do this conversion, we take advantage of the fact that EXIF tags are typically stored in a human-readable (and text-based) format. We convert each tag to text, and then concatenate them together. Our model thus closely resembles contrastive vision-and-language models, such as CLIP [62], but with EXIF-derived text in place of natural language.", + "bbox": [ + 75, + 90, + 472, + 271 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "We show that our model can successfully estimate camera properties solely from images, and that it provides a useful representation for a variety of image forensics and camera calibration tasks. Our approaches to these tasks do not require camera metadata at test time. Instead, camera properties are estimated implicitly from image content via multimodal embeddings.", + "bbox": [ + 75, + 272, + 472, + 377 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "We evaluate the learned feature of our model on two classification tasks that benefit from a low-level understanding of images: estimating an image's radial distortion parameter, and distinguishing real and manipulated images. We find that our features significantly outperform alternative supervised and self-supervised feature sets.", + "bbox": [ + 75, + 377, + 472, + 468 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "We also show that our embeddings can be used to detect image splicing \"zero shot\" (i.e., without labeled data), drawing on recent work [8, 33, 54] that detects inconsistencies in camera fingerprints hidden within image patches. Spliced images contain content from multiple real images, each potentially captured with a different camera and imaging pipeline. Thus, the embeddings that our model assigns to their patches, which convey camera properties, will have less consistency than those of real images. We detect manipulations by flagging images whose patch embeddings do not fit into a single, compact cluster. We also localize spliced regions by clustering the embeddings within an image (Fig. 1b).", + "bbox": [ + 75, + 468, + 472, + 664 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "We show through our experiments that:", + "bbox": [ + 76, + 665, + 339, + 679 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- Camera metadata provides supervision for self-supervised representation learning.", + "- Image patches can be successfully associated with camera metadata via joint embeddings.", + "- Image-metadata embeddings are a useful representation for forensics and camera understanding tasks.", + "- Image manipulations can be identified \"zero shot\" by identifying inconsistencies in patch embeddings." + ], + "bbox": [ + 76, + 681, + 468, + 801 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 76, + 814, + 218, + 830 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Estimating camera properties. Camera metadata has been used for a range of tasks in computer vision, such as for predicting focal length [1, 31, 50, 71], performing white balancing [20, 49] and estimating camera models", + "bbox": [ + 75, + 840, + 470, + 901 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/a311051a7dfabe693642f97231795852484542022e18ea42544732dab992e320.jpg", + "image_caption": [ + "Figure 2. Cross-modal image and camera metadata model. We use contrastive learning to associate each image patch with the EXIF metadata that was extracted from its image file. We represent the metadata as text, which is obtained by concatenating the EXIF tags together. We then process it using a transformer." + ], + "image_footnote": [], + "bbox": [ + 501, + 79, + 890, + 275 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "[7, 39, 74]. It has also been used as extra input for recognition tasks [19, 72]. Instead of estimating camera properties directly (which can be highly error prone [33]), our model predicts an embedding that distinguishes a patch's camera properties from that of other patches in the dataset.", + "bbox": [ + 496, + 364, + 893, + 441 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Image forensics. Early work used physically motivated cues, such as misaligned JPEG blocks [6, 21], color filter array mismatches [3,4,23,78], inconsistencies in noise patterns [37, 47, 48, 61], and compression or boundary artifacts [5, 26, 32, 82]. Other works use supervised learning methods [40, 53, 64, 66, 76, 77, 79-81, 85]. The challenge of collecting large datasets of fake images has led to alternative approaches, such as synthetic examples [53, 79, 81, 85]. Other work uses self-supervised learning, such as methods based on denoising [13], or that detect image manipulations by identifying image content that appears to come from different camera models [7, 9, 54]. Huh et al. [33] learned a patch similarity metric in two steps: they determined which EXIF tags are shared between the patches, then use these binary predictions as features for a second classifier that predicts whether two patches come from the same (or different) images. In contrast, we obtain a visual similarity metric that is well-suited to splice localization directly from our multimodal embeddings.", + "bbox": [ + 496, + 450, + 893, + 739 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Language supervision in vision. Recent works have obtained visual supervision from language. The formulation includes specific keyword prediction [55], bag-of-word multilabel classification [36], $n$ -gram classification [46] and autoregressive language models [16, 68, 84]. Recently, Radford et al. [62] obtained strong performance by training a contrastive model on a large image-and-language dataset. Our technical approach is similar, but uses text from camera metadata in lieu of image captions.", + "bbox": [ + 496, + 750, + 893, + 883 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Work in text-to-image synthesis often exploits camera", + "bbox": [ + 519, + 885, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "6946", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "information through prompting, such as by adding text like \"DSLR photo of...\" or \"Sigma 500mm f/5\" to prompts [59]. These methods, however, learn these camera associations through the (relatively rare) descriptions of cameras provided by humans, while ours learns them from an abundant and complementary learning signal, camera metadata.", + "bbox": [ + 75, + 90, + 468, + 181 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Associating Images with Camera Metadata", + "text_level": 1, + "bbox": [ + 76, + 194, + 464, + 212 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We desire a visual representation that captures low level imaging properties, such as the settings of the camera that were used to shoot the photo. We then apply this learned representation to downstream tasks that require an understanding of camera properties.", + "bbox": [ + 75, + 220, + 468, + 297 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Learning Cross-Modal Embeddings", + "text_level": 1, + "bbox": [ + 76, + 304, + 388, + 321 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We train a model to predict camera metadata from image content, thereby obtaining a representation that conveys camera properties. Following previous work in multimodal contrastive learning [62], we train a joint embedding between the two modalities, allowing our model to avoid the (error prone) task of directly predicting the attributes. Specifically, we want to jointly learn an image encoder and metadata encoder such that, given $N$ images and $N$ pieces of metadata information, the corresponding image–metadata pairs can be recognized by the model by maximizing embedding similarity. We use full-resolution image patches rather than resized images, so that our model can analyze low-level details that may be lost during down-sampling.", + "bbox": [ + 75, + 328, + 468, + 539 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Given a dataset of image patches and their corresponding camera metadata $\\{(\\mathbf{v}_i,\\mathbf{m}_i)\\}_{i = 1}^N$ , we learn visual and EXIF representations $f_{\\theta}(\\mathbf{v})$ and $g_{\\phi}(\\mathbf{m})$ by jointly training $f_{\\theta}$ and $g_{\\phi}$ using a contrastive loss [57]:", + "bbox": [ + 75, + 539, + 468, + 599 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {i} ^ {V, M} = - \\log \\frac {\\exp \\left(f _ {\\theta} \\left(\\mathbf {v} _ {i}\\right) \\cdot g _ {\\phi} \\left(\\mathbf {m} _ {i}\\right) / \\tau\\right)}{\\sum_ {j = 1} ^ {N} \\exp \\left(f _ {\\theta} \\left(\\mathbf {v} _ {i}\\right) \\cdot g _ {\\phi} \\left(\\mathbf {m} _ {j}\\right) / \\tau\\right)}, \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 104, + 609, + 468, + 647 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\tau$ is a small constant. Following prior work [62], we define an analogous loss $\\mathcal{L}^{M,V}$ that sums over visual (rather than metadata) examples in the denominator, and minimize a combined loss $\\mathcal{L} = \\mathcal{L}^{V,M} + \\mathcal{L}^{M,V}$ .", + "bbox": [ + 75, + 656, + 468, + 717 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. Representing the Camera Metadata", + "text_level": 1, + "bbox": [ + 76, + 726, + 387, + 742 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "This formulation raises a natural question: how should we represent the metadata? The metadata within photos is stored as a set of EXIF tags, each indicating a different image property as shown in Table 1. EXIF tags span a range of formats and data types, and the set of tags that are present in a given photo can be highly inconsistent. Previous works that predict camera properties from images typically extract attributes of interest from the EXIF tags, and cast them to an appropriate data format — e.g., extracting a scalar-valued focal length category. This tag-specific processing limits", + "bbox": [ + 75, + 750, + 470, + 902 + ], + "page_idx": 2 + }, + { + "type": "table", + "img_path": "images/c4530ad312368d19084577523fa295bd5e779986500bb366bb0277668132a3dc.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
EXIF tagExample values#values
Camera MakeCanon, NIKON Corporation, Apple312
Camera ModelNIKON D90, Canon EOS 73071
SoftwarePicasa, Adobe Photoshop, QuickTime1711
Exposure Time1/60 sec, 1/125 sec, 1/250 sec2062
Focal Length18.0 mm, 50.0 mm, 6.3 mm931
Aperture ValueF2.8, F4, F5.6, F3.5137
Scene Capture TypeLandscape, Portrait, Night Scene5
Exposure ProgramAperture priority, Manual control9
White Balance ModeAuto, Manual3
Thumbnail CompressionJPEG, Uncompressed3
Digital Zoom Ratio1, 1.5, 2, 1.249
ISO speed Ratings100, 400, 300460
Shutter Speed Value1/60 sec, 1/63 sec, 1/124 sec1161
Date/Time Digitized2013:03:28 04:20:4695932
", + "bbox": [ + 504, + 82, + 893, + 281 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Table 1. What information is contained within photo EXIF metadata? We list several of the most common EXIF tags, along with the common values and number of values they contain in the YFCC100M dataset [73].", + "bbox": [ + 498, + 286, + 890, + 342 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "the amount of metadata information that can be used as part of learning, and requires special-purpose architectures.", + "bbox": [ + 496, + 364, + 890, + 395 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We exploit the fact that EXIF tags are typically stored in a human-readable format and can be straightforwardly converted to text (Fig. 2). This allows us to directly process camera metadata using models from natural language processing — an approach that has successfully been applied to processing various text-like inputs other than language, such as math [45] and code [11]. Specifically, we create a long piece of text from a photo's metadata by converting each tag's name and value to strings, and concatenating them together. We separate each tag name and value with a colon and space, and separate different tags with a space. We evaluate a number of design decisions for this model in Sec. 4.4, such as the text format, choice of tags, and network architecture.", + "bbox": [ + 496, + 396, + 892, + 606 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.3. Application: Zero-shot Image Forensics", + "text_level": 1, + "bbox": [ + 498, + 619, + 841, + 635 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "After learning cross-modal representations from images and camera metadata, we can use them for downstream tasks that require an understanding of camera properties. One way to do this is by using the learned visual network features as a representation for classification tasks, following other work in self-supervised representation learning [12, 29]. We can also use our learned visual embeddings to perform \"zero shot\" image splice detection, by detecting inconsistencies in an input image's imputed camera properties.", + "bbox": [ + 496, + 643, + 890, + 792 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Spliced images are composed of regions from multiple real images. Since they are typically designed to fool humans, forensic models need to rely more on subtle (often non-semantic) cues to detect them. We got inspiration from Huh et al. [33], which predicts whether two image patches share the same camera properties. If two patches are predicted to have very different camera properties, then this", + "bbox": [ + 496, + 795, + 890, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "6947", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/c45b0d3dfa2aef94de38260ae828c1ac3341bd2dd57bd75b825da4a493857113.jpg", + "image_caption": [ + "Figure 3. Zero shot splice localization. Given a spliced image (left), we compute our cross-modal embeddings for each image patch, which we visualize here using projections onto the top 3 principal components. We then compute the affinity matrix by taking dot product for every pair of patches. We localize the spliced region by clustering these embedding vectors." + ], + "image_footnote": [], + "bbox": [ + 80, + 74, + 883, + 256 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "provides evidence that they come from different images. In our work, we can naturally obtain this patch similarity by computing the dot product between two patches' embeddings, since they have been trained to convey camera properties. We note that, unlike Huh et al. [33], we do not train a second, special-purpose classifier for this task, nor do we use augmentation to provide synthetic training examples (e.g., by applying different types of compression to the patches).", + "bbox": [ + 75, + 316, + 468, + 450 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "To determine whether an image is likely to contain a splice, we first compute an affinity matrix $A_{ij} = f_{\\theta}(\\mathbf{v}_i) \\cdot f_{\\theta}(\\mathbf{v}_j)$ whose entries are the dot product between patches' normalized embedding vectors. We score an image $\\mathbf{v}$ using the sum of the exponentiated dot products between embeddings, $\\phi (\\mathbf{v}) = \\sum_{i,j}\\exp (A_{ij} / \\tau)$ . This score indicates the likelihood that the image is unmodified, since high dot products indicate high similarity in imputed camera properties. To localize the spliced image regions within an image, we aggregate the similarity scores in $A_{ij}$ by clustering the rows using mean shift, following [33]. This results in a similarity map indicating the likelihood that each patch was extracted from the largest source photo that was used to create the composite. Alternatively, we can visualize the spliced region by performing spectral clustering via normalized cuts [33, 69], using $A_{ij}$ as an affinity matrix between patches. We visualize this approach in Fig. 3.", + "bbox": [ + 75, + 452, + 468, + 710 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4. Results", + "text_level": 1, + "bbox": [ + 76, + 728, + 161, + 744 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4.1. Implementation", + "text_level": 1, + "bbox": [ + 76, + 753, + 235, + 771 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Architecture. We use ResNet-50 pretrained on ImageNet as our image encoder. We found that the text encoder in models trained on captioning, such as CLIP [62], were not well-suited to our task, since they place low limits on the number of tokens. For the EXIF text encoder, we use DistilBERT [67] pretrained on Wikipedia and the Toronto Book Corpus [86]. We compute the feature representation of the EXIF as the activations for the end-of-sentence token from", + "bbox": [ + 75, + 779, + 468, + 898 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "the last layer which is layer normalized and then linearly projected into multi-modal embedding space.", + "bbox": [ + 498, + 316, + 890, + 345 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Training. To train our model, we use 1.5M full-resolution images and EXIF pairs from a random subset of YFCC100M [73]. We discard images that have less than 10 of the EXIF tags. Because many images only have a small number of EXIF tags available, we only use tags that are present in more than half of these images. This results in 44 EXIF tags (see supplementary for the complete list). In contrast to other work [33], we do not rebalance the images to increase the rate of rare tags. During training, we randomly crop $124 \\times 124$ patches from high-resolution images. We use the AdamW optimizer [38] with a learning rate of $10^{-4}$ , weight decay of $10^{-3}$ , and mixed precision training. We use a cosine annealing learning rate schedule [51]. The batch size is set to 1024, and we train our model for 50 epochs.", + "bbox": [ + 496, + 356, + 892, + 568 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Other model variations. To study the importance of metadata supervision on the learned representation, we train a similar model that performs contrastive learning but does not use metadata. The model resembles image-image contrastive learning [12,29,33,87], which has been shown to be highly effective for representation learning, and which may learn low-level camera information [17]. Different from typical contrastive learning approaches, we use strict cropping augmentation so that the views for our model (Eq. 1) come from different crops of the same image, to encourage it to learn low-level image features. We call this model CropCLR. Additionally, we evaluate a number of ablations of our model, including models that are trained with individual EXIF tags, that use different formats for the EXIF-derived text, and different network architectures (Table 5).", + "bbox": [ + 496, + 578, + 890, + 805 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4.2. Evaluating the learned features", + "text_level": 1, + "bbox": [ + 500, + 816, + 774, + 830 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "First, we want to measure how well the learned features convey camera properties. Since EXIF file is already embedded with a lot of camera properties such as camera model, focal length, shuttle speed, etc., it should be unsur", + "bbox": [ + 498, + 840, + 890, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "6948", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 3 + }, + { + "type": "table", + "img_path": "images/d2e278303c7ab9d39e3716dd6c88260021e82917ff10a222d8e7155744701de3.jpg", + "table_caption": [], + "table_footnote": [ + "Table 2. We do linear probing on top of learned representation to predict two camera related properties that are not presented in EXIF files. The good performance indicates that our model learns general imaging properties. resize and crop denote the image preprocessing applied." + ], + "table_body": "
ModelsForensicsRadial Distortion
CASIA ICASIA IIDresdenRAISE
resizecropresizecropresizeresize
ImageNet pretrained0.690.640.710.720.230.24
MoCo0.670.670.680.690.240.28
CLIP0.710.820.840.810.210.22
Ours - CropCLR0.700.810.860.800.280.32
Ours - Full0.750.850.870.840.310.35
", + "bbox": [ + 84, + 88, + 470, + 239 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "prising if we can predict those properties from images (we provide such results in Sec. 4.4). Instead, we want to study if the feature learned by the model can be generalized to other imaging properties that are not provided in the EXIF file. Specifically, we fit a linear classifier to our learned features on two prediction tasks: radial distortion estimation and forensic feature evaluation.", + "bbox": [ + 75, + 324, + 468, + 429 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We compare the features from our image encoder with several other approaches, including supervised ImageNet pretraining [65], a state-of-the-art self-supervised model MoCo [29], CLIP [62], which obtains strong semantic representations using natural language supervision (rather than EXIF supervision), and finally the CropCLR variation of our model. To ensure a fair comparison, the backbone architectures for all approaches are the same (ResNet-50).", + "bbox": [ + 75, + 431, + 468, + 551 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Radial distortion estimation. Imperfections in camera lens production often lead to radial distortion artifacts in captured images. These artifacts are often removed as part of multi-view 3D reconstruction [27, 70], using methods that model distortion as a 4th-order polynomial of pixel position. Radial distortion is not typically specified directly by the camera metadata, and is thus often must be estimated through calibration [10], bundle adjustment [70], or from monocular cues [50].", + "bbox": [ + 75, + 566, + 468, + 702 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We followed the evaluation setup of Lopez et al. [50], which estimates the quadratic term of the radial distortion model, $k_{1}$ , directly from synthetically distorted images. This term can be used to provide an estimate of radial distortion that is sufficient for many tasks [50, 60]. We synthesized the $512 \\times 512$ images from the Dresden Image Database [25] and RAISE dataset [14] using $k_{1}$ parameters uniformly sampled in the range $[-0.4, 0]$ . To predict $k_{1}$ , we used a regression-by-classification approach, quantizing the values of $k_{1}$ into 20 bins (We also show result in regression RMSE metrics in supplementary). We extracted features from different models, and trained a linear classifier on this 20-way classification problem. We provided", + "bbox": [ + 75, + 704, + 468, + 901 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "them with a $512 \\times 512$ image as input, and obtained image features from the global average pooling layer after the final convolutional layer (i.e., the penultimate layer of a typical ResNet).", + "bbox": [ + 496, + 90, + 890, + 151 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Representation learning for image forensics. We evaluate our model's ability to distinguish real and manipulated images. This is a task that requires a broader understanding of low level imaging properties, such as spotting unusual image statistics. We use the CASIA I [18] and CASIA II [43] datasets. The former contains only spliced fakes, while the latter contains a wider variety of manipulations. We again perform linear classification using the features provided by different models. We evaluate two types of preprocessing, resizing and center cropping, to test whether this low level task is sensitive to these details.", + "bbox": [ + 496, + 157, + 890, + 323 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In both tasks, we found that our model's features significantly outperformed those of the other models (Table 2). Our method achieves much better performance than traditional representational learning methods [29, 30, 62], perhaps because these models are encouraged to discard low-level details, while for our training task they are crucially important. Interestingly, the variation of our model that does not use EXIF metadata, CropCLR, outperforms the supervised [30] and self-supervised baselines [29], but significantly lags behind our full method. This is perhaps because it often suffices to use high-level cues (e.g. color histograms and object co-occurrence) to solve CropCLR's pretext task. This suggests metadata supervision is an important learning signal and can effectively guide our model to learn general imaging information.", + "bbox": [ + 496, + 324, + 892, + 551 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.3. Zero Shot Splice Detection and Localization", + "text_level": 1, + "bbox": [ + 500, + 560, + 872, + 575 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We evaluate our model on the task of detecting spliced images without any labeled training data. This is in contrast to Sec. 4.2, which used labeled data. We perform both splice detection (distinguish an image being spliced or not) and splice localization (localize spliced region within an image).", + "bbox": [ + 496, + 583, + 890, + 659 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Implementation. For fair evaluation, we closely follow the approach of Huh et al. [33]. Given an image, we sample patches in a grid, using a stride such that the number of patches sampled along the longest image dimension is 25. To increase the spatial resolution of each similarity map, we average the predictions of overlapping patches. We consider the smaller of the two detected regions to be the splice.", + "bbox": [ + 496, + 666, + 890, + 772 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Evaluation. In splice localization task, we compare our model to a variety of forensics methods. These include traditional methods that use handcrafted features [24, 52, 83], supervised methods [41, 79, 80], and self-supervised approaches [13, 33]. The datasets we use include Columbia [56], DSO [15], Realistic Tampering (RT) [42], In-the-Wild [33] and Hays and Efros inpainting images [28]. Columbia and DSO are created purely", + "bbox": [ + 496, + 779, + 892, + 901 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "6949", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/55e60366c47fbeba4f99df68cf42da6103b59b4c6f7a0104ba190c168674debc.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
StyleMethodColumbia [56]DSO [15]RT [42]In-the-Wild [33]Hays [28]
p-mAPcIoUp-mAPcIoUp-mAPcIoUp-mAPcIoUp-mAPcIoU
HandcraftedCFA [24]0.760.750.240.460.400.630.270.450.220.45
DCT [83]0.430.410.320.510.120.500.410.510.210.47
NOI [52]0.560.470.380.500.190.500.420.520.270.47
SupervisedMantraNet [80]0.780.880.530.780.500.540.500.630.270.56
MAG [41]0.690.770.480.560.510.550.470.590.300.61
OSN [79]0.680.900.550.850.510.810.660.880.280.57
UnsupervisedNoiseprint [13]0.710.830.660.900.290.800.500.780.220.53
EXIF-SC [33]0.890.970.470.810.220.750.490.790.260.54
Ours - CropCLR0.870.960.480.810.230.740.470.800.260.55
Ours - Full0.920.980.560.850.230.740.510.820.300.58
", + "bbox": [ + 88, + 88, + 883, + 300 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/df2258c5cd7b816ef62f0c1d0a52d622872993a3a4d53577168ac776fc582ec5.jpg", + "table_caption": [ + "Table 3. Zero shot splice localization. We evaluate our model on several datasets using permutation-invariant mean average precision (p-mAP) over pixels and class-balanced IOU (cIoU) with optimal threshold selected per image. The result indicates that our model is comparable to state-of-the-art methods, although not specially optimized for this task." + ], + "table_footnote": [], + "table_body": "
DatasetColumbia [56]DSO [15]RT [42]
CFA [24]0.830.490.54
DCT [83]0.580.480.52
NOI [52]0.730.510.52
EXIF-SC0.980.610.55
Ours - CropCLR0.960.620.52
Ours - Full0.990.660.53
", + "bbox": [ + 81, + 359, + 470, + 481 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 4. Zero-shot splice detection: We compare our splice detection accuracy on 3 datasets. We measure the mean average precision (mAP) of detecting whether an image has been spliced.", + "bbox": [ + 75, + 489, + 468, + 532 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "via image splicing, while Realistic Tampering contains a diverse set of manipulations. In-the-Wild is a splicing image dataset composed of internet images, which may also contain a variety of other manipulations. Hays and Efros [28] perform data-driven image inpainting. The quantitative comparison in terms of permuted-mAP $(\\mathbf{p} - \\mathbf{mAP})$ and class-balanced IoU (cIoU) following [33] are presented in Table 3. We also include splice image detection result in Table 4, where we compare our model to methods that enable splice detection.", + "bbox": [ + 75, + 537, + 468, + 686 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Our model ranks first or second place for metrics in most datasets, and obtains performance comparable to top self-supervised methods that are specially designed for this task. In particular, our model significantly outperforms the most related technique, EXIF-SC [33]. We note that both our method and EXIF-SC get relatively low performance on the Realistic Tampering dataset. This may be due to the fact that this dataset contains manipulations such as copy-move that we do not expect to detect (since both regions share the same camera properties). In contrast to methods based on segmentation [13, 79, 80], we do not aim to have spatially precise matches, and output relatively low-resolution localization maps based on large patches. Consequently, our model is not well-suited to detecting very small", + "bbox": [ + 75, + 688, + 470, + 901 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "spices, which also commonly occur in the Realistic Tampering dataset.", + "bbox": [ + 496, + 362, + 890, + 392 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "In Fig. 4, we show qualitative results, including both similarity maps and spectral clustering results. In Fig. 6, we compare our model with those of several other techniques. Interestingly, EXIF-SC has false positives in overexposed regions (as pointed out by [33]), since its classifier cannot infer whether these regions are (or are not) part of the rest of the scene. In contrast, our model successfully handles these regions. CropCLR incorrectly flags regions that are semantically different from the background, because this is a strong indication that the patches come from different images. In contrast, we successfully handle these cases, since our model has no such \"shortcut\" in its learning task.", + "bbox": [ + 496, + 395, + 892, + 578 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.4. Ablation Study", + "text_level": 1, + "bbox": [ + 500, + 597, + 653, + 614 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "To help understand which aspects of our approach are responsible for its performance, we evaluated a variety of variations of our model, including different training supervision, representations for the camera metadata, and network architectures.", + "bbox": [ + 496, + 625, + 893, + 700 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We evaluated each model's features quality using linear probing on the radial distortion estimation and splice detection task (same as Sec. 4.2). As an additional evaluation, we classify the values of common EXIF tags by applying linear classifiers to our visual representation. We convert the values of each EXIF tag into discrete categories, by quantizing common values and removing examples that do not fit into any category. We average prediction accuracies over 44 EXIF tags to obtain overall accuracy. We provide more details in the supplementary. All models were trained for 30 epochs on 800K images on a subset of YFCC100M dataset. The associated texts are obtained from the image descriptions and EXIF data provided by the dataset.", + "bbox": [ + 496, + 703, + 893, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "6950", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/ad43f539a6a81ed62d5ea60505b180782851f8f671a91761b9762c5599d766af.jpg", + "image_caption": [ + "Figure 4" + ], + "image_footnote": [], + "bbox": [ + 81, + 71, + 477, + 410 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/2fdfb8966aba1879abc2cac9b2139ba104fc5a9586e835e19b7def0ef6ad3dd1.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 491, + 71, + 888, + 410 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/e0ae17366cf28d7dfcc687f45ca50f4d14088da45cfa1dec18ea5a932587e1ad.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodEXIFRadialForens.
Majority class baseline0.120.050.50
SupervisionAll EXIF tags0.350.290.85
CropCLR0.290.220.84
“Camera Model” tag only0.310.270.80
“Color Space” tag only0.120.120.61
YFCC image descriptions0.150.160.70
Tag formatFixed order, w/ tag name0.350.290.85
Fixed order, w/o tag name0.350.280.86
Rand. order, w/ tag name0.340.260.77
Rand. order, w/o tag name0.330.260.76
ArchitectureDistilBERT, w/ pretrained0.350.290.85
DistilBERT, w/o pretrained0.360.250.77
ALBERT, w/ pretrained0.330.290.84
ALBERT, w/o pretrained0.340.260.79
", + "bbox": [ + 93, + 450, + 455, + 690 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 5. Model ablations. Downstream accuracy for versions of the model trained with different text supervision, representations of camera metadata, and architectures. We use linear probing to evaluate the average prediction accuracy of EXIF tag values on our YFCC test set, radial distortion estimation on Dresden dataset, and real-or-fake classification on CASIA I dataset. Rows with gray background (replicated for ease of comparison) represent the same model which is our \"full\" model.", + "bbox": [ + 75, + 694, + 468, + 805 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Metadata supervision. We evaluate a variation of our model that trains using the image descriptions provided by YFCC100M in lieu of camera metadata, as well as models supervised by individual EXIF tags (Table 5). For the variations supervised by a single EXIF tag, we chose 14", + "bbox": [ + 75, + 824, + 470, + 902 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/108d56afff7567abaa79042cb074497735b9a497d35be336e2114c60cc61e394.jpg", + "image_caption": [ + "Figure 5. Per-tag forensics task accuracy. We train various models supervised by individual EXIF tags, then evaluate the learned representations for splice detection task on CASIA I." + ], + "image_footnote": [], + "bbox": [ + 504, + 450, + 888, + 558 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "common tags for this experiment, training a separate network for each one. The results of the per-tag evaluation is shown in Fig. 5. These results suggest that having access to the full metadata provides significantly better performance than using individual tags. Moreover, there is a wide variation in the performance of models that use different tag. This may be because the high performing tags, such as Camera Model, convey significantly more information about the full range of camera properties than others, such as Color Space and Sensing Method. These results suggest that a model that simply uses the full range of tags can extract significantly more camera information from the metadata. We also found that the variation trained on image descriptions (rather than EXIF text) performed significantly worse than other models.", + "bbox": [ + 496, + 618, + 892, + 845 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Tag format. Since EXIF does not have a natural order of tags, we ask what will happen if we randomize the EXIF tag order during training. Table 5 shows the performance drops", + "bbox": [ + 498, + 854, + 893, + 902 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "6951", + "bbox": [ + 482, + 944, + 513, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/525314fda64912fce106de0e71d26e85a57f9d756a95f87618c480c017fc4709.jpg", + "image_caption": [ + "Image", + "EXIF-SC", + "Noiseprint", + "OSN", + "CropCLR", + "Ours", + "Ground Truth", + "Figure 6. Qualitative comparison to other methods. Our method can correctly localize splices in many scenarios where other methods fail. For example, EXIF-SC [33] fails on overexposed image regions; OSN [79] and CropCLR often segment scenes based on semantics." + ], + "image_footnote": [], + "bbox": [ + 91, + 94, + 883, + 501 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "for all three evaluations in this case. This may be due to the fact that the Transformer model is forced to learn meaningful positional embeddings corresponding to each EXIF tag if their order keeps on changing. We also tried removing the tag names from the camera metadata and just provide the values for those keys, e.g. replacing Make: Apple with Apple. Interestingly, this model performs on par with the model that has tag names, suggesting that the network can discern information about the tags from the values alone.", + "bbox": [ + 75, + 537, + 472, + 674 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Text encoder architecture. To test whether performance of our model tied to a specific transformer architecture, we experimented with two different transformer models, DistilBERT [67] and ALBERT [44]. We see that both architectures obtain similar performance on all three tasks with DistilBERT slightly outperforming ALBERT. We also test how much pretraining the text encoder helps with the performance. From Table 5, we can see pretraining improves performance on the radial distortion and forensics tasks.", + "bbox": [ + 75, + 681, + 468, + 816 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Discussion", + "text_level": 1, + "bbox": [ + 76, + 829, + 191, + 845 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this paper, we proposed to learn camera properties by training models to find cross-modal correspondences between images and camera metadata. To achieve this, we", + "bbox": [ + 75, + 854, + 470, + 900 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "created a model that exploits the fact that EXIF metadata can easily be represented and processed as text. Our model achieves strong performance amongst self-supervised methods on a variety of downstream tasks that require understanding camera properties, including zero shot image forensics and radial distortion estimation. We see our work opening several possible directions. First, it opens the possibility of creating multimodal learning systems that use camera metadata as another form of supervision, providing complementary information to high-level modalities like language and sound. Second, it opens applications that require an understanding of low level sensor information, which may benefit from our feature sets.", + "bbox": [ + 496, + 537, + 893, + 734 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Limitations and Broader Impacts. We have shown that our learned features are useful for image forensics, which has potential to reduce the spread of disinformation [22]. The model that we will release may not be fully representative of the cameras in the wild, since it was trained only on photos available in the YFCC100M dataset [73].", + "bbox": [ + 496, + 742, + 893, + 834 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 500, + 847, + 596, + 863 + ], + "page_idx": 7 + }, + { + "type": "ref_text", + "text": "[1] Ali Azarbayejani and Alex P Pentland. Recursive estimation of motion, structure, and focal length. IEEE Transactions on", + "bbox": [ + 506, + 872, + 892, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "6952", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 7 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "Pattern Analysis and Machine Intelligence, 17(6):562-575, 1995. 2", + "[2] Tadas Baltrusaitis, Chaitanya Ahuja, and Louis-Philippe Morency. Multimodal machine learning: A survey and taxonomy. 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Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.221, + 0.131, + 0.75, + 0.175 + ], + "angle": 0, + "content": "EXIF as Language: Learning Cross-Modal Associations Between Images and Camera Metadata" + }, + { + "type": "text", + "bbox": [ + 0.241, + 0.204, + 0.371, + 0.222 + ], + "angle": 0, + "content": "Chenhao Zheng" + }, + { + "type": "text", + "bbox": [ + 0.411, + 0.205, + 0.558, + 0.222 + ], + "angle": 0, + "content": "Ayush Shrivastava" + }, + { + "type": "text", + "bbox": [ + 0.391, + 0.226, + 0.576, + 0.243 + ], + "angle": 0, + "content": "University of Michigan" + }, + { + "type": "text", + "bbox": [ + 0.347, + 0.25, + 0.618, + 0.264 + ], + "angle": 0, + "content": "https://hellomuffin.github.io/exif-as-language" + }, + { + "type": "image", + "bbox": [ + 0.086, + 0.303, + 0.378, + 0.43 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.113, + 0.435, + 0.353, + 0.448 + ], + "angle": 0, + "content": "(a) Multimodal image-metadata embeddings" + }, + { + "type": "image", + "bbox": [ + 0.396, + 0.303, + 0.499, + 0.41 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.399, + 0.411, + 0.495, + 0.421 + ], + "angle": 0, + "content": "Manipulated image" + }, + { + "type": "image", + "bbox": [ + 0.5, + 0.304, + 0.602, + 0.41 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.505, + 0.411, + 0.597, + 0.421 + ], + "angle": 0, + "content": "Patch embeddings" + }, + { + "type": "image", + "bbox": [ + 0.603, + 0.304, + 0.706, + 0.41 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.617, + 0.411, + 0.693, + 0.421 + ], + "angle": 0, + "content": "Detected splice" + }, + { + "type": "image", + "bbox": [ + 0.708, + 0.304, + 0.811, + 0.41 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.727, + 0.411, + 0.792, + 0.421 + ], + "angle": 0, + "content": "Ground truth" + }, + { + "type": "image_caption", + "bbox": [ + 0.41, + 0.435, + 0.796, + 0.448 + ], + "angle": 0, + "content": "(b) Detecting spliced images by spotting inconsistent patch embeddings" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.46, + 0.892, + 0.543 + ], + "angle": 0, + "content": "Figure 1. (a) We learn a joint embedding between image patches and the EXIF metadata that cameras automatically insert into image files. Our model treats this metadata as a language-like modality: we convert the EXIF tags to text, concatenate them together, and then processes the result with a transformer. (b) We apply our representation to tasks that require understanding camera properties. For example, we can detect image splicing \"zero shot\" (and without metadata at test time) by finding inconsistent embeddings within an image. We show a manipulated image that contains content from two source photos. Since these photos were captured with different cameras, the two regions have dissimilar embeddings (visualized by PCA). We localize the splice by clustering the image's patch embeddings." + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.565, + 0.314, + 0.58 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.598, + 0.471, + 0.78 + ], + "angle": 0, + "content": "We learn a visual representation that captures information about the camera that recorded a given photo. To do this, we train a multimodal embedding between image patches and the EXIF metadata that cameras automatically insert into image files. Our model represents this metadata by simply converting it to text and then processing it with a transformer. The features that we learn significantly outperform other self-supervised and supervised features on downstream image forensics and calibration tasks. In particular, we successfully localize spliced image regions \"zero shot\" by clustering the visual embeddings for all of the patches within an image." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.815, + 0.208, + 0.83 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.842, + 0.47, + 0.903 + ], + "angle": 0, + "content": "A major goal of the computer vision community has been to use cross-modal associations to learn concepts that would be hard to glean from images alone [2]. A particular focus has been on learning high level semantics, such as" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.566, + 0.892, + 0.656 + ], + "angle": 0, + "content": "objects, from other rich sensory signals, like language and sound [58, 62]. By design, the representations learned by these approaches typically discard imaging properties, such as the type of camera that shot the photo, its lens, and the exposure settings, which are not useful for their cross-modal prediction tasks [17]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.659, + 0.893, + 0.81 + ], + "angle": 0, + "content": "We argue that obtaining a complete understanding of an image requires both capabilities — for our models to perceive not only the semantic content of a scene, but also the properties of the camera that captured it. This type of low level understanding has proven crucial for a variety of tasks, from image forensics [33, 52, 80] to 3D reconstruction [34, 35], yet it has not typically been a focus of representation learning. It is also widely used in image generation, such as when users of text-to-image tools specify camera properties with phrases like \"DSLR photo\" [59, 63]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.812, + 0.894, + 0.903 + ], + "angle": 0, + "content": "We propose to learn low level imaging properties from the abundantly available (but often neglected) camera metadata that is added to the image file at the moment of capture. This metadata is typically represented as dozens of Exchangeable Image File Format (EXIF) tags that describe the camera, its settings, and postprocessing operations that" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "6945" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.272 + ], + "angle": 0, + "content": "were applied to the image: e.g., Model: \"iPhone 4s\" or Focal Length: \\(35.0 \\, \\text{mm}\\). We train a joint embedding through contrastive learning that puts image patches into correspondence with camera metadata (Fig. 1a). Our model processes the metadata with a transformer [75] after converting it to a language-like representation. To do this conversion, we take advantage of the fact that EXIF tags are typically stored in a human-readable (and text-based) format. We convert each tag to text, and then concatenate them together. Our model thus closely resembles contrastive vision-and-language models, such as CLIP [62], but with EXIF-derived text in place of natural language." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.273, + 0.473, + 0.378 + ], + "angle": 0, + "content": "We show that our model can successfully estimate camera properties solely from images, and that it provides a useful representation for a variety of image forensics and camera calibration tasks. Our approaches to these tasks do not require camera metadata at test time. Instead, camera properties are estimated implicitly from image content via multimodal embeddings." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.378, + 0.473, + 0.469 + ], + "angle": 0, + "content": "We evaluate the learned feature of our model on two classification tasks that benefit from a low-level understanding of images: estimating an image's radial distortion parameter, and distinguishing real and manipulated images. We find that our features significantly outperform alternative supervised and self-supervised feature sets." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.469, + 0.473, + 0.665 + ], + "angle": 0, + "content": "We also show that our embeddings can be used to detect image splicing \"zero shot\" (i.e., without labeled data), drawing on recent work [8, 33, 54] that detects inconsistencies in camera fingerprints hidden within image patches. Spliced images contain content from multiple real images, each potentially captured with a different camera and imaging pipeline. Thus, the embeddings that our model assigns to their patches, which convey camera properties, will have less consistency than those of real images. We detect manipulations by flagging images whose patch embeddings do not fit into a single, compact cluster. We also localize spliced regions by clustering the embeddings within an image (Fig. 1b)." + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.666, + 0.341, + 0.68 + ], + "angle": 0, + "content": "We show through our experiments that:" + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.682, + 0.469, + 0.711 + ], + "angle": 0, + "content": "- Camera metadata provides supervision for self-supervised representation learning." + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.712, + 0.469, + 0.741 + ], + "angle": 0, + "content": "- Image patches can be successfully associated with camera metadata via joint embeddings." + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.742, + 0.468, + 0.771 + ], + "angle": 0, + "content": "- Image-metadata embeddings are a useful representation for forensics and camera understanding tasks." + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.772, + 0.468, + 0.802 + ], + "angle": 0, + "content": "- Image manipulations can be identified \"zero shot\" by identifying inconsistencies in patch embeddings." + }, + { + "type": "list", + "bbox": [ + 0.078, + 0.682, + 0.469, + 0.802 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.815, + 0.22, + 0.831 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.841, + 0.472, + 0.902 + ], + "angle": 0, + "content": "Estimating camera properties. Camera metadata has been used for a range of tasks in computer vision, such as for predicting focal length [1, 31, 50, 71], performing white balancing [20, 49] and estimating camera models" + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.08, + 0.891, + 0.276 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.283, + 0.895, + 0.354 + ], + "angle": 0, + "content": "Figure 2. Cross-modal image and camera metadata model. We use contrastive learning to associate each image patch with the EXIF metadata that was extracted from its image file. We represent the metadata as text, which is obtained by concatenating the EXIF tags together. We then process it using a transformer." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.366, + 0.894, + 0.442 + ], + "angle": 0, + "content": "[7, 39, 74]. It has also been used as extra input for recognition tasks [19, 72]. Instead of estimating camera properties directly (which can be highly error prone [33]), our model predicts an embedding that distinguishes a patch's camera properties from that of other patches in the dataset." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.452, + 0.895, + 0.74 + ], + "angle": 0, + "content": "Image forensics. Early work used physically motivated cues, such as misaligned JPEG blocks [6, 21], color filter array mismatches [3,4,23,78], inconsistencies in noise patterns [37, 47, 48, 61], and compression or boundary artifacts [5, 26, 32, 82]. Other works use supervised learning methods [40, 53, 64, 66, 76, 77, 79-81, 85]. The challenge of collecting large datasets of fake images has led to alternative approaches, such as synthetic examples [53, 79, 81, 85]. Other work uses self-supervised learning, such as methods based on denoising [13], or that detect image manipulations by identifying image content that appears to come from different camera models [7, 9, 54]. Huh et al. [33] learned a patch similarity metric in two steps: they determined which EXIF tags are shared between the patches, then use these binary predictions as features for a second classifier that predicts whether two patches come from the same (or different) images. In contrast, we obtain a visual similarity metric that is well-suited to splice localization directly from our multimodal embeddings." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.75, + 0.894, + 0.885 + ], + "angle": 0, + "content": "Language supervision in vision. Recent works have obtained visual supervision from language. The formulation includes specific keyword prediction [55], bag-of-word multilabel classification [36], \\( n \\)-gram classification [46] and autoregressive language models [16, 68, 84]. Recently, Radford et al. [62] obtained strong performance by training a contrastive model on a large image-and-language dataset. Our technical approach is similar, but uses text from camera metadata in lieu of image captions." + }, + { + "type": "text", + "bbox": [ + 0.52, + 0.886, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Work in text-to-image synthesis often exploits camera" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "6946" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.182 + ], + "angle": 0, + "content": "information through prompting, such as by adding text like \"DSLR photo of...\" or \"Sigma 500mm f/5\" to prompts [59]. These methods, however, learn these camera associations through the (relatively rare) descriptions of cameras provided by humans, while ours learns them from an abundant and complementary learning signal, camera metadata." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.195, + 0.465, + 0.213 + ], + "angle": 0, + "content": "3. Associating Images with Camera Metadata" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.221, + 0.47, + 0.298 + ], + "angle": 0, + "content": "We desire a visual representation that captures low level imaging properties, such as the settings of the camera that were used to shoot the photo. We then apply this learned representation to downstream tasks that require an understanding of camera properties." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.305, + 0.39, + 0.323 + ], + "angle": 0, + "content": "3.1. Learning Cross-Modal Embeddings" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.329, + 0.47, + 0.54 + ], + "angle": 0, + "content": "We train a model to predict camera metadata from image content, thereby obtaining a representation that conveys camera properties. Following previous work in multimodal contrastive learning [62], we train a joint embedding between the two modalities, allowing our model to avoid the (error prone) task of directly predicting the attributes. Specifically, we want to jointly learn an image encoder and metadata encoder such that, given \\( N \\) images and \\( N \\) pieces of metadata information, the corresponding image–metadata pairs can be recognized by the model by maximizing embedding similarity. We use full-resolution image patches rather than resized images, so that our model can analyze low-level details that may be lost during down-sampling." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.54, + 0.47, + 0.601 + ], + "angle": 0, + "content": "Given a dataset of image patches and their corresponding camera metadata \\(\\{(\\mathbf{v}_i,\\mathbf{m}_i)\\}_{i = 1}^N\\), we learn visual and EXIF representations \\(f_{\\theta}(\\mathbf{v})\\) and \\(g_{\\phi}(\\mathbf{m})\\) by jointly training \\(f_{\\theta}\\) and \\(g_{\\phi}\\) using a contrastive loss [57]:" + }, + { + "type": "equation", + "bbox": [ + 0.105, + 0.61, + 0.47, + 0.648 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {i} ^ {V, M} = - \\log \\frac {\\exp \\left(f _ {\\theta} \\left(\\mathbf {v} _ {i}\\right) \\cdot g _ {\\phi} \\left(\\mathbf {m} _ {i}\\right) / \\tau\\right)}{\\sum_ {j = 1} ^ {N} \\exp \\left(f _ {\\theta} \\left(\\mathbf {v} _ {i}\\right) \\cdot g _ {\\phi} \\left(\\mathbf {m} _ {j}\\right) / \\tau\\right)}, \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.657, + 0.47, + 0.718 + ], + "angle": 0, + "content": "where \\(\\tau\\) is a small constant. Following prior work [62], we define an analogous loss \\(\\mathcal{L}^{M,V}\\) that sums over visual (rather than metadata) examples in the denominator, and minimize a combined loss \\(\\mathcal{L} = \\mathcal{L}^{V,M} + \\mathcal{L}^{M,V}\\)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.727, + 0.388, + 0.743 + ], + "angle": 0, + "content": "3.2. Representing the Camera Metadata" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.75, + 0.471, + 0.903 + ], + "angle": 0, + "content": "This formulation raises a natural question: how should we represent the metadata? The metadata within photos is stored as a set of EXIF tags, each indicating a different image property as shown in Table 1. EXIF tags span a range of formats and data types, and the set of tags that are present in a given photo can be highly inconsistent. Previous works that predict camera properties from images typically extract attributes of interest from the EXIF tags, and cast them to an appropriate data format — e.g., extracting a scalar-valued focal length category. This tag-specific processing limits" + }, + { + "type": "table", + "bbox": [ + 0.505, + 0.083, + 0.895, + 0.282 + ], + "angle": 0, + "content": "
EXIF tagExample values#values
Camera MakeCanon, NIKON Corporation, Apple312
Camera ModelNIKON D90, Canon EOS 73071
SoftwarePicasa, Adobe Photoshop, QuickTime1711
Exposure Time1/60 sec, 1/125 sec, 1/250 sec2062
Focal Length18.0 mm, 50.0 mm, 6.3 mm931
Aperture ValueF2.8, F4, F5.6, F3.5137
Scene Capture TypeLandscape, Portrait, Night Scene5
Exposure ProgramAperture priority, Manual control9
White Balance ModeAuto, Manual3
Thumbnail CompressionJPEG, Uncompressed3
Digital Zoom Ratio1, 1.5, 2, 1.249
ISO speed Ratings100, 400, 300460
Shutter Speed Value1/60 sec, 1/63 sec, 1/124 sec1161
Date/Time Digitized2013:03:28 04:20:4695932
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.287, + 0.892, + 0.343 + ], + "angle": 0, + "content": "Table 1. What information is contained within photo EXIF metadata? We list several of the most common EXIF tags, along with the common values and number of values they contain in the YFCC100M dataset [73]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.366, + 0.892, + 0.396 + ], + "angle": 0, + "content": "the amount of metadata information that can be used as part of learning, and requires special-purpose architectures." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.397, + 0.893, + 0.607 + ], + "angle": 0, + "content": "We exploit the fact that EXIF tags are typically stored in a human-readable format and can be straightforwardly converted to text (Fig. 2). This allows us to directly process camera metadata using models from natural language processing — an approach that has successfully been applied to processing various text-like inputs other than language, such as math [45] and code [11]. Specifically, we create a long piece of text from a photo's metadata by converting each tag's name and value to strings, and concatenating them together. We separate each tag name and value with a colon and space, and separate different tags with a space. We evaluate a number of design decisions for this model in Sec. 4.4, such as the text format, choice of tags, and network architecture." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.62, + 0.842, + 0.636 + ], + "angle": 0, + "content": "3.3. Application: Zero-shot Image Forensics" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.644, + 0.892, + 0.793 + ], + "angle": 0, + "content": "After learning cross-modal representations from images and camera metadata, we can use them for downstream tasks that require an understanding of camera properties. One way to do this is by using the learned visual network features as a representation for classification tasks, following other work in self-supervised representation learning [12, 29]. We can also use our learned visual embeddings to perform \"zero shot\" image splice detection, by detecting inconsistencies in an input image's imputed camera properties." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.796, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Spliced images are composed of regions from multiple real images. Since they are typically designed to fool humans, forensic models need to rely more on subtle (often non-semantic) cues to detect them. We got inspiration from Huh et al. [33], which predicts whether two image patches share the same camera properties. If two patches are predicted to have very different camera properties, then this" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "6947" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.081, + 0.075, + 0.885, + 0.257 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.265, + 0.893, + 0.308 + ], + "angle": 0, + "content": "Figure 3. Zero shot splice localization. Given a spliced image (left), we compute our cross-modal embeddings for each image patch, which we visualize here using projections onto the top 3 principal components. We then compute the affinity matrix by taking dot product for every pair of patches. We localize the spliced region by clustering these embedding vectors." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.317, + 0.469, + 0.451 + ], + "angle": 0, + "content": "provides evidence that they come from different images. In our work, we can naturally obtain this patch similarity by computing the dot product between two patches' embeddings, since they have been trained to convey camera properties. We note that, unlike Huh et al. [33], we do not train a second, special-purpose classifier for this task, nor do we use augmentation to provide synthetic training examples (e.g., by applying different types of compression to the patches)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.453, + 0.47, + 0.711 + ], + "angle": 0, + "content": "To determine whether an image is likely to contain a splice, we first compute an affinity matrix \\( A_{ij} = f_{\\theta}(\\mathbf{v}_i) \\cdot f_{\\theta}(\\mathbf{v}_j) \\) whose entries are the dot product between patches' normalized embedding vectors. We score an image \\( \\mathbf{v} \\) using the sum of the exponentiated dot products between embeddings, \\( \\phi (\\mathbf{v}) = \\sum_{i,j}\\exp (A_{ij} / \\tau) \\). This score indicates the likelihood that the image is unmodified, since high dot products indicate high similarity in imputed camera properties. To localize the spliced image regions within an image, we aggregate the similarity scores in \\( A_{ij} \\) by clustering the rows using mean shift, following [33]. This results in a similarity map indicating the likelihood that each patch was extracted from the largest source photo that was used to create the composite. Alternatively, we can visualize the spliced region by performing spectral clustering via normalized cuts [33, 69], using \\( A_{ij} \\) as an affinity matrix between patches. We visualize this approach in Fig. 3." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.729, + 0.163, + 0.745 + ], + "angle": 0, + "content": "4. Results" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.755, + 0.236, + 0.772 + ], + "angle": 0, + "content": "4.1. Implementation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.78, + 0.47, + 0.9 + ], + "angle": 0, + "content": "Architecture. We use ResNet-50 pretrained on ImageNet as our image encoder. We found that the text encoder in models trained on captioning, such as CLIP [62], were not well-suited to our task, since they place low limits on the number of tokens. For the EXIF text encoder, we use DistilBERT [67] pretrained on Wikipedia and the Toronto Book Corpus [86]. We compute the feature representation of the EXIF as the activations for the end-of-sentence token from" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.317, + 0.892, + 0.347 + ], + "angle": 0, + "content": "the last layer which is layer normalized and then linearly projected into multi-modal embedding space." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.357, + 0.893, + 0.569 + ], + "angle": 0, + "content": "Training. To train our model, we use 1.5M full-resolution images and EXIF pairs from a random subset of YFCC100M [73]. We discard images that have less than 10 of the EXIF tags. Because many images only have a small number of EXIF tags available, we only use tags that are present in more than half of these images. This results in 44 EXIF tags (see supplementary for the complete list). In contrast to other work [33], we do not rebalance the images to increase the rate of rare tags. During training, we randomly crop \\(124 \\times 124\\) patches from high-resolution images. We use the AdamW optimizer [38] with a learning rate of \\(10^{-4}\\), weight decay of \\(10^{-3}\\), and mixed precision training. We use a cosine annealing learning rate schedule [51]. The batch size is set to 1024, and we train our model for 50 epochs." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.579, + 0.892, + 0.806 + ], + "angle": 0, + "content": "Other model variations. To study the importance of metadata supervision on the learned representation, we train a similar model that performs contrastive learning but does not use metadata. The model resembles image-image contrastive learning [12,29,33,87], which has been shown to be highly effective for representation learning, and which may learn low-level camera information [17]. Different from typical contrastive learning approaches, we use strict cropping augmentation so that the views for our model (Eq. 1) come from different crops of the same image, to encourage it to learn low-level image features. We call this model CropCLR. Additionally, we evaluate a number of ablations of our model, including models that are trained with individual EXIF tags, that use different formats for the EXIF-derived text, and different network architectures (Table 5)." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.817, + 0.776, + 0.832 + ], + "angle": 0, + "content": "4.2. Evaluating the learned features" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.841, + 0.892, + 0.901 + ], + "angle": 0, + "content": "First, we want to measure how well the learned features convey camera properties. Since EXIF file is already embedded with a lot of camera properties such as camera model, focal length, shuttle speed, etc., it should be unsur" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "6948" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.086, + 0.089, + 0.472, + 0.24 + ], + "angle": 0, + "content": "
ModelsForensicsRadial Distortion
CASIA ICASIA IIDresdenRAISE
resizecropresizecropresizeresize
ImageNet pretrained0.690.640.710.720.230.24
MoCo0.670.670.680.690.240.28
CLIP0.710.820.840.810.210.22
Ours - CropCLR0.700.810.860.800.280.32
Ours - Full0.750.850.870.840.310.35
" + }, + { + "type": "table_footnote", + "bbox": [ + 0.076, + 0.244, + 0.47, + 0.314 + ], + "angle": 0, + "content": "Table 2. We do linear probing on top of learned representation to predict two camera related properties that are not presented in EXIF files. The good performance indicates that our model learns general imaging properties. resize and crop denote the image preprocessing applied." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.325, + 0.469, + 0.43 + ], + "angle": 0, + "content": "prising if we can predict those properties from images (we provide such results in Sec. 4.4). Instead, we want to study if the feature learned by the model can be generalized to other imaging properties that are not provided in the EXIF file. Specifically, we fit a linear classifier to our learned features on two prediction tasks: radial distortion estimation and forensic feature evaluation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.432, + 0.47, + 0.553 + ], + "angle": 0, + "content": "We compare the features from our image encoder with several other approaches, including supervised ImageNet pretraining [65], a state-of-the-art self-supervised model MoCo [29], CLIP [62], which obtains strong semantic representations using natural language supervision (rather than EXIF supervision), and finally the CropCLR variation of our model. To ensure a fair comparison, the backbone architectures for all approaches are the same (ResNet-50)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.568, + 0.469, + 0.703 + ], + "angle": 0, + "content": "Radial distortion estimation. Imperfections in camera lens production often lead to radial distortion artifacts in captured images. These artifacts are often removed as part of multi-view 3D reconstruction [27, 70], using methods that model distortion as a 4th-order polynomial of pixel position. Radial distortion is not typically specified directly by the camera metadata, and is thus often must be estimated through calibration [10], bundle adjustment [70], or from monocular cues [50]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.705, + 0.47, + 0.902 + ], + "angle": 0, + "content": "We followed the evaluation setup of Lopez et al. [50], which estimates the quadratic term of the radial distortion model, \\( k_{1} \\), directly from synthetically distorted images. This term can be used to provide an estimate of radial distortion that is sufficient for many tasks [50, 60]. We synthesized the \\( 512 \\times 512 \\) images from the Dresden Image Database [25] and RAISE dataset [14] using \\( k_{1} \\) parameters uniformly sampled in the range \\([-0.4, 0]\\). To predict \\( k_{1} \\), we used a regression-by-classification approach, quantizing the values of \\( k_{1} \\) into 20 bins (We also show result in regression RMSE metrics in supplementary). We extracted features from different models, and trained a linear classifier on this 20-way classification problem. We provided" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.152 + ], + "angle": 0, + "content": "them with a \\(512 \\times 512\\) image as input, and obtained image features from the global average pooling layer after the final convolutional layer (i.e., the penultimate layer of a typical ResNet)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.159, + 0.892, + 0.324 + ], + "angle": 0, + "content": "Representation learning for image forensics. We evaluate our model's ability to distinguish real and manipulated images. This is a task that requires a broader understanding of low level imaging properties, such as spotting unusual image statistics. We use the CASIA I [18] and CASIA II [43] datasets. The former contains only spliced fakes, while the latter contains a wider variety of manipulations. We again perform linear classification using the features provided by different models. We evaluate two types of preprocessing, resizing and center cropping, to test whether this low level task is sensitive to these details." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.325, + 0.893, + 0.552 + ], + "angle": 0, + "content": "In both tasks, we found that our model's features significantly outperformed those of the other models (Table 2). Our method achieves much better performance than traditional representational learning methods [29, 30, 62], perhaps because these models are encouraged to discard low-level details, while for our training task they are crucially important. Interestingly, the variation of our model that does not use EXIF metadata, CropCLR, outperforms the supervised [30] and self-supervised baselines [29], but significantly lags behind our full method. This is perhaps because it often suffices to use high-level cues (e.g. color histograms and object co-occurrence) to solve CropCLR's pretext task. This suggests metadata supervision is an important learning signal and can effectively guide our model to learn general imaging information." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.561, + 0.874, + 0.577 + ], + "angle": 0, + "content": "4.3. Zero Shot Splice Detection and Localization" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.584, + 0.892, + 0.66 + ], + "angle": 0, + "content": "We evaluate our model on the task of detecting spliced images without any labeled training data. This is in contrast to Sec. 4.2, which used labeled data. We perform both splice detection (distinguish an image being spliced or not) and splice localization (localize spliced region within an image)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.667, + 0.892, + 0.773 + ], + "angle": 0, + "content": "Implementation. For fair evaluation, we closely follow the approach of Huh et al. [33]. Given an image, we sample patches in a grid, using a stride such that the number of patches sampled along the longest image dimension is 25. To increase the spatial resolution of each similarity map, we average the predictions of overlapping patches. We consider the smaller of the two detected regions to be the splice." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.893, + 0.902 + ], + "angle": 0, + "content": "Evaluation. In splice localization task, we compare our model to a variety of forensics methods. These include traditional methods that use handcrafted features [24, 52, 83], supervised methods [41, 79, 80], and self-supervised approaches [13, 33]. The datasets we use include Columbia [56], DSO [15], Realistic Tampering (RT) [42], In-the-Wild [33] and Hays and Efros inpainting images [28]. Columbia and DSO are created purely" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.956 + ], + "angle": 0, + "content": "6949" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.089, + 0.089, + 0.885, + 0.301 + ], + "angle": 0, + "content": "
StyleMethodColumbia [56]DSO [15]RT [42]In-the-Wild [33]Hays [28]
p-mAPcIoUp-mAPcIoUp-mAPcIoUp-mAPcIoUp-mAPcIoU
HandcraftedCFA [24]0.760.750.240.460.400.630.270.450.220.45
DCT [83]0.430.410.320.510.120.500.410.510.210.47
NOI [52]0.560.470.380.500.190.500.420.520.270.47
SupervisedMantraNet [80]0.780.880.530.780.500.540.500.630.270.56
MAG [41]0.690.770.480.560.510.550.470.590.300.61
OSN [79]0.680.900.550.850.510.810.660.880.280.57
UnsupervisedNoiseprint [13]0.710.830.660.900.290.800.500.780.220.53
EXIF-SC [33]0.890.970.470.810.220.750.490.790.260.54
Ours - CropCLR0.870.960.480.810.230.740.470.800.260.55
Ours - Full0.920.980.560.850.230.740.510.820.300.58
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.304, + 0.895, + 0.348 + ], + "angle": 0, + "content": "Table 3. Zero shot splice localization. We evaluate our model on several datasets using permutation-invariant mean average precision (p-mAP) over pixels and class-balanced IOU (cIoU) with optimal threshold selected per image. The result indicates that our model is comparable to state-of-the-art methods, although not specially optimized for this task." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.36, + 0.472, + 0.482 + ], + "angle": 0, + "content": "
DatasetColumbia [56]DSO [15]RT [42]
CFA [24]0.830.490.54
DCT [83]0.580.480.52
NOI [52]0.730.510.52
EXIF-SC0.980.610.55
Ours - CropCLR0.960.620.52
Ours - Full0.990.660.53
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.49, + 0.47, + 0.533 + ], + "angle": 0, + "content": "Table 4. Zero-shot splice detection: We compare our splice detection accuracy on 3 datasets. We measure the mean average precision (mAP) of detecting whether an image has been spliced." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.538, + 0.47, + 0.688 + ], + "angle": 0, + "content": "via image splicing, while Realistic Tampering contains a diverse set of manipulations. In-the-Wild is a splicing image dataset composed of internet images, which may also contain a variety of other manipulations. Hays and Efros [28] perform data-driven image inpainting. The quantitative comparison in terms of permuted-mAP \\((\\mathbf{p} - \\mathbf{mAP})\\) and class-balanced IoU (cIoU) following [33] are presented in Table 3. We also include splice image detection result in Table 4, where we compare our model to methods that enable splice detection." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.689, + 0.471, + 0.902 + ], + "angle": 0, + "content": "Our model ranks first or second place for metrics in most datasets, and obtains performance comparable to top self-supervised methods that are specially designed for this task. In particular, our model significantly outperforms the most related technique, EXIF-SC [33]. We note that both our method and EXIF-SC get relatively low performance on the Realistic Tampering dataset. This may be due to the fact that this dataset contains manipulations such as copy-move that we do not expect to detect (since both regions share the same camera properties). In contrast to methods based on segmentation [13, 79, 80], we do not aim to have spatially precise matches, and output relatively low-resolution localization maps based on large patches. Consequently, our model is not well-suited to detecting very small" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.363, + 0.892, + 0.393 + ], + "angle": 0, + "content": "spices, which also commonly occur in the Realistic Tampering dataset." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.396, + 0.893, + 0.579 + ], + "angle": 0, + "content": "In Fig. 4, we show qualitative results, including both similarity maps and spectral clustering results. In Fig. 6, we compare our model with those of several other techniques. Interestingly, EXIF-SC has false positives in overexposed regions (as pointed out by [33]), since its classifier cannot infer whether these regions are (or are not) part of the rest of the scene. In contrast, our model successfully handles these regions. CropCLR incorrectly flags regions that are semantically different from the background, because this is a strong indication that the patches come from different images. In contrast, we successfully handle these cases, since our model has no such \"shortcut\" in its learning task." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.598, + 0.655, + 0.615 + ], + "angle": 0, + "content": "4.4. Ablation Study" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.625, + 0.894, + 0.701 + ], + "angle": 0, + "content": "To help understand which aspects of our approach are responsible for its performance, we evaluated a variety of variations of our model, including different training supervision, representations for the camera metadata, and network architectures." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.704, + 0.895, + 0.901 + ], + "angle": 0, + "content": "We evaluated each model's features quality using linear probing on the radial distortion estimation and splice detection task (same as Sec. 4.2). As an additional evaluation, we classify the values of common EXIF tags by applying linear classifiers to our visual representation. We convert the values of each EXIF tag into discrete categories, by quantizing common values and removing examples that do not fit into any category. We average prediction accuracies over 44 EXIF tags to obtain overall accuracy. We provide more details in the supplementary. All models were trained for 30 epochs on 800K images on a subset of YFCC100M dataset. The associated texts are obtained from the image descriptions and EXIF data provided by the dataset." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "6950" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.072, + 0.478, + 0.411 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.493, + 0.072, + 0.889, + 0.411 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.459, + 0.42, + 0.512, + 0.434 + ], + "angle": 0, + "content": "Figure 4" + }, + { + "type": "table", + "bbox": [ + 0.094, + 0.451, + 0.457, + 0.691 + ], + "angle": 0, + "content": "
MethodEXIFRadialForens.
Majority class baseline0.120.050.50
SupervisionAll EXIF tags0.350.290.85
CropCLR0.290.220.84
“Camera Model” tag only0.310.270.80
“Color Space” tag only0.120.120.61
YFCC image descriptions0.150.160.70
Tag formatFixed order, w/ tag name0.350.290.85
Fixed order, w/o tag name0.350.280.86
Rand. order, w/ tag name0.340.260.77
Rand. order, w/o tag name0.330.260.76
ArchitectureDistilBERT, w/ pretrained0.350.290.85
DistilBERT, w/o pretrained0.360.250.77
ALBERT, w/ pretrained0.330.290.84
ALBERT, w/o pretrained0.340.260.79
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.695, + 0.47, + 0.806 + ], + "angle": 0, + "content": "Table 5. Model ablations. Downstream accuracy for versions of the model trained with different text supervision, representations of camera metadata, and architectures. We use linear probing to evaluate the average prediction accuracy of EXIF tag values on our YFCC test set, radial distortion estimation on Dresden dataset, and real-or-fake classification on CASIA I dataset. Rows with gray background (replicated for ease of comparison) represent the same model which is our \"full\" model." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.825, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Metadata supervision. We evaluate a variation of our model that trains using the image descriptions provided by YFCC100M in lieu of camera metadata, as well as models supervised by individual EXIF tags (Table 5). For the variations supervised by a single EXIF tag, we chose 14" + }, + { + "type": "image", + "bbox": [ + 0.505, + 0.452, + 0.89, + 0.559 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.568, + 0.892, + 0.61 + ], + "angle": 0, + "content": "Figure 5. Per-tag forensics task accuracy. We train various models supervised by individual EXIF tags, then evaluate the learned representations for splice detection task on CASIA I." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.619, + 0.893, + 0.846 + ], + "angle": 0, + "content": "common tags for this experiment, training a separate network for each one. The results of the per-tag evaluation is shown in Fig. 5. These results suggest that having access to the full metadata provides significantly better performance than using individual tags. Moreover, there is a wide variation in the performance of models that use different tag. This may be because the high performing tags, such as Camera Model, convey significantly more information about the full range of camera properties than others, such as Color Space and Sensing Method. These results suggest that a model that simply uses the full range of tags can extract significantly more camera information from the metadata. We also found that the variation trained on image descriptions (rather than EXIF text) performed significantly worse than other models." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.856, + 0.894, + 0.903 + ], + "angle": 0, + "content": "Tag format. Since EXIF does not have a natural order of tags, we ask what will happen if we randomize the EXIF tag order during training. Table 5 shows the performance drops" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.514, + 0.957 + ], + "angle": 0, + "content": "6951" + } + ], + [ + { + "type": "image_caption", + "bbox": [ + 0.125, + 0.077, + 0.171, + 0.091 + ], + "angle": 0, + "content": "Image" + }, + { + "type": "image_caption", + "bbox": [ + 0.233, + 0.077, + 0.292, + 0.09 + ], + "angle": 0, + "content": "EXIF-SC" + }, + { + "type": "image_caption", + "bbox": [ + 0.338, + 0.078, + 0.412, + 0.091 + ], + "angle": 0, + "content": "Noiseprint" + }, + { + "type": "image_caption", + "bbox": [ + 0.468, + 0.078, + 0.502, + 0.09 + ], + "angle": 0, + "content": "OSN" + }, + { + "type": "image_caption", + "bbox": [ + 0.568, + 0.078, + 0.632, + 0.09 + ], + "angle": 0, + "content": "CropCLR" + }, + { + "type": "image_caption", + "bbox": [ + 0.695, + 0.078, + 0.73, + 0.09 + ], + "angle": 0, + "content": "Ours" + }, + { + "type": "image_caption", + "bbox": [ + 0.78, + 0.078, + 0.873, + 0.09 + ], + "angle": 0, + "content": "Ground Truth" + }, + { + "type": "image", + "bbox": [ + 0.092, + 0.095, + 0.885, + 0.502 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.505, + 0.893, + 0.534 + ], + "angle": 0, + "content": "Figure 6. Qualitative comparison to other methods. Our method can correctly localize splices in many scenarios where other methods fail. For example, EXIF-SC [33] fails on overexposed image regions; OSN [79] and CropCLR often segment scenes based on semantics." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.539, + 0.473, + 0.675 + ], + "angle": 0, + "content": "for all three evaluations in this case. This may be due to the fact that the Transformer model is forced to learn meaningful positional embeddings corresponding to each EXIF tag if their order keeps on changing. We also tried removing the tag names from the camera metadata and just provide the values for those keys, e.g. replacing Make: Apple with Apple. Interestingly, this model performs on par with the model that has tag names, suggesting that the network can discern information about the tags from the values alone." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.682, + 0.47, + 0.818 + ], + "angle": 0, + "content": "Text encoder architecture. To test whether performance of our model tied to a specific transformer architecture, we experimented with two different transformer models, DistilBERT [67] and ALBERT [44]. We see that both architectures obtain similar performance on all three tasks with DistilBERT slightly outperforming ALBERT. We also test how much pretraining the text encoder helps with the performance. From Table 5, we can see pretraining improves performance on the radial distortion and forensics tasks." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.83, + 0.192, + 0.846 + ], + "angle": 0, + "content": "5. Discussion" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.471, + 0.901 + ], + "angle": 0, + "content": "In this paper, we proposed to learn camera properties by training models to find cross-modal correspondences between images and camera metadata. To achieve this, we" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.539, + 0.895, + 0.736 + ], + "angle": 0, + "content": "created a model that exploits the fact that EXIF metadata can easily be represented and processed as text. Our model achieves strong performance amongst self-supervised methods on a variety of downstream tasks that require understanding camera properties, including zero shot image forensics and radial distortion estimation. We see our work opening several possible directions. First, it opens the possibility of creating multimodal learning systems that use camera metadata as another form of supervision, providing complementary information to high-level modalities like language and sound. Second, it opens applications that require an understanding of low level sensor information, which may benefit from our feature sets." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.743, + 0.894, + 0.835 + ], + "angle": 0, + "content": "Limitations and Broader Impacts. We have shown that our learned features are useful for image forensics, which has potential to reduce the spread of disinformation [22]. The model that we will release may not be fully representative of the cameras in the wild, since it was trained only on photos available in the YFCC100M dataset [73]." + }, + { + "type": "title", + "bbox": [ + 0.501, + 0.848, + 0.597, + 0.864 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.508, + 0.873, + 0.893, + 0.901 + ], + "angle": 0, + "content": "[1] Ali Azarbayejani and Alex P Pentland. Recursive estimation of motion, structure, and focal length. 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(a) We learn a joint embedding between image patches and the EXIF metadata that cameras automatically insert into image files. Our model treats this metadata as a language-like modality: we convert the EXIF tags to text, concatenate them together, and then processes the result with a transformer. (b) We apply our representation to tasks that require understanding camera properties. For example, we can detect image splicing "zero shot" (and without metadata at test time) by finding inconsistent embeddings within an image. We show a manipulated image that contains content from two source photos. Since these photos were captured with different cameras, the two regions have dissimilar embeddings (visualized by PCA). We localize the splice by clustering the image's patch embeddings. + +![](images/ce5e683e3ffb1d50f9ccbac1261ad00d9adfadb0a4038ce02a7cd4e84148e92c.jpg) +Patch embeddings + +![](images/94dcea636089c61a35addffb94f89c231e103c1ef8b43f81b6147292fe09e32f.jpg) +Detected splice + +![](images/c7ab03850a618e033c7aa01b66bad2b73ca07cea7d06f61e485bb1ffd89bc8ef.jpg) +Ground truth + +# Abstract + +We learn a visual representation that captures information about the camera that recorded a given photo. To do this, we train a multimodal embedding between image patches and the EXIF metadata that cameras automatically insert into image files. Our model represents this metadata by simply converting it to text and then processing it with a transformer. The features that we learn significantly outperform other self-supervised and supervised features on downstream image forensics and calibration tasks. In particular, we successfully localize spliced image regions "zero shot" by clustering the visual embeddings for all of the patches within an image. + +# 1. Introduction + +A major goal of the computer vision community has been to use cross-modal associations to learn concepts that would be hard to glean from images alone [2]. A particular focus has been on learning high level semantics, such as + +objects, from other rich sensory signals, like language and sound [58, 62]. By design, the representations learned by these approaches typically discard imaging properties, such as the type of camera that shot the photo, its lens, and the exposure settings, which are not useful for their cross-modal prediction tasks [17]. + +We argue that obtaining a complete understanding of an image requires both capabilities — for our models to perceive not only the semantic content of a scene, but also the properties of the camera that captured it. This type of low level understanding has proven crucial for a variety of tasks, from image forensics [33, 52, 80] to 3D reconstruction [34, 35], yet it has not typically been a focus of representation learning. It is also widely used in image generation, such as when users of text-to-image tools specify camera properties with phrases like "DSLR photo" [59, 63]. + +We propose to learn low level imaging properties from the abundantly available (but often neglected) camera metadata that is added to the image file at the moment of capture. This metadata is typically represented as dozens of Exchangeable Image File Format (EXIF) tags that describe the camera, its settings, and postprocessing operations that + +were applied to the image: e.g., Model: "iPhone 4s" or Focal Length: $35.0 \, \text{mm}$ . We train a joint embedding through contrastive learning that puts image patches into correspondence with camera metadata (Fig. 1a). Our model processes the metadata with a transformer [75] after converting it to a language-like representation. To do this conversion, we take advantage of the fact that EXIF tags are typically stored in a human-readable (and text-based) format. We convert each tag to text, and then concatenate them together. Our model thus closely resembles contrastive vision-and-language models, such as CLIP [62], but with EXIF-derived text in place of natural language. + +We show that our model can successfully estimate camera properties solely from images, and that it provides a useful representation for a variety of image forensics and camera calibration tasks. Our approaches to these tasks do not require camera metadata at test time. Instead, camera properties are estimated implicitly from image content via multimodal embeddings. + +We evaluate the learned feature of our model on two classification tasks that benefit from a low-level understanding of images: estimating an image's radial distortion parameter, and distinguishing real and manipulated images. We find that our features significantly outperform alternative supervised and self-supervised feature sets. + +We also show that our embeddings can be used to detect image splicing "zero shot" (i.e., without labeled data), drawing on recent work [8, 33, 54] that detects inconsistencies in camera fingerprints hidden within image patches. Spliced images contain content from multiple real images, each potentially captured with a different camera and imaging pipeline. Thus, the embeddings that our model assigns to their patches, which convey camera properties, will have less consistency than those of real images. We detect manipulations by flagging images whose patch embeddings do not fit into a single, compact cluster. We also localize spliced regions by clustering the embeddings within an image (Fig. 1b). + +We show through our experiments that: + +- Camera metadata provides supervision for self-supervised representation learning. +- Image patches can be successfully associated with camera metadata via joint embeddings. +- Image-metadata embeddings are a useful representation for forensics and camera understanding tasks. +- Image manipulations can be identified "zero shot" by identifying inconsistencies in patch embeddings. + +# 2. Related Work + +Estimating camera properties. Camera metadata has been used for a range of tasks in computer vision, such as for predicting focal length [1, 31, 50, 71], performing white balancing [20, 49] and estimating camera models + +![](images/a311051a7dfabe693642f97231795852484542022e18ea42544732dab992e320.jpg) +Figure 2. Cross-modal image and camera metadata model. We use contrastive learning to associate each image patch with the EXIF metadata that was extracted from its image file. We represent the metadata as text, which is obtained by concatenating the EXIF tags together. We then process it using a transformer. + +[7, 39, 74]. It has also been used as extra input for recognition tasks [19, 72]. Instead of estimating camera properties directly (which can be highly error prone [33]), our model predicts an embedding that distinguishes a patch's camera properties from that of other patches in the dataset. + +Image forensics. Early work used physically motivated cues, such as misaligned JPEG blocks [6, 21], color filter array mismatches [3,4,23,78], inconsistencies in noise patterns [37, 47, 48, 61], and compression or boundary artifacts [5, 26, 32, 82]. Other works use supervised learning methods [40, 53, 64, 66, 76, 77, 79-81, 85]. The challenge of collecting large datasets of fake images has led to alternative approaches, such as synthetic examples [53, 79, 81, 85]. Other work uses self-supervised learning, such as methods based on denoising [13], or that detect image manipulations by identifying image content that appears to come from different camera models [7, 9, 54]. Huh et al. [33] learned a patch similarity metric in two steps: they determined which EXIF tags are shared between the patches, then use these binary predictions as features for a second classifier that predicts whether two patches come from the same (or different) images. In contrast, we obtain a visual similarity metric that is well-suited to splice localization directly from our multimodal embeddings. + +Language supervision in vision. Recent works have obtained visual supervision from language. The formulation includes specific keyword prediction [55], bag-of-word multilabel classification [36], $n$ -gram classification [46] and autoregressive language models [16, 68, 84]. Recently, Radford et al. [62] obtained strong performance by training a contrastive model on a large image-and-language dataset. Our technical approach is similar, but uses text from camera metadata in lieu of image captions. + +Work in text-to-image synthesis often exploits camera + +information through prompting, such as by adding text like "DSLR photo of..." or "Sigma 500mm f/5" to prompts [59]. These methods, however, learn these camera associations through the (relatively rare) descriptions of cameras provided by humans, while ours learns them from an abundant and complementary learning signal, camera metadata. + +# 3. Associating Images with Camera Metadata + +We desire a visual representation that captures low level imaging properties, such as the settings of the camera that were used to shoot the photo. We then apply this learned representation to downstream tasks that require an understanding of camera properties. + +# 3.1. Learning Cross-Modal Embeddings + +We train a model to predict camera metadata from image content, thereby obtaining a representation that conveys camera properties. Following previous work in multimodal contrastive learning [62], we train a joint embedding between the two modalities, allowing our model to avoid the (error prone) task of directly predicting the attributes. Specifically, we want to jointly learn an image encoder and metadata encoder such that, given $N$ images and $N$ pieces of metadata information, the corresponding image–metadata pairs can be recognized by the model by maximizing embedding similarity. We use full-resolution image patches rather than resized images, so that our model can analyze low-level details that may be lost during down-sampling. + +Given a dataset of image patches and their corresponding camera metadata $\{(\mathbf{v}_i,\mathbf{m}_i)\}_{i = 1}^N$ , we learn visual and EXIF representations $f_{\theta}(\mathbf{v})$ and $g_{\phi}(\mathbf{m})$ by jointly training $f_{\theta}$ and $g_{\phi}$ using a contrastive loss [57]: + +$$ +\mathcal {L} _ {i} ^ {V, M} = - \log \frac {\exp \left(f _ {\theta} \left(\mathbf {v} _ {i}\right) \cdot g _ {\phi} \left(\mathbf {m} _ {i}\right) / \tau\right)}{\sum_ {j = 1} ^ {N} \exp \left(f _ {\theta} \left(\mathbf {v} _ {i}\right) \cdot g _ {\phi} \left(\mathbf {m} _ {j}\right) / \tau\right)}, \tag {1} +$$ + +where $\tau$ is a small constant. Following prior work [62], we define an analogous loss $\mathcal{L}^{M,V}$ that sums over visual (rather than metadata) examples in the denominator, and minimize a combined loss $\mathcal{L} = \mathcal{L}^{V,M} + \mathcal{L}^{M,V}$ . + +# 3.2. Representing the Camera Metadata + +This formulation raises a natural question: how should we represent the metadata? The metadata within photos is stored as a set of EXIF tags, each indicating a different image property as shown in Table 1. EXIF tags span a range of formats and data types, and the set of tags that are present in a given photo can be highly inconsistent. Previous works that predict camera properties from images typically extract attributes of interest from the EXIF tags, and cast them to an appropriate data format — e.g., extracting a scalar-valued focal length category. This tag-specific processing limits + +
EXIF tagExample values#values
Camera MakeCanon, NIKON Corporation, Apple312
Camera ModelNIKON D90, Canon EOS 73071
SoftwarePicasa, Adobe Photoshop, QuickTime1711
Exposure Time1/60 sec, 1/125 sec, 1/250 sec2062
Focal Length18.0 mm, 50.0 mm, 6.3 mm931
Aperture ValueF2.8, F4, F5.6, F3.5137
Scene Capture TypeLandscape, Portrait, Night Scene5
Exposure ProgramAperture priority, Manual control9
White Balance ModeAuto, Manual3
Thumbnail CompressionJPEG, Uncompressed3
Digital Zoom Ratio1, 1.5, 2, 1.249
ISO speed Ratings100, 400, 300460
Shutter Speed Value1/60 sec, 1/63 sec, 1/124 sec1161
Date/Time Digitized2013:03:28 04:20:4695932
+ +Table 1. What information is contained within photo EXIF metadata? We list several of the most common EXIF tags, along with the common values and number of values they contain in the YFCC100M dataset [73]. + +the amount of metadata information that can be used as part of learning, and requires special-purpose architectures. + +We exploit the fact that EXIF tags are typically stored in a human-readable format and can be straightforwardly converted to text (Fig. 2). This allows us to directly process camera metadata using models from natural language processing — an approach that has successfully been applied to processing various text-like inputs other than language, such as math [45] and code [11]. Specifically, we create a long piece of text from a photo's metadata by converting each tag's name and value to strings, and concatenating them together. We separate each tag name and value with a colon and space, and separate different tags with a space. We evaluate a number of design decisions for this model in Sec. 4.4, such as the text format, choice of tags, and network architecture. + +# 3.3. Application: Zero-shot Image Forensics + +After learning cross-modal representations from images and camera metadata, we can use them for downstream tasks that require an understanding of camera properties. One way to do this is by using the learned visual network features as a representation for classification tasks, following other work in self-supervised representation learning [12, 29]. We can also use our learned visual embeddings to perform "zero shot" image splice detection, by detecting inconsistencies in an input image's imputed camera properties. + +Spliced images are composed of regions from multiple real images. Since they are typically designed to fool humans, forensic models need to rely more on subtle (often non-semantic) cues to detect them. We got inspiration from Huh et al. [33], which predicts whether two image patches share the same camera properties. If two patches are predicted to have very different camera properties, then this + +![](images/c45b0d3dfa2aef94de38260ae828c1ac3341bd2dd57bd75b825da4a493857113.jpg) +Figure 3. Zero shot splice localization. Given a spliced image (left), we compute our cross-modal embeddings for each image patch, which we visualize here using projections onto the top 3 principal components. We then compute the affinity matrix by taking dot product for every pair of patches. We localize the spliced region by clustering these embedding vectors. + +provides evidence that they come from different images. In our work, we can naturally obtain this patch similarity by computing the dot product between two patches' embeddings, since they have been trained to convey camera properties. We note that, unlike Huh et al. [33], we do not train a second, special-purpose classifier for this task, nor do we use augmentation to provide synthetic training examples (e.g., by applying different types of compression to the patches). + +To determine whether an image is likely to contain a splice, we first compute an affinity matrix $A_{ij} = f_{\theta}(\mathbf{v}_i) \cdot f_{\theta}(\mathbf{v}_j)$ whose entries are the dot product between patches' normalized embedding vectors. We score an image $\mathbf{v}$ using the sum of the exponentiated dot products between embeddings, $\phi (\mathbf{v}) = \sum_{i,j}\exp (A_{ij} / \tau)$ . This score indicates the likelihood that the image is unmodified, since high dot products indicate high similarity in imputed camera properties. To localize the spliced image regions within an image, we aggregate the similarity scores in $A_{ij}$ by clustering the rows using mean shift, following [33]. This results in a similarity map indicating the likelihood that each patch was extracted from the largest source photo that was used to create the composite. Alternatively, we can visualize the spliced region by performing spectral clustering via normalized cuts [33, 69], using $A_{ij}$ as an affinity matrix between patches. We visualize this approach in Fig. 3. + +# 4. Results + +# 4.1. Implementation + +Architecture. We use ResNet-50 pretrained on ImageNet as our image encoder. We found that the text encoder in models trained on captioning, such as CLIP [62], were not well-suited to our task, since they place low limits on the number of tokens. For the EXIF text encoder, we use DistilBERT [67] pretrained on Wikipedia and the Toronto Book Corpus [86]. We compute the feature representation of the EXIF as the activations for the end-of-sentence token from + +the last layer which is layer normalized and then linearly projected into multi-modal embedding space. + +Training. To train our model, we use 1.5M full-resolution images and EXIF pairs from a random subset of YFCC100M [73]. We discard images that have less than 10 of the EXIF tags. Because many images only have a small number of EXIF tags available, we only use tags that are present in more than half of these images. This results in 44 EXIF tags (see supplementary for the complete list). In contrast to other work [33], we do not rebalance the images to increase the rate of rare tags. During training, we randomly crop $124 \times 124$ patches from high-resolution images. We use the AdamW optimizer [38] with a learning rate of $10^{-4}$ , weight decay of $10^{-3}$ , and mixed precision training. We use a cosine annealing learning rate schedule [51]. The batch size is set to 1024, and we train our model for 50 epochs. + +Other model variations. To study the importance of metadata supervision on the learned representation, we train a similar model that performs contrastive learning but does not use metadata. The model resembles image-image contrastive learning [12,29,33,87], which has been shown to be highly effective for representation learning, and which may learn low-level camera information [17]. Different from typical contrastive learning approaches, we use strict cropping augmentation so that the views for our model (Eq. 1) come from different crops of the same image, to encourage it to learn low-level image features. We call this model CropCLR. Additionally, we evaluate a number of ablations of our model, including models that are trained with individual EXIF tags, that use different formats for the EXIF-derived text, and different network architectures (Table 5). + +# 4.2. Evaluating the learned features + +First, we want to measure how well the learned features convey camera properties. Since EXIF file is already embedded with a lot of camera properties such as camera model, focal length, shuttle speed, etc., it should be unsur + +
ModelsForensicsRadial Distortion
CASIA ICASIA IIDresdenRAISE
resizecropresizecropresizeresize
ImageNet pretrained0.690.640.710.720.230.24
MoCo0.670.670.680.690.240.28
CLIP0.710.820.840.810.210.22
Ours - CropCLR0.700.810.860.800.280.32
Ours - Full0.750.850.870.840.310.35
+ +Table 2. We do linear probing on top of learned representation to predict two camera related properties that are not presented in EXIF files. The good performance indicates that our model learns general imaging properties. resize and crop denote the image preprocessing applied. + +prising if we can predict those properties from images (we provide such results in Sec. 4.4). Instead, we want to study if the feature learned by the model can be generalized to other imaging properties that are not provided in the EXIF file. Specifically, we fit a linear classifier to our learned features on two prediction tasks: radial distortion estimation and forensic feature evaluation. + +We compare the features from our image encoder with several other approaches, including supervised ImageNet pretraining [65], a state-of-the-art self-supervised model MoCo [29], CLIP [62], which obtains strong semantic representations using natural language supervision (rather than EXIF supervision), and finally the CropCLR variation of our model. To ensure a fair comparison, the backbone architectures for all approaches are the same (ResNet-50). + +Radial distortion estimation. Imperfections in camera lens production often lead to radial distortion artifacts in captured images. These artifacts are often removed as part of multi-view 3D reconstruction [27, 70], using methods that model distortion as a 4th-order polynomial of pixel position. Radial distortion is not typically specified directly by the camera metadata, and is thus often must be estimated through calibration [10], bundle adjustment [70], or from monocular cues [50]. + +We followed the evaluation setup of Lopez et al. [50], which estimates the quadratic term of the radial distortion model, $k_{1}$ , directly from synthetically distorted images. This term can be used to provide an estimate of radial distortion that is sufficient for many tasks [50, 60]. We synthesized the $512 \times 512$ images from the Dresden Image Database [25] and RAISE dataset [14] using $k_{1}$ parameters uniformly sampled in the range $[-0.4, 0]$ . To predict $k_{1}$ , we used a regression-by-classification approach, quantizing the values of $k_{1}$ into 20 bins (We also show result in regression RMSE metrics in supplementary). We extracted features from different models, and trained a linear classifier on this 20-way classification problem. We provided + +them with a $512 \times 512$ image as input, and obtained image features from the global average pooling layer after the final convolutional layer (i.e., the penultimate layer of a typical ResNet). + +Representation learning for image forensics. We evaluate our model's ability to distinguish real and manipulated images. This is a task that requires a broader understanding of low level imaging properties, such as spotting unusual image statistics. We use the CASIA I [18] and CASIA II [43] datasets. The former contains only spliced fakes, while the latter contains a wider variety of manipulations. We again perform linear classification using the features provided by different models. We evaluate two types of preprocessing, resizing and center cropping, to test whether this low level task is sensitive to these details. + +In both tasks, we found that our model's features significantly outperformed those of the other models (Table 2). Our method achieves much better performance than traditional representational learning methods [29, 30, 62], perhaps because these models are encouraged to discard low-level details, while for our training task they are crucially important. Interestingly, the variation of our model that does not use EXIF metadata, CropCLR, outperforms the supervised [30] and self-supervised baselines [29], but significantly lags behind our full method. This is perhaps because it often suffices to use high-level cues (e.g. color histograms and object co-occurrence) to solve CropCLR's pretext task. This suggests metadata supervision is an important learning signal and can effectively guide our model to learn general imaging information. + +# 4.3. Zero Shot Splice Detection and Localization + +We evaluate our model on the task of detecting spliced images without any labeled training data. This is in contrast to Sec. 4.2, which used labeled data. We perform both splice detection (distinguish an image being spliced or not) and splice localization (localize spliced region within an image). + +Implementation. For fair evaluation, we closely follow the approach of Huh et al. [33]. Given an image, we sample patches in a grid, using a stride such that the number of patches sampled along the longest image dimension is 25. To increase the spatial resolution of each similarity map, we average the predictions of overlapping patches. We consider the smaller of the two detected regions to be the splice. + +Evaluation. In splice localization task, we compare our model to a variety of forensics methods. These include traditional methods that use handcrafted features [24, 52, 83], supervised methods [41, 79, 80], and self-supervised approaches [13, 33]. The datasets we use include Columbia [56], DSO [15], Realistic Tampering (RT) [42], In-the-Wild [33] and Hays and Efros inpainting images [28]. Columbia and DSO are created purely + +
StyleMethodColumbia [56]DSO [15]RT [42]In-the-Wild [33]Hays [28]
p-mAPcIoUp-mAPcIoUp-mAPcIoUp-mAPcIoUp-mAPcIoU
HandcraftedCFA [24]0.760.750.240.460.400.630.270.450.220.45
DCT [83]0.430.410.320.510.120.500.410.510.210.47
NOI [52]0.560.470.380.500.190.500.420.520.270.47
SupervisedMantraNet [80]0.780.880.530.780.500.540.500.630.270.56
MAG [41]0.690.770.480.560.510.550.470.590.300.61
OSN [79]0.680.900.550.850.510.810.660.880.280.57
UnsupervisedNoiseprint [13]0.710.830.660.900.290.800.500.780.220.53
EXIF-SC [33]0.890.970.470.810.220.750.490.790.260.54
Ours - CropCLR0.870.960.480.810.230.740.470.800.260.55
Ours - Full0.920.980.560.850.230.740.510.820.300.58
+ +Table 3. Zero shot splice localization. We evaluate our model on several datasets using permutation-invariant mean average precision (p-mAP) over pixels and class-balanced IOU (cIoU) with optimal threshold selected per image. The result indicates that our model is comparable to state-of-the-art methods, although not specially optimized for this task. + +
DatasetColumbia [56]DSO [15]RT [42]
CFA [24]0.830.490.54
DCT [83]0.580.480.52
NOI [52]0.730.510.52
EXIF-SC0.980.610.55
Ours - CropCLR0.960.620.52
Ours - Full0.990.660.53
+ +Table 4. Zero-shot splice detection: We compare our splice detection accuracy on 3 datasets. We measure the mean average precision (mAP) of detecting whether an image has been spliced. + +via image splicing, while Realistic Tampering contains a diverse set of manipulations. In-the-Wild is a splicing image dataset composed of internet images, which may also contain a variety of other manipulations. Hays and Efros [28] perform data-driven image inpainting. The quantitative comparison in terms of permuted-mAP $(\mathbf{p} - \mathbf{mAP})$ and class-balanced IoU (cIoU) following [33] are presented in Table 3. We also include splice image detection result in Table 4, where we compare our model to methods that enable splice detection. + +Our model ranks first or second place for metrics in most datasets, and obtains performance comparable to top self-supervised methods that are specially designed for this task. In particular, our model significantly outperforms the most related technique, EXIF-SC [33]. We note that both our method and EXIF-SC get relatively low performance on the Realistic Tampering dataset. This may be due to the fact that this dataset contains manipulations such as copy-move that we do not expect to detect (since both regions share the same camera properties). In contrast to methods based on segmentation [13, 79, 80], we do not aim to have spatially precise matches, and output relatively low-resolution localization maps based on large patches. Consequently, our model is not well-suited to detecting very small + +spices, which also commonly occur in the Realistic Tampering dataset. + +In Fig. 4, we show qualitative results, including both similarity maps and spectral clustering results. In Fig. 6, we compare our model with those of several other techniques. Interestingly, EXIF-SC has false positives in overexposed regions (as pointed out by [33]), since its classifier cannot infer whether these regions are (or are not) part of the rest of the scene. In contrast, our model successfully handles these regions. CropCLR incorrectly flags regions that are semantically different from the background, because this is a strong indication that the patches come from different images. In contrast, we successfully handle these cases, since our model has no such "shortcut" in its learning task. + +# 4.4. Ablation Study + +To help understand which aspects of our approach are responsible for its performance, we evaluated a variety of variations of our model, including different training supervision, representations for the camera metadata, and network architectures. + +We evaluated each model's features quality using linear probing on the radial distortion estimation and splice detection task (same as Sec. 4.2). As an additional evaluation, we classify the values of common EXIF tags by applying linear classifiers to our visual representation. We convert the values of each EXIF tag into discrete categories, by quantizing common values and removing examples that do not fit into any category. We average prediction accuracies over 44 EXIF tags to obtain overall accuracy. We provide more details in the supplementary. All models were trained for 30 epochs on 800K images on a subset of YFCC100M dataset. The associated texts are obtained from the image descriptions and EXIF data provided by the dataset. + +![](images/ad43f539a6a81ed62d5ea60505b180782851f8f671a91761b9762c5599d766af.jpg) +Figure 4 + +![](images/2fdfb8966aba1879abc2cac9b2139ba104fc5a9586e835e19b7def0ef6ad3dd1.jpg) + +
MethodEXIFRadialForens.
Majority class baseline0.120.050.50
SupervisionAll EXIF tags0.350.290.85
CropCLR0.290.220.84
“Camera Model” tag only0.310.270.80
“Color Space” tag only0.120.120.61
YFCC image descriptions0.150.160.70
Tag formatFixed order, w/ tag name0.350.290.85
Fixed order, w/o tag name0.350.280.86
Rand. order, w/ tag name0.340.260.77
Rand. order, w/o tag name0.330.260.76
ArchitectureDistilBERT, w/ pretrained0.350.290.85
DistilBERT, w/o pretrained0.360.250.77
ALBERT, w/ pretrained0.330.290.84
ALBERT, w/o pretrained0.340.260.79
+ +Table 5. Model ablations. Downstream accuracy for versions of the model trained with different text supervision, representations of camera metadata, and architectures. We use linear probing to evaluate the average prediction accuracy of EXIF tag values on our YFCC test set, radial distortion estimation on Dresden dataset, and real-or-fake classification on CASIA I dataset. Rows with gray background (replicated for ease of comparison) represent the same model which is our "full" model. + +Metadata supervision. We evaluate a variation of our model that trains using the image descriptions provided by YFCC100M in lieu of camera metadata, as well as models supervised by individual EXIF tags (Table 5). For the variations supervised by a single EXIF tag, we chose 14 + +![](images/108d56afff7567abaa79042cb074497735b9a497d35be336e2114c60cc61e394.jpg) +Figure 5. Per-tag forensics task accuracy. We train various models supervised by individual EXIF tags, then evaluate the learned representations for splice detection task on CASIA I. + +common tags for this experiment, training a separate network for each one. The results of the per-tag evaluation is shown in Fig. 5. These results suggest that having access to the full metadata provides significantly better performance than using individual tags. Moreover, there is a wide variation in the performance of models that use different tag. This may be because the high performing tags, such as Camera Model, convey significantly more information about the full range of camera properties than others, such as Color Space and Sensing Method. These results suggest that a model that simply uses the full range of tags can extract significantly more camera information from the metadata. We also found that the variation trained on image descriptions (rather than EXIF text) performed significantly worse than other models. + +Tag format. Since EXIF does not have a natural order of tags, we ask what will happen if we randomize the EXIF tag order during training. Table 5 shows the performance drops + +![](images/525314fda64912fce106de0e71d26e85a57f9d756a95f87618c480c017fc4709.jpg) +Image +EXIF-SC +Noiseprint +OSN +CropCLR +Ours +Ground Truth +Figure 6. Qualitative comparison to other methods. Our method can correctly localize splices in many scenarios where other methods fail. For example, EXIF-SC [33] fails on overexposed image regions; OSN [79] and CropCLR often segment scenes based on semantics. + +for all three evaluations in this case. This may be due to the fact that the Transformer model is forced to learn meaningful positional embeddings corresponding to each EXIF tag if their order keeps on changing. We also tried removing the tag names from the camera metadata and just provide the values for those keys, e.g. replacing Make: Apple with Apple. Interestingly, this model performs on par with the model that has tag names, suggesting that the network can discern information about the tags from the values alone. + +Text encoder architecture. To test whether performance of our model tied to a specific transformer architecture, we experimented with two different transformer models, DistilBERT [67] and ALBERT [44]. We see that both architectures obtain similar performance on all three tasks with DistilBERT slightly outperforming ALBERT. We also test how much pretraining the text encoder helps with the performance. From Table 5, we can see pretraining improves performance on the radial distortion and forensics tasks. + +# 5. Discussion + +In this paper, we proposed to learn camera properties by training models to find cross-modal correspondences between images and camera metadata. To achieve this, we + +created a model that exploits the fact that EXIF metadata can easily be represented and processed as text. Our model achieves strong performance amongst self-supervised methods on a variety of downstream tasks that require understanding camera properties, including zero shot image forensics and radial distortion estimation. We see our work opening several possible directions. First, it opens the possibility of creating multimodal learning systems that use camera metadata as another form of supervision, providing complementary information to high-level modalities like language and sound. Second, it opens applications that require an understanding of low level sensor information, which may benefit from our feature sets. + +Limitations and Broader Impacts. We have shown that our learned features are useful for image forensics, which has potential to reduce the spread of disinformation [22]. The model that we will release may not be fully representative of the cameras in the wild, since it was trained only on photos available in the YFCC100M dataset [73]. + +# References + +[1] Ali Azarbayejani and Alex P Pentland. Recursive estimation of motion, structure, and focal length. IEEE Transactions on + +Pattern Analysis and Machine Intelligence, 17(6):562-575, 1995. 2 +[2] Tadas Baltrusaitis, Chaitanya Ahuja, and Louis-Philippe Morency. Multimodal machine learning: A survey and taxonomy. IEEE transactions on pattern analysis and machine intelligence, 41(2):423-443, 2018. 1 +[3] Quentin Bamney, Rafael Grompone von Gioi, and Jean-Michel Morel. An adaptive neural network for unsupervised mosaic consistency analysis in image forensics. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 14194-14204, 2020. 2 +[4] Quentin Bammey, Rafael Grompone von Gioi, and Jean-Michel Morel. 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In Proceedings of the IEEE international conference on computer vision, pages 388-396, 2015. 4 \ No newline at end of file diff --git a/2023/EXIF As Language_ Learning Cross-Modal Associations Between Images and Camera Metadata/images.zip b/2023/EXIF As Language_ Learning Cross-Modal Associations Between Images and Camera Metadata/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..01a4c17332346ea11933a092612a2fd77f18be48 --- /dev/null +++ b/2023/EXIF As Language_ Learning Cross-Modal Associations Between Images and Camera Metadata/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:dfb13345283da9192bf979f05d356e540b488498fb1cb2873d99d89a77f18d19 +size 783137 diff --git a/2023/EXIF As Language_ Learning Cross-Modal Associations Between Images and Camera Metadata/layout.json b/2023/EXIF As Language_ Learning Cross-Modal Associations Between Images and Camera Metadata/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..7a54028b288139e229198d2b6550d59fbba494e9 --- /dev/null +++ b/2023/EXIF As Language_ Learning Cross-Modal Associations Between Images and Camera Metadata/layout.json @@ -0,0 +1,8386 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 135, + 103, + 459, + 138 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 135, + 103, + 459, + 138 + ], + "spans": [ + { + "bbox": [ + 135, + 103, + 459, + 138 + ], + "type": "text", + "content": "EXIF as Language: Learning Cross-Modal Associations Between Images and Camera Metadata" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 147, + 161, + 227, + 175 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 147, + 161, + 227, + 175 + ], + "spans": [ + { + "bbox": [ + 147, + 161, + 227, + 175 + ], + "type": "text", + "content": "Chenhao Zheng" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 251, + 162, + 341, + 175 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 251, + 162, + 341, + 175 + ], + "spans": [ + { + "bbox": [ + 251, + 162, + 341, + 175 + ], + "type": "text", + "content": "Ayush Shrivastava" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 239, + 178, + 352, + 192 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 239, + 178, + 352, + 192 + ], + "spans": [ + { + "bbox": [ + 239, + 178, + 352, + 192 + ], + "type": "text", + "content": "University of Michigan" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 212, + 198, + 378, + 209 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 212, + 198, + 378, + 209 + ], + "spans": [ + { + "bbox": [ + 212, + 198, + 378, + 209 + ], + "type": "text", + "content": "https://hellomuffin.github.io/exif-as-language" + } + ] + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 52, + 239, + 231, + 340 + ], + "blocks": [ + { + "bbox": [ + 52, + 239, + 231, + 340 + ], + "lines": [ + { + "bbox": [ + 52, + 239, + 231, + 340 + ], + "spans": [ + { + "bbox": [ + 52, + 239, + 231, + 340 + ], + "type": "image", + "image_path": "a17b7c3c4b4f0f67f778a72abc66db20f513e2004c75ecac18f19e931bb6803f.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 69, + 344, + 216, + 354 + ], + "lines": [ + { + "bbox": [ + 69, + 344, + 216, + 354 + ], + "spans": [ + { + "bbox": [ + 69, + 344, + 216, + 354 + ], + "type": "text", + "content": "(a) Multimodal image-metadata embeddings" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 250, + 344, + 487, + 354 + ], + "lines": [ + { + "bbox": [ + 250, + 344, + 487, + 354 + ], + "spans": [ + { + "bbox": [ + 250, + 344, + 487, + 354 + ], + "type": "text", + "content": "(b) Detecting spliced images by spotting inconsistent patch embeddings" + } + ] + } + ], + "index": 17, + "angle": 0, + "type": "image_caption" + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 242, + 239, + 305, + 324 + ], + "blocks": [ + { + "bbox": [ + 242, + 239, + 305, + 324 + ], + "lines": [ + { + "bbox": [ + 242, + 239, + 305, + 324 + ], + "spans": [ + { + "bbox": [ + 242, + 239, + 305, + 324 + ], + "type": "image", + "image_path": "4713c221b7d18df1b160a60779165e07f4da8bdff0c2ecd3db83817558b0813b.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 244, + 325, + 302, + 333 + ], + "lines": [ + { + "bbox": [ + 244, + 325, + 302, + 333 + ], + "spans": [ + { + "bbox": [ + 244, + 325, + 302, + 333 + ], + "type": "text", + "content": "Manipulated image" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 46, + 364, + 545, + 430 + ], + "lines": [ + { + "bbox": [ + 46, + 364, + 545, + 430 + ], + "spans": [ + { + "bbox": [ + 46, + 364, + 545, + 430 + ], + "type": "text", + "content": "Figure 1. (a) We learn a joint embedding between image patches and the EXIF metadata that cameras automatically insert into image files. Our model treats this metadata as a language-like modality: we convert the EXIF tags to text, concatenate them together, and then processes the result with a transformer. (b) We apply our representation to tasks that require understanding camera properties. For example, we can detect image splicing \"zero shot\" (and without metadata at test time) by finding inconsistent embeddings within an image. We show a manipulated image that contains content from two source photos. Since these photos were captured with different cameras, the two regions have dissimilar embeddings (visualized by PCA). We localize the splice by clustering the image's patch embeddings." + } + ] + } + ], + "index": 18, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 306, + 240, + 368, + 324 + ], + "blocks": [ + { + "bbox": [ + 306, + 240, + 368, + 324 + ], + "lines": [ + { + "bbox": [ + 306, + 240, + 368, + 324 + ], + "spans": [ + { + "bbox": [ + 306, + 240, + 368, + 324 + ], + "type": "image", + "image_path": "ce5e683e3ffb1d50f9ccbac1261ad00d9adfadb0a4038ce02a7cd4e84148e92c.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 309, + 325, + 365, + 333 + ], + "lines": [ + { + "bbox": [ + 309, + 325, + 365, + 333 + ], + "spans": [ + { + "bbox": [ + 309, + 325, + 365, + 333 + ], + "type": "text", + "content": "Patch embeddings" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 11 + }, + { + "type": "image", + "bbox": [ + 369, + 240, + 432, + 324 + ], + "blocks": [ + { + "bbox": [ + 369, + 240, + 432, + 324 + ], + "lines": [ + { + "bbox": [ + 369, + 240, + 432, + 324 + ], + "spans": [ + { + "bbox": [ + 369, + 240, + 432, + 324 + ], + "type": "image", + "image_path": "94dcea636089c61a35addffb94f89c231e103c1ef8b43f81b6147292fe09e32f.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 377, + 325, + 424, + 333 + ], + "lines": [ + { + "bbox": [ + 377, + 325, + 424, + 333 + ], + "spans": [ + { + "bbox": [ + 377, + 325, + 424, + 333 + ], + "type": "text", + "content": "Detected splice" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_caption" + } + ], + "index": 13 + }, + { + "type": "image", + "bbox": [ + 433, + 240, + 496, + 324 + ], + "blocks": [ + { + "bbox": [ + 433, + 240, + 496, + 324 + ], + "lines": [ + { + "bbox": [ + 433, + 240, + 496, + 324 + ], + "spans": [ + { + "bbox": [ + 433, + 240, + 496, + 324 + ], + "type": "image", + "image_path": "c7ab03850a618e033c7aa01b66bad2b73ca07cea7d06f61e485bb1ffd89bc8ef.jpg" + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 444, + 325, + 484, + 333 + ], + "lines": [ + { + "bbox": [ + 444, + 325, + 484, + 333 + ], + "spans": [ + { + "bbox": [ + 444, + 325, + 484, + 333 + ], + "type": "text", + "content": "Ground truth" + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "image_caption" + } + ], + "index": 15 + }, + { + "bbox": [ + 143, + 447, + 192, + 459 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 447, + 192, + 459 + ], + "spans": [ + { + "bbox": [ + 143, + 447, + 192, + 459 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 46, + 473, + 288, + 617 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 473, + 288, + 617 + ], + "spans": [ + { + "bbox": [ + 46, + 473, + 288, + 617 + ], + "type": "text", + "content": "We learn a visual representation that captures information about the camera that recorded a given photo. To do this, we train a multimodal embedding between image patches and the EXIF metadata that cameras automatically insert into image files. Our model represents this metadata by simply converting it to text and then processing it with a transformer. The features that we learn significantly outperform other self-supervised and supervised features on downstream image forensics and calibration tasks. In particular, we successfully localize spliced image regions \"zero shot\" by clustering the visual embeddings for all of the patches within an image." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 47, + 645, + 127, + 657 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 645, + 127, + 657 + ], + "spans": [ + { + "bbox": [ + 47, + 645, + 127, + 657 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 46, + 666, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 666, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 666, + 287, + 715 + ], + "type": "text", + "content": "A major goal of the computer vision community has been to use cross-modal associations to learn concepts that would be hard to glean from images alone [2]. A particular focus has been on learning high level semantics, such as" + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 304, + 448, + 545, + 519 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 448, + 545, + 519 + ], + "spans": [ + { + "bbox": [ + 304, + 448, + 545, + 519 + ], + "type": "text", + "content": "objects, from other rich sensory signals, like language and sound [58, 62]. By design, the representations learned by these approaches typically discard imaging properties, such as the type of camera that shot the photo, its lens, and the exposure settings, which are not useful for their cross-modal prediction tasks [17]." + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 304, + 521, + 546, + 641 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 521, + 546, + 641 + ], + "spans": [ + { + "bbox": [ + 304, + 521, + 546, + 641 + ], + "type": "text", + "content": "We argue that obtaining a complete understanding of an image requires both capabilities — for our models to perceive not only the semantic content of a scene, but also the properties of the camera that captured it. This type of low level understanding has proven crucial for a variety of tasks, from image forensics [33, 52, 80] to 3D reconstruction [34, 35], yet it has not typically been a focus of representation learning. It is also widely used in image generation, such as when users of text-to-image tools specify camera properties with phrases like \"DSLR photo\" [59, 63]." + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 304, + 643, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 643, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 643, + 547, + 715 + ], + "type": "text", + "content": "We propose to learn low level imaging properties from the abundantly available (but often neglected) camera metadata that is added to the image file at the moment of capture. This metadata is typically represented as dozens of Exchangeable Image File Format (EXIF) tags that describe the camera, its settings, and postprocessing operations that" + } + ] + } + ], + "index": 25 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 496, + 35 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 496, + 35 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 496, + 35 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "6945" + } + ] + } + ], + "index": 26 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 215 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 215 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 215 + ], + "type": "text", + "content": "were applied to the image: e.g., Model: \"iPhone 4s\" or Focal Length: " + }, + { + "bbox": [ + 46, + 72, + 289, + 215 + ], + "type": "inline_equation", + "content": "35.0 \\, \\text{mm}" + }, + { + "bbox": [ + 46, + 72, + 289, + 215 + ], + "type": "text", + "content": ". We train a joint embedding through contrastive learning that puts image patches into correspondence with camera metadata (Fig. 1a). Our model processes the metadata with a transformer [75] after converting it to a language-like representation. To do this conversion, we take advantage of the fact that EXIF tags are typically stored in a human-readable (and text-based) format. We convert each tag to text, and then concatenate them together. Our model thus closely resembles contrastive vision-and-language models, such as CLIP [62], but with EXIF-derived text in place of natural language." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 216, + 289, + 299 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 216, + 289, + 299 + ], + "spans": [ + { + "bbox": [ + 46, + 216, + 289, + 299 + ], + "type": "text", + "content": "We show that our model can successfully estimate camera properties solely from images, and that it provides a useful representation for a variety of image forensics and camera calibration tasks. Our approaches to these tasks do not require camera metadata at test time. Instead, camera properties are estimated implicitly from image content via multimodal embeddings." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 299, + 289, + 371 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 299, + 289, + 371 + ], + "spans": [ + { + "bbox": [ + 46, + 299, + 289, + 371 + ], + "type": "text", + "content": "We evaluate the learned feature of our model on two classification tasks that benefit from a low-level understanding of images: estimating an image's radial distortion parameter, and distinguishing real and manipulated images. We find that our features significantly outperform alternative supervised and self-supervised feature sets." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 371, + 289, + 526 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 371, + 289, + 526 + ], + "spans": [ + { + "bbox": [ + 46, + 371, + 289, + 526 + ], + "type": "text", + "content": "We also show that our embeddings can be used to detect image splicing \"zero shot\" (i.e., without labeled data), drawing on recent work [8, 33, 54] that detects inconsistencies in camera fingerprints hidden within image patches. Spliced images contain content from multiple real images, each potentially captured with a different camera and imaging pipeline. Thus, the embeddings that our model assigns to their patches, which convey camera properties, will have less consistency than those of real images. We detect manipulations by flagging images whose patch embeddings do not fit into a single, compact cluster. We also localize spliced regions by clustering the embeddings within an image (Fig. 1b)." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 527, + 208, + 538 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 527, + 208, + 538 + ], + "spans": [ + { + "bbox": [ + 47, + 527, + 208, + 538 + ], + "type": "text", + "content": "We show through our experiments that:" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 540, + 287, + 635 + ], + "type": "list", + "angle": 0, + "index": 9, + "blocks": [ + { + "bbox": [ + 47, + 540, + 287, + 563 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 540, + 287, + 563 + ], + "spans": [ + { + "bbox": [ + 47, + 540, + 287, + 563 + ], + "type": "text", + "content": "- Camera metadata provides supervision for self-supervised representation learning." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 563, + 287, + 586 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 563, + 287, + 586 + ], + "spans": [ + { + "bbox": [ + 47, + 563, + 287, + 586 + ], + "type": "text", + "content": "- Image patches can be successfully associated with camera metadata via joint embeddings." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 587, + 286, + 610 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 587, + 286, + 610 + ], + "spans": [ + { + "bbox": [ + 47, + 587, + 286, + 610 + ], + "type": "text", + "content": "- Image-metadata embeddings are a useful representation for forensics and camera understanding tasks." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 611, + 286, + 635 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 611, + 286, + 635 + ], + "spans": [ + { + "bbox": [ + 47, + 611, + 286, + 635 + ], + "type": "text", + "content": "- Image manipulations can be identified \"zero shot\" by identifying inconsistencies in patch embeddings." + } + ] + } + ], + "index": 8 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 47, + 645, + 134, + 658 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 645, + 134, + 658 + ], + "spans": [ + { + "bbox": [ + 47, + 645, + 134, + 658 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 666, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 666, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 666, + 288, + 714 + ], + "type": "text", + "content": "Estimating camera properties. Camera metadata has been used for a range of tasks in computer vision, such as for predicting focal length [1, 31, 50, 71], performing white balancing [20, 49] and estimating camera models" + } + ] + } + ], + "index": 11 + }, + { + "type": "image", + "bbox": [ + 307, + 63, + 545, + 218 + ], + "blocks": [ + { + "bbox": [ + 307, + 63, + 545, + 218 + ], + "lines": [ + { + "bbox": [ + 307, + 63, + 545, + 218 + ], + "spans": [ + { + "bbox": [ + 307, + 63, + 545, + 218 + ], + "type": "image", + "image_path": "a311051a7dfabe693642f97231795852484542022e18ea42544732dab992e320.jpg" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 224, + 547, + 280 + ], + "lines": [ + { + "bbox": [ + 304, + 224, + 547, + 280 + ], + "spans": [ + { + "bbox": [ + 304, + 224, + 547, + 280 + ], + "type": "text", + "content": "Figure 2. Cross-modal image and camera metadata model. We use contrastive learning to associate each image patch with the EXIF metadata that was extracted from its image file. We represent the metadata as text, which is obtained by concatenating the EXIF tags together. We then process it using a transformer." + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_caption" + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 289, + 547, + 350 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 289, + 547, + 350 + ], + "spans": [ + { + "bbox": [ + 304, + 289, + 547, + 350 + ], + "type": "text", + "content": "[7, 39, 74]. It has also been used as extra input for recognition tasks [19, 72]. Instead of estimating camera properties directly (which can be highly error prone [33]), our model predicts an embedding that distinguishes a patch's camera properties from that of other patches in the dataset." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 357, + 547, + 586 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 357, + 547, + 586 + ], + "spans": [ + { + "bbox": [ + 304, + 357, + 547, + 586 + ], + "type": "text", + "content": "Image forensics. Early work used physically motivated cues, such as misaligned JPEG blocks [6, 21], color filter array mismatches [3,4,23,78], inconsistencies in noise patterns [37, 47, 48, 61], and compression or boundary artifacts [5, 26, 32, 82]. Other works use supervised learning methods [40, 53, 64, 66, 76, 77, 79-81, 85]. The challenge of collecting large datasets of fake images has led to alternative approaches, such as synthetic examples [53, 79, 81, 85]. Other work uses self-supervised learning, such as methods based on denoising [13], or that detect image manipulations by identifying image content that appears to come from different camera models [7, 9, 54]. Huh et al. [33] learned a patch similarity metric in two steps: they determined which EXIF tags are shared between the patches, then use these binary predictions as features for a second classifier that predicts whether two patches come from the same (or different) images. In contrast, we obtain a visual similarity metric that is well-suited to splice localization directly from our multimodal embeddings." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 594, + 547, + 700 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 594, + 547, + 700 + ], + "spans": [ + { + "bbox": [ + 304, + 594, + 547, + 700 + ], + "type": "text", + "content": "Language supervision in vision. Recent works have obtained visual supervision from language. The formulation includes specific keyword prediction [55], bag-of-word multilabel classification [36], " + }, + { + "bbox": [ + 304, + 594, + 547, + 700 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 304, + 594, + 547, + 700 + ], + "type": "text", + "content": "-gram classification [46] and autoregressive language models [16, 68, 84]. Recently, Radford et al. [62] obtained strong performance by training a contrastive model on a large image-and-language dataset. Our technical approach is similar, but uses text from camera metadata in lieu of image captions." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 318, + 701, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 318, + 701, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 318, + 701, + 545, + 713 + ], + "type": "text", + "content": "Work in text-to-image synthesis often exploits camera" + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "6946" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "type": "text", + "content": "information through prompting, such as by adding text like \"DSLR photo of...\" or \"Sigma 500mm f/5\" to prompts [59]. These methods, however, learn these camera associations through the (relatively rare) descriptions of cameras provided by humans, while ours learns them from an abundant and complementary learning signal, camera metadata." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 154, + 284, + 168 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 154, + 284, + 168 + ], + "spans": [ + { + "bbox": [ + 47, + 154, + 284, + 168 + ], + "type": "text", + "content": "3. Associating Images with Camera Metadata" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 175, + 287, + 236 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 175, + 287, + 236 + ], + "spans": [ + { + "bbox": [ + 46, + 175, + 287, + 236 + ], + "type": "text", + "content": "We desire a visual representation that captures low level imaging properties, such as the settings of the camera that were used to shoot the photo. We then apply this learned representation to downstream tasks that require an understanding of camera properties." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 241, + 238, + 255 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 241, + 238, + 255 + ], + "spans": [ + { + "bbox": [ + 47, + 241, + 238, + 255 + ], + "type": "text", + "content": "3.1. Learning Cross-Modal Embeddings" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 260, + 287, + 427 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 260, + 287, + 427 + ], + "spans": [ + { + "bbox": [ + 46, + 260, + 287, + 427 + ], + "type": "text", + "content": "We train a model to predict camera metadata from image content, thereby obtaining a representation that conveys camera properties. Following previous work in multimodal contrastive learning [62], we train a joint embedding between the two modalities, allowing our model to avoid the (error prone) task of directly predicting the attributes. Specifically, we want to jointly learn an image encoder and metadata encoder such that, given " + }, + { + "bbox": [ + 46, + 260, + 287, + 427 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 260, + 287, + 427 + ], + "type": "text", + "content": " images and " + }, + { + "bbox": [ + 46, + 260, + 287, + 427 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 260, + 287, + 427 + ], + "type": "text", + "content": " pieces of metadata information, the corresponding image–metadata pairs can be recognized by the model by maximizing embedding similarity. We use full-resolution image patches rather than resized images, so that our model can analyze low-level details that may be lost during down-sampling." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 427, + 287, + 475 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 427, + 287, + 475 + ], + "spans": [ + { + "bbox": [ + 46, + 427, + 287, + 475 + ], + "type": "text", + "content": "Given a dataset of image patches and their corresponding camera metadata " + }, + { + "bbox": [ + 46, + 427, + 287, + 475 + ], + "type": "inline_equation", + "content": "\\{(\\mathbf{v}_i,\\mathbf{m}_i)\\}_{i = 1}^N" + }, + { + "bbox": [ + 46, + 427, + 287, + 475 + ], + "type": "text", + "content": ", we learn visual and EXIF representations " + }, + { + "bbox": [ + 46, + 427, + 287, + 475 + ], + "type": "inline_equation", + "content": "f_{\\theta}(\\mathbf{v})" + }, + { + "bbox": [ + 46, + 427, + 287, + 475 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 427, + 287, + 475 + ], + "type": "inline_equation", + "content": "g_{\\phi}(\\mathbf{m})" + }, + { + "bbox": [ + 46, + 427, + 287, + 475 + ], + "type": "text", + "content": " by jointly training " + }, + { + "bbox": [ + 46, + 427, + 287, + 475 + ], + "type": "inline_equation", + "content": "f_{\\theta}" + }, + { + "bbox": [ + 46, + 427, + 287, + 475 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 427, + 287, + 475 + ], + "type": "inline_equation", + "content": "g_{\\phi}" + }, + { + "bbox": [ + 46, + 427, + 287, + 475 + ], + "type": "text", + "content": " using a contrastive loss [57]:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 64, + 483, + 287, + 513 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 64, + 483, + 287, + 513 + ], + "spans": [ + { + "bbox": [ + 64, + 483, + 287, + 513 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {i} ^ {V, M} = - \\log \\frac {\\exp \\left(f _ {\\theta} \\left(\\mathbf {v} _ {i}\\right) \\cdot g _ {\\phi} \\left(\\mathbf {m} _ {i}\\right) / \\tau\\right)}{\\sum_ {j = 1} ^ {N} \\exp \\left(f _ {\\theta} \\left(\\mathbf {v} _ {i}\\right) \\cdot g _ {\\phi} \\left(\\mathbf {m} _ {j}\\right) / \\tau\\right)}, \\tag {1}", + "image_path": "b63c4d068e2ecfd172d64e633e85fb01d4a4932b6d72a2c58a36d67463fbb348.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 520, + 287, + 568 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 520, + 287, + 568 + ], + "spans": [ + { + "bbox": [ + 46, + 520, + 287, + 568 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 520, + 287, + 568 + ], + "type": "inline_equation", + "content": "\\tau" + }, + { + "bbox": [ + 46, + 520, + 287, + 568 + ], + "type": "text", + "content": " is a small constant. Following prior work [62], we define an analogous loss " + }, + { + "bbox": [ + 46, + 520, + 287, + 568 + ], + "type": "inline_equation", + "content": "\\mathcal{L}^{M,V}" + }, + { + "bbox": [ + 46, + 520, + 287, + 568 + ], + "type": "text", + "content": " that sums over visual (rather than metadata) examples in the denominator, and minimize a combined loss " + }, + { + "bbox": [ + 46, + 520, + 287, + 568 + ], + "type": "inline_equation", + "content": "\\mathcal{L} = \\mathcal{L}^{V,M} + \\mathcal{L}^{M,V}" + }, + { + "bbox": [ + 46, + 520, + 287, + 568 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 575, + 237, + 588 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 575, + 237, + 588 + ], + "spans": [ + { + "bbox": [ + 47, + 575, + 237, + 588 + ], + "type": "text", + "content": "3.2. Representing the Camera Metadata" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 594, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 594, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 288, + 715 + ], + "type": "text", + "content": "This formulation raises a natural question: how should we represent the metadata? The metadata within photos is stored as a set of EXIF tags, each indicating a different image property as shown in Table 1. EXIF tags span a range of formats and data types, and the set of tags that are present in a given photo can be highly inconsistent. Previous works that predict camera properties from images typically extract attributes of interest from the EXIF tags, and cast them to an appropriate data format — e.g., extracting a scalar-valued focal length category. This tag-specific processing limits" + } + ] + } + ], + "index": 9 + }, + { + "type": "table", + "bbox": [ + 309, + 65, + 547, + 223 + ], + "blocks": [ + { + "bbox": [ + 309, + 65, + 547, + 223 + ], + "lines": [ + { + "bbox": [ + 309, + 65, + 547, + 223 + ], + "spans": [ + { + "bbox": [ + 309, + 65, + 547, + 223 + ], + "type": "table", + "html": "
EXIF tagExample values#values
Camera MakeCanon, NIKON Corporation, Apple312
Camera ModelNIKON D90, Canon EOS 73071
SoftwarePicasa, Adobe Photoshop, QuickTime1711
Exposure Time1/60 sec, 1/125 sec, 1/250 sec2062
Focal Length18.0 mm, 50.0 mm, 6.3 mm931
Aperture ValueF2.8, F4, F5.6, F3.5137
Scene Capture TypeLandscape, Portrait, Night Scene5
Exposure ProgramAperture priority, Manual control9
White Balance ModeAuto, Manual3
Thumbnail CompressionJPEG, Uncompressed3
Digital Zoom Ratio1, 1.5, 2, 1.249
ISO speed Ratings100, 400, 300460
Shutter Speed Value1/60 sec, 1/63 sec, 1/124 sec1161
Date/Time Digitized2013:03:28 04:20:4695932
", + "image_path": "c4530ad312368d19084577523fa295bd5e779986500bb366bb0277668132a3dc.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "table_body" + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 227, + 545, + 271 + ], + "lines": [ + { + "bbox": [ + 305, + 227, + 545, + 271 + ], + "spans": [ + { + "bbox": [ + 305, + 227, + 545, + 271 + ], + "type": "text", + "content": "Table 1. What information is contained within photo EXIF metadata? We list several of the most common EXIF tags, along with the common values and number of values they contain in the YFCC100M dataset [73]." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 304, + 289, + 545, + 313 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 289, + 545, + 313 + ], + "spans": [ + { + "bbox": [ + 304, + 289, + 545, + 313 + ], + "type": "text", + "content": "the amount of metadata information that can be used as part of learning, and requires special-purpose architectures." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 314, + 546, + 480 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 314, + 546, + 480 + ], + "spans": [ + { + "bbox": [ + 304, + 314, + 546, + 480 + ], + "type": "text", + "content": "We exploit the fact that EXIF tags are typically stored in a human-readable format and can be straightforwardly converted to text (Fig. 2). This allows us to directly process camera metadata using models from natural language processing — an approach that has successfully been applied to processing various text-like inputs other than language, such as math [45] and code [11]. Specifically, we create a long piece of text from a photo's metadata by converting each tag's name and value to strings, and concatenating them together. We separate each tag name and value with a colon and space, and separate different tags with a space. We evaluate a number of design decisions for this model in Sec. 4.4, such as the text format, choice of tags, and network architecture." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 491, + 515, + 503 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 491, + 515, + 503 + ], + "spans": [ + { + "bbox": [ + 305, + 491, + 515, + 503 + ], + "type": "text", + "content": "3.3. Application: Zero-shot Image Forensics" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 510, + 545, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 510, + 545, + 628 + ], + "spans": [ + { + "bbox": [ + 304, + 510, + 545, + 628 + ], + "type": "text", + "content": "After learning cross-modal representations from images and camera metadata, we can use them for downstream tasks that require an understanding of camera properties. One way to do this is by using the learned visual network features as a representation for classification tasks, following other work in self-supervised representation learning [12, 29]. We can also use our learned visual embeddings to perform \"zero shot\" image splice detection, by detecting inconsistencies in an input image's imputed camera properties." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "content": "Spliced images are composed of regions from multiple real images. Since they are typically designed to fool humans, forensic models need to rely more on subtle (often non-semantic) cues to detect them. We got inspiration from Huh et al. [33], which predicts whether two image patches share the same camera properties. If two patches are predicted to have very different camera properties, then this" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "6947" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 49, + 59, + 541, + 203 + ], + "blocks": [ + { + "bbox": [ + 49, + 59, + 541, + 203 + ], + "lines": [ + { + "bbox": [ + 49, + 59, + 541, + 203 + ], + "spans": [ + { + "bbox": [ + 49, + 59, + 541, + 203 + ], + "type": "image", + "image_path": "c45b0d3dfa2aef94de38260ae828c1ac3341bd2dd57bd75b825da4a493857113.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 209, + 546, + 243 + ], + "lines": [ + { + "bbox": [ + 46, + 209, + 546, + 243 + ], + "spans": [ + { + "bbox": [ + 46, + 209, + 546, + 243 + ], + "type": "text", + "content": "Figure 3. Zero shot splice localization. Given a spliced image (left), we compute our cross-modal embeddings for each image patch, which we visualize here using projections onto the top 3 principal components. We then compute the affinity matrix by taking dot product for every pair of patches. We localize the spliced region by clustering these embedding vectors." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 251, + 287, + 357 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 251, + 287, + 357 + ], + "spans": [ + { + "bbox": [ + 46, + 251, + 287, + 357 + ], + "type": "text", + "content": "provides evidence that they come from different images. In our work, we can naturally obtain this patch similarity by computing the dot product between two patches' embeddings, since they have been trained to convey camera properties. We note that, unlike Huh et al. [33], we do not train a second, special-purpose classifier for this task, nor do we use augmentation to provide synthetic training examples (e.g., by applying different types of compression to the patches)." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 358, + 287, + 563 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 358, + 287, + 563 + ], + "spans": [ + { + "bbox": [ + 46, + 358, + 287, + 563 + ], + "type": "text", + "content": "To determine whether an image is likely to contain a splice, we first compute an affinity matrix " + }, + { + "bbox": [ + 46, + 358, + 287, + 563 + ], + "type": "inline_equation", + "content": "A_{ij} = f_{\\theta}(\\mathbf{v}_i) \\cdot f_{\\theta}(\\mathbf{v}_j)" + }, + { + "bbox": [ + 46, + 358, + 287, + 563 + ], + "type": "text", + "content": " whose entries are the dot product between patches' normalized embedding vectors. We score an image " + }, + { + "bbox": [ + 46, + 358, + 287, + 563 + ], + "type": "inline_equation", + "content": "\\mathbf{v}" + }, + { + "bbox": [ + 46, + 358, + 287, + 563 + ], + "type": "text", + "content": " using the sum of the exponentiated dot products between embeddings, " + }, + { + "bbox": [ + 46, + 358, + 287, + 563 + ], + "type": "inline_equation", + "content": "\\phi (\\mathbf{v}) = \\sum_{i,j}\\exp (A_{ij} / \\tau)" + }, + { + "bbox": [ + 46, + 358, + 287, + 563 + ], + "type": "text", + "content": ". This score indicates the likelihood that the image is unmodified, since high dot products indicate high similarity in imputed camera properties. To localize the spliced image regions within an image, we aggregate the similarity scores in " + }, + { + "bbox": [ + 46, + 358, + 287, + 563 + ], + "type": "inline_equation", + "content": "A_{ij}" + }, + { + "bbox": [ + 46, + 358, + 287, + 563 + ], + "type": "text", + "content": " by clustering the rows using mean shift, following [33]. This results in a similarity map indicating the likelihood that each patch was extracted from the largest source photo that was used to create the composite. Alternatively, we can visualize the spliced region by performing spectral clustering via normalized cuts [33, 69], using " + }, + { + "bbox": [ + 46, + 358, + 287, + 563 + ], + "type": "inline_equation", + "content": "A_{ij}" + }, + { + "bbox": [ + 46, + 358, + 287, + 563 + ], + "type": "text", + "content": " as an affinity matrix between patches. We visualize this approach in Fig. 3." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 577, + 99, + 590 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 577, + 99, + 590 + ], + "spans": [ + { + "bbox": [ + 47, + 577, + 99, + 590 + ], + "type": "text", + "content": "4. Results" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 597, + 144, + 611 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 597, + 144, + 611 + ], + "spans": [ + { + "bbox": [ + 47, + 597, + 144, + 611 + ], + "type": "text", + "content": "4.1. Implementation" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 617, + 287, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 617, + 287, + 712 + ], + "spans": [ + { + "bbox": [ + 46, + 617, + 287, + 712 + ], + "type": "text", + "content": "Architecture. We use ResNet-50 pretrained on ImageNet as our image encoder. We found that the text encoder in models trained on captioning, such as CLIP [62], were not well-suited to our task, since they place low limits on the number of tokens. For the EXIF text encoder, we use DistilBERT [67] pretrained on Wikipedia and the Toronto Book Corpus [86]. We compute the feature representation of the EXIF as the activations for the end-of-sentence token from" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 305, + 251, + 545, + 274 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 251, + 545, + 274 + ], + "spans": [ + { + "bbox": [ + 305, + 251, + 545, + 274 + ], + "type": "text", + "content": "the last layer which is layer normalized and then linearly projected into multi-modal embedding space." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 282, + 546, + 450 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 282, + 546, + 450 + ], + "spans": [ + { + "bbox": [ + 304, + 282, + 546, + 450 + ], + "type": "text", + "content": "Training. To train our model, we use 1.5M full-resolution images and EXIF pairs from a random subset of YFCC100M [73]. We discard images that have less than 10 of the EXIF tags. Because many images only have a small number of EXIF tags available, we only use tags that are present in more than half of these images. This results in 44 EXIF tags (see supplementary for the complete list). In contrast to other work [33], we do not rebalance the images to increase the rate of rare tags. During training, we randomly crop " + }, + { + "bbox": [ + 304, + 282, + 546, + 450 + ], + "type": "inline_equation", + "content": "124 \\times 124" + }, + { + "bbox": [ + 304, + 282, + 546, + 450 + ], + "type": "text", + "content": " patches from high-resolution images. We use the AdamW optimizer [38] with a learning rate of " + }, + { + "bbox": [ + 304, + 282, + 546, + 450 + ], + "type": "inline_equation", + "content": "10^{-4}" + }, + { + "bbox": [ + 304, + 282, + 546, + 450 + ], + "type": "text", + "content": ", weight decay of " + }, + { + "bbox": [ + 304, + 282, + 546, + 450 + ], + "type": "inline_equation", + "content": "10^{-3}" + }, + { + "bbox": [ + 304, + 282, + 546, + 450 + ], + "type": "text", + "content": ", and mixed precision training. We use a cosine annealing learning rate schedule [51]. The batch size is set to 1024, and we train our model for 50 epochs." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 458, + 545, + 638 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 458, + 545, + 638 + ], + "spans": [ + { + "bbox": [ + 304, + 458, + 545, + 638 + ], + "type": "text", + "content": "Other model variations. To study the importance of metadata supervision on the learned representation, we train a similar model that performs contrastive learning but does not use metadata. The model resembles image-image contrastive learning [12,29,33,87], which has been shown to be highly effective for representation learning, and which may learn low-level camera information [17]. Different from typical contrastive learning approaches, we use strict cropping augmentation so that the views for our model (Eq. 1) come from different crops of the same image, to encourage it to learn low-level image features. We call this model CropCLR. Additionally, we evaluate a number of ablations of our model, including models that are trained with individual EXIF tags, that use different formats for the EXIF-derived text, and different network architectures (Table 5)." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 647, + 474, + 658 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 647, + 474, + 658 + ], + "spans": [ + { + "bbox": [ + 306, + 647, + 474, + 658 + ], + "type": "text", + "content": "4.2. Evaluating the learned features" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 666, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 666, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 666, + 545, + 713 + ], + "type": "text", + "content": "First, we want to measure how well the learned features convey camera properties. Since EXIF file is already embedded with a lot of camera properties such as camera model, focal length, shuttle speed, etc., it should be unsur" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "6948" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 52, + 70, + 288, + 190 + ], + "blocks": [ + { + "bbox": [ + 52, + 70, + 288, + 190 + ], + "lines": [ + { + "bbox": [ + 52, + 70, + 288, + 190 + ], + "spans": [ + { + "bbox": [ + 52, + 70, + 288, + 190 + ], + "type": "table", + "html": "
ModelsForensicsRadial Distortion
CASIA ICASIA IIDresdenRAISE
resizecropresizecropresizeresize
ImageNet pretrained0.690.640.710.720.230.24
MoCo0.670.670.680.690.240.28
CLIP0.710.820.840.810.210.22
Ours - CropCLR0.700.810.860.800.280.32
Ours - Full0.750.850.870.840.310.35
", + "image_path": "d2e278303c7ab9d39e3716dd6c88260021e82917ff10a222d8e7155744701de3.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + }, + { + "bbox": [ + 46, + 193, + 287, + 248 + ], + "lines": [ + { + "bbox": [ + 46, + 193, + 287, + 248 + ], + "spans": [ + { + "bbox": [ + 46, + 193, + 287, + 248 + ], + "type": "text", + "content": "Table 2. We do linear probing on top of learned representation to predict two camera related properties that are not presented in EXIF files. The good performance indicates that our model learns general imaging properties. resize and crop denote the image preprocessing applied." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_footnote" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 257, + 287, + 340 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 257, + 287, + 340 + ], + "spans": [ + { + "bbox": [ + 46, + 257, + 287, + 340 + ], + "type": "text", + "content": "prising if we can predict those properties from images (we provide such results in Sec. 4.4). Instead, we want to study if the feature learned by the model can be generalized to other imaging properties that are not provided in the EXIF file. Specifically, we fit a linear classifier to our learned features on two prediction tasks: radial distortion estimation and forensic feature evaluation." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 342, + 287, + 437 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 342, + 287, + 437 + ], + "spans": [ + { + "bbox": [ + 46, + 342, + 287, + 437 + ], + "type": "text", + "content": "We compare the features from our image encoder with several other approaches, including supervised ImageNet pretraining [65], a state-of-the-art self-supervised model MoCo [29], CLIP [62], which obtains strong semantic representations using natural language supervision (rather than EXIF supervision), and finally the CropCLR variation of our model. To ensure a fair comparison, the backbone architectures for all approaches are the same (ResNet-50)." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 449, + 287, + 556 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 449, + 287, + 556 + ], + "spans": [ + { + "bbox": [ + 46, + 449, + 287, + 556 + ], + "type": "text", + "content": "Radial distortion estimation. Imperfections in camera lens production often lead to radial distortion artifacts in captured images. These artifacts are often removed as part of multi-view 3D reconstruction [27, 70], using methods that model distortion as a 4th-order polynomial of pixel position. Radial distortion is not typically specified directly by the camera metadata, and is thus often must be estimated through calibration [10], bundle adjustment [70], or from monocular cues [50]." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 558, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 558, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 558, + 287, + 714 + ], + "type": "text", + "content": "We followed the evaluation setup of Lopez et al. [50], which estimates the quadratic term of the radial distortion model, " + }, + { + "bbox": [ + 46, + 558, + 287, + 714 + ], + "type": "inline_equation", + "content": "k_{1}" + }, + { + "bbox": [ + 46, + 558, + 287, + 714 + ], + "type": "text", + "content": ", directly from synthetically distorted images. This term can be used to provide an estimate of radial distortion that is sufficient for many tasks [50, 60]. We synthesized the " + }, + { + "bbox": [ + 46, + 558, + 287, + 714 + ], + "type": "inline_equation", + "content": "512 \\times 512" + }, + { + "bbox": [ + 46, + 558, + 287, + 714 + ], + "type": "text", + "content": " images from the Dresden Image Database [25] and RAISE dataset [14] using " + }, + { + "bbox": [ + 46, + 558, + 287, + 714 + ], + "type": "inline_equation", + "content": "k_{1}" + }, + { + "bbox": [ + 46, + 558, + 287, + 714 + ], + "type": "text", + "content": " parameters uniformly sampled in the range " + }, + { + "bbox": [ + 46, + 558, + 287, + 714 + ], + "type": "inline_equation", + "content": "[-0.4, 0]" + }, + { + "bbox": [ + 46, + 558, + 287, + 714 + ], + "type": "text", + "content": ". To predict " + }, + { + "bbox": [ + 46, + 558, + 287, + 714 + ], + "type": "inline_equation", + "content": "k_{1}" + }, + { + "bbox": [ + 46, + 558, + 287, + 714 + ], + "type": "text", + "content": ", we used a regression-by-classification approach, quantizing the values of " + }, + { + "bbox": [ + 46, + 558, + 287, + 714 + ], + "type": "inline_equation", + "content": "k_{1}" + }, + { + "bbox": [ + 46, + 558, + 287, + 714 + ], + "type": "text", + "content": " into 20 bins (We also show result in regression RMSE metrics in supplementary). We extracted features from different models, and trained a linear classifier on this 20-way classification problem. We provided" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "text", + "content": "them with a " + }, + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "inline_equation", + "content": "512 \\times 512" + }, + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "text", + "content": " image as input, and obtained image features from the global average pooling layer after the final convolutional layer (i.e., the penultimate layer of a typical ResNet)." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 125, + 545, + 256 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 125, + 545, + 256 + ], + "spans": [ + { + "bbox": [ + 304, + 125, + 545, + 256 + ], + "type": "text", + "content": "Representation learning for image forensics. We evaluate our model's ability to distinguish real and manipulated images. This is a task that requires a broader understanding of low level imaging properties, such as spotting unusual image statistics. We use the CASIA I [18] and CASIA II [43] datasets. The former contains only spliced fakes, while the latter contains a wider variety of manipulations. We again perform linear classification using the features provided by different models. We evaluate two types of preprocessing, resizing and center cropping, to test whether this low level task is sensitive to these details." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 257, + 546, + 437 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 257, + 546, + 437 + ], + "spans": [ + { + "bbox": [ + 304, + 257, + 546, + 437 + ], + "type": "text", + "content": "In both tasks, we found that our model's features significantly outperformed those of the other models (Table 2). Our method achieves much better performance than traditional representational learning methods [29, 30, 62], perhaps because these models are encouraged to discard low-level details, while for our training task they are crucially important. Interestingly, the variation of our model that does not use EXIF metadata, CropCLR, outperforms the supervised [30] and self-supervised baselines [29], but significantly lags behind our full method. This is perhaps because it often suffices to use high-level cues (e.g. color histograms and object co-occurrence) to solve CropCLR's pretext task. This suggests metadata supervision is an important learning signal and can effectively guide our model to learn general imaging information." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 444, + 534, + 456 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 444, + 534, + 456 + ], + "spans": [ + { + "bbox": [ + 306, + 444, + 534, + 456 + ], + "type": "text", + "content": "4.3. Zero Shot Splice Detection and Localization" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 462, + 545, + 522 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 462, + 545, + 522 + ], + "spans": [ + { + "bbox": [ + 304, + 462, + 545, + 522 + ], + "type": "text", + "content": "We evaluate our model on the task of detecting spliced images without any labeled training data. This is in contrast to Sec. 4.2, which used labeled data. We perform both splice detection (distinguish an image being spliced or not) and splice localization (localize spliced region within an image)." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 528, + 545, + 612 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 528, + 545, + 612 + ], + "spans": [ + { + "bbox": [ + 304, + 528, + 545, + 612 + ], + "type": "text", + "content": "Implementation. For fair evaluation, we closely follow the approach of Huh et al. [33]. Given an image, we sample patches in a grid, using a stride such that the number of patches sampled along the longest image dimension is 25. To increase the spatial resolution of each similarity map, we average the predictions of overlapping patches. We consider the smaller of the two detected regions to be the splice." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 617, + 546, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 546, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 546, + 714 + ], + "type": "text", + "content": "Evaluation. In splice localization task, we compare our model to a variety of forensics methods. These include traditional methods that use handcrafted features [24, 52, 83], supervised methods [41, 79, 80], and self-supervised approaches [13, 33]. The datasets we use include Columbia [56], DSO [15], Realistic Tampering (RT) [42], In-the-Wild [33] and Hays and Efros inpainting images [28]. Columbia and DSO are created purely" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "6949" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 54, + 70, + 541, + 238 + ], + "blocks": [ + { + "bbox": [ + 54, + 70, + 541, + 238 + ], + "lines": [ + { + "bbox": [ + 54, + 70, + 541, + 238 + ], + "spans": [ + { + "bbox": [ + 54, + 70, + 541, + 238 + ], + "type": "table", + "html": "
StyleMethodColumbia [56]DSO [15]RT [42]In-the-Wild [33]Hays [28]
p-mAPcIoUp-mAPcIoUp-mAPcIoUp-mAPcIoUp-mAPcIoU
HandcraftedCFA [24]0.760.750.240.460.400.630.270.450.220.45
DCT [83]0.430.410.320.510.120.500.410.510.210.47
NOI [52]0.560.470.380.500.190.500.420.520.270.47
SupervisedMantraNet [80]0.780.880.530.780.500.540.500.630.270.56
MAG [41]0.690.770.480.560.510.550.470.590.300.61
OSN [79]0.680.900.550.850.510.810.660.880.280.57
UnsupervisedNoiseprint [13]0.710.830.660.900.290.800.500.780.220.53
EXIF-SC [33]0.890.970.470.810.220.750.490.790.260.54
Ours - CropCLR0.870.960.480.810.230.740.470.800.260.55
Ours - Full0.920.980.560.850.230.740.510.820.300.58
", + "image_path": "55e60366c47fbeba4f99df68cf42da6103b59b4c6f7a0104ba190c168674debc.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 50, + 285, + 288, + 381 + ], + "blocks": [ + { + "bbox": [ + 46, + 240, + 547, + 275 + ], + "lines": [ + { + "bbox": [ + 46, + 240, + 547, + 275 + ], + "spans": [ + { + "bbox": [ + 46, + 240, + 547, + 275 + ], + "type": "text", + "content": "Table 3. Zero shot splice localization. We evaluate our model on several datasets using permutation-invariant mean average precision (p-mAP) over pixels and class-balanced IOU (cIoU) with optimal threshold selected per image. The result indicates that our model is comparable to state-of-the-art methods, although not specially optimized for this task." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 50, + 285, + 288, + 381 + ], + "lines": [ + { + "bbox": [ + 50, + 285, + 288, + 381 + ], + "spans": [ + { + "bbox": [ + 50, + 285, + 288, + 381 + ], + "type": "table", + "html": "
DatasetColumbia [56]DSO [15]RT [42]
CFA [24]0.830.490.54
DCT [83]0.580.480.52
NOI [52]0.730.510.52
EXIF-SC0.980.610.55
Ours - CropCLR0.960.620.52
Ours - Full0.990.660.53
", + "image_path": "df2258c5cd7b816ef62f0c1d0a52d622872993a3a4d53577168ac776fc582ec5.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 388, + 287, + 422 + ], + "lines": [ + { + "bbox": [ + 46, + 388, + 287, + 422 + ], + "spans": [ + { + "bbox": [ + 46, + 388, + 287, + 422 + ], + "type": "text", + "content": "Table 4. Zero-shot splice detection: We compare our splice detection accuracy on 3 datasets. We measure the mean average precision (mAP) of detecting whether an image has been spliced." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 426, + 287, + 544 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 426, + 287, + 544 + ], + "spans": [ + { + "bbox": [ + 46, + 426, + 287, + 544 + ], + "type": "text", + "content": "via image splicing, while Realistic Tampering contains a diverse set of manipulations. In-the-Wild is a splicing image dataset composed of internet images, which may also contain a variety of other manipulations. Hays and Efros [28] perform data-driven image inpainting. The quantitative comparison in terms of permuted-mAP " + }, + { + "bbox": [ + 46, + 426, + 287, + 544 + ], + "type": "inline_equation", + "content": "(\\mathbf{p} - \\mathbf{mAP})" + }, + { + "bbox": [ + 46, + 426, + 287, + 544 + ], + "type": "text", + "content": " and class-balanced IoU (cIoU) following [33] are presented in Table 3. We also include splice image detection result in Table 4, where we compare our model to methods that enable splice detection." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 545, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 545, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 545, + 288, + 714 + ], + "type": "text", + "content": "Our model ranks first or second place for metrics in most datasets, and obtains performance comparable to top self-supervised methods that are specially designed for this task. In particular, our model significantly outperforms the most related technique, EXIF-SC [33]. We note that both our method and EXIF-SC get relatively low performance on the Realistic Tampering dataset. This may be due to the fact that this dataset contains manipulations such as copy-move that we do not expect to detect (since both regions share the same camera properties). In contrast to methods based on segmentation [13, 79, 80], we do not aim to have spatially precise matches, and output relatively low-resolution localization maps based on large patches. Consequently, our model is not well-suited to detecting very small" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 287, + 545, + 311 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 287, + 545, + 311 + ], + "spans": [ + { + "bbox": [ + 304, + 287, + 545, + 311 + ], + "type": "text", + "content": "spices, which also commonly occur in the Realistic Tampering dataset." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 313, + 546, + 458 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 313, + 546, + 458 + ], + "spans": [ + { + "bbox": [ + 304, + 313, + 546, + 458 + ], + "type": "text", + "content": "In Fig. 4, we show qualitative results, including both similarity maps and spectral clustering results. In Fig. 6, we compare our model with those of several other techniques. Interestingly, EXIF-SC has false positives in overexposed regions (as pointed out by [33]), since its classifier cannot infer whether these regions are (or are not) part of the rest of the scene. In contrast, our model successfully handles these regions. CropCLR incorrectly flags regions that are semantically different from the background, because this is a strong indication that the patches come from different images. In contrast, we successfully handle these cases, since our model has no such \"shortcut\" in its learning task." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 473, + 400, + 487 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 473, + 400, + 487 + ], + "spans": [ + { + "bbox": [ + 306, + 473, + 400, + 487 + ], + "type": "text", + "content": "4.4. Ablation Study" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 495, + 547, + 555 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 495, + 547, + 555 + ], + "spans": [ + { + "bbox": [ + 304, + 495, + 547, + 555 + ], + "type": "text", + "content": "To help understand which aspects of our approach are responsible for its performance, we evaluated a variety of variations of our model, including different training supervision, representations for the camera metadata, and network architectures." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 557, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 557, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 557, + 547, + 713 + ], + "type": "text", + "content": "We evaluated each model's features quality using linear probing on the radial distortion estimation and splice detection task (same as Sec. 4.2). As an additional evaluation, we classify the values of common EXIF tags by applying linear classifiers to our visual representation. We convert the values of each EXIF tag into discrete categories, by quantizing common values and removing examples that do not fit into any category. We average prediction accuracies over 44 EXIF tags to obtain overall accuracy. We provide more details in the supplementary. All models were trained for 30 epochs on 800K images on a subset of YFCC100M dataset. The associated texts are obtained from the image descriptions and EXIF data provided by the dataset." + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "6950" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 50, + 57, + 292, + 325 + ], + "blocks": [ + { + "bbox": [ + 50, + 57, + 292, + 325 + ], + "lines": [ + { + "bbox": [ + 50, + 57, + 292, + 325 + ], + "spans": [ + { + "bbox": [ + 50, + 57, + 292, + 325 + ], + "type": "image", + "image_path": "ad43f539a6a81ed62d5ea60505b180782851f8f671a91761b9762c5599d766af.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 280, + 332, + 313, + 343 + ], + "lines": [ + { + "bbox": [ + 280, + 332, + 313, + 343 + ], + "spans": [ + { + "bbox": [ + 280, + 332, + 313, + 343 + ], + "type": "text", + "content": "Figure 4" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 301, + 57, + 544, + 325 + ], + "blocks": [ + { + "bbox": [ + 301, + 57, + 544, + 325 + ], + "lines": [ + { + "bbox": [ + 301, + 57, + 544, + 325 + ], + "spans": [ + { + "bbox": [ + 301, + 57, + 544, + 325 + ], + "type": "image", + "image_path": "2fdfb8966aba1879abc2cac9b2139ba104fc5a9586e835e19b7def0ef6ad3dd1.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "type": "table", + "bbox": [ + 57, + 357, + 279, + 547 + ], + "blocks": [ + { + "bbox": [ + 57, + 357, + 279, + 547 + ], + "lines": [ + { + "bbox": [ + 57, + 357, + 279, + 547 + ], + "spans": [ + { + "bbox": [ + 57, + 357, + 279, + 547 + ], + "type": "table", + "html": "
MethodEXIFRadialForens.
Majority class baseline0.120.050.50
SupervisionAll EXIF tags0.350.290.85
CropCLR0.290.220.84
“Camera Model” tag only0.310.270.80
“Color Space” tag only0.120.120.61
YFCC image descriptions0.150.160.70
Tag formatFixed order, w/ tag name0.350.290.85
Fixed order, w/o tag name0.350.280.86
Rand. order, w/ tag name0.340.260.77
Rand. order, w/o tag name0.330.260.76
ArchitectureDistilBERT, w/ pretrained0.350.290.85
DistilBERT, w/o pretrained0.360.250.77
ALBERT, w/ pretrained0.330.290.84
ALBERT, w/o pretrained0.340.260.79
", + "image_path": "e0ae17366cf28d7dfcc687f45ca50f4d14088da45cfa1dec18ea5a932587e1ad.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 550, + 287, + 638 + ], + "lines": [ + { + "bbox": [ + 46, + 550, + 287, + 638 + ], + "spans": [ + { + "bbox": [ + 46, + 550, + 287, + 638 + ], + "type": "text", + "content": "Table 5. Model ablations. Downstream accuracy for versions of the model trained with different text supervision, representations of camera metadata, and architectures. We use linear probing to evaluate the average prediction accuracy of EXIF tag values on our YFCC test set, radial distortion estimation on Dresden dataset, and real-or-fake classification on CASIA I dataset. Rows with gray background (replicated for ease of comparison) represent the same model which is our \"full\" model." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 653, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 653, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 653, + 288, + 715 + ], + "type": "text", + "content": "Metadata supervision. We evaluate a variation of our model that trains using the image descriptions provided by YFCC100M in lieu of camera metadata, as well as models supervised by individual EXIF tags (Table 5). For the variations supervised by a single EXIF tag, we chose 14" + } + ] + } + ], + "index": 5 + }, + { + "type": "image", + "bbox": [ + 309, + 357, + 544, + 442 + ], + "blocks": [ + { + "bbox": [ + 309, + 357, + 544, + 442 + ], + "lines": [ + { + "bbox": [ + 309, + 357, + 544, + 442 + ], + "spans": [ + { + "bbox": [ + 309, + 357, + 544, + 442 + ], + "type": "image", + "image_path": "108d56afff7567abaa79042cb074497735b9a497d35be336e2114c60cc61e394.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 449, + 545, + 483 + ], + "lines": [ + { + "bbox": [ + 305, + 449, + 545, + 483 + ], + "spans": [ + { + "bbox": [ + 305, + 449, + 545, + 483 + ], + "type": "text", + "content": "Figure 5. Per-tag forensics task accuracy. We train various models supervised by individual EXIF tags, then evaluate the learned representations for splice detection task on CASIA I." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_caption" + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 490, + 546, + 670 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 490, + 546, + 670 + ], + "spans": [ + { + "bbox": [ + 304, + 490, + 546, + 670 + ], + "type": "text", + "content": "common tags for this experiment, training a separate network for each one. The results of the per-tag evaluation is shown in Fig. 5. These results suggest that having access to the full metadata provides significantly better performance than using individual tags. Moreover, there is a wide variation in the performance of models that use different tag. This may be because the high performing tags, such as Camera Model, convey significantly more information about the full range of camera properties than others, such as Color Space and Sensing Method. These results suggest that a model that simply uses the full range of tags can extract significantly more camera information from the metadata. We also found that the variation trained on image descriptions (rather than EXIF text) performed significantly worse than other models." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 677, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 677, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 305, + 677, + 547, + 715 + ], + "type": "text", + "content": "Tag format. Since EXIF does not have a natural order of tags, we ask what will happen if we randomize the EXIF tag order during training. Table 5 shows the performance drops" + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "type": "text", + "content": "6951" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 56, + 75, + 541, + 397 + ], + "blocks": [ + { + "bbox": [ + 76, + 60, + 104, + 72 + ], + "lines": [ + { + "bbox": [ + 76, + 60, + 104, + 72 + ], + "spans": [ + { + "bbox": [ + 76, + 60, + 104, + 72 + ], + "type": "text", + "content": "Image" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 142, + 60, + 178, + 71 + ], + "lines": [ + { + "bbox": [ + 142, + 60, + 178, + 71 + ], + "spans": [ + { + "bbox": [ + 142, + 60, + 178, + 71 + ], + "type": "text", + "content": "EXIF-SC" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 206, + 61, + 252, + 72 + ], + "lines": [ + { + "bbox": [ + 206, + 61, + 252, + 72 + ], + "spans": [ + { + "bbox": [ + 206, + 61, + 252, + 72 + ], + "type": "text", + "content": "Noiseprint" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 286, + 61, + 307, + 71 + ], + "lines": [ + { + "bbox": [ + 286, + 61, + 307, + 71 + ], + "spans": [ + { + "bbox": [ + 286, + 61, + 307, + 71 + ], + "type": "text", + "content": "OSN" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 347, + 61, + 386, + 71 + ], + "lines": [ + { + "bbox": [ + 347, + 61, + 386, + 71 + ], + "spans": [ + { + "bbox": [ + 347, + 61, + 386, + 71 + ], + "type": "text", + "content": "CropCLR" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 425, + 61, + 446, + 71 + ], + "lines": [ + { + "bbox": [ + 425, + 61, + 446, + 71 + ], + "spans": [ + { + "bbox": [ + 425, + 61, + 446, + 71 + ], + "type": "text", + "content": "Ours" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 477, + 61, + 534, + 71 + ], + "lines": [ + { + "bbox": [ + 477, + 61, + 534, + 71 + ], + "spans": [ + { + "bbox": [ + 477, + 61, + 534, + 71 + ], + "type": "text", + "content": "Ground Truth" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 56, + 75, + 541, + 397 + ], + "lines": [ + { + "bbox": [ + 56, + 75, + 541, + 397 + ], + "spans": [ + { + "bbox": [ + 56, + 75, + 541, + 397 + ], + "type": "image", + "image_path": "525314fda64912fce106de0e71d26e85a57f9d756a95f87618c480c017fc4709.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 399, + 546, + 422 + ], + "lines": [ + { + "bbox": [ + 46, + 399, + 546, + 422 + ], + "spans": [ + { + "bbox": [ + 46, + 399, + 546, + 422 + ], + "type": "text", + "content": "Figure 6. Qualitative comparison to other methods. Our method can correctly localize splices in many scenarios where other methods fail. For example, EXIF-SC [33] fails on overexposed image regions; OSN [79] and CropCLR often segment scenes based on semantics." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_caption" + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 426, + 289, + 534 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 426, + 289, + 534 + ], + "spans": [ + { + "bbox": [ + 46, + 426, + 289, + 534 + ], + "type": "text", + "content": "for all three evaluations in this case. This may be due to the fact that the Transformer model is forced to learn meaningful positional embeddings corresponding to each EXIF tag if their order keeps on changing. We also tried removing the tag names from the camera metadata and just provide the values for those keys, e.g. replacing Make: Apple with Apple. Interestingly, this model performs on par with the model that has tag names, suggesting that the network can discern information about the tags from the values alone." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 540, + 287, + 647 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 540, + 287, + 647 + ], + "spans": [ + { + "bbox": [ + 46, + 540, + 287, + 647 + ], + "type": "text", + "content": "Text encoder architecture. To test whether performance of our model tied to a specific transformer architecture, we experimented with two different transformer models, DistilBERT [67] and ALBERT [44]. We see that both architectures obtain similar performance on all three tasks with DistilBERT slightly outperforming ALBERT. We also test how much pretraining the text encoder helps with the performance. From Table 5, we can see pretraining improves performance on the radial distortion and forensics tasks." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 47, + 657, + 117, + 670 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 657, + 117, + 670 + ], + "spans": [ + { + "bbox": [ + 47, + 657, + 117, + 670 + ], + "type": "text", + "content": "5. Discussion" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 46, + 677, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 288, + 713 + ], + "type": "text", + "content": "In this paper, we proposed to learn camera properties by training models to find cross-modal correspondences between images and camera metadata. To achieve this, we" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 426, + 547, + 582 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 426, + 547, + 582 + ], + "spans": [ + { + "bbox": [ + 304, + 426, + 547, + 582 + ], + "type": "text", + "content": "created a model that exploits the fact that EXIF metadata can easily be represented and processed as text. Our model achieves strong performance amongst self-supervised methods on a variety of downstream tasks that require understanding camera properties, including zero shot image forensics and radial distortion estimation. We see our work opening several possible directions. First, it opens the possibility of creating multimodal learning systems that use camera metadata as another form of supervision, providing complementary information to high-level modalities like language and sound. Second, it opens applications that require an understanding of low level sensor information, which may benefit from our feature sets." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 588, + 547, + 661 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 588, + 547, + 661 + ], + "spans": [ + { + "bbox": [ + 304, + 588, + 547, + 661 + ], + "type": "text", + "content": "Limitations and Broader Impacts. We have shown that our learned features are useful for image forensics, which has potential to reduce the spread of disinformation [22]. The model that we will release may not be fully representative of the cameras in the wild, since it was trained only on photos available in the YFCC100M dataset [73]." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 671, + 365, + 684 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 671, + 365, + 684 + ], + "spans": [ + { + "bbox": [ + 306, + 671, + 365, + 684 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 310, + 691, + 546, + 713 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 310, + 691, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 310, + 691, + 546, + 713 + ], + "type": "text", + "content": "[1] Ali Azarbayejani and Alex P Pentland. Recursive estimation of motion, structure, and focal length. 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TTA may primarily be conducted on edge devices with limited memory, so reducing memory is crucial but has been overlooked in previous TTA studies. In addition, long-term adaptation often leads to catastrophic forgetting and error accumulation, which hinders applying TTA in real-world deployments. Our approach consists of two components to address these issues. First, we present lightweight meta networks that can adapt the frozen original networks to the target domain. This novel architecture minimizes memory consumption by decreasing the size of intermediate activations required for backpropagation. Second, our novel self-distilled regularization controls the output of the meta networks not to deviate significantly from the output of the frozen original networks, thereby preserving well-trained knowledge from the source domain. Without additional memory, this regularization prevents error accumulation and catastrophic forgetting, resulting in stable performance even in long-term test-time adaptation. We demonstrate that our simple yet effective strategy outperforms other state-of-the-art methods on various benchmarks for image classification and semantic segmentation tasks. Notably, our proposed method with ResNet-50 and WideResNet-40 takes $86\\%$ and $80\\%$ less memory than the recent state-of-the-art method, CoTTA.", + "bbox": [ + 75, + 305, + 473, + 698 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 722, + 209, + 738 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Despite recent advances in deep learning [14, 21, 20, 19], deep neural networks often suffer from performance degradation when the source and target domains differ significantly [8, 36, 31]. Among several tasks addressing such domain shifts, test-time adaptation (TTA) has recently received a significant amount of attention due to its practicality and wide applicability especially in on-device set", + "bbox": [ + 75, + 747, + 468, + 854 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/ba36850b7bda142cabb71e0f3d8ae8bebcb23f4846ad4de3776a42f9ba2d3d9d.jpg", + "image_caption": [ + "Figure 1. (a) Memory cost comparison between TTA methods. The size of activations, not the parameters, is the primary memory bottleneck during training. (b) CIFAR-C adaptation performance. We perform the continual online adaptation on CIFAR-C dataset. The x- and y-axis are the average error of all corruptions and the total memory consumption including the parameters and activations, respectively. Our approach, EcoTTA, achieves the best results while consuming the least amount of memory, where K is the model partition factor used in our method." + ], + "image_footnote": [], + "bbox": [ + 503, + 273, + 890, + 627 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "tings [53, 35, 26, 15]. This task focuses on adapting the model to unlabeled online data from the target domain without access to the source data.", + "bbox": [ + 496, + 773, + 893, + 820 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "While existing TTA methods show improved TTA performances, minimizing the sizes of memory resources have been relatively under-explored, which is crucial considering the applicability of TTA in on-device settings. For example, several studies [54, 35, 9] update entire model parameters", + "bbox": [ + 496, + 824, + 893, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 810, + 44 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Work done during an internship at Qualcomm AI Research.", + "bbox": [ + 94, + 862, + 416, + 875 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "†Corresponding author. ‡ Qualcomm AI Research is an initiative of Qualcomm Technologies, Inc.", + "bbox": [ + 78, + 875, + 468, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "11920", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/493762fb42517322de7e130c1a0e54c2a211b6b1c3b21a05c05291aaf8f8730c.jpg", + "image_caption": [ + "Figure 2. Architecture for test-time adaptation. We illustrate TTA methods: TENT [53], EATA [41], CoTTA [54], and Ours (EcoTTA). TENT and EATA update multiple batch norm layers, in which large activations have to be stored for gradient calculation. In CoTTA, an entire network is trained with additional strategies for continual adaptation that requires a significant amount of both memory and time. In contrast, our approach requires a minimum size of activations by updating only a few layers. Also, stable long-term adaptation is performed by our proposed regularization, named self-distilled regularization." + ], + "image_footnote": [], + "bbox": [ + 84, + 85, + 883, + 209 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "to achieve large performance improvements, which may be impractical when the available memory sizes are limited. Meanwhile, several TTA approaches update only the batch normalization (BN) parameters [53, 41, 16] to make the optimization efficient and stable. However, even updating only BN parameters is not memory efficient enough since the amount of memory required for training models significantly depends on the size of intermediate activations rather than the learnable parameters [4, 13, 57]. Throughout the paper, activations refer to the intermediate features stored during the forward propagation, which are used for gradient calculations during backpropagation. Fig. 1 (a) demonstrates such an issue.", + "bbox": [ + 75, + 295, + 472, + 489 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Moreover, a non-trivial number of TTA studies assume a stationary target domain [53, 35, 9, 48], but the target domain may continuously change in the real world (e.g., continuous changes in weather conditions, illuminations, and location [8] in autonomous driving). Therefore, it is necessary to consider long-term TTA in an environment where the target domain constantly varies. However, there exist two challenging issues: 1) catastrophic forgetting [54, 41] and 2) error accumulation. Catastrophic forgetting refers to degraded performance on the source domain due to long-term adaptation to target domains [54, 41]. Such an issue is important since the test samples in the real world may come from diverse domains, including the source and target domains [41]. Also, since target labels are unavailable, TTA relies on noisy unsupervised losses, such as entropy minimization [17], so long-term continual TTA may lead to error accumulation [63, 2].", + "bbox": [ + 75, + 492, + 468, + 748 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To address these challenges, we propose memory-Efficient continual Test-Time Adaptation (EcoTTA), a simple yet effective approach for 1) enhancing memory efficiency and 2) preventing catastrophic forgetting and error accumulation. First, we present a memory-efficient architecture consisting of frozen original networks and our proposed meta networks attached to the original ones. During the test time, we freeze the original networks to discard the intermediate activations that occupy a significant amount of memory. Instead, we only adapt lightweight meta networks", + "bbox": [ + 75, + 750, + 472, + 902 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "to the target domain, composed of only one batch normalization and one convolution block. Surprisingly, updating only the meta networks, not the original ones, can result in significant performance improvement as well as considerable memory savings. Moreover, we propose a self-distilled regularization method to prevent catastrophic forgetting and error accumulation. Our regularization leverages the preserved source knowledge distilled from the frozen original networks to regularize the meta networks. Specifically, we control the output of the meta networks not to deviate from the one extracted by the original networks significantly. Notably, our regularization leads to negligible overhead because it requires no extra memory and is performed in parallel with adaptation loss, such as entropy minimization.", + "bbox": [ + 496, + 295, + 893, + 507 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Recent TTA studies require access to the source data before model deployments [35, 9, 28, 1, 33, 41]. Similarly, our method uses the source data to warm up the newly attached meta networks for a small number of epochs before model deployment. If the source dataset is publicly available or the owner of the pre-trained model tries to adapt the model to a target domain, access to the source data is feasible [9]. Here, we emphasize that pre-trained original networks are frozen throughout our process, and our method is applicable to any pre-trained model because it is agnostic to the architecture and pre-training method of the original networks.", + "bbox": [ + 496, + 507, + 893, + 672 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Our paper presents the following contributions:", + "bbox": [ + 517, + 672, + 834, + 686 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- We present novel meta networks that help the frozen original networks adapt to the target domain. This architecture significantly minimize memory consumption up to $86\\%$ by reducing the activation sizes of the original networks.", + "- We propose a self-distilled regularization that controls the output of meta networks by leveraging the output of frozen original networks to preserve the source knowledge and prevent error accumulation.", + "- We improve both memory efficiency and TTA performance compared to existing state-of-the-art methods on 1) image classification task (e.g., CIFAR10/100-C and ImageNet-C) and 2) semantic segmentation task (e.g., Cityscapes with weather corruption)" + ], + "bbox": [ + 517, + 688, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "11921", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 76, + 89, + 218, + 104 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Mitigating domain shift. One of the fundamental issues of DNNs is the performance degradation due to the domain shift between the train (i.e. source) and test (i.e. target) distributions. Several research fields attempt to address this problem, such as unsupervised domain adaptation [52, 6, 44, 47, 38, 49] and domain generalization [64, 8]. In particular, domain generalization aims to learn invariant representation so as to cover the possible shifts of test data. They simulate the possible shifts using a single or multiple source dataset [64, 62, 32] or force to minimize the dependence on style information [43, 8]. However, it is challenging to handle all potential test shifts using the given source datasets [18]. Thus, instead of enhancing generalization ability during the training time, TTA [53] overcomes the domain shift by directly adapting to the test data.", + "bbox": [ + 75, + 118, + 472, + 347 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Test-time adaptation. Test-time adaptation allows the model to adapt to the test data (i.e., target domain) in a source-free and online manner [27, 50, 53]. Existing works improve TTA performance with sophisticated designs of unsupervised loss [39, 60, 35, 9, 37, 48, 5, 15, 1, 3, 12] or enhance the usability of small batch sizes [30, 58, 25, 42, 33] considering streaming test data. They focus on improving the adaptation performance with a stationary target domain (i.e., single domain TTA setup). In such a setting, the model that finished adaptation to a given target domain is reset to the original model pre-trained with the source domain in order to adapt to the next target domain.", + "bbox": [ + 75, + 349, + 472, + 532 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Recently, CoTTA [54] has proposed continual TTA setup to address TTA under a continuously changing target domain which also involves a long-term adaptation. This setup frequently suffers from error accumulation [63, 2, 51] and catastrophic forgetting [54, 29, 41]. Specifically, performing a long-term adaptation exposes the model to unsupervised loss from unlabeled test data for a long time, so errors are accumulated significantly. Also, the model focuses on learning new knowledge and forgets about the source knowledge, which becomes problematic when the model needs to correctly classify the test sample as similar to the source distribution. To address such issues, CoTTA [54] randomly restores the updated parameters to the source one, while EATA [41] proposed a weight regularization loss.", + "bbox": [ + 75, + 532, + 472, + 744 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Efficient on-device learning. Since the edge device is likely to be memory constrained (e.g., a Raspberry Pi with 512MB and iPhone 13 with 4GB), it is necessary to take account of the memory usage when deploying the models on the device [34]. TinyTL [4], a seminal work in on-device learning, shows that the activation size, not learnable parameters, bottlenecks the training memory. Following this, recent on-device learning studies [4, 56, 57] targeting fine-tuning task attempt to decrease the size of intermediate activations. In contrast, previous TTA studies [53, 41]", + "bbox": [ + 75, + 750, + 472, + 902 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "have overlooked these facts and instead focused on reducing learnable parameters. This paper, therefore, proposes a method that not only reduces the high activation sizes required for TTA, but also improves adaptation performance.", + "bbox": [ + 496, + 90, + 893, + 152 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Approach", + "text_level": 1, + "bbox": [ + 498, + 165, + 609, + 181 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Fig. 3 illustrates our simple yet effective approach which only updates the newly added meta networks on the target domain while regularizing them with the knowledge distilled from the frozen original network. This section describes how such a design promotes memory efficiency and prevents error accumulation and catastrophic forgetting which are frequently observed in long-term adaptation.", + "bbox": [ + 496, + 190, + 893, + 297 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Memory-efficient Architecture", + "text_level": 1, + "bbox": [ + 498, + 306, + 769, + 321 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Prerequisite. We first formulate the forward and the backward propagation. Assume that the $i^{th}$ linear layer in the model consists of weight $\\mathcal{W}$ and bias $b$ , and the input and output features of this layer are $f_{i}$ and $f_{i+1}$ , respectively. Given that the forward propagation of $f_{i+1} = f_{i}\\mathcal{W} + b$ , the backward propagation from the $i+1^{th}$ layer to the $i^{th}$ layer, and the weight gradient are respectively formulated as:", + "bbox": [ + 496, + 330, + 893, + 439 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\frac {\\partial \\mathcal {L}}{\\partial f _ {i}} = \\frac {\\partial \\mathcal {L}}{\\partial f _ {i + 1}} \\mathcal {W} ^ {T}, \\quad \\frac {\\partial \\mathcal {L}}{\\partial \\mathcal {W}} = f _ {i} ^ {T} \\frac {\\partial \\mathcal {L}}{\\partial f _ {i + 1}}. \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 562, + 446, + 890, + 479 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Eq. (1) means that the learnable layers whose weight $\\mathcal{W}$ need to be updated must store intermediate activations $f_{i}$ to compute the weight gradient. In contrast, the backward propagation in frozen layers can be accomplished without saving the activations, only requiring its weight $\\mathcal{W}$ . Further descriptions are provided in Appendix A.", + "bbox": [ + 496, + 489, + 893, + 580 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "TinyTL [4] shows that activations occupy the majority of the memory required for training the model rather than learnable parameters. Due to this fact, updating the entire model (e.g., CoTTA [54]) requires a substantial amount of memory. Also, updating only parameters in batch normalization (BN) layers (e.g., TENT [53] and EATA [41]) is not an effective approach enough since they still save the large intermediate activations for multiple BN layers. While previous studies fail to reduce memory by utilizing large activations, this work proposes a simple yet effective way to reduce a significant amount of memory by discarding them.", + "bbox": [ + 496, + 580, + 895, + 747 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Before deployment. As illustrated in Fig. 3 (a, b), we first take a pre-trained model using any pre-training method. We divide the encoder of the pre-trained model into K number of parts and attach lightweight meta networks to each part of the original network. The details of how to divide the model into K number of parts are explained in the next section. One group of meta network composes of one batch normalization layer and one convolution block (i.e., ConvBN-Relu). Before the deployment, we pre-train the meta networks on the source dataset $\\mathcal{D}_s$ for a small number of", + "bbox": [ + 496, + 750, + 895, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "11922", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/56a26da2f31e21cda5365271ebbc6dea1a73b27e339c98de81f36d456d03d7dc.jpg", + "image_caption": [ + "Figure 3. Overview of our approach. (a) The encoder of the pre-trained model is divided into K parts (i.e., model partition factor K). (b) Before deployment, the meta networks are attached to each part of the original networks and pre-trained with source dataset $\\mathcal{D}_s$ . (c) After the model is deployed, only the meta networks are updated with unsupervised loss (i.e., entropy minimization) on target data $\\mathcal{D}_t$ , while the original networks are frozen. To avoid error accumulation and catastrophic forgetting by the long-term adaptation, we regularize the output $\\tilde{x}_k$ of each group of the meta networks leveraging the output $x_k$ of the frozen original network, which preserves the source knowledge." + ], + "image_footnote": [], + "bbox": [ + 84, + 95, + 888, + 284 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "epochs (e.g., 10 epochs for CIFAR dataset) while freezing the original networks. Such a warm-up process is completed before the model deployment, similarly done in several TTA works [9, 28, 33, 41]. Note that we do not require source dataset $\\mathcal{D}_s$ during test time.", + "bbox": [ + 75, + 373, + 468, + 448 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Pre-trained model partition. Previous TTA studies addressing domain shifts [9, 39] indicate that updating shallow layers is more crucial for improving the adaptation performance than updating the deep layers. Inspired by such a finding, given that the encoder of the pre-trained model is split into model partition factor K (e.g., 4 or 5), we partition the shallow parts of the encoder more (i.e., densely) compared to the deep parts of it. Table 4c shows how performance changes as we vary the model partition factor K.", + "bbox": [ + 75, + 450, + 468, + 587 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "After deployment. During the test-time adaptation, we only adapt meta networks to target domains while freezing the original networks. Following EATA [41], we use the entropy minimization $H(\\hat{y}) = -\\sum_{c} p(\\hat{y}) \\log p(\\hat{y})$ to the samples achieving entropy less than the pre-defined entropy threshold $H_0$ , where $\\hat{y}$ is the prediction output of a test image from test dataset $\\mathcal{D}_t$ and $\\mathrm{p}(\\cdot)$ is the softmax function. Thus, the main task loss for adaptation is defined as", + "bbox": [ + 75, + 589, + 468, + 710 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} ^ {e n t} = \\mathbb {I} _ {\\{H (\\hat {y}) < H _ {0} \\}} \\cdot H (\\hat {y}), \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 179, + 715, + 468, + 734 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\mathbb{I}_{\\{\\cdot \\}}$ is an indicator function. In addition, in order to prevent catastrophic forgetting and error accumulation, we apply our proposed regularization loss $\\mathcal{R}^k$ , which is described next in detail. Consequently, the overall loss of our method is formulated as,", + "bbox": [ + 75, + 741, + 468, + 816 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\theta} ^ {t o t a l} = \\mathcal {L} _ {\\theta} ^ {e n t} + \\lambda \\sum_ {k} ^ {K} \\mathcal {R} _ {\\theta_ {k}} ^ {k}, \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 174, + 821, + 468, + 863 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\theta$ and $\\theta_{k}$ denotes parameters of all meta networks and those of k-th group of meta networks, respectively, and", + "bbox": [ + 76, + 869, + 468, + 901 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "$\\lambda$ is used to balance the scale of the two loss functions. Note that our architecture requires less memory than previous works [54, 53] since we use frozen original networks and discard its intermediate activations. To be more specific, our architecture uses $82\\%$ and $60\\%$ less memory on average than CoTTA and TENT/EATA.", + "bbox": [ + 496, + 373, + 892, + 464 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. Self-distilled Regularization", + "text_level": 1, + "bbox": [ + 498, + 474, + 751, + 489 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The unsupervised loss from unlabeled test data $\\mathcal{D}_t$ is likely to provide a false signal (i.e., noise) to the model ( $\\hat{y} \\neq y_t$ where $y_t$ is the ground truth test label). Previous works have verified that long-term adaptation with unsupervised loss causes overfitting due to error accumulation [63, 2] and catastrophic forgetting [54, 29]. To prevent the critical issues, we propose a self-distilled regularization utilizing our architecture. As shown in Fig. 3, we regularize the output $\\tilde{x}_k$ of each $k$ -th group of the meta networks not to deviate from the output $x_k$ of the $k$ -th part of frozen original networks. Our regularization loss which computes the mean absolute error (i.e., L1 loss) is formulated as follows:", + "bbox": [ + 496, + 498, + 892, + 679 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {R} _ {\\theta_ {k}} ^ {k} = \\left\\| \\tilde {x} _ {k} - x _ {k} \\right\\| _ {1}. \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 624, + 693, + 890, + 712 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Since the original networks are not updated, the output $x_{k,k\\sim K}$ extracted from them can be considered as containing the knowledge learned from the source domain. Taking advantage of this fact, we let the output of meta networks $\\tilde{x}_k$ be regularized with knowledge distilled from the original networks. By preventing the adapted model to not significantly deviate from the original model, we can prevent 1) catastrophic forgetting by maintaining the source domain knowledge and 2) error accumulation by utilizing the class discriminability of the original model. Remarkably, unlike previous works [54, 41], our regularization does not require saving additional original networks, which accompanies ex", + "bbox": [ + 496, + 719, + 892, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "11923", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 3 + }, + { + "type": "table", + "img_path": "images/23c309bc5801ff067fb67f17c3ab64e6b94a6111883a162aecfdc3a1608ab15b.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodWideResNet-40 (AugMix)WideResNet-28ResNet-50
Avg. err↓Mem. (MB)Avg. err↓Mem. (MB)Avg. err↓Mem. (MB)
Source36.71143.55848.891
BN Stats Adapt [40]15.41120.95816.691
Single do. TENT [53]12.718819.264615.0925
Continual TENT13.318820.064615.2925
TTT++ [35]14.639120.3140516.11877
SWR&NSP [9]12.140017.2155115.41971
NOTE [16]13.418820.2646--
EATA [41]13.018818.664614.2925
CoTTA [54]14.040917.0169714.42066
Ours (K=4)12.280 (80,58%↓)16.9404 (76,38%↓)14.4296 (86,68%↓)
Ours (K=5)12.192 (77,51%↓)16.8471 (72,27%↓)14.1498 (76,46%↓)
", + "bbox": [ + 84, + 89, + 545, + 258 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/af58b3a023ed41fc79b83721e6545ca2504675e10cdb153ba908bd928fbf1a05.jpg", + "table_caption": [ + "(a) CIFAR10-C with severity level 5" + ], + "table_footnote": [], + "table_body": "
MethodWideResNet-40 (AugMix)ResNet-50
Avg. err↓Mem. (MB)Avg. err↓Mem. (MB)
Source69.71173.891
BN Stats Adapt [40]41.11144.591
Single do. TENT [53]36.718840.1926
Continual TENT38.318845.9926
TTT++ [35]41.039144.21876
SWR&NSP [9]36.640044.11970
NOTE [16]42.8188--
EATA [41]37.118839.9926
CoTTA [54]38.140940.22064
Ours (K=4)36.480 (80,58%↓)39.5296 (86,68%↓)
Ours (K=5)36.392 (77,51%↓)39.3498 (76,46%↓)
", + "bbox": [ + 553, + 90, + 897, + 257 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/eaef079754a9d0b085603d07d4a71578d7f8f80edf991dd02e1657b0ed318aa3.jpg", + "table_caption": [ + "(b) CIFAR100-C with severity level 5", + "Table 1. Comparison of error rate (\\%) on CIFAR-C. We report an average error of 15 corruptions on continual TTA and a memory requirement including model parameters and activation sizes. The lowest error is in bold, and the second lowest error is underlined. The memory reduction rates compared to CoTTA and TENT are presented sequentially. WideResNet-40 was pre-trained with AugMix [23] that is a data processing to increase the robustness of the model. Source denotes the pre-trained model without adaptation. Single domain (in short, single do.) TENT resets the model when adapting to a new target domain, so the domain labels are required." + ], + "table_footnote": [], + "table_body": "
MethodResNet-50 (AugMix) \nAvg. err ↓ResNet-50 \nAvg. err ↓(MB) \nTotal Mem. ↓
Source74.3682.3591
BN Stats Adapt [40]57.8772.1891
Continual TENT [53]56.1 (0.6)66.2 (1.1)1486
EATA [41]54.9 (2.3)63.8 (2.7)1486
CoTTA [54]54.6 (3.9)62.6 (3.1)3132
Ours (K=4)55.2 (3.0)64.6 (3.2)438 (86, 72%↓)
Ours (K=5)54.4 (2.7)63.4 (3.0)747 (75, 51%↓)
", + "bbox": [ + 84, + 352, + 460, + 474 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/cf2eb6ef6b69896dc615da14f071498b7669952bd10dae67ff5e2bd5ea0904ec.jpg", + "table_caption": [ + "Table 2. Comparison of error rate (\\%) on ImageNet-C with severity level 5. Standard deviation for ten diverse corruption sequences is denoted by the parentheses values. The total memory refers to the sum of model parameters and activations." + ], + "table_footnote": [], + "table_body": "
Avg. err (%) \nMethodMem. (MB)CIFAR10-CCIFAR100-C
single do.continualsingle do.continual
BN Stats Adapt [40]9116.616.644.544.5
TinyTL† [4]37915.821.940.577.4
RepNet† [57]50815.220.941.552.1
AuxAdapt† [61]20716.016.744.045.8
Ours (K=4)29614.414.439.539.2
", + "bbox": [ + 81, + 545, + 464, + 645 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Table 3. Comparison with methods for on-device learning. The backbone is ResNet-50. $\\dagger$ denotes our own re-implemented models. single do. indicates the single domain TTA setup.", + "bbox": [ + 75, + 648, + 468, + 691 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "tra memory usage. Moreover, it only needs a negligible amount of computational overhead because it is performed in parallel with the entropy minimization loss $\\mathcal{L}^{ent}$ .", + "bbox": [ + 75, + 702, + 468, + 748 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Classification Experiments", + "text_level": 1, + "bbox": [ + 76, + 763, + 326, + 782 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We evaluate our approach to image classification tasks based on the continual test-time adaptation setup with three datasets: CIFAR10-C, CIFAR100-C, and ImageNet-C.", + "bbox": [ + 75, + 791, + 468, + 837 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Experimental setup. Following CoTTA [54], we conduct most experiments on the continual TTA task, where we continually adapt the deployed model to each corruption type sequentially without resetting the model. This task is", + "bbox": [ + 75, + 839, + 468, + 901 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "more challenging but more realistic than single domain TTA task [53] in which the adapted model is periodically reset to the original pre-trained model after finishing adaptation to each target, so they require additional domain information. Moreover, we evaluate our approach on the long-term TTA setup, which is detailed in Section 4.2.", + "bbox": [ + 496, + 354, + 890, + 446 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Following the previous TTA studies [53, 54], we evaluate models with {CIFAR10, CIFAR10-C}, {CIFAR100, CIFAR100-C}, and {ImageNet, ImageNet-C} where the first and the second dataset in each bracket refers to the source and the target domain, respectively. The target domains include 15 types of corruptions (e.g. noise, blur, weather, and digital) with 5 levels of severity, which are widely used in conventional benchmarks [22].", + "bbox": [ + 496, + 449, + 892, + 571 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Implementation Details. We evaluate our approach within the frameworks officially provided by previous state-of-the-art methods [54, 41]. For fair comparisons, we use the same pre-trained model, which are WideResNet-28 and WideResNet-40 [59] models from the RobustBench [11], and ResNet-50 [21] model from TTT++ [35, 9]. Before the deployment, we pre-train the meta networks on the source dataset using a cross-entropy loss with SGD optimizer with the learning rate of 5e-2. Since the meta networks contain only a few layers, we pre-train them with a small number of epochs: 10 and 3 epochs for CIFAR and ImageNet, respectively. After deployment, similar to EATA [41], we use the same SGD optimizer with the learning rate of 5e-3. In Eq. (2), the entropy threshold $H_0$ is set to $0.4 \\times \\ln C$ where $C$ denotes the number of task classes. The batch size is 64 and 32 for CIFAR and ImageNet, respectively. We set the importance of the regularization $\\lambda$ in Eq. (3) to 0.5 to balance it with the entropy minimization loss. Additional implementation details can be found in Appendix C.", + "bbox": [ + 496, + 577, + 892, + 864 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Evaluation Metric. For all the experiments, we report error rates calculated during testing and the memory consump", + "bbox": [ + 498, + 869, + 890, + 901 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "11924", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/108e5cc8efab6f0d685ee38581c3595d9729997d22f52770326c9dc7502caeba.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 102, + 89, + 398, + 244 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/66fadca6d25b4e1992ecf5d1f1fdf3b65c78fd867f1d3481e30dc055e2b7e7e5.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
Avr. errArchCIFAR10-C WRN-28CIFAR10-C WRN-40CIFAR100-C WRN-40
(i)18.112.637.2
(ii) Ours w\\o BN18.713.738.2
(iii) Ours w\\o Conv20.714.940.1
(iv) Conv60.673.377.2
(v) CBAM [55]21.415.140.9
(vi) SE [24]22.316.240.5
Ours16.812.136.3
", + "bbox": [ + 408, + 99, + 679, + 244 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/2a5ee4fc38b6dd56ffdf53eddf32f58ac014fb0220f2bc0d26194d8c4616179a.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
Model#BlockAvg. err
WRN-28 (12) CIFAR10-C3,3,3,317.3
4,4,2,217.9
2,2,4,416.9
WRN-40 (18) CIFAR10-C4,4,5,512.8
6,6,3,313.7
3,3,6,612.2
WRN-40 (18) CIFAR100-C4,4,5,536.9
6,6,3,338.5
3,3,6,636.4
", + "bbox": [ + 687, + 92, + 870, + 244 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 4. Architecture ablation experiments. (a,b) We compare continual TTA performance on several memory-efficient designs. WRN refers to WideResNet [59] backbone. (c) We report the performance based on different designs of partitioning the model. The value next to the backbone's name denotes the total number of residual blocks of a model.", + "bbox": [ + 75, + 250, + 893, + 292 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "tion, including the model parameter and the activation storage. We demonstrate the memory efficiency of our work by using the official code provided by TinyTL [4].", + "bbox": [ + 75, + 297, + 470, + 345 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.1. Comparisons", + "text_level": 1, + "bbox": [ + 76, + 356, + 215, + 372 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Comparisons with TTA methods. We compare our approach to competing TTA methods on extensive benchmarks and various pre-trained models. The results of CIFAR10/100-C are detailed in Table 1. The model partition factor K are set to 4 and 5. Our approach outperforms existing TTA methods with the lowest memory usage in all pre-trained models. Specifically, in WideResNet-40, our method achieves superior performance while requiring $80\\%$ and $58\\%$ less memory than CoTTA [54] and EATA [41], respectively, which are also designed for continual TTA. Approaches targeting single domain TTA [53, 35, 9] show poor performance due to error accumulation and catastrophic forgetting, as observed in CoTTA. The error rates for each corruption type are provided in Appendix F.", + "bbox": [ + 75, + 383, + 468, + 594 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 2 shows the experiment for ImageNet-C. Two ResNet-50 backbones from RobustBench [11] are leveraged. Following CoTTA, evaluations are conducted on ten diverse corruption-type sequences. We achieve comparable performance to CoTTA while utilizing $86\\%$ and $75\\%$ less memory with $\\mathrm{K} = 4$ and 5, respectively. In addition, we observe that our approach shows superior performance when adopting the model pre-trained with strong data augmentation methods (e.g., Augmix [23]).", + "bbox": [ + 75, + 595, + 468, + 731 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Comparisons with on-device learning methods. We compare our approach with methods for memory-efficient on-device learning. TinyTL [4] and RepNet [57] focus on supervised on-device learning (i.e., requiring labeled target data). However, since TTA assumes that we do not have access to the target labels, utilizing such methods to TTA directly is infeasible. Therefore, we experimented by replacing supervised loss (i.e., cross-entropy) with unsupervised loss (i.e., entropy minimization) in TinyTL and RepNet. As shown in Table 3, they suffer from performance degradation in continual TTA, showing inferior performance compared", + "bbox": [ + 75, + 734, + 470, + 902 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/83e81d67edc2a25632cf40d7d634c94dc13cd356f02709442d7b73705f56250a.jpg", + "image_caption": [ + "Figure 4. Ablation study of K. We uniformly divide the encoder of the pre-trained model into the model partition factor K. The x-axis indicates the memory size including both model parameter size and activation size while the y-axis indicates the average error rate. The values in parentheses show the rate of increase for the model parameters compared to the original model." + ], + "image_footnote": [], + "bbox": [ + 501, + 299, + 893, + 414 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "to our proposed approach even in the single domain TTA.", + "bbox": [ + 498, + 508, + 879, + 525 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Similar to ours, AuxAdapt [61] adds and updates a small network (i.e., ResNet-18) while freezing the pre-trained model. Unlike our approach, they only modify a prediction output, not intermediate features. While AuxAdapt requires the least memory usage, it fails to improve TTA performance in single domain TTA. Nevertheless, since the original model is frozen, it suffers less from catastrophic forgetting and error accumulation than TinyTL [4] and RepNet [57] in the continual TTA. Through the results, we confirm that our proposed method brings both memory efficiency and a significant performance improvement in both TTA setups.", + "bbox": [ + 496, + 526, + 890, + 693 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.2. Empirical Study", + "text_level": 1, + "bbox": [ + 500, + 705, + 661, + 722 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Architecture design. An important design of our meta networks is injecting a single BN layer before the original networks and utilizing a residual connection with one conv block. Table 4b studies the effectiveness of the proposed design by comparing it with six different variants. From the results, we observe that using only either conv block (ii) or BN (iii) aggravates the performance: error rate increases by $1.4\\%$ and $3.8\\%$ on CIFAR-100-C with WideResNet-40.", + "bbox": [ + 496, + 732, + 890, + 852 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "In design (i), we enforce both BN parameters and Conv layers in the meta networks to take the output of the original networks as inputs. Such a design brings performance", + "bbox": [ + 496, + 854, + 890, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "11925", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/fe046384f813c599986604b0b12e513e8a90bf17056e94e892127b798d978701.jpg", + "image_caption": [ + "(a) Catastrophic forgetting effect" + ], + "image_footnote": [], + "bbox": [ + 84, + 90, + 488, + 261 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/7371792345457b4221cf7c8650380a80927486101bf247b8bcef57df6d3e3116.jpg", + "image_caption": [ + "(b) Error accumulation effect", + "Figure 5. Regularization ablation experiments. We conduct experiments with WideResNet-40 on CIFAR100-C. (a) We utilize a test set of the CIFAR-100 dataset to measure clean error after adapting to each corruption. Maintaining clean errors at a stable level indicates that our approach helps the model robust to catastrophic forgetting. (b) We simulate a long-term adaptation scenario by repeating 100 rounds of 15 corruption sequences. In the absence of regularization, error accumulation can lead to overfitting (i.e., the case of the error increases exponentially). However, our approach does not suffer from such an error accumulation. We set K to 5 in the above experiments." + ], + "image_footnote": [], + "bbox": [ + 506, + 90, + 887, + 258 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/8f24365dbbfac4a05ddfb4987005d8e6d33fe5ca7f980efa384d2bfce76755ce.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
Batch size168421
Non trainingSource69.769.769.769.769.7
BN Stats Adapt [40]41.150.259.981.099.1
AdaptBN [46]39.141.245.249.054.0
TrainingCon. TENT [53]40.947.858.682.299.0
Con. TENT+AdaptBN38.240.243.247.752.2
Ours (K=5)40.045.863.480.899.0
Ours (K=5)+AdaptBN36.939.342.246.551.8
", + "bbox": [ + 81, + 359, + 464, + 469 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 5. Experiments with small batch sizes. We evaluate all baselines with WideResNet-40 on CIFAR100-C. Con. TENT is the abbreviation for continual TENT.", + "bbox": [ + 75, + 476, + 468, + 517 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "drop. We speculate that it is because the original network, which is not adapted to the target domain, lacks the ability to extract sufficiently meaningful features from the target image. Also, we observed a significant performance degradation after removing the residual connection in design (iv). In addition, since attention mechanisms [55, 24] generally have improved classification accuracy, we study how attention mechanisms can further boost TTA performance of our approach in design (v, vi). The results show that it is difficult for the attention module to train ideally in TTA setup using unsupervised learning, unlike when applying it to supervised learning. An ablation study on each element of meta networks can be found in Appendix D.", + "bbox": [ + 75, + 521, + 468, + 717 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Number of blocks in each partition. ResNet [21] consists of multiple residual blocks (e.g., BasicBlock and Bottleneck in Pytorch [45]). For instance, WideResNet-28 has 12 residual blocks. By varying the number of blocks for each part of the original networks, we analyze TTA performance in Table 4c. We observe that splitting the shallow parts of the encoder densely (e.g., 2,2,4,4 blocks, from the shallow to the deep parts sequentially) brings more performance gain than splitting the deep layers densely (e.g., 4,4,2,2 blocks). We suggest that it is because we modify the lower-level feature more as we split shallow layers densely. Our observation is aligned with the finding of previous TTA works [9, 39],", + "bbox": [ + 75, + 719, + 468, + 900 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "which show that updating the shallow layers more than the deep layers improves TTA performance.", + "bbox": [ + 498, + 358, + 888, + 388 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Number of model partition K. Fig. 4 shows both memory requirement and adaptation performance according to the model partition factor K. With a small K (e.g., 1 or 2), the intermediate outputs are barely modified, making it difficult to achieve a reasonable level of performance. We achieve the best TTA performance with K of 4 or 5 as adjusting a greater numver of intermediate features. In the meanwhile, we observe that the average error rate is saturated and remains consistent when K is set to large values (e.g. 6,7 or 8) even with the increased amount of activations and learnable parameters. Therefore, we set K to 4 and 5.", + "bbox": [ + 496, + 393, + 890, + 559 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Catastrophic forgetting. We conduct experiments to confirm the catastrophic forgetting effect (Fig. 5a). Once finishing adaptation to each corruption, we evaluate the model on clean target data (i.e., test-set of CIFAR dataset) without updating the model. For TENT with no regularization, the error rates for the clean target data (i.e., clean error $(\\%)$ ) increase gradually, which can be seen as the phenomenon of catastrophic forgetting. In contrast, our approach consistently maintains the error rates for the clean target data, proving that our regularization loss effectively prevents catastrophic forgetting. These results indicate that our method can be reliably utilized in various domains, including the source and target domains.", + "bbox": [ + 496, + 564, + 890, + 760 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Error accumulation in long-term adaptation. To evaluate the error accumulation effect, we repeat all the corruption sequences for 100 rounds. The results are described in Fig. 5b. For TENT, a gradual increase in error rates is observed in later rounds, even with small learning rates. For example, TENT [53] with the learning rate of 1e-5 achieves the error rate of $39.7\\%$ , and reached its lowest error rate of $36.5\\%$ after 8 rounds. However, it shows increased error rate of $38.6\\%$ after 100 rounds due to overfitting. It suggests", + "bbox": [ + 496, + 763, + 890, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "11926", + "bbox": [ + 480, + 945, + 517, + 955 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/e70ad4c28636c80e8a9aa745fe2753a4f884d79288abc8088cb57186567f61a3.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
Timet
Round14710All
MethodMem. (MB)Brig.FogFros.SnowBrig.FogFros.SnowBrig.FogFros.SnowBrig.FogFros.SnowMean
Source28060.454.330.04.160.454.330.04.160.454.330.04.160.454.330.04.137.2
BN Stats Adapt [40]28069.161.044.839.169.161.044.839.169.161.044.839.169.161.044.839.153.6
Continual TENT [53]272170.162.146.140.262.253.744.437.950.041.531.626.639.232.625.322.442.9
Ours (K=4)918 (66‰)70.262.446.341.970.062.846.542.270.062.846.542.170.162.846.642.255.3
", + "bbox": [ + 81, + 89, + 885, + 186 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "that without regularization, TTA methods eventually face overfitting in long-term adaptation [63, 2, 29]. Our method in the absence of regularization $(\\lambda = 0)$ also causes overfitting. On the other hand, when self-distilled regularization is involved $(\\lambda > 0)$ , the performance remains consistent even in the long-term adaptation.", + "bbox": [ + 75, + 243, + 470, + 335 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Small batch size. We examine the scalability of our approach with a TTA method designed for small batches size, named adapting BN statistics (i.e., AdaptBN [46, 60]). When the number of batches is too small, the estimated statistics can be unreliable [46]. Thus, they calibrate the source and target statistics for the normalization of BN layers so as to alleviate the domain shift and preserve the discriminative structures. As shown in Table 5, training models with small batch sizes (e.g., 2 or 1) generally increase the error rates. However, such an issue can be addressed by applying AdaptBN to our method. To be more sepcific, we achieve an absolute improvement of $17.9\\%$ and $2.2\\%$ from Source and AdaptBN, respectively, in the batch size of 1.", + "bbox": [ + 75, + 337, + 468, + 532 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Number of the source samples for meta networks. Like previous TTA works [9, 35, 28, 33] including EATA [41], our approach requires access to the source data for pretraining our proposed meta networks before model deployment. In order to cope with the situation where we can only make use of a subset of the source dataset, we study the TTA performance of our method according to the number of accessible source samples. The results are specified in Table 7 where we use WideResNet-40. We observe that our method outperforms the baseline model even with small number of training samples (e.g., $10\\%$ or $20\\%$ ) while showing comparable performance with excessively small numbers (e.g. $5\\%$ ). Note that we still reduce the memory usage of about $51\\%$ compared to EATA.", + "bbox": [ + 75, + 536, + 470, + 748 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Segmentation Experiments", + "text_level": 1, + "bbox": [ + 76, + 758, + 328, + 776 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We investigate our approach in semantic segmentation. First, we create Cityscapes-C by applying the weather corruptions (brightness, fog, frost, and snow [22]) to the validation set of Cityscapes [10]. Then, to simulate continual distribution shifts, we repeat the four types of Cityscapes-C ten times. In this scenario, we conduct continual TTA using the publicly-available ResNet-50-based DeepLabV3+ [7], which is pre-trained on Cityscapes for domain generaliza", + "bbox": [ + 75, + 780, + 470, + 902 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/592eafbed8630e47ce20586a4485c2cb832b811fcbe839f40b6d81df8daba6de.jpg", + "table_caption": [ + "Table 6. Semantic segmentation results in continual test-time adaptation tasks. We conduct experiments on Cityscapes [10] with four weather corruptions [22] applied. The four conditions are repeated ten times to simulate continual domain shifts. All results are evaluated based on DeepLabV3Plus-ResNet-50. Among above methods, only single domain TENT requires domain labels." + ], + "table_footnote": [], + "table_body": "
Target domainEATA [41] (188MB)Ours (K=5) (92MB)# of source samples
10k (20%)5k (10%)2.5k (5%)
CIFAR10-C13.012.112.412.913.1
CIFAR100-C37.136.336.436.637.2
", + "bbox": [ + 504, + 241, + 887, + 297 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 7. Ablation of # of source samples to warm up the meta networks. Before deployment, we pre-trained the meta networks using only a subset of the source dataset (e.g., $20\\%$ , $10\\%$ , and $5\\%$ ). The memory usage (MB) of each method is also presented.", + "bbox": [ + 498, + 301, + 890, + 358 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "tion task [8] in semantic segmentation. For TTA, we use the batch size of 2. More details are specified in Appendix C.", + "bbox": [ + 498, + 363, + 890, + 393 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Results. We report the results based on mean intersection over union (mIoU) in Table 6. It demonstrates that our approach helps to both minimize memory consumption and performs long-term adaptation stably for semantic segmentation. Unlike continual TENT, our method avoids catastrophic forgetting and error accumulation, allowing us to achieve the highest mIoU score while using $66\\%$ less memory usage in a continual TTA setup. Additional experiment results can be found in Appendix B.", + "bbox": [ + 498, + 396, + 892, + 532 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "6. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 541, + 617, + 556 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "This paper proposed a simple yet effective approach that improves continual TTA performance and saves a significant amount of memory, which can be applied to edge devices with limited memory. First, we presented a memory-efficient architecture that consists of original networks and meta networks. This architecture requires much less memory size than the previous TTA methods by decreasing the intermediate activations used for gradient calculations. Second, in order to preserve the source knowledge and prevent error accumulation during long-term adaptation with noisy unsupervised loss, we proposed self-distilled regularization that controls the output of meta networks not to deviate significantly from the output of the original networks. With extensive experiments on diverse datasets and backbone networks, we verified the memory efficiency and TTA performance of our approach. In this regard, we hope that our efforts will facilitate a variety of studies that make test-time adaptation for edge devices feasible in practice.", + "bbox": [ + 496, + 561, + 890, + 834 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgments. We would like to thank Kyuwoong Hwang, Simyung Chang, and Byeonggeun Kim for their valuable feedback. We are also grateful for the helpful discussions from Qualcomm AI Research teams.", + "bbox": [ + 498, + 839, + 892, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "11927", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 174, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Kazuki Adachi, Shin'ya Yamaguchi, and Atsutoshi Kumagai. Covariance-aware feature alignment with pre-computed source statistics for test-time adaptation. arXiv preprint arXiv:2204.13263, 2022. 2, 3", + "[2] Eric Arazo, Diego Ortego, Paul Albert, Noel E O'Connor, and Kevin McGuinness. Pseudo-labeling and confirmation bias in deep semi-supervised learning. In IJCNN, 2020. 2, 3, 4, 8", + "[3] Kambiz Azarian, Debasmit Das, Hyojin Park, and Fatih Porikli. 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Domain generalization with mixstyle. In ICLR, 2021. 3" + ], + "bbox": [ + 501, + 90, + 892, + 875 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "11929", + "bbox": [ + 480, + 945, + 519, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/EcoTTA_ Memory-Efficient Continual Test-Time Adaptation via Self-Distilled Regularization/62c54281-c979-438c-bdac-9fc9ff81d220_model.json b/2023/EcoTTA_ Memory-Efficient Continual Test-Time Adaptation via Self-Distilled Regularization/62c54281-c979-438c-bdac-9fc9ff81d220_model.json new file mode 100644 index 0000000000000000000000000000000000000000..00befaab23832dd8e921e0afc4f61e94088dcc32 --- /dev/null +++ b/2023/EcoTTA_ Memory-Efficient Continual Test-Time Adaptation via Self-Distilled Regularization/62c54281-c979-438c-bdac-9fc9ff81d220_model.json @@ -0,0 +1,2167 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.0, + 0.812, + 0.045 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.183, + 0.131, + 0.79, + 0.177 + ], + "angle": 0, + "content": "EcoTTA: Memory-Efficient Continual Test-time Adaptation via Self-distilled Regularization" + }, + { + "type": "text", + "bbox": [ + 0.234, + 0.203, + 0.744, + 0.24 + ], + "angle": 0, + "content": "Junha Song\\(^{1,2*}\\), Jungsoo Lee\\(^{1}\\), In So Kweon\\(^{2}\\), Sungha Choi\\(^{1\\dagger}\\) \n\\(^{1}\\)Qualcomm AI Research\\(\\ddagger\\), \\(^{2}\\)KAIST" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.274, + 0.314, + 0.29 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.306, + 0.474, + 0.699 + ], + "angle": 0, + "content": "This paper presents a simple yet effective approach that improves continual test-time adaptation (TTA) in a memory-efficient manner. TTA may primarily be conducted on edge devices with limited memory, so reducing memory is crucial but has been overlooked in previous TTA studies. In addition, long-term adaptation often leads to catastrophic forgetting and error accumulation, which hinders applying TTA in real-world deployments. Our approach consists of two components to address these issues. First, we present lightweight meta networks that can adapt the frozen original networks to the target domain. This novel architecture minimizes memory consumption by decreasing the size of intermediate activations required for backpropagation. Second, our novel self-distilled regularization controls the output of the meta networks not to deviate significantly from the output of the frozen original networks, thereby preserving well-trained knowledge from the source domain. Without additional memory, this regularization prevents error accumulation and catastrophic forgetting, resulting in stable performance even in long-term test-time adaptation. We demonstrate that our simple yet effective strategy outperforms other state-of-the-art methods on various benchmarks for image classification and semantic segmentation tasks. Notably, our proposed method with ResNet-50 and WideResNet-40 takes \\(86\\%\\) and \\(80\\%\\) less memory than the recent state-of-the-art method, CoTTA." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.723, + 0.21, + 0.739 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.748, + 0.47, + 0.856 + ], + "angle": 0, + "content": "Despite recent advances in deep learning [14, 21, 20, 19], deep neural networks often suffer from performance degradation when the source and target domains differ significantly [8, 36, 31]. Among several tasks addressing such domain shifts, test-time adaptation (TTA) has recently received a significant amount of attention due to its practicality and wide applicability especially in on-device set" + }, + { + "type": "image", + "bbox": [ + 0.504, + 0.274, + 0.892, + 0.628 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.634, + 0.895, + 0.76 + ], + "angle": 0, + "content": "Figure 1. (a) Memory cost comparison between TTA methods. The size of activations, not the parameters, is the primary memory bottleneck during training. (b) CIFAR-C adaptation performance. We perform the continual online adaptation on CIFAR-C dataset. The x- and y-axis are the average error of all corruptions and the total memory consumption including the parameters and activations, respectively. Our approach, EcoTTA, achieves the best results while consuming the least amount of memory, where K is the model partition factor used in our method." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.775, + 0.895, + 0.821 + ], + "angle": 0, + "content": "tings [53, 35, 26, 15]. This task focuses on adapting the model to unlabeled online data from the target domain without access to the source data." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.825, + 0.895, + 0.903 + ], + "angle": 0, + "content": "While existing TTA methods show improved TTA performances, minimizing the sizes of memory resources have been relatively under-explored, which is crucial considering the applicability of TTA in on-device settings. For example, several studies [54, 35, 9] update entire model parameters" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.863, + 0.418, + 0.875 + ], + "angle": 0, + "content": "*Work done during an internship at Qualcomm AI Research." + }, + { + "type": "page_footnote", + "bbox": [ + 0.079, + 0.876, + 0.47, + 0.9 + ], + "angle": 0, + "content": "†Corresponding author. ‡ Qualcomm AI Research is an initiative of Qualcomm Technologies, Inc." + }, + { + "type": "list", + "bbox": [ + 0.079, + 0.863, + 0.47, + 0.9 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "11920" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.086, + 0.086, + 0.885, + 0.21 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.218, + 0.896, + 0.288 + ], + "angle": 0, + "content": "Figure 2. Architecture for test-time adaptation. We illustrate TTA methods: TENT [53], EATA [41], CoTTA [54], and Ours (EcoTTA). TENT and EATA update multiple batch norm layers, in which large activations have to be stored for gradient calculation. In CoTTA, an entire network is trained with additional strategies for continual adaptation that requires a significant amount of both memory and time. In contrast, our approach requires a minimum size of activations by updating only a few layers. Also, stable long-term adaptation is performed by our proposed regularization, named self-distilled regularization." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.296, + 0.473, + 0.491 + ], + "angle": 0, + "content": "to achieve large performance improvements, which may be impractical when the available memory sizes are limited. Meanwhile, several TTA approaches update only the batch normalization (BN) parameters [53, 41, 16] to make the optimization efficient and stable. However, even updating only BN parameters is not memory efficient enough since the amount of memory required for training models significantly depends on the size of intermediate activations rather than the learnable parameters [4, 13, 57]. Throughout the paper, activations refer to the intermediate features stored during the forward propagation, which are used for gradient calculations during backpropagation. Fig. 1 (a) demonstrates such an issue." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.493, + 0.47, + 0.749 + ], + "angle": 0, + "content": "Moreover, a non-trivial number of TTA studies assume a stationary target domain [53, 35, 9, 48], but the target domain may continuously change in the real world (e.g., continuous changes in weather conditions, illuminations, and location [8] in autonomous driving). Therefore, it is necessary to consider long-term TTA in an environment where the target domain constantly varies. However, there exist two challenging issues: 1) catastrophic forgetting [54, 41] and 2) error accumulation. Catastrophic forgetting refers to degraded performance on the source domain due to long-term adaptation to target domains [54, 41]. Such an issue is important since the test samples in the real world may come from diverse domains, including the source and target domains [41]. Also, since target labels are unavailable, TTA relies on noisy unsupervised losses, such as entropy minimization [17], so long-term continual TTA may lead to error accumulation [63, 2]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.75, + 0.473, + 0.904 + ], + "angle": 0, + "content": "To address these challenges, we propose memory-Efficient continual Test-Time Adaptation (EcoTTA), a simple yet effective approach for 1) enhancing memory efficiency and 2) preventing catastrophic forgetting and error accumulation. First, we present a memory-efficient architecture consisting of frozen original networks and our proposed meta networks attached to the original ones. During the test time, we freeze the original networks to discard the intermediate activations that occupy a significant amount of memory. Instead, we only adapt lightweight meta networks" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.296, + 0.895, + 0.508 + ], + "angle": 0, + "content": "to the target domain, composed of only one batch normalization and one convolution block. Surprisingly, updating only the meta networks, not the original ones, can result in significant performance improvement as well as considerable memory savings. Moreover, we propose a self-distilled regularization method to prevent catastrophic forgetting and error accumulation. Our regularization leverages the preserved source knowledge distilled from the frozen original networks to regularize the meta networks. Specifically, we control the output of the meta networks not to deviate from the one extracted by the original networks significantly. Notably, our regularization leads to negligible overhead because it requires no extra memory and is performed in parallel with adaptation loss, such as entropy minimization." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.508, + 0.895, + 0.674 + ], + "angle": 0, + "content": "Recent TTA studies require access to the source data before model deployments [35, 9, 28, 1, 33, 41]. Similarly, our method uses the source data to warm up the newly attached meta networks for a small number of epochs before model deployment. If the source dataset is publicly available or the owner of the pre-trained model tries to adapt the model to a target domain, access to the source data is feasible [9]. Here, we emphasize that pre-trained original networks are frozen throughout our process, and our method is applicable to any pre-trained model because it is agnostic to the architecture and pre-training method of the original networks." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.674, + 0.835, + 0.688 + ], + "angle": 0, + "content": "Our paper presents the following contributions:" + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.689, + 0.892, + 0.763 + ], + "angle": 0, + "content": "- We present novel meta networks that help the frozen original networks adapt to the target domain. This architecture significantly minimize memory consumption up to \\(86\\%\\) by reducing the activation sizes of the original networks." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.765, + 0.892, + 0.825 + ], + "angle": 0, + "content": "- We propose a self-distilled regularization that controls the output of meta networks by leveraging the output of frozen original networks to preserve the source knowledge and prevent error accumulation." + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.826, + 0.892, + 0.901 + ], + "angle": 0, + "content": "- We improve both memory efficiency and TTA performance compared to existing state-of-the-art methods on 1) image classification task (e.g., CIFAR10/100-C and ImageNet-C) and 2) semantic segmentation task (e.g., Cityscapes with weather corruption)" + }, + { + "type": "list", + "bbox": [ + 0.518, + 0.689, + 0.892, + 0.901 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "11921" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.078, + 0.09, + 0.22, + 0.106 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.119, + 0.473, + 0.348 + ], + "angle": 0, + "content": "Mitigating domain shift. One of the fundamental issues of DNNs is the performance degradation due to the domain shift between the train (i.e. source) and test (i.e. target) distributions. Several research fields attempt to address this problem, such as unsupervised domain adaptation [52, 6, 44, 47, 38, 49] and domain generalization [64, 8]. In particular, domain generalization aims to learn invariant representation so as to cover the possible shifts of test data. They simulate the possible shifts using a single or multiple source dataset [64, 62, 32] or force to minimize the dependence on style information [43, 8]. However, it is challenging to handle all potential test shifts using the given source datasets [18]. Thus, instead of enhancing generalization ability during the training time, TTA [53] overcomes the domain shift by directly adapting to the test data." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.351, + 0.473, + 0.533 + ], + "angle": 0, + "content": "Test-time adaptation. Test-time adaptation allows the model to adapt to the test data (i.e., target domain) in a source-free and online manner [27, 50, 53]. Existing works improve TTA performance with sophisticated designs of unsupervised loss [39, 60, 35, 9, 37, 48, 5, 15, 1, 3, 12] or enhance the usability of small batch sizes [30, 58, 25, 42, 33] considering streaming test data. They focus on improving the adaptation performance with a stationary target domain (i.e., single domain TTA setup). In such a setting, the model that finished adaptation to a given target domain is reset to the original model pre-trained with the source domain in order to adapt to the next target domain." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.534, + 0.473, + 0.746 + ], + "angle": 0, + "content": "Recently, CoTTA [54] has proposed continual TTA setup to address TTA under a continuously changing target domain which also involves a long-term adaptation. This setup frequently suffers from error accumulation [63, 2, 51] and catastrophic forgetting [54, 29, 41]. Specifically, performing a long-term adaptation exposes the model to unsupervised loss from unlabeled test data for a long time, so errors are accumulated significantly. Also, the model focuses on learning new knowledge and forgets about the source knowledge, which becomes problematic when the model needs to correctly classify the test sample as similar to the source distribution. To address such issues, CoTTA [54] randomly restores the updated parameters to the source one, while EATA [41] proposed a weight regularization loss." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.75, + 0.473, + 0.903 + ], + "angle": 0, + "content": "Efficient on-device learning. Since the edge device is likely to be memory constrained (e.g., a Raspberry Pi with 512MB and iPhone 13 with 4GB), it is necessary to take account of the memory usage when deploying the models on the device [34]. TinyTL [4], a seminal work in on-device learning, shows that the activation size, not learnable parameters, bottlenecks the training memory. Following this, recent on-device learning studies [4, 56, 57] targeting fine-tuning task attempt to decrease the size of intermediate activations. In contrast, previous TTA studies [53, 41]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.894, + 0.153 + ], + "angle": 0, + "content": "have overlooked these facts and instead focused on reducing learnable parameters. This paper, therefore, proposes a method that not only reduces the high activation sizes required for TTA, but also improves adaptation performance." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.166, + 0.61, + 0.183 + ], + "angle": 0, + "content": "3. Approach" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.191, + 0.895, + 0.299 + ], + "angle": 0, + "content": "Fig. 3 illustrates our simple yet effective approach which only updates the newly added meta networks on the target domain while regularizing them with the knowledge distilled from the frozen original network. This section describes how such a design promotes memory efficiency and prevents error accumulation and catastrophic forgetting which are frequently observed in long-term adaptation." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.307, + 0.771, + 0.323 + ], + "angle": 0, + "content": "3.1. Memory-efficient Architecture" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.332, + 0.895, + 0.44 + ], + "angle": 0, + "content": "Prerequisite. We first formulate the forward and the backward propagation. Assume that the \\(i^{th}\\) linear layer in the model consists of weight \\(\\mathcal{W}\\) and bias \\(b\\), and the input and output features of this layer are \\(f_{i}\\) and \\(f_{i+1}\\), respectively. Given that the forward propagation of \\(f_{i+1} = f_{i}\\mathcal{W} + b\\), the backward propagation from the \\(i+1^{th}\\) layer to the \\(i^{th}\\) layer, and the weight gradient are respectively formulated as:" + }, + { + "type": "equation", + "bbox": [ + 0.563, + 0.448, + 0.892, + 0.481 + ], + "angle": 0, + "content": "\\[\n\\frac {\\partial \\mathcal {L}}{\\partial f _ {i}} = \\frac {\\partial \\mathcal {L}}{\\partial f _ {i + 1}} \\mathcal {W} ^ {T}, \\quad \\frac {\\partial \\mathcal {L}}{\\partial \\mathcal {W}} = f _ {i} ^ {T} \\frac {\\partial \\mathcal {L}}{\\partial f _ {i + 1}}. \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.491, + 0.895, + 0.581 + ], + "angle": 0, + "content": "Eq. (1) means that the learnable layers whose weight \\(\\mathcal{W}\\) need to be updated must store intermediate activations \\(f_{i}\\) to compute the weight gradient. In contrast, the backward propagation in frozen layers can be accomplished without saving the activations, only requiring its weight \\(\\mathcal{W}\\). Further descriptions are provided in Appendix A." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.582, + 0.896, + 0.748 + ], + "angle": 0, + "content": "TinyTL [4] shows that activations occupy the majority of the memory required for training the model rather than learnable parameters. Due to this fact, updating the entire model (e.g., CoTTA [54]) requires a substantial amount of memory. Also, updating only parameters in batch normalization (BN) layers (e.g., TENT [53] and EATA [41]) is not an effective approach enough since they still save the large intermediate activations for multiple BN layers. While previous studies fail to reduce memory by utilizing large activations, this work proposes a simple yet effective way to reduce a significant amount of memory by discarding them." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.75, + 0.897, + 0.901 + ], + "angle": 0, + "content": "Before deployment. As illustrated in Fig. 3 (a, b), we first take a pre-trained model using any pre-training method. We divide the encoder of the pre-trained model into K number of parts and attach lightweight meta networks to each part of the original network. The details of how to divide the model into K number of parts are explained in the next section. One group of meta network composes of one batch normalization layer and one convolution block (i.e., ConvBN-Relu). Before the deployment, we pre-train the meta networks on the source dataset \\(\\mathcal{D}_s\\) for a small number of" + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "11922" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.086, + 0.097, + 0.89, + 0.285 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.296, + 0.893, + 0.368 + ], + "angle": 0, + "content": "Figure 3. Overview of our approach. (a) The encoder of the pre-trained model is divided into K parts (i.e., model partition factor K). (b) Before deployment, the meta networks are attached to each part of the original networks and pre-trained with source dataset \\(\\mathcal{D}_s\\). (c) After the model is deployed, only the meta networks are updated with unsupervised loss (i.e., entropy minimization) on target data \\(\\mathcal{D}_t\\), while the original networks are frozen. To avoid error accumulation and catastrophic forgetting by the long-term adaptation, we regularize the output \\(\\tilde{x}_k\\) of each group of the meta networks leveraging the output \\(x_k\\) of the frozen original network, which preserves the source knowledge." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.374, + 0.47, + 0.449 + ], + "angle": 0, + "content": "epochs (e.g., 10 epochs for CIFAR dataset) while freezing the original networks. Such a warm-up process is completed before the model deployment, similarly done in several TTA works [9, 28, 33, 41]. Note that we do not require source dataset \\(\\mathcal{D}_s\\) during test time." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.451, + 0.47, + 0.588 + ], + "angle": 0, + "content": "Pre-trained model partition. Previous TTA studies addressing domain shifts [9, 39] indicate that updating shallow layers is more crucial for improving the adaptation performance than updating the deep layers. Inspired by such a finding, given that the encoder of the pre-trained model is split into model partition factor K (e.g., 4 or 5), we partition the shallow parts of the encoder more (i.e., densely) compared to the deep parts of it. Table 4c shows how performance changes as we vary the model partition factor K." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.59, + 0.47, + 0.711 + ], + "angle": 0, + "content": "After deployment. During the test-time adaptation, we only adapt meta networks to target domains while freezing the original networks. Following EATA [41], we use the entropy minimization \\( H(\\hat{y}) = -\\sum_{c} p(\\hat{y}) \\log p(\\hat{y}) \\) to the samples achieving entropy less than the pre-defined entropy threshold \\( H_0 \\), where \\( \\hat{y} \\) is the prediction output of a test image from test dataset \\( \\mathcal{D}_t \\) and \\( \\mathrm{p}(\\cdot) \\) is the softmax function. Thus, the main task loss for adaptation is defined as" + }, + { + "type": "equation", + "bbox": [ + 0.18, + 0.717, + 0.47, + 0.736 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} ^ {e n t} = \\mathbb {I} _ {\\{H (\\hat {y}) < H _ {0} \\}} \\cdot H (\\hat {y}), \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.742, + 0.47, + 0.817 + ], + "angle": 0, + "content": "where \\(\\mathbb{I}_{\\{\\cdot \\}}\\) is an indicator function. In addition, in order to prevent catastrophic forgetting and error accumulation, we apply our proposed regularization loss \\(\\mathcal{R}^k\\), which is described next in detail. Consequently, the overall loss of our method is formulated as," + }, + { + "type": "equation", + "bbox": [ + 0.176, + 0.823, + 0.47, + 0.864 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\theta} ^ {t o t a l} = \\mathcal {L} _ {\\theta} ^ {e n t} + \\lambda \\sum_ {k} ^ {K} \\mathcal {R} _ {\\theta_ {k}} ^ {k}, \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.47, + 0.902 + ], + "angle": 0, + "content": "where \\(\\theta\\) and \\(\\theta_{k}\\) denotes parameters of all meta networks and those of k-th group of meta networks, respectively, and" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.374, + 0.893, + 0.465 + ], + "angle": 0, + "content": "\\(\\lambda\\) is used to balance the scale of the two loss functions. Note that our architecture requires less memory than previous works [54, 53] since we use frozen original networks and discard its intermediate activations. To be more specific, our architecture uses \\(82\\%\\) and \\(60\\%\\) less memory on average than CoTTA and TENT/EATA." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.475, + 0.753, + 0.491 + ], + "angle": 0, + "content": "3.2. Self-distilled Regularization" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.499, + 0.893, + 0.68 + ], + "angle": 0, + "content": "The unsupervised loss from unlabeled test data \\(\\mathcal{D}_t\\) is likely to provide a false signal (i.e., noise) to the model (\\(\\hat{y} \\neq y_t\\) where \\(y_t\\) is the ground truth test label). Previous works have verified that long-term adaptation with unsupervised loss causes overfitting due to error accumulation [63, 2] and catastrophic forgetting [54, 29]. To prevent the critical issues, we propose a self-distilled regularization utilizing our architecture. As shown in Fig. 3, we regularize the output \\(\\tilde{x}_k\\) of each \\(k\\)-th group of the meta networks not to deviate from the output \\(x_k\\) of the \\(k\\)-th part of frozen original networks. Our regularization loss which computes the mean absolute error (i.e., L1 loss) is formulated as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.625, + 0.694, + 0.891, + 0.713 + ], + "angle": 0, + "content": "\\[\n\\mathcal {R} _ {\\theta_ {k}} ^ {k} = \\left\\| \\tilde {x} _ {k} - x _ {k} \\right\\| _ {1}. \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.893, + 0.901 + ], + "angle": 0, + "content": "Since the original networks are not updated, the output \\( x_{k,k\\sim K} \\) extracted from them can be considered as containing the knowledge learned from the source domain. Taking advantage of this fact, we let the output of meta networks \\( \\tilde{x}_k \\) be regularized with knowledge distilled from the original networks. By preventing the adapted model to not significantly deviate from the original model, we can prevent 1) catastrophic forgetting by maintaining the source domain knowledge and 2) error accumulation by utilizing the class discriminability of the original model. Remarkably, unlike previous works [54, 41], our regularization does not require saving additional original networks, which accompanies ex" + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "11923" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.086, + 0.09, + 0.546, + 0.259 + ], + "angle": 0, + "content": "
MethodWideResNet-40 (AugMix)WideResNet-28ResNet-50
Avg. err↓Mem. (MB)Avg. err↓Mem. (MB)Avg. err↓Mem. (MB)
Source36.71143.55848.891
BN Stats Adapt [40]15.41120.95816.691
Single do. TENT [53]12.718819.264615.0925
Continual TENT13.318820.064615.2925
TTT++ [35]14.639120.3140516.11877
SWR&NSP [9]12.140017.2155115.41971
NOTE [16]13.418820.2646--
EATA [41]13.018818.664614.2925
CoTTA [54]14.040917.0169714.42066
Ours (K=4)12.280 (80,58%↓)16.9404 (76,38%↓)14.4296 (86,68%↓)
Ours (K=5)12.192 (77,51%↓)16.8471 (72,27%↓)14.1498 (76,46%↓)
" + }, + { + "type": "table_caption", + "bbox": [ + 0.212, + 0.261, + 0.412, + 0.274 + ], + "angle": 0, + "content": "(a) CIFAR10-C with severity level 5" + }, + { + "type": "table", + "bbox": [ + 0.554, + 0.091, + 0.898, + 0.258 + ], + "angle": 0, + "content": "
MethodWideResNet-40 (AugMix)ResNet-50
Avg. err↓Mem. (MB)Avg. err↓Mem. (MB)
Source69.71173.891
BN Stats Adapt [40]41.11144.591
Single do. TENT [53]36.718840.1926
Continual TENT38.318845.9926
TTT++ [35]41.039144.21876
SWR&NSP [9]36.640044.11970
NOTE [16]42.8188--
EATA [41]37.118839.9926
CoTTA [54]38.140940.22064
Ours (K=4)36.480 (80,58%↓)39.5296 (86,68%↓)
Ours (K=5)36.392 (77,51%↓)39.3498 (76,46%↓)
" + }, + { + "type": "table_caption", + "bbox": [ + 0.617, + 0.261, + 0.824, + 0.274 + ], + "angle": 0, + "content": "(b) CIFAR100-C with severity level 5" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.277, + 0.895, + 0.348 + ], + "angle": 0, + "content": "Table 1. Comparison of error rate (\\%) on CIFAR-C. We report an average error of 15 corruptions on continual TTA and a memory requirement including model parameters and activation sizes. The lowest error is in bold, and the second lowest error is underlined. The memory reduction rates compared to CoTTA and TENT are presented sequentially. WideResNet-40 was pre-trained with AugMix [23] that is a data processing to increase the robustness of the model. Source denotes the pre-trained model without adaptation. Single domain (in short, single do.) TENT resets the model when adapting to a new target domain, so the domain labels are required." + }, + { + "type": "table", + "bbox": [ + 0.086, + 0.353, + 0.462, + 0.475 + ], + "angle": 0, + "content": "
MethodResNet-50 (AugMix) \nAvg. err ↓ResNet-50 \nAvg. err ↓(MB) \nTotal Mem. ↓
Source74.3682.3591
BN Stats Adapt [40]57.8772.1891
Continual TENT [53]56.1 (0.6)66.2 (1.1)1486
EATA [41]54.9 (2.3)63.8 (2.7)1486
CoTTA [54]54.6 (3.9)62.6 (3.1)3132
Ours (K=4)55.2 (3.0)64.6 (3.2)438 (86, 72%↓)
Ours (K=5)54.4 (2.7)63.4 (3.0)747 (75, 51%↓)
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.479, + 0.47, + 0.535 + ], + "angle": 0, + "content": "Table 2. Comparison of error rate (\\%) on ImageNet-C with severity level 5. Standard deviation for ten diverse corruption sequences is denoted by the parentheses values. The total memory refers to the sum of model parameters and activations." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.546, + 0.465, + 0.646 + ], + "angle": 0, + "content": "
Avg. err (%) \nMethodMem. (MB)CIFAR10-CCIFAR100-C
single do.continualsingle do.continual
BN Stats Adapt [40]9116.616.644.544.5
TinyTL† [4]37915.821.940.577.4
RepNet† [57]50815.220.941.552.1
AuxAdapt† [61]20716.016.744.045.8
Ours (K=4)29614.414.439.539.2
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.65, + 0.47, + 0.693 + ], + "angle": 0, + "content": "Table 3. Comparison with methods for on-device learning. The backbone is ResNet-50. \\(\\dagger\\) denotes our own re-implemented models. single do. indicates the single domain TTA setup." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.703, + 0.47, + 0.749 + ], + "angle": 0, + "content": "tra memory usage. Moreover, it only needs a negligible amount of computational overhead because it is performed in parallel with the entropy minimization loss \\(\\mathcal{L}^{ent}\\)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.765, + 0.327, + 0.784 + ], + "angle": 0, + "content": "4. Classification Experiments" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.792, + 0.469, + 0.838 + ], + "angle": 0, + "content": "We evaluate our approach to image classification tasks based on the continual test-time adaptation setup with three datasets: CIFAR10-C, CIFAR100-C, and ImageNet-C." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.47, + 0.902 + ], + "angle": 0, + "content": "Experimental setup. Following CoTTA [54], we conduct most experiments on the continual TTA task, where we continually adapt the deployed model to each corruption type sequentially without resetting the model. This task is" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.356, + 0.892, + 0.447 + ], + "angle": 0, + "content": "more challenging but more realistic than single domain TTA task [53] in which the adapted model is periodically reset to the original pre-trained model after finishing adaptation to each target, so they require additional domain information. Moreover, we evaluate our approach on the long-term TTA setup, which is detailed in Section 4.2." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.45, + 0.893, + 0.572 + ], + "angle": 0, + "content": "Following the previous TTA studies [53, 54], we evaluate models with {CIFAR10, CIFAR10-C}, {CIFAR100, CIFAR100-C}, and {ImageNet, ImageNet-C} where the first and the second dataset in each bracket refers to the source and the target domain, respectively. The target domains include 15 types of corruptions (e.g. noise, blur, weather, and digital) with 5 levels of severity, which are widely used in conventional benchmarks [22]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.578, + 0.893, + 0.866 + ], + "angle": 0, + "content": "Implementation Details. We evaluate our approach within the frameworks officially provided by previous state-of-the-art methods [54, 41]. For fair comparisons, we use the same pre-trained model, which are WideResNet-28 and WideResNet-40 [59] models from the RobustBench [11], and ResNet-50 [21] model from TTT++ [35, 9]. Before the deployment, we pre-train the meta networks on the source dataset using a cross-entropy loss with SGD optimizer with the learning rate of 5e-2. Since the meta networks contain only a few layers, we pre-train them with a small number of epochs: 10 and 3 epochs for CIFAR and ImageNet, respectively. After deployment, similar to EATA [41], we use the same SGD optimizer with the learning rate of 5e-3. In Eq. (2), the entropy threshold \\( H_0 \\) is set to \\( 0.4 \\times \\ln C \\) where \\( C \\) denotes the number of task classes. The batch size is 64 and 32 for CIFAR and ImageNet, respectively. We set the importance of the regularization \\( \\lambda \\) in Eq. (3) to 0.5 to balance it with the entropy minimization loss. Additional implementation details can be found in Appendix C." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.871, + 0.892, + 0.902 + ], + "angle": 0, + "content": "Evaluation Metric. For all the experiments, we report error rates calculated during testing and the memory consump" + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "11924" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.104, + 0.09, + 0.4, + 0.245 + ], + "angle": 0, + "content": null + }, + { + "type": "table", + "bbox": [ + 0.409, + 0.101, + 0.681, + 0.246 + ], + "angle": 0, + "content": "
Avr. errArchCIFAR10-C WRN-28CIFAR10-C WRN-40CIFAR100-C WRN-40
(i)18.112.637.2
(ii) Ours w\\o BN18.713.738.2
(iii) Ours w\\o Conv20.714.940.1
(iv) Conv60.673.377.2
(v) CBAM [55]21.415.140.9
(vi) SE [24]22.316.240.5
Ours16.812.136.3
" + }, + { + "type": "table", + "bbox": [ + 0.689, + 0.093, + 0.871, + 0.246 + ], + "angle": 0, + "content": "
Model#BlockAvg. err
WRN-28 (12) CIFAR10-C3,3,3,317.3
4,4,2,217.9
2,2,4,416.9
WRN-40 (18) CIFAR10-C4,4,5,512.8
6,6,3,313.7
3,3,6,612.2
WRN-40 (18) CIFAR100-C4,4,5,536.9
6,6,3,338.5
3,3,6,636.4
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.25, + 0.895, + 0.293 + ], + "angle": 0, + "content": "Table 4. Architecture ablation experiments. (a,b) We compare continual TTA performance on several memory-efficient designs. WRN refers to WideResNet [59] backbone. (c) We report the performance based on different designs of partitioning the model. The value next to the backbone's name denotes the total number of residual blocks of a model." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.299, + 0.471, + 0.346 + ], + "angle": 0, + "content": "tion, including the model parameter and the activation storage. We demonstrate the memory efficiency of our work by using the official code provided by TinyTL [4]." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.357, + 0.216, + 0.373 + ], + "angle": 0, + "content": "4.1. Comparisons" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.384, + 0.47, + 0.595 + ], + "angle": 0, + "content": "Comparisons with TTA methods. We compare our approach to competing TTA methods on extensive benchmarks and various pre-trained models. The results of CIFAR10/100-C are detailed in Table 1. The model partition factor K are set to 4 and 5. Our approach outperforms existing TTA methods with the lowest memory usage in all pre-trained models. Specifically, in WideResNet-40, our method achieves superior performance while requiring \\(80\\%\\) and \\(58\\%\\) less memory than CoTTA [54] and EATA [41], respectively, which are also designed for continual TTA. Approaches targeting single domain TTA [53, 35, 9] show poor performance due to error accumulation and catastrophic forgetting, as observed in CoTTA. The error rates for each corruption type are provided in Appendix F." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.596, + 0.47, + 0.732 + ], + "angle": 0, + "content": "Table 2 shows the experiment for ImageNet-C. Two ResNet-50 backbones from RobustBench [11] are leveraged. Following CoTTA, evaluations are conducted on ten diverse corruption-type sequences. We achieve comparable performance to CoTTA while utilizing \\(86\\%\\) and \\(75\\%\\) less memory with \\(\\mathrm{K} = 4\\) and 5, respectively. In addition, we observe that our approach shows superior performance when adopting the model pre-trained with strong data augmentation methods (e.g., Augmix [23])." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.735, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Comparisons with on-device learning methods. We compare our approach with methods for memory-efficient on-device learning. TinyTL [4] and RepNet [57] focus on supervised on-device learning (i.e., requiring labeled target data). However, since TTA assumes that we do not have access to the target labels, utilizing such methods to TTA directly is infeasible. Therefore, we experimented by replacing supervised loss (i.e., cross-entropy) with unsupervised loss (i.e., entropy minimization) in TinyTL and RepNet. As shown in Table 3, they suffer from performance degradation in continual TTA, showing inferior performance compared" + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.3, + 0.895, + 0.415 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.416, + 0.895, + 0.5 + ], + "angle": 0, + "content": "Figure 4. Ablation study of K. We uniformly divide the encoder of the pre-trained model into the model partition factor K. The x-axis indicates the memory size including both model parameter size and activation size while the y-axis indicates the average error rate. The values in parentheses show the rate of increase for the model parameters compared to the original model." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.51, + 0.88, + 0.526 + ], + "angle": 0, + "content": "to our proposed approach even in the single domain TTA." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.527, + 0.892, + 0.694 + ], + "angle": 0, + "content": "Similar to ours, AuxAdapt [61] adds and updates a small network (i.e., ResNet-18) while freezing the pre-trained model. Unlike our approach, they only modify a prediction output, not intermediate features. While AuxAdapt requires the least memory usage, it fails to improve TTA performance in single domain TTA. Nevertheless, since the original model is frozen, it suffers less from catastrophic forgetting and error accumulation than TinyTL [4] and RepNet [57] in the continual TTA. Through the results, we confirm that our proposed method brings both memory efficiency and a significant performance improvement in both TTA setups." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.707, + 0.663, + 0.723 + ], + "angle": 0, + "content": "4.2. Empirical Study" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.733, + 0.892, + 0.853 + ], + "angle": 0, + "content": "Architecture design. An important design of our meta networks is injecting a single BN layer before the original networks and utilizing a residual connection with one conv block. Table 4b studies the effectiveness of the proposed design by comparing it with six different variants. From the results, we observe that using only either conv block (ii) or BN (iii) aggravates the performance: error rate increases by \\(1.4\\%\\) and \\(3.8\\%\\) on CIFAR-100-C with WideResNet-40." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.856, + 0.892, + 0.901 + ], + "angle": 0, + "content": "In design (i), we enforce both BN parameters and Conv layers in the meta networks to take the output of the original networks as inputs. Such a design brings performance" + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "11925" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.086, + 0.092, + 0.49, + 0.262 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.195, + 0.267, + 0.378, + 0.279 + ], + "angle": 0, + "content": "(a) Catastrophic forgetting effect" + }, + { + "type": "image", + "bbox": [ + 0.507, + 0.091, + 0.888, + 0.26 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.614, + 0.267, + 0.779, + 0.278 + ], + "angle": 0, + "content": "(b) Error accumulation effect" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.285, + 0.892, + 0.354 + ], + "angle": 0, + "content": "Figure 5. Regularization ablation experiments. We conduct experiments with WideResNet-40 on CIFAR100-C. (a) We utilize a test set of the CIFAR-100 dataset to measure clean error after adapting to each corruption. Maintaining clean errors at a stable level indicates that our approach helps the model robust to catastrophic forgetting. (b) We simulate a long-term adaptation scenario by repeating 100 rounds of 15 corruption sequences. In the absence of regularization, error accumulation can lead to overfitting (i.e., the case of the error increases exponentially). However, our approach does not suffer from such an error accumulation. We set K to 5 in the above experiments." + }, + { + "type": "table", + "bbox": [ + 0.083, + 0.361, + 0.465, + 0.47 + ], + "angle": 0, + "content": "
Batch size168421
Non trainingSource69.769.769.769.769.7
BN Stats Adapt [40]41.150.259.981.099.1
AdaptBN [46]39.141.245.249.054.0
TrainingCon. TENT [53]40.947.858.682.299.0
Con. TENT+AdaptBN38.240.243.247.752.2
Ours (K=5)40.045.863.480.899.0
Ours (K=5)+AdaptBN36.939.342.246.551.8
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.477, + 0.469, + 0.518 + ], + "angle": 0, + "content": "Table 5. Experiments with small batch sizes. We evaluate all baselines with WideResNet-40 on CIFAR100-C. Con. TENT is the abbreviation for continual TENT." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.522, + 0.469, + 0.718 + ], + "angle": 0, + "content": "drop. We speculate that it is because the original network, which is not adapted to the target domain, lacks the ability to extract sufficiently meaningful features from the target image. Also, we observed a significant performance degradation after removing the residual connection in design (iv). In addition, since attention mechanisms [55, 24] generally have improved classification accuracy, we study how attention mechanisms can further boost TTA performance of our approach in design (v, vi). The results show that it is difficult for the attention module to train ideally in TTA setup using unsupervised learning, unlike when applying it to supervised learning. An ablation study on each element of meta networks can be found in Appendix D." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.72, + 0.469, + 0.901 + ], + "angle": 0, + "content": "Number of blocks in each partition. ResNet [21] consists of multiple residual blocks (e.g., BasicBlock and Bottleneck in Pytorch [45]). For instance, WideResNet-28 has 12 residual blocks. By varying the number of blocks for each part of the original networks, we analyze TTA performance in Table 4c. We observe that splitting the shallow parts of the encoder densely (e.g., 2,2,4,4 blocks, from the shallow to the deep parts sequentially) brings more performance gain than splitting the deep layers densely (e.g., 4,4,2,2 blocks). We suggest that it is because we modify the lower-level feature more as we split shallow layers densely. Our observation is aligned with the finding of previous TTA works [9, 39]," + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.359, + 0.89, + 0.39 + ], + "angle": 0, + "content": "which show that updating the shallow layers more than the deep layers improves TTA performance." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.394, + 0.892, + 0.56 + ], + "angle": 0, + "content": "Number of model partition K. Fig. 4 shows both memory requirement and adaptation performance according to the model partition factor K. With a small K (e.g., 1 or 2), the intermediate outputs are barely modified, making it difficult to achieve a reasonable level of performance. We achieve the best TTA performance with K of 4 or 5 as adjusting a greater numver of intermediate features. In the meanwhile, we observe that the average error rate is saturated and remains consistent when K is set to large values (e.g. 6,7 or 8) even with the increased amount of activations and learnable parameters. Therefore, we set K to 4 and 5." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.565, + 0.892, + 0.761 + ], + "angle": 0, + "content": "Catastrophic forgetting. We conduct experiments to confirm the catastrophic forgetting effect (Fig. 5a). Once finishing adaptation to each corruption, we evaluate the model on clean target data (i.e., test-set of CIFAR dataset) without updating the model. For TENT with no regularization, the error rates for the clean target data (i.e., clean error \\((\\%)\\)) increase gradually, which can be seen as the phenomenon of catastrophic forgetting. In contrast, our approach consistently maintains the error rates for the clean target data, proving that our regularization loss effectively prevents catastrophic forgetting. These results indicate that our method can be reliably utilized in various domains, including the source and target domains." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Error accumulation in long-term adaptation. To evaluate the error accumulation effect, we repeat all the corruption sequences for 100 rounds. The results are described in Fig. 5b. For TENT, a gradual increase in error rates is observed in later rounds, even with small learning rates. For example, TENT [53] with the learning rate of 1e-5 achieves the error rate of \\(39.7\\%\\), and reached its lowest error rate of \\(36.5\\%\\) after 8 rounds. However, it shows increased error rate of \\(38.6\\%\\) after 100 rounds due to overfitting. It suggests" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.946, + 0.519, + 0.957 + ], + "angle": 0, + "content": "11926" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.082, + 0.09, + 0.887, + 0.188 + ], + "angle": 0, + "content": "
Timet
Round14710All
MethodMem. (MB)Brig.FogFros.SnowBrig.FogFros.SnowBrig.FogFros.SnowBrig.FogFros.SnowMean
Source28060.454.330.04.160.454.330.04.160.454.330.04.160.454.330.04.137.2
BN Stats Adapt [40]28069.161.044.839.169.161.044.839.169.161.044.839.169.161.044.839.153.6
Continual TENT [53]272170.162.146.140.262.253.744.437.950.041.531.626.639.232.625.322.442.9
Ours (K=4)918 (66‰)70.262.446.341.970.062.846.542.270.062.846.542.170.162.846.642.255.3
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.191, + 0.895, + 0.234 + ], + "angle": 0, + "content": "Table 6. Semantic segmentation results in continual test-time adaptation tasks. We conduct experiments on Cityscapes [10] with four weather corruptions [22] applied. The four conditions are repeated ten times to simulate continual domain shifts. All results are evaluated based on DeepLabV3Plus-ResNet-50. Among above methods, only single domain TENT requires domain labels." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.244, + 0.471, + 0.336 + ], + "angle": 0, + "content": "that without regularization, TTA methods eventually face overfitting in long-term adaptation [63, 2, 29]. Our method in the absence of regularization \\((\\lambda = 0)\\) also causes overfitting. On the other hand, when self-distilled regularization is involved \\((\\lambda > 0)\\), the performance remains consistent even in the long-term adaptation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.338, + 0.47, + 0.534 + ], + "angle": 0, + "content": "Small batch size. We examine the scalability of our approach with a TTA method designed for small batches size, named adapting BN statistics (i.e., AdaptBN [46, 60]). When the number of batches is too small, the estimated statistics can be unreliable [46]. Thus, they calibrate the source and target statistics for the normalization of BN layers so as to alleviate the domain shift and preserve the discriminative structures. As shown in Table 5, training models with small batch sizes (e.g., 2 or 1) generally increase the error rates. However, such an issue can be addressed by applying AdaptBN to our method. To be more sepcific, we achieve an absolute improvement of \\(17.9\\%\\) and \\(2.2\\%\\) from Source and AdaptBN, respectively, in the batch size of 1." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.537, + 0.471, + 0.749 + ], + "angle": 0, + "content": "Number of the source samples for meta networks. Like previous TTA works [9, 35, 28, 33] including EATA [41], our approach requires access to the source data for pretraining our proposed meta networks before model deployment. In order to cope with the situation where we can only make use of a subset of the source dataset, we study the TTA performance of our method according to the number of accessible source samples. The results are specified in Table 7 where we use WideResNet-40. We observe that our method outperforms the baseline model even with small number of training samples (e.g., \\(10\\%\\) or \\(20\\%\\)) while showing comparable performance with excessively small numbers (e.g. \\(5\\%\\)). Note that we still reduce the memory usage of about \\(51\\%\\) compared to EATA." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.759, + 0.329, + 0.777 + ], + "angle": 0, + "content": "5. Segmentation Experiments" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.781, + 0.471, + 0.903 + ], + "angle": 0, + "content": "We investigate our approach in semantic segmentation. First, we create Cityscapes-C by applying the weather corruptions (brightness, fog, frost, and snow [22]) to the validation set of Cityscapes [10]. Then, to simulate continual distribution shifts, we repeat the four types of Cityscapes-C ten times. In this scenario, we conduct continual TTA using the publicly-available ResNet-50-based DeepLabV3+ [7], which is pre-trained on Cityscapes for domain generaliza" + }, + { + "type": "table", + "bbox": [ + 0.505, + 0.242, + 0.888, + 0.299 + ], + "angle": 0, + "content": "
Target domainEATA [41] (188MB)Ours (K=5) (92MB)# of source samples
10k (20%)5k (10%)2.5k (5%)
CIFAR10-C13.012.112.412.913.1
CIFAR100-C37.136.336.436.637.2
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.302, + 0.892, + 0.359 + ], + "angle": 0, + "content": "Table 7. Ablation of # of source samples to warm up the meta networks. Before deployment, we pre-trained the meta networks using only a subset of the source dataset (e.g., \\(20\\%\\), \\(10\\%\\), and \\(5\\%\\)). The memory usage (MB) of each method is also presented." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.364, + 0.892, + 0.395 + ], + "angle": 0, + "content": "tion task [8] in semantic segmentation. For TTA, we use the batch size of 2. More details are specified in Appendix C." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.397, + 0.893, + 0.533 + ], + "angle": 0, + "content": "Results. We report the results based on mean intersection over union (mIoU) in Table 6. It demonstrates that our approach helps to both minimize memory consumption and performs long-term adaptation stably for semantic segmentation. Unlike continual TENT, our method avoids catastrophic forgetting and error accumulation, allowing us to achieve the highest mIoU score while using \\(66\\%\\) less memory usage in a continual TTA setup. Additional experiment results can be found in Appendix B." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.542, + 0.619, + 0.557 + ], + "angle": 0, + "content": "6. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.563, + 0.892, + 0.835 + ], + "angle": 0, + "content": "This paper proposed a simple yet effective approach that improves continual TTA performance and saves a significant amount of memory, which can be applied to edge devices with limited memory. First, we presented a memory-efficient architecture that consists of original networks and meta networks. This architecture requires much less memory size than the previous TTA methods by decreasing the intermediate activations used for gradient calculations. Second, in order to preserve the source knowledge and prevent error accumulation during long-term adaptation with noisy unsupervised loss, we proposed self-distilled regularization that controls the output of meta networks not to deviate significantly from the output of the original networks. With extensive experiments on diverse datasets and backbone networks, we verified the memory efficiency and TTA performance of our approach. In this regard, we hope that our efforts will facilitate a variety of studies that make test-time adaptation for edge devices feasible in practice." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.84, + 0.893, + 0.901 + ], + "angle": 0, + "content": "Acknowledgments. We would like to thank Kyuwoong Hwang, Simyung Chang, and Byeonggeun Kim for their valuable feedback. We are also grateful for the helpful discussions from Qualcomm AI Research teams." + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "11927" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.175, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.116, + 0.47, + 0.171 + ], + "angle": 0, + "content": "[1] Kazuki Adachi, Shin'ya Yamaguchi, and Atsutoshi Kumagai. Covariance-aware feature alignment with pre-computed source statistics for test-time adaptation. arXiv preprint arXiv:2204.13263, 2022. 2, 3" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.173, + 0.472, + 0.227 + ], + "angle": 0, + "content": "[2] Eric Arazo, Diego Ortego, Paul Albert, Noel E O'Connor, and Kevin McGuinness. Pseudo-labeling and confirmation bias in deep semi-supervised learning. 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TTA may primarily be conducted on edge devices with limited memory, so reducing memory is crucial but has been overlooked in previous TTA studies. In addition, long-term adaptation often leads to catastrophic forgetting and error accumulation, which hinders applying TTA in real-world deployments. Our approach consists of two components to address these issues. First, we present lightweight meta networks that can adapt the frozen original networks to the target domain. This novel architecture minimizes memory consumption by decreasing the size of intermediate activations required for backpropagation. Second, our novel self-distilled regularization controls the output of the meta networks not to deviate significantly from the output of the frozen original networks, thereby preserving well-trained knowledge from the source domain. Without additional memory, this regularization prevents error accumulation and catastrophic forgetting, resulting in stable performance even in long-term test-time adaptation. We demonstrate that our simple yet effective strategy outperforms other state-of-the-art methods on various benchmarks for image classification and semantic segmentation tasks. Notably, our proposed method with ResNet-50 and WideResNet-40 takes $86\%$ and $80\%$ less memory than the recent state-of-the-art method, CoTTA. + +# 1. Introduction + +Despite recent advances in deep learning [14, 21, 20, 19], deep neural networks often suffer from performance degradation when the source and target domains differ significantly [8, 36, 31]. Among several tasks addressing such domain shifts, test-time adaptation (TTA) has recently received a significant amount of attention due to its practicality and wide applicability especially in on-device set + +![](images/ba36850b7bda142cabb71e0f3d8ae8bebcb23f4846ad4de3776a42f9ba2d3d9d.jpg) +Figure 1. (a) Memory cost comparison between TTA methods. The size of activations, not the parameters, is the primary memory bottleneck during training. (b) CIFAR-C adaptation performance. We perform the continual online adaptation on CIFAR-C dataset. The x- and y-axis are the average error of all corruptions and the total memory consumption including the parameters and activations, respectively. Our approach, EcoTTA, achieves the best results while consuming the least amount of memory, where K is the model partition factor used in our method. + +tings [53, 35, 26, 15]. This task focuses on adapting the model to unlabeled online data from the target domain without access to the source data. + +While existing TTA methods show improved TTA performances, minimizing the sizes of memory resources have been relatively under-explored, which is crucial considering the applicability of TTA in on-device settings. For example, several studies [54, 35, 9] update entire model parameters + +![](images/493762fb42517322de7e130c1a0e54c2a211b6b1c3b21a05c05291aaf8f8730c.jpg) +Figure 2. Architecture for test-time adaptation. We illustrate TTA methods: TENT [53], EATA [41], CoTTA [54], and Ours (EcoTTA). TENT and EATA update multiple batch norm layers, in which large activations have to be stored for gradient calculation. In CoTTA, an entire network is trained with additional strategies for continual adaptation that requires a significant amount of both memory and time. In contrast, our approach requires a minimum size of activations by updating only a few layers. Also, stable long-term adaptation is performed by our proposed regularization, named self-distilled regularization. + +to achieve large performance improvements, which may be impractical when the available memory sizes are limited. Meanwhile, several TTA approaches update only the batch normalization (BN) parameters [53, 41, 16] to make the optimization efficient and stable. However, even updating only BN parameters is not memory efficient enough since the amount of memory required for training models significantly depends on the size of intermediate activations rather than the learnable parameters [4, 13, 57]. Throughout the paper, activations refer to the intermediate features stored during the forward propagation, which are used for gradient calculations during backpropagation. Fig. 1 (a) demonstrates such an issue. + +Moreover, a non-trivial number of TTA studies assume a stationary target domain [53, 35, 9, 48], but the target domain may continuously change in the real world (e.g., continuous changes in weather conditions, illuminations, and location [8] in autonomous driving). Therefore, it is necessary to consider long-term TTA in an environment where the target domain constantly varies. However, there exist two challenging issues: 1) catastrophic forgetting [54, 41] and 2) error accumulation. Catastrophic forgetting refers to degraded performance on the source domain due to long-term adaptation to target domains [54, 41]. Such an issue is important since the test samples in the real world may come from diverse domains, including the source and target domains [41]. Also, since target labels are unavailable, TTA relies on noisy unsupervised losses, such as entropy minimization [17], so long-term continual TTA may lead to error accumulation [63, 2]. + +To address these challenges, we propose memory-Efficient continual Test-Time Adaptation (EcoTTA), a simple yet effective approach for 1) enhancing memory efficiency and 2) preventing catastrophic forgetting and error accumulation. First, we present a memory-efficient architecture consisting of frozen original networks and our proposed meta networks attached to the original ones. During the test time, we freeze the original networks to discard the intermediate activations that occupy a significant amount of memory. Instead, we only adapt lightweight meta networks + +to the target domain, composed of only one batch normalization and one convolution block. Surprisingly, updating only the meta networks, not the original ones, can result in significant performance improvement as well as considerable memory savings. Moreover, we propose a self-distilled regularization method to prevent catastrophic forgetting and error accumulation. Our regularization leverages the preserved source knowledge distilled from the frozen original networks to regularize the meta networks. Specifically, we control the output of the meta networks not to deviate from the one extracted by the original networks significantly. Notably, our regularization leads to negligible overhead because it requires no extra memory and is performed in parallel with adaptation loss, such as entropy minimization. + +Recent TTA studies require access to the source data before model deployments [35, 9, 28, 1, 33, 41]. Similarly, our method uses the source data to warm up the newly attached meta networks for a small number of epochs before model deployment. If the source dataset is publicly available or the owner of the pre-trained model tries to adapt the model to a target domain, access to the source data is feasible [9]. Here, we emphasize that pre-trained original networks are frozen throughout our process, and our method is applicable to any pre-trained model because it is agnostic to the architecture and pre-training method of the original networks. + +Our paper presents the following contributions: + +- We present novel meta networks that help the frozen original networks adapt to the target domain. This architecture significantly minimize memory consumption up to $86\%$ by reducing the activation sizes of the original networks. +- We propose a self-distilled regularization that controls the output of meta networks by leveraging the output of frozen original networks to preserve the source knowledge and prevent error accumulation. +- We improve both memory efficiency and TTA performance compared to existing state-of-the-art methods on 1) image classification task (e.g., CIFAR10/100-C and ImageNet-C) and 2) semantic segmentation task (e.g., Cityscapes with weather corruption) + +# 2. Related Work + +Mitigating domain shift. One of the fundamental issues of DNNs is the performance degradation due to the domain shift between the train (i.e. source) and test (i.e. target) distributions. Several research fields attempt to address this problem, such as unsupervised domain adaptation [52, 6, 44, 47, 38, 49] and domain generalization [64, 8]. In particular, domain generalization aims to learn invariant representation so as to cover the possible shifts of test data. They simulate the possible shifts using a single or multiple source dataset [64, 62, 32] or force to minimize the dependence on style information [43, 8]. However, it is challenging to handle all potential test shifts using the given source datasets [18]. Thus, instead of enhancing generalization ability during the training time, TTA [53] overcomes the domain shift by directly adapting to the test data. + +Test-time adaptation. Test-time adaptation allows the model to adapt to the test data (i.e., target domain) in a source-free and online manner [27, 50, 53]. Existing works improve TTA performance with sophisticated designs of unsupervised loss [39, 60, 35, 9, 37, 48, 5, 15, 1, 3, 12] or enhance the usability of small batch sizes [30, 58, 25, 42, 33] considering streaming test data. They focus on improving the adaptation performance with a stationary target domain (i.e., single domain TTA setup). In such a setting, the model that finished adaptation to a given target domain is reset to the original model pre-trained with the source domain in order to adapt to the next target domain. + +Recently, CoTTA [54] has proposed continual TTA setup to address TTA under a continuously changing target domain which also involves a long-term adaptation. This setup frequently suffers from error accumulation [63, 2, 51] and catastrophic forgetting [54, 29, 41]. Specifically, performing a long-term adaptation exposes the model to unsupervised loss from unlabeled test data for a long time, so errors are accumulated significantly. Also, the model focuses on learning new knowledge and forgets about the source knowledge, which becomes problematic when the model needs to correctly classify the test sample as similar to the source distribution. To address such issues, CoTTA [54] randomly restores the updated parameters to the source one, while EATA [41] proposed a weight regularization loss. + +Efficient on-device learning. Since the edge device is likely to be memory constrained (e.g., a Raspberry Pi with 512MB and iPhone 13 with 4GB), it is necessary to take account of the memory usage when deploying the models on the device [34]. TinyTL [4], a seminal work in on-device learning, shows that the activation size, not learnable parameters, bottlenecks the training memory. Following this, recent on-device learning studies [4, 56, 57] targeting fine-tuning task attempt to decrease the size of intermediate activations. In contrast, previous TTA studies [53, 41] + +have overlooked these facts and instead focused on reducing learnable parameters. This paper, therefore, proposes a method that not only reduces the high activation sizes required for TTA, but also improves adaptation performance. + +# 3. Approach + +Fig. 3 illustrates our simple yet effective approach which only updates the newly added meta networks on the target domain while regularizing them with the knowledge distilled from the frozen original network. This section describes how such a design promotes memory efficiency and prevents error accumulation and catastrophic forgetting which are frequently observed in long-term adaptation. + +# 3.1. Memory-efficient Architecture + +Prerequisite. We first formulate the forward and the backward propagation. Assume that the $i^{th}$ linear layer in the model consists of weight $\mathcal{W}$ and bias $b$ , and the input and output features of this layer are $f_{i}$ and $f_{i+1}$ , respectively. Given that the forward propagation of $f_{i+1} = f_{i}\mathcal{W} + b$ , the backward propagation from the $i+1^{th}$ layer to the $i^{th}$ layer, and the weight gradient are respectively formulated as: + +$$ +\frac {\partial \mathcal {L}}{\partial f _ {i}} = \frac {\partial \mathcal {L}}{\partial f _ {i + 1}} \mathcal {W} ^ {T}, \quad \frac {\partial \mathcal {L}}{\partial \mathcal {W}} = f _ {i} ^ {T} \frac {\partial \mathcal {L}}{\partial f _ {i + 1}}. \tag {1} +$$ + +Eq. (1) means that the learnable layers whose weight $\mathcal{W}$ need to be updated must store intermediate activations $f_{i}$ to compute the weight gradient. In contrast, the backward propagation in frozen layers can be accomplished without saving the activations, only requiring its weight $\mathcal{W}$ . Further descriptions are provided in Appendix A. + +TinyTL [4] shows that activations occupy the majority of the memory required for training the model rather than learnable parameters. Due to this fact, updating the entire model (e.g., CoTTA [54]) requires a substantial amount of memory. Also, updating only parameters in batch normalization (BN) layers (e.g., TENT [53] and EATA [41]) is not an effective approach enough since they still save the large intermediate activations for multiple BN layers. While previous studies fail to reduce memory by utilizing large activations, this work proposes a simple yet effective way to reduce a significant amount of memory by discarding them. + +Before deployment. As illustrated in Fig. 3 (a, b), we first take a pre-trained model using any pre-training method. We divide the encoder of the pre-trained model into K number of parts and attach lightweight meta networks to each part of the original network. The details of how to divide the model into K number of parts are explained in the next section. One group of meta network composes of one batch normalization layer and one convolution block (i.e., ConvBN-Relu). Before the deployment, we pre-train the meta networks on the source dataset $\mathcal{D}_s$ for a small number of + +![](images/56a26da2f31e21cda5365271ebbc6dea1a73b27e339c98de81f36d456d03d7dc.jpg) +Figure 3. Overview of our approach. (a) The encoder of the pre-trained model is divided into K parts (i.e., model partition factor K). (b) Before deployment, the meta networks are attached to each part of the original networks and pre-trained with source dataset $\mathcal{D}_s$ . (c) After the model is deployed, only the meta networks are updated with unsupervised loss (i.e., entropy minimization) on target data $\mathcal{D}_t$ , while the original networks are frozen. To avoid error accumulation and catastrophic forgetting by the long-term adaptation, we regularize the output $\tilde{x}_k$ of each group of the meta networks leveraging the output $x_k$ of the frozen original network, which preserves the source knowledge. + +epochs (e.g., 10 epochs for CIFAR dataset) while freezing the original networks. Such a warm-up process is completed before the model deployment, similarly done in several TTA works [9, 28, 33, 41]. Note that we do not require source dataset $\mathcal{D}_s$ during test time. + +Pre-trained model partition. Previous TTA studies addressing domain shifts [9, 39] indicate that updating shallow layers is more crucial for improving the adaptation performance than updating the deep layers. Inspired by such a finding, given that the encoder of the pre-trained model is split into model partition factor K (e.g., 4 or 5), we partition the shallow parts of the encoder more (i.e., densely) compared to the deep parts of it. Table 4c shows how performance changes as we vary the model partition factor K. + +After deployment. During the test-time adaptation, we only adapt meta networks to target domains while freezing the original networks. Following EATA [41], we use the entropy minimization $H(\hat{y}) = -\sum_{c} p(\hat{y}) \log p(\hat{y})$ to the samples achieving entropy less than the pre-defined entropy threshold $H_0$ , where $\hat{y}$ is the prediction output of a test image from test dataset $\mathcal{D}_t$ and $\mathrm{p}(\cdot)$ is the softmax function. Thus, the main task loss for adaptation is defined as + +$$ +\mathcal {L} ^ {e n t} = \mathbb {I} _ {\{H (\hat {y}) < H _ {0} \}} \cdot H (\hat {y}), \tag {2} +$$ + +where $\mathbb{I}_{\{\cdot \}}$ is an indicator function. In addition, in order to prevent catastrophic forgetting and error accumulation, we apply our proposed regularization loss $\mathcal{R}^k$ , which is described next in detail. Consequently, the overall loss of our method is formulated as, + +$$ +\mathcal {L} _ {\theta} ^ {t o t a l} = \mathcal {L} _ {\theta} ^ {e n t} + \lambda \sum_ {k} ^ {K} \mathcal {R} _ {\theta_ {k}} ^ {k}, \tag {3} +$$ + +where $\theta$ and $\theta_{k}$ denotes parameters of all meta networks and those of k-th group of meta networks, respectively, and + +$\lambda$ is used to balance the scale of the two loss functions. Note that our architecture requires less memory than previous works [54, 53] since we use frozen original networks and discard its intermediate activations. To be more specific, our architecture uses $82\%$ and $60\%$ less memory on average than CoTTA and TENT/EATA. + +# 3.2. Self-distilled Regularization + +The unsupervised loss from unlabeled test data $\mathcal{D}_t$ is likely to provide a false signal (i.e., noise) to the model ( $\hat{y} \neq y_t$ where $y_t$ is the ground truth test label). Previous works have verified that long-term adaptation with unsupervised loss causes overfitting due to error accumulation [63, 2] and catastrophic forgetting [54, 29]. To prevent the critical issues, we propose a self-distilled regularization utilizing our architecture. As shown in Fig. 3, we regularize the output $\tilde{x}_k$ of each $k$ -th group of the meta networks not to deviate from the output $x_k$ of the $k$ -th part of frozen original networks. Our regularization loss which computes the mean absolute error (i.e., L1 loss) is formulated as follows: + +$$ +\mathcal {R} _ {\theta_ {k}} ^ {k} = \left\| \tilde {x} _ {k} - x _ {k} \right\| _ {1}. \tag {4} +$$ + +Since the original networks are not updated, the output $x_{k,k\sim K}$ extracted from them can be considered as containing the knowledge learned from the source domain. Taking advantage of this fact, we let the output of meta networks $\tilde{x}_k$ be regularized with knowledge distilled from the original networks. By preventing the adapted model to not significantly deviate from the original model, we can prevent 1) catastrophic forgetting by maintaining the source domain knowledge and 2) error accumulation by utilizing the class discriminability of the original model. Remarkably, unlike previous works [54, 41], our regularization does not require saving additional original networks, which accompanies ex + +
MethodWideResNet-40 (AugMix)WideResNet-28ResNet-50
Avg. err↓Mem. (MB)Avg. err↓Mem. (MB)Avg. err↓Mem. (MB)
Source36.71143.55848.891
BN Stats Adapt [40]15.41120.95816.691
Single do. TENT [53]12.718819.264615.0925
Continual TENT13.318820.064615.2925
TTT++ [35]14.639120.3140516.11877
SWR&NSP [9]12.140017.2155115.41971
NOTE [16]13.418820.2646--
EATA [41]13.018818.664614.2925
CoTTA [54]14.040917.0169714.42066
Ours (K=4)12.280 (80,58%↓)16.9404 (76,38%↓)14.4296 (86,68%↓)
Ours (K=5)12.192 (77,51%↓)16.8471 (72,27%↓)14.1498 (76,46%↓)
+ +(a) CIFAR10-C with severity level 5 + +
MethodWideResNet-40 (AugMix)ResNet-50
Avg. err↓Mem. (MB)Avg. err↓Mem. (MB)
Source69.71173.891
BN Stats Adapt [40]41.11144.591
Single do. TENT [53]36.718840.1926
Continual TENT38.318845.9926
TTT++ [35]41.039144.21876
SWR&NSP [9]36.640044.11970
NOTE [16]42.8188--
EATA [41]37.118839.9926
CoTTA [54]38.140940.22064
Ours (K=4)36.480 (80,58%↓)39.5296 (86,68%↓)
Ours (K=5)36.392 (77,51%↓)39.3498 (76,46%↓)
+ +(b) CIFAR100-C with severity level 5 +Table 1. Comparison of error rate (\%) on CIFAR-C. We report an average error of 15 corruptions on continual TTA and a memory requirement including model parameters and activation sizes. The lowest error is in bold, and the second lowest error is underlined. The memory reduction rates compared to CoTTA and TENT are presented sequentially. WideResNet-40 was pre-trained with AugMix [23] that is a data processing to increase the robustness of the model. Source denotes the pre-trained model without adaptation. Single domain (in short, single do.) TENT resets the model when adapting to a new target domain, so the domain labels are required. + +
MethodResNet-50 (AugMix) +Avg. err ↓ResNet-50 +Avg. err ↓(MB) +Total Mem. ↓
Source74.3682.3591
BN Stats Adapt [40]57.8772.1891
Continual TENT [53]56.1 (0.6)66.2 (1.1)1486
EATA [41]54.9 (2.3)63.8 (2.7)1486
CoTTA [54]54.6 (3.9)62.6 (3.1)3132
Ours (K=4)55.2 (3.0)64.6 (3.2)438 (86, 72%↓)
Ours (K=5)54.4 (2.7)63.4 (3.0)747 (75, 51%↓)
+ +Table 2. Comparison of error rate (\%) on ImageNet-C with severity level 5. Standard deviation for ten diverse corruption sequences is denoted by the parentheses values. The total memory refers to the sum of model parameters and activations. + +
Avg. err (%) +MethodMem. (MB)CIFAR10-CCIFAR100-C
single do.continualsingle do.continual
BN Stats Adapt [40]9116.616.644.544.5
TinyTL† [4]37915.821.940.577.4
RepNet† [57]50815.220.941.552.1
AuxAdapt† [61]20716.016.744.045.8
Ours (K=4)29614.414.439.539.2
+ +Table 3. Comparison with methods for on-device learning. The backbone is ResNet-50. $\dagger$ denotes our own re-implemented models. single do. indicates the single domain TTA setup. + +tra memory usage. Moreover, it only needs a negligible amount of computational overhead because it is performed in parallel with the entropy minimization loss $\mathcal{L}^{ent}$ . + +# 4. Classification Experiments + +We evaluate our approach to image classification tasks based on the continual test-time adaptation setup with three datasets: CIFAR10-C, CIFAR100-C, and ImageNet-C. + +Experimental setup. Following CoTTA [54], we conduct most experiments on the continual TTA task, where we continually adapt the deployed model to each corruption type sequentially without resetting the model. This task is + +more challenging but more realistic than single domain TTA task [53] in which the adapted model is periodically reset to the original pre-trained model after finishing adaptation to each target, so they require additional domain information. Moreover, we evaluate our approach on the long-term TTA setup, which is detailed in Section 4.2. + +Following the previous TTA studies [53, 54], we evaluate models with {CIFAR10, CIFAR10-C}, {CIFAR100, CIFAR100-C}, and {ImageNet, ImageNet-C} where the first and the second dataset in each bracket refers to the source and the target domain, respectively. The target domains include 15 types of corruptions (e.g. noise, blur, weather, and digital) with 5 levels of severity, which are widely used in conventional benchmarks [22]. + +Implementation Details. We evaluate our approach within the frameworks officially provided by previous state-of-the-art methods [54, 41]. For fair comparisons, we use the same pre-trained model, which are WideResNet-28 and WideResNet-40 [59] models from the RobustBench [11], and ResNet-50 [21] model from TTT++ [35, 9]. Before the deployment, we pre-train the meta networks on the source dataset using a cross-entropy loss with SGD optimizer with the learning rate of 5e-2. Since the meta networks contain only a few layers, we pre-train them with a small number of epochs: 10 and 3 epochs for CIFAR and ImageNet, respectively. After deployment, similar to EATA [41], we use the same SGD optimizer with the learning rate of 5e-3. In Eq. (2), the entropy threshold $H_0$ is set to $0.4 \times \ln C$ where $C$ denotes the number of task classes. The batch size is 64 and 32 for CIFAR and ImageNet, respectively. We set the importance of the regularization $\lambda$ in Eq. (3) to 0.5 to balance it with the entropy minimization loss. Additional implementation details can be found in Appendix C. + +Evaluation Metric. For all the experiments, we report error rates calculated during testing and the memory consump + +![](images/108e5cc8efab6f0d685ee38581c3595d9729997d22f52770326c9dc7502caeba.jpg) + +
Avr. errArchCIFAR10-C WRN-28CIFAR10-C WRN-40CIFAR100-C WRN-40
(i)18.112.637.2
(ii) Ours w\o BN18.713.738.2
(iii) Ours w\o Conv20.714.940.1
(iv) Conv60.673.377.2
(v) CBAM [55]21.415.140.9
(vi) SE [24]22.316.240.5
Ours16.812.136.3
+ +
Model#BlockAvg. err
WRN-28 (12) CIFAR10-C3,3,3,317.3
4,4,2,217.9
2,2,4,416.9
WRN-40 (18) CIFAR10-C4,4,5,512.8
6,6,3,313.7
3,3,6,612.2
WRN-40 (18) CIFAR100-C4,4,5,536.9
6,6,3,338.5
3,3,6,636.4
+ +Table 4. Architecture ablation experiments. (a,b) We compare continual TTA performance on several memory-efficient designs. WRN refers to WideResNet [59] backbone. (c) We report the performance based on different designs of partitioning the model. The value next to the backbone's name denotes the total number of residual blocks of a model. + +tion, including the model parameter and the activation storage. We demonstrate the memory efficiency of our work by using the official code provided by TinyTL [4]. + +# 4.1. Comparisons + +Comparisons with TTA methods. We compare our approach to competing TTA methods on extensive benchmarks and various pre-trained models. The results of CIFAR10/100-C are detailed in Table 1. The model partition factor K are set to 4 and 5. Our approach outperforms existing TTA methods with the lowest memory usage in all pre-trained models. Specifically, in WideResNet-40, our method achieves superior performance while requiring $80\%$ and $58\%$ less memory than CoTTA [54] and EATA [41], respectively, which are also designed for continual TTA. Approaches targeting single domain TTA [53, 35, 9] show poor performance due to error accumulation and catastrophic forgetting, as observed in CoTTA. The error rates for each corruption type are provided in Appendix F. + +Table 2 shows the experiment for ImageNet-C. Two ResNet-50 backbones from RobustBench [11] are leveraged. Following CoTTA, evaluations are conducted on ten diverse corruption-type sequences. We achieve comparable performance to CoTTA while utilizing $86\%$ and $75\%$ less memory with $\mathrm{K} = 4$ and 5, respectively. In addition, we observe that our approach shows superior performance when adopting the model pre-trained with strong data augmentation methods (e.g., Augmix [23]). + +Comparisons with on-device learning methods. We compare our approach with methods for memory-efficient on-device learning. TinyTL [4] and RepNet [57] focus on supervised on-device learning (i.e., requiring labeled target data). However, since TTA assumes that we do not have access to the target labels, utilizing such methods to TTA directly is infeasible. Therefore, we experimented by replacing supervised loss (i.e., cross-entropy) with unsupervised loss (i.e., entropy minimization) in TinyTL and RepNet. As shown in Table 3, they suffer from performance degradation in continual TTA, showing inferior performance compared + +![](images/83e81d67edc2a25632cf40d7d634c94dc13cd356f02709442d7b73705f56250a.jpg) +Figure 4. Ablation study of K. We uniformly divide the encoder of the pre-trained model into the model partition factor K. The x-axis indicates the memory size including both model parameter size and activation size while the y-axis indicates the average error rate. The values in parentheses show the rate of increase for the model parameters compared to the original model. + +to our proposed approach even in the single domain TTA. + +Similar to ours, AuxAdapt [61] adds and updates a small network (i.e., ResNet-18) while freezing the pre-trained model. Unlike our approach, they only modify a prediction output, not intermediate features. While AuxAdapt requires the least memory usage, it fails to improve TTA performance in single domain TTA. Nevertheless, since the original model is frozen, it suffers less from catastrophic forgetting and error accumulation than TinyTL [4] and RepNet [57] in the continual TTA. Through the results, we confirm that our proposed method brings both memory efficiency and a significant performance improvement in both TTA setups. + +# 4.2. Empirical Study + +Architecture design. An important design of our meta networks is injecting a single BN layer before the original networks and utilizing a residual connection with one conv block. Table 4b studies the effectiveness of the proposed design by comparing it with six different variants. From the results, we observe that using only either conv block (ii) or BN (iii) aggravates the performance: error rate increases by $1.4\%$ and $3.8\%$ on CIFAR-100-C with WideResNet-40. + +In design (i), we enforce both BN parameters and Conv layers in the meta networks to take the output of the original networks as inputs. Such a design brings performance + +![](images/fe046384f813c599986604b0b12e513e8a90bf17056e94e892127b798d978701.jpg) +(a) Catastrophic forgetting effect + +![](images/7371792345457b4221cf7c8650380a80927486101bf247b8bcef57df6d3e3116.jpg) +(b) Error accumulation effect +Figure 5. Regularization ablation experiments. We conduct experiments with WideResNet-40 on CIFAR100-C. (a) We utilize a test set of the CIFAR-100 dataset to measure clean error after adapting to each corruption. Maintaining clean errors at a stable level indicates that our approach helps the model robust to catastrophic forgetting. (b) We simulate a long-term adaptation scenario by repeating 100 rounds of 15 corruption sequences. In the absence of regularization, error accumulation can lead to overfitting (i.e., the case of the error increases exponentially). However, our approach does not suffer from such an error accumulation. We set K to 5 in the above experiments. + +
Batch size168421
Non trainingSource69.769.769.769.769.7
BN Stats Adapt [40]41.150.259.981.099.1
AdaptBN [46]39.141.245.249.054.0
TrainingCon. TENT [53]40.947.858.682.299.0
Con. TENT+AdaptBN38.240.243.247.752.2
Ours (K=5)40.045.863.480.899.0
Ours (K=5)+AdaptBN36.939.342.246.551.8
+ +Table 5. Experiments with small batch sizes. We evaluate all baselines with WideResNet-40 on CIFAR100-C. Con. TENT is the abbreviation for continual TENT. + +drop. We speculate that it is because the original network, which is not adapted to the target domain, lacks the ability to extract sufficiently meaningful features from the target image. Also, we observed a significant performance degradation after removing the residual connection in design (iv). In addition, since attention mechanisms [55, 24] generally have improved classification accuracy, we study how attention mechanisms can further boost TTA performance of our approach in design (v, vi). The results show that it is difficult for the attention module to train ideally in TTA setup using unsupervised learning, unlike when applying it to supervised learning. An ablation study on each element of meta networks can be found in Appendix D. + +Number of blocks in each partition. ResNet [21] consists of multiple residual blocks (e.g., BasicBlock and Bottleneck in Pytorch [45]). For instance, WideResNet-28 has 12 residual blocks. By varying the number of blocks for each part of the original networks, we analyze TTA performance in Table 4c. We observe that splitting the shallow parts of the encoder densely (e.g., 2,2,4,4 blocks, from the shallow to the deep parts sequentially) brings more performance gain than splitting the deep layers densely (e.g., 4,4,2,2 blocks). We suggest that it is because we modify the lower-level feature more as we split shallow layers densely. Our observation is aligned with the finding of previous TTA works [9, 39], + +which show that updating the shallow layers more than the deep layers improves TTA performance. + +Number of model partition K. Fig. 4 shows both memory requirement and adaptation performance according to the model partition factor K. With a small K (e.g., 1 or 2), the intermediate outputs are barely modified, making it difficult to achieve a reasonable level of performance. We achieve the best TTA performance with K of 4 or 5 as adjusting a greater numver of intermediate features. In the meanwhile, we observe that the average error rate is saturated and remains consistent when K is set to large values (e.g. 6,7 or 8) even with the increased amount of activations and learnable parameters. Therefore, we set K to 4 and 5. + +Catastrophic forgetting. We conduct experiments to confirm the catastrophic forgetting effect (Fig. 5a). Once finishing adaptation to each corruption, we evaluate the model on clean target data (i.e., test-set of CIFAR dataset) without updating the model. For TENT with no regularization, the error rates for the clean target data (i.e., clean error $(\%)$ ) increase gradually, which can be seen as the phenomenon of catastrophic forgetting. In contrast, our approach consistently maintains the error rates for the clean target data, proving that our regularization loss effectively prevents catastrophic forgetting. These results indicate that our method can be reliably utilized in various domains, including the source and target domains. + +Error accumulation in long-term adaptation. To evaluate the error accumulation effect, we repeat all the corruption sequences for 100 rounds. The results are described in Fig. 5b. For TENT, a gradual increase in error rates is observed in later rounds, even with small learning rates. For example, TENT [53] with the learning rate of 1e-5 achieves the error rate of $39.7\%$ , and reached its lowest error rate of $36.5\%$ after 8 rounds. However, it shows increased error rate of $38.6\%$ after 100 rounds due to overfitting. It suggests + +
Timet
Round14710All
MethodMem. (MB)Brig.FogFros.SnowBrig.FogFros.SnowBrig.FogFros.SnowBrig.FogFros.SnowMean
Source28060.454.330.04.160.454.330.04.160.454.330.04.160.454.330.04.137.2
BN Stats Adapt [40]28069.161.044.839.169.161.044.839.169.161.044.839.169.161.044.839.153.6
Continual TENT [53]272170.162.146.140.262.253.744.437.950.041.531.626.639.232.625.322.442.9
Ours (K=4)918 (66‰)70.262.446.341.970.062.846.542.270.062.846.542.170.162.846.642.255.3
+ +that without regularization, TTA methods eventually face overfitting in long-term adaptation [63, 2, 29]. Our method in the absence of regularization $(\lambda = 0)$ also causes overfitting. On the other hand, when self-distilled regularization is involved $(\lambda > 0)$ , the performance remains consistent even in the long-term adaptation. + +Small batch size. We examine the scalability of our approach with a TTA method designed for small batches size, named adapting BN statistics (i.e., AdaptBN [46, 60]). When the number of batches is too small, the estimated statistics can be unreliable [46]. Thus, they calibrate the source and target statistics for the normalization of BN layers so as to alleviate the domain shift and preserve the discriminative structures. As shown in Table 5, training models with small batch sizes (e.g., 2 or 1) generally increase the error rates. However, such an issue can be addressed by applying AdaptBN to our method. To be more sepcific, we achieve an absolute improvement of $17.9\%$ and $2.2\%$ from Source and AdaptBN, respectively, in the batch size of 1. + +Number of the source samples for meta networks. Like previous TTA works [9, 35, 28, 33] including EATA [41], our approach requires access to the source data for pretraining our proposed meta networks before model deployment. In order to cope with the situation where we can only make use of a subset of the source dataset, we study the TTA performance of our method according to the number of accessible source samples. The results are specified in Table 7 where we use WideResNet-40. We observe that our method outperforms the baseline model even with small number of training samples (e.g., $10\%$ or $20\%$ ) while showing comparable performance with excessively small numbers (e.g. $5\%$ ). Note that we still reduce the memory usage of about $51\%$ compared to EATA. + +# 5. Segmentation Experiments + +We investigate our approach in semantic segmentation. First, we create Cityscapes-C by applying the weather corruptions (brightness, fog, frost, and snow [22]) to the validation set of Cityscapes [10]. Then, to simulate continual distribution shifts, we repeat the four types of Cityscapes-C ten times. In this scenario, we conduct continual TTA using the publicly-available ResNet-50-based DeepLabV3+ [7], which is pre-trained on Cityscapes for domain generaliza + +Table 6. Semantic segmentation results in continual test-time adaptation tasks. We conduct experiments on Cityscapes [10] with four weather corruptions [22] applied. The four conditions are repeated ten times to simulate continual domain shifts. All results are evaluated based on DeepLabV3Plus-ResNet-50. Among above methods, only single domain TENT requires domain labels. + +
Target domainEATA [41] (188MB)Ours (K=5) (92MB)# of source samples
10k (20%)5k (10%)2.5k (5%)
CIFAR10-C13.012.112.412.913.1
CIFAR100-C37.136.336.436.637.2
+ +Table 7. Ablation of # of source samples to warm up the meta networks. Before deployment, we pre-trained the meta networks using only a subset of the source dataset (e.g., $20\%$ , $10\%$ , and $5\%$ ). The memory usage (MB) of each method is also presented. + +tion task [8] in semantic segmentation. For TTA, we use the batch size of 2. More details are specified in Appendix C. + +Results. We report the results based on mean intersection over union (mIoU) in Table 6. It demonstrates that our approach helps to both minimize memory consumption and performs long-term adaptation stably for semantic segmentation. Unlike continual TENT, our method avoids catastrophic forgetting and error accumulation, allowing us to achieve the highest mIoU score while using $66\%$ less memory usage in a continual TTA setup. Additional experiment results can be found in Appendix B. + +# 6. Conclusion + +This paper proposed a simple yet effective approach that improves continual TTA performance and saves a significant amount of memory, which can be applied to edge devices with limited memory. First, we presented a memory-efficient architecture that consists of original networks and meta networks. This architecture requires much less memory size than the previous TTA methods by decreasing the intermediate activations used for gradient calculations. Second, in order to preserve the source knowledge and prevent error accumulation during long-term adaptation with noisy unsupervised loss, we proposed self-distilled regularization that controls the output of meta networks not to deviate significantly from the output of the original networks. With extensive experiments on diverse datasets and backbone networks, we verified the memory efficiency and TTA performance of our approach. In this regard, we hope that our efforts will facilitate a variety of studies that make test-time adaptation for edge devices feasible in practice. + +Acknowledgments. We would like to thank Kyuwoong Hwang, Simyung Chang, and Byeonggeun Kim for their valuable feedback. We are also grateful for the helpful discussions from Qualcomm AI Research teams. + +# References + +[1] Kazuki Adachi, Shin'ya Yamaguchi, and Atsutoshi Kumagai. Covariance-aware feature alignment with pre-computed source statistics for test-time adaptation. arXiv preprint arXiv:2204.13263, 2022. 2, 3 +[2] Eric Arazo, Diego Ortego, Paul Albert, Noel E O'Connor, and Kevin McGuinness. Pseudo-labeling and confirmation bias in deep semi-supervised learning. In IJCNN, 2020. 2, 3, 4, 8 +[3] Kambiz Azarian, Debasmit Das, Hyojin Park, and Fatih Porikli. Test-time adaptation vs. training-time generalization: A case study in human instance segmentation using keypoints estimation. 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TTA may primarily be conducted on edge devices with limited memory, so reducing memory is crucial but has been overlooked in previous TTA studies. In addition, long-term adaptation often leads to catastrophic forgetting and error accumulation, which hinders applying TTA in real-world deployments. Our approach consists of two components to address these issues. First, we present lightweight meta networks that can adapt the frozen original networks to the target domain. This novel architecture minimizes memory consumption by decreasing the size of intermediate activations required for backpropagation. Second, our novel self-distilled regularization controls the output of the meta networks not to deviate significantly from the output of the frozen original networks, thereby preserving well-trained knowledge from the source domain. Without additional memory, this regularization prevents error accumulation and catastrophic forgetting, resulting in stable performance even in long-term test-time adaptation. We demonstrate that our simple yet effective strategy outperforms other state-of-the-art methods on various benchmarks for image classification and semantic segmentation tasks. Notably, our proposed method with ResNet-50 and WideResNet-40 takes " + }, + { + "bbox": [ + 46, + 242, + 290, + 553 + ], + "type": "inline_equation", + "content": "86\\%" + }, + { + "bbox": [ + 46, + 242, + 290, + 553 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 242, + 290, + 553 + ], + "type": "inline_equation", + "content": "80\\%" + }, + { + "bbox": [ + 46, + 242, + 290, + 553 + ], + "type": "text", + "content": " less memory than the recent state-of-the-art method, CoTTA." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 572, + 128, + 585 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 572, + 128, + 585 + ], + "spans": [ + { + "bbox": [ + 47, + 572, + 128, + 585 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 592, + 287, + 677 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 592, + 287, + 677 + ], + "spans": [ + { + "bbox": [ + 46, + 592, + 287, + 677 + ], + "type": "text", + "content": "Despite recent advances in deep learning [14, 21, 20, 19], deep neural networks often suffer from performance degradation when the source and target domains differ significantly [8, 36, 31]. Among several tasks addressing such domain shifts, test-time adaptation (TTA) has recently received a significant amount of attention due to its practicality and wide applicability especially in on-device set" + } + ] + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 308, + 217, + 545, + 497 + ], + "blocks": [ + { + "bbox": [ + 308, + 217, + 545, + 497 + ], + "lines": [ + { + "bbox": [ + 308, + 217, + 545, + 497 + ], + "spans": [ + { + "bbox": [ + 308, + 217, + 545, + 497 + ], + "type": "image", + "image_path": "ba36850b7bda142cabb71e0f3d8ae8bebcb23f4846ad4de3776a42f9ba2d3d9d.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 502, + 547, + 601 + ], + "lines": [ + { + "bbox": [ + 304, + 502, + 547, + 601 + ], + "spans": [ + { + "bbox": [ + 304, + 502, + 547, + 601 + ], + "type": "text", + "content": "Figure 1. (a) Memory cost comparison between TTA methods. The size of activations, not the parameters, is the primary memory bottleneck during training. (b) CIFAR-C adaptation performance. We perform the continual online adaptation on CIFAR-C dataset. The x- and y-axis are the average error of all corruptions and the total memory consumption including the parameters and activations, respectively. Our approach, EcoTTA, achieves the best results while consuming the least amount of memory, where K is the model partition factor used in our method." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 613, + 547, + 650 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 613, + 547, + 650 + ], + "spans": [ + { + "bbox": [ + 304, + 613, + 547, + 650 + ], + "type": "text", + "content": "tings [53, 35, 26, 15]. This task focuses on adapting the model to unlabeled online data from the target domain without access to the source data." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 653, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 653, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 653, + 547, + 715 + ], + "type": "text", + "content": "While existing TTA methods show improved TTA performances, minimizing the sizes of memory resources have been relatively under-explored, which is crucial considering the applicability of TTA in on-device settings. For example, several studies [54, 35, 9] update entire model parameters" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 496, + 35 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 496, + 35 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 496, + 35 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 683, + 255, + 693 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 683, + 255, + 693 + ], + "spans": [ + { + "bbox": [ + 58, + 683, + 255, + 693 + ], + "type": "text", + "content": "*Work done during an internship at Qualcomm AI Research." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 48, + 693, + 287, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 693, + 287, + 712 + ], + "spans": [ + { + "bbox": [ + 48, + 693, + 287, + 712 + ], + "type": "text", + "content": "†Corresponding author. ‡ Qualcomm AI Research is an initiative of Qualcomm Technologies, Inc." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "11920" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 52, + 68, + 541, + 166 + ], + "blocks": [ + { + "bbox": [ + 52, + 68, + 541, + 166 + ], + "lines": [ + { + "bbox": [ + 52, + 68, + 541, + 166 + ], + "spans": [ + { + "bbox": [ + 52, + 68, + 541, + 166 + ], + "type": "image", + "image_path": "493762fb42517322de7e130c1a0e54c2a211b6b1c3b21a05c05291aaf8f8730c.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 172, + 548, + 228 + ], + "lines": [ + { + "bbox": [ + 46, + 172, + 548, + 228 + ], + "spans": [ + { + "bbox": [ + 46, + 172, + 548, + 228 + ], + "type": "text", + "content": "Figure 2. Architecture for test-time adaptation. We illustrate TTA methods: TENT [53], EATA [41], CoTTA [54], and Ours (EcoTTA). TENT and EATA update multiple batch norm layers, in which large activations have to be stored for gradient calculation. In CoTTA, an entire network is trained with additional strategies for continual adaptation that requires a significant amount of both memory and time. In contrast, our approach requires a minimum size of activations by updating only a few layers. Also, stable long-term adaptation is performed by our proposed regularization, named self-distilled regularization." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 234, + 289, + 388 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 234, + 289, + 388 + ], + "spans": [ + { + "bbox": [ + 46, + 234, + 289, + 388 + ], + "type": "text", + "content": "to achieve large performance improvements, which may be impractical when the available memory sizes are limited. Meanwhile, several TTA approaches update only the batch normalization (BN) parameters [53, 41, 16] to make the optimization efficient and stable. However, even updating only BN parameters is not memory efficient enough since the amount of memory required for training models significantly depends on the size of intermediate activations rather than the learnable parameters [4, 13, 57]. Throughout the paper, activations refer to the intermediate features stored during the forward propagation, which are used for gradient calculations during backpropagation. Fig. 1 (a) demonstrates such an issue." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 390, + 287, + 593 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 390, + 287, + 593 + ], + "spans": [ + { + "bbox": [ + 46, + 390, + 287, + 593 + ], + "type": "text", + "content": "Moreover, a non-trivial number of TTA studies assume a stationary target domain [53, 35, 9, 48], but the target domain may continuously change in the real world (e.g., continuous changes in weather conditions, illuminations, and location [8] in autonomous driving). Therefore, it is necessary to consider long-term TTA in an environment where the target domain constantly varies. However, there exist two challenging issues: 1) catastrophic forgetting [54, 41] and 2) error accumulation. Catastrophic forgetting refers to degraded performance on the source domain due to long-term adaptation to target domains [54, 41]. Such an issue is important since the test samples in the real world may come from diverse domains, including the source and target domains [41]. Also, since target labels are unavailable, TTA relies on noisy unsupervised losses, such as entropy minimization [17], so long-term continual TTA may lead to error accumulation [63, 2]." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 594, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 594, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 289, + 715 + ], + "type": "text", + "content": "To address these challenges, we propose memory-Efficient continual Test-Time Adaptation (EcoTTA), a simple yet effective approach for 1) enhancing memory efficiency and 2) preventing catastrophic forgetting and error accumulation. First, we present a memory-efficient architecture consisting of frozen original networks and our proposed meta networks attached to the original ones. During the test time, we freeze the original networks to discard the intermediate activations that occupy a significant amount of memory. Instead, we only adapt lightweight meta networks" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 234, + 547, + 402 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 234, + 547, + 402 + ], + "spans": [ + { + "bbox": [ + 304, + 234, + 547, + 402 + ], + "type": "text", + "content": "to the target domain, composed of only one batch normalization and one convolution block. Surprisingly, updating only the meta networks, not the original ones, can result in significant performance improvement as well as considerable memory savings. Moreover, we propose a self-distilled regularization method to prevent catastrophic forgetting and error accumulation. Our regularization leverages the preserved source knowledge distilled from the frozen original networks to regularize the meta networks. Specifically, we control the output of the meta networks not to deviate from the one extracted by the original networks significantly. Notably, our regularization leads to negligible overhead because it requires no extra memory and is performed in parallel with adaptation loss, such as entropy minimization." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 402, + 547, + 533 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 402, + 547, + 533 + ], + "spans": [ + { + "bbox": [ + 304, + 402, + 547, + 533 + ], + "type": "text", + "content": "Recent TTA studies require access to the source data before model deployments [35, 9, 28, 1, 33, 41]. Similarly, our method uses the source data to warm up the newly attached meta networks for a small number of epochs before model deployment. If the source dataset is publicly available or the owner of the pre-trained model tries to adapt the model to a target domain, access to the source data is feasible [9]. Here, we emphasize that pre-trained original networks are frozen throughout our process, and our method is applicable to any pre-trained model because it is agnostic to the architecture and pre-training method of the original networks." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 317, + 533, + 511, + 544 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 533, + 511, + 544 + ], + "spans": [ + { + "bbox": [ + 317, + 533, + 511, + 544 + ], + "type": "text", + "content": "Our paper presents the following contributions:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 317, + 545, + 545, + 713 + ], + "type": "list", + "angle": 0, + "index": 11, + "blocks": [ + { + "bbox": [ + 317, + 545, + 545, + 604 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 545, + 545, + 604 + ], + "spans": [ + { + "bbox": [ + 317, + 545, + 545, + 604 + ], + "type": "text", + "content": "- We present novel meta networks that help the frozen original networks adapt to the target domain. This architecture significantly minimize memory consumption up to " + }, + { + "bbox": [ + 317, + 545, + 545, + 604 + ], + "type": "inline_equation", + "content": "86\\%" + }, + { + "bbox": [ + 317, + 545, + 545, + 604 + ], + "type": "text", + "content": " by reducing the activation sizes of the original networks." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 317, + 605, + 545, + 653 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 605, + 545, + 653 + ], + "spans": [ + { + "bbox": [ + 317, + 605, + 545, + 653 + ], + "type": "text", + "content": "- We propose a self-distilled regularization that controls the output of meta networks by leveraging the output of frozen original networks to preserve the source knowledge and prevent error accumulation." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 317, + 654, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 654, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 317, + 654, + 545, + 713 + ], + "type": "text", + "content": "- We improve both memory efficiency and TTA performance compared to existing state-of-the-art methods on 1) image classification task (e.g., CIFAR10/100-C and ImageNet-C) and 2) semantic segmentation task (e.g., Cityscapes with weather corruption)" + } + ] + } + ], + "index": 10 + } + ], + "sub_type": "text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "11921" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 71, + 134, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 71, + 134, + 83 + ], + "spans": [ + { + "bbox": [ + 47, + 71, + 134, + 83 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 94, + 289, + 275 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 94, + 289, + 275 + ], + "spans": [ + { + "bbox": [ + 46, + 94, + 289, + 275 + ], + "type": "text", + "content": "Mitigating domain shift. One of the fundamental issues of DNNs is the performance degradation due to the domain shift between the train (i.e. source) and test (i.e. target) distributions. Several research fields attempt to address this problem, such as unsupervised domain adaptation [52, 6, 44, 47, 38, 49] and domain generalization [64, 8]. In particular, domain generalization aims to learn invariant representation so as to cover the possible shifts of test data. They simulate the possible shifts using a single or multiple source dataset [64, 62, 32] or force to minimize the dependence on style information [43, 8]. However, it is challenging to handle all potential test shifts using the given source datasets [18]. Thus, instead of enhancing generalization ability during the training time, TTA [53] overcomes the domain shift by directly adapting to the test data." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 277, + 289, + 422 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 277, + 289, + 422 + ], + "spans": [ + { + "bbox": [ + 46, + 277, + 289, + 422 + ], + "type": "text", + "content": "Test-time adaptation. Test-time adaptation allows the model to adapt to the test data (i.e., target domain) in a source-free and online manner [27, 50, 53]. Existing works improve TTA performance with sophisticated designs of unsupervised loss [39, 60, 35, 9, 37, 48, 5, 15, 1, 3, 12] or enhance the usability of small batch sizes [30, 58, 25, 42, 33] considering streaming test data. They focus on improving the adaptation performance with a stationary target domain (i.e., single domain TTA setup). In such a setting, the model that finished adaptation to a given target domain is reset to the original model pre-trained with the source domain in order to adapt to the next target domain." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 422, + 289, + 590 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 422, + 289, + 590 + ], + "spans": [ + { + "bbox": [ + 46, + 422, + 289, + 590 + ], + "type": "text", + "content": "Recently, CoTTA [54] has proposed continual TTA setup to address TTA under a continuously changing target domain which also involves a long-term adaptation. This setup frequently suffers from error accumulation [63, 2, 51] and catastrophic forgetting [54, 29, 41]. Specifically, performing a long-term adaptation exposes the model to unsupervised loss from unlabeled test data for a long time, so errors are accumulated significantly. Also, the model focuses on learning new knowledge and forgets about the source knowledge, which becomes problematic when the model needs to correctly classify the test sample as similar to the source distribution. To address such issues, CoTTA [54] randomly restores the updated parameters to the source one, while EATA [41] proposed a weight regularization loss." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 594, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 594, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 289, + 715 + ], + "type": "text", + "content": "Efficient on-device learning. Since the edge device is likely to be memory constrained (e.g., a Raspberry Pi with 512MB and iPhone 13 with 4GB), it is necessary to take account of the memory usage when deploying the models on the device [34]. TinyTL [4], a seminal work in on-device learning, shows that the activation size, not learnable parameters, bottlenecks the training memory. Following this, recent on-device learning studies [4, 56, 57] targeting fine-tuning task attempt to decrease the size of intermediate activations. In contrast, previous TTA studies [53, 41]" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 72, + 547, + 121 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 121 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 121 + ], + "type": "text", + "content": "have overlooked these facts and instead focused on reducing learnable parameters. This paper, therefore, proposes a method that not only reduces the high activation sizes required for TTA, but also improves adaptation performance." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 305, + 131, + 373, + 144 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 131, + 373, + 144 + ], + "spans": [ + { + "bbox": [ + 305, + 131, + 373, + 144 + ], + "type": "text", + "content": "3. Approach" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 151, + 547, + 236 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 151, + 547, + 236 + ], + "spans": [ + { + "bbox": [ + 304, + 151, + 547, + 236 + ], + "type": "text", + "content": "Fig. 3 illustrates our simple yet effective approach which only updates the newly added meta networks on the target domain while regularizing them with the knowledge distilled from the frozen original network. This section describes how such a design promotes memory efficiency and prevents error accumulation and catastrophic forgetting which are frequently observed in long-term adaptation." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 305, + 243, + 471, + 255 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 243, + 471, + 255 + ], + "spans": [ + { + "bbox": [ + 305, + 243, + 471, + 255 + ], + "type": "text", + "content": "3.1. Memory-efficient Architecture" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 262, + 547, + 348 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 262, + 547, + 348 + ], + "spans": [ + { + "bbox": [ + 304, + 262, + 547, + 348 + ], + "type": "text", + "content": "Prerequisite. We first formulate the forward and the backward propagation. Assume that the " + }, + { + "bbox": [ + 304, + 262, + 547, + 348 + ], + "type": "inline_equation", + "content": "i^{th}" + }, + { + "bbox": [ + 304, + 262, + 547, + 348 + ], + "type": "text", + "content": " linear layer in the model consists of weight " + }, + { + "bbox": [ + 304, + 262, + 547, + 348 + ], + "type": "inline_equation", + "content": "\\mathcal{W}" + }, + { + "bbox": [ + 304, + 262, + 547, + 348 + ], + "type": "text", + "content": " and bias " + }, + { + "bbox": [ + 304, + 262, + 547, + 348 + ], + "type": "inline_equation", + "content": "b" + }, + { + "bbox": [ + 304, + 262, + 547, + 348 + ], + "type": "text", + "content": ", and the input and output features of this layer are " + }, + { + "bbox": [ + 304, + 262, + 547, + 348 + ], + "type": "inline_equation", + "content": "f_{i}" + }, + { + "bbox": [ + 304, + 262, + 547, + 348 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 262, + 547, + 348 + ], + "type": "inline_equation", + "content": "f_{i+1}" + }, + { + "bbox": [ + 304, + 262, + 547, + 348 + ], + "type": "text", + "content": ", respectively. Given that the forward propagation of " + }, + { + "bbox": [ + 304, + 262, + 547, + 348 + ], + "type": "inline_equation", + "content": "f_{i+1} = f_{i}\\mathcal{W} + b" + }, + { + "bbox": [ + 304, + 262, + 547, + 348 + ], + "type": "text", + "content": ", the backward propagation from the " + }, + { + "bbox": [ + 304, + 262, + 547, + 348 + ], + "type": "inline_equation", + "content": "i+1^{th}" + }, + { + "bbox": [ + 304, + 262, + 547, + 348 + ], + "type": "text", + "content": " layer to the " + }, + { + "bbox": [ + 304, + 262, + 547, + 348 + ], + "type": "inline_equation", + "content": "i^{th}" + }, + { + "bbox": [ + 304, + 262, + 547, + 348 + ], + "type": "text", + "content": " layer, and the weight gradient are respectively formulated as:" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 344, + 354, + 545, + 380 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 344, + 354, + 545, + 380 + ], + "spans": [ + { + "bbox": [ + 344, + 354, + 545, + 380 + ], + "type": "interline_equation", + "content": "\\frac {\\partial \\mathcal {L}}{\\partial f _ {i}} = \\frac {\\partial \\mathcal {L}}{\\partial f _ {i + 1}} \\mathcal {W} ^ {T}, \\quad \\frac {\\partial \\mathcal {L}}{\\partial \\mathcal {W}} = f _ {i} ^ {T} \\frac {\\partial \\mathcal {L}}{\\partial f _ {i + 1}}. \\tag {1}", + "image_path": "8270289d4defbf9e0f7fb96d91f2e3bea3cae104624965dc4d4299884e1f0960.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 388, + 547, + 460 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 388, + 547, + 460 + ], + "spans": [ + { + "bbox": [ + 304, + 388, + 547, + 460 + ], + "type": "text", + "content": "Eq. (1) means that the learnable layers whose weight " + }, + { + "bbox": [ + 304, + 388, + 547, + 460 + ], + "type": "inline_equation", + "content": "\\mathcal{W}" + }, + { + "bbox": [ + 304, + 388, + 547, + 460 + ], + "type": "text", + "content": " need to be updated must store intermediate activations " + }, + { + "bbox": [ + 304, + 388, + 547, + 460 + ], + "type": "inline_equation", + "content": "f_{i}" + }, + { + "bbox": [ + 304, + 388, + 547, + 460 + ], + "type": "text", + "content": " to compute the weight gradient. In contrast, the backward propagation in frozen layers can be accomplished without saving the activations, only requiring its weight " + }, + { + "bbox": [ + 304, + 388, + 547, + 460 + ], + "type": "inline_equation", + "content": "\\mathcal{W}" + }, + { + "bbox": [ + 304, + 388, + 547, + 460 + ], + "type": "text", + "content": ". Further descriptions are provided in Appendix A." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 460, + 548, + 592 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 460, + 548, + 592 + ], + "spans": [ + { + "bbox": [ + 304, + 460, + 548, + 592 + ], + "type": "text", + "content": "TinyTL [4] shows that activations occupy the majority of the memory required for training the model rather than learnable parameters. Due to this fact, updating the entire model (e.g., CoTTA [54]) requires a substantial amount of memory. Also, updating only parameters in batch normalization (BN) layers (e.g., TENT [53] and EATA [41]) is not an effective approach enough since they still save the large intermediate activations for multiple BN layers. While previous studies fail to reduce memory by utilizing large activations, this work proposes a simple yet effective way to reduce a significant amount of memory by discarding them." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 594, + 548, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 594, + 548, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 594, + 548, + 713 + ], + "type": "text", + "content": "Before deployment. As illustrated in Fig. 3 (a, b), we first take a pre-trained model using any pre-training method. We divide the encoder of the pre-trained model into K number of parts and attach lightweight meta networks to each part of the original network. The details of how to divide the model into K number of parts are explained in the next section. One group of meta network composes of one batch normalization layer and one convolution block (i.e., ConvBN-Relu). Before the deployment, we pre-train the meta networks on the source dataset " + }, + { + "bbox": [ + 304, + 594, + 548, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{D}_s" + }, + { + "bbox": [ + 304, + 594, + 548, + 713 + ], + "type": "text", + "content": " for a small number of" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "11922" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 52, + 76, + 544, + 225 + ], + "blocks": [ + { + "bbox": [ + 52, + 76, + 544, + 225 + ], + "lines": [ + { + "bbox": [ + 52, + 76, + 544, + 225 + ], + "spans": [ + { + "bbox": [ + 52, + 76, + 544, + 225 + ], + "type": "image", + "image_path": "56a26da2f31e21cda5365271ebbc6dea1a73b27e339c98de81f36d456d03d7dc.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 234, + 546, + 291 + ], + "lines": [ + { + "bbox": [ + 46, + 234, + 546, + 291 + ], + "spans": [ + { + "bbox": [ + 46, + 234, + 546, + 291 + ], + "type": "text", + "content": "Figure 3. Overview of our approach. (a) The encoder of the pre-trained model is divided into K parts (i.e., model partition factor K). (b) Before deployment, the meta networks are attached to each part of the original networks and pre-trained with source dataset " + }, + { + "bbox": [ + 46, + 234, + 546, + 291 + ], + "type": "inline_equation", + "content": "\\mathcal{D}_s" + }, + { + "bbox": [ + 46, + 234, + 546, + 291 + ], + "type": "text", + "content": ". (c) After the model is deployed, only the meta networks are updated with unsupervised loss (i.e., entropy minimization) on target data " + }, + { + "bbox": [ + 46, + 234, + 546, + 291 + ], + "type": "inline_equation", + "content": "\\mathcal{D}_t" + }, + { + "bbox": [ + 46, + 234, + 546, + 291 + ], + "type": "text", + "content": ", while the original networks are frozen. To avoid error accumulation and catastrophic forgetting by the long-term adaptation, we regularize the output " + }, + { + "bbox": [ + 46, + 234, + 546, + 291 + ], + "type": "inline_equation", + "content": "\\tilde{x}_k" + }, + { + "bbox": [ + 46, + 234, + 546, + 291 + ], + "type": "text", + "content": " of each group of the meta networks leveraging the output " + }, + { + "bbox": [ + 46, + 234, + 546, + 291 + ], + "type": "inline_equation", + "content": "x_k" + }, + { + "bbox": [ + 46, + 234, + 546, + 291 + ], + "type": "text", + "content": " of the frozen original network, which preserves the source knowledge." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 296, + 287, + 355 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 296, + 287, + 355 + ], + "spans": [ + { + "bbox": [ + 46, + 296, + 287, + 355 + ], + "type": "text", + "content": "epochs (e.g., 10 epochs for CIFAR dataset) while freezing the original networks. Such a warm-up process is completed before the model deployment, similarly done in several TTA works [9, 28, 33, 41]. Note that we do not require source dataset " + }, + { + "bbox": [ + 46, + 296, + 287, + 355 + ], + "type": "inline_equation", + "content": "\\mathcal{D}_s" + }, + { + "bbox": [ + 46, + 296, + 287, + 355 + ], + "type": "text", + "content": " during test time." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 357, + 287, + 465 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 357, + 287, + 465 + ], + "spans": [ + { + "bbox": [ + 46, + 357, + 287, + 465 + ], + "type": "text", + "content": "Pre-trained model partition. Previous TTA studies addressing domain shifts [9, 39] indicate that updating shallow layers is more crucial for improving the adaptation performance than updating the deep layers. Inspired by such a finding, given that the encoder of the pre-trained model is split into model partition factor K (e.g., 4 or 5), we partition the shallow parts of the encoder more (i.e., densely) compared to the deep parts of it. Table 4c shows how performance changes as we vary the model partition factor K." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 467, + 287, + 563 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 467, + 287, + 563 + ], + "spans": [ + { + "bbox": [ + 46, + 467, + 287, + 563 + ], + "type": "text", + "content": "After deployment. During the test-time adaptation, we only adapt meta networks to target domains while freezing the original networks. Following EATA [41], we use the entropy minimization " + }, + { + "bbox": [ + 46, + 467, + 287, + 563 + ], + "type": "inline_equation", + "content": "H(\\hat{y}) = -\\sum_{c} p(\\hat{y}) \\log p(\\hat{y})" + }, + { + "bbox": [ + 46, + 467, + 287, + 563 + ], + "type": "text", + "content": " to the samples achieving entropy less than the pre-defined entropy threshold " + }, + { + "bbox": [ + 46, + 467, + 287, + 563 + ], + "type": "inline_equation", + "content": "H_0" + }, + { + "bbox": [ + 46, + 467, + 287, + 563 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 467, + 287, + 563 + ], + "type": "inline_equation", + "content": "\\hat{y}" + }, + { + "bbox": [ + 46, + 467, + 287, + 563 + ], + "type": "text", + "content": " is the prediction output of a test image from test dataset " + }, + { + "bbox": [ + 46, + 467, + 287, + 563 + ], + "type": "inline_equation", + "content": "\\mathcal{D}_t" + }, + { + "bbox": [ + 46, + 467, + 287, + 563 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 467, + 287, + 563 + ], + "type": "inline_equation", + "content": "\\mathrm{p}(\\cdot)" + }, + { + "bbox": [ + 46, + 467, + 287, + 563 + ], + "type": "text", + "content": " is the softmax function. Thus, the main task loss for adaptation is defined as" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 110, + 567, + 287, + 582 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 110, + 567, + 287, + 582 + ], + "spans": [ + { + "bbox": [ + 110, + 567, + 287, + 582 + ], + "type": "interline_equation", + "content": "\\mathcal {L} ^ {e n t} = \\mathbb {I} _ {\\{H (\\hat {y}) < H _ {0} \\}} \\cdot H (\\hat {y}), \\tag {2}", + "image_path": "144e540f4d42aaa850439e8371ca4cb734d51e008b478fd12b7b6b14b3e40da2.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 587, + 287, + 647 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 587, + 287, + 647 + ], + "spans": [ + { + "bbox": [ + 46, + 587, + 287, + 647 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 587, + 287, + 647 + ], + "type": "inline_equation", + "content": "\\mathbb{I}_{\\{\\cdot \\}}" + }, + { + "bbox": [ + 46, + 587, + 287, + 647 + ], + "type": "text", + "content": " is an indicator function. In addition, in order to prevent catastrophic forgetting and error accumulation, we apply our proposed regularization loss " + }, + { + "bbox": [ + 46, + 587, + 287, + 647 + ], + "type": "inline_equation", + "content": "\\mathcal{R}^k" + }, + { + "bbox": [ + 46, + 587, + 287, + 647 + ], + "type": "text", + "content": ", which is described next in detail. Consequently, the overall loss of our method is formulated as," + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 107, + 651, + 287, + 684 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 107, + 651, + 287, + 684 + ], + "spans": [ + { + "bbox": [ + 107, + 651, + 287, + 684 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\theta} ^ {t o t a l} = \\mathcal {L} _ {\\theta} ^ {e n t} + \\lambda \\sum_ {k} ^ {K} \\mathcal {R} _ {\\theta_ {k}} ^ {k}, \\tag {3}", + "image_path": "e06047a51b3c02a97e947b2ec4c8fac2db8c70a123bdb9dd5e5648d2a7a9f8cd.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "inline_equation", + "content": "\\theta_{k}" + }, + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "text", + "content": " denotes parameters of all meta networks and those of k-th group of meta networks, respectively, and" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 296, + 546, + 368 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 296, + 546, + 368 + ], + "spans": [ + { + "bbox": [ + 304, + 296, + 546, + 368 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 304, + 296, + 546, + 368 + ], + "type": "text", + "content": " is used to balance the scale of the two loss functions. Note that our architecture requires less memory than previous works [54, 53] since we use frozen original networks and discard its intermediate activations. To be more specific, our architecture uses " + }, + { + "bbox": [ + 304, + 296, + 546, + 368 + ], + "type": "inline_equation", + "content": "82\\%" + }, + { + "bbox": [ + 304, + 296, + 546, + 368 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 296, + 546, + 368 + ], + "type": "inline_equation", + "content": "60\\%" + }, + { + "bbox": [ + 304, + 296, + 546, + 368 + ], + "type": "text", + "content": " less memory on average than CoTTA and TENT/EATA." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 376, + 460, + 388 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 376, + 460, + 388 + ], + "spans": [ + { + "bbox": [ + 305, + 376, + 460, + 388 + ], + "type": "text", + "content": "3.2. Self-distilled Regularization" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 395, + 546, + 538 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 395, + 546, + 538 + ], + "spans": [ + { + "bbox": [ + 304, + 395, + 546, + 538 + ], + "type": "text", + "content": "The unsupervised loss from unlabeled test data " + }, + { + "bbox": [ + 304, + 395, + 546, + 538 + ], + "type": "inline_equation", + "content": "\\mathcal{D}_t" + }, + { + "bbox": [ + 304, + 395, + 546, + 538 + ], + "type": "text", + "content": " is likely to provide a false signal (i.e., noise) to the model (" + }, + { + "bbox": [ + 304, + 395, + 546, + 538 + ], + "type": "inline_equation", + "content": "\\hat{y} \\neq y_t" + }, + { + "bbox": [ + 304, + 395, + 546, + 538 + ], + "type": "text", + "content": " where " + }, + { + "bbox": [ + 304, + 395, + 546, + 538 + ], + "type": "inline_equation", + "content": "y_t" + }, + { + "bbox": [ + 304, + 395, + 546, + 538 + ], + "type": "text", + "content": " is the ground truth test label). Previous works have verified that long-term adaptation with unsupervised loss causes overfitting due to error accumulation [63, 2] and catastrophic forgetting [54, 29]. To prevent the critical issues, we propose a self-distilled regularization utilizing our architecture. As shown in Fig. 3, we regularize the output " + }, + { + "bbox": [ + 304, + 395, + 546, + 538 + ], + "type": "inline_equation", + "content": "\\tilde{x}_k" + }, + { + "bbox": [ + 304, + 395, + 546, + 538 + ], + "type": "text", + "content": " of each " + }, + { + "bbox": [ + 304, + 395, + 546, + 538 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 304, + 395, + 546, + 538 + ], + "type": "text", + "content": "-th group of the meta networks not to deviate from the output " + }, + { + "bbox": [ + 304, + 395, + 546, + 538 + ], + "type": "inline_equation", + "content": "x_k" + }, + { + "bbox": [ + 304, + 395, + 546, + 538 + ], + "type": "text", + "content": " of the " + }, + { + "bbox": [ + 304, + 395, + 546, + 538 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 304, + 395, + 546, + 538 + ], + "type": "text", + "content": "-th part of frozen original networks. Our regularization loss which computes the mean absolute error (i.e., L1 loss) is formulated as follows:" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 382, + 549, + 545, + 564 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 382, + 549, + 545, + 564 + ], + "spans": [ + { + "bbox": [ + 382, + 549, + 545, + 564 + ], + "type": "interline_equation", + "content": "\\mathcal {R} _ {\\theta_ {k}} ^ {k} = \\left\\| \\tilde {x} _ {k} - x _ {k} \\right\\| _ {1}. \\tag {4}", + "image_path": "0ce10d4c6f324df0c58478cd96613511b7368abf819d9feaf4acf8774a18adab.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 570, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 546, + 713 + ], + "type": "text", + "content": "Since the original networks are not updated, the output " + }, + { + "bbox": [ + 304, + 570, + 546, + 713 + ], + "type": "inline_equation", + "content": "x_{k,k\\sim K}" + }, + { + "bbox": [ + 304, + 570, + 546, + 713 + ], + "type": "text", + "content": " extracted from them can be considered as containing the knowledge learned from the source domain. Taking advantage of this fact, we let the output of meta networks " + }, + { + "bbox": [ + 304, + 570, + 546, + 713 + ], + "type": "inline_equation", + "content": "\\tilde{x}_k" + }, + { + "bbox": [ + 304, + 570, + 546, + 713 + ], + "type": "text", + "content": " be regularized with knowledge distilled from the original networks. By preventing the adapted model to not significantly deviate from the original model, we can prevent 1) catastrophic forgetting by maintaining the source domain knowledge and 2) error accumulation by utilizing the class discriminability of the original model. Remarkably, unlike previous works [54, 41], our regularization does not require saving additional original networks, which accompanies ex" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "11923" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 52, + 71, + 334, + 205 + ], + "blocks": [ + { + "bbox": [ + 52, + 71, + 334, + 205 + ], + "lines": [ + { + "bbox": [ + 52, + 71, + 334, + 205 + ], + "spans": [ + { + "bbox": [ + 52, + 71, + 334, + 205 + ], + "type": "table", + "html": "
MethodWideResNet-40 (AugMix)WideResNet-28ResNet-50
Avg. err↓Mem. (MB)Avg. err↓Mem. (MB)Avg. err↓Mem. (MB)
Source36.71143.55848.891
BN Stats Adapt [40]15.41120.95816.691
Single do. TENT [53]12.718819.264615.0925
Continual TENT13.318820.064615.2925
TTT++ [35]14.639120.3140516.11877
SWR&NSP [9]12.140017.2155115.41971
NOTE [16]13.418820.2646--
EATA [41]13.018818.664614.2925
CoTTA [54]14.040917.0169714.42066
Ours (K=4)12.280 (80,58%↓)16.9404 (76,38%↓)14.4296 (86,68%↓)
Ours (K=5)12.192 (77,51%↓)16.8471 (72,27%↓)14.1498 (76,46%↓)
", + "image_path": "23c309bc5801ff067fb67f17c3ab64e6b94a6111883a162aecfdc3a1608ab15b.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 339, + 72, + 549, + 204 + ], + "blocks": [ + { + "bbox": [ + 129, + 206, + 252, + 217 + ], + "lines": [ + { + "bbox": [ + 129, + 206, + 252, + 217 + ], + "spans": [ + { + "bbox": [ + 129, + 206, + 252, + 217 + ], + "type": "text", + "content": "(a) CIFAR10-C with severity level 5" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 339, + 72, + 549, + 204 + ], + "lines": [ + { + "bbox": [ + 339, + 72, + 549, + 204 + ], + "spans": [ + { + "bbox": [ + 339, + 72, + 549, + 204 + ], + "type": "table", + "html": "
MethodWideResNet-40 (AugMix)ResNet-50
Avg. err↓Mem. (MB)Avg. err↓Mem. (MB)
Source69.71173.891
BN Stats Adapt [40]41.11144.591
Single do. TENT [53]36.718840.1926
Continual TENT38.318845.9926
TTT++ [35]41.039144.21876
SWR&NSP [9]36.640044.11970
NOTE [16]42.8188--
EATA [41]37.118839.9926
CoTTA [54]38.140940.22064
Ours (K=4)36.480 (80,58%↓)39.5296 (86,68%↓)
Ours (K=5)36.392 (77,51%↓)39.3498 (76,46%↓)
", + "image_path": "af58b3a023ed41fc79b83721e6545ca2504675e10cdb153ba908bd928fbf1a05.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "type": "table", + "bbox": [ + 52, + 279, + 282, + 376 + ], + "blocks": [ + { + "bbox": [ + 377, + 206, + 504, + 217 + ], + "lines": [ + { + "bbox": [ + 377, + 206, + 504, + 217 + ], + "spans": [ + { + "bbox": [ + 377, + 206, + 504, + 217 + ], + "type": "text", + "content": "(b) CIFAR100-C with severity level 5" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 46, + 219, + 547, + 275 + ], + "lines": [ + { + "bbox": [ + 46, + 219, + 547, + 275 + ], + "spans": [ + { + "bbox": [ + 46, + 219, + 547, + 275 + ], + "type": "text", + "content": "Table 1. Comparison of error rate (\\%) on CIFAR-C. We report an average error of 15 corruptions on continual TTA and a memory requirement including model parameters and activation sizes. The lowest error is in bold, and the second lowest error is underlined. The memory reduction rates compared to CoTTA and TENT are presented sequentially. WideResNet-40 was pre-trained with AugMix [23] that is a data processing to increase the robustness of the model. Source denotes the pre-trained model without adaptation. Single domain (in short, single do.) TENT resets the model when adapting to a new target domain, so the domain labels are required." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 52, + 279, + 282, + 376 + ], + "lines": [ + { + "bbox": [ + 52, + 279, + 282, + 376 + ], + "spans": [ + { + "bbox": [ + 52, + 279, + 282, + 376 + ], + "type": "table", + "html": "
MethodResNet-50 (AugMix) \nAvg. err ↓ResNet-50 \nAvg. err ↓(MB) \nTotal Mem. ↓
Source74.3682.3591
BN Stats Adapt [40]57.8772.1891
Continual TENT [53]56.1 (0.6)66.2 (1.1)1486
EATA [41]54.9 (2.3)63.8 (2.7)1486
CoTTA [54]54.6 (3.9)62.6 (3.1)3132
Ours (K=4)55.2 (3.0)64.6 (3.2)438 (86, 72%↓)
Ours (K=5)54.4 (2.7)63.4 (3.0)747 (75, 51%↓)
", + "image_path": "eaef079754a9d0b085603d07d4a71578d7f8f80edf991dd02e1657b0ed318aa3.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "table_body" + } + ], + "index": 5 + }, + { + "type": "table", + "bbox": [ + 50, + 432, + 284, + 511 + ], + "blocks": [ + { + "bbox": [ + 46, + 379, + 287, + 423 + ], + "lines": [ + { + "bbox": [ + 46, + 379, + 287, + 423 + ], + "spans": [ + { + "bbox": [ + 46, + 379, + 287, + 423 + ], + "type": "text", + "content": "Table 2. Comparison of error rate (\\%) on ImageNet-C with severity level 5. Standard deviation for ten diverse corruption sequences is denoted by the parentheses values. The total memory refers to the sum of model parameters and activations." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 50, + 432, + 284, + 511 + ], + "lines": [ + { + "bbox": [ + 50, + 432, + 284, + 511 + ], + "spans": [ + { + "bbox": [ + 50, + 432, + 284, + 511 + ], + "type": "table", + "html": "
Avg. err (%) \nMethodMem. (MB)CIFAR10-CCIFAR100-C
single do.continualsingle do.continual
BN Stats Adapt [40]9116.616.644.544.5
TinyTL† [4]37915.821.940.577.4
RepNet† [57]50815.220.941.552.1
AuxAdapt† [61]20716.016.744.045.8
Ours (K=4)29614.414.439.539.2
", + "image_path": "cf2eb6ef6b69896dc615da14f071498b7669952bd10dae67ff5e2bd5ea0904ec.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "table_body" + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 514, + 287, + 548 + ], + "lines": [ + { + "bbox": [ + 46, + 514, + 287, + 548 + ], + "spans": [ + { + "bbox": [ + 46, + 514, + 287, + 548 + ], + "type": "text", + "content": "Table 3. Comparison with methods for on-device learning. The backbone is ResNet-50. " + }, + { + "bbox": [ + 46, + 514, + 287, + 548 + ], + "type": "inline_equation", + "content": "\\dagger" + }, + { + "bbox": [ + 46, + 514, + 287, + 548 + ], + "type": "text", + "content": " denotes our own re-implemented models. single do. indicates the single domain TTA setup." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 556, + 287, + 593 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 556, + 287, + 593 + ], + "spans": [ + { + "bbox": [ + 46, + 556, + 287, + 593 + ], + "type": "text", + "content": "tra memory usage. Moreover, it only needs a negligible amount of computational overhead because it is performed in parallel with the entropy minimization loss " + }, + { + "bbox": [ + 46, + 556, + 287, + 593 + ], + "type": "inline_equation", + "content": "\\mathcal{L}^{ent}" + }, + { + "bbox": [ + 46, + 556, + 287, + 593 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 605, + 200, + 620 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 605, + 200, + 620 + ], + "spans": [ + { + "bbox": [ + 47, + 605, + 200, + 620 + ], + "type": "text", + "content": "4. Classification Experiments" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 627, + 287, + 663 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 627, + 287, + 663 + ], + "spans": [ + { + "bbox": [ + 46, + 627, + 287, + 663 + ], + "type": "text", + "content": "We evaluate our approach to image classification tasks based on the continual test-time adaptation setup with three datasets: CIFAR10-C, CIFAR100-C, and ImageNet-C." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "text", + "content": "Experimental setup. Following CoTTA [54], we conduct most experiments on the continual TTA task, where we continually adapt the deployed model to each corruption type sequentially without resetting the model. This task is" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 281, + 545, + 354 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 281, + 545, + 354 + ], + "spans": [ + { + "bbox": [ + 304, + 281, + 545, + 354 + ], + "type": "text", + "content": "more challenging but more realistic than single domain TTA task [53] in which the adapted model is periodically reset to the original pre-trained model after finishing adaptation to each target, so they require additional domain information. Moreover, we evaluate our approach on the long-term TTA setup, which is detailed in Section 4.2." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 356, + 546, + 453 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 356, + 546, + 453 + ], + "spans": [ + { + "bbox": [ + 304, + 356, + 546, + 453 + ], + "type": "text", + "content": "Following the previous TTA studies [53, 54], we evaluate models with {CIFAR10, CIFAR10-C}, {CIFAR100, CIFAR100-C}, and {ImageNet, ImageNet-C} where the first and the second dataset in each bracket refers to the source and the target domain, respectively. The target domains include 15 types of corruptions (e.g. noise, blur, weather, and digital) with 5 levels of severity, which are widely used in conventional benchmarks [22]." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 457, + 546, + 685 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 457, + 546, + 685 + ], + "spans": [ + { + "bbox": [ + 304, + 457, + 546, + 685 + ], + "type": "text", + "content": "Implementation Details. We evaluate our approach within the frameworks officially provided by previous state-of-the-art methods [54, 41]. For fair comparisons, we use the same pre-trained model, which are WideResNet-28 and WideResNet-40 [59] models from the RobustBench [11], and ResNet-50 [21] model from TTT++ [35, 9]. Before the deployment, we pre-train the meta networks on the source dataset using a cross-entropy loss with SGD optimizer with the learning rate of 5e-2. Since the meta networks contain only a few layers, we pre-train them with a small number of epochs: 10 and 3 epochs for CIFAR and ImageNet, respectively. After deployment, similar to EATA [41], we use the same SGD optimizer with the learning rate of 5e-3. In Eq. (2), the entropy threshold " + }, + { + "bbox": [ + 304, + 457, + 546, + 685 + ], + "type": "inline_equation", + "content": "H_0" + }, + { + "bbox": [ + 304, + 457, + 546, + 685 + ], + "type": "text", + "content": " is set to " + }, + { + "bbox": [ + 304, + 457, + 546, + 685 + ], + "type": "inline_equation", + "content": "0.4 \\times \\ln C" + }, + { + "bbox": [ + 304, + 457, + 546, + 685 + ], + "type": "text", + "content": " where " + }, + { + "bbox": [ + 304, + 457, + 546, + 685 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 304, + 457, + 546, + 685 + ], + "type": "text", + "content": " denotes the number of task classes. The batch size is 64 and 32 for CIFAR and ImageNet, respectively. We set the importance of the regularization " + }, + { + "bbox": [ + 304, + 457, + 546, + 685 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 304, + 457, + 546, + 685 + ], + "type": "text", + "content": " in Eq. (3) to 0.5 to balance it with the entropy minimization loss. Additional implementation details can be found in Appendix C." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 689, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 689, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 305, + 689, + 545, + 714 + ], + "type": "text", + "content": "Evaluation Metric. For all the experiments, we report error rates calculated during testing and the memory consump" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "11924" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 63, + 71, + 244, + 194 + ], + "blocks": [ + { + "bbox": [ + 63, + 71, + 244, + 194 + ], + "lines": [ + { + "bbox": [ + 63, + 71, + 244, + 194 + ], + "spans": [ + { + "bbox": [ + 63, + 71, + 244, + 194 + ], + "type": "image", + "image_path": "108e5cc8efab6f0d685ee38581c3595d9729997d22f52770326c9dc7502caeba.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 250, + 79, + 416, + 194 + ], + "blocks": [ + { + "bbox": [ + 250, + 79, + 416, + 194 + ], + "lines": [ + { + "bbox": [ + 250, + 79, + 416, + 194 + ], + "spans": [ + { + "bbox": [ + 250, + 79, + 416, + 194 + ], + "type": "table", + "html": "
Avr. errArchCIFAR10-C WRN-28CIFAR10-C WRN-40CIFAR100-C WRN-40
(i)18.112.637.2
(ii) Ours w\\o BN18.713.738.2
(iii) Ours w\\o Conv20.714.940.1
(iv) Conv60.673.377.2
(v) CBAM [55]21.415.140.9
(vi) SE [24]22.316.240.5
Ours16.812.136.3
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Model#BlockAvg. err
WRN-28 (12) CIFAR10-C3,3,3,317.3
4,4,2,217.9
2,2,4,416.9
WRN-40 (18) CIFAR10-C4,4,5,512.8
6,6,3,313.7
3,3,6,612.2
WRN-40 (18) CIFAR100-C4,4,5,536.9
6,6,3,338.5
3,3,6,636.4
", + "image_path": "2a5ee4fc38b6dd56ffdf53eddf32f58ac014fb0220f2bc0d26194d8c4616179a.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 198, + 547, + 232 + ], + "lines": [ + { + "bbox": [ + 46, + 198, + 547, + 232 + ], + "spans": [ + { + "bbox": [ + 46, + 198, + 547, + 232 + ], + "type": "text", + "content": "Table 4. Architecture ablation experiments. (a,b) We compare continual TTA performance on several memory-efficient designs. WRN refers to WideResNet [59] backbone. (c) We report the performance based on different designs of partitioning the model. The value next to the backbone's name denotes the total number of residual blocks of a model." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 236, + 288, + 274 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 236, + 288, + 274 + ], + "spans": [ + { + "bbox": [ + 46, + 236, + 288, + 274 + ], + "type": "text", + "content": "tion, including the model parameter and the activation storage. We demonstrate the memory efficiency of our work by using the official code provided by TinyTL [4]." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 282, + 132, + 295 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 282, + 132, + 295 + ], + "spans": [ + { + "bbox": [ + 47, + 282, + 132, + 295 + ], + "type": "text", + "content": "4.1. Comparisons" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 304, + 287, + 471 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 304, + 287, + 471 + ], + "spans": [ + { + "bbox": [ + 46, + 304, + 287, + 471 + ], + "type": "text", + "content": "Comparisons with TTA methods. We compare our approach to competing TTA methods on extensive benchmarks and various pre-trained models. The results of CIFAR10/100-C are detailed in Table 1. The model partition factor K are set to 4 and 5. Our approach outperforms existing TTA methods with the lowest memory usage in all pre-trained models. Specifically, in WideResNet-40, our method achieves superior performance while requiring " + }, + { + "bbox": [ + 46, + 304, + 287, + 471 + ], + "type": "inline_equation", + "content": "80\\%" + }, + { + "bbox": [ + 46, + 304, + 287, + 471 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 304, + 287, + 471 + ], + "type": "inline_equation", + "content": "58\\%" + }, + { + "bbox": [ + 46, + 304, + 287, + 471 + ], + "type": "text", + "content": " less memory than CoTTA [54] and EATA [41], respectively, which are also designed for continual TTA. Approaches targeting single domain TTA [53, 35, 9] show poor performance due to error accumulation and catastrophic forgetting, as observed in CoTTA. The error rates for each corruption type are provided in Appendix F." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 472, + 287, + 579 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 472, + 287, + 579 + ], + "spans": [ + { + "bbox": [ + 46, + 472, + 287, + 579 + ], + "type": "text", + "content": "Table 2 shows the experiment for ImageNet-C. Two ResNet-50 backbones from RobustBench [11] are leveraged. Following CoTTA, evaluations are conducted on ten diverse corruption-type sequences. We achieve comparable performance to CoTTA while utilizing " + }, + { + "bbox": [ + 46, + 472, + 287, + 579 + ], + "type": "inline_equation", + "content": "86\\%" + }, + { + "bbox": [ + 46, + 472, + 287, + 579 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 472, + 287, + 579 + ], + "type": "inline_equation", + "content": "75\\%" + }, + { + "bbox": [ + 46, + 472, + 287, + 579 + ], + "type": "text", + "content": " less memory with " + }, + { + "bbox": [ + 46, + 472, + 287, + 579 + ], + "type": "inline_equation", + "content": "\\mathrm{K} = 4" + }, + { + "bbox": [ + 46, + 472, + 287, + 579 + ], + "type": "text", + "content": " and 5, respectively. In addition, we observe that our approach shows superior performance when adopting the model pre-trained with strong data augmentation methods (e.g., Augmix [23])." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "content": "Comparisons with on-device learning methods. We compare our approach with methods for memory-efficient on-device learning. TinyTL [4] and RepNet [57] focus on supervised on-device learning (i.e., requiring labeled target data). However, since TTA assumes that we do not have access to the target labels, utilizing such methods to TTA directly is infeasible. Therefore, we experimented by replacing supervised loss (i.e., cross-entropy) with unsupervised loss (i.e., entropy minimization) in TinyTL and RepNet. As shown in Table 3, they suffer from performance degradation in continual TTA, showing inferior performance compared" + } + ] + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 307, + 237, + 547, + 328 + ], + "blocks": [ + { + "bbox": [ + 307, + 237, + 547, + 328 + ], + "lines": [ + { + "bbox": [ + 307, + 237, + 547, + 328 + ], + "spans": [ + { + "bbox": [ + 307, + 237, + 547, + 328 + ], + "type": "image", + "image_path": "83e81d67edc2a25632cf40d7d634c94dc13cd356f02709442d7b73705f56250a.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 329, + 547, + 396 + ], + "lines": [ + { + "bbox": [ + 304, + 329, + 547, + 396 + ], + "spans": [ + { + "bbox": [ + 304, + 329, + 547, + 396 + ], + "type": "text", + "content": "Figure 4. Ablation study of K. We uniformly divide the encoder of the pre-trained model into the model partition factor K. The x-axis indicates the memory size including both model parameter size and activation size while the y-axis indicates the average error rate. The values in parentheses show the rate of increase for the model parameters compared to the original model." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 403, + 538, + 416 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 403, + 538, + 416 + ], + "spans": [ + { + "bbox": [ + 305, + 403, + 538, + 416 + ], + "type": "text", + "content": "to our proposed approach even in the single domain TTA." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 417, + 545, + 549 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 417, + 545, + 549 + ], + "spans": [ + { + "bbox": [ + 304, + 417, + 545, + 549 + ], + "type": "text", + "content": "Similar to ours, AuxAdapt [61] adds and updates a small network (i.e., ResNet-18) while freezing the pre-trained model. Unlike our approach, they only modify a prediction output, not intermediate features. While AuxAdapt requires the least memory usage, it fails to improve TTA performance in single domain TTA. Nevertheless, since the original model is frozen, it suffers less from catastrophic forgetting and error accumulation than TinyTL [4] and RepNet [57] in the continual TTA. Through the results, we confirm that our proposed method brings both memory efficiency and a significant performance improvement in both TTA setups." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 559, + 405, + 572 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 559, + 405, + 572 + ], + "spans": [ + { + "bbox": [ + 306, + 559, + 405, + 572 + ], + "type": "text", + "content": "4.2. Empirical Study" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 580, + 545, + 675 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 580, + 545, + 675 + ], + "spans": [ + { + "bbox": [ + 304, + 580, + 545, + 675 + ], + "type": "text", + "content": "Architecture design. An important design of our meta networks is injecting a single BN layer before the original networks and utilizing a residual connection with one conv block. Table 4b studies the effectiveness of the proposed design by comparing it with six different variants. From the results, we observe that using only either conv block (ii) or BN (iii) aggravates the performance: error rate increases by " + }, + { + "bbox": [ + 304, + 580, + 545, + 675 + ], + "type": "inline_equation", + "content": "1.4\\%" + }, + { + "bbox": [ + 304, + 580, + 545, + 675 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 580, + 545, + 675 + ], + "type": "inline_equation", + "content": "3.8\\%" + }, + { + "bbox": [ + 304, + 580, + 545, + 675 + ], + "type": "text", + "content": " on CIFAR-100-C with WideResNet-40." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "text", + "content": "In design (i), we enforce both BN parameters and Conv layers in the meta networks to take the output of the original networks as inputs. Such a design brings performance" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "11925" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 52, + 72, + 299, + 207 + ], + "blocks": [ + { + "bbox": [ + 52, + 72, + 299, + 207 + ], + "lines": [ + { + "bbox": [ + 52, + 72, + 299, + 207 + ], + "spans": [ + { + "bbox": [ + 52, + 72, + 299, + 207 + ], + "type": "image", + "image_path": "fe046384f813c599986604b0b12e513e8a90bf17056e94e892127b798d978701.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 119, + 211, + 231, + 220 + ], + "lines": [ + { + "bbox": [ + 119, + 211, + 231, + 220 + ], + "spans": [ + { + "bbox": [ + 119, + 211, + 231, + 220 + ], + "type": "text", + "content": "(a) Catastrophic forgetting effect" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 310, + 72, + 543, + 205 + ], + "blocks": [ + { + "bbox": [ + 310, + 72, + 543, + 205 + ], + "lines": [ + { + "bbox": [ + 310, + 72, + 543, + 205 + ], + "spans": [ + { + "bbox": [ + 310, + 72, + 543, + 205 + ], + "type": "image", + "image_path": "7371792345457b4221cf7c8650380a80927486101bf247b8bcef57df6d3e3116.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 375, + 211, + 476, + 220 + ], + "lines": [ + { + "bbox": [ + 375, + 211, + 476, + 220 + ], + "spans": [ + { + "bbox": [ + 375, + 211, + 476, + 220 + ], + "type": "text", + "content": "(b) Error accumulation effect" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 46, + 225, + 545, + 280 + ], + "lines": [ + { + "bbox": [ + 46, + 225, + 545, + 280 + ], + "spans": [ + { + "bbox": [ + 46, + 225, + 545, + 280 + ], + "type": "text", + "content": "Figure 5. Regularization ablation experiments. We conduct experiments with WideResNet-40 on CIFAR100-C. (a) We utilize a test set of the CIFAR-100 dataset to measure clean error after adapting to each corruption. Maintaining clean errors at a stable level indicates that our approach helps the model robust to catastrophic forgetting. (b) We simulate a long-term adaptation scenario by repeating 100 rounds of 15 corruption sequences. In the absence of regularization, error accumulation can lead to overfitting (i.e., the case of the error increases exponentially). However, our approach does not suffer from such an error accumulation. We set K to 5 in the above experiments." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "type": "table", + "bbox": [ + 50, + 285, + 284, + 372 + ], + "blocks": [ + { + "bbox": [ + 50, + 285, + 284, + 372 + ], + "lines": [ + { + "bbox": [ + 50, + 285, + 284, + 372 + ], + "spans": [ + { + "bbox": [ + 50, + 285, + 284, + 372 + ], + "type": "table", + "html": "
Batch size168421
Non trainingSource69.769.769.769.769.7
BN Stats Adapt [40]41.150.259.981.099.1
AdaptBN [46]39.141.245.249.054.0
TrainingCon. TENT [53]40.947.858.682.299.0
Con. TENT+AdaptBN38.240.243.247.752.2
Ours (K=5)40.045.863.480.899.0
Ours (K=5)+AdaptBN36.939.342.246.551.8
", + "image_path": "8f24365dbbfac4a05ddfb4987005d8e6d33fe5ca7f980efa384d2bfce76755ce.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "table_body" + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 377, + 287, + 410 + ], + "lines": [ + { + "bbox": [ + 46, + 377, + 287, + 410 + ], + "spans": [ + { + "bbox": [ + 46, + 377, + 287, + 410 + ], + "type": "text", + "content": "Table 5. Experiments with small batch sizes. We evaluate all baselines with WideResNet-40 on CIFAR100-C. Con. TENT is the abbreviation for continual TENT." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 413, + 287, + 568 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 413, + 287, + 568 + ], + "spans": [ + { + "bbox": [ + 46, + 413, + 287, + 568 + ], + "type": "text", + "content": "drop. We speculate that it is because the original network, which is not adapted to the target domain, lacks the ability to extract sufficiently meaningful features from the target image. Also, we observed a significant performance degradation after removing the residual connection in design (iv). In addition, since attention mechanisms [55, 24] generally have improved classification accuracy, we study how attention mechanisms can further boost TTA performance of our approach in design (v, vi). The results show that it is difficult for the attention module to train ideally in TTA setup using unsupervised learning, unlike when applying it to supervised learning. An ablation study on each element of meta networks can be found in Appendix D." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "text", + "content": "Number of blocks in each partition. ResNet [21] consists of multiple residual blocks (e.g., BasicBlock and Bottleneck in Pytorch [45]). For instance, WideResNet-28 has 12 residual blocks. By varying the number of blocks for each part of the original networks, we analyze TTA performance in Table 4c. We observe that splitting the shallow parts of the encoder densely (e.g., 2,2,4,4 blocks, from the shallow to the deep parts sequentially) brings more performance gain than splitting the deep layers densely (e.g., 4,4,2,2 blocks). We suggest that it is because we modify the lower-level feature more as we split shallow layers densely. Our observation is aligned with the finding of previous TTA works [9, 39]," + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 284, + 544, + 308 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 284, + 544, + 308 + ], + "spans": [ + { + "bbox": [ + 305, + 284, + 544, + 308 + ], + "type": "text", + "content": "which show that updating the shallow layers more than the deep layers improves TTA performance." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 312, + 545, + 443 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 312, + 545, + 443 + ], + "spans": [ + { + "bbox": [ + 304, + 312, + 545, + 443 + ], + "type": "text", + "content": "Number of model partition K. Fig. 4 shows both memory requirement and adaptation performance according to the model partition factor K. With a small K (e.g., 1 or 2), the intermediate outputs are barely modified, making it difficult to achieve a reasonable level of performance. We achieve the best TTA performance with K of 4 or 5 as adjusting a greater numver of intermediate features. In the meanwhile, we observe that the average error rate is saturated and remains consistent when K is set to large values (e.g. 6,7 or 8) even with the increased amount of activations and learnable parameters. Therefore, we set K to 4 and 5." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 447, + 545, + 602 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 447, + 545, + 602 + ], + "spans": [ + { + "bbox": [ + 304, + 447, + 545, + 602 + ], + "type": "text", + "content": "Catastrophic forgetting. We conduct experiments to confirm the catastrophic forgetting effect (Fig. 5a). Once finishing adaptation to each corruption, we evaluate the model on clean target data (i.e., test-set of CIFAR dataset) without updating the model. For TENT with no regularization, the error rates for the clean target data (i.e., clean error " + }, + { + "bbox": [ + 304, + 447, + 545, + 602 + ], + "type": "inline_equation", + "content": "(\\%)" + }, + { + "bbox": [ + 304, + 447, + 545, + 602 + ], + "type": "text", + "content": ") increase gradually, which can be seen as the phenomenon of catastrophic forgetting. In contrast, our approach consistently maintains the error rates for the clean target data, proving that our regularization loss effectively prevents catastrophic forgetting. These results indicate that our method can be reliably utilized in various domains, including the source and target domains." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": "Error accumulation in long-term adaptation. To evaluate the error accumulation effect, we repeat all the corruption sequences for 100 rounds. The results are described in Fig. 5b. For TENT, a gradual increase in error rates is observed in later rounds, even with small learning rates. For example, TENT [53] with the learning rate of 1e-5 achieves the error rate of " + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "inline_equation", + "content": "39.7\\%" + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": ", and reached its lowest error rate of " + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "inline_equation", + "content": "36.5\\%" + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": " after 8 rounds. However, it shows increased error rate of " + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "inline_equation", + "content": "38.6\\%" + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": " after 100 rounds due to overfitting. It suggests" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "type": "text", + "content": "11926" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 50, + 71, + 542, + 148 + ], + "blocks": [ + { + "bbox": [ + 50, + 71, + 542, + 148 + ], + "lines": [ + { + "bbox": [ + 50, + 71, + 542, + 148 + ], + "spans": [ + { + "bbox": [ + 50, + 71, + 542, + 148 + ], + "type": "table", + "html": "
Timet
Round14710All
MethodMem. (MB)Brig.FogFros.SnowBrig.FogFros.SnowBrig.FogFros.SnowBrig.FogFros.SnowMean
Source28060.454.330.04.160.454.330.04.160.454.330.04.160.454.330.04.137.2
BN Stats Adapt [40]28069.161.044.839.169.161.044.839.169.161.044.839.169.161.044.839.153.6
Continual TENT [53]272170.162.146.140.262.253.744.437.950.041.531.626.639.232.625.322.442.9
Ours (K=4)918 (66‰)70.262.446.341.970.062.846.542.270.062.846.542.170.162.846.642.255.3
", + "image_path": "e70ad4c28636c80e8a9aa745fe2753a4f884d79288abc8088cb57186567f61a3.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 193, + 288, + 266 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 193, + 288, + 266 + ], + "spans": [ + { + "bbox": [ + 46, + 193, + 288, + 266 + ], + "type": "text", + "content": "that without regularization, TTA methods eventually face overfitting in long-term adaptation [63, 2, 29]. Our method in the absence of regularization " + }, + { + "bbox": [ + 46, + 193, + 288, + 266 + ], + "type": "inline_equation", + "content": "(\\lambda = 0)" + }, + { + "bbox": [ + 46, + 193, + 288, + 266 + ], + "type": "text", + "content": " also causes overfitting. On the other hand, when self-distilled regularization is involved " + }, + { + "bbox": [ + 46, + 193, + 288, + 266 + ], + "type": "inline_equation", + "content": "(\\lambda > 0)" + }, + { + "bbox": [ + 46, + 193, + 288, + 266 + ], + "type": "text", + "content": ", the performance remains consistent even in the long-term adaptation." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 267, + 287, + 422 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 267, + 287, + 422 + ], + "spans": [ + { + "bbox": [ + 46, + 267, + 287, + 422 + ], + "type": "text", + "content": "Small batch size. We examine the scalability of our approach with a TTA method designed for small batches size, named adapting BN statistics (i.e., AdaptBN [46, 60]). When the number of batches is too small, the estimated statistics can be unreliable [46]. Thus, they calibrate the source and target statistics for the normalization of BN layers so as to alleviate the domain shift and preserve the discriminative structures. As shown in Table 5, training models with small batch sizes (e.g., 2 or 1) generally increase the error rates. However, such an issue can be addressed by applying AdaptBN to our method. To be more sepcific, we achieve an absolute improvement of " + }, + { + "bbox": [ + 46, + 267, + 287, + 422 + ], + "type": "inline_equation", + "content": "17.9\\%" + }, + { + "bbox": [ + 46, + 267, + 287, + 422 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 267, + 287, + 422 + ], + "type": "inline_equation", + "content": "2.2\\%" + }, + { + "bbox": [ + 46, + 267, + 287, + 422 + ], + "type": "text", + "content": " from Source and AdaptBN, respectively, in the batch size of 1." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 425, + 288, + 593 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 425, + 288, + 593 + ], + "spans": [ + { + "bbox": [ + 46, + 425, + 288, + 593 + ], + "type": "text", + "content": "Number of the source samples for meta networks. Like previous TTA works [9, 35, 28, 33] including EATA [41], our approach requires access to the source data for pretraining our proposed meta networks before model deployment. In order to cope with the situation where we can only make use of a subset of the source dataset, we study the TTA performance of our method according to the number of accessible source samples. The results are specified in Table 7 where we use WideResNet-40. We observe that our method outperforms the baseline model even with small number of training samples (e.g., " + }, + { + "bbox": [ + 46, + 425, + 288, + 593 + ], + "type": "inline_equation", + "content": "10\\%" + }, + { + "bbox": [ + 46, + 425, + 288, + 593 + ], + "type": "text", + "content": " or " + }, + { + "bbox": [ + 46, + 425, + 288, + 593 + ], + "type": "inline_equation", + "content": "20\\%" + }, + { + "bbox": [ + 46, + 425, + 288, + 593 + ], + "type": "text", + "content": ") while showing comparable performance with excessively small numbers (e.g. " + }, + { + "bbox": [ + 46, + 425, + 288, + 593 + ], + "type": "inline_equation", + "content": "5\\%" + }, + { + "bbox": [ + 46, + 425, + 288, + 593 + ], + "type": "text", + "content": "). Note that we still reduce the memory usage of about " + }, + { + "bbox": [ + 46, + 425, + 288, + 593 + ], + "type": "inline_equation", + "content": "51\\%" + }, + { + "bbox": [ + 46, + 425, + 288, + 593 + ], + "type": "text", + "content": " compared to EATA." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 601, + 201, + 615 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 601, + 201, + 615 + ], + "spans": [ + { + "bbox": [ + 47, + 601, + 201, + 615 + ], + "type": "text", + "content": "5. Segmentation Experiments" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 618, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 618, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 618, + 288, + 715 + ], + "type": "text", + "content": "We investigate our approach in semantic segmentation. First, we create Cityscapes-C by applying the weather corruptions (brightness, fog, frost, and snow [22]) to the validation set of Cityscapes [10]. Then, to simulate continual distribution shifts, we repeat the four types of Cityscapes-C ten times. In this scenario, we conduct continual TTA using the publicly-available ResNet-50-based DeepLabV3+ [7], which is pre-trained on Cityscapes for domain generaliza" + } + ] + } + ], + "index": 6 + }, + { + "type": "table", + "bbox": [ + 309, + 191, + 543, + 236 + ], + "blocks": [ + { + "bbox": [ + 46, + 151, + 547, + 185 + ], + "lines": [ + { + "bbox": [ + 46, + 151, + 547, + 185 + ], + "spans": [ + { + "bbox": [ + 46, + 151, + 547, + 185 + ], + "type": "text", + "content": "Table 6. Semantic segmentation results in continual test-time adaptation tasks. We conduct experiments on Cityscapes [10] with four weather corruptions [22] applied. The four conditions are repeated ten times to simulate continual domain shifts. All results are evaluated based on DeepLabV3Plus-ResNet-50. Among above methods, only single domain TENT requires domain labels." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 309, + 191, + 543, + 236 + ], + "lines": [ + { + "bbox": [ + 309, + 191, + 543, + 236 + ], + "spans": [ + { + "bbox": [ + 309, + 191, + 543, + 236 + ], + "type": "table", + "html": "
Target domainEATA [41] (188MB)Ours (K=5) (92MB)# of source samples
10k (20%)5k (10%)2.5k (5%)
CIFAR10-C13.012.112.412.913.1
CIFAR100-C37.136.336.436.637.2
", + "image_path": "592eafbed8630e47ce20586a4485c2cb832b811fcbe839f40b6d81df8daba6de.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "table_body" + } + ], + "index": 7 + }, + { + "bbox": [ + 305, + 239, + 545, + 284 + ], + "lines": [ + { + "bbox": [ + 305, + 239, + 545, + 284 + ], + "spans": [ + { + "bbox": [ + 305, + 239, + 545, + 284 + ], + "type": "text", + "content": "Table 7. Ablation of # of source samples to warm up the meta networks. Before deployment, we pre-trained the meta networks using only a subset of the source dataset (e.g., " + }, + { + "bbox": [ + 305, + 239, + 545, + 284 + ], + "type": "inline_equation", + "content": "20\\%" + }, + { + "bbox": [ + 305, + 239, + 545, + 284 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 305, + 239, + 545, + 284 + ], + "type": "inline_equation", + "content": "10\\%" + }, + { + "bbox": [ + 305, + 239, + 545, + 284 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 305, + 239, + 545, + 284 + ], + "type": "inline_equation", + "content": "5\\%" + }, + { + "bbox": [ + 305, + 239, + 545, + 284 + ], + "type": "text", + "content": "). The memory usage (MB) of each method is also presented." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 305, + 288, + 545, + 312 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 288, + 545, + 312 + ], + "spans": [ + { + "bbox": [ + 305, + 288, + 545, + 312 + ], + "type": "text", + "content": "tion task [8] in semantic segmentation. For TTA, we use the batch size of 2. More details are specified in Appendix C." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 314, + 546, + 422 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 314, + 546, + 422 + ], + "spans": [ + { + "bbox": [ + 305, + 314, + 546, + 422 + ], + "type": "text", + "content": "Results. We report the results based on mean intersection over union (mIoU) in Table 6. It demonstrates that our approach helps to both minimize memory consumption and performs long-term adaptation stably for semantic segmentation. Unlike continual TENT, our method avoids catastrophic forgetting and error accumulation, allowing us to achieve the highest mIoU score while using " + }, + { + "bbox": [ + 305, + 314, + 546, + 422 + ], + "type": "inline_equation", + "content": "66\\%" + }, + { + "bbox": [ + 305, + 314, + 546, + 422 + ], + "type": "text", + "content": " less memory usage in a continual TTA setup. Additional experiment results can be found in Appendix B." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 429, + 378, + 441 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 429, + 378, + 441 + ], + "spans": [ + { + "bbox": [ + 306, + 429, + 378, + 441 + ], + "type": "text", + "content": "6. Conclusion" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 445, + 545, + 661 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 445, + 545, + 661 + ], + "spans": [ + { + "bbox": [ + 304, + 445, + 545, + 661 + ], + "type": "text", + "content": "This paper proposed a simple yet effective approach that improves continual TTA performance and saves a significant amount of memory, which can be applied to edge devices with limited memory. First, we presented a memory-efficient architecture that consists of original networks and meta networks. This architecture requires much less memory size than the previous TTA methods by decreasing the intermediate activations used for gradient calculations. Second, in order to preserve the source knowledge and prevent error accumulation during long-term adaptation with noisy unsupervised loss, we proposed self-distilled regularization that controls the output of meta networks not to deviate significantly from the output of the original networks. With extensive experiments on diverse datasets and backbone networks, we verified the memory efficiency and TTA performance of our approach. In this regard, we hope that our efforts will facilitate a variety of studies that make test-time adaptation for edge devices feasible in practice." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 665, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 665, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 665, + 546, + 713 + ], + "type": "text", + "content": "Acknowledgments. We would like to thank Kyuwoong Hwang, Simyung Chang, and Byeonggeun Kim for their valuable feedback. We are also grateful for the helpful discussions from Qualcomm AI Research teams." + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "11927" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 107, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 107, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 107, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 288, + 714 + ], + "type": "list", + "angle": 0, + "index": 15, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 135 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 135 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 135 + ], + "type": "text", + "content": "[1] Kazuki Adachi, Shin'ya Yamaguchi, and Atsutoshi Kumagai. 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In ICLR, 2021. 3" + } + ] + } + ], + "index": 32 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 749, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 749, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 749, + 318, + 757 + ], + "type": "text", + "content": "11929" + } + ] + } + ], + "index": 34 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 9 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Edge-Aware Regional Message Passing Controller for Image Forgery Localization/c5c52750-0529-4615-bd1f-1262f32b5c87_content_list.json b/2023/Edge-Aware Regional Message Passing Controller for Image Forgery Localization/c5c52750-0529-4615-bd1f-1262f32b5c87_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..5478affb942a842a866c2e55e39bcd3f389ed743 --- /dev/null +++ b/2023/Edge-Aware Regional Message Passing Controller for Image Forgery Localization/c5c52750-0529-4615-bd1f-1262f32b5c87_content_list.json @@ -0,0 +1,1691 @@ +[ + { + "type": "text", + "text": "Edge-aware Regional Message Passing Controller for Image Forgery Localization", + "text_level": 1, + "bbox": [ + 217, + 130, + 754, + 176 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Dong Li*, Jiaying Zhu*, Menglu Wang, Jiawei Liu†, Xueyang Fu, Zheng-Jun Zha University of Science and Technology of China, China", + "bbox": [ + 158, + 203, + 808, + 239 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "{dongli6, zhujy53, vault}@mail.ustc.edu.cn, {jwliu6, xyfu, zhazj}@ustc.edu.cn", + "bbox": [ + 143, + 241, + 820, + 258 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 291, + 313, + 306 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Digital image authenticity has promoted research on image forgery localization. Although deep learning-based methods achieve remarkable progress, most of them usually suffer from severe feature coupling between the forged and authentic regions. In this work, we propose a two-step Edge-aware Regional Message Passing Controlling strategy to address the above issue. Specifically, the first step is to account for fully exploiting the edge information. It consists of two core designs: context-enhanced graph construction and threshold-adaptive differentiable binarization edge algorithm. The former assembles the global semantic information to distinguish the features between the forged and authentic regions, while the latter stands on the output of the former to provide the learnable edges. In the second step, guided by the learnable edges, a region message passing controller is devised to weaken the message passing between the forged and authentic regions. In this way, our ERMPC is capable of explicitly modeling the inconsistency between the forged and authentic regions and enabling it to perform well on refined forged images. Extensive experiments on several challenging benchmarks show that our method is superior to state-of-the-art image forgery localization methods qualitatively and quantitatively.", + "bbox": [ + 75, + 323, + 473, + 672 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 700, + 209, + 715 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "The forged or manipulated images pose risks in various fields, such as removing copyright watermarks, generating fake news, and even falsifying evidence in court [32]. The growing technology of forgery will cause a crisis of trust and affect social equity. Therefore, the detection of image forgery is of great significance. The crucial aspect", + "bbox": [ + 75, + 724, + 468, + 818 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/8dc717825240b1d44aa64844e4d505e43c87fee348999bfc6dec9c4460596352.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 501, + 290, + 890, + 393 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/ab176ff3e62eaaa89f24af6f2c8e641eee1a9100591dbdaa492bf1b92ff9845c.jpg", + "image_caption": [ + "Figure 1. The difference between previous methods and ours. Our method controls the message passing between the forged and authentic regions, ignored by the previous method. As shown by $X$ ." + ], + "image_footnote": [], + "bbox": [ + 501, + 396, + 890, + 500 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "of the detection is to model the inconsistency between the forged and authentic regions and to locate the forged regions on the suspicious image, i.e., image forgery localization (IFL). However, as post-processing techniques such as GAN [16, 26, 63], VAE [27, 44] and homogeneous manipulation [7, 33] are wildly utilized, images can be easily tampered in a visually imperceptible way. These techniques constantly aim to couple the forged and authentic regions' features, making image forgery localization challenging. Therefore, in order to accurately locate the image forgery region, it is particularly essential to decouple the features between forged and authentic regions.", + "bbox": [ + 496, + 566, + 890, + 748 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "In recent years, deep-learning techniques have attracted more attention [23, 57, 58, 65, 66]. Due to the development of deep learning, image forgery localization has achieved remarkable results. For example, ManTra-Net [55] treats the forgery localization problem as a local anomaly detection problem and proposes a novel long short-term memory solution to assess local anomalies. To discriminate between heterologous regions, SPAN employs CNNs to extract anomalous local noise features from noise maps. MVSS-Net [5] learns a multiview feature with multi-scale", + "bbox": [ + 496, + 750, + 893, + 900 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 810, + 44 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "* Co-first authors contributed equally, † corresponding author. This work was supported by the National Key R&D Program of China under Grant 2020AAA0105702, the National Natural Science Foundation of China (NSFC) under Grants 62225207, 62276243, 62106245 and U19B2038, the University Synergy Innovation Program of Anhui Province under Grant GXXT-2019-025.", + "bbox": [ + 75, + 825, + 468, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "8222", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "supervised networks to jointly exploit the noise view and the boundary artifacts. However, these methods do not decouple the features between the forged and authentic regions, making it difficult to locate the tampered regions for elaborately forged images accurately. As shown in Figure 1, in the previous method, the features of the forged region are coupled with some of the features of the authentic region, resulting in wrong localization.", + "bbox": [ + 75, + 90, + 468, + 210 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In this work, we propose a novel method to avoid feature coupling of the two regions (forged and authentic) for image forgery localization. One of the keys of this method is to construct a dynamic graph, where the edges between the forged and authentic regions participate in its construction. We control the message passing of regions inside and outside the edges (i.e., forged and authentic) by reconstructing the adjacency matrix of nodes inside and outside the edges, thus achieving effective disentanglement of the features between the forged and authentic regions. Based on its functionality, the edge-aware dynamic graph convolution is named the regional message passing controller (RMPC).", + "bbox": [ + 75, + 212, + 468, + 393 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In order to use the proposed RMPC for image forgery localization, it is necessary to obtain the edge information between the forged and authentic regions, which is the other key of this method. Therefore, an edge reconstruction (ER) module was developed, including a context-enhanced graph (CEG) and a threshold-adaptive differentiable binarization module. We specially design an adjacency matrix learner in the CEG, which encodes global information along the nodes to assemble the global semantic information. Inspired by the Sigmoid function, we develop the threshold-adaptive differentiable binarization edge algorithm, which stands on the output of the CEG to provide the learnable edges.", + "bbox": [ + 75, + 393, + 468, + 574 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In summary, in this work we propose a new two-step framework named Edge-aware Regional Message Passing Controller (ERMPC) for Image Forgery Localization, including RMPC and ER. The ERMPC could effectively control the message passing between the forged and authentic regions to achieve effective disentanglement of the two regions, thus boosting the performance of image forgery localization. We take edge information as the main task and use it as a basis to explicitly model the inconsistency between two regions. To the best of our knowledge, this work is the first attempt to explicitly weaken the message passing between the forged and authentic regions. Our contributions are as follows:", + "bbox": [ + 75, + 575, + 468, + 770 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- We propose ERMPC, a novel two-step coarse-to-fine framework for image forgery localization, explicitly modeling the inconsistency between the forged and authentic regions with edge information.", + "- We propose an edge-aware dynamic graph, also known as RMPC, to control the message passing between two regions (forged and authentic) in the feature map." + ], + "bbox": [ + 96, + 784, + 467, + 900 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- We develop an edge reconstruction module containing a context-enhanced graph and a threshold-adaptive differentiable binarization module to obtain the desired edge information.", + "- We conduct extensive experiments on multiple benchmarks and demonstrate that our method is qualitatively and quantitatively superior to state-of-the-art image forgery localization methods." + ], + "bbox": [ + 517, + 90, + 888, + 226 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Works", + "text_level": 1, + "bbox": [ + 500, + 261, + 648, + 277 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.1. Image Forgery Localization", + "text_level": 1, + "bbox": [ + 500, + 287, + 750, + 303 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Most early works propose to localize a specific type of forgery, including splicing [2, 3, 9, 10, 24, 28, 37, 51, 60], copy-move [8, 14, 25, 48, 52, 54], and removal [1, 50, 56, 64]. While these methods demonstrate satisfactory performance in detecting specific types of forgery, they exhibit limitations in practical applications due to the prevalence of unknown and diverse forgery types. Consequently, recent studies have emphasized the need for an approach to tackle multiple forgery types with one model. RGBN [62] proposes a dual-stream Faster R-CNN network. The first stream is designed to extract RGB features and identify tampering artifacts, while the second stream utilizes noise features to model the noise inconsistency between tampered and authentic regions, thereby localizing image forgery with enhanced accuracy. ManTra-net [55] is an end-to-end network that performs both detection and localization, which treats the problem as anomaly detection and introduces a long short-term memory solution to assess local anomalies. SPAN [22] attempts to model the spatial correlation by constructing a pyramid of local self-attention blocks. MVSS-Net [5] has designed an edge-supervised branch that uses edge residual blocks to capture fine-grained boundary detail in a shallow to deep manner. It is worth noting that edge information is important for image forgery detection and localization, as the tampered regions are commonly surrounded by unnatural artifacts. Nevertheless, most studies only utilize edges in a supervised strategy, such as MVSS-Net [5], MFCN [41], GSR-Net [61], and CAIFL [47]. PSCCNet [35] uses a progressive spatial-channel correlation module that uses features at different scales and dense cross-connections to generate operational masks in a coarse-to-fine fashion. ObjectFormer [46] captures forgery traces by extracting high-frequency parts of the image and combining them with RGB features. In this work, we explicitly employ learnable edges as guiding information to impede the message passing between the forged and untouched regions and employ refined edge reconstruction to achieve inconsistent modeling of the two regions to localize manipulation artifacts.", + "bbox": [ + 496, + 311, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "8223", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/ba984eabd3d397b6adb4d6708b9d7a65875f0767e5428c8d4145c71a8a7c37d9.jpg", + "image_caption": [ + "Figure 2. An overview of the proposed framework ERMPC. The input is a suspicious image $(H\\times W\\times 3)$ , and the output is a predicted mask $(\\mathrm{H}\\times \\mathrm{W}\\times 1)$ , which localizes the forged regions." + ], + "image_footnote": [], + "bbox": [ + 81, + 92, + 890, + 478 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "2.2. Graph Reasoning", + "text_level": 1, + "bbox": [ + 76, + 542, + 250, + 558 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Graph-based approaches have attracted growing attention from the computer vision community these days and have shown to be an effective relational reasoning method with a robust capacity for non-local feature aggregation. Specifically, CDGCNet [21] utilizes a class-wise learning strategy and designs a class-wise graph convolution, which avoids heavy graph concatenation and facilitates feature learning. To overcome the problem that most graph-based approaches assign a fixed number of neighbors for each query item, DAGL [39] proposes a dynamic attentive graph learning model to explore the dynamic non-local property for image restoration. CTL [34] learns a context-reinforced topology to construct multi-scale graphs which have a robust representational capacity by considering both global contextual information and physical connections of the human body. On other tasks in computer vision, e.g., object detection [43], multi-label image recognition [6], and skeleton-based action recognition [36, 59], graph convolutional neural networks have also achieved impressive performance. In contrast, we propose an improved edge-guided graph attention model to obstruct the message passing between forged and untouched regions with dynamic", + "bbox": [ + 75, + 568, + 472, + 902 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "construction for forgery region localization. As graph convolution is an effective relational reasoning method that is very suitable for detecting forgery traces, this paper applies it to the task of image forgery localization for the first time. An improved edge-guided graph attention model is proposed for forgery region localization, which obstructs the message passing between forged and untouched regions with dynamic construction.", + "bbox": [ + 496, + 542, + 893, + 664 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Methodology", + "text_level": 1, + "bbox": [ + 500, + 712, + 633, + 729 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "This section details the scheme of image forgery localization based on edge-aware message passing control. Sec. 3.1 describes an overview of the framework. One of the keys of the scheme is to control the message passing with edge and thus model the inconsistency between the forged and authentic regions (Sec. 3.2). Another key lies in reconstructing accurate edges from coarse features (Sec. 3.3). In addition, following [5, 22, 55, 62], we use the noise branch and fuse it with RGB branch at the end of the network (Sec. 3.4). The optimization is introduced in Sec. 3.5.", + "bbox": [ + 496, + 750, + 893, + 902 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "8224", + "bbox": [ + 480, + 944, + 514, + 955 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Overview", + "text_level": 1, + "bbox": [ + 76, + 90, + 187, + 104 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Figure 2 is an overview of the framework. The input image is represented as $X \\in \\mathbb{R}^{H \\times W \\times 3}$ , where H and W represent the height and width of the image. First, we use two branches to handle RGB and noise separately, obtaining $G_{r} \\in \\mathbb{R}^{H_{s} \\times W_{s} \\times C_{s}}$ and $G_{n} \\in \\mathbb{R}^{H_{s} \\times W_{s} \\times C_{s}}$ respectively. Then, we use ResNet-50 pretrained on ImageNet [11] as the backbone network. Following [4], we adopt atrous spatial pyramid pooling(ASPP) together with ResNet-50 to capture the long-range contextual information. The coarse features extracted from RGB branches are converted into edges through the edge reconstruction block. Meanwhile, the coarse features are constructed as graph structures, guided by the reconstructed edge information. Finally, the RGB features after the graph convolutional network are fused with noise information through dual attention [5] to output the predicted forgery localization map.", + "bbox": [ + 75, + 112, + 472, + 356 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. Region Message Passing Controller", + "text_level": 1, + "bbox": [ + 76, + 364, + 383, + 381 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Most forged images are carefully processed to hide tampering artifacts, making it challenging to model inconsistencies in the RGB branch. To overcome this problem, the edges between the forged and authentic regions are utilized to control the message passing explicitly.", + "bbox": [ + 75, + 387, + 468, + 460 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The edge feature $G_{e} \\in \\mathbb{R}^{H_{e} \\times W_{e} \\times 1}$ comes from the edge reconstruction block (described in detail in the next subsection), where $H_{e} = H_{s}$ and $W_{e} = W_{s}$ . First, we calculate the relationship between two node features $P_{i}, P_{j}$ of the $G_{E}$ using an algorithm similar to XNOR gate:", + "bbox": [ + 75, + 462, + 468, + 537 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathrm {X N} \\left(P _ {i}, P _ {j}\\right) = \\left\\{ \\begin{array}{l l} 0 & \\text {I n s i d e a n d o u t s i d e t h e e d g e s} \\\\ 1 & \\text {O n t h e s a m e s i d e o f e d g e s .} \\end{array} \\right. \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 96, + 547, + 468, + 588 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "If two nodes are inside and outside the edge respectively, then their XN is set to 0. For each of the N ( $N = H_{e} \\times W_{e}$ ) nodes features, we calculate its XN, thus generating a matrix $A_{e} \\in \\mathbb{R}^{N \\times N}$ .", + "bbox": [ + 76, + 597, + 468, + 657 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Next, we apply graph learning to process the $G_{r} \\in \\mathbb{R}^{H_{s} \\times W_{s} \\times C_{s}}$ . Following GAT [45], we calculate the similarity between two nodes as attention coefficients:", + "bbox": [ + 76, + 657, + 468, + 703 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\alpha_ {i, j} = \\psi (x _ {i}) ^ {T} \\psi^ {\\prime} (x _ {j}), \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 191, + 710, + 468, + 731 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\psi, \\psi'$ denotes two learnable linear transformations. Specifically, we utilize $\\psi = Wx$ and $\\psi' = W'x$ , where $W \\in \\mathbb{R}^{C_s \\times C_s}$ and $W' \\in \\mathbb{R}^{C_s \\times C_s}$ are both weight matrices. To make coefficients easier to compare across different nodes, we normalize them using the softmax function:", + "bbox": [ + 76, + 739, + 468, + 816 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nA _ {r _ {i, j}} = \\frac {\\exp (\\alpha_ {i , j})}{\\sum_ {j = 1} ^ {N} \\exp (\\alpha_ {i , j})}, \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 183, + 825, + 468, + 864 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $A_r \\in \\mathbb{R}^{N \\times N}$ is the preliminary adjacency matrix. It reflects the relationship between any two nodes in the fea", + "bbox": [ + 76, + 869, + 468, + 900 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "ture map. Larger values represent a greater flow of information between two nodes. In order to realize message passing control better, a method of dynamically adjusting the adjacency matrix is adopted. Specifically, if two nodes are on and off the boundary respectively, their adjacency is broken due to the dynamic adjustment of the adjacency matrix. In practice, the adjacency matrix is recalculated as follows:", + "bbox": [ + 496, + 90, + 890, + 196 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nA _ {r} ^ {\\prime} = A _ {r} \\odot A _ {e}, \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 640, + 208, + 890, + 224 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\odot$ is the Hadamard product. $A_r' \\in \\mathbb{R}^{N \\times N}$ re-models the weights between nodes in the feature map and severs the connections between the forged and real regions.", + "bbox": [ + 496, + 233, + 890, + 279 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Once the adjacency matrix is obtained, it is weighted by the learnable attention weights. Then the original nodes are updated with the following:", + "bbox": [ + 496, + 280, + 890, + 325 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nZ _ {r} = \\operatorname {R e L U} \\left(A _ {r} ^ {\\prime} G _ {r} ^ {\\prime} W _ {z}\\right), \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 609, + 335, + 890, + 352 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $Z_{r}\\in \\mathbb{R}^{N\\times C_{s}}$ is RGB features after graph reasoning, $W_{z}\\in \\mathbb{R}^{C_{s}\\times C_{s}}$ is the learnable parameter and $G_r^\\prime \\in \\mathbb{R}^{N\\times C_s}$ is the graph representation transformed by $G_{r}$", + "bbox": [ + 496, + 362, + 890, + 407 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "It is worth noting that this work not only introduces the idea of controlling the message passing in image forgery localization for the first time, but also the approach implemented is different from previous research [12, 20]. BFP [12] uses directed acyclic graphs (DAG) for feature propagation and introduces boundary information into the propagation to control the message passing between different segments. However, it has to scan the image pixel by pixel and requires a lot of loops, causing it difficult to implement in real-world applications. BGC [20] emphasizes reducing the weights of the edges and does not really focus on the message passing between regions.", + "bbox": [ + 496, + 407, + 890, + 589 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.3. Edge Reconstruction", + "text_level": 1, + "bbox": [ + 500, + 598, + 694, + 614 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "As described in the previous section, the Edge-aware Message Passing Control Graph requires accurate edge information. Designing such an edge-access network is nontrivial. The main challenge is how to learn edge information from the coarse feature. To this end, a novel approach to edge reconstruction is proposed. Specifically, we started by using the Sobel layer [5] to enhance the edge-related patterns in $G_{r} \\in \\mathbb{R}^{H_{s} \\times W_{s} \\times C_{s}}$ ,", + "bbox": [ + 496, + 621, + 890, + 742 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nG _ {c} = G _ {r} \\odot \\sigma (\\text {N o r m} (S o b e l \\left(G _ {r}\\right)), \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 575, + 753, + 890, + 770 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where Norm is L2 Normalization, $\\sigma$ is Sigmoid and Sobel is the SobelConv [5].", + "bbox": [ + 496, + 779, + 890, + 809 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Then, we explore a Context-Enhanced Graph (CEG), extracting the local and global features separately for $G_{c} \\in \\mathbb{R}^{H_{s} \\times W_{s} \\times C_{s}}$ . Specifically, the local information is extracted by the convolutional layers [5]. For global information, the contextual information of the feature map is encoded as the adjacency matrix $A_{c} \\in \\mathbb{R}^{N \\times N}$ in a simple and", + "bbox": [ + 496, + 810, + 890, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "8225", + "bbox": [ + 480, + 944, + 514, + 955 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/8b02f169471b7653d2c5f6677654f87c42502f3fb2a9e1c10ebfeddd9162723b.jpg", + "image_caption": [ + "Figure 3. Context-Enhanced Graph. Global features are extracted by the specific graph, while local features by the ResBlock." + ], + "image_footnote": [], + "bbox": [ + 76, + 85, + 472, + 281 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "efficient way. As shown in Figure 3, $A_{c}$ is generated by a specially designed adjacency matrix learner which consists of two $1 \\times 1$ convolution layers. The process is written as", + "bbox": [ + 75, + 344, + 470, + 391 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nA _ {c} = \\operatorname {N o r m} \\left(\\operatorname {C o n v} \\left(\\operatorname {C o n v} \\left(\\mathrm {G} _ {\\mathrm {c}} ^ {\\prime}\\right)\\right)\\right), \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 155, + 401, + 468, + 419 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $G_c' \\in \\mathbb{R}^{N \\times C_s}$ is reshaped by $G_c$ . Given the node features of $G_c'$ , we first squeeze the feature dimensions by a $1 \\times 1$ convolution layer. Then, another convolution layer with $1 \\times 1$ kernel is used to transfer the N-dimension feature vector into the $N \\times N$ adjacency matrix. In addition, L2 Normalization is applied to each row of $A_c$ to facilitate stable optimization. Next, we use this adjacency matrix to complete the graph reasoning. In this way, we can obtain a global feature map. The process can be written as", + "bbox": [ + 75, + 428, + 468, + 566 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\operatorname {G l o b a l} \\left(G _ {c} ^ {\\prime}\\right) = A _ {c} G _ {c} ^ {\\prime} W _ {c}, \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 184, + 575, + 468, + 594 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $W_{c}\\in \\mathbb{R}^{C_{s}\\times C_{s}}$ is the learnable parameter. To match with the local information dimension, we reshape Global $(G_c^{\\prime})\\in \\mathbb{R}^{N\\times C_s}$ back to Global' $(G_c^\\prime)\\in$ $\\mathbb{R}^{H_s\\times W_s\\times C_s}$ . Then combining the local and global information, we can obtain the edge probability map $G_{p}\\in$ $\\mathbb{R}^{H_s\\times W_s\\times 1}$ ..", + "bbox": [ + 75, + 603, + 468, + 694 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nG _ {p} = \\sigma \\left(\\mathcal {C} \\left(\\operatorname {C a t} \\left(\\operatorname {L o c a l} \\left(G _ {c}\\right), \\operatorname {G l o b a l} ^ {\\prime} \\left(G _ {c} ^ {\\prime}\\right)\\right)\\right)\\right), \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 104, + 705, + 468, + 724 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\sigma$ denotes the Sigmoid, $\\mathcal{C}$ is a $1\\times 1$ convolution layer, and Local contains ReLU and two convolutional layers.", + "bbox": [ + 75, + 734, + 468, + 763 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Furthermore, in order to determine the edges, a threshold needs to be determined to binarize the probability map. Most previous studies have used fixed thresholds, and the process is non-differentiable. Inspired by [30], we utilize a variable threshold map which is adaptive for each point on the probability map $G_{p}$ . Besides, we propose a variant of the Sigmoid function to complete the binarization, which is capable of participating in the backpropagation involved. Binarize threshold adjustment is achieved by translating the", + "bbox": [ + 75, + 765, + 468, + 901 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Sigmoid function along the x-axis. Therefore, we explore the threshold-adaptive differentiable binarization (TDB) for edge reconstruction. It is computed as follows:", + "bbox": [ + 498, + 90, + 892, + 137 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nG _ {e} = \\frac {1}{1 + e ^ {- k \\left(G _ {p} - \\tau \\left(G _ {p}\\right)\\right)}}, \\tag {10}\n$$\n", + "text_format": "latex", + "bbox": [ + 604, + 145, + 890, + 176 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\tau$ denotes the learnable transformation, which in practice is $3\\times 3$ convolution operators, and $k$ is the amplifying factor. In particular, $k$ is set to 500 empirically.", + "bbox": [ + 498, + 185, + 892, + 231 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.4. Branch Fusion", + "text_level": 1, + "bbox": [ + 500, + 239, + 650, + 253 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Following most studies [5,22,55,62], we also employ the noise branch. However, this is not the focus of this work, so we have used some common methods. As in Figure 2, the noise is extracted with BayarConv [55]. For the fusion of the two branches, we follow [5] and adopt the Dual Attention (DA) [15]. DA includes channel attention module (CAM) and position attention module (PAM). It can effectively fuse two branches. The process can be written as", + "bbox": [ + 498, + 262, + 890, + 383 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nG _ {o} = \\mathrm {D A} \\left(G _ {z}, G _ {n}\\right), \\tag {11}\n$$\n", + "text_format": "latex", + "bbox": [ + 625, + 393, + 890, + 411 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $G_{z} \\in \\mathbb{R}^{H_{s} \\times W_{s} \\times C_{s}}$ is reshaped by the $Z_{r}$ . Finally, we transform $G_{o} \\in \\mathbb{R}^{H_{s} \\times W_{s} \\times 1}$ with bilinear upsampling into the final predicted mask $G_{out} \\in \\mathbb{R}^{H \\times W \\times 1}$ .", + "bbox": [ + 498, + 420, + 892, + 467 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.5. Optimization", + "text_level": 1, + "bbox": [ + 500, + 474, + 638, + 491 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "As shown in Figure 2, we calculate the loss function for three components: the final prediction $G_{out} \\in \\mathbb{R}^{H \\times W \\times 1}$ , the binary edge prediction $G_e \\in \\mathbb{R}^{H_e \\times W_e \\times 1}$ and the edge probability map $G_p \\in \\mathbb{R}^{H_e \\times W_e \\times 1}$ . For edge loss, the ground-truth edge $E \\in \\mathbb{R}^{H \\times W \\times 1}$ is downsampled to a smaller size $E' \\in \\mathbb{R}^{H_e \\times W_e \\times 1}$ to match $G_e$ , $G_p$ . This strategy outperforms upsampling $G_e$ , $G_p$ in terms of computational cost and performance. The overall loss function can be written as:", + "bbox": [ + 498, + 500, + 890, + 633 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {L} = \\lambda_ {1} \\mathcal {L} \\left(\\mathrm {Y}, \\mathrm {G} _ {\\text {o u t}}\\right) + \\lambda_ {2} \\mathcal {L} \\left(\\mathrm {E} ^ {\\prime}, \\mathrm {G} _ {\\mathrm {e}}\\right) + \\lambda_ {3} \\mathcal {L} \\left(\\mathrm {E} ^ {\\prime}, \\mathrm {G} _ {\\mathrm {p}}\\right), \\tag {12}\n$$\n", + "text_format": "latex", + "bbox": [ + 506, + 645, + 890, + 664 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\mathcal{L}$ denotes the Dice loss [5], $Y\\in \\mathbb{R}^{H\\times W\\times 1}$ is the ground-truth mask, and $\\lambda_1,\\lambda_2,\\lambda_3$ are the parameters to balance the three terms in loss function $(\\lambda_{1} + \\lambda_{2} + \\lambda_{3} = 1)$ . In our setting, they are set as 0.50, 0.25 and 0.25 respectively.", + "bbox": [ + 498, + 672, + 890, + 734 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 500, + 746, + 633, + 763 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.1. Experimental Setup", + "text_level": 1, + "bbox": [ + 500, + 771, + 689, + 787 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Pre-training Data We create a sizable image tampering dataset and use it to pre-train our model. This dataset includes three categories: 1) splicing, 2) copy-move, 3) removal. For splicing, we use the MS COCO [31] to generate spliced images, where one annotated region is randomly selected per image and pasted into a different image after several transformations. We use the same transformation as [5],", + "bbox": [ + 498, + 794, + 890, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "8226", + "bbox": [ + 480, + 944, + 514, + 955 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/955e1018d9f9531865694359f9b3254c067e9c55dca32169deba018646881fd6.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodDataColumbiaCoverageCASIANIST16IMD20
ManTraNet64K82.481.981.779.574.8
SPAN96k93.692.279.784.075.0
PSCCNet100k98.284.782.985.580.6
ObjectFormer62K95.592.884.387.282.1
Ours60K96.894.487.689.585.6
", + "bbox": [ + 78, + 88, + 504, + 195 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "including the scale, rotation, shift, and luminance changes. Since the spliced region is not always an object, we create random outlines using the Bezier curve [38] and fill them to create splicing masks. For copy-move, the datasets from MS COCO and [53] are adopted. For removal, we adopt the SOTA inpainting method [29] to fill one annotated region that is randomly removed from each chosen MS COCO image. We randomly add Gaussian noise or apply the JPEG compression algorithm to the generated data to resemble the visual quality of images in real situations.", + "bbox": [ + 75, + 262, + 468, + 412 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Testing Datasets Following [46], we evaluate our model on CASIA [13] dataset, Coverage [49] dataset, Columbia [19] dataset, NIST16 [17] dataset and IMD20 [40] dataset. Specifically, CASIA [13], which contains two types of tampered images (splicing and copy-move), is widely used in the image forgery field. The database V1.0 has fixed size tampered images, which are generated only by using crop-and-paste operation under Adobe Photoshop. The database v2.0 is more comprehensive and challenging, and most tampered examples are generated with post-processing. COVER [49] provides 100 images, and all of them are generated by copy-move tampering technique. Columbia [19] consists of 180 splicing images, whose size ranges from $757 \\times 568$ to $1152 \\times 568$ . In detail, the tampered images in Columbia are all uncompressed and without any post-processing. NIST16 [17] is a high-quality dataset. This dataset contains three types of tampering, and some regions of manipulation are difficult for humans to identify. IMD20 [40] collects real-life manipulated images from the Internet, and involves all three manipulations as well. We apply the same training/testing splits as [22, 46, 62] to fine-tune our model for fair comparisons.", + "bbox": [ + 75, + 415, + 470, + 747 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Evaluation Metrics To quantify the localization performance, following previous works [22, 46], we use pixel-level Area Under Curve (AUC) and F1 score on manipulation masks. And we adopt the Equal Error Rate (EER) threshold to binarize masks because binary masks are necessary to calculate F1 scores.", + "bbox": [ + 75, + 748, + 468, + 838 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Implementation Details The input images are resized to $512 \\times 512$ . In this work, the backbone is ResNet-50 [18], pre-trained on ImageNet [11]. Implemented by PyTorch, our model is trained with GeForce GTX 3090. We use", + "bbox": [ + 75, + 839, + 470, + 900 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/ed7f684086c47859ad8e901f12218252e642ba9f7d2a0bf6dd55899ea4add57e.jpg", + "table_caption": [ + "Table 1. Comparisons of manipulation localization AUC (%) scores of different pre-trained models." + ], + "table_footnote": [], + "table_body": "
MethodsCoverageCASIANIST16
AUCF1AUCF1AUCF1
J-LSTM61.4---76.4-
H-LSTM71.2---79.4-
RGB-N81.743.779.540.893.772.2
SPAN93.755.883.838.296.158.2
PSCCNet94.172.387.555.499.174.2
ObjectFormer95.775.888.257.999.682.4
Ours98.477.390.458.699.783.6
", + "bbox": [ + 521, + 88, + 874, + 234 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/9002029fc96630c5daaaa0434f7a9332b79428afe50d8b6aaf4791f8a078faa4.jpg", + "table_caption": [ + "Table 2. Comparison of manipulation localization results using fine-tuned models." + ], + "table_footnote": [], + "table_body": "
DistortionSPANObjectFormerOurs
no distortion83.9587.1889.49
Resize(0.78×)83.2487.1789.33 0.16↓
Resize(0.25×)80.3286.3387.72 1.77↓
Blur(k=3)83.1085.9789.22 0.27↓
Blur(k=15)79.1580.2687.13 2.36↓
Noise(σ=3)75.1779.5888.25 1.24↓
Noise(σ=15)67.2878.1583.40 6.09↓
Compress(q=100)83.5986.3789.42 0.07↓
Compress(q=50)80.6886.2488.82 0.67↓
", + "bbox": [ + 501, + 287, + 890, + 457 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 3. Localization performance on NIST16 dataset under various distortions. AUC scores are reported (in %), (Blur: Gaussian-Blur, Noise: GaussianNoise, Compress: JPEGCompress.)", + "bbox": [ + 498, + 467, + 890, + 510 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Adam as the optimizer, and the learning rate decays from $10^{-4}$ to $10^{-7}$ . We train 100 epochs with a batch size of 8, and the learning rate decays by 10 times every 30 epochs.", + "bbox": [ + 498, + 535, + 890, + 582 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.2. Comparison with the State-of-the-Art Methods", + "text_level": 1, + "bbox": [ + 498, + 589, + 890, + 606 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Following SPAN [22] and ObjectFormer [46], our model is compared with other state-of-the-art tampering localization methods under two settings: 1) training on the synthetic dataset and evaluating on the full test datasets, and 2) fine-tuning the pre-trained model on the training split of test datasets and evaluating on their test split. The pretrained model will demonstrate each method's generalizability, and the fine-tuned model will demonstrate how well each method performs locally once the domain discrepancy has been significantly reduced.", + "bbox": [ + 496, + 612, + 890, + 763 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Pre-trained Model Table 1 shows the localization performance of pre-trained models for different methods on four standard datasets under pixel-level AUC. We compare our model ERMPC with MantraNet [55], SPAN [22], PSCCNet [35], and ObjectFormer [46] when evaluating pre-trained models. The pre-trained ERMPC achieves the best localization performance on Coverage, CASIA, NIST16 and IMD20, and ranks second on Columbia. Especially, ERMPC achieves $94.4\\%$ on the copy-move dataset", + "bbox": [ + 496, + 763, + 890, + 901 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "8227", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/9924f3f5a4344f8ff617c00235d4a4cf7656ef3eed06003b4d0621735fe143ec.jpg", + "image_caption": [ + "Figure 4. Visualization of the predicted manipulation mask by different methods. From top to bottom, we show forged images, GT masks, predictions of ManTraNet, SPAN, PSCC-Net, and ours." + ], + "image_footnote": [], + "bbox": [ + 137, + 88, + 831, + 444 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/066e0a4b062fc1d9ff0dd6d65cdf85d30c7e692e34e323bb3bc5a309bfa4a7e1.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
VariantsCASIANIST16
AUCF1AUCF1
Baseline71.638.377.152.6
w/o RMPC76.945.686.460.7
w/o CEG85.151.593.475.3
w/o TDB88.657.398.281.9
Ours90.458.699.783.6
", + "bbox": [ + 122, + 494, + 424, + 612 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 4. Ablation results on CASIA and NIST16 dataset using different variants of ERMPC. AUC and F1 scores $(\\%)$ are reported.", + "bbox": [ + 76, + 622, + 468, + 651 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "COVER, whose image forgery regions are indistinguishable from the background. This validates our model owns the superior ability to control message passing between two regions(forged and authentic). We fail to achieve the best performance on Columbia, falling behind PSCCNet $1.4\\%$ under AUC. We contend that the explanation may be that the distribution of their synthesized training data closely resembles that of the Columbia dataset. This is further supported by the results in Table 2, which show that ERMPC performs better than PSCCNet in terms of both AUC and F1 scores. Furthermore, it is important to note that ERMPC attains decent results with less pre-training data.", + "bbox": [ + 75, + 670, + 468, + 851 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Fine-tuned Model The fine-tuned models, which are initiated with the network weights of the pretrained model, will be trained on the training split of Coverage, CASIA, and", + "bbox": [ + 75, + 854, + 470, + 902 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/55343cc4a03e07b2b35355dc1a17b0048c35f1fb3d54ab01fe4d1dcf091255c3.jpg", + "image_caption": [ + "Figure 5. The effect of parameter k in TDB" + ], + "image_footnote": [], + "bbox": [ + 535, + 513, + 841, + 674 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "NIST16 datasets, respectively. We evaluate the fine-tuned models of different methods in Table 2. As for AUC and F1, our model achieves significant performance gains. This validates that ERMPC could capture subtle tampering artifacts by controlling the message passing between two regions (forged and authentic) in the feature map.", + "bbox": [ + 496, + 715, + 893, + 808 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.3. Robustness Evaluation", + "text_level": 1, + "bbox": [ + 500, + 816, + 712, + 830 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We degrade the raw manipulated images from NIST16 using the distortion settings in [46] to analyze the robustness of ERMPC for forgery localization. These distortions types include scaling images to various scales (Re", + "bbox": [ + 496, + 839, + 893, + 902 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "8228", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/5395b7a7779b3aa9fecfebe2010fcd6c38f13b557a08665f8611d1b4c428d44d.jpg", + "image_caption": [ + "Figure 6. Visualization of message passing controller. From left to right, we display the forged images, masks, GradCAM [42] of the feature map without (w/o) and with (w) RMPC, and predictions." + ], + "image_footnote": [], + "bbox": [ + 80, + 88, + 156, + 277 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/d392d13aef3bffac3e6b74cd91af8d8ab5bb5a01931bf77099e737af33a04687.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 158, + 89, + 233, + 279 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/b901ea88b9e5cea5a330264cee2b2b6c13a381909080a697121a1c0a93b66a80.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 235, + 89, + 312, + 277 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/60c8fa84bfa117226ad1d3d46b8de3ac366684152fcf3f3c46094cbb205267b2.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 313, + 89, + 388, + 277 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/e5bba474ca424d4906559f018663504b6dc75cdc9289f612b2d5f15fc49edffd.jpg", + "image_caption": [ + "Figure 7. Visualization of edge reconstruction. From left to right, we display the forged images, masks, the features without (w/o) and with (w) the edge reconstruction module, and prediction." + ], + "image_footnote": [], + "bbox": [ + 390, + 89, + 467, + 277 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "size), applying Gaussian blur with a kernel size $k$ (GaussianBlur), adding Gaussian noise with a standard deviation $\\sigma$ (GaussianNoise), and performing JPEG compression with a quality factor $q$ (JPEGCompress). We compare the forgery localization performance (AUC scores) of our pre-trained models with SPAN [22] and ObjectFormer on these corrupted data and report the results in Table 3. ERMPC demonstrates more resistance to various distortion techniques. It is worth noting that JPEG compression is commonly performed when uploading images to social media. Our model ERMPC performs significantly better on compressed images than other methods.", + "bbox": [ + 75, + 354, + 468, + 535 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.4. Ablation Analysis", + "text_level": 1, + "bbox": [ + 76, + 545, + 250, + 561 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "The Region Message Passing Controller (RMPC) module of our method ERMPC is designed to weaken the message passing between the forged and authentic regions. The Context-Enhanced Graph (CEG) encodes global information along the node to obtain a better edge probability map, while the Threshold-adaptive Differentiable Binarization (TDB) adaptively performs the binarization process for learnable edges. In order to evaluate the effectiveness of RMPC, CEG and TDB, we remove them separately from ERMPC and evaluate the forgery localization performance on CASIA and NIST16 datasets.", + "bbox": [ + 75, + 568, + 468, + 733 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 4 presents the quantitative outcomes. The baseline denotes that we just use ResNet-50. It can be seen that without TDB, the AUC scores decrease by $2.0\\%$ on CASIA and $1.5\\%$ on NIST16, while without CEG, the AUC scores decrease by $5.9\\%$ on CASIA and $6.3\\%$ on NIST16. Furthermore, when RMPC is discarded, serious performance degradation in Table 4, i.e., $14.9\\%$ in terms of AUC and $22.2\\%$ in terms of F1 on CASIA can be observed.", + "bbox": [ + 75, + 734, + 468, + 853 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In Figure 5, we show the different values of parameters $k$ in threshold-adaptive differentiable binarization to verify its effect over three datasets. With its increasing, the curve", + "bbox": [ + 75, + 854, + 468, + 900 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/c440c55cc02b958c84f12ad7a8298234313ef108b88fa94a3cbbb1f86970bb41.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 501, + 89, + 580, + 223 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/237ca72180cfbc71adae202ee6c29ebd2c35637ae08f66909cd87323144b7845.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 581, + 89, + 658, + 223 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/cc251d1431e00b91b31451d1a6049f8dbb791af498e0c71985106b82f62930d8.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 658, + 89, + 733, + 223 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/fe3f7a6cf8ffe68a082603c89741f37670d82c9e50523b58ce6d04f68d152852.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 735, + 89, + 810, + 223 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/824322d2f217507f1e5c57c36d7b87a4d026f715526b6953d38b7481b9c03af2.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 812, + 89, + 890, + 223 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "of binarization becomes steeper. Moreover, being smaller is inadequate for weakening message passing, while being larger will destroy the adaptive capacity of the network. It is obvious that the setting of 500 is the optimal solution.", + "bbox": [ + 498, + 300, + 890, + 361 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.5. Visualization Results", + "text_level": 1, + "bbox": [ + 500, + 369, + 696, + 383 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Qualitative results. As shown in Figure 4, We provide predicted forgery masks of various methods. Since the source code of ObjectFormer [46] is not available, their predictions are not available. The results demonstrate that our method could not only locate the tampering regions more accurately but also develop sharp boundaries. It benefits from the explicit modeling of inconsistencies and the full exploitation of edges by our method.", + "bbox": [ + 496, + 393, + 890, + 513 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Visualization of message passing controller. To verify the usefulness of the region message passing controller (RMPC), we show the change of features before and after the controller in Figure 6. It is clear that RMPC facilitates the learning of forgery features and prevents false alarms. Specifically, the network without RMPC will make false judgments about objects that are similar to the forgery.", + "bbox": [ + 496, + 513, + 890, + 619 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Visualization of edge reconstruction. To verify the effect of the edge reconstruction (ER) module, the change of features before and after EG is shown in Figure 7. The results demonstrate that the EG can effectively acquire accurate edges, thus helping our model to perform well.", + "bbox": [ + 496, + 619, + 890, + 695 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 709, + 617, + 724 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this paper, we propose a novel Image Forgery Localization framework with a two-step Edge-aware Regional Message Passing Controlling strategy. In detail, the first step is to account for fully exploiting the edge information. In the second step, guided by the learnable edges, an edge-aware dynamic graph is devised to weaken the message passing between the forged and authentic regions. Our paper provides a new research strategy to solve the misjudgment problem in the field of IFL. Extensive experimental results on several benchmarks demonstrate the effectiveness of the proposed algorithm.", + "bbox": [ + 496, + 734, + 890, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "8229", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Mohammed Aloraini, Mehdi Sharifzadeh, and Dan Schonfeld. Sequential and patch analyses for object removal video forgery detection and localization. IEEE Transactions on Circuits and Systems for Video Technology, 31(3):917-930, 2020. 2", + "[2] Irene Amerini, Tiberio Uricchio, Lamberto Ballan, and Roberto Caldelli. Localization of jpeg double compression through multi-domain convolutional neural networks. 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Springer, 2023. 1" + ], + "bbox": [ + 501, + 92, + 890, + 204 + ], + "page_idx": 10 + }, + { + "type": "page_number", + "text": "8232", + "bbox": [ + 482, + 945, + 514, + 955 + ], + "page_idx": 10 + } +] \ No newline at end of file diff --git a/2023/Edge-Aware Regional Message Passing Controller for Image Forgery Localization/c5c52750-0529-4615-bd1f-1262f32b5c87_model.json b/2023/Edge-Aware Regional Message Passing Controller for Image Forgery Localization/c5c52750-0529-4615-bd1f-1262f32b5c87_model.json new file mode 100644 index 0000000000000000000000000000000000000000..040812a6d78a6587d49128902c7ca90513c62887 --- /dev/null +++ b/2023/Edge-Aware Regional Message Passing Controller for Image Forgery Localization/c5c52750-0529-4615-bd1f-1262f32b5c87_model.json @@ -0,0 +1,2422 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.0, + 0.812, + 0.045 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.218, + 0.131, + 0.756, + 0.177 + ], + "angle": 0, + "content": "Edge-aware Regional Message Passing Controller for Image Forgery Localization" + }, + { + "type": "text", + "bbox": [ + 0.16, + 0.204, + 0.81, + 0.24 + ], + "angle": 0, + "content": "Dong Li*, Jiaying Zhu*, Menglu Wang, Jiawei Liu†, Xueyang Fu, Zheng-Jun Zha University of Science and Technology of China, China" + }, + { + "type": "text", + "bbox": [ + 0.144, + 0.242, + 0.821, + 0.259 + ], + "angle": 0, + "content": "{dongli6, zhujy53, vault}@mail.ustc.edu.cn, {jwliu6, xyfu, zhazj}@ustc.edu.cn" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.292, + 0.314, + 0.308 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.324, + 0.474, + 0.673 + ], + "angle": 0, + "content": "Digital image authenticity has promoted research on image forgery localization. Although deep learning-based methods achieve remarkable progress, most of them usually suffer from severe feature coupling between the forged and authentic regions. In this work, we propose a two-step Edge-aware Regional Message Passing Controlling strategy to address the above issue. Specifically, the first step is to account for fully exploiting the edge information. It consists of two core designs: context-enhanced graph construction and threshold-adaptive differentiable binarization edge algorithm. The former assembles the global semantic information to distinguish the features between the forged and authentic regions, while the latter stands on the output of the former to provide the learnable edges. In the second step, guided by the learnable edges, a region message passing controller is devised to weaken the message passing between the forged and authentic regions. In this way, our ERMPC is capable of explicitly modeling the inconsistency between the forged and authentic regions and enabling it to perform well on refined forged images. Extensive experiments on several challenging benchmarks show that our method is superior to state-of-the-art image forgery localization methods qualitatively and quantitatively." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.701, + 0.21, + 0.716 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.726, + 0.47, + 0.819 + ], + "angle": 0, + "content": "The forged or manipulated images pose risks in various fields, such as removing copyright watermarks, generating fake news, and even falsifying evidence in court [32]. The growing technology of forgery will cause a crisis of trust and affect social equity. Therefore, the detection of image forgery is of great significance. The crucial aspect" + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.291, + 0.891, + 0.395 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.502, + 0.397, + 0.891, + 0.5 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.51, + 0.894, + 0.553 + ], + "angle": 0, + "content": "Figure 1. The difference between previous methods and ours. Our method controls the message passing between the forged and authentic regions, ignored by the previous method. As shown by \\(X\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.568, + 0.892, + 0.749 + ], + "angle": 0, + "content": "of the detection is to model the inconsistency between the forged and authentic regions and to locate the forged regions on the suspicious image, i.e., image forgery localization (IFL). However, as post-processing techniques such as GAN [16, 26, 63], VAE [27, 44] and homogeneous manipulation [7, 33] are wildly utilized, images can be easily tampered in a visually imperceptible way. These techniques constantly aim to couple the forged and authentic regions' features, making image forgery localization challenging. Therefore, in order to accurately locate the image forgery region, it is particularly essential to decouple the features between forged and authentic regions." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.75, + 0.895, + 0.901 + ], + "angle": 0, + "content": "In recent years, deep-learning techniques have attracted more attention [23, 57, 58, 65, 66]. Due to the development of deep learning, image forgery localization has achieved remarkable results. For example, ManTra-Net [55] treats the forgery localization problem as a local anomaly detection problem and proposes a novel long short-term memory solution to assess local anomalies. To discriminate between heterologous regions, SPAN employs CNNs to extract anomalous local noise features from noise maps. MVSS-Net [5] learns a multiview feature with multi-scale" + }, + { + "type": "page_footnote", + "bbox": [ + 0.076, + 0.827, + 0.47, + 0.9 + ], + "angle": 0, + "content": "* Co-first authors contributed equally, † corresponding author. This work was supported by the National Key R&D Program of China under Grant 2020AAA0105702, the National Natural Science Foundation of China (NSFC) under Grants 62225207, 62276243, 62106245 and U19B2038, the University Synergy Innovation Program of Anhui Province under Grant GXXT-2019-025." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "8222" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.212 + ], + "angle": 0, + "content": "supervised networks to jointly exploit the noise view and the boundary artifacts. However, these methods do not decouple the features between the forged and authentic regions, making it difficult to locate the tampered regions for elaborately forged images accurately. As shown in Figure 1, in the previous method, the features of the forged region are coupled with some of the features of the authentic region, resulting in wrong localization." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.213, + 0.47, + 0.394 + ], + "angle": 0, + "content": "In this work, we propose a novel method to avoid feature coupling of the two regions (forged and authentic) for image forgery localization. One of the keys of this method is to construct a dynamic graph, where the edges between the forged and authentic regions participate in its construction. We control the message passing of regions inside and outside the edges (i.e., forged and authentic) by reconstructing the adjacency matrix of nodes inside and outside the edges, thus achieving effective disentanglement of the features between the forged and authentic regions. Based on its functionality, the edge-aware dynamic graph convolution is named the regional message passing controller (RMPC)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.395, + 0.47, + 0.575 + ], + "angle": 0, + "content": "In order to use the proposed RMPC for image forgery localization, it is necessary to obtain the edge information between the forged and authentic regions, which is the other key of this method. Therefore, an edge reconstruction (ER) module was developed, including a context-enhanced graph (CEG) and a threshold-adaptive differentiable binarization module. We specially design an adjacency matrix learner in the CEG, which encodes global information along the nodes to assemble the global semantic information. Inspired by the Sigmoid function, we develop the threshold-adaptive differentiable binarization edge algorithm, which stands on the output of the CEG to provide the learnable edges." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.576, + 0.47, + 0.771 + ], + "angle": 0, + "content": "In summary, in this work we propose a new two-step framework named Edge-aware Regional Message Passing Controller (ERMPC) for Image Forgery Localization, including RMPC and ER. The ERMPC could effectively control the message passing between the forged and authentic regions to achieve effective disentanglement of the two regions, thus boosting the performance of image forgery localization. We take edge information as the main task and use it as a basis to explicitly model the inconsistency between two regions. To the best of our knowledge, this work is the first attempt to explicitly weaken the message passing between the forged and authentic regions. Our contributions are as follows:" + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.785, + 0.468, + 0.844 + ], + "angle": 0, + "content": "- We propose ERMPC, a novel two-step coarse-to-fine framework for image forgery localization, explicitly modeling the inconsistency between the forged and authentic regions with edge information." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.856, + 0.468, + 0.901 + ], + "angle": 0, + "content": "- We propose an edge-aware dynamic graph, also known as RMPC, to control the message passing between two regions (forged and authentic) in the feature map." + }, + { + "type": "list", + "bbox": [ + 0.097, + 0.785, + 0.468, + 0.901 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.092, + 0.89, + 0.151 + ], + "angle": 0, + "content": "- We develop an edge reconstruction module containing a context-enhanced graph and a threshold-adaptive differentiable binarization module to obtain the desired edge information." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.167, + 0.89, + 0.227 + ], + "angle": 0, + "content": "- We conduct extensive experiments on multiple benchmarks and demonstrate that our method is qualitatively and quantitatively superior to state-of-the-art image forgery localization methods." + }, + { + "type": "list", + "bbox": [ + 0.518, + 0.092, + 0.89, + 0.227 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.262, + 0.65, + 0.278 + ], + "angle": 0, + "content": "2. Related Works" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.288, + 0.75, + 0.304 + ], + "angle": 0, + "content": "2.1. Image Forgery Localization" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.312, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Most early works propose to localize a specific type of forgery, including splicing [2, 3, 9, 10, 24, 28, 37, 51, 60], copy-move [8, 14, 25, 48, 52, 54], and removal [1, 50, 56, 64]. While these methods demonstrate satisfactory performance in detecting specific types of forgery, they exhibit limitations in practical applications due to the prevalence of unknown and diverse forgery types. Consequently, recent studies have emphasized the need for an approach to tackle multiple forgery types with one model. RGBN [62] proposes a dual-stream Faster R-CNN network. The first stream is designed to extract RGB features and identify tampering artifacts, while the second stream utilizes noise features to model the noise inconsistency between tampered and authentic regions, thereby localizing image forgery with enhanced accuracy. ManTra-net [55] is an end-to-end network that performs both detection and localization, which treats the problem as anomaly detection and introduces a long short-term memory solution to assess local anomalies. SPAN [22] attempts to model the spatial correlation by constructing a pyramid of local self-attention blocks. MVSS-Net [5] has designed an edge-supervised branch that uses edge residual blocks to capture fine-grained boundary detail in a shallow to deep manner. It is worth noting that edge information is important for image forgery detection and localization, as the tampered regions are commonly surrounded by unnatural artifacts. Nevertheless, most studies only utilize edges in a supervised strategy, such as MVSS-Net [5], MFCN [41], GSR-Net [61], and CAIFL [47]. PSCCNet [35] uses a progressive spatial-channel correlation module that uses features at different scales and dense cross-connections to generate operational masks in a coarse-to-fine fashion. ObjectFormer [46] captures forgery traces by extracting high-frequency parts of the image and combining them with RGB features. In this work, we explicitly employ learnable edges as guiding information to impede the message passing between the forged and untouched regions and employ refined edge reconstruction to achieve inconsistent modeling of the two regions to localize manipulation artifacts." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "8223" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.093, + 0.891, + 0.479 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.488, + 0.893, + 0.517 + ], + "angle": 0, + "content": "Figure 2. An overview of the proposed framework ERMPC. The input is a suspicious image \\((H\\times W\\times 3)\\), and the output is a predicted mask \\((\\mathrm{H}\\times \\mathrm{W}\\times 1)\\), which localizes the forged regions." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.543, + 0.25, + 0.559 + ], + "angle": 0, + "content": "2.2. Graph Reasoning" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.569, + 0.473, + 0.903 + ], + "angle": 0, + "content": "Graph-based approaches have attracted growing attention from the computer vision community these days and have shown to be an effective relational reasoning method with a robust capacity for non-local feature aggregation. Specifically, CDGCNet [21] utilizes a class-wise learning strategy and designs a class-wise graph convolution, which avoids heavy graph concatenation and facilitates feature learning. To overcome the problem that most graph-based approaches assign a fixed number of neighbors for each query item, DAGL [39] proposes a dynamic attentive graph learning model to explore the dynamic non-local property for image restoration. CTL [34] learns a context-reinforced topology to construct multi-scale graphs which have a robust representational capacity by considering both global contextual information and physical connections of the human body. On other tasks in computer vision, e.g., object detection [43], multi-label image recognition [6], and skeleton-based action recognition [36, 59], graph convolutional neural networks have also achieved impressive performance. In contrast, we propose an improved edge-guided graph attention model to obstruct the message passing between forged and untouched regions with dynamic" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.543, + 0.895, + 0.665 + ], + "angle": 0, + "content": "construction for forgery region localization. As graph convolution is an effective relational reasoning method that is very suitable for detecting forgery traces, this paper applies it to the task of image forgery localization for the first time. An improved edge-guided graph attention model is proposed for forgery region localization, which obstructs the message passing between forged and untouched regions with dynamic construction." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.713, + 0.634, + 0.731 + ], + "angle": 0, + "content": "3. Methodology" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.75, + 0.895, + 0.903 + ], + "angle": 0, + "content": "This section details the scheme of image forgery localization based on edge-aware message passing control. Sec. 3.1 describes an overview of the framework. One of the keys of the scheme is to control the message passing with edge and thus model the inconsistency between the forged and authentic regions (Sec. 3.2). Another key lies in reconstructing accurate edges from coarse features (Sec. 3.3). In addition, following [5, 22, 55, 62], we use the noise branch and fuse it with RGB branch at the end of the network (Sec. 3.4). The optimization is introduced in Sec. 3.5." + }, + { + "type": "page_number", + "bbox": [ + 0.482, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "8224" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.078, + 0.091, + 0.188, + 0.105 + ], + "angle": 0, + "content": "3.1. Overview" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.113, + 0.473, + 0.357 + ], + "angle": 0, + "content": "Figure 2 is an overview of the framework. The input image is represented as \\( X \\in \\mathbb{R}^{H \\times W \\times 3} \\), where H and W represent the height and width of the image. First, we use two branches to handle RGB and noise separately, obtaining \\( G_{r} \\in \\mathbb{R}^{H_{s} \\times W_{s} \\times C_{s}} \\) and \\( G_{n} \\in \\mathbb{R}^{H_{s} \\times W_{s} \\times C_{s}} \\) respectively. Then, we use ResNet-50 pretrained on ImageNet [11] as the backbone network. Following [4], we adopt atrous spatial pyramid pooling(ASPP) together with ResNet-50 to capture the long-range contextual information. The coarse features extracted from RGB branches are converted into edges through the edge reconstruction block. Meanwhile, the coarse features are constructed as graph structures, guided by the reconstructed edge information. Finally, the RGB features after the graph convolutional network are fused with noise information through dual attention [5] to output the predicted forgery localization map." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.365, + 0.384, + 0.382 + ], + "angle": 0, + "content": "3.2. Region Message Passing Controller" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.388, + 0.47, + 0.462 + ], + "angle": 0, + "content": "Most forged images are carefully processed to hide tampering artifacts, making it challenging to model inconsistencies in the RGB branch. To overcome this problem, the edges between the forged and authentic regions are utilized to control the message passing explicitly." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.463, + 0.469, + 0.539 + ], + "angle": 0, + "content": "The edge feature \\( G_{e} \\in \\mathbb{R}^{H_{e} \\times W_{e} \\times 1} \\) comes from the edge reconstruction block (described in detail in the next subsection), where \\( H_{e} = H_{s} \\) and \\( W_{e} = W_{s} \\). First, we calculate the relationship between two node features \\( P_{i}, P_{j} \\) of the \\( G_{E} \\) using an algorithm similar to XNOR gate:" + }, + { + "type": "equation", + "bbox": [ + 0.098, + 0.549, + 0.47, + 0.589 + ], + "angle": 0, + "content": "\\[\n\\mathrm {X N} \\left(P _ {i}, P _ {j}\\right) = \\left\\{ \\begin{array}{l l} 0 & \\text {I n s i d e a n d o u t s i d e t h e e d g e s} \\\\ 1 & \\text {O n t h e s a m e s i d e o f e d g e s .} \\end{array} \\right. \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.598, + 0.469, + 0.658 + ], + "angle": 0, + "content": "If two nodes are inside and outside the edge respectively, then their XN is set to 0. For each of the N (\\(N = H_{e} \\times W_{e}\\)) nodes features, we calculate its XN, thus generating a matrix \\(A_{e} \\in \\mathbb{R}^{N \\times N}\\)." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.659, + 0.469, + 0.704 + ], + "angle": 0, + "content": "Next, we apply graph learning to process the \\(G_{r} \\in \\mathbb{R}^{H_{s} \\times W_{s} \\times C_{s}}\\). Following GAT [45], we calculate the similarity between two nodes as attention coefficients:" + }, + { + "type": "equation", + "bbox": [ + 0.192, + 0.712, + 0.469, + 0.732 + ], + "angle": 0, + "content": "\\[\n\\alpha_ {i, j} = \\psi (x _ {i}) ^ {T} \\psi^ {\\prime} (x _ {j}), \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.741, + 0.469, + 0.817 + ], + "angle": 0, + "content": "where \\(\\psi, \\psi'\\) denotes two learnable linear transformations. Specifically, we utilize \\(\\psi = Wx\\) and \\(\\psi' = W'x\\), where \\(W \\in \\mathbb{R}^{C_s \\times C_s}\\) and \\(W' \\in \\mathbb{R}^{C_s \\times C_s}\\) are both weight matrices. To make coefficients easier to compare across different nodes, we normalize them using the softmax function:" + }, + { + "type": "equation", + "bbox": [ + 0.184, + 0.827, + 0.469, + 0.865 + ], + "angle": 0, + "content": "\\[\nA _ {r _ {i, j}} = \\frac {\\exp (\\alpha_ {i , j})}{\\sum_ {j = 1} ^ {N} \\exp (\\alpha_ {i , j})}, \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.87, + 0.47, + 0.901 + ], + "angle": 0, + "content": "where \\(A_r \\in \\mathbb{R}^{N \\times N}\\) is the preliminary adjacency matrix. It reflects the relationship between any two nodes in the fea" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.198 + ], + "angle": 0, + "content": "ture map. Larger values represent a greater flow of information between two nodes. In order to realize message passing control better, a method of dynamically adjusting the adjacency matrix is adopted. Specifically, if two nodes are on and off the boundary respectively, their adjacency is broken due to the dynamic adjustment of the adjacency matrix. In practice, the adjacency matrix is recalculated as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.642, + 0.209, + 0.892, + 0.226 + ], + "angle": 0, + "content": "\\[\nA _ {r} ^ {\\prime} = A _ {r} \\odot A _ {e}, \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.234, + 0.892, + 0.28 + ], + "angle": 0, + "content": "where \\(\\odot\\) is the Hadamard product. \\(A_r' \\in \\mathbb{R}^{N \\times N}\\) re-models the weights between nodes in the feature map and severs the connections between the forged and real regions." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.281, + 0.892, + 0.326 + ], + "angle": 0, + "content": "Once the adjacency matrix is obtained, it is weighted by the learnable attention weights. Then the original nodes are updated with the following:" + }, + { + "type": "equation", + "bbox": [ + 0.61, + 0.336, + 0.892, + 0.353 + ], + "angle": 0, + "content": "\\[\nZ _ {r} = \\operatorname {R e L U} \\left(A _ {r} ^ {\\prime} G _ {r} ^ {\\prime} W _ {z}\\right), \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.363, + 0.892, + 0.408 + ], + "angle": 0, + "content": "where \\(Z_{r}\\in \\mathbb{R}^{N\\times C_{s}}\\) is RGB features after graph reasoning, \\(W_{z}\\in \\mathbb{R}^{C_{s}\\times C_{s}}\\) is the learnable parameter and \\(G_r^\\prime \\in \\mathbb{R}^{N\\times C_s}\\) is the graph representation transformed by \\(G_{r}\\)" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.409, + 0.892, + 0.59 + ], + "angle": 0, + "content": "It is worth noting that this work not only introduces the idea of controlling the message passing in image forgery localization for the first time, but also the approach implemented is different from previous research [12, 20]. BFP [12] uses directed acyclic graphs (DAG) for feature propagation and introduces boundary information into the propagation to control the message passing between different segments. However, it has to scan the image pixel by pixel and requires a lot of loops, causing it difficult to implement in real-world applications. BGC [20] emphasizes reducing the weights of the edges and does not really focus on the message passing between regions." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.599, + 0.696, + 0.615 + ], + "angle": 0, + "content": "3.3. Edge Reconstruction" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.622, + 0.892, + 0.743 + ], + "angle": 0, + "content": "As described in the previous section, the Edge-aware Message Passing Control Graph requires accurate edge information. Designing such an edge-access network is nontrivial. The main challenge is how to learn edge information from the coarse feature. To this end, a novel approach to edge reconstruction is proposed. Specifically, we started by using the Sobel layer [5] to enhance the edge-related patterns in \\( G_{r} \\in \\mathbb{R}^{H_{s} \\times W_{s} \\times C_{s}} \\)," + }, + { + "type": "equation", + "bbox": [ + 0.576, + 0.754, + 0.892, + 0.771 + ], + "angle": 0, + "content": "\\[\nG _ {c} = G _ {r} \\odot \\sigma (\\text {N o r m} (S o b e l \\left(G _ {r}\\right)), \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.892, + 0.81 + ], + "angle": 0, + "content": "where Norm is L2 Normalization, \\(\\sigma\\) is Sigmoid and Sobel is the SobelConv [5]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.811, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Then, we explore a Context-Enhanced Graph (CEG), extracting the local and global features separately for \\( G_{c} \\in \\mathbb{R}^{H_{s} \\times W_{s} \\times C_{s}} \\). Specifically, the local information is extracted by the convolutional layers [5]. For global information, the contextual information of the feature map is encoded as the adjacency matrix \\( A_{c} \\in \\mathbb{R}^{N \\times N} \\) in a simple and" + }, + { + "type": "page_number", + "bbox": [ + 0.482, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "8225" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.078, + 0.087, + 0.473, + 0.282 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.291, + 0.471, + 0.32 + ], + "angle": 0, + "content": "Figure 3. Context-Enhanced Graph. Global features are extracted by the specific graph, while local features by the ResBlock." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.345, + 0.471, + 0.392 + ], + "angle": 0, + "content": "efficient way. As shown in Figure 3, \\( A_{c} \\) is generated by a specially designed adjacency matrix learner which consists of two \\( 1 \\times 1 \\) convolution layers. The process is written as" + }, + { + "type": "equation", + "bbox": [ + 0.156, + 0.402, + 0.469, + 0.42 + ], + "angle": 0, + "content": "\\[\nA _ {c} = \\operatorname {N o r m} \\left(\\operatorname {C o n v} \\left(\\operatorname {C o n v} \\left(\\mathrm {G} _ {\\mathrm {c}} ^ {\\prime}\\right)\\right)\\right), \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.429, + 0.47, + 0.567 + ], + "angle": 0, + "content": "where \\( G_c' \\in \\mathbb{R}^{N \\times C_s} \\) is reshaped by \\( G_c \\). Given the node features of \\( G_c' \\), we first squeeze the feature dimensions by a \\( 1 \\times 1 \\) convolution layer. Then, another convolution layer with \\( 1 \\times 1 \\) kernel is used to transfer the N-dimension feature vector into the \\( N \\times N \\) adjacency matrix. In addition, L2 Normalization is applied to each row of \\( A_c \\) to facilitate stable optimization. Next, we use this adjacency matrix to complete the graph reasoning. In this way, we can obtain a global feature map. The process can be written as" + }, + { + "type": "equation", + "bbox": [ + 0.186, + 0.577, + 0.469, + 0.595 + ], + "angle": 0, + "content": "\\[\n\\operatorname {G l o b a l} \\left(G _ {c} ^ {\\prime}\\right) = A _ {c} G _ {c} ^ {\\prime} W _ {c}, \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.604, + 0.47, + 0.695 + ], + "angle": 0, + "content": "where \\(W_{c}\\in \\mathbb{R}^{C_{s}\\times C_{s}}\\) is the learnable parameter. To match with the local information dimension, we reshape Global \\((G_c^{\\prime})\\in \\mathbb{R}^{N\\times C_s}\\) back to Global' \\((G_c^\\prime)\\in\\) \\(\\mathbb{R}^{H_s\\times W_s\\times C_s}\\) . Then combining the local and global information, we can obtain the edge probability map \\(G_{p}\\in\\) \\(\\mathbb{R}^{H_s\\times W_s\\times 1}\\) .." + }, + { + "type": "equation", + "bbox": [ + 0.105, + 0.707, + 0.47, + 0.725 + ], + "angle": 0, + "content": "\\[\nG _ {p} = \\sigma \\left(\\mathcal {C} \\left(\\operatorname {C a t} \\left(\\operatorname {L o c a l} \\left(G _ {c}\\right), \\operatorname {G l o b a l} ^ {\\prime} \\left(G _ {c} ^ {\\prime}\\right)\\right)\\right)\\right), \\tag {9}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.735, + 0.469, + 0.765 + ], + "angle": 0, + "content": "where \\(\\sigma\\) denotes the Sigmoid, \\(\\mathcal{C}\\) is a \\(1\\times 1\\) convolution layer, and Local contains ReLU and two convolutional layers." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.766, + 0.47, + 0.902 + ], + "angle": 0, + "content": "Furthermore, in order to determine the edges, a threshold needs to be determined to binarize the probability map. Most previous studies have used fixed thresholds, and the process is non-differentiable. Inspired by [30], we utilize a variable threshold map which is adaptive for each point on the probability map \\( G_{p} \\). Besides, we propose a variant of the Sigmoid function to complete the binarization, which is capable of participating in the backpropagation involved. Binarize threshold adjustment is achieved by translating the" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.092, + 0.893, + 0.138 + ], + "angle": 0, + "content": "Sigmoid function along the x-axis. Therefore, we explore the threshold-adaptive differentiable binarization (TDB) for edge reconstruction. It is computed as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.605, + 0.146, + 0.892, + 0.177 + ], + "angle": 0, + "content": "\\[\nG _ {e} = \\frac {1}{1 + e ^ {- k \\left(G _ {p} - \\tau \\left(G _ {p}\\right)\\right)}}, \\tag {10}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.186, + 0.893, + 0.232 + ], + "angle": 0, + "content": "where \\(\\tau\\) denotes the learnable transformation, which in practice is \\(3\\times 3\\) convolution operators, and \\(k\\) is the amplifying factor. In particular, \\(k\\) is set to 500 empirically." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.24, + 0.651, + 0.255 + ], + "angle": 0, + "content": "3.4. Branch Fusion" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.263, + 0.892, + 0.385 + ], + "angle": 0, + "content": "Following most studies [5,22,55,62], we also employ the noise branch. However, this is not the focus of this work, so we have used some common methods. As in Figure 2, the noise is extracted with BayarConv [55]. For the fusion of the two branches, we follow [5] and adopt the Dual Attention (DA) [15]. DA includes channel attention module (CAM) and position attention module (PAM). It can effectively fuse two branches. The process can be written as" + }, + { + "type": "equation", + "bbox": [ + 0.626, + 0.395, + 0.891, + 0.412 + ], + "angle": 0, + "content": "\\[\nG _ {o} = \\mathrm {D A} \\left(G _ {z}, G _ {n}\\right), \\tag {11}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.421, + 0.893, + 0.468 + ], + "angle": 0, + "content": "where \\( G_{z} \\in \\mathbb{R}^{H_{s} \\times W_{s} \\times C_{s}} \\) is reshaped by the \\( Z_{r} \\). Finally, we transform \\( G_{o} \\in \\mathbb{R}^{H_{s} \\times W_{s} \\times 1} \\) with bilinear upsampling into the final predicted mask \\( G_{out} \\in \\mathbb{R}^{H \\times W \\times 1} \\)." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.476, + 0.64, + 0.492 + ], + "angle": 0, + "content": "3.5. Optimization" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.5, + 0.892, + 0.635 + ], + "angle": 0, + "content": "As shown in Figure 2, we calculate the loss function for three components: the final prediction \\( G_{out} \\in \\mathbb{R}^{H \\times W \\times 1} \\), the binary edge prediction \\( G_e \\in \\mathbb{R}^{H_e \\times W_e \\times 1} \\) and the edge probability map \\( G_p \\in \\mathbb{R}^{H_e \\times W_e \\times 1} \\). For edge loss, the ground-truth edge \\( E \\in \\mathbb{R}^{H \\times W \\times 1} \\) is downsampled to a smaller size \\( E' \\in \\mathbb{R}^{H_e \\times W_e \\times 1} \\) to match \\( G_e \\), \\( G_p \\). This strategy outperforms upsampling \\( G_e \\), \\( G_p \\) in terms of computational cost and performance. The overall loss function can be written as:" + }, + { + "type": "equation", + "bbox": [ + 0.507, + 0.646, + 0.892, + 0.665 + ], + "angle": 0, + "content": "\\[\n\\mathbf {L} = \\lambda_ {1} \\mathcal {L} \\left(\\mathrm {Y}, \\mathrm {G} _ {\\text {o u t}}\\right) + \\lambda_ {2} \\mathcal {L} \\left(\\mathrm {E} ^ {\\prime}, \\mathrm {G} _ {\\mathrm {e}}\\right) + \\lambda_ {3} \\mathcal {L} \\left(\\mathrm {E} ^ {\\prime}, \\mathrm {G} _ {\\mathrm {p}}\\right), \\tag {12}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.673, + 0.892, + 0.735 + ], + "angle": 0, + "content": "where \\(\\mathcal{L}\\) denotes the Dice loss [5], \\(Y\\in \\mathbb{R}^{H\\times W\\times 1}\\) is the ground-truth mask, and \\(\\lambda_1,\\lambda_2,\\lambda_3\\) are the parameters to balance the three terms in loss function \\((\\lambda_{1} + \\lambda_{2} + \\lambda_{3} = 1)\\). In our setting, they are set as 0.50, 0.25 and 0.25 respectively." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.747, + 0.634, + 0.764 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.772, + 0.691, + 0.789 + ], + "angle": 0, + "content": "4.1. Experimental Setup" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.795, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Pre-training Data We create a sizable image tampering dataset and use it to pre-train our model. This dataset includes three categories: 1) splicing, 2) copy-move, 3) removal. For splicing, we use the MS COCO [31] to generate spliced images, where one annotated region is randomly selected per image and pasted into a different image after several transformations. We use the same transformation as [5]," + }, + { + "type": "page_number", + "bbox": [ + 0.482, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "8226" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.08, + 0.089, + 0.505, + 0.196 + ], + "angle": 0, + "content": "
MethodDataColumbiaCoverageCASIANIST16IMD20
ManTraNet64K82.481.981.779.574.8
SPAN96k93.692.279.784.075.0
PSCCNet100k98.284.782.985.580.6
ObjectFormer62K95.592.884.387.282.1
Ours60K96.894.487.689.585.6
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.206, + 0.471, + 0.234 + ], + "angle": 0, + "content": "Table 1. Comparisons of manipulation localization AUC (%) scores of different pre-trained models." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.263, + 0.47, + 0.414 + ], + "angle": 0, + "content": "including the scale, rotation, shift, and luminance changes. Since the spliced region is not always an object, we create random outlines using the Bezier curve [38] and fill them to create splicing masks. For copy-move, the datasets from MS COCO and [53] are adopted. For removal, we adopt the SOTA inpainting method [29] to fill one annotated region that is randomly removed from each chosen MS COCO image. We randomly add Gaussian noise or apply the JPEG compression algorithm to the generated data to resemble the visual quality of images in real situations." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.416, + 0.471, + 0.748 + ], + "angle": 0, + "content": "Testing Datasets Following [46], we evaluate our model on CASIA [13] dataset, Coverage [49] dataset, Columbia [19] dataset, NIST16 [17] dataset and IMD20 [40] dataset. Specifically, CASIA [13], which contains two types of tampered images (splicing and copy-move), is widely used in the image forgery field. The database V1.0 has fixed size tampered images, which are generated only by using crop-and-paste operation under Adobe Photoshop. The database v2.0 is more comprehensive and challenging, and most tampered examples are generated with post-processing. COVER [49] provides 100 images, and all of them are generated by copy-move tampering technique. Columbia [19] consists of 180 splicing images, whose size ranges from \\(757 \\times 568\\) to \\(1152 \\times 568\\). In detail, the tampered images in Columbia are all uncompressed and without any post-processing. NIST16 [17] is a high-quality dataset. This dataset contains three types of tampering, and some regions of manipulation are difficult for humans to identify. IMD20 [40] collects real-life manipulated images from the Internet, and involves all three manipulations as well. We apply the same training/testing splits as [22, 46, 62] to fine-tune our model for fair comparisons." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.749, + 0.47, + 0.839 + ], + "angle": 0, + "content": "Evaluation Metrics To quantify the localization performance, following previous works [22, 46], we use pixel-level Area Under Curve (AUC) and F1 score on manipulation masks. And we adopt the Equal Error Rate (EER) threshold to binarize masks because binary masks are necessary to calculate F1 scores." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.471, + 0.901 + ], + "angle": 0, + "content": "Implementation Details The input images are resized to \\(512 \\times 512\\). In this work, the backbone is ResNet-50 [18], pre-trained on ImageNet [11]. Implemented by PyTorch, our model is trained with GeForce GTX 3090. We use" + }, + { + "type": "table", + "bbox": [ + 0.522, + 0.089, + 0.875, + 0.236 + ], + "angle": 0, + "content": "
MethodsCoverageCASIANIST16
AUCF1AUCF1AUCF1
J-LSTM61.4---76.4-
H-LSTM71.2---79.4-
RGB-N81.743.779.540.893.772.2
SPAN93.755.883.838.296.158.2
PSCCNet94.172.387.555.499.174.2
ObjectFormer95.775.888.257.999.682.4
Ours98.477.390.458.699.783.6
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.246, + 0.892, + 0.273 + ], + "angle": 0, + "content": "Table 2. Comparison of manipulation localization results using fine-tuned models." + }, + { + "type": "table", + "bbox": [ + 0.502, + 0.288, + 0.892, + 0.458 + ], + "angle": 0, + "content": "
DistortionSPANObjectFormerOurs
no distortion83.9587.1889.49
Resize(0.78×)83.2487.1789.33 0.16↓
Resize(0.25×)80.3286.3387.72 1.77↓
Blur(k=3)83.1085.9789.22 0.27↓
Blur(k=15)79.1580.2687.13 2.36↓
Noise(σ=3)75.1779.5888.25 1.24↓
Noise(σ=15)67.2878.1583.40 6.09↓
Compress(q=100)83.5986.3789.42 0.07↓
Compress(q=50)80.6886.2488.82 0.67↓
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.468, + 0.892, + 0.511 + ], + "angle": 0, + "content": "Table 3. Localization performance on NIST16 dataset under various distortions. AUC scores are reported (in %), (Blur: Gaussian-Blur, Noise: GaussianNoise, Compress: JPEGCompress.)" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.536, + 0.892, + 0.583 + ], + "angle": 0, + "content": "Adam as the optimizer, and the learning rate decays from \\(10^{-4}\\) to \\(10^{-7}\\). We train 100 epochs with a batch size of 8, and the learning rate decays by 10 times every 30 epochs." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.59, + 0.892, + 0.607 + ], + "angle": 0, + "content": "4.2. Comparison with the State-of-the-Art Methods" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.613, + 0.892, + 0.765 + ], + "angle": 0, + "content": "Following SPAN [22] and ObjectFormer [46], our model is compared with other state-of-the-art tampering localization methods under two settings: 1) training on the synthetic dataset and evaluating on the full test datasets, and 2) fine-tuning the pre-trained model on the training split of test datasets and evaluating on their test split. The pretrained model will demonstrate each method's generalizability, and the fine-tuned model will demonstrate how well each method performs locally once the domain discrepancy has been significantly reduced." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.892, + 0.902 + ], + "angle": 0, + "content": "Pre-trained Model Table 1 shows the localization performance of pre-trained models for different methods on four standard datasets under pixel-level AUC. We compare our model ERMPC with MantraNet [55], SPAN [22], PSCCNet [35], and ObjectFormer [46] when evaluating pre-trained models. The pre-trained ERMPC achieves the best localization performance on Coverage, CASIA, NIST16 and IMD20, and ranks second on Columbia. Especially, ERMPC achieves \\(94.4\\%\\) on the copy-move dataset" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "8227" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.138, + 0.089, + 0.833, + 0.445 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.455, + 0.895, + 0.484 + ], + "angle": 0, + "content": "Figure 4. Visualization of the predicted manipulation mask by different methods. From top to bottom, we show forged images, GT masks, predictions of ManTraNet, SPAN, PSCC-Net, and ours." + }, + { + "type": "table", + "bbox": [ + 0.124, + 0.495, + 0.426, + 0.613 + ], + "angle": 0, + "content": "
VariantsCASIANIST16
AUCF1AUCF1
Baseline71.638.377.152.6
w/o RMPC76.945.686.460.7
w/o CEG85.151.593.475.3
w/o TDB88.657.398.281.9
Ours90.458.699.783.6
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.623, + 0.47, + 0.652 + ], + "angle": 0, + "content": "Table 4. Ablation results on CASIA and NIST16 dataset using different variants of ERMPC. AUC and F1 scores \\((\\%)\\) are reported." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.671, + 0.47, + 0.852 + ], + "angle": 0, + "content": "COVER, whose image forgery regions are indistinguishable from the background. This validates our model owns the superior ability to control message passing between two regions(forged and authentic). We fail to achieve the best performance on Columbia, falling behind PSCCNet \\(1.4\\%\\) under AUC. We contend that the explanation may be that the distribution of their synthesized training data closely resembles that of the Columbia dataset. This is further supported by the results in Table 2, which show that ERMPC performs better than PSCCNet in terms of both AUC and F1 scores. Furthermore, it is important to note that ERMPC attains decent results with less pre-training data." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Fine-tuned Model The fine-tuned models, which are initiated with the network weights of the pretrained model, will be trained on the training split of Coverage, CASIA, and" + }, + { + "type": "image", + "bbox": [ + 0.536, + 0.515, + 0.843, + 0.675 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.565, + 0.688, + 0.827, + 0.703 + ], + "angle": 0, + "content": "Figure 5. The effect of parameter k in TDB" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.717, + 0.895, + 0.809 + ], + "angle": 0, + "content": "NIST16 datasets, respectively. We evaluate the fine-tuned models of different methods in Table 2. As for AUC and F1, our model achieves significant performance gains. This validates that ERMPC could capture subtle tampering artifacts by controlling the message passing between two regions (forged and authentic) in the feature map." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.817, + 0.714, + 0.832 + ], + "angle": 0, + "content": "4.3. Robustness Evaluation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.895, + 0.903 + ], + "angle": 0, + "content": "We degrade the raw manipulated images from NIST16 using the distortion settings in [46] to analyze the robustness of ERMPC for forgery localization. These distortions types include scaling images to various scales (Re" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "8228" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.081, + 0.089, + 0.157, + 0.279 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.159, + 0.09, + 0.235, + 0.28 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.236, + 0.09, + 0.313, + 0.279 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.314, + 0.09, + 0.389, + 0.279 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.391, + 0.09, + 0.468, + 0.279 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.29, + 0.47, + 0.332 + ], + "angle": 0, + "content": "Figure 6. Visualization of message passing controller. From left to right, we display the forged images, masks, GradCAM [42] of the feature map without (w/o) and with (w) RMPC, and predictions." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.355, + 0.47, + 0.536 + ], + "angle": 0, + "content": "size), applying Gaussian blur with a kernel size \\( k \\) (GaussianBlur), adding Gaussian noise with a standard deviation \\( \\sigma \\) (GaussianNoise), and performing JPEG compression with a quality factor \\( q \\) (JPEGCompress). We compare the forgery localization performance (AUC scores) of our pre-trained models with SPAN [22] and ObjectFormer on these corrupted data and report the results in Table 3. ERMPC demonstrates more resistance to various distortion techniques. It is worth noting that JPEG compression is commonly performed when uploading images to social media. Our model ERMPC performs significantly better on compressed images than other methods." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.546, + 0.25, + 0.563 + ], + "angle": 0, + "content": "4.4. Ablation Analysis" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.569, + 0.47, + 0.734 + ], + "angle": 0, + "content": "The Region Message Passing Controller (RMPC) module of our method ERMPC is designed to weaken the message passing between the forged and authentic regions. The Context-Enhanced Graph (CEG) encodes global information along the node to obtain a better edge probability map, while the Threshold-adaptive Differentiable Binarization (TDB) adaptively performs the binarization process for learnable edges. In order to evaluate the effectiveness of RMPC, CEG and TDB, we remove them separately from ERMPC and evaluate the forgery localization performance on CASIA and NIST16 datasets." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.735, + 0.469, + 0.854 + ], + "angle": 0, + "content": "Table 4 presents the quantitative outcomes. The baseline denotes that we just use ResNet-50. It can be seen that without TDB, the AUC scores decrease by \\(2.0\\%\\) on CASIA and \\(1.5\\%\\) on NIST16, while without CEG, the AUC scores decrease by \\(5.9\\%\\) on CASIA and \\(6.3\\%\\) on NIST16. Furthermore, when RMPC is discarded, serious performance degradation in Table 4, i.e., \\(14.9\\%\\) in terms of AUC and \\(22.2\\%\\) in terms of F1 on CASIA can be observed." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.469, + 0.901 + ], + "angle": 0, + "content": "In Figure 5, we show the different values of parameters \\( k \\) in threshold-adaptive differentiable binarization to verify its effect over three datasets. With its increasing, the curve" + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.09, + 0.581, + 0.224 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.582, + 0.09, + 0.659, + 0.224 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.66, + 0.09, + 0.735, + 0.224 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.736, + 0.09, + 0.812, + 0.224 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.813, + 0.09, + 0.892, + 0.224 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.236, + 0.892, + 0.278 + ], + "angle": 0, + "content": "Figure 7. Visualization of edge reconstruction. From left to right, we display the forged images, masks, the features without (w/o) and with (w) the edge reconstruction module, and prediction." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.301, + 0.892, + 0.362 + ], + "angle": 0, + "content": "of binarization becomes steeper. Moreover, being smaller is inadequate for weakening message passing, while being larger will destroy the adaptive capacity of the network. It is obvious that the setting of 500 is the optimal solution." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.371, + 0.697, + 0.385 + ], + "angle": 0, + "content": "4.5. Visualization Results" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.394, + 0.892, + 0.514 + ], + "angle": 0, + "content": "Qualitative results. As shown in Figure 4, We provide predicted forgery masks of various methods. Since the source code of ObjectFormer [46] is not available, their predictions are not available. The results demonstrate that our method could not only locate the tampering regions more accurately but also develop sharp boundaries. It benefits from the explicit modeling of inconsistencies and the full exploitation of edges by our method." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.515, + 0.892, + 0.621 + ], + "angle": 0, + "content": "Visualization of message passing controller. To verify the usefulness of the region message passing controller (RMPC), we show the change of features before and after the controller in Figure 6. It is clear that RMPC facilitates the learning of forgery features and prevents false alarms. Specifically, the network without RMPC will make false judgments about objects that are similar to the forgery." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.621, + 0.892, + 0.696 + ], + "angle": 0, + "content": "Visualization of edge reconstruction. To verify the effect of the edge reconstruction (ER) module, the change of features before and after EG is shown in Figure 7. The results demonstrate that the EG can effectively acquire accurate edges, thus helping our model to perform well." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.71, + 0.619, + 0.725 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.735, + 0.892, + 0.901 + ], + "angle": 0, + "content": "In this paper, we propose a novel Image Forgery Localization framework with a two-step Edge-aware Regional Message Passing Controlling strategy. In detail, the first step is to account for fully exploiting the edge information. In the second step, guided by the learnable edges, an edge-aware dynamic graph is devised to weaken the message passing between the forged and authentic regions. Our paper provides a new research strategy to solve the misjudgment problem in the field of IFL. 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Springer, 2023. 1" + }, + { + "type": "list", + "bbox": [ + 0.503, + 0.093, + 0.892, + 0.205 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.946, + 0.515, + 0.956 + ], + "angle": 0, + "content": "8232" + } + ] +] \ No newline at end of file diff --git a/2023/Edge-Aware Regional Message Passing Controller for Image Forgery Localization/c5c52750-0529-4615-bd1f-1262f32b5c87_origin.pdf b/2023/Edge-Aware Regional Message Passing Controller for Image Forgery Localization/c5c52750-0529-4615-bd1f-1262f32b5c87_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..2b2c1af34d972a171be1ca5e61b6b74c2f242bd8 --- /dev/null +++ b/2023/Edge-Aware Regional Message Passing Controller for Image Forgery Localization/c5c52750-0529-4615-bd1f-1262f32b5c87_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:63b8de276a1869d1ee1b8c518e6a4d283a2bcbe5ae1b28b6aecd026c7a234822 +size 2723343 diff --git a/2023/Edge-Aware Regional Message Passing Controller for Image Forgery Localization/full.md b/2023/Edge-Aware Regional Message Passing Controller for Image Forgery Localization/full.md new file mode 100644 index 0000000000000000000000000000000000000000..41fe560f0a06b76d567b47ddb0b83dfedb955975 --- /dev/null +++ b/2023/Edge-Aware Regional Message Passing Controller for Image Forgery Localization/full.md @@ -0,0 +1,344 @@ +# Edge-aware Regional Message Passing Controller for Image Forgery Localization + +Dong Li*, Jiaying Zhu*, Menglu Wang, Jiawei Liu†, Xueyang Fu, Zheng-Jun Zha University of Science and Technology of China, China + +{dongli6, zhujy53, vault}@mail.ustc.edu.cn, {jwliu6, xyfu, zhazj}@ustc.edu.cn + +# Abstract + +Digital image authenticity has promoted research on image forgery localization. Although deep learning-based methods achieve remarkable progress, most of them usually suffer from severe feature coupling between the forged and authentic regions. In this work, we propose a two-step Edge-aware Regional Message Passing Controlling strategy to address the above issue. Specifically, the first step is to account for fully exploiting the edge information. It consists of two core designs: context-enhanced graph construction and threshold-adaptive differentiable binarization edge algorithm. The former assembles the global semantic information to distinguish the features between the forged and authentic regions, while the latter stands on the output of the former to provide the learnable edges. In the second step, guided by the learnable edges, a region message passing controller is devised to weaken the message passing between the forged and authentic regions. In this way, our ERMPC is capable of explicitly modeling the inconsistency between the forged and authentic regions and enabling it to perform well on refined forged images. Extensive experiments on several challenging benchmarks show that our method is superior to state-of-the-art image forgery localization methods qualitatively and quantitatively. + +# 1. Introduction + +The forged or manipulated images pose risks in various fields, such as removing copyright watermarks, generating fake news, and even falsifying evidence in court [32]. The growing technology of forgery will cause a crisis of trust and affect social equity. Therefore, the detection of image forgery is of great significance. The crucial aspect + +![](images/8dc717825240b1d44aa64844e4d505e43c87fee348999bfc6dec9c4460596352.jpg) + +![](images/ab176ff3e62eaaa89f24af6f2c8e641eee1a9100591dbdaa492bf1b92ff9845c.jpg) +Figure 1. The difference between previous methods and ours. Our method controls the message passing between the forged and authentic regions, ignored by the previous method. As shown by $X$ . + +of the detection is to model the inconsistency between the forged and authentic regions and to locate the forged regions on the suspicious image, i.e., image forgery localization (IFL). However, as post-processing techniques such as GAN [16, 26, 63], VAE [27, 44] and homogeneous manipulation [7, 33] are wildly utilized, images can be easily tampered in a visually imperceptible way. These techniques constantly aim to couple the forged and authentic regions' features, making image forgery localization challenging. Therefore, in order to accurately locate the image forgery region, it is particularly essential to decouple the features between forged and authentic regions. + +In recent years, deep-learning techniques have attracted more attention [23, 57, 58, 65, 66]. Due to the development of deep learning, image forgery localization has achieved remarkable results. For example, ManTra-Net [55] treats the forgery localization problem as a local anomaly detection problem and proposes a novel long short-term memory solution to assess local anomalies. To discriminate between heterologous regions, SPAN employs CNNs to extract anomalous local noise features from noise maps. MVSS-Net [5] learns a multiview feature with multi-scale + +supervised networks to jointly exploit the noise view and the boundary artifacts. However, these methods do not decouple the features between the forged and authentic regions, making it difficult to locate the tampered regions for elaborately forged images accurately. As shown in Figure 1, in the previous method, the features of the forged region are coupled with some of the features of the authentic region, resulting in wrong localization. + +In this work, we propose a novel method to avoid feature coupling of the two regions (forged and authentic) for image forgery localization. One of the keys of this method is to construct a dynamic graph, where the edges between the forged and authentic regions participate in its construction. We control the message passing of regions inside and outside the edges (i.e., forged and authentic) by reconstructing the adjacency matrix of nodes inside and outside the edges, thus achieving effective disentanglement of the features between the forged and authentic regions. Based on its functionality, the edge-aware dynamic graph convolution is named the regional message passing controller (RMPC). + +In order to use the proposed RMPC for image forgery localization, it is necessary to obtain the edge information between the forged and authentic regions, which is the other key of this method. Therefore, an edge reconstruction (ER) module was developed, including a context-enhanced graph (CEG) and a threshold-adaptive differentiable binarization module. We specially design an adjacency matrix learner in the CEG, which encodes global information along the nodes to assemble the global semantic information. Inspired by the Sigmoid function, we develop the threshold-adaptive differentiable binarization edge algorithm, which stands on the output of the CEG to provide the learnable edges. + +In summary, in this work we propose a new two-step framework named Edge-aware Regional Message Passing Controller (ERMPC) for Image Forgery Localization, including RMPC and ER. The ERMPC could effectively control the message passing between the forged and authentic regions to achieve effective disentanglement of the two regions, thus boosting the performance of image forgery localization. We take edge information as the main task and use it as a basis to explicitly model the inconsistency between two regions. To the best of our knowledge, this work is the first attempt to explicitly weaken the message passing between the forged and authentic regions. Our contributions are as follows: + +- We propose ERMPC, a novel two-step coarse-to-fine framework for image forgery localization, explicitly modeling the inconsistency between the forged and authentic regions with edge information. +- We propose an edge-aware dynamic graph, also known as RMPC, to control the message passing between two regions (forged and authentic) in the feature map. + +- We develop an edge reconstruction module containing a context-enhanced graph and a threshold-adaptive differentiable binarization module to obtain the desired edge information. +- We conduct extensive experiments on multiple benchmarks and demonstrate that our method is qualitatively and quantitatively superior to state-of-the-art image forgery localization methods. + +# 2. Related Works + +# 2.1. Image Forgery Localization + +Most early works propose to localize a specific type of forgery, including splicing [2, 3, 9, 10, 24, 28, 37, 51, 60], copy-move [8, 14, 25, 48, 52, 54], and removal [1, 50, 56, 64]. While these methods demonstrate satisfactory performance in detecting specific types of forgery, they exhibit limitations in practical applications due to the prevalence of unknown and diverse forgery types. Consequently, recent studies have emphasized the need for an approach to tackle multiple forgery types with one model. RGBN [62] proposes a dual-stream Faster R-CNN network. The first stream is designed to extract RGB features and identify tampering artifacts, while the second stream utilizes noise features to model the noise inconsistency between tampered and authentic regions, thereby localizing image forgery with enhanced accuracy. ManTra-net [55] is an end-to-end network that performs both detection and localization, which treats the problem as anomaly detection and introduces a long short-term memory solution to assess local anomalies. SPAN [22] attempts to model the spatial correlation by constructing a pyramid of local self-attention blocks. MVSS-Net [5] has designed an edge-supervised branch that uses edge residual blocks to capture fine-grained boundary detail in a shallow to deep manner. It is worth noting that edge information is important for image forgery detection and localization, as the tampered regions are commonly surrounded by unnatural artifacts. Nevertheless, most studies only utilize edges in a supervised strategy, such as MVSS-Net [5], MFCN [41], GSR-Net [61], and CAIFL [47]. PSCCNet [35] uses a progressive spatial-channel correlation module that uses features at different scales and dense cross-connections to generate operational masks in a coarse-to-fine fashion. ObjectFormer [46] captures forgery traces by extracting high-frequency parts of the image and combining them with RGB features. In this work, we explicitly employ learnable edges as guiding information to impede the message passing between the forged and untouched regions and employ refined edge reconstruction to achieve inconsistent modeling of the two regions to localize manipulation artifacts. + +![](images/ba984eabd3d397b6adb4d6708b9d7a65875f0767e5428c8d4145c71a8a7c37d9.jpg) +Figure 2. An overview of the proposed framework ERMPC. The input is a suspicious image $(H\times W\times 3)$ , and the output is a predicted mask $(\mathrm{H}\times \mathrm{W}\times 1)$ , which localizes the forged regions. + +# 2.2. Graph Reasoning + +Graph-based approaches have attracted growing attention from the computer vision community these days and have shown to be an effective relational reasoning method with a robust capacity for non-local feature aggregation. Specifically, CDGCNet [21] utilizes a class-wise learning strategy and designs a class-wise graph convolution, which avoids heavy graph concatenation and facilitates feature learning. To overcome the problem that most graph-based approaches assign a fixed number of neighbors for each query item, DAGL [39] proposes a dynamic attentive graph learning model to explore the dynamic non-local property for image restoration. CTL [34] learns a context-reinforced topology to construct multi-scale graphs which have a robust representational capacity by considering both global contextual information and physical connections of the human body. On other tasks in computer vision, e.g., object detection [43], multi-label image recognition [6], and skeleton-based action recognition [36, 59], graph convolutional neural networks have also achieved impressive performance. In contrast, we propose an improved edge-guided graph attention model to obstruct the message passing between forged and untouched regions with dynamic + +construction for forgery region localization. As graph convolution is an effective relational reasoning method that is very suitable for detecting forgery traces, this paper applies it to the task of image forgery localization for the first time. An improved edge-guided graph attention model is proposed for forgery region localization, which obstructs the message passing between forged and untouched regions with dynamic construction. + +# 3. Methodology + +This section details the scheme of image forgery localization based on edge-aware message passing control. Sec. 3.1 describes an overview of the framework. One of the keys of the scheme is to control the message passing with edge and thus model the inconsistency between the forged and authentic regions (Sec. 3.2). Another key lies in reconstructing accurate edges from coarse features (Sec. 3.3). In addition, following [5, 22, 55, 62], we use the noise branch and fuse it with RGB branch at the end of the network (Sec. 3.4). The optimization is introduced in Sec. 3.5. + +# 3.1. Overview + +Figure 2 is an overview of the framework. The input image is represented as $X \in \mathbb{R}^{H \times W \times 3}$ , where H and W represent the height and width of the image. First, we use two branches to handle RGB and noise separately, obtaining $G_{r} \in \mathbb{R}^{H_{s} \times W_{s} \times C_{s}}$ and $G_{n} \in \mathbb{R}^{H_{s} \times W_{s} \times C_{s}}$ respectively. Then, we use ResNet-50 pretrained on ImageNet [11] as the backbone network. Following [4], we adopt atrous spatial pyramid pooling(ASPP) together with ResNet-50 to capture the long-range contextual information. The coarse features extracted from RGB branches are converted into edges through the edge reconstruction block. Meanwhile, the coarse features are constructed as graph structures, guided by the reconstructed edge information. Finally, the RGB features after the graph convolutional network are fused with noise information through dual attention [5] to output the predicted forgery localization map. + +# 3.2. Region Message Passing Controller + +Most forged images are carefully processed to hide tampering artifacts, making it challenging to model inconsistencies in the RGB branch. To overcome this problem, the edges between the forged and authentic regions are utilized to control the message passing explicitly. + +The edge feature $G_{e} \in \mathbb{R}^{H_{e} \times W_{e} \times 1}$ comes from the edge reconstruction block (described in detail in the next subsection), where $H_{e} = H_{s}$ and $W_{e} = W_{s}$ . First, we calculate the relationship between two node features $P_{i}, P_{j}$ of the $G_{E}$ using an algorithm similar to XNOR gate: + +$$ +\mathrm {X N} \left(P _ {i}, P _ {j}\right) = \left\{ \begin{array}{l l} 0 & \text {I n s i d e a n d o u t s i d e t h e e d g e s} \\ 1 & \text {O n t h e s a m e s i d e o f e d g e s .} \end{array} \right. \tag {1} +$$ + +If two nodes are inside and outside the edge respectively, then their XN is set to 0. For each of the N ( $N = H_{e} \times W_{e}$ ) nodes features, we calculate its XN, thus generating a matrix $A_{e} \in \mathbb{R}^{N \times N}$ . + +Next, we apply graph learning to process the $G_{r} \in \mathbb{R}^{H_{s} \times W_{s} \times C_{s}}$ . Following GAT [45], we calculate the similarity between two nodes as attention coefficients: + +$$ +\alpha_ {i, j} = \psi (x _ {i}) ^ {T} \psi^ {\prime} (x _ {j}), \tag {2} +$$ + +where $\psi, \psi'$ denotes two learnable linear transformations. Specifically, we utilize $\psi = Wx$ and $\psi' = W'x$ , where $W \in \mathbb{R}^{C_s \times C_s}$ and $W' \in \mathbb{R}^{C_s \times C_s}$ are both weight matrices. To make coefficients easier to compare across different nodes, we normalize them using the softmax function: + +$$ +A _ {r _ {i, j}} = \frac {\exp (\alpha_ {i , j})}{\sum_ {j = 1} ^ {N} \exp (\alpha_ {i , j})}, \tag {3} +$$ + +where $A_r \in \mathbb{R}^{N \times N}$ is the preliminary adjacency matrix. It reflects the relationship between any two nodes in the fea + +ture map. Larger values represent a greater flow of information between two nodes. In order to realize message passing control better, a method of dynamically adjusting the adjacency matrix is adopted. Specifically, if two nodes are on and off the boundary respectively, their adjacency is broken due to the dynamic adjustment of the adjacency matrix. In practice, the adjacency matrix is recalculated as follows: + +$$ +A _ {r} ^ {\prime} = A _ {r} \odot A _ {e}, \tag {4} +$$ + +where $\odot$ is the Hadamard product. $A_r' \in \mathbb{R}^{N \times N}$ re-models the weights between nodes in the feature map and severs the connections between the forged and real regions. + +Once the adjacency matrix is obtained, it is weighted by the learnable attention weights. Then the original nodes are updated with the following: + +$$ +Z _ {r} = \operatorname {R e L U} \left(A _ {r} ^ {\prime} G _ {r} ^ {\prime} W _ {z}\right), \tag {5} +$$ + +where $Z_{r}\in \mathbb{R}^{N\times C_{s}}$ is RGB features after graph reasoning, $W_{z}\in \mathbb{R}^{C_{s}\times C_{s}}$ is the learnable parameter and $G_r^\prime \in \mathbb{R}^{N\times C_s}$ is the graph representation transformed by $G_{r}$ + +It is worth noting that this work not only introduces the idea of controlling the message passing in image forgery localization for the first time, but also the approach implemented is different from previous research [12, 20]. BFP [12] uses directed acyclic graphs (DAG) for feature propagation and introduces boundary information into the propagation to control the message passing between different segments. However, it has to scan the image pixel by pixel and requires a lot of loops, causing it difficult to implement in real-world applications. BGC [20] emphasizes reducing the weights of the edges and does not really focus on the message passing between regions. + +# 3.3. Edge Reconstruction + +As described in the previous section, the Edge-aware Message Passing Control Graph requires accurate edge information. Designing such an edge-access network is nontrivial. The main challenge is how to learn edge information from the coarse feature. To this end, a novel approach to edge reconstruction is proposed. Specifically, we started by using the Sobel layer [5] to enhance the edge-related patterns in $G_{r} \in \mathbb{R}^{H_{s} \times W_{s} \times C_{s}}$ , + +$$ +G _ {c} = G _ {r} \odot \sigma (\text {N o r m} (S o b e l \left(G _ {r}\right)), \tag {6} +$$ + +where Norm is L2 Normalization, $\sigma$ is Sigmoid and Sobel is the SobelConv [5]. + +Then, we explore a Context-Enhanced Graph (CEG), extracting the local and global features separately for $G_{c} \in \mathbb{R}^{H_{s} \times W_{s} \times C_{s}}$ . Specifically, the local information is extracted by the convolutional layers [5]. For global information, the contextual information of the feature map is encoded as the adjacency matrix $A_{c} \in \mathbb{R}^{N \times N}$ in a simple and + +![](images/8b02f169471b7653d2c5f6677654f87c42502f3fb2a9e1c10ebfeddd9162723b.jpg) +Figure 3. Context-Enhanced Graph. Global features are extracted by the specific graph, while local features by the ResBlock. + +efficient way. As shown in Figure 3, $A_{c}$ is generated by a specially designed adjacency matrix learner which consists of two $1 \times 1$ convolution layers. The process is written as + +$$ +A _ {c} = \operatorname {N o r m} \left(\operatorname {C o n v} \left(\operatorname {C o n v} \left(\mathrm {G} _ {\mathrm {c}} ^ {\prime}\right)\right)\right), \tag {7} +$$ + +where $G_c' \in \mathbb{R}^{N \times C_s}$ is reshaped by $G_c$ . Given the node features of $G_c'$ , we first squeeze the feature dimensions by a $1 \times 1$ convolution layer. Then, another convolution layer with $1 \times 1$ kernel is used to transfer the N-dimension feature vector into the $N \times N$ adjacency matrix. In addition, L2 Normalization is applied to each row of $A_c$ to facilitate stable optimization. Next, we use this adjacency matrix to complete the graph reasoning. In this way, we can obtain a global feature map. The process can be written as + +$$ +\operatorname {G l o b a l} \left(G _ {c} ^ {\prime}\right) = A _ {c} G _ {c} ^ {\prime} W _ {c}, \tag {8} +$$ + +where $W_{c}\in \mathbb{R}^{C_{s}\times C_{s}}$ is the learnable parameter. To match with the local information dimension, we reshape Global $(G_c^{\prime})\in \mathbb{R}^{N\times C_s}$ back to Global' $(G_c^\prime)\in$ $\mathbb{R}^{H_s\times W_s\times C_s}$ . Then combining the local and global information, we can obtain the edge probability map $G_{p}\in$ $\mathbb{R}^{H_s\times W_s\times 1}$ .. + +$$ +G _ {p} = \sigma \left(\mathcal {C} \left(\operatorname {C a t} \left(\operatorname {L o c a l} \left(G _ {c}\right), \operatorname {G l o b a l} ^ {\prime} \left(G _ {c} ^ {\prime}\right)\right)\right)\right), \tag {9} +$$ + +where $\sigma$ denotes the Sigmoid, $\mathcal{C}$ is a $1\times 1$ convolution layer, and Local contains ReLU and two convolutional layers. + +Furthermore, in order to determine the edges, a threshold needs to be determined to binarize the probability map. Most previous studies have used fixed thresholds, and the process is non-differentiable. Inspired by [30], we utilize a variable threshold map which is adaptive for each point on the probability map $G_{p}$ . Besides, we propose a variant of the Sigmoid function to complete the binarization, which is capable of participating in the backpropagation involved. Binarize threshold adjustment is achieved by translating the + +Sigmoid function along the x-axis. Therefore, we explore the threshold-adaptive differentiable binarization (TDB) for edge reconstruction. It is computed as follows: + +$$ +G _ {e} = \frac {1}{1 + e ^ {- k \left(G _ {p} - \tau \left(G _ {p}\right)\right)}}, \tag {10} +$$ + +where $\tau$ denotes the learnable transformation, which in practice is $3\times 3$ convolution operators, and $k$ is the amplifying factor. In particular, $k$ is set to 500 empirically. + +# 3.4. Branch Fusion + +Following most studies [5,22,55,62], we also employ the noise branch. However, this is not the focus of this work, so we have used some common methods. As in Figure 2, the noise is extracted with BayarConv [55]. For the fusion of the two branches, we follow [5] and adopt the Dual Attention (DA) [15]. DA includes channel attention module (CAM) and position attention module (PAM). It can effectively fuse two branches. The process can be written as + +$$ +G _ {o} = \mathrm {D A} \left(G _ {z}, G _ {n}\right), \tag {11} +$$ + +where $G_{z} \in \mathbb{R}^{H_{s} \times W_{s} \times C_{s}}$ is reshaped by the $Z_{r}$ . Finally, we transform $G_{o} \in \mathbb{R}^{H_{s} \times W_{s} \times 1}$ with bilinear upsampling into the final predicted mask $G_{out} \in \mathbb{R}^{H \times W \times 1}$ . + +# 3.5. Optimization + +As shown in Figure 2, we calculate the loss function for three components: the final prediction $G_{out} \in \mathbb{R}^{H \times W \times 1}$ , the binary edge prediction $G_e \in \mathbb{R}^{H_e \times W_e \times 1}$ and the edge probability map $G_p \in \mathbb{R}^{H_e \times W_e \times 1}$ . For edge loss, the ground-truth edge $E \in \mathbb{R}^{H \times W \times 1}$ is downsampled to a smaller size $E' \in \mathbb{R}^{H_e \times W_e \times 1}$ to match $G_e$ , $G_p$ . This strategy outperforms upsampling $G_e$ , $G_p$ in terms of computational cost and performance. The overall loss function can be written as: + +$$ +\mathbf {L} = \lambda_ {1} \mathcal {L} \left(\mathrm {Y}, \mathrm {G} _ {\text {o u t}}\right) + \lambda_ {2} \mathcal {L} \left(\mathrm {E} ^ {\prime}, \mathrm {G} _ {\mathrm {e}}\right) + \lambda_ {3} \mathcal {L} \left(\mathrm {E} ^ {\prime}, \mathrm {G} _ {\mathrm {p}}\right), \tag {12} +$$ + +where $\mathcal{L}$ denotes the Dice loss [5], $Y\in \mathbb{R}^{H\times W\times 1}$ is the ground-truth mask, and $\lambda_1,\lambda_2,\lambda_3$ are the parameters to balance the three terms in loss function $(\lambda_{1} + \lambda_{2} + \lambda_{3} = 1)$ . In our setting, they are set as 0.50, 0.25 and 0.25 respectively. + +# 4. Experiments + +# 4.1. Experimental Setup + +Pre-training Data We create a sizable image tampering dataset and use it to pre-train our model. This dataset includes three categories: 1) splicing, 2) copy-move, 3) removal. For splicing, we use the MS COCO [31] to generate spliced images, where one annotated region is randomly selected per image and pasted into a different image after several transformations. We use the same transformation as [5], + +
MethodDataColumbiaCoverageCASIANIST16IMD20
ManTraNet64K82.481.981.779.574.8
SPAN96k93.692.279.784.075.0
PSCCNet100k98.284.782.985.580.6
ObjectFormer62K95.592.884.387.282.1
Ours60K96.894.487.689.585.6
+ +including the scale, rotation, shift, and luminance changes. Since the spliced region is not always an object, we create random outlines using the Bezier curve [38] and fill them to create splicing masks. For copy-move, the datasets from MS COCO and [53] are adopted. For removal, we adopt the SOTA inpainting method [29] to fill one annotated region that is randomly removed from each chosen MS COCO image. We randomly add Gaussian noise or apply the JPEG compression algorithm to the generated data to resemble the visual quality of images in real situations. + +Testing Datasets Following [46], we evaluate our model on CASIA [13] dataset, Coverage [49] dataset, Columbia [19] dataset, NIST16 [17] dataset and IMD20 [40] dataset. Specifically, CASIA [13], which contains two types of tampered images (splicing and copy-move), is widely used in the image forgery field. The database V1.0 has fixed size tampered images, which are generated only by using crop-and-paste operation under Adobe Photoshop. The database v2.0 is more comprehensive and challenging, and most tampered examples are generated with post-processing. COVER [49] provides 100 images, and all of them are generated by copy-move tampering technique. Columbia [19] consists of 180 splicing images, whose size ranges from $757 \times 568$ to $1152 \times 568$ . In detail, the tampered images in Columbia are all uncompressed and without any post-processing. NIST16 [17] is a high-quality dataset. This dataset contains three types of tampering, and some regions of manipulation are difficult for humans to identify. IMD20 [40] collects real-life manipulated images from the Internet, and involves all three manipulations as well. We apply the same training/testing splits as [22, 46, 62] to fine-tune our model for fair comparisons. + +Evaluation Metrics To quantify the localization performance, following previous works [22, 46], we use pixel-level Area Under Curve (AUC) and F1 score on manipulation masks. And we adopt the Equal Error Rate (EER) threshold to binarize masks because binary masks are necessary to calculate F1 scores. + +Implementation Details The input images are resized to $512 \times 512$ . In this work, the backbone is ResNet-50 [18], pre-trained on ImageNet [11]. Implemented by PyTorch, our model is trained with GeForce GTX 3090. We use + +Table 1. Comparisons of manipulation localization AUC (%) scores of different pre-trained models. + +
MethodsCoverageCASIANIST16
AUCF1AUCF1AUCF1
J-LSTM61.4---76.4-
H-LSTM71.2---79.4-
RGB-N81.743.779.540.893.772.2
SPAN93.755.883.838.296.158.2
PSCCNet94.172.387.555.499.174.2
ObjectFormer95.775.888.257.999.682.4
Ours98.477.390.458.699.783.6
+ +Table 2. Comparison of manipulation localization results using fine-tuned models. + +
DistortionSPANObjectFormerOurs
no distortion83.9587.1889.49
Resize(0.78×)83.2487.1789.33 0.16↓
Resize(0.25×)80.3286.3387.72 1.77↓
Blur(k=3)83.1085.9789.22 0.27↓
Blur(k=15)79.1580.2687.13 2.36↓
Noise(σ=3)75.1779.5888.25 1.24↓
Noise(σ=15)67.2878.1583.40 6.09↓
Compress(q=100)83.5986.3789.42 0.07↓
Compress(q=50)80.6886.2488.82 0.67↓
+ +Table 3. Localization performance on NIST16 dataset under various distortions. AUC scores are reported (in %), (Blur: Gaussian-Blur, Noise: GaussianNoise, Compress: JPEGCompress.) + +Adam as the optimizer, and the learning rate decays from $10^{-4}$ to $10^{-7}$ . We train 100 epochs with a batch size of 8, and the learning rate decays by 10 times every 30 epochs. + +# 4.2. Comparison with the State-of-the-Art Methods + +Following SPAN [22] and ObjectFormer [46], our model is compared with other state-of-the-art tampering localization methods under two settings: 1) training on the synthetic dataset and evaluating on the full test datasets, and 2) fine-tuning the pre-trained model on the training split of test datasets and evaluating on their test split. The pretrained model will demonstrate each method's generalizability, and the fine-tuned model will demonstrate how well each method performs locally once the domain discrepancy has been significantly reduced. + +Pre-trained Model Table 1 shows the localization performance of pre-trained models for different methods on four standard datasets under pixel-level AUC. We compare our model ERMPC with MantraNet [55], SPAN [22], PSCCNet [35], and ObjectFormer [46] when evaluating pre-trained models. The pre-trained ERMPC achieves the best localization performance on Coverage, CASIA, NIST16 and IMD20, and ranks second on Columbia. Especially, ERMPC achieves $94.4\%$ on the copy-move dataset + +![](images/9924f3f5a4344f8ff617c00235d4a4cf7656ef3eed06003b4d0621735fe143ec.jpg) +Figure 4. Visualization of the predicted manipulation mask by different methods. From top to bottom, we show forged images, GT masks, predictions of ManTraNet, SPAN, PSCC-Net, and ours. + +
VariantsCASIANIST16
AUCF1AUCF1
Baseline71.638.377.152.6
w/o RMPC76.945.686.460.7
w/o CEG85.151.593.475.3
w/o TDB88.657.398.281.9
Ours90.458.699.783.6
+ +Table 4. Ablation results on CASIA and NIST16 dataset using different variants of ERMPC. AUC and F1 scores $(\%)$ are reported. + +COVER, whose image forgery regions are indistinguishable from the background. This validates our model owns the superior ability to control message passing between two regions(forged and authentic). We fail to achieve the best performance on Columbia, falling behind PSCCNet $1.4\%$ under AUC. We contend that the explanation may be that the distribution of their synthesized training data closely resembles that of the Columbia dataset. This is further supported by the results in Table 2, which show that ERMPC performs better than PSCCNet in terms of both AUC and F1 scores. Furthermore, it is important to note that ERMPC attains decent results with less pre-training data. + +Fine-tuned Model The fine-tuned models, which are initiated with the network weights of the pretrained model, will be trained on the training split of Coverage, CASIA, and + +![](images/55343cc4a03e07b2b35355dc1a17b0048c35f1fb3d54ab01fe4d1dcf091255c3.jpg) +Figure 5. The effect of parameter k in TDB + +NIST16 datasets, respectively. We evaluate the fine-tuned models of different methods in Table 2. As for AUC and F1, our model achieves significant performance gains. This validates that ERMPC could capture subtle tampering artifacts by controlling the message passing between two regions (forged and authentic) in the feature map. + +# 4.3. Robustness Evaluation + +We degrade the raw manipulated images from NIST16 using the distortion settings in [46] to analyze the robustness of ERMPC for forgery localization. These distortions types include scaling images to various scales (Re + +![](images/5395b7a7779b3aa9fecfebe2010fcd6c38f13b557a08665f8611d1b4c428d44d.jpg) +Figure 6. Visualization of message passing controller. From left to right, we display the forged images, masks, GradCAM [42] of the feature map without (w/o) and with (w) RMPC, and predictions. + +![](images/d392d13aef3bffac3e6b74cd91af8d8ab5bb5a01931bf77099e737af33a04687.jpg) + +![](images/b901ea88b9e5cea5a330264cee2b2b6c13a381909080a697121a1c0a93b66a80.jpg) + +![](images/60c8fa84bfa117226ad1d3d46b8de3ac366684152fcf3f3c46094cbb205267b2.jpg) + +![](images/e5bba474ca424d4906559f018663504b6dc75cdc9289f612b2d5f15fc49edffd.jpg) +Figure 7. Visualization of edge reconstruction. From left to right, we display the forged images, masks, the features without (w/o) and with (w) the edge reconstruction module, and prediction. + +size), applying Gaussian blur with a kernel size $k$ (GaussianBlur), adding Gaussian noise with a standard deviation $\sigma$ (GaussianNoise), and performing JPEG compression with a quality factor $q$ (JPEGCompress). We compare the forgery localization performance (AUC scores) of our pre-trained models with SPAN [22] and ObjectFormer on these corrupted data and report the results in Table 3. ERMPC demonstrates more resistance to various distortion techniques. It is worth noting that JPEG compression is commonly performed when uploading images to social media. Our model ERMPC performs significantly better on compressed images than other methods. + +# 4.4. Ablation Analysis + +The Region Message Passing Controller (RMPC) module of our method ERMPC is designed to weaken the message passing between the forged and authentic regions. The Context-Enhanced Graph (CEG) encodes global information along the node to obtain a better edge probability map, while the Threshold-adaptive Differentiable Binarization (TDB) adaptively performs the binarization process for learnable edges. In order to evaluate the effectiveness of RMPC, CEG and TDB, we remove them separately from ERMPC and evaluate the forgery localization performance on CASIA and NIST16 datasets. + +Table 4 presents the quantitative outcomes. The baseline denotes that we just use ResNet-50. It can be seen that without TDB, the AUC scores decrease by $2.0\%$ on CASIA and $1.5\%$ on NIST16, while without CEG, the AUC scores decrease by $5.9\%$ on CASIA and $6.3\%$ on NIST16. Furthermore, when RMPC is discarded, serious performance degradation in Table 4, i.e., $14.9\%$ in terms of AUC and $22.2\%$ in terms of F1 on CASIA can be observed. + +In Figure 5, we show the different values of parameters $k$ in threshold-adaptive differentiable binarization to verify its effect over three datasets. With its increasing, the curve + +![](images/c440c55cc02b958c84f12ad7a8298234313ef108b88fa94a3cbbb1f86970bb41.jpg) + +![](images/237ca72180cfbc71adae202ee6c29ebd2c35637ae08f66909cd87323144b7845.jpg) + +![](images/cc251d1431e00b91b31451d1a6049f8dbb791af498e0c71985106b82f62930d8.jpg) + +![](images/fe3f7a6cf8ffe68a082603c89741f37670d82c9e50523b58ce6d04f68d152852.jpg) + +![](images/824322d2f217507f1e5c57c36d7b87a4d026f715526b6953d38b7481b9c03af2.jpg) + +of binarization becomes steeper. Moreover, being smaller is inadequate for weakening message passing, while being larger will destroy the adaptive capacity of the network. It is obvious that the setting of 500 is the optimal solution. + +# 4.5. Visualization Results + +Qualitative results. As shown in Figure 4, We provide predicted forgery masks of various methods. Since the source code of ObjectFormer [46] is not available, their predictions are not available. The results demonstrate that our method could not only locate the tampering regions more accurately but also develop sharp boundaries. It benefits from the explicit modeling of inconsistencies and the full exploitation of edges by our method. + +Visualization of message passing controller. To verify the usefulness of the region message passing controller (RMPC), we show the change of features before and after the controller in Figure 6. It is clear that RMPC facilitates the learning of forgery features and prevents false alarms. Specifically, the network without RMPC will make false judgments about objects that are similar to the forgery. + +Visualization of edge reconstruction. To verify the effect of the edge reconstruction (ER) module, the change of features before and after EG is shown in Figure 7. The results demonstrate that the EG can effectively acquire accurate edges, thus helping our model to perform well. + +# 5. Conclusion + +In this paper, we propose a novel Image Forgery Localization framework with a two-step Edge-aware Regional Message Passing Controlling strategy. In detail, the first step is to account for fully exploiting the edge information. In the second step, guided by the learnable edges, an edge-aware dynamic graph is devised to weaken the message passing between the forged and authentic regions. Our paper provides a new research strategy to solve the misjudgment problem in the field of IFL. Extensive experimental results on several benchmarks demonstrate the effectiveness of the proposed algorithm. + +# References + +[1] Mohammed Aloraini, Mehdi Sharifzadeh, and Dan Schonfeld. 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In Proceedings of the 30th ACM International Conference on Multimedia, page 6645-6654, 2022. 1 +[59] Xikun Zhang, Chang Xu, and Dacheng Tao. Context aware graph convolution for skeleton-based action recognition. In Proceedings of the IEEE/CVF conference on computer vision and pattern recognition, pages 14333–14342, 2020. 3 +[60] Yulan Zhang, Guopu Zhu, Ligang Wu, Sam Kwong, Hongli Zhang, and Yicong Zhou. Multi-task se-network for image splicing localization. IEEE Transactions on Circuits and Systems for Video Technology, 2021. 2 +[61] Peng Zhou, Bor-Chun Chen, Xintong Han, Mahyar Najibi, Abhinav Shrivastava, Ser-Nam Lim, and Larry Davis. Generate, segment, and refine: Towards generic manipulation segmentation. In Proceedings of the AAAI conference on artificial intelligence, volume 34, pages 13058-13065, 2020. 2 +[62] Peng Zhou, Xintong Han, Vlad I Morariu, and Larry S Davis. Learning rich features for image manipulation detection. In Proceedings of the IEEE conference on computer vision and pattern recognition, pages 1053-1061, 2018. 2, 3, 5, 6 +[63] Jun-Yan Zhu, Taesung Park, Phillip Isola, and Alexei A Efros. Unpaired image-to-image translation using cycle-consistent adversarial networks. In Proceedings of the IEEE international conference on computer vision, pages 2223-2232, 2017. 1 +[64] Xinshan Zhu, Yongjun Qian, Xianfeng Zhao, Biao Sun, and Ya Sun. A deep learning approach to patch-based image inpainting forensics. Signal Processing: Image Communication, 67:90-99, 2018. 2 + +[65] Yurui Zhu, Xueyang Fu, and Aiping Liu. Learning dual transformation networks for image contrast enhancement. IEEE Signal Processing Letters, 27:1999-2003, 2020. 1 +[66] Yurui Zhu, Xi Wang, Xueyang Fu, and Xiaowei Hu. Enhanced coarse-to-fine network for image restoration from under-display cameras. In Computer Vision-ECCV 2022 Workshops: Tel Aviv, Israel, October 23-27, 2022, Proceedings, Part V, pages 130-146. Springer, 2023. 1 \ No newline at end of file diff --git a/2023/Edge-Aware Regional Message Passing Controller for Image Forgery Localization/images.zip b/2023/Edge-Aware Regional Message Passing Controller for Image Forgery Localization/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..e34362c771bd2ff377568f55ff101a3e5fa2b101 --- /dev/null +++ b/2023/Edge-Aware Regional Message Passing Controller for Image Forgery Localization/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:1d3cd8206e0282d4271edf28a787ae04d5fc5ed558d9f2a37059afd81a5743e3 +size 551241 diff --git a/2023/Edge-Aware Regional Message Passing Controller for Image Forgery Localization/layout.json b/2023/Edge-Aware Regional Message Passing Controller for Image Forgery Localization/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..f6125b0aa3ce50fe092158c6574cd80a571eefef --- /dev/null +++ b/2023/Edge-Aware Regional Message Passing Controller for Image Forgery Localization/layout.json @@ -0,0 +1,9155 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 133, + 103, + 462, + 140 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 133, + 103, + 462, + 140 + ], + "spans": [ + { + "bbox": [ + 133, + 103, + 462, + 140 + ], + "type": "text", + "content": "Edge-aware Regional Message Passing Controller for Image Forgery Localization" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 97, + 161, + 495, + 190 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 97, + 161, + 495, + 190 + ], + "spans": [ + { + "bbox": [ + 97, + 161, + 495, + 190 + ], + "type": "text", + "content": "Dong Li*, Jiaying Zhu*, Menglu Wang, Jiawei Liu†, Xueyang Fu, Zheng-Jun Zha University of Science and Technology of China, China" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 88, + 191, + 502, + 205 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 88, + 191, + 502, + 205 + ], + "spans": [ + { + "bbox": [ + 88, + 191, + 502, + 205 + ], + "type": "text", + "content": "{dongli6, zhujy53, vault}@mail.ustc.edu.cn, {jwliu6, xyfu, zhazj}@ustc.edu.cn" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 143, + 231, + 192, + 243 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 231, + 192, + 243 + ], + "spans": [ + { + "bbox": [ + 143, + 231, + 192, + 243 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 256, + 290, + 533 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 256, + 290, + 533 + ], + "spans": [ + { + "bbox": [ + 46, + 256, + 290, + 533 + ], + "type": "text", + "content": "Digital image authenticity has promoted research on image forgery localization. Although deep learning-based methods achieve remarkable progress, most of them usually suffer from severe feature coupling between the forged and authentic regions. In this work, we propose a two-step Edge-aware Regional Message Passing Controlling strategy to address the above issue. Specifically, the first step is to account for fully exploiting the edge information. It consists of two core designs: context-enhanced graph construction and threshold-adaptive differentiable binarization edge algorithm. The former assembles the global semantic information to distinguish the features between the forged and authentic regions, while the latter stands on the output of the former to provide the learnable edges. In the second step, guided by the learnable edges, a region message passing controller is devised to weaken the message passing between the forged and authentic regions. In this way, our ERMPC is capable of explicitly modeling the inconsistency between the forged and authentic regions and enabling it to perform well on refined forged images. Extensive experiments on several challenging benchmarks show that our method is superior to state-of-the-art image forgery localization methods qualitatively and quantitatively." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 555, + 128, + 567 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 555, + 128, + 567 + ], + "spans": [ + { + "bbox": [ + 47, + 555, + 128, + 567 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 574, + 287, + 648 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 574, + 287, + 648 + ], + "spans": [ + { + "bbox": [ + 46, + 574, + 287, + 648 + ], + "type": "text", + "content": "The forged or manipulated images pose risks in various fields, such as removing copyright watermarks, generating fake news, and even falsifying evidence in court [32]. The growing technology of forgery will cause a crisis of trust and affect social equity. Therefore, the detection of image forgery is of great significance. The crucial aspect" + } + ] + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 307, + 230, + 545, + 312 + ], + "blocks": [ + { + "bbox": [ + 307, + 230, + 545, + 312 + ], + "lines": [ + { + "bbox": [ + 307, + 230, + 545, + 312 + ], + "spans": [ + { + "bbox": [ + 307, + 230, + 545, + 312 + ], + "type": "image", + "image_path": "8dc717825240b1d44aa64844e4d505e43c87fee348999bfc6dec9c4460596352.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 307, + 314, + 545, + 396 + ], + "blocks": [ + { + "bbox": [ + 307, + 314, + 545, + 396 + ], + "lines": [ + { + "bbox": [ + 307, + 314, + 545, + 396 + ], + "spans": [ + { + "bbox": [ + 307, + 314, + 545, + 396 + ], + "type": "image", + "image_path": "ab176ff3e62eaaa89f24af6f2c8e641eee1a9100591dbdaa492bf1b92ff9845c.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 403, + 547, + 437 + ], + "lines": [ + { + "bbox": [ + 305, + 403, + 547, + 437 + ], + "spans": [ + { + "bbox": [ + 305, + 403, + 547, + 437 + ], + "type": "text", + "content": "Figure 1. The difference between previous methods and ours. Our method controls the message passing between the forged and authentic regions, ignored by the previous method. As shown by " + }, + { + "bbox": [ + 305, + 403, + 547, + 437 + ], + "type": "inline_equation", + "content": "X" + }, + { + "bbox": [ + 305, + 403, + 547, + 437 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 449, + 545, + 593 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 449, + 545, + 593 + ], + "spans": [ + { + "bbox": [ + 304, + 449, + 545, + 593 + ], + "type": "text", + "content": "of the detection is to model the inconsistency between the forged and authentic regions and to locate the forged regions on the suspicious image, i.e., image forgery localization (IFL). However, as post-processing techniques such as GAN [16, 26, 63], VAE [27, 44] and homogeneous manipulation [7, 33] are wildly utilized, images can be easily tampered in a visually imperceptible way. These techniques constantly aim to couple the forged and authentic regions' features, making image forgery localization challenging. Therefore, in order to accurately locate the image forgery region, it is particularly essential to decouple the features between forged and authentic regions." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 594, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 594, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 594, + 547, + 713 + ], + "type": "text", + "content": "In recent years, deep-learning techniques have attracted more attention [23, 57, 58, 65, 66]. Due to the development of deep learning, image forgery localization has achieved remarkable results. For example, ManTra-Net [55] treats the forgery localization problem as a local anomaly detection problem and proposes a novel long short-term memory solution to assess local anomalies. To discriminate between heterologous regions, SPAN employs CNNs to extract anomalous local noise features from noise maps. MVSS-Net [5] learns a multiview feature with multi-scale" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 496, + 35 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 496, + 35 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 496, + 35 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 654, + 287, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 654, + 287, + 712 + ], + "spans": [ + { + "bbox": [ + 46, + 654, + 287, + 712 + ], + "type": "text", + "content": "* Co-first authors contributed equally, † corresponding author. This work was supported by the National Key R&D Program of China under Grant 2020AAA0105702, the National Natural Science Foundation of China (NSFC) under Grants 62225207, 62276243, 62106245 and U19B2038, the University Synergy Innovation Program of Anhui Province under Grant GXXT-2019-025." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "8222" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 167 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 167 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 167 + ], + "type": "text", + "content": "supervised networks to jointly exploit the noise view and the boundary artifacts. However, these methods do not decouple the features between the forged and authentic regions, making it difficult to locate the tampered regions for elaborately forged images accurately. As shown in Figure 1, in the previous method, the features of the forged region are coupled with some of the features of the authentic region, resulting in wrong localization." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 168, + 287, + 312 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 168, + 287, + 312 + ], + "spans": [ + { + "bbox": [ + 46, + 168, + 287, + 312 + ], + "type": "text", + "content": "In this work, we propose a novel method to avoid feature coupling of the two regions (forged and authentic) for image forgery localization. One of the keys of this method is to construct a dynamic graph, where the edges between the forged and authentic regions participate in its construction. We control the message passing of regions inside and outside the edges (i.e., forged and authentic) by reconstructing the adjacency matrix of nodes inside and outside the edges, thus achieving effective disentanglement of the features between the forged and authentic regions. Based on its functionality, the edge-aware dynamic graph convolution is named the regional message passing controller (RMPC)." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 312, + 287, + 455 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 312, + 287, + 455 + ], + "spans": [ + { + "bbox": [ + 46, + 312, + 287, + 455 + ], + "type": "text", + "content": "In order to use the proposed RMPC for image forgery localization, it is necessary to obtain the edge information between the forged and authentic regions, which is the other key of this method. Therefore, an edge reconstruction (ER) module was developed, including a context-enhanced graph (CEG) and a threshold-adaptive differentiable binarization module. We specially design an adjacency matrix learner in the CEG, which encodes global information along the nodes to assemble the global semantic information. Inspired by the Sigmoid function, we develop the threshold-adaptive differentiable binarization edge algorithm, which stands on the output of the CEG to provide the learnable edges." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 456, + 287, + 610 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 456, + 287, + 610 + ], + "spans": [ + { + "bbox": [ + 46, + 456, + 287, + 610 + ], + "type": "text", + "content": "In summary, in this work we propose a new two-step framework named Edge-aware Regional Message Passing Controller (ERMPC) for Image Forgery Localization, including RMPC and ER. The ERMPC could effectively control the message passing between the forged and authentic regions to achieve effective disentanglement of the two regions, thus boosting the performance of image forgery localization. We take edge information as the main task and use it as a basis to explicitly model the inconsistency between two regions. To the best of our knowledge, this work is the first attempt to explicitly weaken the message passing between the forged and authentic regions. Our contributions are as follows:" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 59, + 621, + 286, + 713 + ], + "type": "list", + "angle": 0, + "index": 6, + "blocks": [ + { + "bbox": [ + 59, + 621, + 286, + 668 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 621, + 286, + 668 + ], + "spans": [ + { + "bbox": [ + 59, + 621, + 286, + 668 + ], + "type": "text", + "content": "- We propose ERMPC, a novel two-step coarse-to-fine framework for image forgery localization, explicitly modeling the inconsistency between the forged and authentic regions with edge information." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 59, + 677, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 677, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 59, + 677, + 286, + 713 + ], + "type": "text", + "content": "- We propose an edge-aware dynamic graph, also known as RMPC, to control the message passing between two regions (forged and authentic) in the feature map." + } + ] + } + ], + "index": 5 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 317, + 72, + 544, + 179 + ], + "type": "list", + "angle": 0, + "index": 9, + "blocks": [ + { + "bbox": [ + 317, + 72, + 544, + 119 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 72, + 544, + 119 + ], + "spans": [ + { + "bbox": [ + 317, + 72, + 544, + 119 + ], + "type": "text", + "content": "- We develop an edge reconstruction module containing a context-enhanced graph and a threshold-adaptive differentiable binarization module to obtain the desired edge information." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 317, + 132, + 544, + 179 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 132, + 544, + 179 + ], + "spans": [ + { + "bbox": [ + 317, + 132, + 544, + 179 + ], + "type": "text", + "content": "- We conduct extensive experiments on multiple benchmarks and demonstrate that our method is qualitatively and quantitatively superior to state-of-the-art image forgery localization methods." + } + ] + } + ], + "index": 8 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 306, + 207, + 397, + 220 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 207, + 397, + 220 + ], + "spans": [ + { + "bbox": [ + 306, + 207, + 397, + 220 + ], + "type": "text", + "content": "2. Related Works" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 228, + 459, + 240 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 228, + 459, + 240 + ], + "spans": [ + { + "bbox": [ + 306, + 228, + 459, + 240 + ], + "type": "text", + "content": "2.1. Image Forgery Localization" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 247, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 247, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 247, + 545, + 713 + ], + "type": "text", + "content": "Most early works propose to localize a specific type of forgery, including splicing [2, 3, 9, 10, 24, 28, 37, 51, 60], copy-move [8, 14, 25, 48, 52, 54], and removal [1, 50, 56, 64]. While these methods demonstrate satisfactory performance in detecting specific types of forgery, they exhibit limitations in practical applications due to the prevalence of unknown and diverse forgery types. Consequently, recent studies have emphasized the need for an approach to tackle multiple forgery types with one model. RGBN [62] proposes a dual-stream Faster R-CNN network. The first stream is designed to extract RGB features and identify tampering artifacts, while the second stream utilizes noise features to model the noise inconsistency between tampered and authentic regions, thereby localizing image forgery with enhanced accuracy. ManTra-net [55] is an end-to-end network that performs both detection and localization, which treats the problem as anomaly detection and introduces a long short-term memory solution to assess local anomalies. SPAN [22] attempts to model the spatial correlation by constructing a pyramid of local self-attention blocks. MVSS-Net [5] has designed an edge-supervised branch that uses edge residual blocks to capture fine-grained boundary detail in a shallow to deep manner. It is worth noting that edge information is important for image forgery detection and localization, as the tampered regions are commonly surrounded by unnatural artifacts. Nevertheless, most studies only utilize edges in a supervised strategy, such as MVSS-Net [5], MFCN [41], GSR-Net [61], and CAIFL [47]. PSCCNet [35] uses a progressive spatial-channel correlation module that uses features at different scales and dense cross-connections to generate operational masks in a coarse-to-fine fashion. ObjectFormer [46] captures forgery traces by extracting high-frequency parts of the image and combining them with RGB features. In this work, we explicitly employ learnable edges as guiding information to impede the message passing between the forged and untouched regions and employ refined edge reconstruction to achieve inconsistent modeling of the two regions to localize manipulation artifacts." + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "8223" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 50, + 73, + 545, + 379 + ], + "blocks": [ + { + "bbox": [ + 50, + 73, + 545, + 379 + ], + "lines": [ + { + "bbox": [ + 50, + 73, + 545, + 379 + ], + "spans": [ + { + "bbox": [ + 50, + 73, + 545, + 379 + ], + "type": "image", + "image_path": "ba984eabd3d397b6adb4d6708b9d7a65875f0767e5428c8d4145c71a8a7c37d9.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 386, + 546, + 409 + ], + "lines": [ + { + "bbox": [ + 46, + 386, + 546, + 409 + ], + "spans": [ + { + "bbox": [ + 46, + 386, + 546, + 409 + ], + "type": "text", + "content": "Figure 2. An overview of the proposed framework ERMPC. The input is a suspicious image " + }, + { + "bbox": [ + 46, + 386, + 546, + 409 + ], + "type": "inline_equation", + "content": "(H\\times W\\times 3)" + }, + { + "bbox": [ + 46, + 386, + 546, + 409 + ], + "type": "text", + "content": ", and the output is a predicted mask " + }, + { + "bbox": [ + 46, + 386, + 546, + 409 + ], + "type": "inline_equation", + "content": "(\\mathrm{H}\\times \\mathrm{W}\\times 1)" + }, + { + "bbox": [ + 46, + 386, + 546, + 409 + ], + "type": "text", + "content": ", which localizes the forged regions." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 430, + 153, + 442 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 430, + 153, + 442 + ], + "spans": [ + { + "bbox": [ + 47, + 430, + 153, + 442 + ], + "type": "text", + "content": "2.2. Graph Reasoning" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 450, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 450, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 450, + 289, + 715 + ], + "type": "text", + "content": "Graph-based approaches have attracted growing attention from the computer vision community these days and have shown to be an effective relational reasoning method with a robust capacity for non-local feature aggregation. Specifically, CDGCNet [21] utilizes a class-wise learning strategy and designs a class-wise graph convolution, which avoids heavy graph concatenation and facilitates feature learning. To overcome the problem that most graph-based approaches assign a fixed number of neighbors for each query item, DAGL [39] proposes a dynamic attentive graph learning model to explore the dynamic non-local property for image restoration. CTL [34] learns a context-reinforced topology to construct multi-scale graphs which have a robust representational capacity by considering both global contextual information and physical connections of the human body. On other tasks in computer vision, e.g., object detection [43], multi-label image recognition [6], and skeleton-based action recognition [36, 59], graph convolutional neural networks have also achieved impressive performance. In contrast, we propose an improved edge-guided graph attention model to obstruct the message passing between forged and untouched regions with dynamic" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 304, + 430, + 547, + 526 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 430, + 547, + 526 + ], + "spans": [ + { + "bbox": [ + 304, + 430, + 547, + 526 + ], + "type": "text", + "content": "construction for forgery region localization. As graph convolution is an effective relational reasoning method that is very suitable for detecting forgery traces, this paper applies it to the task of image forgery localization for the first time. An improved edge-guided graph attention model is proposed for forgery region localization, which obstructs the message passing between forged and untouched regions with dynamic construction." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 306, + 564, + 388, + 578 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 564, + 388, + 578 + ], + "spans": [ + { + "bbox": [ + 306, + 564, + 388, + 578 + ], + "type": "text", + "content": "3. Methodology" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 594, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 594, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 594, + 547, + 715 + ], + "type": "text", + "content": "This section details the scheme of image forgery localization based on edge-aware message passing control. Sec. 3.1 describes an overview of the framework. One of the keys of the scheme is to control the message passing with edge and thus model the inconsistency between the forged and authentic regions (Sec. 3.2). Another key lies in reconstructing accurate edges from coarse features (Sec. 3.3). In addition, following [5, 22, 55, 62], we use the noise branch and fuse it with RGB branch at the end of the network (Sec. 3.4). The optimization is introduced in Sec. 3.5." + } + ] + } + ], + "index": 6 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "text", + "content": "8224" + } + ] + } + ], + "index": 7 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 115, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 115, + 83 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 115, + 83 + ], + "type": "text", + "content": "3.1. Overview" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 89, + 289, + 282 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 89, + 289, + 282 + ], + "spans": [ + { + "bbox": [ + 46, + 89, + 289, + 282 + ], + "type": "text", + "content": "Figure 2 is an overview of the framework. The input image is represented as " + }, + { + "bbox": [ + 46, + 89, + 289, + 282 + ], + "type": "inline_equation", + "content": "X \\in \\mathbb{R}^{H \\times W \\times 3}" + }, + { + "bbox": [ + 46, + 89, + 289, + 282 + ], + "type": "text", + "content": ", where H and W represent the height and width of the image. First, we use two branches to handle RGB and noise separately, obtaining " + }, + { + "bbox": [ + 46, + 89, + 289, + 282 + ], + "type": "inline_equation", + "content": "G_{r} \\in \\mathbb{R}^{H_{s} \\times W_{s} \\times C_{s}}" + }, + { + "bbox": [ + 46, + 89, + 289, + 282 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 89, + 289, + 282 + ], + "type": "inline_equation", + "content": "G_{n} \\in \\mathbb{R}^{H_{s} \\times W_{s} \\times C_{s}}" + }, + { + "bbox": [ + 46, + 89, + 289, + 282 + ], + "type": "text", + "content": " respectively. Then, we use ResNet-50 pretrained on ImageNet [11] as the backbone network. Following [4], we adopt atrous spatial pyramid pooling(ASPP) together with ResNet-50 to capture the long-range contextual information. The coarse features extracted from RGB branches are converted into edges through the edge reconstruction block. Meanwhile, the coarse features are constructed as graph structures, guided by the reconstructed edge information. Finally, the RGB features after the graph convolutional network are fused with noise information through dual attention [5] to output the predicted forgery localization map." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 289, + 235, + 302 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 289, + 235, + 302 + ], + "spans": [ + { + "bbox": [ + 47, + 289, + 235, + 302 + ], + "type": "text", + "content": "3.2. Region Message Passing Controller" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 307, + 287, + 365 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 307, + 287, + 365 + ], + "spans": [ + { + "bbox": [ + 46, + 307, + 287, + 365 + ], + "type": "text", + "content": "Most forged images are carefully processed to hide tampering artifacts, making it challenging to model inconsistencies in the RGB branch. To overcome this problem, the edges between the forged and authentic regions are utilized to control the message passing explicitly." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 366, + 287, + 426 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 366, + 287, + 426 + ], + "spans": [ + { + "bbox": [ + 46, + 366, + 287, + 426 + ], + "type": "text", + "content": "The edge feature " + }, + { + "bbox": [ + 46, + 366, + 287, + 426 + ], + "type": "inline_equation", + "content": "G_{e} \\in \\mathbb{R}^{H_{e} \\times W_{e} \\times 1}" + }, + { + "bbox": [ + 46, + 366, + 287, + 426 + ], + "type": "text", + "content": " comes from the edge reconstruction block (described in detail in the next subsection), where " + }, + { + "bbox": [ + 46, + 366, + 287, + 426 + ], + "type": "inline_equation", + "content": "H_{e} = H_{s}" + }, + { + "bbox": [ + 46, + 366, + 287, + 426 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 366, + 287, + 426 + ], + "type": "inline_equation", + "content": "W_{e} = W_{s}" + }, + { + "bbox": [ + 46, + 366, + 287, + 426 + ], + "type": "text", + "content": ". First, we calculate the relationship between two node features " + }, + { + "bbox": [ + 46, + 366, + 287, + 426 + ], + "type": "inline_equation", + "content": "P_{i}, P_{j}" + }, + { + "bbox": [ + 46, + 366, + 287, + 426 + ], + "type": "text", + "content": " of the " + }, + { + "bbox": [ + 46, + 366, + 287, + 426 + ], + "type": "inline_equation", + "content": "G_{E}" + }, + { + "bbox": [ + 46, + 366, + 287, + 426 + ], + "type": "text", + "content": " using an algorithm similar to XNOR gate:" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 59, + 434, + 287, + 466 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 434, + 287, + 466 + ], + "spans": [ + { + "bbox": [ + 59, + 434, + 287, + 466 + ], + "type": "interline_equation", + "content": "\\mathrm {X N} \\left(P _ {i}, P _ {j}\\right) = \\left\\{ \\begin{array}{l l} 0 & \\text {I n s i d e a n d o u t s i d e t h e e d g e s} \\\\ 1 & \\text {O n t h e s a m e s i d e o f e d g e s .} \\end{array} \\right. \\tag {1}", + "image_path": "6cfd177b6897695130f9876e3c7c09e3c94b989df7c0272233b859a5df57a25f.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 473, + 287, + 521 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 473, + 287, + 521 + ], + "spans": [ + { + "bbox": [ + 47, + 473, + 287, + 521 + ], + "type": "text", + "content": "If two nodes are inside and outside the edge respectively, then their XN is set to 0. For each of the N (" + }, + { + "bbox": [ + 47, + 473, + 287, + 521 + ], + "type": "inline_equation", + "content": "N = H_{e} \\times W_{e}" + }, + { + "bbox": [ + 47, + 473, + 287, + 521 + ], + "type": "text", + "content": ") nodes features, we calculate its XN, thus generating a matrix " + }, + { + "bbox": [ + 47, + 473, + 287, + 521 + ], + "type": "inline_equation", + "content": "A_{e} \\in \\mathbb{R}^{N \\times N}" + }, + { + "bbox": [ + 47, + 473, + 287, + 521 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 521, + 287, + 557 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 521, + 287, + 557 + ], + "spans": [ + { + "bbox": [ + 47, + 521, + 287, + 557 + ], + "type": "text", + "content": "Next, we apply graph learning to process the " + }, + { + "bbox": [ + 47, + 521, + 287, + 557 + ], + "type": "inline_equation", + "content": "G_{r} \\in \\mathbb{R}^{H_{s} \\times W_{s} \\times C_{s}}" + }, + { + "bbox": [ + 47, + 521, + 287, + 557 + ], + "type": "text", + "content": ". Following GAT [45], we calculate the similarity between two nodes as attention coefficients:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 117, + 563, + 287, + 579 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 117, + 563, + 287, + 579 + ], + "spans": [ + { + "bbox": [ + 117, + 563, + 287, + 579 + ], + "type": "interline_equation", + "content": "\\alpha_ {i, j} = \\psi (x _ {i}) ^ {T} \\psi^ {\\prime} (x _ {j}), \\tag {2}", + "image_path": "c6ad1cea273e07b46626b11dd0a310813ba96f89de8597479b4c43c2634a263a.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 586, + 287, + 647 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 586, + 287, + 647 + ], + "spans": [ + { + "bbox": [ + 47, + 586, + 287, + 647 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 586, + 287, + 647 + ], + "type": "inline_equation", + "content": "\\psi, \\psi'" + }, + { + "bbox": [ + 47, + 586, + 287, + 647 + ], + "type": "text", + "content": " denotes two learnable linear transformations. Specifically, we utilize " + }, + { + "bbox": [ + 47, + 586, + 287, + 647 + ], + "type": "inline_equation", + "content": "\\psi = Wx" + }, + { + "bbox": [ + 47, + 586, + 287, + 647 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 586, + 287, + 647 + ], + "type": "inline_equation", + "content": "\\psi' = W'x" + }, + { + "bbox": [ + 47, + 586, + 287, + 647 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 47, + 586, + 287, + 647 + ], + "type": "inline_equation", + "content": "W \\in \\mathbb{R}^{C_s \\times C_s}" + }, + { + "bbox": [ + 47, + 586, + 287, + 647 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 586, + 287, + 647 + ], + "type": "inline_equation", + "content": "W' \\in \\mathbb{R}^{C_s \\times C_s}" + }, + { + "bbox": [ + 47, + 586, + 287, + 647 + ], + "type": "text", + "content": " are both weight matrices. To make coefficients easier to compare across different nodes, we normalize them using the softmax function:" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 112, + 654, + 287, + 685 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 112, + 654, + 287, + 685 + ], + "spans": [ + { + "bbox": [ + 112, + 654, + 287, + 685 + ], + "type": "interline_equation", + "content": "A _ {r _ {i, j}} = \\frac {\\exp (\\alpha_ {i , j})}{\\sum_ {j = 1} ^ {N} \\exp (\\alpha_ {i , j})}, \\tag {3}", + "image_path": "4bb39d5b1dfef01e57932cdcf24fb5b8d6de668e89f7db42c85b479f6be725dd.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "inline_equation", + "content": "A_r \\in \\mathbb{R}^{N \\times N}" + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "content": " is the preliminary adjacency matrix. It reflects the relationship between any two nodes in the fea" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 72, + 545, + 156 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 156 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 156 + ], + "type": "text", + "content": "ture map. Larger values represent a greater flow of information between two nodes. In order to realize message passing control better, a method of dynamically adjusting the adjacency matrix is adopted. Specifically, if two nodes are on and off the boundary respectively, their adjacency is broken due to the dynamic adjustment of the adjacency matrix. In practice, the adjacency matrix is recalculated as follows:" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 392, + 165, + 545, + 178 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 392, + 165, + 545, + 178 + ], + "spans": [ + { + "bbox": [ + 392, + 165, + 545, + 178 + ], + "type": "interline_equation", + "content": "A _ {r} ^ {\\prime} = A _ {r} \\odot A _ {e}, \\tag {4}", + "image_path": "8df01a2fe4e8ad4e353857b1d899ea14163ba98648701f0d32bb2ee5558f61e2.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 185, + 545, + 221 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 185, + 545, + 221 + ], + "spans": [ + { + "bbox": [ + 304, + 185, + 545, + 221 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 185, + 545, + 221 + ], + "type": "inline_equation", + "content": "\\odot" + }, + { + "bbox": [ + 304, + 185, + 545, + 221 + ], + "type": "text", + "content": " is the Hadamard product. " + }, + { + "bbox": [ + 304, + 185, + 545, + 221 + ], + "type": "inline_equation", + "content": "A_r' \\in \\mathbb{R}^{N \\times N}" + }, + { + "bbox": [ + 304, + 185, + 545, + 221 + ], + "type": "text", + "content": " re-models the weights between nodes in the feature map and severs the connections between the forged and real regions." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 222, + 545, + 258 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 222, + 545, + 258 + ], + "spans": [ + { + "bbox": [ + 304, + 222, + 545, + 258 + ], + "type": "text", + "content": "Once the adjacency matrix is obtained, it is weighted by the learnable attention weights. Then the original nodes are updated with the following:" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 373, + 266, + 545, + 279 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 373, + 266, + 545, + 279 + ], + "spans": [ + { + "bbox": [ + 373, + 266, + 545, + 279 + ], + "type": "interline_equation", + "content": "Z _ {r} = \\operatorname {R e L U} \\left(A _ {r} ^ {\\prime} G _ {r} ^ {\\prime} W _ {z}\\right), \\tag {5}", + "image_path": "7acaeba3c23ba43e3bd031eddad3aad06a52f90de039307155cffe857388379b.jpg" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 287, + 545, + 323 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 287, + 545, + 323 + ], + "spans": [ + { + "bbox": [ + 304, + 287, + 545, + 323 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 287, + 545, + 323 + ], + "type": "inline_equation", + "content": "Z_{r}\\in \\mathbb{R}^{N\\times C_{s}}" + }, + { + "bbox": [ + 304, + 287, + 545, + 323 + ], + "type": "text", + "content": " is RGB features after graph reasoning, " + }, + { + "bbox": [ + 304, + 287, + 545, + 323 + ], + "type": "inline_equation", + "content": "W_{z}\\in \\mathbb{R}^{C_{s}\\times C_{s}}" + }, + { + "bbox": [ + 304, + 287, + 545, + 323 + ], + "type": "text", + "content": " is the learnable parameter and " + }, + { + "bbox": [ + 304, + 287, + 545, + 323 + ], + "type": "inline_equation", + "content": "G_r^\\prime \\in \\mathbb{R}^{N\\times C_s}" + }, + { + "bbox": [ + 304, + 287, + 545, + 323 + ], + "type": "text", + "content": " is the graph representation transformed by " + }, + { + "bbox": [ + 304, + 287, + 545, + 323 + ], + "type": "inline_equation", + "content": "G_{r}" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 323, + 545, + 467 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 323, + 545, + 467 + ], + "spans": [ + { + "bbox": [ + 304, + 323, + 545, + 467 + ], + "type": "text", + "content": "It is worth noting that this work not only introduces the idea of controlling the message passing in image forgery localization for the first time, but also the approach implemented is different from previous research [12, 20]. BFP [12] uses directed acyclic graphs (DAG) for feature propagation and introduces boundary information into the propagation to control the message passing between different segments. However, it has to scan the image pixel by pixel and requires a lot of loops, causing it difficult to implement in real-world applications. BGC [20] emphasizes reducing the weights of the edges and does not really focus on the message passing between regions." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 306, + 474, + 425, + 487 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 474, + 425, + 487 + ], + "spans": [ + { + "bbox": [ + 306, + 474, + 425, + 487 + ], + "type": "text", + "content": "3.3. Edge Reconstruction" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 492, + 545, + 588 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 492, + 545, + 588 + ], + "spans": [ + { + "bbox": [ + 304, + 492, + 545, + 588 + ], + "type": "text", + "content": "As described in the previous section, the Edge-aware Message Passing Control Graph requires accurate edge information. Designing such an edge-access network is nontrivial. The main challenge is how to learn edge information from the coarse feature. To this end, a novel approach to edge reconstruction is proposed. Specifically, we started by using the Sobel layer [5] to enhance the edge-related patterns in " + }, + { + "bbox": [ + 304, + 492, + 545, + 588 + ], + "type": "inline_equation", + "content": "G_{r} \\in \\mathbb{R}^{H_{s} \\times W_{s} \\times C_{s}}" + }, + { + "bbox": [ + 304, + 492, + 545, + 588 + ], + "type": "text", + "content": "," + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 352, + 597, + 545, + 610 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 352, + 597, + 545, + 610 + ], + "spans": [ + { + "bbox": [ + 352, + 597, + 545, + 610 + ], + "type": "interline_equation", + "content": "G _ {c} = G _ {r} \\odot \\sigma (\\text {N o r m} (S o b e l \\left(G _ {r}\\right)), \\tag {6}", + "image_path": "7a9e5d5d97b541b7f03e574387ea5e6398f00db928a129f97c569264ee881460.jpg" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 304, + 617, + 545, + 641 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 545, + 641 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 545, + 641 + ], + "type": "text", + "content": "where Norm is L2 Normalization, " + }, + { + "bbox": [ + 304, + 617, + 545, + 641 + ], + "type": "inline_equation", + "content": "\\sigma" + }, + { + "bbox": [ + 304, + 617, + 545, + 641 + ], + "type": "text", + "content": " is Sigmoid and Sobel is the SobelConv [5]." + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 304, + 642, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 642, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 642, + 545, + 713 + ], + "type": "text", + "content": "Then, we explore a Context-Enhanced Graph (CEG), extracting the local and global features separately for " + }, + { + "bbox": [ + 304, + 642, + 545, + 713 + ], + "type": "inline_equation", + "content": "G_{c} \\in \\mathbb{R}^{H_{s} \\times W_{s} \\times C_{s}}" + }, + { + "bbox": [ + 304, + 642, + 545, + 713 + ], + "type": "text", + "content": ". Specifically, the local information is extracted by the convolutional layers [5]. For global information, the contextual information of the feature map is encoded as the adjacency matrix " + }, + { + "bbox": [ + 304, + 642, + 545, + 713 + ], + "type": "inline_equation", + "content": "A_{c} \\in \\mathbb{R}^{N \\times N}" + }, + { + "bbox": [ + 304, + 642, + 545, + 713 + ], + "type": "text", + "content": " in a simple and" + } + ] + } + ], + "index": 23 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "text", + "content": "8225" + } + ] + } + ], + "index": 24 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 47, + 68, + 289, + 223 + ], + "blocks": [ + { + "bbox": [ + 47, + 68, + 289, + 223 + ], + "lines": [ + { + "bbox": [ + 47, + 68, + 289, + 223 + ], + "spans": [ + { + "bbox": [ + 47, + 68, + 289, + 223 + ], + "type": "image", + "image_path": "8b02f169471b7653d2c5f6677654f87c42502f3fb2a9e1c10ebfeddd9162723b.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 230, + 288, + 253 + ], + "lines": [ + { + "bbox": [ + 46, + 230, + 288, + 253 + ], + "spans": [ + { + "bbox": [ + 46, + 230, + 288, + 253 + ], + "type": "text", + "content": "Figure 3. Context-Enhanced Graph. Global features are extracted by the specific graph, while local features by the ResBlock." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 273, + 288, + 310 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 273, + 288, + 310 + ], + "spans": [ + { + "bbox": [ + 46, + 273, + 288, + 310 + ], + "type": "text", + "content": "efficient way. As shown in Figure 3, " + }, + { + "bbox": [ + 46, + 273, + 288, + 310 + ], + "type": "inline_equation", + "content": "A_{c}" + }, + { + "bbox": [ + 46, + 273, + 288, + 310 + ], + "type": "text", + "content": " is generated by a specially designed adjacency matrix learner which consists of two " + }, + { + "bbox": [ + 46, + 273, + 288, + 310 + ], + "type": "inline_equation", + "content": "1 \\times 1" + }, + { + "bbox": [ + 46, + 273, + 288, + 310 + ], + "type": "text", + "content": " convolution layers. The process is written as" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 95, + 318, + 287, + 332 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 95, + 318, + 287, + 332 + ], + "spans": [ + { + "bbox": [ + 95, + 318, + 287, + 332 + ], + "type": "interline_equation", + "content": "A _ {c} = \\operatorname {N o r m} \\left(\\operatorname {C o n v} \\left(\\operatorname {C o n v} \\left(\\mathrm {G} _ {\\mathrm {c}} ^ {\\prime}\\right)\\right)\\right), \\tag {7}", + "image_path": "6efc29a54fe3883641698f6fa139c6a988d33d2a33e1a006da12138ce9bf1130.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 339, + 287, + 449 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 339, + 287, + 449 + ], + "spans": [ + { + "bbox": [ + 46, + 339, + 287, + 449 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 339, + 287, + 449 + ], + "type": "inline_equation", + "content": "G_c' \\in \\mathbb{R}^{N \\times C_s}" + }, + { + "bbox": [ + 46, + 339, + 287, + 449 + ], + "type": "text", + "content": " is reshaped by " + }, + { + "bbox": [ + 46, + 339, + 287, + 449 + ], + "type": "inline_equation", + "content": "G_c" + }, + { + "bbox": [ + 46, + 339, + 287, + 449 + ], + "type": "text", + "content": ". Given the node features of " + }, + { + "bbox": [ + 46, + 339, + 287, + 449 + ], + "type": "inline_equation", + "content": "G_c'" + }, + { + "bbox": [ + 46, + 339, + 287, + 449 + ], + "type": "text", + "content": ", we first squeeze the feature dimensions by a " + }, + { + "bbox": [ + 46, + 339, + 287, + 449 + ], + "type": "inline_equation", + "content": "1 \\times 1" + }, + { + "bbox": [ + 46, + 339, + 287, + 449 + ], + "type": "text", + "content": " convolution layer. Then, another convolution layer with " + }, + { + "bbox": [ + 46, + 339, + 287, + 449 + ], + "type": "inline_equation", + "content": "1 \\times 1" + }, + { + "bbox": [ + 46, + 339, + 287, + 449 + ], + "type": "text", + "content": " kernel is used to transfer the N-dimension feature vector into the " + }, + { + "bbox": [ + 46, + 339, + 287, + 449 + ], + "type": "inline_equation", + "content": "N \\times N" + }, + { + "bbox": [ + 46, + 339, + 287, + 449 + ], + "type": "text", + "content": " adjacency matrix. In addition, L2 Normalization is applied to each row of " + }, + { + "bbox": [ + 46, + 339, + 287, + 449 + ], + "type": "inline_equation", + "content": "A_c" + }, + { + "bbox": [ + 46, + 339, + 287, + 449 + ], + "type": "text", + "content": " to facilitate stable optimization. Next, we use this adjacency matrix to complete the graph reasoning. In this way, we can obtain a global feature map. The process can be written as" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 113, + 456, + 287, + 471 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 113, + 456, + 287, + 471 + ], + "spans": [ + { + "bbox": [ + 113, + 456, + 287, + 471 + ], + "type": "interline_equation", + "content": "\\operatorname {G l o b a l} \\left(G _ {c} ^ {\\prime}\\right) = A _ {c} G _ {c} ^ {\\prime} W _ {c}, \\tag {8}", + "image_path": "ab6ea4c4806e6749075e5fe8773886b7e6610e46133ca7e6b6533aaaa0f99d4a.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 478, + 287, + 550 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 478, + 287, + 550 + ], + "spans": [ + { + "bbox": [ + 46, + 478, + 287, + 550 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 478, + 287, + 550 + ], + "type": "inline_equation", + "content": "W_{c}\\in \\mathbb{R}^{C_{s}\\times C_{s}}" + }, + { + "bbox": [ + 46, + 478, + 287, + 550 + ], + "type": "text", + "content": " is the learnable parameter. To match with the local information dimension, we reshape Global " + }, + { + "bbox": [ + 46, + 478, + 287, + 550 + ], + "type": "inline_equation", + "content": "(G_c^{\\prime})\\in \\mathbb{R}^{N\\times C_s}" + }, + { + "bbox": [ + 46, + 478, + 287, + 550 + ], + "type": "text", + "content": " back to Global' " + }, + { + "bbox": [ + 46, + 478, + 287, + 550 + ], + "type": "inline_equation", + "content": "(G_c^\\prime)\\in" + }, + { + "bbox": [ + 46, + 478, + 287, + 550 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^{H_s\\times W_s\\times C_s}" + }, + { + "bbox": [ + 46, + 478, + 287, + 550 + ], + "type": "text", + "content": " . Then combining the local and global information, we can obtain the edge probability map " + }, + { + "bbox": [ + 46, + 478, + 287, + 550 + ], + "type": "inline_equation", + "content": "G_{p}\\in" + }, + { + "bbox": [ + 46, + 478, + 287, + 550 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^{H_s\\times W_s\\times 1}" + }, + { + "bbox": [ + 46, + 478, + 287, + 550 + ], + "type": "text", + "content": " .." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 64, + 559, + 287, + 574 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 64, + 559, + 287, + 574 + ], + "spans": [ + { + "bbox": [ + 64, + 559, + 287, + 574 + ], + "type": "interline_equation", + "content": "G _ {p} = \\sigma \\left(\\mathcal {C} \\left(\\operatorname {C a t} \\left(\\operatorname {L o c a l} \\left(G _ {c}\\right), \\operatorname {G l o b a l} ^ {\\prime} \\left(G _ {c} ^ {\\prime}\\right)\\right)\\right)\\right), \\tag {9}", + "image_path": "6f8eae6b53d2d56a9a69ea37cce1a235922f80d66983f17e39c138e1a08d4c1c.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 582, + 287, + 605 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 582, + 287, + 605 + ], + "spans": [ + { + "bbox": [ + 46, + 582, + 287, + 605 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 582, + 287, + 605 + ], + "type": "inline_equation", + "content": "\\sigma" + }, + { + "bbox": [ + 46, + 582, + 287, + 605 + ], + "type": "text", + "content": " denotes the Sigmoid, " + }, + { + "bbox": [ + 46, + 582, + 287, + 605 + ], + "type": "inline_equation", + "content": "\\mathcal{C}" + }, + { + "bbox": [ + 46, + 582, + 287, + 605 + ], + "type": "text", + "content": " is a " + }, + { + "bbox": [ + 46, + 582, + 287, + 605 + ], + "type": "inline_equation", + "content": "1\\times 1" + }, + { + "bbox": [ + 46, + 582, + 287, + 605 + ], + "type": "text", + "content": " convolution layer, and Local contains ReLU and two convolutional layers." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 606, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 606, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 606, + 287, + 714 + ], + "type": "text", + "content": "Furthermore, in order to determine the edges, a threshold needs to be determined to binarize the probability map. Most previous studies have used fixed thresholds, and the process is non-differentiable. Inspired by [30], we utilize a variable threshold map which is adaptive for each point on the probability map " + }, + { + "bbox": [ + 46, + 606, + 287, + 714 + ], + "type": "inline_equation", + "content": "G_{p}" + }, + { + "bbox": [ + 46, + 606, + 287, + 714 + ], + "type": "text", + "content": ". Besides, we propose a variant of the Sigmoid function to complete the binarization, which is capable of participating in the backpropagation involved. Binarize threshold adjustment is achieved by translating the" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 72, + 546, + 109 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 546, + 109 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 546, + 109 + ], + "type": "text", + "content": "Sigmoid function along the x-axis. Therefore, we explore the threshold-adaptive differentiable binarization (TDB) for edge reconstruction. It is computed as follows:" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 370, + 115, + 545, + 140 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 370, + 115, + 545, + 140 + ], + "spans": [ + { + "bbox": [ + 370, + 115, + 545, + 140 + ], + "type": "interline_equation", + "content": "G _ {e} = \\frac {1}{1 + e ^ {- k \\left(G _ {p} - \\tau \\left(G _ {p}\\right)\\right)}}, \\tag {10}", + "image_path": "52b3983f4f43557f56b880bf904ead874fb590382d1e4d3783b017ab1fc9b591.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 147, + 546, + 183 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 147, + 546, + 183 + ], + "spans": [ + { + "bbox": [ + 305, + 147, + 546, + 183 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 147, + 546, + 183 + ], + "type": "inline_equation", + "content": "\\tau" + }, + { + "bbox": [ + 305, + 147, + 546, + 183 + ], + "type": "text", + "content": " denotes the learnable transformation, which in practice is " + }, + { + "bbox": [ + 305, + 147, + 546, + 183 + ], + "type": "inline_equation", + "content": "3\\times 3" + }, + { + "bbox": [ + 305, + 147, + 546, + 183 + ], + "type": "text", + "content": " convolution operators, and " + }, + { + "bbox": [ + 305, + 147, + 546, + 183 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 305, + 147, + 546, + 183 + ], + "type": "text", + "content": " is the amplifying factor. In particular, " + }, + { + "bbox": [ + 305, + 147, + 546, + 183 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 305, + 147, + 546, + 183 + ], + "type": "text", + "content": " is set to 500 empirically." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 190, + 398, + 201 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 190, + 398, + 201 + ], + "spans": [ + { + "bbox": [ + 306, + 190, + 398, + 201 + ], + "type": "text", + "content": "3.4. Branch Fusion" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 208, + 545, + 304 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 208, + 545, + 304 + ], + "spans": [ + { + "bbox": [ + 305, + 208, + 545, + 304 + ], + "type": "text", + "content": "Following most studies [5,22,55,62], we also employ the noise branch. However, this is not the focus of this work, so we have used some common methods. As in Figure 2, the noise is extracted with BayarConv [55]. For the fusion of the two branches, we follow [5] and adopt the Dual Attention (DA) [15]. DA includes channel attention module (CAM) and position attention module (PAM). It can effectively fuse two branches. The process can be written as" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 383, + 312, + 545, + 326 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 383, + 312, + 545, + 326 + ], + "spans": [ + { + "bbox": [ + 383, + 312, + 545, + 326 + ], + "type": "interline_equation", + "content": "G _ {o} = \\mathrm {D A} \\left(G _ {z}, G _ {n}\\right), \\tag {11}", + "image_path": "2f3b27d7572b68f6572e59d984d324547a609ea6b46a4ffaf082b54ed1925ef2.jpg" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 333, + 546, + 370 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 333, + 546, + 370 + ], + "spans": [ + { + "bbox": [ + 305, + 333, + 546, + 370 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 333, + 546, + 370 + ], + "type": "inline_equation", + "content": "G_{z} \\in \\mathbb{R}^{H_{s} \\times W_{s} \\times C_{s}}" + }, + { + "bbox": [ + 305, + 333, + 546, + 370 + ], + "type": "text", + "content": " is reshaped by the " + }, + { + "bbox": [ + 305, + 333, + 546, + 370 + ], + "type": "inline_equation", + "content": "Z_{r}" + }, + { + "bbox": [ + 305, + 333, + 546, + 370 + ], + "type": "text", + "content": ". Finally, we transform " + }, + { + "bbox": [ + 305, + 333, + 546, + 370 + ], + "type": "inline_equation", + "content": "G_{o} \\in \\mathbb{R}^{H_{s} \\times W_{s} \\times 1}" + }, + { + "bbox": [ + 305, + 333, + 546, + 370 + ], + "type": "text", + "content": " with bilinear upsampling into the final predicted mask " + }, + { + "bbox": [ + 305, + 333, + 546, + 370 + ], + "type": "inline_equation", + "content": "G_{out} \\in \\mathbb{R}^{H \\times W \\times 1}" + }, + { + "bbox": [ + 305, + 333, + 546, + 370 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 376, + 391, + 389 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 376, + 391, + 389 + ], + "spans": [ + { + "bbox": [ + 306, + 376, + 391, + 389 + ], + "type": "text", + "content": "3.5. Optimization" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 305, + 396, + 545, + 502 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 396, + 545, + 502 + ], + "spans": [ + { + "bbox": [ + 305, + 396, + 545, + 502 + ], + "type": "text", + "content": "As shown in Figure 2, we calculate the loss function for three components: the final prediction " + }, + { + "bbox": [ + 305, + 396, + 545, + 502 + ], + "type": "inline_equation", + "content": "G_{out} \\in \\mathbb{R}^{H \\times W \\times 1}" + }, + { + "bbox": [ + 305, + 396, + 545, + 502 + ], + "type": "text", + "content": ", the binary edge prediction " + }, + { + "bbox": [ + 305, + 396, + 545, + 502 + ], + "type": "inline_equation", + "content": "G_e \\in \\mathbb{R}^{H_e \\times W_e \\times 1}" + }, + { + "bbox": [ + 305, + 396, + 545, + 502 + ], + "type": "text", + "content": " and the edge probability map " + }, + { + "bbox": [ + 305, + 396, + 545, + 502 + ], + "type": "inline_equation", + "content": "G_p \\in \\mathbb{R}^{H_e \\times W_e \\times 1}" + }, + { + "bbox": [ + 305, + 396, + 545, + 502 + ], + "type": "text", + "content": ". For edge loss, the ground-truth edge " + }, + { + "bbox": [ + 305, + 396, + 545, + 502 + ], + "type": "inline_equation", + "content": "E \\in \\mathbb{R}^{H \\times W \\times 1}" + }, + { + "bbox": [ + 305, + 396, + 545, + 502 + ], + "type": "text", + "content": " is downsampled to a smaller size " + }, + { + "bbox": [ + 305, + 396, + 545, + 502 + ], + "type": "inline_equation", + "content": "E' \\in \\mathbb{R}^{H_e \\times W_e \\times 1}" + }, + { + "bbox": [ + 305, + 396, + 545, + 502 + ], + "type": "text", + "content": " to match " + }, + { + "bbox": [ + 305, + 396, + 545, + 502 + ], + "type": "inline_equation", + "content": "G_e" + }, + { + "bbox": [ + 305, + 396, + 545, + 502 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 305, + 396, + 545, + 502 + ], + "type": "inline_equation", + "content": "G_p" + }, + { + "bbox": [ + 305, + 396, + 545, + 502 + ], + "type": "text", + "content": ". This strategy outperforms upsampling " + }, + { + "bbox": [ + 305, + 396, + 545, + 502 + ], + "type": "inline_equation", + "content": "G_e" + }, + { + "bbox": [ + 305, + 396, + 545, + 502 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 305, + 396, + 545, + 502 + ], + "type": "inline_equation", + "content": "G_p" + }, + { + "bbox": [ + 305, + 396, + 545, + 502 + ], + "type": "text", + "content": " in terms of computational cost and performance. The overall loss function can be written as:" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 310, + 511, + 545, + 526 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 310, + 511, + 545, + 526 + ], + "spans": [ + { + "bbox": [ + 310, + 511, + 545, + 526 + ], + "type": "interline_equation", + "content": "\\mathbf {L} = \\lambda_ {1} \\mathcal {L} \\left(\\mathrm {Y}, \\mathrm {G} _ {\\text {o u t}}\\right) + \\lambda_ {2} \\mathcal {L} \\left(\\mathrm {E} ^ {\\prime}, \\mathrm {G} _ {\\mathrm {e}}\\right) + \\lambda_ {3} \\mathcal {L} \\left(\\mathrm {E} ^ {\\prime}, \\mathrm {G} _ {\\mathrm {p}}\\right), \\tag {12}", + "image_path": "2672d2ea20b373e09f176879c18c897b0786c61f4f124d9c7fdb97f2746f5d18.jpg" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 305, + 533, + 545, + 582 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 533, + 545, + 582 + ], + "spans": [ + { + "bbox": [ + 305, + 533, + 545, + 582 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 533, + 545, + 582 + ], + "type": "inline_equation", + "content": "\\mathcal{L}" + }, + { + "bbox": [ + 305, + 533, + 545, + 582 + ], + "type": "text", + "content": " denotes the Dice loss [5], " + }, + { + "bbox": [ + 305, + 533, + 545, + 582 + ], + "type": "inline_equation", + "content": "Y\\in \\mathbb{R}^{H\\times W\\times 1}" + }, + { + "bbox": [ + 305, + 533, + 545, + 582 + ], + "type": "text", + "content": " is the ground-truth mask, and " + }, + { + "bbox": [ + 305, + 533, + 545, + 582 + ], + "type": "inline_equation", + "content": "\\lambda_1,\\lambda_2,\\lambda_3" + }, + { + "bbox": [ + 305, + 533, + 545, + 582 + ], + "type": "text", + "content": " are the parameters to balance the three terms in loss function " + }, + { + "bbox": [ + 305, + 533, + 545, + 582 + ], + "type": "inline_equation", + "content": "(\\lambda_{1} + \\lambda_{2} + \\lambda_{3} = 1)" + }, + { + "bbox": [ + 305, + 533, + 545, + 582 + ], + "type": "text", + "content": ". In our setting, they are set as 0.50, 0.25 and 0.25 respectively." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 306, + 591, + 388, + 605 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 591, + 388, + 605 + ], + "spans": [ + { + "bbox": [ + 306, + 591, + 388, + 605 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 306, + 611, + 422, + 624 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 611, + 422, + 624 + ], + "spans": [ + { + "bbox": [ + 306, + 611, + 422, + 624 + ], + "type": "text", + "content": "4.1. Experimental Setup" + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 305, + 629, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 629, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 629, + 545, + 713 + ], + "type": "text", + "content": "Pre-training Data We create a sizable image tampering dataset and use it to pre-train our model. This dataset includes three categories: 1) splicing, 2) copy-move, 3) removal. For splicing, we use the MS COCO [31] to generate spliced images, where one annotated region is randomly selected per image and pasted into a different image after several transformations. We use the same transformation as [5]," + } + ] + } + ], + "index": 23 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "text", + "content": "8226" + } + ] + } + ], + "index": 24 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 48, + 70, + 309, + 155 + ], + "blocks": [ + { + "bbox": [ + 48, + 70, + 309, + 155 + ], + "lines": [ + { + "bbox": [ + 48, + 70, + 309, + 155 + ], + "spans": [ + { + "bbox": [ + 48, + 70, + 309, + 155 + ], + "type": "table", + "html": "
MethodDataColumbiaCoverageCASIANIST16IMD20
ManTraNet64K82.481.981.779.574.8
SPAN96k93.692.279.784.075.0
PSCCNet100k98.284.782.985.580.6
ObjectFormer62K95.592.884.387.282.1
Ours60K96.894.487.689.585.6
", + "image_path": "955e1018d9f9531865694359f9b3254c067e9c55dca32169deba018646881fd6.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 208, + 287, + 327 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 208, + 287, + 327 + ], + "spans": [ + { + "bbox": [ + 46, + 208, + 287, + 327 + ], + "type": "text", + "content": "including the scale, rotation, shift, and luminance changes. Since the spliced region is not always an object, we create random outlines using the Bezier curve [38] and fill them to create splicing masks. For copy-move, the datasets from MS COCO and [53] are adopted. For removal, we adopt the SOTA inpainting method [29] to fill one annotated region that is randomly removed from each chosen MS COCO image. We randomly add Gaussian noise or apply the JPEG compression algorithm to the generated data to resemble the visual quality of images in real situations." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 329, + 288, + 592 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 329, + 288, + 592 + ], + "spans": [ + { + "bbox": [ + 46, + 329, + 288, + 592 + ], + "type": "text", + "content": "Testing Datasets Following [46], we evaluate our model on CASIA [13] dataset, Coverage [49] dataset, Columbia [19] dataset, NIST16 [17] dataset and IMD20 [40] dataset. Specifically, CASIA [13], which contains two types of tampered images (splicing and copy-move), is widely used in the image forgery field. The database V1.0 has fixed size tampered images, which are generated only by using crop-and-paste operation under Adobe Photoshop. The database v2.0 is more comprehensive and challenging, and most tampered examples are generated with post-processing. COVER [49] provides 100 images, and all of them are generated by copy-move tampering technique. Columbia [19] consists of 180 splicing images, whose size ranges from " + }, + { + "bbox": [ + 46, + 329, + 288, + 592 + ], + "type": "inline_equation", + "content": "757 \\times 568" + }, + { + "bbox": [ + 46, + 329, + 288, + 592 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 46, + 329, + 288, + 592 + ], + "type": "inline_equation", + "content": "1152 \\times 568" + }, + { + "bbox": [ + 46, + 329, + 288, + 592 + ], + "type": "text", + "content": ". In detail, the tampered images in Columbia are all uncompressed and without any post-processing. NIST16 [17] is a high-quality dataset. This dataset contains three types of tampering, and some regions of manipulation are difficult for humans to identify. IMD20 [40] collects real-life manipulated images from the Internet, and involves all three manipulations as well. We apply the same training/testing splits as [22, 46, 62] to fine-tune our model for fair comparisons." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 593, + 287, + 664 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 593, + 287, + 664 + ], + "spans": [ + { + "bbox": [ + 46, + 593, + 287, + 664 + ], + "type": "text", + "content": "Evaluation Metrics To quantify the localization performance, following previous works [22, 46], we use pixel-level Area Under Curve (AUC) and F1 score on manipulation masks. And we adopt the Equal Error Rate (EER) threshold to binarize masks because binary masks are necessary to calculate F1 scores." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 665, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 288, + 713 + ], + "type": "text", + "content": "Implementation Details The input images are resized to " + }, + { + "bbox": [ + 46, + 665, + 288, + 713 + ], + "type": "inline_equation", + "content": "512 \\times 512" + }, + { + "bbox": [ + 46, + 665, + 288, + 713 + ], + "type": "text", + "content": ". In this work, the backbone is ResNet-50 [18], pre-trained on ImageNet [11]. Implemented by PyTorch, our model is trained with GeForce GTX 3090. We use" + } + ] + } + ], + "index": 5 + }, + { + "type": "table", + "bbox": [ + 319, + 70, + 535, + 186 + ], + "blocks": [ + { + "bbox": [ + 46, + 163, + 288, + 185 + ], + "lines": [ + { + "bbox": [ + 46, + 163, + 288, + 185 + ], + "spans": [ + { + "bbox": [ + 46, + 163, + 288, + 185 + ], + "type": "text", + "content": "Table 1. Comparisons of manipulation localization AUC (%) scores of different pre-trained models." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 319, + 70, + 535, + 186 + ], + "lines": [ + { + "bbox": [ + 319, + 70, + 535, + 186 + ], + "spans": [ + { + "bbox": [ + 319, + 70, + 535, + 186 + ], + "type": "table", + "html": "
MethodsCoverageCASIANIST16
AUCF1AUCF1AUCF1
J-LSTM61.4---76.4-
H-LSTM71.2---79.4-
RGB-N81.743.779.540.893.772.2
SPAN93.755.883.838.296.158.2
PSCCNet94.172.387.555.499.174.2
ObjectFormer95.775.888.257.999.682.4
Ours98.477.390.458.699.783.6
", + "image_path": "ed7f684086c47859ad8e901f12218252e642ba9f7d2a0bf6dd55899ea4add57e.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "table_body" + } + ], + "index": 6 + }, + { + "type": "table", + "bbox": [ + 307, + 228, + 545, + 362 + ], + "blocks": [ + { + "bbox": [ + 305, + 194, + 545, + 216 + ], + "lines": [ + { + "bbox": [ + 305, + 194, + 545, + 216 + ], + "spans": [ + { + "bbox": [ + 305, + 194, + 545, + 216 + ], + "type": "text", + "content": "Table 2. Comparison of manipulation localization results using fine-tuned models." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 307, + 228, + 545, + 362 + ], + "lines": [ + { + "bbox": [ + 307, + 228, + 545, + 362 + ], + "spans": [ + { + "bbox": [ + 307, + 228, + 545, + 362 + ], + "type": "table", + "html": "
DistortionSPANObjectFormerOurs
no distortion83.9587.1889.49
Resize(0.78×)83.2487.1789.33 0.16↓
Resize(0.25×)80.3286.3387.72 1.77↓
Blur(k=3)83.1085.9789.22 0.27↓
Blur(k=15)79.1580.2687.13 2.36↓
Noise(σ=3)75.1779.5888.25 1.24↓
Noise(σ=15)67.2878.1583.40 6.09↓
Compress(q=100)83.5986.3789.42 0.07↓
Compress(q=50)80.6886.2488.82 0.67↓
", + "image_path": "9002029fc96630c5daaaa0434f7a9332b79428afe50d8b6aaf4791f8a078faa4.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "table_body" + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 370, + 545, + 404 + ], + "lines": [ + { + "bbox": [ + 305, + 370, + 545, + 404 + ], + "spans": [ + { + "bbox": [ + 305, + 370, + 545, + 404 + ], + "type": "text", + "content": "Table 3. Localization performance on NIST16 dataset under various distortions. AUC scores are reported (in %), (Blur: Gaussian-Blur, Noise: GaussianNoise, Compress: JPEGCompress.)" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 305, + 424, + 545, + 461 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 424, + 545, + 461 + ], + "spans": [ + { + "bbox": [ + 305, + 424, + 545, + 461 + ], + "type": "text", + "content": "Adam as the optimizer, and the learning rate decays from " + }, + { + "bbox": [ + 305, + 424, + 545, + 461 + ], + "type": "inline_equation", + "content": "10^{-4}" + }, + { + "bbox": [ + 305, + 424, + 545, + 461 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 305, + 424, + 545, + 461 + ], + "type": "inline_equation", + "content": "10^{-7}" + }, + { + "bbox": [ + 305, + 424, + 545, + 461 + ], + "type": "text", + "content": ". We train 100 epochs with a batch size of 8, and the learning rate decays by 10 times every 30 epochs." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 467, + 545, + 480 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 467, + 545, + 480 + ], + "spans": [ + { + "bbox": [ + 305, + 467, + 545, + 480 + ], + "type": "text", + "content": "4.2. Comparison with the State-of-the-Art Methods" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 485, + 545, + 605 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 485, + 545, + 605 + ], + "spans": [ + { + "bbox": [ + 304, + 485, + 545, + 605 + ], + "type": "text", + "content": "Following SPAN [22] and ObjectFormer [46], our model is compared with other state-of-the-art tampering localization methods under two settings: 1) training on the synthetic dataset and evaluating on the full test datasets, and 2) fine-tuning the pre-trained model on the training split of test datasets and evaluating on their test split. The pretrained model will demonstrate each method's generalizability, and the fine-tuned model will demonstrate how well each method performs locally once the domain discrepancy has been significantly reduced." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 605, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 545, + 714 + ], + "type": "text", + "content": "Pre-trained Model Table 1 shows the localization performance of pre-trained models for different methods on four standard datasets under pixel-level AUC. We compare our model ERMPC with MantraNet [55], SPAN [22], PSCCNet [35], and ObjectFormer [46] when evaluating pre-trained models. The pre-trained ERMPC achieves the best localization performance on Coverage, CASIA, NIST16 and IMD20, and ranks second on Columbia. Especially, ERMPC achieves " + }, + { + "bbox": [ + 304, + 605, + 545, + 714 + ], + "type": "inline_equation", + "content": "94.4\\%" + }, + { + "bbox": [ + 304, + 605, + 545, + 714 + ], + "type": "text", + "content": " on the copy-move dataset" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "8227" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 84, + 70, + 509, + 352 + ], + "blocks": [ + { + "bbox": [ + 84, + 70, + 509, + 352 + ], + "lines": [ + { + "bbox": [ + 84, + 70, + 509, + 352 + ], + "spans": [ + { + "bbox": [ + 84, + 70, + 509, + 352 + ], + "type": "image", + "image_path": "9924f3f5a4344f8ff617c00235d4a4cf7656ef3eed06003b4d0621735fe143ec.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 360, + 547, + 383 + ], + "lines": [ + { + "bbox": [ + 46, + 360, + 547, + 383 + ], + "spans": [ + { + "bbox": [ + 46, + 360, + 547, + 383 + ], + "type": "text", + "content": "Figure 4. Visualization of the predicted manipulation mask by different methods. From top to bottom, we show forged images, GT masks, predictions of ManTraNet, SPAN, PSCC-Net, and ours." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 75, + 392, + 260, + 485 + ], + "blocks": [ + { + "bbox": [ + 75, + 392, + 260, + 485 + ], + "lines": [ + { + "bbox": [ + 75, + 392, + 260, + 485 + ], + "spans": [ + { + "bbox": [ + 75, + 392, + 260, + 485 + ], + "type": "table", + "html": "
VariantsCASIANIST16
AUCF1AUCF1
Baseline71.638.377.152.6
w/o RMPC76.945.686.460.7
w/o CEG85.151.593.475.3
w/o TDB88.657.398.281.9
Ours90.458.699.783.6
", + "image_path": "066e0a4b062fc1d9ff0dd6d65cdf85d30c7e692e34e323bb3bc5a309bfa4a7e1.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 493, + 287, + 516 + ], + "lines": [ + { + "bbox": [ + 47, + 493, + 287, + 516 + ], + "spans": [ + { + "bbox": [ + 47, + 493, + 287, + 516 + ], + "type": "text", + "content": "Table 4. Ablation results on CASIA and NIST16 dataset using different variants of ERMPC. AUC and F1 scores " + }, + { + "bbox": [ + 47, + 493, + 287, + 516 + ], + "type": "inline_equation", + "content": "(\\%)" + }, + { + "bbox": [ + 47, + 493, + 287, + 516 + ], + "type": "text", + "content": " are reported." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 531, + 287, + 674 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 531, + 287, + 674 + ], + "spans": [ + { + "bbox": [ + 46, + 531, + 287, + 674 + ], + "type": "text", + "content": "COVER, whose image forgery regions are indistinguishable from the background. This validates our model owns the superior ability to control message passing between two regions(forged and authentic). We fail to achieve the best performance on Columbia, falling behind PSCCNet " + }, + { + "bbox": [ + 46, + 531, + 287, + 674 + ], + "type": "inline_equation", + "content": "1.4\\%" + }, + { + "bbox": [ + 46, + 531, + 287, + 674 + ], + "type": "text", + "content": " under AUC. We contend that the explanation may be that the distribution of their synthesized training data closely resembles that of the Columbia dataset. This is further supported by the results in Table 2, which show that ERMPC performs better than PSCCNet in terms of both AUC and F1 scores. Furthermore, it is important to note that ERMPC attains decent results with less pre-training data." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 677, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 288, + 715 + ], + "type": "text", + "content": "Fine-tuned Model The fine-tuned models, which are initiated with the network weights of the pretrained model, will be trained on the training split of Coverage, CASIA, and" + } + ] + } + ], + "index": 5 + }, + { + "type": "image", + "bbox": [ + 328, + 407, + 515, + 534 + ], + "blocks": [ + { + "bbox": [ + 328, + 407, + 515, + 534 + ], + "lines": [ + { + "bbox": [ + 328, + 407, + 515, + 534 + ], + "spans": [ + { + "bbox": [ + 328, + 407, + 515, + 534 + ], + "type": "image", + "image_path": "55343cc4a03e07b2b35355dc1a17b0048c35f1fb3d54ab01fe4d1dcf091255c3.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 345, + 544, + 506, + 556 + ], + "lines": [ + { + "bbox": [ + 345, + 544, + 506, + 556 + ], + "spans": [ + { + "bbox": [ + 345, + 544, + 506, + 556 + ], + "type": "text", + "content": "Figure 5. The effect of parameter k in TDB" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_caption" + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 567, + 547, + 640 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 567, + 547, + 640 + ], + "spans": [ + { + "bbox": [ + 304, + 567, + 547, + 640 + ], + "type": "text", + "content": "NIST16 datasets, respectively. We evaluate the fine-tuned models of different methods in Table 2. As for AUC and F1, our model achieves significant performance gains. This validates that ERMPC could capture subtle tampering artifacts by controlling the message passing between two regions (forged and authentic) in the feature map." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 647, + 436, + 658 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 647, + 436, + 658 + ], + "spans": [ + { + "bbox": [ + 306, + 647, + 436, + 658 + ], + "type": "text", + "content": "4.3. Robustness Evaluation" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 665, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 547, + 715 + ], + "type": "text", + "content": "We degrade the raw manipulated images from NIST16 using the distortion settings in [46] to analyze the robustness of ERMPC for forgery localization. These distortions types include scaling images to various scales (Re" + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "8228" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 49, + 70, + 96, + 220 + ], + "blocks": [ + { + "bbox": [ + 49, + 70, + 96, + 220 + ], + "lines": [ + { + "bbox": [ + 49, + 70, + 96, + 220 + ], + "spans": [ + { + "bbox": [ + 49, + 70, + 96, + 220 + ], + "type": "image", + "image_path": "5395b7a7779b3aa9fecfebe2010fcd6c38f13b557a08665f8611d1b4c428d44d.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 47, + 229, + 287, + 262 + ], + "lines": [ + { + "bbox": [ + 47, + 229, + 287, + 262 + ], + "spans": [ + { + "bbox": [ + 47, + 229, + 287, + 262 + ], + "type": "text", + "content": "Figure 6. Visualization of message passing controller. From left to right, we display the forged images, masks, GradCAM [42] of the feature map without (w/o) and with (w) RMPC, and predictions." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 97, + 71, + 143, + 221 + ], + "blocks": [ + { + "bbox": [ + 97, + 71, + 143, + 221 + ], + "lines": [ + { + "bbox": [ + 97, + 71, + 143, + 221 + ], + "spans": [ + { + "bbox": [ + 97, + 71, + 143, + 221 + ], + "type": "image", + "image_path": "d392d13aef3bffac3e6b74cd91af8d8ab5bb5a01931bf77099e737af33a04687.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 144, + 71, + 191, + 220 + ], + "blocks": [ + { + "bbox": [ + 144, + 71, + 191, + 220 + ], + "lines": [ + { + "bbox": [ + 144, + 71, + 191, + 220 + ], + "spans": [ + { + "bbox": [ + 144, + 71, + 191, + 220 + ], + "type": "image", + "image_path": "b901ea88b9e5cea5a330264cee2b2b6c13a381909080a697121a1c0a93b66a80.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 192, + 71, + 238, + 220 + ], + "blocks": [ + { + "bbox": [ + 192, + 71, + 238, + 220 + ], + "lines": [ + { + "bbox": [ + 192, + 71, + 238, + 220 + ], + "spans": [ + { + "bbox": [ + 192, + 71, + 238, + 220 + ], + "type": "image", + "image_path": "60c8fa84bfa117226ad1d3d46b8de3ac366684152fcf3f3c46094cbb205267b2.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + } + ], + "index": 3 + }, + { + "type": "image", + "bbox": [ + 239, + 71, + 286, + 220 + ], + "blocks": [ + { + "bbox": [ + 239, + 71, + 286, + 220 + ], + "lines": [ + { + "bbox": [ + 239, + 71, + 286, + 220 + ], + "spans": [ + { + "bbox": [ + 239, + 71, + 286, + 220 + ], + "type": "image", + "image_path": "e5bba474ca424d4906559f018663504b6dc75cdc9289f612b2d5f15fc49edffd.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 186, + 545, + 220 + ], + "lines": [ + { + "bbox": [ + 305, + 186, + 545, + 220 + ], + "spans": [ + { + "bbox": [ + 305, + 186, + 545, + 220 + ], + "type": "text", + "content": "Figure 7. Visualization of edge reconstruction. From left to right, we display the forged images, masks, the features without (w/o) and with (w) the edge reconstruction module, and prediction." + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 281, + 287, + 424 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 281, + 287, + 424 + ], + "spans": [ + { + "bbox": [ + 46, + 281, + 287, + 424 + ], + "type": "text", + "content": "size), applying Gaussian blur with a kernel size " + }, + { + "bbox": [ + 46, + 281, + 287, + 424 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 281, + 287, + 424 + ], + "type": "text", + "content": " (GaussianBlur), adding Gaussian noise with a standard deviation " + }, + { + "bbox": [ + 46, + 281, + 287, + 424 + ], + "type": "inline_equation", + "content": "\\sigma" + }, + { + "bbox": [ + 46, + 281, + 287, + 424 + ], + "type": "text", + "content": " (GaussianNoise), and performing JPEG compression with a quality factor " + }, + { + "bbox": [ + 46, + 281, + 287, + 424 + ], + "type": "inline_equation", + "content": "q" + }, + { + "bbox": [ + 46, + 281, + 287, + 424 + ], + "type": "text", + "content": " (JPEGCompress). We compare the forgery localization performance (AUC scores) of our pre-trained models with SPAN [22] and ObjectFormer on these corrupted data and report the results in Table 3. ERMPC demonstrates more resistance to various distortion techniques. It is worth noting that JPEG compression is commonly performed when uploading images to social media. Our model ERMPC performs significantly better on compressed images than other methods." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 432, + 153, + 445 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 432, + 153, + 445 + ], + "spans": [ + { + "bbox": [ + 47, + 432, + 153, + 445 + ], + "type": "text", + "content": "4.4. Ablation Analysis" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 450, + 287, + 581 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 450, + 287, + 581 + ], + "spans": [ + { + "bbox": [ + 46, + 450, + 287, + 581 + ], + "type": "text", + "content": "The Region Message Passing Controller (RMPC) module of our method ERMPC is designed to weaken the message passing between the forged and authentic regions. The Context-Enhanced Graph (CEG) encodes global information along the node to obtain a better edge probability map, while the Threshold-adaptive Differentiable Binarization (TDB) adaptively performs the binarization process for learnable edges. In order to evaluate the effectiveness of RMPC, CEG and TDB, we remove them separately from ERMPC and evaluate the forgery localization performance on CASIA and NIST16 datasets." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 582, + 287, + 676 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 582, + 287, + 676 + ], + "spans": [ + { + "bbox": [ + 46, + 582, + 287, + 676 + ], + "type": "text", + "content": "Table 4 presents the quantitative outcomes. The baseline denotes that we just use ResNet-50. It can be seen that without TDB, the AUC scores decrease by " + }, + { + "bbox": [ + 46, + 582, + 287, + 676 + ], + "type": "inline_equation", + "content": "2.0\\%" + }, + { + "bbox": [ + 46, + 582, + 287, + 676 + ], + "type": "text", + "content": " on CASIA and " + }, + { + "bbox": [ + 46, + 582, + 287, + 676 + ], + "type": "inline_equation", + "content": "1.5\\%" + }, + { + "bbox": [ + 46, + 582, + 287, + 676 + ], + "type": "text", + "content": " on NIST16, while without CEG, the AUC scores decrease by " + }, + { + "bbox": [ + 46, + 582, + 287, + 676 + ], + "type": "inline_equation", + "content": "5.9\\%" + }, + { + "bbox": [ + 46, + 582, + 287, + 676 + ], + "type": "text", + "content": " on CASIA and " + }, + { + "bbox": [ + 46, + 582, + 287, + 676 + ], + "type": "inline_equation", + "content": "6.3\\%" + }, + { + "bbox": [ + 46, + 582, + 287, + 676 + ], + "type": "text", + "content": " on NIST16. Furthermore, when RMPC is discarded, serious performance degradation in Table 4, i.e., " + }, + { + "bbox": [ + 46, + 582, + 287, + 676 + ], + "type": "inline_equation", + "content": "14.9\\%" + }, + { + "bbox": [ + 46, + 582, + 287, + 676 + ], + "type": "text", + "content": " in terms of AUC and " + }, + { + "bbox": [ + 46, + 582, + 287, + 676 + ], + "type": "inline_equation", + "content": "22.2\\%" + }, + { + "bbox": [ + 46, + 582, + 287, + 676 + ], + "type": "text", + "content": " in terms of F1 on CASIA can be observed." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "text", + "content": "In Figure 5, we show the different values of parameters " + }, + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "text", + "content": " in threshold-adaptive differentiable binarization to verify its effect over three datasets. With its increasing, the curve" + } + ] + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 307, + 71, + 355, + 177 + ], + "blocks": [ + { + "bbox": [ + 307, + 71, + 355, + 177 + ], + "lines": [ + { + "bbox": [ + 307, + 71, + 355, + 177 + ], + "spans": [ + { + "bbox": [ + 307, + 71, + 355, + 177 + ], + "type": "image", + "image_path": "c440c55cc02b958c84f12ad7a8298234313ef108b88fa94a3cbbb1f86970bb41.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + } + ], + "index": 11 + }, + { + "type": "image", + "bbox": [ + 356, + 71, + 403, + 177 + ], + "blocks": [ + { + "bbox": [ + 356, + 71, + 403, + 177 + ], + "lines": [ + { + "bbox": [ + 356, + 71, + 403, + 177 + ], + "spans": [ + { + "bbox": [ + 356, + 71, + 403, + 177 + ], + "type": "image", + "image_path": "237ca72180cfbc71adae202ee6c29ebd2c35637ae08f66909cd87323144b7845.jpg" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_body" + } + ], + "index": 12 + }, + { + "type": "image", + "bbox": [ + 403, + 71, + 449, + 177 + ], + "blocks": [ + { + "bbox": [ + 403, + 71, + 449, + 177 + ], + "lines": [ + { + "bbox": [ + 403, + 71, + 449, + 177 + ], + "spans": [ + { + "bbox": [ + 403, + 71, + 449, + 177 + ], + "type": "image", + "image_path": "cc251d1431e00b91b31451d1a6049f8dbb791af498e0c71985106b82f62930d8.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_body" + } + ], + "index": 13 + }, + { + "type": "image", + "bbox": [ + 450, + 71, + 496, + 177 + ], + "blocks": [ + { + "bbox": [ + 450, + 71, + 496, + 177 + ], + "lines": [ + { + "bbox": [ + 450, + 71, + 496, + 177 + ], + "spans": [ + { + "bbox": [ + 450, + 71, + 496, + 177 + ], + "type": "image", + "image_path": "fe3f7a6cf8ffe68a082603c89741f37670d82c9e50523b58ce6d04f68d152852.jpg" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_body" + } + ], + "index": 14 + }, + { + "type": "image", + "bbox": [ + 497, + 71, + 545, + 177 + ], + "blocks": [ + { + "bbox": [ + 497, + 71, + 545, + 177 + ], + "lines": [ + { + "bbox": [ + 497, + 71, + 545, + 177 + ], + "spans": [ + { + "bbox": [ + 497, + 71, + 545, + 177 + ], + "type": "image", + "image_path": "824322d2f217507f1e5c57c36d7b87a4d026f715526b6953d38b7481b9c03af2.jpg" + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_body" + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 238, + 545, + 286 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 238, + 545, + 286 + ], + "spans": [ + { + "bbox": [ + 305, + 238, + 545, + 286 + ], + "type": "text", + "content": "of binarization becomes steeper. Moreover, being smaller is inadequate for weakening message passing, while being larger will destroy the adaptive capacity of the network. It is obvious that the setting of 500 is the optimal solution." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 306, + 293, + 426, + 304 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 293, + 426, + 304 + ], + "spans": [ + { + "bbox": [ + 306, + 293, + 426, + 304 + ], + "type": "text", + "content": "4.5. Visualization Results" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 312, + 545, + 407 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 312, + 545, + 407 + ], + "spans": [ + { + "bbox": [ + 304, + 312, + 545, + 407 + ], + "type": "text", + "content": "Qualitative results. As shown in Figure 4, We provide predicted forgery masks of various methods. Since the source code of ObjectFormer [46] is not available, their predictions are not available. The results demonstrate that our method could not only locate the tampering regions more accurately but also develop sharp boundaries. It benefits from the explicit modeling of inconsistencies and the full exploitation of edges by our method." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 407, + 545, + 491 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 407, + 545, + 491 + ], + "spans": [ + { + "bbox": [ + 304, + 407, + 545, + 491 + ], + "type": "text", + "content": "Visualization of message passing controller. To verify the usefulness of the region message passing controller (RMPC), we show the change of features before and after the controller in Figure 6. It is clear that RMPC facilitates the learning of forgery features and prevents false alarms. Specifically, the network without RMPC will make false judgments about objects that are similar to the forgery." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 304, + 491, + 545, + 551 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 491, + 545, + 551 + ], + "spans": [ + { + "bbox": [ + 304, + 491, + 545, + 551 + ], + "type": "text", + "content": "Visualization of edge reconstruction. To verify the effect of the edge reconstruction (ER) module, the change of features before and after EG is shown in Figure 7. The results demonstrate that the EG can effectively acquire accurate edges, thus helping our model to perform well." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 306, + 562, + 378, + 574 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 562, + 378, + 574 + ], + "spans": [ + { + "bbox": [ + 306, + 562, + 378, + 574 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "content": "In this paper, we propose a novel Image Forgery Localization framework with a two-step Edge-aware Regional Message Passing Controlling strategy. In detail, the first step is to account for fully exploiting the edge information. In the second step, guided by the learnable edges, an edge-aware dynamic graph is devised to weaken the message passing between the forged and authentic regions. Our paper provides a new research strategy to solve the misjudgment problem in the field of IFL. Extensive experimental results on several benchmarks demonstrate the effectiveness of the proposed algorithm." + } + ] + } + ], + "index": 23 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "8229" + } + ] + } + ], + "index": 24 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 288, + 715 + ], + "type": "list", + "angle": 0, + "index": 14, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 145 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 145 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 145 + ], + "type": "text", + "content": "[1] Mohammed Aloraini, Mehdi Sharifzadeh, and Dan Schonfeld. 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Springer, 2023. 1" + } + ] + } + ], + "index": 15 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "type": "text", + "content": "8232" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 10 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Edges to Shapes to Concepts_ Adversarial Augmentation for Robust Vision/d0d50664-1fef-4fb1-8679-7306724f6c4b_content_list.json b/2023/Edges to Shapes to Concepts_ Adversarial Augmentation for Robust Vision/d0d50664-1fef-4fb1-8679-7306724f6c4b_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..f3eb92828e3bfde09952adcf7b0dd34a9cbc108e --- /dev/null +++ b/2023/Edges to Shapes to Concepts_ Adversarial Augmentation for Robust Vision/d0d50664-1fef-4fb1-8679-7306724f6c4b_content_list.json @@ -0,0 +1,1400 @@ +[ + { + "type": "text", + "text": "Edges to Shapes to Concepts: Adversarial Augmentation for Robust Vision", + "text_level": 1, + "bbox": [ + 107, + 130, + 861, + 152 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Aditay Tripathi $^{1*}$ Rishubh Singh $^{2}$ Anirban Chakraborty $^{1}$ Pradeep Shenoy $^{2}$ $^{1}$ CDS, Indian Institute of Science $^{2}$ Google Research India shenoypradeep@gmail.com", + "bbox": [ + 117, + 178, + 849, + 233 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 268, + 313, + 285 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Recent work has shown that deep vision models tend to be overly dependent on low-level or \"texture\" features, leading to poor generalization. Various data augmentation strategies have been proposed to overcome this so-called texture bias in DNNs. We propose a simple, lightweight adversarial augmentation technique that explicitly incentivizes the network to learn holistic shapes for accurate prediction in an object classification setting. Our augmentations superpose edgemaps from one image onto another image with shuffled patches, using a randomly determined mixing proportion, with the image label of the edgemap image. To classify these augmented images, the model needs to not only detect and focus on edges but distinguish between relevant and spurious edges. We show that our augmentations significantly improve classification accuracy and robustness measures on a range of datasets and neural architectures. As an example, for ViT-S, We obtain absolute gains on classification accuracy gains up to $6\\%$ . We also obtain gains of up to $28\\%$ and $8.5\\%$ on natural adversarial and out-of-distribution datasets like ImageNet-A (for ViT-B) and ImageNet-R (for ViT-S), respectively. Analysis using a range of probe datasets shows substantially increased shape sensitivity in our trained models, explaining the observed improvement in robustness and classification accuracy.", + "bbox": [ + 76, + 301, + 473, + 680 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 710, + 209, + 726 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "A growing body of research catalogues and analyzes apparent failure modes of deep vision models. For instance, work on texture bias [1,7,12] suggests that image classifiers are overdependent on textural cues and fail against simple (adversarial) texture substitutions. Relatedly, the idea of simplicity bias [25] captures the tendency of deep models to use weakly predictive \"simple\" features such as color or texture, even in the presence of strongly predictive complex features. In psychology & neuroscience, too, evidence", + "bbox": [ + 76, + 737, + 468, + 875 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/1c5ac6a664b11df457ab1af568be30eabe35746be11f2d742b77e5e003b2ea62.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 501, + 276, + 906, + 448 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/0d4cf708e57e24be696e6f614c301a61e31234ae913c7fc46d7ae53708e7691d.jpg", + "image_caption": [ + "Figure 1. Comparison of the models on robustness and shape-bias. The shape factor gives the fraction of dimensions that encode shape cues [17]. Backbone(T) denotes texture shape debiased (TSD) models [21]. In comparison, ELEAS denoted by Backbone(E) is more shape biased and shows better performance on ImageNet-C and ImageNet-A datasets." + ], + "image_footnote": [], + "bbox": [ + 501, + 453, + 908, + 636 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "suggests that deep networks focus more on \"local\" features rather than global features and differ from human behavior in related tasks [19]. More broadly speaking, there is a mismatch between the cognitive concepts and associated world knowledge implied by the category labels in image datasets such as Imagenet and the actual information content made available to a model via one-hot vectors encoding these labels. In the face of under-determined learning problems, we need to introduce inductive biases to guide", + "bbox": [ + 496, + 763, + 893, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 810, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Work done at Google Research India.", + "bbox": [ + 94, + 886, + 300, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "24470", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/5c0a254668a3da9bd24bf823a5852d733ab8e379a3c94ac932f00efa25595541.jpg", + "image_caption": [ + "Figure 2. Representative performance comparison of our model, with the 'Debiased' models (TSD [21]) on ImageNet-A, R, C, and Sketch datasets. The models trained using ELEAS show improved performance on out-of-distribution robustness datasets. The large performance improvement on the ImageNet-A dataset indicates better robustness to natural adversarial examples." + ], + "image_footnote": [], + "bbox": [ + 81, + 88, + 285, + 281 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/57527a133e97d646058114dbc503af3a36941281e51c7f397fded698786c14c7.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 290, + 88, + 483, + 281 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/a6fb6d8dce5602d9295c32affce1376036a18bbc55752dcb19da6178618a67a6.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 488, + 88, + 681, + 281 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/bf59e34cc2a795bc93e2c0aaf37dbcc32f80699161d6ccba19aad7d9fa29e1e4.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 689, + 88, + 885, + 281 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "the learning process. To this end, Geirhos et al. [7] proposed a data augmentation method wherein the texture of an image was replaced with that of a painting through stylization. Follow-on work improved upon this approach by replacing textures from other objects (instead of paintings) and teaching the model to separately label the outer shape and the substituted texture according to their source image categories [21]. Both these approaches discourage overdependence on textural features in the learned model; however, they do not explicitly incentivize shape recognition.", + "bbox": [ + 75, + 363, + 472, + 515 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "We propose a lightweight adversarial augmentation technique ELEAS (Edge Learning for Shape sensitivity) that is designed to increase shape sensitivity in vision models. Specifically, we augment a dataset with superpositions of random pairs of images from the dataset, where one image is processed to produce an edge map, and the other is modified by shuffling the location of image patches within the image. The two images are superposed using a randomly sampled relative mixing weight (similar to Mixup [30]), and the new superposed image is assigned the label of the edgemap image. ELEAS is designed to specifically incentivize not only edge detection but shape sensitivity: 1) classifying the edgemap image requires the model to extract and exploit edges - the only features available in the image, 2) distinguishing the edgemap object category from the superposed shuffled image requires the model to distinguish the overall edgemap object shape (relevant edges) from the shuffled image edges (irrelevant edges, less likely to be \"shape like\"). We perform extensive experiments over a range of model architectures, image classification datasets, and probe datasets, comparing ELEAS against recent baselines. Figure 1 provides a small visual sample of our findings and results; across various models, a measure of shape sensitivity [17] correlates very strongly with measures of classifier robustness [11, 12] (see Results", + "bbox": [ + 75, + 523, + 472, + 902 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "for more details), validating the shape sensitivity inductive bias. In addition, for a number of model architectures, models trained with ELEAS significantly improve both measures compared to the previous SOTA data augmentation approach [21].", + "bbox": [ + 496, + 363, + 893, + 438 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Summing up, we make the following contributions:", + "bbox": [ + 517, + 439, + 861, + 455 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- We propose an adversarial augmentation technique, ELEAS, designed to incentivize shape sensitivity in vision models. Our augmentation technique is lightweight (needing only an off-the-shelf edge detection method) compared to previous proposals that require expensive GAN-based image synthesis [7, 21].", + "- In experiments, ELEAS shows increased shape sensitivity on a wide range of tasks designed to probe this property. Consequently, we obtain increased accuracy in object classification with a $6\\%$ improvement on ImageNet-1K classification accuracy for ViT-Small among others.", + "- ELEAS shows high generalizability and out of distribution robustness with $14.2\\%$ improvement in ImageNet-C classification performance and $5.89\\%$ increase in shape-bias for Resnet152." + ], + "bbox": [ + 517, + 464, + 890, + 724 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related work", + "text_level": 1, + "bbox": [ + 500, + 739, + 638, + 755 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Texture bias in vision models. In [1,7], convolutional neural networks are shown to be more sensitive towards the texture present in the image to classify the object correctly. Further, in order to mitigate the texture bias, they have suggested a training strategy where they have used modified images with random texture along with the natural images during training. However, utilizing images with conflicting textures leads to an unnatural shift in data distribution, leading to drops in performance on natural images. Instead, sim", + "bbox": [ + 496, + 763, + 893, + 902 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "24471", + "bbox": [ + 478, + 944, + 517, + 957 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "ple and naturalistic data augmentations strategies can also lead to an increase in shape bias of the CNNs without much loss in performance on natural images [13]. An increase in shape-bias in the CNN models is associated with an increase in the robustness of the models [7, 26], however [22] suggested that a more balanced shape or texture biased models also leads to increase in the model robustness. The study of texture bias in vision models has been extended to the vision transformers (ViT) [3], where the transformer models are found to be less texture biased than the convolutional models [27].", + "bbox": [ + 75, + 90, + 472, + 256 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "A measure of shape/texture bias is proposed in [7], where they used images with conflicting textures obtained using style-transfer methods. However, this measure ignores a large portion of test images and is biased toward models trained using images modified by style-transfer methods. In [14], Hermann et al. proposed a linear classification layer in order to measure the shape decodability of the representations learned by the model. A more fine-grained shape evaluation measure was proposed in [18] where they compute the number of dimensions in the image representation that correlate with the shape features. Further, they proposed a shallow read-out module that takes feature representations from the model and predicts a segmentation map.", + "bbox": [ + 75, + 257, + 472, + 454 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Data Augmentation for improving shape-bias In [2, 7], authors suggested a data augmentation strategy in order to increase the shape bias in the trained models. They proposed the Stylized-ImageNet dataset, where they strip each image of its original texture and replace it with the style of a randomly selected painting through AdaIN style transfer [16]. During training, the model is trained to predict the category corresponding to the shape in the model, ignoring the texture, thus leading to an increase in the shape bias of the models. However, instead of changing the distribution of training images through style transfer, naturalistic data augmentation techniques such as can also lead to improvement in the shape bias of the model [13].", + "bbox": [ + 75, + 454, + 472, + 650 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Methodology", + "text_level": 1, + "bbox": [ + 76, + 662, + 212, + 681 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We now describe the training strategy used in ELEAS to increase the shape sensitivity of deep image classifiers.", + "bbox": [ + 75, + 688, + 468, + 718 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Let $\\mathcal{I}$ , and $\\mathcal{C}$ be the set of all images and their corresponding categories in the dataset. In standard classifier training, a classifier $\\Theta$ is trained to predict the category $c \\in \\mathcal{C}$ of the image $i \\in \\mathcal{I}$ . However, the image classifiers trained in this way are sensitive to the texture present in the natural images. In this work, we propose to use edge maps along with textures from natural images to increase the shape sensitivity of image classifiers.", + "bbox": [ + 75, + 719, + 468, + 840 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Obtaining shapes and textures: We approximate the shapes of objects by extracting edge-maps from images and natural textures by shuffling patches within images. In particular, for each image $i \\in \\mathcal{I}$ , an edge-map is constructed", + "bbox": [ + 75, + 840, + 470, + 901 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "using an edge detection kernel (i.e., Laplacian kernel) to produce the set of all edge-maps or \"shapes\" $S$ . Similarly, a \"texture\" dataset $\\mathcal{T}$ is generated by first dividing an image in $\\mathcal{I}$ into $4 \\times 4$ patches and then randomly shuffling the patches within the image to obtain a patch-shuffled image.", + "bbox": [ + 496, + 90, + 890, + 167 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Generating augmentations: We superimpose randomly selected pairs of images $s \\in S$ and $t \\in \\mathcal{T}$ to create new images, or augmentations, to add to the training dataset. Each such augmented image is assigned the label of the shape image $s$ . The superimposed image is obtained as follows:", + "bbox": [ + 496, + 167, + 890, + 242 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\ni _ {s} = \\lambda * t + (1 - \\lambda) * s \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 612, + 253, + 890, + 270 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\lambda$ is drawn randomly from a $\\operatorname{Beta}(\\alpha, \\beta)$ distribution. The parameters $\\alpha$ and $\\beta$ are chosen such that a higher weight is given to the samples from set $T$ . The random weighing parameter $\\lambda$ introduces variation in the augmented image set and helps to obtain better edge-map classification. Let's call the set of superimposed images $\\mathcal{B}$ .", + "bbox": [ + 496, + 281, + 890, + 372 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Training procedure: Training proceeds via minibatch gradient descent, as is standard in current machine learning literature. We construct each mini-batch to have half of its images from the set of natural images $I \\subset \\mathcal{I}$ and the rest from the augmented dataset $B \\subset \\mathcal{B}$ . During training, we minimize the cross-entropy loss on natural image samples as well as our augmentations. In order to carefully control the degree of shape sensitivity induced by this process, we compute a weighted mixture of cross-entropy loss on these two image sets denoted here by $L$ :", + "bbox": [ + 496, + 372, + 890, + 523 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nL (I, B, y _ {I}, y _ {B}) = \\eta * C E (I, y _ {I}) + 1 - \\eta * C E (B, y _ {B}) \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 506, + 534, + 890, + 551 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\eta$ is varied to control the shape sensitivity, $CE$ is the cross-entropy loss, $y_{I}, y_{B}$ are the labels corresponding to the natural and augmented image sets $I, B$ respectively. To predict augmented images correctly, the model needs to interpret the edge-map present in the superimposed sample while at the same time ignoring distracting edges and textures from the other superimposed image. In this manner, we induce shape sensitivity in learned classifiers. The minibatch-mixing strategy encourages the model to generalize learned representations across natural and augmented images, thereby improving shape bias (and consequently overall accuracy) on natural images as well.", + "bbox": [ + 496, + 561, + 890, + 744 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "4. Experimental setup", + "text_level": 1, + "bbox": [ + 498, + 757, + 689, + 773 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "4.1. Models and training setup", + "text_level": 1, + "bbox": [ + 498, + 782, + 736, + 799 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We train convolutional neural networks (CNNs) and Vision Transformers (ViTs) using our methodology. Among the CNN models, similar to [21], we show results on ResNet50, ResNet101, and ResNet152. For training the", + "bbox": [ + 496, + 805, + 890, + 866 + ], + "page_idx": 2 + }, + { + "type": "page_footnote", + "text": "1Refer to Fig. 1 in the supplementary material for examples of ELEAS images.", + "bbox": [ + 500, + 875, + 893, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "24472", + "bbox": [ + 478, + 944, + 519, + 955 + ], + "page_idx": 2 + }, + { + "type": "table", + "img_path": "images/fbccdfe57fcdd54e4040fa3644af0cfb6ba4c7d51faec5394cea573391c8010e.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
ModelMethodIN-A(↑)IN-R(↑)IN-C(↓)IN-Sketch(↑)IN-1K(↑)
Resnet50Vanilla2.036.275.023.576.4
TSD [21]3.340.867.528.376.9
ELEAS5.441.758.529.777.1
Resnet101Vanilla5.639.369.827.178.0
TSD [21]8.844.362.232.378.8
ELEAS13.444.453.532.478.6
Resnet152Vanilla5.941.367.228.478.6
TSD [21]12.545.558.933.379.7
ELEAS15.445.753.034.779.0
ViT-SVanilla16.636.155.133.274.6
TSD [21]27.444.442.232.476.4
ELEAS28.344.741.534.780.6
ViT-BVanilla34.640.750.845.879.5
ELEAS62.956.435.946.485.5
ViT-LVanilla63.463.333.152.785.8
ELEAS67.465.929.554.186.2
", + "bbox": [ + 196, + 88, + 772, + 392 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Table 1. Performance comparison on the ImageNet and the robustness datasets. The models trained using ELEAS show an improvement in the ImageNet performance along with better robustness. Except for IN-C the performance is measured in Accuracy@1 (higher is better). For IN-C, the performance is measured in mean corruption error (mCE) (lower is better). (Refer to Sections 5.1 and 5.2.1)", + "bbox": [ + 75, + 402, + 893, + 446 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "ResNet models, we supplemented ImageNet data with an equal number of augmented images. We trained them for 100 epochs with a starting learning rate of 0.2 which is reduced by a factor of 10 at the 30th, 60th and 90th epoch. Similar to TSD, while training the ResNet models, we also use auxiliary batch norm [29]. As ViTs are compute-intensive, we finetune ImageNet pretrained ViT models for 20k steps with a cosine learning rate schedule with a starting learning rate of 0.01. The stochastic gradient descent (SGD) with a momentum of 0.9 is used to train the models. We train all our models on 8 A100 GPUs with a batch size of 512 for ResNets, 256 for ViT-Small and ViT-Base and 128 for ViT-Large. We find that values $\\alpha = 4$ , $\\beta = 1$ , and $\\eta = 0.65$ produce the best results for all models.", + "bbox": [ + 75, + 472, + 472, + 684 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4.2. Datasets and evaluation protocol", + "text_level": 1, + "bbox": [ + 76, + 695, + 364, + 710 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The models are trained on the ILSVRC 2012 [24] dataset with 1.28M training and 50k validation images. We evaluate and compare our trained models to answer the following questions: (i) Does ELEAS lead to an increase in the shape-sensitivity of a model? (ii) Does the increased shape sensitivity result in better classification performance? (iii) Does the robustness of the models to distribution shift improve with increased shape sensitivity? and (iv) Does an increase in shape sensitivity lead to improvement in downstream tasks such as object detection and instance segmentation?", + "bbox": [ + 75, + 718, + 468, + 883 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The shape sensitivity of the models is first evaluated us", + "bbox": [ + 96, + 885, + 468, + 900 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "ing the metric proposed in [7]. The authors first created an image dataset called cue-conflict, using a style-transfer method to transfer texture from one image to another. They then defined shape bias as the fraction of the shape decision when the model predicts either the shape or the texture category. However, this metric ignores many a lot of images and is biased toward the methods that used Stylized-ImageNet during the training of the models. Further, authors in [17] proposed a method to quantify the number of dimensions in the image representation that encode the object's shape. They take a pair of images with similar semantic concepts (i.e., shape) and then count the number of neurons that encode that specific concept. They have used Pascal VOC [4] and Stylized Pascal VOC dataset to create pair of images with particular semantic concepts. We have used these metrics to evaluate the shape bias in this work. Further, similar to [17], we also evaluate the quality of the shape encoding from these models by performing the binary and semantic segmentation on the frozen representations. PASCAL VOC is image segmentation dataset [4, 8], with 10,582 training images and 1,449 validation images spanning across 20 object categories.", + "bbox": [ + 496, + 472, + 890, + 805 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The out-of-distribution generalization of the trained models is evaluated on four publicly available datasets, which are, ImageNet-A [12], ImageNet-R [10], ImageNet-C [11], and ImageNet-Sketch [28]. The ImageNet-A dataset consists of real-world natural adversarial images and is a challenging classification dataset. The ImageNet-R dataset", + "bbox": [ + 496, + 809, + 893, + 902 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "24473", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 3 + }, + { + "type": "table", + "img_path": "images/7e7bb236cbf78499bb76fc932e1eb1aa84d8da3faafdfc04b59ef53c47b6e1f9.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
ModelMethodEdgeSilhouetteCue-conflictSketchStylized-IN
Resnet50Vanilla13.7554.3818.2059.6237.13
TSD [21]22.555.6221.4067.056.13
ELEAS35.6254.3721.4167.8846.0
Resnet101Vanilla23.8549.3719.9263.1241.75
TSD [21]31.2551.8724.9270.1259.37
ELEAS45.0061.2524.0671.8848.25
Resnet152Vanilla20.6356.2520.7066.7541.63
TSD [21]22.558.12525.3169.1357.67
ELEAS41.8856.8823.8373.3848.75
ViT-SVanilla25.026.2522.9649.1244.25
TSD [21]22.546.8731.7168.6277.5
ELEAS34.3843.1327.6669.6353.00
ViT-BVanilla13.7512.0528.0551.6350.08
ELEAS41.2566.2534.9282.0059.38
ViT-LVanilla55.6268.7540.3983.7565.50
ELEAS75.0069.3842.1185.8866.50
", + "bbox": [ + 197, + 88, + 772, + 393 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Table 2. Performance comparison on out-of-distribution benchmark proposed in [6]. The proposed method significantly improves performance over vanilla ResNet models. Debiased models, trained on stylized images, show high performance on datasets utilizing stylized images for evaluation, such as Cue-Conflict and Stylized-IN. (Refer to Section 5.2.2)", + "bbox": [ + 75, + 402, + 893, + 446 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "consists of images with various renditions, such as cartoon art, DeviantArt, graphics, paintings, origami, etc., of the objects present in the original ImageNet dataset. The ImageNet-Sketch dataset consists of sketches of 1000 ImageNet object categories. Both ImageNet-R and ImageNet-Sketch are used to evaluate the out-of-distribution generalization capability of the models. The ImageNet-C dataset consists of images with varying degrees of artificial distortions like 'Gaussian Noise', 'Motion Blur', 'Speckle Noise', etc. Hence, it evaluates the robustness of the model to added distortions.", + "bbox": [ + 75, + 472, + 472, + 637 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Besides using classification accuracy for most datasets, ImageNet-C's performance is measured using mean corruption error (mCE). Additionally, we evaluated the models on the out-of-distribution benchmark proposed in [6].", + "bbox": [ + 76, + 638, + 470, + 700 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.2.1 Baselines", + "text_level": 1, + "bbox": [ + 76, + 724, + 194, + 738 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We compare the performance of ELEAS with Shape-Texture Debiased (TSD) trained models [21], which focus on both shape and texture cues. TSD uses stylized ImageNet images with conflicting shape and texture cues, and the models are trained using supervision from both semantic cues. Among ViTs, only ViT-S is trained with TSD due to the large computation overhead involved in training ViT-B and ViT-L. In contrast, ELEAS learns the overall object shape in the presence of conflicting, less 'shape-like' edges, leading to increased shape sensitivity in the trained models.", + "bbox": [ + 75, + 750, + 472, + 902 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "5. Results and discussion", + "text_level": 1, + "bbox": [ + 498, + 470, + 712, + 486 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Our experiments study the impact of ELEAS in the following stages: we show classification accuracy gains on the ImageNet dataset; we measure the robustness of trained models to a range of prediction challenges; and we examine ELEAS's influence on shape-sensitivity of trained models and its effect on performance.", + "bbox": [ + 496, + 496, + 890, + 588 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "5.1. Classification", + "text_level": 1, + "bbox": [ + 498, + 595, + 638, + 609 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Along with the increase in shape bias, ELEAS also improves classification performance on the ImageNet dataset, in many cases by very large margins (Refer Table 1). For instance, we see $5.96\\%$ and $5.93\\%$ absolute improvement in ImageNet classification accuracy for ViT-S and ViT-B respectively, compared to vanilla baseline, and a smaller but still significant $4.22\\%$ gain in accuracy compared to TSD on ViT-S. We also see $0.6\\%$ , $0.62\\%$ , and $0.44\\%$ increase in performance for ResNet50, ResNet101, and ResNet152 models respectively.", + "bbox": [ + 496, + 618, + 890, + 771 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "5.2. Out-of-distribution robustness", + "text_level": 1, + "bbox": [ + 498, + 777, + 769, + 792 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "5.2.1 Evaluation on ImageNet-A, R, C, and Sketch datasets.", + "text_level": 1, + "bbox": [ + 498, + 800, + 890, + 830 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "As shown in Table 1, ELEAS significantly improves accuracy over both vanilla and TSD-trained models at these robustness challenges. For ImageNet-A, the considerable improvement (4.54% vs. TSD on ResNet101) indicates bet", + "bbox": [ + 496, + 839, + 890, + 902 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "24474", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/4221d130efa72ff6569ecbb78627dd6db5ce0b350b3d626cf55927fa39068ba9.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 76, + 88, + 343, + 258 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/56dff3c237e7d5bf7e279e1ae6ac5c23189b669a12695dd4ae4f26ebecfa3aa7.jpg", + "image_caption": [ + "(a) True vs. false color", + "(d) Uniform Noise" + ], + "image_footnote": [], + "bbox": [ + 76, + 273, + 343, + 446 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/ffdd3c6786cfeeb9435ba2ea783bf404175216e5ad008ed72227d5596d9f4762.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 76, + 460, + 343, + 632 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/d898887f6e5c3d0e5ab4e7308b1b599f909d4c625aa4ea6ebc906bbc6bd56406.jpg", + "image_caption": [ + "(g) Phase-noise", + "(j) EidolonI", + "Figure 3. Robustness comparison of ELEAS trained Resnet152 and ViT-B with the human subjects. ELEAS leads to trained models which are more robust to added distortion and for many of the noise types it is more robust than the human subjects. (Refer to Section 5.2.1)" + ], + "image_footnote": [], + "bbox": [ + 76, + 646, + 344, + 819 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/3419d55fd5362e83a812fc16c020eda605d4a89b5fb91be5fbbcc6727c9e1fef.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 351, + 87, + 616, + 260 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/0c869195544fe46778f95167853f5bfa8af8593e9f4f44fad5381d83ca859343.jpg", + "image_caption": [ + "(b) Contrast", + "(e) Low-pass" + ], + "image_footnote": [], + "bbox": [ + 351, + 273, + 616, + 446 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/273e60621679449ce0ccdf7e96411191016759a2773c23023394508cb69b0859.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 351, + 463, + 616, + 632 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/cf62a73de5c92603787d63864a051a2cfd777d8aae20d00b012e6a79a572cfec.jpg", + "image_caption": [ + "(h) Power Equalisation", + "(k) EidolonII" + ], + "image_footnote": [], + "bbox": [ + 351, + 646, + 616, + 819 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/96a0bd5ccf6ee5f3749816f0fce86c8437b209b5a6520a800cdfb384d7d6d7a7.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 627, + 90, + 890, + 258 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/f416cd6bfe7874aa099b218e9c1877be243c71e2e705e209cbf0d6d0ea0b1fe7.jpg", + "image_caption": [ + "(c) Color vs greyscale" + ], + "image_footnote": [], + "bbox": [ + 627, + 273, + 890, + 446 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/268b7a49e2d285f7d0609203644485ebe8bba93339c65ad9a106bde73d6f67c1.jpg", + "image_caption": [ + "(f) High-pass", + "(i) Rotation" + ], + "image_footnote": [], + "bbox": [ + 627, + 460, + 890, + 632 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/cb547ba58ca320e73ef83a1825899b2a497afde1d0a54336c9e8821f1d4f397e.jpg", + "image_caption": [ + "(1) EidolonIII" + ], + "image_footnote": [], + "bbox": [ + 627, + 646, + 890, + 819 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "24475", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/ec33ffabf7e9648432bdd66f4e67cc8162b900f85804f6ba3ce34382569b8bb3.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
ModelMethodShape-biasFactor |zk|
Shape dimTexture dim
Res50Vanilla19.750.1700.338
TSD [21]23.110.1850.285
ELEAS23.530.1950.299
Res101Vanilla22.440.1780.323
TSD [21]27.690.2040.256
ELEAS26.040.2220.259
Res152Vanilla21.740.1800.298
TSD [21]28.780.2070.236
ELEAS27.860.2280.249
ViT-SVanilla33.330.2140.210
TSD [21]36.560.2160.213
ELEAS34.640.2210.217
ViT-BVanilla33.120.2190.212
ELEAS37.900.2390.205
ViT-LVanilla47.040.2160.221
ELEAS48.100.2250.207
", + "bbox": [ + 84, + 88, + 460, + 385 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 3. Comparison of the shape-bias of the models. The vision models trained using our strategy shows an increase in the fraction of 'Shape' dimensions. However, the shape-bias metric proposed by Geirhos et al. [7] is biased towards the models trained using style-transfer datasets. (Refer to Section 5.3)", + "bbox": [ + 75, + 396, + 468, + 465 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "ter robustness to naturally occurring adversarial examples. Similarly, the improvement in mCE on ImageNet-C (8.72% vs. TSD on ResNet101) showcases robustness to added distortions of various degrees. Similarly, ELEAS shows robustness performance improvements on the ViT models. These large gains are driven primarily by ELEAS's ability to better encode object shape (Refer Figure 1 for evidence supporting this causal link.)", + "bbox": [ + 75, + 493, + 467, + 612 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.2.2 Evaluation on OOD benchmark [6]", + "text_level": 1, + "bbox": [ + 76, + 633, + 375, + 648 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We also evaluated trained models on the OOD benchmark proposed in [6]; results are in Table 2. The datasets in this benchmark consist of images from different domains such as 'Edge', 'Silhouette', 'Sketch', 'Stylized', and 'Cue-conflict', which require stronger shape sensitivity for correct classification. The 'Cue-conflict' dataset is generated using iterative style transfer [5], where the texture from a source image is transferred to a target image. Since these images contain cues corresponding to different objects, it is challenging to classify them without good shape-sensitive representations. Similarly, the Stylized imagenet (SIN) is generated by replacing the texture present in an image with style from a randomly selected painting using the AdaIN style transfer method [16]. Models trained using ELEAS can better encode object shapes in images, leading to large performance improvements on these datasets over", + "bbox": [ + 75, + 657, + 468, + 900 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/157199e1430337ca7081323849a7278d5a75a508f461bf00aa232e845563f208.jpg", + "image_caption": [ + "Figure 4. Shape vs. texture bias for the vision models: The images with conflicting shape and texture cues are used to calculate the shape bias of the trained models. The ELEAS trained models show improvement in shape-bias. We have shown results for ResNet152 and ViT-B in this figure.(Refer to Section 5.3)" + ], + "image_footnote": [], + "bbox": [ + 500, + 88, + 890, + 417 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "the vanilla model. The better performance of TSD is expected as these models are trained using images from similar domains, i.e., the Stylized ImageNet dataset.", + "bbox": [ + 498, + 537, + 890, + 583 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We further evaluated robustness to distortion using the proposed benchmarks (Refer to Figure 3), which shows improved robustness to added distortions of varying degrees for ELEAS.", + "bbox": [ + 498, + 583, + 890, + 642 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.3. Increasing shape sensitivity", + "text_level": 1, + "bbox": [ + 500, + 652, + 745, + 669 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We measure shape-sensitivity using the datasets and protocols described in Section 4.2; the results are in Tables 3 and 4. Models trained using ELEAS show a large $6.12\\%$ and $4.78\\%$ increase in shape-bias for ResNet152 and ViT-L models, respectively, compared to vanilla baselines and are comparable to the shape-bias of models trained using TSD. We further added class-wise shape bias comparison with human subjects in Figure 4.", + "bbox": [ + 498, + 676, + 890, + 795 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "An alternative measure, the shape factor [17], counts the number of dimensions in the image representation that encodes shape. ELEAS substantially increases the number of", + "bbox": [ + 498, + 797, + 890, + 842 + ], + "page_idx": 6 + }, + { + "type": "page_footnote", + "text": "2Note that shape bias [7] has limitations: since it is defined in terms of a Stylized-ImageNet test set, the metric is biased towards methods that use SIN as a training augmentation. Further, it ignores images on which neither of the true shape/texture categories is predicted.", + "bbox": [ + 498, + 849, + 890, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "24476", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/e6c1eeabc986144a98b336e1f40a92e99011de754179b23f5022c30575ee3719.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
ModelMethodBinSem
Resnet50Vanilla79.861.6
TSD [21]78.961.1
ELEAS79.261.9
Resnet101Vanilla80.463.4
TSD [21]80.064.7
ELEAS81.065.9
Resnet152Vanilla80.364.4
TSD [21]79.865.5
ELEAS81.066.6
", + "bbox": [ + 138, + 88, + 410, + 268 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "shape dimensions in trained models (Table 3). We further evaluated shape decodability from learned representations by predicting the binary and semantic mask of the object in the image (Table 4). The segmentation is performed by adding a three-layer readout module on top of the learned representations. The read-out module is trained on PASCAL VOC 2012 dataset [4].", + "bbox": [ + 75, + 390, + 468, + 496 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Resnet(TSD) [21] shows a significant worsening of binary segmentation performance for all models and semantic segmentation performance for ResNet50, suggesting that their learned representations cannot predict pixel-wise object categories. ELEAS-trained model shows an increase in Semantic segmentation performance, indicating better decodingability of pixel-wise semantic categories of objects.", + "bbox": [ + 75, + 497, + 468, + 604 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5.4. Instance Segmentation and Object detection performance", + "text_level": 1, + "bbox": [ + 76, + 614, + 468, + 647 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "To evaluate the effectiveness of the shape-sensitive image representations in downstream tasks such as object detection and segmentation, we trained the MaskRCNN [9] model using ResNet101 as the backbone. Results are reported in Tables 5 for models trained on the MS-COCO dataset. The model trained using ELEAS outperformed other models by a significant margin in both object detection $(\\approx 1.8\\mathrm{mAP})$ and instance segmentation tasks $(\\approx 1.3\\mathrm{mAP})$ , indicating that learned shape-sensitive representations can improve performance in these tasks. In contrast, TSD showed decreased performance even when compared to the Vanilla backbone.", + "bbox": [ + 75, + 652, + 470, + 834 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5.5. Lightweightness of ELEAS", + "text_level": 1, + "bbox": [ + 76, + 845, + 312, + 863 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Compared to previous augmentation methods, ELEAS is lightweight. Edge maps and shuffled patch images can be", + "bbox": [ + 76, + 869, + 468, + 902 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/8a6963dfc9fc069098d9581898a2fd7532f9894ccacb01f78ea702d017c30b6f.jpg", + "table_caption": [ + "Table 4. Shape decodability of the learned representations: To evaluate the amount of shape information, read-out modules are added to the frozen learned representation and used to predict binary (Bin) and semantic (Sem) segmentation masks [17], with performance measured by mIoU. The shape decodability of the models is evaluated using the Pascal VOC dataset. (Section 5.3)" + ], + "table_footnote": [], + "table_body": "
ModelObject DetectionInstance Segmentation
mAPAP@0.50AP@0.75mAPAP@0.50AP@0.75
Vanilla39.8760.2143.3336.3557.3938.79
TSD [21]37.8258.9841.2933.8755.4135.85
ELEAS41.6561.8345.4337.6358.9940.33
", + "bbox": [ + 501, + 89, + 893, + 156 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 5. Effect of shape sensitivity on Object Detection and Segmentation performance. The shapes-sensitive ResNet101 (i.e. ELEAS) backbone leads to improvement in object detection and instance segmentation performance. The models are evaluated on the COCO-Val2017 dataset.", + "bbox": [ + 498, + 166, + 890, + 234 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "precomputed and stored on disk, and obtaining adversarial augmented images requires only a few operations. In contrast, TSD [21] runs a GAN-based stylization to generate every augmented image, which is much slower.", + "bbox": [ + 496, + 265, + 890, + 325 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "GAN-based stylized image generation takes almost twice the time (with all other factors constant - 8 A100 GPUs in our case) compared to computing all edge maps and shuffled patch images. Both ELEAS and TSD require new augmented images with different source and texture images every epoch, but GAN-based augmentation must be run every time, making it expensive. Therefore, the per epoch cost of ELEAS is negligible compared to TSD.", + "bbox": [ + 496, + 327, + 890, + 446 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Further, once computed, the edge maps and shuffled patch images used by ELEAS can be reused to train other models, further reducing the average data generation cost.", + "bbox": [ + 496, + 449, + 890, + 494 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "6. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 511, + 617, + 527 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We propose and evaluate ELEAS - a lightweight adversarial augmentation technique for image classification in order to induce a shape bias in learned models. Previous work in this area [7,21] identified the need for such inductive biases due to the apparent dependence of deep models on textural features; however, their proposed augmentation techniques have drawbacks—first, they primarily sever the dependence on texture, while not explicitly enforcing processing and representation of shape, and second, the proposed augmentation process is very expensive. Although our work, too, proposes only data augmentation and does not come with guarantees on learned representations, the augmentations are simple to compute and are designed to encourage holistic shape representation. Extensive experimentation shows both the value of this inductive bias (shape factors correlate with model robustness and accuracy across models) and the substantial gains of our proposal, including over $5\\%$ absolute accuracy improvements on ImageNet using vision transformers. An interesting direction for future work is to explore richer ways of specifying \"shape\" to the models—for instance, using off-the-shelf segmentation or depth estimation models—and also to explore other inductive biases that can profitably be incorporated into vision models.", + "bbox": [ + 496, + 537, + 890, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "24477", + "bbox": [ + 478, + 944, + 517, + 957 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Nicholas Baker, Hongjing Lu, Gennady Erlikhman, and Philip J. Kellman. Deep convolutional networks do not classify based on global object shape. PLoS Comput. Biol., 14(12), 2018.", + "[2] Sanghyuk Chun and Song Park. Styleaugment: Learning texture de-biased representations by style augmentation without pre-defined textures. 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OpenReview.net, 2018." + ], + "bbox": [ + 78, + 90, + 468, + 694 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "24479", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/Edges to Shapes to Concepts_ Adversarial Augmentation for Robust Vision/d0d50664-1fef-4fb1-8679-7306724f6c4b_model.json b/2023/Edges to Shapes to Concepts_ Adversarial Augmentation for Robust Vision/d0d50664-1fef-4fb1-8679-7306724f6c4b_model.json new file mode 100644 index 0000000000000000000000000000000000000000..609021c8436c5d537265f325370d2ed1b25b145f --- /dev/null +++ b/2023/Edges to Shapes to Concepts_ Adversarial Augmentation for Robust Vision/d0d50664-1fef-4fb1-8679-7306724f6c4b_model.json @@ -0,0 +1,1837 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.044 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.001, + 0.812, + 0.047 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.109, + 0.131, + 0.862, + 0.154 + ], + "angle": 0, + "content": "Edges to Shapes to Concepts: Adversarial Augmentation for Robust Vision" + }, + { + "type": "text", + "bbox": [ + 0.119, + 0.179, + 0.851, + 0.234 + ], + "angle": 0, + "content": "Aditay Tripathi\\(^{1*}\\) Rishubh Singh\\(^{2}\\) Anirban Chakraborty\\(^{1}\\) Pradeep Shenoy\\(^{2}\\) \n\\(^{1}\\)CDS, Indian Institute of Science \\(^{2}\\)Google Research India shenoypradeep@gmail.com" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.269, + 0.314, + 0.286 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.302, + 0.474, + 0.681 + ], + "angle": 0, + "content": "Recent work has shown that deep vision models tend to be overly dependent on low-level or \"texture\" features, leading to poor generalization. Various data augmentation strategies have been proposed to overcome this so-called texture bias in DNNs. We propose a simple, lightweight adversarial augmentation technique that explicitly incentivizes the network to learn holistic shapes for accurate prediction in an object classification setting. Our augmentations superpose edgemaps from one image onto another image with shuffled patches, using a randomly determined mixing proportion, with the image label of the edgemap image. To classify these augmented images, the model needs to not only detect and focus on edges but distinguish between relevant and spurious edges. We show that our augmentations significantly improve classification accuracy and robustness measures on a range of datasets and neural architectures. As an example, for ViT-S, We obtain absolute gains on classification accuracy gains up to \\(6\\%\\). We also obtain gains of up to \\(28\\%\\) and \\(8.5\\%\\) on natural adversarial and out-of-distribution datasets like ImageNet-A (for ViT-B) and ImageNet-R (for ViT-S), respectively. Analysis using a range of probe datasets shows substantially increased shape sensitivity in our trained models, explaining the observed improvement in robustness and classification accuracy." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.712, + 0.21, + 0.727 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.738, + 0.47, + 0.875 + ], + "angle": 0, + "content": "A growing body of research catalogues and analyzes apparent failure modes of deep vision models. For instance, work on texture bias [1,7,12] suggests that image classifiers are overdependent on textural cues and fail against simple (adversarial) texture substitutions. Relatedly, the idea of simplicity bias [25] captures the tendency of deep models to use weakly predictive \"simple\" features such as color or texture, even in the presence of strongly predictive complex features. In psychology & neuroscience, too, evidence" + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.277, + 0.907, + 0.449 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.502, + 0.454, + 0.909, + 0.637 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.652, + 0.895, + 0.736 + ], + "angle": 0, + "content": "Figure 1. Comparison of the models on robustness and shape-bias. The shape factor gives the fraction of dimensions that encode shape cues [17]. Backbone(T) denotes texture shape debiased (TSD) models [21]. In comparison, ELEAS denoted by Backbone(E) is more shape biased and shows better performance on ImageNet-C and ImageNet-A datasets." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.895, + 0.903 + ], + "angle": 0, + "content": "suggests that deep networks focus more on \"local\" features rather than global features and differ from human behavior in related tasks [19]. More broadly speaking, there is a mismatch between the cognitive concepts and associated world knowledge implied by the category labels in image datasets such as Imagenet and the actual information content made available to a model via one-hot vectors encoding these labels. In the face of under-determined learning problems, we need to introduce inductive biases to guide" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.887, + 0.302, + 0.9 + ], + "angle": 0, + "content": "*Work done at Google Research India." + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "24470" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.089, + 0.287, + 0.282 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.291, + 0.089, + 0.485, + 0.282 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.49, + 0.089, + 0.682, + 0.282 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.69, + 0.089, + 0.887, + 0.282 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.295, + 0.895, + 0.34 + ], + "angle": 0, + "content": "Figure 2. Representative performance comparison of our model, with the 'Debiased' models (TSD [21]) on ImageNet-A, R, C, and Sketch datasets. The models trained using ELEAS show improved performance on out-of-distribution robustness datasets. The large performance improvement on the ImageNet-A dataset indicates better robustness to natural adversarial examples." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.364, + 0.473, + 0.516 + ], + "angle": 0, + "content": "the learning process. To this end, Geirhos et al. [7] proposed a data augmentation method wherein the texture of an image was replaced with that of a painting through stylization. Follow-on work improved upon this approach by replacing textures from other objects (instead of paintings) and teaching the model to separately label the outer shape and the substituted texture according to their source image categories [21]. Both these approaches discourage overdependence on textural features in the learned model; however, they do not explicitly incentivize shape recognition." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.524, + 0.473, + 0.903 + ], + "angle": 0, + "content": "We propose a lightweight adversarial augmentation technique ELEAS (Edge Learning for Shape sensitivity) that is designed to increase shape sensitivity in vision models. Specifically, we augment a dataset with superpositions of random pairs of images from the dataset, where one image is processed to produce an edge map, and the other is modified by shuffling the location of image patches within the image. The two images are superposed using a randomly sampled relative mixing weight (similar to Mixup [30]), and the new superposed image is assigned the label of the edgemap image. ELEAS is designed to specifically incentivize not only edge detection but shape sensitivity: 1) classifying the edgemap image requires the model to extract and exploit edges - the only features available in the image, 2) distinguishing the edgemap object category from the superposed shuffled image requires the model to distinguish the overall edgemap object shape (relevant edges) from the shuffled image edges (irrelevant edges, less likely to be \"shape like\"). We perform extensive experiments over a range of model architectures, image classification datasets, and probe datasets, comparing ELEAS against recent baselines. Figure 1 provides a small visual sample of our findings and results; across various models, a measure of shape sensitivity [17] correlates very strongly with measures of classifier robustness [11, 12] (see Results" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.364, + 0.895, + 0.439 + ], + "angle": 0, + "content": "for more details), validating the shape sensitivity inductive bias. In addition, for a number of model architectures, models trained with ELEAS significantly improve both measures compared to the previous SOTA data augmentation approach [21]." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.44, + 0.862, + 0.456 + ], + "angle": 0, + "content": "Summing up, we make the following contributions:" + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.465, + 0.892, + 0.556 + ], + "angle": 0, + "content": "- We propose an adversarial augmentation technique, ELEAS, designed to incentivize shape sensitivity in vision models. Our augmentation technique is lightweight (needing only an off-the-shelf edge detection method) compared to previous proposals that require expensive GAN-based image synthesis [7, 21]." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.565, + 0.892, + 0.656 + ], + "angle": 0, + "content": "- In experiments, ELEAS shows increased shape sensitivity on a wide range of tasks designed to probe this property. Consequently, we obtain increased accuracy in object classification with a \\(6\\%\\) improvement on ImageNet-1K classification accuracy for ViT-Small among others." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.665, + 0.892, + 0.726 + ], + "angle": 0, + "content": "- ELEAS shows high generalizability and out of distribution robustness with \\(14.2\\%\\) improvement in ImageNet-C classification performance and \\(5.89\\%\\) increase in shape-bias for Resnet152." + }, + { + "type": "list", + "bbox": [ + 0.518, + 0.465, + 0.892, + 0.726 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.74, + 0.64, + 0.756 + ], + "angle": 0, + "content": "2. Related work" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Texture bias in vision models. In [1,7], convolutional neural networks are shown to be more sensitive towards the texture present in the image to classify the object correctly. Further, in order to mitigate the texture bias, they have suggested a training strategy where they have used modified images with random texture along with the natural images during training. However, utilizing images with conflicting textures leads to an unnatural shift in data distribution, leading to drops in performance on natural images. Instead, sim" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.519, + 0.958 + ], + "angle": 0, + "content": "24471" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.257 + ], + "angle": 0, + "content": "ple and naturalistic data augmentations strategies can also lead to an increase in shape bias of the CNNs without much loss in performance on natural images [13]. An increase in shape-bias in the CNN models is associated with an increase in the robustness of the models [7, 26], however [22] suggested that a more balanced shape or texture biased models also leads to increase in the model robustness. The study of texture bias in vision models has been extended to the vision transformers (ViT) [3], where the transformer models are found to be less texture biased than the convolutional models [27]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.258, + 0.473, + 0.455 + ], + "angle": 0, + "content": "A measure of shape/texture bias is proposed in [7], where they used images with conflicting textures obtained using style-transfer methods. However, this measure ignores a large portion of test images and is biased toward models trained using images modified by style-transfer methods. In [14], Hermann et al. proposed a linear classification layer in order to measure the shape decodability of the representations learned by the model. A more fine-grained shape evaluation measure was proposed in [18] where they compute the number of dimensions in the image representation that correlate with the shape features. Further, they proposed a shallow read-out module that takes feature representations from the model and predicts a segmentation map." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.455, + 0.473, + 0.651 + ], + "angle": 0, + "content": "Data Augmentation for improving shape-bias In [2, 7], authors suggested a data augmentation strategy in order to increase the shape bias in the trained models. They proposed the Stylized-ImageNet dataset, where they strip each image of its original texture and replace it with the style of a randomly selected painting through AdaIN style transfer [16]. During training, the model is trained to predict the category corresponding to the shape in the model, ignoring the texture, thus leading to an increase in the shape bias of the models. However, instead of changing the distribution of training images through style transfer, naturalistic data augmentation techniques such as can also lead to improvement in the shape bias of the model [13]." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.664, + 0.214, + 0.682 + ], + "angle": 0, + "content": "3. Methodology" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.689, + 0.47, + 0.719 + ], + "angle": 0, + "content": "We now describe the training strategy used in ELEAS to increase the shape sensitivity of deep image classifiers." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.72, + 0.47, + 0.841 + ], + "angle": 0, + "content": "Let \\(\\mathcal{I}\\), and \\(\\mathcal{C}\\) be the set of all images and their corresponding categories in the dataset. In standard classifier training, a classifier \\(\\Theta\\) is trained to predict the category \\(c \\in \\mathcal{C}\\) of the image \\(i \\in \\mathcal{I}\\). However, the image classifiers trained in this way are sensitive to the texture present in the natural images. In this work, we propose to use edge maps along with textures from natural images to increase the shape sensitivity of image classifiers." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.841, + 0.471, + 0.902 + ], + "angle": 0, + "content": "Obtaining shapes and textures: We approximate the shapes of objects by extracting edge-maps from images and natural textures by shuffling patches within images. In particular, for each image \\(i \\in \\mathcal{I}\\), an edge-map is constructed" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.168 + ], + "angle": 0, + "content": "using an edge detection kernel (i.e., Laplacian kernel) to produce the set of all edge-maps or \"shapes\" \\( S \\). Similarly, a \"texture\" dataset \\( \\mathcal{T} \\) is generated by first dividing an image in \\( \\mathcal{I} \\) into \\( 4 \\times 4 \\) patches and then randomly shuffling the patches within the image to obtain a patch-shuffled image." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.168, + 0.892, + 0.243 + ], + "angle": 0, + "content": "Generating augmentations: We superimpose randomly selected pairs of images \\( s \\in S \\) and \\( t \\in \\mathcal{T} \\) to create new images, or augmentations, to add to the training dataset. Each such augmented image is assigned the label of the shape image \\( s \\). The superimposed image is obtained as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.614, + 0.255, + 0.892, + 0.271 + ], + "angle": 0, + "content": "\\[\ni _ {s} = \\lambda * t + (1 - \\lambda) * s \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.282, + 0.892, + 0.373 + ], + "angle": 0, + "content": "where \\(\\lambda\\) is drawn randomly from a \\(\\operatorname{Beta}(\\alpha, \\beta)\\) distribution. The parameters \\(\\alpha\\) and \\(\\beta\\) are chosen such that a higher weight is given to the samples from set \\(T\\). The random weighing parameter \\(\\lambda\\) introduces variation in the augmented image set and helps to obtain better edge-map classification. Let's call the set of superimposed images \\(\\mathcal{B}\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.373, + 0.892, + 0.525 + ], + "angle": 0, + "content": "Training procedure: Training proceeds via minibatch gradient descent, as is standard in current machine learning literature. We construct each mini-batch to have half of its images from the set of natural images \\( I \\subset \\mathcal{I} \\) and the rest from the augmented dataset \\( B \\subset \\mathcal{B} \\). During training, we minimize the cross-entropy loss on natural image samples as well as our augmentations. In order to carefully control the degree of shape sensitivity induced by this process, we compute a weighted mixture of cross-entropy loss on these two image sets denoted here by \\( L \\):" + }, + { + "type": "equation", + "bbox": [ + 0.508, + 0.535, + 0.892, + 0.553 + ], + "angle": 0, + "content": "\\[\nL (I, B, y _ {I}, y _ {B}) = \\eta * C E (I, y _ {I}) + 1 - \\eta * C E (B, y _ {B}) \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.563, + 0.892, + 0.745 + ], + "angle": 0, + "content": "where \\(\\eta\\) is varied to control the shape sensitivity, \\(CE\\) is the cross-entropy loss, \\(y_{I}, y_{B}\\) are the labels corresponding to the natural and augmented image sets \\(I, B\\) respectively. To predict augmented images correctly, the model needs to interpret the edge-map present in the superimposed sample while at the same time ignoring distracting edges and textures from the other superimposed image. In this manner, we induce shape sensitivity in learned classifiers. The minibatch-mixing strategy encourages the model to generalize learned representations across natural and augmented images, thereby improving shape bias (and consequently overall accuracy) on natural images as well." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.758, + 0.691, + 0.775 + ], + "angle": 0, + "content": "4. Experimental setup" + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.783, + 0.738, + 0.8 + ], + "angle": 0, + "content": "4.1. Models and training setup" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.806, + 0.892, + 0.867 + ], + "angle": 0, + "content": "We train convolutional neural networks (CNNs) and Vision Transformers (ViTs) using our methodology. Among the CNN models, similar to [21], we show results on ResNet50, ResNet101, and ResNet152. For training the" + }, + { + "type": "page_footnote", + "bbox": [ + 0.5, + 0.875, + 0.894, + 0.901 + ], + "angle": 0, + "content": "1Refer to Fig. 1 in the supplementary material for examples of ELEAS images." + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.957 + ], + "angle": 0, + "content": "24472" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.197, + 0.089, + 0.773, + 0.393 + ], + "angle": 0, + "content": "
ModelMethodIN-A(↑)IN-R(↑)IN-C(↓)IN-Sketch(↑)IN-1K(↑)
Resnet50Vanilla2.036.275.023.576.4
TSD [21]3.340.867.528.376.9
ELEAS5.441.758.529.777.1
Resnet101Vanilla5.639.369.827.178.0
TSD [21]8.844.362.232.378.8
ELEAS13.444.453.532.478.6
Resnet152Vanilla5.941.367.228.478.6
TSD [21]12.545.558.933.379.7
ELEAS15.445.753.034.779.0
ViT-SVanilla16.636.155.133.274.6
TSD [21]27.444.442.232.476.4
ELEAS28.344.741.534.780.6
ViT-BVanilla34.640.750.845.879.5
ELEAS62.956.435.946.485.5
ViT-LVanilla63.463.333.152.785.8
ELEAS67.465.929.554.186.2
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.404, + 0.894, + 0.448 + ], + "angle": 0, + "content": "Table 1. Performance comparison on the ImageNet and the robustness datasets. The models trained using ELEAS show an improvement in the ImageNet performance along with better robustness. Except for IN-C the performance is measured in Accuracy@1 (higher is better). For IN-C, the performance is measured in mean corruption error (mCE) (lower is better). (Refer to Sections 5.1 and 5.2.1)" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.473, + 0.473, + 0.685 + ], + "angle": 0, + "content": "ResNet models, we supplemented ImageNet data with an equal number of augmented images. We trained them for 100 epochs with a starting learning rate of 0.2 which is reduced by a factor of 10 at the 30th, 60th and 90th epoch. Similar to TSD, while training the ResNet models, we also use auxiliary batch norm [29]. As ViTs are compute-intensive, we finetune ImageNet pretrained ViT models for 20k steps with a cosine learning rate schedule with a starting learning rate of 0.01. The stochastic gradient descent (SGD) with a momentum of 0.9 is used to train the models. We train all our models on 8 A100 GPUs with a batch size of 512 for ResNets, 256 for ViT-Small and ViT-Base and 128 for ViT-Large. We find that values \\(\\alpha = 4\\), \\(\\beta = 1\\), and \\(\\eta = 0.65\\) produce the best results for all models." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.696, + 0.365, + 0.712 + ], + "angle": 0, + "content": "4.2. Datasets and evaluation protocol" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.719, + 0.47, + 0.884 + ], + "angle": 0, + "content": "The models are trained on the ILSVRC 2012 [24] dataset with 1.28M training and 50k validation images. We evaluate and compare our trained models to answer the following questions: (i) Does ELEAS lead to an increase in the shape-sensitivity of a model? (ii) Does the increased shape sensitivity result in better classification performance? (iii) Does the robustness of the models to distribution shift improve with increased shape sensitivity? and (iv) Does an increase in shape sensitivity lead to improvement in downstream tasks such as object detection and instance segmentation?" + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.886, + 0.47, + 0.901 + ], + "angle": 0, + "content": "The shape sensitivity of the models is first evaluated us" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.473, + 0.892, + 0.806 + ], + "angle": 0, + "content": "ing the metric proposed in [7]. The authors first created an image dataset called cue-conflict, using a style-transfer method to transfer texture from one image to another. They then defined shape bias as the fraction of the shape decision when the model predicts either the shape or the texture category. However, this metric ignores many a lot of images and is biased toward the methods that used Stylized-ImageNet during the training of the models. Further, authors in [17] proposed a method to quantify the number of dimensions in the image representation that encode the object's shape. They take a pair of images with similar semantic concepts (i.e., shape) and then count the number of neurons that encode that specific concept. They have used Pascal VOC [4] and Stylized Pascal VOC dataset to create pair of images with particular semantic concepts. We have used these metrics to evaluate the shape bias in this work. Further, similar to [17], we also evaluate the quality of the shape encoding from these models by performing the binary and semantic segmentation on the frozen representations. PASCAL VOC is image segmentation dataset [4, 8], with 10,582 training images and 1,449 validation images spanning across 20 object categories." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.81, + 0.895, + 0.903 + ], + "angle": 0, + "content": "The out-of-distribution generalization of the trained models is evaluated on four publicly available datasets, which are, ImageNet-A [12], ImageNet-R [10], ImageNet-C [11], and ImageNet-Sketch [28]. The ImageNet-A dataset consists of real-world natural adversarial images and is a challenging classification dataset. The ImageNet-R dataset" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "24473" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.198, + 0.089, + 0.773, + 0.394 + ], + "angle": 0, + "content": "
ModelMethodEdgeSilhouetteCue-conflictSketchStylized-IN
Resnet50Vanilla13.7554.3818.2059.6237.13
TSD [21]22.555.6221.4067.056.13
ELEAS35.6254.3721.4167.8846.0
Resnet101Vanilla23.8549.3719.9263.1241.75
TSD [21]31.2551.8724.9270.1259.37
ELEAS45.0061.2524.0671.8848.25
Resnet152Vanilla20.6356.2520.7066.7541.63
TSD [21]22.558.12525.3169.1357.67
ELEAS41.8856.8823.8373.3848.75
ViT-SVanilla25.026.2522.9649.1244.25
TSD [21]22.546.8731.7168.6277.5
ELEAS34.3843.1327.6669.6353.00
ViT-BVanilla13.7512.0528.0551.6350.08
ELEAS41.2566.2534.9282.0059.38
ViT-LVanilla55.6268.7540.3983.7565.50
ELEAS75.0069.3842.1185.8866.50
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.404, + 0.895, + 0.448 + ], + "angle": 0, + "content": "Table 2. Performance comparison on out-of-distribution benchmark proposed in [6]. The proposed method significantly improves performance over vanilla ResNet models. Debiased models, trained on stylized images, show high performance on datasets utilizing stylized images for evaluation, such as Cue-Conflict and Stylized-IN. (Refer to Section 5.2.2)" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.473, + 0.473, + 0.638 + ], + "angle": 0, + "content": "consists of images with various renditions, such as cartoon art, DeviantArt, graphics, paintings, origami, etc., of the objects present in the original ImageNet dataset. The ImageNet-Sketch dataset consists of sketches of 1000 ImageNet object categories. Both ImageNet-R and ImageNet-Sketch are used to evaluate the out-of-distribution generalization capability of the models. The ImageNet-C dataset consists of images with varying degrees of artificial distortions like 'Gaussian Noise', 'Motion Blur', 'Speckle Noise', etc. Hence, it evaluates the robustness of the model to added distortions." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.64, + 0.471, + 0.702 + ], + "angle": 0, + "content": "Besides using classification accuracy for most datasets, ImageNet-C's performance is measured using mean corruption error (mCE). Additionally, we evaluated the models on the out-of-distribution benchmark proposed in [6]." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.725, + 0.196, + 0.739 + ], + "angle": 0, + "content": "4.2.1 Baselines" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.75, + 0.473, + 0.903 + ], + "angle": 0, + "content": "We compare the performance of ELEAS with Shape-Texture Debiased (TSD) trained models [21], which focus on both shape and texture cues. TSD uses stylized ImageNet images with conflicting shape and texture cues, and the models are trained using supervision from both semantic cues. Among ViTs, only ViT-S is trained with TSD due to the large computation overhead involved in training ViT-B and ViT-L. In contrast, ELEAS learns the overall object shape in the presence of conflicting, less 'shape-like' edges, leading to increased shape sensitivity in the trained models." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.471, + 0.713, + 0.487 + ], + "angle": 0, + "content": "5. Results and discussion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.497, + 0.892, + 0.589 + ], + "angle": 0, + "content": "Our experiments study the impact of ELEAS in the following stages: we show classification accuracy gains on the ImageNet dataset; we measure the robustness of trained models to a range of prediction challenges; and we examine ELEAS's influence on shape-sensitivity of trained models and its effect on performance." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.596, + 0.64, + 0.611 + ], + "angle": 0, + "content": "5.1. Classification" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.619, + 0.892, + 0.772 + ], + "angle": 0, + "content": "Along with the increase in shape bias, ELEAS also improves classification performance on the ImageNet dataset, in many cases by very large margins (Refer Table 1). For instance, we see \\(5.96\\%\\) and \\(5.93\\%\\) absolute improvement in ImageNet classification accuracy for ViT-S and ViT-B respectively, compared to vanilla baseline, and a smaller but still significant \\(4.22\\%\\) gain in accuracy compared to TSD on ViT-S. We also see \\(0.6\\%\\), \\(0.62\\%\\), and \\(0.44\\%\\) increase in performance for ResNet50, ResNet101, and ResNet152 models respectively." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.778, + 0.771, + 0.793 + ], + "angle": 0, + "content": "5.2. Out-of-distribution robustness" + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.801, + 0.892, + 0.831 + ], + "angle": 0, + "content": "5.2.1 Evaluation on ImageNet-A, R, C, and Sketch datasets." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.892, + 0.903 + ], + "angle": 0, + "content": "As shown in Table 1, ELEAS significantly improves accuracy over both vanilla and TSD-trained models at these robustness challenges. For ImageNet-A, the considerable improvement (4.54% vs. TSD on ResNet101) indicates bet" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "24474" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.078, + 0.089, + 0.344, + 0.26 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.15, + 0.263, + 0.272, + 0.274 + ], + "angle": 0, + "content": "(a) True vs. false color" + }, + { + "type": "image", + "bbox": [ + 0.078, + 0.275, + 0.344, + 0.447 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.16, + 0.449, + 0.261, + 0.459 + ], + "angle": 0, + "content": "(d) Uniform Noise" + }, + { + "type": "image", + "bbox": [ + 0.078, + 0.461, + 0.344, + 0.633 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.169, + 0.635, + 0.253, + 0.647 + ], + "angle": 0, + "content": "(g) Phase-noise" + }, + { + "type": "image", + "bbox": [ + 0.078, + 0.647, + 0.345, + 0.82 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.179, + 0.822, + 0.242, + 0.833 + ], + "angle": 0, + "content": "(j) EidolonI" + }, + { + "type": "image", + "bbox": [ + 0.352, + 0.088, + 0.617, + 0.261 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.453, + 0.263, + 0.518, + 0.275 + ], + "angle": 0, + "content": "(b) Contrast" + }, + { + "type": "image", + "bbox": [ + 0.352, + 0.275, + 0.617, + 0.447 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.45, + 0.449, + 0.521, + 0.461 + ], + "angle": 0, + "content": "(e) Low-pass" + }, + { + "type": "image", + "bbox": [ + 0.352, + 0.464, + 0.617, + 0.633 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.425, + 0.635, + 0.547, + 0.647 + ], + "angle": 0, + "content": "(h) Power Equalisation" + }, + { + "type": "image", + "bbox": [ + 0.352, + 0.647, + 0.617, + 0.82 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.45, + 0.821, + 0.521, + 0.833 + ], + "angle": 0, + "content": "(k) EidolonII" + }, + { + "type": "image", + "bbox": [ + 0.629, + 0.092, + 0.892, + 0.26 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.702, + 0.263, + 0.819, + 0.275 + ], + "angle": 0, + "content": "(c) Color vs greyscale" + }, + { + "type": "image", + "bbox": [ + 0.629, + 0.275, + 0.892, + 0.447 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.725, + 0.449, + 0.796, + 0.461 + ], + "angle": 0, + "content": "(f) High-pass" + }, + { + "type": "image", + "bbox": [ + 0.629, + 0.461, + 0.892, + 0.633 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.729, + 0.635, + 0.792, + 0.646 + ], + "angle": 0, + "content": "(i) Rotation" + }, + { + "type": "image", + "bbox": [ + 0.629, + 0.647, + 0.892, + 0.82 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.725, + 0.821, + 0.796, + 0.833 + ], + "angle": 0, + "content": "(1) EidolonIII" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.845, + 0.894, + 0.874 + ], + "angle": 0, + "content": "Figure 3. Robustness comparison of ELEAS trained Resnet152 and ViT-B with the human subjects. ELEAS leads to trained models which are more robust to added distortion and for many of the noise types it is more robust than the human subjects. (Refer to Section 5.2.1)" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "24475" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.086, + 0.089, + 0.462, + 0.386 + ], + "angle": 0, + "content": "
ModelMethodShape-biasFactor |zk|
Shape dimTexture dim
Res50Vanilla19.750.1700.338
TSD [21]23.110.1850.285
ELEAS23.530.1950.299
Res101Vanilla22.440.1780.323
TSD [21]27.690.2040.256
ELEAS26.040.2220.259
Res152Vanilla21.740.1800.298
TSD [21]28.780.2070.236
ELEAS27.860.2280.249
ViT-SVanilla33.330.2140.210
TSD [21]36.560.2160.213
ELEAS34.640.2210.217
ViT-BVanilla33.120.2190.212
ELEAS37.900.2390.205
ViT-LVanilla47.040.2160.221
ELEAS48.100.2250.207
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.397, + 0.47, + 0.466 + ], + "angle": 0, + "content": "Table 3. Comparison of the shape-bias of the models. The vision models trained using our strategy shows an increase in the fraction of 'Shape' dimensions. However, the shape-bias metric proposed by Geirhos et al. [7] is biased towards the models trained using style-transfer datasets. (Refer to Section 5.3)" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.494, + 0.468, + 0.613 + ], + "angle": 0, + "content": "ter robustness to naturally occurring adversarial examples. Similarly, the improvement in mCE on ImageNet-C (8.72% vs. TSD on ResNet101) showcases robustness to added distortions of various degrees. Similarly, ELEAS shows robustness performance improvements on the ViT models. These large gains are driven primarily by ELEAS's ability to better encode object shape (Refer Figure 1 for evidence supporting this causal link.)" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.635, + 0.377, + 0.65 + ], + "angle": 0, + "content": "5.2.2 Evaluation on OOD benchmark [6]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.659, + 0.47, + 0.901 + ], + "angle": 0, + "content": "We also evaluated trained models on the OOD benchmark proposed in [6]; results are in Table 2. The datasets in this benchmark consist of images from different domains such as 'Edge', 'Silhouette', 'Sketch', 'Stylized', and 'Cue-conflict', which require stronger shape sensitivity for correct classification. The 'Cue-conflict' dataset is generated using iterative style transfer [5], where the texture from a source image is transferred to a target image. Since these images contain cues corresponding to different objects, it is challenging to classify them without good shape-sensitive representations. Similarly, the Stylized imagenet (SIN) is generated by replacing the texture present in an image with style from a randomly selected painting using the AdaIN style transfer method [16]. Models trained using ELEAS can better encode object shapes in images, leading to large performance improvements on these datasets over" + }, + { + "type": "image", + "bbox": [ + 0.501, + 0.089, + 0.892, + 0.419 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.443, + 0.892, + 0.514 + ], + "angle": 0, + "content": "Figure 4. Shape vs. texture bias for the vision models: The images with conflicting shape and texture cues are used to calculate the shape bias of the trained models. The ELEAS trained models show improvement in shape-bias. We have shown results for ResNet152 and ViT-B in this figure.(Refer to Section 5.3)" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.539, + 0.891, + 0.584 + ], + "angle": 0, + "content": "the vanilla model. The better performance of TSD is expected as these models are trained using images from similar domains, i.e., the Stylized ImageNet dataset." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.584, + 0.892, + 0.643 + ], + "angle": 0, + "content": "We further evaluated robustness to distortion using the proposed benchmarks (Refer to Figure 3), which shows improved robustness to added distortions of varying degrees for ELEAS." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.654, + 0.746, + 0.67 + ], + "angle": 0, + "content": "5.3. Increasing shape sensitivity" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.677, + 0.892, + 0.796 + ], + "angle": 0, + "content": "We measure shape-sensitivity using the datasets and protocols described in Section 4.2; the results are in Tables 3 and 4. Models trained using ELEAS show a large \\(6.12\\%\\) and \\(4.78\\%\\) increase in shape-bias for ResNet152 and ViT-L models, respectively, compared to vanilla baselines and are comparable to the shape-bias of models trained using TSD. We further added class-wise shape bias comparison with human subjects in Figure 4." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.798, + 0.892, + 0.843 + ], + "angle": 0, + "content": "An alternative measure, the shape factor [17], counts the number of dimensions in the image representation that encodes shape. ELEAS substantially increases the number of" + }, + { + "type": "page_footnote", + "bbox": [ + 0.499, + 0.851, + 0.892, + 0.901 + ], + "angle": 0, + "content": "2Note that shape bias [7] has limitations: since it is defined in terms of a Stylized-ImageNet test set, the metric is biased towards methods that use SIN as a training augmentation. Further, it ignores images on which neither of the true shape/texture categories is predicted." + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "24476" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.14, + 0.089, + 0.411, + 0.27 + ], + "angle": 0, + "content": "
ModelMethodBinSem
Resnet50Vanilla79.861.6
TSD [21]78.961.1
ELEAS79.261.9
Resnet101Vanilla80.463.4
TSD [21]80.064.7
ELEAS81.065.9
Resnet152Vanilla80.364.4
TSD [21]79.865.5
ELEAS81.066.6
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.28, + 0.47, + 0.365 + ], + "angle": 0, + "content": "Table 4. Shape decodability of the learned representations: To evaluate the amount of shape information, read-out modules are added to the frozen learned representation and used to predict binary (Bin) and semantic (Sem) segmentation masks [17], with performance measured by mIoU. The shape decodability of the models is evaluated using the Pascal VOC dataset. (Section 5.3)" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.391, + 0.47, + 0.497 + ], + "angle": 0, + "content": "shape dimensions in trained models (Table 3). We further evaluated shape decodability from learned representations by predicting the binary and semantic mask of the object in the image (Table 4). The segmentation is performed by adding a three-layer readout module on top of the learned representations. The read-out module is trained on PASCAL VOC 2012 dataset [4]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.498, + 0.47, + 0.605 + ], + "angle": 0, + "content": "Resnet(TSD) [21] shows a significant worsening of binary segmentation performance for all models and semantic segmentation performance for ResNet50, suggesting that their learned representations cannot predict pixel-wise object categories. ELEAS-trained model shows an increase in Semantic segmentation performance, indicating better decodingability of pixel-wise semantic categories of objects." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.615, + 0.47, + 0.648 + ], + "angle": 0, + "content": "5.4. Instance Segmentation and Object detection performance" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.654, + 0.471, + 0.835 + ], + "angle": 0, + "content": "To evaluate the effectiveness of the shape-sensitive image representations in downstream tasks such as object detection and segmentation, we trained the MaskRCNN [9] model using ResNet101 as the backbone. Results are reported in Tables 5 for models trained on the MS-COCO dataset. The model trained using ELEAS outperformed other models by a significant margin in both object detection \\((\\approx 1.8\\mathrm{mAP})\\) and instance segmentation tasks \\((\\approx 1.3\\mathrm{mAP})\\), indicating that learned shape-sensitive representations can improve performance in these tasks. In contrast, TSD showed decreased performance even when compared to the Vanilla backbone." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.847, + 0.313, + 0.864 + ], + "angle": 0, + "content": "5.5. Lightweightness of ELEAS" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.47, + 0.903 + ], + "angle": 0, + "content": "Compared to previous augmentation methods, ELEAS is lightweight. Edge maps and shuffled patch images can be" + }, + { + "type": "table", + "bbox": [ + 0.502, + 0.09, + 0.895, + 0.157 + ], + "angle": 0, + "content": "
ModelObject DetectionInstance Segmentation
mAPAP@0.50AP@0.75mAPAP@0.50AP@0.75
Vanilla39.8760.2143.3336.3557.3938.79
TSD [21]37.8258.9841.2933.8755.4135.85
ELEAS41.6561.8345.4337.6358.9940.33
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.167, + 0.892, + 0.235 + ], + "angle": 0, + "content": "Table 5. Effect of shape sensitivity on Object Detection and Segmentation performance. The shapes-sensitive ResNet101 (i.e. ELEAS) backbone leads to improvement in object detection and instance segmentation performance. The models are evaluated on the COCO-Val2017 dataset." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.266, + 0.892, + 0.327 + ], + "angle": 0, + "content": "precomputed and stored on disk, and obtaining adversarial augmented images requires only a few operations. In contrast, TSD [21] runs a GAN-based stylization to generate every augmented image, which is much slower." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.328, + 0.892, + 0.448 + ], + "angle": 0, + "content": "GAN-based stylized image generation takes almost twice the time (with all other factors constant - 8 A100 GPUs in our case) compared to computing all edge maps and shuffled patch images. Both ELEAS and TSD require new augmented images with different source and texture images every epoch, but GAN-based augmentation must be run every time, making it expensive. Therefore, the per epoch cost of ELEAS is negligible compared to TSD." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.45, + 0.892, + 0.495 + ], + "angle": 0, + "content": "Further, once computed, the edge maps and shuffled patch images used by ELEAS can be reused to train other models, further reducing the average data generation cost." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.512, + 0.619, + 0.529 + ], + "angle": 0, + "content": "6. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.539, + 0.892, + 0.901 + ], + "angle": 0, + "content": "We propose and evaluate ELEAS - a lightweight adversarial augmentation technique for image classification in order to induce a shape bias in learned models. Previous work in this area [7,21] identified the need for such inductive biases due to the apparent dependence of deep models on textural features; however, their proposed augmentation techniques have drawbacks—first, they primarily sever the dependence on texture, while not explicitly enforcing processing and representation of shape, and second, the proposed augmentation process is very expensive. Although our work, too, proposes only data augmentation and does not come with guarantees on learned representations, the augmentations are simple to compute and are designed to encourage holistic shape representation. Extensive experimentation shows both the value of this inductive bias (shape factors correlate with model robustness and accuracy across models) and the substantial gains of our proposal, including over \\(5\\%\\) absolute accuracy improvements on ImageNet using vision transformers. An interesting direction for future work is to explore richer ways of specifying \"shape\" to the models—for instance, using off-the-shelf segmentation or depth estimation models—and also to explore other inductive biases that can profitably be incorporated into vision models." + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.519, + 0.958 + ], + "angle": 0, + "content": "24477" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.115, + 0.47, + 0.17 + ], + "angle": 0, + "content": "[1] Nicholas Baker, Hongjing Lu, Gennady Erlikhman, and Philip J. Kellman. Deep convolutional networks do not classify based on global object shape. PLoS Comput. Biol., 14(12), 2018." + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.172, + 0.47, + 0.213 + ], + "angle": 0, + "content": "[2] Sanghyuk Chun and Song Park. 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OpenReview.net, 2018." + }, + { + "type": "list", + "bbox": [ + 0.08, + 0.092, + 0.47, + 0.695 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "24479" + } + ] +] \ No newline at end of file diff --git a/2023/Edges to Shapes to Concepts_ Adversarial Augmentation for Robust Vision/d0d50664-1fef-4fb1-8679-7306724f6c4b_origin.pdf b/2023/Edges to Shapes to Concepts_ Adversarial Augmentation for Robust Vision/d0d50664-1fef-4fb1-8679-7306724f6c4b_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..f0fab6f5f08339dab2a5b7077cd3b87ff055b160 --- /dev/null +++ b/2023/Edges to Shapes to Concepts_ Adversarial Augmentation for Robust Vision/d0d50664-1fef-4fb1-8679-7306724f6c4b_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:f9dd22028a10b7e9e19d19c38bfd909433592d85c0e7b65db337daab8f9ea6e2 +size 440520 diff --git a/2023/Edges to Shapes to Concepts_ Adversarial Augmentation for Robust Vision/full.md b/2023/Edges to Shapes to Concepts_ Adversarial Augmentation for Robust Vision/full.md new file mode 100644 index 0000000000000000000000000000000000000000..7ec8288e1fea53ca99468701fd3e4d772669be07 --- /dev/null +++ b/2023/Edges to Shapes to Concepts_ Adversarial Augmentation for Robust Vision/full.md @@ -0,0 +1,249 @@ +# Edges to Shapes to Concepts: Adversarial Augmentation for Robust Vision + +Aditay Tripathi $^{1*}$ Rishubh Singh $^{2}$ Anirban Chakraborty $^{1}$ Pradeep Shenoy $^{2}$ $^{1}$ CDS, Indian Institute of Science $^{2}$ Google Research India shenoypradeep@gmail.com + +# Abstract + +Recent work has shown that deep vision models tend to be overly dependent on low-level or "texture" features, leading to poor generalization. Various data augmentation strategies have been proposed to overcome this so-called texture bias in DNNs. We propose a simple, lightweight adversarial augmentation technique that explicitly incentivizes the network to learn holistic shapes for accurate prediction in an object classification setting. Our augmentations superpose edgemaps from one image onto another image with shuffled patches, using a randomly determined mixing proportion, with the image label of the edgemap image. To classify these augmented images, the model needs to not only detect and focus on edges but distinguish between relevant and spurious edges. We show that our augmentations significantly improve classification accuracy and robustness measures on a range of datasets and neural architectures. As an example, for ViT-S, We obtain absolute gains on classification accuracy gains up to $6\%$ . We also obtain gains of up to $28\%$ and $8.5\%$ on natural adversarial and out-of-distribution datasets like ImageNet-A (for ViT-B) and ImageNet-R (for ViT-S), respectively. Analysis using a range of probe datasets shows substantially increased shape sensitivity in our trained models, explaining the observed improvement in robustness and classification accuracy. + +# 1. Introduction + +A growing body of research catalogues and analyzes apparent failure modes of deep vision models. For instance, work on texture bias [1,7,12] suggests that image classifiers are overdependent on textural cues and fail against simple (adversarial) texture substitutions. Relatedly, the idea of simplicity bias [25] captures the tendency of deep models to use weakly predictive "simple" features such as color or texture, even in the presence of strongly predictive complex features. In psychology & neuroscience, too, evidence + +![](images/1c5ac6a664b11df457ab1af568be30eabe35746be11f2d742b77e5e003b2ea62.jpg) + +![](images/0d4cf708e57e24be696e6f614c301a61e31234ae913c7fc46d7ae53708e7691d.jpg) +Figure 1. Comparison of the models on robustness and shape-bias. The shape factor gives the fraction of dimensions that encode shape cues [17]. Backbone(T) denotes texture shape debiased (TSD) models [21]. In comparison, ELEAS denoted by Backbone(E) is more shape biased and shows better performance on ImageNet-C and ImageNet-A datasets. + +suggests that deep networks focus more on "local" features rather than global features and differ from human behavior in related tasks [19]. More broadly speaking, there is a mismatch between the cognitive concepts and associated world knowledge implied by the category labels in image datasets such as Imagenet and the actual information content made available to a model via one-hot vectors encoding these labels. In the face of under-determined learning problems, we need to introduce inductive biases to guide + +![](images/5c0a254668a3da9bd24bf823a5852d733ab8e379a3c94ac932f00efa25595541.jpg) +Figure 2. Representative performance comparison of our model, with the 'Debiased' models (TSD [21]) on ImageNet-A, R, C, and Sketch datasets. The models trained using ELEAS show improved performance on out-of-distribution robustness datasets. The large performance improvement on the ImageNet-A dataset indicates better robustness to natural adversarial examples. + +![](images/57527a133e97d646058114dbc503af3a36941281e51c7f397fded698786c14c7.jpg) + +![](images/a6fb6d8dce5602d9295c32affce1376036a18bbc55752dcb19da6178618a67a6.jpg) + +![](images/bf59e34cc2a795bc93e2c0aaf37dbcc32f80699161d6ccba19aad7d9fa29e1e4.jpg) + +the learning process. To this end, Geirhos et al. [7] proposed a data augmentation method wherein the texture of an image was replaced with that of a painting through stylization. Follow-on work improved upon this approach by replacing textures from other objects (instead of paintings) and teaching the model to separately label the outer shape and the substituted texture according to their source image categories [21]. Both these approaches discourage overdependence on textural features in the learned model; however, they do not explicitly incentivize shape recognition. + +We propose a lightweight adversarial augmentation technique ELEAS (Edge Learning for Shape sensitivity) that is designed to increase shape sensitivity in vision models. Specifically, we augment a dataset with superpositions of random pairs of images from the dataset, where one image is processed to produce an edge map, and the other is modified by shuffling the location of image patches within the image. The two images are superposed using a randomly sampled relative mixing weight (similar to Mixup [30]), and the new superposed image is assigned the label of the edgemap image. ELEAS is designed to specifically incentivize not only edge detection but shape sensitivity: 1) classifying the edgemap image requires the model to extract and exploit edges - the only features available in the image, 2) distinguishing the edgemap object category from the superposed shuffled image requires the model to distinguish the overall edgemap object shape (relevant edges) from the shuffled image edges (irrelevant edges, less likely to be "shape like"). We perform extensive experiments over a range of model architectures, image classification datasets, and probe datasets, comparing ELEAS against recent baselines. Figure 1 provides a small visual sample of our findings and results; across various models, a measure of shape sensitivity [17] correlates very strongly with measures of classifier robustness [11, 12] (see Results + +for more details), validating the shape sensitivity inductive bias. In addition, for a number of model architectures, models trained with ELEAS significantly improve both measures compared to the previous SOTA data augmentation approach [21]. + +Summing up, we make the following contributions: + +- We propose an adversarial augmentation technique, ELEAS, designed to incentivize shape sensitivity in vision models. Our augmentation technique is lightweight (needing only an off-the-shelf edge detection method) compared to previous proposals that require expensive GAN-based image synthesis [7, 21]. +- In experiments, ELEAS shows increased shape sensitivity on a wide range of tasks designed to probe this property. Consequently, we obtain increased accuracy in object classification with a $6\%$ improvement on ImageNet-1K classification accuracy for ViT-Small among others. +- ELEAS shows high generalizability and out of distribution robustness with $14.2\%$ improvement in ImageNet-C classification performance and $5.89\%$ increase in shape-bias for Resnet152. + +# 2. Related work + +Texture bias in vision models. In [1,7], convolutional neural networks are shown to be more sensitive towards the texture present in the image to classify the object correctly. Further, in order to mitigate the texture bias, they have suggested a training strategy where they have used modified images with random texture along with the natural images during training. However, utilizing images with conflicting textures leads to an unnatural shift in data distribution, leading to drops in performance on natural images. Instead, sim + +ple and naturalistic data augmentations strategies can also lead to an increase in shape bias of the CNNs without much loss in performance on natural images [13]. An increase in shape-bias in the CNN models is associated with an increase in the robustness of the models [7, 26], however [22] suggested that a more balanced shape or texture biased models also leads to increase in the model robustness. The study of texture bias in vision models has been extended to the vision transformers (ViT) [3], where the transformer models are found to be less texture biased than the convolutional models [27]. + +A measure of shape/texture bias is proposed in [7], where they used images with conflicting textures obtained using style-transfer methods. However, this measure ignores a large portion of test images and is biased toward models trained using images modified by style-transfer methods. In [14], Hermann et al. proposed a linear classification layer in order to measure the shape decodability of the representations learned by the model. A more fine-grained shape evaluation measure was proposed in [18] where they compute the number of dimensions in the image representation that correlate with the shape features. Further, they proposed a shallow read-out module that takes feature representations from the model and predicts a segmentation map. + +Data Augmentation for improving shape-bias In [2, 7], authors suggested a data augmentation strategy in order to increase the shape bias in the trained models. They proposed the Stylized-ImageNet dataset, where they strip each image of its original texture and replace it with the style of a randomly selected painting through AdaIN style transfer [16]. During training, the model is trained to predict the category corresponding to the shape in the model, ignoring the texture, thus leading to an increase in the shape bias of the models. However, instead of changing the distribution of training images through style transfer, naturalistic data augmentation techniques such as can also lead to improvement in the shape bias of the model [13]. + +# 3. Methodology + +We now describe the training strategy used in ELEAS to increase the shape sensitivity of deep image classifiers. + +Let $\mathcal{I}$ , and $\mathcal{C}$ be the set of all images and their corresponding categories in the dataset. In standard classifier training, a classifier $\Theta$ is trained to predict the category $c \in \mathcal{C}$ of the image $i \in \mathcal{I}$ . However, the image classifiers trained in this way are sensitive to the texture present in the natural images. In this work, we propose to use edge maps along with textures from natural images to increase the shape sensitivity of image classifiers. + +Obtaining shapes and textures: We approximate the shapes of objects by extracting edge-maps from images and natural textures by shuffling patches within images. In particular, for each image $i \in \mathcal{I}$ , an edge-map is constructed + +using an edge detection kernel (i.e., Laplacian kernel) to produce the set of all edge-maps or "shapes" $S$ . Similarly, a "texture" dataset $\mathcal{T}$ is generated by first dividing an image in $\mathcal{I}$ into $4 \times 4$ patches and then randomly shuffling the patches within the image to obtain a patch-shuffled image. + +Generating augmentations: We superimpose randomly selected pairs of images $s \in S$ and $t \in \mathcal{T}$ to create new images, or augmentations, to add to the training dataset. Each such augmented image is assigned the label of the shape image $s$ . The superimposed image is obtained as follows: + +$$ +i _ {s} = \lambda * t + (1 - \lambda) * s \tag {1} +$$ + +where $\lambda$ is drawn randomly from a $\operatorname{Beta}(\alpha, \beta)$ distribution. The parameters $\alpha$ and $\beta$ are chosen such that a higher weight is given to the samples from set $T$ . The random weighing parameter $\lambda$ introduces variation in the augmented image set and helps to obtain better edge-map classification. Let's call the set of superimposed images $\mathcal{B}$ . + +Training procedure: Training proceeds via minibatch gradient descent, as is standard in current machine learning literature. We construct each mini-batch to have half of its images from the set of natural images $I \subset \mathcal{I}$ and the rest from the augmented dataset $B \subset \mathcal{B}$ . During training, we minimize the cross-entropy loss on natural image samples as well as our augmentations. In order to carefully control the degree of shape sensitivity induced by this process, we compute a weighted mixture of cross-entropy loss on these two image sets denoted here by $L$ : + +$$ +L (I, B, y _ {I}, y _ {B}) = \eta * C E (I, y _ {I}) + 1 - \eta * C E (B, y _ {B}) \tag {2} +$$ + +where $\eta$ is varied to control the shape sensitivity, $CE$ is the cross-entropy loss, $y_{I}, y_{B}$ are the labels corresponding to the natural and augmented image sets $I, B$ respectively. To predict augmented images correctly, the model needs to interpret the edge-map present in the superimposed sample while at the same time ignoring distracting edges and textures from the other superimposed image. In this manner, we induce shape sensitivity in learned classifiers. The minibatch-mixing strategy encourages the model to generalize learned representations across natural and augmented images, thereby improving shape bias (and consequently overall accuracy) on natural images as well. + +# 4. Experimental setup + +# 4.1. Models and training setup + +We train convolutional neural networks (CNNs) and Vision Transformers (ViTs) using our methodology. Among the CNN models, similar to [21], we show results on ResNet50, ResNet101, and ResNet152. For training the + +
ModelMethodIN-A(↑)IN-R(↑)IN-C(↓)IN-Sketch(↑)IN-1K(↑)
Resnet50Vanilla2.036.275.023.576.4
TSD [21]3.340.867.528.376.9
ELEAS5.441.758.529.777.1
Resnet101Vanilla5.639.369.827.178.0
TSD [21]8.844.362.232.378.8
ELEAS13.444.453.532.478.6
Resnet152Vanilla5.941.367.228.478.6
TSD [21]12.545.558.933.379.7
ELEAS15.445.753.034.779.0
ViT-SVanilla16.636.155.133.274.6
TSD [21]27.444.442.232.476.4
ELEAS28.344.741.534.780.6
ViT-BVanilla34.640.750.845.879.5
ELEAS62.956.435.946.485.5
ViT-LVanilla63.463.333.152.785.8
ELEAS67.465.929.554.186.2
+ +Table 1. Performance comparison on the ImageNet and the robustness datasets. The models trained using ELEAS show an improvement in the ImageNet performance along with better robustness. Except for IN-C the performance is measured in Accuracy@1 (higher is better). For IN-C, the performance is measured in mean corruption error (mCE) (lower is better). (Refer to Sections 5.1 and 5.2.1) + +ResNet models, we supplemented ImageNet data with an equal number of augmented images. We trained them for 100 epochs with a starting learning rate of 0.2 which is reduced by a factor of 10 at the 30th, 60th and 90th epoch. Similar to TSD, while training the ResNet models, we also use auxiliary batch norm [29]. As ViTs are compute-intensive, we finetune ImageNet pretrained ViT models for 20k steps with a cosine learning rate schedule with a starting learning rate of 0.01. The stochastic gradient descent (SGD) with a momentum of 0.9 is used to train the models. We train all our models on 8 A100 GPUs with a batch size of 512 for ResNets, 256 for ViT-Small and ViT-Base and 128 for ViT-Large. We find that values $\alpha = 4$ , $\beta = 1$ , and $\eta = 0.65$ produce the best results for all models. + +# 4.2. Datasets and evaluation protocol + +The models are trained on the ILSVRC 2012 [24] dataset with 1.28M training and 50k validation images. We evaluate and compare our trained models to answer the following questions: (i) Does ELEAS lead to an increase in the shape-sensitivity of a model? (ii) Does the increased shape sensitivity result in better classification performance? (iii) Does the robustness of the models to distribution shift improve with increased shape sensitivity? and (iv) Does an increase in shape sensitivity lead to improvement in downstream tasks such as object detection and instance segmentation? + +The shape sensitivity of the models is first evaluated us + +ing the metric proposed in [7]. The authors first created an image dataset called cue-conflict, using a style-transfer method to transfer texture from one image to another. They then defined shape bias as the fraction of the shape decision when the model predicts either the shape or the texture category. However, this metric ignores many a lot of images and is biased toward the methods that used Stylized-ImageNet during the training of the models. Further, authors in [17] proposed a method to quantify the number of dimensions in the image representation that encode the object's shape. They take a pair of images with similar semantic concepts (i.e., shape) and then count the number of neurons that encode that specific concept. They have used Pascal VOC [4] and Stylized Pascal VOC dataset to create pair of images with particular semantic concepts. We have used these metrics to evaluate the shape bias in this work. Further, similar to [17], we also evaluate the quality of the shape encoding from these models by performing the binary and semantic segmentation on the frozen representations. PASCAL VOC is image segmentation dataset [4, 8], with 10,582 training images and 1,449 validation images spanning across 20 object categories. + +The out-of-distribution generalization of the trained models is evaluated on four publicly available datasets, which are, ImageNet-A [12], ImageNet-R [10], ImageNet-C [11], and ImageNet-Sketch [28]. The ImageNet-A dataset consists of real-world natural adversarial images and is a challenging classification dataset. The ImageNet-R dataset + +
ModelMethodEdgeSilhouetteCue-conflictSketchStylized-IN
Resnet50Vanilla13.7554.3818.2059.6237.13
TSD [21]22.555.6221.4067.056.13
ELEAS35.6254.3721.4167.8846.0
Resnet101Vanilla23.8549.3719.9263.1241.75
TSD [21]31.2551.8724.9270.1259.37
ELEAS45.0061.2524.0671.8848.25
Resnet152Vanilla20.6356.2520.7066.7541.63
TSD [21]22.558.12525.3169.1357.67
ELEAS41.8856.8823.8373.3848.75
ViT-SVanilla25.026.2522.9649.1244.25
TSD [21]22.546.8731.7168.6277.5
ELEAS34.3843.1327.6669.6353.00
ViT-BVanilla13.7512.0528.0551.6350.08
ELEAS41.2566.2534.9282.0059.38
ViT-LVanilla55.6268.7540.3983.7565.50
ELEAS75.0069.3842.1185.8866.50
+ +Table 2. Performance comparison on out-of-distribution benchmark proposed in [6]. The proposed method significantly improves performance over vanilla ResNet models. Debiased models, trained on stylized images, show high performance on datasets utilizing stylized images for evaluation, such as Cue-Conflict and Stylized-IN. (Refer to Section 5.2.2) + +consists of images with various renditions, such as cartoon art, DeviantArt, graphics, paintings, origami, etc., of the objects present in the original ImageNet dataset. The ImageNet-Sketch dataset consists of sketches of 1000 ImageNet object categories. Both ImageNet-R and ImageNet-Sketch are used to evaluate the out-of-distribution generalization capability of the models. The ImageNet-C dataset consists of images with varying degrees of artificial distortions like 'Gaussian Noise', 'Motion Blur', 'Speckle Noise', etc. Hence, it evaluates the robustness of the model to added distortions. + +Besides using classification accuracy for most datasets, ImageNet-C's performance is measured using mean corruption error (mCE). Additionally, we evaluated the models on the out-of-distribution benchmark proposed in [6]. + +# 4.2.1 Baselines + +We compare the performance of ELEAS with Shape-Texture Debiased (TSD) trained models [21], which focus on both shape and texture cues. TSD uses stylized ImageNet images with conflicting shape and texture cues, and the models are trained using supervision from both semantic cues. Among ViTs, only ViT-S is trained with TSD due to the large computation overhead involved in training ViT-B and ViT-L. In contrast, ELEAS learns the overall object shape in the presence of conflicting, less 'shape-like' edges, leading to increased shape sensitivity in the trained models. + +# 5. Results and discussion + +Our experiments study the impact of ELEAS in the following stages: we show classification accuracy gains on the ImageNet dataset; we measure the robustness of trained models to a range of prediction challenges; and we examine ELEAS's influence on shape-sensitivity of trained models and its effect on performance. + +# 5.1. Classification + +Along with the increase in shape bias, ELEAS also improves classification performance on the ImageNet dataset, in many cases by very large margins (Refer Table 1). For instance, we see $5.96\%$ and $5.93\%$ absolute improvement in ImageNet classification accuracy for ViT-S and ViT-B respectively, compared to vanilla baseline, and a smaller but still significant $4.22\%$ gain in accuracy compared to TSD on ViT-S. We also see $0.6\%$ , $0.62\%$ , and $0.44\%$ increase in performance for ResNet50, ResNet101, and ResNet152 models respectively. + +# 5.2. Out-of-distribution robustness + +# 5.2.1 Evaluation on ImageNet-A, R, C, and Sketch datasets. + +As shown in Table 1, ELEAS significantly improves accuracy over both vanilla and TSD-trained models at these robustness challenges. For ImageNet-A, the considerable improvement (4.54% vs. TSD on ResNet101) indicates bet + +![](images/4221d130efa72ff6569ecbb78627dd6db5ce0b350b3d626cf55927fa39068ba9.jpg) + +![](images/56dff3c237e7d5bf7e279e1ae6ac5c23189b669a12695dd4ae4f26ebecfa3aa7.jpg) +(a) True vs. false color +(d) Uniform Noise + +![](images/ffdd3c6786cfeeb9435ba2ea783bf404175216e5ad008ed72227d5596d9f4762.jpg) + +![](images/d898887f6e5c3d0e5ab4e7308b1b599f909d4c625aa4ea6ebc906bbc6bd56406.jpg) +(g) Phase-noise +(j) EidolonI +Figure 3. Robustness comparison of ELEAS trained Resnet152 and ViT-B with the human subjects. ELEAS leads to trained models which are more robust to added distortion and for many of the noise types it is more robust than the human subjects. (Refer to Section 5.2.1) + +![](images/3419d55fd5362e83a812fc16c020eda605d4a89b5fb91be5fbbcc6727c9e1fef.jpg) + +![](images/0c869195544fe46778f95167853f5bfa8af8593e9f4f44fad5381d83ca859343.jpg) +(b) Contrast +(e) Low-pass + +![](images/273e60621679449ce0ccdf7e96411191016759a2773c23023394508cb69b0859.jpg) + +![](images/cf62a73de5c92603787d63864a051a2cfd777d8aae20d00b012e6a79a572cfec.jpg) +(h) Power Equalisation +(k) EidolonII + +![](images/96a0bd5ccf6ee5f3749816f0fce86c8437b209b5a6520a800cdfb384d7d6d7a7.jpg) + +![](images/f416cd6bfe7874aa099b218e9c1877be243c71e2e705e209cbf0d6d0ea0b1fe7.jpg) +(c) Color vs greyscale + +![](images/268b7a49e2d285f7d0609203644485ebe8bba93339c65ad9a106bde73d6f67c1.jpg) +(f) High-pass +(i) Rotation + +![](images/cb547ba58ca320e73ef83a1825899b2a497afde1d0a54336c9e8821f1d4f397e.jpg) +(1) EidolonIII + +
ModelMethodShape-biasFactor |zk|
Shape dimTexture dim
Res50Vanilla19.750.1700.338
TSD [21]23.110.1850.285
ELEAS23.530.1950.299
Res101Vanilla22.440.1780.323
TSD [21]27.690.2040.256
ELEAS26.040.2220.259
Res152Vanilla21.740.1800.298
TSD [21]28.780.2070.236
ELEAS27.860.2280.249
ViT-SVanilla33.330.2140.210
TSD [21]36.560.2160.213
ELEAS34.640.2210.217
ViT-BVanilla33.120.2190.212
ELEAS37.900.2390.205
ViT-LVanilla47.040.2160.221
ELEAS48.100.2250.207
+ +Table 3. Comparison of the shape-bias of the models. The vision models trained using our strategy shows an increase in the fraction of 'Shape' dimensions. However, the shape-bias metric proposed by Geirhos et al. [7] is biased towards the models trained using style-transfer datasets. (Refer to Section 5.3) + +ter robustness to naturally occurring adversarial examples. Similarly, the improvement in mCE on ImageNet-C (8.72% vs. TSD on ResNet101) showcases robustness to added distortions of various degrees. Similarly, ELEAS shows robustness performance improvements on the ViT models. These large gains are driven primarily by ELEAS's ability to better encode object shape (Refer Figure 1 for evidence supporting this causal link.) + +# 5.2.2 Evaluation on OOD benchmark [6] + +We also evaluated trained models on the OOD benchmark proposed in [6]; results are in Table 2. The datasets in this benchmark consist of images from different domains such as 'Edge', 'Silhouette', 'Sketch', 'Stylized', and 'Cue-conflict', which require stronger shape sensitivity for correct classification. The 'Cue-conflict' dataset is generated using iterative style transfer [5], where the texture from a source image is transferred to a target image. Since these images contain cues corresponding to different objects, it is challenging to classify them without good shape-sensitive representations. Similarly, the Stylized imagenet (SIN) is generated by replacing the texture present in an image with style from a randomly selected painting using the AdaIN style transfer method [16]. Models trained using ELEAS can better encode object shapes in images, leading to large performance improvements on these datasets over + +![](images/157199e1430337ca7081323849a7278d5a75a508f461bf00aa232e845563f208.jpg) +Figure 4. Shape vs. texture bias for the vision models: The images with conflicting shape and texture cues are used to calculate the shape bias of the trained models. The ELEAS trained models show improvement in shape-bias. We have shown results for ResNet152 and ViT-B in this figure.(Refer to Section 5.3) + +the vanilla model. The better performance of TSD is expected as these models are trained using images from similar domains, i.e., the Stylized ImageNet dataset. + +We further evaluated robustness to distortion using the proposed benchmarks (Refer to Figure 3), which shows improved robustness to added distortions of varying degrees for ELEAS. + +# 5.3. Increasing shape sensitivity + +We measure shape-sensitivity using the datasets and protocols described in Section 4.2; the results are in Tables 3 and 4. Models trained using ELEAS show a large $6.12\%$ and $4.78\%$ increase in shape-bias for ResNet152 and ViT-L models, respectively, compared to vanilla baselines and are comparable to the shape-bias of models trained using TSD. We further added class-wise shape bias comparison with human subjects in Figure 4. + +An alternative measure, the shape factor [17], counts the number of dimensions in the image representation that encodes shape. ELEAS substantially increases the number of + +
ModelMethodBinSem
Resnet50Vanilla79.861.6
TSD [21]78.961.1
ELEAS79.261.9
Resnet101Vanilla80.463.4
TSD [21]80.064.7
ELEAS81.065.9
Resnet152Vanilla80.364.4
TSD [21]79.865.5
ELEAS81.066.6
+ +shape dimensions in trained models (Table 3). We further evaluated shape decodability from learned representations by predicting the binary and semantic mask of the object in the image (Table 4). The segmentation is performed by adding a three-layer readout module on top of the learned representations. The read-out module is trained on PASCAL VOC 2012 dataset [4]. + +Resnet(TSD) [21] shows a significant worsening of binary segmentation performance for all models and semantic segmentation performance for ResNet50, suggesting that their learned representations cannot predict pixel-wise object categories. ELEAS-trained model shows an increase in Semantic segmentation performance, indicating better decodingability of pixel-wise semantic categories of objects. + +# 5.4. Instance Segmentation and Object detection performance + +To evaluate the effectiveness of the shape-sensitive image representations in downstream tasks such as object detection and segmentation, we trained the MaskRCNN [9] model using ResNet101 as the backbone. Results are reported in Tables 5 for models trained on the MS-COCO dataset. The model trained using ELEAS outperformed other models by a significant margin in both object detection $(\approx 1.8\mathrm{mAP})$ and instance segmentation tasks $(\approx 1.3\mathrm{mAP})$ , indicating that learned shape-sensitive representations can improve performance in these tasks. In contrast, TSD showed decreased performance even when compared to the Vanilla backbone. + +# 5.5. Lightweightness of ELEAS + +Compared to previous augmentation methods, ELEAS is lightweight. Edge maps and shuffled patch images can be + +Table 4. Shape decodability of the learned representations: To evaluate the amount of shape information, read-out modules are added to the frozen learned representation and used to predict binary (Bin) and semantic (Sem) segmentation masks [17], with performance measured by mIoU. The shape decodability of the models is evaluated using the Pascal VOC dataset. (Section 5.3) + +
ModelObject DetectionInstance Segmentation
mAPAP@0.50AP@0.75mAPAP@0.50AP@0.75
Vanilla39.8760.2143.3336.3557.3938.79
TSD [21]37.8258.9841.2933.8755.4135.85
ELEAS41.6561.8345.4337.6358.9940.33
+ +Table 5. Effect of shape sensitivity on Object Detection and Segmentation performance. The shapes-sensitive ResNet101 (i.e. ELEAS) backbone leads to improvement in object detection and instance segmentation performance. The models are evaluated on the COCO-Val2017 dataset. + +precomputed and stored on disk, and obtaining adversarial augmented images requires only a few operations. In contrast, TSD [21] runs a GAN-based stylization to generate every augmented image, which is much slower. + +GAN-based stylized image generation takes almost twice the time (with all other factors constant - 8 A100 GPUs in our case) compared to computing all edge maps and shuffled patch images. Both ELEAS and TSD require new augmented images with different source and texture images every epoch, but GAN-based augmentation must be run every time, making it expensive. Therefore, the per epoch cost of ELEAS is negligible compared to TSD. + +Further, once computed, the edge maps and shuffled patch images used by ELEAS can be reused to train other models, further reducing the average data generation cost. + +# 6. Conclusion + +We propose and evaluate ELEAS - a lightweight adversarial augmentation technique for image classification in order to induce a shape bias in learned models. Previous work in this area [7,21] identified the need for such inductive biases due to the apparent dependence of deep models on textural features; however, their proposed augmentation techniques have drawbacks—first, they primarily sever the dependence on texture, while not explicitly enforcing processing and representation of shape, and second, the proposed augmentation process is very expensive. Although our work, too, proposes only data augmentation and does not come with guarantees on learned representations, the augmentations are simple to compute and are designed to encourage holistic shape representation. Extensive experimentation shows both the value of this inductive bias (shape factors correlate with model robustness and accuracy across models) and the substantial gains of our proposal, including over $5\%$ absolute accuracy improvements on ImageNet using vision transformers. An interesting direction for future work is to explore richer ways of specifying "shape" to the models—for instance, using off-the-shelf segmentation or depth estimation models—and also to explore other inductive biases that can profitably be incorporated into vision models. + +# References + +[1] Nicholas Baker, Hongjing Lu, Gennady Erlikhman, and Philip J. Kellman. Deep convolutional networks do not classify based on global object shape. PLoS Comput. Biol., 14(12), 2018. +[2] Sanghyuk Chun and Song Park. Styleaugment: Learning texture de-biased representations by style augmentation without pre-defined textures. CoRR, abs/2108.10549, 2021. +[3] Alexey Dosovitskiy, Lucas Beyer, Alexander Kolesnikov, Dirk Weissenborn, Xiaohua Zhai, Thomas Unterthiner, Mostafa Dehghani, Matthias Minderer, Georg Heigold, Sylvain Gelly, Jakob Uszkoreit, and Neil Houlsby. An image is worth 16x16 words: Transformers for image recognition at scale. In 9th International Conference on Learning Representations, ICLR 2021, Virtual Event, Austria, May 3-7, 2021. OpenReview.net, 2021. +[4] M. Everingham, L. Van Gool, C. K. I. Williams, J. Winn, and A. Zisserman. The Pascal visual object classes (voc) challenge. International Journal of Computer Vision, 88(2):303-338, June 2010. +[5] Leon A. Gatys. Texture synthesis and style transfer using perceptual image representations from convolutional neural networks. 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Dauphin, and David Lopez-Paz. mixup: Beyond empirical risk minimization. In 6th International Conference on Learning Representations, ICLR 2018, Vancouver, BC, Canada, April 30 - May 3, 2018, Conference Track Proceedings. 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Various data augmentation strategies have been proposed to overcome this so-called texture bias in DNNs. We propose a simple, lightweight adversarial augmentation technique that explicitly incentivizes the network to learn holistic shapes for accurate prediction in an object classification setting. Our augmentations superpose edgemaps from one image onto another image with shuffled patches, using a randomly determined mixing proportion, with the image label of the edgemap image. To classify these augmented images, the model needs to not only detect and focus on edges but distinguish between relevant and spurious edges. We show that our augmentations significantly improve classification accuracy and robustness measures on a range of datasets and neural architectures. As an example, for ViT-S, We obtain absolute gains on classification accuracy gains up to " + }, + { + "bbox": [ + 47, + 239, + 290, + 539 + ], + "type": "inline_equation", + "content": "6\\%" + }, + { + "bbox": [ + 47, + 239, + 290, + 539 + ], + "type": "text", + "content": ". We also obtain gains of up to " + }, + { + "bbox": [ + 47, + 239, + 290, + 539 + ], + "type": "inline_equation", + "content": "28\\%" + }, + { + "bbox": [ + 47, + 239, + 290, + 539 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 239, + 290, + 539 + ], + "type": "inline_equation", + "content": "8.5\\%" + }, + { + "bbox": [ + 47, + 239, + 290, + 539 + ], + "type": "text", + "content": " on natural adversarial and out-of-distribution datasets like ImageNet-A (for ViT-B) and ImageNet-R (for ViT-S), respectively. Analysis using a range of probe datasets shows substantially increased shape sensitivity in our trained models, explaining the observed improvement in robustness and classification accuracy." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 563, + 128, + 575 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 563, + 128, + 575 + ], + "spans": [ + { + "bbox": [ + 47, + 563, + 128, + 575 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 584, + 287, + 693 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 584, + 287, + 693 + ], + "spans": [ + { + "bbox": [ + 47, + 584, + 287, + 693 + ], + "type": "text", + "content": "A growing body of research catalogues and analyzes apparent failure modes of deep vision models. For instance, work on texture bias [1,7,12] suggests that image classifiers are overdependent on textural cues and fail against simple (adversarial) texture substitutions. Relatedly, the idea of simplicity bias [25] captures the tendency of deep models to use weakly predictive \"simple\" features such as color or texture, even in the presence of strongly predictive complex features. In psychology & neuroscience, too, evidence" + } + ] + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 307, + 219, + 555, + 355 + ], + "blocks": [ + { + "bbox": [ + 307, + 219, + 555, + 355 + ], + "lines": [ + { + "bbox": [ + 307, + 219, + 555, + 355 + ], + "spans": [ + { + "bbox": [ + 307, + 219, + 555, + 355 + ], + "type": "image", + "image_path": "1c5ac6a664b11df457ab1af568be30eabe35746be11f2d742b77e5e003b2ea62.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 307, + 359, + 556, + 504 + ], + "blocks": [ + { + "bbox": [ + 307, + 359, + 556, + 504 + ], + "lines": [ + { + "bbox": [ + 307, + 359, + 556, + 504 + ], + "spans": [ + { + "bbox": [ + 307, + 359, + 556, + 504 + ], + "type": "image", + "image_path": "0d4cf708e57e24be696e6f614c301a61e31234ae913c7fc46d7ae53708e7691d.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 516, + 547, + 582 + ], + "lines": [ + { + "bbox": [ + 304, + 516, + 547, + 582 + ], + "spans": [ + { + "bbox": [ + 304, + 516, + 547, + 582 + ], + "type": "text", + "content": "Figure 1. Comparison of the models on robustness and shape-bias. The shape factor gives the fraction of dimensions that encode shape cues [17]. Backbone(T) denotes texture shape debiased (TSD) models [21]. In comparison, ELEAS denoted by Backbone(E) is more shape biased and shows better performance on ImageNet-C and ImageNet-A datasets." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 605, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 547, + 715 + ], + "type": "text", + "content": "suggests that deep networks focus more on \"local\" features rather than global features and differ from human behavior in related tasks [19]. More broadly speaking, there is a mismatch between the cognitive concepts and associated world knowledge implied by the category labels in image datasets such as Imagenet and the actual information content made available to a model via one-hot vectors encoding these labels. In the face of under-determined learning problems, we need to introduce inductive biases to guide" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 702, + 184, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 702, + 184, + 712 + ], + "spans": [ + { + "bbox": [ + 58, + 702, + 184, + 712 + ], + "type": "text", + "content": "*Work done at Google Research India." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "24470" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 50, + 70, + 175, + 223 + ], + "blocks": [ + { + "bbox": [ + 50, + 70, + 175, + 223 + ], + "lines": [ + { + "bbox": [ + 50, + 70, + 175, + 223 + ], + "spans": [ + { + "bbox": [ + 50, + 70, + 175, + 223 + ], + "type": "image", + "image_path": "5c0a254668a3da9bd24bf823a5852d733ab8e379a3c94ac932f00efa25595541.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 233, + 547, + 269 + ], + "lines": [ + { + "bbox": [ + 46, + 233, + 547, + 269 + ], + "spans": [ + { + "bbox": [ + 46, + 233, + 547, + 269 + ], + "type": "text", + "content": "Figure 2. Representative performance comparison of our model, with the 'Debiased' models (TSD [21]) on ImageNet-A, R, C, and Sketch datasets. The models trained using ELEAS show improved performance on out-of-distribution robustness datasets. The large performance improvement on the ImageNet-A dataset indicates better robustness to natural adversarial examples." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 178, + 70, + 296, + 223 + ], + "blocks": [ + { + "bbox": [ + 178, + 70, + 296, + 223 + ], + "lines": [ + { + "bbox": [ + 178, + 70, + 296, + 223 + ], + "spans": [ + { + "bbox": [ + 178, + 70, + 296, + 223 + ], + "type": "image", + "image_path": "57527a133e97d646058114dbc503af3a36941281e51c7f397fded698786c14c7.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 299, + 70, + 417, + 223 + ], + "blocks": [ + { + "bbox": [ + 299, + 70, + 417, + 223 + ], + "lines": [ + { + "bbox": [ + 299, + 70, + 417, + 223 + ], + "spans": [ + { + "bbox": [ + 299, + 70, + 417, + 223 + ], + "type": "image", + "image_path": "a6fb6d8dce5602d9295c32affce1376036a18bbc55752dcb19da6178618a67a6.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 422, + 70, + 542, + 223 + ], + "blocks": [ + { + "bbox": [ + 422, + 70, + 542, + 223 + ], + "lines": [ + { + "bbox": [ + 422, + 70, + 542, + 223 + ], + "spans": [ + { + "bbox": [ + 422, + 70, + 542, + 223 + ], + "type": "image", + "image_path": "bf59e34cc2a795bc93e2c0aaf37dbcc32f80699161d6ccba19aad7d9fa29e1e4.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 288, + 289, + 408 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 288, + 289, + 408 + ], + "spans": [ + { + "bbox": [ + 46, + 288, + 289, + 408 + ], + "type": "text", + "content": "the learning process. To this end, Geirhos et al. [7] proposed a data augmentation method wherein the texture of an image was replaced with that of a painting through stylization. Follow-on work improved upon this approach by replacing textures from other objects (instead of paintings) and teaching the model to separately label the outer shape and the substituted texture according to their source image categories [21]. Both these approaches discourage overdependence on textural features in the learned model; however, they do not explicitly incentivize shape recognition." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 415, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 415, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 415, + 289, + 715 + ], + "type": "text", + "content": "We propose a lightweight adversarial augmentation technique ELEAS (Edge Learning for Shape sensitivity) that is designed to increase shape sensitivity in vision models. Specifically, we augment a dataset with superpositions of random pairs of images from the dataset, where one image is processed to produce an edge map, and the other is modified by shuffling the location of image patches within the image. The two images are superposed using a randomly sampled relative mixing weight (similar to Mixup [30]), and the new superposed image is assigned the label of the edgemap image. ELEAS is designed to specifically incentivize not only edge detection but shape sensitivity: 1) classifying the edgemap image requires the model to extract and exploit edges - the only features available in the image, 2) distinguishing the edgemap object category from the superposed shuffled image requires the model to distinguish the overall edgemap object shape (relevant edges) from the shuffled image edges (irrelevant edges, less likely to be \"shape like\"). We perform extensive experiments over a range of model architectures, image classification datasets, and probe datasets, comparing ELEAS against recent baselines. Figure 1 provides a small visual sample of our findings and results; across various models, a measure of shape sensitivity [17] correlates very strongly with measures of classifier robustness [11, 12] (see Results" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 288, + 547, + 347 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 288, + 547, + 347 + ], + "spans": [ + { + "bbox": [ + 304, + 288, + 547, + 347 + ], + "type": "text", + "content": "for more details), validating the shape sensitivity inductive bias. In addition, for a number of model architectures, models trained with ELEAS significantly improve both measures compared to the previous SOTA data augmentation approach [21]." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 317, + 348, + 527, + 361 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 348, + 527, + 361 + ], + "spans": [ + { + "bbox": [ + 317, + 348, + 527, + 361 + ], + "type": "text", + "content": "Summing up, we make the following contributions:" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 317, + 368, + 545, + 574 + ], + "type": "list", + "angle": 0, + "index": 12, + "blocks": [ + { + "bbox": [ + 317, + 368, + 545, + 440 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 368, + 545, + 440 + ], + "spans": [ + { + "bbox": [ + 317, + 368, + 545, + 440 + ], + "type": "text", + "content": "- We propose an adversarial augmentation technique, ELEAS, designed to incentivize shape sensitivity in vision models. Our augmentation technique is lightweight (needing only an off-the-shelf edge detection method) compared to previous proposals that require expensive GAN-based image synthesis [7, 21]." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 317, + 447, + 545, + 519 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 447, + 545, + 519 + ], + "spans": [ + { + "bbox": [ + 317, + 447, + 545, + 519 + ], + "type": "text", + "content": "- In experiments, ELEAS shows increased shape sensitivity on a wide range of tasks designed to probe this property. Consequently, we obtain increased accuracy in object classification with a " + }, + { + "bbox": [ + 317, + 447, + 545, + 519 + ], + "type": "inline_equation", + "content": "6\\%" + }, + { + "bbox": [ + 317, + 447, + 545, + 519 + ], + "type": "text", + "content": " improvement on ImageNet-1K classification accuracy for ViT-Small among others." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 317, + 526, + 545, + 574 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 526, + 545, + 574 + ], + "spans": [ + { + "bbox": [ + 317, + 526, + 545, + 574 + ], + "type": "text", + "content": "- ELEAS shows high generalizability and out of distribution robustness with " + }, + { + "bbox": [ + 317, + 526, + 545, + 574 + ], + "type": "inline_equation", + "content": "14.2\\%" + }, + { + "bbox": [ + 317, + 526, + 545, + 574 + ], + "type": "text", + "content": " improvement in ImageNet-C classification performance and " + }, + { + "bbox": [ + 317, + 526, + 545, + 574 + ], + "type": "inline_equation", + "content": "5.89\\%" + }, + { + "bbox": [ + 317, + 526, + 545, + 574 + ], + "type": "text", + "content": " increase in shape-bias for Resnet152." + } + ] + } + ], + "index": 11 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 306, + 586, + 391, + 598 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 586, + 391, + 598 + ], + "spans": [ + { + "bbox": [ + 306, + 586, + 391, + 598 + ], + "type": "text", + "content": "2. Related work" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 605, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 547, + 715 + ], + "type": "text", + "content": "Texture bias in vision models. In [1,7], convolutional neural networks are shown to be more sensitive towards the texture present in the image to classify the object correctly. Further, in order to mitigate the texture bias, they have suggested a training strategy where they have used modified images with random texture along with the natural images during training. However, utilizing images with conflicting textures leads to an unnatural shift in data distribution, leading to drops in performance on natural images. Instead, sim" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 758 + ], + "type": "text", + "content": "24471" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 203 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 203 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 203 + ], + "type": "text", + "content": "ple and naturalistic data augmentations strategies can also lead to an increase in shape bias of the CNNs without much loss in performance on natural images [13]. An increase in shape-bias in the CNN models is associated with an increase in the robustness of the models [7, 26], however [22] suggested that a more balanced shape or texture biased models also leads to increase in the model robustness. The study of texture bias in vision models has been extended to the vision transformers (ViT) [3], where the transformer models are found to be less texture biased than the convolutional models [27]." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 204, + 289, + 360 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 204, + 289, + 360 + ], + "spans": [ + { + "bbox": [ + 46, + 204, + 289, + 360 + ], + "type": "text", + "content": "A measure of shape/texture bias is proposed in [7], where they used images with conflicting textures obtained using style-transfer methods. However, this measure ignores a large portion of test images and is biased toward models trained using images modified by style-transfer methods. In [14], Hermann et al. proposed a linear classification layer in order to measure the shape decodability of the representations learned by the model. A more fine-grained shape evaluation measure was proposed in [18] where they compute the number of dimensions in the image representation that correlate with the shape features. Further, they proposed a shallow read-out module that takes feature representations from the model and predicts a segmentation map." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 360, + 289, + 515 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 360, + 289, + 515 + ], + "spans": [ + { + "bbox": [ + 46, + 360, + 289, + 515 + ], + "type": "text", + "content": "Data Augmentation for improving shape-bias In [2, 7], authors suggested a data augmentation strategy in order to increase the shape bias in the trained models. They proposed the Stylized-ImageNet dataset, where they strip each image of its original texture and replace it with the style of a randomly selected painting through AdaIN style transfer [16]. During training, the model is trained to predict the category corresponding to the shape in the model, ignoring the texture, thus leading to an increase in the shape bias of the models. However, instead of changing the distribution of training images through style transfer, naturalistic data augmentation techniques such as can also lead to improvement in the shape bias of the model [13]." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 525, + 130, + 540 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 525, + 130, + 540 + ], + "spans": [ + { + "bbox": [ + 47, + 525, + 130, + 540 + ], + "type": "text", + "content": "3. Methodology" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 545, + 287, + 569 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 545, + 287, + 569 + ], + "spans": [ + { + "bbox": [ + 46, + 545, + 287, + 569 + ], + "type": "text", + "content": "We now describe the training strategy used in ELEAS to increase the shape sensitivity of deep image classifiers." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 570, + 287, + 666 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 570, + 287, + 666 + ], + "spans": [ + { + "bbox": [ + 46, + 570, + 287, + 666 + ], + "type": "text", + "content": "Let " + }, + { + "bbox": [ + 46, + 570, + 287, + 666 + ], + "type": "inline_equation", + "content": "\\mathcal{I}" + }, + { + "bbox": [ + 46, + 570, + 287, + 666 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 46, + 570, + 287, + 666 + ], + "type": "inline_equation", + "content": "\\mathcal{C}" + }, + { + "bbox": [ + 46, + 570, + 287, + 666 + ], + "type": "text", + "content": " be the set of all images and their corresponding categories in the dataset. In standard classifier training, a classifier " + }, + { + "bbox": [ + 46, + 570, + 287, + 666 + ], + "type": "inline_equation", + "content": "\\Theta" + }, + { + "bbox": [ + 46, + 570, + 287, + 666 + ], + "type": "text", + "content": " is trained to predict the category " + }, + { + "bbox": [ + 46, + 570, + 287, + 666 + ], + "type": "inline_equation", + "content": "c \\in \\mathcal{C}" + }, + { + "bbox": [ + 46, + 570, + 287, + 666 + ], + "type": "text", + "content": " of the image " + }, + { + "bbox": [ + 46, + 570, + 287, + 666 + ], + "type": "inline_equation", + "content": "i \\in \\mathcal{I}" + }, + { + "bbox": [ + 46, + 570, + 287, + 666 + ], + "type": "text", + "content": ". However, the image classifiers trained in this way are sensitive to the texture present in the natural images. In this work, we propose to use edge maps along with textures from natural images to increase the shape sensitivity of image classifiers." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 666, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 666, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 666, + 288, + 714 + ], + "type": "text", + "content": "Obtaining shapes and textures: We approximate the shapes of objects by extracting edge-maps from images and natural textures by shuffling patches within images. In particular, for each image " + }, + { + "bbox": [ + 46, + 666, + 288, + 714 + ], + "type": "inline_equation", + "content": "i \\in \\mathcal{I}" + }, + { + "bbox": [ + 46, + 666, + 288, + 714 + ], + "type": "text", + "content": ", an edge-map is constructed" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 72, + 545, + 133 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 133 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 133 + ], + "type": "text", + "content": "using an edge detection kernel (i.e., Laplacian kernel) to produce the set of all edge-maps or \"shapes\" " + }, + { + "bbox": [ + 304, + 72, + 545, + 133 + ], + "type": "inline_equation", + "content": "S" + }, + { + "bbox": [ + 304, + 72, + 545, + 133 + ], + "type": "text", + "content": ". Similarly, a \"texture\" dataset " + }, + { + "bbox": [ + 304, + 72, + 545, + 133 + ], + "type": "inline_equation", + "content": "\\mathcal{T}" + }, + { + "bbox": [ + 304, + 72, + 545, + 133 + ], + "type": "text", + "content": " is generated by first dividing an image in " + }, + { + "bbox": [ + 304, + 72, + 545, + 133 + ], + "type": "inline_equation", + "content": "\\mathcal{I}" + }, + { + "bbox": [ + 304, + 72, + 545, + 133 + ], + "type": "text", + "content": " into " + }, + { + "bbox": [ + 304, + 72, + 545, + 133 + ], + "type": "inline_equation", + "content": "4 \\times 4" + }, + { + "bbox": [ + 304, + 72, + 545, + 133 + ], + "type": "text", + "content": " patches and then randomly shuffling the patches within the image to obtain a patch-shuffled image." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 133, + 545, + 192 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 133, + 545, + 192 + ], + "spans": [ + { + "bbox": [ + 304, + 133, + 545, + 192 + ], + "type": "text", + "content": "Generating augmentations: We superimpose randomly selected pairs of images " + }, + { + "bbox": [ + 304, + 133, + 545, + 192 + ], + "type": "inline_equation", + "content": "s \\in S" + }, + { + "bbox": [ + 304, + 133, + 545, + 192 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 133, + 545, + 192 + ], + "type": "inline_equation", + "content": "t \\in \\mathcal{T}" + }, + { + "bbox": [ + 304, + 133, + 545, + 192 + ], + "type": "text", + "content": " to create new images, or augmentations, to add to the training dataset. Each such augmented image is assigned the label of the shape image " + }, + { + "bbox": [ + 304, + 133, + 545, + 192 + ], + "type": "inline_equation", + "content": "s" + }, + { + "bbox": [ + 304, + 133, + 545, + 192 + ], + "type": "text", + "content": ". The superimposed image is obtained as follows:" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 375, + 201, + 545, + 214 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 375, + 201, + 545, + 214 + ], + "spans": [ + { + "bbox": [ + 375, + 201, + 545, + 214 + ], + "type": "interline_equation", + "content": "i _ {s} = \\lambda * t + (1 - \\lambda) * s \\tag {1}", + "image_path": "44c6ddaaaab813f68ca4078a8252f39c27645485bb128ffb35a5c4c6fd0ca05d.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 223, + 545, + 295 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 223, + 545, + 295 + ], + "spans": [ + { + "bbox": [ + 304, + 223, + 545, + 295 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 223, + 545, + 295 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 304, + 223, + 545, + 295 + ], + "type": "text", + "content": " is drawn randomly from a " + }, + { + "bbox": [ + 304, + 223, + 545, + 295 + ], + "type": "inline_equation", + "content": "\\operatorname{Beta}(\\alpha, \\beta)" + }, + { + "bbox": [ + 304, + 223, + 545, + 295 + ], + "type": "text", + "content": " distribution. The parameters " + }, + { + "bbox": [ + 304, + 223, + 545, + 295 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 304, + 223, + 545, + 295 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 223, + 545, + 295 + ], + "type": "inline_equation", + "content": "\\beta" + }, + { + "bbox": [ + 304, + 223, + 545, + 295 + ], + "type": "text", + "content": " are chosen such that a higher weight is given to the samples from set " + }, + { + "bbox": [ + 304, + 223, + 545, + 295 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 304, + 223, + 545, + 295 + ], + "type": "text", + "content": ". The random weighing parameter " + }, + { + "bbox": [ + 304, + 223, + 545, + 295 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 304, + 223, + 545, + 295 + ], + "type": "text", + "content": " introduces variation in the augmented image set and helps to obtain better edge-map classification. Let's call the set of superimposed images " + }, + { + "bbox": [ + 304, + 223, + 545, + 295 + ], + "type": "inline_equation", + "content": "\\mathcal{B}" + }, + { + "bbox": [ + 304, + 223, + 545, + 295 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 295, + 545, + 415 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 295, + 545, + 415 + ], + "spans": [ + { + "bbox": [ + 304, + 295, + 545, + 415 + ], + "type": "text", + "content": "Training procedure: Training proceeds via minibatch gradient descent, as is standard in current machine learning literature. We construct each mini-batch to have half of its images from the set of natural images " + }, + { + "bbox": [ + 304, + 295, + 545, + 415 + ], + "type": "inline_equation", + "content": "I \\subset \\mathcal{I}" + }, + { + "bbox": [ + 304, + 295, + 545, + 415 + ], + "type": "text", + "content": " and the rest from the augmented dataset " + }, + { + "bbox": [ + 304, + 295, + 545, + 415 + ], + "type": "inline_equation", + "content": "B \\subset \\mathcal{B}" + }, + { + "bbox": [ + 304, + 295, + 545, + 415 + ], + "type": "text", + "content": ". During training, we minimize the cross-entropy loss on natural image samples as well as our augmentations. In order to carefully control the degree of shape sensitivity induced by this process, we compute a weighted mixture of cross-entropy loss on these two image sets denoted here by " + }, + { + "bbox": [ + 304, + 295, + 545, + 415 + ], + "type": "inline_equation", + "content": "L" + }, + { + "bbox": [ + 304, + 295, + 545, + 415 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 310, + 423, + 545, + 437 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 310, + 423, + 545, + 437 + ], + "spans": [ + { + "bbox": [ + 310, + 423, + 545, + 437 + ], + "type": "interline_equation", + "content": "L (I, B, y _ {I}, y _ {B}) = \\eta * C E (I, y _ {I}) + 1 - \\eta * C E (B, y _ {B}) \\tag {2}", + "image_path": "65bcf4f8aec2c6f1aefa8eda82f11e7079c771940db18dca8b97a27e0363e36b.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 445, + 545, + 590 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 445, + 545, + 590 + ], + "spans": [ + { + "bbox": [ + 304, + 445, + 545, + 590 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 445, + 545, + 590 + ], + "type": "inline_equation", + "content": "\\eta" + }, + { + "bbox": [ + 304, + 445, + 545, + 590 + ], + "type": "text", + "content": " is varied to control the shape sensitivity, " + }, + { + "bbox": [ + 304, + 445, + 545, + 590 + ], + "type": "inline_equation", + "content": "CE" + }, + { + "bbox": [ + 304, + 445, + 545, + 590 + ], + "type": "text", + "content": " is the cross-entropy loss, " + }, + { + "bbox": [ + 304, + 445, + 545, + 590 + ], + "type": "inline_equation", + "content": "y_{I}, y_{B}" + }, + { + "bbox": [ + 304, + 445, + 545, + 590 + ], + "type": "text", + "content": " are the labels corresponding to the natural and augmented image sets " + }, + { + "bbox": [ + 304, + 445, + 545, + 590 + ], + "type": "inline_equation", + "content": "I, B" + }, + { + "bbox": [ + 304, + 445, + 545, + 590 + ], + "type": "text", + "content": " respectively. To predict augmented images correctly, the model needs to interpret the edge-map present in the superimposed sample while at the same time ignoring distracting edges and textures from the other superimposed image. In this manner, we induce shape sensitivity in learned classifiers. The minibatch-mixing strategy encourages the model to generalize learned representations across natural and augmented images, thereby improving shape bias (and consequently overall accuracy) on natural images as well." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 600, + 422, + 613 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 600, + 422, + 613 + ], + "spans": [ + { + "bbox": [ + 305, + 600, + 422, + 613 + ], + "type": "text", + "content": "4. Experimental setup" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 620, + 451, + 633 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 620, + 451, + 633 + ], + "spans": [ + { + "bbox": [ + 305, + 620, + 451, + 633 + ], + "type": "text", + "content": "4.1. Models and training setup" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 638, + 545, + 686 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 638, + 545, + 686 + ], + "spans": [ + { + "bbox": [ + 304, + 638, + 545, + 686 + ], + "type": "text", + "content": "We train convolutional neural networks (CNNs) and Vision Transformers (ViTs) using our methodology. Among the CNN models, similar to [21], we show results on ResNet50, ResNet101, and ResNet152. For training the" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 306, + 693, + 547, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 693, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 306, + 693, + 547, + 713 + ], + "type": "text", + "content": "1Refer to Fig. 1 in the supplementary material for examples of ELEAS images." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "type": "text", + "content": "24472" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 120, + 70, + 473, + 311 + ], + "blocks": [ + { + "bbox": [ + 120, + 70, + 473, + 311 + ], + "lines": [ + { + "bbox": [ + 120, + 70, + 473, + 311 + ], + "spans": [ + { + "bbox": [ + 120, + 70, + 473, + 311 + ], + "type": "table", + "html": "
ModelMethodIN-A(↑)IN-R(↑)IN-C(↓)IN-Sketch(↑)IN-1K(↑)
Resnet50Vanilla2.036.275.023.576.4
TSD [21]3.340.867.528.376.9
ELEAS5.441.758.529.777.1
Resnet101Vanilla5.639.369.827.178.0
TSD [21]8.844.362.232.378.8
ELEAS13.444.453.532.478.6
Resnet152Vanilla5.941.367.228.478.6
TSD [21]12.545.558.933.379.7
ELEAS15.445.753.034.779.0
ViT-SVanilla16.636.155.133.274.6
TSD [21]27.444.442.232.476.4
ELEAS28.344.741.534.780.6
ViT-BVanilla34.640.750.845.879.5
ELEAS62.956.435.946.485.5
ViT-LVanilla63.463.333.152.785.8
ELEAS67.465.929.554.186.2
", + "image_path": "fbccdfe57fcdd54e4040fa3644af0cfb6ba4c7d51faec5394cea573391c8010e.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 319, + 547, + 354 + ], + "lines": [ + { + "bbox": [ + 46, + 319, + 547, + 354 + ], + "spans": [ + { + "bbox": [ + 46, + 319, + 547, + 354 + ], + "type": "text", + "content": "Table 1. Performance comparison on the ImageNet and the robustness datasets. The models trained using ELEAS show an improvement in the ImageNet performance along with better robustness. Except for IN-C the performance is measured in Accuracy@1 (higher is better). For IN-C, the performance is measured in mean corruption error (mCE) (lower is better). (Refer to Sections 5.1 and 5.2.1)" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 374, + 289, + 542 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 374, + 289, + 542 + ], + "spans": [ + { + "bbox": [ + 46, + 374, + 289, + 542 + ], + "type": "text", + "content": "ResNet models, we supplemented ImageNet data with an equal number of augmented images. We trained them for 100 epochs with a starting learning rate of 0.2 which is reduced by a factor of 10 at the 30th, 60th and 90th epoch. Similar to TSD, while training the ResNet models, we also use auxiliary batch norm [29]. As ViTs are compute-intensive, we finetune ImageNet pretrained ViT models for 20k steps with a cosine learning rate schedule with a starting learning rate of 0.01. The stochastic gradient descent (SGD) with a momentum of 0.9 is used to train the models. We train all our models on 8 A100 GPUs with a batch size of 512 for ResNets, 256 for ViT-Small and ViT-Base and 128 for ViT-Large. We find that values " + }, + { + "bbox": [ + 46, + 374, + 289, + 542 + ], + "type": "inline_equation", + "content": "\\alpha = 4" + }, + { + "bbox": [ + 46, + 374, + 289, + 542 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 374, + 289, + 542 + ], + "type": "inline_equation", + "content": "\\beta = 1" + }, + { + "bbox": [ + 46, + 374, + 289, + 542 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 46, + 374, + 289, + 542 + ], + "type": "inline_equation", + "content": "\\eta = 0.65" + }, + { + "bbox": [ + 46, + 374, + 289, + 542 + ], + "type": "text", + "content": " produce the best results for all models." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 551, + 223, + 563 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 551, + 223, + 563 + ], + "spans": [ + { + "bbox": [ + 47, + 551, + 223, + 563 + ], + "type": "text", + "content": "4.2. Datasets and evaluation protocol" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 569, + 287, + 700 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 569, + 287, + 700 + ], + "spans": [ + { + "bbox": [ + 46, + 569, + 287, + 700 + ], + "type": "text", + "content": "The models are trained on the ILSVRC 2012 [24] dataset with 1.28M training and 50k validation images. We evaluate and compare our trained models to answer the following questions: (i) Does ELEAS lead to an increase in the shape-sensitivity of a model? (ii) Does the increased shape sensitivity result in better classification performance? (iii) Does the robustness of the models to distribution shift improve with increased shape sensitivity? and (iv) Does an increase in shape sensitivity lead to improvement in downstream tasks such as object detection and instance segmentation?" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 59, + 701, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 701, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 59, + 701, + 287, + 713 + ], + "type": "text", + "content": "The shape sensitivity of the models is first evaluated us" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 374, + 545, + 638 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 374, + 545, + 638 + ], + "spans": [ + { + "bbox": [ + 304, + 374, + 545, + 638 + ], + "type": "text", + "content": "ing the metric proposed in [7]. The authors first created an image dataset called cue-conflict, using a style-transfer method to transfer texture from one image to another. They then defined shape bias as the fraction of the shape decision when the model predicts either the shape or the texture category. However, this metric ignores many a lot of images and is biased toward the methods that used Stylized-ImageNet during the training of the models. Further, authors in [17] proposed a method to quantify the number of dimensions in the image representation that encode the object's shape. They take a pair of images with similar semantic concepts (i.e., shape) and then count the number of neurons that encode that specific concept. They have used Pascal VOC [4] and Stylized Pascal VOC dataset to create pair of images with particular semantic concepts. We have used these metrics to evaluate the shape bias in this work. Further, similar to [17], we also evaluate the quality of the shape encoding from these models by performing the binary and semantic segmentation on the frozen representations. PASCAL VOC is image segmentation dataset [4, 8], with 10,582 training images and 1,449 validation images spanning across 20 object categories." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 641, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 641, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 641, + 547, + 715 + ], + "type": "text", + "content": "The out-of-distribution generalization of the trained models is evaluated on four publicly available datasets, which are, ImageNet-A [12], ImageNet-R [10], ImageNet-C [11], and ImageNet-Sketch [28]. The ImageNet-A dataset consists of real-world natural adversarial images and is a challenging classification dataset. The ImageNet-R dataset" + } + ] + } + ], + "index": 7 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "24473" + } + ] + } + ], + "index": 8 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 121, + 70, + 473, + 312 + ], + "blocks": [ + { + "bbox": [ + 121, + 70, + 473, + 312 + ], + "lines": [ + { + "bbox": [ + 121, + 70, + 473, + 312 + ], + "spans": [ + { + "bbox": [ + 121, + 70, + 473, + 312 + ], + "type": "table", + "html": "
ModelMethodEdgeSilhouetteCue-conflictSketchStylized-IN
Resnet50Vanilla13.7554.3818.2059.6237.13
TSD [21]22.555.6221.4067.056.13
ELEAS35.6254.3721.4167.8846.0
Resnet101Vanilla23.8549.3719.9263.1241.75
TSD [21]31.2551.8724.9270.1259.37
ELEAS45.0061.2524.0671.8848.25
Resnet152Vanilla20.6356.2520.7066.7541.63
TSD [21]22.558.12525.3169.1357.67
ELEAS41.8856.8823.8373.3848.75
ViT-SVanilla25.026.2522.9649.1244.25
TSD [21]22.546.8731.7168.6277.5
ELEAS34.3843.1327.6669.6353.00
ViT-BVanilla13.7512.0528.0551.6350.08
ELEAS41.2566.2534.9282.0059.38
ViT-LVanilla55.6268.7540.3983.7565.50
ELEAS75.0069.3842.1185.8866.50
", + "image_path": "7e7bb236cbf78499bb76fc932e1eb1aa84d8da3faafdfc04b59ef53c47b6e1f9.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 319, + 547, + 354 + ], + "lines": [ + { + "bbox": [ + 46, + 319, + 547, + 354 + ], + "spans": [ + { + "bbox": [ + 46, + 319, + 547, + 354 + ], + "type": "text", + "content": "Table 2. Performance comparison on out-of-distribution benchmark proposed in [6]. The proposed method significantly improves performance over vanilla ResNet models. Debiased models, trained on stylized images, show high performance on datasets utilizing stylized images for evaluation, such as Cue-Conflict and Stylized-IN. (Refer to Section 5.2.2)" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 374, + 289, + 505 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 374, + 289, + 505 + ], + "spans": [ + { + "bbox": [ + 46, + 374, + 289, + 505 + ], + "type": "text", + "content": "consists of images with various renditions, such as cartoon art, DeviantArt, graphics, paintings, origami, etc., of the objects present in the original ImageNet dataset. The ImageNet-Sketch dataset consists of sketches of 1000 ImageNet object categories. Both ImageNet-R and ImageNet-Sketch are used to evaluate the out-of-distribution generalization capability of the models. The ImageNet-C dataset consists of images with varying degrees of artificial distortions like 'Gaussian Noise', 'Motion Blur', 'Speckle Noise', etc. Hence, it evaluates the robustness of the model to added distortions." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 506, + 288, + 555 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 506, + 288, + 555 + ], + "spans": [ + { + "bbox": [ + 47, + 506, + 288, + 555 + ], + "type": "text", + "content": "Besides using classification accuracy for most datasets, ImageNet-C's performance is measured using mean corruption error (mCE). Additionally, we evaluated the models on the out-of-distribution benchmark proposed in [6]." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 574, + 119, + 585 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 574, + 119, + 585 + ], + "spans": [ + { + "bbox": [ + 47, + 574, + 119, + 585 + ], + "type": "text", + "content": "4.2.1 Baselines" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 594, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 594, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 289, + 715 + ], + "type": "text", + "content": "We compare the performance of ELEAS with Shape-Texture Debiased (TSD) trained models [21], which focus on both shape and texture cues. TSD uses stylized ImageNet images with conflicting shape and texture cues, and the models are trained using supervision from both semantic cues. Among ViTs, only ViT-S is trained with TSD due to the large computation overhead involved in training ViT-B and ViT-L. In contrast, ELEAS learns the overall object shape in the presence of conflicting, less 'shape-like' edges, leading to increased shape sensitivity in the trained models." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 305, + 373, + 436, + 385 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 373, + 436, + 385 + ], + "spans": [ + { + "bbox": [ + 305, + 373, + 436, + 385 + ], + "type": "text", + "content": "5. Results and discussion" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 393, + 545, + 466 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 393, + 545, + 466 + ], + "spans": [ + { + "bbox": [ + 304, + 393, + 545, + 466 + ], + "type": "text", + "content": "Our experiments study the impact of ELEAS in the following stages: we show classification accuracy gains on the ImageNet dataset; we measure the robustness of trained models to a range of prediction challenges; and we examine ELEAS's influence on shape-sensitivity of trained models and its effect on performance." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 305, + 472, + 391, + 483 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 472, + 391, + 483 + ], + "spans": [ + { + "bbox": [ + 305, + 472, + 391, + 483 + ], + "type": "text", + "content": "5.1. Classification" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 490, + 545, + 611 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 490, + 545, + 611 + ], + "spans": [ + { + "bbox": [ + 304, + 490, + 545, + 611 + ], + "type": "text", + "content": "Along with the increase in shape bias, ELEAS also improves classification performance on the ImageNet dataset, in many cases by very large margins (Refer Table 1). For instance, we see " + }, + { + "bbox": [ + 304, + 490, + 545, + 611 + ], + "type": "inline_equation", + "content": "5.96\\%" + }, + { + "bbox": [ + 304, + 490, + 545, + 611 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 490, + 545, + 611 + ], + "type": "inline_equation", + "content": "5.93\\%" + }, + { + "bbox": [ + 304, + 490, + 545, + 611 + ], + "type": "text", + "content": " absolute improvement in ImageNet classification accuracy for ViT-S and ViT-B respectively, compared to vanilla baseline, and a smaller but still significant " + }, + { + "bbox": [ + 304, + 490, + 545, + 611 + ], + "type": "inline_equation", + "content": "4.22\\%" + }, + { + "bbox": [ + 304, + 490, + 545, + 611 + ], + "type": "text", + "content": " gain in accuracy compared to TSD on ViT-S. We also see " + }, + { + "bbox": [ + 304, + 490, + 545, + 611 + ], + "type": "inline_equation", + "content": "0.6\\%" + }, + { + "bbox": [ + 304, + 490, + 545, + 611 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 490, + 545, + 611 + ], + "type": "inline_equation", + "content": "0.62\\%" + }, + { + "bbox": [ + 304, + 490, + 545, + 611 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 304, + 490, + 545, + 611 + ], + "type": "inline_equation", + "content": "0.44\\%" + }, + { + "bbox": [ + 304, + 490, + 545, + 611 + ], + "type": "text", + "content": " increase in performance for ResNet50, ResNet101, and ResNet152 models respectively." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 616, + 471, + 628 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 616, + 471, + 628 + ], + "spans": [ + { + "bbox": [ + 305, + 616, + 471, + 628 + ], + "type": "text", + "content": "5.2. Out-of-distribution robustness" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 634, + 545, + 658 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 634, + 545, + 658 + ], + "spans": [ + { + "bbox": [ + 305, + 634, + 545, + 658 + ], + "type": "text", + "content": "5.2.1 Evaluation on ImageNet-A, R, C, and Sketch datasets." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 665, + 545, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 545, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 545, + 715 + ], + "type": "text", + "content": "As shown in Table 1, ELEAS significantly improves accuracy over both vanilla and TSD-trained models at these robustness challenges. For ImageNet-A, the considerable improvement (4.54% vs. TSD on ResNet101) indicates bet" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "24474" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 47, + 70, + 210, + 205 + ], + "blocks": [ + { + "bbox": [ + 47, + 70, + 210, + 205 + ], + "lines": [ + { + "bbox": [ + 47, + 70, + 210, + 205 + ], + "spans": [ + { + "bbox": [ + 47, + 70, + 210, + 205 + ], + "type": "image", + "image_path": "4221d130efa72ff6569ecbb78627dd6db5ce0b350b3d626cf55927fa39068ba9.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 47, + 217, + 210, + 354 + ], + "blocks": [ + { + "bbox": [ + 91, + 208, + 166, + 217 + ], + "lines": [ + { + "bbox": [ + 91, + 208, + 166, + 217 + ], + "spans": [ + { + "bbox": [ + 91, + 208, + 166, + 217 + ], + "type": "text", + "content": "(a) True vs. false color" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 47, + 217, + 210, + 354 + ], + "lines": [ + { + "bbox": [ + 47, + 217, + 210, + 354 + ], + "spans": [ + { + "bbox": [ + 47, + 217, + 210, + 354 + ], + "type": "image", + "image_path": "56dff3c237e7d5bf7e279e1ae6ac5c23189b669a12695dd4ae4f26ebecfa3aa7.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 97, + 355, + 159, + 363 + ], + "lines": [ + { + "bbox": [ + 97, + 355, + 159, + 363 + ], + "spans": [ + { + "bbox": [ + 97, + 355, + 159, + 363 + ], + "type": "text", + "content": "(d) Uniform Noise" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 47, + 365, + 210, + 501 + ], + "blocks": [ + { + "bbox": [ + 47, + 365, + 210, + 501 + ], + "lines": [ + { + "bbox": [ + 47, + 365, + 210, + 501 + ], + "spans": [ + { + "bbox": [ + 47, + 365, + 210, + 501 + ], + "type": "image", + "image_path": "ffdd3c6786cfeeb9435ba2ea783bf404175216e5ad008ed72227d5596d9f4762.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + } + ], + "index": 4 + }, + { + "type": "image", + "bbox": [ + 47, + 512, + 211, + 649 + ], + "blocks": [ + { + "bbox": [ + 103, + 502, + 154, + 512 + ], + "lines": [ + { + "bbox": [ + 103, + 502, + 154, + 512 + ], + "spans": [ + { + "bbox": [ + 103, + 502, + 154, + 512 + ], + "type": "text", + "content": "(g) Phase-noise" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 47, + 512, + 211, + 649 + ], + "lines": [ + { + "bbox": [ + 47, + 512, + 211, + 649 + ], + "spans": [ + { + "bbox": [ + 47, + 512, + 211, + 649 + ], + "type": "image", + "image_path": "d898887f6e5c3d0e5ab4e7308b1b599f909d4c625aa4ea6ebc906bbc6bd56406.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 109, + 651, + 148, + 659 + ], + "lines": [ + { + "bbox": [ + 109, + 651, + 148, + 659 + ], + "spans": [ + { + "bbox": [ + 109, + 651, + 148, + 659 + ], + "type": "text", + "content": "(j) EidolonI" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 46, + 669, + 547, + 692 + ], + "lines": [ + { + "bbox": [ + 46, + 669, + 547, + 692 + ], + "spans": [ + { + "bbox": [ + 46, + 669, + 547, + 692 + ], + "type": "text", + "content": "Figure 3. Robustness comparison of ELEAS trained Resnet152 and ViT-B with the human subjects. ELEAS leads to trained models which are more robust to added distortion and for many of the noise types it is more robust than the human subjects. 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ModelMethodShape-biasFactor |zk|
Shape dimTexture dim
Res50Vanilla19.750.1700.338
TSD [21]23.110.1850.285
ELEAS23.530.1950.299
Res101Vanilla22.440.1780.323
TSD [21]27.690.2040.256
ELEAS26.040.2220.259
Res152Vanilla21.740.1800.298
TSD [21]28.780.2070.236
ELEAS27.860.2280.249
ViT-SVanilla33.330.2140.210
TSD [21]36.560.2160.213
ELEAS34.640.2210.217
ViT-BVanilla33.120.2190.212
ELEAS37.900.2390.205
ViT-LVanilla47.040.2160.221
ELEAS48.100.2250.207
", + "image_path": "ec33ffabf7e9648432bdd66f4e67cc8162b900f85804f6ba3ce34382569b8bb3.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 314, + 287, + 369 + ], + "lines": [ + { + "bbox": [ + 46, + 314, + 287, + 369 + ], + "spans": [ + { + "bbox": [ + 46, + 314, + 287, + 369 + ], + "type": "text", + "content": "Table 3. Comparison of the shape-bias of the models. The vision models trained using our strategy shows an increase in the fraction of 'Shape' dimensions. However, the shape-bias metric proposed by Geirhos et al. [7] is biased towards the models trained using style-transfer datasets. (Refer to Section 5.3)" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 391, + 286, + 485 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 391, + 286, + 485 + ], + "spans": [ + { + "bbox": [ + 46, + 391, + 286, + 485 + ], + "type": "text", + "content": "ter robustness to naturally occurring adversarial examples. Similarly, the improvement in mCE on ImageNet-C (8.72% vs. TSD on ResNet101) showcases robustness to added distortions of various degrees. Similarly, ELEAS shows robustness performance improvements on the ViT models. These large gains are driven primarily by ELEAS's ability to better encode object shape (Refer Figure 1 for evidence supporting this causal link.)" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 502, + 230, + 514 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 502, + 230, + 514 + ], + "spans": [ + { + "bbox": [ + 47, + 502, + 230, + 514 + ], + "type": "text", + "content": "5.2.2 Evaluation on OOD benchmark [6]" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 521, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 521, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 521, + 287, + 713 + ], + "type": "text", + "content": "We also evaluated trained models on the OOD benchmark proposed in [6]; results are in Table 2. The datasets in this benchmark consist of images from different domains such as 'Edge', 'Silhouette', 'Sketch', 'Stylized', and 'Cue-conflict', which require stronger shape sensitivity for correct classification. The 'Cue-conflict' dataset is generated using iterative style transfer [5], where the texture from a source image is transferred to a target image. Since these images contain cues corresponding to different objects, it is challenging to classify them without good shape-sensitive representations. Similarly, the Stylized imagenet (SIN) is generated by replacing the texture present in an image with style from a randomly selected painting using the AdaIN style transfer method [16]. Models trained using ELEAS can better encode object shapes in images, leading to large performance improvements on these datasets over" + } + ] + } + ], + "index": 4 + }, + { + "type": "image", + "bbox": [ + 306, + 70, + 545, + 331 + ], + "blocks": [ + { + "bbox": [ + 306, + 70, + 545, + 331 + ], + "lines": [ + { + "bbox": [ + 306, + 70, + 545, + 331 + ], + "spans": [ + { + "bbox": [ + 306, + 70, + 545, + 331 + ], + "type": "image", + "image_path": "157199e1430337ca7081323849a7278d5a75a508f461bf00aa232e845563f208.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 350, + 545, + 407 + ], + "lines": [ + { + "bbox": [ + 305, + 350, + 545, + 407 + ], + "spans": [ + { + "bbox": [ + 305, + 350, + 545, + 407 + ], + "type": "text", + "content": "Figure 4. Shape vs. texture bias for the vision models: The images with conflicting shape and texture cues are used to calculate the shape bias of the trained models. The ELEAS trained models show improvement in shape-bias. We have shown results for ResNet152 and ViT-B in this figure.(Refer to Section 5.3)" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_caption" + } + ], + "index": 5 + }, + { + "bbox": [ + 305, + 426, + 545, + 462 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 426, + 545, + 462 + ], + "spans": [ + { + "bbox": [ + 305, + 426, + 545, + 462 + ], + "type": "text", + "content": "the vanilla model. The better performance of TSD is expected as these models are trained using images from similar domains, i.e., the Stylized ImageNet dataset." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 305, + 462, + 545, + 509 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 462, + 545, + 509 + ], + "spans": [ + { + "bbox": [ + 305, + 462, + 545, + 509 + ], + "type": "text", + "content": "We further evaluated robustness to distortion using the proposed benchmarks (Refer to Figure 3), which shows improved robustness to added distortions of varying degrees for ELEAS." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 517, + 456, + 530 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 517, + 456, + 530 + ], + "spans": [ + { + "bbox": [ + 306, + 517, + 456, + 530 + ], + "type": "text", + "content": "5.3. Increasing shape sensitivity" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 536, + 545, + 630 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 536, + 545, + 630 + ], + "spans": [ + { + "bbox": [ + 305, + 536, + 545, + 630 + ], + "type": "text", + "content": "We measure shape-sensitivity using the datasets and protocols described in Section 4.2; the results are in Tables 3 and 4. Models trained using ELEAS show a large " + }, + { + "bbox": [ + 305, + 536, + 545, + 630 + ], + "type": "inline_equation", + "content": "6.12\\%" + }, + { + "bbox": [ + 305, + 536, + 545, + 630 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 536, + 545, + 630 + ], + "type": "inline_equation", + "content": "4.78\\%" + }, + { + "bbox": [ + 305, + 536, + 545, + 630 + ], + "type": "text", + "content": " increase in shape-bias for ResNet152 and ViT-L models, respectively, compared to vanilla baselines and are comparable to the shape-bias of models trained using TSD. We further added class-wise shape bias comparison with human subjects in Figure 4." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 632, + 545, + 667 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 632, + 545, + 667 + ], + "spans": [ + { + "bbox": [ + 305, + 632, + 545, + 667 + ], + "type": "text", + "content": "An alternative measure, the shape factor [17], counts the number of dimensions in the image representation that encodes shape. ELEAS substantially increases the number of" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 305, + 673, + 545, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 673, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 673, + 545, + 713 + ], + "type": "text", + "content": "2Note that shape bias [7] has limitations: since it is defined in terms of a Stylized-ImageNet test set, the metric is biased towards methods that use SIN as a training augmentation. Further, it ignores images on which neither of the true shape/texture categories is predicted." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "24476" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 85, + 70, + 251, + 213 + ], + "blocks": [ + { + "bbox": [ + 85, + 70, + 251, + 213 + ], + "lines": [ + { + "bbox": [ + 85, + 70, + 251, + 213 + ], + "spans": [ + { + "bbox": [ + 85, + 70, + 251, + 213 + ], + "type": "table", + "html": "
ModelMethodBinSem
Resnet50Vanilla79.861.6
TSD [21]78.961.1
ELEAS79.261.9
Resnet101Vanilla80.463.4
TSD [21]80.064.7
ELEAS81.065.9
Resnet152Vanilla80.364.4
TSD [21]79.865.5
ELEAS81.066.6
", + "image_path": "e6c1eeabc986144a98b336e1f40a92e99011de754179b23f5022c30575ee3719.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 309, + 287, + 393 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 309, + 287, + 393 + ], + "spans": [ + { + "bbox": [ + 46, + 309, + 287, + 393 + ], + "type": "text", + "content": "shape dimensions in trained models (Table 3). We further evaluated shape decodability from learned representations by predicting the binary and semantic mask of the object in the image (Table 4). The segmentation is performed by adding a three-layer readout module on top of the learned representations. The read-out module is trained on PASCAL VOC 2012 dataset [4]." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 394, + 287, + 479 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 394, + 287, + 479 + ], + "spans": [ + { + "bbox": [ + 46, + 394, + 287, + 479 + ], + "type": "text", + "content": "Resnet(TSD) [21] shows a significant worsening of binary segmentation performance for all models and semantic segmentation performance for ResNet50, suggesting that their learned representations cannot predict pixel-wise object categories. ELEAS-trained model shows an increase in Semantic segmentation performance, indicating better decodingability of pixel-wise semantic categories of objects." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 487, + 287, + 513 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 487, + 287, + 513 + ], + "spans": [ + { + "bbox": [ + 47, + 487, + 287, + 513 + ], + "type": "text", + "content": "5.4. Instance Segmentation and Object detection performance" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 517, + 288, + 661 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 517, + 288, + 661 + ], + "spans": [ + { + "bbox": [ + 46, + 517, + 288, + 661 + ], + "type": "text", + "content": "To evaluate the effectiveness of the shape-sensitive image representations in downstream tasks such as object detection and segmentation, we trained the MaskRCNN [9] model using ResNet101 as the backbone. Results are reported in Tables 5 for models trained on the MS-COCO dataset. The model trained using ELEAS outperformed other models by a significant margin in both object detection " + }, + { + "bbox": [ + 46, + 517, + 288, + 661 + ], + "type": "inline_equation", + "content": "(\\approx 1.8\\mathrm{mAP})" + }, + { + "bbox": [ + 46, + 517, + 288, + 661 + ], + "type": "text", + "content": " and instance segmentation tasks " + }, + { + "bbox": [ + 46, + 517, + 288, + 661 + ], + "type": "inline_equation", + "content": "(\\approx 1.3\\mathrm{mAP})" + }, + { + "bbox": [ + 46, + 517, + 288, + 661 + ], + "type": "text", + "content": ", indicating that learned shape-sensitive representations can improve performance in these tasks. In contrast, TSD showed decreased performance even when compared to the Vanilla backbone." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 670, + 191, + 684 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 670, + 191, + 684 + ], + "spans": [ + { + "bbox": [ + 47, + 670, + 191, + 684 + ], + "type": "text", + "content": "5.5. Lightweightness of ELEAS" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 689, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 715 + ], + "type": "text", + "content": "Compared to previous augmentation methods, ELEAS is lightweight. Edge maps and shuffled patch images can be" + } + ] + } + ], + "index": 7 + }, + { + "type": "table", + "bbox": [ + 307, + 71, + 547, + 124 + ], + "blocks": [ + { + "bbox": [ + 46, + 221, + 287, + 289 + ], + "lines": [ + { + "bbox": [ + 46, + 221, + 287, + 289 + ], + "spans": [ + { + "bbox": [ + 46, + 221, + 287, + 289 + ], + "type": "text", + "content": "Table 4. Shape decodability of the learned representations: To evaluate the amount of shape information, read-out modules are added to the frozen learned representation and used to predict binary (Bin) and semantic (Sem) segmentation masks [17], with performance measured by mIoU. The shape decodability of the models is evaluated using the Pascal VOC dataset. (Section 5.3)" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 307, + 71, + 547, + 124 + ], + "lines": [ + { + "bbox": [ + 307, + 71, + 547, + 124 + ], + "spans": [ + { + "bbox": [ + 307, + 71, + 547, + 124 + ], + "type": "table", + "html": "
ModelObject DetectionInstance Segmentation
mAPAP@0.50AP@0.75mAPAP@0.50AP@0.75
Vanilla39.8760.2143.3336.3557.3938.79
TSD [21]37.8258.9841.2933.8755.4135.85
ELEAS41.6561.8345.4337.6358.9940.33
", + "image_path": "8a6963dfc9fc069098d9581898a2fd7532f9894ccacb01f78ea702d017c30b6f.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "table_body" + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 132, + 545, + 186 + ], + "lines": [ + { + "bbox": [ + 305, + 132, + 545, + 186 + ], + "spans": [ + { + "bbox": [ + 305, + 132, + 545, + 186 + ], + "type": "text", + "content": "Table 5. Effect of shape sensitivity on Object Detection and Segmentation performance. The shapes-sensitive ResNet101 (i.e. ELEAS) backbone leads to improvement in object detection and instance segmentation performance. The models are evaluated on the COCO-Val2017 dataset." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 304, + 210, + 545, + 258 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 210, + 545, + 258 + ], + "spans": [ + { + "bbox": [ + 304, + 210, + 545, + 258 + ], + "type": "text", + "content": "precomputed and stored on disk, and obtaining adversarial augmented images requires only a few operations. In contrast, TSD [21] runs a GAN-based stylization to generate every augmented image, which is much slower." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 259, + 545, + 354 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 259, + 545, + 354 + ], + "spans": [ + { + "bbox": [ + 304, + 259, + 545, + 354 + ], + "type": "text", + "content": "GAN-based stylized image generation takes almost twice the time (with all other factors constant - 8 A100 GPUs in our case) compared to computing all edge maps and shuffled patch images. Both ELEAS and TSD require new augmented images with different source and texture images every epoch, but GAN-based augmentation must be run every time, making it expensive. Therefore, the per epoch cost of ELEAS is negligible compared to TSD." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 356, + 545, + 392 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 356, + 545, + 392 + ], + "spans": [ + { + "bbox": [ + 304, + 356, + 545, + 392 + ], + "type": "text", + "content": "Further, once computed, the edge maps and shuffled patch images used by ELEAS can be reused to train other models, further reducing the average data generation cost." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 405, + 378, + 418 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 405, + 378, + 418 + ], + "spans": [ + { + "bbox": [ + 306, + 405, + 378, + 418 + ], + "type": "text", + "content": "6. Conclusion" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 426, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 426, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 426, + 545, + 713 + ], + "type": "text", + "content": "We propose and evaluate ELEAS - a lightweight adversarial augmentation technique for image classification in order to induce a shape bias in learned models. Previous work in this area [7,21] identified the need for such inductive biases due to the apparent dependence of deep models on textural features; however, their proposed augmentation techniques have drawbacks—first, they primarily sever the dependence on texture, while not explicitly enforcing processing and representation of shape, and second, the proposed augmentation process is very expensive. Although our work, too, proposes only data augmentation and does not come with guarantees on learned representations, the augmentations are simple to compute and are designed to encourage holistic shape representation. Extensive experimentation shows both the value of this inductive bias (shape factors correlate with model robustness and accuracy across models) and the substantial gains of our proposal, including over " + }, + { + "bbox": [ + 304, + 426, + 545, + 713 + ], + "type": "inline_equation", + "content": "5\\%" + }, + { + "bbox": [ + 304, + 426, + 545, + 713 + ], + "type": "text", + "content": " absolute accuracy improvements on ImageNet using vision transformers. An interesting direction for future work is to explore richer ways of specifying \"shape\" to the models—for instance, using off-the-shelf segmentation or depth estimation models—and also to explore other inductive biases that can profitably be incorporated into vision models." + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 758 + ], + "type": "text", + "content": "24477" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 287, + 713 + ], + "type": "list", + "angle": 0, + "index": 12, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 134 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 134 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 134 + ], + "type": "text", + "content": "[1] Nicholas Baker, Hongjing Lu, Gennady Erlikhman, and Philip J. 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Taking an image sequence (a) as input, EditableNeRF is trained fully automatically to reconstruct the captured scene (b) and can handle topological changes. After training, end-users are able to edit the scene (c) by controlling the automatically picked-out key points (circled in green in (b)). Our method enables multi-dimensional editing and can generate novel scenes that are unseen during training." + ], + "image_footnote": [], + "bbox": [ + 78, + 393, + 328, + 474 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/9caabbe6869a4ade2db67c689db708436ef64f674bccff38a0c618a3ad943175.jpg", + "image_caption": [ + "Editing by Key Points", + "Novel view (2 key points)" + ], + "image_footnote": [], + "bbox": [ + 331, + 393, + 486, + 474 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/82721d89e2fbc9c8a0aca20b18a4c331ce23465c878098bd19fe9dea9e520476.jpg", + "image_caption": [ + "(c) Editing Results", + "Playing a piece of music" + ], + "image_footnote": [], + "bbox": [ + 571, + 287, + 728, + 369 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/e54a0f5bf7aa269d65bf0ab7ec1dd3c1952088fe6a3b39791517e72b71672201.jpg", + "image_caption": [ + "Sliding on the piano keys" + ], + "image_footnote": [], + "bbox": [ + 733, + 287, + 890, + 369 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/744553ac3f971806fee6acdb1e4b59db7e817dd8bf8ae2931e503ea6b2bf0ab1.jpg", + "image_caption": [ + "Freely moving for two dice cups" + ], + "image_footnote": [], + "bbox": [ + 571, + 393, + 728, + 474 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/8e8d7a1d966ea3ca80f1827eb137ce6e735a2519cf7a9f85d778634d9ae95ed6.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 733, + 393, + 890, + 474 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 564, + 313, + 580 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Neural radiance fields (NeRF) achieve highly photorealistic novel-view synthesis, but it's a challenging problem to edit the scenes modeled by NeRF-based methods, especially for dynamic scenes. We propose editable neural radiance fields that enable end-users to easily edit dynamic scenes and even support topological changes. Input with an image sequence from a single camera, our network is trained fully automatically and models topologically varying dynamics using our picked-out surface key points. Then end-users can edit the scene by easily dragging the key points to desired new positions. To achieve this, we propose a scene analysis method to detect and initialize key points by considering the dynamics in the scene, and a weighted key points strategy to model topologically varying dynamics by joint key points and weights optimization. Our method supports intuitive multi-dimensional (up to 3D) editing and can generate novel scenes that are unseen in the input sequence. Experiments demonstrate that our method achieves high-quality editing on various dynamic scenes and outperforms the state-of-the-art. Our code and captured data are", + "bbox": [ + 73, + 598, + 473, + 902 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "available at https://chengwei-zheng.github.io/EditableNeRF/.", + "bbox": [ + 500, + 566, + 888, + 595 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 500, + 630, + 632, + 645 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Neural radiance fields (NeRF) [23] have shown great power in novel-view synthesis and enable many applications as this method achieves photo-realistic rendering [9]. Recent techniques have further improved NeRF by extending it to handle dynamic scenes [27, 30, 40] and even topologically varying scenes [28]. However, these works mainly focus on reconstruction itself but do not consider scene editing. Thus, for rendering, only the camera views can be changed, while the modeled scenes cannot be edited.", + "bbox": [ + 496, + 657, + 892, + 792 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Recently, some frameworks have been proposed to make neural radiance fields editable in different aspects. Some of them aim to edit the reconstructed appearance and enable relighting [2,35,54]; some allow controlling the shapes and colors of objects from a specific category [15, 20, 44, 47]; and some divide the scene into different parts and the location of each part can be modified [48, 49, 52]. However, the", + "bbox": [ + 496, + 795, + 893, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 810, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "8317", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "dynamics of moving objects cannot be edited by the previous methods. And this task becomes much more challenging when the dynamics contain topological changes. Topological changes can lead to motion discontinuities (e.g., between the hammer and the piano keys, between the cups and the table in Fig. 1) in 3D space and further cause noticeable artifacts if they are not modeled well. A state-of-the-art framework CoNeRF [16] tries to resolve this problem by using manual supervision. However, it only supports limited and one-dimensional editing for each scene part, requiring user annotations as supervision.", + "bbox": [ + 75, + 90, + 472, + 257 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "We propose EditableNeRF, editable topologically varying neural radiance fields that are trained without manual supervision and support intuitive multi-dimensional (up to three-dimensional) editing. The key of our method is to represent motions and topological changes by the movements of some sparse surface key points. Each key point is able to control the topologically varying dynamics of a moving part, as well as other effects like shadow and reflection changes through the neural radiance fields. This key-point-based method enables end-users to edit the scene by easily dragging the key points to their desired new positions.", + "bbox": [ + 75, + 258, + 472, + 425 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To achieve this, we first apply a scene analysis method to detect key points in the canonical space and track them in the full sequence for key point initialization. We introduce a network to estimate spatially-varying weights for all scene points and use the weighted key points to model the dynamics in the scene, including topological changes. In the training stage, our network is trained to reconstruct the scene using the supervision from the input image sequence, and the key point positions are also optimized by taking motion (optical flow) and geometry (depth maps) constraints as additional supervision. After training, the scene can be edited by controlling the key points' positions, and novel scenes that are unseen during training can also be generated.", + "bbox": [ + 75, + 425, + 472, + 621 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "The contribution of this paper lies in the following aspects:", + "bbox": [ + 76, + 623, + 470, + 654 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- Key-point-driven neural radiance fields achieving intuitive multi-dimensional editing even with topological changes, without requiring annotated training data.", + "- A weighted key points strategy modeling topologically varying dynamics by joint key points and weights optimization.", + "- A scene analysis method to detect and initialize key points by considering the dynamics in the scene." + ], + "bbox": [ + 94, + 666, + 467, + 785 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 76, + 804, + 218, + 819 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.1. Novel-View Synthesis", + "text_level": 1, + "bbox": [ + 76, + 830, + 277, + 845 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Many methods achieve rendering novel-view images by reconstructing scenes and objects into meshes [5, 6, 12, 39, 55], neural voxels [21, 33], and multi-plane images", + "bbox": [ + 76, + 854, + 470, + 902 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "[7, 24, 58]. Besides these methods based on discrete representations, some methods also achieve novel-view synthesis by using continuous representations [26, 34] and have shown great potential in this task.", + "bbox": [ + 496, + 90, + 890, + 150 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Neural radiance fields (NeRF) [23] achieve photorealistic rendering in novel-view synthesis by leveraging continuous implicit functions of density and view-dependent color to represent static scenes. To handle dynamic scenes, time-variant latent codes could be used to encode time-variant components based on NeRF, but requiring multi-view video inputs [17]. To further enable dynamic reconstructions from a single-view sequence, deformation fields implemented by MLPs are applied to warp objects in each frame into a canonical space [27, 30, 40]. Some methods also utilize estimated depth maps [45], ToF depth images [1], or optical scene flow [18] to improve the performance of dynamic neural radiance fields. HyperNeRF [28] further extends dynamic NeRF to reconstruct topologically varying scenes by modeling canonical spaces with different topology states into a unified continuous hyperspace, and the discontinuous deformations in 3D space caused by topological changes can be modeled by continuous functions in hyperspace. However, unlike traditional explicit representations such as triangular meshes, NeRF-based methods represent the scenes by implicit functions, making the modeled scenes difficult to be edited.", + "bbox": [ + 496, + 152, + 892, + 484 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.2. Editing on Neural Radiance Fields", + "text_level": 1, + "bbox": [ + 500, + 496, + 802, + 512 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "As our method focuses on NeRF editing, we mainly discuss NeRF-based methods that support user editing in this section. For editing on explicit representations or other implicit representations, please refer to [4, 32, 50, 57].", + "bbox": [ + 496, + 520, + 890, + 580 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "One approach to edit neural radiance fields is to segment the scene into different components and build MLP for each component [48, 49, 52]. Assuming that different components are individual, this representation allows control of the placements and the relative positions of these components, as well as deleting or reduplicating a component. But these methods do not support editing the dynamics inside a component and only result in limited applications.", + "bbox": [ + 496, + 582, + 892, + 702 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In addition, some methods achieve relighting and material editing on neural fields [2, 35, 54] by decomposing the scene into surface normals, lights, albedo, and material. Texture editing can also be accomplished by a 3D-to-2D texture mapping [46].", + "bbox": [ + 496, + 704, + 890, + 779 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Besides, there are also some methods that focus on modeling a specific category of objects [15, 20, 44, 47] instead of general objects. A common solution for this problem is to model the category of objects with conditional NeRF and use latent codes as conditions to encode the variations of different objects in this category. Then the shape and appearance can be edited by changing the latent codes or by fine-tuning the network [20], and even controlled by", + "bbox": [ + 496, + 780, + 892, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "8318", + "bbox": [ + 480, + 944, + 514, + 955 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/0fbcb3804d096948293b5c6f6437fee61c1346c2aeaef660118ec73096fdeef6.jpg", + "image_caption": [ + "Figure 2. EditableNeRF pipeline. The query point $x$ is first warped into the canonical space by a warp field and a latent code $\\beta_{t}$ in frame $t$ . Next, we compute the key point weights of this canonical point $x'$ and use it to calculate a linear combination of all key point positions $k_{t}$ , called weighted key points. After that, we feed the following NeRF MLP with the weighted key points and $x'$ , then the output density and color are used for volumetric rendering. In the training stage, optical flow and depth maps are used to supervise key point positions." + ], + "image_footnote": [], + "bbox": [ + 81, + 71, + 883, + 343 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "text [41] with the help of a multi-modal model. And many methods also focus on modeling editable human bodies or human faces based on NeRF representation. By using human body parametric models and skinning techniques such as SMPL [22], neural radiance fields have been extended to model the human body and can be animated by controlling skeleton poses [3, 19, 25, 29, 36]. Human face parametric models also contribute to extending NeRF for human face modeling and controlling [8, 10, 14, 37, 42, 56], and even driven by audio [13]. However, general objects cannot be handled by these methods.", + "bbox": [ + 75, + 430, + 470, + 595 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Recently, NeRF-editing [51] proposes to deform NeRF on static objects by extracting explicit meshes, deforming the meshes, and transferring the deformations back into the implicit representations. However, this method cannot handle dynamic scenes. CoNeRF [16] proposes an attribute re-rendering method based on dynamic NeRF. This method requires users to provide annotations in several frames, including masks for every dynamic part and their corresponding attribute values, for network training. Then these parts could be edited by controlling the one-dimensional attribute values. We will show our advantages against CoNeRF in Sec. 4.2.", + "bbox": [ + 75, + 598, + 468, + 779 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. EditableNeRF", + "text_level": 1, + "bbox": [ + 76, + 797, + 220, + 813 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Input with color image sequence, our method can reconstruct the captured scene fully automatically based on neural radiance fields, and the topologically varying dynamics are modeled using surface key points. After reconstruction, end-users can edit the scene by controlling the key points.", + "bbox": [ + 75, + 825, + 468, + 902 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Our pipeline is shown in Fig. 2. First, We use two methods, HyperNeRF [28] and RAFT [38], to derive the depth maps of input frames and optical flow between adjacent input images, respectively. Then we apply a scene analysis method to detect and initialize key points for each frame (Sec. 3.3). After that, our NeRF-based network (Sec. 3.1) can be trained fully automatically (Sec. 3.2) to model the captured scene based on our weighted key points strategy. When the reconstruction is finished, the reconstructed scene can be edited by dragging the key points to desired positions (Sec. 3.4).", + "bbox": [ + 496, + 430, + 890, + 597 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Network", + "text_level": 1, + "bbox": [ + 500, + 607, + 602, + 622 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We first introduce our network architecture, which is shown in Fig. 2. Our network represents the scene as a field of density and radiance [23]. Given a query point, similarly to other dynamic NeRF methods [27,28], we first use a warp field to model slight movements:", + "bbox": [ + 496, + 631, + 890, + 705 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nx ^ {\\prime} = T (x, \\beta_ {t}). \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 643, + 719, + 890, + 736 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Here the warp filed $T$ maps a query 3D point $x$ to its canonical location $x'$ , and $\\beta_{t}$ is the warp latent code in frame $t$ . This warp field ensures that the scene in different frames is aligned despite some errors in input camera parameters, by using slight movements. While as discussed in [28], it's hard for this continuous warp field to model discontinuous movements caused by topological changes.", + "bbox": [ + 496, + 750, + 890, + 854 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Then we need to model different topology and motion states in the canonical space. We find that motions and topological changes are always related to some movements", + "bbox": [ + 496, + 854, + 890, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "8319", + "bbox": [ + 480, + 944, + 514, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/0d13091c8dada144e1a06bec9c96a1014f63ad95f503079e3644743d43f28df5.jpg", + "image_caption": [ + "(a)" + ], + "image_footnote": [], + "bbox": [ + 78, + 88, + 207, + 154 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/fc6baad63057c4bde083c3688c40c4f18e066486e19348f3472f3b062105af07.jpg", + "image_caption": [ + "(b)" + ], + "image_footnote": [], + "bbox": [ + 210, + 88, + 338, + 154 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/f5204edd2630f4cc3f1ff1f9b435b378528fb851ccec093a1811584a27b3e001.jpg", + "image_caption": [ + "(c)", + "Figure 3. Examples of key points and key point weights. (a) shows an input frame and its corresponding key points (circled in green). (b) and (c) demonstrate the weights of the two key points, respectively. These weights are obtained by using the surface points corresponding to the pixels as query points." + ], + "image_footnote": [], + "bbox": [ + 339, + 88, + 468, + 155 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "of surface points, so we achieve this modeling by making use of sparse surface key points. These 3D key points are attached to the objects' surfaces and also move with the objects. Each key point is able to control the topologically varying dynamics of a moving part and also some effects like shadow and reflection changes. An example of key points is shown in (a) of Fig. 3. For each moving part in the scene, we automatically select one corresponding key point, which will be detailed in Sec. 3.3, and the number of key points is denoted as $N$ . The key points' positions in each input frame will be optimized automatically in our training stage to achieve this modeling.", + "bbox": [ + 75, + 277, + 468, + 459 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We assume that different locations in the canonical space are affected by different key points. So for a query point $x'$ , an MLP followed by softmax is used to decide which key point should control its dynamics. We call this network weight estimating network, which takes canonical coordinate $x'$ as input and outputs a weight vector $w \\in \\mathbb{R}^N$ , indicating how each key point affects the query point $x'$ .", + "bbox": [ + 75, + 460, + 468, + 566 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nw = W \\left(x ^ {\\prime}\\right). \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 228, + 578, + 468, + 595 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "An example of these spatially-varying key point weights is shown in (b) and (c) of Fig. 3.", + "bbox": [ + 76, + 608, + 468, + 638 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We then construct a weighted key points vector $p$ by taking a linear combination of all key point positions $k$ to model the topologically varying dynamics at $x'$ .", + "bbox": [ + 76, + 638, + 468, + 684 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\np _ {t} \\left(x ^ {\\prime}\\right) = \\sum_ {i = 1} ^ {N} w ^ {i} \\left(x ^ {\\prime}\\right) \\cdot k _ {t} ^ {i}. \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 187, + 696, + 468, + 736 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The superscript $i$ is the index of key points, and the subscript $t$ is the frame index. If there is only one object that moves and causes topological changes, our method will model this scene with only one key point $(N = 1)$ , and (3) becomes $p_t(x') = k_t$ because the softmax always outputs a scalar 1. So we directly set $p_t(x')$ to be $k_t$ in this situation.", + "bbox": [ + 76, + 750, + 468, + 839 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Next, the 3D canonical coordinate $x'$ and the weighted key points $p$ are concatenated to construct a coordinate in hyperspace for topologically varying scene modeling. This hyperspace is proposed in HyperNeRF [28]. In addition", + "bbox": [ + 75, + 839, + 468, + 901 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "to 3D space, HyperNeRF makes use of ambient dimensions to model objects in hyperspace, and different topology states are encoded with different ambient coordinates. Discontinuous deformations caused by topological changes in 3D space can be modeled by continuous functions (such as MLP) in hyperspace, and more details can be found in [28]. Here we use the weighted key points $p$ as ambient coordinates, modeling topologically varying dynamics.", + "bbox": [ + 496, + 90, + 890, + 210 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Finally, the following NeRF MLP is fed with this 6D coordinate in hyperspace:", + "bbox": [ + 496, + 210, + 890, + 242 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n(c, \\sigma) = H \\left(x ^ {\\prime} \\oplus p _ {t} \\left(x ^ {\\prime}\\right), d, \\alpha_ {t}\\right). \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 589, + 248, + 890, + 265 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Here $d$ is the view direction, and $\\alpha_{t}$ is the appearance latent code as in [28]. This NeRF MLP outputs the color $c$ and the density $\\sigma$ that can be used in volumetric rendering. To render an image, we should trace the camera rays of all pixels, sample points along these rays, obtain their colors and densities, and run the volumetric rendering, which are the same as in the original NeRF [23].", + "bbox": [ + 496, + 271, + 890, + 377 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. Loss Functions and Training", + "text_level": 1, + "bbox": [ + 498, + 383, + 756, + 400 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "All the latent codes and MLP parameters are optimized in the training stage to model the scene. As we use key points to encode topologically varying dynamics, we need to additionally optimize key point positions in each input frame. To keep our key points on the object surfaces and to be time-consistent, novel losses are added in our training stage.", + "bbox": [ + 496, + 407, + 890, + 513 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "First, we propose a motion loss, which constrains that the key point positions in two adjacent frames should be consistent with the optical flow from pre-trained RAFT [38].", + "bbox": [ + 496, + 513, + 890, + 559 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nL _ {\\text {m o t i o n}} (t, i) = \\left\\| \\Pi_ {t + 1} \\left(k _ {t + 1} ^ {i}\\right) - \\Pi_ {t} \\left(k _ {t} ^ {i}\\right) - F _ {t} ^ {t + 1} \\left(\\Pi_ {t} \\left(k _ {t} ^ {i}\\right)\\right) \\right\\| ^ {2}, \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 503, + 565, + 890, + 598 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\Pi_t$ is the projection function using the camera pose of frame $t$ , and $F_t^{t+1}$ is the optical flow from frame $t$ to frame $t+1$ . This loss ensures that the 2D key point positions in different frames correspond to the same surface point.", + "bbox": [ + 496, + 599, + 890, + 659 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The motion loss provides good supervision in 2D image space, while the key points are in the 3D space. Thus, a geometry loss can help to keep the key points on the object surfaces.", + "bbox": [ + 496, + 659, + 890, + 718 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nL _ {g e o} (t, i) = \\left\\| \\Phi_ {t} \\left(k _ {t} ^ {i}\\right) - D _ {t} \\left(\\Pi_ {t} \\left(k _ {t} ^ {i}\\right)\\right) \\right\\| ^ {2}. \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 563, + 723, + 890, + 744 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Here the function $\\Phi_t(k_t^i)$ calculates the distance from the key point $k_{t}^{i}$ to the camera position in frame $t$ , and $D_{t}$ denotes the depth map rendered from HyperNeRF [28] in the original camera view. This HyperNeRF is pre-trained before our training stage and takes the same input as ours.", + "bbox": [ + 496, + 750, + 890, + 824 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Besides, we also apply a reconstruction loss between the rendered RGB images $C$ and the input images $\\widetilde{C}$ , as well as a warp regularization loss.", + "bbox": [ + 496, + 825, + 890, + 869 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nL _ {r e c} (t) = \\left\\| C _ {t} \\left(k _ {t}, \\alpha_ {t}, \\beta_ {t}\\right) - \\widetilde {C} _ {t} \\right\\| ^ {2}, \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 576, + 876, + 890, + 904 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "8320", + "bbox": [ + 480, + 944, + 514, + 955 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/b8d373e7e770c410c39f0efd993e94b22cb0b1ff408f5d9cbb095cd5abf08dbc.jpg", + "image_caption": [ + "Figure 4. A 2D visualization of our key point detection method. For each point $x$ , we compute the variance of its ambient coordinates $a$ in the full sequence. Then the points with local maximum variances after a 2D Gaussian filter will be selected as our reference key points." + ], + "image_footnote": [], + "bbox": [ + 78, + 80, + 472, + 204 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nL _ {r e g} (t) = \\frac {1}{\\| S _ {t} \\|} \\sum_ {x \\in S _ {t}} \\| x - T (x, \\beta_ {t}) \\| ^ {2}, \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 140, + 301, + 468, + 340 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $S_{t}$ is the set of surface points in frame $t$ . This warp regularization loss makes sure that the warp field only models slight movements to compensate for the errors in the input camera parameters and distortions in the input images. Thus, it can avoid the ambiguity between the warp field and our weighted key points model.", + "bbox": [ + 75, + 348, + 468, + 439 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.3. Key Point Detection and Initialization", + "text_level": 1, + "bbox": [ + 76, + 450, + 403, + 467 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "To initialize the network training, we need to determine the key point number $N$ and obtain the initial 3D locations of key points. To achieve this, we apply a scene analysis method, which first finds reference key points in canonical space and reference frames where these reference key points are on the object surfaces, then initializes key points' positions in each frame.", + "bbox": [ + 75, + 474, + 468, + 580 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "As our key points are used to model topologically varying dynamics, we find the 3D points in the canonical space with dramatic dynamics including topological changes as our reference key points. Recall that HyperNeRF [28] uses different ambient coordinates $a$ to encode different topology and motion states at a position. And we have already trained a HyperNeRF for depth maps in (6). So we can detect key points by making use of the ambient dimensions $a$ from this pre-trained HyperNeRF. For a point $x$ , great varying of its $a$ in different frames indicates great dynamics at $x$ , so we use all the positions with locally greatest variations of ambient coordinates as our reference key points.", + "bbox": [ + 75, + 582, + 468, + 763 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "To be specific, for each input frame, we trace the original camera rays of all pixels and find the corresponding surface points. A 3D voxel volume in the canonical space is then built to record the ambient coordinates of these surface points. After traversing the whole input sequence, we compute the variance of ambient coordinates for every voxel, followed by a 3D Gaussian filter. And the center points of the voxels with local maximum variances after Gaussian blur will be selected as the reference key points $k_{ref}$ . As", + "bbox": [ + 75, + 763, + 470, + 902 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/54f8e0de88053fd3d01380f6647d12911ebf5985e2f3ab15563ac6ab8fc3b0a7.jpg", + "image_caption": [ + "Figure 5. Propagating the reference key point in the reference frame to other frames for initialization. Skipping propagation is only used for some long input sequences." + ], + "image_footnote": [], + "bbox": [ + 511, + 83, + 880, + 186 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "our 3D version is difficult to visualize, we show a 2D version of this process in Fig. 4 by rendering all frames in a fixed camera view and computing the variance for each pixel, followed by a 2D Gaussian filter.", + "bbox": [ + 496, + 255, + 890, + 316 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Then for each reference key point, we need to select a reference frame in which the reference key point is on the object surface. We use a similar formulation with the geometry loss in (6) to decide this. (Here we omit the index of key points as they are handled individually.)", + "bbox": [ + 496, + 316, + 890, + 392 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\left\\| \\Phi_ {t} \\left(k _ {r e f}\\right) - D _ {t} \\left(\\Pi_ {t} \\left(k _ {r e f}\\right)\\right) \\right\\| ^ {2} < \\delta , \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 578, + 400, + 890, + 419 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\delta$ is a pre-defined threshold. The first frame $t$ that satisfies (9) will be selected as the reference frame $t_{ref}$ .", + "bbox": [ + 496, + 428, + 890, + 458 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Now for each key point, we have a reference key point position and a corresponding reference frame. To initialize key point positions in the whole sequence, we propagate this reference key point to other frames by optical flow from pre-trained RAFT [38]. The reference key point is first projected into the input image of the reference frame to get its 2D position, and the 2D position is propagated frame by frame using optical flow as shown in Fig. 5. Then these 2D positions are projected back into 3D space by depth maps from HyperNeRF. Note that there are accumulative errors in this initialization due to frame-by-frame propagation, while these errors will be eliminated in our training stage.", + "bbox": [ + 496, + 458, + 892, + 638 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "For some very long input sequences, we found that the initialization method above may not perform well. This is because the accumulative errors may become too large, and the key points in the image space may be propagated into other objects (e.g., background). So we propose a skipping propagation method as shown in Fig. 5. For each key point, we additionally propagate the reference key point in the reference frame every $M$ frames (i.e., $t_{ref}$ to $t_{ref} + M$ , $t_{ref}$ to $t_{ref} + 2M$ , and so on), and replace the frame-by-frame positions if their confidence are greater than a threshold. This confidence is calculated by the consistency between the forward optical flow and the backward optical flow:", + "bbox": [ + 496, + 640, + 893, + 821 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nC o n f (t) = \\left\\| F _ {t} ^ {t _ {r e f}} \\left(F _ {t _ {r e f}} ^ {t} \\left(\\widehat {k} _ {r e f}\\right)\\right) - \\widehat {k} _ {r e f} \\right\\| ^ {- 1}, \\tag {10}\n$$\n", + "text_format": "latex", + "bbox": [ + 527, + 830, + 890, + 859 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $t = t_{ref} + iM$ , $i \\in \\mathbb{Z}$ , and the hat of $\\widehat{k}_{ref}$ indicates that it is a 2D position in the reference frame.", + "bbox": [ + 496, + 868, + 890, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "8321", + "bbox": [ + 480, + 944, + 513, + 955 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/fba6fbb97b40ddce58b3912e8d0dc54f4779dd59f977d37694315350c02f7992.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 81, + 80, + 212, + 146 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/1e7e7e63ca4e7e764ca465382812eec6cae872102b1115d3bbf8500c3fefcc91.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 215, + 80, + 346, + 146 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/553b16ec89092ac373182297da050ab3172b643b7b4b582fc79e75014de88f33.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 346, + 80, + 478, + 146 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/ab9bbd7d300151772c4240a29f0cb90cb081b24fcb8b1b838060d8be77ebcdf6.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 81, + 154, + 212, + 223 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/af51d24e43cff56d970057c2c1d0c799fd7b1ba30d4d19a4d0b7f3dcb60c6144.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 215, + 154, + 346, + 223 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/146aee400fcf3c01804b6445ae67c1b6ee1db932e5ee91549b35b1455b69d46a.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 346, + 154, + 478, + 223 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/882129139b6476e978b92e0653c2952e9fad0ef43c6408cc8f866d1133bc5afb.jpg", + "image_caption": [ + "Figure 6. Our editing results on various scenes. The first image of each scene also shows the key points (circled in red or green). The car transformer sequence on the right side is provided by CoNeRF [16]. The last row on the right side is from a synthetic sequence." + ], + "image_footnote": [], + "bbox": [ + 81, + 229, + 212, + 299 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/e250b184b060a3fcd49e6df634c3eb1ca4005c49590a7d3cfad0da580ac5d4d5.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 215, + 229, + 346, + 299 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/0494f95ab79dd755d2e5750322c20c527475cd02f867966e7f4c6c86d306f15e.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 346, + 229, + 478, + 299 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/0576e082343392d027f856082e957aba0dc563cc4b0a09bc310e67cd13994c4d.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 491, + 80, + 622, + 148 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/1d1eb32f4c9d3dedb7ee09642d1f6a324d434ac6688d753b08dd01367b549b43.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 625, + 80, + 756, + 148 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/01def44dbc4256d2f45cde36cd405e56ab23178915d98c366bc12d2408c35d7d.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 756, + 80, + 888, + 148 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/588b218b0c3af7d5e308a08e884b039f2a958238282f664f8100b4a6952b9f82.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 491, + 155, + 622, + 223 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/a95c7ef52a1d5c3f8f6b17cd79f42d78512f5ea2799f2c61ba069734dca1f86d.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 625, + 155, + 754, + 223 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/7695cbc09b4eea706c286c4c76411b7f398f05f43a16145711c046619a504979.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 756, + 155, + 888, + 223 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/a023505157b2cc1a45ab04dd6adce991770e5ab6efd5e9c5b3b8a2b1ff1e6abe.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 491, + 229, + 622, + 297 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/0ee35c4e1e7c5c88d0f5c7ecc3ddfdf8ff748c2f95e5be62d4dafeccdce5cbd9.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 625, + 229, + 754, + 297 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/80f884738bab625ed99c5aa8d98d4ed368b94b0b4acbb47fbb90da91be9e1095.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 756, + 229, + 888, + 297 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "3.4. Editing by Key Points", + "text_level": 1, + "bbox": [ + 76, + 352, + 281, + 368 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "After training, users can easily edit the modeled scenes by feeding the network with desired key point positions. As the key points are in the 3D space, our method supports up to three-dimensional editing for each part. We also provide a graphical user interface (GUI) in Sec. 4.4.", + "bbox": [ + 75, + 376, + 468, + 452 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 76, + 468, + 209, + 486 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We show some results after editing in Fig. 6. Some effects, like shadow and reflection changes, can also be edited correctly. And please refer to our accompanying video and supplementary materials for more results and experiments.", + "bbox": [ + 75, + 494, + 468, + 556 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.1. Implementation Details", + "text_level": 1, + "bbox": [ + 76, + 566, + 294, + 583 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We set the weight of motion loss to $10^{-4}$ , the weight of geometry loss to 0.5, and the weight of warp regularization loss to 0.1. The real data is captured in a resolution of $1280 \\times 720$ and down-sampled to $320 \\times 180$ for network training. Our network is trained on 4 NVIDIA GeForce RTX 3090 graphics cards, and takes around 5 hours for training with 250k iterations. Our code is based on HyperNeRF [28]. And the camera poses of input frames are solved by COLMAP [31]. More details and discussions of our method are provided in our supplementary materials.", + "bbox": [ + 75, + 590, + 470, + 743 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.2. Comparisons", + "text_level": 1, + "bbox": [ + 76, + 755, + 215, + 771 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Here we compare our method with state-of-the-art methods HyperNeRF [28] and CoNeRF [16]. HyperNeRF is capable of topologically varying scene reconstruction but does not enable scene editing. CoNeRF allows topologically varying editing but only supports one-dimensional editing for each dynamic part, and user annotations, including masks for every part and their attribute values, are necessary for its pipeline. For example, to train a CoNeRF", + "bbox": [ + 75, + 779, + 468, + 902 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "network on an opening mouth sequence, users have to select some input frames, mask the mouth regions in these frames, and set the corresponding attribute values to 1 when the mouth is open and $-1$ when the mouth is closed.", + "bbox": [ + 496, + 353, + 890, + 412 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Qualitative results. As our method focuses on editing, we first evaluate the editing ability of our method. We compare our method with CoNeRF, while HyperNeRF does not support editing.", + "bbox": [ + 496, + 414, + 890, + 474 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We show some editing results of ours and CoNeRF in Fig. 7. Firstly, as shown in the (a) results, our method based on 3D key points enables up to three-dimensional editing, while CoNeRF fails to encode multi-dimensional dynamics by using one-dimensional attribute values. Secondly, our training stage is fully automatic without user annotations. Especially when different parts are close to each other, it becomes quite difficult for end-users to provide very accurate masks at the boundaries, which further leads to artifacts in CoNeRF as shown in (c) of Fig. 7. In contrast, ours can distinguish different parts automatically. Besides, our editing method allows users to drag the key points to their desired positions, which is more intuitive than inputting attribute values as in CoNeRF.", + "bbox": [ + 496, + 476, + 892, + 686 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Quantitative results on synthetic data. Here we compare our method with HyperNeRF and CoNeRF on synthetic data. We use three data sequences synthesized by Kubric [11], and each contains 400 frames for training. Some results on one of these sequences are shown in Fig. 6. For CoNeRF training, we annotate $5\\%$ frames in the training set using ground truth masks and ground truth attribute values, which are the same as the experiment settings in CoNeRF paper [16]. While for our method, we still use the optical flow from RAFT and depth maps from HyperNeRF. We do not use ground truth optical flow or ground truth depth maps, keeping these settings the same as for real data. Both compared methods are implemented by the original authors and are trained with the same batch size and", + "bbox": [ + 496, + 689, + 893, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "8322", + "bbox": [ + 480, + 944, + 514, + 955 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/75397d95a2cd4c76370f4d3e76de992f43ef652f34790c9de01caad52df58efa.jpg", + "image_caption": [ + "(a)" + ], + "image_footnote": [], + "bbox": [ + 76, + 84, + 194, + 154 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/6f48bae6015e71543c675ea4778306fe5228ef4d9b23ff190b85bc9a05ac6897.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 194, + 84, + 310, + 154 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/8dafaddcca698f27cf7d38e289e27293b7477480ef390748a6b98d792a58c635.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 78, + 155, + 194, + 224 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/e66cba270694d9a34a51bb7352278b981e2ae9d2311c5dd08f6ca627453b7a56.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 194, + 155, + 310, + 224 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/8fb6d98214cd3416e4fe5fa592f4ba8a54b70c7c787bcf9441320480bfb252d9.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 78, + 226, + 192, + 308 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/ee834b1b73f2b127ea35a21250f593d410a527e5a82f82efd93a133c68f751aa.jpg", + "image_caption": [ + "Figure 7. Qualitative comparisons with CoNeRF [16]. Our method does not require user annotations for training and supports multidimensional editing. Note that the rotations in (b) also cannot be represented by the one-dimensional attribute values in CoNeRF." + ], + "image_footnote": [], + "bbox": [ + 194, + 226, + 310, + 309 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/a6e959666fb26d13a6ed23ccd348afa8cb2a82d257bc13b1245de25b21c09c94.jpg", + "image_caption": [ + "(b)" + ], + "image_footnote": [], + "bbox": [ + 326, + 83, + 439, + 154 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/e1d0f9d1e3be1e700affac32bf5517a6cc89c4f032ee22a7c37b02979d1706a0.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 326, + 154, + 439, + 224 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/4a4ac7da46535237f080e87e78867c0d8c9b37483c69b6185604e97b2e5f090e.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 326, + 226, + 439, + 308 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/857f9d0251912feba980bd239602b4a270cb665dfae038983f7ffed72411e57e.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 442, + 83, + 558, + 152 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/a30b6e352aa5ec093bf9afcce5b9da2d839b3b58a8e7a3db4b0b4969ecaab208.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 442, + 154, + 557, + 224 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/9a209c84ddcb2bb2828a64b06470373403a8596c91042d2aca59276d47efdd38.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 442, + 226, + 558, + 308 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/60231bdbee4727a829deeabfeb34a70f85fd63c97a9c026a9057bd49c1de98f0.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 573, + 83, + 686, + 154 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/3ceb39c16922937cf154ffaf6ee7684283a6f486e4b0e2fabc381424f9bd9013.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 573, + 154, + 686, + 224 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/1305dc93c18f8ed34a952dee238989a00559b51fe5e43d7292d9981581350d06.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 573, + 226, + 686, + 308 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/8911f79e7a0737fca7506e1d0a959c72e3aa4ae38e1bc5439a31384d19540168.jpg", + "image_caption": [ + "(c)" + ], + "image_footnote": [], + "bbox": [ + 674, + 83, + 730, + 154 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/1415bef1f8d2699d4348cbbf310fe57d14b3415cfe22d30a9f8c0e21d78f4a72.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 674, + 154, + 730, + 226 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/f7e49c2593c93bbb1bd42d1f15cffe3bc3c008969e02a39707be7238d3fc27ac.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 674, + 226, + 730, + 299 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/1ccc9cf76a9b21e4fc89549acacb760497c32b0a07a99a4a0c1cc974debc8c78.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 732, + 83, + 890, + 154 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/e61fbeca508cb5a0a9d6b2e61547472918f30d895ad3310a54b4779d5d052bb0.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 732, + 154, + 890, + 226 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/6c9a27e98e3a52ae4d73c10c23e27898d489a8221b41ccad5a381eb92e4775b8.jpg", + "image_caption": [ + "CoNeRF" + ], + "image_footnote": [], + "bbox": [ + 732, + 226, + 890, + 299 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/c34da815d1a90fb9ba5c00d3860005926cd4fa580cc08ae778d19dea0f29d603.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodReconstructionEditing
PSNR ↑MS-SSIM ↑LPIPS ↓PSNR ↑MS-SSIM ↑LPIPS ↓
HyperNeRF [28]42.670.99640.0823---
CoNeRF [16]40.400.98910.094739.790.98860.0949
Ours44.350.99730.080840.010.99560.0822
", + "bbox": [ + 102, + 354, + 867, + 441 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "iteration step as ours.", + "bbox": [ + 76, + 508, + 220, + 522 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "First, we compare the reconstruction qualities of these methods by rendering the same synthetic scenes in novel viewpoints and evaluating the novel-view synthesis abilities. As shown in Table 1, our method reaches the best performance. Note that our method even slightly outperforms HyperNeRF on this task. This is because, in our method, the frames with similar motions are initialized with similar key point positions, while HyperNeRF uses random initialization. Thus, it is easier for our network to integrate the information from the frames with similar motions but in different viewpoints. An experiment on this is further provided in our supplementary materials.", + "bbox": [ + 75, + 523, + 468, + 703 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Next, we compare the editing qualities of our method and CoNeRF, while HyperNeRF cannot be used for editing. We derive ground truth key point positions and attribute values from ground truth motions, then use them to edit the scenes in our method and CoNeRF, respectively. Errors are computed between the ground truth images and the rendered images after editing. Our method also outperforms CoNeRF as shown in Table 1.", + "bbox": [ + 75, + 704, + 468, + 823 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Quantitative results on real data. As it is difficult to obtain novel-view ground truth for real data sequences, we turn to compare the interpolation qualities on real data. For a real data sequence with $2N$ frames, we pick out $N$ frames with even indices as the training set, and the other $N$ frames", + "bbox": [ + 75, + 825, + 468, + 900 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/ea987e06de9fa50f43c8d98353d5c97365db46642fc5fcaa66244bedeb6d5e75.jpg", + "table_caption": [ + "Table 1. Quantitative comparisons of reconstruction and editing qualities on synthetic data. The reconstruction qualities are measured by the errors in novel-view synthesis. We report PSNR, MS-SSIM [43], and LPIPS [53]. Our method performs the best." + ], + "table_footnote": [], + "table_body": "
MethodPSNR ↑MS-SSIM ↑LPIPS ↓
HyperNeRF [28]30.560.98640.1281
CoNeRF [16]30.650.98690.1307
Ours30.670.98690.1314
", + "bbox": [ + 506, + 505, + 887, + 575 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 2. Quantitative comparisons of interpolation qualities on real data.", + "bbox": [ + 498, + 585, + 890, + 613 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "with odd indices are used as ground truth for testing. Table 2 demonstrates that all the compared methods get similar quantitative results on this task. Key point positions for our method, attribute values for CoNeRF, and all the latent codes are interpolated in this task. In CoNeRF training, we select $1\\%$ frames with extreme attribute values for annotations, as recommended by CoNeRF [16].", + "bbox": [ + 496, + 641, + 890, + 746 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Besides, when rendering the same real scene with two dynamic parts in the same resolution, CoNeRF takes 1.77s, HyperNeRF takes 0.95s, while ours takes 0.90s. And CoNeRF needs to add a new MLP for each dynamic part, which makes its network not as compact as the other methods.", + "bbox": [ + 496, + 747, + 890, + 821 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.3. Ablation Studies", + "text_level": 1, + "bbox": [ + 500, + 832, + 663, + 845 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Our method makes use of 3D key points with the help of 2D optical flow and 1D depth maps. They are first utilized to initialize key point positions, then to formulate the mo", + "bbox": [ + 498, + 854, + 892, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "8323", + "bbox": [ + 480, + 944, + 514, + 955 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/d4460df6614fd1a7524feb83b9bae95e97c86d574111f1f16e62a3ad6a50b19b.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodPSNR ↑MS-SSIM ↑LPIPS ↓
Base (w/o supervision)24.600.85400.1680
+ Lmotion29.790.94290.1150
+ Lmotion + Lgeo32.590.96700.1013
+ Lmotion + Lgeo + init40.010.99560.0822
", + "bbox": [ + 83, + 75, + 464, + 154 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 3. Ablation studies. We evaluate the motion loss, the geometry loss, and the initialization stage. Our final method in the last row performs the best.", + "bbox": [ + 76, + 166, + 468, + 207 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/6c5787515f91a2a6123abc2e3dd0f5167590a0b6b718eac0847d8ba0a5be05b2.jpg", + "image_caption": [ + "Figure 8. Graphical user interface. The left widget shows the rendered image and the corresponding draggable key points. The right widget allows the user to change the viewpoint. Our GUI also supports drawing a trail of key points, then rendering a video." + ], + "image_footnote": [], + "bbox": [ + 81, + 224, + 467, + 358 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "tion loss and the geometry loss. We evaluate the two losses and the initialization stage in Table 3 by measuring the editing qualities on synthetic data. The base method does not use any information from optical flow or depth maps, and its modeled scene changes randomly according to key point movements, while our final method in the last row of Table 3 reaches the best performance.", + "bbox": [ + 75, + 453, + 468, + 559 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.4. Applications", + "text_level": 1, + "bbox": [ + 76, + 571, + 210, + 588 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Graphical user interface. We implement a graphical user interface (GUI) for editing and novel-view synthesis, which is shown in Fig. 8 and in our accompanying video. Note that end-users actually drag the key points in the 2D interface, so we provide 1D default depth values for key points to form 3D positions, and we also allow end-users to further edit these depth values. The default depth value for a pixel position is obtained by finding $K$ closest key point positions in the input sequence after projecting into the current view and computing their average depth.", + "bbox": [ + 75, + 595, + 468, + 747 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Novel scenes generation. Novel scenes that are unseen in the training sequence can also be generated by our method. For example, in the piano toy sequence of Fig. 1, the input data only contains knocking on each piano key, while our method can generate sliding on the piano keys by interpolation. And our method can also combine various dynamics of different parts to create novel scenes, such as the dice cups sequence results shown in Fig. 1.", + "bbox": [ + 75, + 750, + 468, + 869 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Motion transfer. Once reconstructed, our modeled scenes can be driven by motions from other sequences. We", + "bbox": [ + 76, + 869, + 468, + 900 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/bb81f57567b4c9bc947846a05484a1e64097bc195ad6527161c8787b94d74f78.jpg", + "image_caption": [ + "Figure 9. Editing results on a challenging scene where the selected key point is not always visible in the full sequence." + ], + "image_footnote": [], + "bbox": [ + 503, + 75, + 630, + 138 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/2d3b34b49585f21ff9a9a70668a1e21aa31d980031f5442321a8ecdc3613feb0.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 632, + 75, + 759, + 138 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/6b2f9dc01d5b24951eedbe1a6c42c3a3451da2f57b441b15137fc4510b8d885d.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 761, + 75, + 890, + 138 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "show a phonograph toy driven by a disk in our accompanying video. Optical flow is used to track a manually selected point on the source video and an affine transformation then maps the tracked point into our key point space.", + "bbox": [ + 498, + 205, + 890, + 266 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.5. Discussions", + "text_level": 1, + "bbox": [ + 500, + 273, + 624, + 287 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We build our framework based on surface key points. While in some challenging sequences, there may not exist a proper surface point that is visible in all frames to become a key point. Our method can still get plausible results on these sequences, but the consistency of key points is not as good as in other scenes, as shown in Fig. 9.", + "bbox": [ + 498, + 297, + 890, + 387 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Limitations. We assume that the dynamics of a canonical location mainly depend on one key point. If the scene becomes very complex that does not satisfy this assumption (e.g., a dancing human), our method may fail. Also, it's hard for our method to pick out surface key points for semitransparent objects like smoke. Extrapolation cannot be performed well for our method when the key points are dragged too far away from their positions in the training sequence. Our method supports multi-dimensional editing, but if the captured objects only have one-dimensional dynamics (e.g., drawer only moves in 1D), our method can only generate one-dimensional dynamics. Besides, our method cannot work well when RAFT or HyperNeRF fails.", + "bbox": [ + 496, + 388, + 892, + 584 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusions", + "text_level": 1, + "bbox": [ + 500, + 597, + 625, + 612 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We propose EditableNeRF, editable topologically varying neural radiance fields that enable end-users to easily edit dynamic scenes. The key to achieving this is to build our framework by leveraging weighted key points to model topologically varying dynamics, which further achieves intuitive multi-dimensional editing. And a scene analysis method that can measure the dynamics in the scene is also proposed to detect and further initialize these key points. Our method is trained fully automatically using a single-view input sequence and can be easily used by end-users, bringing new applications for editable photo-realistic novel-view synthesis.", + "bbox": [ + 496, + 622, + 890, + 801 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgements. This work was supported by the National Key R&D Program of China (2018YFA0704000), Beijing Natural Science Foundation (M22024), the NSFC (No.62021002), and the Key Research and Development Project of Tibet Autonomous Region (XZ202101ZY0019G). This work was also supported by THUIBCS, Tsinghua University, and BLBCI, Beijing Municipal Education Commission. 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ACM Transactions on Graphics (TOG), 37(4):1-12, 2018. 2" + ], + "bbox": [ + 78, + 90, + 470, + 796 + ], + "page_idx": 10 + }, + { + "type": "page_number", + "text": "8327", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 10 + } +] \ No newline at end of file diff --git a/2023/EditableNeRF_ Editing Topologically Varying Neural Radiance Fields by Key Points/891f5efd-20c5-4d2e-bc9c-a2da74e10197_model.json b/2023/EditableNeRF_ Editing Topologically Varying Neural Radiance Fields by Key Points/891f5efd-20c5-4d2e-bc9c-a2da74e10197_model.json new file mode 100644 index 0000000000000000000000000000000000000000..84bf76baebb2807885444d40e338a0c2e3124189 --- /dev/null +++ b/2023/EditableNeRF_ Editing Topologically Varying Neural Radiance Fields by Key Points/891f5efd-20c5-4d2e-bc9c-a2da74e10197_model.json @@ -0,0 +1,3071 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.044 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.001, + 0.812, + 0.047 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.135, + 0.13, + 0.838, + 0.177 + ], + "angle": 0, + "content": "EditableNeRF: Editing Topologically Varying Neural Radiance Fields by Key Points" + }, + { + "type": "text", + "bbox": [ + 0.257, + 0.204, + 0.397, + 0.222 + ], + "angle": 0, + "content": "Chengwei Zheng" + }, + { + "type": "text", + "bbox": [ + 0.47, + 0.204, + 0.566, + 0.221 + ], + "angle": 0, + "content": "Wenbin Lin" + }, + { + "type": "text", + "bbox": [ + 0.64, + 0.205, + 0.713, + 0.222 + ], + "angle": 0, + "content": "Feng Xu" + }, + { + "type": "text", + "bbox": [ + 0.275, + 0.223, + 0.696, + 0.241 + ], + "angle": 0, + "content": "School of Software and BNrist, Tsinghua University" + }, + { + "type": "image_caption", + "bbox": [ + 0.099, + 0.271, + 0.218, + 0.285 + ], + "angle": 0, + "content": "(a) Input Sequence" + }, + { + "type": "image", + "bbox": [ + 0.078, + 0.289, + 0.329, + 0.371 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.085, + 0.371, + 0.23, + 0.383 + ], + "angle": 0, + "content": "Knocking on each piano key" + }, + { + "type": "image_caption", + "bbox": [ + 0.352, + 0.271, + 0.468, + 0.285 + ], + "angle": 0, + "content": "(b) Reconstruction" + }, + { + "type": "image", + "bbox": [ + 0.331, + 0.289, + 0.488, + 0.372 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.351, + 0.371, + 0.468, + 0.383 + ], + "angle": 0, + "content": "Novel view (key point)" + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.318, + 0.554, + 0.34 + ], + "angle": 0, + "content": "Editing by Key Points" + }, + { + "type": "image", + "bbox": [ + 0.498, + 0.362, + 0.566, + 0.405 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.503, + 0.426, + 0.556, + 0.448 + ], + "angle": 0, + "content": "Editing by Key Points" + }, + { + "type": "image", + "bbox": [ + 0.079, + 0.395, + 0.33, + 0.476 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.083, + 0.477, + 0.24, + 0.499 + ], + "angle": 0, + "content": "Shaking and lifting either cup (one moves, the other stands)" + }, + { + "type": "image", + "bbox": [ + 0.332, + 0.395, + 0.488, + 0.476 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.344, + 0.478, + 0.475, + 0.489 + ], + "angle": 0, + "content": "Novel view (2 key points)" + }, + { + "type": "image_caption", + "bbox": [ + 0.676, + 0.271, + 0.788, + 0.285 + ], + "angle": 0, + "content": "(c) Editing Results" + }, + { + "type": "image", + "bbox": [ + 0.572, + 0.289, + 0.73, + 0.371 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.588, + 0.371, + 0.712, + 0.382 + ], + "angle": 0, + "content": "Playing a piece of music" + }, + { + "type": "image", + "bbox": [ + 0.735, + 0.289, + 0.892, + 0.37 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.75, + 0.371, + 0.88, + 0.383 + ], + "angle": 0, + "content": "Sliding on the piano keys" + }, + { + "type": "image", + "bbox": [ + 0.572, + 0.395, + 0.73, + 0.476 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.649, + 0.477, + 0.816, + 0.489 + ], + "angle": 0, + "content": "Freely moving for two dice cups" + }, + { + "type": "image", + "bbox": [ + 0.735, + 0.395, + 0.892, + 0.476 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.51, + 0.894, + 0.553 + ], + "angle": 0, + "content": "Figure 1. Taking an image sequence (a) as input, EditableNeRF is trained fully automatically to reconstruct the captured scene (b) and can handle topological changes. After training, end-users are able to edit the scene (c) by controlling the automatically picked-out key points (circled in green in (b)). Our method enables multi-dimensional editing and can generate novel scenes that are unseen during training." + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.565, + 0.314, + 0.581 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.075, + 0.599, + 0.474, + 0.903 + ], + "angle": 0, + "content": "Neural radiance fields (NeRF) achieve highly photorealistic novel-view synthesis, but it's a challenging problem to edit the scenes modeled by NeRF-based methods, especially for dynamic scenes. We propose editable neural radiance fields that enable end-users to easily edit dynamic scenes and even support topological changes. Input with an image sequence from a single camera, our network is trained fully automatically and models topologically varying dynamics using our picked-out surface key points. Then end-users can edit the scene by easily dragging the key points to desired new positions. To achieve this, we propose a scene analysis method to detect and initialize key points by considering the dynamics in the scene, and a weighted key points strategy to model topologically varying dynamics by joint key points and weights optimization. Our method supports intuitive multi-dimensional (up to 3D) editing and can generate novel scenes that are unseen in the input sequence. Experiments demonstrate that our method achieves high-quality editing on various dynamic scenes and outperforms the state-of-the-art. Our code and captured data are" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.567, + 0.89, + 0.596 + ], + "angle": 0, + "content": "available at https://chengwei-zheng.github.io/EditableNeRF/." + }, + { + "type": "title", + "bbox": [ + 0.501, + 0.631, + 0.633, + 0.646 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.658, + 0.893, + 0.793 + ], + "angle": 0, + "content": "Neural radiance fields (NeRF) [23] have shown great power in novel-view synthesis and enable many applications as this method achieves photo-realistic rendering [9]. Recent techniques have further improved NeRF by extending it to handle dynamic scenes [27, 30, 40] and even topologically varying scenes [28]. However, these works mainly focus on reconstruction itself but do not consider scene editing. Thus, for rendering, only the camera views can be changed, while the modeled scenes cannot be edited." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.796, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Recently, some frameworks have been proposed to make neural radiance fields editable in different aspects. Some of them aim to edit the reconstructed appearance and enable relighting [2,35,54]; some allow controlling the shapes and colors of objects from a specific category [15, 20, 44, 47]; and some divide the scene into different parts and the location of each part can be modified [48, 49, 52]. However, the" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "8317" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.258 + ], + "angle": 0, + "content": "dynamics of moving objects cannot be edited by the previous methods. And this task becomes much more challenging when the dynamics contain topological changes. Topological changes can lead to motion discontinuities (e.g., between the hammer and the piano keys, between the cups and the table in Fig. 1) in 3D space and further cause noticeable artifacts if they are not modeled well. A state-of-the-art framework CoNeRF [16] tries to resolve this problem by using manual supervision. However, it only supports limited and one-dimensional editing for each scene part, requiring user annotations as supervision." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.259, + 0.473, + 0.426 + ], + "angle": 0, + "content": "We propose EditableNeRF, editable topologically varying neural radiance fields that are trained without manual supervision and support intuitive multi-dimensional (up to three-dimensional) editing. The key of our method is to represent motions and topological changes by the movements of some sparse surface key points. Each key point is able to control the topologically varying dynamics of a moving part, as well as other effects like shadow and reflection changes through the neural radiance fields. This key-point-based method enables end-users to edit the scene by easily dragging the key points to their desired new positions." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.426, + 0.473, + 0.622 + ], + "angle": 0, + "content": "To achieve this, we first apply a scene analysis method to detect key points in the canonical space and track them in the full sequence for key point initialization. We introduce a network to estimate spatially-varying weights for all scene points and use the weighted key points to model the dynamics in the scene, including topological changes. In the training stage, our network is trained to reconstruct the scene using the supervision from the input image sequence, and the key point positions are also optimized by taking motion (optical flow) and geometry (depth maps) constraints as additional supervision. After training, the scene can be edited by controlling the key points' positions, and novel scenes that are unseen during training can also be generated." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.624, + 0.472, + 0.655 + ], + "angle": 0, + "content": "The contribution of this paper lies in the following aspects:" + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.667, + 0.468, + 0.711 + ], + "angle": 0, + "content": "- Key-point-driven neural radiance fields achieving intuitive multi-dimensional editing even with topological changes, without requiring annotated training data." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.713, + 0.468, + 0.755 + ], + "angle": 0, + "content": "- A weighted key points strategy modeling topologically varying dynamics by joint key points and weights optimization." + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.758, + 0.467, + 0.786 + ], + "angle": 0, + "content": "- A scene analysis method to detect and initialize key points by considering the dynamics in the scene." + }, + { + "type": "list", + "bbox": [ + 0.096, + 0.667, + 0.468, + 0.786 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.805, + 0.22, + 0.82 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.831, + 0.279, + 0.847 + ], + "angle": 0, + "content": "2.1. Novel-View Synthesis" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.856, + 0.472, + 0.903 + ], + "angle": 0, + "content": "Many methods achieve rendering novel-view images by reconstructing scenes and objects into meshes [5, 6, 12, 39, 55], neural voxels [21, 33], and multi-plane images" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.151 + ], + "angle": 0, + "content": "[7, 24, 58]. Besides these methods based on discrete representations, some methods also achieve novel-view synthesis by using continuous representations [26, 34] and have shown great potential in this task." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.153, + 0.893, + 0.485 + ], + "angle": 0, + "content": "Neural radiance fields (NeRF) [23] achieve photorealistic rendering in novel-view synthesis by leveraging continuous implicit functions of density and view-dependent color to represent static scenes. To handle dynamic scenes, time-variant latent codes could be used to encode time-variant components based on NeRF, but requiring multi-view video inputs [17]. To further enable dynamic reconstructions from a single-view sequence, deformation fields implemented by MLPs are applied to warp objects in each frame into a canonical space [27, 30, 40]. Some methods also utilize estimated depth maps [45], ToF depth images [1], or optical scene flow [18] to improve the performance of dynamic neural radiance fields. HyperNeRF [28] further extends dynamic NeRF to reconstruct topologically varying scenes by modeling canonical spaces with different topology states into a unified continuous hyperspace, and the discontinuous deformations in 3D space caused by topological changes can be modeled by continuous functions in hyperspace. However, unlike traditional explicit representations such as triangular meshes, NeRF-based methods represent the scenes by implicit functions, making the modeled scenes difficult to be edited." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.497, + 0.803, + 0.513 + ], + "angle": 0, + "content": "2.2. Editing on Neural Radiance Fields" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.521, + 0.892, + 0.581 + ], + "angle": 0, + "content": "As our method focuses on NeRF editing, we mainly discuss NeRF-based methods that support user editing in this section. For editing on explicit representations or other implicit representations, please refer to [4, 32, 50, 57]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.583, + 0.893, + 0.703 + ], + "angle": 0, + "content": "One approach to edit neural radiance fields is to segment the scene into different components and build MLP for each component [48, 49, 52]. Assuming that different components are individual, this representation allows control of the placements and the relative positions of these components, as well as deleting or reduplicating a component. But these methods do not support editing the dynamics inside a component and only result in limited applications." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.705, + 0.892, + 0.78 + ], + "angle": 0, + "content": "In addition, some methods achieve relighting and material editing on neural fields [2, 35, 54] by decomposing the scene into surface normals, lights, albedo, and material. Texture editing can also be accomplished by a 3D-to-2D texture mapping [46]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.781, + 0.893, + 0.901 + ], + "angle": 0, + "content": "Besides, there are also some methods that focus on modeling a specific category of objects [15, 20, 44, 47] instead of general objects. A common solution for this problem is to model the category of objects with conditional NeRF and use latent codes as conditions to encode the variations of different objects in this category. Then the shape and appearance can be edited by changing the latent codes or by fine-tuning the network [20], and even controlled by" + }, + { + "type": "page_number", + "bbox": [ + 0.482, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "8318" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.072, + 0.885, + 0.344 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.354, + 0.895, + 0.412 + ], + "angle": 0, + "content": "Figure 2. EditableNeRF pipeline. The query point \\( x \\) is first warped into the canonical space by a warp field and a latent code \\( \\beta_{t} \\) in frame \\( t \\). Next, we compute the key point weights of this canonical point \\( x' \\) and use it to calculate a linear combination of all key point positions \\( k_{t} \\), called weighted key points. After that, we feed the following NeRF MLP with the weighted key points and \\( x' \\), then the output density and color are used for volumetric rendering. In the training stage, optical flow and depth maps are used to supervise key point positions." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.431, + 0.471, + 0.596 + ], + "angle": 0, + "content": "text [41] with the help of a multi-modal model. And many methods also focus on modeling editable human bodies or human faces based on NeRF representation. By using human body parametric models and skinning techniques such as SMPL [22], neural radiance fields have been extended to model the human body and can be animated by controlling skeleton poses [3, 19, 25, 29, 36]. Human face parametric models also contribute to extending NeRF for human face modeling and controlling [8, 10, 14, 37, 42, 56], and even driven by audio [13]. However, general objects cannot be handled by these methods." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.599, + 0.47, + 0.78 + ], + "angle": 0, + "content": "Recently, NeRF-editing [51] proposes to deform NeRF on static objects by extracting explicit meshes, deforming the meshes, and transferring the deformations back into the implicit representations. However, this method cannot handle dynamic scenes. CoNeRF [16] proposes an attribute re-rendering method based on dynamic NeRF. This method requires users to provide annotations in several frames, including masks for every dynamic part and their corresponding attribute values, for network training. Then these parts could be edited by controlling the one-dimensional attribute values. We will show our advantages against CoNeRF in Sec. 4.2." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.798, + 0.222, + 0.814 + ], + "angle": 0, + "content": "3. EditableNeRF" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.826, + 0.469, + 0.903 + ], + "angle": 0, + "content": "Input with color image sequence, our method can reconstruct the captured scene fully automatically based on neural radiance fields, and the topologically varying dynamics are modeled using surface key points. After reconstruction, end-users can edit the scene by controlling the key points." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.431, + 0.892, + 0.598 + ], + "angle": 0, + "content": "Our pipeline is shown in Fig. 2. First, We use two methods, HyperNeRF [28] and RAFT [38], to derive the depth maps of input frames and optical flow between adjacent input images, respectively. Then we apply a scene analysis method to detect and initialize key points for each frame (Sec. 3.3). After that, our NeRF-based network (Sec. 3.1) can be trained fully automatically (Sec. 3.2) to model the captured scene based on our weighted key points strategy. When the reconstruction is finished, the reconstructed scene can be edited by dragging the key points to desired positions (Sec. 3.4)." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.608, + 0.604, + 0.623 + ], + "angle": 0, + "content": "3.1. Network" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.632, + 0.892, + 0.707 + ], + "angle": 0, + "content": "We first introduce our network architecture, which is shown in Fig. 2. Our network represents the scene as a field of density and radiance [23]. Given a query point, similarly to other dynamic NeRF methods [27,28], we first use a warp field to model slight movements:" + }, + { + "type": "equation", + "bbox": [ + 0.644, + 0.72, + 0.891, + 0.737 + ], + "angle": 0, + "content": "\\[\nx ^ {\\prime} = T (x, \\beta_ {t}). \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.75, + 0.892, + 0.856 + ], + "angle": 0, + "content": "Here the warp filed \\( T \\) maps a query 3D point \\( x \\) to its canonical location \\( x' \\), and \\( \\beta_{t} \\) is the warp latent code in frame \\( t \\). This warp field ensures that the scene in different frames is aligned despite some errors in input camera parameters, by using slight movements. While as discussed in [28], it's hard for this continuous warp field to model discontinuous movements caused by topological changes." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.856, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Then we need to model different topology and motion states in the canonical space. We find that motions and topological changes are always related to some movements" + }, + { + "type": "page_number", + "bbox": [ + 0.482, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "8319" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.08, + 0.089, + 0.209, + 0.155 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.136, + 0.157, + 0.155, + 0.17 + ], + "angle": 0, + "content": "(a)" + }, + { + "type": "image", + "bbox": [ + 0.211, + 0.089, + 0.339, + 0.155 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.265, + 0.157, + 0.285, + 0.17 + ], + "angle": 0, + "content": "(b)" + }, + { + "type": "image", + "bbox": [ + 0.34, + 0.089, + 0.469, + 0.156 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.395, + 0.158, + 0.413, + 0.17 + ], + "angle": 0, + "content": "(c)" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.182, + 0.47, + 0.252 + ], + "angle": 0, + "content": "Figure 3. Examples of key points and key point weights. (a) shows an input frame and its corresponding key points (circled in green). (b) and (c) demonstrate the weights of the two key points, respectively. These weights are obtained by using the surface points corresponding to the pixels as query points." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.279, + 0.469, + 0.46 + ], + "angle": 0, + "content": "of surface points, so we achieve this modeling by making use of sparse surface key points. These 3D key points are attached to the objects' surfaces and also move with the objects. Each key point is able to control the topologically varying dynamics of a moving part and also some effects like shadow and reflection changes. An example of key points is shown in (a) of Fig. 3. For each moving part in the scene, we automatically select one corresponding key point, which will be detailed in Sec. 3.3, and the number of key points is denoted as \\( N \\). The key points' positions in each input frame will be optimized automatically in our training stage to achieve this modeling." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.461, + 0.469, + 0.567 + ], + "angle": 0, + "content": "We assume that different locations in the canonical space are affected by different key points. So for a query point \\( x' \\), an MLP followed by softmax is used to decide which key point should control its dynamics. We call this network weight estimating network, which takes canonical coordinate \\( x' \\) as input and outputs a weight vector \\( w \\in \\mathbb{R}^N \\), indicating how each key point affects the query point \\( x' \\)." + }, + { + "type": "equation", + "bbox": [ + 0.229, + 0.579, + 0.469, + 0.596 + ], + "angle": 0, + "content": "\\[\nw = W \\left(x ^ {\\prime}\\right). \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.609, + 0.469, + 0.639 + ], + "angle": 0, + "content": "An example of these spatially-varying key point weights is shown in (b) and (c) of Fig. 3." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.64, + 0.469, + 0.685 + ], + "angle": 0, + "content": "We then construct a weighted key points vector \\( p \\) by taking a linear combination of all key point positions \\( k \\) to model the topologically varying dynamics at \\( x' \\)." + }, + { + "type": "equation", + "bbox": [ + 0.188, + 0.697, + 0.469, + 0.737 + ], + "angle": 0, + "content": "\\[\np _ {t} \\left(x ^ {\\prime}\\right) = \\sum_ {i = 1} ^ {N} w ^ {i} \\left(x ^ {\\prime}\\right) \\cdot k _ {t} ^ {i}. \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.75, + 0.469, + 0.84 + ], + "angle": 0, + "content": "The superscript \\(i\\) is the index of key points, and the subscript \\(t\\) is the frame index. If there is only one object that moves and causes topological changes, our method will model this scene with only one key point \\((N = 1)\\), and (3) becomes \\(p_t(x') = k_t\\) because the softmax always outputs a scalar 1. So we directly set \\(p_t(x')\\) to be \\(k_t\\) in this situation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.469, + 0.902 + ], + "angle": 0, + "content": "Next, the 3D canonical coordinate \\( x' \\) and the weighted key points \\( p \\) are concatenated to construct a coordinate in hyperspace for topologically varying scene modeling. This hyperspace is proposed in HyperNeRF [28]. In addition" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.212 + ], + "angle": 0, + "content": "to 3D space, HyperNeRF makes use of ambient dimensions to model objects in hyperspace, and different topology states are encoded with different ambient coordinates. Discontinuous deformations caused by topological changes in 3D space can be modeled by continuous functions (such as MLP) in hyperspace, and more details can be found in [28]. Here we use the weighted key points \\( p \\) as ambient coordinates, modeling topologically varying dynamics." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.212, + 0.892, + 0.243 + ], + "angle": 0, + "content": "Finally, the following NeRF MLP is fed with this 6D coordinate in hyperspace:" + }, + { + "type": "equation", + "bbox": [ + 0.591, + 0.249, + 0.892, + 0.266 + ], + "angle": 0, + "content": "\\[\n(c, \\sigma) = H \\left(x ^ {\\prime} \\oplus p _ {t} \\left(x ^ {\\prime}\\right), d, \\alpha_ {t}\\right). \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.272, + 0.892, + 0.378 + ], + "angle": 0, + "content": "Here \\(d\\) is the view direction, and \\(\\alpha_{t}\\) is the appearance latent code as in [28]. This NeRF MLP outputs the color \\(c\\) and the density \\(\\sigma\\) that can be used in volumetric rendering. To render an image, we should trace the camera rays of all pixels, sample points along these rays, obtain their colors and densities, and run the volumetric rendering, which are the same as in the original NeRF [23]." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.385, + 0.757, + 0.401 + ], + "angle": 0, + "content": "3.2. Loss Functions and Training" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.409, + 0.892, + 0.514 + ], + "angle": 0, + "content": "All the latent codes and MLP parameters are optimized in the training stage to model the scene. As we use key points to encode topologically varying dynamics, we need to additionally optimize key point positions in each input frame. To keep our key points on the object surfaces and to be time-consistent, novel losses are added in our training stage." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.514, + 0.892, + 0.56 + ], + "angle": 0, + "content": "First, we propose a motion loss, which constrains that the key point positions in two adjacent frames should be consistent with the optical flow from pre-trained RAFT [38]." + }, + { + "type": "equation", + "bbox": [ + 0.504, + 0.566, + 0.891, + 0.599 + ], + "angle": 0, + "content": "\\[\nL _ {\\text {m o t i o n}} (t, i) = \\left\\| \\Pi_ {t + 1} \\left(k _ {t + 1} ^ {i}\\right) - \\Pi_ {t} \\left(k _ {t} ^ {i}\\right) - F _ {t} ^ {t + 1} \\left(\\Pi_ {t} \\left(k _ {t} ^ {i}\\right)\\right) \\right\\| ^ {2}, \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.6, + 0.892, + 0.66 + ], + "angle": 0, + "content": "where \\(\\Pi_t\\) is the projection function using the camera pose of frame \\(t\\), and \\(F_t^{t+1}\\) is the optical flow from frame \\(t\\) to frame \\(t+1\\). This loss ensures that the 2D key point positions in different frames correspond to the same surface point." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.66, + 0.892, + 0.719 + ], + "angle": 0, + "content": "The motion loss provides good supervision in 2D image space, while the key points are in the 3D space. Thus, a geometry loss can help to keep the key points on the object surfaces." + }, + { + "type": "equation", + "bbox": [ + 0.564, + 0.724, + 0.891, + 0.745 + ], + "angle": 0, + "content": "\\[\nL _ {g e o} (t, i) = \\left\\| \\Phi_ {t} \\left(k _ {t} ^ {i}\\right) - D _ {t} \\left(\\Pi_ {t} \\left(k _ {t} ^ {i}\\right)\\right) \\right\\| ^ {2}. \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.75, + 0.892, + 0.825 + ], + "angle": 0, + "content": "Here the function \\(\\Phi_t(k_t^i)\\) calculates the distance from the key point \\(k_{t}^{i}\\) to the camera position in frame \\(t\\), and \\(D_{t}\\) denotes the depth map rendered from HyperNeRF [28] in the original camera view. This HyperNeRF is pre-trained before our training stage and takes the same input as ours." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.826, + 0.892, + 0.871 + ], + "angle": 0, + "content": "Besides, we also apply a reconstruction loss between the rendered RGB images \\( C \\) and the input images \\( \\widetilde{C} \\), as well as a warp regularization loss." + }, + { + "type": "equation", + "bbox": [ + 0.577, + 0.877, + 0.891, + 0.905 + ], + "angle": 0, + "content": "\\[\nL _ {r e c} (t) = \\left\\| C _ {t} \\left(k _ {t}, \\alpha_ {t}, \\beta_ {t}\\right) - \\widetilde {C} _ {t} \\right\\| ^ {2}, \\tag {7}\n\\]" + }, + { + "type": "page_number", + "bbox": [ + 0.482, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "8320" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.079, + 0.082, + 0.473, + 0.205 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.215, + 0.47, + 0.286 + ], + "angle": 0, + "content": "Figure 4. A 2D visualization of our key point detection method. For each point \\( x \\), we compute the variance of its ambient coordinates \\( a \\) in the full sequence. Then the points with local maximum variances after a 2D Gaussian filter will be selected as our reference key points." + }, + { + "type": "equation", + "bbox": [ + 0.141, + 0.303, + 0.47, + 0.341 + ], + "angle": 0, + "content": "\\[\nL _ {r e g} (t) = \\frac {1}{\\| S _ {t} \\|} \\sum_ {x \\in S _ {t}} \\| x - T (x, \\beta_ {t}) \\| ^ {2}, \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.349, + 0.47, + 0.44 + ], + "angle": 0, + "content": "where \\( S_{t} \\) is the set of surface points in frame \\( t \\). This warp regularization loss makes sure that the warp field only models slight movements to compensate for the errors in the input camera parameters and distortions in the input images. Thus, it can avoid the ambiguity between the warp field and our weighted key points model." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.452, + 0.405, + 0.468 + ], + "angle": 0, + "content": "3.3. Key Point Detection and Initialization" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.476, + 0.47, + 0.581 + ], + "angle": 0, + "content": "To initialize the network training, we need to determine the key point number \\(N\\) and obtain the initial 3D locations of key points. To achieve this, we apply a scene analysis method, which first finds reference key points in canonical space and reference frames where these reference key points are on the object surfaces, then initializes key points' positions in each frame." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.583, + 0.47, + 0.764 + ], + "angle": 0, + "content": "As our key points are used to model topologically varying dynamics, we find the 3D points in the canonical space with dramatic dynamics including topological changes as our reference key points. Recall that HyperNeRF [28] uses different ambient coordinates \\( a \\) to encode different topology and motion states at a position. And we have already trained a HyperNeRF for depth maps in (6). So we can detect key points by making use of the ambient dimensions \\( a \\) from this pre-trained HyperNeRF. For a point \\( x \\), great varying of its \\( a \\) in different frames indicates great dynamics at \\( x \\), so we use all the positions with locally greatest variations of ambient coordinates as our reference key points." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.765, + 0.471, + 0.904 + ], + "angle": 0, + "content": "To be specific, for each input frame, we trace the original camera rays of all pixels and find the corresponding surface points. A 3D voxel volume in the canonical space is then built to record the ambient coordinates of these surface points. After traversing the whole input sequence, we compute the variance of ambient coordinates for every voxel, followed by a 3D Gaussian filter. And the center points of the voxels with local maximum variances after Gaussian blur will be selected as the reference key points \\( k_{ref} \\). As" + }, + { + "type": "image", + "bbox": [ + 0.513, + 0.084, + 0.882, + 0.188 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.195, + 0.894, + 0.238 + ], + "angle": 0, + "content": "Figure 5. Propagating the reference key point in the reference frame to other frames for initialization. Skipping propagation is only used for some long input sequences." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.256, + 0.892, + 0.317 + ], + "angle": 0, + "content": "our 3D version is difficult to visualize, we show a 2D version of this process in Fig. 4 by rendering all frames in a fixed camera view and computing the variance for each pixel, followed by a 2D Gaussian filter." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.317, + 0.892, + 0.393 + ], + "angle": 0, + "content": "Then for each reference key point, we need to select a reference frame in which the reference key point is on the object surface. We use a similar formulation with the geometry loss in (6) to decide this. (Here we omit the index of key points as they are handled individually.)" + }, + { + "type": "equation", + "bbox": [ + 0.579, + 0.401, + 0.892, + 0.42 + ], + "angle": 0, + "content": "\\[\n\\left\\| \\Phi_ {t} \\left(k _ {r e f}\\right) - D _ {t} \\left(\\Pi_ {t} \\left(k _ {r e f}\\right)\\right) \\right\\| ^ {2} < \\delta , \\tag {9}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.429, + 0.892, + 0.459 + ], + "angle": 0, + "content": "where \\(\\delta\\) is a pre-defined threshold. The first frame \\(t\\) that satisfies (9) will be selected as the reference frame \\(t_{ref}\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.459, + 0.893, + 0.64 + ], + "angle": 0, + "content": "Now for each key point, we have a reference key point position and a corresponding reference frame. To initialize key point positions in the whole sequence, we propagate this reference key point to other frames by optical flow from pre-trained RAFT [38]. The reference key point is first projected into the input image of the reference frame to get its 2D position, and the 2D position is propagated frame by frame using optical flow as shown in Fig. 5. Then these 2D positions are projected back into 3D space by depth maps from HyperNeRF. Note that there are accumulative errors in this initialization due to frame-by-frame propagation, while these errors will be eliminated in our training stage." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.641, + 0.894, + 0.822 + ], + "angle": 0, + "content": "For some very long input sequences, we found that the initialization method above may not perform well. This is because the accumulative errors may become too large, and the key points in the image space may be propagated into other objects (e.g., background). So we propose a skipping propagation method as shown in Fig. 5. For each key point, we additionally propagate the reference key point in the reference frame every \\(M\\) frames (i.e., \\(t_{ref}\\) to \\(t_{ref} + M\\), \\(t_{ref}\\) to \\(t_{ref} + 2M\\), and so on), and replace the frame-by-frame positions if their confidence are greater than a threshold. This confidence is calculated by the consistency between the forward optical flow and the backward optical flow:" + }, + { + "type": "equation", + "bbox": [ + 0.529, + 0.831, + 0.892, + 0.86 + ], + "angle": 0, + "content": "\\[\nC o n f (t) = \\left\\| F _ {t} ^ {t _ {r e f}} \\left(F _ {t _ {r e f}} ^ {t} \\left(\\widehat {k} _ {r e f}\\right)\\right) - \\widehat {k} _ {r e f} \\right\\| ^ {- 1}, \\tag {10}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.869, + 0.892, + 0.901 + ], + "angle": 0, + "content": "where \\(t = t_{ref} + iM\\), \\(i \\in \\mathbb{Z}\\), and the hat of \\(\\widehat{k}_{ref}\\) indicates that it is a 2D position in the reference frame." + }, + { + "type": "page_number", + "bbox": [ + 0.482, + 0.945, + 0.514, + 0.957 + ], + "angle": 0, + "content": "8321" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.081, + 0.214, + 0.147 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.216, + 0.081, + 0.348, + 0.147 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.348, + 0.081, + 0.48, + 0.147 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.082, + 0.155, + 0.214, + 0.224 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.216, + 0.155, + 0.347, + 0.224 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.348, + 0.155, + 0.48, + 0.224 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.082, + 0.231, + 0.214, + 0.3 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.216, + 0.231, + 0.347, + 0.3 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.348, + 0.231, + 0.48, + 0.3 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.493, + 0.081, + 0.624, + 0.149 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.626, + 0.081, + 0.757, + 0.149 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.758, + 0.081, + 0.889, + 0.149 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.493, + 0.156, + 0.624, + 0.224 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.626, + 0.156, + 0.756, + 0.224 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.758, + 0.156, + 0.889, + 0.224 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.493, + 0.231, + 0.624, + 0.299 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.626, + 0.231, + 0.756, + 0.299 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.758, + 0.231, + 0.889, + 0.299 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.305, + 0.893, + 0.334 + ], + "angle": 0, + "content": "Figure 6. Our editing results on various scenes. The first image of each scene also shows the key points (circled in red or green). The car transformer sequence on the right side is provided by CoNeRF [16]. The last row on the right side is from a synthetic sequence." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.353, + 0.282, + 0.369 + ], + "angle": 0, + "content": "3.4. Editing by Key Points" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.377, + 0.47, + 0.453 + ], + "angle": 0, + "content": "After training, users can easily edit the modeled scenes by feeding the network with desired key point positions. As the key points are in the 3D space, our method supports up to three-dimensional editing for each part. We also provide a graphical user interface (GUI) in Sec. 4.4." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.469, + 0.21, + 0.487 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.495, + 0.47, + 0.557 + ], + "angle": 0, + "content": "We show some results after editing in Fig. 6. Some effects, like shadow and reflection changes, can also be edited correctly. And please refer to our accompanying video and supplementary materials for more results and experiments." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.568, + 0.295, + 0.584 + ], + "angle": 0, + "content": "4.1. Implementation Details" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.592, + 0.471, + 0.744 + ], + "angle": 0, + "content": "We set the weight of motion loss to \\(10^{-4}\\), the weight of geometry loss to 0.5, and the weight of warp regularization loss to 0.1. The real data is captured in a resolution of \\(1280 \\times 720\\) and down-sampled to \\(320 \\times 180\\) for network training. Our network is trained on 4 NVIDIA GeForce RTX 3090 graphics cards, and takes around 5 hours for training with 250k iterations. Our code is based on HyperNeRF [28]. And the camera poses of input frames are solved by COLMAP [31]. More details and discussions of our method are provided in our supplementary materials." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.756, + 0.216, + 0.772 + ], + "angle": 0, + "content": "4.2. Comparisons" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.78, + 0.47, + 0.903 + ], + "angle": 0, + "content": "Here we compare our method with state-of-the-art methods HyperNeRF [28] and CoNeRF [16]. HyperNeRF is capable of topologically varying scene reconstruction but does not enable scene editing. CoNeRF allows topologically varying editing but only supports one-dimensional editing for each dynamic part, and user annotations, including masks for every part and their attribute values, are necessary for its pipeline. For example, to train a CoNeRF" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.354, + 0.892, + 0.413 + ], + "angle": 0, + "content": "network on an opening mouth sequence, users have to select some input frames, mask the mouth regions in these frames, and set the corresponding attribute values to 1 when the mouth is open and \\(-1\\) when the mouth is closed." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.415, + 0.892, + 0.476 + ], + "angle": 0, + "content": "Qualitative results. As our method focuses on editing, we first evaluate the editing ability of our method. We compare our method with CoNeRF, while HyperNeRF does not support editing." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.477, + 0.893, + 0.688 + ], + "angle": 0, + "content": "We show some editing results of ours and CoNeRF in Fig. 7. Firstly, as shown in the (a) results, our method based on 3D key points enables up to three-dimensional editing, while CoNeRF fails to encode multi-dimensional dynamics by using one-dimensional attribute values. Secondly, our training stage is fully automatic without user annotations. Especially when different parts are close to each other, it becomes quite difficult for end-users to provide very accurate masks at the boundaries, which further leads to artifacts in CoNeRF as shown in (c) of Fig. 7. In contrast, ours can distinguish different parts automatically. Besides, our editing method allows users to drag the key points to their desired positions, which is more intuitive than inputting attribute values as in CoNeRF." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.69, + 0.895, + 0.901 + ], + "angle": 0, + "content": "Quantitative results on synthetic data. Here we compare our method with HyperNeRF and CoNeRF on synthetic data. We use three data sequences synthesized by Kubric [11], and each contains 400 frames for training. Some results on one of these sequences are shown in Fig. 6. For CoNeRF training, we annotate \\(5\\%\\) frames in the training set using ground truth masks and ground truth attribute values, which are the same as the experiment settings in CoNeRF paper [16]. While for our method, we still use the optical flow from RAFT and depth maps from HyperNeRF. We do not use ground truth optical flow or ground truth depth maps, keeping these settings the same as for real data. Both compared methods are implemented by the original authors and are trained with the same batch size and" + }, + { + "type": "page_number", + "bbox": [ + 0.482, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "8322" + } + ], + [ + { + "type": "image_caption", + "bbox": [ + 0.186, + 0.071, + 0.204, + 0.085 + ], + "angle": 0, + "content": "(a)" + }, + { + "type": "image", + "bbox": [ + 0.078, + 0.085, + 0.195, + 0.155 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.196, + 0.085, + 0.312, + 0.155 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.079, + 0.156, + 0.195, + 0.226 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.196, + 0.156, + 0.312, + 0.226 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.079, + 0.227, + 0.194, + 0.309 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.196, + 0.227, + 0.312, + 0.31 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.434, + 0.071, + 0.453, + 0.084 + ], + "angle": 0, + "content": "(b)" + }, + { + "type": "image", + "bbox": [ + 0.328, + 0.084, + 0.441, + 0.155 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.328, + 0.155, + 0.441, + 0.226 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.328, + 0.227, + 0.441, + 0.309 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.443, + 0.084, + 0.559, + 0.154 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.443, + 0.155, + 0.558, + 0.226 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.443, + 0.227, + 0.559, + 0.309 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.708, + 0.071, + 0.726, + 0.085 + ], + "angle": 0, + "content": "(c)" + }, + { + "type": "image", + "bbox": [ + 0.574, + 0.084, + 0.687, + 0.155 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.574, + 0.155, + 0.687, + 0.226 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.574, + 0.227, + 0.687, + 0.309 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.676, + 0.084, + 0.731, + 0.155 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.676, + 0.155, + 0.731, + 0.227 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.676, + 0.227, + 0.731, + 0.3 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.733, + 0.084, + 0.892, + 0.155 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.733, + 0.155, + 0.892, + 0.227 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.733, + 0.227, + 0.892, + 0.3 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.78, + 0.298, + 0.83, + 0.308 + ], + "angle": 0, + "content": "CoNeRF" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.321, + 0.892, + 0.35 + ], + "angle": 0, + "content": "Figure 7. Qualitative comparisons with CoNeRF [16]. Our method does not require user annotations for training and supports multidimensional editing. Note that the rotations in (b) also cannot be represented by the one-dimensional attribute values in CoNeRF." + }, + { + "type": "table", + "bbox": [ + 0.104, + 0.356, + 0.868, + 0.442 + ], + "angle": 0, + "content": "
MethodReconstructionEditing
PSNR ↑MS-SSIM ↑LPIPS ↓PSNR ↑MS-SSIM ↑LPIPS ↓
HyperNeRF [28]42.670.99640.0823---
CoNeRF [16]40.400.98910.094739.790.98860.0949
Ours44.350.99730.080840.010.99560.0822
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.454, + 0.893, + 0.482 + ], + "angle": 0, + "content": "Table 1. Quantitative comparisons of reconstruction and editing qualities on synthetic data. The reconstruction qualities are measured by the errors in novel-view synthesis. We report PSNR, MS-SSIM [43], and LPIPS [53]. Our method performs the best." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.509, + 0.221, + 0.523 + ], + "angle": 0, + "content": "iteration step as ours." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.524, + 0.47, + 0.704 + ], + "angle": 0, + "content": "First, we compare the reconstruction qualities of these methods by rendering the same synthetic scenes in novel viewpoints and evaluating the novel-view synthesis abilities. As shown in Table 1, our method reaches the best performance. Note that our method even slightly outperforms HyperNeRF on this task. This is because, in our method, the frames with similar motions are initialized with similar key point positions, while HyperNeRF uses random initialization. Thus, it is easier for our network to integrate the information from the frames with similar motions but in different viewpoints. An experiment on this is further provided in our supplementary materials." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.705, + 0.47, + 0.824 + ], + "angle": 0, + "content": "Next, we compare the editing qualities of our method and CoNeRF, while HyperNeRF cannot be used for editing. We derive ground truth key point positions and attribute values from ground truth motions, then use them to edit the scenes in our method and CoNeRF, respectively. Errors are computed between the ground truth images and the rendered images after editing. Our method also outperforms CoNeRF as shown in Table 1." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.826, + 0.47, + 0.901 + ], + "angle": 0, + "content": "Quantitative results on real data. As it is difficult to obtain novel-view ground truth for real data sequences, we turn to compare the interpolation qualities on real data. For a real data sequence with \\(2N\\) frames, we pick out \\(N\\) frames with even indices as the training set, and the other \\(N\\) frames" + }, + { + "type": "table", + "bbox": [ + 0.507, + 0.506, + 0.888, + 0.577 + ], + "angle": 0, + "content": "
MethodPSNR ↑MS-SSIM ↑LPIPS ↓
HyperNeRF [28]30.560.98640.1281
CoNeRF [16]30.650.98690.1307
Ours30.670.98690.1314
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.587, + 0.892, + 0.614 + ], + "angle": 0, + "content": "Table 2. Quantitative comparisons of interpolation qualities on real data." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.642, + 0.892, + 0.747 + ], + "angle": 0, + "content": "with odd indices are used as ground truth for testing. Table 2 demonstrates that all the compared methods get similar quantitative results on this task. Key point positions for our method, attribute values for CoNeRF, and all the latent codes are interpolated in this task. In CoNeRF training, we select \\(1\\%\\) frames with extreme attribute values for annotations, as recommended by CoNeRF [16]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.748, + 0.892, + 0.823 + ], + "angle": 0, + "content": "Besides, when rendering the same real scene with two dynamic parts in the same resolution, CoNeRF takes 1.77s, HyperNeRF takes 0.95s, while ours takes 0.90s. And CoNeRF needs to add a new MLP for each dynamic part, which makes its network not as compact as the other methods." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.833, + 0.665, + 0.847 + ], + "angle": 0, + "content": "4.3. Ablation Studies" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.856, + 0.893, + 0.901 + ], + "angle": 0, + "content": "Our method makes use of 3D key points with the help of 2D optical flow and 1D depth maps. They are first utilized to initialize key point positions, then to formulate the mo" + }, + { + "type": "page_number", + "bbox": [ + 0.482, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "8323" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.084, + 0.077, + 0.465, + 0.155 + ], + "angle": 0, + "content": "
MethodPSNR ↑MS-SSIM ↑LPIPS ↓
Base (w/o supervision)24.600.85400.1680
+ Lmotion29.790.94290.1150
+ Lmotion + Lgeo32.590.96700.1013
+ Lmotion + Lgeo + init40.010.99560.0822
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.167, + 0.47, + 0.208 + ], + "angle": 0, + "content": "Table 3. Ablation studies. We evaluate the motion loss, the geometry loss, and the initialization stage. Our final method in the last row performs the best." + }, + { + "type": "image", + "bbox": [ + 0.082, + 0.226, + 0.468, + 0.359 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.37, + 0.47, + 0.426 + ], + "angle": 0, + "content": "Figure 8. Graphical user interface. The left widget shows the rendered image and the corresponding draggable key points. The right widget allows the user to change the viewpoint. Our GUI also supports drawing a trail of key points, then rendering a video." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.454, + 0.47, + 0.56 + ], + "angle": 0, + "content": "tion loss and the geometry loss. We evaluate the two losses and the initialization stage in Table 3 by measuring the editing qualities on synthetic data. The base method does not use any information from optical flow or depth maps, and its modeled scene changes randomly according to key point movements, while our final method in the last row of Table 3 reaches the best performance." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.572, + 0.212, + 0.589 + ], + "angle": 0, + "content": "4.4. Applications" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.597, + 0.469, + 0.748 + ], + "angle": 0, + "content": "Graphical user interface. We implement a graphical user interface (GUI) for editing and novel-view synthesis, which is shown in Fig. 8 and in our accompanying video. Note that end-users actually drag the key points in the 2D interface, so we provide 1D default depth values for key points to form 3D positions, and we also allow end-users to further edit these depth values. The default depth value for a pixel position is obtained by finding \\( K \\) closest key point positions in the input sequence after projecting into the current view and computing their average depth." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.75, + 0.469, + 0.87 + ], + "angle": 0, + "content": "Novel scenes generation. Novel scenes that are unseen in the training sequence can also be generated by our method. For example, in the piano toy sequence of Fig. 1, the input data only contains knocking on each piano key, while our method can generate sliding on the piano keys by interpolation. And our method can also combine various dynamics of different parts to create novel scenes, such as the dice cups sequence results shown in Fig. 1." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.469, + 0.901 + ], + "angle": 0, + "content": "Motion transfer. Once reconstructed, our modeled scenes can be driven by motions from other sequences. We" + }, + { + "type": "image", + "bbox": [ + 0.504, + 0.077, + 0.631, + 0.14 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.633, + 0.077, + 0.761, + 0.14 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.763, + 0.077, + 0.891, + 0.14 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.152, + 0.892, + 0.18 + ], + "angle": 0, + "content": "Figure 9. Editing results on a challenging scene where the selected key point is not always visible in the full sequence." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.206, + 0.892, + 0.267 + ], + "angle": 0, + "content": "show a phonograph toy driven by a disk in our accompanying video. Optical flow is used to track a manually selected point on the source video and an affine transformation then maps the tracked point into our key point space." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.275, + 0.625, + 0.289 + ], + "angle": 0, + "content": "4.5. Discussions" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.298, + 0.892, + 0.388 + ], + "angle": 0, + "content": "We build our framework based on surface key points. While in some challenging sequences, there may not exist a proper surface point that is visible in all frames to become a key point. Our method can still get plausible results on these sequences, but the consistency of key points is not as good as in other scenes, as shown in Fig. 9." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.389, + 0.893, + 0.585 + ], + "angle": 0, + "content": "Limitations. We assume that the dynamics of a canonical location mainly depend on one key point. If the scene becomes very complex that does not satisfy this assumption (e.g., a dancing human), our method may fail. Also, it's hard for our method to pick out surface key points for semitransparent objects like smoke. Extrapolation cannot be performed well for our method when the key points are dragged too far away from their positions in the training sequence. Our method supports multi-dimensional editing, but if the captured objects only have one-dimensional dynamics (e.g., drawer only moves in 1D), our method can only generate one-dimensional dynamics. Besides, our method cannot work well when RAFT or HyperNeRF fails." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.598, + 0.627, + 0.613 + ], + "angle": 0, + "content": "5. Conclusions" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.623, + 0.892, + 0.803 + ], + "angle": 0, + "content": "We propose EditableNeRF, editable topologically varying neural radiance fields that enable end-users to easily edit dynamic scenes. The key to achieving this is to build our framework by leveraging weighted key points to model topologically varying dynamics, which further achieves intuitive multi-dimensional editing. And a scene analysis method that can measure the dynamics in the scene is also proposed to detect and further initialize these key points. Our method is trained fully automatically using a single-view input sequence and can be easily used by end-users, bringing new applications for editable photo-realistic novel-view synthesis." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.804, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Acknowledgements. This work was supported by the National Key R&D Program of China (2018YFA0704000), Beijing Natural Science Foundation (M22024), the NSFC (No.62021002), and the Key Research and Development Project of Tibet Autonomous Region (XZ202101ZY0019G). This work was also supported by THUIBCS, Tsinghua University, and BLBCI, Beijing Municipal Education Commission. 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Taking an image sequence (a) as input, EditableNeRF is trained fully automatically to reconstruct the captured scene (b) and can handle topological changes. After training, end-users are able to edit the scene (c) by controlling the automatically picked-out key points (circled in green in (b)). Our method enables multi-dimensional editing and can generate novel scenes that are unseen during training. + +![](images/9caabbe6869a4ade2db67c689db708436ef64f674bccff38a0c618a3ad943175.jpg) +Editing by Key Points +Novel view (2 key points) + +![](images/82721d89e2fbc9c8a0aca20b18a4c331ce23465c878098bd19fe9dea9e520476.jpg) +(c) Editing Results +Playing a piece of music + +![](images/e54a0f5bf7aa269d65bf0ab7ec1dd3c1952088fe6a3b39791517e72b71672201.jpg) +Sliding on the piano keys + +![](images/744553ac3f971806fee6acdb1e4b59db7e817dd8bf8ae2931e503ea6b2bf0ab1.jpg) +Freely moving for two dice cups + +![](images/8e8d7a1d966ea3ca80f1827eb137ce6e735a2519cf7a9f85d778634d9ae95ed6.jpg) + +# Abstract + +Neural radiance fields (NeRF) achieve highly photorealistic novel-view synthesis, but it's a challenging problem to edit the scenes modeled by NeRF-based methods, especially for dynamic scenes. We propose editable neural radiance fields that enable end-users to easily edit dynamic scenes and even support topological changes. Input with an image sequence from a single camera, our network is trained fully automatically and models topologically varying dynamics using our picked-out surface key points. Then end-users can edit the scene by easily dragging the key points to desired new positions. To achieve this, we propose a scene analysis method to detect and initialize key points by considering the dynamics in the scene, and a weighted key points strategy to model topologically varying dynamics by joint key points and weights optimization. Our method supports intuitive multi-dimensional (up to 3D) editing and can generate novel scenes that are unseen in the input sequence. Experiments demonstrate that our method achieves high-quality editing on various dynamic scenes and outperforms the state-of-the-art. Our code and captured data are + +available at https://chengwei-zheng.github.io/EditableNeRF/. + +# 1. Introduction + +Neural radiance fields (NeRF) [23] have shown great power in novel-view synthesis and enable many applications as this method achieves photo-realistic rendering [9]. Recent techniques have further improved NeRF by extending it to handle dynamic scenes [27, 30, 40] and even topologically varying scenes [28]. However, these works mainly focus on reconstruction itself but do not consider scene editing. Thus, for rendering, only the camera views can be changed, while the modeled scenes cannot be edited. + +Recently, some frameworks have been proposed to make neural radiance fields editable in different aspects. Some of them aim to edit the reconstructed appearance and enable relighting [2,35,54]; some allow controlling the shapes and colors of objects from a specific category [15, 20, 44, 47]; and some divide the scene into different parts and the location of each part can be modified [48, 49, 52]. However, the + +dynamics of moving objects cannot be edited by the previous methods. And this task becomes much more challenging when the dynamics contain topological changes. Topological changes can lead to motion discontinuities (e.g., between the hammer and the piano keys, between the cups and the table in Fig. 1) in 3D space and further cause noticeable artifacts if they are not modeled well. A state-of-the-art framework CoNeRF [16] tries to resolve this problem by using manual supervision. However, it only supports limited and one-dimensional editing for each scene part, requiring user annotations as supervision. + +We propose EditableNeRF, editable topologically varying neural radiance fields that are trained without manual supervision and support intuitive multi-dimensional (up to three-dimensional) editing. The key of our method is to represent motions and topological changes by the movements of some sparse surface key points. Each key point is able to control the topologically varying dynamics of a moving part, as well as other effects like shadow and reflection changes through the neural radiance fields. This key-point-based method enables end-users to edit the scene by easily dragging the key points to their desired new positions. + +To achieve this, we first apply a scene analysis method to detect key points in the canonical space and track them in the full sequence for key point initialization. We introduce a network to estimate spatially-varying weights for all scene points and use the weighted key points to model the dynamics in the scene, including topological changes. In the training stage, our network is trained to reconstruct the scene using the supervision from the input image sequence, and the key point positions are also optimized by taking motion (optical flow) and geometry (depth maps) constraints as additional supervision. After training, the scene can be edited by controlling the key points' positions, and novel scenes that are unseen during training can also be generated. + +The contribution of this paper lies in the following aspects: + +- Key-point-driven neural radiance fields achieving intuitive multi-dimensional editing even with topological changes, without requiring annotated training data. +- A weighted key points strategy modeling topologically varying dynamics by joint key points and weights optimization. +- A scene analysis method to detect and initialize key points by considering the dynamics in the scene. + +# 2. Related Work + +# 2.1. Novel-View Synthesis + +Many methods achieve rendering novel-view images by reconstructing scenes and objects into meshes [5, 6, 12, 39, 55], neural voxels [21, 33], and multi-plane images + +[7, 24, 58]. Besides these methods based on discrete representations, some methods also achieve novel-view synthesis by using continuous representations [26, 34] and have shown great potential in this task. + +Neural radiance fields (NeRF) [23] achieve photorealistic rendering in novel-view synthesis by leveraging continuous implicit functions of density and view-dependent color to represent static scenes. To handle dynamic scenes, time-variant latent codes could be used to encode time-variant components based on NeRF, but requiring multi-view video inputs [17]. To further enable dynamic reconstructions from a single-view sequence, deformation fields implemented by MLPs are applied to warp objects in each frame into a canonical space [27, 30, 40]. Some methods also utilize estimated depth maps [45], ToF depth images [1], or optical scene flow [18] to improve the performance of dynamic neural radiance fields. HyperNeRF [28] further extends dynamic NeRF to reconstruct topologically varying scenes by modeling canonical spaces with different topology states into a unified continuous hyperspace, and the discontinuous deformations in 3D space caused by topological changes can be modeled by continuous functions in hyperspace. However, unlike traditional explicit representations such as triangular meshes, NeRF-based methods represent the scenes by implicit functions, making the modeled scenes difficult to be edited. + +# 2.2. Editing on Neural Radiance Fields + +As our method focuses on NeRF editing, we mainly discuss NeRF-based methods that support user editing in this section. For editing on explicit representations or other implicit representations, please refer to [4, 32, 50, 57]. + +One approach to edit neural radiance fields is to segment the scene into different components and build MLP for each component [48, 49, 52]. Assuming that different components are individual, this representation allows control of the placements and the relative positions of these components, as well as deleting or reduplicating a component. But these methods do not support editing the dynamics inside a component and only result in limited applications. + +In addition, some methods achieve relighting and material editing on neural fields [2, 35, 54] by decomposing the scene into surface normals, lights, albedo, and material. Texture editing can also be accomplished by a 3D-to-2D texture mapping [46]. + +Besides, there are also some methods that focus on modeling a specific category of objects [15, 20, 44, 47] instead of general objects. A common solution for this problem is to model the category of objects with conditional NeRF and use latent codes as conditions to encode the variations of different objects in this category. Then the shape and appearance can be edited by changing the latent codes or by fine-tuning the network [20], and even controlled by + +![](images/0fbcb3804d096948293b5c6f6437fee61c1346c2aeaef660118ec73096fdeef6.jpg) +Figure 2. EditableNeRF pipeline. The query point $x$ is first warped into the canonical space by a warp field and a latent code $\beta_{t}$ in frame $t$ . Next, we compute the key point weights of this canonical point $x'$ and use it to calculate a linear combination of all key point positions $k_{t}$ , called weighted key points. After that, we feed the following NeRF MLP with the weighted key points and $x'$ , then the output density and color are used for volumetric rendering. In the training stage, optical flow and depth maps are used to supervise key point positions. + +text [41] with the help of a multi-modal model. And many methods also focus on modeling editable human bodies or human faces based on NeRF representation. By using human body parametric models and skinning techniques such as SMPL [22], neural radiance fields have been extended to model the human body and can be animated by controlling skeleton poses [3, 19, 25, 29, 36]. Human face parametric models also contribute to extending NeRF for human face modeling and controlling [8, 10, 14, 37, 42, 56], and even driven by audio [13]. However, general objects cannot be handled by these methods. + +Recently, NeRF-editing [51] proposes to deform NeRF on static objects by extracting explicit meshes, deforming the meshes, and transferring the deformations back into the implicit representations. However, this method cannot handle dynamic scenes. CoNeRF [16] proposes an attribute re-rendering method based on dynamic NeRF. This method requires users to provide annotations in several frames, including masks for every dynamic part and their corresponding attribute values, for network training. Then these parts could be edited by controlling the one-dimensional attribute values. We will show our advantages against CoNeRF in Sec. 4.2. + +# 3. EditableNeRF + +Input with color image sequence, our method can reconstruct the captured scene fully automatically based on neural radiance fields, and the topologically varying dynamics are modeled using surface key points. After reconstruction, end-users can edit the scene by controlling the key points. + +Our pipeline is shown in Fig. 2. First, We use two methods, HyperNeRF [28] and RAFT [38], to derive the depth maps of input frames and optical flow between adjacent input images, respectively. Then we apply a scene analysis method to detect and initialize key points for each frame (Sec. 3.3). After that, our NeRF-based network (Sec. 3.1) can be trained fully automatically (Sec. 3.2) to model the captured scene based on our weighted key points strategy. When the reconstruction is finished, the reconstructed scene can be edited by dragging the key points to desired positions (Sec. 3.4). + +# 3.1. Network + +We first introduce our network architecture, which is shown in Fig. 2. Our network represents the scene as a field of density and radiance [23]. Given a query point, similarly to other dynamic NeRF methods [27,28], we first use a warp field to model slight movements: + +$$ +x ^ {\prime} = T (x, \beta_ {t}). \tag {1} +$$ + +Here the warp filed $T$ maps a query 3D point $x$ to its canonical location $x'$ , and $\beta_{t}$ is the warp latent code in frame $t$ . This warp field ensures that the scene in different frames is aligned despite some errors in input camera parameters, by using slight movements. While as discussed in [28], it's hard for this continuous warp field to model discontinuous movements caused by topological changes. + +Then we need to model different topology and motion states in the canonical space. We find that motions and topological changes are always related to some movements + +![](images/0d13091c8dada144e1a06bec9c96a1014f63ad95f503079e3644743d43f28df5.jpg) +(a) + +![](images/fc6baad63057c4bde083c3688c40c4f18e066486e19348f3472f3b062105af07.jpg) +(b) + +![](images/f5204edd2630f4cc3f1ff1f9b435b378528fb851ccec093a1811584a27b3e001.jpg) +(c) +Figure 3. Examples of key points and key point weights. (a) shows an input frame and its corresponding key points (circled in green). (b) and (c) demonstrate the weights of the two key points, respectively. These weights are obtained by using the surface points corresponding to the pixels as query points. + +of surface points, so we achieve this modeling by making use of sparse surface key points. These 3D key points are attached to the objects' surfaces and also move with the objects. Each key point is able to control the topologically varying dynamics of a moving part and also some effects like shadow and reflection changes. An example of key points is shown in (a) of Fig. 3. For each moving part in the scene, we automatically select one corresponding key point, which will be detailed in Sec. 3.3, and the number of key points is denoted as $N$ . The key points' positions in each input frame will be optimized automatically in our training stage to achieve this modeling. + +We assume that different locations in the canonical space are affected by different key points. So for a query point $x'$ , an MLP followed by softmax is used to decide which key point should control its dynamics. We call this network weight estimating network, which takes canonical coordinate $x'$ as input and outputs a weight vector $w \in \mathbb{R}^N$ , indicating how each key point affects the query point $x'$ . + +$$ +w = W \left(x ^ {\prime}\right). \tag {2} +$$ + +An example of these spatially-varying key point weights is shown in (b) and (c) of Fig. 3. + +We then construct a weighted key points vector $p$ by taking a linear combination of all key point positions $k$ to model the topologically varying dynamics at $x'$ . + +$$ +p _ {t} \left(x ^ {\prime}\right) = \sum_ {i = 1} ^ {N} w ^ {i} \left(x ^ {\prime}\right) \cdot k _ {t} ^ {i}. \tag {3} +$$ + +The superscript $i$ is the index of key points, and the subscript $t$ is the frame index. If there is only one object that moves and causes topological changes, our method will model this scene with only one key point $(N = 1)$ , and (3) becomes $p_t(x') = k_t$ because the softmax always outputs a scalar 1. So we directly set $p_t(x')$ to be $k_t$ in this situation. + +Next, the 3D canonical coordinate $x'$ and the weighted key points $p$ are concatenated to construct a coordinate in hyperspace for topologically varying scene modeling. This hyperspace is proposed in HyperNeRF [28]. In addition + +to 3D space, HyperNeRF makes use of ambient dimensions to model objects in hyperspace, and different topology states are encoded with different ambient coordinates. Discontinuous deformations caused by topological changes in 3D space can be modeled by continuous functions (such as MLP) in hyperspace, and more details can be found in [28]. Here we use the weighted key points $p$ as ambient coordinates, modeling topologically varying dynamics. + +Finally, the following NeRF MLP is fed with this 6D coordinate in hyperspace: + +$$ +(c, \sigma) = H \left(x ^ {\prime} \oplus p _ {t} \left(x ^ {\prime}\right), d, \alpha_ {t}\right). \tag {4} +$$ + +Here $d$ is the view direction, and $\alpha_{t}$ is the appearance latent code as in [28]. This NeRF MLP outputs the color $c$ and the density $\sigma$ that can be used in volumetric rendering. To render an image, we should trace the camera rays of all pixels, sample points along these rays, obtain their colors and densities, and run the volumetric rendering, which are the same as in the original NeRF [23]. + +# 3.2. Loss Functions and Training + +All the latent codes and MLP parameters are optimized in the training stage to model the scene. As we use key points to encode topologically varying dynamics, we need to additionally optimize key point positions in each input frame. To keep our key points on the object surfaces and to be time-consistent, novel losses are added in our training stage. + +First, we propose a motion loss, which constrains that the key point positions in two adjacent frames should be consistent with the optical flow from pre-trained RAFT [38]. + +$$ +L _ {\text {m o t i o n}} (t, i) = \left\| \Pi_ {t + 1} \left(k _ {t + 1} ^ {i}\right) - \Pi_ {t} \left(k _ {t} ^ {i}\right) - F _ {t} ^ {t + 1} \left(\Pi_ {t} \left(k _ {t} ^ {i}\right)\right) \right\| ^ {2}, \tag {5} +$$ + +where $\Pi_t$ is the projection function using the camera pose of frame $t$ , and $F_t^{t+1}$ is the optical flow from frame $t$ to frame $t+1$ . This loss ensures that the 2D key point positions in different frames correspond to the same surface point. + +The motion loss provides good supervision in 2D image space, while the key points are in the 3D space. Thus, a geometry loss can help to keep the key points on the object surfaces. + +$$ +L _ {g e o} (t, i) = \left\| \Phi_ {t} \left(k _ {t} ^ {i}\right) - D _ {t} \left(\Pi_ {t} \left(k _ {t} ^ {i}\right)\right) \right\| ^ {2}. \tag {6} +$$ + +Here the function $\Phi_t(k_t^i)$ calculates the distance from the key point $k_{t}^{i}$ to the camera position in frame $t$ , and $D_{t}$ denotes the depth map rendered from HyperNeRF [28] in the original camera view. This HyperNeRF is pre-trained before our training stage and takes the same input as ours. + +Besides, we also apply a reconstruction loss between the rendered RGB images $C$ and the input images $\widetilde{C}$ , as well as a warp regularization loss. + +$$ +L _ {r e c} (t) = \left\| C _ {t} \left(k _ {t}, \alpha_ {t}, \beta_ {t}\right) - \widetilde {C} _ {t} \right\| ^ {2}, \tag {7} +$$ + +![](images/b8d373e7e770c410c39f0efd993e94b22cb0b1ff408f5d9cbb095cd5abf08dbc.jpg) +Figure 4. A 2D visualization of our key point detection method. For each point $x$ , we compute the variance of its ambient coordinates $a$ in the full sequence. Then the points with local maximum variances after a 2D Gaussian filter will be selected as our reference key points. + +$$ +L _ {r e g} (t) = \frac {1}{\| S _ {t} \|} \sum_ {x \in S _ {t}} \| x - T (x, \beta_ {t}) \| ^ {2}, \tag {8} +$$ + +where $S_{t}$ is the set of surface points in frame $t$ . This warp regularization loss makes sure that the warp field only models slight movements to compensate for the errors in the input camera parameters and distortions in the input images. Thus, it can avoid the ambiguity between the warp field and our weighted key points model. + +# 3.3. Key Point Detection and Initialization + +To initialize the network training, we need to determine the key point number $N$ and obtain the initial 3D locations of key points. To achieve this, we apply a scene analysis method, which first finds reference key points in canonical space and reference frames where these reference key points are on the object surfaces, then initializes key points' positions in each frame. + +As our key points are used to model topologically varying dynamics, we find the 3D points in the canonical space with dramatic dynamics including topological changes as our reference key points. Recall that HyperNeRF [28] uses different ambient coordinates $a$ to encode different topology and motion states at a position. And we have already trained a HyperNeRF for depth maps in (6). So we can detect key points by making use of the ambient dimensions $a$ from this pre-trained HyperNeRF. For a point $x$ , great varying of its $a$ in different frames indicates great dynamics at $x$ , so we use all the positions with locally greatest variations of ambient coordinates as our reference key points. + +To be specific, for each input frame, we trace the original camera rays of all pixels and find the corresponding surface points. A 3D voxel volume in the canonical space is then built to record the ambient coordinates of these surface points. After traversing the whole input sequence, we compute the variance of ambient coordinates for every voxel, followed by a 3D Gaussian filter. And the center points of the voxels with local maximum variances after Gaussian blur will be selected as the reference key points $k_{ref}$ . As + +![](images/54f8e0de88053fd3d01380f6647d12911ebf5985e2f3ab15563ac6ab8fc3b0a7.jpg) +Figure 5. Propagating the reference key point in the reference frame to other frames for initialization. Skipping propagation is only used for some long input sequences. + +our 3D version is difficult to visualize, we show a 2D version of this process in Fig. 4 by rendering all frames in a fixed camera view and computing the variance for each pixel, followed by a 2D Gaussian filter. + +Then for each reference key point, we need to select a reference frame in which the reference key point is on the object surface. We use a similar formulation with the geometry loss in (6) to decide this. (Here we omit the index of key points as they are handled individually.) + +$$ +\left\| \Phi_ {t} \left(k _ {r e f}\right) - D _ {t} \left(\Pi_ {t} \left(k _ {r e f}\right)\right) \right\| ^ {2} < \delta , \tag {9} +$$ + +where $\delta$ is a pre-defined threshold. The first frame $t$ that satisfies (9) will be selected as the reference frame $t_{ref}$ . + +Now for each key point, we have a reference key point position and a corresponding reference frame. To initialize key point positions in the whole sequence, we propagate this reference key point to other frames by optical flow from pre-trained RAFT [38]. The reference key point is first projected into the input image of the reference frame to get its 2D position, and the 2D position is propagated frame by frame using optical flow as shown in Fig. 5. Then these 2D positions are projected back into 3D space by depth maps from HyperNeRF. Note that there are accumulative errors in this initialization due to frame-by-frame propagation, while these errors will be eliminated in our training stage. + +For some very long input sequences, we found that the initialization method above may not perform well. This is because the accumulative errors may become too large, and the key points in the image space may be propagated into other objects (e.g., background). So we propose a skipping propagation method as shown in Fig. 5. For each key point, we additionally propagate the reference key point in the reference frame every $M$ frames (i.e., $t_{ref}$ to $t_{ref} + M$ , $t_{ref}$ to $t_{ref} + 2M$ , and so on), and replace the frame-by-frame positions if their confidence are greater than a threshold. This confidence is calculated by the consistency between the forward optical flow and the backward optical flow: + +$$ +C o n f (t) = \left\| F _ {t} ^ {t _ {r e f}} \left(F _ {t _ {r e f}} ^ {t} \left(\widehat {k} _ {r e f}\right)\right) - \widehat {k} _ {r e f} \right\| ^ {- 1}, \tag {10} +$$ + +where $t = t_{ref} + iM$ , $i \in \mathbb{Z}$ , and the hat of $\widehat{k}_{ref}$ indicates that it is a 2D position in the reference frame. + +![](images/fba6fbb97b40ddce58b3912e8d0dc54f4779dd59f977d37694315350c02f7992.jpg) + +![](images/1e7e7e63ca4e7e764ca465382812eec6cae872102b1115d3bbf8500c3fefcc91.jpg) + +![](images/553b16ec89092ac373182297da050ab3172b643b7b4b582fc79e75014de88f33.jpg) + +![](images/ab9bbd7d300151772c4240a29f0cb90cb081b24fcb8b1b838060d8be77ebcdf6.jpg) + +![](images/af51d24e43cff56d970057c2c1d0c799fd7b1ba30d4d19a4d0b7f3dcb60c6144.jpg) + +![](images/146aee400fcf3c01804b6445ae67c1b6ee1db932e5ee91549b35b1455b69d46a.jpg) + +![](images/882129139b6476e978b92e0653c2952e9fad0ef43c6408cc8f866d1133bc5afb.jpg) +Figure 6. Our editing results on various scenes. The first image of each scene also shows the key points (circled in red or green). The car transformer sequence on the right side is provided by CoNeRF [16]. The last row on the right side is from a synthetic sequence. + +![](images/e250b184b060a3fcd49e6df634c3eb1ca4005c49590a7d3cfad0da580ac5d4d5.jpg) + +![](images/0494f95ab79dd755d2e5750322c20c527475cd02f867966e7f4c6c86d306f15e.jpg) + +![](images/0576e082343392d027f856082e957aba0dc563cc4b0a09bc310e67cd13994c4d.jpg) + +![](images/1d1eb32f4c9d3dedb7ee09642d1f6a324d434ac6688d753b08dd01367b549b43.jpg) + +![](images/01def44dbc4256d2f45cde36cd405e56ab23178915d98c366bc12d2408c35d7d.jpg) + +![](images/588b218b0c3af7d5e308a08e884b039f2a958238282f664f8100b4a6952b9f82.jpg) + +![](images/a95c7ef52a1d5c3f8f6b17cd79f42d78512f5ea2799f2c61ba069734dca1f86d.jpg) + +![](images/7695cbc09b4eea706c286c4c76411b7f398f05f43a16145711c046619a504979.jpg) + +![](images/a023505157b2cc1a45ab04dd6adce991770e5ab6efd5e9c5b3b8a2b1ff1e6abe.jpg) + +![](images/0ee35c4e1e7c5c88d0f5c7ecc3ddfdf8ff748c2f95e5be62d4dafeccdce5cbd9.jpg) + +![](images/80f884738bab625ed99c5aa8d98d4ed368b94b0b4acbb47fbb90da91be9e1095.jpg) + +# 3.4. Editing by Key Points + +After training, users can easily edit the modeled scenes by feeding the network with desired key point positions. As the key points are in the 3D space, our method supports up to three-dimensional editing for each part. We also provide a graphical user interface (GUI) in Sec. 4.4. + +# 4. Experiments + +We show some results after editing in Fig. 6. Some effects, like shadow and reflection changes, can also be edited correctly. And please refer to our accompanying video and supplementary materials for more results and experiments. + +# 4.1. Implementation Details + +We set the weight of motion loss to $10^{-4}$ , the weight of geometry loss to 0.5, and the weight of warp regularization loss to 0.1. The real data is captured in a resolution of $1280 \times 720$ and down-sampled to $320 \times 180$ for network training. Our network is trained on 4 NVIDIA GeForce RTX 3090 graphics cards, and takes around 5 hours for training with 250k iterations. Our code is based on HyperNeRF [28]. And the camera poses of input frames are solved by COLMAP [31]. More details and discussions of our method are provided in our supplementary materials. + +# 4.2. Comparisons + +Here we compare our method with state-of-the-art methods HyperNeRF [28] and CoNeRF [16]. HyperNeRF is capable of topologically varying scene reconstruction but does not enable scene editing. CoNeRF allows topologically varying editing but only supports one-dimensional editing for each dynamic part, and user annotations, including masks for every part and their attribute values, are necessary for its pipeline. For example, to train a CoNeRF + +network on an opening mouth sequence, users have to select some input frames, mask the mouth regions in these frames, and set the corresponding attribute values to 1 when the mouth is open and $-1$ when the mouth is closed. + +Qualitative results. As our method focuses on editing, we first evaluate the editing ability of our method. We compare our method with CoNeRF, while HyperNeRF does not support editing. + +We show some editing results of ours and CoNeRF in Fig. 7. Firstly, as shown in the (a) results, our method based on 3D key points enables up to three-dimensional editing, while CoNeRF fails to encode multi-dimensional dynamics by using one-dimensional attribute values. Secondly, our training stage is fully automatic without user annotations. Especially when different parts are close to each other, it becomes quite difficult for end-users to provide very accurate masks at the boundaries, which further leads to artifacts in CoNeRF as shown in (c) of Fig. 7. In contrast, ours can distinguish different parts automatically. Besides, our editing method allows users to drag the key points to their desired positions, which is more intuitive than inputting attribute values as in CoNeRF. + +Quantitative results on synthetic data. Here we compare our method with HyperNeRF and CoNeRF on synthetic data. We use three data sequences synthesized by Kubric [11], and each contains 400 frames for training. Some results on one of these sequences are shown in Fig. 6. For CoNeRF training, we annotate $5\%$ frames in the training set using ground truth masks and ground truth attribute values, which are the same as the experiment settings in CoNeRF paper [16]. While for our method, we still use the optical flow from RAFT and depth maps from HyperNeRF. We do not use ground truth optical flow or ground truth depth maps, keeping these settings the same as for real data. Both compared methods are implemented by the original authors and are trained with the same batch size and + +![](images/75397d95a2cd4c76370f4d3e76de992f43ef652f34790c9de01caad52df58efa.jpg) +(a) + +![](images/6f48bae6015e71543c675ea4778306fe5228ef4d9b23ff190b85bc9a05ac6897.jpg) + +![](images/8dafaddcca698f27cf7d38e289e27293b7477480ef390748a6b98d792a58c635.jpg) + +![](images/e66cba270694d9a34a51bb7352278b981e2ae9d2311c5dd08f6ca627453b7a56.jpg) + +![](images/8fb6d98214cd3416e4fe5fa592f4ba8a54b70c7c787bcf9441320480bfb252d9.jpg) + +![](images/ee834b1b73f2b127ea35a21250f593d410a527e5a82f82efd93a133c68f751aa.jpg) +Figure 7. Qualitative comparisons with CoNeRF [16]. Our method does not require user annotations for training and supports multidimensional editing. Note that the rotations in (b) also cannot be represented by the one-dimensional attribute values in CoNeRF. + +![](images/a6e959666fb26d13a6ed23ccd348afa8cb2a82d257bc13b1245de25b21c09c94.jpg) +(b) + +![](images/e1d0f9d1e3be1e700affac32bf5517a6cc89c4f032ee22a7c37b02979d1706a0.jpg) + +![](images/4a4ac7da46535237f080e87e78867c0d8c9b37483c69b6185604e97b2e5f090e.jpg) + +![](images/857f9d0251912feba980bd239602b4a270cb665dfae038983f7ffed72411e57e.jpg) + +![](images/a30b6e352aa5ec093bf9afcce5b9da2d839b3b58a8e7a3db4b0b4969ecaab208.jpg) + +![](images/9a209c84ddcb2bb2828a64b06470373403a8596c91042d2aca59276d47efdd38.jpg) + +![](images/60231bdbee4727a829deeabfeb34a70f85fd63c97a9c026a9057bd49c1de98f0.jpg) + +![](images/3ceb39c16922937cf154ffaf6ee7684283a6f486e4b0e2fabc381424f9bd9013.jpg) + +![](images/1305dc93c18f8ed34a952dee238989a00559b51fe5e43d7292d9981581350d06.jpg) + +![](images/8911f79e7a0737fca7506e1d0a959c72e3aa4ae38e1bc5439a31384d19540168.jpg) +(c) + +![](images/1415bef1f8d2699d4348cbbf310fe57d14b3415cfe22d30a9f8c0e21d78f4a72.jpg) + +![](images/f7e49c2593c93bbb1bd42d1f15cffe3bc3c008969e02a39707be7238d3fc27ac.jpg) + +![](images/1ccc9cf76a9b21e4fc89549acacb760497c32b0a07a99a4a0c1cc974debc8c78.jpg) + +![](images/e61fbeca508cb5a0a9d6b2e61547472918f30d895ad3310a54b4779d5d052bb0.jpg) + +![](images/6c9a27e98e3a52ae4d73c10c23e27898d489a8221b41ccad5a381eb92e4775b8.jpg) +CoNeRF + +
MethodReconstructionEditing
PSNR ↑MS-SSIM ↑LPIPS ↓PSNR ↑MS-SSIM ↑LPIPS ↓
HyperNeRF [28]42.670.99640.0823---
CoNeRF [16]40.400.98910.094739.790.98860.0949
Ours44.350.99730.080840.010.99560.0822
+ +iteration step as ours. + +First, we compare the reconstruction qualities of these methods by rendering the same synthetic scenes in novel viewpoints and evaluating the novel-view synthesis abilities. As shown in Table 1, our method reaches the best performance. Note that our method even slightly outperforms HyperNeRF on this task. This is because, in our method, the frames with similar motions are initialized with similar key point positions, while HyperNeRF uses random initialization. Thus, it is easier for our network to integrate the information from the frames with similar motions but in different viewpoints. An experiment on this is further provided in our supplementary materials. + +Next, we compare the editing qualities of our method and CoNeRF, while HyperNeRF cannot be used for editing. We derive ground truth key point positions and attribute values from ground truth motions, then use them to edit the scenes in our method and CoNeRF, respectively. Errors are computed between the ground truth images and the rendered images after editing. Our method also outperforms CoNeRF as shown in Table 1. + +Quantitative results on real data. As it is difficult to obtain novel-view ground truth for real data sequences, we turn to compare the interpolation qualities on real data. For a real data sequence with $2N$ frames, we pick out $N$ frames with even indices as the training set, and the other $N$ frames + +Table 1. Quantitative comparisons of reconstruction and editing qualities on synthetic data. The reconstruction qualities are measured by the errors in novel-view synthesis. We report PSNR, MS-SSIM [43], and LPIPS [53]. Our method performs the best. + +
MethodPSNR ↑MS-SSIM ↑LPIPS ↓
HyperNeRF [28]30.560.98640.1281
CoNeRF [16]30.650.98690.1307
Ours30.670.98690.1314
+ +Table 2. Quantitative comparisons of interpolation qualities on real data. + +with odd indices are used as ground truth for testing. Table 2 demonstrates that all the compared methods get similar quantitative results on this task. Key point positions for our method, attribute values for CoNeRF, and all the latent codes are interpolated in this task. In CoNeRF training, we select $1\%$ frames with extreme attribute values for annotations, as recommended by CoNeRF [16]. + +Besides, when rendering the same real scene with two dynamic parts in the same resolution, CoNeRF takes 1.77s, HyperNeRF takes 0.95s, while ours takes 0.90s. And CoNeRF needs to add a new MLP for each dynamic part, which makes its network not as compact as the other methods. + +# 4.3. Ablation Studies + +Our method makes use of 3D key points with the help of 2D optical flow and 1D depth maps. They are first utilized to initialize key point positions, then to formulate the mo + +
MethodPSNR ↑MS-SSIM ↑LPIPS ↓
Base (w/o supervision)24.600.85400.1680
+ Lmotion29.790.94290.1150
+ Lmotion + Lgeo32.590.96700.1013
+ Lmotion + Lgeo + init40.010.99560.0822
+ +Table 3. Ablation studies. We evaluate the motion loss, the geometry loss, and the initialization stage. Our final method in the last row performs the best. + +![](images/6c5787515f91a2a6123abc2e3dd0f5167590a0b6b718eac0847d8ba0a5be05b2.jpg) +Figure 8. Graphical user interface. The left widget shows the rendered image and the corresponding draggable key points. The right widget allows the user to change the viewpoint. Our GUI also supports drawing a trail of key points, then rendering a video. + +tion loss and the geometry loss. We evaluate the two losses and the initialization stage in Table 3 by measuring the editing qualities on synthetic data. The base method does not use any information from optical flow or depth maps, and its modeled scene changes randomly according to key point movements, while our final method in the last row of Table 3 reaches the best performance. + +# 4.4. Applications + +Graphical user interface. We implement a graphical user interface (GUI) for editing and novel-view synthesis, which is shown in Fig. 8 and in our accompanying video. Note that end-users actually drag the key points in the 2D interface, so we provide 1D default depth values for key points to form 3D positions, and we also allow end-users to further edit these depth values. The default depth value for a pixel position is obtained by finding $K$ closest key point positions in the input sequence after projecting into the current view and computing their average depth. + +Novel scenes generation. Novel scenes that are unseen in the training sequence can also be generated by our method. For example, in the piano toy sequence of Fig. 1, the input data only contains knocking on each piano key, while our method can generate sliding on the piano keys by interpolation. And our method can also combine various dynamics of different parts to create novel scenes, such as the dice cups sequence results shown in Fig. 1. + +Motion transfer. Once reconstructed, our modeled scenes can be driven by motions from other sequences. We + +![](images/bb81f57567b4c9bc947846a05484a1e64097bc195ad6527161c8787b94d74f78.jpg) +Figure 9. Editing results on a challenging scene where the selected key point is not always visible in the full sequence. + +![](images/2d3b34b49585f21ff9a9a70668a1e21aa31d980031f5442321a8ecdc3613feb0.jpg) + +![](images/6b2f9dc01d5b24951eedbe1a6c42c3a3451da2f57b441b15137fc4510b8d885d.jpg) + +show a phonograph toy driven by a disk in our accompanying video. Optical flow is used to track a manually selected point on the source video and an affine transformation then maps the tracked point into our key point space. + +# 4.5. Discussions + +We build our framework based on surface key points. While in some challenging sequences, there may not exist a proper surface point that is visible in all frames to become a key point. Our method can still get plausible results on these sequences, but the consistency of key points is not as good as in other scenes, as shown in Fig. 9. + +Limitations. We assume that the dynamics of a canonical location mainly depend on one key point. If the scene becomes very complex that does not satisfy this assumption (e.g., a dancing human), our method may fail. Also, it's hard for our method to pick out surface key points for semitransparent objects like smoke. Extrapolation cannot be performed well for our method when the key points are dragged too far away from their positions in the training sequence. Our method supports multi-dimensional editing, but if the captured objects only have one-dimensional dynamics (e.g., drawer only moves in 1D), our method can only generate one-dimensional dynamics. Besides, our method cannot work well when RAFT or HyperNeRF fails. + +# 5. Conclusions + +We propose EditableNeRF, editable topologically varying neural radiance fields that enable end-users to easily edit dynamic scenes. The key to achieving this is to build our framework by leveraging weighted key points to model topologically varying dynamics, which further achieves intuitive multi-dimensional editing. And a scene analysis method that can measure the dynamics in the scene is also proposed to detect and further initialize these key points. Our method is trained fully automatically using a single-view input sequence and can be easily used by end-users, bringing new applications for editable photo-realistic novel-view synthesis. + +Acknowledgements. This work was supported by the National Key R&D Program of China (2018YFA0704000), Beijing Natural Science Foundation (M22024), the NSFC (No.62021002), and the Key Research and Development Project of Tibet Autonomous Region (XZ202101ZY0019G). This work was also supported by THUIBCS, Tsinghua University, and BLBCI, Beijing Municipal Education Commission. Feng Xu is the corresponding author. + +# References + +[1] Benjamin Attal, Eliot Laidlaw, Aaron Gokaslan, Changil Kim, Christian Richardt, James Tompkin, and Matthew O'Toole. Törf: Time-of-flight radiance fields for dynamic scene view synthesis. Advances in Neural Information Processing Systems, 34:26289-26301, 2021. 2 +[2] Mark Boss, Raphael Braun, Varun Jampani, Jonathan T Barron, Ce Liu, and Hendrik Lensch. Nerd: Neural reflectance decomposition from image collections. 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Taking an image sequence (a) as input, EditableNeRF is trained fully automatically to reconstruct the captured scene (b) and can handle topological changes. After training, end-users are able to edit the scene (c) by controlling the automatically picked-out key points (circled in green in (b)). Our method enables multi-dimensional editing and can generate novel scenes that are unseen during training." + } + ] + } + ], + "index": 28, + "angle": 0, + "type": "image_caption" + } + ], + "index": 16 + }, + { + "type": "image", + "bbox": [ + 203, + 312, + 298, + 376 + ], + "blocks": [ + { + "bbox": [ + 307, + 337, + 340, + 354 + ], + "lines": [ + { + "bbox": [ + 307, + 337, + 340, + 354 + ], + "spans": [ + { + "bbox": [ + 307, + 337, + 340, + 354 + ], + "type": "text", + "content": "Editing by Key Points" + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 203, + 312, + 298, + 376 + ], + "lines": [ + { + "bbox": [ + 203, + 312, + 298, + 376 + ], + "spans": [ + { + "bbox": [ + 203, + 312, + 298, + 376 + ], + "type": "image", + "image_path": "9caabbe6869a4ade2db67c689db708436ef64f674bccff38a0c618a3ad943175.jpg" + } + ] + } + ], + "index": 18, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 210, + 378, + 290, + 387 + ], + "lines": [ + { + "bbox": [ + 210, + 378, + 290, + 387 + ], + "spans": [ + { + "bbox": [ + 210, + 378, + 290, + 387 + ], + "type": "text", + "content": "Novel view (2 key points)" + } + ] + } + ], + "index": 19, + "angle": 0, + "type": "image_caption" + } + ], + "index": 18 + }, + { + "type": "image", + "bbox": [ + 350, + 228, + 446, + 293 + ], + "blocks": [ + { + "bbox": [ + 413, + 214, + 482, + 225 + ], + "lines": [ + { + "bbox": [ + 413, + 214, + 482, + 225 + ], + "spans": [ + { + "bbox": [ + 413, + 214, + 482, + 225 + ], + "type": "text", + "content": "(c) Editing Results" + } + ] + } + ], + "index": 20, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 350, + 228, + 446, + 293 + ], + "lines": [ + { + "bbox": [ + 350, + 228, + 446, + 293 + ], + "spans": [ + { + "bbox": [ + 350, + 228, + 446, + 293 + ], + "type": "image", + "image_path": "82721d89e2fbc9c8a0aca20b18a4c331ce23465c878098bd19fe9dea9e520476.jpg" + } + ] + } + ], + "index": 21, + "angle": 0, + "type": "image_body" + }, 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+ ], + "index": 24, + "angle": 0, + "type": "image_caption" + } + ], + "index": 23 + }, + { + "type": "image", + "bbox": [ + 350, + 312, + 446, + 376 + ], + "blocks": [ + { + "bbox": [ + 350, + 312, + 446, + 376 + ], + "lines": [ + { + "bbox": [ + 350, + 312, + 446, + 376 + ], + "spans": [ + { + "bbox": [ + 350, + 312, + 446, + 376 + ], + "type": "image", + "image_path": "744553ac3f971806fee6acdb1e4b59db7e817dd8bf8ae2931e503ea6b2bf0ab1.jpg" + } + ] + } + ], + "index": 25, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 397, + 377, + 499, + 387 + ], + "lines": [ + { + "bbox": [ + 397, + 377, + 499, + 387 + ], + "spans": [ + { + "bbox": [ + 397, + 377, + 499, + 387 + ], + "type": "text", + "content": "Freely moving for two dice cups" + } + ] + } + ], + "index": 26, + "angle": 0, + "type": "image_caption" + } + ], + "index": 25 + }, + { + "type": "image", + "bbox": [ + 449, + 312, + 545, + 376 + ], + "blocks": [ + { + "bbox": [ + 449, + 312, + 545, + 376 + ], + "lines": [ + { + "bbox": [ + 449, + 312, + 545, + 376 + ], + "spans": [ + { + "bbox": [ + 449, + 312, + 545, + 376 + ], + "type": "image", + "image_path": "8e8d7a1d966ea3ca80f1827eb137ce6e735a2519cf7a9f85d778634d9ae95ed6.jpg" + } + ] + } + ], + "index": 27, + "angle": 0, + "type": "image_body" + } + ], + "index": 27 + }, + { + "bbox": [ + 143, + 447, + 192, + 460 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 447, + 192, + 460 + ], + "spans": [ + { + "bbox": [ + 143, + 447, + 192, + 460 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 29 + }, + { + "bbox": [ + 45, + 474, + 290, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 474, + 290, + 715 + ], + "spans": [ + { + "bbox": [ + 45, + 474, + 290, + 715 + ], + "type": "text", + "content": "Neural radiance fields (NeRF) achieve highly photorealistic novel-view synthesis, but it's a challenging problem to edit the scenes modeled by NeRF-based methods, especially for dynamic scenes. We propose editable neural radiance fields that enable end-users to easily edit dynamic scenes and even support topological changes. Input with an image sequence from a single camera, our network is trained fully automatically and models topologically varying dynamics using our picked-out surface key points. Then end-users can edit the scene by easily dragging the key points to desired new positions. To achieve this, we propose a scene analysis method to detect and initialize key points by considering the dynamics in the scene, and a weighted key points strategy to model topologically varying dynamics by joint key points and weights optimization. Our method supports intuitive multi-dimensional (up to 3D) editing and can generate novel scenes that are unseen in the input sequence. Experiments demonstrate that our method achieves high-quality editing on various dynamic scenes and outperforms the state-of-the-art. Our code and captured data are" + } + ] + } + ], + "index": 30 + }, + { + "bbox": [ + 306, + 449, + 544, + 472 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 449, + 544, + 472 + ], + "spans": [ + { + "bbox": [ + 306, + 449, + 544, + 472 + ], + "type": "text", + "content": "available at https://chengwei-zheng.github.io/EditableNeRF/." + } + ] + } + ], + "index": 31 + }, + { + "bbox": [ + 306, + 499, + 387, + 511 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 499, + 387, + 511 + ], + "spans": [ + { + "bbox": [ + 306, + 499, + 387, + 511 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 32 + }, + { + "bbox": [ + 304, + 521, + 546, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 521, + 546, + 628 + ], + "spans": [ + { + "bbox": [ + 304, + 521, + 546, + 628 + ], + "type": "text", + "content": "Neural radiance fields (NeRF) [23] have shown great power in novel-view synthesis and enable many applications as this method achieves photo-realistic rendering [9]. Recent techniques have further improved NeRF by extending it to handle dynamic scenes [27, 30, 40] and even topologically varying scenes [28]. However, these works mainly focus on reconstruction itself but do not consider scene editing. Thus, for rendering, only the camera views can be changed, while the modeled scenes cannot be edited." + } + ] + } + ], + "index": 33 + }, + { + "bbox": [ + 304, + 630, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 630, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 630, + 547, + 715 + ], + "type": "text", + "content": "Recently, some frameworks have been proposed to make neural radiance fields editable in different aspects. Some of them aim to edit the reconstructed appearance and enable relighting [2,35,54]; some allow controlling the shapes and colors of objects from a specific category [15, 20, 44, 47]; and some divide the scene into different parts and the location of each part can be modified [48, 49, 52]. However, the" + } + ] + } + ], + "index": 34 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "8317" + } + ] + } + ], + "index": 35 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "text", + "content": "dynamics of moving objects cannot be edited by the previous methods. And this task becomes much more challenging when the dynamics contain topological changes. Topological changes can lead to motion discontinuities (e.g., between the hammer and the piano keys, between the cups and the table in Fig. 1) in 3D space and further cause noticeable artifacts if they are not modeled well. A state-of-the-art framework CoNeRF [16] tries to resolve this problem by using manual supervision. However, it only supports limited and one-dimensional editing for each scene part, requiring user annotations as supervision." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 205, + 289, + 337 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 205, + 289, + 337 + ], + "spans": [ + { + "bbox": [ + 46, + 205, + 289, + 337 + ], + "type": "text", + "content": "We propose EditableNeRF, editable topologically varying neural radiance fields that are trained without manual supervision and support intuitive multi-dimensional (up to three-dimensional) editing. The key of our method is to represent motions and topological changes by the movements of some sparse surface key points. Each key point is able to control the topologically varying dynamics of a moving part, as well as other effects like shadow and reflection changes through the neural radiance fields. This key-point-based method enables end-users to edit the scene by easily dragging the key points to their desired new positions." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 337, + 289, + 492 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 337, + 289, + 492 + ], + "spans": [ + { + "bbox": [ + 46, + 337, + 289, + 492 + ], + "type": "text", + "content": "To achieve this, we first apply a scene analysis method to detect key points in the canonical space and track them in the full sequence for key point initialization. We introduce a network to estimate spatially-varying weights for all scene points and use the weighted key points to model the dynamics in the scene, including topological changes. In the training stage, our network is trained to reconstruct the scene using the supervision from the input image sequence, and the key point positions are also optimized by taking motion (optical flow) and geometry (depth maps) constraints as additional supervision. After training, the scene can be edited by controlling the key points' positions, and novel scenes that are unseen during training can also be generated." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 494, + 288, + 518 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 494, + 288, + 518 + ], + "spans": [ + { + "bbox": [ + 47, + 494, + 288, + 518 + ], + "type": "text", + "content": "The contribution of this paper lies in the following aspects:" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 58, + 528, + 286, + 622 + ], + "type": "list", + "angle": 0, + "index": 7, + "blocks": [ + { + "bbox": [ + 59, + 528, + 286, + 563 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 528, + 286, + 563 + ], + "spans": [ + { + "bbox": [ + 59, + 528, + 286, + 563 + ], + "type": "text", + "content": "- Key-point-driven neural radiance fields achieving intuitive multi-dimensional editing even with topological changes, without requiring annotated training data." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 59, + 564, + 286, + 597 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 564, + 286, + 597 + ], + "spans": [ + { + "bbox": [ + 59, + 564, + 286, + 597 + ], + "type": "text", + "content": "- A weighted key points strategy modeling topologically varying dynamics by joint key points and weights optimization." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 58, + 600, + 285, + 622 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 600, + 285, + 622 + ], + "spans": [ + { + "bbox": [ + 58, + 600, + 285, + 622 + ], + "type": "text", + "content": "- A scene analysis method to detect and initialize key points by considering the dynamics in the scene." + } + ] + } + ], + "index": 6 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 47, + 637, + 134, + 649 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 637, + 134, + 649 + ], + "spans": [ + { + "bbox": [ + 47, + 637, + 134, + 649 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 658, + 170, + 670 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 658, + 170, + 670 + ], + "spans": [ + { + "bbox": [ + 47, + 658, + 170, + 670 + ], + "type": "text", + "content": "2.1. Novel-View Synthesis" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 677, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 677, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 47, + 677, + 288, + 715 + ], + "type": "text", + "content": "Many methods achieve rendering novel-view images by reconstructing scenes and objects into meshes [5, 6, 12, 39, 55], neural voxels [21, 33], and multi-plane images" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 72, + 545, + 119 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 119 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 119 + ], + "type": "text", + "content": "[7, 24, 58]. Besides these methods based on discrete representations, some methods also achieve novel-view synthesis by using continuous representations [26, 34] and have shown great potential in this task." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 121, + 546, + 384 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 121, + 546, + 384 + ], + "spans": [ + { + "bbox": [ + 304, + 121, + 546, + 384 + ], + "type": "text", + "content": "Neural radiance fields (NeRF) [23] achieve photorealistic rendering in novel-view synthesis by leveraging continuous implicit functions of density and view-dependent color to represent static scenes. To handle dynamic scenes, time-variant latent codes could be used to encode time-variant components based on NeRF, but requiring multi-view video inputs [17]. To further enable dynamic reconstructions from a single-view sequence, deformation fields implemented by MLPs are applied to warp objects in each frame into a canonical space [27, 30, 40]. Some methods also utilize estimated depth maps [45], ToF depth images [1], or optical scene flow [18] to improve the performance of dynamic neural radiance fields. HyperNeRF [28] further extends dynamic NeRF to reconstruct topologically varying scenes by modeling canonical spaces with different topology states into a unified continuous hyperspace, and the discontinuous deformations in 3D space caused by topological changes can be modeled by continuous functions in hyperspace. However, unlike traditional explicit representations such as triangular meshes, NeRF-based methods represent the scenes by implicit functions, making the modeled scenes difficult to be edited." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 393, + 491, + 406 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 393, + 491, + 406 + ], + "spans": [ + { + "bbox": [ + 306, + 393, + 491, + 406 + ], + "type": "text", + "content": "2.2. Editing on Neural Radiance Fields" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 412, + 545, + 460 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 412, + 545, + 460 + ], + "spans": [ + { + "bbox": [ + 304, + 412, + 545, + 460 + ], + "type": "text", + "content": "As our method focuses on NeRF editing, we mainly discuss NeRF-based methods that support user editing in this section. For editing on explicit representations or other implicit representations, please refer to [4, 32, 50, 57]." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 461, + 546, + 556 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 461, + 546, + 556 + ], + "spans": [ + { + "bbox": [ + 304, + 461, + 546, + 556 + ], + "type": "text", + "content": "One approach to edit neural radiance fields is to segment the scene into different components and build MLP for each component [48, 49, 52]. Assuming that different components are individual, this representation allows control of the placements and the relative positions of these components, as well as deleting or reduplicating a component. But these methods do not support editing the dynamics inside a component and only result in limited applications." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 558, + 545, + 617 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 558, + 545, + 617 + ], + "spans": [ + { + "bbox": [ + 304, + 558, + 545, + 617 + ], + "type": "text", + "content": "In addition, some methods achieve relighting and material editing on neural fields [2, 35, 54] by decomposing the scene into surface normals, lights, albedo, and material. Texture editing can also be accomplished by a 3D-to-2D texture mapping [46]." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 618, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 618, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 618, + 546, + 713 + ], + "type": "text", + "content": "Besides, there are also some methods that focus on modeling a specific category of objects [15, 20, 44, 47] instead of general objects. A common solution for this problem is to model the category of objects with conditional NeRF and use latent codes as conditions to encode the variations of different objects in this category. Then the shape and appearance can be edited by changing the latent codes or by fine-tuning the network [20], and even controlled by" + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "text", + "content": "8318" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 50, + 57, + 541, + 272 + ], + "blocks": [ + { + "bbox": [ + 50, + 57, + 541, + 272 + ], + "lines": [ + { + "bbox": [ + 50, + 57, + 541, + 272 + ], + "spans": [ + { + "bbox": [ + 50, + 57, + 541, + 272 + ], + "type": "image", + "image_path": "0fbcb3804d096948293b5c6f6437fee61c1346c2aeaef660118ec73096fdeef6.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 280, + 547, + 326 + ], + "lines": [ + { + "bbox": [ + 46, + 280, + 547, + 326 + ], + "spans": [ + { + "bbox": [ + 46, + 280, + 547, + 326 + ], + "type": "text", + "content": "Figure 2. EditableNeRF pipeline. The query point " + }, + { + "bbox": [ + 46, + 280, + 547, + 326 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 46, + 280, + 547, + 326 + ], + "type": "text", + "content": " is first warped into the canonical space by a warp field and a latent code " + }, + { + "bbox": [ + 46, + 280, + 547, + 326 + ], + "type": "inline_equation", + "content": "\\beta_{t}" + }, + { + "bbox": [ + 46, + 280, + 547, + 326 + ], + "type": "text", + "content": " in frame " + }, + { + "bbox": [ + 46, + 280, + 547, + 326 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 280, + 547, + 326 + ], + "type": "text", + "content": ". Next, we compute the key point weights of this canonical point " + }, + { + "bbox": [ + 46, + 280, + 547, + 326 + ], + "type": "inline_equation", + "content": "x'" + }, + { + "bbox": [ + 46, + 280, + 547, + 326 + ], + "type": "text", + "content": " and use it to calculate a linear combination of all key point positions " + }, + { + "bbox": [ + 46, + 280, + 547, + 326 + ], + "type": "inline_equation", + "content": "k_{t}" + }, + { + "bbox": [ + 46, + 280, + 547, + 326 + ], + "type": "text", + "content": ", called weighted key points. After that, we feed the following NeRF MLP with the weighted key points and " + }, + { + "bbox": [ + 46, + 280, + 547, + 326 + ], + "type": "inline_equation", + "content": "x'" + }, + { + "bbox": [ + 46, + 280, + 547, + 326 + ], + "type": "text", + "content": ", then the output density and color are used for volumetric rendering. In the training stage, optical flow and depth maps are used to supervise key point positions." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 341, + 288, + 472 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 341, + 288, + 472 + ], + "spans": [ + { + "bbox": [ + 46, + 341, + 288, + 472 + ], + "type": "text", + "content": "text [41] with the help of a multi-modal model. And many methods also focus on modeling editable human bodies or human faces based on NeRF representation. By using human body parametric models and skinning techniques such as SMPL [22], neural radiance fields have been extended to model the human body and can be animated by controlling skeleton poses [3, 19, 25, 29, 36]. Human face parametric models also contribute to extending NeRF for human face modeling and controlling [8, 10, 14, 37, 42, 56], and even driven by audio [13]. However, general objects cannot be handled by these methods." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 474, + 287, + 617 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 474, + 287, + 617 + ], + "spans": [ + { + "bbox": [ + 46, + 474, + 287, + 617 + ], + "type": "text", + "content": "Recently, NeRF-editing [51] proposes to deform NeRF on static objects by extracting explicit meshes, deforming the meshes, and transferring the deformations back into the implicit representations. However, this method cannot handle dynamic scenes. CoNeRF [16] proposes an attribute re-rendering method based on dynamic NeRF. This method requires users to provide annotations in several frames, including masks for every dynamic part and their corresponding attribute values, for network training. Then these parts could be edited by controlling the one-dimensional attribute values. We will show our advantages against CoNeRF in Sec. 4.2." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 632, + 135, + 644 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 632, + 135, + 644 + ], + "spans": [ + { + "bbox": [ + 47, + 632, + 135, + 644 + ], + "type": "text", + "content": "3. EditableNeRF" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 654, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 654, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 654, + 287, + 715 + ], + "type": "text", + "content": "Input with color image sequence, our method can reconstruct the captured scene fully automatically based on neural radiance fields, and the topologically varying dynamics are modeled using surface key points. After reconstruction, end-users can edit the scene by controlling the key points." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 341, + 545, + 473 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 341, + 545, + 473 + ], + "spans": [ + { + "bbox": [ + 304, + 341, + 545, + 473 + ], + "type": "text", + "content": "Our pipeline is shown in Fig. 2. First, We use two methods, HyperNeRF [28] and RAFT [38], to derive the depth maps of input frames and optical flow between adjacent input images, respectively. Then we apply a scene analysis method to detect and initialize key points for each frame (Sec. 3.3). After that, our NeRF-based network (Sec. 3.1) can be trained fully automatically (Sec. 3.2) to model the captured scene based on our weighted key points strategy. When the reconstruction is finished, the reconstructed scene can be edited by dragging the key points to desired positions (Sec. 3.4)." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 481, + 369, + 493 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 481, + 369, + 493 + ], + "spans": [ + { + "bbox": [ + 306, + 481, + 369, + 493 + ], + "type": "text", + "content": "3.1. Network" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 500, + 545, + 559 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 500, + 545, + 559 + ], + "spans": [ + { + "bbox": [ + 304, + 500, + 545, + 559 + ], + "type": "text", + "content": "We first introduce our network architecture, which is shown in Fig. 2. Our network represents the scene as a field of density and radiance [23]. Given a query point, similarly to other dynamic NeRF methods [27,28], we first use a warp field to model slight movements:" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 394, + 570, + 545, + 583 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 394, + 570, + 545, + 583 + ], + "spans": [ + { + "bbox": [ + 394, + 570, + 545, + 583 + ], + "type": "interline_equation", + "content": "x ^ {\\prime} = T (x, \\beta_ {t}). \\tag {1}", + "image_path": "d02220c9596f0549b0a7276c0fc59a5c4904a5ed905596ca90a2eb0eef69e877.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 594, + 545, + 677 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 594, + 545, + 677 + ], + "spans": [ + { + "bbox": [ + 304, + 594, + 545, + 677 + ], + "type": "text", + "content": "Here the warp filed " + }, + { + "bbox": [ + 304, + 594, + 545, + 677 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 304, + 594, + 545, + 677 + ], + "type": "text", + "content": " maps a query 3D point " + }, + { + "bbox": [ + 304, + 594, + 545, + 677 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 304, + 594, + 545, + 677 + ], + "type": "text", + "content": " to its canonical location " + }, + { + "bbox": [ + 304, + 594, + 545, + 677 + ], + "type": "inline_equation", + "content": "x'" + }, + { + "bbox": [ + 304, + 594, + 545, + 677 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 304, + 594, + 545, + 677 + ], + "type": "inline_equation", + "content": "\\beta_{t}" + }, + { + "bbox": [ + 304, + 594, + 545, + 677 + ], + "type": "text", + "content": " is the warp latent code in frame " + }, + { + "bbox": [ + 304, + 594, + 545, + 677 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 594, + 545, + 677 + ], + "type": "text", + "content": ". This warp field ensures that the scene in different frames is aligned despite some errors in input camera parameters, by using slight movements. While as discussed in [28], it's hard for this continuous warp field to model discontinuous movements caused by topological changes." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "text", + "content": "Then we need to model different topology and motion states in the canonical space. We find that motions and topological changes are always related to some movements" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "text", + "content": "8319" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 48, + 70, + 127, + 122 + ], + "blocks": [ + { + "bbox": [ + 48, + 70, + 127, + 122 + ], + "lines": [ + { + "bbox": [ + 48, + 70, + 127, + 122 + ], + "spans": [ + { + "bbox": [ + 48, + 70, + 127, + 122 + ], + "type": "image", + "image_path": "0d13091c8dada144e1a06bec9c96a1014f63ad95f503079e3644743d43f28df5.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 83, + 124, + 94, + 134 + ], + "lines": [ + { + "bbox": [ + 83, + 124, + 94, + 134 + ], + "spans": [ + { + "bbox": [ + 83, + 124, + 94, + 134 + ], + "type": "text", + "content": "(a)" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 129, + 70, + 207, + 122 + ], + "blocks": [ + { + "bbox": [ + 129, + 70, + 207, + 122 + ], + "lines": [ + { + "bbox": [ + 129, + 70, + 207, + 122 + ], + "spans": [ + { + "bbox": [ + 129, + 70, + 207, + 122 + ], + "type": "image", + "image_path": "fc6baad63057c4bde083c3688c40c4f18e066486e19348f3472f3b062105af07.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 162, + 124, + 174, + 134 + ], + "lines": [ + { + "bbox": [ + 162, + 124, + 174, + 134 + ], + "spans": [ + { + "bbox": [ + 162, + 124, + 174, + 134 + ], + "type": "text", + "content": "(b)" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 208, + 70, + 287, + 123 + ], + "blocks": [ + { + "bbox": [ + 208, + 70, + 287, + 123 + ], + "lines": [ + { + "bbox": [ + 208, + 70, + 287, + 123 + ], + "spans": [ + { + "bbox": [ + 208, + 70, + 287, + 123 + ], + "type": "image", + "image_path": "f5204edd2630f4cc3f1ff1f9b435b378528fb851ccec093a1811584a27b3e001.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 241, + 125, + 252, + 134 + ], + "lines": [ + { + "bbox": [ + 241, + 125, + 252, + 134 + ], + "spans": [ + { + "bbox": [ + 241, + 125, + 252, + 134 + ], + "type": "text", + "content": "(c)" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 46, + 144, + 287, + 199 + ], + "lines": [ + { + "bbox": [ + 46, + 144, + 287, + 199 + ], + "spans": [ + { + "bbox": [ + 46, + 144, + 287, + 199 + ], + "type": "text", + "content": "Figure 3. Examples of key points and key point weights. (a) shows an input frame and its corresponding key points (circled in green). (b) and (c) demonstrate the weights of the two key points, respectively. These weights are obtained by using the surface points corresponding to the pixels as query points." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 220, + 287, + 364 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 220, + 287, + 364 + ], + "spans": [ + { + "bbox": [ + 46, + 220, + 287, + 364 + ], + "type": "text", + "content": "of surface points, so we achieve this modeling by making use of sparse surface key points. These 3D key points are attached to the objects' surfaces and also move with the objects. Each key point is able to control the topologically varying dynamics of a moving part and also some effects like shadow and reflection changes. An example of key points is shown in (a) of Fig. 3. For each moving part in the scene, we automatically select one corresponding key point, which will be detailed in Sec. 3.3, and the number of key points is denoted as " + }, + { + "bbox": [ + 46, + 220, + 287, + 364 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 220, + 287, + 364 + ], + "type": "text", + "content": ". The key points' positions in each input frame will be optimized automatically in our training stage to achieve this modeling." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 365, + 287, + 449 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 365, + 287, + 449 + ], + "spans": [ + { + "bbox": [ + 46, + 365, + 287, + 449 + ], + "type": "text", + "content": "We assume that different locations in the canonical space are affected by different key points. So for a query point " + }, + { + "bbox": [ + 46, + 365, + 287, + 449 + ], + "type": "inline_equation", + "content": "x'" + }, + { + "bbox": [ + 46, + 365, + 287, + 449 + ], + "type": "text", + "content": ", an MLP followed by softmax is used to decide which key point should control its dynamics. We call this network weight estimating network, which takes canonical coordinate " + }, + { + "bbox": [ + 46, + 365, + 287, + 449 + ], + "type": "inline_equation", + "content": "x'" + }, + { + "bbox": [ + 46, + 365, + 287, + 449 + ], + "type": "text", + "content": " as input and outputs a weight vector " + }, + { + "bbox": [ + 46, + 365, + 287, + 449 + ], + "type": "inline_equation", + "content": "w \\in \\mathbb{R}^N" + }, + { + "bbox": [ + 46, + 365, + 287, + 449 + ], + "type": "text", + "content": ", indicating how each key point affects the query point " + }, + { + "bbox": [ + 46, + 365, + 287, + 449 + ], + "type": "inline_equation", + "content": "x'" + }, + { + "bbox": [ + 46, + 365, + 287, + 449 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 140, + 458, + 287, + 472 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 140, + 458, + 287, + 472 + ], + "spans": [ + { + "bbox": [ + 140, + 458, + 287, + 472 + ], + "type": "interline_equation", + "content": "w = W \\left(x ^ {\\prime}\\right). \\tag {2}", + "image_path": "0744ee366fff00ab217544f1f61e78dd433574e7b3b320496d980dba8af1976f.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 482, + 287, + 506 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 482, + 287, + 506 + ], + "spans": [ + { + "bbox": [ + 47, + 482, + 287, + 506 + ], + "type": "text", + "content": "An example of these spatially-varying key point weights is shown in (b) and (c) of Fig. 3." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 47, + 506, + 287, + 542 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 506, + 287, + 542 + ], + "spans": [ + { + "bbox": [ + 47, + 506, + 287, + 542 + ], + "type": "text", + "content": "We then construct a weighted key points vector " + }, + { + "bbox": [ + 47, + 506, + 287, + 542 + ], + "type": "inline_equation", + "content": "p" + }, + { + "bbox": [ + 47, + 506, + 287, + 542 + ], + "type": "text", + "content": " by taking a linear combination of all key point positions " + }, + { + "bbox": [ + 47, + 506, + 287, + 542 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 47, + 506, + 287, + 542 + ], + "type": "text", + "content": " to model the topologically varying dynamics at " + }, + { + "bbox": [ + 47, + 506, + 287, + 542 + ], + "type": "inline_equation", + "content": "x'" + }, + { + "bbox": [ + 47, + 506, + 287, + 542 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 115, + 552, + 287, + 583 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 115, + 552, + 287, + 583 + ], + "spans": [ + { + "bbox": [ + 115, + 552, + 287, + 583 + ], + "type": "interline_equation", + "content": "p _ {t} \\left(x ^ {\\prime}\\right) = \\sum_ {i = 1} ^ {N} w ^ {i} \\left(x ^ {\\prime}\\right) \\cdot k _ {t} ^ {i}. \\tag {3}", + "image_path": "bd11c8168b4762b048d2bd965cf99239b841e34bdb9feb1768e221e452e65750.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 47, + 594, + 287, + 665 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 594, + 287, + 665 + ], + "spans": [ + { + "bbox": [ + 47, + 594, + 287, + 665 + ], + "type": "text", + "content": "The superscript " + }, + { + "bbox": [ + 47, + 594, + 287, + 665 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 47, + 594, + 287, + 665 + ], + "type": "text", + "content": " is the index of key points, and the subscript " + }, + { + "bbox": [ + 47, + 594, + 287, + 665 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 47, + 594, + 287, + 665 + ], + "type": "text", + "content": " is the frame index. If there is only one object that moves and causes topological changes, our method will model this scene with only one key point " + }, + { + "bbox": [ + 47, + 594, + 287, + 665 + ], + "type": "inline_equation", + "content": "(N = 1)" + }, + { + "bbox": [ + 47, + 594, + 287, + 665 + ], + "type": "text", + "content": ", and (3) becomes " + }, + { + "bbox": [ + 47, + 594, + 287, + 665 + ], + "type": "inline_equation", + "content": "p_t(x') = k_t" + }, + { + "bbox": [ + 47, + 594, + 287, + 665 + ], + "type": "text", + "content": " because the softmax always outputs a scalar 1. So we directly set " + }, + { + "bbox": [ + 47, + 594, + 287, + 665 + ], + "type": "inline_equation", + "content": "p_t(x')" + }, + { + "bbox": [ + 47, + 594, + 287, + 665 + ], + "type": "text", + "content": " to be " + }, + { + "bbox": [ + 47, + 594, + 287, + 665 + ], + "type": "inline_equation", + "content": "k_t" + }, + { + "bbox": [ + 47, + 594, + 287, + 665 + ], + "type": "text", + "content": " in this situation." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "text", + "content": "Next, the 3D canonical coordinate " + }, + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "inline_equation", + "content": "x'" + }, + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "text", + "content": " and the weighted key points " + }, + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "inline_equation", + "content": "p" + }, + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "text", + "content": " are concatenated to construct a coordinate in hyperspace for topologically varying scene modeling. This hyperspace is proposed in HyperNeRF [28]. In addition" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 72, + 545, + 167 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 167 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 167 + ], + "type": "text", + "content": "to 3D space, HyperNeRF makes use of ambient dimensions to model objects in hyperspace, and different topology states are encoded with different ambient coordinates. Discontinuous deformations caused by topological changes in 3D space can be modeled by continuous functions (such as MLP) in hyperspace, and more details can be found in [28]. Here we use the weighted key points " + }, + { + "bbox": [ + 304, + 72, + 545, + 167 + ], + "type": "inline_equation", + "content": "p" + }, + { + "bbox": [ + 304, + 72, + 545, + 167 + ], + "type": "text", + "content": " as ambient coordinates, modeling topologically varying dynamics." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 167, + 545, + 192 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 167, + 545, + 192 + ], + "spans": [ + { + "bbox": [ + 304, + 167, + 545, + 192 + ], + "type": "text", + "content": "Finally, the following NeRF MLP is fed with this 6D coordinate in hyperspace:" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 361, + 197, + 545, + 210 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 361, + 197, + 545, + 210 + ], + "spans": [ + { + "bbox": [ + 361, + 197, + 545, + 210 + ], + "type": "interline_equation", + "content": "(c, \\sigma) = H \\left(x ^ {\\prime} \\oplus p _ {t} \\left(x ^ {\\prime}\\right), d, \\alpha_ {t}\\right). \\tag {4}", + "image_path": "b05207918b0bd1818bb6d612dc853da6bc91126d9ff92e17363d679be2301415.jpg" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 215, + 545, + 299 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 215, + 545, + 299 + ], + "spans": [ + { + "bbox": [ + 304, + 215, + 545, + 299 + ], + "type": "text", + "content": "Here " + }, + { + "bbox": [ + 304, + 215, + 545, + 299 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 304, + 215, + 545, + 299 + ], + "type": "text", + "content": " is the view direction, and " + }, + { + "bbox": [ + 304, + 215, + 545, + 299 + ], + "type": "inline_equation", + "content": "\\alpha_{t}" + }, + { + "bbox": [ + 304, + 215, + 545, + 299 + ], + "type": "text", + "content": " is the appearance latent code as in [28]. This NeRF MLP outputs the color " + }, + { + "bbox": [ + 304, + 215, + 545, + 299 + ], + "type": "inline_equation", + "content": "c" + }, + { + "bbox": [ + 304, + 215, + 545, + 299 + ], + "type": "text", + "content": " and the density " + }, + { + "bbox": [ + 304, + 215, + 545, + 299 + ], + "type": "inline_equation", + "content": "\\sigma" + }, + { + "bbox": [ + 304, + 215, + 545, + 299 + ], + "type": "text", + "content": " that can be used in volumetric rendering. To render an image, we should trace the camera rays of all pixels, sample points along these rays, obtain their colors and densities, and run the volumetric rendering, which are the same as in the original NeRF [23]." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 305, + 304, + 463, + 317 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 304, + 463, + 317 + ], + "spans": [ + { + "bbox": [ + 305, + 304, + 463, + 317 + ], + "type": "text", + "content": "3.2. Loss Functions and Training" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 323, + 545, + 407 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 323, + 545, + 407 + ], + "spans": [ + { + "bbox": [ + 304, + 323, + 545, + 407 + ], + "type": "text", + "content": "All the latent codes and MLP parameters are optimized in the training stage to model the scene. As we use key points to encode topologically varying dynamics, we need to additionally optimize key point positions in each input frame. To keep our key points on the object surfaces and to be time-consistent, novel losses are added in our training stage." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 304, + 407, + 545, + 443 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 407, + 545, + 443 + ], + "spans": [ + { + "bbox": [ + 304, + 407, + 545, + 443 + ], + "type": "text", + "content": "First, we propose a motion loss, which constrains that the key point positions in two adjacent frames should be consistent with the optical flow from pre-trained RAFT [38]." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 308, + 448, + 545, + 474 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 448, + 545, + 474 + ], + "spans": [ + { + "bbox": [ + 308, + 448, + 545, + 474 + ], + "type": "interline_equation", + "content": "L _ {\\text {m o t i o n}} (t, i) = \\left\\| \\Pi_ {t + 1} \\left(k _ {t + 1} ^ {i}\\right) - \\Pi_ {t} \\left(k _ {t} ^ {i}\\right) - F _ {t} ^ {t + 1} \\left(\\Pi_ {t} \\left(k _ {t} ^ {i}\\right)\\right) \\right\\| ^ {2}, \\tag {5}", + "image_path": "f654f11a2d294fe4263e0eef57091311ce8e4397ba1d8b1da2cd1cc937cb77cf.jpg" + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 304, + 475, + 545, + 522 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 475, + 545, + 522 + ], + "spans": [ + { + "bbox": [ + 304, + 475, + 545, + 522 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 475, + 545, + 522 + ], + "type": "inline_equation", + "content": "\\Pi_t" + }, + { + "bbox": [ + 304, + 475, + 545, + 522 + ], + "type": "text", + "content": " is the projection function using the camera pose of frame " + }, + { + "bbox": [ + 304, + 475, + 545, + 522 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 475, + 545, + 522 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 304, + 475, + 545, + 522 + ], + "type": "inline_equation", + "content": "F_t^{t+1}" + }, + { + "bbox": [ + 304, + 475, + 545, + 522 + ], + "type": "text", + "content": " is the optical flow from frame " + }, + { + "bbox": [ + 304, + 475, + 545, + 522 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 475, + 545, + 522 + ], + "type": "text", + "content": " to frame " + }, + { + "bbox": [ + 304, + 475, + 545, + 522 + ], + "type": "inline_equation", + "content": "t+1" + }, + { + "bbox": [ + 304, + 475, + 545, + 522 + ], + "type": "text", + "content": ". This loss ensures that the 2D key point positions in different frames correspond to the same surface point." + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 304, + 522, + 545, + 569 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 522, + 545, + 569 + ], + "spans": [ + { + "bbox": [ + 304, + 522, + 545, + 569 + ], + "type": "text", + "content": "The motion loss provides good supervision in 2D image space, while the key points are in the 3D space. Thus, a geometry loss can help to keep the key points on the object surfaces." + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 345, + 573, + 545, + 590 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 345, + 573, + 545, + 590 + ], + "spans": [ + { + "bbox": [ + 345, + 573, + 545, + 590 + ], + "type": "interline_equation", + "content": "L _ {g e o} (t, i) = \\left\\| \\Phi_ {t} \\left(k _ {t} ^ {i}\\right) - D _ {t} \\left(\\Pi_ {t} \\left(k _ {t} ^ {i}\\right)\\right) \\right\\| ^ {2}. \\tag {6}", + "image_path": "ae33e9d05f1d7452fee68fe08766dfb3af6a37cd856f1cda5849352262a6c142.jpg" + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 304, + 594, + 545, + 653 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 594, + 545, + 653 + ], + "spans": [ + { + "bbox": [ + 304, + 594, + 545, + 653 + ], + "type": "text", + "content": "Here the function " + }, + { + "bbox": [ + 304, + 594, + 545, + 653 + ], + "type": "inline_equation", + "content": "\\Phi_t(k_t^i)" + }, + { + "bbox": [ + 304, + 594, + 545, + 653 + ], + "type": "text", + "content": " calculates the distance from the key point " + }, + { + "bbox": [ + 304, + 594, + 545, + 653 + ], + "type": "inline_equation", + "content": "k_{t}^{i}" + }, + { + "bbox": [ + 304, + 594, + 545, + 653 + ], + "type": "text", + "content": " to the camera position in frame " + }, + { + "bbox": [ + 304, + 594, + 545, + 653 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 594, + 545, + 653 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 304, + 594, + 545, + 653 + ], + "type": "inline_equation", + "content": "D_{t}" + }, + { + "bbox": [ + 304, + 594, + 545, + 653 + ], + "type": "text", + "content": " denotes the depth map rendered from HyperNeRF [28] in the original camera view. This HyperNeRF is pre-trained before our training stage and takes the same input as ours." + } + ] + } + ], + "index": 26 + }, + { + "bbox": [ + 304, + 654, + 545, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 654, + 545, + 689 + ], + "spans": [ + { + "bbox": [ + 304, + 654, + 545, + 689 + ], + "type": "text", + "content": "Besides, we also apply a reconstruction loss between the rendered RGB images " + }, + { + "bbox": [ + 304, + 654, + 545, + 689 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 304, + 654, + 545, + 689 + ], + "type": "text", + "content": " and the input images " + }, + { + "bbox": [ + 304, + 654, + 545, + 689 + ], + "type": "inline_equation", + "content": "\\widetilde{C}" + }, + { + "bbox": [ + 304, + 654, + 545, + 689 + ], + "type": "text", + "content": ", as well as a warp regularization loss." + } + ] + } + ], + "index": 27 + }, + { + "bbox": [ + 353, + 694, + 545, + 716 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 353, + 694, + 545, + 716 + ], + "spans": [ + { + "bbox": [ + 353, + 694, + 545, + 716 + ], + "type": "interline_equation", + "content": "L _ {r e c} (t) = \\left\\| C _ {t} \\left(k _ {t}, \\alpha_ {t}, \\beta_ {t}\\right) - \\widetilde {C} _ {t} \\right\\| ^ {2}, \\tag {7}", + "image_path": "3271be6f1a86213ceb78131abbdb166ac5bf68c610729d6c75965055cf3259e3.jpg" + } + ] + } + ], + "index": 28 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "text", + "content": "8320" + } + ] + } + ], + "index": 29 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 48, + 64, + 289, + 162 + ], + "blocks": [ + { + "bbox": [ + 48, + 64, + 289, + 162 + ], + "lines": [ + { + "bbox": [ + 48, + 64, + 289, + 162 + ], + "spans": [ + { + "bbox": [ + 48, + 64, + 289, + 162 + ], + "type": "image", + "image_path": "b8d373e7e770c410c39f0efd993e94b22cb0b1ff408f5d9cbb095cd5abf08dbc.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 170, + 287, + 226 + ], + "lines": [ + { + "bbox": [ + 46, + 170, + 287, + 226 + ], + "spans": [ + { + "bbox": [ + 46, + 170, + 287, + 226 + ], + "type": "text", + "content": "Figure 4. A 2D visualization of our key point detection method. For each point " + }, + { + "bbox": [ + 46, + 170, + 287, + 226 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 46, + 170, + 287, + 226 + ], + "type": "text", + "content": ", we compute the variance of its ambient coordinates " + }, + { + "bbox": [ + 46, + 170, + 287, + 226 + ], + "type": "inline_equation", + "content": "a" + }, + { + "bbox": [ + 46, + 170, + 287, + 226 + ], + "type": "text", + "content": " in the full sequence. Then the points with local maximum variances after a 2D Gaussian filter will be selected as our reference key points." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 86, + 239, + 287, + 270 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 86, + 239, + 287, + 270 + ], + "spans": [ + { + "bbox": [ + 86, + 239, + 287, + 270 + ], + "type": "interline_equation", + "content": "L _ {r e g} (t) = \\frac {1}{\\| S _ {t} \\|} \\sum_ {x \\in S _ {t}} \\| x - T (x, \\beta_ {t}) \\| ^ {2}, \\tag {8}", + "image_path": "9045577d5d707db35e93408cd846451f6c2654813ca2c3327006c117910fe4e5.jpg" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 276, + 287, + 348 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 276, + 287, + 348 + ], + "spans": [ + { + "bbox": [ + 46, + 276, + 287, + 348 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 276, + 287, + 348 + ], + "type": "inline_equation", + "content": "S_{t}" + }, + { + "bbox": [ + 46, + 276, + 287, + 348 + ], + "type": "text", + "content": " is the set of surface points in frame " + }, + { + "bbox": [ + 46, + 276, + 287, + 348 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 276, + 287, + 348 + ], + "type": "text", + "content": ". This warp regularization loss makes sure that the warp field only models slight movements to compensate for the errors in the input camera parameters and distortions in the input images. Thus, it can avoid the ambiguity between the warp field and our weighted key points model." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 357, + 247, + 370 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 357, + 247, + 370 + ], + "spans": [ + { + "bbox": [ + 47, + 357, + 247, + 370 + ], + "type": "text", + "content": "3.3. Key Point Detection and Initialization" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 376, + 287, + 460 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 376, + 287, + 460 + ], + "spans": [ + { + "bbox": [ + 46, + 376, + 287, + 460 + ], + "type": "text", + "content": "To initialize the network training, we need to determine the key point number " + }, + { + "bbox": [ + 46, + 376, + 287, + 460 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 376, + 287, + 460 + ], + "type": "text", + "content": " and obtain the initial 3D locations of key points. To achieve this, we apply a scene analysis method, which first finds reference key points in canonical space and reference frames where these reference key points are on the object surfaces, then initializes key points' positions in each frame." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 461, + 287, + 605 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 461, + 287, + 605 + ], + "spans": [ + { + "bbox": [ + 46, + 461, + 287, + 605 + ], + "type": "text", + "content": "As our key points are used to model topologically varying dynamics, we find the 3D points in the canonical space with dramatic dynamics including topological changes as our reference key points. Recall that HyperNeRF [28] uses different ambient coordinates " + }, + { + "bbox": [ + 46, + 461, + 287, + 605 + ], + "type": "inline_equation", + "content": "a" + }, + { + "bbox": [ + 46, + 461, + 287, + 605 + ], + "type": "text", + "content": " to encode different topology and motion states at a position. And we have already trained a HyperNeRF for depth maps in (6). So we can detect key points by making use of the ambient dimensions " + }, + { + "bbox": [ + 46, + 461, + 287, + 605 + ], + "type": "inline_equation", + "content": "a" + }, + { + "bbox": [ + 46, + 461, + 287, + 605 + ], + "type": "text", + "content": " from this pre-trained HyperNeRF. For a point " + }, + { + "bbox": [ + 46, + 461, + 287, + 605 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 46, + 461, + 287, + 605 + ], + "type": "text", + "content": ", great varying of its " + }, + { + "bbox": [ + 46, + 461, + 287, + 605 + ], + "type": "inline_equation", + "content": "a" + }, + { + "bbox": [ + 46, + 461, + 287, + 605 + ], + "type": "text", + "content": " in different frames indicates great dynamics at " + }, + { + "bbox": [ + 46, + 461, + 287, + 605 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 46, + 461, + 287, + 605 + ], + "type": "text", + "content": ", so we use all the positions with locally greatest variations of ambient coordinates as our reference key points." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "text", + "content": "To be specific, for each input frame, we trace the original camera rays of all pixels and find the corresponding surface points. A 3D voxel volume in the canonical space is then built to record the ambient coordinates of these surface points. After traversing the whole input sequence, we compute the variance of ambient coordinates for every voxel, followed by a 3D Gaussian filter. And the center points of the voxels with local maximum variances after Gaussian blur will be selected as the reference key points " + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "inline_equation", + "content": "k_{ref}" + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "text", + "content": ". As" + } + ] + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 313, + 66, + 539, + 148 + ], + "blocks": [ + { + "bbox": [ + 313, + 66, + 539, + 148 + ], + "lines": [ + { + "bbox": [ + 313, + 66, + 539, + 148 + ], + "spans": [ + { + "bbox": [ + 313, + 66, + 539, + 148 + ], + "type": "image", + "image_path": "54f8e0de88053fd3d01380f6647d12911ebf5985e2f3ab15563ac6ab8fc3b0a7.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 154, + 547, + 188 + ], + "lines": [ + { + "bbox": [ + 304, + 154, + 547, + 188 + ], + "spans": [ + { + "bbox": [ + 304, + 154, + 547, + 188 + ], + "type": "text", + "content": "Figure 5. Propagating the reference key point in the reference frame to other frames for initialization. Skipping propagation is only used for some long input sequences." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 202, + 545, + 251 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 202, + 545, + 251 + ], + "spans": [ + { + "bbox": [ + 304, + 202, + 545, + 251 + ], + "type": "text", + "content": "our 3D version is difficult to visualize, we show a 2D version of this process in Fig. 4 by rendering all frames in a fixed camera view and computing the variance for each pixel, followed by a 2D Gaussian filter." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 251, + 545, + 311 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 251, + 545, + 311 + ], + "spans": [ + { + "bbox": [ + 304, + 251, + 545, + 311 + ], + "type": "text", + "content": "Then for each reference key point, we need to select a reference frame in which the reference key point is on the object surface. We use a similar formulation with the geometry loss in (6) to decide this. (Here we omit the index of key points as they are handled individually.)" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 354, + 317, + 545, + 332 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 354, + 317, + 545, + 332 + ], + "spans": [ + { + "bbox": [ + 354, + 317, + 545, + 332 + ], + "type": "interline_equation", + "content": "\\left\\| \\Phi_ {t} \\left(k _ {r e f}\\right) - D _ {t} \\left(\\Pi_ {t} \\left(k _ {r e f}\\right)\\right) \\right\\| ^ {2} < \\delta , \\tag {9}", + "image_path": "d9742a98e5dbcca1210e4b53a03504a521cbef96c4160073463f6258278318fd.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 339, + 545, + 363 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 339, + 545, + 363 + ], + "spans": [ + { + "bbox": [ + 304, + 339, + 545, + 363 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 339, + 545, + 363 + ], + "type": "inline_equation", + "content": "\\delta" + }, + { + "bbox": [ + 304, + 339, + 545, + 363 + ], + "type": "text", + "content": " is a pre-defined threshold. The first frame " + }, + { + "bbox": [ + 304, + 339, + 545, + 363 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 339, + 545, + 363 + ], + "type": "text", + "content": " that satisfies (9) will be selected as the reference frame " + }, + { + "bbox": [ + 304, + 339, + 545, + 363 + ], + "type": "inline_equation", + "content": "t_{ref}" + }, + { + "bbox": [ + 304, + 339, + 545, + 363 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 363, + 546, + 506 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 363, + 546, + 506 + ], + "spans": [ + { + "bbox": [ + 304, + 363, + 546, + 506 + ], + "type": "text", + "content": "Now for each key point, we have a reference key point position and a corresponding reference frame. To initialize key point positions in the whole sequence, we propagate this reference key point to other frames by optical flow from pre-trained RAFT [38]. The reference key point is first projected into the input image of the reference frame to get its 2D position, and the 2D position is propagated frame by frame using optical flow as shown in Fig. 5. Then these 2D positions are projected back into 3D space by depth maps from HyperNeRF. Note that there are accumulative errors in this initialization due to frame-by-frame propagation, while these errors will be eliminated in our training stage." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 507, + 547, + 651 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 507, + 547, + 651 + ], + "spans": [ + { + "bbox": [ + 304, + 507, + 547, + 651 + ], + "type": "text", + "content": "For some very long input sequences, we found that the initialization method above may not perform well. This is because the accumulative errors may become too large, and the key points in the image space may be propagated into other objects (e.g., background). So we propose a skipping propagation method as shown in Fig. 5. For each key point, we additionally propagate the reference key point in the reference frame every " + }, + { + "bbox": [ + 304, + 507, + 547, + 651 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 304, + 507, + 547, + 651 + ], + "type": "text", + "content": " frames (i.e., " + }, + { + "bbox": [ + 304, + 507, + 547, + 651 + ], + "type": "inline_equation", + "content": "t_{ref}" + }, + { + "bbox": [ + 304, + 507, + 547, + 651 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 304, + 507, + 547, + 651 + ], + "type": "inline_equation", + "content": "t_{ref} + M" + }, + { + "bbox": [ + 304, + 507, + 547, + 651 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 507, + 547, + 651 + ], + "type": "inline_equation", + "content": "t_{ref}" + }, + { + "bbox": [ + 304, + 507, + 547, + 651 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 304, + 507, + 547, + 651 + ], + "type": "inline_equation", + "content": "t_{ref} + 2M" + }, + { + "bbox": [ + 304, + 507, + 547, + 651 + ], + "type": "text", + "content": ", and so on), and replace the frame-by-frame positions if their confidence are greater than a threshold. This confidence is calculated by the consistency between the forward optical flow and the backward optical flow:" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 323, + 658, + 545, + 681 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 323, + 658, + 545, + 681 + ], + "spans": [ + { + "bbox": [ + 323, + 658, + 545, + 681 + ], + "type": "interline_equation", + "content": "C o n f (t) = \\left\\| F _ {t} ^ {t _ {r e f}} \\left(F _ {t _ {r e f}} ^ {t} \\left(\\widehat {k} _ {r e f}\\right)\\right) - \\widehat {k} _ {r e f} \\right\\| ^ {- 1}, \\tag {10}", + "image_path": "42998f28deda41d67faf3221060d4274fa184ea6340db773f5483a9dc59a149c.jpg" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 688, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 688, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 688, + 545, + 713 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 688, + 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Our editing results on various scenes. The first image of each scene also shows the key points (circled in red or green). The car transformer sequence on the right side is provided by CoNeRF [16]. 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Editing by Key Points" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 46, + 298, + 287, + 358 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 298, + 287, + 358 + ], + "spans": [ + { + "bbox": [ + 46, + 298, + 287, + 358 + ], + "type": "text", + "content": "After training, users can easily edit the modeled scenes by feeding the network with desired key point positions. As the key points are in the 3D space, our method supports up to three-dimensional editing for each part. We also provide a graphical user interface (GUI) in Sec. 4.4." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 47, + 371, + 128, + 385 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 371, + 128, + 385 + ], + "spans": [ + { + "bbox": [ + 47, + 371, + 128, + 385 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 46, + 392, + 287, + 441 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 392, + 287, + 441 + ], + "spans": [ + { + "bbox": [ + 46, + 392, + 287, + 441 + ], + "type": "text", + "content": "We show some results after editing in Fig. 6. Some effects, like shadow and reflection changes, can also be edited correctly. And please refer to our accompanying video and supplementary materials for more results and experiments." + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 47, + 449, + 180, + 462 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 449, + 180, + 462 + ], + "spans": [ + { + "bbox": [ + 47, + 449, + 180, + 462 + ], + "type": "text", + "content": "4.1. Implementation Details" + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 46, + 468, + 288, + 589 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 468, + 288, + 589 + ], + "spans": [ + { + "bbox": [ + 46, + 468, + 288, + 589 + ], + "type": "text", + "content": "We set the weight of motion loss to " + }, + { + "bbox": [ + 46, + 468, + 288, + 589 + ], + "type": "inline_equation", + "content": "10^{-4}" + }, + { + "bbox": [ + 46, + 468, + 288, + 589 + ], + "type": "text", + "content": ", the weight of geometry loss to 0.5, and the weight of warp regularization loss to 0.1. The real data is captured in a resolution of " + }, + { + "bbox": [ + 46, + 468, + 288, + 589 + ], + "type": "inline_equation", + "content": "1280 \\times 720" + }, + { + "bbox": [ + 46, + 468, + 288, + 589 + ], + "type": "text", + "content": " and down-sampled to " + }, + { + "bbox": [ + 46, + 468, + 288, + 589 + ], + "type": "inline_equation", + "content": "320 \\times 180" + }, + { + "bbox": [ + 46, + 468, + 288, + 589 + ], + "type": "text", + "content": " for network training. Our network is trained on 4 NVIDIA GeForce RTX 3090 graphics cards, and takes around 5 hours for training with 250k iterations. Our code is based on HyperNeRF [28]. And the camera poses of input frames are solved by COLMAP [31]. More details and discussions of our method are provided in our supplementary materials." + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 47, + 598, + 132, + 611 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 598, + 132, + 611 + ], + "spans": [ + { + "bbox": [ + 47, + 598, + 132, + 611 + ], + "type": "text", + "content": "4.2. Comparisons" + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 46, + 617, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 617, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 617, + 287, + 715 + ], + "type": "text", + "content": "Here we compare our method with state-of-the-art methods HyperNeRF [28] and CoNeRF [16]. HyperNeRF is capable of topologically varying scene reconstruction but does not enable scene editing. CoNeRF allows topologically varying editing but only supports one-dimensional editing for each dynamic part, and user annotations, including masks for every part and their attribute values, are necessary for its pipeline. For example, to train a CoNeRF" + } + ] + } + ], + "index": 26 + }, + { + "bbox": [ + 304, + 280, + 545, + 327 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 280, + 545, + 327 + ], + "spans": [ + { + "bbox": [ + 304, + 280, + 545, + 327 + ], + "type": "text", + "content": "network on an opening mouth sequence, users have to select some input frames, mask the mouth regions in these frames, and set the corresponding attribute values to 1 when the mouth is open and " + }, + { + "bbox": [ + 304, + 280, + 545, + 327 + ], + "type": "inline_equation", + "content": "-1" + }, + { + "bbox": [ + 304, + 280, + 545, + 327 + ], + "type": "text", + "content": " when the mouth is closed." + } + ] + } + ], + "index": 27 + }, + { + "bbox": [ + 304, + 328, + 545, + 376 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 328, + 545, + 376 + ], + "spans": [ + { + "bbox": [ + 304, + 328, + 545, + 376 + ], + "type": "text", + "content": "Qualitative results. As our method focuses on editing, we first evaluate the editing ability of our method. We compare our method with CoNeRF, while HyperNeRF does not support editing." + } + ] + } + ], + "index": 28 + }, + { + "bbox": [ + 304, + 377, + 546, + 544 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 377, + 546, + 544 + ], + "spans": [ + { + "bbox": [ + 304, + 377, + 546, + 544 + ], + "type": "text", + "content": "We show some editing results of ours and CoNeRF in Fig. 7. Firstly, as shown in the (a) results, our method based on 3D key points enables up to three-dimensional editing, while CoNeRF fails to encode multi-dimensional dynamics by using one-dimensional attribute values. Secondly, our training stage is fully automatic without user annotations. Especially when different parts are close to each other, it becomes quite difficult for end-users to provide very accurate masks at the boundaries, which further leads to artifacts in CoNeRF as shown in (c) of Fig. 7. In contrast, ours can distinguish different parts automatically. Besides, our editing method allows users to drag the key points to their desired positions, which is more intuitive than inputting attribute values as in CoNeRF." + } + ] + } + ], + "index": 29 + }, + { + "bbox": [ + 304, + 546, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 546, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 546, + 547, + 713 + ], + "type": "text", + "content": "Quantitative results on synthetic data. Here we compare our method with HyperNeRF and CoNeRF on synthetic data. We use three data sequences synthesized by Kubric [11], and each contains 400 frames for training. Some results on one of these sequences are shown in Fig. 6. For CoNeRF training, we annotate " + }, + { + "bbox": [ + 304, + 546, + 547, + 713 + ], + "type": "inline_equation", + "content": "5\\%" + }, + { + "bbox": [ + 304, + 546, + 547, + 713 + ], + "type": "text", + "content": " frames in the training set using ground truth masks and ground truth attribute values, which are the same as the experiment settings in CoNeRF paper [16]. While for our method, we still use the optical flow from RAFT and depth maps from HyperNeRF. We do not use ground truth optical flow or ground truth depth maps, keeping these settings the same as for real data. 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MethodReconstructionEditing
PSNR ↑MS-SSIM ↑LPIPS ↓PSNR ↑MS-SSIM ↑LPIPS ↓
HyperNeRF [28]42.670.99640.0823---
CoNeRF [16]40.400.98910.094739.790.98860.0949
Ours44.350.99730.080840.010.99560.0822
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MethodPSNR ↑MS-SSIM ↑LPIPS ↓
HyperNeRF [28]30.560.98640.1281
CoNeRF [16]30.650.98690.1307
Ours30.670.98690.1314
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MethodPSNR ↑MS-SSIM ↑LPIPS ↓
Base (w/o supervision)24.600.85400.1680
+ Lmotion29.790.94290.1150
+ Lmotion + Lgeo32.590.96700.1013
+ Lmotion + Lgeo + init40.010.99560.0822
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Our final method in the last row performs the best." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "text" + }, + { + "type": "image", + "bbox": [ + 50, + 178, + 286, + 284 + ], + "blocks": [ + { + "bbox": [ + 50, + 178, + 286, + 284 + ], + "lines": [ + { + "bbox": [ + 50, + 178, + 286, + 284 + ], + "spans": [ + { + "bbox": [ + 50, + 178, + 286, + 284 + ], + "type": "image", + "image_path": "6c5787515f91a2a6123abc2e3dd0f5167590a0b6b718eac0847d8ba0a5be05b2.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 293, + 287, + 337 + ], + "lines": [ + { + "bbox": [ + 46, + 293, + 287, + 337 + ], + "spans": [ + { + "bbox": [ + 46, + 293, + 287, + 337 + ], + "type": "text", + "content": "Figure 8. Graphical user interface. The left widget shows the rendered image and the corresponding draggable key points. The right widget allows the user to change the viewpoint. Our GUI also supports drawing a trail of key points, then rendering a video." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 359, + 287, + 443 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 359, + 287, + 443 + ], + "spans": [ + { + "bbox": [ + 46, + 359, + 287, + 443 + ], + "type": "text", + "content": "tion loss and the geometry loss. We evaluate the two losses and the initialization stage in Table 3 by measuring the editing qualities on synthetic data. The base method does not use any information from optical flow or depth maps, and its modeled scene changes randomly according to key point movements, while our final method in the last row of Table 3 reaches the best performance." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 453, + 129, + 466 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 453, + 129, + 466 + ], + "spans": [ + { + "bbox": [ + 47, + 453, + 129, + 466 + ], + "type": "text", + "content": "4.4. Applications" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 472, + 287, + 592 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 472, + 287, + 592 + ], + "spans": [ + { + "bbox": [ + 46, + 472, + 287, + 592 + ], + "type": "text", + "content": "Graphical user interface. We implement a graphical user interface (GUI) for editing and novel-view synthesis, which is shown in Fig. 8 and in our accompanying video. Note that end-users actually drag the key points in the 2D interface, so we provide 1D default depth values for key points to form 3D positions, and we also allow end-users to further edit these depth values. The default depth value for a pixel position is obtained by finding " + }, + { + "bbox": [ + 46, + 472, + 287, + 592 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 46, + 472, + 287, + 592 + ], + "type": "text", + "content": " closest key point positions in the input sequence after projecting into the current view and computing their average depth." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 594, + 287, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 594, + 287, + 689 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 287, + 689 + ], + "type": "text", + "content": "Novel scenes generation. Novel scenes that are unseen in the training sequence can also be generated by our method. For example, in the piano toy sequence of Fig. 1, the input data only contains knocking on each piano key, while our method can generate sliding on the piano keys by interpolation. And our method can also combine various dynamics of different parts to create novel scenes, such as the dice cups sequence results shown in Fig. 1." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "content": "Motion transfer. Once reconstructed, our modeled scenes can be driven by motions from other sequences. We" + } + ] + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 308, + 60, + 386, + 110 + ], + "blocks": [ + { + "bbox": [ + 308, + 60, + 386, + 110 + ], + "lines": [ + { + "bbox": [ + 308, + 60, + 386, + 110 + ], + "spans": [ + { + "bbox": [ + 308, + 60, + 386, + 110 + ], + "type": "image", + "image_path": "bb81f57567b4c9bc947846a05484a1e64097bc195ad6527161c8787b94d74f78.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 120, + 545, + 142 + ], + "lines": [ + { + "bbox": [ + 305, + 120, + 545, + 142 + ], + "spans": [ + { + "bbox": [ + 305, + 120, + 545, + 142 + ], + "type": "text", + "content": "Figure 9. Editing results on a challenging scene where the selected key point is not always visible in the full sequence." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 387, + 60, + 465, + 110 + ], + "blocks": [ + { + "bbox": [ + 387, + 60, + 465, + 110 + ], + "lines": [ + { + "bbox": [ + 387, + 60, + 465, + 110 + ], + "spans": [ + { + "bbox": [ + 387, + 60, + 465, + 110 + ], + "type": "image", + "image_path": "2d3b34b49585f21ff9a9a70668a1e21aa31d980031f5442321a8ecdc3613feb0.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 466, + 60, + 545, + 110 + ], + "blocks": [ + { + "bbox": [ + 466, + 60, + 545, + 110 + ], + "lines": [ + { + "bbox": [ + 466, + 60, + 545, + 110 + ], + "spans": [ + { + "bbox": [ + 466, + 60, + 545, + 110 + ], + "type": "image", + "image_path": "6b2f9dc01d5b24951eedbe1a6c42c3a3451da2f57b441b15137fc4510b8d885d.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 163, + 545, + 211 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 163, + 545, + 211 + ], + "spans": [ + { + "bbox": [ + 305, + 163, + 545, + 211 + ], + "type": "text", + "content": "show a phonograph toy driven by a disk in our accompanying video. Optical flow is used to track a manually selected point on the source video and an affine transformation then maps the tracked point into our key point space." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 217, + 382, + 228 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 217, + 382, + 228 + ], + "spans": [ + { + "bbox": [ + 306, + 217, + 382, + 228 + ], + "type": "text", + "content": "4.5. Discussions" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 236, + 545, + 307 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 236, + 545, + 307 + ], + "spans": [ + { + "bbox": [ + 305, + 236, + 545, + 307 + ], + "type": "text", + "content": "We build our framework based on surface key points. While in some challenging sequences, there may not exist a proper surface point that is visible in all frames to become a key point. Our method can still get plausible results on these sequences, but the consistency of key points is not as good as in other scenes, as shown in Fig. 9." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 308, + 546, + 463 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 308, + 546, + 463 + ], + "spans": [ + { + "bbox": [ + 304, + 308, + 546, + 463 + ], + "type": "text", + "content": "Limitations. We assume that the dynamics of a canonical location mainly depend on one key point. If the scene becomes very complex that does not satisfy this assumption (e.g., a dancing human), our method may fail. Also, it's hard for our method to pick out surface key points for semitransparent objects like smoke. Extrapolation cannot be performed well for our method when the key points are dragged too far away from their positions in the training sequence. Our method supports multi-dimensional editing, but if the captured objects only have one-dimensional dynamics (e.g., drawer only moves in 1D), our method can only generate one-dimensional dynamics. Besides, our method cannot work well when RAFT or HyperNeRF fails." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 473, + 383, + 485 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 473, + 383, + 485 + ], + "spans": [ + { + "bbox": [ + 306, + 473, + 383, + 485 + ], + "type": "text", + "content": "5. Conclusions" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 493, + 545, + 635 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 493, + 545, + 635 + ], + "spans": [ + { + "bbox": [ + 304, + 493, + 545, + 635 + ], + "type": "text", + "content": "We propose EditableNeRF, editable topologically varying neural radiance fields that enable end-users to easily edit dynamic scenes. The key to achieving this is to build our framework by leveraging weighted key points to model topologically varying dynamics, which further achieves intuitive multi-dimensional editing. And a scene analysis method that can measure the dynamics in the scene is also proposed to detect and further initialize these key points. Our method is trained fully automatically using a single-view input sequence and can be easily used by end-users, bringing new applications for editable photo-realistic novel-view synthesis." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 636, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 636, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 636, + 545, + 713 + ], + "type": "text", + "content": "Acknowledgements. This work was supported by the National Key R&D Program of China (2018YFA0704000), Beijing Natural Science Foundation (M22024), the NSFC (No.62021002), and the Key Research and Development Project of Tibet Autonomous Region (XZ202101ZY0019G). This work was also supported by THUIBCS, Tsinghua University, and BLBCI, Beijing Municipal Education Commission. Feng Xu is the corresponding author." + } + ] + } + ], + "index": 19 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "text", + "content": "8324" + } + ] + } + ], + "index": 20 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 92, + 288, + 712 + ], + "type": "list", + "angle": 0, + "index": 12, + "blocks": [ + { + "bbox": [ + 53, + 92, + 287, + 147 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 92, + 287, + 147 + ], + "spans": [ + { + "bbox": [ + 53, + 92, + 287, + 147 + ], + "type": "text", + "content": "[1] Benjamin Attal, Eliot Laidlaw, Aaron Gokaslan, Changil Kim, Christian Richardt, James Tompkin, and Matthew O'Toole. 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The IP protection associated with deep models has been receiving increasing attentions in recent years. Passport-based method, which replaces normalization layers with passport layers, has been one of the few protection solutions that are claimed to be secure against advanced attacks. In this work, we tackle the issue of evaluating the security of passport-based IP protection methods. We propose a novel and effective ambiguity attack against passport-based method, capable of successfully forging multiple valid passports with a small training dataset. This is accomplished by inserting a specially designed accessory block ahead of the passport parameters. Using less than $10\\%$ of training data, with the forged passport, the model exhibits almost indistinguishable performance difference (less than $2\\%$ ) compared with that of the authorized passport. In addition, it is shown that our attack strategy can be readily generalized to attack other IP protection methods based on watermark embedding. Directions for potential remedy solutions are also given.", + "bbox": [ + 75, + 383, + 472, + 702 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 729, + 209, + 744 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "With the geometric growth of computing power of computational devices in recent decades, there have emerged many deep learning applications that have contributed to the human world such as super-resolution reconstruction [7, 9, 30], image inpainting [31, 34, 35] and forgery detection [32]. It usually costs many resources to develop new DNN models and developers will not tolerate the act of theft of their IP. The IP protection problem of deep models be", + "bbox": [ + 75, + 755, + 468, + 878 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "comes more severe with the birth of Machine Learning as a Service (MLaaS) [26]. Preventing the infringement behavior of deep models now emerges as a necessary concern when developing new algorithms and systems.", + "bbox": [ + 500, + 353, + 890, + 412 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Model watermark [20, 25, 27, 28, 37] has been a popular method to protect the IP of DNN models. In the embedding process, the owners embed the secret signatures (watermarks), and then in the verification process, they can claim their ownership to the model by matching the extracted signatures with the original versions. The existing model watermark methods can be roughly divided into two categories [10, 11]: feature-based and trigger-based methods. Specifically, feature-based methods [4, 8, 24, 29] applied a regularizer to embed the secret watermark into the activation functions or model weights. Uchida et al. [29] proposed to use a regularizer to embed a watermark into the model weights. Darvish et al. [8] embedded the fingerprints in the Probability Density Function of trainable weights instead. Aramoon et al. [3] inserted the signature into the gradient of the cross-entropy loss function with respect to the inputs. In contrast, trigger-based methods make the output target respond to specific inputs. Along this line, Adi et al. [1] used the backdoor attack as a means to watermark the model. Merrer et al. [18] designed a zero-bit watermarking algorithm that uses adversarial samples as watermarks to claim the ownership. Zhang et al. [39] applied watermarks to images and then trained the network to output target labels when input images carry these watermarks.", + "bbox": [ + 496, + 415, + 892, + 777 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Despite the strength in retaining ownership of DNN models, most existing model watermark methods are shown to be vulnerable to the so-called ambiguity attack, in which the attacker manages to cast doubts on the ownership verification by crafting counterfeit (forged) watermarks [11]. Recently, Fan et al. [10] first designed a series of ambiguity attacks, which are effective in attacking DNN watermark methods. It was stated that for conventional watermark", + "bbox": [ + 496, + 779, + 893, + 900 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "† Corresponding author.", + "bbox": [ + 94, + 886, + 220, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "8123", + "bbox": [ + 480, + 944, + 514, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "methods, a counterfeit watermark can be forged as along as the model performance is independent of the signature [11]. Following this proposition, Fan et al. designed a passport layer through which the functionality of the model is controlled by the signature called passport. However, Fan et al. encountered a heavy performance drop when batch normalization layers exist. To solve this problem, Zhang et al. [38] added learnable affine transformations to the scale and bias factors. It was claimed that an attacker cannot find a substitute passport that maintains the model performance, which ensures the security of these passport-based methods against existing ambiguity attacks.", + "bbox": [ + 75, + 90, + 472, + 271 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In this work, we aim to design an advanced ambiguity attack to the passport-based method, capable of generating valid substitute passports with only a small number of data. Here, valid substitute passports are defined as those leading to an indistinguishable model performance, but sufficiently different from the original authorized passports. Clearly, with such valid substitute passports, an attacker can claim the ownership of the model. To this end, we first experimentally justify the existence of multiple valid substitute passports. Noticing the fact that it is easy to localize the passport layers, we then propose our ambiguity attack by replacing passport layers with our designed two types of structures, namely Individual Expanded Residual Block (IERB) and Collective Expanded Residual Block (CERB). Both structures are built in a way to encourage the significant changes of the parameters in the passport layers during the training, which could help us search for valid substitute passports. Benefiting from these two structures and assisting with a small amount training data, we can obtain valid substitute passports, and hence, defeat the passport-based methods which are the only type of method claimed to be immune to existing ambiguity attacks.", + "bbox": [ + 75, + 272, + 472, + 604 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Our major contributions can be summarized as follows:", + "bbox": [ + 96, + 604, + 462, + 618 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- We propose a novel and effective ambiguity attack against the passport-based IP protection schemes. With less than $10\\%$ of training data, our ambiguity attack on passport-layer protected model can restore the functionality of the model with a less than $2\\%$ performance gap from the original accuracy.", + "- We design two novel structures for replacing the passport layers, based on the multi-layer perceptron (MLP) and skip connection to assist with our ambiguity attack for searching valid substitute passports with a small amount of training data.", + "- Experiments on both overlapping (attacker's training dataset is part of the original training dataset) and non-overlapping datasets (attacker's dataset and the original one come from the same source but no overlap exists), and on different network structures have proved the effectiveness of our ambiguity attack.", + "- Our attack method can be readily generalized to attack other DNN watermark methods [8, 21, 29]." + ], + "bbox": [ + 96, + 618, + 467, + 900 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Works", + "text_level": 1, + "bbox": [ + 500, + 89, + 650, + 106 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "DNN watermark methods have been popular solutions for DNN model IP protection. However, these techniques might still be vulnerable to flagrant infringement from notorious adversaries. In this section, we review the two types of representative attack methods, namely, removal attack [2, 5, 6, 14, 22, 33] and ambiguity attack [10, 11, 38], along with the passport-based method attempting to defend against ambiguity attacks [11].", + "bbox": [ + 496, + 118, + 890, + 239 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Removal Attack: This type of attack tries to remove the watermark from the protected model, malfunctioning the ownership verification mechanism. Along this line, many fine-tuning based methods have been proposed. Chen et al. [5] combined a redesigned elastic weight consolidation algorithm and unlabeled data augmentation to achieve unified model watermark removal with limited data. Guo et al. [14] used a dataset transformation method called PST (Pattern embedding and Spatial-level Transformation) to preprocess the data before fine-tuning. Chen et al. [6] utilized auxiliary unlabeled data to decrease the amount of labeled training data required for effective watermark removal. Aiken et al. [2] provided a three-stage scheme to remove backdoor-based watermarks by exploiting another trigger-free dataset from the same domain. Liu et al. [22] designed a framework to remove backdoor-based watermarks, in which a data augmentation was proposed to imitate the behavior of the backdoor triggers. Yan et al. [33] attempted to break the passport-based method by scaling the neurons and flipping the signs of parameters. However, this method assumed that the authorized passports are available to the attacker, which is not realistic in practice. Also, these aforementioned attack methods only enable the attackers to remove the watermarks, while unable to claim the ownership.", + "bbox": [ + 496, + 243, + 892, + 604 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Ambiguity Attack: Another more threatening attack is the ambiguity attack, where the attacker can forge another substitute watermark to claim the model ownership. The concept of ambiguity attack originally appeared in image watermark community [19, 23], and recently has been extended to the DNN watermark methods. The pioneering work was conducted by Fan et al. in [10], which pointed out the vulnerability of Uchida's watermark method [29] under the ambiguity attack. They also showed that the same weakness of Adi's DNN watermark method [1] exists, by proving that another trigger can be optimized exclusively to cause the same model response as the original one.", + "bbox": [ + 496, + 609, + 890, + 790 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Passport-based method: Passport-based method was originally proposed by Fan et al. [11] as a remedy enabling DNN watermark methods to defeat the ambiguity attack. This is achieved by replacing the traditional normalization layer with the so-called passport layer, whose difference mainly lies in how the affine factors are obtained. In passport layer, the scale factor $\\gamma$ and bias factor $\\beta$ are computed", + "bbox": [ + 496, + 795, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "8124", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "with the passport as follows:", + "bbox": [ + 76, + 90, + 269, + 104 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\gamma = \\operatorname {A v g} \\left(\\mathbf {W} _ {\\text {c o n v}} * \\mathbf {s} _ {\\gamma}\\right), \\beta = \\operatorname {A v g} \\left(\\mathbf {W} _ {\\text {c o n v}} * \\mathbf {s} _ {\\beta}\\right), \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 102, + 116, + 468, + 133 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\mathbf{s} = \\{\\mathbf{s}_{\\gamma},\\mathbf{s}_{\\beta}\\}$ is called the passport, $\\mathbf{W}_{conv}$ is the convolutional layer weight before this layer, and $Avg(\\cdot)$ represents the average pooling function.", + "bbox": [ + 76, + 142, + 468, + 186 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "To embed the passport $s$ into the model, the network $\\mathbb{N}_p$ is optimized on the training set $\\mathcal{D} = \\{(x_i,y_i)\\}_{i = 1}^N$ , where $x_{i}$ is the input and $y_{i}$ is the corresponding label, using the following loss:", + "bbox": [ + 76, + 188, + 468, + 251 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} = \\mathcal {L} _ {r} \\left(\\mathbb {N} _ {p} [ \\mathbf {W}, \\mathbf {s} ] \\left(x _ {i}, y _ {i}\\right)\\right) + \\alpha \\mathcal {L} _ {\\text {s i g n}} (\\operatorname {s g n} (\\gamma), \\mathbf {b}), \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 99, + 262, + 468, + 279 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\mathbb{N}_p[\\mathbf{W},\\mathbf{s}]$ denotes the model $\\mathbb{N}$ with the weight $\\mathbf{W}$ and the passport s. The first term $\\mathcal{L}_r(\\cdot)$ is the classification loss, and the second term $\\mathcal{L}_{sign}(\\cdot)$ is a sign loss regularization constraining the sign sequence of scale factors to be a predefined $C$ -bit signature $\\mathbf{b} = \\{b_1,\\dots,b_C\\} \\in \\{-1,1\\} ^C$ Here, $\\mathrm{sgn}(\\cdot)$ is the sign function.", + "bbox": [ + 76, + 287, + 468, + 378 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Denote $\\mathcal{Q}(\\mathbb{N}_p[\\mathbf{W},\\mathbf{s}])$ as the inference performance of model $\\mathbb{N}_p$ with the passport s. The verification process mainly relies on the assumption that the performance $\\mathcal{Q}(\\mathbb{N}_p[\\mathbf{W},\\mathbf{s}])$ seriously deteriorates when an unauthorized passport is presented. Hence, the model ownership using passport-based method is conducted by matching the signs of scale factors $\\mathrm{sgn}(\\gamma)$ with the predefined signature b and checking the DNN model inference performance.", + "bbox": [ + 76, + 378, + 468, + 500 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Proposed Ambiguity Attack", + "text_level": 1, + "bbox": [ + 76, + 513, + 334, + 530 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Though the passport-based methods [11, 38] have been claimed to be immune to the existing ambiguity attacks [10], they do not preclude the existence of more advanced ambiguity attacks. In this work, we cast doubt on the security of the passport-based methods, and propose a simple yet effective ambiguity attack, capable of crafting valid substitute passports. Before diving into the detailed design of our ambiguity attack, let us clarify our attack goal and the information assumed to be available to the attacker.", + "bbox": [ + 76, + 537, + 468, + 672 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Attack Goal: Essentially, the attack goal is to generate substitute passport $\\mathbf{s}_t$ , with which the model $\\mathbb{N}_p[\\mathbf{W},\\mathbf{s}_t]$ has indistinguishable performance with that of applying the authorized passport $\\mathbf{s}_o$ , i.e., $\\mathcal{Q}(\\mathbb{N}_p[\\mathbf{W},\\mathbf{s}_o])$ . Specifically, following the ambiguity attack setting in [11], we assume that the attacker has access to the model weights $\\mathbf{W}$ except from the passport. Note that, without the passport, the affine factors are missing in the normalization layer, through which the attacker can easily localize the passport layers. Also, the attacker is allowed to have a small number of training data, namely, $\\mathcal{D}_s = \\{(\\hat{x}_i,\\hat{y}_i)\\}_{i = 1}^n$ , where $n < N$ . Formally, we have the following Definition 1, explicitly explaining the successful ambiguity attack on passport-based method.", + "bbox": [ + 76, + 674, + 468, + 869 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Definition 1: An ambiguity attack on passport layer protected model is successful, if", + "bbox": [ + 76, + 869, + 467, + 898 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/ca37740f9804932d5ba28bd3b64fe307437b2f7bc1050b439db8f9de990b62e2.jpg", + "image_caption": [ + "(a)" + ], + "image_footnote": [], + "bbox": [ + 506, + 93, + 679, + 191 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/23fc951b0b62eb96324a24893ccc4e6abcb8a4b9ffc4155a68b9dedeece37028.jpg", + "image_caption": [ + "(b)", + "Figure 1. Valid substitute passports obtained by initializing scale factors with different signs from the authorized $\\mathbf{s}_o$ and retraining. Horizontal axis denotes the number of different signs from $\\mathbf{s}_o$ ." + ], + "image_footnote": [], + "bbox": [ + 700, + 93, + 880, + 191 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "I) DNN inference accuracy with the substitute passport $\\mathbf{s}_t$ is close to that with the authorized passport $\\mathbf{s}_o$ , i.e.,", + "bbox": [ + 514, + 277, + 890, + 309 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\left| \\mathcal {Q} \\left(\\mathbb {N} _ {p} [ \\mathbf {W}, \\mathbf {s} _ {t} ]\\right) - \\mathcal {Q} \\left(\\mathbb {N} _ {p} [ \\mathbf {W}, \\mathbf {s} _ {o} ]\\right) \\right| < \\epsilon . \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 584, + 318, + 890, + 343 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "II) Dissimilarity between the substitute passport $\\mathbf{s}_t$ and the authorized $\\mathbf{s}_o$ should be large enough, i.e.:", + "bbox": [ + 511, + 354, + 890, + 385 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\left| \\mathbf {s} _ {t} - \\mathbf {s} _ {o} \\right| > \\delta . \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 665, + 393, + 890, + 420 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Before presenting the details of our ambiguity attack, let us first justify the existence of multiple valid substitute passports satisfying the conditions given in (3) and (4). To this end, we here adopt an experimental approach and leave the theoretical justification in our future work. Assume now that we are given the complete training data $\\mathcal{D}$ , though this large amount of data are not required when launching the attack. We initialize scale factors with different combinations of $\\{+1, -1\\}$ and fine-tune the model based on $\\mathcal{D}$ . In Fig. 1, we give the experimental results on ResNet18 trained on the CIFAR10 dataset, where the passport layer is placed after the first convolutional layer and the length of the scale factor is 64. The model with the authorized passport leads to an inference performance of $94.70\\%$ . As can be seen, the accuracy of the models after retraining is still close to $94.70\\%$ (red line, see Fig. 1(a)). More importantly, the signs of retained affine factors only have low coincidence rate (around $60\\%$ , see Fig. 1(b)) with the original ones, implying that retained affine factors differ significantly from the authorized affine factors. Therefore, these retrained affine factors could simultaneously satisfy the conditions (3) and (4), and hence are valid substitute passports.", + "bbox": [ + 496, + 431, + 892, + 763 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Though the existence of substitute passports has been justified, the difficulty of directly optimizing a passport remains unsolved for very limited number of training data. Clearly, in practical attacks, the attacker is only allowed to have access to very limited data; otherwise, he can retrain the entire model. Fan et al. [11] ascribed the robustness of passport-based method against fine-tuning the scale factors to the lazy-to-flip property, with which the scale factors are rarely updated to cross the zero during the training.", + "bbox": [ + 496, + 763, + 890, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "8125", + "bbox": [ + 480, + 944, + 514, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/0d6c6dec4ddb15efac8c1f92f3f3c693602be9671a54bc0f6235c27e57149806.jpg", + "image_caption": [ + "Figure 2. The structures of the ResNet18 with passport layer and our designed CERB/IERB structures." + ], + "image_footnote": [], + "bbox": [ + 127, + 92, + 834, + 402 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "To overcome the lazy-to-flip property for the scale factors, we attempt to add a trainable block after it, encouraging scale factors to go across the zeros by non-linear transformations. For efficiency, we adopt MLP for designing the trainable blocks. Following this line, we design two structures namely IERB and CERB to replace the passport layer.", + "bbox": [ + 75, + 441, + 468, + 532 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The overall structure: Motivated by the above observations, we now design a novel ambiguity attack on passport-based method. The overall structure is given in Fig. 2, where we use the ResNet18 embedded with passport layers for the illustration. Specifically, the protected ResNet18 is comprised of multiple residual blocks, each containing several convolutional layers followed by the passport layer. As aforementioned, the locations of the passport layers can be easily determined. We can then insert either IERB or CERB structure into these locations. In our structure, the scale factor $\\gamma$ is the output of the IERB/CERB. For the bias factor $\\beta$ , we do not add our new structure; but instead we optimize it directly. We are now ready to introduce the details of CERB and IERB structures. After that, we will give the complete algorithm of our ambiguity attack.", + "bbox": [ + 75, + 536, + 470, + 762 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.1. Individually Expanded Residual Block (IERB)", + "text_level": 1, + "bbox": [ + 76, + 771, + 468, + 787 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In this subsection, we present the details of the IERB block. As showed in Fig. 3 (a), the $i$ -th scale factor $\\gamma_i^l$ in the $l$ -th passport layer is transformed by a Two-Layer Perceptron (TLP) with FC-LeakyReLU-FC structure where the FC refers to fully connected layer. For the simplicity of notations, we omit the superscript in $\\gamma_i^l$ in the sequel. The output of this TLP is then used for the affine transformation", + "bbox": [ + 75, + 795, + 470, + 900 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/f9d4362759c2f927f6f8b080aaba8bae7619506c3817638ede184111cc751187.jpg", + "image_caption": [ + "(a)", + "Figure 3. Details of (a) IERB and (b) CERB." + ], + "image_footnote": [], + "bbox": [ + 516, + 443, + 710, + 630 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/7fff39d03ef4a583f4b1402d23e3e7649ce6e1c4eab05046a73165ce52161342.jpg", + "image_caption": [ + "(b)" + ], + "image_footnote": [], + "bbox": [ + 730, + 443, + 870, + 628 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "later. The first linear layer $FC_{1\\rightarrow h}$ with learnable parameters maps the scale factor into a $h$ -dimensional vector, while the second linear layer $FC_{h\\rightarrow 1}$ maps the dimension back to 1, where $h$ is the hidden layer size. A larger $h$ brings a larger optimization space in the hidden layer; but could add burden to the training process. We empirically set $h = 10$ striking a good balance between these two factors. In addition, a skip connection is added aside with the TLP structure to facilitate the back-propagation. Benefiting from the expanded parameter space brought by the TLP structure, the output scale factor would more likely go across the zero during the updating. This helps the attacker search for an appropriate $\\mathbf{s}_t$ satisfying (4).", + "bbox": [ + 496, + 688, + 890, + 883 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Let $\\{\\mathbf{W}_{i,j},\\mathbf{b}_{i,j}\\}$ be the weights of the $j$ -th linear", + "bbox": [ + 517, + 885, + 890, + 901 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "8126", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "layer connected after the $i$ -th scale factor, where $i \\in \\{1,2,\\dots,C\\}$ and $j \\in \\{1,2\\}$ . In IERB, the output of the first linear layer taking the $i$ -th scale factor as input is:", + "bbox": [ + 76, + 90, + 468, + 136 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\gamma_ {i} ^ {\\prime} = \\mathbf {W} _ {i, 1} ^ {T} * \\gamma_ {i} + \\mathbf {b} _ {i, 1} ^ {T}, \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 192, + 138, + 468, + 157 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $*$ denotes the matrix multiplication operator. After the activation function LeakyReLU, the output of the second linear layer with the shortcut can be expressed as:", + "bbox": [ + 75, + 162, + 468, + 208 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\gamma_ {i} ^ {\\prime \\prime} = \\mathbf {W} _ {i, 2} ^ {T} * \\left(L R e L U \\left(\\gamma_ {i} ^ {\\prime}\\right)\\right) + \\mathbf {b} _ {i, 2} ^ {T} + \\gamma_ {i}. \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 135, + 210, + 468, + 229 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.2. Collective Expanded Residual Block (CERB)", + "text_level": 1, + "bbox": [ + 76, + 236, + 457, + 253 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The IERB discussed above handles each scale factor individually, but may ignore the inter-channel relationship among scale factors. Instead of using isolated propagation paths for each scale factor, we now attempt to enhance the inter-channel relationship and optimize the scale factors in a collective manner. As can be observed from Fig. 3 (b), we choose to use a unified TLP structure to deal with all the $C$ scale factors as a whole. The output of the TLP structure is then summed with the input scale factors to get the updated ones. Different from the IERB, each activation in the hidden layer is now related to all the input scale factors, and the fully connected structure ensures the exploitation of the inter-channel information. Mathematically, the output scale factors can be computed by:", + "bbox": [ + 75, + 260, + 472, + 472 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\gamma^ {\\prime \\prime} = \\left(\\mathbf {W} _ {2} ^ {T} * \\left(L R e L U \\left(\\mathbf {W} _ {1} ^ {T} * \\gamma + \\mathbf {b} _ {1} ^ {T}\\right)\\right) + \\mathbf {b} _ {2} ^ {T}\\right) + \\gamma , (7)\n$$\n", + "text_format": "latex", + "bbox": [ + 84, + 478, + 468, + 500 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\mathbf{W}_1$ and $\\mathbf{W}_2$ represent the parameters in the first and second linear layers. Here we set the hidden layer size to be $C / 8$ , where $C$ is the number of channels in this layer.", + "bbox": [ + 76, + 508, + 468, + 555 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.3. Algorithm of Our Ambiguity Attack", + "text_level": 1, + "bbox": [ + 76, + 561, + 393, + 579 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "With these newly proposed structures, we can summarize our ambiguity attack strategy on the passport-based method in Algorithm 1. For simplicity, we use $\\mathbf{W}_{\\gamma}$ to represent all the parameters in IERB or CERB. Let us briefly explain our workflow for better understanding. In Algorithm 1, lines $1\\sim 4$ are devoted to the model loading, normalization layer substitution, CERB/IERB insertion, and parameter initialization. The $\\gamma, \\beta$ and $\\mathbf{W}_{\\gamma}$ are then updated in lines $5\\sim 14$ using the gradients with respect to each parameter by back-propagating the cross entropy loss:", + "bbox": [ + 75, + 585, + 468, + 737 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\gamma = \\gamma - \\nabla_ {\\gamma} l o s s,\n$$\n", + "text_format": "latex", + "bbox": [ + 205, + 742, + 323, + 758 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\beta = \\beta - \\nabla_ {\\beta} \\text {l o s s}, \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 207, + 760, + 468, + 776 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {W} _ {\\gamma} = \\mathbf {W} _ {\\gamma} - \\nabla_ {\\mathbf {W} _ {\\gamma}} l o s s.\n$$\n", + "text_format": "latex", + "bbox": [ + 189, + 779, + 356, + 796 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Eventually, the algorithm outputs the substitute scale and bias factors $\\gamma''$ and $\\beta$ .", + "bbox": [ + 76, + 801, + 468, + 830 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Experimental Results", + "text_level": 1, + "bbox": [ + 76, + 844, + 282, + 861 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In this section, we evaluate the effectiveness of our ambiguity attack from different perspectives. Before present", + "bbox": [ + 76, + 869, + 468, + 901 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Algorithm 1 Proposed Ambiguity Attack", + "bbox": [ + 500, + 90, + 777, + 106 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Input: Protected network $\\mathbb{N}_p[\\mathbf{W}]$ with passport layers excluded; training dataset $\\mathcal{D}_s = \\{(\\hat{x}_i,\\hat{y}_i)\\}_{i = 1}^n$ ; checkpoint state_dict; training epoch $M$", + "bbox": [ + 500, + 108, + 890, + 152 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Output: substitute scale and bias factors $\\gamma^{\\prime \\prime}$ $\\beta$", + "bbox": [ + 500, + 152, + 813, + 167 + ], + "page_idx": 4 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "1: Use normalization layers in the locations of the passport layers.", + "2: Insert CERB/IERB structures after the scale factors of these normalization layers.", + "3: Load weight $\\mathbf{W}$ of $\\mathbb{N}_p[\\mathbf{W}]$ from state_dict.", + "4: Initialize normalization layer weights $\\gamma$ and $\\beta$ with 1 and 0, respectively." + ], + "bbox": [ + 508, + 171, + 890, + 276 + ], + "page_idx": 4 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "5: for epoch $= 1$ to $M$ do", + "6: for minibatch $(\\hat{x}_i,\\hat{y}_i)\\subset \\mathcal{D}_s$ do", + "7: for each normalization layer with IERB/CERB do", + "8: $\\gamma^{\\prime \\prime} = \\mathrm{CERB / IERB}(\\gamma ,\\mathbf{W}_{\\gamma}).$ $\\triangleright$ Eq. (5/7).", + "9: Use $\\gamma''$ and $\\beta$ for affine transformation in normalization layer.", + "10: end for", + "11: loss=cross_entropy $(\\mathbb{N}_p[\\mathbf{W}](\\hat{x}_i),\\hat{y}_i)$", + "12: Update $\\gamma, \\beta$ and $\\mathbf{W}_{\\gamma} \\triangleright$ Eq. (8).", + "13: end for", + "14: end for" + ], + "bbox": [ + 506, + 277, + 890, + 441 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "ing the detailed results, let us clarify the experimental settings including the datasets, target models, and the evaluation metrics.", + "bbox": [ + 496, + 465, + 890, + 508 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Dataset: Four image classification datasets: CIFAR10 [16], CIFAR100 [16], Caltech-101 [12], and Caltech-256 [13], are selected. Unless stated, the dataset used in the attack process only accounts for $10\\%$ at maximum of the full training set and does not overlap with the test set.", + "bbox": [ + 496, + 511, + 890, + 585 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "DNN architectures: Three DNN architectures, AlexNet [17], ResNet-18 [15] and Wide-Residual Network [36] are used in our experiments, following the tradition of passport-based works [10, 11, 38]. To demonstrate that our attack strategy remains effective for different number of passport layers, we perform the experiments on AlexNet and ResNet18, with at most 5 and 18 passport layers, respectively. For notation convenience, we use a suffix to determine the indices of the passport layers. For instance, AlexNet-4 denotes the AlexNet with the first 4 normalization layers replaced by the passport layers, and AlexNet-last3 represents the version in which the last 3 normalization layers are replaced by the passport layers.", + "bbox": [ + 496, + 587, + 890, + 782 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Evaluation metrics: Prediction accuracy (ACC) of the model is a natural choice for evaluating the attack effectiveness, since a successfully forged passport is expected to achieve similar performance as an authorized passport (see Definition 1). Another metric considered is the bit dissimilarity rate (BDR) of the signature derived from the forged passport, with respect to the authorized one. Specifically, let $\\gamma'$ and $\\gamma^o$ be the forged and authorized scale factors, re", + "bbox": [ + 496, + 782, + 890, + 904 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "8127", + "bbox": [ + 480, + 944, + 514, + 955 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "spectively. Note that the sign of $\\gamma^o$ is used as the signature. The BDR is then defined as:", + "bbox": [ + 76, + 90, + 468, + 119 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\nB D R = \\frac {1}{C} \\sum_ {i = 1} ^ {C} \\mathcal {I} \\left[ \\operatorname {s g n} \\left(\\gamma_ {i} ^ {\\prime}\\right) \\neq \\operatorname {s g n} \\left(\\gamma_ {i} ^ {o}\\right) \\right], \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 138, + 125, + 468, + 167 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where the indicator function $\\mathcal{I}[\\cdot]$ returns 1 when the condition is true and 0 otherwise. A high BDR also implies the large dissimilarity with the authorized passport, which in turn indicates a better performance of the ambiguity attack.", + "bbox": [ + 76, + 172, + 468, + 234 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.1. Attack performance using IERB/CERB", + "text_level": 1, + "bbox": [ + 76, + 242, + 416, + 258 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We now give the details on the effectiveness of our ambiguity attack by replacing the passport layers of the protected model with our proposed IERB or CERB blocks. All protected models with passport layers are trained over the training dataset of CIFAR10. We randomly select $10\\%$ of examples from this dataset for launching the ambiguity attack, i.e., training the IERB or CERB blocks.", + "bbox": [ + 75, + 266, + 470, + 371 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "The attack results on AlexNet and ResNet18 are reported in Table 1. Since our ambiguity attack is the first one attacking passport-based methods, there are no comparative algorithms available so far. It can be seen that, by using the proposed CERB, our ambiguity attack is capable of achieving high ACC and BDR values for all the settings. Specifically, for AlexNet, the ACC gap is less than $1\\%$ , compared with the case of the authorized passport. Also, the BDR can be as large as $80.30\\%$ . For the more complex ResNet18, similar observations can be obtained, where the ACC gap is still less than $3\\%$ , and the BDR could approach $50\\%$ . We even encounter several cases (AlexNet-1 and ResNet18-1), in which the attacked models perform even better than the original ones. These results imply that our proposed ambiguity attack is successful in finding the valid substitute passports with a small number of training data.", + "bbox": [ + 75, + 371, + 468, + 613 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "As a comparison, we also present the results of the ambiguity attack with the IERB structure. It can be observed that this variant attack is still somewhat effective with reasonably high ACC and BDR values; but the attack performance is much inferior to the attack with CERB, especially when there are many passport layers. We attribute this phenomenon to the capability of CERB in exploiting the interchannel relationship. For IERB, it is likely to optimize towards the original sign of the scale factor, which naturally results in similar signatures (small BDR) to the original passports. In CERB, however, the collective optimization mechanism explores more possibly optimal pairs of the sign of scale factors, potentially leading to larger BDR of signature and higher ACC.", + "bbox": [ + 75, + 614, + 468, + 824 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "To further show the effectiveness of our proposed attack strategy, we now compare the attack performance of the models with and without CERB/IERB structures. As will be clear soon, directly updating the affine factors cannot retrieve valid passports, especially when the available data is", + "bbox": [ + 75, + 824, + 468, + 902 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/6c46aa20e1ef287654b1da29e94d97256a89e3c2a4f4e2992c58e27f187550bf.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
NameOriginal ACCIERBCERB
ACCBDRACCBDR
AlexNet-190.2089.5416.0090.2624.67
AlexNet-288.7386.019.7688.3746.10
AlexNet-390.0887.4812.9688.9541.41
AlexNet-488.2586.5216.9688.0179.80
AlexNet-588.8882.4927.9588.2080.30
ResNet18-194.8993.853.1394.9425.00
ResNet18-394.8093.4626.5794.2250.0
ResNet18-494.6792.9224.6194.0933.98
ResNet18-594.3990.0426.0593.7534.69
ResNet18-694.4593.4830.1392.4443.31
ResNet18-894.4191.2244.0492.6647.87
ResNet18-1094.3088.9644.5992.8738.55
ResNet18-1294.9687.3640.9092.3437.19
ResNet18-1494.6886.6335.4892.1843.04
ResNet18-1894.8183.9236.5292.1146.79
", + "bbox": [ + 522, + 89, + 874, + 327 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/c52e18a089e61483de0e0f04e376f4d4e0aa34d802365ee60421a60c23526454.jpg", + "table_caption": [ + "Table 1. ACC (\\%) and BDR (\\%) performance of ambiguity attacks using IERB/CERB structure for AlexNet and ResNet18 with different number of passport layers on CIFAR10." + ], + "table_footnote": [], + "table_body": "
Dataset-NetOriginalDataSizePlainCERBIERB
CIFAR10 \nAlexNet90.205000 (10%)83.6288.1687.30
2500 (5%)73.8286.7078.91
2000 (4%)73.4886.3076.73
1500 (3%)72.0986.7871.38
1000 (2%)64.8284.2263.71
CIFAR100 \nResNet1875.055000 (10%)70.7373.2670.51
3000 (6%)69.1472.2669.35
2000 (4%)62.8171.4268.89
1500 (3%)62.8671.6968.50
1000 (2%)53.9170.1268.44
", + "bbox": [ + 517, + 385, + 879, + 536 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/a79e1d3b5b23ae567d64689174b3e40be9008b6cf7c5d3c1d67ed8bb052f9497.jpg", + "table_caption": [ + "Table 2. ACC (%) comparison with Plain attack for CIFAR10-AlexNet and CIFAR100-ResNet18." + ], + "table_footnote": [], + "table_body": "
DatasetPassport LayerOriginalPlainCERBIERB
Caltech101Last 3 layers72.5471.0172.2667.79
Last 5 layers68.3059.8966.7860.73
Last 8 layers72.4959.9469.3859.32
Last 10 layers70.9057.1766.8957.06
Caltech256Last 5 layers54.3438.6452.2351.02
Last 7 layers53.9536.7249.5549.36
Last 10 layers55.4324.9347.8544.19
", + "bbox": [ + 503, + 585, + 879, + 695 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 3. ACC (%) comparison with Plain attack on Caltech-101 and Caltech-256, where $10\\%$ training data are used. Here the network is fixed to be ResNet18.", + "bbox": [ + 498, + 704, + 890, + 747 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "rather limited. To this end, we embed 5 passport layers in AlexNet and 10 passport layers in ResNet18, and train them on CIFAR10 and CIFAR100, respectively. Let Plain attack refer to the case without using our proposed structures. Table 2 gives the ACC results of Plain attack and our ambiguity attacks using CERB and IERB. For the simple AlexNet, the performance of our attack with CERB overwhelms that of Plain attack, and the performance gain becomes more significant when smaller number of training data is avail", + "bbox": [ + 496, + 763, + 890, + 902 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "8128", + "bbox": [ + 480, + 944, + 514, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/6bb3f42f3e3e249da86e0a0f510af87a4c622ecf1f4efe569ff7543bfcdbcde1.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
DataSizeIERBCERB
ACCBDRACCBDR
10000 (25%)90.4740.2492.1791.77
5000 (12.5%)88.2642.8291.0592.82
4000 (10%)87.4347.7190.0792.61
3000 (7.5%)86.3048.3489.4993.65
2500 (6.25%)86.2348.9687.0093.44
2000 (5%)85.2649.2085.6793.44
", + "bbox": [ + 120, + 88, + 431, + 213 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 4. ACC (%) and BDR (%) performance of ambiguity attacks with IERB and CERB using non-overlapping CIFAR10 dataset.", + "bbox": [ + 76, + 223, + 468, + 251 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "able. For instance, when $2\\%$ training data are used, the ACC gap is almost $20\\%$ . Such a property is very valuable in practice, as attacks are usually launched with very limited number of data; otherwise, re-training an entire model could be feasible as well. Also, for this simple AlexNet, our attack with IERB has similar performance with Plain attack. For the relatively large network ResNet18, our attack with CERB achieves $4.93\\%$ ACC drop, compared with the original accuracy, when only $2\\%$ training data are used. This drop shrinks to $1.79\\%$ when $10\\%$ training data are available. Compared with Plain attack, the ACC gains of our attack with CERB can be as large as $16.21\\%$ . In addition, it is noted that our attack with IERB becomes much superior to Plain attack, when very limited training data are adopted; the ACC gain can be up to $14.53\\%$ . More results on more complicated datasets including Caltech-101 and Caltech-256 can be found in Table 3, and similar conclusions can be drawn.", + "bbox": [ + 75, + 263, + 470, + 534 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.2. Attack with non-overlapping dataset", + "text_level": 1, + "bbox": [ + 76, + 545, + 393, + 561 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "In the above experiments, we consider the case that the attacker has access to a part of the original training data, namely, the dataset for launching the attack overlaps with the original one. We now investigate the attack performance under a more challenging scenario, i.e., the dataset available to the attacker and the original dataset come from the same source; but do not overlap. This non-overlapping dataset mimics the practical scenario that the attacker may not be able to exactly access a part of the original training data; but rather can only access some similar ones.", + "bbox": [ + 75, + 568, + 468, + 717 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We randomly divide CIFAR10 into non-overlapping two subsets: 40000 for training the passport-based network and the remaining 10000 for the attack. Specifically, the attacking model is a ResNet18 with 10 passport layers, and the accuracy of the trained model is $93.12\\%$ . The attack performance of our ambiguity attacks with IERB and CERB under this new setting is tabulated in Table 4. With these 10000 non-overlapping data, our ambiguity attack with CERB reaches a $92.17\\%$ accuracy, only $0.95\\%$ away from the original one. Also, the BDR in this case is as high as $91.77\\%$ , indicating the recovered scale factors are very different from the authorized ones. When less number of non-", + "bbox": [ + 75, + 719, + 470, + 900 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "overlapping data are used, the ACC values drop while the accompanied BDRs tend to improve. Even when only $5\\%$ non-overlapping data are available, the ACC value can still be $85.67\\%$ with BDR being $93.44\\%$ . Similar results can be obtained by our ambiguity attack with IERB, but with a much lowered BDR of around $40\\%$ . Another interesting phenomenon is that the ambiguity attack with CEBR using non-overlapping dataset leads to slightly worse ACC, but much better BDR performance, compared with the same attack with overlapping dataset. These results, again, show that our proposed ambiguity attacks are still very effective even in the challenging non-overlapping scenarios.", + "bbox": [ + 496, + 90, + 890, + 272 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.3. Result of ambiguity attack with CERB on other DNN watermark methods", + "text_level": 1, + "bbox": [ + 498, + 282, + 890, + 311 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We now show that our proposed attack strategy can be generalized well to other DNN watermark methods. As the ambiguity attack with CERB overwhelms the one with IEBR, we adopt it in the following evaluations. The three DNN watermarking methods considered are: Greedy-Residual [21], DeepSigns [8], and Uchida [29], which used specific layer weights for the watermark embedding. For Greedy-Residual, the watermark was embedded into the first convolutional layer weight of the network, while for DeepSigns, the watermark was hidden in the flattened features before the last linear layer. Regarding Uchida's method, the watermark was injected into the third convolutional layer weights of the network.", + "bbox": [ + 496, + 320, + 892, + 516 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We flexibly adapt our CERB structure for different types of embedded intermediaries such as model weights and features in three DNN watermark methods. Following the attack setting of Fan et al. [11], we assume that the network structure and model weights except those from the watermark are available to the attacker. As a result, for Greedy-Residual, we can replace the normalization layer after the embedded convolutional parameters with the CERB. Similarly, for DeepSigns, the normalization layer before the embedded feature map is replaced by our CERB. For Uchida's method, a CERB structure is added after the embedded convolutional parameters. We preset a different signature and only train the parameters embedded with the watermarks and the CERB parameters to match this new signature. More implementation details can be found in Appendix A.", + "bbox": [ + 496, + 517, + 890, + 743 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We introduce signature detection rate (SDR) to evaluate if a signature is successfully embedded in the model. The SDR is defined as the percentage of the watermark bits $\\mathbf{wm} = \\{wm_1, \\dots, WM_C\\}$ extracted from the model that are coincident with the signature $\\mathbf{sig} = \\{sig_1, \\dots, sig_C\\}$ used during the embedding process, i.e.,", + "bbox": [ + 496, + 743, + 890, + 834 + ], + "page_idx": 6 + }, + { + "type": "equation", + "text": "\n$$\nS D R = \\frac {1}{C} \\sum_ {i = 1} ^ {C} \\mathcal {I} \\left[ w m _ {i} = s i g _ {i} \\right]. \\tag {10}\n$$\n", + "text_format": "latex", + "bbox": [ + 586, + 838, + 890, + 880 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "The attack results on three watermark methods are pre", + "bbox": [ + 519, + 885, + 890, + 901 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "8129", + "bbox": [ + 480, + 944, + 514, + 955 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/d36f89f33c5150c42ccf3864e0a8770ddd608c6e56f691d9b6556e59d294155b.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
WM methodDataset-NetEmbed-PositionDataSizeOriginal ACCAttack ACCBDRSDR
Greedy-ResidualCaltech256-ResNet18First Conv layer10%54.9854.3749.22100
DeepSignsCIFAR10-WRNLast Linear layer10%91.3091.1537.5100
UchidaCIFAR10-WRNThird Conv layer10%90.1189.7745.31100
", + "bbox": [ + 114, + 88, + 857, + 159 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/e1cc3092f30b91eb288e209aac4c3c79f01c3bf1a68e860a5cc9d6442fe55b05.jpg", + "table_caption": [ + "Table 5. Results of our ambiguity attack on other DNN watermark methods, in terms of ACC (%), BDR (%), and SDR (%)." + ], + "table_footnote": [], + "table_body": "
# of CERBOriginal046810
ACC (%)55.4225.0328.9938.5042.5847.07
", + "bbox": [ + 102, + 196, + 446, + 232 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "sented in Table 5. For Greedy-Residual method, the inference performance of the model after the attack is quite similar to that of the original one, with a very slight drop of $0.61\\%$ . In addition, the SDR is $100\\%$ , implying that the attacker can claim the ownership to this model with the new signature. Meanwhile, a high BDR of $49.22\\%$ well demonstrates the high dissimilarity between the forged and original watermarks. Very similar observations can be made when attacking DeepSigns and Uchida's methods. Therefore, we validate the generalization capability of our attack strategy to other DNN watermark methods.", + "bbox": [ + 75, + 279, + 470, + 445 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.4. Ablation study", + "text_level": 1, + "bbox": [ + 76, + 454, + 227, + 470 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Different number of CERB structures: To study the effect on attack performance with different number of CERB structures, we use a ResNet18 with the last 10 layers embedded with passports for the illustration. As can be seen from Table 6, the original performance evaluated on Caltech-256 is $55.42\\%$ . For Plain attack with 0 CERB structure, the ACC is very low, i.e., $25.05\\%$ . By gradually applying more CERB structures, the ACC values improve constantly. Eventually, with all 10 passport layers replaced by our CERB structures, the ACC of our ambiguity attack reaches $47.07\\%$ .", + "bbox": [ + 75, + 477, + 468, + 642 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Increasing the depth of CERB: The CERB in the default setting is a two-layer perceptron with LeakyReLU. We now try to testify if using perceptron with more layers leads to better attack performance. To this end, we experiment on the ResNet18 with 10 passport layers trained on CIFAR10, and launch the ambiguity attacks by varying the number of layers in CERB. As can be seen from Table 7, the ACC restored by CERB with 2 layers is the highest, reaching $92.24\\%$ . With more layers being involved, the ACC performance actually drops surprisingly. We conjecture that the two-layer perceptron is enough for our ambiguity attack; while increasing the number of layers places heavier burden to the training and eventually affects the performance of the ambiguity attack.", + "bbox": [ + 75, + 643, + 468, + 854 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Using other activation functions in CERB: We also evaluate the impact of the activation functions in CERB on the overall attack performance. Again, we experiment on", + "bbox": [ + 76, + 854, + 468, + 900 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/c18ec8120af143e3ef3a677a30568c34832a14e848c3561405941da5e961ad13.jpg", + "table_caption": [ + "Table 6. Results of using different number of CERB on Caltech-256 with ResNet18." + ], + "table_footnote": [], + "table_body": "
# of MLP layers in CERBOriginal2345
ACC (%)94.4092.2486.8584.1886.45
", + "bbox": [ + 511, + 196, + 883, + 233 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/8d53990b98c7a0e0dd71a11c6a6b63cb4465c98dd73a0522685fbfa6ce1c75e9.jpg", + "table_caption": [ + "Table 7. Results of changing the number of layer in CERB." + ], + "table_footnote": [], + "table_body": "
Activation FunctionsLeakyReLUtanhSigmoid
ACC (%)92.8792.5492.80
", + "bbox": [ + 521, + 271, + 874, + 314 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 8. Result of using different activation functions.", + "bbox": [ + 534, + 324, + 854, + 339 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "the ResNet18 with 10 passport layers trained on CIFAR10. We then replace every passport layer with CERB, and adopt different activation functions in CERB. We list the ACC results by using tanh and Sigmoid, in addition to our default LeakyReLU in Table 8. As can be noticed, all ACC results with different activation functions are similar. This implies that the attack performance is not sensitive to the activation functions adopted.", + "bbox": [ + 496, + 347, + 890, + 468 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 482, + 617, + 498 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this paper, we propose an advanced ambiguity attack that defeats the passport-based model IP protection scheme. We combine multi-layer perceptron with skip connection to find valid substitute passports using less than $10\\%$ of the training dataset. Extensive experimental results validate the effectiveness of our ambiguity attack. Further, it is demonstrated that our attack strategy can be easily extended to other DNN watermark methods.", + "bbox": [ + 496, + 508, + 890, + 628 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Regarding the remedy solutions, one potential direction is to exploit random locations for inserting the passport-layers, in which the randomness is controlled by a secret key. Additionally, another promising attempt is to change the embedding position from model weights to the activations. To make sure the next convolutional layer can extract proper features from the activation, the statistic of the activation should stay in a restricted scope. Such a statistic could be unique for a given signature, which may be helpful to resist our ambiguity attack.", + "bbox": [ + 496, + 628, + 890, + 779 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgments: This work was supported in part by Macau Science and Technology Development Fund under SKLIOTSC-2021-2023, 0072/2020/AMJ, and 0022/2022/A1; in part by Research Committee at University of Macau under MYRG2020-00101-FST and MYRG2022-00152-FST; in part by Natural Science Foundation of China under 61971476; and in part by Alibaba Group through Alibaba Innovative Research Program.", + "bbox": [ + 496, + 780, + 890, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "8130", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Yossi Adi, Carsten Baum, Moustapha Cisse, Benny Pinkas, and Joseph Keshet. 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In Proceedings of the ACM Asia Conference on Computer and Communications Security, pages 159-172, 2018. 1" + ], + "bbox": [ + 78, + 90, + 468, + 811 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "8132", + "bbox": [ + 482, + 945, + 514, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/Effective Ambiguity Attack Against Passport-Based DNN Intellectual Property Protection Schemes Through Fully Connected Layer Substitution/e387fd7f-d2cf-442f-899c-5257e75d504c_model.json b/2023/Effective Ambiguity Attack Against Passport-Based DNN Intellectual Property Protection Schemes Through Fully Connected Layer Substitution/e387fd7f-d2cf-442f-899c-5257e75d504c_model.json new file mode 100644 index 0000000000000000000000000000000000000000..fabc7a521fb956f627d7853727b4b7af660e905f --- /dev/null +++ b/2023/Effective Ambiguity Attack Against Passport-Based DNN Intellectual Property Protection Schemes Through Fully Connected Layer Substitution/e387fd7f-d2cf-442f-899c-5257e75d504c_model.json @@ -0,0 +1,2255 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.09, + 0.13, + 0.882, + 0.177 + ], + "angle": 0, + "content": "Effective Ambiguity Attack Against Passport-based DNN Intellectual Property Protection Schemes through Fully Connected Layer Substitution" + }, + { + "type": "text", + "bbox": [ + 0.228, + 0.21, + 0.744, + 0.229 + ], + "angle": 0, + "content": "Yiming Chen\\(^{1}\\), Jinyu Tian\\(^{2}\\), Xiangyu Chen\\(^{1,3}\\), and Jiantao Zhou\\(^{1,\\dagger}\\)" + }, + { + "type": "text", + "bbox": [ + 0.254, + 0.23, + 0.717, + 0.248 + ], + "angle": 0, + "content": "1State Key Laboratory of Internet of Things for Smart City" + }, + { + "type": "text", + "bbox": [ + 0.202, + 0.248, + 0.769, + 0.265 + ], + "angle": 0, + "content": "Department of Computer and Information Science, University of Macau" + }, + { + "type": "text", + "bbox": [ + 0.163, + 0.265, + 0.808, + 0.282 + ], + "angle": 0, + "content": "\\(^{2}\\)Faculty of Innovation Engineering, Macau University of Science and Technology" + }, + { + "type": "text", + "bbox": [ + 0.18, + 0.283, + 0.791, + 0.3 + ], + "angle": 0, + "content": "3Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences" + }, + { + "type": "text", + "bbox": [ + 0.212, + 0.303, + 0.753, + 0.318 + ], + "angle": 0, + "content": "{yc17486, jtzhou}@umac.mo, jytian@must.edu.mo, chxy95@gmail.com" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.352, + 0.314, + 0.369 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.385, + 0.473, + 0.703 + ], + "angle": 0, + "content": "Since training a deep neural network (DNN) is costly, the well-trained deep models can be regarded as valuable intellectual property (IP) assets. The IP protection associated with deep models has been receiving increasing attentions in recent years. Passport-based method, which replaces normalization layers with passport layers, has been one of the few protection solutions that are claimed to be secure against advanced attacks. In this work, we tackle the issue of evaluating the security of passport-based IP protection methods. We propose a novel and effective ambiguity attack against passport-based method, capable of successfully forging multiple valid passports with a small training dataset. This is accomplished by inserting a specially designed accessory block ahead of the passport parameters. Using less than \\(10\\%\\) of training data, with the forged passport, the model exhibits almost indistinguishable performance difference (less than \\(2\\%\\)) compared with that of the authorized passport. In addition, it is shown that our attack strategy can be readily generalized to attack other IP protection methods based on watermark embedding. Directions for potential remedy solutions are also given." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.731, + 0.21, + 0.746 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.756, + 0.47, + 0.879 + ], + "angle": 0, + "content": "With the geometric growth of computing power of computational devices in recent decades, there have emerged many deep learning applications that have contributed to the human world such as super-resolution reconstruction [7, 9, 30], image inpainting [31, 34, 35] and forgery detection [32]. It usually costs many resources to develop new DNN models and developers will not tolerate the act of theft of their IP. The IP protection problem of deep models be" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.354, + 0.892, + 0.414 + ], + "angle": 0, + "content": "comes more severe with the birth of Machine Learning as a Service (MLaaS) [26]. Preventing the infringement behavior of deep models now emerges as a necessary concern when developing new algorithms and systems." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.416, + 0.893, + 0.779 + ], + "angle": 0, + "content": "Model watermark [20, 25, 27, 28, 37] has been a popular method to protect the IP of DNN models. In the embedding process, the owners embed the secret signatures (watermarks), and then in the verification process, they can claim their ownership to the model by matching the extracted signatures with the original versions. The existing model watermark methods can be roughly divided into two categories [10, 11]: feature-based and trigger-based methods. Specifically, feature-based methods [4, 8, 24, 29] applied a regularizer to embed the secret watermark into the activation functions or model weights. Uchida et al. [29] proposed to use a regularizer to embed a watermark into the model weights. Darvish et al. [8] embedded the fingerprints in the Probability Density Function of trainable weights instead. Aramoon et al. [3] inserted the signature into the gradient of the cross-entropy loss function with respect to the inputs. In contrast, trigger-based methods make the output target respond to specific inputs. Along this line, Adi et al. [1] used the backdoor attack as a means to watermark the model. Merrer et al. [18] designed a zero-bit watermarking algorithm that uses adversarial samples as watermarks to claim the ownership. Zhang et al. [39] applied watermarks to images and then trained the network to output target labels when input images carry these watermarks." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.895, + 0.901 + ], + "angle": 0, + "content": "Despite the strength in retaining ownership of DNN models, most existing model watermark methods are shown to be vulnerable to the so-called ambiguity attack, in which the attacker manages to cast doubts on the ownership verification by crafting counterfeit (forged) watermarks [11]. Recently, Fan et al. [10] first designed a series of ambiguity attacks, which are effective in attacking DNN watermark methods. It was stated that for conventional watermark" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.887, + 0.222, + 0.9 + ], + "angle": 0, + "content": "† Corresponding author." + }, + { + "type": "page_number", + "bbox": [ + 0.482, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "8123" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.272 + ], + "angle": 0, + "content": "methods, a counterfeit watermark can be forged as along as the model performance is independent of the signature [11]. Following this proposition, Fan et al. designed a passport layer through which the functionality of the model is controlled by the signature called passport. However, Fan et al. encountered a heavy performance drop when batch normalization layers exist. To solve this problem, Zhang et al. [38] added learnable affine transformations to the scale and bias factors. It was claimed that an attacker cannot find a substitute passport that maintains the model performance, which ensures the security of these passport-based methods against existing ambiguity attacks." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.273, + 0.473, + 0.605 + ], + "angle": 0, + "content": "In this work, we aim to design an advanced ambiguity attack to the passport-based method, capable of generating valid substitute passports with only a small number of data. Here, valid substitute passports are defined as those leading to an indistinguishable model performance, but sufficiently different from the original authorized passports. Clearly, with such valid substitute passports, an attacker can claim the ownership of the model. To this end, we first experimentally justify the existence of multiple valid substitute passports. Noticing the fact that it is easy to localize the passport layers, we then propose our ambiguity attack by replacing passport layers with our designed two types of structures, namely Individual Expanded Residual Block (IERB) and Collective Expanded Residual Block (CERB). Both structures are built in a way to encourage the significant changes of the parameters in the passport layers during the training, which could help us search for valid substitute passports. Benefiting from these two structures and assisting with a small amount training data, we can obtain valid substitute passports, and hence, defeat the passport-based methods which are the only type of method claimed to be immune to existing ambiguity attacks." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.606, + 0.464, + 0.619 + ], + "angle": 0, + "content": "Our major contributions can be summarized as follows:" + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.619, + 0.468, + 0.708 + ], + "angle": 0, + "content": "- We propose a novel and effective ambiguity attack against the passport-based IP protection schemes. With less than \\(10\\%\\) of training data, our ambiguity attack on passport-layer protected model can restore the functionality of the model with a less than \\(2\\%\\) performance gap from the original accuracy." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.708, + 0.468, + 0.782 + ], + "angle": 0, + "content": "- We design two novel structures for replacing the passport layers, based on the multi-layer perceptron (MLP) and skip connection to assist with our ambiguity attack for searching valid substitute passports with a small amount of training data." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.782, + 0.468, + 0.871 + ], + "angle": 0, + "content": "- Experiments on both overlapping (attacker's training dataset is part of the original training dataset) and non-overlapping datasets (attacker's dataset and the original one come from the same source but no overlap exists), and on different network structures have proved the effectiveness of our ambiguity attack." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.871, + 0.468, + 0.901 + ], + "angle": 0, + "content": "- Our attack method can be readily generalized to attack other DNN watermark methods [8, 21, 29]." + }, + { + "type": "list", + "bbox": [ + 0.097, + 0.619, + 0.468, + 0.901 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.501, + 0.09, + 0.651, + 0.107 + ], + "angle": 0, + "content": "2. Related Works" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.119, + 0.892, + 0.24 + ], + "angle": 0, + "content": "DNN watermark methods have been popular solutions for DNN model IP protection. However, these techniques might still be vulnerable to flagrant infringement from notorious adversaries. In this section, we review the two types of representative attack methods, namely, removal attack [2, 5, 6, 14, 22, 33] and ambiguity attack [10, 11, 38], along with the passport-based method attempting to defend against ambiguity attacks [11]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.244, + 0.893, + 0.606 + ], + "angle": 0, + "content": "Removal Attack: This type of attack tries to remove the watermark from the protected model, malfunctioning the ownership verification mechanism. Along this line, many fine-tuning based methods have been proposed. Chen et al. [5] combined a redesigned elastic weight consolidation algorithm and unlabeled data augmentation to achieve unified model watermark removal with limited data. Guo et al. [14] used a dataset transformation method called PST (Pattern embedding and Spatial-level Transformation) to preprocess the data before fine-tuning. Chen et al. [6] utilized auxiliary unlabeled data to decrease the amount of labeled training data required for effective watermark removal. Aiken et al. [2] provided a three-stage scheme to remove backdoor-based watermarks by exploiting another trigger-free dataset from the same domain. Liu et al. [22] designed a framework to remove backdoor-based watermarks, in which a data augmentation was proposed to imitate the behavior of the backdoor triggers. Yan et al. [33] attempted to break the passport-based method by scaling the neurons and flipping the signs of parameters. However, this method assumed that the authorized passports are available to the attacker, which is not realistic in practice. Also, these aforementioned attack methods only enable the attackers to remove the watermarks, while unable to claim the ownership." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.611, + 0.892, + 0.791 + ], + "angle": 0, + "content": "Ambiguity Attack: Another more threatening attack is the ambiguity attack, where the attacker can forge another substitute watermark to claim the model ownership. The concept of ambiguity attack originally appeared in image watermark community [19, 23], and recently has been extended to the DNN watermark methods. The pioneering work was conducted by Fan et al. in [10], which pointed out the vulnerability of Uchida's watermark method [29] under the ambiguity attack. They also showed that the same weakness of Adi's DNN watermark method [1] exists, by proving that another trigger can be optimized exclusively to cause the same model response as the original one." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.796, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Passport-based method: Passport-based method was originally proposed by Fan et al. [11] as a remedy enabling DNN watermark methods to defeat the ambiguity attack. This is achieved by replacing the traditional normalization layer with the so-called passport layer, whose difference mainly lies in how the affine factors are obtained. In passport layer, the scale factor \\(\\gamma\\) and bias factor \\(\\beta\\) are computed" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "8124" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.078, + 0.092, + 0.27, + 0.106 + ], + "angle": 0, + "content": "with the passport as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.103, + 0.117, + 0.47, + 0.134 + ], + "angle": 0, + "content": "\\[\n\\gamma = \\operatorname {A v g} \\left(\\mathbf {W} _ {\\text {c o n v}} * \\mathbf {s} _ {\\gamma}\\right), \\beta = \\operatorname {A v g} \\left(\\mathbf {W} _ {\\text {c o n v}} * \\mathbf {s} _ {\\beta}\\right), \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.143, + 0.469, + 0.188 + ], + "angle": 0, + "content": "where \\(\\mathbf{s} = \\{\\mathbf{s}_{\\gamma},\\mathbf{s}_{\\beta}\\}\\) is called the passport, \\(\\mathbf{W}_{conv}\\) is the convolutional layer weight before this layer, and \\(Avg(\\cdot)\\) represents the average pooling function." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.189, + 0.469, + 0.252 + ], + "angle": 0, + "content": "To embed the passport \\(s\\) into the model, the network \\(\\mathbb{N}_p\\) is optimized on the training set \\(\\mathcal{D} = \\{(x_i,y_i)\\}_{i = 1}^N\\), where \\(x_{i}\\) is the input and \\(y_{i}\\) is the corresponding label, using the following loss:" + }, + { + "type": "equation", + "bbox": [ + 0.1, + 0.263, + 0.469, + 0.28 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} = \\mathcal {L} _ {r} \\left(\\mathbb {N} _ {p} [ \\mathbf {W}, \\mathbf {s} ] \\left(x _ {i}, y _ {i}\\right)\\right) + \\alpha \\mathcal {L} _ {\\text {s i g n}} (\\operatorname {s g n} (\\gamma), \\mathbf {b}), \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.289, + 0.469, + 0.379 + ], + "angle": 0, + "content": "where \\(\\mathbb{N}_p[\\mathbf{W},\\mathbf{s}]\\) denotes the model \\(\\mathbb{N}\\) with the weight \\(\\mathbf{W}\\) and the passport s. The first term \\(\\mathcal{L}_r(\\cdot)\\) is the classification loss, and the second term \\(\\mathcal{L}_{sign}(\\cdot)\\) is a sign loss regularization constraining the sign sequence of scale factors to be a predefined \\(C\\) -bit signature \\(\\mathbf{b} = \\{b_1,\\dots,b_C\\} \\in \\{-1,1\\} ^C\\) Here, \\(\\mathrm{sgn}(\\cdot)\\) is the sign function." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.379, + 0.47, + 0.501 + ], + "angle": 0, + "content": "Denote \\(\\mathcal{Q}(\\mathbb{N}_p[\\mathbf{W},\\mathbf{s}])\\) as the inference performance of model \\(\\mathbb{N}_p\\) with the passport s. The verification process mainly relies on the assumption that the performance \\(\\mathcal{Q}(\\mathbb{N}_p[\\mathbf{W},\\mathbf{s}])\\) seriously deteriorates when an unauthorized passport is presented. Hence, the model ownership using passport-based method is conducted by matching the signs of scale factors \\(\\mathrm{sgn}(\\gamma)\\) with the predefined signature b and checking the DNN model inference performance." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.514, + 0.336, + 0.531 + ], + "angle": 0, + "content": "3. Proposed Ambiguity Attack" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.539, + 0.469, + 0.674 + ], + "angle": 0, + "content": "Though the passport-based methods [11, 38] have been claimed to be immune to the existing ambiguity attacks [10], they do not preclude the existence of more advanced ambiguity attacks. In this work, we cast doubt on the security of the passport-based methods, and propose a simple yet effective ambiguity attack, capable of crafting valid substitute passports. Before diving into the detailed design of our ambiguity attack, let us clarify our attack goal and the information assumed to be available to the attacker." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.675, + 0.469, + 0.87 + ], + "angle": 0, + "content": "Attack Goal: Essentially, the attack goal is to generate substitute passport \\(\\mathbf{s}_t\\), with which the model \\(\\mathbb{N}_p[\\mathbf{W},\\mathbf{s}_t]\\) has indistinguishable performance with that of applying the authorized passport \\(\\mathbf{s}_o\\), i.e., \\(\\mathcal{Q}(\\mathbb{N}_p[\\mathbf{W},\\mathbf{s}_o])\\). Specifically, following the ambiguity attack setting in [11], we assume that the attacker has access to the model weights \\(\\mathbf{W}\\) except from the passport. Note that, without the passport, the affine factors are missing in the normalization layer, through which the attacker can easily localize the passport layers. Also, the attacker is allowed to have a small number of training data, namely, \\(\\mathcal{D}_s = \\{(\\hat{x}_i,\\hat{y}_i)\\}_{i = 1}^n\\), where \\(n < N\\). Formally, we have the following Definition 1, explicitly explaining the successful ambiguity attack on passport-based method." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.468, + 0.9 + ], + "angle": 0, + "content": "Definition 1: An ambiguity attack on passport layer protected model is successful, if" + }, + { + "type": "image", + "bbox": [ + 0.508, + 0.094, + 0.681, + 0.193 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.601, + 0.2, + 0.615, + 0.21 + ], + "angle": 0, + "content": "(a)" + }, + { + "type": "image", + "bbox": [ + 0.702, + 0.094, + 0.882, + 0.193 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.807, + 0.199, + 0.822, + 0.21 + ], + "angle": 0, + "content": "(b)" + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.22, + 0.892, + 0.262 + ], + "angle": 0, + "content": "Figure 1. Valid substitute passports obtained by initializing scale factors with different signs from the authorized \\(\\mathbf{s}_o\\) and retraining. Horizontal axis denotes the number of different signs from \\(\\mathbf{s}_o\\)." + }, + { + "type": "text", + "bbox": [ + 0.516, + 0.279, + 0.892, + 0.31 + ], + "angle": 0, + "content": "I) DNN inference accuracy with the substitute passport \\(\\mathbf{s}_t\\) is close to that with the authorized passport \\(\\mathbf{s}_o\\), i.e.," + }, + { + "type": "equation", + "bbox": [ + 0.585, + 0.319, + 0.892, + 0.344 + ], + "angle": 0, + "content": "\\[\n\\left| \\mathcal {Q} \\left(\\mathbb {N} _ {p} [ \\mathbf {W}, \\mathbf {s} _ {t} ]\\right) - \\mathcal {Q} \\left(\\mathbb {N} _ {p} [ \\mathbf {W}, \\mathbf {s} _ {o} ]\\right) \\right| < \\epsilon . \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.512, + 0.356, + 0.892, + 0.386 + ], + "angle": 0, + "content": "II) Dissimilarity between the substitute passport \\(\\mathbf{s}_t\\) and the authorized \\(\\mathbf{s}_o\\) should be large enough, i.e.:" + }, + { + "type": "equation", + "bbox": [ + 0.666, + 0.395, + 0.892, + 0.421 + ], + "angle": 0, + "content": "\\[\n\\left| \\mathbf {s} _ {t} - \\mathbf {s} _ {o} \\right| > \\delta . \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.433, + 0.893, + 0.764 + ], + "angle": 0, + "content": "Before presenting the details of our ambiguity attack, let us first justify the existence of multiple valid substitute passports satisfying the conditions given in (3) and (4). To this end, we here adopt an experimental approach and leave the theoretical justification in our future work. Assume now that we are given the complete training data \\(\\mathcal{D}\\), though this large amount of data are not required when launching the attack. We initialize scale factors with different combinations of \\(\\{+1, -1\\}\\) and fine-tune the model based on \\(\\mathcal{D}\\). In Fig. 1, we give the experimental results on ResNet18 trained on the CIFAR10 dataset, where the passport layer is placed after the first convolutional layer and the length of the scale factor is 64. The model with the authorized passport leads to an inference performance of \\(94.70\\%\\). As can be seen, the accuracy of the models after retraining is still close to \\(94.70\\%\\) (red line, see Fig. 1(a)). More importantly, the signs of retained affine factors only have low coincidence rate (around \\(60\\%\\), see Fig. 1(b)) with the original ones, implying that retained affine factors differ significantly from the authorized affine factors. Therefore, these retrained affine factors could simultaneously satisfy the conditions (3) and (4), and hence are valid substitute passports." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Though the existence of substitute passports has been justified, the difficulty of directly optimizing a passport remains unsolved for very limited number of training data. Clearly, in practical attacks, the attacker is only allowed to have access to very limited data; otherwise, he can retrain the entire model. Fan et al. [11] ascribed the robustness of passport-based method against fine-tuning the scale factors to the lazy-to-flip property, with which the scale factors are rarely updated to cross the zero during the training." + }, + { + "type": "page_number", + "bbox": [ + 0.482, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "8125" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.129, + 0.093, + 0.836, + 0.403 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.18, + 0.411, + 0.79, + 0.427 + ], + "angle": 0, + "content": "Figure 2. The structures of the ResNet18 with passport layer and our designed CERB/IERB structures." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.442, + 0.47, + 0.533 + ], + "angle": 0, + "content": "To overcome the lazy-to-flip property for the scale factors, we attempt to add a trainable block after it, encouraging scale factors to go across the zeros by non-linear transformations. For efficiency, we adopt MLP for designing the trainable blocks. Following this line, we design two structures namely IERB and CERB to replace the passport layer." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.537, + 0.471, + 0.763 + ], + "angle": 0, + "content": "The overall structure: Motivated by the above observations, we now design a novel ambiguity attack on passport-based method. The overall structure is given in Fig. 2, where we use the ResNet18 embedded with passport layers for the illustration. Specifically, the protected ResNet18 is comprised of multiple residual blocks, each containing several convolutional layers followed by the passport layer. As aforementioned, the locations of the passport layers can be easily determined. We can then insert either IERB or CERB structure into these locations. In our structure, the scale factor \\(\\gamma\\) is the output of the IERB/CERB. For the bias factor \\(\\beta\\), we do not add our new structure; but instead we optimize it directly. We are now ready to introduce the details of CERB and IERB structures. After that, we will give the complete algorithm of our ambiguity attack." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.772, + 0.47, + 0.789 + ], + "angle": 0, + "content": "3.1. Individually Expanded Residual Block (IERB)" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.796, + 0.471, + 0.901 + ], + "angle": 0, + "content": "In this subsection, we present the details of the IERB block. As showed in Fig. 3 (a), the \\(i\\)-th scale factor \\(\\gamma_i^l\\) in the \\(l\\)-th passport layer is transformed by a Two-Layer Perceptron (TLP) with FC-LeakyReLU-FC structure where the FC refers to fully connected layer. For the simplicity of notations, we omit the superscript in \\(\\gamma_i^l\\) in the sequel. The output of this TLP is then used for the affine transformation" + }, + { + "type": "image", + "bbox": [ + 0.517, + 0.444, + 0.712, + 0.631 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.617, + 0.635, + 0.635, + 0.647 + ], + "angle": 0, + "content": "(a)" + }, + { + "type": "image", + "bbox": [ + 0.731, + 0.444, + 0.871, + 0.63 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.781, + 0.635, + 0.799, + 0.647 + ], + "angle": 0, + "content": "(b)" + }, + { + "type": "image_caption", + "bbox": [ + 0.561, + 0.658, + 0.831, + 0.673 + ], + "angle": 0, + "content": "Figure 3. Details of (a) IERB and (b) CERB." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.689, + 0.892, + 0.885 + ], + "angle": 0, + "content": "later. The first linear layer \\(FC_{1\\rightarrow h}\\) with learnable parameters maps the scale factor into a \\(h\\) -dimensional vector, while the second linear layer \\(FC_{h\\rightarrow 1}\\) maps the dimension back to 1, where \\(h\\) is the hidden layer size. A larger \\(h\\) brings a larger optimization space in the hidden layer; but could add burden to the training process. We empirically set \\(h = 10\\) striking a good balance between these two factors. In addition, a skip connection is added aside with the TLP structure to facilitate the back-propagation. Benefiting from the expanded parameter space brought by the TLP structure, the output scale factor would more likely go across the zero during the updating. This helps the attacker search for an appropriate \\(\\mathbf{s}_t\\) satisfying (4)." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.886, + 0.892, + 0.902 + ], + "angle": 0, + "content": "Let \\(\\{\\mathbf{W}_{i,j},\\mathbf{b}_{i,j}\\}\\) be the weights of the \\(j\\) -th linear" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "8126" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.47, + 0.137 + ], + "angle": 0, + "content": "layer connected after the \\(i\\)-th scale factor, where \\(i \\in \\{1,2,\\dots,C\\}\\) and \\(j \\in \\{1,2\\}\\). In IERB, the output of the first linear layer taking the \\(i\\)-th scale factor as input is:" + }, + { + "type": "equation", + "bbox": [ + 0.194, + 0.139, + 0.469, + 0.158 + ], + "angle": 0, + "content": "\\[\n\\gamma_ {i} ^ {\\prime} = \\mathbf {W} _ {i, 1} ^ {T} * \\gamma_ {i} + \\mathbf {b} _ {i, 1} ^ {T}, \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.164, + 0.47, + 0.209 + ], + "angle": 0, + "content": "where \\(*\\) denotes the matrix multiplication operator. After the activation function LeakyReLU, the output of the second linear layer with the shortcut can be expressed as:" + }, + { + "type": "equation", + "bbox": [ + 0.136, + 0.211, + 0.469, + 0.23 + ], + "angle": 0, + "content": "\\[\n\\gamma_ {i} ^ {\\prime \\prime} = \\mathbf {W} _ {i, 2} ^ {T} * \\left(L R e L U \\left(\\gamma_ {i} ^ {\\prime}\\right)\\right) + \\mathbf {b} _ {i, 2} ^ {T} + \\gamma_ {i}. \\tag {6}\n\\]" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.237, + 0.458, + 0.254 + ], + "angle": 0, + "content": "3.2. Collective Expanded Residual Block (CERB)" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.261, + 0.473, + 0.473 + ], + "angle": 0, + "content": "The IERB discussed above handles each scale factor individually, but may ignore the inter-channel relationship among scale factors. Instead of using isolated propagation paths for each scale factor, we now attempt to enhance the inter-channel relationship and optimize the scale factors in a collective manner. As can be observed from Fig. 3 (b), we choose to use a unified TLP structure to deal with all the \\(C\\) scale factors as a whole. The output of the TLP structure is then summed with the input scale factors to get the updated ones. Different from the IERB, each activation in the hidden layer is now related to all the input scale factors, and the fully connected structure ensures the exploitation of the inter-channel information. Mathematically, the output scale factors can be computed by:" + }, + { + "type": "equation", + "bbox": [ + 0.086, + 0.479, + 0.47, + 0.5 + ], + "angle": 0, + "content": "\\[\n\\gamma^ {\\prime \\prime} = \\left(\\mathbf {W} _ {2} ^ {T} * \\left(L R e L U \\left(\\mathbf {W} _ {1} ^ {T} * \\gamma + \\mathbf {b} _ {1} ^ {T}\\right)\\right) + \\mathbf {b} _ {2} ^ {T}\\right) + \\gamma , (7)\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.509, + 0.47, + 0.556 + ], + "angle": 0, + "content": "where \\(\\mathbf{W}_1\\) and \\(\\mathbf{W}_2\\) represent the parameters in the first and second linear layers. Here we set the hidden layer size to be \\(C / 8\\), where \\(C\\) is the number of channels in this layer." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.563, + 0.394, + 0.58 + ], + "angle": 0, + "content": "3.3. Algorithm of Our Ambiguity Attack" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.587, + 0.47, + 0.738 + ], + "angle": 0, + "content": "With these newly proposed structures, we can summarize our ambiguity attack strategy on the passport-based method in Algorithm 1. For simplicity, we use \\(\\mathbf{W}_{\\gamma}\\) to represent all the parameters in IERB or CERB. Let us briefly explain our workflow for better understanding. In Algorithm 1, lines \\(1\\sim 4\\) are devoted to the model loading, normalization layer substitution, CERB/IERB insertion, and parameter initialization. The \\(\\gamma, \\beta\\) and \\(\\mathbf{W}_{\\gamma}\\) are then updated in lines \\(5\\sim 14\\) using the gradients with respect to each parameter by back-propagating the cross entropy loss:" + }, + { + "type": "equation", + "bbox": [ + 0.206, + 0.743, + 0.324, + 0.759 + ], + "angle": 0, + "content": "\\[\n\\gamma = \\gamma - \\nabla_ {\\gamma} l o s s,\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.208, + 0.761, + 0.469, + 0.777 + ], + "angle": 0, + "content": "\\[\n\\beta = \\beta - \\nabla_ {\\beta} \\text {l o s s}, \\tag {8}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.19, + 0.78, + 0.357, + 0.797 + ], + "angle": 0, + "content": "\\[\n\\mathbf {W} _ {\\gamma} = \\mathbf {W} _ {\\gamma} - \\nabla_ {\\mathbf {W} _ {\\gamma}} l o s s.\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.802, + 0.469, + 0.832 + ], + "angle": 0, + "content": "Eventually, the algorithm outputs the substitute scale and bias factors \\(\\gamma''\\) and \\(\\beta\\)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.845, + 0.283, + 0.862 + ], + "angle": 0, + "content": "4. Experimental Results" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.469, + 0.902 + ], + "angle": 0, + "content": "In this section, we evaluate the effectiveness of our ambiguity attack from different perspectives. Before present" + }, + { + "type": "code_caption", + "bbox": [ + 0.501, + 0.091, + 0.778, + 0.107 + ], + "angle": 0, + "content": "Algorithm 1 Proposed Ambiguity Attack" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.109, + 0.892, + 0.154 + ], + "angle": 0, + "content": "Input: Protected network \\(\\mathbb{N}_p[\\mathbf{W}]\\) with passport layers excluded; training dataset \\(\\mathcal{D}_s = \\{(\\hat{x}_i,\\hat{y}_i)\\}_{i = 1}^n\\); checkpoint state_dict; training epoch \\(M\\)" + }, + { + "type": "text", + "bbox": [ + 0.501, + 0.154, + 0.815, + 0.169 + ], + "angle": 0, + "content": "Output: substitute scale and bias factors \\(\\gamma^{\\prime \\prime}\\) \\(\\beta\\)" + }, + { + "type": "text", + "bbox": [ + 0.509, + 0.172, + 0.892, + 0.202 + ], + "angle": 0, + "content": "1: Use normalization layers in the locations of the passport layers." + }, + { + "type": "text", + "bbox": [ + 0.509, + 0.203, + 0.892, + 0.232 + ], + "angle": 0, + "content": "2: Insert CERB/IERB structures after the scale factors of these normalization layers." + }, + { + "type": "text", + "bbox": [ + 0.509, + 0.233, + 0.813, + 0.247 + ], + "angle": 0, + "content": "3: Load weight \\(\\mathbf{W}\\) of \\(\\mathbb{N}_p[\\mathbf{W}]\\) from state_dict." + }, + { + "type": "text", + "bbox": [ + 0.509, + 0.248, + 0.891, + 0.277 + ], + "angle": 0, + "content": "4: Initialize normalization layer weights \\(\\gamma\\) and \\(\\beta\\) with 1 and 0, respectively." + }, + { + "type": "list", + "bbox": [ + 0.509, + 0.172, + 0.892, + 0.277 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.51, + 0.278, + 0.682, + 0.292 + ], + "angle": 0, + "content": "5: for epoch \\(= 1\\) to \\(M\\) do" + }, + { + "type": "text", + "bbox": [ + 0.51, + 0.293, + 0.753, + 0.308 + ], + "angle": 0, + "content": "6: for minibatch \\((\\hat{x}_i,\\hat{y}_i)\\subset \\mathcal{D}_s\\) do" + }, + { + "type": "text", + "bbox": [ + 0.51, + 0.309, + 0.888, + 0.322 + ], + "angle": 0, + "content": "7: for each normalization layer with IERB/CERB do" + }, + { + "type": "text", + "bbox": [ + 0.51, + 0.323, + 0.886, + 0.338 + ], + "angle": 0, + "content": "8: \\(\\gamma^{\\prime \\prime} = \\mathrm{CERB / IERB}(\\gamma ,\\mathbf{W}_{\\gamma}).\\) \\(\\triangleright\\) Eq. (5/7)." + }, + { + "type": "text", + "bbox": [ + 0.509, + 0.338, + 0.891, + 0.368 + ], + "angle": 0, + "content": "9: Use \\(\\gamma''\\) and \\(\\beta\\) for affine transformation in normalization layer." + }, + { + "type": "text", + "bbox": [ + 0.508, + 0.37, + 0.616, + 0.381 + ], + "angle": 0, + "content": "10: end for" + }, + { + "type": "text", + "bbox": [ + 0.507, + 0.383, + 0.807, + 0.399 + ], + "angle": 0, + "content": "11: loss=cross_entropy \\((\\mathbb{N}_p[\\mathbf{W}](\\hat{x}_i),\\hat{y}_i)\\)" + }, + { + "type": "text", + "bbox": [ + 0.507, + 0.399, + 0.774, + 0.414 + ], + "angle": 0, + "content": "12: Update \\(\\gamma, \\beta\\) and \\(\\mathbf{W}_{\\gamma} \\triangleright\\) Eq. (8)." + }, + { + "type": "text", + "bbox": [ + 0.507, + 0.415, + 0.599, + 0.426 + ], + "angle": 0, + "content": "13: end for" + }, + { + "type": "text", + "bbox": [ + 0.507, + 0.429, + 0.583, + 0.442 + ], + "angle": 0, + "content": "14: end for" + }, + { + "type": "list", + "bbox": [ + 0.507, + 0.278, + 0.891, + 0.442 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.467, + 0.892, + 0.51 + ], + "angle": 0, + "content": "ing the detailed results, let us clarify the experimental settings including the datasets, target models, and the evaluation metrics." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.512, + 0.892, + 0.587 + ], + "angle": 0, + "content": "Dataset: Four image classification datasets: CIFAR10 [16], CIFAR100 [16], Caltech-101 [12], and Caltech-256 [13], are selected. Unless stated, the dataset used in the attack process only accounts for \\(10\\%\\) at maximum of the full training set and does not overlap with the test set." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.588, + 0.892, + 0.784 + ], + "angle": 0, + "content": "DNN architectures: Three DNN architectures, AlexNet [17], ResNet-18 [15] and Wide-Residual Network [36] are used in our experiments, following the tradition of passport-based works [10, 11, 38]. To demonstrate that our attack strategy remains effective for different number of passport layers, we perform the experiments on AlexNet and ResNet18, with at most 5 and 18 passport layers, respectively. For notation convenience, we use a suffix to determine the indices of the passport layers. For instance, AlexNet-4 denotes the AlexNet with the first 4 normalization layers replaced by the passport layers, and AlexNet-last3 represents the version in which the last 3 normalization layers are replaced by the passport layers." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.784, + 0.892, + 0.905 + ], + "angle": 0, + "content": "Evaluation metrics: Prediction accuracy (ACC) of the model is a natural choice for evaluating the attack effectiveness, since a successfully forged passport is expected to achieve similar performance as an authorized passport (see Definition 1). Another metric considered is the bit dissimilarity rate (BDR) of the signature derived from the forged passport, with respect to the authorized one. Specifically, let \\(\\gamma'\\) and \\(\\gamma^o\\) be the forged and authorized scale factors, re" + }, + { + "type": "page_number", + "bbox": [ + 0.482, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "8127" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.47, + 0.121 + ], + "angle": 0, + "content": "spectively. Note that the sign of \\(\\gamma^o\\) is used as the signature. The BDR is then defined as:" + }, + { + "type": "equation", + "bbox": [ + 0.14, + 0.126, + 0.47, + 0.168 + ], + "angle": 0, + "content": "\\[\nB D R = \\frac {1}{C} \\sum_ {i = 1} ^ {C} \\mathcal {I} \\left[ \\operatorname {s g n} \\left(\\gamma_ {i} ^ {\\prime}\\right) \\neq \\operatorname {s g n} \\left(\\gamma_ {i} ^ {o}\\right) \\right], \\tag {9}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.173, + 0.47, + 0.235 + ], + "angle": 0, + "content": "where the indicator function \\(\\mathcal{I}[\\cdot]\\) returns 1 when the condition is true and 0 otherwise. A high BDR also implies the large dissimilarity with the authorized passport, which in turn indicates a better performance of the ambiguity attack." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.243, + 0.418, + 0.26 + ], + "angle": 0, + "content": "4.1. Attack performance using IERB/CERB" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.267, + 0.471, + 0.372 + ], + "angle": 0, + "content": "We now give the details on the effectiveness of our ambiguity attack by replacing the passport layers of the protected model with our proposed IERB or CERB blocks. All protected models with passport layers are trained over the training dataset of CIFAR10. We randomly select \\(10\\%\\) of examples from this dataset for launching the ambiguity attack, i.e., training the IERB or CERB blocks." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.372, + 0.47, + 0.614 + ], + "angle": 0, + "content": "The attack results on AlexNet and ResNet18 are reported in Table 1. Since our ambiguity attack is the first one attacking passport-based methods, there are no comparative algorithms available so far. It can be seen that, by using the proposed CERB, our ambiguity attack is capable of achieving high ACC and BDR values for all the settings. Specifically, for AlexNet, the ACC gap is less than \\(1\\%\\), compared with the case of the authorized passport. Also, the BDR can be as large as \\(80.30\\%\\). For the more complex ResNet18, similar observations can be obtained, where the ACC gap is still less than \\(3\\%\\), and the BDR could approach \\(50\\%\\). We even encounter several cases (AlexNet-1 and ResNet18-1), in which the attacked models perform even better than the original ones. These results imply that our proposed ambiguity attack is successful in finding the valid substitute passports with a small number of training data." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.615, + 0.47, + 0.825 + ], + "angle": 0, + "content": "As a comparison, we also present the results of the ambiguity attack with the IERB structure. It can be observed that this variant attack is still somewhat effective with reasonably high ACC and BDR values; but the attack performance is much inferior to the attack with CERB, especially when there are many passport layers. We attribute this phenomenon to the capability of CERB in exploiting the interchannel relationship. For IERB, it is likely to optimize towards the original sign of the scale factor, which naturally results in similar signatures (small BDR) to the original passports. In CERB, however, the collective optimization mechanism explores more possibly optimal pairs of the sign of scale factors, potentially leading to larger BDR of signature and higher ACC." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.825, + 0.47, + 0.903 + ], + "angle": 0, + "content": "To further show the effectiveness of our proposed attack strategy, we now compare the attack performance of the models with and without CERB/IERB structures. As will be clear soon, directly updating the affine factors cannot retrieve valid passports, especially when the available data is" + }, + { + "type": "table", + "bbox": [ + 0.524, + 0.09, + 0.875, + 0.328 + ], + "angle": 0, + "content": "
NameOriginal ACCIERBCERB
ACCBDRACCBDR
AlexNet-190.2089.5416.0090.2624.67
AlexNet-288.7386.019.7688.3746.10
AlexNet-390.0887.4812.9688.9541.41
AlexNet-488.2586.5216.9688.0179.80
AlexNet-588.8882.4927.9588.2080.30
ResNet18-194.8993.853.1394.9425.00
ResNet18-394.8093.4626.5794.2250.0
ResNet18-494.6792.9224.6194.0933.98
ResNet18-594.3990.0426.0593.7534.69
ResNet18-694.4593.4830.1392.4443.31
ResNet18-894.4191.2244.0492.6647.87
ResNet18-1094.3088.9644.5992.8738.55
ResNet18-1294.9687.3640.9092.3437.19
ResNet18-1494.6886.6335.4892.1843.04
ResNet18-1894.8183.9236.5292.1146.79
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.34, + 0.892, + 0.382 + ], + "angle": 0, + "content": "Table 1. ACC (\\%) and BDR (\\%) performance of ambiguity attacks using IERB/CERB structure for AlexNet and ResNet18 with different number of passport layers on CIFAR10." + }, + { + "type": "table", + "bbox": [ + 0.518, + 0.386, + 0.88, + 0.537 + ], + "angle": 0, + "content": "
Dataset-NetOriginalDataSizePlainCERBIERB
CIFAR10 \nAlexNet90.205000 (10%)83.6288.1687.30
2500 (5%)73.8286.7078.91
2000 (4%)73.4886.3076.73
1500 (3%)72.0986.7871.38
1000 (2%)64.8284.2263.71
CIFAR100 \nResNet1875.055000 (10%)70.7373.2670.51
3000 (6%)69.1472.2669.35
2000 (4%)62.8171.4268.89
1500 (3%)62.8671.6968.50
1000 (2%)53.9170.1268.44
" + }, + { + "type": "table_caption", + "bbox": [ + 0.5, + 0.547, + 0.892, + 0.574 + ], + "angle": 0, + "content": "Table 2. ACC (%) comparison with Plain attack for CIFAR10-AlexNet and CIFAR100-ResNet18." + }, + { + "type": "table", + "bbox": [ + 0.504, + 0.587, + 0.88, + 0.696 + ], + "angle": 0, + "content": "
DatasetPassport LayerOriginalPlainCERBIERB
Caltech101Last 3 layers72.5471.0172.2667.79
Last 5 layers68.3059.8966.7860.73
Last 8 layers72.4959.9469.3859.32
Last 10 layers70.9057.1766.8957.06
Caltech256Last 5 layers54.3438.6452.2351.02
Last 7 layers53.9536.7249.5549.36
Last 10 layers55.4324.9347.8544.19
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.705, + 0.892, + 0.748 + ], + "angle": 0, + "content": "Table 3. ACC (%) comparison with Plain attack on Caltech-101 and Caltech-256, where \\(10\\%\\) training data are used. Here the network is fixed to be ResNet18." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.892, + 0.903 + ], + "angle": 0, + "content": "rather limited. To this end, we embed 5 passport layers in AlexNet and 10 passport layers in ResNet18, and train them on CIFAR10 and CIFAR100, respectively. Let Plain attack refer to the case without using our proposed structures. Table 2 gives the ACC results of Plain attack and our ambiguity attacks using CERB and IERB. For the simple AlexNet, the performance of our attack with CERB overwhelms that of Plain attack, and the performance gain becomes more significant when smaller number of training data is avail" + }, + { + "type": "page_number", + "bbox": [ + 0.482, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "8128" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.122, + 0.089, + 0.432, + 0.214 + ], + "angle": 0, + "content": "
DataSizeIERBCERB
ACCBDRACCBDR
10000 (25%)90.4740.2492.1791.77
5000 (12.5%)88.2642.8291.0592.82
4000 (10%)87.4347.7190.0792.61
3000 (7.5%)86.3048.3489.4993.65
2500 (6.25%)86.2348.9687.0093.44
2000 (5%)85.2649.2085.6793.44
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.224, + 0.47, + 0.252 + ], + "angle": 0, + "content": "Table 4. ACC (%) and BDR (%) performance of ambiguity attacks with IERB and CERB using non-overlapping CIFAR10 dataset." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.264, + 0.471, + 0.535 + ], + "angle": 0, + "content": "able. For instance, when \\(2\\%\\) training data are used, the ACC gap is almost \\(20\\%\\). Such a property is very valuable in practice, as attacks are usually launched with very limited number of data; otherwise, re-training an entire model could be feasible as well. Also, for this simple AlexNet, our attack with IERB has similar performance with Plain attack. For the relatively large network ResNet18, our attack with CERB achieves \\(4.93\\%\\) ACC drop, compared with the original accuracy, when only \\(2\\%\\) training data are used. This drop shrinks to \\(1.79\\%\\) when \\(10\\%\\) training data are available. Compared with Plain attack, the ACC gains of our attack with CERB can be as large as \\(16.21\\%\\). In addition, it is noted that our attack with IERB becomes much superior to Plain attack, when very limited training data are adopted; the ACC gain can be up to \\(14.53\\%\\). More results on more complicated datasets including Caltech-101 and Caltech-256 can be found in Table 3, and similar conclusions can be drawn." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.546, + 0.395, + 0.563 + ], + "angle": 0, + "content": "4.2. Attack with non-overlapping dataset" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.569, + 0.47, + 0.718 + ], + "angle": 0, + "content": "In the above experiments, we consider the case that the attacker has access to a part of the original training data, namely, the dataset for launching the attack overlaps with the original one. We now investigate the attack performance under a more challenging scenario, i.e., the dataset available to the attacker and the original dataset come from the same source; but do not overlap. This non-overlapping dataset mimics the practical scenario that the attacker may not be able to exactly access a part of the original training data; but rather can only access some similar ones." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.72, + 0.471, + 0.901 + ], + "angle": 0, + "content": "We randomly divide CIFAR10 into non-overlapping two subsets: 40000 for training the passport-based network and the remaining 10000 for the attack. Specifically, the attacking model is a ResNet18 with 10 passport layers, and the accuracy of the trained model is \\(93.12\\%\\). The attack performance of our ambiguity attacks with IERB and CERB under this new setting is tabulated in Table 4. With these 10000 non-overlapping data, our ambiguity attack with CERB reaches a \\(92.17\\%\\) accuracy, only \\(0.95\\%\\) away from the original one. Also, the BDR in this case is as high as \\(91.77\\%\\), indicating the recovered scale factors are very different from the authorized ones. When less number of non-" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.273 + ], + "angle": 0, + "content": "overlapping data are used, the ACC values drop while the accompanied BDRs tend to improve. Even when only \\(5\\%\\) non-overlapping data are available, the ACC value can still be \\(85.67\\%\\) with BDR being \\(93.44\\%\\). Similar results can be obtained by our ambiguity attack with IERB, but with a much lowered BDR of around \\(40\\%\\). Another interesting phenomenon is that the ambiguity attack with CEBR using non-overlapping dataset leads to slightly worse ACC, but much better BDR performance, compared with the same attack with overlapping dataset. These results, again, show that our proposed ambiguity attacks are still very effective even in the challenging non-overlapping scenarios." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.283, + 0.892, + 0.313 + ], + "angle": 0, + "content": "4.3. Result of ambiguity attack with CERB on other DNN watermark methods" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.321, + 0.893, + 0.517 + ], + "angle": 0, + "content": "We now show that our proposed attack strategy can be generalized well to other DNN watermark methods. As the ambiguity attack with CERB overwhelms the one with IEBR, we adopt it in the following evaluations. The three DNN watermarking methods considered are: Greedy-Residual [21], DeepSigns [8], and Uchida [29], which used specific layer weights for the watermark embedding. For Greedy-Residual, the watermark was embedded into the first convolutional layer weight of the network, while for DeepSigns, the watermark was hidden in the flattened features before the last linear layer. Regarding Uchida's method, the watermark was injected into the third convolutional layer weights of the network." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.518, + 0.892, + 0.744 + ], + "angle": 0, + "content": "We flexibly adapt our CERB structure for different types of embedded intermediaries such as model weights and features in three DNN watermark methods. Following the attack setting of Fan et al. [11], we assume that the network structure and model weights except those from the watermark are available to the attacker. As a result, for Greedy-Residual, we can replace the normalization layer after the embedded convolutional parameters with the CERB. Similarly, for DeepSigns, the normalization layer before the embedded feature map is replaced by our CERB. For Uchida's method, a CERB structure is added after the embedded convolutional parameters. We preset a different signature and only train the parameters embedded with the watermarks and the CERB parameters to match this new signature. More implementation details can be found in Appendix A." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.744, + 0.892, + 0.835 + ], + "angle": 0, + "content": "We introduce signature detection rate (SDR) to evaluate if a signature is successfully embedded in the model. The SDR is defined as the percentage of the watermark bits \\(\\mathbf{wm} = \\{wm_1, \\dots, WM_C\\}\\) extracted from the model that are coincident with the signature \\(\\mathbf{sig} = \\{sig_1, \\dots, sig_C\\}\\) used during the embedding process, i.e.," + }, + { + "type": "equation", + "bbox": [ + 0.588, + 0.839, + 0.892, + 0.881 + ], + "angle": 0, + "content": "\\[\nS D R = \\frac {1}{C} \\sum_ {i = 1} ^ {C} \\mathcal {I} \\left[ w m _ {i} = s i g _ {i} \\right]. \\tag {10}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.52, + 0.886, + 0.892, + 0.902 + ], + "angle": 0, + "content": "The attack results on three watermark methods are pre" + }, + { + "type": "page_number", + "bbox": [ + 0.482, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "8129" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.116, + 0.089, + 0.859, + 0.16 + ], + "angle": 0, + "content": "
WM methodDataset-NetEmbed-PositionDataSizeOriginal ACCAttack ACCBDRSDR
Greedy-ResidualCaltech256-ResNet18First Conv layer10%54.9854.3749.22100
DeepSignsCIFAR10-WRNLast Linear layer10%91.3091.1537.5100
UchidaCIFAR10-WRNThird Conv layer10%90.1189.7745.31100
" + }, + { + "type": "table_caption", + "bbox": [ + 0.119, + 0.17, + 0.85, + 0.184 + ], + "angle": 0, + "content": "Table 5. Results of our ambiguity attack on other DNN watermark methods, in terms of ACC (%), BDR (%), and SDR (%)." + }, + { + "type": "table", + "bbox": [ + 0.104, + 0.197, + 0.447, + 0.233 + ], + "angle": 0, + "content": "
# of CERBOriginal046810
ACC (%)55.4225.0328.9938.5042.5847.07
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.243, + 0.47, + 0.271 + ], + "angle": 0, + "content": "Table 6. Results of using different number of CERB on Caltech-256 with ResNet18." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.28, + 0.471, + 0.446 + ], + "angle": 0, + "content": "sented in Table 5. For Greedy-Residual method, the inference performance of the model after the attack is quite similar to that of the original one, with a very slight drop of \\(0.61\\%\\). In addition, the SDR is \\(100\\%\\), implying that the attacker can claim the ownership to this model with the new signature. Meanwhile, a high BDR of \\(49.22\\%\\) well demonstrates the high dissimilarity between the forged and original watermarks. Very similar observations can be made when attacking DeepSigns and Uchida's methods. Therefore, we validate the generalization capability of our attack strategy to other DNN watermark methods." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.455, + 0.228, + 0.471 + ], + "angle": 0, + "content": "4.4. Ablation study" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.478, + 0.47, + 0.643 + ], + "angle": 0, + "content": "Different number of CERB structures: To study the effect on attack performance with different number of CERB structures, we use a ResNet18 with the last 10 layers embedded with passports for the illustration. As can be seen from Table 6, the original performance evaluated on Caltech-256 is \\(55.42\\%\\). For Plain attack with 0 CERB structure, the ACC is very low, i.e., \\(25.05\\%\\). By gradually applying more CERB structures, the ACC values improve constantly. Eventually, with all 10 passport layers replaced by our CERB structures, the ACC of our ambiguity attack reaches \\(47.07\\%\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.645, + 0.47, + 0.856 + ], + "angle": 0, + "content": "Increasing the depth of CERB: The CERB in the default setting is a two-layer perceptron with LeakyReLU. We now try to testify if using perceptron with more layers leads to better attack performance. To this end, we experiment on the ResNet18 with 10 passport layers trained on CIFAR10, and launch the ambiguity attacks by varying the number of layers in CERB. As can be seen from Table 7, the ACC restored by CERB with 2 layers is the highest, reaching \\(92.24\\%\\). With more layers being involved, the ACC performance actually drops surprisingly. We conjecture that the two-layer perceptron is enough for our ambiguity attack; while increasing the number of layers places heavier burden to the training and eventually affects the performance of the ambiguity attack." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.856, + 0.47, + 0.901 + ], + "angle": 0, + "content": "Using other activation functions in CERB: We also evaluate the impact of the activation functions in CERB on the overall attack performance. Again, we experiment on" + }, + { + "type": "table", + "bbox": [ + 0.513, + 0.197, + 0.885, + 0.234 + ], + "angle": 0, + "content": "
# of MLP layers in CERBOriginal2345
ACC (%)94.4092.2486.8584.1886.45
" + }, + { + "type": "table_caption", + "bbox": [ + 0.519, + 0.244, + 0.872, + 0.258 + ], + "angle": 0, + "content": "Table 7. Results of changing the number of layer in CERB." + }, + { + "type": "table", + "bbox": [ + 0.522, + 0.272, + 0.875, + 0.315 + ], + "angle": 0, + "content": "
Activation FunctionsLeakyReLUtanhSigmoid
ACC (%)92.8792.5492.80
" + }, + { + "type": "table_caption", + "bbox": [ + 0.535, + 0.325, + 0.856, + 0.34 + ], + "angle": 0, + "content": "Table 8. Result of using different activation functions." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.348, + 0.892, + 0.469 + ], + "angle": 0, + "content": "the ResNet18 with 10 passport layers trained on CIFAR10. We then replace every passport layer with CERB, and adopt different activation functions in CERB. We list the ACC results by using tanh and Sigmoid, in addition to our default LeakyReLU in Table 8. As can be noticed, all ACC results with different activation functions are similar. This implies that the attack performance is not sensitive to the activation functions adopted." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.483, + 0.619, + 0.499 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.509, + 0.892, + 0.629 + ], + "angle": 0, + "content": "In this paper, we propose an advanced ambiguity attack that defeats the passport-based model IP protection scheme. We combine multi-layer perceptron with skip connection to find valid substitute passports using less than \\(10\\%\\) of the training dataset. Extensive experimental results validate the effectiveness of our ambiguity attack. Further, it is demonstrated that our attack strategy can be easily extended to other DNN watermark methods." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.63, + 0.892, + 0.78 + ], + "angle": 0, + "content": "Regarding the remedy solutions, one potential direction is to exploit random locations for inserting the passport-layers, in which the randomness is controlled by a secret key. Additionally, another promising attempt is to change the embedding position from model weights to the activations. To make sure the next convolutional layer can extract proper features from the activation, the statistic of the activation should stay in a restricted scope. Such a statistic could be unique for a given signature, which may be helpful to resist our ambiguity attack." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.781, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Acknowledgments: This work was supported in part by Macau Science and Technology Development Fund under SKLIOTSC-2021-2023, 0072/2020/AMJ, and 0022/2022/A1; in part by Research Committee at University of Macau under MYRG2020-00101-FST and MYRG2022-00152-FST; in part by Natural Science Foundation of China under 61971476; and in part by Alibaba Group through Alibaba Innovative Research Program." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "8130" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.105 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.115, + 0.47, + 0.183 + ], + "angle": 0, + "content": "[1] Yossi Adi, Carsten Baum, Moustapha Cisse, Benny Pinkas, and Joseph Keshet. 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In Proceedings of the ACM Asia Conference on Computer and Communications Security, pages 159-172, 2018. 1" + }, + { + "type": "list", + "bbox": [ + 0.08, + 0.092, + 0.47, + 0.812 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.946, + 0.516, + 0.956 + ], + "angle": 0, + "content": "8132" + } + ] +] \ No newline at end of file diff --git a/2023/Effective Ambiguity Attack Against Passport-Based DNN Intellectual Property Protection Schemes Through Fully Connected Layer Substitution/e387fd7f-d2cf-442f-899c-5257e75d504c_origin.pdf b/2023/Effective Ambiguity Attack Against Passport-Based DNN Intellectual Property Protection Schemes Through Fully Connected Layer Substitution/e387fd7f-d2cf-442f-899c-5257e75d504c_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..7dd498a1975a75e25d2a0955339d66cbcf42cca9 --- /dev/null +++ b/2023/Effective Ambiguity Attack Against Passport-Based DNN Intellectual Property Protection Schemes Through Fully Connected Layer Substitution/e387fd7f-d2cf-442f-899c-5257e75d504c_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:8567398208d227982f2d753b596a6bdf432b0b6a0fb3c9befa68a269659e5875 +size 3263901 diff --git a/2023/Effective Ambiguity Attack Against Passport-Based DNN Intellectual Property Protection Schemes Through Fully Connected Layer Substitution/full.md b/2023/Effective Ambiguity Attack Against Passport-Based DNN Intellectual Property Protection Schemes Through Fully Connected Layer Substitution/full.md new file mode 100644 index 0000000000000000000000000000000000000000..eb202683eaa505aa57ce5f1d49d5e06bf8e30205 --- /dev/null +++ b/2023/Effective Ambiguity Attack Against Passport-Based DNN Intellectual Property Protection Schemes Through Fully Connected Layer Substitution/full.md @@ -0,0 +1,335 @@ +# Effective Ambiguity Attack Against Passport-based DNN Intellectual Property Protection Schemes through Fully Connected Layer Substitution + +Yiming Chen $^{1}$ , Jinyu Tian $^{2}$ , Xiangyu Chen $^{1,3}$ , and Jiantao Zhou $^{1,\dagger}$ + +1State Key Laboratory of Internet of Things for Smart City + +Department of Computer and Information Science, University of Macau + +$^{2}$ Faculty of Innovation Engineering, Macau University of Science and Technology + +3Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences + +{yc17486, jtzhou}@umac.mo, jytian@must.edu.mo, chxy95@gmail.com + +# Abstract + +Since training a deep neural network (DNN) is costly, the well-trained deep models can be regarded as valuable intellectual property (IP) assets. The IP protection associated with deep models has been receiving increasing attentions in recent years. Passport-based method, which replaces normalization layers with passport layers, has been one of the few protection solutions that are claimed to be secure against advanced attacks. In this work, we tackle the issue of evaluating the security of passport-based IP protection methods. We propose a novel and effective ambiguity attack against passport-based method, capable of successfully forging multiple valid passports with a small training dataset. This is accomplished by inserting a specially designed accessory block ahead of the passport parameters. Using less than $10\%$ of training data, with the forged passport, the model exhibits almost indistinguishable performance difference (less than $2\%$ ) compared with that of the authorized passport. In addition, it is shown that our attack strategy can be readily generalized to attack other IP protection methods based on watermark embedding. Directions for potential remedy solutions are also given. + +# 1. Introduction + +With the geometric growth of computing power of computational devices in recent decades, there have emerged many deep learning applications that have contributed to the human world such as super-resolution reconstruction [7, 9, 30], image inpainting [31, 34, 35] and forgery detection [32]. It usually costs many resources to develop new DNN models and developers will not tolerate the act of theft of their IP. The IP protection problem of deep models be + +comes more severe with the birth of Machine Learning as a Service (MLaaS) [26]. Preventing the infringement behavior of deep models now emerges as a necessary concern when developing new algorithms and systems. + +Model watermark [20, 25, 27, 28, 37] has been a popular method to protect the IP of DNN models. In the embedding process, the owners embed the secret signatures (watermarks), and then in the verification process, they can claim their ownership to the model by matching the extracted signatures with the original versions. The existing model watermark methods can be roughly divided into two categories [10, 11]: feature-based and trigger-based methods. Specifically, feature-based methods [4, 8, 24, 29] applied a regularizer to embed the secret watermark into the activation functions or model weights. Uchida et al. [29] proposed to use a regularizer to embed a watermark into the model weights. Darvish et al. [8] embedded the fingerprints in the Probability Density Function of trainable weights instead. Aramoon et al. [3] inserted the signature into the gradient of the cross-entropy loss function with respect to the inputs. In contrast, trigger-based methods make the output target respond to specific inputs. Along this line, Adi et al. [1] used the backdoor attack as a means to watermark the model. Merrer et al. [18] designed a zero-bit watermarking algorithm that uses adversarial samples as watermarks to claim the ownership. Zhang et al. [39] applied watermarks to images and then trained the network to output target labels when input images carry these watermarks. + +Despite the strength in retaining ownership of DNN models, most existing model watermark methods are shown to be vulnerable to the so-called ambiguity attack, in which the attacker manages to cast doubts on the ownership verification by crafting counterfeit (forged) watermarks [11]. Recently, Fan et al. [10] first designed a series of ambiguity attacks, which are effective in attacking DNN watermark methods. It was stated that for conventional watermark + +methods, a counterfeit watermark can be forged as along as the model performance is independent of the signature [11]. Following this proposition, Fan et al. designed a passport layer through which the functionality of the model is controlled by the signature called passport. However, Fan et al. encountered a heavy performance drop when batch normalization layers exist. To solve this problem, Zhang et al. [38] added learnable affine transformations to the scale and bias factors. It was claimed that an attacker cannot find a substitute passport that maintains the model performance, which ensures the security of these passport-based methods against existing ambiguity attacks. + +In this work, we aim to design an advanced ambiguity attack to the passport-based method, capable of generating valid substitute passports with only a small number of data. Here, valid substitute passports are defined as those leading to an indistinguishable model performance, but sufficiently different from the original authorized passports. Clearly, with such valid substitute passports, an attacker can claim the ownership of the model. To this end, we first experimentally justify the existence of multiple valid substitute passports. Noticing the fact that it is easy to localize the passport layers, we then propose our ambiguity attack by replacing passport layers with our designed two types of structures, namely Individual Expanded Residual Block (IERB) and Collective Expanded Residual Block (CERB). Both structures are built in a way to encourage the significant changes of the parameters in the passport layers during the training, which could help us search for valid substitute passports. Benefiting from these two structures and assisting with a small amount training data, we can obtain valid substitute passports, and hence, defeat the passport-based methods which are the only type of method claimed to be immune to existing ambiguity attacks. + +Our major contributions can be summarized as follows: + +- We propose a novel and effective ambiguity attack against the passport-based IP protection schemes. With less than $10\%$ of training data, our ambiguity attack on passport-layer protected model can restore the functionality of the model with a less than $2\%$ performance gap from the original accuracy. +- We design two novel structures for replacing the passport layers, based on the multi-layer perceptron (MLP) and skip connection to assist with our ambiguity attack for searching valid substitute passports with a small amount of training data. +- Experiments on both overlapping (attacker's training dataset is part of the original training dataset) and non-overlapping datasets (attacker's dataset and the original one come from the same source but no overlap exists), and on different network structures have proved the effectiveness of our ambiguity attack. +- Our attack method can be readily generalized to attack other DNN watermark methods [8, 21, 29]. + +# 2. Related Works + +DNN watermark methods have been popular solutions for DNN model IP protection. However, these techniques might still be vulnerable to flagrant infringement from notorious adversaries. In this section, we review the two types of representative attack methods, namely, removal attack [2, 5, 6, 14, 22, 33] and ambiguity attack [10, 11, 38], along with the passport-based method attempting to defend against ambiguity attacks [11]. + +Removal Attack: This type of attack tries to remove the watermark from the protected model, malfunctioning the ownership verification mechanism. Along this line, many fine-tuning based methods have been proposed. Chen et al. [5] combined a redesigned elastic weight consolidation algorithm and unlabeled data augmentation to achieve unified model watermark removal with limited data. Guo et al. [14] used a dataset transformation method called PST (Pattern embedding and Spatial-level Transformation) to preprocess the data before fine-tuning. Chen et al. [6] utilized auxiliary unlabeled data to decrease the amount of labeled training data required for effective watermark removal. Aiken et al. [2] provided a three-stage scheme to remove backdoor-based watermarks by exploiting another trigger-free dataset from the same domain. Liu et al. [22] designed a framework to remove backdoor-based watermarks, in which a data augmentation was proposed to imitate the behavior of the backdoor triggers. Yan et al. [33] attempted to break the passport-based method by scaling the neurons and flipping the signs of parameters. However, this method assumed that the authorized passports are available to the attacker, which is not realistic in practice. Also, these aforementioned attack methods only enable the attackers to remove the watermarks, while unable to claim the ownership. + +Ambiguity Attack: Another more threatening attack is the ambiguity attack, where the attacker can forge another substitute watermark to claim the model ownership. The concept of ambiguity attack originally appeared in image watermark community [19, 23], and recently has been extended to the DNN watermark methods. The pioneering work was conducted by Fan et al. in [10], which pointed out the vulnerability of Uchida's watermark method [29] under the ambiguity attack. They also showed that the same weakness of Adi's DNN watermark method [1] exists, by proving that another trigger can be optimized exclusively to cause the same model response as the original one. + +Passport-based method: Passport-based method was originally proposed by Fan et al. [11] as a remedy enabling DNN watermark methods to defeat the ambiguity attack. This is achieved by replacing the traditional normalization layer with the so-called passport layer, whose difference mainly lies in how the affine factors are obtained. In passport layer, the scale factor $\gamma$ and bias factor $\beta$ are computed + +with the passport as follows: + +$$ +\gamma = \operatorname {A v g} \left(\mathbf {W} _ {\text {c o n v}} * \mathbf {s} _ {\gamma}\right), \beta = \operatorname {A v g} \left(\mathbf {W} _ {\text {c o n v}} * \mathbf {s} _ {\beta}\right), \tag {1} +$$ + +where $\mathbf{s} = \{\mathbf{s}_{\gamma},\mathbf{s}_{\beta}\}$ is called the passport, $\mathbf{W}_{conv}$ is the convolutional layer weight before this layer, and $Avg(\cdot)$ represents the average pooling function. + +To embed the passport $s$ into the model, the network $\mathbb{N}_p$ is optimized on the training set $\mathcal{D} = \{(x_i,y_i)\}_{i = 1}^N$ , where $x_{i}$ is the input and $y_{i}$ is the corresponding label, using the following loss: + +$$ +\mathcal {L} = \mathcal {L} _ {r} \left(\mathbb {N} _ {p} [ \mathbf {W}, \mathbf {s} ] \left(x _ {i}, y _ {i}\right)\right) + \alpha \mathcal {L} _ {\text {s i g n}} (\operatorname {s g n} (\gamma), \mathbf {b}), \tag {2} +$$ + +where $\mathbb{N}_p[\mathbf{W},\mathbf{s}]$ denotes the model $\mathbb{N}$ with the weight $\mathbf{W}$ and the passport s. The first term $\mathcal{L}_r(\cdot)$ is the classification loss, and the second term $\mathcal{L}_{sign}(\cdot)$ is a sign loss regularization constraining the sign sequence of scale factors to be a predefined $C$ -bit signature $\mathbf{b} = \{b_1,\dots,b_C\} \in \{-1,1\} ^C$ Here, $\mathrm{sgn}(\cdot)$ is the sign function. + +Denote $\mathcal{Q}(\mathbb{N}_p[\mathbf{W},\mathbf{s}])$ as the inference performance of model $\mathbb{N}_p$ with the passport s. The verification process mainly relies on the assumption that the performance $\mathcal{Q}(\mathbb{N}_p[\mathbf{W},\mathbf{s}])$ seriously deteriorates when an unauthorized passport is presented. Hence, the model ownership using passport-based method is conducted by matching the signs of scale factors $\mathrm{sgn}(\gamma)$ with the predefined signature b and checking the DNN model inference performance. + +# 3. Proposed Ambiguity Attack + +Though the passport-based methods [11, 38] have been claimed to be immune to the existing ambiguity attacks [10], they do not preclude the existence of more advanced ambiguity attacks. In this work, we cast doubt on the security of the passport-based methods, and propose a simple yet effective ambiguity attack, capable of crafting valid substitute passports. Before diving into the detailed design of our ambiguity attack, let us clarify our attack goal and the information assumed to be available to the attacker. + +Attack Goal: Essentially, the attack goal is to generate substitute passport $\mathbf{s}_t$ , with which the model $\mathbb{N}_p[\mathbf{W},\mathbf{s}_t]$ has indistinguishable performance with that of applying the authorized passport $\mathbf{s}_o$ , i.e., $\mathcal{Q}(\mathbb{N}_p[\mathbf{W},\mathbf{s}_o])$ . Specifically, following the ambiguity attack setting in [11], we assume that the attacker has access to the model weights $\mathbf{W}$ except from the passport. Note that, without the passport, the affine factors are missing in the normalization layer, through which the attacker can easily localize the passport layers. Also, the attacker is allowed to have a small number of training data, namely, $\mathcal{D}_s = \{(\hat{x}_i,\hat{y}_i)\}_{i = 1}^n$ , where $n < N$ . Formally, we have the following Definition 1, explicitly explaining the successful ambiguity attack on passport-based method. + +Definition 1: An ambiguity attack on passport layer protected model is successful, if + +![](images/ca37740f9804932d5ba28bd3b64fe307437b2f7bc1050b439db8f9de990b62e2.jpg) +(a) + +![](images/23fc951b0b62eb96324a24893ccc4e6abcb8a4b9ffc4155a68b9dedeece37028.jpg) +(b) +Figure 1. Valid substitute passports obtained by initializing scale factors with different signs from the authorized $\mathbf{s}_o$ and retraining. Horizontal axis denotes the number of different signs from $\mathbf{s}_o$ . + +I) DNN inference accuracy with the substitute passport $\mathbf{s}_t$ is close to that with the authorized passport $\mathbf{s}_o$ , i.e., + +$$ +\left| \mathcal {Q} \left(\mathbb {N} _ {p} [ \mathbf {W}, \mathbf {s} _ {t} ]\right) - \mathcal {Q} \left(\mathbb {N} _ {p} [ \mathbf {W}, \mathbf {s} _ {o} ]\right) \right| < \epsilon . \tag {3} +$$ + +II) Dissimilarity between the substitute passport $\mathbf{s}_t$ and the authorized $\mathbf{s}_o$ should be large enough, i.e.: + +$$ +\left| \mathbf {s} _ {t} - \mathbf {s} _ {o} \right| > \delta . \tag {4} +$$ + +Before presenting the details of our ambiguity attack, let us first justify the existence of multiple valid substitute passports satisfying the conditions given in (3) and (4). To this end, we here adopt an experimental approach and leave the theoretical justification in our future work. Assume now that we are given the complete training data $\mathcal{D}$ , though this large amount of data are not required when launching the attack. We initialize scale factors with different combinations of $\{+1, -1\}$ and fine-tune the model based on $\mathcal{D}$ . In Fig. 1, we give the experimental results on ResNet18 trained on the CIFAR10 dataset, where the passport layer is placed after the first convolutional layer and the length of the scale factor is 64. The model with the authorized passport leads to an inference performance of $94.70\%$ . As can be seen, the accuracy of the models after retraining is still close to $94.70\%$ (red line, see Fig. 1(a)). More importantly, the signs of retained affine factors only have low coincidence rate (around $60\%$ , see Fig. 1(b)) with the original ones, implying that retained affine factors differ significantly from the authorized affine factors. Therefore, these retrained affine factors could simultaneously satisfy the conditions (3) and (4), and hence are valid substitute passports. + +Though the existence of substitute passports has been justified, the difficulty of directly optimizing a passport remains unsolved for very limited number of training data. Clearly, in practical attacks, the attacker is only allowed to have access to very limited data; otherwise, he can retrain the entire model. Fan et al. [11] ascribed the robustness of passport-based method against fine-tuning the scale factors to the lazy-to-flip property, with which the scale factors are rarely updated to cross the zero during the training. + +![](images/0d6c6dec4ddb15efac8c1f92f3f3c693602be9671a54bc0f6235c27e57149806.jpg) +Figure 2. The structures of the ResNet18 with passport layer and our designed CERB/IERB structures. + +To overcome the lazy-to-flip property for the scale factors, we attempt to add a trainable block after it, encouraging scale factors to go across the zeros by non-linear transformations. For efficiency, we adopt MLP for designing the trainable blocks. Following this line, we design two structures namely IERB and CERB to replace the passport layer. + +The overall structure: Motivated by the above observations, we now design a novel ambiguity attack on passport-based method. The overall structure is given in Fig. 2, where we use the ResNet18 embedded with passport layers for the illustration. Specifically, the protected ResNet18 is comprised of multiple residual blocks, each containing several convolutional layers followed by the passport layer. As aforementioned, the locations of the passport layers can be easily determined. We can then insert either IERB or CERB structure into these locations. In our structure, the scale factor $\gamma$ is the output of the IERB/CERB. For the bias factor $\beta$ , we do not add our new structure; but instead we optimize it directly. We are now ready to introduce the details of CERB and IERB structures. After that, we will give the complete algorithm of our ambiguity attack. + +# 3.1. Individually Expanded Residual Block (IERB) + +In this subsection, we present the details of the IERB block. As showed in Fig. 3 (a), the $i$ -th scale factor $\gamma_i^l$ in the $l$ -th passport layer is transformed by a Two-Layer Perceptron (TLP) with FC-LeakyReLU-FC structure where the FC refers to fully connected layer. For the simplicity of notations, we omit the superscript in $\gamma_i^l$ in the sequel. The output of this TLP is then used for the affine transformation + +![](images/f9d4362759c2f927f6f8b080aaba8bae7619506c3817638ede184111cc751187.jpg) +(a) +Figure 3. Details of (a) IERB and (b) CERB. + +![](images/7fff39d03ef4a583f4b1402d23e3e7649ce6e1c4eab05046a73165ce52161342.jpg) +(b) + +later. The first linear layer $FC_{1\rightarrow h}$ with learnable parameters maps the scale factor into a $h$ -dimensional vector, while the second linear layer $FC_{h\rightarrow 1}$ maps the dimension back to 1, where $h$ is the hidden layer size. A larger $h$ brings a larger optimization space in the hidden layer; but could add burden to the training process. We empirically set $h = 10$ striking a good balance between these two factors. In addition, a skip connection is added aside with the TLP structure to facilitate the back-propagation. Benefiting from the expanded parameter space brought by the TLP structure, the output scale factor would more likely go across the zero during the updating. This helps the attacker search for an appropriate $\mathbf{s}_t$ satisfying (4). + +Let $\{\mathbf{W}_{i,j},\mathbf{b}_{i,j}\}$ be the weights of the $j$ -th linear + +layer connected after the $i$ -th scale factor, where $i \in \{1,2,\dots,C\}$ and $j \in \{1,2\}$ . In IERB, the output of the first linear layer taking the $i$ -th scale factor as input is: + +$$ +\gamma_ {i} ^ {\prime} = \mathbf {W} _ {i, 1} ^ {T} * \gamma_ {i} + \mathbf {b} _ {i, 1} ^ {T}, \tag {5} +$$ + +where $*$ denotes the matrix multiplication operator. After the activation function LeakyReLU, the output of the second linear layer with the shortcut can be expressed as: + +$$ +\gamma_ {i} ^ {\prime \prime} = \mathbf {W} _ {i, 2} ^ {T} * \left(L R e L U \left(\gamma_ {i} ^ {\prime}\right)\right) + \mathbf {b} _ {i, 2} ^ {T} + \gamma_ {i}. \tag {6} +$$ + +# 3.2. Collective Expanded Residual Block (CERB) + +The IERB discussed above handles each scale factor individually, but may ignore the inter-channel relationship among scale factors. Instead of using isolated propagation paths for each scale factor, we now attempt to enhance the inter-channel relationship and optimize the scale factors in a collective manner. As can be observed from Fig. 3 (b), we choose to use a unified TLP structure to deal with all the $C$ scale factors as a whole. The output of the TLP structure is then summed with the input scale factors to get the updated ones. Different from the IERB, each activation in the hidden layer is now related to all the input scale factors, and the fully connected structure ensures the exploitation of the inter-channel information. Mathematically, the output scale factors can be computed by: + +$$ +\gamma^ {\prime \prime} = \left(\mathbf {W} _ {2} ^ {T} * \left(L R e L U \left(\mathbf {W} _ {1} ^ {T} * \gamma + \mathbf {b} _ {1} ^ {T}\right)\right) + \mathbf {b} _ {2} ^ {T}\right) + \gamma , (7) +$$ + +where $\mathbf{W}_1$ and $\mathbf{W}_2$ represent the parameters in the first and second linear layers. Here we set the hidden layer size to be $C / 8$ , where $C$ is the number of channels in this layer. + +# 3.3. Algorithm of Our Ambiguity Attack + +With these newly proposed structures, we can summarize our ambiguity attack strategy on the passport-based method in Algorithm 1. For simplicity, we use $\mathbf{W}_{\gamma}$ to represent all the parameters in IERB or CERB. Let us briefly explain our workflow for better understanding. In Algorithm 1, lines $1\sim 4$ are devoted to the model loading, normalization layer substitution, CERB/IERB insertion, and parameter initialization. The $\gamma, \beta$ and $\mathbf{W}_{\gamma}$ are then updated in lines $5\sim 14$ using the gradients with respect to each parameter by back-propagating the cross entropy loss: + +$$ +\gamma = \gamma - \nabla_ {\gamma} l o s s, +$$ + +$$ +\beta = \beta - \nabla_ {\beta} \text {l o s s}, \tag {8} +$$ + +$$ +\mathbf {W} _ {\gamma} = \mathbf {W} _ {\gamma} - \nabla_ {\mathbf {W} _ {\gamma}} l o s s. +$$ + +Eventually, the algorithm outputs the substitute scale and bias factors $\gamma''$ and $\beta$ . + +# 4. Experimental Results + +In this section, we evaluate the effectiveness of our ambiguity attack from different perspectives. Before present + +Algorithm 1 Proposed Ambiguity Attack + +Input: Protected network $\mathbb{N}_p[\mathbf{W}]$ with passport layers excluded; training dataset $\mathcal{D}_s = \{(\hat{x}_i,\hat{y}_i)\}_{i = 1}^n$ ; checkpoint state_dict; training epoch $M$ + +Output: substitute scale and bias factors $\gamma^{\prime \prime}$ $\beta$ + +1: Use normalization layers in the locations of the passport layers. +2: Insert CERB/IERB structures after the scale factors of these normalization layers. +3: Load weight $\mathbf{W}$ of $\mathbb{N}_p[\mathbf{W}]$ from state_dict. +4: Initialize normalization layer weights $\gamma$ and $\beta$ with 1 and 0, respectively. + +5: for epoch $= 1$ to $M$ do +6: for minibatch $(\hat{x}_i,\hat{y}_i)\subset \mathcal{D}_s$ do +7: for each normalization layer with IERB/CERB do +8: $\gamma^{\prime \prime} = \mathrm{CERB / IERB}(\gamma ,\mathbf{W}_{\gamma}).$ $\triangleright$ Eq. (5/7). +9: Use $\gamma''$ and $\beta$ for affine transformation in normalization layer. +10: end for +11: loss=cross_entropy $(\mathbb{N}_p[\mathbf{W}](\hat{x}_i),\hat{y}_i)$ +12: Update $\gamma, \beta$ and $\mathbf{W}_{\gamma} \triangleright$ Eq. (8). +13: end for +14: end for + +ing the detailed results, let us clarify the experimental settings including the datasets, target models, and the evaluation metrics. + +Dataset: Four image classification datasets: CIFAR10 [16], CIFAR100 [16], Caltech-101 [12], and Caltech-256 [13], are selected. Unless stated, the dataset used in the attack process only accounts for $10\%$ at maximum of the full training set and does not overlap with the test set. + +DNN architectures: Three DNN architectures, AlexNet [17], ResNet-18 [15] and Wide-Residual Network [36] are used in our experiments, following the tradition of passport-based works [10, 11, 38]. To demonstrate that our attack strategy remains effective for different number of passport layers, we perform the experiments on AlexNet and ResNet18, with at most 5 and 18 passport layers, respectively. For notation convenience, we use a suffix to determine the indices of the passport layers. For instance, AlexNet-4 denotes the AlexNet with the first 4 normalization layers replaced by the passport layers, and AlexNet-last3 represents the version in which the last 3 normalization layers are replaced by the passport layers. + +Evaluation metrics: Prediction accuracy (ACC) of the model is a natural choice for evaluating the attack effectiveness, since a successfully forged passport is expected to achieve similar performance as an authorized passport (see Definition 1). Another metric considered is the bit dissimilarity rate (BDR) of the signature derived from the forged passport, with respect to the authorized one. Specifically, let $\gamma'$ and $\gamma^o$ be the forged and authorized scale factors, re + +spectively. Note that the sign of $\gamma^o$ is used as the signature. The BDR is then defined as: + +$$ +B D R = \frac {1}{C} \sum_ {i = 1} ^ {C} \mathcal {I} \left[ \operatorname {s g n} \left(\gamma_ {i} ^ {\prime}\right) \neq \operatorname {s g n} \left(\gamma_ {i} ^ {o}\right) \right], \tag {9} +$$ + +where the indicator function $\mathcal{I}[\cdot]$ returns 1 when the condition is true and 0 otherwise. A high BDR also implies the large dissimilarity with the authorized passport, which in turn indicates a better performance of the ambiguity attack. + +# 4.1. Attack performance using IERB/CERB + +We now give the details on the effectiveness of our ambiguity attack by replacing the passport layers of the protected model with our proposed IERB or CERB blocks. All protected models with passport layers are trained over the training dataset of CIFAR10. We randomly select $10\%$ of examples from this dataset for launching the ambiguity attack, i.e., training the IERB or CERB blocks. + +The attack results on AlexNet and ResNet18 are reported in Table 1. Since our ambiguity attack is the first one attacking passport-based methods, there are no comparative algorithms available so far. It can be seen that, by using the proposed CERB, our ambiguity attack is capable of achieving high ACC and BDR values for all the settings. Specifically, for AlexNet, the ACC gap is less than $1\%$ , compared with the case of the authorized passport. Also, the BDR can be as large as $80.30\%$ . For the more complex ResNet18, similar observations can be obtained, where the ACC gap is still less than $3\%$ , and the BDR could approach $50\%$ . We even encounter several cases (AlexNet-1 and ResNet18-1), in which the attacked models perform even better than the original ones. These results imply that our proposed ambiguity attack is successful in finding the valid substitute passports with a small number of training data. + +As a comparison, we also present the results of the ambiguity attack with the IERB structure. It can be observed that this variant attack is still somewhat effective with reasonably high ACC and BDR values; but the attack performance is much inferior to the attack with CERB, especially when there are many passport layers. We attribute this phenomenon to the capability of CERB in exploiting the interchannel relationship. For IERB, it is likely to optimize towards the original sign of the scale factor, which naturally results in similar signatures (small BDR) to the original passports. In CERB, however, the collective optimization mechanism explores more possibly optimal pairs of the sign of scale factors, potentially leading to larger BDR of signature and higher ACC. + +To further show the effectiveness of our proposed attack strategy, we now compare the attack performance of the models with and without CERB/IERB structures. As will be clear soon, directly updating the affine factors cannot retrieve valid passports, especially when the available data is + +
NameOriginal ACCIERBCERB
ACCBDRACCBDR
AlexNet-190.2089.5416.0090.2624.67
AlexNet-288.7386.019.7688.3746.10
AlexNet-390.0887.4812.9688.9541.41
AlexNet-488.2586.5216.9688.0179.80
AlexNet-588.8882.4927.9588.2080.30
ResNet18-194.8993.853.1394.9425.00
ResNet18-394.8093.4626.5794.2250.0
ResNet18-494.6792.9224.6194.0933.98
ResNet18-594.3990.0426.0593.7534.69
ResNet18-694.4593.4830.1392.4443.31
ResNet18-894.4191.2244.0492.6647.87
ResNet18-1094.3088.9644.5992.8738.55
ResNet18-1294.9687.3640.9092.3437.19
ResNet18-1494.6886.6335.4892.1843.04
ResNet18-1894.8183.9236.5292.1146.79
+ +Table 1. ACC (\%) and BDR (\%) performance of ambiguity attacks using IERB/CERB structure for AlexNet and ResNet18 with different number of passport layers on CIFAR10. + +
Dataset-NetOriginalDataSizePlainCERBIERB
CIFAR10 +AlexNet90.205000 (10%)83.6288.1687.30
2500 (5%)73.8286.7078.91
2000 (4%)73.4886.3076.73
1500 (3%)72.0986.7871.38
1000 (2%)64.8284.2263.71
CIFAR100 +ResNet1875.055000 (10%)70.7373.2670.51
3000 (6%)69.1472.2669.35
2000 (4%)62.8171.4268.89
1500 (3%)62.8671.6968.50
1000 (2%)53.9170.1268.44
+ +Table 2. ACC (%) comparison with Plain attack for CIFAR10-AlexNet and CIFAR100-ResNet18. + +
DatasetPassport LayerOriginalPlainCERBIERB
Caltech101Last 3 layers72.5471.0172.2667.79
Last 5 layers68.3059.8966.7860.73
Last 8 layers72.4959.9469.3859.32
Last 10 layers70.9057.1766.8957.06
Caltech256Last 5 layers54.3438.6452.2351.02
Last 7 layers53.9536.7249.5549.36
Last 10 layers55.4324.9347.8544.19
+ +Table 3. ACC (%) comparison with Plain attack on Caltech-101 and Caltech-256, where $10\%$ training data are used. Here the network is fixed to be ResNet18. + +rather limited. To this end, we embed 5 passport layers in AlexNet and 10 passport layers in ResNet18, and train them on CIFAR10 and CIFAR100, respectively. Let Plain attack refer to the case without using our proposed structures. Table 2 gives the ACC results of Plain attack and our ambiguity attacks using CERB and IERB. For the simple AlexNet, the performance of our attack with CERB overwhelms that of Plain attack, and the performance gain becomes more significant when smaller number of training data is avail + +
DataSizeIERBCERB
ACCBDRACCBDR
10000 (25%)90.4740.2492.1791.77
5000 (12.5%)88.2642.8291.0592.82
4000 (10%)87.4347.7190.0792.61
3000 (7.5%)86.3048.3489.4993.65
2500 (6.25%)86.2348.9687.0093.44
2000 (5%)85.2649.2085.6793.44
+ +Table 4. ACC (%) and BDR (%) performance of ambiguity attacks with IERB and CERB using non-overlapping CIFAR10 dataset. + +able. For instance, when $2\%$ training data are used, the ACC gap is almost $20\%$ . Such a property is very valuable in practice, as attacks are usually launched with very limited number of data; otherwise, re-training an entire model could be feasible as well. Also, for this simple AlexNet, our attack with IERB has similar performance with Plain attack. For the relatively large network ResNet18, our attack with CERB achieves $4.93\%$ ACC drop, compared with the original accuracy, when only $2\%$ training data are used. This drop shrinks to $1.79\%$ when $10\%$ training data are available. Compared with Plain attack, the ACC gains of our attack with CERB can be as large as $16.21\%$ . In addition, it is noted that our attack with IERB becomes much superior to Plain attack, when very limited training data are adopted; the ACC gain can be up to $14.53\%$ . More results on more complicated datasets including Caltech-101 and Caltech-256 can be found in Table 3, and similar conclusions can be drawn. + +# 4.2. Attack with non-overlapping dataset + +In the above experiments, we consider the case that the attacker has access to a part of the original training data, namely, the dataset for launching the attack overlaps with the original one. We now investigate the attack performance under a more challenging scenario, i.e., the dataset available to the attacker and the original dataset come from the same source; but do not overlap. This non-overlapping dataset mimics the practical scenario that the attacker may not be able to exactly access a part of the original training data; but rather can only access some similar ones. + +We randomly divide CIFAR10 into non-overlapping two subsets: 40000 for training the passport-based network and the remaining 10000 for the attack. Specifically, the attacking model is a ResNet18 with 10 passport layers, and the accuracy of the trained model is $93.12\%$ . The attack performance of our ambiguity attacks with IERB and CERB under this new setting is tabulated in Table 4. With these 10000 non-overlapping data, our ambiguity attack with CERB reaches a $92.17\%$ accuracy, only $0.95\%$ away from the original one. Also, the BDR in this case is as high as $91.77\%$ , indicating the recovered scale factors are very different from the authorized ones. When less number of non- + +overlapping data are used, the ACC values drop while the accompanied BDRs tend to improve. Even when only $5\%$ non-overlapping data are available, the ACC value can still be $85.67\%$ with BDR being $93.44\%$ . Similar results can be obtained by our ambiguity attack with IERB, but with a much lowered BDR of around $40\%$ . Another interesting phenomenon is that the ambiguity attack with CEBR using non-overlapping dataset leads to slightly worse ACC, but much better BDR performance, compared with the same attack with overlapping dataset. These results, again, show that our proposed ambiguity attacks are still very effective even in the challenging non-overlapping scenarios. + +# 4.3. Result of ambiguity attack with CERB on other DNN watermark methods + +We now show that our proposed attack strategy can be generalized well to other DNN watermark methods. As the ambiguity attack with CERB overwhelms the one with IEBR, we adopt it in the following evaluations. The three DNN watermarking methods considered are: Greedy-Residual [21], DeepSigns [8], and Uchida [29], which used specific layer weights for the watermark embedding. For Greedy-Residual, the watermark was embedded into the first convolutional layer weight of the network, while for DeepSigns, the watermark was hidden in the flattened features before the last linear layer. Regarding Uchida's method, the watermark was injected into the third convolutional layer weights of the network. + +We flexibly adapt our CERB structure for different types of embedded intermediaries such as model weights and features in three DNN watermark methods. Following the attack setting of Fan et al. [11], we assume that the network structure and model weights except those from the watermark are available to the attacker. As a result, for Greedy-Residual, we can replace the normalization layer after the embedded convolutional parameters with the CERB. Similarly, for DeepSigns, the normalization layer before the embedded feature map is replaced by our CERB. For Uchida's method, a CERB structure is added after the embedded convolutional parameters. We preset a different signature and only train the parameters embedded with the watermarks and the CERB parameters to match this new signature. More implementation details can be found in Appendix A. + +We introduce signature detection rate (SDR) to evaluate if a signature is successfully embedded in the model. The SDR is defined as the percentage of the watermark bits $\mathbf{wm} = \{wm_1, \dots, WM_C\}$ extracted from the model that are coincident with the signature $\mathbf{sig} = \{sig_1, \dots, sig_C\}$ used during the embedding process, i.e., + +$$ +S D R = \frac {1}{C} \sum_ {i = 1} ^ {C} \mathcal {I} \left[ w m _ {i} = s i g _ {i} \right]. \tag {10} +$$ + +The attack results on three watermark methods are pre + +
WM methodDataset-NetEmbed-PositionDataSizeOriginal ACCAttack ACCBDRSDR
Greedy-ResidualCaltech256-ResNet18First Conv layer10%54.9854.3749.22100
DeepSignsCIFAR10-WRNLast Linear layer10%91.3091.1537.5100
UchidaCIFAR10-WRNThird Conv layer10%90.1189.7745.31100
+ +Table 5. Results of our ambiguity attack on other DNN watermark methods, in terms of ACC (%), BDR (%), and SDR (%). + +
# of CERBOriginal046810
ACC (%)55.4225.0328.9938.5042.5847.07
+ +sented in Table 5. For Greedy-Residual method, the inference performance of the model after the attack is quite similar to that of the original one, with a very slight drop of $0.61\%$ . In addition, the SDR is $100\%$ , implying that the attacker can claim the ownership to this model with the new signature. Meanwhile, a high BDR of $49.22\%$ well demonstrates the high dissimilarity between the forged and original watermarks. Very similar observations can be made when attacking DeepSigns and Uchida's methods. Therefore, we validate the generalization capability of our attack strategy to other DNN watermark methods. + +# 4.4. Ablation study + +Different number of CERB structures: To study the effect on attack performance with different number of CERB structures, we use a ResNet18 with the last 10 layers embedded with passports for the illustration. As can be seen from Table 6, the original performance evaluated on Caltech-256 is $55.42\%$ . For Plain attack with 0 CERB structure, the ACC is very low, i.e., $25.05\%$ . By gradually applying more CERB structures, the ACC values improve constantly. Eventually, with all 10 passport layers replaced by our CERB structures, the ACC of our ambiguity attack reaches $47.07\%$ . + +Increasing the depth of CERB: The CERB in the default setting is a two-layer perceptron with LeakyReLU. We now try to testify if using perceptron with more layers leads to better attack performance. To this end, we experiment on the ResNet18 with 10 passport layers trained on CIFAR10, and launch the ambiguity attacks by varying the number of layers in CERB. As can be seen from Table 7, the ACC restored by CERB with 2 layers is the highest, reaching $92.24\%$ . With more layers being involved, the ACC performance actually drops surprisingly. We conjecture that the two-layer perceptron is enough for our ambiguity attack; while increasing the number of layers places heavier burden to the training and eventually affects the performance of the ambiguity attack. + +Using other activation functions in CERB: We also evaluate the impact of the activation functions in CERB on the overall attack performance. Again, we experiment on + +Table 6. Results of using different number of CERB on Caltech-256 with ResNet18. + +
# of MLP layers in CERBOriginal2345
ACC (%)94.4092.2486.8584.1886.45
+ +Table 7. Results of changing the number of layer in CERB. + +
Activation FunctionsLeakyReLUtanhSigmoid
ACC (%)92.8792.5492.80
+ +Table 8. Result of using different activation functions. + +the ResNet18 with 10 passport layers trained on CIFAR10. We then replace every passport layer with CERB, and adopt different activation functions in CERB. We list the ACC results by using tanh and Sigmoid, in addition to our default LeakyReLU in Table 8. As can be noticed, all ACC results with different activation functions are similar. This implies that the attack performance is not sensitive to the activation functions adopted. + +# 5. Conclusion + +In this paper, we propose an advanced ambiguity attack that defeats the passport-based model IP protection scheme. We combine multi-layer perceptron with skip connection to find valid substitute passports using less than $10\%$ of the training dataset. Extensive experimental results validate the effectiveness of our ambiguity attack. Further, it is demonstrated that our attack strategy can be easily extended to other DNN watermark methods. + +Regarding the remedy solutions, one potential direction is to exploit random locations for inserting the passport-layers, in which the randomness is controlled by a secret key. Additionally, another promising attempt is to change the embedding position from model weights to the activations. To make sure the next convolutional layer can extract proper features from the activation, the statistic of the activation should stay in a restricted scope. Such a statistic could be unique for a given signature, which may be helpful to resist our ambiguity attack. + +Acknowledgments: This work was supported in part by Macau Science and Technology Development Fund under SKLIOTSC-2021-2023, 0072/2020/AMJ, and 0022/2022/A1; in part by Research Committee at University of Macau under MYRG2020-00101-FST and MYRG2022-00152-FST; in part by Natural Science Foundation of China under 61971476; and in part by Alibaba Group through Alibaba Innovative Research Program. + +# References + +[1] Yossi Adi, Carsten Baum, Moustapha Cisse, Benny Pinkas, and Joseph Keshet. Turning your weakness into a strength: Watermarking deep neural networks by backdooring. In USENIX Security Symposium, pages 1615-1631, 2018. 1, 2 +[2] William Aiken, Hyoungshick Kim, Simon Woo, and Jungwoo Ryoo. Neural network laundering: Removing black-box backdoor watermarks from deep neural networks. Computers & Security, page 102277, 2021. 2 +[3] Omid Aramoon, Pin-Yu Chen, and Gang Qu. 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+ "content": "Abstract" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 304, + 289, + 556 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 304, + 289, + 556 + ], + "spans": [ + { + "bbox": [ + 46, + 304, + 289, + 556 + ], + "type": "text", + "content": "Since training a deep neural network (DNN) is costly, the well-trained deep models can be regarded as valuable intellectual property (IP) assets. The IP protection associated with deep models has been receiving increasing attentions in recent years. Passport-based method, which replaces normalization layers with passport layers, has been one of the few protection solutions that are claimed to be secure against advanced attacks. In this work, we tackle the issue of evaluating the security of passport-based IP protection methods. We propose a novel and effective ambiguity attack against passport-based method, capable of successfully forging multiple valid passports with a small training dataset. This is accomplished by inserting a specially designed accessory block ahead of the passport parameters. Using less than " + }, + { + "bbox": [ + 46, + 304, + 289, + 556 + ], + "type": "inline_equation", + "content": "10\\%" + }, + { + "bbox": [ + 46, + 304, + 289, + 556 + ], + "type": "text", + "content": " of training data, with the forged passport, the model exhibits almost indistinguishable performance difference (less than " + }, + { + "bbox": [ + 46, + 304, + 289, + 556 + ], + "type": "inline_equation", + "content": "2\\%" + }, + { + "bbox": [ + 46, + 304, + 289, + 556 + ], + "type": "text", + "content": ") compared with that of the authorized passport. In addition, it is shown that our attack strategy can be readily generalized to attack other IP protection methods based on watermark embedding. Directions for potential remedy solutions are also given." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 47, + 578, + 128, + 590 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 578, + 128, + 590 + ], + "spans": [ + { + "bbox": [ + 47, + 578, + 128, + 590 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 46, + 598, + 287, + 696 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 598, + 287, + 696 + ], + "spans": [ + { + "bbox": [ + 46, + 598, + 287, + 696 + ], + "type": "text", + "content": "With the geometric growth of computing power of computational devices in recent decades, there have emerged many deep learning applications that have contributed to the human world such as super-resolution reconstruction [7, 9, 30], image inpainting [31, 34, 35] and forgery detection [32]. It usually costs many resources to develop new DNN models and developers will not tolerate the act of theft of their IP. The IP protection problem of deep models be" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 280, + 545, + 327 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 280, + 545, + 327 + ], + "spans": [ + { + "bbox": [ + 306, + 280, + 545, + 327 + ], + "type": "text", + "content": "comes more severe with the birth of Machine Learning as a Service (MLaaS) [26]. Preventing the infringement behavior of deep models now emerges as a necessary concern when developing new algorithms and systems." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 329, + 546, + 616 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 329, + 546, + 616 + ], + "spans": [ + { + "bbox": [ + 304, + 329, + 546, + 616 + ], + "type": "text", + "content": "Model watermark [20, 25, 27, 28, 37] has been a popular method to protect the IP of DNN models. In the embedding process, the owners embed the secret signatures (watermarks), and then in the verification process, they can claim their ownership to the model by matching the extracted signatures with the original versions. The existing model watermark methods can be roughly divided into two categories [10, 11]: feature-based and trigger-based methods. Specifically, feature-based methods [4, 8, 24, 29] applied a regularizer to embed the secret watermark into the activation functions or model weights. Uchida et al. [29] proposed to use a regularizer to embed a watermark into the model weights. Darvish et al. [8] embedded the fingerprints in the Probability Density Function of trainable weights instead. Aramoon et al. [3] inserted the signature into the gradient of the cross-entropy loss function with respect to the inputs. In contrast, trigger-based methods make the output target respond to specific inputs. Along this line, Adi et al. [1] used the backdoor attack as a means to watermark the model. Merrer et al. [18] designed a zero-bit watermarking algorithm that uses adversarial samples as watermarks to claim the ownership. Zhang et al. [39] applied watermarks to images and then trained the network to output target labels when input images carry these watermarks." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 617, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 547, + 713 + ], + "type": "text", + "content": "Despite the strength in retaining ownership of DNN models, most existing model watermark methods are shown to be vulnerable to the so-called ambiguity attack, in which the attacker manages to cast doubts on the ownership verification by crafting counterfeit (forged) watermarks [11]. Recently, Fan et al. [10] first designed a series of ambiguity attacks, which are effective in attacking DNN watermark methods. It was stated that for conventional watermark" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 702, + 135, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 702, + 135, + 712 + ], + "spans": [ + { + "bbox": [ + 58, + 702, + 135, + 712 + ], + "type": "text", + "content": "† Corresponding author." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "text", + "content": "8123" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 215 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 215 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 215 + ], + "type": "text", + "content": "methods, a counterfeit watermark can be forged as along as the model performance is independent of the signature [11]. Following this proposition, Fan et al. designed a passport layer through which the functionality of the model is controlled by the signature called passport. However, Fan et al. encountered a heavy performance drop when batch normalization layers exist. To solve this problem, Zhang et al. [38] added learnable affine transformations to the scale and bias factors. It was claimed that an attacker cannot find a substitute passport that maintains the model performance, which ensures the security of these passport-based methods against existing ambiguity attacks." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 216, + 289, + 479 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 216, + 289, + 479 + ], + "spans": [ + { + "bbox": [ + 46, + 216, + 289, + 479 + ], + "type": "text", + "content": "In this work, we aim to design an advanced ambiguity attack to the passport-based method, capable of generating valid substitute passports with only a small number of data. Here, valid substitute passports are defined as those leading to an indistinguishable model performance, but sufficiently different from the original authorized passports. Clearly, with such valid substitute passports, an attacker can claim the ownership of the model. To this end, we first experimentally justify the existence of multiple valid substitute passports. Noticing the fact that it is easy to localize the passport layers, we then propose our ambiguity attack by replacing passport layers with our designed two types of structures, namely Individual Expanded Residual Block (IERB) and Collective Expanded Residual Block (CERB). Both structures are built in a way to encourage the significant changes of the parameters in the passport layers during the training, which could help us search for valid substitute passports. Benefiting from these two structures and assisting with a small amount training data, we can obtain valid substitute passports, and hence, defeat the passport-based methods which are the only type of method claimed to be immune to existing ambiguity attacks." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 59, + 479, + 283, + 490 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 479, + 283, + 490 + ], + "spans": [ + { + "bbox": [ + 59, + 479, + 283, + 490 + ], + "type": "text", + "content": "Our major contributions can be summarized as follows:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 59, + 490, + 286, + 713 + ], + "type": "list", + "angle": 0, + "index": 7, + "blocks": [ + { + "bbox": [ + 59, + 490, + 286, + 560 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 490, + 286, + 560 + ], + "spans": [ + { + "bbox": [ + 59, + 490, + 286, + 560 + ], + "type": "text", + "content": "- We propose a novel and effective ambiguity attack against the passport-based IP protection schemes. With less than " + }, + { + "bbox": [ + 59, + 490, + 286, + 560 + ], + "type": "inline_equation", + "content": "10\\%" + }, + { + "bbox": [ + 59, + 490, + 286, + 560 + ], + "type": "text", + "content": " of training data, our ambiguity attack on passport-layer protected model can restore the functionality of the model with a less than " + }, + { + "bbox": [ + 59, + 490, + 286, + 560 + ], + "type": "inline_equation", + "content": "2\\%" + }, + { + "bbox": [ + 59, + 490, + 286, + 560 + ], + "type": "text", + "content": " performance gap from the original accuracy." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 59, + 560, + 286, + 619 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 560, + 286, + 619 + ], + "spans": [ + { + "bbox": [ + 59, + 560, + 286, + 619 + ], + "type": "text", + "content": "- We design two novel structures for replacing the passport layers, based on the multi-layer perceptron (MLP) and skip connection to assist with our ambiguity attack for searching valid substitute passports with a small amount of training data." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 59, + 619, + 286, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 619, + 286, + 689 + ], + "spans": [ + { + "bbox": [ + 59, + 619, + 286, + 689 + ], + "type": "text", + "content": "- Experiments on both overlapping (attacker's training dataset is part of the original training dataset) and non-overlapping datasets (attacker's dataset and the original one come from the same source but no overlap exists), and on different network structures have proved the effectiveness of our ambiguity attack." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 59, + 689, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 689, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 59, + 689, + 286, + 713 + ], + "type": "text", + "content": "- Our attack method can be readily generalized to attack other DNN watermark methods [8, 21, 29]." + } + ] + } + ], + "index": 6 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 306, + 71, + 398, + 84 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 71, + 398, + 84 + ], + "spans": [ + { + "bbox": [ + 306, + 71, + 398, + 84 + ], + "type": "text", + "content": "2. Related Works" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 94, + 545, + 190 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 94, + 545, + 190 + ], + "spans": [ + { + "bbox": [ + 304, + 94, + 545, + 190 + ], + "type": "text", + "content": "DNN watermark methods have been popular solutions for DNN model IP protection. However, these techniques might still be vulnerable to flagrant infringement from notorious adversaries. In this section, we review the two types of representative attack methods, namely, removal attack [2, 5, 6, 14, 22, 33] and ambiguity attack [10, 11, 38], along with the passport-based method attempting to defend against ambiguity attacks [11]." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 193, + 546, + 479 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 193, + 546, + 479 + ], + "spans": [ + { + "bbox": [ + 304, + 193, + 546, + 479 + ], + "type": "text", + "content": "Removal Attack: This type of attack tries to remove the watermark from the protected model, malfunctioning the ownership verification mechanism. Along this line, many fine-tuning based methods have been proposed. Chen et al. [5] combined a redesigned elastic weight consolidation algorithm and unlabeled data augmentation to achieve unified model watermark removal with limited data. Guo et al. [14] used a dataset transformation method called PST (Pattern embedding and Spatial-level Transformation) to preprocess the data before fine-tuning. Chen et al. [6] utilized auxiliary unlabeled data to decrease the amount of labeled training data required for effective watermark removal. Aiken et al. [2] provided a three-stage scheme to remove backdoor-based watermarks by exploiting another trigger-free dataset from the same domain. Liu et al. [22] designed a framework to remove backdoor-based watermarks, in which a data augmentation was proposed to imitate the behavior of the backdoor triggers. Yan et al. [33] attempted to break the passport-based method by scaling the neurons and flipping the signs of parameters. However, this method assumed that the authorized passports are available to the attacker, which is not realistic in practice. Also, these aforementioned attack methods only enable the attackers to remove the watermarks, while unable to claim the ownership." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 483, + 545, + 626 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 483, + 545, + 626 + ], + "spans": [ + { + "bbox": [ + 304, + 483, + 545, + 626 + ], + "type": "text", + "content": "Ambiguity Attack: Another more threatening attack is the ambiguity attack, where the attacker can forge another substitute watermark to claim the model ownership. The concept of ambiguity attack originally appeared in image watermark community [19, 23], and recently has been extended to the DNN watermark methods. The pioneering work was conducted by Fan et al. in [10], which pointed out the vulnerability of Uchida's watermark method [29] under the ambiguity attack. They also showed that the same weakness of Adi's DNN watermark method [1] exists, by proving that another trigger can be optimized exclusively to cause the same model response as the original one." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "content": "Passport-based method: Passport-based method was originally proposed by Fan et al. [11] as a remedy enabling DNN watermark methods to defeat the ambiguity attack. This is achieved by replacing the traditional normalization layer with the so-called passport layer, whose difference mainly lies in how the affine factors are obtained. In passport layer, the scale factor " + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\gamma" + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "content": " and bias factor " + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\beta" + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "content": " are computed" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "8124" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 165, + 83 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 165, + 83 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 165, + 83 + ], + "type": "text", + "content": "with the passport as follows:" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 63, + 92, + 287, + 106 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 63, + 92, + 287, + 106 + ], + "spans": [ + { + "bbox": [ + 63, + 92, + 287, + 106 + ], + "type": "interline_equation", + "content": "\\gamma = \\operatorname {A v g} \\left(\\mathbf {W} _ {\\text {c o n v}} * \\mathbf {s} _ {\\gamma}\\right), \\beta = \\operatorname {A v g} \\left(\\mathbf {W} _ {\\text {c o n v}} * \\mathbf {s} _ {\\beta}\\right), \\tag {1}", + "image_path": "430f1922cca86d14783ed7bdb8ea709028b3704115c594769a5341c990a2182d.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 113, + 287, + 148 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 113, + 287, + 148 + ], + "spans": [ + { + "bbox": [ + 47, + 113, + 287, + 148 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 113, + 287, + 148 + ], + "type": "inline_equation", + "content": "\\mathbf{s} = \\{\\mathbf{s}_{\\gamma},\\mathbf{s}_{\\beta}\\}" + }, + { + "bbox": [ + 47, + 113, + 287, + 148 + ], + "type": "text", + "content": " is called the passport, " + }, + { + "bbox": [ + 47, + 113, + 287, + 148 + ], + "type": "inline_equation", + "content": "\\mathbf{W}_{conv}" + }, + { + "bbox": [ + 47, + 113, + 287, + 148 + ], + "type": "text", + "content": " is the convolutional layer weight before this layer, and " + }, + { + "bbox": [ + 47, + 113, + 287, + 148 + ], + "type": "inline_equation", + "content": "Avg(\\cdot)" + }, + { + "bbox": [ + 47, + 113, + 287, + 148 + ], + "type": "text", + "content": " represents the average pooling function." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 149, + 287, + 199 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 149, + 287, + 199 + ], + "spans": [ + { + "bbox": [ + 47, + 149, + 287, + 199 + ], + "type": "text", + "content": "To embed the passport " + }, + { + "bbox": [ + 47, + 149, + 287, + 199 + ], + "type": "inline_equation", + "content": "s" + }, + { + "bbox": [ + 47, + 149, + 287, + 199 + ], + "type": "text", + "content": " into the model, the network " + }, + { + "bbox": [ + 47, + 149, + 287, + 199 + ], + "type": "inline_equation", + "content": "\\mathbb{N}_p" + }, + { + "bbox": [ + 47, + 149, + 287, + 199 + ], + "type": "text", + "content": " is optimized on the training set " + }, + { + "bbox": [ + 47, + 149, + 287, + 199 + ], + "type": "inline_equation", + "content": "\\mathcal{D} = \\{(x_i,y_i)\\}_{i = 1}^N" + }, + { + "bbox": [ + 47, + 149, + 287, + 199 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 47, + 149, + 287, + 199 + ], + "type": "inline_equation", + "content": "x_{i}" + }, + { + "bbox": [ + 47, + 149, + 287, + 199 + ], + "type": "text", + "content": " is the input and " + }, + { + "bbox": [ + 47, + 149, + 287, + 199 + ], + "type": "inline_equation", + "content": "y_{i}" + }, + { + "bbox": [ + 47, + 149, + 287, + 199 + ], + "type": "text", + "content": " is the corresponding label, using the following loss:" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 61, + 208, + 287, + 221 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 61, + 208, + 287, + 221 + ], + "spans": [ + { + "bbox": [ + 61, + 208, + 287, + 221 + ], + "type": "interline_equation", + "content": "\\mathcal {L} = \\mathcal {L} _ {r} \\left(\\mathbb {N} _ {p} [ \\mathbf {W}, \\mathbf {s} ] \\left(x _ {i}, y _ {i}\\right)\\right) + \\alpha \\mathcal {L} _ {\\text {s i g n}} (\\operatorname {s g n} (\\gamma), \\mathbf {b}), \\tag {2}", + "image_path": "5a31f07beb799e59885014b410594cc8be2fd457b7a48f4531ceba031885081e.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 228, + 287, + 300 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 228, + 287, + 300 + ], + "spans": [ + { + "bbox": [ + 47, + 228, + 287, + 300 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 228, + 287, + 300 + ], + "type": "inline_equation", + "content": "\\mathbb{N}_p[\\mathbf{W},\\mathbf{s}]" + }, + { + "bbox": [ + 47, + 228, + 287, + 300 + ], + "type": "text", + "content": " denotes the model " + }, + { + "bbox": [ + 47, + 228, + 287, + 300 + ], + "type": "inline_equation", + "content": "\\mathbb{N}" + }, + { + "bbox": [ + 47, + 228, + 287, + 300 + ], + "type": "text", + "content": " with the weight " + }, + { + "bbox": [ + 47, + 228, + 287, + 300 + ], + "type": "inline_equation", + "content": "\\mathbf{W}" + }, + { + "bbox": [ + 47, + 228, + 287, + 300 + ], + "type": "text", + "content": " and the passport s. The first term " + }, + { + "bbox": [ + 47, + 228, + 287, + 300 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_r(\\cdot)" + }, + { + "bbox": [ + 47, + 228, + 287, + 300 + ], + "type": "text", + "content": " is the classification loss, and the second term " + }, + { + "bbox": [ + 47, + 228, + 287, + 300 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{sign}(\\cdot)" + }, + { + "bbox": [ + 47, + 228, + 287, + 300 + ], + "type": "text", + "content": " is a sign loss regularization constraining the sign sequence of scale factors to be a predefined " + }, + { + "bbox": [ + 47, + 228, + 287, + 300 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 47, + 228, + 287, + 300 + ], + "type": "text", + "content": " -bit signature " + }, + { + "bbox": [ + 47, + 228, + 287, + 300 + ], + "type": "inline_equation", + "content": "\\mathbf{b} = \\{b_1,\\dots,b_C\\} \\in \\{-1,1\\} ^C" + }, + { + "bbox": [ + 47, + 228, + 287, + 300 + ], + "type": "text", + "content": " Here, " + }, + { + "bbox": [ + 47, + 228, + 287, + 300 + ], + "type": "inline_equation", + "content": "\\mathrm{sgn}(\\cdot)" + }, + { + "bbox": [ + 47, + 228, + 287, + 300 + ], + "type": "text", + "content": " is the sign function." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 300, + 287, + 396 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 300, + 287, + 396 + ], + "spans": [ + { + "bbox": [ + 47, + 300, + 287, + 396 + ], + "type": "text", + "content": "Denote " + }, + { + "bbox": [ + 47, + 300, + 287, + 396 + ], + "type": "inline_equation", + "content": "\\mathcal{Q}(\\mathbb{N}_p[\\mathbf{W},\\mathbf{s}])" + }, + { + "bbox": [ + 47, + 300, + 287, + 396 + ], + "type": "text", + "content": " as the inference performance of model " + }, + { + "bbox": [ + 47, + 300, + 287, + 396 + ], + "type": "inline_equation", + "content": "\\mathbb{N}_p" + }, + { + "bbox": [ + 47, + 300, + 287, + 396 + ], + "type": "text", + "content": " with the passport s. The verification process mainly relies on the assumption that the performance " + }, + { + "bbox": [ + 47, + 300, + 287, + 396 + ], + "type": "inline_equation", + "content": "\\mathcal{Q}(\\mathbb{N}_p[\\mathbf{W},\\mathbf{s}])" + }, + { + "bbox": [ + 47, + 300, + 287, + 396 + ], + "type": "text", + "content": " seriously deteriorates when an unauthorized passport is presented. Hence, the model ownership using passport-based method is conducted by matching the signs of scale factors " + }, + { + "bbox": [ + 47, + 300, + 287, + 396 + ], + "type": "inline_equation", + "content": "\\mathrm{sgn}(\\gamma)" + }, + { + "bbox": [ + 47, + 300, + 287, + 396 + ], + "type": "text", + "content": " with the predefined signature b and checking the DNN model inference performance." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 407, + 205, + 420 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 407, + 205, + 420 + ], + "spans": [ + { + "bbox": [ + 47, + 407, + 205, + 420 + ], + "type": "text", + "content": "3. Proposed Ambiguity Attack" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 426, + 287, + 533 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 426, + 287, + 533 + ], + "spans": [ + { + "bbox": [ + 47, + 426, + 287, + 533 + ], + "type": "text", + "content": "Though the passport-based methods [11, 38] have been claimed to be immune to the existing ambiguity attacks [10], they do not preclude the existence of more advanced ambiguity attacks. In this work, we cast doubt on the security of the passport-based methods, and propose a simple yet effective ambiguity attack, capable of crafting valid substitute passports. Before diving into the detailed design of our ambiguity attack, let us clarify our attack goal and the information assumed to be available to the attacker." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 534, + 287, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 534, + 287, + 689 + ], + "spans": [ + { + "bbox": [ + 47, + 534, + 287, + 689 + ], + "type": "text", + "content": "Attack Goal: Essentially, the attack goal is to generate substitute passport " + }, + { + "bbox": [ + 47, + 534, + 287, + 689 + ], + "type": "inline_equation", + "content": "\\mathbf{s}_t" + }, + { + "bbox": [ + 47, + 534, + 287, + 689 + ], + "type": "text", + "content": ", with which the model " + }, + { + "bbox": [ + 47, + 534, + 287, + 689 + ], + "type": "inline_equation", + "content": "\\mathbb{N}_p[\\mathbf{W},\\mathbf{s}_t]" + }, + { + "bbox": [ + 47, + 534, + 287, + 689 + ], + "type": "text", + "content": " has indistinguishable performance with that of applying the authorized passport " + }, + { + "bbox": [ + 47, + 534, + 287, + 689 + ], + "type": "inline_equation", + "content": "\\mathbf{s}_o" + }, + { + "bbox": [ + 47, + 534, + 287, + 689 + ], + "type": "text", + "content": ", i.e., " + }, + { + "bbox": [ + 47, + 534, + 287, + 689 + ], + "type": "inline_equation", + "content": "\\mathcal{Q}(\\mathbb{N}_p[\\mathbf{W},\\mathbf{s}_o])" + }, + { + "bbox": [ + 47, + 534, + 287, + 689 + ], + "type": "text", + "content": ". Specifically, following the ambiguity attack setting in [11], we assume that the attacker has access to the model weights " + }, + { + "bbox": [ + 47, + 534, + 287, + 689 + ], + "type": "inline_equation", + "content": "\\mathbf{W}" + }, + { + "bbox": [ + 47, + 534, + 287, + 689 + ], + "type": "text", + "content": " except from the passport. Note that, without the passport, the affine factors are missing in the normalization layer, through which the attacker can easily localize the passport layers. Also, the attacker is allowed to have a small number of training data, namely, " + }, + { + "bbox": [ + 47, + 534, + 287, + 689 + ], + "type": "inline_equation", + "content": "\\mathcal{D}_s = \\{(\\hat{x}_i,\\hat{y}_i)\\}_{i = 1}^n" + }, + { + "bbox": [ + 47, + 534, + 287, + 689 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 47, + 534, + 287, + 689 + ], + "type": "inline_equation", + "content": "n < N" + }, + { + "bbox": [ + 47, + 534, + 287, + 689 + ], + "type": "text", + "content": ". Formally, we have the following Definition 1, explicitly explaining the successful ambiguity attack on passport-based method." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 689, + 286, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 286, + 712 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 286, + 712 + ], + "type": "text", + "content": "Definition 1: An ambiguity attack on passport layer protected model is successful, if" + } + ] + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 310, + 74, + 416, + 152 + ], + "blocks": [ + { + "bbox": [ + 310, + 74, + 416, + 152 + ], + "lines": [ + { + "bbox": [ + 310, + 74, + 416, + 152 + ], + "spans": [ + { + "bbox": [ + 310, + 74, + 416, + 152 + ], + "type": "image", + "image_path": "ca37740f9804932d5ba28bd3b64fe307437b2f7bc1050b439db8f9de990b62e2.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 367, + 158, + 376, + 166 + ], + "lines": [ + { + "bbox": [ + 367, + 158, + 376, + 166 + ], + "spans": [ + { + "bbox": [ + 367, + 158, + 376, + 166 + ], + "type": "text", + "content": "(a)" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 11 + }, + { + "type": "image", + "bbox": [ + 429, + 74, + 539, + 152 + ], + "blocks": [ + { + "bbox": [ + 429, + 74, + 539, + 152 + ], + "lines": [ + { + "bbox": [ + 429, + 74, + 539, + 152 + ], + "spans": [ + { + "bbox": [ + 429, + 74, + 539, + 152 + ], + "type": "image", + "image_path": "23fc951b0b62eb96324a24893ccc4e6abcb8a4b9ffc4155a68b9dedeece37028.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 493, + 157, + 503, + 166 + ], + "lines": [ + { + "bbox": [ + 493, + 157, + 503, + 166 + ], + "spans": [ + { + "bbox": [ + 493, + 157, + 503, + 166 + ], + "type": "text", + "content": "(b)" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 305, + 174, + 545, + 207 + ], + "lines": [ + { + "bbox": [ + 305, + 174, + 545, + 207 + ], + "spans": [ + { + "bbox": [ + 305, + 174, + 545, + 207 + ], + "type": "text", + "content": "Figure 1. Valid substitute passports obtained by initializing scale factors with different signs from the authorized " + }, + { + "bbox": [ + 305, + 174, + 545, + 207 + ], + "type": "inline_equation", + "content": "\\mathbf{s}_o" + }, + { + "bbox": [ + 305, + 174, + 545, + 207 + ], + "type": "text", + "content": " and retraining. Horizontal axis denotes the number of different signs from " + }, + { + "bbox": [ + 305, + 174, + 545, + 207 + ], + "type": "inline_equation", + "content": "\\mathbf{s}_o" + }, + { + "bbox": [ + 305, + 174, + 545, + 207 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_caption" + } + ], + "index": 13 + }, + { + "bbox": [ + 315, + 220, + 545, + 245 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 315, + 220, + 545, + 245 + ], + "spans": [ + { + "bbox": [ + 315, + 220, + 545, + 245 + ], + "type": "text", + "content": "I) DNN inference accuracy with the substitute passport " + }, + { + "bbox": [ + 315, + 220, + 545, + 245 + ], + "type": "inline_equation", + "content": "\\mathbf{s}_t" + }, + { + "bbox": [ + 315, + 220, + 545, + 245 + ], + "type": "text", + "content": " is close to that with the authorized passport " + }, + { + "bbox": [ + 315, + 220, + 545, + 245 + ], + "type": "inline_equation", + "content": "\\mathbf{s}_o" + }, + { + "bbox": [ + 315, + 220, + 545, + 245 + ], + "type": "text", + "content": ", i.e.," + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 358, + 252, + 545, + 272 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 358, + 252, + 545, + 272 + ], + "spans": [ + { + "bbox": [ + 358, + 252, + 545, + 272 + ], + "type": "interline_equation", + "content": "\\left| \\mathcal {Q} \\left(\\mathbb {N} _ {p} [ \\mathbf {W}, \\mathbf {s} _ {t} ]\\right) - \\mathcal {Q} \\left(\\mathbb {N} _ {p} [ \\mathbf {W}, \\mathbf {s} _ {o} ]\\right) \\right| < \\epsilon . \\tag {3}", + "image_path": "e78276c901845760054e8917134406360c46a5bc1ffaf75318d9ee002f1f486e.jpg" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 313, + 281, + 545, + 305 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 313, + 281, + 545, + 305 + ], + "spans": [ + { + "bbox": [ + 313, + 281, + 545, + 305 + ], + "type": "text", + "content": "II) Dissimilarity between the substitute passport " + }, + { + "bbox": [ + 313, + 281, + 545, + 305 + ], + "type": "inline_equation", + "content": "\\mathbf{s}_t" + }, + { + "bbox": [ + 313, + 281, + 545, + 305 + ], + "type": "text", + "content": " and the authorized " + }, + { + "bbox": [ + 313, + 281, + 545, + 305 + ], + "type": "inline_equation", + "content": "\\mathbf{s}_o" + }, + { + "bbox": [ + 313, + 281, + 545, + 305 + ], + "type": "text", + "content": " should be large enough, i.e.:" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 407, + 312, + 545, + 333 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 407, + 312, + 545, + 333 + ], + "spans": [ + { + "bbox": [ + 407, + 312, + 545, + 333 + ], + "type": "interline_equation", + "content": "\\left| \\mathbf {s} _ {t} - \\mathbf {s} _ {o} \\right| > \\delta . \\tag {4}", + "image_path": "ad7676a2f128208346bb921bea34d67fd35c94833d8ca3aa462d8b1191cacc0b.jpg" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 342, + 546, + 605 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 342, + 546, + 605 + ], + "spans": [ + { + "bbox": [ + 304, + 342, + 546, + 605 + ], + "type": "text", + "content": "Before presenting the details of our ambiguity attack, let us first justify the existence of multiple valid substitute passports satisfying the conditions given in (3) and (4). To this end, we here adopt an experimental approach and leave the theoretical justification in our future work. Assume now that we are given the complete training data " + }, + { + "bbox": [ + 304, + 342, + 546, + 605 + ], + "type": "inline_equation", + "content": "\\mathcal{D}" + }, + { + "bbox": [ + 304, + 342, + 546, + 605 + ], + "type": "text", + "content": ", though this large amount of data are not required when launching the attack. We initialize scale factors with different combinations of " + }, + { + "bbox": [ + 304, + 342, + 546, + 605 + ], + "type": "inline_equation", + "content": "\\{+1, -1\\}" + }, + { + "bbox": [ + 304, + 342, + 546, + 605 + ], + "type": "text", + "content": " and fine-tune the model based on " + }, + { + "bbox": [ + 304, + 342, + 546, + 605 + ], + "type": "inline_equation", + "content": "\\mathcal{D}" + }, + { + "bbox": [ + 304, + 342, + 546, + 605 + ], + "type": "text", + "content": ". In Fig. 1, we give the experimental results on ResNet18 trained on the CIFAR10 dataset, where the passport layer is placed after the first convolutional layer and the length of the scale factor is 64. The model with the authorized passport leads to an inference performance of " + }, + { + "bbox": [ + 304, + 342, + 546, + 605 + ], + "type": "inline_equation", + "content": "94.70\\%" + }, + { + "bbox": [ + 304, + 342, + 546, + 605 + ], + "type": "text", + "content": ". As can be seen, the accuracy of the models after retraining is still close to " + }, + { + "bbox": [ + 304, + 342, + 546, + 605 + ], + "type": "inline_equation", + "content": "94.70\\%" + }, + { + "bbox": [ + 304, + 342, + 546, + 605 + ], + "type": "text", + "content": " (red line, see Fig. 1(a)). More importantly, the signs of retained affine factors only have low coincidence rate (around " + }, + { + "bbox": [ + 304, + 342, + 546, + 605 + ], + "type": "inline_equation", + "content": "60\\%" + }, + { + "bbox": [ + 304, + 342, + 546, + 605 + ], + "type": "text", + "content": ", see Fig. 1(b)) with the original ones, implying that retained affine factors differ significantly from the authorized affine factors. Therefore, these retrained affine factors could simultaneously satisfy the conditions (3) and (4), and hence are valid substitute passports." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": "Though the existence of substitute passports has been justified, the difficulty of directly optimizing a passport remains unsolved for very limited number of training data. Clearly, in practical attacks, the attacker is only allowed to have access to very limited data; otherwise, he can retrain the entire model. Fan et al. [11] ascribed the robustness of passport-based method against fine-tuning the scale factors to the lazy-to-flip property, with which the scale factors are rarely updated to cross the zero during the training." + } + ] + } + ], + "index": 21 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "text", + "content": "8125" + } + ] + } + ], + "index": 22 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 78, + 73, + 511, + 319 + ], + "blocks": [ + { + "bbox": [ + 78, + 73, + 511, + 319 + ], + "lines": [ + { + "bbox": [ + 78, + 73, + 511, + 319 + ], + "spans": [ + { + "bbox": [ + 78, + 73, + 511, + 319 + ], + "type": "image", + "image_path": "0d6c6dec4ddb15efac8c1f92f3f3c693602be9671a54bc0f6235c27e57149806.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 110, + 325, + 483, + 338 + ], + "lines": [ + { + "bbox": [ + 110, + 325, + 483, + 338 + ], + "spans": [ + { + "bbox": [ + 110, + 325, + 483, + 338 + ], + "type": "text", + "content": "Figure 2. The structures of the ResNet18 with passport layer and our designed CERB/IERB structures." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 350, + 287, + 422 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 350, + 287, + 422 + ], + "spans": [ + { + "bbox": [ + 46, + 350, + 287, + 422 + ], + "type": "text", + "content": "To overcome the lazy-to-flip property for the scale factors, we attempt to add a trainable block after it, encouraging scale factors to go across the zeros by non-linear transformations. For efficiency, we adopt MLP for designing the trainable blocks. Following this line, we design two structures namely IERB and CERB to replace the passport layer." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 425, + 288, + 604 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 425, + 288, + 604 + ], + "spans": [ + { + "bbox": [ + 46, + 425, + 288, + 604 + ], + "type": "text", + "content": "The overall structure: Motivated by the above observations, we now design a novel ambiguity attack on passport-based method. The overall structure is given in Fig. 2, where we use the ResNet18 embedded with passport layers for the illustration. Specifically, the protected ResNet18 is comprised of multiple residual blocks, each containing several convolutional layers followed by the passport layer. As aforementioned, the locations of the passport layers can be easily determined. We can then insert either IERB or CERB structure into these locations. In our structure, the scale factor " + }, + { + "bbox": [ + 46, + 425, + 288, + 604 + ], + "type": "inline_equation", + "content": "\\gamma" + }, + { + "bbox": [ + 46, + 425, + 288, + 604 + ], + "type": "text", + "content": " is the output of the IERB/CERB. For the bias factor " + }, + { + "bbox": [ + 46, + 425, + 288, + 604 + ], + "type": "inline_equation", + "content": "\\beta" + }, + { + "bbox": [ + 46, + 425, + 288, + 604 + ], + "type": "text", + "content": ", we do not add our new structure; but instead we optimize it directly. We are now ready to introduce the details of CERB and IERB structures. After that, we will give the complete algorithm of our ambiguity attack." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 611, + 287, + 624 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 611, + 287, + 624 + ], + "spans": [ + { + "bbox": [ + 47, + 611, + 287, + 624 + ], + "type": "text", + "content": "3.1. Individually Expanded Residual Block (IERB)" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 630, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 630, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 630, + 288, + 713 + ], + "type": "text", + "content": "In this subsection, we present the details of the IERB block. As showed in Fig. 3 (a), the " + }, + { + "bbox": [ + 46, + 630, + 288, + 713 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 630, + 288, + 713 + ], + "type": "text", + "content": "-th scale factor " + }, + { + "bbox": [ + 46, + 630, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\gamma_i^l" + }, + { + "bbox": [ + 46, + 630, + 288, + 713 + ], + "type": "text", + "content": " in the " + }, + { + "bbox": [ + 46, + 630, + 288, + 713 + ], + "type": "inline_equation", + "content": "l" + }, + { + "bbox": [ + 46, + 630, + 288, + 713 + ], + "type": "text", + "content": "-th passport layer is transformed by a Two-Layer Perceptron (TLP) with FC-LeakyReLU-FC structure where the FC refers to fully connected layer. For the simplicity of notations, we omit the superscript in " + }, + { + "bbox": [ + 46, + 630, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\gamma_i^l" + }, + { + "bbox": [ + 46, + 630, + 288, + 713 + ], + "type": "text", + "content": " in the sequel. The output of this TLP is then used for the affine transformation" + } + ] + } + ], + "index": 5 + }, + { + "type": "image", + "bbox": [ + 316, + 351, + 435, + 499 + ], + "blocks": [ + { + "bbox": [ + 316, + 351, + 435, + 499 + ], + "lines": [ + { + "bbox": [ + 316, + 351, + 435, + 499 + ], + "spans": [ + { + "bbox": [ + 316, + 351, + 435, + 499 + ], + "type": "image", + "image_path": "f9d4362759c2f927f6f8b080aaba8bae7619506c3817638ede184111cc751187.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 377, + 502, + 388, + 512 + ], + "lines": [ + { + "bbox": [ + 377, + 502, + 388, + 512 + ], + "spans": [ + { + "bbox": [ + 377, + 502, + 388, + 512 + ], + "type": "text", + "content": "(a)" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 343, + 521, + 508, + 533 + ], + "lines": [ + { + "bbox": [ + 343, + 521, + 508, + 533 + ], + "spans": [ + { + "bbox": [ + 343, + 521, + 508, + 533 + ], + "type": "text", + "content": "Figure 3. Details of (a) IERB and (b) CERB." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 447, + 351, + 533, + 498 + ], + "blocks": [ + { + "bbox": [ + 447, + 351, + 533, + 498 + ], + "lines": [ + { + "bbox": [ + 447, + 351, + 533, + 498 + ], + "spans": [ + { + "bbox": [ + 447, + 351, + 533, + 498 + ], + "type": "image", + "image_path": "7fff39d03ef4a583f4b1402d23e3e7649ce6e1c4eab05046a73165ce52161342.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 477, + 502, + 488, + 512 + ], + "lines": [ + { + "bbox": [ + 477, + 502, + 488, + 512 + ], + "spans": [ + { + "bbox": [ + 477, + 502, + 488, + 512 + ], + "type": "text", + "content": "(b)" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 545, + 545, + 700 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 545, + 545, + 700 + ], + "spans": [ + { + "bbox": [ + 304, + 545, + 545, + 700 + ], + "type": "text", + "content": "later. The first linear layer " + }, + { + "bbox": [ + 304, + 545, + 545, + 700 + ], + "type": "inline_equation", + "content": "FC_{1\\rightarrow h}" + }, + { + "bbox": [ + 304, + 545, + 545, + 700 + ], + "type": "text", + "content": " with learnable parameters maps the scale factor into a " + }, + { + "bbox": [ + 304, + 545, + 545, + 700 + ], + "type": "inline_equation", + "content": "h" + }, + { + "bbox": [ + 304, + 545, + 545, + 700 + ], + "type": "text", + "content": " -dimensional vector, while the second linear layer " + }, + { + "bbox": [ + 304, + 545, + 545, + 700 + ], + "type": "inline_equation", + "content": "FC_{h\\rightarrow 1}" + }, + { + "bbox": [ + 304, + 545, + 545, + 700 + ], + "type": "text", + "content": " maps the dimension back to 1, where " + }, + { + "bbox": [ + 304, + 545, + 545, + 700 + ], + "type": "inline_equation", + "content": "h" + }, + { + "bbox": [ + 304, + 545, + 545, + 700 + ], + "type": "text", + "content": " is the hidden layer size. A larger " + }, + { + "bbox": [ + 304, + 545, + 545, + 700 + ], + "type": "inline_equation", + "content": "h" + }, + { + "bbox": [ + 304, + 545, + 545, + 700 + ], + "type": "text", + "content": " brings a larger optimization space in the hidden layer; but could add burden to the training process. We empirically set " + }, + { + "bbox": [ + 304, + 545, + 545, + 700 + ], + "type": "inline_equation", + "content": "h = 10" + }, + { + "bbox": [ + 304, + 545, + 545, + 700 + ], + "type": "text", + "content": " striking a good balance between these two factors. In addition, a skip connection is added aside with the TLP structure to facilitate the back-propagation. Benefiting from the expanded parameter space brought by the TLP structure, the output scale factor would more likely go across the zero during the updating. This helps the attacker search for an appropriate " + }, + { + "bbox": [ + 304, + 545, + 545, + 700 + ], + "type": "inline_equation", + "content": "\\mathbf{s}_t" + }, + { + "bbox": [ + 304, + 545, + 545, + 700 + ], + "type": "text", + "content": " satisfying (4)." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 317, + 701, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 701, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 317, + 701, + 545, + 714 + ], + "type": "text", + "content": "Let " + }, + { + "bbox": [ + 317, + 701, + 545, + 714 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{W}_{i,j},\\mathbf{b}_{i,j}\\}" + }, + { + "bbox": [ + 317, + 701, + 545, + 714 + ], + "type": "text", + "content": " be the weights of the " + }, + { + "bbox": [ + 317, + 701, + 545, + 714 + ], + "type": "inline_equation", + "content": "j" + }, + { + "bbox": [ + 317, + 701, + 545, + 714 + ], + "type": "text", + "content": " -th linear" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "8126" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 287, + 108 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 287, + 108 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 287, + 108 + ], + "type": "text", + "content": "layer connected after the " + }, + { + "bbox": [ + 47, + 72, + 287, + 108 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 47, + 72, + 287, + 108 + ], + "type": "text", + "content": "-th scale factor, where " + }, + { + "bbox": [ + 47, + 72, + 287, + 108 + ], + "type": "inline_equation", + "content": "i \\in \\{1,2,\\dots,C\\}" + }, + { + "bbox": [ + 47, + 72, + 287, + 108 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 72, + 287, + 108 + ], + "type": "inline_equation", + "content": "j \\in \\{1,2\\}" + }, + { + "bbox": [ + 47, + 72, + 287, + 108 + ], + "type": "text", + "content": ". In IERB, the output of the first linear layer taking the " + }, + { + "bbox": [ + 47, + 72, + 287, + 108 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 47, + 72, + 287, + 108 + ], + "type": "text", + "content": "-th scale factor as input is:" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 118, + 110, + 287, + 125 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 118, + 110, + 287, + 125 + ], + "spans": [ + { + "bbox": [ + 118, + 110, + 287, + 125 + ], + "type": "interline_equation", + "content": "\\gamma_ {i} ^ {\\prime} = \\mathbf {W} _ {i, 1} ^ {T} * \\gamma_ {i} + \\mathbf {b} _ {i, 1} ^ {T}, \\tag {5}", + "image_path": "c06048f4e2bef08f356c9806e9a1b6bb1cdb5244fa3d4fb396c982a0c562bde8.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 129, + 287, + 165 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 129, + 287, + 165 + ], + "spans": [ + { + "bbox": [ + 46, + 129, + 287, + 165 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 129, + 287, + 165 + ], + "type": "inline_equation", + "content": "*" + }, + { + "bbox": [ + 46, + 129, + 287, + 165 + ], + "type": "text", + "content": " denotes the matrix multiplication operator. After the activation function LeakyReLU, the output of the second linear layer with the shortcut can be expressed as:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 83, + 167, + 287, + 182 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 83, + 167, + 287, + 182 + ], + "spans": [ + { + "bbox": [ + 83, + 167, + 287, + 182 + ], + "type": "interline_equation", + "content": "\\gamma_ {i} ^ {\\prime \\prime} = \\mathbf {W} _ {i, 2} ^ {T} * \\left(L R e L U \\left(\\gamma_ {i} ^ {\\prime}\\right)\\right) + \\mathbf {b} _ {i, 2} ^ {T} + \\gamma_ {i}. \\tag {6}", + "image_path": "54beed6aa4329ac48d556bcda81d45f6056f657e6f107eb3850b4b5b70575ff9.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 187, + 280, + 201 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 187, + 280, + 201 + ], + "spans": [ + { + "bbox": [ + 47, + 187, + 280, + 201 + ], + "type": "text", + "content": "3.2. Collective Expanded Residual Block (CERB)" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 206, + 289, + 374 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 206, + 289, + 374 + ], + "spans": [ + { + "bbox": [ + 46, + 206, + 289, + 374 + ], + "type": "text", + "content": "The IERB discussed above handles each scale factor individually, but may ignore the inter-channel relationship among scale factors. Instead of using isolated propagation paths for each scale factor, we now attempt to enhance the inter-channel relationship and optimize the scale factors in a collective manner. As can be observed from Fig. 3 (b), we choose to use a unified TLP structure to deal with all the " + }, + { + "bbox": [ + 46, + 206, + 289, + 374 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 46, + 206, + 289, + 374 + ], + "type": "text", + "content": " scale factors as a whole. The output of the TLP structure is then summed with the input scale factors to get the updated ones. Different from the IERB, each activation in the hidden layer is now related to all the input scale factors, and the fully connected structure ensures the exploitation of the inter-channel information. Mathematically, the output scale factors can be computed by:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 52, + 379, + 287, + 396 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 52, + 379, + 287, + 396 + ], + "spans": [ + { + "bbox": [ + 52, + 379, + 287, + 396 + ], + "type": "interline_equation", + "content": "\\gamma^ {\\prime \\prime} = \\left(\\mathbf {W} _ {2} ^ {T} * \\left(L R e L U \\left(\\mathbf {W} _ {1} ^ {T} * \\gamma + \\mathbf {b} _ {1} ^ {T}\\right)\\right) + \\mathbf {b} _ {2} ^ {T}\\right) + \\gamma , (7)", + "image_path": "351b0451696d99643e648e0af0490199229d14ee0c57a847232f678981c3db32.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 403, + 287, + 440 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 403, + 287, + 440 + ], + "spans": [ + { + "bbox": [ + 47, + 403, + 287, + 440 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 403, + 287, + 440 + ], + "type": "inline_equation", + "content": "\\mathbf{W}_1" + }, + { + "bbox": [ + 47, + 403, + 287, + 440 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 403, + 287, + 440 + ], + "type": "inline_equation", + "content": "\\mathbf{W}_2" + }, + { + "bbox": [ + 47, + 403, + 287, + 440 + ], + "type": "text", + "content": " represent the parameters in the first and second linear layers. Here we set the hidden layer size to be " + }, + { + "bbox": [ + 47, + 403, + 287, + 440 + ], + "type": "inline_equation", + "content": "C / 8" + }, + { + "bbox": [ + 47, + 403, + 287, + 440 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 47, + 403, + 287, + 440 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 47, + 403, + 287, + 440 + ], + "type": "text", + "content": " is the number of channels in this layer." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 445, + 241, + 459 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 445, + 241, + 459 + ], + "spans": [ + { + "bbox": [ + 47, + 445, + 241, + 459 + ], + "type": "text", + "content": "3.3. Algorithm of Our Ambiguity Attack" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 464, + 287, + 584 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 464, + 287, + 584 + ], + "spans": [ + { + "bbox": [ + 46, + 464, + 287, + 584 + ], + "type": "text", + "content": "With these newly proposed structures, we can summarize our ambiguity attack strategy on the passport-based method in Algorithm 1. For simplicity, we use " + }, + { + "bbox": [ + 46, + 464, + 287, + 584 + ], + "type": "inline_equation", + "content": "\\mathbf{W}_{\\gamma}" + }, + { + "bbox": [ + 46, + 464, + 287, + 584 + ], + "type": "text", + "content": " to represent all the parameters in IERB or CERB. Let us briefly explain our workflow for better understanding. In Algorithm 1, lines " + }, + { + "bbox": [ + 46, + 464, + 287, + 584 + ], + "type": "inline_equation", + "content": "1\\sim 4" + }, + { + "bbox": [ + 46, + 464, + 287, + 584 + ], + "type": "text", + "content": " are devoted to the model loading, normalization layer substitution, CERB/IERB insertion, and parameter initialization. The " + }, + { + "bbox": [ + 46, + 464, + 287, + 584 + ], + "type": "inline_equation", + "content": "\\gamma, \\beta" + }, + { + "bbox": [ + 46, + 464, + 287, + 584 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 464, + 287, + 584 + ], + "type": "inline_equation", + "content": "\\mathbf{W}_{\\gamma}" + }, + { + "bbox": [ + 46, + 464, + 287, + 584 + ], + "type": "text", + "content": " are then updated in lines " + }, + { + "bbox": [ + 46, + 464, + 287, + 584 + ], + "type": "inline_equation", + "content": "5\\sim 14" + }, + { + "bbox": [ + 46, + 464, + 287, + 584 + ], + "type": "text", + "content": " using the gradients with respect to each parameter by back-propagating the cross entropy loss:" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 126, + 588, + 198, + 601 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 126, + 588, + 198, + 601 + ], + "spans": [ + { + "bbox": [ + 126, + 588, + 198, + 601 + ], + "type": "interline_equation", + "content": "\\gamma = \\gamma - \\nabla_ {\\gamma} l o s s,", + "image_path": "049fe62dc6cf945e1d49d192b500e2ece2516d4121d68f13074ee6135de4d6d7.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 127, + 602, + 287, + 615 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 127, + 602, + 287, + 615 + ], + "spans": [ + { + "bbox": [ + 127, + 602, + 287, + 615 + ], + "type": "interline_equation", + "content": "\\beta = \\beta - \\nabla_ {\\beta} \\text {l o s s}, \\tag {8}", + "image_path": "58f14966c85e1a11c1bc53221b1c45d2e492a3b88e56aede94909f82e91e14fd.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 116, + 617, + 218, + 631 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 116, + 617, + 218, + 631 + ], + "spans": [ + { + "bbox": [ + 116, + 617, + 218, + 631 + ], + "type": "interline_equation", + "content": "\\mathbf {W} _ {\\gamma} = \\mathbf {W} _ {\\gamma} - \\nabla_ {\\mathbf {W} _ {\\gamma}} l o s s.", + "image_path": "2b93fcb6b54f5fcab0390796fb48d095207c1ddc2cd583239f647e486738689b.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 47, + 635, + 287, + 658 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 635, + 287, + 658 + ], + "spans": [ + { + "bbox": [ + 47, + 635, + 287, + 658 + ], + "type": "text", + "content": "Eventually, the algorithm outputs the substitute scale and bias factors " + }, + { + "bbox": [ + 47, + 635, + 287, + 658 + ], + "type": "inline_equation", + "content": "\\gamma''" + }, + { + "bbox": [ + 47, + 635, + 287, + 658 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 635, + 287, + 658 + ], + "type": "inline_equation", + "content": "\\beta" + }, + { + "bbox": [ + 47, + 635, + 287, + 658 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 47, + 669, + 173, + 682 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 669, + 173, + 682 + ], + "spans": [ + { + "bbox": [ + 47, + 669, + 173, + 682 + ], + "type": "text", + "content": "4. Experimental Results" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "text", + "content": "In this section, we evaluate the effectiveness of our ambiguity attack from different perspectives. Before present" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 306, + 72, + 476, + 84 + ], + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 72, + 476, + 84 + ], + "spans": [ + { + "bbox": [ + 306, + 72, + 476, + 84 + ], + "type": "text", + "content": "Algorithm 1 Proposed Ambiguity Attack" + } + ] + } + ], + "index": 16, + "type": "text" + }, + { + "bbox": [ + 306, + 86, + 545, + 121 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 86, + 545, + 121 + ], + "spans": [ + { + "bbox": [ + 306, + 86, + 545, + 121 + ], + "type": "text", + "content": "Input: Protected network " + }, + { + "bbox": [ + 306, + 86, + 545, + 121 + ], + "type": "inline_equation", + "content": "\\mathbb{N}_p[\\mathbf{W}]" + }, + { + "bbox": [ + 306, + 86, + 545, + 121 + ], + "type": "text", + "content": " with passport layers excluded; training dataset " + }, + { + "bbox": [ + 306, + 86, + 545, + 121 + ], + "type": "inline_equation", + "content": "\\mathcal{D}_s = \\{(\\hat{x}_i,\\hat{y}_i)\\}_{i = 1}^n" + }, + { + "bbox": [ + 306, + 86, + 545, + 121 + ], + "type": "text", + "content": "; checkpoint state_dict; training epoch " + }, + { + "bbox": [ + 306, + 86, + 545, + 121 + ], + "type": "inline_equation", + "content": "M" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 306, + 121, + 498, + 133 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 121, + 498, + 133 + ], + "spans": [ + { + "bbox": [ + 306, + 121, + 498, + 133 + ], + "type": "text", + "content": "Output: substitute scale and bias factors " + }, + { + "bbox": [ + 306, + 121, + 498, + 133 + ], + "type": "inline_equation", + "content": "\\gamma^{\\prime \\prime}" + }, + { + "bbox": [ + 306, + 121, + 498, + 133 + ], + "type": "inline_equation", + "content": "\\beta" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 311, + 136, + 545, + 219 + ], + "type": "list", + "angle": 0, + "index": 23, + "blocks": [ + { + "bbox": [ + 311, + 136, + 545, + 159 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 311, + 136, + 545, + 159 + ], + "spans": [ + { + "bbox": [ + 311, + 136, + 545, + 159 + ], + "type": "text", + "content": "1: Use normalization layers in the locations of the passport layers." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 311, + 160, + 545, + 183 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 311, + 160, + 545, + 183 + ], + "spans": [ + { + "bbox": [ + 311, + 160, + 545, + 183 + ], + "type": "text", + "content": "2: Insert CERB/IERB structures after the scale factors of these normalization layers." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 311, + 184, + 497, + 195 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 311, + 184, + 497, + 195 + ], + "spans": [ + { + "bbox": [ + 311, + 184, + 497, + 195 + ], + "type": "text", + "content": "3: Load weight " + }, + { + "bbox": [ + 311, + 184, + 497, + 195 + ], + "type": "inline_equation", + "content": "\\mathbf{W}" + }, + { + "bbox": [ + 311, + 184, + 497, + 195 + ], + "type": "text", + "content": " of " + }, + { + "bbox": [ + 311, + 184, + 497, + 195 + ], + "type": "inline_equation", + "content": "\\mathbb{N}_p[\\mathbf{W}]" + }, + { + "bbox": [ + 311, + 184, + 497, + 195 + ], + "type": "text", + "content": " from state_dict." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 311, + 196, + 545, + 219 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 311, + 196, + 545, + 219 + ], + "spans": [ + { + "bbox": [ + 311, + 196, + 545, + 219 + ], + "type": "text", + "content": "4: Initialize normalization layer weights " + }, + { + "bbox": [ + 311, + 196, + 545, + 219 + ], + "type": "inline_equation", + "content": "\\gamma" + }, + { + "bbox": [ + 311, + 196, + 545, + 219 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 311, + 196, + 545, + 219 + ], + "type": "inline_equation", + "content": "\\beta" + }, + { + "bbox": [ + 311, + 196, + 545, + 219 + ], + "type": "text", + "content": " with 1 and 0, respectively." + } + ] + } + ], + "index": 22 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 310, + 220, + 545, + 350 + ], + "type": "list", + "angle": 0, + "index": 34, + "blocks": [ + { + "bbox": [ + 312, + 220, + 417, + 231 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 220, + 417, + 231 + ], + "spans": [ + { + "bbox": [ + 312, + 220, + 417, + 231 + ], + "type": "text", + "content": "5: for epoch " + }, + { + "bbox": [ + 312, + 220, + 417, + 231 + ], + "type": "inline_equation", + "content": "= 1" + }, + { + "bbox": [ + 312, + 220, + 417, + 231 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 312, + 220, + 417, + 231 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 312, + 220, + 417, + 231 + ], + "type": "text", + "content": " do" + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 312, + 232, + 460, + 243 + ], + "type": "text", + "angle": 0, + "lines": [ + { 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"bbox": [ + 312, + 255, + 542, + 267 + ], + "type": "inline_equation", + "content": "\\gamma^{\\prime \\prime} = \\mathrm{CERB / IERB}(\\gamma ,\\mathbf{W}_{\\gamma})." + }, + { + "bbox": [ + 312, + 255, + 542, + 267 + ], + "type": "inline_equation", + "content": "\\triangleright" + }, + { + "bbox": [ + 312, + 255, + 542, + 267 + ], + "type": "text", + "content": " Eq. (5/7)." + } + ] + } + ], + "index": 27 + }, + { + "bbox": [ + 311, + 267, + 545, + 291 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 311, + 267, + 545, + 291 + ], + "spans": [ + { + "bbox": [ + 311, + 267, + 545, + 291 + ], + "type": "text", + "content": "9: Use " + }, + { + "bbox": [ + 311, + 267, + 545, + 291 + ], + "type": "inline_equation", + "content": "\\gamma''" + }, + { + "bbox": [ + 311, + 267, + 545, + 291 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 311, + 267, + 545, + 291 + ], + "type": "inline_equation", + "content": "\\beta" + }, + { + "bbox": [ + 311, + 267, + 545, + 291 + ], + "type": "text", + "content": " for affine transformation in normalization layer." + } + ] + } + ], + "index": 28 + }, + { + "bbox": [ + 310, + 293, + 376, + 301 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 310, + 293, + 376, + 301 + ], + "spans": [ + { + "bbox": [ + 310, + 293, + 376, + 301 + ], + "type": "text", + "content": "10: end for" + } + ] + } + ], + "index": 29 + }, + { + "bbox": [ + 310, + 303, + 493, + 316 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 310, + 303, + 493, + 316 + ], + "spans": [ + { + "bbox": [ + 310, + 303, + 493, + 316 + ], + "type": "text", + "content": "11: loss=cross_entropy " + }, + { + "bbox": [ + 310, + 303, + 493, + 316 + ], + "type": "inline_equation", + "content": "(\\mathbb{N}_p[\\mathbf{W}](\\hat{x}_i),\\hat{y}_i)" + } + ] + } + ], + "index": 30 + }, + { + "bbox": [ + 310, + 316, + 473, + 327 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 310, + 316, + 473, + 327 + ], + "spans": [ + { + "bbox": [ + 310, + 316, + 473, + 327 + ], + "type": "text", + "content": "12: Update " + }, + { + "bbox": [ + 310, + 316, + 473, + 327 + ], + "type": "inline_equation", + "content": "\\gamma, \\beta" + }, + { + "bbox": [ + 310, + 316, + 473, + 327 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 310, + 316, + 473, + 327 + ], + "type": "inline_equation", + "content": "\\mathbf{W}_{\\gamma} \\triangleright" + }, + { + "bbox": [ + 310, + 316, + 473, + 327 + ], + "type": "text", + "content": " Eq. (8)." + } + ] + } + ], + "index": 31 + }, + { + "bbox": [ + 310, + 328, + 366, + 337 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 310, + 328, + 366, + 337 + ], + "spans": [ + { + "bbox": [ + 310, + 328, + 366, + 337 + ], + "type": "text", + "content": "13: end for" + } + ] + } + ], + "index": 32 + }, + { + "bbox": [ + 310, + 339, + 356, + 350 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 310, + 339, + 356, + 350 + ], + "spans": [ + { + "bbox": [ + 310, + 339, + 356, + 350 + ], + "type": "text", + "content": "14: end for" + } + ] + } + ], + "index": 33 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 304, + 369, + 545, + 403 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 369, + 545, + 403 + ], + "spans": [ + { + "bbox": [ + 304, + 369, + 545, + 403 + ], + "type": "text", + "content": "ing the detailed results, let us clarify the experimental settings including the datasets, target models, and the evaluation metrics." + } + ] + } + ], + "index": 35 + }, + { + "bbox": [ + 304, + 405, + 545, + 464 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 405, + 545, + 464 + ], + "spans": [ + { + "bbox": [ + 304, + 405, + 545, + 464 + ], + "type": "text", + "content": "Dataset: Four image classification datasets: CIFAR10 [16], CIFAR100 [16], Caltech-101 [12], and Caltech-256 [13], are selected. Unless stated, the dataset used in the attack process only accounts for " + }, + { + "bbox": [ + 304, + 405, + 545, + 464 + ], + "type": "inline_equation", + "content": "10\\%" + }, + { + "bbox": [ + 304, + 405, + 545, + 464 + ], + "type": "text", + "content": " at maximum of the full training set and does not overlap with the test set." + } + ] + } + ], + "index": 36 + }, + { + "bbox": [ + 304, + 465, + 545, + 620 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 465, + 545, + 620 + ], + "spans": [ + { + "bbox": [ + 304, + 465, + 545, + 620 + ], + "type": "text", + "content": "DNN architectures: Three DNN architectures, AlexNet [17], ResNet-18 [15] and Wide-Residual Network [36] are used in our experiments, following the tradition of passport-based works [10, 11, 38]. To demonstrate that our attack strategy remains effective for different number of passport layers, we perform the experiments on AlexNet and ResNet18, with at most 5 and 18 passport layers, respectively. For notation convenience, we use a suffix to determine the indices of the passport layers. For instance, AlexNet-4 denotes the AlexNet with the first 4 normalization layers replaced by the passport layers, and AlexNet-last3 represents the version in which the last 3 normalization layers are replaced by the passport layers." + } + ] + } + ], + "index": 37 + }, + { + "bbox": [ + 304, + 620, + 545, + 716 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 620, + 545, + 716 + ], + "spans": [ + { + "bbox": [ + 304, + 620, + 545, + 716 + ], + "type": "text", + "content": "Evaluation metrics: Prediction accuracy (ACC) of the model is a natural choice for evaluating the attack effectiveness, since a successfully forged passport is expected to achieve similar performance as an authorized passport (see Definition 1). Another metric considered is the bit dissimilarity rate (BDR) of the signature derived from the forged passport, with respect to the authorized one. Specifically, let " + }, + { + "bbox": [ + 304, + 620, + 545, + 716 + ], + "type": "inline_equation", + "content": "\\gamma'" + }, + { + "bbox": [ + 304, + 620, + 545, + 716 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 620, + 545, + 716 + ], + "type": "inline_equation", + "content": "\\gamma^o" + }, + { + "bbox": [ + 304, + 620, + 545, + 716 + ], + "type": "text", + "content": " be the forged and authorized scale factors, re" + } + ] + } + ], + "index": 38 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "text", + "content": "8127" + } + ] + } + ], + "index": 39 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 287, + 95 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 287, + 95 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 287, + 95 + ], + "type": "text", + "content": "spectively. Note that the sign of " + }, + { + "bbox": [ + 47, + 72, + 287, + 95 + ], + "type": "inline_equation", + "content": "\\gamma^o" + }, + { + "bbox": [ + 47, + 72, + 287, + 95 + ], + "type": "text", + "content": " is used as the signature. The BDR is then defined as:" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 85, + 99, + 287, + 133 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 85, + 99, + 287, + 133 + ], + "spans": [ + { + "bbox": [ + 85, + 99, + 287, + 133 + ], + "type": "interline_equation", + "content": "B D R = \\frac {1}{C} \\sum_ {i = 1} ^ {C} \\mathcal {I} \\left[ \\operatorname {s g n} \\left(\\gamma_ {i} ^ {\\prime}\\right) \\neq \\operatorname {s g n} \\left(\\gamma_ {i} ^ {o}\\right) \\right], \\tag {9}", + "image_path": "1903ce1b85a70d3a3437ad3c223ffc0108346e2d730be48875a678c7dddde1d3.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 137, + 287, + 186 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 137, + 287, + 186 + ], + "spans": [ + { + "bbox": [ + 47, + 137, + 287, + 186 + ], + "type": "text", + "content": "where the indicator function " + }, + { + "bbox": [ + 47, + 137, + 287, + 186 + ], + "type": "inline_equation", + "content": "\\mathcal{I}[\\cdot]" + }, + { + "bbox": [ + 47, + 137, + 287, + 186 + ], + "type": "text", + "content": " returns 1 when the condition is true and 0 otherwise. A high BDR also implies the large dissimilarity with the authorized passport, which in turn indicates a better performance of the ambiguity attack." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 192, + 255, + 205 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 192, + 255, + 205 + ], + "spans": [ + { + "bbox": [ + 47, + 192, + 255, + 205 + ], + "type": "text", + "content": "4.1. Attack performance using IERB/CERB" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 211, + 288, + 294 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 211, + 288, + 294 + ], + "spans": [ + { + "bbox": [ + 46, + 211, + 288, + 294 + ], + "type": "text", + "content": "We now give the details on the effectiveness of our ambiguity attack by replacing the passport layers of the protected model with our proposed IERB or CERB blocks. All protected models with passport layers are trained over the training dataset of CIFAR10. We randomly select " + }, + { + "bbox": [ + 46, + 211, + 288, + 294 + ], + "type": "inline_equation", + "content": "10\\%" + }, + { + "bbox": [ + 46, + 211, + 288, + 294 + ], + "type": "text", + "content": " of examples from this dataset for launching the ambiguity attack, i.e., training the IERB or CERB blocks." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 294, + 287, + 486 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 294, + 287, + 486 + ], + "spans": [ + { + "bbox": [ + 46, + 294, + 287, + 486 + ], + "type": "text", + "content": "The attack results on AlexNet and ResNet18 are reported in Table 1. Since our ambiguity attack is the first one attacking passport-based methods, there are no comparative algorithms available so far. It can be seen that, by using the proposed CERB, our ambiguity attack is capable of achieving high ACC and BDR values for all the settings. Specifically, for AlexNet, the ACC gap is less than " + }, + { + "bbox": [ + 46, + 294, + 287, + 486 + ], + "type": "inline_equation", + "content": "1\\%" + }, + { + "bbox": [ + 46, + 294, + 287, + 486 + ], + "type": "text", + "content": ", compared with the case of the authorized passport. Also, the BDR can be as large as " + }, + { + "bbox": [ + 46, + 294, + 287, + 486 + ], + "type": "inline_equation", + "content": "80.30\\%" + }, + { + "bbox": [ + 46, + 294, + 287, + 486 + ], + "type": "text", + "content": ". For the more complex ResNet18, similar observations can be obtained, where the ACC gap is still less than " + }, + { + "bbox": [ + 46, + 294, + 287, + 486 + ], + "type": "inline_equation", + "content": "3\\%" + }, + { + "bbox": [ + 46, + 294, + 287, + 486 + ], + "type": "text", + "content": ", and the BDR could approach " + }, + { + "bbox": [ + 46, + 294, + 287, + 486 + ], + "type": "inline_equation", + "content": "50\\%" + }, + { + "bbox": [ + 46, + 294, + 287, + 486 + ], + "type": "text", + "content": ". We even encounter several cases (AlexNet-1 and ResNet18-1), in which the attacked models perform even better than the original ones. These results imply that our proposed ambiguity attack is successful in finding the valid substitute passports with a small number of training data." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 487, + 287, + 653 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 487, + 287, + 653 + ], + "spans": [ + { + "bbox": [ + 46, + 487, + 287, + 653 + ], + "type": "text", + "content": "As a comparison, we also present the results of the ambiguity attack with the IERB structure. It can be observed that this variant attack is still somewhat effective with reasonably high ACC and BDR values; but the attack performance is much inferior to the attack with CERB, especially when there are many passport layers. We attribute this phenomenon to the capability of CERB in exploiting the interchannel relationship. For IERB, it is likely to optimize towards the original sign of the scale factor, which naturally results in similar signatures (small BDR) to the original passports. In CERB, however, the collective optimization mechanism explores more possibly optimal pairs of the sign of scale factors, potentially leading to larger BDR of signature and higher ACC." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "type": "text", + "content": "To further show the effectiveness of our proposed attack strategy, we now compare the attack performance of the models with and without CERB/IERB structures. As will be clear soon, directly updating the affine factors cannot retrieve valid passports, especially when the available data is" + } + ] + } + ], + "index": 7 + }, + { + "type": "table", + "bbox": [ + 320, + 71, + 535, + 259 + ], + "blocks": [ + { + "bbox": [ + 320, + 71, + 535, + 259 + ], + "lines": [ + { + "bbox": [ + 320, + 71, + 535, + 259 + ], + "spans": [ + { + "bbox": [ + 320, + 71, + 535, + 259 + ], + "type": "table", + "html": "
NameOriginal ACCIERBCERB
ACCBDRACCBDR
AlexNet-190.2089.5416.0090.2624.67
AlexNet-288.7386.019.7688.3746.10
AlexNet-390.0887.4812.9688.9541.41
AlexNet-488.2586.5216.9688.0179.80
AlexNet-588.8882.4927.9588.2080.30
ResNet18-194.8993.853.1394.9425.00
ResNet18-394.8093.4626.5794.2250.0
ResNet18-494.6792.9224.6194.0933.98
ResNet18-594.3990.0426.0593.7534.69
ResNet18-694.4593.4830.1392.4443.31
ResNet18-894.4191.2244.0492.6647.87
ResNet18-1094.3088.9644.5992.8738.55
ResNet18-1294.9687.3640.9092.3437.19
ResNet18-1494.6886.6335.4892.1843.04
ResNet18-1894.8183.9236.5292.1146.79
", + "image_path": "6c46aa20e1ef287654b1da29e94d97256a89e3c2a4f4e2992c58e27f187550bf.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "table_body" + } + ], + "index": 8 + }, + { + "type": "table", + "bbox": [ + 317, + 305, + 538, + 425 + ], + "blocks": [ + { + "bbox": [ + 305, + 269, + 545, + 302 + ], + "lines": [ + { + "bbox": [ + 305, + 269, + 545, + 302 + ], + "spans": [ + { + "bbox": [ + 305, + 269, + 545, + 302 + ], + "type": "text", + "content": "Table 1. ACC (\\%) and BDR (\\%) performance of ambiguity attacks using IERB/CERB structure for AlexNet and ResNet18 with different number of passport layers on CIFAR10." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 317, + 305, + 538, + 425 + ], + "lines": [ + { + "bbox": [ + 317, + 305, + 538, + 425 + ], + "spans": [ + { + "bbox": [ + 317, + 305, + 538, + 425 + ], + "type": "table", + "html": "
Dataset-NetOriginalDataSizePlainCERBIERB
CIFAR10 \nAlexNet90.205000 (10%)83.6288.1687.30
2500 (5%)73.8286.7078.91
2000 (4%)73.4886.3076.73
1500 (3%)72.0986.7871.38
1000 (2%)64.8284.2263.71
CIFAR100 \nResNet1875.055000 (10%)70.7373.2670.51
3000 (6%)69.1472.2669.35
2000 (4%)62.8171.4268.89
1500 (3%)62.8671.6968.50
1000 (2%)53.9170.1268.44
", + "image_path": "c52e18a089e61483de0e0f04e376f4d4e0aa34d802365ee60421a60c23526454.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "table_body" + } + ], + "index": 10 + }, + { + "type": "table", + "bbox": [ + 308, + 464, + 538, + 551 + ], + "blocks": [ + { + "bbox": [ + 306, + 433, + 545, + 454 + ], + "lines": [ + { + "bbox": [ + 306, + 433, + 545, + 454 + ], + "spans": [ + { + "bbox": [ + 306, + 433, + 545, + 454 + ], + "type": "text", + "content": "Table 2. ACC (%) comparison with Plain attack for CIFAR10-AlexNet and CIFAR100-ResNet18." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 308, + 464, + 538, + 551 + ], + "lines": [ + { + "bbox": [ + 308, + 464, + 538, + 551 + ], + "spans": [ + { + "bbox": [ + 308, + 464, + 538, + 551 + ], + "type": "table", + "html": "
DatasetPassport LayerOriginalPlainCERBIERB
Caltech101Last 3 layers72.5471.0172.2667.79
Last 5 layers68.3059.8966.7860.73
Last 8 layers72.4959.9469.3859.32
Last 10 layers70.9057.1766.8957.06
Caltech256Last 5 layers54.3438.6452.2351.02
Last 7 layers53.9536.7249.5549.36
Last 10 layers55.4324.9347.8544.19
", + "image_path": "a79e1d3b5b23ae567d64689174b3e40be9008b6cf7c5d3c1d67ed8bb052f9497.jpg" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "table_body" + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 558, + 545, + 592 + ], + "lines": [ + { + "bbox": [ + 305, + 558, + 545, + 592 + ], + "spans": [ + { + "bbox": [ + 305, + 558, + 545, + 592 + ], + "type": "text", + "content": "Table 3. ACC (%) comparison with Plain attack on Caltech-101 and Caltech-256, where " + }, + { + "bbox": [ + 305, + 558, + 545, + 592 + ], + "type": "inline_equation", + "content": "10\\%" + }, + { + "bbox": [ + 305, + 558, + 545, + 592 + ], + "type": "text", + "content": " training data are used. Here the network is fixed to be ResNet18." + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 304, + 605, + 545, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 545, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 545, + 715 + ], + "type": "text", + "content": "rather limited. To this end, we embed 5 passport layers in AlexNet and 10 passport layers in ResNet18, and train them on CIFAR10 and CIFAR100, respectively. Let Plain attack refer to the case without using our proposed structures. Table 2 gives the ACC results of Plain attack and our ambiguity attacks using CERB and IERB. For the simple AlexNet, the performance of our attack with CERB overwhelms that of Plain attack, and the performance gain becomes more significant when smaller number of training data is avail" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "text", + "content": "8128" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 74, + 70, + 264, + 169 + ], + "blocks": [ + { + "bbox": [ + 74, + 70, + 264, + 169 + ], + "lines": [ + { + "bbox": [ + 74, + 70, + 264, + 169 + ], + "spans": [ + { + "bbox": [ + 74, + 70, + 264, + 169 + ], + "type": "table", + "html": "
DataSizeIERBCERB
ACCBDRACCBDR
10000 (25%)90.4740.2492.1791.77
5000 (12.5%)88.2642.8291.0592.82
4000 (10%)87.4347.7190.0792.61
3000 (7.5%)86.3048.3489.4993.65
2500 (6.25%)86.2348.9687.0093.44
2000 (5%)85.2649.2085.6793.44
", + "image_path": "6bb3f42f3e3e249da86e0a0f510af87a4c622ecf1f4efe569ff7543bfcdbcde1.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 177, + 287, + 199 + ], + "lines": [ + { + "bbox": [ + 47, + 177, + 287, + 199 + ], + "spans": [ + { + "bbox": [ + 47, + 177, + 287, + 199 + ], + "type": "text", + "content": "Table 4. ACC (%) and BDR (%) performance of ambiguity attacks with IERB and CERB using non-overlapping CIFAR10 dataset." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 209, + 288, + 423 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 209, + 288, + 423 + ], + "spans": [ + { + "bbox": [ + 46, + 209, + 288, + 423 + ], + "type": "text", + "content": "able. For instance, when " + }, + { + "bbox": [ + 46, + 209, + 288, + 423 + ], + "type": "inline_equation", + "content": "2\\%" + }, + { + "bbox": [ + 46, + 209, + 288, + 423 + ], + "type": "text", + "content": " training data are used, the ACC gap is almost " + }, + { + "bbox": [ + 46, + 209, + 288, + 423 + ], + "type": "inline_equation", + "content": "20\\%" + }, + { + "bbox": [ + 46, + 209, + 288, + 423 + ], + "type": "text", + "content": ". Such a property is very valuable in practice, as attacks are usually launched with very limited number of data; otherwise, re-training an entire model could be feasible as well. Also, for this simple AlexNet, our attack with IERB has similar performance with Plain attack. For the relatively large network ResNet18, our attack with CERB achieves " + }, + { + "bbox": [ + 46, + 209, + 288, + 423 + ], + "type": "inline_equation", + "content": "4.93\\%" + }, + { + "bbox": [ + 46, + 209, + 288, + 423 + ], + "type": "text", + "content": " ACC drop, compared with the original accuracy, when only " + }, + { + "bbox": [ + 46, + 209, + 288, + 423 + ], + "type": "inline_equation", + "content": "2\\%" + }, + { + "bbox": [ + 46, + 209, + 288, + 423 + ], + "type": "text", + "content": " training data are used. This drop shrinks to " + }, + { + "bbox": [ + 46, + 209, + 288, + 423 + ], + "type": "inline_equation", + "content": "1.79\\%" + }, + { + "bbox": [ + 46, + 209, + 288, + 423 + ], + "type": "text", + "content": " when " + }, + { + "bbox": [ + 46, + 209, + 288, + 423 + ], + "type": "inline_equation", + "content": "10\\%" + }, + { + "bbox": [ + 46, + 209, + 288, + 423 + ], + "type": "text", + "content": " training data are available. Compared with Plain attack, the ACC gains of our attack with CERB can be as large as " + }, + { + "bbox": [ + 46, + 209, + 288, + 423 + ], + "type": "inline_equation", + "content": "16.21\\%" + }, + { + "bbox": [ + 46, + 209, + 288, + 423 + ], + "type": "text", + "content": ". In addition, it is noted that our attack with IERB becomes much superior to Plain attack, when very limited training data are adopted; the ACC gain can be up to " + }, + { + "bbox": [ + 46, + 209, + 288, + 423 + ], + "type": "inline_equation", + "content": "14.53\\%" + }, + { + "bbox": [ + 46, + 209, + 288, + 423 + ], + "type": "text", + "content": ". More results on more complicated datasets including Caltech-101 and Caltech-256 can be found in Table 3, and similar conclusions can be drawn." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 432, + 241, + 445 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 432, + 241, + 445 + ], + "spans": [ + { + "bbox": [ + 47, + 432, + 241, + 445 + ], + "type": "text", + "content": "4.2. Attack with non-overlapping dataset" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 450, + 287, + 568 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 450, + 287, + 568 + ], + "spans": [ + { + "bbox": [ + 46, + 450, + 287, + 568 + ], + "type": "text", + "content": "In the above experiments, we consider the case that the attacker has access to a part of the original training data, namely, the dataset for launching the attack overlaps with the original one. We now investigate the attack performance under a more challenging scenario, i.e., the dataset available to the attacker and the original dataset come from the same source; but do not overlap. This non-overlapping dataset mimics the practical scenario that the attacker may not be able to exactly access a part of the original training data; but rather can only access some similar ones." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 570, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 570, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 570, + 288, + 713 + ], + "type": "text", + "content": "We randomly divide CIFAR10 into non-overlapping two subsets: 40000 for training the passport-based network and the remaining 10000 for the attack. Specifically, the attacking model is a ResNet18 with 10 passport layers, and the accuracy of the trained model is " + }, + { + "bbox": [ + 46, + 570, + 288, + 713 + ], + "type": "inline_equation", + "content": "93.12\\%" + }, + { + "bbox": [ + 46, + 570, + 288, + 713 + ], + "type": "text", + "content": ". The attack performance of our ambiguity attacks with IERB and CERB under this new setting is tabulated in Table 4. With these 10000 non-overlapping data, our ambiguity attack with CERB reaches a " + }, + { + "bbox": [ + 46, + 570, + 288, + 713 + ], + "type": "inline_equation", + "content": "92.17\\%" + }, + { + "bbox": [ + 46, + 570, + 288, + 713 + ], + "type": "text", + "content": " accuracy, only " + }, + { + "bbox": [ + 46, + 570, + 288, + 713 + ], + "type": "inline_equation", + "content": "0.95\\%" + }, + { + "bbox": [ + 46, + 570, + 288, + 713 + ], + "type": "text", + "content": " away from the original one. Also, the BDR in this case is as high as " + }, + { + "bbox": [ + 46, + 570, + 288, + 713 + ], + "type": "inline_equation", + "content": "91.77\\%" + }, + { + "bbox": [ + 46, + 570, + 288, + 713 + ], + "type": "text", + "content": ", indicating the recovered scale factors are very different from the authorized ones. When less number of non-" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 72, + 545, + 216 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 216 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 216 + ], + "type": "text", + "content": "overlapping data are used, the ACC values drop while the accompanied BDRs tend to improve. Even when only " + }, + { + "bbox": [ + 304, + 72, + 545, + 216 + ], + "type": "inline_equation", + "content": "5\\%" + }, + { + "bbox": [ + 304, + 72, + 545, + 216 + ], + "type": "text", + "content": " non-overlapping data are available, the ACC value can still be " + }, + { + "bbox": [ + 304, + 72, + 545, + 216 + ], + "type": "inline_equation", + "content": "85.67\\%" + }, + { + "bbox": [ + 304, + 72, + 545, + 216 + ], + "type": "text", + "content": " with BDR being " + }, + { + "bbox": [ + 304, + 72, + 545, + 216 + ], + "type": "inline_equation", + "content": "93.44\\%" + }, + { + "bbox": [ + 304, + 72, + 545, + 216 + ], + "type": "text", + "content": ". Similar results can be obtained by our ambiguity attack with IERB, but with a much lowered BDR of around " + }, + { + "bbox": [ + 304, + 72, + 545, + 216 + ], + "type": "inline_equation", + "content": "40\\%" + }, + { + "bbox": [ + 304, + 72, + 545, + 216 + ], + "type": "text", + "content": ". Another interesting phenomenon is that the ambiguity attack with CEBR using non-overlapping dataset leads to slightly worse ACC, but much better BDR performance, compared with the same attack with overlapping dataset. These results, again, show that our proposed ambiguity attacks are still very effective even in the challenging non-overlapping scenarios." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 305, + 224, + 545, + 247 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 224, + 545, + 247 + ], + "spans": [ + { + "bbox": [ + 305, + 224, + 545, + 247 + ], + "type": "text", + "content": "4.3. Result of ambiguity attack with CERB on other DNN watermark methods" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 254, + 546, + 409 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 254, + 546, + 409 + ], + "spans": [ + { + "bbox": [ + 304, + 254, + 546, + 409 + ], + "type": "text", + "content": "We now show that our proposed attack strategy can be generalized well to other DNN watermark methods. As the ambiguity attack with CERB overwhelms the one with IEBR, we adopt it in the following evaluations. The three DNN watermarking methods considered are: Greedy-Residual [21], DeepSigns [8], and Uchida [29], which used specific layer weights for the watermark embedding. For Greedy-Residual, the watermark was embedded into the first convolutional layer weight of the network, while for DeepSigns, the watermark was hidden in the flattened features before the last linear layer. Regarding Uchida's method, the watermark was injected into the third convolutional layer weights of the network." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 410, + 545, + 589 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 410, + 545, + 589 + ], + "spans": [ + { + "bbox": [ + 304, + 410, + 545, + 589 + ], + "type": "text", + "content": "We flexibly adapt our CERB structure for different types of embedded intermediaries such as model weights and features in three DNN watermark methods. Following the attack setting of Fan et al. [11], we assume that the network structure and model weights except those from the watermark are available to the attacker. As a result, for Greedy-Residual, we can replace the normalization layer after the embedded convolutional parameters with the CERB. Similarly, for DeepSigns, the normalization layer before the embedded feature map is replaced by our CERB. For Uchida's method, a CERB structure is added after the embedded convolutional parameters. We preset a different signature and only train the parameters embedded with the watermarks and the CERB parameters to match this new signature. More implementation details can be found in Appendix A." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 589, + 545, + 661 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 589, + 545, + 661 + ], + "spans": [ + { + "bbox": [ + 304, + 589, + 545, + 661 + ], + "type": "text", + "content": "We introduce signature detection rate (SDR) to evaluate if a signature is successfully embedded in the model. The SDR is defined as the percentage of the watermark bits " + }, + { + "bbox": [ + 304, + 589, + 545, + 661 + ], + "type": "inline_equation", + "content": "\\mathbf{wm} = \\{wm_1, \\dots, WM_C\\}" + }, + { + "bbox": [ + 304, + 589, + 545, + 661 + ], + "type": "text", + "content": " extracted from the model that are coincident with the signature " + }, + { + "bbox": [ + 304, + 589, + 545, + 661 + ], + "type": "inline_equation", + "content": "\\mathbf{sig} = \\{sig_1, \\dots, sig_C\\}" + }, + { + "bbox": [ + 304, + 589, + 545, + 661 + ], + "type": "text", + "content": " used during the embedding process, i.e.," + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 359, + 664, + 545, + 697 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 359, + 664, + 545, + 697 + ], + "spans": [ + { + "bbox": [ + 359, + 664, + 545, + 697 + ], + "type": "interline_equation", + "content": "S D R = \\frac {1}{C} \\sum_ {i = 1} ^ {C} \\mathcal {I} \\left[ w m _ {i} = s i g _ {i} \\right]. \\tag {10}", + "image_path": "8574a92b746804981ba299d764d818631870e82319555a2abfbd5274c43d4615.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 318, + 701, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 318, + 701, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 318, + 701, + 545, + 714 + ], + "type": "text", + "content": "The attack results on three watermark methods are pre" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "text", + "content": "8129" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 70, + 70, + 525, + 126 + ], + "blocks": [ + { + "bbox": [ + 70, + 70, + 525, + 126 + ], + "lines": [ + { + "bbox": [ + 70, + 70, + 525, + 126 + ], + "spans": [ + { + "bbox": [ + 70, + 70, + 525, + 126 + ], + "type": "table", + "html": "
WM methodDataset-NetEmbed-PositionDataSizeOriginal ACCAttack ACCBDRSDR
Greedy-ResidualCaltech256-ResNet18First Conv layer10%54.9854.3749.22100
DeepSignsCIFAR10-WRNLast Linear layer10%91.3091.1537.5100
UchidaCIFAR10-WRNThird Conv layer10%90.1189.7745.31100
", + "image_path": "d36f89f33c5150c42ccf3864e0a8770ddd608c6e56f691d9b6556e59d294155b.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 63, + 156, + 273, + 184 + ], + "blocks": [ + { + "bbox": [ + 72, + 134, + 520, + 145 + ], + "lines": [ + { + "bbox": [ + 72, + 134, + 520, + 145 + ], + "spans": [ + { + "bbox": [ + 72, + 134, + 520, + 145 + ], + "type": "text", + "content": "Table 5. Results of our ambiguity attack on other DNN watermark methods, in terms of ACC (%), BDR (%), and SDR (%)." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 63, + 156, + 273, + 184 + ], + "lines": [ + { + "bbox": [ + 63, + 156, + 273, + 184 + ], + "spans": [ + { + "bbox": [ + 63, + 156, + 273, + 184 + ], + "type": "table", + "html": "
# of CERBOriginal046810
ACC (%)55.4225.0328.9938.5042.5847.07
", + "image_path": "e1cc3092f30b91eb288e209aac4c3c79f01c3bf1a68e860a5cc9d6442fe55b05.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 221, + 288, + 353 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 221, + 288, + 353 + ], + "spans": [ + { + "bbox": [ + 46, + 221, + 288, + 353 + ], + "type": "text", + "content": "sented in Table 5. For Greedy-Residual method, the inference performance of the model after the attack is quite similar to that of the original one, with a very slight drop of " + }, + { + "bbox": [ + 46, + 221, + 288, + 353 + ], + "type": "inline_equation", + "content": "0.61\\%" + }, + { + "bbox": [ + 46, + 221, + 288, + 353 + ], + "type": "text", + "content": ". In addition, the SDR is " + }, + { + "bbox": [ + 46, + 221, + 288, + 353 + ], + "type": "inline_equation", + "content": "100\\%" + }, + { + "bbox": [ + 46, + 221, + 288, + 353 + ], + "type": "text", + "content": ", implying that the attacker can claim the ownership to this model with the new signature. Meanwhile, a high BDR of " + }, + { + "bbox": [ + 46, + 221, + 288, + 353 + ], + "type": "inline_equation", + "content": "49.22\\%" + }, + { + "bbox": [ + 46, + 221, + 288, + 353 + ], + "type": "text", + "content": " well demonstrates the high dissimilarity between the forged and original watermarks. Very similar observations can be made when attacking DeepSigns and Uchida's methods. Therefore, we validate the generalization capability of our attack strategy to other DNN watermark methods." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 360, + 139, + 373 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 360, + 139, + 373 + ], + "spans": [ + { + "bbox": [ + 47, + 360, + 139, + 373 + ], + "type": "text", + "content": "4.4. Ablation study" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 378, + 287, + 509 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 378, + 287, + 509 + ], + "spans": [ + { + "bbox": [ + 46, + 378, + 287, + 509 + ], + "type": "text", + "content": "Different number of CERB structures: To study the effect on attack performance with different number of CERB structures, we use a ResNet18 with the last 10 layers embedded with passports for the illustration. As can be seen from Table 6, the original performance evaluated on Caltech-256 is " + }, + { + "bbox": [ + 46, + 378, + 287, + 509 + ], + "type": "inline_equation", + "content": "55.42\\%" + }, + { + "bbox": [ + 46, + 378, + 287, + 509 + ], + "type": "text", + "content": ". For Plain attack with 0 CERB structure, the ACC is very low, i.e., " + }, + { + "bbox": [ + 46, + 378, + 287, + 509 + ], + "type": "inline_equation", + "content": "25.05\\%" + }, + { + "bbox": [ + 46, + 378, + 287, + 509 + ], + "type": "text", + "content": ". By gradually applying more CERB structures, the ACC values improve constantly. Eventually, with all 10 passport layers replaced by our CERB structures, the ACC of our ambiguity attack reaches " + }, + { + "bbox": [ + 46, + 378, + 287, + 509 + ], + "type": "inline_equation", + "content": "47.07\\%" + }, + { + "bbox": [ + 46, + 378, + 287, + 509 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 510, + 287, + 677 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 510, + 287, + 677 + ], + "spans": [ + { + "bbox": [ + 46, + 510, + 287, + 677 + ], + "type": "text", + "content": "Increasing the depth of CERB: The CERB in the default setting is a two-layer perceptron with LeakyReLU. We now try to testify if using perceptron with more layers leads to better attack performance. To this end, we experiment on the ResNet18 with 10 passport layers trained on CIFAR10, and launch the ambiguity attacks by varying the number of layers in CERB. As can be seen from Table 7, the ACC restored by CERB with 2 layers is the highest, reaching " + }, + { + "bbox": [ + 46, + 510, + 287, + 677 + ], + "type": "inline_equation", + "content": "92.24\\%" + }, + { + "bbox": [ + 46, + 510, + 287, + 677 + ], + "type": "text", + "content": ". With more layers being involved, the ACC performance actually drops surprisingly. We conjecture that the two-layer perceptron is enough for our ambiguity attack; while increasing the number of layers places heavier burden to the training and eventually affects the performance of the ambiguity attack." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 677, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 677, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 677, + 287, + 713 + ], + "type": "text", + "content": "Using other activation functions in CERB: We also evaluate the impact of the activation functions in CERB on the overall attack performance. Again, we experiment on" + } + ] + } + ], + "index": 8 + }, + { + "type": "table", + "bbox": [ + 313, + 156, + 541, + 185 + ], + "blocks": [ + { + "bbox": [ + 47, + 192, + 287, + 214 + ], + "lines": [ + { + "bbox": [ + 47, + 192, + 287, + 214 + ], + "spans": [ + { + "bbox": [ + 47, + 192, + 287, + 214 + ], + "type": "text", + "content": "Table 6. Results of using different number of CERB on Caltech-256 with ResNet18." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 313, + 156, + 541, + 185 + ], + "lines": [ + { + "bbox": [ + 313, + 156, + 541, + 185 + ], + "spans": [ + { + "bbox": [ + 313, + 156, + 541, + 185 + ], + "type": "table", + "html": "
# of MLP layers in CERBOriginal2345
ACC (%)94.4092.2486.8584.1886.45
", + "image_path": "c18ec8120af143e3ef3a677a30568c34832a14e848c3561405941da5e961ad13.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "table_body" + } + ], + "index": 9 + }, + { + "type": "table", + "bbox": [ + 319, + 215, + 535, + 249 + ], + "blocks": [ + { + "bbox": [ + 317, + 193, + 533, + 204 + ], + "lines": [ + { + "bbox": [ + 317, + 193, + 533, + 204 + ], + "spans": [ + { + "bbox": [ + 317, + 193, + 533, + 204 + ], + "type": "text", + "content": "Table 7. Results of changing the number of layer in CERB." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 319, + 215, + 535, + 249 + ], + "lines": [ + { + "bbox": [ + 319, + 215, + 535, + 249 + ], + "spans": [ + { + "bbox": [ + 319, + 215, + 535, + 249 + ], + "type": "table", + "html": "
Activation FunctionsLeakyReLUtanhSigmoid
ACC (%)92.8792.5492.80
", + "image_path": "8d53990b98c7a0e0dd71a11c6a6b63cb4465c98dd73a0522685fbfa6ce1c75e9.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "table_body" + } + ], + "index": 11 + }, + { + "bbox": [ + 327, + 257, + 523, + 269 + ], + "lines": [ + { + "bbox": [ + 327, + 257, + 523, + 269 + ], + "spans": [ + { + "bbox": [ + 327, + 257, + 523, + 269 + ], + "type": "text", + "content": "Table 8. Result of using different activation functions." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 304, + 275, + 545, + 371 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 275, + 545, + 371 + ], + "spans": [ + { + "bbox": [ + 304, + 275, + 545, + 371 + ], + "type": "text", + "content": "the ResNet18 with 10 passport layers trained on CIFAR10. We then replace every passport layer with CERB, and adopt different activation functions in CERB. We list the ACC results by using tanh and Sigmoid, in addition to our default LeakyReLU in Table 8. As can be noticed, all ACC results with different activation functions are similar. This implies that the attack performance is not sensitive to the activation functions adopted." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 382, + 378, + 395 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 382, + 378, + 395 + ], + "spans": [ + { + "bbox": [ + 306, + 382, + 378, + 395 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 403, + 545, + 498 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 403, + 545, + 498 + ], + "spans": [ + { + "bbox": [ + 304, + 403, + 545, + 498 + ], + "type": "text", + "content": "In this paper, we propose an advanced ambiguity attack that defeats the passport-based model IP protection scheme. We combine multi-layer perceptron with skip connection to find valid substitute passports using less than " + }, + { + "bbox": [ + 304, + 403, + 545, + 498 + ], + "type": "inline_equation", + "content": "10\\%" + }, + { + "bbox": [ + 304, + 403, + 545, + 498 + ], + "type": "text", + "content": " of the training dataset. Extensive experimental results validate the effectiveness of our ambiguity attack. Further, it is demonstrated that our attack strategy can be easily extended to other DNN watermark methods." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 498, + 545, + 617 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 498, + 545, + 617 + ], + "spans": [ + { + "bbox": [ + 304, + 498, + 545, + 617 + ], + "type": "text", + "content": "Regarding the remedy solutions, one potential direction is to exploit random locations for inserting the passport-layers, in which the randomness is controlled by a secret key. Additionally, another promising attempt is to change the embedding position from model weights to the activations. To make sure the next convolutional layer can extract proper features from the activation, the statistic of the activation should stay in a restricted scope. Such a statistic could be unique for a given signature, which may be helpful to resist our ambiguity attack." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 618, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 618, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 618, + 545, + 713 + ], + "type": "text", + "content": "Acknowledgments: This work was supported in part by Macau Science and Technology Development Fund under SKLIOTSC-2021-2023, 0072/2020/AMJ, and 0022/2022/A1; in part by Research Committee at University of Macau under MYRG2020-00101-FST and MYRG2022-00152-FST; in part by Natural Science Foundation of China under 61971476; and in part by Alibaba Group through Alibaba Innovative Research Program." + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "8130" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 288, + 714 + ], + "type": "list", + "angle": 0, + "index": 13, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 144 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 144 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 144 + ], + "type": "text", + "content": "[1] Yossi Adi, Carsten Baum, Moustapha Cisse, Benny Pinkas, and Joseph Keshet. 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In Proceedings of the ACM Asia Conference on Computer and Communications Security, pages 159-172, 2018. 1" + } + ] + } + ], + "index": 11 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "type": "text", + "content": "8132" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 9 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Efficient Frequency Domain-Based Transformers for High-Quality Image Deblurring/c856a1da-867e-42ea-84a9-c14d1b12f290_content_list.json b/2023/Efficient Frequency Domain-Based Transformers for High-Quality Image Deblurring/c856a1da-867e-42ea-84a9-c14d1b12f290_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..51b2d91709c794812fe23841158459a2fefe91ae --- /dev/null +++ b/2023/Efficient Frequency Domain-Based Transformers for High-Quality Image Deblurring/c856a1da-867e-42ea-84a9-c14d1b12f290_content_list.json @@ -0,0 +1,1921 @@ +[ + { + "type": "text", + "text": "Efficient Frequency Domain-based Transformers for High-Quality Image Deblurring", + "text_level": 1, + "bbox": [ + 236, + 130, + 736, + 176 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Lingshun Kong $^{1}$ , Jiangxin Dong $^{1*}$ , Jianjun Ge $^{2}$ , Mingqiang Li $^{2}$ , and Jinshan Pan $^{1*}$ $^{1}$ School of Computer Science and Engineering, Nanjing University of Science and Technology \n $^{2}$ Information Science Academy, China Electronics Technology Group Corporation", + "bbox": [ + 109, + 202, + 857, + 258 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 308, + 313, + 325 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "We present an effective and efficient method that explores the properties of Transformers in the frequency domain for high-quality image deblurring. Our method is motivated by the convolution theorem that the correlation or convolution of two signals in the spatial domain is equivalent to an element-wise product of them in the frequency domain. This inspires us to develop an efficient frequency domain-based self-attention solver (FSAS) to estimate the scaled dot-product attention by an element-wise product operation instead of the matrix multiplication in the spatial domain. In addition, we note that simply using the naive feed-forward network (FFN) in Transformers does not generate good deblurred results. To overcome this problem, we propose a simple yet effective discriminative frequency domain-based FFN (DFFN), where we introduce a gated mechanism in the FFN based on the Joint Photographic Experts Group (JPEG) compression algorithm to discriminatively determine which low- and high-frequency information of the features should be preserved for latent clear image restoration. We formulate the proposed FSAS and DFFN into an asymmetrical network based on an encoder and decoder architecture, where the FSAS is only used in the decoder module for better image deblurring. Experimental results show that the proposed method performs favorably against the state-of-the-art approaches.", + "bbox": [ + 75, + 340, + 473, + 719 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 731, + 209, + 747 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Image deblurring aims to restore high-quality images from blurred ones. This problem has achieved significant progress due to the development of various effective deep models with large-scale training datasets.", + "bbox": [ + 75, + 753, + 468, + 814 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Most state-of-the-art methods for image deblurring are mainly based on deep convolutional neural networks (CNNs). The main success of these methods is due to developing kinds of network architectural designs, for example, the multi-", + "bbox": [ + 75, + 814, + 472, + 876 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/b611b7e74183e61962acbb8c333c1d664239b3d51cf2a59c7c5217d79fcac314.jpg", + "image_caption": [ + "Figure 1. Comparisons of the proposed method and state-of-the-art ones on the GoPro dataset [16] in terms of accuracy, floating point operations (FLOPs), and network parameters. The circle size indicates the number of the network parameter." + ], + "image_footnote": [], + "bbox": [ + 498, + 306, + 895, + 503 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "scale [4, 16, 22] or multi-stage [31, 32] network architectures, generative adversarial learning [11, 12], physics model inspired network structures [6-8, 17, 33], and so on. As the basic operation in these networks, the convolution operation is a spatially-invariant local operation, which does not model the spatially variant properties of the image contents. Most of them use larger and deeper models to remedy the limitation of the convolution. However, simply increasing the capacity of deep models does not always lead to better performance as shown in [17, 33].", + "bbox": [ + 496, + 566, + 895, + 715 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Different from the convolution operation that models the local connectivity, Transformers are able to model the global contexts by computing the correlations of one token to all other tokens. They have been shown to be an effective approach in lots of high-level vision tasks and also have great potential to be the alternatives of deep CNN models. In image deblurring, the methods based on Transformers [27, 30] also achieve better performance than the CNN-based methods. However, the computation of the scaled dot-product attention in Transformers leads to quadratic space and time complexity in terms of the number of tokens. Although using smaller and fewer tokens can reduce the space and", + "bbox": [ + 496, + 719, + 895, + 901 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 810, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Corresponding author: Jiangxin Dong and Jinshan Pan.", + "bbox": [ + 93, + 886, + 393, + 900 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "5886", + "bbox": [ + 482, + 944, + 516, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "time complexity, such strategy cannot model the long-range information of features well and usually leads to significant artifacts when handling high-resolution images, which thus limits the performance improvement.", + "bbox": [ + 75, + 90, + 468, + 151 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To alleviate this problem, most approaches use the down-sampling strategy to reduce the spatial resolution of features [26]. However, reducing the spatial resolution of features will cause information loss and thus affect the image deblurring. Several methods reduce the computational cost by computing the scaled dot-product attention in terms of the number of features [29, 30]. Although the computational cost is reduced, the spatial information is well not explored, which may affect the deblurring performance.", + "bbox": [ + 75, + 154, + 470, + 289 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In this paper, we develop an effective and efficient method that explores the properties of Transformers for high-quality image deblurring. We note that the scaled dot-product attention computation is actually to estimate the correlation of one token from the query and all the tokens from the key. This process can be achieved by a convolution operation when rearranging the permutations of tokens. Based on this observation and the convolution theorem that the convolution in the spatial domain equals a point-wise multiplication in the frequency domain, we develop an efficient frequency domain-based self-attention solver (FSAS) to estimate the scaled dot-product attention by an element-wise product operation instead of the matrix multiplication. Therefore, the space and time complexity can be reduced to $O(N)$ $O(N\\log N)$ for each feature channel, where $N$ is the number of the pixels.", + "bbox": [ + 75, + 291, + 470, + 532 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In addition, we note that simply using the feed-forward network (FFN) by [30] does not generate good deblurred results. To generate better features for latent clear image restoration, we develop a simple yet effective discriminative frequency domain-based FFN (DFFN). Our DFFN is motivated by the Joint Photographic Experts Group (JPEG) compression algorithm. It introduces a gated mechanism in the FFN to discriminatively determine which low- and high-frequency information should be preserved for latent clear image restoration.", + "bbox": [ + 75, + 536, + 468, + 686 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "We formulate the proposed FSAS and DFFN into an end-to-end trainable network based on an encoder and decoder architecture to solve image deblurring. However, we find that as features of shallow layers usually contain blur effects, applying the scaled dot-product attention to shallow features does not effectively explore global clear contents. As the features from deep layers are usually clearer than those from shallow layers, we develop an asymmetric network architecture, where the FSAS is only used in the decoder module for better image deblurring. We analyze that the exploring properties of Transformers in the frequency domain is able to facilitate blur removal. Experimental results demonstrate that the proposed method generates favorable results against state-of-the-art methods in terms of accuracy and efficiency", + "bbox": [ + 75, + 688, + 470, + 900 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "(Figure 1).", + "text_level": 1, + "bbox": [ + 500, + 90, + 573, + 106 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "The main contributions are summarized as follows:", + "- We develop an efficient frequency domain-based self-attention solver to estimate the scaled dot-product attention. Our analysis demonstrates that using the frequency domain-based solver reduces the space and time complexity and is much more effective and efficient.", + "- We propose a simple yet effective discriminative frequency domain-based FFN based on the JPEG compression algorithm to discriminatively determine which low and high-frequency information should be preserved for latent clear image restoration.", + "- We develop an asymmetric network architecture based on an encoder and decoder network, where the frequency domain-based self-attention solver is only used in the decoder module for better image deblurring.", + "- We analyze that the exploring properties of Transformers in the frequency domain is able to facilitate blur removal and show that our approach performs favorably against state-of-the-art methods." + ], + "bbox": [ + 516, + 107, + 893, + 392 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 500, + 398, + 640, + 412 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Deep CNN-based Image deblurring methods. In recent years, we have witnessed significant advances in image deblurring due to the development of different deep CNN models [3, 4, 9, 16, 22, 31, 32]. In [16], Nah et al. propose a deep CNN based on a multi-scale framework to directly estimate clear images from blurred ones. To better utilize the information of each scale in multi-scale framework, Tao et al. [22] develop an effective scale recurrent network. Gao et al. [9] propose a selective network parameter sharing method to improve [16, 22].", + "bbox": [ + 496, + 419, + 893, + 569 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "As using more scales does not improve the performance significantly, Zhang et al. [32] develop an effective network based on multi-patch strategy. The deblurring process is achieved stage by stage. To better explore the features from different stages, Zamir et al. [31] propose a cross-stage feature fusion for better performance. In order to reduce the computational cost of the methods based on multi-scale framework, Cho et al. [4] present a multi-input and multi-output network. Chen et al. [3] analyze the baseline modules and simplify them for better image restoration. As demonstrated in [30], the convolution operation is spatial invariant and does not effectively model the global contexts for image deblurring.", + "bbox": [ + 496, + 570, + 893, + 765 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Transformers and their applications to image deblurring. As the Transformer [25] can model the global contexts and achieves significant progress in lots of high-level vision tasks (e.g., image classification [14], object detection [1, 34] and semantic segmentation [28, 35]), it has been developed to solve image super-resolution [13], image deblurring [24, 30] and image denoise [2, 27]. To reduce the computational cost of Transformer, Zamir et al. [30] propose an efficient Transformer model by computing the scaled dot-product attention", + "bbox": [ + 496, + 763, + 893, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "5887", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "in the feature depth domain. This method can effectively explore information from different features along the channel dimension. However, the spatial information that is vital for image restoration is not fully explored. Tsai et al. [24] simplify the calculation of self-attention by constructing intra and inter strip tokens to replace the global attention. Wang et al. [27] propose a Transformer based on a UNet which uses non-overlapping window-based self-attention for single image deblurring. Although using the splitting strategy reduces the computational cost, the coarse splitting does not fully explore the information of each patch. Moreover, the scaled dot-product attention in these methods usually needs the complex matrix multiplication whose the space and time complexity is quadratic.", + "bbox": [ + 75, + 90, + 472, + 301 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Different from these methods, we develop an efficient Transformer-based method that explores the property of the frequency domain to avoid the complex matrix multiplication for the scaled dot-product attention.", + "bbox": [ + 75, + 301, + 468, + 363 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Proposed Method", + "text_level": 1, + "bbox": [ + 76, + 369, + 250, + 386 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Our goal is to present an effective and efficient method to explore the properties of Transformers for high-quality image deblurring. To this end, we first develop an efficient frequency domain-based self-attention solver to estimate the scaled dot-product attention. To refine the features estimated by the frequency domain-based solver, we further develop a discriminative frequency domain-based feed-forward network. We formulate these above approaches into an end-to-end trainable network based on an encoder and decoder architecture to solve image deblurring, where the frequency domain-based self-attention solver for the estimation of the scaled dot-product attention is used in the decoder module for better feature representation. Figure 2(a) shows the overview of the proposed method. In the following, we present the details of each component.", + "bbox": [ + 75, + 392, + 472, + 619 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Frequency domain-based self-attention solver", + "text_level": 1, + "bbox": [ + 76, + 626, + 464, + 642 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Given the input feature $X$ with a spatial resolution of $H\\times W$ pixels and $C$ channels, existing vision Transformers usually first compute the features $F_{q},F_{k}$ ,and $F_{v}$ by applying linear transformations $W_{q}$ $W_{k}$ ,and $W_{v}$ to $X$ . Then, they apply the unfolding function to the features $F_{q},F_{k}$ ,and $F_{v}$ to extract image patches $\\{q_i\\}_{i = 1}^N,\\{k_i\\}_{i = 1}^N$ ,and $\\{v_i\\}_{i = 1}^N$ ,where $N$ denotes the number of extracted patches. By applying a reshape operation to the extracted patches, the query Q, key K, and value V can be obtained by:", + "bbox": [ + 76, + 645, + 472, + 781 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {Q} = \\mathcal {R} \\left(\\left\\{q _ {i} \\right\\} _ {i = 1} ^ {N}\\right), \\mathbf {K} = \\mathcal {R} \\left(\\left\\{k _ {i} \\right\\} _ {i = 1} ^ {N}\\right), \\mathbf {V} = \\mathcal {R} \\left(\\left\\{v _ {i} \\right\\} _ {i = 1} ^ {N}\\right), \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 83, + 792, + 468, + 824 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\mathcal{R}$ denotes the reshape function which ensures that $\\{\\mathbf{K},\\mathbf{Q},\\mathbf{V}\\} \\in R^{N\\times (CH_pW_p)}$ , $H_{p}$ and $W_{p}$ denote the height and width of extracted patches. Based on the obtained query $\\mathbf{Q}$ , key $\\mathbf{K}$ , and value $\\mathbf{V}$ , the scaled dot-product attention is achieved by:", + "bbox": [ + 76, + 825, + 468, + 901 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nV _ {a t t} = \\operatorname {s o f t m a x} \\left(\\frac {\\mathbf {Q K} ^ {\\top}}{\\sqrt {C H _ {p} W _ {p}}}\\right) V. \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 578, + 88, + 890, + 128 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The attention map computation involves the matrix multiplication of $\\mathbf{Q}\\mathbf{K}^{\\top}$ whose space complexity and time complexity are $O(N^{2})$ and $O(N^{2}C)$ . It is not affordable if the image resolution and the number of the extracted patches are large. Although using downsampling operation to reduce the image resolution or non-overlapping method to extract fewer patches will alleviate the problem, these strategies would lead to information loss and limit the ability to model details within and across each patch [29].", + "bbox": [ + 496, + 133, + 893, + 268 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We note that each element of $\\mathbf{Q}\\mathbf{K}^{\\top}$ is obtained by the inner product:", + "bbox": [ + 498, + 268, + 890, + 299 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\left(\\mathbf {Q} \\mathbf {K} ^ {\\top}\\right) _ {i j} = \\langle \\mathbf {q} _ {i}, \\mathbf {k} _ {j} \\rangle , \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 619, + 305, + 890, + 333 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\mathbf{q}_i$ and $\\mathbf{k}_j$ are the vectorized forms of $i$ -th and $j$ -th patches from $F_{q}$ and $F_{k}$ . Based on (3), if we apply reshape functions to $\\mathbf{q}_i$ and all the patches $\\mathbf{k}_j$ , respectively, all the $i$ -th column elements of $\\mathbf{QK}^{\\top}$ can be obtained by a convolution operation, i.e., $\\widetilde{q}_i \\otimes \\widetilde{K}$ , where $\\widetilde{q}_i$ and $\\widetilde{K}$ denote the reshaped results of $\\mathbf{q}_i$ and $\\mathbf{k}_j$ ; $\\otimes$ denotes the convolution operation.", + "bbox": [ + 496, + 337, + 893, + 430 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "According to the convolution theorem, the correlation or convolution of two signals in the spatial domain is equivalent to an element-wise product of them in the frequency domain. Therefore, a natural question is that can we efficiently estimate the attention map by an element-wise product operation in a frequency domain instead of computing the matrix multiplication of $\\mathbf{Q}\\mathbf{K}^{\\top}$ in the spatial domain?", + "bbox": [ + 496, + 430, + 893, + 535 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "To this end, we develop an effective frequency domain-based self-attention solver. Specifically, we first obtain $F_{q}$ , $F_{k}$ , and $F_{v}$ by a $1 \\times 1$ point-wise convolution and $3 \\times 3$ depth-wise convolution. Then, we apply the fast Fourier transform (FFT) to the estimated features $F_{q}$ and $F_{k}$ and estimate the correlation of $F_{q}$ and $F_{k}$ in the frequency domain by:", + "bbox": [ + 498, + 536, + 893, + 626 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nA = \\mathcal {F} ^ {- 1} \\left(\\mathcal {F} \\left(F _ {q}\\right) \\overline {{\\mathcal {F} \\left(F _ {k}\\right)}}\\right), \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 599, + 633, + 890, + 657 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\mathcal{F}(\\cdot)$ denotes the FFT, $\\mathcal{F}^{-1}(\\cdot)$ denotes the inverse FFT, and $\\overline{\\mathcal{F}(\\cdot)}$ denotes the conjugate transpose operation. Finally, we estimate the aggregated feature by:", + "bbox": [ + 496, + 664, + 893, + 710 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nV _ {a t t} = \\mathcal {L} (A) F _ {v}, \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 635, + 717, + 890, + 733 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where a layer norm $\\mathcal{L}(\\cdot)$ is used to normalize $A$ . Finally, we generate the output feature of FSAS by:", + "bbox": [ + 496, + 739, + 890, + 770 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nX _ {a t t} = X + \\operatorname {C o n v} _ {1 \\times 1} \\left(V _ {a t t}\\right), \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 596, + 777, + 890, + 792 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\mathrm{Conv}_{1\\times 1}(\\cdot)$ denotes a convolution with filter size of $1\\times 1$ pixel. The detailed network architecture of the proposed FSAS is shown in Figure 2(b).", + "bbox": [ + 496, + 799, + 893, + 845 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. Discriminative frequency domain-based FFN", + "text_level": 1, + "bbox": [ + 500, + 849, + 880, + 866 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The FFN is used to improve the features by the scaled dot-product attention. Thus, it is important to develop an", + "bbox": [ + 498, + 869, + 890, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "5888", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/449efbfdd40dfc847e99bfd25a9c3177a45ac771dcdc69d13ec61095b0173f50.jpg", + "image_caption": [ + "Figure 2. Network architectures. (a) The proposed asymmetric encoder-decoder network that only contains DFFN in the encoder module and both FSAS and DFFN in the decoder module for image deblurring. (b) The proposed FSAS module. (c) The proposed DFFN module." + ], + "image_footnote": [], + "bbox": [ + 101, + 88, + 459, + 314 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/9617f88a384dc068920468f0db287e28971a8e1a2e0576f0eead493a72a69c4b.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 464, + 87, + 635, + 314 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/d217644bdbccaee5334259ea53062598d2f112272bebdf1c89f90499f919085a.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 640, + 88, + 866, + 314 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "effective FFN to generate the features that facilitate the latent clear image reconstruction. As not all the low-frequency information and high-frequency information help latent clear image restoration, we develop a DFFN that can adaptively determine which frequency information should be preserved. However, how to effectively determine which frequency information is important. Motivated by the JPEG compression algorithm, we introduce a learnable quantization matrix $\\mathbf{W}$ and learn it by an inverse method of JPEG compression to determine which frequency information should be preserved. The proposed DFFN can be formulated by:", + "bbox": [ + 75, + 347, + 473, + 513 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nX _ {1} = \\operatorname {C o n v} _ {1 \\times 1} (\\mathcal {L} (X _ {\\text {a t t}}))\n$$\n", + "text_format": "latex", + "bbox": [ + 166, + 516, + 344, + 532 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nX _ {1} ^ {f} = \\mathcal {F} \\left(\\mathcal {P} \\left(X _ {1}\\right)\\right) \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 169, + 536, + 468, + 563 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nX _ {2} = \\mathcal {F} ^ {- 1} \\left(\\mathbf {W} X _ {1} ^ {f}\\right)\n$$\n", + "text_format": "latex", + "bbox": [ + 169, + 558, + 302, + 577 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nX _ {o u t} = \\mathcal {G} \\left(\\mathcal {P} ^ {- 1} \\left(X _ {2}\\right)\\right) + X _ {a t t},\n$$\n", + "text_format": "latex", + "bbox": [ + 169, + 579, + 375, + 598 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\mathcal{P}(\\cdot)$ and $\\mathcal{P}^{-1}(\\cdot)$ denote the patch unfolding and folding operations in the JPEG compression method; $\\mathcal{G}$ denotes GEGLU function by [19]. The detailed network architecture of the proposed DFFN is shown in Figure 2(c).", + "bbox": [ + 75, + 608, + 468, + 669 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.3. Asymmetric encoder-decoder network", + "text_level": 1, + "bbox": [ + 76, + 671, + 406, + 686 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We embed the proposed FSAS and DFFN into a network based on an encoder and decoder architecture. We note that most existing methods usually use symmetric architectures in the encoder and decoder modules. For example, if the FSAS and DFFN are used in the encoder module, they are also used in the decoder module. We note that the features extracted by encoder module are shallow ones, which usually contain blur effects compared to the deep features from the decoder module. However, the blur usually changes similarity of two similar patches from clear features. Thus, using the FSAS in the encoder module may not estimate the similarity correctly, which accordingly affects image restoration. To overcome this problem, we embed the FSAS into the decoder module, which leads to an asymmetric architecture for better image", + "bbox": [ + 75, + 688, + 470, + 900 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "deblurring. Figure 2(a) shows the network architecture of the proposed asymmetric encoder-decoder network.", + "bbox": [ + 496, + 347, + 892, + 377 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Finally, given a blurred image $B$ , the restored image $I$ is estimated by the asymmetric encoder-decoder network:", + "bbox": [ + 496, + 378, + 890, + 407 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nI = \\mathcal {N} (B) + B, \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 638, + 414, + 890, + 431 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\mathcal{N}$ denotes the asymmetric encoder-decoder network.", + "bbox": [ + 498, + 441, + 893, + 455 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4. Experimental Results", + "text_level": 1, + "bbox": [ + 498, + 465, + 705, + 482 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In this section, we evaluate our method and compare it with state-of-the-art ones using public benchmark datasets.", + "bbox": [ + 496, + 484, + 890, + 515 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4.1. Datasets and parameter settings", + "text_level": 1, + "bbox": [ + 498, + 520, + 782, + 536 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Datasets. We evaluate our method on commonly used image deblurring datasets including the GoPro dataset [16], the HIDe dataset [20], and the RealBlur dataset [18]. We follow the protocols of existing methods for fair comparisons.", + "bbox": [ + 496, + 537, + 890, + 598 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Parameter settings. We use the same loss function as [4] to constrain the network and train it using the Adam [10] optimizer with default parameters. The initial value of the learning rate is $10^{-3}$ and is updated with the cosine annealing strategy after 600,000 iterations. The minimum value of the learning rate is $10^{-7}$ . The patch size is empirically set to be $256 \\times 256$ pixels and the batch size is set to be 16. We adopt the same data augmentation method as [30] during the training. The patch size for the quantization matrix estimation is empirically set to be $8 \\times 8$ based on the JPEG compression method. In the implementation, the tensor form of the quantization matrix is set as [batch_size, channel_num, 8, 8], where batch_size and channel_num are the number of batches and features. The quantization matrix is jointly learned with other parameters by solving loss functions during the training. Similarity, we also use the patch size of $8 \\times 8$ pixels when computing the self-attention (4). Due to the page limit, we include more experimental results in the supplemental material. The training code and models are available at https://github.com/kkkls/FFTformer.", + "bbox": [ + 496, + 604, + 893, + 905 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "5889", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/451bd253d42c6abf52b0cfc97893610d7c6414344676ca28e0e8ac93d7a588b4.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 91, + 88, + 285, + 215 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/74cb9d826e7bc61ca50ffe75480252d28137b5df96d67818e1945bdd033830b2.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 287, + 88, + 482, + 215 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/16b200b4c21552650b77904c7bed316d46b8198653f0ed0777fe43a0f646eb7f.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 483, + 88, + 679, + 215 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/3f9b52f1e843819375fccddbba7daa3fe0b1920482f7cbbe9748de2394870fdd.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 679, + 88, + 875, + 215 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/9a90f446fa2d656748d434e6036198e13b684dfaf44ad63521799441277fb0b6.jpg", + "image_caption": [ + "(a) Blurred image", + "(e) Stripformer [24]", + "Figure 3. Deblurred results on the GoPro dataset [16]. The deblurred results in (c)-(g) still contain significant blur effects. The proposed method generates a clearer image. For example, the characters and boundaries are much clearer." + ], + "image_footnote": [], + "bbox": [ + 89, + 229, + 287, + 357 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/0dfa20e30f8b057bd54d6d0922bd2b5cf4fbe61c81ccd89f6f2f529f59bf2d3a.jpg", + "image_caption": [ + "(b) GT", + "(f) Restormer-local [5]" + ], + "image_footnote": [], + "bbox": [ + 287, + 229, + 482, + 357 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/14ea27bae754bbbc1abaa2b79b2442d4dce2b1a866512e9db84f3ea97c4a7582.jpg", + "image_caption": [ + "(c) MIMO-Unet+ [4]", + "(g) NAFNet [3]" + ], + "image_footnote": [], + "bbox": [ + 483, + 229, + 679, + 357 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/1d1292b3236808f90eb204eca634bbcc27bc2ffaa959c82f6099f2b3067baac9.jpg", + "image_caption": [ + "(d) Restormer [30]", + "(h) Ours" + ], + "image_footnote": [], + "bbox": [ + 679, + 229, + 875, + 357 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/695231ac748724df3f75c6d098a1e4f849fe7c08739fb611ea8c4f97b3d579f0.jpg", + "table_caption": [ + "Table 1. Quantitative evaluations on the GoPro dataset [16]. The average runtime is tested on images with size of $256 \\times 256$ pixels." + ], + "table_footnote": [], + "table_body": "
MethodsPSNRsSSIMsParameters (M)Avg. runtime
DeblurGAN-v2 [12]29.550.934060.90.04s
SRN [22]30.260.93426.80.07s
DMPHN [32]31.200.945321.70.21s
SAPHN [21]31.850.948023.0-
MIMO-Unet+ [4]32.450.956716.10.02s
MPRNet [31]32.660.958920.10.09s
IPT [2]--1140.50s
DeepRFT+ [15]33.230.963223.00.09s
Restormer [30]32.920.961126.10.08s
Uformer-B [27]33.060.967050.90.07s
Stripformer [24]33.080.962419.70.04s
MPRNet-local [5]33.310.963720.10.11s
Restormer-local [5]33.570.965626.10.42s
NAFNet [3]33.710.966867.90.04s
Ours34.210.969216.60.13s
", + "bbox": [ + 80, + 438, + 468, + 623 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.2. Comparisons with the state of the arts", + "text_level": 1, + "bbox": [ + 76, + 625, + 403, + 638 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We compare our method with state-of-the-art ones and use the PSNR and SSIM to evaluate the quality of restored images.", + "bbox": [ + 75, + 641, + 468, + 685 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "**Evaluations on the GoPro dataset.** We first evaluate our method on the commonly used GoPro dataset by [16]. For fair comparisons, we follow the protocols of this dataset and retrain or fine-tune the deep learning methods that are not trained on this dataset. Table 1 shows the quantitative evaluation results. Our method generates the results with the highest PSNR and SSIM values. Compared to the state-of-the-art CNN-based methods, NAFNet [3], the PSNR gain of our method is at least 0.5dB higher than NAFNet, while the number of the proposed model parameters is a quarter of the NAFNet. In addition, compared to the Transformer-based methods [24,27,30], our method has fewer model parameters while the performance is better.", + "bbox": [ + 75, + 688, + 468, + 883 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "As the FFT implementation is not optimized well in Py-", + "bbox": [ + 96, + 885, + 470, + 900 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/38b4e5a0d88683de76036be4bbfca0ac06da72acb67004876e7e8de62aefa406.jpg", + "table_caption": [ + "Table 2. Quantitative evaluations on the RealBlur dataset [18] in terms of PSNR and SSIM." + ], + "table_footnote": [], + "table_body": "
MethodsRealblur-RRealblur-J
PSNRsSSIMsPSNRsSSIMs
DeblurGAN-v2 [12]36.440.934729.690.8703
SRN [22]38.650.965231.380.9091
MIMO-Unet+ [4]--31.920.9190
BANet [23]39.550.971032.000.9230
DeepRFT+ [15]39.840.972132.190.9305
Stripformer [24]39.840.973732.480.9290
Ours40.110.973232.620.9326
", + "bbox": [ + 503, + 436, + 885, + 561 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Torch, using FFTs in PyTorch needs more runtime. However, the runtime of our method is still competitive against state-of-art methods. Moreover, our method is at least $4 \\times$ faster than IPT [2] that is based on the original self-attention.", + "bbox": [ + 496, + 563, + 893, + 622 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Figure 3 shows visual comparisons of the proposed method and the evaluated ones on the GoPro dataset. As demonstrated by [30], the CNN-based methods [3,4] do not effectively explore non-local information for latent clear image restoration. Therefore, the deblurred results by the methods [3,4] still contain significant blur effect as shown in Figure 3(c) and (g). The Transformer-based methods [5,24,30] are able to model the global contexts for image deblurring. However, some main structures, e.g., characters and chairs, are not recovered well (see Figure 3(d)-(f)).", + "bbox": [ + 496, + 623, + 893, + 773 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In contrast to existing Transformer-based methods that are based on the spatial domain, we develop an efficient frequency domain-based Transformer, where the proposed DFFN is able to discriminately estimate useful frequency information for latent clear image restoration. Thus, the deblurred results contain clear structures, and the characters are much clearer as shown in Figure 3(h).", + "bbox": [ + 496, + 775, + 890, + 881 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Evaluations on the RealBlur dataset. We further evaluate", + "bbox": [ + 500, + 885, + 890, + 898 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "5890", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/e0abd2f730e1282a7e0486f884a0a893698007a4d89dbdb734c067cf8ec0665c.jpg", + "image_caption": [ + "(a) Blurred image" + ], + "image_footnote": [], + "bbox": [ + 91, + 88, + 285, + 272 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/dd5bf27376ba19fa35c1383a11bd1ba44edf85471c704aa6099460cf0bb6bb2b.jpg", + "image_caption": [ + "(b) GT" + ], + "image_footnote": [], + "bbox": [ + 287, + 88, + 482, + 271 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/a1dae926d2171004d12a0f0c5c9ade50d2917adbdfed5d672e75a0a63c810df1.jpg", + "image_caption": [ + "(c) DeblurGAN-v2 [11]" + ], + "image_footnote": [], + "bbox": [ + 483, + 89, + 679, + 271 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/e00f85579c3f7f53439a284eb0832faf229fa3ca6ab3b7558815493016231f8a.jpg", + "image_caption": [ + "(d) SRN [22]" + ], + "image_footnote": [], + "bbox": [ + 679, + 90, + 875, + 271 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/46704e1e9f5baa2d8d703d5da0bb64137af57bd43e47dd2304f9be37a4df5be5.jpg", + "image_caption": [ + "(e) MIMO-Unet+ [4]" + ], + "image_footnote": [], + "bbox": [ + 89, + 286, + 285, + 468 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/3a1b7a6aa4c21bbd1446ce81e2abc14f3c1b4706a740190894490bc3d2a2d1a1.jpg", + "image_caption": [ + "(f) DeepRFT+ [15]" + ], + "image_footnote": [], + "bbox": [ + 285, + 286, + 482, + 468 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/4649ab62271b77e781aae6109fc2ee51d04ff6209e858ec91b3f257af18db455.jpg", + "image_caption": [ + "(g) Stripformer [24]" + ], + "image_footnote": [], + "bbox": [ + 483, + 286, + 679, + 468 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/2a71d775ccaaf0e055fd221b6728860acac580a5c7a5f88a8999450d19c33ee8.jpg", + "image_caption": [ + "(h) Ours", + "Figure 4. Deblurred results on the RealBlur dataset [18]. The characters or the structural details in (c)-(g) are not recovered well. The proposed method generates an image with much clearer characters and structural details." + ], + "image_footnote": [], + "bbox": [ + 679, + 286, + 875, + 468 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/ee30f8e12ec9f99993992617875362c2f45b49af3be79ac3c69ba6748973f548.jpg", + "table_caption": [ + "Table 3. Quantitative evaluations on the Hide dataset [20]. We use the models trained on the GoPro dataset [16] for fair comparisons." + ], + "table_footnote": [], + "table_body": "
MethodsPSNRsSSIMsParameters (M)
DeblurGAN-v2 [12]26.610.875060.9
SRN [22]28.360.90406.8
DMPHN [32]29.090.924021.7
SAPHN [21]29.980.930023.0
MIMO-Unet+ [4]29.990.930416.1
MPRNet [31]30.960.939720.1
Stripformer [24]31.030.939519.7
MPRNet-local [5]31.190.941820.1
Restormer [30]31.220.942326.1
NAFNet [3]31.310.942767.9
Restormer-local [5]31.490.944726.1
Ours31.620.945516.6
", + "bbox": [ + 89, + 551, + 454, + 723 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "our method on the RealBlur dataset by [18] and follow the protocols of this dataset for fair comparisons. The test dataset of [18] includes a RealBlur-R test set from the raw images and RealBlur-J test set from the JPEG images. Table 2 summarizes the quantitative evaluation results on the above mentioned test sets. The proposed method generates the results with higher PSNR values.", + "bbox": [ + 75, + 726, + 467, + 830 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Figure 4 shows the visual comparisons on the RealBlur dataset, where our method generates the results with clearer characters and finer structural details (Figure 4(h)).", + "bbox": [ + 75, + 833, + 468, + 878 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Evaluations on the HIDe dataset. We then evaluate our", + "bbox": [ + 76, + 885, + 468, + 898 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "method on the Hide dataset [20], which mainly contains humans. Similar to state-of-the-art methods [4, 31], we directly use the models of the evaluated methods, which are trained on the GoPro dataset for test. Table 3 shows that the quality of the deblurred images generated by the proposed method is better than the evaluated methods, suggesting that our method has a better generalization ability as models are not trained on this dataset.", + "bbox": [ + 496, + 523, + 892, + 645 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We show some visual comparisons in Figure 5. We note that the evaluated methods do not recover the humans well. In contrast, our method generates better images. For example, the faces and zipper of clothes are much clearer.", + "bbox": [ + 496, + 646, + 893, + 705 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5. Analysis and Discussion", + "text_level": 1, + "bbox": [ + 500, + 710, + 723, + 728 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We have shown that exploring the properties of Transformers in the frequency domain generates favorable results against state-of-the-art methods. In this section, we provide deeper analysis on the proposed method and demonstrate the effect of the main components. For the ablation studies in this section, we train our method and all the baselines on the GoPro dataset using the batch size of 8 to illustrate the effect of each component in our method.", + "bbox": [ + 496, + 729, + 892, + 851 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Effect of FSAS. The proposed FSAS is used to reduce the computational cost. According to the properties of FFT, the space and time complexity of the FSAS are $O(N)$ and", + "bbox": [ + 496, + 854, + 893, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "5891", + "bbox": [ + 482, + 944, + 513, + 955 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/69f92d39d74e2fa5ebcfeccc2d6d8024a2b0fc9a7f669c80ddd25caf50b309e2.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 89, + 87, + 285, + 223 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/2d2f3ef00f2e4c7934488eb6c0c5e9c40ba94722102eba78dc10eba222b49410.jpg", + "image_caption": [ + "(b) GT" + ], + "image_footnote": [], + "bbox": [ + 287, + 88, + 482, + 223 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/57f04088f0d5a1ad44a2218966ecd02d0b494f2cab2d3f528c11940e7ffea69e.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 483, + 88, + 679, + 223 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/c6bb3b4f34da0ac2bb3ba97a8cc60e6f756f4f2eac4dca461b09440e3caedda2.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 679, + 88, + 875, + 223 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/9bfb7051f9c07e94ea29d8d4efb593652f80218c9b2e630de810de7063abf412.jpg", + "image_caption": [ + "(a) Blurred image", + "(e) Stripformer [24]", + "Figure 5. Deblurred results on the HID dataset [20]. The deblurred results in (c)-(g) still contain significant blur effects. The proposed method generates much clearer images." + ], + "image_footnote": [], + "bbox": [ + 89, + 237, + 287, + 372 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/4360d278caabde2650ed43c9ca06f646c04f55f005d0e0f999af9f47a8d3658c.jpg", + "image_caption": [ + "(f) NAFNet [3]" + ], + "image_footnote": [], + "bbox": [ + 287, + 237, + 482, + 372 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/545d76defbeaf7cb56668160fcd53369ea8a47bf2c05727e79e181a4c54fd5bc.jpg", + "image_caption": [ + "(c) MPRNet [31]", + "(g) Restormer-local [5]" + ], + "image_footnote": [], + "bbox": [ + 483, + 237, + 679, + 372 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/14290ec445988f0e46846cae611638da398fa4e4145a97e898281b042afddeeb.jpg", + "image_caption": [ + "(d) Restormer [30]", + "(h) Ours" + ], + "image_footnote": [], + "bbox": [ + 679, + 237, + 875, + 372 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/797e8e3e5bd914fbb31234fee3a645c9e38020ace7c39a3c68925088f9623645.jpg", + "table_caption": [ + "Table 4. Memory and running time comparisons of the Transformer based on our method and the window methods [14,27]. The size of the test image is $1280 \\times 720$ pixels. The test environment is based on a machine with an NVIDIA GeForce RTX 3090 GPU. \"GPU memory\" denotes the maximum GPU memory consumption that is computed by the \"torch.cuda.max_memory_allocated( )\" function." + ], + "table_footnote": [], + "table_body": "
Window sizeWindow-based method [27]Ours
Avg. runtimeGPU memoryAvg. runtimeGPU memory
8 × 853ms6.3G44ms6.5G
16 × 1656ms7.1G44ms6.2G
32 × 3289ms12.0G43ms6.0G
64 × 64-Out of memory42ms5.9G
1280 × 720-Out of memory42ms5.9G
", + "bbox": [ + 81, + 511, + 475, + 597 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "$O(NC\\log N)$ , which are much lower than $O(N^2)$ and $O(N^{2}C)$ in the original computation of the scaled dot-product attention, where $C$ is the number of features. We further examine the space and time complexity of the FSAS and the window-based strategy [14, 27] for Transformers. Although the tensors in the frequency domain contain real part and imaginary part, the memory consumption does not increase as we only store half parts of the tensors by FFT based on the conjugate symmetry of FFT in our implementations. Table 4 shows that using the proposed FSAS needs a small GPU memory and is much more efficient compared to the window-based strategy [27]. In addition, as the memory of the FSAS is independent of window size, the memory usage of the FSAS does not increase when the window size becomes larger.", + "bbox": [ + 75, + 609, + 468, + 837 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Moreover, as the proposed FSAS is performed in the frequency domain, one may wonder whether the scaled dot-product attention estimated in the spatial domain performs better or not. To answer this question, we compare the F-", + "bbox": [ + 75, + 839, + 470, + 901 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/cd90ef32c29999db296617e538dcad7d0a6e20b1096adb13ac7ebc579310ca87.jpg", + "table_caption": [ + "Table 5. Quantitative evaluations of each component in the proposed method on the GoPro dataset [16]." + ], + "table_footnote": [], + "table_body": "
FSASSwin attentionFFNDFFNPSNRs/SSIMs
w/ only FFN✘✘✓✘33.19/0.9626
w/ only DFFN✘✘✘✓33.55/0.9651
SA w/ SD✘✓✘✓33.46/0.9645
FSAS+FFN✓✘✓✘33.61/0.9654
FSAS+DFFN✓✘✘✓33.73/0.9663
", + "bbox": [ + 503, + 455, + 890, + 536 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "SAS with the baseline method that performs in the spatial domain (SA w/ SD for short). As the space complexity of the original scaled dot-product attention is $O(N^2)$ , it is not affordable to train \"SA w/ SD\" when using the same settings as the proposed FSAS. We use the Swin Transformer [14] for comparison as it is much more efficient. Table 5 shows the quantitative evaluation results on the GoPro dataset. The method that computes the scaled dot-product attention in the spatial domain does not generate good deblurred results, where its PSNR value is 0.27 lower (see comparisons of \"SA w/ SD\" and \"FSAS+DFFN\" in Table 5). The main reason is that although using the shifted window partitioning method reduces the computational cost, it does not fully explore the useful information across different windows. In contrast, the space complexity of the proposed FSAS is $O(N)$ and does not need the shifted window partitioning as an approximation, thus leading to better deblurred results. Figure 6(b) further shows that using the shifted window partitioning method as an approximation of scaled dot-product attention in the spatial domain does not remove blur effectively. In contrast, the proposed FSAS generates clearer images.", + "bbox": [ + 496, + 537, + 892, + 853 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Moreover, compared to the baseline method only using FFN (\"w/ only FFN\"), using the proposed FSAS in this baseline generates much better results, where the PSNR", + "bbox": [ + 496, + 854, + 892, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "5892", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/128744473ea93513c52c9e6aaca03d5db4eaed5dab1680adbcb53285d8cc145f.jpg", + "image_caption": [ + "(a) Blurred image" + ], + "image_footnote": [], + "bbox": [ + 83, + 88, + 207, + 165 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/3e3b5a814b68060738f41b8369376727d3b9954da72fc4bd54537963a2f858f9.jpg", + "image_caption": [ + "(b) Spatial domain" + ], + "image_footnote": [], + "bbox": [ + 209, + 88, + 331, + 165 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/a09b6e556183a636be7de6bc7ae3dac3c187d276d22570a8c0606e42796702be.jpg", + "image_caption": [ + "(c) Frequency domain" + ], + "image_footnote": [], + "bbox": [ + 334, + 88, + 457, + 165 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/0e5595647369251d3eafb9c3a0f474e71046c0dd0aa2f185ede665a5be135523.jpg", + "image_caption": [ + "Figure 6. Effectiveness of the scaled dot-product attention computation in the spatial and frequency domains. Computing the scaled dot-product attention using the FSAS in the frequency domain generates a clearer image.", + "(a) Blurred image" + ], + "image_footnote": [], + "bbox": [ + 81, + 243, + 207, + 337 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/fb580b54fa2a0c13ad823e6d133fb5efcd1a24cda044c0c651657a2d85ced954.jpg", + "image_caption": [ + "(b) Ours w/o FSAS" + ], + "image_footnote": [], + "bbox": [ + 209, + 247, + 331, + 337 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/8d9059818c7eb609503c6ae9fe30d1af6a1cbd6903897d1c50bd88b0d2b230e8.jpg", + "image_caption": [ + "(c) Ours" + ], + "image_footnote": [], + "bbox": [ + 334, + 247, + 457, + 337 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/cb6773d0a2ac0879dd7ecc3e4bde89d173391e410ef5283f4845a13d96c44d3e.jpg", + "image_caption": [ + "Figure 7. Effectiveness of the proposed FSAS on image deblurring. Using the proposed FSAS generates a clearer image.", + "(a) Blurred image", + "Figure 8. Effectiveness of the proposed DFFN on image deblurring. value is $0.42\\mathrm{dB}$ higher (see comparisons of \"w/ only FFN\" and \"FSAS+FFN\" in Table 5). The visual comparisons in Figure 7(b) and (c) further demonstrate that using the proposed FSAS facilitates the blur removal well, where the boundaries are recovered well as shown in Figure 7(c)." + ], + "image_footnote": [], + "bbox": [ + 81, + 385, + 205, + 501 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/3038c7f3e5e6817a02120af391b0c76ae080dc2586e5ab35e3143fa5d4ec4b7e.jpg", + "image_caption": [ + "(b) w/ only FFN" + ], + "image_footnote": [], + "bbox": [ + 209, + 385, + 331, + 501 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/4594999a5bdbad73cc23f5ec41413962eed7a6febcf2ca4c72a1bf92a16795fd.jpg", + "image_caption": [ + "(c) w/ only DFFN" + ], + "image_footnote": [], + "bbox": [ + 334, + 385, + 457, + 501 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Effect of DFFN. The proposed DFFN is used to discriminatively estimate useful frequency information for latent clear image restoration. To demonstrate its effectiveness on image deblurring, we compare the proposed method with two baselines. For the first baseline, we compare the proposed method only using the DFFN (w/ only DFFN for short) and the proposed method only using the original FFN (w/ only FFN for short). For the second baseline, we compare the proposed method with the one that replaces the DFFN with the original FFN in the proposed method (FSAS+FFN). The comparisons of \"w/ only DFFN\" and \"w/ only FFN\" in Table 5 show that using the proposed DFFN generates better results, where the PSNR value is 0.36dB higher.", + "bbox": [ + 75, + 613, + 470, + 809 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In addition, the comparisons of \"FSAS+FFN\" and \"F-SAS+DFFN\" in Table 5 show that using the proposed DFFN further improves the performance.", + "bbox": [ + 76, + 810, + 470, + 854 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Figure 8 shows the visualization results by these above mentioned baseline methods. Using the proposed DFFN generates better deblurred images, where the windows are", + "bbox": [ + 76, + 854, + 470, + 900 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/fef8694a71860c1ecd55aee943c7a5e22bbdc490bf0f0528b420b9e1793a3e40.jpg", + "table_caption": [ + "Table 6. Quantitative evaluations of the asymmetric encoder-decoder network on the GoPro dataset." + ], + "table_footnote": [], + "table_body": "
MethodsFSAS in enc&decFSAS in dec (Ours)
PSNRs33.5633.73
SSIMs0.96530.9663
", + "bbox": [ + 503, + 117, + 885, + 164 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/1effbcebb58a0780dc4cc518e38985e51e55680c0acdc5f20373cb17745fd224.jpg", + "image_caption": [ + "(a) Blurred image", + "Figure 9. Effectiveness of the asymmetric encoder-decoder network on image deblurring." + ], + "image_footnote": [], + "bbox": [ + 506, + 166, + 629, + 263 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/87ab1364ba958b607ef74e3c489883d6b1d9a0d10c4905d59a964995abdd20db.jpg", + "image_caption": [ + "(b) FSAS in enc&dec" + ], + "image_footnote": [], + "bbox": [ + 630, + 166, + 754, + 263 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/1c9088dff19043022d2757d857bbd51981a983459a909d06ef3bf7c9171e7ff1.jpg", + "image_caption": [ + "(c) FSAS in dec (Ours)" + ], + "image_footnote": [], + "bbox": [ + 756, + 166, + 880, + 263 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "recovered well shown in Figure 8(c).", + "bbox": [ + 500, + 310, + 743, + 325 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Effect of the asymmetric encoder-decoder network. As demonstrated in Section 3.3, the shallow features extracted by encoder module usually contain blur effects that affect the estimations of FSAS. We thus embed it into the decoder module, which leads to an asymmetric encoder-decoder network for better image deblurring. To examine the effect of this network design, we compare the network that puts the FSAS into both the encoder and decoder modules (\"FSAS in enc&dec\" in Table 6). Table 6 shows that using the FSAS in the decoder module generates better results, where the PSNR value is at least 0.17dB higher. The visual comparisons in Figure 9(b) and (c) further demonstrate that using the FSAS in the decoder module generates better clear images.", + "bbox": [ + 498, + 328, + 893, + 523 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "6. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 530, + 617, + 544 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Motivated by the convolution theorem, we have presented an effective and efficient method that explores the properties of Transformers for high-quality image deblurring. We have developed an efficient frequency domain-based self-attention solver (FSAS) to estimate the scaled dot-product attention by an element-wise product operation instead of the matrix multiplication in the spatial domain, where we show that the spatial complexity and the computational complexity are significantly reduced. We further propose a DFFN to discriminatively determine which low and high frequency information of the features should be preserved for latent clear image restoration. Moreover, we develop an asymmetrical network based on an encoder and decoder architecture, where the FSAS is only used in the decoder module for better image deblurring. By training our method in an end-to-end manner, we show that it performs favorably against the state-of-the-art approaches in terms of accuracy and efficiency.", + "bbox": [ + 496, + 549, + 893, + 806 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgements. This work has been partly supported by the National Key R&D Program of China (No. 2018AAA0102001), the National Natural Science Foundation of China (Nos. U22B2049, 62272233, 61922043, U19B2040), and the Fundamental Research Funds for the Central Universities (No. 30920041109).", + "bbox": [ + 496, + 809, + 893, + 898 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "5893", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 174, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Nicolas Carion, Francisco Massa, Gabriel Synnaeve, Nicolas Usunier, Alexander Kirillov, and Sergey Zagoruyko. End-to-end object detection with transformers. In ECCV, 2020. 2", + "[2] Hanting Chen, Yunhe Wang, Tianyu Guo, Chang Xu, Yiping Deng, Zhenhua Liu, Siwei Ma, Chunjing Xu, Chao Xu, and Wen Gao. Pre-trained image processing transformer. In CVPR, 2021. 2, 5", + "[3] Liangyu Chen, Xiaojie Chu, Xiangyu Zhang, and Jian Sun. Simple baselines for image restoration. 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In CVPR, 2021. 2", + "bbox": [ + 78, + 90, + 470, + 160 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "5895", + "bbox": [ + 482, + 945, + 514, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/Efficient Frequency Domain-Based Transformers for High-Quality Image Deblurring/c856a1da-867e-42ea-84a9-c14d1b12f290_model.json b/2023/Efficient Frequency Domain-Based Transformers for High-Quality Image Deblurring/c856a1da-867e-42ea-84a9-c14d1b12f290_model.json new file mode 100644 index 0000000000000000000000000000000000000000..d057b19f3fc30fb39bd013f84921b7f492528181 --- /dev/null +++ b/2023/Efficient Frequency Domain-Based Transformers for High-Quality Image Deblurring/c856a1da-867e-42ea-84a9-c14d1b12f290_model.json @@ -0,0 +1,2684 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.0, + 0.812, + 0.047 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.238, + 0.131, + 0.737, + 0.177 + ], + "angle": 0, + "content": "Efficient Frequency Domain-based Transformers for High-Quality Image Deblurring" + }, + { + "type": "text", + "bbox": [ + 0.111, + 0.203, + 0.859, + 0.259 + ], + "angle": 0, + "content": "Lingshun Kong\\(^{1}\\), Jiangxin Dong\\(^{1*}\\), Jianjun Ge\\(^{2}\\), Mingqiang Li\\(^{2}\\), and Jinshan Pan\\(^{1*}\\) \n\\(^{1}\\)School of Computer Science and Engineering, Nanjing University of Science and Technology \n\\(^{2}\\)Information Science Academy, China Electronics Technology Group Corporation" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.309, + 0.314, + 0.327 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.342, + 0.474, + 0.72 + ], + "angle": 0, + "content": "We present an effective and efficient method that explores the properties of Transformers in the frequency domain for high-quality image deblurring. Our method is motivated by the convolution theorem that the correlation or convolution of two signals in the spatial domain is equivalent to an element-wise product of them in the frequency domain. This inspires us to develop an efficient frequency domain-based self-attention solver (FSAS) to estimate the scaled dot-product attention by an element-wise product operation instead of the matrix multiplication in the spatial domain. In addition, we note that simply using the naive feed-forward network (FFN) in Transformers does not generate good deblurred results. To overcome this problem, we propose a simple yet effective discriminative frequency domain-based FFN (DFFN), where we introduce a gated mechanism in the FFN based on the Joint Photographic Experts Group (JPEG) compression algorithm to discriminatively determine which low- and high-frequency information of the features should be preserved for latent clear image restoration. We formulate the proposed FSAS and DFFN into an asymmetrical network based on an encoder and decoder architecture, where the FSAS is only used in the decoder module for better image deblurring. Experimental results show that the proposed method performs favorably against the state-of-the-art approaches." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.732, + 0.21, + 0.748 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.754, + 0.47, + 0.815 + ], + "angle": 0, + "content": "Image deblurring aims to restore high-quality images from blurred ones. This problem has achieved significant progress due to the development of various effective deep models with large-scale training datasets." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.815, + 0.473, + 0.877 + ], + "angle": 0, + "content": "Most state-of-the-art methods for image deblurring are mainly based on deep convolutional neural networks (CNNs). The main success of these methods is due to developing kinds of network architectural designs, for example, the multi-" + }, + { + "type": "image", + "bbox": [ + 0.499, + 0.307, + 0.897, + 0.504 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.508, + 0.895, + 0.564 + ], + "angle": 0, + "content": "Figure 1. Comparisons of the proposed method and state-of-the-art ones on the GoPro dataset [16] in terms of accuracy, floating point operations (FLOPs), and network parameters. The circle size indicates the number of the network parameter." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.567, + 0.896, + 0.717 + ], + "angle": 0, + "content": "scale [4, 16, 22] or multi-stage [31, 32] network architectures, generative adversarial learning [11, 12], physics model inspired network structures [6-8, 17, 33], and so on. As the basic operation in these networks, the convolution operation is a spatially-invariant local operation, which does not model the spatially variant properties of the image contents. Most of them use larger and deeper models to remedy the limitation of the convolution. However, simply increasing the capacity of deep models does not always lead to better performance as shown in [17, 33]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.897, + 0.902 + ], + "angle": 0, + "content": "Different from the convolution operation that models the local connectivity, Transformers are able to model the global contexts by computing the correlations of one token to all other tokens. They have been shown to be an effective approach in lots of high-level vision tasks and also have great potential to be the alternatives of deep CNN models. In image deblurring, the methods based on Transformers [27, 30] also achieve better performance than the CNN-based methods. However, the computation of the scaled dot-product attention in Transformers leads to quadratic space and time complexity in terms of the number of tokens. Although using smaller and fewer tokens can reduce the space and" + }, + { + "type": "page_footnote", + "bbox": [ + 0.094, + 0.887, + 0.395, + 0.901 + ], + "angle": 0, + "content": "*Corresponding author: Jiangxin Dong and Jinshan Pan." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.517, + 0.957 + ], + "angle": 0, + "content": "5886" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.152 + ], + "angle": 0, + "content": "time complexity, such strategy cannot model the long-range information of features well and usually leads to significant artifacts when handling high-resolution images, which thus limits the performance improvement." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.155, + 0.471, + 0.29 + ], + "angle": 0, + "content": "To alleviate this problem, most approaches use the down-sampling strategy to reduce the spatial resolution of features [26]. However, reducing the spatial resolution of features will cause information loss and thus affect the image deblurring. Several methods reduce the computational cost by computing the scaled dot-product attention in terms of the number of features [29, 30]. Although the computational cost is reduced, the spatial information is well not explored, which may affect the deblurring performance." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.292, + 0.471, + 0.534 + ], + "angle": 0, + "content": "In this paper, we develop an effective and efficient method that explores the properties of Transformers for high-quality image deblurring. We note that the scaled dot-product attention computation is actually to estimate the correlation of one token from the query and all the tokens from the key. This process can be achieved by a convolution operation when rearranging the permutations of tokens. Based on this observation and the convolution theorem that the convolution in the spatial domain equals a point-wise multiplication in the frequency domain, we develop an efficient frequency domain-based self-attention solver (FSAS) to estimate the scaled dot-product attention by an element-wise product operation instead of the matrix multiplication. Therefore, the space and time complexity can be reduced to \\( O(N) \\) \\( O(N\\log N) \\) for each feature channel, where \\( N \\) is the number of the pixels." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.537, + 0.47, + 0.687 + ], + "angle": 0, + "content": "In addition, we note that simply using the feed-forward network (FFN) by [30] does not generate good deblurred results. To generate better features for latent clear image restoration, we develop a simple yet effective discriminative frequency domain-based FFN (DFFN). Our DFFN is motivated by the Joint Photographic Experts Group (JPEG) compression algorithm. It introduces a gated mechanism in the FFN to discriminatively determine which low- and high-frequency information should be preserved for latent clear image restoration." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.689, + 0.471, + 0.901 + ], + "angle": 0, + "content": "We formulate the proposed FSAS and DFFN into an end-to-end trainable network based on an encoder and decoder architecture to solve image deblurring. However, we find that as features of shallow layers usually contain blur effects, applying the scaled dot-product attention to shallow features does not effectively explore global clear contents. As the features from deep layers are usually clearer than those from shallow layers, we develop an asymmetric network architecture, where the FSAS is only used in the decoder module for better image deblurring. We analyze that the exploring properties of Transformers in the frequency domain is able to facilitate blur removal. Experimental results demonstrate that the proposed method generates favorable results against state-of-the-art methods in terms of accuracy and efficiency" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.092, + 0.575, + 0.107 + ], + "angle": 0, + "content": "(Figure 1)." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.108, + 0.858, + 0.121 + ], + "angle": 0, + "content": "The main contributions are summarized as follows:" + }, + { + "type": "text", + "bbox": [ + 0.517, + 0.122, + 0.894, + 0.197 + ], + "angle": 0, + "content": "- We develop an efficient frequency domain-based self-attention solver to estimate the scaled dot-product attention. Our analysis demonstrates that using the frequency domain-based solver reduces the space and time complexity and is much more effective and efficient." + }, + { + "type": "text", + "bbox": [ + 0.517, + 0.198, + 0.894, + 0.272 + ], + "angle": 0, + "content": "- We propose a simple yet effective discriminative frequency domain-based FFN based on the JPEG compression algorithm to discriminatively determine which low and high-frequency information should be preserved for latent clear image restoration." + }, + { + "type": "text", + "bbox": [ + 0.517, + 0.273, + 0.894, + 0.332 + ], + "angle": 0, + "content": "- We develop an asymmetric network architecture based on an encoder and decoder network, where the frequency domain-based self-attention solver is only used in the decoder module for better image deblurring." + }, + { + "type": "text", + "bbox": [ + 0.517, + 0.334, + 0.894, + 0.393 + ], + "angle": 0, + "content": "- We analyze that the exploring properties of Transformers in the frequency domain is able to facilitate blur removal and show that our approach performs favorably against state-of-the-art methods." + }, + { + "type": "list", + "bbox": [ + 0.517, + 0.108, + 0.894, + 0.393 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.399, + 0.642, + 0.414 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.42, + 0.894, + 0.57 + ], + "angle": 0, + "content": "Deep CNN-based Image deblurring methods. In recent years, we have witnessed significant advances in image deblurring due to the development of different deep CNN models [3, 4, 9, 16, 22, 31, 32]. In [16], Nah et al. propose a deep CNN based on a multi-scale framework to directly estimate clear images from blurred ones. To better utilize the information of each scale in multi-scale framework, Tao et al. [22] develop an effective scale recurrent network. Gao et al. [9] propose a selective network parameter sharing method to improve [16, 22]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.571, + 0.894, + 0.766 + ], + "angle": 0, + "content": "As using more scales does not improve the performance significantly, Zhang et al. [32] develop an effective network based on multi-patch strategy. The deblurring process is achieved stage by stage. To better explore the features from different stages, Zamir et al. [31] propose a cross-stage feature fusion for better performance. In order to reduce the computational cost of the methods based on multi-scale framework, Cho et al. [4] present a multi-input and multi-output network. Chen et al. [3] analyze the baseline modules and simplify them for better image restoration. As demonstrated in [30], the convolution operation is spatial invariant and does not effectively model the global contexts for image deblurring." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.894, + 0.901 + ], + "angle": 0, + "content": "Transformers and their applications to image deblurring. As the Transformer [25] can model the global contexts and achieves significant progress in lots of high-level vision tasks (e.g., image classification [14], object detection [1, 34] and semantic segmentation [28, 35]), it has been developed to solve image super-resolution [13], image deblurring [24, 30] and image denoise [2, 27]. To reduce the computational cost of Transformer, Zamir et al. [30] propose an efficient Transformer model by computing the scaled dot-product attention" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "5887" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.302 + ], + "angle": 0, + "content": "in the feature depth domain. This method can effectively explore information from different features along the channel dimension. However, the spatial information that is vital for image restoration is not fully explored. Tsai et al. [24] simplify the calculation of self-attention by constructing intra and inter strip tokens to replace the global attention. Wang et al. [27] propose a Transformer based on a UNet which uses non-overlapping window-based self-attention for single image deblurring. Although using the splitting strategy reduces the computational cost, the coarse splitting does not fully explore the information of each patch. Moreover, the scaled dot-product attention in these methods usually needs the complex matrix multiplication whose the space and time complexity is quadratic." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.303, + 0.47, + 0.364 + ], + "angle": 0, + "content": "Different from these methods, we develop an efficient Transformer-based method that explores the property of the frequency domain to avoid the complex matrix multiplication for the scaled dot-product attention." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.371, + 0.251, + 0.387 + ], + "angle": 0, + "content": "3. Proposed Method" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.393, + 0.473, + 0.62 + ], + "angle": 0, + "content": "Our goal is to present an effective and efficient method to explore the properties of Transformers for high-quality image deblurring. To this end, we first develop an efficient frequency domain-based self-attention solver to estimate the scaled dot-product attention. To refine the features estimated by the frequency domain-based solver, we further develop a discriminative frequency domain-based feed-forward network. We formulate these above approaches into an end-to-end trainable network based on an encoder and decoder architecture to solve image deblurring, where the frequency domain-based self-attention solver for the estimation of the scaled dot-product attention is used in the decoder module for better feature representation. Figure 2(a) shows the overview of the proposed method. In the following, we present the details of each component." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.627, + 0.465, + 0.643 + ], + "angle": 0, + "content": "3.1. Frequency domain-based self-attention solver" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.646, + 0.473, + 0.782 + ], + "angle": 0, + "content": "Given the input feature \\(X\\) with a spatial resolution of \\(H\\times W\\) pixels and \\(C\\) channels, existing vision Transformers usually first compute the features \\(F_{q},F_{k}\\) ,and \\(F_{v}\\) by applying linear transformations \\(W_{q}\\) \\(W_{k}\\) ,and \\(W_{v}\\) to \\(X\\) . Then, they apply the unfolding function to the features \\(F_{q},F_{k}\\) ,and \\(F_{v}\\) to extract image patches \\(\\{q_i\\}_{i = 1}^N,\\{k_i\\}_{i = 1}^N\\) ,and \\(\\{v_i\\}_{i = 1}^N\\) ,where \\(N\\) denotes the number of extracted patches. By applying a reshape operation to the extracted patches, the query Q, key K, and value V can be obtained by:" + }, + { + "type": "equation", + "bbox": [ + 0.084, + 0.793, + 0.469, + 0.825 + ], + "angle": 0, + "content": "\\[\n\\mathbf {Q} = \\mathcal {R} \\left(\\left\\{q _ {i} \\right\\} _ {i = 1} ^ {N}\\right), \\mathbf {K} = \\mathcal {R} \\left(\\left\\{k _ {i} \\right\\} _ {i = 1} ^ {N}\\right), \\mathbf {V} = \\mathcal {R} \\left(\\left\\{v _ {i} \\right\\} _ {i = 1} ^ {N}\\right), \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.826, + 0.47, + 0.902 + ], + "angle": 0, + "content": "where \\(\\mathcal{R}\\) denotes the reshape function which ensures that \\(\\{\\mathbf{K},\\mathbf{Q},\\mathbf{V}\\} \\in R^{N\\times (CH_pW_p)}\\), \\(H_{p}\\) and \\(W_{p}\\) denote the height and width of extracted patches. Based on the obtained query \\(\\mathbf{Q}\\), key \\(\\mathbf{K}\\), and value \\(\\mathbf{V}\\), the scaled dot-product attention is achieved by:" + }, + { + "type": "equation", + "bbox": [ + 0.579, + 0.089, + 0.892, + 0.129 + ], + "angle": 0, + "content": "\\[\nV _ {a t t} = \\operatorname {s o f t m a x} \\left(\\frac {\\mathbf {Q K} ^ {\\top}}{\\sqrt {C H _ {p} W _ {p}}}\\right) V. \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.134, + 0.895, + 0.269 + ], + "angle": 0, + "content": "The attention map computation involves the matrix multiplication of \\(\\mathbf{Q}\\mathbf{K}^{\\top}\\) whose space complexity and time complexity are \\(O(N^{2})\\) and \\(O(N^{2}C)\\). It is not affordable if the image resolution and the number of the extracted patches are large. Although using downsampling operation to reduce the image resolution or non-overlapping method to extract fewer patches will alleviate the problem, these strategies would lead to information loss and limit the ability to model details within and across each patch [29]." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.269, + 0.892, + 0.3 + ], + "angle": 0, + "content": "We note that each element of \\(\\mathbf{Q}\\mathbf{K}^{\\top}\\) is obtained by the inner product:" + }, + { + "type": "equation", + "bbox": [ + 0.62, + 0.306, + 0.892, + 0.334 + ], + "angle": 0, + "content": "\\[\n\\left(\\mathbf {Q} \\mathbf {K} ^ {\\top}\\right) _ {i j} = \\langle \\mathbf {q} _ {i}, \\mathbf {k} _ {j} \\rangle , \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.338, + 0.894, + 0.431 + ], + "angle": 0, + "content": "where \\(\\mathbf{q}_i\\) and \\(\\mathbf{k}_j\\) are the vectorized forms of \\(i\\)-th and \\(j\\)-th patches from \\(F_{q}\\) and \\(F_{k}\\). Based on (3), if we apply reshape functions to \\(\\mathbf{q}_i\\) and all the patches \\(\\mathbf{k}_j\\), respectively, all the \\(i\\)-th column elements of \\(\\mathbf{QK}^{\\top}\\) can be obtained by a convolution operation, i.e., \\(\\widetilde{q}_i \\otimes \\widetilde{K}\\), where \\(\\widetilde{q}_i\\) and \\(\\widetilde{K}\\) denote the reshaped results of \\(\\mathbf{q}_i\\) and \\(\\mathbf{k}_j\\); \\(\\otimes\\) denotes the convolution operation." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.431, + 0.895, + 0.536 + ], + "angle": 0, + "content": "According to the convolution theorem, the correlation or convolution of two signals in the spatial domain is equivalent to an element-wise product of them in the frequency domain. Therefore, a natural question is that can we efficiently estimate the attention map by an element-wise product operation in a frequency domain instead of computing the matrix multiplication of \\(\\mathbf{Q}\\mathbf{K}^{\\top}\\) in the spatial domain?" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.537, + 0.895, + 0.627 + ], + "angle": 0, + "content": "To this end, we develop an effective frequency domain-based self-attention solver. Specifically, we first obtain \\( F_{q} \\), \\( F_{k} \\), and \\( F_{v} \\) by a \\( 1 \\times 1 \\) point-wise convolution and \\( 3 \\times 3 \\) depth-wise convolution. Then, we apply the fast Fourier transform (FFT) to the estimated features \\( F_{q} \\) and \\( F_{k} \\) and estimate the correlation of \\( F_{q} \\) and \\( F_{k} \\) in the frequency domain by:" + }, + { + "type": "equation", + "bbox": [ + 0.601, + 0.634, + 0.892, + 0.659 + ], + "angle": 0, + "content": "\\[\nA = \\mathcal {F} ^ {- 1} \\left(\\mathcal {F} \\left(F _ {q}\\right) \\overline {{\\mathcal {F} \\left(F _ {k}\\right)}}\\right), \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.665, + 0.894, + 0.711 + ], + "angle": 0, + "content": "where \\(\\mathcal{F}(\\cdot)\\) denotes the FFT, \\(\\mathcal{F}^{-1}(\\cdot)\\) denotes the inverse FFT, and \\(\\overline{\\mathcal{F}(\\cdot)}\\) denotes the conjugate transpose operation. Finally, we estimate the aggregated feature by:" + }, + { + "type": "equation", + "bbox": [ + 0.637, + 0.718, + 0.891, + 0.734 + ], + "angle": 0, + "content": "\\[\nV _ {a t t} = \\mathcal {L} (A) F _ {v}, \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.74, + 0.892, + 0.771 + ], + "angle": 0, + "content": "where a layer norm \\(\\mathcal{L}(\\cdot)\\) is used to normalize \\(A\\). Finally, we generate the output feature of FSAS by:" + }, + { + "type": "equation", + "bbox": [ + 0.597, + 0.778, + 0.891, + 0.794 + ], + "angle": 0, + "content": "\\[\nX _ {a t t} = X + \\operatorname {C o n v} _ {1 \\times 1} \\left(V _ {a t t}\\right), \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.8, + 0.894, + 0.846 + ], + "angle": 0, + "content": "where \\(\\mathrm{Conv}_{1\\times 1}(\\cdot)\\) denotes a convolution with filter size of \\(1\\times 1\\) pixel. The detailed network architecture of the proposed FSAS is shown in Figure 2(b)." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.851, + 0.882, + 0.867 + ], + "angle": 0, + "content": "3.2. Discriminative frequency domain-based FFN" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.871, + 0.892, + 0.901 + ], + "angle": 0, + "content": "The FFN is used to improve the features by the scaled dot-product attention. Thus, it is important to develop an" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.956 + ], + "angle": 0, + "content": "5888" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.102, + 0.089, + 0.46, + 0.315 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.465, + 0.088, + 0.637, + 0.315 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.641, + 0.089, + 0.867, + 0.315 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.315, + 0.892, + 0.343 + ], + "angle": 0, + "content": "Figure 2. Network architectures. (a) The proposed asymmetric encoder-decoder network that only contains DFFN in the encoder module and both FSAS and DFFN in the decoder module for image deblurring. (b) The proposed FSAS module. (c) The proposed DFFN module." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.348, + 0.474, + 0.514 + ], + "angle": 0, + "content": "effective FFN to generate the features that facilitate the latent clear image reconstruction. As not all the low-frequency information and high-frequency information help latent clear image restoration, we develop a DFFN that can adaptively determine which frequency information should be preserved. However, how to effectively determine which frequency information is important. Motivated by the JPEG compression algorithm, we introduce a learnable quantization matrix \\(\\mathbf{W}\\) and learn it by an inverse method of JPEG compression to determine which frequency information should be preserved. The proposed DFFN can be formulated by:" + }, + { + "type": "equation", + "bbox": [ + 0.168, + 0.517, + 0.346, + 0.534 + ], + "angle": 0, + "content": "\\[\nX _ {1} = \\operatorname {C o n v} _ {1 \\times 1} (\\mathcal {L} (X _ {\\text {a t t}}))\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.17, + 0.537, + 0.469, + 0.564 + ], + "angle": 0, + "content": "\\[\nX _ {1} ^ {f} = \\mathcal {F} \\left(\\mathcal {P} \\left(X _ {1}\\right)\\right) \\tag {7}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.17, + 0.559, + 0.303, + 0.578 + ], + "angle": 0, + "content": "\\[\nX _ {2} = \\mathcal {F} ^ {- 1} \\left(\\mathbf {W} X _ {1} ^ {f}\\right)\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.17, + 0.58, + 0.376, + 0.599 + ], + "angle": 0, + "content": "\\[\nX _ {o u t} = \\mathcal {G} \\left(\\mathcal {P} ^ {- 1} \\left(X _ {2}\\right)\\right) + X _ {a t t},\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.609, + 0.47, + 0.67 + ], + "angle": 0, + "content": "where \\(\\mathcal{P}(\\cdot)\\) and \\(\\mathcal{P}^{-1}(\\cdot)\\) denote the patch unfolding and folding operations in the JPEG compression method; \\(\\mathcal{G}\\) denotes GEGLU function by [19]. The detailed network architecture of the proposed DFFN is shown in Figure 2(c)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.672, + 0.407, + 0.687 + ], + "angle": 0, + "content": "3.3. Asymmetric encoder-decoder network" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.689, + 0.471, + 0.901 + ], + "angle": 0, + "content": "We embed the proposed FSAS and DFFN into a network based on an encoder and decoder architecture. We note that most existing methods usually use symmetric architectures in the encoder and decoder modules. For example, if the FSAS and DFFN are used in the encoder module, they are also used in the decoder module. We note that the features extracted by encoder module are shallow ones, which usually contain blur effects compared to the deep features from the decoder module. However, the blur usually changes similarity of two similar patches from clear features. Thus, using the FSAS in the encoder module may not estimate the similarity correctly, which accordingly affects image restoration. To overcome this problem, we embed the FSAS into the decoder module, which leads to an asymmetric architecture for better image" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.348, + 0.893, + 0.378 + ], + "angle": 0, + "content": "deblurring. Figure 2(a) shows the network architecture of the proposed asymmetric encoder-decoder network." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.379, + 0.892, + 0.409 + ], + "angle": 0, + "content": "Finally, given a blurred image \\( B \\), the restored image \\( I \\) is estimated by the asymmetric encoder-decoder network:" + }, + { + "type": "equation", + "bbox": [ + 0.639, + 0.415, + 0.892, + 0.432 + ], + "angle": 0, + "content": "\\[\nI = \\mathcal {N} (B) + B, \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.442, + 0.894, + 0.457 + ], + "angle": 0, + "content": "where \\(\\mathcal{N}\\) denotes the asymmetric encoder-decoder network." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.467, + 0.706, + 0.483 + ], + "angle": 0, + "content": "4. Experimental Results" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.486, + 0.892, + 0.516 + ], + "angle": 0, + "content": "In this section, we evaluate our method and compare it with state-of-the-art ones using public benchmark datasets." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.521, + 0.783, + 0.537 + ], + "angle": 0, + "content": "4.1. Datasets and parameter settings" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.538, + 0.892, + 0.599 + ], + "angle": 0, + "content": "Datasets. We evaluate our method on commonly used image deblurring datasets including the GoPro dataset [16], the HIDe dataset [20], and the RealBlur dataset [18]. We follow the protocols of existing methods for fair comparisons." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.605, + 0.895, + 0.906 + ], + "angle": 0, + "content": "Parameter settings. We use the same loss function as [4] to constrain the network and train it using the Adam [10] optimizer with default parameters. The initial value of the learning rate is \\( 10^{-3} \\) and is updated with the cosine annealing strategy after 600,000 iterations. The minimum value of the learning rate is \\( 10^{-7} \\). The patch size is empirically set to be \\( 256 \\times 256 \\) pixels and the batch size is set to be 16. We adopt the same data augmentation method as [30] during the training. The patch size for the quantization matrix estimation is empirically set to be \\( 8 \\times 8 \\) based on the JPEG compression method. In the implementation, the tensor form of the quantization matrix is set as [batch_size, channel_num, 8, 8], where batch_size and channel_num are the number of batches and features. The quantization matrix is jointly learned with other parameters by solving loss functions during the training. Similarity, we also use the patch size of \\( 8 \\times 8 \\) pixels when computing the self-attention (4). Due to the page limit, we include more experimental results in the supplemental material. The training code and models are available at https://github.com/kkkls/FFTformer." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "5889" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.092, + 0.089, + 0.287, + 0.216 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.132, + 0.219, + 0.227, + 0.23 + ], + "angle": 0, + "content": "(a) Blurred image" + }, + { + "type": "image", + "bbox": [ + 0.289, + 0.089, + 0.483, + 0.216 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.367, + 0.219, + 0.405, + 0.23 + ], + "angle": 0, + "content": "(b) GT" + }, + { + "type": "image", + "bbox": [ + 0.484, + 0.089, + 0.68, + 0.216 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.524, + 0.219, + 0.636, + 0.23 + ], + "angle": 0, + "content": "(c) MIMO-Unet+ [4]" + }, + { + "type": "image", + "bbox": [ + 0.68, + 0.089, + 0.876, + 0.216 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.726, + 0.219, + 0.826, + 0.23 + ], + "angle": 0, + "content": "(d) Restormer [30]" + }, + { + "type": "image", + "bbox": [ + 0.091, + 0.231, + 0.288, + 0.358 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.128, + 0.36, + 0.234, + 0.372 + ], + "angle": 0, + "content": "(e) Stripformer [24]" + }, + { + "type": "image", + "bbox": [ + 0.289, + 0.231, + 0.483, + 0.358 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.326, + 0.36, + 0.446, + 0.372 + ], + "angle": 0, + "content": "(f) Restormer-local [5]" + }, + { + "type": "image", + "bbox": [ + 0.484, + 0.231, + 0.68, + 0.358 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.54, + 0.36, + 0.624, + 0.372 + ], + "angle": 0, + "content": "(g) NAFNet [3]" + }, + { + "type": "image", + "bbox": [ + 0.681, + 0.231, + 0.876, + 0.358 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.755, + 0.36, + 0.801, + 0.371 + ], + "angle": 0, + "content": "(h) Ours" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.377, + 0.891, + 0.404 + ], + "angle": 0, + "content": "Figure 3. Deblurred results on the GoPro dataset [16]. The deblurred results in (c)-(g) still contain significant blur effects. The proposed method generates a clearer image. For example, the characters and boundaries are much clearer." + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.409, + 0.468, + 0.437 + ], + "angle": 0, + "content": "Table 1. Quantitative evaluations on the GoPro dataset [16]. The average runtime is tested on images with size of \\(256 \\times 256\\) pixels." + }, + { + "type": "table", + "bbox": [ + 0.081, + 0.439, + 0.469, + 0.624 + ], + "angle": 0, + "content": "
MethodsPSNRsSSIMsParameters (M)Avg. runtime
DeblurGAN-v2 [12]29.550.934060.90.04s
SRN [22]30.260.93426.80.07s
DMPHN [32]31.200.945321.70.21s
SAPHN [21]31.850.948023.0-
MIMO-Unet+ [4]32.450.956716.10.02s
MPRNet [31]32.660.958920.10.09s
IPT [2]--1140.50s
DeepRFT+ [15]33.230.963223.00.09s
Restormer [30]32.920.961126.10.08s
Uformer-B [27]33.060.967050.90.07s
Stripformer [24]33.080.962419.70.04s
MPRNet-local [5]33.310.963720.10.11s
Restormer-local [5]33.570.965626.10.42s
NAFNet [3]33.710.966867.90.04s
Ours34.210.969216.60.13s
" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.625, + 0.405, + 0.64 + ], + "angle": 0, + "content": "4.2. Comparisons with the state of the arts" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.642, + 0.47, + 0.686 + ], + "angle": 0, + "content": "We compare our method with state-of-the-art ones and use the PSNR and SSIM to evaluate the quality of restored images." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.689, + 0.47, + 0.884 + ], + "angle": 0, + "content": "**Evaluations on the GoPro dataset.** We first evaluate our method on the commonly used GoPro dataset by [16]. For fair comparisons, we follow the protocols of this dataset and retrain or fine-tune the deep learning methods that are not trained on this dataset. Table 1 shows the quantitative evaluation results. Our method generates the results with the highest PSNR and SSIM values. Compared to the state-of-the-art CNN-based methods, NAFNet [3], the PSNR gain of our method is at least 0.5dB higher than NAFNet, while the number of the proposed model parameters is a quarter of the NAFNet. In addition, compared to the Transformer-based methods [24,27,30], our method has fewer model parameters while the performance is better." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.886, + 0.471, + 0.901 + ], + "angle": 0, + "content": "As the FFT implementation is not optimized well in Py-" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.409, + 0.892, + 0.435 + ], + "angle": 0, + "content": "Table 2. Quantitative evaluations on the RealBlur dataset [18] in terms of PSNR and SSIM." + }, + { + "type": "table", + "bbox": [ + 0.504, + 0.438, + 0.887, + 0.562 + ], + "angle": 0, + "content": "
MethodsRealblur-RRealblur-J
PSNRsSSIMsPSNRsSSIMs
DeblurGAN-v2 [12]36.440.934729.690.8703
SRN [22]38.650.965231.380.9091
MIMO-Unet+ [4]--31.920.9190
BANet [23]39.550.971032.000.9230
DeepRFT+ [15]39.840.972132.190.9305
Stripformer [24]39.840.973732.480.9290
Ours40.110.973232.620.9326
" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.564, + 0.894, + 0.623 + ], + "angle": 0, + "content": "Torch, using FFTs in PyTorch needs more runtime. However, the runtime of our method is still competitive against state-of-art methods. Moreover, our method is at least \\(4 \\times\\) faster than IPT [2] that is based on the original self-attention." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.624, + 0.895, + 0.775 + ], + "angle": 0, + "content": "Figure 3 shows visual comparisons of the proposed method and the evaluated ones on the GoPro dataset. As demonstrated by [30], the CNN-based methods [3,4] do not effectively explore non-local information for latent clear image restoration. Therefore, the deblurred results by the methods [3,4] still contain significant blur effect as shown in Figure 3(c) and (g). The Transformer-based methods [5,24,30] are able to model the global contexts for image deblurring. However, some main structures, e.g., characters and chairs, are not recovered well (see Figure 3(d)-(f))." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.776, + 0.892, + 0.882 + ], + "angle": 0, + "content": "In contrast to existing Transformer-based methods that are based on the spatial domain, we develop an efficient frequency domain-based Transformer, where the proposed DFFN is able to discriminately estimate useful frequency information for latent clear image restoration. Thus, the deblurred results contain clear structures, and the characters are much clearer as shown in Figure 3(h)." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.886, + 0.891, + 0.9 + ], + "angle": 0, + "content": "Evaluations on the RealBlur dataset. We further evaluate" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "5890" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.092, + 0.089, + 0.287, + 0.273 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.133, + 0.275, + 0.229, + 0.286 + ], + "angle": 0, + "content": "(a) Blurred image" + }, + { + "type": "image", + "bbox": [ + 0.289, + 0.089, + 0.483, + 0.272 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.367, + 0.275, + 0.405, + 0.285 + ], + "angle": 0, + "content": "(b) GT" + }, + { + "type": "image", + "bbox": [ + 0.484, + 0.09, + 0.68, + 0.272 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.518, + 0.275, + 0.645, + 0.286 + ], + "angle": 0, + "content": "(c) DeblurGAN-v2 [11]" + }, + { + "type": "image", + "bbox": [ + 0.68, + 0.091, + 0.876, + 0.272 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.743, + 0.275, + 0.813, + 0.286 + ], + "angle": 0, + "content": "(d) SRN [22]" + }, + { + "type": "image", + "bbox": [ + 0.091, + 0.287, + 0.287, + 0.469 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.125, + 0.471, + 0.236, + 0.483 + ], + "angle": 0, + "content": "(e) MIMO-Unet+ [4]" + }, + { + "type": "image", + "bbox": [ + 0.287, + 0.287, + 0.483, + 0.469 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.335, + 0.471, + 0.437, + 0.484 + ], + "angle": 0, + "content": "(f) DeepRFT+ [15]" + }, + { + "type": "image", + "bbox": [ + 0.484, + 0.287, + 0.68, + 0.469 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.529, + 0.471, + 0.636, + 0.484 + ], + "angle": 0, + "content": "(g) Stripformer [24]" + }, + { + "type": "image", + "bbox": [ + 0.68, + 0.287, + 0.876, + 0.469 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.756, + 0.471, + 0.801, + 0.482 + ], + "angle": 0, + "content": "(h) Ours" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.489, + 0.891, + 0.517 + ], + "angle": 0, + "content": "Figure 4. Deblurred results on the RealBlur dataset [18]. The characters or the structural details in (c)-(g) are not recovered well. The proposed method generates an image with much clearer characters and structural details." + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.524, + 0.468, + 0.551 + ], + "angle": 0, + "content": "Table 3. Quantitative evaluations on the Hide dataset [20]. We use the models trained on the GoPro dataset [16] for fair comparisons." + }, + { + "type": "table", + "bbox": [ + 0.09, + 0.553, + 0.455, + 0.724 + ], + "angle": 0, + "content": "
MethodsPSNRsSSIMsParameters (M)
DeblurGAN-v2 [12]26.610.875060.9
SRN [22]28.360.90406.8
DMPHN [32]29.090.924021.7
SAPHN [21]29.980.930023.0
MIMO-Unet+ [4]29.990.930416.1
MPRNet [31]30.960.939720.1
Stripformer [24]31.030.939519.7
MPRNet-local [5]31.190.941820.1
Restormer [30]31.220.942326.1
NAFNet [3]31.310.942767.9
Restormer-local [5]31.490.944726.1
Ours31.620.945516.6
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.727, + 0.468, + 0.832 + ], + "angle": 0, + "content": "our method on the RealBlur dataset by [18] and follow the protocols of this dataset for fair comparisons. The test dataset of [18] includes a RealBlur-R test set from the raw images and RealBlur-J test set from the JPEG images. Table 2 summarizes the quantitative evaluation results on the above mentioned test sets. The proposed method generates the results with higher PSNR values." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.834, + 0.469, + 0.879 + ], + "angle": 0, + "content": "Figure 4 shows the visual comparisons on the RealBlur dataset, where our method generates the results with clearer characters and finer structural details (Figure 4(h))." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.886, + 0.469, + 0.9 + ], + "angle": 0, + "content": "Evaluations on the HIDe dataset. We then evaluate our" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.525, + 0.893, + 0.646 + ], + "angle": 0, + "content": "method on the Hide dataset [20], which mainly contains humans. Similar to state-of-the-art methods [4, 31], we directly use the models of the evaluated methods, which are trained on the GoPro dataset for test. Table 3 shows that the quality of the deblurred images generated by the proposed method is better than the evaluated methods, suggesting that our method has a better generalization ability as models are not trained on this dataset." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.647, + 0.894, + 0.707 + ], + "angle": 0, + "content": "We show some visual comparisons in Figure 5. We note that the evaluated methods do not recover the humans well. In contrast, our method generates better images. For example, the faces and zipper of clothes are much clearer." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.712, + 0.725, + 0.729 + ], + "angle": 0, + "content": "5. Analysis and Discussion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.731, + 0.893, + 0.852 + ], + "angle": 0, + "content": "We have shown that exploring the properties of Transformers in the frequency domain generates favorable results against state-of-the-art methods. In this section, we provide deeper analysis on the proposed method and demonstrate the effect of the main components. For the ablation studies in this section, we train our method and all the baselines on the GoPro dataset using the batch size of 8 to illustrate the effect of each component in our method." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.856, + 0.894, + 0.901 + ], + "angle": 0, + "content": "Effect of FSAS. The proposed FSAS is used to reduce the computational cost. According to the properties of FFT, the space and time complexity of the FSAS are \\(O(N)\\) and" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.514, + 0.957 + ], + "angle": 0, + "content": "5891" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.091, + 0.088, + 0.287, + 0.224 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.132, + 0.226, + 0.227, + 0.238 + ], + "angle": 0, + "content": "(a) Blurred image" + }, + { + "type": "image", + "bbox": [ + 0.289, + 0.089, + 0.483, + 0.224 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.367, + 0.226, + 0.405, + 0.237 + ], + "angle": 0, + "content": "(b) GT" + }, + { + "type": "image", + "bbox": [ + 0.484, + 0.089, + 0.68, + 0.224 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.536, + 0.226, + 0.626, + 0.238 + ], + "angle": 0, + "content": "(c) MPRNet [31]" + }, + { + "type": "image", + "bbox": [ + 0.681, + 0.089, + 0.877, + 0.224 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.727, + 0.226, + 0.826, + 0.238 + ], + "angle": 0, + "content": "(d) Restormer [30]" + }, + { + "type": "image", + "bbox": [ + 0.091, + 0.238, + 0.288, + 0.373 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.128, + 0.375, + 0.234, + 0.387 + ], + "angle": 0, + "content": "(e) Stripformer [24]" + }, + { + "type": "image", + "bbox": [ + 0.289, + 0.238, + 0.483, + 0.373 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.345, + 0.375, + 0.426, + 0.387 + ], + "angle": 0, + "content": "(f) NAFNet [3]" + }, + { + "type": "image", + "bbox": [ + 0.484, + 0.238, + 0.68, + 0.373 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.521, + 0.375, + 0.643, + 0.387 + ], + "angle": 0, + "content": "(g) Restormer-local [5]" + }, + { + "type": "image", + "bbox": [ + 0.681, + 0.238, + 0.877, + 0.373 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.756, + 0.375, + 0.801, + 0.387 + ], + "angle": 0, + "content": "(h) Ours" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.392, + 0.893, + 0.421 + ], + "angle": 0, + "content": "Figure 5. Deblurred results on the HID dataset [20]. The deblurred results in (c)-(g) still contain significant blur effects. The proposed method generates much clearer images." + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.427, + 0.473, + 0.51 + ], + "angle": 0, + "content": "Table 4. Memory and running time comparisons of the Transformer based on our method and the window methods [14,27]. The size of the test image is \\(1280 \\times 720\\) pixels. The test environment is based on a machine with an NVIDIA GeForce RTX 3090 GPU. \"GPU memory\" denotes the maximum GPU memory consumption that is computed by the \"torch.cuda.max_memory_allocated( )\" function." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.512, + 0.477, + 0.598 + ], + "angle": 0, + "content": "
Window sizeWindow-based method [27]Ours
Avg. runtimeGPU memoryAvg. runtimeGPU memory
8 × 853ms6.3G44ms6.5G
16 × 1656ms7.1G44ms6.2G
32 × 3289ms12.0G43ms6.0G
64 × 64-Out of memory42ms5.9G
1280 × 720-Out of memory42ms5.9G
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.611, + 0.47, + 0.838 + ], + "angle": 0, + "content": "\\(O(NC\\log N)\\), which are much lower than \\(O(N^2)\\) and \\(O(N^{2}C)\\) in the original computation of the scaled dot-product attention, where \\(C\\) is the number of features. We further examine the space and time complexity of the FSAS and the window-based strategy [14, 27] for Transformers. Although the tensors in the frequency domain contain real part and imaginary part, the memory consumption does not increase as we only store half parts of the tensors by FFT based on the conjugate symmetry of FFT in our implementations. Table 4 shows that using the proposed FSAS needs a small GPU memory and is much more efficient compared to the window-based strategy [27]. In addition, as the memory of the FSAS is independent of window size, the memory usage of the FSAS does not increase when the window size becomes larger." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.471, + 0.902 + ], + "angle": 0, + "content": "Moreover, as the proposed FSAS is performed in the frequency domain, one may wonder whether the scaled dot-product attention estimated in the spatial domain performs better or not. To answer this question, we compare the F-" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.428, + 0.894, + 0.455 + ], + "angle": 0, + "content": "Table 5. Quantitative evaluations of each component in the proposed method on the GoPro dataset [16]." + }, + { + "type": "table", + "bbox": [ + 0.504, + 0.456, + 0.892, + 0.537 + ], + "angle": 0, + "content": "
FSASSwin attentionFFNDFFNPSNRs/SSIMs
w/ only FFN✘✘✓✘33.19/0.9626
w/ only DFFN✘✘✘✓33.55/0.9651
SA w/ SD✘✓✘✓33.46/0.9645
FSAS+FFN✓✘✓✘33.61/0.9654
FSAS+DFFN✓✘✘✓33.73/0.9663
" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.538, + 0.893, + 0.854 + ], + "angle": 0, + "content": "SAS with the baseline method that performs in the spatial domain (SA w/ SD for short). As the space complexity of the original scaled dot-product attention is \\( O(N^2) \\), it is not affordable to train \"SA w/ SD\" when using the same settings as the proposed FSAS. We use the Swin Transformer [14] for comparison as it is much more efficient. Table 5 shows the quantitative evaluation results on the GoPro dataset. The method that computes the scaled dot-product attention in the spatial domain does not generate good deblurred results, where its PSNR value is 0.27 lower (see comparisons of \"SA w/ SD\" and \"FSAS+DFFN\" in Table 5). The main reason is that although using the shifted window partitioning method reduces the computational cost, it does not fully explore the useful information across different windows. In contrast, the space complexity of the proposed FSAS is \\( O(N) \\) and does not need the shifted window partitioning as an approximation, thus leading to better deblurred results. Figure 6(b) further shows that using the shifted window partitioning method as an approximation of scaled dot-product attention in the spatial domain does not remove blur effectively. In contrast, the proposed FSAS generates clearer images." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.856, + 0.893, + 0.901 + ], + "angle": 0, + "content": "Moreover, compared to the baseline method only using FFN (\"w/ only FFN\"), using the proposed FSAS in this baseline generates much better results, where the PSNR" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "5892" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.084, + 0.089, + 0.208, + 0.166 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.094, + 0.169, + 0.19, + 0.18 + ], + "angle": 0, + "content": "(a) Blurred image" + }, + { + "type": "image", + "bbox": [ + 0.21, + 0.089, + 0.332, + 0.166 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.221, + 0.169, + 0.321, + 0.18 + ], + "angle": 0, + "content": "(b) Spatial domain" + }, + { + "type": "image", + "bbox": [ + 0.335, + 0.089, + 0.458, + 0.166 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.338, + 0.169, + 0.455, + 0.18 + ], + "angle": 0, + "content": "(c) Frequency domain" + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.183, + 0.471, + 0.239 + ], + "angle": 0, + "content": "Figure 6. Effectiveness of the scaled dot-product attention computation in the spatial and frequency domains. Computing the scaled dot-product attention using the FSAS in the frequency domain generates a clearer image." + }, + { + "type": "image", + "bbox": [ + 0.083, + 0.244, + 0.208, + 0.338 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.094, + 0.34, + 0.19, + 0.352 + ], + "angle": 0, + "content": "(a) Blurred image" + }, + { + "type": "image", + "bbox": [ + 0.21, + 0.248, + 0.332, + 0.338 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.22, + 0.34, + 0.323, + 0.351 + ], + "angle": 0, + "content": "(b) Ours w/o FSAS" + }, + { + "type": "image", + "bbox": [ + 0.335, + 0.248, + 0.458, + 0.338 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.375, + 0.34, + 0.42, + 0.351 + ], + "angle": 0, + "content": "(c) Ours" + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.355, + 0.47, + 0.383 + ], + "angle": 0, + "content": "Figure 7. Effectiveness of the proposed FSAS on image deblurring. Using the proposed FSAS generates a clearer image." + }, + { + "type": "image", + "bbox": [ + 0.083, + 0.386, + 0.207, + 0.502 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.094, + 0.504, + 0.189, + 0.516 + ], + "angle": 0, + "content": "(a) Blurred image" + }, + { + "type": "image", + "bbox": [ + 0.21, + 0.386, + 0.332, + 0.502 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.228, + 0.504, + 0.315, + 0.516 + ], + "angle": 0, + "content": "(b) w/ only FFN" + }, + { + "type": "image", + "bbox": [ + 0.335, + 0.386, + 0.458, + 0.502 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.35, + 0.504, + 0.445, + 0.516 + ], + "angle": 0, + "content": "(c) w/ only DFFN" + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.519, + 0.47, + 0.613 + ], + "angle": 0, + "content": "Figure 8. Effectiveness of the proposed DFFN on image deblurring. value is \\(0.42\\mathrm{dB}\\) higher (see comparisons of \"w/ only FFN\" and \"FSAS+FFN\" in Table 5). The visual comparisons in Figure 7(b) and (c) further demonstrate that using the proposed FSAS facilitates the blur removal well, where the boundaries are recovered well as shown in Figure 7(c)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.614, + 0.471, + 0.81 + ], + "angle": 0, + "content": "Effect of DFFN. The proposed DFFN is used to discriminatively estimate useful frequency information for latent clear image restoration. To demonstrate its effectiveness on image deblurring, we compare the proposed method with two baselines. For the first baseline, we compare the proposed method only using the DFFN (w/ only DFFN for short) and the proposed method only using the original FFN (w/ only FFN for short). For the second baseline, we compare the proposed method with the one that replaces the DFFN with the original FFN in the proposed method (FSAS+FFN). The comparisons of \"w/ only DFFN\" and \"w/ only FFN\" in Table 5 show that using the proposed DFFN generates better results, where the PSNR value is 0.36dB higher." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.811, + 0.471, + 0.856 + ], + "angle": 0, + "content": "In addition, the comparisons of \"FSAS+FFN\" and \"F-SAS+DFFN\" in Table 5 show that using the proposed DFFN further improves the performance." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.856, + 0.471, + 0.901 + ], + "angle": 0, + "content": "Figure 8 shows the visualization results by these above mentioned baseline methods. Using the proposed DFFN generates better deblurred images, where the windows are" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.09, + 0.894, + 0.116 + ], + "angle": 0, + "content": "Table 6. Quantitative evaluations of the asymmetric encoder-decoder network on the GoPro dataset." + }, + { + "type": "table", + "bbox": [ + 0.504, + 0.118, + 0.887, + 0.165 + ], + "angle": 0, + "content": "
MethodsFSAS in enc&decFSAS in dec (Ours)
PSNRs33.5633.73
SSIMs0.96530.9663
" + }, + { + "type": "image", + "bbox": [ + 0.507, + 0.167, + 0.63, + 0.264 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.516, + 0.266, + 0.612, + 0.278 + ], + "angle": 0, + "content": "(a) Blurred image" + }, + { + "type": "image", + "bbox": [ + 0.632, + 0.167, + 0.756, + 0.264 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.637, + 0.266, + 0.751, + 0.278 + ], + "angle": 0, + "content": "(b) FSAS in enc&dec" + }, + { + "type": "image", + "bbox": [ + 0.758, + 0.167, + 0.882, + 0.264 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.759, + 0.266, + 0.882, + 0.278 + ], + "angle": 0, + "content": "(c) FSAS in dec (Ours)" + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.281, + 0.892, + 0.308 + ], + "angle": 0, + "content": "Figure 9. Effectiveness of the asymmetric encoder-decoder network on image deblurring." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.311, + 0.744, + 0.326 + ], + "angle": 0, + "content": "recovered well shown in Figure 8(c)." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.329, + 0.894, + 0.525 + ], + "angle": 0, + "content": "Effect of the asymmetric encoder-decoder network. As demonstrated in Section 3.3, the shallow features extracted by encoder module usually contain blur effects that affect the estimations of FSAS. We thus embed it into the decoder module, which leads to an asymmetric encoder-decoder network for better image deblurring. To examine the effect of this network design, we compare the network that puts the FSAS into both the encoder and decoder modules (\"FSAS in enc&dec\" in Table 6). Table 6 shows that using the FSAS in the decoder module generates better results, where the PSNR value is at least 0.17dB higher. The visual comparisons in Figure 9(b) and (c) further demonstrate that using the FSAS in the decoder module generates better clear images." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.531, + 0.619, + 0.545 + ], + "angle": 0, + "content": "6. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.55, + 0.895, + 0.807 + ], + "angle": 0, + "content": "Motivated by the convolution theorem, we have presented an effective and efficient method that explores the properties of Transformers for high-quality image deblurring. We have developed an efficient frequency domain-based self-attention solver (FSAS) to estimate the scaled dot-product attention by an element-wise product operation instead of the matrix multiplication in the spatial domain, where we show that the spatial complexity and the computational complexity are significantly reduced. We further propose a DFFN to discriminatively determine which low and high frequency information of the features should be preserved for latent clear image restoration. Moreover, we develop an asymmetrical network based on an encoder and decoder architecture, where the FSAS is only used in the decoder module for better image deblurring. By training our method in an end-to-end manner, we show that it performs favorably against the state-of-the-art approaches in terms of accuracy and efficiency." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.81, + 0.895, + 0.9 + ], + "angle": 0, + "content": "Acknowledgements. This work has been partly supported by the National Key R&D Program of China (No. 2018AAA0102001), the National Natural Science Foundation of China (Nos. U22B2049, 62272233, 61922043, U19B2040), and the Fundamental Research Funds for the Central Universities (No. 30920041109)." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "5893" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.175, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.117, + 0.471, + 0.17 + ], + "angle": 0, + "content": "[1] Nicolas Carion, Francisco Massa, Gabriel Synnaeve, Nicolas Usunier, Alexander Kirillov, and Sergey Zagoruyko. End-to-end object detection with transformers. In ECCV, 2020. 2" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.174, + 0.472, + 0.229 + ], + "angle": 0, + "content": "[2] Hanting Chen, Yunhe Wang, Tianyu Guo, Chang Xu, Yiping Deng, Zhenhua Liu, Siwei Ma, Chunjing Xu, Chao Xu, and Wen Gao. Pre-trained image processing transformer. 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In CVPR, 2021. 2" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.946, + 0.515, + 0.956 + ], + "angle": 0, + "content": "5895" + } + ] +] \ No newline at end of file diff --git a/2023/Efficient Frequency Domain-Based Transformers for High-Quality Image Deblurring/c856a1da-867e-42ea-84a9-c14d1b12f290_origin.pdf b/2023/Efficient Frequency Domain-Based Transformers for High-Quality Image Deblurring/c856a1da-867e-42ea-84a9-c14d1b12f290_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..b370200db4d95535e58a8afe9c3315a6ece6ffdd --- /dev/null +++ b/2023/Efficient Frequency Domain-Based Transformers for High-Quality Image Deblurring/c856a1da-867e-42ea-84a9-c14d1b12f290_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:2d320a87ffcba00b1d5de0744dda58d189b87ef4ccbb6bf9d815e598f47af2c3 +size 3039996 diff --git a/2023/Efficient Frequency Domain-Based Transformers for High-Quality Image Deblurring/full.md b/2023/Efficient Frequency Domain-Based Transformers for High-Quality Image Deblurring/full.md new file mode 100644 index 0000000000000000000000000000000000000000..7eb7f3d4da89e25c889de0f19f31c69661d47a06 --- /dev/null +++ b/2023/Efficient Frequency Domain-Based Transformers for High-Quality Image Deblurring/full.md @@ -0,0 +1,392 @@ +# Efficient Frequency Domain-based Transformers for High-Quality Image Deblurring + +Lingshun Kong $^{1}$ , Jiangxin Dong $^{1*}$ , Jianjun Ge $^{2}$ , Mingqiang Li $^{2}$ , and Jinshan Pan $^{1*}$ $^{1}$ School of Computer Science and Engineering, Nanjing University of Science and Technology + $^{2}$ Information Science Academy, China Electronics Technology Group Corporation + +# Abstract + +We present an effective and efficient method that explores the properties of Transformers in the frequency domain for high-quality image deblurring. Our method is motivated by the convolution theorem that the correlation or convolution of two signals in the spatial domain is equivalent to an element-wise product of them in the frequency domain. This inspires us to develop an efficient frequency domain-based self-attention solver (FSAS) to estimate the scaled dot-product attention by an element-wise product operation instead of the matrix multiplication in the spatial domain. In addition, we note that simply using the naive feed-forward network (FFN) in Transformers does not generate good deblurred results. To overcome this problem, we propose a simple yet effective discriminative frequency domain-based FFN (DFFN), where we introduce a gated mechanism in the FFN based on the Joint Photographic Experts Group (JPEG) compression algorithm to discriminatively determine which low- and high-frequency information of the features should be preserved for latent clear image restoration. We formulate the proposed FSAS and DFFN into an asymmetrical network based on an encoder and decoder architecture, where the FSAS is only used in the decoder module for better image deblurring. Experimental results show that the proposed method performs favorably against the state-of-the-art approaches. + +# 1. Introduction + +Image deblurring aims to restore high-quality images from blurred ones. This problem has achieved significant progress due to the development of various effective deep models with large-scale training datasets. + +Most state-of-the-art methods for image deblurring are mainly based on deep convolutional neural networks (CNNs). The main success of these methods is due to developing kinds of network architectural designs, for example, the multi- + +![](images/b611b7e74183e61962acbb8c333c1d664239b3d51cf2a59c7c5217d79fcac314.jpg) +Figure 1. Comparisons of the proposed method and state-of-the-art ones on the GoPro dataset [16] in terms of accuracy, floating point operations (FLOPs), and network parameters. The circle size indicates the number of the network parameter. + +scale [4, 16, 22] or multi-stage [31, 32] network architectures, generative adversarial learning [11, 12], physics model inspired network structures [6-8, 17, 33], and so on. As the basic operation in these networks, the convolution operation is a spatially-invariant local operation, which does not model the spatially variant properties of the image contents. Most of them use larger and deeper models to remedy the limitation of the convolution. However, simply increasing the capacity of deep models does not always lead to better performance as shown in [17, 33]. + +Different from the convolution operation that models the local connectivity, Transformers are able to model the global contexts by computing the correlations of one token to all other tokens. They have been shown to be an effective approach in lots of high-level vision tasks and also have great potential to be the alternatives of deep CNN models. In image deblurring, the methods based on Transformers [27, 30] also achieve better performance than the CNN-based methods. However, the computation of the scaled dot-product attention in Transformers leads to quadratic space and time complexity in terms of the number of tokens. Although using smaller and fewer tokens can reduce the space and + +time complexity, such strategy cannot model the long-range information of features well and usually leads to significant artifacts when handling high-resolution images, which thus limits the performance improvement. + +To alleviate this problem, most approaches use the down-sampling strategy to reduce the spatial resolution of features [26]. However, reducing the spatial resolution of features will cause information loss and thus affect the image deblurring. Several methods reduce the computational cost by computing the scaled dot-product attention in terms of the number of features [29, 30]. Although the computational cost is reduced, the spatial information is well not explored, which may affect the deblurring performance. + +In this paper, we develop an effective and efficient method that explores the properties of Transformers for high-quality image deblurring. We note that the scaled dot-product attention computation is actually to estimate the correlation of one token from the query and all the tokens from the key. This process can be achieved by a convolution operation when rearranging the permutations of tokens. Based on this observation and the convolution theorem that the convolution in the spatial domain equals a point-wise multiplication in the frequency domain, we develop an efficient frequency domain-based self-attention solver (FSAS) to estimate the scaled dot-product attention by an element-wise product operation instead of the matrix multiplication. Therefore, the space and time complexity can be reduced to $O(N)$ $O(N\log N)$ for each feature channel, where $N$ is the number of the pixels. + +In addition, we note that simply using the feed-forward network (FFN) by [30] does not generate good deblurred results. To generate better features for latent clear image restoration, we develop a simple yet effective discriminative frequency domain-based FFN (DFFN). Our DFFN is motivated by the Joint Photographic Experts Group (JPEG) compression algorithm. It introduces a gated mechanism in the FFN to discriminatively determine which low- and high-frequency information should be preserved for latent clear image restoration. + +We formulate the proposed FSAS and DFFN into an end-to-end trainable network based on an encoder and decoder architecture to solve image deblurring. However, we find that as features of shallow layers usually contain blur effects, applying the scaled dot-product attention to shallow features does not effectively explore global clear contents. As the features from deep layers are usually clearer than those from shallow layers, we develop an asymmetric network architecture, where the FSAS is only used in the decoder module for better image deblurring. We analyze that the exploring properties of Transformers in the frequency domain is able to facilitate blur removal. Experimental results demonstrate that the proposed method generates favorable results against state-of-the-art methods in terms of accuracy and efficiency + +# (Figure 1). + +The main contributions are summarized as follows: +- We develop an efficient frequency domain-based self-attention solver to estimate the scaled dot-product attention. Our analysis demonstrates that using the frequency domain-based solver reduces the space and time complexity and is much more effective and efficient. +- We propose a simple yet effective discriminative frequency domain-based FFN based on the JPEG compression algorithm to discriminatively determine which low and high-frequency information should be preserved for latent clear image restoration. +- We develop an asymmetric network architecture based on an encoder and decoder network, where the frequency domain-based self-attention solver is only used in the decoder module for better image deblurring. +- We analyze that the exploring properties of Transformers in the frequency domain is able to facilitate blur removal and show that our approach performs favorably against state-of-the-art methods. + +# 2. Related Work + +Deep CNN-based Image deblurring methods. In recent years, we have witnessed significant advances in image deblurring due to the development of different deep CNN models [3, 4, 9, 16, 22, 31, 32]. In [16], Nah et al. propose a deep CNN based on a multi-scale framework to directly estimate clear images from blurred ones. To better utilize the information of each scale in multi-scale framework, Tao et al. [22] develop an effective scale recurrent network. Gao et al. [9] propose a selective network parameter sharing method to improve [16, 22]. + +As using more scales does not improve the performance significantly, Zhang et al. [32] develop an effective network based on multi-patch strategy. The deblurring process is achieved stage by stage. To better explore the features from different stages, Zamir et al. [31] propose a cross-stage feature fusion for better performance. In order to reduce the computational cost of the methods based on multi-scale framework, Cho et al. [4] present a multi-input and multi-output network. Chen et al. [3] analyze the baseline modules and simplify them for better image restoration. As demonstrated in [30], the convolution operation is spatial invariant and does not effectively model the global contexts for image deblurring. + +Transformers and their applications to image deblurring. As the Transformer [25] can model the global contexts and achieves significant progress in lots of high-level vision tasks (e.g., image classification [14], object detection [1, 34] and semantic segmentation [28, 35]), it has been developed to solve image super-resolution [13], image deblurring [24, 30] and image denoise [2, 27]. To reduce the computational cost of Transformer, Zamir et al. [30] propose an efficient Transformer model by computing the scaled dot-product attention + +in the feature depth domain. This method can effectively explore information from different features along the channel dimension. However, the spatial information that is vital for image restoration is not fully explored. Tsai et al. [24] simplify the calculation of self-attention by constructing intra and inter strip tokens to replace the global attention. Wang et al. [27] propose a Transformer based on a UNet which uses non-overlapping window-based self-attention for single image deblurring. Although using the splitting strategy reduces the computational cost, the coarse splitting does not fully explore the information of each patch. Moreover, the scaled dot-product attention in these methods usually needs the complex matrix multiplication whose the space and time complexity is quadratic. + +Different from these methods, we develop an efficient Transformer-based method that explores the property of the frequency domain to avoid the complex matrix multiplication for the scaled dot-product attention. + +# 3. Proposed Method + +Our goal is to present an effective and efficient method to explore the properties of Transformers for high-quality image deblurring. To this end, we first develop an efficient frequency domain-based self-attention solver to estimate the scaled dot-product attention. To refine the features estimated by the frequency domain-based solver, we further develop a discriminative frequency domain-based feed-forward network. We formulate these above approaches into an end-to-end trainable network based on an encoder and decoder architecture to solve image deblurring, where the frequency domain-based self-attention solver for the estimation of the scaled dot-product attention is used in the decoder module for better feature representation. Figure 2(a) shows the overview of the proposed method. In the following, we present the details of each component. + +# 3.1. Frequency domain-based self-attention solver + +Given the input feature $X$ with a spatial resolution of $H\times W$ pixels and $C$ channels, existing vision Transformers usually first compute the features $F_{q},F_{k}$ ,and $F_{v}$ by applying linear transformations $W_{q}$ $W_{k}$ ,and $W_{v}$ to $X$ . Then, they apply the unfolding function to the features $F_{q},F_{k}$ ,and $F_{v}$ to extract image patches $\{q_i\}_{i = 1}^N,\{k_i\}_{i = 1}^N$ ,and $\{v_i\}_{i = 1}^N$ ,where $N$ denotes the number of extracted patches. By applying a reshape operation to the extracted patches, the query Q, key K, and value V can be obtained by: + +$$ +\mathbf {Q} = \mathcal {R} \left(\left\{q _ {i} \right\} _ {i = 1} ^ {N}\right), \mathbf {K} = \mathcal {R} \left(\left\{k _ {i} \right\} _ {i = 1} ^ {N}\right), \mathbf {V} = \mathcal {R} \left(\left\{v _ {i} \right\} _ {i = 1} ^ {N}\right), \tag {1} +$$ + +where $\mathcal{R}$ denotes the reshape function which ensures that $\{\mathbf{K},\mathbf{Q},\mathbf{V}\} \in R^{N\times (CH_pW_p)}$ , $H_{p}$ and $W_{p}$ denote the height and width of extracted patches. Based on the obtained query $\mathbf{Q}$ , key $\mathbf{K}$ , and value $\mathbf{V}$ , the scaled dot-product attention is achieved by: + +$$ +V _ {a t t} = \operatorname {s o f t m a x} \left(\frac {\mathbf {Q K} ^ {\top}}{\sqrt {C H _ {p} W _ {p}}}\right) V. \tag {2} +$$ + +The attention map computation involves the matrix multiplication of $\mathbf{Q}\mathbf{K}^{\top}$ whose space complexity and time complexity are $O(N^{2})$ and $O(N^{2}C)$ . It is not affordable if the image resolution and the number of the extracted patches are large. Although using downsampling operation to reduce the image resolution or non-overlapping method to extract fewer patches will alleviate the problem, these strategies would lead to information loss and limit the ability to model details within and across each patch [29]. + +We note that each element of $\mathbf{Q}\mathbf{K}^{\top}$ is obtained by the inner product: + +$$ +\left(\mathbf {Q} \mathbf {K} ^ {\top}\right) _ {i j} = \langle \mathbf {q} _ {i}, \mathbf {k} _ {j} \rangle , \tag {3} +$$ + +where $\mathbf{q}_i$ and $\mathbf{k}_j$ are the vectorized forms of $i$ -th and $j$ -th patches from $F_{q}$ and $F_{k}$ . Based on (3), if we apply reshape functions to $\mathbf{q}_i$ and all the patches $\mathbf{k}_j$ , respectively, all the $i$ -th column elements of $\mathbf{QK}^{\top}$ can be obtained by a convolution operation, i.e., $\widetilde{q}_i \otimes \widetilde{K}$ , where $\widetilde{q}_i$ and $\widetilde{K}$ denote the reshaped results of $\mathbf{q}_i$ and $\mathbf{k}_j$ ; $\otimes$ denotes the convolution operation. + +According to the convolution theorem, the correlation or convolution of two signals in the spatial domain is equivalent to an element-wise product of them in the frequency domain. Therefore, a natural question is that can we efficiently estimate the attention map by an element-wise product operation in a frequency domain instead of computing the matrix multiplication of $\mathbf{Q}\mathbf{K}^{\top}$ in the spatial domain? + +To this end, we develop an effective frequency domain-based self-attention solver. Specifically, we first obtain $F_{q}$ , $F_{k}$ , and $F_{v}$ by a $1 \times 1$ point-wise convolution and $3 \times 3$ depth-wise convolution. Then, we apply the fast Fourier transform (FFT) to the estimated features $F_{q}$ and $F_{k}$ and estimate the correlation of $F_{q}$ and $F_{k}$ in the frequency domain by: + +$$ +A = \mathcal {F} ^ {- 1} \left(\mathcal {F} \left(F _ {q}\right) \overline {{\mathcal {F} \left(F _ {k}\right)}}\right), \tag {4} +$$ + +where $\mathcal{F}(\cdot)$ denotes the FFT, $\mathcal{F}^{-1}(\cdot)$ denotes the inverse FFT, and $\overline{\mathcal{F}(\cdot)}$ denotes the conjugate transpose operation. Finally, we estimate the aggregated feature by: + +$$ +V _ {a t t} = \mathcal {L} (A) F _ {v}, \tag {5} +$$ + +where a layer norm $\mathcal{L}(\cdot)$ is used to normalize $A$ . Finally, we generate the output feature of FSAS by: + +$$ +X _ {a t t} = X + \operatorname {C o n v} _ {1 \times 1} \left(V _ {a t t}\right), \tag {6} +$$ + +where $\mathrm{Conv}_{1\times 1}(\cdot)$ denotes a convolution with filter size of $1\times 1$ pixel. The detailed network architecture of the proposed FSAS is shown in Figure 2(b). + +# 3.2. Discriminative frequency domain-based FFN + +The FFN is used to improve the features by the scaled dot-product attention. Thus, it is important to develop an + +![](images/449efbfdd40dfc847e99bfd25a9c3177a45ac771dcdc69d13ec61095b0173f50.jpg) +Figure 2. Network architectures. (a) The proposed asymmetric encoder-decoder network that only contains DFFN in the encoder module and both FSAS and DFFN in the decoder module for image deblurring. (b) The proposed FSAS module. (c) The proposed DFFN module. + +![](images/9617f88a384dc068920468f0db287e28971a8e1a2e0576f0eead493a72a69c4b.jpg) + +![](images/d217644bdbccaee5334259ea53062598d2f112272bebdf1c89f90499f919085a.jpg) + +effective FFN to generate the features that facilitate the latent clear image reconstruction. As not all the low-frequency information and high-frequency information help latent clear image restoration, we develop a DFFN that can adaptively determine which frequency information should be preserved. However, how to effectively determine which frequency information is important. Motivated by the JPEG compression algorithm, we introduce a learnable quantization matrix $\mathbf{W}$ and learn it by an inverse method of JPEG compression to determine which frequency information should be preserved. The proposed DFFN can be formulated by: + +$$ +X _ {1} = \operatorname {C o n v} _ {1 \times 1} (\mathcal {L} (X _ {\text {a t t}})) +$$ + +$$ +X _ {1} ^ {f} = \mathcal {F} \left(\mathcal {P} \left(X _ {1}\right)\right) \tag {7} +$$ + +$$ +X _ {2} = \mathcal {F} ^ {- 1} \left(\mathbf {W} X _ {1} ^ {f}\right) +$$ + +$$ +X _ {o u t} = \mathcal {G} \left(\mathcal {P} ^ {- 1} \left(X _ {2}\right)\right) + X _ {a t t}, +$$ + +where $\mathcal{P}(\cdot)$ and $\mathcal{P}^{-1}(\cdot)$ denote the patch unfolding and folding operations in the JPEG compression method; $\mathcal{G}$ denotes GEGLU function by [19]. The detailed network architecture of the proposed DFFN is shown in Figure 2(c). + +# 3.3. Asymmetric encoder-decoder network + +We embed the proposed FSAS and DFFN into a network based on an encoder and decoder architecture. We note that most existing methods usually use symmetric architectures in the encoder and decoder modules. For example, if the FSAS and DFFN are used in the encoder module, they are also used in the decoder module. We note that the features extracted by encoder module are shallow ones, which usually contain blur effects compared to the deep features from the decoder module. However, the blur usually changes similarity of two similar patches from clear features. Thus, using the FSAS in the encoder module may not estimate the similarity correctly, which accordingly affects image restoration. To overcome this problem, we embed the FSAS into the decoder module, which leads to an asymmetric architecture for better image + +deblurring. Figure 2(a) shows the network architecture of the proposed asymmetric encoder-decoder network. + +Finally, given a blurred image $B$ , the restored image $I$ is estimated by the asymmetric encoder-decoder network: + +$$ +I = \mathcal {N} (B) + B, \tag {8} +$$ + +where $\mathcal{N}$ denotes the asymmetric encoder-decoder network. + +# 4. Experimental Results + +In this section, we evaluate our method and compare it with state-of-the-art ones using public benchmark datasets. + +# 4.1. Datasets and parameter settings + +Datasets. We evaluate our method on commonly used image deblurring datasets including the GoPro dataset [16], the HIDe dataset [20], and the RealBlur dataset [18]. We follow the protocols of existing methods for fair comparisons. + +Parameter settings. We use the same loss function as [4] to constrain the network and train it using the Adam [10] optimizer with default parameters. The initial value of the learning rate is $10^{-3}$ and is updated with the cosine annealing strategy after 600,000 iterations. The minimum value of the learning rate is $10^{-7}$ . The patch size is empirically set to be $256 \times 256$ pixels and the batch size is set to be 16. We adopt the same data augmentation method as [30] during the training. The patch size for the quantization matrix estimation is empirically set to be $8 \times 8$ based on the JPEG compression method. In the implementation, the tensor form of the quantization matrix is set as [batch_size, channel_num, 8, 8], where batch_size and channel_num are the number of batches and features. The quantization matrix is jointly learned with other parameters by solving loss functions during the training. Similarity, we also use the patch size of $8 \times 8$ pixels when computing the self-attention (4). Due to the page limit, we include more experimental results in the supplemental material. The training code and models are available at https://github.com/kkkls/FFTformer. + +![](images/451bd253d42c6abf52b0cfc97893610d7c6414344676ca28e0e8ac93d7a588b4.jpg) + +![](images/74cb9d826e7bc61ca50ffe75480252d28137b5df96d67818e1945bdd033830b2.jpg) + +![](images/16b200b4c21552650b77904c7bed316d46b8198653f0ed0777fe43a0f646eb7f.jpg) + +![](images/3f9b52f1e843819375fccddbba7daa3fe0b1920482f7cbbe9748de2394870fdd.jpg) + +![](images/9a90f446fa2d656748d434e6036198e13b684dfaf44ad63521799441277fb0b6.jpg) +(a) Blurred image +(e) Stripformer [24] +Figure 3. Deblurred results on the GoPro dataset [16]. The deblurred results in (c)-(g) still contain significant blur effects. The proposed method generates a clearer image. For example, the characters and boundaries are much clearer. + +![](images/0dfa20e30f8b057bd54d6d0922bd2b5cf4fbe61c81ccd89f6f2f529f59bf2d3a.jpg) +(b) GT +(f) Restormer-local [5] + +![](images/14ea27bae754bbbc1abaa2b79b2442d4dce2b1a866512e9db84f3ea97c4a7582.jpg) +(c) MIMO-Unet+ [4] +(g) NAFNet [3] + +![](images/1d1292b3236808f90eb204eca634bbcc27bc2ffaa959c82f6099f2b3067baac9.jpg) +(d) Restormer [30] +(h) Ours + +Table 1. Quantitative evaluations on the GoPro dataset [16]. The average runtime is tested on images with size of $256 \times 256$ pixels. + +
MethodsPSNRsSSIMsParameters (M)Avg. runtime
DeblurGAN-v2 [12]29.550.934060.90.04s
SRN [22]30.260.93426.80.07s
DMPHN [32]31.200.945321.70.21s
SAPHN [21]31.850.948023.0-
MIMO-Unet+ [4]32.450.956716.10.02s
MPRNet [31]32.660.958920.10.09s
IPT [2]--1140.50s
DeepRFT+ [15]33.230.963223.00.09s
Restormer [30]32.920.961126.10.08s
Uformer-B [27]33.060.967050.90.07s
Stripformer [24]33.080.962419.70.04s
MPRNet-local [5]33.310.963720.10.11s
Restormer-local [5]33.570.965626.10.42s
NAFNet [3]33.710.966867.90.04s
Ours34.210.969216.60.13s
+ +# 4.2. Comparisons with the state of the arts + +We compare our method with state-of-the-art ones and use the PSNR and SSIM to evaluate the quality of restored images. + +**Evaluations on the GoPro dataset.** We first evaluate our method on the commonly used GoPro dataset by [16]. For fair comparisons, we follow the protocols of this dataset and retrain or fine-tune the deep learning methods that are not trained on this dataset. Table 1 shows the quantitative evaluation results. Our method generates the results with the highest PSNR and SSIM values. Compared to the state-of-the-art CNN-based methods, NAFNet [3], the PSNR gain of our method is at least 0.5dB higher than NAFNet, while the number of the proposed model parameters is a quarter of the NAFNet. In addition, compared to the Transformer-based methods [24,27,30], our method has fewer model parameters while the performance is better. + +As the FFT implementation is not optimized well in Py- + +Table 2. Quantitative evaluations on the RealBlur dataset [18] in terms of PSNR and SSIM. + +
MethodsRealblur-RRealblur-J
PSNRsSSIMsPSNRsSSIMs
DeblurGAN-v2 [12]36.440.934729.690.8703
SRN [22]38.650.965231.380.9091
MIMO-Unet+ [4]--31.920.9190
BANet [23]39.550.971032.000.9230
DeepRFT+ [15]39.840.972132.190.9305
Stripformer [24]39.840.973732.480.9290
Ours40.110.973232.620.9326
+ +Torch, using FFTs in PyTorch needs more runtime. However, the runtime of our method is still competitive against state-of-art methods. Moreover, our method is at least $4 \times$ faster than IPT [2] that is based on the original self-attention. + +Figure 3 shows visual comparisons of the proposed method and the evaluated ones on the GoPro dataset. As demonstrated by [30], the CNN-based methods [3,4] do not effectively explore non-local information for latent clear image restoration. Therefore, the deblurred results by the methods [3,4] still contain significant blur effect as shown in Figure 3(c) and (g). The Transformer-based methods [5,24,30] are able to model the global contexts for image deblurring. However, some main structures, e.g., characters and chairs, are not recovered well (see Figure 3(d)-(f)). + +In contrast to existing Transformer-based methods that are based on the spatial domain, we develop an efficient frequency domain-based Transformer, where the proposed DFFN is able to discriminately estimate useful frequency information for latent clear image restoration. Thus, the deblurred results contain clear structures, and the characters are much clearer as shown in Figure 3(h). + +Evaluations on the RealBlur dataset. We further evaluate + +![](images/e0abd2f730e1282a7e0486f884a0a893698007a4d89dbdb734c067cf8ec0665c.jpg) +(a) Blurred image + +![](images/dd5bf27376ba19fa35c1383a11bd1ba44edf85471c704aa6099460cf0bb6bb2b.jpg) +(b) GT + +![](images/a1dae926d2171004d12a0f0c5c9ade50d2917adbdfed5d672e75a0a63c810df1.jpg) +(c) DeblurGAN-v2 [11] + +![](images/e00f85579c3f7f53439a284eb0832faf229fa3ca6ab3b7558815493016231f8a.jpg) +(d) SRN [22] + +![](images/46704e1e9f5baa2d8d703d5da0bb64137af57bd43e47dd2304f9be37a4df5be5.jpg) +(e) MIMO-Unet+ [4] + +![](images/3a1b7a6aa4c21bbd1446ce81e2abc14f3c1b4706a740190894490bc3d2a2d1a1.jpg) +(f) DeepRFT+ [15] + +![](images/4649ab62271b77e781aae6109fc2ee51d04ff6209e858ec91b3f257af18db455.jpg) +(g) Stripformer [24] + +![](images/2a71d775ccaaf0e055fd221b6728860acac580a5c7a5f88a8999450d19c33ee8.jpg) +(h) Ours +Figure 4. Deblurred results on the RealBlur dataset [18]. The characters or the structural details in (c)-(g) are not recovered well. The proposed method generates an image with much clearer characters and structural details. + +Table 3. Quantitative evaluations on the Hide dataset [20]. We use the models trained on the GoPro dataset [16] for fair comparisons. + +
MethodsPSNRsSSIMsParameters (M)
DeblurGAN-v2 [12]26.610.875060.9
SRN [22]28.360.90406.8
DMPHN [32]29.090.924021.7
SAPHN [21]29.980.930023.0
MIMO-Unet+ [4]29.990.930416.1
MPRNet [31]30.960.939720.1
Stripformer [24]31.030.939519.7
MPRNet-local [5]31.190.941820.1
Restormer [30]31.220.942326.1
NAFNet [3]31.310.942767.9
Restormer-local [5]31.490.944726.1
Ours31.620.945516.6
+ +our method on the RealBlur dataset by [18] and follow the protocols of this dataset for fair comparisons. The test dataset of [18] includes a RealBlur-R test set from the raw images and RealBlur-J test set from the JPEG images. Table 2 summarizes the quantitative evaluation results on the above mentioned test sets. The proposed method generates the results with higher PSNR values. + +Figure 4 shows the visual comparisons on the RealBlur dataset, where our method generates the results with clearer characters and finer structural details (Figure 4(h)). + +Evaluations on the HIDe dataset. We then evaluate our + +method on the Hide dataset [20], which mainly contains humans. Similar to state-of-the-art methods [4, 31], we directly use the models of the evaluated methods, which are trained on the GoPro dataset for test. Table 3 shows that the quality of the deblurred images generated by the proposed method is better than the evaluated methods, suggesting that our method has a better generalization ability as models are not trained on this dataset. + +We show some visual comparisons in Figure 5. We note that the evaluated methods do not recover the humans well. In contrast, our method generates better images. For example, the faces and zipper of clothes are much clearer. + +# 5. Analysis and Discussion + +We have shown that exploring the properties of Transformers in the frequency domain generates favorable results against state-of-the-art methods. In this section, we provide deeper analysis on the proposed method and demonstrate the effect of the main components. For the ablation studies in this section, we train our method and all the baselines on the GoPro dataset using the batch size of 8 to illustrate the effect of each component in our method. + +Effect of FSAS. The proposed FSAS is used to reduce the computational cost. According to the properties of FFT, the space and time complexity of the FSAS are $O(N)$ and + +![](images/69f92d39d74e2fa5ebcfeccc2d6d8024a2b0fc9a7f669c80ddd25caf50b309e2.jpg) + +![](images/2d2f3ef00f2e4c7934488eb6c0c5e9c40ba94722102eba78dc10eba222b49410.jpg) +(b) GT + +![](images/57f04088f0d5a1ad44a2218966ecd02d0b494f2cab2d3f528c11940e7ffea69e.jpg) + +![](images/c6bb3b4f34da0ac2bb3ba97a8cc60e6f756f4f2eac4dca461b09440e3caedda2.jpg) + +![](images/9bfb7051f9c07e94ea29d8d4efb593652f80218c9b2e630de810de7063abf412.jpg) +(a) Blurred image +(e) Stripformer [24] +Figure 5. Deblurred results on the HID dataset [20]. The deblurred results in (c)-(g) still contain significant blur effects. The proposed method generates much clearer images. + +![](images/4360d278caabde2650ed43c9ca06f646c04f55f005d0e0f999af9f47a8d3658c.jpg) +(f) NAFNet [3] + +![](images/545d76defbeaf7cb56668160fcd53369ea8a47bf2c05727e79e181a4c54fd5bc.jpg) +(c) MPRNet [31] +(g) Restormer-local [5] + +![](images/14290ec445988f0e46846cae611638da398fa4e4145a97e898281b042afddeeb.jpg) +(d) Restormer [30] +(h) Ours + +Table 4. Memory and running time comparisons of the Transformer based on our method and the window methods [14,27]. The size of the test image is $1280 \times 720$ pixels. The test environment is based on a machine with an NVIDIA GeForce RTX 3090 GPU. "GPU memory" denotes the maximum GPU memory consumption that is computed by the "torch.cuda.max_memory_allocated( )" function. + +
Window sizeWindow-based method [27]Ours
Avg. runtimeGPU memoryAvg. runtimeGPU memory
8 × 853ms6.3G44ms6.5G
16 × 1656ms7.1G44ms6.2G
32 × 3289ms12.0G43ms6.0G
64 × 64-Out of memory42ms5.9G
1280 × 720-Out of memory42ms5.9G
+ +$O(NC\log N)$ , which are much lower than $O(N^2)$ and $O(N^{2}C)$ in the original computation of the scaled dot-product attention, where $C$ is the number of features. We further examine the space and time complexity of the FSAS and the window-based strategy [14, 27] for Transformers. Although the tensors in the frequency domain contain real part and imaginary part, the memory consumption does not increase as we only store half parts of the tensors by FFT based on the conjugate symmetry of FFT in our implementations. Table 4 shows that using the proposed FSAS needs a small GPU memory and is much more efficient compared to the window-based strategy [27]. In addition, as the memory of the FSAS is independent of window size, the memory usage of the FSAS does not increase when the window size becomes larger. + +Moreover, as the proposed FSAS is performed in the frequency domain, one may wonder whether the scaled dot-product attention estimated in the spatial domain performs better or not. To answer this question, we compare the F- + +Table 5. Quantitative evaluations of each component in the proposed method on the GoPro dataset [16]. + +
FSASSwin attentionFFNDFFNPSNRs/SSIMs
w/ only FFN✘✘✓✘33.19/0.9626
w/ only DFFN✘✘✘✓33.55/0.9651
SA w/ SD✘✓✘✓33.46/0.9645
FSAS+FFN✓✘✓✘33.61/0.9654
FSAS+DFFN✓✘✘✓33.73/0.9663
+ +SAS with the baseline method that performs in the spatial domain (SA w/ SD for short). As the space complexity of the original scaled dot-product attention is $O(N^2)$ , it is not affordable to train "SA w/ SD" when using the same settings as the proposed FSAS. We use the Swin Transformer [14] for comparison as it is much more efficient. Table 5 shows the quantitative evaluation results on the GoPro dataset. The method that computes the scaled dot-product attention in the spatial domain does not generate good deblurred results, where its PSNR value is 0.27 lower (see comparisons of "SA w/ SD" and "FSAS+DFFN" in Table 5). The main reason is that although using the shifted window partitioning method reduces the computational cost, it does not fully explore the useful information across different windows. In contrast, the space complexity of the proposed FSAS is $O(N)$ and does not need the shifted window partitioning as an approximation, thus leading to better deblurred results. Figure 6(b) further shows that using the shifted window partitioning method as an approximation of scaled dot-product attention in the spatial domain does not remove blur effectively. In contrast, the proposed FSAS generates clearer images. + +Moreover, compared to the baseline method only using FFN ("w/ only FFN"), using the proposed FSAS in this baseline generates much better results, where the PSNR + +![](images/128744473ea93513c52c9e6aaca03d5db4eaed5dab1680adbcb53285d8cc145f.jpg) +(a) Blurred image + +![](images/3e3b5a814b68060738f41b8369376727d3b9954da72fc4bd54537963a2f858f9.jpg) +(b) Spatial domain + +![](images/a09b6e556183a636be7de6bc7ae3dac3c187d276d22570a8c0606e42796702be.jpg) +(c) Frequency domain + +![](images/0e5595647369251d3eafb9c3a0f474e71046c0dd0aa2f185ede665a5be135523.jpg) +Figure 6. Effectiveness of the scaled dot-product attention computation in the spatial and frequency domains. Computing the scaled dot-product attention using the FSAS in the frequency domain generates a clearer image. +(a) Blurred image + +![](images/fb580b54fa2a0c13ad823e6d133fb5efcd1a24cda044c0c651657a2d85ced954.jpg) +(b) Ours w/o FSAS + +![](images/8d9059818c7eb609503c6ae9fe30d1af6a1cbd6903897d1c50bd88b0d2b230e8.jpg) +(c) Ours + +![](images/cb6773d0a2ac0879dd7ecc3e4bde89d173391e410ef5283f4845a13d96c44d3e.jpg) +Figure 7. Effectiveness of the proposed FSAS on image deblurring. Using the proposed FSAS generates a clearer image. +(a) Blurred image +Figure 8. Effectiveness of the proposed DFFN on image deblurring. value is $0.42\mathrm{dB}$ higher (see comparisons of "w/ only FFN" and "FSAS+FFN" in Table 5). The visual comparisons in Figure 7(b) and (c) further demonstrate that using the proposed FSAS facilitates the blur removal well, where the boundaries are recovered well as shown in Figure 7(c). + +![](images/3038c7f3e5e6817a02120af391b0c76ae080dc2586e5ab35e3143fa5d4ec4b7e.jpg) +(b) w/ only FFN + +![](images/4594999a5bdbad73cc23f5ec41413962eed7a6febcf2ca4c72a1bf92a16795fd.jpg) +(c) w/ only DFFN + +Effect of DFFN. The proposed DFFN is used to discriminatively estimate useful frequency information for latent clear image restoration. To demonstrate its effectiveness on image deblurring, we compare the proposed method with two baselines. For the first baseline, we compare the proposed method only using the DFFN (w/ only DFFN for short) and the proposed method only using the original FFN (w/ only FFN for short). For the second baseline, we compare the proposed method with the one that replaces the DFFN with the original FFN in the proposed method (FSAS+FFN). The comparisons of "w/ only DFFN" and "w/ only FFN" in Table 5 show that using the proposed DFFN generates better results, where the PSNR value is 0.36dB higher. + +In addition, the comparisons of "FSAS+FFN" and "F-SAS+DFFN" in Table 5 show that using the proposed DFFN further improves the performance. + +Figure 8 shows the visualization results by these above mentioned baseline methods. Using the proposed DFFN generates better deblurred images, where the windows are + +Table 6. Quantitative evaluations of the asymmetric encoder-decoder network on the GoPro dataset. + +
MethodsFSAS in enc&decFSAS in dec (Ours)
PSNRs33.5633.73
SSIMs0.96530.9663
+ +![](images/1effbcebb58a0780dc4cc518e38985e51e55680c0acdc5f20373cb17745fd224.jpg) +(a) Blurred image +Figure 9. Effectiveness of the asymmetric encoder-decoder network on image deblurring. + +![](images/87ab1364ba958b607ef74e3c489883d6b1d9a0d10c4905d59a964995abdd20db.jpg) +(b) FSAS in enc&dec + +![](images/1c9088dff19043022d2757d857bbd51981a983459a909d06ef3bf7c9171e7ff1.jpg) +(c) FSAS in dec (Ours) + +recovered well shown in Figure 8(c). + +Effect of the asymmetric encoder-decoder network. As demonstrated in Section 3.3, the shallow features extracted by encoder module usually contain blur effects that affect the estimations of FSAS. We thus embed it into the decoder module, which leads to an asymmetric encoder-decoder network for better image deblurring. To examine the effect of this network design, we compare the network that puts the FSAS into both the encoder and decoder modules ("FSAS in enc&dec" in Table 6). Table 6 shows that using the FSAS in the decoder module generates better results, where the PSNR value is at least 0.17dB higher. The visual comparisons in Figure 9(b) and (c) further demonstrate that using the FSAS in the decoder module generates better clear images. + +# 6. Conclusion + +Motivated by the convolution theorem, we have presented an effective and efficient method that explores the properties of Transformers for high-quality image deblurring. We have developed an efficient frequency domain-based self-attention solver (FSAS) to estimate the scaled dot-product attention by an element-wise product operation instead of the matrix multiplication in the spatial domain, where we show that the spatial complexity and the computational complexity are significantly reduced. We further propose a DFFN to discriminatively determine which low and high frequency information of the features should be preserved for latent clear image restoration. Moreover, we develop an asymmetrical network based on an encoder and decoder architecture, where the FSAS is only used in the decoder module for better image deblurring. By training our method in an end-to-end manner, we show that it performs favorably against the state-of-the-art approaches in terms of accuracy and efficiency. + +Acknowledgements. This work has been partly supported by the National Key R&D Program of China (No. 2018AAA0102001), the National Natural Science Foundation of China (Nos. U22B2049, 62272233, 61922043, U19B2040), and the Fundamental Research Funds for the Central Universities (No. 30920041109). + +# References + +[1] Nicolas Carion, Francisco Massa, Gabriel Synnaeve, Nicolas Usunier, Alexander Kirillov, and Sergey Zagoruyko. End-to-end object detection with transformers. In ECCV, 2020. 2 +[2] Hanting Chen, Yunhe Wang, Tianyu Guo, Chang Xu, Yiping Deng, Zhenhua Liu, Siwei Ma, Chunjing Xu, Chao Xu, and Wen Gao. Pre-trained image processing transformer. 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Our method is motivated by the convolution theorem that the correlation or convolution of two signals in the spatial domain is equivalent to an element-wise product of them in the frequency domain. This inspires us to develop an efficient frequency domain-based self-attention solver (FSAS) to estimate the scaled dot-product attention by an element-wise product operation instead of the matrix multiplication in the spatial domain. In addition, we note that simply using the naive feed-forward network (FFN) in Transformers does not generate good deblurred results. To overcome this problem, we propose a simple yet effective discriminative frequency domain-based FFN (DFFN), where we introduce a gated mechanism in the FFN based on the Joint Photographic Experts Group (JPEG) compression algorithm to discriminatively determine which low- and high-frequency information of the features should be preserved for latent clear image restoration. We formulate the proposed FSAS and DFFN into an asymmetrical network based on an encoder and decoder architecture, where the FSAS is only used in the decoder module for better image deblurring. Experimental results show that the proposed method performs favorably against the state-of-the-art approaches." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 579, + 128, + 592 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 579, + 128, + 592 + ], + "spans": [ + { + "bbox": [ + 47, + 579, + 128, + 592 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 597, + 287, + 645 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 597, + 287, + 645 + ], + "spans": [ + { + "bbox": [ + 46, + 597, + 287, + 645 + ], + "type": "text", + "content": "Image deblurring aims to restore high-quality images from blurred ones. This problem has achieved significant progress due to the development of various effective deep models with large-scale training datasets." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 645, + 289, + 694 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 645, + 289, + 694 + ], + "spans": [ + { + "bbox": [ + 46, + 645, + 289, + 694 + ], + "type": "text", + "content": "Most state-of-the-art methods for image deblurring are mainly based on deep convolutional neural networks (CNNs). The main success of these methods is due to developing kinds of network architectural designs, for example, the multi-" + } + ] + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 305, + 243, + 548, + 399 + ], + "blocks": [ + { + "bbox": [ + 305, + 243, + 548, + 399 + ], + "lines": [ + { + "bbox": [ + 305, + 243, + 548, + 399 + ], + "spans": [ + { + "bbox": [ + 305, + 243, + 548, + 399 + ], + "type": "image", + "image_path": "b611b7e74183e61962acbb8c333c1d664239b3d51cf2a59c7c5217d79fcac314.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 402, + 547, + 446 + ], + "lines": [ + { + "bbox": [ + 304, + 402, + 547, + 446 + ], + "spans": [ + { + "bbox": [ + 304, + 402, + 547, + 446 + ], + "type": "text", + "content": "Figure 1. Comparisons of the proposed method and state-of-the-art ones on the GoPro dataset [16] in terms of accuracy, floating point operations (FLOPs), and network parameters. The circle size indicates the number of the network parameter." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 449, + 548, + 567 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 449, + 548, + 567 + ], + "spans": [ + { + "bbox": [ + 304, + 449, + 548, + 567 + ], + "type": "text", + "content": "scale [4, 16, 22] or multi-stage [31, 32] network architectures, generative adversarial learning [11, 12], physics model inspired network structures [6-8, 17, 33], and so on. As the basic operation in these networks, the convolution operation is a spatially-invariant local operation, which does not model the spatially variant properties of the image contents. Most of them use larger and deeper models to remedy the limitation of the convolution. However, simply increasing the capacity of deep models does not always lead to better performance as shown in [17, 33]." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 570, + 548, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 548, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 548, + 714 + ], + "type": "text", + "content": "Different from the convolution operation that models the local connectivity, Transformers are able to model the global contexts by computing the correlations of one token to all other tokens. They have been shown to be an effective approach in lots of high-level vision tasks and also have great potential to be the alternatives of deep CNN models. In image deblurring, the methods based on Transformers [27, 30] also achieve better performance than the CNN-based methods. However, the computation of the scaled dot-product attention in Transformers leads to quadratic space and time complexity in terms of the number of tokens. Although using smaller and fewer tokens can reduce the space and" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 57, + 702, + 241, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 57, + 702, + 241, + 713 + ], + "spans": [ + { + "bbox": [ + 57, + 702, + 241, + 713 + ], + "type": "text", + "content": "*Corresponding author: Jiangxin Dong and Jinshan Pan." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 295, + 748, + 316, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 316, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 316, + 757 + ], + "type": "text", + "content": "5886" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 120 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 120 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 120 + ], + "type": "text", + "content": "time complexity, such strategy cannot model the long-range information of features well and usually leads to significant artifacts when handling high-resolution images, which thus limits the performance improvement." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 122, + 288, + 229 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 122, + 288, + 229 + ], + "spans": [ + { + "bbox": [ + 46, + 122, + 288, + 229 + ], + "type": "text", + "content": "To alleviate this problem, most approaches use the down-sampling strategy to reduce the spatial resolution of features [26]. However, reducing the spatial resolution of features will cause information loss and thus affect the image deblurring. Several methods reduce the computational cost by computing the scaled dot-product attention in terms of the number of features [29, 30]. Although the computational cost is reduced, the spatial information is well not explored, which may affect the deblurring performance." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 231, + 288, + 422 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 231, + 288, + 422 + ], + "spans": [ + { + "bbox": [ + 46, + 231, + 288, + 422 + ], + "type": "text", + "content": "In this paper, we develop an effective and efficient method that explores the properties of Transformers for high-quality image deblurring. We note that the scaled dot-product attention computation is actually to estimate the correlation of one token from the query and all the tokens from the key. This process can be achieved by a convolution operation when rearranging the permutations of tokens. Based on this observation and the convolution theorem that the convolution in the spatial domain equals a point-wise multiplication in the frequency domain, we develop an efficient frequency domain-based self-attention solver (FSAS) to estimate the scaled dot-product attention by an element-wise product operation instead of the matrix multiplication. Therefore, the space and time complexity can be reduced to " + }, + { + "bbox": [ + 46, + 231, + 288, + 422 + ], + "type": "inline_equation", + "content": "O(N)" + }, + { + "bbox": [ + 46, + 231, + 288, + 422 + ], + "type": "inline_equation", + "content": "O(N\\log N)" + }, + { + "bbox": [ + 46, + 231, + 288, + 422 + ], + "type": "text", + "content": " for each feature channel, where " + }, + { + "bbox": [ + 46, + 231, + 288, + 422 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 231, + 288, + 422 + ], + "type": "text", + "content": " is the number of the pixels." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 425, + 287, + 544 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 425, + 287, + 544 + ], + "spans": [ + { + "bbox": [ + 46, + 425, + 287, + 544 + ], + "type": "text", + "content": "In addition, we note that simply using the feed-forward network (FFN) by [30] does not generate good deblurred results. To generate better features for latent clear image restoration, we develop a simple yet effective discriminative frequency domain-based FFN (DFFN). Our DFFN is motivated by the Joint Photographic Experts Group (JPEG) compression algorithm. It introduces a gated mechanism in the FFN to discriminatively determine which low- and high-frequency information should be preserved for latent clear image restoration." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "content": "We formulate the proposed FSAS and DFFN into an end-to-end trainable network based on an encoder and decoder architecture to solve image deblurring. However, we find that as features of shallow layers usually contain blur effects, applying the scaled dot-product attention to shallow features does not effectively explore global clear contents. As the features from deep layers are usually clearer than those from shallow layers, we develop an asymmetric network architecture, where the FSAS is only used in the decoder module for better image deblurring. We analyze that the exploring properties of Transformers in the frequency domain is able to facilitate blur removal. Experimental results demonstrate that the proposed method generates favorable results against state-of-the-art methods in terms of accuracy and efficiency" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 306, + 72, + 351, + 84 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 72, + 351, + 84 + ], + "spans": [ + { + "bbox": [ + 306, + 72, + 351, + 84 + ], + "type": "text", + "content": "(Figure 1)." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 316, + 85, + 547, + 311 + ], + "type": "list", + "angle": 0, + "index": 11, + "blocks": [ + { + "bbox": [ + 317, + 85, + 525, + 95 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 85, + 525, + 95 + ], + "spans": [ + { + "bbox": [ + 317, + 85, + 525, + 95 + ], + "type": "text", + "content": "The main contributions are summarized as follows:" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 316, + 96, + 547, + 156 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 316, + 96, + 547, + 156 + ], + "spans": [ + { + "bbox": [ + 316, + 96, + 547, + 156 + ], + "type": "text", + "content": "- We develop an efficient frequency domain-based self-attention solver to estimate the scaled dot-product attention. Our analysis demonstrates that using the frequency domain-based solver reduces the space and time complexity and is much more effective and efficient." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 316, + 156, + 547, + 215 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 316, + 156, + 547, + 215 + ], + "spans": [ + { + "bbox": [ + 316, + 156, + 547, + 215 + ], + "type": "text", + "content": "- We propose a simple yet effective discriminative frequency domain-based FFN based on the JPEG compression algorithm to discriminatively determine which low and high-frequency information should be preserved for latent clear image restoration." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 316, + 216, + 547, + 262 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 316, + 216, + 547, + 262 + ], + "spans": [ + { + "bbox": [ + 316, + 216, + 547, + 262 + ], + "type": "text", + "content": "- We develop an asymmetric network architecture based on an encoder and decoder network, where the frequency domain-based self-attention solver is only used in the decoder module for better image deblurring." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 316, + 264, + 547, + 311 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 316, + 264, + 547, + 311 + ], + "spans": [ + { + "bbox": [ + 316, + 264, + 547, + 311 + ], + "type": "text", + "content": "- We analyze that the exploring properties of Transformers in the frequency domain is able to facilitate blur removal and show that our approach performs favorably against state-of-the-art methods." + } + ] + } + ], + "index": 10 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 306, + 316, + 392, + 327 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 316, + 392, + 327 + ], + "spans": [ + { + "bbox": [ + 306, + 316, + 392, + 327 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 332, + 547, + 451 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 332, + 547, + 451 + ], + "spans": [ + { + "bbox": [ + 304, + 332, + 547, + 451 + ], + "type": "text", + "content": "Deep CNN-based Image deblurring methods. In recent years, we have witnessed significant advances in image deblurring due to the development of different deep CNN models [3, 4, 9, 16, 22, 31, 32]. In [16], Nah et al. propose a deep CNN based on a multi-scale framework to directly estimate clear images from blurred ones. To better utilize the information of each scale in multi-scale framework, Tao et al. [22] develop an effective scale recurrent network. Gao et al. [9] propose a selective network parameter sharing method to improve [16, 22]." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 452, + 547, + 606 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 452, + 547, + 606 + ], + "spans": [ + { + "bbox": [ + 304, + 452, + 547, + 606 + ], + "type": "text", + "content": "As using more scales does not improve the performance significantly, Zhang et al. [32] develop an effective network based on multi-patch strategy. The deblurring process is achieved stage by stage. To better explore the features from different stages, Zamir et al. [31] propose a cross-stage feature fusion for better performance. In order to reduce the computational cost of the methods based on multi-scale framework, Cho et al. [4] present a multi-input and multi-output network. Chen et al. [3] analyze the baseline modules and simplify them for better image restoration. As demonstrated in [30], the convolution operation is spatial invariant and does not effectively model the global contexts for image deblurring." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 605, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 547, + 713 + ], + "type": "text", + "content": "Transformers and their applications to image deblurring. As the Transformer [25] can model the global contexts and achieves significant progress in lots of high-level vision tasks (e.g., image classification [14], object detection [1, 34] and semantic segmentation [28, 35]), it has been developed to solve image super-resolution [13], image deblurring [24, 30] and image denoise [2, 27]. To reduce the computational cost of Transformer, Zamir et al. [30] propose an efficient Transformer model by computing the scaled dot-product attention" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "5887" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 239 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 239 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 239 + ], + "type": "text", + "content": "in the feature depth domain. This method can effectively explore information from different features along the channel dimension. However, the spatial information that is vital for image restoration is not fully explored. Tsai et al. [24] simplify the calculation of self-attention by constructing intra and inter strip tokens to replace the global attention. Wang et al. [27] propose a Transformer based on a UNet which uses non-overlapping window-based self-attention for single image deblurring. Although using the splitting strategy reduces the computational cost, the coarse splitting does not fully explore the information of each patch. Moreover, the scaled dot-product attention in these methods usually needs the complex matrix multiplication whose the space and time complexity is quadratic." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 239, + 287, + 288 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 239, + 287, + 288 + ], + "spans": [ + { + "bbox": [ + 46, + 239, + 287, + 288 + ], + "type": "text", + "content": "Different from these methods, we develop an efficient Transformer-based method that explores the property of the frequency domain to avoid the complex matrix multiplication for the scaled dot-product attention." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 293, + 153, + 306 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 293, + 153, + 306 + ], + "spans": [ + { + "bbox": [ + 47, + 293, + 153, + 306 + ], + "type": "text", + "content": "3. Proposed Method" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 311, + 289, + 491 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 311, + 289, + 491 + ], + "spans": [ + { + "bbox": [ + 46, + 311, + 289, + 491 + ], + "type": "text", + "content": "Our goal is to present an effective and efficient method to explore the properties of Transformers for high-quality image deblurring. To this end, we first develop an efficient frequency domain-based self-attention solver to estimate the scaled dot-product attention. To refine the features estimated by the frequency domain-based solver, we further develop a discriminative frequency domain-based feed-forward network. We formulate these above approaches into an end-to-end trainable network based on an encoder and decoder architecture to solve image deblurring, where the frequency domain-based self-attention solver for the estimation of the scaled dot-product attention is used in the decoder module for better feature representation. Figure 2(a) shows the overview of the proposed method. In the following, we present the details of each component." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 496, + 284, + 509 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 496, + 284, + 509 + ], + "spans": [ + { + "bbox": [ + 47, + 496, + 284, + 509 + ], + "type": "text", + "content": "3.1. Frequency domain-based self-attention solver" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 511, + 289, + 619 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 511, + 289, + 619 + ], + "spans": [ + { + "bbox": [ + 47, + 511, + 289, + 619 + ], + "type": "text", + "content": "Given the input feature " + }, + { + "bbox": [ + 47, + 511, + 289, + 619 + ], + "type": "inline_equation", + "content": "X" + }, + { + "bbox": [ + 47, + 511, + 289, + 619 + ], + "type": "text", + "content": " with a spatial resolution of " + }, + { + "bbox": [ + 47, + 511, + 289, + 619 + ], + "type": "inline_equation", + "content": "H\\times W" + }, + { + "bbox": [ + 47, + 511, + 289, + 619 + ], + "type": "text", + "content": " pixels and " + }, + { + "bbox": [ + 47, + 511, + 289, + 619 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 47, + 511, + 289, + 619 + ], + "type": "text", + "content": " channels, existing vision Transformers usually first compute the features " + }, + { + "bbox": [ + 47, + 511, + 289, + 619 + ], + "type": "inline_equation", + "content": "F_{q},F_{k}" + }, + { + "bbox": [ + 47, + 511, + 289, + 619 + ], + "type": "text", + "content": " ,and " + }, + { + "bbox": [ + 47, + 511, + 289, + 619 + ], + "type": "inline_equation", + "content": "F_{v}" + }, + { + "bbox": [ + 47, + 511, + 289, + 619 + ], + "type": "text", + "content": " by applying linear transformations " + }, + { + "bbox": [ + 47, + 511, + 289, + 619 + ], + "type": "inline_equation", + "content": "W_{q}" + }, + { + "bbox": [ + 47, + 511, + 289, + 619 + ], + "type": "inline_equation", + "content": "W_{k}" + }, + { + "bbox": [ + 47, + 511, + 289, + 619 + ], + "type": "text", + "content": " ,and " + }, + { + "bbox": [ + 47, + 511, + 289, + 619 + ], + "type": "inline_equation", + "content": "W_{v}" + }, + { + "bbox": [ + 47, + 511, + 289, + 619 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 47, + 511, + 289, + 619 + ], + "type": "inline_equation", + "content": "X" + }, + { + "bbox": [ + 47, + 511, + 289, + 619 + ], + "type": "text", + "content": " . Then, they apply the unfolding function to the features " + }, + { + "bbox": [ + 47, + 511, + 289, + 619 + ], + "type": "inline_equation", + "content": "F_{q},F_{k}" + }, + { + "bbox": [ + 47, + 511, + 289, + 619 + ], + "type": "text", + "content": " ,and " + }, + { + "bbox": [ + 47, + 511, + 289, + 619 + ], + "type": "inline_equation", + "content": "F_{v}" + }, + { + "bbox": [ + 47, + 511, + 289, + 619 + ], + "type": "text", + "content": " to extract image patches " + }, + { + "bbox": [ + 47, + 511, + 289, + 619 + ], + "type": "inline_equation", + "content": "\\{q_i\\}_{i = 1}^N,\\{k_i\\}_{i = 1}^N" + }, + { + "bbox": [ + 47, + 511, + 289, + 619 + ], + "type": "text", + "content": " ,and " + }, + { + "bbox": [ + 47, + 511, + 289, + 619 + ], + "type": "inline_equation", + "content": "\\{v_i\\}_{i = 1}^N" + }, + { + "bbox": [ + 47, + 511, + 289, + 619 + ], + "type": "text", + "content": " ,where " + }, + { + "bbox": [ + 47, + 511, + 289, + 619 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 47, + 511, + 289, + 619 + ], + "type": "text", + "content": " denotes the number of extracted patches. By applying a reshape operation to the extracted patches, the query Q, key K, and value V can be obtained by:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 51, + 628, + 287, + 653 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 51, + 628, + 287, + 653 + ], + "spans": [ + { + "bbox": [ + 51, + 628, + 287, + 653 + ], + "type": "interline_equation", + "content": "\\mathbf {Q} = \\mathcal {R} \\left(\\left\\{q _ {i} \\right\\} _ {i = 1} ^ {N}\\right), \\mathbf {K} = \\mathcal {R} \\left(\\left\\{k _ {i} \\right\\} _ {i = 1} ^ {N}\\right), \\mathbf {V} = \\mathcal {R} \\left(\\left\\{v _ {i} \\right\\} _ {i = 1} ^ {N}\\right), \\tag {1}", + "image_path": "bae8e7fa604d2cbe13fd0df511386ab95b0d682211129df47d3c544793aa008c.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 654, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 654, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 47, + 654, + 287, + 714 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 654, + 287, + 714 + ], + "type": "inline_equation", + "content": "\\mathcal{R}" + }, + { + "bbox": [ + 47, + 654, + 287, + 714 + ], + "type": "text", + "content": " denotes the reshape function which ensures that " + }, + { + "bbox": [ + 47, + 654, + 287, + 714 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{K},\\mathbf{Q},\\mathbf{V}\\} \\in R^{N\\times (CH_pW_p)}" + }, + { + "bbox": [ + 47, + 654, + 287, + 714 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 654, + 287, + 714 + ], + "type": "inline_equation", + "content": "H_{p}" + }, + { + "bbox": [ + 47, + 654, + 287, + 714 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 654, + 287, + 714 + ], + "type": "inline_equation", + "content": "W_{p}" + }, + { + "bbox": [ + 47, + 654, + 287, + 714 + ], + "type": "text", + "content": " denote the height and width of extracted patches. Based on the obtained query " + }, + { + "bbox": [ + 47, + 654, + 287, + 714 + ], + "type": "inline_equation", + "content": "\\mathbf{Q}" + }, + { + "bbox": [ + 47, + 654, + 287, + 714 + ], + "type": "text", + "content": ", key " + }, + { + "bbox": [ + 47, + 654, + 287, + 714 + ], + "type": "inline_equation", + "content": "\\mathbf{K}" + }, + { + "bbox": [ + 47, + 654, + 287, + 714 + ], + "type": "text", + "content": ", and value " + }, + { + "bbox": [ + 47, + 654, + 287, + 714 + ], + "type": "inline_equation", + "content": "\\mathbf{V}" + }, + { + "bbox": [ + 47, + 654, + 287, + 714 + ], + "type": "text", + "content": ", the scaled dot-product attention is achieved by:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 354, + 70, + 545, + 102 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 354, + 70, + 545, + 102 + ], + "spans": [ + { + "bbox": [ + 354, + 70, + 545, + 102 + ], + "type": "interline_equation", + "content": "V _ {a t t} = \\operatorname {s o f t m a x} \\left(\\frac {\\mathbf {Q K} ^ {\\top}}{\\sqrt {C H _ {p} W _ {p}}}\\right) V. \\tag {2}", + "image_path": "dee0f90ab640a9d9914bcdbfcb5073e830cb3b5589f4162e414e5b6a357fc208.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 106, + 547, + 213 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 106, + 547, + 213 + ], + "spans": [ + { + "bbox": [ + 304, + 106, + 547, + 213 + ], + "type": "text", + "content": "The attention map computation involves the matrix multiplication of " + }, + { + "bbox": [ + 304, + 106, + 547, + 213 + ], + "type": "inline_equation", + "content": "\\mathbf{Q}\\mathbf{K}^{\\top}" + }, + { + "bbox": [ + 304, + 106, + 547, + 213 + ], + "type": "text", + "content": " whose space complexity and time complexity are " + }, + { + "bbox": [ + 304, + 106, + 547, + 213 + ], + "type": "inline_equation", + "content": "O(N^{2})" + }, + { + "bbox": [ + 304, + 106, + 547, + 213 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 106, + 547, + 213 + ], + "type": "inline_equation", + "content": "O(N^{2}C)" + }, + { + "bbox": [ + 304, + 106, + 547, + 213 + ], + "type": "text", + "content": ". It is not affordable if the image resolution and the number of the extracted patches are large. Although using downsampling operation to reduce the image resolution or non-overlapping method to extract fewer patches will alleviate the problem, these strategies would lead to information loss and limit the ability to model details within and across each patch [29]." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 213, + 545, + 237 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 213, + 545, + 237 + ], + "spans": [ + { + "bbox": [ + 305, + 213, + 545, + 237 + ], + "type": "text", + "content": "We note that each element of " + }, + { + "bbox": [ + 305, + 213, + 545, + 237 + ], + "type": "inline_equation", + "content": "\\mathbf{Q}\\mathbf{K}^{\\top}" + }, + { + "bbox": [ + 305, + 213, + 545, + 237 + ], + "type": "text", + "content": " is obtained by the inner product:" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 379, + 242, + 545, + 264 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 379, + 242, + 545, + 264 + ], + "spans": [ + { + "bbox": [ + 379, + 242, + 545, + 264 + ], + "type": "interline_equation", + "content": "\\left(\\mathbf {Q} \\mathbf {K} ^ {\\top}\\right) _ {i j} = \\langle \\mathbf {q} _ {i}, \\mathbf {k} _ {j} \\rangle , \\tag {3}", + "image_path": "2c41f16d9dda31e8e219f0ea02dadebaa5a2f61dc82f9cf90cb54f68aeca8ad1.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 267, + 547, + 341 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 267, + 547, + 341 + ], + "spans": [ + { + "bbox": [ + 304, + 267, + 547, + 341 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 267, + 547, + 341 + ], + "type": "inline_equation", + "content": "\\mathbf{q}_i" + }, + { + "bbox": [ + 304, + 267, + 547, + 341 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 267, + 547, + 341 + ], + "type": "inline_equation", + "content": "\\mathbf{k}_j" + }, + { + "bbox": [ + 304, + 267, + 547, + 341 + ], + "type": "text", + "content": " are the vectorized forms of " + }, + { + "bbox": [ + 304, + 267, + 547, + 341 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 304, + 267, + 547, + 341 + ], + "type": "text", + "content": "-th and " + }, + { + "bbox": [ + 304, + 267, + 547, + 341 + ], + "type": "inline_equation", + "content": "j" + }, + { + "bbox": [ + 304, + 267, + 547, + 341 + ], + "type": "text", + "content": "-th patches from " + }, + { + "bbox": [ + 304, + 267, + 547, + 341 + ], + "type": "inline_equation", + "content": "F_{q}" + }, + { + "bbox": [ + 304, + 267, + 547, + 341 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 267, + 547, + 341 + ], + "type": "inline_equation", + "content": "F_{k}" + }, + { + "bbox": [ + 304, + 267, + 547, + 341 + ], + "type": "text", + "content": ". Based on (3), if we apply reshape functions to " + }, + { + "bbox": [ + 304, + 267, + 547, + 341 + ], + "type": "inline_equation", + "content": "\\mathbf{q}_i" + }, + { + "bbox": [ + 304, + 267, + 547, + 341 + ], + "type": "text", + "content": " and all the patches " + }, + { + "bbox": [ + 304, + 267, + 547, + 341 + ], + "type": "inline_equation", + "content": "\\mathbf{k}_j" + }, + { + "bbox": [ + 304, + 267, + 547, + 341 + ], + "type": "text", + "content": ", respectively, all the " + }, + { + "bbox": [ + 304, + 267, + 547, + 341 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 304, + 267, + 547, + 341 + ], + "type": "text", + "content": "-th column elements of " + }, + { + "bbox": [ + 304, + 267, + 547, + 341 + ], + "type": "inline_equation", + "content": "\\mathbf{QK}^{\\top}" + }, + { + "bbox": [ + 304, + 267, + 547, + 341 + ], + "type": "text", + "content": " can be obtained by a convolution operation, i.e., " + }, + { + "bbox": [ + 304, + 267, + 547, + 341 + ], + "type": "inline_equation", + "content": "\\widetilde{q}_i \\otimes \\widetilde{K}" + }, + { + "bbox": [ + 304, + 267, + 547, + 341 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 267, + 547, + 341 + ], + "type": "inline_equation", + "content": "\\widetilde{q}_i" + }, + { + "bbox": [ + 304, + 267, + 547, + 341 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 267, + 547, + 341 + ], + "type": "inline_equation", + "content": "\\widetilde{K}" + }, + { + "bbox": [ + 304, + 267, + 547, + 341 + ], + "type": "text", + "content": " denote the reshaped results of " + }, + { + "bbox": [ + 304, + 267, + 547, + 341 + ], + "type": "inline_equation", + "content": "\\mathbf{q}_i" + }, + { + "bbox": [ + 304, + 267, + 547, + 341 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 267, + 547, + 341 + ], + "type": "inline_equation", + "content": "\\mathbf{k}_j" + }, + { + "bbox": [ + 304, + 267, + 547, + 341 + ], + "type": "text", + "content": "; " + }, + { + "bbox": [ + 304, + 267, + 547, + 341 + ], + "type": "inline_equation", + "content": "\\otimes" + }, + { + "bbox": [ + 304, + 267, + 547, + 341 + ], + "type": "text", + "content": " denotes the convolution operation." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 341, + 547, + 424 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 341, + 547, + 424 + ], + "spans": [ + { + "bbox": [ + 304, + 341, + 547, + 424 + ], + "type": "text", + "content": "According to the convolution theorem, the correlation or convolution of two signals in the spatial domain is equivalent to an element-wise product of them in the frequency domain. Therefore, a natural question is that can we efficiently estimate the attention map by an element-wise product operation in a frequency domain instead of computing the matrix multiplication of " + }, + { + "bbox": [ + 304, + 341, + 547, + 424 + ], + "type": "inline_equation", + "content": "\\mathbf{Q}\\mathbf{K}^{\\top}" + }, + { + "bbox": [ + 304, + 341, + 547, + 424 + ], + "type": "text", + "content": " in the spatial domain?" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 425, + 547, + 496 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 425, + 547, + 496 + ], + "spans": [ + { + "bbox": [ + 305, + 425, + 547, + 496 + ], + "type": "text", + "content": "To this end, we develop an effective frequency domain-based self-attention solver. Specifically, we first obtain " + }, + { + "bbox": [ + 305, + 425, + 547, + 496 + ], + "type": "inline_equation", + "content": "F_{q}" + }, + { + "bbox": [ + 305, + 425, + 547, + 496 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 305, + 425, + 547, + 496 + ], + "type": "inline_equation", + "content": "F_{k}" + }, + { + "bbox": [ + 305, + 425, + 547, + 496 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 305, + 425, + 547, + 496 + ], + "type": "inline_equation", + "content": "F_{v}" + }, + { + "bbox": [ + 305, + 425, + 547, + 496 + ], + "type": "text", + "content": " by a " + }, + { + "bbox": [ + 305, + 425, + 547, + 496 + ], + "type": "inline_equation", + "content": "1 \\times 1" + }, + { + "bbox": [ + 305, + 425, + 547, + 496 + ], + "type": "text", + "content": " point-wise convolution and " + }, + { + "bbox": [ + 305, + 425, + 547, + 496 + ], + "type": "inline_equation", + "content": "3 \\times 3" + }, + { + "bbox": [ + 305, + 425, + 547, + 496 + ], + "type": "text", + "content": " depth-wise convolution. Then, we apply the fast Fourier transform (FFT) to the estimated features " + }, + { + "bbox": [ + 305, + 425, + 547, + 496 + ], + "type": "inline_equation", + "content": "F_{q}" + }, + { + "bbox": [ + 305, + 425, + 547, + 496 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 425, + 547, + 496 + ], + "type": "inline_equation", + "content": "F_{k}" + }, + { + "bbox": [ + 305, + 425, + 547, + 496 + ], + "type": "text", + "content": " and estimate the correlation of " + }, + { + "bbox": [ + 305, + 425, + 547, + 496 + ], + "type": "inline_equation", + "content": "F_{q}" + }, + { + "bbox": [ + 305, + 425, + 547, + 496 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 425, + 547, + 496 + ], + "type": "inline_equation", + "content": "F_{k}" + }, + { + "bbox": [ + 305, + 425, + 547, + 496 + ], + "type": "text", + "content": " in the frequency domain by:" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 367, + 502, + 545, + 521 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 367, + 502, + 545, + 521 + ], + "spans": [ + { + "bbox": [ + 367, + 502, + 545, + 521 + ], + "type": "interline_equation", + "content": "A = \\mathcal {F} ^ {- 1} \\left(\\mathcal {F} \\left(F _ {q}\\right) \\overline {{\\mathcal {F} \\left(F _ {k}\\right)}}\\right), \\tag {4}", + "image_path": "1fd755aab566aa8f919ad98703cfac2c37365c43a756bb4614787e39d3223481.jpg" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 526, + 547, + 563 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 526, + 547, + 563 + ], + "spans": [ + { + "bbox": [ + 304, + 526, + 547, + 563 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 526, + 547, + 563 + ], + "type": "inline_equation", + "content": "\\mathcal{F}(\\cdot)" + }, + { + "bbox": [ + 304, + 526, + 547, + 563 + ], + "type": "text", + "content": " denotes the FFT, " + }, + { + "bbox": [ + 304, + 526, + 547, + 563 + ], + "type": "inline_equation", + "content": "\\mathcal{F}^{-1}(\\cdot)" + }, + { + "bbox": [ + 304, + 526, + 547, + 563 + ], + "type": "text", + "content": " denotes the inverse FFT, and " + }, + { + "bbox": [ + 304, + 526, + 547, + 563 + ], + "type": "inline_equation", + "content": "\\overline{\\mathcal{F}(\\cdot)}" + }, + { + "bbox": [ + 304, + 526, + 547, + 563 + ], + "type": "text", + "content": " denotes the conjugate transpose operation. Finally, we estimate the aggregated feature by:" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 389, + 568, + 545, + 581 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 389, + 568, + 545, + 581 + ], + "spans": [ + { + "bbox": [ + 389, + 568, + 545, + 581 + ], + "type": "interline_equation", + "content": "V _ {a t t} = \\mathcal {L} (A) F _ {v}, \\tag {5}", + "image_path": "c2bb1ffa54f09e98b651c30688c417f716731b376f7f7a0efa50b4e9b91868b5.jpg" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 586, + 545, + 610 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 586, + 545, + 610 + ], + "spans": [ + { + "bbox": [ + 304, + 586, + 545, + 610 + ], + "type": "text", + "content": "where a layer norm " + }, + { + "bbox": [ + 304, + 586, + 545, + 610 + ], + "type": "inline_equation", + "content": "\\mathcal{L}(\\cdot)" + }, + { + "bbox": [ + 304, + 586, + 545, + 610 + ], + "type": "text", + "content": " is used to normalize " + }, + { + "bbox": [ + 304, + 586, + 545, + 610 + ], + "type": "inline_equation", + "content": "A" + }, + { + "bbox": [ + 304, + 586, + 545, + 610 + ], + "type": "text", + "content": ". Finally, we generate the output feature of FSAS by:" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 365, + 616, + 545, + 628 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 365, + 616, + 545, + 628 + ], + "spans": [ + { + "bbox": [ + 365, + 616, + 545, + 628 + ], + "type": "interline_equation", + "content": "X _ {a t t} = X + \\operatorname {C o n v} _ {1 \\times 1} \\left(V _ {a t t}\\right), \\tag {6}", + "image_path": "6674d806c87580daa534e3b4fe208c2fc914c1729fcb13dd21adc7115a0a2d9f.jpg" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 633, + 547, + 670 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 633, + 547, + 670 + ], + "spans": [ + { + "bbox": [ + 304, + 633, + 547, + 670 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 633, + 547, + 670 + ], + "type": "inline_equation", + "content": "\\mathrm{Conv}_{1\\times 1}(\\cdot)" + }, + { + "bbox": [ + 304, + 633, + 547, + 670 + ], + "type": "text", + "content": " denotes a convolution with filter size of " + }, + { + "bbox": [ + 304, + 633, + 547, + 670 + ], + "type": "inline_equation", + "content": "1\\times 1" + }, + { + "bbox": [ + 304, + 633, + 547, + 670 + ], + "type": "text", + "content": " pixel. The detailed network architecture of the proposed FSAS is shown in Figure 2(b)." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 306, + 673, + 539, + 686 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 673, + 539, + 686 + ], + "spans": [ + { + "bbox": [ + 306, + 673, + 539, + 686 + ], + "type": "text", + "content": "3.2. Discriminative frequency domain-based FFN" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "type": "text", + "content": "The FFN is used to improve the features by the scaled dot-product attention. Thus, it is important to develop an" + } + ] + } + ], + "index": 22 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "5888" + } + ] + } + ], + "index": 23 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 62, + 70, + 281, + 249 + ], + "blocks": [ + { + "bbox": [ + 62, + 70, + 281, + 249 + ], + "lines": [ + { + "bbox": [ + 62, + 70, + 281, + 249 + ], + "spans": [ + { + "bbox": [ + 62, + 70, + 281, + 249 + ], + "type": "image", + "image_path": "449efbfdd40dfc847e99bfd25a9c3177a45ac771dcdc69d13ec61095b0173f50.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 249, + 545, + 271 + ], + "lines": [ + { + "bbox": [ + 46, + 249, + 545, + 271 + ], + "spans": [ + { + "bbox": [ + 46, + 249, + 545, + 271 + ], + "type": "text", + "content": "Figure 2. Network architectures. (a) The proposed asymmetric encoder-decoder network that only contains DFFN in the encoder module and both FSAS and DFFN in the decoder module for image deblurring. (b) The proposed FSAS module. (c) The proposed DFFN module." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 284, + 69, + 389, + 249 + ], + "blocks": [ + { + "bbox": [ + 284, + 69, + 389, + 249 + ], + "lines": [ + { + "bbox": [ + 284, + 69, + 389, + 249 + ], + "spans": [ + { + "bbox": [ + 284, + 69, + 389, + 249 + ], + "type": "image", + "image_path": "9617f88a384dc068920468f0db287e28971a8e1a2e0576f0eead493a72a69c4b.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 392, + 70, + 530, + 249 + ], + "blocks": [ + { + "bbox": [ + 392, + 70, + 530, + 249 + ], + "lines": [ + { + "bbox": [ + 392, + 70, + 530, + 249 + ], + "spans": [ + { + "bbox": [ + 392, + 70, + 530, + 249 + ], + "type": "image", + "image_path": "d217644bdbccaee5334259ea53062598d2f112272bebdf1c89f90499f919085a.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 275, + 290, + 407 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 275, + 290, + 407 + ], + "spans": [ + { + "bbox": [ + 46, + 275, + 290, + 407 + ], + "type": "text", + "content": "effective FFN to generate the features that facilitate the latent clear image reconstruction. As not all the low-frequency information and high-frequency information help latent clear image restoration, we develop a DFFN that can adaptively determine which frequency information should be preserved. However, how to effectively determine which frequency information is important. Motivated by the JPEG compression algorithm, we introduce a learnable quantization matrix " + }, + { + "bbox": [ + 46, + 275, + 290, + 407 + ], + "type": "inline_equation", + "content": "\\mathbf{W}" + }, + { + "bbox": [ + 46, + 275, + 290, + 407 + ], + "type": "text", + "content": " and learn it by an inverse method of JPEG compression to determine which frequency information should be preserved. The proposed DFFN can be formulated by:" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 102, + 409, + 211, + 422 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 102, + 409, + 211, + 422 + ], + "spans": [ + { + "bbox": [ + 102, + 409, + 211, + 422 + ], + "type": "interline_equation", + "content": "X _ {1} = \\operatorname {C o n v} _ {1 \\times 1} (\\mathcal {L} (X _ {\\text {a t t}}))", + "image_path": "c155ed2d3144425ee6a0485d1c0d792f5a7c3d1eebf6b7da0e57554322ce6af0.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 104, + 425, + 287, + 446 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 104, + 425, + 287, + 446 + ], + "spans": [ + { + "bbox": [ + 104, + 425, + 287, + 446 + ], + "type": "interline_equation", + "content": "X _ {1} ^ {f} = \\mathcal {F} \\left(\\mathcal {P} \\left(X _ {1}\\right)\\right) \\tag {7}", + "image_path": "31b4288d139da40dec1b5fcfaa2634c0f224e28d5b7890e81e38e6bbcf1fec7b.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 104, + 442, + 185, + 457 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 104, + 442, + 185, + 457 + ], + "spans": [ + { + "bbox": [ + 104, + 442, + 185, + 457 + ], + "type": "interline_equation", + "content": "X _ {2} = \\mathcal {F} ^ {- 1} \\left(\\mathbf {W} X _ {1} ^ {f}\\right)", + "image_path": "014919a4d71d9237ec19a86066d7b0b55f6cbc7129f9cb38febf74417016768a.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 104, + 459, + 230, + 474 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 104, + 459, + 230, + 474 + ], + "spans": [ + { + "bbox": [ + 104, + 459, + 230, + 474 + ], + "type": "interline_equation", + "content": "X _ {o u t} = \\mathcal {G} \\left(\\mathcal {P} ^ {- 1} \\left(X _ {2}\\right)\\right) + X _ {a t t},", + "image_path": "14c8a28befe48ee7d51d4dce82f4633272a4aa95a69bb510b0276b2294e2af2e.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 482, + 287, + 530 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 482, + 287, + 530 + ], + "spans": [ + { + "bbox": [ + 46, + 482, + 287, + 530 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 482, + 287, + 530 + ], + "type": "inline_equation", + "content": "\\mathcal{P}(\\cdot)" + }, + { + "bbox": [ + 46, + 482, + 287, + 530 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 482, + 287, + 530 + ], + "type": "inline_equation", + "content": "\\mathcal{P}^{-1}(\\cdot)" + }, + { + "bbox": [ + 46, + 482, + 287, + 530 + ], + "type": "text", + "content": " denote the patch unfolding and folding operations in the JPEG compression method; " + }, + { + "bbox": [ + 46, + 482, + 287, + 530 + ], + "type": "inline_equation", + "content": "\\mathcal{G}" + }, + { + "bbox": [ + 46, + 482, + 287, + 530 + ], + "type": "text", + "content": " denotes GEGLU function by [19]. The detailed network architecture of the proposed DFFN is shown in Figure 2(c)." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 532, + 249, + 544 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 532, + 249, + 544 + ], + "spans": [ + { + "bbox": [ + 47, + 532, + 249, + 544 + ], + "type": "text", + "content": "3.3. Asymmetric encoder-decoder network" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "content": "We embed the proposed FSAS and DFFN into a network based on an encoder and decoder architecture. We note that most existing methods usually use symmetric architectures in the encoder and decoder modules. For example, if the FSAS and DFFN are used in the encoder module, they are also used in the decoder module. We note that the features extracted by encoder module are shallow ones, which usually contain blur effects compared to the deep features from the decoder module. However, the blur usually changes similarity of two similar patches from clear features. Thus, using the FSAS in the encoder module may not estimate the similarity correctly, which accordingly affects image restoration. To overcome this problem, we embed the FSAS into the decoder module, which leads to an asymmetric architecture for better image" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 275, + 546, + 299 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 275, + 546, + 299 + ], + "spans": [ + { + "bbox": [ + 304, + 275, + 546, + 299 + ], + "type": "text", + "content": "deblurring. Figure 2(a) shows the network architecture of the proposed asymmetric encoder-decoder network." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 300, + 545, + 323 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 300, + 545, + 323 + ], + "spans": [ + { + "bbox": [ + 304, + 300, + 545, + 323 + ], + "type": "text", + "content": "Finally, given a blurred image " + }, + { + "bbox": [ + 304, + 300, + 545, + 323 + ], + "type": "inline_equation", + "content": "B" + }, + { + "bbox": [ + 304, + 300, + 545, + 323 + ], + "type": "text", + "content": ", the restored image " + }, + { + "bbox": [ + 304, + 300, + 545, + 323 + ], + "type": "inline_equation", + "content": "I" + }, + { + "bbox": [ + 304, + 300, + 545, + 323 + ], + "type": "text", + "content": " is estimated by the asymmetric encoder-decoder network:" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 391, + 328, + 545, + 342 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 391, + 328, + 545, + 342 + ], + "spans": [ + { + "bbox": [ + 391, + 328, + 545, + 342 + ], + "type": "interline_equation", + "content": "I = \\mathcal {N} (B) + B, \\tag {8}", + "image_path": "e9a0497f959fc34f83db2d9eb90ad84d197725d442542135d2fc20b4a13c149d.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 350, + 547, + 361 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 350, + 547, + 361 + ], + "spans": [ + { + "bbox": [ + 305, + 350, + 547, + 361 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 350, + 547, + 361 + ], + "type": "inline_equation", + "content": "\\mathcal{N}" + }, + { + "bbox": [ + 305, + 350, + 547, + 361 + ], + "type": "text", + "content": " denotes the asymmetric encoder-decoder network." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 369, + 432, + 382 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 369, + 432, + 382 + ], + "spans": [ + { + "bbox": [ + 305, + 369, + 432, + 382 + ], + "type": "text", + "content": "4. Experimental Results" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 384, + 545, + 408 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 384, + 545, + 408 + ], + "spans": [ + { + "bbox": [ + 304, + 384, + 545, + 408 + ], + "type": "text", + "content": "In this section, we evaluate our method and compare it with state-of-the-art ones using public benchmark datasets." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 305, + 412, + 479, + 425 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 412, + 479, + 425 + ], + "spans": [ + { + "bbox": [ + 305, + 412, + 479, + 425 + ], + "type": "text", + "content": "4.1. Datasets and parameter settings" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 426, + 545, + 474 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 426, + 545, + 474 + ], + "spans": [ + { + "bbox": [ + 304, + 426, + 545, + 474 + ], + "type": "text", + "content": "Datasets. We evaluate our method on commonly used image deblurring datasets including the GoPro dataset [16], the HIDe dataset [20], and the RealBlur dataset [18]. We follow the protocols of existing methods for fair comparisons." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 479, + 547, + 717 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 479, + 547, + 717 + ], + "spans": [ + { + "bbox": [ + 304, + 479, + 547, + 717 + ], + "type": "text", + "content": "Parameter settings. We use the same loss function as [4] to constrain the network and train it using the Adam [10] optimizer with default parameters. The initial value of the learning rate is " + }, + { + "bbox": [ + 304, + 479, + 547, + 717 + ], + "type": "inline_equation", + "content": "10^{-3}" + }, + { + "bbox": [ + 304, + 479, + 547, + 717 + ], + "type": "text", + "content": " and is updated with the cosine annealing strategy after 600,000 iterations. The minimum value of the learning rate is " + }, + { + "bbox": [ + 304, + 479, + 547, + 717 + ], + "type": "inline_equation", + "content": "10^{-7}" + }, + { + "bbox": [ + 304, + 479, + 547, + 717 + ], + "type": "text", + "content": ". The patch size is empirically set to be " + }, + { + "bbox": [ + 304, + 479, + 547, + 717 + ], + "type": "inline_equation", + "content": "256 \\times 256" + }, + { + "bbox": [ + 304, + 479, + 547, + 717 + ], + "type": "text", + "content": " pixels and the batch size is set to be 16. We adopt the same data augmentation method as [30] during the training. The patch size for the quantization matrix estimation is empirically set to be " + }, + { + "bbox": [ + 304, + 479, + 547, + 717 + ], + "type": "inline_equation", + "content": "8 \\times 8" + }, + { + "bbox": [ + 304, + 479, + 547, + 717 + ], + "type": "text", + "content": " based on the JPEG compression method. In the implementation, the tensor form of the quantization matrix is set as [batch_size, channel_num, 8, 8], where batch_size and channel_num are the number of batches and features. The quantization matrix is jointly learned with other parameters by solving loss functions during the training. Similarity, we also use the patch size of " + }, + { + "bbox": [ + 304, + 479, + 547, + 717 + ], + "type": "inline_equation", + "content": "8 \\times 8" + }, + { + "bbox": [ + 304, + 479, + 547, + 717 + ], + "type": "text", + "content": " pixels when computing the self-attention (4). Due to the page limit, we include more experimental results in the supplemental material. The training code and models are available at https://github.com/kkkls/FFTformer." + } + ] + } + ], + "index": 20 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "5889" + } + ] + } + ], + "index": 21 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 56, + 70, + 175, + 171 + ], + "blocks": [ + { + "bbox": [ + 56, + 70, + 175, + 171 + ], + "lines": [ + { + "bbox": [ + 56, + 70, + 175, + 171 + ], + "spans": [ + { + "bbox": [ + 56, + 70, + 175, + 171 + ], + "type": "image", + "image_path": "451bd253d42c6abf52b0cfc97893610d7c6414344676ca28e0e8ac93d7a588b4.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 176, + 70, + 295, + 171 + ], + "blocks": [ + { + "bbox": [ + 176, + 70, + 295, + 171 + ], + "lines": [ + { + "bbox": [ + 176, + 70, + 295, + 171 + ], + "spans": [ + { + "bbox": [ + 176, + 70, + 295, + 171 + ], + "type": "image", + "image_path": "74cb9d826e7bc61ca50ffe75480252d28137b5df96d67818e1945bdd033830b2.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 296, + 70, + 416, + 171 + ], + "blocks": [ + { + "bbox": [ + 296, + 70, + 416, + 171 + ], + "lines": [ + { + "bbox": [ + 296, + 70, + 416, + 171 + ], + "spans": [ + { + "bbox": [ + 296, + 70, + 416, + 171 + ], + "type": "image", + "image_path": "16b200b4c21552650b77904c7bed316d46b8198653f0ed0777fe43a0f646eb7f.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + } + ], + "index": 4 + }, + { + "type": "image", + "bbox": [ + 416, + 70, + 536, + 171 + ], + "blocks": [ + { + "bbox": [ + 416, + 70, + 536, + 171 + ], + "lines": [ + { + "bbox": [ + 416, + 70, + 536, + 171 + ], + "spans": [ + { + "bbox": [ + 416, + 70, + 536, + 171 + ], + "type": "image", + "image_path": "3f9b52f1e843819375fccddbba7daa3fe0b1920482f7cbbe9748de2394870fdd.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_body" + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 55, + 182, + 176, + 283 + ], + "blocks": [ + { + "bbox": [ + 80, + 173, + 138, + 182 + ], + "lines": [ + { + "bbox": [ + 80, + 173, + 138, + 182 + ], + "spans": [ + { + "bbox": [ + 80, + 173, + 138, + 182 + ], + "type": "text", + "content": "(a) Blurred image" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 55, + 182, + 176, + 283 + ], + "lines": [ + { + "bbox": [ + 55, + 182, + 176, + 283 + ], + "spans": [ + { + "bbox": [ + 55, + 182, + 176, + 283 + ], + "type": "image", + "image_path": "9a90f446fa2d656748d434e6036198e13b684dfaf44ad63521799441277fb0b6.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 78, + 285, + 143, + 294 + ], + "lines": [ + { + "bbox": [ + 78, + 285, + 143, + 294 + ], + "spans": [ + { + "bbox": [ + 78, + 285, + 143, + 294 + ], + "type": "text", + "content": "(e) Stripformer [24]" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 46, + 298, + 545, + 319 + ], + "lines": [ + { + "bbox": [ + 46, + 298, + 545, + 319 + ], + "spans": [ + { + "bbox": [ + 46, + 298, + 545, + 319 + ], + "type": "text", + "content": "Figure 3. Deblurred results on the GoPro dataset [16]. The deblurred results in (c)-(g) still contain significant blur effects. The proposed method generates a clearer image. For example, the characters and boundaries are much clearer." + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 176, + 182, + 295, + 283 + ], + "blocks": [ + { + "bbox": [ + 224, + 173, + 247, + 182 + ], + "lines": [ + { + "bbox": [ + 224, + 173, + 247, + 182 + ], + "spans": [ + { + "bbox": [ + 224, + 173, + 247, + 182 + ], + "type": "text", + "content": "(b) GT" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 176, + 182, + 295, + 283 + ], + "lines": [ + { + "bbox": [ + 176, + 182, + 295, + 283 + ], + "spans": [ + { + "bbox": [ + 176, + 182, + 295, + 283 + ], + "type": "image", + "image_path": "0dfa20e30f8b057bd54d6d0922bd2b5cf4fbe61c81ccd89f6f2f529f59bf2d3a.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 199, + 285, + 272, + 294 + ], + "lines": [ + { + "bbox": [ + 199, + 285, + 272, + 294 + ], + "spans": [ + { + "bbox": [ + 199, + 285, + 272, + 294 + ], + "type": "text", + "content": "(f) Restormer-local [5]" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 296, + 182, + 416, + 283 + ], + "blocks": [ + { + "bbox": [ + 320, + 173, + 389, + 182 + ], + "lines": [ + { + "bbox": [ + 320, + 173, + 389, + 182 + ], + "spans": [ + { + "bbox": [ + 320, + 173, + 389, + 182 + ], + "type": "text", + "content": "(c) MIMO-Unet+ [4]" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 296, + 182, + 416, + 283 + ], + "lines": [ + { + "bbox": [ + 296, + 182, + 416, + 283 + ], + "spans": [ + { + "bbox": [ + 296, + 182, + 416, + 283 + ], + "type": "image", + "image_path": "14ea27bae754bbbc1abaa2b79b2442d4dce2b1a866512e9db84f3ea97c4a7582.jpg" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 330, + 285, + 381, + 294 + ], + "lines": [ + { + "bbox": [ + 330, + 285, + 381, + 294 + ], + "spans": [ + { + "bbox": [ + 330, + 285, + 381, + 294 + ], + "type": "text", + "content": "(g) NAFNet [3]" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_caption" + } + ], + "index": 12 + }, + { + "type": "image", + "bbox": [ + 416, + 182, + 536, + 283 + ], + "blocks": [ + { + "bbox": [ + 444, + 173, + 505, + 182 + ], + "lines": [ + { + "bbox": [ + 444, + 173, + 505, + 182 + ], + "spans": [ + { + "bbox": [ + 444, + 173, + 505, + 182 + ], + "type": "text", + "content": "(d) Restormer [30]" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 416, + 182, + 536, + 283 + ], + "lines": [ + { + "bbox": [ + 416, + 182, + 536, + 283 + ], + "spans": [ + { + "bbox": [ + 416, + 182, + 536, + 283 + ], + "type": "image", + "image_path": "1d1292b3236808f90eb204eca634bbcc27bc2ffaa959c82f6099f2b3067baac9.jpg" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 462, + 285, + 490, + 293 + ], + "lines": [ + { + "bbox": [ + 462, + 285, + 490, + 293 + ], + "spans": [ + { + "bbox": [ + 462, + 285, + 490, + 293 + ], + "type": "text", + "content": "(h) Ours" + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_caption" + } + ], + "index": 14 + }, + { + "type": "table", + "bbox": [ + 49, + 347, + 287, + 494 + ], + "blocks": [ + { + "bbox": [ + 47, + 323, + 286, + 346 + ], + "lines": [ + { + "bbox": [ + 47, + 323, + 286, + 346 + ], + "spans": [ + { + "bbox": [ + 47, + 323, + 286, + 346 + ], + "type": "text", + "content": "Table 1. Quantitative evaluations on the GoPro dataset [16]. The average runtime is tested on images with size of " + }, + { + "bbox": [ + 47, + 323, + 286, + 346 + ], + "type": "inline_equation", + "content": "256 \\times 256" + }, + { + "bbox": [ + 47, + 323, + 286, + 346 + ], + "type": "text", + "content": " pixels." + } + ] + } + ], + "index": 17, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 49, + 347, + 287, + 494 + ], + "lines": [ + { + "bbox": [ + 49, + 347, + 287, + 494 + ], + "spans": [ + { + "bbox": [ + 49, + 347, + 287, + 494 + ], + "type": "table", + "html": "
MethodsPSNRsSSIMsParameters (M)Avg. runtime
DeblurGAN-v2 [12]29.550.934060.90.04s
SRN [22]30.260.93426.80.07s
DMPHN [32]31.200.945321.70.21s
SAPHN [21]31.850.948023.0-
MIMO-Unet+ [4]32.450.956716.10.02s
MPRNet [31]32.660.958920.10.09s
IPT [2]--1140.50s
DeepRFT+ [15]33.230.963223.00.09s
Restormer [30]32.920.961126.10.08s
Uformer-B [27]33.060.967050.90.07s
Stripformer [24]33.080.962419.70.04s
MPRNet-local [5]33.310.963720.10.11s
Restormer-local [5]33.570.965626.10.42s
NAFNet [3]33.710.966867.90.04s
Ours34.210.969216.60.13s
", + "image_path": "695231ac748724df3f75c6d098a1e4f849fe7c08739fb611ea8c4f97b3d579f0.jpg" + } + ] + } + ], + "index": 18, + "angle": 0, + "type": "table_body" + } + ], + "index": 18 + }, + { + "bbox": [ + 47, + 495, + 247, + 506 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 495, + 247, + 506 + ], + "spans": [ + { + "bbox": [ + 47, + 495, + 247, + 506 + ], + "type": "text", + "content": "4.2. Comparisons with the state of the arts" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 46, + 508, + 287, + 543 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 508, + 287, + 543 + ], + "spans": [ + { + "bbox": [ + 46, + 508, + 287, + 543 + ], + "type": "text", + "content": "We compare our method with state-of-the-art ones and use the PSNR and SSIM to evaluate the quality of restored images." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 46, + 545, + 287, + 700 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 545, + 287, + 700 + ], + "spans": [ + { + "bbox": [ + 46, + 545, + 287, + 700 + ], + "type": "text", + "content": "**Evaluations on the GoPro dataset.** We first evaluate our method on the commonly used GoPro dataset by [16]. For fair comparisons, we follow the protocols of this dataset and retrain or fine-tune the deep learning methods that are not trained on this dataset. Table 1 shows the quantitative evaluation results. Our method generates the results with the highest PSNR and SSIM values. Compared to the state-of-the-art CNN-based methods, NAFNet [3], the PSNR gain of our method is at least 0.5dB higher than NAFNet, while the number of the proposed model parameters is a quarter of the NAFNet. In addition, compared to the Transformer-based methods [24,27,30], our method has fewer model parameters while the performance is better." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 59, + 701, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 701, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 59, + 701, + 288, + 713 + ], + "type": "text", + "content": "As the FFT implementation is not optimized well in Py-" + } + ] + } + ], + "index": 22 + }, + { + "type": "table", + "bbox": [ + 308, + 346, + 542, + 445 + ], + "blocks": [ + { + "bbox": [ + 305, + 323, + 545, + 344 + ], + "lines": [ + { + "bbox": [ + 305, + 323, + 545, + 344 + ], + "spans": [ + { + "bbox": [ + 305, + 323, + 545, + 344 + ], + "type": "text", + "content": "Table 2. Quantitative evaluations on the RealBlur dataset [18] in terms of PSNR and SSIM." + } + ] + } + ], + "index": 23, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 308, + 346, + 542, + 445 + ], + "lines": [ + { + "bbox": [ + 308, + 346, + 542, + 445 + ], + "spans": [ + { + "bbox": [ + 308, + 346, + 542, + 445 + ], + "type": "table", + "html": "
MethodsRealblur-RRealblur-J
PSNRsSSIMsPSNRsSSIMs
DeblurGAN-v2 [12]36.440.934729.690.8703
SRN [22]38.650.965231.380.9091
MIMO-Unet+ [4]--31.920.9190
BANet [23]39.550.971032.000.9230
DeepRFT+ [15]39.840.972132.190.9305
Stripformer [24]39.840.973732.480.9290
Ours40.110.973232.620.9326
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Moreover, our method is at least " + }, + { + "bbox": [ + 304, + 446, + 547, + 493 + ], + "type": "inline_equation", + "content": "4 \\times" + }, + { + "bbox": [ + 304, + 446, + 547, + 493 + ], + "type": "text", + "content": " faster than IPT [2] that is based on the original self-attention." + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 304, + 494, + 547, + 613 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 494, + 547, + 613 + ], + "spans": [ + { + "bbox": [ + 304, + 494, + 547, + 613 + ], + "type": "text", + "content": "Figure 3 shows visual comparisons of the proposed method and the evaluated ones on the GoPro dataset. As demonstrated by [30], the CNN-based methods [3,4] do not effectively explore non-local information for latent clear image restoration. Therefore, the deblurred results by the methods [3,4] still contain significant blur effect as shown in Figure 3(c) and (g). The Transformer-based methods [5,24,30] are able to model the global contexts for image deblurring. However, some main structures, e.g., characters and chairs, are not recovered well (see Figure 3(d)-(f))." + } + ] + } + ], + "index": 26 + }, + { + "bbox": [ + 304, + 614, + 545, + 698 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 614, + 545, + 698 + ], + "spans": [ + { + "bbox": [ + 304, + 614, + 545, + 698 + ], + "type": "text", + "content": "In contrast to existing Transformer-based methods that are based on the spatial domain, we develop an efficient frequency domain-based Transformer, where the proposed DFFN is able to discriminately estimate useful frequency information for latent clear image restoration. Thus, the deblurred results contain clear structures, and the characters are much clearer as shown in Figure 3(h)." + } + ] + } + ], + "index": 27 + }, + { + "bbox": [ + 306, + 701, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 701, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 306, + 701, + 545, + 712 + ], + "type": "text", + "content": "Evaluations on the RealBlur dataset. We further evaluate" + } + ] + } + ], + "index": 28 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "5890" + } + ] + } + ], + "index": 29 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 56, + 70, + 175, + 216 + ], + "blocks": [ + { + "bbox": [ + 56, + 70, + 175, + 216 + ], + "lines": [ + { + "bbox": [ + 56, + 70, + 175, + 216 + ], + "spans": [ + { + "bbox": [ + 56, + 70, + 175, + 216 + ], + "type": "image", + "image_path": "e0abd2f730e1282a7e0486f884a0a893698007a4d89dbdb734c067cf8ec0665c.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 81, + 217, + 140, + 226 + ], + "lines": [ + { + "bbox": [ + 81, + 217, + 140, + 226 + ], + "spans": [ + { + 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"image_path": "2a71d775ccaaf0e055fd221b6728860acac580a5c7a5f88a8999450d19c33ee8.jpg" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 462, + 373, + 490, + 381 + ], + "lines": [ + { + "bbox": [ + 462, + 373, + 490, + 381 + ], + "spans": [ + { + "bbox": [ + 462, + 373, + 490, + 381 + ], + "type": "text", + "content": "(h) Ours" + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 46, + 387, + 545, + 409 + ], + "lines": [ + { + "bbox": [ + 46, + 387, + 545, + 409 + ], + "spans": [ + { + "bbox": [ + 46, + 387, + 545, + 409 + ], + "type": "text", + "content": "Figure 4. Deblurred results on the RealBlur dataset [18]. The characters or the structural details in (c)-(g) are not recovered well. The proposed method generates an image with much clearer characters and structural details." + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "image_caption" + } + ], + "index": 14 + }, + { + "type": "table", + "bbox": [ + 55, + 437, + 278, + 573 + ], + "blocks": [ + { + "bbox": [ + 47, + 415, + 286, + 436 + ], + "lines": [ + { + "bbox": [ + 47, + 415, + 286, + 436 + ], + "spans": [ + { + "bbox": [ + 47, + 415, + 286, + 436 + ], + "type": "text", + "content": "Table 3. Quantitative evaluations on the Hide dataset [20]. We use the models trained on the GoPro dataset [16] for fair comparisons." + } + ] + } + ], + "index": 17, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 55, + 437, + 278, + 573 + ], + "lines": [ + { + "bbox": [ + 55, + 437, + 278, + 573 + ], + "spans": [ + { + "bbox": [ + 55, + 437, + 278, + 573 + ], + "type": "table", + "html": "
MethodsPSNRsSSIMsParameters (M)
DeblurGAN-v2 [12]26.610.875060.9
SRN [22]28.360.90406.8
DMPHN [32]29.090.924021.7
SAPHN [21]29.980.930023.0
MIMO-Unet+ [4]29.990.930416.1
MPRNet [31]30.960.939720.1
Stripformer [24]31.030.939519.7
MPRNet-local [5]31.190.941820.1
Restormer [30]31.220.942326.1
NAFNet [3]31.310.942767.9
Restormer-local [5]31.490.944726.1
Ours31.620.945516.6
", + "image_path": "ee30f8e12ec9f99993992617875362c2f45b49af3be79ac3c69ba6748973f548.jpg" + } + ] + } + ], + "index": 18, + "angle": 0, + "type": "table_body" + } + ], + "index": 18 + }, + { + "bbox": [ + 46, + 575, + 286, + 658 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 575, + 286, + 658 + ], + "spans": [ + { + "bbox": [ + 46, + 575, + 286, + 658 + ], + "type": "text", + "content": "our method on the RealBlur dataset by [18] and follow the protocols of this dataset for fair comparisons. The test dataset of [18] includes a RealBlur-R test set from the raw images and RealBlur-J test set from the JPEG images. Table 2 summarizes the quantitative evaluation results on the above mentioned test sets. The proposed method generates the results with higher PSNR values." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 46, + 660, + 287, + 696 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 660, + 287, + 696 + ], + "spans": [ + { + "bbox": [ + 46, + 660, + 287, + 696 + ], + "type": "text", + "content": "Figure 4 shows the visual comparisons on the RealBlur dataset, where our method generates the results with clearer characters and finer structural details (Figure 4(h))." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 47, + 701, + 287, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 701, + 287, + 712 + ], + "spans": [ + { + "bbox": [ + 47, + 701, + 287, + 712 + ], + "type": "text", + "content": "Evaluations on the HIDe dataset. We then evaluate our" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 304, + 415, + 546, + 511 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 415, + 546, + 511 + ], + "spans": [ + { + "bbox": [ + 304, + 415, + 546, + 511 + ], + "type": "text", + "content": "method on the Hide dataset [20], which mainly contains humans. Similar to state-of-the-art methods [4, 31], we directly use the models of the evaluated methods, which are trained on the GoPro dataset for test. Table 3 shows that the quality of the deblurred images generated by the proposed method is better than the evaluated methods, suggesting that our method has a better generalization ability as models are not trained on this dataset." + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 304, + 512, + 547, + 559 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 512, + 547, + 559 + ], + "spans": [ + { + "bbox": [ + 304, + 512, + 547, + 559 + ], + "type": "text", + "content": "We show some visual comparisons in Figure 5. We note that the evaluated methods do not recover the humans well. In contrast, our method generates better images. For example, the faces and zipper of clothes are much clearer." + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 306, + 563, + 443, + 577 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 563, + 443, + 577 + ], + "spans": [ + { + "bbox": [ + 306, + 563, + 443, + 577 + ], + "type": "text", + "content": "5. Analysis and Discussion" + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 304, + 578, + 546, + 674 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 578, + 546, + 674 + ], + "spans": [ + { + "bbox": [ + 304, + 578, + 546, + 674 + ], + "type": "text", + "content": "We have shown that exploring the properties of Transformers in the frequency domain generates favorable results against state-of-the-art methods. In this section, we provide deeper analysis on the proposed method and demonstrate the effect of the main components. For the ablation studies in this section, we train our method and all the baselines on the GoPro dataset using the batch size of 8 to illustrate the effect of each component in our method." + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 304, + 677, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 547, + 713 + ], + "type": "text", + "content": "Effect of FSAS. The proposed FSAS is used to reduce the computational cost. According to the properties of FFT, the space and time complexity of the FSAS are " + }, + { + "bbox": [ + 304, + 677, + 547, + 713 + ], + "type": "inline_equation", + "content": "O(N)" + }, + { + "bbox": [ + 304, + 677, + 547, + 713 + ], + "type": "text", + "content": " and" + } + ] + } + ], + "index": 26 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "type": "text", + "content": "5891" + } + ] + } + ], + "index": 27 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 55, + 69, + 175, + 177 + ], + "blocks": [ + { + "bbox": [ + 55, + 69, + 175, + 177 + ], + "lines": [ + { + "bbox": [ + 55, + 69, + 175, + 177 + ], + "spans": [ + { + "bbox": [ + 55, + 69, + 175, + 177 + ], + "type": "image", + "image_path": "69f92d39d74e2fa5ebcfeccc2d6d8024a2b0fc9a7f669c80ddd25caf50b309e2.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 176, + 70, + 295, + 177 + ], + "blocks": [ + { + "bbox": [ + 176, + 70, + 295, + 177 + ], + "lines": [ + { + "bbox": [ + 176, + 70, + 295, + 177 + ], + "spans": [ + { + "bbox": [ + 176, + 70, + 295, + 177 + ], + "type": "image", + "image_path": "2d2f3ef00f2e4c7934488eb6c0c5e9c40ba94722102eba78dc10eba222b49410.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 224, + 178, + 247, + 187 + ], + "lines": [ + { + "bbox": [ + 224, + 178, + 247, + 187 + ], + "spans": [ + { + "bbox": [ + 224, + 178, + 247, + 187 + ], + "type": "text", + "content": "(b) GT" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 296, + 70, + 416, + 177 + ], + "blocks": [ + { + "bbox": [ + 296, + 70, + 416, + 177 + ], + "lines": [ + { + "bbox": [ + 296, + 70, + 416, + 177 + ], + "spans": [ + { + "bbox": [ + 296, + 70, + 416, + 177 + ], + "type": "image", + "image_path": "57f04088f0d5a1ad44a2218966ecd02d0b494f2cab2d3f528c11940e7ffea69e.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + } + ], + "index": 4 + }, + { + "type": "image", + "bbox": [ + 416, + 70, + 536, + 177 + ], + "blocks": [ + { + "bbox": [ + 416, + 70, + 536, + 177 + ], + "lines": [ + { + "bbox": [ + 416, + 70, + 536, + 177 + ], + "spans": [ + { + "bbox": [ + 416, + 70, + 536, + 177 + ], + "type": "image", + "image_path": "c6bb3b4f34da0ac2bb3ba97a8cc60e6f756f4f2eac4dca461b09440e3caedda2.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_body" + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 55, + 188, + 176, + 295 + ], + "blocks": [ + { + "bbox": [ + 80, + 178, + 138, + 188 + ], + "lines": [ + { + "bbox": [ + 80, + 178, + 138, + 188 + ], + "spans": [ + { + "bbox": [ + 80, + 178, + 138, + 188 + ], + "type": "text", + "content": "(a) Blurred image" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 55, + 188, + 176, + 295 + ], + "lines": [ + { + "bbox": [ + 55, + 188, + 176, + 295 + ], + "spans": [ + { + "bbox": [ + 55, + 188, + 176, + 295 + ], + "type": "image", + "image_path": "9bfb7051f9c07e94ea29d8d4efb593652f80218c9b2e630de810de7063abf412.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 78, + 297, + 143, + 306 + ], + "lines": [ + { + "bbox": [ + 78, + 297, + 143, + 306 + ], + "spans": [ + { + "bbox": [ + 78, + 297, + 143, + 306 + ], + "type": "text", + "content": "(e) Stripformer [24]" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 46, + 310, + 546, + 333 + ], + "lines": [ + { + "bbox": [ + 46, + 310, + 546, + 333 + ], + "spans": [ + { + "bbox": [ + 46, + 310, + 546, + 333 + ], + "type": "text", + "content": "Figure 5. Deblurred results on the HID dataset [20]. The deblurred results in (c)-(g) still contain significant blur effects. 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Memory and running time comparisons of the Transformer based on our method and the window methods [14,27]. The size of the test image is " + }, + { + "bbox": [ + 46, + 338, + 289, + 403 + ], + "type": "inline_equation", + "content": "1280 \\times 720" + }, + { + "bbox": [ + 46, + 338, + 289, + 403 + ], + "type": "text", + "content": " pixels. The test environment is based on a machine with an NVIDIA GeForce RTX 3090 GPU. \"GPU memory\" denotes the maximum GPU memory consumption that is computed by the \"torch.cuda.max_memory_allocated( )\" function." + } + ] + } + ], + "index": 17, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 50, + 405, + 291, + 473 + ], + "lines": [ + { + "bbox": [ + 50, + 405, + 291, + 473 + ], + "spans": [ + { + "bbox": [ + 50, + 405, + 291, + 473 + ], + "type": "table", + "html": "
Window sizeWindow-based method [27]Ours
Avg. runtimeGPU memoryAvg. runtimeGPU memory
8 × 853ms6.3G44ms6.5G
16 × 1656ms7.1G44ms6.2G
32 × 3289ms12.0G43ms6.0G
64 × 64-Out of memory42ms5.9G
1280 × 720-Out of memory42ms5.9G
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FSASSwin attentionFFNDFFNPSNRs/SSIMs
w/ only FFN✘✘✓✘33.19/0.9626
w/ only DFFN✘✘✘✓33.55/0.9651
SA w/ SD✘✓✘✓33.46/0.9645
FSAS+FFN✓✘✓✘33.61/0.9654
FSAS+DFFN✓✘✘✓33.73/0.9663
", + "image_path": "cd90ef32c29999db296617e538dcad7d0a6e20b1096adb13ac7ebc579310ca87.jpg" + } + ] + } + ], + "index": 22, + "angle": 0, + "type": "table_body" + } + ], + "index": 22 + }, + { + "bbox": [ + 304, + 426, + 546, + 676 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 426, + 546, + 676 + ], + "spans": [ + { + "bbox": [ + 304, + 426, + 546, + 676 + ], + "type": "text", + "content": "SAS with the baseline method that performs in the spatial domain (SA w/ SD for short). As the space complexity of the original scaled dot-product attention is " + }, + { + "bbox": [ + 304, + 426, + 546, + 676 + ], + "type": "inline_equation", + "content": "O(N^2)" + }, + { + "bbox": [ + 304, + 426, + 546, + 676 + ], + "type": "text", + "content": ", it is not affordable to train \"SA w/ SD\" when using the same settings as the proposed FSAS. We use the Swin Transformer [14] for comparison as it is much more efficient. Table 5 shows the quantitative evaluation results on the GoPro dataset. The method that computes the scaled dot-product attention in the spatial domain does not generate good deblurred results, where its PSNR value is 0.27 lower (see comparisons of \"SA w/ SD\" and \"FSAS+DFFN\" in Table 5). The main reason is that although using the shifted window partitioning method reduces the computational cost, it does not fully explore the useful information across different windows. In contrast, the space complexity of the proposed FSAS is " + }, + { + "bbox": [ + 304, + 426, + 546, + 676 + ], + "type": "inline_equation", + "content": "O(N)" + }, + { + "bbox": [ + 304, + 426, + 546, + 676 + ], + "type": "text", + "content": " and does not need the shifted window partitioning as an approximation, thus leading to better deblurred results. Figure 6(b) further shows that using the shifted window partitioning method as an approximation of scaled dot-product attention in the spatial domain does not remove blur effectively. In contrast, the proposed FSAS generates clearer images." + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 304, + 677, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 546, + 713 + ], + "type": "text", + "content": "Moreover, compared to the baseline method only using FFN (\"w/ only FFN\"), using the proposed FSAS in this baseline generates much better results, where the PSNR" + } + ] + } + ], + "index": 24 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "5892" + } + ] + } + ], + "index": 25 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 51, + 70, + 127, + 131 + ], + "blocks": [ + { + "bbox": [ + 51, + 70, + 127, + 131 + ], + "lines": [ + { + "bbox": [ + 51, + 70, + 127, + 131 + ], + "spans": [ + { + "bbox": [ + 51, + 70, + 127, + 131 + ], + "type": "image", + "image_path": "128744473ea93513c52c9e6aaca03d5db4eaed5dab1680adbcb53285d8cc145f.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 57, + 133, + 116, + 142 + ], + "lines": [ + { + "bbox": [ + 57, + 133, + 116, + 142 + ], + "spans": [ + { + "bbox": [ + 57, + 133, + 116, + 142 + ], + "type": "text", + "content": "(a) Blurred image" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 128, + 70, + 203, + 131 + ], + "blocks": [ + { + "bbox": [ + 128, + 70, + 203, + 131 + ], + "lines": [ + { + "bbox": [ + 128, + 70, + 203, + 131 + ], + "spans": [ + { + "bbox": [ + 128, + 70, + 203, + 131 + ], + "type": "image", + "image_path": "3e3b5a814b68060738f41b8369376727d3b9954da72fc4bd54537963a2f858f9.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 135, + 133, + 196, + 142 + ], + "lines": [ + { + "bbox": [ + 135, + 133, + 196, + 142 + ], + "spans": [ + { + "bbox": [ + 135, + 133, + 196, + 142 + ], + "type": "text", + "content": "(b) Spatial domain" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 205, + 70, + 280, + 131 + ], + "blocks": [ + { + "bbox": [ + 205, + 70, + 280, + 131 + ], + "lines": [ + { + "bbox": [ + 205, + 70, + 280, + 131 + ], + "spans": [ + { + "bbox": [ + 205, + 70, + 280, + 131 + ], + "type": "image", + "image_path": "a09b6e556183a636be7de6bc7ae3dac3c187d276d22570a8c0606e42796702be.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 206, + 133, + 278, + 142 + ], + "lines": [ + { + "bbox": [ + 206, + 133, + 278, + 142 + ], + "spans": [ + { + "bbox": [ + 206, + 133, + 278, + 142 + ], + "type": "text", + "content": "(c) Frequency domain" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "type": "image", + "bbox": [ + 50, + 193, + 127, + 267 + ], + "blocks": [ + { + "bbox": [ + 47, + 144, + 288, + 189 + ], + "lines": [ + { + "bbox": [ + 47, + 144, + 288, + 189 + ], + "spans": [ + { + "bbox": [ + 47, + 144, + 288, + 189 + ], + "type": "text", + "content": "Figure 6. Effectiveness of the scaled dot-product attention computation in the spatial and frequency domains. Computing the scaled dot-product attention using the FSAS in the frequency domain generates a clearer image." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 50, + 193, + 127, + 267 + ], + "lines": [ + { + "bbox": [ + 50, + 193, + 127, + 267 + ], + "spans": [ + { + "bbox": [ + 50, + 193, + 127, + 267 + ], + "type": "image", + "image_path": "0e5595647369251d3eafb9c3a0f474e71046c0dd0aa2f185ede665a5be135523.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 57, + 269, + 116, + 278 + ], + "lines": [ + { + "bbox": [ + 57, + 269, + 116, + 278 + ], + "spans": [ + { + "bbox": [ + 57, + 269, + 116, + 278 + ], + "type": "text", + "content": "(a) Blurred image" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_caption" + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 128, + 196, + 203, + 267 + ], + "blocks": [ + { + "bbox": [ + 128, + 196, + 203, + 267 + ], + "lines": [ + { + "bbox": [ + 128, + 196, + 203, + 267 + ], + "spans": [ + { + "bbox": [ + 128, + 196, + 203, + 267 + ], + "type": "image", + "image_path": "fb580b54fa2a0c13ad823e6d133fb5efcd1a24cda044c0c651657a2d85ced954.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 134, + 269, + 197, + 277 + ], + "lines": [ + { + "bbox": [ + 134, + 269, + 197, + 277 + ], + "spans": [ + { + "bbox": [ + 134, + 269, + 197, + 277 + ], + "type": "text", + "content": "(b) Ours w/o FSAS" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 205, + 196, + 280, + 267 + ], + "blocks": [ + { + "bbox": [ + 205, + 196, + 280, + 267 + ], + "lines": [ + { + "bbox": [ + 205, + 196, + 280, + 267 + ], + "spans": [ + { + "bbox": [ + 205, + 196, + 280, + 267 + ], + "type": "image", + "image_path": "8d9059818c7eb609503c6ae9fe30d1af6a1cbd6903897d1c50bd88b0d2b230e8.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 229, + 269, + 257, + 277 + ], + "lines": [ + { + "bbox": [ + 229, + 269, + 257, + 277 + ], + "spans": [ + { + "bbox": [ + 229, + 269, + 257, + 277 + ], + "type": "text", + "content": "(c) Ours" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 11 + }, + { + "type": "image", + "bbox": [ + 50, + 305, + 126, + 397 + ], + "blocks": [ + { + "bbox": [ + 47, + 281, + 287, + 303 + ], + "lines": [ + { + "bbox": [ + 47, + 281, + 287, + 303 + ], + "spans": [ + { + "bbox": [ + 47, + 281, + 287, + 303 + ], + "type": "text", + "content": "Figure 7. Effectiveness of the proposed FSAS on image deblurring. Using the proposed FSAS generates a clearer image." + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 50, + 305, + 126, + 397 + ], + "lines": [ + { + "bbox": [ + 50, + 305, + 126, + 397 + ], + "spans": [ + { + "bbox": [ + 50, + 305, + 126, + 397 + ], + "type": "image", + "image_path": "cb6773d0a2ac0879dd7ecc3e4bde89d173391e410ef5283f4845a13d96c44d3e.jpg" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 57, + 399, + 115, + 408 + ], + "lines": [ + { + "bbox": [ + 57, + 399, + 115, + 408 + ], + "spans": [ + { + "bbox": [ + 57, + 399, + 115, + 408 + ], + "type": "text", + "content": "(a) Blurred image" + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 47, + 411, + 287, + 485 + ], + "lines": [ + { + "bbox": [ + 47, + 411, + 287, + 485 + ], + "spans": [ + { + "bbox": [ + 47, + 411, + 287, + 485 + ], + "type": "text", + "content": "Figure 8. Effectiveness of the proposed DFFN on image deblurring. value is " + }, + { + "bbox": [ + 47, + 411, + 287, + 485 + ], + "type": "inline_equation", + "content": "0.42\\mathrm{dB}" + }, + { + "bbox": [ + 47, + 411, + 287, + 485 + ], + "type": "text", + "content": " higher (see comparisons of \"w/ only FFN\" and \"FSAS+FFN\" in Table 5). The visual comparisons in Figure 7(b) and (c) further demonstrate that using the proposed FSAS facilitates the blur removal well, where the boundaries are recovered well as shown in Figure 7(c)." + } + ] + } + ], + "index": 20, + "angle": 0, + "type": "image_caption" + } + ], + "index": 14 + }, + { + "type": "image", + "bbox": [ + 128, + 305, + 203, + 397 + ], + "blocks": [ + { + "bbox": [ + 128, + 305, + 203, + 397 + ], + "lines": [ + { + "bbox": [ + 128, + 305, + 203, + 397 + ], + "spans": [ + { + "bbox": [ + 128, + 305, + 203, + 397 + ], + "type": "image", + "image_path": "3038c7f3e5e6817a02120af391b0c76ae080dc2586e5ab35e3143fa5d4ec4b7e.jpg" + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 139, + 399, + 192, + 408 + ], + "lines": [ + { + "bbox": [ + 139, + 399, + 192, + 408 + ], + "spans": [ + { + "bbox": [ + 139, + 399, + 192, + 408 + ], + "type": "text", + "content": "(b) w/ only FFN" + } + ] + } + ], + "index": 17, + "angle": 0, + "type": "image_caption" + } + ], + "index": 16 + }, + { + "type": "image", + "bbox": [ + 205, + 305, + 280, + 397 + ], + "blocks": [ + { + "bbox": [ + 205, + 305, + 280, + 397 + ], + "lines": [ + { + "bbox": [ + 205, + 305, + 280, + 397 + ], + "spans": [ + { + "bbox": [ + 205, + 305, + 280, + 397 + ], + "type": "image", + "image_path": "4594999a5bdbad73cc23f5ec41413962eed7a6febcf2ca4c72a1bf92a16795fd.jpg" + } + ] + } + ], + "index": 18, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 214, + 399, + 272, + 408 + ], + "lines": [ + { + "bbox": [ + 214, + 399, + 272, + 408 + ], + "spans": [ + { + "bbox": [ + 214, + 399, + 272, + 408 + ], + "type": "text", + "content": "(c) w/ only DFFN" + } + ] + } + ], + "index": 19, + "angle": 0, + "type": "image_caption" + } + ], + "index": 18 + }, + { + "bbox": [ + 46, + 486, + 288, + 641 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 486, + 288, + 641 + ], + "spans": [ + { + "bbox": [ + 46, + 486, + 288, + 641 + ], + "type": "text", + "content": "Effect of DFFN. The proposed DFFN is used to discriminatively estimate useful frequency information for latent clear image restoration. To demonstrate its effectiveness on image deblurring, we compare the proposed method with two baselines. For the first baseline, we compare the proposed method only using the DFFN (w/ only DFFN for short) and the proposed method only using the original FFN (w/ only FFN for short). For the second baseline, we compare the proposed method with the one that replaces the DFFN with the original FFN in the proposed method (FSAS+FFN). The comparisons of \"w/ only DFFN\" and \"w/ only FFN\" in Table 5 show that using the proposed DFFN generates better results, where the PSNR value is 0.36dB higher." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 47, + 642, + 288, + 677 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 642, + 288, + 677 + ], + "spans": [ + { + "bbox": [ + 47, + 642, + 288, + 677 + ], + "type": "text", + "content": "In addition, the comparisons of \"FSAS+FFN\" and \"F-SAS+DFFN\" in Table 5 show that using the proposed DFFN further improves the performance." + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 47, + 677, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 677, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 677, + 288, + 713 + ], + "type": "text", + "content": "Figure 8 shows the visualization results by these above mentioned baseline methods. Using the proposed DFFN generates better deblurred images, where the windows are" + } + ] + } + ], + "index": 23 + }, + { + "type": "table", + "bbox": [ + 308, + 93, + 542, + 130 + ], + "blocks": [ + { + "bbox": [ + 305, + 71, + 547, + 91 + ], + "lines": [ + { + "bbox": [ + 305, + 71, + 547, + 91 + ], + "spans": [ + { + "bbox": [ + 305, + 71, + 547, + 91 + ], + "type": "text", + "content": "Table 6. Quantitative evaluations of the asymmetric encoder-decoder network on the GoPro dataset." + } + ] + } + ], + "index": 24, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 308, + 93, + 542, + 130 + ], + "lines": [ + { + "bbox": [ + 308, + 93, + 542, + 130 + ], + "spans": [ + { + "bbox": [ + 308, + 93, + 542, + 130 + ], + "type": "table", + "html": "
MethodsFSAS in enc&decFSAS in dec (Ours)
PSNRs33.5633.73
SSIMs0.96530.9663
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Effectiveness of the asymmetric encoder-decoder network on image deblurring." + } + ] + } + ], + "index": 32, + "angle": 0, + "type": "image_caption" + } + ], + "index": 26 + }, + { + "type": "image", + "bbox": [ + 386, + 132, + 462, + 209 + ], + "blocks": [ + { + "bbox": [ + 386, + 132, + 462, + 209 + ], + "lines": [ + { + "bbox": [ + 386, + 132, + 462, + 209 + ], + "spans": [ + { + "bbox": [ + 386, + 132, + 462, + 209 + ], + "type": "image", + "image_path": "87ab1364ba958b607ef74e3c489883d6b1d9a0d10c4905d59a964995abdd20db.jpg" + } + ] + } + ], + "index": 28, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 389, + 210, + 459, + 220 + ], + "lines": [ + { + "bbox": [ + 389, + 210, + 459, + 220 + ], + "spans": [ + { + "bbox": [ + 389, + 210, + 459, + 220 + ], + "type": "text", + "content": "(b) FSAS in enc&dec" + } + ] + } + ], + "index": 29, + "angle": 0, + "type": "image_caption" + } + ], + "index": 28 + }, + { + "type": "image", + "bbox": [ + 463, + 132, + 539, + 209 + ], + "blocks": [ + { + "bbox": [ + 463, + 132, + 539, + 209 + ], + "lines": [ + { + "bbox": [ + 463, + 132, + 539, + 209 + ], + "spans": [ + { + "bbox": [ + 463, + 132, + 539, + 209 + ], + "type": "image", + "image_path": "1c9088dff19043022d2757d857bbd51981a983459a909d06ef3bf7c9171e7ff1.jpg" + } + ] + } + ], + "index": 30, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 464, + 210, + 539, + 220 + ], + "lines": [ + { + "bbox": [ + 464, + 210, + 539, + 220 + ], + "spans": [ + { + "bbox": [ + 464, + 210, + 539, + 220 + ], + "type": "text", + "content": "(c) FSAS in dec (Ours)" + } + ] + } + ], + "index": 31, + "angle": 0, + "type": "image_caption" + } + ], + "index": 30 + }, + { + "bbox": [ + 306, + 246, + 455, + 258 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 246, + 455, + 258 + ], + "spans": [ + { + "bbox": [ + 306, + 246, + 455, + 258 + ], + "type": "text", + "content": "recovered well shown in Figure 8(c)." + } + ] + } + ], + "index": 33 + }, + { + "bbox": [ + 305, + 260, + 547, + 415 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 260, + 547, + 415 + ], + "spans": [ + { + "bbox": [ + 305, + 260, + 547, + 415 + ], + "type": "text", + "content": "Effect of the asymmetric encoder-decoder network. As demonstrated in Section 3.3, the shallow features extracted by encoder module usually contain blur effects that affect the estimations of FSAS. We thus embed it into the decoder module, which leads to an asymmetric encoder-decoder network for better image deblurring. To examine the effect of this network design, we compare the network that puts the FSAS into both the encoder and decoder modules (\"FSAS in enc&dec\" in Table 6). Table 6 shows that using the FSAS in the decoder module generates better results, where the PSNR value is at least 0.17dB higher. The visual comparisons in Figure 9(b) and (c) further demonstrate that using the FSAS in the decoder module generates better clear images." + } + ] + } + ], + "index": 34 + }, + { + "bbox": [ + 306, + 420, + 378, + 431 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 420, + 378, + 431 + ], + "spans": [ + { + "bbox": [ + 306, + 420, + 378, + 431 + ], + "type": "text", + "content": "6. Conclusion" + } + ] + } + ], + "index": 35 + }, + { + "bbox": [ + 304, + 435, + 547, + 639 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 435, + 547, + 639 + ], + "spans": [ + { + "bbox": [ + 304, + 435, + 547, + 639 + ], + "type": "text", + "content": "Motivated by the convolution theorem, we have presented an effective and efficient method that explores the properties of Transformers for high-quality image deblurring. We have developed an efficient frequency domain-based self-attention solver (FSAS) to estimate the scaled dot-product attention by an element-wise product operation instead of the matrix multiplication in the spatial domain, where we show that the spatial complexity and the computational complexity are significantly reduced. We further propose a DFFN to discriminatively determine which low and high frequency information of the features should be preserved for latent clear image restoration. Moreover, we develop an asymmetrical network based on an encoder and decoder architecture, where the FSAS is only used in the decoder module for better image deblurring. By training our method in an end-to-end manner, we show that it performs favorably against the state-of-the-art approaches in terms of accuracy and efficiency." + } + ] + } + ], + "index": 36 + }, + { + "bbox": [ + 304, + 641, + 547, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 641, + 547, + 712 + ], + "spans": [ + { + "bbox": [ + 304, + 641, + 547, + 712 + ], + "type": "text", + "content": "Acknowledgements. This work has been partly supported by the National Key R&D Program of China (No. 2018AAA0102001), the National Natural Science Foundation of China (Nos. 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Recently, the octree-based auto-regressive entropy model which adopts the self-attention mechanism to explore dependencies in a large-scale context is proved to be promising. However, heavy global attention computations and auto-regressive contexts are inefficient for practical applications. To improve the efficiency of the attention model, we propose a hierarchical attention structure that has a linear complexity to the context scale and maintains the global receptive field. Furthermore, we present a grouped context structure to address the serial decoding issue caused by the auto-regression while preserving the compression performance. Experiments demonstrate that the proposed entropy model achieves superior rate-distortion performance and significant decoding latency reduction compared with the state-of-the-art large-scale auto-regressive entropy model.", + "bbox": [ + 75, + 318, + 473, + 575 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 621, + 209, + 636 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Point cloud is a fundamental data structure to represent 3D scenes. It has been widely applied in 3D vision systems such as autonomous driving and immersive applications. The large-scale point cloud typically contains millions of points [36]. It is challenging to store and transmit such massive data. Hence, efficient point cloud compression that reduces memory footprints and transmission bandwidth is necessary to develop practical point cloud applications.", + "bbox": [ + 75, + 647, + 468, + 768 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Recently, deep learning methods have promoted the development of point cloud compression [4, 9, 10, 16, 31, 36, 40, 43]. It is a common pipeline to learn an octree-based entropy model to estimate octree node symbol (i.e., occupancy symbol) distributions. The point cloud is first organized as an octree, and occupancy symbols are then encoded into the bitstream losslessly by an entropy coder (e.g., arithmetic", + "bbox": [ + 75, + 768, + 468, + 876 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/dd10b2b2886ee02b32a621ee036207fd249ece4002772f83f089636dc4c67f66.jpg", + "image_caption": [ + "Figure 1. Bitrate and decoding speed in the log scale for lossless compression on 16-bit quantized SemanticKITTI. The proposed method EHEM yields state-of-the-art performance with a comparable decoding latency to the efficient traditional method G-PCC." + ], + "image_footnote": [], + "bbox": [ + 504, + 284, + 885, + 518 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "coder [47]). An accurate entropy model is required since it reduces the cross entropy between the estimated distribution and ground truth, which is corresponding to actual bitrates. Various attempts have been made to improve the accuracy by designing different context structures [4, 10, 16, 37]. The key of these advances is to increase the context capacity and introduce references from high-resolution octree representations. For example, the context in OctAttention [10] includes hundreds of previously decoded siblings (i.e., nodes at the same octree level). The large-scale context incorporates more references for the entropy coder, and the high-resolution context preserves detailed features of the point cloud. Both of them contribute to building informative contexts and effective entropy models.", + "bbox": [ + 496, + 612, + 892, + 824 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "However, large-scale context requires heavy computations to model dependencies among numerous references. The previous work [10] uses the global self-attention mechanism to model long-range dependencies within the context, and its complexity is quadratic to the length of the", + "bbox": [ + 496, + 824, + 893, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 810, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Corresponding author.", + "bbox": [ + 94, + 886, + 220, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "14368", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "large-scale context. Furthermore, considering the efficiency issue, it is infeasible to build a deeper entropy model or extend the context scale to enhance the modeling capability based on global attention. Another concern is the serial decoding process caused by the inclusion of previously decoded siblings. This auto-regressive context structure incurs a practically unacceptable decoding latency (e.g., around 700 seconds per frame).", + "bbox": [ + 78, + 90, + 467, + 210 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To address these issues, we build an entropy model with an efficient hierarchical attention model and a parallel-friendly grouped context structure. The hierarchical attention model partitions the context into local windows and computes attention within these windows independently. Therefore, the complexity is linear to the context scale, which allows the further extension of network depth and context capacity to improve performance. Since the receptive field of the localized attention is limited, we adopt a multi-scale network structure to query features across different windows. The context is progressively downsampled by merging neighboring nodes to generate a new token. Then, cross-window dependencies can be captured by incorporating these new tokens in the same window. The grouped context divides the occupancy symbol sequence into two groups. Each group is conditioned on ancestral features and previously decoded groups, and hence nodes in the same group can be coded in parallel. Furthermore, in contrast to the previous auto-regressive context that only exploits causal parts of the ancestral context [10], the grouped context allows to make use of a complete ancestral context.", + "bbox": [ + 80, + 212, + 467, + 527 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "The proposed efficient hierarchical entropy model called EHEM is evaluated on SemanticKITTI [3] and Ford [32] benchmarks. It surpasses state-of-the-art methods in terms of both compression performance and efficiency. Contributions of this work can be summarized from the following perspectives:", + "bbox": [ + 78, + 529, + 467, + 619 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- We propose a hierarchical attention model, which yields improved compression performance by extending model and context while keeping the efficiency.", + "- We design a grouped context structure that enables parallel decoding. It adapts the entropy model using high-resolution references to practical applications.", + "- The proposed method achieves state-of-the-art RD performance with a practically applicable coding speed." + ], + "bbox": [ + 96, + 627, + 467, + 763 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 80, + 777, + 217, + 792 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.1. Learned Point Cloud Compression", + "text_level": 1, + "bbox": [ + 80, + 801, + 377, + 816 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Point cloud compression is an active research area in both industry and academia. Traditional point cloud compression codecs are generally interpretable, robust, and efficient [11,25,39,41]. However, neural codecs have shown better rate-distortion performance recently.", + "bbox": [ + 80, + 825, + 467, + 898 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Various data structures and models have been developed to boost the rate-distortion performance for learned point cloud compression. The pioneering works [15,17,36,44,48] construct analysis and synthesis transforms to compress point clouds to latent representations. These transforms are learned on point sets with the PointNet backbone [33, 34] or on the voxel structure using 3D convolution. However, distortions are inevitable in these transforms. It is therefore difficult to preserve high-frequency information in latent vectors. Hence, these structures are preferable to lossy compression at low bitrates.", + "bbox": [ + 501, + 90, + 890, + 256 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Learned entropy model is another effective pipeline to reduce bitrates without introducing distortion. Since the inference of the entropy model depends on the context, it is important to build an informative context. A typical entropy model predicts the binary occupancy status of the voxel based on the context of several adjacent voxels [30, 31]. Similarly, entropy model can be established on the octree by estimating occupancy symbol distributions. Early tree-structured entropy models exploit references from ancestor nodes [4, 16, 37]. Later works introduce adjacent voxels that have the same resolution as the currently coded octree node to provide high-resolution references [18]. A recent work replaces neighboring voxels with decoded siblings to extend the context [10], and it yields state-of-the-art performance. However, its efficiency is limited by the expensive global attention computation and auto-regressive processing.", + "bbox": [ + 503, + 258, + 890, + 500 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.2. Learned Image Compression", + "text_level": 1, + "bbox": [ + 503, + 510, + 754, + 526 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "The typical learned image compression pipeline is based on non-linear transforms and hyperprior-based entropy models [1,2,5,19,21,26,27,35,49]. In addition, decoded latent elements also can be introduced into the context to generate parameters for entropy coding, leading to improved performance with an auto-regressive coding process [28]. To accelerate the coding, a few parallel solutions have been developed [13, 14, 29]. The key of these modifications is performing auto-regression at the level of groups instead of pixels to parallelize coding within each group. For example, the checkerboard context model divides latent elements into two groups in the spatial domain [14]. A checkerboard mask is employed to constrain that the inference of the second group only refers to the decoded first group. Despite the data structures of point clouds and images are different, these strategies are instructive to solve the serial coding problem in point cloud compression.", + "bbox": [ + 503, + 534, + 890, + 790 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "3. Preliminary", + "text_level": 1, + "bbox": [ + 503, + 806, + 622, + 823 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "3.1. Octree Structure", + "text_level": 1, + "bbox": [ + 503, + 832, + 663, + 845 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "The octree [24] provides a progressive representation of the point cloud, where each level represents the point cloud with a certain resolution. An octree recursively divides oc", + "bbox": [ + 503, + 856, + 890, + 898 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "14369", + "bbox": [ + 480, + 945, + 517, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "cupied voxels into 8 equal-sized subvoxels until the required resolution is reached. The occupancy symbol is composed of 8 bits (1 to 255 in decimal), where each bit indicates the occupancy status of the corresponding subvoxel. It is an effective data structure to represent large regions, since neighboring nodes in the breadth-first traversal order might locate at distant locations.", + "bbox": [ + 75, + 90, + 468, + 195 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The octree-based point cloud compression transmits an octree to the receiver instead of point coordinates [38, 39]. The octree is represented by a breadth-first traversed occupancy symbol sequence. An entropy coder is adopted to encode these symbols into the bitstream losslessly. At the receiver, an identical octree is reconstructed, which restores the geometry structure of the original point cloud.", + "bbox": [ + 75, + 196, + 467, + 303 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. Large-scale Auto-regressive Entropy Model", + "text_level": 1, + "bbox": [ + 76, + 310, + 444, + 325 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The entropy coder encodes the occupancy symbol sequence $\\mathbf{x} = \\{x_{1},\\ldots ,x_{n}\\}$ according to the distribution $\\tilde{p} (\\mathbf{x})$ estimated by a learned entropy model. The joint distribution is factorized as the product of probability of each node:", + "bbox": [ + 75, + 333, + 467, + 393 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\tilde {p} (\\mathbf {x}) = \\prod_ {i} \\tilde {p} _ {i} \\left(x _ {i} \\mid \\mathbf {C} _ {i}\\right), \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 191, + 401, + 467, + 431 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\mathbf{C}_i$ is the contextual information for predicting $x_{i}$ . Here, nodes are considered to be conditionally independent. Consumed bitrates are given by the cross entropy between the estimated distribution $\\tilde{p} (\\mathbf{x})$ and ground truth $p(\\mathbf{x})$ , formulated as $\\mathbb{E}_{\\mathbf{x}\\sim p}\\left[-\\log_2\\tilde{p} (\\mathbf{x})\\right]$ . An accurate entropy model that minimizes this entropy is helpful to reduce bitrates.", + "bbox": [ + 75, + 440, + 467, + 530 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "To formulate the context structure, we characterize each octree node $n_i$ by features $\\mathbf{u}_i$ including its occupancy symbol $x_i$ , level index, octant index, and parent bounding box coordinates. The ancestral context collects features from the currently coded node and its $K$ ancestors as:", + "bbox": [ + 75, + 531, + 467, + 606 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {a} _ {i} = \\left\\{\\mathbf {u} _ {i} ^ {\\emptyset}, \\mathbf {u} _ {\\text {a n c} (i)}, \\dots , \\mathbf {u} _ {\\text {a n c} (\\dots \\text {a n c} (i))} \\right\\}, \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 143, + 613, + 467, + 633 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\mathbf{u}_i^\\varnothing$ excludes $x_{i}$ from $\\mathbf{u}_i$ since it is unknown when decoding $x_{i}$ . The ancestor-dependent methods [4, 16] predict the occupancy distribution $\\tilde{p}_i(x_i)$ based on the ancestral context $\\mathbf{a}_i$ .", + "bbox": [ + 75, + 640, + 467, + 700 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The large-scale auto-regressive entropy model [10] constructs an extensive context to incorporate more information for inference. It combines the occupancy symbol of the previous sibling with the ancestral context as $\\mathbf{v}_i = \\{x_{i - 1},\\mathbf{a}_i\\}$ . Besides, the context is extended by introducing features from $N - 1$ previously decoded sibling nodes and their ancestors to build a context window with length $N$ :", + "bbox": [ + 75, + 700, + 467, + 806 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {C} _ {i} = \\left\\{\\mathbf {v} _ {i - N + 1}, \\dots , \\mathbf {v} _ {i} \\right\\}. \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 184, + 815, + 467, + 832 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "$\\mathbf{C}_i$ is then embedded to features $\\mathbf{F}_i = \\{\\mathbf{f}_{i - N + 1},\\dots ,\\mathbf{f}_i\\}$ and a self-attention module [42] is adopted to model dependencies among $N$ embedded features. A mask is employed to constrain that only causal contexts $\\mathbf{f}_{< i}$ are visible.", + "bbox": [ + 75, + 839, + 467, + 900 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Finally, attention-weighted features $\\tilde{\\mathbf{f}}_i$ are projected to the distribution $\\tilde{p}_i(x_i)$ , which is used for entropy coding.", + "bbox": [ + 498, + 90, + 888, + 121 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Since the octree is coded in a breadth-first manner, ancestral contexts are completely known while coding any node. Therefore, the ancestor-dependent entropy model can decode multiple nodes at the same octree level in parallel. In contrast, the auto-regressive context model is conditioned on previously decoded siblings (e.g., $x_{i-1}$ ). It hence requires a serial decoding process. The global attention computation among $N$ elements in $\\mathbf{F}_i$ also limits its efficiency. However, large-scale contexts and sibling references are still effective to improve performance. Therefore, we aim to build an efficient entropy model while preserving these advantages.", + "bbox": [ + 496, + 122, + 890, + 303 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "4. Efficient Hierarchical Entropy Model", + "text_level": 1, + "bbox": [ + 498, + 320, + 834, + 338 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "4.1. Overall Architecture", + "text_level": 1, + "bbox": [ + 498, + 345, + 694, + 361 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The overview of the proposed entropy model is shown in Fig. 2. It is composed of a grouped context structure and a hierarchical attention model. The occupancy sequence $\\mathbf{x}$ is divided into a series of non-overlapped subsequences $\\mathbf{x}_i = \\{x_{i-N+1},\\dots,x_i\\}$ with length $N$ . Contextual information for each subsequence is called a context window. The grouped context equally partitions $\\mathbf{x}_i$ into two groups $\\mathbf{x}_{i_1}$ and $\\mathbf{x}_{i_2}$ . The first group $\\mathbf{x}_{i_1}$ is only conditioned on the ancestral context $\\mathbf{A}_i = \\{\\mathbf{a}_{i-N+1},\\dots,\\mathbf{a}_i\\}$ , where $\\mathbf{a}_i$ is defined in Eq. (2). The second group $\\mathbf{x}_{i_2}$ is conditioned on both siblings $\\mathbf{x}_{i_1}$ and ancestors $\\mathbf{A}_i$ .", + "bbox": [ + 496, + 371, + 890, + 537 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The hierarchical attention model computes dependencies within local windows to improve the efficiency. The self-attention model discovers dependencies among $N$ ancestral features. The ancestral context $\\mathbf{A}_i$ is partitioned into $\\frac{N}{L}$ non-overlapped local windows with length $L$ . Then we regard parent coordinates in the same window as a point cloud, and feed $\\mathbf{A}_i$ to a DGCNN-based [46] feature extractor to generate $C$ -dimensional geometry-aware features $\\mathbf{F}_i^a$ from local windows separately. $\\mathbf{F}_i^a$ is then passed to successive localized self-attention blocks. Weighted ancestral features of the first group are projected to occupancy distributions $\\tilde{p} (\\mathbf{x}_{i_1})$ using a multi-layer perceptron (MLP). Then $\\mathbf{x}_{i_1}$ is coded and we predict the second group $\\mathbf{x}_{i_2}$ . $\\mathbf{x}_{i_1}$ is embedded to $\\mathbf{F}_{i_1}^s$ and concatenated to its ancestral features $\\tilde{\\mathbf{F}}_{i_1}^a$ as $\\mathbf{F}_{i_1}$ . Subsequently, we adopt a hierarchical cross-attention model to introduce sibling-involved features $\\mathbf{F}_{i_1}$ to ancestral features $\\tilde{\\mathbf{F}}_{i_2}^a$ . Finally, an MLP produces distributions $\\tilde{p} (\\mathbf{x}_{i_2})$ based on sibling features $\\tilde{\\mathbf{F}}_{i_2}^s$ and ancestral features $\\tilde{\\mathbf{F}}_{i_2}^a$ .", + "bbox": [ + 496, + 539, + 890, + 835 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "4.2. Grouped Context", + "text_level": 1, + "bbox": [ + 500, + 845, + 669, + 861 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The auto-regressive context model requires serial decoding since it depends on the previous sibling $x_{i-1}$ . To", + "bbox": [ + 498, + 869, + 890, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "14370", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/79d266ca715e8b069a33ad493e6c141a58f4628ffe96b043eae646dcf915a9f3.jpg", + "image_caption": [ + "Figure 2. Left: The architecture of EHEM for context window length $N = 4$ and local window length $L = 2$ . Red, blue, and yellow nodes denote ancestral features, sibling-involved features, and estimated distributions, respectively. Attention is computed within local windows (dashed boxes). Right: The encoding and decoding process following the grouped context structure. The occupancy sequence $\\mathbf{x}_i$ is split into two disjoint groups and coded in turn." + ], + "image_footnote": [], + "bbox": [ + 81, + 88, + 630, + 299 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/d42bb57a02c632986e5aadc02082862532df9ba6c6ad9079cfa23906b5f4b64f.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 666, + 88, + 888, + 181 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/cfd524b3df22712003e28bfa86eadaf5a48a20bf8a4cd3bca185f2ed67f52992.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 666, + 183, + 887, + 297 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/f3f07b64a301cf3897e3e12d849aa69d4d15ee271d70566c251632086fe48e7f.jpg", + "image_caption": [ + "Figure 3. Illustration of auto-regressive (left) and grouped (right) context structures." + ], + "image_footnote": [], + "bbox": [ + 84, + 388, + 460, + 491 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "address this issue, we decompose the occupancy subsequence into two groups and remove dependencies within each group. As shown in Fig. 3, $\\mathbf{x}_{i_1}$ is first decoded based on the ancestral context $\\mathbf{A}_i$ , then it is introduced as sibling priors to predict $\\mathbf{x}_{i_2}$ . Since the required contexts are completely known before decoding each group, nodes in the same group can be decoded in parallel. The auto-regressive entropy model requires $N$ sequential steps to decode the subsequence $\\mathbf{x}_i$ , while the grouped context only takes 2 steps to decode two groups in turn.", + "bbox": [ + 75, + 564, + 467, + 715 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The prediction of $\\mathbf{x}_{i_2}$ depends on $\\mathbf{x}_{i_1}$ , and hence it is important to design an effective decomposition pattern. We visualize ancestral dependencies among the first 16 siblings in the context window in Fig. 4b. Dependencies are represented by normalized attention scores computed on $\\mathbf{F}_i^a$ , and results are averaged over all self-attention layers from around 200 SemanticKITTI scans. Fig. 4b reveals that closer neighbors have stronger dependencies, and dependency activations at more distant locations are weak and uniform. This distribution is consistent with both intuitions and experiences in learned image compression [14]. We assume that dependencies computed on ancestral and sibling", + "bbox": [ + 75, + 719, + 467, + 900 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/45ddc2833a4ed01fef535418ebb5495ed7d3dbdda2df8a630540f6120d8f8b28.jpg", + "image_caption": [ + "Figure 4. Visualization of dependencies discovered by different methods. Deep colors indicate strong dependencies." + ], + "image_footnote": [], + "bbox": [ + 504, + 388, + 694, + 525 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/ab6324581e1ff62d1c29a10b97683c169e361298a94a04f3e22a8a41280ddd2d.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 697, + 388, + 890, + 523 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "involved contexts have similar distributions. With this property, we use a uniform decomposition pattern expressed as:", + "bbox": [ + 498, + 593, + 890, + 625 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\left\\{ \\begin{array}{l} \\mathbf {x} _ {i _ {1}} = \\left\\{x _ {1}, \\dots , x _ {2 j - 1}, \\dots , x _ {i - 1} \\right\\}, \\mathbf {C} _ {i _ {1}} = \\left\\{\\mathbf {A} _ {i} \\right\\}, \\\\ \\mathbf {x} _ {i _ {2}} = \\left\\{x _ {2}, \\dots , x _ {2 j}, \\dots , x _ {i} \\right\\}, \\mathbf {C} _ {i _ {2}} = \\left\\{\\mathbf {A} _ {i}, \\mathbf {x} _ {i _ {1}} \\right\\}. \\end{array} \\right. \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 509, + 636, + 890, + 676 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "It preserves two most important neighbors $x_{2j-1}$ and $x_{2j+1}$ for $x_{2j}$ and uniformly samples $\\mathbf{x}_{i_1}$ at more distant locations.", + "bbox": [ + 498, + 688, + 888, + 718 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In addition, the grouped context separates ancestral and sibling priors to utilize a complete ancestral context. For the auto-regressive context in OctAttention, ancestral and sibling features are concatenated when computing dependencies (see Eq. (3)). To keep the causality, both ancestral and sibling features from non-causal positions (i.e., $\\mathbf{f}_{>i}$ ) are discarded, as shown in Fig. 4a. However, these ancestral features are actually available. As illustrated in Fig. 4b, $\\mathbf{f}_{>i}^{a}$ have similar dependency activations to $\\mathbf{f}_{< i}^{a}$ . Therefore, they are equivalently important to compute dependencies. The grouped context structure accesses to more ancestral features, which leads to better compression performance.", + "bbox": [ + 496, + 719, + 890, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "14371", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/5f88752a9cf67363d186a35e0fe4340a13b6d12b273a2edd76f93744b148248c.jpg", + "image_caption": [ + "Figure 5. Illustration of two successive localized attention layers for the case of $N = 8$ and $L = 2$ . MSA represents the multi-head self-attention." + ], + "image_footnote": [], + "bbox": [ + 84, + 87, + 464, + 212 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "From the perspective of context modeling, this grouped context can be interpreted as the space-channel context in image compression [13]. As shown in Eq. (3), $N$ nodes constitute the spatial domain, and each spatial position has $K + 1$ channels, consisting of $K$ ancestors and 1 sibling. The grouped context partitions on both channel and spatial dimensions. Available contexts for each element are decoded channels (ancestors) from all spatial positions, and elements in the same channel (siblings) at decoded spatial positions. Therefore, it is feasible to use similar context structures for point cloud and image compression, and both domains might benefit from advances of each other.", + "bbox": [ + 75, + 290, + 472, + 474 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.3. Hierarchical Attention", + "text_level": 1, + "bbox": [ + 76, + 483, + 287, + 498 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "To reduce the complexity, we discover dependencies within local windows and model long-range dependencies with a multi-scale network structure. It is inspired by vision transformers designed for 2D images [8, 22, 23, 45]. Since the localized attention can not exploit long-range dependencies in the large-scale context, we gradually downsample the context to represent numerous nodes with $L$ tokens. The downsampling is implemented by a node merging operation. Two neighboring nodes are merged by concatenating their features on the channel dimension. Then, $2C$ -dimensional concatenated features are passed to an MLP to shrink the channel dimension to $C$ . In this way, features from distant nodes can be computed in the same window and the receptive field is increased. Furthermore, dependencies are estimated at different scales, and closer neighbors are computed with fine-grained representations. It is reasonable since closer neighbors are more informative. In contrast, distant nodes can be coarsely characterized. We further introduce the shifted window strategy [23] to capture dependencies across neighboring local windows. Dependencies are computed with a window partition alternating between two patterns, as shown in Fig. 5.", + "bbox": [ + 75, + 507, + 468, + 839 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "A self-attention block is composed of various localized attention layers and one node merging module (except for the last block). The hierarchical attention model is a stack of $\\log_2\\frac{N}{L} + 1$ blocks to capture all $N$ nodes in the last block.", + "bbox": [ + 75, + 839, + 468, + 902 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The number of blocks can be further reduced by aggregating more than two nodes in a single node merging module. We produce a hierarchical representation $\\bar{\\mathbf{F}}_i^a$ by aggregating features and dependencies from different scales. Therefore, we refer to this model as a hierarchical attention model.", + "bbox": [ + 496, + 90, + 890, + 165 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "By performing attention operations within local windows, the hierarchical attention model reduces the complexity from quadratic to linear scale. Complexities of attention computations in global and localized self-attention are:", + "bbox": [ + 496, + 167, + 890, + 227 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\Omega (\\text {G l o b a l}) = 2 N ^ {2} C, \\quad \\Omega (\\text {L o c a l i z e d}) = 2 L N C. \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 537, + 238, + 890, + 256 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "It allows us to build a much deeper entropy model with reasonable computational costs to enhance the modeling capability, or substantially expand the context scale to introduce more potentially useful references.", + "bbox": [ + 496, + 267, + 890, + 327 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The hierarchical cross-attention follows a similar localized attention practice. Since the decomposition pattern is uniform, each local window includes $\\frac{L}{2}$ nodes from $\\mathbf{x}_{i_1}$ and another $\\frac{L}{2}$ nodes from $\\mathbf{x}_{i_2}$ . They are regarded as key and query features, respectively. We compute dependencies among keys and queries within each local window, and weight keys according to their dependencies to queries. To extend the receptive field, neighboring keys (and queries) are progressively merged into new key (and query) tokens. Finally, features from different scales are concatenated, which are then exploited to predict $x_{i_2}$ with ancestral features $\\tilde{\\mathbf{F}}_{i_2}^a$ jointly.", + "bbox": [ + 496, + 327, + 890, + 512 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.4. Learning", + "text_level": 1, + "bbox": [ + 500, + 518, + 607, + 536 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The optimization objective of the octree-based entropy model is to minimize the total bitrates for communicating octree nodes. The bitrate is given by the cross entropy between the estimated distribution $\\tilde{p} (\\mathbf{x})$ and the ground truth $p(\\mathbf{x})$ at each node:", + "bbox": [ + 496, + 542, + 890, + 619 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\ell = - \\sum_ {i} \\log \\tilde {p} _ {i} \\left(x _ {i} \\mid \\mathbf {C} _ {i}\\right), \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 606, + 628, + 890, + 661 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\tilde{p}_i(x_i\\mid \\mathbf{C}_i)$ is the distribution estimated by the proposed entropy model based on the context $\\mathbf{C}_i$", + "bbox": [ + 496, + 672, + 890, + 704 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "5. Experiments", + "text_level": 1, + "bbox": [ + 500, + 715, + 632, + 733 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "5.1. Experimental Settings", + "text_level": 1, + "bbox": [ + 500, + 741, + 705, + 758 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Datasets Experiments are conducted on two large-scale point cloud datasets SemanticKITTI [3] and Ford [32]. SemanticKITTI is composed of 43552 LiDAR scans acquired from autonomous driving scenes, which are divided into 22 sequences. We follow the default split to perform training on sequences 00 to 10 and evaluation on sequences 11 to 21. Ford is another LiDAR point cloud dataset used in MPEG point cloud compression standardization. It includes 3 sequences, each consists of 1500 scans. On the Ford dataset,", + "bbox": [ + 496, + 763, + 890, + 902 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "14372", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/de2a17434b604c200dd6f99e282cab9a543b2202b492a96776cf516e0b4dfe12.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 84, + 87, + 343, + 253 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/c0ee82cd88e021dfbc338b65caec9c9a74db5790fc4053e2e07e8e718e80198a.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 354, + 87, + 612, + 253 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/4d35d2aabc046b8ef7a80ba9f7b373077fe7bb4f1314a88ee9002d83c471616f.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 625, + 88, + 883, + 255 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/b4a36def1db17bcbca32e704059b0e579f0e092cde6472bdbe131d2a7a61d5d7.jpg", + "image_caption": [ + "Figure 6. Rate-distortion performance of different methods on SemanticKITTI (top) and Ford (bottom)." + ], + "image_footnote": [], + "bbox": [ + 81, + 263, + 344, + 429 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/5c148f59cc31e7be5ca4478bf54ba6db83a0b926e41e9e97f99127adf65b9a00.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 354, + 263, + 612, + 429 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/cbb657c583b33283971c92cb3c15a04414c9b41b43f3ec2ece5a7609ec9868d6.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 625, + 263, + 883, + 429 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "we follow the suggested dataset partition in MPEG standardization [7], where sequence 01 is used for training and sequences 02 and 03 are used for evaluation.", + "bbox": [ + 75, + 479, + 468, + 526 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Baselines To verify the effectiveness of the proposed model, we compare it with the state-of-the-art octree-based learned entropy model OctAttention [10] and the competitive voxel-based learned method SparsePCGC [43]. We also provide comparisons with the representative handcrafted compression method MPEG G-PCC [12].", + "bbox": [ + 75, + 529, + 468, + 621 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Implementation settings Quantization is necessary to construct octrees from point clouds. For SemanticKITTI, we follow the quantization settings in OctSqueeze [16], where the quantization step is set to $\\frac{400}{2^{D} - 1}$ to build an octree with the depth of $D$ . Octrees are truncated with a maximum depth of 16 for training and evaluation. We set the quantization step to $2^{18 - D}$ and construct octrees with the maximum depth of 18 on Ford. Since the original Ford dataset has been quantized with 18-bit precision, compression is lossless at the highest octree level.", + "bbox": [ + 75, + 625, + 468, + 775 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "The hierarchical self-attention model has 5 blocks including 4, 4, 4, 4, 2 layers, respectively. The hierarchical cross-attention model consists of 4 blocks with 2, 2, 1, 1 layers. The head number is set to 4 for all attention layers. The channel dimension $C$ is set to 256, and the ancestor depth $K$ is set to 3. The context window length $N$ is set to 8192, which is initially divided into 16 local windows with the length $L$ of 512. To further achieve speed-accuracy trade", + "bbox": [ + 75, + 779, + 470, + 902 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/5b94bb553ca3b20760f67f6334b73721989231196cd702116b872aaa0599eccb.jpg", + "table_caption": [ + "Table 1. Inference times (in seconds) for encoding/decoding a D-depth octree on SemanticKITTI. Runtimes for G-PCC are total times." + ], + "table_footnote": [], + "table_body": "
MethodD=12D=14D=16
G-PCC0.25 / 0.120.66 / 0.321.07 / 0.54
SparsePCGC1.14 / 0.861.76 / 1.432.43 / 2.04
OctAttention0.08 / 830.31 / 3210.66 / 708
EHEM0.40 / 0.431.21 / 1.392.53 / 3.01
Light EHEM0.29 / 0.330.79 / 0.921.63 / 1.94
", + "bbox": [ + 504, + 531, + 883, + 628 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "offs, we present a lightweight EHEM model called Light EHEM. It has the same network structure as EHEM except that its 5 self-attention blocks have 2, 2, 2, 2, 2 layers and its channel dimension $C$ is set to 192.", + "bbox": [ + 496, + 662, + 890, + 723 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We adopt an Adam optimizer [20] with a learning rate of $10^{-4}$ to train two models for 10 and 50 epochs on SemanticKITTI and Ford datasets, respectively. The evaluation is implemented on the NVIDIA V100 GPU.", + "bbox": [ + 496, + 729, + 890, + 789 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Metrics We adopt the point-to-point PSNR (D1 PSNR), point-to-plane PSNR (D2 PSNR) [6], and Chamfer distance (CD) to measure the distortion. Experiments on SemanticKITTI follow the PSNR calculations in OctSqueeze and MuSCLE [4, 16], where the peak value is set to 59.70. On the Ford dataset, we set the peak value to 30000 [6]. Consumed bitrates are measured by bits per point (bpp).", + "bbox": [ + 496, + 794, + 890, + 901 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "14373", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/ffb363dd884c3ec22b6d204a213f75fb75915f8f2677bb8f4124f9065d9ad5a6.jpg", + "table_caption": [ + "Table 2. Complexity comparison on encoding/decoding time, theoretical computation cost (FLOPs), parameters, and memory usage among OctAttention, EHEM, and Light EHEM." + ], + "table_footnote": [], + "table_body": "
MethodEnc / DecFLOPs#param.Mem.
OctAttn0.66s / 708s124.3G4.23M1.3G
EHEM2.53s / 3.01s184.4G13.01M2.9G
L-EHEM1.63s / 1.94s102.9G6.34M2.6G
", + "bbox": [ + 78, + 141, + 467, + 207 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/e111aa5ad9e7fa0f07677ecd391997037cde7a7b4cceb57a8321db4c428ca22d.jpg", + "table_caption": [ + "Table 3. Comparison of FLOPs among OctAttention, EHEM, and Light EHEM with respect to the context length $N$ ." + ], + "table_footnote": [], + "table_body": "
Method5121024204840968192
OctAttn6.0G15.5G45.0G145.7G514.0G
EHEM9.0G18.4G38.1G81.5G184.4G
L-EHEM5.2G10.7G21.9G46.4G102.9G
", + "bbox": [ + 78, + 263, + 470, + 329 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.2. Performance Evaluation", + "text_level": 1, + "bbox": [ + 76, + 357, + 302, + 372 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "The quantitative results of the rate-distortion performance are shown in Fig. 6. The proposed method EHEM achieves significant improvements over other baselines. For example, on SemanticKITTI, EHEM achieves an average gain of $28.89\\%$ to G-PCC, and $19.47\\%$ bitrate reduction on average compared with OctAttention. Furthermore, Light EHEM also preserves satisfactory performance and outperforms other baselines.", + "bbox": [ + 75, + 383, + 468, + 503 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "To evaluate the efficiency of EHEM, we report inference times at different quantization steps in Tab. 1. EHEM achieves notable decoding time reduction over the autoregressive context model OctAttention. The encoding time increases compared with OctAttention since the grouped context requires a two-step inference (for $\\mathbf{x}_{i_1}$ and $\\mathbf{x}_{i_2}$ ), while OctAttention only requires one step. However, this encoding time is still practically acceptable and the grouped context is effective to speed up decoding. We further represent both rate-distortion performance and decoding time in Fig. 1. It is shown that EHEM is effective regarding both compression performance and decoding speed.", + "bbox": [ + 75, + 505, + 468, + 686 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We provide the complexity analysis of EHEM and OctAttention in Tab. 2 and Tab. 3. Here, we report required FLOPs to infer a single context window. Note that larger context predicts more nodes with one forward pass. For example, EHEM requires $81.5 \\times 2$ and $184.4 \\times 1$ GFLOPs to predict 8192 nodes when $N$ is set to 4096 and 8192, respectively. It is shown that EHEM has comparable FLOPs to OctAttention when the context capacity is 1024, which is the default setting for OctAttention. However, EHEM contains 24 hierarchical attention layers while OctAttention only includes 2 global attention layers. It proves the superiority of the localized attention structure in terms of extending the network depth. Furthermore, localized attention is also effective to enlarge the context due to the linear com", + "bbox": [ + 75, + 688, + 470, + 900 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/231266a08d05b49923d280eabadfafa9d9eaeee281eb992a289a4d60fa6d956b.jpg", + "image_caption": [ + "Figure 7. Ablation studies on attention models, context scales, and context structures." + ], + "image_footnote": [], + "bbox": [ + 506, + 85, + 883, + 304 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/b53bf97dc1eb8c5a2c7a2ed96ef713bd90c565af1294313fb8cacd7ccb10d6ff.jpg", + "image_caption": [ + "Figure 8. Contexts with different capacities $N$ on 16-bit quantized SemanticKITTI. Points in the context are colored in blue." + ], + "image_footnote": [], + "bbox": [ + 501, + 356, + 694, + 470 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/e1f9957123d0d73c6c05581814b1295da7fd8383787ed761d67fc53560999519.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 697, + 356, + 890, + 470 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "plexity. FLOPs of EHEM increase 2.26 times as the context is enlarged from 4096 to 8192. In contrast, the complexity of OctAttention increases 3.53 times with the same extension. Besides, Light EHEM achieves lower FLOPs at all context window length settings compared to OctAttention. EHEM has slightly larger model size and memory usage compared with OctAttention. These increases are due to the extension of model capacity and context scale, but it is still reasonable for practical use.", + "bbox": [ + 496, + 535, + 890, + 671 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.3. Ablation Studies and Analysis", + "text_level": 1, + "bbox": [ + 500, + 680, + 767, + 696 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Hierarchical attention structure To verify the effectiveness of the hierarchical attention structure, we replace the hierarchical self-attention model with global self-attention layers to build a counterpart with similar FLOPs. Since it is impractical to compute global self-attention with $N = 8192$ , we conduct experiments with $N = 1024$ . Here, EHEM still has 18 localized self-attention layers, and the global-attention counterpart contains 5 layers. The comparison between EHEM ( $N = 1024$ ) and Global Self-Attn in Fig. 7 proves that the hierarchical attention model with a much deeper network achieves considerable improvements. Network depth With the same network structure, the comparison between EHEM and Light EHEM shows that the", + "bbox": [ + 496, + 703, + 890, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "14374", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/48b6b6d53dc05c5f9f0da23f43e3598ae46623b66bdc4110d00a2ae953b0fbec.jpg", + "image_caption": [ + "Figure 9. Visualized compression results of G-PCC, OctAttention, and our method on the SemanticKITTI dataset." + ], + "image_footnote": [], + "bbox": [ + 106, + 92, + 864, + 385 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "deeper network leads to better performance. Therefore, it is helpful to enhance the expressiveness of the model by stacking more layers within a reasonable range.", + "bbox": [ + 75, + 436, + 470, + 482 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Context scale The linear complexity of the hierarchical attention also allows the further extension of the context scale $N$ . Contexts with different capacities are visualized in Fig. 8. It is shown that captured regions are significantly enlarged when $N$ increases from 1024 to 8192. The extended context includes the complete geometry pattern of the vehicle and introduces references from the neighboring similar vehicle. This is beneficial to improve the rate-distortion performance, as shown in Fig. 7.", + "bbox": [ + 75, + 487, + 468, + 625 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Grouped context structure The grouped context structure allows a two-step parallel decoding procedure. Here, we examine its influence on rate-distortion performance. To this end, we train a baseline with an auto-regressive context used in OctAttention. The hierarchical attention is unavailable to this context structure since the node merging operation uses non-causal ancestral references. For a fair comparison, we use global attention to compute dependencies for both grouped and auto-regressive context structures. The grouped context introduces features from the first group via global cross-attention layers. The comparison between AR Context and Grouped Context in Fig. 7 demonstrates that although only half of the nodes access to siblings, the grouped context structure achieves comparable performance. It is because the grouped context preserves ancestral features from non-causal references, as shown in Fig. 4b. Besides, it proves that the grouped context structure does not significantly improve compression performance. Therefore, im", + "bbox": [ + 75, + 628, + 470, + 902 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "provements of EHEM are mainly due to stronger hierarchical attention blocks.", + "bbox": [ + 498, + 436, + 890, + 465 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5.4. Qualitative Results", + "text_level": 1, + "bbox": [ + 500, + 481, + 683, + 498 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In Fig. 9, we show the visualized compression distortions of different methods at similar bitrates. It indicates that our method provides better reconstructions compared with other baselines. For example, EHEM outperforms G-PCC by roughly 10 dB D1 PSNR improvements.", + "bbox": [ + 498, + 506, + 890, + 583 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "6. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 601, + 619, + 617 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We proposed an efficient learned entropy model for point cloud compression. It adopts a hierarchical attention structure, which allows us to substantially extend the network depth and context capacity to improve the rate-distortion performance with reasonable complexity. We further developed a grouped context structure to realize a parallel decoding procedure. Moreover, this context aligns the context modeling regimes of point cloud and image compression, and we hope it would be helpful to bridge the gap between two communities. The proposed model is proved to yield superior compression performance and significantly reduce the decoding time compared to the state-of-the-art auto-regressive method.", + "bbox": [ + 496, + 628, + 890, + 824 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgement", + "text_level": 1, + "bbox": [ + 500, + 843, + 660, + 859 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "This work was supported by National Natural Science Foundation of China (No. 62172021).", + "bbox": [ + 500, + 869, + 890, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "14375", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Johannes Balle, Valero Laparra, and Eero P Simoncelli. End-to-end optimized image compression. 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In International Conference on Learning Representations, 2022." + ], + "bbox": [ + 501, + 92, + 890, + 571 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "14377", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/Efficient Hierarchical Entropy Model for Learned Point Cloud Compression/cb22330c-c1cc-443f-b5db-982a0288da0a_model.json b/2023/Efficient Hierarchical Entropy Model for Learned Point Cloud Compression/cb22330c-c1cc-443f-b5db-982a0288da0a_model.json new file mode 100644 index 0000000000000000000000000000000000000000..721213e1bff8018b6179c66e89cd9fad95fb9c42 --- /dev/null +++ b/2023/Efficient Hierarchical Entropy Model for Learned Point Cloud Compression/cb22330c-c1cc-443f-b5db-982a0288da0a_model.json @@ -0,0 +1,2167 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.001, + 0.812, + 0.047 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.102, + 0.13, + 0.872, + 0.154 + ], + "angle": 0, + "content": "Efficient Hierarchical Entropy Model for Learned Point Cloud Compression" + }, + { + "type": "text", + "bbox": [ + 0.109, + 0.18, + 0.86, + 0.233 + ], + "angle": 0, + "content": "Rui Song\\(^{1}\\), Chunyang Fu\\(^{1}\\), Shan Liu\\(^{2}\\), Ge Li\\(^{1*}\\) \nSchool of Electronic and Computer Engineering, Shenzhen Graduate School, Peking University\\(^{1}\\) \nTencent America\\(^{2}\\)" + }, + { + "type": "text", + "bbox": [ + 0.119, + 0.238, + 0.846, + 0.252 + ], + "angle": 0, + "content": "rsong@stu.pku.edu.cn, fuchy@stu.pku.edu.cn, shanl@tencent.com, geli@ece.pku.edu.cn" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.287, + 0.314, + 0.303 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.319, + 0.474, + 0.577 + ], + "angle": 0, + "content": "Learning an accurate entropy model is a fundamental way to remove the redundancy in point cloud compression. Recently, the octree-based auto-regressive entropy model which adopts the self-attention mechanism to explore dependencies in a large-scale context is proved to be promising. However, heavy global attention computations and auto-regressive contexts are inefficient for practical applications. To improve the efficiency of the attention model, we propose a hierarchical attention structure that has a linear complexity to the context scale and maintains the global receptive field. Furthermore, we present a grouped context structure to address the serial decoding issue caused by the auto-regression while preserving the compression performance. Experiments demonstrate that the proposed entropy model achieves superior rate-distortion performance and significant decoding latency reduction compared with the state-of-the-art large-scale auto-regressive entropy model." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.622, + 0.21, + 0.637 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.648, + 0.47, + 0.77 + ], + "angle": 0, + "content": "Point cloud is a fundamental data structure to represent 3D scenes. It has been widely applied in 3D vision systems such as autonomous driving and immersive applications. The large-scale point cloud typically contains millions of points [36]. It is challenging to store and transmit such massive data. Hence, efficient point cloud compression that reduces memory footprints and transmission bandwidth is necessary to develop practical point cloud applications." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.77, + 0.47, + 0.877 + ], + "angle": 0, + "content": "Recently, deep learning methods have promoted the development of point cloud compression [4, 9, 10, 16, 31, 36, 40, 43]. It is a common pipeline to learn an octree-based entropy model to estimate octree node symbol (i.e., occupancy symbol) distributions. The point cloud is first organized as an octree, and occupancy symbols are then encoded into the bitstream losslessly by an entropy coder (e.g., arithmetic" + }, + { + "type": "image", + "bbox": [ + 0.505, + 0.285, + 0.887, + 0.52 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.529, + 0.894, + 0.586 + ], + "angle": 0, + "content": "Figure 1. Bitrate and decoding speed in the log scale for lossless compression on 16-bit quantized SemanticKITTI. The proposed method EHEM yields state-of-the-art performance with a comparable decoding latency to the efficient traditional method G-PCC." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.613, + 0.893, + 0.825 + ], + "angle": 0, + "content": "coder [47]). An accurate entropy model is required since it reduces the cross entropy between the estimated distribution and ground truth, which is corresponding to actual bitrates. Various attempts have been made to improve the accuracy by designing different context structures [4, 10, 16, 37]. The key of these advances is to increase the context capacity and introduce references from high-resolution octree representations. For example, the context in OctAttention [10] includes hundreds of previously decoded siblings (i.e., nodes at the same octree level). The large-scale context incorporates more references for the entropy coder, and the high-resolution context preserves detailed features of the point cloud. Both of them contribute to building informative contexts and effective entropy models." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.825, + 0.894, + 0.903 + ], + "angle": 0, + "content": "However, large-scale context requires heavy computations to model dependencies among numerous references. The previous work [10] uses the global self-attention mechanism to model long-range dependencies within the context, and its complexity is quadratic to the length of the" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.887, + 0.222, + 0.9 + ], + "angle": 0, + "content": "*Corresponding author." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "14368" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.08, + 0.092, + 0.468, + 0.212 + ], + "angle": 0, + "content": "large-scale context. Furthermore, considering the efficiency issue, it is infeasible to build a deeper entropy model or extend the context scale to enhance the modeling capability based on global attention. Another concern is the serial decoding process caused by the inclusion of previously decoded siblings. This auto-regressive context structure incurs a practically unacceptable decoding latency (e.g., around 700 seconds per frame)." + }, + { + "type": "text", + "bbox": [ + 0.081, + 0.213, + 0.468, + 0.529 + ], + "angle": 0, + "content": "To address these issues, we build an entropy model with an efficient hierarchical attention model and a parallel-friendly grouped context structure. The hierarchical attention model partitions the context into local windows and computes attention within these windows independently. Therefore, the complexity is linear to the context scale, which allows the further extension of network depth and context capacity to improve performance. Since the receptive field of the localized attention is limited, we adopt a multi-scale network structure to query features across different windows. The context is progressively downsampled by merging neighboring nodes to generate a new token. Then, cross-window dependencies can be captured by incorporating these new tokens in the same window. The grouped context divides the occupancy symbol sequence into two groups. Each group is conditioned on ancestral features and previously decoded groups, and hence nodes in the same group can be coded in parallel. Furthermore, in contrast to the previous auto-regressive context that only exploits causal parts of the ancestral context [10], the grouped context allows to make use of a complete ancestral context." + }, + { + "type": "text", + "bbox": [ + 0.08, + 0.53, + 0.468, + 0.62 + ], + "angle": 0, + "content": "The proposed efficient hierarchical entropy model called EHEM is evaluated on SemanticKITTI [3] and Ford [32] benchmarks. It surpasses state-of-the-art methods in terms of both compression performance and efficiency. Contributions of this work can be summarized from the following perspectives:" + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.628, + 0.468, + 0.673 + ], + "angle": 0, + "content": "- We propose a hierarchical attention model, which yields improved compression performance by extending model and context while keeping the efficiency." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.682, + 0.468, + 0.727 + ], + "angle": 0, + "content": "- We design a grouped context structure that enables parallel decoding. It adapts the entropy model using high-resolution references to practical applications." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.735, + 0.468, + 0.765 + ], + "angle": 0, + "content": "- The proposed method achieves state-of-the-art RD performance with a practically applicable coding speed." + }, + { + "type": "list", + "bbox": [ + 0.097, + 0.628, + 0.468, + 0.765 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.081, + 0.778, + 0.218, + 0.793 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "title", + "bbox": [ + 0.081, + 0.803, + 0.378, + 0.818 + ], + "angle": 0, + "content": "2.1. Learned Point Cloud Compression" + }, + { + "type": "text", + "bbox": [ + 0.081, + 0.826, + 0.468, + 0.9 + ], + "angle": 0, + "content": "Point cloud compression is an active research area in both industry and academia. Traditional point cloud compression codecs are generally interpretable, robust, and efficient [11,25,39,41]. However, neural codecs have shown better rate-distortion performance recently." + }, + { + "type": "text", + "bbox": [ + 0.503, + 0.092, + 0.891, + 0.257 + ], + "angle": 0, + "content": "Various data structures and models have been developed to boost the rate-distortion performance for learned point cloud compression. The pioneering works [15,17,36,44,48] construct analysis and synthesis transforms to compress point clouds to latent representations. These transforms are learned on point sets with the PointNet backbone [33, 34] or on the voxel structure using 3D convolution. However, distortions are inevitable in these transforms. It is therefore difficult to preserve high-frequency information in latent vectors. Hence, these structures are preferable to lossy compression at low bitrates." + }, + { + "type": "text", + "bbox": [ + 0.504, + 0.259, + 0.891, + 0.5 + ], + "angle": 0, + "content": "Learned entropy model is another effective pipeline to reduce bitrates without introducing distortion. Since the inference of the entropy model depends on the context, it is important to build an informative context. A typical entropy model predicts the binary occupancy status of the voxel based on the context of several adjacent voxels [30, 31]. Similarly, entropy model can be established on the octree by estimating occupancy symbol distributions. Early tree-structured entropy models exploit references from ancestor nodes [4, 16, 37]. Later works introduce adjacent voxels that have the same resolution as the currently coded octree node to provide high-resolution references [18]. A recent work replaces neighboring voxels with decoded siblings to extend the context [10], and it yields state-of-the-art performance. However, its efficiency is limited by the expensive global attention computation and auto-regressive processing." + }, + { + "type": "title", + "bbox": [ + 0.504, + 0.511, + 0.756, + 0.527 + ], + "angle": 0, + "content": "2.2. Learned Image Compression" + }, + { + "type": "text", + "bbox": [ + 0.504, + 0.535, + 0.891, + 0.791 + ], + "angle": 0, + "content": "The typical learned image compression pipeline is based on non-linear transforms and hyperprior-based entropy models [1,2,5,19,21,26,27,35,49]. In addition, decoded latent elements also can be introduced into the context to generate parameters for entropy coding, leading to improved performance with an auto-regressive coding process [28]. To accelerate the coding, a few parallel solutions have been developed [13, 14, 29]. The key of these modifications is performing auto-regression at the level of groups instead of pixels to parallelize coding within each group. For example, the checkerboard context model divides latent elements into two groups in the spatial domain [14]. A checkerboard mask is employed to constrain that the inference of the second group only refers to the decoded first group. Despite the data structures of point clouds and images are different, these strategies are instructive to solve the serial coding problem in point cloud compression." + }, + { + "type": "title", + "bbox": [ + 0.504, + 0.807, + 0.623, + 0.824 + ], + "angle": 0, + "content": "3. Preliminary" + }, + { + "type": "title", + "bbox": [ + 0.504, + 0.833, + 0.665, + 0.847 + ], + "angle": 0, + "content": "3.1. Octree Structure" + }, + { + "type": "text", + "bbox": [ + 0.504, + 0.857, + 0.891, + 0.9 + ], + "angle": 0, + "content": "The octree [24] provides a progressive representation of the point cloud, where each level represents the point cloud with a certain resolution. An octree recursively divides oc" + }, + { + "type": "page_number", + "bbox": [ + 0.482, + 0.946, + 0.518, + 0.956 + ], + "angle": 0, + "content": "14369" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.196 + ], + "angle": 0, + "content": "cupied voxels into 8 equal-sized subvoxels until the required resolution is reached. The occupancy symbol is composed of 8 bits (1 to 255 in decimal), where each bit indicates the occupancy status of the corresponding subvoxel. It is an effective data structure to represent large regions, since neighboring nodes in the breadth-first traversal order might locate at distant locations." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.197, + 0.468, + 0.304 + ], + "angle": 0, + "content": "The octree-based point cloud compression transmits an octree to the receiver instead of point coordinates [38, 39]. The octree is represented by a breadth-first traversed occupancy symbol sequence. An entropy coder is adopted to encode these symbols into the bitstream losslessly. At the receiver, an identical octree is reconstructed, which restores the geometry structure of the original point cloud." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.311, + 0.446, + 0.327 + ], + "angle": 0, + "content": "3.2. Large-scale Auto-regressive Entropy Model" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.334, + 0.468, + 0.395 + ], + "angle": 0, + "content": "The entropy coder encodes the occupancy symbol sequence \\(\\mathbf{x} = \\{x_{1},\\ldots ,x_{n}\\}\\) according to the distribution \\(\\tilde{p} (\\mathbf{x})\\) estimated by a learned entropy model. The joint distribution is factorized as the product of probability of each node:" + }, + { + "type": "equation", + "bbox": [ + 0.192, + 0.402, + 0.468, + 0.433 + ], + "angle": 0, + "content": "\\[\n\\tilde {p} (\\mathbf {x}) = \\prod_ {i} \\tilde {p} _ {i} \\left(x _ {i} \\mid \\mathbf {C} _ {i}\\right), \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.441, + 0.468, + 0.531 + ], + "angle": 0, + "content": "where \\(\\mathbf{C}_i\\) is the contextual information for predicting \\(x_{i}\\). Here, nodes are considered to be conditionally independent. Consumed bitrates are given by the cross entropy between the estimated distribution \\(\\tilde{p} (\\mathbf{x})\\) and ground truth \\(p(\\mathbf{x})\\), formulated as \\(\\mathbb{E}_{\\mathbf{x}\\sim p}\\left[-\\log_2\\tilde{p} (\\mathbf{x})\\right]\\). An accurate entropy model that minimizes this entropy is helpful to reduce bitrates." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.532, + 0.468, + 0.607 + ], + "angle": 0, + "content": "To formulate the context structure, we characterize each octree node \\( n_i \\) by features \\( \\mathbf{u}_i \\) including its occupancy symbol \\( x_i \\), level index, octant index, and parent bounding box coordinates. The ancestral context collects features from the currently coded node and its \\( K \\) ancestors as:" + }, + { + "type": "equation", + "bbox": [ + 0.145, + 0.614, + 0.468, + 0.634 + ], + "angle": 0, + "content": "\\[\n\\mathbf {a} _ {i} = \\left\\{\\mathbf {u} _ {i} ^ {\\emptyset}, \\mathbf {u} _ {\\text {a n c} (i)}, \\dots , \\mathbf {u} _ {\\text {a n c} (\\dots \\text {a n c} (i))} \\right\\}, \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.641, + 0.468, + 0.701 + ], + "angle": 0, + "content": "where \\(\\mathbf{u}_i^\\varnothing\\) excludes \\(x_{i}\\) from \\(\\mathbf{u}_i\\) since it is unknown when decoding \\(x_{i}\\). The ancestor-dependent methods [4, 16] predict the occupancy distribution \\(\\tilde{p}_i(x_i)\\) based on the ancestral context \\(\\mathbf{a}_i\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.702, + 0.468, + 0.807 + ], + "angle": 0, + "content": "The large-scale auto-regressive entropy model [10] constructs an extensive context to incorporate more information for inference. It combines the occupancy symbol of the previous sibling with the ancestral context as \\(\\mathbf{v}_i = \\{x_{i - 1},\\mathbf{a}_i\\}\\). Besides, the context is extended by introducing features from \\(N - 1\\) previously decoded sibling nodes and their ancestors to build a context window with length \\(N\\):" + }, + { + "type": "equation", + "bbox": [ + 0.185, + 0.816, + 0.468, + 0.833 + ], + "angle": 0, + "content": "\\[\n\\mathbf {C} _ {i} = \\left\\{\\mathbf {v} _ {i - N + 1}, \\dots , \\mathbf {v} _ {i} \\right\\}. \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.468, + 0.901 + ], + "angle": 0, + "content": "\\(\\mathbf{C}_i\\) is then embedded to features \\(\\mathbf{F}_i = \\{\\mathbf{f}_{i - N + 1},\\dots ,\\mathbf{f}_i\\}\\) and a self-attention module [42] is adopted to model dependencies among \\(N\\) embedded features. A mask is employed to constrain that only causal contexts \\(\\mathbf{f}_{< i}\\) are visible." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.091, + 0.89, + 0.122 + ], + "angle": 0, + "content": "Finally, attention-weighted features \\(\\tilde{\\mathbf{f}}_i\\) are projected to the distribution \\(\\tilde{p}_i(x_i)\\), which is used for entropy coding." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.123, + 0.892, + 0.304 + ], + "angle": 0, + "content": "Since the octree is coded in a breadth-first manner, ancestral contexts are completely known while coding any node. Therefore, the ancestor-dependent entropy model can decode multiple nodes at the same octree level in parallel. In contrast, the auto-regressive context model is conditioned on previously decoded siblings (e.g., \\( x_{i-1} \\)). It hence requires a serial decoding process. The global attention computation among \\( N \\) elements in \\( \\mathbf{F}_i \\) also limits its efficiency. However, large-scale contexts and sibling references are still effective to improve performance. Therefore, we aim to build an efficient entropy model while preserving these advantages." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.321, + 0.836, + 0.339 + ], + "angle": 0, + "content": "4. Efficient Hierarchical Entropy Model" + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.347, + 0.696, + 0.362 + ], + "angle": 0, + "content": "4.1. Overall Architecture" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.372, + 0.892, + 0.538 + ], + "angle": 0, + "content": "The overview of the proposed entropy model is shown in Fig. 2. It is composed of a grouped context structure and a hierarchical attention model. The occupancy sequence \\(\\mathbf{x}\\) is divided into a series of non-overlapped subsequences \\(\\mathbf{x}_i = \\{x_{i-N+1},\\dots,x_i\\}\\) with length \\(N\\). Contextual information for each subsequence is called a context window. The grouped context equally partitions \\(\\mathbf{x}_i\\) into two groups \\(\\mathbf{x}_{i_1}\\) and \\(\\mathbf{x}_{i_2}\\). The first group \\(\\mathbf{x}_{i_1}\\) is only conditioned on the ancestral context \\(\\mathbf{A}_i = \\{\\mathbf{a}_{i-N+1},\\dots,\\mathbf{a}_i\\}\\), where \\(\\mathbf{a}_i\\) is defined in Eq. (2). The second group \\(\\mathbf{x}_{i_2}\\) is conditioned on both siblings \\(\\mathbf{x}_{i_1}\\) and ancestors \\(\\mathbf{A}_i\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.54, + 0.892, + 0.836 + ], + "angle": 0, + "content": "The hierarchical attention model computes dependencies within local windows to improve the efficiency. The self-attention model discovers dependencies among \\(N\\) ancestral features. The ancestral context \\(\\mathbf{A}_i\\) is partitioned into \\(\\frac{N}{L}\\) non-overlapped local windows with length \\(L\\). Then we regard parent coordinates in the same window as a point cloud, and feed \\(\\mathbf{A}_i\\) to a DGCNN-based [46] feature extractor to generate \\(C\\)-dimensional geometry-aware features \\(\\mathbf{F}_i^a\\) from local windows separately. \\(\\mathbf{F}_i^a\\) is then passed to successive localized self-attention blocks. Weighted ancestral features of the first group are projected to occupancy distributions \\(\\tilde{p} (\\mathbf{x}_{i_1})\\) using a multi-layer perceptron (MLP). Then \\(\\mathbf{x}_{i_1}\\) is coded and we predict the second group \\(\\mathbf{x}_{i_2}\\). \\(\\mathbf{x}_{i_1}\\) is embedded to \\(\\mathbf{F}_{i_1}^s\\) and concatenated to its ancestral features \\(\\tilde{\\mathbf{F}}_{i_1}^a\\) as \\(\\mathbf{F}_{i_1}\\). Subsequently, we adopt a hierarchical cross-attention model to introduce sibling-involved features \\(\\mathbf{F}_{i_1}\\) to ancestral features \\(\\tilde{\\mathbf{F}}_{i_2}^a\\). Finally, an MLP produces distributions \\(\\tilde{p} (\\mathbf{x}_{i_2})\\) based on sibling features \\(\\tilde{\\mathbf{F}}_{i_2}^s\\) and ancestral features \\(\\tilde{\\mathbf{F}}_{i_2}^a\\)." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.846, + 0.671, + 0.862 + ], + "angle": 0, + "content": "4.2. Grouped Context" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.871, + 0.892, + 0.901 + ], + "angle": 0, + "content": "The auto-regressive context model requires serial decoding since it depends on the previous sibling \\( x_{i-1} \\). To" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "14370" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.089, + 0.631, + 0.3 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.668, + 0.089, + 0.889, + 0.182 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.668, + 0.184, + 0.888, + 0.299 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.311, + 0.893, + 0.368 + ], + "angle": 0, + "content": "Figure 2. Left: The architecture of EHEM for context window length \\( N = 4 \\) and local window length \\( L = 2 \\). Red, blue, and yellow nodes denote ancestral features, sibling-involved features, and estimated distributions, respectively. Attention is computed within local windows (dashed boxes). Right: The encoding and decoding process following the grouped context structure. The occupancy sequence \\( \\mathbf{x}_i \\) is split into two disjoint groups and coded in turn." + }, + { + "type": "image", + "bbox": [ + 0.085, + 0.389, + 0.462, + 0.492 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.501, + 0.468, + 0.528 + ], + "angle": 0, + "content": "Figure 3. Illustration of auto-regressive (left) and grouped (right) context structures." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.565, + 0.468, + 0.716 + ], + "angle": 0, + "content": "address this issue, we decompose the occupancy subsequence into two groups and remove dependencies within each group. As shown in Fig. 3, \\(\\mathbf{x}_{i_1}\\) is first decoded based on the ancestral context \\(\\mathbf{A}_i\\), then it is introduced as sibling priors to predict \\(\\mathbf{x}_{i_2}\\). Since the required contexts are completely known before decoding each group, nodes in the same group can be decoded in parallel. The auto-regressive entropy model requires \\(N\\) sequential steps to decode the subsequence \\(\\mathbf{x}_i\\), while the grouped context only takes 2 steps to decode two groups in turn." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.72, + 0.468, + 0.901 + ], + "angle": 0, + "content": "The prediction of \\(\\mathbf{x}_{i_2}\\) depends on \\(\\mathbf{x}_{i_1}\\), and hence it is important to design an effective decomposition pattern. We visualize ancestral dependencies among the first 16 siblings in the context window in Fig. 4b. Dependencies are represented by normalized attention scores computed on \\(\\mathbf{F}_i^a\\), and results are averaged over all self-attention layers from around 200 SemanticKITTI scans. Fig. 4b reveals that closer neighbors have stronger dependencies, and dependency activations at more distant locations are weak and uniform. This distribution is consistent with both intuitions and experiences in learned image compression [14]. We assume that dependencies computed on ancestral and sibling" + }, + { + "type": "image", + "bbox": [ + 0.505, + 0.39, + 0.695, + 0.526 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.699, + 0.389, + 0.892, + 0.525 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.5, + 0.537, + 0.892, + 0.565 + ], + "angle": 0, + "content": "Figure 4. Visualization of dependencies discovered by different methods. Deep colors indicate strong dependencies." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.594, + 0.891, + 0.625 + ], + "angle": 0, + "content": "involved contexts have similar distributions. With this property, we use a uniform decomposition pattern expressed as:" + }, + { + "type": "equation", + "bbox": [ + 0.51, + 0.637, + 0.891, + 0.677 + ], + "angle": 0, + "content": "\\[\n\\left\\{ \\begin{array}{l} \\mathbf {x} _ {i _ {1}} = \\left\\{x _ {1}, \\dots , x _ {2 j - 1}, \\dots , x _ {i - 1} \\right\\}, \\mathbf {C} _ {i _ {1}} = \\left\\{\\mathbf {A} _ {i} \\right\\}, \\\\ \\mathbf {x} _ {i _ {2}} = \\left\\{x _ {2}, \\dots , x _ {2 j}, \\dots , x _ {i} \\right\\}, \\mathbf {C} _ {i _ {2}} = \\left\\{\\mathbf {A} _ {i}, \\mathbf {x} _ {i _ {1}} \\right\\}. \\end{array} \\right. \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.689, + 0.89, + 0.719 + ], + "angle": 0, + "content": "It preserves two most important neighbors \\( x_{2j-1} \\) and \\( x_{2j+1} \\) for \\( x_{2j} \\) and uniformly samples \\( \\mathbf{x}_{i_1} \\) at more distant locations." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.892, + 0.901 + ], + "angle": 0, + "content": "In addition, the grouped context separates ancestral and sibling priors to utilize a complete ancestral context. For the auto-regressive context in OctAttention, ancestral and sibling features are concatenated when computing dependencies (see Eq. (3)). To keep the causality, both ancestral and sibling features from non-causal positions (i.e., \\( \\mathbf{f}_{>i} \\)) are discarded, as shown in Fig. 4a. However, these ancestral features are actually available. As illustrated in Fig. 4b, \\( \\mathbf{f}_{>i}^{a} \\) have similar dependency activations to \\( \\mathbf{f}_{< i}^{a} \\). Therefore, they are equivalently important to compute dependencies. The grouped context structure accesses to more ancestral features, which leads to better compression performance." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "14371" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.086, + 0.088, + 0.465, + 0.213 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.222, + 0.47, + 0.263 + ], + "angle": 0, + "content": "Figure 5. Illustration of two successive localized attention layers for the case of \\( N = 8 \\) and \\( L = 2 \\). MSA represents the multi-head self-attention." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.291, + 0.473, + 0.475 + ], + "angle": 0, + "content": "From the perspective of context modeling, this grouped context can be interpreted as the space-channel context in image compression [13]. As shown in Eq. (3), \\( N \\) nodes constitute the spatial domain, and each spatial position has \\( K + 1 \\) channels, consisting of \\( K \\) ancestors and 1 sibling. The grouped context partitions on both channel and spatial dimensions. Available contexts for each element are decoded channels (ancestors) from all spatial positions, and elements in the same channel (siblings) at decoded spatial positions. Therefore, it is feasible to use similar context structures for point cloud and image compression, and both domains might benefit from advances of each other." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.484, + 0.288, + 0.499 + ], + "angle": 0, + "content": "4.3. Hierarchical Attention" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.508, + 0.47, + 0.84 + ], + "angle": 0, + "content": "To reduce the complexity, we discover dependencies within local windows and model long-range dependencies with a multi-scale network structure. It is inspired by vision transformers designed for 2D images [8, 22, 23, 45]. Since the localized attention can not exploit long-range dependencies in the large-scale context, we gradually downsample the context to represent numerous nodes with \\( L \\) tokens. The downsampling is implemented by a node merging operation. Two neighboring nodes are merged by concatenating their features on the channel dimension. Then, \\( 2C \\)-dimensional concatenated features are passed to an MLP to shrink the channel dimension to \\( C \\). In this way, features from distant nodes can be computed in the same window and the receptive field is increased. Furthermore, dependencies are estimated at different scales, and closer neighbors are computed with fine-grained representations. It is reasonable since closer neighbors are more informative. In contrast, distant nodes can be coarsely characterized. We further introduce the shifted window strategy [23] to capture dependencies across neighboring local windows. Dependencies are computed with a window partition alternating between two patterns, as shown in Fig. 5." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.47, + 0.904 + ], + "angle": 0, + "content": "A self-attention block is composed of various localized attention layers and one node merging module (except for the last block). The hierarchical attention model is a stack of \\(\\log_2\\frac{N}{L} + 1\\) blocks to capture all \\(N\\) nodes in the last block." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.166 + ], + "angle": 0, + "content": "The number of blocks can be further reduced by aggregating more than two nodes in a single node merging module. We produce a hierarchical representation \\(\\bar{\\mathbf{F}}_i^a\\) by aggregating features and dependencies from different scales. Therefore, we refer to this model as a hierarchical attention model." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.168, + 0.892, + 0.228 + ], + "angle": 0, + "content": "By performing attention operations within local windows, the hierarchical attention model reduces the complexity from quadratic to linear scale. Complexities of attention computations in global and localized self-attention are:" + }, + { + "type": "equation", + "bbox": [ + 0.538, + 0.239, + 0.892, + 0.257 + ], + "angle": 0, + "content": "\\[\n\\Omega (\\text {G l o b a l}) = 2 N ^ {2} C, \\quad \\Omega (\\text {L o c a l i z e d}) = 2 L N C. \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.268, + 0.892, + 0.328 + ], + "angle": 0, + "content": "It allows us to build a much deeper entropy model with reasonable computational costs to enhance the modeling capability, or substantially expand the context scale to introduce more potentially useful references." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.328, + 0.892, + 0.513 + ], + "angle": 0, + "content": "The hierarchical cross-attention follows a similar localized attention practice. Since the decomposition pattern is uniform, each local window includes \\(\\frac{L}{2}\\) nodes from \\(\\mathbf{x}_{i_1}\\) and another \\(\\frac{L}{2}\\) nodes from \\(\\mathbf{x}_{i_2}\\). They are regarded as key and query features, respectively. We compute dependencies among keys and queries within each local window, and weight keys according to their dependencies to queries. To extend the receptive field, neighboring keys (and queries) are progressively merged into new key (and query) tokens. Finally, features from different scales are concatenated, which are then exploited to predict \\(x_{i_2}\\) with ancestral features \\(\\tilde{\\mathbf{F}}_{i_2}^a\\) jointly." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.52, + 0.609, + 0.537 + ], + "angle": 0, + "content": "4.4. Learning" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.544, + 0.892, + 0.62 + ], + "angle": 0, + "content": "The optimization objective of the octree-based entropy model is to minimize the total bitrates for communicating octree nodes. The bitrate is given by the cross entropy between the estimated distribution \\(\\tilde{p} (\\mathbf{x})\\) and the ground truth \\(p(\\mathbf{x})\\) at each node:" + }, + { + "type": "equation", + "bbox": [ + 0.607, + 0.63, + 0.892, + 0.662 + ], + "angle": 0, + "content": "\\[\n\\ell = - \\sum_ {i} \\log \\tilde {p} _ {i} \\left(x _ {i} \\mid \\mathbf {C} _ {i}\\right), \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.673, + 0.891, + 0.705 + ], + "angle": 0, + "content": "where \\(\\tilde{p}_i(x_i\\mid \\mathbf{C}_i)\\) is the distribution estimated by the proposed entropy model based on the context \\(\\mathbf{C}_i\\)" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.717, + 0.633, + 0.734 + ], + "angle": 0, + "content": "5. Experiments" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.742, + 0.707, + 0.759 + ], + "angle": 0, + "content": "5.1. Experimental Settings" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.892, + 0.903 + ], + "angle": 0, + "content": "Datasets Experiments are conducted on two large-scale point cloud datasets SemanticKITTI [3] and Ford [32]. SemanticKITTI is composed of 43552 LiDAR scans acquired from autonomous driving scenes, which are divided into 22 sequences. We follow the default split to perform training on sequences 00 to 10 and evaluation on sequences 11 to 21. Ford is another LiDAR point cloud dataset used in MPEG point cloud compression standardization. It includes 3 sequences, each consists of 1500 scans. On the Ford dataset," + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "14372" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.086, + 0.088, + 0.344, + 0.255 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.356, + 0.088, + 0.613, + 0.255 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.626, + 0.089, + 0.885, + 0.256 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.082, + 0.264, + 0.345, + 0.43 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.355, + 0.264, + 0.613, + 0.43 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.626, + 0.264, + 0.884, + 0.43 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.178, + 0.441, + 0.792, + 0.456 + ], + "angle": 0, + "content": "Figure 6. Rate-distortion performance of different methods on SemanticKITTI (top) and Ford (bottom)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.481, + 0.47, + 0.527 + ], + "angle": 0, + "content": "we follow the suggested dataset partition in MPEG standardization [7], where sequence 01 is used for training and sequences 02 and 03 are used for evaluation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.53, + 0.47, + 0.622 + ], + "angle": 0, + "content": "Baselines To verify the effectiveness of the proposed model, we compare it with the state-of-the-art octree-based learned entropy model OctAttention [10] and the competitive voxel-based learned method SparsePCGC [43]. We also provide comparisons with the representative handcrafted compression method MPEG G-PCC [12]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.626, + 0.47, + 0.776 + ], + "angle": 0, + "content": "Implementation settings Quantization is necessary to construct octrees from point clouds. For SemanticKITTI, we follow the quantization settings in OctSqueeze [16], where the quantization step is set to \\(\\frac{400}{2^{D} - 1}\\) to build an octree with the depth of \\(D\\). Octrees are truncated with a maximum depth of 16 for training and evaluation. We set the quantization step to \\(2^{18 - D}\\) and construct octrees with the maximum depth of 18 on Ford. Since the original Ford dataset has been quantized with 18-bit precision, compression is lossless at the highest octree level." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.78, + 0.471, + 0.903 + ], + "angle": 0, + "content": "The hierarchical self-attention model has 5 blocks including 4, 4, 4, 4, 2 layers, respectively. The hierarchical cross-attention model consists of 4 blocks with 2, 2, 1, 1 layers. The head number is set to 4 for all attention layers. The channel dimension \\( C \\) is set to 256, and the ancestor depth \\( K \\) is set to 3. The context window length \\( N \\) is set to 8192, which is initially divided into 16 local windows with the length \\( L \\) of 512. To further achieve speed-accuracy trade" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.48, + 0.892, + 0.52 + ], + "angle": 0, + "content": "Table 1. Inference times (in seconds) for encoding/decoding a D-depth octree on SemanticKITTI. Runtimes for G-PCC are total times." + }, + { + "type": "table", + "bbox": [ + 0.506, + 0.532, + 0.885, + 0.629 + ], + "angle": 0, + "content": "
MethodD=12D=14D=16
G-PCC0.25 / 0.120.66 / 0.321.07 / 0.54
SparsePCGC1.14 / 0.861.76 / 1.432.43 / 2.04
OctAttention0.08 / 830.31 / 3210.66 / 708
EHEM0.40 / 0.431.21 / 1.392.53 / 3.01
Light EHEM0.29 / 0.330.79 / 0.921.63 / 1.94
" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.664, + 0.892, + 0.724 + ], + "angle": 0, + "content": "offs, we present a lightweight EHEM model called Light EHEM. It has the same network structure as EHEM except that its 5 self-attention blocks have 2, 2, 2, 2, 2 layers and its channel dimension \\( C \\) is set to 192." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.73, + 0.892, + 0.79 + ], + "angle": 0, + "content": "We adopt an Adam optimizer [20] with a learning rate of \\(10^{-4}\\) to train two models for 10 and 50 epochs on SemanticKITTI and Ford datasets, respectively. The evaluation is implemented on the NVIDIA V100 GPU." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.795, + 0.892, + 0.902 + ], + "angle": 0, + "content": "Metrics We adopt the point-to-point PSNR (D1 PSNR), point-to-plane PSNR (D2 PSNR) [6], and Chamfer distance (CD) to measure the distortion. Experiments on SemanticKITTI follow the PSNR calculations in OctSqueeze and MuSCLE [4, 16], where the peak value is set to 59.70. On the Ford dataset, we set the peak value to 30000 [6]. Consumed bitrates are measured by bits per point (bpp)." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "14373" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.089, + 0.472, + 0.132 + ], + "angle": 0, + "content": "Table 2. Complexity comparison on encoding/decoding time, theoretical computation cost (FLOPs), parameters, and memory usage among OctAttention, EHEM, and Light EHEM." + }, + { + "type": "table", + "bbox": [ + 0.079, + 0.142, + 0.468, + 0.208 + ], + "angle": 0, + "content": "
MethodEnc / DecFLOPs#param.Mem.
OctAttn0.66s / 708s124.3G4.23M1.3G
EHEM2.53s / 3.01s184.4G13.01M2.9G
L-EHEM1.63s / 1.94s102.9G6.34M2.6G
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.224, + 0.47, + 0.253 + ], + "angle": 0, + "content": "Table 3. Comparison of FLOPs among OctAttention, EHEM, and Light EHEM with respect to the context length \\( N \\) ." + }, + { + "type": "table", + "bbox": [ + 0.079, + 0.264, + 0.472, + 0.33 + ], + "angle": 0, + "content": "
Method5121024204840968192
OctAttn6.0G15.5G45.0G145.7G514.0G
EHEM9.0G18.4G38.1G81.5G184.4G
L-EHEM5.2G10.7G21.9G46.4G102.9G
" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.358, + 0.303, + 0.373 + ], + "angle": 0, + "content": "5.2. Performance Evaluation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.384, + 0.47, + 0.504 + ], + "angle": 0, + "content": "The quantitative results of the rate-distortion performance are shown in Fig. 6. The proposed method EHEM achieves significant improvements over other baselines. For example, on SemanticKITTI, EHEM achieves an average gain of \\(28.89\\%\\) to G-PCC, and \\(19.47\\%\\) bitrate reduction on average compared with OctAttention. Furthermore, Light EHEM also preserves satisfactory performance and outperforms other baselines." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.506, + 0.47, + 0.688 + ], + "angle": 0, + "content": "To evaluate the efficiency of EHEM, we report inference times at different quantization steps in Tab. 1. EHEM achieves notable decoding time reduction over the autoregressive context model OctAttention. The encoding time increases compared with OctAttention since the grouped context requires a two-step inference (for \\( \\mathbf{x}_{i_1} \\) and \\( \\mathbf{x}_{i_2} \\)), while OctAttention only requires one step. However, this encoding time is still practically acceptable and the grouped context is effective to speed up decoding. We further represent both rate-distortion performance and decoding time in Fig. 1. It is shown that EHEM is effective regarding both compression performance and decoding speed." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.689, + 0.471, + 0.901 + ], + "angle": 0, + "content": "We provide the complexity analysis of EHEM and OctAttention in Tab. 2 and Tab. 3. Here, we report required FLOPs to infer a single context window. Note that larger context predicts more nodes with one forward pass. For example, EHEM requires \\(81.5 \\times 2\\) and \\(184.4 \\times 1\\) GFLOPs to predict 8192 nodes when \\(N\\) is set to 4096 and 8192, respectively. It is shown that EHEM has comparable FLOPs to OctAttention when the context capacity is 1024, which is the default setting for OctAttention. However, EHEM contains 24 hierarchical attention layers while OctAttention only includes 2 global attention layers. It proves the superiority of the localized attention structure in terms of extending the network depth. Furthermore, localized attention is also effective to enlarge the context due to the linear com" + }, + { + "type": "image", + "bbox": [ + 0.507, + 0.087, + 0.885, + 0.305 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.314, + 0.892, + 0.342 + ], + "angle": 0, + "content": "Figure 7. Ablation studies on attention models, context scales, and context structures." + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.357, + 0.695, + 0.471 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.699, + 0.357, + 0.892, + 0.471 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.5, + 0.481, + 0.892, + 0.508 + ], + "angle": 0, + "content": "Figure 8. Contexts with different capacities \\( N \\) on 16-bit quantized SemanticKITTI. Points in the context are colored in blue." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.536, + 0.892, + 0.672 + ], + "angle": 0, + "content": "plexity. FLOPs of EHEM increase 2.26 times as the context is enlarged from 4096 to 8192. In contrast, the complexity of OctAttention increases 3.53 times with the same extension. Besides, Light EHEM achieves lower FLOPs at all context window length settings compared to OctAttention. EHEM has slightly larger model size and memory usage compared with OctAttention. These increases are due to the extension of model capacity and context scale, but it is still reasonable for practical use." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.681, + 0.768, + 0.697 + ], + "angle": 0, + "content": "5.3. Ablation Studies and Analysis" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.704, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Hierarchical attention structure To verify the effectiveness of the hierarchical attention structure, we replace the hierarchical self-attention model with global self-attention layers to build a counterpart with similar FLOPs. Since it is impractical to compute global self-attention with \\( N = 8192 \\), we conduct experiments with \\( N = 1024 \\). Here, EHEM still has 18 localized self-attention layers, and the global-attention counterpart contains 5 layers. The comparison between EHEM (\\( N = 1024 \\)) and Global Self-Attn in Fig. 7 proves that the hierarchical attention model with a much deeper network achieves considerable improvements. Network depth With the same network structure, the comparison between EHEM and Light EHEM shows that the" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "14374" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.107, + 0.093, + 0.865, + 0.386 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.146, + 0.396, + 0.822, + 0.412 + ], + "angle": 0, + "content": "Figure 9. Visualized compression results of G-PCC, OctAttention, and our method on the SemanticKITTI dataset." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.437, + 0.471, + 0.483 + ], + "angle": 0, + "content": "deeper network leads to better performance. Therefore, it is helpful to enhance the expressiveness of the model by stacking more layers within a reasonable range." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.488, + 0.47, + 0.625 + ], + "angle": 0, + "content": "Context scale The linear complexity of the hierarchical attention also allows the further extension of the context scale \\( N \\). Contexts with different capacities are visualized in Fig. 8. It is shown that captured regions are significantly enlarged when \\( N \\) increases from 1024 to 8192. The extended context includes the complete geometry pattern of the vehicle and introduces references from the neighboring similar vehicle. This is beneficial to improve the rate-distortion performance, as shown in Fig. 7." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.629, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Grouped context structure The grouped context structure allows a two-step parallel decoding procedure. Here, we examine its influence on rate-distortion performance. To this end, we train a baseline with an auto-regressive context used in OctAttention. The hierarchical attention is unavailable to this context structure since the node merging operation uses non-causal ancestral references. For a fair comparison, we use global attention to compute dependencies for both grouped and auto-regressive context structures. The grouped context introduces features from the first group via global cross-attention layers. The comparison between AR Context and Grouped Context in Fig. 7 demonstrates that although only half of the nodes access to siblings, the grouped context structure achieves comparable performance. It is because the grouped context preserves ancestral features from non-causal references, as shown in Fig. 4b. Besides, it proves that the grouped context structure does not significantly improve compression performance. Therefore, im" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.437, + 0.892, + 0.467 + ], + "angle": 0, + "content": "provements of EHEM are mainly due to stronger hierarchical attention blocks." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.482, + 0.684, + 0.499 + ], + "angle": 0, + "content": "5.4. Qualitative Results" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.507, + 0.892, + 0.584 + ], + "angle": 0, + "content": "In Fig. 9, we show the visualized compression distortions of different methods at similar bitrates. It indicates that our method provides better reconstructions compared with other baselines. For example, EHEM outperforms G-PCC by roughly 10 dB D1 PSNR improvements." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.602, + 0.62, + 0.618 + ], + "angle": 0, + "content": "6. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.629, + 0.892, + 0.825 + ], + "angle": 0, + "content": "We proposed an efficient learned entropy model for point cloud compression. It adopts a hierarchical attention structure, which allows us to substantially extend the network depth and context capacity to improve the rate-distortion performance with reasonable complexity. We further developed a grouped context structure to realize a parallel decoding procedure. Moreover, this context aligns the context modeling regimes of point cloud and image compression, and we hope it would be helpful to bridge the gap between two communities. The proposed model is proved to yield superior compression performance and significantly reduce the decoding time compared to the state-of-the-art auto-regressive method." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.844, + 0.661, + 0.861 + ], + "angle": 0, + "content": "Acknowledgement" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.871, + 0.892, + 0.901 + ], + "angle": 0, + "content": "This work was supported by National Natural Science Foundation of China (No. 62172021)." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "14375" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.115, + 0.468, + 0.156 + ], + "angle": 0, + "content": "[1] Johannes Balle, Valero Laparra, and Eero P Simoncelli. End-to-end optimized image compression. 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Recently, the octree-based auto-regressive entropy model which adopts the self-attention mechanism to explore dependencies in a large-scale context is proved to be promising. However, heavy global attention computations and auto-regressive contexts are inefficient for practical applications. To improve the efficiency of the attention model, we propose a hierarchical attention structure that has a linear complexity to the context scale and maintains the global receptive field. Furthermore, we present a grouped context structure to address the serial decoding issue caused by the auto-regression while preserving the compression performance. Experiments demonstrate that the proposed entropy model achieves superior rate-distortion performance and significant decoding latency reduction compared with the state-of-the-art large-scale auto-regressive entropy model. + +# 1. Introduction + +Point cloud is a fundamental data structure to represent 3D scenes. It has been widely applied in 3D vision systems such as autonomous driving and immersive applications. The large-scale point cloud typically contains millions of points [36]. It is challenging to store and transmit such massive data. Hence, efficient point cloud compression that reduces memory footprints and transmission bandwidth is necessary to develop practical point cloud applications. + +Recently, deep learning methods have promoted the development of point cloud compression [4, 9, 10, 16, 31, 36, 40, 43]. It is a common pipeline to learn an octree-based entropy model to estimate octree node symbol (i.e., occupancy symbol) distributions. The point cloud is first organized as an octree, and occupancy symbols are then encoded into the bitstream losslessly by an entropy coder (e.g., arithmetic + +![](images/dd10b2b2886ee02b32a621ee036207fd249ece4002772f83f089636dc4c67f66.jpg) +Figure 1. Bitrate and decoding speed in the log scale for lossless compression on 16-bit quantized SemanticKITTI. The proposed method EHEM yields state-of-the-art performance with a comparable decoding latency to the efficient traditional method G-PCC. + +coder [47]). An accurate entropy model is required since it reduces the cross entropy between the estimated distribution and ground truth, which is corresponding to actual bitrates. Various attempts have been made to improve the accuracy by designing different context structures [4, 10, 16, 37]. The key of these advances is to increase the context capacity and introduce references from high-resolution octree representations. For example, the context in OctAttention [10] includes hundreds of previously decoded siblings (i.e., nodes at the same octree level). The large-scale context incorporates more references for the entropy coder, and the high-resolution context preserves detailed features of the point cloud. Both of them contribute to building informative contexts and effective entropy models. + +However, large-scale context requires heavy computations to model dependencies among numerous references. The previous work [10] uses the global self-attention mechanism to model long-range dependencies within the context, and its complexity is quadratic to the length of the + +large-scale context. Furthermore, considering the efficiency issue, it is infeasible to build a deeper entropy model or extend the context scale to enhance the modeling capability based on global attention. Another concern is the serial decoding process caused by the inclusion of previously decoded siblings. This auto-regressive context structure incurs a practically unacceptable decoding latency (e.g., around 700 seconds per frame). + +To address these issues, we build an entropy model with an efficient hierarchical attention model and a parallel-friendly grouped context structure. The hierarchical attention model partitions the context into local windows and computes attention within these windows independently. Therefore, the complexity is linear to the context scale, which allows the further extension of network depth and context capacity to improve performance. Since the receptive field of the localized attention is limited, we adopt a multi-scale network structure to query features across different windows. The context is progressively downsampled by merging neighboring nodes to generate a new token. Then, cross-window dependencies can be captured by incorporating these new tokens in the same window. The grouped context divides the occupancy symbol sequence into two groups. Each group is conditioned on ancestral features and previously decoded groups, and hence nodes in the same group can be coded in parallel. Furthermore, in contrast to the previous auto-regressive context that only exploits causal parts of the ancestral context [10], the grouped context allows to make use of a complete ancestral context. + +The proposed efficient hierarchical entropy model called EHEM is evaluated on SemanticKITTI [3] and Ford [32] benchmarks. It surpasses state-of-the-art methods in terms of both compression performance and efficiency. Contributions of this work can be summarized from the following perspectives: + +- We propose a hierarchical attention model, which yields improved compression performance by extending model and context while keeping the efficiency. +- We design a grouped context structure that enables parallel decoding. It adapts the entropy model using high-resolution references to practical applications. +- The proposed method achieves state-of-the-art RD performance with a practically applicable coding speed. + +# 2. Related Work + +# 2.1. Learned Point Cloud Compression + +Point cloud compression is an active research area in both industry and academia. Traditional point cloud compression codecs are generally interpretable, robust, and efficient [11,25,39,41]. However, neural codecs have shown better rate-distortion performance recently. + +Various data structures and models have been developed to boost the rate-distortion performance for learned point cloud compression. The pioneering works [15,17,36,44,48] construct analysis and synthesis transforms to compress point clouds to latent representations. These transforms are learned on point sets with the PointNet backbone [33, 34] or on the voxel structure using 3D convolution. However, distortions are inevitable in these transforms. It is therefore difficult to preserve high-frequency information in latent vectors. Hence, these structures are preferable to lossy compression at low bitrates. + +Learned entropy model is another effective pipeline to reduce bitrates without introducing distortion. Since the inference of the entropy model depends on the context, it is important to build an informative context. A typical entropy model predicts the binary occupancy status of the voxel based on the context of several adjacent voxels [30, 31]. Similarly, entropy model can be established on the octree by estimating occupancy symbol distributions. Early tree-structured entropy models exploit references from ancestor nodes [4, 16, 37]. Later works introduce adjacent voxels that have the same resolution as the currently coded octree node to provide high-resolution references [18]. A recent work replaces neighboring voxels with decoded siblings to extend the context [10], and it yields state-of-the-art performance. However, its efficiency is limited by the expensive global attention computation and auto-regressive processing. + +# 2.2. Learned Image Compression + +The typical learned image compression pipeline is based on non-linear transforms and hyperprior-based entropy models [1,2,5,19,21,26,27,35,49]. In addition, decoded latent elements also can be introduced into the context to generate parameters for entropy coding, leading to improved performance with an auto-regressive coding process [28]. To accelerate the coding, a few parallel solutions have been developed [13, 14, 29]. The key of these modifications is performing auto-regression at the level of groups instead of pixels to parallelize coding within each group. For example, the checkerboard context model divides latent elements into two groups in the spatial domain [14]. A checkerboard mask is employed to constrain that the inference of the second group only refers to the decoded first group. Despite the data structures of point clouds and images are different, these strategies are instructive to solve the serial coding problem in point cloud compression. + +# 3. Preliminary + +# 3.1. Octree Structure + +The octree [24] provides a progressive representation of the point cloud, where each level represents the point cloud with a certain resolution. An octree recursively divides oc + +cupied voxels into 8 equal-sized subvoxels until the required resolution is reached. The occupancy symbol is composed of 8 bits (1 to 255 in decimal), where each bit indicates the occupancy status of the corresponding subvoxel. It is an effective data structure to represent large regions, since neighboring nodes in the breadth-first traversal order might locate at distant locations. + +The octree-based point cloud compression transmits an octree to the receiver instead of point coordinates [38, 39]. The octree is represented by a breadth-first traversed occupancy symbol sequence. An entropy coder is adopted to encode these symbols into the bitstream losslessly. At the receiver, an identical octree is reconstructed, which restores the geometry structure of the original point cloud. + +# 3.2. Large-scale Auto-regressive Entropy Model + +The entropy coder encodes the occupancy symbol sequence $\mathbf{x} = \{x_{1},\ldots ,x_{n}\}$ according to the distribution $\tilde{p} (\mathbf{x})$ estimated by a learned entropy model. The joint distribution is factorized as the product of probability of each node: + +$$ +\tilde {p} (\mathbf {x}) = \prod_ {i} \tilde {p} _ {i} \left(x _ {i} \mid \mathbf {C} _ {i}\right), \tag {1} +$$ + +where $\mathbf{C}_i$ is the contextual information for predicting $x_{i}$ . Here, nodes are considered to be conditionally independent. Consumed bitrates are given by the cross entropy between the estimated distribution $\tilde{p} (\mathbf{x})$ and ground truth $p(\mathbf{x})$ , formulated as $\mathbb{E}_{\mathbf{x}\sim p}\left[-\log_2\tilde{p} (\mathbf{x})\right]$ . An accurate entropy model that minimizes this entropy is helpful to reduce bitrates. + +To formulate the context structure, we characterize each octree node $n_i$ by features $\mathbf{u}_i$ including its occupancy symbol $x_i$ , level index, octant index, and parent bounding box coordinates. The ancestral context collects features from the currently coded node and its $K$ ancestors as: + +$$ +\mathbf {a} _ {i} = \left\{\mathbf {u} _ {i} ^ {\emptyset}, \mathbf {u} _ {\text {a n c} (i)}, \dots , \mathbf {u} _ {\text {a n c} (\dots \text {a n c} (i))} \right\}, \tag {2} +$$ + +where $\mathbf{u}_i^\varnothing$ excludes $x_{i}$ from $\mathbf{u}_i$ since it is unknown when decoding $x_{i}$ . The ancestor-dependent methods [4, 16] predict the occupancy distribution $\tilde{p}_i(x_i)$ based on the ancestral context $\mathbf{a}_i$ . + +The large-scale auto-regressive entropy model [10] constructs an extensive context to incorporate more information for inference. It combines the occupancy symbol of the previous sibling with the ancestral context as $\mathbf{v}_i = \{x_{i - 1},\mathbf{a}_i\}$ . Besides, the context is extended by introducing features from $N - 1$ previously decoded sibling nodes and their ancestors to build a context window with length $N$ : + +$$ +\mathbf {C} _ {i} = \left\{\mathbf {v} _ {i - N + 1}, \dots , \mathbf {v} _ {i} \right\}. \tag {3} +$$ + +$\mathbf{C}_i$ is then embedded to features $\mathbf{F}_i = \{\mathbf{f}_{i - N + 1},\dots ,\mathbf{f}_i\}$ and a self-attention module [42] is adopted to model dependencies among $N$ embedded features. A mask is employed to constrain that only causal contexts $\mathbf{f}_{< i}$ are visible. + +Finally, attention-weighted features $\tilde{\mathbf{f}}_i$ are projected to the distribution $\tilde{p}_i(x_i)$ , which is used for entropy coding. + +Since the octree is coded in a breadth-first manner, ancestral contexts are completely known while coding any node. Therefore, the ancestor-dependent entropy model can decode multiple nodes at the same octree level in parallel. In contrast, the auto-regressive context model is conditioned on previously decoded siblings (e.g., $x_{i-1}$ ). It hence requires a serial decoding process. The global attention computation among $N$ elements in $\mathbf{F}_i$ also limits its efficiency. However, large-scale contexts and sibling references are still effective to improve performance. Therefore, we aim to build an efficient entropy model while preserving these advantages. + +# 4. Efficient Hierarchical Entropy Model + +# 4.1. Overall Architecture + +The overview of the proposed entropy model is shown in Fig. 2. It is composed of a grouped context structure and a hierarchical attention model. The occupancy sequence $\mathbf{x}$ is divided into a series of non-overlapped subsequences $\mathbf{x}_i = \{x_{i-N+1},\dots,x_i\}$ with length $N$ . Contextual information for each subsequence is called a context window. The grouped context equally partitions $\mathbf{x}_i$ into two groups $\mathbf{x}_{i_1}$ and $\mathbf{x}_{i_2}$ . The first group $\mathbf{x}_{i_1}$ is only conditioned on the ancestral context $\mathbf{A}_i = \{\mathbf{a}_{i-N+1},\dots,\mathbf{a}_i\}$ , where $\mathbf{a}_i$ is defined in Eq. (2). The second group $\mathbf{x}_{i_2}$ is conditioned on both siblings $\mathbf{x}_{i_1}$ and ancestors $\mathbf{A}_i$ . + +The hierarchical attention model computes dependencies within local windows to improve the efficiency. The self-attention model discovers dependencies among $N$ ancestral features. The ancestral context $\mathbf{A}_i$ is partitioned into $\frac{N}{L}$ non-overlapped local windows with length $L$ . Then we regard parent coordinates in the same window as a point cloud, and feed $\mathbf{A}_i$ to a DGCNN-based [46] feature extractor to generate $C$ -dimensional geometry-aware features $\mathbf{F}_i^a$ from local windows separately. $\mathbf{F}_i^a$ is then passed to successive localized self-attention blocks. Weighted ancestral features of the first group are projected to occupancy distributions $\tilde{p} (\mathbf{x}_{i_1})$ using a multi-layer perceptron (MLP). Then $\mathbf{x}_{i_1}$ is coded and we predict the second group $\mathbf{x}_{i_2}$ . $\mathbf{x}_{i_1}$ is embedded to $\mathbf{F}_{i_1}^s$ and concatenated to its ancestral features $\tilde{\mathbf{F}}_{i_1}^a$ as $\mathbf{F}_{i_1}$ . Subsequently, we adopt a hierarchical cross-attention model to introduce sibling-involved features $\mathbf{F}_{i_1}$ to ancestral features $\tilde{\mathbf{F}}_{i_2}^a$ . Finally, an MLP produces distributions $\tilde{p} (\mathbf{x}_{i_2})$ based on sibling features $\tilde{\mathbf{F}}_{i_2}^s$ and ancestral features $\tilde{\mathbf{F}}_{i_2}^a$ . + +# 4.2. Grouped Context + +The auto-regressive context model requires serial decoding since it depends on the previous sibling $x_{i-1}$ . To + +![](images/79d266ca715e8b069a33ad493e6c141a58f4628ffe96b043eae646dcf915a9f3.jpg) +Figure 2. Left: The architecture of EHEM for context window length $N = 4$ and local window length $L = 2$ . Red, blue, and yellow nodes denote ancestral features, sibling-involved features, and estimated distributions, respectively. Attention is computed within local windows (dashed boxes). Right: The encoding and decoding process following the grouped context structure. The occupancy sequence $\mathbf{x}_i$ is split into two disjoint groups and coded in turn. + +![](images/d42bb57a02c632986e5aadc02082862532df9ba6c6ad9079cfa23906b5f4b64f.jpg) + +![](images/cfd524b3df22712003e28bfa86eadaf5a48a20bf8a4cd3bca185f2ed67f52992.jpg) + +![](images/f3f07b64a301cf3897e3e12d849aa69d4d15ee271d70566c251632086fe48e7f.jpg) +Figure 3. Illustration of auto-regressive (left) and grouped (right) context structures. + +address this issue, we decompose the occupancy subsequence into two groups and remove dependencies within each group. As shown in Fig. 3, $\mathbf{x}_{i_1}$ is first decoded based on the ancestral context $\mathbf{A}_i$ , then it is introduced as sibling priors to predict $\mathbf{x}_{i_2}$ . Since the required contexts are completely known before decoding each group, nodes in the same group can be decoded in parallel. The auto-regressive entropy model requires $N$ sequential steps to decode the subsequence $\mathbf{x}_i$ , while the grouped context only takes 2 steps to decode two groups in turn. + +The prediction of $\mathbf{x}_{i_2}$ depends on $\mathbf{x}_{i_1}$ , and hence it is important to design an effective decomposition pattern. We visualize ancestral dependencies among the first 16 siblings in the context window in Fig. 4b. Dependencies are represented by normalized attention scores computed on $\mathbf{F}_i^a$ , and results are averaged over all self-attention layers from around 200 SemanticKITTI scans. Fig. 4b reveals that closer neighbors have stronger dependencies, and dependency activations at more distant locations are weak and uniform. This distribution is consistent with both intuitions and experiences in learned image compression [14]. We assume that dependencies computed on ancestral and sibling + +![](images/45ddc2833a4ed01fef535418ebb5495ed7d3dbdda2df8a630540f6120d8f8b28.jpg) +Figure 4. Visualization of dependencies discovered by different methods. Deep colors indicate strong dependencies. + +![](images/ab6324581e1ff62d1c29a10b97683c169e361298a94a04f3e22a8a41280ddd2d.jpg) + +involved contexts have similar distributions. With this property, we use a uniform decomposition pattern expressed as: + +$$ +\left\{ \begin{array}{l} \mathbf {x} _ {i _ {1}} = \left\{x _ {1}, \dots , x _ {2 j - 1}, \dots , x _ {i - 1} \right\}, \mathbf {C} _ {i _ {1}} = \left\{\mathbf {A} _ {i} \right\}, \\ \mathbf {x} _ {i _ {2}} = \left\{x _ {2}, \dots , x _ {2 j}, \dots , x _ {i} \right\}, \mathbf {C} _ {i _ {2}} = \left\{\mathbf {A} _ {i}, \mathbf {x} _ {i _ {1}} \right\}. \end{array} \right. \tag {4} +$$ + +It preserves two most important neighbors $x_{2j-1}$ and $x_{2j+1}$ for $x_{2j}$ and uniformly samples $\mathbf{x}_{i_1}$ at more distant locations. + +In addition, the grouped context separates ancestral and sibling priors to utilize a complete ancestral context. For the auto-regressive context in OctAttention, ancestral and sibling features are concatenated when computing dependencies (see Eq. (3)). To keep the causality, both ancestral and sibling features from non-causal positions (i.e., $\mathbf{f}_{>i}$ ) are discarded, as shown in Fig. 4a. However, these ancestral features are actually available. As illustrated in Fig. 4b, $\mathbf{f}_{>i}^{a}$ have similar dependency activations to $\mathbf{f}_{< i}^{a}$ . Therefore, they are equivalently important to compute dependencies. The grouped context structure accesses to more ancestral features, which leads to better compression performance. + +![](images/5f88752a9cf67363d186a35e0fe4340a13b6d12b273a2edd76f93744b148248c.jpg) +Figure 5. Illustration of two successive localized attention layers for the case of $N = 8$ and $L = 2$ . MSA represents the multi-head self-attention. + +From the perspective of context modeling, this grouped context can be interpreted as the space-channel context in image compression [13]. As shown in Eq. (3), $N$ nodes constitute the spatial domain, and each spatial position has $K + 1$ channels, consisting of $K$ ancestors and 1 sibling. The grouped context partitions on both channel and spatial dimensions. Available contexts for each element are decoded channels (ancestors) from all spatial positions, and elements in the same channel (siblings) at decoded spatial positions. Therefore, it is feasible to use similar context structures for point cloud and image compression, and both domains might benefit from advances of each other. + +# 4.3. Hierarchical Attention + +To reduce the complexity, we discover dependencies within local windows and model long-range dependencies with a multi-scale network structure. It is inspired by vision transformers designed for 2D images [8, 22, 23, 45]. Since the localized attention can not exploit long-range dependencies in the large-scale context, we gradually downsample the context to represent numerous nodes with $L$ tokens. The downsampling is implemented by a node merging operation. Two neighboring nodes are merged by concatenating their features on the channel dimension. Then, $2C$ -dimensional concatenated features are passed to an MLP to shrink the channel dimension to $C$ . In this way, features from distant nodes can be computed in the same window and the receptive field is increased. Furthermore, dependencies are estimated at different scales, and closer neighbors are computed with fine-grained representations. It is reasonable since closer neighbors are more informative. In contrast, distant nodes can be coarsely characterized. We further introduce the shifted window strategy [23] to capture dependencies across neighboring local windows. Dependencies are computed with a window partition alternating between two patterns, as shown in Fig. 5. + +A self-attention block is composed of various localized attention layers and one node merging module (except for the last block). The hierarchical attention model is a stack of $\log_2\frac{N}{L} + 1$ blocks to capture all $N$ nodes in the last block. + +The number of blocks can be further reduced by aggregating more than two nodes in a single node merging module. We produce a hierarchical representation $\bar{\mathbf{F}}_i^a$ by aggregating features and dependencies from different scales. Therefore, we refer to this model as a hierarchical attention model. + +By performing attention operations within local windows, the hierarchical attention model reduces the complexity from quadratic to linear scale. Complexities of attention computations in global and localized self-attention are: + +$$ +\Omega (\text {G l o b a l}) = 2 N ^ {2} C, \quad \Omega (\text {L o c a l i z e d}) = 2 L N C. \tag {5} +$$ + +It allows us to build a much deeper entropy model with reasonable computational costs to enhance the modeling capability, or substantially expand the context scale to introduce more potentially useful references. + +The hierarchical cross-attention follows a similar localized attention practice. Since the decomposition pattern is uniform, each local window includes $\frac{L}{2}$ nodes from $\mathbf{x}_{i_1}$ and another $\frac{L}{2}$ nodes from $\mathbf{x}_{i_2}$ . They are regarded as key and query features, respectively. We compute dependencies among keys and queries within each local window, and weight keys according to their dependencies to queries. To extend the receptive field, neighboring keys (and queries) are progressively merged into new key (and query) tokens. Finally, features from different scales are concatenated, which are then exploited to predict $x_{i_2}$ with ancestral features $\tilde{\mathbf{F}}_{i_2}^a$ jointly. + +# 4.4. Learning + +The optimization objective of the octree-based entropy model is to minimize the total bitrates for communicating octree nodes. The bitrate is given by the cross entropy between the estimated distribution $\tilde{p} (\mathbf{x})$ and the ground truth $p(\mathbf{x})$ at each node: + +$$ +\ell = - \sum_ {i} \log \tilde {p} _ {i} \left(x _ {i} \mid \mathbf {C} _ {i}\right), \tag {6} +$$ + +where $\tilde{p}_i(x_i\mid \mathbf{C}_i)$ is the distribution estimated by the proposed entropy model based on the context $\mathbf{C}_i$ + +# 5. Experiments + +# 5.1. Experimental Settings + +Datasets Experiments are conducted on two large-scale point cloud datasets SemanticKITTI [3] and Ford [32]. SemanticKITTI is composed of 43552 LiDAR scans acquired from autonomous driving scenes, which are divided into 22 sequences. We follow the default split to perform training on sequences 00 to 10 and evaluation on sequences 11 to 21. Ford is another LiDAR point cloud dataset used in MPEG point cloud compression standardization. It includes 3 sequences, each consists of 1500 scans. On the Ford dataset, + +![](images/de2a17434b604c200dd6f99e282cab9a543b2202b492a96776cf516e0b4dfe12.jpg) + +![](images/c0ee82cd88e021dfbc338b65caec9c9a74db5790fc4053e2e07e8e718e80198a.jpg) + +![](images/4d35d2aabc046b8ef7a80ba9f7b373077fe7bb4f1314a88ee9002d83c471616f.jpg) + +![](images/b4a36def1db17bcbca32e704059b0e579f0e092cde6472bdbe131d2a7a61d5d7.jpg) +Figure 6. Rate-distortion performance of different methods on SemanticKITTI (top) and Ford (bottom). + +![](images/5c148f59cc31e7be5ca4478bf54ba6db83a0b926e41e9e97f99127adf65b9a00.jpg) + +![](images/cbb657c583b33283971c92cb3c15a04414c9b41b43f3ec2ece5a7609ec9868d6.jpg) + +we follow the suggested dataset partition in MPEG standardization [7], where sequence 01 is used for training and sequences 02 and 03 are used for evaluation. + +Baselines To verify the effectiveness of the proposed model, we compare it with the state-of-the-art octree-based learned entropy model OctAttention [10] and the competitive voxel-based learned method SparsePCGC [43]. We also provide comparisons with the representative handcrafted compression method MPEG G-PCC [12]. + +Implementation settings Quantization is necessary to construct octrees from point clouds. For SemanticKITTI, we follow the quantization settings in OctSqueeze [16], where the quantization step is set to $\frac{400}{2^{D} - 1}$ to build an octree with the depth of $D$ . Octrees are truncated with a maximum depth of 16 for training and evaluation. We set the quantization step to $2^{18 - D}$ and construct octrees with the maximum depth of 18 on Ford. Since the original Ford dataset has been quantized with 18-bit precision, compression is lossless at the highest octree level. + +The hierarchical self-attention model has 5 blocks including 4, 4, 4, 4, 2 layers, respectively. The hierarchical cross-attention model consists of 4 blocks with 2, 2, 1, 1 layers. The head number is set to 4 for all attention layers. The channel dimension $C$ is set to 256, and the ancestor depth $K$ is set to 3. The context window length $N$ is set to 8192, which is initially divided into 16 local windows with the length $L$ of 512. To further achieve speed-accuracy trade + +Table 1. Inference times (in seconds) for encoding/decoding a D-depth octree on SemanticKITTI. Runtimes for G-PCC are total times. + +
MethodD=12D=14D=16
G-PCC0.25 / 0.120.66 / 0.321.07 / 0.54
SparsePCGC1.14 / 0.861.76 / 1.432.43 / 2.04
OctAttention0.08 / 830.31 / 3210.66 / 708
EHEM0.40 / 0.431.21 / 1.392.53 / 3.01
Light EHEM0.29 / 0.330.79 / 0.921.63 / 1.94
+ +offs, we present a lightweight EHEM model called Light EHEM. It has the same network structure as EHEM except that its 5 self-attention blocks have 2, 2, 2, 2, 2 layers and its channel dimension $C$ is set to 192. + +We adopt an Adam optimizer [20] with a learning rate of $10^{-4}$ to train two models for 10 and 50 epochs on SemanticKITTI and Ford datasets, respectively. The evaluation is implemented on the NVIDIA V100 GPU. + +Metrics We adopt the point-to-point PSNR (D1 PSNR), point-to-plane PSNR (D2 PSNR) [6], and Chamfer distance (CD) to measure the distortion. Experiments on SemanticKITTI follow the PSNR calculations in OctSqueeze and MuSCLE [4, 16], where the peak value is set to 59.70. On the Ford dataset, we set the peak value to 30000 [6]. Consumed bitrates are measured by bits per point (bpp). + +Table 2. Complexity comparison on encoding/decoding time, theoretical computation cost (FLOPs), parameters, and memory usage among OctAttention, EHEM, and Light EHEM. + +
MethodEnc / DecFLOPs#param.Mem.
OctAttn0.66s / 708s124.3G4.23M1.3G
EHEM2.53s / 3.01s184.4G13.01M2.9G
L-EHEM1.63s / 1.94s102.9G6.34M2.6G
+ +Table 3. Comparison of FLOPs among OctAttention, EHEM, and Light EHEM with respect to the context length $N$ . + +
Method5121024204840968192
OctAttn6.0G15.5G45.0G145.7G514.0G
EHEM9.0G18.4G38.1G81.5G184.4G
L-EHEM5.2G10.7G21.9G46.4G102.9G
+ +# 5.2. Performance Evaluation + +The quantitative results of the rate-distortion performance are shown in Fig. 6. The proposed method EHEM achieves significant improvements over other baselines. For example, on SemanticKITTI, EHEM achieves an average gain of $28.89\%$ to G-PCC, and $19.47\%$ bitrate reduction on average compared with OctAttention. Furthermore, Light EHEM also preserves satisfactory performance and outperforms other baselines. + +To evaluate the efficiency of EHEM, we report inference times at different quantization steps in Tab. 1. EHEM achieves notable decoding time reduction over the autoregressive context model OctAttention. The encoding time increases compared with OctAttention since the grouped context requires a two-step inference (for $\mathbf{x}_{i_1}$ and $\mathbf{x}_{i_2}$ ), while OctAttention only requires one step. However, this encoding time is still practically acceptable and the grouped context is effective to speed up decoding. We further represent both rate-distortion performance and decoding time in Fig. 1. It is shown that EHEM is effective regarding both compression performance and decoding speed. + +We provide the complexity analysis of EHEM and OctAttention in Tab. 2 and Tab. 3. Here, we report required FLOPs to infer a single context window. Note that larger context predicts more nodes with one forward pass. For example, EHEM requires $81.5 \times 2$ and $184.4 \times 1$ GFLOPs to predict 8192 nodes when $N$ is set to 4096 and 8192, respectively. It is shown that EHEM has comparable FLOPs to OctAttention when the context capacity is 1024, which is the default setting for OctAttention. However, EHEM contains 24 hierarchical attention layers while OctAttention only includes 2 global attention layers. It proves the superiority of the localized attention structure in terms of extending the network depth. Furthermore, localized attention is also effective to enlarge the context due to the linear com + +![](images/231266a08d05b49923d280eabadfafa9d9eaeee281eb992a289a4d60fa6d956b.jpg) +Figure 7. Ablation studies on attention models, context scales, and context structures. + +![](images/b53bf97dc1eb8c5a2c7a2ed96ef713bd90c565af1294313fb8cacd7ccb10d6ff.jpg) +Figure 8. Contexts with different capacities $N$ on 16-bit quantized SemanticKITTI. Points in the context are colored in blue. + +![](images/e1f9957123d0d73c6c05581814b1295da7fd8383787ed761d67fc53560999519.jpg) + +plexity. FLOPs of EHEM increase 2.26 times as the context is enlarged from 4096 to 8192. In contrast, the complexity of OctAttention increases 3.53 times with the same extension. Besides, Light EHEM achieves lower FLOPs at all context window length settings compared to OctAttention. EHEM has slightly larger model size and memory usage compared with OctAttention. These increases are due to the extension of model capacity and context scale, but it is still reasonable for practical use. + +# 5.3. Ablation Studies and Analysis + +Hierarchical attention structure To verify the effectiveness of the hierarchical attention structure, we replace the hierarchical self-attention model with global self-attention layers to build a counterpart with similar FLOPs. Since it is impractical to compute global self-attention with $N = 8192$ , we conduct experiments with $N = 1024$ . Here, EHEM still has 18 localized self-attention layers, and the global-attention counterpart contains 5 layers. The comparison between EHEM ( $N = 1024$ ) and Global Self-Attn in Fig. 7 proves that the hierarchical attention model with a much deeper network achieves considerable improvements. Network depth With the same network structure, the comparison between EHEM and Light EHEM shows that the + +![](images/48b6b6d53dc05c5f9f0da23f43e3598ae46623b66bdc4110d00a2ae953b0fbec.jpg) +Figure 9. Visualized compression results of G-PCC, OctAttention, and our method on the SemanticKITTI dataset. + +deeper network leads to better performance. Therefore, it is helpful to enhance the expressiveness of the model by stacking more layers within a reasonable range. + +Context scale The linear complexity of the hierarchical attention also allows the further extension of the context scale $N$ . Contexts with different capacities are visualized in Fig. 8. It is shown that captured regions are significantly enlarged when $N$ increases from 1024 to 8192. The extended context includes the complete geometry pattern of the vehicle and introduces references from the neighboring similar vehicle. This is beneficial to improve the rate-distortion performance, as shown in Fig. 7. + +Grouped context structure The grouped context structure allows a two-step parallel decoding procedure. Here, we examine its influence on rate-distortion performance. To this end, we train a baseline with an auto-regressive context used in OctAttention. The hierarchical attention is unavailable to this context structure since the node merging operation uses non-causal ancestral references. For a fair comparison, we use global attention to compute dependencies for both grouped and auto-regressive context structures. The grouped context introduces features from the first group via global cross-attention layers. The comparison between AR Context and Grouped Context in Fig. 7 demonstrates that although only half of the nodes access to siblings, the grouped context structure achieves comparable performance. It is because the grouped context preserves ancestral features from non-causal references, as shown in Fig. 4b. Besides, it proves that the grouped context structure does not significantly improve compression performance. Therefore, im + +provements of EHEM are mainly due to stronger hierarchical attention blocks. + +# 5.4. Qualitative Results + +In Fig. 9, we show the visualized compression distortions of different methods at similar bitrates. It indicates that our method provides better reconstructions compared with other baselines. For example, EHEM outperforms G-PCC by roughly 10 dB D1 PSNR improvements. + +# 6. Conclusion + +We proposed an efficient learned entropy model for point cloud compression. It adopts a hierarchical attention structure, which allows us to substantially extend the network depth and context capacity to improve the rate-distortion performance with reasonable complexity. We further developed a grouped context structure to realize a parallel decoding procedure. Moreover, this context aligns the context modeling regimes of point cloud and image compression, and we hope it would be helpful to bridge the gap between two communities. The proposed model is proved to yield superior compression performance and significantly reduce the decoding time compared to the state-of-the-art auto-regressive method. + +# Acknowledgement + +This work was supported by National Natural Science Foundation of China (No. 62172021). + +# References + +[1] Johannes Balle, Valero Laparra, and Eero P Simoncelli. End-to-end optimized image compression. In International Conference on Learning Representations, 2017. +[2] Johannes Ballé, David Minnen, Saurabh Singh, Sung Jin Hwang, and Nick Johnston. Variational image compression with a scale hyperprior. 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Recently, the octree-based auto-regressive entropy model which adopts the self-attention mechanism to explore dependencies in a large-scale context is proved to be promising. However, heavy global attention computations and auto-regressive contexts are inefficient for practical applications. To improve the efficiency of the attention model, we propose a hierarchical attention structure that has a linear complexity to the context scale and maintains the global receptive field. Furthermore, we present a grouped context structure to address the serial decoding issue caused by the auto-regression while preserving the compression performance. Experiments demonstrate that the proposed entropy model achieves superior rate-distortion performance and significant decoding latency reduction compared with the state-of-the-art large-scale auto-regressive entropy model." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 492, + 128, + 504 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 492, + 128, + 504 + ], + "spans": [ + { + "bbox": [ + 47, + 492, + 128, + 504 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 513, + 287, + 609 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 513, + 287, + 609 + ], + "spans": [ + { + "bbox": [ + 46, + 513, + 287, + 609 + ], + "type": "text", + "content": "Point cloud is a fundamental data structure to represent 3D scenes. It has been widely applied in 3D vision systems such as autonomous driving and immersive applications. The large-scale point cloud typically contains millions of points [36]. It is challenging to store and transmit such massive data. Hence, efficient point cloud compression that reduces memory footprints and transmission bandwidth is necessary to develop practical point cloud applications." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 609, + 287, + 694 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 609, + 287, + 694 + ], + "spans": [ + { + "bbox": [ + 46, + 609, + 287, + 694 + ], + "type": "text", + "content": "Recently, deep learning methods have promoted the development of point cloud compression [4, 9, 10, 16, 31, 36, 40, 43]. It is a common pipeline to learn an octree-based entropy model to estimate octree node symbol (i.e., occupancy symbol) distributions. The point cloud is first organized as an octree, and occupancy symbols are then encoded into the bitstream losslessly by an entropy coder (e.g., arithmetic" + } + ] + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 309, + 225, + 542, + 411 + ], + "blocks": [ + { + "bbox": [ + 309, + 225, + 542, + 411 + ], + "lines": [ + { + "bbox": [ + 309, + 225, + 542, + 411 + ], + "spans": [ + { + "bbox": [ + 309, + 225, + 542, + 411 + ], + "type": "image", + "image_path": "dd10b2b2886ee02b32a621ee036207fd249ece4002772f83f089636dc4c67f66.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 418, + 547, + 464 + ], + "lines": [ + { + "bbox": [ + 304, + 418, + 547, + 464 + ], + "spans": [ + { + "bbox": [ + 304, + 418, + 547, + 464 + ], + "type": "text", + "content": "Figure 1. Bitrate and decoding speed in the log scale for lossless compression on 16-bit quantized SemanticKITTI. The proposed method EHEM yields state-of-the-art performance with a comparable decoding latency to the efficient traditional method G-PCC." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 485, + 546, + 653 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 485, + 546, + 653 + ], + "spans": [ + { + "bbox": [ + 304, + 485, + 546, + 653 + ], + "type": "text", + "content": "coder [47]). An accurate entropy model is required since it reduces the cross entropy between the estimated distribution and ground truth, which is corresponding to actual bitrates. Various attempts have been made to improve the accuracy by designing different context structures [4, 10, 16, 37]. The key of these advances is to increase the context capacity and introduce references from high-resolution octree representations. For example, the context in OctAttention [10] includes hundreds of previously decoded siblings (i.e., nodes at the same octree level). The large-scale context incorporates more references for the entropy coder, and the high-resolution context preserves detailed features of the point cloud. Both of them contribute to building informative contexts and effective entropy models." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 653, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 653, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 653, + 547, + 715 + ], + "type": "text", + "content": "However, large-scale context requires heavy computations to model dependencies among numerous references. The previous work [10] uses the global self-attention mechanism to model long-range dependencies within the context, and its complexity is quadratic to the length of the" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 702, + 135, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 702, + 135, + 712 + ], + "spans": [ + { + "bbox": [ + 58, + 702, + 135, + 712 + ], + "type": "text", + "content": "*Corresponding author." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "14368" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 72, + 286, + 167 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 72, + 286, + 167 + ], + "spans": [ + { + "bbox": [ + 48, + 72, + 286, + 167 + ], + "type": "text", + "content": "large-scale context. Furthermore, considering the efficiency issue, it is infeasible to build a deeper entropy model or extend the context scale to enhance the modeling capability based on global attention. Another concern is the serial decoding process caused by the inclusion of previously decoded siblings. This auto-regressive context structure incurs a practically unacceptable decoding latency (e.g., around 700 seconds per frame)." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 49, + 168, + 286, + 418 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 168, + 286, + 418 + ], + "spans": [ + { + "bbox": [ + 49, + 168, + 286, + 418 + ], + "type": "text", + "content": "To address these issues, we build an entropy model with an efficient hierarchical attention model and a parallel-friendly grouped context structure. The hierarchical attention model partitions the context into local windows and computes attention within these windows independently. Therefore, the complexity is linear to the context scale, which allows the further extension of network depth and context capacity to improve performance. Since the receptive field of the localized attention is limited, we adopt a multi-scale network structure to query features across different windows. The context is progressively downsampled by merging neighboring nodes to generate a new token. Then, cross-window dependencies can be captured by incorporating these new tokens in the same window. The grouped context divides the occupancy symbol sequence into two groups. Each group is conditioned on ancestral features and previously decoded groups, and hence nodes in the same group can be coded in parallel. Furthermore, in contrast to the previous auto-regressive context that only exploits causal parts of the ancestral context [10], the grouped context allows to make use of a complete ancestral context." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 48, + 419, + 286, + 491 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 419, + 286, + 491 + ], + "spans": [ + { + "bbox": [ + 48, + 419, + 286, + 491 + ], + "type": "text", + "content": "The proposed efficient hierarchical entropy model called EHEM is evaluated on SemanticKITTI [3] and Ford [32] benchmarks. It surpasses state-of-the-art methods in terms of both compression performance and efficiency. Contributions of this work can be summarized from the following perspectives:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 59, + 497, + 286, + 605 + ], + "type": "list", + "angle": 0, + "index": 6, + "blocks": [ + { + "bbox": [ + 59, + 497, + 286, + 533 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 497, + 286, + 533 + ], + "spans": [ + { + "bbox": [ + 59, + 497, + 286, + 533 + ], + "type": "text", + "content": "- We propose a hierarchical attention model, which yields improved compression performance by extending model and context while keeping the efficiency." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 59, + 540, + 286, + 575 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 540, + 286, + 575 + ], + "spans": [ + { + "bbox": [ + 59, + 540, + 286, + 575 + ], + "type": "text", + "content": "- We design a grouped context structure that enables parallel decoding. It adapts the entropy model using high-resolution references to practical applications." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 59, + 582, + 286, + 605 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 582, + 286, + 605 + ], + "spans": [ + { + "bbox": [ + 59, + 582, + 286, + 605 + ], + "type": "text", + "content": "- The proposed method achieves state-of-the-art RD performance with a practically applicable coding speed." + } + ] + } + ], + "index": 5 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 49, + 616, + 133, + 628 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 616, + 133, + 628 + ], + "spans": [ + { + "bbox": [ + 49, + 616, + 133, + 628 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 49, + 635, + 231, + 647 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 635, + 231, + 647 + ], + "spans": [ + { + "bbox": [ + 49, + 635, + 231, + 647 + ], + "type": "text", + "content": "2.1. Learned Point Cloud Compression" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 49, + 654, + 286, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 654, + 286, + 712 + ], + "spans": [ + { + "bbox": [ + 49, + 654, + 286, + 712 + ], + "type": "text", + "content": "Point cloud compression is an active research area in both industry and academia. Traditional point cloud compression codecs are generally interpretable, robust, and efficient [11,25,39,41]. However, neural codecs have shown better rate-distortion performance recently." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 307, + 72, + 545, + 203 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 307, + 72, + 545, + 203 + ], + "spans": [ + { + "bbox": [ + 307, + 72, + 545, + 203 + ], + "type": "text", + "content": "Various data structures and models have been developed to boost the rate-distortion performance for learned point cloud compression. The pioneering works [15,17,36,44,48] construct analysis and synthesis transforms to compress point clouds to latent representations. These transforms are learned on point sets with the PointNet backbone [33, 34] or on the voxel structure using 3D convolution. However, distortions are inevitable in these transforms. It is therefore difficult to preserve high-frequency information in latent vectors. Hence, these structures are preferable to lossy compression at low bitrates." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 308, + 205, + 545, + 396 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 205, + 545, + 396 + ], + "spans": [ + { + "bbox": [ + 308, + 205, + 545, + 396 + ], + "type": "text", + "content": "Learned entropy model is another effective pipeline to reduce bitrates without introducing distortion. Since the inference of the entropy model depends on the context, it is important to build an informative context. A typical entropy model predicts the binary occupancy status of the voxel based on the context of several adjacent voxels [30, 31]. Similarly, entropy model can be established on the octree by estimating occupancy symbol distributions. Early tree-structured entropy models exploit references from ancestor nodes [4, 16, 37]. Later works introduce adjacent voxels that have the same resolution as the currently coded octree node to provide high-resolution references [18]. A recent work replaces neighboring voxels with decoded siblings to extend the context [10], and it yields state-of-the-art performance. However, its efficiency is limited by the expensive global attention computation and auto-regressive processing." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 308, + 404, + 462, + 417 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 404, + 462, + 417 + ], + "spans": [ + { + "bbox": [ + 308, + 404, + 462, + 417 + ], + "type": "text", + "content": "2.2. Learned Image Compression" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 308, + 423, + 545, + 626 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 423, + 545, + 626 + ], + "spans": [ + { + "bbox": [ + 308, + 423, + 545, + 626 + ], + "type": "text", + "content": "The typical learned image compression pipeline is based on non-linear transforms and hyperprior-based entropy models [1,2,5,19,21,26,27,35,49]. In addition, decoded latent elements also can be introduced into the context to generate parameters for entropy coding, leading to improved performance with an auto-regressive coding process [28]. To accelerate the coding, a few parallel solutions have been developed [13, 14, 29]. The key of these modifications is performing auto-regression at the level of groups instead of pixels to parallelize coding within each group. For example, the checkerboard context model divides latent elements into two groups in the spatial domain [14]. A checkerboard mask is employed to constrain that the inference of the second group only refers to the decoded first group. Despite the data structures of point clouds and images are different, these strategies are instructive to solve the serial coding problem in point cloud compression." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 308, + 639, + 381, + 652 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 639, + 381, + 652 + ], + "spans": [ + { + "bbox": [ + 308, + 639, + 381, + 652 + ], + "type": "text", + "content": "3. Preliminary" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 308, + 659, + 406, + 670 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 659, + 406, + 670 + ], + "spans": [ + { + "bbox": [ + 308, + 659, + 406, + 670 + ], + "type": "text", + "content": "3.1. 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It is an effective data structure to represent large regions, since neighboring nodes in the breadth-first traversal order might locate at distant locations." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 156, + 286, + 240 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 156, + 286, + 240 + ], + "spans": [ + { + "bbox": [ + 46, + 156, + 286, + 240 + ], + "type": "text", + "content": "The octree-based point cloud compression transmits an octree to the receiver instead of point coordinates [38, 39]. The octree is represented by a breadth-first traversed occupancy symbol sequence. An entropy coder is adopted to encode these symbols into the bitstream losslessly. 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Here, nodes are considered to be conditionally independent. Consumed bitrates are given by the cross entropy between the estimated distribution " + }, + { + "bbox": [ + 46, + 349, + 286, + 420 + ], + "type": "inline_equation", + "content": "\\tilde{p} (\\mathbf{x})" + }, + { + "bbox": [ + 46, + 349, + 286, + 420 + ], + "type": "text", + "content": " and ground truth " + }, + { + "bbox": [ + 46, + 349, + 286, + 420 + ], + "type": "inline_equation", + "content": "p(\\mathbf{x})" + }, + { + "bbox": [ + 46, + 349, + 286, + 420 + ], + "type": "text", + "content": ", formulated as " + }, + { + "bbox": [ + 46, + 349, + 286, + 420 + ], + "type": "inline_equation", + "content": "\\mathbb{E}_{\\mathbf{x}\\sim p}\\left[-\\log_2\\tilde{p} (\\mathbf{x})\\right]" + }, + { + "bbox": [ + 46, + 349, + 286, + 420 + ], + "type": "text", + "content": ". An accurate entropy model that minimizes this entropy is helpful to reduce bitrates." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 421, + 286, + 480 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 421, + 286, + 480 + ], + "spans": [ + { + "bbox": [ + 46, + 421, + 286, + 480 + ], + "type": "text", + "content": "To formulate the context structure, we characterize each octree node " + }, + { + "bbox": [ + 46, + 421, + 286, + 480 + ], + "type": "inline_equation", + "content": "n_i" + }, + { + "bbox": [ + 46, + 421, + 286, + 480 + ], + "type": "text", + "content": " by features " + }, + { + "bbox": [ + 46, + 421, + 286, + 480 + ], + "type": "inline_equation", + "content": "\\mathbf{u}_i" + }, + { + "bbox": [ + 46, + 421, + 286, + 480 + ], + "type": "text", + "content": " including its occupancy symbol " + }, + { + "bbox": [ + 46, + 421, + 286, + 480 + ], + "type": "inline_equation", + "content": "x_i" + }, + { + "bbox": [ + 46, + 421, + 286, + 480 + ], + "type": "text", + "content": ", level index, octant index, and parent bounding box coordinates. The ancestral context collects features from the currently coded node and its " + }, + { + "bbox": [ + 46, + 421, + 286, + 480 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 46, + 421, + 286, + 480 + ], + "type": "text", + "content": " ancestors as:" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 88, + 486, + 286, + 502 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 88, + 486, + 286, + 502 + ], + "spans": [ + { + "bbox": [ + 88, + 486, + 286, + 502 + ], + "type": "interline_equation", + "content": "\\mathbf {a} _ {i} = \\left\\{\\mathbf {u} _ {i} ^ {\\emptyset}, \\mathbf {u} _ {\\text {a n c} (i)}, \\dots , \\mathbf {u} _ {\\text {a n c} (\\dots \\text {a n c} (i))} \\right\\}, \\tag {2}", + "image_path": "e56dd8375d24eff8f9018c07c78d60809def2d4baadf1e62e876c84f77711fae.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 507, + 286, + 555 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 507, + 286, + 555 + ], + "spans": [ + { + "bbox": [ + 46, + 507, + 286, + 555 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 507, + 286, + 555 + ], + "type": "inline_equation", + "content": "\\mathbf{u}_i^\\varnothing" + }, + { + "bbox": [ + 46, + 507, + 286, + 555 + ], + "type": "text", + "content": " excludes " + }, + { + "bbox": [ + 46, + 507, + 286, + 555 + ], + "type": "inline_equation", + "content": "x_{i}" + }, + { + "bbox": [ + 46, + 507, + 286, + 555 + ], + "type": "text", + "content": " from " + }, + { + "bbox": [ + 46, + 507, + 286, + 555 + ], + "type": "inline_equation", + "content": "\\mathbf{u}_i" + }, + { + "bbox": [ + 46, + 507, + 286, + 555 + ], + "type": "text", + "content": " since it is unknown when decoding " + }, + { + "bbox": [ + 46, + 507, + 286, + 555 + ], + "type": "inline_equation", + "content": "x_{i}" + }, + { + "bbox": [ + 46, + 507, + 286, + 555 + ], + "type": "text", + "content": ". The ancestor-dependent methods [4, 16] predict the occupancy distribution " + }, + { + "bbox": [ + 46, + 507, + 286, + 555 + ], + "type": "inline_equation", + "content": "\\tilde{p}_i(x_i)" + }, + { + "bbox": [ + 46, + 507, + 286, + 555 + ], + "type": "text", + "content": " based on the ancestral context " + }, + { + "bbox": [ + 46, + 507, + 286, + 555 + ], + "type": "inline_equation", + "content": "\\mathbf{a}_i" + }, + { + "bbox": [ + 46, + 507, + 286, + 555 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 555, + 286, + 639 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 555, + 286, + 639 + ], + "spans": [ + { + "bbox": [ + 46, + 555, + 286, + 639 + ], + "type": "text", + "content": "The large-scale auto-regressive entropy model [10] constructs an extensive context to incorporate more information for inference. It combines the occupancy symbol of the previous sibling with the ancestral context as " + }, + { + "bbox": [ + 46, + 555, + 286, + 639 + ], + "type": "inline_equation", + "content": "\\mathbf{v}_i = \\{x_{i - 1},\\mathbf{a}_i\\}" + }, + { + "bbox": [ + 46, + 555, + 286, + 639 + ], + "type": "text", + "content": ". Besides, the context is extended by introducing features from " + }, + { + "bbox": [ + 46, + 555, + 286, + 639 + ], + "type": "inline_equation", + "content": "N - 1" + }, + { + "bbox": [ + 46, + 555, + 286, + 639 + ], + "type": "text", + "content": " previously decoded sibling nodes and their ancestors to build a context window with length " + }, + { + "bbox": [ + 46, + 555, + 286, + 639 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 555, + 286, + 639 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 113, + 646, + 286, + 659 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 113, + 646, + 286, + 659 + ], + "spans": [ + { + "bbox": [ + 113, + 646, + 286, + 659 + ], + "type": "interline_equation", + "content": "\\mathbf {C} _ {i} = \\left\\{\\mathbf {v} _ {i - N + 1}, \\dots , \\mathbf {v} _ {i} \\right\\}. \\tag {3}", + "image_path": "f97725c966178eaaac92d46a7822d0b3a101ae31448a51b98466c9dd572c10b8.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 665, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 286, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{C}_i" + }, + { + "bbox": [ + 46, + 665, + 286, + 713 + ], + "type": "text", + "content": " is then embedded to features " + }, + { + "bbox": [ + 46, + 665, + 286, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_i = \\{\\mathbf{f}_{i - N + 1},\\dots ,\\mathbf{f}_i\\}" + }, + { + "bbox": [ + 46, + 665, + 286, + 713 + ], + "type": "text", + "content": " and a self-attention module [42] is adopted to model dependencies among " + }, + { + "bbox": [ + 46, + 665, + 286, + 713 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 665, + 286, + 713 + ], + "type": "text", + "content": " embedded features. A mask is employed to constrain that only causal contexts " + }, + { + "bbox": [ + 46, + 665, + 286, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{f}_{< i}" + }, + { + "bbox": [ + 46, + 665, + 286, + 713 + ], + "type": "text", + "content": " are visible." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 72, + 544, + 96 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 544, + 96 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 544, + 96 + ], + "type": "text", + "content": "Finally, attention-weighted features " + }, + { + "bbox": [ + 305, + 72, + 544, + 96 + ], + "type": "inline_equation", + "content": "\\tilde{\\mathbf{f}}_i" + }, + { + "bbox": [ + 305, + 72, + 544, + 96 + ], + "type": "text", + "content": " are projected to the distribution " + }, + { + "bbox": [ + 305, + 72, + 544, + 96 + ], + "type": "inline_equation", + "content": "\\tilde{p}_i(x_i)" + }, + { + "bbox": [ + 305, + 72, + 544, + 96 + ], + "type": "text", + "content": ", which is used for entropy coding." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 97, + 545, + 240 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 97, + 545, + 240 + ], + "spans": [ + { + "bbox": [ + 304, + 97, + 545, + 240 + ], + "type": "text", + "content": "Since the octree is coded in a breadth-first manner, ancestral contexts are completely known while coding any node. Therefore, the ancestor-dependent entropy model can decode multiple nodes at the same octree level in parallel. In contrast, the auto-regressive context model is conditioned on previously decoded siblings (e.g., " + }, + { + "bbox": [ + 304, + 97, + 545, + 240 + ], + "type": "inline_equation", + "content": "x_{i-1}" + }, + { + "bbox": [ + 304, + 97, + 545, + 240 + ], + "type": "text", + "content": "). It hence requires a serial decoding process. The global attention computation among " + }, + { + "bbox": [ + 304, + 97, + 545, + 240 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 304, + 97, + 545, + 240 + ], + "type": "text", + "content": " elements in " + }, + { + "bbox": [ + 304, + 97, + 545, + 240 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_i" + }, + { + "bbox": [ + 304, + 97, + 545, + 240 + ], + "type": "text", + "content": " also limits its efficiency. However, large-scale contexts and sibling references are still effective to improve performance. Therefore, we aim to build an efficient entropy model while preserving these advantages." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 254, + 511, + 268 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 254, + 511, + 268 + ], + "spans": [ + { + "bbox": [ + 305, + 254, + 511, + 268 + ], + "type": "text", + "content": "4. Efficient Hierarchical Entropy Model" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 274, + 425, + 286 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 274, + 425, + 286 + ], + "spans": [ + { + "bbox": [ + 305, + 274, + 425, + 286 + ], + "type": "text", + "content": "4.1. Overall Architecture" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 294, + 545, + 426 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 294, + 545, + 426 + ], + "spans": [ + { + "bbox": [ + 304, + 294, + 545, + 426 + ], + "type": "text", + "content": "The overview of the proposed entropy model is shown in Fig. 2. It is composed of a grouped context structure and a hierarchical attention model. The occupancy sequence " + }, + { + "bbox": [ + 304, + 294, + 545, + 426 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 304, + 294, + 545, + 426 + ], + "type": "text", + "content": " is divided into a series of non-overlapped subsequences " + }, + { + "bbox": [ + 304, + 294, + 545, + 426 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_i = \\{x_{i-N+1},\\dots,x_i\\}" + }, + { + "bbox": [ + 304, + 294, + 545, + 426 + ], + "type": "text", + "content": " with length " + }, + { + "bbox": [ + 304, + 294, + 545, + 426 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 304, + 294, + 545, + 426 + ], + "type": "text", + "content": ". Contextual information for each subsequence is called a context window. The grouped context equally partitions " + }, + { + "bbox": [ + 304, + 294, + 545, + 426 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_i" + }, + { + "bbox": [ + 304, + 294, + 545, + 426 + ], + "type": "text", + "content": " into two groups " + }, + { + "bbox": [ + 304, + 294, + 545, + 426 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_{i_1}" + }, + { + "bbox": [ + 304, + 294, + 545, + 426 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 294, + 545, + 426 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_{i_2}" + }, + { + "bbox": [ + 304, + 294, + 545, + 426 + ], + "type": "text", + "content": ". The first group " + }, + { + "bbox": [ + 304, + 294, + 545, + 426 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_{i_1}" + }, + { + "bbox": [ + 304, + 294, + 545, + 426 + ], + "type": "text", + "content": " is only conditioned on the ancestral context " + }, + { + "bbox": [ + 304, + 294, + 545, + 426 + ], + "type": "inline_equation", + "content": "\\mathbf{A}_i = \\{\\mathbf{a}_{i-N+1},\\dots,\\mathbf{a}_i\\}" + }, + { + "bbox": [ + 304, + 294, + 545, + 426 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 294, + 545, + 426 + ], + "type": "inline_equation", + "content": "\\mathbf{a}_i" + }, + { + "bbox": [ + 304, + 294, + 545, + 426 + ], + "type": "text", + "content": " is defined in Eq. (2). The second group " + }, + { + "bbox": [ + 304, + 294, + 545, + 426 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_{i_2}" + }, + { + "bbox": [ + 304, + 294, + 545, + 426 + ], + "type": "text", + "content": " is conditioned on both siblings " + }, + { + "bbox": [ + 304, + 294, + 545, + 426 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_{i_1}" + }, + { + "bbox": [ + 304, + 294, + 545, + 426 + ], + "type": "text", + "content": " and ancestors " + }, + { + "bbox": [ + 304, + 294, + 545, + 426 + ], + "type": "inline_equation", + "content": "\\mathbf{A}_i" + }, + { + "bbox": [ + 304, + 294, + 545, + 426 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 427, + 545, + 662 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 427, + 545, + 662 + ], + "spans": [ + { + "bbox": [ + 304, + 427, + 545, + 662 + ], + "type": "text", + "content": "The hierarchical attention model computes dependencies within local windows to improve the efficiency. The self-attention model discovers dependencies among " + }, + { + "bbox": [ + 304, + 427, + 545, + 662 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 304, + 427, + 545, + 662 + ], + "type": "text", + "content": " ancestral features. The ancestral context " + }, + { + "bbox": [ + 304, + 427, + 545, + 662 + ], + "type": "inline_equation", + "content": "\\mathbf{A}_i" + }, + { + "bbox": [ + 304, + 427, + 545, + 662 + ], + "type": "text", + "content": " is partitioned into " + }, + { + "bbox": [ + 304, + 427, + 545, + 662 + ], + "type": "inline_equation", + "content": "\\frac{N}{L}" + }, + { + "bbox": [ + 304, + 427, + 545, + 662 + ], + "type": "text", + "content": " non-overlapped local windows with length " + }, + { + "bbox": [ + 304, + 427, + 545, + 662 + ], + "type": "inline_equation", + "content": "L" + }, + { + "bbox": [ + 304, + 427, + 545, + 662 + ], + "type": "text", + "content": ". Then we regard parent coordinates in the same window as a point cloud, and feed " + }, + { + "bbox": [ + 304, + 427, + 545, + 662 + ], + "type": "inline_equation", + "content": "\\mathbf{A}_i" + }, + { + "bbox": [ + 304, + 427, + 545, + 662 + ], + "type": "text", + "content": " to a DGCNN-based [46] feature extractor to generate " + }, + { + "bbox": [ + 304, + 427, + 545, + 662 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 304, + 427, + 545, + 662 + ], + "type": "text", + "content": "-dimensional geometry-aware features " + }, + { + "bbox": [ + 304, + 427, + 545, + 662 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_i^a" + }, + { + "bbox": [ + 304, + 427, + 545, + 662 + ], + "type": "text", + "content": " from local windows separately. " + }, + { + "bbox": [ + 304, + 427, + 545, + 662 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_i^a" + }, + { + "bbox": [ + 304, + 427, + 545, + 662 + ], + "type": "text", + "content": " is then passed to successive localized self-attention blocks. Weighted ancestral features of the first group are projected to occupancy distributions " + }, + { + "bbox": [ + 304, + 427, + 545, + 662 + ], + "type": "inline_equation", + "content": "\\tilde{p} (\\mathbf{x}_{i_1})" + }, + { + "bbox": [ + 304, + 427, + 545, + 662 + ], + "type": "text", + "content": " using a multi-layer perceptron (MLP). Then " + }, + { + "bbox": [ + 304, + 427, + 545, + 662 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_{i_1}" + }, + { + "bbox": [ + 304, + 427, + 545, + 662 + ], + "type": "text", + "content": " is coded and we predict the second group " + }, + { + "bbox": [ + 304, + 427, + 545, + 662 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_{i_2}" + }, + { + "bbox": [ + 304, + 427, + 545, + 662 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 304, + 427, + 545, + 662 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_{i_1}" + }, + { + "bbox": [ + 304, + 427, + 545, + 662 + ], + "type": "text", + "content": " is embedded to " + }, + { + "bbox": [ + 304, + 427, + 545, + 662 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_{i_1}^s" + }, + { + "bbox": [ + 304, + 427, + 545, + 662 + ], + "type": "text", + "content": " and concatenated to its ancestral features " + }, + { + "bbox": [ + 304, + 427, + 545, + 662 + ], + "type": "inline_equation", + "content": "\\tilde{\\mathbf{F}}_{i_1}^a" + }, + { + "bbox": [ + 304, + 427, + 545, + 662 + ], + "type": "text", + "content": " as " + }, + { + "bbox": [ + 304, + 427, + 545, + 662 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_{i_1}" + }, + { + "bbox": [ + 304, + 427, + 545, + 662 + ], + "type": "text", + "content": ". Subsequently, we adopt a hierarchical cross-attention model to introduce sibling-involved features " + }, + { + "bbox": [ + 304, + 427, + 545, + 662 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_{i_1}" + }, + { + "bbox": [ + 304, + 427, + 545, + 662 + ], + "type": "text", + "content": " to ancestral features " + }, + { + "bbox": [ + 304, + 427, + 545, + 662 + ], + "type": "inline_equation", + "content": "\\tilde{\\mathbf{F}}_{i_2}^a" + }, + { + "bbox": [ + 304, + 427, + 545, + 662 + ], + "type": "text", + "content": ". Finally, an MLP produces distributions " + }, + { + "bbox": [ + 304, + 427, + 545, + 662 + ], + "type": "inline_equation", + "content": "\\tilde{p} (\\mathbf{x}_{i_2})" + }, + { + "bbox": [ + 304, + 427, + 545, + 662 + ], + "type": "text", + "content": " based on sibling features " + }, + { + "bbox": [ + 304, + 427, + 545, + 662 + ], + "type": "inline_equation", + "content": "\\tilde{\\mathbf{F}}_{i_2}^s" + }, + { + "bbox": [ + 304, + 427, + 545, + 662 + ], + "type": "text", + "content": " and ancestral features " + }, + { + "bbox": [ + 304, + 427, + 545, + 662 + ], + "type": "inline_equation", + "content": "\\tilde{\\mathbf{F}}_{i_2}^a" + }, + { + "bbox": [ + 304, + 427, + 545, + 662 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 306, + 670, + 410, + 682 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 670, + 410, + 682 + ], + "spans": [ + { + "bbox": [ + 306, + 670, + 410, + 682 + ], + "type": "text", + "content": "4.2. Grouped Context" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "type": "text", + "content": "The auto-regressive context model requires serial decoding since it depends on the previous sibling " + }, + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "type": "inline_equation", + "content": "x_{i-1}" + }, + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "type": "text", + "content": ". To" + } + ] + } + ], + "index": 19 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "14370" + } + ] + } + ], + "index": 20 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 50, + 70, + 386, + 237 + ], + "blocks": [ + { + "bbox": [ + 50, + 70, + 386, + 237 + ], + "lines": [ + { + "bbox": [ + 50, + 70, + 386, + 237 + ], + "spans": [ + { + "bbox": [ + 50, + 70, + 386, + 237 + ], + "type": "image", + "image_path": "79d266ca715e8b069a33ad493e6c141a58f4628ffe96b043eae646dcf915a9f3.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 246, + 546, + 291 + ], + "lines": [ + { + "bbox": [ + 46, + 246, + 546, + 291 + ], + "spans": [ + { + "bbox": [ + 46, + 246, + 546, + 291 + ], + "type": "text", + "content": "Figure 2. Left: The architecture of EHEM for context window length " + }, + { + "bbox": [ + 46, + 246, + 546, + 291 + ], + "type": "inline_equation", + "content": "N = 4" + }, + { + "bbox": [ + 46, + 246, + 546, + 291 + ], + "type": "text", + "content": " and local window length " + }, + { + "bbox": [ + 46, + 246, + 546, + 291 + ], + "type": "inline_equation", + "content": "L = 2" + }, + { + "bbox": [ + 46, + 246, + 546, + 291 + ], + "type": "text", + "content": ". Red, blue, and yellow nodes denote ancestral features, sibling-involved features, and estimated distributions, respectively. Attention is computed within local windows (dashed boxes). Right: The encoding and decoding process following the grouped context structure. The occupancy sequence " + }, + { + "bbox": [ + 46, + 246, + 546, + 291 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_i" + }, + { + "bbox": [ + 46, + 246, + 546, + 291 + ], + "type": "text", + "content": " is split into two disjoint groups and coded in turn." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 408, + 70, + 544, + 144 + ], + "blocks": [ + { + "bbox": [ + 408, + 70, + 544, + 144 + ], + "lines": [ + { + "bbox": [ + 408, + 70, + 544, + 144 + ], + "spans": [ + { + "bbox": [ + 408, + 70, + 544, + 144 + ], + "type": "image", + "image_path": "d42bb57a02c632986e5aadc02082862532df9ba6c6ad9079cfa23906b5f4b64f.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 408, + 145, + 543, + 236 + ], + "blocks": [ + { + "bbox": [ + 408, + 145, + 543, + 236 + ], + "lines": [ + { + "bbox": [ + 408, + 145, + 543, + 236 + ], + "spans": [ + { + "bbox": [ + 408, + 145, + 543, + 236 + ], + "type": "image", + "image_path": "cfd524b3df22712003e28bfa86eadaf5a48a20bf8a4cd3bca185f2ed67f52992.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 52, + 308, + 282, + 389 + ], + "blocks": [ + { + "bbox": [ + 52, + 308, + 282, + 389 + ], + "lines": [ + { + "bbox": [ + 52, + 308, + 282, + 389 + ], + "spans": [ + { + "bbox": [ + 52, + 308, + 282, + 389 + ], + "type": "image", + "image_path": "f3f07b64a301cf3897e3e12d849aa69d4d15ee271d70566c251632086fe48e7f.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 396, + 286, + 418 + ], + "lines": [ + { + "bbox": [ + 46, + 396, + 286, + 418 + ], + "spans": [ + { + "bbox": [ + 46, + 396, + 286, + 418 + ], + "type": "text", + "content": "Figure 3. Illustration of auto-regressive (left) and grouped (right) context structures." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 447, + 286, + 567 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 447, + 286, + 567 + ], + "spans": [ + { + "bbox": [ + 46, + 447, + 286, + 567 + ], + "type": "text", + "content": "address this issue, we decompose the occupancy subsequence into two groups and remove dependencies within each group. As shown in Fig. 3, " + }, + { + "bbox": [ + 46, + 447, + 286, + 567 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_{i_1}" + }, + { + "bbox": [ + 46, + 447, + 286, + 567 + ], + "type": "text", + "content": " is first decoded based on the ancestral context " + }, + { + "bbox": [ + 46, + 447, + 286, + 567 + ], + "type": "inline_equation", + "content": "\\mathbf{A}_i" + }, + { + "bbox": [ + 46, + 447, + 286, + 567 + ], + "type": "text", + "content": ", then it is introduced as sibling priors to predict " + }, + { + "bbox": [ + 46, + 447, + 286, + 567 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_{i_2}" + }, + { + "bbox": [ + 46, + 447, + 286, + 567 + ], + "type": "text", + "content": ". Since the required contexts are completely known before decoding each group, nodes in the same group can be decoded in parallel. The auto-regressive entropy model requires " + }, + { + "bbox": [ + 46, + 447, + 286, + 567 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 447, + 286, + 567 + ], + "type": "text", + "content": " sequential steps to decode the subsequence " + }, + { + "bbox": [ + 46, + 447, + 286, + 567 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_i" + }, + { + "bbox": [ + 46, + 447, + 286, + 567 + ], + "type": "text", + "content": ", while the grouped context only takes 2 steps to decode two groups in turn." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 570, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 570, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 570, + 286, + 713 + ], + "type": "text", + "content": "The prediction of " + }, + { + "bbox": [ + 46, + 570, + 286, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_{i_2}" + }, + { + "bbox": [ + 46, + 570, + 286, + 713 + ], + "type": "text", + "content": " depends on " + }, + { + "bbox": [ + 46, + 570, + 286, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_{i_1}" + }, + { + "bbox": [ + 46, + 570, + 286, + 713 + ], + "type": "text", + "content": ", and hence it is important to design an effective decomposition pattern. We visualize ancestral dependencies among the first 16 siblings in the context window in Fig. 4b. Dependencies are represented by normalized attention scores computed on " + }, + { + "bbox": [ + 46, + 570, + 286, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_i^a" + }, + { + "bbox": [ + 46, + 570, + 286, + 713 + ], + "type": "text", + "content": ", and results are averaged over all self-attention layers from around 200 SemanticKITTI scans. Fig. 4b reveals that closer neighbors have stronger dependencies, and dependency activations at more distant locations are weak and uniform. This distribution is consistent with both intuitions and experiences in learned image compression [14]. We assume that dependencies computed on ancestral and sibling" + } + ] + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 309, + 308, + 425, + 416 + ], + "blocks": [ + { + "bbox": [ + 309, + 308, + 425, + 416 + ], + "lines": [ + { + "bbox": [ + 309, + 308, + 425, + 416 + ], + "spans": [ + { + "bbox": [ + 309, + 308, + 425, + 416 + ], + "type": "image", + "image_path": "45ddc2833a4ed01fef535418ebb5495ed7d3dbdda2df8a630540f6120d8f8b28.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 306, + 425, + 545, + 447 + ], + "lines": [ + { + "bbox": [ + 306, + 425, + 545, + 447 + ], + "spans": [ + { + "bbox": [ + 306, + 425, + 545, + 447 + ], + "type": "text", + "content": "Figure 4. Visualization of dependencies discovered by different methods. Deep colors indicate strong dependencies." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 427, + 308, + 545, + 415 + ], + "blocks": [ + { + "bbox": [ + 427, + 308, + 545, + 415 + ], + "lines": [ + { + "bbox": [ + 427, + 308, + 545, + 415 + ], + "spans": [ + { + "bbox": [ + 427, + 308, + 545, + 415 + ], + "type": "image", + "image_path": "ab6324581e1ff62d1c29a10b97683c169e361298a94a04f3e22a8a41280ddd2d.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 470, + 545, + 495 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 470, + 545, + 495 + ], + "spans": [ + { + "bbox": [ + 305, + 470, + 545, + 495 + ], + "type": "text", + "content": "involved contexts have similar distributions. With this property, we use a uniform decomposition pattern expressed as:" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 312, + 504, + 545, + 536 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 504, + 545, + 536 + ], + "spans": [ + { + "bbox": [ + 312, + 504, + 545, + 536 + ], + "type": "interline_equation", + "content": "\\left\\{ \\begin{array}{l} \\mathbf {x} _ {i _ {1}} = \\left\\{x _ {1}, \\dots , x _ {2 j - 1}, \\dots , x _ {i - 1} \\right\\}, \\mathbf {C} _ {i _ {1}} = \\left\\{\\mathbf {A} _ {i} \\right\\}, \\\\ \\mathbf {x} _ {i _ {2}} = \\left\\{x _ {2}, \\dots , x _ {2 j}, \\dots , x _ {i} \\right\\}, \\mathbf {C} _ {i _ {2}} = \\left\\{\\mathbf {A} _ {i}, \\mathbf {x} _ {i _ {1}} \\right\\}. \\end{array} \\right. \\tag {4}", + "image_path": "21923a116eb66006c803f9dad9d13362a4b7bff1e379811ea733fd7b33c16248.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 545, + 544, + 569 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 545, + 544, + 569 + ], + "spans": [ + { + "bbox": [ + 305, + 545, + 544, + 569 + ], + "type": "text", + "content": "It preserves two most important neighbors " + }, + { + "bbox": [ + 305, + 545, + 544, + 569 + ], + "type": "inline_equation", + "content": "x_{2j-1}" + }, + { + "bbox": [ + 305, + 545, + 544, + 569 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 545, + 544, + 569 + ], + "type": "inline_equation", + "content": "x_{2j+1}" + }, + { + "bbox": [ + 305, + 545, + 544, + 569 + ], + "type": "text", + "content": " for " + }, + { + "bbox": [ + 305, + 545, + 544, + 569 + ], + "type": "inline_equation", + "content": "x_{2j}" + }, + { + "bbox": [ + 305, + 545, + 544, + 569 + ], + "type": "text", + "content": " and uniformly samples " + }, + { + "bbox": [ + 305, + 545, + 544, + 569 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_{i_1}" + }, + { + "bbox": [ + 305, + 545, + 544, + 569 + ], + "type": "text", + "content": " at more distant locations." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "content": "In addition, the grouped context separates ancestral and sibling priors to utilize a complete ancestral context. For the auto-regressive context in OctAttention, ancestral and sibling features are concatenated when computing dependencies (see Eq. (3)). To keep the causality, both ancestral and sibling features from non-causal positions (i.e., " + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{f}_{>i}" + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "content": ") are discarded, as shown in Fig. 4a. However, these ancestral features are actually available. As illustrated in Fig. 4b, " + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{f}_{>i}^{a}" + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "content": " have similar dependency activations to " + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{f}_{< i}^{a}" + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "content": ". Therefore, they are equivalently important to compute dependencies. The grouped context structure accesses to more ancestral features, which leads to better compression performance." + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "14371" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 52, + 69, + 284, + 168 + ], + "blocks": [ + { + "bbox": [ + 52, + 69, + 284, + 168 + ], + "lines": [ + { + "bbox": [ + 52, + 69, + 284, + 168 + ], + "spans": [ + { + "bbox": [ + 52, + 69, + 284, + 168 + ], + "type": "image", + "image_path": "5f88752a9cf67363d186a35e0fe4340a13b6d12b273a2edd76f93744b148248c.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 175, + 287, + 208 + ], + "lines": [ + { + "bbox": [ + 46, + 175, + 287, + 208 + ], + "spans": [ + { + "bbox": [ + 46, + 175, + 287, + 208 + ], + "type": "text", + "content": "Figure 5. Illustration of two successive localized attention layers for the case of " + }, + { + "bbox": [ + 46, + 175, + 287, + 208 + ], + "type": "inline_equation", + "content": "N = 8" + }, + { + "bbox": [ + 46, + 175, + 287, + 208 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 175, + 287, + 208 + ], + "type": "inline_equation", + "content": "L = 2" + }, + { + "bbox": [ + 46, + 175, + 287, + 208 + ], + "type": "text", + "content": ". MSA represents the multi-head self-attention." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 230, + 289, + 376 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 230, + 289, + 376 + ], + "spans": [ + { + "bbox": [ + 46, + 230, + 289, + 376 + ], + "type": "text", + "content": "From the perspective of context modeling, this grouped context can be interpreted as the space-channel context in image compression [13]. As shown in Eq. (3), " + }, + { + "bbox": [ + 46, + 230, + 289, + 376 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 230, + 289, + 376 + ], + "type": "text", + "content": " nodes constitute the spatial domain, and each spatial position has " + }, + { + "bbox": [ + 46, + 230, + 289, + 376 + ], + "type": "inline_equation", + "content": "K + 1" + }, + { + "bbox": [ + 46, + 230, + 289, + 376 + ], + "type": "text", + "content": " channels, consisting of " + }, + { + "bbox": [ + 46, + 230, + 289, + 376 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 46, + 230, + 289, + 376 + ], + "type": "text", + "content": " ancestors and 1 sibling. The grouped context partitions on both channel and spatial dimensions. Available contexts for each element are decoded channels (ancestors) from all spatial positions, and elements in the same channel (siblings) at decoded spatial positions. Therefore, it is feasible to use similar context structures for point cloud and image compression, and both domains might benefit from advances of each other." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 383, + 176, + 395 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 383, + 176, + 395 + ], + "spans": [ + { + "bbox": [ + 47, + 383, + 176, + 395 + ], + "type": "text", + "content": "4.3. Hierarchical Attention" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 402, + 287, + 665 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 402, + 287, + 665 + ], + "spans": [ + { + "bbox": [ + 46, + 402, + 287, + 665 + ], + "type": "text", + "content": "To reduce the complexity, we discover dependencies within local windows and model long-range dependencies with a multi-scale network structure. It is inspired by vision transformers designed for 2D images [8, 22, 23, 45]. Since the localized attention can not exploit long-range dependencies in the large-scale context, we gradually downsample the context to represent numerous nodes with " + }, + { + "bbox": [ + 46, + 402, + 287, + 665 + ], + "type": "inline_equation", + "content": "L" + }, + { + "bbox": [ + 46, + 402, + 287, + 665 + ], + "type": "text", + "content": " tokens. The downsampling is implemented by a node merging operation. Two neighboring nodes are merged by concatenating their features on the channel dimension. Then, " + }, + { + "bbox": [ + 46, + 402, + 287, + 665 + ], + "type": "inline_equation", + "content": "2C" + }, + { + "bbox": [ + 46, + 402, + 287, + 665 + ], + "type": "text", + "content": "-dimensional concatenated features are passed to an MLP to shrink the channel dimension to " + }, + { + "bbox": [ + 46, + 402, + 287, + 665 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 46, + 402, + 287, + 665 + ], + "type": "text", + "content": ". In this way, features from distant nodes can be computed in the same window and the receptive field is increased. Furthermore, dependencies are estimated at different scales, and closer neighbors are computed with fine-grained representations. It is reasonable since closer neighbors are more informative. In contrast, distant nodes can be coarsely characterized. We further introduce the shifted window strategy [23] to capture dependencies across neighboring local windows. Dependencies are computed with a window partition alternating between two patterns, as shown in Fig. 5." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 665, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 287, + 715 + ], + "type": "text", + "content": "A self-attention block is composed of various localized attention layers and one node merging module (except for the last block). The hierarchical attention model is a stack of " + }, + { + "bbox": [ + 46, + 665, + 287, + 715 + ], + "type": "inline_equation", + "content": "\\log_2\\frac{N}{L} + 1" + }, + { + "bbox": [ + 46, + 665, + 287, + 715 + ], + "type": "text", + "content": " blocks to capture all " + }, + { + "bbox": [ + 46, + 665, + 287, + 715 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 665, + 287, + 715 + ], + "type": "text", + "content": " nodes in the last block." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 72, + 545, + 131 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 131 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 131 + ], + "type": "text", + "content": "The number of blocks can be further reduced by aggregating more than two nodes in a single node merging module. We produce a hierarchical representation " + }, + { + "bbox": [ + 304, + 72, + 545, + 131 + ], + "type": "inline_equation", + "content": "\\bar{\\mathbf{F}}_i^a" + }, + { + "bbox": [ + 304, + 72, + 545, + 131 + ], + "type": "text", + "content": " by aggregating features and dependencies from different scales. Therefore, we refer to this model as a hierarchical attention model." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 133, + 545, + 180 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 133, + 545, + 180 + ], + "spans": [ + { + "bbox": [ + 304, + 133, + 545, + 180 + ], + "type": "text", + "content": "By performing attention operations within local windows, the hierarchical attention model reduces the complexity from quadratic to linear scale. Complexities of attention computations in global and localized self-attention are:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 329, + 189, + 545, + 203 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 329, + 189, + 545, + 203 + ], + "spans": [ + { + "bbox": [ + 329, + 189, + 545, + 203 + ], + "type": "interline_equation", + "content": "\\Omega (\\text {G l o b a l}) = 2 N ^ {2} C, \\quad \\Omega (\\text {L o c a l i z e d}) = 2 L N C. \\tag {5}", + "image_path": "e6f0fd15b0824d676024ef887d1a797cda08544120a73739c3900eec1768dc32.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 212, + 545, + 259 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 212, + 545, + 259 + ], + "spans": [ + { + "bbox": [ + 304, + 212, + 545, + 259 + ], + "type": "text", + "content": "It allows us to build a much deeper entropy model with reasonable computational costs to enhance the modeling capability, or substantially expand the context scale to introduce more potentially useful references." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 259, + 545, + 406 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 259, + 545, + 406 + ], + "spans": [ + { + "bbox": [ + 304, + 259, + 545, + 406 + ], + "type": "text", + "content": "The hierarchical cross-attention follows a similar localized attention practice. Since the decomposition pattern is uniform, each local window includes " + }, + { + "bbox": [ + 304, + 259, + 545, + 406 + ], + "type": "inline_equation", + "content": "\\frac{L}{2}" + }, + { + "bbox": [ + 304, + 259, + 545, + 406 + ], + "type": "text", + "content": " nodes from " + }, + { + "bbox": [ + 304, + 259, + 545, + 406 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_{i_1}" + }, + { + "bbox": [ + 304, + 259, + 545, + 406 + ], + "type": "text", + "content": " and another " + }, + { + "bbox": [ + 304, + 259, + 545, + 406 + ], + "type": "inline_equation", + "content": "\\frac{L}{2}" + }, + { + "bbox": [ + 304, + 259, + 545, + 406 + ], + "type": "text", + "content": " nodes from " + }, + { + "bbox": [ + 304, + 259, + 545, + 406 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_{i_2}" + }, + { + "bbox": [ + 304, + 259, + 545, + 406 + ], + "type": "text", + "content": ". They are regarded as key and query features, respectively. We compute dependencies among keys and queries within each local window, and weight keys according to their dependencies to queries. To extend the receptive field, neighboring keys (and queries) are progressively merged into new key (and query) tokens. Finally, features from different scales are concatenated, which are then exploited to predict " + }, + { + "bbox": [ + 304, + 259, + 545, + 406 + ], + "type": "inline_equation", + "content": "x_{i_2}" + }, + { + "bbox": [ + 304, + 259, + 545, + 406 + ], + "type": "text", + "content": " with ancestral features " + }, + { + "bbox": [ + 304, + 259, + 545, + 406 + ], + "type": "inline_equation", + "content": "\\tilde{\\mathbf{F}}_{i_2}^a" + }, + { + "bbox": [ + 304, + 259, + 545, + 406 + ], + "type": "text", + "content": " jointly." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 411, + 372, + 425 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 411, + 372, + 425 + ], + "spans": [ + { + "bbox": [ + 306, + 411, + 372, + 425 + ], + "type": "text", + "content": "4.4. Learning" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 430, + 545, + 491 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 430, + 545, + 491 + ], + "spans": [ + { + "bbox": [ + 304, + 430, + 545, + 491 + ], + "type": "text", + "content": "The optimization objective of the octree-based entropy model is to minimize the total bitrates for communicating octree nodes. The bitrate is given by the cross entropy between the estimated distribution " + }, + { + "bbox": [ + 304, + 430, + 545, + 491 + ], + "type": "inline_equation", + "content": "\\tilde{p} (\\mathbf{x})" + }, + { + "bbox": [ + 304, + 430, + 545, + 491 + ], + "type": "text", + "content": " and the ground truth " + }, + { + "bbox": [ + 304, + 430, + 545, + 491 + ], + "type": "inline_equation", + "content": "p(\\mathbf{x})" + }, + { + "bbox": [ + 304, + 430, + 545, + 491 + ], + "type": "text", + "content": " at each node:" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 371, + 498, + 545, + 524 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 371, + 498, + 545, + 524 + ], + "spans": [ + { + "bbox": [ + 371, + 498, + 545, + 524 + ], + "type": "interline_equation", + "content": "\\ell = - \\sum_ {i} \\log \\tilde {p} _ {i} \\left(x _ {i} \\mid \\mathbf {C} _ {i}\\right), \\tag {6}", + "image_path": "3a2824f0ed0b13525eee631a17ad1974a63f01b46e4adcba1037b963dd77e54f.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 533, + 545, + 558 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 533, + 545, + 558 + ], + "spans": [ + { + "bbox": [ + 304, + 533, + 545, + 558 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 533, + 545, + 558 + ], + "type": "inline_equation", + "content": "\\tilde{p}_i(x_i\\mid \\mathbf{C}_i)" + }, + { + "bbox": [ + 304, + 533, + 545, + 558 + ], + "type": "text", + "content": " is the distribution estimated by the proposed entropy model based on the context " + }, + { + "bbox": [ + 304, + 533, + 545, + 558 + ], + "type": "inline_equation", + "content": "\\mathbf{C}_i" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 567, + 387, + 581 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 567, + 387, + 581 + ], + "spans": [ + { + "bbox": [ + 306, + 567, + 387, + 581 + ], + "type": "text", + "content": "5. Experiments" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 306, + 587, + 432, + 601 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 587, + 432, + 601 + ], + "spans": [ + { + "bbox": [ + 306, + 587, + 432, + 601 + ], + "type": "text", + "content": "5.1. Experimental Settings" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 605, + 545, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 545, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 545, + 715 + ], + "type": "text", + "content": "Datasets Experiments are conducted on two large-scale point cloud datasets SemanticKITTI [3] and Ford [32]. SemanticKITTI is composed of 43552 LiDAR scans acquired from autonomous driving scenes, which are divided into 22 sequences. We follow the default split to perform training on sequences 00 to 10 and evaluation on sequences 11 to 21. Ford is another LiDAR point cloud dataset used in MPEG point cloud compression standardization. It includes 3 sequences, each consists of 1500 scans. On the Ford dataset," + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "14372" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 52, + 69, + 210, + 201 + ], + "blocks": [ + { + "bbox": [ + 52, + 69, + 210, + 201 + ], + "lines": [ + { + "bbox": [ + 52, + 69, + 210, + 201 + ], + "spans": [ + { + "bbox": [ + 52, + 69, + 210, + 201 + ], + "type": "image", + "image_path": "de2a17434b604c200dd6f99e282cab9a543b2202b492a96776cf516e0b4dfe12.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 217, + 69, + 375, + 201 + ], + "blocks": [ + { + "bbox": [ + 217, + 69, + 375, + 201 + ], + "lines": [ + { + "bbox": [ + 217, + 69, + 375, + 201 + ], + "spans": [ + { + "bbox": [ + 217, + 69, + 375, + 201 + ], + "type": "image", + "image_path": "c0ee82cd88e021dfbc338b65caec9c9a74db5790fc4053e2e07e8e718e80198a.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 383, + 70, + 541, + 202 + ], + "blocks": [ + { + "bbox": [ + 383, + 70, + 541, + 202 + ], + "lines": [ + { + "bbox": [ + 383, + 70, + 541, + 202 + ], + "spans": [ + { + "bbox": [ + 383, + 70, + 541, + 202 + ], + "type": "image", + "image_path": "4d35d2aabc046b8ef7a80ba9f7b373077fe7bb4f1314a88ee9002d83c471616f.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 50, + 209, + 211, + 340 + ], + "blocks": [ + { + "bbox": [ + 50, + 209, + 211, + 340 + ], + "lines": [ + { + "bbox": [ + 50, + 209, + 211, + 340 + ], + "spans": [ + { + "bbox": [ + 50, + 209, + 211, + 340 + ], + "type": "image", + "image_path": "b4a36def1db17bcbca32e704059b0e579f0e092cde6472bdbe131d2a7a61d5d7.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 108, + 349, + 484, + 361 + ], + "lines": [ + { + "bbox": [ + 108, + 349, + 484, + 361 + ], + "spans": [ + { + "bbox": [ + 108, + 349, + 484, + 361 + ], + "type": "text", + "content": "Figure 6. Rate-distortion performance of different methods on SemanticKITTI (top) and Ford (bottom)." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_caption" + } + ], + "index": 3 + }, + { + "type": "image", + "bbox": [ + 217, + 209, + 375, + 340 + ], + "blocks": [ + { + "bbox": [ + 217, + 209, + 375, + 340 + ], + "lines": [ + { + "bbox": [ + 217, + 209, + 375, + 340 + ], + "spans": [ + { + "bbox": [ + 217, + 209, + 375, + 340 + ], + "type": "image", + "image_path": "5c148f59cc31e7be5ca4478bf54ba6db83a0b926e41e9e97f99127adf65b9a00.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + } + ], + "index": 4 + }, + { + "type": "image", + "bbox": [ + 383, + 209, + 541, + 340 + ], + "blocks": [ + { + "bbox": [ + 383, + 209, + 541, + 340 + ], + "lines": [ + { + "bbox": [ + 383, + 209, + 541, + 340 + ], + "spans": [ + { + "bbox": [ + 383, + 209, + 541, + 340 + ], + "type": "image", + "image_path": "cbb657c583b33283971c92cb3c15a04414c9b41b43f3ec2ece5a7609ec9868d6.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_body" + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 380, + 287, + 417 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 380, + 287, + 417 + ], + "spans": [ + { + "bbox": [ + 46, + 380, + 287, + 417 + ], + "type": "text", + "content": "we follow the suggested dataset partition in MPEG standardization [7], where sequence 01 is used for training and sequences 02 and 03 are used for evaluation." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 419, + 287, + 492 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 419, + 287, + 492 + ], + "spans": [ + { + "bbox": [ + 46, + 419, + 287, + 492 + ], + "type": "text", + "content": "Baselines To verify the effectiveness of the proposed model, we compare it with the state-of-the-art octree-based learned entropy model OctAttention [10] and the competitive voxel-based learned method SparsePCGC [43]. We also provide comparisons with the representative handcrafted compression method MPEG G-PCC [12]." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 495, + 287, + 614 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 495, + 287, + 614 + ], + "spans": [ + { + "bbox": [ + 46, + 495, + 287, + 614 + ], + "type": "text", + "content": "Implementation settings Quantization is necessary to construct octrees from point clouds. For SemanticKITTI, we follow the quantization settings in OctSqueeze [16], where the quantization step is set to " + }, + { + "bbox": [ + 46, + 495, + 287, + 614 + ], + "type": "inline_equation", + "content": "\\frac{400}{2^{D} - 1}" + }, + { + "bbox": [ + 46, + 495, + 287, + 614 + ], + "type": "text", + "content": " to build an octree with the depth of " + }, + { + "bbox": [ + 46, + 495, + 287, + 614 + ], + "type": "inline_equation", + "content": "D" + }, + { + "bbox": [ + 46, + 495, + 287, + 614 + ], + "type": "text", + "content": ". Octrees are truncated with a maximum depth of 16 for training and evaluation. We set the quantization step to " + }, + { + "bbox": [ + 46, + 495, + 287, + 614 + ], + "type": "inline_equation", + "content": "2^{18 - D}" + }, + { + "bbox": [ + 46, + 495, + 287, + 614 + ], + "type": "text", + "content": " and construct octrees with the maximum depth of 18 on Ford. Since the original Ford dataset has been quantized with 18-bit precision, compression is lossless at the highest octree level." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 617, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 617, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 617, + 288, + 715 + ], + "type": "text", + "content": "The hierarchical self-attention model has 5 blocks including 4, 4, 4, 4, 2 layers, respectively. The hierarchical cross-attention model consists of 4 blocks with 2, 2, 1, 1 layers. The head number is set to 4 for all attention layers. The channel dimension " + }, + { + "bbox": [ + 46, + 617, + 288, + 715 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 46, + 617, + 288, + 715 + ], + "type": "text", + "content": " is set to 256, and the ancestor depth " + }, + { + "bbox": [ + 46, + 617, + 288, + 715 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 46, + 617, + 288, + 715 + ], + "type": "text", + "content": " is set to 3. The context window length " + }, + { + "bbox": [ + 46, + 617, + 288, + 715 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 617, + 288, + 715 + ], + "type": "text", + "content": " is set to 8192, which is initially divided into 16 local windows with the length " + }, + { + "bbox": [ + 46, + 617, + 288, + 715 + ], + "type": "inline_equation", + "content": "L" + }, + { + "bbox": [ + 46, + 617, + 288, + 715 + ], + "type": "text", + "content": " of 512. To further achieve speed-accuracy trade" + } + ] + } + ], + "index": 10 + }, + { + "type": "table", + "bbox": [ + 309, + 421, + 541, + 498 + ], + "blocks": [ + { + "bbox": [ + 305, + 380, + 545, + 411 + ], + "lines": [ + { + "bbox": [ + 305, + 380, + 545, + 411 + ], + "spans": [ + { + "bbox": [ + 305, + 380, + 545, + 411 + ], + "type": "text", + "content": "Table 1. Inference times (in seconds) for encoding/decoding a D-depth octree on SemanticKITTI. Runtimes for G-PCC are total times." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 309, + 421, + 541, + 498 + ], + "lines": [ + { + "bbox": [ + 309, + 421, + 541, + 498 + ], + "spans": [ + { + "bbox": [ + 309, + 421, + 541, + 498 + ], + "type": "table", + "html": "
MethodD=12D=14D=16
G-PCC0.25 / 0.120.66 / 0.321.07 / 0.54
SparsePCGC1.14 / 0.861.76 / 1.432.43 / 2.04
OctAttention0.08 / 830.31 / 3210.66 / 708
EHEM0.40 / 0.431.21 / 1.392.53 / 3.01
Light EHEM0.29 / 0.330.79 / 0.921.63 / 1.94
", + "image_path": "5b94bb553ca3b20760f67f6334b73721989231196cd702116b872aaa0599eccb.jpg" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "table_body" + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 525, + 545, + 573 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 525, + 545, + 573 + ], + "spans": [ + { + "bbox": [ + 304, + 525, + 545, + 573 + ], + "type": "text", + "content": "offs, we present a lightweight EHEM model called Light EHEM. It has the same network structure as EHEM except that its 5 self-attention blocks have 2, 2, 2, 2, 2 layers and its channel dimension " + }, + { + "bbox": [ + 304, + 525, + 545, + 573 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 304, + 525, + 545, + 573 + ], + "type": "text", + "content": " is set to 192." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 578, + 545, + 625 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 578, + 545, + 625 + ], + "spans": [ + { + "bbox": [ + 304, + 578, + 545, + 625 + ], + "type": "text", + "content": "We adopt an Adam optimizer [20] with a learning rate of " + }, + { + "bbox": [ + 304, + 578, + 545, + 625 + ], + "type": "inline_equation", + "content": "10^{-4}" + }, + { + "bbox": [ + 304, + 578, + 545, + 625 + ], + "type": "text", + "content": " to train two models for 10 and 50 epochs on SemanticKITTI and Ford datasets, respectively. The evaluation is implemented on the NVIDIA V100 GPU." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 629, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 629, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 629, + 545, + 714 + ], + "type": "text", + "content": "Metrics We adopt the point-to-point PSNR (D1 PSNR), point-to-plane PSNR (D2 PSNR) [6], and Chamfer distance (CD) to measure the distortion. Experiments on SemanticKITTI follow the PSNR calculations in OctSqueeze and MuSCLE [4, 16], where the peak value is set to 59.70. On the Ford dataset, we set the peak value to 30000 [6]. Consumed bitrates are measured by bits per point (bpp)." + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "14373" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 48, + 112, + 286, + 164 + ], + "blocks": [ + { + "bbox": [ + 47, + 70, + 288, + 104 + ], + "lines": [ + { + "bbox": [ + 47, + 70, + 288, + 104 + ], + "spans": [ + { + "bbox": [ + 47, + 70, + 288, + 104 + ], + "type": "text", + "content": "Table 2. Complexity comparison on encoding/decoding time, theoretical computation cost (FLOPs), parameters, and memory usage among OctAttention, EHEM, and Light EHEM." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 48, + 112, + 286, + 164 + ], + "lines": [ + { + "bbox": [ + 48, + 112, + 286, + 164 + ], + "spans": [ + { + "bbox": [ + 48, + 112, + 286, + 164 + ], + "type": "table", + "html": "
MethodEnc / DecFLOPs#param.Mem.
OctAttn0.66s / 708s124.3G4.23M1.3G
EHEM2.53s / 3.01s184.4G13.01M2.9G
L-EHEM1.63s / 1.94s102.9G6.34M2.6G
", + "image_path": "ffb363dd884c3ec22b6d204a213f75fb75915f8f2677bb8f4124f9065d9ad5a6.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "type": "table", + "bbox": [ + 48, + 209, + 288, + 261 + ], + "blocks": [ + { + "bbox": [ + 47, + 177, + 287, + 200 + ], + "lines": [ + { + "bbox": [ + 47, + 177, + 287, + 200 + ], + "spans": [ + { + "bbox": [ + 47, + 177, + 287, + 200 + ], + "type": "text", + "content": "Table 3. Comparison of FLOPs among OctAttention, EHEM, and Light EHEM with respect to the context length " + }, + { + "bbox": [ + 47, + 177, + 287, + 200 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 47, + 177, + 287, + 200 + ], + "type": "text", + "content": " ." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 48, + 209, + 288, + 261 + ], + "lines": [ + { + "bbox": [ + 48, + 209, + 288, + 261 + ], + "spans": [ + { + "bbox": [ + 48, + 209, + 288, + 261 + ], + "type": "table", + "html": "
Method5121024204840968192
OctAttn6.0G15.5G45.0G145.7G514.0G
EHEM9.0G18.4G38.1G81.5G184.4G
L-EHEM5.2G10.7G21.9G46.4G102.9G
", + "image_path": "e111aa5ad9e7fa0f07677ecd391997037cde7a7b4cceb57a8321db4c428ca22d.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 283, + 185, + 295 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 283, + 185, + 295 + ], + "spans": [ + { + "bbox": [ + 47, + 283, + 185, + 295 + ], + "type": "text", + "content": "5.2. Performance Evaluation" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 304, + 287, + 399 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 304, + 287, + 399 + ], + "spans": [ + { + "bbox": [ + 46, + 304, + 287, + 399 + ], + "type": "text", + "content": "The quantitative results of the rate-distortion performance are shown in Fig. 6. The proposed method EHEM achieves significant improvements over other baselines. For example, on SemanticKITTI, EHEM achieves an average gain of " + }, + { + "bbox": [ + 46, + 304, + 287, + 399 + ], + "type": "inline_equation", + "content": "28.89\\%" + }, + { + "bbox": [ + 46, + 304, + 287, + 399 + ], + "type": "text", + "content": " to G-PCC, and " + }, + { + "bbox": [ + 46, + 304, + 287, + 399 + ], + "type": "inline_equation", + "content": "19.47\\%" + }, + { + "bbox": [ + 46, + 304, + 287, + 399 + ], + "type": "text", + "content": " bitrate reduction on average compared with OctAttention. Furthermore, Light EHEM also preserves satisfactory performance and outperforms other baselines." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 400, + 287, + 544 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 400, + 287, + 544 + ], + "spans": [ + { + "bbox": [ + 46, + 400, + 287, + 544 + ], + "type": "text", + "content": "To evaluate the efficiency of EHEM, we report inference times at different quantization steps in Tab. 1. EHEM achieves notable decoding time reduction over the autoregressive context model OctAttention. The encoding time increases compared with OctAttention since the grouped context requires a two-step inference (for " + }, + { + "bbox": [ + 46, + 400, + 287, + 544 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_{i_1}" + }, + { + "bbox": [ + 46, + 400, + 287, + 544 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 400, + 287, + 544 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_{i_2}" + }, + { + "bbox": [ + 46, + 400, + 287, + 544 + ], + "type": "text", + "content": "), while OctAttention only requires one step. However, this encoding time is still practically acceptable and the grouped context is effective to speed up decoding. We further represent both rate-distortion performance and decoding time in Fig. 1. It is shown that EHEM is effective regarding both compression performance and decoding speed." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "content": "We provide the complexity analysis of EHEM and OctAttention in Tab. 2 and Tab. 3. Here, we report required FLOPs to infer a single context window. Note that larger context predicts more nodes with one forward pass. For example, EHEM requires " + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "inline_equation", + "content": "81.5 \\times 2" + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "inline_equation", + "content": "184.4 \\times 1" + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "content": " GFLOPs to predict 8192 nodes when " + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "content": " is set to 4096 and 8192, respectively. It is shown that EHEM has comparable FLOPs to OctAttention when the context capacity is 1024, which is the default setting for OctAttention. However, EHEM contains 24 hierarchical attention layers while OctAttention only includes 2 global attention layers. It proves the superiority of the localized attention structure in terms of extending the network depth. Furthermore, localized attention is also effective to enlarge the context due to the linear com" + } + ] + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 310, + 68, + 541, + 241 + ], + "blocks": [ + { + "bbox": [ + 310, + 68, + 541, + 241 + ], + "lines": [ + { + "bbox": [ + 310, + 68, + 541, + 241 + ], + "spans": [ + { + "bbox": [ + 310, + 68, + 541, + 241 + ], + "type": "image", + "image_path": "231266a08d05b49923d280eabadfafa9d9eaeee281eb992a289a4d60fa6d956b.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 248, + 545, + 270 + ], + "lines": [ + { + "bbox": [ + 305, + 248, + 545, + 270 + ], + "spans": [ + { + "bbox": [ + 305, + 248, + 545, + 270 + ], + "type": "text", + "content": "Figure 7. Ablation studies on attention models, context scales, and context structures." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 307, + 282, + 425, + 373 + ], + "blocks": [ + { + "bbox": [ + 307, + 282, + 425, + 373 + ], + "lines": [ + { + "bbox": [ + 307, + 282, + 425, + 373 + ], + "spans": [ + { + "bbox": [ + 307, + 282, + 425, + 373 + ], + "type": "image", + "image_path": "b53bf97dc1eb8c5a2c7a2ed96ef713bd90c565af1294313fb8cacd7ccb10d6ff.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 306, + 380, + 545, + 402 + ], + "lines": [ + { + "bbox": [ + 306, + 380, + 545, + 402 + ], + "spans": [ + { + "bbox": [ + 306, + 380, + 545, + 402 + ], + "type": "text", + "content": "Figure 8. Contexts with different capacities " + }, + { + "bbox": [ + 306, + 380, + 545, + 402 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 306, + 380, + 545, + 402 + ], + "type": "text", + "content": " on 16-bit quantized SemanticKITTI. Points in the context are colored in blue." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 427, + 282, + 545, + 373 + ], + "blocks": [ + { + "bbox": [ + 427, + 282, + 545, + 373 + ], + "lines": [ + { + "bbox": [ + 427, + 282, + 545, + 373 + ], + "spans": [ + { + "bbox": [ + 427, + 282, + 545, + 373 + ], + "type": "image", + "image_path": "e1f9957123d0d73c6c05581814b1295da7fd8383787ed761d67fc53560999519.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 424, + 545, + 532 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 424, + 545, + 532 + ], + "spans": [ + { + "bbox": [ + 304, + 424, + 545, + 532 + ], + "type": "text", + "content": "plexity. FLOPs of EHEM increase 2.26 times as the context is enlarged from 4096 to 8192. In contrast, the complexity of OctAttention increases 3.53 times with the same extension. Besides, Light EHEM achieves lower FLOPs at all context window length settings compared to OctAttention. EHEM has slightly larger model size and memory usage compared with OctAttention. These increases are due to the extension of model capacity and context scale, but it is still reasonable for practical use." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 539, + 470, + 552 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 539, + 470, + 552 + ], + "spans": [ + { + "bbox": [ + 306, + 539, + 470, + 552 + ], + "type": "text", + "content": "5.3. Ablation Studies and Analysis" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 557, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 557, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 557, + 545, + 713 + ], + "type": "text", + "content": "Hierarchical attention structure To verify the effectiveness of the hierarchical attention structure, we replace the hierarchical self-attention model with global self-attention layers to build a counterpart with similar FLOPs. Since it is impractical to compute global self-attention with " + }, + { + "bbox": [ + 304, + 557, + 545, + 713 + ], + "type": "inline_equation", + "content": "N = 8192" + }, + { + "bbox": [ + 304, + 557, + 545, + 713 + ], + "type": "text", + "content": ", we conduct experiments with " + }, + { + "bbox": [ + 304, + 557, + 545, + 713 + ], + "type": "inline_equation", + "content": "N = 1024" + }, + { + "bbox": [ + 304, + 557, + 545, + 713 + ], + "type": "text", + "content": ". Here, EHEM still has 18 localized self-attention layers, and the global-attention counterpart contains 5 layers. The comparison between EHEM (" + }, + { + "bbox": [ + 304, + 557, + 545, + 713 + ], + "type": "inline_equation", + "content": "N = 1024" + }, + { + "bbox": [ + 304, + 557, + 545, + 713 + ], + "type": "text", + "content": ") and Global Self-Attn in Fig. 7 proves that the hierarchical attention model with a much deeper network achieves considerable improvements. Network depth With the same network structure, the comparison between EHEM and Light EHEM shows that the" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "14374" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 65, + 73, + 529, + 305 + ], + "blocks": [ + { + "bbox": [ + 65, + 73, + 529, + 305 + ], + "lines": [ + { + "bbox": [ + 65, + 73, + 529, + 305 + ], + "spans": [ + { + "bbox": [ + 65, + 73, + 529, + 305 + ], + "type": "image", + "image_path": "48b6b6d53dc05c5f9f0da23f43e3598ae46623b66bdc4110d00a2ae953b0fbec.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 89, + 313, + 503, + 326 + ], + "lines": [ + { + "bbox": [ + 89, + 313, + 503, + 326 + ], + "spans": [ + { + "bbox": [ + 89, + 313, + 503, + 326 + ], + "type": "text", + "content": "Figure 9. Visualized compression results of G-PCC, OctAttention, and our method on the SemanticKITTI dataset." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 346, + 288, + 382 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 346, + 288, + 382 + ], + "spans": [ + { + "bbox": [ + 46, + 346, + 288, + 382 + ], + "type": "text", + "content": "deeper network leads to better performance. Therefore, it is helpful to enhance the expressiveness of the model by stacking more layers within a reasonable range." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 386, + 287, + 495 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 386, + 287, + 495 + ], + "spans": [ + { + "bbox": [ + 46, + 386, + 287, + 495 + ], + "type": "text", + "content": "Context scale The linear complexity of the hierarchical attention also allows the further extension of the context scale " + }, + { + "bbox": [ + 46, + 386, + 287, + 495 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 386, + 287, + 495 + ], + "type": "text", + "content": ". Contexts with different capacities are visualized in Fig. 8. It is shown that captured regions are significantly enlarged when " + }, + { + "bbox": [ + 46, + 386, + 287, + 495 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 386, + 287, + 495 + ], + "type": "text", + "content": " increases from 1024 to 8192. The extended context includes the complete geometry pattern of the vehicle and introduces references from the neighboring similar vehicle. This is beneficial to improve the rate-distortion performance, as shown in Fig. 7." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 498, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 498, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 498, + 288, + 715 + ], + "type": "text", + "content": "Grouped context structure The grouped context structure allows a two-step parallel decoding procedure. Here, we examine its influence on rate-distortion performance. To this end, we train a baseline with an auto-regressive context used in OctAttention. The hierarchical attention is unavailable to this context structure since the node merging operation uses non-causal ancestral references. For a fair comparison, we use global attention to compute dependencies for both grouped and auto-regressive context structures. The grouped context introduces features from the first group via global cross-attention layers. The comparison between AR Context and Grouped Context in Fig. 7 demonstrates that although only half of the nodes access to siblings, the grouped context structure achieves comparable performance. It is because the grouped context preserves ancestral features from non-causal references, as shown in Fig. 4b. Besides, it proves that the grouped context structure does not significantly improve compression performance. Therefore, im" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 305, + 346, + 545, + 369 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 346, + 545, + 369 + ], + "spans": [ + { + "bbox": [ + 305, + 346, + 545, + 369 + ], + "type": "text", + "content": "provements of EHEM are mainly due to stronger hierarchical attention blocks." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 306, + 381, + 418, + 395 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 381, + 418, + 395 + ], + "spans": [ + { + "bbox": [ + 306, + 381, + 418, + 395 + ], + "type": "text", + "content": "5.4. Qualitative Results" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 305, + 401, + 545, + 462 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 401, + 545, + 462 + ], + "spans": [ + { + "bbox": [ + 305, + 401, + 545, + 462 + ], + "type": "text", + "content": "In Fig. 9, we show the visualized compression distortions of different methods at similar bitrates. It indicates that our method provides better reconstructions compared with other baselines. For example, EHEM outperforms G-PCC by roughly 10 dB D1 PSNR improvements." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 476, + 379, + 489 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 476, + 379, + 489 + ], + "spans": [ + { + "bbox": [ + 306, + 476, + 379, + 489 + ], + "type": "text", + "content": "6. Conclusion" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 498, + 545, + 653 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 498, + 545, + 653 + ], + "spans": [ + { + "bbox": [ + 304, + 498, + 545, + 653 + ], + "type": "text", + "content": "We proposed an efficient learned entropy model for point cloud compression. It adopts a hierarchical attention structure, which allows us to substantially extend the network depth and context capacity to improve the rate-distortion performance with reasonable complexity. We further developed a grouped context structure to realize a parallel decoding procedure. Moreover, this context aligns the context modeling regimes of point cloud and image compression, and we hope it would be helpful to bridge the gap between two communities. The proposed model is proved to yield superior compression performance and significantly reduce the decoding time compared to the state-of-the-art auto-regressive method." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 668, + 404, + 681 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 668, + 404, + 681 + ], + "spans": [ + { + "bbox": [ + 306, + 668, + 404, + 681 + ], + "type": "text", + "content": "Acknowledgement" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "text", + "content": "This work was supported by National Natural Science Foundation of China (No. 62172021)." + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "14375" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 286, + 713 + ], + "type": "list", + "angle": 0, + "index": 15, + "blocks": [ + { + "bbox": [ + 53, + 91, + 286, + 123 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 286, + 123 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 286, + 123 + ], + "type": "text", + "content": "[1] Johannes Balle, Valero Laparra, and Eero P Simoncelli. 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Many attack techniques have been proposed to evaluate the model's robustness. Gradient-based attacks suffer from severely overestimating the robustness. This paper identifies that the relative error in calculated gradients caused by floating-point errors, including floating-point underflow and rounding errors, is a fundamental reason why gradient-based attacks fail to accurately assess the model's robustness. Although it is hard to eliminate the relative error in the gradients, we can control its effect on the gradient-based attacks. Correspondingly, we propose an efficient loss function by minimizing the detrimental impact of the floating-point errors on the attacks. Experimental results show that it is more efficient and reliable than other loss functions when examined across a wide range of defence mechanisms.", + "bbox": [ + 75, + 358, + 473, + 630 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 659, + 209, + 674 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "AI with deep neural networks (DNNs) as the core [24] has achieved great success in different research directions and has been widely used in many safety-critical systems, such as aviation [1,8,35], medical diagnosis [27, 49], self-driving [4,26,47], etc. However, a severe problem with current DNNs is that they are vulnerable to adversarial attacks. Adding human imperceptive perturbations to input data can mislead the model to output incorrect results [16, 45]. Such vulnerability poses a significant security risk to all DNN-based systems. Therefore, increasing the models' robustness and providing efficient and reliable evaluation methods are becoming increasingly urgent and vital.", + "bbox": [ + 75, + 684, + 468, + 864 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/bda904398ffe2aa928830752bebe4d7f281be5f97d93bf99c2f5c0211310e755.jpg", + "image_caption": [ + "Figure 1. Comparison of the effectiveness of non-targeted and multi-targeted PGD 100 iterations attacks using various loss functions on the CIFAR-10 dataset. The best results were obtained from RobustBench using an ensemble attack with a minimum of 4900 iterations. The defence model is from [59]." + ], + "image_footnote": [], + "bbox": [ + 511, + 333, + 880, + 498 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Numerous defence strategies [6, 10, 13, 16, 29, 31, 55] to improve the model's robustness and many attacks [2, 29, 33, 41, 50, 52, 54, 59] to evaluate these strategies have been proposed. Currently, the most efficient attack method is known as white-box attack, where the attacker has complete knowledge of the target defending strategy, including its model architecture, parameters, detail of the training algorithm, dataset, etc. A typical example is Projective gradient descent (PGD) [29] for evaluating the model's robustness. However, studies have shown that PGD with cross-entropy (CE) loss fails to provide accurate evaluation results [6, 41] and significantly overestimates the model's robustness (Figure 1). To enhance the evaluation accuracy, recent powerful evaluation methods were proposed to ensemble diverse attack algorithms [10, 30]. However, their performance is at the cost of high computational overhead.", + "bbox": [ + 496, + 609, + 893, + 852 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "The research community attributes the failure of gradient-based attacks to gradient masking [15]. The core of gradient masking is that the calculated gradients are not", + "bbox": [ + 498, + 854, + 893, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 810, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Corresponding author. \n1https://robustbench.github.io/", + "bbox": [ + 94, + 875, + 339, + 900 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "4056", + "bbox": [ + 482, + 944, + 516, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "necessarily efficient in guiding the generation of adversarial examples. The causes of inefficient gradients may be related to floating-point errors or other factors. This paper reveals that the relative error in the gradients caused by floating-point errors is one of the fundamental reasons for the failure of gradient-based attacks, and the relative error is directly affected by the value of the difference of the first and second largest in logits(DFSL). Although it is hard to eliminate the relative error in the gradients caused by floating-point errors completely, we can control its effect on the gradient-based attacks. Thus, we propose a new efficient loss function by minimizing the impact of floating-point errors (MIFPE) on gradient-based attacks. To summarize, our main contributions are as follows:", + "bbox": [ + 75, + 90, + 472, + 303 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- We provide a comprehensive demonstration of how the presence of floating-point errors leads to the failure of gradient-based attacks due to the relative error in calculated gradients.", + "- We show that the floating-point rounding errors may lead to attack's failure due to growing relative errors as samples reach the classification boundary.", + "- We demonstrate that when the model's robustness is overestimated primarily due to floating-point errors, the loss function discarding partial elements of logits causes performance degradation in the gradient-based attack.", + "- We show that minimizing the impact of floating-point errors can improve the efficiency and accuracy of gradient-based attacks.", + "- Empirical results demonstrate that MIFPE tends to outperform the competing loss functions in terms of attack performance and computational efficiency." + ], + "bbox": [ + 94, + 311, + 468, + 619 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Preliminaries & Related Work", + "text_level": 1, + "bbox": [ + 76, + 633, + 357, + 648 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "We define the classification model as $f_{\\theta}(\\mathbf{x})$ , where $\\pmb{\\theta}$ represents the model parameters. $f_{\\theta}:\\mathbf{x}\\subset \\mathbb{R}^{C\\times H\\times W}\\to$ $\\mathbf{z}\\subset \\mathbb{R}^k$ is a classifier that maps input data $\\mathbf{x}$ to output logits $\\mathbf{z}$ ,where $C,H$ ,and $W$ are parameters that describe the input data's channel number, height, and width, respectively. Additionally, $K$ represents the number of classes from the model's output. We define the label of the input data as $y$", + "bbox": [ + 75, + 657, + 468, + 763 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Attackers aim to breach defence strategies by generating adversarial examples $\\hat{\\mathbf{x}}$ , which can maximize the loss function $L(f_{\\theta}(\\hat{\\mathbf{x}}),y)$ and deceive the model into producing incorrect results, arg max $f_{\\theta}(\\hat{\\mathbf{x}})\\neq y$ . Achieving this requires the attackers to find imperceptible perturbations $\\delta = \\hat{\\mathbf{x}} -\\mathbf{x}$ that satisfy the constraint $\\| \\delta \\| p\\leq \\varepsilon$ , where $\\varepsilon$ is the magnitude and $p$ is the norm of the perturbation. Various perturbation options have been explored in literature, including the one-pixel attack [44, 44], $l_{2}$ attacks [6, 31, 45], and $l\\infty$", + "bbox": [ + 75, + 765, + 468, + 900 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "attacks [16, 29]. The attackers can find an adversarial example $\\hat{\\mathbf{x}} \\in \\mathcal{I}$ by maximizing the loss. This process can be formulated as:", + "bbox": [ + 498, + 90, + 890, + 135 + ], + "page_idx": 1 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {\\mathbf {x}} = \\mathbf {x} + \\max _ {\\| \\delta \\| _ {p} \\in \\varepsilon} L \\left(f _ {\\boldsymbol {\\theta}} (\\mathbf {x} + \\delta), y\\right), \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 576, + 147, + 890, + 172 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "The white-box scenario is the most rigorous test for defence strategies, as attackers have complete knowledge about the models' architecture, parameters, training data, and algorithm implementation details. This is a highly challenging situation for defence strategies. Attackers can exploit nearly all vulnerabilities in the defence strategies and perform tailored attacks. If defence strategies remain robust against white-box attacks, they can ensure the system's security even in the worst-case scenario. In practice, the gradient-based method is commonly used to solve (1).", + "bbox": [ + 496, + 181, + 890, + 332 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Many gradient-based white-box attacks methods have been proposed, which include fast gradient-sign method (FGSM) [16], basic iterative method (BIM) [23], projected gradient descent (PGD) [29], momentum iterative method (MIM) [13] and fast adaptive boundary attack (FAB) [9] for $\\ell_{\\infty}$ -norm attacks. Carlini and Wagner (C&W) [6] and DeepFool [31] can additionally carry out $\\ell_{2}$ -norm attacks. PGD is one of the widely used methods to evaluate the model's robustness in the white box scenario, which finds an adversarial example by performing the following iterative update:", + "bbox": [ + 496, + 334, + 890, + 500 + ], + "page_idx": 1 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {\\mathbf {x}} _ {i + 1} = \\mathcal {P} _ {\\epsilon , \\mathbf {x}} \\left(\\hat {\\mathbf {x}} _ {i} + \\alpha_ {i} \\operatorname {s i g n} \\left(\\nabla_ {\\hat {\\mathbf {x}} _ {i}} \\mathcal {L} ^ {\\mathrm {c e}} \\left(f _ {\\boldsymbol {\\theta}} \\left(\\hat {\\mathbf {x}} _ {i}\\right), y\\right)\\right)\\right), \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 516, + 510, + 890, + 527 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Initially, $\\hat{\\mathbf{x}}_0 = \\mathcal{P}_{\\epsilon,\\mathbf{x}}(\\mathbf{x} + \\mathbf{u})$ , where $\\mathbf{u} \\sim \\mathcal{U}([- \\epsilon, \\epsilon])$ , i.e. $\\mathbf{u}$ is a uniform random noise bounded by $[- \\epsilon, \\epsilon]$ . The function $\\mathcal{P}_{\\epsilon,\\mathbf{x}}: \\mathbb{R}^{C \\times H \\times W} \\to \\mathcal{I}$ first clips the range of its input into the $\\epsilon$ -ball $\\ell_p$ -distance neighbour of the original image $\\mathbf{x}$ and then clips its input into the range of $\\mathcal{I}$ . The term $\\nabla_{\\hat{\\mathbf{x}}_i} \\mathcal{L}^{\\mathrm{ce}}(f_\\theta(\\hat{\\mathbf{x}}_i), y)$ computes the gradient of the loss w.r.t. the input $\\hat{\\mathbf{x}}_i$ . Finally, $\\alpha_i$ is the step size, and for each element in the tensor $g$ , $\\operatorname{sign}(g)$ returns one of 1, 0 or -1, if the value is positive, zero or negative, respectively.", + "bbox": [ + 496, + 537, + 890, + 672 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "CE is a commonly used loss function for training deep neural network models and evaluating their robustness in classification tasks. However, the presence of exponential operations in CE makes it vulnerable to underflow and rounding errors with limited floating-point precision. Gradient-based attacks with the CE loss may experience vanishing/inefficient gradients and difficulty converging while suffering from a severe overestimation of the model's robustness. [6, 10]. Recent attack methods use surrogate losses for gradient computation [6, 18] and optimize an alternative target by replacing $\\mathcal{L}^{\\mathrm{ce}}$ with a custom surrogate loss function. $\\mathbf{z} = f_{\\theta}(\\hat{\\mathbf{x}})$ is output logits of the model, and $\\mathbf{z}_i$ is the $i^{\\mathrm{th}}$ component of $\\mathbf{z}$ , two typical examples to replace the CE objective include the difference-of-logits (DL) [6], also known as hinge loss, where $i \\in \\{1,2,\\dots,K\\}$", + "bbox": [ + 496, + 674, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "4057", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "and $i\\neq y$", + "bbox": [ + 76, + 90, + 151, + 106 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} ^ {\\mathrm {c w}} (\\mathbf {z}, \\mathrm {y}) = - \\mathbf {z} _ {y} + \\max _ {i \\neq y} \\mathbf {z} _ {i}, \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 179, + 112, + 468, + 136 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "and the difference-of-logits ratio (DLR) loss [10]:", + "bbox": [ + 76, + 142, + 406, + 157 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} ^ {\\mathrm {d l r}} (\\mathbf {z}, \\mathrm {y}) = \\frac {- \\mathbf {z} _ {y} + \\max _ {i \\neq y} \\mathbf {z} _ {i}}{\\mathbf {z} _ {\\pi 1} - \\mathbf {z} _ {\\pi 3}}, \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 165, + 162, + 468, + 193 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\mathbf{z}_{\\pi_1}$ and $\\mathbf{z}_{\\pi_3}$ respectively denote the $1^{\\mathrm{th}}$ and $3^{\\mathrm{th}}$ largest components of $\\mathbf{z}$ . It is clear that maximizing the alternative goals is consistent with the original objective of making $\\arg \\max f(\\hat{\\mathbf{x}})\\neq y$ . In addition, since surrogate losses avoid exponential operations, they are not prone to underflow, allowing gradient-based optimization to escape suffering from the overestimation caused by the floating-point underflow errors. However, the floating-point underflow errors are not the sole reason for all overestimations related to floating-point errors. At the same time, the new loss function discards some elements of $\\mathbf{z}$ , reducing the effectiveness of the attack and causing gradient-based attacks with surrogate losses to overestimate the model's robustness.", + "bbox": [ + 75, + 198, + 468, + 393 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Many auxiliary techniques can assist existing attack methods to improve their performance. For example, momentum-based updates can improve the attack's convergence rate and are widely used by white-box attacks [13, 18]. A step schedule with decreasing step size based on the number of iterations can improve the overall success rate [10, 18, 56]. Multi-target attacks can outperform nontarget attacks in the evaluation results at the cost of more iterations since they require enumerating multiple most likely target labels [18, 33, 34]. In addition to the above strategies, multiple restarts can also improve the effectiveness of gradient-based attacks by adding different random initial perturbations to the input data to diversify the starting point of the attack and reduce the impact of suboptimal solutions [5, 46]. Finally, several recent publications have shown that leveraging latent features in attacks can enhance the transferability of black-box attacks [21, 22] and the performance of white-box attacks [56].", + "bbox": [ + 75, + 395, + 468, + 667 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "However, even with so many auxiliary strategies mentioned above, using any single attack is still challenging to accurately evaluate the model's robustness. Attackers start using an ensemble of multiple attack strategies to improve the attack's performance by introducing diversity [5,10,28]. They often suffer from high computational costs. Even though these ensemble strategies are more powerful than any single attack, they still fail to provide an assessment of the ensemble defence strategy's robustness accurately [48,57].", + "bbox": [ + 75, + 667, + 468, + 818 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Efficient Loss Function", + "text_level": 1, + "bbox": [ + 76, + 829, + 295, + 845 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Assuming that the input $\\hat{\\mathbf{x}}$ has the correct label $y$ , we compute $\\mathbf{z} = f_{\\theta}(\\hat{\\mathbf{x}})$ , where $\\pmb{\\theta}$ represents the model parameters. Next, we sort the values in $\\mathbf{z}$ in a descending order,", + "bbox": [ + 75, + 854, + 468, + 901 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\mathbf{z}_{\\pi 1}$ is the maximum value. We define $\\Delta$ as the difference between the maximum and the second maximum value, i.e., $\\Delta = \\mathbf{z}_{\\pi 1} - \\mathbf{z}_{\\pi 2} \\geq 0$ . The cross-entropy loss at $\\mathbf{z}$ becomes", + "bbox": [ + 498, + 90, + 890, + 148 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nC E (\\mathbf {z}, y) = - \\log p _ {y} = - \\log \\frac {e ^ {\\mathbf {z} _ {y} - \\mathbf {z} _ {\\pi 1}}}{\\sum_ {i = 1} ^ {K} e ^ {\\mathbf {z} _ {i} - \\mathbf {z} _ {\\pi 1}}}, \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 542, + 157, + 890, + 196 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\nabla_ {\\hat {\\mathbf {x}}} C E (\\mathbf {z}, y) = (- 1 + p _ {y}) \\nabla_ {\\hat {\\mathbf {x}}} \\left(\\mathbf {z} _ {y} - \\mathbf {z} _ {\\pi 1}\\right) \\\\ + \\sum_ {i \\neq y} p _ {i} \\nabla_ {\\hat {\\mathbf {x}}} \\left(\\mathbf {z} _ {i} - \\mathbf {z} _ {\\pi 1}\\right), \\tag {6} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 555, + 215, + 890, + 268 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $p_i = e^{\\mathbf{z}_i - \\mathbf{z}_{\\pi 1}} / \\sum_{j = 1}^{K}e^{\\mathbf{z}_j - \\mathbf{z}_{\\pi 1}}$ $i\\in \\{1,2,3,\\dots,K\\}$", + "bbox": [ + 498, + 279, + 875, + 297 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Exponential operations in Equation (5), specifically $e^{\\mathbf{z}_{\\pi i} - \\mathbf{z}_{\\pi 1}},i\\in \\{2,\\dots,K\\}$ , where $\\mathbf{z}_{\\pi i} - \\mathbf{z}_{\\pi 1}\\leq \\mathbf{z}_{\\pi 2} - \\mathbf{z}_{\\pi 1} =$ $-\\Delta \\leq 0$ , can cause floating-point underflow errors in the CE loss gradient. To investigate this issue, we analyze the properties of $e^{-\\Delta}$ and observe that when $\\Delta$ surpasses a threshold value denoted by $\\lambda$ $e^{-\\Delta}$ underflows and leads to significant inaccuracies in the gradient calculation. Specifically, when $\\Delta \\geq \\lambda$ and $\\mathbf{z}_y = \\mathbf{z}_{\\pi 1}$ , the predicted probability $p_{y} = 1$ and the calculated gradient $\\nabla_{\\hat{\\mathbf{x}}}CE(\\mathbf{z},y) = 0$ The value of $\\lambda$ varies with different floating-point arithmetic precisions, with approximate values of 16.64, 103.28, and 744.44 for half-precision, single-precision, and double-precision, respectively.", + "bbox": [ + 498, + 297, + 890, + 492 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Based on the findings, we identify that the root cause of the calculated gradient being equal to zero is the result of $\\Delta$ exceeding $\\lambda$ . To further investigate the relationship between the value of $\\Delta$ and the overestimation of the model's robustness, we analyze the distribution of $\\Delta$ values in defence models that tend to be overestimated by gradient-based attacks under single-precision. The results in Figure 2 indicate that the range of $\\Delta$ values varies significantly among different defence models. Notably, the values of $\\Delta$ in 2a and 2b do not exceed 10, which is significantly smaller than $\\lambda \\approx 103.28$ for single-precision. As a result, these models do not suffer from floating-point underflow errors. In contrast, most of the $\\Delta$ values in 2c exceed the threshold that leads to floating-point underflow errors. It is evident that not all models suffer from floating-point underflow errors, and other reasons associated with floating-point errors cause gradient-based attacks to fail. This is because in addition to floating-point underflow errors, floating-point errors have another component: floating-point rounding errors when $\\Delta < \\lambda$ . These errors result in a non-negligible relative error in $\\nabla_{\\hat{\\mathbf{x}}}CE(\\mathbf{z},y)$ . We define the relative error as $\\delta_{CE} = \\delta (\\nabla_{\\hat{\\mathbf{x}}}CE(\\mathbf{z},y))$ .", + "bbox": [ + 496, + 493, + 892, + 824 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We know that $\\delta_{CE} = 100\\%$ when $\\Delta \\geq \\lambda$ . We need to further analyze the change pattern of $\\delta_{CE}$ when $\\Delta < \\lambda$ . A multi-iteration gradient-based attack involves adding perturbations to $\\hat{\\mathbf{x}}$ at each iteration, leading to constant changes in $\\mathbf{z}$ , $\\Delta$ , and $\\nabla_{\\hat{\\mathbf{x}}}(\\mathbf{z}_{\\pi i} - \\mathbf{z}_{\\pi 1})$ for $i \\in 1,2,\\dots,K$ after each", + "bbox": [ + 496, + 825, + 890, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "4058", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/0ab137cb715c73ef94d939c8cfc537e53e3b472c0f632faa1eb2558a518b75bb.jpg", + "image_caption": [ + "(a) The $\\Delta$ distribution of [33]" + ], + "image_footnote": [], + "bbox": [ + 86, + 94, + 343, + 263 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/eec3ef563842dce2633a4eae2a74f3696a65dda253ce5c4a87a006c78c6d6471.jpg", + "image_caption": [ + "(b) The $\\Delta$ distribution of [59]" + ], + "image_footnote": [], + "bbox": [ + 357, + 94, + 612, + 263 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/7f86c89dec6dd32c29c06404bf30c2c6852b0e052e60bde1251996165148457b.jpg", + "image_caption": [ + "(c) The $\\Delta$ distribution of [3]" + ], + "image_footnote": [], + "bbox": [ + 627, + 94, + 880, + 263 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "modification. This makes it difficult to analyze how $\\delta_{CE}$ changes when $\\Delta < \\lambda$ . However, we can indirectly examine the effect of floating-point errors on the attack's performance by analyzing the impact of such errors on a single step. To do so, we introduce a scaling factor $c$ and define the scaled value of $\\Delta$ as $T = c\\Delta$ . By varying $c$ while keeping $\\hat{\\mathbf{x}}$ , $\\mathbf{z}$ , and $\\nabla_{\\hat{\\mathbf{x}}}(\\mathbf{z}_{\\pi i} - \\mathbf{z}_{\\pi 1})$ fixed during gradient calculation, we can investigate the relationship between $\\delta_{CE}$ and $T$ for different values of $T$ .", + "bbox": [ + 75, + 339, + 468, + 473 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "To compute the scale factor, we need to detach the gradient information from $\\Delta$ since $\\mathbf{z}$ contains the gradient information during the actual program running. Thus, we define the scale factor as $c = T / \\Delta_{\\mathrm{detach}}$ . The use of the detach operation in the calculation of $c$ removes the gradient information from the $\\Delta_{\\mathrm{detach}}$ , making it distinct from the $\\Delta$ that retains gradient information. When $\\mathbf{z}_y \\neq \\mathbf{z}_{\\pi 1}$ , the model output is already incorrect. Therefore, we only focus on the relationship between $\\delta_{CE}$ and $T$ when $\\mathbf{z}_y = \\mathbf{z}_{\\pi 1}$ , at which point $\\nabla_{\\hat{\\mathbf{z}}}CE(c\\mathbf{z},y) = c\\sum_{i \\neq y}p_i^c\\nabla_{\\hat{\\mathbf{x}}}(\\mathbf{z}_i - \\mathbf{z}_{\\pi 1})$ , where $p_i^c = e^{c(\\mathbf{z}_i - \\mathbf{z}_{\\pi 1})} / \\sum_{j=1}^{K}e^{c(\\mathbf{z}_j - \\mathbf{z}_{\\pi 1})}$ .", + "bbox": [ + 75, + 479, + 468, + 651 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "To get a more intuitive picture of the relationship between $\\delta_{CE}$ and $T$ , we plotted the figure of $\\delta_{CE}$ on the binary classification task with $K = 2$ . At this point, $\\nabla_{\\hat{\\mathbf{z}}}CE(\\mathbf{cz},y) = c\\sum_{i\\neq y}p_i^c\\nabla_{\\hat{\\mathbf{x}}}\\left(\\mathbf{z}_i - \\mathbf{z}_{\\pi 1}\\right) = cp_2^c\\nabla_{\\hat{\\mathbf{x}}}\\left(\\mathbf{z}_{\\pi 2} - \\mathbf{z}_{\\pi 1}\\right)\\propto cp_2^c$ . Therefore, $\\delta_{CE}\\propto \\delta (cp_2^c)$ . In Figure 3, we can see that for the same $\\hat{\\mathbf{x}}$ , when $\\mathbf{z}$ and $\\nabla_{\\hat{\\mathbf{x}}}\\left(\\mathbf{z}_i - \\mathbf{z}_{\\pi 1}\\right)$ , $i\\in \\{1,2,\\dots,K\\}$ are all fixed, $\\delta_{CE}$ varies with $T$ . When $T\\geq \\lambda$ , $\\delta_{CE} = 100\\%$ In contrast, When $T < \\lambda$ , The relative error $\\delta_{CE}$ caused by the floating-point rounding errors is much more minor, varies continuously with T, and reaches the minimum when $T$ is approximately 1. But one thing that needs to be highlighted is that after the relative error reaches the minimum, it starts to increase as $T$ gets closer to 0.", + "bbox": [ + 75, + 654, + 468, + 864 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Following the same operation, we add a scale factor $c$ to $\\Delta$ and hold $T = c\\Delta$ constant during each iteration of the", + "bbox": [ + 76, + 869, + 468, + 900 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/d95af38b41c36f9eb37c4797d3eab35679b7ce2f952d071ecd6328714713887a.jpg", + "image_caption": [ + "Figure 2. The distributions of $\\Delta = \\mathbf{z}_{\\pi 1} - \\mathbf{z}_{\\pi 2}$ for the defending models on the CIFAR-10 dataset are averaged across 100 bins.", + "Figure 3. The relative error of the gradient information computed using half-precision floating-point operations on a binary classification task with the CE loss varies with $T$ for a given adversarial example within a single iteration." + ], + "image_footnote": [], + "bbox": [ + 511, + 343, + 883, + 507 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "multi-iteration attack. This technique, which we refer to as FT-PGD, allows us to assess the model's robustness with a fixed $T$ value. In Figure 4, we evaluate the model's robustness using FT-PGD at various $T$ values. By comparing the relative floating-point error in Figure 3 with the attack's performance in Figure 4, we observe a strong correlation between the relative error $\\delta_{CE}$ and the attack's effectiveness. Thus, the relative error is a critical factor that contributes to overestimating the model's robustness. Furthermore, we identify two distinct phases in the impact of floating-point errors on gradient-based attacks due to the CE loss, which depend on the relationship between $T$ and $\\lambda$ .", + "bbox": [ + 496, + 609, + 890, + 790 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "(a) The attack failed due to floating-point underflow errors. When $T \\geq \\lambda$ , floating-point underflow causes the calculated gradient equal to zero and $\\delta_{CE} = 100\\%$ . As a result, the input perturbation becomes zero, and the model's robustness is measured to be equal to its clean accuracy, which leads to a significant overestimation of the model's robustness.", + "bbox": [ + 496, + 795, + 890, + 898 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "4059", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/b0b8ab6948caca79330c28616c95877a9f7f6cf30e7bcee041befb84223822f3.jpg", + "image_caption": [ + "Figure 4. A higher zero ratio, which represents the proportion of zero elements in the perturbation, leads to larger overestimations when evaluating model robustness. We assess model robustness using 100 iterations of FT-PGD with CE loss on the CIFAR-10 dataset under half-precision floating-point arithmetic. The model is obtained from [59]." + ], + "image_footnote": [], + "bbox": [ + 88, + 95, + 459, + 258 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "(b) The attack's performance fluctuates with the small relative error caused by floating-point rounding errors. When $0 \\leq T < \\lambda$ , the computed gradient's relative error due to the floating-point rounding error is small and has the same variation pattern as the zero ratio and attack performance. The smallest relative error occurs around $T = 1$ . However, it's crucial to note that at the bottom left of Figure 3 and Figure 4, the relative error and its detrimental effect on the gradient-based attack increase as $T$ approaches zero after reaching the minimum.", + "bbox": [ + 75, + 383, + 468, + 536 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "It is straightforward to assume that since floating-point errors cause the above problem, it should be possible to solve the problem by simply increasing the precision of floating-point arithmetics because it can effectively reduce the floating-point errors. To test whether this simple idea works, we evaluated the impact of different floating-point arithmetics precisions, including half-precision, single-precision, and double-precision, on the model's robustness against FT-PGD with 100 iterations. As depicted in Figure 5, the attack's performance exhibits a similar variation pattern across different precisions, and the model's robustness measured with PGD remains nearly unchanged. While increasing the floating-point precision can delay attack failure due to floating-point underflow errors, it incurs significant computational overhead. Therefore, increasing the floating-point precision is not a viable solution to address the problem.", + "bbox": [ + 75, + 537, + 470, + 792 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Surrogate loss functions(3,4) have been proposed [6, 10, 18] to work around floating-point underflow errors. They avoid suffering from floating-point underflow errors by discarding softmax operations. At the same time, they only use partial $\\mathbf{z}$ elements in the new loss function. To demonstrate the effect of discarding elements of $\\mathbf{z}$ on the attack's performance, We designed an experiment to make only a fixed", + "bbox": [ + 75, + 795, + 468, + 902 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/c9c9e888fdb5a71a6da290d8d2d9f7340e414777a2ac14d5de2eca4cedead01b.jpg", + "image_caption": [ + "Figure 5. The model's robustness test results on the CIFAR-10 dataset under Float16, Float32, and Float64 follow a similar pattern of variation, except that the thresholds that lead to the attack's failure are different, the model obtained from [59]." + ], + "image_footnote": [], + "bbox": [ + 511, + 95, + 882, + 261 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "number of $\\mathbf{z}$ elements participate in the calculation of the gradients by exploiting floating-point underflow errors. To achieve this goal we scale the logits $\\mathbf{z}_{\\pi 1} - \\mathbf{z}_{\\pi i}$ by a scale factor $c$ to make $c(\\mathbf{z}_{\\pi 1} - \\mathbf{z}_{\\pi i}) = \\lambda$ , such that $p_{\\pi j}^{c} = 0$ if $j \\geq i$ and $p_{\\pi j}^{c} > 0$ if $j < i$ , where $i \\in \\{2,3,\\dots,K\\}$ and $j \\in \\{1,2,3,\\dots,K\\}$ . So that only $i - 1$ number of $\\mathbf{z}$ elements are involved in the gradient calculation, thus giving PGD the ability to attack the network with a fixed number of $\\mathbf{z}$ elements, which we now call FNZ-PGD. We use FNZ-PGD with different numbers of $\\mathbf{z}$ elements to evaluate the model's robustness which is overestimated mainly due to floating-point errors. From Figure 6, we can see that the more $\\mathbf{z}$ elements involved in the attack, the more potent the attack will be. So discarding the $\\mathbf{z}$ element in the loss function will impair the attack's performance when model robustness is overestimated mainly due to floating-point errors.", + "bbox": [ + 496, + 363, + 893, + 619 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In summary, the relative error in the calculated gradients due to the floating-point errors, which include floating-point underflow errors and floating-point rounding errors, is the critical factor contributing to the overestimation of the model's robustness. While floating-point errors are a primary cause of gradient-based attacks' failure, they are not the sole cause. Reducing their impact can only address the portion of model robustness that is overestimated due to them. Therefore, it is unrealistic to expect that solely reducing the impact of floating-point errors alone will eliminate all problems related to overestimating model robustness.", + "bbox": [ + 496, + 625, + 893, + 790 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Although we cannot eliminate the relative error in the gradients caused by floating-point errors, we can control it's side effect and significantly increase the power of gradient-based attacks. As a result, we propose the Minimize the impact of floating-point errors (MIFPE) loss, a small modification to the original CE loss, which scales the logits adaptively before the softmax operation. For untargeted and tar", + "bbox": [ + 496, + 795, + 893, + 902 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "4060", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/694ce9b0c918646cac4415f771ff25ccb1d1c3c6cb15b66c232525d0946a79e7.jpg", + "image_caption": [ + "Figure 6. Using more $\\mathbf{z}$ elements increases attack potency when model robustness is overestimated mainly due to floating-point errors. We utilized FNZ-PGD with 100 iterations, CE loss, and a baseline of PGD-100 with CE, C&W, and DLR loss under CIFAR10. All floating-point operations were single-precision, and the model was obtained from [59]. Here, $n$ refers to the number of $\\mathbf{z}$ elements used." + ], + "image_footnote": [], + "bbox": [ + 88, + 95, + 468, + 261 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "geted attacks, the targets are as follows respectively:", + "bbox": [ + 76, + 395, + 426, + 412 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} ^ {\\mathrm {M I F P E}} (\\mathbf {z}, y) \\triangleq \\mathcal {L} ^ {\\mathrm {c e}} \\left(T \\mathbf {z} / \\Delta_ {\\text {d e t a c h}}, y\\right), \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 147, + 419, + 468, + 439 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\text {t a r g e t}} ^ {\\mathrm {M I F P E}} \\left(\\mathbf {z}, y _ {\\mathrm {t}}\\right) = - \\mathcal {L} ^ {\\mathrm {c e}} \\left(T \\mathbf {z} / \\Delta_ {\\text {d e t a c h}}, y _ {\\mathrm {t}}\\right), \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 138, + 460, + 468, + 479 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Where $y_{t}$ is a predefined class target, $t \\in \\{1, 2, \\dots, K\\}$ and $y_{t} \\neq y$ . In our experiments, the factor $T$ was set to around 1 to minimize the detrimental effect of floating-point errors on the gradient-based attacks.", + "bbox": [ + 76, + 484, + 468, + 544 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "The new surrogate loss $\\mathcal{L}^{\\mathrm{MIFPE}}$ has fourfold advantages. First, it can eliminate the failure of gradient-based attacks due to floating-point underflow errors. Second, it can minimize the impact of the small relative error due to floating-point rounding errors and significantly improve the performance of gradient-based attacks. Third, it provides the flexibility to adjust the number of logit elements involved in the attack simply by changing the value of T. Finally, unlike the C&W or DLR loss, it still represents the original CE loss faithfully, and all values in the logit vector can still contribute to the gradient calculation.", + "bbox": [ + 75, + 545, + 472, + 712 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 76, + 724, + 210, + 742 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "To ensure a fair comparison against other loss functions in our evaluation and to make our evaluation as comprehensive as possible, we conducted tests on different threat models and datasets. Specifically, we tested the $\\ell_{\\infty}$ -norm bounded perturbation on the CIFAR-10, CIFAR-100, MNIST [25] and ImageNet datasets [11], and the $\\ell_{2}$ -norm threat model on the CIFAR-10 dataset. For each test, we ran the PGD with different loss functions, including the cross-entropy (CE) loss function, the C&W loss function [6], the DLR loss function [10], and our proposed MIFPE. We kept", + "bbox": [ + 75, + 750, + 472, + 902 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "all other settings the same across the tests. Firstly, we used 100 iterations for each test. Secondly, we adopted the same step-size schedule with a linear decay [56], which updates the perturbation boundary $\\epsilon$ at each iteration $i$ according to the formula $2\\epsilon (1 - i / I)$ , where $I$ denotes the total number of iterations. Thirdly, we employed momentum-based updates [10] with a momentum factor of $\\nu = 0.75$ for all tests. Lastly, we saved the best adversarial examples generated during the attack. To demonstrate the effectiveness of MIFPE in achieving near-state-of-the-art robustness with only 100 iterations, we compare our results with the best robust accuracy reported on RobustBench1, which uses an ensemble of attacks and a minimum of 4900 iterations. We also compared the attack performance of MIFPE with GAMA_PGD [43] under the same 100-iteration constraint.", + "bbox": [ + 496, + 90, + 893, + 318 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "In Table 1, we present a comprehensive comparison showing that MIFPE outperforms CE, C&W, and DLR loss functions on all tested models. Additionally, we found that when PGD with momentum and step schedule using MIFPE as the loss function outperforms GAMA_PGD on all tested models by at least more than $0.1\\%$ under 100 iterations constraint, which is impossible when PGD with momentum and step schedule using CE, C&W and DLR as the loss function. Remarkably, even with only 100 iterations, MIFPE achieves results that are very close to the best results obtained with at least 4900 iterations on some models, such as Uncovering limits [17] and Proper definition [32] for CIFAR10, $l_{\\infty}$ , $\\varepsilon = 8/255$ . Our findings also reveal that C&W and DLR perform even worse than CE in some cases, such as on Robustness library [14] and Fast adversarial training [51] for CIFAR10, $l_{\\infty}$ , $\\varepsilon = 8/255$ . This suggests that discarding partial logit elements in the loss function would decrease the effectiveness of gradient-based attacks.", + "bbox": [ + 496, + 319, + 893, + 592 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Faster convergence. We want to highlight that the effectiveness of MIFPE is not achieved by increasing the computational cost compared to other loss functions. We found that minimising the effect of the floating-point errors leads to faster convergence speed than competing loss functions. Figure 7 shows that for all two defending models, MIFPE loss performs more efficiently, and often with orders of magnitude faster than other loss functions for successful attacks. Finally, minimising the effect of floating-point error operation introduces no overhead and imposes no impact on the iteration time.", + "bbox": [ + 496, + 594, + 895, + 758 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Boost the capability of existing attack strategies. Because MIFPE is a loss function, it can be easily integrated with existing attack strategies by replacing the original loss function. The results in Table 2 show that using MIFPE boosts the attack's effectiveness.", + "bbox": [ + 496, + 762, + 893, + 837 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Ablation analysis. Our ablation experiments, presented in Table 3, investigated the effect of momentum and step-size schedule on PGD using different loss functions with 100 iterations. The results show that the MIFPE consist", + "bbox": [ + 496, + 839, + 893, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "4061", + "bbox": [ + 482, + 944, + 513, + 957 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/83b7d990ada4c8d4f82ad14f456a1450212fb2df50899a56031be26ffb8aa8b6.jpg", + "table_caption": [ + "Table 1. Comparing the proposed MIFPE loss $(\\mathcal{L}^{\\mathrm{MIFPE}})$ , against CE $(\\mathcal{L}^{\\mathrm{ce}})$ , C&W $(\\mathcal{L}^{\\mathrm{cw}})$ , and DLR $(\\mathcal{L}^{\\mathrm{dlr}})$ losses. For each surrogate loss, we use PGD-100 with the step-size schedule $2\\epsilon (1 - i / I)$ and momentum $\\nu = 0.75$ . Models marked with $\\dagger$ were trained with extra data. Models marked with $\\ddagger$ , which used $\\varepsilon = 0.031$ as originally reported by the authors. Numbers in parentheses indicate the improvement w.r.t. the CE baseline. The best, calculated using an ensemble of attacks and a minimum of 4900 iterations, is reported from RobustBench1 to demonstrate how closely MIFPE can approach the lowest known robustness accuracy with only 100 iterations." + ], + "table_footnote": [], + "table_body": "
Defense methodArchitectureCleanCE (Lce)100C&W (Lcw)100DLR (Ldir)100GAMA_PGD100MIFPE (LMIFPE)100Best4900
MNIST, ℓ∞, ε = 0.3
Uncovering limits [17]WRN-28-1099.2696.5596.64(+0.09)96.71(+0.16)96.69(+0.14)96.53(-0.02)96.31
MMA training [12]†LeNet5Madry98.9895.6695.60(-0.06)95.56(-0.10)95.96(+0.13)95.50(-0.16)93.51
MMA training [12]LeNet5Madry98.9595.0995.33(+0.24)95.59(+0.50)95.74(+0.19)94.88(-0.21)91.40
Neural level sets [3]SmallCNN99.3599.2894.68(-4.60)95.09(-4.19)99.29(+0.01)94.67(-4.61)90.85
TRADES [59]SmallCNN99.4893.6993.88(+0.19)94.49(+0.80)93.82(+0.13)93.67(-0.02)92.71
Robust optimization [29]SmallCNN99.3593.0693.19(+0.13)93.63(+0.57)93.39(+0.33)92.88(-0.18)90.85
Fast adversarial training [51]SmallCNN98.5086.8286.96(+0.14)87.42(+0.60)87.62(+0.80)86.57(-0.25)82.93
CIFAR-10, ℓ∞, ε = 8/255
Uncovering limits [17]†WRN-70-1691.1067.9666.70(-1.26)66.78(-1.18)66.08(-1.88)65.96(-2.00)65.87
Fixing data augmentation [36]WRN-106-1688.5067.5765.55(-2.02)65.61(-1.96)64.94(-2.63)64.75(-2.82)64.58
Fixing data augmentation [36]WRN-70-1688.5467.2765.23(-2.04)65.32(-1.95)64.57(-2.70)64.46(-2.81)64.20
Proper definition [32]WRN-70-1689.0166.6663.94(-2.72)64.01(-2.65)63.65(-3.01)63.49(-3.17)63.35
Uncovering limits [17]†WRN-28-1089.4865.5963.62(-1.97)63.82(-1.77)63.05(-2.90)62.96(-2.63)62.76
Proper definition [32]WRN-28-1088.6164.6661.55(-3.11)61.62(-3.04)61.19(-3.47)61.12(-3.54)61.04
Adversarial weight perturbation [53]†WRN-28-1088.2563.1860.51(-2.67)60.60(-2.58)60.18(-3.00)60.09(-3.09)60.04
Unlabeled data [7]†WRN-28-1089.6961.6060.47(-1.13)60.67(-0.93)59.82(-1.78)59.72(-1.88)59.53
HYDRA [40]†WRN-28-1088.9859.5358.21(-1.32)58.30(-1.23)57.52(-2.01)57.38(-2.15)57.14
Misclassification-aware [50]WRN-28-1087.5061.6058.03(-3.57)58.73(-2.87)57.20(-4.40)56.88(-4.72)56.29
Pre-training [19]†WRN-28-1087.1157.0756.27(-0.80)57.07(0.00)55.22(-1.85)55.10(-1.97)54.92
Hypersphere embedding [33]WRN-34-2085.1461.4355.35(-6.08)56.21(-5.22)54.37(-7.06)53.85(-7.58)53.74
Overfitting [37]WRN-34-2085.3456.8555.22(-1.63)55.97(-0.88)53.87(-2.98)53.62(-3.23)53.42
Self-adaptive training [20]‡WRN-34-1083.4856.1254.30(-1.82)54.73(-1.39)53.64(-2.48)53.48(-2.64)53.34
TRADES [59]‡WRN-34-1084.9255.2153.94(-1.27)54.11(-1.10)53.38(-1.83)53.22(-1.99)53.08
Robustness library [14]RN-5087.0351.5652.07(+0.51)52.81(+1.25)50.04(-1.52)49.84(-1.72)49.25
Neural level sets [3]‡RN-1881.3079.1240.07(-39.05)45.10(-34.02)79.69(+0.57)40.06(-39.06)39.77
YOPO [58]WRN-34-1087.2046.0547.02(+0.97)47.55(+1.50)45.30(-0.75)45.19(-0.86)44.83
Fast adversarial training [51]RN-1883.3445.7545.81(+0.06)46.89(+1.14)43.71(-2.04)43.57(-2.18)43.21
CIFAR-10, ℓ∞, ε = 8/255
Adversarial weight perturbation [54]WRN-34-1060.3833.0930.74(-2.35)31.13(-1.96)29.44(-3.65)29.35(-3.74)28.86
Pre-training [19]†WRN-28-1059.2332.8230.58(-2.24)31.83(-0.99)29.22(-3.60)29.02(-3.80)28.42
Progressive Hardening [42]WRN-34-1062.8226.1826.69(+0.51)27.26(+1.08)24.97(-1.21)24.91(-1.27)24.57
Overfitting [37]RN-1853.8320.4720.17(-0.30)20.30(-0.17)19.20(-1.27)19.16(-1.31)18.95
ImageNet, ℓ∞, ε = 4/255
Transfer Better [39]RN-5064.0238.4437.26(-1.18)37.72(-0.72)34.94(-3.50)34.84(-3.60)34.96
Robustness library [14]RN-5062.5632.1632.24(+0.08)32.80(+0.64)29.72(-2.44)29.60(-2.56)29.22
Transfer Better [39]RN-1852.9229.3027.14(-2.16)27.40(1.90)25.56(-3.74)25.40(-3.90)18.95
CIFAR-10, ℓ2, ε = 0.5
Uncovering limits [17]†WRN-70-1694.7481.7180.93(-0.78)80.94(-0.77)87.74(+6.03)80.57(-1.14)80.53
Uncovering limits [17]WRN-70-1690.9075.2074.89(-0.31)74.95(-0.25)81.78(+6.58)74.56(-0.64)74.50
Adversarial weight perturbation [54]WRN-34-1088.5174.7773.88(-0.89)73.89(-0.88)79.38(+4.61)73.67(-1.10)73.66
Robustness library [14]RN-5090.8369.6570.13(+0.48)70.25(+0.60)78.15(+8.50)69.29(-0.36)69.24
Overfitting [37]RN-1888.6768.6668.74(+0.08)69.03(+0.37)76.19(+7.53)67.87(-0.79)67.68
Decoupling direction and norm [38]WRN-28-1089.0566.5667.00(+0.44)67.02(+0.46)74.61(+8.05)66.48(-0.08)66.44
MMA training [12]WRN-28-488.0266.2266.58(+0.36)66.60(+0.38)71.44(+5.22)66.16(-0.06)66.09
", + "bbox": [ + 76, + 170, + 890, + 739 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "tently outperforms the other loss functions, and shows the least variance across different setups. These findings suggest that the effectiveness of the MIFPE should not be dependent on the momentum and step-size schedule.", + "bbox": [ + 75, + 766, + 468, + 828 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "To analyze the reasons for the failure of the attack due to floating-point rounding errors, we selected $\\mathbb{Z} = \\mathbf{z}_y - \\max_{i\\neq y}\\mathbf{z}_i$ because its sign indicates if the attack is successful or not. We compared the change of $\\mathbb{Z}$ for samples", + "bbox": [ + 75, + 839, + 470, + 902 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "attacked by PGD-100 with CE loss but failed, and PGD-100 with MIFPE loss and succeeded. Figure 8 demonstrates that for samples attacked with CE loss, the value of $\\mathbb{Z}$ rapidly approaches 0 in the first few iterations and then remains positive afterwards. On the other hand, when attacked with MIFPE loss $\\mathbb{Z}$ smoothly drops below 0 after approaching 0. This phenomenon suggests that the floating-point rounding error primarily may cause attack failure when the samples", + "bbox": [ + 496, + 766, + 893, + 888 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "4062", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/22f4e9b5f5dc78cafba4055356ed916a85bf9b502249809575bea5b1b69f8a15.jpg", + "image_caption": [ + "Figure 7. We compare MIFPE to standard CE loss and other surrogate loss functions (C&W [6] and DLR [10]) on defenders [58,59]. The graph shows iterations on the horizontal axis and the percentage of unsuccessful examples on the vertical axis." + ], + "image_footnote": [], + "bbox": [ + 86, + 94, + 267, + 232 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/4175ca8ed00fddb62a84ad39eadc7f4a91c86d20fcccdec3b45b11f3d9169ad1.jpg", + "image_caption": [ + "Figure 8. The changing process of the value of $\\mathbb{Z} = \\mathbf{z}_y - \\max_{i\\neq y}\\mathbf{z}_i$ with the number of iterations during the attack on the CIFAR10 dataset using the model from TRADES [59] and single-precision arithmetic. The horizontal axes show the number of iterations used so far, and the vertical axes show the value of $\\mathbb{Z}$ ." + ], + "image_footnote": [], + "bbox": [ + 271, + 95, + 459, + 232 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/65ae8b783808adaaaed1bfb3fe0290bccf7c28107b0daed4ada6c834522cb1d0.jpg", + "table_caption": [ + "Table 2. The comparison of attack performances for FGSM [16], PGD [29], APGD_DLR [10] and AA [10] using original loss functions versus MIFPE loss on CIFAR10 dataset and $\\varepsilon = 0.031$ with the model obtained from TRADES [59]. with the $\\nabla$ row representing the improvement achieved with MIFPE." + ], + "table_footnote": [], + "table_body": "
Attack \niterationFGSM \n1PGD \n100APGD_DLR \n100AA \n4900
Original \nMIFPE79.8379.7945.9040.22
49.7640.0640.4939.89
V30.0739.735.410.33
", + "bbox": [ + 94, + 392, + 452, + 474 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/d6f3fee9083c859473393d9ef36fcf70a07d437da9bbbcd45225074ee9334b0c.jpg", + "table_caption": [ + "Table 3. Ablation study on the effect of momentum and step-size schedule on the PGD with different loss functions and under 100 iterations on CIFAR10 dataset with the model obtained from Neural level sets [3]. New components are added in consecutive rows." + ], + "table_footnote": [], + "table_body": "
Accuracy under attack(%)Loss Function
CEC&WDLRMIFPE
PGD55.4654.2354.3953.42
+Momentum55.2554.0254.1853.23
+Step-size schedule55.2153.9454.1153.22
", + "bbox": [ + 78, + 555, + 470, + 637 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "become close to the classification boundary due to the relative error and its detrimental effect on the gradient-based attack would increase as $T$ approaches zero after reaching the minimum.", + "bbox": [ + 75, + 662, + 468, + 722 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 76, + 738, + 194, + 753 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "This paper reveals that relative error in calculated gradient caused by floating-point errors is a fundamental reason why gradient-based attacks fail to accurately evaluate the model's robustness. To efficiently and accurately evaluate the model's robustness, we introduce MIFPE, a new loss function that minimises the impact of floating-point errors on gradient-based attacks. Compared with other loss functions, MIFPE enjoys higher accuracy and faster convergence speed. Moreover, we find several surprising ob", + "bbox": [ + 75, + 763, + 468, + 902 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/e183c12478a4a3af2f7b4e348fc6bede55785c12f70708d0e56269976073adee.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 513, + 95, + 882, + 261 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "servations related to adversarial attacks: (1)Discarding partial elements of logits in the loss will impair the attack's performance; (2)The floating-point rounding errors lead to the attack's failure by causing an increasing relative error as the samples get closer to the classification boundary; (3)Increasing the precision of floating-point arithmetic cannot solve the problem of overestimating the model's robustness caused by floating-point errors, etc. We hope that the above observations will help discover more efficient and reliable loss functions in the future. Finally, MIFPE is open source with reproducible results2.", + "bbox": [ + 496, + 392, + 892, + 556 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgments", + "text_level": 1, + "bbox": [ + 500, + 571, + 660, + 588 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "This work is supported in part by Science and Technology Development Fund of Macao S.A.R (FDCT) under No. 0015/2019/AKP, 0123/2022/AFJ, and 0081/2022/A2. This work was carried out in part at SICC which is supported by SKL-IOTSC, University of Macau.", + "bbox": [ + 498, + 595, + 890, + 667 + ], + "page_idx": 7 + }, + { + "type": "page_footnote", + "text": "2Available at: https://github.com/MIFPE/Efficient-Loss-Function.", + "bbox": [ + 500, + 875, + 890, + 898 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "4063", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Samet Akçay, Mikolaj E Kundegorski, Michael Devereux, and Toby P Breckon. Transfer learning using convolutional neural networks for object classification within X-ray baggage security imagery. In 2016 IEEE International Conference on Image Processing (ICIP), pages 1057-1061. 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In ICML, 2019, 1, 4, 5, 6, 7, 8" + ], + "bbox": [ + 78, + 90, + 468, + 358 + ], + "page_idx": 10 + }, + { + "type": "page_number", + "text": "4066", + "bbox": [ + 482, + 945, + 516, + 955 + ], + "page_idx": 10 + } +] \ No newline at end of file diff --git a/2023/Efficient Loss Function by Minimizing the Detrimental Effect of Floating-Point Errors on Gradient-Based Attacks/e43d26b1-1945-4f4e-bd26-fe5c4d18f332_model.json b/2023/Efficient Loss Function by Minimizing the Detrimental Effect of Floating-Point Errors on Gradient-Based Attacks/e43d26b1-1945-4f4e-bd26-fe5c4d18f332_model.json new file mode 100644 index 0000000000000000000000000000000000000000..91b9923ec999499179639b121cc05b05493b716f --- /dev/null +++ b/2023/Efficient Loss Function by Minimizing the Detrimental Effect of Floating-Point Errors on Gradient-Based Attacks/e43d26b1-1945-4f4e-bd26-fe5c4d18f332_model.json @@ -0,0 +1,2059 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.001, + 0.812, + 0.047 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.089, + 0.13, + 0.885, + 0.175 + ], + "angle": 0, + "content": "Efficient Loss Function by Minimizing the Detrimental Effect of Floating-point Errors on Gradient-based Attacks" + }, + { + "type": "text", + "bbox": [ + 0.132, + 0.204, + 0.464, + 0.276 + ], + "angle": 0, + "content": "Yunrui Yu \nDepartment of Computer Science \nState Key Lab of IOTSC \nUniversity of Macau, Macau SAR, China." + }, + { + "type": "text", + "bbox": [ + 0.221, + 0.278, + 0.376, + 0.292 + ], + "angle": 0, + "content": "yb97445@um.edu.mo" + }, + { + "type": "text", + "bbox": [ + 0.507, + 0.204, + 0.841, + 0.275 + ], + "angle": 0, + "content": "Cheng-Zhong Xu* \nDepartment of Computer Science \nState Key Lab of IOTSC \nUniversity of Macau, Macau SAR, China." + }, + { + "type": "text", + "bbox": [ + 0.607, + 0.279, + 0.734, + 0.291 + ], + "angle": 0, + "content": "czxu@um.edu.mo" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.327, + 0.314, + 0.344 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.359, + 0.474, + 0.631 + ], + "angle": 0, + "content": "Attackers can deceive neural networks by adding human imperative perturbations to their input data; this reveals the vulnerability and weak robustness of current deep-learning networks. Many attack techniques have been proposed to evaluate the model's robustness. Gradient-based attacks suffer from severely overestimating the robustness. This paper identifies that the relative error in calculated gradients caused by floating-point errors, including floating-point underflow and rounding errors, is a fundamental reason why gradient-based attacks fail to accurately assess the model's robustness. Although it is hard to eliminate the relative error in the gradients, we can control its effect on the gradient-based attacks. Correspondingly, we propose an efficient loss function by minimizing the detrimental impact of the floating-point errors on the attacks. Experimental results show that it is more efficient and reliable than other loss functions when examined across a wide range of defence mechanisms." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.66, + 0.21, + 0.675 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.685, + 0.47, + 0.866 + ], + "angle": 0, + "content": "AI with deep neural networks (DNNs) as the core [24] has achieved great success in different research directions and has been widely used in many safety-critical systems, such as aviation [1,8,35], medical diagnosis [27, 49], self-driving [4,26,47], etc. However, a severe problem with current DNNs is that they are vulnerable to adversarial attacks. Adding human imperceptive perturbations to input data can mislead the model to output incorrect results [16, 45]. Such vulnerability poses a significant security risk to all DNN-based systems. Therefore, increasing the models' robustness and providing efficient and reliable evaluation methods are becoming increasingly urgent and vital." + }, + { + "type": "image", + "bbox": [ + 0.512, + 0.334, + 0.882, + 0.499 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.51, + 0.895, + 0.581 + ], + "angle": 0, + "content": "Figure 1. Comparison of the effectiveness of non-targeted and multi-targeted PGD 100 iterations attacks using various loss functions on the CIFAR-10 dataset. The best results were obtained from RobustBench using an ensemble attack with a minimum of 4900 iterations. The defence model is from [59]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.611, + 0.895, + 0.853 + ], + "angle": 0, + "content": "Numerous defence strategies [6, 10, 13, 16, 29, 31, 55] to improve the model's robustness and many attacks [2, 29, 33, 41, 50, 52, 54, 59] to evaluate these strategies have been proposed. Currently, the most efficient attack method is known as white-box attack, where the attacker has complete knowledge of the target defending strategy, including its model architecture, parameters, detail of the training algorithm, dataset, etc. A typical example is Projective gradient descent (PGD) [29] for evaluating the model's robustness. However, studies have shown that PGD with cross-entropy (CE) loss fails to provide accurate evaluation results [6, 41] and significantly overestimates the model's robustness (Figure 1). To enhance the evaluation accuracy, recent powerful evaluation methods were proposed to ensemble diverse attack algorithms [10, 30]. However, their performance is at the cost of high computational overhead." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.856, + 0.895, + 0.903 + ], + "angle": 0, + "content": "The research community attributes the failure of gradient-based attacks to gradient masking [15]. The core of gradient masking is that the calculated gradients are not" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.875, + 0.341, + 0.901 + ], + "angle": 0, + "content": "*Corresponding author. \n1https://robustbench.github.io/" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.517, + 0.957 + ], + "angle": 0, + "content": "4056" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.304 + ], + "angle": 0, + "content": "necessarily efficient in guiding the generation of adversarial examples. The causes of inefficient gradients may be related to floating-point errors or other factors. This paper reveals that the relative error in the gradients caused by floating-point errors is one of the fundamental reasons for the failure of gradient-based attacks, and the relative error is directly affected by the value of the difference of the first and second largest in logits(DFSL). Although it is hard to eliminate the relative error in the gradients caused by floating-point errors completely, we can control its effect on the gradient-based attacks. Thus, we propose a new efficient loss function by minimizing the impact of floating-point errors (MIFPE) on gradient-based attacks. To summarize, our main contributions are as follows:" + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.312, + 0.47, + 0.372 + ], + "angle": 0, + "content": "- We provide a comprehensive demonstration of how the presence of floating-point errors leads to the failure of gradient-based attacks due to the relative error in calculated gradients." + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.381, + 0.469, + 0.427 + ], + "angle": 0, + "content": "- We show that the floating-point rounding errors may lead to attack's failure due to growing relative errors as samples reach the classification boundary." + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.436, + 0.469, + 0.511 + ], + "angle": 0, + "content": "- We demonstrate that when the model's robustness is overestimated primarily due to floating-point errors, the loss function discarding partial elements of logits causes performance degradation in the gradient-based attack." + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.521, + 0.469, + 0.566 + ], + "angle": 0, + "content": "- We show that minimizing the impact of floating-point errors can improve the efficiency and accuracy of gradient-based attacks." + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.576, + 0.469, + 0.621 + ], + "angle": 0, + "content": "- Empirical results demonstrate that MIFPE tends to outperform the competing loss functions in terms of attack performance and computational efficiency." + }, + { + "type": "list", + "bbox": [ + 0.096, + 0.312, + 0.47, + 0.621 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.634, + 0.358, + 0.65 + ], + "angle": 0, + "content": "2. Preliminaries & Related Work" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.659, + 0.469, + 0.765 + ], + "angle": 0, + "content": "We define the classification model as \\(f_{\\theta}(\\mathbf{x})\\) , where \\(\\pmb{\\theta}\\) represents the model parameters. \\(f_{\\theta}:\\mathbf{x}\\subset \\mathbb{R}^{C\\times H\\times W}\\to\\) \\(\\mathbf{z}\\subset \\mathbb{R}^k\\) is a classifier that maps input data \\(\\mathbf{x}\\) to output logits \\(\\mathbf{z}\\) ,where \\(C,H\\) ,and \\(W\\) are parameters that describe the input data's channel number, height, and width, respectively. Additionally, \\(K\\) represents the number of classes from the model's output. We define the label of the input data as \\(y\\)" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.766, + 0.469, + 0.901 + ], + "angle": 0, + "content": "Attackers aim to breach defence strategies by generating adversarial examples \\(\\hat{\\mathbf{x}}\\), which can maximize the loss function \\(L(f_{\\theta}(\\hat{\\mathbf{x}}),y)\\) and deceive the model into producing incorrect results, arg max \\(f_{\\theta}(\\hat{\\mathbf{x}})\\neq y\\). Achieving this requires the attackers to find imperceptible perturbations \\(\\delta = \\hat{\\mathbf{x}} -\\mathbf{x}\\) that satisfy the constraint \\(\\| \\delta \\| p\\leq \\varepsilon\\), where \\(\\varepsilon\\) is the magnitude and \\(p\\) is the norm of the perturbation. Various perturbation options have been explored in literature, including the one-pixel attack [44, 44], \\(l_{2}\\) attacks [6, 31, 45], and \\(l\\infty\\)" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.092, + 0.892, + 0.136 + ], + "angle": 0, + "content": "attacks [16, 29]. The attackers can find an adversarial example \\(\\hat{\\mathbf{x}} \\in \\mathcal{I}\\) by maximizing the loss. This process can be formulated as:" + }, + { + "type": "equation", + "bbox": [ + 0.578, + 0.148, + 0.892, + 0.173 + ], + "angle": 0, + "content": "\\[\n\\hat {\\mathbf {x}} = \\mathbf {x} + \\max _ {\\| \\delta \\| _ {p} \\in \\varepsilon} L \\left(f _ {\\boldsymbol {\\theta}} (\\mathbf {x} + \\delta), y\\right), \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.183, + 0.892, + 0.333 + ], + "angle": 0, + "content": "The white-box scenario is the most rigorous test for defence strategies, as attackers have complete knowledge about the models' architecture, parameters, training data, and algorithm implementation details. This is a highly challenging situation for defence strategies. Attackers can exploit nearly all vulnerabilities in the defence strategies and perform tailored attacks. If defence strategies remain robust against white-box attacks, they can ensure the system's security even in the worst-case scenario. In practice, the gradient-based method is commonly used to solve (1)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.335, + 0.892, + 0.501 + ], + "angle": 0, + "content": "Many gradient-based white-box attacks methods have been proposed, which include fast gradient-sign method (FGSM) [16], basic iterative method (BIM) [23], projected gradient descent (PGD) [29], momentum iterative method (MIM) [13] and fast adaptive boundary attack (FAB) [9] for \\(\\ell_{\\infty}\\)-norm attacks. Carlini and Wagner (C&W) [6] and DeepFool [31] can additionally carry out \\(\\ell_{2}\\)-norm attacks. PGD is one of the widely used methods to evaluate the model's robustness in the white box scenario, which finds an adversarial example by performing the following iterative update:" + }, + { + "type": "equation", + "bbox": [ + 0.517, + 0.511, + 0.892, + 0.528 + ], + "angle": 0, + "content": "\\[\n\\hat {\\mathbf {x}} _ {i + 1} = \\mathcal {P} _ {\\epsilon , \\mathbf {x}} \\left(\\hat {\\mathbf {x}} _ {i} + \\alpha_ {i} \\operatorname {s i g n} \\left(\\nabla_ {\\hat {\\mathbf {x}} _ {i}} \\mathcal {L} ^ {\\mathrm {c e}} \\left(f _ {\\boldsymbol {\\theta}} \\left(\\hat {\\mathbf {x}} _ {i}\\right), y\\right)\\right)\\right), \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.538, + 0.892, + 0.674 + ], + "angle": 0, + "content": "Initially, \\(\\hat{\\mathbf{x}}_0 = \\mathcal{P}_{\\epsilon,\\mathbf{x}}(\\mathbf{x} + \\mathbf{u})\\), where \\(\\mathbf{u} \\sim \\mathcal{U}([- \\epsilon, \\epsilon])\\), i.e. \\(\\mathbf{u}\\) is a uniform random noise bounded by \\([- \\epsilon, \\epsilon]\\). The function \\(\\mathcal{P}_{\\epsilon,\\mathbf{x}}: \\mathbb{R}^{C \\times H \\times W} \\to \\mathcal{I}\\) first clips the range of its input into the \\(\\epsilon\\)-ball \\(\\ell_p\\)-distance neighbour of the original image \\(\\mathbf{x}\\) and then clips its input into the range of \\(\\mathcal{I}\\). The term \\(\\nabla_{\\hat{\\mathbf{x}}_i} \\mathcal{L}^{\\mathrm{ce}}(f_\\theta(\\hat{\\mathbf{x}}_i), y)\\) computes the gradient of the loss w.r.t. the input \\(\\hat{\\mathbf{x}}_i\\). Finally, \\(\\alpha_i\\) is the step size, and for each element in the tensor \\(g\\), \\(\\operatorname{sign}(g)\\) returns one of 1, 0 or -1, if the value is positive, zero or negative, respectively." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.675, + 0.892, + 0.901 + ], + "angle": 0, + "content": "CE is a commonly used loss function for training deep neural network models and evaluating their robustness in classification tasks. However, the presence of exponential operations in CE makes it vulnerable to underflow and rounding errors with limited floating-point precision. Gradient-based attacks with the CE loss may experience vanishing/inefficient gradients and difficulty converging while suffering from a severe overestimation of the model's robustness. [6, 10]. Recent attack methods use surrogate losses for gradient computation [6, 18] and optimize an alternative target by replacing \\(\\mathcal{L}^{\\mathrm{ce}}\\) with a custom surrogate loss function. \\(\\mathbf{z} = f_{\\theta}(\\hat{\\mathbf{x}})\\) is output logits of the model, and \\(\\mathbf{z}_i\\) is the \\(i^{\\mathrm{th}}\\) component of \\(\\mathbf{z}\\), two typical examples to replace the CE objective include the difference-of-logits (DL) [6], also known as hinge loss, where \\(i \\in \\{1,2,\\dots,K\\}\\)" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "4057" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.152, + 0.107 + ], + "angle": 0, + "content": "and \\(i\\neq y\\)" + }, + { + "type": "equation", + "bbox": [ + 0.18, + 0.113, + 0.47, + 0.137 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} ^ {\\mathrm {c w}} (\\mathbf {z}, \\mathrm {y}) = - \\mathbf {z} _ {y} + \\max _ {i \\neq y} \\mathbf {z} _ {i}, \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.143, + 0.408, + 0.158 + ], + "angle": 0, + "content": "and the difference-of-logits ratio (DLR) loss [10]:" + }, + { + "type": "equation", + "bbox": [ + 0.166, + 0.163, + 0.469, + 0.194 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} ^ {\\mathrm {d l r}} (\\mathbf {z}, \\mathrm {y}) = \\frac {- \\mathbf {z} _ {y} + \\max _ {i \\neq y} \\mathbf {z} _ {i}}{\\mathbf {z} _ {\\pi 1} - \\mathbf {z} _ {\\pi 3}}, \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.199, + 0.469, + 0.395 + ], + "angle": 0, + "content": "where \\(\\mathbf{z}_{\\pi_1}\\) and \\(\\mathbf{z}_{\\pi_3}\\) respectively denote the \\(1^{\\mathrm{th}}\\) and \\(3^{\\mathrm{th}}\\) largest components of \\(\\mathbf{z}\\). It is clear that maximizing the alternative goals is consistent with the original objective of making \\(\\arg \\max f(\\hat{\\mathbf{x}})\\neq y\\). In addition, since surrogate losses avoid exponential operations, they are not prone to underflow, allowing gradient-based optimization to escape suffering from the overestimation caused by the floating-point underflow errors. However, the floating-point underflow errors are not the sole reason for all overestimations related to floating-point errors. At the same time, the new loss function discards some elements of \\(\\mathbf{z}\\), reducing the effectiveness of the attack and causing gradient-based attacks with surrogate losses to overestimate the model's robustness." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.396, + 0.47, + 0.668 + ], + "angle": 0, + "content": "Many auxiliary techniques can assist existing attack methods to improve their performance. For example, momentum-based updates can improve the attack's convergence rate and are widely used by white-box attacks [13, 18]. A step schedule with decreasing step size based on the number of iterations can improve the overall success rate [10, 18, 56]. Multi-target attacks can outperform nontarget attacks in the evaluation results at the cost of more iterations since they require enumerating multiple most likely target labels [18, 33, 34]. In addition to the above strategies, multiple restarts can also improve the effectiveness of gradient-based attacks by adding different random initial perturbations to the input data to diversify the starting point of the attack and reduce the impact of suboptimal solutions [5, 46]. Finally, several recent publications have shown that leveraging latent features in attacks can enhance the transferability of black-box attacks [21, 22] and the performance of white-box attacks [56]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.668, + 0.47, + 0.819 + ], + "angle": 0, + "content": "However, even with so many auxiliary strategies mentioned above, using any single attack is still challenging to accurately evaluate the model's robustness. Attackers start using an ensemble of multiple attack strategies to improve the attack's performance by introducing diversity [5,10,28]. They often suffer from high computational costs. Even though these ensemble strategies are more powerful than any single attack, they still fail to provide an assessment of the ensemble defence strategy's robustness accurately [48,57]." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.83, + 0.296, + 0.847 + ], + "angle": 0, + "content": "3. Efficient Loss Function" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.469, + 0.902 + ], + "angle": 0, + "content": "Assuming that the input \\(\\hat{\\mathbf{x}}\\) has the correct label \\(y\\), we compute \\(\\mathbf{z} = f_{\\theta}(\\hat{\\mathbf{x}})\\), where \\(\\pmb{\\theta}\\) represents the model parameters. Next, we sort the values in \\(\\mathbf{z}\\) in a descending order," + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.092, + 0.892, + 0.15 + ], + "angle": 0, + "content": "where \\(\\mathbf{z}_{\\pi 1}\\) is the maximum value. We define \\(\\Delta\\) as the difference between the maximum and the second maximum value, i.e., \\(\\Delta = \\mathbf{z}_{\\pi 1} - \\mathbf{z}_{\\pi 2} \\geq 0\\). The cross-entropy loss at \\(\\mathbf{z}\\) becomes" + }, + { + "type": "equation", + "bbox": [ + 0.543, + 0.159, + 0.892, + 0.197 + ], + "angle": 0, + "content": "\\[\nC E (\\mathbf {z}, y) = - \\log p _ {y} = - \\log \\frac {e ^ {\\mathbf {z} _ {y} - \\mathbf {z} _ {\\pi 1}}}{\\sum_ {i = 1} ^ {K} e ^ {\\mathbf {z} _ {i} - \\mathbf {z} _ {\\pi 1}}}, \\tag {5}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.556, + 0.216, + 0.891, + 0.269 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\nabla_ {\\hat {\\mathbf {x}}} C E (\\mathbf {z}, y) = (- 1 + p _ {y}) \\nabla_ {\\hat {\\mathbf {x}}} \\left(\\mathbf {z} _ {y} - \\mathbf {z} _ {\\pi 1}\\right) \\\\ + \\sum_ {i \\neq y} p _ {i} \\nabla_ {\\hat {\\mathbf {x}}} \\left(\\mathbf {z} _ {i} - \\mathbf {z} _ {\\pi 1}\\right), \\tag {6} \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.28, + 0.876, + 0.298 + ], + "angle": 0, + "content": "where \\(p_i = e^{\\mathbf{z}_i - \\mathbf{z}_{\\pi 1}} / \\sum_{j = 1}^{K}e^{\\mathbf{z}_j - \\mathbf{z}_{\\pi 1}}\\) \\(i\\in \\{1,2,3,\\dots,K\\}\\)" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.298, + 0.892, + 0.493 + ], + "angle": 0, + "content": "Exponential operations in Equation (5), specifically \\(e^{\\mathbf{z}_{\\pi i} - \\mathbf{z}_{\\pi 1}},i\\in \\{2,\\dots,K\\}\\) , where \\(\\mathbf{z}_{\\pi i} - \\mathbf{z}_{\\pi 1}\\leq \\mathbf{z}_{\\pi 2} - \\mathbf{z}_{\\pi 1} =\\) \\(-\\Delta \\leq 0\\) , can cause floating-point underflow errors in the CE loss gradient. To investigate this issue, we analyze the properties of \\(e^{-\\Delta}\\) and observe that when \\(\\Delta\\) surpasses a threshold value denoted by \\(\\lambda\\) \\(e^{-\\Delta}\\) underflows and leads to significant inaccuracies in the gradient calculation. Specifically, when \\(\\Delta \\geq \\lambda\\) and \\(\\mathbf{z}_y = \\mathbf{z}_{\\pi 1}\\) , the predicted probability \\(p_{y} = 1\\) and the calculated gradient \\(\\nabla_{\\hat{\\mathbf{x}}}CE(\\mathbf{z},y) = 0\\) The value of \\(\\lambda\\) varies with different floating-point arithmetic precisions, with approximate values of 16.64, 103.28, and 744.44 for half-precision, single-precision, and double-precision, respectively." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.494, + 0.893, + 0.825 + ], + "angle": 0, + "content": "Based on the findings, we identify that the root cause of the calculated gradient being equal to zero is the result of \\(\\Delta\\) exceeding \\(\\lambda\\). To further investigate the relationship between the value of \\(\\Delta\\) and the overestimation of the model's robustness, we analyze the distribution of \\(\\Delta\\) values in defence models that tend to be overestimated by gradient-based attacks under single-precision. The results in Figure 2 indicate that the range of \\(\\Delta\\) values varies significantly among different defence models. Notably, the values of \\(\\Delta\\) in 2a and 2b do not exceed 10, which is significantly smaller than \\(\\lambda \\approx 103.28\\) for single-precision. As a result, these models do not suffer from floating-point underflow errors. In contrast, most of the \\(\\Delta\\) values in 2c exceed the threshold that leads to floating-point underflow errors. It is evident that not all models suffer from floating-point underflow errors, and other reasons associated with floating-point errors cause gradient-based attacks to fail. This is because in addition to floating-point underflow errors, floating-point errors have another component: floating-point rounding errors when \\(\\Delta < \\lambda\\). These errors result in a non-negligible relative error in \\(\\nabla_{\\hat{\\mathbf{x}}}CE(\\mathbf{z},y)\\). We define the relative error as \\(\\delta_{CE} = \\delta (\\nabla_{\\hat{\\mathbf{x}}}CE(\\mathbf{z},y))\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.826, + 0.892, + 0.901 + ], + "angle": 0, + "content": "We know that \\(\\delta_{CE} = 100\\%\\) when \\(\\Delta \\geq \\lambda\\). We need to further analyze the change pattern of \\(\\delta_{CE}\\) when \\(\\Delta < \\lambda\\). A multi-iteration gradient-based attack involves adding perturbations to \\(\\hat{\\mathbf{x}}\\) at each iteration, leading to constant changes in \\(\\mathbf{z}\\), \\(\\Delta\\), and \\(\\nabla_{\\hat{\\mathbf{x}}}(\\mathbf{z}_{\\pi i} - \\mathbf{z}_{\\pi 1})\\) for \\(i \\in 1,2,\\dots,K\\) after each" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "4058" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.088, + 0.095, + 0.344, + 0.265 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.134, + 0.274, + 0.294, + 0.287 + ], + "angle": 0, + "content": "(a) The \\(\\Delta\\) distribution of [33]" + }, + { + "type": "image", + "bbox": [ + 0.359, + 0.095, + 0.614, + 0.264 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.405, + 0.274, + 0.566, + 0.287 + ], + "angle": 0, + "content": "(b) The \\(\\Delta\\) distribution of [59]" + }, + { + "type": "image", + "bbox": [ + 0.629, + 0.095, + 0.882, + 0.264 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.681, + 0.274, + 0.832, + 0.287 + ], + "angle": 0, + "content": "(c) The \\(\\Delta\\) distribution of [3]" + }, + { + "type": "image_caption", + "bbox": [ + 0.107, + 0.299, + 0.86, + 0.313 + ], + "angle": 0, + "content": "Figure 2. The distributions of \\(\\Delta = \\mathbf{z}_{\\pi 1} - \\mathbf{z}_{\\pi 2}\\) for the defending models on the CIFAR-10 dataset are averaged across 100 bins." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.34, + 0.47, + 0.474 + ], + "angle": 0, + "content": "modification. This makes it difficult to analyze how \\(\\delta_{CE}\\) changes when \\(\\Delta < \\lambda\\). However, we can indirectly examine the effect of floating-point errors on the attack's performance by analyzing the impact of such errors on a single step. To do so, we introduce a scaling factor \\(c\\) and define the scaled value of \\(\\Delta\\) as \\(T = c\\Delta\\). By varying \\(c\\) while keeping \\(\\hat{\\mathbf{x}}\\), \\(\\mathbf{z}\\), and \\(\\nabla_{\\hat{\\mathbf{x}}}(\\mathbf{z}_{\\pi i} - \\mathbf{z}_{\\pi 1})\\) fixed during gradient calculation, we can investigate the relationship between \\(\\delta_{CE}\\) and \\(T\\) for different values of \\(T\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.48, + 0.47, + 0.652 + ], + "angle": 0, + "content": "To compute the scale factor, we need to detach the gradient information from \\(\\Delta\\) since \\(\\mathbf{z}\\) contains the gradient information during the actual program running. Thus, we define the scale factor as \\(c = T / \\Delta_{\\mathrm{detach}}\\). The use of the detach operation in the calculation of \\(c\\) removes the gradient information from the \\(\\Delta_{\\mathrm{detach}}\\), making it distinct from the \\(\\Delta\\) that retains gradient information. When \\(\\mathbf{z}_y \\neq \\mathbf{z}_{\\pi 1}\\), the model output is already incorrect. Therefore, we only focus on the relationship between \\(\\delta_{CE}\\) and \\(T\\) when \\(\\mathbf{z}_y = \\mathbf{z}_{\\pi 1}\\), at which point \\(\\nabla_{\\hat{\\mathbf{z}}}CE(c\\mathbf{z},y) = c\\sum_{i \\neq y}p_i^c\\nabla_{\\hat{\\mathbf{x}}}(\\mathbf{z}_i - \\mathbf{z}_{\\pi 1})\\), where \\(p_i^c = e^{c(\\mathbf{z}_i - \\mathbf{z}_{\\pi 1})} / \\sum_{j=1}^{K}e^{c(\\mathbf{z}_j - \\mathbf{z}_{\\pi 1})}\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.655, + 0.47, + 0.866 + ], + "angle": 0, + "content": "To get a more intuitive picture of the relationship between \\(\\delta_{CE}\\) and \\(T\\), we plotted the figure of \\(\\delta_{CE}\\) on the binary classification task with \\(K = 2\\). At this point, \\(\\nabla_{\\hat{\\mathbf{z}}}CE(\\mathbf{cz},y) = c\\sum_{i\\neq y}p_i^c\\nabla_{\\hat{\\mathbf{x}}}\\left(\\mathbf{z}_i - \\mathbf{z}_{\\pi 1}\\right) = cp_2^c\\nabla_{\\hat{\\mathbf{x}}}\\left(\\mathbf{z}_{\\pi 2} - \\mathbf{z}_{\\pi 1}\\right)\\propto cp_2^c\\). Therefore, \\(\\delta_{CE}\\propto \\delta (cp_2^c)\\). In Figure 3, we can see that for the same \\(\\hat{\\mathbf{x}}\\), when \\(\\mathbf{z}\\) and \\(\\nabla_{\\hat{\\mathbf{x}}}\\left(\\mathbf{z}_i - \\mathbf{z}_{\\pi 1}\\right)\\), \\(i\\in \\{1,2,\\dots,K\\}\\) are all fixed, \\(\\delta_{CE}\\) varies with \\(T\\). When \\(T\\geq \\lambda\\), \\(\\delta_{CE} = 100\\%\\) In contrast, When \\(T < \\lambda\\), The relative error \\(\\delta_{CE}\\) caused by the floating-point rounding errors is much more minor, varies continuously with T, and reaches the minimum when \\(T\\) is approximately 1. But one thing that needs to be highlighted is that after the relative error reaches the minimum, it starts to increase as \\(T\\) gets closer to 0." + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.871, + 0.469, + 0.901 + ], + "angle": 0, + "content": "Following the same operation, we add a scale factor \\(c\\) to \\(\\Delta\\) and hold \\(T = c\\Delta\\) constant during each iteration of the" + }, + { + "type": "image", + "bbox": [ + 0.513, + 0.344, + 0.885, + 0.508 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.521, + 0.893, + 0.577 + ], + "angle": 0, + "content": "Figure 3. The relative error of the gradient information computed using half-precision floating-point operations on a binary classification task with the CE loss varies with \\( T \\) for a given adversarial example within a single iteration." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.611, + 0.892, + 0.791 + ], + "angle": 0, + "content": "multi-iteration attack. This technique, which we refer to as FT-PGD, allows us to assess the model's robustness with a fixed \\( T \\) value. In Figure 4, we evaluate the model's robustness using FT-PGD at various \\( T \\) values. By comparing the relative floating-point error in Figure 3 with the attack's performance in Figure 4, we observe a strong correlation between the relative error \\( \\delta_{CE} \\) and the attack's effectiveness. Thus, the relative error is a critical factor that contributes to overestimating the model's robustness. Furthermore, we identify two distinct phases in the impact of floating-point errors on gradient-based attacks due to the CE loss, which depend on the relationship between \\( T \\) and \\( \\lambda \\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.796, + 0.892, + 0.9 + ], + "angle": 0, + "content": "(a) The attack failed due to floating-point underflow errors. When \\( T \\geq \\lambda \\), floating-point underflow causes the calculated gradient equal to zero and \\( \\delta_{CE} = 100\\% \\). As a result, the input perturbation becomes zero, and the model's robustness is measured to be equal to its clean accuracy, which leads to a significant overestimation of the model's robustness." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.956 + ], + "angle": 0, + "content": "4059" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.089, + 0.097, + 0.46, + 0.26 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.273, + 0.473, + 0.357 + ], + "angle": 0, + "content": "Figure 4. A higher zero ratio, which represents the proportion of zero elements in the perturbation, leads to larger overestimations when evaluating model robustness. We assess model robustness using 100 iterations of FT-PGD with CE loss on the CIFAR-10 dataset under half-precision floating-point arithmetic. The model is obtained from [59]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.385, + 0.47, + 0.537 + ], + "angle": 0, + "content": "(b) The attack's performance fluctuates with the small relative error caused by floating-point rounding errors. When \\(0 \\leq T < \\lambda\\), the computed gradient's relative error due to the floating-point rounding error is small and has the same variation pattern as the zero ratio and attack performance. The smallest relative error occurs around \\(T = 1\\). However, it's crucial to note that at the bottom left of Figure 3 and Figure 4, the relative error and its detrimental effect on the gradient-based attack increase as \\(T\\) approaches zero after reaching the minimum." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.538, + 0.471, + 0.794 + ], + "angle": 0, + "content": "It is straightforward to assume that since floating-point errors cause the above problem, it should be possible to solve the problem by simply increasing the precision of floating-point arithmetics because it can effectively reduce the floating-point errors. To test whether this simple idea works, we evaluated the impact of different floating-point arithmetics precisions, including half-precision, single-precision, and double-precision, on the model's robustness against FT-PGD with 100 iterations. As depicted in Figure 5, the attack's performance exhibits a similar variation pattern across different precisions, and the model's robustness measured with PGD remains nearly unchanged. While increasing the floating-point precision can delay attack failure due to floating-point underflow errors, it incurs significant computational overhead. Therefore, increasing the floating-point precision is not a viable solution to address the problem." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.796, + 0.47, + 0.903 + ], + "angle": 0, + "content": "Surrogate loss functions(3,4) have been proposed [6, 10, 18] to work around floating-point underflow errors. They avoid suffering from floating-point underflow errors by discarding softmax operations. At the same time, they only use partial \\(\\mathbf{z}\\) elements in the new loss function. To demonstrate the effect of discarding elements of \\(\\mathbf{z}\\) on the attack's performance, We designed an experiment to make only a fixed" + }, + { + "type": "image", + "bbox": [ + 0.513, + 0.097, + 0.883, + 0.262 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.273, + 0.895, + 0.33 + ], + "angle": 0, + "content": "Figure 5. The model's robustness test results on the CIFAR-10 dataset under Float16, Float32, and Float64 follow a similar pattern of variation, except that the thresholds that lead to the attack's failure are different, the model obtained from [59]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.364, + 0.895, + 0.621 + ], + "angle": 0, + "content": "number of \\(\\mathbf{z}\\) elements participate in the calculation of the gradients by exploiting floating-point underflow errors. To achieve this goal we scale the logits \\(\\mathbf{z}_{\\pi 1} - \\mathbf{z}_{\\pi i}\\) by a scale factor \\(c\\) to make \\(c(\\mathbf{z}_{\\pi 1} - \\mathbf{z}_{\\pi i}) = \\lambda\\), such that \\(p_{\\pi j}^{c} = 0\\) if \\(j \\geq i\\) and \\(p_{\\pi j}^{c} > 0\\) if \\(j < i\\), where \\(i \\in \\{2,3,\\dots,K\\}\\) and \\(j \\in \\{1,2,3,\\dots,K\\}\\). So that only \\(i - 1\\) number of \\(\\mathbf{z}\\) elements are involved in the gradient calculation, thus giving PGD the ability to attack the network with a fixed number of \\(\\mathbf{z}\\) elements, which we now call FNZ-PGD. We use FNZ-PGD with different numbers of \\(\\mathbf{z}\\) elements to evaluate the model's robustness which is overestimated mainly due to floating-point errors. From Figure 6, we can see that the more \\(\\mathbf{z}\\) elements involved in the attack, the more potent the attack will be. So discarding the \\(\\mathbf{z}\\) element in the loss function will impair the attack's performance when model robustness is overestimated mainly due to floating-point errors." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.625, + 0.895, + 0.791 + ], + "angle": 0, + "content": "In summary, the relative error in the calculated gradients due to the floating-point errors, which include floating-point underflow errors and floating-point rounding errors, is the critical factor contributing to the overestimation of the model's robustness. While floating-point errors are a primary cause of gradient-based attacks' failure, they are not the sole cause. Reducing their impact can only address the portion of model robustness that is overestimated due to them. Therefore, it is unrealistic to expect that solely reducing the impact of floating-point errors alone will eliminate all problems related to overestimating model robustness." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.796, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Although we cannot eliminate the relative error in the gradients caused by floating-point errors, we can control it's side effect and significantly increase the power of gradient-based attacks. As a result, we propose the Minimize the impact of floating-point errors (MIFPE) loss, a small modification to the original CE loss, which scales the logits adaptively before the softmax operation. For untargeted and tar" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.956 + ], + "angle": 0, + "content": "4060" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.089, + 0.096, + 0.469, + 0.262 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.273, + 0.475, + 0.373 + ], + "angle": 0, + "content": "Figure 6. Using more \\(\\mathbf{z}\\) elements increases attack potency when model robustness is overestimated mainly due to floating-point errors. We utilized FNZ-PGD with 100 iterations, CE loss, and a baseline of PGD-100 with CE, C&W, and DLR loss under CIFAR10. All floating-point operations were single-precision, and the model was obtained from [59]. Here, \\(n\\) refers to the number of \\(\\mathbf{z}\\) elements used." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.396, + 0.427, + 0.413 + ], + "angle": 0, + "content": "geted attacks, the targets are as follows respectively:" + }, + { + "type": "equation", + "bbox": [ + 0.148, + 0.42, + 0.47, + 0.44 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} ^ {\\mathrm {M I F P E}} (\\mathbf {z}, y) \\triangleq \\mathcal {L} ^ {\\mathrm {c e}} \\left(T \\mathbf {z} / \\Delta_ {\\text {d e t a c h}}, y\\right), \\tag {7}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.139, + 0.461, + 0.47, + 0.481 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\text {t a r g e t}} ^ {\\mathrm {M I F P E}} \\left(\\mathbf {z}, y _ {\\mathrm {t}}\\right) = - \\mathcal {L} ^ {\\mathrm {c e}} \\left(T \\mathbf {z} / \\Delta_ {\\text {d e t a c h}}, y _ {\\mathrm {t}}\\right), \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.485, + 0.47, + 0.545 + ], + "angle": 0, + "content": "Where \\( y_{t} \\) is a predefined class target, \\( t \\in \\{1, 2, \\dots, K\\} \\) and \\( y_{t} \\neq y \\). In our experiments, the factor \\( T \\) was set to around 1 to minimize the detrimental effect of floating-point errors on the gradient-based attacks." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.546, + 0.473, + 0.713 + ], + "angle": 0, + "content": "The new surrogate loss \\(\\mathcal{L}^{\\mathrm{MIFPE}}\\) has fourfold advantages. First, it can eliminate the failure of gradient-based attacks due to floating-point underflow errors. Second, it can minimize the impact of the small relative error due to floating-point rounding errors and significantly improve the performance of gradient-based attacks. Third, it provides the flexibility to adjust the number of logit elements involved in the attack simply by changing the value of T. Finally, unlike the C&W or DLR loss, it still represents the original CE loss faithfully, and all values in the logit vector can still contribute to the gradient calculation." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.725, + 0.212, + 0.743 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.75, + 0.473, + 0.903 + ], + "angle": 0, + "content": "To ensure a fair comparison against other loss functions in our evaluation and to make our evaluation as comprehensive as possible, we conducted tests on different threat models and datasets. Specifically, we tested the \\(\\ell_{\\infty}\\)-norm bounded perturbation on the CIFAR-10, CIFAR-100, MNIST [25] and ImageNet datasets [11], and the \\(\\ell_{2}\\)-norm threat model on the CIFAR-10 dataset. For each test, we ran the PGD with different loss functions, including the cross-entropy (CE) loss function, the C&W loss function [6], the DLR loss function [10], and our proposed MIFPE. We kept" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.895, + 0.319 + ], + "angle": 0, + "content": "all other settings the same across the tests. Firstly, we used 100 iterations for each test. Secondly, we adopted the same step-size schedule with a linear decay [56], which updates the perturbation boundary \\(\\epsilon\\) at each iteration \\(i\\) according to the formula \\(2\\epsilon (1 - i / I)\\), where \\(I\\) denotes the total number of iterations. Thirdly, we employed momentum-based updates [10] with a momentum factor of \\(\\nu = 0.75\\) for all tests. Lastly, we saved the best adversarial examples generated during the attack. To demonstrate the effectiveness of MIFPE in achieving near-state-of-the-art robustness with only 100 iterations, we compare our results with the best robust accuracy reported on RobustBench1, which uses an ensemble of attacks and a minimum of 4900 iterations. We also compared the attack performance of MIFPE with GAMA_PGD [43] under the same 100-iteration constraint." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.32, + 0.895, + 0.593 + ], + "angle": 0, + "content": "In Table 1, we present a comprehensive comparison showing that MIFPE outperforms CE, C&W, and DLR loss functions on all tested models. Additionally, we found that when PGD with momentum and step schedule using MIFPE as the loss function outperforms GAMA_PGD on all tested models by at least more than \\(0.1\\%\\) under 100 iterations constraint, which is impossible when PGD with momentum and step schedule using CE, C&W and DLR as the loss function. Remarkably, even with only 100 iterations, MIFPE achieves results that are very close to the best results obtained with at least 4900 iterations on some models, such as Uncovering limits [17] and Proper definition [32] for CIFAR10, \\(l_{\\infty}\\), \\(\\varepsilon = 8/255\\). Our findings also reveal that C&W and DLR perform even worse than CE in some cases, such as on Robustness library [14] and Fast adversarial training [51] for CIFAR10, \\(l_{\\infty}\\), \\(\\varepsilon = 8/255\\). This suggests that discarding partial logit elements in the loss function would decrease the effectiveness of gradient-based attacks." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.595, + 0.896, + 0.76 + ], + "angle": 0, + "content": "Faster convergence. We want to highlight that the effectiveness of MIFPE is not achieved by increasing the computational cost compared to other loss functions. We found that minimising the effect of the floating-point errors leads to faster convergence speed than competing loss functions. Figure 7 shows that for all two defending models, MIFPE loss performs more efficiently, and often with orders of magnitude faster than other loss functions for successful attacks. Finally, minimising the effect of floating-point error operation introduces no overhead and imposes no impact on the iteration time." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.763, + 0.895, + 0.838 + ], + "angle": 0, + "content": "Boost the capability of existing attack strategies. Because MIFPE is a loss function, it can be easily integrated with existing attack strategies by replacing the original loss function. The results in Table 2 show that using MIFPE boosts the attack's effectiveness." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.895, + 0.901 + ], + "angle": 0, + "content": "Ablation analysis. Our ablation experiments, presented in Table 3, investigated the effect of momentum and step-size schedule on PGD using different loss functions with 100 iterations. The results show that the MIFPE consist" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.514, + 0.958 + ], + "angle": 0, + "content": "4061" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.089, + 0.892, + 0.16 + ], + "angle": 0, + "content": "Table 1. Comparing the proposed MIFPE loss \\((\\mathcal{L}^{\\mathrm{MIFPE}})\\), against CE \\((\\mathcal{L}^{\\mathrm{ce}})\\), C&W \\((\\mathcal{L}^{\\mathrm{cw}})\\), and DLR \\((\\mathcal{L}^{\\mathrm{dlr}})\\) losses. For each surrogate loss, we use PGD-100 with the step-size schedule \\(2\\epsilon (1 - i / I)\\) and momentum \\(\\nu = 0.75\\). Models marked with \\(\\dagger\\) were trained with extra data. Models marked with \\(\\ddagger\\), which used \\(\\varepsilon = 0.031\\) as originally reported by the authors. Numbers in parentheses indicate the improvement w.r.t. the CE baseline. The best, calculated using an ensemble of attacks and a minimum of 4900 iterations, is reported from RobustBench1 to demonstrate how closely MIFPE can approach the lowest known robustness accuracy with only 100 iterations." + }, + { + "type": "table", + "bbox": [ + 0.078, + 0.171, + 0.892, + 0.741 + ], + "angle": 0, + "content": "
Defense methodArchitectureCleanCE (Lce)100C&W (Lcw)100DLR (Ldir)100GAMA_PGD100MIFPE (LMIFPE)100Best4900
MNIST, ℓ∞, ε = 0.3
Uncovering limits [17]WRN-28-1099.2696.5596.64(+0.09)96.71(+0.16)96.69(+0.14)96.53(-0.02)96.31
MMA training [12]†LeNet5Madry98.9895.6695.60(-0.06)95.56(-0.10)95.96(+0.13)95.50(-0.16)93.51
MMA training [12]LeNet5Madry98.9595.0995.33(+0.24)95.59(+0.50)95.74(+0.19)94.88(-0.21)91.40
Neural level sets [3]SmallCNN99.3599.2894.68(-4.60)95.09(-4.19)99.29(+0.01)94.67(-4.61)90.85
TRADES [59]SmallCNN99.4893.6993.88(+0.19)94.49(+0.80)93.82(+0.13)93.67(-0.02)92.71
Robust optimization [29]SmallCNN99.3593.0693.19(+0.13)93.63(+0.57)93.39(+0.33)92.88(-0.18)90.85
Fast adversarial training [51]SmallCNN98.5086.8286.96(+0.14)87.42(+0.60)87.62(+0.80)86.57(-0.25)82.93
CIFAR-10, ℓ∞, ε = 8/255
Uncovering limits [17]†WRN-70-1691.1067.9666.70(-1.26)66.78(-1.18)66.08(-1.88)65.96(-2.00)65.87
Fixing data augmentation [36]WRN-106-1688.5067.5765.55(-2.02)65.61(-1.96)64.94(-2.63)64.75(-2.82)64.58
Fixing data augmentation [36]WRN-70-1688.5467.2765.23(-2.04)65.32(-1.95)64.57(-2.70)64.46(-2.81)64.20
Proper definition [32]WRN-70-1689.0166.6663.94(-2.72)64.01(-2.65)63.65(-3.01)63.49(-3.17)63.35
Uncovering limits [17]†WRN-28-1089.4865.5963.62(-1.97)63.82(-1.77)63.05(-2.90)62.96(-2.63)62.76
Proper definition [32]WRN-28-1088.6164.6661.55(-3.11)61.62(-3.04)61.19(-3.47)61.12(-3.54)61.04
Adversarial weight perturbation [53]†WRN-28-1088.2563.1860.51(-2.67)60.60(-2.58)60.18(-3.00)60.09(-3.09)60.04
Unlabeled data [7]†WRN-28-1089.6961.6060.47(-1.13)60.67(-0.93)59.82(-1.78)59.72(-1.88)59.53
HYDRA [40]†WRN-28-1088.9859.5358.21(-1.32)58.30(-1.23)57.52(-2.01)57.38(-2.15)57.14
Misclassification-aware [50]WRN-28-1087.5061.6058.03(-3.57)58.73(-2.87)57.20(-4.40)56.88(-4.72)56.29
Pre-training [19]†WRN-28-1087.1157.0756.27(-0.80)57.07(0.00)55.22(-1.85)55.10(-1.97)54.92
Hypersphere embedding [33]WRN-34-2085.1461.4355.35(-6.08)56.21(-5.22)54.37(-7.06)53.85(-7.58)53.74
Overfitting [37]WRN-34-2085.3456.8555.22(-1.63)55.97(-0.88)53.87(-2.98)53.62(-3.23)53.42
Self-adaptive training [20]‡WRN-34-1083.4856.1254.30(-1.82)54.73(-1.39)53.64(-2.48)53.48(-2.64)53.34
TRADES [59]‡WRN-34-1084.9255.2153.94(-1.27)54.11(-1.10)53.38(-1.83)53.22(-1.99)53.08
Robustness library [14]RN-5087.0351.5652.07(+0.51)52.81(+1.25)50.04(-1.52)49.84(-1.72)49.25
Neural level sets [3]‡RN-1881.3079.1240.07(-39.05)45.10(-34.02)79.69(+0.57)40.06(-39.06)39.77
YOPO [58]WRN-34-1087.2046.0547.02(+0.97)47.55(+1.50)45.30(-0.75)45.19(-0.86)44.83
Fast adversarial training [51]RN-1883.3445.7545.81(+0.06)46.89(+1.14)43.71(-2.04)43.57(-2.18)43.21
CIFAR-10, ℓ∞, ε = 8/255
Adversarial weight perturbation [54]WRN-34-1060.3833.0930.74(-2.35)31.13(-1.96)29.44(-3.65)29.35(-3.74)28.86
Pre-training [19]†WRN-28-1059.2332.8230.58(-2.24)31.83(-0.99)29.22(-3.60)29.02(-3.80)28.42
Progressive Hardening [42]WRN-34-1062.8226.1826.69(+0.51)27.26(+1.08)24.97(-1.21)24.91(-1.27)24.57
Overfitting [37]RN-1853.8320.4720.17(-0.30)20.30(-0.17)19.20(-1.27)19.16(-1.31)18.95
ImageNet, ℓ∞, ε = 4/255
Transfer Better [39]RN-5064.0238.4437.26(-1.18)37.72(-0.72)34.94(-3.50)34.84(-3.60)34.96
Robustness library [14]RN-5062.5632.1632.24(+0.08)32.80(+0.64)29.72(-2.44)29.60(-2.56)29.22
Transfer Better [39]RN-1852.9229.3027.14(-2.16)27.40(1.90)25.56(-3.74)25.40(-3.90)18.95
CIFAR-10, ℓ2, ε = 0.5
Uncovering limits [17]†WRN-70-1694.7481.7180.93(-0.78)80.94(-0.77)87.74(+6.03)80.57(-1.14)80.53
Uncovering limits [17]WRN-70-1690.9075.2074.89(-0.31)74.95(-0.25)81.78(+6.58)74.56(-0.64)74.50
Adversarial weight perturbation [54]WRN-34-1088.5174.7773.88(-0.89)73.89(-0.88)79.38(+4.61)73.67(-1.10)73.66
Robustness library [14]RN-5090.8369.6570.13(+0.48)70.25(+0.60)78.15(+8.50)69.29(-0.36)69.24
Overfitting [37]RN-1888.6768.6668.74(+0.08)69.03(+0.37)76.19(+7.53)67.87(-0.79)67.68
Decoupling direction and norm [38]WRN-28-1089.0566.5667.00(+0.44)67.02(+0.46)74.61(+8.05)66.48(-0.08)66.44
MMA training [12]WRN-28-488.0266.2266.58(+0.36)66.60(+0.38)71.44(+5.22)66.16(-0.06)66.09
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.767, + 0.47, + 0.829 + ], + "angle": 0, + "content": "tently outperforms the other loss functions, and shows the least variance across different setups. These findings suggest that the effectiveness of the MIFPE should not be dependent on the momentum and step-size schedule." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.471, + 0.903 + ], + "angle": 0, + "content": "To analyze the reasons for the failure of the attack due to floating-point rounding errors, we selected \\(\\mathbb{Z} = \\mathbf{z}_y - \\max_{i\\neq y}\\mathbf{z}_i\\) because its sign indicates if the attack is successful or not. We compared the change of \\(\\mathbb{Z}\\) for samples" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.767, + 0.895, + 0.89 + ], + "angle": 0, + "content": "attacked by PGD-100 with CE loss but failed, and PGD-100 with MIFPE loss and succeeded. Figure 8 demonstrates that for samples attacked with CE loss, the value of \\(\\mathbb{Z}\\) rapidly approaches 0 in the first few iterations and then remains positive afterwards. On the other hand, when attacked with MIFPE loss \\(\\mathbb{Z}\\) smoothly drops below 0 after approaching 0. This phenomenon suggests that the floating-point rounding error primarily may cause attack failure when the samples" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "4062" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.088, + 0.095, + 0.268, + 0.233 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.272, + 0.096, + 0.46, + 0.233 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.241, + 0.47, + 0.298 + ], + "angle": 0, + "content": "Figure 7. We compare MIFPE to standard CE loss and other surrogate loss functions (C&W [6] and DLR [10]) on defenders [58,59]. The graph shows iterations on the horizontal axis and the percentage of unsuccessful examples on the vertical axis." + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.313, + 0.471, + 0.385 + ], + "angle": 0, + "content": "Table 2. The comparison of attack performances for FGSM [16], PGD [29], APGD_DLR [10] and AA [10] using original loss functions versus MIFPE loss on CIFAR10 dataset and \\(\\varepsilon = 0.031\\) with the model obtained from TRADES [59]. with the \\(\\nabla\\) row representing the improvement achieved with MIFPE." + }, + { + "type": "table", + "bbox": [ + 0.095, + 0.393, + 0.454, + 0.476 + ], + "angle": 0, + "content": "
Attack \niterationFGSM \n1PGD \n100APGD_DLR \n100AA \n4900
Original \nMIFPE79.8379.7945.9040.22
49.7640.0640.4939.89
V30.0739.735.410.33
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.489, + 0.47, + 0.545 + ], + "angle": 0, + "content": "Table 3. Ablation study on the effect of momentum and step-size schedule on the PGD with different loss functions and under 100 iterations on CIFAR10 dataset with the model obtained from Neural level sets [3]. New components are added in consecutive rows." + }, + { + "type": "table", + "bbox": [ + 0.079, + 0.556, + 0.472, + 0.638 + ], + "angle": 0, + "content": "
Accuracy under attack(%)Loss Function
CEC&WDLRMIFPE
PGD55.4654.2354.3953.42
+Momentum55.2554.0254.1853.23
+Step-size schedule55.2153.9454.1153.22
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.663, + 0.47, + 0.723 + ], + "angle": 0, + "content": "become close to the classification boundary due to the relative error and its detrimental effect on the gradient-based attack would increase as \\( T \\) approaches zero after reaching the minimum." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.739, + 0.196, + 0.755 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.765, + 0.47, + 0.903 + ], + "angle": 0, + "content": "This paper reveals that relative error in calculated gradient caused by floating-point errors is a fundamental reason why gradient-based attacks fail to accurately evaluate the model's robustness. To efficiently and accurately evaluate the model's robustness, we introduce MIFPE, a new loss function that minimises the impact of floating-point errors on gradient-based attacks. Compared with other loss functions, MIFPE enjoys higher accuracy and faster convergence speed. Moreover, we find several surprising ob" + }, + { + "type": "image", + "bbox": [ + 0.514, + 0.097, + 0.883, + 0.262 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.296, + 0.893, + 0.366 + ], + "angle": 0, + "content": "Figure 8. The changing process of the value of \\(\\mathbb{Z} = \\mathbf{z}_y - \\max_{i\\neq y}\\mathbf{z}_i\\) with the number of iterations during the attack on the CIFAR10 dataset using the model from TRADES [59] and single-precision arithmetic. The horizontal axes show the number of iterations used so far, and the vertical axes show the value of \\(\\mathbb{Z}\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.393, + 0.893, + 0.558 + ], + "angle": 0, + "content": "servations related to adversarial attacks: (1)Discarding partial elements of logits in the loss will impair the attack's performance; (2)The floating-point rounding errors lead to the attack's failure by causing an increasing relative error as the samples get closer to the classification boundary; (3)Increasing the precision of floating-point arithmetic cannot solve the problem of overestimating the model's robustness caused by floating-point errors, etc. We hope that the above observations will help discover more efficient and reliable loss functions in the future. Finally, MIFPE is open source with reproducible results2." + }, + { + "type": "title", + "bbox": [ + 0.501, + 0.572, + 0.661, + 0.589 + ], + "angle": 0, + "content": "Acknowledgments" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.597, + 0.892, + 0.668 + ], + "angle": 0, + "content": "This work is supported in part by Science and Technology Development Fund of Macao S.A.R (FDCT) under No. 0015/2019/AKP, 0123/2022/AFJ, and 0081/2022/A2. This work was carried out in part at SICC which is supported by SKL-IOTSC, University of Macau." + }, + { + "type": "page_footnote", + "bbox": [ + 0.5, + 0.875, + 0.892, + 0.9 + ], + "angle": 0, + "content": "2Available at: https://github.com/MIFPE/Efficient-Loss-Function." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "4063" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.115, + 0.47, + 0.198 + ], + "angle": 0, + "content": "[1] Samet Akçay, Mikolaj E Kundegorski, Michael Devereux, and Toby P Breckon. Transfer learning using convolutional neural networks for object classification within X-ray baggage security imagery. In 2016 IEEE International Conference on Image Processing (ICIP), pages 1057-1061. 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Many attack techniques have been proposed to evaluate the model's robustness. Gradient-based attacks suffer from severely overestimating the robustness. This paper identifies that the relative error in calculated gradients caused by floating-point errors, including floating-point underflow and rounding errors, is a fundamental reason why gradient-based attacks fail to accurately assess the model's robustness. Although it is hard to eliminate the relative error in the gradients, we can control its effect on the gradient-based attacks. Correspondingly, we propose an efficient loss function by minimizing the detrimental impact of the floating-point errors on the attacks. Experimental results show that it is more efficient and reliable than other loss functions when examined across a wide range of defence mechanisms. + +# 1. Introduction + +AI with deep neural networks (DNNs) as the core [24] has achieved great success in different research directions and has been widely used in many safety-critical systems, such as aviation [1,8,35], medical diagnosis [27, 49], self-driving [4,26,47], etc. However, a severe problem with current DNNs is that they are vulnerable to adversarial attacks. Adding human imperceptive perturbations to input data can mislead the model to output incorrect results [16, 45]. Such vulnerability poses a significant security risk to all DNN-based systems. Therefore, increasing the models' robustness and providing efficient and reliable evaluation methods are becoming increasingly urgent and vital. + +![](images/bda904398ffe2aa928830752bebe4d7f281be5f97d93bf99c2f5c0211310e755.jpg) +Figure 1. Comparison of the effectiveness of non-targeted and multi-targeted PGD 100 iterations attacks using various loss functions on the CIFAR-10 dataset. The best results were obtained from RobustBench using an ensemble attack with a minimum of 4900 iterations. The defence model is from [59]. + +Numerous defence strategies [6, 10, 13, 16, 29, 31, 55] to improve the model's robustness and many attacks [2, 29, 33, 41, 50, 52, 54, 59] to evaluate these strategies have been proposed. Currently, the most efficient attack method is known as white-box attack, where the attacker has complete knowledge of the target defending strategy, including its model architecture, parameters, detail of the training algorithm, dataset, etc. A typical example is Projective gradient descent (PGD) [29] for evaluating the model's robustness. However, studies have shown that PGD with cross-entropy (CE) loss fails to provide accurate evaluation results [6, 41] and significantly overestimates the model's robustness (Figure 1). To enhance the evaluation accuracy, recent powerful evaluation methods were proposed to ensemble diverse attack algorithms [10, 30]. However, their performance is at the cost of high computational overhead. + +The research community attributes the failure of gradient-based attacks to gradient masking [15]. The core of gradient masking is that the calculated gradients are not + +necessarily efficient in guiding the generation of adversarial examples. The causes of inefficient gradients may be related to floating-point errors or other factors. This paper reveals that the relative error in the gradients caused by floating-point errors is one of the fundamental reasons for the failure of gradient-based attacks, and the relative error is directly affected by the value of the difference of the first and second largest in logits(DFSL). Although it is hard to eliminate the relative error in the gradients caused by floating-point errors completely, we can control its effect on the gradient-based attacks. Thus, we propose a new efficient loss function by minimizing the impact of floating-point errors (MIFPE) on gradient-based attacks. To summarize, our main contributions are as follows: + +- We provide a comprehensive demonstration of how the presence of floating-point errors leads to the failure of gradient-based attacks due to the relative error in calculated gradients. +- We show that the floating-point rounding errors may lead to attack's failure due to growing relative errors as samples reach the classification boundary. +- We demonstrate that when the model's robustness is overestimated primarily due to floating-point errors, the loss function discarding partial elements of logits causes performance degradation in the gradient-based attack. +- We show that minimizing the impact of floating-point errors can improve the efficiency and accuracy of gradient-based attacks. +- Empirical results demonstrate that MIFPE tends to outperform the competing loss functions in terms of attack performance and computational efficiency. + +# 2. Preliminaries & Related Work + +We define the classification model as $f_{\theta}(\mathbf{x})$ , where $\pmb{\theta}$ represents the model parameters. $f_{\theta}:\mathbf{x}\subset \mathbb{R}^{C\times H\times W}\to$ $\mathbf{z}\subset \mathbb{R}^k$ is a classifier that maps input data $\mathbf{x}$ to output logits $\mathbf{z}$ ,where $C,H$ ,and $W$ are parameters that describe the input data's channel number, height, and width, respectively. Additionally, $K$ represents the number of classes from the model's output. We define the label of the input data as $y$ + +Attackers aim to breach defence strategies by generating adversarial examples $\hat{\mathbf{x}}$ , which can maximize the loss function $L(f_{\theta}(\hat{\mathbf{x}}),y)$ and deceive the model into producing incorrect results, arg max $f_{\theta}(\hat{\mathbf{x}})\neq y$ . Achieving this requires the attackers to find imperceptible perturbations $\delta = \hat{\mathbf{x}} -\mathbf{x}$ that satisfy the constraint $\| \delta \| p\leq \varepsilon$ , where $\varepsilon$ is the magnitude and $p$ is the norm of the perturbation. Various perturbation options have been explored in literature, including the one-pixel attack [44, 44], $l_{2}$ attacks [6, 31, 45], and $l\infty$ + +attacks [16, 29]. The attackers can find an adversarial example $\hat{\mathbf{x}} \in \mathcal{I}$ by maximizing the loss. This process can be formulated as: + +$$ +\hat {\mathbf {x}} = \mathbf {x} + \max _ {\| \delta \| _ {p} \in \varepsilon} L \left(f _ {\boldsymbol {\theta}} (\mathbf {x} + \delta), y\right), \tag {1} +$$ + +The white-box scenario is the most rigorous test for defence strategies, as attackers have complete knowledge about the models' architecture, parameters, training data, and algorithm implementation details. This is a highly challenging situation for defence strategies. Attackers can exploit nearly all vulnerabilities in the defence strategies and perform tailored attacks. If defence strategies remain robust against white-box attacks, they can ensure the system's security even in the worst-case scenario. In practice, the gradient-based method is commonly used to solve (1). + +Many gradient-based white-box attacks methods have been proposed, which include fast gradient-sign method (FGSM) [16], basic iterative method (BIM) [23], projected gradient descent (PGD) [29], momentum iterative method (MIM) [13] and fast adaptive boundary attack (FAB) [9] for $\ell_{\infty}$ -norm attacks. Carlini and Wagner (C&W) [6] and DeepFool [31] can additionally carry out $\ell_{2}$ -norm attacks. PGD is one of the widely used methods to evaluate the model's robustness in the white box scenario, which finds an adversarial example by performing the following iterative update: + +$$ +\hat {\mathbf {x}} _ {i + 1} = \mathcal {P} _ {\epsilon , \mathbf {x}} \left(\hat {\mathbf {x}} _ {i} + \alpha_ {i} \operatorname {s i g n} \left(\nabla_ {\hat {\mathbf {x}} _ {i}} \mathcal {L} ^ {\mathrm {c e}} \left(f _ {\boldsymbol {\theta}} \left(\hat {\mathbf {x}} _ {i}\right), y\right)\right)\right), \tag {2} +$$ + +Initially, $\hat{\mathbf{x}}_0 = \mathcal{P}_{\epsilon,\mathbf{x}}(\mathbf{x} + \mathbf{u})$ , where $\mathbf{u} \sim \mathcal{U}([- \epsilon, \epsilon])$ , i.e. $\mathbf{u}$ is a uniform random noise bounded by $[- \epsilon, \epsilon]$ . The function $\mathcal{P}_{\epsilon,\mathbf{x}}: \mathbb{R}^{C \times H \times W} \to \mathcal{I}$ first clips the range of its input into the $\epsilon$ -ball $\ell_p$ -distance neighbour of the original image $\mathbf{x}$ and then clips its input into the range of $\mathcal{I}$ . The term $\nabla_{\hat{\mathbf{x}}_i} \mathcal{L}^{\mathrm{ce}}(f_\theta(\hat{\mathbf{x}}_i), y)$ computes the gradient of the loss w.r.t. the input $\hat{\mathbf{x}}_i$ . Finally, $\alpha_i$ is the step size, and for each element in the tensor $g$ , $\operatorname{sign}(g)$ returns one of 1, 0 or -1, if the value is positive, zero or negative, respectively. + +CE is a commonly used loss function for training deep neural network models and evaluating their robustness in classification tasks. However, the presence of exponential operations in CE makes it vulnerable to underflow and rounding errors with limited floating-point precision. Gradient-based attacks with the CE loss may experience vanishing/inefficient gradients and difficulty converging while suffering from a severe overestimation of the model's robustness. [6, 10]. Recent attack methods use surrogate losses for gradient computation [6, 18] and optimize an alternative target by replacing $\mathcal{L}^{\mathrm{ce}}$ with a custom surrogate loss function. $\mathbf{z} = f_{\theta}(\hat{\mathbf{x}})$ is output logits of the model, and $\mathbf{z}_i$ is the $i^{\mathrm{th}}$ component of $\mathbf{z}$ , two typical examples to replace the CE objective include the difference-of-logits (DL) [6], also known as hinge loss, where $i \in \{1,2,\dots,K\}$ + +and $i\neq y$ + +$$ +\mathcal {L} ^ {\mathrm {c w}} (\mathbf {z}, \mathrm {y}) = - \mathbf {z} _ {y} + \max _ {i \neq y} \mathbf {z} _ {i}, \tag {3} +$$ + +and the difference-of-logits ratio (DLR) loss [10]: + +$$ +\mathcal {L} ^ {\mathrm {d l r}} (\mathbf {z}, \mathrm {y}) = \frac {- \mathbf {z} _ {y} + \max _ {i \neq y} \mathbf {z} _ {i}}{\mathbf {z} _ {\pi 1} - \mathbf {z} _ {\pi 3}}, \tag {4} +$$ + +where $\mathbf{z}_{\pi_1}$ and $\mathbf{z}_{\pi_3}$ respectively denote the $1^{\mathrm{th}}$ and $3^{\mathrm{th}}$ largest components of $\mathbf{z}$ . It is clear that maximizing the alternative goals is consistent with the original objective of making $\arg \max f(\hat{\mathbf{x}})\neq y$ . In addition, since surrogate losses avoid exponential operations, they are not prone to underflow, allowing gradient-based optimization to escape suffering from the overestimation caused by the floating-point underflow errors. However, the floating-point underflow errors are not the sole reason for all overestimations related to floating-point errors. At the same time, the new loss function discards some elements of $\mathbf{z}$ , reducing the effectiveness of the attack and causing gradient-based attacks with surrogate losses to overestimate the model's robustness. + +Many auxiliary techniques can assist existing attack methods to improve their performance. For example, momentum-based updates can improve the attack's convergence rate and are widely used by white-box attacks [13, 18]. A step schedule with decreasing step size based on the number of iterations can improve the overall success rate [10, 18, 56]. Multi-target attacks can outperform nontarget attacks in the evaluation results at the cost of more iterations since they require enumerating multiple most likely target labels [18, 33, 34]. In addition to the above strategies, multiple restarts can also improve the effectiveness of gradient-based attacks by adding different random initial perturbations to the input data to diversify the starting point of the attack and reduce the impact of suboptimal solutions [5, 46]. Finally, several recent publications have shown that leveraging latent features in attacks can enhance the transferability of black-box attacks [21, 22] and the performance of white-box attacks [56]. + +However, even with so many auxiliary strategies mentioned above, using any single attack is still challenging to accurately evaluate the model's robustness. Attackers start using an ensemble of multiple attack strategies to improve the attack's performance by introducing diversity [5,10,28]. They often suffer from high computational costs. Even though these ensemble strategies are more powerful than any single attack, they still fail to provide an assessment of the ensemble defence strategy's robustness accurately [48,57]. + +# 3. Efficient Loss Function + +Assuming that the input $\hat{\mathbf{x}}$ has the correct label $y$ , we compute $\mathbf{z} = f_{\theta}(\hat{\mathbf{x}})$ , where $\pmb{\theta}$ represents the model parameters. Next, we sort the values in $\mathbf{z}$ in a descending order, + +where $\mathbf{z}_{\pi 1}$ is the maximum value. We define $\Delta$ as the difference between the maximum and the second maximum value, i.e., $\Delta = \mathbf{z}_{\pi 1} - \mathbf{z}_{\pi 2} \geq 0$ . The cross-entropy loss at $\mathbf{z}$ becomes + +$$ +C E (\mathbf {z}, y) = - \log p _ {y} = - \log \frac {e ^ {\mathbf {z} _ {y} - \mathbf {z} _ {\pi 1}}}{\sum_ {i = 1} ^ {K} e ^ {\mathbf {z} _ {i} - \mathbf {z} _ {\pi 1}}}, \tag {5} +$$ + +$$ +\begin{array}{l} \nabla_ {\hat {\mathbf {x}}} C E (\mathbf {z}, y) = (- 1 + p _ {y}) \nabla_ {\hat {\mathbf {x}}} \left(\mathbf {z} _ {y} - \mathbf {z} _ {\pi 1}\right) \\ + \sum_ {i \neq y} p _ {i} \nabla_ {\hat {\mathbf {x}}} \left(\mathbf {z} _ {i} - \mathbf {z} _ {\pi 1}\right), \tag {6} \\ \end{array} +$$ + +where $p_i = e^{\mathbf{z}_i - \mathbf{z}_{\pi 1}} / \sum_{j = 1}^{K}e^{\mathbf{z}_j - \mathbf{z}_{\pi 1}}$ $i\in \{1,2,3,\dots,K\}$ + +Exponential operations in Equation (5), specifically $e^{\mathbf{z}_{\pi i} - \mathbf{z}_{\pi 1}},i\in \{2,\dots,K\}$ , where $\mathbf{z}_{\pi i} - \mathbf{z}_{\pi 1}\leq \mathbf{z}_{\pi 2} - \mathbf{z}_{\pi 1} =$ $-\Delta \leq 0$ , can cause floating-point underflow errors in the CE loss gradient. To investigate this issue, we analyze the properties of $e^{-\Delta}$ and observe that when $\Delta$ surpasses a threshold value denoted by $\lambda$ $e^{-\Delta}$ underflows and leads to significant inaccuracies in the gradient calculation. Specifically, when $\Delta \geq \lambda$ and $\mathbf{z}_y = \mathbf{z}_{\pi 1}$ , the predicted probability $p_{y} = 1$ and the calculated gradient $\nabla_{\hat{\mathbf{x}}}CE(\mathbf{z},y) = 0$ The value of $\lambda$ varies with different floating-point arithmetic precisions, with approximate values of 16.64, 103.28, and 744.44 for half-precision, single-precision, and double-precision, respectively. + +Based on the findings, we identify that the root cause of the calculated gradient being equal to zero is the result of $\Delta$ exceeding $\lambda$ . To further investigate the relationship between the value of $\Delta$ and the overestimation of the model's robustness, we analyze the distribution of $\Delta$ values in defence models that tend to be overestimated by gradient-based attacks under single-precision. The results in Figure 2 indicate that the range of $\Delta$ values varies significantly among different defence models. Notably, the values of $\Delta$ in 2a and 2b do not exceed 10, which is significantly smaller than $\lambda \approx 103.28$ for single-precision. As a result, these models do not suffer from floating-point underflow errors. In contrast, most of the $\Delta$ values in 2c exceed the threshold that leads to floating-point underflow errors. It is evident that not all models suffer from floating-point underflow errors, and other reasons associated with floating-point errors cause gradient-based attacks to fail. This is because in addition to floating-point underflow errors, floating-point errors have another component: floating-point rounding errors when $\Delta < \lambda$ . These errors result in a non-negligible relative error in $\nabla_{\hat{\mathbf{x}}}CE(\mathbf{z},y)$ . We define the relative error as $\delta_{CE} = \delta (\nabla_{\hat{\mathbf{x}}}CE(\mathbf{z},y))$ . + +We know that $\delta_{CE} = 100\%$ when $\Delta \geq \lambda$ . We need to further analyze the change pattern of $\delta_{CE}$ when $\Delta < \lambda$ . A multi-iteration gradient-based attack involves adding perturbations to $\hat{\mathbf{x}}$ at each iteration, leading to constant changes in $\mathbf{z}$ , $\Delta$ , and $\nabla_{\hat{\mathbf{x}}}(\mathbf{z}_{\pi i} - \mathbf{z}_{\pi 1})$ for $i \in 1,2,\dots,K$ after each + +![](images/0ab137cb715c73ef94d939c8cfc537e53e3b472c0f632faa1eb2558a518b75bb.jpg) +(a) The $\Delta$ distribution of [33] + +![](images/eec3ef563842dce2633a4eae2a74f3696a65dda253ce5c4a87a006c78c6d6471.jpg) +(b) The $\Delta$ distribution of [59] + +![](images/7f86c89dec6dd32c29c06404bf30c2c6852b0e052e60bde1251996165148457b.jpg) +(c) The $\Delta$ distribution of [3] + +modification. This makes it difficult to analyze how $\delta_{CE}$ changes when $\Delta < \lambda$ . However, we can indirectly examine the effect of floating-point errors on the attack's performance by analyzing the impact of such errors on a single step. To do so, we introduce a scaling factor $c$ and define the scaled value of $\Delta$ as $T = c\Delta$ . By varying $c$ while keeping $\hat{\mathbf{x}}$ , $\mathbf{z}$ , and $\nabla_{\hat{\mathbf{x}}}(\mathbf{z}_{\pi i} - \mathbf{z}_{\pi 1})$ fixed during gradient calculation, we can investigate the relationship between $\delta_{CE}$ and $T$ for different values of $T$ . + +To compute the scale factor, we need to detach the gradient information from $\Delta$ since $\mathbf{z}$ contains the gradient information during the actual program running. Thus, we define the scale factor as $c = T / \Delta_{\mathrm{detach}}$ . The use of the detach operation in the calculation of $c$ removes the gradient information from the $\Delta_{\mathrm{detach}}$ , making it distinct from the $\Delta$ that retains gradient information. When $\mathbf{z}_y \neq \mathbf{z}_{\pi 1}$ , the model output is already incorrect. Therefore, we only focus on the relationship between $\delta_{CE}$ and $T$ when $\mathbf{z}_y = \mathbf{z}_{\pi 1}$ , at which point $\nabla_{\hat{\mathbf{z}}}CE(c\mathbf{z},y) = c\sum_{i \neq y}p_i^c\nabla_{\hat{\mathbf{x}}}(\mathbf{z}_i - \mathbf{z}_{\pi 1})$ , where $p_i^c = e^{c(\mathbf{z}_i - \mathbf{z}_{\pi 1})} / \sum_{j=1}^{K}e^{c(\mathbf{z}_j - \mathbf{z}_{\pi 1})}$ . + +To get a more intuitive picture of the relationship between $\delta_{CE}$ and $T$ , we plotted the figure of $\delta_{CE}$ on the binary classification task with $K = 2$ . At this point, $\nabla_{\hat{\mathbf{z}}}CE(\mathbf{cz},y) = c\sum_{i\neq y}p_i^c\nabla_{\hat{\mathbf{x}}}\left(\mathbf{z}_i - \mathbf{z}_{\pi 1}\right) = cp_2^c\nabla_{\hat{\mathbf{x}}}\left(\mathbf{z}_{\pi 2} - \mathbf{z}_{\pi 1}\right)\propto cp_2^c$ . Therefore, $\delta_{CE}\propto \delta (cp_2^c)$ . In Figure 3, we can see that for the same $\hat{\mathbf{x}}$ , when $\mathbf{z}$ and $\nabla_{\hat{\mathbf{x}}}\left(\mathbf{z}_i - \mathbf{z}_{\pi 1}\right)$ , $i\in \{1,2,\dots,K\}$ are all fixed, $\delta_{CE}$ varies with $T$ . When $T\geq \lambda$ , $\delta_{CE} = 100\%$ In contrast, When $T < \lambda$ , The relative error $\delta_{CE}$ caused by the floating-point rounding errors is much more minor, varies continuously with T, and reaches the minimum when $T$ is approximately 1. But one thing that needs to be highlighted is that after the relative error reaches the minimum, it starts to increase as $T$ gets closer to 0. + +Following the same operation, we add a scale factor $c$ to $\Delta$ and hold $T = c\Delta$ constant during each iteration of the + +![](images/d95af38b41c36f9eb37c4797d3eab35679b7ce2f952d071ecd6328714713887a.jpg) +Figure 2. The distributions of $\Delta = \mathbf{z}_{\pi 1} - \mathbf{z}_{\pi 2}$ for the defending models on the CIFAR-10 dataset are averaged across 100 bins. +Figure 3. The relative error of the gradient information computed using half-precision floating-point operations on a binary classification task with the CE loss varies with $T$ for a given adversarial example within a single iteration. + +multi-iteration attack. This technique, which we refer to as FT-PGD, allows us to assess the model's robustness with a fixed $T$ value. In Figure 4, we evaluate the model's robustness using FT-PGD at various $T$ values. By comparing the relative floating-point error in Figure 3 with the attack's performance in Figure 4, we observe a strong correlation between the relative error $\delta_{CE}$ and the attack's effectiveness. Thus, the relative error is a critical factor that contributes to overestimating the model's robustness. Furthermore, we identify two distinct phases in the impact of floating-point errors on gradient-based attacks due to the CE loss, which depend on the relationship between $T$ and $\lambda$ . + +(a) The attack failed due to floating-point underflow errors. When $T \geq \lambda$ , floating-point underflow causes the calculated gradient equal to zero and $\delta_{CE} = 100\%$ . As a result, the input perturbation becomes zero, and the model's robustness is measured to be equal to its clean accuracy, which leads to a significant overestimation of the model's robustness. + +![](images/b0b8ab6948caca79330c28616c95877a9f7f6cf30e7bcee041befb84223822f3.jpg) +Figure 4. A higher zero ratio, which represents the proportion of zero elements in the perturbation, leads to larger overestimations when evaluating model robustness. We assess model robustness using 100 iterations of FT-PGD with CE loss on the CIFAR-10 dataset under half-precision floating-point arithmetic. The model is obtained from [59]. + +(b) The attack's performance fluctuates with the small relative error caused by floating-point rounding errors. When $0 \leq T < \lambda$ , the computed gradient's relative error due to the floating-point rounding error is small and has the same variation pattern as the zero ratio and attack performance. The smallest relative error occurs around $T = 1$ . However, it's crucial to note that at the bottom left of Figure 3 and Figure 4, the relative error and its detrimental effect on the gradient-based attack increase as $T$ approaches zero after reaching the minimum. + +It is straightforward to assume that since floating-point errors cause the above problem, it should be possible to solve the problem by simply increasing the precision of floating-point arithmetics because it can effectively reduce the floating-point errors. To test whether this simple idea works, we evaluated the impact of different floating-point arithmetics precisions, including half-precision, single-precision, and double-precision, on the model's robustness against FT-PGD with 100 iterations. As depicted in Figure 5, the attack's performance exhibits a similar variation pattern across different precisions, and the model's robustness measured with PGD remains nearly unchanged. While increasing the floating-point precision can delay attack failure due to floating-point underflow errors, it incurs significant computational overhead. Therefore, increasing the floating-point precision is not a viable solution to address the problem. + +Surrogate loss functions(3,4) have been proposed [6, 10, 18] to work around floating-point underflow errors. They avoid suffering from floating-point underflow errors by discarding softmax operations. At the same time, they only use partial $\mathbf{z}$ elements in the new loss function. To demonstrate the effect of discarding elements of $\mathbf{z}$ on the attack's performance, We designed an experiment to make only a fixed + +![](images/c9c9e888fdb5a71a6da290d8d2d9f7340e414777a2ac14d5de2eca4cedead01b.jpg) +Figure 5. The model's robustness test results on the CIFAR-10 dataset under Float16, Float32, and Float64 follow a similar pattern of variation, except that the thresholds that lead to the attack's failure are different, the model obtained from [59]. + +number of $\mathbf{z}$ elements participate in the calculation of the gradients by exploiting floating-point underflow errors. To achieve this goal we scale the logits $\mathbf{z}_{\pi 1} - \mathbf{z}_{\pi i}$ by a scale factor $c$ to make $c(\mathbf{z}_{\pi 1} - \mathbf{z}_{\pi i}) = \lambda$ , such that $p_{\pi j}^{c} = 0$ if $j \geq i$ and $p_{\pi j}^{c} > 0$ if $j < i$ , where $i \in \{2,3,\dots,K\}$ and $j \in \{1,2,3,\dots,K\}$ . So that only $i - 1$ number of $\mathbf{z}$ elements are involved in the gradient calculation, thus giving PGD the ability to attack the network with a fixed number of $\mathbf{z}$ elements, which we now call FNZ-PGD. We use FNZ-PGD with different numbers of $\mathbf{z}$ elements to evaluate the model's robustness which is overestimated mainly due to floating-point errors. From Figure 6, we can see that the more $\mathbf{z}$ elements involved in the attack, the more potent the attack will be. So discarding the $\mathbf{z}$ element in the loss function will impair the attack's performance when model robustness is overestimated mainly due to floating-point errors. + +In summary, the relative error in the calculated gradients due to the floating-point errors, which include floating-point underflow errors and floating-point rounding errors, is the critical factor contributing to the overestimation of the model's robustness. While floating-point errors are a primary cause of gradient-based attacks' failure, they are not the sole cause. Reducing their impact can only address the portion of model robustness that is overestimated due to them. Therefore, it is unrealistic to expect that solely reducing the impact of floating-point errors alone will eliminate all problems related to overestimating model robustness. + +Although we cannot eliminate the relative error in the gradients caused by floating-point errors, we can control it's side effect and significantly increase the power of gradient-based attacks. As a result, we propose the Minimize the impact of floating-point errors (MIFPE) loss, a small modification to the original CE loss, which scales the logits adaptively before the softmax operation. For untargeted and tar + +![](images/694ce9b0c918646cac4415f771ff25ccb1d1c3c6cb15b66c232525d0946a79e7.jpg) +Figure 6. Using more $\mathbf{z}$ elements increases attack potency when model robustness is overestimated mainly due to floating-point errors. We utilized FNZ-PGD with 100 iterations, CE loss, and a baseline of PGD-100 with CE, C&W, and DLR loss under CIFAR10. All floating-point operations were single-precision, and the model was obtained from [59]. Here, $n$ refers to the number of $\mathbf{z}$ elements used. + +geted attacks, the targets are as follows respectively: + +$$ +\mathcal {L} ^ {\mathrm {M I F P E}} (\mathbf {z}, y) \triangleq \mathcal {L} ^ {\mathrm {c e}} \left(T \mathbf {z} / \Delta_ {\text {d e t a c h}}, y\right), \tag {7} +$$ + +$$ +\mathcal {L} _ {\text {t a r g e t}} ^ {\mathrm {M I F P E}} \left(\mathbf {z}, y _ {\mathrm {t}}\right) = - \mathcal {L} ^ {\mathrm {c e}} \left(T \mathbf {z} / \Delta_ {\text {d e t a c h}}, y _ {\mathrm {t}}\right), \tag {8} +$$ + +Where $y_{t}$ is a predefined class target, $t \in \{1, 2, \dots, K\}$ and $y_{t} \neq y$ . In our experiments, the factor $T$ was set to around 1 to minimize the detrimental effect of floating-point errors on the gradient-based attacks. + +The new surrogate loss $\mathcal{L}^{\mathrm{MIFPE}}$ has fourfold advantages. First, it can eliminate the failure of gradient-based attacks due to floating-point underflow errors. Second, it can minimize the impact of the small relative error due to floating-point rounding errors and significantly improve the performance of gradient-based attacks. Third, it provides the flexibility to adjust the number of logit elements involved in the attack simply by changing the value of T. Finally, unlike the C&W or DLR loss, it still represents the original CE loss faithfully, and all values in the logit vector can still contribute to the gradient calculation. + +# 4. Experiments + +To ensure a fair comparison against other loss functions in our evaluation and to make our evaluation as comprehensive as possible, we conducted tests on different threat models and datasets. Specifically, we tested the $\ell_{\infty}$ -norm bounded perturbation on the CIFAR-10, CIFAR-100, MNIST [25] and ImageNet datasets [11], and the $\ell_{2}$ -norm threat model on the CIFAR-10 dataset. For each test, we ran the PGD with different loss functions, including the cross-entropy (CE) loss function, the C&W loss function [6], the DLR loss function [10], and our proposed MIFPE. We kept + +all other settings the same across the tests. Firstly, we used 100 iterations for each test. Secondly, we adopted the same step-size schedule with a linear decay [56], which updates the perturbation boundary $\epsilon$ at each iteration $i$ according to the formula $2\epsilon (1 - i / I)$ , where $I$ denotes the total number of iterations. Thirdly, we employed momentum-based updates [10] with a momentum factor of $\nu = 0.75$ for all tests. Lastly, we saved the best adversarial examples generated during the attack. To demonstrate the effectiveness of MIFPE in achieving near-state-of-the-art robustness with only 100 iterations, we compare our results with the best robust accuracy reported on RobustBench1, which uses an ensemble of attacks and a minimum of 4900 iterations. We also compared the attack performance of MIFPE with GAMA_PGD [43] under the same 100-iteration constraint. + +In Table 1, we present a comprehensive comparison showing that MIFPE outperforms CE, C&W, and DLR loss functions on all tested models. Additionally, we found that when PGD with momentum and step schedule using MIFPE as the loss function outperforms GAMA_PGD on all tested models by at least more than $0.1\%$ under 100 iterations constraint, which is impossible when PGD with momentum and step schedule using CE, C&W and DLR as the loss function. Remarkably, even with only 100 iterations, MIFPE achieves results that are very close to the best results obtained with at least 4900 iterations on some models, such as Uncovering limits [17] and Proper definition [32] for CIFAR10, $l_{\infty}$ , $\varepsilon = 8/255$ . Our findings also reveal that C&W and DLR perform even worse than CE in some cases, such as on Robustness library [14] and Fast adversarial training [51] for CIFAR10, $l_{\infty}$ , $\varepsilon = 8/255$ . This suggests that discarding partial logit elements in the loss function would decrease the effectiveness of gradient-based attacks. + +Faster convergence. We want to highlight that the effectiveness of MIFPE is not achieved by increasing the computational cost compared to other loss functions. We found that minimising the effect of the floating-point errors leads to faster convergence speed than competing loss functions. Figure 7 shows that for all two defending models, MIFPE loss performs more efficiently, and often with orders of magnitude faster than other loss functions for successful attacks. Finally, minimising the effect of floating-point error operation introduces no overhead and imposes no impact on the iteration time. + +Boost the capability of existing attack strategies. Because MIFPE is a loss function, it can be easily integrated with existing attack strategies by replacing the original loss function. The results in Table 2 show that using MIFPE boosts the attack's effectiveness. + +Ablation analysis. Our ablation experiments, presented in Table 3, investigated the effect of momentum and step-size schedule on PGD using different loss functions with 100 iterations. The results show that the MIFPE consist + +Table 1. Comparing the proposed MIFPE loss $(\mathcal{L}^{\mathrm{MIFPE}})$ , against CE $(\mathcal{L}^{\mathrm{ce}})$ , C&W $(\mathcal{L}^{\mathrm{cw}})$ , and DLR $(\mathcal{L}^{\mathrm{dlr}})$ losses. For each surrogate loss, we use PGD-100 with the step-size schedule $2\epsilon (1 - i / I)$ and momentum $\nu = 0.75$ . Models marked with $\dagger$ were trained with extra data. Models marked with $\ddagger$ , which used $\varepsilon = 0.031$ as originally reported by the authors. Numbers in parentheses indicate the improvement w.r.t. the CE baseline. The best, calculated using an ensemble of attacks and a minimum of 4900 iterations, is reported from RobustBench1 to demonstrate how closely MIFPE can approach the lowest known robustness accuracy with only 100 iterations. + +
Defense methodArchitectureCleanCE (Lce)100C&W (Lcw)100DLR (Ldir)100GAMA_PGD100MIFPE (LMIFPE)100Best4900
MNIST, ℓ∞, ε = 0.3
Uncovering limits [17]WRN-28-1099.2696.5596.64(+0.09)96.71(+0.16)96.69(+0.14)96.53(-0.02)96.31
MMA training [12]†LeNet5Madry98.9895.6695.60(-0.06)95.56(-0.10)95.96(+0.13)95.50(-0.16)93.51
MMA training [12]LeNet5Madry98.9595.0995.33(+0.24)95.59(+0.50)95.74(+0.19)94.88(-0.21)91.40
Neural level sets [3]SmallCNN99.3599.2894.68(-4.60)95.09(-4.19)99.29(+0.01)94.67(-4.61)90.85
TRADES [59]SmallCNN99.4893.6993.88(+0.19)94.49(+0.80)93.82(+0.13)93.67(-0.02)92.71
Robust optimization [29]SmallCNN99.3593.0693.19(+0.13)93.63(+0.57)93.39(+0.33)92.88(-0.18)90.85
Fast adversarial training [51]SmallCNN98.5086.8286.96(+0.14)87.42(+0.60)87.62(+0.80)86.57(-0.25)82.93
CIFAR-10, ℓ∞, ε = 8/255
Uncovering limits [17]†WRN-70-1691.1067.9666.70(-1.26)66.78(-1.18)66.08(-1.88)65.96(-2.00)65.87
Fixing data augmentation [36]WRN-106-1688.5067.5765.55(-2.02)65.61(-1.96)64.94(-2.63)64.75(-2.82)64.58
Fixing data augmentation [36]WRN-70-1688.5467.2765.23(-2.04)65.32(-1.95)64.57(-2.70)64.46(-2.81)64.20
Proper definition [32]WRN-70-1689.0166.6663.94(-2.72)64.01(-2.65)63.65(-3.01)63.49(-3.17)63.35
Uncovering limits [17]†WRN-28-1089.4865.5963.62(-1.97)63.82(-1.77)63.05(-2.90)62.96(-2.63)62.76
Proper definition [32]WRN-28-1088.6164.6661.55(-3.11)61.62(-3.04)61.19(-3.47)61.12(-3.54)61.04
Adversarial weight perturbation [53]†WRN-28-1088.2563.1860.51(-2.67)60.60(-2.58)60.18(-3.00)60.09(-3.09)60.04
Unlabeled data [7]†WRN-28-1089.6961.6060.47(-1.13)60.67(-0.93)59.82(-1.78)59.72(-1.88)59.53
HYDRA [40]†WRN-28-1088.9859.5358.21(-1.32)58.30(-1.23)57.52(-2.01)57.38(-2.15)57.14
Misclassification-aware [50]WRN-28-1087.5061.6058.03(-3.57)58.73(-2.87)57.20(-4.40)56.88(-4.72)56.29
Pre-training [19]†WRN-28-1087.1157.0756.27(-0.80)57.07(0.00)55.22(-1.85)55.10(-1.97)54.92
Hypersphere embedding [33]WRN-34-2085.1461.4355.35(-6.08)56.21(-5.22)54.37(-7.06)53.85(-7.58)53.74
Overfitting [37]WRN-34-2085.3456.8555.22(-1.63)55.97(-0.88)53.87(-2.98)53.62(-3.23)53.42
Self-adaptive training [20]‡WRN-34-1083.4856.1254.30(-1.82)54.73(-1.39)53.64(-2.48)53.48(-2.64)53.34
TRADES [59]‡WRN-34-1084.9255.2153.94(-1.27)54.11(-1.10)53.38(-1.83)53.22(-1.99)53.08
Robustness library [14]RN-5087.0351.5652.07(+0.51)52.81(+1.25)50.04(-1.52)49.84(-1.72)49.25
Neural level sets [3]‡RN-1881.3079.1240.07(-39.05)45.10(-34.02)79.69(+0.57)40.06(-39.06)39.77
YOPO [58]WRN-34-1087.2046.0547.02(+0.97)47.55(+1.50)45.30(-0.75)45.19(-0.86)44.83
Fast adversarial training [51]RN-1883.3445.7545.81(+0.06)46.89(+1.14)43.71(-2.04)43.57(-2.18)43.21
CIFAR-10, ℓ∞, ε = 8/255
Adversarial weight perturbation [54]WRN-34-1060.3833.0930.74(-2.35)31.13(-1.96)29.44(-3.65)29.35(-3.74)28.86
Pre-training [19]†WRN-28-1059.2332.8230.58(-2.24)31.83(-0.99)29.22(-3.60)29.02(-3.80)28.42
Progressive Hardening [42]WRN-34-1062.8226.1826.69(+0.51)27.26(+1.08)24.97(-1.21)24.91(-1.27)24.57
Overfitting [37]RN-1853.8320.4720.17(-0.30)20.30(-0.17)19.20(-1.27)19.16(-1.31)18.95
ImageNet, ℓ∞, ε = 4/255
Transfer Better [39]RN-5064.0238.4437.26(-1.18)37.72(-0.72)34.94(-3.50)34.84(-3.60)34.96
Robustness library [14]RN-5062.5632.1632.24(+0.08)32.80(+0.64)29.72(-2.44)29.60(-2.56)29.22
Transfer Better [39]RN-1852.9229.3027.14(-2.16)27.40(1.90)25.56(-3.74)25.40(-3.90)18.95
CIFAR-10, ℓ2, ε = 0.5
Uncovering limits [17]†WRN-70-1694.7481.7180.93(-0.78)80.94(-0.77)87.74(+6.03)80.57(-1.14)80.53
Uncovering limits [17]WRN-70-1690.9075.2074.89(-0.31)74.95(-0.25)81.78(+6.58)74.56(-0.64)74.50
Adversarial weight perturbation [54]WRN-34-1088.5174.7773.88(-0.89)73.89(-0.88)79.38(+4.61)73.67(-1.10)73.66
Robustness library [14]RN-5090.8369.6570.13(+0.48)70.25(+0.60)78.15(+8.50)69.29(-0.36)69.24
Overfitting [37]RN-1888.6768.6668.74(+0.08)69.03(+0.37)76.19(+7.53)67.87(-0.79)67.68
Decoupling direction and norm [38]WRN-28-1089.0566.5667.00(+0.44)67.02(+0.46)74.61(+8.05)66.48(-0.08)66.44
MMA training [12]WRN-28-488.0266.2266.58(+0.36)66.60(+0.38)71.44(+5.22)66.16(-0.06)66.09
+ +tently outperforms the other loss functions, and shows the least variance across different setups. These findings suggest that the effectiveness of the MIFPE should not be dependent on the momentum and step-size schedule. + +To analyze the reasons for the failure of the attack due to floating-point rounding errors, we selected $\mathbb{Z} = \mathbf{z}_y - \max_{i\neq y}\mathbf{z}_i$ because its sign indicates if the attack is successful or not. We compared the change of $\mathbb{Z}$ for samples + +attacked by PGD-100 with CE loss but failed, and PGD-100 with MIFPE loss and succeeded. Figure 8 demonstrates that for samples attacked with CE loss, the value of $\mathbb{Z}$ rapidly approaches 0 in the first few iterations and then remains positive afterwards. On the other hand, when attacked with MIFPE loss $\mathbb{Z}$ smoothly drops below 0 after approaching 0. This phenomenon suggests that the floating-point rounding error primarily may cause attack failure when the samples + +![](images/22f4e9b5f5dc78cafba4055356ed916a85bf9b502249809575bea5b1b69f8a15.jpg) +Figure 7. We compare MIFPE to standard CE loss and other surrogate loss functions (C&W [6] and DLR [10]) on defenders [58,59]. The graph shows iterations on the horizontal axis and the percentage of unsuccessful examples on the vertical axis. + +![](images/4175ca8ed00fddb62a84ad39eadc7f4a91c86d20fcccdec3b45b11f3d9169ad1.jpg) +Figure 8. The changing process of the value of $\mathbb{Z} = \mathbf{z}_y - \max_{i\neq y}\mathbf{z}_i$ with the number of iterations during the attack on the CIFAR10 dataset using the model from TRADES [59] and single-precision arithmetic. The horizontal axes show the number of iterations used so far, and the vertical axes show the value of $\mathbb{Z}$ . + +Table 2. The comparison of attack performances for FGSM [16], PGD [29], APGD_DLR [10] and AA [10] using original loss functions versus MIFPE loss on CIFAR10 dataset and $\varepsilon = 0.031$ with the model obtained from TRADES [59]. with the $\nabla$ row representing the improvement achieved with MIFPE. + +
Attack +iterationFGSM +1PGD +100APGD_DLR +100AA +4900
Original +MIFPE79.8379.7945.9040.22
49.7640.0640.4939.89
V30.0739.735.410.33
+ +Table 3. Ablation study on the effect of momentum and step-size schedule on the PGD with different loss functions and under 100 iterations on CIFAR10 dataset with the model obtained from Neural level sets [3]. New components are added in consecutive rows. + +
Accuracy under attack(%)Loss Function
CEC&WDLRMIFPE
PGD55.4654.2354.3953.42
+Momentum55.2554.0254.1853.23
+Step-size schedule55.2153.9454.1153.22
+ +become close to the classification boundary due to the relative error and its detrimental effect on the gradient-based attack would increase as $T$ approaches zero after reaching the minimum. + +# 5. Conclusion + +This paper reveals that relative error in calculated gradient caused by floating-point errors is a fundamental reason why gradient-based attacks fail to accurately evaluate the model's robustness. To efficiently and accurately evaluate the model's robustness, we introduce MIFPE, a new loss function that minimises the impact of floating-point errors on gradient-based attacks. Compared with other loss functions, MIFPE enjoys higher accuracy and faster convergence speed. Moreover, we find several surprising ob + +![](images/e183c12478a4a3af2f7b4e348fc6bede55785c12f70708d0e56269976073adee.jpg) + +servations related to adversarial attacks: (1)Discarding partial elements of logits in the loss will impair the attack's performance; (2)The floating-point rounding errors lead to the attack's failure by causing an increasing relative error as the samples get closer to the classification boundary; (3)Increasing the precision of floating-point arithmetic cannot solve the problem of overestimating the model's robustness caused by floating-point errors, etc. We hope that the above observations will help discover more efficient and reliable loss functions in the future. Finally, MIFPE is open source with reproducible results2. + +# Acknowledgments + +This work is supported in part by Science and Technology Development Fund of Macao S.A.R (FDCT) under No. 0015/2019/AKP, 0123/2022/AFJ, and 0081/2022/A2. 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In ICML, 2019, 1, 4, 5, 6, 7, 8 \ No newline at end of file diff --git a/2023/Efficient Loss Function by Minimizing the Detrimental Effect of Floating-Point Errors on Gradient-Based Attacks/images.zip b/2023/Efficient Loss Function by Minimizing the Detrimental Effect of Floating-Point Errors on Gradient-Based Attacks/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..1a288c4fe8fd0199f85c6f8bf9cecc31aa3a103e --- /dev/null +++ b/2023/Efficient Loss Function by Minimizing the Detrimental Effect of Floating-Point Errors on Gradient-Based Attacks/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:87348a825743215438de9c5c2376d483b927307b6e7524439881b9c1716662b0 +size 675165 diff --git a/2023/Efficient Loss Function by Minimizing the Detrimental Effect of Floating-Point Errors on Gradient-Based Attacks/layout.json b/2023/Efficient Loss Function by Minimizing the Detrimental Effect of Floating-Point Errors on Gradient-Based Attacks/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..9aa0f3d64699ff0ff1c1990ebaffc4822fcfc117 --- /dev/null +++ b/2023/Efficient Loss Function by Minimizing the Detrimental Effect of Floating-Point Errors on Gradient-Based Attacks/layout.json @@ -0,0 +1,10387 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 54, + 102, + 541, + 138 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 54, + 102, + 541, + 138 + ], + "spans": [ + { + "bbox": [ + 54, + 102, + 541, + 138 + ], + "type": "text", + "content": "Efficient Loss Function by Minimizing the Detrimental Effect of Floating-point Errors on Gradient-based Attacks" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 80, + 161, + 283, + 218 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 80, + 161, + 283, + 218 + ], + "spans": [ + { + "bbox": [ + 80, + 161, + 283, + 218 + ], + "type": "text", + "content": "Yunrui Yu \nDepartment of Computer Science \nState Key Lab of IOTSC \nUniversity of Macau, Macau SAR, China." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 135, + 220, + 230, + 231 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 135, + 220, + 230, + 231 + ], + "spans": [ + { + "bbox": [ + 135, + 220, + 230, + 231 + ], + "type": "text", + "content": "yb97445@um.edu.mo" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 310, + 161, + 514, + 217 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 310, + 161, + 514, + 217 + ], + "spans": [ + { + "bbox": [ + 310, + 161, + 514, + 217 + ], + "type": "text", + "content": "Cheng-Zhong Xu* \nDepartment of Computer Science \nState Key Lab of IOTSC \nUniversity of Macau, Macau SAR, China." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 371, + 220, + 449, + 230 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 371, + 220, + 449, + 230 + ], + "spans": [ + { + "bbox": [ + 371, + 220, + 449, + 230 + ], + "type": "text", + "content": "czxu@um.edu.mo" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 143, + 258, + 192, + 272 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 258, + 192, + 272 + ], + "spans": [ + { + "bbox": [ + 143, + 258, + 192, + 272 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 284, + 290, + 499 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 284, + 290, + 499 + ], + "spans": [ + { + "bbox": [ + 46, + 284, + 290, + 499 + ], + "type": "text", + "content": "Attackers can deceive neural networks by adding human imperative perturbations to their input data; this reveals the vulnerability and weak robustness of current deep-learning networks. Many attack techniques have been proposed to evaluate the model's robustness. Gradient-based attacks suffer from severely overestimating the robustness. This paper identifies that the relative error in calculated gradients caused by floating-point errors, including floating-point underflow and rounding errors, is a fundamental reason why gradient-based attacks fail to accurately assess the model's robustness. Although it is hard to eliminate the relative error in the gradients, we can control its effect on the gradient-based attacks. Correspondingly, we propose an efficient loss function by minimizing the detrimental impact of the floating-point errors on the attacks. Experimental results show that it is more efficient and reliable than other loss functions when examined across a wide range of defence mechanisms." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 522, + 128, + 534 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 522, + 128, + 534 + ], + "spans": [ + { + "bbox": [ + 47, + 522, + 128, + 534 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 542, + 287, + 685 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 542, + 287, + 685 + ], + "spans": [ + { + "bbox": [ + 46, + 542, + 287, + 685 + ], + "type": "text", + "content": "AI with deep neural networks (DNNs) as the core [24] has achieved great success in different research directions and has been widely used in many safety-critical systems, such as aviation [1,8,35], medical diagnosis [27, 49], self-driving [4,26,47], etc. However, a severe problem with current DNNs is that they are vulnerable to adversarial attacks. Adding human imperceptive perturbations to input data can mislead the model to output incorrect results [16, 45]. Such vulnerability poses a significant security risk to all DNN-based systems. Therefore, increasing the models' robustness and providing efficient and reliable evaluation methods are becoming increasingly urgent and vital." + } + ] + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 313, + 264, + 539, + 395 + ], + "blocks": [ + { + "bbox": [ + 313, + 264, + 539, + 395 + ], + "lines": [ + { + "bbox": [ + 313, + 264, + 539, + 395 + ], + "spans": [ + { + "bbox": [ + 313, + 264, + 539, + 395 + ], + "type": "image", + "image_path": "bda904398ffe2aa928830752bebe4d7f281be5f97d93bf99c2f5c0211310e755.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 403, + 547, + 460 + ], + "lines": [ + { + "bbox": [ + 305, + 403, + 547, + 460 + ], + "spans": [ + { + "bbox": [ + 305, + 403, + 547, + 460 + ], + "type": "text", + "content": "Figure 1. Comparison of the effectiveness of non-targeted and multi-targeted PGD 100 iterations attacks using various loss functions on the CIFAR-10 dataset. The best results were obtained from RobustBench using an ensemble attack with a minimum of 4900 iterations. The defence model is from [59]." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 483, + 547, + 675 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 483, + 547, + 675 + ], + "spans": [ + { + "bbox": [ + 304, + 483, + 547, + 675 + ], + "type": "text", + "content": "Numerous defence strategies [6, 10, 13, 16, 29, 31, 55] to improve the model's robustness and many attacks [2, 29, 33, 41, 50, 52, 54, 59] to evaluate these strategies have been proposed. Currently, the most efficient attack method is known as white-box attack, where the attacker has complete knowledge of the target defending strategy, including its model architecture, parameters, detail of the training algorithm, dataset, etc. A typical example is Projective gradient descent (PGD) [29] for evaluating the model's robustness. However, studies have shown that PGD with cross-entropy (CE) loss fails to provide accurate evaluation results [6, 41] and significantly overestimates the model's robustness (Figure 1). To enhance the evaluation accuracy, recent powerful evaluation methods were proposed to ensemble diverse attack algorithms [10, 30]. However, their performance is at the cost of high computational overhead." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 677, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 677, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 305, + 677, + 547, + 715 + ], + "type": "text", + "content": "The research community attributes the failure of gradient-based attacks to gradient masking [15]. The core of gradient masking is that the calculated gradients are not" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 693, + 208, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 693, + 208, + 713 + ], + "spans": [ + { + "bbox": [ + 58, + 693, + 208, + 713 + ], + "type": "text", + "content": "*Corresponding author. \n1https://robustbench.github.io/" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 295, + 748, + 316, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 316, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 316, + 757 + ], + "type": "text", + "content": "4056" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 240 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 240 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 240 + ], + "type": "text", + "content": "necessarily efficient in guiding the generation of adversarial examples. The causes of inefficient gradients may be related to floating-point errors or other factors. This paper reveals that the relative error in the gradients caused by floating-point errors is one of the fundamental reasons for the failure of gradient-based attacks, and the relative error is directly affected by the value of the difference of the first and second largest in logits(DFSL). Although it is hard to eliminate the relative error in the gradients caused by floating-point errors completely, we can control its effect on the gradient-based attacks. Thus, we propose a new efficient loss function by minimizing the impact of floating-point errors (MIFPE) on gradient-based attacks. To summarize, our main contributions are as follows:" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 58, + 247, + 287, + 491 + ], + "type": "list", + "angle": 0, + "index": 6, + "blocks": [ + { + "bbox": [ + 58, + 247, + 287, + 294 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 247, + 287, + 294 + ], + "spans": [ + { + "bbox": [ + 58, + 247, + 287, + 294 + ], + "type": "text", + "content": "- We provide a comprehensive demonstration of how the presence of floating-point errors leads to the failure of gradient-based attacks due to the relative error in calculated gradients." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 301, + 287, + 338 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 301, + 287, + 338 + ], + "spans": [ + { + "bbox": [ + 58, + 301, + 287, + 338 + ], + "type": "text", + "content": "- We show that the floating-point rounding errors may lead to attack's failure due to growing relative errors as samples reach the classification boundary." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 58, + 345, + 287, + 404 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 345, + 287, + 404 + ], + "spans": [ + { + "bbox": [ + 58, + 345, + 287, + 404 + ], + "type": "text", + "content": "- We demonstrate that when the model's robustness is overestimated primarily due to floating-point errors, the loss function discarding partial elements of logits causes performance degradation in the gradient-based attack." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 58, + 412, + 287, + 448 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 412, + 287, + 448 + ], + "spans": [ + { + "bbox": [ + 58, + 412, + 287, + 448 + ], + "type": "text", + "content": "- We show that minimizing the impact of floating-point errors can improve the efficiency and accuracy of gradient-based attacks." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 58, + 456, + 287, + 491 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 456, + 287, + 491 + ], + "spans": [ + { + "bbox": [ + 58, + 456, + 287, + 491 + ], + "type": "text", + "content": "- Empirical results demonstrate that MIFPE tends to outperform the competing loss functions in terms of attack performance and computational efficiency." + } + ] + } + ], + "index": 5 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 47, + 502, + 219, + 514 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 502, + 219, + 514 + ], + "spans": [ + { + "bbox": [ + 47, + 502, + 219, + 514 + ], + "type": "text", + "content": "2. Preliminaries & Related Work" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 521, + 287, + 605 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 521, + 287, + 605 + ], + "spans": [ + { + "bbox": [ + 46, + 521, + 287, + 605 + ], + "type": "text", + "content": "We define the classification model as " + }, + { + "bbox": [ + 46, + 521, + 287, + 605 + ], + "type": "inline_equation", + "content": "f_{\\theta}(\\mathbf{x})" + }, + { + "bbox": [ + 46, + 521, + 287, + 605 + ], + "type": "text", + "content": " , where " + }, + { + "bbox": [ + 46, + 521, + 287, + 605 + ], + "type": "inline_equation", + "content": "\\pmb{\\theta}" + }, + { + "bbox": [ + 46, + 521, + 287, + 605 + ], + "type": "text", + "content": " represents the model parameters. " + }, + { + "bbox": [ + 46, + 521, + 287, + 605 + ], + "type": "inline_equation", + "content": "f_{\\theta}:\\mathbf{x}\\subset \\mathbb{R}^{C\\times H\\times W}\\to" + }, + { + "bbox": [ + 46, + 521, + 287, + 605 + ], + "type": "inline_equation", + "content": "\\mathbf{z}\\subset \\mathbb{R}^k" + }, + { + "bbox": [ + 46, + 521, + 287, + 605 + ], + "type": "text", + "content": " is a classifier that maps input data " + }, + { + "bbox": [ + 46, + 521, + 287, + 605 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 46, + 521, + 287, + 605 + ], + "type": "text", + "content": " to output logits " + }, + { + "bbox": [ + 46, + 521, + 287, + 605 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 46, + 521, + 287, + 605 + ], + "type": "text", + "content": " ,where " + }, + { + "bbox": [ + 46, + 521, + 287, + 605 + ], + "type": "inline_equation", + "content": "C,H" + }, + { + "bbox": [ + 46, + 521, + 287, + 605 + ], + "type": "text", + "content": " ,and " + }, + { + "bbox": [ + 46, + 521, + 287, + 605 + ], + "type": "inline_equation", + "content": "W" + }, + { + "bbox": [ + 46, + 521, + 287, + 605 + ], + "type": "text", + "content": " are parameters that describe the input data's channel number, height, and width, respectively. Additionally, " + }, + { + "bbox": [ + 46, + 521, + 287, + 605 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 46, + 521, + 287, + 605 + ], + "type": "text", + "content": " represents the number of classes from the model's output. We define the label of the input data as " + }, + { + "bbox": [ + 46, + 521, + 287, + 605 + ], + "type": "inline_equation", + "content": "y" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 606, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 606, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 606, + 287, + 713 + ], + "type": "text", + "content": "Attackers aim to breach defence strategies by generating adversarial examples " + }, + { + "bbox": [ + 46, + 606, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{x}}" + }, + { + "bbox": [ + 46, + 606, + 287, + 713 + ], + "type": "text", + "content": ", which can maximize the loss function " + }, + { + "bbox": [ + 46, + 606, + 287, + 713 + ], + "type": "inline_equation", + "content": "L(f_{\\theta}(\\hat{\\mathbf{x}}),y)" + }, + { + "bbox": [ + 46, + 606, + 287, + 713 + ], + "type": "text", + "content": " and deceive the model into producing incorrect results, arg max " + }, + { + "bbox": [ + 46, + 606, + 287, + 713 + ], + "type": "inline_equation", + "content": "f_{\\theta}(\\hat{\\mathbf{x}})\\neq y" + }, + { + "bbox": [ + 46, + 606, + 287, + 713 + ], + "type": "text", + "content": ". Achieving this requires the attackers to find imperceptible perturbations " + }, + { + "bbox": [ + 46, + 606, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\delta = \\hat{\\mathbf{x}} -\\mathbf{x}" + }, + { + "bbox": [ + 46, + 606, + 287, + 713 + ], + "type": "text", + "content": " that satisfy the constraint " + }, + { + "bbox": [ + 46, + 606, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\| \\delta \\| p\\leq \\varepsilon" + }, + { + "bbox": [ + 46, + 606, + 287, + 713 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 606, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\varepsilon" + }, + { + "bbox": [ + 46, + 606, + 287, + 713 + ], + "type": "text", + "content": " is the magnitude and " + }, + { + "bbox": [ + 46, + 606, + 287, + 713 + ], + "type": "inline_equation", + "content": "p" + }, + { + "bbox": [ + 46, + 606, + 287, + 713 + ], + "type": "text", + "content": " is the norm of the perturbation. Various perturbation options have been explored in literature, including the one-pixel attack [44, 44], " + }, + { + "bbox": [ + 46, + 606, + 287, + 713 + ], + "type": "inline_equation", + "content": "l_{2}" + }, + { + "bbox": [ + 46, + 606, + 287, + 713 + ], + "type": "text", + "content": " attacks [6, 31, 45], and " + }, + { + "bbox": [ + 46, + 606, + 287, + 713 + ], + "type": "inline_equation", + "content": "l\\infty" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 72, + 545, + 107 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 545, + 107 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 545, + 107 + ], + "type": "text", + "content": "attacks [16, 29]. The attackers can find an adversarial example " + }, + { + "bbox": [ + 305, + 72, + 545, + 107 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{x}} \\in \\mathcal{I}" + }, + { + "bbox": [ + 305, + 72, + 545, + 107 + ], + "type": "text", + "content": " by maximizing the loss. This process can be formulated as:" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 353, + 117, + 545, + 137 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 353, + 117, + 545, + 137 + ], + "spans": [ + { + "bbox": [ + 353, + 117, + 545, + 137 + ], + "type": "interline_equation", + "content": "\\hat {\\mathbf {x}} = \\mathbf {x} + \\max _ {\\| \\delta \\| _ {p} \\in \\varepsilon} L \\left(f _ {\\boldsymbol {\\theta}} (\\mathbf {x} + \\delta), y\\right), \\tag {1}", + "image_path": "07cf5fd384f2af4a283212f8dd48a527023b65538282f7abeb1e9a16a20c2f8d.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 144, + 545, + 263 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 144, + 545, + 263 + ], + "spans": [ + { + "bbox": [ + 304, + 144, + 545, + 263 + ], + "type": "text", + "content": "The white-box scenario is the most rigorous test for defence strategies, as attackers have complete knowledge about the models' architecture, parameters, training data, and algorithm implementation details. This is a highly challenging situation for defence strategies. Attackers can exploit nearly all vulnerabilities in the defence strategies and perform tailored attacks. If defence strategies remain robust against white-box attacks, they can ensure the system's security even in the worst-case scenario. In practice, the gradient-based method is commonly used to solve (1)." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 265, + 545, + 396 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 265, + 545, + 396 + ], + "spans": [ + { + "bbox": [ + 304, + 265, + 545, + 396 + ], + "type": "text", + "content": "Many gradient-based white-box attacks methods have been proposed, which include fast gradient-sign method (FGSM) [16], basic iterative method (BIM) [23], projected gradient descent (PGD) [29], momentum iterative method (MIM) [13] and fast adaptive boundary attack (FAB) [9] for " + }, + { + "bbox": [ + 304, + 265, + 545, + 396 + ], + "type": "inline_equation", + "content": "\\ell_{\\infty}" + }, + { + "bbox": [ + 304, + 265, + 545, + 396 + ], + "type": "text", + "content": "-norm attacks. Carlini and Wagner (C&W) [6] and DeepFool [31] can additionally carry out " + }, + { + "bbox": [ + 304, + 265, + 545, + 396 + ], + "type": "inline_equation", + "content": "\\ell_{2}" + }, + { + "bbox": [ + 304, + 265, + 545, + 396 + ], + "type": "text", + "content": "-norm attacks. PGD is one of the widely used methods to evaluate the model's robustness in the white box scenario, which finds an adversarial example by performing the following iterative update:" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 316, + 404, + 545, + 418 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 316, + 404, + 545, + 418 + ], + "spans": [ + { + "bbox": [ + 316, + 404, + 545, + 418 + ], + "type": "interline_equation", + "content": "\\hat {\\mathbf {x}} _ {i + 1} = \\mathcal {P} _ {\\epsilon , \\mathbf {x}} \\left(\\hat {\\mathbf {x}} _ {i} + \\alpha_ {i} \\operatorname {s i g n} \\left(\\nabla_ {\\hat {\\mathbf {x}} _ {i}} \\mathcal {L} ^ {\\mathrm {c e}} \\left(f _ {\\boldsymbol {\\theta}} \\left(\\hat {\\mathbf {x}} _ {i}\\right), y\\right)\\right)\\right), \\tag {2}", + "image_path": "7182489a513dcc317863821714a339bec3023b3a8f0839c6c093a788104dc67d.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 426, + 545, + 533 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 426, + 545, + 533 + ], + "spans": [ + { + "bbox": [ + 304, + 426, + 545, + 533 + ], + "type": "text", + "content": "Initially, " + }, + { + "bbox": [ + 304, + 426, + 545, + 533 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{x}}_0 = \\mathcal{P}_{\\epsilon,\\mathbf{x}}(\\mathbf{x} + \\mathbf{u})" + }, + { + "bbox": [ + 304, + 426, + 545, + 533 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 426, + 545, + 533 + ], + "type": "inline_equation", + "content": "\\mathbf{u} \\sim \\mathcal{U}([- \\epsilon, \\epsilon])" + }, + { + "bbox": [ + 304, + 426, + 545, + 533 + ], + "type": "text", + "content": ", i.e. " + }, + { + "bbox": [ + 304, + 426, + 545, + 533 + ], + "type": "inline_equation", + "content": "\\mathbf{u}" + }, + { + "bbox": [ + 304, + 426, + 545, + 533 + ], + "type": "text", + "content": " is a uniform random noise bounded by " + }, + { + "bbox": [ + 304, + 426, + 545, + 533 + ], + "type": "inline_equation", + "content": "[- \\epsilon, \\epsilon]" + }, + { + "bbox": [ + 304, + 426, + 545, + 533 + ], + "type": "text", + "content": ". The function " + }, + { + "bbox": [ + 304, + 426, + 545, + 533 + ], + "type": "inline_equation", + "content": "\\mathcal{P}_{\\epsilon,\\mathbf{x}}: \\mathbb{R}^{C \\times H \\times W} \\to \\mathcal{I}" + }, + { + "bbox": [ + 304, + 426, + 545, + 533 + ], + "type": "text", + "content": " first clips the range of its input into the " + }, + { + "bbox": [ + 304, + 426, + 545, + 533 + ], + "type": "inline_equation", + "content": "\\epsilon" + }, + { + "bbox": [ + 304, + 426, + 545, + 533 + ], + "type": "text", + "content": "-ball " + }, + { + "bbox": [ + 304, + 426, + 545, + 533 + ], + "type": "inline_equation", + "content": "\\ell_p" + }, + { + "bbox": [ + 304, + 426, + 545, + 533 + ], + "type": "text", + "content": "-distance neighbour of the original image " + }, + { + "bbox": [ + 304, + 426, + 545, + 533 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 304, + 426, + 545, + 533 + ], + "type": "text", + "content": " and then clips its input into the range of " + }, + { + "bbox": [ + 304, + 426, + 545, + 533 + ], + "type": "inline_equation", + "content": "\\mathcal{I}" + }, + { + "bbox": [ + 304, + 426, + 545, + 533 + ], + "type": "text", + "content": ". The term " + }, + { + "bbox": [ + 304, + 426, + 545, + 533 + ], + "type": "inline_equation", + "content": "\\nabla_{\\hat{\\mathbf{x}}_i} \\mathcal{L}^{\\mathrm{ce}}(f_\\theta(\\hat{\\mathbf{x}}_i), y)" + }, + { + "bbox": [ + 304, + 426, + 545, + 533 + ], + "type": "text", + "content": " computes the gradient of the loss w.r.t. the input " + }, + { + "bbox": [ + 304, + 426, + 545, + 533 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{x}}_i" + }, + { + "bbox": [ + 304, + 426, + 545, + 533 + ], + "type": "text", + "content": ". Finally, " + }, + { + "bbox": [ + 304, + 426, + 545, + 533 + ], + "type": "inline_equation", + "content": "\\alpha_i" + }, + { + "bbox": [ + 304, + 426, + 545, + 533 + ], + "type": "text", + "content": " is the step size, and for each element in the tensor " + }, + { + "bbox": [ + 304, + 426, + 545, + 533 + ], + "type": "inline_equation", + "content": "g" + }, + { + "bbox": [ + 304, + 426, + 545, + 533 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 426, + 545, + 533 + ], + "type": "inline_equation", + "content": "\\operatorname{sign}(g)" + }, + { + "bbox": [ + 304, + 426, + 545, + 533 + ], + "type": "text", + "content": " returns one of 1, 0 or -1, if the value is positive, zero or negative, respectively." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 534, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 534, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 534, + 545, + 713 + ], + "type": "text", + "content": "CE is a commonly used loss function for training deep neural network models and evaluating their robustness in classification tasks. However, the presence of exponential operations in CE makes it vulnerable to underflow and rounding errors with limited floating-point precision. Gradient-based attacks with the CE loss may experience vanishing/inefficient gradients and difficulty converging while suffering from a severe overestimation of the model's robustness. [6, 10]. Recent attack methods use surrogate losses for gradient computation [6, 18] and optimize an alternative target by replacing " + }, + { + "bbox": [ + 304, + 534, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{L}^{\\mathrm{ce}}" + }, + { + "bbox": [ + 304, + 534, + 545, + 713 + ], + "type": "text", + "content": " with a custom surrogate loss function. " + }, + { + "bbox": [ + 304, + 534, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{z} = f_{\\theta}(\\hat{\\mathbf{x}})" + }, + { + "bbox": [ + 304, + 534, + 545, + 713 + ], + "type": "text", + "content": " is output logits of the model, and " + }, + { + "bbox": [ + 304, + 534, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_i" + }, + { + "bbox": [ + 304, + 534, + 545, + 713 + ], + "type": "text", + "content": " is the " + }, + { + "bbox": [ + 304, + 534, + 545, + 713 + ], + "type": "inline_equation", + "content": "i^{\\mathrm{th}}" + }, + { + "bbox": [ + 304, + 534, + 545, + 713 + ], + "type": "text", + "content": " component of " + }, + { + "bbox": [ + 304, + 534, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 304, + 534, + 545, + 713 + ], + "type": "text", + "content": ", two typical examples to replace the CE objective include the difference-of-logits (DL) [6], also known as hinge loss, where " + }, + { + "bbox": [ + 304, + 534, + 545, + 713 + ], + "type": "inline_equation", + "content": "i \\in \\{1,2,\\dots,K\\}" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "4057" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 93, + 84 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 93, + 84 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 93, + 84 + ], + "type": "text", + "content": "and " + }, + { + "bbox": [ + 47, + 72, + 93, + 84 + ], + "type": "inline_equation", + "content": "i\\neq y" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 110, + 89, + 287, + 108 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 110, + 89, + 287, + 108 + ], + "spans": [ + { + "bbox": [ + 110, + 89, + 287, + 108 + ], + "type": "interline_equation", + "content": "\\mathcal {L} ^ {\\mathrm {c w}} (\\mathbf {z}, \\mathrm {y}) = - \\mathbf {z} _ {y} + \\max _ {i \\neq y} \\mathbf {z} _ {i}, \\tag {3}", + "image_path": "969295652cb1fddced27742d02ec533e09f790c5e639e46e0be53a89f3c0d5b9.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 113, + 249, + 125 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 113, + 249, + 125 + ], + "spans": [ + { + "bbox": [ + 47, + 113, + 249, + 125 + ], + "type": "text", + "content": "and the difference-of-logits ratio (DLR) loss [10]:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 101, + 129, + 287, + 153 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 101, + 129, + 287, + 153 + ], + "spans": [ + { + "bbox": [ + 101, + 129, + 287, + 153 + ], + "type": "interline_equation", + "content": "\\mathcal {L} ^ {\\mathrm {d l r}} (\\mathbf {z}, \\mathrm {y}) = \\frac {- \\mathbf {z} _ {y} + \\max _ {i \\neq y} \\mathbf {z} _ {i}}{\\mathbf {z} _ {\\pi 1} - \\mathbf {z} _ {\\pi 3}}, \\tag {4}", + "image_path": "ba09c4c108a3e5d699017e582a4f3510cffccdfb70aa14093c3292a989d509a3.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 157, + 287, + 312 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 157, + 287, + 312 + ], + "spans": [ + { + "bbox": [ + 46, + 157, + 287, + 312 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 157, + 287, + 312 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_{\\pi_1}" + }, + { + "bbox": [ + 46, + 157, + 287, + 312 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 157, + 287, + 312 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_{\\pi_3}" + }, + { + "bbox": [ + 46, + 157, + 287, + 312 + ], + "type": "text", + "content": " respectively denote the " + }, + { + "bbox": [ + 46, + 157, + 287, + 312 + ], + "type": "inline_equation", + "content": "1^{\\mathrm{th}}" + }, + { + "bbox": [ + 46, + 157, + 287, + 312 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 157, + 287, + 312 + ], + "type": "inline_equation", + "content": "3^{\\mathrm{th}}" + }, + { + "bbox": [ + 46, + 157, + 287, + 312 + ], + "type": "text", + "content": " largest components of " + }, + { + "bbox": [ + 46, + 157, + 287, + 312 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 46, + 157, + 287, + 312 + ], + "type": "text", + "content": ". It is clear that maximizing the alternative goals is consistent with the original objective of making " + }, + { + "bbox": [ + 46, + 157, + 287, + 312 + ], + "type": "inline_equation", + "content": "\\arg \\max f(\\hat{\\mathbf{x}})\\neq y" + }, + { + "bbox": [ + 46, + 157, + 287, + 312 + ], + "type": "text", + "content": ". In addition, since surrogate losses avoid exponential operations, they are not prone to underflow, allowing gradient-based optimization to escape suffering from the overestimation caused by the floating-point underflow errors. However, the floating-point underflow errors are not the sole reason for all overestimations related to floating-point errors. At the same time, the new loss function discards some elements of " + }, + { + "bbox": [ + 46, + 157, + 287, + 312 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 46, + 157, + 287, + 312 + ], + "type": "text", + "content": ", reducing the effectiveness of the attack and causing gradient-based attacks with surrogate losses to overestimate the model's robustness." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 313, + 287, + 529 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 313, + 287, + 529 + ], + "spans": [ + { + "bbox": [ + 46, + 313, + 287, + 529 + ], + "type": "text", + "content": "Many auxiliary techniques can assist existing attack methods to improve their performance. For example, momentum-based updates can improve the attack's convergence rate and are widely used by white-box attacks [13, 18]. A step schedule with decreasing step size based on the number of iterations can improve the overall success rate [10, 18, 56]. Multi-target attacks can outperform nontarget attacks in the evaluation results at the cost of more iterations since they require enumerating multiple most likely target labels [18, 33, 34]. In addition to the above strategies, multiple restarts can also improve the effectiveness of gradient-based attacks by adding different random initial perturbations to the input data to diversify the starting point of the attack and reduce the impact of suboptimal solutions [5, 46]. Finally, several recent publications have shown that leveraging latent features in attacks can enhance the transferability of black-box attacks [21, 22] and the performance of white-box attacks [56]." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 529, + 287, + 648 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 529, + 287, + 648 + ], + "spans": [ + { + "bbox": [ + 46, + 529, + 287, + 648 + ], + "type": "text", + "content": "However, even with so many auxiliary strategies mentioned above, using any single attack is still challenging to accurately evaluate the model's robustness. Attackers start using an ensemble of multiple attack strategies to improve the attack's performance by introducing diversity [5,10,28]. They often suffer from high computational costs. Even though these ensemble strategies are more powerful than any single attack, they still fail to provide an assessment of the ensemble defence strategy's robustness accurately [48,57]." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 657, + 181, + 670 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 657, + 181, + 670 + ], + "spans": [ + { + "bbox": [ + 47, + 657, + 181, + 670 + ], + "type": "text", + "content": "3. Efficient Loss Function" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 677, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 287, + 714 + ], + "type": "text", + "content": "Assuming that the input " + }, + { + "bbox": [ + 46, + 677, + 287, + 714 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{x}}" + }, + { + "bbox": [ + 46, + 677, + 287, + 714 + ], + "type": "text", + "content": " has the correct label " + }, + { + "bbox": [ + 46, + 677, + 287, + 714 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 46, + 677, + 287, + 714 + ], + "type": "text", + "content": ", we compute " + }, + { + "bbox": [ + 46, + 677, + 287, + 714 + ], + "type": "inline_equation", + "content": "\\mathbf{z} = f_{\\theta}(\\hat{\\mathbf{x}})" + }, + { + "bbox": [ + 46, + 677, + 287, + 714 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 677, + 287, + 714 + ], + "type": "inline_equation", + "content": "\\pmb{\\theta}" + }, + { + "bbox": [ + 46, + 677, + 287, + 714 + ], + "type": "text", + "content": " represents the model parameters. Next, we sort the values in " + }, + { + "bbox": [ + 46, + 677, + 287, + 714 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 46, + 677, + 287, + 714 + ], + "type": "text", + "content": " in a descending order," + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 72, + 545, + 118 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 545, + 118 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 545, + 118 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 72, + 545, + 118 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_{\\pi 1}" + }, + { + "bbox": [ + 305, + 72, + 545, + 118 + ], + "type": "text", + "content": " is the maximum value. We define " + }, + { + "bbox": [ + 305, + 72, + 545, + 118 + ], + "type": "inline_equation", + "content": "\\Delta" + }, + { + "bbox": [ + 305, + 72, + 545, + 118 + ], + "type": "text", + "content": " as the difference between the maximum and the second maximum value, i.e., " + }, + { + "bbox": [ + 305, + 72, + 545, + 118 + ], + "type": "inline_equation", + "content": "\\Delta = \\mathbf{z}_{\\pi 1} - \\mathbf{z}_{\\pi 2} \\geq 0" + }, + { + "bbox": [ + 305, + 72, + 545, + 118 + ], + "type": "text", + "content": ". The cross-entropy loss at " + }, + { + "bbox": [ + 305, + 72, + 545, + 118 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 305, + 72, + 545, + 118 + ], + "type": "text", + "content": " becomes" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 332, + 125, + 545, + 156 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 332, + 125, + 545, + 156 + ], + "spans": [ + { + "bbox": [ + 332, + 125, + 545, + 156 + ], + "type": "interline_equation", + "content": "C E (\\mathbf {z}, y) = - \\log p _ {y} = - \\log \\frac {e ^ {\\mathbf {z} _ {y} - \\mathbf {z} _ {\\pi 1}}}{\\sum_ {i = 1} ^ {K} e ^ {\\mathbf {z} _ {i} - \\mathbf {z} _ {\\pi 1}}}, \\tag {5}", + "image_path": "0ed24a616d57327d8c573fb569e66de921797abf57a1ecf655633a857feb0110.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 340, + 171, + 545, + 213 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 340, + 171, + 545, + 213 + ], + "spans": [ + { + "bbox": [ + 340, + 171, + 545, + 213 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\nabla_ {\\hat {\\mathbf {x}}} C E (\\mathbf {z}, y) = (- 1 + p _ {y}) \\nabla_ {\\hat {\\mathbf {x}}} \\left(\\mathbf {z} _ {y} - \\mathbf {z} _ {\\pi 1}\\right) \\\\ + \\sum_ {i \\neq y} p _ {i} \\nabla_ {\\hat {\\mathbf {x}}} \\left(\\mathbf {z} _ {i} - \\mathbf {z} _ {\\pi 1}\\right), \\tag {6} \\\\ \\end{array}", + "image_path": "6d3a22405697d9cd6163d8cd3baa71b4b2e7ddb65f422ea26a8170d77e6eb246.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 221, + 536, + 236 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 221, + 536, + 236 + ], + "spans": [ + { + "bbox": [ + 305, + 221, + 536, + 236 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 221, + 536, + 236 + ], + "type": "inline_equation", + "content": "p_i = e^{\\mathbf{z}_i - \\mathbf{z}_{\\pi 1}} / \\sum_{j = 1}^{K}e^{\\mathbf{z}_j - \\mathbf{z}_{\\pi 1}}" + }, + { + "bbox": [ + 305, + 221, + 536, + 236 + ], + "type": "inline_equation", + "content": "i\\in \\{1,2,3,\\dots,K\\}" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 236, + 545, + 390 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 236, + 545, + 390 + ], + "spans": [ + { + "bbox": [ + 305, + 236, + 545, + 390 + ], + "type": "text", + "content": "Exponential operations in Equation (5), specifically " + }, + { + "bbox": [ + 305, + 236, + 545, + 390 + ], + "type": "inline_equation", + "content": "e^{\\mathbf{z}_{\\pi i} - \\mathbf{z}_{\\pi 1}},i\\in \\{2,\\dots,K\\}" + }, + { + "bbox": [ + 305, + 236, + 545, + 390 + ], + "type": "text", + "content": " , where " + }, + { + "bbox": [ + 305, + 236, + 545, + 390 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_{\\pi i} - \\mathbf{z}_{\\pi 1}\\leq \\mathbf{z}_{\\pi 2} - \\mathbf{z}_{\\pi 1} =" + }, + { + "bbox": [ + 305, + 236, + 545, + 390 + ], + "type": "inline_equation", + "content": "-\\Delta \\leq 0" + }, + { + "bbox": [ + 305, + 236, + 545, + 390 + ], + "type": "text", + "content": " , can cause floating-point underflow errors in the CE loss gradient. To investigate this issue, we analyze the properties of " + }, + { + "bbox": [ + 305, + 236, + 545, + 390 + ], + "type": "inline_equation", + "content": "e^{-\\Delta}" + }, + { + "bbox": [ + 305, + 236, + 545, + 390 + ], + "type": "text", + "content": " and observe that when " + }, + { + "bbox": [ + 305, + 236, + 545, + 390 + ], + "type": "inline_equation", + "content": "\\Delta" + }, + { + "bbox": [ + 305, + 236, + 545, + 390 + ], + "type": "text", + "content": " surpasses a threshold value denoted by " + }, + { + "bbox": [ + 305, + 236, + 545, + 390 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 305, + 236, + 545, + 390 + ], + "type": "inline_equation", + "content": "e^{-\\Delta}" + }, + { + "bbox": [ + 305, + 236, + 545, + 390 + ], + "type": "text", + "content": " underflows and leads to significant inaccuracies in the gradient calculation. Specifically, when " + }, + { + "bbox": [ + 305, + 236, + 545, + 390 + ], + "type": "inline_equation", + "content": "\\Delta \\geq \\lambda" + }, + { + "bbox": [ + 305, + 236, + 545, + 390 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 236, + 545, + 390 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_y = \\mathbf{z}_{\\pi 1}" + }, + { + "bbox": [ + 305, + 236, + 545, + 390 + ], + "type": "text", + "content": " , the predicted probability " + }, + { + "bbox": [ + 305, + 236, + 545, + 390 + ], + "type": "inline_equation", + "content": "p_{y} = 1" + }, + { + "bbox": [ + 305, + 236, + 545, + 390 + ], + "type": "text", + "content": " and the calculated gradient " + }, + { + "bbox": [ + 305, + 236, + 545, + 390 + ], + "type": "inline_equation", + "content": "\\nabla_{\\hat{\\mathbf{x}}}CE(\\mathbf{z},y) = 0" + }, + { + "bbox": [ + 305, + 236, + 545, + 390 + ], + "type": "text", + "content": " The value of " + }, + { + "bbox": [ + 305, + 236, + 545, + 390 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 305, + 236, + 545, + 390 + ], + "type": "text", + "content": " varies with different floating-point arithmetic precisions, with approximate values of 16.64, 103.28, and 744.44 for half-precision, single-precision, and double-precision, respectively." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 391, + 546, + 653 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 391, + 546, + 653 + ], + "spans": [ + { + "bbox": [ + 304, + 391, + 546, + 653 + ], + "type": "text", + "content": "Based on the findings, we identify that the root cause of the calculated gradient being equal to zero is the result of " + }, + { + "bbox": [ + 304, + 391, + 546, + 653 + ], + "type": "inline_equation", + "content": "\\Delta" + }, + { + "bbox": [ + 304, + 391, + 546, + 653 + ], + "type": "text", + "content": " exceeding " + }, + { + "bbox": [ + 304, + 391, + 546, + 653 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 304, + 391, + 546, + 653 + ], + "type": "text", + "content": ". To further investigate the relationship between the value of " + }, + { + "bbox": [ + 304, + 391, + 546, + 653 + ], + "type": "inline_equation", + "content": "\\Delta" + }, + { + "bbox": [ + 304, + 391, + 546, + 653 + ], + "type": "text", + "content": " and the overestimation of the model's robustness, we analyze the distribution of " + }, + { + "bbox": [ + 304, + 391, + 546, + 653 + ], + "type": "inline_equation", + "content": "\\Delta" + }, + { + "bbox": [ + 304, + 391, + 546, + 653 + ], + "type": "text", + "content": " values in defence models that tend to be overestimated by gradient-based attacks under single-precision. The results in Figure 2 indicate that the range of " + }, + { + "bbox": [ + 304, + 391, + 546, + 653 + ], + "type": "inline_equation", + "content": "\\Delta" + }, + { + "bbox": [ + 304, + 391, + 546, + 653 + ], + "type": "text", + "content": " values varies significantly among different defence models. Notably, the values of " + }, + { + "bbox": [ + 304, + 391, + 546, + 653 + ], + "type": "inline_equation", + "content": "\\Delta" + }, + { + "bbox": [ + 304, + 391, + 546, + 653 + ], + "type": "text", + "content": " in 2a and 2b do not exceed 10, which is significantly smaller than " + }, + { + "bbox": [ + 304, + 391, + 546, + 653 + ], + "type": "inline_equation", + "content": "\\lambda \\approx 103.28" + }, + { + "bbox": [ + 304, + 391, + 546, + 653 + ], + "type": "text", + "content": " for single-precision. As a result, these models do not suffer from floating-point underflow errors. In contrast, most of the " + }, + { + "bbox": [ + 304, + 391, + 546, + 653 + ], + "type": "inline_equation", + "content": "\\Delta" + }, + { + "bbox": [ + 304, + 391, + 546, + 653 + ], + "type": "text", + "content": " values in 2c exceed the threshold that leads to floating-point underflow errors. It is evident that not all models suffer from floating-point underflow errors, and other reasons associated with floating-point errors cause gradient-based attacks to fail. This is because in addition to floating-point underflow errors, floating-point errors have another component: floating-point rounding errors when " + }, + { + "bbox": [ + 304, + 391, + 546, + 653 + ], + "type": "inline_equation", + "content": "\\Delta < \\lambda" + }, + { + "bbox": [ + 304, + 391, + 546, + 653 + ], + "type": "text", + "content": ". These errors result in a non-negligible relative error in " + }, + { + "bbox": [ + 304, + 391, + 546, + 653 + ], + "type": "inline_equation", + "content": "\\nabla_{\\hat{\\mathbf{x}}}CE(\\mathbf{z},y)" + }, + { + "bbox": [ + 304, + 391, + 546, + 653 + ], + "type": "text", + "content": ". We define the relative error as " + }, + { + "bbox": [ + 304, + 391, + 546, + 653 + ], + "type": "inline_equation", + "content": "\\delta_{CE} = \\delta (\\nabla_{\\hat{\\mathbf{x}}}CE(\\mathbf{z},y))" + }, + { + "bbox": [ + 304, + 391, + 546, + 653 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 654, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 654, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 654, + 545, + 713 + ], + "type": "text", + "content": "We know that " + }, + { + "bbox": [ + 304, + 654, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\delta_{CE} = 100\\%" + }, + { + "bbox": [ + 304, + 654, + 545, + 713 + ], + "type": "text", + "content": " when " + }, + { + "bbox": [ + 304, + 654, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\Delta \\geq \\lambda" + }, + { + "bbox": [ + 304, + 654, + 545, + 713 + ], + "type": "text", + "content": ". We need to further analyze the change pattern of " + }, + { + "bbox": [ + 304, + 654, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\delta_{CE}" + }, + { + "bbox": [ + 304, + 654, + 545, + 713 + ], + "type": "text", + "content": " when " + }, + { + "bbox": [ + 304, + 654, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\Delta < \\lambda" + }, + { + "bbox": [ + 304, + 654, + 545, + 713 + ], + "type": "text", + "content": ". A multi-iteration gradient-based attack involves adding perturbations to " + }, + { + "bbox": [ + 304, + 654, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{x}}" + }, + { + "bbox": [ + 304, + 654, + 545, + 713 + ], + "type": "text", + "content": " at each iteration, leading to constant changes in " + }, + { + "bbox": [ + 304, + 654, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 304, + 654, + 545, + 713 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 654, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\Delta" + }, + { + "bbox": [ + 304, + 654, + 545, + 713 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 304, + 654, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\nabla_{\\hat{\\mathbf{x}}}(\\mathbf{z}_{\\pi i} - \\mathbf{z}_{\\pi 1})" + }, + { + "bbox": [ + 304, + 654, + 545, + 713 + ], + "type": "text", + "content": " for " + }, + { + "bbox": [ + 304, + 654, + 545, + 713 + ], + "type": "inline_equation", + "content": "i \\in 1,2,\\dots,K" + }, + { + "bbox": [ + 304, + 654, + 545, + 713 + ], + "type": "text", + "content": " after each" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "4058" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 53, + 75, + 210, + 209 + ], + "blocks": [ + { + "bbox": [ + 53, + 75, + 210, + 209 + ], + "lines": [ + { + "bbox": [ + 53, + 75, + 210, + 209 + ], + "spans": [ + { + "bbox": [ + 53, + 75, + 210, + 209 + ], + "type": "image", + "image_path": "0ab137cb715c73ef94d939c8cfc537e53e3b472c0f632faa1eb2558a518b75bb.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 82, + 217, + 179, + 227 + ], + "lines": [ + { + "bbox": [ + 82, + 217, + 179, + 227 + ], + "spans": [ + { + "bbox": [ + 82, + 217, + 179, + 227 + ], + "type": "text", + "content": "(a) The " + }, + { + "bbox": [ + 82, + 217, + 179, + 227 + ], + "type": "inline_equation", + "content": "\\Delta" + }, + { + "bbox": [ + 82, + 217, + 179, + 227 + ], + "type": "text", + "content": " distribution of [33]" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 219, + 75, + 375, + 209 + ], + "blocks": [ + { + "bbox": [ + 219, + 75, + 375, + 209 + ], + "lines": [ + { + "bbox": [ + 219, + 75, + 375, + 209 + ], + "spans": [ + { + "bbox": [ + 219, + 75, + 375, + 209 + ], + "type": "image", + "image_path": "eec3ef563842dce2633a4eae2a74f3696a65dda253ce5c4a87a006c78c6d6471.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 247, + 217, + 346, + 227 + ], + "lines": [ + { + "bbox": [ + 247, + 217, + 346, + 227 + ], + "spans": [ + { + "bbox": [ + 247, + 217, + 346, + 227 + ], + "type": "text", + "content": "(b) The " + }, + { + "bbox": [ + 247, + 217, + 346, + 227 + ], + "type": "inline_equation", + "content": "\\Delta" + }, + { + "bbox": [ + 247, + 217, + 346, + 227 + ], + "type": "text", + "content": " distribution of [59]" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 384, + 75, + 539, + 209 + ], + "blocks": [ + { + "bbox": [ + 384, + 75, + 539, + 209 + ], + "lines": [ + { + "bbox": [ + 384, + 75, + 539, + 209 + ], + "spans": [ + { + "bbox": [ + 384, + 75, + 539, + 209 + ], + "type": "image", + "image_path": "7f86c89dec6dd32c29c06404bf30c2c6852b0e052e60bde1251996165148457b.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 416, + 217, + 509, + 227 + ], + "lines": [ + { + "bbox": [ + 416, + 217, + 509, + 227 + ], + "spans": [ + { + "bbox": [ + 416, + 217, + 509, + 227 + ], + "type": "text", + "content": "(c) The " + }, + { + "bbox": [ + 416, + 217, + 509, + 227 + ], + "type": "inline_equation", + "content": "\\Delta" + }, + { + "bbox": [ + 416, + 217, + 509, + 227 + ], + "type": "text", + "content": " distribution of [3]" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 269, + 287, + 375 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 269, + 287, + 375 + ], + "spans": [ + { + "bbox": [ + 46, + 269, + 287, + 375 + ], + "type": "text", + "content": "modification. This makes it difficult to analyze how " + }, + { + "bbox": [ + 46, + 269, + 287, + 375 + ], + "type": "inline_equation", + "content": "\\delta_{CE}" + }, + { + "bbox": [ + 46, + 269, + 287, + 375 + ], + "type": "text", + "content": " changes when " + }, + { + "bbox": [ + 46, + 269, + 287, + 375 + ], + "type": "inline_equation", + "content": "\\Delta < \\lambda" + }, + { + "bbox": [ + 46, + 269, + 287, + 375 + ], + "type": "text", + "content": ". However, we can indirectly examine the effect of floating-point errors on the attack's performance by analyzing the impact of such errors on a single step. To do so, we introduce a scaling factor " + }, + { + "bbox": [ + 46, + 269, + 287, + 375 + ], + "type": "inline_equation", + "content": "c" + }, + { + "bbox": [ + 46, + 269, + 287, + 375 + ], + "type": "text", + "content": " and define the scaled value of " + }, + { + "bbox": [ + 46, + 269, + 287, + 375 + ], + "type": "inline_equation", + "content": "\\Delta" + }, + { + "bbox": [ + 46, + 269, + 287, + 375 + ], + "type": "text", + "content": " as " + }, + { + "bbox": [ + 46, + 269, + 287, + 375 + ], + "type": "inline_equation", + "content": "T = c\\Delta" + }, + { + "bbox": [ + 46, + 269, + 287, + 375 + ], + "type": "text", + "content": ". By varying " + }, + { + "bbox": [ + 46, + 269, + 287, + 375 + ], + "type": "inline_equation", + "content": "c" + }, + { + "bbox": [ + 46, + 269, + 287, + 375 + ], + "type": "text", + "content": " while keeping " + }, + { + "bbox": [ + 46, + 269, + 287, + 375 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{x}}" + }, + { + "bbox": [ + 46, + 269, + 287, + 375 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 269, + 287, + 375 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 46, + 269, + 287, + 375 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 46, + 269, + 287, + 375 + ], + "type": "inline_equation", + "content": "\\nabla_{\\hat{\\mathbf{x}}}(\\mathbf{z}_{\\pi i} - \\mathbf{z}_{\\pi 1})" + }, + { + "bbox": [ + 46, + 269, + 287, + 375 + ], + "type": "text", + "content": " fixed during gradient calculation, we can investigate the relationship between " + }, + { + "bbox": [ + 46, + 269, + 287, + 375 + ], + "type": "inline_equation", + "content": "\\delta_{CE}" + }, + { + "bbox": [ + 46, + 269, + 287, + 375 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 269, + 287, + 375 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 46, + 269, + 287, + 375 + ], + "type": "text", + "content": " for different values of " + }, + { + "bbox": [ + 46, + 269, + 287, + 375 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 46, + 269, + 287, + 375 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 380, + 287, + 516 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 380, + 287, + 516 + ], + "spans": [ + { + "bbox": [ + 46, + 380, + 287, + 516 + ], + "type": "text", + "content": "To compute the scale factor, we need to detach the gradient information from " + }, + { + "bbox": [ + 46, + 380, + 287, + 516 + ], + "type": "inline_equation", + "content": "\\Delta" + }, + { + "bbox": [ + 46, + 380, + 287, + 516 + ], + "type": "text", + "content": " since " + }, + { + "bbox": [ + 46, + 380, + 287, + 516 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 46, + 380, + 287, + 516 + ], + "type": "text", + "content": " contains the gradient information during the actual program running. Thus, we define the scale factor as " + }, + { + "bbox": [ + 46, + 380, + 287, + 516 + ], + "type": "inline_equation", + "content": "c = T / \\Delta_{\\mathrm{detach}}" + }, + { + "bbox": [ + 46, + 380, + 287, + 516 + ], + "type": "text", + "content": ". The use of the detach operation in the calculation of " + }, + { + "bbox": [ + 46, + 380, + 287, + 516 + ], + "type": "inline_equation", + "content": "c" + }, + { + "bbox": [ + 46, + 380, + 287, + 516 + ], + "type": "text", + "content": " removes the gradient information from the " + }, + { + "bbox": [ + 46, + 380, + 287, + 516 + ], + "type": "inline_equation", + "content": "\\Delta_{\\mathrm{detach}}" + }, + { + "bbox": [ + 46, + 380, + 287, + 516 + ], + "type": "text", + "content": ", making it distinct from the " + }, + { + "bbox": [ + 46, + 380, + 287, + 516 + ], + "type": "inline_equation", + "content": "\\Delta" + }, + { + "bbox": [ + 46, + 380, + 287, + 516 + ], + "type": "text", + "content": " that retains gradient information. When " + }, + { + "bbox": [ + 46, + 380, + 287, + 516 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_y \\neq \\mathbf{z}_{\\pi 1}" + }, + { + "bbox": [ + 46, + 380, + 287, + 516 + ], + "type": "text", + "content": ", the model output is already incorrect. Therefore, we only focus on the relationship between " + }, + { + "bbox": [ + 46, + 380, + 287, + 516 + ], + "type": "inline_equation", + "content": "\\delta_{CE}" + }, + { + "bbox": [ + 46, + 380, + 287, + 516 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 380, + 287, + 516 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 46, + 380, + 287, + 516 + ], + "type": "text", + "content": " when " + }, + { + "bbox": [ + 46, + 380, + 287, + 516 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_y = \\mathbf{z}_{\\pi 1}" + }, + { + "bbox": [ + 46, + 380, + 287, + 516 + ], + "type": "text", + "content": ", at which point " + }, + { + "bbox": [ + 46, + 380, + 287, + 516 + ], + "type": "inline_equation", + "content": "\\nabla_{\\hat{\\mathbf{z}}}CE(c\\mathbf{z},y) = c\\sum_{i \\neq y}p_i^c\\nabla_{\\hat{\\mathbf{x}}}(\\mathbf{z}_i - \\mathbf{z}_{\\pi 1})" + }, + { + "bbox": [ + 46, + 380, + 287, + 516 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 380, + 287, + 516 + ], + "type": "inline_equation", + "content": "p_i^c = e^{c(\\mathbf{z}_i - \\mathbf{z}_{\\pi 1})} / \\sum_{j=1}^{K}e^{c(\\mathbf{z}_j - \\mathbf{z}_{\\pi 1})}" + }, + { + "bbox": [ + 46, + 380, + 287, + 516 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 518, + 287, + 685 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 518, + 287, + 685 + ], + "spans": [ + { + "bbox": [ + 46, + 518, + 287, + 685 + ], + "type": "text", + "content": "To get a more intuitive picture of the relationship between " + }, + { + "bbox": [ + 46, + 518, + 287, + 685 + ], + "type": "inline_equation", + "content": "\\delta_{CE}" + }, + { + "bbox": [ + 46, + 518, + 287, + 685 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 518, + 287, + 685 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 46, + 518, + 287, + 685 + ], + "type": "text", + "content": ", we plotted the figure of " + }, + { + "bbox": [ + 46, + 518, + 287, + 685 + ], + "type": "inline_equation", + "content": "\\delta_{CE}" + }, + { + "bbox": [ + 46, + 518, + 287, + 685 + ], + "type": "text", + "content": " on the binary classification task with " + }, + { + "bbox": [ + 46, + 518, + 287, + 685 + ], + "type": "inline_equation", + "content": "K = 2" + }, + { + "bbox": [ + 46, + 518, + 287, + 685 + ], + "type": "text", + "content": ". At this point, " + }, + { + "bbox": [ + 46, + 518, + 287, + 685 + ], + "type": "inline_equation", + "content": "\\nabla_{\\hat{\\mathbf{z}}}CE(\\mathbf{cz},y) = c\\sum_{i\\neq y}p_i^c\\nabla_{\\hat{\\mathbf{x}}}\\left(\\mathbf{z}_i - \\mathbf{z}_{\\pi 1}\\right) = cp_2^c\\nabla_{\\hat{\\mathbf{x}}}\\left(\\mathbf{z}_{\\pi 2} - \\mathbf{z}_{\\pi 1}\\right)\\propto cp_2^c" + }, + { + "bbox": [ + 46, + 518, + 287, + 685 + ], + "type": "text", + "content": ". Therefore, " + }, + { + "bbox": [ + 46, + 518, + 287, + 685 + ], + "type": "inline_equation", + "content": "\\delta_{CE}\\propto \\delta (cp_2^c)" + }, + { + "bbox": [ + 46, + 518, + 287, + 685 + ], + "type": "text", + "content": ". In Figure 3, we can see that for the same " + }, + { + "bbox": [ + 46, + 518, + 287, + 685 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{x}}" + }, + { + "bbox": [ + 46, + 518, + 287, + 685 + ], + "type": "text", + "content": ", when " + }, + { + "bbox": [ + 46, + 518, + 287, + 685 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 46, + 518, + 287, + 685 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 518, + 287, + 685 + ], + "type": "inline_equation", + "content": "\\nabla_{\\hat{\\mathbf{x}}}\\left(\\mathbf{z}_i - \\mathbf{z}_{\\pi 1}\\right)" + }, + { + "bbox": [ + 46, + 518, + 287, + 685 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 518, + 287, + 685 + ], + "type": "inline_equation", + "content": "i\\in \\{1,2,\\dots,K\\}" + }, + { + "bbox": [ + 46, + 518, + 287, + 685 + ], + "type": "text", + "content": " are all fixed, " + }, + { + "bbox": [ + 46, + 518, + 287, + 685 + ], + "type": "inline_equation", + "content": "\\delta_{CE}" + }, + { + "bbox": [ + 46, + 518, + 287, + 685 + ], + "type": "text", + "content": " varies with " + }, + { + "bbox": [ + 46, + 518, + 287, + 685 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 46, + 518, + 287, + 685 + ], + "type": "text", + "content": ". When " + }, + { + "bbox": [ + 46, + 518, + 287, + 685 + ], + "type": "inline_equation", + "content": "T\\geq \\lambda" + }, + { + "bbox": [ + 46, + 518, + 287, + 685 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 518, + 287, + 685 + ], + "type": "inline_equation", + "content": "\\delta_{CE} = 100\\%" + }, + { + "bbox": [ + 46, + 518, + 287, + 685 + ], + "type": "text", + "content": " In contrast, When " + }, + { + "bbox": [ + 46, + 518, + 287, + 685 + ], + "type": "inline_equation", + "content": "T < \\lambda" + }, + { + "bbox": [ + 46, + 518, + 287, + 685 + ], + "type": "text", + "content": ", The relative error " + }, + { + "bbox": [ + 46, + 518, + 287, + 685 + ], + "type": "inline_equation", + "content": "\\delta_{CE}" + }, + { + "bbox": [ + 46, + 518, + 287, + 685 + ], + "type": "text", + "content": " caused by the floating-point rounding errors is much more minor, varies continuously with T, and reaches the minimum when " + }, + { + "bbox": [ + 46, + 518, + 287, + 685 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 46, + 518, + 287, + 685 + ], + "type": "text", + "content": " is approximately 1. But one thing that needs to be highlighted is that after the relative error reaches the minimum, it starts to increase as " + }, + { + "bbox": [ + 46, + 518, + 287, + 685 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 46, + 518, + 287, + 685 + ], + "type": "text", + "content": " gets closer to 0." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "content": "Following the same operation, we add a scale factor " + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "inline_equation", + "content": "c" + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\Delta" + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "content": " and hold " + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "inline_equation", + "content": "T = c\\Delta" + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "content": " constant during each iteration of the" + } + ] + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 313, + 272, + 541, + 402 + ], + "blocks": [ + { + "bbox": [ + 65, + 236, + 526, + 247 + ], + "lines": [ + { + "bbox": [ + 65, + 236, + 526, + 247 + ], + "spans": [ + { + "bbox": [ + 65, + 236, + 526, + 247 + ], + "type": "text", + "content": "Figure 2. The distributions of " + }, + { + "bbox": [ + 65, + 236, + 526, + 247 + ], + "type": "inline_equation", + "content": "\\Delta = \\mathbf{z}_{\\pi 1} - \\mathbf{z}_{\\pi 2}" + }, + { + "bbox": [ + 65, + 236, + 526, + 247 + ], + "type": "text", + "content": " for the defending models on the CIFAR-10 dataset are averaged across 100 bins." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 313, + 272, + 541, + 402 + ], + "lines": [ + { + "bbox": [ + 313, + 272, + 541, + 402 + ], + "spans": [ + { + "bbox": [ + 313, + 272, + 541, + 402 + ], + "type": "image", + "image_path": "d95af38b41c36f9eb37c4797d3eab35679b7ce2f952d071ecd6328714713887a.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 412, + 546, + 456 + ], + "lines": [ + { + "bbox": [ + 305, + 412, + 546, + 456 + ], + "spans": [ + { + "bbox": [ + 305, + 412, + 546, + 456 + ], + "type": "text", + "content": "Figure 3. The relative error of the gradient information computed using half-precision floating-point operations on a binary classification task with the CE loss varies with " + }, + { + "bbox": [ + 305, + 412, + 546, + 456 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 305, + 412, + 546, + 456 + ], + "type": "text", + "content": " for a given adversarial example within a single iteration." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 483, + 545, + 626 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 483, + 545, + 626 + ], + "spans": [ + { + "bbox": [ + 304, + 483, + 545, + 626 + ], + "type": "text", + "content": "multi-iteration attack. This technique, which we refer to as FT-PGD, allows us to assess the model's robustness with a fixed " + }, + { + "bbox": [ + 304, + 483, + 545, + 626 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 304, + 483, + 545, + 626 + ], + "type": "text", + "content": " value. In Figure 4, we evaluate the model's robustness using FT-PGD at various " + }, + { + "bbox": [ + 304, + 483, + 545, + 626 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 304, + 483, + 545, + 626 + ], + "type": "text", + "content": " values. By comparing the relative floating-point error in Figure 3 with the attack's performance in Figure 4, we observe a strong correlation between the relative error " + }, + { + "bbox": [ + 304, + 483, + 545, + 626 + ], + "type": "inline_equation", + "content": "\\delta_{CE}" + }, + { + "bbox": [ + 304, + 483, + 545, + 626 + ], + "type": "text", + "content": " and the attack's effectiveness. Thus, the relative error is a critical factor that contributes to overestimating the model's robustness. Furthermore, we identify two distinct phases in the impact of floating-point errors on gradient-based attacks due to the CE loss, which depend on the relationship between " + }, + { + "bbox": [ + 304, + 483, + 545, + 626 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 304, + 483, + 545, + 626 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 483, + 545, + 626 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 304, + 483, + 545, + 626 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 630, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 630, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 304, + 630, + 545, + 712 + ], + "type": "text", + "content": "(a) The attack failed due to floating-point underflow errors. When " + }, + { + "bbox": [ + 304, + 630, + 545, + 712 + ], + "type": "inline_equation", + "content": "T \\geq \\lambda" + }, + { + "bbox": [ + 304, + 630, + 545, + 712 + ], + "type": "text", + "content": ", floating-point underflow causes the calculated gradient equal to zero and " + }, + { + "bbox": [ + 304, + 630, + 545, + 712 + ], + "type": "inline_equation", + "content": "\\delta_{CE} = 100\\%" + }, + { + "bbox": [ + 304, + 630, + 545, + 712 + ], + "type": "text", + "content": ". As a result, the input perturbation becomes zero, and the model's robustness is measured to be equal to its clean accuracy, which leads to a significant overestimation of the model's robustness." + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "4059" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 54, + 76, + 281, + 205 + ], + "blocks": [ + { + "bbox": [ + 54, + 76, + 281, + 205 + ], + "lines": [ + { + "bbox": [ + 54, + 76, + 281, + 205 + ], + "spans": [ + { + "bbox": [ + 54, + 76, + 281, + 205 + ], + "type": "image", + "image_path": "b0b8ab6948caca79330c28616c95877a9f7f6cf30e7bcee041befb84223822f3.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 216, + 289, + 282 + ], + "lines": [ + { + "bbox": [ + 46, + 216, + 289, + 282 + ], + "spans": [ + { + "bbox": [ + 46, + 216, + 289, + 282 + ], + "type": "text", + "content": "Figure 4. A higher zero ratio, which represents the proportion of zero elements in the perturbation, leads to larger overestimations when evaluating model robustness. We assess model robustness using 100 iterations of FT-PGD with CE loss on the CIFAR-10 dataset under half-precision floating-point arithmetic. The model is obtained from [59]." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 304, + 287, + 425 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 304, + 287, + 425 + ], + "spans": [ + { + "bbox": [ + 46, + 304, + 287, + 425 + ], + "type": "text", + "content": "(b) The attack's performance fluctuates with the small relative error caused by floating-point rounding errors. When " + }, + { + "bbox": [ + 46, + 304, + 287, + 425 + ], + "type": "inline_equation", + "content": "0 \\leq T < \\lambda" + }, + { + "bbox": [ + 46, + 304, + 287, + 425 + ], + "type": "text", + "content": ", the computed gradient's relative error due to the floating-point rounding error is small and has the same variation pattern as the zero ratio and attack performance. The smallest relative error occurs around " + }, + { + "bbox": [ + 46, + 304, + 287, + 425 + ], + "type": "inline_equation", + "content": "T = 1" + }, + { + "bbox": [ + 46, + 304, + 287, + 425 + ], + "type": "text", + "content": ". However, it's crucial to note that at the bottom left of Figure 3 and Figure 4, the relative error and its detrimental effect on the gradient-based attack increase as " + }, + { + "bbox": [ + 46, + 304, + 287, + 425 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 46, + 304, + 287, + 425 + ], + "type": "text", + "content": " approaches zero after reaching the minimum." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 426, + 288, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 426, + 288, + 628 + ], + "spans": [ + { + "bbox": [ + 46, + 426, + 288, + 628 + ], + "type": "text", + "content": "It is straightforward to assume that since floating-point errors cause the above problem, it should be possible to solve the problem by simply increasing the precision of floating-point arithmetics because it can effectively reduce the floating-point errors. To test whether this simple idea works, we evaluated the impact of different floating-point arithmetics precisions, including half-precision, single-precision, and double-precision, on the model's robustness against FT-PGD with 100 iterations. As depicted in Figure 5, the attack's performance exhibits a similar variation pattern across different precisions, and the model's robustness measured with PGD remains nearly unchanged. While increasing the floating-point precision can delay attack failure due to floating-point underflow errors, it incurs significant computational overhead. Therefore, increasing the floating-point precision is not a viable solution to address the problem." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 630, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 630, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 630, + 287, + 715 + ], + "type": "text", + "content": "Surrogate loss functions(3,4) have been proposed [6, 10, 18] to work around floating-point underflow errors. They avoid suffering from floating-point underflow errors by discarding softmax operations. At the same time, they only use partial " + }, + { + "bbox": [ + 46, + 630, + 287, + 715 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 46, + 630, + 287, + 715 + ], + "type": "text", + "content": " elements in the new loss function. To demonstrate the effect of discarding elements of " + }, + { + "bbox": [ + 46, + 630, + 287, + 715 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 46, + 630, + 287, + 715 + ], + "type": "text", + "content": " on the attack's performance, We designed an experiment to make only a fixed" + } + ] + } + ], + "index": 4 + }, + { + "type": "image", + "bbox": [ + 313, + 76, + 540, + 207 + ], + "blocks": [ + { + "bbox": [ + 313, + 76, + 540, + 207 + ], + "lines": [ + { + "bbox": [ + 313, + 76, + 540, + 207 + ], + "spans": [ + { + "bbox": [ + 313, + 76, + 540, + 207 + ], + "type": "image", + "image_path": "c9c9e888fdb5a71a6da290d8d2d9f7340e414777a2ac14d5de2eca4cedead01b.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 216, + 547, + 261 + ], + "lines": [ + { + "bbox": [ + 305, + 216, + 547, + 261 + ], + "spans": [ + { + "bbox": [ + 305, + 216, + 547, + 261 + ], + "type": "text", + "content": "Figure 5. The model's robustness test results on the CIFAR-10 dataset under Float16, Float32, and Float64 follow a similar pattern of variation, except that the thresholds that lead to the attack's failure are different, the model obtained from [59]." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_caption" + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 288, + 547, + 491 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 288, + 547, + 491 + ], + "spans": [ + { + "bbox": [ + 304, + 288, + 547, + 491 + ], + "type": "text", + "content": "number of " + }, + { + "bbox": [ + 304, + 288, + 547, + 491 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 304, + 288, + 547, + 491 + ], + "type": "text", + "content": " elements participate in the calculation of the gradients by exploiting floating-point underflow errors. To achieve this goal we scale the logits " + }, + { + "bbox": [ + 304, + 288, + 547, + 491 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_{\\pi 1} - \\mathbf{z}_{\\pi i}" + }, + { + "bbox": [ + 304, + 288, + 547, + 491 + ], + "type": "text", + "content": " by a scale factor " + }, + { + "bbox": [ + 304, + 288, + 547, + 491 + ], + "type": "inline_equation", + "content": "c" + }, + { + "bbox": [ + 304, + 288, + 547, + 491 + ], + "type": "text", + "content": " to make " + }, + { + "bbox": [ + 304, + 288, + 547, + 491 + ], + "type": "inline_equation", + "content": "c(\\mathbf{z}_{\\pi 1} - \\mathbf{z}_{\\pi i}) = \\lambda" + }, + { + "bbox": [ + 304, + 288, + 547, + 491 + ], + "type": "text", + "content": ", such that " + }, + { + "bbox": [ + 304, + 288, + 547, + 491 + ], + "type": "inline_equation", + "content": "p_{\\pi j}^{c} = 0" + }, + { + "bbox": [ + 304, + 288, + 547, + 491 + ], + "type": "text", + "content": " if " + }, + { + "bbox": [ + 304, + 288, + 547, + 491 + ], + "type": "inline_equation", + "content": "j \\geq i" + }, + { + "bbox": [ + 304, + 288, + 547, + 491 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 288, + 547, + 491 + ], + "type": "inline_equation", + "content": "p_{\\pi j}^{c} > 0" + }, + { + "bbox": [ + 304, + 288, + 547, + 491 + ], + "type": "text", + "content": " if " + }, + { + "bbox": [ + 304, + 288, + 547, + 491 + ], + "type": "inline_equation", + "content": "j < i" + }, + { + "bbox": [ + 304, + 288, + 547, + 491 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 288, + 547, + 491 + ], + "type": "inline_equation", + "content": "i \\in \\{2,3,\\dots,K\\}" + }, + { + "bbox": [ + 304, + 288, + 547, + 491 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 288, + 547, + 491 + ], + "type": "inline_equation", + "content": "j \\in \\{1,2,3,\\dots,K\\}" + }, + { + "bbox": [ + 304, + 288, + 547, + 491 + ], + "type": "text", + "content": ". So that only " + }, + { + "bbox": [ + 304, + 288, + 547, + 491 + ], + "type": "inline_equation", + "content": "i - 1" + }, + { + "bbox": [ + 304, + 288, + 547, + 491 + ], + "type": "text", + "content": " number of " + }, + { + "bbox": [ + 304, + 288, + 547, + 491 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 304, + 288, + 547, + 491 + ], + "type": "text", + "content": " elements are involved in the gradient calculation, thus giving PGD the ability to attack the network with a fixed number of " + }, + { + "bbox": [ + 304, + 288, + 547, + 491 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 304, + 288, + 547, + 491 + ], + "type": "text", + "content": " elements, which we now call FNZ-PGD. We use FNZ-PGD with different numbers of " + }, + { + "bbox": [ + 304, + 288, + 547, + 491 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 304, + 288, + 547, + 491 + ], + "type": "text", + "content": " elements to evaluate the model's robustness which is overestimated mainly due to floating-point errors. From Figure 6, we can see that the more " + }, + { + "bbox": [ + 304, + 288, + 547, + 491 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 304, + 288, + 547, + 491 + ], + "type": "text", + "content": " elements involved in the attack, the more potent the attack will be. So discarding the " + }, + { + "bbox": [ + 304, + 288, + 547, + 491 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 304, + 288, + 547, + 491 + ], + "type": "text", + "content": " element in the loss function will impair the attack's performance when model robustness is overestimated mainly due to floating-point errors." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 495, + 547, + 626 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 495, + 547, + 626 + ], + "spans": [ + { + "bbox": [ + 304, + 495, + 547, + 626 + ], + "type": "text", + "content": "In summary, the relative error in the calculated gradients due to the floating-point errors, which include floating-point underflow errors and floating-point rounding errors, is the critical factor contributing to the overestimation of the model's robustness. While floating-point errors are a primary cause of gradient-based attacks' failure, they are not the sole cause. Reducing their impact can only address the portion of model robustness that is overestimated due to them. Therefore, it is unrealistic to expect that solely reducing the impact of floating-point errors alone will eliminate all problems related to overestimating model robustness." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 630, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 630, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 630, + 547, + 715 + ], + "type": "text", + "content": "Although we cannot eliminate the relative error in the gradients caused by floating-point errors, we can control it's side effect and significantly increase the power of gradient-based attacks. As a result, we propose the Minimize the impact of floating-point errors (MIFPE) loss, a small modification to the original CE loss, which scales the logits adaptively before the softmax operation. For untargeted and tar" + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "4060" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 54, + 76, + 287, + 207 + ], + "blocks": [ + { + "bbox": [ + 54, + 76, + 287, + 207 + ], + "lines": [ + { + "bbox": [ + 54, + 76, + 287, + 207 + ], + "spans": [ + { + "bbox": [ + 54, + 76, + 287, + 207 + ], + "type": "image", + "image_path": "694ce9b0c918646cac4415f771ff25ccb1d1c3c6cb15b66c232525d0946a79e7.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 216, + 290, + 295 + ], + "lines": [ + { + "bbox": [ + 46, + 216, + 290, + 295 + ], + "spans": [ + { + "bbox": [ + 46, + 216, + 290, + 295 + ], + "type": "text", + "content": "Figure 6. Using more " + }, + { + "bbox": [ + 46, + 216, + 290, + 295 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 46, + 216, + 290, + 295 + ], + "type": "text", + "content": " elements increases attack potency when model robustness is overestimated mainly due to floating-point errors. We utilized FNZ-PGD with 100 iterations, CE loss, and a baseline of PGD-100 with CE, C&W, and DLR loss under CIFAR10. All floating-point operations were single-precision, and the model was obtained from [59]. Here, " + }, + { + "bbox": [ + 46, + 216, + 290, + 295 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 46, + 216, + 290, + 295 + ], + "type": "text", + "content": " refers to the number of " + }, + { + "bbox": [ + 46, + 216, + 290, + 295 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 46, + 216, + 290, + 295 + ], + "type": "text", + "content": " elements used." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 313, + 261, + 327 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 313, + 261, + 327 + ], + "spans": [ + { + "bbox": [ + 47, + 313, + 261, + 327 + ], + "type": "text", + "content": "geted attacks, the targets are as follows respectively:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 90, + 332, + 287, + 348 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 90, + 332, + 287, + 348 + ], + "spans": [ + { + "bbox": [ + 90, + 332, + 287, + 348 + ], + "type": "interline_equation", + "content": "\\mathcal {L} ^ {\\mathrm {M I F P E}} (\\mathbf {z}, y) \\triangleq \\mathcal {L} ^ {\\mathrm {c e}} \\left(T \\mathbf {z} / \\Delta_ {\\text {d e t a c h}}, y\\right), \\tag {7}", + "image_path": "39ce14776a02bc55fe726f0582e545bd42643ce5fea7a86057cc1caca5262922.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 85, + 365, + 287, + 380 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 85, + 365, + 287, + 380 + ], + "spans": [ + { + "bbox": [ + 85, + 365, + 287, + 380 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\text {t a r g e t}} ^ {\\mathrm {M I F P E}} \\left(\\mathbf {z}, y _ {\\mathrm {t}}\\right) = - \\mathcal {L} ^ {\\mathrm {c e}} \\left(T \\mathbf {z} / \\Delta_ {\\text {d e t a c h}}, y _ {\\mathrm {t}}\\right), \\tag {8}", + "image_path": "213fd04280be64b05e6076b4e2bfbd69316df2bdf1a2ee2b97ce423e0de747cc.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 384, + 287, + 431 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 384, + 287, + 431 + ], + "spans": [ + { + "bbox": [ + 47, + 384, + 287, + 431 + ], + "type": "text", + "content": "Where " + }, + { + "bbox": [ + 47, + 384, + 287, + 431 + ], + "type": "inline_equation", + "content": "y_{t}" + }, + { + "bbox": [ + 47, + 384, + 287, + 431 + ], + "type": "text", + "content": " is a predefined class target, " + }, + { + "bbox": [ + 47, + 384, + 287, + 431 + ], + "type": "inline_equation", + "content": "t \\in \\{1, 2, \\dots, K\\}" + }, + { + "bbox": [ + 47, + 384, + 287, + 431 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 384, + 287, + 431 + ], + "type": "inline_equation", + "content": "y_{t} \\neq y" + }, + { + "bbox": [ + 47, + 384, + 287, + 431 + ], + "type": "text", + "content": ". In our experiments, the factor " + }, + { + "bbox": [ + 47, + 384, + 287, + 431 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 47, + 384, + 287, + 431 + ], + "type": "text", + "content": " was set to around 1 to minimize the detrimental effect of floating-point errors on the gradient-based attacks." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 432, + 289, + 564 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 432, + 289, + 564 + ], + "spans": [ + { + "bbox": [ + 46, + 432, + 289, + 564 + ], + "type": "text", + "content": "The new surrogate loss " + }, + { + "bbox": [ + 46, + 432, + 289, + 564 + ], + "type": "inline_equation", + "content": "\\mathcal{L}^{\\mathrm{MIFPE}}" + }, + { + "bbox": [ + 46, + 432, + 289, + 564 + ], + "type": "text", + "content": " has fourfold advantages. First, it can eliminate the failure of gradient-based attacks due to floating-point underflow errors. Second, it can minimize the impact of the small relative error due to floating-point rounding errors and significantly improve the performance of gradient-based attacks. Third, it provides the flexibility to adjust the number of logit elements involved in the attack simply by changing the value of T. Finally, unlike the C&W or DLR loss, it still represents the original CE loss faithfully, and all values in the logit vector can still contribute to the gradient calculation." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 574, + 129, + 588 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 574, + 129, + 588 + ], + "spans": [ + { + "bbox": [ + 47, + 574, + 129, + 588 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 594, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 594, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 289, + 715 + ], + "type": "text", + "content": "To ensure a fair comparison against other loss functions in our evaluation and to make our evaluation as comprehensive as possible, we conducted tests on different threat models and datasets. Specifically, we tested the " + }, + { + "bbox": [ + 46, + 594, + 289, + 715 + ], + "type": "inline_equation", + "content": "\\ell_{\\infty}" + }, + { + "bbox": [ + 46, + 594, + 289, + 715 + ], + "type": "text", + "content": "-norm bounded perturbation on the CIFAR-10, CIFAR-100, MNIST [25] and ImageNet datasets [11], and the " + }, + { + "bbox": [ + 46, + 594, + 289, + 715 + ], + "type": "inline_equation", + "content": "\\ell_{2}" + }, + { + "bbox": [ + 46, + 594, + 289, + 715 + ], + "type": "text", + "content": "-norm threat model on the CIFAR-10 dataset. For each test, we ran the PGD with different loss functions, including the cross-entropy (CE) loss function, the C&W loss function [6], the DLR loss function [10], and our proposed MIFPE. We kept" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 72, + 547, + 252 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 252 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 252 + ], + "type": "text", + "content": "all other settings the same across the tests. Firstly, we used 100 iterations for each test. Secondly, we adopted the same step-size schedule with a linear decay [56], which updates the perturbation boundary " + }, + { + "bbox": [ + 304, + 72, + 547, + 252 + ], + "type": "inline_equation", + "content": "\\epsilon" + }, + { + "bbox": [ + 304, + 72, + 547, + 252 + ], + "type": "text", + "content": " at each iteration " + }, + { + "bbox": [ + 304, + 72, + 547, + 252 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 304, + 72, + 547, + 252 + ], + "type": "text", + "content": " according to the formula " + }, + { + "bbox": [ + 304, + 72, + 547, + 252 + ], + "type": "inline_equation", + "content": "2\\epsilon (1 - i / I)" + }, + { + "bbox": [ + 304, + 72, + 547, + 252 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 72, + 547, + 252 + ], + "type": "inline_equation", + "content": "I" + }, + { + "bbox": [ + 304, + 72, + 547, + 252 + ], + "type": "text", + "content": " denotes the total number of iterations. Thirdly, we employed momentum-based updates [10] with a momentum factor of " + }, + { + "bbox": [ + 304, + 72, + 547, + 252 + ], + "type": "inline_equation", + "content": "\\nu = 0.75" + }, + { + "bbox": [ + 304, + 72, + 547, + 252 + ], + "type": "text", + "content": " for all tests. Lastly, we saved the best adversarial examples generated during the attack. To demonstrate the effectiveness of MIFPE in achieving near-state-of-the-art robustness with only 100 iterations, we compare our results with the best robust accuracy reported on RobustBench1, which uses an ensemble of attacks and a minimum of 4900 iterations. We also compared the attack performance of MIFPE with GAMA_PGD [43] under the same 100-iteration constraint." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 253, + 547, + 469 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 253, + 547, + 469 + ], + "spans": [ + { + "bbox": [ + 304, + 253, + 547, + 469 + ], + "type": "text", + "content": "In Table 1, we present a comprehensive comparison showing that MIFPE outperforms CE, C&W, and DLR loss functions on all tested models. Additionally, we found that when PGD with momentum and step schedule using MIFPE as the loss function outperforms GAMA_PGD on all tested models by at least more than " + }, + { + "bbox": [ + 304, + 253, + 547, + 469 + ], + "type": "inline_equation", + "content": "0.1\\%" + }, + { + "bbox": [ + 304, + 253, + 547, + 469 + ], + "type": "text", + "content": " under 100 iterations constraint, which is impossible when PGD with momentum and step schedule using CE, C&W and DLR as the loss function. Remarkably, even with only 100 iterations, MIFPE achieves results that are very close to the best results obtained with at least 4900 iterations on some models, such as Uncovering limits [17] and Proper definition [32] for CIFAR10, " + }, + { + "bbox": [ + 304, + 253, + 547, + 469 + ], + "type": "inline_equation", + "content": "l_{\\infty}" + }, + { + "bbox": [ + 304, + 253, + 547, + 469 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 253, + 547, + 469 + ], + "type": "inline_equation", + "content": "\\varepsilon = 8/255" + }, + { + "bbox": [ + 304, + 253, + 547, + 469 + ], + "type": "text", + "content": ". Our findings also reveal that C&W and DLR perform even worse than CE in some cases, such as on Robustness library [14] and Fast adversarial training [51] for CIFAR10, " + }, + { + "bbox": [ + 304, + 253, + 547, + 469 + ], + "type": "inline_equation", + "content": "l_{\\infty}" + }, + { + "bbox": [ + 304, + 253, + 547, + 469 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 253, + 547, + 469 + ], + "type": "inline_equation", + "content": "\\varepsilon = 8/255" + }, + { + "bbox": [ + 304, + 253, + 547, + 469 + ], + "type": "text", + "content": ". This suggests that discarding partial logit elements in the loss function would decrease the effectiveness of gradient-based attacks." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 471, + 548, + 601 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 471, + 548, + 601 + ], + "spans": [ + { + "bbox": [ + 304, + 471, + 548, + 601 + ], + "type": "text", + "content": "Faster convergence. We want to highlight that the effectiveness of MIFPE is not achieved by increasing the computational cost compared to other loss functions. We found that minimising the effect of the floating-point errors leads to faster convergence speed than competing loss functions. Figure 7 shows that for all two defending models, MIFPE loss performs more efficiently, and often with orders of magnitude faster than other loss functions for successful attacks. Finally, minimising the effect of floating-point error operation introduces no overhead and imposes no impact on the iteration time." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 604, + 547, + 663 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 604, + 547, + 663 + ], + "spans": [ + { + "bbox": [ + 304, + 604, + 547, + 663 + ], + "type": "text", + "content": "Boost the capability of existing attack strategies. Because MIFPE is a loss function, it can be easily integrated with existing attack strategies by replacing the original loss function. The results in Table 2 show that using MIFPE boosts the attack's effectiveness." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 665, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 547, + 713 + ], + "type": "text", + "content": "Ablation analysis. Our ablation experiments, presented in Table 3, investigated the effect of momentum and step-size schedule on PGD using different loss functions with 100 iterations. The results show that the MIFPE consist" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 314, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 314, + 758 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 314, + 758 + ], + "type": "text", + "content": "4061" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 47, + 135, + 545, + 586 + ], + "blocks": [ + { + "bbox": [ + 46, + 70, + 545, + 126 + ], + "lines": [ + { + "bbox": [ + 46, + 70, + 545, + 126 + ], + "spans": [ + { + "bbox": [ + 46, + 70, + 545, + 126 + ], + "type": "text", + "content": "Table 1. Comparing the proposed MIFPE loss " + }, + { + "bbox": [ + 46, + 70, + 545, + 126 + ], + "type": "inline_equation", + "content": "(\\mathcal{L}^{\\mathrm{MIFPE}})" + }, + { + "bbox": [ + 46, + 70, + 545, + 126 + ], + "type": "text", + "content": ", against CE " + }, + { + "bbox": [ + 46, + 70, + 545, + 126 + ], + "type": "inline_equation", + "content": "(\\mathcal{L}^{\\mathrm{ce}})" + }, + { + "bbox": [ + 46, + 70, + 545, + 126 + ], + "type": "text", + "content": ", C&W " + }, + { + "bbox": [ + 46, + 70, + 545, + 126 + ], + "type": "inline_equation", + "content": "(\\mathcal{L}^{\\mathrm{cw}})" + }, + { + "bbox": [ + 46, + 70, + 545, + 126 + ], + "type": "text", + "content": ", and DLR " + }, + { + "bbox": [ + 46, + 70, + 545, + 126 + ], + "type": "inline_equation", + "content": "(\\mathcal{L}^{\\mathrm{dlr}})" + }, + { + "bbox": [ + 46, + 70, + 545, + 126 + ], + "type": "text", + "content": " losses. For each surrogate loss, we use PGD-100 with the step-size schedule " + }, + { + "bbox": [ + 46, + 70, + 545, + 126 + ], + "type": "inline_equation", + "content": "2\\epsilon (1 - i / I)" + }, + { + "bbox": [ + 46, + 70, + 545, + 126 + ], + "type": "text", + "content": " and momentum " + }, + { + "bbox": [ + 46, + 70, + 545, + 126 + ], + "type": "inline_equation", + "content": "\\nu = 0.75" + }, + { + "bbox": [ + 46, + 70, + 545, + 126 + ], + "type": "text", + "content": ". Models marked with " + }, + { + "bbox": [ + 46, + 70, + 545, + 126 + ], + "type": "inline_equation", + "content": "\\dagger" + }, + { + "bbox": [ + 46, + 70, + 545, + 126 + ], + "type": "text", + "content": " were trained with extra data. Models marked with " + }, + { + "bbox": [ + 46, + 70, + 545, + 126 + ], + "type": "inline_equation", + "content": "\\ddagger" + }, + { + "bbox": [ + 46, + 70, + 545, + 126 + ], + "type": "text", + "content": ", which used " + }, + { + "bbox": [ + 46, + 70, + 545, + 126 + ], + "type": "inline_equation", + "content": "\\varepsilon = 0.031" + }, + { + "bbox": [ + 46, + 70, + 545, + 126 + ], + "type": "text", + "content": " as originally reported by the authors. Numbers in parentheses indicate the improvement w.r.t. the CE baseline. The best, calculated using an ensemble of attacks and a minimum of 4900 iterations, is reported from RobustBench1 to demonstrate how closely MIFPE can approach the lowest known robustness accuracy with only 100 iterations." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 47, + 135, + 545, + 586 + ], + "lines": [ + { + "bbox": [ + 47, + 135, + 545, + 586 + ], + "spans": [ + { + "bbox": [ + 47, + 135, + 545, + 586 + ], + "type": "table", + "html": "
Defense methodArchitectureCleanCE (Lce)100C&W (Lcw)100DLR (Ldir)100GAMA_PGD100MIFPE (LMIFPE)100Best4900
MNIST, ℓ∞, ε = 0.3
Uncovering limits [17]WRN-28-1099.2696.5596.64(+0.09)96.71(+0.16)96.69(+0.14)96.53(-0.02)96.31
MMA training [12]†LeNet5Madry98.9895.6695.60(-0.06)95.56(-0.10)95.96(+0.13)95.50(-0.16)93.51
MMA training [12]LeNet5Madry98.9595.0995.33(+0.24)95.59(+0.50)95.74(+0.19)94.88(-0.21)91.40
Neural level sets [3]SmallCNN99.3599.2894.68(-4.60)95.09(-4.19)99.29(+0.01)94.67(-4.61)90.85
TRADES [59]SmallCNN99.4893.6993.88(+0.19)94.49(+0.80)93.82(+0.13)93.67(-0.02)92.71
Robust optimization [29]SmallCNN99.3593.0693.19(+0.13)93.63(+0.57)93.39(+0.33)92.88(-0.18)90.85
Fast adversarial training [51]SmallCNN98.5086.8286.96(+0.14)87.42(+0.60)87.62(+0.80)86.57(-0.25)82.93
CIFAR-10, ℓ∞, ε = 8/255
Uncovering limits [17]†WRN-70-1691.1067.9666.70(-1.26)66.78(-1.18)66.08(-1.88)65.96(-2.00)65.87
Fixing data augmentation [36]WRN-106-1688.5067.5765.55(-2.02)65.61(-1.96)64.94(-2.63)64.75(-2.82)64.58
Fixing data augmentation [36]WRN-70-1688.5467.2765.23(-2.04)65.32(-1.95)64.57(-2.70)64.46(-2.81)64.20
Proper definition [32]WRN-70-1689.0166.6663.94(-2.72)64.01(-2.65)63.65(-3.01)63.49(-3.17)63.35
Uncovering limits [17]†WRN-28-1089.4865.5963.62(-1.97)63.82(-1.77)63.05(-2.90)62.96(-2.63)62.76
Proper definition [32]WRN-28-1088.6164.6661.55(-3.11)61.62(-3.04)61.19(-3.47)61.12(-3.54)61.04
Adversarial weight perturbation [53]†WRN-28-1088.2563.1860.51(-2.67)60.60(-2.58)60.18(-3.00)60.09(-3.09)60.04
Unlabeled data [7]†WRN-28-1089.6961.6060.47(-1.13)60.67(-0.93)59.82(-1.78)59.72(-1.88)59.53
HYDRA [40]†WRN-28-1088.9859.5358.21(-1.32)58.30(-1.23)57.52(-2.01)57.38(-2.15)57.14
Misclassification-aware [50]WRN-28-1087.5061.6058.03(-3.57)58.73(-2.87)57.20(-4.40)56.88(-4.72)56.29
Pre-training [19]†WRN-28-1087.1157.0756.27(-0.80)57.07(0.00)55.22(-1.85)55.10(-1.97)54.92
Hypersphere embedding [33]WRN-34-2085.1461.4355.35(-6.08)56.21(-5.22)54.37(-7.06)53.85(-7.58)53.74
Overfitting [37]WRN-34-2085.3456.8555.22(-1.63)55.97(-0.88)53.87(-2.98)53.62(-3.23)53.42
Self-adaptive training [20]‡WRN-34-1083.4856.1254.30(-1.82)54.73(-1.39)53.64(-2.48)53.48(-2.64)53.34
TRADES [59]‡WRN-34-1084.9255.2153.94(-1.27)54.11(-1.10)53.38(-1.83)53.22(-1.99)53.08
Robustness library [14]RN-5087.0351.5652.07(+0.51)52.81(+1.25)50.04(-1.52)49.84(-1.72)49.25
Neural level sets [3]‡RN-1881.3079.1240.07(-39.05)45.10(-34.02)79.69(+0.57)40.06(-39.06)39.77
YOPO [58]WRN-34-1087.2046.0547.02(+0.97)47.55(+1.50)45.30(-0.75)45.19(-0.86)44.83
Fast adversarial training [51]RN-1883.3445.7545.81(+0.06)46.89(+1.14)43.71(-2.04)43.57(-2.18)43.21
CIFAR-10, ℓ∞, ε = 8/255
Adversarial weight perturbation [54]WRN-34-1060.3833.0930.74(-2.35)31.13(-1.96)29.44(-3.65)29.35(-3.74)28.86
Pre-training [19]†WRN-28-1059.2332.8230.58(-2.24)31.83(-0.99)29.22(-3.60)29.02(-3.80)28.42
Progressive Hardening [42]WRN-34-1062.8226.1826.69(+0.51)27.26(+1.08)24.97(-1.21)24.91(-1.27)24.57
Overfitting [37]RN-1853.8320.4720.17(-0.30)20.30(-0.17)19.20(-1.27)19.16(-1.31)18.95
ImageNet, ℓ∞, ε = 4/255
Transfer Better [39]RN-5064.0238.4437.26(-1.18)37.72(-0.72)34.94(-3.50)34.84(-3.60)34.96
Robustness library [14]RN-5062.5632.1632.24(+0.08)32.80(+0.64)29.72(-2.44)29.60(-2.56)29.22
Transfer Better [39]RN-1852.9229.3027.14(-2.16)27.40(1.90)25.56(-3.74)25.40(-3.90)18.95
CIFAR-10, ℓ2, ε = 0.5
Uncovering limits [17]†WRN-70-1694.7481.7180.93(-0.78)80.94(-0.77)87.74(+6.03)80.57(-1.14)80.53
Uncovering limits [17]WRN-70-1690.9075.2074.89(-0.31)74.95(-0.25)81.78(+6.58)74.56(-0.64)74.50
Adversarial weight perturbation [54]WRN-34-1088.5174.7773.88(-0.89)73.89(-0.88)79.38(+4.61)73.67(-1.10)73.66
Robustness library [14]RN-5090.8369.6570.13(+0.48)70.25(+0.60)78.15(+8.50)69.29(-0.36)69.24
Overfitting [37]RN-1888.6768.6668.74(+0.08)69.03(+0.37)76.19(+7.53)67.87(-0.79)67.68
Decoupling direction and norm [38]WRN-28-1089.0566.5667.00(+0.44)67.02(+0.46)74.61(+8.05)66.48(-0.08)66.44
MMA training [12]WRN-28-488.0266.2266.58(+0.36)66.60(+0.38)71.44(+5.22)66.16(-0.06)66.09
", + "image_path": "83b7d990ada4c8d4f82ad14f456a1450212fb2df50899a56031be26ffb8aa8b6.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 607, + 287, + 656 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 607, + 287, + 656 + ], + "spans": [ + { + "bbox": [ + 46, + 607, + 287, + 656 + ], + "type": "text", + "content": "tently outperforms the other loss functions, and shows the least variance across different setups. These findings suggest that the effectiveness of the MIFPE should not be dependent on the momentum and step-size schedule." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "text", + "content": "To analyze the reasons for the failure of the attack due to floating-point rounding errors, we selected " + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\mathbb{Z} = \\mathbf{z}_y - \\max_{i\\neq y}\\mathbf{z}_i" + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "text", + "content": " because its sign indicates if the attack is successful or not. We compared the change of " + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\mathbb{Z}" + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "text", + "content": " for samples" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 304, + 607, + 547, + 704 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 607, + 547, + 704 + ], + "spans": [ + { + "bbox": [ + 304, + 607, + 547, + 704 + ], + "type": "text", + "content": "attacked by PGD-100 with CE loss but failed, and PGD-100 with MIFPE loss and succeeded. Figure 8 demonstrates that for samples attacked with CE loss, the value of " + }, + { + "bbox": [ + 304, + 607, + 547, + 704 + ], + "type": "inline_equation", + "content": "\\mathbb{Z}" + }, + { + "bbox": [ + 304, + 607, + 547, + 704 + ], + "type": "text", + "content": " rapidly approaches 0 in the first few iterations and then remains positive afterwards. On the other hand, when attacked with MIFPE loss " + }, + { + "bbox": [ + 304, + 607, + 547, + 704 + ], + "type": "inline_equation", + "content": "\\mathbb{Z}" + }, + { + "bbox": [ + 304, + 607, + 547, + 704 + ], + "type": "text", + "content": " smoothly drops below 0 after approaching 0. This phenomenon suggests that the floating-point rounding error primarily may cause attack failure when the samples" + } + ] + } + ], + "index": 4 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "4062" + } + ] + } + ], + "index": 5 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 53, + 75, + 164, + 184 + ], + "blocks": [ + { + "bbox": [ + 53, + 75, + 164, + 184 + ], + "lines": [ + { + "bbox": [ + 53, + 75, + 164, + 184 + ], + "spans": [ + { + "bbox": [ + 53, + 75, + 164, + 184 + ], + "type": "image", + "image_path": "22f4e9b5f5dc78cafba4055356ed916a85bf9b502249809575bea5b1b69f8a15.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 190, + 287, + 236 + ], + "lines": [ + { + "bbox": [ + 46, + 190, + 287, + 236 + ], + "spans": [ + { + "bbox": [ + 46, + 190, + 287, + 236 + ], + "type": "text", + "content": "Figure 7. We compare MIFPE to standard CE loss and other surrogate loss functions (C&W [6] and DLR [10]) on defenders [58,59]. The graph shows iterations on the horizontal axis and the percentage of unsuccessful examples on the vertical axis." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 166, + 76, + 281, + 184 + ], + "blocks": [ + { + "bbox": [ + 166, + 76, + 281, + 184 + ], + "lines": [ + { + "bbox": [ + 166, + 76, + 281, + 184 + ], + "spans": [ + { + "bbox": [ + 166, + 76, + 281, + 184 + ], + "type": "image", + "image_path": "4175ca8ed00fddb62a84ad39eadc7f4a91c86d20fcccdec3b45b11f3d9169ad1.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 234, + 546, + 289 + ], + "lines": [ + { + "bbox": [ + 305, + 234, + 546, + 289 + ], + "spans": [ + { + "bbox": [ + 305, + 234, + 546, + 289 + ], + "type": "text", + "content": "Figure 8. The changing process of the value of " + }, + { + "bbox": [ + 305, + 234, + 546, + 289 + ], + "type": "inline_equation", + "content": "\\mathbb{Z} = \\mathbf{z}_y - \\max_{i\\neq y}\\mathbf{z}_i" + }, + { + "bbox": [ + 305, + 234, + 546, + 289 + ], + "type": "text", + "content": " with the number of iterations during the attack on the CIFAR10 dataset using the model from TRADES [59] and single-precision arithmetic. The horizontal axes show the number of iterations used so far, and the vertical axes show the value of " + }, + { + "bbox": [ + 305, + 234, + 546, + 289 + ], + "type": "inline_equation", + "content": "\\mathbb{Z}" + }, + { + "bbox": [ + 305, + 234, + 546, + 289 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_caption" + } + ], + "index": 1 + }, + { + "type": "table", + "bbox": [ + 58, + 311, + 277, + 376 + ], + "blocks": [ + { + "bbox": [ + 46, + 247, + 288, + 304 + ], + "lines": [ + { + "bbox": [ + 46, + 247, + 288, + 304 + ], + "spans": [ + { + "bbox": [ + 46, + 247, + 288, + 304 + ], + "type": "text", + "content": "Table 2. The comparison of attack performances for FGSM [16], PGD [29], APGD_DLR [10] and AA [10] using original loss functions versus MIFPE loss on CIFAR10 dataset and " + }, + { + "bbox": [ + 46, + 247, + 288, + 304 + ], + "type": "inline_equation", + "content": "\\varepsilon = 0.031" + }, + { + "bbox": [ + 46, + 247, + 288, + 304 + ], + "type": "text", + "content": " with the model obtained from TRADES [59]. with the " + }, + { + "bbox": [ + 46, + 247, + 288, + 304 + ], + "type": "inline_equation", + "content": "\\nabla" + }, + { + "bbox": [ + 46, + 247, + 288, + 304 + ], + "type": "text", + "content": " row representing the improvement achieved with MIFPE." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 58, + 311, + 277, + 376 + ], + "lines": [ + { + "bbox": [ + 58, + 311, + 277, + 376 + ], + "spans": [ + { + "bbox": [ + 58, + 311, + 277, + 376 + ], + "type": "table", + "html": "
Attack \niterationFGSM \n1PGD \n100APGD_DLR \n100AA \n4900
Original \nMIFPE79.8379.7945.9040.22
49.7640.0640.4939.89
V30.0739.735.410.33
", + "image_path": "65ae8b783808adaaaed1bfb3fe0290bccf7c28107b0daed4ada6c834522cb1d0.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_body" + } + ], + "index": 4 + }, + { + "type": "table", + "bbox": [ + 48, + 440, + 288, + 505 + ], + "blocks": [ + { + "bbox": [ + 46, + 387, + 287, + 431 + ], + "lines": [ + { + "bbox": [ + 46, + 387, + 287, + 431 + ], + "spans": [ + { + "bbox": [ + 46, + 387, + 287, + 431 + ], + "type": "text", + "content": "Table 3. Ablation study on the effect of momentum and step-size schedule on the PGD with different loss functions and under 100 iterations on CIFAR10 dataset with the model obtained from Neural level sets [3]. New components are added in consecutive rows." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 48, + 440, + 288, + 505 + ], + "lines": [ + { + "bbox": [ + 48, + 440, + 288, + 505 + ], + "spans": [ + { + "bbox": [ + 48, + 440, + 288, + 505 + ], + "type": "table", + "html": "
Accuracy under attack(%)Loss Function
CEC&WDLRMIFPE
PGD55.4654.2354.3953.42
+Momentum55.2554.0254.1853.23
+Step-size schedule55.2153.9454.1153.22
", + "image_path": "d6f3fee9083c859473393d9ef36fcf70a07d437da9bbbcd45225074ee9334b0c.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "table_body" + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 525, + 287, + 572 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 525, + 287, + 572 + ], + "spans": [ + { + "bbox": [ + 46, + 525, + 287, + 572 + ], + "type": "text", + "content": "become close to the classification boundary due to the relative error and its detrimental effect on the gradient-based attack would increase as " + }, + { + "bbox": [ + 46, + 525, + 287, + 572 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 46, + 525, + 287, + 572 + ], + "type": "text", + "content": " approaches zero after reaching the minimum." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 585, + 119, + 597 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 585, + 119, + 597 + ], + "spans": [ + { + "bbox": [ + 47, + 585, + 119, + 597 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 605, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 605, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 605, + 287, + 715 + ], + "type": "text", + "content": "This paper reveals that relative error in calculated gradient caused by floating-point errors is a fundamental reason why gradient-based attacks fail to accurately evaluate the model's robustness. To efficiently and accurately evaluate the model's robustness, we introduce MIFPE, a new loss function that minimises the impact of floating-point errors on gradient-based attacks. Compared with other loss functions, MIFPE enjoys higher accuracy and faster convergence speed. Moreover, we find several surprising ob" + } + ] + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 314, + 76, + 540, + 207 + ], + "blocks": [ + { + "bbox": [ + 314, + 76, + 540, + 207 + ], + "lines": [ + { + "bbox": [ + 314, + 76, + 540, + 207 + ], + "spans": [ + { + "bbox": [ + 314, + 76, + 540, + 207 + ], + "type": "image", + "image_path": "e183c12478a4a3af2f7b4e348fc6bede55785c12f70708d0e56269976073adee.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 311, + 546, + 441 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 311, + 546, + 441 + ], + "spans": [ + { + "bbox": [ + 304, + 311, + 546, + 441 + ], + "type": "text", + "content": "servations related to adversarial attacks: (1)Discarding partial elements of logits in the loss will impair the attack's performance; (2)The floating-point rounding errors lead to the attack's failure by causing an increasing relative error as the samples get closer to the classification boundary; (3)Increasing the precision of floating-point arithmetic cannot solve the problem of overestimating the model's robustness caused by floating-point errors, etc. We hope that the above observations will help discover more efficient and reliable loss functions in the future. Finally, MIFPE is open source with reproducible results2." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 453, + 404, + 466 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 453, + 404, + 466 + ], + "spans": [ + { + "bbox": [ + 306, + 453, + 404, + 466 + ], + "type": "text", + "content": "Acknowledgments" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 472, + 545, + 529 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 472, + 545, + 529 + ], + "spans": [ + { + "bbox": [ + 305, + 472, + 545, + 529 + ], + "type": "text", + "content": "This work is supported in part by Science and Technology Development Fund of Macao S.A.R (FDCT) under No. 0015/2019/AKP, 0123/2022/AFJ, and 0081/2022/A2. This work was carried out in part at SICC which is supported by SKL-IOTSC, University of Macau." + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 306, + 693, + 545, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 693, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 306, + 693, + 545, + 712 + ], + "type": "text", + "content": "2Available at: https://github.com/MIFPE/Efficient-Loss-Function." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "4063" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 288, + 713 + ], + "type": "list", + "angle": 0, + "index": 14, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 156 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 156 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 156 + ], + "type": "text", + "content": "[1] Samet Akçay, Mikolaj E Kundegorski, Michael Devereux, and Toby P Breckon. 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In ICML, 2019, 1, 4, 5, 6, 7, 8" + } + ] + } + ], + "index": 3 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 749, + 316, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 749, + 316, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 749, + 316, + 757 + ], + "type": "text", + "content": "4066" + } + ] + } + ], + "index": 5 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 10 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Efficient Map Sparsification Based on 2D and 3D Discretized Grids/4f0f1ce5-d45d-4b52-a587-2da996f0a8b8_content_list.json b/2023/Efficient Map Sparsification Based on 2D and 3D Discretized Grids/4f0f1ce5-d45d-4b52-a587-2da996f0a8b8_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..4a8d80bbc3cf5bb83f574b7c4bba97218eb398d0 --- /dev/null +++ b/2023/Efficient Map Sparsification Based on 2D and 3D Discretized Grids/4f0f1ce5-d45d-4b52-a587-2da996f0a8b8_content_list.json @@ -0,0 +1,1371 @@ +[ + { + "type": "text", + "text": "Efficient Map Sparsification Based on 2D and 3D Discretized Grids", + "text_level": 1, + "bbox": [ + 147, + 130, + 821, + 151 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Xiaoyu Zhang Yun-Hui Liu T Stone Robotics Institute, Chinese University of Hong Kong Hong Kong Centre for Logistics Robotics", + "bbox": [ + 241, + 181, + 725, + 233 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "zhang.xy@link.cuhk.edu.hk yhliu@mae.cuhk.edu.hk", + "bbox": [ + 258, + 237, + 705, + 250 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 286, + 312, + 301 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Localization in a pre-built map is a basic technique for robot autonomous navigation. Existing mapping and localization methods commonly work well in small-scale environments. As a map grows larger, however, more memory is required and localization becomes inefficient. To solve these problems, map sparsification becomes a practical necessity to acquire a subset of the original map for localization. Previous map sparsification methods add a quadratic term in mixed-integer programming to enforce a uniform distribution of selected landmarks, which requires high memory capacity and heavy computation. In this paper, we formulate map sparsification in an efficient linear form and select uniformly distributed landmarks based on 2D discretized grids. Furthermore, to reduce the influence of different spatial distributions between the mapping and query sequences, which is not considered in previous methods, we also introduce a space constraint term based on 3D discretized grids. The exhaustive experiments in different datasets demonstrate the superiority of the proposed methods in both efficiency and localization performance. The relevant codes will be released at https://github.com/fishmarch/SLAM_Map_Compression.", + "bbox": [ + 75, + 316, + 473, + 650 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 679, + 207, + 694 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "To realize autonomous navigation for robots, localization in a pre-built map is a basic technique. Lots of algorithms have been proposed for mapping and localization using different sensors, including camera [20] and lidar [27]. These algorithms commonly work well in some small-scale environments now. When applied in large-scale environments or in long-term, however, new challenges appear and need to be settled for practical applications. Some of these problems are time and memory consuming.", + "bbox": [ + 75, + 703, + 468, + 839 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "When using cameras, visual simultaneous localization and mapping (SLAM) is a commonly used method to build maps. In visual SLAM, redundant features are extracted from images and then constructed as landmarks in a map,", + "bbox": [ + 75, + 839, + 470, + 901 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/ac61547f118e7710f3f157276dd2e0e2ed91856d569186ae85e84c5169c78734.jpg", + "image_caption": [ + "Figure 1. Localization results in a compact map. The original map is constructed from sequence 00 of the KITTI dataset [14]. The original map consists of 141K landmarks, indicated by gray points; while the compact map consists of only 5K landmarks, indicated by blue points. $96.15\\%$ of the query images are localized successfully in the compact map, indicted by green poses." + ], + "image_footnote": [], + "bbox": [ + 519, + 282, + 875, + 529 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "such that camera poses can be tracked robustly and accurately. These redundant landmarks promise good localization results in small-scale environments. As more and more images are received when working in large-scale environments or in long-term, however, memory consumption is increasing unboundedly. Localizing in such large maps will also be more time-consuming. These problems are especially severe for some low-cost robots.", + "bbox": [ + 496, + 641, + 890, + 761 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Actually, not all landmarks are necessary for robots to localize in pre-built maps. In theory, even only 4 matched landmarks can determine a camera pose using EPnP [16] (more landmarks are commonly used for robust and accurate estimation). This reveals that maps can be compressed and still retain comparable performance for localization. Map compression can be classified into two types: descriptor compression [5, 18, 22] and landmark sparsification [17, 23]. The research of this paper falls in the latter", + "bbox": [ + 496, + 763, + 892, + 900 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "12470", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "one, which is to find a subset of an original map while maintaining comparable localization performance. A subset map is called compact map in this paper. For example, as indicated in Fig. 1, only $3.91\\%$ of the original landmarks are selected as the compact map, in which more than $96\\%$ of the query images can still be localized successfully.", + "bbox": [ + 78, + 90, + 467, + 181 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To select an optimal subset for localization, map sparsification is related to a $K$ -cover problem [17], which means the number of landmarks in a compact map is minimized while keeping the number of associated landmarks in each image larger than a threshold (i.e., $K$ ). To solve the $K$ -cover problem, it can be formulated as mixed-integer linear programming, through which an optimal subset is obtained. The original formulation only considers the number of landmarks for localization, while their distribution also affects localization performance. Therefore, some works design and add quadratic terms, formulating mixed-integer quadratic programming to enforce a more uniform distribution of selected landmarks [11, 23]. However, these quadratic terms slow down the optimization speed heavily. The required high memory capacity and heavy computation become severe limitations of these map sparsification methods. For example, in our experiments, the mixed-integer quadratic programming methods cannot be used for the maps containing more than 55K landmarks, because all computer memory has been consumed.", + "bbox": [ + 80, + 184, + 467, + 484 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To select uniformly distributed landmarks and at the same time maintain the computation efficiency, we keep map sparsification formulation in a linear form in this paper. We firstly discretize images into 2D fix-sized grids. Then for all observed landmarks, we can find which cells they fall in. Therefore, more occupied cells reflect a more uniform distribution of landmarks. This can be formulated in a linear form easily. In this way, uniformly distributed landmarks are selected efficiently, and thus the localization performance in compact maps will be better.", + "bbox": [ + 80, + 488, + 467, + 638 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Another severe limitation is that all of past works assume the spatial distribution of the query sequence is close to that of the mapping sequence. Then landmarks are selected only based on their association with the images of the mapping sequence. However, this assumption cannot be guaranteed in real robotic applications. The perspective difference between query and mapping sequences may cause the localization in compact maps to fail unexpectedly.", + "bbox": [ + 80, + 642, + 467, + 761 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To ensure more query images from whole 3D space can be localized successfully in compact maps, we propose to select landmarks based on not only their association with mapping images but also their visibility in 3D space. The visibility region of a landmark is defined based on its viewing angle and distance. The 3D space is also discretized into a 3D discretized grid. For each 3D cell, all visible landmarks are collected, and a constraint on the number of visible landmarks is added into map sparsification formulation.", + "bbox": [ + 80, + 763, + 467, + 898 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In this way, landmarks are selected to maintain localization performance for query images from the whole space.", + "bbox": [ + 503, + 90, + 888, + 119 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In summary, the contributions of this paper are as follows: 1) We propose an efficient map sparsification method formulating uniform landmark distribution in a linear form to keep the computation efficiency. 2) We propose to perform map sparsification involving the visibility of landmarks to achieve better localization results for the query images from the whole space. 3) We conduct exhaustive experiments in different datasets and compare with other state-of-the-art methods, showing the effectiveness and superiority of our methods for different kinds of query sequences.", + "bbox": [ + 503, + 122, + 888, + 271 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 503, + 286, + 638, + 301 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Map compression or sparsification has received many research attention in SLAM and structure from motion (SfM) because of the burden of maintaining and utilizing a large map. Different methods are also proposed to solve this problem. In [5,18,22], the descriptors are quantized to compact forms to reduce memory consumption. Mera-Trujillo et al. [19] propose a constrained quadratic program method and design an efficient solver to select landmarks. Contreras et al. [8] develop a map compression method based on traveled trajectories, and they also propose an online system performing SLAM and map compression simultaneously [9]. Some SLAM systems [7, 26, 28] are also designed to select and build a compact map online, but much more landmarks are still remained compared with the offline methods. Recently, some learning-based map sparsification methods have also appeared and achieved good results [4, 25], but they require high-cost GPUs to train and struggle to be applied in different unseen scenes.", + "bbox": [ + 503, + 311, + 888, + 580 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Map sparsification is more commonly regarded as a $K$ -cover problem. Since $K$ -cover is an NP-hard problem, Li et al. [17] propose to use a greedy algorithm to select the landmark observed by the largest number of not-yet-fully covered frames. Cao et al. [3] also use a greedy algorithm to select landmarks, considering both the coverage and distinctiveness. In [6], the original $K$ -cover method is improved by predicting the parameter $K$ . Similarly, the landmarks are scored and sampled based on the observation count, covariance, and descriptor stability in [12]. Moreover, the authors come up with more scoring factors to rank landmarks for selecting in [13]. These methods can provide compact maps for localization, but depend on a careful design of selecting methods and cannot get the optimal solution.", + "bbox": [ + 503, + 584, + 888, + 792 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Another $K$ -cover based map sparsification solution is to be formulated as a mixed-integer programming problem, which is introduced in detail in [23]. The linear formulation does not consider the distribution of the selected landmarks but can be solved efficiently, and therefore it is adopted in some later works [13, 24]. The mixed-integer quadratic programming formulation encourages the uniformly dis", + "bbox": [ + 503, + 795, + 888, + 898 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "12471", + "bbox": [ + 480, + 945, + 517, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "tributed landmarks but requires a high capacity of memory and heavy computation [23] and becomes impractical for large maps. To improve the computation efficiency, Dymczyk et al. [11] have to divide the whole map into several small parts and perform map sparsification separately. Camposeco et al. [2] keep the linear form of map sparsification but divide each image into $q$ uniformly-sized cells and let each cell be covered by $K / q$ landmarks. This method seems reasonable, but we find in the experiments that the number of corresponding selected landmarks in some images is much less than $K$ actually, and thus the localization results get worse. Similarly, the proposed method also makes use of discretized images, but the image is still considered as a whole and thus avoids the above problems.", + "bbox": [ + 75, + 90, + 472, + 301 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "All of the above methods are based on the existing association between landmarks and images, thus landmarks are selected only to ensure localization performance of these images. For an arbitrary query image with a different viewing perspective, localization may fail unexpectedly, especially when the compression ratio is high. To solve this problem, the proposed method considers landmark visibility in the 3D space and adds constraints to preserve enough visible landmarks for the whole space in compact maps.", + "bbox": [ + 75, + 301, + 472, + 439 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Map Sparsification Formulation", + "text_level": 1, + "bbox": [ + 76, + 450, + 372, + 468 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The proposed method is designed mainly for the maps built from feature-based visual SLAM systems (e.g., ORBSLAM [20]). Receiving sequences of images, the feature points observed by keyframes are constructed as landmarks. Thus, an original map $\\mathcal{M}$ consists of landmarks $\\{\\pmb {p}_i\\}_{i = 1,2,\\dots,N}$ , keyframes $\\{F_j\\}_{j = 1,2,\\dots,M}$ , and their association. The map sparsification aims to decrease the number of landmarks. We firstly introduce commonly used formulations of map sparsification in past works [23].", + "bbox": [ + 75, + 476, + 468, + 611 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Using mixed-integer programming, map sparsification can be formulated as:", + "bbox": [ + 75, + 612, + 468, + 642 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\underset {\\mathbf {x}, \\boldsymbol {\\xi}} {\\text {m i n i m i z e}} \\quad \\mathbf {q} ^ {\\top} \\mathbf {x} + \\lambda \\mathbf {1} ^ {\\top} \\boldsymbol {\\xi} \\\\ \\mathbf {A} \\mathbf {x} \\geq K \\mathbf {1} - \\boldsymbol {\\xi} \\tag {1} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 181, + 648, + 468, + 691 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\begin{array}{l} \\text {s u b j e c t t o} \\quad \\mathbf {x} \\in \\{0, 1 \\} ^ {N} \\end{array} \\\\ \\boldsymbol {\\xi} \\in \\{0, \\mathbb {Z} _ {+} \\} ^ {M} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 179, + 689, + 362, + 722 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\mathbf{x}$ is a binary vector whose $i^{\\mathrm{th}}$ element indicates whether the landmark $\\pmb{p}_i$ is selected or not. $\\mathbf{q}$ is a weight vector to select landmarks. $\\mathbf{A}$ is a binary matrix describing the association between landmarks and keyframes, i.e., the element $\\mathbf{A}_{ij}$ indicates whether the landmark $\\pmb{p}_j$ is visible in the keyframe $\\pmb{F}_i$ . $K$ is the desired minimum number of visible landmarks in each keyframe and can be used to adjust compression ratio. To handle the situation when the total number of associated landmarks of a keyframe is less than $K$ , a slack variable $\\xi$ is used to relax the hard constraints, and $\\lambda$ determines the hardness of the constraints.", + "bbox": [ + 75, + 734, + 472, + 900 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Therefore, Eq. (1) describes the mixed-integer linear programming method for map sparsification. The distribution of selected landmarks is not considered in this method. To involve the distribution of landmarks, quadratic terms are commonly used:", + "bbox": [ + 496, + 90, + 890, + 167 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\underset {\\mathbf {x}, \\boldsymbol {\\xi}} {\\text {m i n i m i z e}} \\quad \\frac {1}{2} \\mathbf {x} ^ {\\top} \\mathbf {Q} \\mathbf {x} + \\mathbf {q} ^ {\\top} \\mathbf {x} + \\lambda \\mathbf {1} ^ {\\top} \\boldsymbol {\\xi} \\\\ \\mathbf {A} \\mathbf {x} \\geq K \\mathbf {1} _ {N} - \\boldsymbol {\\xi} \\tag {2} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 571, + 175, + 890, + 217 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\begin{array}{l} \\text {s u b j e c t t o} \\quad \\mathbf {x} \\in \\{0, 1 \\} ^ {N} \\end{array} \\\\ \\boldsymbol {\\xi} \\in \\{0, \\mathbb {Z} _ {+} \\} ^ {M} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 568, + 214, + 753, + 247 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\mathbf{Q}$ is a symmetric matrix. The element $\\mathbf{Q}_{ij}$ indicates the relation between $\\pmb{p}_i$ and $\\pmb{p}_j$ . For example, it can be the number of common observations for each pair of landmarks. Therefore, the landmarks that are observed together with others frequently would be discarded. As a result, selected landmarks are distributed more uniformly. Eq. (2) describes the commonly used map sparsification formulation in past works, which considers both the number and distribution of landmarks for localization.", + "bbox": [ + 496, + 256, + 890, + 392 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "4. Map Sparsification Based on 2D Grids", + "text_level": 1, + "bbox": [ + 498, + 405, + 844, + 422 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Uniformly distributed landmarks commonly provide better localization results. Because of the quadratic terms, however, the computation complexity increases largely. Besides, Eq. (2) encourages selection of rarely observed landmarks, which may have larger errors and be detrimental for localization [11].", + "bbox": [ + 496, + 430, + 890, + 521 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "To solve these problems, we design a linear term to encourage a uniform distribution of selected landmarks. As illustrated in Fig. 2, the image is discretized into fixed-size grids (e.g., $C \\times R$ cells). Each cell has two stats: empty or occupied. Based on the camera model, projected positions of landmarks can be computed easily. Then a cell is occupied if at least one landmark is projected into it; otherwise, it is empty. Therefore, to acquire uniformly distributed landmarks, we encourage selecting the landmarks that make more cells to be occupied. This concept can be easily formulated into Eq. (1), which becomes:", + "bbox": [ + 496, + 521, + 890, + 688 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\underset {\\mathbf {x}, \\boldsymbol {\\xi}, \\boldsymbol {\\phi}} {\\text {m i n i m i z e}} \\quad \\mathbf {q} ^ {\\top} \\mathbf {x} + \\lambda_ {1} \\mathbf {1} ^ {\\top} \\boldsymbol {\\xi} + \\lambda_ {2} \\mathbf {1} ^ {\\top} \\boldsymbol {\\phi} \\\\ \\mathbf {A} \\mathbf {x} \\geq K \\mathbf {1} - \\boldsymbol {\\xi} \\\\ \\mathrm {B x} \\geq 1 - \\phi \\tag {3} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 571, + 696, + 890, + 753 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\begin{array}{l} \\text {s u b j e c t t o} \\quad \\mathbf {x} \\in \\{0, 1 \\} ^ {N} \\end{array} \\\\ \\boldsymbol {\\xi} \\in \\{0, \\mathbb {Z} _ {+} \\} ^ {M} \\\\ \\phi \\in \\{0, 1 \\} ^ {M \\times C \\times R} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 568, + 750, + 784, + 800 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\mathbf{B}$ is a binary matrix describing the association between the landmarks and all cells, i.e., the element $\\mathbf{B}_{ij}$ indicates whether the projected position of the landmark $p_j$ falls within the cell $c_i$ . We encourage every cell to keep at least one corresponding landmark and use the slack variable $\\phi$ to relax this constraint. An example is illustrated in", + "bbox": [ + 496, + 809, + 890, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "12472", + "bbox": [ + 478, + 944, + 519, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/f210f16341cfc302c78164256d3237949714bde17207944b5b66083b7836c58f.jpg", + "image_caption": [ + "Figure 2. Illustration of discretized images and associated landmarks. The occupied cells are drawn in deeper color. The red points represent the projected position of associated landmarks. Dotted points can be discarded without changing occupancy." + ], + "image_footnote": [], + "bbox": [ + 109, + 87, + 436, + 218 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Fig. 2, the dotted points can be discarded without changing the number of occupied cells.", + "bbox": [ + 75, + 299, + 468, + 329 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Eq. (3) formulates map sparsification as a mixed-integer linear programming problem and thus can be solved efficiently. The selected landmarks are directly encouraged to spread uniformly in all corresponding keyframes. Thus better localization performance will be achieved.", + "bbox": [ + 75, + 329, + 468, + 405 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "5. Map Sparsification In 3D Space", + "text_level": 1, + "bbox": [ + 76, + 417, + 369, + 436 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "From the previous section, it is noticed that map sparsification is formulated based on the association between landmarks and keyframes. This association can be easily constructed from feature matching during mapping. All past works are based on such association and assume the spatial distribution of the query sequence will be close to that of the mapping sequence. Thus selected landmarks can be matched again in query images. Obviously, this assumption cannot be promised in real robotic applications. Some selected landmarks would not be matched in query images because of different viewing perspectives, and thus, the localization may fail unexpectedly.", + "bbox": [ + 75, + 444, + 468, + 625 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In this section, we will introduce our proposed map sparsification method that involves landmark visibility in 3D space and thus improves localization performance for query images from the whole space.", + "bbox": [ + 75, + 626, + 468, + 686 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "5.1. Landmark Visibility", + "text_level": 1, + "bbox": [ + 76, + 696, + 269, + 713 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Feature points (e.g., ORB [21]) are commonly extracted and constructed as landmarks in visual SLAM. One of the basic requirements of used features is robust matching from different viewing perspectives. In other words, it is assumed that a valid feature point is visible and can be matched within a certain region. Specifically, we assume a feature point can be matched when the viewing angle and distance are within certain thresholds. Such specific regions can be approximated from mapping process. Similarly defined visibility is also used for efficient feature matching [20]. Deng et al. [10] also predict such feature matching to ensure localization performance in an active SLAM framework.", + "bbox": [ + 75, + 719, + 470, + 901 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/df77f14592e6993b2eaebd4529850f6024f5accc56bf42baeb3e9191f4bd663f.jpg", + "image_caption": [ + "Figure 3. 3D cells in which the landmark $\\pmb{p}$ is visible." + ], + "image_footnote": [], + "bbox": [ + 578, + 87, + 816, + 258 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "For a landmark $\\pmb{p}$ observed by multiple keyframes, an average viewing direction $\\bar{\\pmb{v}}^p$ can be computed from all viewing directions, pointing from $\\pmb{p}$ to the optical centers of these keyframes. Therefore, the first condition for $\\pmb{p}$ to be visible is that the viewing angle is within the threshold,", + "bbox": [ + 498, + 295, + 890, + 371 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\langle \\bar {\\boldsymbol {v}} ^ {p}, \\boldsymbol {v} ^ {i} \\rangle < \\theta_ {t h} ^ {p} \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 645, + 380, + 890, + 398 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\pmb{v}^i$ is the viewing direction for a query position. In our experiments, $\\theta_{th}^{p}$ is set according to the largest viewing angle during mapping.", + "bbox": [ + 498, + 407, + 890, + 453 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Besides, an image pyramid is commonly employed for matching features from different distance. Therefore, the second condition for $\\pmb{p}$ to be visible is that the viewing distance $d_{i}^{p}$ from a query position is within the following range,", + "bbox": [ + 498, + 454, + 890, + 515 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nd _ {\\min } ^ {p} < d _ {i} ^ {p} < d _ {\\max } ^ {p} \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 630, + 527, + 890, + 546 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $d_{\\mathrm{min}}^p$ and $d_{\\mathrm{max}}^p$ are also set according to the smallest and largest viewing distance during mapping.", + "bbox": [ + 498, + 550, + 890, + 580 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Therefore, a landmark is assumed to be visible when meeting the conditions Eq. (4) and Eq. (5). The visible region forms a truncated spherical cone, as indicated in Fig. 3.", + "bbox": [ + 498, + 580, + 890, + 628 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "5.2. Map Sparsification Based on 3D Grid", + "text_level": 1, + "bbox": [ + 500, + 635, + 823, + 652 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "For map sparsification methods described in Sec. 3, enough visible landmarks are preserved for every keyframe based on the constraint $\\mathbf{A}\\mathbf{x} \\geq K\\mathbf{1} - \\boldsymbol{\\xi}$ . Therefore, the compact map can be used to localize the query images that are close to the mapping sequence as expected. However, for query images taken from different viewing perspectives, which is common in practical robotic applications, the number of matched visible landmarks may decrease, and thus the localization may fail unexpectedly.", + "bbox": [ + 496, + 659, + 890, + 794 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "To solve the above problem, we propose a map sparsification method considering landmark visibility in 3D space. We firstly discretize the whole space into a 3D grid. The corresponding 3D cells from which it is visible are collected for each landmark, as indicated in Fig. 3. Therefore, each cell stores all visible landmarks from that position. To decrease computation, we define a threshold $K_{2}$ , and the", + "bbox": [ + 496, + 795, + 890, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "12473", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3D cell is valid only if the number of corresponding visible landmarks is larger than $K_{2}$ .", + "bbox": [ + 76, + 90, + 468, + 119 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In the proposed map sparsification method, landmarks are selected to keep as many valid 3D cells as possible. Therefore, an extra constraint is introduced into the formulation for each valid 3D cell:", + "bbox": [ + 76, + 121, + 467, + 181 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\underset {\\mathbf {x}, \\boldsymbol {\\xi}, \\boldsymbol {\\phi}, \\boldsymbol {\\varphi}} {\\text {m i n i m i z e}} \\quad \\mathbf {q} ^ {\\top} \\mathbf {x} + \\lambda_ {1} \\mathbf {1} ^ {\\top} \\boldsymbol {\\xi} + \\lambda_ {2} \\mathbf {1} ^ {\\top} \\boldsymbol {\\phi} + \\lambda_ {3} \\mathbf {1} ^ {\\top} \\boldsymbol {\\varphi} \\\\ \\mathbf {A} \\mathbf {x} \\geq K _ {1} \\mathbf {1} - \\boldsymbol {\\xi} \\\\ \\mathrm {B x} \\geq 1 - \\phi \\\\ \\mathbf {C x} \\geq K _ {2} \\mathbf {1} - \\varphi \\tag {6} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 102, + 188, + 468, + 266 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "subject to $\\mathbf{x}\\in \\{0,1\\} ^N$ (6)", + "bbox": [ + 102, + 260, + 468, + 275 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\boldsymbol {\\xi} \\in \\left\\{0, \\mathbb {Z} _ {+} \\right\\} ^ {M} \\\\ \\phi \\in \\{0, 1 \\} ^ {M \\times C \\times R} \\\\ \\boldsymbol {\\varphi} \\in \\{0, \\mathbb {Z} _ {+} \\} ^ {S} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 102, + 260, + 468, + 325 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\mathbf{C}$ is a binary matrix describing the association between landmarks and valid 3D cells, i.e., the element $\\mathbf{C}_{ij}$ indicates whether the landmark $p_j$ is visible for the 3D cell $g_i$ . As before, the slack variable $\\varphi$ is used to relax the constraints.", + "bbox": [ + 76, + 337, + 468, + 411 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Therefore, the proposed map sparsification method aims to preserve enough visible landmarks not only for mapping keyframes but also for the whole 3D space. As a result, more query images from the whole space can be localized successfully.", + "bbox": [ + 75, + 412, + 468, + 488 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "6. Experiments", + "text_level": 1, + "bbox": [ + 76, + 502, + 209, + 518 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The proposed map sparsification based on 2D grids (i.e., Eq. (3)) is firstly compared with previous works to show its superiority in performance and efficiency for localizing query images close to mapping sequences. Then we demonstrate the effectiveness of map sparsification involving the visibility of landmarks in 3D space (i.e., Eq. (6)) and its superiority when query images are not close to mapping sequences. More experimental results can be found in the supplementary material, including visualization results and the comparison between original and compact maps in terms of memory consumption and localization efficiency.", + "bbox": [ + 75, + 527, + 468, + 694 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "6.1. Experimental Setup", + "text_level": 1, + "bbox": [ + 76, + 703, + 266, + 719 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "All experiments are tested on a laptop with an i7- 7700HQ $2.80\\mathrm{Hz}$ CPU and 16GB RAM. The mixed-integer programming problem is solved using Gurobi1.", + "bbox": [ + 76, + 726, + 468, + 771 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The proposed methods are tested on three commonly used SLAM datasets: ICL-NUIM [15], EuRoC [1], and KITTI [14]. These datasets cover indoor and outdoor, small-scale and large-scale environments; the number of landmarks in original maps changes from thousands to more than one hundred thousand. The original map is constructed by running a state-of-the-art visual SLAM system", + "bbox": [ + 76, + 772, + 468, + 877 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "(i.e., ORB-SLAM2 [20]). Query images are localized in the map based on the re-localization module in ORB-SLAM2, in which localization is successful when enough inliers are matched. Different map sparsification methods are compared in terms of localization rate and run-time. Localization rate is the ratio of the number of successfully localized images to the number of all query images in one sequence.", + "bbox": [ + 500, + 90, + 890, + 196 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The weight vector $\\mathbf{q}$ in all methods is set based on the number of matched times for each landmark, just like in [23]. The proposed method based only on 2D grids (i.e., Eq. (3)) is denoted as Ours-2D, while the method based on 2D and 3D grids (i.e., Eq. (6)) is denoted as Ours-3D. The proposed methods are compared with several state-of-the-art $K$ -cover-based map sparsification methods. The map sparsification using mixed-integer linear programming (i.e., Eq. (1)) is denoted as LP. For the methods using mixed-integer quadratic programming (i.e., Eq. (2)), the weight matrix $\\mathbf{Q}$ is set according to the number of co-observation times [23] or average projected distance [11], and these two methods are denoted as QP1 and QP2 respectively. The map sparsification based on divided images [2] is denoted as DI.", + "bbox": [ + 498, + 198, + 890, + 409 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "6.2. Map Sparsification Based on 2D Grids", + "text_level": 1, + "bbox": [ + 500, + 421, + 830, + 436 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Since previous methods assume the spatial distribution of the query sequence is close to that of the mapping sequence, one sequence is firstly used to build an original map and then the images from the same mapping sequence are re-localized in compact maps. In this subsection, the proposed map sparsification method is only based on 2D discretized grids (i.e., Eq. (3)). Tab. 1 compares the localization rates in different maps obtained by different methods. An example of the selected sparse landmarks is illustrated by blue points in Fig. 1.", + "bbox": [ + 498, + 445, + 890, + 595 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The experimental results demonstrate that the number of landmarks can be reduced largely while the localization is still successful for most query images. For example, only $4.37\\%$ landmarks are selected from the map of sequence off2 and $3.46\\%$ for sequence 04, but more than $90\\%$ of the query images can still be localized successfully. The compression ratio is mainly controlled by the threshold $K$ in Eq. (1), Eq. (2), and Eq. (3), and we use $K = 50$ in our experiments. With a larger $K$ , more landmarks will be selected in compact maps, and localization rate will be higher.", + "bbox": [ + 498, + 598, + 890, + 748 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "For more sequences, our proposed method achieves the highest localization rate (labelled in bold), especially compared with the method only considering the number of landmarks for map sparsification (i.e., LP). Our method also gets slightly better results than other methods that consider landmark distribution (i.e., QP1, QP2, and DI). In QP1, the weight matrix $\\mathbf{Q}$ is set according to the number of co-observation times between landmarks and as a result, rarely observed landmarks are preferred, which may be detrimental for localization [11]. To overcome this limitation, QP2", + "bbox": [ + 498, + 750, + 890, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_footnote", + "text": "1https://www.gurobi.com", + "bbox": [ + 94, + 886, + 232, + 898 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "12474", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/3bcf0908d7462c99d4a350899774ce8ca7f3d2837d1eaf85e9a5acefe40e3d52.jpg", + "table_caption": [ + "Table 1. Comparison of different map sparsification methods in terms of localization rate. Num denotes the number of landmarks in the mam, Rate denotes the localization rate in the corresponding map. The highest localization rates in compact maps are labelled in bold. -' means the method cannot work because of memory limit." + ], + "table_footnote": [], + "table_body": "
DatasetOriginal MapOurs-2DLP [23]QP1 [23]QP2 [11]DI [2]
NumRateNumRateNumRateNumRateNumRateNumRate
ICL-NUIM [15]liv0406198.34%51979.97%51979.51%51979.64%51978.65%73477.39%
liv1411299.89%44587.47%44586.23%44587.37%44585.51%51655.59%
liv26435100.0%31291.36%31089.77%31090.57%31091.02%83389.89%
liv3617393.38%53276.21%53173.71%53175.32%53173.55%98761.85%
off0587599.93%39895.62%39895.42%39895.76%39895.76%79184.88%
off1599293.57%48580.00%48577.93%48579.07%48476.89%73637.20%
off26838100.0%29992.27%29891.02%29890.34%29891.36%75990.45%
off3536799.52%39683.47%39583.06%39578.31%39683.15%43051.05%
EuRoC [1]MH11250699.04%297897.33%297697.03%297696.76%297796.54%421094.56%
MH21130699.73%254698.17%254496.43%254798.33%254798.30%366593.30%
MH31523497.34%210595.32%210495.32%210795.44%210595.17%372091.30%
MH41749099.69%74497.37%74397.32%74297.27%74297.01%249396.05%
MH51695699.77%111698.87%111698.69%111698.60%111698.60%293396.08%
V101686499.03%46186.04%46084.92%46185.52%46186.35%101179.14%
V102987898.12%50785.93%50784.86%50685.87%50685.49%125584.17%
V1031151893.22%114083.76%114083.91%114083.09%114083.05%166177.89%
V201734694.69%56579.64%56478.75%56478.62%56478.97%99078.75%
V2021179199.48%125493.25%125492.86%125493.07%125493.42%228590.39%
V2031455787.51%179681.48%179581.27%179681.11%179581.48%238475.45%
KITTI [14]00141673100.0%553696.15%552495.68%----1854291.15%
018944391.01%421876.02%421676.02%----1020471.84%
0218249999.96%766097.47%766197.15%----2513386.76%
0324284100.0%83796.00%83695.63%83796.13%83695.76%295288.76%
0416824100.0%58399.63%58599.26%57299.63%57299.63%201997.41%
0574158100.0%273797.46%273897.25%----965590.62%
0642522100.0%187998.27%187898.09%187898.18%187798.18%563595.82%
0727036100.0%124292.28%124091.28%124091.73%124092.55%351792.01%
08119323100.0%590394.87%589994.82%----1687283.03%
095598499.94%294595.79%294495.60%294295.85%294395.79%822488.37%
103093399.92%172997.09%172896.67%172896.83%172996.42%474386.34%
", + "bbox": [ + 76, + 141, + 890, + 651 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "sets the weight matrix $\\mathbf{Q}$ based on the average distance between projected positions. But instead of uniform distribution, QP2 actually prefers to select landmarks that are projected far from the image center. Unlike these quadratic programming-based methods, our method formulates uniform distribution in a more clear and simple way, achieving better results.", + "bbox": [ + 75, + 664, + 468, + 770 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "DI gets unexpected bad performance in these testings. DI divides images into $q$ cells and forces each cell is covered by at least $K / q$ landmarks. Therefore, DI also achieves map sparsification in a linear programming form and considers both the number and distribution of landmarks. But we find in these testings that the slack variable $\\lambda$ in Eq. (1) needs to be small for DI to get a high compression ratio. As a result, the number of selected landmarks is much less", + "bbox": [ + 75, + 779, + 470, + 900 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "than $K$ for some images, where localization would fail. Although based on similar discretized grids, our method still considers an image as a whole and thus avoids this problem.", + "bbox": [ + 496, + 664, + 890, + 710 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Another superiority of our method is computational efficiency. The comparison of run-time and memory consumption on different sequences is shown in Tab. 2. The run-time for map sparsification depends on the number of landmarks, keyframes and associations among them. As the number of landmarks or keyframes increases, the run-time will commonly increase quickly. It is clear that the methods using quadratic programming are much slower, especially for the maps containing a large number of landmarks (e.g., sequence 09). In addition to solving more complex optimization problems, QP1 and QP2 also need much more time to set the weight matrix $\\mathbf{Q}$ , since the relation between every", + "bbox": [ + 496, + 719, + 890, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "12475", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/da65ae7cadf3e664eb9d46844de4d319b662ffdf51759cd83b39b47a97ff0ffc.jpg", + "table_caption": [ + "Table 2. Comparison of different map sparsification methods in terms of run-time and consumed memory. $N$ denotes the number of landmarks, ${N}_{k}$ denotes the number of keyframes." + ], + "table_footnote": [], + "table_body": "
Seq.Original MapRun-time (s)
NNkOursLPQP1QP2DI
liv04.1K1070.20.113.612.50.2
off05.9K1330.30.127.918.90.2
V10311.5K2161.10.359.836.30.6
MH517.0K3694.52.210761.51.2
0727.0K2582.61.112795.50.7
0956.0K6037.79.97544911.8
08119K126933.219.2--4.9
02182K179469.663.2--7.9
NNkConsumed memory (MB)
liv04.1K107351455547633
off05.9K133612784270821
V10311.5K216128563048136783
MH517.0K3692551073532165677
0727.0K2581416263155766100
0956.0K6036762301300510952211
08119K12691162637--512
02182K179434941502--1187
", + "bbox": [ + 78, + 142, + 468, + 450 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "pair of landmarks needs to be found and this is not recorded in original maps. In our method, both the matrix $\\mathbf{A}$ and $\\mathbf{B}$ in Eq. (3) are set according to the relation between landmarks and keyframes, which can be retrieved from original maps directly and efficiently. In addition, since formulated in a linear form, our method can also be solved efficiently and is only slightly slower than LP.", + "bbox": [ + 75, + 460, + 468, + 566 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Similarly for memory consumption, ours consumes much less memory than quadratic programming. QP1 and QP2 cannot work for some sequences (e.g., 00) on our device with 16 GB memory. The testing for sequence 09 consumes nearly all of the memory when using QP1 and QP2, in which the original map contains 56K landmarks.", + "bbox": [ + 75, + 566, + 468, + 656 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Therefore, if the mapping sequence has covered most of the query space for localization, the proposed map sparsification based on 2D discretized grids can be used to decrease the number of landmarks to save memory and improve localization efficiency.", + "bbox": [ + 75, + 656, + 468, + 734 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "6.3. Map Sparsification Based on 2D and 3D Grids", + "text_level": 1, + "bbox": [ + 76, + 741, + 467, + 758 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We have demonstrated that compact maps with much fewer landmarks achieve good localization performance when the spatial distribution of the query sequence is close to that of the mapping sequence. In this subsection, we continue to test the localization performance for query images from different distributions.", + "bbox": [ + 75, + 763, + 467, + 853 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "In ICL-NUIM [15] and EuRoC [1] datasets, different sequences are recorded in the same environments. Therefore, one sequence is used to build original maps and then query", + "bbox": [ + 75, + 854, + 467, + 901 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/1138bf57ffe456e409696f5a01ffcc53d943db2707dcb38d36a5b19310f956f0.jpg", + "image_caption": [ + "Figure 4. Comparison of map sparsification results. The original map is constructed from sequence V201. There are 3401 blue points indicating valid 3D cells of the compact map acquired by Ours-2D; while there are 6468 green points indicating valid 3D cells of the compact map acquired by Ours-3D." + ], + "image_footnote": [], + "bbox": [ + 517, + 88, + 883, + 284 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "images of other sequences are also localized in compact maps. The comparison of experimental results is presented in Table 3. For example, sequence off0 is used to build the map, and then sequence off0, off2 and off3 are used as query sequences to be localized in the original and compact maps. Not all sequences of these two datasets are used in this experiment since the successful localization is very low even in original maps for some sequences.", + "bbox": [ + 496, + 382, + 890, + 503 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "As shown in Tab. 3, compact maps commonly achieve good localization performance for query images from mapping sequences, while localization rates may decrease largely for other query sequences. Because the map sparsification is mainly selecting landmarks to maintain the observations in keyframes of the mapping sequences, and thus discarding other redundant landmarks which may be useful for localizing query images from the whole space. Our proposed map sparsification method in Eq. (6) aims to add such extra constraints for the whole space. In most testings, ours-3D achieves higher localization rates for the query sequences that are different from mapping sequences. For the query images from the mapping sequence, ours-3D also achieves comparable localization performance with other map sparsification methods. Other map sparsification methods achieve similar results as Ours-2D, which are included in the supplementary material.", + "bbox": [ + 496, + 505, + 892, + 762 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "A comparison of compact maps acquired by ours-2D and ours-3D is illustrated in Fig. 4. The blue points indicate the valid 3D cells of ours-2D, while the green points indicate the valid 3D cells of ours-3D. The numbers of selected landmarks are similar using these two methods. But it is clear that much more valid 3D cells are kept using ours-3D and they are spreading over a larger space. As a result, more query images from the whole 3D space can be localized successfully.", + "bbox": [ + 496, + 763, + 890, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "12476", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/9fe051df7a19af953cb555e21a1d713a8de3daad9e629c672b2834375c133d64.jpg", + "table_caption": [ + "Table 3. Comparison of different map sparsification methods in terms of localization rate. Num denotes the number of landmarks in the map, Rate denotes the localization rate in the corresponding map. The sequence for mapping is indicated in bold and the images from several different sequences are localized in the map. The highest localization rates in compact maps are labelled in bold." + ], + "table_footnote": [], + "table_body": "
off0off2liv2
MapNumoff0Rate off2off3NumRate off0off2NumRate liv1liv2
Original587599.93%66.70%52.26%683865.65%100.00%643555.80%100.00%
Ours-2D39895.62%27.95%7.74%2994.31%92.27%3122.48%91.36%
Ours-3D39995.49%28.52%7.98%3016.17%91.70%3144.04%90.68%
MH1MH4MH5
MapNumRateNumRateNumRate
MH1MH2MH3MH4MH5MH4MH5
Original1250699.04%87.10%52.53%1749099.69%84.20%1695682.34%99.77%
Ours-2D297897.33%73.67%45.76%74497.37%63.77%111674.75%98.87%
Ours-3D298296.78%73.97%46.18%74597.06%64.27%112175.71%98.74%
MH2V101V102
MapNumRateNumRateNumRate
MH1MH2MH3V101V102V101V102
Original1130691.78%99.73%51.81%686499.03%61.56%987872.25%98.12%
Ours-2D254674.80%98.17%35.50%46186.04%32.60%50734.61%85.93%
Ours-3D255077.41%97.77%38.69%46285.79%34.61%50637.67%85.99%
MH3V201V202
MapNumRateNumRateNumRate
MH1MH2MH3V201V202V201V202
Original1523459.93%52.80%97.34%734694.69%52.77%1179175.22%99.48%
Ours-2D210546.85%37.23%95.32%56579.64%19.48%125449.82%93.25%
Ours-3D210846.94%37.60%95.25%56980.00%22.77%125650.04%93.46%
", + "bbox": [ + 89, + 142, + 877, + 560 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/caa6124029b3eb7cbad22a0bb927eb027dd12b53312992d82eb5e47e2873888f.jpg", + "table_caption": [ + "Table 4. Comparison of average run-time (s) in different scenes." + ], + "table_footnote": [], + "table_body": "
SceneResolution (m)Ours-2DOurs-3D
liv0.150.251.00
off0.150.201.19
V10.200.998.06
V20.201.2410.36
MH0.403.6211.34
", + "bbox": [ + 102, + 595, + 439, + 698 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Since Ours-3D is also formulated in a linear form, it can also be solved efficiently. Tab. 4 shows the average run-time in different scenes. The run-time of Ours-3D is related to the resolution of the 3D grids. In the experiment, we choose different resolutions for different scenes and thousands of valid cells are used for map sparsification. The run-time of Ours-3D does not increase much compared with Ours-2D, and Ours-3D is still much faster than QP1 and QP2.", + "bbox": [ + 75, + 715, + 470, + 838 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Therefore, if the mapping sequence has not covered the whole query space and query images may be taken with different viewing perspectives, the map sparsification involving the constraints from the 3D discretized grid is a better", + "bbox": [ + 75, + 839, + 470, + 902 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "choice to select landmarks.", + "bbox": [ + 500, + 571, + 681, + 585 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "7. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 607, + 619, + 625 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this paper, we propose two novel terms for efficient map sparsification. The first term is to enforce a uniform distribution of selected landmarks based on 2D discretized grids. The second one adds a space constraint based on landmark visibility to weaken the assumption that the spatial distribution of the query sequence is close to that of the mapping sequence. Both two terms are formulated in efficient linear forms, and thus avoid heavy computation. The proposed terms can be chosen and set according to different conditions of query sequences. The exhaustive experiments have demonstrated the effectiveness and superiority of the proposed method, especially the computation efficiency compared with previous QP methods.", + "bbox": [ + 496, + 635, + 893, + 832 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgments: This work is supported by the CUHK T Sone Robotics Institute, and the InnoHK of the Government of Hong Kong via the Hong Kong Centre for Logistics Robotics.", + "bbox": [ + 496, + 839, + 893, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "12477", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Michael Burri, Janosch Nikolic, Pascal Gohl, Thomas Schneider, Joern Rehder, Sammy Omari, Markus W Achtelik, and Roland Siegwart. 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TIP, 26(1):262-275, 2017. 2", + "[7] Siddharth Choudhary, Vadim Indelman, Henrik I Christensen, and Frank Dellaert. Information-based reduced landmark SLAM. In ICRA, pages 4620-4627, 2015. 2", + "[8] Luis Contreras and Walterio Mayol-Cuevas. Trajectory-driven point cloud compression techniques for visual SLAM. In IROS, pages 133-140, 2015. 2", + "[9] Luis Contreras and Walterio Mayol-Cuevas. O-POCO: Online point cloud compression mapping for visual odometry and SLAM. In ICRA, pages 4509–4514, 2017. 2", + "[10] Xinke Deng, Zixu Zhang, Avishai Sintov, Jing Huang, and Timothy Bretl. Feature-constrained active visual SLAM for mobile robot navigation. In ICRA, pages 7233-7238, 2018. 4", + "[11] Marcin Dymczyk, Simon Lynen, Michael Bosse, and Roland Siegwart. Keep it brief: Scalable creation of compressed localization maps. In IROS, pages 2536-2542, 2015. 2, 3, 5, 6", + "[12] Marcin Dymczyk, Simon Lynen, Titus Cieslewski, Michael Bosse, Roland Siegwart, and Paul Furgale. The gist of mapsummarizing experience for lifelong localization. In ICRA, pages 2767-2773, 2015. 2", + "[13] Marcin Dymczyk, Thomas Schneider, Igor Gilitschenski, Roland Siegwart, and Elena Stumm. Erasing bad memories: Agent-side summarization for long-term mapping. In IROS, pages 4572-4579, 2016. 2", + "[14] Andreas Geiger, Philip Lenz, and Raquel Urtasun. Are we ready for autonomous driving? The KITTI vision benchmark suite. In CVPR, pages 3354-3361, 2012. 1, 5, 6", + "[15] Ankur Handa, Thomas Whelan, John McDonald, and Andrew J Davison. A benchmark for RGB-D visual odometry, 3D reconstruction and SLAM. In ICRA, pages 1524-1531, 2014. 5, 6, 7", + "[16] Vincent Lepetit, Francesc Moreno-Noguer, and Pascal Fua. Epnp: An accurate o (n) solution to the pnp problem. IJCV, 81(2):155-166, 2009. 1" + ], + "bbox": [ + 78, + 114, + 470, + 900 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[17] Yunpeng Li, Noah Snavely, and Daniel P Huttenlocher. Location recognition using prioritized feature matching. In ECCV, pages 791-804. Springer, 2010. 1, 2", + "[18] Simon Lynen, Torsten Sattler, Michael Bosse, Joel A Hesch, Marc Pollefeys, and Roland Siegwart. Get out of my lab: Large-scale, real-time visual-inertial localization. In RSS, 2015. 1, 2", + "[19] Marcela Mera-Trujillo, Benjamin Smith, and Victor Fragoso. Efficient scene compression for visual-based localization. In 3DV, pages 1-10, 2020. 2", + "[20] Raul Mur-Artal and Juan D Tardos. ORB-SLAM2: An opensource SLAM system for monocular, stereo, and RGB-D cameras. IEEE Transactions on Robotics, 33(5):1255-1262, 2017. 1, 3, 4, 5", + "[21] Ethan Rublee, Vincent Rabaud, Kurt Konolige, and Gary Bradski. ORB: An efficient alternative to SIFT or SURF. In ICCV, pages 2564-2571, 2011. 4", + "[22] Torsten Sattler, Michal Havlena, Filip Radenovic, Konrad Schindler, and Marc Pollefeys. Hyperpoints and fine vocabularies for large-scale location recognition. 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Good feature matching: Toward accurate, robust VO/VSLAM with low latency. IEEE Transactions on Robotics, 36(3):657-675, 2020. 2" + ], + "bbox": [ + 501, + 92, + 890, + 672 + ], + "page_idx": 8 + }, + { + "type": "page_number", + "text": "12478", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 8 + } +] \ No newline at end of file diff --git a/2023/Efficient Map Sparsification Based on 2D and 3D Discretized Grids/4f0f1ce5-d45d-4b52-a587-2da996f0a8b8_model.json b/2023/Efficient Map Sparsification Based on 2D and 3D Discretized Grids/4f0f1ce5-d45d-4b52-a587-2da996f0a8b8_model.json new file mode 100644 index 0000000000000000000000000000000000000000..4e736d08d052f30544931543c4df653459184701 --- /dev/null +++ b/2023/Efficient Map Sparsification Based on 2D and 3D Discretized Grids/4f0f1ce5-d45d-4b52-a587-2da996f0a8b8_model.json @@ -0,0 +1,1692 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.148, + 0.131, + 0.823, + 0.152 + ], + "angle": 0, + "content": "Efficient Map Sparsification Based on 2D and 3D Discretized Grids" + }, + { + "type": "text", + "bbox": [ + 0.242, + 0.182, + 0.727, + 0.234 + ], + "angle": 0, + "content": "Xiaoyu Zhang Yun-Hui Liu T Stone Robotics Institute, Chinese University of Hong Kong Hong Kong Centre for Logistics Robotics" + }, + { + "type": "text", + "bbox": [ + 0.259, + 0.238, + 0.706, + 0.251 + ], + "angle": 0, + "content": "zhang.xy@link.cuhk.edu.hk yhliu@mae.cuhk.edu.hk" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.287, + 0.313, + 0.303 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.318, + 0.474, + 0.651 + ], + "angle": 0, + "content": "Localization in a pre-built map is a basic technique for robot autonomous navigation. Existing mapping and localization methods commonly work well in small-scale environments. As a map grows larger, however, more memory is required and localization becomes inefficient. To solve these problems, map sparsification becomes a practical necessity to acquire a subset of the original map for localization. Previous map sparsification methods add a quadratic term in mixed-integer programming to enforce a uniform distribution of selected landmarks, which requires high memory capacity and heavy computation. In this paper, we formulate map sparsification in an efficient linear form and select uniformly distributed landmarks based on 2D discretized grids. Furthermore, to reduce the influence of different spatial distributions between the mapping and query sequences, which is not considered in previous methods, we also introduce a space constraint term based on 3D discretized grids. The exhaustive experiments in different datasets demonstrate the superiority of the proposed methods in both efficiency and localization performance. The relevant codes will be released at https://github.com/fishmarch/SLAM_Map_Compression." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.68, + 0.208, + 0.695 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.704, + 0.47, + 0.84 + ], + "angle": 0, + "content": "To realize autonomous navigation for robots, localization in a pre-built map is a basic technique. Lots of algorithms have been proposed for mapping and localization using different sensors, including camera [20] and lidar [27]. These algorithms commonly work well in some small-scale environments now. When applied in large-scale environments or in long-term, however, new challenges appear and need to be settled for practical applications. Some of these problems are time and memory consuming." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.471, + 0.902 + ], + "angle": 0, + "content": "When using cameras, visual simultaneous localization and mapping (SLAM) is a commonly used method to build maps. In visual SLAM, redundant features are extracted from images and then constructed as landmarks in a map," + }, + { + "type": "image", + "bbox": [ + 0.52, + 0.283, + 0.876, + 0.53 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.539, + 0.892, + 0.622 + ], + "angle": 0, + "content": "Figure 1. Localization results in a compact map. The original map is constructed from sequence 00 of the KITTI dataset [14]. The original map consists of 141K landmarks, indicated by gray points; while the compact map consists of only 5K landmarks, indicated by blue points. \\(96.15\\%\\) of the query images are localized successfully in the compact map, indicted by green poses." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.642, + 0.892, + 0.762 + ], + "angle": 0, + "content": "such that camera poses can be tracked robustly and accurately. These redundant landmarks promise good localization results in small-scale environments. As more and more images are received when working in large-scale environments or in long-term, however, memory consumption is increasing unboundedly. Localizing in such large maps will also be more time-consuming. These problems are especially severe for some low-cost robots." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.893, + 0.901 + ], + "angle": 0, + "content": "Actually, not all landmarks are necessary for robots to localize in pre-built maps. In theory, even only 4 matched landmarks can determine a camera pose using EPnP [16] (more landmarks are commonly used for robust and accurate estimation). This reveals that maps can be compressed and still retain comparable performance for localization. Map compression can be classified into two types: descriptor compression [5, 18, 22] and landmark sparsification [17, 23]. The research of this paper falls in the latter" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "12470" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.08, + 0.092, + 0.468, + 0.182 + ], + "angle": 0, + "content": "one, which is to find a subset of an original map while maintaining comparable localization performance. A subset map is called compact map in this paper. For example, as indicated in Fig. 1, only \\(3.91\\%\\) of the original landmarks are selected as the compact map, in which more than \\(96\\%\\) of the query images can still be localized successfully." + }, + { + "type": "text", + "bbox": [ + 0.081, + 0.185, + 0.468, + 0.486 + ], + "angle": 0, + "content": "To select an optimal subset for localization, map sparsification is related to a \\(K\\)-cover problem [17], which means the number of landmarks in a compact map is minimized while keeping the number of associated landmarks in each image larger than a threshold (i.e., \\(K\\)). To solve the \\(K\\)-cover problem, it can be formulated as mixed-integer linear programming, through which an optimal subset is obtained. The original formulation only considers the number of landmarks for localization, while their distribution also affects localization performance. Therefore, some works design and add quadratic terms, formulating mixed-integer quadratic programming to enforce a more uniform distribution of selected landmarks [11, 23]. However, these quadratic terms slow down the optimization speed heavily. The required high memory capacity and heavy computation become severe limitations of these map sparsification methods. For example, in our experiments, the mixed-integer quadratic programming methods cannot be used for the maps containing more than 55K landmarks, because all computer memory has been consumed." + }, + { + "type": "text", + "bbox": [ + 0.081, + 0.489, + 0.468, + 0.639 + ], + "angle": 0, + "content": "To select uniformly distributed landmarks and at the same time maintain the computation efficiency, we keep map sparsification formulation in a linear form in this paper. We firstly discretize images into 2D fix-sized grids. Then for all observed landmarks, we can find which cells they fall in. Therefore, more occupied cells reflect a more uniform distribution of landmarks. This can be formulated in a linear form easily. In this way, uniformly distributed landmarks are selected efficiently, and thus the localization performance in compact maps will be better." + }, + { + "type": "text", + "bbox": [ + 0.081, + 0.643, + 0.468, + 0.762 + ], + "angle": 0, + "content": "Another severe limitation is that all of past works assume the spatial distribution of the query sequence is close to that of the mapping sequence. Then landmarks are selected only based on their association with the images of the mapping sequence. However, this assumption cannot be guaranteed in real robotic applications. The perspective difference between query and mapping sequences may cause the localization in compact maps to fail unexpectedly." + }, + { + "type": "text", + "bbox": [ + 0.081, + 0.765, + 0.468, + 0.9 + ], + "angle": 0, + "content": "To ensure more query images from whole 3D space can be localized successfully in compact maps, we propose to select landmarks based on not only their association with mapping images but also their visibility in 3D space. The visibility region of a landmark is defined based on its viewing angle and distance. The 3D space is also discretized into a 3D discretized grid. For each 3D cell, all visible landmarks are collected, and a constraint on the number of visible landmarks is added into map sparsification formulation." + }, + { + "type": "text", + "bbox": [ + 0.504, + 0.092, + 0.89, + 0.121 + ], + "angle": 0, + "content": "In this way, landmarks are selected to maintain localization performance for query images from the whole space." + }, + { + "type": "text", + "bbox": [ + 0.504, + 0.123, + 0.89, + 0.272 + ], + "angle": 0, + "content": "In summary, the contributions of this paper are as follows: 1) We propose an efficient map sparsification method formulating uniform landmark distribution in a linear form to keep the computation efficiency. 2) We propose to perform map sparsification involving the visibility of landmarks to achieve better localization results for the query images from the whole space. 3) We conduct exhaustive experiments in different datasets and compare with other state-of-the-art methods, showing the effectiveness and superiority of our methods for different kinds of query sequences." + }, + { + "type": "title", + "bbox": [ + 0.504, + 0.287, + 0.64, + 0.302 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.504, + 0.313, + 0.89, + 0.582 + ], + "angle": 0, + "content": "Map compression or sparsification has received many research attention in SLAM and structure from motion (SfM) because of the burden of maintaining and utilizing a large map. Different methods are also proposed to solve this problem. In [5,18,22], the descriptors are quantized to compact forms to reduce memory consumption. Mera-Trujillo et al. [19] propose a constrained quadratic program method and design an efficient solver to select landmarks. Contreras et al. [8] develop a map compression method based on traveled trajectories, and they also propose an online system performing SLAM and map compression simultaneously [9]. Some SLAM systems [7, 26, 28] are also designed to select and build a compact map online, but much more landmarks are still remained compared with the offline methods. Recently, some learning-based map sparsification methods have also appeared and achieved good results [4, 25], but they require high-cost GPUs to train and struggle to be applied in different unseen scenes." + }, + { + "type": "text", + "bbox": [ + 0.504, + 0.585, + 0.89, + 0.794 + ], + "angle": 0, + "content": "Map sparsification is more commonly regarded as a \\(K\\)-cover problem. Since \\(K\\)-cover is an NP-hard problem, Li et al. [17] propose to use a greedy algorithm to select the landmark observed by the largest number of not-yet-fully covered frames. Cao et al. [3] also use a greedy algorithm to select landmarks, considering both the coverage and distinctiveness. In [6], the original \\(K\\)-cover method is improved by predicting the parameter \\(K\\). Similarly, the landmarks are scored and sampled based on the observation count, covariance, and descriptor stability in [12]. Moreover, the authors come up with more scoring factors to rank landmarks for selecting in [13]. These methods can provide compact maps for localization, but depend on a careful design of selecting methods and cannot get the optimal solution." + }, + { + "type": "text", + "bbox": [ + 0.504, + 0.796, + 0.89, + 0.9 + ], + "angle": 0, + "content": "Another \\(K\\)-cover based map sparsification solution is to be formulated as a mixed-integer programming problem, which is introduced in detail in [23]. The linear formulation does not consider the distribution of the selected landmarks but can be solved efficiently, and therefore it is adopted in some later works [13, 24]. The mixed-integer quadratic programming formulation encourages the uniformly dis" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.946, + 0.518, + 0.957 + ], + "angle": 0, + "content": "12471" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.302 + ], + "angle": 0, + "content": "tributed landmarks but requires a high capacity of memory and heavy computation [23] and becomes impractical for large maps. To improve the computation efficiency, Dymczyk et al. [11] have to divide the whole map into several small parts and perform map sparsification separately. Camposeco et al. [2] keep the linear form of map sparsification but divide each image into \\( q \\) uniformly-sized cells and let each cell be covered by \\( K / q \\) landmarks. This method seems reasonable, but we find in the experiments that the number of corresponding selected landmarks in some images is much less than \\( K \\) actually, and thus the localization results get worse. Similarly, the proposed method also makes use of discretized images, but the image is still considered as a whole and thus avoids the above problems." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.303, + 0.473, + 0.44 + ], + "angle": 0, + "content": "All of the above methods are based on the existing association between landmarks and images, thus landmarks are selected only to ensure localization performance of these images. For an arbitrary query image with a different viewing perspective, localization may fail unexpectedly, especially when the compression ratio is high. To solve this problem, the proposed method considers landmark visibility in the 3D space and adds constraints to preserve enough visible landmarks for the whole space in compact maps." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.452, + 0.373, + 0.469 + ], + "angle": 0, + "content": "3. Map Sparsification Formulation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.477, + 0.47, + 0.612 + ], + "angle": 0, + "content": "The proposed method is designed mainly for the maps built from feature-based visual SLAM systems (e.g., ORBSLAM [20]). Receiving sequences of images, the feature points observed by keyframes are constructed as landmarks. Thus, an original map \\(\\mathcal{M}\\) consists of landmarks \\(\\{\\pmb {p}_i\\}_{i = 1,2,\\dots,N}\\), keyframes \\(\\{F_j\\}_{j = 1,2,\\dots,M}\\), and their association. The map sparsification aims to decrease the number of landmarks. We firstly introduce commonly used formulations of map sparsification in past works [23]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.613, + 0.47, + 0.643 + ], + "angle": 0, + "content": "Using mixed-integer programming, map sparsification can be formulated as:" + }, + { + "type": "equation", + "bbox": [ + 0.183, + 0.65, + 0.469, + 0.693 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\underset {\\mathbf {x}, \\boldsymbol {\\xi}} {\\text {m i n i m i z e}} \\quad \\mathbf {q} ^ {\\top} \\mathbf {x} + \\lambda \\mathbf {1} ^ {\\top} \\boldsymbol {\\xi} \\\\ \\mathbf {A} \\mathbf {x} \\geq K \\mathbf {1} - \\boldsymbol {\\xi} \\tag {1} \\\\ \\end{array}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.18, + 0.69, + 0.364, + 0.723 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\begin{array}{l} \\text {s u b j e c t t o} \\quad \\mathbf {x} \\in \\{0, 1 \\} ^ {N} \\end{array} \\\\ \\boldsymbol {\\xi} \\in \\{0, \\mathbb {Z} _ {+} \\} ^ {M} \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.735, + 0.473, + 0.901 + ], + "angle": 0, + "content": "where \\(\\mathbf{x}\\) is a binary vector whose \\(i^{\\mathrm{th}}\\) element indicates whether the landmark \\(\\pmb{p}_i\\) is selected or not. \\(\\mathbf{q}\\) is a weight vector to select landmarks. \\(\\mathbf{A}\\) is a binary matrix describing the association between landmarks and keyframes, i.e., the element \\(\\mathbf{A}_{ij}\\) indicates whether the landmark \\(\\pmb{p}_j\\) is visible in the keyframe \\(\\pmb{F}_i\\). \\(K\\) is the desired minimum number of visible landmarks in each keyframe and can be used to adjust compression ratio. To handle the situation when the total number of associated landmarks of a keyframe is less than \\(K\\), a slack variable \\(\\xi\\) is used to relax the hard constraints, and \\(\\lambda\\) determines the hardness of the constraints." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.168 + ], + "angle": 0, + "content": "Therefore, Eq. (1) describes the mixed-integer linear programming method for map sparsification. The distribution of selected landmarks is not considered in this method. To involve the distribution of landmarks, quadratic terms are commonly used:" + }, + { + "type": "equation", + "bbox": [ + 0.573, + 0.176, + 0.891, + 0.218 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\underset {\\mathbf {x}, \\boldsymbol {\\xi}} {\\text {m i n i m i z e}} \\quad \\frac {1}{2} \\mathbf {x} ^ {\\top} \\mathbf {Q} \\mathbf {x} + \\mathbf {q} ^ {\\top} \\mathbf {x} + \\lambda \\mathbf {1} ^ {\\top} \\boldsymbol {\\xi} \\\\ \\mathbf {A} \\mathbf {x} \\geq K \\mathbf {1} _ {N} - \\boldsymbol {\\xi} \\tag {2} \\\\ \\end{array}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.57, + 0.215, + 0.754, + 0.248 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\begin{array}{l} \\text {s u b j e c t t o} \\quad \\mathbf {x} \\in \\{0, 1 \\} ^ {N} \\end{array} \\\\ \\boldsymbol {\\xi} \\in \\{0, \\mathbb {Z} _ {+} \\} ^ {M} \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.257, + 0.892, + 0.393 + ], + "angle": 0, + "content": "where \\(\\mathbf{Q}\\) is a symmetric matrix. The element \\(\\mathbf{Q}_{ij}\\) indicates the relation between \\(\\pmb{p}_i\\) and \\(\\pmb{p}_j\\). For example, it can be the number of common observations for each pair of landmarks. Therefore, the landmarks that are observed together with others frequently would be discarded. As a result, selected landmarks are distributed more uniformly. Eq. (2) describes the commonly used map sparsification formulation in past works, which considers both the number and distribution of landmarks for localization." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.406, + 0.846, + 0.423 + ], + "angle": 0, + "content": "4. Map Sparsification Based on 2D Grids" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.431, + 0.892, + 0.522 + ], + "angle": 0, + "content": "Uniformly distributed landmarks commonly provide better localization results. Because of the quadratic terms, however, the computation complexity increases largely. Besides, Eq. (2) encourages selection of rarely observed landmarks, which may have larger errors and be detrimental for localization [11]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.522, + 0.892, + 0.689 + ], + "angle": 0, + "content": "To solve these problems, we design a linear term to encourage a uniform distribution of selected landmarks. As illustrated in Fig. 2, the image is discretized into fixed-size grids (e.g., \\( C \\times R \\) cells). Each cell has two stats: empty or occupied. Based on the camera model, projected positions of landmarks can be computed easily. Then a cell is occupied if at least one landmark is projected into it; otherwise, it is empty. Therefore, to acquire uniformly distributed landmarks, we encourage selecting the landmarks that make more cells to be occupied. This concept can be easily formulated into Eq. (1), which becomes:" + }, + { + "type": "equation", + "bbox": [ + 0.573, + 0.697, + 0.892, + 0.755 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\underset {\\mathbf {x}, \\boldsymbol {\\xi}, \\boldsymbol {\\phi}} {\\text {m i n i m i z e}} \\quad \\mathbf {q} ^ {\\top} \\mathbf {x} + \\lambda_ {1} \\mathbf {1} ^ {\\top} \\boldsymbol {\\xi} + \\lambda_ {2} \\mathbf {1} ^ {\\top} \\boldsymbol {\\phi} \\\\ \\mathbf {A} \\mathbf {x} \\geq K \\mathbf {1} - \\boldsymbol {\\xi} \\\\ \\mathrm {B x} \\geq 1 - \\phi \\tag {3} \\\\ \\end{array}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.57, + 0.751, + 0.785, + 0.801 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\begin{array}{l} \\text {s u b j e c t t o} \\quad \\mathbf {x} \\in \\{0, 1 \\} ^ {N} \\end{array} \\\\ \\boldsymbol {\\xi} \\in \\{0, \\mathbb {Z} _ {+} \\} ^ {M} \\\\ \\phi \\in \\{0, 1 \\} ^ {M \\times C \\times R} \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.81, + 0.892, + 0.901 + ], + "angle": 0, + "content": "where \\(\\mathbf{B}\\) is a binary matrix describing the association between the landmarks and all cells, i.e., the element \\(\\mathbf{B}_{ij}\\) indicates whether the projected position of the landmark \\(p_j\\) falls within the cell \\(c_i\\). We encourage every cell to keep at least one corresponding landmark and use the slack variable \\(\\phi\\) to relax this constraint. An example is illustrated in" + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "12472" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.11, + 0.088, + 0.437, + 0.219 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.229, + 0.473, + 0.288 + ], + "angle": 0, + "content": "Figure 2. Illustration of discretized images and associated landmarks. The occupied cells are drawn in deeper color. The red points represent the projected position of associated landmarks. Dotted points can be discarded without changing occupancy." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.3, + 0.47, + 0.33 + ], + "angle": 0, + "content": "Fig. 2, the dotted points can be discarded without changing the number of occupied cells." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.33, + 0.47, + 0.406 + ], + "angle": 0, + "content": "Eq. (3) formulates map sparsification as a mixed-integer linear programming problem and thus can be solved efficiently. The selected landmarks are directly encouraged to spread uniformly in all corresponding keyframes. Thus better localization performance will be achieved." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.419, + 0.37, + 0.438 + ], + "angle": 0, + "content": "5. Map Sparsification In 3D Space" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.445, + 0.47, + 0.626 + ], + "angle": 0, + "content": "From the previous section, it is noticed that map sparsification is formulated based on the association between landmarks and keyframes. This association can be easily constructed from feature matching during mapping. All past works are based on such association and assume the spatial distribution of the query sequence will be close to that of the mapping sequence. Thus selected landmarks can be matched again in query images. Obviously, this assumption cannot be promised in real robotic applications. Some selected landmarks would not be matched in query images because of different viewing perspectives, and thus, the localization may fail unexpectedly." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.627, + 0.47, + 0.687 + ], + "angle": 0, + "content": "In this section, we will introduce our proposed map sparsification method that involves landmark visibility in 3D space and thus improves localization performance for query images from the whole space." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.697, + 0.27, + 0.714 + ], + "angle": 0, + "content": "5.1. Landmark Visibility" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.72, + 0.471, + 0.902 + ], + "angle": 0, + "content": "Feature points (e.g., ORB [21]) are commonly extracted and constructed as landmarks in visual SLAM. One of the basic requirements of used features is robust matching from different viewing perspectives. In other words, it is assumed that a valid feature point is visible and can be matched within a certain region. Specifically, we assume a feature point can be matched when the viewing angle and distance are within certain thresholds. Such specific regions can be approximated from mapping process. Similarly defined visibility is also used for efficient feature matching [20]. Deng et al. [10] also predict such feature matching to ensure localization performance in an active SLAM framework." + }, + { + "type": "image", + "bbox": [ + 0.58, + 0.088, + 0.818, + 0.259 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.536, + 0.268, + 0.856, + 0.283 + ], + "angle": 0, + "content": "Figure 3. 3D cells in which the landmark \\( \\pmb{p} \\) is visible." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.296, + 0.892, + 0.372 + ], + "angle": 0, + "content": "For a landmark \\( \\pmb{p} \\) observed by multiple keyframes, an average viewing direction \\( \\bar{\\pmb{v}}^p \\) can be computed from all viewing directions, pointing from \\( \\pmb{p} \\) to the optical centers of these keyframes. Therefore, the first condition for \\( \\pmb{p} \\) to be visible is that the viewing angle is within the threshold," + }, + { + "type": "equation", + "bbox": [ + 0.647, + 0.381, + 0.892, + 0.4 + ], + "angle": 0, + "content": "\\[\n\\langle \\bar {\\boldsymbol {v}} ^ {p}, \\boldsymbol {v} ^ {i} \\rangle < \\theta_ {t h} ^ {p} \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.409, + 0.892, + 0.454 + ], + "angle": 0, + "content": "where \\(\\pmb{v}^i\\) is the viewing direction for a query position. In our experiments, \\(\\theta_{th}^{p}\\) is set according to the largest viewing angle during mapping." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.455, + 0.892, + 0.516 + ], + "angle": 0, + "content": "Besides, an image pyramid is commonly employed for matching features from different distance. Therefore, the second condition for \\( \\pmb{p} \\) to be visible is that the viewing distance \\( d_{i}^{p} \\) from a query position is within the following range," + }, + { + "type": "equation", + "bbox": [ + 0.631, + 0.529, + 0.891, + 0.547 + ], + "angle": 0, + "content": "\\[\nd _ {\\min } ^ {p} < d _ {i} ^ {p} < d _ {\\max } ^ {p} \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.551, + 0.892, + 0.582 + ], + "angle": 0, + "content": "where \\(d_{\\mathrm{min}}^p\\) and \\(d_{\\mathrm{max}}^p\\) are also set according to the smallest and largest viewing distance during mapping." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.582, + 0.892, + 0.629 + ], + "angle": 0, + "content": "Therefore, a landmark is assumed to be visible when meeting the conditions Eq. (4) and Eq. (5). The visible region forms a truncated spherical cone, as indicated in Fig. 3." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.636, + 0.825, + 0.653 + ], + "angle": 0, + "content": "5.2. Map Sparsification Based on 3D Grid" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.66, + 0.892, + 0.795 + ], + "angle": 0, + "content": "For map sparsification methods described in Sec. 3, enough visible landmarks are preserved for every keyframe based on the constraint \\(\\mathbf{A}\\mathbf{x} \\geq K\\mathbf{1} - \\boldsymbol{\\xi}\\). Therefore, the compact map can be used to localize the query images that are close to the mapping sequence as expected. However, for query images taken from different viewing perspectives, which is common in practical robotic applications, the number of matched visible landmarks may decrease, and thus the localization may fail unexpectedly." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.796, + 0.892, + 0.901 + ], + "angle": 0, + "content": "To solve the above problem, we propose a map sparsification method considering landmark visibility in 3D space. We firstly discretize the whole space into a 3D grid. The corresponding 3D cells from which it is visible are collected for each landmark, as indicated in Fig. 3. Therefore, each cell stores all visible landmarks from that position. To decrease computation, we define a threshold \\( K_{2} \\), and the" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "12473" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.47, + 0.121 + ], + "angle": 0, + "content": "3D cell is valid only if the number of corresponding visible landmarks is larger than \\( K_{2} \\)." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.122, + 0.468, + 0.182 + ], + "angle": 0, + "content": "In the proposed map sparsification method, landmarks are selected to keep as many valid 3D cells as possible. Therefore, an extra constraint is introduced into the formulation for each valid 3D cell:" + }, + { + "type": "equation", + "bbox": [ + 0.104, + 0.189, + 0.469, + 0.267 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\underset {\\mathbf {x}, \\boldsymbol {\\xi}, \\boldsymbol {\\phi}, \\boldsymbol {\\varphi}} {\\text {m i n i m i z e}} \\quad \\mathbf {q} ^ {\\top} \\mathbf {x} + \\lambda_ {1} \\mathbf {1} ^ {\\top} \\boldsymbol {\\xi} + \\lambda_ {2} \\mathbf {1} ^ {\\top} \\boldsymbol {\\phi} + \\lambda_ {3} \\mathbf {1} ^ {\\top} \\boldsymbol {\\varphi} \\\\ \\mathbf {A} \\mathbf {x} \\geq K _ {1} \\mathbf {1} - \\boldsymbol {\\xi} \\\\ \\mathrm {B x} \\geq 1 - \\phi \\\\ \\mathbf {C x} \\geq K _ {2} \\mathbf {1} - \\varphi \\tag {6} \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.103, + 0.261, + 0.47, + 0.276 + ], + "angle": 0, + "content": "subject to \\(\\mathbf{x}\\in \\{0,1\\} ^N\\) (6)" + }, + { + "type": "equation", + "bbox": [ + 0.103, + 0.261, + 0.47, + 0.327 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\boldsymbol {\\xi} \\in \\left\\{0, \\mathbb {Z} _ {+} \\right\\} ^ {M} \\\\ \\phi \\in \\{0, 1 \\} ^ {M \\times C \\times R} \\\\ \\boldsymbol {\\varphi} \\in \\{0, \\mathbb {Z} _ {+} \\} ^ {S} \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.338, + 0.469, + 0.412 + ], + "angle": 0, + "content": "where \\(\\mathbf{C}\\) is a binary matrix describing the association between landmarks and valid 3D cells, i.e., the element \\(\\mathbf{C}_{ij}\\) indicates whether the landmark \\(p_j\\) is visible for the 3D cell \\(g_i\\). As before, the slack variable \\(\\varphi\\) is used to relax the constraints." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.414, + 0.469, + 0.489 + ], + "angle": 0, + "content": "Therefore, the proposed map sparsification method aims to preserve enough visible landmarks not only for mapping keyframes but also for the whole 3D space. As a result, more query images from the whole space can be localized successfully." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.503, + 0.21, + 0.52 + ], + "angle": 0, + "content": "6. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.528, + 0.47, + 0.695 + ], + "angle": 0, + "content": "The proposed map sparsification based on 2D grids (i.e., Eq. (3)) is firstly compared with previous works to show its superiority in performance and efficiency for localizing query images close to mapping sequences. Then we demonstrate the effectiveness of map sparsification involving the visibility of landmarks in 3D space (i.e., Eq. (6)) and its superiority when query images are not close to mapping sequences. More experimental results can be found in the supplementary material, including visualization results and the comparison between original and compact maps in terms of memory consumption and localization efficiency." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.704, + 0.267, + 0.72 + ], + "angle": 0, + "content": "6.1. Experimental Setup" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.727, + 0.469, + 0.772 + ], + "angle": 0, + "content": "All experiments are tested on a laptop with an i7- 7700HQ \\(2.80\\mathrm{Hz}\\) CPU and 16GB RAM. The mixed-integer programming problem is solved using Gurobi1." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.773, + 0.469, + 0.878 + ], + "angle": 0, + "content": "The proposed methods are tested on three commonly used SLAM datasets: ICL-NUIM [15], EuRoC [1], and KITTI [14]. These datasets cover indoor and outdoor, small-scale and large-scale environments; the number of landmarks in original maps changes from thousands to more than one hundred thousand. The original map is constructed by running a state-of-the-art visual SLAM system" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.092, + 0.892, + 0.198 + ], + "angle": 0, + "content": "(i.e., ORB-SLAM2 [20]). Query images are localized in the map based on the re-localization module in ORB-SLAM2, in which localization is successful when enough inliers are matched. Different map sparsification methods are compared in terms of localization rate and run-time. Localization rate is the ratio of the number of successfully localized images to the number of all query images in one sequence." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.199, + 0.892, + 0.41 + ], + "angle": 0, + "content": "The weight vector \\(\\mathbf{q}\\) in all methods is set based on the number of matched times for each landmark, just like in [23]. The proposed method based only on 2D grids (i.e., Eq. (3)) is denoted as Ours-2D, while the method based on 2D and 3D grids (i.e., Eq. (6)) is denoted as Ours-3D. The proposed methods are compared with several state-of-the-art \\(K\\)-cover-based map sparsification methods. The map sparsification using mixed-integer linear programming (i.e., Eq. (1)) is denoted as LP. For the methods using mixed-integer quadratic programming (i.e., Eq. (2)), the weight matrix \\(\\mathbf{Q}\\) is set according to the number of co-observation times [23] or average projected distance [11], and these two methods are denoted as QP1 and QP2 respectively. The map sparsification based on divided images [2] is denoted as DI." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.422, + 0.831, + 0.438 + ], + "angle": 0, + "content": "6.2. Map Sparsification Based on 2D Grids" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.446, + 0.892, + 0.597 + ], + "angle": 0, + "content": "Since previous methods assume the spatial distribution of the query sequence is close to that of the mapping sequence, one sequence is firstly used to build an original map and then the images from the same mapping sequence are re-localized in compact maps. In this subsection, the proposed map sparsification method is only based on 2D discretized grids (i.e., Eq. (3)). Tab. 1 compares the localization rates in different maps obtained by different methods. An example of the selected sparse landmarks is illustrated by blue points in Fig. 1." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.599, + 0.892, + 0.749 + ], + "angle": 0, + "content": "The experimental results demonstrate that the number of landmarks can be reduced largely while the localization is still successful for most query images. For example, only \\(4.37\\%\\) landmarks are selected from the map of sequence off2 and \\(3.46\\%\\) for sequence 04, but more than \\(90\\%\\) of the query images can still be localized successfully. The compression ratio is mainly controlled by the threshold \\(K\\) in Eq. (1), Eq. (2), and Eq. (3), and we use \\(K = 50\\) in our experiments. With a larger \\(K\\), more landmarks will be selected in compact maps, and localization rate will be higher." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.75, + 0.892, + 0.901 + ], + "angle": 0, + "content": "For more sequences, our proposed method achieves the highest localization rate (labelled in bold), especially compared with the method only considering the number of landmarks for map sparsification (i.e., LP). Our method also gets slightly better results than other methods that consider landmark distribution (i.e., QP1, QP2, and DI). In QP1, the weight matrix \\(\\mathbf{Q}\\) is set according to the number of co-observation times between landmarks and as a result, rarely observed landmarks are preferred, which may be detrimental for localization [11]. To overcome this limitation, QP2" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.887, + 0.233, + 0.9 + ], + "angle": 0, + "content": "1https://www.gurobi.com" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "12474" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.078, + 0.089, + 0.892, + 0.131 + ], + "angle": 0, + "content": "Table 1. Comparison of different map sparsification methods in terms of localization rate. Num denotes the number of landmarks in the mam, Rate denotes the localization rate in the corresponding map. The highest localization rates in compact maps are labelled in bold. -' means the method cannot work because of memory limit." + }, + { + "type": "table", + "bbox": [ + 0.078, + 0.142, + 0.892, + 0.652 + ], + "angle": 0, + "content": "
DatasetOriginal MapOurs-2DLP [23]QP1 [23]QP2 [11]DI [2]
NumRateNumRateNumRateNumRateNumRateNumRate
ICL-NUIM [15]liv0406198.34%51979.97%51979.51%51979.64%51978.65%73477.39%
liv1411299.89%44587.47%44586.23%44587.37%44585.51%51655.59%
liv26435100.0%31291.36%31089.77%31090.57%31091.02%83389.89%
liv3617393.38%53276.21%53173.71%53175.32%53173.55%98761.85%
off0587599.93%39895.62%39895.42%39895.76%39895.76%79184.88%
off1599293.57%48580.00%48577.93%48579.07%48476.89%73637.20%
off26838100.0%29992.27%29891.02%29890.34%29891.36%75990.45%
off3536799.52%39683.47%39583.06%39578.31%39683.15%43051.05%
EuRoC [1]MH11250699.04%297897.33%297697.03%297696.76%297796.54%421094.56%
MH21130699.73%254698.17%254496.43%254798.33%254798.30%366593.30%
MH31523497.34%210595.32%210495.32%210795.44%210595.17%372091.30%
MH41749099.69%74497.37%74397.32%74297.27%74297.01%249396.05%
MH51695699.77%111698.87%111698.69%111698.60%111698.60%293396.08%
V101686499.03%46186.04%46084.92%46185.52%46186.35%101179.14%
V102987898.12%50785.93%50784.86%50685.87%50685.49%125584.17%
V1031151893.22%114083.76%114083.91%114083.09%114083.05%166177.89%
V201734694.69%56579.64%56478.75%56478.62%56478.97%99078.75%
V2021179199.48%125493.25%125492.86%125493.07%125493.42%228590.39%
V2031455787.51%179681.48%179581.27%179681.11%179581.48%238475.45%
KITTI [14]00141673100.0%553696.15%552495.68%----1854291.15%
018944391.01%421876.02%421676.02%----1020471.84%
0218249999.96%766097.47%766197.15%----2513386.76%
0324284100.0%83796.00%83695.63%83796.13%83695.76%295288.76%
0416824100.0%58399.63%58599.26%57299.63%57299.63%201997.41%
0574158100.0%273797.46%273897.25%----965590.62%
0642522100.0%187998.27%187898.09%187898.18%187798.18%563595.82%
0727036100.0%124292.28%124091.28%124091.73%124092.55%351792.01%
08119323100.0%590394.87%589994.82%----1687283.03%
095598499.94%294595.79%294495.60%294295.85%294395.79%822488.37%
103093399.92%172997.09%172896.67%172896.83%172996.42%474386.34%
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.665, + 0.47, + 0.771 + ], + "angle": 0, + "content": "sets the weight matrix \\(\\mathbf{Q}\\) based on the average distance between projected positions. But instead of uniform distribution, QP2 actually prefers to select landmarks that are projected far from the image center. Unlike these quadratic programming-based methods, our method formulates uniform distribution in a more clear and simple way, achieving better results." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.78, + 0.471, + 0.901 + ], + "angle": 0, + "content": "DI gets unexpected bad performance in these testings. DI divides images into \\( q \\) cells and forces each cell is covered by at least \\( K / q \\) landmarks. Therefore, DI also achieves map sparsification in a linear programming form and considers both the number and distribution of landmarks. But we find in these testings that the slack variable \\( \\lambda \\) in Eq. (1) needs to be small for DI to get a high compression ratio. As a result, the number of selected landmarks is much less" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.665, + 0.892, + 0.711 + ], + "angle": 0, + "content": "than \\( K \\) for some images, where localization would fail. Although based on similar discretized grids, our method still considers an image as a whole and thus avoids this problem." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Another superiority of our method is computational efficiency. The comparison of run-time and memory consumption on different sequences is shown in Tab. 2. The run-time for map sparsification depends on the number of landmarks, keyframes and associations among them. As the number of landmarks or keyframes increases, the run-time will commonly increase quickly. It is clear that the methods using quadratic programming are much slower, especially for the maps containing a large number of landmarks (e.g., sequence 09). In addition to solving more complex optimization problems, QP1 and QP2 also need much more time to set the weight matrix \\(\\mathbf{Q}\\), since the relation between every" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "12475" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.089, + 0.472, + 0.132 + ], + "angle": 0, + "content": "Table 2. Comparison of different map sparsification methods in terms of run-time and consumed memory. \\( N \\) denotes the number of landmarks, \\( {N}_{k} \\) denotes the number of keyframes." + }, + { + "type": "table", + "bbox": [ + 0.08, + 0.143, + 0.47, + 0.451 + ], + "angle": 0, + "content": "
Seq.Original MapRun-time (s)
NNkOursLPQP1QP2DI
liv04.1K1070.20.113.612.50.2
off05.9K1330.30.127.918.90.2
V10311.5K2161.10.359.836.30.6
MH517.0K3694.52.210761.51.2
0727.0K2582.61.112795.50.7
0956.0K6037.79.97544911.8
08119K126933.219.2--4.9
02182K179469.663.2--7.9
NNkConsumed memory (MB)
liv04.1K107351455547633
off05.9K133612784270821
V10311.5K216128563048136783
MH517.0K3692551073532165677
0727.0K2581416263155766100
0956.0K6036762301300510952211
08119K12691162637--512
02182K179434941502--1187
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.461, + 0.47, + 0.567 + ], + "angle": 0, + "content": "pair of landmarks needs to be found and this is not recorded in original maps. In our method, both the matrix \\(\\mathbf{A}\\) and \\(\\mathbf{B}\\) in Eq. (3) are set according to the relation between landmarks and keyframes, which can be retrieved from original maps directly and efficiently. In addition, since formulated in a linear form, our method can also be solved efficiently and is only slightly slower than LP." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.567, + 0.47, + 0.657 + ], + "angle": 0, + "content": "Similarly for memory consumption, ours consumes much less memory than quadratic programming. QP1 and QP2 cannot work for some sequences (e.g., 00) on our device with 16 GB memory. The testing for sequence 09 consumes nearly all of the memory when using QP1 and QP2, in which the original map contains 56K landmarks." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.657, + 0.47, + 0.735 + ], + "angle": 0, + "content": "Therefore, if the mapping sequence has covered most of the query space for localization, the proposed map sparsification based on 2D discretized grids can be used to decrease the number of landmarks to save memory and improve localization efficiency." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.742, + 0.468, + 0.759 + ], + "angle": 0, + "content": "6.3. Map Sparsification Based on 2D and 3D Grids" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.765, + 0.468, + 0.854 + ], + "angle": 0, + "content": "We have demonstrated that compact maps with much fewer landmarks achieve good localization performance when the spatial distribution of the query sequence is close to that of the mapping sequence. In this subsection, we continue to test the localization performance for query images from different distributions." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.468, + 0.902 + ], + "angle": 0, + "content": "In ICL-NUIM [15] and EuRoC [1] datasets, different sequences are recorded in the same environments. Therefore, one sequence is used to build original maps and then query" + }, + { + "type": "image", + "bbox": [ + 0.518, + 0.089, + 0.885, + 0.285 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.295, + 0.892, + 0.366 + ], + "angle": 0, + "content": "Figure 4. Comparison of map sparsification results. The original map is constructed from sequence V201. There are 3401 blue points indicating valid 3D cells of the compact map acquired by Ours-2D; while there are 6468 green points indicating valid 3D cells of the compact map acquired by Ours-3D." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.383, + 0.892, + 0.504 + ], + "angle": 0, + "content": "images of other sequences are also localized in compact maps. The comparison of experimental results is presented in Table 3. For example, sequence off0 is used to build the map, and then sequence off0, off2 and off3 are used as query sequences to be localized in the original and compact maps. Not all sequences of these two datasets are used in this experiment since the successful localization is very low even in original maps for some sequences." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.506, + 0.893, + 0.763 + ], + "angle": 0, + "content": "As shown in Tab. 3, compact maps commonly achieve good localization performance for query images from mapping sequences, while localization rates may decrease largely for other query sequences. Because the map sparsification is mainly selecting landmarks to maintain the observations in keyframes of the mapping sequences, and thus discarding other redundant landmarks which may be useful for localizing query images from the whole space. Our proposed map sparsification method in Eq. (6) aims to add such extra constraints for the whole space. In most testings, ours-3D achieves higher localization rates for the query sequences that are different from mapping sequences. For the query images from the mapping sequence, ours-3D also achieves comparable localization performance with other map sparsification methods. Other map sparsification methods achieve similar results as Ours-2D, which are included in the supplementary material." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.892, + 0.901 + ], + "angle": 0, + "content": "A comparison of compact maps acquired by ours-2D and ours-3D is illustrated in Fig. 4. The blue points indicate the valid 3D cells of ours-2D, while the green points indicate the valid 3D cells of ours-3D. The numbers of selected landmarks are similar using these two methods. But it is clear that much more valid 3D cells are kept using ours-3D and they are spreading over a larger space. As a result, more query images from the whole 3D space can be localized successfully." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "12476" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.089, + 0.895, + 0.133 + ], + "angle": 0, + "content": "Table 3. Comparison of different map sparsification methods in terms of localization rate. Num denotes the number of landmarks in the map, Rate denotes the localization rate in the corresponding map. The sequence for mapping is indicated in bold and the images from several different sequences are localized in the map. The highest localization rates in compact maps are labelled in bold." + }, + { + "type": "table", + "bbox": [ + 0.091, + 0.143, + 0.878, + 0.561 + ], + "angle": 0, + "content": "
off0off2liv2
MapNumoff0Rate off2off3NumRate off0off2NumRate liv1liv2
Original587599.93%66.70%52.26%683865.65%100.00%643555.80%100.00%
Ours-2D39895.62%27.95%7.74%2994.31%92.27%3122.48%91.36%
Ours-3D39995.49%28.52%7.98%3016.17%91.70%3144.04%90.68%
MH1MH4MH5
MapNumRateNumRateNumRate
MH1MH2MH3MH4MH5MH4MH5
Original1250699.04%87.10%52.53%1749099.69%84.20%1695682.34%99.77%
Ours-2D297897.33%73.67%45.76%74497.37%63.77%111674.75%98.87%
Ours-3D298296.78%73.97%46.18%74597.06%64.27%112175.71%98.74%
MH2V101V102
MapNumRateNumRateNumRate
MH1MH2MH3V101V102V101V102
Original1130691.78%99.73%51.81%686499.03%61.56%987872.25%98.12%
Ours-2D254674.80%98.17%35.50%46186.04%32.60%50734.61%85.93%
Ours-3D255077.41%97.77%38.69%46285.79%34.61%50637.67%85.99%
MH3V201V202
MapNumRateNumRateNumRate
MH1MH2MH3V201V202V201V202
Original1523459.93%52.80%97.34%734694.69%52.77%1179175.22%99.48%
Ours-2D210546.85%37.23%95.32%56579.64%19.48%125449.82%93.25%
Ours-3D210846.94%37.60%95.25%56980.00%22.77%125650.04%93.46%
" + }, + { + "type": "table_caption", + "bbox": [ + 0.083, + 0.571, + 0.465, + 0.585 + ], + "angle": 0, + "content": "Table 4. Comparison of average run-time (s) in different scenes." + }, + { + "type": "table", + "bbox": [ + 0.104, + 0.596, + 0.44, + 0.699 + ], + "angle": 0, + "content": "
SceneResolution (m)Ours-2DOurs-3D
liv0.150.251.00
off0.150.201.19
V10.200.998.06
V20.201.2410.36
MH0.403.6211.34
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.717, + 0.471, + 0.839 + ], + "angle": 0, + "content": "Since Ours-3D is also formulated in a linear form, it can also be solved efficiently. Tab. 4 shows the average run-time in different scenes. The run-time of Ours-3D is related to the resolution of the 3D grids. In the experiment, we choose different resolutions for different scenes and thousands of valid cells are used for map sparsification. The run-time of Ours-3D does not increase much compared with Ours-2D, and Ours-3D is still much faster than QP1 and QP2." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.472, + 0.903 + ], + "angle": 0, + "content": "Therefore, if the mapping sequence has not covered the whole query space and query images may be taken with different viewing perspectives, the map sparsification involving the constraints from the 3D discretized grid is a better" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.572, + 0.682, + 0.587 + ], + "angle": 0, + "content": "choice to select landmarks." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.608, + 0.62, + 0.625 + ], + "angle": 0, + "content": "7. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.636, + 0.895, + 0.833 + ], + "angle": 0, + "content": "In this paper, we propose two novel terms for efficient map sparsification. The first term is to enforce a uniform distribution of selected landmarks based on 2D discretized grids. The second one adds a space constraint based on landmark visibility to weaken the assumption that the spatial distribution of the query sequence is close to that of the mapping sequence. Both two terms are formulated in efficient linear forms, and thus avoid heavy computation. The proposed terms can be chosen and set according to different conditions of query sequences. The exhaustive experiments have demonstrated the effectiveness and superiority of the proposed method, especially the computation efficiency compared with previous QP methods." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.895, + 0.901 + ], + "angle": 0, + "content": "Acknowledgments: This work is supported by the CUHK T Sone Robotics Institute, and the InnoHK of the Government of Hong Kong via the Hong Kong Centre for Logistics Robotics." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "12477" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.115, + 0.47, + 0.184 + ], + "angle": 0, + "content": "[1] Michael Burri, Janosch Nikolic, Pascal Gohl, Thomas Schneider, Joern Rehder, Sammy Omari, Markus W Achtelik, and Roland Siegwart. The EuRoC micro aerial vehicle datasets. 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Existing mapping and localization methods commonly work well in small-scale environments. As a map grows larger, however, more memory is required and localization becomes inefficient. To solve these problems, map sparsification becomes a practical necessity to acquire a subset of the original map for localization. Previous map sparsification methods add a quadratic term in mixed-integer programming to enforce a uniform distribution of selected landmarks, which requires high memory capacity and heavy computation. In this paper, we formulate map sparsification in an efficient linear form and select uniformly distributed landmarks based on 2D discretized grids. Furthermore, to reduce the influence of different spatial distributions between the mapping and query sequences, which is not considered in previous methods, we also introduce a space constraint term based on 3D discretized grids. The exhaustive experiments in different datasets demonstrate the superiority of the proposed methods in both efficiency and localization performance. The relevant codes will be released at https://github.com/fishmarch/SLAM_Map_Compression. + +# 1. Introduction + +To realize autonomous navigation for robots, localization in a pre-built map is a basic technique. Lots of algorithms have been proposed for mapping and localization using different sensors, including camera [20] and lidar [27]. These algorithms commonly work well in some small-scale environments now. When applied in large-scale environments or in long-term, however, new challenges appear and need to be settled for practical applications. Some of these problems are time and memory consuming. + +When using cameras, visual simultaneous localization and mapping (SLAM) is a commonly used method to build maps. In visual SLAM, redundant features are extracted from images and then constructed as landmarks in a map, + +![](images/ac61547f118e7710f3f157276dd2e0e2ed91856d569186ae85e84c5169c78734.jpg) +Figure 1. Localization results in a compact map. The original map is constructed from sequence 00 of the KITTI dataset [14]. The original map consists of 141K landmarks, indicated by gray points; while the compact map consists of only 5K landmarks, indicated by blue points. $96.15\%$ of the query images are localized successfully in the compact map, indicted by green poses. + +such that camera poses can be tracked robustly and accurately. These redundant landmarks promise good localization results in small-scale environments. As more and more images are received when working in large-scale environments or in long-term, however, memory consumption is increasing unboundedly. Localizing in such large maps will also be more time-consuming. These problems are especially severe for some low-cost robots. + +Actually, not all landmarks are necessary for robots to localize in pre-built maps. In theory, even only 4 matched landmarks can determine a camera pose using EPnP [16] (more landmarks are commonly used for robust and accurate estimation). This reveals that maps can be compressed and still retain comparable performance for localization. Map compression can be classified into two types: descriptor compression [5, 18, 22] and landmark sparsification [17, 23]. The research of this paper falls in the latter + +one, which is to find a subset of an original map while maintaining comparable localization performance. A subset map is called compact map in this paper. For example, as indicated in Fig. 1, only $3.91\%$ of the original landmarks are selected as the compact map, in which more than $96\%$ of the query images can still be localized successfully. + +To select an optimal subset for localization, map sparsification is related to a $K$ -cover problem [17], which means the number of landmarks in a compact map is minimized while keeping the number of associated landmarks in each image larger than a threshold (i.e., $K$ ). To solve the $K$ -cover problem, it can be formulated as mixed-integer linear programming, through which an optimal subset is obtained. The original formulation only considers the number of landmarks for localization, while their distribution also affects localization performance. Therefore, some works design and add quadratic terms, formulating mixed-integer quadratic programming to enforce a more uniform distribution of selected landmarks [11, 23]. However, these quadratic terms slow down the optimization speed heavily. The required high memory capacity and heavy computation become severe limitations of these map sparsification methods. For example, in our experiments, the mixed-integer quadratic programming methods cannot be used for the maps containing more than 55K landmarks, because all computer memory has been consumed. + +To select uniformly distributed landmarks and at the same time maintain the computation efficiency, we keep map sparsification formulation in a linear form in this paper. We firstly discretize images into 2D fix-sized grids. Then for all observed landmarks, we can find which cells they fall in. Therefore, more occupied cells reflect a more uniform distribution of landmarks. This can be formulated in a linear form easily. In this way, uniformly distributed landmarks are selected efficiently, and thus the localization performance in compact maps will be better. + +Another severe limitation is that all of past works assume the spatial distribution of the query sequence is close to that of the mapping sequence. Then landmarks are selected only based on their association with the images of the mapping sequence. However, this assumption cannot be guaranteed in real robotic applications. The perspective difference between query and mapping sequences may cause the localization in compact maps to fail unexpectedly. + +To ensure more query images from whole 3D space can be localized successfully in compact maps, we propose to select landmarks based on not only their association with mapping images but also their visibility in 3D space. The visibility region of a landmark is defined based on its viewing angle and distance. The 3D space is also discretized into a 3D discretized grid. For each 3D cell, all visible landmarks are collected, and a constraint on the number of visible landmarks is added into map sparsification formulation. + +In this way, landmarks are selected to maintain localization performance for query images from the whole space. + +In summary, the contributions of this paper are as follows: 1) We propose an efficient map sparsification method formulating uniform landmark distribution in a linear form to keep the computation efficiency. 2) We propose to perform map sparsification involving the visibility of landmarks to achieve better localization results for the query images from the whole space. 3) We conduct exhaustive experiments in different datasets and compare with other state-of-the-art methods, showing the effectiveness and superiority of our methods for different kinds of query sequences. + +# 2. Related Work + +Map compression or sparsification has received many research attention in SLAM and structure from motion (SfM) because of the burden of maintaining and utilizing a large map. Different methods are also proposed to solve this problem. In [5,18,22], the descriptors are quantized to compact forms to reduce memory consumption. Mera-Trujillo et al. [19] propose a constrained quadratic program method and design an efficient solver to select landmarks. Contreras et al. [8] develop a map compression method based on traveled trajectories, and they also propose an online system performing SLAM and map compression simultaneously [9]. Some SLAM systems [7, 26, 28] are also designed to select and build a compact map online, but much more landmarks are still remained compared with the offline methods. Recently, some learning-based map sparsification methods have also appeared and achieved good results [4, 25], but they require high-cost GPUs to train and struggle to be applied in different unseen scenes. + +Map sparsification is more commonly regarded as a $K$ -cover problem. Since $K$ -cover is an NP-hard problem, Li et al. [17] propose to use a greedy algorithm to select the landmark observed by the largest number of not-yet-fully covered frames. Cao et al. [3] also use a greedy algorithm to select landmarks, considering both the coverage and distinctiveness. In [6], the original $K$ -cover method is improved by predicting the parameter $K$ . Similarly, the landmarks are scored and sampled based on the observation count, covariance, and descriptor stability in [12]. Moreover, the authors come up with more scoring factors to rank landmarks for selecting in [13]. These methods can provide compact maps for localization, but depend on a careful design of selecting methods and cannot get the optimal solution. + +Another $K$ -cover based map sparsification solution is to be formulated as a mixed-integer programming problem, which is introduced in detail in [23]. The linear formulation does not consider the distribution of the selected landmarks but can be solved efficiently, and therefore it is adopted in some later works [13, 24]. The mixed-integer quadratic programming formulation encourages the uniformly dis + +tributed landmarks but requires a high capacity of memory and heavy computation [23] and becomes impractical for large maps. To improve the computation efficiency, Dymczyk et al. [11] have to divide the whole map into several small parts and perform map sparsification separately. Camposeco et al. [2] keep the linear form of map sparsification but divide each image into $q$ uniformly-sized cells and let each cell be covered by $K / q$ landmarks. This method seems reasonable, but we find in the experiments that the number of corresponding selected landmarks in some images is much less than $K$ actually, and thus the localization results get worse. Similarly, the proposed method also makes use of discretized images, but the image is still considered as a whole and thus avoids the above problems. + +All of the above methods are based on the existing association between landmarks and images, thus landmarks are selected only to ensure localization performance of these images. For an arbitrary query image with a different viewing perspective, localization may fail unexpectedly, especially when the compression ratio is high. To solve this problem, the proposed method considers landmark visibility in the 3D space and adds constraints to preserve enough visible landmarks for the whole space in compact maps. + +# 3. Map Sparsification Formulation + +The proposed method is designed mainly for the maps built from feature-based visual SLAM systems (e.g., ORBSLAM [20]). Receiving sequences of images, the feature points observed by keyframes are constructed as landmarks. Thus, an original map $\mathcal{M}$ consists of landmarks $\{\pmb {p}_i\}_{i = 1,2,\dots,N}$ , keyframes $\{F_j\}_{j = 1,2,\dots,M}$ , and their association. The map sparsification aims to decrease the number of landmarks. We firstly introduce commonly used formulations of map sparsification in past works [23]. + +Using mixed-integer programming, map sparsification can be formulated as: + +$$ +\begin{array}{l} \underset {\mathbf {x}, \boldsymbol {\xi}} {\text {m i n i m i z e}} \quad \mathbf {q} ^ {\top} \mathbf {x} + \lambda \mathbf {1} ^ {\top} \boldsymbol {\xi} \\ \mathbf {A} \mathbf {x} \geq K \mathbf {1} - \boldsymbol {\xi} \tag {1} \\ \end{array} +$$ + +$$ +\begin{array}{l} \begin{array}{l} \text {s u b j e c t t o} \quad \mathbf {x} \in \{0, 1 \} ^ {N} \end{array} \\ \boldsymbol {\xi} \in \{0, \mathbb {Z} _ {+} \} ^ {M} \\ \end{array} +$$ + +where $\mathbf{x}$ is a binary vector whose $i^{\mathrm{th}}$ element indicates whether the landmark $\pmb{p}_i$ is selected or not. $\mathbf{q}$ is a weight vector to select landmarks. $\mathbf{A}$ is a binary matrix describing the association between landmarks and keyframes, i.e., the element $\mathbf{A}_{ij}$ indicates whether the landmark $\pmb{p}_j$ is visible in the keyframe $\pmb{F}_i$ . $K$ is the desired minimum number of visible landmarks in each keyframe and can be used to adjust compression ratio. To handle the situation when the total number of associated landmarks of a keyframe is less than $K$ , a slack variable $\xi$ is used to relax the hard constraints, and $\lambda$ determines the hardness of the constraints. + +Therefore, Eq. (1) describes the mixed-integer linear programming method for map sparsification. The distribution of selected landmarks is not considered in this method. To involve the distribution of landmarks, quadratic terms are commonly used: + +$$ +\begin{array}{l} \underset {\mathbf {x}, \boldsymbol {\xi}} {\text {m i n i m i z e}} \quad \frac {1}{2} \mathbf {x} ^ {\top} \mathbf {Q} \mathbf {x} + \mathbf {q} ^ {\top} \mathbf {x} + \lambda \mathbf {1} ^ {\top} \boldsymbol {\xi} \\ \mathbf {A} \mathbf {x} \geq K \mathbf {1} _ {N} - \boldsymbol {\xi} \tag {2} \\ \end{array} +$$ + +$$ +\begin{array}{l} \begin{array}{l} \text {s u b j e c t t o} \quad \mathbf {x} \in \{0, 1 \} ^ {N} \end{array} \\ \boldsymbol {\xi} \in \{0, \mathbb {Z} _ {+} \} ^ {M} \\ \end{array} +$$ + +where $\mathbf{Q}$ is a symmetric matrix. The element $\mathbf{Q}_{ij}$ indicates the relation between $\pmb{p}_i$ and $\pmb{p}_j$ . For example, it can be the number of common observations for each pair of landmarks. Therefore, the landmarks that are observed together with others frequently would be discarded. As a result, selected landmarks are distributed more uniformly. Eq. (2) describes the commonly used map sparsification formulation in past works, which considers both the number and distribution of landmarks for localization. + +# 4. Map Sparsification Based on 2D Grids + +Uniformly distributed landmarks commonly provide better localization results. Because of the quadratic terms, however, the computation complexity increases largely. Besides, Eq. (2) encourages selection of rarely observed landmarks, which may have larger errors and be detrimental for localization [11]. + +To solve these problems, we design a linear term to encourage a uniform distribution of selected landmarks. As illustrated in Fig. 2, the image is discretized into fixed-size grids (e.g., $C \times R$ cells). Each cell has two stats: empty or occupied. Based on the camera model, projected positions of landmarks can be computed easily. Then a cell is occupied if at least one landmark is projected into it; otherwise, it is empty. Therefore, to acquire uniformly distributed landmarks, we encourage selecting the landmarks that make more cells to be occupied. This concept can be easily formulated into Eq. (1), which becomes: + +$$ +\begin{array}{l} \underset {\mathbf {x}, \boldsymbol {\xi}, \boldsymbol {\phi}} {\text {m i n i m i z e}} \quad \mathbf {q} ^ {\top} \mathbf {x} + \lambda_ {1} \mathbf {1} ^ {\top} \boldsymbol {\xi} + \lambda_ {2} \mathbf {1} ^ {\top} \boldsymbol {\phi} \\ \mathbf {A} \mathbf {x} \geq K \mathbf {1} - \boldsymbol {\xi} \\ \mathrm {B x} \geq 1 - \phi \tag {3} \\ \end{array} +$$ + +$$ +\begin{array}{l} \begin{array}{l} \text {s u b j e c t t o} \quad \mathbf {x} \in \{0, 1 \} ^ {N} \end{array} \\ \boldsymbol {\xi} \in \{0, \mathbb {Z} _ {+} \} ^ {M} \\ \phi \in \{0, 1 \} ^ {M \times C \times R} \\ \end{array} +$$ + +where $\mathbf{B}$ is a binary matrix describing the association between the landmarks and all cells, i.e., the element $\mathbf{B}_{ij}$ indicates whether the projected position of the landmark $p_j$ falls within the cell $c_i$ . We encourage every cell to keep at least one corresponding landmark and use the slack variable $\phi$ to relax this constraint. An example is illustrated in + +![](images/f210f16341cfc302c78164256d3237949714bde17207944b5b66083b7836c58f.jpg) +Figure 2. Illustration of discretized images and associated landmarks. The occupied cells are drawn in deeper color. The red points represent the projected position of associated landmarks. Dotted points can be discarded without changing occupancy. + +Fig. 2, the dotted points can be discarded without changing the number of occupied cells. + +Eq. (3) formulates map sparsification as a mixed-integer linear programming problem and thus can be solved efficiently. The selected landmarks are directly encouraged to spread uniformly in all corresponding keyframes. Thus better localization performance will be achieved. + +# 5. Map Sparsification In 3D Space + +From the previous section, it is noticed that map sparsification is formulated based on the association between landmarks and keyframes. This association can be easily constructed from feature matching during mapping. All past works are based on such association and assume the spatial distribution of the query sequence will be close to that of the mapping sequence. Thus selected landmarks can be matched again in query images. Obviously, this assumption cannot be promised in real robotic applications. Some selected landmarks would not be matched in query images because of different viewing perspectives, and thus, the localization may fail unexpectedly. + +In this section, we will introduce our proposed map sparsification method that involves landmark visibility in 3D space and thus improves localization performance for query images from the whole space. + +# 5.1. Landmark Visibility + +Feature points (e.g., ORB [21]) are commonly extracted and constructed as landmarks in visual SLAM. One of the basic requirements of used features is robust matching from different viewing perspectives. In other words, it is assumed that a valid feature point is visible and can be matched within a certain region. Specifically, we assume a feature point can be matched when the viewing angle and distance are within certain thresholds. Such specific regions can be approximated from mapping process. Similarly defined visibility is also used for efficient feature matching [20]. Deng et al. [10] also predict such feature matching to ensure localization performance in an active SLAM framework. + +![](images/df77f14592e6993b2eaebd4529850f6024f5accc56bf42baeb3e9191f4bd663f.jpg) +Figure 3. 3D cells in which the landmark $\pmb{p}$ is visible. + +For a landmark $\pmb{p}$ observed by multiple keyframes, an average viewing direction $\bar{\pmb{v}}^p$ can be computed from all viewing directions, pointing from $\pmb{p}$ to the optical centers of these keyframes. Therefore, the first condition for $\pmb{p}$ to be visible is that the viewing angle is within the threshold, + +$$ +\langle \bar {\boldsymbol {v}} ^ {p}, \boldsymbol {v} ^ {i} \rangle < \theta_ {t h} ^ {p} \tag {4} +$$ + +where $\pmb{v}^i$ is the viewing direction for a query position. In our experiments, $\theta_{th}^{p}$ is set according to the largest viewing angle during mapping. + +Besides, an image pyramid is commonly employed for matching features from different distance. Therefore, the second condition for $\pmb{p}$ to be visible is that the viewing distance $d_{i}^{p}$ from a query position is within the following range, + +$$ +d _ {\min } ^ {p} < d _ {i} ^ {p} < d _ {\max } ^ {p} \tag {5} +$$ + +where $d_{\mathrm{min}}^p$ and $d_{\mathrm{max}}^p$ are also set according to the smallest and largest viewing distance during mapping. + +Therefore, a landmark is assumed to be visible when meeting the conditions Eq. (4) and Eq. (5). The visible region forms a truncated spherical cone, as indicated in Fig. 3. + +# 5.2. Map Sparsification Based on 3D Grid + +For map sparsification methods described in Sec. 3, enough visible landmarks are preserved for every keyframe based on the constraint $\mathbf{A}\mathbf{x} \geq K\mathbf{1} - \boldsymbol{\xi}$ . Therefore, the compact map can be used to localize the query images that are close to the mapping sequence as expected. However, for query images taken from different viewing perspectives, which is common in practical robotic applications, the number of matched visible landmarks may decrease, and thus the localization may fail unexpectedly. + +To solve the above problem, we propose a map sparsification method considering landmark visibility in 3D space. We firstly discretize the whole space into a 3D grid. The corresponding 3D cells from which it is visible are collected for each landmark, as indicated in Fig. 3. Therefore, each cell stores all visible landmarks from that position. To decrease computation, we define a threshold $K_{2}$ , and the + +3D cell is valid only if the number of corresponding visible landmarks is larger than $K_{2}$ . + +In the proposed map sparsification method, landmarks are selected to keep as many valid 3D cells as possible. Therefore, an extra constraint is introduced into the formulation for each valid 3D cell: + +$$ +\begin{array}{l} \underset {\mathbf {x}, \boldsymbol {\xi}, \boldsymbol {\phi}, \boldsymbol {\varphi}} {\text {m i n i m i z e}} \quad \mathbf {q} ^ {\top} \mathbf {x} + \lambda_ {1} \mathbf {1} ^ {\top} \boldsymbol {\xi} + \lambda_ {2} \mathbf {1} ^ {\top} \boldsymbol {\phi} + \lambda_ {3} \mathbf {1} ^ {\top} \boldsymbol {\varphi} \\ \mathbf {A} \mathbf {x} \geq K _ {1} \mathbf {1} - \boldsymbol {\xi} \\ \mathrm {B x} \geq 1 - \phi \\ \mathbf {C x} \geq K _ {2} \mathbf {1} - \varphi \tag {6} \\ \end{array} +$$ + +subject to $\mathbf{x}\in \{0,1\} ^N$ (6) + +$$ +\begin{array}{l} \boldsymbol {\xi} \in \left\{0, \mathbb {Z} _ {+} \right\} ^ {M} \\ \phi \in \{0, 1 \} ^ {M \times C \times R} \\ \boldsymbol {\varphi} \in \{0, \mathbb {Z} _ {+} \} ^ {S} \\ \end{array} +$$ + +where $\mathbf{C}$ is a binary matrix describing the association between landmarks and valid 3D cells, i.e., the element $\mathbf{C}_{ij}$ indicates whether the landmark $p_j$ is visible for the 3D cell $g_i$ . As before, the slack variable $\varphi$ is used to relax the constraints. + +Therefore, the proposed map sparsification method aims to preserve enough visible landmarks not only for mapping keyframes but also for the whole 3D space. As a result, more query images from the whole space can be localized successfully. + +# 6. Experiments + +The proposed map sparsification based on 2D grids (i.e., Eq. (3)) is firstly compared with previous works to show its superiority in performance and efficiency for localizing query images close to mapping sequences. Then we demonstrate the effectiveness of map sparsification involving the visibility of landmarks in 3D space (i.e., Eq. (6)) and its superiority when query images are not close to mapping sequences. More experimental results can be found in the supplementary material, including visualization results and the comparison between original and compact maps in terms of memory consumption and localization efficiency. + +# 6.1. Experimental Setup + +All experiments are tested on a laptop with an i7- 7700HQ $2.80\mathrm{Hz}$ CPU and 16GB RAM. The mixed-integer programming problem is solved using Gurobi1. + +The proposed methods are tested on three commonly used SLAM datasets: ICL-NUIM [15], EuRoC [1], and KITTI [14]. These datasets cover indoor and outdoor, small-scale and large-scale environments; the number of landmarks in original maps changes from thousands to more than one hundred thousand. The original map is constructed by running a state-of-the-art visual SLAM system + +(i.e., ORB-SLAM2 [20]). Query images are localized in the map based on the re-localization module in ORB-SLAM2, in which localization is successful when enough inliers are matched. Different map sparsification methods are compared in terms of localization rate and run-time. Localization rate is the ratio of the number of successfully localized images to the number of all query images in one sequence. + +The weight vector $\mathbf{q}$ in all methods is set based on the number of matched times for each landmark, just like in [23]. The proposed method based only on 2D grids (i.e., Eq. (3)) is denoted as Ours-2D, while the method based on 2D and 3D grids (i.e., Eq. (6)) is denoted as Ours-3D. The proposed methods are compared with several state-of-the-art $K$ -cover-based map sparsification methods. The map sparsification using mixed-integer linear programming (i.e., Eq. (1)) is denoted as LP. For the methods using mixed-integer quadratic programming (i.e., Eq. (2)), the weight matrix $\mathbf{Q}$ is set according to the number of co-observation times [23] or average projected distance [11], and these two methods are denoted as QP1 and QP2 respectively. The map sparsification based on divided images [2] is denoted as DI. + +# 6.2. Map Sparsification Based on 2D Grids + +Since previous methods assume the spatial distribution of the query sequence is close to that of the mapping sequence, one sequence is firstly used to build an original map and then the images from the same mapping sequence are re-localized in compact maps. In this subsection, the proposed map sparsification method is only based on 2D discretized grids (i.e., Eq. (3)). Tab. 1 compares the localization rates in different maps obtained by different methods. An example of the selected sparse landmarks is illustrated by blue points in Fig. 1. + +The experimental results demonstrate that the number of landmarks can be reduced largely while the localization is still successful for most query images. For example, only $4.37\%$ landmarks are selected from the map of sequence off2 and $3.46\%$ for sequence 04, but more than $90\%$ of the query images can still be localized successfully. The compression ratio is mainly controlled by the threshold $K$ in Eq. (1), Eq. (2), and Eq. (3), and we use $K = 50$ in our experiments. With a larger $K$ , more landmarks will be selected in compact maps, and localization rate will be higher. + +For more sequences, our proposed method achieves the highest localization rate (labelled in bold), especially compared with the method only considering the number of landmarks for map sparsification (i.e., LP). Our method also gets slightly better results than other methods that consider landmark distribution (i.e., QP1, QP2, and DI). In QP1, the weight matrix $\mathbf{Q}$ is set according to the number of co-observation times between landmarks and as a result, rarely observed landmarks are preferred, which may be detrimental for localization [11]. To overcome this limitation, QP2 + +Table 1. Comparison of different map sparsification methods in terms of localization rate. Num denotes the number of landmarks in the mam, Rate denotes the localization rate in the corresponding map. The highest localization rates in compact maps are labelled in bold. -' means the method cannot work because of memory limit. + +
DatasetOriginal MapOurs-2DLP [23]QP1 [23]QP2 [11]DI [2]
NumRateNumRateNumRateNumRateNumRateNumRate
ICL-NUIM [15]liv0406198.34%51979.97%51979.51%51979.64%51978.65%73477.39%
liv1411299.89%44587.47%44586.23%44587.37%44585.51%51655.59%
liv26435100.0%31291.36%31089.77%31090.57%31091.02%83389.89%
liv3617393.38%53276.21%53173.71%53175.32%53173.55%98761.85%
off0587599.93%39895.62%39895.42%39895.76%39895.76%79184.88%
off1599293.57%48580.00%48577.93%48579.07%48476.89%73637.20%
off26838100.0%29992.27%29891.02%29890.34%29891.36%75990.45%
off3536799.52%39683.47%39583.06%39578.31%39683.15%43051.05%
EuRoC [1]MH11250699.04%297897.33%297697.03%297696.76%297796.54%421094.56%
MH21130699.73%254698.17%254496.43%254798.33%254798.30%366593.30%
MH31523497.34%210595.32%210495.32%210795.44%210595.17%372091.30%
MH41749099.69%74497.37%74397.32%74297.27%74297.01%249396.05%
MH51695699.77%111698.87%111698.69%111698.60%111698.60%293396.08%
V101686499.03%46186.04%46084.92%46185.52%46186.35%101179.14%
V102987898.12%50785.93%50784.86%50685.87%50685.49%125584.17%
V1031151893.22%114083.76%114083.91%114083.09%114083.05%166177.89%
V201734694.69%56579.64%56478.75%56478.62%56478.97%99078.75%
V2021179199.48%125493.25%125492.86%125493.07%125493.42%228590.39%
V2031455787.51%179681.48%179581.27%179681.11%179581.48%238475.45%
KITTI [14]00141673100.0%553696.15%552495.68%----1854291.15%
018944391.01%421876.02%421676.02%----1020471.84%
0218249999.96%766097.47%766197.15%----2513386.76%
0324284100.0%83796.00%83695.63%83796.13%83695.76%295288.76%
0416824100.0%58399.63%58599.26%57299.63%57299.63%201997.41%
0574158100.0%273797.46%273897.25%----965590.62%
0642522100.0%187998.27%187898.09%187898.18%187798.18%563595.82%
0727036100.0%124292.28%124091.28%124091.73%124092.55%351792.01%
08119323100.0%590394.87%589994.82%----1687283.03%
095598499.94%294595.79%294495.60%294295.85%294395.79%822488.37%
103093399.92%172997.09%172896.67%172896.83%172996.42%474386.34%
+ +sets the weight matrix $\mathbf{Q}$ based on the average distance between projected positions. But instead of uniform distribution, QP2 actually prefers to select landmarks that are projected far from the image center. Unlike these quadratic programming-based methods, our method formulates uniform distribution in a more clear and simple way, achieving better results. + +DI gets unexpected bad performance in these testings. DI divides images into $q$ cells and forces each cell is covered by at least $K / q$ landmarks. Therefore, DI also achieves map sparsification in a linear programming form and considers both the number and distribution of landmarks. But we find in these testings that the slack variable $\lambda$ in Eq. (1) needs to be small for DI to get a high compression ratio. As a result, the number of selected landmarks is much less + +than $K$ for some images, where localization would fail. Although based on similar discretized grids, our method still considers an image as a whole and thus avoids this problem. + +Another superiority of our method is computational efficiency. The comparison of run-time and memory consumption on different sequences is shown in Tab. 2. The run-time for map sparsification depends on the number of landmarks, keyframes and associations among them. As the number of landmarks or keyframes increases, the run-time will commonly increase quickly. It is clear that the methods using quadratic programming are much slower, especially for the maps containing a large number of landmarks (e.g., sequence 09). In addition to solving more complex optimization problems, QP1 and QP2 also need much more time to set the weight matrix $\mathbf{Q}$ , since the relation between every + +Table 2. Comparison of different map sparsification methods in terms of run-time and consumed memory. $N$ denotes the number of landmarks, ${N}_{k}$ denotes the number of keyframes. + +
Seq.Original MapRun-time (s)
NNkOursLPQP1QP2DI
liv04.1K1070.20.113.612.50.2
off05.9K1330.30.127.918.90.2
V10311.5K2161.10.359.836.30.6
MH517.0K3694.52.210761.51.2
0727.0K2582.61.112795.50.7
0956.0K6037.79.97544911.8
08119K126933.219.2--4.9
02182K179469.663.2--7.9
NNkConsumed memory (MB)
liv04.1K107351455547633
off05.9K133612784270821
V10311.5K216128563048136783
MH517.0K3692551073532165677
0727.0K2581416263155766100
0956.0K6036762301300510952211
08119K12691162637--512
02182K179434941502--1187
+ +pair of landmarks needs to be found and this is not recorded in original maps. In our method, both the matrix $\mathbf{A}$ and $\mathbf{B}$ in Eq. (3) are set according to the relation between landmarks and keyframes, which can be retrieved from original maps directly and efficiently. In addition, since formulated in a linear form, our method can also be solved efficiently and is only slightly slower than LP. + +Similarly for memory consumption, ours consumes much less memory than quadratic programming. QP1 and QP2 cannot work for some sequences (e.g., 00) on our device with 16 GB memory. The testing for sequence 09 consumes nearly all of the memory when using QP1 and QP2, in which the original map contains 56K landmarks. + +Therefore, if the mapping sequence has covered most of the query space for localization, the proposed map sparsification based on 2D discretized grids can be used to decrease the number of landmarks to save memory and improve localization efficiency. + +# 6.3. Map Sparsification Based on 2D and 3D Grids + +We have demonstrated that compact maps with much fewer landmarks achieve good localization performance when the spatial distribution of the query sequence is close to that of the mapping sequence. In this subsection, we continue to test the localization performance for query images from different distributions. + +In ICL-NUIM [15] and EuRoC [1] datasets, different sequences are recorded in the same environments. Therefore, one sequence is used to build original maps and then query + +![](images/1138bf57ffe456e409696f5a01ffcc53d943db2707dcb38d36a5b19310f956f0.jpg) +Figure 4. Comparison of map sparsification results. The original map is constructed from sequence V201. There are 3401 blue points indicating valid 3D cells of the compact map acquired by Ours-2D; while there are 6468 green points indicating valid 3D cells of the compact map acquired by Ours-3D. + +images of other sequences are also localized in compact maps. The comparison of experimental results is presented in Table 3. For example, sequence off0 is used to build the map, and then sequence off0, off2 and off3 are used as query sequences to be localized in the original and compact maps. Not all sequences of these two datasets are used in this experiment since the successful localization is very low even in original maps for some sequences. + +As shown in Tab. 3, compact maps commonly achieve good localization performance for query images from mapping sequences, while localization rates may decrease largely for other query sequences. Because the map sparsification is mainly selecting landmarks to maintain the observations in keyframes of the mapping sequences, and thus discarding other redundant landmarks which may be useful for localizing query images from the whole space. Our proposed map sparsification method in Eq. (6) aims to add such extra constraints for the whole space. In most testings, ours-3D achieves higher localization rates for the query sequences that are different from mapping sequences. For the query images from the mapping sequence, ours-3D also achieves comparable localization performance with other map sparsification methods. Other map sparsification methods achieve similar results as Ours-2D, which are included in the supplementary material. + +A comparison of compact maps acquired by ours-2D and ours-3D is illustrated in Fig. 4. The blue points indicate the valid 3D cells of ours-2D, while the green points indicate the valid 3D cells of ours-3D. The numbers of selected landmarks are similar using these two methods. But it is clear that much more valid 3D cells are kept using ours-3D and they are spreading over a larger space. As a result, more query images from the whole 3D space can be localized successfully. + +Table 3. Comparison of different map sparsification methods in terms of localization rate. Num denotes the number of landmarks in the map, Rate denotes the localization rate in the corresponding map. The sequence for mapping is indicated in bold and the images from several different sequences are localized in the map. The highest localization rates in compact maps are labelled in bold. + +
off0off2liv2
MapNumoff0Rate off2off3NumRate off0off2NumRate liv1liv2
Original587599.93%66.70%52.26%683865.65%100.00%643555.80%100.00%
Ours-2D39895.62%27.95%7.74%2994.31%92.27%3122.48%91.36%
Ours-3D39995.49%28.52%7.98%3016.17%91.70%3144.04%90.68%
MH1MH4MH5
MapNumRateNumRateNumRate
MH1MH2MH3MH4MH5MH4MH5
Original1250699.04%87.10%52.53%1749099.69%84.20%1695682.34%99.77%
Ours-2D297897.33%73.67%45.76%74497.37%63.77%111674.75%98.87%
Ours-3D298296.78%73.97%46.18%74597.06%64.27%112175.71%98.74%
MH2V101V102
MapNumRateNumRateNumRate
MH1MH2MH3V101V102V101V102
Original1130691.78%99.73%51.81%686499.03%61.56%987872.25%98.12%
Ours-2D254674.80%98.17%35.50%46186.04%32.60%50734.61%85.93%
Ours-3D255077.41%97.77%38.69%46285.79%34.61%50637.67%85.99%
MH3V201V202
MapNumRateNumRateNumRate
MH1MH2MH3V201V202V201V202
Original1523459.93%52.80%97.34%734694.69%52.77%1179175.22%99.48%
Ours-2D210546.85%37.23%95.32%56579.64%19.48%125449.82%93.25%
Ours-3D210846.94%37.60%95.25%56980.00%22.77%125650.04%93.46%
+ +Table 4. Comparison of average run-time (s) in different scenes. + +
SceneResolution (m)Ours-2DOurs-3D
liv0.150.251.00
off0.150.201.19
V10.200.998.06
V20.201.2410.36
MH0.403.6211.34
+ +Since Ours-3D is also formulated in a linear form, it can also be solved efficiently. Tab. 4 shows the average run-time in different scenes. The run-time of Ours-3D is related to the resolution of the 3D grids. In the experiment, we choose different resolutions for different scenes and thousands of valid cells are used for map sparsification. The run-time of Ours-3D does not increase much compared with Ours-2D, and Ours-3D is still much faster than QP1 and QP2. + +Therefore, if the mapping sequence has not covered the whole query space and query images may be taken with different viewing perspectives, the map sparsification involving the constraints from the 3D discretized grid is a better + +choice to select landmarks. + +# 7. Conclusion + +In this paper, we propose two novel terms for efficient map sparsification. The first term is to enforce a uniform distribution of selected landmarks based on 2D discretized grids. 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IEEE Transactions on Robotics, 36(3):657-675, 2020. 2 \ No newline at end of file diff --git a/2023/Efficient Map Sparsification Based on 2D and 3D Discretized Grids/images.zip b/2023/Efficient Map Sparsification Based on 2D and 3D Discretized Grids/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..f50aae9d5e5883b496f32ba3f416592bdd3010e9 --- /dev/null +++ b/2023/Efficient Map Sparsification Based on 2D and 3D Discretized Grids/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:4603430622a5bbd29c4106de2ec6f2d38bd954bbd14b86cc66a4b725f8281fdf +size 805419 diff --git a/2023/Efficient Map Sparsification Based on 2D and 3D Discretized Grids/layout.json b/2023/Efficient Map Sparsification Based on 2D and 3D Discretized Grids/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..f3bb1f588275655310bd742806ac95c54de8c40e --- /dev/null +++ b/2023/Efficient Map Sparsification Based on 2D and 3D Discretized Grids/layout.json @@ -0,0 +1,6793 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 90, + 103, + 503, + 120 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 90, + 103, + 503, + 120 + ], + "spans": [ + { + "bbox": [ + 90, + 103, + 503, + 120 + ], + "type": "text", + "content": "Efficient Map Sparsification Based on 2D and 3D Discretized Grids" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 148, + 144, + 444, + 185 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 148, + 144, + 444, + 185 + ], + "spans": [ + { + "bbox": [ + 148, + 144, + 444, + 185 + ], + "type": "text", + "content": "Xiaoyu Zhang Yun-Hui Liu T Stone Robotics Institute, Chinese University of Hong Kong Hong Kong Centre for Logistics Robotics" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 158, + 188, + 432, + 198 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 158, + 188, + 432, + 198 + ], + "spans": [ + { + "bbox": [ + 158, + 188, + 432, + 198 + ], + "type": "text", + "content": "zhang.xy@link.cuhk.edu.hk yhliu@mae.cuhk.edu.hk" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 143, + 227, + 191, + 239 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 227, + 191, + 239 + ], + "spans": [ + { + "bbox": [ + 143, + 227, + 191, + 239 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 251, + 290, + 515 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 251, + 290, + 515 + ], + "spans": [ + { + "bbox": [ + 46, + 251, + 290, + 515 + ], + "type": "text", + "content": "Localization in a pre-built map is a basic technique for robot autonomous navigation. Existing mapping and localization methods commonly work well in small-scale environments. As a map grows larger, however, more memory is required and localization becomes inefficient. To solve these problems, map sparsification becomes a practical necessity to acquire a subset of the original map for localization. Previous map sparsification methods add a quadratic term in mixed-integer programming to enforce a uniform distribution of selected landmarks, which requires high memory capacity and heavy computation. In this paper, we formulate map sparsification in an efficient linear form and select uniformly distributed landmarks based on 2D discretized grids. Furthermore, to reduce the influence of different spatial distributions between the mapping and query sequences, which is not considered in previous methods, we also introduce a space constraint term based on 3D discretized grids. The exhaustive experiments in different datasets demonstrate the superiority of the proposed methods in both efficiency and localization performance. The relevant codes will be released at https://github.com/fishmarch/SLAM_Map_Compression." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 538, + 127, + 550 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 538, + 127, + 550 + ], + "spans": [ + { + "bbox": [ + 47, + 538, + 127, + 550 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 557, + 287, + 665 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 557, + 287, + 665 + ], + "spans": [ + { + "bbox": [ + 46, + 557, + 287, + 665 + ], + "type": "text", + "content": "To realize autonomous navigation for robots, localization in a pre-built map is a basic technique. Lots of algorithms have been proposed for mapping and localization using different sensors, including camera [20] and lidar [27]. These algorithms commonly work well in some small-scale environments now. When applied in large-scale environments or in long-term, however, new challenges appear and need to be settled for practical applications. Some of these problems are time and memory consuming." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 665, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 288, + 714 + ], + "type": "text", + "content": "When using cameras, visual simultaneous localization and mapping (SLAM) is a commonly used method to build maps. In visual SLAM, redundant features are extracted from images and then constructed as landmarks in a map," + } + ] + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 318, + 224, + 536, + 419 + ], + "blocks": [ + { + "bbox": [ + 318, + 224, + 536, + 419 + ], + "lines": [ + { + "bbox": [ + 318, + 224, + 536, + 419 + ], + "spans": [ + { + "bbox": [ + 318, + 224, + 536, + 419 + ], + "type": "image", + "image_path": "ac61547f118e7710f3f157276dd2e0e2ed91856d569186ae85e84c5169c78734.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 426, + 545, + 492 + ], + "lines": [ + { + "bbox": [ + 305, + 426, + 545, + 492 + ], + "spans": [ + { + "bbox": [ + 305, + 426, + 545, + 492 + ], + "type": "text", + "content": "Figure 1. Localization results in a compact map. The original map is constructed from sequence 00 of the KITTI dataset [14]. The original map consists of 141K landmarks, indicated by gray points; while the compact map consists of only 5K landmarks, indicated by blue points. " + }, + { + "bbox": [ + 305, + 426, + 545, + 492 + ], + "type": "inline_equation", + "content": "96.15\\%" + }, + { + "bbox": [ + 305, + 426, + 545, + 492 + ], + "type": "text", + "content": " of the query images are localized successfully in the compact map, indicted by green poses." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 508, + 545, + 603 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 508, + 545, + 603 + ], + "spans": [ + { + "bbox": [ + 304, + 508, + 545, + 603 + ], + "type": "text", + "content": "such that camera poses can be tracked robustly and accurately. These redundant landmarks promise good localization results in small-scale environments. As more and more images are received when working in large-scale environments or in long-term, however, memory consumption is increasing unboundedly. Localizing in such large maps will also be more time-consuming. These problems are especially severe for some low-cost robots." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 605, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 546, + 713 + ], + "type": "text", + "content": "Actually, not all landmarks are necessary for robots to localize in pre-built maps. In theory, even only 4 matched landmarks can determine a camera pose using EPnP [16] (more landmarks are commonly used for robust and accurate estimation). This reveals that maps can be compressed and still retain comparable performance for localization. Map compression can be classified into two types: descriptor compression [5, 18, 22] and landmark sparsification [17, 23]. The research of this paper falls in the latter" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "12470" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 72, + 286, + 144 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 72, + 286, + 144 + ], + "spans": [ + { + "bbox": [ + 48, + 72, + 286, + 144 + ], + "type": "text", + "content": "one, which is to find a subset of an original map while maintaining comparable localization performance. A subset map is called compact map in this paper. For example, as indicated in Fig. 1, only " + }, + { + "bbox": [ + 48, + 72, + 286, + 144 + ], + "type": "inline_equation", + "content": "3.91\\%" + }, + { + "bbox": [ + 48, + 72, + 286, + 144 + ], + "type": "text", + "content": " of the original landmarks are selected as the compact map, in which more than " + }, + { + "bbox": [ + 48, + 72, + 286, + 144 + ], + "type": "inline_equation", + "content": "96\\%" + }, + { + "bbox": [ + 48, + 72, + 286, + 144 + ], + "type": "text", + "content": " of the query images can still be localized successfully." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 49, + 146, + 286, + 384 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 146, + 286, + 384 + ], + "spans": [ + { + "bbox": [ + 49, + 146, + 286, + 384 + ], + "type": "text", + "content": "To select an optimal subset for localization, map sparsification is related to a " + }, + { + "bbox": [ + 49, + 146, + 286, + 384 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 49, + 146, + 286, + 384 + ], + "type": "text", + "content": "-cover problem [17], which means the number of landmarks in a compact map is minimized while keeping the number of associated landmarks in each image larger than a threshold (i.e., " + }, + { + "bbox": [ + 49, + 146, + 286, + 384 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 49, + 146, + 286, + 384 + ], + "type": "text", + "content": "). To solve the " + }, + { + "bbox": [ + 49, + 146, + 286, + 384 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 49, + 146, + 286, + 384 + ], + "type": "text", + "content": "-cover problem, it can be formulated as mixed-integer linear programming, through which an optimal subset is obtained. The original formulation only considers the number of landmarks for localization, while their distribution also affects localization performance. Therefore, some works design and add quadratic terms, formulating mixed-integer quadratic programming to enforce a more uniform distribution of selected landmarks [11, 23]. However, these quadratic terms slow down the optimization speed heavily. The required high memory capacity and heavy computation become severe limitations of these map sparsification methods. For example, in our experiments, the mixed-integer quadratic programming methods cannot be used for the maps containing more than 55K landmarks, because all computer memory has been consumed." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 49, + 387, + 286, + 506 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 387, + 286, + 506 + ], + "spans": [ + { + "bbox": [ + 49, + 387, + 286, + 506 + ], + "type": "text", + "content": "To select uniformly distributed landmarks and at the same time maintain the computation efficiency, we keep map sparsification formulation in a linear form in this paper. We firstly discretize images into 2D fix-sized grids. Then for all observed landmarks, we can find which cells they fall in. Therefore, more occupied cells reflect a more uniform distribution of landmarks. This can be formulated in a linear form easily. In this way, uniformly distributed landmarks are selected efficiently, and thus the localization performance in compact maps will be better." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 49, + 509, + 286, + 603 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 509, + 286, + 603 + ], + "spans": [ + { + "bbox": [ + 49, + 509, + 286, + 603 + ], + "type": "text", + "content": "Another severe limitation is that all of past works assume the spatial distribution of the query sequence is close to that of the mapping sequence. Then landmarks are selected only based on their association with the images of the mapping sequence. However, this assumption cannot be guaranteed in real robotic applications. The perspective difference between query and mapping sequences may cause the localization in compact maps to fail unexpectedly." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 49, + 605, + 286, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 605, + 286, + 712 + ], + "spans": [ + { + "bbox": [ + 49, + 605, + 286, + 712 + ], + "type": "text", + "content": "To ensure more query images from whole 3D space can be localized successfully in compact maps, we propose to select landmarks based on not only their association with mapping images but also their visibility in 3D space. The visibility region of a landmark is defined based on its viewing angle and distance. The 3D space is also discretized into a 3D discretized grid. For each 3D cell, all visible landmarks are collected, and a constraint on the number of visible landmarks is added into map sparsification formulation." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 308, + 72, + 544, + 95 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 72, + 544, + 95 + ], + "spans": [ + { + "bbox": [ + 308, + 72, + 544, + 95 + ], + "type": "text", + "content": "In this way, landmarks are selected to maintain localization performance for query images from the whole space." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 308, + 97, + 544, + 215 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 97, + 544, + 215 + ], + "spans": [ + { + "bbox": [ + 308, + 97, + 544, + 215 + ], + "type": "text", + "content": "In summary, the contributions of this paper are as follows: 1) We propose an efficient map sparsification method formulating uniform landmark distribution in a linear form to keep the computation efficiency. 2) We propose to perform map sparsification involving the visibility of landmarks to achieve better localization results for the query images from the whole space. 3) We conduct exhaustive experiments in different datasets and compare with other state-of-the-art methods, showing the effectiveness and superiority of our methods for different kinds of query sequences." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 308, + 227, + 391, + 239 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 227, + 391, + 239 + ], + "spans": [ + { + "bbox": [ + 308, + 227, + 391, + 239 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 308, + 247, + 544, + 460 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 247, + 544, + 460 + ], + "spans": [ + { + "bbox": [ + 308, + 247, + 544, + 460 + ], + "type": "text", + "content": "Map compression or sparsification has received many research attention in SLAM and structure from motion (SfM) because of the burden of maintaining and utilizing a large map. Different methods are also proposed to solve this problem. In [5,18,22], the descriptors are quantized to compact forms to reduce memory consumption. Mera-Trujillo et al. [19] propose a constrained quadratic program method and design an efficient solver to select landmarks. Contreras et al. [8] develop a map compression method based on traveled trajectories, and they also propose an online system performing SLAM and map compression simultaneously [9]. Some SLAM systems [7, 26, 28] are also designed to select and build a compact map online, but much more landmarks are still remained compared with the offline methods. Recently, some learning-based map sparsification methods have also appeared and achieved good results [4, 25], but they require high-cost GPUs to train and struggle to be applied in different unseen scenes." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 308, + 463, + 544, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 463, + 544, + 628 + ], + "spans": [ + { + "bbox": [ + 308, + 463, + 544, + 628 + ], + "type": "text", + "content": "Map sparsification is more commonly regarded as a " + }, + { + "bbox": [ + 308, + 463, + 544, + 628 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 308, + 463, + 544, + 628 + ], + "type": "text", + "content": "-cover problem. Since " + }, + { + "bbox": [ + 308, + 463, + 544, + 628 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 308, + 463, + 544, + 628 + ], + "type": "text", + "content": "-cover is an NP-hard problem, Li et al. [17] propose to use a greedy algorithm to select the landmark observed by the largest number of not-yet-fully covered frames. Cao et al. [3] also use a greedy algorithm to select landmarks, considering both the coverage and distinctiveness. In [6], the original " + }, + { + "bbox": [ + 308, + 463, + 544, + 628 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 308, + 463, + 544, + 628 + ], + "type": "text", + "content": "-cover method is improved by predicting the parameter " + }, + { + "bbox": [ + 308, + 463, + 544, + 628 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 308, + 463, + 544, + 628 + ], + "type": "text", + "content": ". Similarly, the landmarks are scored and sampled based on the observation count, covariance, and descriptor stability in [12]. Moreover, the authors come up with more scoring factors to rank landmarks for selecting in [13]. These methods can provide compact maps for localization, but depend on a careful design of selecting methods and cannot get the optimal solution." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 308, + 630, + 544, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 630, + 544, + 712 + ], + "spans": [ + { + "bbox": [ + 308, + 630, + 544, + 712 + ], + "type": "text", + "content": "Another " + }, + { + "bbox": [ + 308, + 630, + 544, + 712 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 308, + 630, + 544, + 712 + ], + "type": "text", + "content": "-cover based map sparsification solution is to be formulated as a mixed-integer programming problem, which is introduced in detail in [23]. The linear formulation does not consider the distribution of the selected landmarks but can be solved efficiently, and therefore it is adopted in some later works [13, 24]. The mixed-integer quadratic programming formulation encourages the uniformly dis" + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "type": "text", + "content": "12471" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 239 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 239 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 239 + ], + "type": "text", + "content": "tributed landmarks but requires a high capacity of memory and heavy computation [23] and becomes impractical for large maps. To improve the computation efficiency, Dymczyk et al. [11] have to divide the whole map into several small parts and perform map sparsification separately. Camposeco et al. [2] keep the linear form of map sparsification but divide each image into " + }, + { + "bbox": [ + 46, + 72, + 289, + 239 + ], + "type": "inline_equation", + "content": "q" + }, + { + "bbox": [ + 46, + 72, + 289, + 239 + ], + "type": "text", + "content": " uniformly-sized cells and let each cell be covered by " + }, + { + "bbox": [ + 46, + 72, + 289, + 239 + ], + "type": "inline_equation", + "content": "K / q" + }, + { + "bbox": [ + 46, + 72, + 289, + 239 + ], + "type": "text", + "content": " landmarks. This method seems reasonable, but we find in the experiments that the number of corresponding selected landmarks in some images is much less than " + }, + { + "bbox": [ + 46, + 72, + 289, + 239 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 46, + 72, + 289, + 239 + ], + "type": "text", + "content": " actually, and thus the localization results get worse. Similarly, the proposed method also makes use of discretized images, but the image is still considered as a whole and thus avoids the above problems." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 239, + 289, + 348 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 239, + 289, + 348 + ], + "spans": [ + { + "bbox": [ + 46, + 239, + 289, + 348 + ], + "type": "text", + "content": "All of the above methods are based on the existing association between landmarks and images, thus landmarks are selected only to ensure localization performance of these images. For an arbitrary query image with a different viewing perspective, localization may fail unexpectedly, especially when the compression ratio is high. To solve this problem, the proposed method considers landmark visibility in the 3D space and adds constraints to preserve enough visible landmarks for the whole space in compact maps." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 357, + 228, + 371 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 357, + 228, + 371 + ], + "spans": [ + { + "bbox": [ + 47, + 357, + 228, + 371 + ], + "type": "text", + "content": "3. Map Sparsification Formulation" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 377, + 287, + 484 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 377, + 287, + 484 + ], + "spans": [ + { + "bbox": [ + 46, + 377, + 287, + 484 + ], + "type": "text", + "content": "The proposed method is designed mainly for the maps built from feature-based visual SLAM systems (e.g., ORBSLAM [20]). Receiving sequences of images, the feature points observed by keyframes are constructed as landmarks. Thus, an original map " + }, + { + "bbox": [ + 46, + 377, + 287, + 484 + ], + "type": "inline_equation", + "content": "\\mathcal{M}" + }, + { + "bbox": [ + 46, + 377, + 287, + 484 + ], + "type": "text", + "content": " consists of landmarks " + }, + { + "bbox": [ + 46, + 377, + 287, + 484 + ], + "type": "inline_equation", + "content": "\\{\\pmb {p}_i\\}_{i = 1,2,\\dots,N}" + }, + { + "bbox": [ + 46, + 377, + 287, + 484 + ], + "type": "text", + "content": ", keyframes " + }, + { + "bbox": [ + 46, + 377, + 287, + 484 + ], + "type": "inline_equation", + "content": "\\{F_j\\}_{j = 1,2,\\dots,M}" + }, + { + "bbox": [ + 46, + 377, + 287, + 484 + ], + "type": "text", + "content": ", and their association. The map sparsification aims to decrease the number of landmarks. We firstly introduce commonly used formulations of map sparsification in past works [23]." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 485, + 287, + 509 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 485, + 287, + 509 + ], + "spans": [ + { + "bbox": [ + 46, + 485, + 287, + 509 + ], + "type": "text", + "content": "Using mixed-integer programming, map sparsification can be formulated as:" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 111, + 514, + 287, + 548 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 111, + 514, + 287, + 548 + ], + "spans": [ + { + "bbox": [ + 111, + 514, + 287, + 548 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\underset {\\mathbf {x}, \\boldsymbol {\\xi}} {\\text {m i n i m i z e}} \\quad \\mathbf {q} ^ {\\top} \\mathbf {x} + \\lambda \\mathbf {1} ^ {\\top} \\boldsymbol {\\xi} \\\\ \\mathbf {A} \\mathbf {x} \\geq K \\mathbf {1} - \\boldsymbol {\\xi} \\tag {1} \\\\ \\end{array}", + "image_path": "8b2bd31885c7ce6e6027329d9612e07389725b13f6388e03eadb1d4b3af7708b.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 110, + 546, + 222, + 572 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 110, + 546, + 222, + 572 + ], + "spans": [ + { + "bbox": [ + 110, + 546, + 222, + 572 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\begin{array}{l} \\text {s u b j e c t t o} \\quad \\mathbf {x} \\in \\{0, 1 \\} ^ {N} \\end{array} \\\\ \\boldsymbol {\\xi} \\in \\{0, \\mathbb {Z} _ {+} \\} ^ {M} \\\\ \\end{array}", + "image_path": "73002bb3f510664a450ba8943b5d15a174f98420e0b12a75c176175545c5ab13.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 582, + 289, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 582, + 289, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 582, + 289, + 713 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 582, + 289, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 46, + 582, + 289, + 713 + ], + "type": "text", + "content": " is a binary vector whose " + }, + { + "bbox": [ + 46, + 582, + 289, + 713 + ], + "type": "inline_equation", + "content": "i^{\\mathrm{th}}" + }, + { + "bbox": [ + 46, + 582, + 289, + 713 + ], + "type": "text", + "content": " element indicates whether the landmark " + }, + { + "bbox": [ + 46, + 582, + 289, + 713 + ], + "type": "inline_equation", + "content": "\\pmb{p}_i" + }, + { + "bbox": [ + 46, + 582, + 289, + 713 + ], + "type": "text", + "content": " is selected or not. " + }, + { + "bbox": [ + 46, + 582, + 289, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{q}" + }, + { + "bbox": [ + 46, + 582, + 289, + 713 + ], + "type": "text", + "content": " is a weight vector to select landmarks. " + }, + { + "bbox": [ + 46, + 582, + 289, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{A}" + }, + { + "bbox": [ + 46, + 582, + 289, + 713 + ], + "type": "text", + "content": " is a binary matrix describing the association between landmarks and keyframes, i.e., the element " + }, + { + "bbox": [ + 46, + 582, + 289, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{A}_{ij}" + }, + { + "bbox": [ + 46, + 582, + 289, + 713 + ], + "type": "text", + "content": " indicates whether the landmark " + }, + { + "bbox": [ + 46, + 582, + 289, + 713 + ], + "type": "inline_equation", + "content": "\\pmb{p}_j" + }, + { + "bbox": [ + 46, + 582, + 289, + 713 + ], + "type": "text", + "content": " is visible in the keyframe " + }, + { + "bbox": [ + 46, + 582, + 289, + 713 + ], + "type": "inline_equation", + "content": "\\pmb{F}_i" + }, + { + "bbox": [ + 46, + 582, + 289, + 713 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 46, + 582, + 289, + 713 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 46, + 582, + 289, + 713 + ], + "type": "text", + "content": " is the desired minimum number of visible landmarks in each keyframe and can be used to adjust compression ratio. To handle the situation when the total number of associated landmarks of a keyframe is less than " + }, + { + "bbox": [ + 46, + 582, + 289, + 713 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 46, + 582, + 289, + 713 + ], + "type": "text", + "content": ", a slack variable " + }, + { + "bbox": [ + 46, + 582, + 289, + 713 + ], + "type": "inline_equation", + "content": "\\xi" + }, + { + "bbox": [ + 46, + 582, + 289, + 713 + ], + "type": "text", + "content": " is used to relax the hard constraints, and " + }, + { + "bbox": [ + 46, + 582, + 289, + 713 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 46, + 582, + 289, + 713 + ], + "type": "text", + "content": " determines the hardness of the constraints." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 72, + 545, + 133 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 133 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 133 + ], + "type": "text", + "content": "Therefore, Eq. (1) describes the mixed-integer linear programming method for map sparsification. The distribution of selected landmarks is not considered in this method. To involve the distribution of landmarks, quadratic terms are commonly used:" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 350, + 139, + 545, + 172 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 350, + 139, + 545, + 172 + ], + "spans": [ + { + "bbox": [ + 350, + 139, + 545, + 172 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\underset {\\mathbf {x}, \\boldsymbol {\\xi}} {\\text {m i n i m i z e}} \\quad \\frac {1}{2} \\mathbf {x} ^ {\\top} \\mathbf {Q} \\mathbf {x} + \\mathbf {q} ^ {\\top} \\mathbf {x} + \\lambda \\mathbf {1} ^ {\\top} \\boldsymbol {\\xi} \\\\ \\mathbf {A} \\mathbf {x} \\geq K \\mathbf {1} _ {N} - \\boldsymbol {\\xi} \\tag {2} \\\\ \\end{array}", + "image_path": "f90fe4ac917aa8b6eba5fdd2b6f598fb95388105bde98638bbb9eb440c0590bb.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 348, + 170, + 461, + 196 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 348, + 170, + 461, + 196 + ], + "spans": [ + { + "bbox": [ + 348, + 170, + 461, + 196 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\begin{array}{l} \\text {s u b j e c t t o} \\quad \\mathbf {x} \\in \\{0, 1 \\} ^ {N} \\end{array} \\\\ \\boldsymbol {\\xi} \\in \\{0, \\mathbb {Z} _ {+} \\} ^ {M} \\\\ \\end{array}", + "image_path": "39fe467273b1569262f243125446db0aec76289b49820cc97dcfc98ebdaea9b7.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 203, + 545, + 311 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 203, + 545, + 311 + ], + "spans": [ + { + "bbox": [ + 304, + 203, + 545, + 311 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 203, + 545, + 311 + ], + "type": "inline_equation", + "content": "\\mathbf{Q}" + }, + { + "bbox": [ + 304, + 203, + 545, + 311 + ], + "type": "text", + "content": " is a symmetric matrix. The element " + }, + { + "bbox": [ + 304, + 203, + 545, + 311 + ], + "type": "inline_equation", + "content": "\\mathbf{Q}_{ij}" + }, + { + "bbox": [ + 304, + 203, + 545, + 311 + ], + "type": "text", + "content": " indicates the relation between " + }, + { + "bbox": [ + 304, + 203, + 545, + 311 + ], + "type": "inline_equation", + "content": "\\pmb{p}_i" + }, + { + "bbox": [ + 304, + 203, + 545, + 311 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 203, + 545, + 311 + ], + "type": "inline_equation", + "content": "\\pmb{p}_j" + }, + { + "bbox": [ + 304, + 203, + 545, + 311 + ], + "type": "text", + "content": ". For example, it can be the number of common observations for each pair of landmarks. Therefore, the landmarks that are observed together with others frequently would be discarded. As a result, selected landmarks are distributed more uniformly. Eq. (2) describes the commonly used map sparsification formulation in past works, which considers both the number and distribution of landmarks for localization." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 321, + 517, + 335 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 321, + 517, + 335 + ], + "spans": [ + { + "bbox": [ + 305, + 321, + 517, + 335 + ], + "type": "text", + "content": "4. Map Sparsification Based on 2D Grids" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 341, + 545, + 413 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 341, + 545, + 413 + ], + "spans": [ + { + "bbox": [ + 304, + 341, + 545, + 413 + ], + "type": "text", + "content": "Uniformly distributed landmarks commonly provide better localization results. Because of the quadratic terms, however, the computation complexity increases largely. Besides, Eq. (2) encourages selection of rarely observed landmarks, which may have larger errors and be detrimental for localization [11]." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 413, + 545, + 545 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 413, + 545, + 545 + ], + "spans": [ + { + "bbox": [ + 304, + 413, + 545, + 545 + ], + "type": "text", + "content": "To solve these problems, we design a linear term to encourage a uniform distribution of selected landmarks. As illustrated in Fig. 2, the image is discretized into fixed-size grids (e.g., " + }, + { + "bbox": [ + 304, + 413, + 545, + 545 + ], + "type": "inline_equation", + "content": "C \\times R" + }, + { + "bbox": [ + 304, + 413, + 545, + 545 + ], + "type": "text", + "content": " cells). Each cell has two stats: empty or occupied. Based on the camera model, projected positions of landmarks can be computed easily. Then a cell is occupied if at least one landmark is projected into it; otherwise, it is empty. Therefore, to acquire uniformly distributed landmarks, we encourage selecting the landmarks that make more cells to be occupied. This concept can be easily formulated into Eq. (1), which becomes:" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 350, + 552, + 545, + 597 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 350, + 552, + 545, + 597 + ], + "spans": [ + { + "bbox": [ + 350, + 552, + 545, + 597 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\underset {\\mathbf {x}, \\boldsymbol {\\xi}, \\boldsymbol {\\phi}} {\\text {m i n i m i z e}} \\quad \\mathbf {q} ^ {\\top} \\mathbf {x} + \\lambda_ {1} \\mathbf {1} ^ {\\top} \\boldsymbol {\\xi} + \\lambda_ {2} \\mathbf {1} ^ {\\top} \\boldsymbol {\\phi} \\\\ \\mathbf {A} \\mathbf {x} \\geq K \\mathbf {1} - \\boldsymbol {\\xi} \\\\ \\mathrm {B x} \\geq 1 - \\phi \\tag {3} \\\\ \\end{array}", + "image_path": "b01a7b4b100e055d548a5972d39d4efda62b5a84edbc40f953d60afc06ca237c.jpg" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 348, + 594, + 480, + 634 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 348, + 594, + 480, + 634 + ], + "spans": [ + { + "bbox": [ + 348, + 594, + 480, + 634 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\begin{array}{l} \\text {s u b j e c t t o} \\quad \\mathbf {x} \\in \\{0, 1 \\} ^ {N} \\end{array} \\\\ \\boldsymbol {\\xi} \\in \\{0, \\mathbb {Z} _ {+} \\} ^ {M} \\\\ \\phi \\in \\{0, 1 \\} ^ {M \\times C \\times R} \\\\ \\end{array}", + "image_path": "18b1a1f8fac485c895e7ac5af1eabcf4d045a23b840d9733b680e73a116d4f78.jpg" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{B}" + }, + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "type": "text", + "content": " is a binary matrix describing the association between the landmarks and all cells, i.e., the element " + }, + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{B}_{ij}" + }, + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "type": "text", + "content": " indicates whether the projected position of the landmark " + }, + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "type": "inline_equation", + "content": "p_j" + }, + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "type": "text", + "content": " falls within the cell " + }, + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "type": "inline_equation", + "content": "c_i" + }, + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "type": "text", + "content": ". We encourage every cell to keep at least one corresponding landmark and use the slack variable " + }, + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\phi" + }, + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "type": "text", + "content": " to relax this constraint. An example is illustrated in" + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "type": "text", + "content": "12472" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 67, + 69, + 267, + 173 + ], + "blocks": [ + { + "bbox": [ + 67, + 69, + 267, + 173 + ], + "lines": [ + { + "bbox": [ + 67, + 69, + 267, + 173 + ], + "spans": [ + { + "bbox": [ + 67, + 69, + 267, + 173 + ], + "type": "image", + "image_path": "f210f16341cfc302c78164256d3237949714bde17207944b5b66083b7836c58f.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 181, + 289, + 228 + ], + "lines": [ + { + "bbox": [ + 46, + 181, + 289, + 228 + ], + "spans": [ + { + "bbox": [ + 46, + 181, + 289, + 228 + ], + "type": "text", + "content": "Figure 2. Illustration of discretized images and associated landmarks. The occupied cells are drawn in deeper color. The red points represent the projected position of associated landmarks. Dotted points can be discarded without changing occupancy." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 237, + 287, + 261 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 237, + 287, + 261 + ], + "spans": [ + { + "bbox": [ + 46, + 237, + 287, + 261 + ], + "type": "text", + "content": "Fig. 2, the dotted points can be discarded without changing the number of occupied cells." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 261, + 287, + 321 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 261, + 287, + 321 + ], + "spans": [ + { + "bbox": [ + 46, + 261, + 287, + 321 + ], + "type": "text", + "content": "Eq. (3) formulates map sparsification as a mixed-integer linear programming problem and thus can be solved efficiently. The selected landmarks are directly encouraged to spread uniformly in all corresponding keyframes. Thus better localization performance will be achieved." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 331, + 226, + 346 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 331, + 226, + 346 + ], + "spans": [ + { + "bbox": [ + 47, + 331, + 226, + 346 + ], + "type": "text", + "content": "5. Map Sparsification In 3D Space" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 352, + 287, + 495 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 352, + 287, + 495 + ], + "spans": [ + { + "bbox": [ + 46, + 352, + 287, + 495 + ], + "type": "text", + "content": "From the previous section, it is noticed that map sparsification is formulated based on the association between landmarks and keyframes. This association can be easily constructed from feature matching during mapping. All past works are based on such association and assume the spatial distribution of the query sequence will be close to that of the mapping sequence. Thus selected landmarks can be matched again in query images. Obviously, this assumption cannot be promised in real robotic applications. Some selected landmarks would not be matched in query images because of different viewing perspectives, and thus, the localization may fail unexpectedly." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 496, + 287, + 544 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 496, + 287, + 544 + ], + "spans": [ + { + "bbox": [ + 46, + 496, + 287, + 544 + ], + "type": "text", + "content": "In this section, we will introduce our proposed map sparsification method that involves landmark visibility in 3D space and thus improves localization performance for query images from the whole space." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 552, + 165, + 565 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 552, + 165, + 565 + ], + "spans": [ + { + "bbox": [ + 47, + 552, + 165, + 565 + ], + "type": "text", + "content": "5.1. Landmark Visibility" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 570, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 570, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 570, + 288, + 714 + ], + "type": "text", + "content": "Feature points (e.g., ORB [21]) are commonly extracted and constructed as landmarks in visual SLAM. One of the basic requirements of used features is robust matching from different viewing perspectives. In other words, it is assumed that a valid feature point is visible and can be matched within a certain region. Specifically, we assume a feature point can be matched when the viewing angle and distance are within certain thresholds. Such specific regions can be approximated from mapping process. Similarly defined visibility is also used for efficient feature matching [20]. Deng et al. [10] also predict such feature matching to ensure localization performance in an active SLAM framework." + } + ] + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 354, + 69, + 500, + 205 + ], + "blocks": [ + { + "bbox": [ + 354, + 69, + 500, + 205 + ], + "lines": [ + { + "bbox": [ + 354, + 69, + 500, + 205 + ], + "spans": [ + { + "bbox": [ + 354, + 69, + 500, + 205 + ], + "type": "image", + "image_path": "df77f14592e6993b2eaebd4529850f6024f5accc56bf42baeb3e9191f4bd663f.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 328, + 212, + 523, + 224 + ], + "lines": [ + { + "bbox": [ + 328, + 212, + 523, + 224 + ], + "spans": [ + { + "bbox": [ + 328, + 212, + 523, + 224 + ], + "type": "text", + "content": "Figure 3. 3D cells in which the landmark " + }, + { + "bbox": [ + 328, + 212, + 523, + 224 + ], + "type": "inline_equation", + "content": "\\pmb{p}" + }, + { + "bbox": [ + 328, + 212, + 523, + 224 + ], + "type": "text", + "content": " is visible." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 234, + 545, + 294 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 234, + 545, + 294 + ], + "spans": [ + { + "bbox": [ + 305, + 234, + 545, + 294 + ], + "type": "text", + "content": "For a landmark " + }, + { + "bbox": [ + 305, + 234, + 545, + 294 + ], + "type": "inline_equation", + "content": "\\pmb{p}" + }, + { + "bbox": [ + 305, + 234, + 545, + 294 + ], + "type": "text", + "content": " observed by multiple keyframes, an average viewing direction " + }, + { + "bbox": [ + 305, + 234, + 545, + 294 + ], + "type": "inline_equation", + "content": "\\bar{\\pmb{v}}^p" + }, + { + "bbox": [ + 305, + 234, + 545, + 294 + ], + "type": "text", + "content": " can be computed from all viewing directions, pointing from " + }, + { + "bbox": [ + 305, + 234, + 545, + 294 + ], + "type": "inline_equation", + "content": "\\pmb{p}" + }, + { + "bbox": [ + 305, + 234, + 545, + 294 + ], + "type": "text", + "content": " to the optical centers of these keyframes. Therefore, the first condition for " + }, + { + "bbox": [ + 305, + 234, + 545, + 294 + ], + "type": "inline_equation", + "content": "\\pmb{p}" + }, + { + "bbox": [ + 305, + 234, + 545, + 294 + ], + "type": "text", + "content": " to be visible is that the viewing angle is within the threshold," + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 395, + 301, + 545, + 316 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 395, + 301, + 545, + 316 + ], + "spans": [ + { + "bbox": [ + 395, + 301, + 545, + 316 + ], + "type": "interline_equation", + "content": "\\langle \\bar {\\boldsymbol {v}} ^ {p}, \\boldsymbol {v} ^ {i} \\rangle < \\theta_ {t h} ^ {p} \\tag {4}", + "image_path": "f399b80c413fcfede53b8514d52d96cc3db2184851dafe5e6040e58cf952406f.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 323, + 545, + 359 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 323, + 545, + 359 + ], + "spans": [ + { + "bbox": [ + 305, + 323, + 545, + 359 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 323, + 545, + 359 + ], + "type": "inline_equation", + "content": "\\pmb{v}^i" + }, + { + "bbox": [ + 305, + 323, + 545, + 359 + ], + "type": "text", + "content": " is the viewing direction for a query position. In our experiments, " + }, + { + "bbox": [ + 305, + 323, + 545, + 359 + ], + "type": "inline_equation", + "content": "\\theta_{th}^{p}" + }, + { + "bbox": [ + 305, + 323, + 545, + 359 + ], + "type": "text", + "content": " is set according to the largest viewing angle during mapping." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 360, + 545, + 408 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 360, + 545, + 408 + ], + "spans": [ + { + "bbox": [ + 305, + 360, + 545, + 408 + ], + "type": "text", + "content": "Besides, an image pyramid is commonly employed for matching features from different distance. Therefore, the second condition for " + }, + { + "bbox": [ + 305, + 360, + 545, + 408 + ], + "type": "inline_equation", + "content": "\\pmb{p}" + }, + { + "bbox": [ + 305, + 360, + 545, + 408 + ], + "type": "text", + "content": " to be visible is that the viewing distance " + }, + { + "bbox": [ + 305, + 360, + 545, + 408 + ], + "type": "inline_equation", + "content": "d_{i}^{p}" + }, + { + "bbox": [ + 305, + 360, + 545, + 408 + ], + "type": "text", + "content": " from a query position is within the following range," + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 386, + 418, + 545, + 433 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 386, + 418, + 545, + 433 + ], + "spans": [ + { + "bbox": [ + 386, + 418, + 545, + 433 + ], + "type": "interline_equation", + "content": "d _ {\\min } ^ {p} < d _ {i} ^ {p} < d _ {\\max } ^ {p} \\tag {5}", + "image_path": "c81704ac3fd79c883b34f6b1d8671451187ca8f4dfe1513588207c5663c8c452.jpg" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 436, + 545, + 460 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 436, + 545, + 460 + ], + "spans": [ + { + "bbox": [ + 305, + 436, + 545, + 460 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 436, + 545, + 460 + ], + "type": "inline_equation", + "content": "d_{\\mathrm{min}}^p" + }, + { + "bbox": [ + 305, + 436, + 545, + 460 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 436, + 545, + 460 + ], + "type": "inline_equation", + "content": "d_{\\mathrm{max}}^p" + }, + { + "bbox": [ + 305, + 436, + 545, + 460 + ], + "type": "text", + "content": " are also set according to the smallest and largest viewing distance during mapping." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 305, + 460, + 545, + 498 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 460, + 545, + 498 + ], + "spans": [ + { + "bbox": [ + 305, + 460, + 545, + 498 + ], + "type": "text", + "content": "Therefore, a landmark is assumed to be visible when meeting the conditions Eq. (4) and Eq. (5). The visible region forms a truncated spherical cone, as indicated in Fig. 3." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 306, + 503, + 504, + 517 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 503, + 504, + 517 + ], + "spans": [ + { + "bbox": [ + 306, + 503, + 504, + 517 + ], + "type": "text", + "content": "5.2. Map Sparsification Based on 3D Grid" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 522, + 545, + 629 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 522, + 545, + 629 + ], + "spans": [ + { + "bbox": [ + 304, + 522, + 545, + 629 + ], + "type": "text", + "content": "For map sparsification methods described in Sec. 3, enough visible landmarks are preserved for every keyframe based on the constraint " + }, + { + "bbox": [ + 304, + 522, + 545, + 629 + ], + "type": "inline_equation", + "content": "\\mathbf{A}\\mathbf{x} \\geq K\\mathbf{1} - \\boldsymbol{\\xi}" + }, + { + "bbox": [ + 304, + 522, + 545, + 629 + ], + "type": "text", + "content": ". Therefore, the compact map can be used to localize the query images that are close to the mapping sequence as expected. However, for query images taken from different viewing perspectives, which is common in practical robotic applications, the number of matched visible landmarks may decrease, and thus the localization may fail unexpectedly." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "content": "To solve the above problem, we propose a map sparsification method considering landmark visibility in 3D space. We firstly discretize the whole space into a 3D grid. The corresponding 3D cells from which it is visible are collected for each landmark, as indicated in Fig. 3. Therefore, each cell stores all visible landmarks from that position. To decrease computation, we define a threshold " + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "inline_equation", + "content": "K_{2}" + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "content": ", and the" + } + ] + } + ], + "index": 20 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "12473" + } + ] + } + ], + "index": 21 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 287, + 95 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 287, + 95 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 287, + 95 + ], + "type": "text", + "content": "3D cell is valid only if the number of corresponding visible landmarks is larger than " + }, + { + "bbox": [ + 47, + 72, + 287, + 95 + ], + "type": "inline_equation", + "content": "K_{2}" + }, + { + "bbox": [ + 47, + 72, + 287, + 95 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 96, + 286, + 144 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 96, + 286, + 144 + ], + "spans": [ + { + "bbox": [ + 47, + 96, + 286, + 144 + ], + "type": "text", + "content": "In the proposed map sparsification method, landmarks are selected to keep as many valid 3D cells as possible. Therefore, an extra constraint is introduced into the formulation for each valid 3D cell:" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 63, + 149, + 287, + 211 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 63, + 149, + 287, + 211 + ], + "spans": [ + { + "bbox": [ + 63, + 149, + 287, + 211 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\underset {\\mathbf {x}, \\boldsymbol {\\xi}, \\boldsymbol {\\phi}, \\boldsymbol {\\varphi}} {\\text {m i n i m i z e}} \\quad \\mathbf {q} ^ {\\top} \\mathbf {x} + \\lambda_ {1} \\mathbf {1} ^ {\\top} \\boldsymbol {\\xi} + \\lambda_ {2} \\mathbf {1} ^ {\\top} \\boldsymbol {\\phi} + \\lambda_ {3} \\mathbf {1} ^ {\\top} \\boldsymbol {\\varphi} \\\\ \\mathbf {A} \\mathbf {x} \\geq K _ {1} \\mathbf {1} - \\boldsymbol {\\xi} \\\\ \\mathrm {B x} \\geq 1 - \\phi \\\\ \\mathbf {C x} \\geq K _ {2} \\mathbf {1} - \\varphi \\tag {6} \\\\ \\end{array}", + "image_path": "449a09e425d9de1384bfd44958ed1004f0e0a8207b69515b285b20fff5336268.jpg" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 63, + 206, + 287, + 218 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 63, + 206, + 287, + 218 + ], + "spans": [ + { + "bbox": [ + 63, + 206, + 287, + 218 + ], + "type": "text", + "content": "subject to " + }, + { + "bbox": [ + 63, + 206, + 287, + 218 + ], + "type": "inline_equation", + "content": "\\mathbf{x}\\in \\{0,1\\} ^N" + }, + { + "bbox": [ + 63, + 206, + 287, + 218 + ], + "type": "text", + "content": " (6)" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 63, + 206, + 287, + 258 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 63, + 206, + 287, + 258 + ], + "spans": [ + { + "bbox": [ + 63, + 206, + 287, + 258 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\boldsymbol {\\xi} \\in \\left\\{0, \\mathbb {Z} _ {+} \\right\\} ^ {M} \\\\ \\phi \\in \\{0, 1 \\} ^ {M \\times C \\times R} \\\\ \\boldsymbol {\\varphi} \\in \\{0, \\mathbb {Z} _ {+} \\} ^ {S} \\\\ \\end{array}", + "image_path": "d78a318b7b70e943c2259583cfa9a3ca5a338920fe04e37139ad50517b9ca4d8.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 267, + 287, + 326 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 267, + 287, + 326 + ], + "spans": [ + { + "bbox": [ + 47, + 267, + 287, + 326 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 267, + 287, + 326 + ], + "type": "inline_equation", + "content": "\\mathbf{C}" + }, + { + "bbox": [ + 47, + 267, + 287, + 326 + ], + "type": "text", + "content": " is a binary matrix describing the association between landmarks and valid 3D cells, i.e., the element " + }, + { + "bbox": [ + 47, + 267, + 287, + 326 + ], + "type": "inline_equation", + "content": "\\mathbf{C}_{ij}" + }, + { + "bbox": [ + 47, + 267, + 287, + 326 + ], + "type": "text", + "content": " indicates whether the landmark " + }, + { + "bbox": [ + 47, + 267, + 287, + 326 + ], + "type": "inline_equation", + "content": "p_j" + }, + { + "bbox": [ + 47, + 267, + 287, + 326 + ], + "type": "text", + "content": " is visible for the 3D cell " + }, + { + "bbox": [ + 47, + 267, + 287, + 326 + ], + "type": "inline_equation", + "content": "g_i" + }, + { + "bbox": [ + 47, + 267, + 287, + 326 + ], + "type": "text", + "content": ". As before, the slack variable " + }, + { + "bbox": [ + 47, + 267, + 287, + 326 + ], + "type": "inline_equation", + "content": "\\varphi" + }, + { + "bbox": [ + 47, + 267, + 287, + 326 + ], + "type": "text", + "content": " is used to relax the constraints." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 327, + 287, + 387 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 327, + 287, + 387 + ], + "spans": [ + { + "bbox": [ + 46, + 327, + 287, + 387 + ], + "type": "text", + "content": "Therefore, the proposed map sparsification method aims to preserve enough visible landmarks not only for mapping keyframes but also for the whole 3D space. As a result, more query images from the whole space can be localized successfully." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 398, + 128, + 411 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 398, + 128, + 411 + ], + "spans": [ + { + "bbox": [ + 47, + 398, + 128, + 411 + ], + "type": "text", + "content": "6. Experiments" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 418, + 287, + 550 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 418, + 287, + 550 + ], + "spans": [ + { + "bbox": [ + 46, + 418, + 287, + 550 + ], + "type": "text", + "content": "The proposed map sparsification based on 2D grids (i.e., Eq. (3)) is firstly compared with previous works to show its superiority in performance and efficiency for localizing query images close to mapping sequences. Then we demonstrate the effectiveness of map sparsification involving the visibility of landmarks in 3D space (i.e., Eq. (6)) and its superiority when query images are not close to mapping sequences. More experimental results can be found in the supplementary material, including visualization results and the comparison between original and compact maps in terms of memory consumption and localization efficiency." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 557, + 163, + 570 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 557, + 163, + 570 + ], + "spans": [ + { + "bbox": [ + 47, + 557, + 163, + 570 + ], + "type": "text", + "content": "6.1. Experimental Setup" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 575, + 287, + 611 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 575, + 287, + 611 + ], + "spans": [ + { + "bbox": [ + 47, + 575, + 287, + 611 + ], + "type": "text", + "content": "All experiments are tested on a laptop with an i7- 7700HQ " + }, + { + "bbox": [ + 47, + 575, + 287, + 611 + ], + "type": "inline_equation", + "content": "2.80\\mathrm{Hz}" + }, + { + "bbox": [ + 47, + 575, + 287, + 611 + ], + "type": "text", + "content": " CPU and 16GB RAM. The mixed-integer programming problem is solved using Gurobi1." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 47, + 612, + 287, + 695 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 612, + 287, + 695 + ], + "spans": [ + { + "bbox": [ + 47, + 612, + 287, + 695 + ], + "type": "text", + "content": "The proposed methods are tested on three commonly used SLAM datasets: ICL-NUIM [15], EuRoC [1], and KITTI [14]. These datasets cover indoor and outdoor, small-scale and large-scale environments; the number of landmarks in original maps changes from thousands to more than one hundred thousand. The original map is constructed by running a state-of-the-art visual SLAM system" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 72, + 545, + 156 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 72, + 545, + 156 + ], + "spans": [ + { + "bbox": [ + 306, + 72, + 545, + 156 + ], + "type": "text", + "content": "(i.e., ORB-SLAM2 [20]). Query images are localized in the map based on the re-localization module in ORB-SLAM2, in which localization is successful when enough inliers are matched. Different map sparsification methods are compared in terms of localization rate and run-time. Localization rate is the ratio of the number of successfully localized images to the number of all query images in one sequence." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 157, + 545, + 324 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 157, + 545, + 324 + ], + "spans": [ + { + "bbox": [ + 305, + 157, + 545, + 324 + ], + "type": "text", + "content": "The weight vector " + }, + { + "bbox": [ + 305, + 157, + 545, + 324 + ], + "type": "inline_equation", + "content": "\\mathbf{q}" + }, + { + "bbox": [ + 305, + 157, + 545, + 324 + ], + "type": "text", + "content": " in all methods is set based on the number of matched times for each landmark, just like in [23]. The proposed method based only on 2D grids (i.e., Eq. (3)) is denoted as Ours-2D, while the method based on 2D and 3D grids (i.e., Eq. (6)) is denoted as Ours-3D. The proposed methods are compared with several state-of-the-art " + }, + { + "bbox": [ + 305, + 157, + 545, + 324 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 305, + 157, + 545, + 324 + ], + "type": "text", + "content": "-cover-based map sparsification methods. The map sparsification using mixed-integer linear programming (i.e., Eq. (1)) is denoted as LP. For the methods using mixed-integer quadratic programming (i.e., Eq. (2)), the weight matrix " + }, + { + "bbox": [ + 305, + 157, + 545, + 324 + ], + "type": "inline_equation", + "content": "\\mathbf{Q}" + }, + { + "bbox": [ + 305, + 157, + 545, + 324 + ], + "type": "text", + "content": " is set according to the number of co-observation times [23] or average projected distance [11], and these two methods are denoted as QP1 and QP2 respectively. The map sparsification based on divided images [2] is denoted as DI." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 334, + 508, + 346 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 334, + 508, + 346 + ], + "spans": [ + { + "bbox": [ + 306, + 334, + 508, + 346 + ], + "type": "text", + "content": "6.2. Map Sparsification Based on 2D Grids" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 353, + 545, + 472 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 353, + 545, + 472 + ], + "spans": [ + { + "bbox": [ + 305, + 353, + 545, + 472 + ], + "type": "text", + "content": "Since previous methods assume the spatial distribution of the query sequence is close to that of the mapping sequence, one sequence is firstly used to build an original map and then the images from the same mapping sequence are re-localized in compact maps. In this subsection, the proposed map sparsification method is only based on 2D discretized grids (i.e., Eq. (3)). Tab. 1 compares the localization rates in different maps obtained by different methods. An example of the selected sparse landmarks is illustrated by blue points in Fig. 1." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 474, + 545, + 593 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 474, + 545, + 593 + ], + "spans": [ + { + "bbox": [ + 305, + 474, + 545, + 593 + ], + "type": "text", + "content": "The experimental results demonstrate that the number of landmarks can be reduced largely while the localization is still successful for most query images. For example, only " + }, + { + "bbox": [ + 305, + 474, + 545, + 593 + ], + "type": "inline_equation", + "content": "4.37\\%" + }, + { + "bbox": [ + 305, + 474, + 545, + 593 + ], + "type": "text", + "content": " landmarks are selected from the map of sequence off2 and " + }, + { + "bbox": [ + 305, + 474, + 545, + 593 + ], + "type": "inline_equation", + "content": "3.46\\%" + }, + { + "bbox": [ + 305, + 474, + 545, + 593 + ], + "type": "text", + "content": " for sequence 04, but more than " + }, + { + "bbox": [ + 305, + 474, + 545, + 593 + ], + "type": "inline_equation", + "content": "90\\%" + }, + { + "bbox": [ + 305, + 474, + 545, + 593 + ], + "type": "text", + "content": " of the query images can still be localized successfully. The compression ratio is mainly controlled by the threshold " + }, + { + "bbox": [ + 305, + 474, + 545, + 593 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 305, + 474, + 545, + 593 + ], + "type": "text", + "content": " in Eq. (1), Eq. (2), and Eq. (3), and we use " + }, + { + "bbox": [ + 305, + 474, + 545, + 593 + ], + "type": "inline_equation", + "content": "K = 50" + }, + { + "bbox": [ + 305, + 474, + 545, + 593 + ], + "type": "text", + "content": " in our experiments. With a larger " + }, + { + "bbox": [ + 305, + 474, + 545, + 593 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 305, + 474, + 545, + 593 + ], + "type": "text", + "content": ", more landmarks will be selected in compact maps, and localization rate will be higher." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 305, + 594, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 594, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 594, + 545, + 713 + ], + "type": "text", + "content": "For more sequences, our proposed method achieves the highest localization rate (labelled in bold), especially compared with the method only considering the number of landmarks for map sparsification (i.e., LP). Our method also gets slightly better results than other methods that consider landmark distribution (i.e., QP1, QP2, and DI). In QP1, the weight matrix " + }, + { + "bbox": [ + 305, + 594, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{Q}" + }, + { + "bbox": [ + 305, + 594, + 545, + 713 + ], + "type": "text", + "content": " is set according to the number of co-observation times between landmarks and as a result, rarely observed landmarks are preferred, which may be detrimental for localization [11]. To overcome this limitation, QP2" + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 58, + 702, + 142, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 702, + 142, + 712 + ], + "spans": [ + { + "bbox": [ + 58, + 702, + 142, + 712 + ], + "type": "text", + "content": "1https://www.gurobi.com" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "12474" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 47, + 112, + 545, + 516 + ], + "blocks": [ + { + "bbox": [ + 47, + 70, + 545, + 103 + ], + "lines": [ + { + "bbox": [ + 47, + 70, + 545, + 103 + ], + "spans": [ + { + "bbox": [ + 47, + 70, + 545, + 103 + ], + "type": "text", + "content": "Table 1. Comparison of different map sparsification methods in terms of localization rate. Num denotes the number of landmarks in the mam, Rate denotes the localization rate in the corresponding map. The highest localization rates in compact maps are labelled in bold. -' means the method cannot work because of memory limit." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 47, + 112, + 545, + 516 + ], + "lines": [ + { + "bbox": [ + 47, + 112, + 545, + 516 + ], + "spans": [ + { + "bbox": [ + 47, + 112, + 545, + 516 + ], + "type": "table", + "html": "
DatasetOriginal MapOurs-2DLP [23]QP1 [23]QP2 [11]DI [2]
NumRateNumRateNumRateNumRateNumRateNumRate
ICL-NUIM [15]liv0406198.34%51979.97%51979.51%51979.64%51978.65%73477.39%
liv1411299.89%44587.47%44586.23%44587.37%44585.51%51655.59%
liv26435100.0%31291.36%31089.77%31090.57%31091.02%83389.89%
liv3617393.38%53276.21%53173.71%53175.32%53173.55%98761.85%
off0587599.93%39895.62%39895.42%39895.76%39895.76%79184.88%
off1599293.57%48580.00%48577.93%48579.07%48476.89%73637.20%
off26838100.0%29992.27%29891.02%29890.34%29891.36%75990.45%
off3536799.52%39683.47%39583.06%39578.31%39683.15%43051.05%
EuRoC [1]MH11250699.04%297897.33%297697.03%297696.76%297796.54%421094.56%
MH21130699.73%254698.17%254496.43%254798.33%254798.30%366593.30%
MH31523497.34%210595.32%210495.32%210795.44%210595.17%372091.30%
MH41749099.69%74497.37%74397.32%74297.27%74297.01%249396.05%
MH51695699.77%111698.87%111698.69%111698.60%111698.60%293396.08%
V101686499.03%46186.04%46084.92%46185.52%46186.35%101179.14%
V102987898.12%50785.93%50784.86%50685.87%50685.49%125584.17%
V1031151893.22%114083.76%114083.91%114083.09%114083.05%166177.89%
V201734694.69%56579.64%56478.75%56478.62%56478.97%99078.75%
V2021179199.48%125493.25%125492.86%125493.07%125493.42%228590.39%
V2031455787.51%179681.48%179581.27%179681.11%179581.48%238475.45%
KITTI [14]00141673100.0%553696.15%552495.68%----1854291.15%
018944391.01%421876.02%421676.02%----1020471.84%
0218249999.96%766097.47%766197.15%----2513386.76%
0324284100.0%83796.00%83695.63%83796.13%83695.76%295288.76%
0416824100.0%58399.63%58599.26%57299.63%57299.63%201997.41%
0574158100.0%273797.46%273897.25%----965590.62%
0642522100.0%187998.27%187898.09%187898.18%187798.18%563595.82%
0727036100.0%124292.28%124091.28%124091.73%124092.55%351792.01%
08119323100.0%590394.87%589994.82%----1687283.03%
095598499.94%294595.79%294495.60%294295.85%294395.79%822488.37%
103093399.92%172997.09%172896.67%172896.83%172996.42%474386.34%
", + "image_path": "3bcf0908d7462c99d4a350899774ce8ca7f3d2837d1eaf85e9a5acefe40e3d52.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 526, + 287, + 610 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 526, + 287, + 610 + ], + "spans": [ + { + "bbox": [ + 46, + 526, + 287, + 610 + ], + "type": "text", + "content": "sets the weight matrix " + }, + { + "bbox": [ + 46, + 526, + 287, + 610 + ], + "type": "inline_equation", + "content": "\\mathbf{Q}" + }, + { + "bbox": [ + 46, + 526, + 287, + 610 + ], + "type": "text", + "content": " based on the average distance between projected positions. But instead of uniform distribution, QP2 actually prefers to select landmarks that are projected far from the image center. Unlike these quadratic programming-based methods, our method formulates uniform distribution in a more clear and simple way, achieving better results." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 617, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 617, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 617, + 288, + 713 + ], + "type": "text", + "content": "DI gets unexpected bad performance in these testings. DI divides images into " + }, + { + "bbox": [ + 46, + 617, + 288, + 713 + ], + "type": "inline_equation", + "content": "q" + }, + { + "bbox": [ + 46, + 617, + 288, + 713 + ], + "type": "text", + "content": " cells and forces each cell is covered by at least " + }, + { + "bbox": [ + 46, + 617, + 288, + 713 + ], + "type": "inline_equation", + "content": "K / q" + }, + { + "bbox": [ + 46, + 617, + 288, + 713 + ], + "type": "text", + "content": " landmarks. Therefore, DI also achieves map sparsification in a linear programming form and considers both the number and distribution of landmarks. But we find in these testings that the slack variable " + }, + { + "bbox": [ + 46, + 617, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 46, + 617, + 288, + 713 + ], + "type": "text", + "content": " in Eq. (1) needs to be small for DI to get a high compression ratio. As a result, the number of selected landmarks is much less" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 304, + 526, + 545, + 563 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 526, + 545, + 563 + ], + "spans": [ + { + "bbox": [ + 304, + 526, + 545, + 563 + ], + "type": "text", + "content": "than " + }, + { + "bbox": [ + 304, + 526, + 545, + 563 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 304, + 526, + 545, + 563 + ], + "type": "text", + "content": " for some images, where localization would fail. Although based on similar discretized grids, our method still considers an image as a whole and thus avoids this problem." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "content": "Another superiority of our method is computational efficiency. The comparison of run-time and memory consumption on different sequences is shown in Tab. 2. The run-time for map sparsification depends on the number of landmarks, keyframes and associations among them. As the number of landmarks or keyframes increases, the run-time will commonly increase quickly. It is clear that the methods using quadratic programming are much slower, especially for the maps containing a large number of landmarks (e.g., sequence 09). In addition to solving more complex optimization problems, QP1 and QP2 also need much more time to set the weight matrix " + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{Q}" + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "content": ", since the relation between every" + } + ] + } + ], + "index": 5 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "12475" + } + ] + } + ], + "index": 6 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 48, + 113, + 287, + 357 + ], + "blocks": [ + { + "bbox": [ + 47, + 70, + 288, + 104 + ], + "lines": [ + { + "bbox": [ + 47, + 70, + 288, + 104 + ], + "spans": [ + { + "bbox": [ + 47, + 70, + 288, + 104 + ], + "type": "text", + "content": "Table 2. Comparison of different map sparsification methods in terms of run-time and consumed memory. " + }, + { + "bbox": [ + 47, + 70, + 288, + 104 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 47, + 70, + 288, + 104 + ], + "type": "text", + "content": " denotes the number of landmarks, " + }, + { + "bbox": [ + 47, + 70, + 288, + 104 + ], + "type": "inline_equation", + "content": "{N}_{k}" + }, + { + "bbox": [ + 47, + 70, + 288, + 104 + ], + "type": "text", + "content": " denotes the number of keyframes." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 48, + 113, + 287, + 357 + ], + "lines": [ + { + "bbox": [ + 48, + 113, + 287, + 357 + ], + "spans": [ + { + "bbox": [ + 48, + 113, + 287, + 357 + ], + "type": "table", + "html": "
Seq.Original MapRun-time (s)
NNkOursLPQP1QP2DI
liv04.1K1070.20.113.612.50.2
off05.9K1330.30.127.918.90.2
V10311.5K2161.10.359.836.30.6
MH517.0K3694.52.210761.51.2
0727.0K2582.61.112795.50.7
0956.0K6037.79.97544911.8
08119K126933.219.2--4.9
02182K179469.663.2--7.9
NNkConsumed memory (MB)
liv04.1K107351455547633
off05.9K133612784270821
V10311.5K216128563048136783
MH517.0K3692551073532165677
0727.0K2581416263155766100
0956.0K6036762301300510952211
08119K12691162637--512
02182K179434941502--1187
", + "image_path": "da65ae7cadf3e664eb9d46844de4d319b662ffdf51759cd83b39b47a97ff0ffc.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 365, + 287, + 449 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 365, + 287, + 449 + ], + "spans": [ + { + "bbox": [ + 46, + 365, + 287, + 449 + ], + "type": "text", + "content": "pair of landmarks needs to be found and this is not recorded in original maps. In our method, both the matrix " + }, + { + "bbox": [ + 46, + 365, + 287, + 449 + ], + "type": "inline_equation", + "content": "\\mathbf{A}" + }, + { + "bbox": [ + 46, + 365, + 287, + 449 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 365, + 287, + 449 + ], + "type": "inline_equation", + "content": "\\mathbf{B}" + }, + { + "bbox": [ + 46, + 365, + 287, + 449 + ], + "type": "text", + "content": " in Eq. (3) are set according to the relation between landmarks and keyframes, which can be retrieved from original maps directly and efficiently. In addition, since formulated in a linear form, our method can also be solved efficiently and is only slightly slower than LP." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 449, + 287, + 520 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 449, + 287, + 520 + ], + "spans": [ + { + "bbox": [ + 46, + 449, + 287, + 520 + ], + "type": "text", + "content": "Similarly for memory consumption, ours consumes much less memory than quadratic programming. QP1 and QP2 cannot work for some sequences (e.g., 00) on our device with 16 GB memory. The testing for sequence 09 consumes nearly all of the memory when using QP1 and QP2, in which the original map contains 56K landmarks." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 520, + 287, + 582 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 520, + 287, + 582 + ], + "spans": [ + { + "bbox": [ + 46, + 520, + 287, + 582 + ], + "type": "text", + "content": "Therefore, if the mapping sequence has covered most of the query space for localization, the proposed map sparsification based on 2D discretized grids can be used to decrease the number of landmarks to save memory and improve localization efficiency." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 587, + 286, + 601 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 587, + 286, + 601 + ], + "spans": [ + { + "bbox": [ + 47, + 587, + 286, + 601 + ], + "type": "text", + "content": "6.3. Map Sparsification Based on 2D and 3D Grids" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 605, + 286, + 676 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 605, + 286, + 676 + ], + "spans": [ + { + "bbox": [ + 46, + 605, + 286, + 676 + ], + "type": "text", + "content": "We have demonstrated that compact maps with much fewer landmarks achieve good localization performance when the spatial distribution of the query sequence is close to that of the mapping sequence. In this subsection, we continue to test the localization performance for query images from different distributions." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 677, + 286, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 286, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 286, + 714 + ], + "type": "text", + "content": "In ICL-NUIM [15] and EuRoC [1] datasets, different sequences are recorded in the same environments. Therefore, one sequence is used to build original maps and then query" + } + ] + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 317, + 70, + 541, + 225 + ], + "blocks": [ + { + "bbox": [ + 317, + 70, + 541, + 225 + ], + "lines": [ + { + "bbox": [ + 317, + 70, + 541, + 225 + ], + "spans": [ + { + "bbox": [ + 317, + 70, + 541, + 225 + ], + "type": "image", + "image_path": "1138bf57ffe456e409696f5a01ffcc53d943db2707dcb38d36a5b19310f956f0.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 233, + 545, + 289 + ], + "lines": [ + { + "bbox": [ + 305, + 233, + 545, + 289 + ], + "spans": [ + { + "bbox": [ + 305, + 233, + 545, + 289 + ], + "type": "text", + "content": "Figure 4. Comparison of map sparsification results. The original map is constructed from sequence V201. There are 3401 blue points indicating valid 3D cells of the compact map acquired by Ours-2D; while there are 6468 green points indicating valid 3D cells of the compact map acquired by Ours-3D." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 303, + 545, + 399 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 303, + 545, + 399 + ], + "spans": [ + { + "bbox": [ + 304, + 303, + 545, + 399 + ], + "type": "text", + "content": "images of other sequences are also localized in compact maps. The comparison of experimental results is presented in Table 3. For example, sequence off0 is used to build the map, and then sequence off0, off2 and off3 are used as query sequences to be localized in the original and compact maps. Not all sequences of these two datasets are used in this experiment since the successful localization is very low even in original maps for some sequences." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 400, + 546, + 604 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 400, + 546, + 604 + ], + "spans": [ + { + "bbox": [ + 304, + 400, + 546, + 604 + ], + "type": "text", + "content": "As shown in Tab. 3, compact maps commonly achieve good localization performance for query images from mapping sequences, while localization rates may decrease largely for other query sequences. Because the map sparsification is mainly selecting landmarks to maintain the observations in keyframes of the mapping sequences, and thus discarding other redundant landmarks which may be useful for localizing query images from the whole space. Our proposed map sparsification method in Eq. (6) aims to add such extra constraints for the whole space. In most testings, ours-3D achieves higher localization rates for the query sequences that are different from mapping sequences. For the query images from the mapping sequence, ours-3D also achieves comparable localization performance with other map sparsification methods. Other map sparsification methods achieve similar results as Ours-2D, which are included in the supplementary material." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": "A comparison of compact maps acquired by ours-2D and ours-3D is illustrated in Fig. 4. The blue points indicate the valid 3D cells of ours-2D, while the green points indicate the valid 3D cells of ours-3D. The numbers of selected landmarks are similar using these two methods. But it is clear that much more valid 3D cells are kept using ours-3D and they are spreading over a larger space. As a result, more query images from the whole 3D space can be localized successfully." + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "12476" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 55, + 113, + 537, + 444 + ], + "blocks": [ + { + "bbox": [ + 46, + 70, + 547, + 105 + ], + "lines": [ + { + "bbox": [ + 46, + 70, + 547, + 105 + ], + "spans": [ + { + "bbox": [ + 46, + 70, + 547, + 105 + ], + "type": "text", + "content": "Table 3. Comparison of different map sparsification methods in terms of localization rate. Num denotes the number of landmarks in the map, Rate denotes the localization rate in the corresponding map. The sequence for mapping is indicated in bold and the images from several different sequences are localized in the map. The highest localization rates in compact maps are labelled in bold." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 55, + 113, + 537, + 444 + ], + "lines": [ + { + "bbox": [ + 55, + 113, + 537, + 444 + ], + "spans": [ + { + "bbox": [ + 55, + 113, + 537, + 444 + ], + "type": "table", + "html": "
off0off2liv2
MapNumoff0Rate off2off3NumRate off0off2NumRate liv1liv2
Original587599.93%66.70%52.26%683865.65%100.00%643555.80%100.00%
Ours-2D39895.62%27.95%7.74%2994.31%92.27%3122.48%91.36%
Ours-3D39995.49%28.52%7.98%3016.17%91.70%3144.04%90.68%
MH1MH4MH5
MapNumRateNumRateNumRate
MH1MH2MH3MH4MH5MH4MH5
Original1250699.04%87.10%52.53%1749099.69%84.20%1695682.34%99.77%
Ours-2D297897.33%73.67%45.76%74497.37%63.77%111674.75%98.87%
Ours-3D298296.78%73.97%46.18%74597.06%64.27%112175.71%98.74%
MH2V101V102
MapNumRateNumRateNumRate
MH1MH2MH3V101V102V101V102
Original1130691.78%99.73%51.81%686499.03%61.56%987872.25%98.12%
Ours-2D254674.80%98.17%35.50%46186.04%32.60%50734.61%85.93%
Ours-3D255077.41%97.77%38.69%46285.79%34.61%50637.67%85.99%
MH3V201V202
MapNumRateNumRateNumRate
MH1MH2MH3V201V202V201V202
Original1523459.93%52.80%97.34%734694.69%52.77%1179175.22%99.48%
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", + "image_path": "9fe051df7a19af953cb555e21a1d713a8de3daad9e629c672b2834375c133d64.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "type": "table", + "bbox": [ + 63, + 472, + 269, + 553 + ], + "blocks": [ + { + "bbox": [ + 50, + 452, + 284, + 463 + ], + "lines": [ + { + "bbox": [ + 50, + 452, + 284, + 463 + ], + "spans": [ + { + "bbox": [ + 50, + 452, + 284, + 463 + ], + "type": "text", + "content": "Table 4. Comparison of average run-time (s) in different scenes." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 63, + 472, + 269, + 553 + ], + "lines": [ + { + "bbox": [ + 63, + 472, + 269, + 553 + ], + "spans": [ + { + "bbox": [ + 63, + 472, + 269, + 553 + ], + "type": "table", + "html": "
SceneResolution (m)Ours-2DOurs-3D
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", + "image_path": "caa6124029b3eb7cbad22a0bb927eb027dd12b53312992d82eb5e47e2873888f.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 567, + 288, + 664 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 567, + 288, + 664 + ], + "spans": [ + { + "bbox": [ + 46, + 567, + 288, + 664 + ], + "type": "text", + "content": "Since Ours-3D is also formulated in a linear form, it can also be solved efficiently. Tab. 4 shows the average run-time in different scenes. The run-time of Ours-3D is related to the resolution of the 3D grids. In the experiment, we choose different resolutions for different scenes and thousands of valid cells are used for map sparsification. The run-time of Ours-3D does not increase much compared with Ours-2D, and Ours-3D is still much faster than QP1 and QP2." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "text", + "content": "Therefore, if the mapping sequence has not covered the whole query space and query images may be taken with different viewing perspectives, the map sparsification involving the constraints from the 3D discretized grid is a better" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 306, + 453, + 417, + 464 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 453, + 417, + 464 + ], + "spans": [ + { + "bbox": [ + 306, + 453, + 417, + 464 + ], + "type": "text", + "content": "choice to select landmarks." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 481, + 379, + 495 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 481, + 379, + 495 + ], + "spans": [ + { + "bbox": [ + 306, + 481, + 379, + 495 + ], + "type": "text", + "content": "7. Conclusion" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 503, + 547, + 659 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 503, + 547, + 659 + ], + "spans": [ + { + "bbox": [ + 304, + 503, + 547, + 659 + ], + "type": "text", + "content": "In this paper, we propose two novel terms for efficient map sparsification. The first term is to enforce a uniform distribution of selected landmarks based on 2D discretized grids. The second one adds a space constraint based on landmark visibility to weaken the assumption that the spatial distribution of the query sequence is close to that of the mapping sequence. Both two terms are formulated in efficient linear forms, and thus avoid heavy computation. The proposed terms can be chosen and set according to different conditions of query sequences. The exhaustive experiments have demonstrated the effectiveness and superiority of the proposed method, especially the computation efficiency compared with previous QP methods." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 665, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 547, + 713 + ], + "type": "text", + "content": "Acknowledgments: This work is supported by the CUHK T Sone Robotics Institute, and the InnoHK of the Government of Hong Kong via the Hong Kong Centre for Logistics Robotics." + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "12477" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 288, + 713 + ], + "type": "list", + "angle": 0, + "index": 17, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 145 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 145 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 145 + ], + "type": "text", + "content": "[1] Michael Burri, Janosch Nikolic, Pascal Gohl, Thomas Schneider, Joern Rehder, Sammy Omari, Markus W Achtelik, and Roland Siegwart. 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IEEE Transactions on Robotics, 36(3):657-675, 2020. 2" + } + ] + } + ], + "index": 29 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "12478" + } + ] + } + ], + "index": 31 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 8 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Efficient Mask Correction for Click-Based Interactive Image Segmentation/0a4cc1dd-64c3-44d2-8dfa-4f17be83df54_content_list.json b/2023/Efficient Mask Correction for Click-Based Interactive Image Segmentation/0a4cc1dd-64c3-44d2-8dfa-4f17be83df54_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..d13e5dd9fe35af5daef2baf39c9d2044fc3b73f4 --- /dev/null +++ b/2023/Efficient Mask Correction for Click-Based Interactive Image Segmentation/0a4cc1dd-64c3-44d2-8dfa-4f17be83df54_content_list.json @@ -0,0 +1,1343 @@ +[ + { + "type": "text", + "text": "Efficient Mask Correction for Click-Based Interactive Image Segmentation", + "text_level": 1, + "bbox": [ + 107, + 128, + 861, + 152 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Fei Du, Jianlong Yuan, Zhibin Wang, Fan Wang Alibaba Group", + "bbox": [ + 294, + 180, + 673, + 217 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "{dufei.cf, gongyuan.yjl, zhibin.waz, fan.w}@alibaba-inc.com", + "bbox": [ + 222, + 218, + 743, + 233 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 268, + 313, + 284 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "The goal of click-based interactive image segmentation is to extract target masks with the input of positive/negative clicks. Every time a new click is placed, existing methods run the whole segmentation network to obtain a corrected mask, which is inefficient since several clicks may be needed to reach satisfactory accuracy. To this end, we propose an efficient method to correct the mask with a lightweight mask correction network. The whole network remains a low computational cost from the second click, even if we have a large backbone. However, a simple correction network with limited capacity is not likely to achieve comparable performance with a classic segmentation network. Thus, we propose a click-guided self-attention module and a click-guided correlation module to effectively exploits the click information to boost performance. First, several templates are selected based on the semantic similarity with click features. Then the self-attention module propagates the template information to other pixels, while the correlation module directly uses the templates to obtain target outlines. With the efficient architecture and two click-guided modules, our method shows preferable performance and efficiency compared to existing methods. The code will be released at https://github.com/feiaxyt/EMC-Click.", + "bbox": [ + 75, + 300, + 473, + 661 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 691, + 209, + 709 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Interactive image segmentation aims to select the object of interest with minimal iterative interactions, which can benefit various computer vision tasks, such as semantic segmentation [30], instance segmentation [17], and medical image analysis [28]. As the success of these tasks often requires large-scale mask-level annotations and it is time-consuming to annotate the image manually, interactive segmentation is an attractive way to simplify the annotation process and alleviate the annotation cost.", + "bbox": [ + 75, + 719, + 468, + 853 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Different interaction strategies have been studied to simplify the interactive process, including bounding boxes [23, 37, 48], clicks [33, 40, 47], scribbles [1, 2], boundary", + "bbox": [ + 76, + 854, + 468, + 901 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/432df18341de00bb3b099453c2cc7530ba416a9d5665ac997eebaec2382b7a9c.jpg", + "image_caption": [ + "Figure 1. Comparison between the architectures of our method and classic methods. Classic methods run the segmentation network in every iteration, which is inefficient if a large network is adopted. We update the mask via a lightweight mask correction network, enabling an efficient interaction." + ], + "image_footnote": [], + "bbox": [ + 506, + 268, + 890, + 431 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "points [32], and extreme points [34]. However, due to the complexity of the object boundary and appearance, the performance of methods based on bounding boxes may drop if the bounding boxes are not tightly drawn [48]. Besides, it requires more effort to identify the object boundary and place bounding boxes, boundary points, or extreme points on the image. In contrast, the click-based method only requires the users to progressively place positive and negative clicks on the foreground and background areas, respectively. It has recently attracted more attention due to its simplicity and well-established training and evaluation protocols [40, 47]. Hence, we focus on the click-based method.", + "bbox": [ + 496, + 547, + 892, + 731 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "In click-based interactive segmentation methods, the model returns a corrected prediction mask after each click from the users. Efficiency is of great importance to interactive segmentation methods since a typical segmentation process requires several interactive iterations. In recent years, deep learning-based interactive segmentation methods have achieved considerably better performance compared to traditional methods. However, some recent works [20, 22, 39] achieve state-of-the-art performance by employing inference-time optimization to refine the masks, which significantly increases the computational cost. To", + "bbox": [ + 496, + 734, + 893, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "22773", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "eliminate online optimization, RITM [40] investigates different designs for interactive segmentation and achieves state-of-the-art results with a classic segmentation network. To improve efficiency, FocalClick [8] proposes target crop and focus crop strategies to segment two selected local regions efficiently. Most click-based methods [7, 8, 27, 31, 40, 47] iteratively run the whole segmentation network to update the masks with the input of user clicks, which is time-consuming especially when we have a strong segmentation network. Majumder et al. [32] proposes to refine the mask with a lightweight refinement network. However, the network requires the user to place boundary points, which is not user-friendly. Therefore, more efficient click-based interactive segmentation methods are still required to reach a better trade-off between performance and efficiency.", + "bbox": [ + 75, + 90, + 472, + 316 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "With the above consideration, in this work, we develop an efficient click-based interactive segmentation model based on an Efficient Mask Correction network (EMC-Click). The model consists of a base segmentation network and a lightweight mask correction network. The base network takes the first click as input and outputs target-aware features and a coarse prediction. The mask correction network iteratively updates the prediction whenever a new click is placed. The difference between our network and the classic network is shown in Fig. 1. This decoupled design ensures that the computational cost of each iteration is relatively low from the second click. However, using a simply designed mask correction network to update the prediction can hardly achieve comparable performance with classic methods that use a strong segmentation network. Thus, we propose two feature augmentation modules, including a click-guided self-attention module and a click-guided correlation module, to effectively exploit the click information to augment the features in the mask correction network. We first extract the click features and enrich them by selecting several template features based on the semantic similarity between the clicks and other pixels. The self-attention module propagates the information of the template features to other pixels, and the correlation model directly learns target contours. Both modules effectively and efficiently augment the features and improve the segmentation performance. Experiments on five benchmarks demonstrate that our method achieves competitive performance and higher efficiency compared with state-of-the-art click-based interactive segmentation methods.", + "bbox": [ + 75, + 316, + 472, + 770 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Our contribution can be summarized as follows:", + "bbox": [ + 96, + 771, + 415, + 785 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- We propose EMC-Click, an efficient click-based interactive method, to correct the masks via a lightweight mask correction network interactively. Our method significantly reduces computational cost from the second click especially when we have a large backbone.", + "- We propose two feature augmentation modules to im" + ], + "bbox": [ + 94, + 797, + 468, + 901 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "prove the segmentation accuracy by effectively exploiting the click information.", + "bbox": [ + 529, + 90, + 890, + 122 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "- We build EMC-Click on different base segmentation networks and evaluate our models on several benchmarks. The results show that our method achieves preferable performance and efficiency compared to state-of-the-art methods.", + "bbox": [ + 517, + 135, + 893, + 210 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related works", + "text_level": 1, + "bbox": [ + 500, + 239, + 645, + 255 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.1. Interactive image segmentation", + "text_level": 1, + "bbox": [ + 500, + 265, + 774, + 281 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Interactive image segmentation is a longstanding research topic in computer vision. In the early years, methods based on optimization on a graph over image pixels were the mainstream. GrabCut [37] is a classic method that extend [5] to an iterative energy minimization problem. Methods based on random walk [13,21] build an undirected graph on the image to estimate the probability of each pixel. Since early methods use handcrafted features, they can hardly generalize to complex scenes.", + "bbox": [ + 496, + 289, + 890, + 425 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Deep learning has been applied in many fields due to its high representation power and the ability to model complex structures. Xu et al. [47] are the first to propose a CNN-based interactive segmentation method. They encode the positive/negative clicks as positive/negative distance maps and concatenate them with the image to feed them into the network. They also design strategies to sample clicks for training, which are adopted by many subsequent works [8, 15, 40]. Later, Mahadevan et al. [31] add an iterative sampling strategy on [47] during training. BRS [20] proposes optimizing the network online based on user-specified location information during the annotation process. f-BRS [39] accelerates BRS [20] by optimizing a small part of the network. Recently, RITM [40] conducts comprehensive experiments to investigate the design principle of an end-to-end click-based interactive segmentation method. Although the click-based method is the mainstream due to its simplicity and well-established training and evaluation protocols, other interactive methods are also exploited, such as extreme points [34], boundary points [32], and bounding boxes [46]. Despite the impressive progress made by deep learning-based methods, most of them suffer from a high computational cost especially when they have a strong backbone like ResNet101 [18].", + "bbox": [ + 496, + 426, + 892, + 787 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.2. Mask refinement in interactive segmentation", + "text_level": 1, + "bbox": [ + 500, + 800, + 877, + 816 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Mask refinement is commonly used in interactive segmentation to get fine-level results. They often follow the coarse-to-fine schema and crop a local region to make local corrections. For example, RIS-Net [24] samples multiple regions based on the click positions for local refinement.", + "bbox": [ + 496, + 825, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "22774", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/da493adfb7b4825f87f46ce03eaa3866b53cd96ae2b5b26c8b10eec825a45f2e.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 80, + 88, + 890, + 195 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/9508ab7d2201089c732dcd4bd1f5cff842e86a7d82dfc79e7f1dc4588b016ae0.jpg", + "image_caption": [ + "Figure 2. The framework of the proposed EMC-Click. We adopt a base segmentation network to extract target-aware features and make the first prediction by taking the first click as input. The mask correction network is responsible for updating the mask when a new click is placed. In this mask correction network, we first map the click location to the feature map and extract the click features. Then we sample several template features that are similar to the click features. The click-guided self-attention module propagates the template information to other pixels, while the click-guided correlation module extracts target outlines via the correlation between the templates and the feature map. Both modules augment the features, and the combined features are used to predict the mask." + ], + "image_footnote": [], + "bbox": [ + 80, + 196, + 887, + 306 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "FocalClick [8] crops a region based on the difference between the previous mask and the coarsely predicted mask to refine the details. Zhang et al. [50] refines a local area centered on the target based on the coarse segmentation results. There are also methods to refine the global mask, such as EdgeFlow [15] and $99\\%$ AccuracyNet [12]. One common property of these refinement methods is that they run the whole segmentation and refinement networks to get the results in each interactive iteration. It is too costly compared with a simple feedforward segmentation network. FocusCut [26] trains a segmentation network to not only segment the target object but also refine local details. However, it is still not efficient enough to run the whole segmentation network in each iteration. Our mask correction network is somewhat like a refinement network. The difference is that we directly use this network to correct masks when a new click is placed, and the base segmentation network only runs for the first click. This architecture reduces the inference time significantly compared with traditional methods.", + "bbox": [ + 75, + 431, + 472, + 719 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "2.3. Exploitation of click information", + "text_level": 1, + "bbox": [ + 76, + 726, + 366, + 742 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The clicks provide key information for locating the foreground and background areas. Most methods encode the clicks as click maps where the regions around the clicks are highlighted. However, the click information is not explicitly exploited. To better exploit the click information, CDNet [7] propagates the click information to other pixels via two non-local networks [43]. It constructs weight maps based on the click locations to re-weight the affinity matrix, which is not computational efficiency since it needs to model the affinity between every two pixels. IFPN [50]", + "bbox": [ + 75, + 750, + 472, + 902 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "learns a sparse graph model to perform click feature propagation. It only models the dependencies between the clicks and other pixels. Inspired by the two methods, we construct a multi-head self-attention module to propagate the click information to other pixels. Different from CDNet and IFPN, we select several templates to enrich the click features. Thus, our method is more efficient compared to CDNet [7] and can exploit more information compared to IFPN [50]. Besides, we also propose a correlation module to exploit the click information explicitly.", + "bbox": [ + 496, + 431, + 893, + 583 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Proposed method", + "text_level": 1, + "bbox": [ + 498, + 597, + 671, + 616 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We propose to iteratively correct the segmentation mask using a lightweight mask correction network, which exploits the information of the clicks to boost the performance via a click-guided self-attention module and a click-guided correlation module. We first briefly revisit the traditional pipeline of the interactive segmentation model, then introduce our pipeline and elaborate on the mask correction network.", + "bbox": [ + 496, + 623, + 893, + 743 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. The standard pipeline", + "text_level": 1, + "bbox": [ + 498, + 755, + 705, + 772 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Interactive segmentation is often regarded as a special type of segmentation task. Different from classic segmentation, the input of the interactive segmentation network contains not only the image but also the click maps and previously predicted mask. When segmenting the object of interest, the user decides where to place the next click based on the current segmentation mask. All positive/negative clicks are encoded as positive/negative click maps that are usual", + "bbox": [ + 496, + 780, + 893, + 902 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "22775", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "ally defined as distance maps [47] or binary disks [3]. The click maps are then concatenated with the image and previously predicted mask to be fed to the segmentation network. After each click, the user obtains an updated segmentation mask by running the whole segmentation network. Usually, a strong segmentation network like DeepLabv3+ [6] is required to achieve satisfactory results since the segmentation accuracy directly depends on it. However, running a strong segmentation network several times is often time-consuming, especially on low-power devices, which makes this standard pipeline inefficient in practice.", + "bbox": [ + 75, + 90, + 472, + 257 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. Efficient pipeline", + "text_level": 1, + "bbox": [ + 76, + 265, + 243, + 281 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "To avoid running the whole segmentation network for each click, we build a lightweight network to correct the segmentation mask in each iteration. The pipeline is shown in Fig. 2. Our network consists of a base segmentation network and a lightweight mask correction network. As observed in FCA-Net [27], the first click is responsible for locating the target object. Thus, we input the first click into the segmentation network to generate target-aware features. When the user places the first click, the base segmentation network extracts the target-aware feature and generates a coarse mask, and the mask correction network corrects the coarse mask. Starting from the second click, we no longer run the base segmentation network. Instead, we directly feed all clicks into the mask correction network to correct the previously predicted mask.", + "bbox": [ + 75, + 287, + 472, + 513 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Specifically, we denote the input image as $I$ and the click set at the $t$ -th iteration as $C^t$ . The base segmentation network takes the input image and the first click $C^1$ as input and generates target-aware features $F_{t}$ and a coarse mask $M_{c}$ , which can be formulated as follows,", + "bbox": [ + 76, + 515, + 470, + 590 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nF _ {t}, M _ {c} = \\Phi_ {S} (I, E n c \\left(C ^ {1}\\right); \\theta_ {s}), \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 166, + 599, + 468, + 616 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $Enc$ denotes the click encoding function, and $\\Phi_S$ and $\\theta_s$ denote the base segmentation network and its parameters, respectively. In this work, we adopt disks with a small radius [3,40] to encode the clicks. The mask correction network takes the click set $C^t$ , the target-aware feature $F_t$ , the original image $I$ , and the previously predicted mask $M^{t-1}$ as input and outputs an updated mask, which can be written as follows,", + "bbox": [ + 76, + 625, + 468, + 744 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nM ^ {t} = \\Phi_ {R} (I, E n c \\left(C ^ {t}\\right), M ^ {t - 1}, F _ {t}; \\theta_ {r}), \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 143, + 753, + 468, + 771 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\Phi_R$ and $\\theta_r$ denote the mask correction network and its parameters, respectively. For the first click (i.e. $t = 1$ ), the previous mask $M^0$ input to the mask correction network is equal to the coarse mask $M_c$ . The mask correction network can also take as input a preexisting mask generated from other forms of pre-processing.", + "bbox": [ + 76, + 780, + 468, + 869 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Note that our pipeline differs from FCA-Net [27] which also treats the first click differently from other clicks. Our", + "bbox": [ + 76, + 869, + 468, + 900 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "network only runs the mask correction network after the first click, while FCA-Net still needs to run the whole network for each click.", + "bbox": [ + 498, + 90, + 890, + 135 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.3. Efficient and effective mask correction network", + "text_level": 1, + "bbox": [ + 498, + 156, + 890, + 171 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "A simple mask correction network with limited parameters and computational cost can hardly achieve comparable performance with a traditional segmentation network. Therefore, we propose to exploit the click information better to boost performance with the click-guided self-attention module and the click-guided correlation module. Before performing correlation and self-attention, we first concatenate the image, positive/negative click maps, and previous mask to extract the low-level features $F_{l}$ from them. We also adjust the channel number of target-aware features $F_{t}$ via a convolutional layer with a kernel size of $1 \\times 1$ . Then we concatenate $F_{l}$ with $F_{t}$ from the backbone to learn the fused features $F_{u}$ .", + "bbox": [ + 496, + 183, + 890, + 378 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "To exploit the click information, we map the location of clicks onto the feature maps and extract the features with a shape of $1 \\times 1 \\times C$ for each click, where $C$ is the number of channels. These click features are regarded as templates. The click-guided self-attention module propagates the information of these templates to other locations via multi-head attention, while the click-guided correlation attention module uses them to learn target outlines via correlation. Since the number of clicks used to obtain a satisfactory segmentation accuracy is often less than 20, it may not be sufficient only to extract templates from the location of clicks. Thus, we first enrich the templates by selecting some informative locations based on their semantic similarity to the clicks.", + "bbox": [ + 496, + 383, + 892, + 595 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Template selection. The strategy to select templates is based on the observation that pixels on the same object show higher similarity than pixels from different objects. We separately select positive and negative templates by identifying pixels that are more likely to be the object and the background, respectively. To select positive templates, we assign a score for each pixel to indicate the likelihood of being the object and select the top $K_{p}$ pixels. The score is calculated by considering three factors: the similarity to positive clicks, the similarity to negative clicks, and the distance from the positive clicks. A pixel with a short distance and a high similarity to one of the positive clicks and a low similarity to one of the negative clicks is more likely to be located in the object region and vice versa. We use the Cosine similarity between features of two pixels to measure their similarity and the Euclidean distance to measure the distance. Let $H_{f} \\times W_{f}$ denote the size of the feature map, where $H_{f}$ and $W_{f}$ are respectively the height and width, and we can obtain a positive score map $O_{p} \\in \\mathbb{R}^{H_{f} \\times W_{f}}$ as", + "bbox": [ + 496, + 613, + 892, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "22776", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "follows,", + "bbox": [ + 76, + 90, + 133, + 104 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nO _ {p} = \\left(V _ {p} + \\left(1 - V _ {n}\\right)\\right) * \\left(1 - D _ {p}\\right), \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 153, + 114, + 468, + 133 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $V_{p}\\in \\mathbb{R}^{H_{f}\\times W_{f}}$ and $V_{n}\\in \\mathbb{R}^{H_{f}\\times W_{f}}$ respectively denote the positive and negative Cosine similarity maps, and $D_{p}\\in \\mathbb{R}^{H_{f}\\times W_{f}}$ denotes the normalized distance map. Note that the similarity scores $V_{p}^{u,v} / V_{n}^{u,v}$ respectively represent the maximum similarity between the pixel $(u,v)$ and positive/negative clicks, while $D_p^{u,v}$ represents the normalized minimum distance between $(u,v)$ and positive clicks. Similarly, we can obtain a negative score map $O_{n}$ by", + "bbox": [ + 76, + 141, + 468, + 263 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nO _ {n} = \\left(V _ {n} + \\left(1 - V _ {p}\\right)\\right) * \\left(1 - D _ {n}\\right), \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 151, + 273, + 468, + 290 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $D_{n}$ denotes the normalized negative distance map, which measures the normalized minimum distance between each pixel and negative clicks. After obtaining the score maps, we select positive templates from the top $K_{p}$ locations of the positive score map and $K_{n}$ negative templates from the top $K_{n}$ locations of the negative score map. The positive and negative template features are represented as $F_{pt} \\in \\mathbb{R}^{K_p \\times C}$ and $F_{nt} \\in \\mathbb{R}^{K_n \\times C}$ , respectively.", + "bbox": [ + 76, + 299, + 468, + 420 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Click-guided self-attention. Our first way to exploit the click information is to propagate their information to other pixels via a self-attention module. Multi-head attention is widely used in computer vision to capture long-range dependencies among different pixels [9, 19]. We adopt the standard $qkv$ multi-head attention [41] to augment the representation of each pixel with the selected templates. Multi-head attention helps each pixel attend to the templates, which is beneficial to the identification of the target. To perform multi-head attention, we first reshape the feature $F_{u}$ to a size of $H_{f}W_{f}\\times C$ , then we learn the self-attention-based augmented feature $F_{s}$ by", + "bbox": [ + 76, + 435, + 468, + 617 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nF _ {s} = F _ {u} + \\text {A t t e n t i o n} (Q, K, V), \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 158, + 626, + 468, + 642 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nQ = \\phi_ {Q} \\left(F _ {u}\\right), K = \\phi_ {K} \\left(F _ {p n t}\\right), V = \\phi_ {V} \\left(F _ {p n t}\\right), \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 114, + 652, + 468, + 667 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\phi_{Q},\\phi_{K}$ , and $\\phi_V$ are linear transformations, and $F_{pnt}$ is the concatenation of positive templates $F_{pt}$ and negative templates $F_{nt}$ . $F_{s}$ is further reshaped to $H_{f}\\times W_{f}\\times C$ As the template features are selected from $F_{u}$ , and the attention is guided by the click information, we denote this attention module as a click-guided self-attention module.", + "bbox": [ + 76, + 674, + 468, + 763 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Click-guided correlation. To further exploit the click information, we propose a click-guided correlation attention module to learn the contour of the object of interest explicitly. Correlation is widely used in the Siamese object tracking archietecture [4] to locate the position of the target in a search area. Siamese tracking calculates similarity maps between a target template and the search area. In video object segmentation, RANet [44] treats target features from", + "bbox": [ + 76, + 779, + 468, + 900 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "the first frame as the template to learn pixel-wise similarity maps. In RANet, pixel-wise correlation is shown to be able to learn the contour of the target with the target features as templates. In this work, we extract target semantic features based on the location of the clicks and employ the pixel-wise correlation to learn target outlines to improve the segmentation performance. For the $j$ -th positive template feature $F_{pt}^{j}\\in \\mathbb{R}^{1\\times C}$ , we can get a similarity map via the correlation between it and $F_{u}\\in \\mathbb{R}^{H_{f}W_{f}\\times C}$ . Thus, we have", + "bbox": [ + 496, + 90, + 890, + 229 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nS _ {p} = \\left\\{S _ {p} ^ {j} \\mid S _ {p} ^ {j} = \\phi_ {q} \\left(F _ {p t} ^ {j}\\right) * \\phi_ {k} \\left(F _ {u}\\right) \\right\\} _ {j \\in \\{1, \\dots , K _ {p} \\}}, \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 526, + 239, + 890, + 260 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nS _ {n} = \\left\\{S _ {n} ^ {j} \\mid S _ {n} ^ {j} = \\phi_ {q} \\left(F _ {n t} ^ {j}\\right) * \\phi_ {k} \\left(F _ {u}\\right) \\right\\} _ {j \\in \\{1, \\dots , K _ {n} \\}}, \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 524, + 272, + 890, + 290 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $*$ denotes the correlation operation, $S_{p}$ and $S_{n}$ respectively denote the set of positive and negative correlation similarity maps, and $\\phi_q$ and $\\phi_k$ denote two linear transformations. We then transform the positive/negative similarity maps into features for segmentation via a shared convolutional layer. Then positive and negative features are concatenated and followed by the second convolutional layer to fuse them. In this manner, we get the correlation-based augmented feature $F_{c}$ as follows,", + "bbox": [ + 496, + 297, + 890, + 433 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nF _ {c} = \\phi_ {f} (\\operatorname {C o n c a t} \\left(\\phi_ {s} \\left(S _ {p}\\right), \\phi_ {s} \\left(S _ {n}\\right)\\right)), \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 571, + 445, + 890, + 462 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\phi_s$ and $\\phi_f$ denote two convolutional layers.", + "bbox": [ + 496, + 474, + 830, + 489 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "After learning the two augmented features $F_{s}$ and $F_{c}$ , we concatenate them and use four convolutional layers to predict the segmentation mask. Our mask correction network is efficient since the resolution of the features is just 1/4 of the image, and the whole structure is lightweight. It is also effective since the click information is exploited explicitly via two modules to improve performance.", + "bbox": [ + 496, + 489, + 890, + 595 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 498, + 609, + 633, + 627 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.1. Experimental Configuration", + "text_level": 1, + "bbox": [ + 498, + 635, + 754, + 651 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Implementation details. Our pipeline can be built on different existing segmentation networks. Following FocalClick [8], we choose HRNet+OCR [42, 49] and SegFormer [45] series as our base segmentation networks to show the effectiveness of the proposed method. For lightweight models like SegFormerB0 and HRNet18s, the mask correction network first transforms the number of backbone feature channels to 64. For larger models like SegFormerB3, HRNet18, and HRNet32, the channel is transformed to 96. The number of selected templates $K_{p}$ and $K_{n}$ is set to be equal to the channel number.", + "bbox": [ + 496, + 657, + 890, + 824 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We train our model on a combination of COCO [25] and LVIS [14] datasets, following RITM [40]. For a fair comparison of some previous methods, we also report the performance of our model trained on SBD [16]. We use the normalized focal loss [38] for both the base segmentation", + "bbox": [ + 496, + 825, + 890, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "22777", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/831d890cf1ae9216ea0199c27750de48c0398bec4a4745e0b6fba80f677361b7.jpg", + "table_caption": [], + "table_footnote": [ + "Table 1. Comparison of the computational cost for different methods. The speed represents the average inference time per click and is measured on a CPU laptop with $2\\mathrm{GHz}$ , $4\\times$ Intel Core i5. From the second click, we only run the mask correction network, significantly reducing the inference time compared to other methods." + ], + "table_body": "
MethodParams/MBFLOPs/GSpeed/ms
CDNet-ResNet34384 [7]23.556.73339
f-BRS-ResNet50400 [39]31.484.62373
RITM-hrnet18s400 [40]4.228.96634
RITM-hrnet18400 [40]10.015.41103
RITM-hrnet32400 [40]31.040.41635
Flickr-hrnet18s256 [8]4.233.82358
Flickr-hrnet32256 [8]31.017.1728
Flickr-SegB0256 [8]3.741.94207
Flickr-SegB3256 [8]45.612.9805
Ours-hrnet18s-FirstClick3844.339.35752
Ours-hrnet18-FirstClick38410.315.31237
Ours-hrnet32-FirstClick38431.240.51745
Ours-SegB0-FirstClick3843.845.38528
Ours-SegB3-FirstClick38445.932.32006
Ours-MaskCorrection-C643840.111.09183
Ours-MaskCorrection-C963840.222.25280
", + "bbox": [ + 81, + 88, + 465, + 352 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "and mask correction networks. We adopt the iterative training strategy [31] by randomly sampling the first positive click in the target area and progressively adding clicks based on the errors in the network's predictions during training. Our lightweight mask correction network enables efficient iterative training. We use the Adam optimizer with $\\beta_{1} = 0.9$ and $\\beta_{2} = 0.999$ to train the network. As in FocalClick [8], we sample 30000 images in one epoch and train our model for 230 epochs. We use an initial learning rate of $1e - 3$ for the HRNet+OCR series and $2e - 3$ for the SegFormer series, and decay them by ten times on the 200th and 220th epochs. We train the network with an image size of $320\\times 480$ and a batch size of 64. We add data augmentation strategies, including random resizing in a range of [0.75, 1.40], horizontal flip, random jittering of brightness, contrast, and RGB values. All our models are implemented in Python using Pytorch.", + "bbox": [ + 76, + 460, + 468, + 719 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Evaluation datasets and metrics. We evaluate our method on five commonly used datasets, including GrabCut [37], Berkeley [35], DAVIS [36], SBD [16], and Pascal VOC [10]. The GrabCut dataset contains 50 images with one single target in each image. The test set of the Berkeley dataset contains 100 object masks for 96 images. The DAVIS dataset is originally constructed for the evaluation of video object segmentation methods. We sample 345 frames to evaluate our method as in [8,40]. The SBD dataset is the largest and has been widely used to evaluate the interactive segmentation methods since [47]. It contains 6671 object", + "bbox": [ + 76, + 734, + 468, + 902 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/b1a4d2b50fad6906e0a84a5ff0d79b0f835fc61151ece6b92d62c12ddf086a6c.jpg", + "table_caption": [], + "table_footnote": [ + "Table 2. Comparison of the total inference time to reach different IoU thresholds on the largest SBD dataset. The time is measured on an NVIDIA V100 GPU." + ], + "table_body": "
NoC@90Time@90NoC@95Time@95
FocalClick-hrnet18s6.7934min12.7862min
FocalClick-hrnet326.5149min12.5085min
FocalClick-SegB06.8623min12.7339min
FocalClick-SegB35.5934min11.5563min
Ours-hrnet18s6.1619min12.4730min
Ours-hrnet325.6521min11.9032min
Ours-SegB06.2116min12.4527min
Ours-SegB35.5720min11.6529min
", + "bbox": [ + 504, + 88, + 890, + 234 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "masks for 2820 images. The validation set of the Pascal VOC dataset is also used, which consists of 1449 images with 3427 object masks.", + "bbox": [ + 498, + 316, + 890, + 362 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We use the commonly used evaluation protocol to make a fair comparison. During the evaluation, the clicks are simulated based on the difference between the current prediction and the ground truth. The first click is placed in the center of the target, and other clicks are placed in the center of the largest erroneous region. Following [26], the image is resized to a fixed length of 384 as the short side during evaluation. We use the standard Number of Clicks (NoC) metric to compare different methods. The NoC measures the number of clicks required to reach a predefined Intersection over Union (IoU) threshold between the predicted mask and the ground truth. Following most methods, the thresholds of $85\\%$ and $90\\%$ are used, and the metrics are denoted as NoC@85 and NoC@90.", + "bbox": [ + 496, + 364, + 890, + 575 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.2. Comparison with state-of-the-art methods", + "text_level": 1, + "bbox": [ + 500, + 589, + 857, + 606 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Computational comparison. We compare the parameters, FLOPs, and inference speed on CPUs of representative methods in Tab. 1. MaskCorrection-C64 denotes that we set the channel of the mask correction network to 64, which is used for HRNet18s and SegFormerB0. MaskCorrection-C96 is used for HRNet18, HRNet32, and SegFormerB3. The computational cost of our method is different between the first click and other clicks. For the first click, our method needs to run the base segmentation network and the mask correction network, resulting in slightly higher inference time compared with RITM [40]. However, our method shows higher efficiency from the second click even compared with FocalClick [8] which uses a small resolution since our mask correction network is lightweight. The computational cost of the mask correction network will not change with the base segmentation network if we fix the configuration, which is a good property since we can use a stronger segmentation network to reduce the number of interactions without a significant increase in the inference", + "bbox": [ + 496, + 613, + 890, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "22778", + "bbox": [ + 478, + 945, + 517, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/0c49a61b8ec62993ac855e9b6af0263aa72fa4d597880ef2a0f5f4addfb5286f.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodsGrabCutBerkeleySBDDAVISPascal
Train DataNoC@85NoC@90NoC@90NoC@85NoC@90NoC@85NoC@90NoC@90NoC@85
f-BRS-B-ResNet50 [39]SBD2.502.984.345.068.085.397.81
CDNet-ResNet50 [7]SBD2.222.643.694.377.875.176.66-
FocusCut-ResNet50 [26]SBD1.601.783.443.625.665.006.38-
FocalClick-hrnet18s [8]SBD1.862.063.144.306.524.926.48-
RITM-hrnet18 [40]SBD1.762.043.223.395.434.946.71-
Ours-hrnet18sSBD1.821.923.263.585.795.236.882.47
Ours-hrnet18SBD1.741.843.033.385.515.056.712.37
TransClick-segformerB4 [11]C+L1.521.601.603.445.633.685.062.08
FocalClick-segformerB0 [8]C+L1.401.662.274.566.864.045.492.97
Ours-segformerB0C+L1.561.642.403.956.214.485.532.65
FocalClick-segformerB3 [8]C+L1.441.501.923.535.593.614.902.46
Ours-segformerB3C+L1.421.482.353.445.574.495.692.23
RITM-hrnet18s [40]C+L1.541.682.604.046.484.705.982.57
FocalClick-hrnet18s [8]C+L1.481.622.664.436.793.905.252.93
Ours-hrnet18sC+L1.401.522.683.866.164.425.662.37
RITM-hrnet18 [40]C+L1.421.542.263.806.064.365.742.28
EdgeFlow-hrnet18 [15]C+L1.601.722.40--4.545.772.50
Ours-hrnet18C+L1.381.502.303.695.934.345.592.37
RITM-hrnet32 [40]C+L1.461.562.103.595.714.115.342.57
FocalClick-hrnet32 [8]C+L1.641.802.364.246.514.015.392.80
PseudoClick-hrnet32 [29]C+L-1.502.08-5.684.095.271.94
Ours-hrnet32C+L1.301.422.353.555.654.295.332.22
", + "bbox": [ + 76, + 88, + 890, + 505 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 3. Comparison results on five benchmarks. NoC@85 and NoC@90 respectively denote the number of clicks required to reach the IoU of $85\\%$ and $90\\%$ , and lower is better for the value. C+L means the combination of COCO and LVIS.", + "bbox": [ + 75, + 515, + 892, + 544 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "time. We demonstrate the total inference time to reach $90\\%$ and $95\\%$ IoU on the largest dataset SBD in Tab. 2. To save evaluation time, all models are evaluated on an NVIDIA V100 GPU. Our method spends less time reaching a predefined IoU threshold for all versions. Notably, although the number of clicks required to reach $90\\%$ (NoC@90) and $95\\%$ (NoC@95) IoUs is similar for FocalClick-SegB3 and Ours-SegB3, the inference time of our method is significantly lower because the computational cost of Ours-SegB3 from the second click is considerably lower than FocalClick-SegB3. And the gap between our method and FocalClick is larger when the threshold changes from $90\\%$ to $95\\%$ . Thus, our method is more suitable for challenging images and scenarios where we want to get a high IoU.", + "bbox": [ + 75, + 570, + 472, + 782 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Performance Comparison. We compare our method with existing methods on five benchmarks in Tab. 3. Some methods use the SBD [16] dataset to train their network, while RITM suggests training on COCO [25] and LVIS [14]. We report the results of our method equipped with different base segmentation networks and trained on different", + "bbox": [ + 75, + 809, + 470, + 901 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "datasets. Compared with some early methods like CD-Net [7] and f-BRS [39], different versions of our method show superior performance and efficiency. Compared with recent state-of-the-art methods RITM [40], FocalClick [8], FocusCut [26], PseudoClick [29], and TransClick [11], our method demonstrates competitive performance. Especially, our method achieves outstanding performance on the largest SBD dataset. Overall, the proposed method demonstrates preferable performance considering that the inference time is significantly low from the second click.", + "bbox": [ + 496, + 570, + 893, + 722 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.3. Method analysis", + "text_level": 1, + "bbox": [ + 500, + 738, + 661, + 753 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Ablation study. We conduct ablation studies to verify the effectiveness of each component in our method. The results on three challenging datasets in presented in Tab. 4. We first construct a network with only a simple convolutional mask correction network as our baseline. The first point is not fed to the base segmentation network (HRNet18s) in this baseline. As shown in Tab. 4, a simple mask correction network can hardly achieve high performance. The input of the first click to the base segmentation network helps", + "bbox": [ + 496, + 763, + 893, + 902 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "22779", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/4f92cbe5b66dbae3b0682e2a83843108315c0fcee2339d9e064a0ee221dcbba6.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
1st ClickCorrSelf-AttTSDAVIS NoC@90SBD NoC@90Pascal NoC@90
7.118.324.38
✓6.986.833.19
✓✓6.326.303.09
✓✓6.026.332.98
✓✓✓5.866.242.89
✓✓✓✓5.666.162.84
", + "bbox": [ + 86, + 88, + 459, + 215 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/cb49fe975800e71a79e0a60ffb17f9a7abb4fe11e8904192025fdd5b7392b28c.jpg", + "table_caption": [ + "Table 4. Ablation study on three challenging benchmarks. HR-Net18s is used as the base segmentation network. 1st Click denotes that we input the first click to the base segmentation network, Corr denotes the correlation module, Self-Att denotes the self-attention module, and TS denotes the template selection module." + ], + "table_footnote": [], + "table_body": "
Negative TemplatesDAVIS NoC@90SBD NoC@90Pascal NoC@90
Correlation Module✓6.106.393.01
6.096.262.96
Self-Attention Module✓6.046.553.22
5.926.292.99
", + "bbox": [ + 91, + 311, + 455, + 417 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 5. The performance of the correlation and self-attention modules with and without the adoption of the negative templates.", + "bbox": [ + 75, + 429, + 467, + 458 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/1650afc9121aaa13cb26562151a851cc12b72f27328bc0246e93dcf9e378224e.jpg", + "image_caption": [ + "Figure 3. Illustration of the positive/negative score maps for template selection and positive/negative correlation similarity maps in click-guided correlation module." + ], + "image_footnote": [], + "bbox": [ + 83, + 474, + 464, + 619 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "extract target-aware features to boost the performance. However, the performance is still relatively low. Both the introduction of the click-guided self-attention module and the click-guided correlation module bring significant improvements over the simple mask correction network, indicating that they both effectively exploit the click information. Their combination achieves the best performance, showing that they learn complementary augmented features and can be combined to boost performance. The template selection module further improves performance by sampling several templates to enrich the click features.", + "bbox": [ + 75, + 703, + 468, + 869 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "The necessity of negative templates. All positive and", + "bbox": [ + 76, + 885, + 468, + 901 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "negative templates are input to the self-attention and correlation modules. The adoption of positive templates is a natural choice since they contain rich information regarding the target. However, the negative templates are also vital since negative clicks are often selected in distractor areas, and they contain information that can discriminate the target from the background. Tab. 5 demonstrates the performance of the two modules with and without the negative templates. The employment of the negative templates effectively improves the performance of both the correlation and self-attention modules.", + "bbox": [ + 496, + 90, + 890, + 257 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Qualitative analysis. We show the change of the positive/negative score maps for template selection and positive/negative correlation similarity maps in Fig. 3. After placing the first positive click, the model predicts an erroneous area that shows high semantic similarity to the target. After placing two more negative clicks in the erroneous area, the model successfully segments the target. In the interactive process, the score maps change with the clicks and can effectively discriminate the areas of the target of interest and other objects, which helps select meaningful and correct templates. The change in the correlation similarity maps shows that we can learn the target contours by correlating the templates with the feature maps. Fig. 3 only shows the similarity maps of two templates. Since we select several templates, the correlation results provide rich information to discriminate the target from other areas. Directly employing the correlation results as features helps better segment the target.", + "bbox": [ + 496, + 277, + 890, + 549 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Limitation analysis. Our method still requires a relatively high computational cost in the first click, which may not be suitable for some simple annotation scenarios where only one or two clicks are needed. Maybe this can be solved by reducing the resolution of the base segmentation network as in FocalClick [8] and locally updating the mask with the mask correlation network. We leave this for future research.", + "bbox": [ + 496, + 569, + 890, + 675 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 704, + 617, + 719 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this paper, we propose an efficient EMC-Click method for click-based interactive segmentation. A lightweight mask correction network is constructed to iteratively update the mask, which significantly reduces the computational cost from the second click. A click-guided correlation module and a click-guided self-attention module are proposed to effectively exploit the click information to boost the performance of the mask correction network. Experiments on five benchmarks demonstrate that our method achieves competitive performance and higher efficiency compared with state-of-the-art methods.", + "bbox": [ + 496, + 734, + 890, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "22780", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 174, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Eirikur Agustsson, Jasper RR Uijlings, and Vittorio Ferrari. Interactive full image segmentation by considering all regions jointly. In CVPR, pages 11622-11631, 2019. 1", + "[2] Junjie Bai and Xiaodong Wu. Error-tolerant scribbles based interactive image segmentation. In CVPR, pages 392-399, 2014. 1", + "[3] Rodrigo Benenson, Stefan Popov, and Vittorio Ferrari. Large-scale interactive object segmentation with human annotators. 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Intention-aware feature propagation network for interactive segmentation. arXiv:2203.05145, 2022. 3", + "bbox": [ + 501, + 90, + 892, + 133 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "22782", + "bbox": [ + 478, + 945, + 519, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/Efficient Mask Correction for Click-Based Interactive Image Segmentation/0a4cc1dd-64c3-44d2-8dfa-4f17be83df54_model.json b/2023/Efficient Mask Correction for Click-Based Interactive Image Segmentation/0a4cc1dd-64c3-44d2-8dfa-4f17be83df54_model.json new file mode 100644 index 0000000000000000000000000000000000000000..b0c27892f57c3e9e5a987d7816ffaab4dcf44920 --- /dev/null +++ b/2023/Efficient Mask Correction for Click-Based Interactive Image Segmentation/0a4cc1dd-64c3-44d2-8dfa-4f17be83df54_model.json @@ -0,0 +1,1870 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.109, + 0.13, + 0.862, + 0.154 + ], + "angle": 0, + "content": "Efficient Mask Correction for Click-Based Interactive Image Segmentation" + }, + { + "type": "text", + "bbox": [ + 0.295, + 0.181, + 0.674, + 0.218 + ], + "angle": 0, + "content": "Fei Du, Jianlong Yuan, Zhibin Wang, Fan Wang Alibaba Group" + }, + { + "type": "text", + "bbox": [ + 0.223, + 0.219, + 0.744, + 0.234 + ], + "angle": 0, + "content": "{dufei.cf, gongyuan.yjl, zhibin.waz, fan.w}@alibaba-inc.com" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.269, + 0.314, + 0.285 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.301, + 0.474, + 0.662 + ], + "angle": 0, + "content": "The goal of click-based interactive image segmentation is to extract target masks with the input of positive/negative clicks. Every time a new click is placed, existing methods run the whole segmentation network to obtain a corrected mask, which is inefficient since several clicks may be needed to reach satisfactory accuracy. To this end, we propose an efficient method to correct the mask with a lightweight mask correction network. The whole network remains a low computational cost from the second click, even if we have a large backbone. However, a simple correction network with limited capacity is not likely to achieve comparable performance with a classic segmentation network. Thus, we propose a click-guided self-attention module and a click-guided correlation module to effectively exploits the click information to boost performance. First, several templates are selected based on the semantic similarity with click features. Then the self-attention module propagates the template information to other pixels, while the correlation module directly uses the templates to obtain target outlines. With the efficient architecture and two click-guided modules, our method shows preferable performance and efficiency compared to existing methods. The code will be released at https://github.com/feiaxyt/EMC-Click." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.693, + 0.21, + 0.71 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.72, + 0.47, + 0.854 + ], + "angle": 0, + "content": "Interactive image segmentation aims to select the object of interest with minimal iterative interactions, which can benefit various computer vision tasks, such as semantic segmentation [30], instance segmentation [17], and medical image analysis [28]. As the success of these tasks often requires large-scale mask-level annotations and it is time-consuming to annotate the image manually, interactive segmentation is an attractive way to simplify the annotation process and alleviate the annotation cost." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.856, + 0.47, + 0.902 + ], + "angle": 0, + "content": "Different interaction strategies have been studied to simplify the interactive process, including bounding boxes [23, 37, 48], clicks [33, 40, 47], scribbles [1, 2], boundary" + }, + { + "type": "image", + "bbox": [ + 0.508, + 0.269, + 0.891, + 0.433 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.443, + 0.895, + 0.514 + ], + "angle": 0, + "content": "Figure 1. Comparison between the architectures of our method and classic methods. Classic methods run the segmentation network in every iteration, which is inefficient if a large network is adopted. We update the mask via a lightweight mask correction network, enabling an efficient interaction." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.549, + 0.893, + 0.732 + ], + "angle": 0, + "content": "points [32], and extreme points [34]. However, due to the complexity of the object boundary and appearance, the performance of methods based on bounding boxes may drop if the bounding boxes are not tightly drawn [48]. Besides, it requires more effort to identify the object boundary and place bounding boxes, boundary points, or extreme points on the image. In contrast, the click-based method only requires the users to progressively place positive and negative clicks on the foreground and background areas, respectively. It has recently attracted more attention due to its simplicity and well-established training and evaluation protocols [40, 47]. Hence, we focus on the click-based method." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.735, + 0.895, + 0.903 + ], + "angle": 0, + "content": "In click-based interactive segmentation methods, the model returns a corrected prediction mask after each click from the users. Efficiency is of great importance to interactive segmentation methods since a typical segmentation process requires several interactive iterations. In recent years, deep learning-based interactive segmentation methods have achieved considerably better performance compared to traditional methods. However, some recent works [20, 22, 39] achieve state-of-the-art performance by employing inference-time optimization to refine the masks, which significantly increases the computational cost. To" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "22773" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.318 + ], + "angle": 0, + "content": "eliminate online optimization, RITM [40] investigates different designs for interactive segmentation and achieves state-of-the-art results with a classic segmentation network. To improve efficiency, FocalClick [8] proposes target crop and focus crop strategies to segment two selected local regions efficiently. Most click-based methods [7, 8, 27, 31, 40, 47] iteratively run the whole segmentation network to update the masks with the input of user clicks, which is time-consuming especially when we have a strong segmentation network. Majumder et al. [32] proposes to refine the mask with a lightweight refinement network. However, the network requires the user to place boundary points, which is not user-friendly. Therefore, more efficient click-based interactive segmentation methods are still required to reach a better trade-off between performance and efficiency." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.318, + 0.473, + 0.771 + ], + "angle": 0, + "content": "With the above consideration, in this work, we develop an efficient click-based interactive segmentation model based on an Efficient Mask Correction network (EMC-Click). The model consists of a base segmentation network and a lightweight mask correction network. The base network takes the first click as input and outputs target-aware features and a coarse prediction. The mask correction network iteratively updates the prediction whenever a new click is placed. The difference between our network and the classic network is shown in Fig. 1. This decoupled design ensures that the computational cost of each iteration is relatively low from the second click. However, using a simply designed mask correction network to update the prediction can hardly achieve comparable performance with classic methods that use a strong segmentation network. Thus, we propose two feature augmentation modules, including a click-guided self-attention module and a click-guided correlation module, to effectively exploit the click information to augment the features in the mask correction network. We first extract the click features and enrich them by selecting several template features based on the semantic similarity between the clicks and other pixels. The self-attention module propagates the information of the template features to other pixels, and the correlation model directly learns target contours. Both modules effectively and efficiently augment the features and improve the segmentation performance. Experiments on five benchmarks demonstrate that our method achieves competitive performance and higher efficiency compared with state-of-the-art click-based interactive segmentation methods." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.772, + 0.416, + 0.786 + ], + "angle": 0, + "content": "Our contribution can be summarized as follows:" + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.798, + 0.47, + 0.875 + ], + "angle": 0, + "content": "- We propose EMC-Click, an efficient click-based interactive method, to correct the masks via a lightweight mask correction network interactively. Our method significantly reduces computational cost from the second click especially when we have a large backbone." + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.886, + 0.47, + 0.902 + ], + "angle": 0, + "content": "- We propose two feature augmentation modules to im" + }, + { + "type": "list", + "bbox": [ + 0.096, + 0.798, + 0.47, + 0.902 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.531, + 0.092, + 0.892, + 0.123 + ], + "angle": 0, + "content": "prove the segmentation accuracy by effectively exploiting the click information." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.136, + 0.895, + 0.212 + ], + "angle": 0, + "content": "- We build EMC-Click on different base segmentation networks and evaluate our models on several benchmarks. The results show that our method achieves preferable performance and efficiency compared to state-of-the-art methods." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.24, + 0.646, + 0.256 + ], + "angle": 0, + "content": "2. Related works" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.266, + 0.776, + 0.282 + ], + "angle": 0, + "content": "2.1. Interactive image segmentation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.29, + 0.892, + 0.426 + ], + "angle": 0, + "content": "Interactive image segmentation is a longstanding research topic in computer vision. In the early years, methods based on optimization on a graph over image pixels were the mainstream. GrabCut [37] is a classic method that extend [5] to an iterative energy minimization problem. Methods based on random walk [13,21] build an undirected graph on the image to estimate the probability of each pixel. Since early methods use handcrafted features, they can hardly generalize to complex scenes." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.427, + 0.893, + 0.789 + ], + "angle": 0, + "content": "Deep learning has been applied in many fields due to its high representation power and the ability to model complex structures. Xu et al. [47] are the first to propose a CNN-based interactive segmentation method. They encode the positive/negative clicks as positive/negative distance maps and concatenate them with the image to feed them into the network. They also design strategies to sample clicks for training, which are adopted by many subsequent works [8, 15, 40]. Later, Mahadevan et al. [31] add an iterative sampling strategy on [47] during training. BRS [20] proposes optimizing the network online based on user-specified location information during the annotation process. f-BRS [39] accelerates BRS [20] by optimizing a small part of the network. Recently, RITM [40] conducts comprehensive experiments to investigate the design principle of an end-to-end click-based interactive segmentation method. Although the click-based method is the mainstream due to its simplicity and well-established training and evaluation protocols, other interactive methods are also exploited, such as extreme points [34], boundary points [32], and bounding boxes [46]. Despite the impressive progress made by deep learning-based methods, most of them suffer from a high computational cost especially when they have a strong backbone like ResNet101 [18]." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.801, + 0.878, + 0.817 + ], + "angle": 0, + "content": "2.2. Mask refinement in interactive segmentation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.826, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Mask refinement is commonly used in interactive segmentation to get fine-level results. They often follow the coarse-to-fine schema and crop a local region to make local corrections. For example, RIS-Net [24] samples multiple regions based on the click positions for local refinement." + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "22774" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.081, + 0.089, + 0.891, + 0.196 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.081, + 0.197, + 0.888, + 0.307 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.321, + 0.896, + 0.406 + ], + "angle": 0, + "content": "Figure 2. The framework of the proposed EMC-Click. We adopt a base segmentation network to extract target-aware features and make the first prediction by taking the first click as input. The mask correction network is responsible for updating the mask when a new click is placed. In this mask correction network, we first map the click location to the feature map and extract the click features. Then we sample several template features that are similar to the click features. The click-guided self-attention module propagates the template information to other pixels, while the click-guided correlation module extracts target outlines via the correlation between the templates and the feature map. Both modules augment the features, and the combined features are used to predict the mask." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.432, + 0.473, + 0.72 + ], + "angle": 0, + "content": "FocalClick [8] crops a region based on the difference between the previous mask and the coarsely predicted mask to refine the details. Zhang et al. [50] refines a local area centered on the target based on the coarse segmentation results. There are also methods to refine the global mask, such as EdgeFlow [15] and \\(99\\%\\) AccuracyNet [12]. One common property of these refinement methods is that they run the whole segmentation and refinement networks to get the results in each interactive iteration. It is too costly compared with a simple feedforward segmentation network. FocusCut [26] trains a segmentation network to not only segment the target object but also refine local details. However, it is still not efficient enough to run the whole segmentation network in each iteration. Our mask correction network is somewhat like a refinement network. The difference is that we directly use this network to correct masks when a new click is placed, and the base segmentation network only runs for the first click. This architecture reduces the inference time significantly compared with traditional methods." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.727, + 0.367, + 0.743 + ], + "angle": 0, + "content": "2.3. Exploitation of click information" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.75, + 0.473, + 0.903 + ], + "angle": 0, + "content": "The clicks provide key information for locating the foreground and background areas. Most methods encode the clicks as click maps where the regions around the clicks are highlighted. However, the click information is not explicitly exploited. To better exploit the click information, CDNet [7] propagates the click information to other pixels via two non-local networks [43]. It constructs weight maps based on the click locations to re-weight the affinity matrix, which is not computational efficiency since it needs to model the affinity between every two pixels. IFPN [50]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.432, + 0.895, + 0.584 + ], + "angle": 0, + "content": "learns a sparse graph model to perform click feature propagation. It only models the dependencies between the clicks and other pixels. Inspired by the two methods, we construct a multi-head self-attention module to propagate the click information to other pixels. Different from CDNet and IFPN, we select several templates to enrich the click features. Thus, our method is more efficient compared to CDNet [7] and can exploit more information compared to IFPN [50]. Besides, we also propose a correlation module to exploit the click information explicitly." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.598, + 0.673, + 0.617 + ], + "angle": 0, + "content": "3. Proposed method" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.624, + 0.895, + 0.744 + ], + "angle": 0, + "content": "We propose to iteratively correct the segmentation mask using a lightweight mask correction network, which exploits the information of the clicks to boost the performance via a click-guided self-attention module and a click-guided correlation module. We first briefly revisit the traditional pipeline of the interactive segmentation model, then introduce our pipeline and elaborate on the mask correction network." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.756, + 0.707, + 0.773 + ], + "angle": 0, + "content": "3.1. The standard pipeline" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.781, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Interactive segmentation is often regarded as a special type of segmentation task. Different from classic segmentation, the input of the interactive segmentation network contains not only the image but also the click maps and previously predicted mask. When segmenting the object of interest, the user decides where to place the next click based on the current segmentation mask. All positive/negative clicks are encoded as positive/negative click maps that are usual" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "22775" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.258 + ], + "angle": 0, + "content": "ally defined as distance maps [47] or binary disks [3]. The click maps are then concatenated with the image and previously predicted mask to be fed to the segmentation network. After each click, the user obtains an updated segmentation mask by running the whole segmentation network. Usually, a strong segmentation network like DeepLabv3+ [6] is required to achieve satisfactory results since the segmentation accuracy directly depends on it. However, running a strong segmentation network several times is often time-consuming, especially on low-power devices, which makes this standard pipeline inefficient in practice." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.266, + 0.245, + 0.282 + ], + "angle": 0, + "content": "3.2. Efficient pipeline" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.289, + 0.473, + 0.515 + ], + "angle": 0, + "content": "To avoid running the whole segmentation network for each click, we build a lightweight network to correct the segmentation mask in each iteration. The pipeline is shown in Fig. 2. Our network consists of a base segmentation network and a lightweight mask correction network. As observed in FCA-Net [27], the first click is responsible for locating the target object. Thus, we input the first click into the segmentation network to generate target-aware features. When the user places the first click, the base segmentation network extracts the target-aware feature and generates a coarse mask, and the mask correction network corrects the coarse mask. Starting from the second click, we no longer run the base segmentation network. Instead, we directly feed all clicks into the mask correction network to correct the previously predicted mask." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.516, + 0.471, + 0.591 + ], + "angle": 0, + "content": "Specifically, we denote the input image as \\(I\\) and the click set at the \\(t\\)-th iteration as \\(C^t\\). The base segmentation network takes the input image and the first click \\(C^1\\) as input and generates target-aware features \\(F_{t}\\) and a coarse mask \\(M_{c}\\), which can be formulated as follows," + }, + { + "type": "equation", + "bbox": [ + 0.168, + 0.6, + 0.47, + 0.617 + ], + "angle": 0, + "content": "\\[\nF _ {t}, M _ {c} = \\Phi_ {S} (I, E n c \\left(C ^ {1}\\right); \\theta_ {s}), \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.626, + 0.47, + 0.746 + ], + "angle": 0, + "content": "where \\( Enc \\) denotes the click encoding function, and \\( \\Phi_S \\) and \\( \\theta_s \\) denote the base segmentation network and its parameters, respectively. In this work, we adopt disks with a small radius [3,40] to encode the clicks. The mask correction network takes the click set \\( C^t \\), the target-aware feature \\( F_t \\), the original image \\( I \\), and the previously predicted mask \\( M^{t-1} \\) as input and outputs an updated mask, which can be written as follows," + }, + { + "type": "equation", + "bbox": [ + 0.144, + 0.754, + 0.469, + 0.772 + ], + "angle": 0, + "content": "\\[\nM ^ {t} = \\Phi_ {R} (I, E n c \\left(C ^ {t}\\right), M ^ {t - 1}, F _ {t}; \\theta_ {r}), \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.781, + 0.47, + 0.87 + ], + "angle": 0, + "content": "where \\(\\Phi_R\\) and \\(\\theta_r\\) denote the mask correction network and its parameters, respectively. For the first click (i.e. \\(t = 1\\)), the previous mask \\(M^0\\) input to the mask correction network is equal to the coarse mask \\(M_c\\). The mask correction network can also take as input a preexisting mask generated from other forms of pre-processing." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.47, + 0.901 + ], + "angle": 0, + "content": "Note that our pipeline differs from FCA-Net [27] which also treats the first click differently from other clicks. Our" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.092, + 0.892, + 0.136 + ], + "angle": 0, + "content": "network only runs the mask correction network after the first click, while FCA-Net still needs to run the whole network for each click." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.157, + 0.892, + 0.172 + ], + "angle": 0, + "content": "3.3. Efficient and effective mask correction network" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.184, + 0.892, + 0.38 + ], + "angle": 0, + "content": "A simple mask correction network with limited parameters and computational cost can hardly achieve comparable performance with a traditional segmentation network. Therefore, we propose to exploit the click information better to boost performance with the click-guided self-attention module and the click-guided correlation module. Before performing correlation and self-attention, we first concatenate the image, positive/negative click maps, and previous mask to extract the low-level features \\( F_{l} \\) from them. We also adjust the channel number of target-aware features \\( F_{t} \\) via a convolutional layer with a kernel size of \\( 1 \\times 1 \\). Then we concatenate \\( F_{l} \\) with \\( F_{t} \\) from the backbone to learn the fused features \\( F_{u} \\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.384, + 0.893, + 0.596 + ], + "angle": 0, + "content": "To exploit the click information, we map the location of clicks onto the feature maps and extract the features with a shape of \\( 1 \\times 1 \\times C \\) for each click, where \\( C \\) is the number of channels. These click features are regarded as templates. The click-guided self-attention module propagates the information of these templates to other locations via multi-head attention, while the click-guided correlation attention module uses them to learn target outlines via correlation. Since the number of clicks used to obtain a satisfactory segmentation accuracy is often less than 20, it may not be sufficient only to extract templates from the location of clicks. Thus, we first enrich the templates by selecting some informative locations based on their semantic similarity to the clicks." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.614, + 0.893, + 0.901 + ], + "angle": 0, + "content": "Template selection. The strategy to select templates is based on the observation that pixels on the same object show higher similarity than pixels from different objects. We separately select positive and negative templates by identifying pixels that are more likely to be the object and the background, respectively. To select positive templates, we assign a score for each pixel to indicate the likelihood of being the object and select the top \\( K_{p} \\) pixels. The score is calculated by considering three factors: the similarity to positive clicks, the similarity to negative clicks, and the distance from the positive clicks. A pixel with a short distance and a high similarity to one of the positive clicks and a low similarity to one of the negative clicks is more likely to be located in the object region and vice versa. We use the Cosine similarity between features of two pixels to measure their similarity and the Euclidean distance to measure the distance. Let \\( H_{f} \\times W_{f} \\) denote the size of the feature map, where \\( H_{f} \\) and \\( W_{f} \\) are respectively the height and width, and we can obtain a positive score map \\( O_{p} \\in \\mathbb{R}^{H_{f} \\times W_{f}} \\) as" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "22776" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.078, + 0.092, + 0.135, + 0.105 + ], + "angle": 0, + "content": "follows," + }, + { + "type": "equation", + "bbox": [ + 0.154, + 0.116, + 0.47, + 0.134 + ], + "angle": 0, + "content": "\\[\nO _ {p} = \\left(V _ {p} + \\left(1 - V _ {n}\\right)\\right) * \\left(1 - D _ {p}\\right), \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.142, + 0.47, + 0.264 + ], + "angle": 0, + "content": "where \\(V_{p}\\in \\mathbb{R}^{H_{f}\\times W_{f}}\\) and \\(V_{n}\\in \\mathbb{R}^{H_{f}\\times W_{f}}\\) respectively denote the positive and negative Cosine similarity maps, and \\(D_{p}\\in \\mathbb{R}^{H_{f}\\times W_{f}}\\) denotes the normalized distance map. Note that the similarity scores \\(V_{p}^{u,v} / V_{n}^{u,v}\\) respectively represent the maximum similarity between the pixel \\((u,v)\\) and positive/negative clicks, while \\(D_p^{u,v}\\) represents the normalized minimum distance between \\((u,v)\\) and positive clicks. Similarly, we can obtain a negative score map \\(O_{n}\\) by" + }, + { + "type": "equation", + "bbox": [ + 0.153, + 0.274, + 0.469, + 0.291 + ], + "angle": 0, + "content": "\\[\nO _ {n} = \\left(V _ {n} + \\left(1 - V _ {p}\\right)\\right) * \\left(1 - D _ {n}\\right), \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.3, + 0.469, + 0.421 + ], + "angle": 0, + "content": "where \\(D_{n}\\) denotes the normalized negative distance map, which measures the normalized minimum distance between each pixel and negative clicks. After obtaining the score maps, we select positive templates from the top \\(K_{p}\\) locations of the positive score map and \\(K_{n}\\) negative templates from the top \\(K_{n}\\) locations of the negative score map. The positive and negative template features are represented as \\(F_{pt} \\in \\mathbb{R}^{K_p \\times C}\\) and \\(F_{nt} \\in \\mathbb{R}^{K_n \\times C}\\), respectively." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.436, + 0.469, + 0.618 + ], + "angle": 0, + "content": "Click-guided self-attention. Our first way to exploit the click information is to propagate their information to other pixels via a self-attention module. Multi-head attention is widely used in computer vision to capture long-range dependencies among different pixels [9, 19]. We adopt the standard \\( qkv \\) multi-head attention [41] to augment the representation of each pixel with the selected templates. Multi-head attention helps each pixel attend to the templates, which is beneficial to the identification of the target. To perform multi-head attention, we first reshape the feature \\( F_{u} \\) to a size of \\( H_{f}W_{f}\\times C \\), then we learn the self-attention-based augmented feature \\( F_{s} \\) by" + }, + { + "type": "equation", + "bbox": [ + 0.16, + 0.627, + 0.469, + 0.643 + ], + "angle": 0, + "content": "\\[\nF _ {s} = F _ {u} + \\text {A t t e n t i o n} (Q, K, V), \\tag {5}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.116, + 0.653, + 0.469, + 0.669 + ], + "angle": 0, + "content": "\\[\nQ = \\phi_ {Q} \\left(F _ {u}\\right), K = \\phi_ {K} \\left(F _ {p n t}\\right), V = \\phi_ {V} \\left(F _ {p n t}\\right), \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.675, + 0.469, + 0.765 + ], + "angle": 0, + "content": "where \\(\\phi_{Q},\\phi_{K}\\) , and \\(\\phi_V\\) are linear transformations, and \\(F_{pnt}\\) is the concatenation of positive templates \\(F_{pt}\\) and negative templates \\(F_{nt}\\) . \\(F_{s}\\) is further reshaped to \\(H_{f}\\times W_{f}\\times C\\) As the template features are selected from \\(F_{u}\\) , and the attention is guided by the click information, we denote this attention module as a click-guided self-attention module." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.78, + 0.469, + 0.901 + ], + "angle": 0, + "content": "Click-guided correlation. To further exploit the click information, we propose a click-guided correlation attention module to learn the contour of the object of interest explicitly. Correlation is widely used in the Siamese object tracking archietecture [4] to locate the position of the target in a search area. Siamese tracking calculates similarity maps between a target template and the search area. In video object segmentation, RANet [44] treats target features from" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.23 + ], + "angle": 0, + "content": "the first frame as the template to learn pixel-wise similarity maps. In RANet, pixel-wise correlation is shown to be able to learn the contour of the target with the target features as templates. In this work, we extract target semantic features based on the location of the clicks and employ the pixel-wise correlation to learn target outlines to improve the segmentation performance. For the \\(j\\)-th positive template feature \\(F_{pt}^{j}\\in \\mathbb{R}^{1\\times C}\\), we can get a similarity map via the correlation between it and \\(F_{u}\\in \\mathbb{R}^{H_{f}W_{f}\\times C}\\). Thus, we have" + }, + { + "type": "equation", + "bbox": [ + 0.527, + 0.241, + 0.892, + 0.261 + ], + "angle": 0, + "content": "\\[\nS _ {p} = \\left\\{S _ {p} ^ {j} \\mid S _ {p} ^ {j} = \\phi_ {q} \\left(F _ {p t} ^ {j}\\right) * \\phi_ {k} \\left(F _ {u}\\right) \\right\\} _ {j \\in \\{1, \\dots , K _ {p} \\}}, \\tag {7}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.525, + 0.273, + 0.892, + 0.291 + ], + "angle": 0, + "content": "\\[\nS _ {n} = \\left\\{S _ {n} ^ {j} \\mid S _ {n} ^ {j} = \\phi_ {q} \\left(F _ {n t} ^ {j}\\right) * \\phi_ {k} \\left(F _ {u}\\right) \\right\\} _ {j \\in \\{1, \\dots , K _ {n} \\}}, \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.298, + 0.892, + 0.434 + ], + "angle": 0, + "content": "where \\(*\\) denotes the correlation operation, \\(S_{p}\\) and \\(S_{n}\\) respectively denote the set of positive and negative correlation similarity maps, and \\(\\phi_q\\) and \\(\\phi_k\\) denote two linear transformations. We then transform the positive/negative similarity maps into features for segmentation via a shared convolutional layer. Then positive and negative features are concatenated and followed by the second convolutional layer to fuse them. In this manner, we get the correlation-based augmented feature \\(F_{c}\\) as follows," + }, + { + "type": "equation", + "bbox": [ + 0.573, + 0.446, + 0.892, + 0.463 + ], + "angle": 0, + "content": "\\[\nF _ {c} = \\phi_ {f} (\\operatorname {C o n c a t} \\left(\\phi_ {s} \\left(S _ {p}\\right), \\phi_ {s} \\left(S _ {n}\\right)\\right)), \\tag {9}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.475, + 0.831, + 0.49 + ], + "angle": 0, + "content": "where \\(\\phi_s\\) and \\(\\phi_f\\) denote two convolutional layers." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.491, + 0.892, + 0.596 + ], + "angle": 0, + "content": "After learning the two augmented features \\( F_{s} \\) and \\( F_{c} \\), we concatenate them and use four convolutional layers to predict the segmentation mask. Our mask correction network is efficient since the resolution of the features is just 1/4 of the image, and the whole structure is lightweight. It is also effective since the click information is exploited explicitly via two modules to improve performance." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.611, + 0.634, + 0.628 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.636, + 0.755, + 0.652 + ], + "angle": 0, + "content": "4.1. Experimental Configuration" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.659, + 0.892, + 0.825 + ], + "angle": 0, + "content": "Implementation details. Our pipeline can be built on different existing segmentation networks. Following FocalClick [8], we choose HRNet+OCR [42, 49] and SegFormer [45] series as our base segmentation networks to show the effectiveness of the proposed method. For lightweight models like SegFormerB0 and HRNet18s, the mask correction network first transforms the number of backbone feature channels to 64. For larger models like SegFormerB3, HRNet18, and HRNet32, the channel is transformed to 96. The number of selected templates \\( K_{p} \\) and \\( K_{n} \\) is set to be equal to the channel number." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.826, + 0.892, + 0.901 + ], + "angle": 0, + "content": "We train our model on a combination of COCO [25] and LVIS [14] datasets, following RITM [40]. For a fair comparison of some previous methods, we also report the performance of our model trained on SBD [16]. We use the normalized focal loss [38] for both the base segmentation" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "22777" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.082, + 0.089, + 0.467, + 0.353 + ], + "angle": 0, + "content": "
MethodParams/MBFLOPs/GSpeed/ms
CDNet-ResNet34384 [7]23.556.73339
f-BRS-ResNet50400 [39]31.484.62373
RITM-hrnet18s400 [40]4.228.96634
RITM-hrnet18400 [40]10.015.41103
RITM-hrnet32400 [40]31.040.41635
Flickr-hrnet18s256 [8]4.233.82358
Flickr-hrnet32256 [8]31.017.1728
Flickr-SegB0256 [8]3.741.94207
Flickr-SegB3256 [8]45.612.9805
Ours-hrnet18s-FirstClick3844.339.35752
Ours-hrnet18-FirstClick38410.315.31237
Ours-hrnet32-FirstClick38431.240.51745
Ours-SegB0-FirstClick3843.845.38528
Ours-SegB3-FirstClick38445.932.32006
Ours-MaskCorrection-C643840.111.09183
Ours-MaskCorrection-C963840.222.25280
" + }, + { + "type": "table_footnote", + "bbox": [ + 0.077, + 0.364, + 0.47, + 0.435 + ], + "angle": 0, + "content": "Table 1. Comparison of the computational cost for different methods. The speed represents the average inference time per click and is measured on a CPU laptop with \\(2\\mathrm{GHz}\\), \\(4\\times\\) Intel Core i5. From the second click, we only run the mask correction network, significantly reducing the inference time compared to other methods." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.462, + 0.47, + 0.72 + ], + "angle": 0, + "content": "and mask correction networks. We adopt the iterative training strategy [31] by randomly sampling the first positive click in the target area and progressively adding clicks based on the errors in the network's predictions during training. Our lightweight mask correction network enables efficient iterative training. We use the Adam optimizer with \\(\\beta_{1} = 0.9\\) and \\(\\beta_{2} = 0.999\\) to train the network. As in FocalClick [8], we sample 30000 images in one epoch and train our model for 230 epochs. We use an initial learning rate of \\(1e - 3\\) for the HRNet+OCR series and \\(2e - 3\\) for the SegFormer series, and decay them by ten times on the 200th and 220th epochs. We train the network with an image size of \\(320\\times 480\\) and a batch size of 64. We add data augmentation strategies, including random resizing in a range of [0.75, 1.40], horizontal flip, random jittering of brightness, contrast, and RGB values. All our models are implemented in Python using Pytorch." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.735, + 0.47, + 0.903 + ], + "angle": 0, + "content": "Evaluation datasets and metrics. We evaluate our method on five commonly used datasets, including GrabCut [37], Berkeley [35], DAVIS [36], SBD [16], and Pascal VOC [10]. The GrabCut dataset contains 50 images with one single target in each image. The test set of the Berkeley dataset contains 100 object masks for 96 images. The DAVIS dataset is originally constructed for the evaluation of video object segmentation methods. We sample 345 frames to evaluate our method as in [8,40]. The SBD dataset is the largest and has been widely used to evaluate the interactive segmentation methods since [47]. It contains 6671 object" + }, + { + "type": "table", + "bbox": [ + 0.505, + 0.089, + 0.891, + 0.236 + ], + "angle": 0, + "content": "
NoC@90Time@90NoC@95Time@95
FocalClick-hrnet18s6.7934min12.7862min
FocalClick-hrnet326.5149min12.5085min
FocalClick-SegB06.8623min12.7339min
FocalClick-SegB35.5934min11.5563min
Ours-hrnet18s6.1619min12.4730min
Ours-hrnet325.6521min11.9032min
Ours-SegB06.2116min12.4527min
Ours-SegB35.5720min11.6529min
" + }, + { + "type": "table_footnote", + "bbox": [ + 0.499, + 0.247, + 0.892, + 0.289 + ], + "angle": 0, + "content": "Table 2. Comparison of the total inference time to reach different IoU thresholds on the largest SBD dataset. The time is measured on an NVIDIA V100 GPU." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.318, + 0.892, + 0.363 + ], + "angle": 0, + "content": "masks for 2820 images. The validation set of the Pascal VOC dataset is also used, which consists of 1449 images with 3427 object masks." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.365, + 0.892, + 0.576 + ], + "angle": 0, + "content": "We use the commonly used evaluation protocol to make a fair comparison. During the evaluation, the clicks are simulated based on the difference between the current prediction and the ground truth. The first click is placed in the center of the target, and other clicks are placed in the center of the largest erroneous region. Following [26], the image is resized to a fixed length of 384 as the short side during evaluation. We use the standard Number of Clicks (NoC) metric to compare different methods. The NoC measures the number of clicks required to reach a predefined Intersection over Union (IoU) threshold between the predicted mask and the ground truth. Following most methods, the thresholds of \\(85\\%\\) and \\(90\\%\\) are used, and the metrics are denoted as NoC@85 and NoC@90." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.59, + 0.859, + 0.607 + ], + "angle": 0, + "content": "4.2. Comparison with state-of-the-art methods" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.614, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Computational comparison. We compare the parameters, FLOPs, and inference speed on CPUs of representative methods in Tab. 1. MaskCorrection-C64 denotes that we set the channel of the mask correction network to 64, which is used for HRNet18s and SegFormerB0. MaskCorrection-C96 is used for HRNet18, HRNet32, and SegFormerB3. The computational cost of our method is different between the first click and other clicks. For the first click, our method needs to run the base segmentation network and the mask correction network, resulting in slightly higher inference time compared with RITM [40]. However, our method shows higher efficiency from the second click even compared with FocalClick [8] which uses a small resolution since our mask correction network is lightweight. The computational cost of the mask correction network will not change with the base segmentation network if we fix the configuration, which is a good property since we can use a stronger segmentation network to reduce the number of interactions without a significant increase in the inference" + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.946, + 0.519, + 0.957 + ], + "angle": 0, + "content": "22778" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.078, + 0.089, + 0.892, + 0.506 + ], + "angle": 0, + "content": "
MethodsGrabCutBerkeleySBDDAVISPascal
Train DataNoC@85NoC@90NoC@90NoC@85NoC@90NoC@85NoC@90NoC@90NoC@85
f-BRS-B-ResNet50 [39]SBD2.502.984.345.068.085.397.81
CDNet-ResNet50 [7]SBD2.222.643.694.377.875.176.66-
FocusCut-ResNet50 [26]SBD1.601.783.443.625.665.006.38-
FocalClick-hrnet18s [8]SBD1.862.063.144.306.524.926.48-
RITM-hrnet18 [40]SBD1.762.043.223.395.434.946.71-
Ours-hrnet18sSBD1.821.923.263.585.795.236.882.47
Ours-hrnet18SBD1.741.843.033.385.515.056.712.37
TransClick-segformerB4 [11]C+L1.521.601.603.445.633.685.062.08
FocalClick-segformerB0 [8]C+L1.401.662.274.566.864.045.492.97
Ours-segformerB0C+L1.561.642.403.956.214.485.532.65
FocalClick-segformerB3 [8]C+L1.441.501.923.535.593.614.902.46
Ours-segformerB3C+L1.421.482.353.445.574.495.692.23
RITM-hrnet18s [40]C+L1.541.682.604.046.484.705.982.57
FocalClick-hrnet18s [8]C+L1.481.622.664.436.793.905.252.93
Ours-hrnet18sC+L1.401.522.683.866.164.425.662.37
RITM-hrnet18 [40]C+L1.421.542.263.806.064.365.742.28
EdgeFlow-hrnet18 [15]C+L1.601.722.40--4.545.772.50
Ours-hrnet18C+L1.381.502.303.695.934.345.592.37
RITM-hrnet32 [40]C+L1.461.562.103.595.714.115.342.57
FocalClick-hrnet32 [8]C+L1.641.802.364.246.514.015.392.80
PseudoClick-hrnet32 [29]C+L-1.502.08-5.684.095.271.94
Ours-hrnet32C+L1.301.422.353.555.654.295.332.22
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.516, + 0.893, + 0.545 + ], + "angle": 0, + "content": "Table 3. Comparison results on five benchmarks. NoC@85 and NoC@90 respectively denote the number of clicks required to reach the IoU of \\(85\\%\\) and \\(90\\%\\), and lower is better for the value. C+L means the combination of COCO and LVIS." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.571, + 0.473, + 0.784 + ], + "angle": 0, + "content": "time. We demonstrate the total inference time to reach \\(90\\%\\) and \\(95\\%\\) IoU on the largest dataset SBD in Tab. 2. To save evaluation time, all models are evaluated on an NVIDIA V100 GPU. Our method spends less time reaching a predefined IoU threshold for all versions. Notably, although the number of clicks required to reach \\(90\\%\\) (NoC@90) and \\(95\\%\\) (NoC@95) IoUs is similar for FocalClick-SegB3 and Ours-SegB3, the inference time of our method is significantly lower because the computational cost of Ours-SegB3 from the second click is considerably lower than FocalClick-SegB3. And the gap between our method and FocalClick is larger when the threshold changes from \\(90\\%\\) to \\(95\\%\\). Thus, our method is more suitable for challenging images and scenarios where we want to get a high IoU." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.81, + 0.471, + 0.902 + ], + "angle": 0, + "content": "Performance Comparison. We compare our method with existing methods on five benchmarks in Tab. 3. Some methods use the SBD [16] dataset to train their network, while RITM suggests training on COCO [25] and LVIS [14]. We report the results of our method equipped with different base segmentation networks and trained on different" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.571, + 0.895, + 0.723 + ], + "angle": 0, + "content": "datasets. Compared with some early methods like CD-Net [7] and f-BRS [39], different versions of our method show superior performance and efficiency. Compared with recent state-of-the-art methods RITM [40], FocalClick [8], FocusCut [26], PseudoClick [29], and TransClick [11], our method demonstrates competitive performance. Especially, our method achieves outstanding performance on the largest SBD dataset. Overall, the proposed method demonstrates preferable performance considering that the inference time is significantly low from the second click." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.739, + 0.663, + 0.755 + ], + "angle": 0, + "content": "4.3. Method analysis" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Ablation study. We conduct ablation studies to verify the effectiveness of each component in our method. The results on three challenging datasets in presented in Tab. 4. We first construct a network with only a simple convolutional mask correction network as our baseline. The first point is not fed to the base segmentation network (HRNet18s) in this baseline. As shown in Tab. 4, a simple mask correction network can hardly achieve high performance. The input of the first click to the base segmentation network helps" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "22779" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.088, + 0.089, + 0.46, + 0.216 + ], + "angle": 0, + "content": "
1st ClickCorrSelf-AttTSDAVIS NoC@90SBD NoC@90Pascal NoC@90
7.118.324.38
✓6.986.833.19
✓✓6.326.303.09
✓✓6.026.332.98
✓✓✓5.866.242.89
✓✓✓✓5.666.162.84
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.226, + 0.47, + 0.298 + ], + "angle": 0, + "content": "Table 4. Ablation study on three challenging benchmarks. HR-Net18s is used as the base segmentation network. 1st Click denotes that we input the first click to the base segmentation network, Corr denotes the correlation module, Self-Att denotes the self-attention module, and TS denotes the template selection module." + }, + { + "type": "table", + "bbox": [ + 0.092, + 0.313, + 0.457, + 0.419 + ], + "angle": 0, + "content": "
Negative TemplatesDAVIS NoC@90SBD NoC@90Pascal NoC@90
Correlation Module✓6.106.393.01
6.096.262.96
Self-Attention Module✓6.046.553.22
5.926.292.99
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.43, + 0.468, + 0.459 + ], + "angle": 0, + "content": "Table 5. The performance of the correlation and self-attention modules with and without the adoption of the negative templates." + }, + { + "type": "image", + "bbox": [ + 0.084, + 0.476, + 0.465, + 0.621 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.632, + 0.47, + 0.675 + ], + "angle": 0, + "content": "Figure 3. Illustration of the positive/negative score maps for template selection and positive/negative correlation similarity maps in click-guided correlation module." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.704, + 0.47, + 0.87 + ], + "angle": 0, + "content": "extract target-aware features to boost the performance. However, the performance is still relatively low. Both the introduction of the click-guided self-attention module and the click-guided correlation module bring significant improvements over the simple mask correction network, indicating that they both effectively exploit the click information. Their combination achieves the best performance, showing that they learn complementary augmented features and can be combined to boost performance. The template selection module further improves performance by sampling several templates to enrich the click features." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.886, + 0.47, + 0.902 + ], + "angle": 0, + "content": "The necessity of negative templates. All positive and" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.258 + ], + "angle": 0, + "content": "negative templates are input to the self-attention and correlation modules. The adoption of positive templates is a natural choice since they contain rich information regarding the target. However, the negative templates are also vital since negative clicks are often selected in distractor areas, and they contain information that can discriminate the target from the background. Tab. 5 demonstrates the performance of the two modules with and without the negative templates. The employment of the negative templates effectively improves the performance of both the correlation and self-attention modules." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.278, + 0.892, + 0.55 + ], + "angle": 0, + "content": "Qualitative analysis. We show the change of the positive/negative score maps for template selection and positive/negative correlation similarity maps in Fig. 3. After placing the first positive click, the model predicts an erroneous area that shows high semantic similarity to the target. After placing two more negative clicks in the erroneous area, the model successfully segments the target. In the interactive process, the score maps change with the clicks and can effectively discriminate the areas of the target of interest and other objects, which helps select meaningful and correct templates. The change in the correlation similarity maps shows that we can learn the target contours by correlating the templates with the feature maps. Fig. 3 only shows the similarity maps of two templates. Since we select several templates, the correlation results provide rich information to discriminate the target from other areas. Directly employing the correlation results as features helps better segment the target." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.57, + 0.892, + 0.676 + ], + "angle": 0, + "content": "Limitation analysis. Our method still requires a relatively high computational cost in the first click, which may not be suitable for some simple annotation scenarios where only one or two clicks are needed. Maybe this can be solved by reducing the resolution of the base segmentation network as in FocalClick [8] and locally updating the mask with the mask correlation network. We leave this for future research." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.705, + 0.619, + 0.72 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.735, + 0.892, + 0.901 + ], + "angle": 0, + "content": "In this paper, we propose an efficient EMC-Click method for click-based interactive segmentation. A lightweight mask correction network is constructed to iteratively update the mask, which significantly reduces the computational cost from the second click. A click-guided correlation module and a click-guided self-attention module are proposed to effectively exploit the click information to boost the performance of the mask correction network. Experiments on five benchmarks demonstrate that our method achieves competitive performance and higher efficiency compared with state-of-the-art methods." + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "22780" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.175, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.115, + 0.468, + 0.157 + ], + "angle": 0, + "content": "[1] Eirikur Agustsson, Jasper RR Uijlings, and Vittorio Ferrari. Interactive full image segmentation by considering all regions jointly. In CVPR, pages 11622-11631, 2019. 1" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.157, + 0.468, + 0.198 + ], + "angle": 0, + "content": "[2] Junjie Bai and Xiaodong Wu. Error-tolerant scribbles based interactive image segmentation. 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Intention-aware feature propagation network for interactive segmentation. arXiv:2203.05145, 2022. 3" + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.946, + 0.52, + 0.957 + ], + "angle": 0, + "content": "22782" + } + ] +] \ No newline at end of file diff --git a/2023/Efficient Mask Correction for Click-Based Interactive Image Segmentation/0a4cc1dd-64c3-44d2-8dfa-4f17be83df54_origin.pdf b/2023/Efficient Mask Correction for Click-Based Interactive Image Segmentation/0a4cc1dd-64c3-44d2-8dfa-4f17be83df54_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..e1770da8cc18e28691b44cfc3d01fe1e792b6413 --- /dev/null +++ b/2023/Efficient Mask Correction for Click-Based Interactive Image Segmentation/0a4cc1dd-64c3-44d2-8dfa-4f17be83df54_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:503aede08429f5ae3a7c62bd49fc6dd94c4dfa2bc66ab8fd69db771f6f30bd70 +size 2704321 diff --git a/2023/Efficient Mask Correction for Click-Based Interactive Image Segmentation/full.md b/2023/Efficient Mask Correction for Click-Based Interactive Image Segmentation/full.md new file mode 100644 index 0000000000000000000000000000000000000000..ff5d52f7e07865325ebdafa1c9649e20b5fa81fb --- /dev/null +++ b/2023/Efficient Mask Correction for Click-Based Interactive Image Segmentation/full.md @@ -0,0 +1,271 @@ +# Efficient Mask Correction for Click-Based Interactive Image Segmentation + +Fei Du, Jianlong Yuan, Zhibin Wang, Fan Wang Alibaba Group + +{dufei.cf, gongyuan.yjl, zhibin.waz, fan.w}@alibaba-inc.com + +# Abstract + +The goal of click-based interactive image segmentation is to extract target masks with the input of positive/negative clicks. Every time a new click is placed, existing methods run the whole segmentation network to obtain a corrected mask, which is inefficient since several clicks may be needed to reach satisfactory accuracy. To this end, we propose an efficient method to correct the mask with a lightweight mask correction network. The whole network remains a low computational cost from the second click, even if we have a large backbone. However, a simple correction network with limited capacity is not likely to achieve comparable performance with a classic segmentation network. Thus, we propose a click-guided self-attention module and a click-guided correlation module to effectively exploits the click information to boost performance. First, several templates are selected based on the semantic similarity with click features. Then the self-attention module propagates the template information to other pixels, while the correlation module directly uses the templates to obtain target outlines. With the efficient architecture and two click-guided modules, our method shows preferable performance and efficiency compared to existing methods. The code will be released at https://github.com/feiaxyt/EMC-Click. + +# 1. Introduction + +Interactive image segmentation aims to select the object of interest with minimal iterative interactions, which can benefit various computer vision tasks, such as semantic segmentation [30], instance segmentation [17], and medical image analysis [28]. As the success of these tasks often requires large-scale mask-level annotations and it is time-consuming to annotate the image manually, interactive segmentation is an attractive way to simplify the annotation process and alleviate the annotation cost. + +Different interaction strategies have been studied to simplify the interactive process, including bounding boxes [23, 37, 48], clicks [33, 40, 47], scribbles [1, 2], boundary + +![](images/432df18341de00bb3b099453c2cc7530ba416a9d5665ac997eebaec2382b7a9c.jpg) +Figure 1. Comparison between the architectures of our method and classic methods. Classic methods run the segmentation network in every iteration, which is inefficient if a large network is adopted. We update the mask via a lightweight mask correction network, enabling an efficient interaction. + +points [32], and extreme points [34]. However, due to the complexity of the object boundary and appearance, the performance of methods based on bounding boxes may drop if the bounding boxes are not tightly drawn [48]. Besides, it requires more effort to identify the object boundary and place bounding boxes, boundary points, or extreme points on the image. In contrast, the click-based method only requires the users to progressively place positive and negative clicks on the foreground and background areas, respectively. It has recently attracted more attention due to its simplicity and well-established training and evaluation protocols [40, 47]. Hence, we focus on the click-based method. + +In click-based interactive segmentation methods, the model returns a corrected prediction mask after each click from the users. Efficiency is of great importance to interactive segmentation methods since a typical segmentation process requires several interactive iterations. In recent years, deep learning-based interactive segmentation methods have achieved considerably better performance compared to traditional methods. However, some recent works [20, 22, 39] achieve state-of-the-art performance by employing inference-time optimization to refine the masks, which significantly increases the computational cost. To + +eliminate online optimization, RITM [40] investigates different designs for interactive segmentation and achieves state-of-the-art results with a classic segmentation network. To improve efficiency, FocalClick [8] proposes target crop and focus crop strategies to segment two selected local regions efficiently. Most click-based methods [7, 8, 27, 31, 40, 47] iteratively run the whole segmentation network to update the masks with the input of user clicks, which is time-consuming especially when we have a strong segmentation network. Majumder et al. [32] proposes to refine the mask with a lightweight refinement network. However, the network requires the user to place boundary points, which is not user-friendly. Therefore, more efficient click-based interactive segmentation methods are still required to reach a better trade-off between performance and efficiency. + +With the above consideration, in this work, we develop an efficient click-based interactive segmentation model based on an Efficient Mask Correction network (EMC-Click). The model consists of a base segmentation network and a lightweight mask correction network. The base network takes the first click as input and outputs target-aware features and a coarse prediction. The mask correction network iteratively updates the prediction whenever a new click is placed. The difference between our network and the classic network is shown in Fig. 1. This decoupled design ensures that the computational cost of each iteration is relatively low from the second click. However, using a simply designed mask correction network to update the prediction can hardly achieve comparable performance with classic methods that use a strong segmentation network. Thus, we propose two feature augmentation modules, including a click-guided self-attention module and a click-guided correlation module, to effectively exploit the click information to augment the features in the mask correction network. We first extract the click features and enrich them by selecting several template features based on the semantic similarity between the clicks and other pixels. The self-attention module propagates the information of the template features to other pixels, and the correlation model directly learns target contours. Both modules effectively and efficiently augment the features and improve the segmentation performance. Experiments on five benchmarks demonstrate that our method achieves competitive performance and higher efficiency compared with state-of-the-art click-based interactive segmentation methods. + +Our contribution can be summarized as follows: + +- We propose EMC-Click, an efficient click-based interactive method, to correct the masks via a lightweight mask correction network interactively. Our method significantly reduces computational cost from the second click especially when we have a large backbone. +- We propose two feature augmentation modules to im + +prove the segmentation accuracy by effectively exploiting the click information. + +- We build EMC-Click on different base segmentation networks and evaluate our models on several benchmarks. The results show that our method achieves preferable performance and efficiency compared to state-of-the-art methods. + +# 2. Related works + +# 2.1. Interactive image segmentation + +Interactive image segmentation is a longstanding research topic in computer vision. In the early years, methods based on optimization on a graph over image pixels were the mainstream. GrabCut [37] is a classic method that extend [5] to an iterative energy minimization problem. Methods based on random walk [13,21] build an undirected graph on the image to estimate the probability of each pixel. Since early methods use handcrafted features, they can hardly generalize to complex scenes. + +Deep learning has been applied in many fields due to its high representation power and the ability to model complex structures. Xu et al. [47] are the first to propose a CNN-based interactive segmentation method. They encode the positive/negative clicks as positive/negative distance maps and concatenate them with the image to feed them into the network. They also design strategies to sample clicks for training, which are adopted by many subsequent works [8, 15, 40]. Later, Mahadevan et al. [31] add an iterative sampling strategy on [47] during training. BRS [20] proposes optimizing the network online based on user-specified location information during the annotation process. f-BRS [39] accelerates BRS [20] by optimizing a small part of the network. Recently, RITM [40] conducts comprehensive experiments to investigate the design principle of an end-to-end click-based interactive segmentation method. Although the click-based method is the mainstream due to its simplicity and well-established training and evaluation protocols, other interactive methods are also exploited, such as extreme points [34], boundary points [32], and bounding boxes [46]. Despite the impressive progress made by deep learning-based methods, most of them suffer from a high computational cost especially when they have a strong backbone like ResNet101 [18]. + +# 2.2. Mask refinement in interactive segmentation + +Mask refinement is commonly used in interactive segmentation to get fine-level results. They often follow the coarse-to-fine schema and crop a local region to make local corrections. For example, RIS-Net [24] samples multiple regions based on the click positions for local refinement. + +![](images/da493adfb7b4825f87f46ce03eaa3866b53cd96ae2b5b26c8b10eec825a45f2e.jpg) + +![](images/9508ab7d2201089c732dcd4bd1f5cff842e86a7d82dfc79e7f1dc4588b016ae0.jpg) +Figure 2. The framework of the proposed EMC-Click. We adopt a base segmentation network to extract target-aware features and make the first prediction by taking the first click as input. The mask correction network is responsible for updating the mask when a new click is placed. In this mask correction network, we first map the click location to the feature map and extract the click features. Then we sample several template features that are similar to the click features. The click-guided self-attention module propagates the template information to other pixels, while the click-guided correlation module extracts target outlines via the correlation between the templates and the feature map. Both modules augment the features, and the combined features are used to predict the mask. + +FocalClick [8] crops a region based on the difference between the previous mask and the coarsely predicted mask to refine the details. Zhang et al. [50] refines a local area centered on the target based on the coarse segmentation results. There are also methods to refine the global mask, such as EdgeFlow [15] and $99\%$ AccuracyNet [12]. One common property of these refinement methods is that they run the whole segmentation and refinement networks to get the results in each interactive iteration. It is too costly compared with a simple feedforward segmentation network. FocusCut [26] trains a segmentation network to not only segment the target object but also refine local details. However, it is still not efficient enough to run the whole segmentation network in each iteration. Our mask correction network is somewhat like a refinement network. The difference is that we directly use this network to correct masks when a new click is placed, and the base segmentation network only runs for the first click. This architecture reduces the inference time significantly compared with traditional methods. + +# 2.3. Exploitation of click information + +The clicks provide key information for locating the foreground and background areas. Most methods encode the clicks as click maps where the regions around the clicks are highlighted. However, the click information is not explicitly exploited. To better exploit the click information, CDNet [7] propagates the click information to other pixels via two non-local networks [43]. It constructs weight maps based on the click locations to re-weight the affinity matrix, which is not computational efficiency since it needs to model the affinity between every two pixels. IFPN [50] + +learns a sparse graph model to perform click feature propagation. It only models the dependencies between the clicks and other pixels. Inspired by the two methods, we construct a multi-head self-attention module to propagate the click information to other pixels. Different from CDNet and IFPN, we select several templates to enrich the click features. Thus, our method is more efficient compared to CDNet [7] and can exploit more information compared to IFPN [50]. Besides, we also propose a correlation module to exploit the click information explicitly. + +# 3. Proposed method + +We propose to iteratively correct the segmentation mask using a lightweight mask correction network, which exploits the information of the clicks to boost the performance via a click-guided self-attention module and a click-guided correlation module. We first briefly revisit the traditional pipeline of the interactive segmentation model, then introduce our pipeline and elaborate on the mask correction network. + +# 3.1. The standard pipeline + +Interactive segmentation is often regarded as a special type of segmentation task. Different from classic segmentation, the input of the interactive segmentation network contains not only the image but also the click maps and previously predicted mask. When segmenting the object of interest, the user decides where to place the next click based on the current segmentation mask. All positive/negative clicks are encoded as positive/negative click maps that are usual + +ally defined as distance maps [47] or binary disks [3]. The click maps are then concatenated with the image and previously predicted mask to be fed to the segmentation network. After each click, the user obtains an updated segmentation mask by running the whole segmentation network. Usually, a strong segmentation network like DeepLabv3+ [6] is required to achieve satisfactory results since the segmentation accuracy directly depends on it. However, running a strong segmentation network several times is often time-consuming, especially on low-power devices, which makes this standard pipeline inefficient in practice. + +# 3.2. Efficient pipeline + +To avoid running the whole segmentation network for each click, we build a lightweight network to correct the segmentation mask in each iteration. The pipeline is shown in Fig. 2. Our network consists of a base segmentation network and a lightweight mask correction network. As observed in FCA-Net [27], the first click is responsible for locating the target object. Thus, we input the first click into the segmentation network to generate target-aware features. When the user places the first click, the base segmentation network extracts the target-aware feature and generates a coarse mask, and the mask correction network corrects the coarse mask. Starting from the second click, we no longer run the base segmentation network. Instead, we directly feed all clicks into the mask correction network to correct the previously predicted mask. + +Specifically, we denote the input image as $I$ and the click set at the $t$ -th iteration as $C^t$ . The base segmentation network takes the input image and the first click $C^1$ as input and generates target-aware features $F_{t}$ and a coarse mask $M_{c}$ , which can be formulated as follows, + +$$ +F _ {t}, M _ {c} = \Phi_ {S} (I, E n c \left(C ^ {1}\right); \theta_ {s}), \tag {1} +$$ + +where $Enc$ denotes the click encoding function, and $\Phi_S$ and $\theta_s$ denote the base segmentation network and its parameters, respectively. In this work, we adopt disks with a small radius [3,40] to encode the clicks. The mask correction network takes the click set $C^t$ , the target-aware feature $F_t$ , the original image $I$ , and the previously predicted mask $M^{t-1}$ as input and outputs an updated mask, which can be written as follows, + +$$ +M ^ {t} = \Phi_ {R} (I, E n c \left(C ^ {t}\right), M ^ {t - 1}, F _ {t}; \theta_ {r}), \tag {2} +$$ + +where $\Phi_R$ and $\theta_r$ denote the mask correction network and its parameters, respectively. For the first click (i.e. $t = 1$ ), the previous mask $M^0$ input to the mask correction network is equal to the coarse mask $M_c$ . The mask correction network can also take as input a preexisting mask generated from other forms of pre-processing. + +Note that our pipeline differs from FCA-Net [27] which also treats the first click differently from other clicks. Our + +network only runs the mask correction network after the first click, while FCA-Net still needs to run the whole network for each click. + +# 3.3. Efficient and effective mask correction network + +A simple mask correction network with limited parameters and computational cost can hardly achieve comparable performance with a traditional segmentation network. Therefore, we propose to exploit the click information better to boost performance with the click-guided self-attention module and the click-guided correlation module. Before performing correlation and self-attention, we first concatenate the image, positive/negative click maps, and previous mask to extract the low-level features $F_{l}$ from them. We also adjust the channel number of target-aware features $F_{t}$ via a convolutional layer with a kernel size of $1 \times 1$ . Then we concatenate $F_{l}$ with $F_{t}$ from the backbone to learn the fused features $F_{u}$ . + +To exploit the click information, we map the location of clicks onto the feature maps and extract the features with a shape of $1 \times 1 \times C$ for each click, where $C$ is the number of channels. These click features are regarded as templates. The click-guided self-attention module propagates the information of these templates to other locations via multi-head attention, while the click-guided correlation attention module uses them to learn target outlines via correlation. Since the number of clicks used to obtain a satisfactory segmentation accuracy is often less than 20, it may not be sufficient only to extract templates from the location of clicks. Thus, we first enrich the templates by selecting some informative locations based on their semantic similarity to the clicks. + +Template selection. The strategy to select templates is based on the observation that pixels on the same object show higher similarity than pixels from different objects. We separately select positive and negative templates by identifying pixels that are more likely to be the object and the background, respectively. To select positive templates, we assign a score for each pixel to indicate the likelihood of being the object and select the top $K_{p}$ pixels. The score is calculated by considering three factors: the similarity to positive clicks, the similarity to negative clicks, and the distance from the positive clicks. A pixel with a short distance and a high similarity to one of the positive clicks and a low similarity to one of the negative clicks is more likely to be located in the object region and vice versa. We use the Cosine similarity between features of two pixels to measure their similarity and the Euclidean distance to measure the distance. Let $H_{f} \times W_{f}$ denote the size of the feature map, where $H_{f}$ and $W_{f}$ are respectively the height and width, and we can obtain a positive score map $O_{p} \in \mathbb{R}^{H_{f} \times W_{f}}$ as + +follows, + +$$ +O _ {p} = \left(V _ {p} + \left(1 - V _ {n}\right)\right) * \left(1 - D _ {p}\right), \tag {3} +$$ + +where $V_{p}\in \mathbb{R}^{H_{f}\times W_{f}}$ and $V_{n}\in \mathbb{R}^{H_{f}\times W_{f}}$ respectively denote the positive and negative Cosine similarity maps, and $D_{p}\in \mathbb{R}^{H_{f}\times W_{f}}$ denotes the normalized distance map. Note that the similarity scores $V_{p}^{u,v} / V_{n}^{u,v}$ respectively represent the maximum similarity between the pixel $(u,v)$ and positive/negative clicks, while $D_p^{u,v}$ represents the normalized minimum distance between $(u,v)$ and positive clicks. Similarly, we can obtain a negative score map $O_{n}$ by + +$$ +O _ {n} = \left(V _ {n} + \left(1 - V _ {p}\right)\right) * \left(1 - D _ {n}\right), \tag {4} +$$ + +where $D_{n}$ denotes the normalized negative distance map, which measures the normalized minimum distance between each pixel and negative clicks. After obtaining the score maps, we select positive templates from the top $K_{p}$ locations of the positive score map and $K_{n}$ negative templates from the top $K_{n}$ locations of the negative score map. The positive and negative template features are represented as $F_{pt} \in \mathbb{R}^{K_p \times C}$ and $F_{nt} \in \mathbb{R}^{K_n \times C}$ , respectively. + +Click-guided self-attention. Our first way to exploit the click information is to propagate their information to other pixels via a self-attention module. Multi-head attention is widely used in computer vision to capture long-range dependencies among different pixels [9, 19]. We adopt the standard $qkv$ multi-head attention [41] to augment the representation of each pixel with the selected templates. Multi-head attention helps each pixel attend to the templates, which is beneficial to the identification of the target. To perform multi-head attention, we first reshape the feature $F_{u}$ to a size of $H_{f}W_{f}\times C$ , then we learn the self-attention-based augmented feature $F_{s}$ by + +$$ +F _ {s} = F _ {u} + \text {A t t e n t i o n} (Q, K, V), \tag {5} +$$ + +$$ +Q = \phi_ {Q} \left(F _ {u}\right), K = \phi_ {K} \left(F _ {p n t}\right), V = \phi_ {V} \left(F _ {p n t}\right), \tag {6} +$$ + +where $\phi_{Q},\phi_{K}$ , and $\phi_V$ are linear transformations, and $F_{pnt}$ is the concatenation of positive templates $F_{pt}$ and negative templates $F_{nt}$ . $F_{s}$ is further reshaped to $H_{f}\times W_{f}\times C$ As the template features are selected from $F_{u}$ , and the attention is guided by the click information, we denote this attention module as a click-guided self-attention module. + +Click-guided correlation. To further exploit the click information, we propose a click-guided correlation attention module to learn the contour of the object of interest explicitly. Correlation is widely used in the Siamese object tracking archietecture [4] to locate the position of the target in a search area. Siamese tracking calculates similarity maps between a target template and the search area. In video object segmentation, RANet [44] treats target features from + +the first frame as the template to learn pixel-wise similarity maps. In RANet, pixel-wise correlation is shown to be able to learn the contour of the target with the target features as templates. In this work, we extract target semantic features based on the location of the clicks and employ the pixel-wise correlation to learn target outlines to improve the segmentation performance. For the $j$ -th positive template feature $F_{pt}^{j}\in \mathbb{R}^{1\times C}$ , we can get a similarity map via the correlation between it and $F_{u}\in \mathbb{R}^{H_{f}W_{f}\times C}$ . Thus, we have + +$$ +S _ {p} = \left\{S _ {p} ^ {j} \mid S _ {p} ^ {j} = \phi_ {q} \left(F _ {p t} ^ {j}\right) * \phi_ {k} \left(F _ {u}\right) \right\} _ {j \in \{1, \dots , K _ {p} \}}, \tag {7} +$$ + +$$ +S _ {n} = \left\{S _ {n} ^ {j} \mid S _ {n} ^ {j} = \phi_ {q} \left(F _ {n t} ^ {j}\right) * \phi_ {k} \left(F _ {u}\right) \right\} _ {j \in \{1, \dots , K _ {n} \}}, \tag {8} +$$ + +where $*$ denotes the correlation operation, $S_{p}$ and $S_{n}$ respectively denote the set of positive and negative correlation similarity maps, and $\phi_q$ and $\phi_k$ denote two linear transformations. We then transform the positive/negative similarity maps into features for segmentation via a shared convolutional layer. Then positive and negative features are concatenated and followed by the second convolutional layer to fuse them. In this manner, we get the correlation-based augmented feature $F_{c}$ as follows, + +$$ +F _ {c} = \phi_ {f} (\operatorname {C o n c a t} \left(\phi_ {s} \left(S _ {p}\right), \phi_ {s} \left(S _ {n}\right)\right)), \tag {9} +$$ + +where $\phi_s$ and $\phi_f$ denote two convolutional layers. + +After learning the two augmented features $F_{s}$ and $F_{c}$ , we concatenate them and use four convolutional layers to predict the segmentation mask. Our mask correction network is efficient since the resolution of the features is just 1/4 of the image, and the whole structure is lightweight. It is also effective since the click information is exploited explicitly via two modules to improve performance. + +# 4. Experiments + +# 4.1. Experimental Configuration + +Implementation details. Our pipeline can be built on different existing segmentation networks. Following FocalClick [8], we choose HRNet+OCR [42, 49] and SegFormer [45] series as our base segmentation networks to show the effectiveness of the proposed method. For lightweight models like SegFormerB0 and HRNet18s, the mask correction network first transforms the number of backbone feature channels to 64. For larger models like SegFormerB3, HRNet18, and HRNet32, the channel is transformed to 96. The number of selected templates $K_{p}$ and $K_{n}$ is set to be equal to the channel number. + +We train our model on a combination of COCO [25] and LVIS [14] datasets, following RITM [40]. For a fair comparison of some previous methods, we also report the performance of our model trained on SBD [16]. We use the normalized focal loss [38] for both the base segmentation + +
MethodParams/MBFLOPs/GSpeed/ms
CDNet-ResNet34384 [7]23.556.73339
f-BRS-ResNet50400 [39]31.484.62373
RITM-hrnet18s400 [40]4.228.96634
RITM-hrnet18400 [40]10.015.41103
RITM-hrnet32400 [40]31.040.41635
Flickr-hrnet18s256 [8]4.233.82358
Flickr-hrnet32256 [8]31.017.1728
Flickr-SegB0256 [8]3.741.94207
Flickr-SegB3256 [8]45.612.9805
Ours-hrnet18s-FirstClick3844.339.35752
Ours-hrnet18-FirstClick38410.315.31237
Ours-hrnet32-FirstClick38431.240.51745
Ours-SegB0-FirstClick3843.845.38528
Ours-SegB3-FirstClick38445.932.32006
Ours-MaskCorrection-C643840.111.09183
Ours-MaskCorrection-C963840.222.25280
+ +Table 1. Comparison of the computational cost for different methods. The speed represents the average inference time per click and is measured on a CPU laptop with $2\mathrm{GHz}$ , $4\times$ Intel Core i5. From the second click, we only run the mask correction network, significantly reducing the inference time compared to other methods. + +and mask correction networks. We adopt the iterative training strategy [31] by randomly sampling the first positive click in the target area and progressively adding clicks based on the errors in the network's predictions during training. Our lightweight mask correction network enables efficient iterative training. We use the Adam optimizer with $\beta_{1} = 0.9$ and $\beta_{2} = 0.999$ to train the network. As in FocalClick [8], we sample 30000 images in one epoch and train our model for 230 epochs. We use an initial learning rate of $1e - 3$ for the HRNet+OCR series and $2e - 3$ for the SegFormer series, and decay them by ten times on the 200th and 220th epochs. We train the network with an image size of $320\times 480$ and a batch size of 64. We add data augmentation strategies, including random resizing in a range of [0.75, 1.40], horizontal flip, random jittering of brightness, contrast, and RGB values. All our models are implemented in Python using Pytorch. + +Evaluation datasets and metrics. We evaluate our method on five commonly used datasets, including GrabCut [37], Berkeley [35], DAVIS [36], SBD [16], and Pascal VOC [10]. The GrabCut dataset contains 50 images with one single target in each image. The test set of the Berkeley dataset contains 100 object masks for 96 images. The DAVIS dataset is originally constructed for the evaluation of video object segmentation methods. We sample 345 frames to evaluate our method as in [8,40]. The SBD dataset is the largest and has been widely used to evaluate the interactive segmentation methods since [47]. It contains 6671 object + +
NoC@90Time@90NoC@95Time@95
FocalClick-hrnet18s6.7934min12.7862min
FocalClick-hrnet326.5149min12.5085min
FocalClick-SegB06.8623min12.7339min
FocalClick-SegB35.5934min11.5563min
Ours-hrnet18s6.1619min12.4730min
Ours-hrnet325.6521min11.9032min
Ours-SegB06.2116min12.4527min
Ours-SegB35.5720min11.6529min
+ +Table 2. Comparison of the total inference time to reach different IoU thresholds on the largest SBD dataset. The time is measured on an NVIDIA V100 GPU. + +masks for 2820 images. The validation set of the Pascal VOC dataset is also used, which consists of 1449 images with 3427 object masks. + +We use the commonly used evaluation protocol to make a fair comparison. During the evaluation, the clicks are simulated based on the difference between the current prediction and the ground truth. The first click is placed in the center of the target, and other clicks are placed in the center of the largest erroneous region. Following [26], the image is resized to a fixed length of 384 as the short side during evaluation. We use the standard Number of Clicks (NoC) metric to compare different methods. The NoC measures the number of clicks required to reach a predefined Intersection over Union (IoU) threshold between the predicted mask and the ground truth. Following most methods, the thresholds of $85\%$ and $90\%$ are used, and the metrics are denoted as NoC@85 and NoC@90. + +# 4.2. Comparison with state-of-the-art methods + +Computational comparison. We compare the parameters, FLOPs, and inference speed on CPUs of representative methods in Tab. 1. MaskCorrection-C64 denotes that we set the channel of the mask correction network to 64, which is used for HRNet18s and SegFormerB0. MaskCorrection-C96 is used for HRNet18, HRNet32, and SegFormerB3. The computational cost of our method is different between the first click and other clicks. For the first click, our method needs to run the base segmentation network and the mask correction network, resulting in slightly higher inference time compared with RITM [40]. However, our method shows higher efficiency from the second click even compared with FocalClick [8] which uses a small resolution since our mask correction network is lightweight. The computational cost of the mask correction network will not change with the base segmentation network if we fix the configuration, which is a good property since we can use a stronger segmentation network to reduce the number of interactions without a significant increase in the inference + +
MethodsGrabCutBerkeleySBDDAVISPascal
Train DataNoC@85NoC@90NoC@90NoC@85NoC@90NoC@85NoC@90NoC@90NoC@85
f-BRS-B-ResNet50 [39]SBD2.502.984.345.068.085.397.81
CDNet-ResNet50 [7]SBD2.222.643.694.377.875.176.66-
FocusCut-ResNet50 [26]SBD1.601.783.443.625.665.006.38-
FocalClick-hrnet18s [8]SBD1.862.063.144.306.524.926.48-
RITM-hrnet18 [40]SBD1.762.043.223.395.434.946.71-
Ours-hrnet18sSBD1.821.923.263.585.795.236.882.47
Ours-hrnet18SBD1.741.843.033.385.515.056.712.37
TransClick-segformerB4 [11]C+L1.521.601.603.445.633.685.062.08
FocalClick-segformerB0 [8]C+L1.401.662.274.566.864.045.492.97
Ours-segformerB0C+L1.561.642.403.956.214.485.532.65
FocalClick-segformerB3 [8]C+L1.441.501.923.535.593.614.902.46
Ours-segformerB3C+L1.421.482.353.445.574.495.692.23
RITM-hrnet18s [40]C+L1.541.682.604.046.484.705.982.57
FocalClick-hrnet18s [8]C+L1.481.622.664.436.793.905.252.93
Ours-hrnet18sC+L1.401.522.683.866.164.425.662.37
RITM-hrnet18 [40]C+L1.421.542.263.806.064.365.742.28
EdgeFlow-hrnet18 [15]C+L1.601.722.40--4.545.772.50
Ours-hrnet18C+L1.381.502.303.695.934.345.592.37
RITM-hrnet32 [40]C+L1.461.562.103.595.714.115.342.57
FocalClick-hrnet32 [8]C+L1.641.802.364.246.514.015.392.80
PseudoClick-hrnet32 [29]C+L-1.502.08-5.684.095.271.94
Ours-hrnet32C+L1.301.422.353.555.654.295.332.22
+ +Table 3. Comparison results on five benchmarks. NoC@85 and NoC@90 respectively denote the number of clicks required to reach the IoU of $85\%$ and $90\%$ , and lower is better for the value. C+L means the combination of COCO and LVIS. + +time. We demonstrate the total inference time to reach $90\%$ and $95\%$ IoU on the largest dataset SBD in Tab. 2. To save evaluation time, all models are evaluated on an NVIDIA V100 GPU. Our method spends less time reaching a predefined IoU threshold for all versions. Notably, although the number of clicks required to reach $90\%$ (NoC@90) and $95\%$ (NoC@95) IoUs is similar for FocalClick-SegB3 and Ours-SegB3, the inference time of our method is significantly lower because the computational cost of Ours-SegB3 from the second click is considerably lower than FocalClick-SegB3. And the gap between our method and FocalClick is larger when the threshold changes from $90\%$ to $95\%$ . Thus, our method is more suitable for challenging images and scenarios where we want to get a high IoU. + +Performance Comparison. We compare our method with existing methods on five benchmarks in Tab. 3. Some methods use the SBD [16] dataset to train their network, while RITM suggests training on COCO [25] and LVIS [14]. We report the results of our method equipped with different base segmentation networks and trained on different + +datasets. Compared with some early methods like CD-Net [7] and f-BRS [39], different versions of our method show superior performance and efficiency. Compared with recent state-of-the-art methods RITM [40], FocalClick [8], FocusCut [26], PseudoClick [29], and TransClick [11], our method demonstrates competitive performance. Especially, our method achieves outstanding performance on the largest SBD dataset. Overall, the proposed method demonstrates preferable performance considering that the inference time is significantly low from the second click. + +# 4.3. Method analysis + +Ablation study. We conduct ablation studies to verify the effectiveness of each component in our method. The results on three challenging datasets in presented in Tab. 4. We first construct a network with only a simple convolutional mask correction network as our baseline. The first point is not fed to the base segmentation network (HRNet18s) in this baseline. As shown in Tab. 4, a simple mask correction network can hardly achieve high performance. The input of the first click to the base segmentation network helps + +
1st ClickCorrSelf-AttTSDAVIS NoC@90SBD NoC@90Pascal NoC@90
7.118.324.38
✓6.986.833.19
✓✓6.326.303.09
✓✓6.026.332.98
✓✓✓5.866.242.89
✓✓✓✓5.666.162.84
+ +Table 4. Ablation study on three challenging benchmarks. HR-Net18s is used as the base segmentation network. 1st Click denotes that we input the first click to the base segmentation network, Corr denotes the correlation module, Self-Att denotes the self-attention module, and TS denotes the template selection module. + +
Negative TemplatesDAVIS NoC@90SBD NoC@90Pascal NoC@90
Correlation Module✓6.106.393.01
6.096.262.96
Self-Attention Module✓6.046.553.22
5.926.292.99
+ +Table 5. The performance of the correlation and self-attention modules with and without the adoption of the negative templates. + +![](images/1650afc9121aaa13cb26562151a851cc12b72f27328bc0246e93dcf9e378224e.jpg) +Figure 3. Illustration of the positive/negative score maps for template selection and positive/negative correlation similarity maps in click-guided correlation module. + +extract target-aware features to boost the performance. However, the performance is still relatively low. Both the introduction of the click-guided self-attention module and the click-guided correlation module bring significant improvements over the simple mask correction network, indicating that they both effectively exploit the click information. Their combination achieves the best performance, showing that they learn complementary augmented features and can be combined to boost performance. The template selection module further improves performance by sampling several templates to enrich the click features. + +The necessity of negative templates. All positive and + +negative templates are input to the self-attention and correlation modules. The adoption of positive templates is a natural choice since they contain rich information regarding the target. However, the negative templates are also vital since negative clicks are often selected in distractor areas, and they contain information that can discriminate the target from the background. Tab. 5 demonstrates the performance of the two modules with and without the negative templates. The employment of the negative templates effectively improves the performance of both the correlation and self-attention modules. + +Qualitative analysis. We show the change of the positive/negative score maps for template selection and positive/negative correlation similarity maps in Fig. 3. After placing the first positive click, the model predicts an erroneous area that shows high semantic similarity to the target. After placing two more negative clicks in the erroneous area, the model successfully segments the target. In the interactive process, the score maps change with the clicks and can effectively discriminate the areas of the target of interest and other objects, which helps select meaningful and correct templates. The change in the correlation similarity maps shows that we can learn the target contours by correlating the templates with the feature maps. Fig. 3 only shows the similarity maps of two templates. Since we select several templates, the correlation results provide rich information to discriminate the target from other areas. Directly employing the correlation results as features helps better segment the target. + +Limitation analysis. Our method still requires a relatively high computational cost in the first click, which may not be suitable for some simple annotation scenarios where only one or two clicks are needed. Maybe this can be solved by reducing the resolution of the base segmentation network as in FocalClick [8] and locally updating the mask with the mask correlation network. We leave this for future research. + +# 5. Conclusion + +In this paper, we propose an efficient EMC-Click method for click-based interactive segmentation. A lightweight mask correction network is constructed to iteratively update the mask, which significantly reduces the computational cost from the second click. A click-guided correlation module and a click-guided self-attention module are proposed to effectively exploit the click information to boost the performance of the mask correction network. 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Intention-aware feature propagation network for interactive segmentation. arXiv:2203.05145, 2022. 3 \ No newline at end of file diff --git a/2023/Efficient Mask Correction for Click-Based Interactive Image Segmentation/images.zip b/2023/Efficient Mask Correction for Click-Based Interactive Image Segmentation/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..04d38139af06a252a085bd675156d644916b8e16 --- /dev/null +++ b/2023/Efficient Mask Correction for Click-Based Interactive Image Segmentation/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:bebb0135d5cccef1bed2c3b016e8728bab3e8254cf768e2da71d24cda02bcf93 +size 517137 diff --git a/2023/Efficient Mask Correction for Click-Based Interactive Image Segmentation/layout.json b/2023/Efficient Mask Correction for Click-Based Interactive Image Segmentation/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..11bc66fa234e9024186da7f479344d5229b2bd46 --- /dev/null +++ b/2023/Efficient Mask Correction for Click-Based Interactive Image Segmentation/layout.json @@ -0,0 +1,7526 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 66, + 102, + 527, + 121 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 66, + 102, + 527, + 121 + ], + "spans": [ + { + "bbox": [ + 66, + 102, + 527, + 121 + ], + "type": "text", + "content": "Efficient Mask Correction for Click-Based Interactive Image Segmentation" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 180, + 143, + 412, + 172 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 180, + 143, + 412, + 172 + ], + "spans": [ + { + "bbox": [ + 180, + 143, + 412, + 172 + ], + "type": "text", + "content": "Fei Du, Jianlong Yuan, Zhibin Wang, Fan Wang Alibaba Group" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 136, + 173, + 455, + 185 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 136, + 173, + 455, + 185 + ], + "spans": [ + { + "bbox": [ + 136, + 173, + 455, + 185 + ], + "type": "text", + "content": "{dufei.cf, gongyuan.yjl, zhibin.waz, fan.w}@alibaba-inc.com" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 143, + 213, + 192, + 225 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 213, + 192, + 225 + ], + "spans": [ + { + "bbox": [ + 143, + 213, + 192, + 225 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 238, + 290, + 524 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 238, + 290, + 524 + ], + "spans": [ + { + "bbox": [ + 46, + 238, + 290, + 524 + ], + "type": "text", + "content": "The goal of click-based interactive image segmentation is to extract target masks with the input of positive/negative clicks. Every time a new click is placed, existing methods run the whole segmentation network to obtain a corrected mask, which is inefficient since several clicks may be needed to reach satisfactory accuracy. To this end, we propose an efficient method to correct the mask with a lightweight mask correction network. The whole network remains a low computational cost from the second click, even if we have a large backbone. However, a simple correction network with limited capacity is not likely to achieve comparable performance with a classic segmentation network. Thus, we propose a click-guided self-attention module and a click-guided correlation module to effectively exploits the click information to boost performance. First, several templates are selected based on the semantic similarity with click features. Then the self-attention module propagates the template information to other pixels, while the correlation module directly uses the templates to obtain target outlines. With the efficient architecture and two click-guided modules, our method shows preferable performance and efficiency compared to existing methods. The code will be released at https://github.com/feiaxyt/EMC-Click." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 548, + 128, + 562 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 548, + 128, + 562 + ], + "spans": [ + { + "bbox": [ + 47, + 548, + 128, + 562 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 570, + 287, + 676 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 570, + 287, + 676 + ], + "spans": [ + { + "bbox": [ + 46, + 570, + 287, + 676 + ], + "type": "text", + "content": "Interactive image segmentation aims to select the object of interest with minimal iterative interactions, which can benefit various computer vision tasks, such as semantic segmentation [30], instance segmentation [17], and medical image analysis [28]. As the success of these tasks often requires large-scale mask-level annotations and it is time-consuming to annotate the image manually, interactive segmentation is an attractive way to simplify the annotation process and alleviate the annotation cost." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 677, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 677, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 47, + 677, + 287, + 714 + ], + "type": "text", + "content": "Different interaction strategies have been studied to simplify the interactive process, including bounding boxes [23, 37, 48], clicks [33, 40, 47], scribbles [1, 2], boundary" + } + ] + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 310, + 213, + 545, + 342 + ], + "blocks": [ + { + "bbox": [ + 310, + 213, + 545, + 342 + ], + "lines": [ + { + "bbox": [ + 310, + 213, + 545, + 342 + ], + "spans": [ + { + "bbox": [ + 310, + 213, + 545, + 342 + ], + "type": "image", + "image_path": "432df18341de00bb3b099453c2cc7530ba416a9d5665ac997eebaec2382b7a9c.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 350, + 547, + 407 + ], + "lines": [ + { + "bbox": [ + 304, + 350, + 547, + 407 + ], + "spans": [ + { + "bbox": [ + 304, + 350, + 547, + 407 + ], + "type": "text", + "content": "Figure 1. Comparison between the architectures of our method and classic methods. Classic methods run the segmentation network in every iteration, which is inefficient if a large network is adopted. We update the mask via a lightweight mask correction network, enabling an efficient interaction." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 434, + 546, + 579 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 434, + 546, + 579 + ], + "spans": [ + { + "bbox": [ + 304, + 434, + 546, + 579 + ], + "type": "text", + "content": "points [32], and extreme points [34]. However, due to the complexity of the object boundary and appearance, the performance of methods based on bounding boxes may drop if the bounding boxes are not tightly drawn [48]. Besides, it requires more effort to identify the object boundary and place bounding boxes, boundary points, or extreme points on the image. In contrast, the click-based method only requires the users to progressively place positive and negative clicks on the foreground and background areas, respectively. It has recently attracted more attention due to its simplicity and well-established training and evaluation protocols [40, 47]. Hence, we focus on the click-based method." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 582, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 547, + 715 + ], + "type": "text", + "content": "In click-based interactive segmentation methods, the model returns a corrected prediction mask after each click from the users. Efficiency is of great importance to interactive segmentation methods since a typical segmentation process requires several interactive iterations. In recent years, deep learning-based interactive segmentation methods have achieved considerably better performance compared to traditional methods. However, some recent works [20, 22, 39] achieve state-of-the-art performance by employing inference-time optimization to refine the masks, which significantly increases the computational cost. To" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "22773" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "text", + "content": "eliminate online optimization, RITM [40] investigates different designs for interactive segmentation and achieves state-of-the-art results with a classic segmentation network. To improve efficiency, FocalClick [8] proposes target crop and focus crop strategies to segment two selected local regions efficiently. Most click-based methods [7, 8, 27, 31, 40, 47] iteratively run the whole segmentation network to update the masks with the input of user clicks, which is time-consuming especially when we have a strong segmentation network. Majumder et al. [32] proposes to refine the mask with a lightweight refinement network. However, the network requires the user to place boundary points, which is not user-friendly. Therefore, more efficient click-based interactive segmentation methods are still required to reach a better trade-off between performance and efficiency." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 251, + 289, + 610 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 251, + 289, + 610 + ], + "spans": [ + { + "bbox": [ + 46, + 251, + 289, + 610 + ], + "type": "text", + "content": "With the above consideration, in this work, we develop an efficient click-based interactive segmentation model based on an Efficient Mask Correction network (EMC-Click). The model consists of a base segmentation network and a lightweight mask correction network. The base network takes the first click as input and outputs target-aware features and a coarse prediction. The mask correction network iteratively updates the prediction whenever a new click is placed. The difference between our network and the classic network is shown in Fig. 1. This decoupled design ensures that the computational cost of each iteration is relatively low from the second click. However, using a simply designed mask correction network to update the prediction can hardly achieve comparable performance with classic methods that use a strong segmentation network. Thus, we propose two feature augmentation modules, including a click-guided self-attention module and a click-guided correlation module, to effectively exploit the click information to augment the features in the mask correction network. We first extract the click features and enrich them by selecting several template features based on the semantic similarity between the clicks and other pixels. The self-attention module propagates the information of the template features to other pixels, and the correlation model directly learns target contours. Both modules effectively and efficiently augment the features and improve the segmentation performance. Experiments on five benchmarks demonstrate that our method achieves competitive performance and higher efficiency compared with state-of-the-art click-based interactive segmentation methods." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 59, + 611, + 254, + 622 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 611, + 254, + 622 + ], + "spans": [ + { + "bbox": [ + 59, + 611, + 254, + 622 + ], + "type": "text", + "content": "Our contribution can be summarized as follows:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 58, + 632, + 287, + 714 + ], + "type": "list", + "angle": 0, + "index": 5, + "blocks": [ + { + "bbox": [ + 58, + 632, + 287, + 693 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 632, + 287, + 693 + ], + "spans": [ + { + "bbox": [ + 58, + 632, + 287, + 693 + ], + "type": "text", + "content": "- We propose EMC-Click, an efficient click-based interactive method, to correct the masks via a lightweight mask correction network interactively. Our method significantly reduces computational cost from the second click especially when we have a large backbone." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 58, + 701, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 701, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 58, + 701, + 287, + 714 + ], + "type": "text", + "content": "- We propose two feature augmentation modules to im" + } + ] + } + ], + "index": 4 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 324, + 72, + 545, + 97 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 324, + 72, + 545, + 97 + ], + "spans": [ + { + "bbox": [ + 324, + 72, + 545, + 97 + ], + "type": "text", + "content": "prove the segmentation accuracy by effectively exploiting the click information." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 317, + 107, + 547, + 167 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 107, + 547, + 167 + ], + "spans": [ + { + "bbox": [ + 317, + 107, + 547, + 167 + ], + "type": "text", + "content": "- We build EMC-Click on different base segmentation networks and evaluate our models on several benchmarks. The results show that our method achieves preferable performance and efficiency compared to state-of-the-art methods." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 190, + 395, + 202 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 190, + 395, + 202 + ], + "spans": [ + { + "bbox": [ + 306, + 190, + 395, + 202 + ], + "type": "text", + "content": "2. Related works" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 210, + 474, + 223 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 210, + 474, + 223 + ], + "spans": [ + { + "bbox": [ + 306, + 210, + 474, + 223 + ], + "type": "text", + "content": "2.1. Interactive image segmentation" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 229, + 545, + 337 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 229, + 545, + 337 + ], + "spans": [ + { + "bbox": [ + 304, + 229, + 545, + 337 + ], + "type": "text", + "content": "Interactive image segmentation is a longstanding research topic in computer vision. In the early years, methods based on optimization on a graph over image pixels were the mainstream. GrabCut [37] is a classic method that extend [5] to an iterative energy minimization problem. Methods based on random walk [13,21] build an undirected graph on the image to estimate the probability of each pixel. Since early methods use handcrafted features, they can hardly generalize to complex scenes." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 338, + 546, + 624 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 338, + 546, + 624 + ], + "spans": [ + { + "bbox": [ + 304, + 338, + 546, + 624 + ], + "type": "text", + "content": "Deep learning has been applied in many fields due to its high representation power and the ability to model complex structures. Xu et al. [47] are the first to propose a CNN-based interactive segmentation method. They encode the positive/negative clicks as positive/negative distance maps and concatenate them with the image to feed them into the network. They also design strategies to sample clicks for training, which are adopted by many subsequent works [8, 15, 40]. Later, Mahadevan et al. [31] add an iterative sampling strategy on [47] during training. BRS [20] proposes optimizing the network online based on user-specified location information during the annotation process. f-BRS [39] accelerates BRS [20] by optimizing a small part of the network. Recently, RITM [40] conducts comprehensive experiments to investigate the design principle of an end-to-end click-based interactive segmentation method. Although the click-based method is the mainstream due to its simplicity and well-established training and evaluation protocols, other interactive methods are also exploited, such as extreme points [34], boundary points [32], and bounding boxes [46]. Despite the impressive progress made by deep learning-based methods, most of them suffer from a high computational cost especially when they have a strong backbone like ResNet101 [18]." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 634, + 537, + 647 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 634, + 537, + 647 + ], + "spans": [ + { + "bbox": [ + 306, + 634, + 537, + 647 + ], + "type": "text", + "content": "2.2. Mask refinement in interactive segmentation" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 654, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 654, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 654, + 545, + 713 + ], + "type": "text", + "content": "Mask refinement is commonly used in interactive segmentation to get fine-level results. They often follow the coarse-to-fine schema and crop a local region to make local corrections. For example, RIS-Net [24] samples multiple regions based on the click positions for local refinement." + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "22774" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 49, + 70, + 545, + 155 + ], + "blocks": [ + { + "bbox": [ + 49, + 70, + 545, + 155 + ], + "lines": [ + { + "bbox": [ + 49, + 70, + 545, + 155 + ], + "spans": [ + { + "bbox": [ + 49, + 70, + 545, + 155 + ], + "type": "image", + "image_path": "da493adfb7b4825f87f46ce03eaa3866b53cd96ae2b5b26c8b10eec825a45f2e.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 49, + 156, + 543, + 243 + ], + "blocks": [ + { + "bbox": [ + 49, + 156, + 543, + 243 + ], + "lines": [ + { + "bbox": [ + 49, + 156, + 543, + 243 + ], + "spans": [ + { + "bbox": [ + 49, + 156, + 543, + 243 + ], + "type": "image", + "image_path": "9508ab7d2201089c732dcd4bd1f5cff842e86a7d82dfc79e7f1dc4588b016ae0.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 254, + 548, + 321 + ], + "lines": [ + { + "bbox": [ + 46, + 254, + 548, + 321 + ], + "spans": [ + { + "bbox": [ + 46, + 254, + 548, + 321 + ], + "type": "text", + "content": "Figure 2. The framework of the proposed EMC-Click. We adopt a base segmentation network to extract target-aware features and make the first prediction by taking the first click as input. The mask correction network is responsible for updating the mask when a new click is placed. In this mask correction network, we first map the click location to the feature map and extract the click features. Then we sample several template features that are similar to the click features. The click-guided self-attention module propagates the template information to other pixels, while the click-guided correlation module extracts target outlines via the correlation between the templates and the feature map. Both modules augment the features, and the combined features are used to predict the mask." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_caption" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 342, + 289, + 570 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 342, + 289, + 570 + ], + "spans": [ + { + "bbox": [ + 46, + 342, + 289, + 570 + ], + "type": "text", + "content": "FocalClick [8] crops a region based on the difference between the previous mask and the coarsely predicted mask to refine the details. Zhang et al. [50] refines a local area centered on the target based on the coarse segmentation results. There are also methods to refine the global mask, such as EdgeFlow [15] and " + }, + { + "bbox": [ + 46, + 342, + 289, + 570 + ], + "type": "inline_equation", + "content": "99\\%" + }, + { + "bbox": [ + 46, + 342, + 289, + 570 + ], + "type": "text", + "content": " AccuracyNet [12]. One common property of these refinement methods is that they run the whole segmentation and refinement networks to get the results in each interactive iteration. It is too costly compared with a simple feedforward segmentation network. FocusCut [26] trains a segmentation network to not only segment the target object but also refine local details. However, it is still not efficient enough to run the whole segmentation network in each iteration. Our mask correction network is somewhat like a refinement network. The difference is that we directly use this network to correct masks when a new click is placed, and the base segmentation network only runs for the first click. This architecture reduces the inference time significantly compared with traditional methods." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 575, + 224, + 588 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 575, + 224, + 588 + ], + "spans": [ + { + "bbox": [ + 47, + 575, + 224, + 588 + ], + "type": "text", + "content": "2.3. Exploitation of click information" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 594, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 594, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 289, + 715 + ], + "type": "text", + "content": "The clicks provide key information for locating the foreground and background areas. Most methods encode the clicks as click maps where the regions around the clicks are highlighted. However, the click information is not explicitly exploited. To better exploit the click information, CDNet [7] propagates the click information to other pixels via two non-local networks [43]. It constructs weight maps based on the click locations to re-weight the affinity matrix, which is not computational efficiency since it needs to model the affinity between every two pixels. IFPN [50]" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 342, + 547, + 462 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 342, + 547, + 462 + ], + "spans": [ + { + "bbox": [ + 304, + 342, + 547, + 462 + ], + "type": "text", + "content": "learns a sparse graph model to perform click feature propagation. It only models the dependencies between the clicks and other pixels. Inspired by the two methods, we construct a multi-head self-attention module to propagate the click information to other pixels. Different from CDNet and IFPN, we select several templates to enrich the click features. Thus, our method is more efficient compared to CDNet [7] and can exploit more information compared to IFPN [50]. Besides, we also propose a correlation module to exploit the click information explicitly." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 305, + 473, + 411, + 488 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 473, + 411, + 488 + ], + "spans": [ + { + "bbox": [ + 305, + 473, + 411, + 488 + ], + "type": "text", + "content": "3. Proposed method" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 494, + 547, + 589 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 494, + 547, + 589 + ], + "spans": [ + { + "bbox": [ + 304, + 494, + 547, + 589 + ], + "type": "text", + "content": "We propose to iteratively correct the segmentation mask using a lightweight mask correction network, which exploits the information of the clicks to boost the performance via a click-guided self-attention module and a click-guided correlation module. We first briefly revisit the traditional pipeline of the interactive segmentation model, then introduce our pipeline and elaborate on the mask correction network." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 598, + 432, + 612 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 598, + 432, + 612 + ], + "spans": [ + { + "bbox": [ + 305, + 598, + 432, + 612 + ], + "type": "text", + "content": "3.1. The standard pipeline" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 618, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 618, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 618, + 547, + 715 + ], + "type": "text", + "content": "Interactive segmentation is often regarded as a special type of segmentation task. Different from classic segmentation, the input of the interactive segmentation network contains not only the image but also the click maps and previously predicted mask. When segmenting the object of interest, the user decides where to place the next click based on the current segmentation mask. All positive/negative clicks are encoded as positive/negative click maps that are usual" + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "22775" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "text", + "content": "ally defined as distance maps [47] or binary disks [3]. The click maps are then concatenated with the image and previously predicted mask to be fed to the segmentation network. After each click, the user obtains an updated segmentation mask by running the whole segmentation network. Usually, a strong segmentation network like DeepLabv3+ [6] is required to achieve satisfactory results since the segmentation accuracy directly depends on it. However, running a strong segmentation network several times is often time-consuming, especially on low-power devices, which makes this standard pipeline inefficient in practice." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 210, + 149, + 223 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 210, + 149, + 223 + ], + "spans": [ + { + "bbox": [ + 47, + 210, + 149, + 223 + ], + "type": "text", + "content": "3.2. Efficient pipeline" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 228, + 289, + 407 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 228, + 289, + 407 + ], + "spans": [ + { + "bbox": [ + 46, + 228, + 289, + 407 + ], + "type": "text", + "content": "To avoid running the whole segmentation network for each click, we build a lightweight network to correct the segmentation mask in each iteration. The pipeline is shown in Fig. 2. Our network consists of a base segmentation network and a lightweight mask correction network. As observed in FCA-Net [27], the first click is responsible for locating the target object. Thus, we input the first click into the segmentation network to generate target-aware features. When the user places the first click, the base segmentation network extracts the target-aware feature and generates a coarse mask, and the mask correction network corrects the coarse mask. Starting from the second click, we no longer run the base segmentation network. Instead, we directly feed all clicks into the mask correction network to correct the previously predicted mask." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 408, + 288, + 468 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 408, + 288, + 468 + ], + "spans": [ + { + "bbox": [ + 47, + 408, + 288, + 468 + ], + "type": "text", + "content": "Specifically, we denote the input image as " + }, + { + "bbox": [ + 47, + 408, + 288, + 468 + ], + "type": "inline_equation", + "content": "I" + }, + { + "bbox": [ + 47, + 408, + 288, + 468 + ], + "type": "text", + "content": " and the click set at the " + }, + { + "bbox": [ + 47, + 408, + 288, + 468 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 47, + 408, + 288, + 468 + ], + "type": "text", + "content": "-th iteration as " + }, + { + "bbox": [ + 47, + 408, + 288, + 468 + ], + "type": "inline_equation", + "content": "C^t" + }, + { + "bbox": [ + 47, + 408, + 288, + 468 + ], + "type": "text", + "content": ". The base segmentation network takes the input image and the first click " + }, + { + "bbox": [ + 47, + 408, + 288, + 468 + ], + "type": "inline_equation", + "content": "C^1" + }, + { + "bbox": [ + 47, + 408, + 288, + 468 + ], + "type": "text", + "content": " as input and generates target-aware features " + }, + { + "bbox": [ + 47, + 408, + 288, + 468 + ], + "type": "inline_equation", + "content": "F_{t}" + }, + { + "bbox": [ + 47, + 408, + 288, + 468 + ], + "type": "text", + "content": " and a coarse mask " + }, + { + "bbox": [ + 47, + 408, + 288, + 468 + ], + "type": "inline_equation", + "content": "M_{c}" + }, + { + "bbox": [ + 47, + 408, + 288, + 468 + ], + "type": "text", + "content": ", which can be formulated as follows," + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 102, + 475, + 287, + 488 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 102, + 475, + 287, + 488 + ], + "spans": [ + { + "bbox": [ + 102, + 475, + 287, + 488 + ], + "type": "interline_equation", + "content": "F _ {t}, M _ {c} = \\Phi_ {S} (I, E n c \\left(C ^ {1}\\right); \\theta_ {s}), \\tag {1}", + "image_path": "8702058a89b60062bd63cd50dc6c4bc7345d6db48bb7345dce4097399e5f0b32.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 495, + 287, + 590 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 495, + 287, + 590 + ], + "spans": [ + { + "bbox": [ + 47, + 495, + 287, + 590 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 495, + 287, + 590 + ], + "type": "inline_equation", + "content": "Enc" + }, + { + "bbox": [ + 47, + 495, + 287, + 590 + ], + "type": "text", + "content": " denotes the click encoding function, and " + }, + { + "bbox": [ + 47, + 495, + 287, + 590 + ], + "type": "inline_equation", + "content": "\\Phi_S" + }, + { + "bbox": [ + 47, + 495, + 287, + 590 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 495, + 287, + 590 + ], + "type": "inline_equation", + "content": "\\theta_s" + }, + { + "bbox": [ + 47, + 495, + 287, + 590 + ], + "type": "text", + "content": " denote the base segmentation network and its parameters, respectively. In this work, we adopt disks with a small radius [3,40] to encode the clicks. The mask correction network takes the click set " + }, + { + "bbox": [ + 47, + 495, + 287, + 590 + ], + "type": "inline_equation", + "content": "C^t" + }, + { + "bbox": [ + 47, + 495, + 287, + 590 + ], + "type": "text", + "content": ", the target-aware feature " + }, + { + "bbox": [ + 47, + 495, + 287, + 590 + ], + "type": "inline_equation", + "content": "F_t" + }, + { + "bbox": [ + 47, + 495, + 287, + 590 + ], + "type": "text", + "content": ", the original image " + }, + { + "bbox": [ + 47, + 495, + 287, + 590 + ], + "type": "inline_equation", + "content": "I" + }, + { + "bbox": [ + 47, + 495, + 287, + 590 + ], + "type": "text", + "content": ", and the previously predicted mask " + }, + { + "bbox": [ + 47, + 495, + 287, + 590 + ], + "type": "inline_equation", + "content": "M^{t-1}" + }, + { + "bbox": [ + 47, + 495, + 287, + 590 + ], + "type": "text", + "content": " as input and outputs an updated mask, which can be written as follows," + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 88, + 597, + 287, + 611 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 88, + 597, + 287, + 611 + ], + "spans": [ + { + "bbox": [ + 88, + 597, + 287, + 611 + ], + "type": "interline_equation", + "content": "M ^ {t} = \\Phi_ {R} (I, E n c \\left(C ^ {t}\\right), M ^ {t - 1}, F _ {t}; \\theta_ {r}), \\tag {2}", + "image_path": "161650d67c43551da7494b487367be8a4101742f0fdcdc72c2634f4bcbeaed69.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 618, + 287, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 618, + 287, + 689 + ], + "spans": [ + { + "bbox": [ + 47, + 618, + 287, + 689 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 618, + 287, + 689 + ], + "type": "inline_equation", + "content": "\\Phi_R" + }, + { + "bbox": [ + 47, + 618, + 287, + 689 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 618, + 287, + 689 + ], + "type": "inline_equation", + "content": "\\theta_r" + }, + { + "bbox": [ + 47, + 618, + 287, + 689 + ], + "type": "text", + "content": " denote the mask correction network and its parameters, respectively. For the first click (i.e. " + }, + { + "bbox": [ + 47, + 618, + 287, + 689 + ], + "type": "inline_equation", + "content": "t = 1" + }, + { + "bbox": [ + 47, + 618, + 287, + 689 + ], + "type": "text", + "content": "), the previous mask " + }, + { + "bbox": [ + 47, + 618, + 287, + 689 + ], + "type": "inline_equation", + "content": "M^0" + }, + { + "bbox": [ + 47, + 618, + 287, + 689 + ], + "type": "text", + "content": " input to the mask correction network is equal to the coarse mask " + }, + { + "bbox": [ + 47, + 618, + 287, + 689 + ], + "type": "inline_equation", + "content": "M_c" + }, + { + "bbox": [ + 47, + 618, + 287, + 689 + ], + "type": "text", + "content": ". The mask correction network can also take as input a preexisting mask generated from other forms of pre-processing." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "content": "Note that our pipeline differs from FCA-Net [27] which also treats the first click differently from other clicks. Our" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 72, + 545, + 107 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 545, + 107 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 545, + 107 + ], + "type": "text", + "content": "network only runs the mask correction network after the first click, while FCA-Net still needs to run the whole network for each click." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 124, + 545, + 136 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 124, + 545, + 136 + ], + "spans": [ + { + "bbox": [ + 305, + 124, + 545, + 136 + ], + "type": "text", + "content": "3.3. Efficient and effective mask correction network" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 145, + 545, + 300 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 145, + 545, + 300 + ], + "spans": [ + { + "bbox": [ + 304, + 145, + 545, + 300 + ], + "type": "text", + "content": "A simple mask correction network with limited parameters and computational cost can hardly achieve comparable performance with a traditional segmentation network. Therefore, we propose to exploit the click information better to boost performance with the click-guided self-attention module and the click-guided correlation module. Before performing correlation and self-attention, we first concatenate the image, positive/negative click maps, and previous mask to extract the low-level features " + }, + { + "bbox": [ + 304, + 145, + 545, + 300 + ], + "type": "inline_equation", + "content": "F_{l}" + }, + { + "bbox": [ + 304, + 145, + 545, + 300 + ], + "type": "text", + "content": " from them. We also adjust the channel number of target-aware features " + }, + { + "bbox": [ + 304, + 145, + 545, + 300 + ], + "type": "inline_equation", + "content": "F_{t}" + }, + { + "bbox": [ + 304, + 145, + 545, + 300 + ], + "type": "text", + "content": " via a convolutional layer with a kernel size of " + }, + { + "bbox": [ + 304, + 145, + 545, + 300 + ], + "type": "inline_equation", + "content": "1 \\times 1" + }, + { + "bbox": [ + 304, + 145, + 545, + 300 + ], + "type": "text", + "content": ". Then we concatenate " + }, + { + "bbox": [ + 304, + 145, + 545, + 300 + ], + "type": "inline_equation", + "content": "F_{l}" + }, + { + "bbox": [ + 304, + 145, + 545, + 300 + ], + "type": "text", + "content": " with " + }, + { + "bbox": [ + 304, + 145, + 545, + 300 + ], + "type": "inline_equation", + "content": "F_{t}" + }, + { + "bbox": [ + 304, + 145, + 545, + 300 + ], + "type": "text", + "content": " from the backbone to learn the fused features " + }, + { + "bbox": [ + 304, + 145, + 545, + 300 + ], + "type": "inline_equation", + "content": "F_{u}" + }, + { + "bbox": [ + 304, + 145, + 545, + 300 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 304, + 546, + 472 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 304, + 546, + 472 + ], + "spans": [ + { + "bbox": [ + 304, + 304, + 546, + 472 + ], + "type": "text", + "content": "To exploit the click information, we map the location of clicks onto the feature maps and extract the features with a shape of " + }, + { + "bbox": [ + 304, + 304, + 546, + 472 + ], + "type": "inline_equation", + "content": "1 \\times 1 \\times C" + }, + { + "bbox": [ + 304, + 304, + 546, + 472 + ], + "type": "text", + "content": " for each click, where " + }, + { + "bbox": [ + 304, + 304, + 546, + 472 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 304, + 304, + 546, + 472 + ], + "type": "text", + "content": " is the number of channels. These click features are regarded as templates. The click-guided self-attention module propagates the information of these templates to other locations via multi-head attention, while the click-guided correlation attention module uses them to learn target outlines via correlation. Since the number of clicks used to obtain a satisfactory segmentation accuracy is often less than 20, it may not be sufficient only to extract templates from the location of clicks. Thus, we first enrich the templates by selecting some informative locations based on their semantic similarity to the clicks." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 486, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 486, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 486, + 546, + 713 + ], + "type": "text", + "content": "Template selection. The strategy to select templates is based on the observation that pixels on the same object show higher similarity than pixels from different objects. We separately select positive and negative templates by identifying pixels that are more likely to be the object and the background, respectively. To select positive templates, we assign a score for each pixel to indicate the likelihood of being the object and select the top " + }, + { + "bbox": [ + 304, + 486, + 546, + 713 + ], + "type": "inline_equation", + "content": "K_{p}" + }, + { + "bbox": [ + 304, + 486, + 546, + 713 + ], + "type": "text", + "content": " pixels. The score is calculated by considering three factors: the similarity to positive clicks, the similarity to negative clicks, and the distance from the positive clicks. A pixel with a short distance and a high similarity to one of the positive clicks and a low similarity to one of the negative clicks is more likely to be located in the object region and vice versa. We use the Cosine similarity between features of two pixels to measure their similarity and the Euclidean distance to measure the distance. Let " + }, + { + "bbox": [ + 304, + 486, + 546, + 713 + ], + "type": "inline_equation", + "content": "H_{f} \\times W_{f}" + }, + { + "bbox": [ + 304, + 486, + 546, + 713 + ], + "type": "text", + "content": " denote the size of the feature map, where " + }, + { + "bbox": [ + 304, + 486, + 546, + 713 + ], + "type": "inline_equation", + "content": "H_{f}" + }, + { + "bbox": [ + 304, + 486, + 546, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 486, + 546, + 713 + ], + "type": "inline_equation", + "content": "W_{f}" + }, + { + "bbox": [ + 304, + 486, + 546, + 713 + ], + "type": "text", + "content": " are respectively the height and width, and we can obtain a positive score map " + }, + { + "bbox": [ + 304, + 486, + 546, + 713 + ], + "type": "inline_equation", + "content": "O_{p} \\in \\mathbb{R}^{H_{f} \\times W_{f}}" + }, + { + "bbox": [ + 304, + 486, + 546, + 713 + ], + "type": "text", + "content": " as" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "22776" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 82, + 83 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 82, + 83 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 82, + 83 + ], + "type": "text", + "content": "follows," + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 94, + 91, + 287, + 106 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 94, + 91, + 287, + 106 + ], + "spans": [ + { + "bbox": [ + 94, + 91, + 287, + 106 + ], + "type": "interline_equation", + "content": "O _ {p} = \\left(V _ {p} + \\left(1 - V _ {n}\\right)\\right) * \\left(1 - D _ {p}\\right), \\tag {3}", + "image_path": "df58c37bba57484ed1e4bde73dfe2f4301a49d96b4401a73d588f1fc76f27f4f.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 112, + 287, + 209 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 112, + 287, + 209 + ], + "spans": [ + { + "bbox": [ + 47, + 112, + 287, + 209 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 112, + 287, + 209 + ], + "type": "inline_equation", + "content": "V_{p}\\in \\mathbb{R}^{H_{f}\\times W_{f}}" + }, + { + "bbox": [ + 47, + 112, + 287, + 209 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 112, + 287, + 209 + ], + "type": "inline_equation", + "content": "V_{n}\\in \\mathbb{R}^{H_{f}\\times W_{f}}" + }, + { + "bbox": [ + 47, + 112, + 287, + 209 + ], + "type": "text", + "content": " respectively denote the positive and negative Cosine similarity maps, and " + }, + { + "bbox": [ + 47, + 112, + 287, + 209 + ], + "type": "inline_equation", + "content": "D_{p}\\in \\mathbb{R}^{H_{f}\\times W_{f}}" + }, + { + "bbox": [ + 47, + 112, + 287, + 209 + ], + "type": "text", + "content": " denotes the normalized distance map. Note that the similarity scores " + }, + { + "bbox": [ + 47, + 112, + 287, + 209 + ], + "type": "inline_equation", + "content": "V_{p}^{u,v} / V_{n}^{u,v}" + }, + { + "bbox": [ + 47, + 112, + 287, + 209 + ], + "type": "text", + "content": " respectively represent the maximum similarity between the pixel " + }, + { + "bbox": [ + 47, + 112, + 287, + 209 + ], + "type": "inline_equation", + "content": "(u,v)" + }, + { + "bbox": [ + 47, + 112, + 287, + 209 + ], + "type": "text", + "content": " and positive/negative clicks, while " + }, + { + "bbox": [ + 47, + 112, + 287, + 209 + ], + "type": "inline_equation", + "content": "D_p^{u,v}" + }, + { + "bbox": [ + 47, + 112, + 287, + 209 + ], + "type": "text", + "content": " represents the normalized minimum distance between " + }, + { + "bbox": [ + 47, + 112, + 287, + 209 + ], + "type": "inline_equation", + "content": "(u,v)" + }, + { + "bbox": [ + 47, + 112, + 287, + 209 + ], + "type": "text", + "content": " and positive clicks. Similarly, we can obtain a negative score map " + }, + { + "bbox": [ + 47, + 112, + 287, + 209 + ], + "type": "inline_equation", + "content": "O_{n}" + }, + { + "bbox": [ + 47, + 112, + 287, + 209 + ], + "type": "text", + "content": " by" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 93, + 217, + 287, + 230 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 93, + 217, + 287, + 230 + ], + "spans": [ + { + "bbox": [ + 93, + 217, + 287, + 230 + ], + "type": "interline_equation", + "content": "O _ {n} = \\left(V _ {n} + \\left(1 - V _ {p}\\right)\\right) * \\left(1 - D _ {n}\\right), \\tag {4}", + "image_path": "f73a3ad0eee696a670fe2f343ebd32df75fb6f5320a3b5c80ec21616dd5a3fae.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 237, + 287, + 333 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 237, + 287, + 333 + ], + "spans": [ + { + "bbox": [ + 47, + 237, + 287, + 333 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 237, + 287, + 333 + ], + "type": "inline_equation", + "content": "D_{n}" + }, + { + "bbox": [ + 47, + 237, + 287, + 333 + ], + "type": "text", + "content": " denotes the normalized negative distance map, which measures the normalized minimum distance between each pixel and negative clicks. After obtaining the score maps, we select positive templates from the top " + }, + { + "bbox": [ + 47, + 237, + 287, + 333 + ], + "type": "inline_equation", + "content": "K_{p}" + }, + { + "bbox": [ + 47, + 237, + 287, + 333 + ], + "type": "text", + "content": " locations of the positive score map and " + }, + { + "bbox": [ + 47, + 237, + 287, + 333 + ], + "type": "inline_equation", + "content": "K_{n}" + }, + { + "bbox": [ + 47, + 237, + 287, + 333 + ], + "type": "text", + "content": " negative templates from the top " + }, + { + "bbox": [ + 47, + 237, + 287, + 333 + ], + "type": "inline_equation", + "content": "K_{n}" + }, + { + "bbox": [ + 47, + 237, + 287, + 333 + ], + "type": "text", + "content": " locations of the negative score map. The positive and negative template features are represented as " + }, + { + "bbox": [ + 47, + 237, + 287, + 333 + ], + "type": "inline_equation", + "content": "F_{pt} \\in \\mathbb{R}^{K_p \\times C}" + }, + { + "bbox": [ + 47, + 237, + 287, + 333 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 237, + 287, + 333 + ], + "type": "inline_equation", + "content": "F_{nt} \\in \\mathbb{R}^{K_n \\times C}" + }, + { + "bbox": [ + 47, + 237, + 287, + 333 + ], + "type": "text", + "content": ", respectively." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 345, + 287, + 489 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 345, + 287, + 489 + ], + "spans": [ + { + "bbox": [ + 47, + 345, + 287, + 489 + ], + "type": "text", + "content": "Click-guided self-attention. Our first way to exploit the click information is to propagate their information to other pixels via a self-attention module. Multi-head attention is widely used in computer vision to capture long-range dependencies among different pixels [9, 19]. We adopt the standard " + }, + { + "bbox": [ + 47, + 345, + 287, + 489 + ], + "type": "inline_equation", + "content": "qkv" + }, + { + "bbox": [ + 47, + 345, + 287, + 489 + ], + "type": "text", + "content": " multi-head attention [41] to augment the representation of each pixel with the selected templates. Multi-head attention helps each pixel attend to the templates, which is beneficial to the identification of the target. To perform multi-head attention, we first reshape the feature " + }, + { + "bbox": [ + 47, + 345, + 287, + 489 + ], + "type": "inline_equation", + "content": "F_{u}" + }, + { + "bbox": [ + 47, + 345, + 287, + 489 + ], + "type": "text", + "content": " to a size of " + }, + { + "bbox": [ + 47, + 345, + 287, + 489 + ], + "type": "inline_equation", + "content": "H_{f}W_{f}\\times C" + }, + { + "bbox": [ + 47, + 345, + 287, + 489 + ], + "type": "text", + "content": ", then we learn the self-attention-based augmented feature " + }, + { + "bbox": [ + 47, + 345, + 287, + 489 + ], + "type": "inline_equation", + "content": "F_{s}" + }, + { + "bbox": [ + 47, + 345, + 287, + 489 + ], + "type": "text", + "content": " by" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 97, + 496, + 287, + 509 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 97, + 496, + 287, + 509 + ], + "spans": [ + { + "bbox": [ + 97, + 496, + 287, + 509 + ], + "type": "interline_equation", + "content": "F _ {s} = F _ {u} + \\text {A t t e n t i o n} (Q, K, V), \\tag {5}", + "image_path": "1fe7779b483401618eaddfccbfe6bdf8a32369842c29d387222a2cac0f3cc6e8.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 70, + 517, + 287, + 529 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 70, + 517, + 287, + 529 + ], + "spans": [ + { + "bbox": [ + 70, + 517, + 287, + 529 + ], + "type": "interline_equation", + "content": "Q = \\phi_ {Q} \\left(F _ {u}\\right), K = \\phi_ {K} \\left(F _ {p n t}\\right), V = \\phi_ {V} \\left(F _ {p n t}\\right), \\tag {6}", + "image_path": "2b974bf22533b919f619360ea0a1ece70b9981bef4a2f04a81e69e9584f3d9b4.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 534, + 287, + 605 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 534, + 287, + 605 + ], + "spans": [ + { + "bbox": [ + 47, + 534, + 287, + 605 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 534, + 287, + 605 + ], + "type": "inline_equation", + "content": "\\phi_{Q},\\phi_{K}" + }, + { + "bbox": [ + 47, + 534, + 287, + 605 + ], + "type": "text", + "content": " , and " + }, + { + "bbox": [ + 47, + 534, + 287, + 605 + ], + "type": "inline_equation", + "content": "\\phi_V" + }, + { + "bbox": [ + 47, + 534, + 287, + 605 + ], + "type": "text", + "content": " are linear transformations, and " + }, + { + "bbox": [ + 47, + 534, + 287, + 605 + ], + "type": "inline_equation", + "content": "F_{pnt}" + }, + { + "bbox": [ + 47, + 534, + 287, + 605 + ], + "type": "text", + "content": " is the concatenation of positive templates " + }, + { + "bbox": [ + 47, + 534, + 287, + 605 + ], + "type": "inline_equation", + "content": "F_{pt}" + }, + { + "bbox": [ + 47, + 534, + 287, + 605 + ], + "type": "text", + "content": " and negative templates " + }, + { + "bbox": [ + 47, + 534, + 287, + 605 + ], + "type": "inline_equation", + "content": "F_{nt}" + }, + { + "bbox": [ + 47, + 534, + 287, + 605 + ], + "type": "text", + "content": " . " + }, + { + "bbox": [ + 47, + 534, + 287, + 605 + ], + "type": "inline_equation", + "content": "F_{s}" + }, + { + "bbox": [ + 47, + 534, + 287, + 605 + ], + "type": "text", + "content": " is further reshaped to " + }, + { + "bbox": [ + 47, + 534, + 287, + 605 + ], + "type": "inline_equation", + "content": "H_{f}\\times W_{f}\\times C" + }, + { + "bbox": [ + 47, + 534, + 287, + 605 + ], + "type": "text", + "content": " As the template features are selected from " + }, + { + "bbox": [ + 47, + 534, + 287, + 605 + ], + "type": "inline_equation", + "content": "F_{u}" + }, + { + "bbox": [ + 47, + 534, + 287, + 605 + ], + "type": "text", + "content": " , and the attention is guided by the click information, we denote this attention module as a click-guided self-attention module." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 617, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 617, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 617, + 287, + 713 + ], + "type": "text", + "content": "Click-guided correlation. To further exploit the click information, we propose a click-guided correlation attention module to learn the contour of the object of interest explicitly. Correlation is widely used in the Siamese object tracking archietecture [4] to locate the position of the target in a search area. Siamese tracking calculates similarity maps between a target template and the search area. In video object segmentation, RANet [44] treats target features from" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 72, + 545, + 182 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 182 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 182 + ], + "type": "text", + "content": "the first frame as the template to learn pixel-wise similarity maps. In RANet, pixel-wise correlation is shown to be able to learn the contour of the target with the target features as templates. In this work, we extract target semantic features based on the location of the clicks and employ the pixel-wise correlation to learn target outlines to improve the segmentation performance. For the " + }, + { + "bbox": [ + 304, + 72, + 545, + 182 + ], + "type": "inline_equation", + "content": "j" + }, + { + "bbox": [ + 304, + 72, + 545, + 182 + ], + "type": "text", + "content": "-th positive template feature " + }, + { + "bbox": [ + 304, + 72, + 545, + 182 + ], + "type": "inline_equation", + "content": "F_{pt}^{j}\\in \\mathbb{R}^{1\\times C}" + }, + { + "bbox": [ + 304, + 72, + 545, + 182 + ], + "type": "text", + "content": ", we can get a similarity map via the correlation between it and " + }, + { + "bbox": [ + 304, + 72, + 545, + 182 + ], + "type": "inline_equation", + "content": "F_{u}\\in \\mathbb{R}^{H_{f}W_{f}\\times C}" + }, + { + "bbox": [ + 304, + 72, + 545, + 182 + ], + "type": "text", + "content": ". Thus, we have" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 322, + 190, + 545, + 206 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 322, + 190, + 545, + 206 + ], + "spans": [ + { + "bbox": [ + 322, + 190, + 545, + 206 + ], + "type": "interline_equation", + "content": "S _ {p} = \\left\\{S _ {p} ^ {j} \\mid S _ {p} ^ {j} = \\phi_ {q} \\left(F _ {p t} ^ {j}\\right) * \\phi_ {k} \\left(F _ {u}\\right) \\right\\} _ {j \\in \\{1, \\dots , K _ {p} \\}}, \\tag {7}", + "image_path": "f2e3b8c66662b54179f6a8fa0dd59bdc7d20beaba65a276dd5089f8c1beec8a0.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 321, + 216, + 545, + 230 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 321, + 216, + 545, + 230 + ], + "spans": [ + { + "bbox": [ + 321, + 216, + 545, + 230 + ], + "type": "interline_equation", + "content": "S _ {n} = \\left\\{S _ {n} ^ {j} \\mid S _ {n} ^ {j} = \\phi_ {q} \\left(F _ {n t} ^ {j}\\right) * \\phi_ {k} \\left(F _ {u}\\right) \\right\\} _ {j \\in \\{1, \\dots , K _ {n} \\}}, \\tag {8}", + "image_path": "23e762d530b589ddb5a1a1f8e36642b0490b3cbf0bb0ce7038dc238c4ef41714.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 236, + 545, + 343 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 236, + 545, + 343 + ], + "spans": [ + { + "bbox": [ + 304, + 236, + 545, + 343 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 236, + 545, + 343 + ], + "type": "inline_equation", + "content": "*" + }, + { + "bbox": [ + 304, + 236, + 545, + 343 + ], + "type": "text", + "content": " denotes the correlation operation, " + }, + { + "bbox": [ + 304, + 236, + 545, + 343 + ], + "type": "inline_equation", + "content": "S_{p}" + }, + { + "bbox": [ + 304, + 236, + 545, + 343 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 236, + 545, + 343 + ], + "type": "inline_equation", + "content": "S_{n}" + }, + { + "bbox": [ + 304, + 236, + 545, + 343 + ], + "type": "text", + "content": " respectively denote the set of positive and negative correlation similarity maps, and " + }, + { + "bbox": [ + 304, + 236, + 545, + 343 + ], + "type": "inline_equation", + "content": "\\phi_q" + }, + { + "bbox": [ + 304, + 236, + 545, + 343 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 236, + 545, + 343 + ], + "type": "inline_equation", + "content": "\\phi_k" + }, + { + "bbox": [ + 304, + 236, + 545, + 343 + ], + "type": "text", + "content": " denote two linear transformations. We then transform the positive/negative similarity maps into features for segmentation via a shared convolutional layer. Then positive and negative features are concatenated and followed by the second convolutional layer to fuse them. In this manner, we get the correlation-based augmented feature " + }, + { + "bbox": [ + 304, + 236, + 545, + 343 + ], + "type": "inline_equation", + "content": "F_{c}" + }, + { + "bbox": [ + 304, + 236, + 545, + 343 + ], + "type": "text", + "content": " as follows," + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 350, + 353, + 545, + 366 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 350, + 353, + 545, + 366 + ], + "spans": [ + { + "bbox": [ + 350, + 353, + 545, + 366 + ], + "type": "interline_equation", + "content": "F _ {c} = \\phi_ {f} (\\operatorname {C o n c a t} \\left(\\phi_ {s} \\left(S _ {p}\\right), \\phi_ {s} \\left(S _ {n}\\right)\\right)), \\tag {9}", + "image_path": "9640b2f0c75bba747f9ac93260cd9f12b8612c1abaf2fc348d8d6c9665bce2f0.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 376, + 508, + 388 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 376, + 508, + 388 + ], + "spans": [ + { + "bbox": [ + 304, + 376, + 508, + 388 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 376, + 508, + 388 + ], + "type": "inline_equation", + "content": "\\phi_s" + }, + { + "bbox": [ + 304, + 376, + 508, + 388 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 376, + 508, + 388 + ], + "type": "inline_equation", + "content": "\\phi_f" + }, + { + "bbox": [ + 304, + 376, + 508, + 388 + ], + "type": "text", + "content": " denote two convolutional layers." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 388, + 545, + 472 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 388, + 545, + 472 + ], + "spans": [ + { + "bbox": [ + 304, + 388, + 545, + 472 + ], + "type": "text", + "content": "After learning the two augmented features " + }, + { + "bbox": [ + 304, + 388, + 545, + 472 + ], + "type": "inline_equation", + "content": "F_{s}" + }, + { + "bbox": [ + 304, + 388, + 545, + 472 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 388, + 545, + 472 + ], + "type": "inline_equation", + "content": "F_{c}" + }, + { + "bbox": [ + 304, + 388, + 545, + 472 + ], + "type": "text", + "content": ", we concatenate them and use four convolutional layers to predict the segmentation mask. Our mask correction network is efficient since the resolution of the features is just 1/4 of the image, and the whole structure is lightweight. It is also effective since the click information is exploited explicitly via two modules to improve performance." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 305, + 483, + 388, + 497 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 483, + 388, + 497 + ], + "spans": [ + { + "bbox": [ + 305, + 483, + 388, + 497 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 305, + 503, + 462, + 516 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 503, + 462, + 516 + ], + "spans": [ + { + "bbox": [ + 305, + 503, + 462, + 516 + ], + "type": "text", + "content": "4.1. Experimental Configuration" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 521, + 545, + 653 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 521, + 545, + 653 + ], + "spans": [ + { + "bbox": [ + 304, + 521, + 545, + 653 + ], + "type": "text", + "content": "Implementation details. Our pipeline can be built on different existing segmentation networks. Following FocalClick [8], we choose HRNet+OCR [42, 49] and SegFormer [45] series as our base segmentation networks to show the effectiveness of the proposed method. For lightweight models like SegFormerB0 and HRNet18s, the mask correction network first transforms the number of backbone feature channels to 64. For larger models like SegFormerB3, HRNet18, and HRNet32, the channel is transformed to 96. The number of selected templates " + }, + { + "bbox": [ + 304, + 521, + 545, + 653 + ], + "type": "inline_equation", + "content": "K_{p}" + }, + { + "bbox": [ + 304, + 521, + 545, + 653 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 521, + 545, + 653 + ], + "type": "inline_equation", + "content": "K_{n}" + }, + { + "bbox": [ + 304, + 521, + 545, + 653 + ], + "type": "text", + "content": " is set to be equal to the channel number." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 654, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 654, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 654, + 545, + 713 + ], + "type": "text", + "content": "We train our model on a combination of COCO [25] and LVIS [14] datasets, following RITM [40]. For a fair comparison of some previous methods, we also report the performance of our model trained on SBD [16]. We use the normalized focal loss [38] for both the base segmentation" + } + ] + } + ], + "index": 20 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "22777" + } + ] + } + ], + "index": 21 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 50, + 70, + 285, + 279 + ], + "blocks": [ + { + "bbox": [ + 50, + 70, + 285, + 279 + ], + "lines": [ + { + "bbox": [ + 50, + 70, + 285, + 279 + ], + "spans": [ + { + "bbox": [ + 50, + 70, + 285, + 279 + ], + "type": "table", + "html": "
MethodParams/MBFLOPs/GSpeed/ms
CDNet-ResNet34384 [7]23.556.73339
f-BRS-ResNet50400 [39]31.484.62373
RITM-hrnet18s400 [40]4.228.96634
RITM-hrnet18400 [40]10.015.41103
RITM-hrnet32400 [40]31.040.41635
Flickr-hrnet18s256 [8]4.233.82358
Flickr-hrnet32256 [8]31.017.1728
Flickr-SegB0256 [8]3.741.94207
Flickr-SegB3256 [8]45.612.9805
Ours-hrnet18s-FirstClick3844.339.35752
Ours-hrnet18-FirstClick38410.315.31237
Ours-hrnet32-FirstClick38431.240.51745
Ours-SegB0-FirstClick3843.845.38528
Ours-SegB3-FirstClick38445.932.32006
Ours-MaskCorrection-C643840.111.09183
Ours-MaskCorrection-C963840.222.25280
", + "image_path": "831d890cf1ae9216ea0199c27750de48c0398bec4a4745e0b6fba80f677361b7.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + }, + { + "bbox": [ + 47, + 288, + 287, + 344 + ], + "lines": [ + { + "bbox": [ + 47, + 288, + 287, + 344 + ], + "spans": [ + { + "bbox": [ + 47, + 288, + 287, + 344 + ], + "type": "text", + "content": "Table 1. Comparison of the computational cost for different methods. The speed represents the average inference time per click and is measured on a CPU laptop with " + }, + { + "bbox": [ + 47, + 288, + 287, + 344 + ], + "type": "inline_equation", + "content": "2\\mathrm{GHz}" + }, + { + "bbox": [ + 47, + 288, + 287, + 344 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 288, + 287, + 344 + ], + "type": "inline_equation", + "content": "4\\times" + }, + { + "bbox": [ + 47, + 288, + 287, + 344 + ], + "type": "text", + "content": " Intel Core i5. From the second click, we only run the mask correction network, significantly reducing the inference time compared to other methods." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_footnote" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 365, + 287, + 570 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 365, + 287, + 570 + ], + "spans": [ + { + "bbox": [ + 47, + 365, + 287, + 570 + ], + "type": "text", + "content": "and mask correction networks. We adopt the iterative training strategy [31] by randomly sampling the first positive click in the target area and progressively adding clicks based on the errors in the network's predictions during training. Our lightweight mask correction network enables efficient iterative training. We use the Adam optimizer with " + }, + { + "bbox": [ + 47, + 365, + 287, + 570 + ], + "type": "inline_equation", + "content": "\\beta_{1} = 0.9" + }, + { + "bbox": [ + 47, + 365, + 287, + 570 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 365, + 287, + 570 + ], + "type": "inline_equation", + "content": "\\beta_{2} = 0.999" + }, + { + "bbox": [ + 47, + 365, + 287, + 570 + ], + "type": "text", + "content": " to train the network. As in FocalClick [8], we sample 30000 images in one epoch and train our model for 230 epochs. We use an initial learning rate of " + }, + { + "bbox": [ + 47, + 365, + 287, + 570 + ], + "type": "inline_equation", + "content": "1e - 3" + }, + { + "bbox": [ + 47, + 365, + 287, + 570 + ], + "type": "text", + "content": " for the HRNet+OCR series and " + }, + { + "bbox": [ + 47, + 365, + 287, + 570 + ], + "type": "inline_equation", + "content": "2e - 3" + }, + { + "bbox": [ + 47, + 365, + 287, + 570 + ], + "type": "text", + "content": " for the SegFormer series, and decay them by ten times on the 200th and 220th epochs. We train the network with an image size of " + }, + { + "bbox": [ + 47, + 365, + 287, + 570 + ], + "type": "inline_equation", + "content": "320\\times 480" + }, + { + "bbox": [ + 47, + 365, + 287, + 570 + ], + "type": "text", + "content": " and a batch size of 64. We add data augmentation strategies, including random resizing in a range of [0.75, 1.40], horizontal flip, random jittering of brightness, contrast, and RGB values. All our models are implemented in Python using Pytorch." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 582, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 582, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 47, + 582, + 287, + 715 + ], + "type": "text", + "content": "Evaluation datasets and metrics. We evaluate our method on five commonly used datasets, including GrabCut [37], Berkeley [35], DAVIS [36], SBD [16], and Pascal VOC [10]. The GrabCut dataset contains 50 images with one single target in each image. The test set of the Berkeley dataset contains 100 object masks for 96 images. The DAVIS dataset is originally constructed for the evaluation of video object segmentation methods. We sample 345 frames to evaluate our method as in [8,40]. The SBD dataset is the largest and has been widely used to evaluate the interactive segmentation methods since [47]. It contains 6671 object" + } + ] + } + ], + "index": 3 + }, + { + "type": "table", + "bbox": [ + 309, + 70, + 545, + 186 + ], + "blocks": [ + { + "bbox": [ + 309, + 70, + 545, + 186 + ], + "lines": [ + { + "bbox": [ + 309, + 70, + 545, + 186 + ], + "spans": [ + { + "bbox": [ + 309, + 70, + 545, + 186 + ], + "type": "table", + "html": "
NoC@90Time@90NoC@95Time@95
FocalClick-hrnet18s6.7934min12.7862min
FocalClick-hrnet326.5149min12.5085min
FocalClick-SegB06.8623min12.7339min
FocalClick-SegB35.5934min11.5563min
Ours-hrnet18s6.1619min12.4730min
Ours-hrnet325.6521min11.9032min
Ours-SegB06.2116min12.4527min
Ours-SegB35.5720min11.6529min
", + "image_path": "b1a4d2b50fad6906e0a84a5ff0d79b0f835fc61151ece6b92d62c12ddf086a6c.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_body" + }, + { + "bbox": [ + 305, + 195, + 545, + 228 + ], + "lines": [ + { + "bbox": [ + 305, + 195, + 545, + 228 + ], + "spans": [ + { + "bbox": [ + 305, + 195, + 545, + 228 + ], + "type": "text", + "content": "Table 2. Comparison of the total inference time to reach different IoU thresholds on the largest SBD dataset. The time is measured on an NVIDIA V100 GPU." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "table_footnote" + } + ], + "index": 4 + }, + { + "bbox": [ + 305, + 251, + 545, + 287 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 251, + 545, + 287 + ], + "spans": [ + { + "bbox": [ + 305, + 251, + 545, + 287 + ], + "type": "text", + "content": "masks for 2820 images. The validation set of the Pascal VOC dataset is also used, which consists of 1449 images with 3427 object masks." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 289, + 545, + 456 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 289, + 545, + 456 + ], + "spans": [ + { + "bbox": [ + 304, + 289, + 545, + 456 + ], + "type": "text", + "content": "We use the commonly used evaluation protocol to make a fair comparison. During the evaluation, the clicks are simulated based on the difference between the current prediction and the ground truth. The first click is placed in the center of the target, and other clicks are placed in the center of the largest erroneous region. Following [26], the image is resized to a fixed length of 384 as the short side during evaluation. We use the standard Number of Clicks (NoC) metric to compare different methods. The NoC measures the number of clicks required to reach a predefined Intersection over Union (IoU) threshold between the predicted mask and the ground truth. Following most methods, the thresholds of " + }, + { + "bbox": [ + 304, + 289, + 545, + 456 + ], + "type": "inline_equation", + "content": "85\\%" + }, + { + "bbox": [ + 304, + 289, + 545, + 456 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 289, + 545, + 456 + ], + "type": "inline_equation", + "content": "90\\%" + }, + { + "bbox": [ + 304, + 289, + 545, + 456 + ], + "type": "text", + "content": " are used, and the metrics are denoted as NoC@85 and NoC@90." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 467, + 525, + 480 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 467, + 525, + 480 + ], + "spans": [ + { + "bbox": [ + 306, + 467, + 525, + 480 + ], + "type": "text", + "content": "4.2. Comparison with state-of-the-art methods" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 486, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 486, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 486, + 545, + 713 + ], + "type": "text", + "content": "Computational comparison. We compare the parameters, FLOPs, and inference speed on CPUs of representative methods in Tab. 1. MaskCorrection-C64 denotes that we set the channel of the mask correction network to 64, which is used for HRNet18s and SegFormerB0. MaskCorrection-C96 is used for HRNet18, HRNet32, and SegFormerB3. The computational cost of our method is different between the first click and other clicks. For the first click, our method needs to run the base segmentation network and the mask correction network, resulting in slightly higher inference time compared with RITM [40]. However, our method shows higher efficiency from the second click even compared with FocalClick [8] which uses a small resolution since our mask correction network is lightweight. The computational cost of the mask correction network will not change with the base segmentation network if we fix the configuration, which is a good property since we can use a stronger segmentation network to reduce the number of interactions without a significant increase in the inference" + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 749, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 749, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 749, + 317, + 757 + ], + "type": "text", + "content": "22778" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 47, + 70, + 545, + 400 + ], + "blocks": [ + { + "bbox": [ + 47, + 70, + 545, + 400 + ], + "lines": [ + { + "bbox": [ + 47, + 70, + 545, + 400 + ], + "spans": [ + { + "bbox": [ + 47, + 70, + 545, + 400 + ], + "type": "table", + "html": "
MethodsGrabCutBerkeleySBDDAVISPascal
Train DataNoC@85NoC@90NoC@90NoC@85NoC@90NoC@85NoC@90NoC@90NoC@85
f-BRS-B-ResNet50 [39]SBD2.502.984.345.068.085.397.81
CDNet-ResNet50 [7]SBD2.222.643.694.377.875.176.66-
FocusCut-ResNet50 [26]SBD1.601.783.443.625.665.006.38-
FocalClick-hrnet18s [8]SBD1.862.063.144.306.524.926.48-
RITM-hrnet18 [40]SBD1.762.043.223.395.434.946.71-
Ours-hrnet18sSBD1.821.923.263.585.795.236.882.47
Ours-hrnet18SBD1.741.843.033.385.515.056.712.37
TransClick-segformerB4 [11]C+L1.521.601.603.445.633.685.062.08
FocalClick-segformerB0 [8]C+L1.401.662.274.566.864.045.492.97
Ours-segformerB0C+L1.561.642.403.956.214.485.532.65
FocalClick-segformerB3 [8]C+L1.441.501.923.535.593.614.902.46
Ours-segformerB3C+L1.421.482.353.445.574.495.692.23
RITM-hrnet18s [40]C+L1.541.682.604.046.484.705.982.57
FocalClick-hrnet18s [8]C+L1.481.622.664.436.793.905.252.93
Ours-hrnet18sC+L1.401.522.683.866.164.425.662.37
RITM-hrnet18 [40]C+L1.421.542.263.806.064.365.742.28
EdgeFlow-hrnet18 [15]C+L1.601.722.40--4.545.772.50
Ours-hrnet18C+L1.381.502.303.695.934.345.592.37
RITM-hrnet32 [40]C+L1.461.562.103.595.714.115.342.57
FocalClick-hrnet32 [8]C+L1.641.802.364.246.514.015.392.80
PseudoClick-hrnet32 [29]C+L-1.502.08-5.684.095.271.94
Ours-hrnet32C+L1.301.422.353.555.654.295.332.22
", + "image_path": "0c49a61b8ec62993ac855e9b6af0263aa72fa4d597880ef2a0f5f4addfb5286f.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 408, + 546, + 431 + ], + "lines": [ + { + "bbox": [ + 46, + 408, + 546, + 431 + ], + "spans": [ + { + "bbox": [ + 46, + 408, + 546, + 431 + ], + "type": "text", + "content": "Table 3. Comparison results on five benchmarks. NoC@85 and NoC@90 respectively denote the number of clicks required to reach the IoU of " + }, + { + "bbox": [ + 46, + 408, + 546, + 431 + ], + "type": "inline_equation", + "content": "85\\%" + }, + { + "bbox": [ + 46, + 408, + 546, + 431 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 408, + 546, + 431 + ], + "type": "inline_equation", + "content": "90\\%" + }, + { + "bbox": [ + 46, + 408, + 546, + 431 + ], + "type": "text", + "content": ", and lower is better for the value. C+L means the combination of COCO and LVIS." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 452, + 289, + 620 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 452, + 289, + 620 + ], + "spans": [ + { + "bbox": [ + 46, + 452, + 289, + 620 + ], + "type": "text", + "content": "time. We demonstrate the total inference time to reach " + }, + { + "bbox": [ + 46, + 452, + 289, + 620 + ], + "type": "inline_equation", + "content": "90\\%" + }, + { + "bbox": [ + 46, + 452, + 289, + 620 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 452, + 289, + 620 + ], + "type": "inline_equation", + "content": "95\\%" + }, + { + "bbox": [ + 46, + 452, + 289, + 620 + ], + "type": "text", + "content": " IoU on the largest dataset SBD in Tab. 2. To save evaluation time, all models are evaluated on an NVIDIA V100 GPU. Our method spends less time reaching a predefined IoU threshold for all versions. Notably, although the number of clicks required to reach " + }, + { + "bbox": [ + 46, + 452, + 289, + 620 + ], + "type": "inline_equation", + "content": "90\\%" + }, + { + "bbox": [ + 46, + 452, + 289, + 620 + ], + "type": "text", + "content": " (NoC@90) and " + }, + { + "bbox": [ + 46, + 452, + 289, + 620 + ], + "type": "inline_equation", + "content": "95\\%" + }, + { + "bbox": [ + 46, + 452, + 289, + 620 + ], + "type": "text", + "content": " (NoC@95) IoUs is similar for FocalClick-SegB3 and Ours-SegB3, the inference time of our method is significantly lower because the computational cost of Ours-SegB3 from the second click is considerably lower than FocalClick-SegB3. And the gap between our method and FocalClick is larger when the threshold changes from " + }, + { + "bbox": [ + 46, + 452, + 289, + 620 + ], + "type": "inline_equation", + "content": "90\\%" + }, + { + "bbox": [ + 46, + 452, + 289, + 620 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 46, + 452, + 289, + 620 + ], + "type": "inline_equation", + "content": "95\\%" + }, + { + "bbox": [ + 46, + 452, + 289, + 620 + ], + "type": "text", + "content": ". Thus, our method is more suitable for challenging images and scenarios where we want to get a high IoU." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 641, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 641, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 641, + 288, + 714 + ], + "type": "text", + "content": "Performance Comparison. We compare our method with existing methods on five benchmarks in Tab. 3. Some methods use the SBD [16] dataset to train their network, while RITM suggests training on COCO [25] and LVIS [14]. We report the results of our method equipped with different base segmentation networks and trained on different" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 304, + 452, + 547, + 572 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 452, + 547, + 572 + ], + "spans": [ + { + "bbox": [ + 304, + 452, + 547, + 572 + ], + "type": "text", + "content": "datasets. Compared with some early methods like CD-Net [7] and f-BRS [39], different versions of our method show superior performance and efficiency. Compared with recent state-of-the-art methods RITM [40], FocalClick [8], FocusCut [26], PseudoClick [29], and TransClick [11], our method demonstrates competitive performance. Especially, our method achieves outstanding performance on the largest SBD dataset. Overall, the proposed method demonstrates preferable performance considering that the inference time is significantly low from the second click." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 306, + 585, + 405, + 597 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 585, + 405, + 597 + ], + "spans": [ + { + "bbox": [ + 306, + 585, + 405, + 597 + ], + "type": "text", + "content": "4.3. Method analysis" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 605, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 547, + 715 + ], + "type": "text", + "content": "Ablation study. We conduct ablation studies to verify the effectiveness of each component in our method. The results on three challenging datasets in presented in Tab. 4. We first construct a network with only a simple convolutional mask correction network as our baseline. The first point is not fed to the base segmentation network (HRNet18s) in this baseline. As shown in Tab. 4, a simple mask correction network can hardly achieve high performance. The input of the first click to the base segmentation network helps" + } + ] + } + ], + "index": 6 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "22779" + } + ] + } + ], + "index": 7 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 53, + 70, + 281, + 171 + ], + "blocks": [ + { + "bbox": [ + 53, + 70, + 281, + 171 + ], + "lines": [ + { + "bbox": [ + 53, + 70, + 281, + 171 + ], + "spans": [ + { + "bbox": [ + 53, + 70, + 281, + 171 + ], + "type": "table", + "html": "
1st ClickCorrSelf-AttTSDAVIS NoC@90SBD NoC@90Pascal NoC@90
7.118.324.38
✓6.986.833.19
✓✓6.326.303.09
✓✓6.026.332.98
✓✓✓5.866.242.89
✓✓✓✓5.666.162.84
", + "image_path": "4f92cbe5b66dbae3b0682e2a83843108315c0fcee2339d9e064a0ee221dcbba6.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 56, + 247, + 279, + 331 + ], + "blocks": [ + { + "bbox": [ + 46, + 178, + 287, + 236 + ], + "lines": [ + { + "bbox": [ + 46, + 178, + 287, + 236 + ], + "spans": [ + { + "bbox": [ + 46, + 178, + 287, + 236 + ], + "type": "text", + "content": "Table 4. Ablation study on three challenging benchmarks. HR-Net18s is used as the base segmentation network. 1st Click denotes that we input the first click to the base segmentation network, Corr denotes the correlation module, Self-Att denotes the self-attention module, and TS denotes the template selection module." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 56, + 247, + 279, + 331 + ], + "lines": [ + { + "bbox": [ + 56, + 247, + 279, + 331 + ], + "spans": [ + { + "bbox": [ + 56, + 247, + 279, + 331 + ], + "type": "table", + "html": "
Negative TemplatesDAVIS NoC@90SBD NoC@90Pascal NoC@90
Correlation Module✓6.106.393.01
6.096.262.96
Self-Attention Module✓6.046.553.22
5.926.292.99
", + "image_path": "cb49fe975800e71a79e0a60ffb17f9a7abb4fe11e8904192025fdd5b7392b28c.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 340, + 286, + 363 + ], + "lines": [ + { + "bbox": [ + 46, + 340, + 286, + 363 + ], + "spans": [ + { + "bbox": [ + 46, + 340, + 286, + 363 + ], + "type": "text", + "content": "Table 5. The performance of the correlation and self-attention modules with and without the adoption of the negative templates." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "text" + }, + { + "type": "image", + "bbox": [ + 51, + 376, + 284, + 491 + ], + "blocks": [ + { + "bbox": [ + 51, + 376, + 284, + 491 + ], + "lines": [ + { + "bbox": [ + 51, + 376, + 284, + 491 + ], + "spans": [ + { + "bbox": [ + 51, + 376, + 284, + 491 + ], + "type": "image", + "image_path": "1650afc9121aaa13cb26562151a851cc12b72f27328bc0246e93dcf9e378224e.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 500, + 287, + 534 + ], + "lines": [ + { + "bbox": [ + 46, + 500, + 287, + 534 + ], + "spans": [ + { + "bbox": [ + 46, + 500, + 287, + 534 + ], + "type": "text", + "content": "Figure 3. Illustration of the positive/negative score maps for template selection and positive/negative correlation similarity maps in click-guided correlation module." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 557, + 287, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 557, + 287, + 689 + ], + "spans": [ + { + "bbox": [ + 46, + 557, + 287, + 689 + ], + "type": "text", + "content": "extract target-aware features to boost the performance. However, the performance is still relatively low. Both the introduction of the click-guided self-attention module and the click-guided correlation module bring significant improvements over the simple mask correction network, indicating that they both effectively exploit the click information. Their combination achieves the best performance, showing that they learn complementary augmented features and can be combined to boost performance. The template selection module further improves performance by sampling several templates to enrich the click features." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 701, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 701, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 47, + 701, + 287, + 714 + ], + "type": "text", + "content": "The necessity of negative templates. All positive and" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 72, + 545, + 204 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 204 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 204 + ], + "type": "text", + "content": "negative templates are input to the self-attention and correlation modules. The adoption of positive templates is a natural choice since they contain rich information regarding the target. However, the negative templates are also vital since negative clicks are often selected in distractor areas, and they contain information that can discriminate the target from the background. Tab. 5 demonstrates the performance of the two modules with and without the negative templates. The employment of the negative templates effectively improves the performance of both the correlation and self-attention modules." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 220, + 545, + 435 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 220, + 545, + 435 + ], + "spans": [ + { + "bbox": [ + 304, + 220, + 545, + 435 + ], + "type": "text", + "content": "Qualitative analysis. We show the change of the positive/negative score maps for template selection and positive/negative correlation similarity maps in Fig. 3. After placing the first positive click, the model predicts an erroneous area that shows high semantic similarity to the target. After placing two more negative clicks in the erroneous area, the model successfully segments the target. In the interactive process, the score maps change with the clicks and can effectively discriminate the areas of the target of interest and other objects, which helps select meaningful and correct templates. The change in the correlation similarity maps shows that we can learn the target contours by correlating the templates with the feature maps. Fig. 3 only shows the similarity maps of two templates. Since we select several templates, the correlation results provide rich information to discriminate the target from other areas. Directly employing the correlation results as features helps better segment the target." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 451, + 545, + 535 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 451, + 545, + 535 + ], + "spans": [ + { + "bbox": [ + 304, + 451, + 545, + 535 + ], + "type": "text", + "content": "Limitation analysis. Our method still requires a relatively high computational cost in the first click, which may not be suitable for some simple annotation scenarios where only one or two clicks are needed. Maybe this can be solved by reducing the resolution of the base segmentation network as in FocalClick [8] and locally updating the mask with the mask correlation network. We leave this for future research." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 558, + 378, + 570 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 558, + 378, + 570 + ], + "spans": [ + { + "bbox": [ + 306, + 558, + 378, + 570 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "content": "In this paper, we propose an efficient EMC-Click method for click-based interactive segmentation. A lightweight mask correction network is constructed to iteratively update the mask, which significantly reduces the computational cost from the second click. A click-guided correlation module and a click-guided self-attention module are proposed to effectively exploit the click information to boost the performance of the mask correction network. Experiments on five benchmarks demonstrate that our method achieves competitive performance and higher efficiency compared with state-of-the-art methods." + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "22780" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 107, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 107, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 107, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 286, + 713 + ], + "type": "list", + "angle": 0, + "index": 17, + "blocks": [ + { + "bbox": [ + 53, + 91, + 286, + 124 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 286, + 124 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 286, + 124 + ], + "type": "text", + "content": "[1] Eirikur Agustsson, Jasper RR Uijlings, and Vittorio Ferrari. 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Intention-aware feature propagation network for interactive segmentation. arXiv:2203.05145, 2022. 3" + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 749, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 749, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 749, + 318, + 757 + ], + "type": "text", + "content": "22782" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 9 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Efficient Movie Scene Detection Using State-Space Transformers/b626675b-8b28-4fca-aa4b-1742033f43ec_content_list.json b/2023/Efficient Movie Scene Detection Using State-Space Transformers/b626675b-8b28-4fca-aa4b-1742033f43ec_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..c78a83d7d9a7bddbdeb3b91cf36e67df48f8cdfc --- /dev/null +++ b/2023/Efficient Movie Scene Detection Using State-Space Transformers/b626675b-8b28-4fca-aa4b-1742033f43ec_content_list.json @@ -0,0 +1,1835 @@ +[ + { + "type": "text", + "text": "Efficient Movie Scene Detection using State-Space Transformers", + "text_level": 1, + "bbox": [ + 161, + 130, + 808, + 152 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Md Mohaiminul Islam $^{1*}$ Mahmudul Hasan $^{2}$ Kishan Shamsundar Athrey $^{2}$ \nTony Braskich $^{2}$ Gedas Bertasius $^{1}$ $^{1}$ UNC Chapel Hill ${}^{2}$ Comcast Labs", + "bbox": [ + 179, + 179, + 787, + 233 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 268, + 313, + 284 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "The ability to distinguish between different movie scenes is critical for understanding the storyline of a movie. However, accurately detecting movie scenes is often challenging as it requires the ability to reason over very long movie segments. This contrasts with most existing video recognition models, which are typically designed for short-range video analysis. This work proposes a State-Space Transformer model that can efficiently capture dependencies in long movie videos for accurate movie scene detection. Our model, called TranS4mer, is built using a novel S4A building block, combining the strengths of structured state-space sequence (S4) and self-attention (A) layers. Given a sequence of frames divided into movie shots (uninterrupted periods where the camera position does not change), the S4A block first applies self-attention to capture short-range intra-shot dependencies. Afterward, the state-space operation in the S4A block aggregates long-range inter-shot cues. The final TranS4mer model, which can be trained end-to-end, is obtained by stacking the S4A blocks one after the other multiple times. Our proposed TranS4mer outperforms all prior methods in three movie scene detection datasets, including MovieNet, BBC, and OVSD, while being $2 \\times$ faster and requiring $3 \\times$ less GPU memory than standard Transformer models. We will release our code and models.", + "bbox": [ + 75, + 301, + 473, + 662 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 696, + 209, + 710 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Imagine watching The Godfather movie as illustrated in Figure 1. The first scene starts in the office room of mafia boss Don Vito Corleone, where he is discussing family business affairs with his eldest son Sonny Corleone and the family lawyer Tom Hagen. Then in the second scene, the family meets Virgil Sollozzo to hear about his business proposition. Afterward, the movie transitions into a third scene, where Don Vito chides his son Sonny for interfering. All of these movie scenes are inherently connected and create a complex storyline. Thus, the ability to recognize such", + "bbox": [ + 75, + 722, + 468, + 875 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "movie scenes is essential for understanding the plot of a movie. Moreover, identifying movie scenes enables broader applications, such as content-driven video search, preview generation, and minimally disruptive ad insertion.", + "bbox": [ + 500, + 270, + 890, + 330 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Unlike standard video recognition tasks (e.g., action recognition), which require a short-range analysis of video clips lasting only 5-10 seconds, movie scene detection requires short- and long-range understanding, where videos might last several minutes. For instance, to successfully recognize the scenes in Figure 1, we need to identify the visual concepts in each frame, such as characters, objects, and backgrounds (short-range modeling), while also reasoning about complex temporal events and activities (long-range modeling). For example, if we only look at the boundary frames of the first and second scenes of Figure 1 and identify the local properties (e.g., characters, objects, and backgrounds), it is quite difficult to determine the transition between the two scenes. However, considering longer temporal windows with frames from both scenes, we can recognize global events and identify their boundaries.", + "bbox": [ + 496, + 334, + 892, + 575 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "We also note that models that only use short-range temporal context typically produce many false positives due to abrupt low-level changes in the scene dynamics (e.g., camera switching between characters). For example, if we look at the middle two frames of scene 2 in Figure 1, we might mistake them for a scene boundary since the frames contain two characters. However, looking at all the frames in scene 2 makes it clear that they belong to the same scene. Therefore, a successful movie scene detection model should identify the short-range visual elements and also reason about their long-range temporal dependencies in a movie segment.", + "bbox": [ + 496, + 579, + 893, + 747 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "However, most existing movie scene detection methods [11, 35] are built using convolutional neural networks (CNNs), which are inherently designed using local operators (i.e., convolution kernels) for short-range video analysis. Thus, such models often fail to capture the long-range dependencies crucial for accurate movie scene detection. Recently, transformers have been shown to effectively model short-range and long-range dependencies in various Natural Language Processing (NLP) tasks [1,7,14, 15, 32, 37, 47, 49]. Inspired by the success of transform", + "bbox": [ + 496, + 750, + 893, + 901 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Research done while MI was an intern at Comcast Labs.", + "bbox": [ + 94, + 886, + 400, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "18749", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/7ea336fad0d749db3aa00c8718839cb5a8724c676bb4d154054a6f6a80a1257a.jpg", + "image_caption": [ + "Figure 1. Three scenes from the movie The Godfather. In the first scene, The Godfather (Don Vito Corleone) discusses family business affairs with his eldest son Sony and family lawyer Tom Hagen. Then the movie transitions into the second scene, where the mafia family meets Virgil Sollozzo to hear his business proposition. Afterward, in the third scene, Don Vito chides his son Sonny for interfering in the middle of his talk. Generally, movies are composed of well-defined scenes, and detecting those scenes is essential to high-level movie understanding. Therefore, this work aims to detect high-level scenes from a long-range movie video." + ], + "image_footnote": [], + "bbox": [ + 84, + 90, + 171, + 138 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/360c0ea64e987272d73fd417d0887368103d39162c9087447e77880dd45621fc.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 173, + 90, + 259, + 138 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/76e35dc1eb455ce7f1cf4319c9612ae2dab0a2f436837b5ab54b99409716724b.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 261, + 90, + 348, + 138 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/4ab128512689b67d329614cbec82a633b3e33e15e42a63a09d563fc15cb5a8c8.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 351, + 90, + 437, + 138 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/d11d77dbb3111a71ae320628023621bb00b172fa0d21f9330edeee51c54dfed6.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 439, + 90, + 524, + 138 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/f8b340fb3a939c73adeb338a223ad9676823a817550cd5b1b8a0a2f1c1dbb549.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 527, + 90, + 612, + 138 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/e93756d965d9d01f14cc3d1a3816d0eb6c4480f657f48c9dc1c052e15bde724c.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 614, + 90, + 702, + 138 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/9c0fda13a18abd58e5f36db1bfc5117353259d181c2a117544f895046c67fb77.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 705, + 90, + 792, + 138 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/a234ab7b4f27ba0626e083710298dcd678b28f6cfb5539b9ee698a95f7b7c0db.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 795, + 90, + 880, + 138 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "ers in NLP, subsequent works have shown the remarkable success of using transformers in several short-range vision tasks [8, 16]. However, applying Transformers to long video sequences remains challenging due to the quadratic cost of self-attention. To overcome these issues, recent work proposed a structured state-space sequence (S4) operator [18, 19, 33] for efficient long-range sequence analysis.", + "bbox": [ + 75, + 227, + 467, + 333 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Motivated by the developments in transformer and S4-based architectures, we present TranS4mer, an efficient end-to-end model for movie scene boundary detection, which combines the strengths of transformers for short-range modeling and S4 operators for long-range modeling. Specifically, we propose a novel state-space self-attention (S4A) block and build our TranS4mer model by stacking multiple S4A blocks on top of each other. Our model takes a sequence of frames divided into movie shots as input, where a shot is defined as a series of frames captured by the same camera over an uninterrupted period [46]. The S4A block first captures the short-range intra-shot dependencies by applying self-attention over the frames in each shot. Subsequently, it aggregates the inter-shot interactions over long movie segments by employing the state-space operator over all shots in a given movie video.", + "bbox": [ + 75, + 335, + 467, + 575 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "One key property of our model is that it independently applies self-attention to each shot, significantly reducing the cost of standard self-attention. For instance, if we have a video of 25 shots and each shot contains 3 frames, applying a standard vision transformer [16] with a patch size of $32 \\times 32$ will result in 3,675 tokens and a single self-attention operation will require $\\sim 13.5\\mathrm{M}$ pairwise comparisons. In contrast, applying self-attention within each shot parallelly reduces the number of comparisons $25 \\times$ times. Simultaneously, TranS4mer attains long-range modeling ability through the efficient state-space layers that do not require costly pairwise comparisons and operate over the entire input video. As a result, the proposed TranS4mer model can be efficiently applied to long movie videos.", + "bbox": [ + 75, + 580, + 467, + 791 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "We experiment with three movie scene detection datasets: MovieNet [25], BBC [3], and OVSD [40], and report that our method outperforms prior approaches by large margins $(+3.38\\%)$ AP, $+4.66\\%$ and $+7.36\\%$ respectively). TranS4mer is also $2\\times$ faster and requires $3\\times$ less GPU memory than the pure Transformer-based models. Moreover, to evaluate the generalizability of our model,", + "bbox": [ + 75, + 795, + 467, + 900 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "we experiment with several long-range video understanding tasks, such as movie clip classification and procedural activity recognition. TranS4mer performs the best in 5 out of 7 movie clip classification tasks on LVU [48], the best in procedural activity classification on Breakfast [30], and the second-best in procedural activity classification on COIN [43] datasets.", + "bbox": [ + 496, + 227, + 890, + 332 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related works", + "text_level": 1, + "bbox": [ + 500, + 345, + 643, + 361 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Long Sequence Modeling. Many modern approaches to long sequence modeling started in the field of Natural Language Processing (NLP). Bahdanau et al. [1] introduced an RNN architecture with an attention mechanism for machine translation. Afterward, Vaswani et al. [47] proposed the transformer model for capturing long-range dependencies in text sequences. Following this work, various improved transformer architectures were proposed [7, 14, 15, 32, 37, 49]. However, despite these advances, applying transformers to very long sequences is still challenging because of the quadratic cost of the self-attention operation. Consequently, many recent methods have developed efficient variations of standard self-attention [12, 26, 29, 36, 50]. Furthermore, the recent work of Gu et al. [17-19] proposed a structured statespace sequence (S4) model for long sequence analysis. The S4 models have achieved impressive results in many NLP tasks [17-20, 33], while having only linear memory and computation costs (w.r.t the sequence length). Building on this work, Islam et al. [34] proposed a model that applies S4 on pre-extracted video features for long-range video classification. In contrast, we propose an end-to-end trainable movie scene detection model that combines S4 and self-attention into a novel S4A block, which we use to build our TranS4mer model.", + "bbox": [ + 496, + 372, + 890, + 733 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Movie Scene Detection. The early approaches for movie scene detection consisted predominantly of unsupervised clustering-based methods [2,4,10,39,40,42,52] built using hand-crafted features. Recently, Huang et al. [25] introduced a large-scale dataset for movie scene detection called MovieNet, which became the most popular benchmark for this problem. Subsequently, Huang et al. [25] and Rao et al. [38] proposed an LSTM-based model for movie scene detection, which is applied on top of preextracted CNN features. Most recently, Chen et al. [11] and Mun et al. [35] introduced several end-to-end movie", + "bbox": [ + 496, + 734, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "header", + "text": "Scene 1 (250 seconds)", + "bbox": [ + 133, + 74, + 297, + 89 + ], + "page_idx": 1 + }, + { + "type": "header", + "text": "Scene 2 (310 seconds)", + "bbox": [ + 442, + 74, + 606, + 89 + ], + "page_idx": 1 + }, + { + "type": "header", + "text": "Scene 3 (200 seconds)", + "bbox": [ + 709, + 74, + 872, + 89 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "18750", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/b601745f8402a6727a45a986b65fb91f00347d29bd0eb0c9ca7a7c20e258f832.jpg", + "image_caption": [ + "Figure 2. The hierarchical structure of long movie videos. First, multiple consecutive frames captured from the same camera position depict a shot. Next, multiple neighboring shots constitute a movie scene. Finally, a movie is composed of a collection of scenes. Here, we show one scene that contains N shots with $K$ frames in each shot." + ], + "image_footnote": [], + "bbox": [ + 80, + 92, + 467, + 152 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "scene detection approaches built using 2D/3D CNN architectures. However, these CNN-based models are limited by the smaller receptive fields of the local convolution operations. In contrast, our TranS4mer model is constructed using global operators (state-space and self-attention), which are more effective for long-range modeling.", + "bbox": [ + 75, + 248, + 468, + 339 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Background", + "text_level": 1, + "bbox": [ + 76, + 352, + 205, + 369 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The State-Space Model (SSM) is a fundamental model used in many scientific fields, such as control theory and computational neuroscience. We can define the SSM in continuous time using the following equations:", + "bbox": [ + 75, + 377, + 468, + 439 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nh ^ {\\prime} (t) = A h (t) + B x (t) \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 189, + 449, + 468, + 474 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\ny (t) = C h (t) + D x (t)\n$$\n", + "text_format": "latex", + "bbox": [ + 197, + 469, + 352, + 484 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Here, $x(t)$ is the input signal, $h(t)$ is a latent state, $h'(t)$ is the first order derivative of $h(t)$ wrt $t$ , i.e., $h'(t) = \\frac{dh}{dt}$ , $y(t)$ is the output signal, and $A$ is the state matrix. Equation (1) can be discretized by sampling the underlying input signal $u(t)$ with a step size $\\Delta$ .", + "bbox": [ + 76, + 491, + 468, + 566 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nh _ {k} = \\bar {A} h _ {k - 1} + \\bar {B} x _ {k} \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 200, + 578, + 468, + 603 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\ny _ {k} = \\overline {{C}} h _ {k} + \\bar {D} x _ {k}\n$$\n", + "text_format": "latex", + "bbox": [ + 205, + 599, + 326, + 616 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Here, $\\overline{A}$ , $\\overline{B}$ , $\\overline{C}$ , and $\\overline{D}$ are the discrete versions of $A$ , $B$ , $C$ and $D$ . Furthermore, the equation (2) can be expressed as a convolution operation $(*)$ :", + "bbox": [ + 76, + 628, + 468, + 675 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\ny = \\bar {K} * x \\quad \\bar {K} = (\\bar {C B}, \\bar {C A B}, \\dots , \\bar {C A} ^ {L - 1} \\bar {B}), \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 94, + 686, + 468, + 705 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\overline{K}$ is a kernel, and $L$ is the sequence length.", + "bbox": [ + 76, + 718, + 410, + 734 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "S4 Model. The Structured State Space (S4) model is a particular class of SSM that requires the state matrix $A$ to be diagonal and low-rank. Because of the specific structure of the state matrix $A$ , we can derive a closed-form formula for the convolutional kernel $\\overline{K}$ in equation (3) [18], which then facilitates an efficient computation of $\\overline{K}$ without having to multiply the matrix $A$ , $L - 1$ times.", + "bbox": [ + 75, + 734, + 468, + 839 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Gated S4 Model. Borrowing the idea from Gated Attention [24], Metha at el. [33] introduced a Gated S4 model, which first uses linear layers to compute two latent representations $(u$ and $v)$ from the input sequences $x$ , and then", + "bbox": [ + 75, + 839, + 468, + 900 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "applies an S4 layer to obtain a contextualized representation $\\hat{u}$ . Finally, the tokens from $\\hat{u}$ are used to gate $v$ :", + "bbox": [ + 500, + 90, + 890, + 121 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nu = \\phi (W _ {u} x) \\quad v = \\phi (W _ {v} x)\n$$\n", + "text_format": "latex", + "bbox": [ + 589, + 132, + 799, + 148 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nh = S 4 (u) \\quad \\hat {u} = W _ {h} x \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 591, + 150, + 890, + 166 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\ny = W _ {y} (\\hat {u} \\odot v)\n$$\n", + "text_format": "latex", + "bbox": [ + 591, + 169, + 700, + 186 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Here, $W_{u}, W_{v}, W_{h}, W_{y}$ are the weight matrices of linear layers, $\\phi$ denotes GELU nonlinearity [23], $\\odot$ is elementwise multiplication, and S4 denotes an S4 layer described above.", + "bbox": [ + 498, + 195, + 890, + 239 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "4. Technical Approach", + "text_level": 1, + "bbox": [ + 498, + 253, + 692, + 271 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We aim to develop an efficient scene detection method for long movie videos. Movie videos have a specific hierarchical structure consisting of three semantic levels: (i) frames, (ii) shots, and (iii) scenes (See Figure 2). First, multiple consecutive frames constitute a shot, where the frames are captured from the same camera position over an uninterrupted period [46]. Second, multiple consecutive shots construct a scene, where a scene is a semantically cohesive unit of the storyline [27, 41]. Finally, a movie is composed of a collection of scenes. Shots can be easily recognized by detecting the changes in low-level visual cues [9, 13, 42]. However, identifying the scene boundary is more challenging as it requires high-level semantic understanding.", + "bbox": [ + 496, + 279, + 890, + 474 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Problem Overview. First, we formally define the problem of movie scene detection. We are given a movie video $V$ divided into $T$ non-overlapping automatically-detected shots, $V = \\{s_1,\\ldots ,s_i,\\ldots ,s_T\\}$ . We can then uniformly sample $K$ frames from each shot. Therefore, a shot is represented as $s_i = \\{f_1,\\dots ,f_j,\\dots ,f_K\\}$ , where $f_{j}\\in \\mathbb{R}^{3\\times H\\times W}$ depicts an RGB frame, $H$ is the height, and $W$ is the width of each frame. Following these definitions, we can then formulate the movie scene detection problem as a prediction task, where we need to produce a binary output $y_{i}\\in \\{0,1\\}$ for each video shot $s_i$ (i.e., whether a given shot is at a movie scene boundary or not).", + "bbox": [ + 496, + 476, + 890, + 656 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "**Approach Overview.** Our movie scene detection model, called the State-Space Transformer (TranS4mer), is built using our proposed S4A blocks that combine the strengths of structured state-space sequence (S4) and self-attention (A) layers. The S4A block utilizes the self-attention layer to encode short-range dependencies between frames in each shot and the S4 layer for capturing long-range dependencies between shots far away from each other. A detailed illustration of our model is presented in Figure 3. Below, we describe each component of our model in more detail.", + "bbox": [ + 496, + 657, + 890, + 806 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "4.1. The TranS4mer Model", + "text_level": 1, + "bbox": [ + 500, + 816, + 710, + 830 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Following previous methods [11,35,38], our model takes as input $N = 2m + 1$ temporally adjacent shots, $\\mathcal{V}_i = \\{s_{i - m},\\ldots ,s_i,\\ldots ,s_{i + m}\\}$ , and outputs a binary prediction $y_{i}\\in \\{0,1\\}$ for the shot $s_i$ . The neighboring shots provide", + "bbox": [ + 500, + 839, + 890, + 901 + ], + "page_idx": 2 + }, + { + "type": "header", + "text": "Scene S", + "bbox": [ + 254, + 78, + 297, + 88 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "18751", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/25feea89ec1c422697255ef8ed0724b5c0af5a4e57b00176e95a91475dfb592f.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 102, + 71, + 509, + 367 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/fc1d6e927c049e2f33b13d193633eaa1ce640b2f5f55a42037aa1bfa98846afb.jpg", + "image_caption": [ + "Figure 3. Overview of the TranS4mer model. Left: Our model takes a sequence of frames divided into automatically-detected shots. Following the ViT [16], the frames are decomposed into non-overlapping patches and passed through a linear projection layer. Afterward, we feed these patch-level embeddings through our TranS4mer model, which consists of $B$ state-space self-attention (S4A) blocks stacked on top of each other. Finally, the CLS tokens of all shots are passed to two linear layers, i.e., the boundary prediction head (which outputs a binary label indicating the boundary shot) and the contrastive head (which maximizes intra-shot similarity). Right: Each of our proposed S4A blocks contains a self-attention-based intra-shot module that models the interaction among frames in the same shot and a Gated S4-based inter-shot module that aggregates long-range temporal cues from shots far away from each other." + ], + "image_footnote": [], + "bbox": [ + 517, + 71, + 864, + 409 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "long-range contextual cues for predicting the boundary at shot $s_i$ . Here, $\\mathcal{V}_i \\in \\mathbb{R}^{N \\times K \\times 3 \\times H \\times W}$ is composed of $K$ frames from each of $N$ consecutive shots, where $H$ is the height, and $W$ is the width of each frame.", + "bbox": [ + 75, + 521, + 468, + 580 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Following ViT [16], we divide each frame into $P$ nonoverlapping patches of size $p \\times p$ , where $P = HW / p^2$ . Then we use a linear layer to project each patch into a hidden dimension $D$ , and a positional embedding is added to each patch token. As a result, we obtain a tensor of shape $\\mathbf{V}_i \\in \\mathbb{R}^{N \\times K \\times P \\times D}$ , which is fed to our TranS4mer model.", + "bbox": [ + 76, + 582, + 468, + 672 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The S4A Block. Our proposed S4A block enables us to compute a strong short-range feature representation and model long-range temporal dependencies among shots. It consists of two modules: a short-range intra-shot module and a long-range inter-shot module.", + "bbox": [ + 75, + 672, + 468, + 748 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Intra-Shot Module. The intra-shot module takes the input tensor $\\mathbf{V}_i\\in \\mathbb{R}^{N\\times K\\times P\\times D}$ , which we can think of as a collection of $N$ shots, where a sequence of tokens represents each shot $S_{i} = x_{1},\\ldots ,x_{L}$ , where $x_{i}\\in \\mathbb{R}^{D}$ , $L = K\\times P$ . The intra-shot module models the sequence of tokens from each shot independently. To this end, it first applies a multi-layer perceptron (MLP) layer and a residual connection. Afterward, it applies a Multiheaded Self Attention (MSA) layer and another residual connection. Layer Normalization (LN) is applied before the MLP", + "bbox": [ + 75, + 750, + 468, + 900 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "and the MSA layers. The module can be defined as follows:", + "bbox": [ + 500, + 521, + 888, + 536 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {x} ^ {\\prime} = \\operatorname {M H A} \\left(\\operatorname {L N} \\left(\\mathbf {x} _ {i n}\\right)\\right) + \\mathbf {x} _ {i n} \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 599, + 551, + 888, + 575 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {x} _ {\\text {o u t}} = \\operatorname {M L P} \\left(\\operatorname {L N} \\left(\\mathbf {x} ^ {\\prime}\\right)\\right) + \\mathbf {x} ^ {\\prime}\n$$\n", + "text_format": "latex", + "bbox": [ + 601, + 571, + 782, + 585 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The output of the intra-shot module $\\mathbf{V}'_i \\in \\mathbb{R}^{N \\times K \\times P \\times D}$ , is then passed to the inter-shot module.", + "bbox": [ + 498, + 603, + 888, + 635 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Note that applying self-attention to tokens from each shot separately reduces the computation cost to $O(NL^2)$ . In contrast, applying self-attention to the entire sequence of tokens in $\\mathbf{V}_{\\mathrm{i}}$ would cost $O(N^{2}L^{2})$ .", + "bbox": [ + 498, + 638, + 890, + 698 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Inter-Shot Module. Our previously defined intra-shot module only models short-range dependencies and, thus, lacks the ability for long-range temporal understanding, which is crucial for the movie scene detection task. To address this limitation, we propose an efficient inter-shot module based on the Gated S4 operator that aggregates long-range inter-shot cues.", + "bbox": [ + 496, + 700, + 890, + 806 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "First, we unroll the input tensor $\\mathbf{V}'_i$ into a sequence $z_{1},\\ldots ,z_{L'}$ , where $z_{i}\\in \\mathbb{R}^{D}$ , $L^{\\prime} = N\\times K\\times P$ . Then, we pass the sequence to a multi-layer perceptron (MLP) layer and a residual connection. Afterward, we apply a Gated S4 (GS4) layer and another residual connection. Layer Normalization (LN) is applied before MLP and GS4 layers:", + "bbox": [ + 496, + 809, + 890, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "18752", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\mathbf {z} ^ {\\prime} = \\operatorname {G S 4} \\left(\\operatorname {L N} \\left(\\mathbf {z} _ {i n}\\right)\\right) + \\mathbf {z} _ {i n} \\tag {6} \\\\ \\mathbf {z} _ {\\text {o u t}} = \\operatorname {M L P} \\left(\\operatorname {L N} \\left(\\mathbf {z} ^ {\\prime}\\right)\\right) + \\mathbf {z} ^ {\\prime} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 187, + 104, + 467, + 136 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The output of this operation is then passed into the next S4A block. Unlike the intra-shot module, which operates on a short sequence of length $L = K \\times P$ , the inter-shot module operates on much longer sequences of $L' = N \\times K \\times P$ . Our model can efficiently process such long sequences due to the Gated S4 layers in the inter-shot module.", + "bbox": [ + 76, + 147, + 467, + 237 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.2. Training and Loss Functions", + "text_level": 1, + "bbox": [ + 76, + 247, + 333, + 263 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Most prior works in move scene detection use self-supervised pretraining [11, 35]. Thus, we also adopt the self-supervised pretraining strategy of Mun at et al. [35], which uses pseudo boundaries of move scenes from the Dynamic Time Warping algorithm as a supervisory signal. Afterward, we finetune our pretrained model using the labeled subset of the data. Note that we do not claim technical novelty over the pretraining strategy. Instead, our main goal is to develop an efficient state-space transformer backbone for movie scene detection. Below, we provide more details related to the pretraining and fine-tuning protocols.", + "bbox": [ + 75, + 271, + 467, + 436 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Pretraining. Leveraging the pseudo movie scene boundaries, we optimize our model using the following two losses: (i) a shot-scene contrastive loss and (ii) a pseudoboundary prediction loss. The contrastive loss maximizes the similarity between the representations of a shot and its corresponding pseudo ground truth scene while also minimizing the similarity of a shot with all the other scenes. We represent each shot with its respective CLS token, whereas each scene is represented by mean-pooling the CLS tokens of all shots in that scene. The DTW algorithm divides the input video $\\mathcal{V}_i = \\{s_{i - m},\\dots ,s_i,\\dots ,s_{i + m}\\}$ into two pseudo-scenes $\\mathcal{V}_L = \\{s_{i - m},\\dots ,s_{i^*}\\}$ and $\\mathcal{V}_R = s_{i^{*} + 1},\\ldots ,s_{i + m}\\}$ , here $s_{i^*}$ is the pseudo-boundary shot. We can then define the shot-scene contrastive loss as:", + "bbox": [ + 75, + 438, + 467, + 648 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nl _ {\\mathrm {C}} (\\mathbf {r}, \\bar {\\mathbf {r}}) = - \\log \\frac {\\mathcal {S} (\\mathbf {r} , \\bar {\\mathbf {r}})}{\\mathcal {S} (\\mathbf {r} , \\bar {\\mathbf {r}}) + \\sum_ {\\mathbf {r} _ {n}} \\mathcal {S} (\\mathbf {r} _ {n} , \\bar {\\mathbf {r}}) + \\sum_ {\\bar {\\mathbf {r}} _ {n}} \\mathcal {S} (\\mathbf {r} , \\bar {\\mathbf {r}} _ {n})} \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 86, + 662, + 467, + 703 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Here, $\\mathbf{r}$ is a shot representation obtained by applying a linear layer on the CLS token of that shot, $\\bar{\\mathbf{r}}_L$ and $\\bar{\\mathbf{r}}_R$ are the scene-level representations of pseudo-scenes $\\nu_{L}$ and $\\nu_{R}$ , $\\mathbf{r}_n$ and $\\bar{\\mathbf{r}}_n$ are the negative shots and scenes from the minibatch. Similarity between two representations is calculated as: $S(\\mathbf{x},\\mathbf{y}) = \\exp ((\\mathbf{x}^{\\top}\\mathbf{y}) / (\\| \\mathbf{x}\\| \\| \\mathbf{y}\\|))$ . The first loss term can then be written as: $\\mathcal{L}_{\\mathrm{C}} = l_{\\mathrm{C}}(\\mathbf{r}_{i - m},\\bar{\\mathbf{r}}_L) + l_{\\mathrm{C}}(\\mathbf{r}_{i + m},\\bar{\\mathbf{r}}_R)$ .", + "bbox": [ + 76, + 710, + 467, + 815 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The second loss function of pseudo-boundary prediction is a simple objective that guides the model to predict a pseudo-boundary from a given shot representation. We can define this loss as a binary cross-entropy loss:", + "bbox": [ + 75, + 816, + 467, + 876 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\mathrm {B}} = - \\log \\left(\\rho_ {b} \\left(\\mathbf {r} _ {i ^ {*}}\\right)\\right) - \\log \\left(1 - \\rho_ {b} \\left(\\mathbf {r} _ {\\tilde {b}}\\right)\\right) \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 138, + 886, + 467, + 901 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Here, $\\mathbf{r}_{i^*}$ is the CLS representation of the pseudoboundary shot $s_{i^*}$ , $\\mathbf{r}_{\\bar{b}}$ is the representation of a randomly selected non-boundary shot $s_{\\bar{b}}$ , $\\rho_{b}$ is a projection layer that outputs the probability of a shot being the pseudo-boundary.", + "bbox": [ + 501, + 99, + 890, + 159 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The overall pretraining loss is the sum of the shot-scene contrastive loss and the pseudo-boundary loss.", + "bbox": [ + 501, + 160, + 888, + 188 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Finetuning. After the self-supervised pretraining, we finetune our model using the subset of the dataset with ground truth annotations. We use a binary cross-entropy loss as in [35] to finetune our model.", + "bbox": [ + 501, + 189, + 890, + 248 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.3. Implementation Details", + "text_level": 1, + "bbox": [ + 501, + 258, + 714, + 272 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Following the ViT [16], we resize video frames to a spatial dimension of $224 \\times 224$ and divide using a patch size of $32 \\times 32$ . Our model contains 12 S4A blocks and uses a hidden dimension of 384. It takes 25 neighboring shots as input, where each shot contains 3 frames. We use four data augmentation techniques: random crop, flip, color jitter, and Gaussian blur. We use a batch size of 256 and pretrain our model for 10 epochs before finetuning for 20 epochs. During pretraining, we use a base learning rate of 0.3, which we reduce using a cosine schedule after a linear warmup strategy of 1 epoch. During finetuning, we use a learning rate of $10^{-6}$ . We use the Adam [28] optimizer with a momentum of 0.9 and weight decay of $10^{-6}$ . We train our models using 8 NVIDIA RTX A6000 GPUs.", + "bbox": [ + 501, + 281, + 890, + 491 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "5. Experimental Setup", + "text_level": 1, + "bbox": [ + 501, + 503, + 689, + 520 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "5.1. Datasets", + "text_level": 1, + "bbox": [ + 501, + 529, + 599, + 542 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "MovieNet [25] is a large-scale dataset containing 1100 movies with 1.6 million shots, and 318 of these movies have ground-truth scene boundary annotation. The annotated subset of the dataset is divided into 190, 64, and 64 movies for training, validation, and testing. Following the previous approaches, we pretrain our model using all the movies, finetune using the standard training split of the annotated subset, and report the result on the test split.", + "bbox": [ + 501, + 551, + 890, + 672 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "BBC [3] contains 11 episodes from the BBC TV series Planet Earth [5]. The average duration of the videos is 50 minutes. The dataset contains 670 scenes and 4.9K shots.", + "bbox": [ + 501, + 672, + 888, + 717 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "OVSD [40] contains 21 short films with an average duration of 30 minutes. It has a total of 10K shots and 300 scenes extracted from movie scripts.", + "bbox": [ + 501, + 718, + 888, + 762 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "5.2. Evaluation Metrics", + "text_level": 1, + "bbox": [ + 501, + 771, + 681, + 785 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "AP measures the weighted average of precisions at different thresholds.", + "bbox": [ + 501, + 795, + 888, + 823 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "mIoU is the average intersection over union of predicted scene boundaries with the closest ground truth boundaries.", + "bbox": [ + 501, + 825, + 888, + 854 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "AUC-ROC is calculated as the True Positive Rate with respect to the False Positive Rate at different thresholds.", + "bbox": [ + 501, + 854, + 888, + 883 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "F1-Score is the harmonic mean of precision and recall.", + "bbox": [ + 522, + 885, + 880, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "18753", + "bbox": [ + 480, + 945, + 517, + 955 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/ac019eb0e17c68d5065fb2d64eb8c007f0904733c7d3a32a8e027094a9b98ed0.jpg", + "table_caption": [], + "table_footnote": [ + "Table 1. Results on MovieNet [25]. Horizontal lines in both Unsupervised and Supervised rows separate prior works from our implemented baselines. First, our method achieves state-of-the-art performance, outperforming the previous best method (BaSSL) by a significant margin of $3.38\\%$ AP. Second, compared to prior unsupervised approaches, the unsupervised TranS4mer model achieves better performance in all metrics. Finally, TranS4mer is $2.68 \\times$ faster and requires $3.38 \\times$ less GPU memory than the previous SOTA methods (ShotCol and BaSSL), while also being faster and more memory efficient than the transformer and state-space baselines." + ], + "table_body": "
MethodAP (↑)mIoU (↑)AUC-ROC (↑)F1 (↑)Memory (GB) (↓)Samples/s (↑)
UnsupervisedGraphCut [39]14.1029.70----
SCSA [10]14.7030.50----
DP [21]15.5032.00----
Story Graph [45]25.1035.70----
Grouping [40]33.6037.20----
BaSSL [35]31.5539.3671.6732.5534.280.96
Transformer [16]32.1637.2470.2331.2430.281.27
TimeSformer [6]32.4737.7670.9531.4528.121.47
Vanilla S4 [18]33.3438.1271.8632.2115.621.83
TranS4mer34.4539.6073.2533.4110.132.57
SupervisedSiamese [3]35.8039.60----
MS-LSTM [25]46.5046.20----
LGSS [38]47.1048.80----
ViS4mer [34]55.1348.2788.7446.15
ShotCoL [11]53.40---34.280.96
BaSSL [35]57.4050.6990.5447.0234.280.96
Transformer [16]58.8151.2190.8447.8830.281.27
TimeSformer [6]59.6250.7590.6648.0228.121.47
Vanilla S4 [18]59.7151.3290.9647.8515.621.83
TranS4mer60.7851.9191.8948.3610.132.57
", + "bbox": [ + 86, + 85, + 879, + 422 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5.3. Baselines", + "text_level": 1, + "bbox": [ + 76, + 517, + 186, + 531 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Prior Methods. In our comparisons, we include several unsupervised approaches such as GraphCut [39], SCSA [10], DP [21], Story Graph [45], and Grouping [40]. These methods use various clustering techniques using pre-extracted features. Moreover, we compare our approach with supervised approaches, such as Siamese [3], MS-LSTM [25], and LGSS [38], which also use pre-extracted CNN features. We also compare against the long-range video model ViS4mer [34], which uses S4 layers as a late-fusion strategy. Finally, we include two recent end-to-end trainable models that use self-supervised pretraining, namely, ShotCoL [11] and BaSSL [35]. Both models use CNN models based on ResNet-50 [22].", + "bbox": [ + 75, + 537, + 470, + 734 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Our Implemented Baselines. To make our comparisons more complete, we implement three additional baselines: 1) Transformer: We construct this baseline by following the standard Vision Transformer [16]. In particular, we replace the Gated S4 layers of the TranS4mer model with self-attention layers and keep everything else unchanged. 2) TimeSformer: We construct this baseline by replacing the Gated S4 layers of our model with the divided space-time attention proposed by Bertasius at et al. [6]. 3) Vanilla S4: We develop this baseline by replacing the Gated S4 layers of the TranS4mer model with the S4 layers [18].", + "bbox": [ + 75, + 734, + 470, + 902 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "6. Results and Analysis", + "text_level": 1, + "bbox": [ + 500, + 517, + 697, + 534 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "6.1. Main Results on the MovieNet Dataset", + "text_level": 1, + "bbox": [ + 500, + 542, + 831, + 558 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Comparison to the State-of-the-Art. We present the results on MovieNet [25] in Table 1. We first compare our method with the unsupervised approaches, including GraphCut [39], SCSA [10], DP [21], Story Graph [45], Grouping [40], and BaSSL (unsupervised) [35]. For a fair comparison, we train an unsupervised variant of our TranS4mer model using pseudo-boundary loss without ground-truth annotations and report the result without supervised finetuning. Our results suggest that our unsupervised TranS4mer model achieves the best performance according to all metrics and outperforms the prior best method Grouping by $+0.85\\%$ AP. Next, we compare the supervised variant of our model (i.e., finetuned with ground truth annotations) with the state-of-the-art supervised methods (ShotCol [11] and BaSSL [35])). We also compare with the state-space-based long-range video classification model ViS4mer [34]. We observe that TranS4mer achieves the best performance in all metrics and outperforms the previous best method (BaSSL) by a large margin $(+3.38\\%)$ AP.", + "bbox": [ + 496, + 566, + 890, + 852 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Comparison with Transformer and State-space Baselines. In Table 1, we also compare our TranS4mer model with the Transformer and State-space baselines: Trans-", + "bbox": [ + 496, + 854, + 893, + 902 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "18754", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "former, TimeSformer, and Vanilla S4 (See subsection 5.3). Note that all three baselines use intra-shot and inter-shot modules; however, instead of a Gated S4 layer, Transformer uses standard self-attention [16], TimeSformer uses divided space-time attention [18], and Vanilla S4 uses standard S4 [18] at the inter-shot module. Moreover, similar to the TranS4mer-Unsupervised method, we train unsupervised variants of these baselines without any ground-truth annotation. First, we observe that all three baselines outperform the previous state-of-the-art method (BaSSL [35]) in both supervised and unsupervised settings, indicating the effectiveness of our proposed intra-shot and inter-shot block designs. Second, TranS4mer performs better than all three of these baselines, outperforming Transformer by $+1.97\\%$ and $+2.29\\%$ , TimeSformer by $+1.16\\%$ and $+1.98\\%$ , and Vanilla S4 by $+1.07\\%$ and $+1.11\\%$ in supervised and unsupervised approaches, respectively. These experiments indicate that TranS4mer is better suited for movie scene detection than the standard self-attention and state-space models.", + "bbox": [ + 76, + 90, + 472, + 378 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Computational Cost Analysis. We compare the GPU memory consumption (in gigabytes) and the training speed (samples/s) of our model with the previous best methods as well as our implemented baselines in Table 1. First, we observe that, in addition to achieving the best performance, our method also requires $3.38 \\times$ less memory and is $2.68 \\times$ faster than the previous state-of-the-art method BaSSL [35]. Second, compared to the standard Transformer baseline, TranS4mer is $2 \\times$ faster and requires $3 \\times$ less GPU memory. Finally, our model is significantly cheaper than efficient self-attention and state-space models such as TimeSformer and Vanilla S4. Whereas TimeSformer and Vanilla S4 require 28.12 GB and 15.62 GB of memory, our TranS4mer requires only 10.13 GB of memory. Moreover, the training speed of TranS4mer is 2.57 samples/second compared to the 1.47 and 1.82 samples/second speed of TimeSformer and Vanilla S4, respectively. These observations suggest that TranS4mer is much more efficient than prior methods and standard self-attention and state-space-based models.", + "bbox": [ + 76, + 381, + 472, + 667 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Comparison Using the Same Backbone Model. For a fair comparison, we also experiment with a previous-best BaSSL [35] method that uses the same backbone as our model (i.e., ViT-S/32). We report that our TranS4mer outperforms this BaSSL variant by $+2.77\\%$ AP.", + "bbox": [ + 76, + 672, + 470, + 748 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "6.2. Scene Detection on Other Datasets", + "text_level": 1, + "bbox": [ + 76, + 767, + 379, + 782 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We experiment with two additional movie scene detection datasets, BBC [3] and OVSD [40]. We present these results in Table 2, which shows that TranS4mer achieves the best result among all methods, outperforming the previous best BaSSL [35] method by $4.66\\%$ AP on the BBC and $7.36\\%$ AP on the OVSD datasets. These results demonstrate our method's ability to generalize to other datasets.", + "bbox": [ + 76, + 794, + 468, + 902 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/ad53d515baddd5ff2151c533e296024274b79247e29d8a3d3c2d9aaddf89fc9d.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodAP (↑)
BaSSL [35]39.98
Transformer [16]41.86
TimeSformer [6]42.23
Vanilla S4 [18]42.56
TranS4mer43.64
", + "bbox": [ + 506, + 75, + 689, + 167 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/2ffac1e28fbebe48937d44bf49e470f3139519eb9807468052d1e8a3310cd736.jpg", + "table_caption": [ + "(a) Performance on BBC [3]." + ], + "table_footnote": [], + "table_body": "
MethodAP (↑)
BaSSL [35]28.68
Transformer [16]33.12
TimeSformer [6]33.87
Vanilla S4 [18]34.21
TranS4mer36.04
", + "bbox": [ + 699, + 77, + 885, + 169 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/a8fb60ec44e5742f9382d646d9ac87c912c9a6a94cdf843bdfce8b426c76145d.jpg", + "table_caption": [ + "(b) Performance on OVSD [40].", + "Table 2. Scene Detection on additional datasets. TranS4mer outperforms the prior method (BaSSL) by a large margin of $4.66\\%$ AP on BBC [3] and $7.36\\%$ AP on OVSD [40] datasets." + ], + "table_footnote": [], + "table_body": "
MethodRelationSpeakSceneDirectorGenreWriterYear
ObjTrans. [48]53.1039.4056.9051.2054.6034.5039.10
ViS4mer [34]57.1440.7967.4462.6154.7148.8044.75
TranS4mer59.5239.2170.9363.8655.8546.9345.45
(a) Performance on LVU [48]
", + "bbox": [ + 503, + 244, + 887, + 306 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/ae04e349d6ab5960a70c3164b6868f77e4d36f0bcf784bd484ef8540c80dcf2b.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
Model#Data(↓)Acc.(↑)
GHRM [51]306K75.50
Dist.Sup. [31]136M89.90
ViS4mer [34]495K88.17
TranS4mer495K90.27
", + "bbox": [ + 504, + 309, + 689, + 372 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/12fbfe926002b07937de1a4c850da7eb27f017ccc3f933e236e97eb5a9c39f80.jpg", + "table_caption": [ + "(b) Performance on Breakfast [30]" + ], + "table_footnote": [], + "table_body": "
Model#Data(↓)Acc.(↑)
TSN [44]306K73.40
Dist.Sup. [31]136M90.00
ViS4mer [34]495K88.41
TranS4mer495K89.23
", + "bbox": [ + 700, + 309, + 885, + 373 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "(c) Performance on COIN [43]", + "bbox": [ + 709, + 373, + 877, + 385 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 3. Long-range video classification. (a) TranS4mer achieves best performance in 5 out of 7 classification tasks in LVU benchmark [48]. Moreover, (b) it performs best on the Breakfast [30] and (c) second-best on the COIN [43] datasets, while using significantly less pretraining data (middle column).", + "bbox": [ + 498, + 388, + 890, + 459 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "6.3. Long-range Video Classification", + "text_level": 1, + "bbox": [ + 500, + 476, + 782, + 492 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "In addition to move scene detection, we also experiment with other tasks including long-form movie clip classification in the LVU [48] dataset, and long-range procedural activity classification on Breakfast [30] and COIN [43] datasets. LVU contains $30K$ videos from $3K$ movies, Breakfast has 1,712 videos of 10 cooking activities, and COIN contains 11,827 videos of 180 different procedural activities. Videos of each dataset are $2 - 3$ minutes long. We present the results in Table 3. On LVU, TranS4mer achieves the best performance in 5 out of 7 tasks (Table 3(a)). Moreover, TranS4mer also achieves the best performance on Breakfast (Table 3(b)) and the second-best performance on COIN (Table 3(c)) while using significantly fewer pretraining samples than the state-of-the-art Distant Supervision [31] approach. These results indicate that TranS4mer can be effectively applied to other domains and tasks.", + "bbox": [ + 496, + 501, + 890, + 743 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "6.4. Ablation Studies", + "text_level": 1, + "bbox": [ + 500, + 755, + 663, + 768 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Temporal Extent Ablation. To verify our hypothesis that long-range temporal context is critical for accurate movie scene detection, we experiment with video inputs of different lengths (i.e., video inputs containing 9, 17, 25, and 33 contextual shots) while predicting the boundary for the middle shot. Note that videos with more input shots denote longer input videos. We present these results in Figure 4a. First, we notice that a short temporal window of 9 context", + "bbox": [ + 496, + 779, + 890, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "18755", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/73508bc8858b27ae82cb8df775b54f351b5bde2180e51ff6844172a75811449b.jpg", + "image_caption": [ + "(a) Performance $\\uparrow$ TranS4mer achieves much better performance for longer videos.", + "Table 4. Ablation studies with (a) TranS4mer modules, (b) (c) positioning, and (d) variants of S4 layers. Intra-shot and inter-shot modules are complementary, and TranS4mer with Gated S4 layers at every S4A block yields the best performance." + ], + "image_footnote": [], + "bbox": [ + 120, + 63, + 349, + 200 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/7edc9edbe6d125fe50678b1bc28e2171ce5cd8ddcfc02c658adb5c05e5ab0a89.jpg", + "image_caption": [ + "(b) Training Speed $\\uparrow$ TranS4mer is significantly faster than the Transformer baseline.", + "Figure 4. (a) Performance (AP), (b) Training Speed (Samples/Second), and (c) Memory Requirements (GigaBytes), and as a function of the number of input shots. Note that videos with more input shots denote longer input videos." + ], + "image_footnote": [], + "bbox": [ + 372, + 65, + 612, + 200 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/9b52f9a383728fdc8562c2a8366a40731997d54aa7e605822d2c684a82864365.jpg", + "image_caption": [ + "(c) Memory Requirements $\\downarrow$ TranS4mer requires significantly less GPU memory." + ], + "image_footnote": [], + "bbox": [ + 625, + 69, + 852, + 200 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/dee39f14b602b1821733080f5853bb53198a3b6e908393c017377da51c65c054.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
Intra-ShotInter-ShotAp (↑)
✓✗57.80
✗✓55.59
✓✓60.78
", + "bbox": [ + 117, + 277, + 346, + 349 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/4d530835e22c8d9ef4bb6b268857d999c76c645ead46108fca9cea795342702c.jpg", + "table_caption": [ + "(a)TranS4mer modules." + ], + "table_footnote": [], + "table_body": "
S4 layersAP (↑)
1-658.31
7-1258.82
1-1260.78
", + "bbox": [ + 367, + 277, + 514, + 349 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/9d02b436da756ac3abff8d0d4ac9118a5da6425bf9018db795d38128030d38d8.jpg", + "table_caption": [ + "(b) S4 in different layers." + ], + "table_footnote": [], + "table_body": "
S4 layersAP (↑)
every 2nd59.82
every 4th58.01
all60.78
", + "bbox": [ + 535, + 277, + 687, + 349 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/3518ffc92b2beb7ff4835c90396d871bbb8dacf58deaf330704f186aaa641f37.jpg", + "table_caption": [ + "(c) S4 in every $k^{th}$ layer." + ], + "table_footnote": [], + "table_body": "
S4 layersAP (↑)
S459.71
DS460.13
GS460.78
", + "bbox": [ + 710, + 277, + 857, + 349 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "(d) Different S4 variants.", + "bbox": [ + 712, + 351, + 844, + 363 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "tual shots produces a suboptimal performance of $53.29\\%$ AP. Increasing the temporal extent to 25 contextual shots increases the performance to $60.78\\%$ AP $(+7.49\\%$ boost). Adding more contextual shots does not yield any significant improvements. These results verify the importance of long-range temporal modeling for movie scene detection.", + "bbox": [ + 75, + 424, + 468, + 515 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Detailed Comparison with Transformer. We next present a detailed comparison of our model with the Transformer baseline [16]. In particular, we experiment with videos that contain a different number of input shots and plot the accuracy in AP as a function of the number of input shots (see Figure 4). Although the Transformer baseline performs better for shorter video inputs, our TranS4mer model achieves much better performance using longer videos. Specifically, TranS4mer yields $+2.07\\%$ larger AP than the transformer model when using the longest video inputs. This suggests that TranS4mer is more effective at capturing long-range dependencies for the movie scene detection task. Moreover, we also illustrate the training speed (Samples/Second) and the memory requirement (GigaBytes) as a function of the number of input shots (see Figures 4b and 4c). We observe that as we increase the video length, the training speed of the Transformer baseline drops drastically, and the memory requirement grows rapidly. Overall, our proposed TranS4mer model is $2.7\\times$ faster and requires $3.38\\times$ less GPU memory than the Transformer baseline while using the longest video inputs.", + "bbox": [ + 75, + 518, + 468, + 835 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Ablation with Intra-Shot and Inter-Shot Modules. In Table 4a, we analyze the significance of our (i) self-attention-based intra-shot module and (ii) state-space-based inter-shot module. We observe that removing the inter-shot", + "bbox": [ + 75, + 839, + 468, + 900 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "module drops the performance by $2.98\\%$ AP, whereas discarding the intra-shot module decreases the performance by $5.19\\%$ AP. Therefore, based on these results, we can conclude that both the intra-shot and inter-shot modules are essential for good movie scene detection performance. We also note that they are complementary to each other, which aligns with our intuition of the intra-shot module being responsible for short-range representations while the intershot module is dedicated to long-range temporal reasoning.", + "bbox": [ + 496, + 424, + 890, + 559 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Ablation with S4 Layers. We experiment with injecting our proposed S4A block into different encoder layers (Table 4b). We also evaluate a sparser TranS4mer variant with our S4A block injected into every $k^{th}$ layer of the network (Table 4c). Lastly, we experiment with different S4 variants (i.e., Diagonal S4 (DS4) [20], Gated S4 (GS4) [33]) (Table 4d). Our results suggest that using S4A with Gated S4 in every layer of the network leads to the best accuracy.", + "bbox": [ + 496, + 560, + 892, + 681 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "7. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 694, + 617, + 709 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this work, we propose an efficient movie scene segmentation method which combines the strengths of selfattention for short-range modeling and state-space models for long-range modeling. Our method, named TranS4mer, achieves state-of-the-art results in three different movie scene segmentation datasets (MovieNet, BBC, and OVSD). Moreover, our model is significantly faster and requires less GPU memory than previous approaches and the standard vision transformer models. In future, we will extend our model to other long-range video understanding and multimodal tasks such as movie summarization, movie trailer generation, and natural language grounding in long videos.", + "bbox": [ + 496, + 719, + 890, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "18756", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Dzmitry Bahdanau, Kyunghyun Cho, et al. Neural machine translation by jointly learning to align and translate. arXiv preprint arXiv: 1409.0473, 2014. 1, 2", + "[2] Lorenzo Baraldi, Costantino Grana, and Rita Cucchiara. Analysis and re-use of videos in educational digital libraries with automatic scene detection. In *Italian Research Conference on Digital Libraries*, pages 155–164. 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In Exploration of Visual Data, pages 53-73. Springer, 2003. 2" + ], + "bbox": [ + 501, + 92, + 892, + 642 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "18758", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/Efficient Movie Scene Detection Using State-Space Transformers/b626675b-8b28-4fca-aa4b-1742033f43ec_model.json b/2023/Efficient Movie Scene Detection Using State-Space Transformers/b626675b-8b28-4fca-aa4b-1742033f43ec_model.json new file mode 100644 index 0000000000000000000000000000000000000000..48a8887ca7e9b17db3731ab83c836c530eba28cf --- /dev/null +++ b/2023/Efficient Movie Scene Detection Using State-Space Transformers/b626675b-8b28-4fca-aa4b-1742033f43ec_model.json @@ -0,0 +1,2431 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.163, + 0.131, + 0.809, + 0.154 + ], + "angle": 0, + "content": "Efficient Movie Scene Detection using State-Space Transformers" + }, + { + "type": "text", + "bbox": [ + 0.18, + 0.18, + 0.788, + 0.234 + ], + "angle": 0, + "content": "Md Mohaiminul Islam\\(^{1*}\\) Mahmudul Hasan\\(^{2}\\) Kishan Shamsundar Athrey\\(^{2}\\) \nTony Braskich\\(^{2}\\) Gedas Bertasius\\(^{1}\\) \n\\(^{1}\\)UNC Chapel Hill \\({}^{2}\\)Comcast Labs" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.269, + 0.314, + 0.285 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.302, + 0.474, + 0.664 + ], + "angle": 0, + "content": "The ability to distinguish between different movie scenes is critical for understanding the storyline of a movie. However, accurately detecting movie scenes is often challenging as it requires the ability to reason over very long movie segments. This contrasts with most existing video recognition models, which are typically designed for short-range video analysis. This work proposes a State-Space Transformer model that can efficiently capture dependencies in long movie videos for accurate movie scene detection. Our model, called TranS4mer, is built using a novel S4A building block, combining the strengths of structured state-space sequence (S4) and self-attention (A) layers. Given a sequence of frames divided into movie shots (uninterrupted periods where the camera position does not change), the S4A block first applies self-attention to capture short-range intra-shot dependencies. Afterward, the state-space operation in the S4A block aggregates long-range inter-shot cues. The final TranS4mer model, which can be trained end-to-end, is obtained by stacking the S4A blocks one after the other multiple times. Our proposed TranS4mer outperforms all prior methods in three movie scene detection datasets, including MovieNet, BBC, and OVSD, while being \\(2 \\times\\) faster and requiring \\(3 \\times\\) less GPU memory than standard Transformer models. We will release our code and models." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.697, + 0.21, + 0.712 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.723, + 0.47, + 0.875 + ], + "angle": 0, + "content": "Imagine watching The Godfather movie as illustrated in Figure 1. The first scene starts in the office room of mafia boss Don Vito Corleone, where he is discussing family business affairs with his eldest son Sonny Corleone and the family lawyer Tom Hagen. Then in the second scene, the family meets Virgil Sollozzo to hear about his business proposition. Afterward, the movie transitions into a third scene, where Don Vito chides his son Sonny for interfering. All of these movie scenes are inherently connected and create a complex storyline. Thus, the ability to recognize such" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.271, + 0.892, + 0.332 + ], + "angle": 0, + "content": "movie scenes is essential for understanding the plot of a movie. Moreover, identifying movie scenes enables broader applications, such as content-driven video search, preview generation, and minimally disruptive ad insertion." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.335, + 0.893, + 0.576 + ], + "angle": 0, + "content": "Unlike standard video recognition tasks (e.g., action recognition), which require a short-range analysis of video clips lasting only 5-10 seconds, movie scene detection requires short- and long-range understanding, where videos might last several minutes. For instance, to successfully recognize the scenes in Figure 1, we need to identify the visual concepts in each frame, such as characters, objects, and backgrounds (short-range modeling), while also reasoning about complex temporal events and activities (long-range modeling). For example, if we only look at the boundary frames of the first and second scenes of Figure 1 and identify the local properties (e.g., characters, objects, and backgrounds), it is quite difficult to determine the transition between the two scenes. However, considering longer temporal windows with frames from both scenes, we can recognize global events and identify their boundaries." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.58, + 0.895, + 0.748 + ], + "angle": 0, + "content": "We also note that models that only use short-range temporal context typically produce many false positives due to abrupt low-level changes in the scene dynamics (e.g., camera switching between characters). For example, if we look at the middle two frames of scene 2 in Figure 1, we might mistake them for a scene boundary since the frames contain two characters. However, looking at all the frames in scene 2 makes it clear that they belong to the same scene. Therefore, a successful movie scene detection model should identify the short-range visual elements and also reason about their long-range temporal dependencies in a movie segment." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.75, + 0.895, + 0.902 + ], + "angle": 0, + "content": "However, most existing movie scene detection methods [11, 35] are built using convolutional neural networks (CNNs), which are inherently designed using local operators (i.e., convolution kernels) for short-range video analysis. Thus, such models often fail to capture the long-range dependencies crucial for accurate movie scene detection. Recently, transformers have been shown to effectively model short-range and long-range dependencies in various Natural Language Processing (NLP) tasks [1,7,14, 15, 32, 37, 47, 49]. Inspired by the success of transform" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.887, + 0.401, + 0.9 + ], + "angle": 0, + "content": "*Research done while MI was an intern at Comcast Labs." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "18749" + } + ], + [ + { + "type": "header", + "bbox": [ + 0.135, + 0.075, + 0.298, + 0.09 + ], + "angle": 0, + "content": "Scene 1 (250 seconds)" + }, + { + "type": "header", + "bbox": [ + 0.443, + 0.075, + 0.607, + 0.09 + ], + "angle": 0, + "content": "Scene 2 (310 seconds)" + }, + { + "type": "header", + "bbox": [ + 0.71, + 0.075, + 0.874, + 0.09 + ], + "angle": 0, + "content": "Scene 3 (200 seconds)" + }, + { + "type": "image", + "bbox": [ + 0.086, + 0.092, + 0.172, + 0.14 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.174, + 0.092, + 0.261, + 0.14 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.263, + 0.092, + 0.349, + 0.14 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.352, + 0.092, + 0.439, + 0.14 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.441, + 0.092, + 0.526, + 0.14 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.528, + 0.092, + 0.614, + 0.14 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.616, + 0.092, + 0.703, + 0.14 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.706, + 0.092, + 0.793, + 0.14 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.796, + 0.092, + 0.882, + 0.14 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.146, + 0.894, + 0.217 + ], + "angle": 0, + "content": "Figure 1. Three scenes from the movie The Godfather. In the first scene, The Godfather (Don Vito Corleone) discusses family business affairs with his eldest son Sony and family lawyer Tom Hagen. Then the movie transitions into the second scene, where the mafia family meets Virgil Sollozzo to hear his business proposition. Afterward, in the third scene, Don Vito chides his son Sonny for interfering in the middle of his talk. Generally, movies are composed of well-defined scenes, and detecting those scenes is essential to high-level movie understanding. Therefore, this work aims to detect high-level scenes from a long-range movie video." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.228, + 0.468, + 0.334 + ], + "angle": 0, + "content": "ers in NLP, subsequent works have shown the remarkable success of using transformers in several short-range vision tasks [8, 16]. However, applying Transformers to long video sequences remains challenging due to the quadratic cost of self-attention. To overcome these issues, recent work proposed a structured state-space sequence (S4) operator [18, 19, 33] for efficient long-range sequence analysis." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.337, + 0.468, + 0.577 + ], + "angle": 0, + "content": "Motivated by the developments in transformer and S4-based architectures, we present TranS4mer, an efficient end-to-end model for movie scene boundary detection, which combines the strengths of transformers for short-range modeling and S4 operators for long-range modeling. Specifically, we propose a novel state-space self-attention (S4A) block and build our TranS4mer model by stacking multiple S4A blocks on top of each other. Our model takes a sequence of frames divided into movie shots as input, where a shot is defined as a series of frames captured by the same camera over an uninterrupted period [46]. The S4A block first captures the short-range intra-shot dependencies by applying self-attention over the frames in each shot. Subsequently, it aggregates the inter-shot interactions over long movie segments by employing the state-space operator over all shots in a given movie video." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.581, + 0.468, + 0.792 + ], + "angle": 0, + "content": "One key property of our model is that it independently applies self-attention to each shot, significantly reducing the cost of standard self-attention. For instance, if we have a video of 25 shots and each shot contains 3 frames, applying a standard vision transformer [16] with a patch size of \\(32 \\times 32\\) will result in 3,675 tokens and a single self-attention operation will require \\(\\sim 13.5\\mathrm{M}\\) pairwise comparisons. In contrast, applying self-attention within each shot parallelly reduces the number of comparisons \\(25 \\times\\) times. Simultaneously, TranS4mer attains long-range modeling ability through the efficient state-space layers that do not require costly pairwise comparisons and operate over the entire input video. As a result, the proposed TranS4mer model can be efficiently applied to long movie videos." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.796, + 0.468, + 0.901 + ], + "angle": 0, + "content": "We experiment with three movie scene detection datasets: MovieNet [25], BBC [3], and OVSD [40], and report that our method outperforms prior approaches by large margins \\((+3.38\\%)\\) AP, \\(+4.66\\%\\) and \\(+7.36\\%\\) respectively). TranS4mer is also \\(2\\times\\) faster and requires \\(3\\times\\) less GPU memory than the pure Transformer-based models. Moreover, to evaluate the generalizability of our model," + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.228, + 0.892, + 0.333 + ], + "angle": 0, + "content": "we experiment with several long-range video understanding tasks, such as movie clip classification and procedural activity recognition. TranS4mer performs the best in 5 out of 7 movie clip classification tasks on LVU [48], the best in procedural activity classification on Breakfast [30], and the second-best in procedural activity classification on COIN [43] datasets." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.347, + 0.644, + 0.362 + ], + "angle": 0, + "content": "2. Related works" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.373, + 0.892, + 0.734 + ], + "angle": 0, + "content": "Long Sequence Modeling. Many modern approaches to long sequence modeling started in the field of Natural Language Processing (NLP). Bahdanau et al. [1] introduced an RNN architecture with an attention mechanism for machine translation. Afterward, Vaswani et al. [47] proposed the transformer model for capturing long-range dependencies in text sequences. Following this work, various improved transformer architectures were proposed [7, 14, 15, 32, 37, 49]. However, despite these advances, applying transformers to very long sequences is still challenging because of the quadratic cost of the self-attention operation. Consequently, many recent methods have developed efficient variations of standard self-attention [12, 26, 29, 36, 50]. Furthermore, the recent work of Gu et al. [17-19] proposed a structured statespace sequence (S4) model for long sequence analysis. The S4 models have achieved impressive results in many NLP tasks [17-20, 33], while having only linear memory and computation costs (w.r.t the sequence length). Building on this work, Islam et al. [34] proposed a model that applies S4 on pre-extracted video features for long-range video classification. In contrast, we propose an end-to-end trainable movie scene detection model that combines S4 and self-attention into a novel S4A block, which we use to build our TranS4mer model." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.735, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Movie Scene Detection. The early approaches for movie scene detection consisted predominantly of unsupervised clustering-based methods [2,4,10,39,40,42,52] built using hand-crafted features. Recently, Huang et al. [25] introduced a large-scale dataset for movie scene detection called MovieNet, which became the most popular benchmark for this problem. Subsequently, Huang et al. [25] and Rao et al. [38] proposed an LSTM-based model for movie scene detection, which is applied on top of preextracted CNN features. Most recently, Chen et al. [11] and Mun et al. [35] introduced several end-to-end movie" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "18750" + } + ], + [ + { + "type": "header", + "bbox": [ + 0.255, + 0.079, + 0.298, + 0.089 + ], + "angle": 0, + "content": "Scene S" + }, + { + "type": "image", + "bbox": [ + 0.081, + 0.093, + 0.468, + 0.153 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.157, + 0.47, + 0.24 + ], + "angle": 0, + "content": "Figure 2. The hierarchical structure of long movie videos. First, multiple consecutive frames captured from the same camera position depict a shot. Next, multiple neighboring shots constitute a movie scene. Finally, a movie is composed of a collection of scenes. Here, we show one scene that contains N shots with \\( K \\) frames in each shot." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.249, + 0.469, + 0.34 + ], + "angle": 0, + "content": "scene detection approaches built using 2D/3D CNN architectures. However, these CNN-based models are limited by the smaller receptive fields of the local convolution operations. In contrast, our TranS4mer model is constructed using global operators (state-space and self-attention), which are more effective for long-range modeling." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.353, + 0.206, + 0.37 + ], + "angle": 0, + "content": "3. Background" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.378, + 0.469, + 0.44 + ], + "angle": 0, + "content": "The State-Space Model (SSM) is a fundamental model used in many scientific fields, such as control theory and computational neuroscience. We can define the SSM in continuous time using the following equations:" + }, + { + "type": "equation", + "bbox": [ + 0.191, + 0.45, + 0.469, + 0.475 + ], + "angle": 0, + "content": "\\[\nh ^ {\\prime} (t) = A h (t) + B x (t) \\tag {1}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.199, + 0.47, + 0.353, + 0.485 + ], + "angle": 0, + "content": "\\[\ny (t) = C h (t) + D x (t)\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.492, + 0.469, + 0.568 + ], + "angle": 0, + "content": "Here, \\( x(t) \\) is the input signal, \\( h(t) \\) is a latent state, \\( h'(t) \\) is the first order derivative of \\( h(t) \\) wrt \\( t \\), i.e., \\( h'(t) = \\frac{dh}{dt} \\), \\( y(t) \\) is the output signal, and \\( A \\) is the state matrix. Equation (1) can be discretized by sampling the underlying input signal \\( u(t) \\) with a step size \\( \\Delta \\)." + }, + { + "type": "equation", + "bbox": [ + 0.202, + 0.579, + 0.469, + 0.604 + ], + "angle": 0, + "content": "\\[\nh _ {k} = \\bar {A} h _ {k - 1} + \\bar {B} x _ {k} \\tag {2}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.206, + 0.601, + 0.328, + 0.617 + ], + "angle": 0, + "content": "\\[\ny _ {k} = \\overline {{C}} h _ {k} + \\bar {D} x _ {k}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.629, + 0.469, + 0.676 + ], + "angle": 0, + "content": "Here, \\(\\overline{A}\\), \\(\\overline{B}\\), \\(\\overline{C}\\), and \\(\\overline{D}\\) are the discrete versions of \\(A\\), \\(B\\), \\(C\\) and \\(D\\). Furthermore, the equation (2) can be expressed as a convolution operation \\((*)\\):" + }, + { + "type": "equation", + "bbox": [ + 0.095, + 0.687, + 0.469, + 0.707 + ], + "angle": 0, + "content": "\\[\ny = \\bar {K} * x \\quad \\bar {K} = (\\bar {C B}, \\bar {C A B}, \\dots , \\bar {C A} ^ {L - 1} \\bar {B}), \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.719, + 0.411, + 0.735 + ], + "angle": 0, + "content": "where \\(\\overline{K}\\) is a kernel, and \\(L\\) is the sequence length." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.735, + 0.469, + 0.84 + ], + "angle": 0, + "content": "S4 Model. The Structured State Space (S4) model is a particular class of SSM that requires the state matrix \\( A \\) to be diagonal and low-rank. Because of the specific structure of the state matrix \\( A \\), we can derive a closed-form formula for the convolutional kernel \\( \\overline{K} \\) in equation (3) [18], which then facilitates an efficient computation of \\( \\overline{K} \\) without having to multiply the matrix \\( A \\), \\( L - 1 \\) times." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.469, + 0.901 + ], + "angle": 0, + "content": "Gated S4 Model. Borrowing the idea from Gated Attention [24], Metha at el. [33] introduced a Gated S4 model, which first uses linear layers to compute two latent representations \\((u\\) and \\(v)\\) from the input sequences \\(x\\), and then" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.092, + 0.892, + 0.122 + ], + "angle": 0, + "content": "applies an S4 layer to obtain a contextualized representation \\(\\hat{u}\\). Finally, the tokens from \\(\\hat{u}\\) are used to gate \\(v\\):" + }, + { + "type": "equation", + "bbox": [ + 0.591, + 0.133, + 0.8, + 0.149 + ], + "angle": 0, + "content": "\\[\nu = \\phi (W _ {u} x) \\quad v = \\phi (W _ {v} x)\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.593, + 0.151, + 0.891, + 0.167 + ], + "angle": 0, + "content": "\\[\nh = S 4 (u) \\quad \\hat {u} = W _ {h} x \\tag {4}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.593, + 0.17, + 0.701, + 0.187 + ], + "angle": 0, + "content": "\\[\ny = W _ {y} (\\hat {u} \\odot v)\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.196, + 0.892, + 0.241 + ], + "angle": 0, + "content": "Here, \\( W_{u}, W_{v}, W_{h}, W_{y} \\) are the weight matrices of linear layers, \\( \\phi \\) denotes GELU nonlinearity [23], \\( \\odot \\) is elementwise multiplication, and S4 denotes an S4 layer described above." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.255, + 0.693, + 0.272 + ], + "angle": 0, + "content": "4. Technical Approach" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.28, + 0.892, + 0.476 + ], + "angle": 0, + "content": "We aim to develop an efficient scene detection method for long movie videos. Movie videos have a specific hierarchical structure consisting of three semantic levels: (i) frames, (ii) shots, and (iii) scenes (See Figure 2). First, multiple consecutive frames constitute a shot, where the frames are captured from the same camera position over an uninterrupted period [46]. Second, multiple consecutive shots construct a scene, where a scene is a semantically cohesive unit of the storyline [27, 41]. Finally, a movie is composed of a collection of scenes. Shots can be easily recognized by detecting the changes in low-level visual cues [9, 13, 42]. However, identifying the scene boundary is more challenging as it requires high-level semantic understanding." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.477, + 0.892, + 0.657 + ], + "angle": 0, + "content": "Problem Overview. First, we formally define the problem of movie scene detection. We are given a movie video \\(V\\) divided into \\(T\\) non-overlapping automatically-detected shots, \\(V = \\{s_1,\\ldots ,s_i,\\ldots ,s_T\\}\\). We can then uniformly sample \\(K\\) frames from each shot. Therefore, a shot is represented as \\(s_i = \\{f_1,\\dots ,f_j,\\dots ,f_K\\}\\), where \\(f_{j}\\in \\mathbb{R}^{3\\times H\\times W}\\) depicts an RGB frame, \\(H\\) is the height, and \\(W\\) is the width of each frame. Following these definitions, we can then formulate the movie scene detection problem as a prediction task, where we need to produce a binary output \\(y_{i}\\in \\{0,1\\}\\) for each video shot \\(s_i\\) (i.e., whether a given shot is at a movie scene boundary or not)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.658, + 0.892, + 0.808 + ], + "angle": 0, + "content": "**Approach Overview.** Our movie scene detection model, called the State-Space Transformer (TranS4mer), is built using our proposed S4A blocks that combine the strengths of structured state-space sequence (S4) and self-attention (A) layers. The S4A block utilizes the self-attention layer to encode short-range dependencies between frames in each shot and the S4 layer for capturing long-range dependencies between shots far away from each other. A detailed illustration of our model is presented in Figure 3. Below, we describe each component of our model in more detail." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.817, + 0.712, + 0.832 + ], + "angle": 0, + "content": "4.1. The TranS4mer Model" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.84, + 0.892, + 0.902 + ], + "angle": 0, + "content": "Following previous methods [11,35,38], our model takes as input \\(N = 2m + 1\\) temporally adjacent shots, \\(\\mathcal{V}_i = \\{s_{i - m},\\ldots ,s_i,\\ldots ,s_{i + m}\\}\\), and outputs a binary prediction \\(y_{i}\\in \\{0,1\\}\\) for the shot \\(s_i\\). The neighboring shots provide" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "18751" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.104, + 0.073, + 0.511, + 0.368 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.518, + 0.073, + 0.865, + 0.41 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.412, + 0.892, + 0.51 + ], + "angle": 0, + "content": "Figure 3. Overview of the TranS4mer model. Left: Our model takes a sequence of frames divided into automatically-detected shots. Following the ViT [16], the frames are decomposed into non-overlapping patches and passed through a linear projection layer. Afterward, we feed these patch-level embeddings through our TranS4mer model, which consists of \\( B \\) state-space self-attention (S4A) blocks stacked on top of each other. Finally, the CLS tokens of all shots are passed to two linear layers, i.e., the boundary prediction head (which outputs a binary label indicating the boundary shot) and the contrastive head (which maximizes intra-shot similarity). Right: Each of our proposed S4A blocks contains a self-attention-based intra-shot module that models the interaction among frames in the same shot and a Gated S4-based inter-shot module that aggregates long-range temporal cues from shots far away from each other." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.522, + 0.469, + 0.581 + ], + "angle": 0, + "content": "long-range contextual cues for predicting the boundary at shot \\( s_i \\). Here, \\( \\mathcal{V}_i \\in \\mathbb{R}^{N \\times K \\times 3 \\times H \\times W} \\) is composed of \\( K \\) frames from each of \\( N \\) consecutive shots, where \\( H \\) is the height, and \\( W \\) is the width of each frame." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.583, + 0.469, + 0.673 + ], + "angle": 0, + "content": "Following ViT [16], we divide each frame into \\(P\\) nonoverlapping patches of size \\(p \\times p\\), where \\(P = HW / p^2\\). Then we use a linear layer to project each patch into a hidden dimension \\(D\\), and a positional embedding is added to each patch token. As a result, we obtain a tensor of shape \\(\\mathbf{V}_i \\in \\mathbb{R}^{N \\times K \\times P \\times D}\\), which is fed to our TranS4mer model." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.673, + 0.469, + 0.749 + ], + "angle": 0, + "content": "The S4A Block. Our proposed S4A block enables us to compute a strong short-range feature representation and model long-range temporal dependencies among shots. It consists of two modules: a short-range intra-shot module and a long-range inter-shot module." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.75, + 0.47, + 0.901 + ], + "angle": 0, + "content": "Intra-Shot Module. The intra-shot module takes the input tensor \\(\\mathbf{V}_i\\in \\mathbb{R}^{N\\times K\\times P\\times D}\\), which we can think of as a collection of \\(N\\) shots, where a sequence of tokens represents each shot \\(S_{i} = x_{1},\\ldots ,x_{L}\\), where \\(x_{i}\\in \\mathbb{R}^{D}\\), \\(L = K\\times P\\). The intra-shot module models the sequence of tokens from each shot independently. To this end, it first applies a multi-layer perceptron (MLP) layer and a residual connection. Afterward, it applies a Multiheaded Self Attention (MSA) layer and another residual connection. Layer Normalization (LN) is applied before the MLP" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.522, + 0.89, + 0.537 + ], + "angle": 0, + "content": "and the MSA layers. The module can be defined as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.6, + 0.553, + 0.89, + 0.577 + ], + "angle": 0, + "content": "\\[\n\\mathbf {x} ^ {\\prime} = \\operatorname {M H A} \\left(\\operatorname {L N} \\left(\\mathbf {x} _ {i n}\\right)\\right) + \\mathbf {x} _ {i n} \\tag {5}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.602, + 0.572, + 0.783, + 0.587 + ], + "angle": 0, + "content": "\\[\n\\mathbf {x} _ {\\text {o u t}} = \\operatorname {M L P} \\left(\\operatorname {L N} \\left(\\mathbf {x} ^ {\\prime}\\right)\\right) + \\mathbf {x} ^ {\\prime}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.604, + 0.89, + 0.636 + ], + "angle": 0, + "content": "The output of the intra-shot module \\(\\mathbf{V}'_i \\in \\mathbb{R}^{N \\times K \\times P \\times D}\\), is then passed to the inter-shot module." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.639, + 0.892, + 0.699 + ], + "angle": 0, + "content": "Note that applying self-attention to tokens from each shot separately reduces the computation cost to \\( O(NL^2) \\). In contrast, applying self-attention to the entire sequence of tokens in \\( \\mathbf{V}_{\\mathrm{i}} \\) would cost \\( O(N^{2}L^{2}) \\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.701, + 0.892, + 0.807 + ], + "angle": 0, + "content": "Inter-Shot Module. Our previously defined intra-shot module only models short-range dependencies and, thus, lacks the ability for long-range temporal understanding, which is crucial for the movie scene detection task. To address this limitation, we propose an efficient inter-shot module based on the Gated S4 operator that aggregates long-range inter-shot cues." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.81, + 0.892, + 0.901 + ], + "angle": 0, + "content": "First, we unroll the input tensor \\(\\mathbf{V}'_i\\) into a sequence \\(z_{1},\\ldots ,z_{L'}\\), where \\(z_{i}\\in \\mathbb{R}^{D}\\), \\(L^{\\prime} = N\\times K\\times P\\). Then, we pass the sequence to a multi-layer perceptron (MLP) layer and a residual connection. Afterward, we apply a Gated S4 (GS4) layer and another residual connection. Layer Normalization (LN) is applied before MLP and GS4 layers:" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "18752" + } + ], + [ + { + "type": "equation", + "bbox": [ + 0.188, + 0.105, + 0.468, + 0.137 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\mathbf {z} ^ {\\prime} = \\operatorname {G S 4} \\left(\\operatorname {L N} \\left(\\mathbf {z} _ {i n}\\right)\\right) + \\mathbf {z} _ {i n} \\tag {6} \\\\ \\mathbf {z} _ {\\text {o u t}} = \\operatorname {M L P} \\left(\\operatorname {L N} \\left(\\mathbf {z} ^ {\\prime}\\right)\\right) + \\mathbf {z} ^ {\\prime} \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.148, + 0.468, + 0.238 + ], + "angle": 0, + "content": "The output of this operation is then passed into the next S4A block. Unlike the intra-shot module, which operates on a short sequence of length \\( L = K \\times P \\), the inter-shot module operates on much longer sequences of \\( L' = N \\times K \\times P \\). Our model can efficiently process such long sequences due to the Gated S4 layers in the inter-shot module." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.248, + 0.334, + 0.264 + ], + "angle": 0, + "content": "4.2. Training and Loss Functions" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.272, + 0.468, + 0.437 + ], + "angle": 0, + "content": "Most prior works in move scene detection use self-supervised pretraining [11, 35]. Thus, we also adopt the self-supervised pretraining strategy of Mun at et al. [35], which uses pseudo boundaries of move scenes from the Dynamic Time Warping algorithm as a supervisory signal. Afterward, we finetune our pretrained model using the labeled subset of the data. Note that we do not claim technical novelty over the pretraining strategy. Instead, our main goal is to develop an efficient state-space transformer backbone for movie scene detection. Below, we provide more details related to the pretraining and fine-tuning protocols." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.439, + 0.468, + 0.649 + ], + "angle": 0, + "content": "Pretraining. Leveraging the pseudo movie scene boundaries, we optimize our model using the following two losses: (i) a shot-scene contrastive loss and (ii) a pseudoboundary prediction loss. The contrastive loss maximizes the similarity between the representations of a shot and its corresponding pseudo ground truth scene while also minimizing the similarity of a shot with all the other scenes. We represent each shot with its respective CLS token, whereas each scene is represented by mean-pooling the CLS tokens of all shots in that scene. The DTW algorithm divides the input video \\(\\mathcal{V}_i = \\{s_{i - m},\\dots ,s_i,\\dots ,s_{i + m}\\}\\) into two pseudo-scenes \\(\\mathcal{V}_L = \\{s_{i - m},\\dots ,s_{i^*}\\}\\) and \\(\\mathcal{V}_R = s_{i^{*} + 1},\\ldots ,s_{i + m}\\}\\), here \\(s_{i^*}\\) is the pseudo-boundary shot. We can then define the shot-scene contrastive loss as:" + }, + { + "type": "equation", + "bbox": [ + 0.088, + 0.663, + 0.468, + 0.704 + ], + "angle": 0, + "content": "\\[\nl _ {\\mathrm {C}} (\\mathbf {r}, \\bar {\\mathbf {r}}) = - \\log \\frac {\\mathcal {S} (\\mathbf {r} , \\bar {\\mathbf {r}})}{\\mathcal {S} (\\mathbf {r} , \\bar {\\mathbf {r}}) + \\sum_ {\\mathbf {r} _ {n}} \\mathcal {S} (\\mathbf {r} _ {n} , \\bar {\\mathbf {r}}) + \\sum_ {\\bar {\\mathbf {r}} _ {n}} \\mathcal {S} (\\mathbf {r} , \\bar {\\mathbf {r}} _ {n})} \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.711, + 0.468, + 0.816 + ], + "angle": 0, + "content": "Here, \\(\\mathbf{r}\\) is a shot representation obtained by applying a linear layer on the CLS token of that shot, \\(\\bar{\\mathbf{r}}_L\\) and \\(\\bar{\\mathbf{r}}_R\\) are the scene-level representations of pseudo-scenes \\(\\nu_{L}\\) and \\(\\nu_{R}\\), \\(\\mathbf{r}_n\\) and \\(\\bar{\\mathbf{r}}_n\\) are the negative shots and scenes from the minibatch. Similarity between two representations is calculated as: \\(S(\\mathbf{x},\\mathbf{y}) = \\exp ((\\mathbf{x}^{\\top}\\mathbf{y}) / (\\| \\mathbf{x}\\| \\| \\mathbf{y}\\|))\\). The first loss term can then be written as: \\(\\mathcal{L}_{\\mathrm{C}} = l_{\\mathrm{C}}(\\mathbf{r}_{i - m},\\bar{\\mathbf{r}}_L) + l_{\\mathrm{C}}(\\mathbf{r}_{i + m},\\bar{\\mathbf{r}}_R)\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.818, + 0.468, + 0.877 + ], + "angle": 0, + "content": "The second loss function of pseudo-boundary prediction is a simple objective that guides the model to predict a pseudo-boundary from a given shot representation. We can define this loss as a binary cross-entropy loss:" + }, + { + "type": "equation", + "bbox": [ + 0.14, + 0.887, + 0.468, + 0.902 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\mathrm {B}} = - \\log \\left(\\rho_ {b} \\left(\\mathbf {r} _ {i ^ {*}}\\right)\\right) - \\log \\left(1 - \\rho_ {b} \\left(\\mathbf {r} _ {\\tilde {b}}\\right)\\right) \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.502, + 0.1, + 0.891, + 0.16 + ], + "angle": 0, + "content": "Here, \\(\\mathbf{r}_{i^*}\\) is the CLS representation of the pseudoboundary shot \\(s_{i^*}\\), \\(\\mathbf{r}_{\\bar{b}}\\) is the representation of a randomly selected non-boundary shot \\(s_{\\bar{b}}\\), \\(\\rho_{b}\\) is a projection layer that outputs the probability of a shot being the pseudo-boundary." + }, + { + "type": "text", + "bbox": [ + 0.502, + 0.161, + 0.89, + 0.189 + ], + "angle": 0, + "content": "The overall pretraining loss is the sum of the shot-scene contrastive loss and the pseudo-boundary loss." + }, + { + "type": "text", + "bbox": [ + 0.502, + 0.19, + 0.891, + 0.249 + ], + "angle": 0, + "content": "Finetuning. After the self-supervised pretraining, we finetune our model using the subset of the dataset with ground truth annotations. We use a binary cross-entropy loss as in [35] to finetune our model." + }, + { + "type": "title", + "bbox": [ + 0.502, + 0.259, + 0.715, + 0.273 + ], + "angle": 0, + "content": "4.3. Implementation Details" + }, + { + "type": "text", + "bbox": [ + 0.502, + 0.282, + 0.891, + 0.492 + ], + "angle": 0, + "content": "Following the ViT [16], we resize video frames to a spatial dimension of \\(224 \\times 224\\) and divide using a patch size of \\(32 \\times 32\\). Our model contains 12 S4A blocks and uses a hidden dimension of 384. It takes 25 neighboring shots as input, where each shot contains 3 frames. We use four data augmentation techniques: random crop, flip, color jitter, and Gaussian blur. We use a batch size of 256 and pretrain our model for 10 epochs before finetuning for 20 epochs. During pretraining, we use a base learning rate of 0.3, which we reduce using a cosine schedule after a linear warmup strategy of 1 epoch. During finetuning, we use a learning rate of \\(10^{-6}\\). We use the Adam [28] optimizer with a momentum of 0.9 and weight decay of \\(10^{-6}\\). We train our models using 8 NVIDIA RTX A6000 GPUs." + }, + { + "type": "title", + "bbox": [ + 0.502, + 0.505, + 0.691, + 0.521 + ], + "angle": 0, + "content": "5. Experimental Setup" + }, + { + "type": "title", + "bbox": [ + 0.502, + 0.53, + 0.6, + 0.544 + ], + "angle": 0, + "content": "5.1. Datasets" + }, + { + "type": "text", + "bbox": [ + 0.502, + 0.553, + 0.891, + 0.673 + ], + "angle": 0, + "content": "MovieNet [25] is a large-scale dataset containing 1100 movies with 1.6 million shots, and 318 of these movies have ground-truth scene boundary annotation. The annotated subset of the dataset is divided into 190, 64, and 64 movies for training, validation, and testing. Following the previous approaches, we pretrain our model using all the movies, finetune using the standard training split of the annotated subset, and report the result on the test split." + }, + { + "type": "text", + "bbox": [ + 0.502, + 0.674, + 0.89, + 0.718 + ], + "angle": 0, + "content": "BBC [3] contains 11 episodes from the BBC TV series Planet Earth [5]. The average duration of the videos is 50 minutes. The dataset contains 670 scenes and 4.9K shots." + }, + { + "type": "text", + "bbox": [ + 0.502, + 0.719, + 0.89, + 0.763 + ], + "angle": 0, + "content": "OVSD [40] contains 21 short films with an average duration of 30 minutes. It has a total of 10K shots and 300 scenes extracted from movie scripts." + }, + { + "type": "title", + "bbox": [ + 0.502, + 0.772, + 0.682, + 0.786 + ], + "angle": 0, + "content": "5.2. Evaluation Metrics" + }, + { + "type": "text", + "bbox": [ + 0.502, + 0.796, + 0.89, + 0.824 + ], + "angle": 0, + "content": "AP measures the weighted average of precisions at different thresholds." + }, + { + "type": "text", + "bbox": [ + 0.502, + 0.826, + 0.89, + 0.855 + ], + "angle": 0, + "content": "mIoU is the average intersection over union of predicted scene boundaries with the closest ground truth boundaries." + }, + { + "type": "text", + "bbox": [ + 0.502, + 0.856, + 0.89, + 0.885 + ], + "angle": 0, + "content": "AUC-ROC is calculated as the True Positive Rate with respect to the False Positive Rate at different thresholds." + }, + { + "type": "text", + "bbox": [ + 0.523, + 0.886, + 0.882, + 0.901 + ], + "angle": 0, + "content": "F1-Score is the harmonic mean of precision and recall." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.946, + 0.518, + 0.956 + ], + "angle": 0, + "content": "18753" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.087, + 0.087, + 0.88, + 0.423 + ], + "angle": 0, + "content": "
MethodAP (↑)mIoU (↑)AUC-ROC (↑)F1 (↑)Memory (GB) (↓)Samples/s (↑)
UnsupervisedGraphCut [39]14.1029.70----
SCSA [10]14.7030.50----
DP [21]15.5032.00----
Story Graph [45]25.1035.70----
Grouping [40]33.6037.20----
BaSSL [35]31.5539.3671.6732.5534.280.96
Transformer [16]32.1637.2470.2331.2430.281.27
TimeSformer [6]32.4737.7670.9531.4528.121.47
Vanilla S4 [18]33.3438.1271.8632.2115.621.83
TranS4mer34.4539.6073.2533.4110.132.57
SupervisedSiamese [3]35.8039.60----
MS-LSTM [25]46.5046.20----
LGSS [38]47.1048.80----
ViS4mer [34]55.1348.2788.7446.15
ShotCoL [11]53.40---34.280.96
BaSSL [35]57.4050.6990.5447.0234.280.96
Transformer [16]58.8151.2190.8447.8830.281.27
TimeSformer [6]59.6250.7590.6648.0228.121.47
Vanilla S4 [18]59.7151.3290.9647.8515.621.83
TranS4mer60.7851.9191.8948.3610.132.57
" + }, + { + "type": "table_footnote", + "bbox": [ + 0.076, + 0.429, + 0.895, + 0.501 + ], + "angle": 0, + "content": "Table 1. Results on MovieNet [25]. Horizontal lines in both Unsupervised and Supervised rows separate prior works from our implemented baselines. First, our method achieves state-of-the-art performance, outperforming the previous best method (BaSSL) by a significant margin of \\(3.38\\%\\) AP. Second, compared to prior unsupervised approaches, the unsupervised TranS4mer model achieves better performance in all metrics. Finally, TranS4mer is \\(2.68 \\times\\) faster and requires \\(3.38 \\times\\) less GPU memory than the previous SOTA methods (ShotCol and BaSSL), while also being faster and more memory efficient than the transformer and state-space baselines." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.518, + 0.187, + 0.532 + ], + "angle": 0, + "content": "5.3. Baselines" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.538, + 0.471, + 0.735 + ], + "angle": 0, + "content": "Prior Methods. In our comparisons, we include several unsupervised approaches such as GraphCut [39], SCSA [10], DP [21], Story Graph [45], and Grouping [40]. These methods use various clustering techniques using pre-extracted features. Moreover, we compare our approach with supervised approaches, such as Siamese [3], MS-LSTM [25], and LGSS [38], which also use pre-extracted CNN features. We also compare against the long-range video model ViS4mer [34], which uses S4 layers as a late-fusion strategy. Finally, we include two recent end-to-end trainable models that use self-supervised pretraining, namely, ShotCoL [11] and BaSSL [35]. Both models use CNN models based on ResNet-50 [22]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.735, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Our Implemented Baselines. To make our comparisons more complete, we implement three additional baselines: 1) Transformer: We construct this baseline by following the standard Vision Transformer [16]. In particular, we replace the Gated S4 layers of the TranS4mer model with self-attention layers and keep everything else unchanged. 2) TimeSformer: We construct this baseline by replacing the Gated S4 layers of our model with the divided space-time attention proposed by Bertasius at et al. [6]. 3) Vanilla S4: We develop this baseline by replacing the Gated S4 layers of the TranS4mer model with the S4 layers [18]." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.518, + 0.698, + 0.535 + ], + "angle": 0, + "content": "6. Results and Analysis" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.543, + 0.833, + 0.559 + ], + "angle": 0, + "content": "6.1. Main Results on the MovieNet Dataset" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.567, + 0.892, + 0.853 + ], + "angle": 0, + "content": "Comparison to the State-of-the-Art. We present the results on MovieNet [25] in Table 1. We first compare our method with the unsupervised approaches, including GraphCut [39], SCSA [10], DP [21], Story Graph [45], Grouping [40], and BaSSL (unsupervised) [35]. For a fair comparison, we train an unsupervised variant of our TranS4mer model using pseudo-boundary loss without ground-truth annotations and report the result without supervised finetuning. Our results suggest that our unsupervised TranS4mer model achieves the best performance according to all metrics and outperforms the prior best method Grouping by \\(+0.85\\%\\) AP. Next, we compare the supervised variant of our model (i.e., finetuned with ground truth annotations) with the state-of-the-art supervised methods (ShotCol [11] and BaSSL [35])). We also compare with the state-space-based long-range video classification model ViS4mer [34]. We observe that TranS4mer achieves the best performance in all metrics and outperforms the previous best method (BaSSL) by a large margin \\((+3.38\\%)\\) AP." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.856, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Comparison with Transformer and State-space Baselines. In Table 1, we also compare our TranS4mer model with the Transformer and State-space baselines: Trans-" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "18754" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.091, + 0.473, + 0.379 + ], + "angle": 0, + "content": "former, TimeSformer, and Vanilla S4 (See subsection 5.3). Note that all three baselines use intra-shot and inter-shot modules; however, instead of a Gated S4 layer, Transformer uses standard self-attention [16], TimeSformer uses divided space-time attention [18], and Vanilla S4 uses standard S4 [18] at the inter-shot module. Moreover, similar to the TranS4mer-Unsupervised method, we train unsupervised variants of these baselines without any ground-truth annotation. First, we observe that all three baselines outperform the previous state-of-the-art method (BaSSL [35]) in both supervised and unsupervised settings, indicating the effectiveness of our proposed intra-shot and inter-shot block designs. Second, TranS4mer performs better than all three of these baselines, outperforming Transformer by \\(+1.97\\%\\) and \\(+2.29\\%\\), TimeSformer by \\(+1.16\\%\\) and \\(+1.98\\%\\), and Vanilla S4 by \\(+1.07\\%\\) and \\(+1.11\\%\\) in supervised and unsupervised approaches, respectively. These experiments indicate that TranS4mer is better suited for movie scene detection than the standard self-attention and state-space models." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.382, + 0.473, + 0.669 + ], + "angle": 0, + "content": "Computational Cost Analysis. We compare the GPU memory consumption (in gigabytes) and the training speed (samples/s) of our model with the previous best methods as well as our implemented baselines in Table 1. First, we observe that, in addition to achieving the best performance, our method also requires \\(3.38 \\times\\) less memory and is \\(2.68 \\times\\) faster than the previous state-of-the-art method BaSSL [35]. Second, compared to the standard Transformer baseline, TranS4mer is \\(2 \\times\\) faster and requires \\(3 \\times\\) less GPU memory. Finally, our model is significantly cheaper than efficient self-attention and state-space models such as TimeSformer and Vanilla S4. Whereas TimeSformer and Vanilla S4 require 28.12 GB and 15.62 GB of memory, our TranS4mer requires only 10.13 GB of memory. Moreover, the training speed of TranS4mer is 2.57 samples/second compared to the 1.47 and 1.82 samples/second speed of TimeSformer and Vanilla S4, respectively. These observations suggest that TranS4mer is much more efficient than prior methods and standard self-attention and state-space-based models." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.673, + 0.472, + 0.749 + ], + "angle": 0, + "content": "Comparison Using the Same Backbone Model. For a fair comparison, we also experiment with a previous-best BaSSL [35] method that uses the same backbone as our model (i.e., ViT-S/32). We report that our TranS4mer outperforms this BaSSL variant by \\(+2.77\\%\\) AP." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.768, + 0.38, + 0.784 + ], + "angle": 0, + "content": "6.2. Scene Detection on Other Datasets" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.795, + 0.47, + 0.903 + ], + "angle": 0, + "content": "We experiment with two additional movie scene detection datasets, BBC [3] and OVSD [40]. We present these results in Table 2, which shows that TranS4mer achieves the best result among all methods, outperforming the previous best BaSSL [35] method by \\(4.66\\%\\) AP on the BBC and \\(7.36\\%\\) AP on the OVSD datasets. These results demonstrate our method's ability to generalize to other datasets." + }, + { + "type": "table", + "bbox": [ + 0.508, + 0.077, + 0.691, + 0.169 + ], + "angle": 0, + "content": "
MethodAP (↑)
BaSSL [35]39.98
Transformer [16]41.86
TimeSformer [6]42.23
Vanilla S4 [18]42.56
TranS4mer43.64
" + }, + { + "type": "table_caption", + "bbox": [ + 0.511, + 0.17, + 0.684, + 0.184 + ], + "angle": 0, + "content": "(a) Performance on BBC [3]." + }, + { + "type": "table", + "bbox": [ + 0.7, + 0.078, + 0.887, + 0.17 + ], + "angle": 0, + "content": "
MethodAP (↑)
BaSSL [35]28.68
Transformer [16]33.12
TimeSformer [6]33.87
Vanilla S4 [18]34.21
TranS4mer36.04
" + }, + { + "type": "table_caption", + "bbox": [ + 0.699, + 0.17, + 0.886, + 0.184 + ], + "angle": 0, + "content": "(b) Performance on OVSD [40]." + }, + { + "type": "table_caption", + "bbox": [ + 0.5, + 0.189, + 0.892, + 0.231 + ], + "angle": 0, + "content": "Table 2. Scene Detection on additional datasets. TranS4mer outperforms the prior method (BaSSL) by a large margin of \\(4.66\\%\\) AP on BBC [3] and \\(7.36\\%\\) AP on OVSD [40] datasets." + }, + { + "type": "table", + "bbox": [ + 0.504, + 0.246, + 0.888, + 0.308 + ], + "angle": 0, + "content": "
MethodRelationSpeakSceneDirectorGenreWriterYear
ObjTrans. [48]53.1039.4056.9051.2054.6034.5039.10
ViS4mer [34]57.1440.7967.4462.6154.7148.8044.75
TranS4mer59.5239.2170.9363.8655.8546.9345.45
(a) Performance on LVU [48]
" + }, + { + "type": "table", + "bbox": [ + 0.505, + 0.31, + 0.69, + 0.373 + ], + "angle": 0, + "content": "
Model#Data(↓)Acc.(↑)
GHRM [51]306K75.50
Dist.Sup. [31]136M89.90
ViS4mer [34]495K88.17
TranS4mer495K90.27
" + }, + { + "type": "table_caption", + "bbox": [ + 0.507, + 0.373, + 0.688, + 0.385 + ], + "angle": 0, + "content": "(b) Performance on Breakfast [30]" + }, + { + "type": "table", + "bbox": [ + 0.701, + 0.31, + 0.886, + 0.374 + ], + "angle": 0, + "content": "
Model#Data(↓)Acc.(↑)
TSN [44]306K73.40
Dist.Sup. [31]136M90.00
ViS4mer [34]495K88.41
TranS4mer495K89.23
" + }, + { + "type": "table_caption", + "bbox": [ + 0.71, + 0.374, + 0.878, + 0.386 + ], + "angle": 0, + "content": "(c) Performance on COIN [43]" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.39, + 0.892, + 0.46 + ], + "angle": 0, + "content": "Table 3. Long-range video classification. (a) TranS4mer achieves best performance in 5 out of 7 classification tasks in LVU benchmark [48]. Moreover, (b) it performs best on the Breakfast [30] and (c) second-best on the COIN [43] datasets, while using significantly less pretraining data (middle column)." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.477, + 0.783, + 0.493 + ], + "angle": 0, + "content": "6.3. Long-range Video Classification" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.502, + 0.892, + 0.744 + ], + "angle": 0, + "content": "In addition to move scene detection, we also experiment with other tasks including long-form movie clip classification in the LVU [48] dataset, and long-range procedural activity classification on Breakfast [30] and COIN [43] datasets. LVU contains \\(30K\\) videos from \\(3K\\) movies, Breakfast has 1,712 videos of 10 cooking activities, and COIN contains 11,827 videos of 180 different procedural activities. Videos of each dataset are \\(2 - 3\\) minutes long. We present the results in Table 3. On LVU, TranS4mer achieves the best performance in 5 out of 7 tasks (Table 3(a)). Moreover, TranS4mer also achieves the best performance on Breakfast (Table 3(b)) and the second-best performance on COIN (Table 3(c)) while using significantly fewer pretraining samples than the state-of-the-art Distant Supervision [31] approach. These results indicate that TranS4mer can be effectively applied to other domains and tasks." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.756, + 0.665, + 0.77 + ], + "angle": 0, + "content": "6.4. Ablation Studies" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Temporal Extent Ablation. To verify our hypothesis that long-range temporal context is critical for accurate movie scene detection, we experiment with video inputs of different lengths (i.e., video inputs containing 9, 17, 25, and 33 contextual shots) while predicting the boundary for the middle shot. Note that videos with more input shots denote longer input videos. We present these results in Figure 4a. First, we notice that a short temporal window of 9 context" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "18755" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.121, + 0.064, + 0.35, + 0.201 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.127, + 0.205, + 0.361, + 0.229 + ], + "angle": 0, + "content": "(a) Performance \\(\\uparrow\\) TranS4mer achieves much better performance for longer videos." + }, + { + "type": "image", + "bbox": [ + 0.373, + 0.066, + 0.614, + 0.201 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.379, + 0.204, + 0.614, + 0.229 + ], + "angle": 0, + "content": "(b) Training Speed \\(\\uparrow\\) TranS4mer is significantly faster than the Transformer baseline." + }, + { + "type": "image", + "bbox": [ + 0.626, + 0.07, + 0.853, + 0.201 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.632, + 0.205, + 0.866, + 0.229 + ], + "angle": 0, + "content": "(c) Memory Requirements \\(\\downarrow\\) TranS4mer requires significantly less GPU memory." + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.238, + 0.895, + 0.267 + ], + "angle": 0, + "content": "Figure 4. (a) Performance (AP), (b) Training Speed (Samples/Second), and (c) Memory Requirements (GigaBytes), and as a function of the number of input shots. Note that videos with more input shots denote longer input videos." + }, + { + "type": "table", + "bbox": [ + 0.118, + 0.279, + 0.348, + 0.351 + ], + "angle": 0, + "content": "
Intra-ShotInter-ShotAp (↑)
✓✗57.80
✗✓55.59
✓✓60.78
" + }, + { + "type": "table_caption", + "bbox": [ + 0.163, + 0.353, + 0.292, + 0.364 + ], + "angle": 0, + "content": "(a)TranS4mer modules." + }, + { + "type": "table", + "bbox": [ + 0.368, + 0.279, + 0.516, + 0.35 + ], + "angle": 0, + "content": "
S4 layersAP (↑)
1-658.31
7-1258.82
1-1260.78
" + }, + { + "type": "table_caption", + "bbox": [ + 0.37, + 0.352, + 0.504, + 0.365 + ], + "angle": 0, + "content": "(b) S4 in different layers." + }, + { + "type": "table", + "bbox": [ + 0.536, + 0.279, + 0.689, + 0.35 + ], + "angle": 0, + "content": "
S4 layersAP (↑)
every 2nd59.82
every 4th58.01
all60.78
" + }, + { + "type": "table_caption", + "bbox": [ + 0.541, + 0.352, + 0.676, + 0.365 + ], + "angle": 0, + "content": "(c) S4 in every \\(k^{th}\\) layer." + }, + { + "type": "table", + "bbox": [ + 0.711, + 0.279, + 0.858, + 0.351 + ], + "angle": 0, + "content": "
S4 layersAP (↑)
S459.71
DS460.13
GS460.78
" + }, + { + "type": "table_caption", + "bbox": [ + 0.713, + 0.352, + 0.845, + 0.364 + ], + "angle": 0, + "content": "(d) Different S4 variants." + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.373, + 0.893, + 0.403 + ], + "angle": 0, + "content": "Table 4. Ablation studies with (a) TranS4mer modules, (b) (c) positioning, and (d) variants of S4 layers. Intra-shot and inter-shot modules are complementary, and TranS4mer with Gated S4 layers at every S4A block yields the best performance." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.425, + 0.469, + 0.516 + ], + "angle": 0, + "content": "tual shots produces a suboptimal performance of \\(53.29\\%\\) AP. Increasing the temporal extent to 25 contextual shots increases the performance to \\(60.78\\%\\) AP \\((+7.49\\%\\) boost). Adding more contextual shots does not yield any significant improvements. These results verify the importance of long-range temporal modeling for movie scene detection." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.52, + 0.47, + 0.837 + ], + "angle": 0, + "content": "Detailed Comparison with Transformer. We next present a detailed comparison of our model with the Transformer baseline [16]. In particular, we experiment with videos that contain a different number of input shots and plot the accuracy in AP as a function of the number of input shots (see Figure 4). Although the Transformer baseline performs better for shorter video inputs, our TranS4mer model achieves much better performance using longer videos. Specifically, TranS4mer yields \\(+2.07\\%\\) larger AP than the transformer model when using the longest video inputs. This suggests that TranS4mer is more effective at capturing long-range dependencies for the movie scene detection task. Moreover, we also illustrate the training speed (Samples/Second) and the memory requirement (GigaBytes) as a function of the number of input shots (see Figures 4b and 4c). We observe that as we increase the video length, the training speed of the Transformer baseline drops drastically, and the memory requirement grows rapidly. Overall, our proposed TranS4mer model is \\(2.7\\times\\) faster and requires \\(3.38\\times\\) less GPU memory than the Transformer baseline while using the longest video inputs." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.47, + 0.901 + ], + "angle": 0, + "content": "Ablation with Intra-Shot and Inter-Shot Modules. In Table 4a, we analyze the significance of our (i) self-attention-based intra-shot module and (ii) state-space-based inter-shot module. We observe that removing the inter-shot" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.425, + 0.892, + 0.56 + ], + "angle": 0, + "content": "module drops the performance by \\(2.98\\%\\) AP, whereas discarding the intra-shot module decreases the performance by \\(5.19\\%\\) AP. Therefore, based on these results, we can conclude that both the intra-shot and inter-shot modules are essential for good movie scene detection performance. We also note that they are complementary to each other, which aligns with our intuition of the intra-shot module being responsible for short-range representations while the intershot module is dedicated to long-range temporal reasoning." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.561, + 0.893, + 0.682 + ], + "angle": 0, + "content": "Ablation with S4 Layers. We experiment with injecting our proposed S4A block into different encoder layers (Table 4b). We also evaluate a sparser TranS4mer variant with our S4A block injected into every \\( k^{th} \\) layer of the network (Table 4c). Lastly, we experiment with different S4 variants (i.e., Diagonal S4 (DS4) [20], Gated S4 (GS4) [33]) (Table 4d). Our results suggest that using S4A with Gated S4 in every layer of the network leads to the best accuracy." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.695, + 0.619, + 0.71 + ], + "angle": 0, + "content": "7. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.892, + 0.901 + ], + "angle": 0, + "content": "In this work, we propose an efficient movie scene segmentation method which combines the strengths of selfattention for short-range modeling and state-space models for long-range modeling. Our method, named TranS4mer, achieves state-of-the-art results in three different movie scene segmentation datasets (MovieNet, BBC, and OVSD). Moreover, our model is significantly faster and requires less GPU memory than previous approaches and the standard vision transformer models. In future, we will extend our model to other long-range video understanding and multimodal tasks such as movie summarization, movie trailer generation, and natural language grounding in long videos." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "18756" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.115, + 0.47, + 0.157 + ], + "angle": 0, + "content": "[1] Dzmitry Bahdanau, Kyunghyun Cho, et al. 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However, accurately detecting movie scenes is often challenging as it requires the ability to reason over very long movie segments. This contrasts with most existing video recognition models, which are typically designed for short-range video analysis. This work proposes a State-Space Transformer model that can efficiently capture dependencies in long movie videos for accurate movie scene detection. Our model, called TranS4mer, is built using a novel S4A building block, combining the strengths of structured state-space sequence (S4) and self-attention (A) layers. Given a sequence of frames divided into movie shots (uninterrupted periods where the camera position does not change), the S4A block first applies self-attention to capture short-range intra-shot dependencies. Afterward, the state-space operation in the S4A block aggregates long-range inter-shot cues. The final TranS4mer model, which can be trained end-to-end, is obtained by stacking the S4A blocks one after the other multiple times. Our proposed TranS4mer outperforms all prior methods in three movie scene detection datasets, including MovieNet, BBC, and OVSD, while being $2 \times$ faster and requiring $3 \times$ less GPU memory than standard Transformer models. We will release our code and models. + +# 1. Introduction + +Imagine watching The Godfather movie as illustrated in Figure 1. The first scene starts in the office room of mafia boss Don Vito Corleone, where he is discussing family business affairs with his eldest son Sonny Corleone and the family lawyer Tom Hagen. Then in the second scene, the family meets Virgil Sollozzo to hear about his business proposition. Afterward, the movie transitions into a third scene, where Don Vito chides his son Sonny for interfering. All of these movie scenes are inherently connected and create a complex storyline. Thus, the ability to recognize such + +movie scenes is essential for understanding the plot of a movie. Moreover, identifying movie scenes enables broader applications, such as content-driven video search, preview generation, and minimally disruptive ad insertion. + +Unlike standard video recognition tasks (e.g., action recognition), which require a short-range analysis of video clips lasting only 5-10 seconds, movie scene detection requires short- and long-range understanding, where videos might last several minutes. For instance, to successfully recognize the scenes in Figure 1, we need to identify the visual concepts in each frame, such as characters, objects, and backgrounds (short-range modeling), while also reasoning about complex temporal events and activities (long-range modeling). For example, if we only look at the boundary frames of the first and second scenes of Figure 1 and identify the local properties (e.g., characters, objects, and backgrounds), it is quite difficult to determine the transition between the two scenes. However, considering longer temporal windows with frames from both scenes, we can recognize global events and identify their boundaries. + +We also note that models that only use short-range temporal context typically produce many false positives due to abrupt low-level changes in the scene dynamics (e.g., camera switching between characters). For example, if we look at the middle two frames of scene 2 in Figure 1, we might mistake them for a scene boundary since the frames contain two characters. However, looking at all the frames in scene 2 makes it clear that they belong to the same scene. Therefore, a successful movie scene detection model should identify the short-range visual elements and also reason about their long-range temporal dependencies in a movie segment. + +However, most existing movie scene detection methods [11, 35] are built using convolutional neural networks (CNNs), which are inherently designed using local operators (i.e., convolution kernels) for short-range video analysis. Thus, such models often fail to capture the long-range dependencies crucial for accurate movie scene detection. Recently, transformers have been shown to effectively model short-range and long-range dependencies in various Natural Language Processing (NLP) tasks [1,7,14, 15, 32, 37, 47, 49]. Inspired by the success of transform + +![](images/7ea336fad0d749db3aa00c8718839cb5a8724c676bb4d154054a6f6a80a1257a.jpg) +Figure 1. Three scenes from the movie The Godfather. In the first scene, The Godfather (Don Vito Corleone) discusses family business affairs with his eldest son Sony and family lawyer Tom Hagen. Then the movie transitions into the second scene, where the mafia family meets Virgil Sollozzo to hear his business proposition. Afterward, in the third scene, Don Vito chides his son Sonny for interfering in the middle of his talk. Generally, movies are composed of well-defined scenes, and detecting those scenes is essential to high-level movie understanding. Therefore, this work aims to detect high-level scenes from a long-range movie video. + +![](images/360c0ea64e987272d73fd417d0887368103d39162c9087447e77880dd45621fc.jpg) + +![](images/76e35dc1eb455ce7f1cf4319c9612ae2dab0a2f436837b5ab54b99409716724b.jpg) + +![](images/4ab128512689b67d329614cbec82a633b3e33e15e42a63a09d563fc15cb5a8c8.jpg) + +![](images/d11d77dbb3111a71ae320628023621bb00b172fa0d21f9330edeee51c54dfed6.jpg) + +![](images/f8b340fb3a939c73adeb338a223ad9676823a817550cd5b1b8a0a2f1c1dbb549.jpg) + +![](images/e93756d965d9d01f14cc3d1a3816d0eb6c4480f657f48c9dc1c052e15bde724c.jpg) + +![](images/9c0fda13a18abd58e5f36db1bfc5117353259d181c2a117544f895046c67fb77.jpg) + +![](images/a234ab7b4f27ba0626e083710298dcd678b28f6cfb5539b9ee698a95f7b7c0db.jpg) + +ers in NLP, subsequent works have shown the remarkable success of using transformers in several short-range vision tasks [8, 16]. However, applying Transformers to long video sequences remains challenging due to the quadratic cost of self-attention. To overcome these issues, recent work proposed a structured state-space sequence (S4) operator [18, 19, 33] for efficient long-range sequence analysis. + +Motivated by the developments in transformer and S4-based architectures, we present TranS4mer, an efficient end-to-end model for movie scene boundary detection, which combines the strengths of transformers for short-range modeling and S4 operators for long-range modeling. Specifically, we propose a novel state-space self-attention (S4A) block and build our TranS4mer model by stacking multiple S4A blocks on top of each other. Our model takes a sequence of frames divided into movie shots as input, where a shot is defined as a series of frames captured by the same camera over an uninterrupted period [46]. The S4A block first captures the short-range intra-shot dependencies by applying self-attention over the frames in each shot. Subsequently, it aggregates the inter-shot interactions over long movie segments by employing the state-space operator over all shots in a given movie video. + +One key property of our model is that it independently applies self-attention to each shot, significantly reducing the cost of standard self-attention. For instance, if we have a video of 25 shots and each shot contains 3 frames, applying a standard vision transformer [16] with a patch size of $32 \times 32$ will result in 3,675 tokens and a single self-attention operation will require $\sim 13.5\mathrm{M}$ pairwise comparisons. In contrast, applying self-attention within each shot parallelly reduces the number of comparisons $25 \times$ times. Simultaneously, TranS4mer attains long-range modeling ability through the efficient state-space layers that do not require costly pairwise comparisons and operate over the entire input video. As a result, the proposed TranS4mer model can be efficiently applied to long movie videos. + +We experiment with three movie scene detection datasets: MovieNet [25], BBC [3], and OVSD [40], and report that our method outperforms prior approaches by large margins $(+3.38\%)$ AP, $+4.66\%$ and $+7.36\%$ respectively). TranS4mer is also $2\times$ faster and requires $3\times$ less GPU memory than the pure Transformer-based models. Moreover, to evaluate the generalizability of our model, + +we experiment with several long-range video understanding tasks, such as movie clip classification and procedural activity recognition. TranS4mer performs the best in 5 out of 7 movie clip classification tasks on LVU [48], the best in procedural activity classification on Breakfast [30], and the second-best in procedural activity classification on COIN [43] datasets. + +# 2. Related works + +Long Sequence Modeling. Many modern approaches to long sequence modeling started in the field of Natural Language Processing (NLP). Bahdanau et al. [1] introduced an RNN architecture with an attention mechanism for machine translation. Afterward, Vaswani et al. [47] proposed the transformer model for capturing long-range dependencies in text sequences. Following this work, various improved transformer architectures were proposed [7, 14, 15, 32, 37, 49]. However, despite these advances, applying transformers to very long sequences is still challenging because of the quadratic cost of the self-attention operation. Consequently, many recent methods have developed efficient variations of standard self-attention [12, 26, 29, 36, 50]. Furthermore, the recent work of Gu et al. [17-19] proposed a structured statespace sequence (S4) model for long sequence analysis. The S4 models have achieved impressive results in many NLP tasks [17-20, 33], while having only linear memory and computation costs (w.r.t the sequence length). Building on this work, Islam et al. [34] proposed a model that applies S4 on pre-extracted video features for long-range video classification. In contrast, we propose an end-to-end trainable movie scene detection model that combines S4 and self-attention into a novel S4A block, which we use to build our TranS4mer model. + +Movie Scene Detection. The early approaches for movie scene detection consisted predominantly of unsupervised clustering-based methods [2,4,10,39,40,42,52] built using hand-crafted features. Recently, Huang et al. [25] introduced a large-scale dataset for movie scene detection called MovieNet, which became the most popular benchmark for this problem. Subsequently, Huang et al. [25] and Rao et al. [38] proposed an LSTM-based model for movie scene detection, which is applied on top of preextracted CNN features. Most recently, Chen et al. [11] and Mun et al. [35] introduced several end-to-end movie + +![](images/b601745f8402a6727a45a986b65fb91f00347d29bd0eb0c9ca7a7c20e258f832.jpg) +Figure 2. The hierarchical structure of long movie videos. First, multiple consecutive frames captured from the same camera position depict a shot. Next, multiple neighboring shots constitute a movie scene. Finally, a movie is composed of a collection of scenes. Here, we show one scene that contains N shots with $K$ frames in each shot. + +scene detection approaches built using 2D/3D CNN architectures. However, these CNN-based models are limited by the smaller receptive fields of the local convolution operations. In contrast, our TranS4mer model is constructed using global operators (state-space and self-attention), which are more effective for long-range modeling. + +# 3. Background + +The State-Space Model (SSM) is a fundamental model used in many scientific fields, such as control theory and computational neuroscience. We can define the SSM in continuous time using the following equations: + +$$ +h ^ {\prime} (t) = A h (t) + B x (t) \tag {1} +$$ + +$$ +y (t) = C h (t) + D x (t) +$$ + +Here, $x(t)$ is the input signal, $h(t)$ is a latent state, $h'(t)$ is the first order derivative of $h(t)$ wrt $t$ , i.e., $h'(t) = \frac{dh}{dt}$ , $y(t)$ is the output signal, and $A$ is the state matrix. Equation (1) can be discretized by sampling the underlying input signal $u(t)$ with a step size $\Delta$ . + +$$ +h _ {k} = \bar {A} h _ {k - 1} + \bar {B} x _ {k} \tag {2} +$$ + +$$ +y _ {k} = \overline {{C}} h _ {k} + \bar {D} x _ {k} +$$ + +Here, $\overline{A}$ , $\overline{B}$ , $\overline{C}$ , and $\overline{D}$ are the discrete versions of $A$ , $B$ , $C$ and $D$ . Furthermore, the equation (2) can be expressed as a convolution operation $(*)$ : + +$$ +y = \bar {K} * x \quad \bar {K} = (\bar {C B}, \bar {C A B}, \dots , \bar {C A} ^ {L - 1} \bar {B}), \tag {3} +$$ + +where $\overline{K}$ is a kernel, and $L$ is the sequence length. + +S4 Model. The Structured State Space (S4) model is a particular class of SSM that requires the state matrix $A$ to be diagonal and low-rank. Because of the specific structure of the state matrix $A$ , we can derive a closed-form formula for the convolutional kernel $\overline{K}$ in equation (3) [18], which then facilitates an efficient computation of $\overline{K}$ without having to multiply the matrix $A$ , $L - 1$ times. + +Gated S4 Model. Borrowing the idea from Gated Attention [24], Metha at el. [33] introduced a Gated S4 model, which first uses linear layers to compute two latent representations $(u$ and $v)$ from the input sequences $x$ , and then + +applies an S4 layer to obtain a contextualized representation $\hat{u}$ . Finally, the tokens from $\hat{u}$ are used to gate $v$ : + +$$ +u = \phi (W _ {u} x) \quad v = \phi (W _ {v} x) +$$ + +$$ +h = S 4 (u) \quad \hat {u} = W _ {h} x \tag {4} +$$ + +$$ +y = W _ {y} (\hat {u} \odot v) +$$ + +Here, $W_{u}, W_{v}, W_{h}, W_{y}$ are the weight matrices of linear layers, $\phi$ denotes GELU nonlinearity [23], $\odot$ is elementwise multiplication, and S4 denotes an S4 layer described above. + +# 4. Technical Approach + +We aim to develop an efficient scene detection method for long movie videos. Movie videos have a specific hierarchical structure consisting of three semantic levels: (i) frames, (ii) shots, and (iii) scenes (See Figure 2). First, multiple consecutive frames constitute a shot, where the frames are captured from the same camera position over an uninterrupted period [46]. Second, multiple consecutive shots construct a scene, where a scene is a semantically cohesive unit of the storyline [27, 41]. Finally, a movie is composed of a collection of scenes. Shots can be easily recognized by detecting the changes in low-level visual cues [9, 13, 42]. However, identifying the scene boundary is more challenging as it requires high-level semantic understanding. + +Problem Overview. First, we formally define the problem of movie scene detection. We are given a movie video $V$ divided into $T$ non-overlapping automatically-detected shots, $V = \{s_1,\ldots ,s_i,\ldots ,s_T\}$ . We can then uniformly sample $K$ frames from each shot. Therefore, a shot is represented as $s_i = \{f_1,\dots ,f_j,\dots ,f_K\}$ , where $f_{j}\in \mathbb{R}^{3\times H\times W}$ depicts an RGB frame, $H$ is the height, and $W$ is the width of each frame. Following these definitions, we can then formulate the movie scene detection problem as a prediction task, where we need to produce a binary output $y_{i}\in \{0,1\}$ for each video shot $s_i$ (i.e., whether a given shot is at a movie scene boundary or not). + +**Approach Overview.** Our movie scene detection model, called the State-Space Transformer (TranS4mer), is built using our proposed S4A blocks that combine the strengths of structured state-space sequence (S4) and self-attention (A) layers. The S4A block utilizes the self-attention layer to encode short-range dependencies between frames in each shot and the S4 layer for capturing long-range dependencies between shots far away from each other. A detailed illustration of our model is presented in Figure 3. Below, we describe each component of our model in more detail. + +# 4.1. The TranS4mer Model + +Following previous methods [11,35,38], our model takes as input $N = 2m + 1$ temporally adjacent shots, $\mathcal{V}_i = \{s_{i - m},\ldots ,s_i,\ldots ,s_{i + m}\}$ , and outputs a binary prediction $y_{i}\in \{0,1\}$ for the shot $s_i$ . The neighboring shots provide + +![](images/25feea89ec1c422697255ef8ed0724b5c0af5a4e57b00176e95a91475dfb592f.jpg) + +![](images/fc1d6e927c049e2f33b13d193633eaa1ce640b2f5f55a42037aa1bfa98846afb.jpg) +Figure 3. Overview of the TranS4mer model. Left: Our model takes a sequence of frames divided into automatically-detected shots. Following the ViT [16], the frames are decomposed into non-overlapping patches and passed through a linear projection layer. Afterward, we feed these patch-level embeddings through our TranS4mer model, which consists of $B$ state-space self-attention (S4A) blocks stacked on top of each other. Finally, the CLS tokens of all shots are passed to two linear layers, i.e., the boundary prediction head (which outputs a binary label indicating the boundary shot) and the contrastive head (which maximizes intra-shot similarity). Right: Each of our proposed S4A blocks contains a self-attention-based intra-shot module that models the interaction among frames in the same shot and a Gated S4-based inter-shot module that aggregates long-range temporal cues from shots far away from each other. + +long-range contextual cues for predicting the boundary at shot $s_i$ . Here, $\mathcal{V}_i \in \mathbb{R}^{N \times K \times 3 \times H \times W}$ is composed of $K$ frames from each of $N$ consecutive shots, where $H$ is the height, and $W$ is the width of each frame. + +Following ViT [16], we divide each frame into $P$ nonoverlapping patches of size $p \times p$ , where $P = HW / p^2$ . Then we use a linear layer to project each patch into a hidden dimension $D$ , and a positional embedding is added to each patch token. As a result, we obtain a tensor of shape $\mathbf{V}_i \in \mathbb{R}^{N \times K \times P \times D}$ , which is fed to our TranS4mer model. + +The S4A Block. Our proposed S4A block enables us to compute a strong short-range feature representation and model long-range temporal dependencies among shots. It consists of two modules: a short-range intra-shot module and a long-range inter-shot module. + +Intra-Shot Module. The intra-shot module takes the input tensor $\mathbf{V}_i\in \mathbb{R}^{N\times K\times P\times D}$ , which we can think of as a collection of $N$ shots, where a sequence of tokens represents each shot $S_{i} = x_{1},\ldots ,x_{L}$ , where $x_{i}\in \mathbb{R}^{D}$ , $L = K\times P$ . The intra-shot module models the sequence of tokens from each shot independently. To this end, it first applies a multi-layer perceptron (MLP) layer and a residual connection. Afterward, it applies a Multiheaded Self Attention (MSA) layer and another residual connection. Layer Normalization (LN) is applied before the MLP + +and the MSA layers. The module can be defined as follows: + +$$ +\mathbf {x} ^ {\prime} = \operatorname {M H A} \left(\operatorname {L N} \left(\mathbf {x} _ {i n}\right)\right) + \mathbf {x} _ {i n} \tag {5} +$$ + +$$ +\mathbf {x} _ {\text {o u t}} = \operatorname {M L P} \left(\operatorname {L N} \left(\mathbf {x} ^ {\prime}\right)\right) + \mathbf {x} ^ {\prime} +$$ + +The output of the intra-shot module $\mathbf{V}'_i \in \mathbb{R}^{N \times K \times P \times D}$ , is then passed to the inter-shot module. + +Note that applying self-attention to tokens from each shot separately reduces the computation cost to $O(NL^2)$ . In contrast, applying self-attention to the entire sequence of tokens in $\mathbf{V}_{\mathrm{i}}$ would cost $O(N^{2}L^{2})$ . + +Inter-Shot Module. Our previously defined intra-shot module only models short-range dependencies and, thus, lacks the ability for long-range temporal understanding, which is crucial for the movie scene detection task. To address this limitation, we propose an efficient inter-shot module based on the Gated S4 operator that aggregates long-range inter-shot cues. + +First, we unroll the input tensor $\mathbf{V}'_i$ into a sequence $z_{1},\ldots ,z_{L'}$ , where $z_{i}\in \mathbb{R}^{D}$ , $L^{\prime} = N\times K\times P$ . Then, we pass the sequence to a multi-layer perceptron (MLP) layer and a residual connection. Afterward, we apply a Gated S4 (GS4) layer and another residual connection. Layer Normalization (LN) is applied before MLP and GS4 layers: + +$$ +\begin{array}{l} \mathbf {z} ^ {\prime} = \operatorname {G S 4} \left(\operatorname {L N} \left(\mathbf {z} _ {i n}\right)\right) + \mathbf {z} _ {i n} \tag {6} \\ \mathbf {z} _ {\text {o u t}} = \operatorname {M L P} \left(\operatorname {L N} \left(\mathbf {z} ^ {\prime}\right)\right) + \mathbf {z} ^ {\prime} \\ \end{array} +$$ + +The output of this operation is then passed into the next S4A block. Unlike the intra-shot module, which operates on a short sequence of length $L = K \times P$ , the inter-shot module operates on much longer sequences of $L' = N \times K \times P$ . Our model can efficiently process such long sequences due to the Gated S4 layers in the inter-shot module. + +# 4.2. Training and Loss Functions + +Most prior works in move scene detection use self-supervised pretraining [11, 35]. Thus, we also adopt the self-supervised pretraining strategy of Mun at et al. [35], which uses pseudo boundaries of move scenes from the Dynamic Time Warping algorithm as a supervisory signal. Afterward, we finetune our pretrained model using the labeled subset of the data. Note that we do not claim technical novelty over the pretraining strategy. Instead, our main goal is to develop an efficient state-space transformer backbone for movie scene detection. Below, we provide more details related to the pretraining and fine-tuning protocols. + +Pretraining. Leveraging the pseudo movie scene boundaries, we optimize our model using the following two losses: (i) a shot-scene contrastive loss and (ii) a pseudoboundary prediction loss. The contrastive loss maximizes the similarity between the representations of a shot and its corresponding pseudo ground truth scene while also minimizing the similarity of a shot with all the other scenes. We represent each shot with its respective CLS token, whereas each scene is represented by mean-pooling the CLS tokens of all shots in that scene. The DTW algorithm divides the input video $\mathcal{V}_i = \{s_{i - m},\dots ,s_i,\dots ,s_{i + m}\}$ into two pseudo-scenes $\mathcal{V}_L = \{s_{i - m},\dots ,s_{i^*}\}$ and $\mathcal{V}_R = s_{i^{*} + 1},\ldots ,s_{i + m}\}$ , here $s_{i^*}$ is the pseudo-boundary shot. We can then define the shot-scene contrastive loss as: + +$$ +l _ {\mathrm {C}} (\mathbf {r}, \bar {\mathbf {r}}) = - \log \frac {\mathcal {S} (\mathbf {r} , \bar {\mathbf {r}})}{\mathcal {S} (\mathbf {r} , \bar {\mathbf {r}}) + \sum_ {\mathbf {r} _ {n}} \mathcal {S} (\mathbf {r} _ {n} , \bar {\mathbf {r}}) + \sum_ {\bar {\mathbf {r}} _ {n}} \mathcal {S} (\mathbf {r} , \bar {\mathbf {r}} _ {n})} \tag {7} +$$ + +Here, $\mathbf{r}$ is a shot representation obtained by applying a linear layer on the CLS token of that shot, $\bar{\mathbf{r}}_L$ and $\bar{\mathbf{r}}_R$ are the scene-level representations of pseudo-scenes $\nu_{L}$ and $\nu_{R}$ , $\mathbf{r}_n$ and $\bar{\mathbf{r}}_n$ are the negative shots and scenes from the minibatch. Similarity between two representations is calculated as: $S(\mathbf{x},\mathbf{y}) = \exp ((\mathbf{x}^{\top}\mathbf{y}) / (\| \mathbf{x}\| \| \mathbf{y}\|))$ . The first loss term can then be written as: $\mathcal{L}_{\mathrm{C}} = l_{\mathrm{C}}(\mathbf{r}_{i - m},\bar{\mathbf{r}}_L) + l_{\mathrm{C}}(\mathbf{r}_{i + m},\bar{\mathbf{r}}_R)$ . + +The second loss function of pseudo-boundary prediction is a simple objective that guides the model to predict a pseudo-boundary from a given shot representation. We can define this loss as a binary cross-entropy loss: + +$$ +\mathcal {L} _ {\mathrm {B}} = - \log \left(\rho_ {b} \left(\mathbf {r} _ {i ^ {*}}\right)\right) - \log \left(1 - \rho_ {b} \left(\mathbf {r} _ {\tilde {b}}\right)\right) \tag {8} +$$ + +Here, $\mathbf{r}_{i^*}$ is the CLS representation of the pseudoboundary shot $s_{i^*}$ , $\mathbf{r}_{\bar{b}}$ is the representation of a randomly selected non-boundary shot $s_{\bar{b}}$ , $\rho_{b}$ is a projection layer that outputs the probability of a shot being the pseudo-boundary. + +The overall pretraining loss is the sum of the shot-scene contrastive loss and the pseudo-boundary loss. + +Finetuning. After the self-supervised pretraining, we finetune our model using the subset of the dataset with ground truth annotations. We use a binary cross-entropy loss as in [35] to finetune our model. + +# 4.3. Implementation Details + +Following the ViT [16], we resize video frames to a spatial dimension of $224 \times 224$ and divide using a patch size of $32 \times 32$ . Our model contains 12 S4A blocks and uses a hidden dimension of 384. It takes 25 neighboring shots as input, where each shot contains 3 frames. We use four data augmentation techniques: random crop, flip, color jitter, and Gaussian blur. We use a batch size of 256 and pretrain our model for 10 epochs before finetuning for 20 epochs. During pretraining, we use a base learning rate of 0.3, which we reduce using a cosine schedule after a linear warmup strategy of 1 epoch. During finetuning, we use a learning rate of $10^{-6}$ . We use the Adam [28] optimizer with a momentum of 0.9 and weight decay of $10^{-6}$ . We train our models using 8 NVIDIA RTX A6000 GPUs. + +# 5. Experimental Setup + +# 5.1. Datasets + +MovieNet [25] is a large-scale dataset containing 1100 movies with 1.6 million shots, and 318 of these movies have ground-truth scene boundary annotation. The annotated subset of the dataset is divided into 190, 64, and 64 movies for training, validation, and testing. Following the previous approaches, we pretrain our model using all the movies, finetune using the standard training split of the annotated subset, and report the result on the test split. + +BBC [3] contains 11 episodes from the BBC TV series Planet Earth [5]. The average duration of the videos is 50 minutes. The dataset contains 670 scenes and 4.9K shots. + +OVSD [40] contains 21 short films with an average duration of 30 minutes. It has a total of 10K shots and 300 scenes extracted from movie scripts. + +# 5.2. Evaluation Metrics + +AP measures the weighted average of precisions at different thresholds. + +mIoU is the average intersection over union of predicted scene boundaries with the closest ground truth boundaries. + +AUC-ROC is calculated as the True Positive Rate with respect to the False Positive Rate at different thresholds. + +F1-Score is the harmonic mean of precision and recall. + +
MethodAP (↑)mIoU (↑)AUC-ROC (↑)F1 (↑)Memory (GB) (↓)Samples/s (↑)
UnsupervisedGraphCut [39]14.1029.70----
SCSA [10]14.7030.50----
DP [21]15.5032.00----
Story Graph [45]25.1035.70----
Grouping [40]33.6037.20----
BaSSL [35]31.5539.3671.6732.5534.280.96
Transformer [16]32.1637.2470.2331.2430.281.27
TimeSformer [6]32.4737.7670.9531.4528.121.47
Vanilla S4 [18]33.3438.1271.8632.2115.621.83
TranS4mer34.4539.6073.2533.4110.132.57
SupervisedSiamese [3]35.8039.60----
MS-LSTM [25]46.5046.20----
LGSS [38]47.1048.80----
ViS4mer [34]55.1348.2788.7446.15
ShotCoL [11]53.40---34.280.96
BaSSL [35]57.4050.6990.5447.0234.280.96
Transformer [16]58.8151.2190.8447.8830.281.27
TimeSformer [6]59.6250.7590.6648.0228.121.47
Vanilla S4 [18]59.7151.3290.9647.8515.621.83
TranS4mer60.7851.9191.8948.3610.132.57
+ +Table 1. Results on MovieNet [25]. Horizontal lines in both Unsupervised and Supervised rows separate prior works from our implemented baselines. First, our method achieves state-of-the-art performance, outperforming the previous best method (BaSSL) by a significant margin of $3.38\%$ AP. Second, compared to prior unsupervised approaches, the unsupervised TranS4mer model achieves better performance in all metrics. Finally, TranS4mer is $2.68 \times$ faster and requires $3.38 \times$ less GPU memory than the previous SOTA methods (ShotCol and BaSSL), while also being faster and more memory efficient than the transformer and state-space baselines. + +# 5.3. Baselines + +Prior Methods. In our comparisons, we include several unsupervised approaches such as GraphCut [39], SCSA [10], DP [21], Story Graph [45], and Grouping [40]. These methods use various clustering techniques using pre-extracted features. Moreover, we compare our approach with supervised approaches, such as Siamese [3], MS-LSTM [25], and LGSS [38], which also use pre-extracted CNN features. We also compare against the long-range video model ViS4mer [34], which uses S4 layers as a late-fusion strategy. Finally, we include two recent end-to-end trainable models that use self-supervised pretraining, namely, ShotCoL [11] and BaSSL [35]. Both models use CNN models based on ResNet-50 [22]. + +Our Implemented Baselines. To make our comparisons more complete, we implement three additional baselines: 1) Transformer: We construct this baseline by following the standard Vision Transformer [16]. In particular, we replace the Gated S4 layers of the TranS4mer model with self-attention layers and keep everything else unchanged. 2) TimeSformer: We construct this baseline by replacing the Gated S4 layers of our model with the divided space-time attention proposed by Bertasius at et al. [6]. 3) Vanilla S4: We develop this baseline by replacing the Gated S4 layers of the TranS4mer model with the S4 layers [18]. + +# 6. Results and Analysis + +# 6.1. Main Results on the MovieNet Dataset + +Comparison to the State-of-the-Art. We present the results on MovieNet [25] in Table 1. We first compare our method with the unsupervised approaches, including GraphCut [39], SCSA [10], DP [21], Story Graph [45], Grouping [40], and BaSSL (unsupervised) [35]. For a fair comparison, we train an unsupervised variant of our TranS4mer model using pseudo-boundary loss without ground-truth annotations and report the result without supervised finetuning. Our results suggest that our unsupervised TranS4mer model achieves the best performance according to all metrics and outperforms the prior best method Grouping by $+0.85\%$ AP. Next, we compare the supervised variant of our model (i.e., finetuned with ground truth annotations) with the state-of-the-art supervised methods (ShotCol [11] and BaSSL [35])). We also compare with the state-space-based long-range video classification model ViS4mer [34]. We observe that TranS4mer achieves the best performance in all metrics and outperforms the previous best method (BaSSL) by a large margin $(+3.38\%)$ AP. + +Comparison with Transformer and State-space Baselines. In Table 1, we also compare our TranS4mer model with the Transformer and State-space baselines: Trans- + +former, TimeSformer, and Vanilla S4 (See subsection 5.3). Note that all three baselines use intra-shot and inter-shot modules; however, instead of a Gated S4 layer, Transformer uses standard self-attention [16], TimeSformer uses divided space-time attention [18], and Vanilla S4 uses standard S4 [18] at the inter-shot module. Moreover, similar to the TranS4mer-Unsupervised method, we train unsupervised variants of these baselines without any ground-truth annotation. First, we observe that all three baselines outperform the previous state-of-the-art method (BaSSL [35]) in both supervised and unsupervised settings, indicating the effectiveness of our proposed intra-shot and inter-shot block designs. Second, TranS4mer performs better than all three of these baselines, outperforming Transformer by $+1.97\%$ and $+2.29\%$ , TimeSformer by $+1.16\%$ and $+1.98\%$ , and Vanilla S4 by $+1.07\%$ and $+1.11\%$ in supervised and unsupervised approaches, respectively. These experiments indicate that TranS4mer is better suited for movie scene detection than the standard self-attention and state-space models. + +Computational Cost Analysis. We compare the GPU memory consumption (in gigabytes) and the training speed (samples/s) of our model with the previous best methods as well as our implemented baselines in Table 1. First, we observe that, in addition to achieving the best performance, our method also requires $3.38 \times$ less memory and is $2.68 \times$ faster than the previous state-of-the-art method BaSSL [35]. Second, compared to the standard Transformer baseline, TranS4mer is $2 \times$ faster and requires $3 \times$ less GPU memory. Finally, our model is significantly cheaper than efficient self-attention and state-space models such as TimeSformer and Vanilla S4. Whereas TimeSformer and Vanilla S4 require 28.12 GB and 15.62 GB of memory, our TranS4mer requires only 10.13 GB of memory. Moreover, the training speed of TranS4mer is 2.57 samples/second compared to the 1.47 and 1.82 samples/second speed of TimeSformer and Vanilla S4, respectively. These observations suggest that TranS4mer is much more efficient than prior methods and standard self-attention and state-space-based models. + +Comparison Using the Same Backbone Model. For a fair comparison, we also experiment with a previous-best BaSSL [35] method that uses the same backbone as our model (i.e., ViT-S/32). We report that our TranS4mer outperforms this BaSSL variant by $+2.77\%$ AP. + +# 6.2. Scene Detection on Other Datasets + +We experiment with two additional movie scene detection datasets, BBC [3] and OVSD [40]. We present these results in Table 2, which shows that TranS4mer achieves the best result among all methods, outperforming the previous best BaSSL [35] method by $4.66\%$ AP on the BBC and $7.36\%$ AP on the OVSD datasets. These results demonstrate our method's ability to generalize to other datasets. + +
MethodAP (↑)
BaSSL [35]39.98
Transformer [16]41.86
TimeSformer [6]42.23
Vanilla S4 [18]42.56
TranS4mer43.64
+ +(a) Performance on BBC [3]. + +
MethodAP (↑)
BaSSL [35]28.68
Transformer [16]33.12
TimeSformer [6]33.87
Vanilla S4 [18]34.21
TranS4mer36.04
+ +(b) Performance on OVSD [40]. +Table 2. Scene Detection on additional datasets. TranS4mer outperforms the prior method (BaSSL) by a large margin of $4.66\%$ AP on BBC [3] and $7.36\%$ AP on OVSD [40] datasets. + +
MethodRelationSpeakSceneDirectorGenreWriterYear
ObjTrans. [48]53.1039.4056.9051.2054.6034.5039.10
ViS4mer [34]57.1440.7967.4462.6154.7148.8044.75
TranS4mer59.5239.2170.9363.8655.8546.9345.45
(a) Performance on LVU [48]
+ +
Model#Data(↓)Acc.(↑)
GHRM [51]306K75.50
Dist.Sup. [31]136M89.90
ViS4mer [34]495K88.17
TranS4mer495K90.27
+ +(b) Performance on Breakfast [30] + +
Model#Data(↓)Acc.(↑)
TSN [44]306K73.40
Dist.Sup. [31]136M90.00
ViS4mer [34]495K88.41
TranS4mer495K89.23
+ +(c) Performance on COIN [43] + +Table 3. Long-range video classification. (a) TranS4mer achieves best performance in 5 out of 7 classification tasks in LVU benchmark [48]. Moreover, (b) it performs best on the Breakfast [30] and (c) second-best on the COIN [43] datasets, while using significantly less pretraining data (middle column). + +# 6.3. Long-range Video Classification + +In addition to move scene detection, we also experiment with other tasks including long-form movie clip classification in the LVU [48] dataset, and long-range procedural activity classification on Breakfast [30] and COIN [43] datasets. LVU contains $30K$ videos from $3K$ movies, Breakfast has 1,712 videos of 10 cooking activities, and COIN contains 11,827 videos of 180 different procedural activities. Videos of each dataset are $2 - 3$ minutes long. We present the results in Table 3. On LVU, TranS4mer achieves the best performance in 5 out of 7 tasks (Table 3(a)). Moreover, TranS4mer also achieves the best performance on Breakfast (Table 3(b)) and the second-best performance on COIN (Table 3(c)) while using significantly fewer pretraining samples than the state-of-the-art Distant Supervision [31] approach. These results indicate that TranS4mer can be effectively applied to other domains and tasks. + +# 6.4. Ablation Studies + +Temporal Extent Ablation. To verify our hypothesis that long-range temporal context is critical for accurate movie scene detection, we experiment with video inputs of different lengths (i.e., video inputs containing 9, 17, 25, and 33 contextual shots) while predicting the boundary for the middle shot. Note that videos with more input shots denote longer input videos. We present these results in Figure 4a. First, we notice that a short temporal window of 9 context + +![](images/73508bc8858b27ae82cb8df775b54f351b5bde2180e51ff6844172a75811449b.jpg) +(a) Performance $\uparrow$ TranS4mer achieves much better performance for longer videos. +Table 4. Ablation studies with (a) TranS4mer modules, (b) (c) positioning, and (d) variants of S4 layers. Intra-shot and inter-shot modules are complementary, and TranS4mer with Gated S4 layers at every S4A block yields the best performance. + +![](images/7edc9edbe6d125fe50678b1bc28e2171ce5cd8ddcfc02c658adb5c05e5ab0a89.jpg) +(b) Training Speed $\uparrow$ TranS4mer is significantly faster than the Transformer baseline. +Figure 4. (a) Performance (AP), (b) Training Speed (Samples/Second), and (c) Memory Requirements (GigaBytes), and as a function of the number of input shots. Note that videos with more input shots denote longer input videos. + +![](images/9b52f9a383728fdc8562c2a8366a40731997d54aa7e605822d2c684a82864365.jpg) +(c) Memory Requirements $\downarrow$ TranS4mer requires significantly less GPU memory. + +
Intra-ShotInter-ShotAp (↑)
✓✗57.80
✗✓55.59
✓✓60.78
+ +(a)TranS4mer modules. + +
S4 layersAP (↑)
1-658.31
7-1258.82
1-1260.78
+ +(b) S4 in different layers. + +
S4 layersAP (↑)
every 2nd59.82
every 4th58.01
all60.78
+ +(c) S4 in every $k^{th}$ layer. + +
S4 layersAP (↑)
S459.71
DS460.13
GS460.78
+ +(d) Different S4 variants. + +tual shots produces a suboptimal performance of $53.29\%$ AP. Increasing the temporal extent to 25 contextual shots increases the performance to $60.78\%$ AP $(+7.49\%$ boost). Adding more contextual shots does not yield any significant improvements. These results verify the importance of long-range temporal modeling for movie scene detection. + +Detailed Comparison with Transformer. We next present a detailed comparison of our model with the Transformer baseline [16]. In particular, we experiment with videos that contain a different number of input shots and plot the accuracy in AP as a function of the number of input shots (see Figure 4). Although the Transformer baseline performs better for shorter video inputs, our TranS4mer model achieves much better performance using longer videos. Specifically, TranS4mer yields $+2.07\%$ larger AP than the transformer model when using the longest video inputs. This suggests that TranS4mer is more effective at capturing long-range dependencies for the movie scene detection task. Moreover, we also illustrate the training speed (Samples/Second) and the memory requirement (GigaBytes) as a function of the number of input shots (see Figures 4b and 4c). We observe that as we increase the video length, the training speed of the Transformer baseline drops drastically, and the memory requirement grows rapidly. Overall, our proposed TranS4mer model is $2.7\times$ faster and requires $3.38\times$ less GPU memory than the Transformer baseline while using the longest video inputs. + +Ablation with Intra-Shot and Inter-Shot Modules. In Table 4a, we analyze the significance of our (i) self-attention-based intra-shot module and (ii) state-space-based inter-shot module. We observe that removing the inter-shot + +module drops the performance by $2.98\%$ AP, whereas discarding the intra-shot module decreases the performance by $5.19\%$ AP. Therefore, based on these results, we can conclude that both the intra-shot and inter-shot modules are essential for good movie scene detection performance. We also note that they are complementary to each other, which aligns with our intuition of the intra-shot module being responsible for short-range representations while the intershot module is dedicated to long-range temporal reasoning. + +Ablation with S4 Layers. We experiment with injecting our proposed S4A block into different encoder layers (Table 4b). We also evaluate a sparser TranS4mer variant with our S4A block injected into every $k^{th}$ layer of the network (Table 4c). Lastly, we experiment with different S4 variants (i.e., Diagonal S4 (DS4) [20], Gated S4 (GS4) [33]) (Table 4d). Our results suggest that using S4A with Gated S4 in every layer of the network leads to the best accuracy. + +# 7. Conclusion + +In this work, we propose an efficient movie scene segmentation method which combines the strengths of selfattention for short-range modeling and state-space models for long-range modeling. Our method, named TranS4mer, achieves state-of-the-art results in three different movie scene segmentation datasets (MovieNet, BBC, and OVSD). Moreover, our model is significantly faster and requires less GPU memory than previous approaches and the standard vision transformer models. In future, we will extend our model to other long-range video understanding and multimodal tasks such as movie summarization, movie trailer generation, and natural language grounding in long videos. + +# References + +[1] Dzmitry Bahdanau, Kyunghyun Cho, et al. Neural machine translation by jointly learning to align and translate. arXiv preprint arXiv: 1409.0473, 2014. 1, 2 +[2] Lorenzo Baraldi, Costantino Grana, and Rita Cucchiara. 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However, accurately detecting movie scenes is often challenging as it requires the ability to reason over very long movie segments. This contrasts with most existing video recognition models, which are typically designed for short-range video analysis. This work proposes a State-Space Transformer model that can efficiently capture dependencies in long movie videos for accurate movie scene detection. Our model, called TranS4mer, is built using a novel S4A building block, combining the strengths of structured state-space sequence (S4) and self-attention (A) layers. Given a sequence of frames divided into movie shots (uninterrupted periods where the camera position does not change), the S4A block first applies self-attention to capture short-range intra-shot dependencies. Afterward, the state-space operation in the S4A block aggregates long-range inter-shot cues. The final TranS4mer model, which can be trained end-to-end, is obtained by stacking the S4A blocks one after the other multiple times. Our proposed TranS4mer outperforms all prior methods in three movie scene detection datasets, including MovieNet, BBC, and OVSD, while being " + }, + { + "bbox": [ + 46, + 239, + 290, + 525 + ], + "type": "inline_equation", + "content": "2 \\times" + }, + { + "bbox": [ + 46, + 239, + 290, + 525 + ], + "type": "text", + "content": " faster and requiring " + }, + { + "bbox": [ + 46, + 239, + 290, + 525 + ], + "type": "inline_equation", + "content": "3 \\times" + }, + { + "bbox": [ + 46, + 239, + 290, + 525 + ], + "type": "text", + "content": " less GPU memory than standard Transformer models. We will release our code and models." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 552, + 128, + 563 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 552, + 128, + 563 + ], + "spans": [ + { + "bbox": [ + 47, + 552, + 128, + 563 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 572, + 287, + 693 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 572, + 287, + 693 + ], + "spans": [ + { + "bbox": [ + 46, + 572, + 287, + 693 + ], + "type": "text", + "content": "Imagine watching The Godfather movie as illustrated in Figure 1. The first scene starts in the office room of mafia boss Don Vito Corleone, where he is discussing family business affairs with his eldest son Sonny Corleone and the family lawyer Tom Hagen. Then in the second scene, the family meets Virgil Sollozzo to hear about his business proposition. Afterward, the movie transitions into a third scene, where Don Vito chides his son Sonny for interfering. All of these movie scenes are inherently connected and create a complex storyline. Thus, the ability to recognize such" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 214, + 545, + 262 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 214, + 545, + 262 + ], + "spans": [ + { + "bbox": [ + 306, + 214, + 545, + 262 + ], + "type": "text", + "content": "movie scenes is essential for understanding the plot of a movie. Moreover, identifying movie scenes enables broader applications, such as content-driven video search, preview generation, and minimally disruptive ad insertion." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 265, + 546, + 456 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 265, + 546, + 456 + ], + "spans": [ + { + "bbox": [ + 304, + 265, + 546, + 456 + ], + "type": "text", + "content": "Unlike standard video recognition tasks (e.g., action recognition), which require a short-range analysis of video clips lasting only 5-10 seconds, movie scene detection requires short- and long-range understanding, where videos might last several minutes. For instance, to successfully recognize the scenes in Figure 1, we need to identify the visual concepts in each frame, such as characters, objects, and backgrounds (short-range modeling), while also reasoning about complex temporal events and activities (long-range modeling). For example, if we only look at the boundary frames of the first and second scenes of Figure 1 and identify the local properties (e.g., characters, objects, and backgrounds), it is quite difficult to determine the transition between the two scenes. However, considering longer temporal windows with frames from both scenes, we can recognize global events and identify their boundaries." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 459, + 547, + 592 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 459, + 547, + 592 + ], + "spans": [ + { + "bbox": [ + 304, + 459, + 547, + 592 + ], + "type": "text", + "content": "We also note that models that only use short-range temporal context typically produce many false positives due to abrupt low-level changes in the scene dynamics (e.g., camera switching between characters). For example, if we look at the middle two frames of scene 2 in Figure 1, we might mistake them for a scene boundary since the frames contain two characters. However, looking at all the frames in scene 2 makes it clear that they belong to the same scene. Therefore, a successful movie scene detection model should identify the short-range visual elements and also reason about their long-range temporal dependencies in a movie segment." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 594, + 547, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 594, + 547, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 594, + 547, + 714 + ], + "type": "text", + "content": "However, most existing movie scene detection methods [11, 35] are built using convolutional neural networks (CNNs), which are inherently designed using local operators (i.e., convolution kernels) for short-range video analysis. Thus, such models often fail to capture the long-range dependencies crucial for accurate movie scene detection. Recently, transformers have been shown to effectively model short-range and long-range dependencies in various Natural Language Processing (NLP) tasks [1,7,14, 15, 32, 37, 47, 49]. Inspired by the success of transform" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 702, + 245, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 702, + 245, + 712 + ], + "spans": [ + { + "bbox": [ + 58, + 702, + 245, + 712 + ], + "type": "text", + "content": "*Research done while MI was an intern at Comcast Labs." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "18749" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 52, + 72, + 105, + 110 + ], + "blocks": [ + { + "bbox": [ + 52, + 72, + 105, + 110 + ], + "lines": [ + { + "bbox": [ + 52, + 72, + 105, + 110 + ], + "spans": [ + { + "bbox": [ + 52, + 72, + 105, + 110 + ], + "type": "image", + "image_path": "7ea336fad0d749db3aa00c8718839cb5a8724c676bb4d154054a6f6a80a1257a.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 115, + 547, + 171 + ], + "lines": [ + { + "bbox": [ + 46, + 115, + 547, + 171 + ], + "spans": [ + { + "bbox": [ + 46, + 115, + 547, + 171 + ], + "type": "text", + "content": "Figure 1. Three scenes from the movie The Godfather. In the first scene, The Godfather (Don Vito Corleone) discusses family business affairs with his eldest son Sony and family lawyer Tom Hagen. Then the movie transitions into the second scene, where the mafia family meets Virgil Sollozzo to hear his business proposition. Afterward, in the third scene, Don Vito chides his son Sonny for interfering in the middle of his talk. Generally, movies are composed of well-defined scenes, and detecting those scenes is essential to high-level movie understanding. Therefore, this work aims to detect high-level scenes from a long-range movie video." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 3 + }, + { + "type": "image", + "bbox": [ + 106, + 72, + 159, + 110 + ], + "blocks": [ + { + "bbox": [ + 106, + 72, + 159, + 110 + ], + "lines": [ + { + "bbox": [ + 106, + 72, + 159, + 110 + ], + "spans": [ + { + "bbox": [ + 106, + 72, + 159, + 110 + ], + "type": "image", + "image_path": "360c0ea64e987272d73fd417d0887368103d39162c9087447e77880dd45621fc.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + } + ], + "index": 4 + }, + { + "type": "image", + "bbox": [ + 160, + 72, + 213, + 110 + ], + "blocks": [ + { + "bbox": [ + 160, + 72, + 213, + 110 + ], + "lines": [ + { + "bbox": [ + 160, + 72, + 213, + 110 + ], + "spans": [ + { + "bbox": [ + 160, + 72, + 213, + 110 + ], + "type": "image", + "image_path": "76e35dc1eb455ce7f1cf4319c9612ae2dab0a2f436837b5ab54b99409716724b.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_body" + } + ], + "index": 5 + }, + { + "type": "image", + "bbox": [ + 215, + 72, + 268, + 110 + ], + "blocks": [ + { + "bbox": [ + 215, + 72, + 268, + 110 + ], + "lines": [ + { + "bbox": [ + 215, + 72, + 268, + 110 + ], + "spans": [ + { + "bbox": [ + 215, + 72, + 268, + 110 + ], + "type": "image", + "image_path": "4ab128512689b67d329614cbec82a633b3e33e15e42a63a09d563fc15cb5a8c8.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_body" + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 269, + 72, + 321, + 110 + ], + "blocks": [ + { + "bbox": [ + 269, + 72, + 321, + 110 + ], + "lines": [ + { + "bbox": [ + 269, + 72, + 321, + 110 + ], + "spans": [ + { + "bbox": [ + 269, + 72, + 321, + 110 + ], + "type": "image", + "image_path": "d11d77dbb3111a71ae320628023621bb00b172fa0d21f9330edeee51c54dfed6.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_body" + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 323, + 72, + 375, + 110 + ], + "blocks": [ + { + "bbox": [ + 323, + 72, + 375, + 110 + ], + "lines": [ + { + "bbox": [ + 323, + 72, + 375, + 110 + ], + "spans": [ + { + "bbox": [ + 323, + 72, + 375, + 110 + ], + "type": "image", + "image_path": "f8b340fb3a939c73adeb338a223ad9676823a817550cd5b1b8a0a2f1c1dbb549.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 376, + 72, + 430, + 110 + ], + "blocks": [ + { + "bbox": [ + 376, + 72, + 430, + 110 + ], + "lines": [ + { + "bbox": [ + 376, + 72, + 430, + 110 + ], + "spans": [ + { + "bbox": [ + 376, + 72, + 430, + 110 + ], + "type": "image", + "image_path": "e93756d965d9d01f14cc3d1a3816d0eb6c4480f657f48c9dc1c052e15bde724c.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 432, + 72, + 485, + 110 + ], + "blocks": [ + { + "bbox": [ + 432, + 72, + 485, + 110 + ], + "lines": [ + { + "bbox": [ + 432, + 72, + 485, + 110 + ], + "spans": [ + { + "bbox": [ + 432, + 72, + 485, + 110 + ], + "type": "image", + "image_path": "9c0fda13a18abd58e5f36db1bfc5117353259d181c2a117544f895046c67fb77.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 487, + 72, + 539, + 110 + ], + "blocks": [ + { + "bbox": [ + 487, + 72, + 539, + 110 + ], + "lines": [ + { + "bbox": [ + 487, + 72, + 539, + 110 + ], + "spans": [ + { + "bbox": [ + 487, + 72, + 539, + 110 + ], + "type": "image", + "image_path": "a234ab7b4f27ba0626e083710298dcd678b28f6cfb5539b9ee698a95f7b7c0db.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + } + ], + "index": 11 + }, + { + "bbox": [ + 46, + 180, + 286, + 264 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 180, + 286, + 264 + ], + "spans": [ + { + "bbox": [ + 46, + 180, + 286, + 264 + ], + "type": "text", + "content": "ers in NLP, subsequent works have shown the remarkable success of using transformers in several short-range vision tasks [8, 16]. However, applying Transformers to long video sequences remains challenging due to the quadratic cost of self-attention. To overcome these issues, recent work proposed a structured state-space sequence (S4) operator [18, 19, 33] for efficient long-range sequence analysis." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 46, + 266, + 286, + 456 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 266, + 286, + 456 + ], + "spans": [ + { + "bbox": [ + 46, + 266, + 286, + 456 + ], + "type": "text", + "content": "Motivated by the developments in transformer and S4-based architectures, we present TranS4mer, an efficient end-to-end model for movie scene boundary detection, which combines the strengths of transformers for short-range modeling and S4 operators for long-range modeling. Specifically, we propose a novel state-space self-attention (S4A) block and build our TranS4mer model by stacking multiple S4A blocks on top of each other. Our model takes a sequence of frames divided into movie shots as input, where a shot is defined as a series of frames captured by the same camera over an uninterrupted period [46]. The S4A block first captures the short-range intra-shot dependencies by applying self-attention over the frames in each shot. Subsequently, it aggregates the inter-shot interactions over long movie segments by employing the state-space operator over all shots in a given movie video." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 46, + 460, + 286, + 627 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 460, + 286, + 627 + ], + "spans": [ + { + "bbox": [ + 46, + 460, + 286, + 627 + ], + "type": "text", + "content": "One key property of our model is that it independently applies self-attention to each shot, significantly reducing the cost of standard self-attention. For instance, if we have a video of 25 shots and each shot contains 3 frames, applying a standard vision transformer [16] with a patch size of " + }, + { + "bbox": [ + 46, + 460, + 286, + 627 + ], + "type": "inline_equation", + "content": "32 \\times 32" + }, + { + "bbox": [ + 46, + 460, + 286, + 627 + ], + "type": "text", + "content": " will result in 3,675 tokens and a single self-attention operation will require " + }, + { + "bbox": [ + 46, + 460, + 286, + 627 + ], + "type": "inline_equation", + "content": "\\sim 13.5\\mathrm{M}" + }, + { + "bbox": [ + 46, + 460, + 286, + 627 + ], + "type": "text", + "content": " pairwise comparisons. In contrast, applying self-attention within each shot parallelly reduces the number of comparisons " + }, + { + "bbox": [ + 46, + 460, + 286, + 627 + ], + "type": "inline_equation", + "content": "25 \\times" + }, + { + "bbox": [ + 46, + 460, + 286, + 627 + ], + "type": "text", + "content": " times. Simultaneously, TranS4mer attains long-range modeling ability through the efficient state-space layers that do not require costly pairwise comparisons and operate over the entire input video. As a result, the proposed TranS4mer model can be efficiently applied to long movie videos." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 46, + 630, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 630, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 630, + 286, + 713 + ], + "type": "text", + "content": "We experiment with three movie scene detection datasets: MovieNet [25], BBC [3], and OVSD [40], and report that our method outperforms prior approaches by large margins " + }, + { + "bbox": [ + 46, + 630, + 286, + 713 + ], + "type": "inline_equation", + "content": "(+3.38\\%)" + }, + { + "bbox": [ + 46, + 630, + 286, + 713 + ], + "type": "text", + "content": " AP, " + }, + { + "bbox": [ + 46, + 630, + 286, + 713 + ], + "type": "inline_equation", + "content": "+4.66\\%" + }, + { + "bbox": [ + 46, + 630, + 286, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 630, + 286, + 713 + ], + "type": "inline_equation", + "content": "+7.36\\%" + }, + { + "bbox": [ + 46, + 630, + 286, + 713 + ], + "type": "text", + "content": " respectively). TranS4mer is also " + }, + { + "bbox": [ + 46, + 630, + 286, + 713 + ], + "type": "inline_equation", + "content": "2\\times" + }, + { + "bbox": [ + 46, + 630, + 286, + 713 + ], + "type": "text", + "content": " faster and requires " + }, + { + "bbox": [ + 46, + 630, + 286, + 713 + ], + "type": "inline_equation", + "content": "3\\times" + }, + { + "bbox": [ + 46, + 630, + 286, + 713 + ], + "type": "text", + "content": " less GPU memory than the pure Transformer-based models. Moreover, to evaluate the generalizability of our model," + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 180, + 545, + 263 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 180, + 545, + 263 + ], + "spans": [ + { + "bbox": [ + 304, + 180, + 545, + 263 + ], + "type": "text", + "content": "we experiment with several long-range video understanding tasks, such as movie clip classification and procedural activity recognition. TranS4mer performs the best in 5 out of 7 movie clip classification tasks on LVU [48], the best in procedural activity classification on Breakfast [30], and the second-best in procedural activity classification on COIN [43] datasets." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 306, + 274, + 394, + 286 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 274, + 394, + 286 + ], + "spans": [ + { + "bbox": [ + 306, + 274, + 394, + 286 + ], + "type": "text", + "content": "2. Related works" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 295, + 545, + 581 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 295, + 545, + 581 + ], + "spans": [ + { + "bbox": [ + 304, + 295, + 545, + 581 + ], + "type": "text", + "content": "Long Sequence Modeling. Many modern approaches to long sequence modeling started in the field of Natural Language Processing (NLP). Bahdanau et al. [1] introduced an RNN architecture with an attention mechanism for machine translation. Afterward, Vaswani et al. [47] proposed the transformer model for capturing long-range dependencies in text sequences. Following this work, various improved transformer architectures were proposed [7, 14, 15, 32, 37, 49]. However, despite these advances, applying transformers to very long sequences is still challenging because of the quadratic cost of the self-attention operation. Consequently, many recent methods have developed efficient variations of standard self-attention [12, 26, 29, 36, 50]. Furthermore, the recent work of Gu et al. [17-19] proposed a structured statespace sequence (S4) model for long sequence analysis. The S4 models have achieved impressive results in many NLP tasks [17-20, 33], while having only linear memory and computation costs (w.r.t the sequence length). Building on this work, Islam et al. [34] proposed a model that applies S4 on pre-extracted video features for long-range video classification. In contrast, we propose an end-to-end trainable movie scene detection model that combines S4 and self-attention into a novel S4A block, which we use to build our TranS4mer model." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "content": "Movie Scene Detection. The early approaches for movie scene detection consisted predominantly of unsupervised clustering-based methods [2,4,10,39,40,42,52] built using hand-crafted features. Recently, Huang et al. [25] introduced a large-scale dataset for movie scene detection called MovieNet, which became the most popular benchmark for this problem. Subsequently, Huang et al. [25] and Rao et al. [38] proposed an LSTM-based model for movie scene detection, which is applied on top of preextracted CNN features. Most recently, Chen et al. [11] and Mun et al. [35] introduced several end-to-end movie" + } + ] + } + ], + "index": 20 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 82, + 59, + 182, + 71 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 82, + 59, + 182, + 71 + ], + "spans": [ + { + "bbox": [ + 82, + 59, + 182, + 71 + ], + "type": "text", + "content": "Scene 1 (250 seconds)" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 271, + 59, + 371, + 71 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 271, + 59, + 371, + 71 + ], + "spans": [ + { + "bbox": [ + 271, + 59, + 371, + 71 + ], + "type": "text", + "content": "Scene 2 (310 seconds)" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 434, + 59, + 534, + 71 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 434, + 59, + 534, + 71 + ], + "spans": [ + { + "bbox": [ + 434, + 59, + 534, + 71 + ], + "type": "text", + "content": "Scene 3 (200 seconds)" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "18750" + } + ] + } + ], + "index": 21 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 49, + 73, + 286, + 121 + ], + "blocks": [ + { + "bbox": [ + 49, + 73, + 286, + 121 + ], + "lines": [ + { + "bbox": [ + 49, + 73, + 286, + 121 + ], + "spans": [ + { + "bbox": [ + 49, + 73, + 286, + 121 + ], + "type": "image", + "image_path": "b601745f8402a6727a45a986b65fb91f00347d29bd0eb0c9ca7a7c20e258f832.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 124, + 287, + 190 + ], + "lines": [ + { + "bbox": [ + 46, + 124, + 287, + 190 + ], + "spans": [ + { + "bbox": [ + 46, + 124, + 287, + 190 + ], + "type": "text", + "content": "Figure 2. The hierarchical structure of long movie videos. First, multiple consecutive frames captured from the same camera position depict a shot. Next, multiple neighboring shots constitute a movie scene. Finally, a movie is composed of a collection of scenes. Here, we show one scene that contains N shots with " + }, + { + "bbox": [ + 46, + 124, + 287, + 190 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 46, + 124, + 287, + 190 + ], + "type": "text", + "content": " frames in each shot." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_caption" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 197, + 287, + 269 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 197, + 287, + 269 + ], + "spans": [ + { + "bbox": [ + 46, + 197, + 287, + 269 + ], + "type": "text", + "content": "scene detection approaches built using 2D/3D CNN architectures. However, these CNN-based models are limited by the smaller receptive fields of the local convolution operations. In contrast, our TranS4mer model is constructed using global operators (state-space and self-attention), which are more effective for long-range modeling." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 279, + 126, + 293 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 279, + 126, + 293 + ], + "spans": [ + { + "bbox": [ + 47, + 279, + 126, + 293 + ], + "type": "text", + "content": "3. Background" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 299, + 287, + 348 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 299, + 287, + 348 + ], + "spans": [ + { + "bbox": [ + 46, + 299, + 287, + 348 + ], + "type": "text", + "content": "The State-Space Model (SSM) is a fundamental model used in many scientific fields, such as control theory and computational neuroscience. We can define the SSM in continuous time using the following equations:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 116, + 356, + 287, + 376 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 116, + 356, + 287, + 376 + ], + "spans": [ + { + "bbox": [ + 116, + 356, + 287, + 376 + ], + "type": "interline_equation", + "content": "h ^ {\\prime} (t) = A h (t) + B x (t) \\tag {1}", + "image_path": "ff74f4093e7dcad6c548930c765e4fc6f167b72c18c5ae1730e558709c914a81.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 121, + 372, + 216, + 384 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 121, + 372, + 216, + 384 + ], + "spans": [ + { + "bbox": [ + 121, + 372, + 216, + 384 + ], + "type": "interline_equation", + "content": "y (t) = C h (t) + D x (t)", + "image_path": "0033bd61ae408b5adcf33765a3872ca2e1eb30eeafba3a9da688a302bca5710c.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 389, + 287, + 449 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 389, + 287, + 449 + ], + "spans": [ + { + "bbox": [ + 47, + 389, + 287, + 449 + ], + "type": "text", + "content": "Here, " + }, + { + "bbox": [ + 47, + 389, + 287, + 449 + ], + "type": "inline_equation", + "content": "x(t)" + }, + { + "bbox": [ + 47, + 389, + 287, + 449 + ], + "type": "text", + "content": " is the input signal, " + }, + { + "bbox": [ + 47, + 389, + 287, + 449 + ], + "type": "inline_equation", + "content": "h(t)" + }, + { + "bbox": [ + 47, + 389, + 287, + 449 + ], + "type": "text", + "content": " is a latent state, " + }, + { + "bbox": [ + 47, + 389, + 287, + 449 + ], + "type": "inline_equation", + "content": "h'(t)" + }, + { + "bbox": [ + 47, + 389, + 287, + 449 + ], + "type": "text", + "content": " is the first order derivative of " + }, + { + "bbox": [ + 47, + 389, + 287, + 449 + ], + "type": "inline_equation", + "content": "h(t)" + }, + { + "bbox": [ + 47, + 389, + 287, + 449 + ], + "type": "text", + "content": " wrt " + }, + { + "bbox": [ + 47, + 389, + 287, + 449 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 47, + 389, + 287, + 449 + ], + "type": "text", + "content": ", i.e., " + }, + { + "bbox": [ + 47, + 389, + 287, + 449 + ], + "type": "inline_equation", + "content": "h'(t) = \\frac{dh}{dt}" + }, + { + "bbox": [ + 47, + 389, + 287, + 449 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 389, + 287, + 449 + ], + "type": "inline_equation", + "content": "y(t)" + }, + { + "bbox": [ + 47, + 389, + 287, + 449 + ], + "type": "text", + "content": " is the output signal, and " + }, + { + "bbox": [ + 47, + 389, + 287, + 449 + ], + "type": "inline_equation", + "content": "A" + }, + { + "bbox": [ + 47, + 389, + 287, + 449 + ], + "type": "text", + "content": " is the state matrix. Equation (1) can be discretized by sampling the underlying input signal " + }, + { + "bbox": [ + 47, + 389, + 287, + 449 + ], + "type": "inline_equation", + "content": "u(t)" + }, + { + "bbox": [ + 47, + 389, + 287, + 449 + ], + "type": "text", + "content": " with a step size " + }, + { + "bbox": [ + 47, + 389, + 287, + 449 + ], + "type": "inline_equation", + "content": "\\Delta" + }, + { + "bbox": [ + 47, + 389, + 287, + 449 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 123, + 458, + 287, + 478 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 123, + 458, + 287, + 478 + ], + "spans": [ + { + "bbox": [ + 123, + 458, + 287, + 478 + ], + "type": "interline_equation", + "content": "h _ {k} = \\bar {A} h _ {k - 1} + \\bar {B} x _ {k} \\tag {2}", + "image_path": "1a8cb5fa876e5b88f7f2d3ffde2065e940e76dff21356d8db2c2e03a8450256d.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 126, + 475, + 200, + 488 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 126, + 475, + 200, + 488 + ], + "spans": [ + { + "bbox": [ + 126, + 475, + 200, + 488 + ], + "type": "interline_equation", + "content": "y _ {k} = \\overline {{C}} h _ {k} + \\bar {D} x _ {k}", + "image_path": "352bae8ae0b90c2bdfba5d1b7cdead3efdc29f9a0cfb68d065895d6fe5d1471f.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 47, + 498, + 287, + 535 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 498, + 287, + 535 + ], + "spans": [ + { + "bbox": [ + 47, + 498, + 287, + 535 + ], + "type": "text", + "content": "Here, " + }, + { + "bbox": [ + 47, + 498, + 287, + 535 + ], + "type": "inline_equation", + "content": "\\overline{A}" + }, + { + "bbox": [ + 47, + 498, + 287, + 535 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 498, + 287, + 535 + ], + "type": "inline_equation", + "content": "\\overline{B}" + }, + { + "bbox": [ + 47, + 498, + 287, + 535 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 498, + 287, + 535 + ], + "type": "inline_equation", + "content": "\\overline{C}" + }, + { + "bbox": [ + 47, + 498, + 287, + 535 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 47, + 498, + 287, + 535 + ], + "type": "inline_equation", + "content": "\\overline{D}" + }, + { + "bbox": [ + 47, + 498, + 287, + 535 + ], + "type": "text", + "content": " are the discrete versions of " + }, + { + "bbox": [ + 47, + 498, + 287, + 535 + ], + "type": "inline_equation", + "content": "A" + }, + { + "bbox": [ + 47, + 498, + 287, + 535 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 498, + 287, + 535 + ], + "type": "inline_equation", + "content": "B" + }, + { + "bbox": [ + 47, + 498, + 287, + 535 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 498, + 287, + 535 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 47, + 498, + 287, + 535 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 498, + 287, + 535 + ], + "type": "inline_equation", + "content": "D" + }, + { + "bbox": [ + 47, + 498, + 287, + 535 + ], + "type": "text", + "content": ". Furthermore, the equation (2) can be expressed as a convolution operation " + }, + { + "bbox": [ + 47, + 498, + 287, + 535 + ], + "type": "inline_equation", + "content": "(*)" + }, + { + "bbox": [ + 47, + 498, + 287, + 535 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 58, + 544, + 287, + 559 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 544, + 287, + 559 + ], + "spans": [ + { + "bbox": [ + 58, + 544, + 287, + 559 + ], + "type": "interline_equation", + "content": "y = \\bar {K} * x \\quad \\bar {K} = (\\bar {C B}, \\bar {C A B}, \\dots , \\bar {C A} ^ {L - 1} \\bar {B}), \\tag {3}", + "image_path": "fb50382d6b2d520058acf2d3d025b5e253d4be41b2026767270b51ff54a9b902.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 47, + 569, + 251, + 582 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 569, + 251, + 582 + ], + "spans": [ + { + "bbox": [ + 47, + 569, + 251, + 582 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 569, + 251, + 582 + ], + "type": "inline_equation", + "content": "\\overline{K}" + }, + { + "bbox": [ + 47, + 569, + 251, + 582 + ], + "type": "text", + "content": " is a kernel, and " + }, + { + "bbox": [ + 47, + 569, + 251, + 582 + ], + "type": "inline_equation", + "content": "L" + }, + { + "bbox": [ + 47, + 569, + 251, + 582 + ], + "type": "text", + "content": " is the sequence length." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 46, + 582, + 287, + 665 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 582, + 287, + 665 + ], + "spans": [ + { + "bbox": [ + 46, + 582, + 287, + 665 + ], + "type": "text", + "content": "S4 Model. The Structured State Space (S4) model is a particular class of SSM that requires the state matrix " + }, + { + "bbox": [ + 46, + 582, + 287, + 665 + ], + "type": "inline_equation", + "content": "A" + }, + { + "bbox": [ + 46, + 582, + 287, + 665 + ], + "type": "text", + "content": " to be diagonal and low-rank. Because of the specific structure of the state matrix " + }, + { + "bbox": [ + 46, + 582, + 287, + 665 + ], + "type": "inline_equation", + "content": "A" + }, + { + "bbox": [ + 46, + 582, + 287, + 665 + ], + "type": "text", + "content": ", we can derive a closed-form formula for the convolutional kernel " + }, + { + "bbox": [ + 46, + 582, + 287, + 665 + ], + "type": "inline_equation", + "content": "\\overline{K}" + }, + { + "bbox": [ + 46, + 582, + 287, + 665 + ], + "type": "text", + "content": " in equation (3) [18], which then facilitates an efficient computation of " + }, + { + "bbox": [ + 46, + 582, + 287, + 665 + ], + "type": "inline_equation", + "content": "\\overline{K}" + }, + { + "bbox": [ + 46, + 582, + 287, + 665 + ], + "type": "text", + "content": " without having to multiply the matrix " + }, + { + "bbox": [ + 46, + 582, + 287, + 665 + ], + "type": "inline_equation", + "content": "A" + }, + { + "bbox": [ + 46, + 582, + 287, + 665 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 582, + 287, + 665 + ], + "type": "inline_equation", + "content": "L - 1" + }, + { + "bbox": [ + 46, + 582, + 287, + 665 + ], + "type": "text", + "content": " times." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "text", + "content": "Gated S4 Model. Borrowing the idea from Gated Attention [24], Metha at el. [33] introduced a Gated S4 model, which first uses linear layers to compute two latent representations " + }, + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "inline_equation", + "content": "(u" + }, + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "inline_equation", + "content": "v)" + }, + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "text", + "content": " from the input sequences " + }, + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "text", + "content": ", and then" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 306, + 72, + 545, + 96 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 72, + 545, + 96 + ], + "spans": [ + { + "bbox": [ + 306, + 72, + 545, + 96 + ], + "type": "text", + "content": "applies an S4 layer to obtain a contextualized representation " + }, + { + "bbox": [ + 306, + 72, + 545, + 96 + ], + "type": "inline_equation", + "content": "\\hat{u}" + }, + { + "bbox": [ + 306, + 72, + 545, + 96 + ], + "type": "text", + "content": ". Finally, the tokens from " + }, + { + "bbox": [ + 306, + 72, + 545, + 96 + ], + "type": "inline_equation", + "content": "\\hat{u}" + }, + { + "bbox": [ + 306, + 72, + 545, + 96 + ], + "type": "text", + "content": " are used to gate " + }, + { + "bbox": [ + 306, + 72, + 545, + 96 + ], + "type": "inline_equation", + "content": "v" + }, + { + "bbox": [ + 306, + 72, + 545, + 96 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 361, + 105, + 489, + 118 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 361, + 105, + 489, + 118 + ], + "spans": [ + { + "bbox": [ + 361, + 105, + 489, + 118 + ], + "type": "interline_equation", + "content": "u = \\phi (W _ {u} x) \\quad v = \\phi (W _ {v} x)", + "image_path": "15c9ec80d911475da3bcfdeb1ec8c29a47c69b221991a3f7c09164586b1dfb97.jpg" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 362, + 119, + 545, + 132 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 362, + 119, + 545, + 132 + ], + "spans": [ + { + "bbox": [ + 362, + 119, + 545, + 132 + ], + "type": "interline_equation", + "content": "h = S 4 (u) \\quad \\hat {u} = W _ {h} x \\tag {4}", + "image_path": "3bddff8b59398e1d2d57731c8abc718aacaced74832330e80cf2074fcb3f16f6.jpg" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 362, + 134, + 429, + 148 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 362, + 134, + 429, + 148 + ], + "spans": [ + { + "bbox": [ + 362, + 134, + 429, + 148 + ], + "type": "interline_equation", + "content": "y = W _ {y} (\\hat {u} \\odot v)", + "image_path": "ed52169699693071cd44f7314a043e0b4deb87e3af21ba05cfc96fce008bfaa9.jpg" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 305, + 155, + 545, + 190 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 155, + 545, + 190 + ], + "spans": [ + { + "bbox": [ + 305, + 155, + 545, + 190 + ], + "type": "text", + "content": "Here, " + }, + { + "bbox": [ + 305, + 155, + 545, + 190 + ], + "type": "inline_equation", + "content": "W_{u}, W_{v}, W_{h}, W_{y}" + }, + { + "bbox": [ + 305, + 155, + 545, + 190 + ], + "type": "text", + "content": " are the weight matrices of linear layers, " + }, + { + "bbox": [ + 305, + 155, + 545, + 190 + ], + "type": "inline_equation", + "content": "\\phi" + }, + { + "bbox": [ + 305, + 155, + 545, + 190 + ], + "type": "text", + "content": " denotes GELU nonlinearity [23], " + }, + { + "bbox": [ + 305, + 155, + 545, + 190 + ], + "type": "inline_equation", + "content": "\\odot" + }, + { + "bbox": [ + 305, + 155, + 545, + 190 + ], + "type": "text", + "content": " is elementwise multiplication, and S4 denotes an S4 layer described above." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 305, + 201, + 424, + 215 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 201, + 424, + 215 + ], + "spans": [ + { + "bbox": [ + 305, + 201, + 424, + 215 + ], + "type": "text", + "content": "4. Technical Approach" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 304, + 221, + 545, + 376 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 221, + 545, + 376 + ], + "spans": [ + { + "bbox": [ + 304, + 221, + 545, + 376 + ], + "type": "text", + "content": "We aim to develop an efficient scene detection method for long movie videos. Movie videos have a specific hierarchical structure consisting of three semantic levels: (i) frames, (ii) shots, and (iii) scenes (See Figure 2). First, multiple consecutive frames constitute a shot, where the frames are captured from the same camera position over an uninterrupted period [46]. Second, multiple consecutive shots construct a scene, where a scene is a semantically cohesive unit of the storyline [27, 41]. Finally, a movie is composed of a collection of scenes. Shots can be easily recognized by detecting the changes in low-level visual cues [9, 13, 42]. However, identifying the scene boundary is more challenging as it requires high-level semantic understanding." + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 304, + 377, + 545, + 520 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 377, + 545, + 520 + ], + "spans": [ + { + "bbox": [ + 304, + 377, + 545, + 520 + ], + "type": "text", + "content": "Problem Overview. First, we formally define the problem of movie scene detection. We are given a movie video " + }, + { + "bbox": [ + 304, + 377, + 545, + 520 + ], + "type": "inline_equation", + "content": "V" + }, + { + "bbox": [ + 304, + 377, + 545, + 520 + ], + "type": "text", + "content": " divided into " + }, + { + "bbox": [ + 304, + 377, + 545, + 520 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 304, + 377, + 545, + 520 + ], + "type": "text", + "content": " non-overlapping automatically-detected shots, " + }, + { + "bbox": [ + 304, + 377, + 545, + 520 + ], + "type": "inline_equation", + "content": "V = \\{s_1,\\ldots ,s_i,\\ldots ,s_T\\}" + }, + { + "bbox": [ + 304, + 377, + 545, + 520 + ], + "type": "text", + "content": ". We can then uniformly sample " + }, + { + "bbox": [ + 304, + 377, + 545, + 520 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 304, + 377, + 545, + 520 + ], + "type": "text", + "content": " frames from each shot. Therefore, a shot is represented as " + }, + { + "bbox": [ + 304, + 377, + 545, + 520 + ], + "type": "inline_equation", + "content": "s_i = \\{f_1,\\dots ,f_j,\\dots ,f_K\\}" + }, + { + "bbox": [ + 304, + 377, + 545, + 520 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 377, + 545, + 520 + ], + "type": "inline_equation", + "content": "f_{j}\\in \\mathbb{R}^{3\\times H\\times W}" + }, + { + "bbox": [ + 304, + 377, + 545, + 520 + ], + "type": "text", + "content": " depicts an RGB frame, " + }, + { + "bbox": [ + 304, + 377, + 545, + 520 + ], + "type": "inline_equation", + "content": "H" + }, + { + "bbox": [ + 304, + 377, + 545, + 520 + ], + "type": "text", + "content": " is the height, and " + }, + { + "bbox": [ + 304, + 377, + 545, + 520 + ], + "type": "inline_equation", + "content": "W" + }, + { + "bbox": [ + 304, + 377, + 545, + 520 + ], + "type": "text", + "content": " is the width of each frame. Following these definitions, we can then formulate the movie scene detection problem as a prediction task, where we need to produce a binary output " + }, + { + "bbox": [ + 304, + 377, + 545, + 520 + ], + "type": "inline_equation", + "content": "y_{i}\\in \\{0,1\\}" + }, + { + "bbox": [ + 304, + 377, + 545, + 520 + ], + "type": "text", + "content": " for each video shot " + }, + { + "bbox": [ + 304, + 377, + 545, + 520 + ], + "type": "inline_equation", + "content": "s_i" + }, + { + "bbox": [ + 304, + 377, + 545, + 520 + ], + "type": "text", + "content": " (i.e., whether a given shot is at a movie scene boundary or not)." + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 304, + 521, + 545, + 639 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 521, + 545, + 639 + ], + "spans": [ + { + "bbox": [ + 304, + 521, + 545, + 639 + ], + "type": "text", + "content": "**Approach Overview.** Our movie scene detection model, called the State-Space Transformer (TranS4mer), is built using our proposed S4A blocks that combine the strengths of structured state-space sequence (S4) and self-attention (A) layers. The S4A block utilizes the self-attention layer to encode short-range dependencies between frames in each shot and the S4 layer for capturing long-range dependencies between shots far away from each other. A detailed illustration of our model is presented in Figure 3. Below, we describe each component of our model in more detail." + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 306, + 647, + 435, + 658 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 647, + 435, + 658 + ], + "spans": [ + { + "bbox": [ + 306, + 647, + 435, + 658 + ], + "type": "text", + "content": "4.1. The TranS4mer Model" + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 306, + 665, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 665, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 306, + 665, + 545, + 714 + ], + "type": "text", + "content": "Following previous methods [11,35,38], our model takes as input " + }, + { + "bbox": [ + 306, + 665, + 545, + 714 + ], + "type": "inline_equation", + "content": "N = 2m + 1" + }, + { + "bbox": [ + 306, + 665, + 545, + 714 + ], + "type": "text", + "content": " temporally adjacent shots, " + }, + { + "bbox": [ + 306, + 665, + 545, + 714 + ], + "type": "inline_equation", + "content": "\\mathcal{V}_i = \\{s_{i - m},\\ldots ,s_i,\\ldots ,s_{i + m}\\}" + }, + { + "bbox": [ + 306, + 665, + 545, + 714 + ], + "type": "text", + "content": ", and outputs a binary prediction " + }, + { + "bbox": [ + 306, + 665, + 545, + 714 + ], + "type": "inline_equation", + "content": "y_{i}\\in \\{0,1\\}" + }, + { + "bbox": [ + 306, + 665, + 545, + 714 + ], + "type": "text", + "content": " for the shot " + }, + { + "bbox": [ + 306, + 665, + 545, + 714 + ], + "type": "inline_equation", + "content": "s_i" + }, + { + "bbox": [ + 306, + 665, + 545, + 714 + ], + "type": "text", + "content": ". The neighboring shots provide" + } + ] + } + ], + "index": 26 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 156, + 62, + 182, + 70 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 156, + 62, + 182, + 70 + ], + "spans": [ + { + "bbox": [ + 156, + 62, + 182, + 70 + ], + "type": "text", + "content": "Scene S" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "18751" + } + ] + } + ], + "index": 27 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 63, + 57, + 312, + 291 + ], + "blocks": [ + { + "bbox": [ + 63, + 57, + 312, + 291 + ], + "lines": [ + { + "bbox": [ + 63, + 57, + 312, + 291 + ], + "spans": [ + { + "bbox": [ + 63, + 57, + 312, + 291 + ], + "type": "image", + "image_path": "25feea89ec1c422697255ef8ed0724b5c0af5a4e57b00176e95a91475dfb592f.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 317, + 57, + 529, + 324 + ], + "blocks": [ + { + "bbox": [ + 317, + 57, + 529, + 324 + ], + "lines": [ + { + "bbox": [ + 317, + 57, + 529, + 324 + ], + "spans": [ + { + "bbox": [ + 317, + 57, + 529, + 324 + ], + "type": "image", + "image_path": "fc1d6e927c049e2f33b13d193633eaa1ce640b2f5f55a42037aa1bfa98846afb.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 326, + 545, + 403 + ], + "lines": [ + { + "bbox": [ + 46, + 326, + 545, + 403 + ], + "spans": [ + { + "bbox": [ + 46, + 326, + 545, + 403 + ], + "type": "text", + "content": "Figure 3. Overview of the TranS4mer model. Left: Our model takes a sequence of frames divided into automatically-detected shots. Following the ViT [16], the frames are decomposed into non-overlapping patches and passed through a linear projection layer. Afterward, we feed these patch-level embeddings through our TranS4mer model, which consists of " + }, + { + "bbox": [ + 46, + 326, + 545, + 403 + ], + "type": "inline_equation", + "content": "B" + }, + { + "bbox": [ + 46, + 326, + 545, + 403 + ], + "type": "text", + "content": " state-space self-attention (S4A) blocks stacked on top of each other. Finally, the CLS tokens of all shots are passed to two linear layers, i.e., the boundary prediction head (which outputs a binary label indicating the boundary shot) and the contrastive head (which maximizes intra-shot similarity). Right: Each of our proposed S4A blocks contains a self-attention-based intra-shot module that models the interaction among frames in the same shot and a Gated S4-based inter-shot module that aggregates long-range temporal cues from shots far away from each other." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_caption" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 413, + 287, + 460 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 413, + 287, + 460 + ], + "spans": [ + { + "bbox": [ + 46, + 413, + 287, + 460 + ], + "type": "text", + "content": "long-range contextual cues for predicting the boundary at shot " + }, + { + "bbox": [ + 46, + 413, + 287, + 460 + ], + "type": "inline_equation", + "content": "s_i" + }, + { + "bbox": [ + 46, + 413, + 287, + 460 + ], + "type": "text", + "content": ". Here, " + }, + { + "bbox": [ + 46, + 413, + 287, + 460 + ], + "type": "inline_equation", + "content": "\\mathcal{V}_i \\in \\mathbb{R}^{N \\times K \\times 3 \\times H \\times W}" + }, + { + "bbox": [ + 46, + 413, + 287, + 460 + ], + "type": "text", + "content": " is composed of " + }, + { + "bbox": [ + 46, + 413, + 287, + 460 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 46, + 413, + 287, + 460 + ], + "type": "text", + "content": " frames from each of " + }, + { + "bbox": [ + 46, + 413, + 287, + 460 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 413, + 287, + 460 + ], + "type": "text", + "content": " consecutive shots, where " + }, + { + "bbox": [ + 46, + 413, + 287, + 460 + ], + "type": "inline_equation", + "content": "H" + }, + { + "bbox": [ + 46, + 413, + 287, + 460 + ], + "type": "text", + "content": " is the height, and " + }, + { + "bbox": [ + 46, + 413, + 287, + 460 + ], + "type": "inline_equation", + "content": "W" + }, + { + "bbox": [ + 46, + 413, + 287, + 460 + ], + "type": "text", + "content": " is the width of each frame." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 461, + 287, + 533 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 461, + 287, + 533 + ], + "spans": [ + { + "bbox": [ + 47, + 461, + 287, + 533 + ], + "type": "text", + "content": "Following ViT [16], we divide each frame into " + }, + { + "bbox": [ + 47, + 461, + 287, + 533 + ], + "type": "inline_equation", + "content": "P" + }, + { + "bbox": [ + 47, + 461, + 287, + 533 + ], + "type": "text", + "content": " nonoverlapping patches of size " + }, + { + "bbox": [ + 47, + 461, + 287, + 533 + ], + "type": "inline_equation", + "content": "p \\times p" + }, + { + "bbox": [ + 47, + 461, + 287, + 533 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 47, + 461, + 287, + 533 + ], + "type": "inline_equation", + "content": "P = HW / p^2" + }, + { + "bbox": [ + 47, + 461, + 287, + 533 + ], + "type": "text", + "content": ". Then we use a linear layer to project each patch into a hidden dimension " + }, + { + "bbox": [ + 47, + 461, + 287, + 533 + ], + "type": "inline_equation", + "content": "D" + }, + { + "bbox": [ + 47, + 461, + 287, + 533 + ], + "type": "text", + "content": ", and a positional embedding is added to each patch token. As a result, we obtain a tensor of shape " + }, + { + "bbox": [ + 47, + 461, + 287, + 533 + ], + "type": "inline_equation", + "content": "\\mathbf{V}_i \\in \\mathbb{R}^{N \\times K \\times P \\times D}" + }, + { + "bbox": [ + 47, + 461, + 287, + 533 + ], + "type": "text", + "content": ", which is fed to our TranS4mer model." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 533, + 287, + 593 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 533, + 287, + 593 + ], + "spans": [ + { + "bbox": [ + 46, + 533, + 287, + 593 + ], + "type": "text", + "content": "The S4A Block. Our proposed S4A block enables us to compute a strong short-range feature representation and model long-range temporal dependencies among shots. It consists of two modules: a short-range intra-shot module and a long-range inter-shot module." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 594, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 594, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 287, + 713 + ], + "type": "text", + "content": "Intra-Shot Module. The intra-shot module takes the input tensor " + }, + { + "bbox": [ + 46, + 594, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{V}_i\\in \\mathbb{R}^{N\\times K\\times P\\times D}" + }, + { + "bbox": [ + 46, + 594, + 287, + 713 + ], + "type": "text", + "content": ", which we can think of as a collection of " + }, + { + "bbox": [ + 46, + 594, + 287, + 713 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 594, + 287, + 713 + ], + "type": "text", + "content": " shots, where a sequence of tokens represents each shot " + }, + { + "bbox": [ + 46, + 594, + 287, + 713 + ], + "type": "inline_equation", + "content": "S_{i} = x_{1},\\ldots ,x_{L}" + }, + { + "bbox": [ + 46, + 594, + 287, + 713 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 594, + 287, + 713 + ], + "type": "inline_equation", + "content": "x_{i}\\in \\mathbb{R}^{D}" + }, + { + "bbox": [ + 46, + 594, + 287, + 713 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 594, + 287, + 713 + ], + "type": "inline_equation", + "content": "L = K\\times P" + }, + { + "bbox": [ + 46, + 594, + 287, + 713 + ], + "type": "text", + "content": ". The intra-shot module models the sequence of tokens from each shot independently. To this end, it first applies a multi-layer perceptron (MLP) layer and a residual connection. Afterward, it applies a Multiheaded Self Attention (MSA) layer and another residual connection. Layer Normalization (LN) is applied before the MLP" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 413, + 544, + 425 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 413, + 544, + 425 + ], + "spans": [ + { + "bbox": [ + 306, + 413, + 544, + 425 + ], + "type": "text", + "content": "and the MSA layers. The module can be defined as follows:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 367, + 437, + 544, + 456 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 367, + 437, + 544, + 456 + ], + "spans": [ + { + "bbox": [ + 367, + 437, + 544, + 456 + ], + "type": "interline_equation", + "content": "\\mathbf {x} ^ {\\prime} = \\operatorname {M H A} \\left(\\operatorname {L N} \\left(\\mathbf {x} _ {i n}\\right)\\right) + \\mathbf {x} _ {i n} \\tag {5}", + "image_path": "f933f15c3068126166ca785a6e526e70a90a7830e3f1776ae5728574271d202d.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 368, + 453, + 479, + 464 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 368, + 453, + 479, + 464 + ], + "spans": [ + { + "bbox": [ + 368, + 453, + 479, + 464 + ], + "type": "interline_equation", + "content": "\\mathbf {x} _ {\\text {o u t}} = \\operatorname {M L P} \\left(\\operatorname {L N} \\left(\\mathbf {x} ^ {\\prime}\\right)\\right) + \\mathbf {x} ^ {\\prime}", + "image_path": "2c095f67489b65111716b24a1c05fb56ca2b264a2d728f90aa923dd2ee7b03e9.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 478, + 544, + 503 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 478, + 544, + 503 + ], + "spans": [ + { + "bbox": [ + 305, + 478, + 544, + 503 + ], + "type": "text", + "content": "The output of the intra-shot module " + }, + { + "bbox": [ + 305, + 478, + 544, + 503 + ], + "type": "inline_equation", + "content": "\\mathbf{V}'_i \\in \\mathbb{R}^{N \\times K \\times P \\times D}" + }, + { + "bbox": [ + 305, + 478, + 544, + 503 + ], + "type": "text", + "content": ", is then passed to the inter-shot module." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 506, + 545, + 553 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 506, + 545, + 553 + ], + "spans": [ + { + "bbox": [ + 305, + 506, + 545, + 553 + ], + "type": "text", + "content": "Note that applying self-attention to tokens from each shot separately reduces the computation cost to " + }, + { + "bbox": [ + 305, + 506, + 545, + 553 + ], + "type": "inline_equation", + "content": "O(NL^2)" + }, + { + "bbox": [ + 305, + 506, + 545, + 553 + ], + "type": "text", + "content": ". In contrast, applying self-attention to the entire sequence of tokens in " + }, + { + "bbox": [ + 305, + 506, + 545, + 553 + ], + "type": "inline_equation", + "content": "\\mathbf{V}_{\\mathrm{i}}" + }, + { + "bbox": [ + 305, + 506, + 545, + 553 + ], + "type": "text", + "content": " would cost " + }, + { + "bbox": [ + 305, + 506, + 545, + 553 + ], + "type": "inline_equation", + "content": "O(N^{2}L^{2})" + }, + { + "bbox": [ + 305, + 506, + 545, + 553 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 555, + 545, + 639 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 555, + 545, + 639 + ], + "spans": [ + { + "bbox": [ + 304, + 555, + 545, + 639 + ], + "type": "text", + "content": "Inter-Shot Module. Our previously defined intra-shot module only models short-range dependencies and, thus, lacks the ability for long-range temporal understanding, which is crucial for the movie scene detection task. To address this limitation, we propose an efficient inter-shot module based on the Gated S4 operator that aggregates long-range inter-shot cues." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "type": "text", + "content": "First, we unroll the input tensor " + }, + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{V}'_i" + }, + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "type": "text", + "content": " into a sequence " + }, + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "type": "inline_equation", + "content": "z_{1},\\ldots ,z_{L'}" + }, + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "type": "inline_equation", + "content": "z_{i}\\in \\mathbb{R}^{D}" + }, + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "type": "inline_equation", + "content": "L^{\\prime} = N\\times K\\times P" + }, + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "type": "text", + "content": ". Then, we pass the sequence to a multi-layer perceptron (MLP) layer and a residual connection. Afterward, we apply a Gated S4 (GS4) layer and another residual connection. Layer Normalization (LN) is applied before MLP and GS4 layers:" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "18752" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 115, + 83, + 286, + 108 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 115, + 83, + 286, + 108 + ], + "spans": [ + { + "bbox": [ + 115, + 83, + 286, + 108 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\mathbf {z} ^ {\\prime} = \\operatorname {G S 4} \\left(\\operatorname {L N} \\left(\\mathbf {z} _ {i n}\\right)\\right) + \\mathbf {z} _ {i n} \\tag {6} \\\\ \\mathbf {z} _ {\\text {o u t}} = \\operatorname {M L P} \\left(\\operatorname {L N} \\left(\\mathbf {z} ^ {\\prime}\\right)\\right) + \\mathbf {z} ^ {\\prime} \\\\ \\end{array}", + "image_path": "dc52a00074ee811cdbbc8c44ca9af13d2dbb6fa68311f0090cf97e5d2675af0c.jpg" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 117, + 286, + 188 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 117, + 286, + 188 + ], + "spans": [ + { + "bbox": [ + 47, + 117, + 286, + 188 + ], + "type": "text", + "content": "The output of this operation is then passed into the next S4A block. Unlike the intra-shot module, which operates on a short sequence of length " + }, + { + "bbox": [ + 47, + 117, + 286, + 188 + ], + "type": "inline_equation", + "content": "L = K \\times P" + }, + { + "bbox": [ + 47, + 117, + 286, + 188 + ], + "type": "text", + "content": ", the inter-shot module operates on much longer sequences of " + }, + { + "bbox": [ + 47, + 117, + 286, + 188 + ], + "type": "inline_equation", + "content": "L' = N \\times K \\times P" + }, + { + "bbox": [ + 47, + 117, + 286, + 188 + ], + "type": "text", + "content": ". Our model can efficiently process such long sequences due to the Gated S4 layers in the inter-shot module." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 196, + 204, + 209 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 196, + 204, + 209 + ], + "spans": [ + { + "bbox": [ + 47, + 196, + 204, + 209 + ], + "type": "text", + "content": "4.2. Training and Loss Functions" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 215, + 286, + 346 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 215, + 286, + 346 + ], + "spans": [ + { + "bbox": [ + 46, + 215, + 286, + 346 + ], + "type": "text", + "content": "Most prior works in move scene detection use self-supervised pretraining [11, 35]. Thus, we also adopt the self-supervised pretraining strategy of Mun at et al. [35], which uses pseudo boundaries of move scenes from the Dynamic Time Warping algorithm as a supervisory signal. Afterward, we finetune our pretrained model using the labeled subset of the data. Note that we do not claim technical novelty over the pretraining strategy. Instead, our main goal is to develop an efficient state-space transformer backbone for movie scene detection. Below, we provide more details related to the pretraining and fine-tuning protocols." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 347, + 286, + 514 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 347, + 286, + 514 + ], + "spans": [ + { + "bbox": [ + 46, + 347, + 286, + 514 + ], + "type": "text", + "content": "Pretraining. Leveraging the pseudo movie scene boundaries, we optimize our model using the following two losses: (i) a shot-scene contrastive loss and (ii) a pseudoboundary prediction loss. The contrastive loss maximizes the similarity between the representations of a shot and its corresponding pseudo ground truth scene while also minimizing the similarity of a shot with all the other scenes. We represent each shot with its respective CLS token, whereas each scene is represented by mean-pooling the CLS tokens of all shots in that scene. The DTW algorithm divides the input video " + }, + { + "bbox": [ + 46, + 347, + 286, + 514 + ], + "type": "inline_equation", + "content": "\\mathcal{V}_i = \\{s_{i - m},\\dots ,s_i,\\dots ,s_{i + m}\\}" + }, + { + "bbox": [ + 46, + 347, + 286, + 514 + ], + "type": "text", + "content": " into two pseudo-scenes " + }, + { + "bbox": [ + 46, + 347, + 286, + 514 + ], + "type": "inline_equation", + "content": "\\mathcal{V}_L = \\{s_{i - m},\\dots ,s_{i^*}\\}" + }, + { + "bbox": [ + 46, + 347, + 286, + 514 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 347, + 286, + 514 + ], + "type": "inline_equation", + "content": "\\mathcal{V}_R = s_{i^{*} + 1},\\ldots ,s_{i + m}\\}" + }, + { + "bbox": [ + 46, + 347, + 286, + 514 + ], + "type": "text", + "content": ", here " + }, + { + "bbox": [ + 46, + 347, + 286, + 514 + ], + "type": "inline_equation", + "content": "s_{i^*}" + }, + { + "bbox": [ + 46, + 347, + 286, + 514 + ], + "type": "text", + "content": " is the pseudo-boundary shot. We can then define the shot-scene contrastive loss as:" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 53, + 525, + 286, + 557 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 525, + 286, + 557 + ], + "spans": [ + { + "bbox": [ + 53, + 525, + 286, + 557 + ], + "type": "interline_equation", + "content": "l _ {\\mathrm {C}} (\\mathbf {r}, \\bar {\\mathbf {r}}) = - \\log \\frac {\\mathcal {S} (\\mathbf {r} , \\bar {\\mathbf {r}})}{\\mathcal {S} (\\mathbf {r} , \\bar {\\mathbf {r}}) + \\sum_ {\\mathbf {r} _ {n}} \\mathcal {S} (\\mathbf {r} _ {n} , \\bar {\\mathbf {r}}) + \\sum_ {\\bar {\\mathbf {r}} _ {n}} \\mathcal {S} (\\mathbf {r} , \\bar {\\mathbf {r}} _ {n})} \\tag {7}", + "image_path": "4ed468e4136ebe6f721bf0bfec5d114d845473de41e1bd155c866809a23087f9.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 563, + 286, + 646 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 563, + 286, + 646 + ], + "spans": [ + { + "bbox": [ + 47, + 563, + 286, + 646 + ], + "type": "text", + "content": "Here, " + }, + { + "bbox": [ + 47, + 563, + 286, + 646 + ], + "type": "inline_equation", + "content": "\\mathbf{r}" + }, + { + "bbox": [ + 47, + 563, + 286, + 646 + ], + "type": "text", + "content": " is a shot representation obtained by applying a linear layer on the CLS token of that shot, " + }, + { + "bbox": [ + 47, + 563, + 286, + 646 + ], + "type": "inline_equation", + "content": "\\bar{\\mathbf{r}}_L" + }, + { + "bbox": [ + 47, + 563, + 286, + 646 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 563, + 286, + 646 + ], + "type": "inline_equation", + "content": "\\bar{\\mathbf{r}}_R" + }, + { + "bbox": [ + 47, + 563, + 286, + 646 + ], + "type": "text", + "content": " are the scene-level representations of pseudo-scenes " + }, + { + "bbox": [ + 47, + 563, + 286, + 646 + ], + "type": "inline_equation", + "content": "\\nu_{L}" + }, + { + "bbox": [ + 47, + 563, + 286, + 646 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 563, + 286, + 646 + ], + "type": "inline_equation", + "content": "\\nu_{R}" + }, + { + "bbox": [ + 47, + 563, + 286, + 646 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 563, + 286, + 646 + ], + "type": "inline_equation", + "content": "\\mathbf{r}_n" + }, + { + "bbox": [ + 47, + 563, + 286, + 646 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 563, + 286, + 646 + ], + "type": "inline_equation", + "content": "\\bar{\\mathbf{r}}_n" + }, + { + "bbox": [ + 47, + 563, + 286, + 646 + ], + "type": "text", + "content": " are the negative shots and scenes from the minibatch. Similarity between two representations is calculated as: " + }, + { + "bbox": [ + 47, + 563, + 286, + 646 + ], + "type": "inline_equation", + "content": "S(\\mathbf{x},\\mathbf{y}) = \\exp ((\\mathbf{x}^{\\top}\\mathbf{y}) / (\\| \\mathbf{x}\\| \\| \\mathbf{y}\\|))" + }, + { + "bbox": [ + 47, + 563, + 286, + 646 + ], + "type": "text", + "content": ". The first loss term can then be written as: " + }, + { + "bbox": [ + 47, + 563, + 286, + 646 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{C}} = l_{\\mathrm{C}}(\\mathbf{r}_{i - m},\\bar{\\mathbf{r}}_L) + l_{\\mathrm{C}}(\\mathbf{r}_{i + m},\\bar{\\mathbf{r}}_R)" + }, + { + "bbox": [ + 47, + 563, + 286, + 646 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 647, + 286, + 694 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 647, + 286, + 694 + ], + "spans": [ + { + "bbox": [ + 46, + 647, + 286, + 694 + ], + "type": "text", + "content": "The second loss function of pseudo-boundary prediction is a simple objective that guides the model to predict a pseudo-boundary from a given shot representation. We can define this loss as a binary cross-entropy loss:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 85, + 702, + 286, + 714 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 85, + 702, + 286, + 714 + ], + "spans": [ + { + "bbox": [ + 85, + 702, + 286, + 714 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\mathrm {B}} = - \\log \\left(\\rho_ {b} \\left(\\mathbf {r} _ {i ^ {*}}\\right)\\right) - \\log \\left(1 - \\rho_ {b} \\left(\\mathbf {r} _ {\\tilde {b}}\\right)\\right) \\tag {8}", + "image_path": "ee4ee8981f8e265f1e4870250f2704fd9415c5308966ab7f4a70dda877fe3324.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 307, + 79, + 545, + 126 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 307, + 79, + 545, + 126 + ], + "spans": [ + { + "bbox": [ + 307, + 79, + 545, + 126 + ], + "type": "text", + "content": "Here, " + }, + { + "bbox": [ + 307, + 79, + 545, + 126 + ], + "type": "inline_equation", + "content": "\\mathbf{r}_{i^*}" + }, + { + "bbox": [ + 307, + 79, + 545, + 126 + ], + "type": "text", + "content": " is the CLS representation of the pseudoboundary shot " + }, + { + "bbox": [ + 307, + 79, + 545, + 126 + ], + "type": "inline_equation", + "content": "s_{i^*}" + }, + { + "bbox": [ + 307, + 79, + 545, + 126 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 307, + 79, + 545, + 126 + ], + "type": "inline_equation", + "content": "\\mathbf{r}_{\\bar{b}}" + }, + { + "bbox": [ + 307, + 79, + 545, + 126 + ], + "type": "text", + "content": " is the representation of a randomly selected non-boundary shot " + }, + { + "bbox": [ + 307, + 79, + 545, + 126 + ], + "type": "inline_equation", + "content": "s_{\\bar{b}}" + }, + { + "bbox": [ + 307, + 79, + 545, + 126 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 307, + 79, + 545, + 126 + ], + "type": "inline_equation", + "content": "\\rho_{b}" + }, + { + "bbox": [ + 307, + 79, + 545, + 126 + ], + "type": "text", + "content": " is a projection layer that outputs the probability of a shot being the pseudo-boundary." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 307, + 127, + 544, + 149 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 307, + 127, + 544, + 149 + ], + "spans": [ + { + "bbox": [ + 307, + 127, + 544, + 149 + ], + "type": "text", + "content": "The overall pretraining loss is the sum of the shot-scene contrastive loss and the pseudo-boundary loss." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 307, + 150, + 545, + 197 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 307, + 150, + 545, + 197 + ], + "spans": [ + { + "bbox": [ + 307, + 150, + 545, + 197 + ], + "type": "text", + "content": "Finetuning. After the self-supervised pretraining, we finetune our model using the subset of the dataset with ground truth annotations. We use a binary cross-entropy loss as in [35] to finetune our model." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 307, + 205, + 437, + 216 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 307, + 205, + 437, + 216 + ], + "spans": [ + { + "bbox": [ + 307, + 205, + 437, + 216 + ], + "type": "text", + "content": "4.3. Implementation Details" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 307, + 223, + 545, + 389 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 307, + 223, + 545, + 389 + ], + "spans": [ + { + "bbox": [ + 307, + 223, + 545, + 389 + ], + "type": "text", + "content": "Following the ViT [16], we resize video frames to a spatial dimension of " + }, + { + "bbox": [ + 307, + 223, + 545, + 389 + ], + "type": "inline_equation", + "content": "224 \\times 224" + }, + { + "bbox": [ + 307, + 223, + 545, + 389 + ], + "type": "text", + "content": " and divide using a patch size of " + }, + { + "bbox": [ + 307, + 223, + 545, + 389 + ], + "type": "inline_equation", + "content": "32 \\times 32" + }, + { + "bbox": [ + 307, + 223, + 545, + 389 + ], + "type": "text", + "content": ". Our model contains 12 S4A blocks and uses a hidden dimension of 384. It takes 25 neighboring shots as input, where each shot contains 3 frames. We use four data augmentation techniques: random crop, flip, color jitter, and Gaussian blur. We use a batch size of 256 and pretrain our model for 10 epochs before finetuning for 20 epochs. During pretraining, we use a base learning rate of 0.3, which we reduce using a cosine schedule after a linear warmup strategy of 1 epoch. During finetuning, we use a learning rate of " + }, + { + "bbox": [ + 307, + 223, + 545, + 389 + ], + "type": "inline_equation", + "content": "10^{-6}" + }, + { + "bbox": [ + 307, + 223, + 545, + 389 + ], + "type": "text", + "content": ". We use the Adam [28] optimizer with a momentum of 0.9 and weight decay of " + }, + { + "bbox": [ + 307, + 223, + 545, + 389 + ], + "type": "inline_equation", + "content": "10^{-6}" + }, + { + "bbox": [ + 307, + 223, + 545, + 389 + ], + "type": "text", + "content": ". We train our models using 8 NVIDIA RTX A6000 GPUs." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 307, + 399, + 422, + 412 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 307, + 399, + 422, + 412 + ], + "spans": [ + { + "bbox": [ + 307, + 399, + 422, + 412 + ], + "type": "text", + "content": "5. Experimental Setup" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 307, + 419, + 367, + 430 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 307, + 419, + 367, + 430 + ], + "spans": [ + { + "bbox": [ + 307, + 419, + 367, + 430 + ], + "type": "text", + "content": "5.1. Datasets" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 307, + 437, + 545, + 533 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 307, + 437, + 545, + 533 + ], + "spans": [ + { + "bbox": [ + 307, + 437, + 545, + 533 + ], + "type": "text", + "content": "MovieNet [25] is a large-scale dataset containing 1100 movies with 1.6 million shots, and 318 of these movies have ground-truth scene boundary annotation. The annotated subset of the dataset is divided into 190, 64, and 64 movies for training, validation, and testing. Following the previous approaches, we pretrain our model using all the movies, finetune using the standard training split of the annotated subset, and report the result on the test split." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 307, + 533, + 544, + 568 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 307, + 533, + 544, + 568 + ], + "spans": [ + { + "bbox": [ + 307, + 533, + 544, + 568 + ], + "type": "text", + "content": "BBC [3] contains 11 episodes from the BBC TV series Planet Earth [5]. The average duration of the videos is 50 minutes. The dataset contains 670 scenes and 4.9K shots." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 307, + 569, + 544, + 604 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 307, + 569, + 544, + 604 + ], + "spans": [ + { + "bbox": [ + 307, + 569, + 544, + 604 + ], + "type": "text", + "content": "OVSD [40] contains 21 short films with an average duration of 30 minutes. It has a total of 10K shots and 300 scenes extracted from movie scripts." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 307, + 611, + 417, + 622 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 307, + 611, + 417, + 622 + ], + "spans": [ + { + "bbox": [ + 307, + 611, + 417, + 622 + ], + "type": "text", + "content": "5.2. Evaluation Metrics" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 307, + 630, + 544, + 652 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 307, + 630, + 544, + 652 + ], + "spans": [ + { + "bbox": [ + 307, + 630, + 544, + 652 + ], + "type": "text", + "content": "AP measures the weighted average of precisions at different thresholds." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 307, + 654, + 544, + 677 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 307, + 654, + 544, + 677 + ], + "spans": [ + { + "bbox": [ + 307, + 654, + 544, + 677 + ], + "type": "text", + "content": "mIoU is the average intersection over union of predicted scene boundaries with the closest ground truth boundaries." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 307, + 677, + 544, + 700 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 307, + 677, + 544, + 700 + ], + "spans": [ + { + "bbox": [ + 307, + 677, + 544, + 700 + ], + "type": "text", + "content": "AUC-ROC is calculated as the True Positive Rate with respect to the False Positive Rate at different thresholds." + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 320, + 701, + 539, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 320, + 701, + 539, + 713 + ], + "spans": [ + { + "bbox": [ + 320, + 701, + 539, + 713 + ], + "type": "text", + "content": "F1-Score is the harmonic mean of precision and recall." + } + ] + } + ], + "index": 23 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "type": "text", + "content": "18753" + } + ] + } + ], + "index": 24 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 53, + 68, + 538, + 335 + ], + "blocks": [ + { + "bbox": [ + 53, + 68, + 538, + 335 + ], + "lines": [ + { + "bbox": [ + 53, + 68, + 538, + 335 + ], + "spans": [ + { + "bbox": [ + 53, + 68, + 538, + 335 + ], + "type": "table", + "html": "
MethodAP (↑)mIoU (↑)AUC-ROC (↑)F1 (↑)Memory (GB) (↓)Samples/s (↑)
UnsupervisedGraphCut [39]14.1029.70----
SCSA [10]14.7030.50----
DP [21]15.5032.00----
Story Graph [45]25.1035.70----
Grouping [40]33.6037.20----
BaSSL [35]31.5539.3671.6732.5534.280.96
Transformer [16]32.1637.2470.2331.2430.281.27
TimeSformer [6]32.4737.7670.9531.4528.121.47
Vanilla S4 [18]33.3438.1271.8632.2115.621.83
TranS4mer34.4539.6073.2533.4110.132.57
SupervisedSiamese [3]35.8039.60----
MS-LSTM [25]46.5046.20----
LGSS [38]47.1048.80----
ViS4mer [34]55.1348.2788.7446.15
ShotCoL [11]53.40---34.280.96
BaSSL [35]57.4050.6990.5447.0234.280.96
Transformer [16]58.8151.2190.8447.8830.281.27
TimeSformer [6]59.6250.7590.6648.0228.121.47
Vanilla S4 [18]59.7151.3290.9647.8515.621.83
TranS4mer60.7851.9191.8948.3610.132.57
", + "image_path": "ac019eb0e17c68d5065fb2d64eb8c007f0904733c7d3a32a8e027094a9b98ed0.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + }, + { + "bbox": [ + 46, + 339, + 547, + 396 + ], + "lines": [ + { + "bbox": [ + 46, + 339, + 547, + 396 + ], + "spans": [ + { + "bbox": [ + 46, + 339, + 547, + 396 + ], + "type": "text", + "content": "Table 1. Results on MovieNet [25]. Horizontal lines in both Unsupervised and Supervised rows separate prior works from our implemented baselines. First, our method achieves state-of-the-art performance, outperforming the previous best method (BaSSL) by a significant margin of " + }, + { + "bbox": [ + 46, + 339, + 547, + 396 + ], + "type": "inline_equation", + "content": "3.38\\%" + }, + { + "bbox": [ + 46, + 339, + 547, + 396 + ], + "type": "text", + "content": " AP. Second, compared to prior unsupervised approaches, the unsupervised TranS4mer model achieves better performance in all metrics. Finally, TranS4mer is " + }, + { + "bbox": [ + 46, + 339, + 547, + 396 + ], + "type": "inline_equation", + "content": "2.68 \\times" + }, + { + "bbox": [ + 46, + 339, + 547, + 396 + ], + "type": "text", + "content": " faster and requires " + }, + { + "bbox": [ + 46, + 339, + 547, + 396 + ], + "type": "inline_equation", + "content": "3.38 \\times" + }, + { + "bbox": [ + 46, + 339, + 547, + 396 + ], + "type": "text", + "content": " less GPU memory than the previous SOTA methods (ShotCol and BaSSL), while also being faster and more memory efficient than the transformer and state-space baselines." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_footnote" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 410, + 114, + 421 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 410, + 114, + 421 + ], + "spans": [ + { + "bbox": [ + 47, + 410, + 114, + 421 + ], + "type": "text", + "content": "5.3. Baselines" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 426, + 288, + 582 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 426, + 288, + 582 + ], + "spans": [ + { + "bbox": [ + 46, + 426, + 288, + 582 + ], + "type": "text", + "content": "Prior Methods. In our comparisons, we include several unsupervised approaches such as GraphCut [39], SCSA [10], DP [21], Story Graph [45], and Grouping [40]. These methods use various clustering techniques using pre-extracted features. Moreover, we compare our approach with supervised approaches, such as Siamese [3], MS-LSTM [25], and LGSS [38], which also use pre-extracted CNN features. We also compare against the long-range video model ViS4mer [34], which uses S4 layers as a late-fusion strategy. Finally, we include two recent end-to-end trainable models that use self-supervised pretraining, namely, ShotCoL [11] and BaSSL [35]. Both models use CNN models based on ResNet-50 [22]." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "content": "Our Implemented Baselines. To make our comparisons more complete, we implement three additional baselines: 1) Transformer: We construct this baseline by following the standard Vision Transformer [16]. In particular, we replace the Gated S4 layers of the TranS4mer model with self-attention layers and keep everything else unchanged. 2) TimeSformer: We construct this baseline by replacing the Gated S4 layers of our model with the divided space-time attention proposed by Bertasius at et al. [6]. 3) Vanilla S4: We develop this baseline by replacing the Gated S4 layers of the TranS4mer model with the S4 layers [18]." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 306, + 410, + 427, + 423 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 410, + 427, + 423 + ], + "spans": [ + { + "bbox": [ + 306, + 410, + 427, + 423 + ], + "type": "text", + "content": "6. Results and Analysis" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 306, + 430, + 509, + 442 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 430, + 509, + 442 + ], + "spans": [ + { + "bbox": [ + 306, + 430, + 509, + 442 + ], + "type": "text", + "content": "6.1. Main Results on the MovieNet Dataset" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 449, + 545, + 675 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 449, + 545, + 675 + ], + "spans": [ + { + "bbox": [ + 304, + 449, + 545, + 675 + ], + "type": "text", + "content": "Comparison to the State-of-the-Art. We present the results on MovieNet [25] in Table 1. We first compare our method with the unsupervised approaches, including GraphCut [39], SCSA [10], DP [21], Story Graph [45], Grouping [40], and BaSSL (unsupervised) [35]. For a fair comparison, we train an unsupervised variant of our TranS4mer model using pseudo-boundary loss without ground-truth annotations and report the result without supervised finetuning. Our results suggest that our unsupervised TranS4mer model achieves the best performance according to all metrics and outperforms the prior best method Grouping by " + }, + { + "bbox": [ + 304, + 449, + 545, + 675 + ], + "type": "inline_equation", + "content": "+0.85\\%" + }, + { + "bbox": [ + 304, + 449, + 545, + 675 + ], + "type": "text", + "content": " AP. Next, we compare the supervised variant of our model (i.e., finetuned with ground truth annotations) with the state-of-the-art supervised methods (ShotCol [11] and BaSSL [35])). We also compare with the state-space-based long-range video classification model ViS4mer [34]. We observe that TranS4mer achieves the best performance in all metrics and outperforms the previous best method (BaSSL) by a large margin " + }, + { + "bbox": [ + 304, + 449, + 545, + 675 + ], + "type": "inline_equation", + "content": "(+3.38\\%)" + }, + { + "bbox": [ + 304, + 449, + 545, + 675 + ], + "type": "text", + "content": " AP." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 677, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 547, + 715 + ], + "type": "text", + "content": "Comparison with Transformer and State-space Baselines. In Table 1, we also compare our TranS4mer model with the Transformer and State-space baselines: Trans-" + } + ] + } + ], + "index": 8 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "18754" + } + ] + } + ], + "index": 9 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 289, + 300 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 289, + 300 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 289, + 300 + ], + "type": "text", + "content": "former, TimeSformer, and Vanilla S4 (See subsection 5.3). Note that all three baselines use intra-shot and inter-shot modules; however, instead of a Gated S4 layer, Transformer uses standard self-attention [16], TimeSformer uses divided space-time attention [18], and Vanilla S4 uses standard S4 [18] at the inter-shot module. Moreover, similar to the TranS4mer-Unsupervised method, we train unsupervised variants of these baselines without any ground-truth annotation. First, we observe that all three baselines outperform the previous state-of-the-art method (BaSSL [35]) in both supervised and unsupervised settings, indicating the effectiveness of our proposed intra-shot and inter-shot block designs. Second, TranS4mer performs better than all three of these baselines, outperforming Transformer by " + }, + { + "bbox": [ + 47, + 72, + 289, + 300 + ], + "type": "inline_equation", + "content": "+1.97\\%" + }, + { + "bbox": [ + 47, + 72, + 289, + 300 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 72, + 289, + 300 + ], + "type": "inline_equation", + "content": "+2.29\\%" + }, + { + "bbox": [ + 47, + 72, + 289, + 300 + ], + "type": "text", + "content": ", TimeSformer by " + }, + { + "bbox": [ + 47, + 72, + 289, + 300 + ], + "type": "inline_equation", + "content": "+1.16\\%" + }, + { + "bbox": [ + 47, + 72, + 289, + 300 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 72, + 289, + 300 + ], + "type": "inline_equation", + "content": "+1.98\\%" + }, + { + "bbox": [ + 47, + 72, + 289, + 300 + ], + "type": "text", + "content": ", and Vanilla S4 by " + }, + { + "bbox": [ + 47, + 72, + 289, + 300 + ], + "type": "inline_equation", + "content": "+1.07\\%" + }, + { + "bbox": [ + 47, + 72, + 289, + 300 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 72, + 289, + 300 + ], + "type": "inline_equation", + "content": "+1.11\\%" + }, + { + "bbox": [ + 47, + 72, + 289, + 300 + ], + "type": "text", + "content": " in supervised and unsupervised approaches, respectively. These experiments indicate that TranS4mer is better suited for movie scene detection than the standard self-attention and state-space models." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 302, + 289, + 529 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 302, + 289, + 529 + ], + "spans": [ + { + "bbox": [ + 47, + 302, + 289, + 529 + ], + "type": "text", + "content": "Computational Cost Analysis. We compare the GPU memory consumption (in gigabytes) and the training speed (samples/s) of our model with the previous best methods as well as our implemented baselines in Table 1. First, we observe that, in addition to achieving the best performance, our method also requires " + }, + { + "bbox": [ + 47, + 302, + 289, + 529 + ], + "type": "inline_equation", + "content": "3.38 \\times" + }, + { + "bbox": [ + 47, + 302, + 289, + 529 + ], + "type": "text", + "content": " less memory and is " + }, + { + "bbox": [ + 47, + 302, + 289, + 529 + ], + "type": "inline_equation", + "content": "2.68 \\times" + }, + { + "bbox": [ + 47, + 302, + 289, + 529 + ], + "type": "text", + "content": " faster than the previous state-of-the-art method BaSSL [35]. Second, compared to the standard Transformer baseline, TranS4mer is " + }, + { + "bbox": [ + 47, + 302, + 289, + 529 + ], + "type": "inline_equation", + "content": "2 \\times" + }, + { + "bbox": [ + 47, + 302, + 289, + 529 + ], + "type": "text", + "content": " faster and requires " + }, + { + "bbox": [ + 47, + 302, + 289, + 529 + ], + "type": "inline_equation", + "content": "3 \\times" + }, + { + "bbox": [ + 47, + 302, + 289, + 529 + ], + "type": "text", + "content": " less GPU memory. Finally, our model is significantly cheaper than efficient self-attention and state-space models such as TimeSformer and Vanilla S4. Whereas TimeSformer and Vanilla S4 require 28.12 GB and 15.62 GB of memory, our TranS4mer requires only 10.13 GB of memory. Moreover, the training speed of TranS4mer is 2.57 samples/second compared to the 1.47 and 1.82 samples/second speed of TimeSformer and Vanilla S4, respectively. These observations suggest that TranS4mer is much more efficient than prior methods and standard self-attention and state-space-based models." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 533, + 288, + 593 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 533, + 288, + 593 + ], + "spans": [ + { + "bbox": [ + 47, + 533, + 288, + 593 + ], + "type": "text", + "content": "Comparison Using the Same Backbone Model. For a fair comparison, we also experiment with a previous-best BaSSL [35] method that uses the same backbone as our model (i.e., ViT-S/32). We report that our TranS4mer outperforms this BaSSL variant by " + }, + { + "bbox": [ + 47, + 533, + 288, + 593 + ], + "type": "inline_equation", + "content": "+2.77\\%" + }, + { + "bbox": [ + 47, + 533, + 288, + 593 + ], + "type": "text", + "content": " AP." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 608, + 232, + 620 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 608, + 232, + 620 + ], + "spans": [ + { + "bbox": [ + 47, + 608, + 232, + 620 + ], + "type": "text", + "content": "6.2. Scene Detection on Other Datasets" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 629, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 629, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 47, + 629, + 287, + 715 + ], + "type": "text", + "content": "We experiment with two additional movie scene detection datasets, BBC [3] and OVSD [40]. We present these results in Table 2, which shows that TranS4mer achieves the best result among all methods, outperforming the previous best BaSSL [35] method by " + }, + { + "bbox": [ + 47, + 629, + 287, + 715 + ], + "type": "inline_equation", + "content": "4.66\\%" + }, + { + "bbox": [ + 47, + 629, + 287, + 715 + ], + "type": "text", + "content": " AP on the BBC and " + }, + { + "bbox": [ + 47, + 629, + 287, + 715 + ], + "type": "inline_equation", + "content": "7.36\\%" + }, + { + "bbox": [ + 47, + 629, + 287, + 715 + ], + "type": "text", + "content": " AP on the OVSD datasets. These results demonstrate our method's ability to generalize to other datasets." + } + ] + } + ], + "index": 4 + }, + { + "type": "table", + "bbox": [ + 310, + 60, + 422, + 133 + ], + "blocks": [ + { + "bbox": [ + 310, + 60, + 422, + 133 + ], + "lines": [ + { + "bbox": [ + 310, + 60, + 422, + 133 + ], + "spans": [ + { + "bbox": [ + 310, + 60, + 422, + 133 + ], + "type": "table", + "html": "
MethodAP (↑)
BaSSL [35]39.98
Transformer [16]41.86
TimeSformer [6]42.23
Vanilla S4 [18]42.56
TranS4mer43.64
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MethodAP (↑)
BaSSL [35]28.68
Transformer [16]33.12
TimeSformer [6]33.87
Vanilla S4 [18]34.21
TranS4mer36.04
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MethodRelationSpeakSceneDirectorGenreWriterYear
ObjTrans. [48]53.1039.4056.9051.2054.6034.5039.10
ViS4mer [34]57.1440.7967.4462.6154.7148.8044.75
TranS4mer59.5239.2170.9363.8655.8546.9345.45
(a) Performance on LVU [48]
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Model#Data(↓)Acc.(↑)
GHRM [51]306K75.50
Dist.Sup. [31]136M89.90
ViS4mer [34]495K88.17
TranS4mer495K90.27
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Model#Data(↓)Acc.(↑)
TSN [44]306K73.40
Dist.Sup. [31]136M90.00
ViS4mer [34]495K88.41
TranS4mer495K89.23
", + "image_path": "12fbfe926002b07937de1a4c850da7eb27f017ccc3f933e236e97eb5a9c39f80.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "table_body" + } + ], + "index": 13 + }, + { + "bbox": [ + 434, + 296, + 537, + 305 + ], + "lines": [ + { + "bbox": [ + 434, + 296, + 537, + 305 + ], + "spans": [ + { + "bbox": [ + 434, + 296, + 537, + 305 + ], + "type": "text", + "content": "(c) Performance on COIN [43]" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 305, + 308, + 545, + 364 + ], + "lines": [ + { + "bbox": [ + 305, + 308, + 545, + 364 + ], + "spans": [ + { + "bbox": [ + 305, + 308, + 545, + 364 + ], + "type": "text", + "content": "Table 3. Long-range video classification. (a) TranS4mer achieves best performance in 5 out of 7 classification tasks in LVU benchmark [48]. Moreover, (b) it performs best on the Breakfast [30] and (c) second-best on the COIN [43] datasets, while using significantly less pretraining data (middle column)." + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 306, + 377, + 479, + 390 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 377, + 479, + 390 + ], + "spans": [ + { + "bbox": [ + 306, + 377, + 479, + 390 + ], + "type": "text", + "content": "6.3. Long-range Video Classification" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 397, + 545, + 589 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 397, + 545, + 589 + ], + "spans": [ + { + "bbox": [ + 304, + 397, + 545, + 589 + ], + "type": "text", + "content": "In addition to move scene detection, we also experiment with other tasks including long-form movie clip classification in the LVU [48] dataset, and long-range procedural activity classification on Breakfast [30] and COIN [43] datasets. LVU contains " + }, + { + "bbox": [ + 304, + 397, + 545, + 589 + ], + "type": "inline_equation", + "content": "30K" + }, + { + "bbox": [ + 304, + 397, + 545, + 589 + ], + "type": "text", + "content": " videos from " + }, + { + "bbox": [ + 304, + 397, + 545, + 589 + ], + "type": "inline_equation", + "content": "3K" + }, + { + "bbox": [ + 304, + 397, + 545, + 589 + ], + "type": "text", + "content": " movies, Breakfast has 1,712 videos of 10 cooking activities, and COIN contains 11,827 videos of 180 different procedural activities. Videos of each dataset are " + }, + { + "bbox": [ + 304, + 397, + 545, + 589 + ], + "type": "inline_equation", + "content": "2 - 3" + }, + { + "bbox": [ + 304, + 397, + 545, + 589 + ], + "type": "text", + "content": " minutes long. We present the results in Table 3. On LVU, TranS4mer achieves the best performance in 5 out of 7 tasks (Table 3(a)). Moreover, TranS4mer also achieves the best performance on Breakfast (Table 3(b)) and the second-best performance on COIN (Table 3(c)) while using significantly fewer pretraining samples than the state-of-the-art Distant Supervision [31] approach. These results indicate that TranS4mer can be effectively applied to other domains and tasks." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 306, + 598, + 406, + 609 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 598, + 406, + 609 + ], + "spans": [ + { + "bbox": [ + 306, + 598, + 406, + 609 + ], + "type": "text", + "content": "6.4. Ablation Studies" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "type": "text", + "content": "Temporal Extent Ablation. To verify our hypothesis that long-range temporal context is critical for accurate movie scene detection, we experiment with video inputs of different lengths (i.e., video inputs containing 9, 17, 25, and 33 contextual shots) while predicting the boundary for the middle shot. Note that videos with more input shots denote longer input videos. We present these results in Figure 4a. First, we notice that a short temporal window of 9 context" + } + ] + } + ], + "index": 19 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "18755" + } + ] + } + ], + "index": 20 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 74, + 50, + 214, + 159 + ], + "blocks": [ + { + "bbox": [ + 74, + 50, + 214, + 159 + ], + "lines": [ + { + "bbox": [ + 74, + 50, + 214, + 159 + ], + "spans": [ + { + "bbox": [ + 74, + 50, + 214, + 159 + ], + "type": "image", + "image_path": "73508bc8858b27ae82cb8df775b54f351b5bde2180e51ff6844172a75811449b.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 77, + 162, + 220, + 181 + ], + "lines": [ + { + "bbox": [ + 77, + 162, + 220, + 181 + ], + "spans": [ + { + "bbox": [ + 77, + 162, + 220, + 181 + ], + "type": "text", + "content": "(a) Performance " + }, + { + "bbox": [ + 77, + 162, + 220, + 181 + ], + "type": "inline_equation", + "content": "\\uparrow" + }, + { + "bbox": [ + 77, + 162, + 220, + 181 + ], + "type": "text", + "content": " TranS4mer achieves much better performance for longer videos." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 46, + 295, + 546, + 319 + ], + "lines": [ + { + "bbox": [ + 46, + 295, + 546, + 319 + ], + "spans": [ + { + "bbox": [ + 46, + 295, + 546, + 319 + ], + "type": "text", + "content": "Table 4. Ablation studies with (a) TranS4mer modules, (b) (c) positioning, and (d) variants of S4 layers. Intra-shot and inter-shot modules are complementary, and TranS4mer with Gated S4 layers at every S4A block yields the best performance." + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 228, + 52, + 375, + 159 + ], + "blocks": [ + { + "bbox": [ + 228, + 52, + 375, + 159 + ], + "lines": [ + { + "bbox": [ + 228, + 52, + 375, + 159 + ], + "spans": [ + { + "bbox": [ + 228, + 52, + 375, + 159 + ], + "type": "image", + "image_path": "7edc9edbe6d125fe50678b1bc28e2171ce5cd8ddcfc02c658adb5c05e5ab0a89.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 231, + 161, + 375, + 181 + ], + "lines": [ + { + "bbox": [ + 231, + 161, + 375, + 181 + ], + "spans": [ + { + "bbox": [ + 231, + 161, + 375, + 181 + ], + "type": "text", + "content": "(b) Training Speed " + }, + { + "bbox": [ + 231, + 161, + 375, + 181 + ], + "type": "inline_equation", + "content": "\\uparrow" + }, + { + "bbox": [ + 231, + 161, + 375, + 181 + ], + "type": "text", + "content": " TranS4mer is significantly faster than the Transformer baseline." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 46, + 188, + 547, + 211 + ], + "lines": [ + { + "bbox": [ + 46, + 188, + 547, + 211 + ], + "spans": [ + { + "bbox": [ + 46, + 188, + 547, + 211 + ], + "type": "text", + "content": "Figure 4. (a) Performance (AP), (b) Training Speed (Samples/Second), and (c) Memory Requirements (GigaBytes), and as a function of the number of input shots. Note that videos with more input shots denote longer input videos." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 383, + 55, + 522, + 159 + ], + "blocks": [ + { + "bbox": [ + 383, + 55, + 522, + 159 + ], + "lines": [ + { + "bbox": [ + 383, + 55, + 522, + 159 + ], + "spans": [ + { + "bbox": [ + 383, + 55, + 522, + 159 + ], + "type": "image", + "image_path": "9b52f9a383728fdc8562c2a8366a40731997d54aa7e605822d2c684a82864365.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 386, + 162, + 529, + 181 + ], + "lines": [ + { + "bbox": [ + 386, + 162, + 529, + 181 + ], + "spans": [ + { + "bbox": [ + 386, + 162, + 529, + 181 + ], + "type": "text", + "content": "(c) Memory Requirements " + }, + { + "bbox": [ + 386, + 162, + 529, + 181 + ], + "type": "inline_equation", + "content": "\\downarrow" + }, + { + "bbox": [ + 386, + 162, + 529, + 181 + ], + "type": "text", + "content": " TranS4mer requires significantly less GPU memory." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "type": "table", + "bbox": [ + 72, + 220, + 212, + 277 + ], + "blocks": [ + { + "bbox": [ + 72, + 220, + 212, + 277 + ], + "lines": [ + { + "bbox": [ + 72, + 220, + 212, + 277 + ], + "spans": [ + { + "bbox": [ + 72, + 220, + 212, + 277 + ], + "type": "table", + "html": "
Intra-ShotInter-ShotAp (↑)
✓✗57.80
✗✓55.59
✓✓60.78
", + "image_path": "dee39f14b602b1821733080f5853bb53198a3b6e908393c017377da51c65c054.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "table_body" + } + ], + "index": 7 + }, + { + "type": "table", + "bbox": [ + 225, + 220, + 315, + 277 + ], + "blocks": [ + { + "bbox": [ + 99, + 279, + 178, + 288 + ], + "lines": [ + { + "bbox": [ + 99, + 279, + 178, + 288 + ], + "spans": [ + { + "bbox": [ + 99, + 279, + 178, + 288 + ], + "type": "text", + "content": "(a)TranS4mer modules." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 225, + 220, + 315, + 277 + ], + "lines": [ + { + "bbox": [ + 225, + 220, + 315, + 277 + ], + "spans": [ + { + "bbox": [ + 225, + 220, + 315, + 277 + ], + "type": "table", + "html": "
S4 layersAP (↑)
1-658.31
7-1258.82
1-1260.78
", + "image_path": "4d530835e22c8d9ef4bb6b268857d999c76c645ead46108fca9cea795342702c.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "table_body" + } + ], + "index": 9 + }, + { + "type": "table", + "bbox": [ + 328, + 220, + 421, + 277 + ], + "blocks": [ + { + "bbox": [ + 226, + 278, + 308, + 289 + ], + "lines": [ + { + "bbox": [ + 226, + 278, + 308, + 289 + ], + "spans": [ + { + "bbox": [ + 226, + 278, + 308, + 289 + ], + "type": "text", + "content": "(b) S4 in different layers." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 328, + 220, + 421, + 277 + ], + "lines": [ + { + "bbox": [ + 328, + 220, + 421, + 277 + ], + "spans": [ + { + "bbox": [ + 328, + 220, + 421, + 277 + ], + "type": "table", + "html": "
S4 layersAP (↑)
every 2nd59.82
every 4th58.01
all60.78
", + "image_path": "9d02b436da756ac3abff8d0d4ac9118a5da6425bf9018db795d38128030d38d8.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "table_body" + } + ], + "index": 11 + }, + { + "type": "table", + "bbox": [ + 435, + 220, + 525, + 277 + ], + "blocks": [ + { + "bbox": [ + 331, + 278, + 413, + 289 + ], + "lines": [ + { + "bbox": [ + 331, + 278, + 413, + 289 + ], + "spans": [ + { + "bbox": [ + 331, + 278, + 413, + 289 + ], + "type": "text", + "content": "(c) S4 in every " + }, + { + "bbox": [ + 331, + 278, + 413, + 289 + ], + "type": "inline_equation", + "content": "k^{th}" + }, + { + "bbox": [ + 331, + 278, + 413, + 289 + ], + "type": "text", + "content": " layer." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 435, + 220, + 525, + 277 + ], + "lines": [ + { + "bbox": [ + 435, + 220, + 525, + 277 + ], + "spans": [ + { + "bbox": [ + 435, + 220, + 525, + 277 + ], + "type": "table", + "html": "
S4 layersAP (↑)
S459.71
DS460.13
GS460.78
", + "image_path": "3518ffc92b2beb7ff4835c90396d871bbb8dacf58deaf330704f186aaa641f37.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "table_body" + } + ], + "index": 13 + }, + { + "bbox": [ + 436, + 278, + 517, + 288 + ], + "lines": [ + { + "bbox": [ + 436, + 278, + 517, + 288 + ], + "spans": [ + { + "bbox": [ + 436, + 278, + 517, + 288 + ], + "type": "text", + "content": "(d) Different S4 variants." + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 336, + 287, + 408 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 336, + 287, + 408 + ], + "spans": [ + { + "bbox": [ + 46, + 336, + 287, + 408 + ], + "type": "text", + "content": "tual shots produces a suboptimal performance of " + }, + { + "bbox": [ + 46, + 336, + 287, + 408 + ], + "type": "inline_equation", + "content": "53.29\\%" + }, + { + "bbox": [ + 46, + 336, + 287, + 408 + ], + "type": "text", + "content": " AP. Increasing the temporal extent to 25 contextual shots increases the performance to " + }, + { + "bbox": [ + 46, + 336, + 287, + 408 + ], + "type": "inline_equation", + "content": "60.78\\%" + }, + { + "bbox": [ + 46, + 336, + 287, + 408 + ], + "type": "text", + "content": " AP " + }, + { + "bbox": [ + 46, + 336, + 287, + 408 + ], + "type": "inline_equation", + "content": "(+7.49\\%" + }, + { + "bbox": [ + 46, + 336, + 287, + 408 + ], + "type": "text", + "content": " boost). Adding more contextual shots does not yield any significant improvements. These results verify the importance of long-range temporal modeling for movie scene detection." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 46, + 411, + 287, + 662 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 411, + 287, + 662 + ], + "spans": [ + { + "bbox": [ + 46, + 411, + 287, + 662 + ], + "type": "text", + "content": "Detailed Comparison with Transformer. We next present a detailed comparison of our model with the Transformer baseline [16]. In particular, we experiment with videos that contain a different number of input shots and plot the accuracy in AP as a function of the number of input shots (see Figure 4). Although the Transformer baseline performs better for shorter video inputs, our TranS4mer model achieves much better performance using longer videos. Specifically, TranS4mer yields " + }, + { + "bbox": [ + 46, + 411, + 287, + 662 + ], + "type": "inline_equation", + "content": "+2.07\\%" + }, + { + "bbox": [ + 46, + 411, + 287, + 662 + ], + "type": "text", + "content": " larger AP than the transformer model when using the longest video inputs. This suggests that TranS4mer is more effective at capturing long-range dependencies for the movie scene detection task. Moreover, we also illustrate the training speed (Samples/Second) and the memory requirement (GigaBytes) as a function of the number of input shots (see Figures 4b and 4c). We observe that as we increase the video length, the training speed of the Transformer baseline drops drastically, and the memory requirement grows rapidly. Overall, our proposed TranS4mer model is " + }, + { + "bbox": [ + 46, + 411, + 287, + 662 + ], + "type": "inline_equation", + "content": "2.7\\times" + }, + { + "bbox": [ + 46, + 411, + 287, + 662 + ], + "type": "text", + "content": " faster and requires " + }, + { + "bbox": [ + 46, + 411, + 287, + 662 + ], + "type": "inline_equation", + "content": "3.38\\times" + }, + { + "bbox": [ + 46, + 411, + 287, + 662 + ], + "type": "text", + "content": " less GPU memory than the Transformer baseline while using the longest video inputs." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "text", + "content": "Ablation with Intra-Shot and Inter-Shot Modules. In Table 4a, we analyze the significance of our (i) self-attention-based intra-shot module and (ii) state-space-based inter-shot module. We observe that removing the inter-shot" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 336, + 545, + 443 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 336, + 545, + 443 + ], + "spans": [ + { + "bbox": [ + 304, + 336, + 545, + 443 + ], + "type": "text", + "content": "module drops the performance by " + }, + { + "bbox": [ + 304, + 336, + 545, + 443 + ], + "type": "inline_equation", + "content": "2.98\\%" + }, + { + "bbox": [ + 304, + 336, + 545, + 443 + ], + "type": "text", + "content": " AP, whereas discarding the intra-shot module decreases the performance by " + }, + { + "bbox": [ + 304, + 336, + 545, + 443 + ], + "type": "inline_equation", + "content": "5.19\\%" + }, + { + "bbox": [ + 304, + 336, + 545, + 443 + ], + "type": "text", + "content": " AP. Therefore, based on these results, we can conclude that both the intra-shot and inter-shot modules are essential for good movie scene detection performance. We also note that they are complementary to each other, which aligns with our intuition of the intra-shot module being responsible for short-range representations while the intershot module is dedicated to long-range temporal reasoning." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 444, + 546, + 540 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 444, + 546, + 540 + ], + "spans": [ + { + "bbox": [ + 304, + 444, + 546, + 540 + ], + "type": "text", + "content": "Ablation with S4 Layers. We experiment with injecting our proposed S4A block into different encoder layers (Table 4b). We also evaluate a sparser TranS4mer variant with our S4A block injected into every " + }, + { + "bbox": [ + 304, + 444, + 546, + 540 + ], + "type": "inline_equation", + "content": "k^{th}" + }, + { + "bbox": [ + 304, + 444, + 546, + 540 + ], + "type": "text", + "content": " layer of the network (Table 4c). Lastly, we experiment with different S4 variants (i.e., Diagonal S4 (DS4) [20], Gated S4 (GS4) [33]) (Table 4d). Our results suggest that using S4A with Gated S4 in every layer of the network leads to the best accuracy." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 306, + 550, + 378, + 562 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 550, + 378, + 562 + ], + "spans": [ + { + "bbox": [ + 306, + 550, + 378, + 562 + ], + "type": "text", + "content": "7. Conclusion" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "content": "In this work, we propose an efficient movie scene segmentation method which combines the strengths of selfattention for short-range modeling and state-space models for long-range modeling. Our method, named TranS4mer, achieves state-of-the-art results in three different movie scene segmentation datasets (MovieNet, BBC, and OVSD). Moreover, our model is significantly faster and requires less GPU memory than previous approaches and the standard vision transformer models. In future, we will extend our model to other long-range video understanding and multimodal tasks such as movie summarization, movie trailer generation, and natural language grounding in long videos." + } + ] + } + ], + "index": 22 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "18756" + } + ] + } + ], + "index": 23 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 288, + 713 + ], + "type": "list", + "angle": 0, + "index": 15, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 124 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 124 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 124 + ], + "type": "text", + "content": "[1] Dzmitry Bahdanau, Kyunghyun Cho, et al. 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Following this trend, the size of multimodal learning models constantly increases, leading to an urgent need to reduce the massive computational cost of finetuning these models for downstream tasks. In this paper, we propose an efficient and flexible multimodal fusion method, namely PMF, tailored for fusing unimodally pretrained transformers. Specifically, we first present a modular multimodal fusion framework that exhibits high flexibility and facilitates mutual interactions among different modalities. In addition, we disentangle vanilla prompts into three types in order to learn different optimizing objectives for multimodal learning. It is also worth noting that we propose to add prompt vectors only on the deep layers of the unimodal transformers, thus significantly reducing the training memory usage. Experiment results show that our proposed method achieves comparable performance to several other multimodal finetuning methods with less than $3\\%$ trainable parameters and up to $66\\%$ saving of training memory usage.", + "bbox": [ + 75, + 349, + 473, + 667 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 693, + 209, + 709 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Recent years have witnessed the great success of large-scale pretrained language models [8,31,32] and visual models [6,10,23,39], leading to a surge of pretrained multimodal models [13, 14, 43, 47, 48] trying to align different modalities. Many prior methods utilize finetuning to update the entire set of model parameters for every target cross-modal task. Although finetuning can achieve good performance, it requires a large number of computational costs since the gradients and optimizer states for all parameters of multimodal models have to store. Therefore, it encourages researchers to propose more parameter-efficient methods than finetuning for multimodal learning.", + "bbox": [ + 75, + 719, + 470, + 901 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/b9b1b14be11ecd3b076674817ba71900a4293f010ad306256177e5ba35381571.jpg", + "image_caption": [ + "Figure 1. Comparison over three multimodal classification tasks. We compare our proposed PMF and PMF-Large with multiple finetuning (yellow) and prompt-based (purple) methods. The y-axis is the average score of three tasks, and the x-axis is the maximum GPU memory usage during training." + ], + "image_footnote": [], + "bbox": [ + 506, + 321, + 888, + 545 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "More recently, prompting tuning [17, 19, 21, 22, 29] is proposed to address this problem by freezing all parameters of a pretrained model while tuning only the continuous prompts. Specifically, it adds trainable continuous prompts to the original token sequences of input data. During training, only the continuous prompts are updated. For multimodal prompt-based learning, a most recent method [20] proposes to disentangle the functionality of the pretrained model which exhibits high flexibility. Although this method significantly reduces the tuned parameters (e.g., less than $0.1\\%$ of the pretrained model), there still exists a large performance gap between it and the finetuning-based methods. In addition, this method adopts a sequential modular structure that the pretrained image transformer model is followed by a language transformer model, which causes two main problems in cross-modal learning: a one-way path learn", + "bbox": [ + 496, + 657, + 893, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 810, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "2604", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "ing and a significant increase in the number of model layers. Specifically, a one-way path learning in the multimodal model usually forces one modality to align with others, but not vice versa. In this way, cross-modal learning based on multiple different modalities is not fully explored due to the missing mutual alignments. Since the prompts are added to the token sequences of input data and are updated in the training, they require extensive gradient calculations in the backward propagation which cost numerous memory usages. As a result, this kind of method does not reduce the memory usage during training by much (up to $20\\%$ ) though it reduces the number of parameters to update. In other words, this parameter-efficient method still requires massive computational resources which prevents it from being applied to many real-world applications.", + "bbox": [ + 75, + 90, + 472, + 318 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To address these issues, we propose a Prompt-based Multimodal Fusion method with a high memory efficiency, namely PMF. Firstly, we present a new form of modular multimodal fusion framework which demonstrates high flexibility and facilitates a two-way interaction among different modalities. Specifically, we adopt a two-stream structure where the pretrained language model and image model construct the multimodal model in a parallel way. Therefore, tokens of different modalities can learn mutual interactions through a cross-attention-like operation. Such a parallel modular structure brings two benefits. First, unimodal pretraining can be directly utilized for multimodal learning through a parallel combination, eliminating the need for paired multimodal datasets that can be expensive to construct. Also, the type of image or language model can be changed easily (e.g., replacing BERT with T5 for text generation tasks). Furthermore, incorporating extra modalities is made possible based on the parallel modular structure.", + "bbox": [ + 75, + 320, + 472, + 593 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Moreover, we propose to leverage three types of interactive prompts (i.e., query prompts, query context prompts, and fusion context prompts) in order to dynamically learn different objectives for multimodal learning. Intuitively, the query context prompt and query prompt can be seen as a pair of 'questions' and 'answers' with an aim of extracting necessary information for exchange between two modalities. After being translated by a non-linear mapping 'translator', the 'answer' is then delivered to the other modality for better cross-modal understanding. Finally, the fusion context prompts then provide the context to the delivered answer to facilitate the fusion.", + "bbox": [ + 75, + 595, + 472, + 777 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Last but most importantly, PMF is a memory-efficient method that significantly reduces the memory requirements for the large pretrained model. Considering that calculating gradients for prompts for back-propagation is memory-consuming, we propose to add prompts only on the deep layers of the utilized unimodal transformers. Therefore, instead of passing through the entire multimodal model, the backward propagation only needs to pass through the deep", + "bbox": [ + 75, + 779, + 472, + 902 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "few transformer layers to reach all trainable parameters, greatly reducing the training memory usage. We conduct extensive experiments to demonstrate the superior of it in our experiments. As a result, PMF enables large pretrained models to be trained on the GPU with a low memory requirement.", + "bbox": [ + 496, + 90, + 893, + 181 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "We conduct extensive experiments on three vision-language datasets: UPMC-Food101 [38], MM-IMDB [2], and SNLI-VE [41]. Through comparisons with multiple finetuning and prompt tuning methods (see in Fig. 1), we find that: (1) PMF is the most memory-efficient method for cross-modal learning so far, which reduces the training memory usage by up to $66\\%$ compared with finetuning baselines, and by $55\\%$ compared with prompt-based methods. (2) PMF can perform comparably compared to prior fine-tuning methods with much fewer trainable parameters (less than $2.5\\%$ ) and memory usage.", + "bbox": [ + 496, + 181, + 893, + 348 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Concretely, our contributions are as follows: (1) we present a new form of modular multimodal fusion framework which enables two-way interactions between different modalities and high flexibility of the entire model; (2) we disentangle vanilla prompts into three types of prompts, in order to dynamically learn different objectives for multimodal learning; (3) our proposed method is quite memory-efficient yet is able to achieve comparable performance with existing finetuning methods for multimodal fusion.", + "bbox": [ + 496, + 348, + 893, + 484 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related works", + "text_level": 1, + "bbox": [ + 498, + 497, + 645, + 513 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Multimodal Fusion. Multimodal fusion methods aim to simultaneously process the input of different modalities, such as audio-video [27], vision-language [2, 15], and inputs from different types of sensors [42], etc. In this paper, we specifically focus on the fusion of vision-language inputs, though our proposed strategy is compatible with other modality pairs as long as there are unimodally pretrained transformers for these modalities.", + "bbox": [ + 496, + 523, + 893, + 643 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Our work is in line with deep learning-based multimodal fusion strategies [16, 18, 26, 28, 33, 34, 44]. In this line of work, [15] proposed a framework whose vision encoder solely serves as a mapping tool to encode the raw images to the token space of the text encoder. Such an architecture is widely used in the later multimodal fusion research [20, 26, 34]. Differently, [27] used a dual-encoder architecture with bottleneck fusion tokens to exchange information between two encoders for video-audio fusion. Our work has a similar architecture as in [27]. But our proposed method completely freezes the unimodal encoders and uses an interactive prompting technique for more efficient fusion.", + "bbox": [ + 496, + 643, + 895, + 824 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Another important line of multimodal fusion work is through pretraining with the large-scale datasets, mostly achieved by self-supervised learning algorithms [1, 11, 24, 30, 36, 37, 45]. This line of works can be roughly divided into two kinds by their architectures. The first kind has", + "bbox": [ + 496, + 825, + 893, + 902 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "2605", + "bbox": [ + 482, + 944, + 514, + 957 + ], + "page_idx": 1 + }, + { + "type": "table", + "img_path": "images/2dd3c4c8e5f53a75c49360a84f9ef1f68f085bfa7b752b540b23bbc2b1b8de39.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
Task TypePretraining TypeMethod
UnimodalUnimodalP-Tuning [22], VPT [12]
UnimodalMultimodalCoOp [47], MAPLE [14]
MultimodalMultimodalPI-VL [13], PTGM [43]
MultimodalUnimodalBlindPrompt [20], PMF
", + "bbox": [ + 80, + 88, + 467, + 181 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Table 1. Prompt-based methods categorized by model pretraining types and downstream task types. Our proposed PMF falls into the last category which utilize unimodally pretrained transformers for multimodal tasks.", + "bbox": [ + 75, + 190, + 470, + 247 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "a dual-encoder structure where image and text are treated separately, such as CLIP [30] and ALIGN [11]. The other kind simultaneously processes the vision and language inputs with cross-attention or self-attention over a longer sequence from two modalities. Our proposed method differs from these self-supervised architectures in that the individual components used in our model are unimodally pretrained with much less data. This difference directly results in a huge performance gap because of the lack of multimodal information in the pretraining stage. However, using unimodally pretrained models enables a much more flexible architecture. It has great potential in multimodal tasks where modality-paired large-scale pretraining data is not available, or when more advanced unimodal encoders are proposed in the future.", + "bbox": [ + 73, + 277, + 468, + 503 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Prompt Tuning. As shown in Tab. 1, prompt-based methods can be roughly divided into four major categories in terms of the modalities of the pretrained model and the downstream tasks. Prompting techniques originally apply on unimodally pretrained transformers for unimodal natural language processing (NLP) tasks [17, 19, 21, 22, 29]. Pretrained GPT-3 can be simply leveraged with handcrafted prompts, which are some manually chosen words preceding the input text [4]. Then [22] and [17] proposed to change the handcrafted prompt to trainable continuous prompts and only update the prompt vectors during the training. Later on, [19] and [29] proposed to use prompt tuning in every hidden layer in the pretrained transformer instead of the input embeddings only. VPT [12] first applied prompt tuning to the vision transformer.", + "bbox": [ + 73, + 505, + 468, + 731 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "For methods that prompt multimodally pretrained models for unimodal tasks, many recent works apply prompt tuning to pretrained vision-language models (i.e. CLIP [30]) for unimodal vision tasks [3, 14, 25, 46, 47]. Another type of prompt-based method apply to the multimodal pretrained model for multimodal tasks [13, 43]. [13] adds prompts to an encoder-decoder one-for-all multimodal transformer, achieving comparable performance with finetuning with improved robustness against adversarial attacks. The method used in [13] is simple but effective, showing that prompting methods works well with powerful and com", + "bbox": [ + 75, + 734, + 470, + 902 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "plex multimodally pretraining models.", + "bbox": [ + 498, + 90, + 754, + 106 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Our proposed fusion strategy is different from the above methods and falls into the last category where prompts are used to fuse pretrained unimodal models for multimodal tasks. Sharing the same architecture design with [15, 34], [20] uses prompt to align the feature extracted from raw images to the token space of pretrained language model. They achieved comparable performance to several multimodal fusion methods in low-resource settings but underperform fine-tuning baselines by a large margin with full data. Compared with them, our proposed PMF not only is more memory-efficient but can also perform comparably with fine-tuning baselines with full data.", + "bbox": [ + 496, + 107, + 890, + 287 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Prompt-based Multimodal Fusion", + "text_level": 1, + "bbox": [ + 498, + 304, + 808, + 321 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In this section, we describe our proposed Prompt-based Multimodal Fusion strategy (PMF). We begin by summarising unimodal transformers developed for vision and language tasks in Sec. 3.1. Then we describe the base feature extraction process in Sec. 3.2. Lastly, we give a detailed description of how PMF integrates two unimodal transformer layers into a multimodal one via interactive prompting in Sec. 3.3.", + "bbox": [ + 496, + 330, + 890, + 452 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Unimodal Transformers", + "text_level": 1, + "bbox": [ + 498, + 464, + 723, + 479 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Vision Transformer (ViT) [9] adapts the Transformer [35] architecture with minimum modifications. The RGB image input $\\mathbf{x}_{img} \\in \\mathbb{R}^{h,w,c}$ is first cut into $N_{img}$ nonoverlapping patches and then linearly projected into a sequence of embeddings $\\mathbf{z}$ with each $z_i \\in \\mathbb{R}^d$ . Differently, the language Transformer first tokenizes raw text to $N_{txt}$ one-hot word embeddings and then converted these discrete vectors into a sequence of $N_{txt}$ continuous embeddings. The resulting continuous embedding for both Language Transformer and Vision Transformer share the same structure as follows:", + "bbox": [ + 496, + 488, + 890, + 652 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {z} = \\left[ \\mathrm {C L S}, z _ {1}, z _ {2}, \\dots , z _ {N} \\right] \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 609, + 656, + 890, + 672 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where CLS is a special token prepended to the sequence so that its representation at the final layer can be used as the representation of the whole sequence for classification. Please note that the two unimodal transformers have different CLS tokens. The continuous embedding $\\mathbf{z}$ is then fed into a transformer encoder which consists of $L$ transformer layers. For each transformer layer, the input passes through modules including multi-head self-attention, layer normalization, multilayer perceptron, and finally added to the original input with a residual connection.", + "bbox": [ + 496, + 681, + 890, + 834 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. Unimodal Base feature Extraction", + "text_level": 1, + "bbox": [ + 498, + 845, + 799, + 861 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "As shown in Fig. 2, the image and text inputs are first processed and fed into the unimodal transformer layers to", + "bbox": [ + 498, + 869, + 890, + 901 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "2606", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/a7d913cdf02b214f352ce6e81dd4e3b0f695c412a27d26cef071273ec05f4d01.jpg", + "image_caption": [ + "Figure 2. Prompt-based multimodal fusion strategy (PMF) applied to vision-language inputs. In the forward propagation, image and text inputs are first embedded into continuous token sequences and fed to the unimodal transformer layers for base feature extraction. The base features from both modalities then pass through multiple prompt-based multimodal fusion layers to get the feature of two CLS tokens for final classification. In the backward propagation, only multimodal fusion layers take part in the calculation of gradients, greatly saving memory usage during training. All pretrained parameters in both transformers are frozen during the training." + ], + "image_footnote": [], + "bbox": [ + 81, + 92, + 880, + 296 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "extract base features, respectively. At this stage, each encoder works exactly the same as they did in unimodal tasks. Here we denote the starting fusion layer as $L_{f}$ . And the base feature extraction of each encoder can be denoted as:", + "bbox": [ + 75, + 407, + 468, + 467 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {z} ^ {l + 1} = \\operatorname {T r a n s L a y e r} ^ {l} \\left(\\mathbf {z} ^ {l}; \\theta\\right) \\quad \\text {i f} l < L _ {f} \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 140, + 477, + 468, + 496 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\theta$ stands for the pretrained parameters. A smaller $L_{f}$ leads to an earlier fusion and a larger $L_{f}$ leads to a later fusion. A detailed discussion of the impact brought by different $L_{f}$ can be found in Sec. 4.5.", + "bbox": [ + 75, + 505, + 468, + 568 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.3. Multimodal Fusion Layer", + "text_level": 1, + "bbox": [ + 76, + 575, + 312, + 590 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The extracted unimodal base features are then passed through multiple multimodal fusion layers, each consisting of a 'querying stage' and a 'fusion stage', as shown in Fig. 3. The querying stage focus on the extraction of what is necessary to pass, and the fusion stage focus on fusing the extracted information delivered from the other modality.", + "bbox": [ + 75, + 598, + 468, + 688 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "This two-stage setting makes the vanilla prompt training entangled with different learning objectives. Therefore, we propose to decouple the vanilla prompts into three kinds: 'query prompt' (QP, denoted $\\mathbf{z}_{qp}$ ), 'query context prompt' (QCP, denoted $\\mathbf{z}_{qcp}$ ), and 'fusion context prompt' (FCP, denoted $\\mathbf{z}_{fcp}$ ) to dynamically learn different objectives for multimodal learning. According to the modality where prompts are used, each kind of prompt can be further specified as $\\mathbf{z}_*$ and $\\mathbf{z}_*$ to distinguish from each other (e.g. $\\mathbf{z}_{fcp}$ and $\\mathbf{z}_{fcp}^{\\prime}$ ).", + "bbox": [ + 75, + 689, + 468, + 840 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "As shown in Fig. 3, QP and QCP are used in the querying stage and the FCP is used in the fusion stage. As suggested by their names, QP is to query information from the unimodal input sequence, QCP is to help this process by pro", + "bbox": [ + 75, + 840, + 468, + 901 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "viding extra context to the query. QP and QCP like a pair of 'questions' and 'answers', translated by the non-linear mapping. As for FCP, it is responsible for providing the context to the fusion in the fusion stage. We now introduce how these three kinds of prompts interact with each other in the two stages of each multimodal fusion layer.", + "bbox": [ + 496, + 407, + 890, + 497 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Querying Stage. We first concatenate corresponding QP and QCP to the input sequence $\\mathbf{z}$ . The resulting input sequence after the concatenation is:", + "bbox": [ + 496, + 497, + 890, + 542 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n[ \\mathbf {z} ^ {l} | | \\mathbf {z} _ {q c p} ^ {l} | | \\mathbf {z} _ {q p} ^ {l} ] \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 648, + 551, + 890, + 571 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $| \\cdot |$ denotes the concatenation operation. Then we feed the concatenated sequence to the unimodal transformer layer, which can be denoted as:", + "bbox": [ + 496, + 580, + 890, + 626 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n[ \\hat {\\mathbf {z}} ^ {l} | | \\hat {\\mathbf {z}} _ {q c p} ^ {l} | | \\hat {\\mathbf {z}} _ {q p} ^ {l} ] = \\mathrm {T r a n s L a y e r} ^ {l} ([ \\mathbf {z} ^ {l} | | \\mathbf {z} _ {q c p} ^ {l} | | \\mathbf {z} _ {q p} ^ {l} ]; \\theta) \\quad (4)\n$$\n", + "text_format": "latex", + "bbox": [ + 524, + 633, + 890, + 656 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "After the forward propagation, the output of QP $\\hat{\\mathbf{z}}_{qp}^{l}$ is extracted as the queried information to be used in the following fusion operations. It should be noted that though $\\hat{\\mathbf{z}}_{qcp}^{l}$ will not be used in the following fusion operations, it has played an important role by providing the context of query in the querying stage.", + "bbox": [ + 496, + 666, + 890, + 757 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The queried fusion intermediate $\\hat{\\mathbf{z}}_{qp}^{l}$ is then mapped to the representation space of the other modality through a non-linear mapping function:", + "bbox": [ + 496, + 757, + 890, + 801 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {y} _ {q p} ^ {l} = f ^ {l} \\left(\\hat {\\mathbf {z}} _ {q p} ^ {l}\\right) \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 643, + 811, + 890, + 832 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $f$ is a non-linear mapping function. Specifically, a mapping function consists of two linear layers with a bottleneck structure to reduce dimension and only the first linear layer has a ReLu function. Each fusion layer $l$ has two", + "bbox": [ + 496, + 839, + 890, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "2607", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/0c0ac5fefaa70d253a2f34dbef34929ab93671ec95dfc5775f2fc7f60cb07a17.jpg", + "image_caption": [ + "Figure 3. Prompt-based multimodal fusion layer. We propose to use three kinds of interactive prompts to achieve the fusion/exchange of information from two modalities. We use 'query prompt' $(\\mathrm{z}_{qp},\\mathrm{z}_{qp}^{\\prime})$ and 'query context prompt' $(\\mathrm{z}_{qcp},\\mathrm{z}_{qcp}^{\\prime})$ in the querying stage to extract what is necessary, after a non-linear mapping, the extracted information is then fused to the other modality with the help of 'fusion context prompt' $(\\mathrm{z}_{fcp},\\mathrm{z}_{fcp}^{\\prime})$ in the fusion stage. Yellow and green elements stand for language and vision modalities, respectively. Red boxes indicate trainable modules." + ], + "image_footnote": [], + "bbox": [ + 78, + 88, + 893, + 220 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "mapping functions $f^l$ and $f'^l$ , building a two-way interaction among different modalities. Note that the non-linear mapping functions contain more than $95\\%$ of the trainable parameters in PMF.", + "bbox": [ + 75, + 329, + 468, + 390 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Fusion Stage. We first concatenate the mapped fusion intermediates $\\mathbf{y}_{qp}^{l}$ to the original input sequence $\\mathbf{z}^{\\prime l}$ and FCP $\\mathbf{z}_{fcp}^{\\prime l}$ of the other modality. Then we feed the concatenated sequence to the unimodal transformer layer of the other modality to complete a one-way fusion. These two processes can be together denoted as:", + "bbox": [ + 76, + 391, + 468, + 483 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n[ \\mathbf {z} ^ {\\prime l + 1} | | \\hat {\\mathbf {z}} _ {f c p} ^ {\\prime l} | | \\hat {\\mathbf {y}} _ {q p} ^ {l} ] = \\operatorname {T r a n s L a y e r} ^ {l} ([ \\mathbf {z} ^ {\\prime l} | | \\mathbf {z} _ {f c p} ^ {\\prime l} | | \\mathbf {y} _ {q p} ^ {l} ]; \\theta^ {\\prime}) \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 94, + 494, + 468, + 527 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $[\\ast ]'$ means $[\\ast ]$ from the other modality.", + "bbox": [ + 76, + 527, + 380, + 542 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Finally, the output of two unimodal transformer layers $\\mathbf{z}^{l + 1}$ and $\\mathbf{z}^{\\prime l + 1}$ are together as the output of the multimodal fusion layer and fed to the higher layers. The entire multimodal fusion process can be concluded as:", + "bbox": [ + 76, + 542, + 468, + 604 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n[ \\mathbf {z} ^ {l + 1} | | \\mathbf {z} ^ {\\prime l + 1} ] = \\text {F u s i o n L a y e r} ^ {l} ([ \\mathbf {z} ^ {l} | | \\mathbf {z} ^ {\\prime l} ]; \\theta , \\theta^ {\\prime}) \\quad \\text {i f} L _ {f} \\leq l \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 86, + 614, + 468, + 646 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "After the multimodal fusion is complete, we take the output representation of CLS token $z_{CLS}^{L}$ and $z_{CLS}^{\\prime L}$ to two different linear classifiers and average the pre-softmax logits for classification. Mathematically, such a classifier setting is equivalent to feeding the classifier with the concatenated features when a linear classifier is used, except for a different scale of gradient caused by the averaging operation.", + "bbox": [ + 75, + 648, + 468, + 753 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 76, + 768, + 209, + 786 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In this section, we analyze the performance of our proposed PMF on three multimodal datasets and aim to answer the following questions: (1) How efficient is the PMF and does PMF perform well (Sec. 4.4)? (2) What factors affect the effectiveness of PMF (Sec. 4.5)? In addition, we explore the PMF equipped with larger transformers and its impact brought to the performance and memory efficiency in", + "bbox": [ + 75, + 794, + 468, + 900 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Sec. 4.6. Lastly, we introduce a Neural Architecture Search (NAS) method to automatically search for the preferable fusion structure for PMF in Sec. 4.7.", + "bbox": [ + 498, + 329, + 890, + 375 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.1. Datasets and Metrics", + "text_level": 1, + "bbox": [ + 500, + 387, + 697, + 402 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "UPMC Food-101 [38] is a multimodal classification dataset, which contains food images with textual recipe descriptions for 101 kinds of food. UPMC Food-101 contains a total of 90,840 image-text pairs with a size range between 790 and 956 pairs for different classes. As the dataset only has training and testing sets, we follow [15] and create a validation split of 5000 samples from the training set.", + "bbox": [ + 498, + 410, + 890, + 516 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "MM-IMDB [2] is a multimodal multi-label classification dataset, which contains movie plot outlines and movie posters. The task is to predict the genre of movies. This dataset contains 25,956 image-text pairs for 23 classes with a long-tail distribution.", + "bbox": [ + 498, + 517, + 890, + 590 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "SNLI-VE [41] is a multimodal classification dataset for the visual entailment tasks, which is to reason about the relationship between an image premise and a text hypothesis into entailment, contradiction, or neutrality. SNLI-VE contains a total of 565,286 image-text pairs. Please note that we only use image premise and text hypothesis in the input, which is different from the settings in some other papers where text premises are also used in the inputs [43].", + "bbox": [ + 498, + 592, + 890, + 713 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We report accuracy for UPMC Food-101 and SNLI-VE, and Macro/Micro-F1 scores for MM-IMDB as metrics.", + "bbox": [ + 500, + 714, + 890, + 743 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.2. Existing Methods and Baselines", + "text_level": 1, + "bbox": [ + 500, + 755, + 779, + 771 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We report the performance of several baselines and existing methods. First, we report the performance of finetuning unimodal models (i.e. BERT [8], ViT [9]) to verify the effectiveness of multimodal fusion. Specifically, we take the output representation of CLS token of the last layer in ViT and BERT, and feed it into a linear classifier. We also report the performance of VPT [12] and a prompt-based BERT (denoted P-BERT) for a better comparison. For VPT", + "bbox": [ + 498, + 779, + 890, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "2608", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/a3d268425afd033e75912d7dfbfda448c63c9bc90748a913b1d14d93561abdf9.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodUpdated Param. (Million)Memory Usage (GB) Train/InferenceSNLI-VEFood-101MM-IMDBAvg.
Linear-3.76 / 3.2350.0578.9649.76 / 56.8360.77
ViT86.59.36 / 1.9933.3374.6938.39 / 49.8850.72
BERT109.030.82 / 2.7969.8287.4458.91 / 64.3172.96
LateConcat196.038.54 / 3.3670.0193.2959.56 / 64.9275.18
MMBT*196.537.87 / 3.4874.6994.1060.80 / 66.1077.41
MBT*196.038.00 / 4.0674.0293.5659.60 / 64.8176.60
VPT-6.12 / 2.0133.3372.5535.22 / 44.4948.58
P-BERT-28.13 / 2.9963.2881.0748.67 / 54.5865.33
PromptFuse-29.57 / 3.5564.5382.2148.59 / 54.4966.09
BlindPrompt-29.57 / 3.6565.5484.5650.18 / 56.4667.81
P-LateConcat0.330.82 / 3.4363.0589.0353.91 / 59.9369.67
P-MMBT0.930.90 / 3.4867.5886.5852.95 / 59.3070.10
PMF (M=4, Lf=10)2.512.84 / 4.0871.9291.5158.77 / 64.5175.02
PMF-large (M=4, Lf=22)4.518.44 / 6.4272.1091.6861.66 / 66.7275.99
", + "bbox": [ + 76, + 88, + 893, + 354 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 2. Multimodal classification performance. PMF achieve comparable performance to the finetuning baselines with less than $3\\%$ of trainable parameters and up to $66\\%$ of training memory usage. MM-IMDB is F1-Macro / F1-Micro, others are accuracy. We report the maximum memory usage in training and evaluating UPMC Food-101 for each method. We report mean performance over 3 runs with different random seeds. \\* means trainable parameter less than $0.1\\mathrm{M}$ . PMF-Large uses bert-large and vit-large models (24 hidden layers) while others use bert-base and vit-base models (12 hidden layers). $M$ is the prompt length and $L_{f}$ is the starting fusion layer.", + "bbox": [ + 75, + 364, + 893, + 436 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "and P-BERT, the input sequence to each transformer layer is concatenated with a prompt vector, whose length is set to 10. And the concatenated prompt vectors and the final linear classifier are the only updated modules in training.", + "bbox": [ + 75, + 460, + 470, + 521 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "In addition, we compare against a strong baseline method which concatenates the output features of CLS tokens of ViT and BERT, and feed the concatenated feature to a linear classifier, denoted as LateConcat. In this case, the input to the classifier is $(768 + 768)$ -dimensional. Besides, we also introduce Linear, which shares the same architecture with LateConcat with the only difference in the updated modules. Linear only updates the linear classifier while LateConcat updates all parameters during training.", + "bbox": [ + 75, + 522, + 468, + 657 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We reimplement MMBT (denoted $\\mathbf{MMBT}^*$ ) [15] and MBT (denoted $\\mathbf{MBT}^*$ ) [27] with a vit-base model as the vision encoder and a bert-base model as the text encoder for fair and controlled comparison. We set the fusion layer $L_{f} = 8$ and use 4 fusion tokens in MBT as recommended in the original paper.", + "bbox": [ + 75, + 657, + 468, + 750 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We also propose a prompt-based MMBT and a prompt-based LateConcat, denoted as P-MMBT and P-LateConcat, respectively. In P-MMBT and P-LateConcat, we apply deep prompt tuning on both vision and language encoders, which are pretrained backbones with frozen parameters during training. We set the prompt length in each layer of two encoders to 10, totalling 240 prompt vectors. Similar to VPT and P-BERT, P-LateConcat only updates the final linear classifier and prompt vectors during training. Compared with P-LateConcat, P-MMBT have an extra", + "bbox": [ + 75, + 750, + 470, + 902 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "linear projection layer and a smaller linear classifier to train.", + "bbox": [ + 498, + 460, + 890, + 476 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Lastly, we report the performance of PromptFuse and BlindPrompt [20], both proposed in the only existing paper which leverages unimodally pretrained models for multimodal fusion through prompting. We set the prompt length to 20 as recommended in the original paper.", + "bbox": [ + 498, + 477, + 890, + 551 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.3. Implementation Details", + "text_level": 1, + "bbox": [ + 500, + 559, + 718, + 575 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Pretrained Backbone and Initialization. Unless otherwise noted, we use an ImageNet-21k [7] pretrained vit-base model for the vision encoder and a bert-base-uncased model for the language encoder in all experiments. All pretrained checkpoints are from huggingface [40]. All prompt vectors are initialized through a Gaussian distribution (mean=0, std=0.02).", + "bbox": [ + 498, + 582, + 890, + 686 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Network Training. We use SGD optimizer in all experiments with momentum set to 0.9 and weight decay set to $1e^{-4}$ . The batch size is set to 64 for SNLI-VE, and 32 for UPMC Food-101 and MM-IMDB. Cross entropy loss is applied in all experiments and the class labels are weighted by their inverse frequency for UPMC Food-101 and MM-IMDB. More details are in the supplementary material.", + "bbox": [ + 498, + 688, + 890, + 794 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.4. Main Results", + "text_level": 1, + "bbox": [ + 500, + 801, + 638, + 816 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "PMF is most memory-efficient. As shown in Tab. 2, PMF is the most memory-efficient multimodal fusion model of all existing prompt-based methods and baselines. PMF can save up to $66\\%$ of training memory usage compared with finetuning baselines. Even compared with the existing most", + "bbox": [ + 498, + 824, + 893, + 902 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "2609", + "bbox": [ + 482, + 944, + 516, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/6b652dcd559273eacc8ff281e0aa8a79f4372d461b72df7c6388544daf4adf89.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
QPMappingfQCPFCPMM-IMDB
48.80/56.38
✓45.38/53.34
✓43.56/51.43
✓✓54.92/62.25
✓✓✓57.98/63.69
✓✓✓58.30/64.07
✓✓✓58.34/64.15
✓✓✓✓58.63/64.23
", + "bbox": [ + 106, + 88, + 442, + 241 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 3. PMF Component Ablation. There are four types of trainable modules in our proposed PMF. We set the fusion layer $L_{f} = 10$ and add different components one at a time to see their individual impact. All prompts with $\\checkmark$ have a length of 4, and prompts with $\\checkmark \\checkmark$ have a length of 8.", + "bbox": [ + 75, + 251, + 470, + 324 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/04ca90815f5c5c93ede716f7afd0a25e5fe0ca577a3b848ad1df46dbab44461f.jpg", + "image_caption": [ + "Figure 4. Model Performance and Training Memory Usage under different fusion layers $L_{f}$ . We set the prompt length $M = 4$ for every prompt vector with different fusion layer $L_{f} = 0,2,4,6,8,10,12$ ." + ], + "image_footnote": [], + "bbox": [ + 81, + 345, + 464, + 498 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "memory-efficient prompt-based multimodal method, PMF still saves an extra of more than $50\\%$ of training memory.", + "bbox": [ + 75, + 603, + 468, + 635 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "PMF outperforms all existing prompt-based methods. With the same pretrained unimodal transformers, prompt-based methods underperform the full finetuning methods by a large margin. Some prompt-based methods even underperform unimodal finetuning baselines. Our proposed PMF achieves the best performance among all prompt-based methods. Especially, PMF outperforms all unimodal baselines in all experiments, showing that the two modalities are successfully fused.", + "bbox": [ + 75, + 638, + 468, + 776 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "PMF is competitive with finetuning baselines. Tab. 2 shows that PMF achieves comparable performance with full finetuning baselines with less than $3\\%$ trainable parameters while saving $66\\%$ of memory cost, significantly narrowing the gap between finetuning and prompt-based methods. Furthermore, PMF even outperforms the finetuning LateConcat when equipped with larger transformers (i.e. bert-large and vit-large).", + "bbox": [ + 75, + 779, + 470, + 902 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/dbcf0106de26c140db5f3f399107438285fca6c2fbb26fc40a0dd8c648b380d7.jpg", + "image_caption": [ + "Figure 5. Model Performance and Training Memory Usage under different prompt length $M$ . We fix the fusion layer $L_{f} = 10$ and study 1, 4, 8, 16, and 32 tokens for each prompt vector." + ], + "image_footnote": [], + "bbox": [ + 501, + 90, + 890, + 237 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.5. Ablation Study", + "text_level": 1, + "bbox": [ + 500, + 316, + 651, + 333 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "In this section, we investigate the impact of different factors in our proposed fusion strategy. All experiments in this section are conducted on the MM-IMDB dataset.", + "bbox": [ + 496, + 340, + 890, + 385 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Components Ablation. We verify the effectiveness of three kinds of prompts and the non-linear mapping function in this section. The results are shown in Tab. 3. The first row without any components in PMF is equivalent to the Linear model introduced in Sec. 4.2. The comparison between the first three rows shows that merely prompting the top layers of the two transformers not only cannot achieve multimodal fusion. Oppositely, it will disturb the feature space of two transformers, which finally hurts the performance. Though the mapping functions give the biggest boost to the performance, it should be noted that the mapping functions $f$ cannot work without QP querying the fusion intermediates.", + "bbox": [ + 496, + 386, + 892, + 568 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "In addition, the comparison between the last four rows shows that decoupling the prompts into three individual modules with different learning objectives brings a performance gain. More specifically, the comparison between the fifth and sixth row in Tab. 3 shows that an extended QP cannot replace QCP. Since only the output of QP tokens are fused to the other modality while that of QCP discarded, replacing QCP with a longer QP not only increases the computation as the sequences in the fusion stage are longer but also results in a damaged performance. As a result, every module introduced in PMF contributes to the quality of multimodal fusion. The missing of any of the four modules will bring a performance drop at different scales.", + "bbox": [ + 496, + 568, + 893, + 763 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Fusion Layer. We now investigate impacts brought by different fusion layers $L_{f}$ to the fusion performance and memory efficiency. The results are summarized in Fig. 4. As can be seen in the figure, the training memory usage keeps decreasing as the fusion starts later. However, the performance of the fusion model is relatively consistent with $L_{f} \\leq 10$ . Therefore, adding prompts only on the deep layers $(10 < l < L)$ is empirically better for the trade-off between performance and memory efficiency.", + "bbox": [ + 496, + 763, + 893, + 901 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "2610", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/2be1528f5f0ba4cec100172f4e1342ad15ef2e62b09a489c006207b055c0f061.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
Text EncoderImage EncoderMemory Usage Train/InferenceMM-IMDB
bert-basevit-base12.84 / 4.0858.77 / 64.51
bert-basevit-large14.16 / 4.8959.70 / 65.20
bert-largevit-base17.17 / 5.5360.08 / 65.41
bert-largevit-large18.44 / 6.4261.66 / 66.72
", + "bbox": [ + 80, + 88, + 467, + 195 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/f05c7a881e3e36a64cb2ae0350b543550f8eb958b224013ef2c0ebeac63ba04a.jpg", + "table_caption": [ + "Table 4. Comparison of PMF applying to different unimodal transformers. We set the fusion layer $L_{f} = L - 2$ and prompt length $M = 4$ in all experiments. MM-IMDB is reported with F1-Macro / F1-Micro." + ], + "table_footnote": [], + "table_body": "
Training MemorySNLI-VEFood-101MM-IMDBAvg.
33.36 GB72.2792.159.67 / 65.5775.66
", + "bbox": [ + 80, + 285, + 465, + 343 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 5. Performance of PMF applied with NAS. MM-IMDB is F1-Macro / F1-Micro, others are accuracy. We only report the training memory usage.", + "bbox": [ + 76, + 353, + 467, + 396 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Prompt Length. The ablation study on prompt length is carried out with three kinds of prompts set to have the same length (i.e. $M_{qp} = M_{qcp} = M_{fcp}$ ). Fig. 5 summarizes the results. The performance increases as the prompt length grows longer when $M \\leq 16$ , and drops when the prompts are too long ( $M = 32$ ). It should be stressed that the training memory usage only increases around 1 GB as the prompt length grows from 1 to 16, which means the fusion layer $L_f$ is the major factor of the training memory usage instead of prompt length.", + "bbox": [ + 75, + 431, + 467, + 583 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.6. Modularity and Flexibility", + "text_level": 1, + "bbox": [ + 76, + 606, + 316, + 622 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "PMF is highly modular, which means it is trivial to replace the unimodal transformers when there are better ones. In this section, we first describe how to replace the unimodal transformer and then show the benefits of such flexibility through experiments with larger pretrained models.", + "bbox": [ + 75, + 633, + 467, + 710 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Since the total transformer layers, $L_{img}$ and $L_{txt}$ of each unimodal transformer are now different, the unimodal base features of two modalities now take different layers to extract, and the number of remaining layers for fusion stays the same. Simply, the fusion layers $L_{f}$ of two transformers can be further specified as $L_{f - img} = L_{img} - 2$ and $L_{f - txt} = L_{txt} - 2$ . In addition, the difference between different hidden dimensions $d$ is automatically handled by the non-linear mapping functions $f$ .", + "bbox": [ + 75, + 714, + 467, + 851 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "The results shown in Tab. 4 clearly demonstrate that PMF can be empowered by larger unimodal transformers with a very limited increase of training memory usage.", + "bbox": [ + 75, + 854, + 467, + 900 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.7. PMF with NAS", + "text_level": 1, + "bbox": [ + 500, + 90, + 653, + 104 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "The hyper-parameters introduced in the proposed PMF are fusion layer $L_{f}$ and prompt length $M$ . Although PMF works well without exhausting hyper-parameter tuning, it is still preferable to have specific settings for every different task and data distribution. In this section, we experiment with automatic fusion structure search via AutoFormer [5]. A detailed description of the search space and evolution search can be found in the supplementary material.", + "bbox": [ + 496, + 114, + 890, + 236 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Tab. 5 shows the performance of NAS-applied PMF on three datasets. With an increase in training memory usage, PMF-NAS achieves better results than regular PMF with the same vision and language encoders, greatly reducing the workload of finding the preferable fusion structure.", + "bbox": [ + 496, + 237, + 890, + 313 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Limitations and Future Works", + "text_level": 1, + "bbox": [ + 498, + 330, + 779, + 347 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "The first limitation is that PMF's performance on three datasets is still behind finetuning baselines with the same pretrained backbones, indicating more work developing prompt-based methods to fully leverage the knowledge inside the pretrained models in the future, finally achieving equivalent or surpassing results through prompting.", + "bbox": [ + 496, + 357, + 890, + 449 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "The second limitation is about the hyper-parameters tuning: It is preferable to decouple prompts into three kinds by their roles in multimodal fusion. However, it also brings more work to hyper-parameter tuning if someone is expecting the best results via an optimal fusion structure.", + "bbox": [ + 496, + 450, + 890, + 526 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Our future research endeavours will involve further investigation of the PMF in diverse multimodal understanding tasks such as Visual Question Answering, utilizing various model architectures.", + "bbox": [ + 496, + 527, + 890, + 585 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "6. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 606, + 617, + 621 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We propose a new form of modular multimodal fusion framework which demonstrates high flexibility and facilitates a two-way interaction among different modalities, namely PMF. PMF leverages three types of interactive prompts in order to dynamically learn different objectives for multimodal learning. By adding the prompts only on the deep layers of utilized unimodal transformers, PMF can significantly reduce the memory usage of the gradient calculation in the backward propagation. Through extensive experiments, we demonstrate that PMF is quite memory-efficient and yet able to perform comparably with existing finetuning baselines.", + "bbox": [ + 496, + 632, + 890, + 813 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "7. Acknowledgement", + "text_level": 1, + "bbox": [ + 500, + 832, + 679, + 849 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "This work was supported in part by the Australian Research Council (ARC) under Grant DP200100938.", + "bbox": [ + 500, + 857, + 890, + 898 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "2611", + "bbox": [ + 482, + 944, + 513, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Jean-Baptiste Alayrac, Jeff Donahue, Pauline Luc, Antoine Miech, Iain Barr, Yana Hasson, Karel Lenc, Arthur Mensch, Katie Millican, Malcolm Reynolds, et al. Flamingo: a visual language model for few-shot learning. arXiv preprint arXiv:2204.14198, 2022. 2", + "[2] John Arevalo, Thamar Solorio, Manuel Montes-y Gómez, and Fabio A González. 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In Proceedings of the IEEE/CVF conference on computer vision and pattern recognition, pages 8746-8755, 2020. 1" + ], + "bbox": [ + 501, + 90, + 890, + 544 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "2613", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/Efficient Multimodal Fusion via Interactive Prompting/9f845069-d99b-4851-8fff-d097c545215b_model.json b/2023/Efficient Multimodal Fusion via Interactive Prompting/9f845069-d99b-4851-8fff-d097c545215b_model.json new file mode 100644 index 0000000000000000000000000000000000000000..159ee116cb985d82e063b571c3171d23d88f8c92 --- /dev/null +++ b/2023/Efficient Multimodal Fusion via Interactive Prompting/9f845069-d99b-4851-8fff-d097c545215b_model.json @@ -0,0 +1,2068 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.001, + 0.812, + 0.047 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.209, + 0.131, + 0.764, + 0.154 + ], + "angle": 0, + "content": "Efficient Multimodal Fusion via Interactive Prompting" + }, + { + "type": "text", + "bbox": [ + 0.201, + 0.179, + 0.77, + 0.2 + ], + "angle": 0, + "content": "Ruijie Quan² Linchao Zhu² Yi Yang²" + }, + { + "type": "text", + "bbox": [ + 0.206, + 0.224, + 0.765, + 0.244 + ], + "angle": 0, + "content": "yaowei.li@uts.edu.au, {quanruijie, zhulinchao, yangyics} @zju.edu.cn" + }, + { + "type": "text", + "bbox": [ + 0.286, + 0.248, + 0.686, + 0.286 + ], + "angle": 0, + "content": "\\(^{1}\\) ReLER, AAII, University of Technology Sydney \\(^{2}\\) CCAI, Zhejiang University" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.319, + 0.314, + 0.335 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.351, + 0.474, + 0.669 + ], + "angle": 0, + "content": "Large-scale pre-training has brought unimodal fields such as computer vision and natural language processing to a new era. Following this trend, the size of multimodal learning models constantly increases, leading to an urgent need to reduce the massive computational cost of finetuning these models for downstream tasks. In this paper, we propose an efficient and flexible multimodal fusion method, namely PMF, tailored for fusing unimodally pretrained transformers. Specifically, we first present a modular multimodal fusion framework that exhibits high flexibility and facilitates mutual interactions among different modalities. In addition, we disentangle vanilla prompts into three types in order to learn different optimizing objectives for multimodal learning. It is also worth noting that we propose to add prompt vectors only on the deep layers of the unimodal transformers, thus significantly reducing the training memory usage. Experiment results show that our proposed method achieves comparable performance to several other multimodal finetuning methods with less than \\(3\\%\\) trainable parameters and up to \\(66\\%\\) saving of training memory usage." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.694, + 0.21, + 0.71 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.72, + 0.471, + 0.902 + ], + "angle": 0, + "content": "Recent years have witnessed the great success of large-scale pretrained language models [8,31,32] and visual models [6,10,23,39], leading to a surge of pretrained multimodal models [13, 14, 43, 47, 48] trying to align different modalities. Many prior methods utilize finetuning to update the entire set of model parameters for every target cross-modal task. Although finetuning can achieve good performance, it requires a large number of computational costs since the gradients and optimizer states for all parameters of multimodal models have to store. Therefore, it encourages researchers to propose more parameter-efficient methods than finetuning for multimodal learning." + }, + { + "type": "image", + "bbox": [ + 0.507, + 0.322, + 0.889, + 0.546 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.56, + 0.894, + 0.631 + ], + "angle": 0, + "content": "Figure 1. Comparison over three multimodal classification tasks. We compare our proposed PMF and PMF-Large with multiple finetuning (yellow) and prompt-based (purple) methods. The y-axis is the average score of three tasks, and the x-axis is the maximum GPU memory usage during training." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.659, + 0.895, + 0.903 + ], + "angle": 0, + "content": "More recently, prompting tuning [17, 19, 21, 22, 29] is proposed to address this problem by freezing all parameters of a pretrained model while tuning only the continuous prompts. Specifically, it adds trainable continuous prompts to the original token sequences of input data. During training, only the continuous prompts are updated. For multimodal prompt-based learning, a most recent method [20] proposes to disentangle the functionality of the pretrained model which exhibits high flexibility. Although this method significantly reduces the tuned parameters (e.g., less than \\(0.1\\%\\) of the pretrained model), there still exists a large performance gap between it and the finetuning-based methods. In addition, this method adopts a sequential modular structure that the pretrained image transformer model is followed by a language transformer model, which causes two main problems in cross-modal learning: a one-way path learn" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "2604" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.319 + ], + "angle": 0, + "content": "ing and a significant increase in the number of model layers. Specifically, a one-way path learning in the multimodal model usually forces one modality to align with others, but not vice versa. In this way, cross-modal learning based on multiple different modalities is not fully explored due to the missing mutual alignments. Since the prompts are added to the token sequences of input data and are updated in the training, they require extensive gradient calculations in the backward propagation which cost numerous memory usages. As a result, this kind of method does not reduce the memory usage during training by much (up to \\(20\\%\\)) though it reduces the number of parameters to update. In other words, this parameter-efficient method still requires massive computational resources which prevents it from being applied to many real-world applications." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.321, + 0.473, + 0.594 + ], + "angle": 0, + "content": "To address these issues, we propose a Prompt-based Multimodal Fusion method with a high memory efficiency, namely PMF. Firstly, we present a new form of modular multimodal fusion framework which demonstrates high flexibility and facilitates a two-way interaction among different modalities. Specifically, we adopt a two-stream structure where the pretrained language model and image model construct the multimodal model in a parallel way. Therefore, tokens of different modalities can learn mutual interactions through a cross-attention-like operation. Such a parallel modular structure brings two benefits. First, unimodal pretraining can be directly utilized for multimodal learning through a parallel combination, eliminating the need for paired multimodal datasets that can be expensive to construct. Also, the type of image or language model can be changed easily (e.g., replacing BERT with T5 for text generation tasks). Furthermore, incorporating extra modalities is made possible based on the parallel modular structure." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.597, + 0.473, + 0.779 + ], + "angle": 0, + "content": "Moreover, we propose to leverage three types of interactive prompts (i.e., query prompts, query context prompts, and fusion context prompts) in order to dynamically learn different objectives for multimodal learning. Intuitively, the query context prompt and query prompt can be seen as a pair of 'questions' and 'answers' with an aim of extracting necessary information for exchange between two modalities. After being translated by a non-linear mapping 'translator', the 'answer' is then delivered to the other modality for better cross-modal understanding. Finally, the fusion context prompts then provide the context to the delivered answer to facilitate the fusion." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.78, + 0.473, + 0.904 + ], + "angle": 0, + "content": "Last but most importantly, PMF is a memory-efficient method that significantly reduces the memory requirements for the large pretrained model. Considering that calculating gradients for prompts for back-propagation is memory-consuming, we propose to add prompts only on the deep layers of the utilized unimodal transformers. Therefore, instead of passing through the entire multimodal model, the backward propagation only needs to pass through the deep" + }, + { + "type": "text", + "bbox": [ + 0.497, + 0.092, + 0.895, + 0.182 + ], + "angle": 0, + "content": "few transformer layers to reach all trainable parameters, greatly reducing the training memory usage. We conduct extensive experiments to demonstrate the superior of it in our experiments. As a result, PMF enables large pretrained models to be trained on the GPU with a low memory requirement." + }, + { + "type": "text", + "bbox": [ + 0.497, + 0.183, + 0.895, + 0.349 + ], + "angle": 0, + "content": "We conduct extensive experiments on three vision-language datasets: UPMC-Food101 [38], MM-IMDB [2], and SNLI-VE [41]. Through comparisons with multiple finetuning and prompt tuning methods (see in Fig. 1), we find that: (1) PMF is the most memory-efficient method for cross-modal learning so far, which reduces the training memory usage by up to \\(66\\%\\) compared with finetuning baselines, and by \\(55\\%\\) compared with prompt-based methods. (2) PMF can perform comparably compared to prior fine-tuning methods with much fewer trainable parameters (less than \\(2.5\\%\\)) and memory usage." + }, + { + "type": "text", + "bbox": [ + 0.497, + 0.349, + 0.895, + 0.485 + ], + "angle": 0, + "content": "Concretely, our contributions are as follows: (1) we present a new form of modular multimodal fusion framework which enables two-way interactions between different modalities and high flexibility of the entire model; (2) we disentangle vanilla prompts into three types of prompts, in order to dynamically learn different objectives for multimodal learning; (3) our proposed method is quite memory-efficient yet is able to achieve comparable performance with existing finetuning methods for multimodal fusion." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.498, + 0.646, + 0.515 + ], + "angle": 0, + "content": "2. Related works" + }, + { + "type": "text", + "bbox": [ + 0.497, + 0.524, + 0.895, + 0.644 + ], + "angle": 0, + "content": "Multimodal Fusion. Multimodal fusion methods aim to simultaneously process the input of different modalities, such as audio-video [27], vision-language [2, 15], and inputs from different types of sensors [42], etc. In this paper, we specifically focus on the fusion of vision-language inputs, though our proposed strategy is compatible with other modality pairs as long as there are unimodally pretrained transformers for these modalities." + }, + { + "type": "text", + "bbox": [ + 0.497, + 0.645, + 0.896, + 0.825 + ], + "angle": 0, + "content": "Our work is in line with deep learning-based multimodal fusion strategies [16, 18, 26, 28, 33, 34, 44]. In this line of work, [15] proposed a framework whose vision encoder solely serves as a mapping tool to encode the raw images to the token space of the text encoder. Such an architecture is widely used in the later multimodal fusion research [20, 26, 34]. Differently, [27] used a dual-encoder architecture with bottleneck fusion tokens to exchange information between two encoders for video-audio fusion. Our work has a similar architecture as in [27]. But our proposed method completely freezes the unimodal encoders and uses an interactive prompting technique for more efficient fusion." + }, + { + "type": "text", + "bbox": [ + 0.497, + 0.826, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Another important line of multimodal fusion work is through pretraining with the large-scale datasets, mostly achieved by self-supervised learning algorithms [1, 11, 24, 30, 36, 37, 45]. This line of works can be roughly divided into two kinds by their architectures. The first kind has" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.958 + ], + "angle": 0, + "content": "2605" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.081, + 0.089, + 0.468, + 0.182 + ], + "angle": 0, + "content": "
Task TypePretraining TypeMethod
UnimodalUnimodalP-Tuning [22], VPT [12]
UnimodalMultimodalCoOp [47], MAPLE [14]
MultimodalMultimodalPI-VL [13], PTGM [43]
MultimodalUnimodalBlindPrompt [20], PMF
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.191, + 0.472, + 0.248 + ], + "angle": 0, + "content": "Table 1. Prompt-based methods categorized by model pretraining types and downstream task types. Our proposed PMF falls into the last category which utilize unimodally pretrained transformers for multimodal tasks." + }, + { + "type": "text", + "bbox": [ + 0.075, + 0.278, + 0.47, + 0.504 + ], + "angle": 0, + "content": "a dual-encoder structure where image and text are treated separately, such as CLIP [30] and ALIGN [11]. The other kind simultaneously processes the vision and language inputs with cross-attention or self-attention over a longer sequence from two modalities. Our proposed method differs from these self-supervised architectures in that the individual components used in our model are unimodally pretrained with much less data. This difference directly results in a huge performance gap because of the lack of multimodal information in the pretraining stage. However, using unimodally pretrained models enables a much more flexible architecture. It has great potential in multimodal tasks where modality-paired large-scale pretraining data is not available, or when more advanced unimodal encoders are proposed in the future." + }, + { + "type": "text", + "bbox": [ + 0.075, + 0.506, + 0.47, + 0.732 + ], + "angle": 0, + "content": "Prompt Tuning. As shown in Tab. 1, prompt-based methods can be roughly divided into four major categories in terms of the modalities of the pretrained model and the downstream tasks. Prompting techniques originally apply on unimodally pretrained transformers for unimodal natural language processing (NLP) tasks [17, 19, 21, 22, 29]. Pretrained GPT-3 can be simply leveraged with handcrafted prompts, which are some manually chosen words preceding the input text [4]. Then [22] and [17] proposed to change the handcrafted prompt to trainable continuous prompts and only update the prompt vectors during the training. Later on, [19] and [29] proposed to use prompt tuning in every hidden layer in the pretrained transformer instead of the input embeddings only. VPT [12] first applied prompt tuning to the vision transformer." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.735, + 0.471, + 0.903 + ], + "angle": 0, + "content": "For methods that prompt multimodally pretrained models for unimodal tasks, many recent works apply prompt tuning to pretrained vision-language models (i.e. CLIP [30]) for unimodal vision tasks [3, 14, 25, 46, 47]. Another type of prompt-based method apply to the multimodal pretrained model for multimodal tasks [13, 43]. [13] adds prompts to an encoder-decoder one-for-all multimodal transformer, achieving comparable performance with finetuning with improved robustness against adversarial attacks. The method used in [13] is simple but effective, showing that prompting methods works well with powerful and com" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.092, + 0.756, + 0.107 + ], + "angle": 0, + "content": "plex multimodally pretraining models." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.108, + 0.892, + 0.289 + ], + "angle": 0, + "content": "Our proposed fusion strategy is different from the above methods and falls into the last category where prompts are used to fuse pretrained unimodal models for multimodal tasks. Sharing the same architecture design with [15, 34], [20] uses prompt to align the feature extracted from raw images to the token space of pretrained language model. They achieved comparable performance to several multimodal fusion methods in low-resource settings but underperform fine-tuning baselines by a large margin with full data. Compared with them, our proposed PMF not only is more memory-efficient but can also perform comparably with fine-tuning baselines with full data." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.305, + 0.809, + 0.323 + ], + "angle": 0, + "content": "3. Prompt-based Multimodal Fusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.332, + 0.892, + 0.453 + ], + "angle": 0, + "content": "In this section, we describe our proposed Prompt-based Multimodal Fusion strategy (PMF). We begin by summarising unimodal transformers developed for vision and language tasks in Sec. 3.1. Then we describe the base feature extraction process in Sec. 3.2. Lastly, we give a detailed description of how PMF integrates two unimodal transformer layers into a multimodal one via interactive prompting in Sec. 3.3." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.465, + 0.724, + 0.48 + ], + "angle": 0, + "content": "3.1. Unimodal Transformers" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.489, + 0.892, + 0.653 + ], + "angle": 0, + "content": "Vision Transformer (ViT) [9] adapts the Transformer [35] architecture with minimum modifications. The RGB image input \\(\\mathbf{x}_{img} \\in \\mathbb{R}^{h,w,c}\\) is first cut into \\(N_{img}\\) nonoverlapping patches and then linearly projected into a sequence of embeddings \\(\\mathbf{z}\\) with each \\(z_i \\in \\mathbb{R}^d\\). Differently, the language Transformer first tokenizes raw text to \\(N_{txt}\\) one-hot word embeddings and then converted these discrete vectors into a sequence of \\(N_{txt}\\) continuous embeddings. The resulting continuous embedding for both Language Transformer and Vision Transformer share the same structure as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.611, + 0.657, + 0.892, + 0.674 + ], + "angle": 0, + "content": "\\[\n\\mathbf {z} = \\left[ \\mathrm {C L S}, z _ {1}, z _ {2}, \\dots , z _ {N} \\right] \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.683, + 0.892, + 0.835 + ], + "angle": 0, + "content": "where CLS is a special token prepended to the sequence so that its representation at the final layer can be used as the representation of the whole sequence for classification. Please note that the two unimodal transformers have different CLS tokens. The continuous embedding \\(\\mathbf{z}\\) is then fed into a transformer encoder which consists of \\(L\\) transformer layers. For each transformer layer, the input passes through modules including multi-head self-attention, layer normalization, multilayer perceptron, and finally added to the original input with a residual connection." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.847, + 0.8, + 0.862 + ], + "angle": 0, + "content": "3.2. Unimodal Base feature Extraction" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.871, + 0.892, + 0.902 + ], + "angle": 0, + "content": "As shown in Fig. 2, the image and text inputs are first processed and fed into the unimodal transformer layers to" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "2606" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.093, + 0.881, + 0.297 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.311, + 0.895, + 0.382 + ], + "angle": 0, + "content": "Figure 2. Prompt-based multimodal fusion strategy (PMF) applied to vision-language inputs. In the forward propagation, image and text inputs are first embedded into continuous token sequences and fed to the unimodal transformer layers for base feature extraction. The base features from both modalities then pass through multiple prompt-based multimodal fusion layers to get the feature of two CLS tokens for final classification. In the backward propagation, only multimodal fusion layers take part in the calculation of gradients, greatly saving memory usage during training. All pretrained parameters in both transformers are frozen during the training." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.408, + 0.47, + 0.468 + ], + "angle": 0, + "content": "extract base features, respectively. At this stage, each encoder works exactly the same as they did in unimodal tasks. Here we denote the starting fusion layer as \\( L_{f} \\). And the base feature extraction of each encoder can be denoted as:" + }, + { + "type": "equation", + "bbox": [ + 0.142, + 0.478, + 0.47, + 0.497 + ], + "angle": 0, + "content": "\\[\n\\mathbf {z} ^ {l + 1} = \\operatorname {T r a n s L a y e r} ^ {l} \\left(\\mathbf {z} ^ {l}; \\theta\\right) \\quad \\text {i f} l < L _ {f} \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.506, + 0.47, + 0.569 + ], + "angle": 0, + "content": "where \\(\\theta\\) stands for the pretrained parameters. A smaller \\(L_{f}\\) leads to an earlier fusion and a larger \\(L_{f}\\) leads to a later fusion. A detailed discussion of the impact brought by different \\(L_{f}\\) can be found in Sec. 4.5." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.576, + 0.313, + 0.592 + ], + "angle": 0, + "content": "3.3. Multimodal Fusion Layer" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.599, + 0.47, + 0.689 + ], + "angle": 0, + "content": "The extracted unimodal base features are then passed through multiple multimodal fusion layers, each consisting of a 'querying stage' and a 'fusion stage', as shown in Fig. 3. The querying stage focus on the extraction of what is necessary to pass, and the fusion stage focus on fusing the extracted information delivered from the other modality." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.69, + 0.469, + 0.841 + ], + "angle": 0, + "content": "This two-stage setting makes the vanilla prompt training entangled with different learning objectives. Therefore, we propose to decouple the vanilla prompts into three kinds: 'query prompt' (QP, denoted \\(\\mathbf{z}_{qp}\\)), 'query context prompt' (QCP, denoted \\(\\mathbf{z}_{qcp}\\)), and 'fusion context prompt' (FCP, denoted \\(\\mathbf{z}_{fcp}\\)) to dynamically learn different objectives for multimodal learning. According to the modality where prompts are used, each kind of prompt can be further specified as \\(\\mathbf{z}_*\\) and \\(\\mathbf{z}_*\\) to distinguish from each other (e.g. \\(\\mathbf{z}_{fcp}\\) and \\(\\mathbf{z}_{fcp}^{\\prime}\\))." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.841, + 0.47, + 0.902 + ], + "angle": 0, + "content": "As shown in Fig. 3, QP and QCP are used in the querying stage and the FCP is used in the fusion stage. As suggested by their names, QP is to query information from the unimodal input sequence, QCP is to help this process by pro" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.408, + 0.892, + 0.498 + ], + "angle": 0, + "content": "viding extra context to the query. QP and QCP like a pair of 'questions' and 'answers', translated by the non-linear mapping. As for FCP, it is responsible for providing the context to the fusion in the fusion stage. We now introduce how these three kinds of prompts interact with each other in the two stages of each multimodal fusion layer." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.498, + 0.892, + 0.543 + ], + "angle": 0, + "content": "Querying Stage. We first concatenate corresponding QP and QCP to the input sequence \\(\\mathbf{z}\\). The resulting input sequence after the concatenation is:" + }, + { + "type": "equation", + "bbox": [ + 0.649, + 0.553, + 0.892, + 0.573 + ], + "angle": 0, + "content": "\\[\n[ \\mathbf {z} ^ {l} | | \\mathbf {z} _ {q c p} ^ {l} | | \\mathbf {z} _ {q p} ^ {l} ] \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.581, + 0.892, + 0.627 + ], + "angle": 0, + "content": "where \\( | \\cdot | \\) denotes the concatenation operation. Then we feed the concatenated sequence to the unimodal transformer layer, which can be denoted as:" + }, + { + "type": "equation", + "bbox": [ + 0.526, + 0.635, + 0.892, + 0.657 + ], + "angle": 0, + "content": "\\[\n[ \\hat {\\mathbf {z}} ^ {l} | | \\hat {\\mathbf {z}} _ {q c p} ^ {l} | | \\hat {\\mathbf {z}} _ {q p} ^ {l} ] = \\mathrm {T r a n s L a y e r} ^ {l} ([ \\mathbf {z} ^ {l} | | \\mathbf {z} _ {q c p} ^ {l} | | \\mathbf {z} _ {q p} ^ {l} ]; \\theta) \\quad (4)\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.667, + 0.892, + 0.758 + ], + "angle": 0, + "content": "After the forward propagation, the output of QP \\(\\hat{\\mathbf{z}}_{qp}^{l}\\) is extracted as the queried information to be used in the following fusion operations. It should be noted that though \\(\\hat{\\mathbf{z}}_{qcp}^{l}\\) will not be used in the following fusion operations, it has played an important role by providing the context of query in the querying stage." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.758, + 0.892, + 0.803 + ], + "angle": 0, + "content": "The queried fusion intermediate \\(\\hat{\\mathbf{z}}_{qp}^{l}\\) is then mapped to the representation space of the other modality through a non-linear mapping function:" + }, + { + "type": "equation", + "bbox": [ + 0.644, + 0.812, + 0.892, + 0.833 + ], + "angle": 0, + "content": "\\[\n\\mathbf {y} _ {q p} ^ {l} = f ^ {l} \\left(\\hat {\\mathbf {z}} _ {q p} ^ {l}\\right) \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.892, + 0.901 + ], + "angle": 0, + "content": "where \\( f \\) is a non-linear mapping function. Specifically, a mapping function consists of two linear layers with a bottleneck structure to reduce dimension and only the first linear layer has a ReLu function. Each fusion layer \\( l \\) has two" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "2607" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.08, + 0.089, + 0.895, + 0.222 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.235, + 0.895, + 0.304 + ], + "angle": 0, + "content": "Figure 3. Prompt-based multimodal fusion layer. We propose to use three kinds of interactive prompts to achieve the fusion/exchange of information from two modalities. We use 'query prompt' \\((\\mathrm{z}_{qp},\\mathrm{z}_{qp}^{\\prime})\\) and 'query context prompt' \\((\\mathrm{z}_{qcp},\\mathrm{z}_{qcp}^{\\prime})\\) in the querying stage to extract what is necessary, after a non-linear mapping, the extracted information is then fused to the other modality with the help of 'fusion context prompt' \\((\\mathrm{z}_{fcp},\\mathrm{z}_{fcp}^{\\prime})\\) in the fusion stage. Yellow and green elements stand for language and vision modalities, respectively. Red boxes indicate trainable modules." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.33, + 0.469, + 0.391 + ], + "angle": 0, + "content": "mapping functions \\( f^l \\) and \\( f'^l \\), building a two-way interaction among different modalities. Note that the non-linear mapping functions contain more than \\( 95\\% \\) of the trainable parameters in PMF." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.392, + 0.47, + 0.484 + ], + "angle": 0, + "content": "Fusion Stage. We first concatenate the mapped fusion intermediates \\(\\mathbf{y}_{qp}^{l}\\) to the original input sequence \\(\\mathbf{z}^{\\prime l}\\) and FCP \\(\\mathbf{z}_{fcp}^{\\prime l}\\) of the other modality. Then we feed the concatenated sequence to the unimodal transformer layer of the other modality to complete a one-way fusion. These two processes can be together denoted as:" + }, + { + "type": "equation", + "bbox": [ + 0.095, + 0.495, + 0.469, + 0.528 + ], + "angle": 0, + "content": "\\[\n[ \\mathbf {z} ^ {\\prime l + 1} | | \\hat {\\mathbf {z}} _ {f c p} ^ {\\prime l} | | \\hat {\\mathbf {y}} _ {q p} ^ {l} ] = \\operatorname {T r a n s L a y e r} ^ {l} ([ \\mathbf {z} ^ {\\prime l} | | \\mathbf {z} _ {f c p} ^ {\\prime l} | | \\mathbf {y} _ {q p} ^ {l} ]; \\theta^ {\\prime}) \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.528, + 0.381, + 0.544 + ], + "angle": 0, + "content": "where \\([\\ast ]'\\) means \\([\\ast ]\\) from the other modality." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.544, + 0.469, + 0.605 + ], + "angle": 0, + "content": "Finally, the output of two unimodal transformer layers \\(\\mathbf{z}^{l + 1}\\) and \\(\\mathbf{z}^{\\prime l + 1}\\) are together as the output of the multimodal fusion layer and fed to the higher layers. The entire multimodal fusion process can be concluded as:" + }, + { + "type": "equation", + "bbox": [ + 0.087, + 0.615, + 0.469, + 0.647 + ], + "angle": 0, + "content": "\\[\n[ \\mathbf {z} ^ {l + 1} | | \\mathbf {z} ^ {\\prime l + 1} ] = \\text {F u s i o n L a y e r} ^ {l} ([ \\mathbf {z} ^ {l} | | \\mathbf {z} ^ {\\prime l} ]; \\theta , \\theta^ {\\prime}) \\quad \\text {i f} L _ {f} \\leq l \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.649, + 0.469, + 0.755 + ], + "angle": 0, + "content": "After the multimodal fusion is complete, we take the output representation of CLS token \\( z_{CLS}^{L} \\) and \\( z_{CLS}^{\\prime L} \\) to two different linear classifiers and average the pre-softmax logits for classification. Mathematically, such a classifier setting is equivalent to feeding the classifier with the concatenated features when a linear classifier is used, except for a different scale of gradient caused by the averaging operation." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.769, + 0.21, + 0.787 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.795, + 0.469, + 0.901 + ], + "angle": 0, + "content": "In this section, we analyze the performance of our proposed PMF on three multimodal datasets and aim to answer the following questions: (1) How efficient is the PMF and does PMF perform well (Sec. 4.4)? (2) What factors affect the effectiveness of PMF (Sec. 4.5)? In addition, we explore the PMF equipped with larger transformers and its impact brought to the performance and memory efficiency in" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.33, + 0.892, + 0.376 + ], + "angle": 0, + "content": "Sec. 4.6. Lastly, we introduce a Neural Architecture Search (NAS) method to automatically search for the preferable fusion structure for PMF in Sec. 4.7." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.388, + 0.698, + 0.403 + ], + "angle": 0, + "content": "4.1. Datasets and Metrics" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.411, + 0.892, + 0.517 + ], + "angle": 0, + "content": "UPMC Food-101 [38] is a multimodal classification dataset, which contains food images with textual recipe descriptions for 101 kinds of food. UPMC Food-101 contains a total of 90,840 image-text pairs with a size range between 790 and 956 pairs for different classes. As the dataset only has training and testing sets, we follow [15] and create a validation split of 5000 samples from the training set." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.518, + 0.892, + 0.592 + ], + "angle": 0, + "content": "MM-IMDB [2] is a multimodal multi-label classification dataset, which contains movie plot outlines and movie posters. The task is to predict the genre of movies. This dataset contains 25,956 image-text pairs for 23 classes with a long-tail distribution." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.593, + 0.892, + 0.714 + ], + "angle": 0, + "content": "SNLI-VE [41] is a multimodal classification dataset for the visual entailment tasks, which is to reason about the relationship between an image premise and a text hypothesis into entailment, contradiction, or neutrality. SNLI-VE contains a total of 565,286 image-text pairs. Please note that we only use image premise and text hypothesis in the input, which is different from the settings in some other papers where text premises are also used in the inputs [43]." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.715, + 0.891, + 0.744 + ], + "angle": 0, + "content": "We report accuracy for UPMC Food-101 and SNLI-VE, and Macro/Micro-F1 scores for MM-IMDB as metrics." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.756, + 0.78, + 0.772 + ], + "angle": 0, + "content": "4.2. Existing Methods and Baselines" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.78, + 0.892, + 0.901 + ], + "angle": 0, + "content": "We report the performance of several baselines and existing methods. First, we report the performance of finetuning unimodal models (i.e. BERT [8], ViT [9]) to verify the effectiveness of multimodal fusion. Specifically, we take the output representation of CLS token of the last layer in ViT and BERT, and feed it into a linear classifier. We also report the performance of VPT [12] and a prompt-based BERT (denoted P-BERT) for a better comparison. For VPT" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "2608" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.078, + 0.089, + 0.895, + 0.356 + ], + "angle": 0, + "content": "
MethodUpdated Param. (Million)Memory Usage (GB) Train/InferenceSNLI-VEFood-101MM-IMDBAvg.
Linear-3.76 / 3.2350.0578.9649.76 / 56.8360.77
ViT86.59.36 / 1.9933.3374.6938.39 / 49.8850.72
BERT109.030.82 / 2.7969.8287.4458.91 / 64.3172.96
LateConcat196.038.54 / 3.3670.0193.2959.56 / 64.9275.18
MMBT*196.537.87 / 3.4874.6994.1060.80 / 66.1077.41
MBT*196.038.00 / 4.0674.0293.5659.60 / 64.8176.60
VPT-6.12 / 2.0133.3372.5535.22 / 44.4948.58
P-BERT-28.13 / 2.9963.2881.0748.67 / 54.5865.33
PromptFuse-29.57 / 3.5564.5382.2148.59 / 54.4966.09
BlindPrompt-29.57 / 3.6565.5484.5650.18 / 56.4667.81
P-LateConcat0.330.82 / 3.4363.0589.0353.91 / 59.9369.67
P-MMBT0.930.90 / 3.4867.5886.5852.95 / 59.3070.10
PMF (M=4, Lf=10)2.512.84 / 4.0871.9291.5158.77 / 64.5175.02
PMF-large (M=4, Lf=22)4.518.44 / 6.4272.1091.6861.66 / 66.7275.99
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.365, + 0.895, + 0.437 + ], + "angle": 0, + "content": "Table 2. Multimodal classification performance. PMF achieve comparable performance to the finetuning baselines with less than \\(3\\%\\) of trainable parameters and up to \\(66\\%\\) of training memory usage. MM-IMDB is F1-Macro / F1-Micro, others are accuracy. We report the maximum memory usage in training and evaluating UPMC Food-101 for each method. We report mean performance over 3 runs with different random seeds. \\* means trainable parameter less than \\(0.1\\mathrm{M}\\) . PMF-Large uses bert-large and vit-large models (24 hidden layers) while others use bert-base and vit-base models (12 hidden layers). \\(M\\) is the prompt length and \\(L_{f}\\) is the starting fusion layer." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.462, + 0.471, + 0.522 + ], + "angle": 0, + "content": "and P-BERT, the input sequence to each transformer layer is concatenated with a prompt vector, whose length is set to 10. And the concatenated prompt vectors and the final linear classifier are the only updated modules in training." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.523, + 0.47, + 0.659 + ], + "angle": 0, + "content": "In addition, we compare against a strong baseline method which concatenates the output features of CLS tokens of ViT and BERT, and feed the concatenated feature to a linear classifier, denoted as LateConcat. In this case, the input to the classifier is \\((768 + 768)\\)-dimensional. Besides, we also introduce Linear, which shares the same architecture with LateConcat with the only difference in the updated modules. Linear only updates the linear classifier while LateConcat updates all parameters during training." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.659, + 0.47, + 0.75 + ], + "angle": 0, + "content": "We reimplement MMBT (denoted \\(\\mathbf{MMBT}^*\\)) [15] and MBT (denoted \\(\\mathbf{MBT}^*\\)) [27] with a vit-base model as the vision encoder and a bert-base model as the text encoder for fair and controlled comparison. We set the fusion layer \\(L_{f} = 8\\) and use 4 fusion tokens in MBT as recommended in the original paper." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.75, + 0.471, + 0.903 + ], + "angle": 0, + "content": "We also propose a prompt-based MMBT and a prompt-based LateConcat, denoted as P-MMBT and P-LateConcat, respectively. In P-MMBT and P-LateConcat, we apply deep prompt tuning on both vision and language encoders, which are pretrained backbones with frozen parameters during training. We set the prompt length in each layer of two encoders to 10, totalling 240 prompt vectors. Similar to VPT and P-BERT, P-LateConcat only updates the final linear classifier and prompt vectors during training. Compared with P-LateConcat, P-MMBT have an extra" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.462, + 0.892, + 0.477 + ], + "angle": 0, + "content": "linear projection layer and a smaller linear classifier to train." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.478, + 0.892, + 0.553 + ], + "angle": 0, + "content": "Lastly, we report the performance of PromptFuse and BlindPrompt [20], both proposed in the only existing paper which leverages unimodally pretrained models for multimodal fusion through prompting. We set the prompt length to 20 as recommended in the original paper." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.56, + 0.719, + 0.577 + ], + "angle": 0, + "content": "4.3. Implementation Details" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.583, + 0.892, + 0.688 + ], + "angle": 0, + "content": "Pretrained Backbone and Initialization. Unless otherwise noted, we use an ImageNet-21k [7] pretrained vit-base model for the vision encoder and a bert-base-uncased model for the language encoder in all experiments. All pretrained checkpoints are from huggingface [40]. All prompt vectors are initialized through a Gaussian distribution (mean=0, std=0.02)." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.689, + 0.892, + 0.795 + ], + "angle": 0, + "content": "Network Training. We use SGD optimizer in all experiments with momentum set to 0.9 and weight decay set to \\(1e^{-4}\\). The batch size is set to 64 for SNLI-VE, and 32 for UPMC Food-101 and MM-IMDB. Cross entropy loss is applied in all experiments and the class labels are weighted by their inverse frequency for UPMC Food-101 and MM-IMDB. More details are in the supplementary material." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.802, + 0.64, + 0.817 + ], + "angle": 0, + "content": "4.4. Main Results" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.825, + 0.895, + 0.903 + ], + "angle": 0, + "content": "PMF is most memory-efficient. As shown in Tab. 2, PMF is the most memory-efficient multimodal fusion model of all existing prompt-based methods and baselines. PMF can save up to \\(66\\%\\) of training memory usage compared with finetuning baselines. Even compared with the existing most" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.517, + 0.957 + ], + "angle": 0, + "content": "2609" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.107, + 0.089, + 0.444, + 0.242 + ], + "angle": 0, + "content": "
QPMappingfQCPFCPMM-IMDB
48.80/56.38
✓45.38/53.34
✓43.56/51.43
✓✓54.92/62.25
✓✓✓57.98/63.69
✓✓✓58.30/64.07
✓✓✓58.34/64.15
✓✓✓✓58.63/64.23
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.252, + 0.472, + 0.325 + ], + "angle": 0, + "content": "Table 3. PMF Component Ablation. There are four types of trainable modules in our proposed PMF. We set the fusion layer \\( L_{f} = 10 \\) and add different components one at a time to see their individual impact. All prompts with \\( \\checkmark \\) have a length of 4, and prompts with \\( \\checkmark \\checkmark \\) have a length of 8." + }, + { + "type": "image", + "bbox": [ + 0.082, + 0.347, + 0.465, + 0.499 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.511, + 0.471, + 0.568 + ], + "angle": 0, + "content": "Figure 4. Model Performance and Training Memory Usage under different fusion layers \\( L_{f} \\). We set the prompt length \\( M = 4 \\) for every prompt vector with different fusion layer \\( L_{f} = 0,2,4,6,8,10,12 \\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.604, + 0.47, + 0.636 + ], + "angle": 0, + "content": "memory-efficient prompt-based multimodal method, PMF still saves an extra of more than \\(50\\%\\) of training memory." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.64, + 0.47, + 0.777 + ], + "angle": 0, + "content": "PMF outperforms all existing prompt-based methods. With the same pretrained unimodal transformers, prompt-based methods underperform the full finetuning methods by a large margin. Some prompt-based methods even underperform unimodal finetuning baselines. Our proposed PMF achieves the best performance among all prompt-based methods. Especially, PMF outperforms all unimodal baselines in all experiments, showing that the two modalities are successfully fused." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.78, + 0.471, + 0.903 + ], + "angle": 0, + "content": "PMF is competitive with finetuning baselines. Tab. 2 shows that PMF achieves comparable performance with full finetuning baselines with less than \\(3\\%\\) trainable parameters while saving \\(66\\%\\) of memory cost, significantly narrowing the gap between finetuning and prompt-based methods. Furthermore, PMF even outperforms the finetuning LateConcat when equipped with larger transformers (i.e. bert-large and vit-large)." + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.091, + 0.891, + 0.238 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.25, + 0.894, + 0.293 + ], + "angle": 0, + "content": "Figure 5. Model Performance and Training Memory Usage under different prompt length \\( M \\). We fix the fusion layer \\( L_{f} = 10 \\) and study 1, 4, 8, 16, and 32 tokens for each prompt vector." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.318, + 0.653, + 0.334 + ], + "angle": 0, + "content": "4.5. Ablation Study" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.342, + 0.892, + 0.386 + ], + "angle": 0, + "content": "In this section, we investigate the impact of different factors in our proposed fusion strategy. All experiments in this section are conducted on the MM-IMDB dataset." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.387, + 0.893, + 0.569 + ], + "angle": 0, + "content": "Components Ablation. We verify the effectiveness of three kinds of prompts and the non-linear mapping function in this section. The results are shown in Tab. 3. The first row without any components in PMF is equivalent to the Linear model introduced in Sec. 4.2. The comparison between the first three rows shows that merely prompting the top layers of the two transformers not only cannot achieve multimodal fusion. Oppositely, it will disturb the feature space of two transformers, which finally hurts the performance. Though the mapping functions give the biggest boost to the performance, it should be noted that the mapping functions \\( f \\) cannot work without QP querying the fusion intermediates." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.569, + 0.894, + 0.765 + ], + "angle": 0, + "content": "In addition, the comparison between the last four rows shows that decoupling the prompts into three individual modules with different learning objectives brings a performance gain. More specifically, the comparison between the fifth and sixth row in Tab. 3 shows that an extended QP cannot replace QCP. Since only the output of QP tokens are fused to the other modality while that of QCP discarded, replacing QCP with a longer QP not only increases the computation as the sequences in the fusion stage are longer but also results in a damaged performance. As a result, every module introduced in PMF contributes to the quality of multimodal fusion. The missing of any of the four modules will bring a performance drop at different scales." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.894, + 0.902 + ], + "angle": 0, + "content": "Fusion Layer. We now investigate impacts brought by different fusion layers \\( L_{f} \\) to the fusion performance and memory efficiency. The results are summarized in Fig. 4. As can be seen in the figure, the training memory usage keeps decreasing as the fusion starts later. However, the performance of the fusion model is relatively consistent with \\( L_{f} \\leq 10 \\). Therefore, adding prompts only on the deep layers \\( (10 < l < L) \\) is empirically better for the trade-off between performance and memory efficiency." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "2610" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.081, + 0.089, + 0.468, + 0.196 + ], + "angle": 0, + "content": "
Text EncoderImage EncoderMemory Usage Train/InferenceMM-IMDB
bert-basevit-base12.84 / 4.0858.77 / 64.51
bert-basevit-large14.16 / 4.8959.70 / 65.20
bert-largevit-base17.17 / 5.5360.08 / 65.41
bert-largevit-large18.44 / 6.4261.66 / 66.72
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.206, + 0.47, + 0.262 + ], + "angle": 0, + "content": "Table 4. Comparison of PMF applying to different unimodal transformers. We set the fusion layer \\( L_{f} = L - 2 \\) and prompt length \\( M = 4 \\) in all experiments. MM-IMDB is reported with F1-Macro / F1-Micro." + }, + { + "type": "table", + "bbox": [ + 0.081, + 0.286, + 0.466, + 0.344 + ], + "angle": 0, + "content": "
Training MemorySNLI-VEFood-101MM-IMDBAvg.
33.36 GB72.2792.159.67 / 65.5775.66
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.354, + 0.468, + 0.397 + ], + "angle": 0, + "content": "Table 5. Performance of PMF applied with NAS. MM-IMDB is F1-Macro / F1-Micro, others are accuracy. We only report the training memory usage." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.433, + 0.468, + 0.584 + ], + "angle": 0, + "content": "Prompt Length. The ablation study on prompt length is carried out with three kinds of prompts set to have the same length (i.e. \\( M_{qp} = M_{qcp} = M_{fcp} \\)). Fig. 5 summarizes the results. The performance increases as the prompt length grows longer when \\( M \\leq 16 \\), and drops when the prompts are too long (\\( M = 32 \\)). It should be stressed that the training memory usage only increases around 1 GB as the prompt length grows from 1 to 16, which means the fusion layer \\( L_f \\) is the major factor of the training memory usage instead of prompt length." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.607, + 0.317, + 0.623 + ], + "angle": 0, + "content": "4.6. Modularity and Flexibility" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.635, + 0.468, + 0.711 + ], + "angle": 0, + "content": "PMF is highly modular, which means it is trivial to replace the unimodal transformers when there are better ones. In this section, we first describe how to replace the unimodal transformer and then show the benefits of such flexibility through experiments with larger pretrained models." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.715, + 0.468, + 0.852 + ], + "angle": 0, + "content": "Since the total transformer layers, \\( L_{img} \\) and \\( L_{txt} \\) of each unimodal transformer are now different, the unimodal base features of two modalities now take different layers to extract, and the number of remaining layers for fusion stays the same. Simply, the fusion layers \\( L_{f} \\) of two transformers can be further specified as \\( L_{f - img} = L_{img} - 2 \\) and \\( L_{f - txt} = L_{txt} - 2 \\). In addition, the difference between different hidden dimensions \\( d \\) is automatically handled by the non-linear mapping functions \\( f \\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.468, + 0.901 + ], + "angle": 0, + "content": "The results shown in Tab. 4 clearly demonstrate that PMF can be empowered by larger unimodal transformers with a very limited increase of training memory usage." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.091, + 0.655, + 0.106 + ], + "angle": 0, + "content": "4.7. PMF with NAS" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.115, + 0.892, + 0.237 + ], + "angle": 0, + "content": "The hyper-parameters introduced in the proposed PMF are fusion layer \\( L_{f} \\) and prompt length \\( M \\). Although PMF works well without exhausting hyper-parameter tuning, it is still preferable to have specific settings for every different task and data distribution. In this section, we experiment with automatic fusion structure search via AutoFormer [5]. A detailed description of the search space and evolution search can be found in the supplementary material." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.238, + 0.892, + 0.314 + ], + "angle": 0, + "content": "Tab. 5 shows the performance of NAS-applied PMF on three datasets. With an increase in training memory usage, PMF-NAS achieves better results than regular PMF with the same vision and language encoders, greatly reducing the workload of finding the preferable fusion structure." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.332, + 0.78, + 0.348 + ], + "angle": 0, + "content": "5. Limitations and Future Works" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.358, + 0.892, + 0.45 + ], + "angle": 0, + "content": "The first limitation is that PMF's performance on three datasets is still behind finetuning baselines with the same pretrained backbones, indicating more work developing prompt-based methods to fully leverage the knowledge inside the pretrained models in the future, finally achieving equivalent or surpassing results through prompting." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.451, + 0.892, + 0.527 + ], + "angle": 0, + "content": "The second limitation is about the hyper-parameters tuning: It is preferable to decouple prompts into three kinds by their roles in multimodal fusion. However, it also brings more work to hyper-parameter tuning if someone is expecting the best results via an optimal fusion structure." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.528, + 0.892, + 0.587 + ], + "angle": 0, + "content": "Our future research endeavours will involve further investigation of the PMF in diverse multimodal understanding tasks such as Visual Question Answering, utilizing various model architectures." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.607, + 0.619, + 0.622 + ], + "angle": 0, + "content": "6. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.633, + 0.892, + 0.814 + ], + "angle": 0, + "content": "We propose a new form of modular multimodal fusion framework which demonstrates high flexibility and facilitates a two-way interaction among different modalities, namely PMF. PMF leverages three types of interactive prompts in order to dynamically learn different objectives for multimodal learning. By adding the prompts only on the deep layers of utilized unimodal transformers, PMF can significantly reduce the memory usage of the gradient calculation in the backward propagation. Through extensive experiments, we demonstrate that PMF is quite memory-efficient and yet able to perform comparably with existing finetuning baselines." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.833, + 0.68, + 0.85 + ], + "angle": 0, + "content": "7. Acknowledgement" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.858, + 0.892, + 0.9 + ], + "angle": 0, + "content": "This work was supported in part by the Australian Research Council (ARC) under Grant DP200100938." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.514, + 0.957 + ], + "angle": 0, + "content": "2611" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.116, + 0.47, + 0.185 + ], + "angle": 0, + "content": "[1] Jean-Baptiste Alayrac, Jeff Donahue, Pauline Luc, Antoine Miech, Iain Barr, Yana Hasson, Karel Lenc, Arthur Mensch, Katie Millican, Malcolm Reynolds, et al. 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In Proceedings of the IEEE/CVF conference on computer vision and pattern recognition, pages 8746-8755, 2020. 1" + }, + { + "type": "list", + "bbox": [ + 0.503, + 0.092, + 0.892, + 0.545 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "2613" + } + ] +] \ No newline at end of file diff --git a/2023/Efficient Multimodal Fusion via Interactive Prompting/9f845069-d99b-4851-8fff-d097c545215b_origin.pdf b/2023/Efficient Multimodal Fusion via Interactive Prompting/9f845069-d99b-4851-8fff-d097c545215b_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..0112285aad6700f2880b87fd9bc17b732f66233a --- /dev/null +++ b/2023/Efficient Multimodal Fusion via Interactive Prompting/9f845069-d99b-4851-8fff-d097c545215b_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:e5444a2890b3ec76a7b7130c46a22c1626cb70382395c7d0abd732f6e94d7531 +size 1545888 diff --git a/2023/Efficient Multimodal Fusion via Interactive Prompting/full.md b/2023/Efficient Multimodal Fusion via Interactive Prompting/full.md new file mode 100644 index 0000000000000000000000000000000000000000..d423945f7346fd1a059713089b031eee49e6fe35 --- /dev/null +++ b/2023/Efficient Multimodal Fusion via Interactive Prompting/full.md @@ -0,0 +1,304 @@ +# Efficient Multimodal Fusion via Interactive Prompting + +Ruijie Quan² Linchao Zhu² Yi Yang² + +yaowei.li@uts.edu.au, {quanruijie, zhulinchao, yangyics} @zju.edu.cn + +$^{1}$ ReLER, AAII, University of Technology Sydney $^{2}$ CCAI, Zhejiang University + +# Abstract + +Large-scale pre-training has brought unimodal fields such as computer vision and natural language processing to a new era. Following this trend, the size of multimodal learning models constantly increases, leading to an urgent need to reduce the massive computational cost of finetuning these models for downstream tasks. In this paper, we propose an efficient and flexible multimodal fusion method, namely PMF, tailored for fusing unimodally pretrained transformers. Specifically, we first present a modular multimodal fusion framework that exhibits high flexibility and facilitates mutual interactions among different modalities. In addition, we disentangle vanilla prompts into three types in order to learn different optimizing objectives for multimodal learning. It is also worth noting that we propose to add prompt vectors only on the deep layers of the unimodal transformers, thus significantly reducing the training memory usage. Experiment results show that our proposed method achieves comparable performance to several other multimodal finetuning methods with less than $3\%$ trainable parameters and up to $66\%$ saving of training memory usage. + +# 1. Introduction + +Recent years have witnessed the great success of large-scale pretrained language models [8,31,32] and visual models [6,10,23,39], leading to a surge of pretrained multimodal models [13, 14, 43, 47, 48] trying to align different modalities. Many prior methods utilize finetuning to update the entire set of model parameters for every target cross-modal task. Although finetuning can achieve good performance, it requires a large number of computational costs since the gradients and optimizer states for all parameters of multimodal models have to store. Therefore, it encourages researchers to propose more parameter-efficient methods than finetuning for multimodal learning. + +![](images/b9b1b14be11ecd3b076674817ba71900a4293f010ad306256177e5ba35381571.jpg) +Figure 1. Comparison over three multimodal classification tasks. We compare our proposed PMF and PMF-Large with multiple finetuning (yellow) and prompt-based (purple) methods. The y-axis is the average score of three tasks, and the x-axis is the maximum GPU memory usage during training. + +More recently, prompting tuning [17, 19, 21, 22, 29] is proposed to address this problem by freezing all parameters of a pretrained model while tuning only the continuous prompts. Specifically, it adds trainable continuous prompts to the original token sequences of input data. During training, only the continuous prompts are updated. For multimodal prompt-based learning, a most recent method [20] proposes to disentangle the functionality of the pretrained model which exhibits high flexibility. Although this method significantly reduces the tuned parameters (e.g., less than $0.1\%$ of the pretrained model), there still exists a large performance gap between it and the finetuning-based methods. In addition, this method adopts a sequential modular structure that the pretrained image transformer model is followed by a language transformer model, which causes two main problems in cross-modal learning: a one-way path learn + +ing and a significant increase in the number of model layers. Specifically, a one-way path learning in the multimodal model usually forces one modality to align with others, but not vice versa. In this way, cross-modal learning based on multiple different modalities is not fully explored due to the missing mutual alignments. Since the prompts are added to the token sequences of input data and are updated in the training, they require extensive gradient calculations in the backward propagation which cost numerous memory usages. As a result, this kind of method does not reduce the memory usage during training by much (up to $20\%$ ) though it reduces the number of parameters to update. In other words, this parameter-efficient method still requires massive computational resources which prevents it from being applied to many real-world applications. + +To address these issues, we propose a Prompt-based Multimodal Fusion method with a high memory efficiency, namely PMF. Firstly, we present a new form of modular multimodal fusion framework which demonstrates high flexibility and facilitates a two-way interaction among different modalities. Specifically, we adopt a two-stream structure where the pretrained language model and image model construct the multimodal model in a parallel way. Therefore, tokens of different modalities can learn mutual interactions through a cross-attention-like operation. Such a parallel modular structure brings two benefits. First, unimodal pretraining can be directly utilized for multimodal learning through a parallel combination, eliminating the need for paired multimodal datasets that can be expensive to construct. Also, the type of image or language model can be changed easily (e.g., replacing BERT with T5 for text generation tasks). Furthermore, incorporating extra modalities is made possible based on the parallel modular structure. + +Moreover, we propose to leverage three types of interactive prompts (i.e., query prompts, query context prompts, and fusion context prompts) in order to dynamically learn different objectives for multimodal learning. Intuitively, the query context prompt and query prompt can be seen as a pair of 'questions' and 'answers' with an aim of extracting necessary information for exchange between two modalities. After being translated by a non-linear mapping 'translator', the 'answer' is then delivered to the other modality for better cross-modal understanding. Finally, the fusion context prompts then provide the context to the delivered answer to facilitate the fusion. + +Last but most importantly, PMF is a memory-efficient method that significantly reduces the memory requirements for the large pretrained model. Considering that calculating gradients for prompts for back-propagation is memory-consuming, we propose to add prompts only on the deep layers of the utilized unimodal transformers. Therefore, instead of passing through the entire multimodal model, the backward propagation only needs to pass through the deep + +few transformer layers to reach all trainable parameters, greatly reducing the training memory usage. We conduct extensive experiments to demonstrate the superior of it in our experiments. As a result, PMF enables large pretrained models to be trained on the GPU with a low memory requirement. + +We conduct extensive experiments on three vision-language datasets: UPMC-Food101 [38], MM-IMDB [2], and SNLI-VE [41]. Through comparisons with multiple finetuning and prompt tuning methods (see in Fig. 1), we find that: (1) PMF is the most memory-efficient method for cross-modal learning so far, which reduces the training memory usage by up to $66\%$ compared with finetuning baselines, and by $55\%$ compared with prompt-based methods. (2) PMF can perform comparably compared to prior fine-tuning methods with much fewer trainable parameters (less than $2.5\%$ ) and memory usage. + +Concretely, our contributions are as follows: (1) we present a new form of modular multimodal fusion framework which enables two-way interactions between different modalities and high flexibility of the entire model; (2) we disentangle vanilla prompts into three types of prompts, in order to dynamically learn different objectives for multimodal learning; (3) our proposed method is quite memory-efficient yet is able to achieve comparable performance with existing finetuning methods for multimodal fusion. + +# 2. Related works + +Multimodal Fusion. Multimodal fusion methods aim to simultaneously process the input of different modalities, such as audio-video [27], vision-language [2, 15], and inputs from different types of sensors [42], etc. In this paper, we specifically focus on the fusion of vision-language inputs, though our proposed strategy is compatible with other modality pairs as long as there are unimodally pretrained transformers for these modalities. + +Our work is in line with deep learning-based multimodal fusion strategies [16, 18, 26, 28, 33, 34, 44]. In this line of work, [15] proposed a framework whose vision encoder solely serves as a mapping tool to encode the raw images to the token space of the text encoder. Such an architecture is widely used in the later multimodal fusion research [20, 26, 34]. Differently, [27] used a dual-encoder architecture with bottleneck fusion tokens to exchange information between two encoders for video-audio fusion. Our work has a similar architecture as in [27]. But our proposed method completely freezes the unimodal encoders and uses an interactive prompting technique for more efficient fusion. + +Another important line of multimodal fusion work is through pretraining with the large-scale datasets, mostly achieved by self-supervised learning algorithms [1, 11, 24, 30, 36, 37, 45]. This line of works can be roughly divided into two kinds by their architectures. The first kind has + +
Task TypePretraining TypeMethod
UnimodalUnimodalP-Tuning [22], VPT [12]
UnimodalMultimodalCoOp [47], MAPLE [14]
MultimodalMultimodalPI-VL [13], PTGM [43]
MultimodalUnimodalBlindPrompt [20], PMF
+ +Table 1. Prompt-based methods categorized by model pretraining types and downstream task types. Our proposed PMF falls into the last category which utilize unimodally pretrained transformers for multimodal tasks. + +a dual-encoder structure where image and text are treated separately, such as CLIP [30] and ALIGN [11]. The other kind simultaneously processes the vision and language inputs with cross-attention or self-attention over a longer sequence from two modalities. Our proposed method differs from these self-supervised architectures in that the individual components used in our model are unimodally pretrained with much less data. This difference directly results in a huge performance gap because of the lack of multimodal information in the pretraining stage. However, using unimodally pretrained models enables a much more flexible architecture. It has great potential in multimodal tasks where modality-paired large-scale pretraining data is not available, or when more advanced unimodal encoders are proposed in the future. + +Prompt Tuning. As shown in Tab. 1, prompt-based methods can be roughly divided into four major categories in terms of the modalities of the pretrained model and the downstream tasks. Prompting techniques originally apply on unimodally pretrained transformers for unimodal natural language processing (NLP) tasks [17, 19, 21, 22, 29]. Pretrained GPT-3 can be simply leveraged with handcrafted prompts, which are some manually chosen words preceding the input text [4]. Then [22] and [17] proposed to change the handcrafted prompt to trainable continuous prompts and only update the prompt vectors during the training. Later on, [19] and [29] proposed to use prompt tuning in every hidden layer in the pretrained transformer instead of the input embeddings only. VPT [12] first applied prompt tuning to the vision transformer. + +For methods that prompt multimodally pretrained models for unimodal tasks, many recent works apply prompt tuning to pretrained vision-language models (i.e. CLIP [30]) for unimodal vision tasks [3, 14, 25, 46, 47]. Another type of prompt-based method apply to the multimodal pretrained model for multimodal tasks [13, 43]. [13] adds prompts to an encoder-decoder one-for-all multimodal transformer, achieving comparable performance with finetuning with improved robustness against adversarial attacks. The method used in [13] is simple but effective, showing that prompting methods works well with powerful and com + +plex multimodally pretraining models. + +Our proposed fusion strategy is different from the above methods and falls into the last category where prompts are used to fuse pretrained unimodal models for multimodal tasks. Sharing the same architecture design with [15, 34], [20] uses prompt to align the feature extracted from raw images to the token space of pretrained language model. They achieved comparable performance to several multimodal fusion methods in low-resource settings but underperform fine-tuning baselines by a large margin with full data. Compared with them, our proposed PMF not only is more memory-efficient but can also perform comparably with fine-tuning baselines with full data. + +# 3. Prompt-based Multimodal Fusion + +In this section, we describe our proposed Prompt-based Multimodal Fusion strategy (PMF). We begin by summarising unimodal transformers developed for vision and language tasks in Sec. 3.1. Then we describe the base feature extraction process in Sec. 3.2. Lastly, we give a detailed description of how PMF integrates two unimodal transformer layers into a multimodal one via interactive prompting in Sec. 3.3. + +# 3.1. Unimodal Transformers + +Vision Transformer (ViT) [9] adapts the Transformer [35] architecture with minimum modifications. The RGB image input $\mathbf{x}_{img} \in \mathbb{R}^{h,w,c}$ is first cut into $N_{img}$ nonoverlapping patches and then linearly projected into a sequence of embeddings $\mathbf{z}$ with each $z_i \in \mathbb{R}^d$ . Differently, the language Transformer first tokenizes raw text to $N_{txt}$ one-hot word embeddings and then converted these discrete vectors into a sequence of $N_{txt}$ continuous embeddings. The resulting continuous embedding for both Language Transformer and Vision Transformer share the same structure as follows: + +$$ +\mathbf {z} = \left[ \mathrm {C L S}, z _ {1}, z _ {2}, \dots , z _ {N} \right] \tag {1} +$$ + +where CLS is a special token prepended to the sequence so that its representation at the final layer can be used as the representation of the whole sequence for classification. Please note that the two unimodal transformers have different CLS tokens. The continuous embedding $\mathbf{z}$ is then fed into a transformer encoder which consists of $L$ transformer layers. For each transformer layer, the input passes through modules including multi-head self-attention, layer normalization, multilayer perceptron, and finally added to the original input with a residual connection. + +# 3.2. Unimodal Base feature Extraction + +As shown in Fig. 2, the image and text inputs are first processed and fed into the unimodal transformer layers to + +![](images/a7d913cdf02b214f352ce6e81dd4e3b0f695c412a27d26cef071273ec05f4d01.jpg) +Figure 2. Prompt-based multimodal fusion strategy (PMF) applied to vision-language inputs. In the forward propagation, image and text inputs are first embedded into continuous token sequences and fed to the unimodal transformer layers for base feature extraction. The base features from both modalities then pass through multiple prompt-based multimodal fusion layers to get the feature of two CLS tokens for final classification. In the backward propagation, only multimodal fusion layers take part in the calculation of gradients, greatly saving memory usage during training. All pretrained parameters in both transformers are frozen during the training. + +extract base features, respectively. At this stage, each encoder works exactly the same as they did in unimodal tasks. Here we denote the starting fusion layer as $L_{f}$ . And the base feature extraction of each encoder can be denoted as: + +$$ +\mathbf {z} ^ {l + 1} = \operatorname {T r a n s L a y e r} ^ {l} \left(\mathbf {z} ^ {l}; \theta\right) \quad \text {i f} l < L _ {f} \tag {2} +$$ + +where $\theta$ stands for the pretrained parameters. A smaller $L_{f}$ leads to an earlier fusion and a larger $L_{f}$ leads to a later fusion. A detailed discussion of the impact brought by different $L_{f}$ can be found in Sec. 4.5. + +# 3.3. Multimodal Fusion Layer + +The extracted unimodal base features are then passed through multiple multimodal fusion layers, each consisting of a 'querying stage' and a 'fusion stage', as shown in Fig. 3. The querying stage focus on the extraction of what is necessary to pass, and the fusion stage focus on fusing the extracted information delivered from the other modality. + +This two-stage setting makes the vanilla prompt training entangled with different learning objectives. Therefore, we propose to decouple the vanilla prompts into three kinds: 'query prompt' (QP, denoted $\mathbf{z}_{qp}$ ), 'query context prompt' (QCP, denoted $\mathbf{z}_{qcp}$ ), and 'fusion context prompt' (FCP, denoted $\mathbf{z}_{fcp}$ ) to dynamically learn different objectives for multimodal learning. According to the modality where prompts are used, each kind of prompt can be further specified as $\mathbf{z}_*$ and $\mathbf{z}_*$ to distinguish from each other (e.g. $\mathbf{z}_{fcp}$ and $\mathbf{z}_{fcp}^{\prime}$ ). + +As shown in Fig. 3, QP and QCP are used in the querying stage and the FCP is used in the fusion stage. As suggested by their names, QP is to query information from the unimodal input sequence, QCP is to help this process by pro + +viding extra context to the query. QP and QCP like a pair of 'questions' and 'answers', translated by the non-linear mapping. As for FCP, it is responsible for providing the context to the fusion in the fusion stage. We now introduce how these three kinds of prompts interact with each other in the two stages of each multimodal fusion layer. + +Querying Stage. We first concatenate corresponding QP and QCP to the input sequence $\mathbf{z}$ . The resulting input sequence after the concatenation is: + +$$ +[ \mathbf {z} ^ {l} | | \mathbf {z} _ {q c p} ^ {l} | | \mathbf {z} _ {q p} ^ {l} ] \tag {3} +$$ + +where $| \cdot |$ denotes the concatenation operation. Then we feed the concatenated sequence to the unimodal transformer layer, which can be denoted as: + +$$ +[ \hat {\mathbf {z}} ^ {l} | | \hat {\mathbf {z}} _ {q c p} ^ {l} | | \hat {\mathbf {z}} _ {q p} ^ {l} ] = \mathrm {T r a n s L a y e r} ^ {l} ([ \mathbf {z} ^ {l} | | \mathbf {z} _ {q c p} ^ {l} | | \mathbf {z} _ {q p} ^ {l} ]; \theta) \quad (4) +$$ + +After the forward propagation, the output of QP $\hat{\mathbf{z}}_{qp}^{l}$ is extracted as the queried information to be used in the following fusion operations. It should be noted that though $\hat{\mathbf{z}}_{qcp}^{l}$ will not be used in the following fusion operations, it has played an important role by providing the context of query in the querying stage. + +The queried fusion intermediate $\hat{\mathbf{z}}_{qp}^{l}$ is then mapped to the representation space of the other modality through a non-linear mapping function: + +$$ +\mathbf {y} _ {q p} ^ {l} = f ^ {l} \left(\hat {\mathbf {z}} _ {q p} ^ {l}\right) \tag {5} +$$ + +where $f$ is a non-linear mapping function. Specifically, a mapping function consists of two linear layers with a bottleneck structure to reduce dimension and only the first linear layer has a ReLu function. Each fusion layer $l$ has two + +![](images/0c0ac5fefaa70d253a2f34dbef34929ab93671ec95dfc5775f2fc7f60cb07a17.jpg) +Figure 3. Prompt-based multimodal fusion layer. We propose to use three kinds of interactive prompts to achieve the fusion/exchange of information from two modalities. We use 'query prompt' $(\mathrm{z}_{qp},\mathrm{z}_{qp}^{\prime})$ and 'query context prompt' $(\mathrm{z}_{qcp},\mathrm{z}_{qcp}^{\prime})$ in the querying stage to extract what is necessary, after a non-linear mapping, the extracted information is then fused to the other modality with the help of 'fusion context prompt' $(\mathrm{z}_{fcp},\mathrm{z}_{fcp}^{\prime})$ in the fusion stage. Yellow and green elements stand for language and vision modalities, respectively. Red boxes indicate trainable modules. + +mapping functions $f^l$ and $f'^l$ , building a two-way interaction among different modalities. Note that the non-linear mapping functions contain more than $95\%$ of the trainable parameters in PMF. + +Fusion Stage. We first concatenate the mapped fusion intermediates $\mathbf{y}_{qp}^{l}$ to the original input sequence $\mathbf{z}^{\prime l}$ and FCP $\mathbf{z}_{fcp}^{\prime l}$ of the other modality. Then we feed the concatenated sequence to the unimodal transformer layer of the other modality to complete a one-way fusion. These two processes can be together denoted as: + +$$ +[ \mathbf {z} ^ {\prime l + 1} | | \hat {\mathbf {z}} _ {f c p} ^ {\prime l} | | \hat {\mathbf {y}} _ {q p} ^ {l} ] = \operatorname {T r a n s L a y e r} ^ {l} ([ \mathbf {z} ^ {\prime l} | | \mathbf {z} _ {f c p} ^ {\prime l} | | \mathbf {y} _ {q p} ^ {l} ]; \theta^ {\prime}) \tag {6} +$$ + +where $[\ast ]'$ means $[\ast ]$ from the other modality. + +Finally, the output of two unimodal transformer layers $\mathbf{z}^{l + 1}$ and $\mathbf{z}^{\prime l + 1}$ are together as the output of the multimodal fusion layer and fed to the higher layers. The entire multimodal fusion process can be concluded as: + +$$ +[ \mathbf {z} ^ {l + 1} | | \mathbf {z} ^ {\prime l + 1} ] = \text {F u s i o n L a y e r} ^ {l} ([ \mathbf {z} ^ {l} | | \mathbf {z} ^ {\prime l} ]; \theta , \theta^ {\prime}) \quad \text {i f} L _ {f} \leq l \tag {7} +$$ + +After the multimodal fusion is complete, we take the output representation of CLS token $z_{CLS}^{L}$ and $z_{CLS}^{\prime L}$ to two different linear classifiers and average the pre-softmax logits for classification. Mathematically, such a classifier setting is equivalent to feeding the classifier with the concatenated features when a linear classifier is used, except for a different scale of gradient caused by the averaging operation. + +# 4. Experiments + +In this section, we analyze the performance of our proposed PMF on three multimodal datasets and aim to answer the following questions: (1) How efficient is the PMF and does PMF perform well (Sec. 4.4)? (2) What factors affect the effectiveness of PMF (Sec. 4.5)? In addition, we explore the PMF equipped with larger transformers and its impact brought to the performance and memory efficiency in + +Sec. 4.6. Lastly, we introduce a Neural Architecture Search (NAS) method to automatically search for the preferable fusion structure for PMF in Sec. 4.7. + +# 4.1. Datasets and Metrics + +UPMC Food-101 [38] is a multimodal classification dataset, which contains food images with textual recipe descriptions for 101 kinds of food. UPMC Food-101 contains a total of 90,840 image-text pairs with a size range between 790 and 956 pairs for different classes. As the dataset only has training and testing sets, we follow [15] and create a validation split of 5000 samples from the training set. + +MM-IMDB [2] is a multimodal multi-label classification dataset, which contains movie plot outlines and movie posters. The task is to predict the genre of movies. This dataset contains 25,956 image-text pairs for 23 classes with a long-tail distribution. + +SNLI-VE [41] is a multimodal classification dataset for the visual entailment tasks, which is to reason about the relationship between an image premise and a text hypothesis into entailment, contradiction, or neutrality. SNLI-VE contains a total of 565,286 image-text pairs. Please note that we only use image premise and text hypothesis in the input, which is different from the settings in some other papers where text premises are also used in the inputs [43]. + +We report accuracy for UPMC Food-101 and SNLI-VE, and Macro/Micro-F1 scores for MM-IMDB as metrics. + +# 4.2. Existing Methods and Baselines + +We report the performance of several baselines and existing methods. First, we report the performance of finetuning unimodal models (i.e. BERT [8], ViT [9]) to verify the effectiveness of multimodal fusion. Specifically, we take the output representation of CLS token of the last layer in ViT and BERT, and feed it into a linear classifier. We also report the performance of VPT [12] and a prompt-based BERT (denoted P-BERT) for a better comparison. For VPT + +
MethodUpdated Param. (Million)Memory Usage (GB) Train/InferenceSNLI-VEFood-101MM-IMDBAvg.
Linear-3.76 / 3.2350.0578.9649.76 / 56.8360.77
ViT86.59.36 / 1.9933.3374.6938.39 / 49.8850.72
BERT109.030.82 / 2.7969.8287.4458.91 / 64.3172.96
LateConcat196.038.54 / 3.3670.0193.2959.56 / 64.9275.18
MMBT*196.537.87 / 3.4874.6994.1060.80 / 66.1077.41
MBT*196.038.00 / 4.0674.0293.5659.60 / 64.8176.60
VPT-6.12 / 2.0133.3372.5535.22 / 44.4948.58
P-BERT-28.13 / 2.9963.2881.0748.67 / 54.5865.33
PromptFuse-29.57 / 3.5564.5382.2148.59 / 54.4966.09
BlindPrompt-29.57 / 3.6565.5484.5650.18 / 56.4667.81
P-LateConcat0.330.82 / 3.4363.0589.0353.91 / 59.9369.67
P-MMBT0.930.90 / 3.4867.5886.5852.95 / 59.3070.10
PMF (M=4, Lf=10)2.512.84 / 4.0871.9291.5158.77 / 64.5175.02
PMF-large (M=4, Lf=22)4.518.44 / 6.4272.1091.6861.66 / 66.7275.99
+ +Table 2. Multimodal classification performance. PMF achieve comparable performance to the finetuning baselines with less than $3\%$ of trainable parameters and up to $66\%$ of training memory usage. MM-IMDB is F1-Macro / F1-Micro, others are accuracy. We report the maximum memory usage in training and evaluating UPMC Food-101 for each method. We report mean performance over 3 runs with different random seeds. \* means trainable parameter less than $0.1\mathrm{M}$ . PMF-Large uses bert-large and vit-large models (24 hidden layers) while others use bert-base and vit-base models (12 hidden layers). $M$ is the prompt length and $L_{f}$ is the starting fusion layer. + +and P-BERT, the input sequence to each transformer layer is concatenated with a prompt vector, whose length is set to 10. And the concatenated prompt vectors and the final linear classifier are the only updated modules in training. + +In addition, we compare against a strong baseline method which concatenates the output features of CLS tokens of ViT and BERT, and feed the concatenated feature to a linear classifier, denoted as LateConcat. In this case, the input to the classifier is $(768 + 768)$ -dimensional. Besides, we also introduce Linear, which shares the same architecture with LateConcat with the only difference in the updated modules. Linear only updates the linear classifier while LateConcat updates all parameters during training. + +We reimplement MMBT (denoted $\mathbf{MMBT}^*$ ) [15] and MBT (denoted $\mathbf{MBT}^*$ ) [27] with a vit-base model as the vision encoder and a bert-base model as the text encoder for fair and controlled comparison. We set the fusion layer $L_{f} = 8$ and use 4 fusion tokens in MBT as recommended in the original paper. + +We also propose a prompt-based MMBT and a prompt-based LateConcat, denoted as P-MMBT and P-LateConcat, respectively. In P-MMBT and P-LateConcat, we apply deep prompt tuning on both vision and language encoders, which are pretrained backbones with frozen parameters during training. We set the prompt length in each layer of two encoders to 10, totalling 240 prompt vectors. Similar to VPT and P-BERT, P-LateConcat only updates the final linear classifier and prompt vectors during training. Compared with P-LateConcat, P-MMBT have an extra + +linear projection layer and a smaller linear classifier to train. + +Lastly, we report the performance of PromptFuse and BlindPrompt [20], both proposed in the only existing paper which leverages unimodally pretrained models for multimodal fusion through prompting. We set the prompt length to 20 as recommended in the original paper. + +# 4.3. Implementation Details + +Pretrained Backbone and Initialization. Unless otherwise noted, we use an ImageNet-21k [7] pretrained vit-base model for the vision encoder and a bert-base-uncased model for the language encoder in all experiments. All pretrained checkpoints are from huggingface [40]. All prompt vectors are initialized through a Gaussian distribution (mean=0, std=0.02). + +Network Training. We use SGD optimizer in all experiments with momentum set to 0.9 and weight decay set to $1e^{-4}$ . The batch size is set to 64 for SNLI-VE, and 32 for UPMC Food-101 and MM-IMDB. Cross entropy loss is applied in all experiments and the class labels are weighted by their inverse frequency for UPMC Food-101 and MM-IMDB. More details are in the supplementary material. + +# 4.4. Main Results + +PMF is most memory-efficient. As shown in Tab. 2, PMF is the most memory-efficient multimodal fusion model of all existing prompt-based methods and baselines. PMF can save up to $66\%$ of training memory usage compared with finetuning baselines. Even compared with the existing most + +
QPMappingfQCPFCPMM-IMDB
48.80/56.38
✓45.38/53.34
✓43.56/51.43
✓✓54.92/62.25
✓✓✓57.98/63.69
✓✓✓58.30/64.07
✓✓✓58.34/64.15
✓✓✓✓58.63/64.23
+ +Table 3. PMF Component Ablation. There are four types of trainable modules in our proposed PMF. We set the fusion layer $L_{f} = 10$ and add different components one at a time to see their individual impact. All prompts with $\checkmark$ have a length of 4, and prompts with $\checkmark \checkmark$ have a length of 8. + +![](images/04ca90815f5c5c93ede716f7afd0a25e5fe0ca577a3b848ad1df46dbab44461f.jpg) +Figure 4. Model Performance and Training Memory Usage under different fusion layers $L_{f}$ . We set the prompt length $M = 4$ for every prompt vector with different fusion layer $L_{f} = 0,2,4,6,8,10,12$ . + +memory-efficient prompt-based multimodal method, PMF still saves an extra of more than $50\%$ of training memory. + +PMF outperforms all existing prompt-based methods. With the same pretrained unimodal transformers, prompt-based methods underperform the full finetuning methods by a large margin. Some prompt-based methods even underperform unimodal finetuning baselines. Our proposed PMF achieves the best performance among all prompt-based methods. Especially, PMF outperforms all unimodal baselines in all experiments, showing that the two modalities are successfully fused. + +PMF is competitive with finetuning baselines. Tab. 2 shows that PMF achieves comparable performance with full finetuning baselines with less than $3\%$ trainable parameters while saving $66\%$ of memory cost, significantly narrowing the gap between finetuning and prompt-based methods. Furthermore, PMF even outperforms the finetuning LateConcat when equipped with larger transformers (i.e. bert-large and vit-large). + +![](images/dbcf0106de26c140db5f3f399107438285fca6c2fbb26fc40a0dd8c648b380d7.jpg) +Figure 5. Model Performance and Training Memory Usage under different prompt length $M$ . We fix the fusion layer $L_{f} = 10$ and study 1, 4, 8, 16, and 32 tokens for each prompt vector. + +# 4.5. Ablation Study + +In this section, we investigate the impact of different factors in our proposed fusion strategy. All experiments in this section are conducted on the MM-IMDB dataset. + +Components Ablation. We verify the effectiveness of three kinds of prompts and the non-linear mapping function in this section. The results are shown in Tab. 3. The first row without any components in PMF is equivalent to the Linear model introduced in Sec. 4.2. The comparison between the first three rows shows that merely prompting the top layers of the two transformers not only cannot achieve multimodal fusion. Oppositely, it will disturb the feature space of two transformers, which finally hurts the performance. Though the mapping functions give the biggest boost to the performance, it should be noted that the mapping functions $f$ cannot work without QP querying the fusion intermediates. + +In addition, the comparison between the last four rows shows that decoupling the prompts into three individual modules with different learning objectives brings a performance gain. More specifically, the comparison between the fifth and sixth row in Tab. 3 shows that an extended QP cannot replace QCP. Since only the output of QP tokens are fused to the other modality while that of QCP discarded, replacing QCP with a longer QP not only increases the computation as the sequences in the fusion stage are longer but also results in a damaged performance. As a result, every module introduced in PMF contributes to the quality of multimodal fusion. The missing of any of the four modules will bring a performance drop at different scales. + +Fusion Layer. We now investigate impacts brought by different fusion layers $L_{f}$ to the fusion performance and memory efficiency. The results are summarized in Fig. 4. As can be seen in the figure, the training memory usage keeps decreasing as the fusion starts later. However, the performance of the fusion model is relatively consistent with $L_{f} \leq 10$ . Therefore, adding prompts only on the deep layers $(10 < l < L)$ is empirically better for the trade-off between performance and memory efficiency. + +
Text EncoderImage EncoderMemory Usage Train/InferenceMM-IMDB
bert-basevit-base12.84 / 4.0858.77 / 64.51
bert-basevit-large14.16 / 4.8959.70 / 65.20
bert-largevit-base17.17 / 5.5360.08 / 65.41
bert-largevit-large18.44 / 6.4261.66 / 66.72
+ +Table 4. Comparison of PMF applying to different unimodal transformers. We set the fusion layer $L_{f} = L - 2$ and prompt length $M = 4$ in all experiments. MM-IMDB is reported with F1-Macro / F1-Micro. + +
Training MemorySNLI-VEFood-101MM-IMDBAvg.
33.36 GB72.2792.159.67 / 65.5775.66
+ +Table 5. Performance of PMF applied with NAS. MM-IMDB is F1-Macro / F1-Micro, others are accuracy. We only report the training memory usage. + +Prompt Length. The ablation study on prompt length is carried out with three kinds of prompts set to have the same length (i.e. $M_{qp} = M_{qcp} = M_{fcp}$ ). Fig. 5 summarizes the results. The performance increases as the prompt length grows longer when $M \leq 16$ , and drops when the prompts are too long ( $M = 32$ ). It should be stressed that the training memory usage only increases around 1 GB as the prompt length grows from 1 to 16, which means the fusion layer $L_f$ is the major factor of the training memory usage instead of prompt length. + +# 4.6. Modularity and Flexibility + +PMF is highly modular, which means it is trivial to replace the unimodal transformers when there are better ones. In this section, we first describe how to replace the unimodal transformer and then show the benefits of such flexibility through experiments with larger pretrained models. + +Since the total transformer layers, $L_{img}$ and $L_{txt}$ of each unimodal transformer are now different, the unimodal base features of two modalities now take different layers to extract, and the number of remaining layers for fusion stays the same. Simply, the fusion layers $L_{f}$ of two transformers can be further specified as $L_{f - img} = L_{img} - 2$ and $L_{f - txt} = L_{txt} - 2$ . In addition, the difference between different hidden dimensions $d$ is automatically handled by the non-linear mapping functions $f$ . + +The results shown in Tab. 4 clearly demonstrate that PMF can be empowered by larger unimodal transformers with a very limited increase of training memory usage. + +# 4.7. PMF with NAS + +The hyper-parameters introduced in the proposed PMF are fusion layer $L_{f}$ and prompt length $M$ . Although PMF works well without exhausting hyper-parameter tuning, it is still preferable to have specific settings for every different task and data distribution. In this section, we experiment with automatic fusion structure search via AutoFormer [5]. A detailed description of the search space and evolution search can be found in the supplementary material. + +Tab. 5 shows the performance of NAS-applied PMF on three datasets. With an increase in training memory usage, PMF-NAS achieves better results than regular PMF with the same vision and language encoders, greatly reducing the workload of finding the preferable fusion structure. + +# 5. Limitations and Future Works + +The first limitation is that PMF's performance on three datasets is still behind finetuning baselines with the same pretrained backbones, indicating more work developing prompt-based methods to fully leverage the knowledge inside the pretrained models in the future, finally achieving equivalent or surpassing results through prompting. + +The second limitation is about the hyper-parameters tuning: It is preferable to decouple prompts into three kinds by their roles in multimodal fusion. However, it also brings more work to hyper-parameter tuning if someone is expecting the best results via an optimal fusion structure. + +Our future research endeavours will involve further investigation of the PMF in diverse multimodal understanding tasks such as Visual Question Answering, utilizing various model architectures. + +# 6. Conclusion + +We propose a new form of modular multimodal fusion framework which demonstrates high flexibility and facilitates a two-way interaction among different modalities, namely PMF. PMF leverages three types of interactive prompts in order to dynamically learn different objectives for multimodal learning. By adding the prompts only on the deep layers of utilized unimodal transformers, PMF can significantly reduce the memory usage of the gradient calculation in the backward propagation. Through extensive experiments, we demonstrate that PMF is quite memory-efficient and yet able to perform comparably with existing finetuning baselines. + +# 7. Acknowledgement + +This work was supported in part by the Australian Research Council (ARC) under Grant DP200100938. + +# References + +[1] Jean-Baptiste Alayrac, Jeff Donahue, Pauline Luc, Antoine Miech, Iain Barr, Yana Hasson, Karel Lenc, Arthur Mensch, Katie Millican, Malcolm Reynolds, et al. 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In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 14733-14743, 2022. 2 +[38] Xin Wang, Devinder Kumar, Nicolas Thome, Matthieu Cord, and Frederic Precioso. Recipe recognition with large multimodal food dataset. In 2015 IEEE International Conference on Multimedia & Expo Workshops (ICMEW), pages 1-6. IEEE, 2015. 2, 5 +[39] Zejia Weng, Xitong Yang, Ang Li, Zuxuan Wu, and Yu-Gang Jiang. Semi-supervised vision transformers. In ECCV, 2022. 1 +[40] Thomas Wolf, Lysandre Debut, Victor Sanh, Julien Chau-mond, Clement Delangue, Anthony Moi, Pierrick Cistac, Tim Rault, Rémi Louf, Morgan Funtowicz, et al. Transformers: State-of-the-art natural language processing. In Proceedings of the 2020 conference on empirical methods in natural language processing: system demonstrations, pages 38-45, 2020. 6 + +[41] Ning Xie, Farley Lai, Derek Doran, and Asim Kadav. Visual entailment: A novel task for fine-grained image understanding. arXiv preprint arXiv:1901.06706, 2019. 2, 5 +[42] Ning Xiong and Per Svensson. Multi-sensor management for information fusion: issues and approaches. Information fusion, 3(2):163-186, 2002. 2 +[43] Hao Yang, Junyang Lin, An Yang, Peng Wang, Chang Zhou, and Hongxia Yang. Prompt tuning for generative multimodal pretrained models. arXiv preprint arXiv:2208.02532, 2022. 1, 3, 5 +[44] Yi Yang, Yueting Zhuang, and Yunhe Pan. Multiple knowledge representation for big data artificial intelligence: framework, applications, and case studies. Frontiers of Information Technology & Electronic Engineering, 22(12):1551-1558, 2021. 2 +[45] Jiahui Yu, Zirui Wang, Vijay Vasudevan, Legg Yeung, Mojtaba Seyhedhosseini, and Yonghui Wu. Coca: Contrastive captioners are image-text foundation models. arXiv preprint arXiv:2205.01917, 2022. 2 +[46] Kaiyang Zhou, Jingkang Yang, Chen Change Loy, and Ziwei Liu. Conditional prompt learning for vision-language models. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 16816-16825, 2022. 3 +[47] Kaiyang Zhou, Jingkang Yang, Chen Change Loy, and Ziwei Liu. Learning to prompt for vision-language models. International Journal of Computer Vision, 130(9):2337-2348, 2022. 1, 3 +[48] Linchao Zhu and Yi Yang. Actbert: Learning global-local video-text representations. In Proceedings of the IEEE/CVF conference on computer vision and pattern recognition, pages 8746-8755, 2020. 1 \ No newline at end of file diff --git a/2023/Efficient Multimodal Fusion via Interactive Prompting/images.zip b/2023/Efficient Multimodal Fusion via Interactive Prompting/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..d26c94b298ff5913b2bfc6be9dc712195964c397 --- /dev/null +++ b/2023/Efficient Multimodal Fusion via Interactive Prompting/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:d31de48c67d5b76a4dc097828ee3afe57e84170748be34986a5c5f6b2b0c6593 +size 450744 diff --git a/2023/Efficient Multimodal Fusion via Interactive Prompting/layout.json b/2023/Efficient Multimodal Fusion via Interactive Prompting/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..f47fd96494f69cee38e5a779f2b1ae012853f6df --- /dev/null +++ b/2023/Efficient Multimodal Fusion via Interactive Prompting/layout.json @@ -0,0 +1,8140 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 127, + 103, + 467, + 121 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 127, + 103, + 467, + 121 + ], + "spans": [ + { + "bbox": [ + 127, + 103, + 467, + 121 + ], + "type": "text", + "content": "Efficient Multimodal Fusion via Interactive Prompting" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 123, + 141, + 471, + 158 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 123, + 141, + 471, + 158 + ], + "spans": [ + { + "bbox": [ + 123, + 141, + 471, + 158 + ], + "type": "text", + "content": "Ruijie Quan² Linchao Zhu² Yi Yang²" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 126, + 177, + 468, + 193 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 126, + 177, + 468, + 193 + ], + "spans": [ + { + "bbox": [ + 126, + 177, + 468, + 193 + ], + "type": "text", + "content": "yaowei.li@uts.edu.au, {quanruijie, zhulinchao, yangyics} @zju.edu.cn" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 175, + 196, + 419, + 226 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 175, + 196, + 419, + 226 + ], + "spans": [ + { + "bbox": [ + 175, + 196, + 419, + 226 + ], + "type": "inline_equation", + "content": "^{1}" + }, + { + "bbox": [ + 175, + 196, + 419, + 226 + ], + "type": "text", + "content": " ReLER, AAII, University of Technology Sydney " + }, + { + "bbox": [ + 175, + 196, + 419, + 226 + ], + "type": "inline_equation", + "content": "^{2}" + }, + { + "bbox": [ + 175, + 196, + 419, + 226 + ], + "type": "text", + "content": " CCAI, Zhejiang University" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 143, + 252, + 192, + 265 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 252, + 192, + 265 + ], + "spans": [ + { + "bbox": [ + 143, + 252, + 192, + 265 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 277, + 290, + 529 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 277, + 290, + 529 + ], + "spans": [ + { + "bbox": [ + 46, + 277, + 290, + 529 + ], + "type": "text", + "content": "Large-scale pre-training has brought unimodal fields such as computer vision and natural language processing to a new era. Following this trend, the size of multimodal learning models constantly increases, leading to an urgent need to reduce the massive computational cost of finetuning these models for downstream tasks. In this paper, we propose an efficient and flexible multimodal fusion method, namely PMF, tailored for fusing unimodally pretrained transformers. Specifically, we first present a modular multimodal fusion framework that exhibits high flexibility and facilitates mutual interactions among different modalities. In addition, we disentangle vanilla prompts into three types in order to learn different optimizing objectives for multimodal learning. It is also worth noting that we propose to add prompt vectors only on the deep layers of the unimodal transformers, thus significantly reducing the training memory usage. Experiment results show that our proposed method achieves comparable performance to several other multimodal finetuning methods with less than " + }, + { + "bbox": [ + 46, + 277, + 290, + 529 + ], + "type": "inline_equation", + "content": "3\\%" + }, + { + "bbox": [ + 46, + 277, + 290, + 529 + ], + "type": "text", + "content": " trainable parameters and up to " + }, + { + "bbox": [ + 46, + 277, + 290, + 529 + ], + "type": "inline_equation", + "content": "66\\%" + }, + { + "bbox": [ + 46, + 277, + 290, + 529 + ], + "type": "text", + "content": " saving of training memory usage." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 549, + 128, + 562 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 549, + 128, + 562 + ], + "spans": [ + { + "bbox": [ + 47, + 549, + 128, + 562 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 570, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 570, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 570, + 288, + 714 + ], + "type": "text", + "content": "Recent years have witnessed the great success of large-scale pretrained language models [8,31,32] and visual models [6,10,23,39], leading to a surge of pretrained multimodal models [13, 14, 43, 47, 48] trying to align different modalities. Many prior methods utilize finetuning to update the entire set of model parameters for every target cross-modal task. Although finetuning can achieve good performance, it requires a large number of computational costs since the gradients and optimizer states for all parameters of multimodal models have to store. Therefore, it encourages researchers to propose more parameter-efficient methods than finetuning for multimodal learning." + } + ] + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 310, + 255, + 544, + 432 + ], + "blocks": [ + { + "bbox": [ + 310, + 255, + 544, + 432 + ], + "lines": [ + { + "bbox": [ + 310, + 255, + 544, + 432 + ], + "spans": [ + { + "bbox": [ + 310, + 255, + 544, + 432 + ], + "type": "image", + "image_path": "b9b1b14be11ecd3b076674817ba71900a4293f010ad306256177e5ba35381571.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 443, + 547, + 499 + ], + "lines": [ + { + "bbox": [ + 305, + 443, + 547, + 499 + ], + "spans": [ + { + "bbox": [ + 305, + 443, + 547, + 499 + ], + "type": "text", + "content": "Figure 1. Comparison over three multimodal classification tasks. We compare our proposed PMF and PMF-Large with multiple finetuning (yellow) and prompt-based (purple) methods. The y-axis is the average score of three tasks, and the x-axis is the maximum GPU memory usage during training." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 521, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 521, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 521, + 547, + 715 + ], + "type": "text", + "content": "More recently, prompting tuning [17, 19, 21, 22, 29] is proposed to address this problem by freezing all parameters of a pretrained model while tuning only the continuous prompts. Specifically, it adds trainable continuous prompts to the original token sequences of input data. During training, only the continuous prompts are updated. For multimodal prompt-based learning, a most recent method [20] proposes to disentangle the functionality of the pretrained model which exhibits high flexibility. Although this method significantly reduces the tuned parameters (e.g., less than " + }, + { + "bbox": [ + 304, + 521, + 547, + 715 + ], + "type": "inline_equation", + "content": "0.1\\%" + }, + { + "bbox": [ + 304, + 521, + 547, + 715 + ], + "type": "text", + "content": " of the pretrained model), there still exists a large performance gap between it and the finetuning-based methods. In addition, this method adopts a sequential modular structure that the pretrained image transformer model is followed by a language transformer model, which causes two main problems in cross-modal learning: a one-way path learn" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "2604" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 252 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 252 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 252 + ], + "type": "text", + "content": "ing and a significant increase in the number of model layers. Specifically, a one-way path learning in the multimodal model usually forces one modality to align with others, but not vice versa. In this way, cross-modal learning based on multiple different modalities is not fully explored due to the missing mutual alignments. Since the prompts are added to the token sequences of input data and are updated in the training, they require extensive gradient calculations in the backward propagation which cost numerous memory usages. As a result, this kind of method does not reduce the memory usage during training by much (up to " + }, + { + "bbox": [ + 46, + 72, + 289, + 252 + ], + "type": "inline_equation", + "content": "20\\%" + }, + { + "bbox": [ + 46, + 72, + 289, + 252 + ], + "type": "text", + "content": ") though it reduces the number of parameters to update. In other words, this parameter-efficient method still requires massive computational resources which prevents it from being applied to many real-world applications." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 254, + 289, + 470 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 254, + 289, + 470 + ], + "spans": [ + { + "bbox": [ + 46, + 254, + 289, + 470 + ], + "type": "text", + "content": "To address these issues, we propose a Prompt-based Multimodal Fusion method with a high memory efficiency, namely PMF. Firstly, we present a new form of modular multimodal fusion framework which demonstrates high flexibility and facilitates a two-way interaction among different modalities. Specifically, we adopt a two-stream structure where the pretrained language model and image model construct the multimodal model in a parallel way. Therefore, tokens of different modalities can learn mutual interactions through a cross-attention-like operation. Such a parallel modular structure brings two benefits. First, unimodal pretraining can be directly utilized for multimodal learning through a parallel combination, eliminating the need for paired multimodal datasets that can be expensive to construct. Also, the type of image or language model can be changed easily (e.g., replacing BERT with T5 for text generation tasks). Furthermore, incorporating extra modalities is made possible based on the parallel modular structure." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 472, + 289, + 616 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 472, + 289, + 616 + ], + "spans": [ + { + "bbox": [ + 46, + 472, + 289, + 616 + ], + "type": "text", + "content": "Moreover, we propose to leverage three types of interactive prompts (i.e., query prompts, query context prompts, and fusion context prompts) in order to dynamically learn different objectives for multimodal learning. Intuitively, the query context prompt and query prompt can be seen as a pair of 'questions' and 'answers' with an aim of extracting necessary information for exchange between two modalities. After being translated by a non-linear mapping 'translator', the 'answer' is then delivered to the other modality for better cross-modal understanding. Finally, the fusion context prompts then provide the context to the delivered answer to facilitate the fusion." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 617, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 617, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 617, + 289, + 715 + ], + "type": "text", + "content": "Last but most importantly, PMF is a memory-efficient method that significantly reduces the memory requirements for the large pretrained model. Considering that calculating gradients for prompts for back-propagation is memory-consuming, we propose to add prompts only on the deep layers of the utilized unimodal transformers. Therefore, instead of passing through the entire multimodal model, the backward propagation only needs to pass through the deep" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 304, + 72, + 547, + 144 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 144 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 144 + ], + "type": "text", + "content": "few transformer layers to reach all trainable parameters, greatly reducing the training memory usage. We conduct extensive experiments to demonstrate the superior of it in our experiments. As a result, PMF enables large pretrained models to be trained on the GPU with a low memory requirement." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 144, + 547, + 276 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 144, + 547, + 276 + ], + "spans": [ + { + "bbox": [ + 304, + 144, + 547, + 276 + ], + "type": "text", + "content": "We conduct extensive experiments on three vision-language datasets: UPMC-Food101 [38], MM-IMDB [2], and SNLI-VE [41]. Through comparisons with multiple finetuning and prompt tuning methods (see in Fig. 1), we find that: (1) PMF is the most memory-efficient method for cross-modal learning so far, which reduces the training memory usage by up to " + }, + { + "bbox": [ + 304, + 144, + 547, + 276 + ], + "type": "inline_equation", + "content": "66\\%" + }, + { + "bbox": [ + 304, + 144, + 547, + 276 + ], + "type": "text", + "content": " compared with finetuning baselines, and by " + }, + { + "bbox": [ + 304, + 144, + 547, + 276 + ], + "type": "inline_equation", + "content": "55\\%" + }, + { + "bbox": [ + 304, + 144, + 547, + 276 + ], + "type": "text", + "content": " compared with prompt-based methods. (2) PMF can perform comparably compared to prior fine-tuning methods with much fewer trainable parameters (less than " + }, + { + "bbox": [ + 304, + 144, + 547, + 276 + ], + "type": "inline_equation", + "content": "2.5\\%" + }, + { + "bbox": [ + 304, + 144, + 547, + 276 + ], + "type": "text", + "content": ") and memory usage." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 276, + 547, + 384 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 276, + 547, + 384 + ], + "spans": [ + { + "bbox": [ + 304, + 276, + 547, + 384 + ], + "type": "text", + "content": "Concretely, our contributions are as follows: (1) we present a new form of modular multimodal fusion framework which enables two-way interactions between different modalities and high flexibility of the entire model; (2) we disentangle vanilla prompts into three types of prompts, in order to dynamically learn different objectives for multimodal learning; (3) our proposed method is quite memory-efficient yet is able to achieve comparable performance with existing finetuning methods for multimodal fusion." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 305, + 394, + 395, + 407 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 394, + 395, + 407 + ], + "spans": [ + { + "bbox": [ + 305, + 394, + 395, + 407 + ], + "type": "text", + "content": "2. Related works" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 415, + 547, + 510 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 415, + 547, + 510 + ], + "spans": [ + { + "bbox": [ + 304, + 415, + 547, + 510 + ], + "type": "text", + "content": "Multimodal Fusion. Multimodal fusion methods aim to simultaneously process the input of different modalities, such as audio-video [27], vision-language [2, 15], and inputs from different types of sensors [42], etc. In this paper, we specifically focus on the fusion of vision-language inputs, though our proposed strategy is compatible with other modality pairs as long as there are unimodally pretrained transformers for these modalities." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 510, + 548, + 653 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 510, + 548, + 653 + ], + "spans": [ + { + "bbox": [ + 304, + 510, + 548, + 653 + ], + "type": "text", + "content": "Our work is in line with deep learning-based multimodal fusion strategies [16, 18, 26, 28, 33, 34, 44]. In this line of work, [15] proposed a framework whose vision encoder solely serves as a mapping tool to encode the raw images to the token space of the text encoder. Such an architecture is widely used in the later multimodal fusion research [20, 26, 34]. Differently, [27] used a dual-encoder architecture with bottleneck fusion tokens to exchange information between two encoders for video-audio fusion. Our work has a similar architecture as in [27]. But our proposed method completely freezes the unimodal encoders and uses an interactive prompting technique for more efficient fusion." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 654, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 654, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 654, + 547, + 715 + ], + "type": "text", + "content": "Another important line of multimodal fusion work is through pretraining with the large-scale datasets, mostly achieved by self-supervised learning algorithms [1, 11, 24, 30, 36, 37, 45]. This line of works can be roughly divided into two kinds by their architectures. The first kind has" + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 758 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 758 + ], + "type": "text", + "content": "2605" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 49, + 70, + 286, + 144 + ], + "blocks": [ + { + "bbox": [ + 49, + 70, + 286, + 144 + ], + "lines": [ + { + "bbox": [ + 49, + 70, + 286, + 144 + ], + "spans": [ + { + "bbox": [ + 49, + 70, + 286, + 144 + ], + "type": "table", + "html": "
Task TypePretraining TypeMethod
UnimodalUnimodalP-Tuning [22], VPT [12]
UnimodalMultimodalCoOp [47], MAPLE [14]
MultimodalMultimodalPI-VL [13], PTGM [43]
MultimodalUnimodalBlindPrompt [20], PMF
", + "image_path": "2dd3c4c8e5f53a75c49360a84f9ef1f68f085bfa7b752b540b23bbc2b1b8de39.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 151, + 288, + 196 + ], + "lines": [ + { + "bbox": [ + 46, + 151, + 288, + 196 + ], + "spans": [ + { + "bbox": [ + 46, + 151, + 288, + 196 + ], + "type": "text", + "content": "Table 1. Prompt-based methods categorized by model pretraining types and downstream task types. Our proposed PMF falls into the last category which utilize unimodally pretrained transformers for multimodal tasks." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 45, + 220, + 287, + 399 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 220, + 287, + 399 + ], + "spans": [ + { + "bbox": [ + 45, + 220, + 287, + 399 + ], + "type": "text", + "content": "a dual-encoder structure where image and text are treated separately, such as CLIP [30] and ALIGN [11]. The other kind simultaneously processes the vision and language inputs with cross-attention or self-attention over a longer sequence from two modalities. Our proposed method differs from these self-supervised architectures in that the individual components used in our model are unimodally pretrained with much less data. This difference directly results in a huge performance gap because of the lack of multimodal information in the pretraining stage. However, using unimodally pretrained models enables a much more flexible architecture. It has great potential in multimodal tasks where modality-paired large-scale pretraining data is not available, or when more advanced unimodal encoders are proposed in the future." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 45, + 400, + 287, + 579 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 400, + 287, + 579 + ], + "spans": [ + { + "bbox": [ + 45, + 400, + 287, + 579 + ], + "type": "text", + "content": "Prompt Tuning. As shown in Tab. 1, prompt-based methods can be roughly divided into four major categories in terms of the modalities of the pretrained model and the downstream tasks. Prompting techniques originally apply on unimodally pretrained transformers for unimodal natural language processing (NLP) tasks [17, 19, 21, 22, 29]. Pretrained GPT-3 can be simply leveraged with handcrafted prompts, which are some manually chosen words preceding the input text [4]. Then [22] and [17] proposed to change the handcrafted prompt to trainable continuous prompts and only update the prompt vectors during the training. Later on, [19] and [29] proposed to use prompt tuning in every hidden layer in the pretrained transformer instead of the input embeddings only. VPT [12] first applied prompt tuning to the vision transformer." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "content": "For methods that prompt multimodally pretrained models for unimodal tasks, many recent works apply prompt tuning to pretrained vision-language models (i.e. CLIP [30]) for unimodal vision tasks [3, 14, 25, 46, 47]. Another type of prompt-based method apply to the multimodal pretrained model for multimodal tasks [13, 43]. [13] adds prompts to an encoder-decoder one-for-all multimodal transformer, achieving comparable performance with finetuning with improved robustness against adversarial attacks. The method used in [13] is simple but effective, showing that prompting methods works well with powerful and com" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 305, + 72, + 462, + 84 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 462, + 84 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 462, + 84 + ], + "type": "text", + "content": "plex multimodally pretraining models." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 85, + 545, + 228 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 85, + 545, + 228 + ], + "spans": [ + { + "bbox": [ + 304, + 85, + 545, + 228 + ], + "type": "text", + "content": "Our proposed fusion strategy is different from the above methods and falls into the last category where prompts are used to fuse pretrained unimodal models for multimodal tasks. Sharing the same architecture design with [15, 34], [20] uses prompt to align the feature extracted from raw images to the token space of pretrained language model. They achieved comparable performance to several multimodal fusion methods in low-resource settings but underperform fine-tuning baselines by a large margin with full data. Compared with them, our proposed PMF not only is more memory-efficient but can also perform comparably with fine-tuning baselines with full data." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 305, + 241, + 495, + 255 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 241, + 495, + 255 + ], + "spans": [ + { + "bbox": [ + 305, + 241, + 495, + 255 + ], + "type": "text", + "content": "3. Prompt-based Multimodal Fusion" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 262, + 545, + 358 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 262, + 545, + 358 + ], + "spans": [ + { + "bbox": [ + 304, + 262, + 545, + 358 + ], + "type": "text", + "content": "In this section, we describe our proposed Prompt-based Multimodal Fusion strategy (PMF). We begin by summarising unimodal transformers developed for vision and language tasks in Sec. 3.1. Then we describe the base feature extraction process in Sec. 3.2. Lastly, we give a detailed description of how PMF integrates two unimodal transformer layers into a multimodal one via interactive prompting in Sec. 3.3." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 368, + 443, + 380 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 368, + 443, + 380 + ], + "spans": [ + { + "bbox": [ + 305, + 368, + 443, + 380 + ], + "type": "text", + "content": "3.1. Unimodal Transformers" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 387, + 545, + 517 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 387, + 545, + 517 + ], + "spans": [ + { + "bbox": [ + 304, + 387, + 545, + 517 + ], + "type": "text", + "content": "Vision Transformer (ViT) [9] adapts the Transformer [35] architecture with minimum modifications. The RGB image input " + }, + { + "bbox": [ + 304, + 387, + 545, + 517 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_{img} \\in \\mathbb{R}^{h,w,c}" + }, + { + "bbox": [ + 304, + 387, + 545, + 517 + ], + "type": "text", + "content": " is first cut into " + }, + { + "bbox": [ + 304, + 387, + 545, + 517 + ], + "type": "inline_equation", + "content": "N_{img}" + }, + { + "bbox": [ + 304, + 387, + 545, + 517 + ], + "type": "text", + "content": " nonoverlapping patches and then linearly projected into a sequence of embeddings " + }, + { + "bbox": [ + 304, + 387, + 545, + 517 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 304, + 387, + 545, + 517 + ], + "type": "text", + "content": " with each " + }, + { + "bbox": [ + 304, + 387, + 545, + 517 + ], + "type": "inline_equation", + "content": "z_i \\in \\mathbb{R}^d" + }, + { + "bbox": [ + 304, + 387, + 545, + 517 + ], + "type": "text", + "content": ". Differently, the language Transformer first tokenizes raw text to " + }, + { + "bbox": [ + 304, + 387, + 545, + 517 + ], + "type": "inline_equation", + "content": "N_{txt}" + }, + { + "bbox": [ + 304, + 387, + 545, + 517 + ], + "type": "text", + "content": " one-hot word embeddings and then converted these discrete vectors into a sequence of " + }, + { + "bbox": [ + 304, + 387, + 545, + 517 + ], + "type": "inline_equation", + "content": "N_{txt}" + }, + { + "bbox": [ + 304, + 387, + 545, + 517 + ], + "type": "text", + "content": " continuous embeddings. The resulting continuous embedding for both Language Transformer and Vision Transformer share the same structure as follows:" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 373, + 520, + 545, + 533 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 373, + 520, + 545, + 533 + ], + "spans": [ + { + "bbox": [ + 373, + 520, + 545, + 533 + ], + "type": "interline_equation", + "content": "\\mathbf {z} = \\left[ \\mathrm {C L S}, z _ {1}, z _ {2}, \\dots , z _ {N} \\right] \\tag {1}", + "image_path": "825868872cb499e4b9ebc8ce6abc8f0e5e752719246de2f05b321fd1fc116c9f.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 540, + 545, + 661 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 540, + 545, + 661 + ], + "spans": [ + { + "bbox": [ + 304, + 540, + 545, + 661 + ], + "type": "text", + "content": "where CLS is a special token prepended to the sequence so that its representation at the final layer can be used as the representation of the whole sequence for classification. Please note that the two unimodal transformers have different CLS tokens. The continuous embedding " + }, + { + "bbox": [ + 304, + 540, + 545, + 661 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 304, + 540, + 545, + 661 + ], + "type": "text", + "content": " is then fed into a transformer encoder which consists of " + }, + { + "bbox": [ + 304, + 540, + 545, + 661 + ], + "type": "inline_equation", + "content": "L" + }, + { + "bbox": [ + 304, + 540, + 545, + 661 + ], + "type": "text", + "content": " transformer layers. For each transformer layer, the input passes through modules including multi-head self-attention, layer normalization, multilayer perceptron, and finally added to the original input with a residual connection." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 670, + 489, + 682 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 670, + 489, + 682 + ], + "spans": [ + { + "bbox": [ + 305, + 670, + 489, + 682 + ], + "type": "text", + "content": "3.2. Unimodal Base feature Extraction" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 689, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 689, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 305, + 689, + 545, + 714 + ], + "type": "text", + "content": "As shown in Fig. 2, the image and text inputs are first processed and fed into the unimodal transformer layers to" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "2606" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 50, + 73, + 539, + 235 + ], + "blocks": [ + { + "bbox": [ + 50, + 73, + 539, + 235 + ], + "lines": [ + { + "bbox": [ + 50, + 73, + 539, + 235 + ], + "spans": [ + { + "bbox": [ + 50, + 73, + 539, + 235 + ], + "type": "image", + "image_path": "a7d913cdf02b214f352ce6e81dd4e3b0f695c412a27d26cef071273ec05f4d01.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 246, + 547, + 302 + ], + "lines": [ + { + "bbox": [ + 46, + 246, + 547, + 302 + ], + "spans": [ + { + "bbox": [ + 46, + 246, + 547, + 302 + ], + "type": "text", + "content": "Figure 2. Prompt-based multimodal fusion strategy (PMF) applied to vision-language inputs. In the forward propagation, image and text inputs are first embedded into continuous token sequences and fed to the unimodal transformer layers for base feature extraction. The base features from both modalities then pass through multiple prompt-based multimodal fusion layers to get the feature of two CLS tokens for final classification. In the backward propagation, only multimodal fusion layers take part in the calculation of gradients, greatly saving memory usage during training. All pretrained parameters in both transformers are frozen during the training." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 323, + 287, + 370 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 323, + 287, + 370 + ], + "spans": [ + { + "bbox": [ + 46, + 323, + 287, + 370 + ], + "type": "text", + "content": "extract base features, respectively. At this stage, each encoder works exactly the same as they did in unimodal tasks. Here we denote the starting fusion layer as " + }, + { + "bbox": [ + 46, + 323, + 287, + 370 + ], + "type": "inline_equation", + "content": "L_{f}" + }, + { + "bbox": [ + 46, + 323, + 287, + 370 + ], + "type": "text", + "content": ". And the base feature extraction of each encoder can be denoted as:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 86, + 378, + 287, + 393 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 86, + 378, + 287, + 393 + ], + "spans": [ + { + "bbox": [ + 86, + 378, + 287, + 393 + ], + "type": "interline_equation", + "content": "\\mathbf {z} ^ {l + 1} = \\operatorname {T r a n s L a y e r} ^ {l} \\left(\\mathbf {z} ^ {l}; \\theta\\right) \\quad \\text {i f} l < L _ {f} \\tag {2}", + "image_path": "3bdcc1c9ad4e1100c4df5bc0de3981d4df7e2489f2a8765832d01a8fbad0e60b.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 400, + 287, + 450 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 400, + 287, + 450 + ], + "spans": [ + { + "bbox": [ + 46, + 400, + 287, + 450 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 400, + 287, + 450 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 46, + 400, + 287, + 450 + ], + "type": "text", + "content": " stands for the pretrained parameters. A smaller " + }, + { + "bbox": [ + 46, + 400, + 287, + 450 + ], + "type": "inline_equation", + "content": "L_{f}" + }, + { + "bbox": [ + 46, + 400, + 287, + 450 + ], + "type": "text", + "content": " leads to an earlier fusion and a larger " + }, + { + "bbox": [ + 46, + 400, + 287, + 450 + ], + "type": "inline_equation", + "content": "L_{f}" + }, + { + "bbox": [ + 46, + 400, + 287, + 450 + ], + "type": "text", + "content": " leads to a later fusion. A detailed discussion of the impact brought by different " + }, + { + "bbox": [ + 46, + 400, + 287, + 450 + ], + "type": "inline_equation", + "content": "L_{f}" + }, + { + "bbox": [ + 46, + 400, + 287, + 450 + ], + "type": "text", + "content": " can be found in Sec. 4.5." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 456, + 191, + 468 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 456, + 191, + 468 + ], + "spans": [ + { + "bbox": [ + 47, + 456, + 191, + 468 + ], + "type": "text", + "content": "3.3. Multimodal Fusion Layer" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 474, + 287, + 545 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 474, + 287, + 545 + ], + "spans": [ + { + "bbox": [ + 46, + 474, + 287, + 545 + ], + "type": "text", + "content": "The extracted unimodal base features are then passed through multiple multimodal fusion layers, each consisting of a 'querying stage' and a 'fusion stage', as shown in Fig. 3. The querying stage focus on the extraction of what is necessary to pass, and the fusion stage focus on fusing the extracted information delivered from the other modality." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 546, + 287, + 666 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 546, + 287, + 666 + ], + "spans": [ + { + "bbox": [ + 46, + 546, + 287, + 666 + ], + "type": "text", + "content": "This two-stage setting makes the vanilla prompt training entangled with different learning objectives. Therefore, we propose to decouple the vanilla prompts into three kinds: 'query prompt' (QP, denoted " + }, + { + "bbox": [ + 46, + 546, + 287, + 666 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_{qp}" + }, + { + "bbox": [ + 46, + 546, + 287, + 666 + ], + "type": "text", + "content": "), 'query context prompt' (QCP, denoted " + }, + { + "bbox": [ + 46, + 546, + 287, + 666 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_{qcp}" + }, + { + "bbox": [ + 46, + 546, + 287, + 666 + ], + "type": "text", + "content": "), and 'fusion context prompt' (FCP, denoted " + }, + { + "bbox": [ + 46, + 546, + 287, + 666 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_{fcp}" + }, + { + "bbox": [ + 46, + 546, + 287, + 666 + ], + "type": "text", + "content": ") to dynamically learn different objectives for multimodal learning. According to the modality where prompts are used, each kind of prompt can be further specified as " + }, + { + "bbox": [ + 46, + 546, + 287, + 666 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_*" + }, + { + "bbox": [ + 46, + 546, + 287, + 666 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 546, + 287, + 666 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_*" + }, + { + "bbox": [ + 46, + 546, + 287, + 666 + ], + "type": "text", + "content": " to distinguish from each other (e.g. " + }, + { + "bbox": [ + 46, + 546, + 287, + 666 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_{fcp}" + }, + { + "bbox": [ + 46, + 546, + 287, + 666 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 546, + 287, + 666 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_{fcp}^{\\prime}" + }, + { + "bbox": [ + 46, + 546, + 287, + 666 + ], + "type": "text", + "content": ")." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 666, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 666, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 666, + 287, + 714 + ], + "type": "text", + "content": "As shown in Fig. 3, QP and QCP are used in the querying stage and the FCP is used in the fusion stage. As suggested by their names, QP is to query information from the unimodal input sequence, QCP is to help this process by pro" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 323, + 545, + 394 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 323, + 545, + 394 + ], + "spans": [ + { + "bbox": [ + 304, + 323, + 545, + 394 + ], + "type": "text", + "content": "viding extra context to the query. QP and QCP like a pair of 'questions' and 'answers', translated by the non-linear mapping. As for FCP, it is responsible for providing the context to the fusion in the fusion stage. We now introduce how these three kinds of prompts interact with each other in the two stages of each multimodal fusion layer." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 394, + 545, + 430 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 394, + 545, + 430 + ], + "spans": [ + { + "bbox": [ + 304, + 394, + 545, + 430 + ], + "type": "text", + "content": "Querying Stage. We first concatenate corresponding QP and QCP to the input sequence " + }, + { + "bbox": [ + 304, + 394, + 545, + 430 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 304, + 394, + 545, + 430 + ], + "type": "text", + "content": ". The resulting input sequence after the concatenation is:" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 397, + 437, + 545, + 453 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 397, + 437, + 545, + 453 + ], + "spans": [ + { + "bbox": [ + 397, + 437, + 545, + 453 + ], + "type": "interline_equation", + "content": "[ \\mathbf {z} ^ {l} | | \\mathbf {z} _ {q c p} ^ {l} | | \\mathbf {z} _ {q p} ^ {l} ] \\tag {3}", + "image_path": "788713e3b1c591ca844a690e5fa12720dae3c4c8dc28da986a726202e803feee.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 460, + 545, + 496 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 460, + 545, + 496 + ], + "spans": [ + { + "bbox": [ + 304, + 460, + 545, + 496 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 460, + 545, + 496 + ], + "type": "inline_equation", + "content": "| \\cdot |" + }, + { + "bbox": [ + 304, + 460, + 545, + 496 + ], + "type": "text", + "content": " denotes the concatenation operation. Then we feed the concatenated sequence to the unimodal transformer layer, which can be denoted as:" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 321, + 502, + 545, + 520 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 321, + 502, + 545, + 520 + ], + "spans": [ + { + "bbox": [ + 321, + 502, + 545, + 520 + ], + "type": "interline_equation", + "content": "[ \\hat {\\mathbf {z}} ^ {l} | | \\hat {\\mathbf {z}} _ {q c p} ^ {l} | | \\hat {\\mathbf {z}} _ {q p} ^ {l} ] = \\mathrm {T r a n s L a y e r} ^ {l} ([ \\mathbf {z} ^ {l} | | \\mathbf {z} _ {q c p} ^ {l} | | \\mathbf {z} _ {q p} ^ {l} ]; \\theta) \\quad (4)", + "image_path": "8d7ffbfd178d65548eb4d503014af798a5017897cd7661b7b4620245d934f66d.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 528, + 545, + 600 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 528, + 545, + 600 + ], + "spans": [ + { + "bbox": [ + 304, + 528, + 545, + 600 + ], + "type": "text", + "content": "After the forward propagation, the output of QP " + }, + { + "bbox": [ + 304, + 528, + 545, + 600 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{z}}_{qp}^{l}" + }, + { + "bbox": [ + 304, + 528, + 545, + 600 + ], + "type": "text", + "content": " is extracted as the queried information to be used in the following fusion operations. It should be noted that though " + }, + { + "bbox": [ + 304, + 528, + 545, + 600 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{z}}_{qcp}^{l}" + }, + { + "bbox": [ + 304, + 528, + 545, + 600 + ], + "type": "text", + "content": " will not be used in the following fusion operations, it has played an important role by providing the context of query in the querying stage." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 600, + 545, + 635 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 600, + 545, + 635 + ], + "spans": [ + { + "bbox": [ + 304, + 600, + 545, + 635 + ], + "type": "text", + "content": "The queried fusion intermediate " + }, + { + "bbox": [ + 304, + 600, + 545, + 635 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{z}}_{qp}^{l}" + }, + { + "bbox": [ + 304, + 600, + 545, + 635 + ], + "type": "text", + "content": " is then mapped to the representation space of the other modality through a non-linear mapping function:" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 394, + 643, + 545, + 659 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 394, + 643, + 545, + 659 + ], + "spans": [ + { + "bbox": [ + 394, + 643, + 545, + 659 + ], + "type": "interline_equation", + "content": "\\mathbf {y} _ {q p} ^ {l} = f ^ {l} \\left(\\hat {\\mathbf {z}} _ {q p} ^ {l}\\right) \\tag {5}", + "image_path": "d4a321be24e2841ccfa6ebcf5a2d641141799d6031bcb6863fcb1e6d5ec0a041.jpg" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "content": " is a non-linear mapping function. Specifically, a mapping function consists of two linear layers with a bottleneck structure to reduce dimension and only the first linear layer has a ReLu function. Each fusion layer " + }, + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "inline_equation", + "content": "l" + }, + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "content": " has two" + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "2607" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 48, + 70, + 547, + 175 + ], + "blocks": [ + { + "bbox": [ + 48, + 70, + 547, + 175 + ], + "lines": [ + { + "bbox": [ + 48, + 70, + 547, + 175 + ], + "spans": [ + { + "bbox": [ + 48, + 70, + 547, + 175 + ], + "type": "image", + "image_path": "0c0ac5fefaa70d253a2f34dbef34929ab93671ec95dfc5775f2fc7f60cb07a17.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 186, + 547, + 240 + ], + "lines": [ + { + "bbox": [ + 46, + 186, + 547, + 240 + ], + "spans": [ + { + "bbox": [ + 46, + 186, + 547, + 240 + ], + "type": "text", + "content": "Figure 3. Prompt-based multimodal fusion layer. We propose to use three kinds of interactive prompts to achieve the fusion/exchange of information from two modalities. We use 'query prompt' " + }, + { + "bbox": [ + 46, + 186, + 547, + 240 + ], + "type": "inline_equation", + "content": "(\\mathrm{z}_{qp},\\mathrm{z}_{qp}^{\\prime})" + }, + { + "bbox": [ + 46, + 186, + 547, + 240 + ], + "type": "text", + "content": " and 'query context prompt' " + }, + { + "bbox": [ + 46, + 186, + 547, + 240 + ], + "type": "inline_equation", + "content": "(\\mathrm{z}_{qcp},\\mathrm{z}_{qcp}^{\\prime})" + }, + { + "bbox": [ + 46, + 186, + 547, + 240 + ], + "type": "text", + "content": " in the querying stage to extract what is necessary, after a non-linear mapping, the extracted information is then fused to the other modality with the help of 'fusion context prompt' " + }, + { + "bbox": [ + 46, + 186, + 547, + 240 + ], + "type": "inline_equation", + "content": "(\\mathrm{z}_{fcp},\\mathrm{z}_{fcp}^{\\prime})" + }, + { + "bbox": [ + 46, + 186, + 547, + 240 + ], + "type": "text", + "content": " in the fusion stage. Yellow and green elements stand for language and vision modalities, respectively. Red boxes indicate trainable modules." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 261, + 287, + 309 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 261, + 287, + 309 + ], + "spans": [ + { + "bbox": [ + 46, + 261, + 287, + 309 + ], + "type": "text", + "content": "mapping functions " + }, + { + "bbox": [ + 46, + 261, + 287, + 309 + ], + "type": "inline_equation", + "content": "f^l" + }, + { + "bbox": [ + 46, + 261, + 287, + 309 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 261, + 287, + 309 + ], + "type": "inline_equation", + "content": "f'^l" + }, + { + "bbox": [ + 46, + 261, + 287, + 309 + ], + "type": "text", + "content": ", building a two-way interaction among different modalities. Note that the non-linear mapping functions contain more than " + }, + { + "bbox": [ + 46, + 261, + 287, + 309 + ], + "type": "inline_equation", + "content": "95\\%" + }, + { + "bbox": [ + 46, + 261, + 287, + 309 + ], + "type": "text", + "content": " of the trainable parameters in PMF." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 310, + 287, + 383 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 310, + 287, + 383 + ], + "spans": [ + { + "bbox": [ + 47, + 310, + 287, + 383 + ], + "type": "text", + "content": "Fusion Stage. We first concatenate the mapped fusion intermediates " + }, + { + "bbox": [ + 47, + 310, + 287, + 383 + ], + "type": "inline_equation", + "content": "\\mathbf{y}_{qp}^{l}" + }, + { + "bbox": [ + 47, + 310, + 287, + 383 + ], + "type": "text", + "content": " to the original input sequence " + }, + { + "bbox": [ + 47, + 310, + 287, + 383 + ], + "type": "inline_equation", + "content": "\\mathbf{z}^{\\prime l}" + }, + { + "bbox": [ + 47, + 310, + 287, + 383 + ], + "type": "text", + "content": " and FCP " + }, + { + "bbox": [ + 47, + 310, + 287, + 383 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_{fcp}^{\\prime l}" + }, + { + "bbox": [ + 47, + 310, + 287, + 383 + ], + "type": "text", + "content": " of the other modality. Then we feed the concatenated sequence to the unimodal transformer layer of the other modality to complete a one-way fusion. These two processes can be together denoted as:" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 58, + 392, + 287, + 418 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 392, + 287, + 418 + ], + "spans": [ + { + "bbox": [ + 58, + 392, + 287, + 418 + ], + "type": "interline_equation", + "content": "[ \\mathbf {z} ^ {\\prime l + 1} | | \\hat {\\mathbf {z}} _ {f c p} ^ {\\prime l} | | \\hat {\\mathbf {y}} _ {q p} ^ {l} ] = \\operatorname {T r a n s L a y e r} ^ {l} ([ \\mathbf {z} ^ {\\prime l} | | \\mathbf {z} _ {f c p} ^ {\\prime l} | | \\mathbf {y} _ {q p} ^ {l} ]; \\theta^ {\\prime}) \\tag {6}", + "image_path": "906625098b1dec26bd75f31e20d18c0d30179ca7aceabfa60fc02b41369777c7.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 418, + 233, + 430 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 418, + 233, + 430 + ], + "spans": [ + { + "bbox": [ + 47, + 418, + 233, + 430 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 418, + 233, + 430 + ], + "type": "inline_equation", + "content": "[\\ast ]'" + }, + { + "bbox": [ + 47, + 418, + 233, + 430 + ], + "type": "text", + "content": " means " + }, + { + "bbox": [ + 47, + 418, + 233, + 430 + ], + "type": "inline_equation", + "content": "[\\ast ]" + }, + { + "bbox": [ + 47, + 418, + 233, + 430 + ], + "type": "text", + "content": " from the other modality." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 430, + 287, + 479 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 430, + 287, + 479 + ], + "spans": [ + { + "bbox": [ + 47, + 430, + 287, + 479 + ], + "type": "text", + "content": "Finally, the output of two unimodal transformer layers " + }, + { + "bbox": [ + 47, + 430, + 287, + 479 + ], + "type": "inline_equation", + "content": "\\mathbf{z}^{l + 1}" + }, + { + "bbox": [ + 47, + 430, + 287, + 479 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 430, + 287, + 479 + ], + "type": "inline_equation", + "content": "\\mathbf{z}^{\\prime l + 1}" + }, + { + "bbox": [ + 47, + 430, + 287, + 479 + ], + "type": "text", + "content": " are together as the output of the multimodal fusion layer and fed to the higher layers. The entire multimodal fusion process can be concluded as:" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 53, + 487, + 287, + 512 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 487, + 287, + 512 + ], + "spans": [ + { + "bbox": [ + 53, + 487, + 287, + 512 + ], + "type": "interline_equation", + "content": "[ \\mathbf {z} ^ {l + 1} | | \\mathbf {z} ^ {\\prime l + 1} ] = \\text {F u s i o n L a y e r} ^ {l} ([ \\mathbf {z} ^ {l} | | \\mathbf {z} ^ {\\prime l} ]; \\theta , \\theta^ {\\prime}) \\quad \\text {i f} L _ {f} \\leq l \\tag {7}", + "image_path": "521c223e74ecd6e98ef3505805779d033130bc6055071f9ef0d42c6be57504cd.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 514, + 287, + 597 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 514, + 287, + 597 + ], + "spans": [ + { + "bbox": [ + 46, + 514, + 287, + 597 + ], + "type": "text", + "content": "After the multimodal fusion is complete, we take the output representation of CLS token " + }, + { + "bbox": [ + 46, + 514, + 287, + 597 + ], + "type": "inline_equation", + "content": "z_{CLS}^{L}" + }, + { + "bbox": [ + 46, + 514, + 287, + 597 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 514, + 287, + 597 + ], + "type": "inline_equation", + "content": "z_{CLS}^{\\prime L}" + }, + { + "bbox": [ + 46, + 514, + 287, + 597 + ], + "type": "text", + "content": " to two different linear classifiers and average the pre-softmax logits for classification. Mathematically, such a classifier setting is equivalent to feeding the classifier with the concatenated features when a linear classifier is used, except for a different scale of gradient caused by the averaging operation." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 609, + 128, + 623 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 609, + 128, + 623 + ], + "spans": [ + { + "bbox": [ + 47, + 609, + 128, + 623 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 629, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 629, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 629, + 287, + 713 + ], + "type": "text", + "content": "In this section, we analyze the performance of our proposed PMF on three multimodal datasets and aim to answer the following questions: (1) How efficient is the PMF and does PMF perform well (Sec. 4.4)? (2) What factors affect the effectiveness of PMF (Sec. 4.5)? In addition, we explore the PMF equipped with larger transformers and its impact brought to the performance and memory efficiency in" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 261, + 545, + 297 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 261, + 545, + 297 + ], + "spans": [ + { + "bbox": [ + 305, + 261, + 545, + 297 + ], + "type": "text", + "content": "Sec. 4.6. Lastly, we introduce a Neural Architecture Search (NAS) method to automatically search for the preferable fusion structure for PMF in Sec. 4.7." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 307, + 427, + 319 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 307, + 427, + 319 + ], + "spans": [ + { + "bbox": [ + 306, + 307, + 427, + 319 + ], + "type": "text", + "content": "4.1. Datasets and Metrics" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 325, + 545, + 409 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 325, + 545, + 409 + ], + "spans": [ + { + "bbox": [ + 305, + 325, + 545, + 409 + ], + "type": "text", + "content": "UPMC Food-101 [38] is a multimodal classification dataset, which contains food images with textual recipe descriptions for 101 kinds of food. UPMC Food-101 contains a total of 90,840 image-text pairs with a size range between 790 and 956 pairs for different classes. As the dataset only has training and testing sets, we follow [15] and create a validation split of 5000 samples from the training set." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 410, + 545, + 468 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 410, + 545, + 468 + ], + "spans": [ + { + "bbox": [ + 305, + 410, + 545, + 468 + ], + "type": "text", + "content": "MM-IMDB [2] is a multimodal multi-label classification dataset, which contains movie plot outlines and movie posters. The task is to predict the genre of movies. This dataset contains 25,956 image-text pairs for 23 classes with a long-tail distribution." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 469, + 545, + 565 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 469, + 545, + 565 + ], + "spans": [ + { + "bbox": [ + 305, + 469, + 545, + 565 + ], + "type": "text", + "content": "SNLI-VE [41] is a multimodal classification dataset for the visual entailment tasks, which is to reason about the relationship between an image premise and a text hypothesis into entailment, contradiction, or neutrality. SNLI-VE contains a total of 565,286 image-text pairs. Please note that we only use image premise and text hypothesis in the input, which is different from the settings in some other papers where text premises are also used in the inputs [43]." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 306, + 566, + 545, + 589 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 566, + 545, + 589 + ], + "spans": [ + { + "bbox": [ + 306, + 566, + 545, + 589 + ], + "type": "text", + "content": "We report accuracy for UPMC Food-101 and SNLI-VE, and Macro/Micro-F1 scores for MM-IMDB as metrics." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 598, + 477, + 611 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 598, + 477, + 611 + ], + "spans": [ + { + "bbox": [ + 306, + 598, + 477, + 611 + ], + "type": "text", + "content": "4.2. Existing Methods and Baselines" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 305, + 617, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 617, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 617, + 545, + 713 + ], + "type": "text", + "content": "We report the performance of several baselines and existing methods. First, we report the performance of finetuning unimodal models (i.e. BERT [8], ViT [9]) to verify the effectiveness of multimodal fusion. Specifically, we take the output representation of CLS token of the last layer in ViT and BERT, and feed it into a linear classifier. We also report the performance of VPT [12] and a prompt-based BERT (denoted P-BERT) for a better comparison. For VPT" + } + ] + } + ], + "index": 18 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "2608" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 47, + 70, + 547, + 281 + ], + "blocks": [ + { + "bbox": [ + 47, + 70, + 547, + 281 + ], + "lines": [ + { + "bbox": [ + 47, + 70, + 547, + 281 + ], + "spans": [ + { + "bbox": [ + 47, + 70, + 547, + 281 + ], + "type": "table", + "html": "
MethodUpdated Param. (Million)Memory Usage (GB) Train/InferenceSNLI-VEFood-101MM-IMDBAvg.
Linear-3.76 / 3.2350.0578.9649.76 / 56.8360.77
ViT86.59.36 / 1.9933.3374.6938.39 / 49.8850.72
BERT109.030.82 / 2.7969.8287.4458.91 / 64.3172.96
LateConcat196.038.54 / 3.3670.0193.2959.56 / 64.9275.18
MMBT*196.537.87 / 3.4874.6994.1060.80 / 66.1077.41
MBT*196.038.00 / 4.0674.0293.5659.60 / 64.8176.60
VPT-6.12 / 2.0133.3372.5535.22 / 44.4948.58
P-BERT-28.13 / 2.9963.2881.0748.67 / 54.5865.33
PromptFuse-29.57 / 3.5564.5382.2148.59 / 54.4966.09
BlindPrompt-29.57 / 3.6565.5484.5650.18 / 56.4667.81
P-LateConcat0.330.82 / 3.4363.0589.0353.91 / 59.9369.67
P-MMBT0.930.90 / 3.4867.5886.5852.95 / 59.3070.10
PMF (M=4, Lf=10)2.512.84 / 4.0871.9291.5158.77 / 64.5175.02
PMF-large (M=4, Lf=22)4.518.44 / 6.4272.1091.6861.66 / 66.7275.99
", + "image_path": "a3d268425afd033e75912d7dfbfda448c63c9bc90748a913b1d14d93561abdf9.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 289, + 547, + 346 + ], + "lines": [ + { + "bbox": [ + 46, + 289, + 547, + 346 + ], + "spans": [ + { + "bbox": [ + 46, + 289, + 547, + 346 + ], + "type": "text", + "content": "Table 2. Multimodal classification performance. PMF achieve comparable performance to the finetuning baselines with less than " + }, + { + "bbox": [ + 46, + 289, + 547, + 346 + ], + "type": "inline_equation", + "content": "3\\%" + }, + { + "bbox": [ + 46, + 289, + 547, + 346 + ], + "type": "text", + "content": " of trainable parameters and up to " + }, + { + "bbox": [ + 46, + 289, + 547, + 346 + ], + "type": "inline_equation", + "content": "66\\%" + }, + { + "bbox": [ + 46, + 289, + 547, + 346 + ], + "type": "text", + "content": " of training memory usage. MM-IMDB is F1-Macro / F1-Micro, others are accuracy. We report the maximum memory usage in training and evaluating UPMC Food-101 for each method. We report mean performance over 3 runs with different random seeds. \\* means trainable parameter less than " + }, + { + "bbox": [ + 46, + 289, + 547, + 346 + ], + "type": "inline_equation", + "content": "0.1\\mathrm{M}" + }, + { + "bbox": [ + 46, + 289, + 547, + 346 + ], + "type": "text", + "content": " . PMF-Large uses bert-large and vit-large models (24 hidden layers) while others use bert-base and vit-base models (12 hidden layers). " + }, + { + "bbox": [ + 46, + 289, + 547, + 346 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 46, + 289, + 547, + 346 + ], + "type": "text", + "content": " is the prompt length and " + }, + { + "bbox": [ + 46, + 289, + 547, + 346 + ], + "type": "inline_equation", + "content": "L_{f}" + }, + { + "bbox": [ + 46, + 289, + 547, + 346 + ], + "type": "text", + "content": " is the starting fusion layer." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 365, + 288, + 413 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 365, + 288, + 413 + ], + "spans": [ + { + "bbox": [ + 46, + 365, + 288, + 413 + ], + "type": "text", + "content": "and P-BERT, the input sequence to each transformer layer is concatenated with a prompt vector, whose length is set to 10. And the concatenated prompt vectors and the final linear classifier are the only updated modules in training." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 414, + 287, + 521 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 414, + 287, + 521 + ], + "spans": [ + { + "bbox": [ + 46, + 414, + 287, + 521 + ], + "type": "text", + "content": "In addition, we compare against a strong baseline method which concatenates the output features of CLS tokens of ViT and BERT, and feed the concatenated feature to a linear classifier, denoted as LateConcat. In this case, the input to the classifier is " + }, + { + "bbox": [ + 46, + 414, + 287, + 521 + ], + "type": "inline_equation", + "content": "(768 + 768)" + }, + { + "bbox": [ + 46, + 414, + 287, + 521 + ], + "type": "text", + "content": "-dimensional. Besides, we also introduce Linear, which shares the same architecture with LateConcat with the only difference in the updated modules. Linear only updates the linear classifier while LateConcat updates all parameters during training." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 521, + 287, + 594 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 521, + 287, + 594 + ], + "spans": [ + { + "bbox": [ + 46, + 521, + 287, + 594 + ], + "type": "text", + "content": "We reimplement MMBT (denoted " + }, + { + "bbox": [ + 46, + 521, + 287, + 594 + ], + "type": "inline_equation", + "content": "\\mathbf{MMBT}^*" + }, + { + "bbox": [ + 46, + 521, + 287, + 594 + ], + "type": "text", + "content": ") [15] and MBT (denoted " + }, + { + "bbox": [ + 46, + 521, + 287, + 594 + ], + "type": "inline_equation", + "content": "\\mathbf{MBT}^*" + }, + { + "bbox": [ + 46, + 521, + 287, + 594 + ], + "type": "text", + "content": ") [27] with a vit-base model as the vision encoder and a bert-base model as the text encoder for fair and controlled comparison. We set the fusion layer " + }, + { + "bbox": [ + 46, + 521, + 287, + 594 + ], + "type": "inline_equation", + "content": "L_{f} = 8" + }, + { + "bbox": [ + 46, + 521, + 287, + 594 + ], + "type": "text", + "content": " and use 4 fusion tokens in MBT as recommended in the original paper." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 594, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 594, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 288, + 715 + ], + "type": "text", + "content": "We also propose a prompt-based MMBT and a prompt-based LateConcat, denoted as P-MMBT and P-LateConcat, respectively. In P-MMBT and P-LateConcat, we apply deep prompt tuning on both vision and language encoders, which are pretrained backbones with frozen parameters during training. We set the prompt length in each layer of two encoders to 10, totalling 240 prompt vectors. Similar to VPT and P-BERT, P-LateConcat only updates the final linear classifier and prompt vectors during training. Compared with P-LateConcat, P-MMBT have an extra" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 305, + 365, + 545, + 377 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 365, + 545, + 377 + ], + "spans": [ + { + "bbox": [ + 305, + 365, + 545, + 377 + ], + "type": "text", + "content": "linear projection layer and a smaller linear classifier to train." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 305, + 378, + 545, + 437 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 378, + 545, + 437 + ], + "spans": [ + { + "bbox": [ + 305, + 378, + 545, + 437 + ], + "type": "text", + "content": "Lastly, we report the performance of PromptFuse and BlindPrompt [20], both proposed in the only existing paper which leverages unimodally pretrained models for multimodal fusion through prompting. We set the prompt length to 20 as recommended in the original paper." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 443, + 440, + 456 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 443, + 440, + 456 + ], + "spans": [ + { + "bbox": [ + 306, + 443, + 440, + 456 + ], + "type": "text", + "content": "4.3. Implementation Details" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 461, + 545, + 544 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 461, + 545, + 544 + ], + "spans": [ + { + "bbox": [ + 305, + 461, + 545, + 544 + ], + "type": "text", + "content": "Pretrained Backbone and Initialization. Unless otherwise noted, we use an ImageNet-21k [7] pretrained vit-base model for the vision encoder and a bert-base-uncased model for the language encoder in all experiments. All pretrained checkpoints are from huggingface [40]. All prompt vectors are initialized through a Gaussian distribution (mean=0, std=0.02)." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 545, + 545, + 629 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 545, + 545, + 629 + ], + "spans": [ + { + "bbox": [ + 305, + 545, + 545, + 629 + ], + "type": "text", + "content": "Network Training. We use SGD optimizer in all experiments with momentum set to 0.9 and weight decay set to " + }, + { + "bbox": [ + 305, + 545, + 545, + 629 + ], + "type": "inline_equation", + "content": "1e^{-4}" + }, + { + "bbox": [ + 305, + 545, + 545, + 629 + ], + "type": "text", + "content": ". The batch size is set to 64 for SNLI-VE, and 32 for UPMC Food-101 and MM-IMDB. Cross entropy loss is applied in all experiments and the class labels are weighted by their inverse frequency for UPMC Food-101 and MM-IMDB. More details are in the supplementary material." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 635, + 391, + 647 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 635, + 391, + 647 + ], + "spans": [ + { + "bbox": [ + 306, + 635, + 391, + 647 + ], + "type": "text", + "content": "4.4. Main Results" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 653, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 653, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 305, + 653, + 547, + 715 + ], + "type": "text", + "content": "PMF is most memory-efficient. As shown in Tab. 2, PMF is the most memory-efficient multimodal fusion model of all existing prompt-based methods and baselines. PMF can save up to " + }, + { + "bbox": [ + 305, + 653, + 547, + 715 + ], + "type": "inline_equation", + "content": "66\\%" + }, + { + "bbox": [ + 305, + 653, + 547, + 715 + ], + "type": "text", + "content": " of training memory usage compared with finetuning baselines. Even compared with the existing most" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 316, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 316, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 316, + 757 + ], + "type": "text", + "content": "2609" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 65, + 70, + 271, + 191 + ], + "blocks": [ + { + "bbox": [ + 65, + 70, + 271, + 191 + ], + "lines": [ + { + "bbox": [ + 65, + 70, + 271, + 191 + ], + "spans": [ + { + "bbox": [ + 65, + 70, + 271, + 191 + ], + "type": "table", + "html": "
QPMappingfQCPFCPMM-IMDB
48.80/56.38
✓45.38/53.34
✓43.56/51.43
✓✓54.92/62.25
✓✓✓57.98/63.69
✓✓✓58.30/64.07
✓✓✓58.34/64.15
✓✓✓✓58.63/64.23
", + "image_path": "6b652dcd559273eacc8ff281e0aa8a79f4372d461b72df7c6388544daf4adf89.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 199, + 288, + 257 + ], + "lines": [ + { + "bbox": [ + 46, + 199, + 288, + 257 + ], + "spans": [ + { + "bbox": [ + 46, + 199, + 288, + 257 + ], + "type": "text", + "content": "Table 3. PMF Component Ablation. There are four types of trainable modules in our proposed PMF. We set the fusion layer " + }, + { + "bbox": [ + 46, + 199, + 288, + 257 + ], + "type": "inline_equation", + "content": "L_{f} = 10" + }, + { + "bbox": [ + 46, + 199, + 288, + 257 + ], + "type": "text", + "content": " and add different components one at a time to see their individual impact. All prompts with " + }, + { + "bbox": [ + 46, + 199, + 288, + 257 + ], + "type": "inline_equation", + "content": "\\checkmark" + }, + { + "bbox": [ + 46, + 199, + 288, + 257 + ], + "type": "text", + "content": " have a length of 4, and prompts with " + }, + { + "bbox": [ + 46, + 199, + 288, + 257 + ], + "type": "inline_equation", + "content": "\\checkmark \\checkmark" + }, + { + "bbox": [ + 46, + 199, + 288, + 257 + ], + "type": "text", + "content": " have a length of 8." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "text" + }, + { + "type": "image", + "bbox": [ + 50, + 274, + 284, + 395 + ], + "blocks": [ + { + "bbox": [ + 50, + 274, + 284, + 395 + ], + "lines": [ + { + "bbox": [ + 50, + 274, + 284, + 395 + ], + "spans": [ + { + "bbox": [ + 50, + 274, + 284, + 395 + ], + "type": "image", + "image_path": "04ca90815f5c5c93ede716f7afd0a25e5fe0ca577a3b848ad1df46dbab44461f.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 404, + 288, + 449 + ], + "lines": [ + { + "bbox": [ + 46, + 404, + 288, + 449 + ], + "spans": [ + { + "bbox": [ + 46, + 404, + 288, + 449 + ], + "type": "text", + "content": "Figure 4. Model Performance and Training Memory Usage under different fusion layers " + }, + { + "bbox": [ + 46, + 404, + 288, + 449 + ], + "type": "inline_equation", + "content": "L_{f}" + }, + { + "bbox": [ + 46, + 404, + 288, + 449 + ], + "type": "text", + "content": ". We set the prompt length " + }, + { + "bbox": [ + 46, + 404, + 288, + 449 + ], + "type": "inline_equation", + "content": "M = 4" + }, + { + "bbox": [ + 46, + 404, + 288, + 449 + ], + "type": "text", + "content": " for every prompt vector with different fusion layer " + }, + { + "bbox": [ + 46, + 404, + 288, + 449 + ], + "type": "inline_equation", + "content": "L_{f} = 0,2,4,6,8,10,12" + }, + { + "bbox": [ + 46, + 404, + 288, + 449 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 478, + 287, + 503 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 478, + 287, + 503 + ], + "spans": [ + { + "bbox": [ + 46, + 478, + 287, + 503 + ], + "type": "text", + "content": "memory-efficient prompt-based multimodal method, PMF still saves an extra of more than " + }, + { + "bbox": [ + 46, + 478, + 287, + 503 + ], + "type": "inline_equation", + "content": "50\\%" + }, + { + "bbox": [ + 46, + 478, + 287, + 503 + ], + "type": "text", + "content": " of training memory." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 506, + 287, + 615 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 506, + 287, + 615 + ], + "spans": [ + { + "bbox": [ + 46, + 506, + 287, + 615 + ], + "type": "text", + "content": "PMF outperforms all existing prompt-based methods. With the same pretrained unimodal transformers, prompt-based methods underperform the full finetuning methods by a large margin. Some prompt-based methods even underperform unimodal finetuning baselines. Our proposed PMF achieves the best performance among all prompt-based methods. Especially, PMF outperforms all unimodal baselines in all experiments, showing that the two modalities are successfully fused." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 617, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 617, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 617, + 288, + 715 + ], + "type": "text", + "content": "PMF is competitive with finetuning baselines. Tab. 2 shows that PMF achieves comparable performance with full finetuning baselines with less than " + }, + { + "bbox": [ + 46, + 617, + 288, + 715 + ], + "type": "inline_equation", + "content": "3\\%" + }, + { + "bbox": [ + 46, + 617, + 288, + 715 + ], + "type": "text", + "content": " trainable parameters while saving " + }, + { + "bbox": [ + 46, + 617, + 288, + 715 + ], + "type": "inline_equation", + "content": "66\\%" + }, + { + "bbox": [ + 46, + 617, + 288, + 715 + ], + "type": "text", + "content": " of memory cost, significantly narrowing the gap between finetuning and prompt-based methods. Furthermore, PMF even outperforms the finetuning LateConcat when equipped with larger transformers (i.e. bert-large and vit-large)." + } + ] + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 307, + 72, + 545, + 188 + ], + "blocks": [ + { + "bbox": [ + 307, + 72, + 545, + 188 + ], + "lines": [ + { + "bbox": [ + 307, + 72, + 545, + 188 + ], + "spans": [ + { + "bbox": [ + 307, + 72, + 545, + 188 + ], + "type": "image", + "image_path": "dbcf0106de26c140db5f3f399107438285fca6c2fbb26fc40a0dd8c648b380d7.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 198, + 547, + 232 + ], + "lines": [ + { + "bbox": [ + 305, + 198, + 547, + 232 + ], + "spans": [ + { + "bbox": [ + 305, + 198, + 547, + 232 + ], + "type": "text", + "content": "Figure 5. Model Performance and Training Memory Usage under different prompt length " + }, + { + "bbox": [ + 305, + 198, + 547, + 232 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 305, + 198, + 547, + 232 + ], + "type": "text", + "content": ". We fix the fusion layer " + }, + { + "bbox": [ + 305, + 198, + 547, + 232 + ], + "type": "inline_equation", + "content": "L_{f} = 10" + }, + { + "bbox": [ + 305, + 198, + 547, + 232 + ], + "type": "text", + "content": " and study 1, 4, 8, 16, and 32 tokens for each prompt vector." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_caption" + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 251, + 399, + 264 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 251, + 399, + 264 + ], + "spans": [ + { + "bbox": [ + 306, + 251, + 399, + 264 + ], + "type": "text", + "content": "4.5. Ablation Study" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 270, + 545, + 305 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 270, + 545, + 305 + ], + "spans": [ + { + "bbox": [ + 304, + 270, + 545, + 305 + ], + "type": "text", + "content": "In this section, we investigate the impact of different factors in our proposed fusion strategy. All experiments in this section are conducted on the MM-IMDB dataset." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 306, + 546, + 450 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 306, + 546, + 450 + ], + "spans": [ + { + "bbox": [ + 304, + 306, + 546, + 450 + ], + "type": "text", + "content": "Components Ablation. We verify the effectiveness of three kinds of prompts and the non-linear mapping function in this section. The results are shown in Tab. 3. The first row without any components in PMF is equivalent to the Linear model introduced in Sec. 4.2. The comparison between the first three rows shows that merely prompting the top layers of the two transformers not only cannot achieve multimodal fusion. Oppositely, it will disturb the feature space of two transformers, which finally hurts the performance. Though the mapping functions give the biggest boost to the performance, it should be noted that the mapping functions " + }, + { + "bbox": [ + 304, + 306, + 546, + 450 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 304, + 306, + 546, + 450 + ], + "type": "text", + "content": " cannot work without QP querying the fusion intermediates." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 450, + 547, + 605 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 450, + 547, + 605 + ], + "spans": [ + { + "bbox": [ + 304, + 450, + 547, + 605 + ], + "type": "text", + "content": "In addition, the comparison between the last four rows shows that decoupling the prompts into three individual modules with different learning objectives brings a performance gain. More specifically, the comparison between the fifth and sixth row in Tab. 3 shows that an extended QP cannot replace QCP. Since only the output of QP tokens are fused to the other modality while that of QCP discarded, replacing QCP with a longer QP not only increases the computation as the sequences in the fusion stage are longer but also results in a damaged performance. As a result, every module introduced in PMF contributes to the quality of multimodal fusion. The missing of any of the four modules will bring a performance drop at different scales." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 605, + 547, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 547, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 547, + 714 + ], + "type": "text", + "content": "Fusion Layer. We now investigate impacts brought by different fusion layers " + }, + { + "bbox": [ + 304, + 605, + 547, + 714 + ], + "type": "inline_equation", + "content": "L_{f}" + }, + { + "bbox": [ + 304, + 605, + 547, + 714 + ], + "type": "text", + "content": " to the fusion performance and memory efficiency. The results are summarized in Fig. 4. As can be seen in the figure, the training memory usage keeps decreasing as the fusion starts later. However, the performance of the fusion model is relatively consistent with " + }, + { + "bbox": [ + 304, + 605, + 547, + 714 + ], + "type": "inline_equation", + "content": "L_{f} \\leq 10" + }, + { + "bbox": [ + 304, + 605, + 547, + 714 + ], + "type": "text", + "content": ". Therefore, adding prompts only on the deep layers " + }, + { + "bbox": [ + 304, + 605, + 547, + 714 + ], + "type": "inline_equation", + "content": "(10 < l < L)" + }, + { + "bbox": [ + 304, + 605, + 547, + 714 + ], + "type": "text", + "content": " is empirically better for the trade-off between performance and memory efficiency." + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "2610" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 49, + 70, + 286, + 155 + ], + "blocks": [ + { + "bbox": [ + 49, + 70, + 286, + 155 + ], + "lines": [ + { + "bbox": [ + 49, + 70, + 286, + 155 + ], + "spans": [ + { + "bbox": [ + 49, + 70, + 286, + 155 + ], + "type": "table", + "html": "
Text EncoderImage EncoderMemory Usage Train/InferenceMM-IMDB
bert-basevit-base12.84 / 4.0858.77 / 64.51
bert-basevit-large14.16 / 4.8959.70 / 65.20
bert-largevit-base17.17 / 5.5360.08 / 65.41
bert-largevit-large18.44 / 6.4261.66 / 66.72
", + "image_path": "2be1528f5f0ba4cec100172f4e1342ad15ef2e62b09a489c006207b055c0f061.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 49, + 226, + 285, + 272 + ], + "blocks": [ + { + "bbox": [ + 47, + 163, + 287, + 207 + ], + "lines": [ + { + "bbox": [ + 47, + 163, + 287, + 207 + ], + "spans": [ + { + "bbox": [ + 47, + 163, + 287, + 207 + ], + "type": "text", + "content": "Table 4. Comparison of PMF applying to different unimodal transformers. We set the fusion layer " + }, + { + "bbox": [ + 47, + 163, + 287, + 207 + ], + "type": "inline_equation", + "content": "L_{f} = L - 2" + }, + { + "bbox": [ + 47, + 163, + 287, + 207 + ], + "type": "text", + "content": " and prompt length " + }, + { + "bbox": [ + 47, + 163, + 287, + 207 + ], + "type": "inline_equation", + "content": "M = 4" + }, + { + "bbox": [ + 47, + 163, + 287, + 207 + ], + "type": "text", + "content": " in all experiments. MM-IMDB is reported with F1-Macro / F1-Micro." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 49, + 226, + 285, + 272 + ], + "lines": [ + { + "bbox": [ + 49, + 226, + 285, + 272 + ], + "spans": [ + { + "bbox": [ + 49, + 226, + 285, + 272 + ], + "type": "table", + "html": "
Training MemorySNLI-VEFood-101MM-IMDBAvg.
33.36 GB72.2792.159.67 / 65.5775.66
", + "image_path": "f05c7a881e3e36a64cb2ae0350b543550f8eb958b224013ef2c0ebeac63ba04a.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 280, + 286, + 314 + ], + "lines": [ + { + "bbox": [ + 47, + 280, + 286, + 314 + ], + "spans": [ + { + "bbox": [ + 47, + 280, + 286, + 314 + ], + "type": "text", + "content": "Table 5. Performance of PMF applied with NAS. MM-IMDB is F1-Macro / F1-Micro, others are accuracy. We only report the training memory usage." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 342, + 286, + 462 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 342, + 286, + 462 + ], + "spans": [ + { + "bbox": [ + 46, + 342, + 286, + 462 + ], + "type": "text", + "content": "Prompt Length. The ablation study on prompt length is carried out with three kinds of prompts set to have the same length (i.e. " + }, + { + "bbox": [ + 46, + 342, + 286, + 462 + ], + "type": "inline_equation", + "content": "M_{qp} = M_{qcp} = M_{fcp}" + }, + { + "bbox": [ + 46, + 342, + 286, + 462 + ], + "type": "text", + "content": "). Fig. 5 summarizes the results. The performance increases as the prompt length grows longer when " + }, + { + "bbox": [ + 46, + 342, + 286, + 462 + ], + "type": "inline_equation", + "content": "M \\leq 16" + }, + { + "bbox": [ + 46, + 342, + 286, + 462 + ], + "type": "text", + "content": ", and drops when the prompts are too long (" + }, + { + "bbox": [ + 46, + 342, + 286, + 462 + ], + "type": "inline_equation", + "content": "M = 32" + }, + { + "bbox": [ + 46, + 342, + 286, + 462 + ], + "type": "text", + "content": "). It should be stressed that the training memory usage only increases around 1 GB as the prompt length grows from 1 to 16, which means the fusion layer " + }, + { + "bbox": [ + 46, + 342, + 286, + 462 + ], + "type": "inline_equation", + "content": "L_f" + }, + { + "bbox": [ + 46, + 342, + 286, + 462 + ], + "type": "text", + "content": " is the major factor of the training memory usage instead of prompt length." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 480, + 194, + 493 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 480, + 194, + 493 + ], + "spans": [ + { + "bbox": [ + 47, + 480, + 194, + 493 + ], + "type": "text", + "content": "4.6. Modularity and Flexibility" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 502, + 286, + 563 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 502, + 286, + 563 + ], + "spans": [ + { + "bbox": [ + 46, + 502, + 286, + 563 + ], + "type": "text", + "content": "PMF is highly modular, which means it is trivial to replace the unimodal transformers when there are better ones. In this section, we first describe how to replace the unimodal transformer and then show the benefits of such flexibility through experiments with larger pretrained models." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 566, + 286, + 674 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 566, + 286, + 674 + ], + "spans": [ + { + "bbox": [ + 46, + 566, + 286, + 674 + ], + "type": "text", + "content": "Since the total transformer layers, " + }, + { + "bbox": [ + 46, + 566, + 286, + 674 + ], + "type": "inline_equation", + "content": "L_{img}" + }, + { + "bbox": [ + 46, + 566, + 286, + 674 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 566, + 286, + 674 + ], + "type": "inline_equation", + "content": "L_{txt}" + }, + { + "bbox": [ + 46, + 566, + 286, + 674 + ], + "type": "text", + "content": " of each unimodal transformer are now different, the unimodal base features of two modalities now take different layers to extract, and the number of remaining layers for fusion stays the same. Simply, the fusion layers " + }, + { + "bbox": [ + 46, + 566, + 286, + 674 + ], + "type": "inline_equation", + "content": "L_{f}" + }, + { + "bbox": [ + 46, + 566, + 286, + 674 + ], + "type": "text", + "content": " of two transformers can be further specified as " + }, + { + "bbox": [ + 46, + 566, + 286, + 674 + ], + "type": "inline_equation", + "content": "L_{f - img} = L_{img} - 2" + }, + { + "bbox": [ + 46, + 566, + 286, + 674 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 566, + 286, + 674 + ], + "type": "inline_equation", + "content": "L_{f - txt} = L_{txt} - 2" + }, + { + "bbox": [ + 46, + 566, + 286, + 674 + ], + "type": "text", + "content": ". In addition, the difference between different hidden dimensions " + }, + { + "bbox": [ + 46, + 566, + 286, + 674 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 46, + 566, + 286, + 674 + ], + "type": "text", + "content": " is automatically handled by the non-linear mapping functions " + }, + { + "bbox": [ + 46, + 566, + 286, + 674 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 46, + 566, + 286, + 674 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 677, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 286, + 713 + ], + "type": "text", + "content": "The results shown in Tab. 4 clearly demonstrate that PMF can be empowered by larger unimodal transformers with a very limited increase of training memory usage." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 72, + 400, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 72, + 400, + 83 + ], + "spans": [ + { + "bbox": [ + 306, + 72, + 400, + 83 + ], + "type": "text", + "content": "4.7. PMF with NAS" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 91, + 545, + 187 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 91, + 545, + 187 + ], + "spans": [ + { + "bbox": [ + 304, + 91, + 545, + 187 + ], + "type": "text", + "content": "The hyper-parameters introduced in the proposed PMF are fusion layer " + }, + { + "bbox": [ + 304, + 91, + 545, + 187 + ], + "type": "inline_equation", + "content": "L_{f}" + }, + { + "bbox": [ + 304, + 91, + 545, + 187 + ], + "type": "text", + "content": " and prompt length " + }, + { + "bbox": [ + 304, + 91, + 545, + 187 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 304, + 91, + 545, + 187 + ], + "type": "text", + "content": ". Although PMF works well without exhausting hyper-parameter tuning, it is still preferable to have specific settings for every different task and data distribution. In this section, we experiment with automatic fusion structure search via AutoFormer [5]. A detailed description of the search space and evolution search can be found in the supplementary material." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 188, + 545, + 248 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 188, + 545, + 248 + ], + "spans": [ + { + "bbox": [ + 304, + 188, + 545, + 248 + ], + "type": "text", + "content": "Tab. 5 shows the performance of NAS-applied PMF on three datasets. With an increase in training memory usage, PMF-NAS achieves better results than regular PMF with the same vision and language encoders, greatly reducing the workload of finding the preferable fusion structure." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 262, + 477, + 275 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 262, + 477, + 275 + ], + "spans": [ + { + "bbox": [ + 305, + 262, + 477, + 275 + ], + "type": "text", + "content": "5. Limitations and Future Works" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 283, + 545, + 356 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 283, + 545, + 356 + ], + "spans": [ + { + "bbox": [ + 304, + 283, + 545, + 356 + ], + "type": "text", + "content": "The first limitation is that PMF's performance on three datasets is still behind finetuning baselines with the same pretrained backbones, indicating more work developing prompt-based methods to fully leverage the knowledge inside the pretrained models in the future, finally achieving equivalent or surpassing results through prompting." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 357, + 545, + 417 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 357, + 545, + 417 + ], + "spans": [ + { + "bbox": [ + 304, + 357, + 545, + 417 + ], + "type": "text", + "content": "The second limitation is about the hyper-parameters tuning: It is preferable to decouple prompts into three kinds by their roles in multimodal fusion. However, it also brings more work to hyper-parameter tuning if someone is expecting the best results via an optimal fusion structure." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 418, + 545, + 464 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 418, + 545, + 464 + ], + "spans": [ + { + "bbox": [ + 304, + 418, + 545, + 464 + ], + "type": "text", + "content": "Our future research endeavours will involve further investigation of the PMF in diverse multimodal understanding tasks such as Visual Question Answering, utilizing various model architectures." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 306, + 480, + 378, + 492 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 480, + 378, + 492 + ], + "spans": [ + { + "bbox": [ + 306, + 480, + 378, + 492 + ], + "type": "text", + "content": "6. Conclusion" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 501, + 545, + 644 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 501, + 545, + 644 + ], + "spans": [ + { + "bbox": [ + 304, + 501, + 545, + 644 + ], + "type": "text", + "content": "We propose a new form of modular multimodal fusion framework which demonstrates high flexibility and facilitates a two-way interaction among different modalities, namely PMF. PMF leverages three types of interactive prompts in order to dynamically learn different objectives for multimodal learning. By adding the prompts only on the deep layers of utilized unimodal transformers, PMF can significantly reduce the memory usage of the gradient calculation in the backward propagation. Through extensive experiments, we demonstrate that PMF is quite memory-efficient and yet able to perform comparably with existing finetuning baselines." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 306, + 659, + 416, + 673 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 659, + 416, + 673 + ], + "spans": [ + { + "bbox": [ + 306, + 659, + 416, + 673 + ], + "type": "text", + "content": "7. Acknowledgement" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 306, + 679, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 679, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 306, + 679, + 545, + 712 + ], + "type": "text", + "content": "This work was supported in part by the Australian Research Council (ARC) under Grant DP200100938." + } + ] + } + ], + "index": 19 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "type": "text", + "content": "2611" + } + ] + } + ], + "index": 20 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 288, + 712 + ], + "type": "list", + "angle": 0, + "index": 13, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 146 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 146 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 146 + ], + "type": "text", + "content": "[1] Jean-Baptiste Alayrac, Jeff Donahue, Pauline Luc, Antoine Miech, Iain Barr, Yana Hasson, Karel Lenc, Arthur Mensch, Katie Millican, Malcolm Reynolds, et al. 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The problem stems from the large number of operations (e.g., floating point multiplications and additions) and memory consumption required during training by the back-propagation algorithm. Consequently, in this paper, we propose a new gradient filtering approach which enables on-device CNN model training. More precisely, our approach creates a special structure with fewer unique elements in the gradient map, thus significantly reducing the computational complexity and memory consumption of back propagation during training. Extensive experiments on image classification and semantic segmentation with multiple CNN models (e.g., MobileNet, DeepLabV3, UPerNet) and devices (e.g., Raspberry Pi and Jetson Nano) demonstrate the effectiveness and wide applicability of our approach. For example, compared to SOTA, we achieve up to $19 \\times$ speedup and $77.1\\%$ memory savings on ImageNet classification with only $0.1\\%$ accuracy loss. Finally, our method is easy to implement and deploy; over $20 \\times$ speedup and $90\\%$ energy savings have been observed compared to highly optimized baselines in MKLDNN and CUDNN on NVIDIA Jetson Nano. Consequently, our approach opens up a new direction of research with a huge potential for on-device training. $^{1}$", + "bbox": [ + 76, + 301, + 473, + 680 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 710, + 209, + 726 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Existing approaches for on-device training are neither efficient nor practical enough to satisfy the resource constraints of edge devices (Figure 1). This is because these methods do not properly address a fundamental problem in on-device training, namely the computational and memory complexity of the back-propagation (BP) algorithm. More precisely, although the architecture modification [6] and layer freezing [18, 20] can help skipping the BP for some layers, for other layers, the complexity remains high. Gra", + "bbox": [ + 75, + 736, + 470, + 875 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "dient quantization [4, 7] can reduce the cost of arithmetic operations but cannot reduce the number of operations (e.g., multiplications); thus, the speedup in training remains limited. Moreover, gradient quantization is not supported by existing deep-learning frameworks (e.g., CUDNN [9], MKLDNN [1], PyTorch [25] and Tensorflow [2]). To enable on-device training, there are two important questions must be addressed:", + "bbox": [ + 496, + 268, + 893, + 391 + ], + "page_idx": 0 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- How can we reduce the computational complexity of back propagation through the convolution layers?", + "- How can we reduce the data required by the gradient computation during back propagation?" + ], + "bbox": [ + 517, + 404, + 893, + 479 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "In this paper, we propose gradient filtering, a new research direction, to address both questions. By addressing the first question, we reduce the computational complexity of training; by addressing the second question, we reduce the memory consumption.", + "bbox": [ + 496, + 489, + 892, + 566 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "In general, the gradient propagation through a convolution layer involves multiplying the gradient of the output variable with a Jacobian matrix constructed with data from either the input feature map or the convolution kernel. We aim at simplifying this process with the new gradient filtering approach proposed in Section 3. Intuitively, if the gradient map w.r.t. the output has the same value for all entries, then the computation-intensive matrix multiplication can be greatly simplified, and the data required to construct the Jacobian matrix can be significantly reduced. Thus, our gradient filtering can approximate the gradient w.r.t. the output by creating a new gradient map with a special (i.e., spatial) structure and fewer unique elements. By doing so, the gradient propagation through the convolution layers reduces to cheaper operations, while the data required (hence memory) for the forward propagation also lessens. Through this filtering process, we trade off the gradient precision against the computation complexity during BP. We note that gradient filtering does not necessarily lead to a worse precision, i.e., models sometimes perform better with filtered gradients when compared against models trained with vanilla BP.", + "bbox": [ + 496, + 568, + 893, + 883 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "In summary, our contributions are as follows:", + "bbox": [ + 517, + 885, + 820, + 900 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "$^{1}$ Code: https://github.com/SLDGroup/GradientFilter-CVPR23", + "bbox": [ + 94, + 886, + 426, + 900 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "3811", + "bbox": [ + 482, + 944, + 513, + 955 + ], + "page_idx": 0 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- We propose gradient filtering, which reduces the computation and memory required for BP by more than two orders of magnitude compared to the exact gradient calculation.", + "- We provide a rigorous error analysis which shows that the errors introduced by the gradient filtering have only a limited influence on model accuracy.", + "- Our experiments with multiple CNN models and computer vision tasks show that we can train a neural network with significantly less computation and memory costs, with only a marginal accuracy loss compared to baseline methods. Side-by-side comparisons against other training acceleration techniques also suggest the effectiveness of our method.", + "- Our method is easy to deploy with highly optimized deep learning frameworks (e.g., MKLDNN [1] and CUDNN [9]). Evaluations on resource-constrained edge (Raspberry Pi and Jetson Nano) and high-performance devices (CPU/GPU) show that our method is highly suitable for real life deployment." + ], + "bbox": [ + 96, + 90, + 470, + 428 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "The paper is organized as follows. Section 2 reviews relevant work. Section 3 presents our method in detail. Section 4 discusses error analysis, computation and memory consumption. Experimental results are presented in Section 5. Finally, Section 6 summarizes our main contributions.", + "bbox": [ + 76, + 436, + 468, + 513 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 76, + 526, + 218, + 542 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Architecture Modification: Authors of [6] propose to attach small branches to the original neural network. During training, the attached branches and biases in the original model are updated. Though memory consumption is reduced, updating these branches still needs gradient propagation through the entire network; moreover, a large computational overhead for inference is introduced.", + "bbox": [ + 76, + 551, + 468, + 657 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Layer Freezing: Authors of [18, 20] propose to only train parts of the model. [18] makes layer selection based on layer importance metrics, while [20] uses evolutionary search. However, the layers selected by all these methods are typically computationally heavy layers (e.g., the last few layers in ResNet [14]) which consume most of the resources. Thus, the speedup achieved by these approaches is limited.", + "bbox": [ + 76, + 657, + 468, + 763 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Gradient Quantization: [3,5] quantize gradient after backpropagation, which means these methods cannot accelerate the training on a single device. Work in [4,7,15,17,28, 29, 33] accelerates training by reducing the cost for every arithmetic operation. However, these methods do not reduce the number of operations, which is typically huge for SOTA CNNs, so their achievable speedup is limited. Also, all these methods are not supported by the popular deep learning frameworks [1,2,9,25].", + "bbox": [ + 76, + 763, + 468, + 901 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/73ae460d6f7ea1dfc9ccee277a7dfe2ba9e447c8c043b143039ccc3c61d20a44.jpg", + "image_caption": [ + "Figure 1. Matrix of orthogonal directions for on-device training. \"Arch\" is short for \"architecture\". Our approach opens up a new direction of research for on-device training for EdgeAI." + ], + "image_footnote": [], + "bbox": [ + 498, + 87, + 890, + 306 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In contrast to the prior work, our method opens up a new research direction. More precisely, we reduce the number of computations and memory consumption required for training a single layer via gradient filtering. Thus, our method can be combined with any of the methods mentioned above. For example, in Section H in the Supplementary, we illustrate how our method can work together with the gradient quantization methods to enable a higher speedup.", + "bbox": [ + 498, + 388, + 892, + 510 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "3. Proposed Method", + "text_level": 1, + "bbox": [ + 500, + 530, + 671, + 547 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In this section, we introduce our gradient filtering approach to accelerate BP. To this end, we target the most computation and memory heavy operation, i.e., convolution (Figure 2(a)). Table 1 lists some symbols we use.", + "bbox": [ + 498, + 556, + 890, + 619 + ], + "page_idx": 1 + }, + { + "type": "table", + "img_path": "images/d7c95e0cc4846b3bae26a33e63d83706d275a184ce3c3ce8de226e0812b9540a.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
CxNumber of channels of x
Wx, HxWidth and height of x
θConvolution kernel
θ'Rotated θ, i.e., θ' = rot180(θ)
rPatch size (r × r)
gx, gy, gθGradients w.r.t. x, y, θ
gyApproximated gradient gy
x, θ'Sum of x and θ' over spatial dimensions (height and width)
x[n, ci, h, w]Element for feature map x at batch n, channel ci, pixel (h, w)
θ[c_o, c_i, u, v]Element for convolution kernel θ at output channel co, input channel ci, position (u, v)
", + "bbox": [ + 506, + 643, + 885, + 873 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Table 1. Table of symbols we use.", + "bbox": [ + 591, + 882, + 797, + 896 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "3812", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/8111d331612d65e54228ae093e287e0c50aac9ba36ac30aa6855cc06e9e6fb23.jpg", + "image_caption": [ + "Figure 2. (a) Computation procedures for vanilla training method (upper) and our method (lower). (b) Example of gradient propagation with gradient filtering. Numbers in this example are chosen randomly for illustration purposes. In this case, the patch size selected for the gradient filter is $2 \\times 2$ . Thus, the $4 \\times 4$ gradient map $g_{y}$ is approximated by $\\tilde{g}_{y}$ , which has four $2 \\times 2$ patches with one unique value for each patch. Also, input feature map $x$ and mirrored convolution kernel $\\theta'$ are spatial summed to $\\tilde{x}$ and $\\tilde{\\theta}'$ . Since $\\tilde{x}$ has fewer unique values than $x$ , memory consumption is reduced. Finally, with $\\tilde{g}_{y}, \\tilde{x}$ and $\\tilde{\\theta}$ , we compute the gradient w.r.t. kernel and input feature map with much fewer operations than the standard back propagation method." + ], + "image_footnote": [ + "Forward Propagation", + "Backward Propagation", + "Average Filter", + "$②$ Spatial Sum", + "Convolution", + "Frobenius Inner Product", + "Element-wise Product" + ], + "bbox": [ + 76, + 85, + 504, + 289 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Problem Setup", + "text_level": 1, + "bbox": [ + 76, + 422, + 227, + 439 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The computations for both forward and backward paths are shown in Figure 2(a). For the standard (vanilla) approach (upper Figure 2(a)), starting with input $x$ , the forward propagation convolves the input feature map $x$ with kernel $\\theta$ and returns output $y$ , which is further processed by the other layers in the neural network (dotted arrow) until the loss value $l$ is calculated. As shown in Figure 2(a), the BP of the convolution layer starts with the gradient map w.r.t. output $y(g_{y})$ . The gradient w.r.t. input $(g_{x})$ is calculated by convolving $g_{y}$ with the rotated convolution kernel $\\theta'$ , i.e., $g_{x} = g_{y} \\otimes \\mathrm{rot}180(\\theta) = g_{y} \\otimes \\theta'$ . The gradient w.r.t. convolution kernel, namely $g_{\\theta}$ , is calculated with the Frobenius inner product [16] between $x$ and $g_{y}$ , i.e., $g_{\\theta} = g_{y} \\otimes f(x)$ .", + "bbox": [ + 75, + 446, + 468, + 643 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The lower half of Figure 2(a) shows our method, where several changes are made: We introduce the gradient filter \"A\" after $g_{y}$ to generate the approximate gradient for BP. Also, instead of using the accurate $x$ and $\\theta^{\\prime}$ values for gradient computation, we sum over spatial dimensions (height and width dimensions), i.e., $\\tilde{x}$ and $\\tilde{\\theta}^{\\prime}$ , respectively. Finally, the convolution layer now multiplies the approximate gradient $\\tilde{g}_{y}$ with spatial kernel $\\tilde{\\theta}^{\\prime}$ instead of convolving with it to calculate $\\tilde{g}_x$ . Figure 2(b) shows an example of gradient propagation with our gradient filter.", + "bbox": [ + 75, + 643, + 468, + 792 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. Preliminary Analysis", + "text_level": 1, + "bbox": [ + 76, + 801, + 274, + 816 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Consider the vanilla BP for convolution in Figure 2(a). Equation (1) shows the number of computations (#FLOPs) required to calculate $g_{x}$ given $g_{y}$ :", + "bbox": [ + 75, + 824, + 467, + 871 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\# \\text {F L O P s} = 2 C _ {x} C _ {y} \\cdot W _ {y} H _ {y} \\cdot W _ {\\theta} H _ {\\theta} \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 151, + 883, + 468, + 902 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The computation requirements in Equation (1) belong to three categories: number of channels, number of unique elements per channel in the gradient map, and kernel size. Our method focuses on the last two categories.", + "bbox": [ + 498, + 422, + 890, + 484 + ], + "page_idx": 2 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "i. Unique elements: $(W_yH_y)$ represents the number of unique elements per channel in the gradient w.r.t. output variable $y$ ( $g_y$ ). Given the high-resolution images we use, this term is huge, so if we manage to reduce the number of unique elements in the spatial dimensions (height and width), the computations required are greatly reduced too.", + "ii. Kernel size: $(W_{\\theta}H_{\\theta})$ represents the number of unique elements in the convolution kernel. If the gradient $g_{y}$ has some special structure, for example $g_{y} = 1_{H_{y}\\times W_{y}}\\cdot v$ (i.e., every element in $g_{y}$ has the same value $v$ ), then the convolution can be simplified to $(\\sum \\theta^{\\prime})v1_{H_{y}\\times W_{y}}$ (with boundary elements ignored). With such a special structure, only one multiplication and $(W_{\\theta}H_{\\theta} - 1)$ additions are required. Moreover, $\\sum \\theta^{\\prime}$ is independent of data so the result can be shared across multiple images until $\\theta$ gets updated." + ], + "bbox": [ + 496, + 484, + 890, + 710 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.3. Gradient Filtering", + "text_level": 1, + "bbox": [ + 500, + 719, + 678, + 734 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "To reduce the number of unique elements and create the special structure in the gradient map, we apply the gradient filter after the gradient w.r.t. output $(g_y)$ is provided. During the backward propagation, the gradient filter $\\langle \\mathbf{A}\\rangle$ approximates the gradient $g_{y}$ by spatially cutting the gradient map into $r\\times r$ -pixel patches and then replacing all elements in each patch with their average value (Figure 2(b)):", + "bbox": [ + 496, + 742, + 890, + 848 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\tilde {g} _ {y} [ n, c _ {o}, h, w ] = \\frac {1}{r ^ {2}} \\sum_ {i = \\lfloor h / r \\rfloor r} ^ {\\lceil h / r \\rceil r} \\sum_ {j = \\lfloor w / r \\rfloor r} ^ {\\lceil w / r \\rceil r} g _ {y} [ n, c _ {o}, i, j ] \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 514, + 857, + 890, + 902 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "3813", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "For instance in Figure 2(b), we replace the 16 distinct values in the gradient map $g_{y}$ with 4 average values in $\\tilde{g}_{y}$ . So given a gradient map $g_{y}$ with $N$ images per batch, $C$ channels, and $H \\times W$ pixels per channel, the gradient filter returns a structured approximation of the gradient map containing only $N \\times C \\times \\left\\lceil \\frac{H}{r} \\right\\rceil \\times \\left\\lceil \\frac{W}{r} \\right\\rceil$ blocks, with one unique value per patch. We use this matrix of unique values to represent the approximate gradient map $\\tilde{g}_{y}$ , as shown in Figure 2(b).", + "bbox": [ + 75, + 90, + 472, + 213 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.4. Back Propagation with Gradient Filtering", + "text_level": 1, + "bbox": [ + 76, + 222, + 437, + 239 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We describe now the computation procedure used after applying the gradient filter. Detailed derivations are provided in Supplementary Section B.", + "bbox": [ + 76, + 247, + 468, + 291 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Gradient w.r.t. input: The gradient w.r.t. input is calculated by convolving $\\theta^{\\prime}$ with $g_{y}$ (Figure 2(a)). With the approximate gradient $\\tilde{g}_y$ , this convolution simplifies to:", + "bbox": [ + 76, + 292, + 468, + 339 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\tilde {g} _ {x} [ n, c _ {i}, h, w ] = \\sum_ {c _ {o}} \\tilde {g} _ {y} [ n, c _ {o}, h, w ] \\odot \\tilde {\\theta} ^ {\\prime} [ c _ {o}, c _ {i} ] \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 114, + 351, + 468, + 383 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\tilde{\\theta}^{\\prime}[c_o,c_i] = \\sum_{u,v}\\theta^{\\prime}[c_o,c_i,u,v]$ is the spatial sum of convolution kernel $\\theta$ , as shown in Figure 2(b).", + "bbox": [ + 76, + 397, + 468, + 428 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Gradient w.r.t. kernel: The gradient w.r.t. the kernel is calculated by taking the Frobenius inner product between $x$ and $g_{y}$ , i.e., $g_{\\theta}[c_o, c_i, u, v] = x \\oplus g_{y}$ , namely:", + "bbox": [ + 76, + 429, + 468, + 476 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\ng _ {\\theta} \\left[ c _ {o}, c _ {i}, u, v \\right] = \\sum_ {n, i, j} x \\left[ n, c _ {i}, i + u, j + v \\right] g _ {y} \\left[ n, c _ {o}, i, j \\right] \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 84, + 487, + 468, + 521 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "With the approximate gradient $\\tilde{g}_y$ , the operation can be simplified to:", + "bbox": [ + 76, + 532, + 468, + 563 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\tilde {g} _ {\\theta} \\left[ c _ {o}, c _ {i}, u, v \\right] = \\sum_ {n, i, j} \\tilde {x} [ n, c _ {i}, i, j ] \\tilde {g} _ {y} [ n, c _ {o}, i, j ] \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 119, + 575, + 468, + 609 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "with $\\tilde{x}[n,c_i,i,j] = \\sum_{h = [i / r]\\rfloor r}^{\\lceil i / r\\rceil r}\\sum_{w = \\lfloor j / r\\rfloor r}^{\\lceil j / r\\rceil r}x[n,c_i,h,w].$ As shown in Figure 2(b), $\\tilde{x}[n,c_i,i,j]$ is the spatial sum of $x$ elements in the same patch containing pixel $(i,j)$ .", + "bbox": [ + 76, + 619, + 468, + 672 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4. Analyses of Proposed Approach", + "text_level": 1, + "bbox": [ + 76, + 686, + 369, + 705 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In this section, we analyze our method from three perspectives: gradient filtering approximation error, computation reduction, and memory cost reduction.", + "bbox": [ + 76, + 714, + 468, + 758 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4.1. Error Analysis of Gradient Filtering", + "text_level": 1, + "bbox": [ + 76, + 770, + 393, + 787 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We prove that the approximation error introduced by our gradient filtering is bounded during the gradient propagation. Without losing generality, we consider that all variables have only one channel, i.e., $C_{x_0} = C_{x_1} = 1$ .", + "bbox": [ + 76, + 794, + 468, + 854 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Proposition 1: For any input-output channel pair $(c_{o}, c_{i})$ in the convolution kernel $\\theta$ , assuming the DC component has the largest energy value compared to all components in", + "bbox": [ + 76, + 854, + 468, + 900 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "the spectrum $^2$ , then the signal-to-noise-ratio (SNR) of $\\tilde{g}_x$ is greater than SNR of $\\tilde{g}_y$ .", + "bbox": [ + 498, + 90, + 890, + 121 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Proof: We use $G_{x}, G_{y}$ and $\\Theta$ to denote the gradients $g_{x}, g_{y}$ and the convolution kernel $\\theta$ in the frequency domain; $G_{x}[u, v]$ is the spectrum value at frequency $(u, v)$ and $\\delta$ is the 2D discrete Dirichlet function. To simplify the discussion, we consider only one patch of size $r \\times r$ .", + "bbox": [ + 498, + 121, + 890, + 196 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The gradient returned by the gradient filtering can be written as:", + "bbox": [ + 500, + 196, + 890, + 224 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\tilde {g} _ {y} = \\frac {1}{r ^ {2}} 1 _ {r \\times r} * g _ {y} \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 630, + 222, + 890, + 250 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\circ$ denotes convolution. By applying the discrete Fourier transformation, Equation (6) can be rewritten in the frequency domain as:", + "bbox": [ + 498, + 253, + 890, + 299 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\tilde {G} _ {y} [ u, v ] = \\frac {1}{r ^ {2}} \\delta [ u, v ] G _ {y} [ u, v ] \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 596, + 305, + 890, + 335 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "$\\tilde{g}_y$ is the approximation of $g_{y}$ (i.e., the ground truth for $\\tilde{g}_y$ is $g_{y}$ ), and the SNR of $\\tilde{g}_y$ equals to:", + "bbox": [ + 498, + 340, + 890, + 372 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\mathrm {S N R} _ {\\tilde {g} _ {y}} = \\frac {\\sum_ {(u , v)} G _ {y} ^ {2} [ u , v ]}{\\sum_ {(u , v)} \\left(G _ {y} [ u , v ] - \\frac {1}{r ^ {2}} \\delta [ u , v ] G _ {y} [ u , v ]\\right) ^ {2}} \\tag {8} \\\\ = (1 - \\frac {2 r ^ {2} - 1}{r ^ {4}} \\frac {G _ {y} ^ {2} [ 0 , 0 ]}{\\sum_ {(u , v)} G _ {y} ^ {2} [ u , v ]}) ^ {- 1} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 519, + 378, + 890, + 458 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "For the convolution layer, the gradient w.r.t. the approximate variable $\\tilde{x}$ in the frequency domain is:", + "bbox": [ + 500, + 464, + 890, + 494 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\tilde {G} _ {x} [ u, v ] = \\Theta [ - u, - v ] \\tilde {G} _ {y} [ u, v ] \\\\ = \\frac {1}{r ^ {2}} \\Theta [ - u, - v ] \\delta [ u, v ] G _ {y} [ u, v ] \\tag {9} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 560, + 500, + 890, + 551 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "and its ground truth is:", + "bbox": [ + 500, + 558, + 653, + 571 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nG _ {x} [ u, v ] = \\Theta [ - u, - v ] G _ {y} [ u, v ] \\tag {10}\n$$\n", + "text_format": "latex", + "bbox": [ + 589, + 580, + 890, + 598 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Similar to Equation (8), the SNR of $g_{\\bar{x}}$ is:", + "bbox": [ + 500, + 604, + 777, + 619 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathrm {S N R} _ {\\tilde {g} _ {x}} = \\left(1 - \\frac {2 r ^ {2} - 1}{r ^ {4}} \\frac {(\\Theta [ 0 , 0 ] G _ {y} [ 0 , 0 ]) ^ {2}}{\\sum_ {(u , v)} (\\Theta [ u , v ] G _ {y} [ u , v ]) ^ {2}}\\right) ^ {- 1} \\tag {11}\n$$\n", + "text_format": "latex", + "bbox": [ + 514, + 626, + 890, + 676 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Equation (11) can be rewritten as:", + "bbox": [ + 500, + 676, + 725, + 691 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\frac {r ^ {4} \\left(1 - \\operatorname {S N R} _ {\\hat {g} _ {x}} ^ {- 1}\\right)}{2 r ^ {2} - 1} = \\frac {\\left(\\Theta [ 0 , 0 ] G _ {y} [ 0 , 0 ]\\right) ^ {2}}{\\sum_ {(u , v)} \\left(\\Theta [ - u , - v ] G _ {y} [ u , v ]\\right) ^ {2}} \\tag {12} \\\\ = \\frac {G _ {y} ^ {2} [ 0 , 0 ]}{\\sum_ {(u , v)} (\\frac {\\Theta [ - u , - v ]}{\\Theta [ 0 , 0 ]} G _ {y} [ u , v ]) ^ {2}} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 514, + 698, + 890, + 781 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Furthermore, the main assumption (i.e., the DC component dominates the frequency spectrum of $\\Theta$ ) can be written as:", + "bbox": [ + 500, + 787, + 890, + 816 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\Theta^ {2} [ 0, 0 ] / \\max _ {(u, v) \\neq (0, 0)} \\Theta^ {2} [ u, v ] \\geq 1 \\tag {13}\n$$\n", + "text_format": "latex", + "bbox": [ + 573, + 824, + 890, + 843 + ], + "page_idx": 3 + }, + { + "type": "page_footnote", + "text": "2As a reminder, the energy of a signal is the sum of energy of the DC component and the energy of its AC components.", + "bbox": [ + 500, + 849, + 890, + 875 + ], + "page_idx": 3 + }, + { + "type": "page_footnote", + "text": "3Because $g_{y}$ is convolved with the rotated kernel $\\theta'$ , in the frequency domain, we use $\\Theta[-u, -v]$ instead of $\\Theta[u, v]$ .", + "bbox": [ + 500, + 875, + 890, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "3814", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/091bb923c03287a7b9181226c0aaeffc2670817b0d471d7d830a652be75b22e0.jpg", + "image_caption": [ + "Figure 3. Computation analysis for a specific convolution layer4. Minimum achievable computation is given in Equation (16). By reducing the number of unique elements, computations required by our approach drop to about $1 / r^2$ compared with the standard BP method. By combining it with structured gradient map, computations required by our approach drop further, getting very close to the theoretical limit." + ], + "image_footnote": [], + "bbox": [ + 112, + 95, + 433, + 232 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "that is, $\\forall (u,v),\\frac{\\Theta^2[-u,-v]}{\\Theta^2[0,0]}\\leq 1$ ; thus, by combining Equation (12) and Equation (13), we have:", + "bbox": [ + 75, + 371, + 468, + 406 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\frac {G _ {y} ^ {2} [ 0 , 0 ]}{\\sum_ {(u , v)} \\left(\\frac {\\Theta [ - u , - v ]}{\\Theta [ 0 , 0 ]} G _ {y} [ u , v ]\\right) ^ {2}} \\geq \\frac {G _ {y} ^ {2} [ 0 , 0 ]}{\\sum_ {(u , v)} \\left(G _ {y} [ u , v ]\\right) ^ {2}} \\tag {14} \\\\ \\Leftrightarrow \\frac {r ^ {4} \\left(1 - \\mathrm {S N R} _ {\\tilde {g} _ {x}} ^ {- 1}\\right)}{2 r ^ {2} - 1} \\geq \\frac {r ^ {4} \\left(1 - \\mathrm {S N R} _ {\\tilde {g} _ {y}} ^ {- 1}\\right)}{2 r ^ {2} - 1} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 94, + 417, + 468, + 496 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "which means that: $\\mathrm{SNR}_{\\tilde{g}_x} \\geq \\mathrm{SNR}_{\\tilde{g}_y}$ . This completes our proof for error analysis.", + "bbox": [ + 75, + 505, + 468, + 535 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In conclusion, as the gradient propagates through the network, the noise introduced by our gradient filter becomes weaker compared to the real gradient signal. This property ensures that the error in gradient has only a limited influence on the quality of BP. We validate Proposition 1 later in the experimental section.", + "bbox": [ + 75, + 536, + 468, + 626 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.2. Computation and Overhead Analysis", + "text_level": 1, + "bbox": [ + 76, + 636, + 398, + 652 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In this section, we analyse the computation required to compute $g_{x}$ , the gradient w.r.t. input $x$ . Figure 3 compares the computation required to propagate the gradient through this convolution layer under different patch sizes $r \\times r$ . A patch size $1 \\times 1$ means the vanilla BP algorithm which we use as the baseline. As discussed in the preliminary analysis section (Section 3.2), two terms contribute to the computation savings: fewer unique elements in the gradient map and the structured gradient map.", + "bbox": [ + 75, + 660, + 468, + 795 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Fewer unique elements: In vanilla BP, there are $H_{y}W_{y}$ unique elements in the gradient map. After applying gradient filtering with a patch size $r \\times r$ , the number of unique", + "bbox": [ + 75, + 796, + 468, + 842 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "elements reduces to only $\\lceil \\frac{H_y}{r}\\rceil \\lceil \\frac{W_y}{r}\\rceil$ . This reduction contributes the most to the savings in computation (orange line in Figure 3).", + "bbox": [ + 500, + 88, + 890, + 135 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Structured Gradient Map: By creating the structured gradient map, the convolution over the gradient map $\\tilde{g}_y$ is simplified to the element-wise multiplication and channel-wise addition. Computation is thus reduced to $(H_{\\theta}W_{\\theta})^{-1}$ of its original value. For instance, the example convolution layer in Figure 3 uses a $3\\times 3$ convolution kernel so around $89\\%$ computations are removed. The blue line in Figure 3 shows the #FLOPs after combining both methods. Greater reduction is expected when applying our method with larger convolution kernels. For instance, FastDepth [30] uses $5\\times 5$ convolution kernel so as much as $96\\%$ reduction in computation can be achieved, in principle.", + "bbox": [ + 498, + 136, + 890, + 316 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Minimum Achievable Computation: With the two reductions mentioned above, the computation required to propagate the gradient through the convolution layer is:", + "bbox": [ + 498, + 316, + 890, + 363 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\# \\text {F L O P s} (r) = \\left\\lceil \\frac {H _ {y}}{r} \\right\\rceil \\left\\lceil \\frac {W _ {y}}{r} \\right\\rceil C _ {x} \\left(2 C _ {y} - 1\\right) + o \\left(H _ {y} W _ {y}\\right) \\tag {15}\n$$\n", + "text_format": "latex", + "bbox": [ + 506, + 369, + 890, + 401 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $o(H_yW_y)$ is a constant term which is independent of $r$ and negligible compared to $H_yW_y$ . When the patch is as large as the feature map, our method reaches the minimum achievable computation (blue dashed line in Figure 3):", + "bbox": [ + 498, + 409, + 890, + 470 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\min _ {r} \\# \\text {F L O P s} (r) = 2 C _ {x} C _ {y} - C _ {x} + o \\left(H _ {y} W _ {y}\\right) \\tag {16}\n$$\n", + "text_format": "latex", + "bbox": [ + 526, + 479, + 890, + 497 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In this case, each channel of the gradient map is represented with a single value, so the computation is controlled by the number of input and output channels.", + "bbox": [ + 498, + 506, + 890, + 551 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Overhead: The overhead of our approach comes from approximating the feature map $x$ , gradient $g_{y}$ , and kernel $\\theta$ . As the lower part of Figure 2(a) shows, the approximation for $x$ is considered as part of forward propagation, while the other two as back propagation. Indeed, with the patch size $r$ , the ratio of forward propagation overhead is about $1 / (2C_{o}W_{\\theta}H_{\\theta})$ , while the ratio of backward propagation overhead is about $(r^{2} - 1) / (2C_{x})$ .", + "bbox": [ + 498, + 551, + 890, + 672 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Given the large number of channels and spatial dimensions in typical neural networks, both overhead values take less than $1\\%$ computation in the U-Net example above.", + "bbox": [ + 498, + 672, + 890, + 717 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.3. Memory Analysis", + "text_level": 1, + "bbox": [ + 500, + 726, + 669, + 742 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "As Figure 2(a) shows, the standard back propagation for a convolution layer relies on the input feature map $x$ , which needs to be stored in memory during forward propagation. Since every convolution layer requiring gradient for its kernel needs to save a copy of feature map $x$ , the memory consumption for storing $x$ is huge. With our method, we simplify the feature map $x$ to approximated $\\tilde{x}$ , which has only $\\lceil \\frac{H_x}{r} \\rceil \\lceil \\frac{W_x}{r} \\rceil$ unique elements for every channel. Thus, by saving only these unique values, our method achieves around $(1 - \\frac{1}{r^2})$ memory savings, overall.", + "bbox": [ + 498, + 750, + 890, + 902 + ], + "page_idx": 4 + }, + { + "type": "page_footnote", + "text": "4The layer is from U-Net [26]. The size of the input is assumed to be $120 \\times 160$ pixels with 192 channels; the output has the same resolution, but with only 64 channels. The kernel size of the convolution layer is $3 \\times 3$ . Analysis for ResNet is included in the supplementary material.", + "bbox": [ + 76, + 849, + 468, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "3815", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/4ca6fe4ff02fd04384c037fda6de61dd75046c0361f049b90523657aaae02f5b.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MobileNetV2 [27]#LayersAccuracyFLOPsMemResNet-18 [14]#LayersAccuracyFLOPsMem
No Finetuning04.200No Finetuning04.700
VanillaAll75.11.13G24.33MBVanillaAll73.15.42G8.33MB
263.1113.68M245.00KBBP270.4489.20M196.00KB
BP462.2160.00M459.38KB472.31.14G490.00KB
TinyTL [6]N/A60.2663.51M683.00KBTinyTL [6]N/A69.23.88G1.76MB
Ours263.139.27M80.00KBOurs268.628.32M64.00KB
463.453.96M150.00KB468.561.53M112.00KB
MCUNet [19]#LayersAccuracyFLOPsMemResNet-34 [14]#LayersAccuracyFLOPsMem
No Finetune04.100No Finetune000
VanillaAll68.5231.67M9.17MBVanillaAll70.811.17G13.11MB
262.118.80M220.50KBBP269.6489.20M196.00KB
BP464.933.71M312.38KB472.31.21G392.00KB
TinyTL [6]N/A53.1148.01M571.5KBTinyTL [6]N/A72.98.03G2.95MB
Ours261.86.34M72.00KBOurs268.628.32M64.00KB
464.411.01M102.00KB470.664.07M128.00KB
", + "bbox": [ + 78, + 88, + 893, + 314 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/d5d94509c02b205c1c25ce092f30a0d1014640ac73ce9fe18e567b4916194f03.jpg", + "table_caption": [ + "Table 2. Experimental results for ImageNet classification with four neural networks (MobileNet-V2, ResNet18/34, MCUNet). \"#Layers\" is short for \"the number of active convolutional layers\". For example, #Layers equals to 2 means that only the last two convolutional layers are trained. For memory consumption, we only consider the memory for input feature $x$ . Strategy \"No Finetuning\" shows the accuracy on new datasets without finetuning the pretrained model. Since TinyTL [6] changes the architecture, \"#Layers\" is not applicable (N/A)." + ], + "table_footnote": [], + "table_body": "
PSPNet [32]#LayersGFLOPsmIoUmAccPSPNet-M [32]#LayersGFLOPsmIoUmAccFCN [21]#LayersGFLOPsmIoUmAcc
Calibration0012.8619.74Calibration0014.2020.46Calibration0010.9515.69
Vanilla BPAll166.555.0168.02Vanilla BPAll42.448.4861.48Vanilla BPAll170.345.2258.80
515.039.5451.86512.2236.3547.09559.527.4137.90
10110.653.1567.101022.4646.0158.7010100.943.8757.58
Ours50.1439.3451.86Ours50.1136.1446.86Ours50.5827.4237.88
100.7950.8864.73100.7644.9057.50100.9636.3048.82
DLV3 [8]#LayersGFLOPsmIoUmAccDLV3-M [8]#LayersGFLOPsmIoUmAccUPerNet [31]#LayersGFLOPsmIoUmAcc
Calibration0013.9520.62Calibration0021.9636.15Calibration0014.7121.82
Vanilla BPAll151.258.3271.72Vanilla BPAll54.455.6668.95Vanilla BPAll541.064.8877.13
518.040.8553.16514.838.2149.355503.947.9361.67
10102.054.6568.641033.147.9561.4910507.648.8363.02
Ours50.3133.0944.33Ours50.2635.4746.35Ours51.9747.0460.44
102.9647.1160.28101.4045.5358.99102.2248.0062.07
", + "bbox": [ + 78, + 396, + 892, + 550 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 3. Experimental results for semantic segmentation task on augmented Pascal VOC12 dataset [8]. Model name with postfix \"M\" means the model uses MobileNetV2 as backbone, otherwise ResNet18 is used. \"#Layers\" is short for \"the number of active convolutional layers\" that are trained. All models are pretrained on Cityscapes dataset [11]. Strategy \"Calibration\" shows the accuracy when only the classifier and normalization statistics are updated to adapt different numbers of classes between augmented Pascal VOC12 and Cityscapes.", + "bbox": [ + 75, + 561, + 892, + 617 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5. Experiments", + "text_level": 1, + "bbox": [ + 76, + 642, + 209, + 659 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Our experimental section consists of theoretical and practical evaluations. Sections 5.2-5.4 show the theoretical advantages of our method on image classification and semantic segmentation tasks with implementation-agnostic metrics (e.g., accuracy, FLOPs). Then, in Section 5.5, we show how these theoretical advantages translate into practical advantages (i.e., speedup and memory savings) on real edge devices.", + "bbox": [ + 75, + 667, + 470, + 789 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5.1. Experimental Setup", + "text_level": 1, + "bbox": [ + 76, + 801, + 266, + 816 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Classification: Following [24], we split every dataset into two highly non-i.i.d. partitions with the same size. Then, we pretrain our models on the first partition with a vanilla training strategy, and finetune the model on the other partition with different configurations for the training strat", + "bbox": [ + 75, + 824, + 468, + 902 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "egy (i.e., with/without gradient filtering, hyper-parameters, number of convolution layers to be trained). More details (e.g., hyper-parameters) are in the Supplementary.", + "bbox": [ + 496, + 643, + 890, + 688 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Segmentation: Models are pretrained on Cityscapes [11] by MMSegmentation [10]. Then, we calibrate and finetune these models with different training strategies on the augmented Pascal-VOC12 dataset following [8], which is the combination of Pascal-VOC12 [12] and SBD [13]. More details are included in the supplementary material.", + "bbox": [ + 496, + 688, + 890, + 779 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "On-device Performance Evaluation: For CPU performance evaluation, we implement our method with MKLDNN [1] (a.k.a. OneDNN) v2.6.0 and compare it with the convolution BP method provided by MKLDNN. We test on three CPUs, namely Intel 11900KF, Quad-core Cortex-A72 (Jetson Nano) and Quad-core Cortex-A53 (Raspberry Pi-3b). For GPU performance evaluation, we implement our method on CUDNN v8.2 [9] and compare with the BP", + "bbox": [ + 496, + 779, + 892, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "3816", + "bbox": [ + 482, + 944, + 516, + 955 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "method provided by CUDNN. We test on two GPUs, RTX 3090Ti and the edge GPU on Jetson Nano. Since both MKLDNN and CUDNN only support float32 BP, we test float32 BP only. Additionally, for the experiments on Jetson Nano, we record the energy consumption for CPU and GPU with the embedded power meter. More details (e.g., frequency) are included in the supplementary material.", + "bbox": [ + 75, + 90, + 472, + 196 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.2. ImageNet Classification", + "text_level": 1, + "bbox": [ + 76, + 204, + 295, + 220 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 2 shows our evaluation results on the ImageNet classification task. As shown, our method significantly reduces the FLOPs and memory required for BP, with very little accuracy loss. For example, for ResNet34, our method achieves $18.9 \\times$ speedup with $1.7\\%$ accuracy loss when training four layers; for MobileNetV2, we get a $1.2\\%$ better accuracy with $3.0 \\times$ speedup and $3.1 \\times$ memory savings. These results illustrate the effectiveness of our method. On most networks, TinyTL has a lower accuracy while consuming more resources compared to the baselines methods.", + "bbox": [ + 75, + 227, + 470, + 378 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.3. Semantic Segmentation", + "text_level": 1, + "bbox": [ + 76, + 387, + 294, + 402 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 3 shows our evaluation results on the augmented Pascal-VOC12 dataset. On a wide range of networks, our method constantly achieves significant speedup with marginal accuracy loss. For the large network UPerNet, our method achieves $229 \\times$ speedup with only $1\\%$ mIoU loss. For the small network PSPNet, our method speedups training by $140 \\times$ with only $2.27\\%$ mIoU loss. This shows the effectiveness of our method on a dense prediction task.", + "bbox": [ + 75, + 410, + 468, + 532 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.4. Hyper-Parameter Selection", + "text_level": 1, + "bbox": [ + 76, + 539, + 323, + 556 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Figure 4 shows our experimental results for ResNets under different hyper-parameter selection, i.e. number of convolution layers and patch size of gradient filter $r \\times r$ . Of note, the y-axis (MFLOPs) in Figure 4 is log scale. More results are included in Supplementary Section G. We highlight three qualitative findings in Figure 4:", + "bbox": [ + 75, + 561, + 468, + 654 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "a. For a similar accuracy, our method greatly reduces the number of operations (1 to 2 orders of magnitude), while for a similar number of computations, our method achieves a higher accuracy (2% to 5% better).", + "bbox": [ + 88, + 662, + 468, + 723 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "This finding proves the effectiveness of our method.", + "bbox": [ + 76, + 731, + 419, + 746 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "b. Given the number of convolution layers to be trained, the more accurate method returns a better accuracy. Baseline (i.e., standard BP) uses the most accurate gradient, Ours-R4 (BP with gradient filter with patch size $4 \\times 4$ ) uses the least accurate gradient; thus, Baseline $>$ Ours-R2 $>$ Ours-R4.", + "bbox": [ + 88, + 755, + 468, + 845 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "This finding is intuitive since the more accurate method should introduce smaller noise to the BP, e.g., the gradient filtering with patch size $2 \\times 2$ (Ours-R2) introduces less", + "bbox": [ + 76, + 854, + 468, + 900 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/1416129e05ab5a02b79a1cd3ff2e57355fbb725cdb5ca23f9cc84eea4d7156dc.jpg", + "image_caption": [ + "Figure 4. Computation (#MFLOPs, log scale) and model accuracy $[\\%]$ under different hyper-parameter selection. \"Baseline\" means vanilla BP; \"Ours-R2/4\" uses gradient filtering with patch size $2 \\times 2/4 \\times 4$ during BP." + ], + "image_footnote": [], + "bbox": [ + 498, + 90, + 893, + 287 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "noise than with patch size $4 \\times 4$ (Ours-R4). In Figure 5, we evaluate the relationship between accuracy and noise level introduced by gradient filtering. With a higher SNR (i.e., a lower noise level), a better accuracy is achieved.", + "bbox": [ + 498, + 377, + 892, + 439 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/73bcb391638f29be8c8a17d3f684bca07e65e98fcf947a2d41f3031cd2ff548f.jpg", + "image_caption": [ + "Figure 5. Relationship between accuracy and noise level introduced by the gradient filtering. As shown, accuracy increases as the SNR increases, i.e., noise level decreases." + ], + "image_footnote": [], + "bbox": [ + 544, + 449, + 848, + 530 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "c. Given the number of computations, the less accurate method returns the better accuracy by training more layers, i.e., Ours-R4 > Ours-R2 > baseline.", + "bbox": [ + 511, + 611, + 890, + 657 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "This finding suggests that for neural network training with relatively low computational resources, training more layers with less accurate gradients is preferable than training fewer layers with more accurate gradients.", + "bbox": [ + 498, + 667, + 890, + 729 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.5. On-device Performance Evaluation", + "text_level": 1, + "bbox": [ + 500, + 739, + 805, + 755 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Figure 6 and Table 4 show our evaluation results on real devices. More results are included in the Supplementary Section I. As Figure 6 shows, on CPU, most convolution layers achieve speedups over $20 \\times$ with less than $50\\%$ memory consumption for gradient filtering with patch sizes $2 \\times 2$ ; for gradient filtering with patch size $4 \\times 4$ , the speedups are much higher, namely over $60 \\times$ . On GPU, the speedup is a little bit lower, but still over $10 \\times$ and $25 \\times$ , respectively. Furthermore, as Table 4 shows, our method saves over $95\\%$", + "bbox": [ + 496, + 763, + 890, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "3817", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/b2621cf2d0595e7d12fdc1b7a17dbd2bedcf0002c376b365ea87427e31ff6337.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 106, + 88, + 491, + 205 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/17bfbab6cd32095d7afba678690e120cd59adaf3fc2ea12510c6670e4b04732a.jpg", + "image_caption": [ + "Figure 6. Speedup and normalized memory consumption results on multiple CPUs and GPUs under different test cases (i.e. different input sizes, numbers of channels, etc.) Detailed configuration of these test cases are included in the supplementary material. \"R2\", \"R4\" mean using gradient filtering with $2 \\times 2$ and $4 \\times 4$ patch sizes, respectively. Our method achieves significant speedup with low memory consumption compared to all baseline methods. For example, on Jetson CPU with patch size $4 \\times 4$ (\"Jetson-R4\" in left top figure), our method achieves $114 \\times$ speedup with only $33\\%$ memory consumption for most test cases." + ], + "image_footnote": [], + "bbox": [ + 112, + 208, + 491, + 313 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/ce9a8e3c2f32f5b9947b7d367cadf78fe160db8a107c9eb1eb42fb66e368d32e.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 496, + 88, + 864, + 205 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/5934835918819d8e6eab3b65fb3871333c6e2c82db12a1f6f4a0547a98147fe3.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 500, + 207, + 864, + 313 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/a6ff3b5531118b3eae2c562aed13787df7038bc19495319a7cdc1e68b9e7eea3.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
DevicePatch SizeNormalized Energy Cost [STD]
Edge2 × 24.13% [0.61%]
CPU4 × 41.15% [0.18%]
Edge2 × 23.80% [0.73%]
GPU4 × 41.22% [1.10%]
", + "bbox": [ + 81, + 417, + 467, + 503 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "energy for both CPU and GPU scenarios, which largely resolves one of the most important constraints on edge devices. All these experiments on real devices show that our method is practical for the real deployment of both high-performance and IoT applications.", + "bbox": [ + 75, + 609, + 468, + 686 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/f3d83be387b20b493638d11b392803cb2bfd8a10d408adfc964ef4df899f38f9.jpg", + "table_caption": [ + "Table 4. Normalized energy consumption for BP with gradient filtering for different patch sizes. Results are normalized w.r.t. the energy cost of standard BP methods. For instance, for edge CPU with a $4 \\times 4$ patch, only $1.15\\%$ of energy in standard BP is used. Standard deviations are shown within brackets." + ], + "table_footnote": [], + "table_body": "
ModelRatioModelRatio
(Wide)ResNet18-1521.462VGG(bn)11-191.497
DenseNet121-2012.278EfficientNet b0-b71.240
", + "bbox": [ + 81, + 696, + 468, + 755 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 5. Evaluation of energy ratio defined in Equation (13) on models published on Torchvision. The ratio greater than 1 empirically verifies our assumption.", + "bbox": [ + 75, + 765, + 467, + 808 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5.6. Main Assumption Verification", + "text_level": 1, + "bbox": [ + 76, + 832, + 344, + 848 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We now empirically verify the assumption that the DC component dominates the frequency spectrum of the convolution kernel (Section 4.1). To this end, we collect the en", + "bbox": [ + 75, + 854, + 468, + 900 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "ergy ratio shown in Equation (13) from trained models published in Torchvision [23]. As Table 5 shows, for the convolution kernels in all these networks, we get a ratio greater than one, which means that the energy of DC components is larger than energy of all AC components. Thus, our assumption in Section 4.1 empirically holds true in practice.", + "bbox": [ + 496, + 421, + 890, + 512 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "6. Conclusions", + "text_level": 1, + "bbox": [ + 500, + 526, + 627, + 541 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this paper, we have addressed the on-device model training for resource-constrained edge devices. To this end, a new gradient filtering method has been proposed to systematically reduce the computation and memory consumption for the back-propagation algorithm, which is the key bottleneck for efficient model training.", + "bbox": [ + 496, + 551, + 890, + 642 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In Section 3, a new gradient filtering approach has been proposed to reduce the computation required for propagating gradients through the convolutional layers. The gradient filtering creates an approximate gradient feature map with fewer unique elements and a special structure; this reduces the computation by more than two orders of magnitude. Furthermore, we proved that the error introduced during back-propagation by our gradient filter is bounded so the influence of gradient approximation is limited.", + "bbox": [ + 496, + 643, + 890, + 777 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Extensive experiments in Section 5 have demonstrated the efficiency and wide applicability of our method. Indeed, models can be finetuned with orders of magnitudes fewer computations, while having only a marginal accuracy loss compared to popular baseline methods.", + "bbox": [ + 496, + 779, + 890, + 854 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgements: This work was supported in part by the US National Science Foundation (NSF) grant CNS-2007284.", + "bbox": [ + 496, + 854, + 890, + 898 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "3818", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Intel® oneapi deep neural network library (onednn). https://www.intel.com/content/www/us/en/developer/tools/oneapi/onednn.html. 1,2,6", + "[2] Martin Abadi, Ashish Agarwal, Paul Barham, Eugene Brevdo, Zhifeng Chen, Craig Citro, Greg S. 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In Proceedings of the AAAI Conference on Artificial Intelligence, volume 35, pages 3483-3491, 2021. 2" + ], + "bbox": [ + 78, + 90, + 468, + 792 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "3820", + "bbox": [ + 482, + 944, + 516, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/Efficient On-Device Training via Gradient Filtering/3b76baa7-39c6-473d-83e4-4a2631e20341_model.json b/2023/Efficient On-Device Training via Gradient Filtering/3b76baa7-39c6-473d-83e4-4a2631e20341_model.json new file mode 100644 index 0000000000000000000000000000000000000000..c7c42ce33a714cbd5671a0e8d82e1e57d18bc660 --- /dev/null +++ b/2023/Efficient On-Device Training via Gradient Filtering/3b76baa7-39c6-473d-83e4-4a2631e20341_model.json @@ -0,0 +1,2332 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.228, + 0.131, + 0.745, + 0.154 + ], + "angle": 0, + "content": "Efficient On-device Training via Gradient Filtering" + }, + { + "type": "text", + "bbox": [ + 0.273, + 0.182, + 0.699, + 0.217 + ], + "angle": 0, + "content": "Yuedong Yang Guihong Li Radu Marculescu The University of Texas at Austin" + }, + { + "type": "text", + "bbox": [ + 0.325, + 0.22, + 0.642, + 0.234 + ], + "angle": 0, + "content": "{albertyoung, lgh, radum}@utexas.edu" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.269, + 0.314, + 0.285 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.302, + 0.474, + 0.681 + ], + "angle": 0, + "content": "Despite its importance for federated learning, continuous learning and many other applications, on-device training remains an open problem for EdgeAI. The problem stems from the large number of operations (e.g., floating point multiplications and additions) and memory consumption required during training by the back-propagation algorithm. Consequently, in this paper, we propose a new gradient filtering approach which enables on-device CNN model training. More precisely, our approach creates a special structure with fewer unique elements in the gradient map, thus significantly reducing the computational complexity and memory consumption of back propagation during training. Extensive experiments on image classification and semantic segmentation with multiple CNN models (e.g., MobileNet, DeepLabV3, UPerNet) and devices (e.g., Raspberry Pi and Jetson Nano) demonstrate the effectiveness and wide applicability of our approach. For example, compared to SOTA, we achieve up to \\(19 \\times\\) speedup and \\(77.1\\%\\) memory savings on ImageNet classification with only \\(0.1\\%\\) accuracy loss. Finally, our method is easy to implement and deploy; over \\(20 \\times\\) speedup and \\(90\\%\\) energy savings have been observed compared to highly optimized baselines in MKLDNN and CUDNN on NVIDIA Jetson Nano. Consequently, our approach opens up a new direction of research with a huge potential for on-device training.\\(^{1}\\)" + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.711, + 0.21, + 0.727 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.737, + 0.471, + 0.875 + ], + "angle": 0, + "content": "Existing approaches for on-device training are neither efficient nor practical enough to satisfy the resource constraints of edge devices (Figure 1). This is because these methods do not properly address a fundamental problem in on-device training, namely the computational and memory complexity of the back-propagation (BP) algorithm. More precisely, although the architecture modification [6] and layer freezing [18, 20] can help skipping the BP for some layers, for other layers, the complexity remains high. Gra" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.27, + 0.895, + 0.392 + ], + "angle": 0, + "content": "dient quantization [4, 7] can reduce the cost of arithmetic operations but cannot reduce the number of operations (e.g., multiplications); thus, the speedup in training remains limited. Moreover, gradient quantization is not supported by existing deep-learning frameworks (e.g., CUDNN [9], MKLDNN [1], PyTorch [25] and Tensorflow [2]). To enable on-device training, there are two important questions must be addressed:" + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.405, + 0.895, + 0.435 + ], + "angle": 0, + "content": "- How can we reduce the computational complexity of back propagation through the convolution layers?" + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.449, + 0.895, + 0.48 + ], + "angle": 0, + "content": "- How can we reduce the data required by the gradient computation during back propagation?" + }, + { + "type": "list", + "bbox": [ + 0.518, + 0.405, + 0.895, + 0.48 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.491, + 0.893, + 0.567 + ], + "angle": 0, + "content": "In this paper, we propose gradient filtering, a new research direction, to address both questions. By addressing the first question, we reduce the computational complexity of training; by addressing the second question, we reduce the memory consumption." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.569, + 0.895, + 0.884 + ], + "angle": 0, + "content": "In general, the gradient propagation through a convolution layer involves multiplying the gradient of the output variable with a Jacobian matrix constructed with data from either the input feature map or the convolution kernel. We aim at simplifying this process with the new gradient filtering approach proposed in Section 3. Intuitively, if the gradient map w.r.t. the output has the same value for all entries, then the computation-intensive matrix multiplication can be greatly simplified, and the data required to construct the Jacobian matrix can be significantly reduced. Thus, our gradient filtering can approximate the gradient w.r.t. the output by creating a new gradient map with a special (i.e., spatial) structure and fewer unique elements. By doing so, the gradient propagation through the convolution layers reduces to cheaper operations, while the data required (hence memory) for the forward propagation also lessens. Through this filtering process, we trade off the gradient precision against the computation complexity during BP. We note that gradient filtering does not necessarily lead to a worse precision, i.e., models sometimes perform better with filtered gradients when compared against models trained with vanilla BP." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.886, + 0.821, + 0.901 + ], + "angle": 0, + "content": "In summary, our contributions are as follows:" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.887, + 0.428, + 0.901 + ], + "angle": 0, + "content": "\\(^{1}\\)Code: https://github.com/SLDGroup/GradientFilter-CVPR23" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.514, + 0.957 + ], + "angle": 0, + "content": "3811" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.097, + 0.092, + 0.47, + 0.152 + ], + "angle": 0, + "content": "- We propose gradient filtering, which reduces the computation and memory required for BP by more than two orders of magnitude compared to the exact gradient calculation." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.163, + 0.47, + 0.209 + ], + "angle": 0, + "content": "- We provide a rigorous error analysis which shows that the errors introduced by the gradient filtering have only a limited influence on model accuracy." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.219, + 0.471, + 0.326 + ], + "angle": 0, + "content": "- Our experiments with multiple CNN models and computer vision tasks show that we can train a neural network with significantly less computation and memory costs, with only a marginal accuracy loss compared to baseline methods. Side-by-side comparisons against other training acceleration techniques also suggest the effectiveness of our method." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.336, + 0.47, + 0.429 + ], + "angle": 0, + "content": "- Our method is easy to deploy with highly optimized deep learning frameworks (e.g., MKLDNN [1] and CUDNN [9]). Evaluations on resource-constrained edge (Raspberry Pi and Jetson Nano) and high-performance devices (CPU/GPU) show that our method is highly suitable for real life deployment." + }, + { + "type": "list", + "bbox": [ + 0.097, + 0.092, + 0.471, + 0.429 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.438, + 0.47, + 0.514 + ], + "angle": 0, + "content": "The paper is organized as follows. Section 2 reviews relevant work. Section 3 presents our method in detail. Section 4 discusses error analysis, computation and memory consumption. Experimental results are presented in Section 5. Finally, Section 6 summarizes our main contributions." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.527, + 0.22, + 0.543 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.553, + 0.469, + 0.658 + ], + "angle": 0, + "content": "Architecture Modification: Authors of [6] propose to attach small branches to the original neural network. During training, the attached branches and biases in the original model are updated. Though memory consumption is reduced, updating these branches still needs gradient propagation through the entire network; moreover, a large computational overhead for inference is introduced." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.659, + 0.469, + 0.765 + ], + "angle": 0, + "content": "Layer Freezing: Authors of [18, 20] propose to only train parts of the model. [18] makes layer selection based on layer importance metrics, while [20] uses evolutionary search. However, the layers selected by all these methods are typically computationally heavy layers (e.g., the last few layers in ResNet [14]) which consume most of the resources. Thus, the speedup achieved by these approaches is limited." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.765, + 0.47, + 0.902 + ], + "angle": 0, + "content": "Gradient Quantization: [3,5] quantize gradient after backpropagation, which means these methods cannot accelerate the training on a single device. Work in [4,7,15,17,28, 29, 33] accelerates training by reducing the cost for every arithmetic operation. However, these methods do not reduce the number of operations, which is typically huge for SOTA CNNs, so their achievable speedup is limited. Also, all these methods are not supported by the popular deep learning frameworks [1,2,9,25]." + }, + { + "type": "image", + "bbox": [ + 0.499, + 0.088, + 0.891, + 0.308 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.316, + 0.892, + 0.359 + ], + "angle": 0, + "content": "Figure 1. Matrix of orthogonal directions for on-device training. \"Arch\" is short for \"architecture\". Our approach opens up a new direction of research for on-device training for EdgeAI." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.39, + 0.893, + 0.511 + ], + "angle": 0, + "content": "In contrast to the prior work, our method opens up a new research direction. More precisely, we reduce the number of computations and memory consumption required for training a single layer via gradient filtering. Thus, our method can be combined with any of the methods mentioned above. For example, in Section H in the Supplementary, we illustrate how our method can work together with the gradient quantization methods to enable a higher speedup." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.531, + 0.673, + 0.549 + ], + "angle": 0, + "content": "3. Proposed Method" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.558, + 0.892, + 0.62 + ], + "angle": 0, + "content": "In this section, we introduce our gradient filtering approach to accelerate BP. To this end, we target the most computation and memory heavy operation, i.e., convolution (Figure 2(a)). Table 1 lists some symbols we use." + }, + { + "type": "table", + "bbox": [ + 0.508, + 0.645, + 0.887, + 0.874 + ], + "angle": 0, + "content": "
CxNumber of channels of x
Wx, HxWidth and height of x
θConvolution kernel
θ'Rotated θ, i.e., θ' = rot180(θ)
rPatch size (r × r)
gx, gy, gθGradients w.r.t. x, y, θ
gyApproximated gradient gy
x, θ'Sum of x and θ' over spatial dimensions (height and width)
x[n, ci, h, w]Element for feature map x at batch n, channel ci, pixel (h, w)
θ[c_o, c_i, u, v]Element for convolution kernel θ at output channel co, input channel ci, position (u, v)
" + }, + { + "type": "table_caption", + "bbox": [ + 0.593, + 0.883, + 0.799, + 0.897 + ], + "angle": 0, + "content": "Table 1. Table of symbols we use." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "3812" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.078, + 0.087, + 0.506, + 0.29 + ], + "angle": 0, + "content": null + }, + { + "type": "image_footnote", + "bbox": [ + 0.123, + 0.291, + 0.236, + 0.303 + ], + "angle": 0, + "content": "Forward Propagation" + }, + { + "type": "image_footnote", + "bbox": [ + 0.245, + 0.292, + 0.364, + 0.302 + ], + "angle": 0, + "content": "Backward Propagation" + }, + { + "type": "image_footnote", + "bbox": [ + 0.374, + 0.291, + 0.449, + 0.302 + ], + "angle": 0, + "content": "Average Filter" + }, + { + "type": "image_footnote", + "bbox": [ + 0.458, + 0.292, + 0.522, + 0.302 + ], + "angle": 0, + "content": "\\(②\\) Spatial Sum" + }, + { + "type": "image_footnote", + "bbox": [ + 0.534, + 0.292, + 0.598, + 0.302 + ], + "angle": 0, + "content": "Convolution" + }, + { + "type": "image_footnote", + "bbox": [ + 0.609, + 0.292, + 0.725, + 0.302 + ], + "angle": 0, + "content": "Frobenius Inner Product" + }, + { + "type": "image_footnote", + "bbox": [ + 0.739, + 0.292, + 0.846, + 0.303 + ], + "angle": 0, + "content": "Element-wise Product" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.315, + 0.892, + 0.398 + ], + "angle": 0, + "content": "Figure 2. (a) Computation procedures for vanilla training method (upper) and our method (lower). (b) Example of gradient propagation with gradient filtering. Numbers in this example are chosen randomly for illustration purposes. In this case, the patch size selected for the gradient filter is \\(2 \\times 2\\). Thus, the \\(4 \\times 4\\) gradient map \\(g_{y}\\) is approximated by \\(\\tilde{g}_{y}\\), which has four \\(2 \\times 2\\) patches with one unique value for each patch. Also, input feature map \\(x\\) and mirrored convolution kernel \\(\\theta'\\) are spatial summed to \\(\\tilde{x}\\) and \\(\\tilde{\\theta}'\\). Since \\(\\tilde{x}\\) has fewer unique values than \\(x\\), memory consumption is reduced. Finally, with \\(\\tilde{g}_{y}, \\tilde{x}\\) and \\(\\tilde{\\theta}\\), we compute the gradient w.r.t. kernel and input feature map with much fewer operations than the standard back propagation method." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.424, + 0.228, + 0.44 + ], + "angle": 0, + "content": "3.1. Problem Setup" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.447, + 0.469, + 0.644 + ], + "angle": 0, + "content": "The computations for both forward and backward paths are shown in Figure 2(a). For the standard (vanilla) approach (upper Figure 2(a)), starting with input \\( x \\), the forward propagation convolves the input feature map \\( x \\) with kernel \\( \\theta \\) and returns output \\( y \\), which is further processed by the other layers in the neural network (dotted arrow) until the loss value \\( l \\) is calculated. As shown in Figure 2(a), the BP of the convolution layer starts with the gradient map w.r.t. output \\( y(g_{y}) \\). The gradient w.r.t. input \\( (g_{x}) \\) is calculated by convolving \\( g_{y} \\) with the rotated convolution kernel \\( \\theta' \\), i.e., \\( g_{x} = g_{y} \\otimes \\mathrm{rot}180(\\theta) = g_{y} \\otimes \\theta' \\). The gradient w.r.t. convolution kernel, namely \\( g_{\\theta} \\), is calculated with the Frobenius inner product [16] between \\( x \\) and \\( g_{y} \\), i.e., \\( g_{\\theta} = g_{y} \\otimes f(x) \\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.644, + 0.469, + 0.794 + ], + "angle": 0, + "content": "The lower half of Figure 2(a) shows our method, where several changes are made: We introduce the gradient filter \"A\" after \\(g_{y}\\) to generate the approximate gradient for BP. Also, instead of using the accurate \\(x\\) and \\(\\theta^{\\prime}\\) values for gradient computation, we sum over spatial dimensions (height and width dimensions), i.e., \\(\\tilde{x}\\) and \\(\\tilde{\\theta}^{\\prime}\\), respectively. Finally, the convolution layer now multiplies the approximate gradient \\(\\tilde{g}_{y}\\) with spatial kernel \\(\\tilde{\\theta}^{\\prime}\\) instead of convolving with it to calculate \\(\\tilde{g}_x\\). Figure 2(b) shows an example of gradient propagation with our gradient filter." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.802, + 0.276, + 0.818 + ], + "angle": 0, + "content": "3.2. Preliminary Analysis" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.825, + 0.468, + 0.872 + ], + "angle": 0, + "content": "Consider the vanilla BP for convolution in Figure 2(a). Equation (1) shows the number of computations (#FLOPs) required to calculate \\( g_{x} \\) given \\( g_{y} \\):" + }, + { + "type": "equation", + "bbox": [ + 0.152, + 0.885, + 0.469, + 0.903 + ], + "angle": 0, + "content": "\\[\n\\# \\text {F L O P s} = 2 C _ {x} C _ {y} \\cdot W _ {y} H _ {y} \\cdot W _ {\\theta} H _ {\\theta} \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.424, + 0.892, + 0.485 + ], + "angle": 0, + "content": "The computation requirements in Equation (1) belong to three categories: number of channels, number of unique elements per channel in the gradient map, and kernel size. Our method focuses on the last two categories." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.485, + 0.892, + 0.575 + ], + "angle": 0, + "content": "i. Unique elements: \\((W_yH_y)\\) represents the number of unique elements per channel in the gradient w.r.t. output variable \\(y\\) (\\(g_y\\)). Given the high-resolution images we use, this term is huge, so if we manage to reduce the number of unique elements in the spatial dimensions (height and width), the computations required are greatly reduced too." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.575, + 0.892, + 0.711 + ], + "angle": 0, + "content": "ii. Kernel size: \\((W_{\\theta}H_{\\theta})\\) represents the number of unique elements in the convolution kernel. If the gradient \\(g_{y}\\) has some special structure, for example \\(g_{y} = 1_{H_{y}\\times W_{y}}\\cdot v\\) (i.e., every element in \\(g_{y}\\) has the same value \\(v\\)), then the convolution can be simplified to \\((\\sum \\theta^{\\prime})v1_{H_{y}\\times W_{y}}\\) (with boundary elements ignored). With such a special structure, only one multiplication and \\((W_{\\theta}H_{\\theta} - 1)\\) additions are required. Moreover, \\(\\sum \\theta^{\\prime}\\) is independent of data so the result can be shared across multiple images until \\(\\theta\\) gets updated." + }, + { + "type": "list", + "bbox": [ + 0.498, + 0.485, + 0.892, + 0.711 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.72, + 0.679, + 0.736 + ], + "angle": 0, + "content": "3.3. Gradient Filtering" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.743, + 0.892, + 0.849 + ], + "angle": 0, + "content": "To reduce the number of unique elements and create the special structure in the gradient map, we apply the gradient filter after the gradient w.r.t. output \\((g_y)\\) is provided. During the backward propagation, the gradient filter \\(\\langle \\mathbf{A}\\rangle\\) approximates the gradient \\(g_{y}\\) by spatially cutting the gradient map into \\(r\\times r\\)-pixel patches and then replacing all elements in each patch with their average value (Figure 2(b)):" + }, + { + "type": "equation", + "bbox": [ + 0.515, + 0.858, + 0.892, + 0.904 + ], + "angle": 0, + "content": "\\[\n\\tilde {g} _ {y} [ n, c _ {o}, h, w ] = \\frac {1}{r ^ {2}} \\sum_ {i = \\lfloor h / r \\rfloor r} ^ {\\lceil h / r \\rceil r} \\sum_ {j = \\lfloor w / r \\rfloor r} ^ {\\lceil w / r \\rceil r} g _ {y} [ n, c _ {o}, i, j ] \\tag {2}\n\\]" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "3813" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.214 + ], + "angle": 0, + "content": "For instance in Figure 2(b), we replace the 16 distinct values in the gradient map \\( g_{y} \\) with 4 average values in \\( \\tilde{g}_{y} \\). So given a gradient map \\( g_{y} \\) with \\( N \\) images per batch, \\( C \\) channels, and \\( H \\times W \\) pixels per channel, the gradient filter returns a structured approximation of the gradient map containing only \\( N \\times C \\times \\left\\lceil \\frac{H}{r} \\right\\rceil \\times \\left\\lceil \\frac{W}{r} \\right\\rceil \\) blocks, with one unique value per patch. We use this matrix of unique values to represent the approximate gradient map \\( \\tilde{g}_{y} \\), as shown in Figure 2(b)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.223, + 0.438, + 0.24 + ], + "angle": 0, + "content": "3.4. Back Propagation with Gradient Filtering" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.248, + 0.47, + 0.292 + ], + "angle": 0, + "content": "We describe now the computation procedure used after applying the gradient filter. Detailed derivations are provided in Supplementary Section B." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.294, + 0.47, + 0.34 + ], + "angle": 0, + "content": "Gradient w.r.t. input: The gradient w.r.t. input is calculated by convolving \\(\\theta^{\\prime}\\) with \\(g_{y}\\) (Figure 2(a)). With the approximate gradient \\(\\tilde{g}_y\\), this convolution simplifies to:" + }, + { + "type": "equation", + "bbox": [ + 0.116, + 0.352, + 0.47, + 0.385 + ], + "angle": 0, + "content": "\\[\n\\tilde {g} _ {x} [ n, c _ {i}, h, w ] = \\sum_ {c _ {o}} \\tilde {g} _ {y} [ n, c _ {o}, h, w ] \\odot \\tilde {\\theta} ^ {\\prime} [ c _ {o}, c _ {i} ] \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.398, + 0.47, + 0.429 + ], + "angle": 0, + "content": "where \\(\\tilde{\\theta}^{\\prime}[c_o,c_i] = \\sum_{u,v}\\theta^{\\prime}[c_o,c_i,u,v]\\) is the spatial sum of convolution kernel \\(\\theta\\), as shown in Figure 2(b)." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.43, + 0.47, + 0.477 + ], + "angle": 0, + "content": "Gradient w.r.t. kernel: The gradient w.r.t. the kernel is calculated by taking the Frobenius inner product between \\( x \\) and \\( g_{y} \\), i.e., \\( g_{\\theta}[c_o, c_i, u, v] = x \\oplus g_{y} \\), namely:" + }, + { + "type": "equation", + "bbox": [ + 0.085, + 0.488, + 0.47, + 0.522 + ], + "angle": 0, + "content": "\\[\ng _ {\\theta} \\left[ c _ {o}, c _ {i}, u, v \\right] = \\sum_ {n, i, j} x \\left[ n, c _ {i}, i + u, j + v \\right] g _ {y} \\left[ n, c _ {o}, i, j \\right] \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.534, + 0.469, + 0.564 + ], + "angle": 0, + "content": "With the approximate gradient \\(\\tilde{g}_y\\), the operation can be simplified to:" + }, + { + "type": "equation", + "bbox": [ + 0.12, + 0.577, + 0.469, + 0.61 + ], + "angle": 0, + "content": "\\[\n\\tilde {g} _ {\\theta} \\left[ c _ {o}, c _ {i}, u, v \\right] = \\sum_ {n, i, j} \\tilde {x} [ n, c _ {i}, i, j ] \\tilde {g} _ {y} [ n, c _ {o}, i, j ] \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.621, + 0.469, + 0.674 + ], + "angle": 0, + "content": "with \\(\\tilde{x}[n,c_i,i,j] = \\sum_{h = [i / r]\\rfloor r}^{\\lceil i / r\\rceil r}\\sum_{w = \\lfloor j / r\\rfloor r}^{\\lceil j / r\\rceil r}x[n,c_i,h,w].\\) As shown in Figure 2(b), \\(\\tilde{x}[n,c_i,i,j]\\) is the spatial sum of \\(x\\) elements in the same patch containing pixel \\((i,j)\\)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.688, + 0.37, + 0.707 + ], + "angle": 0, + "content": "4. Analyses of Proposed Approach" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.715, + 0.47, + 0.76 + ], + "angle": 0, + "content": "In this section, we analyze our method from three perspectives: gradient filtering approximation error, computation reduction, and memory cost reduction." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.771, + 0.395, + 0.788 + ], + "angle": 0, + "content": "4.1. Error Analysis of Gradient Filtering" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.795, + 0.469, + 0.855 + ], + "angle": 0, + "content": "We prove that the approximation error introduced by our gradient filtering is bounded during the gradient propagation. Without losing generality, we consider that all variables have only one channel, i.e., \\( C_{x_0} = C_{x_1} = 1 \\)." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.856, + 0.47, + 0.901 + ], + "angle": 0, + "content": "Proposition 1: For any input-output channel pair \\((c_{o}, c_{i})\\) in the convolution kernel \\(\\theta\\), assuming the DC component has the largest energy value compared to all components in" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.092, + 0.892, + 0.122 + ], + "angle": 0, + "content": "the spectrum\\(^2\\), then the signal-to-noise-ratio (SNR) of \\(\\tilde{g}_x\\) is greater than SNR of \\(\\tilde{g}_y\\)." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.122, + 0.892, + 0.197 + ], + "angle": 0, + "content": "Proof: We use \\( G_{x}, G_{y} \\) and \\( \\Theta \\) to denote the gradients \\( g_{x}, g_{y} \\) and the convolution kernel \\( \\theta \\) in the frequency domain; \\( G_{x}[u, v] \\) is the spectrum value at frequency \\( (u, v) \\) and \\( \\delta \\) is the 2D discrete Dirichlet function. To simplify the discussion, we consider only one patch of size \\( r \\times r \\)." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.198, + 0.892, + 0.225 + ], + "angle": 0, + "content": "The gradient returned by the gradient filtering can be written as:" + }, + { + "type": "equation", + "bbox": [ + 0.631, + 0.223, + 0.892, + 0.251 + ], + "angle": 0, + "content": "\\[\n\\tilde {g} _ {y} = \\frac {1}{r ^ {2}} 1 _ {r \\times r} * g _ {y} \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.254, + 0.892, + 0.3 + ], + "angle": 0, + "content": "where \\(\\circ\\) denotes convolution. By applying the discrete Fourier transformation, Equation (6) can be rewritten in the frequency domain as:" + }, + { + "type": "equation", + "bbox": [ + 0.597, + 0.306, + 0.892, + 0.336 + ], + "angle": 0, + "content": "\\[\n\\tilde {G} _ {y} [ u, v ] = \\frac {1}{r ^ {2}} \\delta [ u, v ] G _ {y} [ u, v ] \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.342, + 0.892, + 0.373 + ], + "angle": 0, + "content": "\\(\\tilde{g}_y\\) is the approximation of \\(g_{y}\\) (i.e., the ground truth for \\(\\tilde{g}_y\\) is \\(g_{y}\\)), and the SNR of \\(\\tilde{g}_y\\) equals to:" + }, + { + "type": "equation", + "bbox": [ + 0.52, + 0.379, + 0.892, + 0.459 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\mathrm {S N R} _ {\\tilde {g} _ {y}} = \\frac {\\sum_ {(u , v)} G _ {y} ^ {2} [ u , v ]}{\\sum_ {(u , v)} \\left(G _ {y} [ u , v ] - \\frac {1}{r ^ {2}} \\delta [ u , v ] G _ {y} [ u , v ]\\right) ^ {2}} \\tag {8} \\\\ = (1 - \\frac {2 r ^ {2} - 1}{r ^ {4}} \\frac {G _ {y} ^ {2} [ 0 , 0 ]}{\\sum_ {(u , v)} G _ {y} ^ {2} [ u , v ]}) ^ {- 1} \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.465, + 0.892, + 0.495 + ], + "angle": 0, + "content": "For the convolution layer, the gradient w.r.t. the approximate variable \\(\\tilde{x}\\) in the frequency domain is:" + }, + { + "type": "equation", + "bbox": [ + 0.561, + 0.501, + 0.892, + 0.552 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\tilde {G} _ {x} [ u, v ] = \\Theta [ - u, - v ] \\tilde {G} _ {y} [ u, v ] \\\\ = \\frac {1}{r ^ {2}} \\Theta [ - u, - v ] \\delta [ u, v ] G _ {y} [ u, v ] \\tag {9} \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.559, + 0.654, + 0.573 + ], + "angle": 0, + "content": "and its ground truth is:" + }, + { + "type": "equation", + "bbox": [ + 0.591, + 0.581, + 0.892, + 0.599 + ], + "angle": 0, + "content": "\\[\nG _ {x} [ u, v ] = \\Theta [ - u, - v ] G _ {y} [ u, v ] \\tag {10}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.606, + 0.778, + 0.621 + ], + "angle": 0, + "content": "Similar to Equation (8), the SNR of \\(g_{\\bar{x}}\\) is:" + }, + { + "type": "equation", + "bbox": [ + 0.515, + 0.627, + 0.892, + 0.677 + ], + "angle": 0, + "content": "\\[\n\\mathrm {S N R} _ {\\tilde {g} _ {x}} = \\left(1 - \\frac {2 r ^ {2} - 1}{r ^ {4}} \\frac {(\\Theta [ 0 , 0 ] G _ {y} [ 0 , 0 ]) ^ {2}}{\\sum_ {(u , v)} (\\Theta [ u , v ] G _ {y} [ u , v ]) ^ {2}}\\right) ^ {- 1} \\tag {11}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.678, + 0.726, + 0.692 + ], + "angle": 0, + "content": "Equation (11) can be rewritten as:" + }, + { + "type": "equation", + "bbox": [ + 0.516, + 0.699, + 0.892, + 0.782 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\frac {r ^ {4} \\left(1 - \\operatorname {S N R} _ {\\hat {g} _ {x}} ^ {- 1}\\right)}{2 r ^ {2} - 1} = \\frac {\\left(\\Theta [ 0 , 0 ] G _ {y} [ 0 , 0 ]\\right) ^ {2}}{\\sum_ {(u , v)} \\left(\\Theta [ - u , - v ] G _ {y} [ u , v ]\\right) ^ {2}} \\tag {12} \\\\ = \\frac {G _ {y} ^ {2} [ 0 , 0 ]}{\\sum_ {(u , v)} (\\frac {\\Theta [ - u , - v ]}{\\Theta [ 0 , 0 ]} G _ {y} [ u , v ]) ^ {2}} \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.788, + 0.892, + 0.818 + ], + "angle": 0, + "content": "Furthermore, the main assumption (i.e., the DC component dominates the frequency spectrum of \\(\\Theta\\)) can be written as:" + }, + { + "type": "equation", + "bbox": [ + 0.574, + 0.825, + 0.892, + 0.844 + ], + "angle": 0, + "content": "\\[\n\\Theta^ {2} [ 0, 0 ] / \\max _ {(u, v) \\neq (0, 0)} \\Theta^ {2} [ u, v ] \\geq 1 \\tag {13}\n\\]" + }, + { + "type": "page_footnote", + "bbox": [ + 0.5, + 0.851, + 0.892, + 0.876 + ], + "angle": 0, + "content": "2As a reminder, the energy of a signal is the sum of energy of the DC component and the energy of its AC components." + }, + { + "type": "page_footnote", + "bbox": [ + 0.5, + 0.876, + 0.892, + 0.901 + ], + "angle": 0, + "content": "3Because \\( g_{y} \\) is convolved with the rotated kernel \\( \\theta' \\), in the frequency domain, we use \\( \\Theta[-u, -v] \\) instead of \\( \\Theta[u, v] \\)." + }, + { + "type": "list", + "bbox": [ + 0.5, + 0.851, + 0.892, + 0.901 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "3814" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.113, + 0.096, + 0.434, + 0.233 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.25, + 0.47, + 0.347 + ], + "angle": 0, + "content": "Figure 3. Computation analysis for a specific convolution layer4. Minimum achievable computation is given in Equation (16). By reducing the number of unique elements, computations required by our approach drop to about \\(1 / r^2\\) compared with the standard BP method. By combining it with structured gradient map, computations required by our approach drop further, getting very close to the theoretical limit." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.372, + 0.469, + 0.407 + ], + "angle": 0, + "content": "that is, \\(\\forall (u,v),\\frac{\\Theta^2[-u,-v]}{\\Theta^2[0,0]}\\leq 1\\) ; thus, by combining Equation (12) and Equation (13), we have:" + }, + { + "type": "equation", + "bbox": [ + 0.095, + 0.418, + 0.469, + 0.497 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\frac {G _ {y} ^ {2} [ 0 , 0 ]}{\\sum_ {(u , v)} \\left(\\frac {\\Theta [ - u , - v ]}{\\Theta [ 0 , 0 ]} G _ {y} [ u , v ]\\right) ^ {2}} \\geq \\frac {G _ {y} ^ {2} [ 0 , 0 ]}{\\sum_ {(u , v)} \\left(G _ {y} [ u , v ]\\right) ^ {2}} \\tag {14} \\\\ \\Leftrightarrow \\frac {r ^ {4} \\left(1 - \\mathrm {S N R} _ {\\tilde {g} _ {x}} ^ {- 1}\\right)}{2 r ^ {2} - 1} \\geq \\frac {r ^ {4} \\left(1 - \\mathrm {S N R} _ {\\tilde {g} _ {y}} ^ {- 1}\\right)}{2 r ^ {2} - 1} \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.506, + 0.469, + 0.536 + ], + "angle": 0, + "content": "which means that: \\(\\mathrm{SNR}_{\\tilde{g}_x} \\geq \\mathrm{SNR}_{\\tilde{g}_y}\\). This completes our proof for error analysis." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.537, + 0.469, + 0.627 + ], + "angle": 0, + "content": "In conclusion, as the gradient propagates through the network, the noise introduced by our gradient filter becomes weaker compared to the real gradient signal. This property ensures that the error in gradient has only a limited influence on the quality of BP. We validate Proposition 1 later in the experimental section." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.637, + 0.399, + 0.654 + ], + "angle": 0, + "content": "4.2. Computation and Overhead Analysis" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.661, + 0.469, + 0.796 + ], + "angle": 0, + "content": "In this section, we analyse the computation required to compute \\( g_{x} \\), the gradient w.r.t. input \\( x \\). Figure 3 compares the computation required to propagate the gradient through this convolution layer under different patch sizes \\( r \\times r \\). A patch size \\( 1 \\times 1 \\) means the vanilla BP algorithm which we use as the baseline. As discussed in the preliminary analysis section (Section 3.2), two terms contribute to the computation savings: fewer unique elements in the gradient map and the structured gradient map." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.797, + 0.469, + 0.843 + ], + "angle": 0, + "content": "Fewer unique elements: In vanilla BP, there are \\( H_{y}W_{y} \\) unique elements in the gradient map. After applying gradient filtering with a patch size \\( r \\times r \\), the number of unique" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.089, + 0.891, + 0.136 + ], + "angle": 0, + "content": "elements reduces to only \\(\\lceil \\frac{H_y}{r}\\rceil \\lceil \\frac{W_y}{r}\\rceil\\). This reduction contributes the most to the savings in computation (orange line in Figure 3)." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.137, + 0.892, + 0.318 + ], + "angle": 0, + "content": "Structured Gradient Map: By creating the structured gradient map, the convolution over the gradient map \\(\\tilde{g}_y\\) is simplified to the element-wise multiplication and channel-wise addition. Computation is thus reduced to \\((H_{\\theta}W_{\\theta})^{-1}\\) of its original value. For instance, the example convolution layer in Figure 3 uses a \\(3\\times 3\\) convolution kernel so around \\(89\\%\\) computations are removed. The blue line in Figure 3 shows the #FLOPs after combining both methods. Greater reduction is expected when applying our method with larger convolution kernels. For instance, FastDepth [30] uses \\(5\\times 5\\) convolution kernel so as much as \\(96\\%\\) reduction in computation can be achieved, in principle." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.318, + 0.892, + 0.364 + ], + "angle": 0, + "content": "Minimum Achievable Computation: With the two reductions mentioned above, the computation required to propagate the gradient through the convolution layer is:" + }, + { + "type": "equation", + "bbox": [ + 0.508, + 0.371, + 0.892, + 0.402 + ], + "angle": 0, + "content": "\\[\n\\# \\text {F L O P s} (r) = \\left\\lceil \\frac {H _ {y}}{r} \\right\\rceil \\left\\lceil \\frac {W _ {y}}{r} \\right\\rceil C _ {x} \\left(2 C _ {y} - 1\\right) + o \\left(H _ {y} W _ {y}\\right) \\tag {15}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.41, + 0.892, + 0.471 + ], + "angle": 0, + "content": "where \\( o(H_yW_y) \\) is a constant term which is independent of \\( r \\) and negligible compared to \\( H_yW_y \\). When the patch is as large as the feature map, our method reaches the minimum achievable computation (blue dashed line in Figure 3):" + }, + { + "type": "equation", + "bbox": [ + 0.527, + 0.48, + 0.891, + 0.498 + ], + "angle": 0, + "content": "\\[\n\\min _ {r} \\# \\text {F L O P s} (r) = 2 C _ {x} C _ {y} - C _ {x} + o \\left(H _ {y} W _ {y}\\right) \\tag {16}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.507, + 0.891, + 0.552 + ], + "angle": 0, + "content": "In this case, each channel of the gradient map is represented with a single value, so the computation is controlled by the number of input and output channels." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.553, + 0.892, + 0.673 + ], + "angle": 0, + "content": "Overhead: The overhead of our approach comes from approximating the feature map \\( x \\), gradient \\( g_{y} \\), and kernel \\( \\theta \\). As the lower part of Figure 2(a) shows, the approximation for \\( x \\) is considered as part of forward propagation, while the other two as back propagation. Indeed, with the patch size \\( r \\), the ratio of forward propagation overhead is about \\( 1 / (2C_{o}W_{\\theta}H_{\\theta}) \\), while the ratio of backward propagation overhead is about \\( (r^{2} - 1) / (2C_{x}) \\)." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.673, + 0.891, + 0.718 + ], + "angle": 0, + "content": "Given the large number of channels and spatial dimensions in typical neural networks, both overhead values take less than \\(1\\%\\) computation in the U-Net example above." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.727, + 0.671, + 0.743 + ], + "angle": 0, + "content": "4.3. Memory Analysis" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.75, + 0.892, + 0.903 + ], + "angle": 0, + "content": "As Figure 2(a) shows, the standard back propagation for a convolution layer relies on the input feature map \\( x \\), which needs to be stored in memory during forward propagation. Since every convolution layer requiring gradient for its kernel needs to save a copy of feature map \\( x \\), the memory consumption for storing \\( x \\) is huge. With our method, we simplify the feature map \\( x \\) to approximated \\( \\tilde{x} \\), which has only \\( \\lceil \\frac{H_x}{r} \\rceil \\lceil \\frac{W_x}{r} \\rceil \\) unique elements for every channel. Thus, by saving only these unique values, our method achieves around \\( (1 - \\frac{1}{r^2}) \\) memory savings, overall." + }, + { + "type": "page_footnote", + "bbox": [ + 0.077, + 0.851, + 0.469, + 0.901 + ], + "angle": 0, + "content": "4The layer is from U-Net [26]. The size of the input is assumed to be \\(120 \\times 160\\) pixels with 192 channels; the output has the same resolution, but with only 64 channels. The kernel size of the convolution layer is \\(3 \\times 3\\). Analysis for ResNet is included in the supplementary material." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.515, + 0.957 + ], + "angle": 0, + "content": "3815" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.08, + 0.089, + 0.894, + 0.315 + ], + "angle": 0, + "content": "
MobileNetV2 [27]#LayersAccuracyFLOPsMemResNet-18 [14]#LayersAccuracyFLOPsMem
No Finetuning04.200No Finetuning04.700
VanillaAll75.11.13G24.33MBVanillaAll73.15.42G8.33MB
263.1113.68M245.00KBBP270.4489.20M196.00KB
BP462.2160.00M459.38KB472.31.14G490.00KB
TinyTL [6]N/A60.2663.51M683.00KBTinyTL [6]N/A69.23.88G1.76MB
Ours263.139.27M80.00KBOurs268.628.32M64.00KB
463.453.96M150.00KB468.561.53M112.00KB
MCUNet [19]#LayersAccuracyFLOPsMemResNet-34 [14]#LayersAccuracyFLOPsMem
No Finetune04.100No Finetune000
VanillaAll68.5231.67M9.17MBVanillaAll70.811.17G13.11MB
262.118.80M220.50KBBP269.6489.20M196.00KB
BP464.933.71M312.38KB472.31.21G392.00KB
TinyTL [6]N/A53.1148.01M571.5KBTinyTL [6]N/A72.98.03G2.95MB
Ours261.86.34M72.00KBOurs268.628.32M64.00KB
464.411.01M102.00KB470.664.07M128.00KB
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.325, + 0.893, + 0.381 + ], + "angle": 0, + "content": "Table 2. Experimental results for ImageNet classification with four neural networks (MobileNet-V2, ResNet18/34, MCUNet). \"#Layers\" is short for \"the number of active convolutional layers\". For example, #Layers equals to 2 means that only the last two convolutional layers are trained. For memory consumption, we only consider the memory for input feature \\( x \\). Strategy \"No Finetuning\" shows the accuracy on new datasets without finetuning the pretrained model. Since TinyTL [6] changes the architecture, \"#Layers\" is not applicable (N/A)." + }, + { + "type": "table", + "bbox": [ + 0.079, + 0.397, + 0.893, + 0.551 + ], + "angle": 0, + "content": "
PSPNet [32]#LayersGFLOPsmIoUmAccPSPNet-M [32]#LayersGFLOPsmIoUmAccFCN [21]#LayersGFLOPsmIoUmAcc
Calibration0012.8619.74Calibration0014.2020.46Calibration0010.9515.69
Vanilla BPAll166.555.0168.02Vanilla BPAll42.448.4861.48Vanilla BPAll170.345.2258.80
515.039.5451.86512.2236.3547.09559.527.4137.90
10110.653.1567.101022.4646.0158.7010100.943.8757.58
Ours50.1439.3451.86Ours50.1136.1446.86Ours50.5827.4237.88
100.7950.8864.73100.7644.9057.50100.9636.3048.82
DLV3 [8]#LayersGFLOPsmIoUmAccDLV3-M [8]#LayersGFLOPsmIoUmAccUPerNet [31]#LayersGFLOPsmIoUmAcc
Calibration0013.9520.62Calibration0021.9636.15Calibration0014.7121.82
Vanilla BPAll151.258.3271.72Vanilla BPAll54.455.6668.95Vanilla BPAll541.064.8877.13
518.040.8553.16514.838.2149.355503.947.9361.67
10102.054.6568.641033.147.9561.4910507.648.8363.02
Ours50.3133.0944.33Ours50.2635.4746.35Ours51.9747.0460.44
102.9647.1160.28101.4045.5358.99102.2248.0062.07
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.562, + 0.893, + 0.618 + ], + "angle": 0, + "content": "Table 3. Experimental results for semantic segmentation task on augmented Pascal VOC12 dataset [8]. Model name with postfix \"M\" means the model uses MobileNetV2 as backbone, otherwise ResNet18 is used. \"#Layers\" is short for \"the number of active convolutional layers\" that are trained. All models are pretrained on Cityscapes dataset [11]. Strategy \"Calibration\" shows the accuracy when only the classifier and normalization statistics are updated to adapt different numbers of classes between augmented Pascal VOC12 and Cityscapes." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.643, + 0.21, + 0.66 + ], + "angle": 0, + "content": "5. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.669, + 0.471, + 0.79 + ], + "angle": 0, + "content": "Our experimental section consists of theoretical and practical evaluations. Sections 5.2-5.4 show the theoretical advantages of our method on image classification and semantic segmentation tasks with implementation-agnostic metrics (e.g., accuracy, FLOPs). Then, in Section 5.5, we show how these theoretical advantages translate into practical advantages (i.e., speedup and memory savings) on real edge devices." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.802, + 0.267, + 0.818 + ], + "angle": 0, + "content": "5.1. Experimental Setup" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.825, + 0.47, + 0.903 + ], + "angle": 0, + "content": "Classification: Following [24], we split every dataset into two highly non-i.i.d. partitions with the same size. Then, we pretrain our models on the first partition with a vanilla training strategy, and finetune the model on the other partition with different configurations for the training strat" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.644, + 0.892, + 0.689 + ], + "angle": 0, + "content": "egy (i.e., with/without gradient filtering, hyper-parameters, number of convolution layers to be trained). More details (e.g., hyper-parameters) are in the Supplementary." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.689, + 0.892, + 0.78 + ], + "angle": 0, + "content": "Segmentation: Models are pretrained on Cityscapes [11] by MMSegmentation [10]. Then, we calibrate and finetune these models with different training strategies on the augmented Pascal-VOC12 dataset following [8], which is the combination of Pascal-VOC12 [12] and SBD [13]. More details are included in the supplementary material." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.893, + 0.901 + ], + "angle": 0, + "content": "On-device Performance Evaluation: For CPU performance evaluation, we implement our method with MKLDNN [1] (a.k.a. OneDNN) v2.6.0 and compare it with the convolution BP method provided by MKLDNN. We test on three CPUs, namely Intel 11900KF, Quad-core Cortex-A72 (Jetson Nano) and Quad-core Cortex-A53 (Raspberry Pi-3b). For GPU performance evaluation, we implement our method on CUDNN v8.2 [9] and compare with the BP" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.517, + 0.957 + ], + "angle": 0, + "content": "3816" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.091, + 0.473, + 0.198 + ], + "angle": 0, + "content": "method provided by CUDNN. We test on two GPUs, RTX 3090Ti and the edge GPU on Jetson Nano. Since both MKLDNN and CUDNN only support float32 BP, we test float32 BP only. Additionally, for the experiments on Jetson Nano, we record the energy consumption for CPU and GPU with the embedded power meter. More details (e.g., frequency) are included in the supplementary material." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.205, + 0.296, + 0.221 + ], + "angle": 0, + "content": "5.2. ImageNet Classification" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.228, + 0.471, + 0.38 + ], + "angle": 0, + "content": "Table 2 shows our evaluation results on the ImageNet classification task. As shown, our method significantly reduces the FLOPs and memory required for BP, with very little accuracy loss. For example, for ResNet34, our method achieves \\(18.9 \\times\\) speedup with \\(1.7\\%\\) accuracy loss when training four layers; for MobileNetV2, we get a \\(1.2\\%\\) better accuracy with \\(3.0 \\times\\) speedup and \\(3.1 \\times\\) memory savings. These results illustrate the effectiveness of our method. On most networks, TinyTL has a lower accuracy while consuming more resources compared to the baselines methods." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.388, + 0.295, + 0.403 + ], + "angle": 0, + "content": "5.3. Semantic Segmentation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.411, + 0.47, + 0.533 + ], + "angle": 0, + "content": "Table 3 shows our evaluation results on the augmented Pascal-VOC12 dataset. On a wide range of networks, our method constantly achieves significant speedup with marginal accuracy loss. For the large network UPerNet, our method achieves \\(229 \\times\\) speedup with only \\(1\\%\\) mIoU loss. For the small network PSPNet, our method speedups training by \\(140 \\times\\) with only \\(2.27\\%\\) mIoU loss. This shows the effectiveness of our method on a dense prediction task." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.54, + 0.324, + 0.557 + ], + "angle": 0, + "content": "5.4. Hyper-Parameter Selection" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.563, + 0.47, + 0.655 + ], + "angle": 0, + "content": "Figure 4 shows our experimental results for ResNets under different hyper-parameter selection, i.e. number of convolution layers and patch size of gradient filter \\( r \\times r \\). Of note, the y-axis (MFLOPs) in Figure 4 is log scale. More results are included in Supplementary Section G. We highlight three qualitative findings in Figure 4:" + }, + { + "type": "text", + "bbox": [ + 0.089, + 0.663, + 0.47, + 0.724 + ], + "angle": 0, + "content": "a. For a similar accuracy, our method greatly reduces the number of operations (1 to 2 orders of magnitude), while for a similar number of computations, our method achieves a higher accuracy (2% to 5% better)." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.732, + 0.421, + 0.747 + ], + "angle": 0, + "content": "This finding proves the effectiveness of our method." + }, + { + "type": "text", + "bbox": [ + 0.089, + 0.756, + 0.47, + 0.846 + ], + "angle": 0, + "content": "b. Given the number of convolution layers to be trained, the more accurate method returns a better accuracy. Baseline (i.e., standard BP) uses the most accurate gradient, Ours-R4 (BP with gradient filter with patch size \\( 4 \\times 4 \\)) uses the least accurate gradient; thus, Baseline \\( > \\) Ours-R2 \\( > \\) Ours-R4." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.856, + 0.47, + 0.901 + ], + "angle": 0, + "content": "This finding is intuitive since the more accurate method should introduce smaller noise to the BP, e.g., the gradient filtering with patch size \\(2 \\times 2\\) (Ours-R2) introduces less" + }, + { + "type": "image", + "bbox": [ + 0.499, + 0.091, + 0.895, + 0.288 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.294, + 0.893, + 0.351 + ], + "angle": 0, + "content": "Figure 4. Computation (#MFLOPs, log scale) and model accuracy \\([\\%]\\) under different hyper-parameter selection. \"Baseline\" means vanilla BP; \"Ours-R2/4\" uses gradient filtering with patch size \\(2 \\times 2/4 \\times 4\\) during BP." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.378, + 0.893, + 0.44 + ], + "angle": 0, + "content": "noise than with patch size \\(4 \\times 4\\) (Ours-R4). In Figure 5, we evaluate the relationship between accuracy and noise level introduced by gradient filtering. With a higher SNR (i.e., a lower noise level), a better accuracy is achieved." + }, + { + "type": "image", + "bbox": [ + 0.545, + 0.45, + 0.849, + 0.531 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.54, + 0.893, + 0.582 + ], + "angle": 0, + "content": "Figure 5. Relationship between accuracy and noise level introduced by the gradient filtering. As shown, accuracy increases as the SNR increases, i.e., noise level decreases." + }, + { + "type": "text", + "bbox": [ + 0.513, + 0.612, + 0.892, + 0.658 + ], + "angle": 0, + "content": "c. Given the number of computations, the less accurate method returns the better accuracy by training more layers, i.e., Ours-R4 > Ours-R2 > baseline." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.669, + 0.892, + 0.73 + ], + "angle": 0, + "content": "This finding suggests that for neural network training with relatively low computational resources, training more layers with less accurate gradients is preferable than training fewer layers with more accurate gradients." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.741, + 0.807, + 0.756 + ], + "angle": 0, + "content": "5.5. On-device Performance Evaluation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Figure 6 and Table 4 show our evaluation results on real devices. More results are included in the Supplementary Section I. As Figure 6 shows, on CPU, most convolution layers achieve speedups over \\(20 \\times\\) with less than \\(50\\%\\) memory consumption for gradient filtering with patch sizes \\(2 \\times 2\\); for gradient filtering with patch size \\(4 \\times 4\\), the speedups are much higher, namely over \\(60 \\times\\). On GPU, the speedup is a little bit lower, but still over \\(10 \\times\\) and \\(25 \\times\\), respectively. Furthermore, as Table 4 shows, our method saves over \\(95\\%\\)" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "3817" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.107, + 0.089, + 0.493, + 0.207 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.114, + 0.209, + 0.493, + 0.314 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.498, + 0.089, + 0.865, + 0.207 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.501, + 0.208, + 0.865, + 0.314 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.325, + 0.894, + 0.396 + ], + "angle": 0, + "content": "Figure 6. Speedup and normalized memory consumption results on multiple CPUs and GPUs under different test cases (i.e. different input sizes, numbers of channels, etc.) Detailed configuration of these test cases are included in the supplementary material. \"R2\", \"R4\" mean using gradient filtering with \\(2 \\times 2\\) and \\(4 \\times 4\\) patch sizes, respectively. Our method achieves significant speedup with low memory consumption compared to all baseline methods. For example, on Jetson CPU with patch size \\(4 \\times 4\\) (\"Jetson-R4\" in left top figure), our method achieves \\(114 \\times\\) speedup with only \\(33\\%\\) memory consumption for most test cases." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.419, + 0.468, + 0.505 + ], + "angle": 0, + "content": "
DevicePatch SizeNormalized Energy Cost [STD]
Edge2 × 24.13% [0.61%]
CPU4 × 41.15% [0.18%]
Edge2 × 23.80% [0.73%]
GPU4 × 41.22% [1.10%]
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.516, + 0.47, + 0.585 + ], + "angle": 0, + "content": "Table 4. Normalized energy consumption for BP with gradient filtering for different patch sizes. Results are normalized w.r.t. the energy cost of standard BP methods. For instance, for edge CPU with a \\(4 \\times 4\\) patch, only \\(1.15\\%\\) of energy in standard BP is used. Standard deviations are shown within brackets." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.611, + 0.47, + 0.687 + ], + "angle": 0, + "content": "energy for both CPU and GPU scenarios, which largely resolves one of the most important constraints on edge devices. All these experiments on real devices show that our method is practical for the real deployment of both high-performance and IoT applications." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.698, + 0.47, + 0.756 + ], + "angle": 0, + "content": "
ModelRatioModelRatio
(Wide)ResNet18-1521.462VGG(bn)11-191.497
DenseNet121-2012.278EfficientNet b0-b71.240
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.766, + 0.468, + 0.809 + ], + "angle": 0, + "content": "Table 5. Evaluation of energy ratio defined in Equation (13) on models published on Torchvision. The ratio greater than 1 empirically verifies our assumption." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.833, + 0.345, + 0.849 + ], + "angle": 0, + "content": "5.6. Main Assumption Verification" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.47, + 0.901 + ], + "angle": 0, + "content": "We now empirically verify the assumption that the DC component dominates the frequency spectrum of the convolution kernel (Section 4.1). To this end, we collect the en" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.422, + 0.892, + 0.513 + ], + "angle": 0, + "content": "ergy ratio shown in Equation (13) from trained models published in Torchvision [23]. As Table 5 shows, for the convolution kernels in all these networks, we get a ratio greater than one, which means that the energy of DC components is larger than energy of all AC components. Thus, our assumption in Section 4.1 empirically holds true in practice." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.527, + 0.628, + 0.542 + ], + "angle": 0, + "content": "6. Conclusions" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.553, + 0.892, + 0.643 + ], + "angle": 0, + "content": "In this paper, we have addressed the on-device model training for resource-constrained edge devices. To this end, a new gradient filtering method has been proposed to systematically reduce the computation and memory consumption for the back-propagation algorithm, which is the key bottleneck for efficient model training." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.644, + 0.892, + 0.779 + ], + "angle": 0, + "content": "In Section 3, a new gradient filtering approach has been proposed to reduce the computation required for propagating gradients through the convolutional layers. The gradient filtering creates an approximate gradient feature map with fewer unique elements and a special structure; this reduces the computation by more than two orders of magnitude. Furthermore, we proved that the error introduced during back-propagation by our gradient filter is bounded so the influence of gradient approximation is limited." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.892, + 0.855 + ], + "angle": 0, + "content": "Extensive experiments in Section 5 have demonstrated the efficiency and wide applicability of our method. Indeed, models can be finetuned with orders of magnitudes fewer computations, while having only a marginal accuracy loss compared to popular baseline methods." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.856, + 0.892, + 0.9 + ], + "angle": 0, + "content": "Acknowledgements: This work was supported in part by the US National Science Foundation (NSF) grant CNS-2007284." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "3818" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.117, + 0.468, + 0.158 + ], + "angle": 0, + "content": "[1] Intel® oneapi deep neural network library (onednn). https://www.intel.com/content/www/us/en/developer/tools/oneapi/onednn.html. 1,2,6" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.161, + 0.468, + 0.342 + ], + "angle": 0, + "content": "[2] Martin Abadi, Ashish Agarwal, Paul Barham, Eugene Brevdo, Zhifeng Chen, Craig Citro, Greg S. 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In Proceedings of the AAAI Conference on Artificial Intelligence, volume 35, pages 3483-3491, 2021. 2" + }, + { + "type": "list", + "bbox": [ + 0.08, + 0.092, + 0.47, + 0.794 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.517, + 0.956 + ], + "angle": 0, + "content": "3820" + } + ] +] \ No newline at end of file diff --git a/2023/Efficient On-Device Training via Gradient Filtering/3b76baa7-39c6-473d-83e4-4a2631e20341_origin.pdf b/2023/Efficient On-Device Training via Gradient Filtering/3b76baa7-39c6-473d-83e4-4a2631e20341_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..fc3e4f0fda6246e4483561625cf0addecedcc2c7 --- /dev/null +++ b/2023/Efficient On-Device Training via Gradient Filtering/3b76baa7-39c6-473d-83e4-4a2631e20341_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:208387313aa41064322c43e00460c660bfe1a2a1677f7e019fd16587b8cdd0d4 +size 709846 diff --git a/2023/Efficient On-Device Training via Gradient Filtering/full.md b/2023/Efficient On-Device Training via Gradient Filtering/full.md new file mode 100644 index 0000000000000000000000000000000000000000..13845e67e4494cb2cf47a387aa7a64f52579d61f --- /dev/null +++ b/2023/Efficient On-Device Training via Gradient Filtering/full.md @@ -0,0 +1,357 @@ +# Efficient On-device Training via Gradient Filtering + +Yuedong Yang Guihong Li Radu Marculescu The University of Texas at Austin + +{albertyoung, lgh, radum}@utexas.edu + +# Abstract + +Despite its importance for federated learning, continuous learning and many other applications, on-device training remains an open problem for EdgeAI. The problem stems from the large number of operations (e.g., floating point multiplications and additions) and memory consumption required during training by the back-propagation algorithm. Consequently, in this paper, we propose a new gradient filtering approach which enables on-device CNN model training. More precisely, our approach creates a special structure with fewer unique elements in the gradient map, thus significantly reducing the computational complexity and memory consumption of back propagation during training. Extensive experiments on image classification and semantic segmentation with multiple CNN models (e.g., MobileNet, DeepLabV3, UPerNet) and devices (e.g., Raspberry Pi and Jetson Nano) demonstrate the effectiveness and wide applicability of our approach. For example, compared to SOTA, we achieve up to $19 \times$ speedup and $77.1\%$ memory savings on ImageNet classification with only $0.1\%$ accuracy loss. Finally, our method is easy to implement and deploy; over $20 \times$ speedup and $90\%$ energy savings have been observed compared to highly optimized baselines in MKLDNN and CUDNN on NVIDIA Jetson Nano. Consequently, our approach opens up a new direction of research with a huge potential for on-device training. $^{1}$ + +# 1. Introduction + +Existing approaches for on-device training are neither efficient nor practical enough to satisfy the resource constraints of edge devices (Figure 1). This is because these methods do not properly address a fundamental problem in on-device training, namely the computational and memory complexity of the back-propagation (BP) algorithm. More precisely, although the architecture modification [6] and layer freezing [18, 20] can help skipping the BP for some layers, for other layers, the complexity remains high. Gra + +dient quantization [4, 7] can reduce the cost of arithmetic operations but cannot reduce the number of operations (e.g., multiplications); thus, the speedup in training remains limited. Moreover, gradient quantization is not supported by existing deep-learning frameworks (e.g., CUDNN [9], MKLDNN [1], PyTorch [25] and Tensorflow [2]). To enable on-device training, there are two important questions must be addressed: + +- How can we reduce the computational complexity of back propagation through the convolution layers? +- How can we reduce the data required by the gradient computation during back propagation? + +In this paper, we propose gradient filtering, a new research direction, to address both questions. By addressing the first question, we reduce the computational complexity of training; by addressing the second question, we reduce the memory consumption. + +In general, the gradient propagation through a convolution layer involves multiplying the gradient of the output variable with a Jacobian matrix constructed with data from either the input feature map or the convolution kernel. We aim at simplifying this process with the new gradient filtering approach proposed in Section 3. Intuitively, if the gradient map w.r.t. the output has the same value for all entries, then the computation-intensive matrix multiplication can be greatly simplified, and the data required to construct the Jacobian matrix can be significantly reduced. Thus, our gradient filtering can approximate the gradient w.r.t. the output by creating a new gradient map with a special (i.e., spatial) structure and fewer unique elements. By doing so, the gradient propagation through the convolution layers reduces to cheaper operations, while the data required (hence memory) for the forward propagation also lessens. Through this filtering process, we trade off the gradient precision against the computation complexity during BP. We note that gradient filtering does not necessarily lead to a worse precision, i.e., models sometimes perform better with filtered gradients when compared against models trained with vanilla BP. + +In summary, our contributions are as follows: + +- We propose gradient filtering, which reduces the computation and memory required for BP by more than two orders of magnitude compared to the exact gradient calculation. +- We provide a rigorous error analysis which shows that the errors introduced by the gradient filtering have only a limited influence on model accuracy. +- Our experiments with multiple CNN models and computer vision tasks show that we can train a neural network with significantly less computation and memory costs, with only a marginal accuracy loss compared to baseline methods. Side-by-side comparisons against other training acceleration techniques also suggest the effectiveness of our method. +- Our method is easy to deploy with highly optimized deep learning frameworks (e.g., MKLDNN [1] and CUDNN [9]). Evaluations on resource-constrained edge (Raspberry Pi and Jetson Nano) and high-performance devices (CPU/GPU) show that our method is highly suitable for real life deployment. + +The paper is organized as follows. Section 2 reviews relevant work. Section 3 presents our method in detail. Section 4 discusses error analysis, computation and memory consumption. Experimental results are presented in Section 5. Finally, Section 6 summarizes our main contributions. + +# 2. Related Work + +Architecture Modification: Authors of [6] propose to attach small branches to the original neural network. During training, the attached branches and biases in the original model are updated. Though memory consumption is reduced, updating these branches still needs gradient propagation through the entire network; moreover, a large computational overhead for inference is introduced. + +Layer Freezing: Authors of [18, 20] propose to only train parts of the model. [18] makes layer selection based on layer importance metrics, while [20] uses evolutionary search. However, the layers selected by all these methods are typically computationally heavy layers (e.g., the last few layers in ResNet [14]) which consume most of the resources. Thus, the speedup achieved by these approaches is limited. + +Gradient Quantization: [3,5] quantize gradient after backpropagation, which means these methods cannot accelerate the training on a single device. Work in [4,7,15,17,28, 29, 33] accelerates training by reducing the cost for every arithmetic operation. However, these methods do not reduce the number of operations, which is typically huge for SOTA CNNs, so their achievable speedup is limited. Also, all these methods are not supported by the popular deep learning frameworks [1,2,9,25]. + +![](images/73ae460d6f7ea1dfc9ccee277a7dfe2ba9e447c8c043b143039ccc3c61d20a44.jpg) +Figure 1. Matrix of orthogonal directions for on-device training. "Arch" is short for "architecture". Our approach opens up a new direction of research for on-device training for EdgeAI. + +In contrast to the prior work, our method opens up a new research direction. More precisely, we reduce the number of computations and memory consumption required for training a single layer via gradient filtering. Thus, our method can be combined with any of the methods mentioned above. For example, in Section H in the Supplementary, we illustrate how our method can work together with the gradient quantization methods to enable a higher speedup. + +# 3. Proposed Method + +In this section, we introduce our gradient filtering approach to accelerate BP. To this end, we target the most computation and memory heavy operation, i.e., convolution (Figure 2(a)). Table 1 lists some symbols we use. + +
CxNumber of channels of x
Wx, HxWidth and height of x
θConvolution kernel
θ'Rotated θ, i.e., θ' = rot180(θ)
rPatch size (r × r)
gx, gy, gθGradients w.r.t. x, y, θ
gyApproximated gradient gy
x, θ'Sum of x and θ' over spatial dimensions (height and width)
x[n, ci, h, w]Element for feature map x at batch n, channel ci, pixel (h, w)
θ[c_o, c_i, u, v]Element for convolution kernel θ at output channel co, input channel ci, position (u, v)
+ +Table 1. Table of symbols we use. + +Figure 2. (a) Computation procedures for vanilla training method (upper) and our method (lower). (b) Example of gradient propagation with gradient filtering. Numbers in this example are chosen randomly for illustration purposes. In this case, the patch size selected for the gradient filter is $2 \times 2$ . Thus, the $4 \times 4$ gradient map $g_{y}$ is approximated by $\tilde{g}_{y}$ , which has four $2 \times 2$ patches with one unique value for each patch. Also, input feature map $x$ and mirrored convolution kernel $\theta'$ are spatial summed to $\tilde{x}$ and $\tilde{\theta}'$ . Since $\tilde{x}$ has fewer unique values than $x$ , memory consumption is reduced. Finally, with $\tilde{g}_{y}, \tilde{x}$ and $\tilde{\theta}$ , we compute the gradient w.r.t. kernel and input feature map with much fewer operations than the standard back propagation method. +![](images/8111d331612d65e54228ae093e287e0c50aac9ba36ac30aa6855cc06e9e6fb23.jpg) +Forward Propagation +Backward Propagation +Average Filter +$②$ Spatial Sum +Convolution +Frobenius Inner Product +Element-wise Product + +# 3.1. Problem Setup + +The computations for both forward and backward paths are shown in Figure 2(a). For the standard (vanilla) approach (upper Figure 2(a)), starting with input $x$ , the forward propagation convolves the input feature map $x$ with kernel $\theta$ and returns output $y$ , which is further processed by the other layers in the neural network (dotted arrow) until the loss value $l$ is calculated. As shown in Figure 2(a), the BP of the convolution layer starts with the gradient map w.r.t. output $y(g_{y})$ . The gradient w.r.t. input $(g_{x})$ is calculated by convolving $g_{y}$ with the rotated convolution kernel $\theta'$ , i.e., $g_{x} = g_{y} \otimes \mathrm{rot}180(\theta) = g_{y} \otimes \theta'$ . The gradient w.r.t. convolution kernel, namely $g_{\theta}$ , is calculated with the Frobenius inner product [16] between $x$ and $g_{y}$ , i.e., $g_{\theta} = g_{y} \otimes f(x)$ . + +The lower half of Figure 2(a) shows our method, where several changes are made: We introduce the gradient filter "A" after $g_{y}$ to generate the approximate gradient for BP. Also, instead of using the accurate $x$ and $\theta^{\prime}$ values for gradient computation, we sum over spatial dimensions (height and width dimensions), i.e., $\tilde{x}$ and $\tilde{\theta}^{\prime}$ , respectively. Finally, the convolution layer now multiplies the approximate gradient $\tilde{g}_{y}$ with spatial kernel $\tilde{\theta}^{\prime}$ instead of convolving with it to calculate $\tilde{g}_x$ . Figure 2(b) shows an example of gradient propagation with our gradient filter. + +# 3.2. Preliminary Analysis + +Consider the vanilla BP for convolution in Figure 2(a). Equation (1) shows the number of computations (#FLOPs) required to calculate $g_{x}$ given $g_{y}$ : + +$$ +\# \text {F L O P s} = 2 C _ {x} C _ {y} \cdot W _ {y} H _ {y} \cdot W _ {\theta} H _ {\theta} \tag {1} +$$ + +The computation requirements in Equation (1) belong to three categories: number of channels, number of unique elements per channel in the gradient map, and kernel size. Our method focuses on the last two categories. + +i. Unique elements: $(W_yH_y)$ represents the number of unique elements per channel in the gradient w.r.t. output variable $y$ ( $g_y$ ). Given the high-resolution images we use, this term is huge, so if we manage to reduce the number of unique elements in the spatial dimensions (height and width), the computations required are greatly reduced too. +ii. Kernel size: $(W_{\theta}H_{\theta})$ represents the number of unique elements in the convolution kernel. If the gradient $g_{y}$ has some special structure, for example $g_{y} = 1_{H_{y}\times W_{y}}\cdot v$ (i.e., every element in $g_{y}$ has the same value $v$ ), then the convolution can be simplified to $(\sum \theta^{\prime})v1_{H_{y}\times W_{y}}$ (with boundary elements ignored). With such a special structure, only one multiplication and $(W_{\theta}H_{\theta} - 1)$ additions are required. Moreover, $\sum \theta^{\prime}$ is independent of data so the result can be shared across multiple images until $\theta$ gets updated. + +# 3.3. Gradient Filtering + +To reduce the number of unique elements and create the special structure in the gradient map, we apply the gradient filter after the gradient w.r.t. output $(g_y)$ is provided. During the backward propagation, the gradient filter $\langle \mathbf{A}\rangle$ approximates the gradient $g_{y}$ by spatially cutting the gradient map into $r\times r$ -pixel patches and then replacing all elements in each patch with their average value (Figure 2(b)): + +$$ +\tilde {g} _ {y} [ n, c _ {o}, h, w ] = \frac {1}{r ^ {2}} \sum_ {i = \lfloor h / r \rfloor r} ^ {\lceil h / r \rceil r} \sum_ {j = \lfloor w / r \rfloor r} ^ {\lceil w / r \rceil r} g _ {y} [ n, c _ {o}, i, j ] \tag {2} +$$ + +For instance in Figure 2(b), we replace the 16 distinct values in the gradient map $g_{y}$ with 4 average values in $\tilde{g}_{y}$ . So given a gradient map $g_{y}$ with $N$ images per batch, $C$ channels, and $H \times W$ pixels per channel, the gradient filter returns a structured approximation of the gradient map containing only $N \times C \times \left\lceil \frac{H}{r} \right\rceil \times \left\lceil \frac{W}{r} \right\rceil$ blocks, with one unique value per patch. We use this matrix of unique values to represent the approximate gradient map $\tilde{g}_{y}$ , as shown in Figure 2(b). + +# 3.4. Back Propagation with Gradient Filtering + +We describe now the computation procedure used after applying the gradient filter. Detailed derivations are provided in Supplementary Section B. + +Gradient w.r.t. input: The gradient w.r.t. input is calculated by convolving $\theta^{\prime}$ with $g_{y}$ (Figure 2(a)). With the approximate gradient $\tilde{g}_y$ , this convolution simplifies to: + +$$ +\tilde {g} _ {x} [ n, c _ {i}, h, w ] = \sum_ {c _ {o}} \tilde {g} _ {y} [ n, c _ {o}, h, w ] \odot \tilde {\theta} ^ {\prime} [ c _ {o}, c _ {i} ] \tag {3} +$$ + +where $\tilde{\theta}^{\prime}[c_o,c_i] = \sum_{u,v}\theta^{\prime}[c_o,c_i,u,v]$ is the spatial sum of convolution kernel $\theta$ , as shown in Figure 2(b). + +Gradient w.r.t. kernel: The gradient w.r.t. the kernel is calculated by taking the Frobenius inner product between $x$ and $g_{y}$ , i.e., $g_{\theta}[c_o, c_i, u, v] = x \oplus g_{y}$ , namely: + +$$ +g _ {\theta} \left[ c _ {o}, c _ {i}, u, v \right] = \sum_ {n, i, j} x \left[ n, c _ {i}, i + u, j + v \right] g _ {y} \left[ n, c _ {o}, i, j \right] \tag {4} +$$ + +With the approximate gradient $\tilde{g}_y$ , the operation can be simplified to: + +$$ +\tilde {g} _ {\theta} \left[ c _ {o}, c _ {i}, u, v \right] = \sum_ {n, i, j} \tilde {x} [ n, c _ {i}, i, j ] \tilde {g} _ {y} [ n, c _ {o}, i, j ] \tag {5} +$$ + +with $\tilde{x}[n,c_i,i,j] = \sum_{h = [i / r]\rfloor r}^{\lceil i / r\rceil r}\sum_{w = \lfloor j / r\rfloor r}^{\lceil j / r\rceil r}x[n,c_i,h,w].$ As shown in Figure 2(b), $\tilde{x}[n,c_i,i,j]$ is the spatial sum of $x$ elements in the same patch containing pixel $(i,j)$ . + +# 4. Analyses of Proposed Approach + +In this section, we analyze our method from three perspectives: gradient filtering approximation error, computation reduction, and memory cost reduction. + +# 4.1. Error Analysis of Gradient Filtering + +We prove that the approximation error introduced by our gradient filtering is bounded during the gradient propagation. Without losing generality, we consider that all variables have only one channel, i.e., $C_{x_0} = C_{x_1} = 1$ . + +Proposition 1: For any input-output channel pair $(c_{o}, c_{i})$ in the convolution kernel $\theta$ , assuming the DC component has the largest energy value compared to all components in + +the spectrum $^2$ , then the signal-to-noise-ratio (SNR) of $\tilde{g}_x$ is greater than SNR of $\tilde{g}_y$ . + +Proof: We use $G_{x}, G_{y}$ and $\Theta$ to denote the gradients $g_{x}, g_{y}$ and the convolution kernel $\theta$ in the frequency domain; $G_{x}[u, v]$ is the spectrum value at frequency $(u, v)$ and $\delta$ is the 2D discrete Dirichlet function. To simplify the discussion, we consider only one patch of size $r \times r$ . + +The gradient returned by the gradient filtering can be written as: + +$$ +\tilde {g} _ {y} = \frac {1}{r ^ {2}} 1 _ {r \times r} * g _ {y} \tag {6} +$$ + +where $\circ$ denotes convolution. By applying the discrete Fourier transformation, Equation (6) can be rewritten in the frequency domain as: + +$$ +\tilde {G} _ {y} [ u, v ] = \frac {1}{r ^ {2}} \delta [ u, v ] G _ {y} [ u, v ] \tag {7} +$$ + +$\tilde{g}_y$ is the approximation of $g_{y}$ (i.e., the ground truth for $\tilde{g}_y$ is $g_{y}$ ), and the SNR of $\tilde{g}_y$ equals to: + +$$ +\begin{array}{l} \mathrm {S N R} _ {\tilde {g} _ {y}} = \frac {\sum_ {(u , v)} G _ {y} ^ {2} [ u , v ]}{\sum_ {(u , v)} \left(G _ {y} [ u , v ] - \frac {1}{r ^ {2}} \delta [ u , v ] G _ {y} [ u , v ]\right) ^ {2}} \tag {8} \\ = (1 - \frac {2 r ^ {2} - 1}{r ^ {4}} \frac {G _ {y} ^ {2} [ 0 , 0 ]}{\sum_ {(u , v)} G _ {y} ^ {2} [ u , v ]}) ^ {- 1} \\ \end{array} +$$ + +For the convolution layer, the gradient w.r.t. the approximate variable $\tilde{x}$ in the frequency domain is: + +$$ +\begin{array}{l} \tilde {G} _ {x} [ u, v ] = \Theta [ - u, - v ] \tilde {G} _ {y} [ u, v ] \\ = \frac {1}{r ^ {2}} \Theta [ - u, - v ] \delta [ u, v ] G _ {y} [ u, v ] \tag {9} \\ \end{array} +$$ + +and its ground truth is: + +$$ +G _ {x} [ u, v ] = \Theta [ - u, - v ] G _ {y} [ u, v ] \tag {10} +$$ + +Similar to Equation (8), the SNR of $g_{\bar{x}}$ is: + +$$ +\mathrm {S N R} _ {\tilde {g} _ {x}} = \left(1 - \frac {2 r ^ {2} - 1}{r ^ {4}} \frac {(\Theta [ 0 , 0 ] G _ {y} [ 0 , 0 ]) ^ {2}}{\sum_ {(u , v)} (\Theta [ u , v ] G _ {y} [ u , v ]) ^ {2}}\right) ^ {- 1} \tag {11} +$$ + +Equation (11) can be rewritten as: + +$$ +\begin{array}{l} \frac {r ^ {4} \left(1 - \operatorname {S N R} _ {\hat {g} _ {x}} ^ {- 1}\right)}{2 r ^ {2} - 1} = \frac {\left(\Theta [ 0 , 0 ] G _ {y} [ 0 , 0 ]\right) ^ {2}}{\sum_ {(u , v)} \left(\Theta [ - u , - v ] G _ {y} [ u , v ]\right) ^ {2}} \tag {12} \\ = \frac {G _ {y} ^ {2} [ 0 , 0 ]}{\sum_ {(u , v)} (\frac {\Theta [ - u , - v ]}{\Theta [ 0 , 0 ]} G _ {y} [ u , v ]) ^ {2}} \\ \end{array} +$$ + +Furthermore, the main assumption (i.e., the DC component dominates the frequency spectrum of $\Theta$ ) can be written as: + +$$ +\Theta^ {2} [ 0, 0 ] / \max _ {(u, v) \neq (0, 0)} \Theta^ {2} [ u, v ] \geq 1 \tag {13} +$$ + +![](images/091bb923c03287a7b9181226c0aaeffc2670817b0d471d7d830a652be75b22e0.jpg) +Figure 3. Computation analysis for a specific convolution layer4. Minimum achievable computation is given in Equation (16). By reducing the number of unique elements, computations required by our approach drop to about $1 / r^2$ compared with the standard BP method. By combining it with structured gradient map, computations required by our approach drop further, getting very close to the theoretical limit. + +that is, $\forall (u,v),\frac{\Theta^2[-u,-v]}{\Theta^2[0,0]}\leq 1$ ; thus, by combining Equation (12) and Equation (13), we have: + +$$ +\begin{array}{l} \frac {G _ {y} ^ {2} [ 0 , 0 ]}{\sum_ {(u , v)} \left(\frac {\Theta [ - u , - v ]}{\Theta [ 0 , 0 ]} G _ {y} [ u , v ]\right) ^ {2}} \geq \frac {G _ {y} ^ {2} [ 0 , 0 ]}{\sum_ {(u , v)} \left(G _ {y} [ u , v ]\right) ^ {2}} \tag {14} \\ \Leftrightarrow \frac {r ^ {4} \left(1 - \mathrm {S N R} _ {\tilde {g} _ {x}} ^ {- 1}\right)}{2 r ^ {2} - 1} \geq \frac {r ^ {4} \left(1 - \mathrm {S N R} _ {\tilde {g} _ {y}} ^ {- 1}\right)}{2 r ^ {2} - 1} \\ \end{array} +$$ + +which means that: $\mathrm{SNR}_{\tilde{g}_x} \geq \mathrm{SNR}_{\tilde{g}_y}$ . This completes our proof for error analysis. + +In conclusion, as the gradient propagates through the network, the noise introduced by our gradient filter becomes weaker compared to the real gradient signal. This property ensures that the error in gradient has only a limited influence on the quality of BP. We validate Proposition 1 later in the experimental section. + +# 4.2. Computation and Overhead Analysis + +In this section, we analyse the computation required to compute $g_{x}$ , the gradient w.r.t. input $x$ . Figure 3 compares the computation required to propagate the gradient through this convolution layer under different patch sizes $r \times r$ . A patch size $1 \times 1$ means the vanilla BP algorithm which we use as the baseline. As discussed in the preliminary analysis section (Section 3.2), two terms contribute to the computation savings: fewer unique elements in the gradient map and the structured gradient map. + +Fewer unique elements: In vanilla BP, there are $H_{y}W_{y}$ unique elements in the gradient map. After applying gradient filtering with a patch size $r \times r$ , the number of unique + +elements reduces to only $\lceil \frac{H_y}{r}\rceil \lceil \frac{W_y}{r}\rceil$ . This reduction contributes the most to the savings in computation (orange line in Figure 3). + +Structured Gradient Map: By creating the structured gradient map, the convolution over the gradient map $\tilde{g}_y$ is simplified to the element-wise multiplication and channel-wise addition. Computation is thus reduced to $(H_{\theta}W_{\theta})^{-1}$ of its original value. For instance, the example convolution layer in Figure 3 uses a $3\times 3$ convolution kernel so around $89\%$ computations are removed. The blue line in Figure 3 shows the #FLOPs after combining both methods. Greater reduction is expected when applying our method with larger convolution kernels. For instance, FastDepth [30] uses $5\times 5$ convolution kernel so as much as $96\%$ reduction in computation can be achieved, in principle. + +Minimum Achievable Computation: With the two reductions mentioned above, the computation required to propagate the gradient through the convolution layer is: + +$$ +\# \text {F L O P s} (r) = \left\lceil \frac {H _ {y}}{r} \right\rceil \left\lceil \frac {W _ {y}}{r} \right\rceil C _ {x} \left(2 C _ {y} - 1\right) + o \left(H _ {y} W _ {y}\right) \tag {15} +$$ + +where $o(H_yW_y)$ is a constant term which is independent of $r$ and negligible compared to $H_yW_y$ . When the patch is as large as the feature map, our method reaches the minimum achievable computation (blue dashed line in Figure 3): + +$$ +\min _ {r} \# \text {F L O P s} (r) = 2 C _ {x} C _ {y} - C _ {x} + o \left(H _ {y} W _ {y}\right) \tag {16} +$$ + +In this case, each channel of the gradient map is represented with a single value, so the computation is controlled by the number of input and output channels. + +Overhead: The overhead of our approach comes from approximating the feature map $x$ , gradient $g_{y}$ , and kernel $\theta$ . As the lower part of Figure 2(a) shows, the approximation for $x$ is considered as part of forward propagation, while the other two as back propagation. Indeed, with the patch size $r$ , the ratio of forward propagation overhead is about $1 / (2C_{o}W_{\theta}H_{\theta})$ , while the ratio of backward propagation overhead is about $(r^{2} - 1) / (2C_{x})$ . + +Given the large number of channels and spatial dimensions in typical neural networks, both overhead values take less than $1\%$ computation in the U-Net example above. + +# 4.3. Memory Analysis + +As Figure 2(a) shows, the standard back propagation for a convolution layer relies on the input feature map $x$ , which needs to be stored in memory during forward propagation. Since every convolution layer requiring gradient for its kernel needs to save a copy of feature map $x$ , the memory consumption for storing $x$ is huge. With our method, we simplify the feature map $x$ to approximated $\tilde{x}$ , which has only $\lceil \frac{H_x}{r} \rceil \lceil \frac{W_x}{r} \rceil$ unique elements for every channel. Thus, by saving only these unique values, our method achieves around $(1 - \frac{1}{r^2})$ memory savings, overall. + +
MobileNetV2 [27]#LayersAccuracyFLOPsMemResNet-18 [14]#LayersAccuracyFLOPsMem
No Finetuning04.200No Finetuning04.700
VanillaAll75.11.13G24.33MBVanillaAll73.15.42G8.33MB
263.1113.68M245.00KBBP270.4489.20M196.00KB
BP462.2160.00M459.38KB472.31.14G490.00KB
TinyTL [6]N/A60.2663.51M683.00KBTinyTL [6]N/A69.23.88G1.76MB
Ours263.139.27M80.00KBOurs268.628.32M64.00KB
463.453.96M150.00KB468.561.53M112.00KB
MCUNet [19]#LayersAccuracyFLOPsMemResNet-34 [14]#LayersAccuracyFLOPsMem
No Finetune04.100No Finetune000
VanillaAll68.5231.67M9.17MBVanillaAll70.811.17G13.11MB
262.118.80M220.50KBBP269.6489.20M196.00KB
BP464.933.71M312.38KB472.31.21G392.00KB
TinyTL [6]N/A53.1148.01M571.5KBTinyTL [6]N/A72.98.03G2.95MB
Ours261.86.34M72.00KBOurs268.628.32M64.00KB
464.411.01M102.00KB470.664.07M128.00KB
+ +Table 2. Experimental results for ImageNet classification with four neural networks (MobileNet-V2, ResNet18/34, MCUNet). "#Layers" is short for "the number of active convolutional layers". For example, #Layers equals to 2 means that only the last two convolutional layers are trained. For memory consumption, we only consider the memory for input feature $x$ . Strategy "No Finetuning" shows the accuracy on new datasets without finetuning the pretrained model. Since TinyTL [6] changes the architecture, "#Layers" is not applicable (N/A). + +
PSPNet [32]#LayersGFLOPsmIoUmAccPSPNet-M [32]#LayersGFLOPsmIoUmAccFCN [21]#LayersGFLOPsmIoUmAcc
Calibration0012.8619.74Calibration0014.2020.46Calibration0010.9515.69
Vanilla BPAll166.555.0168.02Vanilla BPAll42.448.4861.48Vanilla BPAll170.345.2258.80
515.039.5451.86512.2236.3547.09559.527.4137.90
10110.653.1567.101022.4646.0158.7010100.943.8757.58
Ours50.1439.3451.86Ours50.1136.1446.86Ours50.5827.4237.88
100.7950.8864.73100.7644.9057.50100.9636.3048.82
DLV3 [8]#LayersGFLOPsmIoUmAccDLV3-M [8]#LayersGFLOPsmIoUmAccUPerNet [31]#LayersGFLOPsmIoUmAcc
Calibration0013.9520.62Calibration0021.9636.15Calibration0014.7121.82
Vanilla BPAll151.258.3271.72Vanilla BPAll54.455.6668.95Vanilla BPAll541.064.8877.13
518.040.8553.16514.838.2149.355503.947.9361.67
10102.054.6568.641033.147.9561.4910507.648.8363.02
Ours50.3133.0944.33Ours50.2635.4746.35Ours51.9747.0460.44
102.9647.1160.28101.4045.5358.99102.2248.0062.07
+ +Table 3. Experimental results for semantic segmentation task on augmented Pascal VOC12 dataset [8]. Model name with postfix "M" means the model uses MobileNetV2 as backbone, otherwise ResNet18 is used. "#Layers" is short for "the number of active convolutional layers" that are trained. All models are pretrained on Cityscapes dataset [11]. Strategy "Calibration" shows the accuracy when only the classifier and normalization statistics are updated to adapt different numbers of classes between augmented Pascal VOC12 and Cityscapes. + +# 5. Experiments + +Our experimental section consists of theoretical and practical evaluations. Sections 5.2-5.4 show the theoretical advantages of our method on image classification and semantic segmentation tasks with implementation-agnostic metrics (e.g., accuracy, FLOPs). Then, in Section 5.5, we show how these theoretical advantages translate into practical advantages (i.e., speedup and memory savings) on real edge devices. + +# 5.1. Experimental Setup + +Classification: Following [24], we split every dataset into two highly non-i.i.d. partitions with the same size. Then, we pretrain our models on the first partition with a vanilla training strategy, and finetune the model on the other partition with different configurations for the training strat + +egy (i.e., with/without gradient filtering, hyper-parameters, number of convolution layers to be trained). More details (e.g., hyper-parameters) are in the Supplementary. + +Segmentation: Models are pretrained on Cityscapes [11] by MMSegmentation [10]. Then, we calibrate and finetune these models with different training strategies on the augmented Pascal-VOC12 dataset following [8], which is the combination of Pascal-VOC12 [12] and SBD [13]. More details are included in the supplementary material. + +On-device Performance Evaluation: For CPU performance evaluation, we implement our method with MKLDNN [1] (a.k.a. OneDNN) v2.6.0 and compare it with the convolution BP method provided by MKLDNN. We test on three CPUs, namely Intel 11900KF, Quad-core Cortex-A72 (Jetson Nano) and Quad-core Cortex-A53 (Raspberry Pi-3b). For GPU performance evaluation, we implement our method on CUDNN v8.2 [9] and compare with the BP + +method provided by CUDNN. We test on two GPUs, RTX 3090Ti and the edge GPU on Jetson Nano. Since both MKLDNN and CUDNN only support float32 BP, we test float32 BP only. Additionally, for the experiments on Jetson Nano, we record the energy consumption for CPU and GPU with the embedded power meter. More details (e.g., frequency) are included in the supplementary material. + +# 5.2. ImageNet Classification + +Table 2 shows our evaluation results on the ImageNet classification task. As shown, our method significantly reduces the FLOPs and memory required for BP, with very little accuracy loss. For example, for ResNet34, our method achieves $18.9 \times$ speedup with $1.7\%$ accuracy loss when training four layers; for MobileNetV2, we get a $1.2\%$ better accuracy with $3.0 \times$ speedup and $3.1 \times$ memory savings. These results illustrate the effectiveness of our method. On most networks, TinyTL has a lower accuracy while consuming more resources compared to the baselines methods. + +# 5.3. Semantic Segmentation + +Table 3 shows our evaluation results on the augmented Pascal-VOC12 dataset. On a wide range of networks, our method constantly achieves significant speedup with marginal accuracy loss. For the large network UPerNet, our method achieves $229 \times$ speedup with only $1\%$ mIoU loss. For the small network PSPNet, our method speedups training by $140 \times$ with only $2.27\%$ mIoU loss. This shows the effectiveness of our method on a dense prediction task. + +# 5.4. Hyper-Parameter Selection + +Figure 4 shows our experimental results for ResNets under different hyper-parameter selection, i.e. number of convolution layers and patch size of gradient filter $r \times r$ . Of note, the y-axis (MFLOPs) in Figure 4 is log scale. More results are included in Supplementary Section G. We highlight three qualitative findings in Figure 4: + +a. For a similar accuracy, our method greatly reduces the number of operations (1 to 2 orders of magnitude), while for a similar number of computations, our method achieves a higher accuracy (2% to 5% better). + +This finding proves the effectiveness of our method. + +b. Given the number of convolution layers to be trained, the more accurate method returns a better accuracy. Baseline (i.e., standard BP) uses the most accurate gradient, Ours-R4 (BP with gradient filter with patch size $4 \times 4$ ) uses the least accurate gradient; thus, Baseline $>$ Ours-R2 $>$ Ours-R4. + +This finding is intuitive since the more accurate method should introduce smaller noise to the BP, e.g., the gradient filtering with patch size $2 \times 2$ (Ours-R2) introduces less + +![](images/1416129e05ab5a02b79a1cd3ff2e57355fbb725cdb5ca23f9cc84eea4d7156dc.jpg) +Figure 4. Computation (#MFLOPs, log scale) and model accuracy $[\%]$ under different hyper-parameter selection. "Baseline" means vanilla BP; "Ours-R2/4" uses gradient filtering with patch size $2 \times 2/4 \times 4$ during BP. + +noise than with patch size $4 \times 4$ (Ours-R4). In Figure 5, we evaluate the relationship between accuracy and noise level introduced by gradient filtering. With a higher SNR (i.e., a lower noise level), a better accuracy is achieved. + +![](images/73bcb391638f29be8c8a17d3f684bca07e65e98fcf947a2d41f3031cd2ff548f.jpg) +Figure 5. Relationship between accuracy and noise level introduced by the gradient filtering. As shown, accuracy increases as the SNR increases, i.e., noise level decreases. + +c. Given the number of computations, the less accurate method returns the better accuracy by training more layers, i.e., Ours-R4 > Ours-R2 > baseline. + +This finding suggests that for neural network training with relatively low computational resources, training more layers with less accurate gradients is preferable than training fewer layers with more accurate gradients. + +# 5.5. On-device Performance Evaluation + +Figure 6 and Table 4 show our evaluation results on real devices. More results are included in the Supplementary Section I. As Figure 6 shows, on CPU, most convolution layers achieve speedups over $20 \times$ with less than $50\%$ memory consumption for gradient filtering with patch sizes $2 \times 2$ ; for gradient filtering with patch size $4 \times 4$ , the speedups are much higher, namely over $60 \times$ . On GPU, the speedup is a little bit lower, but still over $10 \times$ and $25 \times$ , respectively. Furthermore, as Table 4 shows, our method saves over $95\%$ + +![](images/b2621cf2d0595e7d12fdc1b7a17dbd2bedcf0002c376b365ea87427e31ff6337.jpg) + +![](images/17bfbab6cd32095d7afba678690e120cd59adaf3fc2ea12510c6670e4b04732a.jpg) +Figure 6. Speedup and normalized memory consumption results on multiple CPUs and GPUs under different test cases (i.e. different input sizes, numbers of channels, etc.) Detailed configuration of these test cases are included in the supplementary material. "R2", "R4" mean using gradient filtering with $2 \times 2$ and $4 \times 4$ patch sizes, respectively. Our method achieves significant speedup with low memory consumption compared to all baseline methods. For example, on Jetson CPU with patch size $4 \times 4$ ("Jetson-R4" in left top figure), our method achieves $114 \times$ speedup with only $33\%$ memory consumption for most test cases. + +![](images/ce9a8e3c2f32f5b9947b7d367cadf78fe160db8a107c9eb1eb42fb66e368d32e.jpg) + +![](images/5934835918819d8e6eab3b65fb3871333c6e2c82db12a1f6f4a0547a98147fe3.jpg) + +
DevicePatch SizeNormalized Energy Cost [STD]
Edge2 × 24.13% [0.61%]
CPU4 × 41.15% [0.18%]
Edge2 × 23.80% [0.73%]
GPU4 × 41.22% [1.10%]
+ +energy for both CPU and GPU scenarios, which largely resolves one of the most important constraints on edge devices. All these experiments on real devices show that our method is practical for the real deployment of both high-performance and IoT applications. + +Table 4. Normalized energy consumption for BP with gradient filtering for different patch sizes. Results are normalized w.r.t. the energy cost of standard BP methods. For instance, for edge CPU with a $4 \times 4$ patch, only $1.15\%$ of energy in standard BP is used. Standard deviations are shown within brackets. + +
ModelRatioModelRatio
(Wide)ResNet18-1521.462VGG(bn)11-191.497
DenseNet121-2012.278EfficientNet b0-b71.240
+ +Table 5. Evaluation of energy ratio defined in Equation (13) on models published on Torchvision. The ratio greater than 1 empirically verifies our assumption. + +# 5.6. Main Assumption Verification + +We now empirically verify the assumption that the DC component dominates the frequency spectrum of the convolution kernel (Section 4.1). To this end, we collect the en + +ergy ratio shown in Equation (13) from trained models published in Torchvision [23]. As Table 5 shows, for the convolution kernels in all these networks, we get a ratio greater than one, which means that the energy of DC components is larger than energy of all AC components. Thus, our assumption in Section 4.1 empirically holds true in practice. + +# 6. Conclusions + +In this paper, we have addressed the on-device model training for resource-constrained edge devices. To this end, a new gradient filtering method has been proposed to systematically reduce the computation and memory consumption for the back-propagation algorithm, which is the key bottleneck for efficient model training. + +In Section 3, a new gradient filtering approach has been proposed to reduce the computation required for propagating gradients through the convolutional layers. The gradient filtering creates an approximate gradient feature map with fewer unique elements and a special structure; this reduces the computation by more than two orders of magnitude. Furthermore, we proved that the error introduced during back-propagation by our gradient filter is bounded so the influence of gradient approximation is limited. + +Extensive experiments in Section 5 have demonstrated the efficiency and wide applicability of our method. 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Consequently, our approach opens up a new direction of research with a huge potential for on-device training." + }, + { + "bbox": [ + 47, + 239, + 290, + 539 + ], + "type": "inline_equation", + "content": "^{1}" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 563, + 128, + 575 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 563, + 128, + 575 + ], + "spans": [ + { + "bbox": [ + 47, + 563, + 128, + 575 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 583, + 288, + 693 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 583, + 288, + 693 + ], + "spans": [ + { + "bbox": [ + 46, + 583, + 288, + 693 + ], + "type": "text", + "content": "Existing approaches for on-device training are neither efficient nor practical enough to satisfy the resource constraints of edge devices (Figure 1). This is because these methods do not properly address a fundamental problem in on-device training, namely the computational and memory complexity of the back-propagation (BP) algorithm. More precisely, although the architecture modification [6] and layer freezing [18, 20] can help skipping the BP for some layers, for other layers, the complexity remains high. Gra" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 213, + 547, + 310 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 213, + 547, + 310 + ], + "spans": [ + { + "bbox": [ + 304, + 213, + 547, + 310 + ], + "type": "text", + "content": "dient quantization [4, 7] can reduce the cost of arithmetic operations but cannot reduce the number of operations (e.g., multiplications); thus, the speedup in training remains limited. Moreover, gradient quantization is not supported by existing deep-learning frameworks (e.g., CUDNN [9], MKLDNN [1], PyTorch [25] and Tensorflow [2]). To enable on-device training, there are two important questions must be addressed:" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 317, + 320, + 547, + 380 + ], + "type": "list", + "angle": 0, + "index": 12, + "blocks": [ + { + "bbox": [ + 317, + 320, + 547, + 344 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 320, + 547, + 344 + ], + "spans": [ + { + "bbox": [ + 317, + 320, + 547, + 344 + ], + "type": "text", + "content": "- How can we reduce the computational complexity of back propagation through the convolution layers?" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 317, + 355, + 547, + 380 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 355, + 547, + 380 + ], + "spans": [ + { + "bbox": [ + 317, + 355, + 547, + 380 + ], + "type": "text", + "content": "- How can we reduce the data required by the gradient computation during back propagation?" + } + ] + } + ], + "index": 11 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 304, + 388, + 546, + 449 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 388, + 546, + 449 + ], + "spans": [ + { + "bbox": [ + 304, + 388, + 546, + 449 + ], + "type": "text", + "content": "In this paper, we propose gradient filtering, a new research direction, to address both questions. By addressing the first question, we reduce the computational complexity of training; by addressing the second question, we reduce the memory consumption." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 450, + 547, + 700 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 450, + 547, + 700 + ], + "spans": [ + { + "bbox": [ + 304, + 450, + 547, + 700 + ], + "type": "text", + "content": "In general, the gradient propagation through a convolution layer involves multiplying the gradient of the output variable with a Jacobian matrix constructed with data from either the input feature map or the convolution kernel. We aim at simplifying this process with the new gradient filtering approach proposed in Section 3. Intuitively, if the gradient map w.r.t. the output has the same value for all entries, then the computation-intensive matrix multiplication can be greatly simplified, and the data required to construct the Jacobian matrix can be significantly reduced. Thus, our gradient filtering can approximate the gradient w.r.t. the output by creating a new gradient map with a special (i.e., spatial) structure and fewer unique elements. By doing so, the gradient propagation through the convolution layers reduces to cheaper operations, while the data required (hence memory) for the forward propagation also lessens. Through this filtering process, we trade off the gradient precision against the computation complexity during BP. We note that gradient filtering does not necessarily lead to a worse precision, i.e., models sometimes perform better with filtered gradients when compared against models trained with vanilla BP." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 317, + 701, + 502, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 701, + 502, + 713 + ], + "spans": [ + { + "bbox": [ + 317, + 701, + 502, + 713 + ], + "type": "text", + "content": "In summary, our contributions are as follows:" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 702, + 261, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 702, + 261, + 713 + ], + "spans": [ + { + "bbox": [ + 58, + 702, + 261, + 713 + ], + "type": "inline_equation", + "content": "^{1}" + }, + { + "bbox": [ + 58, + 702, + 261, + 713 + ], + "type": "text", + "content": "Code: https://github.com/SLDGroup/GradientFilter-CVPR23" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "type": "text", + "content": "3811" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 59, + 72, + 288, + 339 + ], + "type": "list", + "angle": 0, + "index": 4, + "blocks": [ + { + "bbox": [ + 59, + 72, + 287, + 120 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 72, + 287, + 120 + ], + "spans": [ + { + "bbox": [ + 59, + 72, + 287, + 120 + ], + "type": "text", + "content": "- We propose gradient filtering, which reduces the computation and memory required for BP by more than two orders of magnitude compared to the exact gradient calculation." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 59, + 129, + 287, + 165 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 129, + 287, + 165 + ], + "spans": [ + { + "bbox": [ + 59, + 129, + 287, + 165 + ], + "type": "text", + "content": "- We provide a rigorous error analysis which shows that the errors introduced by the gradient filtering have only a limited influence on model accuracy." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 59, + 173, + 288, + 258 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 173, + 288, + 258 + ], + "spans": [ + { + "bbox": [ + 59, + 173, + 288, + 258 + ], + "type": "text", + "content": "- Our experiments with multiple CNN models and computer vision tasks show that we can train a neural network with significantly less computation and memory costs, with only a marginal accuracy loss compared to baseline methods. Side-by-side comparisons against other training acceleration techniques also suggest the effectiveness of our method." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 59, + 266, + 287, + 339 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 266, + 287, + 339 + ], + "spans": [ + { + "bbox": [ + 59, + 266, + 287, + 339 + ], + "type": "text", + "content": "- Our method is easy to deploy with highly optimized deep learning frameworks (e.g., MKLDNN [1] and CUDNN [9]). Evaluations on resource-constrained edge (Raspberry Pi and Jetson Nano) and high-performance devices (CPU/GPU) show that our method is highly suitable for real life deployment." + } + ] + } + ], + "index": 3 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 47, + 346, + 287, + 407 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 346, + 287, + 407 + ], + "spans": [ + { + "bbox": [ + 47, + 346, + 287, + 407 + ], + "type": "text", + "content": "The paper is organized as follows. Section 2 reviews relevant work. Section 3 presents our method in detail. Section 4 discusses error analysis, computation and memory consumption. Experimental results are presented in Section 5. Finally, Section 6 summarizes our main contributions." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 417, + 134, + 430 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 417, + 134, + 430 + ], + "spans": [ + { + "bbox": [ + 47, + 417, + 134, + 430 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 437, + 287, + 521 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 437, + 287, + 521 + ], + "spans": [ + { + "bbox": [ + 47, + 437, + 287, + 521 + ], + "type": "text", + "content": "Architecture Modification: Authors of [6] propose to attach small branches to the original neural network. During training, the attached branches and biases in the original model are updated. Though memory consumption is reduced, updating these branches still needs gradient propagation through the entire network; moreover, a large computational overhead for inference is introduced." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 521, + 287, + 605 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 521, + 287, + 605 + ], + "spans": [ + { + "bbox": [ + 47, + 521, + 287, + 605 + ], + "type": "text", + "content": "Layer Freezing: Authors of [18, 20] propose to only train parts of the model. [18] makes layer selection based on layer importance metrics, while [20] uses evolutionary search. However, the layers selected by all these methods are typically computationally heavy layers (e.g., the last few layers in ResNet [14]) which consume most of the resources. Thus, the speedup achieved by these approaches is limited." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 605, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 605, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 47, + 605, + 287, + 714 + ], + "type": "text", + "content": "Gradient Quantization: [3,5] quantize gradient after backpropagation, which means these methods cannot accelerate the training on a single device. Work in [4,7,15,17,28, 29, 33] accelerates training by reducing the cost for every arithmetic operation. However, these methods do not reduce the number of operations, which is typically huge for SOTA CNNs, so their achievable speedup is limited. Also, all these methods are not supported by the popular deep learning frameworks [1,2,9,25]." + } + ] + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 305, + 69, + 545, + 243 + ], + "blocks": [ + { + "bbox": [ + 305, + 69, + 545, + 243 + ], + "lines": [ + { + "bbox": [ + 305, + 69, + 545, + 243 + ], + "spans": [ + { + "bbox": [ + 305, + 69, + 545, + 243 + ], + "type": "image", + "image_path": "73ae460d6f7ea1dfc9ccee277a7dfe2ba9e447c8c043b143039ccc3c61d20a44.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 250, + 545, + 284 + ], + "lines": [ + { + "bbox": [ + 305, + 250, + 545, + 284 + ], + "spans": [ + { + "bbox": [ + 305, + 250, + 545, + 284 + ], + "type": "text", + "content": "Figure 1. Matrix of orthogonal directions for on-device training. \"Arch\" is short for \"architecture\". Our approach opens up a new direction of research for on-device training for EdgeAI." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 308, + 546, + 404 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 308, + 546, + 404 + ], + "spans": [ + { + "bbox": [ + 305, + 308, + 546, + 404 + ], + "type": "text", + "content": "In contrast to the prior work, our method opens up a new research direction. More precisely, we reduce the number of computations and memory consumption required for training a single layer via gradient filtering. Thus, our method can be combined with any of the methods mentioned above. For example, in Section H in the Supplementary, we illustrate how our method can work together with the gradient quantization methods to enable a higher speedup." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 420, + 411, + 434 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 420, + 411, + 434 + ], + "spans": [ + { + "bbox": [ + 306, + 420, + 411, + 434 + ], + "type": "text", + "content": "3. Proposed Method" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 441, + 545, + 491 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 441, + 545, + 491 + ], + "spans": [ + { + "bbox": [ + 305, + 441, + 545, + 491 + ], + "type": "text", + "content": "In this section, we introduce our gradient filtering approach to accelerate BP. To this end, we target the most computation and memory heavy operation, i.e., convolution (Figure 2(a)). Table 1 lists some symbols we use." + } + ] + } + ], + "index": 14 + }, + { + "type": "table", + "bbox": [ + 310, + 510, + 542, + 692 + ], + "blocks": [ + { + "bbox": [ + 310, + 510, + 542, + 692 + ], + "lines": [ + { + "bbox": [ + 310, + 510, + 542, + 692 + ], + "spans": [ + { + "bbox": [ + 310, + 510, + 542, + 692 + ], + "type": "table", + "html": "
CxNumber of channels of x
Wx, HxWidth and height of x
θConvolution kernel
θ'Rotated θ, i.e., θ' = rot180(θ)
rPatch size (r × r)
gx, gy, gθGradients w.r.t. x, y, θ
gyApproximated gradient gy
x, θ'Sum of x and θ' over spatial dimensions (height and width)
x[n, ci, h, w]Element for feature map x at batch n, channel ci, pixel (h, w)
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(a) Computation procedures for vanilla training method (upper) and our method (lower). (b) Example of gradient propagation with gradient filtering. Numbers in this example are chosen randomly for illustration purposes. In this case, the patch size selected for the gradient filter is " + }, + { + "bbox": [ + 46, + 249, + 545, + 315 + ], + "type": "inline_equation", + "content": "2 \\times 2" + }, + { + "bbox": [ + 46, + 249, + 545, + 315 + ], + "type": "text", + "content": ". Thus, the " + }, + { + "bbox": [ + 46, + 249, + 545, + 315 + ], + "type": "inline_equation", + "content": "4 \\times 4" + }, + { + "bbox": [ + 46, + 249, + 545, + 315 + ], + "type": "text", + "content": " gradient map " + }, + { + "bbox": [ + 46, + 249, + 545, + 315 + ], + "type": "inline_equation", + "content": "g_{y}" + }, + { + "bbox": [ + 46, + 249, + 545, + 315 + ], + "type": "text", + "content": " is approximated by " + }, + { + "bbox": [ + 46, + 249, + 545, + 315 + ], + "type": "inline_equation", + "content": "\\tilde{g}_{y}" + }, + { + "bbox": [ + 46, + 249, + 545, + 315 + ], + "type": "text", + "content": ", which has four " + }, + { + "bbox": [ + 46, + 249, + 545, + 315 + ], + "type": "inline_equation", + "content": "2 \\times 2" + }, + { + "bbox": [ + 46, + 249, + 545, + 315 + ], + "type": "text", + "content": " patches with one unique value for each patch. Also, input feature map " + }, + { + "bbox": [ + 46, + 249, + 545, + 315 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 46, + 249, + 545, + 315 + ], + "type": "text", + "content": " and mirrored convolution kernel " + }, + { + "bbox": [ + 46, + 249, + 545, + 315 + ], + "type": "inline_equation", + "content": "\\theta'" + }, + { + "bbox": [ + 46, + 249, + 545, + 315 + ], + "type": "text", + "content": " are spatial summed to " + }, + { + "bbox": [ + 46, + 249, + 545, + 315 + ], + "type": "inline_equation", + "content": "\\tilde{x}" + }, + { + "bbox": [ + 46, + 249, + 545, + 315 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 249, + 545, + 315 + ], + "type": "inline_equation", + "content": "\\tilde{\\theta}'" + }, + { + "bbox": [ + 46, + 249, + 545, + 315 + ], + "type": "text", + "content": ". Since " + }, + { + "bbox": [ + 46, + 249, + 545, + 315 + ], + "type": "inline_equation", + "content": "\\tilde{x}" + }, + { + "bbox": [ + 46, + 249, + 545, + 315 + ], + "type": "text", + "content": " has fewer unique values than " + }, + { + "bbox": [ + 46, + 249, + 545, + 315 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 46, + 249, + 545, + 315 + ], + "type": "text", + "content": ", memory consumption is reduced. Finally, with " + }, + { + "bbox": [ + 46, + 249, + 545, + 315 + ], + "type": "inline_equation", + "content": "\\tilde{g}_{y}, \\tilde{x}" + }, + { + "bbox": [ + 46, + 249, + 545, + 315 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 249, + 545, + 315 + ], + "type": "inline_equation", + "content": "\\tilde{\\theta}" + }, + { + "bbox": [ + 46, + 249, + 545, + 315 + ], + "type": "text", + "content": ", we compute the gradient w.r.t. kernel and input feature map with much fewer operations than the standard back propagation method." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 335, + 139, + 348 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 335, + 139, + 348 + ], + "spans": [ + { + "bbox": [ + 47, + 335, + 139, + 348 + ], + "type": "text", + "content": "3.1. Problem Setup" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 354, + 287, + 510 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 354, + 287, + 510 + ], + "spans": [ + { + "bbox": [ + 46, + 354, + 287, + 510 + ], + "type": "text", + "content": "The computations for both forward and backward paths are shown in Figure 2(a). For the standard (vanilla) approach (upper Figure 2(a)), starting with input " + }, + { + "bbox": [ + 46, + 354, + 287, + 510 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 46, + 354, + 287, + 510 + ], + "type": "text", + "content": ", the forward propagation convolves the input feature map " + }, + { + "bbox": [ + 46, + 354, + 287, + 510 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 46, + 354, + 287, + 510 + ], + "type": "text", + "content": " with kernel " + }, + { + "bbox": [ + 46, + 354, + 287, + 510 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 46, + 354, + 287, + 510 + ], + "type": "text", + "content": " and returns output " + }, + { + "bbox": [ + 46, + 354, + 287, + 510 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 46, + 354, + 287, + 510 + ], + "type": "text", + "content": ", which is further processed by the other layers in the neural network (dotted arrow) until the loss value " + }, + { + "bbox": [ + 46, + 354, + 287, + 510 + ], + "type": "inline_equation", + "content": "l" + }, + { + "bbox": [ + 46, + 354, + 287, + 510 + ], + "type": "text", + "content": " is calculated. As shown in Figure 2(a), the BP of the convolution layer starts with the gradient map w.r.t. output " + }, + { + "bbox": [ + 46, + 354, + 287, + 510 + ], + "type": "inline_equation", + "content": "y(g_{y})" + }, + { + "bbox": [ + 46, + 354, + 287, + 510 + ], + "type": "text", + "content": ". The gradient w.r.t. input " + }, + { + "bbox": [ + 46, + 354, + 287, + 510 + ], + "type": "inline_equation", + "content": "(g_{x})" + }, + { + "bbox": [ + 46, + 354, + 287, + 510 + ], + "type": "text", + "content": " is calculated by convolving " + }, + { + "bbox": [ + 46, + 354, + 287, + 510 + ], + "type": "inline_equation", + "content": "g_{y}" + }, + { + "bbox": [ + 46, + 354, + 287, + 510 + ], + "type": "text", + "content": " with the rotated convolution kernel " + }, + { + "bbox": [ + 46, + 354, + 287, + 510 + ], + "type": "inline_equation", + "content": "\\theta'" + }, + { + "bbox": [ + 46, + 354, + 287, + 510 + ], + "type": "text", + "content": ", i.e., " + }, + { + "bbox": [ + 46, + 354, + 287, + 510 + ], + "type": "inline_equation", + "content": "g_{x} = g_{y} \\otimes \\mathrm{rot}180(\\theta) = g_{y} \\otimes \\theta'" + }, + { + "bbox": [ + 46, + 354, + 287, + 510 + ], + "type": "text", + "content": ". The gradient w.r.t. convolution kernel, namely " + }, + { + "bbox": [ + 46, + 354, + 287, + 510 + ], + "type": "inline_equation", + "content": "g_{\\theta}" + }, + { + "bbox": [ + 46, + 354, + 287, + 510 + ], + "type": "text", + "content": ", is calculated with the Frobenius inner product [16] between " + }, + { + "bbox": [ + 46, + 354, + 287, + 510 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 46, + 354, + 287, + 510 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 354, + 287, + 510 + ], + "type": "inline_equation", + "content": "g_{y}" + }, + { + "bbox": [ + 46, + 354, + 287, + 510 + ], + "type": "text", + "content": ", i.e., " + }, + { + "bbox": [ + 46, + 354, + 287, + 510 + ], + "type": "inline_equation", + "content": "g_{\\theta} = g_{y} \\otimes f(x)" + }, + { + "bbox": [ + 46, + 354, + 287, + 510 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 510, + 287, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 510, + 287, + 628 + ], + "spans": [ + { + "bbox": [ + 46, + 510, + 287, + 628 + ], + "type": "text", + "content": "The lower half of Figure 2(a) shows our method, where several changes are made: We introduce the gradient filter \"A\" after " + }, + { + "bbox": [ + 46, + 510, + 287, + 628 + ], + "type": "inline_equation", + "content": "g_{y}" + }, + { + "bbox": [ + 46, + 510, + 287, + 628 + ], + "type": "text", + "content": " to generate the approximate gradient for BP. Also, instead of using the accurate " + }, + { + "bbox": [ + 46, + 510, + 287, + 628 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 46, + 510, + 287, + 628 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 510, + 287, + 628 + ], + "type": "inline_equation", + "content": "\\theta^{\\prime}" + }, + { + "bbox": [ + 46, + 510, + 287, + 628 + ], + "type": "text", + "content": " values for gradient computation, we sum over spatial dimensions (height and width dimensions), i.e., " + }, + { + "bbox": [ + 46, + 510, + 287, + 628 + ], + "type": "inline_equation", + "content": "\\tilde{x}" + }, + { + "bbox": [ + 46, + 510, + 287, + 628 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 510, + 287, + 628 + ], + "type": "inline_equation", + "content": "\\tilde{\\theta}^{\\prime}" + }, + { + "bbox": [ + 46, + 510, + 287, + 628 + ], + "type": "text", + "content": ", respectively. Finally, the convolution layer now multiplies the approximate gradient " + }, + { + "bbox": [ + 46, + 510, + 287, + 628 + ], + "type": "inline_equation", + "content": "\\tilde{g}_{y}" + }, + { + "bbox": [ + 46, + 510, + 287, + 628 + ], + "type": "text", + "content": " with spatial kernel " + }, + { + "bbox": [ + 46, + 510, + 287, + 628 + ], + "type": "inline_equation", + "content": "\\tilde{\\theta}^{\\prime}" + }, + { + "bbox": [ + 46, + 510, + 287, + 628 + ], + "type": "text", + "content": " instead of convolving with it to calculate " + }, + { + "bbox": [ + 46, + 510, + 287, + 628 + ], + "type": "inline_equation", + "content": "\\tilde{g}_x" + }, + { + "bbox": [ + 46, + 510, + 287, + 628 + ], + "type": "text", + "content": ". Figure 2(b) shows an example of gradient propagation with our gradient filter." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 47, + 635, + 168, + 647 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 635, + 168, + 647 + ], + "spans": [ + { + "bbox": [ + 47, + 635, + 168, + 647 + ], + "type": "text", + "content": "3.2. Preliminary Analysis" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 46, + 653, + 286, + 690 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 653, + 286, + 690 + ], + "spans": [ + { + "bbox": [ + 46, + 653, + 286, + 690 + ], + "type": "text", + "content": "Consider the vanilla BP for convolution in Figure 2(a). Equation (1) shows the number of computations (#FLOPs) required to calculate " + }, + { + "bbox": [ + 46, + 653, + 286, + 690 + ], + "type": "inline_equation", + "content": "g_{x}" + }, + { + "bbox": [ + 46, + 653, + 286, + 690 + ], + "type": "text", + "content": " given " + }, + { + "bbox": [ + 46, + 653, + 286, + 690 + ], + "type": "inline_equation", + "content": "g_{y}" + }, + { + "bbox": [ + 46, + 653, + 286, + 690 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 93, + 700, + 287, + 715 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 93, + 700, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 93, + 700, + 287, + 715 + ], + "type": "interline_equation", + "content": "\\# \\text {F L O P s} = 2 C _ {x} C _ {y} \\cdot W _ {y} H _ {y} \\cdot W _ {\\theta} H _ {\\theta} \\tag {1}", + "image_path": "fa067615b8a0c4f31af5c345c2337f24c541b2516a7bf1830732dbbd2ac1014b.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 335, + 545, + 384 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 335, + 545, + 384 + ], + "spans": [ + { + "bbox": [ + 305, + 335, + 545, + 384 + ], + "type": "text", + "content": "The computation requirements in Equation (1) belong to three categories: number of channels, number of unique elements per channel in the gradient map, and kernel size. Our method focuses on the last two categories." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 384, + 545, + 563 + ], + "type": "list", + "angle": 0, + "index": 18, + "blocks": [ + { + "bbox": [ + 304, + 384, + 545, + 455 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 384, + 545, + 455 + ], + "spans": [ + { + "bbox": [ + 304, + 384, + 545, + 455 + ], + "type": "text", + "content": "i. Unique elements: " + }, + { + "bbox": [ + 304, + 384, + 545, + 455 + ], + "type": "inline_equation", + "content": "(W_yH_y)" + }, + { + "bbox": [ + 304, + 384, + 545, + 455 + ], + "type": "text", + "content": " represents the number of unique elements per channel in the gradient w.r.t. output variable " + }, + { + "bbox": [ + 304, + 384, + 545, + 455 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 304, + 384, + 545, + 455 + ], + "type": "text", + "content": " (" + }, + { + "bbox": [ + 304, + 384, + 545, + 455 + ], + "type": "inline_equation", + "content": "g_y" + }, + { + "bbox": [ + 304, + 384, + 545, + 455 + ], + "type": "text", + "content": "). Given the high-resolution images we use, this term is huge, so if we manage to reduce the number of unique elements in the spatial dimensions (height and width), the computations required are greatly reduced too." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 455, + 545, + 563 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 455, + 545, + 563 + ], + "spans": [ + { + "bbox": [ + 304, + 455, + 545, + 563 + ], + "type": "text", + "content": "ii. Kernel size: " + }, + { + "bbox": [ + 304, + 455, + 545, + 563 + ], + "type": "inline_equation", + "content": "(W_{\\theta}H_{\\theta})" + }, + { + "bbox": [ + 304, + 455, + 545, + 563 + ], + "type": "text", + "content": " represents the number of unique elements in the convolution kernel. If the gradient " + }, + { + "bbox": [ + 304, + 455, + 545, + 563 + ], + "type": "inline_equation", + "content": "g_{y}" + }, + { + "bbox": [ + 304, + 455, + 545, + 563 + ], + "type": "text", + "content": " has some special structure, for example " + }, + { + "bbox": [ + 304, + 455, + 545, + 563 + ], + "type": "inline_equation", + "content": "g_{y} = 1_{H_{y}\\times W_{y}}\\cdot v" + }, + { + "bbox": [ + 304, + 455, + 545, + 563 + ], + "type": "text", + "content": " (i.e., every element in " + }, + { + "bbox": [ + 304, + 455, + 545, + 563 + ], + "type": "inline_equation", + "content": "g_{y}" + }, + { + "bbox": [ + 304, + 455, + 545, + 563 + ], + "type": "text", + "content": " has the same value " + }, + { + "bbox": [ + 304, + 455, + 545, + 563 + ], + "type": "inline_equation", + "content": "v" + }, + { + "bbox": [ + 304, + 455, + 545, + 563 + ], + "type": "text", + "content": "), then the convolution can be simplified to " + }, + { + "bbox": [ + 304, + 455, + 545, + 563 + ], + "type": "inline_equation", + "content": "(\\sum \\theta^{\\prime})v1_{H_{y}\\times W_{y}}" + }, + { + "bbox": [ + 304, + 455, + 545, + 563 + ], + "type": "text", + "content": " (with boundary elements ignored). With such a special structure, only one multiplication and " + }, + { + "bbox": [ + 304, + 455, + 545, + 563 + ], + "type": "inline_equation", + "content": "(W_{\\theta}H_{\\theta} - 1)" + }, + { + "bbox": [ + 304, + 455, + 545, + 563 + ], + "type": "text", + "content": " additions are required. Moreover, " + }, + { + "bbox": [ + 304, + 455, + 545, + 563 + ], + "type": "inline_equation", + "content": "\\sum \\theta^{\\prime}" + }, + { + "bbox": [ + 304, + 455, + 545, + 563 + ], + "type": "text", + "content": " is independent of data so the result can be shared across multiple images until " + }, + { + "bbox": [ + 304, + 455, + 545, + 563 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 304, + 455, + 545, + 563 + ], + "type": "text", + "content": " gets updated." + } + ] + } + ], + "index": 17 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 306, + 570, + 415, + 582 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 570, + 415, + 582 + ], + "spans": [ + { + "bbox": [ + 306, + 570, + 415, + 582 + ], + "type": "text", + "content": "3.3. Gradient Filtering" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 588, + 545, + 672 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 588, + 545, + 672 + ], + "spans": [ + { + "bbox": [ + 304, + 588, + 545, + 672 + ], + "type": "text", + "content": "To reduce the number of unique elements and create the special structure in the gradient map, we apply the gradient filter after the gradient w.r.t. output " + }, + { + "bbox": [ + 304, + 588, + 545, + 672 + ], + "type": "inline_equation", + "content": "(g_y)" + }, + { + "bbox": [ + 304, + 588, + 545, + 672 + ], + "type": "text", + "content": " is provided. During the backward propagation, the gradient filter " + }, + { + "bbox": [ + 304, + 588, + 545, + 672 + ], + "type": "inline_equation", + "content": "\\langle \\mathbf{A}\\rangle" + }, + { + "bbox": [ + 304, + 588, + 545, + 672 + ], + "type": "text", + "content": " approximates the gradient " + }, + { + "bbox": [ + 304, + 588, + 545, + 672 + ], + "type": "inline_equation", + "content": "g_{y}" + }, + { + "bbox": [ + 304, + 588, + 545, + 672 + ], + "type": "text", + "content": " by spatially cutting the gradient map into " + }, + { + "bbox": [ + 304, + 588, + 545, + 672 + ], + "type": "inline_equation", + "content": "r\\times r" + }, + { + "bbox": [ + 304, + 588, + 545, + 672 + ], + "type": "text", + "content": "-pixel patches and then replacing all elements in each patch with their average value (Figure 2(b)):" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 315, + 679, + 545, + 715 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 315, + 679, + 545, + 715 + ], + "spans": [ + { + "bbox": [ + 315, + 679, + 545, + 715 + ], + "type": "interline_equation", + "content": "\\tilde {g} _ {y} [ n, c _ {o}, h, w ] = \\frac {1}{r ^ {2}} \\sum_ {i = \\lfloor h / r \\rfloor r} ^ {\\lceil h / r \\rceil r} \\sum_ {j = \\lfloor w / r \\rfloor r} ^ {\\lceil w / r \\rceil r} g _ {y} [ n, c _ {o}, i, j ] \\tag {2}", + "image_path": "e02905d3e97900c61b3e466d90178275a53ffd1c4bdc9349bf0f03baf542908e.jpg" + } + ] + } + ], + "index": 21 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "3813" + } + ] + } + ], + "index": 22 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 169 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 169 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 169 + ], + "type": "text", + "content": "For instance in Figure 2(b), we replace the 16 distinct values in the gradient map " + }, + { + "bbox": [ + 46, + 72, + 289, + 169 + ], + "type": "inline_equation", + "content": "g_{y}" + }, + { + "bbox": [ + 46, + 72, + 289, + 169 + ], + "type": "text", + "content": " with 4 average values in " + }, + { + "bbox": [ + 46, + 72, + 289, + 169 + ], + "type": "inline_equation", + "content": "\\tilde{g}_{y}" + }, + { + "bbox": [ + 46, + 72, + 289, + 169 + ], + "type": "text", + "content": ". So given a gradient map " + }, + { + "bbox": [ + 46, + 72, + 289, + 169 + ], + "type": "inline_equation", + "content": "g_{y}" + }, + { + "bbox": [ + 46, + 72, + 289, + 169 + ], + "type": "text", + "content": " with " + }, + { + "bbox": [ + 46, + 72, + 289, + 169 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 72, + 289, + 169 + ], + "type": "text", + "content": " images per batch, " + }, + { + "bbox": [ + 46, + 72, + 289, + 169 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 46, + 72, + 289, + 169 + ], + "type": "text", + "content": " channels, and " + }, + { + "bbox": [ + 46, + 72, + 289, + 169 + ], + "type": "inline_equation", + "content": "H \\times W" + }, + { + "bbox": [ + 46, + 72, + 289, + 169 + ], + "type": "text", + "content": " pixels per channel, the gradient filter returns a structured approximation of the gradient map containing only " + }, + { + "bbox": [ + 46, + 72, + 289, + 169 + ], + "type": "inline_equation", + "content": "N \\times C \\times \\left\\lceil \\frac{H}{r} \\right\\rceil \\times \\left\\lceil \\frac{W}{r} \\right\\rceil" + }, + { + "bbox": [ + 46, + 72, + 289, + 169 + ], + "type": "text", + "content": " blocks, with one unique value per patch. We use this matrix of unique values to represent the approximate gradient map " + }, + { + "bbox": [ + 46, + 72, + 289, + 169 + ], + "type": "inline_equation", + "content": "\\tilde{g}_{y}" + }, + { + "bbox": [ + 46, + 72, + 289, + 169 + ], + "type": "text", + "content": ", as shown in Figure 2(b)." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 176, + 268, + 190 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 176, + 268, + 190 + ], + "spans": [ + { + "bbox": [ + 47, + 176, + 268, + 190 + ], + "type": "text", + "content": "3.4. Back Propagation with Gradient Filtering" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 196, + 287, + 231 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 196, + 287, + 231 + ], + "spans": [ + { + "bbox": [ + 47, + 196, + 287, + 231 + ], + "type": "text", + "content": "We describe now the computation procedure used after applying the gradient filter. Detailed derivations are provided in Supplementary Section B." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 232, + 287, + 269 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 232, + 287, + 269 + ], + "spans": [ + { + "bbox": [ + 47, + 232, + 287, + 269 + ], + "type": "text", + "content": "Gradient w.r.t. input: The gradient w.r.t. input is calculated by convolving " + }, + { + "bbox": [ + 47, + 232, + 287, + 269 + ], + "type": "inline_equation", + "content": "\\theta^{\\prime}" + }, + { + "bbox": [ + 47, + 232, + 287, + 269 + ], + "type": "text", + "content": " with " + }, + { + "bbox": [ + 47, + 232, + 287, + 269 + ], + "type": "inline_equation", + "content": "g_{y}" + }, + { + "bbox": [ + 47, + 232, + 287, + 269 + ], + "type": "text", + "content": " (Figure 2(a)). With the approximate gradient " + }, + { + "bbox": [ + 47, + 232, + 287, + 269 + ], + "type": "inline_equation", + "content": "\\tilde{g}_y" + }, + { + "bbox": [ + 47, + 232, + 287, + 269 + ], + "type": "text", + "content": ", this convolution simplifies to:" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 70, + 278, + 287, + 304 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 70, + 278, + 287, + 304 + ], + "spans": [ + { + "bbox": [ + 70, + 278, + 287, + 304 + ], + "type": "interline_equation", + "content": "\\tilde {g} _ {x} [ n, c _ {i}, h, w ] = \\sum_ {c _ {o}} \\tilde {g} _ {y} [ n, c _ {o}, h, w ] \\odot \\tilde {\\theta} ^ {\\prime} [ c _ {o}, c _ {i} ] \\tag {3}", + "image_path": "971dbb4d7c13b6adc9b694809f2b7cfc66b657cd50315ddf6d116b3774d851aa.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 315, + 287, + 339 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 315, + 287, + 339 + ], + "spans": [ + { + "bbox": [ + 47, + 315, + 287, + 339 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 315, + 287, + 339 + ], + "type": "inline_equation", + "content": "\\tilde{\\theta}^{\\prime}[c_o,c_i] = \\sum_{u,v}\\theta^{\\prime}[c_o,c_i,u,v]" + }, + { + "bbox": [ + 47, + 315, + 287, + 339 + ], + "type": "text", + "content": " is the spatial sum of convolution kernel " + }, + { + "bbox": [ + 47, + 315, + 287, + 339 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 47, + 315, + 287, + 339 + ], + "type": "text", + "content": ", as shown in Figure 2(b)." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 340, + 287, + 377 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 340, + 287, + 377 + ], + "spans": [ + { + "bbox": [ + 47, + 340, + 287, + 377 + ], + "type": "text", + "content": "Gradient w.r.t. kernel: The gradient w.r.t. the kernel is calculated by taking the Frobenius inner product between " + }, + { + "bbox": [ + 47, + 340, + 287, + 377 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 47, + 340, + 287, + 377 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 340, + 287, + 377 + ], + "type": "inline_equation", + "content": "g_{y}" + }, + { + "bbox": [ + 47, + 340, + 287, + 377 + ], + "type": "text", + "content": ", i.e., " + }, + { + "bbox": [ + 47, + 340, + 287, + 377 + ], + "type": "inline_equation", + "content": "g_{\\theta}[c_o, c_i, u, v] = x \\oplus g_{y}" + }, + { + "bbox": [ + 47, + 340, + 287, + 377 + ], + "type": "text", + "content": ", namely:" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 52, + 386, + 287, + 413 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 52, + 386, + 287, + 413 + ], + "spans": [ + { + "bbox": [ + 52, + 386, + 287, + 413 + ], + "type": "interline_equation", + "content": "g _ {\\theta} \\left[ c _ {o}, c _ {i}, u, v \\right] = \\sum_ {n, i, j} x \\left[ n, c _ {i}, i + u, j + v \\right] g _ {y} \\left[ n, c _ {o}, i, j \\right] \\tag {4}", + "image_path": "87b2138cfed962f29d535ae0e6e4f135afaebae0bbd9f8095dbfd8bed93681b7.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 422, + 287, + 446 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 422, + 287, + 446 + ], + "spans": [ + { + "bbox": [ + 47, + 422, + 287, + 446 + ], + "type": "text", + "content": "With the approximate gradient " + }, + { + "bbox": [ + 47, + 422, + 287, + 446 + ], + "type": "inline_equation", + "content": "\\tilde{g}_y" + }, + { + "bbox": [ + 47, + 422, + 287, + 446 + ], + "type": "text", + "content": ", the operation can be simplified to:" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 73, + 456, + 287, + 483 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 73, + 456, + 287, + 483 + ], + "spans": [ + { + "bbox": [ + 73, + 456, + 287, + 483 + ], + "type": "interline_equation", + "content": "\\tilde {g} _ {\\theta} \\left[ c _ {o}, c _ {i}, u, v \\right] = \\sum_ {n, i, j} \\tilde {x} [ n, c _ {i}, i, j ] \\tilde {g} _ {y} [ n, c _ {o}, i, j ] \\tag {5}", + "image_path": "fed597df9ad03b4e90f211ef54a51d1f45b023f767d07b0eaffd74e72a13913a.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 491, + 287, + 533 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 491, + 287, + 533 + ], + "spans": [ + { + "bbox": [ + 47, + 491, + 287, + 533 + ], + "type": "text", + "content": "with " + }, + { + "bbox": [ + 47, + 491, + 287, + 533 + ], + "type": "inline_equation", + "content": "\\tilde{x}[n,c_i,i,j] = \\sum_{h = [i / r]\\rfloor r}^{\\lceil i / r\\rceil r}\\sum_{w = \\lfloor j / r\\rfloor r}^{\\lceil j / r\\rceil r}x[n,c_i,h,w]." + }, + { + "bbox": [ + 47, + 491, + 287, + 533 + ], + "type": "text", + "content": " As shown in Figure 2(b), " + }, + { + "bbox": [ + 47, + 491, + 287, + 533 + ], + "type": "inline_equation", + "content": "\\tilde{x}[n,c_i,i,j]" + }, + { + "bbox": [ + 47, + 491, + 287, + 533 + ], + "type": "text", + "content": " is the spatial sum of " + }, + { + "bbox": [ + 47, + 491, + 287, + 533 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 47, + 491, + 287, + 533 + ], + "type": "text", + "content": " elements in the same patch containing pixel " + }, + { + "bbox": [ + 47, + 491, + 287, + 533 + ], + "type": "inline_equation", + "content": "(i,j)" + }, + { + "bbox": [ + 47, + 491, + 287, + 533 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 47, + 544, + 226, + 559 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 544, + 226, + 559 + ], + "spans": [ + { + "bbox": [ + 47, + 544, + 226, + 559 + ], + "type": "text", + "content": "4. Analyses of Proposed Approach" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 47, + 566, + 287, + 601 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 566, + 287, + 601 + ], + "spans": [ + { + "bbox": [ + 47, + 566, + 287, + 601 + ], + "type": "text", + "content": "In this section, we analyze our method from three perspectives: gradient filtering approximation error, computation reduction, and memory cost reduction." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 47, + 610, + 241, + 624 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 610, + 241, + 624 + ], + "spans": [ + { + "bbox": [ + 47, + 610, + 241, + 624 + ], + "type": "text", + "content": "4.1. Error Analysis of Gradient Filtering" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 47, + 629, + 287, + 677 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 629, + 287, + 677 + ], + "spans": [ + { + "bbox": [ + 47, + 629, + 287, + 677 + ], + "type": "text", + "content": "We prove that the approximation error introduced by our gradient filtering is bounded during the gradient propagation. Without losing generality, we consider that all variables have only one channel, i.e., " + }, + { + "bbox": [ + 47, + 629, + 287, + 677 + ], + "type": "inline_equation", + "content": "C_{x_0} = C_{x_1} = 1" + }, + { + "bbox": [ + 47, + 629, + 287, + 677 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 47, + 677, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 677, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 677, + 287, + 713 + ], + "type": "text", + "content": "Proposition 1: For any input-output channel pair " + }, + { + "bbox": [ + 47, + 677, + 287, + 713 + ], + "type": "inline_equation", + "content": "(c_{o}, c_{i})" + }, + { + "bbox": [ + 47, + 677, + 287, + 713 + ], + "type": "text", + "content": " in the convolution kernel " + }, + { + "bbox": [ + 47, + 677, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 47, + 677, + 287, + 713 + ], + "type": "text", + "content": ", assuming the DC component has the largest energy value compared to all components in" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "type": "text", + "content": "the spectrum" + }, + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "type": "inline_equation", + "content": "^2" + }, + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "type": "text", + "content": ", then the signal-to-noise-ratio (SNR) of " + }, + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "type": "inline_equation", + "content": "\\tilde{g}_x" + }, + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "type": "text", + "content": " is greater than SNR of " + }, + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "type": "inline_equation", + "content": "\\tilde{g}_y" + }, + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 305, + 96, + 545, + 156 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 96, + 545, + 156 + ], + "spans": [ + { + "bbox": [ + 305, + 96, + 545, + 156 + ], + "type": "text", + "content": "Proof: We use " + }, + { + "bbox": [ + 305, + 96, + 545, + 156 + ], + "type": "inline_equation", + "content": "G_{x}, G_{y}" + }, + { + "bbox": [ + 305, + 96, + 545, + 156 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 96, + 545, + 156 + ], + "type": "inline_equation", + "content": "\\Theta" + }, + { + "bbox": [ + 305, + 96, + 545, + 156 + ], + "type": "text", + "content": " to denote the gradients " + }, + { + "bbox": [ + 305, + 96, + 545, + 156 + ], + "type": "inline_equation", + "content": "g_{x}, g_{y}" + }, + { + "bbox": [ + 305, + 96, + 545, + 156 + ], + "type": "text", + "content": " and the convolution kernel " + }, + { + "bbox": [ + 305, + 96, + 545, + 156 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 305, + 96, + 545, + 156 + ], + "type": "text", + "content": " in the frequency domain; " + }, + { + "bbox": [ + 305, + 96, + 545, + 156 + ], + "type": "inline_equation", + "content": "G_{x}[u, v]" + }, + { + "bbox": [ + 305, + 96, + 545, + 156 + ], + "type": "text", + "content": " is the spectrum value at frequency " + }, + { + "bbox": [ + 305, + 96, + 545, + 156 + ], + "type": "inline_equation", + "content": "(u, v)" + }, + { + "bbox": [ + 305, + 96, + 545, + 156 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 96, + 545, + 156 + ], + "type": "inline_equation", + "content": "\\delta" + }, + { + "bbox": [ + 305, + 96, + 545, + 156 + ], + "type": "text", + "content": " is the 2D discrete Dirichlet function. To simplify the discussion, we consider only one patch of size " + }, + { + "bbox": [ + 305, + 96, + 545, + 156 + ], + "type": "inline_equation", + "content": "r \\times r" + }, + { + "bbox": [ + 305, + 96, + 545, + 156 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 306, + 156, + 545, + 178 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 156, + 545, + 178 + ], + "spans": [ + { + "bbox": [ + 306, + 156, + 545, + 178 + ], + "type": "text", + "content": "The gradient returned by the gradient filtering can be written as:" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 386, + 176, + 545, + 198 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 386, + 176, + 545, + 198 + ], + "spans": [ + { + "bbox": [ + 386, + 176, + 545, + 198 + ], + "type": "interline_equation", + "content": "\\tilde {g} _ {y} = \\frac {1}{r ^ {2}} 1 _ {r \\times r} * g _ {y} \\tag {6}", + "image_path": "d0d9cb63d7da662d82f76d6e0eef8822dbc98cf0d64e28d6af4ab1339123bc4e.jpg" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 305, + 201, + 545, + 237 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 201, + 545, + 237 + ], + "spans": [ + { + "bbox": [ + 305, + 201, + 545, + 237 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 201, + 545, + 237 + ], + "type": "inline_equation", + "content": "\\circ" + }, + { + "bbox": [ + 305, + 201, + 545, + 237 + ], + "type": "text", + "content": " denotes convolution. By applying the discrete Fourier transformation, Equation (6) can be rewritten in the frequency domain as:" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 365, + 242, + 545, + 266 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 365, + 242, + 545, + 266 + ], + "spans": [ + { + "bbox": [ + 365, + 242, + 545, + 266 + ], + "type": "interline_equation", + "content": "\\tilde {G} _ {y} [ u, v ] = \\frac {1}{r ^ {2}} \\delta [ u, v ] G _ {y} [ u, v ] \\tag {7}", + "image_path": "f0704270fb8d248f3c5854fc43ab0d7e2976db2fe771ad5dd1e08a4c0d772c97.jpg" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 305, + 270, + 545, + 295 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 270, + 545, + 295 + ], + "spans": [ + { + "bbox": [ + 305, + 270, + 545, + 295 + ], + "type": "inline_equation", + "content": "\\tilde{g}_y" + }, + { + "bbox": [ + 305, + 270, + 545, + 295 + ], + "type": "text", + "content": " is the approximation of " + }, + { + "bbox": [ + 305, + 270, + 545, + 295 + ], + "type": "inline_equation", + "content": "g_{y}" + }, + { + "bbox": [ + 305, + 270, + 545, + 295 + ], + "type": "text", + "content": " (i.e., the ground truth for " + }, + { + "bbox": [ + 305, + 270, + 545, + 295 + ], + "type": "inline_equation", + "content": "\\tilde{g}_y" + }, + { + "bbox": [ + 305, + 270, + 545, + 295 + ], + "type": "text", + "content": " is " + }, + { + "bbox": [ + 305, + 270, + 545, + 295 + ], + "type": "inline_equation", + "content": "g_{y}" + }, + { + "bbox": [ + 305, + 270, + 545, + 295 + ], + "type": "text", + "content": "), and the SNR of " + }, + { + "bbox": [ + 305, + 270, + 545, + 295 + ], + "type": "inline_equation", + "content": "\\tilde{g}_y" + }, + { + "bbox": [ + 305, + 270, + 545, + 295 + ], + "type": "text", + "content": " equals to:" + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 318, + 300, + 545, + 363 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 318, + 300, + 545, + 363 + ], + "spans": [ + { + "bbox": [ + 318, + 300, + 545, + 363 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\mathrm {S N R} _ {\\tilde {g} _ {y}} = \\frac {\\sum_ {(u , v)} G _ {y} ^ {2} [ u , v ]}{\\sum_ {(u , v)} \\left(G _ {y} [ u , v ] - \\frac {1}{r ^ {2}} \\delta [ u , v ] G _ {y} [ u , v ]\\right) ^ {2}} \\tag {8} \\\\ = (1 - \\frac {2 r ^ {2} - 1}{r ^ {4}} \\frac {G _ {y} ^ {2} [ 0 , 0 ]}{\\sum_ {(u , v)} G _ {y} ^ {2} [ u , v ]}) ^ {- 1} \\\\ \\end{array}", + "image_path": "8605abf7b98badaa97025c0bd1dd2a8d1e2a21adb879f8aedbd0e269428c682b.jpg" + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 306, + 368, + 545, + 392 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 368, + 545, + 392 + ], + "spans": [ + { + "bbox": [ + 306, + 368, + 545, + 392 + ], + "type": "text", + "content": "For the convolution layer, the gradient w.r.t. the approximate variable " + }, + { + "bbox": [ + 306, + 368, + 545, + 392 + ], + "type": "inline_equation", + "content": "\\tilde{x}" + }, + { + "bbox": [ + 306, + 368, + 545, + 392 + ], + "type": "text", + "content": " in the frequency domain is:" + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 343, + 396, + 545, + 437 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 343, + 396, + 545, + 437 + ], + "spans": [ + { + "bbox": [ + 343, + 396, + 545, + 437 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\tilde {G} _ {x} [ u, v ] = \\Theta [ - u, - v ] \\tilde {G} _ {y} [ u, v ] \\\\ = \\frac {1}{r ^ {2}} \\Theta [ - u, - v ] \\delta [ u, v ] G _ {y} [ u, v ] \\tag {9} \\\\ \\end{array}", + "image_path": "4d7b936cdf765094224be77c41069201a71315e86dfe5230c44493625a0a415c.jpg" + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 306, + 442, + 400, + 453 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 442, + 400, + 453 + ], + "spans": [ + { + "bbox": [ + 306, + 442, + 400, + 453 + ], + "type": "text", + "content": "and its ground truth is:" + } + ] + } + ], + "index": 26 + }, + { + "bbox": [ + 361, + 460, + 545, + 474 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 361, + 460, + 545, + 474 + ], + "spans": [ + { + "bbox": [ + 361, + 460, + 545, + 474 + ], + "type": "interline_equation", + "content": "G _ {x} [ u, v ] = \\Theta [ - u, - v ] G _ {y} [ u, v ] \\tag {10}", + "image_path": "e5bf21e6aa03a6a938945176570656e0edc5b753600f596a86b15290ebe53673.jpg" + } + ] + } + ], + "index": 27 + }, + { + "bbox": [ + 306, + 479, + 476, + 491 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 479, + 476, + 491 + ], + "spans": [ + { + "bbox": [ + 306, + 479, + 476, + 491 + ], + "type": "text", + "content": "Similar to Equation (8), the SNR of " + }, + { + "bbox": [ + 306, + 479, + 476, + 491 + ], + "type": "inline_equation", + "content": "g_{\\bar{x}}" + }, + { + "bbox": [ + 306, + 479, + 476, + 491 + ], + "type": "text", + "content": " is:" + } + ] + } + ], + "index": 28 + }, + { + "bbox": [ + 315, + 496, + 545, + 536 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 315, + 496, + 545, + 536 + ], + "spans": [ + { + "bbox": [ + 315, + 496, + 545, + 536 + ], + "type": "interline_equation", + "content": "\\mathrm {S N R} _ {\\tilde {g} _ {x}} = \\left(1 - \\frac {2 r ^ {2} - 1}{r ^ {4}} \\frac {(\\Theta [ 0 , 0 ] G _ {y} [ 0 , 0 ]) ^ {2}}{\\sum_ {(u , v)} (\\Theta [ u , v ] G _ {y} [ u , v ]) ^ {2}}\\right) ^ {- 1} \\tag {11}", + "image_path": "04cce2e637a0496d1ee9557e5bb3390769a8baae1ac6c5535f84c47ad9f31588.jpg" + } + ] + } + ], + "index": 29 + }, + { + "bbox": [ + 306, + 536, + 444, + 548 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 536, + 444, + 548 + ], + "spans": [ + { + "bbox": [ + 306, + 536, + 444, + 548 + ], + "type": "text", + "content": "Equation (11) can be rewritten as:" + } + ] + } + ], + "index": 30 + }, + { + "bbox": [ + 315, + 553, + 545, + 619 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 315, + 553, + 545, + 619 + ], + "spans": [ + { + "bbox": [ + 315, + 553, + 545, + 619 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\frac {r ^ {4} \\left(1 - \\operatorname {S N R} _ {\\hat {g} _ {x}} ^ {- 1}\\right)}{2 r ^ {2} - 1} = \\frac {\\left(\\Theta [ 0 , 0 ] G _ {y} [ 0 , 0 ]\\right) ^ {2}}{\\sum_ {(u , v)} \\left(\\Theta [ - u , - v ] G _ {y} [ u , v ]\\right) ^ {2}} \\tag {12} \\\\ = \\frac {G _ {y} ^ {2} [ 0 , 0 ]}{\\sum_ {(u , v)} (\\frac {\\Theta [ - u , - v ]}{\\Theta [ 0 , 0 ]} G _ {y} [ u , v ]) ^ {2}} \\\\ \\end{array}", + "image_path": "91450a693b240ba8227bd0d4a75eec165006e8c337483b1d6e8307c17bf5f99c.jpg" + } + ] + } + ], + "index": 31 + }, + { + "bbox": [ + 306, + 624, + 545, + 647 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 624, + 545, + 647 + ], + "spans": [ + { + "bbox": [ + 306, + 624, + 545, + 647 + ], + "type": "text", + "content": "Furthermore, the main assumption (i.e., the DC component dominates the frequency spectrum of " + }, + { + "bbox": [ + 306, + 624, + 545, + 647 + ], + "type": "inline_equation", + "content": "\\Theta" + }, + { + "bbox": [ + 306, + 624, + 545, + 647 + ], + "type": "text", + "content": ") can be written as:" + } + ] + } + ], + "index": 32 + }, + { + "bbox": [ + 351, + 653, + 545, + 668 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 351, + 653, + 545, + 668 + ], + "spans": [ + { + "bbox": [ + 351, + 653, + 545, + 668 + ], + "type": "interline_equation", + "content": "\\Theta^ {2} [ 0, 0 ] / \\max _ {(u, v) \\neq (0, 0)} \\Theta^ {2} [ u, v ] \\geq 1 \\tag {13}", + "image_path": "452095a8ac90caadbefcc32862de5074cdff802043d644a6770c143a02f89e4f.jpg" + } + ] + } + ], + "index": 33 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 306, + 673, + 545, + 693 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 673, + 545, + 693 + ], + "spans": [ + { + "bbox": [ + 306, + 673, + 545, + 693 + ], + "type": "text", + "content": "2As a reminder, the energy of a signal is the sum of energy of the DC component and the energy of its AC components." + } + ] + } + ], + "index": 34 + }, + { + "bbox": [ + 306, + 693, + 545, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 693, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 306, + 693, + 545, + 713 + ], + "type": "text", + "content": "3Because " + }, + { + "bbox": [ + 306, + 693, + 545, + 713 + ], + "type": "inline_equation", + "content": "g_{y}" + }, + { + "bbox": [ + 306, + 693, + 545, + 713 + ], + "type": "text", + "content": " is convolved with the rotated kernel " + }, + { + "bbox": [ + 306, + 693, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\theta'" + }, + { + "bbox": [ + 306, + 693, + 545, + 713 + ], + "type": "text", + "content": ", in the frequency domain, we use " + }, + { + "bbox": [ + 306, + 693, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\Theta[-u, -v]" + }, + { + "bbox": [ + 306, + 693, + 545, + 713 + ], + "type": "text", + "content": " instead of " + }, + { + "bbox": [ + 306, + 693, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\Theta[u, v]" + }, + { + "bbox": [ + 306, + 693, + 545, + 713 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 35 + }, + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "3814" + } + ] + } + ], + "index": 37 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 69, + 76, + 265, + 184 + ], + "blocks": [ + { + "bbox": [ + 69, + 76, + 265, + 184 + ], + "lines": [ + { + "bbox": [ + 69, + 76, + 265, + 184 + ], + "spans": [ + { + "bbox": [ + 69, + 76, + 265, + 184 + ], + "type": "image", + "image_path": "091bb923c03287a7b9181226c0aaeffc2670817b0d471d7d830a652be75b22e0.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 198, + 287, + 274 + ], + "lines": [ + { + "bbox": [ + 46, + 198, + 287, + 274 + ], + "spans": [ + { + "bbox": [ + 46, + 198, + 287, + 274 + ], + "type": "text", + "content": "Figure 3. Computation analysis for a specific convolution layer4. Minimum achievable computation is given in Equation (16). By reducing the number of unique elements, computations required by our approach drop to about " + }, + { + "bbox": [ + 46, + 198, + 287, + 274 + ], + "type": "inline_equation", + "content": "1 / r^2" + }, + { + "bbox": [ + 46, + 198, + 287, + 274 + ], + "type": "text", + "content": " compared with the standard BP method. By combining it with structured gradient map, computations required by our approach drop further, getting very close to the theoretical limit." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 294, + 287, + 322 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 294, + 287, + 322 + ], + "spans": [ + { + "bbox": [ + 46, + 294, + 287, + 322 + ], + "type": "text", + "content": "that is, " + }, + { + "bbox": [ + 46, + 294, + 287, + 322 + ], + "type": "inline_equation", + "content": "\\forall (u,v),\\frac{\\Theta^2[-u,-v]}{\\Theta^2[0,0]}\\leq 1" + }, + { + "bbox": [ + 46, + 294, + 287, + 322 + ], + "type": "text", + "content": " ; thus, by combining Equation (12) and Equation (13), we have:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 58, + 331, + 287, + 393 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 331, + 287, + 393 + ], + "spans": [ + { + "bbox": [ + 58, + 331, + 287, + 393 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\frac {G _ {y} ^ {2} [ 0 , 0 ]}{\\sum_ {(u , v)} \\left(\\frac {\\Theta [ - u , - v ]}{\\Theta [ 0 , 0 ]} G _ {y} [ u , v ]\\right) ^ {2}} \\geq \\frac {G _ {y} ^ {2} [ 0 , 0 ]}{\\sum_ {(u , v)} \\left(G _ {y} [ u , v ]\\right) ^ {2}} \\tag {14} \\\\ \\Leftrightarrow \\frac {r ^ {4} \\left(1 - \\mathrm {S N R} _ {\\tilde {g} _ {x}} ^ {- 1}\\right)}{2 r ^ {2} - 1} \\geq \\frac {r ^ {4} \\left(1 - \\mathrm {S N R} _ {\\tilde {g} _ {y}} ^ {- 1}\\right)}{2 r ^ {2} - 1} \\\\ \\end{array}", + "image_path": "4ff83c5cfd4996ff23fe3f0e19c75c43e91817b612b8fcd8f780d8c547a66e9c.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 400, + 287, + 424 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 400, + 287, + 424 + ], + "spans": [ + { + "bbox": [ + 46, + 400, + 287, + 424 + ], + "type": "text", + "content": "which means that: " + }, + { + "bbox": [ + 46, + 400, + 287, + 424 + ], + "type": "inline_equation", + "content": "\\mathrm{SNR}_{\\tilde{g}_x} \\geq \\mathrm{SNR}_{\\tilde{g}_y}" + }, + { + "bbox": [ + 46, + 400, + 287, + 424 + ], + "type": "text", + "content": ". This completes our proof for error analysis." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 425, + 287, + 496 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 425, + 287, + 496 + ], + "spans": [ + { + "bbox": [ + 46, + 425, + 287, + 496 + ], + "type": "text", + "content": "In conclusion, as the gradient propagates through the network, the noise introduced by our gradient filter becomes weaker compared to the real gradient signal. This property ensures that the error in gradient has only a limited influence on the quality of BP. We validate Proposition 1 later in the experimental section." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 504, + 244, + 517 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 504, + 244, + 517 + ], + "spans": [ + { + "bbox": [ + 47, + 504, + 244, + 517 + ], + "type": "text", + "content": "4.2. Computation and Overhead Analysis" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 523, + 287, + 630 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 523, + 287, + 630 + ], + "spans": [ + { + "bbox": [ + 46, + 523, + 287, + 630 + ], + "type": "text", + "content": "In this section, we analyse the computation required to compute " + }, + { + "bbox": [ + 46, + 523, + 287, + 630 + ], + "type": "inline_equation", + "content": "g_{x}" + }, + { + "bbox": [ + 46, + 523, + 287, + 630 + ], + "type": "text", + "content": ", the gradient w.r.t. input " + }, + { + "bbox": [ + 46, + 523, + 287, + 630 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 46, + 523, + 287, + 630 + ], + "type": "text", + "content": ". Figure 3 compares the computation required to propagate the gradient through this convolution layer under different patch sizes " + }, + { + "bbox": [ + 46, + 523, + 287, + 630 + ], + "type": "inline_equation", + "content": "r \\times r" + }, + { + "bbox": [ + 46, + 523, + 287, + 630 + ], + "type": "text", + "content": ". A patch size " + }, + { + "bbox": [ + 46, + 523, + 287, + 630 + ], + "type": "inline_equation", + "content": "1 \\times 1" + }, + { + "bbox": [ + 46, + 523, + 287, + 630 + ], + "type": "text", + "content": " means the vanilla BP algorithm which we use as the baseline. As discussed in the preliminary analysis section (Section 3.2), two terms contribute to the computation savings: fewer unique elements in the gradient map and the structured gradient map." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 631, + 287, + 667 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 631, + 287, + 667 + ], + "spans": [ + { + "bbox": [ + 46, + 631, + 287, + 667 + ], + "type": "text", + "content": "Fewer unique elements: In vanilla BP, there are " + }, + { + "bbox": [ + 46, + 631, + 287, + 667 + ], + "type": "inline_equation", + "content": "H_{y}W_{y}" + }, + { + "bbox": [ + 46, + 631, + 287, + 667 + ], + "type": "text", + "content": " unique elements in the gradient map. After applying gradient filtering with a patch size " + }, + { + "bbox": [ + 46, + 631, + 287, + 667 + ], + "type": "inline_equation", + "content": "r \\times r" + }, + { + "bbox": [ + 46, + 631, + 287, + 667 + ], + "type": "text", + "content": ", the number of unique" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 70, + 545, + 107 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 70, + 545, + 107 + ], + "spans": [ + { + "bbox": [ + 306, + 70, + 545, + 107 + ], + "type": "text", + "content": "elements reduces to only " + }, + { + "bbox": [ + 306, + 70, + 545, + 107 + ], + "type": "inline_equation", + "content": "\\lceil \\frac{H_y}{r}\\rceil \\lceil \\frac{W_y}{r}\\rceil" + }, + { + "bbox": [ + 306, + 70, + 545, + 107 + ], + "type": "text", + "content": ". This reduction contributes the most to the savings in computation (orange line in Figure 3)." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 108, + 545, + 251 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 108, + 545, + 251 + ], + "spans": [ + { + "bbox": [ + 305, + 108, + 545, + 251 + ], + "type": "text", + "content": "Structured Gradient Map: By creating the structured gradient map, the convolution over the gradient map " + }, + { + "bbox": [ + 305, + 108, + 545, + 251 + ], + "type": "inline_equation", + "content": "\\tilde{g}_y" + }, + { + "bbox": [ + 305, + 108, + 545, + 251 + ], + "type": "text", + "content": " is simplified to the element-wise multiplication and channel-wise addition. Computation is thus reduced to " + }, + { + "bbox": [ + 305, + 108, + 545, + 251 + ], + "type": "inline_equation", + "content": "(H_{\\theta}W_{\\theta})^{-1}" + }, + { + "bbox": [ + 305, + 108, + 545, + 251 + ], + "type": "text", + "content": " of its original value. For instance, the example convolution layer in Figure 3 uses a " + }, + { + "bbox": [ + 305, + 108, + 545, + 251 + ], + "type": "inline_equation", + "content": "3\\times 3" + }, + { + "bbox": [ + 305, + 108, + 545, + 251 + ], + "type": "text", + "content": " convolution kernel so around " + }, + { + "bbox": [ + 305, + 108, + 545, + 251 + ], + "type": "inline_equation", + "content": "89\\%" + }, + { + "bbox": [ + 305, + 108, + 545, + 251 + ], + "type": "text", + "content": " computations are removed. The blue line in Figure 3 shows the #FLOPs after combining both methods. Greater reduction is expected when applying our method with larger convolution kernels. For instance, FastDepth [30] uses " + }, + { + "bbox": [ + 305, + 108, + 545, + 251 + ], + "type": "inline_equation", + "content": "5\\times 5" + }, + { + "bbox": [ + 305, + 108, + 545, + 251 + ], + "type": "text", + "content": " convolution kernel so as much as " + }, + { + "bbox": [ + 305, + 108, + 545, + 251 + ], + "type": "inline_equation", + "content": "96\\%" + }, + { + "bbox": [ + 305, + 108, + 545, + 251 + ], + "type": "text", + "content": " reduction in computation can be achieved, in principle." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 251, + 545, + 288 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 251, + 545, + 288 + ], + "spans": [ + { + "bbox": [ + 305, + 251, + 545, + 288 + ], + "type": "text", + "content": "Minimum Achievable Computation: With the two reductions mentioned above, the computation required to propagate the gradient through the convolution layer is:" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 310, + 293, + 545, + 318 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 310, + 293, + 545, + 318 + ], + "spans": [ + { + "bbox": [ + 310, + 293, + 545, + 318 + ], + "type": "interline_equation", + "content": "\\# \\text {F L O P s} (r) = \\left\\lceil \\frac {H _ {y}}{r} \\right\\rceil \\left\\lceil \\frac {W _ {y}}{r} \\right\\rceil C _ {x} \\left(2 C _ {y} - 1\\right) + o \\left(H _ {y} W _ {y}\\right) \\tag {15}", + "image_path": "997b6d48a7d971fc6ef35129f436c18860cb552bb5c60a28ce3d6f5ca61744c3.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 324, + 545, + 373 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 324, + 545, + 373 + ], + "spans": [ + { + "bbox": [ + 305, + 324, + 545, + 373 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 324, + 545, + 373 + ], + "type": "inline_equation", + "content": "o(H_yW_y)" + }, + { + "bbox": [ + 305, + 324, + 545, + 373 + ], + "type": "text", + "content": " is a constant term which is independent of " + }, + { + "bbox": [ + 305, + 324, + 545, + 373 + ], + "type": "inline_equation", + "content": "r" + }, + { + "bbox": [ + 305, + 324, + 545, + 373 + ], + "type": "text", + "content": " and negligible compared to " + }, + { + "bbox": [ + 305, + 324, + 545, + 373 + ], + "type": "inline_equation", + "content": "H_yW_y" + }, + { + "bbox": [ + 305, + 324, + 545, + 373 + ], + "type": "text", + "content": ". When the patch is as large as the feature map, our method reaches the minimum achievable computation (blue dashed line in Figure 3):" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 322, + 380, + 545, + 394 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 322, + 380, + 545, + 394 + ], + "spans": [ + { + "bbox": [ + 322, + 380, + 545, + 394 + ], + "type": "interline_equation", + "content": "\\min _ {r} \\# \\text {F L O P s} (r) = 2 C _ {x} C _ {y} - C _ {x} + o \\left(H _ {y} W _ {y}\\right) \\tag {16}", + "image_path": "ba6a8185ed9210369cdf1bb95eb6b3728e7ae5b2790b8b102438fda707669a53.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 401, + 545, + 437 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 401, + 545, + 437 + ], + "spans": [ + { + "bbox": [ + 305, + 401, + 545, + 437 + ], + "type": "text", + "content": "In this case, each channel of the gradient map is represented with a single value, so the computation is controlled by the number of input and output channels." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 437, + 545, + 533 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 437, + 545, + 533 + ], + "spans": [ + { + "bbox": [ + 305, + 437, + 545, + 533 + ], + "type": "text", + "content": "Overhead: The overhead of our approach comes from approximating the feature map " + }, + { + "bbox": [ + 305, + 437, + 545, + 533 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 305, + 437, + 545, + 533 + ], + "type": "text", + "content": ", gradient " + }, + { + "bbox": [ + 305, + 437, + 545, + 533 + ], + "type": "inline_equation", + "content": "g_{y}" + }, + { + "bbox": [ + 305, + 437, + 545, + 533 + ], + "type": "text", + "content": ", and kernel " + }, + { + "bbox": [ + 305, + 437, + 545, + 533 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 305, + 437, + 545, + 533 + ], + "type": "text", + "content": ". As the lower part of Figure 2(a) shows, the approximation for " + }, + { + "bbox": [ + 305, + 437, + 545, + 533 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 305, + 437, + 545, + 533 + ], + "type": "text", + "content": " is considered as part of forward propagation, while the other two as back propagation. 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Memory Analysis" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 305, + 594, + 545, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 594, + 545, + 715 + ], + "spans": [ + { + "bbox": [ + 305, + 594, + 545, + 715 + ], + "type": "text", + "content": "As Figure 2(a) shows, the standard back propagation for a convolution layer relies on the input feature map " + }, + { + "bbox": [ + 305, + 594, + 545, + 715 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 305, + 594, + 545, + 715 + ], + "type": "text", + "content": ", which needs to be stored in memory during forward propagation. 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Thus, by saving only these unique values, our method achieves around " + }, + { + "bbox": [ + 305, + 594, + 545, + 715 + ], + "type": "inline_equation", + "content": "(1 - \\frac{1}{r^2})" + }, + { + "bbox": [ + 305, + 594, + 545, + 715 + ], + "type": "text", + "content": " memory savings, overall." + } + ] + } + ], + "index": 19 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 47, + 673, + 287, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 673, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 673, + 287, + 713 + ], + "type": "text", + "content": "4The layer is from U-Net [26]. The size of the input is assumed to be " + }, + { + "bbox": [ + 47, + 673, + 287, + 713 + ], + "type": "inline_equation", + "content": "120 \\times 160" + }, + { + "bbox": [ + 47, + 673, + 287, + 713 + ], + "type": "text", + "content": " pixels with 192 channels; the output has the same resolution, but with only 64 channels. 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MobileNetV2 [27]#LayersAccuracyFLOPsMemResNet-18 [14]#LayersAccuracyFLOPsMem
No Finetuning04.200No Finetuning04.700
VanillaAll75.11.13G24.33MBVanillaAll73.15.42G8.33MB
263.1113.68M245.00KBBP270.4489.20M196.00KB
BP462.2160.00M459.38KB472.31.14G490.00KB
TinyTL [6]N/A60.2663.51M683.00KBTinyTL [6]N/A69.23.88G1.76MB
Ours263.139.27M80.00KBOurs268.628.32M64.00KB
463.453.96M150.00KB468.561.53M112.00KB
MCUNet [19]#LayersAccuracyFLOPsMemResNet-34 [14]#LayersAccuracyFLOPsMem
No Finetune04.100No Finetune000
VanillaAll68.5231.67M9.17MBVanillaAll70.811.17G13.11MB
262.118.80M220.50KBBP269.6489.20M196.00KB
BP464.933.71M312.38KB472.31.21G392.00KB
TinyTL [6]N/A53.1148.01M571.5KBTinyTL [6]N/A72.98.03G2.95MB
Ours261.86.34M72.00KBOurs268.628.32M64.00KB
464.411.01M102.00KB470.664.07M128.00KB
", + "image_path": "4ca6fe4ff02fd04384c037fda6de61dd75046c0361f049b90523657aaae02f5b.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 48, + 314, + 546, + 436 + ], + "blocks": [ + { + "bbox": [ + 46, + 257, + 546, + 301 + ], + "lines": [ + { + "bbox": [ + 46, + 257, + 546, + 301 + ], + "spans": [ + { + "bbox": [ + 46, + 257, + 546, + 301 + ], + "type": "text", + "content": "Table 2. Experimental results for ImageNet classification with four neural networks (MobileNet-V2, ResNet18/34, MCUNet). \"#Layers\" is short for \"the number of active convolutional layers\". For example, #Layers equals to 2 means that only the last two convolutional layers are trained. For memory consumption, we only consider the memory for input feature " + }, + { + "bbox": [ + 46, + 257, + 546, + 301 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 46, + 257, + 546, + 301 + ], + "type": "text", + "content": ". Strategy \"No Finetuning\" shows the accuracy on new datasets without finetuning the pretrained model. Since TinyTL [6] changes the architecture, \"#Layers\" is not applicable (N/A)." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 48, + 314, + 546, + 436 + ], + "lines": [ + { + "bbox": [ + 48, + 314, + 546, + 436 + ], + "spans": [ + { + "bbox": [ + 48, + 314, + 546, + 436 + ], + "type": "table", + "html": "
PSPNet [32]#LayersGFLOPsmIoUmAccPSPNet-M [32]#LayersGFLOPsmIoUmAccFCN [21]#LayersGFLOPsmIoUmAcc
Calibration0012.8619.74Calibration0014.2020.46Calibration0010.9515.69
Vanilla BPAll166.555.0168.02Vanilla BPAll42.448.4861.48Vanilla BPAll170.345.2258.80
515.039.5451.86512.2236.3547.09559.527.4137.90
10110.653.1567.101022.4646.0158.7010100.943.8757.58
Ours50.1439.3451.86Ours50.1136.1446.86Ours50.5827.4237.88
100.7950.8864.73100.7644.9057.50100.9636.3048.82
DLV3 [8]#LayersGFLOPsmIoUmAccDLV3-M [8]#LayersGFLOPsmIoUmAccUPerNet [31]#LayersGFLOPsmIoUmAcc
Calibration0013.9520.62Calibration0021.9636.15Calibration0014.7121.82
Vanilla BPAll151.258.3271.72Vanilla BPAll54.455.6668.95Vanilla BPAll541.064.8877.13
518.040.8553.16514.838.2149.355503.947.9361.67
10102.054.6568.641033.147.9561.4910507.648.8363.02
Ours50.3133.0944.33Ours50.2635.4746.35Ours51.9747.0460.44
102.9647.1160.28101.4045.5358.99102.2248.0062.07
", + "image_path": "d5d94509c02b205c1c25ce092f30a0d1014640ac73ce9fe18e567b4916194f03.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 445, + 546, + 489 + ], + "lines": [ + { + "bbox": [ + 46, + 445, + 546, + 489 + ], + "spans": [ + { + "bbox": [ + 46, + 445, + 546, + 489 + ], + "type": "text", + "content": "Table 3. Experimental results for semantic segmentation task on augmented Pascal VOC12 dataset [8]. Model name with postfix \"M\" means the model uses MobileNetV2 as backbone, otherwise ResNet18 is used. \"#Layers\" is short for \"the number of active convolutional layers\" that are trained. All models are pretrained on Cityscapes dataset [11]. Strategy \"Calibration\" shows the accuracy when only the classifier and normalization statistics are updated to adapt different numbers of classes between augmented Pascal VOC12 and Cityscapes." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 47, + 509, + 128, + 522 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 509, + 128, + 522 + ], + "spans": [ + { + "bbox": [ + 47, + 509, + 128, + 522 + ], + "type": "text", + "content": "5. Experiments" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 529, + 288, + 625 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 529, + 288, + 625 + ], + "spans": [ + { + "bbox": [ + 46, + 529, + 288, + 625 + ], + "type": "text", + "content": "Our experimental section consists of theoretical and practical evaluations. Sections 5.2-5.4 show the theoretical advantages of our method on image classification and semantic segmentation tasks with implementation-agnostic metrics (e.g., accuracy, FLOPs). Then, in Section 5.5, we show how these theoretical advantages translate into practical advantages (i.e., speedup and memory savings) on real edge devices." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 635, + 163, + 647 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 635, + 163, + 647 + ], + "spans": [ + { + "bbox": [ + 47, + 635, + 163, + 647 + ], + "type": "text", + "content": "5.1. Experimental Setup" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "type": "text", + "content": "Classification: Following [24], we split every dataset into two highly non-i.i.d. partitions with the same size. Then, we pretrain our models on the first partition with a vanilla training strategy, and finetune the model on the other partition with different configurations for the training strat" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 510, + 545, + 545 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 510, + 545, + 545 + ], + "spans": [ + { + "bbox": [ + 304, + 510, + 545, + 545 + ], + "type": "text", + "content": "egy (i.e., with/without gradient filtering, hyper-parameters, number of convolution layers to be trained). More details (e.g., hyper-parameters) are in the Supplementary." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 545, + 545, + 617 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 545, + 545, + 617 + ], + "spans": [ + { + "bbox": [ + 304, + 545, + 545, + 617 + ], + "type": "text", + "content": "Segmentation: Models are pretrained on Cityscapes [11] by MMSegmentation [10]. Then, we calibrate and finetune these models with different training strategies on the augmented Pascal-VOC12 dataset following [8], which is the combination of Pascal-VOC12 [12] and SBD [13]. More details are included in the supplementary material." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 617, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 546, + 713 + ], + "type": "text", + "content": "On-device Performance Evaluation: For CPU performance evaluation, we implement our method with MKLDNN [1] (a.k.a. OneDNN) v2.6.0 and compare it with the convolution BP method provided by MKLDNN. We test on three CPUs, namely Intel 11900KF, Quad-core Cortex-A72 (Jetson Nano) and Quad-core Cortex-A53 (Raspberry Pi-3b). For GPU performance evaluation, we implement our method on CUDNN v8.2 [9] and compare with the BP" + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 316, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 316, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 316, + 757 + ], + "type": "text", + "content": "3816" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 156 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 156 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 156 + ], + "type": "text", + "content": "method provided by CUDNN. We test on two GPUs, RTX 3090Ti and the edge GPU on Jetson Nano. Since both MKLDNN and CUDNN only support float32 BP, we test float32 BP only. Additionally, for the experiments on Jetson Nano, we record the energy consumption for CPU and GPU with the embedded power meter. More details (e.g., frequency) are included in the supplementary material." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 162, + 181, + 175 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 162, + 181, + 175 + ], + "spans": [ + { + "bbox": [ + 47, + 162, + 181, + 175 + ], + "type": "text", + "content": "5.2. ImageNet Classification" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 180, + 288, + 300 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 180, + 288, + 300 + ], + "spans": [ + { + "bbox": [ + 46, + 180, + 288, + 300 + ], + "type": "text", + "content": "Table 2 shows our evaluation results on the ImageNet classification task. As shown, our method significantly reduces the FLOPs and memory required for BP, with very little accuracy loss. For example, for ResNet34, our method achieves " + }, + { + "bbox": [ + 46, + 180, + 288, + 300 + ], + "type": "inline_equation", + "content": "18.9 \\times" + }, + { + "bbox": [ + 46, + 180, + 288, + 300 + ], + "type": "text", + "content": " speedup with " + }, + { + "bbox": [ + 46, + 180, + 288, + 300 + ], + "type": "inline_equation", + "content": "1.7\\%" + }, + { + "bbox": [ + 46, + 180, + 288, + 300 + ], + "type": "text", + "content": " accuracy loss when training four layers; for MobileNetV2, we get a " + }, + { + "bbox": [ + 46, + 180, + 288, + 300 + ], + "type": "inline_equation", + "content": "1.2\\%" + }, + { + "bbox": [ + 46, + 180, + 288, + 300 + ], + "type": "text", + "content": " better accuracy with " + }, + { + "bbox": [ + 46, + 180, + 288, + 300 + ], + "type": "inline_equation", + "content": "3.0 \\times" + }, + { + "bbox": [ + 46, + 180, + 288, + 300 + ], + "type": "text", + "content": " speedup and " + }, + { + "bbox": [ + 46, + 180, + 288, + 300 + ], + "type": "inline_equation", + "content": "3.1 \\times" + }, + { + "bbox": [ + 46, + 180, + 288, + 300 + ], + "type": "text", + "content": " memory savings. These results illustrate the effectiveness of our method. On most networks, TinyTL has a lower accuracy while consuming more resources compared to the baselines methods." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 307, + 180, + 319 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 307, + 180, + 319 + ], + "spans": [ + { + "bbox": [ + 47, + 307, + 180, + 319 + ], + "type": "text", + "content": "5.3. Semantic Segmentation" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 325, + 287, + 422 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 325, + 287, + 422 + ], + "spans": [ + { + "bbox": [ + 46, + 325, + 287, + 422 + ], + "type": "text", + "content": "Table 3 shows our evaluation results on the augmented Pascal-VOC12 dataset. On a wide range of networks, our method constantly achieves significant speedup with marginal accuracy loss. For the large network UPerNet, our method achieves " + }, + { + "bbox": [ + 46, + 325, + 287, + 422 + ], + "type": "inline_equation", + "content": "229 \\times" + }, + { + "bbox": [ + 46, + 325, + 287, + 422 + ], + "type": "text", + "content": " speedup with only " + }, + { + "bbox": [ + 46, + 325, + 287, + 422 + ], + "type": "inline_equation", + "content": "1\\%" + }, + { + "bbox": [ + 46, + 325, + 287, + 422 + ], + "type": "text", + "content": " mIoU loss. For the small network PSPNet, our method speedups training by " + }, + { + "bbox": [ + 46, + 325, + 287, + 422 + ], + "type": "inline_equation", + "content": "140 \\times" + }, + { + "bbox": [ + 46, + 325, + 287, + 422 + ], + "type": "text", + "content": " with only " + }, + { + "bbox": [ + 46, + 325, + 287, + 422 + ], + "type": "inline_equation", + "content": "2.27\\%" + }, + { + "bbox": [ + 46, + 325, + 287, + 422 + ], + "type": "text", + "content": " mIoU loss. This shows the effectiveness of our method on a dense prediction task." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 427, + 198, + 441 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 427, + 198, + 441 + ], + "spans": [ + { + "bbox": [ + 47, + 427, + 198, + 441 + ], + "type": "text", + "content": "5.4. Hyper-Parameter Selection" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 445, + 287, + 518 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 445, + 287, + 518 + ], + "spans": [ + { + "bbox": [ + 46, + 445, + 287, + 518 + ], + "type": "text", + "content": "Figure 4 shows our experimental results for ResNets under different hyper-parameter selection, i.e. number of convolution layers and patch size of gradient filter " + }, + { + "bbox": [ + 46, + 445, + 287, + 518 + ], + "type": "inline_equation", + "content": "r \\times r" + }, + { + "bbox": [ + 46, + 445, + 287, + 518 + ], + "type": "text", + "content": ". Of note, the y-axis (MFLOPs) in Figure 4 is log scale. More results are included in Supplementary Section G. We highlight three qualitative findings in Figure 4:" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 54, + 525, + 287, + 573 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 54, + 525, + 287, + 573 + ], + "spans": [ + { + "bbox": [ + 54, + 525, + 287, + 573 + ], + "type": "text", + "content": "a. For a similar accuracy, our method greatly reduces the number of operations (1 to 2 orders of magnitude), while for a similar number of computations, our method achieves a higher accuracy (2% to 5% better)." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 579, + 257, + 591 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 579, + 257, + 591 + ], + "spans": [ + { + "bbox": [ + 47, + 579, + 257, + 591 + ], + "type": "text", + "content": "This finding proves the effectiveness of our method." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 54, + 598, + 287, + 670 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 54, + 598, + 287, + 670 + ], + "spans": [ + { + "bbox": [ + 54, + 598, + 287, + 670 + ], + "type": "text", + "content": "b. Given the number of convolution layers to be trained, the more accurate method returns a better accuracy. Baseline (i.e., standard BP) uses the most accurate gradient, Ours-R4 (BP with gradient filter with patch size " + }, + { + "bbox": [ + 54, + 598, + 287, + 670 + ], + "type": "inline_equation", + "content": "4 \\times 4" + }, + { + "bbox": [ + 54, + 598, + 287, + 670 + ], + "type": "text", + "content": ") uses the least accurate gradient; thus, Baseline " + }, + { + "bbox": [ + 54, + 598, + 287, + 670 + ], + "type": "inline_equation", + "content": ">" + }, + { + "bbox": [ + 54, + 598, + 287, + 670 + ], + "type": "text", + "content": " Ours-R2 " + }, + { + "bbox": [ + 54, + 598, + 287, + 670 + ], + "type": "inline_equation", + "content": ">" + }, + { + "bbox": [ + 54, + 598, + 287, + 670 + ], + "type": "text", + "content": " Ours-R4." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 677, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 677, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 677, + 287, + 713 + ], + "type": "text", + "content": "This finding is intuitive since the more accurate method should introduce smaller noise to the BP, e.g., the gradient filtering with patch size " + }, + { + "bbox": [ + 47, + 677, + 287, + 713 + ], + "type": "inline_equation", + "content": "2 \\times 2" + }, + { + "bbox": [ + 47, + 677, + 287, + 713 + ], + "type": "text", + "content": " (Ours-R2) introduces less" + } + ] + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 305, + 72, + 547, + 228 + ], + "blocks": [ + { + "bbox": [ + 305, + 72, + 547, + 228 + ], + "lines": [ + { + "bbox": [ + 305, + 72, + 547, + 228 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 547, + 228 + ], + "type": "image", + "image_path": "1416129e05ab5a02b79a1cd3ff2e57355fbb725cdb5ca23f9cc84eea4d7156dc.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 232, + 546, + 277 + ], + "lines": [ + { + "bbox": [ + 305, + 232, + 546, + 277 + ], + "spans": [ + { + "bbox": [ + 305, + 232, + 546, + 277 + ], + "type": "text", + "content": "Figure 4. Computation (#MFLOPs, log scale) and model accuracy " + }, + { + "bbox": [ + 305, + 232, + 546, + 277 + ], + "type": "inline_equation", + "content": "[\\%]" + }, + { + "bbox": [ + 305, + 232, + 546, + 277 + ], + "type": "text", + "content": " under different hyper-parameter selection. \"Baseline\" means vanilla BP; \"Ours-R2/4\" uses gradient filtering with patch size " + }, + { + "bbox": [ + 305, + 232, + 546, + 277 + ], + "type": "inline_equation", + "content": "2 \\times 2/4 \\times 4" + }, + { + "bbox": [ + 305, + 232, + 546, + 277 + ], + "type": "text", + "content": " during BP." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 299, + 546, + 348 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 299, + 546, + 348 + ], + "spans": [ + { + "bbox": [ + 305, + 299, + 546, + 348 + ], + "type": "text", + "content": "noise than with patch size " + }, + { + "bbox": [ + 305, + 299, + 546, + 348 + ], + "type": "inline_equation", + "content": "4 \\times 4" + }, + { + "bbox": [ + 305, + 299, + 546, + 348 + ], + "type": "text", + "content": " (Ours-R4). In Figure 5, we evaluate the relationship between accuracy and noise level introduced by gradient filtering. With a higher SNR (i.e., a lower noise level), a better accuracy is achieved." + } + ] + } + ], + "index": 13 + }, + { + "type": "image", + "bbox": [ + 333, + 356, + 519, + 420 + ], + "blocks": [ + { + "bbox": [ + 333, + 356, + 519, + 420 + ], + "lines": [ + { + "bbox": [ + 333, + 356, + 519, + 420 + ], + "spans": [ + { + "bbox": [ + 333, + 356, + 519, + 420 + ], + "type": "image", + "image_path": "73bcb391638f29be8c8a17d3f684bca07e65e98fcf947a2d41f3031cd2ff548f.jpg" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 427, + 546, + 460 + ], + "lines": [ + { + "bbox": [ + 305, + 427, + 546, + 460 + ], + "spans": [ + { + "bbox": [ + 305, + 427, + 546, + 460 + ], + "type": "text", + "content": "Figure 5. Relationship between accuracy and noise level introduced by the gradient filtering. As shown, accuracy increases as the SNR increases, i.e., noise level decreases." + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_caption" + } + ], + "index": 14 + }, + { + "bbox": [ + 313, + 484, + 545, + 521 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 313, + 484, + 545, + 521 + ], + "spans": [ + { + "bbox": [ + 313, + 484, + 545, + 521 + ], + "type": "text", + "content": "c. Given the number of computations, the less accurate method returns the better accuracy by training more layers, i.e., Ours-R4 > Ours-R2 > baseline." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 305, + 529, + 545, + 578 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 529, + 545, + 578 + ], + "spans": [ + { + "bbox": [ + 305, + 529, + 545, + 578 + ], + "type": "text", + "content": "This finding suggests that for neural network training with relatively low computational resources, training more layers with less accurate gradients is preferable than training fewer layers with more accurate gradients." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 306, + 586, + 493, + 598 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 586, + 493, + 598 + ], + "spans": [ + { + "bbox": [ + 306, + 586, + 493, + 598 + ], + "type": "text", + "content": "5.5. On-device Performance Evaluation" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": "Figure 6 and Table 4 show our evaluation results on real devices. More results are included in the Supplementary Section I. As Figure 6 shows, on CPU, most convolution layers achieve speedups over " + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "inline_equation", + "content": "20 \\times" + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": " with less than " + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "inline_equation", + "content": "50\\%" + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": " memory consumption for gradient filtering with patch sizes " + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "inline_equation", + "content": "2 \\times 2" + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": "; for gradient filtering with patch size " + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "inline_equation", + "content": "4 \\times 4" + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": ", the speedups are much higher, namely over " + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "inline_equation", + "content": "60 \\times" + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": ". 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Speedup and normalized memory consumption results on multiple CPUs and GPUs under different test cases (i.e. different input sizes, numbers of channels, etc.) Detailed configuration of these test cases are included in the supplementary material. \"R2\", \"R4\" mean using gradient filtering with " + }, + { + "bbox": [ + 46, + 257, + 547, + 313 + ], + "type": "inline_equation", + "content": "2 \\times 2" + }, + { + "bbox": [ + 46, + 257, + 547, + 313 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 257, + 547, + 313 + ], + "type": "inline_equation", + "content": "4 \\times 4" + }, + { + "bbox": [ + 46, + 257, + 547, + 313 + ], + "type": "text", + "content": " patch sizes, respectively. Our method achieves significant speedup with low memory consumption compared to all baseline methods. 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DevicePatch SizeNormalized Energy Cost [STD]
Edge2 × 24.13% [0.61%]
CPU4 × 41.15% [0.18%]
Edge2 × 23.80% [0.73%]
GPU4 × 41.22% [1.10%]
", + "image_path": "a6ff3b5531118b3eae2c562aed13787df7038bc19495319a7cdc1e68b9e7eea3.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "table_body" + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 483, + 287, + 544 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 483, + 287, + 544 + ], + "spans": [ + { + "bbox": [ + 46, + 483, + 287, + 544 + ], + "type": "text", + "content": "energy for both CPU and GPU scenarios, which largely resolves one of the most important constraints on edge devices. All these experiments on real devices show that our method is practical for the real deployment of both high-performance and IoT applications." + } + ] + } + ], + "index": 7 + }, + { + "type": "table", + "bbox": [ + 50, + 552, + 287, + 598 + ], + "blocks": [ + { + "bbox": [ + 46, + 408, + 287, + 463 + ], + "lines": [ + { + "bbox": [ + 46, + 408, + 287, + 463 + ], + "spans": [ + { + "bbox": [ + 46, + 408, + 287, + 463 + ], + "type": "text", + "content": "Table 4. Normalized energy consumption for BP with gradient filtering for different patch sizes. Results are normalized w.r.t. the energy cost of standard BP methods. For instance, for edge CPU with a " + }, + { + "bbox": [ + 46, + 408, + 287, + 463 + ], + "type": "inline_equation", + "content": "4 \\times 4" + }, + { + "bbox": [ + 46, + 408, + 287, + 463 + ], + "type": "text", + "content": " patch, only " + }, + { + "bbox": [ + 46, + 408, + 287, + 463 + ], + "type": "inline_equation", + "content": "1.15\\%" + }, + { + "bbox": [ + 46, + 408, + 287, + 463 + ], + "type": "text", + "content": " of energy in standard BP is used. Standard deviations are shown within brackets." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 50, + 552, + 287, + 598 + ], + "lines": [ + { + "bbox": [ + 50, + 552, + 287, + 598 + ], + "spans": [ + { + "bbox": [ + 50, + 552, + 287, + 598 + ], + "type": "table", + "html": "
ModelRatioModelRatio
(Wide)ResNet18-1521.462VGG(bn)11-191.497
DenseNet121-2012.278EfficientNet b0-b71.240
", + "image_path": "f3d83be387b20b493638d11b392803cb2bfd8a10d408adfc964ef4df899f38f9.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "table_body" + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 606, + 286, + 640 + ], + "lines": [ + { + "bbox": [ + 46, + 606, + 286, + 640 + ], + "spans": [ + { + "bbox": [ + 46, + 606, + 286, + 640 + ], + "type": "text", + "content": "Table 5. Evaluation of energy ratio defined in Equation (13) on models published on Torchvision. The ratio greater than 1 empirically verifies our assumption." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 47, + 659, + 211, + 672 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 659, + 211, + 672 + ], + "spans": [ + { + "bbox": [ + 47, + 659, + 211, + 672 + ], + "type": "text", + "content": "5.6. Main Assumption Verification" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "text", + "content": "We now empirically verify the assumption that the DC component dominates the frequency spectrum of the convolution kernel (Section 4.1). To this end, we collect the en" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 334, + 545, + 406 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 334, + 545, + 406 + ], + "spans": [ + { + "bbox": [ + 304, + 334, + 545, + 406 + ], + "type": "text", + "content": "ergy ratio shown in Equation (13) from trained models published in Torchvision [23]. As Table 5 shows, for the convolution kernels in all these networks, we get a ratio greater than one, which means that the energy of DC components is larger than energy of all AC components. Thus, our assumption in Section 4.1 empirically holds true in practice." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 417, + 384, + 429 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 417, + 384, + 429 + ], + "spans": [ + { + "bbox": [ + 306, + 417, + 384, + 429 + ], + "type": "text", + "content": "6. Conclusions" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 437, + 545, + 509 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 437, + 545, + 509 + ], + "spans": [ + { + "bbox": [ + 304, + 437, + 545, + 509 + ], + "type": "text", + "content": "In this paper, we have addressed the on-device model training for resource-constrained edge devices. To this end, a new gradient filtering method has been proposed to systematically reduce the computation and memory consumption for the back-propagation algorithm, which is the key bottleneck for efficient model training." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 510, + 545, + 616 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 510, + 545, + 616 + ], + "spans": [ + { + "bbox": [ + 304, + 510, + 545, + 616 + ], + "type": "text", + "content": "In Section 3, a new gradient filtering approach has been proposed to reduce the computation required for propagating gradients through the convolutional layers. The gradient filtering creates an approximate gradient feature map with fewer unique elements and a special structure; this reduces the computation by more than two orders of magnitude. Furthermore, we proved that the error introduced during back-propagation by our gradient filter is bounded so the influence of gradient approximation is limited." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 617, + 545, + 677 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 545, + 677 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 545, + 677 + ], + "type": "text", + "content": "Extensive experiments in Section 5 have demonstrated the efficiency and wide applicability of our method. Indeed, models can be finetuned with orders of magnitudes fewer computations, while having only a marginal accuracy loss compared to popular baseline methods." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 677, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 545, + 712 + ], + "type": "text", + "content": "Acknowledgements: This work was supported in part by the US National Science Foundation (NSF) grant CNS-2007284." + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "3818" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 92, + 286, + 713 + ], + "type": "list", + "angle": 0, + "index": 11, + "blocks": [ + { + "bbox": [ + 53, + 92, + 286, + 125 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 92, + 286, + 125 + ], + "spans": [ + { + "bbox": [ + 53, + 92, + 286, + 125 + ], + "type": "text", + "content": "[1] Intel® oneapi deep neural network library (onednn). https://www.intel.com/content/www/us/en/developer/tools/oneapi/onednn.html. 1,2,6" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 53, + 127, + 286, + 270 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 127, + 286, + 270 + ], + "spans": [ + { + "bbox": [ + 53, + 127, + 286, + 270 + ], + "type": "text", + "content": "[2] Martin Abadi, Ashish Agarwal, Paul Barham, Eugene Brevdo, Zhifeng Chen, Craig Citro, Greg S. 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In Proceedings of the AAAI Conference on Artificial Intelligence, volume 35, pages 3483-3491, 2021. 2" + } + ] + } + ], + "index": 8 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 316, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 316, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 316, + 757 + ], + "type": "text", + "content": "3820" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 9 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Efficient RGB-T Tracking via Cross-Modality Distillation/cf5e82ff-3a69-46ad-ac66-64191f806cdf_content_list.json b/2023/Efficient RGB-T Tracking via Cross-Modality Distillation/cf5e82ff-3a69-46ad-ac66-64191f806cdf_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..cb8f5cd95817742a1b1e306efd06b6f498d6f93a --- /dev/null +++ b/2023/Efficient RGB-T Tracking via Cross-Modality Distillation/cf5e82ff-3a69-46ad-ac66-64191f806cdf_content_list.json @@ -0,0 +1,1762 @@ +[ + { + "type": "text", + "text": "Efficient RGB-T Tracking via Cross-Modality Distillation", + "text_level": 1, + "bbox": [ + 194, + 161, + 774, + 181 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Tianlu Zhang $^{1}$ Hongyuan Guo $^{1}$ Qiang Jiao $^{1}$ Qiang Zhang $^{1*}$ Jungong Han $^{2,3}$ $^{1}$ School of Mechano-Electronic Engineering, Xidian University, China \n $^{2}$ Department of Computer Science, the University of Sheffield, UK. \n $^{3}$ Centre for Machine Intelligence, the University of Sheffield, UK.", + "bbox": [ + 159, + 206, + 815, + 273 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "{tianluzhang, hyg}@stu.xidian.edu.cn, {qzhang, qjiao}@xidian.edu.cn, jungonghan77@gmail.com", + "bbox": [ + 87, + 275, + 887, + 289 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 320, + 312, + 334 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Most current RGB-T trackers adopt a two-stream structure to extract unimodal RGB and thermal features and complex fusion strategies to achieve multi-modal feature fusion, which require a huge number of parameters, thus hindering their real-life applications. On the other hand, a compact RGB-T tracker may be computationally efficient but encounter non-negligible performance degradation, due to the weakening of feature representation ability. To remedy this situation, a cross-modality distillation framework is presented to bridge the performance gap between a compact tracker and a powerful tracker. Specifically, a specific-common feature distillation module is proposed to transform the modality-common information as well as the modality-specific information from a deeper two-stream network to a shallower single-stream network. In addition, a multi-path selection distillation module is proposed to instruct a simple fusion module to learn more accurate multi-modal information from a well-designed fusion mechanism by using multiple paths. We validate the effectiveness of our method with extensive experiments on three RGB-T benchmarks, which achieves state-of-the-art performance but consumes much less computational resources.", + "bbox": [ + 75, + 349, + 473, + 654 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 77, + 681, + 208, + 695 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "RGB-T tracking is the task of estimating the state of an arbitrary target in each frame of an RGB-T video sequence [35]. Due to the affordability of thermal infrared (TIR) sensors, RGB-T tracking draws more and more research interest.", + "bbox": [ + 75, + 704, + 468, + 771 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "As shown in Fig. 1 (a), most existing RGB-T tracking models first adopt a two-stream structure to extract multilevel unimodal RGB and TIR features, respectively, and then employ elaborate-designed multi-modal feature fusion modules to exploit complementary information within the", + "bbox": [ + 75, + 774, + 470, + 844 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/59efdeff0171c59731060e780b9a1b5909d0688f8f3c0d58b8b3c9093f46d051.jpg", + "image_caption": [ + "Figure 1. Architectures of different RGB-T tracking models. (a) Two-stream structure. (b) Single-stream structure. (c) Our proposed method." + ], + "image_footnote": [], + "bbox": [ + 519, + 318, + 870, + 429 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "multi-modal data. Finally, they deduce the target state, often represented by a bounding box, from the fused features. Although great progress has been made, these powerful RGB-T tracking models usually require high computational costs and large model sizes to handle the information of two modalities in the stages of unimodal feature extraction and multi-modal feature fusion.", + "bbox": [ + 497, + 473, + 892, + 568 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "There are two straightforward solutions to tackle the complexity and efficiency issues. One is to adopt a single-stream feature extractor with fewer convolutional layers, and the other is to employ simpler multi-modal feature fusion modules, as shown in Fig. 1 (b). Although such compact models can reduce computational complexity, they inevitably bring non-negligible performance degradation due to the weakening of unimodal feature representation ability and multi-modal complementary information exploration ability. For instance, a powerful RGB-T tracker [35] with a two-stream structure and complicated multi-modal feature fusion modules suffers from severe performance degradation after the above model simplification operations (84.4% precision rate vs 78.1% precision rate on RGBT234 dataset [11]), as shown in Fig. 2.", + "bbox": [ + 497, + 573, + 890, + 780 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Now, the research question becomes: can we shrink the RGB-T tracker without sacrificing performance? This paper answers this question using knowledge distillation, which allows a compact model to obtain a similar ability of a complex model at little cost. We call this complex but powerful model the teacher model, and call this", + "bbox": [ + 497, + 783, + 890, + 866 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 129, + 49, + 200, + 84 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 252, + 48, + 791, + 87 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Corresponding author.", + "bbox": [ + 95, + 853, + 223, + 866 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "5404", + "bbox": [ + 468, + 885, + 500, + 897 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/f9915a6f4968cf7eeab4baedcab7a8eb1909bfe67870c1c47d7937043c3058c9.jpg", + "image_caption": [ + "Figure 2. Experimental results of different RGB-T tracking structures on RGBT234 dataset [11]. Teacher denotes the two-stream structure with complex fusion modules. Student denotes a single-stream structure with simple fusion operations. The teacher model employs ResNet50 [7] for feature extraction and fusion modules in [35] for multi-modal feature fusion, respectively. The student model employs ResNet18 [7] for feature extraction and concatenation for multi-modal feature fusion, respectively." + ], + "image_footnote": [], + "bbox": [ + 97, + 124, + 443, + 302 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "compact model the student model. Although some works [15, 19, 20, 29] have made considerable progress on knowledge distillation in multi-modal tasks, they fail to conduct a deep investigation on the huge feature differences between teacher and student in the unimodal feature extraction stage as well as in the multi-modal feature fusion stage, thereby resulting in suboptimal efficiency of the knowledge transformation. For that, a novel teacher-student knowledge distillation training framework, named Cross-Modality Distillation (CMD), is proposed to elaborately guide efficient imitation from three stages: unimodal feature extraction, multi-modal feature fusion and target estimate estimation, as shown in Fig. 1 (c).", + "bbox": [ + 75, + 409, + 468, + 587 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Specifically, in the stage of unimodal feature extraction, as pointed out by many previous works [9, 17], the shallower layers of unimodal features usually contain abundant low-level spatial details, which are usually modality-dependent. Differently, the deeper layers of unimodal features often contain many high-level semantic cues, which tend to be strongly modality-consistent. The student model uses a compact single-stream network to extract both RGB features and TIR features, which not only lacks the ability to extract modality-specific information in the shallower layers, but also insufficiently explores the modality-common information in the deeper layers. These interesting observations inspire us to design a Specific-common Feature Distillation (SCFD) module, which transforms the modality-specific information as well as the modality-common information from a two-stream deeper network to a single-stream shallower network.", + "bbox": [ + 75, + 589, + 468, + 823 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Second, in the stage of multi-modal feature fusion, the complex multi-modal feature fusion modules in the teacher model show great advantages in various scenarios, while", + "bbox": [ + 75, + 824, + 468, + 866 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "the simple fusion strategies in the student model are usually effective in some specific scenarios. It is difficult for a student model with a single simple fusion strategy to learn more effective complementary information mining capabilities from a complex teacher model due to the large feature differences. Therefore, we design a fusion module with multiple simple fusion strategies in the student model, denoted as Multi-path Selection Distillation (MPSD) module. In the process of learning from the teacher model, the student model can adaptively combine different types of fusion features to make up for the lack of complementary information mining capabilities of a single simple fusion strategy.", + "bbox": [ + 497, + 125, + 890, + 290 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Finally, in the stage of target state estimation, with the weakening of the feature representation ability of the student model, the discriminative ability of the tracker for distractors is also reduced. For that, we further present a Hard-focused Response Distillation (HFRD) module to improve the student model's discriminative ability by alleviating the problem of data imbalance between the targets and the backgrounds, which employs the response maps generated by the teacher model to instruct the student to focus on distinguishing targets from hard negative samples.", + "bbox": [ + 497, + 290, + 890, + 429 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "As shown in Fig. 2, each of our proposed modules continuously reduces the performance gap between the student model and the teacher model without increasing the number of parameters obviously. To sum up, our work improves an RGB-T tracker dramatically because of the following two contributions:", + "bbox": [ + 497, + 429, + 890, + 511 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- A Cross-Modality Distillation (CMD) framework is presented to bridge the performance gap between a compact student model and a powerful teacher model through three stages, i.e., unimodal feature extraction, multi-modal feature fusion and target state estimation. To the best of our knowledge, we are the first to introduce knowledge distillation for multi-modal tracking.", + "- Experimental results show that our proposed approach helps a student model achieve the state-of-the-art performance on the challenging GTOT [10], RGBT234 [11] and LasHer [14], while reducing the number of parameters and computational complexity." + ], + "bbox": [ + 517, + 519, + 890, + 693 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 499, + 704, + 638, + 718 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "RGB-T Tracking Methods. The past few years have witnessed the increase of RGB-T tracking algorithms [4, 10, 13, 17, 31, 39]. Among them, numerous RGB-T trackers [6, 17, 30, 39] have been presented based on the MDNet [18]. For instance, in [17], Li et al. introduced a multi-adapter architecture to learn modality-common, modality-specific and instance-aware target representations, respectively. In [39], Zhu et al. first presented a network to aggregate the features from all of the layers and all of the modalities. After that, these aggregated features were further", + "bbox": [ + 497, + 726, + 890, + 866 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "5405", + "bbox": [ + 468, + 885, + 500, + 897 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "pruned to reduce noise and redundancy. Recently, Zhang et al. [35] introduced DiMP [1] as their baseline tracker and achieved promising tracking performance. Meanwhile, aiming to speed up the tracking, some works [36, 37] bring the Siamese networks to RGB-T tracking, where their models are trained in an offline manner. Although some progress has been made, these models still suffer from the limitations of large model sizes and high computation costs.", + "bbox": [ + 75, + 125, + 468, + 235 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Knowledge Distillation Methods. Knowledge Distillation (KD) was first proposed by Hinton et al. [8] to pass dark knowledge from complicated teachers to compact students, enabling students to maintain strong performance as teachers. FitNet [21] proves that the semantic information from intermediate features is also helpful to guide the student model. Besides image classification, KD is widely applied to object detection and object tracking tasks. For instance, [2] and [16] used KD to speed up the detection and segmentation networks, respectively. Furthermore, Wang [24] proposed to learn a more compact backbone for faster feature extraction in correlation filter based trackers. Shen et al. [22] used KD to compress deep Siamese-based trackers for high-performance visual tracking.", + "bbox": [ + 75, + 236, + 470, + 429 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In addition, KD is also employed for some multi-modal tasks, such as RGB-D salient object detection [19, 20] and RGB-T pedestrian detection [15, 29]. Specifically, in [20, 29], the single-stream feature extractors and the early fusion strategies were employed in their student models. However, both of them only simply employ the distillation loss functions to improve the performance of student models by using fused features or label knowledges of teacher models, and pay less attention to the huge differences between the teacher model and the student model in the unimodal feature extraction stage as well as in the multi-modal feature fusion stage. Differently, in this paper, we aim to narrow the feature differences between the student model and the teacher model by specifically learning strategies at multiple stages.", + "bbox": [ + 75, + 429, + 468, + 637 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Distilled RGB-T Tracking", + "text_level": 1, + "bbox": [ + 77, + 648, + 319, + 663 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Given a powerful teacher model for RGB-T tracking, the proposed CMD framework aims to prompt a more efficient student model to learn from the teacher model. The knowledge from the teacher model is transferred to the student model to mimic more effective feature representation. This section starts with an overview of the proposed CMD framework. Then, we briefly provide an introduction of the employed teacher and student models. Finally, the three proposed knowledge distillation modules (i.e., SCFD, MPSD and HFRD) are described in details.", + "bbox": [ + 75, + 671, + 468, + 809 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Overview", + "text_level": 1, + "bbox": [ + 77, + 817, + 186, + 830 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "As illustrated in Fig. 3, the proposed CMD framework includes a teacher model, a student model and three knowl-", + "bbox": [ + 77, + 838, + 468, + 865 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/17a87bcf2b243628ac3e382f991b4ed3d48fc378d3c538126df05682dcb7f8bc.jpg", + "image_caption": [ + "Figure 3. Overview of the proposed CMD framework." + ], + "image_footnote": [], + "bbox": [ + 502, + 123, + 890, + 334 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "edge distillation modules. The teacher model takes a pair of RGB-T images as input, and employs a two-stream feature extractor and several complex multi-modal feature fusion modules for unimodal feature extraction and multi-modal fusion, respectively. Finally, the fused features will be fed into the target state estimation module to obtain the final tracking results. Different from the teacher model, the student model uses a single-stream feature extractor and several efficient multi-modal fusion modules. Although the student model has a higher running speed, the simplification of the model inevitably leads to a decrease in tracking performance.", + "bbox": [ + 497, + 353, + 890, + 517 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "To make up for the huge performance gap between the student model and the teacher model, the proposed CMD framework attempts to coach the learning process of the student model from three stages: unimodal feature extraction, multi-modal feature fusion and target state estimation. Accordingly, in the first stage, by using a proposed SCFD module, the powerful two-stream feature extraction network of the teacher model will transfer such modality-specific information as well as modality-common information into the single-stream network of the student model to enhance its representation ability for unimodal features. In the second stage, we will present an MPSD module to shrink the differences between the fused features obtained by the teacher model and those obtained by the student model via a multipath optimization strategy. In the third stage, with a proposed HFRD module, we will adopt the response map generated by the teacher model in a form of spatial attention to instruct the student model to focus on the discrimination of difficult samples, thereby improving its discrimination ability. The improvements in the above three stages will effectively narrow the performance gap between the student model and the teacher model, enabling the student model to achieve competitive tracking results with the teacher model but with fewer parameters and higher computational efficiency.", + "bbox": [ + 497, + 521, + 890, + 866 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "5406", + "bbox": [ + 468, + 887, + 500, + 897 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/29707099059fed5d853c711e7a9007a825e7326eb4fa95e578e36d90b877647d.jpg", + "image_caption": [ + "Figure 4. Structure of the employed teacher model and the student model." + ], + "image_footnote": [], + "bbox": [ + 85, + 124, + 458, + 273 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. Teacher and Student Model", + "text_level": 1, + "bbox": [ + 77, + 302, + 326, + 315 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In this section, we will describe the architectures of the employed teacher and student models, which are both based on the recent deep RGB tracker DiMP [1]. As shown in Fig. 4, both the teacher model and the student model can be divided into three stages: unimodal feature extraction, multi-modal feature fusion and target state estimation.", + "bbox": [ + 75, + 323, + 468, + 406 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Feature extraction. In the teacher model, two feature extractors, denoted as $E_{rgb}$ and $E_{the}$ , regard RGB and TIR modalities in parallel. The two feature extractors both adopt ResNet50 [7] as the backbone to extract multi-level RGB and TIR features, as shown in Fig. 4 (a). Differently, in the student model, only one feature extractor, denoted as $E_{stu}$ , regards both RGB and TIR modalities simultaneously. As shown in Fig. 4 (b), $E_{stu}$ just adopts ResNet18 [7] as the backbone for simplification. Similar to the original DiMP tracker, in both the teacher model and the student model, we use the features from block3 and block 4 for regression, and those features only from block4 for classification. The extracted RGB and TIR features from the teacher model are denoted as $ft_{rgb}^{i}$ and $ft_{tir}^{i}$ , respectively, and the extracted RGB and TIR features from the student model are denoted as $fs_{rgb}^{i}$ and $fs_{tir}^{i}$ , respectively, where $i \\in \\{1,2,3,4\\}$ indexes the feature level.", + "bbox": [ + 75, + 407, + 468, + 641 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Multi-modal feature fusion. By performing the multi-modal fusion modules on the $3rd$ and $4th$ levels of RGB and TIR features, we obtain the fused features $f t_{f u s}^{3}$ and $f t_{f u s}^{4}$ in the teacher model and the fused features $f s_{f u s}^{3}$ and $f s_{f u s}^{4}$ in the student model, respectively. Our teacher model employs a Modality Difference Compensation (MDC) module and a Feature Re-selection module (FRS) for multi-modal feature fusion [35]. Differently, our student model utilizes the proposed MPSD modules for multi-modal feature fusion. Details of MPSD will be introduced in Section 3.4.", + "bbox": [ + 75, + 642, + 468, + 781 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Classification and regression. Finally, these fused features will be fed to the classification and regression heads, which have the same architectures with those in the original DiMP. Especially, in this stage, the student and teacher models both apply the original classification and regression heads in DiMP. We refer readers to [1, 5] for more details.", + "bbox": [ + 75, + 783, + 468, + 865 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/25e3aa7f8ba10b42c78054b55c7a64b31494edd278591707ea7af8a32bdc26d4.jpg", + "image_caption": [ + "Figure 5. The proposed specific-common feature distillation module for the RGB modality. The SCFD module for the TIR modality employs the same architecture as that in the RGB modality." + ], + "image_footnote": [], + "bbox": [ + 522, + 124, + 734, + 314 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/402ddf399b8a6b0c85c04a8de2333af006806bf3f59788eedd2af2d884b915ff.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 734, + 124, + 870, + 315 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.3. Specific-Common Feature Distillation", + "text_level": 1, + "bbox": [ + 499, + 362, + 823, + 376 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "This section elaborates on the proposed SCFD module for the two-stage unimodal feature distillation, which lets the single-stream feature extraction module in the student model enable to learn the modality-common information as well as the modality-specific information from the teacher model, as shown in Fig. 5 (a).", + "bbox": [ + 497, + 383, + 890, + 465 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We first perform cross-modal interaction on the unimodal RGB features and TIR features from the teacher model to highlight the modality-common information and modality-specific information at different layers, respectively, for better guiding the learning of the student model. Specifically, as shown in Fig. 5 (b), given the unimodal features of shallow layers (i.e., $\\{f t_{r g b}^{i}|i = 1,2,3\\}$ and $\\{f t_{t i r}^{i}|i = 1,2,3\\}$ ) from the teacher model, the proposed Specific Enhanced Modules (SEMs) are employed to obtain such modality-interacted features $f e_{r g b}^{i}$ and $f e_{t i r}^{i}$ ( $i = 1,2,3$ ) with more modality-specific information via subtraction and multiplication. Mathematically,", + "bbox": [ + 497, + 466, + 890, + 634 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} f e _ {r g b} ^ {i} = \\left(f t _ {r g b} ^ {i} * f t _ {t i r} ^ {i}\\right) \\oplus \\left(f t _ {r g b} ^ {i} \\ominus f t _ {t i r} ^ {i}\\right), \\\\ f e _ {t i r} ^ {i} = \\left(f t _ {r g b} ^ {i} * f t _ {t i r} ^ {i}\\right) \\oplus \\left(f t _ {t i r} ^ {i} \\ominus f t _ {r g b} ^ {i}\\right), \\end{array} \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 549, + 638, + 890, + 673 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\ominus$ , $\\oplus$ and $\\circ$ denote element-wise subtraction, element-wise addition and element-wise multiplication, respectively. $f t_{r g b}^{i}\\circ f t_{t i r}^{i}$ reflects the jointly valid information within RGB and TIR features. While, $f t_{r g b}^{i}\\ominus f t_{t i r}^{i}$ represents the modality-specific information of the RGB modality with respect to the TIR modality. Similarly, the modality-specific information of the TIR modality with respect to the RGB modality can be obtained by $f t_{t i r}^{i}\\ominus f t_{r g b}^{i}$ . Accordingly, $f e_{r g b}^{i}$ and $f e_{t i r}^{i}$ highlight such modality-specific information in addition to preserve jointly valid information, which can be applied to guide feature learning of the student model in shallow layers.", + "bbox": [ + 497, + 682, + 890, + 851 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Alternatively, for the RGB and TIR features of deep lay", + "bbox": [ + 519, + 852, + 890, + 866 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "5407", + "bbox": [ + 468, + 885, + 500, + 897 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "ers (i.e., $f t_{r g b}^{4}$ and $f t_{t i r}^{4}$ ), the proposed Consistence Enhanced Module (CEM) is employed to obtain modality-interacted features $f c^{4}$ with more modality-common information via addition and multiplication, as shown in Fig. 5 (c). Mathematically,", + "bbox": [ + 75, + 124, + 468, + 195 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nf c ^ {4} = \\left(f t _ {r g b} ^ {4} * f t _ {t i r} ^ {4}\\right) \\oplus \\left(f t _ {r g b} ^ {4} \\oplus f t _ {t i r} ^ {4}\\right). \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 134, + 197, + 468, + 214 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Here, by applying the element-wise addition on $f t_{r g b}^{4}$ and $f t_{t i r}^{4}$ , the consistency of high-level semantic cues within multi-modal data can be further enhanced. Therefore, $f c^{4}$ can better guide the learning of the student model in deep layer.", + "bbox": [ + 75, + 219, + 468, + 290 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "With the modality-interacted features from the teacher model, the next step is to adjust the feature-channel dimensions of the student model to be consistent with those of the teacher model. Here, inspired by the idea of Knowledge Review [3], we employ a series of attention based fusion (ABF) modules [3] to adjust the channel dimensions of unimodal features and dynamically aggregate the cross-layer features in the student model. The modified features of the student model from ABFs (i.e., $\\{f u_{r g b}^{i}|i = 1,2,3,4\\}$ and $\\{f u_{t i r}^{i}|i = 1,2,3,4\\}$ ) and the modality-interacted features of the teacher model (i.e., $\\{f e_{r g b}^{1},f e_{r g b}^{2},f e_{r g b}^{3},f c^{4}\\}$ and $\\{f e_{t i r}^{1},f e_{t i r}^{2},f e_{t i r}^{3},f c^{4}\\}$ ) will be employed together to force the student model to mimic the specific and common information from the teacher model via a proposed feature-learning distillation loss $L_{SCFD}$ , which is formulated as:", + "bbox": [ + 75, + 290, + 468, + 503 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} L _ {s p e} = \\sum_ {i = 1} ^ {3} l \\left(f e _ {r g b} ^ {i}, f u _ {r g b} ^ {i}\\right) + \\sum_ {i = 1} ^ {3} l \\left(f e _ {t i r} ^ {i}, f u _ {t i r} ^ {i}\\right), \\\\ L _ {c o m} = l \\left(f c ^ {4}, f u _ {r g b} ^ {4}\\right) + l \\left(f c ^ {4}, f u _ {t i r} ^ {4}\\right), \\\\ L _ {S C F D} = L _ {s p e} + L _ {c o m}, \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 84, + 516, + 460, + 562 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $l(*)$ denotes the standard MSE loss used in [21].", + "bbox": [ + 43, + 564, + 468, + 590 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.4. Multi-path Selection Distillation", + "text_level": 1, + "bbox": [ + 77, + 595, + 359, + 609 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In order to learn the exploration ability of complementary information from the teacher model more effectively, we design a fusion module by using multiple fusion strategies, denoted as Multi-path Selection Distillation (MPSD) module, in the student model. In the process of learning from the teacher model, the student model can adaptively optimize the paths to reduce feature differences.", + "bbox": [ + 75, + 616, + 468, + 712 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Specifically, in the student model, the proposed MPSD module first performs multi-modal feature fusion from three typical perspectives: modality differences, modality commonality and modality complementary. Given the original RGB features $f s_{rgb}^{i}$ and TIR features $f s_{tir}^{i}$ from the 3rd and 4th levels in the student model, three types of initially fused features $f s_{fus,1}^{i}, f s_{fus,2}^{i}$ and $f s_{fus,3}^{i}$ are computed by", + "bbox": [ + 75, + 713, + 468, + 821 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} f s _ {f u s, 1} ^ {i} = s a \\left(f s _ {r g b} ^ {i}, f s _ {t i r} ^ {i}\\right), \\\\ f s _ {f u s, 2} ^ {i} = f s _ {r g b} ^ {i} * f s _ {t i r} ^ {i}, \\tag {4} \\\\ f s _ {f u s, 3} ^ {i} = f s _ {r g b} ^ {i} \\ominus f s _ {t i r} ^ {i}. \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 176, + 823, + 468, + 869 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/01677883ff0eb0534384c1630764725674a6adf586ca64564506a3080549fad3.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 504, + 123, + 890, + 247 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/61c42f2c87849d575b5df24b239dc533723c461e31d6aa1be7dc3cfe9c823106.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 505, + 250, + 694, + 328 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/7965819198d60dc6feb71106f58fb003611d106837319eabf193ded3d1b260be.jpg", + "image_caption": [ + "Broadcasting multiplication" + ], + "image_footnote": [], + "bbox": [ + 695, + 250, + 890, + 328 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/267e6b7eb30bfa93061281b9e9e3d67d0277eed328a42b1a93e3c9bcab89a1f6.jpg", + "image_caption": [ + "FC layer" + ], + "image_footnote": [], + "bbox": [ + 507, + 336, + 532, + 353 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/d0e1360210284c64f026fff592caf87140a6c7ba5afb42183c98fe0262e52e9a.jpg", + "image_caption": [ + "Global max pooling" + ], + "image_footnote": [], + "bbox": [ + 591, + 338, + 616, + 353 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/4a2f6d9b6bf4be715a8dc21c531021e5d119f7ce4257bfdef9522e0499c5eb9a.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 690, + 338, + 714, + 353 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/f839172198e89c4bf0f455b27554cc0308c512e36026166841cfb727e019a3c6.jpg", + "image_caption": [ + "Separation operation" + ], + "image_footnote": [], + "bbox": [ + 798, + 338, + 820, + 353 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/2df42faf8cd6b1d51bf366d4b53a218a6fbd5318decd7aee607475a991627cf8.jpg", + "image_caption": [ + "Concatenation Operation" + ], + "image_footnote": [], + "bbox": [ + 507, + 366, + 529, + 382 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/1fb1e3f5b2277228f601eb806818fa1f58436f2d1d91e9059abf6b062f1a5dcd.jpg", + "image_caption": [ + "Sigmoid Function" + ], + "image_footnote": [], + "bbox": [ + 636, + 366, + 660, + 382 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/6d16dbb22edd370a6d27ea299c026e68dd8f440a366421606a6289c7e6ce0ff5.jpg", + "image_caption": [ + "1x1 Convolutional Layer", + "Figure 6. The proposed multi-path selection distillation module." + ], + "image_footnote": [], + "bbox": [ + 739, + 366, + 773, + 383 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Here, $sa(*)$ denotes the spatial attention mechanism, which first utilizes a convolution layer of kernel size $1 \\times 1$ and a softmax layer to get a two-channel weight map. The two-channel weight map is then split into two reliability weight maps for selecting the RGB features and TIR features, respectively. Mathematically, the self-attention mechanism is expressed by:", + "bbox": [ + 497, + 423, + 890, + 520 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} w _ {r g b} ^ {i}, w _ {t} ^ {i} = \\sigma \\left(\\operatorname {c o n v} \\left(\\operatorname {c a t} \\left(f s _ {r g b} ^ {i}, f s _ {t i r} ^ {i}\\right), \\theta_ {1}\\right)\\right), \\\\ f s _ {f u s, 1} ^ {i} = \\left(f s _ {r g b} ^ {i} * w _ {r g b} ^ {i}\\right) \\oplus \\left(f s _ {t i r} ^ {i} * w _ {t i r} ^ {i}\\right), \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 547, + 523, + 867, + 555 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\text{cat}(*)$ denotes the concatenation operation and $\\text{conv}(*, \\theta_1)$ denotes a $1 \\times 1$ convolutional layer with its parameters $\\theta_1$ . $\\sigma(*)$ denotes the sigmoid layer. The features $f s_{fus,1}^{i}$ mainly reflect the complementary information within multi-modal data. Features $f s_{fus,2}^{i}$ and $f s_{fus,3}^{i}$ reflect their interacted information and their differential information, respectively.", + "bbox": [ + 497, + 557, + 890, + 656 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "After that, $f s_{f u s,1}^{i}, f s_{f u s,2}^{i}$ and $f s_{f u s,3}^{i}$ are further combined together by a weighted fusion way, i.e,", + "bbox": [ + 497, + 662, + 890, + 691 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} w _ {1} ^ {i}, w _ {2} ^ {i}, w _ {3} ^ {i} = \\text {s o f t m a x} (f c (g m p (c a t (f s _ {f u s, 1} ^ {i}, f s _ {f u s, 2} ^ {i}, f s _ {f u s, 3} ^ {i})))) \\\\ f s _ {f u s} ^ {i} = \\left(f s _ {f u s, 1} ^ {i} \\odot w _ {1} ^ {i}\\right) \\oplus \\left(f s _ {f u s, 2} ^ {i} \\odot w _ {2} ^ {i}\\right) \\oplus \\left(f s _ {f u s, 3} ^ {i} \\odot w _ {3} ^ {i}\\right). \\tag {6} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 505, + 695, + 890, + 733 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $gmp(*)$ and $fc(*)$ denote the global max pooling layer and the fully connected layers, respectively. $softmax(*)$ denote the softmax operation. The feature-wise weights $w_1^i, w_2^i, w_3^i$ reflect the importance of different fused features for the current scenario. $\\odot$ denotes the broadcasting multiplication operation.", + "bbox": [ + 497, + 735, + 890, + 818 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "With the fused features $\\{ft_{fus}^i | i = 3,4\\}$ and $\\{fs_{fus}^i | i = 3,4\\}$ obtained by the teacher model and the student model, respectively, we calculate the fusion distillation loss $L_{fus}$", + "bbox": [ + 497, + 823, + 890, + 866 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "5408", + "bbox": [ + 468, + 885, + 500, + 897 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "between the fused features:", + "bbox": [ + 77, + 125, + 260, + 138 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\nL _ {f u s} = l \\left(f t _ {f u s} ^ {3}, f s _ {f u s} ^ {3}\\right) + l \\left(f t _ {f u s} ^ {4}, f s _ {f u s} ^ {4}\\right) \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 126, + 142, + 468, + 160 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "What's more, in order to enable the student model to adaptively select a fusion path that is more similar to the teacher model in different scenarios, we introduce an additional penalty $L_{p}$ for the efficiency of knowledge transformation during training. More specifically, we first select the fusion type with the smallest difference between the initially fused features of the student model and the fused features of the teacher model by,", + "bbox": [ + 75, + 162, + 468, + 271 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} L _ {f u s, n} ^ {i} = l \\left(f t _ {f u s} ^ {i}, f s _ {f u s, n} ^ {i}\\right), n = 1, 2, 3 \\tag {8} \\\\ L _ {f u s, \\lambda^ {i}} ^ {i} = \\min (L _ {f u s, 1} ^ {i}, L _ {f u s, 2} ^ {i}, L _ {f u s, 3} ^ {i}), \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 136, + 275, + 468, + 308 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $\\lambda^i = 1$ , 2 or 3 denotes the selected type of initially fused features according to the fused feature difference between the teacher and student models.", + "bbox": [ + 75, + 309, + 468, + 350 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "After that, through the adaptive selection part in MPSD, the student model itself will also predict a type of initially fused features that is suitable for the current tracking scene, i.e.,", + "bbox": [ + 75, + 352, + 468, + 404 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\nw _ {\\nu^ {i}} ^ {i} = \\max \\left(w _ {1} ^ {i}, w _ {2} ^ {i}, w _ {3} ^ {i}\\right), \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 186, + 406, + 468, + 422 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $\\nu^i = 1$ , 2 or 3 denotes the predicted type of initially fused features from the student model.", + "bbox": [ + 75, + 423, + 468, + 451 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "With $w_{\\nu^i}^i$ and $w_{\\lambda^i}^i$ , we can use a penalty to help the student model choose a fusion path that is more suitable for the current scene under the guidance of the teacher model, i.e.,", + "bbox": [ + 75, + 452, + 468, + 494 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\nL _ {p} = \\sum_ {i = 3} ^ {4} \\max \\left(\\left| L _ {f u s, \\lambda^ {i}} ^ {i} w _ {\\nu^ {i}} ^ {i} - L _ {f u s, \\lambda^ {i}} ^ {i} w _ {\\lambda^ {i}} ^ {i} \\right|, 0\\right). \\tag {10}\n$$\n", + "text_format": "latex", + "bbox": [ + 100, + 498, + 468, + 534 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "By minimizing $L_{p}$ , $w_{\\nu^{i}}^{i}$ and $w_{\\lambda^i}^i$ will tend to be consistent, which can enable the student model to adaptively select the fusion path according to the teacher model to improve the exploration ability of complementary information.", + "bbox": [ + 75, + 536, + 468, + 591 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "On top of that, the overall distill loss in the multi-modal fusion stage can be obtained by:", + "bbox": [ + 75, + 592, + 468, + 619 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\nL _ {M P S D} = L _ {f u s} + L _ {p}. \\tag {11}\n$$\n", + "text_format": "latex", + "bbox": [ + 194, + 623, + 468, + 638 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "3.5. Hard-focused Response Distillation", + "text_level": 1, + "bbox": [ + 77, + 643, + 381, + 657 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "To alleviate the data imbalance problem, we propose the Hard-focused Response Distillation (HFRD) module to instruct the student to focus on distinguishing targets from hard negative samples.", + "bbox": [ + 75, + 665, + 468, + 719 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "First, we obtain the response map $R_{t} \\in \\mathbb{R}^{H \\times W}$ from the teacher model. Then, in order to prevent the teacher model from failing to have high responses in the target area within some scenes, we use the Gaussian-shaped mask $R_{g} \\in \\mathbb{R}^{H \\times W}$ constructed by ground-truth bounding box as in [1] to correct the response map of the teacher model $R_{t}$ as follows:", + "bbox": [ + 75, + 719, + 468, + 815 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\nR _ {c} (i, j) = \\left\\{ \\begin{array}{c} R _ {t} (i, j) + R _ {g} (i, j), i f \\left(R _ {t} (i, j) + R _ {g} (i, j)\\right) < 1, \\\\ R _ {g} (i, j), i f \\left(R _ {t} (i, j) + R _ {g} (i, j)\\right) \\geq 1. \\end{array} \\right. \\tag {12}\n$$\n", + "text_format": "latex", + "bbox": [ + 77, + 820, + 468, + 866 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $i,j$ are the horizontal and vertical coordinates of the response map, respectively. The corrected mask $R_{c}\\in \\mathbb{R}^{H\\times W}$ has higher response values not only on the positive samples but also on the hard negative samples.", + "bbox": [ + 499, + 125, + 890, + 181 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "In the training process of the student model, with the assistance of the corrected mask $R_{c}$ from the teacher model, the student model can focus more on distinguishing target from hard negative samples by a proposed Hard-focused Response Distillation loss $L_{HFRD}$ to alleviate the data imbalance problem:", + "bbox": [ + 497, + 182, + 890, + 264 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\nL _ {H F R D} = r \\left(R _ {s} * R _ {c}, R _ {g}\\right), \\tag {13}\n$$\n", + "text_format": "latex", + "bbox": [ + 600, + 269, + 890, + 283 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $r(*)$ denotes the $L_{2}$ loss function [5].", + "bbox": [ + 499, + 286, + 793, + 300 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "3.6. Overall loss", + "text_level": 1, + "bbox": [ + 499, + 314, + 626, + 327 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "The overall distillation loss $L_{distill}$ is the sum of $L_{SCFD}$ , $L_{MPSD}$ and $L_{HFRD}$ . We train the student model with the total loss as follows:", + "bbox": [ + 499, + 337, + 890, + 378 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\nL _ {\\text {d i s t i l l}} = \\alpha \\left(L _ {S C F D} + L _ {M P S D}\\right) + \\beta L _ {H F R D} + L _ {\\text {o r i g i n a l}}, \\tag {14}\n$$\n", + "text_format": "latex", + "bbox": [ + 500, + 382, + 890, + 409 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $\\alpha$ and $\\beta$ are hyper-parameters to balance the distillation loss. $L_{\\text{original}}$ is the original loss for tracking as in [35]. The distillation loss $L_{SCFD}$ and $L_{MPSD}$ are just calculated on feature maps, which can be easily applied to different tackers or other multi-modal vision tasks.", + "bbox": [ + 497, + 410, + 890, + 479 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 499, + 497, + 631, + 513 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Our tracking approach is implemented in Python based on PyTorch. For inference, we test our tracker on a single Nvidia RTX 1080Ti GPU.", + "bbox": [ + 497, + 522, + 890, + 562 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.1. Implementation details", + "text_level": 1, + "bbox": [ + 499, + 578, + 712, + 592 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Training Details. We adopt the training dataset in LasHeR [14], which contains 979 pairs of RGB-T videos, to train the teacher model and student model, respectively. The proposed CMD framework includes two training stages. In the first stage, we train the teacher model as in MFNet [35] and fix its weights after training. In the second stage, the optimization of the student model is jointly supervised by the original tracking loss $L_{\\text{original}}$ as well as the knowledge transfer loss $L_{\\text{SCFD}}$ , $L_{\\text{MPSD}}$ and $L_{\\text{HFRD}}$ . $\\alpha$ and $\\beta$ in Eq. 14 are experimentally set to 0.001 and 100, respectively.", + "bbox": [ + 497, + 600, + 890, + 739 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Online Tracking. In the tracking phase, our method is similar to DiMP [1]. We split tracking into classification and regression subtasks. For classification subtask, we employ data augmentation [1] on the first frame to construct an initial set, which contains 15 initial training samples for initial classification model training. Then the initial classification model is optimized using the augmented training set during tracking. For regression subtask, the same settings as those in [1] are employed.", + "bbox": [ + 497, + 741, + 890, + 866 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "5409", + "bbox": [ + 468, + 885, + 500, + 897 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/80a6918e9aa4c2bc29bca225dd59edd142009c97ac7cdad6dc85da0da761b1b6.jpg", + "table_caption": [ + "Table 1. Ablation study of different components." + ], + "table_footnote": [], + "table_body": "
StudentSCFDMPSDHFRDPR/SRParams(M)FPS
✓78.1/56.019.831
✓✓80.3/57.419.831
✓✓✓82.2/58.319.930
✓✓✓✓82.4/58.419.930
", + "bbox": [ + 100, + 140, + 445, + 209 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.2. Evaluation datasets and metrics", + "text_level": 1, + "bbox": [ + 77, + 214, + 357, + 226 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We evaluate our method on three large-scale benchmark datasets, i.e., GTOT [10], RGBT234 [11] and LasHeR [14]. GTOT is the first standard dataset for RGB-T tracking. It contains 50 RGB-T video sequences annotated with seven challenging attributes. RGBT234 [11] contains 234 pairs of RGB-T videos and 12 annotated attributes. LasHeR is currently the largest RGB-T tracking dataset, which consists of 1244 RGB-T videos with more than 730K frame pairs in total. Among them, 245 videos are used as the testing set, and 979 videos are used as the training set. As in [17], we utilize two widely used metrics, i.e., precision rate (PR) and success rate (SR), to evaluate the tracking performance on GTOT and RGBT234. As in [14], we adopt precision rate (PR), normalized precision rate (NPR) and success rate (SR) to evaluate different trackers on LasHeR.", + "bbox": [ + 75, + 236, + 468, + 442 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.3. Ablation Experiments and Analyses", + "text_level": 1, + "bbox": [ + 77, + 454, + 386, + 469 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We conduct some ablation studies on RGBT234 [11] to discuss the impacts of different components in our CMD framework.", + "bbox": [ + 77, + 477, + 468, + 517 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Ablation experiments for each module. To investigate the impact of each component in our proposed CMD, several versions of our proposed method are provided for comparisons. Specifically, 'Student' denotes the model that without any knowledge transformation. Here, the proposed SCFD, MPSD and HFRD are employed in the unimodal feature extraction stage, multi-modal feature fusion stage and target state estimation stage, respectively. The quantitative results of these models are shown in Table 1. It can be seen that SCFD, MPSD and HFRD can all improve the performance of the student model. This verifies that each proposed component in CMD can effectively inherit the knowledge learnt from a powerful teacher models to a student model without obvious loss.", + "bbox": [ + 75, + 520, + 468, + 712 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Effectiveness of the proposed SCFD module. To further verify the effectiveness of the proposed SCFD module, several variants are also compared with our proposed SCFD module. Here, in the unimodal feature extraction stage, 'AFD', 'SED' and 'CED' denote initially fusing the unimodal features of each layer in the teacher model by using the simple element-wise addition operation, the designed SEM module and the designed CEM module, respectively, and such initially fused features are then employed to guide the student model for single-stream structure learning. As well, ABF modules [3] are employed in all of these vari-", + "bbox": [ + 75, + 714, + 468, + 865 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/1511a550c55ea3a1eca97fcd7b7aeb965ba40de899d662c5dbaaa30258b14b44.jpg", + "table_caption": [ + "Table 2. Ablation study of the proposed SCFD module." + ], + "table_footnote": [], + "table_body": "
StudentAFDSEDCEDSCFDPR/SRParams(M)FPS
✓78.1/56.019.831
✓✓78.7/56.619.831
✓✓79.2/56.519.831
✓✓79.6/56.619.831
✓✓80.3/57.419.831
", + "bbox": [ + 522, + 140, + 868, + 218 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/716f6d0d8be2980c85cf8a184f1d6559252a1e9761522aec0ed2f552e40c72e5.jpg", + "table_caption": [ + "Table 3. Ablation study of the proposed MPSD module." + ], + "table_footnote": [], + "table_body": "
Student+SCFDSAFCAFTFMPSDPR/SRParams(M)FPS
✓80.3/57.419.831
✓✓81.9/58.019.930
✓✓81.1/57.619.930
✓✓82.6/58.625.923
✓✓82.2/58.319.930
", + "bbox": [ + 514, + 239, + 877, + 315 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "ants. As shown in Table 2, the proposed SCFD can better exploit the modality-common and modality-specific information from the teacher model.", + "bbox": [ + 499, + 321, + 890, + 361 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Effectiveness of the proposed MPSD module. As shown in Table 3, several versions of our proposed MPSD module are also conducted to verify its effectiveness. 'SAF' denotes a spatial-wise attention based fusion module. 'CAF' denotes a channel-wise attention based module. 'TF' denotes adopting the same fusion strategy as that in the teacher model [35]. In particular, each layer adopts the same fusion strategy in the student model. It can be seen that the exploitation of the multi-path fusion strategy can well improve the performance of the student model. In addition, the performance gap between 'Student-MPSD' and 'Student-TF' is much smaller, which indicates that our proposed MPSD module can better mimic the fused features in the teacher model to compensate for the performance penalty from simple fusion operations.", + "bbox": [ + 499, + 363, + 890, + 570 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Teacher-Student knowledge distillation experiments. Table 4 shows the performance of using some other knowledge distillation methods in the feature extraction and feature fusion stages for comparisons, including KD [8], Fit-Nets [21], ReviewKD [3] and MD [29]. It is observed from Table 4 that the proposed distillation strategy performs the best. Due to the absence of cross-modal interactions, these existing knowledge distillation methods usually achieve some modest performance gains. In addition, we notice that the student model with a single-stream feature extractor performs obviously well than the student model with a two-stream feature extractor after knowledge distillation. This may be due to the fact that the single-stream network can narrow the modality difference to a certain extent and better acquire the knowledge from the teacher model.", + "bbox": [ + 499, + 571, + 889, + 777 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.4. Comparison with the state-of-the-art", + "text_level": 1, + "bbox": [ + 499, + 789, + 816, + 802 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "To evaluate the superiority of our proposed method, we compare our method with some existing state-of-the-art RGB-T trackers, including MANet [17], DAFNet [6], DAPNet [39], TODA [28], MACNet [30], CAT [12], CEDiMP", + "bbox": [ + 499, + 811, + 890, + 866 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "5410", + "bbox": [ + 468, + 885, + 500, + 897 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/671dad26f739987730771b477662fbb7e133fcc6e4a2552c94ca82962cee8819.jpg", + "table_caption": [ + "Table 4. Ablation study of different knowledge distillation experiments." + ], + "table_footnote": [], + "table_body": "
MethodKD [8]FitNets [21]ReviewKD [3]ReviewKD [3]MD [29]Ours
Backbone2 Res182 Res182 Res181 Res181 Res181 Res18
PR/SR78.4/56.279.3/56.079.9/56.580.5/56.380.0/55.482.4/58.4
FPS272727303030
Params31.631.631.619.919.919.9
", + "bbox": [ + 80, + 150, + 465, + 207 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/dab941b98f8b67f539ec0154d648990eda6203d121b3f88d2a1491ee36ce8ba8.jpg", + "table_caption": [ + "Table 5. Quantitative comparisons of our method with some state-of-the-arts methods on benchmark datasets. Higher values indicate better performance." + ], + "table_footnote": [], + "table_body": "
MethodsYearRGBT234 [11]GTOT [10]LasHeR [14]FPSParams
PR ↑SR ↑PR ↑SR ↑PR ↑NPR ↑SR ↑
DAPNet [39]201976.653.788.270.743.138.431.41-
MANet [17]201977.753.989.472.445.740.833.017.28M
DAFNet [6]201979.654.489.171.644.939.031.1145.50M
mfDiMP [31]201978.655.583.669.744.739.534.422175.82M
TODA [28]201978.754.584.367.7---1-
MACNet [30]202079.055.488.071.448.342.335.2114.86M
CAT [12]202080.456.188.971.745.139.831.7--
FANet [40]202178.755.389.172.844.238.430.91238.44M
SiamCDA [36]202176.056.987.773.2---24107.90M
JMMAC [32]202179.057.390.273.2-----
MANet++ [33]202180.055.488.270.746.740.831.7157.38M
ADRNet [33]202180.957.190.473.9---1568.50M
CBPNet [27]202279.454.188.571.6---3-
TFNet [41]202280.656.088.672.9-----
MFGNet [25]202278.353.588.970.7---38.09M
M5LNet [23]202279.554.289.671.0---9-
HMFT [34]202278.856.891.274.9----127.84M
APFNet [26]202282.757.990.573.950.0-36.2-15.01M
MANet* [17]201978.655.590.072.5---17.28M
DAFNet* [6]201980.054.986.070.048.042.834.5145.50M
mfDiMP* [31]201982.458.387.773.158.354.245.622175.82M
FANet* [40]202179.453.990.172.148.242.534.31238.44M
Teacher [35]202284.460.190.773.559.755.446.71881.01M
Student-Origin202278.156.088.572.355.450.342.33019.90M
Student-Distill202282.458.489.273.459.054.646.43019.90M
", + "bbox": [ + 80, + 261, + 465, + 486 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "[38], SiamCDA [36], mfDiMP [31], FANet [40], CBPNet [27], MANet++ [33], JMMAC [32], ADRNet [33], TFNet [41], MFGNet [25], M5LNet [23], HMFT [34], APFNet [26] and MFNet [35], on three challenging datasets. Considering that existing methods usually employ different training datasets, we use the LasHeR training set to retrain some of these algorithms for fair comparisons, including FANet*, DAFNet*, MANet* and mfDiMP*.", + "bbox": [ + 75, + 492, + 467, + 602 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "On RGBT234. From Table 5, we observe that, in addition to the teacher model, our method achieves the best results with $82.4\\% / 58.4\\%$ in PR/SR. In particular, our tracker achieves $3.0\\% / 4.5\\%$ , $3.8\\% / 2.9\\%$ and $2.4\\% / 3.6\\%$ improvements against FANet* [40], MANet* [17] and DAFNet* [6] in PR/SR, respectively. We should note that some MDNet [18] based trackers [6,17,33] employ merely three convolutional layers for unimodal feature extraction, thus have fewer parameters in the unimodal feature extraction stage with a two-stream structure (e.g., 3.6M in [30, 40]). However, in the multi-modal feature fusion stage, these methods' parameters are significantly higher than those of the proposed MPSD module. Meanwhile, due to the complex updating strategy in MDNet, the above methods cannot meet the needs of real-time operation.", + "bbox": [ + 75, + 603, + 467, + 809 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "On GTOT. From Table 5, we can see that our method obtains competitive performance on GTOT dataset [10] with $73.4\\%$ and $89.2\\%$ in success and precision scores, respectively. Compared with the teacher model, our student", + "bbox": [ + 75, + 811, + 467, + 866 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "model achieves comparable performance but with a $75\\%$ reduction in parameter sizes. Compared with the original student model, our algorithm achieves $1.1\\%$ improvements in success and $0.7\\%$ improvements in precision.", + "bbox": [ + 497, + 125, + 890, + 180 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "On LasHeR. LasHeR [14] is captured from a number of scenes and categories and is highly diverse. A tracker restrained on this dataset usually achieves some improvements. From Table 5, we can also see that, in addition to the teacher model, our tracker still performs the best in terms of all the three metrics with significant performance superiorities on LasHeR. In particular, our tracker achieves $11.0\\% / 11.9\\%$ and $10.8\\% / 12.1\\%$ improvements against DAFNet* [6] and FANet* [40], which are based on MDNet [18]. Compared with mfDiMP* [31], which is based on DiMP [1] and employs two ResNet50 [7] for feature extraction, our PR/SR is $0.7\\% / 0.8\\%$ higher than it. This demonstrates that our proposed method can effectively reduce the performance loss caused by parameter reduction.", + "bbox": [ + 497, + 182, + 890, + 377 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 499, + 395, + 616, + 409 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this paper, a novel teacher-student knowledge distillation training framework is proposed to reduce the performance gap between a powerful teacher model and a compact student model. Specifically, this framework distills the knowledge from a deep two-stream network with complex multi-modal feature fusion modules to a single-stream network with efficient feature fusion modules. By virtue of the proposed SCFD module, the modality-common information as well as the modality-specific information can be transformed from a two-stream network to a single-stream network in the unimodal feature extraction stage, thus enhancing the representations of unimodal features. Besides, by employing the proposed MPSD module, the student model can adaptively combine multiple fused features generated by various simple fusion strategies to explore complementary information from multi-modal data more thoroughly. In addition, an HFRD module is proposed to improve the student model's discriminative ability against the distractors by alleviating the problem of data imbalance in the target state estimation stage. Experimental results show that our approach helps a student model achieve the state-of-the-art performance while reducing the number of parameters and computational complexity dramatically.", + "bbox": [ + 497, + 420, + 890, + 737 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Limitation: The current method dedicated to reducing computational complexity at the stages of unimodal feature extraction and multi-modal feature fusion, but it paid ZERO effort to improve the efficiency of target stage estimation, which is our future work.", + "bbox": [ + 497, + 739, + 890, + 808 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgement: This work is supported by the National Natural Science Foundation of China under Grant No. 61773301. 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IEEE Transactions on Circuits and Systems for Video Technology, 32(2):579-592, 2021. 8" + ], + "bbox": [ + 78, + 125, + 468, + 811 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "5413", + "bbox": [ + 468, + 885, + 500, + 897 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/Efficient RGB-T Tracking via Cross-Modality Distillation/cf5e82ff-3a69-46ad-ac66-64191f806cdf_model.json b/2023/Efficient RGB-T Tracking via Cross-Modality Distillation/cf5e82ff-3a69-46ad-ac66-64191f806cdf_model.json new file mode 100644 index 0000000000000000000000000000000000000000..dc4dd3360bc7637112fc97c2fb2e9e2efac7d79c --- /dev/null +++ b/2023/Efficient RGB-T Tracking via Cross-Modality Distillation/cf5e82ff-3a69-46ad-ac66-64191f806cdf_model.json @@ -0,0 +1,2288 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.13, + 0.051, + 0.201, + 0.085 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.253, + 0.049, + 0.792, + 0.088 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.195, + 0.162, + 0.776, + 0.182 + ], + "angle": 0, + "content": "Efficient RGB-T Tracking via Cross-Modality Distillation" + }, + { + "type": "text", + "bbox": [ + 0.16, + 0.207, + 0.816, + 0.274 + ], + "angle": 0, + "content": "Tianlu Zhang\\(^{1}\\) Hongyuan Guo\\(^{1}\\) Qiang Jiao\\(^{1}\\) Qiang Zhang\\(^{1*}\\) Jungong Han\\(^{2,3}\\) \n\\(^{1}\\)School of Mechano-Electronic Engineering, Xidian University, China \n\\(^{2}\\)Department of Computer Science, the University of Sheffield, UK. \n\\(^{3}\\)Centre for Machine Intelligence, the University of Sheffield, UK." + }, + { + "type": "text", + "bbox": [ + 0.088, + 0.276, + 0.888, + 0.29 + ], + "angle": 0, + "content": "{tianluzhang, hyg}@stu.xidian.edu.cn, {qzhang, qjiao}@xidian.edu.cn, jungonghan77@gmail.com" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.321, + 0.314, + 0.335 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.35, + 0.474, + 0.655 + ], + "angle": 0, + "content": "Most current RGB-T trackers adopt a two-stream structure to extract unimodal RGB and thermal features and complex fusion strategies to achieve multi-modal feature fusion, which require a huge number of parameters, thus hindering their real-life applications. On the other hand, a compact RGB-T tracker may be computationally efficient but encounter non-negligible performance degradation, due to the weakening of feature representation ability. To remedy this situation, a cross-modality distillation framework is presented to bridge the performance gap between a compact tracker and a powerful tracker. Specifically, a specific-common feature distillation module is proposed to transform the modality-common information as well as the modality-specific information from a deeper two-stream network to a shallower single-stream network. In addition, a multi-path selection distillation module is proposed to instruct a simple fusion module to learn more accurate multi-modal information from a well-designed fusion mechanism by using multiple paths. We validate the effectiveness of our method with extensive experiments on three RGB-T benchmarks, which achieves state-of-the-art performance but consumes much less computational resources." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.682, + 0.21, + 0.697 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.705, + 0.47, + 0.773 + ], + "angle": 0, + "content": "RGB-T tracking is the task of estimating the state of an arbitrary target in each frame of an RGB-T video sequence [35]. Due to the affordability of thermal infrared (TIR) sensors, RGB-T tracking draws more and more research interest." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.775, + 0.471, + 0.845 + ], + "angle": 0, + "content": "As shown in Fig. 1 (a), most existing RGB-T tracking models first adopt a two-stream structure to extract multilevel unimodal RGB and TIR features, respectively, and then employ elaborate-designed multi-modal feature fusion modules to exploit complementary information within the" + }, + { + "type": "image", + "bbox": [ + 0.521, + 0.319, + 0.872, + 0.43 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.432, + 0.892, + 0.47 + ], + "angle": 0, + "content": "Figure 1. Architectures of different RGB-T tracking models. (a) Two-stream structure. (b) Single-stream structure. (c) Our proposed method." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.474, + 0.893, + 0.57 + ], + "angle": 0, + "content": "multi-modal data. Finally, they deduce the target state, often represented by a bounding box, from the fused features. Although great progress has been made, these powerful RGB-T tracking models usually require high computational costs and large model sizes to handle the information of two modalities in the stages of unimodal feature extraction and multi-modal feature fusion." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.574, + 0.892, + 0.781 + ], + "angle": 0, + "content": "There are two straightforward solutions to tackle the complexity and efficiency issues. One is to adopt a single-stream feature extractor with fewer convolutional layers, and the other is to employ simpler multi-modal feature fusion modules, as shown in Fig. 1 (b). Although such compact models can reduce computational complexity, they inevitably bring non-negligible performance degradation due to the weakening of unimodal feature representation ability and multi-modal complementary information exploration ability. For instance, a powerful RGB-T tracker [35] with a two-stream structure and complicated multi-modal feature fusion modules suffers from severe performance degradation after the above model simplification operations (84.4% precision rate vs 78.1% precision rate on RGBT234 dataset [11]), as shown in Fig. 2." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.784, + 0.892, + 0.868 + ], + "angle": 0, + "content": "Now, the research question becomes: can we shrink the RGB-T tracker without sacrificing performance? This paper answers this question using knowledge distillation, which allows a compact model to obtain a similar ability of a complex model at little cost. We call this complex but powerful model the teacher model, and call this" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.854, + 0.224, + 0.867 + ], + "angle": 0, + "content": "*Corresponding author." + }, + { + "type": "page_number", + "bbox": [ + 0.469, + 0.887, + 0.502, + 0.898 + ], + "angle": 0, + "content": "5404" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.098, + 0.125, + 0.445, + 0.304 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.306, + 0.47, + 0.408 + ], + "angle": 0, + "content": "Figure 2. Experimental results of different RGB-T tracking structures on RGBT234 dataset [11]. Teacher denotes the two-stream structure with complex fusion modules. Student denotes a single-stream structure with simple fusion operations. The teacher model employs ResNet50 [7] for feature extraction and fusion modules in [35] for multi-modal feature fusion, respectively. The student model employs ResNet18 [7] for feature extraction and concatenation for multi-modal feature fusion, respectively." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.41, + 0.469, + 0.589 + ], + "angle": 0, + "content": "compact model the student model. Although some works [15, 19, 20, 29] have made considerable progress on knowledge distillation in multi-modal tasks, they fail to conduct a deep investigation on the huge feature differences between teacher and student in the unimodal feature extraction stage as well as in the multi-modal feature fusion stage, thereby resulting in suboptimal efficiency of the knowledge transformation. For that, a novel teacher-student knowledge distillation training framework, named Cross-Modality Distillation (CMD), is proposed to elaborately guide efficient imitation from three stages: unimodal feature extraction, multi-modal feature fusion and target estimate estimation, as shown in Fig. 1 (c)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.59, + 0.469, + 0.824 + ], + "angle": 0, + "content": "Specifically, in the stage of unimodal feature extraction, as pointed out by many previous works [9, 17], the shallower layers of unimodal features usually contain abundant low-level spatial details, which are usually modality-dependent. Differently, the deeper layers of unimodal features often contain many high-level semantic cues, which tend to be strongly modality-consistent. The student model uses a compact single-stream network to extract both RGB features and TIR features, which not only lacks the ability to extract modality-specific information in the shallower layers, but also insufficiently explores the modality-common information in the deeper layers. These interesting observations inspire us to design a Specific-common Feature Distillation (SCFD) module, which transforms the modality-specific information as well as the modality-common information from a two-stream deeper network to a single-stream shallower network." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.825, + 0.469, + 0.867 + ], + "angle": 0, + "content": "Second, in the stage of multi-modal feature fusion, the complex multi-modal feature fusion modules in the teacher model show great advantages in various scenarios, while" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.127, + 0.892, + 0.292 + ], + "angle": 0, + "content": "the simple fusion strategies in the student model are usually effective in some specific scenarios. It is difficult for a student model with a single simple fusion strategy to learn more effective complementary information mining capabilities from a complex teacher model due to the large feature differences. Therefore, we design a fusion module with multiple simple fusion strategies in the student model, denoted as Multi-path Selection Distillation (MPSD) module. In the process of learning from the teacher model, the student model can adaptively combine different types of fusion features to make up for the lack of complementary information mining capabilities of a single simple fusion strategy." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.292, + 0.892, + 0.43 + ], + "angle": 0, + "content": "Finally, in the stage of target state estimation, with the weakening of the feature representation ability of the student model, the discriminative ability of the tracker for distractors is also reduced. For that, we further present a Hard-focused Response Distillation (HFRD) module to improve the student model's discriminative ability by alleviating the problem of data imbalance between the targets and the backgrounds, which employs the response maps generated by the teacher model to instruct the student to focus on distinguishing targets from hard negative samples." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.431, + 0.892, + 0.512 + ], + "angle": 0, + "content": "As shown in Fig. 2, each of our proposed modules continuously reduces the performance gap between the student model and the teacher model without increasing the number of parameters obviously. To sum up, our work improves an RGB-T tracker dramatically because of the following two contributions:" + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.52, + 0.892, + 0.617 + ], + "angle": 0, + "content": "- A Cross-Modality Distillation (CMD) framework is presented to bridge the performance gap between a compact student model and a powerful teacher model through three stages, i.e., unimodal feature extraction, multi-modal feature fusion and target state estimation. To the best of our knowledge, we are the first to introduce knowledge distillation for multi-modal tracking." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.625, + 0.892, + 0.694 + ], + "angle": 0, + "content": "- Experimental results show that our proposed approach helps a student model achieve the state-of-the-art performance on the challenging GTOT [10], RGBT234 [11] and LasHer [14], while reducing the number of parameters and computational complexity." + }, + { + "type": "list", + "bbox": [ + 0.518, + 0.52, + 0.892, + 0.694 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.705, + 0.64, + 0.719 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.728, + 0.892, + 0.867 + ], + "angle": 0, + "content": "RGB-T Tracking Methods. The past few years have witnessed the increase of RGB-T tracking algorithms [4, 10, 13, 17, 31, 39]. Among them, numerous RGB-T trackers [6, 17, 30, 39] have been presented based on the MDNet [18]. For instance, in [17], Li et al. introduced a multi-adapter architecture to learn modality-common, modality-specific and instance-aware target representations, respectively. In [39], Zhu et al. first presented a network to aggregate the features from all of the layers and all of the modalities. After that, these aggregated features were further" + }, + { + "type": "page_number", + "bbox": [ + 0.469, + 0.887, + 0.501, + 0.898 + ], + "angle": 0, + "content": "5405" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.127, + 0.47, + 0.236 + ], + "angle": 0, + "content": "pruned to reduce noise and redundancy. Recently, Zhang et al. [35] introduced DiMP [1] as their baseline tracker and achieved promising tracking performance. Meanwhile, aiming to speed up the tracking, some works [36, 37] bring the Siamese networks to RGB-T tracking, where their models are trained in an offline manner. Although some progress has been made, these models still suffer from the limitations of large model sizes and high computation costs." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.237, + 0.471, + 0.43 + ], + "angle": 0, + "content": "Knowledge Distillation Methods. Knowledge Distillation (KD) was first proposed by Hinton et al. [8] to pass dark knowledge from complicated teachers to compact students, enabling students to maintain strong performance as teachers. FitNet [21] proves that the semantic information from intermediate features is also helpful to guide the student model. Besides image classification, KD is widely applied to object detection and object tracking tasks. For instance, [2] and [16] used KD to speed up the detection and segmentation networks, respectively. Furthermore, Wang [24] proposed to learn a more compact backbone for faster feature extraction in correlation filter based trackers. Shen et al. [22] used KD to compress deep Siamese-based trackers for high-performance visual tracking." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.431, + 0.47, + 0.638 + ], + "angle": 0, + "content": "In addition, KD is also employed for some multi-modal tasks, such as RGB-D salient object detection [19, 20] and RGB-T pedestrian detection [15, 29]. Specifically, in [20, 29], the single-stream feature extractors and the early fusion strategies were employed in their student models. However, both of them only simply employ the distillation loss functions to improve the performance of student models by using fused features or label knowledges of teacher models, and pay less attention to the huge differences between the teacher model and the student model in the unimodal feature extraction stage as well as in the multi-modal feature fusion stage. Differently, in this paper, we aim to narrow the feature differences between the student model and the teacher model by specifically learning strategies at multiple stages." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.649, + 0.32, + 0.665 + ], + "angle": 0, + "content": "3. Distilled RGB-T Tracking" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.672, + 0.469, + 0.81 + ], + "angle": 0, + "content": "Given a powerful teacher model for RGB-T tracking, the proposed CMD framework aims to prompt a more efficient student model to learn from the teacher model. The knowledge from the teacher model is transferred to the student model to mimic more effective feature representation. This section starts with an overview of the proposed CMD framework. Then, we briefly provide an introduction of the employed teacher and student models. Finally, the three proposed knowledge distillation modules (i.e., SCFD, MPSD and HFRD) are described in details." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.818, + 0.187, + 0.831 + ], + "angle": 0, + "content": "3.1. Overview" + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.839, + 0.469, + 0.866 + ], + "angle": 0, + "content": "As illustrated in Fig. 3, the proposed CMD framework includes a teacher model, a student model and three knowl-" + }, + { + "type": "image", + "bbox": [ + 0.504, + 0.124, + 0.891, + 0.335 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.534, + 0.338, + 0.856, + 0.351 + ], + "angle": 0, + "content": "Figure 3. Overview of the proposed CMD framework." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.354, + 0.892, + 0.519 + ], + "angle": 0, + "content": "edge distillation modules. The teacher model takes a pair of RGB-T images as input, and employs a two-stream feature extractor and several complex multi-modal feature fusion modules for unimodal feature extraction and multi-modal fusion, respectively. Finally, the fused features will be fed into the target state estimation module to obtain the final tracking results. Different from the teacher model, the student model uses a single-stream feature extractor and several efficient multi-modal fusion modules. Although the student model has a higher running speed, the simplification of the model inevitably leads to a decrease in tracking performance." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.522, + 0.892, + 0.867 + ], + "angle": 0, + "content": "To make up for the huge performance gap between the student model and the teacher model, the proposed CMD framework attempts to coach the learning process of the student model from three stages: unimodal feature extraction, multi-modal feature fusion and target state estimation. Accordingly, in the first stage, by using a proposed SCFD module, the powerful two-stream feature extraction network of the teacher model will transfer such modality-specific information as well as modality-common information into the single-stream network of the student model to enhance its representation ability for unimodal features. In the second stage, we will present an MPSD module to shrink the differences between the fused features obtained by the teacher model and those obtained by the student model via a multipath optimization strategy. In the third stage, with a proposed HFRD module, we will adopt the response map generated by the teacher model in a form of spatial attention to instruct the student model to focus on the discrimination of difficult samples, thereby improving its discrimination ability. The improvements in the above three stages will effectively narrow the performance gap between the student model and the teacher model, enabling the student model to achieve competitive tracking results with the teacher model but with fewer parameters and higher computational efficiency." + }, + { + "type": "page_number", + "bbox": [ + 0.469, + 0.888, + 0.502, + 0.898 + ], + "angle": 0, + "content": "5406" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.087, + 0.125, + 0.46, + 0.274 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.276, + 0.468, + 0.3 + ], + "angle": 0, + "content": "Figure 4. Structure of the employed teacher model and the student model." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.303, + 0.327, + 0.317 + ], + "angle": 0, + "content": "3.2. Teacher and Student Model" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.324, + 0.469, + 0.407 + ], + "angle": 0, + "content": "In this section, we will describe the architectures of the employed teacher and student models, which are both based on the recent deep RGB tracker DiMP [1]. As shown in Fig. 4, both the teacher model and the student model can be divided into three stages: unimodal feature extraction, multi-modal feature fusion and target state estimation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.408, + 0.469, + 0.642 + ], + "angle": 0, + "content": "Feature extraction. In the teacher model, two feature extractors, denoted as \\( E_{rgb} \\) and \\( E_{the} \\), regard RGB and TIR modalities in parallel. The two feature extractors both adopt ResNet50 [7] as the backbone to extract multi-level RGB and TIR features, as shown in Fig. 4 (a). Differently, in the student model, only one feature extractor, denoted as \\( E_{stu} \\), regards both RGB and TIR modalities simultaneously. As shown in Fig. 4 (b), \\( E_{stu} \\) just adopts ResNet18 [7] as the backbone for simplification. Similar to the original DiMP tracker, in both the teacher model and the student model, we use the features from block3 and block 4 for regression, and those features only from block4 for classification. The extracted RGB and TIR features from the teacher model are denoted as \\( ft_{rgb}^{i} \\) and \\( ft_{tir}^{i} \\), respectively, and the extracted RGB and TIR features from the student model are denoted as \\( fs_{rgb}^{i} \\) and \\( fs_{tir}^{i} \\), respectively, where \\( i \\in \\{1,2,3,4\\} \\) indexes the feature level." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.643, + 0.469, + 0.782 + ], + "angle": 0, + "content": "Multi-modal feature fusion. By performing the multi-modal fusion modules on the \\(3rd\\) and \\(4th\\) levels of RGB and TIR features, we obtain the fused features \\(f t_{f u s}^{3}\\) and \\(f t_{f u s}^{4}\\) in the teacher model and the fused features \\(f s_{f u s}^{3}\\) and \\(f s_{f u s}^{4}\\) in the student model, respectively. Our teacher model employs a Modality Difference Compensation (MDC) module and a Feature Re-selection module (FRS) for multi-modal feature fusion [35]. Differently, our student model utilizes the proposed MPSD modules for multi-modal feature fusion. Details of MPSD will be introduced in Section 3.4." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.784, + 0.469, + 0.866 + ], + "angle": 0, + "content": "Classification and regression. Finally, these fused features will be fed to the classification and regression heads, which have the same architectures with those in the original DiMP. Especially, in this stage, the student and teacher models both apply the original classification and regression heads in DiMP. We refer readers to [1, 5] for more details." + }, + { + "type": "image", + "bbox": [ + 0.523, + 0.125, + 0.735, + 0.315 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.736, + 0.125, + 0.871, + 0.316 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.319, + 0.892, + 0.358 + ], + "angle": 0, + "content": "Figure 5. The proposed specific-common feature distillation module for the RGB modality. The SCFD module for the TIR modality employs the same architecture as that in the RGB modality." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.363, + 0.825, + 0.377 + ], + "angle": 0, + "content": "3.3. Specific-Common Feature Distillation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.384, + 0.892, + 0.466 + ], + "angle": 0, + "content": "This section elaborates on the proposed SCFD module for the two-stage unimodal feature distillation, which lets the single-stream feature extraction module in the student model enable to learn the modality-common information as well as the modality-specific information from the teacher model, as shown in Fig. 5 (a)." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.467, + 0.892, + 0.635 + ], + "angle": 0, + "content": "We first perform cross-modal interaction on the unimodal RGB features and TIR features from the teacher model to highlight the modality-common information and modality-specific information at different layers, respectively, for better guiding the learning of the student model. Specifically, as shown in Fig. 5 (b), given the unimodal features of shallow layers (i.e., \\(\\{f t_{r g b}^{i}|i = 1,2,3\\}\\) and \\(\\{f t_{t i r}^{i}|i = 1,2,3\\}\\)) from the teacher model, the proposed Specific Enhanced Modules (SEMs) are employed to obtain such modality-interacted features \\(f e_{r g b}^{i}\\) and \\(f e_{t i r}^{i}\\) (\\(i = 1,2,3\\)) with more modality-specific information via subtraction and multiplication. Mathematically," + }, + { + "type": "equation", + "bbox": [ + 0.55, + 0.64, + 0.892, + 0.674 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} f e _ {r g b} ^ {i} = \\left(f t _ {r g b} ^ {i} * f t _ {t i r} ^ {i}\\right) \\oplus \\left(f t _ {r g b} ^ {i} \\ominus f t _ {t i r} ^ {i}\\right), \\\\ f e _ {t i r} ^ {i} = \\left(f t _ {r g b} ^ {i} * f t _ {t i r} ^ {i}\\right) \\oplus \\left(f t _ {t i r} ^ {i} \\ominus f t _ {r g b} ^ {i}\\right), \\end{array} \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.683, + 0.892, + 0.852 + ], + "angle": 0, + "content": "where \\(\\ominus\\), \\(\\oplus\\) and \\(\\circ\\) denote element-wise subtraction, element-wise addition and element-wise multiplication, respectively. \\(f t_{r g b}^{i}\\circ f t_{t i r}^{i}\\) reflects the jointly valid information within RGB and TIR features. While, \\(f t_{r g b}^{i}\\ominus f t_{t i r}^{i}\\) represents the modality-specific information of the RGB modality with respect to the TIR modality. Similarly, the modality-specific information of the TIR modality with respect to the RGB modality can be obtained by \\(f t_{t i r}^{i}\\ominus f t_{r g b}^{i}\\). Accordingly, \\(f e_{r g b}^{i}\\) and \\(f e_{t i r}^{i}\\) highlight such modality-specific information in addition to preserve jointly valid information, which can be applied to guide feature learning of the student model in shallow layers." + }, + { + "type": "text", + "bbox": [ + 0.52, + 0.853, + 0.892, + 0.867 + ], + "angle": 0, + "content": "Alternatively, for the RGB and TIR features of deep lay" + }, + { + "type": "page_number", + "bbox": [ + 0.469, + 0.887, + 0.501, + 0.898 + ], + "angle": 0, + "content": "5407" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.125, + 0.47, + 0.196 + ], + "angle": 0, + "content": "ers (i.e., \\( f t_{r g b}^{4} \\) and \\( f t_{t i r}^{4} \\)), the proposed Consistence Enhanced Module (CEM) is employed to obtain modality-interacted features \\( f c^{4} \\) with more modality-common information via addition and multiplication, as shown in Fig. 5 (c). Mathematically," + }, + { + "type": "equation", + "bbox": [ + 0.135, + 0.198, + 0.469, + 0.216 + ], + "angle": 0, + "content": "\\[\nf c ^ {4} = \\left(f t _ {r g b} ^ {4} * f t _ {t i r} ^ {4}\\right) \\oplus \\left(f t _ {r g b} ^ {4} \\oplus f t _ {t i r} ^ {4}\\right). \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.22, + 0.469, + 0.291 + ], + "angle": 0, + "content": "Here, by applying the element-wise addition on \\( f t_{r g b}^{4} \\) and \\( f t_{t i r}^{4} \\), the consistency of high-level semantic cues within multi-modal data can be further enhanced. Therefore, \\( f c^{4} \\) can better guide the learning of the student model in deep layer." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.292, + 0.47, + 0.504 + ], + "angle": 0, + "content": "With the modality-interacted features from the teacher model, the next step is to adjust the feature-channel dimensions of the student model to be consistent with those of the teacher model. Here, inspired by the idea of Knowledge Review [3], we employ a series of attention based fusion (ABF) modules [3] to adjust the channel dimensions of unimodal features and dynamically aggregate the cross-layer features in the student model. The modified features of the student model from ABFs (i.e., \\(\\{f u_{r g b}^{i}|i = 1,2,3,4\\}\\) and \\(\\{f u_{t i r}^{i}|i = 1,2,3,4\\}\\)) and the modality-interacted features of the teacher model (i.e., \\(\\{f e_{r g b}^{1},f e_{r g b}^{2},f e_{r g b}^{3},f c^{4}\\}\\) and \\(\\{f e_{t i r}^{1},f e_{t i r}^{2},f e_{t i r}^{3},f c^{4}\\}\\)) will be employed together to force the student model to mimic the specific and common information from the teacher model via a proposed feature-learning distillation loss \\(L_{SCFD}\\), which is formulated as:" + }, + { + "type": "equation", + "bbox": [ + 0.085, + 0.517, + 0.462, + 0.564 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} L _ {s p e} = \\sum_ {i = 1} ^ {3} l \\left(f e _ {r g b} ^ {i}, f u _ {r g b} ^ {i}\\right) + \\sum_ {i = 1} ^ {3} l \\left(f e _ {t i r} ^ {i}, f u _ {t i r} ^ {i}\\right), \\\\ L _ {c o m} = l \\left(f c ^ {4}, f u _ {r g b} ^ {4}\\right) + l \\left(f c ^ {4}, f u _ {t i r} ^ {4}\\right), \\\\ L _ {S C F D} = L _ {s p e} + L _ {c o m}, \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.044, + 0.565, + 0.469, + 0.591 + ], + "angle": 0, + "content": "where \\(l(*)\\) denotes the standard MSE loss used in [21]." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.596, + 0.36, + 0.61 + ], + "angle": 0, + "content": "3.4. Multi-path Selection Distillation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.617, + 0.469, + 0.713 + ], + "angle": 0, + "content": "In order to learn the exploration ability of complementary information from the teacher model more effectively, we design a fusion module by using multiple fusion strategies, denoted as Multi-path Selection Distillation (MPSD) module, in the student model. In the process of learning from the teacher model, the student model can adaptively optimize the paths to reduce feature differences." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.714, + 0.469, + 0.823 + ], + "angle": 0, + "content": "Specifically, in the student model, the proposed MPSD module first performs multi-modal feature fusion from three typical perspectives: modality differences, modality commonality and modality complementary. Given the original RGB features \\( f s_{rgb}^{i} \\) and TIR features \\( f s_{tir}^{i} \\) from the 3rd and 4th levels in the student model, three types of initially fused features \\( f s_{fus,1}^{i}, f s_{fus,2}^{i} \\) and \\( f s_{fus,3}^{i} \\) are computed by" + }, + { + "type": "equation", + "bbox": [ + 0.178, + 0.824, + 0.469, + 0.87 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} f s _ {f u s, 1} ^ {i} = s a \\left(f s _ {r g b} ^ {i}, f s _ {t i r} ^ {i}\\right), \\\\ f s _ {f u s, 2} ^ {i} = f s _ {r g b} ^ {i} * f s _ {t i r} ^ {i}, \\tag {4} \\\\ f s _ {f u s, 3} ^ {i} = f s _ {r g b} ^ {i} \\ominus f s _ {t i r} ^ {i}. \\\\ \\end{array}\n\\]" + }, + { + "type": "image", + "bbox": [ + 0.505, + 0.124, + 0.891, + 0.248 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.506, + 0.251, + 0.695, + 0.329 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.696, + 0.251, + 0.891, + 0.329 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.508, + 0.337, + 0.533, + 0.355 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.54, + 0.343, + 0.585, + 0.354 + ], + "angle": 0, + "content": "FC layer" + }, + { + "type": "image", + "bbox": [ + 0.593, + 0.339, + 0.618, + 0.355 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.621, + 0.338, + 0.677, + 0.358 + ], + "angle": 0, + "content": "Global max pooling" + }, + { + "type": "image", + "bbox": [ + 0.692, + 0.339, + 0.715, + 0.355 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.721, + 0.338, + 0.788, + 0.358 + ], + "angle": 0, + "content": "Broadcasting multiplication" + }, + { + "type": "image", + "bbox": [ + 0.799, + 0.339, + 0.821, + 0.355 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.826, + 0.338, + 0.88, + 0.358 + ], + "angle": 0, + "content": "Separation operation" + }, + { + "type": "image", + "bbox": [ + 0.509, + 0.367, + 0.531, + 0.383 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.537, + 0.366, + 0.608, + 0.385 + ], + "angle": 0, + "content": "Concatenation Operation" + }, + { + "type": "image", + "bbox": [ + 0.638, + 0.367, + 0.661, + 0.383 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.67, + 0.366, + 0.715, + 0.385 + ], + "angle": 0, + "content": "Sigmoid Function" + }, + { + "type": "image", + "bbox": [ + 0.741, + 0.368, + 0.774, + 0.384 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.782, + 0.368, + 0.884, + 0.386 + ], + "angle": 0, + "content": "1x1 Convolutional Layer" + }, + { + "type": "image_caption", + "bbox": [ + 0.505, + 0.393, + 0.885, + 0.406 + ], + "angle": 0, + "content": "Figure 6. The proposed multi-path selection distillation module." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.424, + 0.892, + 0.521 + ], + "angle": 0, + "content": "Here, \\(sa(*)\\) denotes the spatial attention mechanism, which first utilizes a convolution layer of kernel size \\(1 \\times 1\\) and a softmax layer to get a two-channel weight map. The two-channel weight map is then split into two reliability weight maps for selecting the RGB features and TIR features, respectively. Mathematically, the self-attention mechanism is expressed by:" + }, + { + "type": "equation", + "bbox": [ + 0.549, + 0.524, + 0.868, + 0.556 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} w _ {r g b} ^ {i}, w _ {t} ^ {i} = \\sigma \\left(\\operatorname {c o n v} \\left(\\operatorname {c a t} \\left(f s _ {r g b} ^ {i}, f s _ {t i r} ^ {i}\\right), \\theta_ {1}\\right)\\right), \\\\ f s _ {f u s, 1} ^ {i} = \\left(f s _ {r g b} ^ {i} * w _ {r g b} ^ {i}\\right) \\oplus \\left(f s _ {t i r} ^ {i} * w _ {t i r} ^ {i}\\right), \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.558, + 0.892, + 0.657 + ], + "angle": 0, + "content": "where \\( \\text{cat}(*) \\) denotes the concatenation operation and \\( \\text{conv}(*, \\theta_1) \\) denotes a \\( 1 \\times 1 \\) convolutional layer with its parameters \\( \\theta_1 \\). \\( \\sigma(*) \\) denotes the sigmoid layer. The features \\( f s_{fus,1}^{i} \\) mainly reflect the complementary information within multi-modal data. Features \\( f s_{fus,2}^{i} \\) and \\( f s_{fus,3}^{i} \\) reflect their interacted information and their differential information, respectively." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.663, + 0.891, + 0.692 + ], + "angle": 0, + "content": "After that, \\( f s_{f u s,1}^{i}, f s_{f u s,2}^{i} \\) and \\( f s_{f u s,3}^{i} \\) are further combined together by a weighted fusion way, i.e," + }, + { + "type": "equation", + "bbox": [ + 0.507, + 0.697, + 0.891, + 0.735 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} w _ {1} ^ {i}, w _ {2} ^ {i}, w _ {3} ^ {i} = \\text {s o f t m a x} (f c (g m p (c a t (f s _ {f u s, 1} ^ {i}, f s _ {f u s, 2} ^ {i}, f s _ {f u s, 3} ^ {i})))) \\\\ f s _ {f u s} ^ {i} = \\left(f s _ {f u s, 1} ^ {i} \\odot w _ {1} ^ {i}\\right) \\oplus \\left(f s _ {f u s, 2} ^ {i} \\odot w _ {2} ^ {i}\\right) \\oplus \\left(f s _ {f u s, 3} ^ {i} \\odot w _ {3} ^ {i}\\right). \\tag {6} \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.736, + 0.892, + 0.819 + ], + "angle": 0, + "content": "where \\( gmp(*) \\) and \\( fc(*) \\) denote the global max pooling layer and the fully connected layers, respectively. \\( softmax(*) \\) denote the softmax operation. The feature-wise weights \\( w_1^i, w_2^i, w_3^i \\) reflect the importance of different fused features for the current scenario. \\( \\odot \\) denotes the broadcasting multiplication operation." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.824, + 0.892, + 0.868 + ], + "angle": 0, + "content": "With the fused features \\(\\{ft_{fus}^i | i = 3,4\\}\\) and \\(\\{fs_{fus}^i | i = 3,4\\}\\) obtained by the teacher model and the student model, respectively, we calculate the fusion distillation loss \\(L_{fus}\\)" + }, + { + "type": "page_number", + "bbox": [ + 0.469, + 0.887, + 0.501, + 0.898 + ], + "angle": 0, + "content": "5408" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.078, + 0.127, + 0.262, + 0.139 + ], + "angle": 0, + "content": "between the fused features:" + }, + { + "type": "equation", + "bbox": [ + 0.127, + 0.143, + 0.47, + 0.161 + ], + "angle": 0, + "content": "\\[\nL _ {f u s} = l \\left(f t _ {f u s} ^ {3}, f s _ {f u s} ^ {3}\\right) + l \\left(f t _ {f u s} ^ {4}, f s _ {f u s} ^ {4}\\right) \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.163, + 0.47, + 0.273 + ], + "angle": 0, + "content": "What's more, in order to enable the student model to adaptively select a fusion path that is more similar to the teacher model in different scenarios, we introduce an additional penalty \\( L_{p} \\) for the efficiency of knowledge transformation during training. More specifically, we first select the fusion type with the smallest difference between the initially fused features of the student model and the fused features of the teacher model by," + }, + { + "type": "equation", + "bbox": [ + 0.137, + 0.276, + 0.469, + 0.309 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} L _ {f u s, n} ^ {i} = l \\left(f t _ {f u s} ^ {i}, f s _ {f u s, n} ^ {i}\\right), n = 1, 2, 3 \\tag {8} \\\\ L _ {f u s, \\lambda^ {i}} ^ {i} = \\min (L _ {f u s, 1} ^ {i}, L _ {f u s, 2} ^ {i}, L _ {f u s, 3} ^ {i}), \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.311, + 0.469, + 0.351 + ], + "angle": 0, + "content": "where \\(\\lambda^i = 1\\), 2 or 3 denotes the selected type of initially fused features according to the fused feature difference between the teacher and student models." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.353, + 0.469, + 0.406 + ], + "angle": 0, + "content": "After that, through the adaptive selection part in MPSD, the student model itself will also predict a type of initially fused features that is suitable for the current tracking scene, i.e.," + }, + { + "type": "equation", + "bbox": [ + 0.187, + 0.407, + 0.469, + 0.423 + ], + "angle": 0, + "content": "\\[\nw _ {\\nu^ {i}} ^ {i} = \\max \\left(w _ {1} ^ {i}, w _ {2} ^ {i}, w _ {3} ^ {i}\\right), \\tag {9}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.425, + 0.469, + 0.452 + ], + "angle": 0, + "content": "where \\(\\nu^i = 1\\), 2 or 3 denotes the predicted type of initially fused features from the student model." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.453, + 0.469, + 0.495 + ], + "angle": 0, + "content": "With \\( w_{\\nu^i}^i \\) and \\( w_{\\lambda^i}^i \\), we can use a penalty to help the student model choose a fusion path that is more suitable for the current scene under the guidance of the teacher model, i.e.," + }, + { + "type": "equation", + "bbox": [ + 0.102, + 0.499, + 0.469, + 0.535 + ], + "angle": 0, + "content": "\\[\nL _ {p} = \\sum_ {i = 3} ^ {4} \\max \\left(\\left| L _ {f u s, \\lambda^ {i}} ^ {i} w _ {\\nu^ {i}} ^ {i} - L _ {f u s, \\lambda^ {i}} ^ {i} w _ {\\lambda^ {i}} ^ {i} \\right|, 0\\right). \\tag {10}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.538, + 0.469, + 0.592 + ], + "angle": 0, + "content": "By minimizing \\(L_{p}\\), \\(w_{\\nu^{i}}^{i}\\) and \\(w_{\\lambda^i}^i\\) will tend to be consistent, which can enable the student model to adaptively select the fusion path according to the teacher model to improve the exploration ability of complementary information." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.593, + 0.469, + 0.62 + ], + "angle": 0, + "content": "On top of that, the overall distill loss in the multi-modal fusion stage can be obtained by:" + }, + { + "type": "equation", + "bbox": [ + 0.195, + 0.624, + 0.469, + 0.64 + ], + "angle": 0, + "content": "\\[\nL _ {M P S D} = L _ {f u s} + L _ {p}. \\tag {11}\n\\]" + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.644, + 0.383, + 0.659 + ], + "angle": 0, + "content": "3.5. Hard-focused Response Distillation" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.666, + 0.469, + 0.72 + ], + "angle": 0, + "content": "To alleviate the data imbalance problem, we propose the Hard-focused Response Distillation (HFRD) module to instruct the student to focus on distinguishing targets from hard negative samples." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.72, + 0.469, + 0.816 + ], + "angle": 0, + "content": "First, we obtain the response map \\(R_{t} \\in \\mathbb{R}^{H \\times W}\\) from the teacher model. Then, in order to prevent the teacher model from failing to have high responses in the target area within some scenes, we use the Gaussian-shaped mask \\(R_{g} \\in \\mathbb{R}^{H \\times W}\\) constructed by ground-truth bounding box as in [1] to correct the response map of the teacher model \\(R_{t}\\) as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.078, + 0.821, + 0.469, + 0.867 + ], + "angle": 0, + "content": "\\[\nR _ {c} (i, j) = \\left\\{ \\begin{array}{c} R _ {t} (i, j) + R _ {g} (i, j), i f \\left(R _ {t} (i, j) + R _ {g} (i, j)\\right) < 1, \\\\ R _ {g} (i, j), i f \\left(R _ {t} (i, j) + R _ {g} (i, j)\\right) \\geq 1. \\end{array} \\right. \\tag {12}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.127, + 0.892, + 0.182 + ], + "angle": 0, + "content": "where \\(i,j\\) are the horizontal and vertical coordinates of the response map, respectively. The corrected mask \\(R_{c}\\in \\mathbb{R}^{H\\times W}\\) has higher response values not only on the positive samples but also on the hard negative samples." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.184, + 0.892, + 0.266 + ], + "angle": 0, + "content": "In the training process of the student model, with the assistance of the corrected mask \\( R_{c} \\) from the teacher model, the student model can focus more on distinguishing target from hard negative samples by a proposed Hard-focused Response Distillation loss \\( L_{HFRD} \\) to alleviate the data imbalance problem:" + }, + { + "type": "equation", + "bbox": [ + 0.6, + 0.27, + 0.891, + 0.285 + ], + "angle": 0, + "content": "\\[\nL _ {H F R D} = r \\left(R _ {s} * R _ {c}, R _ {g}\\right), \\tag {13}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.287, + 0.794, + 0.301 + ], + "angle": 0, + "content": "where \\(r(*)\\) denotes the \\(L_{2}\\) loss function [5]." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.315, + 0.627, + 0.328 + ], + "angle": 0, + "content": "3.6. Overall loss" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.338, + 0.892, + 0.379 + ], + "angle": 0, + "content": "The overall distillation loss \\( L_{distill} \\) is the sum of \\( L_{SCFD} \\), \\( L_{MPSD} \\) and \\( L_{HFRD} \\). We train the student model with the total loss as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.501, + 0.383, + 0.891, + 0.41 + ], + "angle": 0, + "content": "\\[\nL _ {\\text {d i s t i l l}} = \\alpha \\left(L _ {S C F D} + L _ {M P S D}\\right) + \\beta L _ {H F R D} + L _ {\\text {o r i g i n a l}}, \\tag {14}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.411, + 0.892, + 0.48 + ], + "angle": 0, + "content": "where \\(\\alpha\\) and \\(\\beta\\) are hyper-parameters to balance the distillation loss. \\(L_{\\text{original}}\\) is the original loss for tracking as in [35]. The distillation loss \\(L_{SCFD}\\) and \\(L_{MPSD}\\) are just calculated on feature maps, which can be easily applied to different tackers or other multi-modal vision tasks." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.498, + 0.632, + 0.514 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.523, + 0.892, + 0.564 + ], + "angle": 0, + "content": "Our tracking approach is implemented in Python based on PyTorch. For inference, we test our tracker on a single Nvidia RTX 1080Ti GPU." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.579, + 0.714, + 0.593 + ], + "angle": 0, + "content": "4.1. Implementation details" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.602, + 0.892, + 0.741 + ], + "angle": 0, + "content": "Training Details. We adopt the training dataset in LasHeR [14], which contains 979 pairs of RGB-T videos, to train the teacher model and student model, respectively. The proposed CMD framework includes two training stages. In the first stage, we train the teacher model as in MFNet [35] and fix its weights after training. In the second stage, the optimization of the student model is jointly supervised by the original tracking loss \\( L_{\\text{original}} \\) as well as the knowledge transfer loss \\( L_{\\text{SCFD}} \\), \\( L_{\\text{MPSD}} \\) and \\( L_{\\text{HFRD}} \\). \\( \\alpha \\) and \\( \\beta \\) in Eq. 14 are experimentally set to 0.001 and 100, respectively." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.742, + 0.892, + 0.867 + ], + "angle": 0, + "content": "Online Tracking. In the tracking phase, our method is similar to DiMP [1]. We split tracking into classification and regression subtasks. For classification subtask, we employ data augmentation [1] on the first frame to construct an initial set, which contains 15 initial training samples for initial classification model training. Then the initial classification model is optimized using the augmented training set during tracking. For regression subtask, the same settings as those in [1] are employed." + }, + { + "type": "page_number", + "bbox": [ + 0.469, + 0.887, + 0.502, + 0.898 + ], + "angle": 0, + "content": "5409" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.128, + 0.125, + 0.418, + 0.138 + ], + "angle": 0, + "content": "Table 1. Ablation study of different components." + }, + { + "type": "table", + "bbox": [ + 0.101, + 0.141, + 0.446, + 0.21 + ], + "angle": 0, + "content": "
StudentSCFDMPSDHFRDPR/SRParams(M)FPS
✓78.1/56.019.831
✓✓80.3/57.419.831
✓✓✓82.2/58.319.930
✓✓✓✓82.4/58.419.930
" + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.215, + 0.358, + 0.228 + ], + "angle": 0, + "content": "4.2. Evaluation datasets and metrics" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.237, + 0.47, + 0.444 + ], + "angle": 0, + "content": "We evaluate our method on three large-scale benchmark datasets, i.e., GTOT [10], RGBT234 [11] and LasHeR [14]. GTOT is the first standard dataset for RGB-T tracking. It contains 50 RGB-T video sequences annotated with seven challenging attributes. RGBT234 [11] contains 234 pairs of RGB-T videos and 12 annotated attributes. LasHeR is currently the largest RGB-T tracking dataset, which consists of 1244 RGB-T videos with more than 730K frame pairs in total. Among them, 245 videos are used as the testing set, and 979 videos are used as the training set. As in [17], we utilize two widely used metrics, i.e., precision rate (PR) and success rate (SR), to evaluate the tracking performance on GTOT and RGBT234. As in [14], we adopt precision rate (PR), normalized precision rate (NPR) and success rate (SR) to evaluate different trackers on LasHeR." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.456, + 0.388, + 0.47 + ], + "angle": 0, + "content": "4.3. Ablation Experiments and Analyses" + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.478, + 0.469, + 0.518 + ], + "angle": 0, + "content": "We conduct some ablation studies on RGBT234 [11] to discuss the impacts of different components in our CMD framework." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.521, + 0.469, + 0.713 + ], + "angle": 0, + "content": "Ablation experiments for each module. To investigate the impact of each component in our proposed CMD, several versions of our proposed method are provided for comparisons. Specifically, 'Student' denotes the model that without any knowledge transformation. Here, the proposed SCFD, MPSD and HFRD are employed in the unimodal feature extraction stage, multi-modal feature fusion stage and target state estimation stage, respectively. The quantitative results of these models are shown in Table 1. It can be seen that SCFD, MPSD and HFRD can all improve the performance of the student model. This verifies that each proposed component in CMD can effectively inherit the knowledge learnt from a powerful teacher models to a student model without obvious loss." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.715, + 0.469, + 0.866 + ], + "angle": 0, + "content": "Effectiveness of the proposed SCFD module. To further verify the effectiveness of the proposed SCFD module, several variants are also compared with our proposed SCFD module. Here, in the unimodal feature extraction stage, 'AFD', 'SED' and 'CED' denote initially fusing the unimodal features of each layer in the teacher model by using the simple element-wise addition operation, the designed SEM module and the designed CEM module, respectively, and such initially fused features are then employed to guide the student model for single-stream structure learning. As well, ABF modules [3] are employed in all of these vari-" + }, + { + "type": "table_caption", + "bbox": [ + 0.531, + 0.125, + 0.86, + 0.138 + ], + "angle": 0, + "content": "Table 2. Ablation study of the proposed SCFD module." + }, + { + "type": "table", + "bbox": [ + 0.524, + 0.141, + 0.87, + 0.219 + ], + "angle": 0, + "content": "
StudentAFDSEDCEDSCFDPR/SRParams(M)FPS
✓78.1/56.019.831
✓✓78.7/56.619.831
✓✓79.2/56.519.831
✓✓79.6/56.619.831
✓✓80.3/57.419.831
" + }, + { + "type": "table_caption", + "bbox": [ + 0.53, + 0.225, + 0.86, + 0.238 + ], + "angle": 0, + "content": "Table 3. Ablation study of the proposed MPSD module." + }, + { + "type": "table", + "bbox": [ + 0.515, + 0.241, + 0.878, + 0.317 + ], + "angle": 0, + "content": "
Student+SCFDSAFCAFTFMPSDPR/SRParams(M)FPS
✓80.3/57.419.831
✓✓81.9/58.019.930
✓✓81.1/57.619.930
✓✓82.6/58.625.923
✓✓82.2/58.319.930
" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.322, + 0.891, + 0.362 + ], + "angle": 0, + "content": "ants. As shown in Table 2, the proposed SCFD can better exploit the modality-common and modality-specific information from the teacher model." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.364, + 0.891, + 0.571 + ], + "angle": 0, + "content": "Effectiveness of the proposed MPSD module. As shown in Table 3, several versions of our proposed MPSD module are also conducted to verify its effectiveness. 'SAF' denotes a spatial-wise attention based fusion module. 'CAF' denotes a channel-wise attention based module. 'TF' denotes adopting the same fusion strategy as that in the teacher model [35]. In particular, each layer adopts the same fusion strategy in the student model. It can be seen that the exploitation of the multi-path fusion strategy can well improve the performance of the student model. In addition, the performance gap between 'Student-MPSD' and 'Student-TF' is much smaller, which indicates that our proposed MPSD module can better mimic the fused features in the teacher model to compensate for the performance penalty from simple fusion operations." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.572, + 0.89, + 0.779 + ], + "angle": 0, + "content": "Teacher-Student knowledge distillation experiments. Table 4 shows the performance of using some other knowledge distillation methods in the feature extraction and feature fusion stages for comparisons, including KD [8], Fit-Nets [21], ReviewKD [3] and MD [29]. It is observed from Table 4 that the proposed distillation strategy performs the best. Due to the absence of cross-modal interactions, these existing knowledge distillation methods usually achieve some modest performance gains. In addition, we notice that the student model with a single-stream feature extractor performs obviously well than the student model with a two-stream feature extractor after knowledge distillation. This may be due to the fact that the single-stream network can narrow the modality difference to a certain extent and better acquire the knowledge from the teacher model." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.79, + 0.817, + 0.804 + ], + "angle": 0, + "content": "4.4. Comparison with the state-of-the-art" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.812, + 0.891, + 0.867 + ], + "angle": 0, + "content": "To evaluate the superiority of our proposed method, we compare our method with some existing state-of-the-art RGB-T trackers, including MANet [17], DAFNet [6], DAPNet [39], TODA [28], MACNet [30], CAT [12], CEDiMP" + }, + { + "type": "page_number", + "bbox": [ + 0.469, + 0.887, + 0.502, + 0.898 + ], + "angle": 0, + "content": "5410" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.078, + 0.125, + 0.468, + 0.148 + ], + "angle": 0, + "content": "Table 4. Ablation study of different knowledge distillation experiments." + }, + { + "type": "table", + "bbox": [ + 0.081, + 0.152, + 0.466, + 0.209 + ], + "angle": 0, + "content": "
MethodKD [8]FitNets [21]ReviewKD [3]ReviewKD [3]MD [29]Ours
Backbone2 Res182 Res182 Res181 Res181 Res181 Res18
PR/SR78.4/56.279.3/56.079.9/56.580.5/56.380.0/55.482.4/58.4
FPS272727303030
Params31.631.631.619.919.919.9
" + }, + { + "type": "table_caption", + "bbox": [ + 0.078, + 0.22, + 0.468, + 0.257 + ], + "angle": 0, + "content": "Table 5. Quantitative comparisons of our method with some state-of-the-arts methods on benchmark datasets. Higher values indicate better performance." + }, + { + "type": "table", + "bbox": [ + 0.081, + 0.262, + 0.466, + 0.487 + ], + "angle": 0, + "content": "
MethodsYearRGBT234 [11]GTOT [10]LasHeR [14]FPSParams
PR ↑SR ↑PR ↑SR ↑PR ↑NPR ↑SR ↑
DAPNet [39]201976.653.788.270.743.138.431.41-
MANet [17]201977.753.989.472.445.740.833.017.28M
DAFNet [6]201979.654.489.171.644.939.031.1145.50M
mfDiMP [31]201978.655.583.669.744.739.534.422175.82M
TODA [28]201978.754.584.367.7---1-
MACNet [30]202079.055.488.071.448.342.335.2114.86M
CAT [12]202080.456.188.971.745.139.831.7--
FANet [40]202178.755.389.172.844.238.430.91238.44M
SiamCDA [36]202176.056.987.773.2---24107.90M
JMMAC [32]202179.057.390.273.2-----
MANet++ [33]202180.055.488.270.746.740.831.7157.38M
ADRNet [33]202180.957.190.473.9---1568.50M
CBPNet [27]202279.454.188.571.6---3-
TFNet [41]202280.656.088.672.9-----
MFGNet [25]202278.353.588.970.7---38.09M
M5LNet [23]202279.554.289.671.0---9-
HMFT [34]202278.856.891.274.9----127.84M
APFNet [26]202282.757.990.573.950.0-36.2-15.01M
MANet* [17]201978.655.590.072.5---17.28M
DAFNet* [6]201980.054.986.070.048.042.834.5145.50M
mfDiMP* [31]201982.458.387.773.158.354.245.622175.82M
FANet* [40]202179.453.990.172.148.242.534.31238.44M
Teacher [35]202284.460.190.773.559.755.446.71881.01M
Student-Origin202278.156.088.572.355.450.342.33019.90M
Student-Distill202282.458.489.273.459.054.646.43019.90M
" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.493, + 0.468, + 0.603 + ], + "angle": 0, + "content": "[38], SiamCDA [36], mfDiMP [31], FANet [40], CBPNet [27], MANet++ [33], JMMAC [32], ADRNet [33], TFNet [41], MFGNet [25], M5LNet [23], HMFT [34], APFNet [26] and MFNet [35], on three challenging datasets. Considering that existing methods usually employ different training datasets, we use the LasHeR training set to retrain some of these algorithms for fair comparisons, including FANet*, DAFNet*, MANet* and mfDiMP*." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.604, + 0.468, + 0.811 + ], + "angle": 0, + "content": "On RGBT234. From Table 5, we observe that, in addition to the teacher model, our method achieves the best results with \\(82.4\\% / 58.4\\%\\) in PR/SR. In particular, our tracker achieves \\(3.0\\% / 4.5\\%\\), \\(3.8\\% / 2.9\\%\\) and \\(2.4\\% / 3.6\\%\\) improvements against FANet* [40], MANet* [17] and DAFNet* [6] in PR/SR, respectively. We should note that some MDNet [18] based trackers [6,17,33] employ merely three convolutional layers for unimodal feature extraction, thus have fewer parameters in the unimodal feature extraction stage with a two-stream structure (e.g., 3.6M in [30, 40]). However, in the multi-modal feature fusion stage, these methods' parameters are significantly higher than those of the proposed MPSD module. Meanwhile, due to the complex updating strategy in MDNet, the above methods cannot meet the needs of real-time operation." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.812, + 0.468, + 0.867 + ], + "angle": 0, + "content": "On GTOT. From Table 5, we can see that our method obtains competitive performance on GTOT dataset [10] with \\(73.4\\%\\) and \\(89.2\\%\\) in success and precision scores, respectively. Compared with the teacher model, our student" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.127, + 0.892, + 0.181 + ], + "angle": 0, + "content": "model achieves comparable performance but with a \\(75\\%\\) reduction in parameter sizes. Compared with the original student model, our algorithm achieves \\(1.1\\%\\) improvements in success and \\(0.7\\%\\) improvements in precision." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.184, + 0.892, + 0.378 + ], + "angle": 0, + "content": "On LasHeR. LasHeR [14] is captured from a number of scenes and categories and is highly diverse. A tracker restrained on this dataset usually achieves some improvements. From Table 5, we can also see that, in addition to the teacher model, our tracker still performs the best in terms of all the three metrics with significant performance superiorities on LasHeR. In particular, our tracker achieves \\(11.0\\% / 11.9\\%\\) and \\(10.8\\% / 12.1\\%\\) improvements against DAFNet* [6] and FANet* [40], which are based on MDNet [18]. Compared with mfDiMP* [31], which is based on DiMP [1] and employs two ResNet50 [7] for feature extraction, our PR/SR is \\(0.7\\% / 0.8\\%\\) higher than it. This demonstrates that our proposed method can effectively reduce the performance loss caused by parameter reduction." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.396, + 0.618, + 0.41 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.421, + 0.892, + 0.738 + ], + "angle": 0, + "content": "In this paper, a novel teacher-student knowledge distillation training framework is proposed to reduce the performance gap between a powerful teacher model and a compact student model. Specifically, this framework distills the knowledge from a deep two-stream network with complex multi-modal feature fusion modules to a single-stream network with efficient feature fusion modules. By virtue of the proposed SCFD module, the modality-common information as well as the modality-specific information can be transformed from a two-stream network to a single-stream network in the unimodal feature extraction stage, thus enhancing the representations of unimodal features. Besides, by employing the proposed MPSD module, the student model can adaptively combine multiple fused features generated by various simple fusion strategies to explore complementary information from multi-modal data more thoroughly. In addition, an HFRD module is proposed to improve the student model's discriminative ability against the distractors by alleviating the problem of data imbalance in the target state estimation stage. Experimental results show that our approach helps a student model achieve the state-of-the-art performance while reducing the number of parameters and computational complexity dramatically." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.74, + 0.892, + 0.809 + ], + "angle": 0, + "content": "Limitation: The current method dedicated to reducing computational complexity at the stages of unimodal feature extraction and multi-modal feature fusion, but it paid ZERO effort to improve the efficiency of target stage estimation, which is our future work." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.811, + 0.892, + 0.867 + ], + "angle": 0, + "content": "Acknowledgement: This work is supported by the National Natural Science Foundation of China under Grant No. 61773301. It is also supported by the Shaanxi Innovation Team Project under Grant No.2018TD-012." + }, + { + "type": "page_number", + "bbox": [ + 0.469, + 0.887, + 0.501, + 0.898 + ], + "angle": 0, + "content": "5411" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.125, + 0.174, + 0.139 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.148, + 0.47, + 0.2 + ], + "angle": 0, + "content": "[1] Goutam Bhat, Martin Danelljan, Luc Van Gool, and Radu Timofte. Learning discriminative model prediction for tracking. In Proceedings of the IEEE International Conference on Computer Vision, pages 6182-6191, 2019. 3, 4, 6, 8" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.201, + 0.472, + 0.252 + ], + "angle": 0, + "content": "[2] Guobin Chen, Wongun Choi, Xiang Yu, Tony Han, and Manmohan Chandraker. Learning efficient object detection models with knowledge distillation. 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IEEE Transactions on Circuits and Systems for Video Technology, 32(2):579-592, 2021. 8" + }, + { + "type": "list", + "bbox": [ + 0.08, + 0.127, + 0.47, + 0.812 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.469, + 0.887, + 0.501, + 0.898 + ], + "angle": 0, + "content": "5413" + } + ] +] \ No newline at end of file diff --git a/2023/Efficient RGB-T Tracking via Cross-Modality Distillation/cf5e82ff-3a69-46ad-ac66-64191f806cdf_origin.pdf b/2023/Efficient RGB-T Tracking via Cross-Modality Distillation/cf5e82ff-3a69-46ad-ac66-64191f806cdf_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..53a70b24770484b99c50ec58147d3ea5ab0ca3b3 --- /dev/null +++ b/2023/Efficient RGB-T Tracking via Cross-Modality Distillation/cf5e82ff-3a69-46ad-ac66-64191f806cdf_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:3358e453fb9303b00106bd38bce3db7e0be744994ac6b64a887a4a3c002d538e +size 492051 diff --git a/2023/Efficient RGB-T Tracking via Cross-Modality Distillation/full.md b/2023/Efficient RGB-T Tracking via Cross-Modality Distillation/full.md new file mode 100644 index 0000000000000000000000000000000000000000..a1d7790c02d69c695af13a8634e0bf55df868d35 --- /dev/null +++ b/2023/Efficient RGB-T Tracking via Cross-Modality Distillation/full.md @@ -0,0 +1,355 @@ +# Efficient RGB-T Tracking via Cross-Modality Distillation + +Tianlu Zhang $^{1}$ Hongyuan Guo $^{1}$ Qiang Jiao $^{1}$ Qiang Zhang $^{1*}$ Jungong Han $^{2,3}$ $^{1}$ School of Mechano-Electronic Engineering, Xidian University, China + $^{2}$ Department of Computer Science, the University of Sheffield, UK. + $^{3}$ Centre for Machine Intelligence, the University of Sheffield, UK. + +{tianluzhang, hyg}@stu.xidian.edu.cn, {qzhang, qjiao}@xidian.edu.cn, jungonghan77@gmail.com + +# Abstract + +Most current RGB-T trackers adopt a two-stream structure to extract unimodal RGB and thermal features and complex fusion strategies to achieve multi-modal feature fusion, which require a huge number of parameters, thus hindering their real-life applications. On the other hand, a compact RGB-T tracker may be computationally efficient but encounter non-negligible performance degradation, due to the weakening of feature representation ability. To remedy this situation, a cross-modality distillation framework is presented to bridge the performance gap between a compact tracker and a powerful tracker. Specifically, a specific-common feature distillation module is proposed to transform the modality-common information as well as the modality-specific information from a deeper two-stream network to a shallower single-stream network. In addition, a multi-path selection distillation module is proposed to instruct a simple fusion module to learn more accurate multi-modal information from a well-designed fusion mechanism by using multiple paths. We validate the effectiveness of our method with extensive experiments on three RGB-T benchmarks, which achieves state-of-the-art performance but consumes much less computational resources. + +# 1. Introduction + +RGB-T tracking is the task of estimating the state of an arbitrary target in each frame of an RGB-T video sequence [35]. Due to the affordability of thermal infrared (TIR) sensors, RGB-T tracking draws more and more research interest. + +As shown in Fig. 1 (a), most existing RGB-T tracking models first adopt a two-stream structure to extract multilevel unimodal RGB and TIR features, respectively, and then employ elaborate-designed multi-modal feature fusion modules to exploit complementary information within the + +![](images/59efdeff0171c59731060e780b9a1b5909d0688f8f3c0d58b8b3c9093f46d051.jpg) +Figure 1. Architectures of different RGB-T tracking models. (a) Two-stream structure. (b) Single-stream structure. (c) Our proposed method. + +multi-modal data. Finally, they deduce the target state, often represented by a bounding box, from the fused features. Although great progress has been made, these powerful RGB-T tracking models usually require high computational costs and large model sizes to handle the information of two modalities in the stages of unimodal feature extraction and multi-modal feature fusion. + +There are two straightforward solutions to tackle the complexity and efficiency issues. One is to adopt a single-stream feature extractor with fewer convolutional layers, and the other is to employ simpler multi-modal feature fusion modules, as shown in Fig. 1 (b). Although such compact models can reduce computational complexity, they inevitably bring non-negligible performance degradation due to the weakening of unimodal feature representation ability and multi-modal complementary information exploration ability. For instance, a powerful RGB-T tracker [35] with a two-stream structure and complicated multi-modal feature fusion modules suffers from severe performance degradation after the above model simplification operations (84.4% precision rate vs 78.1% precision rate on RGBT234 dataset [11]), as shown in Fig. 2. + +Now, the research question becomes: can we shrink the RGB-T tracker without sacrificing performance? This paper answers this question using knowledge distillation, which allows a compact model to obtain a similar ability of a complex model at little cost. We call this complex but powerful model the teacher model, and call this + +![](images/f9915a6f4968cf7eeab4baedcab7a8eb1909bfe67870c1c47d7937043c3058c9.jpg) +Figure 2. Experimental results of different RGB-T tracking structures on RGBT234 dataset [11]. Teacher denotes the two-stream structure with complex fusion modules. Student denotes a single-stream structure with simple fusion operations. The teacher model employs ResNet50 [7] for feature extraction and fusion modules in [35] for multi-modal feature fusion, respectively. The student model employs ResNet18 [7] for feature extraction and concatenation for multi-modal feature fusion, respectively. + +compact model the student model. Although some works [15, 19, 20, 29] have made considerable progress on knowledge distillation in multi-modal tasks, they fail to conduct a deep investigation on the huge feature differences between teacher and student in the unimodal feature extraction stage as well as in the multi-modal feature fusion stage, thereby resulting in suboptimal efficiency of the knowledge transformation. For that, a novel teacher-student knowledge distillation training framework, named Cross-Modality Distillation (CMD), is proposed to elaborately guide efficient imitation from three stages: unimodal feature extraction, multi-modal feature fusion and target estimate estimation, as shown in Fig. 1 (c). + +Specifically, in the stage of unimodal feature extraction, as pointed out by many previous works [9, 17], the shallower layers of unimodal features usually contain abundant low-level spatial details, which are usually modality-dependent. Differently, the deeper layers of unimodal features often contain many high-level semantic cues, which tend to be strongly modality-consistent. The student model uses a compact single-stream network to extract both RGB features and TIR features, which not only lacks the ability to extract modality-specific information in the shallower layers, but also insufficiently explores the modality-common information in the deeper layers. These interesting observations inspire us to design a Specific-common Feature Distillation (SCFD) module, which transforms the modality-specific information as well as the modality-common information from a two-stream deeper network to a single-stream shallower network. + +Second, in the stage of multi-modal feature fusion, the complex multi-modal feature fusion modules in the teacher model show great advantages in various scenarios, while + +the simple fusion strategies in the student model are usually effective in some specific scenarios. It is difficult for a student model with a single simple fusion strategy to learn more effective complementary information mining capabilities from a complex teacher model due to the large feature differences. Therefore, we design a fusion module with multiple simple fusion strategies in the student model, denoted as Multi-path Selection Distillation (MPSD) module. In the process of learning from the teacher model, the student model can adaptively combine different types of fusion features to make up for the lack of complementary information mining capabilities of a single simple fusion strategy. + +Finally, in the stage of target state estimation, with the weakening of the feature representation ability of the student model, the discriminative ability of the tracker for distractors is also reduced. For that, we further present a Hard-focused Response Distillation (HFRD) module to improve the student model's discriminative ability by alleviating the problem of data imbalance between the targets and the backgrounds, which employs the response maps generated by the teacher model to instruct the student to focus on distinguishing targets from hard negative samples. + +As shown in Fig. 2, each of our proposed modules continuously reduces the performance gap between the student model and the teacher model without increasing the number of parameters obviously. To sum up, our work improves an RGB-T tracker dramatically because of the following two contributions: + +- A Cross-Modality Distillation (CMD) framework is presented to bridge the performance gap between a compact student model and a powerful teacher model through three stages, i.e., unimodal feature extraction, multi-modal feature fusion and target state estimation. To the best of our knowledge, we are the first to introduce knowledge distillation for multi-modal tracking. +- Experimental results show that our proposed approach helps a student model achieve the state-of-the-art performance on the challenging GTOT [10], RGBT234 [11] and LasHer [14], while reducing the number of parameters and computational complexity. + +# 2. Related Work + +RGB-T Tracking Methods. The past few years have witnessed the increase of RGB-T tracking algorithms [4, 10, 13, 17, 31, 39]. Among them, numerous RGB-T trackers [6, 17, 30, 39] have been presented based on the MDNet [18]. For instance, in [17], Li et al. introduced a multi-adapter architecture to learn modality-common, modality-specific and instance-aware target representations, respectively. In [39], Zhu et al. first presented a network to aggregate the features from all of the layers and all of the modalities. After that, these aggregated features were further + +pruned to reduce noise and redundancy. Recently, Zhang et al. [35] introduced DiMP [1] as their baseline tracker and achieved promising tracking performance. Meanwhile, aiming to speed up the tracking, some works [36, 37] bring the Siamese networks to RGB-T tracking, where their models are trained in an offline manner. Although some progress has been made, these models still suffer from the limitations of large model sizes and high computation costs. + +Knowledge Distillation Methods. Knowledge Distillation (KD) was first proposed by Hinton et al. [8] to pass dark knowledge from complicated teachers to compact students, enabling students to maintain strong performance as teachers. FitNet [21] proves that the semantic information from intermediate features is also helpful to guide the student model. Besides image classification, KD is widely applied to object detection and object tracking tasks. For instance, [2] and [16] used KD to speed up the detection and segmentation networks, respectively. Furthermore, Wang [24] proposed to learn a more compact backbone for faster feature extraction in correlation filter based trackers. Shen et al. [22] used KD to compress deep Siamese-based trackers for high-performance visual tracking. + +In addition, KD is also employed for some multi-modal tasks, such as RGB-D salient object detection [19, 20] and RGB-T pedestrian detection [15, 29]. Specifically, in [20, 29], the single-stream feature extractors and the early fusion strategies were employed in their student models. However, both of them only simply employ the distillation loss functions to improve the performance of student models by using fused features or label knowledges of teacher models, and pay less attention to the huge differences between the teacher model and the student model in the unimodal feature extraction stage as well as in the multi-modal feature fusion stage. Differently, in this paper, we aim to narrow the feature differences between the student model and the teacher model by specifically learning strategies at multiple stages. + +# 3. Distilled RGB-T Tracking + +Given a powerful teacher model for RGB-T tracking, the proposed CMD framework aims to prompt a more efficient student model to learn from the teacher model. The knowledge from the teacher model is transferred to the student model to mimic more effective feature representation. This section starts with an overview of the proposed CMD framework. Then, we briefly provide an introduction of the employed teacher and student models. Finally, the three proposed knowledge distillation modules (i.e., SCFD, MPSD and HFRD) are described in details. + +# 3.1. Overview + +As illustrated in Fig. 3, the proposed CMD framework includes a teacher model, a student model and three knowl- + +![](images/17a87bcf2b243628ac3e382f991b4ed3d48fc378d3c538126df05682dcb7f8bc.jpg) +Figure 3. Overview of the proposed CMD framework. + +edge distillation modules. The teacher model takes a pair of RGB-T images as input, and employs a two-stream feature extractor and several complex multi-modal feature fusion modules for unimodal feature extraction and multi-modal fusion, respectively. Finally, the fused features will be fed into the target state estimation module to obtain the final tracking results. Different from the teacher model, the student model uses a single-stream feature extractor and several efficient multi-modal fusion modules. Although the student model has a higher running speed, the simplification of the model inevitably leads to a decrease in tracking performance. + +To make up for the huge performance gap between the student model and the teacher model, the proposed CMD framework attempts to coach the learning process of the student model from three stages: unimodal feature extraction, multi-modal feature fusion and target state estimation. Accordingly, in the first stage, by using a proposed SCFD module, the powerful two-stream feature extraction network of the teacher model will transfer such modality-specific information as well as modality-common information into the single-stream network of the student model to enhance its representation ability for unimodal features. In the second stage, we will present an MPSD module to shrink the differences between the fused features obtained by the teacher model and those obtained by the student model via a multipath optimization strategy. In the third stage, with a proposed HFRD module, we will adopt the response map generated by the teacher model in a form of spatial attention to instruct the student model to focus on the discrimination of difficult samples, thereby improving its discrimination ability. The improvements in the above three stages will effectively narrow the performance gap between the student model and the teacher model, enabling the student model to achieve competitive tracking results with the teacher model but with fewer parameters and higher computational efficiency. + +![](images/29707099059fed5d853c711e7a9007a825e7326eb4fa95e578e36d90b877647d.jpg) +Figure 4. Structure of the employed teacher model and the student model. + +# 3.2. Teacher and Student Model + +In this section, we will describe the architectures of the employed teacher and student models, which are both based on the recent deep RGB tracker DiMP [1]. As shown in Fig. 4, both the teacher model and the student model can be divided into three stages: unimodal feature extraction, multi-modal feature fusion and target state estimation. + +Feature extraction. In the teacher model, two feature extractors, denoted as $E_{rgb}$ and $E_{the}$ , regard RGB and TIR modalities in parallel. The two feature extractors both adopt ResNet50 [7] as the backbone to extract multi-level RGB and TIR features, as shown in Fig. 4 (a). Differently, in the student model, only one feature extractor, denoted as $E_{stu}$ , regards both RGB and TIR modalities simultaneously. As shown in Fig. 4 (b), $E_{stu}$ just adopts ResNet18 [7] as the backbone for simplification. Similar to the original DiMP tracker, in both the teacher model and the student model, we use the features from block3 and block 4 for regression, and those features only from block4 for classification. The extracted RGB and TIR features from the teacher model are denoted as $ft_{rgb}^{i}$ and $ft_{tir}^{i}$ , respectively, and the extracted RGB and TIR features from the student model are denoted as $fs_{rgb}^{i}$ and $fs_{tir}^{i}$ , respectively, where $i \in \{1,2,3,4\}$ indexes the feature level. + +Multi-modal feature fusion. By performing the multi-modal fusion modules on the $3rd$ and $4th$ levels of RGB and TIR features, we obtain the fused features $f t_{f u s}^{3}$ and $f t_{f u s}^{4}$ in the teacher model and the fused features $f s_{f u s}^{3}$ and $f s_{f u s}^{4}$ in the student model, respectively. Our teacher model employs a Modality Difference Compensation (MDC) module and a Feature Re-selection module (FRS) for multi-modal feature fusion [35]. Differently, our student model utilizes the proposed MPSD modules for multi-modal feature fusion. Details of MPSD will be introduced in Section 3.4. + +Classification and regression. Finally, these fused features will be fed to the classification and regression heads, which have the same architectures with those in the original DiMP. Especially, in this stage, the student and teacher models both apply the original classification and regression heads in DiMP. We refer readers to [1, 5] for more details. + +![](images/25e3aa7f8ba10b42c78054b55c7a64b31494edd278591707ea7af8a32bdc26d4.jpg) +Figure 5. The proposed specific-common feature distillation module for the RGB modality. The SCFD module for the TIR modality employs the same architecture as that in the RGB modality. + +![](images/402ddf399b8a6b0c85c04a8de2333af006806bf3f59788eedd2af2d884b915ff.jpg) + +# 3.3. Specific-Common Feature Distillation + +This section elaborates on the proposed SCFD module for the two-stage unimodal feature distillation, which lets the single-stream feature extraction module in the student model enable to learn the modality-common information as well as the modality-specific information from the teacher model, as shown in Fig. 5 (a). + +We first perform cross-modal interaction on the unimodal RGB features and TIR features from the teacher model to highlight the modality-common information and modality-specific information at different layers, respectively, for better guiding the learning of the student model. Specifically, as shown in Fig. 5 (b), given the unimodal features of shallow layers (i.e., $\{f t_{r g b}^{i}|i = 1,2,3\}$ and $\{f t_{t i r}^{i}|i = 1,2,3\}$ ) from the teacher model, the proposed Specific Enhanced Modules (SEMs) are employed to obtain such modality-interacted features $f e_{r g b}^{i}$ and $f e_{t i r}^{i}$ ( $i = 1,2,3$ ) with more modality-specific information via subtraction and multiplication. Mathematically, + +$$ +\begin{array}{l} f e _ {r g b} ^ {i} = \left(f t _ {r g b} ^ {i} * f t _ {t i r} ^ {i}\right) \oplus \left(f t _ {r g b} ^ {i} \ominus f t _ {t i r} ^ {i}\right), \\ f e _ {t i r} ^ {i} = \left(f t _ {r g b} ^ {i} * f t _ {t i r} ^ {i}\right) \oplus \left(f t _ {t i r} ^ {i} \ominus f t _ {r g b} ^ {i}\right), \end{array} \tag {1} +$$ + +where $\ominus$ , $\oplus$ and $\circ$ denote element-wise subtraction, element-wise addition and element-wise multiplication, respectively. $f t_{r g b}^{i}\circ f t_{t i r}^{i}$ reflects the jointly valid information within RGB and TIR features. While, $f t_{r g b}^{i}\ominus f t_{t i r}^{i}$ represents the modality-specific information of the RGB modality with respect to the TIR modality. Similarly, the modality-specific information of the TIR modality with respect to the RGB modality can be obtained by $f t_{t i r}^{i}\ominus f t_{r g b}^{i}$ . Accordingly, $f e_{r g b}^{i}$ and $f e_{t i r}^{i}$ highlight such modality-specific information in addition to preserve jointly valid information, which can be applied to guide feature learning of the student model in shallow layers. + +Alternatively, for the RGB and TIR features of deep lay + +ers (i.e., $f t_{r g b}^{4}$ and $f t_{t i r}^{4}$ ), the proposed Consistence Enhanced Module (CEM) is employed to obtain modality-interacted features $f c^{4}$ with more modality-common information via addition and multiplication, as shown in Fig. 5 (c). Mathematically, + +$$ +f c ^ {4} = \left(f t _ {r g b} ^ {4} * f t _ {t i r} ^ {4}\right) \oplus \left(f t _ {r g b} ^ {4} \oplus f t _ {t i r} ^ {4}\right). \tag {2} +$$ + +Here, by applying the element-wise addition on $f t_{r g b}^{4}$ and $f t_{t i r}^{4}$ , the consistency of high-level semantic cues within multi-modal data can be further enhanced. Therefore, $f c^{4}$ can better guide the learning of the student model in deep layer. + +With the modality-interacted features from the teacher model, the next step is to adjust the feature-channel dimensions of the student model to be consistent with those of the teacher model. Here, inspired by the idea of Knowledge Review [3], we employ a series of attention based fusion (ABF) modules [3] to adjust the channel dimensions of unimodal features and dynamically aggregate the cross-layer features in the student model. The modified features of the student model from ABFs (i.e., $\{f u_{r g b}^{i}|i = 1,2,3,4\}$ and $\{f u_{t i r}^{i}|i = 1,2,3,4\}$ ) and the modality-interacted features of the teacher model (i.e., $\{f e_{r g b}^{1},f e_{r g b}^{2},f e_{r g b}^{3},f c^{4}\}$ and $\{f e_{t i r}^{1},f e_{t i r}^{2},f e_{t i r}^{3},f c^{4}\}$ ) will be employed together to force the student model to mimic the specific and common information from the teacher model via a proposed feature-learning distillation loss $L_{SCFD}$ , which is formulated as: + +$$ +\begin{array}{l} L _ {s p e} = \sum_ {i = 1} ^ {3} l \left(f e _ {r g b} ^ {i}, f u _ {r g b} ^ {i}\right) + \sum_ {i = 1} ^ {3} l \left(f e _ {t i r} ^ {i}, f u _ {t i r} ^ {i}\right), \\ L _ {c o m} = l \left(f c ^ {4}, f u _ {r g b} ^ {4}\right) + l \left(f c ^ {4}, f u _ {t i r} ^ {4}\right), \\ L _ {S C F D} = L _ {s p e} + L _ {c o m}, \\ \end{array} +$$ + +where $l(*)$ denotes the standard MSE loss used in [21]. + +# 3.4. Multi-path Selection Distillation + +In order to learn the exploration ability of complementary information from the teacher model more effectively, we design a fusion module by using multiple fusion strategies, denoted as Multi-path Selection Distillation (MPSD) module, in the student model. In the process of learning from the teacher model, the student model can adaptively optimize the paths to reduce feature differences. + +Specifically, in the student model, the proposed MPSD module first performs multi-modal feature fusion from three typical perspectives: modality differences, modality commonality and modality complementary. Given the original RGB features $f s_{rgb}^{i}$ and TIR features $f s_{tir}^{i}$ from the 3rd and 4th levels in the student model, three types of initially fused features $f s_{fus,1}^{i}, f s_{fus,2}^{i}$ and $f s_{fus,3}^{i}$ are computed by + +$$ +\begin{array}{l} f s _ {f u s, 1} ^ {i} = s a \left(f s _ {r g b} ^ {i}, f s _ {t i r} ^ {i}\right), \\ f s _ {f u s, 2} ^ {i} = f s _ {r g b} ^ {i} * f s _ {t i r} ^ {i}, \tag {4} \\ f s _ {f u s, 3} ^ {i} = f s _ {r g b} ^ {i} \ominus f s _ {t i r} ^ {i}. \\ \end{array} +$$ + +![](images/01677883ff0eb0534384c1630764725674a6adf586ca64564506a3080549fad3.jpg) + +![](images/61c42f2c87849d575b5df24b239dc533723c461e31d6aa1be7dc3cfe9c823106.jpg) + +![](images/7965819198d60dc6feb71106f58fb003611d106837319eabf193ded3d1b260be.jpg) +Broadcasting multiplication + +![](images/267e6b7eb30bfa93061281b9e9e3d67d0277eed328a42b1a93e3c9bcab89a1f6.jpg) +FC layer + +![](images/d0e1360210284c64f026fff592caf87140a6c7ba5afb42183c98fe0262e52e9a.jpg) +Global max pooling + +![](images/4a2f6d9b6bf4be715a8dc21c531021e5d119f7ce4257bfdef9522e0499c5eb9a.jpg) + +![](images/f839172198e89c4bf0f455b27554cc0308c512e36026166841cfb727e019a3c6.jpg) +Separation operation + +![](images/2df42faf8cd6b1d51bf366d4b53a218a6fbd5318decd7aee607475a991627cf8.jpg) +Concatenation Operation + +![](images/1fb1e3f5b2277228f601eb806818fa1f58436f2d1d91e9059abf6b062f1a5dcd.jpg) +Sigmoid Function + +![](images/6d16dbb22edd370a6d27ea299c026e68dd8f440a366421606a6289c7e6ce0ff5.jpg) +1x1 Convolutional Layer +Figure 6. The proposed multi-path selection distillation module. + +Here, $sa(*)$ denotes the spatial attention mechanism, which first utilizes a convolution layer of kernel size $1 \times 1$ and a softmax layer to get a two-channel weight map. The two-channel weight map is then split into two reliability weight maps for selecting the RGB features and TIR features, respectively. Mathematically, the self-attention mechanism is expressed by: + +$$ +\begin{array}{l} w _ {r g b} ^ {i}, w _ {t} ^ {i} = \sigma \left(\operatorname {c o n v} \left(\operatorname {c a t} \left(f s _ {r g b} ^ {i}, f s _ {t i r} ^ {i}\right), \theta_ {1}\right)\right), \\ f s _ {f u s, 1} ^ {i} = \left(f s _ {r g b} ^ {i} * w _ {r g b} ^ {i}\right) \oplus \left(f s _ {t i r} ^ {i} * w _ {t i r} ^ {i}\right), \\ \end{array} +$$ + +where $\text{cat}(*)$ denotes the concatenation operation and $\text{conv}(*, \theta_1)$ denotes a $1 \times 1$ convolutional layer with its parameters $\theta_1$ . $\sigma(*)$ denotes the sigmoid layer. The features $f s_{fus,1}^{i}$ mainly reflect the complementary information within multi-modal data. Features $f s_{fus,2}^{i}$ and $f s_{fus,3}^{i}$ reflect their interacted information and their differential information, respectively. + +After that, $f s_{f u s,1}^{i}, f s_{f u s,2}^{i}$ and $f s_{f u s,3}^{i}$ are further combined together by a weighted fusion way, i.e, + +$$ +\begin{array}{l} w _ {1} ^ {i}, w _ {2} ^ {i}, w _ {3} ^ {i} = \text {s o f t m a x} (f c (g m p (c a t (f s _ {f u s, 1} ^ {i}, f s _ {f u s, 2} ^ {i}, f s _ {f u s, 3} ^ {i})))) \\ f s _ {f u s} ^ {i} = \left(f s _ {f u s, 1} ^ {i} \odot w _ {1} ^ {i}\right) \oplus \left(f s _ {f u s, 2} ^ {i} \odot w _ {2} ^ {i}\right) \oplus \left(f s _ {f u s, 3} ^ {i} \odot w _ {3} ^ {i}\right). \tag {6} \\ \end{array} +$$ + +where $gmp(*)$ and $fc(*)$ denote the global max pooling layer and the fully connected layers, respectively. $softmax(*)$ denote the softmax operation. The feature-wise weights $w_1^i, w_2^i, w_3^i$ reflect the importance of different fused features for the current scenario. $\odot$ denotes the broadcasting multiplication operation. + +With the fused features $\{ft_{fus}^i | i = 3,4\}$ and $\{fs_{fus}^i | i = 3,4\}$ obtained by the teacher model and the student model, respectively, we calculate the fusion distillation loss $L_{fus}$ + +between the fused features: + +$$ +L _ {f u s} = l \left(f t _ {f u s} ^ {3}, f s _ {f u s} ^ {3}\right) + l \left(f t _ {f u s} ^ {4}, f s _ {f u s} ^ {4}\right) \tag {7} +$$ + +What's more, in order to enable the student model to adaptively select a fusion path that is more similar to the teacher model in different scenarios, we introduce an additional penalty $L_{p}$ for the efficiency of knowledge transformation during training. More specifically, we first select the fusion type with the smallest difference between the initially fused features of the student model and the fused features of the teacher model by, + +$$ +\begin{array}{l} L _ {f u s, n} ^ {i} = l \left(f t _ {f u s} ^ {i}, f s _ {f u s, n} ^ {i}\right), n = 1, 2, 3 \tag {8} \\ L _ {f u s, \lambda^ {i}} ^ {i} = \min (L _ {f u s, 1} ^ {i}, L _ {f u s, 2} ^ {i}, L _ {f u s, 3} ^ {i}), \\ \end{array} +$$ + +where $\lambda^i = 1$ , 2 or 3 denotes the selected type of initially fused features according to the fused feature difference between the teacher and student models. + +After that, through the adaptive selection part in MPSD, the student model itself will also predict a type of initially fused features that is suitable for the current tracking scene, i.e., + +$$ +w _ {\nu^ {i}} ^ {i} = \max \left(w _ {1} ^ {i}, w _ {2} ^ {i}, w _ {3} ^ {i}\right), \tag {9} +$$ + +where $\nu^i = 1$ , 2 or 3 denotes the predicted type of initially fused features from the student model. + +With $w_{\nu^i}^i$ and $w_{\lambda^i}^i$ , we can use a penalty to help the student model choose a fusion path that is more suitable for the current scene under the guidance of the teacher model, i.e., + +$$ +L _ {p} = \sum_ {i = 3} ^ {4} \max \left(\left| L _ {f u s, \lambda^ {i}} ^ {i} w _ {\nu^ {i}} ^ {i} - L _ {f u s, \lambda^ {i}} ^ {i} w _ {\lambda^ {i}} ^ {i} \right|, 0\right). \tag {10} +$$ + +By minimizing $L_{p}$ , $w_{\nu^{i}}^{i}$ and $w_{\lambda^i}^i$ will tend to be consistent, which can enable the student model to adaptively select the fusion path according to the teacher model to improve the exploration ability of complementary information. + +On top of that, the overall distill loss in the multi-modal fusion stage can be obtained by: + +$$ +L _ {M P S D} = L _ {f u s} + L _ {p}. \tag {11} +$$ + +# 3.5. Hard-focused Response Distillation + +To alleviate the data imbalance problem, we propose the Hard-focused Response Distillation (HFRD) module to instruct the student to focus on distinguishing targets from hard negative samples. + +First, we obtain the response map $R_{t} \in \mathbb{R}^{H \times W}$ from the teacher model. Then, in order to prevent the teacher model from failing to have high responses in the target area within some scenes, we use the Gaussian-shaped mask $R_{g} \in \mathbb{R}^{H \times W}$ constructed by ground-truth bounding box as in [1] to correct the response map of the teacher model $R_{t}$ as follows: + +$$ +R _ {c} (i, j) = \left\{ \begin{array}{c} R _ {t} (i, j) + R _ {g} (i, j), i f \left(R _ {t} (i, j) + R _ {g} (i, j)\right) < 1, \\ R _ {g} (i, j), i f \left(R _ {t} (i, j) + R _ {g} (i, j)\right) \geq 1. \end{array} \right. \tag {12} +$$ + +where $i,j$ are the horizontal and vertical coordinates of the response map, respectively. The corrected mask $R_{c}\in \mathbb{R}^{H\times W}$ has higher response values not only on the positive samples but also on the hard negative samples. + +In the training process of the student model, with the assistance of the corrected mask $R_{c}$ from the teacher model, the student model can focus more on distinguishing target from hard negative samples by a proposed Hard-focused Response Distillation loss $L_{HFRD}$ to alleviate the data imbalance problem: + +$$ +L _ {H F R D} = r \left(R _ {s} * R _ {c}, R _ {g}\right), \tag {13} +$$ + +where $r(*)$ denotes the $L_{2}$ loss function [5]. + +# 3.6. Overall loss + +The overall distillation loss $L_{distill}$ is the sum of $L_{SCFD}$ , $L_{MPSD}$ and $L_{HFRD}$ . We train the student model with the total loss as follows: + +$$ +L _ {\text {d i s t i l l}} = \alpha \left(L _ {S C F D} + L _ {M P S D}\right) + \beta L _ {H F R D} + L _ {\text {o r i g i n a l}}, \tag {14} +$$ + +where $\alpha$ and $\beta$ are hyper-parameters to balance the distillation loss. $L_{\text{original}}$ is the original loss for tracking as in [35]. The distillation loss $L_{SCFD}$ and $L_{MPSD}$ are just calculated on feature maps, which can be easily applied to different tackers or other multi-modal vision tasks. + +# 4. Experiments + +Our tracking approach is implemented in Python based on PyTorch. For inference, we test our tracker on a single Nvidia RTX 1080Ti GPU. + +# 4.1. Implementation details + +Training Details. We adopt the training dataset in LasHeR [14], which contains 979 pairs of RGB-T videos, to train the teacher model and student model, respectively. The proposed CMD framework includes two training stages. In the first stage, we train the teacher model as in MFNet [35] and fix its weights after training. In the second stage, the optimization of the student model is jointly supervised by the original tracking loss $L_{\text{original}}$ as well as the knowledge transfer loss $L_{\text{SCFD}}$ , $L_{\text{MPSD}}$ and $L_{\text{HFRD}}$ . $\alpha$ and $\beta$ in Eq. 14 are experimentally set to 0.001 and 100, respectively. + +Online Tracking. In the tracking phase, our method is similar to DiMP [1]. We split tracking into classification and regression subtasks. For classification subtask, we employ data augmentation [1] on the first frame to construct an initial set, which contains 15 initial training samples for initial classification model training. Then the initial classification model is optimized using the augmented training set during tracking. For regression subtask, the same settings as those in [1] are employed. + +Table 1. Ablation study of different components. + +
StudentSCFDMPSDHFRDPR/SRParams(M)FPS
✓78.1/56.019.831
✓✓80.3/57.419.831
✓✓✓82.2/58.319.930
✓✓✓✓82.4/58.419.930
+ +# 4.2. Evaluation datasets and metrics + +We evaluate our method on three large-scale benchmark datasets, i.e., GTOT [10], RGBT234 [11] and LasHeR [14]. GTOT is the first standard dataset for RGB-T tracking. It contains 50 RGB-T video sequences annotated with seven challenging attributes. RGBT234 [11] contains 234 pairs of RGB-T videos and 12 annotated attributes. LasHeR is currently the largest RGB-T tracking dataset, which consists of 1244 RGB-T videos with more than 730K frame pairs in total. Among them, 245 videos are used as the testing set, and 979 videos are used as the training set. As in [17], we utilize two widely used metrics, i.e., precision rate (PR) and success rate (SR), to evaluate the tracking performance on GTOT and RGBT234. As in [14], we adopt precision rate (PR), normalized precision rate (NPR) and success rate (SR) to evaluate different trackers on LasHeR. + +# 4.3. Ablation Experiments and Analyses + +We conduct some ablation studies on RGBT234 [11] to discuss the impacts of different components in our CMD framework. + +Ablation experiments for each module. To investigate the impact of each component in our proposed CMD, several versions of our proposed method are provided for comparisons. Specifically, 'Student' denotes the model that without any knowledge transformation. Here, the proposed SCFD, MPSD and HFRD are employed in the unimodal feature extraction stage, multi-modal feature fusion stage and target state estimation stage, respectively. The quantitative results of these models are shown in Table 1. It can be seen that SCFD, MPSD and HFRD can all improve the performance of the student model. This verifies that each proposed component in CMD can effectively inherit the knowledge learnt from a powerful teacher models to a student model without obvious loss. + +Effectiveness of the proposed SCFD module. To further verify the effectiveness of the proposed SCFD module, several variants are also compared with our proposed SCFD module. Here, in the unimodal feature extraction stage, 'AFD', 'SED' and 'CED' denote initially fusing the unimodal features of each layer in the teacher model by using the simple element-wise addition operation, the designed SEM module and the designed CEM module, respectively, and such initially fused features are then employed to guide the student model for single-stream structure learning. As well, ABF modules [3] are employed in all of these vari- + +Table 2. Ablation study of the proposed SCFD module. + +
StudentAFDSEDCEDSCFDPR/SRParams(M)FPS
✓78.1/56.019.831
✓✓78.7/56.619.831
✓✓79.2/56.519.831
✓✓79.6/56.619.831
✓✓80.3/57.419.831
+ +Table 3. Ablation study of the proposed MPSD module. + +
Student+SCFDSAFCAFTFMPSDPR/SRParams(M)FPS
✓80.3/57.419.831
✓✓81.9/58.019.930
✓✓81.1/57.619.930
✓✓82.6/58.625.923
✓✓82.2/58.319.930
+ +ants. As shown in Table 2, the proposed SCFD can better exploit the modality-common and modality-specific information from the teacher model. + +Effectiveness of the proposed MPSD module. As shown in Table 3, several versions of our proposed MPSD module are also conducted to verify its effectiveness. 'SAF' denotes a spatial-wise attention based fusion module. 'CAF' denotes a channel-wise attention based module. 'TF' denotes adopting the same fusion strategy as that in the teacher model [35]. In particular, each layer adopts the same fusion strategy in the student model. It can be seen that the exploitation of the multi-path fusion strategy can well improve the performance of the student model. In addition, the performance gap between 'Student-MPSD' and 'Student-TF' is much smaller, which indicates that our proposed MPSD module can better mimic the fused features in the teacher model to compensate for the performance penalty from simple fusion operations. + +Teacher-Student knowledge distillation experiments. Table 4 shows the performance of using some other knowledge distillation methods in the feature extraction and feature fusion stages for comparisons, including KD [8], Fit-Nets [21], ReviewKD [3] and MD [29]. It is observed from Table 4 that the proposed distillation strategy performs the best. Due to the absence of cross-modal interactions, these existing knowledge distillation methods usually achieve some modest performance gains. In addition, we notice that the student model with a single-stream feature extractor performs obviously well than the student model with a two-stream feature extractor after knowledge distillation. This may be due to the fact that the single-stream network can narrow the modality difference to a certain extent and better acquire the knowledge from the teacher model. + +# 4.4. Comparison with the state-of-the-art + +To evaluate the superiority of our proposed method, we compare our method with some existing state-of-the-art RGB-T trackers, including MANet [17], DAFNet [6], DAPNet [39], TODA [28], MACNet [30], CAT [12], CEDiMP + +Table 4. Ablation study of different knowledge distillation experiments. + +
MethodKD [8]FitNets [21]ReviewKD [3]ReviewKD [3]MD [29]Ours
Backbone2 Res182 Res182 Res181 Res181 Res181 Res18
PR/SR78.4/56.279.3/56.079.9/56.580.5/56.380.0/55.482.4/58.4
FPS272727303030
Params31.631.631.619.919.919.9
+ +Table 5. Quantitative comparisons of our method with some state-of-the-arts methods on benchmark datasets. Higher values indicate better performance. + +
MethodsYearRGBT234 [11]GTOT [10]LasHeR [14]FPSParams
PR ↑SR ↑PR ↑SR ↑PR ↑NPR ↑SR ↑
DAPNet [39]201976.653.788.270.743.138.431.41-
MANet [17]201977.753.989.472.445.740.833.017.28M
DAFNet [6]201979.654.489.171.644.939.031.1145.50M
mfDiMP [31]201978.655.583.669.744.739.534.422175.82M
TODA [28]201978.754.584.367.7---1-
MACNet [30]202079.055.488.071.448.342.335.2114.86M
CAT [12]202080.456.188.971.745.139.831.7--
FANet [40]202178.755.389.172.844.238.430.91238.44M
SiamCDA [36]202176.056.987.773.2---24107.90M
JMMAC [32]202179.057.390.273.2-----
MANet++ [33]202180.055.488.270.746.740.831.7157.38M
ADRNet [33]202180.957.190.473.9---1568.50M
CBPNet [27]202279.454.188.571.6---3-
TFNet [41]202280.656.088.672.9-----
MFGNet [25]202278.353.588.970.7---38.09M
M5LNet [23]202279.554.289.671.0---9-
HMFT [34]202278.856.891.274.9----127.84M
APFNet [26]202282.757.990.573.950.0-36.2-15.01M
MANet* [17]201978.655.590.072.5---17.28M
DAFNet* [6]201980.054.986.070.048.042.834.5145.50M
mfDiMP* [31]201982.458.387.773.158.354.245.622175.82M
FANet* [40]202179.453.990.172.148.242.534.31238.44M
Teacher [35]202284.460.190.773.559.755.446.71881.01M
Student-Origin202278.156.088.572.355.450.342.33019.90M
Student-Distill202282.458.489.273.459.054.646.43019.90M
+ +[38], SiamCDA [36], mfDiMP [31], FANet [40], CBPNet [27], MANet++ [33], JMMAC [32], ADRNet [33], TFNet [41], MFGNet [25], M5LNet [23], HMFT [34], APFNet [26] and MFNet [35], on three challenging datasets. Considering that existing methods usually employ different training datasets, we use the LasHeR training set to retrain some of these algorithms for fair comparisons, including FANet*, DAFNet*, MANet* and mfDiMP*. + +On RGBT234. From Table 5, we observe that, in addition to the teacher model, our method achieves the best results with $82.4\% / 58.4\%$ in PR/SR. In particular, our tracker achieves $3.0\% / 4.5\%$ , $3.8\% / 2.9\%$ and $2.4\% / 3.6\%$ improvements against FANet* [40], MANet* [17] and DAFNet* [6] in PR/SR, respectively. We should note that some MDNet [18] based trackers [6,17,33] employ merely three convolutional layers for unimodal feature extraction, thus have fewer parameters in the unimodal feature extraction stage with a two-stream structure (e.g., 3.6M in [30, 40]). However, in the multi-modal feature fusion stage, these methods' parameters are significantly higher than those of the proposed MPSD module. Meanwhile, due to the complex updating strategy in MDNet, the above methods cannot meet the needs of real-time operation. + +On GTOT. From Table 5, we can see that our method obtains competitive performance on GTOT dataset [10] with $73.4\%$ and $89.2\%$ in success and precision scores, respectively. Compared with the teacher model, our student + +model achieves comparable performance but with a $75\%$ reduction in parameter sizes. Compared with the original student model, our algorithm achieves $1.1\%$ improvements in success and $0.7\%$ improvements in precision. + +On LasHeR. LasHeR [14] is captured from a number of scenes and categories and is highly diverse. A tracker restrained on this dataset usually achieves some improvements. From Table 5, we can also see that, in addition to the teacher model, our tracker still performs the best in terms of all the three metrics with significant performance superiorities on LasHeR. In particular, our tracker achieves $11.0\% / 11.9\%$ and $10.8\% / 12.1\%$ improvements against DAFNet* [6] and FANet* [40], which are based on MDNet [18]. Compared with mfDiMP* [31], which is based on DiMP [1] and employs two ResNet50 [7] for feature extraction, our PR/SR is $0.7\% / 0.8\%$ higher than it. This demonstrates that our proposed method can effectively reduce the performance loss caused by parameter reduction. + +# 5. Conclusion + +In this paper, a novel teacher-student knowledge distillation training framework is proposed to reduce the performance gap between a powerful teacher model and a compact student model. Specifically, this framework distills the knowledge from a deep two-stream network with complex multi-modal feature fusion modules to a single-stream network with efficient feature fusion modules. By virtue of the proposed SCFD module, the modality-common information as well as the modality-specific information can be transformed from a two-stream network to a single-stream network in the unimodal feature extraction stage, thus enhancing the representations of unimodal features. Besides, by employing the proposed MPSD module, the student model can adaptively combine multiple fused features generated by various simple fusion strategies to explore complementary information from multi-modal data more thoroughly. In addition, an HFRD module is proposed to improve the student model's discriminative ability against the distractors by alleviating the problem of data imbalance in the target state estimation stage. Experimental results show that our approach helps a student model achieve the state-of-the-art performance while reducing the number of parameters and computational complexity dramatically. + +Limitation: The current method dedicated to reducing computational complexity at the stages of unimodal feature extraction and multi-modal feature fusion, but it paid ZERO effort to improve the efficiency of target stage estimation, which is our future work. + +Acknowledgement: This work is supported by the National Natural Science Foundation of China under Grant No. 61773301. It is also supported by the Shaanxi Innovation Team Project under Grant No.2018TD-012. + +# References + +[1] Goutam Bhat, Martin Danelljan, Luc Van Gool, and Radu Timofte. Learning discriminative model prediction for tracking. In Proceedings of the IEEE International Conference on Computer Vision, pages 6182-6191, 2019. 3, 4, 6, 8 +[2] Guobin Chen, Wongun Choi, Xiang Yu, Tony Han, and Manmohan Chandraker. 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On the other hand, a compact RGB-T tracker may be computationally efficient but encounter non-negligible performance degradation, due to the weakening of feature representation ability. To remedy this situation, a cross-modality distillation framework is presented to bridge the performance gap between a compact tracker and a powerful tracker. Specifically, a specific-common feature distillation module is proposed to transform the modality-common information as well as the modality-specific information from a deeper two-stream network to a shallower single-stream network. In addition, a multi-path selection distillation module is proposed to instruct a simple fusion module to learn more accurate multi-modal information from a well-designed fusion mechanism by using multiple paths. We validate the effectiveness of our method with extensive experiments on three RGB-T benchmarks, which achieves state-of-the-art performance but consumes much less computational resources." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 574, + 124, + 586 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 574, + 124, + 586 + ], + "spans": [ + { + "bbox": [ + 46, + 574, + 124, + 586 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 45, + 593, + 279, + 650 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 593, + 279, + 650 + ], + "spans": [ + { + "bbox": [ + 45, + 593, + 279, + 650 + ], + "type": "text", + "content": "RGB-T tracking is the task of estimating the state of an arbitrary target in each frame of an RGB-T video sequence [35]. Due to the affordability of thermal infrared (TIR) sensors, RGB-T tracking draws more and more research interest." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 45, + 652, + 280, + 711 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 652, + 280, + 711 + ], + "spans": [ + { + "bbox": [ + 45, + 652, + 280, + 711 + ], + "type": "text", + "content": "As shown in Fig. 1 (a), most existing RGB-T tracking models first adopt a two-stream structure to extract multilevel unimodal RGB and TIR features, respectively, and then employ elaborate-designed multi-modal feature fusion modules to exploit complementary information within the" + } + ] + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 309, + 268, + 518, + 362 + ], + "blocks": [ + { + "bbox": [ + 309, + 268, + 518, + 362 + ], + "lines": [ + { + "bbox": [ + 309, + 268, + 518, + 362 + ], + "spans": [ + { + "bbox": [ + 309, + 268, + 518, + 362 + ], + "type": "image", + "image_path": "59efdeff0171c59731060e780b9a1b5909d0688f8f3c0d58b8b3c9093f46d051.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 296, + 363, + 530, + 395 + ], + "lines": [ + { + "bbox": [ + 296, + 363, + 530, + 395 + ], + "spans": [ + { + "bbox": [ + 296, + 363, + 530, + 395 + ], + "type": "text", + "content": "Figure 1. Architectures of different RGB-T tracking models. (a) Two-stream structure. (b) Single-stream structure. (c) Our proposed method." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "bbox": [ + 296, + 399, + 531, + 479 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 399, + 531, + 479 + ], + "spans": [ + { + "bbox": [ + 296, + 399, + 531, + 479 + ], + "type": "text", + "content": "multi-modal data. Finally, they deduce the target state, often represented by a bounding box, from the fused features. Although great progress has been made, these powerful RGB-T tracking models usually require high computational costs and large model sizes to handle the information of two modalities in the stages of unimodal feature extraction and multi-modal feature fusion." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 296, + 483, + 530, + 657 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 483, + 530, + 657 + ], + "spans": [ + { + "bbox": [ + 296, + 483, + 530, + 657 + ], + "type": "text", + "content": "There are two straightforward solutions to tackle the complexity and efficiency issues. One is to adopt a single-stream feature extractor with fewer convolutional layers, and the other is to employ simpler multi-modal feature fusion modules, as shown in Fig. 1 (b). Although such compact models can reduce computational complexity, they inevitably bring non-negligible performance degradation due to the weakening of unimodal feature representation ability and multi-modal complementary information exploration ability. For instance, a powerful RGB-T tracker [35] with a two-stream structure and complicated multi-modal feature fusion modules suffers from severe performance degradation after the above model simplification operations (84.4% precision rate vs 78.1% precision rate on RGBT234 dataset [11]), as shown in Fig. 2." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 296, + 660, + 530, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 660, + 530, + 730 + ], + "spans": [ + { + "bbox": [ + 296, + 660, + 530, + 730 + ], + "type": "text", + "content": "Now, the research question becomes: can we shrink the RGB-T tracker without sacrificing performance? This paper answers this question using knowledge distillation, which allows a compact model to obtain a similar ability of a complex model at little cost. We call this complex but powerful model the teacher model, and call this" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 77, + 42, + 119, + 71 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 77, + 42, + 119, + 71 + ], + "spans": [ + { + "bbox": [ + 77, + 42, + 119, + 71 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 150, + 41, + 471, + 74 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 150, + 41, + 471, + 74 + ], + "spans": [ + { + "bbox": [ + 150, + 41, + 471, + 74 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 57, + 719, + 133, + 730 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 57, + 719, + 133, + 730 + ], + "spans": [ + { + "bbox": [ + 57, + 719, + 133, + 730 + ], + "type": "text", + "content": "*Corresponding author." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 279, + 746, + 298, + 756 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 279, + 746, + 298, + 756 + ], + "spans": [ + { + "bbox": [ + 279, + 746, + 298, + 756 + ], + "type": "text", + "content": "5404" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 595, + 842 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 58, + 105, + 264, + 255 + ], + "blocks": [ + { + "bbox": [ + 58, + 105, + 264, + 255 + ], + "lines": [ + { + "bbox": [ + 58, + 105, + 264, + 255 + ], + "spans": [ + { + "bbox": [ + 58, + 105, + 264, + 255 + ], + "type": "image", + "image_path": "f9915a6f4968cf7eeab4baedcab7a8eb1909bfe67870c1c47d7937043c3058c9.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 45, + 257, + 279, + 343 + ], + "lines": [ + { + "bbox": [ + 45, + 257, + 279, + 343 + ], + "spans": [ + { + "bbox": [ + 45, + 257, + 279, + 343 + ], + "type": "text", + "content": "Figure 2. Experimental results of different RGB-T tracking structures on RGBT234 dataset [11]. Teacher denotes the two-stream structure with complex fusion modules. Student denotes a single-stream structure with simple fusion operations. The teacher model employs ResNet50 [7] for feature extraction and fusion modules in [35] for multi-modal feature fusion, respectively. The student model employs ResNet18 [7] for feature extraction and concatenation for multi-modal feature fusion, respectively." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 45, + 345, + 279, + 495 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 345, + 279, + 495 + ], + "spans": [ + { + "bbox": [ + 45, + 345, + 279, + 495 + ], + "type": "text", + "content": "compact model the student model. Although some works [15, 19, 20, 29] have made considerable progress on knowledge distillation in multi-modal tasks, they fail to conduct a deep investigation on the huge feature differences between teacher and student in the unimodal feature extraction stage as well as in the multi-modal feature fusion stage, thereby resulting in suboptimal efficiency of the knowledge transformation. For that, a novel teacher-student knowledge distillation training framework, named Cross-Modality Distillation (CMD), is proposed to elaborately guide efficient imitation from three stages: unimodal feature extraction, multi-modal feature fusion and target estimate estimation, as shown in Fig. 1 (c)." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 45, + 496, + 279, + 693 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 496, + 279, + 693 + ], + "spans": [ + { + "bbox": [ + 45, + 496, + 279, + 693 + ], + "type": "text", + "content": "Specifically, in the stage of unimodal feature extraction, as pointed out by many previous works [9, 17], the shallower layers of unimodal features usually contain abundant low-level spatial details, which are usually modality-dependent. Differently, the deeper layers of unimodal features often contain many high-level semantic cues, which tend to be strongly modality-consistent. The student model uses a compact single-stream network to extract both RGB features and TIR features, which not only lacks the ability to extract modality-specific information in the shallower layers, but also insufficiently explores the modality-common information in the deeper layers. These interesting observations inspire us to design a Specific-common Feature Distillation (SCFD) module, which transforms the modality-specific information as well as the modality-common information from a two-stream deeper network to a single-stream shallower network." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 45, + 694, + 279, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 694, + 279, + 730 + ], + "spans": [ + { + "bbox": [ + 45, + 694, + 279, + 730 + ], + "type": "text", + "content": "Second, in the stage of multi-modal feature fusion, the complex multi-modal feature fusion modules in the teacher model show great advantages in various scenarios, while" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 296, + 106, + 530, + 245 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 106, + 530, + 245 + ], + "spans": [ + { + "bbox": [ + 296, + 106, + 530, + 245 + ], + "type": "text", + "content": "the simple fusion strategies in the student model are usually effective in some specific scenarios. It is difficult for a student model with a single simple fusion strategy to learn more effective complementary information mining capabilities from a complex teacher model due to the large feature differences. Therefore, we design a fusion module with multiple simple fusion strategies in the student model, denoted as Multi-path Selection Distillation (MPSD) module. In the process of learning from the teacher model, the student model can adaptively combine different types of fusion features to make up for the lack of complementary information mining capabilities of a single simple fusion strategy." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 296, + 245, + 530, + 362 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 245, + 530, + 362 + ], + "spans": [ + { + "bbox": [ + 296, + 245, + 530, + 362 + ], + "type": "text", + "content": "Finally, in the stage of target state estimation, with the weakening of the feature representation ability of the student model, the discriminative ability of the tracker for distractors is also reduced. For that, we further present a Hard-focused Response Distillation (HFRD) module to improve the student model's discriminative ability by alleviating the problem of data imbalance between the targets and the backgrounds, which employs the response maps generated by the teacher model to instruct the student to focus on distinguishing targets from hard negative samples." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 296, + 362, + 530, + 431 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 362, + 530, + 431 + ], + "spans": [ + { + "bbox": [ + 296, + 362, + 530, + 431 + ], + "type": "text", + "content": "As shown in Fig. 2, each of our proposed modules continuously reduces the performance gap between the student model and the teacher model without increasing the number of parameters obviously. To sum up, our work improves an RGB-T tracker dramatically because of the following two contributions:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 308, + 437, + 530, + 584 + ], + "type": "list", + "angle": 0, + "index": 10, + "blocks": [ + { + "bbox": [ + 308, + 437, + 530, + 519 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 437, + 530, + 519 + ], + "spans": [ + { + "bbox": [ + 308, + 437, + 530, + 519 + ], + "type": "text", + "content": "- A Cross-Modality Distillation (CMD) framework is presented to bridge the performance gap between a compact student model and a powerful teacher model through three stages, i.e., unimodal feature extraction, multi-modal feature fusion and target state estimation. To the best of our knowledge, we are the first to introduce knowledge distillation for multi-modal tracking." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 308, + 526, + 530, + 584 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 526, + 530, + 584 + ], + "spans": [ + { + "bbox": [ + 308, + 526, + 530, + 584 + ], + "type": "text", + "content": "- Experimental results show that our proposed approach helps a student model achieve the state-of-the-art performance on the challenging GTOT [10], RGBT234 [11] and LasHer [14], while reducing the number of parameters and computational complexity." + } + ] + } + ], + "index": 9 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 297, + 593, + 380, + 605 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 593, + 380, + 605 + ], + "spans": [ + { + "bbox": [ + 297, + 593, + 380, + 605 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 296, + 612, + 530, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 612, + 530, + 730 + ], + "spans": [ + { + "bbox": [ + 296, + 612, + 530, + 730 + ], + "type": "text", + "content": "RGB-T Tracking Methods. The past few years have witnessed the increase of RGB-T tracking algorithms [4, 10, 13, 17, 31, 39]. Among them, numerous RGB-T trackers [6, 17, 30, 39] have been presented based on the MDNet [18]. For instance, in [17], Li et al. introduced a multi-adapter architecture to learn modality-common, modality-specific and instance-aware target representations, respectively. In [39], Zhu et al. first presented a network to aggregate the features from all of the layers and all of the modalities. After that, these aggregated features were further" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 279, + 746, + 298, + 756 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 279, + 746, + 298, + 756 + ], + "spans": [ + { + "bbox": [ + 279, + 746, + 298, + 756 + ], + "type": "text", + "content": "5405" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 595, + 842 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 45, + 106, + 279, + 198 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 106, + 279, + 198 + ], + "spans": [ + { + "bbox": [ + 45, + 106, + 279, + 198 + ], + "type": "text", + "content": "pruned to reduce noise and redundancy. Recently, Zhang et al. [35] introduced DiMP [1] as their baseline tracker and achieved promising tracking performance. Meanwhile, aiming to speed up the tracking, some works [36, 37] bring the Siamese networks to RGB-T tracking, where their models are trained in an offline manner. Although some progress has been made, these models still suffer from the limitations of large model sizes and high computation costs." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 45, + 199, + 280, + 362 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 199, + 280, + 362 + ], + "spans": [ + { + "bbox": [ + 45, + 199, + 280, + 362 + ], + "type": "text", + "content": "Knowledge Distillation Methods. Knowledge Distillation (KD) was first proposed by Hinton et al. [8] to pass dark knowledge from complicated teachers to compact students, enabling students to maintain strong performance as teachers. FitNet [21] proves that the semantic information from intermediate features is also helpful to guide the student model. Besides image classification, KD is widely applied to object detection and object tracking tasks. For instance, [2] and [16] used KD to speed up the detection and segmentation networks, respectively. Furthermore, Wang [24] proposed to learn a more compact backbone for faster feature extraction in correlation filter based trackers. Shen et al. [22] used KD to compress deep Siamese-based trackers for high-performance visual tracking." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 45, + 362, + 279, + 537 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 362, + 279, + 537 + ], + "spans": [ + { + "bbox": [ + 45, + 362, + 279, + 537 + ], + "type": "text", + "content": "In addition, KD is also employed for some multi-modal tasks, such as RGB-D salient object detection [19, 20] and RGB-T pedestrian detection [15, 29]. Specifically, in [20, 29], the single-stream feature extractors and the early fusion strategies were employed in their student models. However, both of them only simply employ the distillation loss functions to improve the performance of student models by using fused features or label knowledges of teacher models, and pay less attention to the huge differences between the teacher model and the student model in the unimodal feature extraction stage as well as in the multi-modal feature fusion stage. Differently, in this paper, we aim to narrow the feature differences between the student model and the teacher model by specifically learning strategies at multiple stages." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 546, + 190, + 559 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 546, + 190, + 559 + ], + "spans": [ + { + "bbox": [ + 46, + 546, + 190, + 559 + ], + "type": "text", + "content": "3. Distilled RGB-T Tracking" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 45, + 565, + 279, + 682 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 565, + 279, + 682 + ], + "spans": [ + { + "bbox": [ + 45, + 565, + 279, + 682 + ], + "type": "text", + "content": "Given a powerful teacher model for RGB-T tracking, the proposed CMD framework aims to prompt a more efficient student model to learn from the teacher model. The knowledge from the teacher model is transferred to the student model to mimic more effective feature representation. This section starts with an overview of the proposed CMD framework. Then, we briefly provide an introduction of the employed teacher and student models. Finally, the three proposed knowledge distillation modules (i.e., SCFD, MPSD and HFRD) are described in details." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 688, + 111, + 699 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 688, + 111, + 699 + ], + "spans": [ + { + "bbox": [ + 46, + 688, + 111, + 699 + ], + "type": "text", + "content": "3.1. Overview" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 706, + 279, + 729 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 706, + 279, + 729 + ], + "spans": [ + { + "bbox": [ + 46, + 706, + 279, + 729 + ], + "type": "text", + "content": "As illustrated in Fig. 3, the proposed CMD framework includes a teacher model, a student model and three knowl-" + } + ] + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 299, + 104, + 530, + 282 + ], + "blocks": [ + { + "bbox": [ + 299, + 104, + 530, + 282 + ], + "lines": [ + { + "bbox": [ + 299, + 104, + 530, + 282 + ], + "spans": [ + { + "bbox": [ + 299, + 104, + 530, + 282 + ], + "type": "image", + "image_path": "17a87bcf2b243628ac3e382f991b4ed3d48fc378d3c538126df05682dcb7f8bc.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 317, + 284, + 509, + 295 + ], + "lines": [ + { + "bbox": [ + 317, + 284, + 509, + 295 + ], + "spans": [ + { + "bbox": [ + 317, + 284, + 509, + 295 + ], + "type": "text", + "content": "Figure 3. Overview of the proposed CMD framework." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_caption" + } + ], + "index": 7 + }, + { + "bbox": [ + 296, + 298, + 530, + 436 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 298, + 530, + 436 + ], + "spans": [ + { + "bbox": [ + 296, + 298, + 530, + 436 + ], + "type": "text", + "content": "edge distillation modules. The teacher model takes a pair of RGB-T images as input, and employs a two-stream feature extractor and several complex multi-modal feature fusion modules for unimodal feature extraction and multi-modal fusion, respectively. Finally, the fused features will be fed into the target state estimation module to obtain the final tracking results. Different from the teacher model, the student model uses a single-stream feature extractor and several efficient multi-modal fusion modules. Although the student model has a higher running speed, the simplification of the model inevitably leads to a decrease in tracking performance." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 296, + 439, + 530, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 439, + 530, + 730 + ], + "spans": [ + { + "bbox": [ + 296, + 439, + 530, + 730 + ], + "type": "text", + "content": "To make up for the huge performance gap between the student model and the teacher model, the proposed CMD framework attempts to coach the learning process of the student model from three stages: unimodal feature extraction, multi-modal feature fusion and target state estimation. Accordingly, in the first stage, by using a proposed SCFD module, the powerful two-stream feature extraction network of the teacher model will transfer such modality-specific information as well as modality-common information into the single-stream network of the student model to enhance its representation ability for unimodal features. In the second stage, we will present an MPSD module to shrink the differences between the fused features obtained by the teacher model and those obtained by the student model via a multipath optimization strategy. In the third stage, with a proposed HFRD module, we will adopt the response map generated by the teacher model in a form of spatial attention to instruct the student model to focus on the discrimination of difficult samples, thereby improving its discrimination ability. The improvements in the above three stages will effectively narrow the performance gap between the student model and the teacher model, enabling the student model to achieve competitive tracking results with the teacher model but with fewer parameters and higher computational efficiency." + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 279, + 747, + 298, + 756 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 279, + 747, + 298, + 756 + ], + "spans": [ + { + "bbox": [ + 279, + 747, + 298, + 756 + ], + "type": "text", + "content": "5406" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 595, + 842 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 51, + 105, + 273, + 230 + ], + "blocks": [ + { + "bbox": [ + 51, + 105, + 273, + 230 + ], + "lines": [ + { + "bbox": [ + 51, + 105, + 273, + 230 + ], + "spans": [ + { + "bbox": [ + 51, + 105, + 273, + 230 + ], + "type": "image", + "image_path": "29707099059fed5d853c711e7a9007a825e7326eb4fa95e578e36d90b877647d.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 45, + 232, + 278, + 252 + ], + "lines": [ + { + "bbox": [ + 45, + 232, + 278, + 252 + ], + "spans": [ + { + "bbox": [ + 45, + 232, + 278, + 252 + ], + "type": "text", + "content": "Figure 4. Structure of the employed teacher model and the student model." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 255, + 194, + 266 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 255, + 194, + 266 + ], + "spans": [ + { + "bbox": [ + 46, + 255, + 194, + 266 + ], + "type": "text", + "content": "3.2. Teacher and Student Model" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 45, + 272, + 279, + 342 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 272, + 279, + 342 + ], + "spans": [ + { + "bbox": [ + 45, + 272, + 279, + 342 + ], + "type": "text", + "content": "In this section, we will describe the architectures of the employed teacher and student models, which are both based on the recent deep RGB tracker DiMP [1]. As shown in Fig. 4, both the teacher model and the student model can be divided into three stages: unimodal feature extraction, multi-modal feature fusion and target state estimation." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 45, + 343, + 279, + 540 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 343, + 279, + 540 + ], + "spans": [ + { + "bbox": [ + 45, + 343, + 279, + 540 + ], + "type": "text", + "content": "Feature extraction. In the teacher model, two feature extractors, denoted as " + }, + { + "bbox": [ + 45, + 343, + 279, + 540 + ], + "type": "inline_equation", + "content": "E_{rgb}" + }, + { + "bbox": [ + 45, + 343, + 279, + 540 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 45, + 343, + 279, + 540 + ], + "type": "inline_equation", + "content": "E_{the}" + }, + { + "bbox": [ + 45, + 343, + 279, + 540 + ], + "type": "text", + "content": ", regard RGB and TIR modalities in parallel. The two feature extractors both adopt ResNet50 [7] as the backbone to extract multi-level RGB and TIR features, as shown in Fig. 4 (a). Differently, in the student model, only one feature extractor, denoted as " + }, + { + "bbox": [ + 45, + 343, + 279, + 540 + ], + "type": "inline_equation", + "content": "E_{stu}" + }, + { + "bbox": [ + 45, + 343, + 279, + 540 + ], + "type": "text", + "content": ", regards both RGB and TIR modalities simultaneously. As shown in Fig. 4 (b), " + }, + { + "bbox": [ + 45, + 343, + 279, + 540 + ], + "type": "inline_equation", + "content": "E_{stu}" + }, + { + "bbox": [ + 45, + 343, + 279, + 540 + ], + "type": "text", + "content": " just adopts ResNet18 [7] as the backbone for simplification. Similar to the original DiMP tracker, in both the teacher model and the student model, we use the features from block3 and block 4 for regression, and those features only from block4 for classification. The extracted RGB and TIR features from the teacher model are denoted as " + }, + { + "bbox": [ + 45, + 343, + 279, + 540 + ], + "type": "inline_equation", + "content": "ft_{rgb}^{i}" + }, + { + "bbox": [ + 45, + 343, + 279, + 540 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 45, + 343, + 279, + 540 + ], + "type": "inline_equation", + "content": "ft_{tir}^{i}" + }, + { + "bbox": [ + 45, + 343, + 279, + 540 + ], + "type": "text", + "content": ", respectively, and the extracted RGB and TIR features from the student model are denoted as " + }, + { + "bbox": [ + 45, + 343, + 279, + 540 + ], + "type": "inline_equation", + "content": "fs_{rgb}^{i}" + }, + { + "bbox": [ + 45, + 343, + 279, + 540 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 45, + 343, + 279, + 540 + ], + "type": "inline_equation", + "content": "fs_{tir}^{i}" + }, + { + "bbox": [ + 45, + 343, + 279, + 540 + ], + "type": "text", + "content": ", respectively, where " + }, + { + "bbox": [ + 45, + 343, + 279, + 540 + ], + "type": "inline_equation", + "content": "i \\in \\{1,2,3,4\\}" + }, + { + "bbox": [ + 45, + 343, + 279, + 540 + ], + "type": "text", + "content": " indexes the feature level." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 45, + 541, + 279, + 658 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 541, + 279, + 658 + ], + "spans": [ + { + "bbox": [ + 45, + 541, + 279, + 658 + ], + "type": "text", + "content": "Multi-modal feature fusion. By performing the multi-modal fusion modules on the " + }, + { + "bbox": [ + 45, + 541, + 279, + 658 + ], + "type": "inline_equation", + "content": "3rd" + }, + { + "bbox": [ + 45, + 541, + 279, + 658 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 45, + 541, + 279, + 658 + ], + "type": "inline_equation", + "content": "4th" + }, + { + "bbox": [ + 45, + 541, + 279, + 658 + ], + "type": "text", + "content": " levels of RGB and TIR features, we obtain the fused features " + }, + { + "bbox": [ + 45, + 541, + 279, + 658 + ], + "type": "inline_equation", + "content": "f t_{f u s}^{3}" + }, + { + "bbox": [ + 45, + 541, + 279, + 658 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 45, + 541, + 279, + 658 + ], + "type": "inline_equation", + "content": "f t_{f u s}^{4}" + }, + { + "bbox": [ + 45, + 541, + 279, + 658 + ], + "type": "text", + "content": " in the teacher model and the fused features " + }, + { + "bbox": [ + 45, + 541, + 279, + 658 + ], + "type": "inline_equation", + "content": "f s_{f u s}^{3}" + }, + { + "bbox": [ + 45, + 541, + 279, + 658 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 45, + 541, + 279, + 658 + ], + "type": "inline_equation", + "content": "f s_{f u s}^{4}" + }, + { + "bbox": [ + 45, + 541, + 279, + 658 + ], + "type": "text", + "content": " in the student model, respectively. Our teacher model employs a Modality Difference Compensation (MDC) module and a Feature Re-selection module (FRS) for multi-modal feature fusion [35]. Differently, our student model utilizes the proposed MPSD modules for multi-modal feature fusion. Details of MPSD will be introduced in Section 3.4." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 45, + 660, + 279, + 729 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 660, + 279, + 729 + ], + "spans": [ + { + "bbox": [ + 45, + 660, + 279, + 729 + ], + "type": "text", + "content": "Classification and regression. Finally, these fused features will be fed to the classification and regression heads, which have the same architectures with those in the original DiMP. Especially, in this stage, the student and teacher models both apply the original classification and regression heads in DiMP. We refer readers to [1, 5] for more details." + } + ] + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 311, + 105, + 437, + 265 + ], + "blocks": [ + { + "bbox": [ + 311, + 105, + 437, + 265 + ], + "lines": [ + { + "bbox": [ + 311, + 105, + 437, + 265 + ], + "spans": [ + { + "bbox": [ + 311, + 105, + 437, + 265 + ], + "type": "image", + "image_path": "25e3aa7f8ba10b42c78054b55c7a64b31494edd278591707ea7af8a32bdc26d4.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 296, + 268, + 530, + 301 + ], + "lines": [ + { + "bbox": [ + 296, + 268, + 530, + 301 + ], + "spans": [ + { + "bbox": [ + 296, + 268, + 530, + 301 + ], + "type": "text", + "content": "Figure 5. The proposed specific-common feature distillation module for the RGB modality. The SCFD module for the TIR modality employs the same architecture as that in the RGB modality." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 437, + 105, + 518, + 266 + ], + "blocks": [ + { + "bbox": [ + 437, + 105, + 518, + 266 + ], + "lines": [ + { + "bbox": [ + 437, + 105, + 518, + 266 + ], + "spans": [ + { + "bbox": [ + 437, + 105, + 518, + 266 + ], + "type": "image", + "image_path": "402ddf399b8a6b0c85c04a8de2333af006806bf3f59788eedd2af2d884b915ff.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + } + ], + "index": 8 + }, + { + "bbox": [ + 297, + 305, + 490, + 317 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 305, + 490, + 317 + ], + "spans": [ + { + "bbox": [ + 297, + 305, + 490, + 317 + ], + "type": "text", + "content": "3.3. Specific-Common Feature Distillation" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 296, + 323, + 530, + 392 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 323, + 530, + 392 + ], + "spans": [ + { + "bbox": [ + 296, + 323, + 530, + 392 + ], + "type": "text", + "content": "This section elaborates on the proposed SCFD module for the two-stage unimodal feature distillation, which lets the single-stream feature extraction module in the student model enable to learn the modality-common information as well as the modality-specific information from the teacher model, as shown in Fig. 5 (a)." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 296, + 393, + 530, + 534 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 393, + 530, + 534 + ], + "spans": [ + { + "bbox": [ + 296, + 393, + 530, + 534 + ], + "type": "text", + "content": "We first perform cross-modal interaction on the unimodal RGB features and TIR features from the teacher model to highlight the modality-common information and modality-specific information at different layers, respectively, for better guiding the learning of the student model. Specifically, as shown in Fig. 5 (b), given the unimodal features of shallow layers (i.e., " + }, + { + "bbox": [ + 296, + 393, + 530, + 534 + ], + "type": "inline_equation", + "content": "\\{f t_{r g b}^{i}|i = 1,2,3\\}" + }, + { + "bbox": [ + 296, + 393, + 530, + 534 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 296, + 393, + 530, + 534 + ], + "type": "inline_equation", + "content": "\\{f t_{t i r}^{i}|i = 1,2,3\\}" + }, + { + "bbox": [ + 296, + 393, + 530, + 534 + ], + "type": "text", + "content": ") from the teacher model, the proposed Specific Enhanced Modules (SEMs) are employed to obtain such modality-interacted features " + }, + { + "bbox": [ + 296, + 393, + 530, + 534 + ], + "type": "inline_equation", + "content": "f e_{r g b}^{i}" + }, + { + "bbox": [ + 296, + 393, + 530, + 534 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 296, + 393, + 530, + 534 + ], + "type": "inline_equation", + "content": "f e_{t i r}^{i}" + }, + { + "bbox": [ + 296, + 393, + 530, + 534 + ], + "type": "text", + "content": " (" + }, + { + "bbox": [ + 296, + 393, + 530, + 534 + ], + "type": "inline_equation", + "content": "i = 1,2,3" + }, + { + "bbox": [ + 296, + 393, + 530, + 534 + ], + "type": "text", + "content": ") with more modality-specific information via subtraction and multiplication. Mathematically," + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 327, + 538, + 530, + 567 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 327, + 538, + 530, + 567 + ], + "spans": [ + { + "bbox": [ + 327, + 538, + 530, + 567 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} f e _ {r g b} ^ {i} = \\left(f t _ {r g b} ^ {i} * f t _ {t i r} ^ {i}\\right) \\oplus \\left(f t _ {r g b} ^ {i} \\ominus f t _ {t i r} ^ {i}\\right), \\\\ f e _ {t i r} ^ {i} = \\left(f t _ {r g b} ^ {i} * f t _ {t i r} ^ {i}\\right) \\oplus \\left(f t _ {t i r} ^ {i} \\ominus f t _ {r g b} ^ {i}\\right), \\end{array} \\tag {1}", + "image_path": "6c208a211df4f3a260c5edcdd3e375c11a0daa5e8605930469afc0085a3f5a8f.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 296, + 575, + 530, + 717 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 575, + 530, + 717 + ], + "spans": [ + { + "bbox": [ + 296, + 575, + 530, + 717 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 296, + 575, + 530, + 717 + ], + "type": "inline_equation", + "content": "\\ominus" + }, + { + "bbox": [ + 296, + 575, + 530, + 717 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 296, + 575, + 530, + 717 + ], + "type": "inline_equation", + "content": "\\oplus" + }, + { + "bbox": [ + 296, + 575, + 530, + 717 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 296, + 575, + 530, + 717 + ], + "type": "inline_equation", + "content": "\\circ" + }, + { + "bbox": [ + 296, + 575, + 530, + 717 + ], + "type": "text", + "content": " denote element-wise subtraction, element-wise addition and element-wise multiplication, respectively. " + }, + { + "bbox": [ + 296, + 575, + 530, + 717 + ], + "type": "inline_equation", + "content": "f t_{r g b}^{i}\\circ f t_{t i r}^{i}" + }, + { + "bbox": [ + 296, + 575, + 530, + 717 + ], + "type": "text", + "content": " reflects the jointly valid information within RGB and TIR features. While, " + }, + { + "bbox": [ + 296, + 575, + 530, + 717 + ], + "type": "inline_equation", + "content": "f t_{r g b}^{i}\\ominus f t_{t i r}^{i}" + }, + { + "bbox": [ + 296, + 575, + 530, + 717 + ], + "type": "text", + "content": " represents the modality-specific information of the RGB modality with respect to the TIR modality. Similarly, the modality-specific information of the TIR modality with respect to the RGB modality can be obtained by " + }, + { + "bbox": [ + 296, + 575, + 530, + 717 + ], + "type": "inline_equation", + "content": "f t_{t i r}^{i}\\ominus f t_{r g b}^{i}" + }, + { + "bbox": [ + 296, + 575, + 530, + 717 + ], + "type": "text", + "content": ". Accordingly, " + }, + { + "bbox": [ + 296, + 575, + 530, + 717 + ], + "type": "inline_equation", + "content": "f e_{r g b}^{i}" + }, + { + "bbox": [ + 296, + 575, + 530, + 717 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 296, + 575, + 530, + 717 + ], + "type": "inline_equation", + "content": "f e_{t i r}^{i}" + }, + { + "bbox": [ + 296, + 575, + 530, + 717 + ], + "type": "text", + "content": " highlight such modality-specific information in addition to preserve jointly valid information, which can be applied to guide feature learning of the student model in shallow layers." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 309, + 718, + 530, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 309, + 718, + 530, + 730 + ], + "spans": [ + { + "bbox": [ + 309, + 718, + 530, + 730 + ], + "type": "text", + "content": "Alternatively, for the RGB and TIR features of deep lay" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 279, + 746, + 298, + 756 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 279, + 746, + 298, + 756 + ], + "spans": [ + { + "bbox": [ + 279, + 746, + 298, + 756 + ], + "type": "text", + "content": "5407" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 595, + 842 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 45, + 105, + 279, + 165 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 105, + 279, + 165 + ], + "spans": [ + { + "bbox": [ + 45, + 105, + 279, + 165 + ], + "type": "text", + "content": "ers (i.e., " + }, + { + "bbox": [ + 45, + 105, + 279, + 165 + ], + "type": "inline_equation", + "content": "f t_{r g b}^{4}" + }, + { + "bbox": [ + 45, + 105, + 279, + 165 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 45, + 105, + 279, + 165 + ], + "type": "inline_equation", + "content": "f t_{t i r}^{4}" + }, + { + "bbox": [ + 45, + 105, + 279, + 165 + ], + "type": "text", + "content": "), the proposed Consistence Enhanced Module (CEM) is employed to obtain modality-interacted features " + }, + { + "bbox": [ + 45, + 105, + 279, + 165 + ], + "type": "inline_equation", + "content": "f c^{4}" + }, + { + "bbox": [ + 45, + 105, + 279, + 165 + ], + "type": "text", + "content": " with more modality-common information via addition and multiplication, as shown in Fig. 5 (c). Mathematically," + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 80, + 166, + 279, + 181 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 80, + 166, + 279, + 181 + ], + "spans": [ + { + "bbox": [ + 80, + 166, + 279, + 181 + ], + "type": "interline_equation", + "content": "f c ^ {4} = \\left(f t _ {r g b} ^ {4} * f t _ {t i r} ^ {4}\\right) \\oplus \\left(f t _ {r g b} ^ {4} \\oplus f t _ {t i r} ^ {4}\\right). \\tag {2}", + "image_path": "148c5d062de702473344193d8b03b8d5fbaf94cb266144088727515801e23c05.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 45, + 185, + 279, + 245 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 185, + 279, + 245 + ], + "spans": [ + { + "bbox": [ + 45, + 185, + 279, + 245 + ], + "type": "text", + "content": "Here, by applying the element-wise addition on " + }, + { + "bbox": [ + 45, + 185, + 279, + 245 + ], + "type": "inline_equation", + "content": "f t_{r g b}^{4}" + }, + { + "bbox": [ + 45, + 185, + 279, + 245 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 45, + 185, + 279, + 245 + ], + "type": "inline_equation", + "content": "f t_{t i r}^{4}" + }, + { + "bbox": [ + 45, + 185, + 279, + 245 + ], + "type": "text", + "content": ", the consistency of high-level semantic cues within multi-modal data can be further enhanced. Therefore, " + }, + { + "bbox": [ + 45, + 185, + 279, + 245 + ], + "type": "inline_equation", + "content": "f c^{4}" + }, + { + "bbox": [ + 45, + 185, + 279, + 245 + ], + "type": "text", + "content": " can better guide the learning of the student model in deep layer." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 45, + 245, + 279, + 424 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 245, + 279, + 424 + ], + "spans": [ + { + "bbox": [ + 45, + 245, + 279, + 424 + ], + "type": "text", + "content": "With the modality-interacted features from the teacher model, the next step is to adjust the feature-channel dimensions of the student model to be consistent with those of the teacher model. Here, inspired by the idea of Knowledge Review [3], we employ a series of attention based fusion (ABF) modules [3] to adjust the channel dimensions of unimodal features and dynamically aggregate the cross-layer features in the student model. The modified features of the student model from ABFs (i.e., " + }, + { + "bbox": [ + 45, + 245, + 279, + 424 + ], + "type": "inline_equation", + "content": "\\{f u_{r g b}^{i}|i = 1,2,3,4\\}" + }, + { + "bbox": [ + 45, + 245, + 279, + 424 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 45, + 245, + 279, + 424 + ], + "type": "inline_equation", + "content": "\\{f u_{t i r}^{i}|i = 1,2,3,4\\}" + }, + { + "bbox": [ + 45, + 245, + 279, + 424 + ], + "type": "text", + "content": ") and the modality-interacted features of the teacher model (i.e., " + }, + { + "bbox": [ + 45, + 245, + 279, + 424 + ], + "type": "inline_equation", + "content": "\\{f e_{r g b}^{1},f e_{r g b}^{2},f e_{r g b}^{3},f c^{4}\\}" + }, + { + "bbox": [ + 45, + 245, + 279, + 424 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 45, + 245, + 279, + 424 + ], + "type": "inline_equation", + "content": "\\{f e_{t i r}^{1},f e_{t i r}^{2},f e_{t i r}^{3},f c^{4}\\}" + }, + { + "bbox": [ + 45, + 245, + 279, + 424 + ], + "type": "text", + "content": ") will be employed together to force the student model to mimic the specific and common information from the teacher model via a proposed feature-learning distillation loss " + }, + { + "bbox": [ + 45, + 245, + 279, + 424 + ], + "type": "inline_equation", + "content": "L_{SCFD}" + }, + { + "bbox": [ + 45, + 245, + 279, + 424 + ], + "type": "text", + "content": ", which is formulated as:" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 50, + 435, + 274, + 474 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 50, + 435, + 274, + 474 + ], + "spans": [ + { + "bbox": [ + 50, + 435, + 274, + 474 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} L _ {s p e} = \\sum_ {i = 1} ^ {3} l \\left(f e _ {r g b} ^ {i}, f u _ {r g b} ^ {i}\\right) + \\sum_ {i = 1} ^ {3} l \\left(f e _ {t i r} ^ {i}, f u _ {t i r} ^ {i}\\right), \\\\ L _ {c o m} = l \\left(f c ^ {4}, f u _ {r g b} ^ {4}\\right) + l \\left(f c ^ {4}, f u _ {t i r} ^ {4}\\right), \\\\ L _ {S C F D} = L _ {s p e} + L _ {c o m}, \\\\ \\end{array}", + "image_path": "4d8028a94699b917526dc66754a430fa774330c316a44a1262fee926982e1ca8.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 26, + 475, + 279, + 497 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 26, + 475, + 279, + 497 + ], + "spans": [ + { + "bbox": [ + 26, + 475, + 279, + 497 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 26, + 475, + 279, + 497 + ], + "type": "inline_equation", + "content": "l(*)" + }, + { + "bbox": [ + 26, + 475, + 279, + 497 + ], + "type": "text", + "content": " denotes the standard MSE loss used in [21]." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 501, + 214, + 513 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 501, + 214, + 513 + ], + "spans": [ + { + "bbox": [ + 46, + 501, + 214, + 513 + ], + "type": "text", + "content": "3.4. Multi-path Selection Distillation" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 45, + 519, + 279, + 600 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 519, + 279, + 600 + ], + "spans": [ + { + "bbox": [ + 45, + 519, + 279, + 600 + ], + "type": "text", + "content": "In order to learn the exploration ability of complementary information from the teacher model more effectively, we design a fusion module by using multiple fusion strategies, denoted as Multi-path Selection Distillation (MPSD) module, in the student model. In the process of learning from the teacher model, the student model can adaptively optimize the paths to reduce feature differences." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 45, + 601, + 279, + 692 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 601, + 279, + 692 + ], + "spans": [ + { + "bbox": [ + 45, + 601, + 279, + 692 + ], + "type": "text", + "content": "Specifically, in the student model, the proposed MPSD module first performs multi-modal feature fusion from three typical perspectives: modality differences, modality commonality and modality complementary. Given the original RGB features " + }, + { + "bbox": [ + 45, + 601, + 279, + 692 + ], + "type": "inline_equation", + "content": "f s_{rgb}^{i}" + }, + { + "bbox": [ + 45, + 601, + 279, + 692 + ], + "type": "text", + "content": " and TIR features " + }, + { + "bbox": [ + 45, + 601, + 279, + 692 + ], + "type": "inline_equation", + "content": "f s_{tir}^{i}" + }, + { + "bbox": [ + 45, + 601, + 279, + 692 + ], + "type": "text", + "content": " from the 3rd and 4th levels in the student model, three types of initially fused features " + }, + { + "bbox": [ + 45, + 601, + 279, + 692 + ], + "type": "inline_equation", + "content": "f s_{fus,1}^{i}, f s_{fus,2}^{i}" + }, + { + "bbox": [ + 45, + 601, + 279, + 692 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 45, + 601, + 279, + 692 + ], + "type": "inline_equation", + "content": "f s_{fus,3}^{i}" + }, + { + "bbox": [ + 45, + 601, + 279, + 692 + ], + "type": "text", + "content": " are computed by" + } + ] + } + ], + "index": 8 + 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The proposed multi-path selection distillation module." + } + ] + } + ], + "index": 27, + "angle": 0, + "type": "image_caption" + } + ], + "index": 25 + }, + { + "bbox": [ + 296, + 357, + 530, + 438 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 357, + 530, + 438 + ], + "spans": [ + { + "bbox": [ + 296, + 357, + 530, + 438 + ], + "type": "text", + "content": "Here, " + }, + { + "bbox": [ + 296, + 357, + 530, + 438 + ], + "type": "inline_equation", + "content": "sa(*)" + }, + { + "bbox": [ + 296, + 357, + 530, + 438 + ], + "type": "text", + "content": " denotes the spatial attention mechanism, which first utilizes a convolution layer of kernel size " + }, + { + "bbox": [ + 296, + 357, + 530, + 438 + ], + "type": "inline_equation", + "content": "1 \\times 1" + }, + { + "bbox": [ + 296, + 357, + 530, + 438 + ], + "type": "text", + "content": " and a softmax layer to get a two-channel weight map. The two-channel weight map is then split into two reliability weight maps for selecting the RGB features and TIR features, respectively. Mathematically, the self-attention mechanism is expressed by:" + } + ] + } + ], + "index": 28 + }, + { + "bbox": [ + 326, + 441, + 516, + 468 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 326, + 441, + 516, + 468 + ], + "spans": [ + { + "bbox": [ + 326, + 441, + 516, + 468 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} w _ {r g b} ^ {i}, w _ {t} ^ {i} = \\sigma \\left(\\operatorname {c o n v} \\left(\\operatorname {c a t} \\left(f s _ {r g b} ^ {i}, f s _ {t i r} ^ {i}\\right), \\theta_ {1}\\right)\\right), \\\\ f s _ {f u s, 1} ^ {i} = \\left(f s _ {r g b} ^ {i} * w _ {r g b} ^ {i}\\right) \\oplus \\left(f s _ {t i r} ^ {i} * w _ {t i r} ^ {i}\\right), \\\\ \\end{array}", + "image_path": "1f81d3461a184399ed086a773ce7f37b6155f7f78ba2c13bb24c3c583837adfa.jpg" + } + ] + } + ], + "index": 29 + }, + { + "bbox": [ + 296, + 469, + 530, + 553 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 469, + 530, + 553 + ], + "spans": [ + { + "bbox": [ + 296, + 469, + 530, + 553 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 296, + 469, + 530, + 553 + ], + "type": "inline_equation", + "content": "\\text{cat}(*)" + }, + { + "bbox": [ + 296, + 469, + 530, + 553 + ], + "type": "text", + "content": " denotes the concatenation operation and " + }, + { + "bbox": [ + 296, + 469, + 530, + 553 + ], + "type": "inline_equation", + "content": "\\text{conv}(*, \\theta_1)" + }, + { + "bbox": [ + 296, + 469, + 530, + 553 + ], + "type": "text", + "content": " denotes a " + }, + { + "bbox": [ + 296, + 469, + 530, + 553 + ], + "type": "inline_equation", + "content": "1 \\times 1" + }, + { + "bbox": [ + 296, + 469, + 530, + 553 + ], + "type": "text", + "content": " convolutional layer with its parameters " + }, + { + "bbox": [ + 296, + 469, + 530, + 553 + ], + "type": "inline_equation", + "content": "\\theta_1" + }, + { + "bbox": [ + 296, + 469, + 530, + 553 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 296, + 469, + 530, + 553 + ], + "type": "inline_equation", + "content": "\\sigma(*)" + }, + { + "bbox": [ + 296, + 469, + 530, + 553 + ], + "type": "text", + "content": " denotes the sigmoid layer. The features " + }, + { + "bbox": [ + 296, + 469, + 530, + 553 + ], + "type": "inline_equation", + "content": "f s_{fus,1}^{i}" + }, + { + "bbox": [ + 296, + 469, + 530, + 553 + ], + "type": "text", + "content": " mainly reflect the complementary information within multi-modal data. Features " + }, + { + "bbox": [ + 296, + 469, + 530, + 553 + ], + "type": "inline_equation", + "content": "f s_{fus,2}^{i}" + }, + { + "bbox": [ + 296, + 469, + 530, + 553 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 296, + 469, + 530, + 553 + ], + "type": "inline_equation", + "content": "f s_{fus,3}^{i}" + }, + { + "bbox": [ + 296, + 469, + 530, + 553 + ], + "type": "text", + "content": " reflect their interacted information and their differential information, respectively." + } + ] + } + ], + "index": 30 + }, + { + "bbox": [ + 296, + 558, + 530, + 582 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 558, + 530, + 582 + ], + "spans": [ + { + "bbox": [ + 296, + 558, + 530, + 582 + ], + "type": "text", + "content": "After that, " + }, + { + "bbox": [ + 296, + 558, + 530, + 582 + ], + "type": "inline_equation", + "content": "f s_{f u s,1}^{i}, f s_{f u s,2}^{i}" + }, + { + "bbox": [ + 296, + 558, + 530, + 582 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 296, + 558, + 530, + 582 + ], + "type": "inline_equation", + "content": "f s_{f u s,3}^{i}" + }, + { + "bbox": [ + 296, + 558, + 530, + 582 + ], + "type": "text", + "content": " are further combined together by a weighted fusion way, i.e," + } + ] + } + ], + "index": 31 + }, + { + "bbox": [ + 301, + 586, + 530, + 618 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 301, + 586, + 530, + 618 + ], + "spans": [ + { + "bbox": [ + 301, + 586, + 530, + 618 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} w _ {1} ^ {i}, w _ {2} ^ {i}, w _ {3} ^ {i} = \\text {s o f t m a x} (f c (g m p (c a t (f s _ {f u s, 1} ^ {i}, f s _ {f u s, 2} ^ {i}, f s _ {f u s, 3} ^ {i})))) \\\\ f s _ {f u s} ^ {i} = \\left(f s _ {f u s, 1} ^ {i} \\odot w _ {1} ^ {i}\\right) \\oplus \\left(f s _ {f u s, 2} ^ {i} \\odot w _ {2} ^ {i}\\right) \\oplus \\left(f s _ {f u s, 3} ^ {i} \\odot w _ {3} ^ {i}\\right). \\tag {6} \\\\ \\end{array}", + "image_path": "93ec87932d41d2166132a20e3f4c189a070da845c9b05dec4d8fdd274c230c82.jpg" + } + ] + } + ], + "index": 32 + }, + { + "bbox": [ + 296, + 619, + 530, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 619, + 530, + 689 + ], + "spans": [ + { + "bbox": [ + 296, + 619, + 530, + 689 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 296, + 619, + 530, + 689 + ], + "type": "inline_equation", + "content": "gmp(*)" + }, + { + "bbox": [ + 296, + 619, + 530, + 689 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 296, + 619, + 530, + 689 + ], + "type": "inline_equation", + "content": "fc(*)" + }, + { + "bbox": [ + 296, + 619, + 530, + 689 + ], + "type": "text", + "content": " denote the global max pooling layer and the fully connected layers, respectively. " + }, + { + "bbox": [ + 296, + 619, + 530, + 689 + ], + "type": "inline_equation", + "content": "softmax(*)" + }, + { + "bbox": [ + 296, + 619, + 530, + 689 + ], + "type": "text", + "content": " denote the softmax operation. The feature-wise weights " + }, + { + "bbox": [ + 296, + 619, + 530, + 689 + ], + "type": "inline_equation", + "content": "w_1^i, w_2^i, w_3^i" + }, + { + "bbox": [ + 296, + 619, + 530, + 689 + ], + "type": "text", + "content": " reflect the importance of different fused features for the current scenario. " + }, + { + "bbox": [ + 296, + 619, + 530, + 689 + ], + "type": "inline_equation", + "content": "\\odot" + }, + { + "bbox": [ + 296, + 619, + 530, + 689 + ], + "type": "text", + "content": " denotes the broadcasting multiplication operation." + } + ] + } + ], + "index": 33 + }, + { + "bbox": [ + 296, + 693, + 530, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 693, + 530, + 730 + ], + "spans": [ + { + "bbox": [ + 296, + 693, + 530, + 730 + ], + "type": "text", + "content": "With the fused features " + }, + { + "bbox": [ + 296, + 693, + 530, + 730 + ], + "type": "inline_equation", + "content": "\\{ft_{fus}^i | i = 3,4\\}" + }, + { + "bbox": [ + 296, + 693, + 530, + 730 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 296, + 693, + 530, + 730 + ], + "type": "inline_equation", + "content": "\\{fs_{fus}^i | i = 3,4\\}" + }, + { + "bbox": [ + 296, + 693, + 530, + 730 + ], + "type": "text", + "content": " obtained by the teacher model and the student model, respectively, we calculate the fusion distillation loss " + }, + { + "bbox": [ + 296, + 693, + 530, + 730 + ], + "type": "inline_equation", + "content": "L_{fus}" + } + ] + } + ], + "index": 34 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 279, + 746, + 298, + 756 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 279, + 746, + 298, + 756 + ], + "spans": [ + { + "bbox": [ + 279, + 746, + 298, + 756 + ], + "type": "text", + "content": "5408" + } + ] + } + ], + "index": 35 + } + ], + "page_size": [ + 595, + 842 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 106, + 155, + 117 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 106, + 155, + 117 + ], + "spans": [ + { + "bbox": [ + 46, + 106, + 155, + 117 + ], + "type": "text", + "content": "between the fused features:" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 75, + 120, + 279, + 135 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 75, + 120, + 279, + 135 + ], + "spans": [ + { + "bbox": [ + 75, + 120, + 279, + 135 + ], + "type": "interline_equation", + "content": "L _ {f u s} = l \\left(f t _ {f u s} ^ {3}, f s _ {f u s} ^ {3}\\right) + l \\left(f t _ {f u s} ^ {4}, f s _ {f u s} ^ {4}\\right) \\tag {7}", + "image_path": "55341a22df36627e560dd270676a38ca65a58332bbc734a704b76599db908aa9.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 45, + 137, + 279, + 229 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 137, + 279, + 229 + ], + "spans": [ + { + "bbox": [ + 45, + 137, + 279, + 229 + ], + "type": "text", + "content": "What's more, in order to enable the student model to adaptively select a fusion path that is more similar to the teacher model in different scenarios, we introduce an additional penalty " + }, + { + "bbox": [ + 45, + 137, + 279, + 229 + ], + "type": "inline_equation", + "content": "L_{p}" + }, + { + "bbox": [ + 45, + 137, + 279, + 229 + ], + "type": "text", + "content": " for the efficiency of knowledge transformation during training. More specifically, we first select the fusion type with the smallest difference between the initially fused features of the student model and the fused features of the teacher model by," + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 81, + 232, + 279, + 260 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 81, + 232, + 279, + 260 + ], + "spans": [ + { + "bbox": [ + 81, + 232, + 279, + 260 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} L _ {f u s, n} ^ {i} = l \\left(f t _ {f u s} ^ {i}, f s _ {f u s, n} ^ {i}\\right), n = 1, 2, 3 \\tag {8} \\\\ L _ {f u s, \\lambda^ {i}} ^ {i} = \\min (L _ {f u s, 1} ^ {i}, L _ {f u s, 2} ^ {i}, L _ {f u s, 3} ^ {i}), \\\\ \\end{array}", + "image_path": "21c76db4c67b5708cb96ca60e987e8e947b0bf0bd4c479a39d2e01f1e7e1cedd.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 45, + 261, + 279, + 295 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 261, + 279, + 295 + ], + "spans": [ + { + "bbox": [ + 45, + 261, + 279, + 295 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 45, + 261, + 279, + 295 + ], + "type": "inline_equation", + "content": "\\lambda^i = 1" + }, + { + "bbox": [ + 45, + 261, + 279, + 295 + ], + "type": "text", + "content": ", 2 or 3 denotes the selected type of initially fused features according to the fused feature difference between the teacher and student models." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 45, + 297, + 279, + 341 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 297, + 279, + 341 + ], + "spans": [ + { + "bbox": [ + 45, + 297, + 279, + 341 + ], + "type": "text", + "content": "After that, through the adaptive selection part in MPSD, the student model itself will also predict a type of initially fused features that is suitable for the current tracking scene, i.e.," + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 111, + 342, + 279, + 356 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 111, + 342, + 279, + 356 + ], + "spans": [ + { + "bbox": [ + 111, + 342, + 279, + 356 + ], + "type": "interline_equation", + "content": "w _ {\\nu^ {i}} ^ {i} = \\max \\left(w _ {1} ^ {i}, w _ {2} ^ {i}, w _ {3} ^ {i}\\right), \\tag {9}", + "image_path": "df836b3c6e93bf3840472b5275d4dfdd97272f551139fb8c3d30df1200583e73.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 45, + 357, + 279, + 380 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 357, + 279, + 380 + ], + "spans": [ + { + "bbox": [ + 45, + 357, + 279, + 380 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 45, + 357, + 279, + 380 + ], + "type": "inline_equation", + "content": "\\nu^i = 1" + }, + { + "bbox": [ + 45, + 357, + 279, + 380 + ], + "type": "text", + "content": ", 2 or 3 denotes the predicted type of initially fused features from the student model." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 45, + 381, + 279, + 416 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 381, + 279, + 416 + ], + "spans": [ + { + "bbox": [ + 45, + 381, + 279, + 416 + ], + "type": "text", + "content": "With " + }, + { + "bbox": [ + 45, + 381, + 279, + 416 + ], + "type": "inline_equation", + "content": "w_{\\nu^i}^i" + }, + { + "bbox": [ + 45, + 381, + 279, + 416 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 45, + 381, + 279, + 416 + ], + "type": "inline_equation", + "content": "w_{\\lambda^i}^i" + }, + { + "bbox": [ + 45, + 381, + 279, + 416 + ], + "type": "text", + "content": ", we can use a penalty to help the student model choose a fusion path that is more suitable for the current scene under the guidance of the teacher model, i.e.," + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 60, + 420, + 279, + 450 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 60, + 420, + 279, + 450 + ], + "spans": [ + { + "bbox": [ + 60, + 420, + 279, + 450 + ], + "type": "interline_equation", + "content": "L _ {p} = \\sum_ {i = 3} ^ {4} \\max \\left(\\left| L _ {f u s, \\lambda^ {i}} ^ {i} w _ {\\nu^ {i}} ^ {i} - L _ {f u s, \\lambda^ {i}} ^ {i} w _ {\\lambda^ {i}} ^ {i} \\right|, 0\\right). \\tag {10}", + "image_path": "6d506537a754ca12828df154ba81475af3e5084e4e570f7730a1311f5cac1fc3.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 45, + 452, + 279, + 498 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 452, + 279, + 498 + ], + "spans": [ + { + "bbox": [ + 45, + 452, + 279, + 498 + ], + "type": "text", + "content": "By minimizing " + }, + { + "bbox": [ + 45, + 452, + 279, + 498 + ], + "type": "inline_equation", + "content": "L_{p}" + }, + { + "bbox": [ + 45, + 452, + 279, + 498 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 45, + 452, + 279, + 498 + ], + "type": "inline_equation", + "content": "w_{\\nu^{i}}^{i}" + }, + { + "bbox": [ + 45, + 452, + 279, + 498 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 45, + 452, + 279, + 498 + ], + "type": "inline_equation", + "content": "w_{\\lambda^i}^i" + }, + { + "bbox": [ + 45, + 452, + 279, + 498 + ], + "type": "text", + "content": " will tend to be consistent, which can enable the student model to adaptively select the fusion path according to the teacher model to improve the exploration ability of complementary information." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 45, + 499, + 279, + 522 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 499, + 279, + 522 + ], + "spans": [ + { + "bbox": [ + 45, + 499, + 279, + 522 + ], + "type": "text", + "content": "On top of that, the overall distill loss in the multi-modal fusion stage can be obtained by:" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 116, + 525, + 279, + 538 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 116, + 525, + 279, + 538 + ], + "spans": [ + { + "bbox": [ + 116, + 525, + 279, + 538 + ], + "type": "interline_equation", + "content": "L _ {M P S D} = L _ {f u s} + L _ {p}. \\tag {11}", + "image_path": "504d0315eb0675f41e4063139d0a84a77406b889a7d80502f494bef5ebb69c1b.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 46, + 542, + 227, + 554 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 542, + 227, + 554 + ], + "spans": [ + { + "bbox": [ + 46, + 542, + 227, + 554 + ], + "type": "text", + "content": "3.5. Hard-focused Response Distillation" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 45, + 560, + 279, + 606 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 560, + 279, + 606 + ], + "spans": [ + { + "bbox": [ + 45, + 560, + 279, + 606 + ], + "type": "text", + "content": "To alleviate the data imbalance problem, we propose the Hard-focused Response Distillation (HFRD) module to instruct the student to focus on distinguishing targets from hard negative samples." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 45, + 606, + 279, + 687 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 606, + 279, + 687 + ], + "spans": [ + { + "bbox": [ + 45, + 606, + 279, + 687 + ], + "type": "text", + "content": "First, we obtain the response map " + }, + { + "bbox": [ + 45, + 606, + 279, + 687 + ], + "type": "inline_equation", + "content": "R_{t} \\in \\mathbb{R}^{H \\times W}" + }, + { + "bbox": [ + 45, + 606, + 279, + 687 + ], + "type": "text", + "content": " from the teacher model. Then, in order to prevent the teacher model from failing to have high responses in the target area within some scenes, we use the Gaussian-shaped mask " + }, + { + "bbox": [ + 45, + 606, + 279, + 687 + ], + "type": "inline_equation", + "content": "R_{g} \\in \\mathbb{R}^{H \\times W}" + }, + { + "bbox": [ + 45, + 606, + 279, + 687 + ], + "type": "text", + "content": " constructed by ground-truth bounding box as in [1] to correct the response map of the teacher model " + }, + { + "bbox": [ + 45, + 606, + 279, + 687 + ], + "type": "inline_equation", + "content": "R_{t}" + }, + { + "bbox": [ + 45, + 606, + 279, + 687 + ], + "type": "text", + "content": " as follows:" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 46, + 691, + 279, + 730 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 691, + 279, + 730 + ], + "spans": [ + { + "bbox": [ + 46, + 691, + 279, + 730 + ], + "type": "interline_equation", + "content": "R _ {c} (i, j) = \\left\\{ \\begin{array}{c} R _ {t} (i, j) + R _ {g} (i, j), i f \\left(R _ {t} (i, j) + R _ {g} (i, j)\\right) < 1, \\\\ R _ {g} (i, j), i f \\left(R _ {t} (i, j) + R _ {g} (i, j)\\right) \\geq 1. \\end{array} \\right. \\tag {12}", + "image_path": "9ccc131a94abffdac14243fa82c053ae1d627ca2684a0551d88bc658e9ea8781.jpg" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 297, + 106, + 530, + 153 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 106, + 530, + 153 + ], + "spans": [ + { + "bbox": [ + 297, + 106, + 530, + 153 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 297, + 106, + 530, + 153 + ], + "type": "inline_equation", + "content": "i,j" + }, + { + "bbox": [ + 297, + 106, + 530, + 153 + ], + "type": "text", + "content": " are the horizontal and vertical coordinates of the response map, respectively. The corrected mask " + }, + { + "bbox": [ + 297, + 106, + 530, + 153 + ], + "type": "inline_equation", + "content": "R_{c}\\in \\mathbb{R}^{H\\times W}" + }, + { + "bbox": [ + 297, + 106, + 530, + 153 + ], + "type": "text", + "content": " has higher response values not only on the positive samples but also on the hard negative samples." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 296, + 154, + 530, + 223 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 154, + 530, + 223 + ], + "spans": [ + { + "bbox": [ + 296, + 154, + 530, + 223 + ], + "type": "text", + "content": "In the training process of the student model, with the assistance of the corrected mask " + }, + { + "bbox": [ + 296, + 154, + 530, + 223 + ], + "type": "inline_equation", + "content": "R_{c}" + }, + { + "bbox": [ + 296, + 154, + 530, + 223 + ], + "type": "text", + "content": " from the teacher model, the student model can focus more on distinguishing target from hard negative samples by a proposed Hard-focused Response Distillation loss " + }, + { + "bbox": [ + 296, + 154, + 530, + 223 + ], + "type": "inline_equation", + "content": "L_{HFRD}" + }, + { + "bbox": [ + 296, + 154, + 530, + 223 + ], + "type": "text", + "content": " to alleviate the data imbalance problem:" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 357, + 227, + 530, + 239 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 357, + 227, + 530, + 239 + ], + "spans": [ + { + "bbox": [ + 357, + 227, + 530, + 239 + ], + "type": "interline_equation", + "content": "L _ {H F R D} = r \\left(R _ {s} * R _ {c}, R _ {g}\\right), \\tag {13}", + "image_path": "4217c184e41d8381ee800af8302febda040fa7073b700350030768f1e4ec28c0.jpg" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 297, + 241, + 472, + 253 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 241, + 472, + 253 + ], + "spans": [ + { + "bbox": [ + 297, + 241, + 472, + 253 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 297, + 241, + 472, + 253 + ], + "type": "inline_equation", + "content": "r(*)" + }, + { + "bbox": [ + 297, + 241, + 472, + 253 + ], + "type": "text", + "content": " denotes the " + }, + { + "bbox": [ + 297, + 241, + 472, + 253 + ], + "type": "inline_equation", + "content": "L_{2}" + }, + { + "bbox": [ + 297, + 241, + 472, + 253 + ], + "type": "text", + "content": " loss function [5]." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 297, + 265, + 373, + 276 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 265, + 373, + 276 + ], + "spans": [ + { + "bbox": [ + 297, + 265, + 373, + 276 + ], + "type": "text", + "content": "3.6. Overall loss" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 297, + 284, + 530, + 319 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 284, + 530, + 319 + ], + "spans": [ + { + "bbox": [ + 297, + 284, + 530, + 319 + ], + "type": "text", + "content": "The overall distillation loss " + }, + { + "bbox": [ + 297, + 284, + 530, + 319 + ], + "type": "inline_equation", + "content": "L_{distill}" + }, + { + "bbox": [ + 297, + 284, + 530, + 319 + ], + "type": "text", + "content": " is the sum of " + }, + { + "bbox": [ + 297, + 284, + 530, + 319 + ], + "type": "inline_equation", + "content": "L_{SCFD}" + }, + { + "bbox": [ + 297, + 284, + 530, + 319 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 297, + 284, + 530, + 319 + ], + "type": "inline_equation", + "content": "L_{MPSD}" + }, + { + "bbox": [ + 297, + 284, + 530, + 319 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 297, + 284, + 530, + 319 + ], + "type": "inline_equation", + "content": "L_{HFRD}" + }, + { + "bbox": [ + 297, + 284, + 530, + 319 + ], + "type": "text", + "content": ". We train the student model with the total loss as follows:" + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 298, + 322, + 530, + 345 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 298, + 322, + 530, + 345 + ], + "spans": [ + { + "bbox": [ + 298, + 322, + 530, + 345 + ], + "type": "interline_equation", + "content": "L _ {\\text {d i s t i l l}} = \\alpha \\left(L _ {S C F D} + L _ {M P S D}\\right) + \\beta L _ {H F R D} + L _ {\\text {o r i g i n a l}}, \\tag {14}", + "image_path": "89aa89bbb9a603efa7a0291f31dce92abc43a4057002f295834f03f6a111d2e7.jpg" + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 296, + 346, + 530, + 404 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 346, + 530, + 404 + ], + "spans": [ + { + "bbox": [ + 296, + 346, + 530, + 404 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 296, + 346, + 530, + 404 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 296, + 346, + 530, + 404 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 296, + 346, + 530, + 404 + ], + "type": "inline_equation", + "content": "\\beta" + }, + { + "bbox": [ + 296, + 346, + 530, + 404 + ], + "type": "text", + "content": " are hyper-parameters to balance the distillation loss. " + }, + { + "bbox": [ + 296, + 346, + 530, + 404 + ], + "type": "inline_equation", + "content": "L_{\\text{original}}" + }, + { + "bbox": [ + 296, + 346, + 530, + 404 + ], + "type": "text", + "content": " is the original loss for tracking as in [35]. The distillation loss " + }, + { + "bbox": [ + 296, + 346, + 530, + 404 + ], + "type": "inline_equation", + "content": "L_{SCFD}" + }, + { + "bbox": [ + 296, + 346, + 530, + 404 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 296, + 346, + 530, + 404 + ], + "type": "inline_equation", + "content": "L_{MPSD}" + }, + { + "bbox": [ + 296, + 346, + 530, + 404 + ], + "type": "text", + "content": " are just calculated on feature maps, which can be easily applied to different tackers or other multi-modal vision tasks." + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 297, + 419, + 376, + 432 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 419, + 376, + 432 + ], + "spans": [ + { + "bbox": [ + 297, + 419, + 376, + 432 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 296, + 440, + 530, + 474 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 440, + 530, + 474 + ], + "spans": [ + { + "bbox": [ + 296, + 440, + 530, + 474 + ], + "type": "text", + "content": "Our tracking approach is implemented in Python based on PyTorch. For inference, we test our tracker on a single Nvidia RTX 1080Ti GPU." + } + ] + } + ], + "index": 26 + }, + { + "bbox": [ + 297, + 487, + 424, + 499 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 487, + 424, + 499 + ], + "spans": [ + { + "bbox": [ + 297, + 487, + 424, + 499 + ], + "type": "text", + "content": "4.1. Implementation details" + } + ] + } + ], + "index": 27 + }, + { + "bbox": [ + 296, + 506, + 530, + 623 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 506, + 530, + 623 + ], + "spans": [ + { + "bbox": [ + 296, + 506, + 530, + 623 + ], + "type": "text", + "content": "Training Details. We adopt the training dataset in LasHeR [14], which contains 979 pairs of RGB-T videos, to train the teacher model and student model, respectively. The proposed CMD framework includes two training stages. In the first stage, we train the teacher model as in MFNet [35] and fix its weights after training. In the second stage, the optimization of the student model is jointly supervised by the original tracking loss " + }, + { + "bbox": [ + 296, + 506, + 530, + 623 + ], + "type": "inline_equation", + "content": "L_{\\text{original}}" + }, + { + "bbox": [ + 296, + 506, + 530, + 623 + ], + "type": "text", + "content": " as well as the knowledge transfer loss " + }, + { + "bbox": [ + 296, + 506, + 530, + 623 + ], + "type": "inline_equation", + "content": "L_{\\text{SCFD}}" + }, + { + "bbox": [ + 296, + 506, + 530, + 623 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 296, + 506, + 530, + 623 + ], + "type": "inline_equation", + "content": "L_{\\text{MPSD}}" + }, + { + "bbox": [ + 296, + 506, + 530, + 623 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 296, + 506, + 530, + 623 + ], + "type": "inline_equation", + "content": "L_{\\text{HFRD}}" + }, + { + "bbox": [ + 296, + 506, + 530, + 623 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 296, + 506, + 530, + 623 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 296, + 506, + 530, + 623 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 296, + 506, + 530, + 623 + ], + "type": "inline_equation", + "content": "\\beta" + }, + { + "bbox": [ + 296, + 506, + 530, + 623 + ], + "type": "text", + "content": " in Eq. 14 are experimentally set to 0.001 and 100, respectively." + } + ] + } + ], + "index": 28 + }, + { + "bbox": [ + 296, + 624, + 530, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 624, + 530, + 730 + ], + "spans": [ + { + "bbox": [ + 296, + 624, + 530, + 730 + ], + "type": "text", + "content": "Online Tracking. In the tracking phase, our method is similar to DiMP [1]. We split tracking into classification and regression subtasks. For classification subtask, we employ data augmentation [1] on the first frame to construct an initial set, which contains 15 initial training samples for initial classification model training. Then the initial classification model is optimized using the augmented training set during tracking. For regression subtask, the same settings as those in [1] are employed." + } + ] + } + ], + "index": 29 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 279, + 746, + 298, + 756 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 279, + 746, + 298, + 756 + ], + "spans": [ + { + "bbox": [ + 279, + 746, + 298, + 756 + ], + "type": "text", + "content": "5409" + } + ] + } + ], + "index": 30 + } + ], + "page_size": [ + 595, + 842 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 60, + 118, + 265, + 176 + ], + "blocks": [ + { + "bbox": [ + 76, + 105, + 248, + 116 + ], + "lines": [ + { + "bbox": [ + 76, + 105, + 248, + 116 + ], + "spans": [ + { + "bbox": [ + 76, + 105, + 248, + 116 + ], + "type": "text", + "content": "Table 1. Ablation study of different components." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 60, + 118, + 265, + 176 + ], + "lines": [ + { + "bbox": [ + 60, + 118, + 265, + 176 + ], + "spans": [ + { + "bbox": [ + 60, + 118, + 265, + 176 + ], + "type": "table", + "html": "
StudentSCFDMPSDHFRDPR/SRParams(M)FPS
✓78.1/56.019.831
✓✓80.3/57.419.831
✓✓✓82.2/58.319.930
✓✓✓✓82.4/58.419.930
", + "image_path": "80a6918e9aa4c2bc29bca225dd59edd142009c97ac7cdad6dc85da0da761b1b6.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 181, + 213, + 191 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 181, + 213, + 191 + ], + "spans": [ + { + "bbox": [ + 46, + 181, + 213, + 191 + ], + "type": "text", + "content": "4.2. Evaluation datasets and metrics" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 45, + 199, + 279, + 373 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 199, + 279, + 373 + ], + "spans": [ + { + "bbox": [ + 45, + 199, + 279, + 373 + ], + "type": "text", + "content": "We evaluate our method on three large-scale benchmark datasets, i.e., GTOT [10], RGBT234 [11] and LasHeR [14]. GTOT is the first standard dataset for RGB-T tracking. It contains 50 RGB-T video sequences annotated with seven challenging attributes. RGBT234 [11] contains 234 pairs of RGB-T videos and 12 annotated attributes. LasHeR is currently the largest RGB-T tracking dataset, which consists of 1244 RGB-T videos with more than 730K frame pairs in total. Among them, 245 videos are used as the testing set, and 979 videos are used as the training set. As in [17], we utilize two widely used metrics, i.e., precision rate (PR) and success rate (SR), to evaluate the tracking performance on GTOT and RGBT234. As in [14], we adopt precision rate (PR), normalized precision rate (NPR) and success rate (SR) to evaluate different trackers on LasHeR." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 383, + 230, + 395 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 383, + 230, + 395 + ], + "spans": [ + { + "bbox": [ + 46, + 383, + 230, + 395 + ], + "type": "text", + "content": "4.3. Ablation Experiments and Analyses" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 402, + 279, + 436 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 402, + 279, + 436 + ], + "spans": [ + { + "bbox": [ + 46, + 402, + 279, + 436 + ], + "type": "text", + "content": "We conduct some ablation studies on RGBT234 [11] to discuss the impacts of different components in our CMD framework." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 45, + 438, + 279, + 600 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 438, + 279, + 600 + ], + "spans": [ + { + "bbox": [ + 45, + 438, + 279, + 600 + ], + "type": "text", + "content": "Ablation experiments for each module. To investigate the impact of each component in our proposed CMD, several versions of our proposed method are provided for comparisons. Specifically, 'Student' denotes the model that without any knowledge transformation. Here, the proposed SCFD, MPSD and HFRD are employed in the unimodal feature extraction stage, multi-modal feature fusion stage and target state estimation stage, respectively. The quantitative results of these models are shown in Table 1. It can be seen that SCFD, MPSD and HFRD can all improve the performance of the student model. This verifies that each proposed component in CMD can effectively inherit the knowledge learnt from a powerful teacher models to a student model without obvious loss." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 45, + 602, + 279, + 729 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 602, + 279, + 729 + ], + "spans": [ + { + "bbox": [ + 45, + 602, + 279, + 729 + ], + "type": "text", + "content": "Effectiveness of the proposed SCFD module. To further verify the effectiveness of the proposed SCFD module, several variants are also compared with our proposed SCFD module. Here, in the unimodal feature extraction stage, 'AFD', 'SED' and 'CED' denote initially fusing the unimodal features of each layer in the teacher model by using the simple element-wise addition operation, the designed SEM module and the designed CEM module, respectively, and such initially fused features are then employed to guide the student model for single-stream structure learning. As well, ABF modules [3] are employed in all of these vari-" + } + ] + } + ], + "index": 7 + }, + { + "type": "table", + "bbox": [ + 311, + 118, + 517, + 184 + ], + "blocks": [ + { + "bbox": [ + 315, + 105, + 511, + 116 + ], + "lines": [ + { + "bbox": [ + 315, + 105, + 511, + 116 + ], + "spans": [ + { + "bbox": [ + 315, + 105, + 511, + 116 + ], + "type": "text", + "content": "Table 2. Ablation study of the proposed SCFD module." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 311, + 118, + 517, + 184 + ], + "lines": [ + { + "bbox": [ + 311, + 118, + 517, + 184 + ], + "spans": [ + { + "bbox": [ + 311, + 118, + 517, + 184 + ], + "type": "table", + "html": "
StudentAFDSEDCEDSCFDPR/SRParams(M)FPS
✓78.1/56.019.831
✓✓78.7/56.619.831
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✓✓79.6/56.619.831
✓✓80.3/57.419.831
", + "image_path": "1511a550c55ea3a1eca97fcd7b7aeb965ba40de899d662c5dbaaa30258b14b44.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "table_body" + } + ], + "index": 9 + }, + { + "type": "table", + "bbox": [ + 306, + 202, + 522, + 266 + ], + "blocks": [ + { + "bbox": [ + 315, + 189, + 511, + 200 + ], + "lines": [ + { + "bbox": [ + 315, + 189, + 511, + 200 + ], + "spans": [ + { + "bbox": [ + 315, + 189, + 511, + 200 + ], + "type": "text", + "content": "Table 3. Ablation study of the proposed MPSD module." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 306, + 202, + 522, + 266 + ], + "lines": [ + { + "bbox": [ + 306, + 202, + 522, + 266 + ], + "spans": [ + { + "bbox": [ + 306, + 202, + 522, + 266 + ], + "type": "table", + "html": "
Student+SCFDSAFCAFTFMPSDPR/SRParams(M)FPS
✓80.3/57.419.831
✓✓81.9/58.019.930
✓✓81.1/57.619.930
✓✓82.6/58.625.923
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", + "image_path": "716f6d0d8be2980c85cf8a184f1d6559252a1e9761522aec0ed2f552e40c72e5.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "table_body" + } + ], + "index": 11 + }, + { + "bbox": [ + 297, + 271, + 530, + 304 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 271, + 530, + 304 + ], + "spans": [ + { + "bbox": [ + 297, + 271, + 530, + 304 + ], + "type": "text", + "content": "ants. As shown in Table 2, the proposed SCFD can better exploit the modality-common and modality-specific information from the teacher model." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 297, + 306, + 530, + 480 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 306, + 530, + 480 + ], + "spans": [ + { + "bbox": [ + 297, + 306, + 530, + 480 + ], + "type": "text", + "content": "Effectiveness of the proposed MPSD module. As shown in Table 3, several versions of our proposed MPSD module are also conducted to verify its effectiveness. 'SAF' denotes a spatial-wise attention based fusion module. 'CAF' denotes a channel-wise attention based module. 'TF' denotes adopting the same fusion strategy as that in the teacher model [35]. In particular, each layer adopts the same fusion strategy in the student model. It can be seen that the exploitation of the multi-path fusion strategy can well improve the performance of the student model. In addition, the performance gap between 'Student-MPSD' and 'Student-TF' is much smaller, which indicates that our proposed MPSD module can better mimic the fused features in the teacher model to compensate for the performance penalty from simple fusion operations." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 297, + 481, + 529, + 655 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 481, + 529, + 655 + ], + "spans": [ + { + "bbox": [ + 297, + 481, + 529, + 655 + ], + "type": "text", + "content": "Teacher-Student knowledge distillation experiments. Table 4 shows the performance of using some other knowledge distillation methods in the feature extraction and feature fusion stages for comparisons, including KD [8], Fit-Nets [21], ReviewKD [3] and MD [29]. It is observed from Table 4 that the proposed distillation strategy performs the best. Due to the absence of cross-modal interactions, these existing knowledge distillation methods usually achieve some modest performance gains. In addition, we notice that the student model with a single-stream feature extractor performs obviously well than the student model with a two-stream feature extractor after knowledge distillation. This may be due to the fact that the single-stream network can narrow the modality difference to a certain extent and better acquire the knowledge from the teacher model." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 297, + 665, + 486, + 676 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 665, + 486, + 676 + ], + "spans": [ + { + "bbox": [ + 297, + 665, + 486, + 676 + ], + "type": "text", + "content": "4.4. Comparison with the state-of-the-art" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 297, + 683, + 530, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 683, + 530, + 730 + ], + "spans": [ + { + "bbox": [ + 297, + 683, + 530, + 730 + ], + "type": "text", + "content": "To evaluate the superiority of our proposed method, we compare our method with some existing state-of-the-art RGB-T trackers, including MANet [17], DAFNet [6], DAPNet [39], TODA [28], MACNet [30], CAT [12], CEDiMP" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 279, + 746, + 298, + 756 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 279, + 746, + 298, + 756 + ], + "spans": [ + { + "bbox": [ + 279, + 746, + 298, + 756 + ], + "type": "text", + "content": "5410" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 595, + 842 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 48, + 127, + 277, + 175 + ], + "blocks": [ + { + "bbox": [ + 46, + 105, + 278, + 124 + ], + "lines": [ + { + "bbox": [ + 46, + 105, + 278, + 124 + ], + "spans": [ + { + "bbox": [ + 46, + 105, + 278, + 124 + ], + "type": "text", + "content": "Table 4. Ablation study of different knowledge distillation experiments." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 48, + 127, + 277, + 175 + ], + "lines": [ + { + "bbox": [ + 48, + 127, + 277, + 175 + ], + "spans": [ + { + "bbox": [ + 48, + 127, + 277, + 175 + ], + "type": "table", + "html": "
MethodKD [8]FitNets [21]ReviewKD [3]ReviewKD [3]MD [29]Ours
Backbone2 Res182 Res182 Res181 Res181 Res181 Res18
PR/SR78.4/56.279.3/56.079.9/56.580.5/56.380.0/55.482.4/58.4
FPS272727303030
Params31.631.631.619.919.919.9
", + "image_path": "671dad26f739987730771b477662fbb7e133fcc6e4a2552c94ca82962cee8819.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "type": "table", + "bbox": [ + 48, + 220, + 277, + 410 + ], + "blocks": [ + { + "bbox": [ + 46, + 185, + 278, + 216 + ], + "lines": [ + { + "bbox": [ + 46, + 185, + 278, + 216 + ], + "spans": [ + { + "bbox": [ + 46, + 185, + 278, + 216 + ], + "type": "text", + "content": "Table 5. Quantitative comparisons of our method with some state-of-the-arts methods on benchmark datasets. Higher values indicate better performance." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 48, + 220, + 277, + 410 + ], + "lines": [ + { + "bbox": [ + 48, + 220, + 277, + 410 + ], + "spans": [ + { + "bbox": [ + 48, + 220, + 277, + 410 + ], + "type": "table", + "html": "
MethodsYearRGBT234 [11]GTOT [10]LasHeR [14]FPSParams
PR ↑SR ↑PR ↑SR ↑PR ↑NPR ↑SR ↑
DAPNet [39]201976.653.788.270.743.138.431.41-
MANet [17]201977.753.989.472.445.740.833.017.28M
DAFNet [6]201979.654.489.171.644.939.031.1145.50M
mfDiMP [31]201978.655.583.669.744.739.534.422175.82M
TODA [28]201978.754.584.367.7---1-
MACNet [30]202079.055.488.071.448.342.335.2114.86M
CAT [12]202080.456.188.971.745.139.831.7--
FANet [40]202178.755.389.172.844.238.430.91238.44M
SiamCDA [36]202176.056.987.773.2---24107.90M
JMMAC [32]202179.057.390.273.2-----
MANet++ [33]202180.055.488.270.746.740.831.7157.38M
ADRNet [33]202180.957.190.473.9---1568.50M
CBPNet [27]202279.454.188.571.6---3-
TFNet [41]202280.656.088.672.9-----
MFGNet [25]202278.353.588.970.7---38.09M
M5LNet [23]202279.554.289.671.0---9-
HMFT [34]202278.856.891.274.9----127.84M
APFNet [26]202282.757.990.573.950.0-36.2-15.01M
MANet* [17]201978.655.590.072.5---17.28M
DAFNet* [6]201980.054.986.070.048.042.834.5145.50M
mfDiMP* [31]201982.458.387.773.158.354.245.622175.82M
FANet* [40]202179.453.990.172.148.242.534.31238.44M
Teacher [35]202284.460.190.773.559.755.446.71881.01M
Student-Origin202278.156.088.572.355.450.342.33019.90M
Student-Distill202282.458.489.273.459.054.646.43019.90M
", + "image_path": "dab941b98f8b67f539ec0154d648990eda6203d121b3f88d2a1491ee36ce8ba8.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 45, + 415, + 278, + 507 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 415, + 278, + 507 + ], + "spans": [ + { + "bbox": [ + 45, + 415, + 278, + 507 + ], + "type": "text", + "content": "[38], SiamCDA [36], mfDiMP [31], FANet [40], CBPNet [27], MANet++ [33], JMMAC [32], ADRNet [33], TFNet [41], MFGNet [25], M5LNet [23], HMFT [34], APFNet [26] and MFNet [35], on three challenging datasets. Considering that existing methods usually employ different training datasets, we use the LasHeR training set to retrain some of these algorithms for fair comparisons, including FANet*, DAFNet*, MANet* and mfDiMP*." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 45, + 508, + 278, + 682 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 508, + 278, + 682 + ], + "spans": [ + { + "bbox": [ + 45, + 508, + 278, + 682 + ], + "type": "text", + "content": "On RGBT234. From Table 5, we observe that, in addition to the teacher model, our method achieves the best results with " + }, + { + "bbox": [ + 45, + 508, + 278, + 682 + ], + "type": "inline_equation", + "content": "82.4\\% / 58.4\\%" + }, + { + "bbox": [ + 45, + 508, + 278, + 682 + ], + "type": "text", + "content": " in PR/SR. In particular, our tracker achieves " + }, + { + "bbox": [ + 45, + 508, + 278, + 682 + ], + "type": "inline_equation", + "content": "3.0\\% / 4.5\\%" + }, + { + "bbox": [ + 45, + 508, + 278, + 682 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 45, + 508, + 278, + 682 + ], + "type": "inline_equation", + "content": "3.8\\% / 2.9\\%" + }, + { + "bbox": [ + 45, + 508, + 278, + 682 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 45, + 508, + 278, + 682 + ], + "type": "inline_equation", + "content": "2.4\\% / 3.6\\%" + }, + { + "bbox": [ + 45, + 508, + 278, + 682 + ], + "type": "text", + "content": " improvements against FANet* [40], MANet* [17] and DAFNet* [6] in PR/SR, respectively. We should note that some MDNet [18] based trackers [6,17,33] employ merely three convolutional layers for unimodal feature extraction, thus have fewer parameters in the unimodal feature extraction stage with a two-stream structure (e.g., 3.6M in [30, 40]). However, in the multi-modal feature fusion stage, these methods' parameters are significantly higher than those of the proposed MPSD module. Meanwhile, due to the complex updating strategy in MDNet, the above methods cannot meet the needs of real-time operation." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 45, + 683, + 278, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 683, + 278, + 730 + ], + "spans": [ + { + "bbox": [ + 45, + 683, + 278, + 730 + ], + "type": "text", + "content": "On GTOT. From Table 5, we can see that our method obtains competitive performance on GTOT dataset [10] with " + }, + { + "bbox": [ + 45, + 683, + 278, + 730 + ], + "type": "inline_equation", + "content": "73.4\\%" + }, + { + "bbox": [ + 45, + 683, + 278, + 730 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 45, + 683, + 278, + 730 + ], + "type": "inline_equation", + "content": "89.2\\%" + }, + { + "bbox": [ + 45, + 683, + 278, + 730 + ], + "type": "text", + "content": " in success and precision scores, respectively. Compared with the teacher model, our student" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 296, + 106, + 530, + 152 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 106, + 530, + 152 + ], + "spans": [ + { + "bbox": [ + 296, + 106, + 530, + 152 + ], + "type": "text", + "content": "model achieves comparable performance but with a " + }, + { + "bbox": [ + 296, + 106, + 530, + 152 + ], + "type": "inline_equation", + "content": "75\\%" + }, + { + "bbox": [ + 296, + 106, + 530, + 152 + ], + "type": "text", + "content": " reduction in parameter sizes. Compared with the original student model, our algorithm achieves " + }, + { + "bbox": [ + 296, + 106, + 530, + 152 + ], + "type": "inline_equation", + "content": "1.1\\%" + }, + { + "bbox": [ + 296, + 106, + 530, + 152 + ], + "type": "text", + "content": " improvements in success and " + }, + { + "bbox": [ + 296, + 106, + 530, + 152 + ], + "type": "inline_equation", + "content": "0.7\\%" + }, + { + "bbox": [ + 296, + 106, + 530, + 152 + ], + "type": "text", + "content": " improvements in precision." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 296, + 154, + 530, + 318 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 154, + 530, + 318 + ], + "spans": [ + { + "bbox": [ + 296, + 154, + 530, + 318 + ], + "type": "text", + "content": "On LasHeR. LasHeR [14] is captured from a number of scenes and categories and is highly diverse. A tracker restrained on this dataset usually achieves some improvements. From Table 5, we can also see that, in addition to the teacher model, our tracker still performs the best in terms of all the three metrics with significant performance superiorities on LasHeR. In particular, our tracker achieves " + }, + { + "bbox": [ + 296, + 154, + 530, + 318 + ], + "type": "inline_equation", + "content": "11.0\\% / 11.9\\%" + }, + { + "bbox": [ + 296, + 154, + 530, + 318 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 296, + 154, + 530, + 318 + ], + "type": "inline_equation", + "content": "10.8\\% / 12.1\\%" + }, + { + "bbox": [ + 296, + 154, + 530, + 318 + ], + "type": "text", + "content": " improvements against DAFNet* [6] and FANet* [40], which are based on MDNet [18]. Compared with mfDiMP* [31], which is based on DiMP [1] and employs two ResNet50 [7] for feature extraction, our PR/SR is " + }, + { + "bbox": [ + 296, + 154, + 530, + 318 + ], + "type": "inline_equation", + "content": "0.7\\% / 0.8\\%" + }, + { + "bbox": [ + 296, + 154, + 530, + 318 + ], + "type": "text", + "content": " higher than it. This demonstrates that our proposed method can effectively reduce the performance loss caused by parameter reduction." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 297, + 333, + 367, + 345 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 333, + 367, + 345 + ], + "spans": [ + { + "bbox": [ + 297, + 333, + 367, + 345 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 296, + 354, + 530, + 621 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 354, + 530, + 621 + ], + "spans": [ + { + "bbox": [ + 296, + 354, + 530, + 621 + ], + "type": "text", + "content": "In this paper, a novel teacher-student knowledge distillation training framework is proposed to reduce the performance gap between a powerful teacher model and a compact student model. Specifically, this framework distills the knowledge from a deep two-stream network with complex multi-modal feature fusion modules to a single-stream network with efficient feature fusion modules. By virtue of the proposed SCFD module, the modality-common information as well as the modality-specific information can be transformed from a two-stream network to a single-stream network in the unimodal feature extraction stage, thus enhancing the representations of unimodal features. Besides, by employing the proposed MPSD module, the student model can adaptively combine multiple fused features generated by various simple fusion strategies to explore complementary information from multi-modal data more thoroughly. In addition, an HFRD module is proposed to improve the student model's discriminative ability against the distractors by alleviating the problem of data imbalance in the target state estimation stage. Experimental results show that our approach helps a student model achieve the state-of-the-art performance while reducing the number of parameters and computational complexity dramatically." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 296, + 623, + 530, + 681 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 623, + 530, + 681 + ], + "spans": [ + { + "bbox": [ + 296, + 623, + 530, + 681 + ], + "type": "text", + "content": "Limitation: The current method dedicated to reducing computational complexity at the stages of unimodal feature extraction and multi-modal feature fusion, but it paid ZERO effort to improve the efficiency of target stage estimation, which is our future work." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 296, + 682, + 530, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 682, + 530, + 730 + ], + "spans": [ + { + "bbox": [ + 296, + 682, + 530, + 730 + ], + "type": "text", + "content": "Acknowledgement: This work is supported by the National Natural Science Foundation of China under Grant No. 61773301. 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IEEE Transactions on Circuits and Systems for Video Technology, 32(2):579-592, 2021. 8" + } + ] + } + ], + "index": 12 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 279, + 746, + 298, + 756 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 279, + 746, + 298, + 756 + ], + "spans": [ + { + "bbox": [ + 279, + 746, + 298, + 756 + ], + "type": "text", + "content": "5413" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 595, + 842 + ], + "page_idx": 9 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Efficient Robust Principal Component Analysis via Block Krylov Iteration and CUR Decomposition/07ab4d04-cd27-49d8-a510-e7e724ff7dc1_content_list.json b/2023/Efficient Robust Principal Component Analysis via Block Krylov Iteration and CUR Decomposition/07ab4d04-cd27-49d8-a510-e7e724ff7dc1_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..0851b805a446b5c7e44306e266fc65a9f29212da --- /dev/null +++ b/2023/Efficient Robust Principal Component Analysis via Block Krylov Iteration and CUR Decomposition/07ab4d04-cd27-49d8-a510-e7e724ff7dc1_content_list.json @@ -0,0 +1,2590 @@ +[ + { + "type": "text", + "text": "Efficient Robust Principal Component Analysis via Block Krylov Iteration and CUR Decomposition", + "text_level": 1, + "bbox": [ + 88, + 128, + 880, + 176 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Shun Fang $^{1,2}$ Zhengqin Xu $^{3}$ Shiqian Wu $^{1,2,4*}$ Shoulie Xie $^{5}$", + "bbox": [ + 241, + 202, + 756, + 220 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "$^{1}$ School of Information Science and Engineering, Wuhan University of Science and Technology, China \n $^{2}$ Institute of Robotics and Intelligent Systems, Wuhan University of Science and Technology, China \n $^{3}$ MoE Key Lab of Artificial Intelligence, AI Institute, Shanghai Jiao Tong University, China \n $^{4}$ Hubei Province Key Laboratory of Intelligent Information Processing and Real-Time Industrial Systems \n $^{5}$ Signal Processing, RF & Optical Dept. Institute for Infocomm Research A*STAR, Singapore", + "bbox": [ + 93, + 220, + 913, + 308 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "fangshun97@wust.edu.cn, fate311@sjtu.edu.cn, shiqian.wu@wust.edu.cn, slxie@i2r.a-star.edu.sg", + "bbox": [ + 89, + 311, + 906, + 325 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 361, + 313, + 378 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Robust principal component analysis (RPCA) is widely studied in computer vision. Recently an adaptive rank estimate based RPCA has achieved top performance in low-level vision tasks without the prior rank, but both the rank estimate and RPCA optimization algorithm involve singular value decomposition, which requires extremely huge computational resource for large-scale matrices. To address these issues, an efficient RPCA (eRPCA) algorithm is proposed based on block Krylov iteration and CUR decomposition in this paper. Specifically, the Krylov iteration method is employed to approximate the eigenvalue decomposition in the rank estimation, which requires $O(ndrq + n(rq)^2)$ for an $(n \\times d)$ input matrix, in which $q$ is a parameter with a small value, $r$ is the target rank. Based on the estimated rank, CUR decomposition is adopted to replace SVD in updating low-rank matrix components, whose complexity reduces from $O(rnd)$ to $O(r^2 n)$ per iteration. Experimental results verify the efficiency and effectiveness of the proposed eRPCA over the state-of-the-art methods in various low-level vision applications.", + "bbox": [ + 75, + 393, + 473, + 698 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 729, + 209, + 744 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Robust principal component analysis (RPCA) aims to recover a low-rank matrix $\\mathbf{L}$ and a sparse matrix $\\mathbf{S}$ from the corrupted observation matrix $\\mathbf{D} \\in \\mathbb{R}^{n \\times d}$ : $\\mathbf{D} = \\mathbf{L} + \\mathbf{S}$ . The RPCA can be formulated as the following optimization problem [1]:", + "bbox": [ + 75, + 756, + 468, + 834 + ], + "page_idx": 0 + }, + { + "type": "equation", + "text": "\n$$\n\\min _ {\\boldsymbol {L}, \\boldsymbol {S}} \\operatorname {r a n k} (\\boldsymbol {L}) + \\lambda \\| \\boldsymbol {S} \\| _ {0} \\quad \\text {s . t .} \\boldsymbol {D} = \\boldsymbol {L} + \\boldsymbol {S} \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 130, + 847, + 468, + 869 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "where $\\ell_0$ -norm is the number of nonzero elements in the matrix, the parameter $\\lambda > 0$ provides the trade-off between the rankness and sparsity.", + "bbox": [ + 500, + 363, + 890, + 407 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "RPCA has been widely studied and applied in computer vision. For example, \"background\" in a video clip captured by a static camera has a low-rank property, which can be considered in background modeling [2]. The requirement of detecting sparse outliers from the observed imagery data leads to RPCA applications in image or video processing [3]. In industry, RPCA is also applicable to point cloud filtering [4], surface defects detection [5], shock sensing [6], etc.", + "bbox": [ + 496, + 409, + 892, + 542 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "It is noted that the optimization problem (1) is NP-hard. The convex relaxation of RPCA has been studied to achieve an exact recovery in [1, 7-12], where the RPCA problem was relaxed as the sum of the nuclear norm and $\\ell_1$ -norm. But the convex methods always have a rate of sublinear convergence and high computation in practice [13]. It is necessary to exploit the structure of the underlying data and develop more efficient algorithms for RPCA. Zhou et al. [14] extended the equality constraint of RPCA to inequality in order to deal with noisy data, thus the RPCA is reformulated as the following constrained non-convex optimization problem:", + "bbox": [ + 496, + 545, + 893, + 727 + ], + "page_idx": 0 + }, + { + "type": "equation", + "text": "\n$$\n\\min _ {\\boldsymbol {L}, \\boldsymbol {S}} \\| \\boldsymbol {D} - \\boldsymbol {L} - \\boldsymbol {S} \\| _ {F} ^ {2} \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 586, + 737, + 890, + 767 + ], + "page_idx": 0 + }, + { + "type": "equation", + "text": "\n$$\n\\text {s . t .} \\operatorname {r a n k} (\\boldsymbol {L}) \\leq r \\text {a n d} \\| \\boldsymbol {S} \\| _ {0} \\leq s\n$$\n", + "text_format": "latex", + "bbox": [ + 588, + 767, + 803, + 781 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "with the target rank $r$ and target sparse number $s$ .", + "bbox": [ + 500, + 794, + 826, + 809 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "The key idea of Eq. (2) is to formulate a constrained nonconvex optimization problem. Among the nonconvex optimization methods of RPCA, Zhou et al. [15] substituted the hard thresholding of Eq. (2) with a soft $\\ell_1$ regularization to reduce the complexity of $S$ . Netrapalli et al. [16] added the deterministic sparsity assumption and devoted themselves", + "bbox": [ + 496, + 810, + 893, + 900 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Shiqian Wu is corresponding author.", + "bbox": [ + 94, + 886, + 295, + 900 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "1348", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "to recovering a low-rank matrix from the sparse corruptions that were of unknown value and support. The RPCA algorithm via gradient descent on the factorized space in [17] achieved linear convergence with proper initialization and step size, whose sparse estimator is to guarantee that the fraction of nonzero entries in each column and row of $S$ is bounded above. Inspired by these methods, GoDec+ [18] made the model become an ordinary low-rank projection problem based on the current entropy of noise and half-quadratic optimization theory. In [19], RPCA problem is considered for the first time without heuristics, such as loss functions, convex and surrogate constraints, which provides a new direction for potential research on online algorithms. In addition, Ornhag et al. [20] used second-order methods to convert the original objectives to differentiable equivalents, benefitting from faster convergence.", + "bbox": [ + 75, + 90, + 472, + 332 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Meanwhile, the efficient algorithms for RPCA have been widely investigated for large-scale matrices. In [16], the developed algorithm involved alternating projections between a set of low-rank matrices and a set of sparse matrices, whose projection idea was also widely studied. Inspired by [16], a proximal block coordinate descent method was proposed in [21] to find an $\\epsilon$ -stationary solution in $O(1/\\epsilon^2)$ iterations. Furthermore, an accelerated alternating projection strategy was studied in [22] for RPCA, which project a matrix onto a specific low-dimensional subspace before obtaining a new estimate of the low-rank matrix via truncated SVD.", + "bbox": [ + 75, + 335, + 472, + 517 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Most of RPCA and its variants contain SVD, which requires significant computational cost for large-scale matrices. Hintermüller [23] directly considered a least-squares problem subject to rank and cardinality constraints based on matrix manifolds, which favorably avoids singular value decompositions in full dimension. Phan et al. [24] proposed an accelerated algorithm with iteratively reweighted nuclear norm to ensure that every limit point is a critical point, which leads to small singular values and obtains fast result. Some different computing strategies were employed to substitute SVD so that the computation of RPCA was significantly reduced. Cai et al. [25] introduced CUR decomposition at each iteration, which only required $O(r^{2}n)$ flops per iteration and preserved more information than SVD.", + "bbox": [ + 75, + 518, + 472, + 733 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Generally, the aforementioned algorithms achieved efficient and effective performance in different computer vision tasks. It is highlighted that these methods require the rank of a low-rank matrix to be known a priori, which is inappropriate in most practical applications. To bridge this gap, Xu et al. [26] proposed a rank estimation method based on Gerschgorin disk theorem (GDE), whose computational complexity is $O((d - 1)^3)$ at each iteration. Furthermore, an adaptive weighting RPCA was developed based on iteratively estimated rank, which outperforms the state-of-the-art RPCA methods in various computer vision applications.", + "bbox": [ + 75, + 734, + 472, + 902 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "More specifically, the adaptive weighting RPCA in [26] was formulated as the following optimization problem:", + "bbox": [ + 498, + 90, + 890, + 122 + ], + "page_idx": 1 + }, + { + "type": "equation", + "text": "\n$$\n\\min _ {\\boldsymbol {L}, \\boldsymbol {S}} \\| \\boldsymbol {L} \\| _ {W} + \\lambda \\| \\boldsymbol {S} \\| _ {1} \\quad \\text {s . t .} \\boldsymbol {D} = \\boldsymbol {L} + \\boldsymbol {S} \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 560, + 136, + 890, + 160 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "where $\\| L\\| _W = \\Sigma_i\\omega_i\\sigma_i(L)$ and $\\omega_{i}$ are non-negative weights. Based on the estimated rank of $L$ , the weights can be updated iteratively.", + "bbox": [ + 496, + 174, + 890, + 219 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Although the adaptive weighting RPCA [26] achieves top performance in recovering a low-rank matrix and a sparse matrix, both the rank estimation and RPCA optimization algorithm contain SVD, which takes significant computational costs for large-scale matrices. Recently, randomized block Krylov iteration [27] was introduced to approximate the singular value decomposition in fewer iterations with better accuracy guarantees. This motivates us to use the block Krylov iteration method to accelerate the GDE-based rank estimation in this work. The computational complexity of the proposed Krylov GDE (KGDE)-based rank estimation is reduced to $O(ndrq + n(rq)^2)$ , where $q$ is a parameter with a small value. On the other hand, CUR decomposition is also adopted to replace SVD in the updates of a low-rank matrix, thus the computational complexity of RPCA is significantly reduced. Since the rank of a matrix is required to be known for CUR decomposition, it is natural that the proposed KGDE is used to adaptively estimate the rank of the low-rank matrix within the iterative RPCA computing. Furthermore, a new non-convex low-rank regularized term is used to replace the weighted nuclear norm in (3) which can improve the low-rank matrix approximation. Compared with the state-of-the-art RPCA approaches, the proposed efficient RPCA (eRPCA) algorithm are fast with better accuracy guarantees. The main contributions of this paper are as follows:", + "bbox": [ + 496, + 220, + 892, + 613 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "1) An efficient rank estimation method based on Gerschgorin disks with block Krylov iteration is proposed to accelerate the rank estimate of low-rank matrices.", + "2) CUR decomposition is adopted to reduce the computation of SVD on a large-scale matrix in the update of the low-rank matrix.", + "3) An efficient non-convex RPCA method with a nonconvex weighted regularizer is proposed to achieve better recovery of the low-rank matrix and the sparse matrix.", + "4) The proposed eRPCA algorithm has been applied to various computer vision scenarios and outperforms the state-of-the-art methods on large-scale data." + ], + "bbox": [ + 509, + 621, + 893, + 816 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In the following section, the improved eRPCA method, which consists of efficient rank estimation and new weight is presented in Section 2. The experimental results are demonstrated in Section 3, and the conclusions are drawn in Section 4.", + "bbox": [ + 496, + 824, + 890, + 898 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "1349", + "bbox": [ + 483, + 944, + 514, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Proposed Method", + "text_level": 1, + "bbox": [ + 76, + 89, + 250, + 106 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "2.1. Efficient Rank Estimation via Block Krylov Iteration", + "text_level": 1, + "bbox": [ + 76, + 113, + 468, + 143 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In [26], GDE was used to estimate the rank of a low-rank matrix, which involves SVD and has the computational complexity $O\\left(\\left(d - 1\\right)^{3}\\right)$ for a matrix $D \\in \\mathbb{R}^{n \\times d}$ . Hence it is time-consuming to estimate the rank of large-scale matrix $D$ . Recently it has been shown that block Krylov iteration (BKI) method [27] gives nearly optimal approximation of singular values and singular vectors with few interations. In this subsection, an efficient rank estimation is proposed by combining BKI and GDE, which is named as KGDE.", + "bbox": [ + 75, + 152, + 468, + 287 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Now we give a brief review on the block Krylov iteration method. For a matrix $D \\in \\mathbb{R}^{n \\times d}$ , the Krylov subspace is obtained by", + "bbox": [ + 75, + 289, + 468, + 335 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {K} := [ \\boldsymbol {v}, \\boldsymbol {D} \\boldsymbol {v}, \\boldsymbol {D} ^ {2} \\boldsymbol {v}, \\dots , \\boldsymbol {D} ^ {q - 1} \\boldsymbol {v} ] \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 158, + 348, + 468, + 364 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\pmb{v}$ is a vector of unit norm, $\\| \\pmb {v}\\| = 1$ , and $q$ is a scalar. In [28], the Krylov subspace was extended to randomized block Krylov subspace:", + "bbox": [ + 75, + 369, + 468, + 416 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {K} := \\left[ \\boldsymbol {V}, \\boldsymbol {D V}, \\boldsymbol {D} ^ {2} \\boldsymbol {V}, \\dots , \\boldsymbol {D} ^ {q - 1} \\boldsymbol {V} \\right] \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 147, + 429, + 468, + 446 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\mathbf{V} = [\\pmb{v}_1, \\dots, \\pmb{v}_b] \\in \\mathbb{R}^{d \\times b}$ is a block of $b$ random vectors.", + "bbox": [ + 75, + 452, + 468, + 481 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "After constructing the block Krylov subspace, the Block Krylov Iteration (BKI) [27] can be used to generate closely approximate eigenpairs within fewer iterations by projecting the matrix onto the randomized block Krylov subspace. Its idea is to take a randomized starting matrix $V = D\\Omega$ as the initial matrix, where $\\Omega$ is a Gaussian random matrix. BKI captures an accurate range space:", + "bbox": [ + 75, + 483, + 468, + 588 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {K} := \\left(\\boldsymbol {D} \\boldsymbol {D} ^ {T}\\right) ^ {q} \\boldsymbol {D} \\boldsymbol {\\Omega} \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 202, + 589, + 468, + 609 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $q \\coloneqq \\Theta \\left( \\frac{\\log d}{\\sqrt{\\varepsilon}} \\right)$ . Orthonormalize the columns of $K$ to obtain $Q$ then compute $M \\coloneqq Q^T D D^T Q$ . Set $\\overline{U}_k$ to the top $k$ singular vectors of $M$ . At last, return the low-dimension matrix $Z$ :", + "bbox": [ + 75, + 609, + 468, + 675 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {Z} = \\boldsymbol {Q} \\bar {\\boldsymbol {U}} _ {k} \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 233, + 678, + 468, + 695 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The following theorem shows that the randomized BKI can get strong relative-error bound.", + "bbox": [ + 75, + 699, + 468, + 729 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Theorem 1 [27] Given data matrix $\\pmb{D} \\in \\mathbb{R}^{n \\times d}$ , $n < d$ with eigenvalues $\\lambda_i, i = 1, 2, \\dots, n$ . Let $\\{\\theta_i, \\varphi_i\\}_{i=1}^k$ be the $k$ eigenpair computed using $q$ steps of Block Krylov Iteration (using the orthonormal basis of $\\pmb{K}$ for $\\pmb{V} \\in \\mathbb{R}^{d \\times b}$ ). If $q = \\frac{\\log d}{\\sqrt{\\varepsilon}}$ for some $0 < \\varepsilon < 1$ , then have", + "bbox": [ + 76, + 738, + 468, + 818 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\left| \\theta_ {i} - \\lambda_ {i} \\right| \\leq \\varepsilon \\lambda_ {k + 1}, i = 1, \\dots , k.\n$$\n", + "text_format": "latex", + "bbox": [ + 163, + 818, + 382, + 834 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In the rest of this subsection, we present a fast rank estimation of low-rank matrices based on the BKI and GDE. Given a low-rank matrix $D \\in \\mathbb{R}^{n \\times d}$ , $n < d$ with rank $r$ . The BKI algorithm outputs a low-dimension matrix", + "bbox": [ + 75, + 839, + 468, + 900 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "$Z \\in \\mathbb{R}^{n \\times k}$ , $k < d$ , which aligns well with the top $k$ singular vectors of $D$ . If $r \\leq k$ , the ranks of $D$ and $Z$ are equal. Hence it reduces the computational complexity when GDE can also be applied to $Z$ to estimate the rank instead of the large-scale matrix $D$ .", + "bbox": [ + 498, + 90, + 890, + 165 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The covariance matrix $\\mathbf{R}_{\\mathbf{Z}} \\in \\mathbb{R}^{k \\times k}$ of the matrix $\\mathbf{Z}$ with a rank $r$ can be defined as:", + "bbox": [ + 498, + 166, + 890, + 195 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {R} _ {Z} = \\boldsymbol {Z} ^ {T} \\boldsymbol {Z} \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 650, + 198, + 890, + 215 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Then the eigenvalue decomposition of $R_Z$ is given by", + "bbox": [ + 517, + 219, + 879, + 234 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nR _ {Z} = U _ {R _ {Z}} \\Sigma_ {R _ {Z}} U _ {R _ {Z}} ^ {H} \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 617, + 236, + 890, + 255 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $U_{R_Z} = [u_1, u_2, \\dots, u_k]$ is the eigenvector matrix, and $\\Sigma_{R_Z} = \\text{diag}(\\sigma_1, \\sigma_2, \\dots, \\sigma_k)$ represents the eigenvalue matrix. According to the Gerschgorin disk theorem [29], $R_Z$ can be transformed as follows:", + "bbox": [ + 498, + 257, + 890, + 316 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {R} _ {\\boldsymbol {Z}} = \\left[ \\begin{array}{c c c c} R _ {1 1} & R _ {1 2} & \\dots & R _ {1 k} \\\\ R _ {2 1} & R _ {2 2} & \\dots & R _ {2 k} \\\\ \\vdots & \\vdots & \\ddots & \\vdots \\\\ R _ {k 1} & R _ {k 2} & \\dots & R _ {k k} \\end{array} \\right] = \\left[ \\begin{array}{c c} \\boldsymbol {R} _ {\\boldsymbol {Z 1}} & \\boldsymbol {R} \\\\ \\boldsymbol {R} ^ {H} & R _ {k k} \\end{array} \\right] \\tag {10}\n$$\n", + "text_format": "latex", + "bbox": [ + 508, + 319, + 890, + 402 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\pmb{R}_{\\pmb{Z1}} \\in \\mathbb{R}^{(k-1) \\times (k-1)}$ is the square matrix by the first $(k-1)$ rows and the first $(k-1)$ columns of $\\pmb{R}_{\\pmb{Z1}}$ , and $\\pmb{R} = [R_{1k}, R_{2k}, \\dots, R_{(k-1)k}]^T$ . Then the eigenvalue decomposition on $\\pmb{R}_{\\pmb{Z1}}$ is obtained as:", + "bbox": [ + 498, + 402, + 890, + 463 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {R} _ {Z 1} = U _ {Z 1} \\boldsymbol {\\Sigma} _ {1} U _ {Z 1} ^ {H} \\tag {11}\n$$\n", + "text_format": "latex", + "bbox": [ + 622, + 465, + 890, + 483 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $U_{\\mathbf{Z1}} = [q_1', q_2', \\dots, q_{k-1}']$ is an $(k-1) \\times (k-1)$ unitary matrix composed of the eigenvectors of $\\mathbf{R}_{\\mathbf{Z1}}$ , and $\\pmb{\\Sigma}_{\\mathbf{1}} = \\text{diag}(\\sigma_1', \\sigma_2', \\dots, \\sigma_{k-1}')$ . Similar to Eq. (10), a unitary transformed matrix $\\mathbf{U} \\in \\mathbb{R}^{k \\times k}(\\mathbf{U}\\mathbf{U}^H = \\mathbf{I})$ is defined as:", + "bbox": [ + 498, + 484, + 890, + 559 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {U} = \\left[ \\begin{array}{c c} U _ {Z 1} & \\mathbf {0} \\\\ \\mathbf {0} ^ {T} & \\mathbf {1} \\end{array} \\right] \\tag {12}\n$$\n", + "text_format": "latex", + "bbox": [ + 627, + 559, + 890, + 592 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The transformed covariance matrix is obtained by:", + "bbox": [ + 517, + 597, + 852, + 612 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\boldsymbol {R} _ {T} = \\boldsymbol {U} ^ {H} \\boldsymbol {R} _ {Z} \\boldsymbol {U} = \\left[ \\begin{array}{c c} \\boldsymbol {U} _ {Z 1} ^ {H} \\boldsymbol {R} _ {Z 1} \\boldsymbol {U} _ {Z 1} & \\boldsymbol {U} _ {Z 1} ^ {H} \\boldsymbol {R} \\\\ \\boldsymbol {R} ^ {H} \\boldsymbol {U} _ {Z 1} & R _ {k k} \\end{array} \\right] \\\\ = \\left[ \\begin{array}{c c c c c c} \\sigma_ {1} ^ {\\prime} & 0 & 0 & \\dots & 0 & \\rho_ {1} \\\\ 0 & \\sigma_ {2} ^ {\\prime} & 0 & \\dots & 0 & \\rho_ {2} \\\\ 0 & 0 & \\sigma_ {3} ^ {\\prime} & \\dots & 0 & \\rho_ {3} \\\\ \\vdots & \\vdots & \\vdots & \\ddots & \\vdots & \\vdots \\\\ 0 & 0 & 0 & \\dots & \\sigma_ {k - 1} ^ {\\prime} & \\rho_ {k - 1} \\\\ \\rho_ {1} ^ {*} & \\rho_ {2} ^ {*} & \\rho_ {3} ^ {*} & \\dots & \\rho_ {k - 1} ^ {*} & R _ {k k} \\end{array} \\right] \\tag {13} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 514, + 613, + 890, + 752 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\rho_{i} = \\pmb{q}_{i}^{\\prime H}\\pmb{R}$ . The eigenvalues of $\\pmb{R}_{T}$ can be estimated using the Gerschgorin disk theorem [29]. Then, the radii of the first $(k - 1)$ Gerschgorin's disk can be written as:", + "bbox": [ + 498, + 755, + 890, + 814 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nr _ {i} = \\left| \\rho_ {i} \\right| = \\left| \\boldsymbol {q} _ {i} ^ {\\prime H} \\boldsymbol {R} \\right| \\tag {14}\n$$\n", + "text_format": "latex", + "bbox": [ + 627, + 814, + 890, + 834 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where the radius $r_i$ of the $i$ th Gerschgorin's disk depends on the size of $\\pmb{q}_i^{\\prime H}\\pmb {R}$", + "bbox": [ + 498, + 839, + 890, + 869 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "To further improve the accuracy of the rank estimation, the radii of the Gerschgorin's disk are shrank in [26]. Then", + "bbox": [ + 498, + 869, + 890, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "1350", + "bbox": [ + 483, + 944, + 514, + 955 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Algorithm 1 KGDE", + "text_level": 1, + "bbox": [ + 78, + 90, + 215, + 104 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Input: $D\\in \\mathbb{R}^{n\\times d}$ , error $\\varepsilon \\in (0,1)$ , $k = 2$ , the $(1 + \\varepsilon)$ relative-error bound for BKI $q = \\frac{\\log d}{\\sqrt{\\varepsilon}}$", + "bbox": [ + 76, + 111, + 467, + 145 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Output: Estimated rank $r$", + "bbox": [ + 78, + 145, + 256, + 157 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Set $gde = \\text{zeros}(d, 1)$", + "bbox": [ + 94, + 160, + 243, + 174 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "for $t = 1$ to $d$ do", + "bbox": [ + 94, + 175, + 209, + 186 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {Z} \\in \\mathbb {R} ^ {n \\times k} \\leftarrow B K I (\\boldsymbol {D} \\in \\mathbb {R} ^ {n \\times d}, \\varepsilon , q)\n$$\n", + "text_format": "latex", + "bbox": [ + 111, + 188, + 362, + 204 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Covariance matrix $\\mathbf{R}_{\\mathbf{Z}} = \\mathbf{Z}^{T}\\mathbf{Z}$", + "bbox": [ + 111, + 204, + 325, + 218 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Obtain the transformed unitary matrix according to Eqs. (10)-(12)", + "bbox": [ + 111, + 220, + 468, + 250 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Calculate the radii $r_i$ of the Gerschgorin's disk according to Eqs. (14)-(15)", + "bbox": [ + 111, + 250, + 468, + 279 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Calculate $gde(t)$ according to Eqs. (16)-(17)", + "bbox": [ + 111, + 280, + 405, + 295 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "if $(t > 1\\& \\& gde(t) < 0)$ then", + "bbox": [ + 111, + 295, + 310, + 310 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "break;", + "bbox": [ + 127, + 311, + 171, + 323 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "else", + "bbox": [ + 111, + 325, + 140, + 337 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nk = k + 1\n$$\n", + "text_format": "latex", + "bbox": [ + 127, + 340, + 197, + 353 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "end if", + "bbox": [ + 111, + 356, + 155, + 368 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "end for", + "bbox": [ + 94, + 372, + 148, + 383 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nr = t - 1\n$$\n", + "text_format": "latex", + "bbox": [ + 94, + 386, + 161, + 398 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "return $r$", + "bbox": [ + 94, + 402, + 148, + 412 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "a new diagonal matrix $\\pmb{\\Sigma}_{\\pmb{T}} = \\text{diag}(\\sigma_{1}', \\sigma_{2}', \\dots, \\sigma_{k-1}', \\sigma_{k}')$ is constructed, where $\\sigma_{k}' = \\sqrt{\\sum_{i=1}^{k-1} \\sigma_{i}'^{2}}$ . Thus, the new transformed matrix $\\pmb{R}_{\\pmb{T}\\pmb{\\Sigma}_{\\pmb{T}}}$ is constructed as follows:", + "bbox": [ + 75, + 444, + 468, + 497 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\boldsymbol {R} _ {T \\Sigma_ {T}} = \\boldsymbol {\\Sigma} _ {T} \\boldsymbol {R} _ {T} \\boldsymbol {\\Sigma} _ {T} ^ {- 1} \\\\ = \\left[ \\begin{array}{c c c c c} \\sigma_ {1} ^ {\\prime} & 0 & \\dots & 0 & \\frac {\\sigma_ {1} ^ {\\prime}}{\\sigma_ {k} ^ {\\prime}} \\rho_ {1} \\\\ 0 & \\sigma_ {2} ^ {\\prime} & \\dots & 0 & \\frac {\\sigma_ {2}}{\\sigma_ {k} ^ {\\prime}} \\rho_ {2} \\\\ \\vdots & \\vdots & \\ddots & \\vdots & \\vdots \\\\ 0 & 0 & \\dots & \\sigma_ {k - 1} ^ {\\prime} & \\frac {\\sigma_ {k - 1} ^ {\\prime}}{\\sigma_ {k} ^ {\\prime}} \\rho_ {k - 1} \\\\ \\frac {\\sigma_ {1} ^ {\\prime}}{\\sigma_ {k} ^ {\\prime}} \\rho_ {1} ^ {*} & \\frac {\\sigma_ {2} ^ {\\prime}}{\\sigma_ {k} ^ {\\prime}} \\rho_ {2} ^ {*} & \\dots & \\frac {\\sigma_ {k - 1} ^ {\\prime}}{\\sigma_ {k} ^ {\\prime}} \\rho_ {k - 1} ^ {*} & R _ {k k} \\end{array} \\right] \\tag {15} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 96, + 500, + 468, + 645 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "$R_{T\\Sigma_T}$ and $R_{T}$ are similar matrices and have the same eigenvalues. In Eq. (15), the radii are compressed to various degrees. Finally, the estimated rank is obtained by the improved heuristic decision rule:", + "bbox": [ + 75, + 646, + 468, + 705 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\ng d e (t) = \\frac {1}{\\sqrt {\\sum_ {i = 1} ^ {k - 1} \\sigma_ {i} ^ {\\prime 2}}} [ | \\sigma_ {t} ^ {\\prime} | r _ {t} - \\frac {H _ {D} ^ {(t)} (M)}{k - 1} \\sum_ {i = 1} ^ {k - 1} \\left| \\sigma_ {i} ^ {\\prime} \\right| r _ {i} ] \\tag {16}\n$$\n", + "text_format": "latex", + "bbox": [ + 84, + 710, + 468, + 756 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $t = 1,2,\\dots ,k - 2$ and $0 < H_D^{(t)}(M) < 1$ is the adjustment factor:", + "bbox": [ + 75, + 760, + 468, + 792 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nH _ {D} ^ {(t)} (M) = \\frac {2 \\left| \\sigma_ {t + 1} ^ {\\prime} \\right|}{\\sqrt {\\sum_ {i = t} ^ {k - 1} \\sigma_ {i} ^ {\\prime 2}}} \\tag {17}\n$$\n", + "text_format": "latex", + "bbox": [ + 184, + 794, + 468, + 838 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "As a result, the rank $r = t - 1$ if the first negative value of (16) is reached at $t$ .", + "bbox": [ + 76, + 839, + 468, + 869 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "When $r \\leq k$ , $D$ is transformed to $Z$ by BKI, then the rank of $Z$ is estimated by GDE. It is noted that while $r > k$ ,", + "bbox": [ + 76, + 869, + 468, + 900 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "GDE can not estimate the true rank of $D$ from $Z$ . To adaptively determine an appropriate $k$ , KGDE is proposed by adopting iteration, and GDE is served as a stopping criterion for such Krylov subspace approximation of $Z$ . The KGDE for rank estimation based on BKI and GDE is summarized in Algorithm 1.", + "bbox": [ + 496, + 90, + 890, + 181 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Remark 1: The computational cost of KGDE is related to BKI. If the estimated $r$ of the input matrix $D \\in \\mathbb{R}^{n \\times d}$ is exact, the computational complexity will be $O(ndrq + n(rq)^2)$ , where $n < d$ . For sparse matrix, the computational cost of KGDE will be $O(nnz(D)rq + n(rq)^2)$ , where $nnz(D)$ is the number of nonzeros in $D$ . Since $r \\leq n$ and $q = \\frac{\\log d}{\\sqrt{\\varepsilon}}$ are small, the KGDE will be inexpensive, especially for sparse matrices.", + "bbox": [ + 496, + 181, + 890, + 306 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Remark 2: The accuracy of the KGDE mainly depends on the BKI. In light of Theorem 1, $Z$ is obtained within a high-quality principal components approximation of $D$ , both its eigenvalues and eigenvectors are highly close to the actual ones of $D$ .", + "bbox": [ + 496, + 306, + 890, + 381 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "2.2. Efficient RPCA based on KGDE and CUR Decomposition", + "text_level": 1, + "bbox": [ + 500, + 393, + 890, + 425 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In this subsection, an efficient RPCA based on the above rank estimation and CUR decomposition is proposed for solving the following optimization problem:", + "bbox": [ + 496, + 431, + 890, + 477 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\min _ {\\boldsymbol {L}, \\boldsymbol {S}} \\| \\boldsymbol {D} - \\boldsymbol {L} - \\boldsymbol {S} \\| _ {F} ^ {2} + \\lambda \\| \\boldsymbol {L} \\| _ {\\gamma} \\quad s. t. \\| \\boldsymbol {S} \\| _ {0} \\leq s \\tag {18}\n$$\n", + "text_format": "latex", + "bbox": [ + 524, + 478, + 890, + 502 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where", + "bbox": [ + 500, + 503, + 544, + 516 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\| \\boldsymbol {L}\\|_{\\gamma} = \\left\\{ \\begin{array}{l}\\sum_{i = 1}\\frac{e^{\\gamma}\\sigma_{i}}{\\gamma + \\sigma_{i}}, i\\leq r\\\\ 0 , i > r \\end{array} \\right.\n$$\n", + "text_format": "latex", + "bbox": [ + 591, + 516, + 797, + 571 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "and $\\sigma_{i}, i = 1,2,\\dots ,r$ , is the singular value, $\\gamma >0$ , and $\\lambda$ is the regularized parameter which provides a trade-off between the recovery of low-rank matrix and sparse matrix.", + "bbox": [ + 496, + 578, + 890, + 623 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The optimization model (18) adds a new non-convex low-rank regularization term to Eq. (2), which adopts the estimated rank to achieve better recovery accuracy of the low-rank matrix than the weighted nuclear norm in (3).", + "bbox": [ + 496, + 625, + 890, + 684 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In this work, the alternating projection method is used to solve the following two sub-problems until convergence:", + "bbox": [ + 496, + 685, + 890, + 715 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {L} _ {\\ell + 1} = \\underset {\\boldsymbol {L}} {\\arg \\min } \\| \\boldsymbol {D} - \\boldsymbol {L} - \\boldsymbol {S} _ {\\ell} \\| _ {F} ^ {2} + \\lambda \\| \\boldsymbol {L} \\| _ {\\gamma} \\tag {19}\n$$\n", + "text_format": "latex", + "bbox": [ + 532, + 742, + 890, + 767 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {S} _ {\\ell + 1} = \\underset {\\boldsymbol {S}: \\| \\boldsymbol {S} \\| _ {0} \\leq s} {\\arg \\min } \\| \\boldsymbol {D} - \\boldsymbol {L} _ {\\ell + 1} - \\boldsymbol {S} \\| _ {F} ^ {2} \\tag {20}\n$$\n", + "text_format": "latex", + "bbox": [ + 566, + 770, + 890, + 797 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Update for L: The traditional solution of (19) often involves SVD, which requires significant computational resource for a large-scale matrix. To efficiently solve the model (19), we replace SVD with CUR decomposition [30], which has been proven to be efficient and effective in solving classical RPCA problem [31]. Mathematically, the CUR", + "bbox": [ + 500, + 810, + 890, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "1351", + "bbox": [ + 483, + 944, + 513, + 955 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/449102a391a1ff7ed034b896a9956b319a0a3ad3bb58041afda27b734ffdb1cd.jpg", + "image_caption": [ + "Figure 1. The numerical rank estimation of sparse data matrices." + ], + "image_footnote": [], + "bbox": [ + 89, + 66, + 272, + 193 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/4574448e17edbfe350785fc482ce96c5f9ab580a8dda0f69355c52e6f79f1a92.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 292, + 66, + 475, + 193 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/3d39cfbde76e612f32f4b5f76c67bebeaf0f64d0ba8f32c6b5c1831f77a59209.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 493, + 66, + 676, + 193 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/62bacbecab044961e7183415c4bc2d11e34f8712604e7447e1bed2f28997fd20.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 694, + 66, + 879, + 193 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "decomposition of (19) can be rewritten as follows:", + "bbox": [ + 76, + 229, + 410, + 244 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {C} _ {\\ell + 1} = \\underset {\\boldsymbol {L} _ {:, \\mathcal {J}}} {\\arg \\min } \\| [ \\boldsymbol {D} - \\boldsymbol {L} - \\boldsymbol {S} _ {\\ell} ] _ {:, \\mathcal {J}} \\| _ {F} ^ {2} + \\lambda \\| \\boldsymbol {L} _ {:, \\mathcal {J}} \\| _ {\\gamma} \\tag {21}\n$$\n", + "text_format": "latex", + "bbox": [ + 84, + 253, + 468, + 281 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {U} _ {\\ell + 1} = \\mathcal {T} \\boldsymbol {S} ([ \\boldsymbol {D} - \\boldsymbol {L} - \\boldsymbol {S} _ {\\ell} ] _ {\\mathcal {I}, \\mathcal {J}}) \\tag {22}\n$$\n", + "text_format": "latex", + "bbox": [ + 163, + 285, + 468, + 303 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {R} _ {\\ell + 1} = \\underset {\\boldsymbol {L} _ {\\mathcal {I},:}} {\\arg \\min } \\| [ \\boldsymbol {D} - \\boldsymbol {L} - \\boldsymbol {S} _ {\\ell} ] _ {\\mathcal {I},:} \\| _ {F} ^ {2} + \\lambda \\| \\boldsymbol {L} _ {\\mathcal {I},:} \\| _ {\\gamma} \\tag {23}\n$$\n", + "text_format": "latex", + "bbox": [ + 89, + 305, + 468, + 332 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $C_{\\ell +1}\\in \\mathbb{R}^{n\\times \\mathcal{I}}$ is $\\mathcal{I}$ columns of (19) via uniform sampling, $R_{\\ell +1}\\in \\mathbb{R}^{\\mathcal{I}\\times d}$ is $\\mathcal{J}$ rows of (19) in the same way, $U_{\\ell +1}\\in \\mathbb{R}^{\\mathcal{I}\\times \\mathcal{I}}$ is the overlap of the column and row indices of $C_{\\ell +1}$ and $R_{\\ell +1}$ . $\\mathcal{T}S(\\cdot)$ denotes the truncated SVD.", + "bbox": [ + 76, + 345, + 468, + 405 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In addition, the rank value $r$ is needed for $\\mathcal{T}S(\\cdot)$ and CUR decomposition, which can be exactly estimated by our proposed KGDE method.", + "bbox": [ + 75, + 406, + 468, + 450 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "As Eqs. (21) and (23) are the combination of concave and convex functions, the Difference of Convex programming [32] is used to solve these problems. Thus, $C_{\\ell + 1}$ can be obtained as follows [33]:", + "bbox": [ + 75, + 450, + 468, + 511 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {C} _ {\\ell + 1} = \\left[ \\boldsymbol {a} \\operatorname {d i a g} \\left\\{\\sigma^ {*} \\right\\} \\boldsymbol {b} ^ {T} \\right] _ {:, \\mathcal {I}} \\tag {24}\n$$\n", + "text_format": "latex", + "bbox": [ + 179, + 513, + 468, + 532 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\mathbf{a}$ and $\\mathbf{b}$ are the left and right singular vectors of $(D - S_{\\ell + 1})$ , respectively, and $\\sigma^*$ has a closed-form solution at each iteration:", + "bbox": [ + 76, + 534, + 468, + 578 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\sigma^ {i + 1} = \\max \\left(\\left(\\sigma_ {\\boldsymbol {D} - \\boldsymbol {S} _ {\\ell + 1}} - \\frac {\\lambda \\omega_ {i}}{\\mu^ {\\ell}}\\right), 0\\right) \\tag {25}\n$$\n", + "text_format": "latex", + "bbox": [ + 151, + 580, + 468, + 609 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\sigma_{D - S_{\\ell +1}}$ is the singular value of $(D - S_{\\ell +1}),\\mu >0,$ and $\\omega_{i} = \\left\\{ \\begin{array}{ll}\\frac{\\gamma e^{\\gamma}}{(\\gamma + \\sigma_{i}(\\gamma))^{2}}, & i\\leq r\\\\ 0, & \\text{others} \\end{array} \\right.$ is the gradient of $\\| L\\|_{\\gamma}$ at", + "bbox": [ + 76, + 612, + 468, + 681 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "$\\sigma^i$ . Obviously, $\\omega_{i}$ is dependent on $r$ , which can be estimated by KGDE at each iteration.", + "bbox": [ + 76, + 681, + 468, + 710 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Similarly,", + "bbox": [ + 96, + 712, + 163, + 727 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {R} _ {\\ell + 1} = \\left[ \\boldsymbol {a} \\operatorname {d i a g} \\left\\{\\sigma^ {*} \\right\\} \\boldsymbol {b} ^ {T} \\right] _ {\\mathcal {I},:} \\tag {26}\n$$\n", + "text_format": "latex", + "bbox": [ + 181, + 729, + 468, + 747 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Hence, the updated for $L$ is:", + "bbox": [ + 76, + 750, + 266, + 763 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {L} _ {\\ell + 1} = \\boldsymbol {C} _ {\\ell + 1} \\boldsymbol {U} _ {\\ell + 1} ^ {\\dagger} \\boldsymbol {R} _ {\\ell + 1} \\tag {27}\n$$\n", + "text_format": "latex", + "bbox": [ + 187, + 767, + 468, + 785 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $(\\cdot)^{\\dagger}$ denotes the Moore-Penrose pseudoinverse.", + "bbox": [ + 76, + 789, + 431, + 804 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Update for S: Similarly, the optimization of (20) can be divided into as:", + "bbox": [ + 76, + 805, + 468, + 833 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n[ \\boldsymbol {S} _ {\\ell + 1} ] _ {:, \\mathcal {J}} = \\underset {\\boldsymbol {S}:, \\mathcal {J}: \\| \\boldsymbol {S} \\| _ {0} \\leq s} {\\arg \\min } \\| [ \\boldsymbol {D} - \\boldsymbol {L} _ {\\ell} - \\boldsymbol {S} ] _ {:, \\mathcal {J}} \\| _ {F} ^ {2} \\tag {28}\n$$\n", + "text_format": "latex", + "bbox": [ + 102, + 837, + 468, + 864 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n[ \\boldsymbol {S} _ {\\ell + 1} ] _ {\\mathcal {I},:} = \\underset {\\boldsymbol {S} _ {\\mathcal {I},:} \\| \\boldsymbol {S} \\| _ {0} \\leq s} {\\arg \\min } \\| [ \\boldsymbol {D} - \\boldsymbol {L} _ {\\ell} - \\boldsymbol {S} ] _ {\\mathcal {I},:} \\| _ {F} ^ {2} \\tag {29}\n$$\n", + "text_format": "latex", + "bbox": [ + 106, + 875, + 468, + 902 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Algorithm 2 eRPCA based on KGDE", + "text_level": 1, + "bbox": [ + 500, + 228, + 754, + 242 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Input: $D \\in \\mathbb{R}^{n \\times d}$ with estimated rank $r$ ; $\\delta$ : error; $\\lambda, \\mu$ : penalty parameter; $\\zeta_0$ : initial thresholding value; $|\\mathcal{I}| = O(r), |\\mathcal{J}| = O(r)$ : sampling number of rows and columns; $\\gamma$ : non-convex regularizer parameter.", + "bbox": [ + 500, + 248, + 890, + 310 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Output: $L, S$", + "text_level": 1, + "bbox": [ + 501, + 311, + 596, + 325 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Uniformly sample row indices $\\mathcal{I}$ and column indices $\\mathcal{J}$ .", + "bbox": [ + 516, + 325, + 885, + 340 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {L} _ {0} = 0, \\boldsymbol {S} _ {0} = 0, k = 0\n$$\n", + "text_format": "latex", + "bbox": [ + 517, + 340, + 674, + 354 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "while not converged do", + "text_level": 1, + "bbox": [ + 517, + 356, + 674, + 369 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Resample $\\mathcal{I}$ and $\\mathcal{J}$", + "bbox": [ + 532, + 371, + 661, + 385 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Update $\\zeta_{k + 1} = \\eta \\zeta_0$", + "bbox": [ + 532, + 386, + 663, + 401 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Update $S_{\\ell +1}$ according to Eqs. (28)-(29)", + "bbox": [ + 532, + 401, + 803, + 416 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Estimate and update $r$ by KGDE", + "bbox": [ + 532, + 416, + 751, + 430 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Update $C_{\\ell +1}$ according to (21)", + "bbox": [ + 532, + 431, + 740, + 446 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Update $R_{\\ell +1}$ according to (23)", + "bbox": [ + 532, + 446, + 741, + 460 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Update $U_{\\ell +1}$ according to (22)", + "bbox": [ + 532, + 462, + 738, + 476 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {L} _ {\\ell + 1} = \\boldsymbol {C} _ {\\ell + 1} \\boldsymbol {U} _ {\\ell + 1} ^ {\\dagger} \\boldsymbol {R} _ {\\ell + 1}\n$$\n", + "text_format": "latex", + "bbox": [ + 532, + 476, + 700, + 492 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\ell = \\ell + 1\n$$\n", + "text_format": "latex", + "bbox": [ + 534, + 492, + 599, + 505 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "end while", + "text_level": 1, + "bbox": [ + 517, + 507, + 586, + 520 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "For $S$ , the hard thresholding operator $\\mathcal{HT}$ is adopted as:", + "bbox": [ + 517, + 550, + 888, + 566 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\left[ \\mathcal {H T} (\\boldsymbol {S}) \\right] _ {i, j} = \\left\\{ \\begin{array}{l} \\boldsymbol {S} _ {i, j}, i f | \\boldsymbol {S} _ {i, j} | > \\zeta , \\\\ 0, o t h e r w i s e. \\end{array} \\right. \\tag {30}\n$$\n", + "text_format": "latex", + "bbox": [ + 570, + 578, + 890, + 618 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\zeta$ is the thresholding value. The hard thresholding is employed for projections on to $(D - L_{\\ell})$ .", + "bbox": [ + 500, + 625, + 888, + 655 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The iteration is terminated when", + "bbox": [ + 519, + 657, + 736, + 669 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\frac {\\left\\| \\left[ \\boldsymbol {D} - \\boldsymbol {L} _ {\\ell} - \\boldsymbol {S} _ {\\ell} \\right] _ {: , \\mathcal {I}} \\right\\| _ {F} + \\left\\| \\left[ \\boldsymbol {D} - \\boldsymbol {L} _ {\\ell} - \\boldsymbol {S} _ {\\ell} \\right] _ {\\mathcal {I} , :} \\right\\| _ {F}}{\\left\\| \\boldsymbol {D} _ {: , \\mathcal {I}} \\right\\| _ {F} + \\left\\| \\boldsymbol {D} _ {\\mathcal {I} , :} \\right\\| _ {F}} < \\delta \\tag {31}\n$$\n", + "text_format": "latex", + "bbox": [ + 521, + 670, + 890, + 715 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The entire procedure to solve the problem (18) is summarized in Algorithm 2.", + "bbox": [ + 500, + 717, + 888, + 747 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Remark 3: The computational complexity of $U$ in CUR decomposition is $O(r^3)$ . Since the sampling numbers of rows and columns are $|\\mathcal{I}| = O(r)$ and $|\\mathcal{J}| = O(r)$ , respectively, updating $L$ requires $O(r^{2}n)$ flops per iteration. In contrast, computing the SVD usually requires $O(rnd)$ . In addition, the runtime of updating $S$ is actually a simple projection, whose computational complexity is further less than that of $L$ . Thus, the computational complexity of the alternating projection procedure is $O\\left(\\frac{d^2r}{\\epsilon} + d \\cdot \\text{poly}(r, \\log(r / \\epsilon), 1 / \\epsilon)\\right)$ , where $0 < \\epsilon < 1$ is an", + "bbox": [ + 496, + 747, + 890, + 902 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "1352", + "bbox": [ + 483, + 944, + 514, + 955 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/ae35347ff9ab07ed21ffb218540d74c34b6798bc25172e17bb58f491841068f0.jpg", + "image_caption": [ + "Figure 2. The numerical rank estimation of video data matrices." + ], + "image_footnote": [], + "bbox": [ + 86, + 80, + 267, + 202 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/7a563cf6a4ef7bf765d8e28c102129d2ad4ffc4bce8da79c9e680ecba716517c.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 282, + 80, + 449, + 202 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "accuracy parameter.", + "bbox": [ + 76, + 239, + 210, + 253 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "3. Experimental Results", + "text_level": 1, + "bbox": [ + 76, + 268, + 281, + 284 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "This section reports the experimental results of our proposed eRPCA and compares it with state-of-the-art algorithms on synthetic datasets and two practical computer vision scenarios. The parameters in our method are listed as follows: $\\gamma = 0.02$ , $\\delta = 10^{-7}$ , $\\lambda = 10^{-3}$ , $\\mu = \\frac{1}{2}$ , $\\zeta_0 = \\max(|D|)$ , and $\\varepsilon = 0.05$ . The parameters in other methods use their default settings. All the experiments are conducted on a laptop with MATLAB 2019 equipped with Windows 10 based on AMD Ryzen 5 CPU with 32G RAM.", + "bbox": [ + 76, + 292, + 468, + 429 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "3.1. The Validation of Rank Estimation Method", + "text_level": 1, + "bbox": [ + 76, + 439, + 444, + 454 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "3.1.1 Public real datasets", + "text_level": 1, + "bbox": [ + 76, + 462, + 266, + 476 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "To validate the efficiency and accuracy of KGDE, the general data matrices are tested to estimate the rank. SuiteSparse Database1 [34] provides general data matrices with low numerical rank, whose Gaussian-type distribution assumptions for the data and noise may not hold. In addition, the video datasets from Scene Background Initialization (SBI) dataset2 [35], which are converted to the full matrix are also tested.", + "bbox": [ + 76, + 486, + 468, + 604 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Fig.1 shows the numerical rank estimation for the SVD curve of sparse data matrices. The singular values of Fig.1(a) and Fig.1(b) have apparent distribution, and KGDE and GDE obtain the exact rank estimation. The singular values of Fig.1(c) and Fig.1(d) are very close, it is therefore hard to bind the rank. The result of Fig.1(c) is the same, and the one of Fig.1(d) is slightly different, while the gap can be ignored in practice.", + "bbox": [ + 75, + 607, + 468, + 728 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Fig.2 shows the rank estimation results of video data matrices. The video datasets have a stable low-rank, and the rank is usually equal to 1. Thus, the distribution of their singular values has a noticeable gap.", + "bbox": [ + 76, + 729, + 468, + 789 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "The comparisons of runtime and estimated rank for different matrices are shown in Table 1. When the matrix scale is small, the execution time is close, but KGDE is still faster than GDE. When the matrix becomes more extensive, the efficiency of KGDE performs better than GDE. Because the", + "bbox": [ + 76, + 789, + 468, + 864 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/a5249b0c51468920d4d5eb4a2c69235f8a8ba00c25f3147e0efd780ad59a3744.jpg", + "image_caption": [ + "Figure 3. The comparison of the average runtime between different algorithms." + ], + "image_footnote": [], + "bbox": [ + 504, + 70, + 880, + 150 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/4cadb674c50bb5a9b0c2502dc4973f43048b5a1a4f5dbdf3385c561031c06173.jpg", + "table_caption": [ + "Table 1. The results of runtime and estimated rank using GDE and KGDE" + ], + "table_footnote": [], + "table_body": "
DatasetGDEKGDE
Runtime(s)RankRuntime(s)Rank
lp Blend0.15630.0943
lp_pilot41.48830.2503
Ipi bgdbg10.27460.2666
Ipi_ceria3d91.18050.2343
IBMtest20.17610.1341
CAVIAR12.23510.7571
", + "bbox": [ + 501, + 220, + 890, + 358 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "computational complexity of KGDE is not too much related to the dimension of the matrix, KGDE can maintain a fast result.", + "bbox": [ + 498, + 368, + 890, + 412 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "3.1.2 Synthetic Datasets", + "text_level": 1, + "bbox": [ + 500, + 435, + 681, + 450 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "For synthetic datasets, our algorithm was compared with the state-of-the-art RPCA-based approaches: RPCA [1], PSSV [36], WNNM [37], and ARE-RPCA [26].", + "bbox": [ + 498, + 459, + 890, + 505 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "The recovery ability and execution time of the algorithms are investigated. The input matrix $D \\in \\mathbb{R}^{n \\times d}$ is corrupted by sparse noise with the corruption rate $\\alpha = \\{0.1, 0.3, 0.5, 0.7\\}$ . The parameters are set: $d = 10000$ , $n = \\{20, 100, 500\\}$ and different ranks $r = \\{1, 3, 5\\}$ . The iteration stop criterion is $10^{-7}$ . Let $L_{sol}$ be the reconstruction of $L$ and the reconstruction error is defined as $\\| L_{sol} - L \\|_F / \\| L \\|_F$ .", + "bbox": [ + 498, + 506, + 890, + 627 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "The comparisons of the average runtime with different ranks $r$ and dimensions $d$ are shown in Fig.3. The eRPCA is faster than others for the average runtime in Fig.3. When the input matrix has a larger scale or rank, the time gap between our method and others is more prominent.", + "bbox": [ + 496, + 627, + 890, + 702 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "The simulation results are shown in Fig.4. It can be seen that eRPCA algorithm is stubborn when the corruption rate is low and has similar results with other algorithms. When the corruption rate rises, the reconstruction error of eRPCA algorithm is larger. eRPCA performs worse when the corruption rate is 0.7 with a large rank.", + "bbox": [ + 496, + 703, + 890, + 792 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 2 shows the desired rank of the low-rank matrix decomposed by different algorithms under different corruption rates. It can be observed that the proposed eRPCA can obtain correct ranks of low-rank matrices in all cases. Other algorithms can get the desired rank correctly only if the corruption rate is low.", + "bbox": [ + 496, + 794, + 890, + 883 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "According to the above analysis, it is observed that eR-", + "bbox": [ + 519, + 885, + 890, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_footnote", + "text": "1https://sparse.tamu.edu/", + "bbox": [ + 94, + 875, + 230, + 887 + ], + "page_idx": 5 + }, + { + "type": "page_footnote", + "text": "$^{2}$ https://sbmi2015.na.icar.cnr.it/SBIdataset.html", + "bbox": [ + 94, + 887, + 346, + 898 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "1353", + "bbox": [ + 483, + 944, + 514, + 955 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/1128a80c9adfbdd6dbe4ad41a0d998905993d0e20473f32beb4d885e47fb25a5.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 187, + 89, + 374, + 212 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/3868c151360f7336ffee565a181cb89f91d8a3684fd3663eee0e9f6fa8fb8009.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 385, + 90, + 573, + 212 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/94a1debc227dad820f2144c8f56bd850804f85c61be6621f905588c729c3a971.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 588, + 90, + 771, + 212 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/4c59e566e933216d645521e6e2900bb6b27c48fb375583898a62b40094f6a011.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 187, + 213, + 372, + 334 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/64e5245212bbe5551cdf9697b43e963330d16b6f11c0967c75fe5bb8e0495245.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 388, + 213, + 573, + 334 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/30b17348bd204304021979b2ec7f48b80297e6853a83c03d5f3b33551fa9c051.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 588, + 213, + 771, + 334 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/23174bc418f4f11341c652a282066900aa1872bbd1dea2dae534945ef2afc38d.jpg", + "image_caption": [ + "Figure 4. Comparison of various algorithms with different dimensions $n$ , matrix ranks $r$ , and corruption rates $\\alpha$ ." + ], + "image_footnote": [], + "bbox": [ + 187, + 335, + 372, + 458 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/7279b9371cf4a6321eee50277c775258059ea506006125fa4b3e15609d7c9ca9.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 388, + 335, + 573, + 458 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/df7d04f3f12663de7310d5317b0f240f1883b3667996f90b6ea72b1123af1eea.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 588, + 335, + 771, + 458 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/a6cfbce333d338d050e9530f5b5f7678178e5ec6e743536e6b3e6790a4e15610.jpg", + "table_caption": [ + "Table 2. The desired rank of low-rank matrix decomposed by different algorithms in different corruption rates and dimensions with different ranks" + ], + "table_footnote": [], + "table_body": "
AlgorithmDimensionr=1r=3r=5
α=0.1α=0.3α=0.5α=0.7α=0.1α=0.3α=0.5α=0.7α=0.1α=0.3α=0.5α=0.7
RPCAn=20116648655656
n=10011123335555552
n=50011173331255516
PSSVn=20111233515551519
n=100111133335558
n=50011163331055513
ARE-RPCAn=20111133355555
n=100111133335555
n=500111133375555
WNNMn=20111133511551520
n=1001111333100555100
n=5001111333500555500
eRPCAn=20111133335555
n=100111133335555
n=500111133335555
", + "bbox": [ + 84, + 526, + 885, + 731 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "PCA has excellent robustness and the fastest execution time.", + "bbox": [ + 75, + 738, + 468, + 767 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "3.2. Foreground-Background Separation", + "text_level": 1, + "bbox": [ + 76, + 792, + 393, + 809 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "In this subsection, we evaluate the proposed eRPCA with the following approaches: ARE-RPCA [26], IRCUR [25], PETRELS [38], and ADW-RPCA [39].", + "bbox": [ + 75, + 820, + 468, + 864 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Foreground-background separation is an important application of RPCA. Scene Background Initialization (SBI)", + "bbox": [ + 76, + 869, + 468, + 901 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "dataset3 [35] is considered. The visual comparisons of the sub-dataset CAVIAR1 are shown in Fig.5, containing 610 frames with size $384 \\times 256$ . The dataset can be represented by a matrix, where each column is a vectorized video frame. Then each algorithm can be applied to decompose the matrix into low-rank parts and sparse ones; that is, this scene can be separated from the moving foreground object from the static background.", + "bbox": [ + 496, + 738, + 890, + 859 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "There are five frames selected in Fig.5, and the upper and", + "bbox": [ + 517, + 859, + 890, + 876 + ], + "page_idx": 6 + }, + { + "type": "page_footnote", + "text": "3https://sbmi2015.na.icar.cnr.it/SBIdataset.html", + "bbox": [ + 517, + 886, + 769, + 898 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "1354", + "bbox": [ + 483, + 944, + 514, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/8f25d0552f440415af5d345500dc32ec85ed24edf98ae7cc8def0545566ebd01.jpg", + "image_caption": [ + "Figure 5. The comparison of visual results on CAVIAR1 between different algorithms." + ], + "image_footnote": [], + "bbox": [ + 80, + 77, + 468, + 412 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/3ba8f610150dfed3d93429e44ef2dbe71a80299f489fd29847ade1250de82d79.jpg", + "table_caption": [ + "Table 3. Performance of one frame from CAVIAR1 dataset among different algorithms" + ], + "table_footnote": [], + "table_body": "
AGEpEPs%pCEPS%MSSSIMPSNRCQMTIME(s)
ARE-RPCA5.26374.07413.48710.856425.441424.787610.78593
IRCUR3.14890.28280.18210.991734.468933.27140.007564
PETRELS4.99725.01614.02220.932929.801729.07731.14708
ADW-RPCA2.640.34990.24820.990534.485333.34026.356669
eRPCA2.63940.26860.16890.991734.862633.57250.034198
", + "bbox": [ + 80, + 488, + 470, + 555 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "lower parts represent the background and foreground. It can be shown that ARE-RPCA and PETRELS yield artifacts in some backgrounds. IRCUR, ADW-RPCA, and eRPCA obtain more distinctive visual results.", + "bbox": [ + 75, + 580, + 468, + 641 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In addition, objective evaluations, i.e. AGE, pEP, pCEP, PSNR, MS-SSIM, CQM, are performed on SBI database where the smaller the first three values, the better the separation results, and the last three ones and vice versa. Table 3 shows the performance evaluation of the above six metrics and runtime. For the first six metrics, eRPCA algorithm obtains better results. Due to the time of estimating the rank, eRPCA algorithm is slower than IRCUR for each frame. However, IRCUR needs to determine the rank in advance, leading to its results being slightly inferior to ours. Moreover, only ARE-RPCA and eRPCA algorithm can obtain the rank prior, but ours are better than ARE-RPCA in all aspects.", + "bbox": [ + 75, + 641, + 468, + 837 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "3.3. Shadow Removal from Face Images", + "text_level": 1, + "bbox": [ + 76, + 847, + 387, + 864 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Face images taken under different lighting conditions always introduce errors, for example, uneven lighting,", + "bbox": [ + 76, + 869, + 468, + 902 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/6d782ff7971e33f8949dad73d5d7357695115e4c47639627c8a5c395754f4c28.jpg", + "image_caption": [ + "Figure 6. The comparison of different algorithms on two images." + ], + "image_footnote": [], + "bbox": [ + 501, + 88, + 893, + 210 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/e71f99c651c2f9046fd5657eceeb814f918a5726e4a453448c9a1587614ff582.jpg", + "table_caption": [ + "Table 4. The comparison of runtime between different algorithms" + ], + "table_footnote": [], + "table_body": "
RPCAPSSVWNNMARE-RPCAeRPCA
yale053.535s0.973s1.113s3.648s0.071s
yaleB023.499s0.962s2.424s3.650s0.081s
", + "bbox": [ + 504, + 262, + 887, + 315 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "shadow etc, which yields challenge for face recognition. Fig.6 (first column) shows two typical examples with size $192 \\times 168$ from the Extended Yale B database[40], a benchmark database in face recognition. Each image is converted to a column vector. The comparisons of these methods are given: RPCA [1], PSSV [36], WNNM [37], and ARE-RPCA [26]. In addition, since the images are aligned, the rank is set to 1, and ARE-RPCA and eRPCA can adaptively estimate the rank.", + "bbox": [ + 496, + 325, + 890, + 460 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Fig.6 shows the shadow removal results of different algorithms. In the visual aspect, the proposed eRPCA algorithm removes the shadow well and does not need to determine the rank. The runtime of different algorithms is shown in Table 4 and ours is the fastest.", + "bbox": [ + 496, + 462, + 890, + 536 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Due to the space limitation, more experimental results are shown in the Supplementary Material.", + "bbox": [ + 498, + 539, + 890, + 570 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 587, + 617, + 603 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this paper, an efficient non-convex RPCA method is proposed for recovering a low-rank matrix and a sparse matrix, especially with large sizes. Specifically, a fast rank estimation method KGDE has been proposed by using Gerschgorin disk theorem with the block Krylov iteration. Based on the estimated rank, a new non-convex regularizer is proposed to achieve better recovery of the low-rank matrices with less computation due to CUR decomposition involved in the iterations. Experimental results demonstrate that the proposed eRPCA algorithm outperforms state-of-the-art algorithms in various vision applications.", + "bbox": [ + 496, + 613, + 890, + 779 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In future, our algorithm will be extended in other applications, such as image recovery and video denoising. However, the accuracy of eRPCA for high corruption rate is still a big challenge. Therefore, we will devote ourselves to improving the robustness of the algorithm. Meanwhile, the parameter adaptability is considered in our future work.", + "bbox": [ + 496, + 781, + 890, + 872 + ], + "page_idx": 7 + }, + { + "type": "page_footnote", + "text": "4http://vision.ucsd.edu/leekc/ExtYaleDatabase/ExtYaleB.html", + "bbox": [ + 514, + 886, + 849, + 898 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "1355", + "bbox": [ + 483, + 944, + 514, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 174, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Emmanuel J Candès, Xiaodong Li, Yi Ma, and John Wright. Robust principal component analysis? Journal of the ACM (JACM), 58(3):1-37, 2011. 1, 6, 8", + "[2] Spencer Markowitz, Corey Snyder, Yonina C Eldar, and Minh N Do. Multimodal unrolled robust PCA for background foreground separation. 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IEEE Transactions on pattern analysis and machine intelligence, 27(5):684-698, 2005. 8", + "bbox": [ + 501, + 90, + 890, + 148 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "1357", + "bbox": [ + 483, + 944, + 514, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/Efficient Robust Principal Component Analysis via Block Krylov Iteration and CUR Decomposition/07ab4d04-cd27-49d8-a510-e7e724ff7dc1_model.json b/2023/Efficient Robust Principal Component Analysis via Block Krylov Iteration and CUR Decomposition/07ab4d04-cd27-49d8-a510-e7e724ff7dc1_model.json new file mode 100644 index 0000000000000000000000000000000000000000..03a676c47b29a23a65ee2a86291113d73db6ed7f --- /dev/null +++ b/2023/Efficient Robust Principal Component Analysis via Block Krylov Iteration and CUR Decomposition/07ab4d04-cd27-49d8-a510-e7e724ff7dc1_model.json @@ -0,0 +1,3036 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.089, + 0.13, + 0.882, + 0.177 + ], + "angle": 0, + "content": "Efficient Robust Principal Component Analysis via Block Krylov Iteration and CUR Decomposition" + }, + { + "type": "text", + "bbox": [ + 0.243, + 0.203, + 0.758, + 0.221 + ], + "angle": 0, + "content": "Shun Fang\\(^{1,2}\\) Zhengqin Xu\\(^{3}\\) Shiqian Wu\\(^{1,2,4*}\\) Shoulie Xie\\(^{5}\\)" + }, + { + "type": "text", + "bbox": [ + 0.094, + 0.221, + 0.914, + 0.309 + ], + "angle": 0, + "content": "\\(^{1}\\)School of Information Science and Engineering, Wuhan University of Science and Technology, China \n\\(^{2}\\)Institute of Robotics and Intelligent Systems, Wuhan University of Science and Technology, China \n\\(^{3}\\)MoE Key Lab of Artificial Intelligence, AI Institute, Shanghai Jiao Tong University, China \n\\(^{4}\\)Hubei Province Key Laboratory of Intelligent Information Processing and Real-Time Industrial Systems \n\\(^{5}\\)Signal Processing, RF & Optical Dept. Institute for Infocomm Research A*STAR, Singapore" + }, + { + "type": "text", + "bbox": [ + 0.091, + 0.313, + 0.908, + 0.327 + ], + "angle": 0, + "content": "fangshun97@wust.edu.cn, fate311@sjtu.edu.cn, shiqian.wu@wust.edu.cn, slxie@i2r.a-star.edu.sg" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.362, + 0.314, + 0.379 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.395, + 0.474, + 0.699 + ], + "angle": 0, + "content": "Robust principal component analysis (RPCA) is widely studied in computer vision. Recently an adaptive rank estimate based RPCA has achieved top performance in low-level vision tasks without the prior rank, but both the rank estimate and RPCA optimization algorithm involve singular value decomposition, which requires extremely huge computational resource for large-scale matrices. To address these issues, an efficient RPCA (eRPCA) algorithm is proposed based on block Krylov iteration and CUR decomposition in this paper. Specifically, the Krylov iteration method is employed to approximate the eigenvalue decomposition in the rank estimation, which requires \\( O(ndrq + n(rq)^2) \\) for an \\( (n \\times d) \\) input matrix, in which \\( q \\) is a parameter with a small value, \\( r \\) is the target rank. Based on the estimated rank, CUR decomposition is adopted to replace SVD in updating low-rank matrix components, whose complexity reduces from \\( O(rnd) \\) to \\( O(r^2 n) \\) per iteration. Experimental results verify the efficiency and effectiveness of the proposed eRPCA over the state-of-the-art methods in various low-level vision applications." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.731, + 0.21, + 0.746 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.757, + 0.47, + 0.835 + ], + "angle": 0, + "content": "Robust principal component analysis (RPCA) aims to recover a low-rank matrix \\( \\mathbf{L} \\) and a sparse matrix \\( \\mathbf{S} \\) from the corrupted observation matrix \\( \\mathbf{D} \\in \\mathbb{R}^{n \\times d} \\): \\( \\mathbf{D} = \\mathbf{L} + \\mathbf{S} \\). The RPCA can be formulated as the following optimization problem [1]:" + }, + { + "type": "equation", + "bbox": [ + 0.132, + 0.848, + 0.47, + 0.871 + ], + "angle": 0, + "content": "\\[\n\\min _ {\\boldsymbol {L}, \\boldsymbol {S}} \\operatorname {r a n k} (\\boldsymbol {L}) + \\lambda \\| \\boldsymbol {S} \\| _ {0} \\quad \\text {s . t .} \\boldsymbol {D} = \\boldsymbol {L} + \\boldsymbol {S} \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.364, + 0.892, + 0.409 + ], + "angle": 0, + "content": "where \\(\\ell_0\\)-norm is the number of nonzero elements in the matrix, the parameter \\(\\lambda > 0\\) provides the trade-off between the rankness and sparsity." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.41, + 0.893, + 0.544 + ], + "angle": 0, + "content": "RPCA has been widely studied and applied in computer vision. For example, \"background\" in a video clip captured by a static camera has a low-rank property, which can be considered in background modeling [2]. The requirement of detecting sparse outliers from the observed imagery data leads to RPCA applications in image or video processing [3]. In industry, RPCA is also applicable to point cloud filtering [4], surface defects detection [5], shock sensing [6], etc." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.546, + 0.895, + 0.728 + ], + "angle": 0, + "content": "It is noted that the optimization problem (1) is NP-hard. The convex relaxation of RPCA has been studied to achieve an exact recovery in [1, 7-12], where the RPCA problem was relaxed as the sum of the nuclear norm and \\(\\ell_1\\)-norm. But the convex methods always have a rate of sublinear convergence and high computation in practice [13]. It is necessary to exploit the structure of the underlying data and develop more efficient algorithms for RPCA. Zhou et al. [14] extended the equality constraint of RPCA to inequality in order to deal with noisy data, thus the RPCA is reformulated as the following constrained non-convex optimization problem:" + }, + { + "type": "equation", + "bbox": [ + 0.588, + 0.738, + 0.892, + 0.768 + ], + "angle": 0, + "content": "\\[\n\\min _ {\\boldsymbol {L}, \\boldsymbol {S}} \\| \\boldsymbol {D} - \\boldsymbol {L} - \\boldsymbol {S} \\| _ {F} ^ {2} \\tag {2}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.589, + 0.768, + 0.805, + 0.782 + ], + "angle": 0, + "content": "\\[\n\\text {s . t .} \\operatorname {r a n k} (\\boldsymbol {L}) \\leq r \\text {a n d} \\| \\boldsymbol {S} \\| _ {0} \\leq s\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.795, + 0.827, + 0.81 + ], + "angle": 0, + "content": "with the target rank \\( r \\) and target sparse number \\( s \\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.811, + 0.894, + 0.901 + ], + "angle": 0, + "content": "The key idea of Eq. (2) is to formulate a constrained nonconvex optimization problem. Among the nonconvex optimization methods of RPCA, Zhou et al. [15] substituted the hard thresholding of Eq. (2) with a soft \\(\\ell_1\\) regularization to reduce the complexity of \\(S\\). Netrapalli et al. [16] added the deterministic sparsity assumption and devoted themselves" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.887, + 0.296, + 0.901 + ], + "angle": 0, + "content": "*Shiqian Wu is corresponding author." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "1348" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.333 + ], + "angle": 0, + "content": "to recovering a low-rank matrix from the sparse corruptions that were of unknown value and support. The RPCA algorithm via gradient descent on the factorized space in [17] achieved linear convergence with proper initialization and step size, whose sparse estimator is to guarantee that the fraction of nonzero entries in each column and row of \\( S \\) is bounded above. Inspired by these methods, GoDec+ [18] made the model become an ordinary low-rank projection problem based on the current entropy of noise and half-quadratic optimization theory. In [19], RPCA problem is considered for the first time without heuristics, such as loss functions, convex and surrogate constraints, which provides a new direction for potential research on online algorithms. In addition, Ornhag et al. [20] used second-order methods to convert the original objectives to differentiable equivalents, benefitting from faster convergence." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.336, + 0.473, + 0.518 + ], + "angle": 0, + "content": "Meanwhile, the efficient algorithms for RPCA have been widely investigated for large-scale matrices. In [16], the developed algorithm involved alternating projections between a set of low-rank matrices and a set of sparse matrices, whose projection idea was also widely studied. Inspired by [16], a proximal block coordinate descent method was proposed in [21] to find an \\(\\epsilon\\)-stationary solution in \\(O(1/\\epsilon^2)\\) iterations. Furthermore, an accelerated alternating projection strategy was studied in [22] for RPCA, which project a matrix onto a specific low-dimensional subspace before obtaining a new estimate of the low-rank matrix via truncated SVD." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.52, + 0.473, + 0.734 + ], + "angle": 0, + "content": "Most of RPCA and its variants contain SVD, which requires significant computational cost for large-scale matrices. Hintermüller [23] directly considered a least-squares problem subject to rank and cardinality constraints based on matrix manifolds, which favorably avoids singular value decompositions in full dimension. Phan et al. [24] proposed an accelerated algorithm with iteratively reweighted nuclear norm to ensure that every limit point is a critical point, which leads to small singular values and obtains fast result. Some different computing strategies were employed to substitute SVD so that the computation of RPCA was significantly reduced. Cai et al. [25] introduced CUR decomposition at each iteration, which only required \\( O(r^{2}n) \\) flops per iteration and preserved more information than SVD." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.735, + 0.473, + 0.903 + ], + "angle": 0, + "content": "Generally, the aforementioned algorithms achieved efficient and effective performance in different computer vision tasks. It is highlighted that these methods require the rank of a low-rank matrix to be known a priori, which is inappropriate in most practical applications. To bridge this gap, Xu et al. [26] proposed a rank estimation method based on Gerschgorin disk theorem (GDE), whose computational complexity is \\( O((d - 1)^3) \\) at each iteration. Furthermore, an adaptive weighting RPCA was developed based on iteratively estimated rank, which outperforms the state-of-the-art RPCA methods in various computer vision applications." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.092, + 0.892, + 0.123 + ], + "angle": 0, + "content": "More specifically, the adaptive weighting RPCA in [26] was formulated as the following optimization problem:" + }, + { + "type": "equation", + "bbox": [ + 0.561, + 0.137, + 0.892, + 0.161 + ], + "angle": 0, + "content": "\\[\n\\min _ {\\boldsymbol {L}, \\boldsymbol {S}} \\| \\boldsymbol {L} \\| _ {W} + \\lambda \\| \\boldsymbol {S} \\| _ {1} \\quad \\text {s . t .} \\boldsymbol {D} = \\boldsymbol {L} + \\boldsymbol {S} \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.175, + 0.892, + 0.22 + ], + "angle": 0, + "content": "where \\(\\| L\\| _W = \\Sigma_i\\omega_i\\sigma_i(L)\\) and \\(\\omega_{i}\\) are non-negative weights. Based on the estimated rank of \\(L\\) , the weights can be updated iteratively." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.222, + 0.893, + 0.614 + ], + "angle": 0, + "content": "Although the adaptive weighting RPCA [26] achieves top performance in recovering a low-rank matrix and a sparse matrix, both the rank estimation and RPCA optimization algorithm contain SVD, which takes significant computational costs for large-scale matrices. Recently, randomized block Krylov iteration [27] was introduced to approximate the singular value decomposition in fewer iterations with better accuracy guarantees. This motivates us to use the block Krylov iteration method to accelerate the GDE-based rank estimation in this work. The computational complexity of the proposed Krylov GDE (KGDE)-based rank estimation is reduced to \\( O(ndrq + n(rq)^2) \\), where \\( q \\) is a parameter with a small value. On the other hand, CUR decomposition is also adopted to replace SVD in the updates of a low-rank matrix, thus the computational complexity of RPCA is significantly reduced. Since the rank of a matrix is required to be known for CUR decomposition, it is natural that the proposed KGDE is used to adaptively estimate the rank of the low-rank matrix within the iterative RPCA computing. Furthermore, a new non-convex low-rank regularized term is used to replace the weighted nuclear norm in (3) which can improve the low-rank matrix approximation. Compared with the state-of-the-art RPCA approaches, the proposed efficient RPCA (eRPCA) algorithm are fast with better accuracy guarantees. The main contributions of this paper are as follows:" + }, + { + "type": "text", + "bbox": [ + 0.512, + 0.622, + 0.892, + 0.667 + ], + "angle": 0, + "content": "1) An efficient rank estimation method based on Gerschgorin disks with block Krylov iteration is proposed to accelerate the rank estimate of low-rank matrices." + }, + { + "type": "text", + "bbox": [ + 0.511, + 0.667, + 0.894, + 0.711 + ], + "angle": 0, + "content": "2) CUR decomposition is adopted to reduce the computation of SVD on a large-scale matrix in the update of the low-rank matrix." + }, + { + "type": "text", + "bbox": [ + 0.511, + 0.713, + 0.892, + 0.771 + ], + "angle": 0, + "content": "3) An efficient non-convex RPCA method with a nonconvex weighted regularizer is proposed to achieve better recovery of the low-rank matrix and the sparse matrix." + }, + { + "type": "text", + "bbox": [ + 0.511, + 0.773, + 0.892, + 0.817 + ], + "angle": 0, + "content": "4) The proposed eRPCA algorithm has been applied to various computer vision scenarios and outperforms the state-of-the-art methods on large-scale data." + }, + { + "type": "list", + "bbox": [ + 0.511, + 0.622, + 0.894, + 0.817 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.825, + 0.892, + 0.9 + ], + "angle": 0, + "content": "In the following section, the improved eRPCA method, which consists of efficient rank estimation and new weight is presented in Section 2. The experimental results are demonstrated in Section 3, and the conclusions are drawn in Section 4." + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "1349" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.078, + 0.09, + 0.251, + 0.107 + ], + "angle": 0, + "content": "2. Proposed Method" + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.114, + 0.47, + 0.145 + ], + "angle": 0, + "content": "2.1. Efficient Rank Estimation via Block Krylov Iteration" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.153, + 0.47, + 0.289 + ], + "angle": 0, + "content": "In [26], GDE was used to estimate the rank of a low-rank matrix, which involves SVD and has the computational complexity \\( O\\left(\\left(d - 1\\right)^{3}\\right) \\) for a matrix \\( D \\in \\mathbb{R}^{n \\times d} \\). Hence it is time-consuming to estimate the rank of large-scale matrix \\( D \\). Recently it has been shown that block Krylov iteration (BKI) method [27] gives nearly optimal approximation of singular values and singular vectors with few interations. In this subsection, an efficient rank estimation is proposed by combining BKI and GDE, which is named as KGDE." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.29, + 0.47, + 0.336 + ], + "angle": 0, + "content": "Now we give a brief review on the block Krylov iteration method. For a matrix \\(D \\in \\mathbb{R}^{n \\times d}\\), the Krylov subspace is obtained by" + }, + { + "type": "equation", + "bbox": [ + 0.16, + 0.349, + 0.469, + 0.366 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {K} := [ \\boldsymbol {v}, \\boldsymbol {D} \\boldsymbol {v}, \\boldsymbol {D} ^ {2} \\boldsymbol {v}, \\dots , \\boldsymbol {D} ^ {q - 1} \\boldsymbol {v} ] \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.371, + 0.469, + 0.417 + ], + "angle": 0, + "content": "where \\(\\pmb{v}\\) is a vector of unit norm, \\(\\| \\pmb {v}\\| = 1\\), and \\(q\\) is a scalar. In [28], the Krylov subspace was extended to randomized block Krylov subspace:" + }, + { + "type": "equation", + "bbox": [ + 0.148, + 0.43, + 0.469, + 0.448 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {K} := \\left[ \\boldsymbol {V}, \\boldsymbol {D V}, \\boldsymbol {D} ^ {2} \\boldsymbol {V}, \\dots , \\boldsymbol {D} ^ {q - 1} \\boldsymbol {V} \\right] \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.453, + 0.469, + 0.482 + ], + "angle": 0, + "content": "where \\(\\mathbf{V} = [\\pmb{v}_1, \\dots, \\pmb{v}_b] \\in \\mathbb{R}^{d \\times b}\\) is a block of \\(b\\) random vectors." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.484, + 0.469, + 0.589 + ], + "angle": 0, + "content": "After constructing the block Krylov subspace, the Block Krylov Iteration (BKI) [27] can be used to generate closely approximate eigenpairs within fewer iterations by projecting the matrix onto the randomized block Krylov subspace. Its idea is to take a randomized starting matrix \\( V = D\\Omega \\) as the initial matrix, where \\( \\Omega \\) is a Gaussian random matrix. BKI captures an accurate range space:" + }, + { + "type": "equation", + "bbox": [ + 0.204, + 0.59, + 0.469, + 0.61 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {K} := \\left(\\boldsymbol {D} \\boldsymbol {D} ^ {T}\\right) ^ {q} \\boldsymbol {D} \\boldsymbol {\\Omega} \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.611, + 0.469, + 0.676 + ], + "angle": 0, + "content": "where \\( q \\coloneqq \\Theta \\left( \\frac{\\log d}{\\sqrt{\\varepsilon}} \\right) \\). Orthonormalize the columns of \\( K \\) to obtain \\( Q \\) then compute \\( M \\coloneqq Q^T D D^T Q \\). Set \\( \\overline{U}_k \\) to the top \\( k \\) singular vectors of \\( M \\). At last, return the low-dimension matrix \\( Z \\):" + }, + { + "type": "equation", + "bbox": [ + 0.235, + 0.679, + 0.469, + 0.696 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {Z} = \\boldsymbol {Q} \\bar {\\boldsymbol {U}} _ {k} \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.7, + 0.469, + 0.73 + ], + "angle": 0, + "content": "The following theorem shows that the randomized BKI can get strong relative-error bound." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.739, + 0.47, + 0.819 + ], + "angle": 0, + "content": "Theorem 1 [27] Given data matrix \\( \\pmb{D} \\in \\mathbb{R}^{n \\times d} \\), \\( n < d \\) with eigenvalues \\( \\lambda_i, i = 1, 2, \\dots, n \\). Let \\( \\{\\theta_i, \\varphi_i\\}_{i=1}^k \\) be the \\( k \\) eigenpair computed using \\( q \\) steps of Block Krylov Iteration (using the orthonormal basis of \\( \\pmb{K} \\) for \\( \\pmb{V} \\in \\mathbb{R}^{d \\times b} \\)). If \\( q = \\frac{\\log d}{\\sqrt{\\varepsilon}} \\) for some \\( 0 < \\varepsilon < 1 \\), then have" + }, + { + "type": "equation", + "bbox": [ + 0.164, + 0.819, + 0.383, + 0.835 + ], + "angle": 0, + "content": "\\[\n\\left| \\theta_ {i} - \\lambda_ {i} \\right| \\leq \\varepsilon \\lambda_ {k + 1}, i = 1, \\dots , k.\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.469, + 0.901 + ], + "angle": 0, + "content": "In the rest of this subsection, we present a fast rank estimation of low-rank matrices based on the BKI and GDE. Given a low-rank matrix \\( D \\in \\mathbb{R}^{n \\times d} \\), \\( n < d \\) with rank \\( r \\). The BKI algorithm outputs a low-dimension matrix" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.091, + 0.892, + 0.166 + ], + "angle": 0, + "content": "\\(Z \\in \\mathbb{R}^{n \\times k}\\), \\(k < d\\), which aligns well with the top \\(k\\) singular vectors of \\(D\\). If \\(r \\leq k\\), the ranks of \\(D\\) and \\(Z\\) are equal. Hence it reduces the computational complexity when GDE can also be applied to \\(Z\\) to estimate the rank instead of the large-scale matrix \\(D\\)." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.167, + 0.892, + 0.196 + ], + "angle": 0, + "content": "The covariance matrix \\( \\mathbf{R}_{\\mathbf{Z}} \\in \\mathbb{R}^{k \\times k} \\) of the matrix \\( \\mathbf{Z} \\) with a rank \\( r \\) can be defined as:" + }, + { + "type": "equation", + "bbox": [ + 0.651, + 0.199, + 0.891, + 0.217 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {R} _ {Z} = \\boldsymbol {Z} ^ {T} \\boldsymbol {Z} \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.22, + 0.88, + 0.235 + ], + "angle": 0, + "content": "Then the eigenvalue decomposition of \\( R_Z \\) is given by" + }, + { + "type": "equation", + "bbox": [ + 0.619, + 0.237, + 0.891, + 0.256 + ], + "angle": 0, + "content": "\\[\nR _ {Z} = U _ {R _ {Z}} \\Sigma_ {R _ {Z}} U _ {R _ {Z}} ^ {H} \\tag {9}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.258, + 0.892, + 0.318 + ], + "angle": 0, + "content": "where \\(U_{R_Z} = [u_1, u_2, \\dots, u_k]\\) is the eigenvector matrix, and \\(\\Sigma_{R_Z} = \\text{diag}(\\sigma_1, \\sigma_2, \\dots, \\sigma_k)\\) represents the eigenvalue matrix. According to the Gerschgorin disk theorem [29], \\(R_Z\\) can be transformed as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.509, + 0.32, + 0.891, + 0.403 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {R} _ {\\boldsymbol {Z}} = \\left[ \\begin{array}{c c c c} R _ {1 1} & R _ {1 2} & \\dots & R _ {1 k} \\\\ R _ {2 1} & R _ {2 2} & \\dots & R _ {2 k} \\\\ \\vdots & \\vdots & \\ddots & \\vdots \\\\ R _ {k 1} & R _ {k 2} & \\dots & R _ {k k} \\end{array} \\right] = \\left[ \\begin{array}{c c} \\boldsymbol {R} _ {\\boldsymbol {Z 1}} & \\boldsymbol {R} \\\\ \\boldsymbol {R} ^ {H} & R _ {k k} \\end{array} \\right] \\tag {10}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.403, + 0.892, + 0.464 + ], + "angle": 0, + "content": "where \\(\\pmb{R}_{\\pmb{Z1}} \\in \\mathbb{R}^{(k-1) \\times (k-1)}\\) is the square matrix by the first \\((k-1)\\) rows and the first \\((k-1)\\) columns of \\(\\pmb{R}_{\\pmb{Z1}}\\), and \\(\\pmb{R} = [R_{1k}, R_{2k}, \\dots, R_{(k-1)k}]^T\\). Then the eigenvalue decomposition on \\(\\pmb{R}_{\\pmb{Z1}}\\) is obtained as:" + }, + { + "type": "equation", + "bbox": [ + 0.624, + 0.466, + 0.891, + 0.484 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {R} _ {Z 1} = U _ {Z 1} \\boldsymbol {\\Sigma} _ {1} U _ {Z 1} ^ {H} \\tag {11}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.486, + 0.892, + 0.56 + ], + "angle": 0, + "content": "where \\(U_{\\mathbf{Z1}} = [q_1', q_2', \\dots, q_{k-1}']\\) is an \\((k-1) \\times (k-1)\\) unitary matrix composed of the eigenvectors of \\(\\mathbf{R}_{\\mathbf{Z1}}\\), and \\(\\pmb{\\Sigma}_{\\mathbf{1}} = \\text{diag}(\\sigma_1', \\sigma_2', \\dots, \\sigma_{k-1}')\\). Similar to Eq. (10), a unitary transformed matrix \\(\\mathbf{U} \\in \\mathbb{R}^{k \\times k}(\\mathbf{U}\\mathbf{U}^H = \\mathbf{I})\\) is defined as:" + }, + { + "type": "equation", + "bbox": [ + 0.629, + 0.56, + 0.891, + 0.593 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {U} = \\left[ \\begin{array}{c c} U _ {Z 1} & \\mathbf {0} \\\\ \\mathbf {0} ^ {T} & \\mathbf {1} \\end{array} \\right] \\tag {12}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.598, + 0.854, + 0.613 + ], + "angle": 0, + "content": "The transformed covariance matrix is obtained by:" + }, + { + "type": "equation", + "bbox": [ + 0.515, + 0.614, + 0.891, + 0.753 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\boldsymbol {R} _ {T} = \\boldsymbol {U} ^ {H} \\boldsymbol {R} _ {Z} \\boldsymbol {U} = \\left[ \\begin{array}{c c} \\boldsymbol {U} _ {Z 1} ^ {H} \\boldsymbol {R} _ {Z 1} \\boldsymbol {U} _ {Z 1} & \\boldsymbol {U} _ {Z 1} ^ {H} \\boldsymbol {R} \\\\ \\boldsymbol {R} ^ {H} \\boldsymbol {U} _ {Z 1} & R _ {k k} \\end{array} \\right] \\\\ = \\left[ \\begin{array}{c c c c c c} \\sigma_ {1} ^ {\\prime} & 0 & 0 & \\dots & 0 & \\rho_ {1} \\\\ 0 & \\sigma_ {2} ^ {\\prime} & 0 & \\dots & 0 & \\rho_ {2} \\\\ 0 & 0 & \\sigma_ {3} ^ {\\prime} & \\dots & 0 & \\rho_ {3} \\\\ \\vdots & \\vdots & \\vdots & \\ddots & \\vdots & \\vdots \\\\ 0 & 0 & 0 & \\dots & \\sigma_ {k - 1} ^ {\\prime} & \\rho_ {k - 1} \\\\ \\rho_ {1} ^ {*} & \\rho_ {2} ^ {*} & \\rho_ {3} ^ {*} & \\dots & \\rho_ {k - 1} ^ {*} & R _ {k k} \\end{array} \\right] \\tag {13} \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.756, + 0.892, + 0.815 + ], + "angle": 0, + "content": "where \\(\\rho_{i} = \\pmb{q}_{i}^{\\prime H}\\pmb{R}\\). The eigenvalues of \\(\\pmb{R}_{T}\\) can be estimated using the Gerschgorin disk theorem [29]. Then, the radii of the first \\((k - 1)\\) Gerschgorin's disk can be written as:" + }, + { + "type": "equation", + "bbox": [ + 0.628, + 0.815, + 0.891, + 0.835 + ], + "angle": 0, + "content": "\\[\nr _ {i} = \\left| \\rho_ {i} \\right| = \\left| \\boldsymbol {q} _ {i} ^ {\\prime H} \\boldsymbol {R} \\right| \\tag {14}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.84, + 0.892, + 0.871 + ], + "angle": 0, + "content": "where the radius \\(r_i\\) of the \\(i\\)th Gerschgorin's disk depends on the size of \\(\\pmb{q}_i^{\\prime H}\\pmb {R}\\)" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.871, + 0.892, + 0.901 + ], + "angle": 0, + "content": "To further improve the accuracy of the rank estimation, the radii of the Gerschgorin's disk are shrank in [26]. Then" + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "1350" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.079, + 0.091, + 0.217, + 0.106 + ], + "angle": 0, + "content": "Algorithm 1 KGDE" + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.112, + 0.468, + 0.146 + ], + "angle": 0, + "content": "Input: \\(D\\in \\mathbb{R}^{n\\times d}\\), error \\(\\varepsilon \\in (0,1)\\), \\(k = 2\\), the \\((1 + \\varepsilon)\\) relative-error bound for BKI \\(q = \\frac{\\log d}{\\sqrt{\\varepsilon}}\\)" + }, + { + "type": "text", + "bbox": [ + 0.079, + 0.146, + 0.258, + 0.159 + ], + "angle": 0, + "content": "Output: Estimated rank \\( r \\)" + }, + { + "type": "text", + "bbox": [ + 0.095, + 0.161, + 0.245, + 0.175 + ], + "angle": 0, + "content": "Set \\( gde = \\text{zeros}(d, 1) \\)" + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.176, + 0.21, + 0.188 + ], + "angle": 0, + "content": "for \\(t = 1\\) to \\(d\\) do" + }, + { + "type": "equation", + "bbox": [ + 0.112, + 0.189, + 0.364, + 0.205 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {Z} \\in \\mathbb {R} ^ {n \\times k} \\leftarrow B K I (\\boldsymbol {D} \\in \\mathbb {R} ^ {n \\times d}, \\varepsilon , q)\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.112, + 0.205, + 0.326, + 0.219 + ], + "angle": 0, + "content": "Covariance matrix \\(\\mathbf{R}_{\\mathbf{Z}} = \\mathbf{Z}^{T}\\mathbf{Z}\\)" + }, + { + "type": "text", + "bbox": [ + 0.112, + 0.221, + 0.469, + 0.25 + ], + "angle": 0, + "content": "Obtain the transformed unitary matrix according to Eqs. (10)-(12)" + }, + { + "type": "text", + "bbox": [ + 0.112, + 0.251, + 0.469, + 0.28 + ], + "angle": 0, + "content": "Calculate the radii \\(r_i\\) of the Gerschgorin's disk according to Eqs. (14)-(15)" + }, + { + "type": "text", + "bbox": [ + 0.112, + 0.281, + 0.406, + 0.296 + ], + "angle": 0, + "content": "Calculate \\( gde(t) \\) according to Eqs. (16)-(17)" + }, + { + "type": "text", + "bbox": [ + 0.112, + 0.296, + 0.311, + 0.311 + ], + "angle": 0, + "content": "if \\((t > 1\\& \\& gde(t) < 0)\\) then" + }, + { + "type": "text", + "bbox": [ + 0.128, + 0.312, + 0.172, + 0.324 + ], + "angle": 0, + "content": "break;" + }, + { + "type": "text", + "bbox": [ + 0.112, + 0.327, + 0.141, + 0.338 + ], + "angle": 0, + "content": "else" + }, + { + "type": "equation", + "bbox": [ + 0.128, + 0.342, + 0.198, + 0.354 + ], + "angle": 0, + "content": "\\[\nk = k + 1\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.112, + 0.357, + 0.156, + 0.369 + ], + "angle": 0, + "content": "end if" + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.373, + 0.15, + 0.384 + ], + "angle": 0, + "content": "end for" + }, + { + "type": "equation", + "bbox": [ + 0.096, + 0.387, + 0.162, + 0.399 + ], + "angle": 0, + "content": "\\[\nr = t - 1\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.403, + 0.15, + 0.414 + ], + "angle": 0, + "content": "return \\( r \\)" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.445, + 0.469, + 0.498 + ], + "angle": 0, + "content": "a new diagonal matrix \\(\\pmb{\\Sigma}_{\\pmb{T}} = \\text{diag}(\\sigma_{1}', \\sigma_{2}', \\dots, \\sigma_{k-1}', \\sigma_{k}')\\) is constructed, where \\(\\sigma_{k}' = \\sqrt{\\sum_{i=1}^{k-1} \\sigma_{i}'^{2}}\\). Thus, the new transformed matrix \\(\\pmb{R}_{\\pmb{T}\\pmb{\\Sigma}_{\\pmb{T}}}\\) is constructed as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.097, + 0.501, + 0.469, + 0.646 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\boldsymbol {R} _ {T \\Sigma_ {T}} = \\boldsymbol {\\Sigma} _ {T} \\boldsymbol {R} _ {T} \\boldsymbol {\\Sigma} _ {T} ^ {- 1} \\\\ = \\left[ \\begin{array}{c c c c c} \\sigma_ {1} ^ {\\prime} & 0 & \\dots & 0 & \\frac {\\sigma_ {1} ^ {\\prime}}{\\sigma_ {k} ^ {\\prime}} \\rho_ {1} \\\\ 0 & \\sigma_ {2} ^ {\\prime} & \\dots & 0 & \\frac {\\sigma_ {2}}{\\sigma_ {k} ^ {\\prime}} \\rho_ {2} \\\\ \\vdots & \\vdots & \\ddots & \\vdots & \\vdots \\\\ 0 & 0 & \\dots & \\sigma_ {k - 1} ^ {\\prime} & \\frac {\\sigma_ {k - 1} ^ {\\prime}}{\\sigma_ {k} ^ {\\prime}} \\rho_ {k - 1} \\\\ \\frac {\\sigma_ {1} ^ {\\prime}}{\\sigma_ {k} ^ {\\prime}} \\rho_ {1} ^ {*} & \\frac {\\sigma_ {2} ^ {\\prime}}{\\sigma_ {k} ^ {\\prime}} \\rho_ {2} ^ {*} & \\dots & \\frac {\\sigma_ {k - 1} ^ {\\prime}}{\\sigma_ {k} ^ {\\prime}} \\rho_ {k - 1} ^ {*} & R _ {k k} \\end{array} \\right] \\tag {15} \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.647, + 0.469, + 0.707 + ], + "angle": 0, + "content": "\\(R_{T\\Sigma_T}\\) and \\(R_{T}\\) are similar matrices and have the same eigenvalues. In Eq. (15), the radii are compressed to various degrees. Finally, the estimated rank is obtained by the improved heuristic decision rule:" + }, + { + "type": "equation", + "bbox": [ + 0.085, + 0.711, + 0.469, + 0.757 + ], + "angle": 0, + "content": "\\[\ng d e (t) = \\frac {1}{\\sqrt {\\sum_ {i = 1} ^ {k - 1} \\sigma_ {i} ^ {\\prime 2}}} [ | \\sigma_ {t} ^ {\\prime} | r _ {t} - \\frac {H _ {D} ^ {(t)} (M)}{k - 1} \\sum_ {i = 1} ^ {k - 1} \\left| \\sigma_ {i} ^ {\\prime} \\right| r _ {i} ] \\tag {16}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.761, + 0.469, + 0.793 + ], + "angle": 0, + "content": "where \\(t = 1,2,\\dots ,k - 2\\) and \\(0 < H_D^{(t)}(M) < 1\\) is the adjustment factor:" + }, + { + "type": "equation", + "bbox": [ + 0.186, + 0.795, + 0.469, + 0.839 + ], + "angle": 0, + "content": "\\[\nH _ {D} ^ {(t)} (M) = \\frac {2 \\left| \\sigma_ {t + 1} ^ {\\prime} \\right|}{\\sqrt {\\sum_ {i = t} ^ {k - 1} \\sigma_ {i} ^ {\\prime 2}}} \\tag {17}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.84, + 0.469, + 0.87 + ], + "angle": 0, + "content": "As a result, the rank \\( r = t - 1 \\) if the first negative value of (16) is reached at \\( t \\)." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.469, + 0.901 + ], + "angle": 0, + "content": "When \\(r \\leq k\\), \\(D\\) is transformed to \\(Z\\) by BKI, then the rank of \\(Z\\) is estimated by GDE. It is noted that while \\(r > k\\)," + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.182 + ], + "angle": 0, + "content": "GDE can not estimate the true rank of \\( D \\) from \\( Z \\). To adaptively determine an appropriate \\( k \\), KGDE is proposed by adopting iteration, and GDE is served as a stopping criterion for such Krylov subspace approximation of \\( Z \\). The KGDE for rank estimation based on BKI and GDE is summarized in Algorithm 1." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.183, + 0.892, + 0.307 + ], + "angle": 0, + "content": "Remark 1: The computational cost of KGDE is related to BKI. If the estimated \\( r \\) of the input matrix \\( D \\in \\mathbb{R}^{n \\times d} \\) is exact, the computational complexity will be \\( O(ndrq + n(rq)^2) \\), where \\( n < d \\). For sparse matrix, the computational cost of KGDE will be \\( O(nnz(D)rq + n(rq)^2) \\), where \\( nnz(D) \\) is the number of nonzeros in \\( D \\). Since \\( r \\leq n \\) and \\( q = \\frac{\\log d}{\\sqrt{\\varepsilon}} \\) are small, the KGDE will be inexpensive, especially for sparse matrices." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.308, + 0.892, + 0.382 + ], + "angle": 0, + "content": "Remark 2: The accuracy of the KGDE mainly depends on the BKI. In light of Theorem 1, \\( Z \\) is obtained within a high-quality principal components approximation of \\( D \\), both its eigenvalues and eigenvectors are highly close to the actual ones of \\( D \\)." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.394, + 0.892, + 0.426 + ], + "angle": 0, + "content": "2.2. Efficient RPCA based on KGDE and CUR Decomposition" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.433, + 0.892, + 0.478 + ], + "angle": 0, + "content": "In this subsection, an efficient RPCA based on the above rank estimation and CUR decomposition is proposed for solving the following optimization problem:" + }, + { + "type": "equation", + "bbox": [ + 0.525, + 0.479, + 0.891, + 0.503 + ], + "angle": 0, + "content": "\\[\n\\min _ {\\boldsymbol {L}, \\boldsymbol {S}} \\| \\boldsymbol {D} - \\boldsymbol {L} - \\boldsymbol {S} \\| _ {F} ^ {2} + \\lambda \\| \\boldsymbol {L} \\| _ {\\gamma} \\quad s. t. \\| \\boldsymbol {S} \\| _ {0} \\leq s \\tag {18}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.505, + 0.545, + 0.517 + ], + "angle": 0, + "content": "where" + }, + { + "type": "equation", + "bbox": [ + 0.592, + 0.517, + 0.799, + 0.573 + ], + "angle": 0, + "content": "\\[\n\\| \\boldsymbol {L}\\|_{\\gamma} = \\left\\{ \\begin{array}{l}\\sum_{i = 1}\\frac{e^{\\gamma}\\sigma_{i}}{\\gamma + \\sigma_{i}}, i\\leq r\\\\ 0 , i > r \\end{array} \\right.\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.579, + 0.892, + 0.624 + ], + "angle": 0, + "content": "and \\(\\sigma_{i}, i = 1,2,\\dots ,r\\), is the singular value, \\(\\gamma >0\\), and \\(\\lambda\\) is the regularized parameter which provides a trade-off between the recovery of low-rank matrix and sparse matrix." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.625, + 0.892, + 0.685 + ], + "angle": 0, + "content": "The optimization model (18) adds a new non-convex low-rank regularization term to Eq. (2), which adopts the estimated rank to achieve better recovery accuracy of the low-rank matrix than the weighted nuclear norm in (3)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.686, + 0.892, + 0.716 + ], + "angle": 0, + "content": "In this work, the alternating projection method is used to solve the following two sub-problems until convergence:" + }, + { + "type": "equation", + "bbox": [ + 0.534, + 0.743, + 0.891, + 0.768 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {L} _ {\\ell + 1} = \\underset {\\boldsymbol {L}} {\\arg \\min } \\| \\boldsymbol {D} - \\boldsymbol {L} - \\boldsymbol {S} _ {\\ell} \\| _ {F} ^ {2} + \\lambda \\| \\boldsymbol {L} \\| _ {\\gamma} \\tag {19}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.568, + 0.771, + 0.891, + 0.798 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {S} _ {\\ell + 1} = \\underset {\\boldsymbol {S}: \\| \\boldsymbol {S} \\| _ {0} \\leq s} {\\arg \\min } \\| \\boldsymbol {D} - \\boldsymbol {L} _ {\\ell + 1} - \\boldsymbol {S} \\| _ {F} ^ {2} \\tag {20}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.811, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Update for L: The traditional solution of (19) often involves SVD, which requires significant computational resource for a large-scale matrix. To efficiently solve the model (19), we replace SVD with CUR decomposition [30], which has been proven to be efficient and effective in solving classical RPCA problem [31]. Mathematically, the CUR" + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.945, + 0.514, + 0.957 + ], + "angle": 0, + "content": "1351" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.09, + 0.068, + 0.273, + 0.194 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.293, + 0.068, + 0.477, + 0.194 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.494, + 0.067, + 0.677, + 0.194 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.695, + 0.067, + 0.88, + 0.194 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.293, + 0.206, + 0.676, + 0.221 + ], + "angle": 0, + "content": "Figure 1. The numerical rank estimation of sparse data matrices." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.23, + 0.411, + 0.245 + ], + "angle": 0, + "content": "decomposition of (19) can be rewritten as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.086, + 0.255, + 0.469, + 0.282 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {C} _ {\\ell + 1} = \\underset {\\boldsymbol {L} _ {:, \\mathcal {J}}} {\\arg \\min } \\| [ \\boldsymbol {D} - \\boldsymbol {L} - \\boldsymbol {S} _ {\\ell} ] _ {:, \\mathcal {J}} \\| _ {F} ^ {2} + \\lambda \\| \\boldsymbol {L} _ {:, \\mathcal {J}} \\| _ {\\gamma} \\tag {21}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.165, + 0.286, + 0.469, + 0.304 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {U} _ {\\ell + 1} = \\mathcal {T} \\boldsymbol {S} ([ \\boldsymbol {D} - \\boldsymbol {L} - \\boldsymbol {S} _ {\\ell} ] _ {\\mathcal {I}, \\mathcal {J}}) \\tag {22}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.09, + 0.306, + 0.469, + 0.333 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {R} _ {\\ell + 1} = \\underset {\\boldsymbol {L} _ {\\mathcal {I},:}} {\\arg \\min } \\| [ \\boldsymbol {D} - \\boldsymbol {L} - \\boldsymbol {S} _ {\\ell} ] _ {\\mathcal {I},:} \\| _ {F} ^ {2} + \\lambda \\| \\boldsymbol {L} _ {\\mathcal {I},:} \\| _ {\\gamma} \\tag {23}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.346, + 0.469, + 0.406 + ], + "angle": 0, + "content": "where \\(C_{\\ell +1}\\in \\mathbb{R}^{n\\times \\mathcal{I}}\\) is \\(\\mathcal{I}\\) columns of (19) via uniform sampling, \\(R_{\\ell +1}\\in \\mathbb{R}^{\\mathcal{I}\\times d}\\) is \\(\\mathcal{J}\\) rows of (19) in the same way, \\(U_{\\ell +1}\\in \\mathbb{R}^{\\mathcal{I}\\times \\mathcal{I}}\\) is the overlap of the column and row indices of \\(C_{\\ell +1}\\) and \\(R_{\\ell +1}\\). \\(\\mathcal{T}S(\\cdot)\\) denotes the truncated SVD." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.407, + 0.469, + 0.451 + ], + "angle": 0, + "content": "In addition, the rank value \\( r \\) is needed for \\( \\mathcal{T}S(\\cdot) \\) and CUR decomposition, which can be exactly estimated by our proposed KGDE method." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.452, + 0.469, + 0.512 + ], + "angle": 0, + "content": "As Eqs. (21) and (23) are the combination of concave and convex functions, the Difference of Convex programming [32] is used to solve these problems. Thus, \\( C_{\\ell + 1} \\) can be obtained as follows [33]:" + }, + { + "type": "equation", + "bbox": [ + 0.18, + 0.515, + 0.469, + 0.533 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {C} _ {\\ell + 1} = \\left[ \\boldsymbol {a} \\operatorname {d i a g} \\left\\{\\sigma^ {*} \\right\\} \\boldsymbol {b} ^ {T} \\right] _ {:, \\mathcal {I}} \\tag {24}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.535, + 0.469, + 0.579 + ], + "angle": 0, + "content": "where \\( \\mathbf{a} \\) and \\( \\mathbf{b} \\) are the left and right singular vectors of \\( (D - S_{\\ell + 1}) \\), respectively, and \\( \\sigma^* \\) has a closed-form solution at each iteration:" + }, + { + "type": "equation", + "bbox": [ + 0.152, + 0.581, + 0.469, + 0.611 + ], + "angle": 0, + "content": "\\[\n\\sigma^ {i + 1} = \\max \\left(\\left(\\sigma_ {\\boldsymbol {D} - \\boldsymbol {S} _ {\\ell + 1}} - \\frac {\\lambda \\omega_ {i}}{\\mu^ {\\ell}}\\right), 0\\right) \\tag {25}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.613, + 0.469, + 0.683 + ], + "angle": 0, + "content": "where \\(\\sigma_{D - S_{\\ell +1}}\\) is the singular value of \\((D - S_{\\ell +1}),\\mu >0,\\) and \\(\\omega_{i} = \\left\\{ \\begin{array}{ll}\\frac{\\gamma e^{\\gamma}}{(\\gamma + \\sigma_{i}(\\gamma))^{2}}, & i\\leq r\\\\ 0, & \\text{others} \\end{array} \\right.\\) is the gradient of \\(\\| L\\|_{\\gamma}\\) at" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.683, + 0.469, + 0.712 + ], + "angle": 0, + "content": "\\(\\sigma^i\\). Obviously, \\(\\omega_{i}\\) is dependent on \\(r\\), which can be estimated by KGDE at each iteration." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.713, + 0.165, + 0.728 + ], + "angle": 0, + "content": "Similarly," + }, + { + "type": "equation", + "bbox": [ + 0.182, + 0.73, + 0.469, + 0.748 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {R} _ {\\ell + 1} = \\left[ \\boldsymbol {a} \\operatorname {d i a g} \\left\\{\\sigma^ {*} \\right\\} \\boldsymbol {b} ^ {T} \\right] _ {\\mathcal {I},:} \\tag {26}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.751, + 0.267, + 0.765 + ], + "angle": 0, + "content": "Hence, the updated for \\(L\\) is:" + }, + { + "type": "equation", + "bbox": [ + 0.188, + 0.768, + 0.469, + 0.786 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {L} _ {\\ell + 1} = \\boldsymbol {C} _ {\\ell + 1} \\boldsymbol {U} _ {\\ell + 1} ^ {\\dagger} \\boldsymbol {R} _ {\\ell + 1} \\tag {27}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.79, + 0.433, + 0.805 + ], + "angle": 0, + "content": "where \\((\\cdot)^{\\dagger}\\) denotes the Moore-Penrose pseudoinverse." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.806, + 0.469, + 0.834 + ], + "angle": 0, + "content": "Update for S: Similarly, the optimization of (20) can be divided into as:" + }, + { + "type": "equation", + "bbox": [ + 0.104, + 0.838, + 0.469, + 0.866 + ], + "angle": 0, + "content": "\\[\n[ \\boldsymbol {S} _ {\\ell + 1} ] _ {:, \\mathcal {J}} = \\underset {\\boldsymbol {S}:, \\mathcal {J}: \\| \\boldsymbol {S} \\| _ {0} \\leq s} {\\arg \\min } \\| [ \\boldsymbol {D} - \\boldsymbol {L} _ {\\ell} - \\boldsymbol {S} ] _ {:, \\mathcal {J}} \\| _ {F} ^ {2} \\tag {28}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.107, + 0.875, + 0.469, + 0.904 + ], + "angle": 0, + "content": "\\[\n[ \\boldsymbol {S} _ {\\ell + 1} ] _ {\\mathcal {I},:} = \\underset {\\boldsymbol {S} _ {\\mathcal {I},:} \\| \\boldsymbol {S} \\| _ {0} \\leq s} {\\arg \\min } \\| [ \\boldsymbol {D} - \\boldsymbol {L} _ {\\ell} - \\boldsymbol {S} ] _ {\\mathcal {I},:} \\| _ {F} ^ {2} \\tag {29}\n\\]" + }, + { + "type": "title", + "bbox": [ + 0.501, + 0.229, + 0.755, + 0.243 + ], + "angle": 0, + "content": "Algorithm 2 eRPCA based on KGDE" + }, + { + "type": "text", + "bbox": [ + 0.501, + 0.249, + 0.892, + 0.311 + ], + "angle": 0, + "content": "Input: \\(D \\in \\mathbb{R}^{n \\times d}\\) with estimated rank \\(r\\); \\(\\delta\\): error; \\(\\lambda, \\mu\\): penalty parameter; \\(\\zeta_0\\): initial thresholding value; \\(|\\mathcal{I}| = O(r), |\\mathcal{J}| = O(r)\\): sampling number of rows and columns; \\(\\gamma\\): non-convex regularizer parameter." + }, + { + "type": "title", + "bbox": [ + 0.502, + 0.312, + 0.598, + 0.326 + ], + "angle": 0, + "content": "Output: \\(L, S\\)" + }, + { + "type": "text", + "bbox": [ + 0.517, + 0.327, + 0.886, + 0.341 + ], + "angle": 0, + "content": "Uniformly sample row indices \\(\\mathcal{I}\\) and column indices \\(\\mathcal{J}\\)." + }, + { + "type": "equation", + "bbox": [ + 0.518, + 0.341, + 0.675, + 0.355 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {L} _ {0} = 0, \\boldsymbol {S} _ {0} = 0, k = 0\n\\]" + }, + { + "type": "title", + "bbox": [ + 0.518, + 0.357, + 0.676, + 0.371 + ], + "angle": 0, + "content": "while not converged do" + }, + { + "type": "text", + "bbox": [ + 0.534, + 0.372, + 0.662, + 0.386 + ], + "angle": 0, + "content": "Resample \\(\\mathcal{I}\\) and \\(\\mathcal{J}\\)" + }, + { + "type": "text", + "bbox": [ + 0.534, + 0.387, + 0.664, + 0.402 + ], + "angle": 0, + "content": "Update \\(\\zeta_{k + 1} = \\eta \\zeta_0\\)" + }, + { + "type": "text", + "bbox": [ + 0.534, + 0.402, + 0.805, + 0.417 + ], + "angle": 0, + "content": "Update \\(S_{\\ell +1}\\) according to Eqs. (28)-(29)" + }, + { + "type": "text", + "bbox": [ + 0.534, + 0.417, + 0.752, + 0.431 + ], + "angle": 0, + "content": "Estimate and update \\( r \\) by KGDE" + }, + { + "type": "text", + "bbox": [ + 0.534, + 0.432, + 0.741, + 0.447 + ], + "angle": 0, + "content": "Update \\(C_{\\ell +1}\\) according to (21)" + }, + { + "type": "text", + "bbox": [ + 0.534, + 0.448, + 0.742, + 0.462 + ], + "angle": 0, + "content": "Update \\(R_{\\ell +1}\\) according to (23)" + }, + { + "type": "text", + "bbox": [ + 0.534, + 0.463, + 0.74, + 0.477 + ], + "angle": 0, + "content": "Update \\(U_{\\ell +1}\\) according to (22)" + }, + { + "type": "equation", + "bbox": [ + 0.534, + 0.477, + 0.702, + 0.493 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {L} _ {\\ell + 1} = \\boldsymbol {C} _ {\\ell + 1} \\boldsymbol {U} _ {\\ell + 1} ^ {\\dagger} \\boldsymbol {R} _ {\\ell + 1}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.535, + 0.493, + 0.6, + 0.506 + ], + "angle": 0, + "content": "\\[\n\\ell = \\ell + 1\n\\]" + }, + { + "type": "title", + "bbox": [ + 0.518, + 0.508, + 0.588, + 0.521 + ], + "angle": 0, + "content": "end while" + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.551, + 0.89, + 0.567 + ], + "angle": 0, + "content": "For \\(S\\), the hard thresholding operator \\(\\mathcal{HT}\\) is adopted as:" + }, + { + "type": "equation", + "bbox": [ + 0.571, + 0.579, + 0.891, + 0.619 + ], + "angle": 0, + "content": "\\[\n\\left[ \\mathcal {H T} (\\boldsymbol {S}) \\right] _ {i, j} = \\left\\{ \\begin{array}{l} \\boldsymbol {S} _ {i, j}, i f | \\boldsymbol {S} _ {i, j} | > \\zeta , \\\\ 0, o t h e r w i s e. \\end{array} \\right. \\tag {30}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.626, + 0.89, + 0.656 + ], + "angle": 0, + "content": "where \\(\\zeta\\) is the thresholding value. The hard thresholding is employed for projections on to \\((D - L_{\\ell})\\)." + }, + { + "type": "text", + "bbox": [ + 0.52, + 0.658, + 0.737, + 0.67 + ], + "angle": 0, + "content": "The iteration is terminated when" + }, + { + "type": "equation", + "bbox": [ + 0.522, + 0.671, + 0.891, + 0.717 + ], + "angle": 0, + "content": "\\[\n\\frac {\\left\\| \\left[ \\boldsymbol {D} - \\boldsymbol {L} _ {\\ell} - \\boldsymbol {S} _ {\\ell} \\right] _ {: , \\mathcal {I}} \\right\\| _ {F} + \\left\\| \\left[ \\boldsymbol {D} - \\boldsymbol {L} _ {\\ell} - \\boldsymbol {S} _ {\\ell} \\right] _ {\\mathcal {I} , :} \\right\\| _ {F}}{\\left\\| \\boldsymbol {D} _ {: , \\mathcal {I}} \\right\\| _ {F} + \\left\\| \\boldsymbol {D} _ {\\mathcal {I} , :} \\right\\| _ {F}} < \\delta \\tag {31}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.718, + 0.89, + 0.748 + ], + "angle": 0, + "content": "The entire procedure to solve the problem (18) is summarized in Algorithm 2." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.748, + 0.892, + 0.903 + ], + "angle": 0, + "content": "Remark 3: The computational complexity of \\( U \\) in CUR decomposition is \\( O(r^3) \\). Since the sampling numbers of rows and columns are \\( |\\mathcal{I}| = O(r) \\) and \\( |\\mathcal{J}| = O(r) \\), respectively, updating \\( L \\) requires \\( O(r^{2}n) \\) flops per iteration. In contrast, computing the SVD usually requires \\( O(rnd) \\). In addition, the runtime of updating \\( S \\) is actually a simple projection, whose computational complexity is further less than that of \\( L \\). Thus, the computational complexity of the alternating projection procedure is \\( O\\left(\\frac{d^2r}{\\epsilon} + d \\cdot \\text{poly}(r, \\log(r / \\epsilon), 1 / \\epsilon)\\right) \\), where \\( 0 < \\epsilon < 1 \\) is an" + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "1352" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.088, + 0.082, + 0.268, + 0.203 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.284, + 0.082, + 0.45, + 0.203 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.082, + 0.216, + 0.462, + 0.23 + ], + "angle": 0, + "content": "Figure 2. The numerical rank estimation of video data matrices." + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.241, + 0.212, + 0.254 + ], + "angle": 0, + "content": "accuracy parameter." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.269, + 0.282, + 0.285 + ], + "angle": 0, + "content": "3. Experimental Results" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.294, + 0.47, + 0.43 + ], + "angle": 0, + "content": "This section reports the experimental results of our proposed eRPCA and compares it with state-of-the-art algorithms on synthetic datasets and two practical computer vision scenarios. The parameters in our method are listed as follows: \\(\\gamma = 0.02\\), \\(\\delta = 10^{-7}\\), \\(\\lambda = 10^{-3}\\), \\(\\mu = \\frac{1}{2}\\), \\(\\zeta_0 = \\max(|D|)\\), and \\(\\varepsilon = 0.05\\). The parameters in other methods use their default settings. All the experiments are conducted on a laptop with MATLAB 2019 equipped with Windows 10 based on AMD Ryzen 5 CPU with 32G RAM." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.44, + 0.445, + 0.455 + ], + "angle": 0, + "content": "3.1. The Validation of Rank Estimation Method" + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.463, + 0.267, + 0.477 + ], + "angle": 0, + "content": "3.1.1 Public real datasets" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.487, + 0.469, + 0.606 + ], + "angle": 0, + "content": "To validate the efficiency and accuracy of KGDE, the general data matrices are tested to estimate the rank. SuiteSparse Database1 [34] provides general data matrices with low numerical rank, whose Gaussian-type distribution assumptions for the data and noise may not hold. In addition, the video datasets from Scene Background Initialization (SBI) dataset2 [35], which are converted to the full matrix are also tested." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.608, + 0.469, + 0.729 + ], + "angle": 0, + "content": "Fig.1 shows the numerical rank estimation for the SVD curve of sparse data matrices. The singular values of Fig.1(a) and Fig.1(b) have apparent distribution, and KGDE and GDE obtain the exact rank estimation. The singular values of Fig.1(c) and Fig.1(d) are very close, it is therefore hard to bind the rank. The result of Fig.1(c) is the same, and the one of Fig.1(d) is slightly different, while the gap can be ignored in practice." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.73, + 0.469, + 0.79 + ], + "angle": 0, + "content": "Fig.2 shows the rank estimation results of video data matrices. The video datasets have a stable low-rank, and the rank is usually equal to 1. Thus, the distribution of their singular values has a noticeable gap." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.79, + 0.469, + 0.865 + ], + "angle": 0, + "content": "The comparisons of runtime and estimated rank for different matrices are shown in Table 1. When the matrix scale is small, the execution time is close, but KGDE is still faster than GDE. When the matrix becomes more extensive, the efficiency of KGDE performs better than GDE. Because the" + }, + { + "type": "image", + "bbox": [ + 0.505, + 0.071, + 0.882, + 0.151 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.16, + 0.892, + 0.188 + ], + "angle": 0, + "content": "Figure 3. The comparison of the average runtime between different algorithms." + }, + { + "type": "table_caption", + "bbox": [ + 0.5, + 0.194, + 0.892, + 0.22 + ], + "angle": 0, + "content": "Table 1. The results of runtime and estimated rank using GDE and KGDE" + }, + { + "type": "table", + "bbox": [ + 0.502, + 0.222, + 0.892, + 0.359 + ], + "angle": 0, + "content": "
DatasetGDEKGDE
Runtime(s)RankRuntime(s)Rank
lp Blend0.15630.0943
lp_pilot41.48830.2503
Ipi bgdbg10.27460.2666
Ipi_ceria3d91.18050.2343
IBMtest20.17610.1341
CAVIAR12.23510.7571
" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.369, + 0.892, + 0.413 + ], + "angle": 0, + "content": "computational complexity of KGDE is not too much related to the dimension of the matrix, KGDE can maintain a fast result." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.436, + 0.682, + 0.451 + ], + "angle": 0, + "content": "3.1.2 Synthetic Datasets" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.46, + 0.892, + 0.506 + ], + "angle": 0, + "content": "For synthetic datasets, our algorithm was compared with the state-of-the-art RPCA-based approaches: RPCA [1], PSSV [36], WNNM [37], and ARE-RPCA [26]." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.507, + 0.892, + 0.628 + ], + "angle": 0, + "content": "The recovery ability and execution time of the algorithms are investigated. The input matrix \\( D \\in \\mathbb{R}^{n \\times d} \\) is corrupted by sparse noise with the corruption rate \\( \\alpha = \\{0.1, 0.3, 0.5, 0.7\\} \\). The parameters are set: \\( d = 10000 \\), \\( n = \\{20, 100, 500\\} \\) and different ranks \\( r = \\{1, 3, 5\\} \\). The iteration stop criterion is \\( 10^{-7} \\). Let \\( L_{sol} \\) be the reconstruction of \\( L \\) and the reconstruction error is defined as \\( \\| L_{sol} - L \\|_F / \\| L \\|_F \\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.628, + 0.892, + 0.703 + ], + "angle": 0, + "content": "The comparisons of the average runtime with different ranks \\( r \\) and dimensions \\( d \\) are shown in Fig.3. The eRPCA is faster than others for the average runtime in Fig.3. When the input matrix has a larger scale or rank, the time gap between our method and others is more prominent." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.704, + 0.892, + 0.794 + ], + "angle": 0, + "content": "The simulation results are shown in Fig.4. It can be seen that eRPCA algorithm is stubborn when the corruption rate is low and has similar results with other algorithms. When the corruption rate rises, the reconstruction error of eRPCA algorithm is larger. eRPCA performs worse when the corruption rate is 0.7 with a large rank." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.795, + 0.892, + 0.884 + ], + "angle": 0, + "content": "Table 2 shows the desired rank of the low-rank matrix decomposed by different algorithms under different corruption rates. It can be observed that the proposed eRPCA can obtain correct ranks of low-rank matrices in all cases. Other algorithms can get the desired rank correctly only if the corruption rate is low." + }, + { + "type": "text", + "bbox": [ + 0.52, + 0.886, + 0.892, + 0.901 + ], + "angle": 0, + "content": "According to the above analysis, it is observed that eR-" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.875, + 0.232, + 0.888 + ], + "angle": 0, + "content": "1https://sparse.tamu.edu/" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.888, + 0.348, + 0.9 + ], + "angle": 0, + "content": "\\(^{2}\\)https://sbmi2015.na.icar.cnr.it/SBIdataset.html" + }, + { + "type": "list", + "bbox": [ + 0.096, + 0.875, + 0.348, + 0.9 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "1353" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.189, + 0.09, + 0.375, + 0.213 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.387, + 0.091, + 0.574, + 0.213 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.589, + 0.091, + 0.772, + 0.213 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.188, + 0.214, + 0.374, + 0.335 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.389, + 0.214, + 0.574, + 0.335 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.589, + 0.214, + 0.772, + 0.335 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.189, + 0.336, + 0.374, + 0.459 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.389, + 0.336, + 0.574, + 0.459 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.589, + 0.336, + 0.772, + 0.459 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.152, + 0.469, + 0.816, + 0.484 + ], + "angle": 0, + "content": "Figure 4. Comparison of various algorithms with different dimensions \\( n \\), matrix ranks \\( r \\), and corruption rates \\( \\alpha \\)." + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.498, + 0.893, + 0.524 + ], + "angle": 0, + "content": "Table 2. The desired rank of low-rank matrix decomposed by different algorithms in different corruption rates and dimensions with different ranks" + }, + { + "type": "table", + "bbox": [ + 0.085, + 0.527, + 0.887, + 0.732 + ], + "angle": 0, + "content": "
AlgorithmDimensionr=1r=3r=5
α=0.1α=0.3α=0.5α=0.7α=0.1α=0.3α=0.5α=0.7α=0.1α=0.3α=0.5α=0.7
RPCAn=20116648655656
n=10011123335555552
n=50011173331255516
PSSVn=20111233515551519
n=100111133335558
n=50011163331055513
ARE-RPCAn=20111133355555
n=100111133335555
n=500111133375555
WNNMn=20111133511551520
n=1001111333100555100
n=5001111333500555500
eRPCAn=20111133335555
n=100111133335555
n=500111133335555
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.739, + 0.47, + 0.768 + ], + "angle": 0, + "content": "PCA has excellent robustness and the fastest execution time." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.793, + 0.394, + 0.81 + ], + "angle": 0, + "content": "3.2. Foreground-Background Separation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.821, + 0.469, + 0.866 + ], + "angle": 0, + "content": "In this subsection, we evaluate the proposed eRPCA with the following approaches: ARE-RPCA [26], IRCUR [25], PETRELS [38], and ADW-RPCA [39]." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.47, + 0.902 + ], + "angle": 0, + "content": "Foreground-background separation is an important application of RPCA. Scene Background Initialization (SBI)" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.739, + 0.892, + 0.86 + ], + "angle": 0, + "content": "dataset3 [35] is considered. The visual comparisons of the sub-dataset CAVIAR1 are shown in Fig.5, containing 610 frames with size \\(384 \\times 256\\). The dataset can be represented by a matrix, where each column is a vectorized video frame. Then each algorithm can be applied to decompose the matrix into low-rank parts and sparse ones; that is, this scene can be separated from the moving foreground object from the static background." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.861, + 0.892, + 0.877 + ], + "angle": 0, + "content": "There are five frames selected in Fig.5, and the upper and" + }, + { + "type": "page_footnote", + "bbox": [ + 0.518, + 0.887, + 0.771, + 0.9 + ], + "angle": 0, + "content": "3https://sbmi2015.na.icar.cnr.it/SBIdataset.html" + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "1354" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.081, + 0.078, + 0.47, + 0.414 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.428, + 0.47, + 0.456 + ], + "angle": 0, + "content": "Figure 5. The comparison of visual results on CAVIAR1 between different algorithms." + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.46, + 0.469, + 0.487 + ], + "angle": 0, + "content": "Table 3. Performance of one frame from CAVIAR1 dataset among different algorithms" + }, + { + "type": "table", + "bbox": [ + 0.081, + 0.489, + 0.472, + 0.556 + ], + "angle": 0, + "content": "
AGEpEPs%pCEPS%MSSSIMPSNRCQMTIME(s)
ARE-RPCA5.26374.07413.48710.856425.441424.787610.78593
IRCUR3.14890.28280.18210.991734.468933.27140.007564
PETRELS4.99725.01614.02220.932929.801729.07731.14708
ADW-RPCA2.640.34990.24820.990534.485333.34026.356669
eRPCA2.63940.26860.16890.991734.862633.57250.034198
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.581, + 0.469, + 0.642 + ], + "angle": 0, + "content": "lower parts represent the background and foreground. It can be shown that ARE-RPCA and PETRELS yield artifacts in some backgrounds. IRCUR, ADW-RPCA, and eRPCA obtain more distinctive visual results." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.642, + 0.47, + 0.838 + ], + "angle": 0, + "content": "In addition, objective evaluations, i.e. AGE, pEP, pCEP, PSNR, MS-SSIM, CQM, are performed on SBI database where the smaller the first three values, the better the separation results, and the last three ones and vice versa. Table 3 shows the performance evaluation of the above six metrics and runtime. For the first six metrics, eRPCA algorithm obtains better results. Due to the time of estimating the rank, eRPCA algorithm is slower than IRCUR for each frame. However, IRCUR needs to determine the rank in advance, leading to its results being slightly inferior to ours. Moreover, only ARE-RPCA and eRPCA algorithm can obtain the rank prior, but ours are better than ARE-RPCA in all aspects." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.848, + 0.388, + 0.865 + ], + "angle": 0, + "content": "3.3. Shadow Removal from Face Images" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.47, + 0.903 + ], + "angle": 0, + "content": "Face images taken under different lighting conditions always introduce errors, for example, uneven lighting," + }, + { + "type": "image", + "bbox": [ + 0.502, + 0.089, + 0.895, + 0.212 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.502, + 0.226, + 0.889, + 0.241 + ], + "angle": 0, + "content": "Figure 6. The comparison of different algorithms on two images." + }, + { + "type": "table_caption", + "bbox": [ + 0.502, + 0.248, + 0.892, + 0.262 + ], + "angle": 0, + "content": "Table 4. The comparison of runtime between different algorithms" + }, + { + "type": "table", + "bbox": [ + 0.505, + 0.263, + 0.888, + 0.316 + ], + "angle": 0, + "content": "
RPCAPSSVWNNMARE-RPCAeRPCA
yale053.535s0.973s1.113s3.648s0.071s
yaleB023.499s0.962s2.424s3.650s0.081s
" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.326, + 0.892, + 0.461 + ], + "angle": 0, + "content": "shadow etc, which yields challenge for face recognition. Fig.6 (first column) shows two typical examples with size \\(192 \\times 168\\) from the Extended Yale B database[40], a benchmark database in face recognition. Each image is converted to a column vector. The comparisons of these methods are given: RPCA [1], PSSV [36], WNNM [37], and ARE-RPCA [26]. In addition, since the images are aligned, the rank is set to 1, and ARE-RPCA and eRPCA can adaptively estimate the rank." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.463, + 0.892, + 0.537 + ], + "angle": 0, + "content": "Fig.6 shows the shadow removal results of different algorithms. In the visual aspect, the proposed eRPCA algorithm removes the shadow well and does not need to determine the rank. The runtime of different algorithms is shown in Table 4 and ours is the fastest." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.54, + 0.892, + 0.571 + ], + "angle": 0, + "content": "Due to the space limitation, more experimental results are shown in the Supplementary Material." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.588, + 0.619, + 0.604 + ], + "angle": 0, + "content": "4. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.614, + 0.892, + 0.78 + ], + "angle": 0, + "content": "In this paper, an efficient non-convex RPCA method is proposed for recovering a low-rank matrix and a sparse matrix, especially with large sizes. Specifically, a fast rank estimation method KGDE has been proposed by using Gerschgorin disk theorem with the block Krylov iteration. Based on the estimated rank, a new non-convex regularizer is proposed to achieve better recovery of the low-rank matrices with less computation due to CUR decomposition involved in the iterations. Experimental results demonstrate that the proposed eRPCA algorithm outperforms state-of-the-art algorithms in various vision applications." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.782, + 0.892, + 0.873 + ], + "angle": 0, + "content": "In future, our algorithm will be extended in other applications, such as image recovery and video denoising. However, the accuracy of eRPCA for high corruption rate is still a big challenge. Therefore, we will devote ourselves to improving the robustness of the algorithm. Meanwhile, the parameter adaptability is considered in our future work." + }, + { + "type": "page_footnote", + "bbox": [ + 0.516, + 0.887, + 0.851, + 0.9 + ], + "angle": 0, + "content": "4http://vision.ucsd.edu/leekc/ExtYaleDatabase/ExtYaleB.html" + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "1355" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.175, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.115, + 0.47, + 0.157 + ], + "angle": 0, + "content": "[1] Emmanuel J Candès, Xiaodong Li, Yi Ma, and John Wright. Robust principal component analysis? Journal of the ACM (JACM), 58(3):1-37, 2011. 1, 6, 8" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.162, + 0.471, + 0.219 + ], + "angle": 0, + "content": "[2] Spencer Markowitz, Corey Snyder, Yonina C Eldar, and Minh N Do. 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Institute for Infocomm Research A*STAR, Singapore + +fangshun97@wust.edu.cn, fate311@sjtu.edu.cn, shiqian.wu@wust.edu.cn, slxie@i2r.a-star.edu.sg + +# Abstract + +Robust principal component analysis (RPCA) is widely studied in computer vision. Recently an adaptive rank estimate based RPCA has achieved top performance in low-level vision tasks without the prior rank, but both the rank estimate and RPCA optimization algorithm involve singular value decomposition, which requires extremely huge computational resource for large-scale matrices. To address these issues, an efficient RPCA (eRPCA) algorithm is proposed based on block Krylov iteration and CUR decomposition in this paper. Specifically, the Krylov iteration method is employed to approximate the eigenvalue decomposition in the rank estimation, which requires $O(ndrq + n(rq)^2)$ for an $(n \times d)$ input matrix, in which $q$ is a parameter with a small value, $r$ is the target rank. Based on the estimated rank, CUR decomposition is adopted to replace SVD in updating low-rank matrix components, whose complexity reduces from $O(rnd)$ to $O(r^2 n)$ per iteration. Experimental results verify the efficiency and effectiveness of the proposed eRPCA over the state-of-the-art methods in various low-level vision applications. + +# 1. Introduction + +Robust principal component analysis (RPCA) aims to recover a low-rank matrix $\mathbf{L}$ and a sparse matrix $\mathbf{S}$ from the corrupted observation matrix $\mathbf{D} \in \mathbb{R}^{n \times d}$ : $\mathbf{D} = \mathbf{L} + \mathbf{S}$ . The RPCA can be formulated as the following optimization problem [1]: + +$$ +\min _ {\boldsymbol {L}, \boldsymbol {S}} \operatorname {r a n k} (\boldsymbol {L}) + \lambda \| \boldsymbol {S} \| _ {0} \quad \text {s . t .} \boldsymbol {D} = \boldsymbol {L} + \boldsymbol {S} \tag {1} +$$ + +where $\ell_0$ -norm is the number of nonzero elements in the matrix, the parameter $\lambda > 0$ provides the trade-off between the rankness and sparsity. + +RPCA has been widely studied and applied in computer vision. For example, "background" in a video clip captured by a static camera has a low-rank property, which can be considered in background modeling [2]. The requirement of detecting sparse outliers from the observed imagery data leads to RPCA applications in image or video processing [3]. In industry, RPCA is also applicable to point cloud filtering [4], surface defects detection [5], shock sensing [6], etc. + +It is noted that the optimization problem (1) is NP-hard. The convex relaxation of RPCA has been studied to achieve an exact recovery in [1, 7-12], where the RPCA problem was relaxed as the sum of the nuclear norm and $\ell_1$ -norm. But the convex methods always have a rate of sublinear convergence and high computation in practice [13]. It is necessary to exploit the structure of the underlying data and develop more efficient algorithms for RPCA. Zhou et al. [14] extended the equality constraint of RPCA to inequality in order to deal with noisy data, thus the RPCA is reformulated as the following constrained non-convex optimization problem: + +$$ +\min _ {\boldsymbol {L}, \boldsymbol {S}} \| \boldsymbol {D} - \boldsymbol {L} - \boldsymbol {S} \| _ {F} ^ {2} \tag {2} +$$ + +$$ +\text {s . t .} \operatorname {r a n k} (\boldsymbol {L}) \leq r \text {a n d} \| \boldsymbol {S} \| _ {0} \leq s +$$ + +with the target rank $r$ and target sparse number $s$ . + +The key idea of Eq. (2) is to formulate a constrained nonconvex optimization problem. Among the nonconvex optimization methods of RPCA, Zhou et al. [15] substituted the hard thresholding of Eq. (2) with a soft $\ell_1$ regularization to reduce the complexity of $S$ . Netrapalli et al. [16] added the deterministic sparsity assumption and devoted themselves + +to recovering a low-rank matrix from the sparse corruptions that were of unknown value and support. The RPCA algorithm via gradient descent on the factorized space in [17] achieved linear convergence with proper initialization and step size, whose sparse estimator is to guarantee that the fraction of nonzero entries in each column and row of $S$ is bounded above. Inspired by these methods, GoDec+ [18] made the model become an ordinary low-rank projection problem based on the current entropy of noise and half-quadratic optimization theory. In [19], RPCA problem is considered for the first time without heuristics, such as loss functions, convex and surrogate constraints, which provides a new direction for potential research on online algorithms. In addition, Ornhag et al. [20] used second-order methods to convert the original objectives to differentiable equivalents, benefitting from faster convergence. + +Meanwhile, the efficient algorithms for RPCA have been widely investigated for large-scale matrices. In [16], the developed algorithm involved alternating projections between a set of low-rank matrices and a set of sparse matrices, whose projection idea was also widely studied. Inspired by [16], a proximal block coordinate descent method was proposed in [21] to find an $\epsilon$ -stationary solution in $O(1/\epsilon^2)$ iterations. Furthermore, an accelerated alternating projection strategy was studied in [22] for RPCA, which project a matrix onto a specific low-dimensional subspace before obtaining a new estimate of the low-rank matrix via truncated SVD. + +Most of RPCA and its variants contain SVD, which requires significant computational cost for large-scale matrices. Hintermüller [23] directly considered a least-squares problem subject to rank and cardinality constraints based on matrix manifolds, which favorably avoids singular value decompositions in full dimension. Phan et al. [24] proposed an accelerated algorithm with iteratively reweighted nuclear norm to ensure that every limit point is a critical point, which leads to small singular values and obtains fast result. Some different computing strategies were employed to substitute SVD so that the computation of RPCA was significantly reduced. Cai et al. [25] introduced CUR decomposition at each iteration, which only required $O(r^{2}n)$ flops per iteration and preserved more information than SVD. + +Generally, the aforementioned algorithms achieved efficient and effective performance in different computer vision tasks. It is highlighted that these methods require the rank of a low-rank matrix to be known a priori, which is inappropriate in most practical applications. To bridge this gap, Xu et al. [26] proposed a rank estimation method based on Gerschgorin disk theorem (GDE), whose computational complexity is $O((d - 1)^3)$ at each iteration. Furthermore, an adaptive weighting RPCA was developed based on iteratively estimated rank, which outperforms the state-of-the-art RPCA methods in various computer vision applications. + +More specifically, the adaptive weighting RPCA in [26] was formulated as the following optimization problem: + +$$ +\min _ {\boldsymbol {L}, \boldsymbol {S}} \| \boldsymbol {L} \| _ {W} + \lambda \| \boldsymbol {S} \| _ {1} \quad \text {s . t .} \boldsymbol {D} = \boldsymbol {L} + \boldsymbol {S} \tag {3} +$$ + +where $\| L\| _W = \Sigma_i\omega_i\sigma_i(L)$ and $\omega_{i}$ are non-negative weights. Based on the estimated rank of $L$ , the weights can be updated iteratively. + +Although the adaptive weighting RPCA [26] achieves top performance in recovering a low-rank matrix and a sparse matrix, both the rank estimation and RPCA optimization algorithm contain SVD, which takes significant computational costs for large-scale matrices. Recently, randomized block Krylov iteration [27] was introduced to approximate the singular value decomposition in fewer iterations with better accuracy guarantees. This motivates us to use the block Krylov iteration method to accelerate the GDE-based rank estimation in this work. The computational complexity of the proposed Krylov GDE (KGDE)-based rank estimation is reduced to $O(ndrq + n(rq)^2)$ , where $q$ is a parameter with a small value. On the other hand, CUR decomposition is also adopted to replace SVD in the updates of a low-rank matrix, thus the computational complexity of RPCA is significantly reduced. Since the rank of a matrix is required to be known for CUR decomposition, it is natural that the proposed KGDE is used to adaptively estimate the rank of the low-rank matrix within the iterative RPCA computing. Furthermore, a new non-convex low-rank regularized term is used to replace the weighted nuclear norm in (3) which can improve the low-rank matrix approximation. Compared with the state-of-the-art RPCA approaches, the proposed efficient RPCA (eRPCA) algorithm are fast with better accuracy guarantees. The main contributions of this paper are as follows: + +1) An efficient rank estimation method based on Gerschgorin disks with block Krylov iteration is proposed to accelerate the rank estimate of low-rank matrices. +2) CUR decomposition is adopted to reduce the computation of SVD on a large-scale matrix in the update of the low-rank matrix. +3) An efficient non-convex RPCA method with a nonconvex weighted regularizer is proposed to achieve better recovery of the low-rank matrix and the sparse matrix. +4) The proposed eRPCA algorithm has been applied to various computer vision scenarios and outperforms the state-of-the-art methods on large-scale data. + +In the following section, the improved eRPCA method, which consists of efficient rank estimation and new weight is presented in Section 2. The experimental results are demonstrated in Section 3, and the conclusions are drawn in Section 4. + +# 2. Proposed Method + +# 2.1. Efficient Rank Estimation via Block Krylov Iteration + +In [26], GDE was used to estimate the rank of a low-rank matrix, which involves SVD and has the computational complexity $O\left(\left(d - 1\right)^{3}\right)$ for a matrix $D \in \mathbb{R}^{n \times d}$ . Hence it is time-consuming to estimate the rank of large-scale matrix $D$ . Recently it has been shown that block Krylov iteration (BKI) method [27] gives nearly optimal approximation of singular values and singular vectors with few interations. In this subsection, an efficient rank estimation is proposed by combining BKI and GDE, which is named as KGDE. + +Now we give a brief review on the block Krylov iteration method. For a matrix $D \in \mathbb{R}^{n \times d}$ , the Krylov subspace is obtained by + +$$ +\boldsymbol {K} := [ \boldsymbol {v}, \boldsymbol {D} \boldsymbol {v}, \boldsymbol {D} ^ {2} \boldsymbol {v}, \dots , \boldsymbol {D} ^ {q - 1} \boldsymbol {v} ] \tag {4} +$$ + +where $\pmb{v}$ is a vector of unit norm, $\| \pmb {v}\| = 1$ , and $q$ is a scalar. In [28], the Krylov subspace was extended to randomized block Krylov subspace: + +$$ +\boldsymbol {K} := \left[ \boldsymbol {V}, \boldsymbol {D V}, \boldsymbol {D} ^ {2} \boldsymbol {V}, \dots , \boldsymbol {D} ^ {q - 1} \boldsymbol {V} \right] \tag {5} +$$ + +where $\mathbf{V} = [\pmb{v}_1, \dots, \pmb{v}_b] \in \mathbb{R}^{d \times b}$ is a block of $b$ random vectors. + +After constructing the block Krylov subspace, the Block Krylov Iteration (BKI) [27] can be used to generate closely approximate eigenpairs within fewer iterations by projecting the matrix onto the randomized block Krylov subspace. Its idea is to take a randomized starting matrix $V = D\Omega$ as the initial matrix, where $\Omega$ is a Gaussian random matrix. BKI captures an accurate range space: + +$$ +\boldsymbol {K} := \left(\boldsymbol {D} \boldsymbol {D} ^ {T}\right) ^ {q} \boldsymbol {D} \boldsymbol {\Omega} \tag {6} +$$ + +where $q \coloneqq \Theta \left( \frac{\log d}{\sqrt{\varepsilon}} \right)$ . Orthonormalize the columns of $K$ to obtain $Q$ then compute $M \coloneqq Q^T D D^T Q$ . Set $\overline{U}_k$ to the top $k$ singular vectors of $M$ . At last, return the low-dimension matrix $Z$ : + +$$ +\boldsymbol {Z} = \boldsymbol {Q} \bar {\boldsymbol {U}} _ {k} \tag {7} +$$ + +The following theorem shows that the randomized BKI can get strong relative-error bound. + +Theorem 1 [27] Given data matrix $\pmb{D} \in \mathbb{R}^{n \times d}$ , $n < d$ with eigenvalues $\lambda_i, i = 1, 2, \dots, n$ . Let $\{\theta_i, \varphi_i\}_{i=1}^k$ be the $k$ eigenpair computed using $q$ steps of Block Krylov Iteration (using the orthonormal basis of $\pmb{K}$ for $\pmb{V} \in \mathbb{R}^{d \times b}$ ). If $q = \frac{\log d}{\sqrt{\varepsilon}}$ for some $0 < \varepsilon < 1$ , then have + +$$ +\left| \theta_ {i} - \lambda_ {i} \right| \leq \varepsilon \lambda_ {k + 1}, i = 1, \dots , k. +$$ + +In the rest of this subsection, we present a fast rank estimation of low-rank matrices based on the BKI and GDE. Given a low-rank matrix $D \in \mathbb{R}^{n \times d}$ , $n < d$ with rank $r$ . The BKI algorithm outputs a low-dimension matrix + +$Z \in \mathbb{R}^{n \times k}$ , $k < d$ , which aligns well with the top $k$ singular vectors of $D$ . If $r \leq k$ , the ranks of $D$ and $Z$ are equal. Hence it reduces the computational complexity when GDE can also be applied to $Z$ to estimate the rank instead of the large-scale matrix $D$ . + +The covariance matrix $\mathbf{R}_{\mathbf{Z}} \in \mathbb{R}^{k \times k}$ of the matrix $\mathbf{Z}$ with a rank $r$ can be defined as: + +$$ +\boldsymbol {R} _ {Z} = \boldsymbol {Z} ^ {T} \boldsymbol {Z} \tag {8} +$$ + +Then the eigenvalue decomposition of $R_Z$ is given by + +$$ +R _ {Z} = U _ {R _ {Z}} \Sigma_ {R _ {Z}} U _ {R _ {Z}} ^ {H} \tag {9} +$$ + +where $U_{R_Z} = [u_1, u_2, \dots, u_k]$ is the eigenvector matrix, and $\Sigma_{R_Z} = \text{diag}(\sigma_1, \sigma_2, \dots, \sigma_k)$ represents the eigenvalue matrix. According to the Gerschgorin disk theorem [29], $R_Z$ can be transformed as follows: + +$$ +\boldsymbol {R} _ {\boldsymbol {Z}} = \left[ \begin{array}{c c c c} R _ {1 1} & R _ {1 2} & \dots & R _ {1 k} \\ R _ {2 1} & R _ {2 2} & \dots & R _ {2 k} \\ \vdots & \vdots & \ddots & \vdots \\ R _ {k 1} & R _ {k 2} & \dots & R _ {k k} \end{array} \right] = \left[ \begin{array}{c c} \boldsymbol {R} _ {\boldsymbol {Z 1}} & \boldsymbol {R} \\ \boldsymbol {R} ^ {H} & R _ {k k} \end{array} \right] \tag {10} +$$ + +where $\pmb{R}_{\pmb{Z1}} \in \mathbb{R}^{(k-1) \times (k-1)}$ is the square matrix by the first $(k-1)$ rows and the first $(k-1)$ columns of $\pmb{R}_{\pmb{Z1}}$ , and $\pmb{R} = [R_{1k}, R_{2k}, \dots, R_{(k-1)k}]^T$ . Then the eigenvalue decomposition on $\pmb{R}_{\pmb{Z1}}$ is obtained as: + +$$ +\boldsymbol {R} _ {Z 1} = U _ {Z 1} \boldsymbol {\Sigma} _ {1} U _ {Z 1} ^ {H} \tag {11} +$$ + +where $U_{\mathbf{Z1}} = [q_1', q_2', \dots, q_{k-1}']$ is an $(k-1) \times (k-1)$ unitary matrix composed of the eigenvectors of $\mathbf{R}_{\mathbf{Z1}}$ , and $\pmb{\Sigma}_{\mathbf{1}} = \text{diag}(\sigma_1', \sigma_2', \dots, \sigma_{k-1}')$ . Similar to Eq. (10), a unitary transformed matrix $\mathbf{U} \in \mathbb{R}^{k \times k}(\mathbf{U}\mathbf{U}^H = \mathbf{I})$ is defined as: + +$$ +\boldsymbol {U} = \left[ \begin{array}{c c} U _ {Z 1} & \mathbf {0} \\ \mathbf {0} ^ {T} & \mathbf {1} \end{array} \right] \tag {12} +$$ + +The transformed covariance matrix is obtained by: + +$$ +\begin{array}{l} \boldsymbol {R} _ {T} = \boldsymbol {U} ^ {H} \boldsymbol {R} _ {Z} \boldsymbol {U} = \left[ \begin{array}{c c} \boldsymbol {U} _ {Z 1} ^ {H} \boldsymbol {R} _ {Z 1} \boldsymbol {U} _ {Z 1} & \boldsymbol {U} _ {Z 1} ^ {H} \boldsymbol {R} \\ \boldsymbol {R} ^ {H} \boldsymbol {U} _ {Z 1} & R _ {k k} \end{array} \right] \\ = \left[ \begin{array}{c c c c c c} \sigma_ {1} ^ {\prime} & 0 & 0 & \dots & 0 & \rho_ {1} \\ 0 & \sigma_ {2} ^ {\prime} & 0 & \dots & 0 & \rho_ {2} \\ 0 & 0 & \sigma_ {3} ^ {\prime} & \dots & 0 & \rho_ {3} \\ \vdots & \vdots & \vdots & \ddots & \vdots & \vdots \\ 0 & 0 & 0 & \dots & \sigma_ {k - 1} ^ {\prime} & \rho_ {k - 1} \\ \rho_ {1} ^ {*} & \rho_ {2} ^ {*} & \rho_ {3} ^ {*} & \dots & \rho_ {k - 1} ^ {*} & R _ {k k} \end{array} \right] \tag {13} \\ \end{array} +$$ + +where $\rho_{i} = \pmb{q}_{i}^{\prime H}\pmb{R}$ . The eigenvalues of $\pmb{R}_{T}$ can be estimated using the Gerschgorin disk theorem [29]. Then, the radii of the first $(k - 1)$ Gerschgorin's disk can be written as: + +$$ +r _ {i} = \left| \rho_ {i} \right| = \left| \boldsymbol {q} _ {i} ^ {\prime H} \boldsymbol {R} \right| \tag {14} +$$ + +where the radius $r_i$ of the $i$ th Gerschgorin's disk depends on the size of $\pmb{q}_i^{\prime H}\pmb {R}$ + +To further improve the accuracy of the rank estimation, the radii of the Gerschgorin's disk are shrank in [26]. Then + +# Algorithm 1 KGDE + +Input: $D\in \mathbb{R}^{n\times d}$ , error $\varepsilon \in (0,1)$ , $k = 2$ , the $(1 + \varepsilon)$ relative-error bound for BKI $q = \frac{\log d}{\sqrt{\varepsilon}}$ + +Output: Estimated rank $r$ + +Set $gde = \text{zeros}(d, 1)$ + +for $t = 1$ to $d$ do + +$$ +\boldsymbol {Z} \in \mathbb {R} ^ {n \times k} \leftarrow B K I (\boldsymbol {D} \in \mathbb {R} ^ {n \times d}, \varepsilon , q) +$$ + +Covariance matrix $\mathbf{R}_{\mathbf{Z}} = \mathbf{Z}^{T}\mathbf{Z}$ + +Obtain the transformed unitary matrix according to Eqs. (10)-(12) + +Calculate the radii $r_i$ of the Gerschgorin's disk according to Eqs. (14)-(15) + +Calculate $gde(t)$ according to Eqs. (16)-(17) + +if $(t > 1\& \& gde(t) < 0)$ then + +break; + +else + +$$ +k = k + 1 +$$ + +end if + +end for + +$$ +r = t - 1 +$$ + +return $r$ + +a new diagonal matrix $\pmb{\Sigma}_{\pmb{T}} = \text{diag}(\sigma_{1}', \sigma_{2}', \dots, \sigma_{k-1}', \sigma_{k}')$ is constructed, where $\sigma_{k}' = \sqrt{\sum_{i=1}^{k-1} \sigma_{i}'^{2}}$ . Thus, the new transformed matrix $\pmb{R}_{\pmb{T}\pmb{\Sigma}_{\pmb{T}}}$ is constructed as follows: + +$$ +\begin{array}{l} \boldsymbol {R} _ {T \Sigma_ {T}} = \boldsymbol {\Sigma} _ {T} \boldsymbol {R} _ {T} \boldsymbol {\Sigma} _ {T} ^ {- 1} \\ = \left[ \begin{array}{c c c c c} \sigma_ {1} ^ {\prime} & 0 & \dots & 0 & \frac {\sigma_ {1} ^ {\prime}}{\sigma_ {k} ^ {\prime}} \rho_ {1} \\ 0 & \sigma_ {2} ^ {\prime} & \dots & 0 & \frac {\sigma_ {2}}{\sigma_ {k} ^ {\prime}} \rho_ {2} \\ \vdots & \vdots & \ddots & \vdots & \vdots \\ 0 & 0 & \dots & \sigma_ {k - 1} ^ {\prime} & \frac {\sigma_ {k - 1} ^ {\prime}}{\sigma_ {k} ^ {\prime}} \rho_ {k - 1} \\ \frac {\sigma_ {1} ^ {\prime}}{\sigma_ {k} ^ {\prime}} \rho_ {1} ^ {*} & \frac {\sigma_ {2} ^ {\prime}}{\sigma_ {k} ^ {\prime}} \rho_ {2} ^ {*} & \dots & \frac {\sigma_ {k - 1} ^ {\prime}}{\sigma_ {k} ^ {\prime}} \rho_ {k - 1} ^ {*} & R _ {k k} \end{array} \right] \tag {15} \\ \end{array} +$$ + +$R_{T\Sigma_T}$ and $R_{T}$ are similar matrices and have the same eigenvalues. In Eq. (15), the radii are compressed to various degrees. Finally, the estimated rank is obtained by the improved heuristic decision rule: + +$$ +g d e (t) = \frac {1}{\sqrt {\sum_ {i = 1} ^ {k - 1} \sigma_ {i} ^ {\prime 2}}} [ | \sigma_ {t} ^ {\prime} | r _ {t} - \frac {H _ {D} ^ {(t)} (M)}{k - 1} \sum_ {i = 1} ^ {k - 1} \left| \sigma_ {i} ^ {\prime} \right| r _ {i} ] \tag {16} +$$ + +where $t = 1,2,\dots ,k - 2$ and $0 < H_D^{(t)}(M) < 1$ is the adjustment factor: + +$$ +H _ {D} ^ {(t)} (M) = \frac {2 \left| \sigma_ {t + 1} ^ {\prime} \right|}{\sqrt {\sum_ {i = t} ^ {k - 1} \sigma_ {i} ^ {\prime 2}}} \tag {17} +$$ + +As a result, the rank $r = t - 1$ if the first negative value of (16) is reached at $t$ . + +When $r \leq k$ , $D$ is transformed to $Z$ by BKI, then the rank of $Z$ is estimated by GDE. It is noted that while $r > k$ , + +GDE can not estimate the true rank of $D$ from $Z$ . To adaptively determine an appropriate $k$ , KGDE is proposed by adopting iteration, and GDE is served as a stopping criterion for such Krylov subspace approximation of $Z$ . The KGDE for rank estimation based on BKI and GDE is summarized in Algorithm 1. + +Remark 1: The computational cost of KGDE is related to BKI. If the estimated $r$ of the input matrix $D \in \mathbb{R}^{n \times d}$ is exact, the computational complexity will be $O(ndrq + n(rq)^2)$ , where $n < d$ . For sparse matrix, the computational cost of KGDE will be $O(nnz(D)rq + n(rq)^2)$ , where $nnz(D)$ is the number of nonzeros in $D$ . Since $r \leq n$ and $q = \frac{\log d}{\sqrt{\varepsilon}}$ are small, the KGDE will be inexpensive, especially for sparse matrices. + +Remark 2: The accuracy of the KGDE mainly depends on the BKI. In light of Theorem 1, $Z$ is obtained within a high-quality principal components approximation of $D$ , both its eigenvalues and eigenvectors are highly close to the actual ones of $D$ . + +# 2.2. Efficient RPCA based on KGDE and CUR Decomposition + +In this subsection, an efficient RPCA based on the above rank estimation and CUR decomposition is proposed for solving the following optimization problem: + +$$ +\min _ {\boldsymbol {L}, \boldsymbol {S}} \| \boldsymbol {D} - \boldsymbol {L} - \boldsymbol {S} \| _ {F} ^ {2} + \lambda \| \boldsymbol {L} \| _ {\gamma} \quad s. t. \| \boldsymbol {S} \| _ {0} \leq s \tag {18} +$$ + +where + +$$ +\| \boldsymbol {L}\|_{\gamma} = \left\{ \begin{array}{l}\sum_{i = 1}\frac{e^{\gamma}\sigma_{i}}{\gamma + \sigma_{i}}, i\leq r\\ 0 , i > r \end{array} \right. +$$ + +and $\sigma_{i}, i = 1,2,\dots ,r$ , is the singular value, $\gamma >0$ , and $\lambda$ is the regularized parameter which provides a trade-off between the recovery of low-rank matrix and sparse matrix. + +The optimization model (18) adds a new non-convex low-rank regularization term to Eq. (2), which adopts the estimated rank to achieve better recovery accuracy of the low-rank matrix than the weighted nuclear norm in (3). + +In this work, the alternating projection method is used to solve the following two sub-problems until convergence: + +$$ +\boldsymbol {L} _ {\ell + 1} = \underset {\boldsymbol {L}} {\arg \min } \| \boldsymbol {D} - \boldsymbol {L} - \boldsymbol {S} _ {\ell} \| _ {F} ^ {2} + \lambda \| \boldsymbol {L} \| _ {\gamma} \tag {19} +$$ + +$$ +\boldsymbol {S} _ {\ell + 1} = \underset {\boldsymbol {S}: \| \boldsymbol {S} \| _ {0} \leq s} {\arg \min } \| \boldsymbol {D} - \boldsymbol {L} _ {\ell + 1} - \boldsymbol {S} \| _ {F} ^ {2} \tag {20} +$$ + +Update for L: The traditional solution of (19) often involves SVD, which requires significant computational resource for a large-scale matrix. To efficiently solve the model (19), we replace SVD with CUR decomposition [30], which has been proven to be efficient and effective in solving classical RPCA problem [31]. Mathematically, the CUR + +![](images/449102a391a1ff7ed034b896a9956b319a0a3ad3bb58041afda27b734ffdb1cd.jpg) +Figure 1. The numerical rank estimation of sparse data matrices. + +![](images/4574448e17edbfe350785fc482ce96c5f9ab580a8dda0f69355c52e6f79f1a92.jpg) + +![](images/3d39cfbde76e612f32f4b5f76c67bebeaf0f64d0ba8f32c6b5c1831f77a59209.jpg) + +![](images/62bacbecab044961e7183415c4bc2d11e34f8712604e7447e1bed2f28997fd20.jpg) + +decomposition of (19) can be rewritten as follows: + +$$ +\boldsymbol {C} _ {\ell + 1} = \underset {\boldsymbol {L} _ {:, \mathcal {J}}} {\arg \min } \| [ \boldsymbol {D} - \boldsymbol {L} - \boldsymbol {S} _ {\ell} ] _ {:, \mathcal {J}} \| _ {F} ^ {2} + \lambda \| \boldsymbol {L} _ {:, \mathcal {J}} \| _ {\gamma} \tag {21} +$$ + +$$ +\boldsymbol {U} _ {\ell + 1} = \mathcal {T} \boldsymbol {S} ([ \boldsymbol {D} - \boldsymbol {L} - \boldsymbol {S} _ {\ell} ] _ {\mathcal {I}, \mathcal {J}}) \tag {22} +$$ + +$$ +\boldsymbol {R} _ {\ell + 1} = \underset {\boldsymbol {L} _ {\mathcal {I},:}} {\arg \min } \| [ \boldsymbol {D} - \boldsymbol {L} - \boldsymbol {S} _ {\ell} ] _ {\mathcal {I},:} \| _ {F} ^ {2} + \lambda \| \boldsymbol {L} _ {\mathcal {I},:} \| _ {\gamma} \tag {23} +$$ + +where $C_{\ell +1}\in \mathbb{R}^{n\times \mathcal{I}}$ is $\mathcal{I}$ columns of (19) via uniform sampling, $R_{\ell +1}\in \mathbb{R}^{\mathcal{I}\times d}$ is $\mathcal{J}$ rows of (19) in the same way, $U_{\ell +1}\in \mathbb{R}^{\mathcal{I}\times \mathcal{I}}$ is the overlap of the column and row indices of $C_{\ell +1}$ and $R_{\ell +1}$ . $\mathcal{T}S(\cdot)$ denotes the truncated SVD. + +In addition, the rank value $r$ is needed for $\mathcal{T}S(\cdot)$ and CUR decomposition, which can be exactly estimated by our proposed KGDE method. + +As Eqs. (21) and (23) are the combination of concave and convex functions, the Difference of Convex programming [32] is used to solve these problems. Thus, $C_{\ell + 1}$ can be obtained as follows [33]: + +$$ +\boldsymbol {C} _ {\ell + 1} = \left[ \boldsymbol {a} \operatorname {d i a g} \left\{\sigma^ {*} \right\} \boldsymbol {b} ^ {T} \right] _ {:, \mathcal {I}} \tag {24} +$$ + +where $\mathbf{a}$ and $\mathbf{b}$ are the left and right singular vectors of $(D - S_{\ell + 1})$ , respectively, and $\sigma^*$ has a closed-form solution at each iteration: + +$$ +\sigma^ {i + 1} = \max \left(\left(\sigma_ {\boldsymbol {D} - \boldsymbol {S} _ {\ell + 1}} - \frac {\lambda \omega_ {i}}{\mu^ {\ell}}\right), 0\right) \tag {25} +$$ + +where $\sigma_{D - S_{\ell +1}}$ is the singular value of $(D - S_{\ell +1}),\mu >0,$ and $\omega_{i} = \left\{ \begin{array}{ll}\frac{\gamma e^{\gamma}}{(\gamma + \sigma_{i}(\gamma))^{2}}, & i\leq r\\ 0, & \text{others} \end{array} \right.$ is the gradient of $\| L\|_{\gamma}$ at + +$\sigma^i$ . Obviously, $\omega_{i}$ is dependent on $r$ , which can be estimated by KGDE at each iteration. + +Similarly, + +$$ +\boldsymbol {R} _ {\ell + 1} = \left[ \boldsymbol {a} \operatorname {d i a g} \left\{\sigma^ {*} \right\} \boldsymbol {b} ^ {T} \right] _ {\mathcal {I},:} \tag {26} +$$ + +Hence, the updated for $L$ is: + +$$ +\boldsymbol {L} _ {\ell + 1} = \boldsymbol {C} _ {\ell + 1} \boldsymbol {U} _ {\ell + 1} ^ {\dagger} \boldsymbol {R} _ {\ell + 1} \tag {27} +$$ + +where $(\cdot)^{\dagger}$ denotes the Moore-Penrose pseudoinverse. + +Update for S: Similarly, the optimization of (20) can be divided into as: + +$$ +[ \boldsymbol {S} _ {\ell + 1} ] _ {:, \mathcal {J}} = \underset {\boldsymbol {S}:, \mathcal {J}: \| \boldsymbol {S} \| _ {0} \leq s} {\arg \min } \| [ \boldsymbol {D} - \boldsymbol {L} _ {\ell} - \boldsymbol {S} ] _ {:, \mathcal {J}} \| _ {F} ^ {2} \tag {28} +$$ + +$$ +[ \boldsymbol {S} _ {\ell + 1} ] _ {\mathcal {I},:} = \underset {\boldsymbol {S} _ {\mathcal {I},:} \| \boldsymbol {S} \| _ {0} \leq s} {\arg \min } \| [ \boldsymbol {D} - \boldsymbol {L} _ {\ell} - \boldsymbol {S} ] _ {\mathcal {I},:} \| _ {F} ^ {2} \tag {29} +$$ + +# Algorithm 2 eRPCA based on KGDE + +Input: $D \in \mathbb{R}^{n \times d}$ with estimated rank $r$ ; $\delta$ : error; $\lambda, \mu$ : penalty parameter; $\zeta_0$ : initial thresholding value; $|\mathcal{I}| = O(r), |\mathcal{J}| = O(r)$ : sampling number of rows and columns; $\gamma$ : non-convex regularizer parameter. + +# Output: $L, S$ + +Uniformly sample row indices $\mathcal{I}$ and column indices $\mathcal{J}$ . + +$$ +\boldsymbol {L} _ {0} = 0, \boldsymbol {S} _ {0} = 0, k = 0 +$$ + +# while not converged do + +Resample $\mathcal{I}$ and $\mathcal{J}$ + +Update $\zeta_{k + 1} = \eta \zeta_0$ + +Update $S_{\ell +1}$ according to Eqs. (28)-(29) + +Estimate and update $r$ by KGDE + +Update $C_{\ell +1}$ according to (21) + +Update $R_{\ell +1}$ according to (23) + +Update $U_{\ell +1}$ according to (22) + +$$ +\boldsymbol {L} _ {\ell + 1} = \boldsymbol {C} _ {\ell + 1} \boldsymbol {U} _ {\ell + 1} ^ {\dagger} \boldsymbol {R} _ {\ell + 1} +$$ + +$$ +\ell = \ell + 1 +$$ + +# end while + +For $S$ , the hard thresholding operator $\mathcal{HT}$ is adopted as: + +$$ +\left[ \mathcal {H T} (\boldsymbol {S}) \right] _ {i, j} = \left\{ \begin{array}{l} \boldsymbol {S} _ {i, j}, i f | \boldsymbol {S} _ {i, j} | > \zeta , \\ 0, o t h e r w i s e. \end{array} \right. \tag {30} +$$ + +where $\zeta$ is the thresholding value. The hard thresholding is employed for projections on to $(D - L_{\ell})$ . + +The iteration is terminated when + +$$ +\frac {\left\| \left[ \boldsymbol {D} - \boldsymbol {L} _ {\ell} - \boldsymbol {S} _ {\ell} \right] _ {: , \mathcal {I}} \right\| _ {F} + \left\| \left[ \boldsymbol {D} - \boldsymbol {L} _ {\ell} - \boldsymbol {S} _ {\ell} \right] _ {\mathcal {I} , :} \right\| _ {F}}{\left\| \boldsymbol {D} _ {: , \mathcal {I}} \right\| _ {F} + \left\| \boldsymbol {D} _ {\mathcal {I} , :} \right\| _ {F}} < \delta \tag {31} +$$ + +The entire procedure to solve the problem (18) is summarized in Algorithm 2. + +Remark 3: The computational complexity of $U$ in CUR decomposition is $O(r^3)$ . Since the sampling numbers of rows and columns are $|\mathcal{I}| = O(r)$ and $|\mathcal{J}| = O(r)$ , respectively, updating $L$ requires $O(r^{2}n)$ flops per iteration. In contrast, computing the SVD usually requires $O(rnd)$ . In addition, the runtime of updating $S$ is actually a simple projection, whose computational complexity is further less than that of $L$ . Thus, the computational complexity of the alternating projection procedure is $O\left(\frac{d^2r}{\epsilon} + d \cdot \text{poly}(r, \log(r / \epsilon), 1 / \epsilon)\right)$ , where $0 < \epsilon < 1$ is an + +![](images/ae35347ff9ab07ed21ffb218540d74c34b6798bc25172e17bb58f491841068f0.jpg) +Figure 2. The numerical rank estimation of video data matrices. + +![](images/7a563cf6a4ef7bf765d8e28c102129d2ad4ffc4bce8da79c9e680ecba716517c.jpg) + +accuracy parameter. + +# 3. Experimental Results + +This section reports the experimental results of our proposed eRPCA and compares it with state-of-the-art algorithms on synthetic datasets and two practical computer vision scenarios. The parameters in our method are listed as follows: $\gamma = 0.02$ , $\delta = 10^{-7}$ , $\lambda = 10^{-3}$ , $\mu = \frac{1}{2}$ , $\zeta_0 = \max(|D|)$ , and $\varepsilon = 0.05$ . The parameters in other methods use their default settings. All the experiments are conducted on a laptop with MATLAB 2019 equipped with Windows 10 based on AMD Ryzen 5 CPU with 32G RAM. + +# 3.1. The Validation of Rank Estimation Method + +# 3.1.1 Public real datasets + +To validate the efficiency and accuracy of KGDE, the general data matrices are tested to estimate the rank. SuiteSparse Database1 [34] provides general data matrices with low numerical rank, whose Gaussian-type distribution assumptions for the data and noise may not hold. In addition, the video datasets from Scene Background Initialization (SBI) dataset2 [35], which are converted to the full matrix are also tested. + +Fig.1 shows the numerical rank estimation for the SVD curve of sparse data matrices. The singular values of Fig.1(a) and Fig.1(b) have apparent distribution, and KGDE and GDE obtain the exact rank estimation. The singular values of Fig.1(c) and Fig.1(d) are very close, it is therefore hard to bind the rank. The result of Fig.1(c) is the same, and the one of Fig.1(d) is slightly different, while the gap can be ignored in practice. + +Fig.2 shows the rank estimation results of video data matrices. The video datasets have a stable low-rank, and the rank is usually equal to 1. Thus, the distribution of their singular values has a noticeable gap. + +The comparisons of runtime and estimated rank for different matrices are shown in Table 1. When the matrix scale is small, the execution time is close, but KGDE is still faster than GDE. When the matrix becomes more extensive, the efficiency of KGDE performs better than GDE. Because the + +![](images/a5249b0c51468920d4d5eb4a2c69235f8a8ba00c25f3147e0efd780ad59a3744.jpg) +Figure 3. The comparison of the average runtime between different algorithms. + +Table 1. The results of runtime and estimated rank using GDE and KGDE + +
DatasetGDEKGDE
Runtime(s)RankRuntime(s)Rank
lp Blend0.15630.0943
lp_pilot41.48830.2503
Ipi bgdbg10.27460.2666
Ipi_ceria3d91.18050.2343
IBMtest20.17610.1341
CAVIAR12.23510.7571
+ +computational complexity of KGDE is not too much related to the dimension of the matrix, KGDE can maintain a fast result. + +# 3.1.2 Synthetic Datasets + +For synthetic datasets, our algorithm was compared with the state-of-the-art RPCA-based approaches: RPCA [1], PSSV [36], WNNM [37], and ARE-RPCA [26]. + +The recovery ability and execution time of the algorithms are investigated. The input matrix $D \in \mathbb{R}^{n \times d}$ is corrupted by sparse noise with the corruption rate $\alpha = \{0.1, 0.3, 0.5, 0.7\}$ . The parameters are set: $d = 10000$ , $n = \{20, 100, 500\}$ and different ranks $r = \{1, 3, 5\}$ . The iteration stop criterion is $10^{-7}$ . Let $L_{sol}$ be the reconstruction of $L$ and the reconstruction error is defined as $\| L_{sol} - L \|_F / \| L \|_F$ . + +The comparisons of the average runtime with different ranks $r$ and dimensions $d$ are shown in Fig.3. The eRPCA is faster than others for the average runtime in Fig.3. When the input matrix has a larger scale or rank, the time gap between our method and others is more prominent. + +The simulation results are shown in Fig.4. It can be seen that eRPCA algorithm is stubborn when the corruption rate is low and has similar results with other algorithms. When the corruption rate rises, the reconstruction error of eRPCA algorithm is larger. eRPCA performs worse when the corruption rate is 0.7 with a large rank. + +Table 2 shows the desired rank of the low-rank matrix decomposed by different algorithms under different corruption rates. It can be observed that the proposed eRPCA can obtain correct ranks of low-rank matrices in all cases. Other algorithms can get the desired rank correctly only if the corruption rate is low. + +According to the above analysis, it is observed that eR- + +![](images/1128a80c9adfbdd6dbe4ad41a0d998905993d0e20473f32beb4d885e47fb25a5.jpg) + +![](images/3868c151360f7336ffee565a181cb89f91d8a3684fd3663eee0e9f6fa8fb8009.jpg) + +![](images/94a1debc227dad820f2144c8f56bd850804f85c61be6621f905588c729c3a971.jpg) + +![](images/4c59e566e933216d645521e6e2900bb6b27c48fb375583898a62b40094f6a011.jpg) + +![](images/64e5245212bbe5551cdf9697b43e963330d16b6f11c0967c75fe5bb8e0495245.jpg) + +![](images/30b17348bd204304021979b2ec7f48b80297e6853a83c03d5f3b33551fa9c051.jpg) + +![](images/23174bc418f4f11341c652a282066900aa1872bbd1dea2dae534945ef2afc38d.jpg) +Figure 4. Comparison of various algorithms with different dimensions $n$ , matrix ranks $r$ , and corruption rates $\alpha$ . + +![](images/7279b9371cf4a6321eee50277c775258059ea506006125fa4b3e15609d7c9ca9.jpg) + +![](images/df7d04f3f12663de7310d5317b0f240f1883b3667996f90b6ea72b1123af1eea.jpg) + +Table 2. The desired rank of low-rank matrix decomposed by different algorithms in different corruption rates and dimensions with different ranks + +
AlgorithmDimensionr=1r=3r=5
α=0.1α=0.3α=0.5α=0.7α=0.1α=0.3α=0.5α=0.7α=0.1α=0.3α=0.5α=0.7
RPCAn=20116648655656
n=10011123335555552
n=50011173331255516
PSSVn=20111233515551519
n=100111133335558
n=50011163331055513
ARE-RPCAn=20111133355555
n=100111133335555
n=500111133375555
WNNMn=20111133511551520
n=1001111333100555100
n=5001111333500555500
eRPCAn=20111133335555
n=100111133335555
n=500111133335555
+ +PCA has excellent robustness and the fastest execution time. + +# 3.2. Foreground-Background Separation + +In this subsection, we evaluate the proposed eRPCA with the following approaches: ARE-RPCA [26], IRCUR [25], PETRELS [38], and ADW-RPCA [39]. + +Foreground-background separation is an important application of RPCA. Scene Background Initialization (SBI) + +dataset3 [35] is considered. The visual comparisons of the sub-dataset CAVIAR1 are shown in Fig.5, containing 610 frames with size $384 \times 256$ . The dataset can be represented by a matrix, where each column is a vectorized video frame. Then each algorithm can be applied to decompose the matrix into low-rank parts and sparse ones; that is, this scene can be separated from the moving foreground object from the static background. + +There are five frames selected in Fig.5, and the upper and + +![](images/8f25d0552f440415af5d345500dc32ec85ed24edf98ae7cc8def0545566ebd01.jpg) +Figure 5. The comparison of visual results on CAVIAR1 between different algorithms. + +Table 3. Performance of one frame from CAVIAR1 dataset among different algorithms + +
AGEpEPs%pCEPS%MSSSIMPSNRCQMTIME(s)
ARE-RPCA5.26374.07413.48710.856425.441424.787610.78593
IRCUR3.14890.28280.18210.991734.468933.27140.007564
PETRELS4.99725.01614.02220.932929.801729.07731.14708
ADW-RPCA2.640.34990.24820.990534.485333.34026.356669
eRPCA2.63940.26860.16890.991734.862633.57250.034198
+ +lower parts represent the background and foreground. It can be shown that ARE-RPCA and PETRELS yield artifacts in some backgrounds. IRCUR, ADW-RPCA, and eRPCA obtain more distinctive visual results. + +In addition, objective evaluations, i.e. AGE, pEP, pCEP, PSNR, MS-SSIM, CQM, are performed on SBI database where the smaller the first three values, the better the separation results, and the last three ones and vice versa. Table 3 shows the performance evaluation of the above six metrics and runtime. For the first six metrics, eRPCA algorithm obtains better results. Due to the time of estimating the rank, eRPCA algorithm is slower than IRCUR for each frame. However, IRCUR needs to determine the rank in advance, leading to its results being slightly inferior to ours. Moreover, only ARE-RPCA and eRPCA algorithm can obtain the rank prior, but ours are better than ARE-RPCA in all aspects. + +# 3.3. Shadow Removal from Face Images + +Face images taken under different lighting conditions always introduce errors, for example, uneven lighting, + +![](images/6d782ff7971e33f8949dad73d5d7357695115e4c47639627c8a5c395754f4c28.jpg) +Figure 6. The comparison of different algorithms on two images. + +Table 4. The comparison of runtime between different algorithms + +
RPCAPSSVWNNMARE-RPCAeRPCA
yale053.535s0.973s1.113s3.648s0.071s
yaleB023.499s0.962s2.424s3.650s0.081s
+ +shadow etc, which yields challenge for face recognition. Fig.6 (first column) shows two typical examples with size $192 \times 168$ from the Extended Yale B database[40], a benchmark database in face recognition. Each image is converted to a column vector. The comparisons of these methods are given: RPCA [1], PSSV [36], WNNM [37], and ARE-RPCA [26]. In addition, since the images are aligned, the rank is set to 1, and ARE-RPCA and eRPCA can adaptively estimate the rank. + +Fig.6 shows the shadow removal results of different algorithms. In the visual aspect, the proposed eRPCA algorithm removes the shadow well and does not need to determine the rank. The runtime of different algorithms is shown in Table 4 and ours is the fastest. + +Due to the space limitation, more experimental results are shown in the Supplementary Material. + +# 4. Conclusion + +In this paper, an efficient non-convex RPCA method is proposed for recovering a low-rank matrix and a sparse matrix, especially with large sizes. Specifically, a fast rank estimation method KGDE has been proposed by using Gerschgorin disk theorem with the block Krylov iteration. Based on the estimated rank, a new non-convex regularizer is proposed to achieve better recovery of the low-rank matrices with less computation due to CUR decomposition involved in the iterations. Experimental results demonstrate that the proposed eRPCA algorithm outperforms state-of-the-art algorithms in various vision applications. + +In future, our algorithm will be extended in other applications, such as image recovery and video denoising. However, the accuracy of eRPCA for high corruption rate is still a big challenge. Therefore, we will devote ourselves to improving the robustness of the algorithm. 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Institute for Infocomm Research A*STAR, Singapore" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 55, + 247, + 555, + 258 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 55, + 247, + 555, + 258 + ], + "spans": [ + { + "bbox": [ + 55, + 247, + 555, + 258 + ], + "type": "text", + "content": "fangshun97@wust.edu.cn, fate311@sjtu.edu.cn, shiqian.wu@wust.edu.cn, slxie@i2r.a-star.edu.sg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 143, + 286, + 192, + 300 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 286, + 192, + 300 + ], + "spans": [ + { + "bbox": [ + 143, + 286, + 192, + 300 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 312, + 290, + 553 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 312, + 290, + 553 + ], + "spans": [ + { + "bbox": [ + 46, + 312, + 290, + 553 + ], + "type": "text", + "content": "Robust principal component analysis (RPCA) is widely studied in computer vision. Recently an adaptive rank estimate based RPCA has achieved top performance in low-level vision tasks without the prior rank, but both the rank estimate and RPCA optimization algorithm involve singular value decomposition, which requires extremely huge computational resource for large-scale matrices. To address these issues, an efficient RPCA (eRPCA) algorithm is proposed based on block Krylov iteration and CUR decomposition in this paper. Specifically, the Krylov iteration method is employed to approximate the eigenvalue decomposition in the rank estimation, which requires " + }, + { + "bbox": [ + 46, + 312, + 290, + 553 + ], + "type": "inline_equation", + "content": "O(ndrq + n(rq)^2)" + }, + { + "bbox": [ + 46, + 312, + 290, + 553 + ], + "type": "text", + "content": " for an " + }, + { + "bbox": [ + 46, + 312, + 290, + 553 + ], + "type": "inline_equation", + "content": "(n \\times d)" + }, + { + "bbox": [ + 46, + 312, + 290, + 553 + ], + "type": "text", + "content": " input matrix, in which " + }, + { + "bbox": [ + 46, + 312, + 290, + 553 + ], + "type": "inline_equation", + "content": "q" + }, + { + "bbox": [ + 46, + 312, + 290, + 553 + ], + "type": "text", + "content": " is a parameter with a small value, " + }, + { + "bbox": [ + 46, + 312, + 290, + 553 + ], + "type": "inline_equation", + "content": "r" + }, + { + "bbox": [ + 46, + 312, + 290, + 553 + ], + "type": "text", + "content": " is the target rank. Based on the estimated rank, CUR decomposition is adopted to replace SVD in updating low-rank matrix components, whose complexity reduces from " + }, + { + "bbox": [ + 46, + 312, + 290, + 553 + ], + "type": "inline_equation", + "content": "O(rnd)" + }, + { + "bbox": [ + 46, + 312, + 290, + 553 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 46, + 312, + 290, + 553 + ], + "type": "inline_equation", + "content": "O(r^2 n)" + }, + { + "bbox": [ + 46, + 312, + 290, + 553 + ], + "type": "text", + "content": " per iteration. Experimental results verify the efficiency and effectiveness of the proposed eRPCA over the state-of-the-art methods in various low-level vision applications." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 578, + 128, + 590 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 578, + 128, + 590 + ], + "spans": [ + { + "bbox": [ + 47, + 578, + 128, + 590 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 599, + 287, + 661 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 599, + 287, + 661 + ], + "spans": [ + { + "bbox": [ + 46, + 599, + 287, + 661 + ], + "type": "text", + "content": "Robust principal component analysis (RPCA) aims to recover a low-rank matrix " + }, + { + "bbox": [ + 46, + 599, + 287, + 661 + ], + "type": "inline_equation", + "content": "\\mathbf{L}" + }, + { + "bbox": [ + 46, + 599, + 287, + 661 + ], + "type": "text", + "content": " and a sparse matrix " + }, + { + "bbox": [ + 46, + 599, + 287, + 661 + ], + "type": "inline_equation", + "content": "\\mathbf{S}" + }, + { + "bbox": [ + 46, + 599, + 287, + 661 + ], + "type": "text", + "content": " from the corrupted observation matrix " + }, + { + "bbox": [ + 46, + 599, + 287, + 661 + ], + "type": "inline_equation", + "content": "\\mathbf{D} \\in \\mathbb{R}^{n \\times d}" + }, + { + "bbox": [ + 46, + 599, + 287, + 661 + ], + "type": "text", + "content": ": " + }, + { + "bbox": [ + 46, + 599, + 287, + 661 + ], + "type": "inline_equation", + "content": "\\mathbf{D} = \\mathbf{L} + \\mathbf{S}" + }, + { + "bbox": [ + 46, + 599, + 287, + 661 + ], + "type": "text", + "content": ". The RPCA can be formulated as the following optimization problem [1]:" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 80, + 671, + 287, + 689 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 80, + 671, + 287, + 689 + ], + "spans": [ + { + "bbox": [ + 80, + 671, + 287, + 689 + ], + "type": "interline_equation", + "content": "\\min _ {\\boldsymbol {L}, \\boldsymbol {S}} \\operatorname {r a n k} (\\boldsymbol {L}) + \\lambda \\| \\boldsymbol {S} \\| _ {0} \\quad \\text {s . t .} \\boldsymbol {D} = \\boldsymbol {L} + \\boldsymbol {S} \\tag {1}", + "image_path": "2cf5cd161ac54ed878fcbb4610ac1df887f5b76197fac17a8f1315edae1a6c17.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 288, + 545, + 323 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 288, + 545, + 323 + ], + "spans": [ + { + "bbox": [ + 306, + 288, + 545, + 323 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 306, + 288, + 545, + 323 + ], + "type": "inline_equation", + "content": "\\ell_0" + }, + { + "bbox": [ + 306, + 288, + 545, + 323 + ], + "type": "text", + "content": "-norm is the number of nonzero elements in the matrix, the parameter " + }, + { + "bbox": [ + 306, + 288, + 545, + 323 + ], + "type": "inline_equation", + "content": "\\lambda > 0" + }, + { + "bbox": [ + 306, + 288, + 545, + 323 + ], + "type": "text", + "content": " provides the trade-off between the rankness and sparsity." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 324, + 546, + 430 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 324, + 546, + 430 + ], + "spans": [ + { + "bbox": [ + 304, + 324, + 546, + 430 + ], + "type": "text", + "content": "RPCA has been widely studied and applied in computer vision. For example, \"background\" in a video clip captured by a static camera has a low-rank property, which can be considered in background modeling [2]. The requirement of detecting sparse outliers from the observed imagery data leads to RPCA applications in image or video processing [3]. In industry, RPCA is also applicable to point cloud filtering [4], surface defects detection [5], shock sensing [6], etc." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 432, + 547, + 576 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 432, + 547, + 576 + ], + "spans": [ + { + "bbox": [ + 304, + 432, + 547, + 576 + ], + "type": "text", + "content": "It is noted that the optimization problem (1) is NP-hard. The convex relaxation of RPCA has been studied to achieve an exact recovery in [1, 7-12], where the RPCA problem was relaxed as the sum of the nuclear norm and " + }, + { + "bbox": [ + 304, + 432, + 547, + 576 + ], + "type": "inline_equation", + "content": "\\ell_1" + }, + { + "bbox": [ + 304, + 432, + 547, + 576 + ], + "type": "text", + "content": "-norm. But the convex methods always have a rate of sublinear convergence and high computation in practice [13]. It is necessary to exploit the structure of the underlying data and develop more efficient algorithms for RPCA. Zhou et al. [14] extended the equality constraint of RPCA to inequality in order to deal with noisy data, thus the RPCA is reformulated as the following constrained non-convex optimization problem:" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 359, + 584, + 545, + 608 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 359, + 584, + 545, + 608 + ], + "spans": [ + { + "bbox": [ + 359, + 584, + 545, + 608 + ], + "type": "interline_equation", + "content": "\\min _ {\\boldsymbol {L}, \\boldsymbol {S}} \\| \\boldsymbol {D} - \\boldsymbol {L} - \\boldsymbol {S} \\| _ {F} ^ {2} \\tag {2}", + "image_path": "99475465cde9a6f54581e4bce523c780971ea70790639e4bab5411abde0da1dc.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 360, + 608, + 492, + 619 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 360, + 608, + 492, + 619 + ], + "spans": [ + { + "bbox": [ + 360, + 608, + 492, + 619 + ], + "type": "interline_equation", + "content": "\\text {s . t .} \\operatorname {r a n k} (\\boldsymbol {L}) \\leq r \\text {a n d} \\| \\boldsymbol {S} \\| _ {0} \\leq s", + "image_path": "ecd230ca0724e8fa696b65433e4c959a38df26be84f197ed7277e3913d972adb.jpg" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 306, + 629, + 506, + 641 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 629, + 506, + 641 + ], + "spans": [ + { + "bbox": [ + 306, + 629, + 506, + 641 + ], + "type": "text", + "content": "with the target rank " + }, + { + "bbox": [ + 306, + 629, + 506, + 641 + ], + "type": "inline_equation", + "content": "r" + }, + { + "bbox": [ + 306, + 629, + 506, + 641 + ], + "type": "text", + "content": " and target sparse number " + }, + { + "bbox": [ + 306, + 629, + 506, + 641 + ], + "type": "inline_equation", + "content": "s" + }, + { + "bbox": [ + 306, + 629, + 506, + 641 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 642, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 642, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 642, + 547, + 713 + ], + "type": "text", + "content": "The key idea of Eq. (2) is to formulate a constrained nonconvex optimization problem. Among the nonconvex optimization methods of RPCA, Zhou et al. [15] substituted the hard thresholding of Eq. (2) with a soft " + }, + { + "bbox": [ + 304, + 642, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\ell_1" + }, + { + "bbox": [ + 304, + 642, + 547, + 713 + ], + "type": "text", + "content": " regularization to reduce the complexity of " + }, + { + "bbox": [ + 304, + 642, + 547, + 713 + ], + "type": "inline_equation", + "content": "S" + }, + { + "bbox": [ + 304, + 642, + 547, + 713 + ], + "type": "text", + "content": ". Netrapalli et al. [16] added the deterministic sparsity assumption and devoted themselves" + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 702, + 181, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 702, + 181, + 713 + ], + "spans": [ + { + "bbox": [ + 58, + 702, + 181, + 713 + ], + "type": "text", + "content": "*Shiqian Wu is corresponding author." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "1348" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 263 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 263 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 263 + ], + "type": "text", + "content": "to recovering a low-rank matrix from the sparse corruptions that were of unknown value and support. The RPCA algorithm via gradient descent on the factorized space in [17] achieved linear convergence with proper initialization and step size, whose sparse estimator is to guarantee that the fraction of nonzero entries in each column and row of " + }, + { + "bbox": [ + 46, + 72, + 289, + 263 + ], + "type": "inline_equation", + "content": "S" + }, + { + "bbox": [ + 46, + 72, + 289, + 263 + ], + "type": "text", + "content": " is bounded above. Inspired by these methods, GoDec+ [18] made the model become an ordinary low-rank projection problem based on the current entropy of noise and half-quadratic optimization theory. In [19], RPCA problem is considered for the first time without heuristics, such as loss functions, convex and surrogate constraints, which provides a new direction for potential research on online algorithms. In addition, Ornhag et al. [20] used second-order methods to convert the original objectives to differentiable equivalents, benefitting from faster convergence." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 266, + 289, + 410 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 266, + 289, + 410 + ], + "spans": [ + { + "bbox": [ + 46, + 266, + 289, + 410 + ], + "type": "text", + "content": "Meanwhile, the efficient algorithms for RPCA have been widely investigated for large-scale matrices. In [16], the developed algorithm involved alternating projections between a set of low-rank matrices and a set of sparse matrices, whose projection idea was also widely studied. Inspired by [16], a proximal block coordinate descent method was proposed in [21] to find an " + }, + { + "bbox": [ + 46, + 266, + 289, + 410 + ], + "type": "inline_equation", + "content": "\\epsilon" + }, + { + "bbox": [ + 46, + 266, + 289, + 410 + ], + "type": "text", + "content": "-stationary solution in " + }, + { + "bbox": [ + 46, + 266, + 289, + 410 + ], + "type": "inline_equation", + "content": "O(1/\\epsilon^2)" + }, + { + "bbox": [ + 46, + 266, + 289, + 410 + ], + "type": "text", + "content": " iterations. Furthermore, an accelerated alternating projection strategy was studied in [22] for RPCA, which project a matrix onto a specific low-dimensional subspace before obtaining a new estimate of the low-rank matrix via truncated SVD." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 411, + 289, + 581 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 411, + 289, + 581 + ], + "spans": [ + { + "bbox": [ + 46, + 411, + 289, + 581 + ], + "type": "text", + "content": "Most of RPCA and its variants contain SVD, which requires significant computational cost for large-scale matrices. Hintermüller [23] directly considered a least-squares problem subject to rank and cardinality constraints based on matrix manifolds, which favorably avoids singular value decompositions in full dimension. Phan et al. [24] proposed an accelerated algorithm with iteratively reweighted nuclear norm to ensure that every limit point is a critical point, which leads to small singular values and obtains fast result. Some different computing strategies were employed to substitute SVD so that the computation of RPCA was significantly reduced. Cai et al. [25] introduced CUR decomposition at each iteration, which only required " + }, + { + "bbox": [ + 46, + 411, + 289, + 581 + ], + "type": "inline_equation", + "content": "O(r^{2}n)" + }, + { + "bbox": [ + 46, + 411, + 289, + 581 + ], + "type": "text", + "content": " flops per iteration and preserved more information than SVD." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "text", + "content": "Generally, the aforementioned algorithms achieved efficient and effective performance in different computer vision tasks. It is highlighted that these methods require the rank of a low-rank matrix to be known a priori, which is inappropriate in most practical applications. To bridge this gap, Xu et al. [26] proposed a rank estimation method based on Gerschgorin disk theorem (GDE), whose computational complexity is " + }, + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "inline_equation", + "content": "O((d - 1)^3)" + }, + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "text", + "content": " at each iteration. Furthermore, an adaptive weighting RPCA was developed based on iteratively estimated rank, which outperforms the state-of-the-art RPCA methods in various computer vision applications." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 305, + 72, + 545, + 97 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 545, + 97 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 545, + 97 + ], + "type": "text", + "content": "More specifically, the adaptive weighting RPCA in [26] was formulated as the following optimization problem:" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 343, + 108, + 545, + 127 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 343, + 108, + 545, + 127 + ], + "spans": [ + { + "bbox": [ + 343, + 108, + 545, + 127 + ], + "type": "interline_equation", + "content": "\\min _ {\\boldsymbol {L}, \\boldsymbol {S}} \\| \\boldsymbol {L} \\| _ {W} + \\lambda \\| \\boldsymbol {S} \\| _ {1} \\quad \\text {s . t .} \\boldsymbol {D} = \\boldsymbol {L} + \\boldsymbol {S} \\tag {3}", + "image_path": "5d4f6b8eb27654481ac9e6ea9a8251adabc78567e72bc95032bad8e5fa6a4013.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 138, + 545, + 174 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 138, + 545, + 174 + ], + "spans": [ + { + "bbox": [ + 304, + 138, + 545, + 174 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 138, + 545, + 174 + ], + "type": "inline_equation", + "content": "\\| L\\| _W = \\Sigma_i\\omega_i\\sigma_i(L)" + }, + { + "bbox": [ + 304, + 138, + 545, + 174 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 138, + 545, + 174 + ], + "type": "inline_equation", + "content": "\\omega_{i}" + }, + { + "bbox": [ + 304, + 138, + 545, + 174 + ], + "type": "text", + "content": " are non-negative weights. Based on the estimated rank of " + }, + { + "bbox": [ + 304, + 138, + 545, + 174 + ], + "type": "inline_equation", + "content": "L" + }, + { + "bbox": [ + 304, + 138, + 545, + 174 + ], + "type": "text", + "content": " , the weights can be updated iteratively." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 175, + 546, + 486 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 175, + 546, + 486 + ], + "spans": [ + { + "bbox": [ + 304, + 175, + 546, + 486 + ], + "type": "text", + "content": "Although the adaptive weighting RPCA [26] achieves top performance in recovering a low-rank matrix and a sparse matrix, both the rank estimation and RPCA optimization algorithm contain SVD, which takes significant computational costs for large-scale matrices. Recently, randomized block Krylov iteration [27] was introduced to approximate the singular value decomposition in fewer iterations with better accuracy guarantees. This motivates us to use the block Krylov iteration method to accelerate the GDE-based rank estimation in this work. The computational complexity of the proposed Krylov GDE (KGDE)-based rank estimation is reduced to " + }, + { + "bbox": [ + 304, + 175, + 546, + 486 + ], + "type": "inline_equation", + "content": "O(ndrq + n(rq)^2)" + }, + { + "bbox": [ + 304, + 175, + 546, + 486 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 175, + 546, + 486 + ], + "type": "inline_equation", + "content": "q" + }, + { + "bbox": [ + 304, + 175, + 546, + 486 + ], + "type": "text", + "content": " is a parameter with a small value. On the other hand, CUR decomposition is also adopted to replace SVD in the updates of a low-rank matrix, thus the computational complexity of RPCA is significantly reduced. Since the rank of a matrix is required to be known for CUR decomposition, it is natural that the proposed KGDE is used to adaptively estimate the rank of the low-rank matrix within the iterative RPCA computing. Furthermore, a new non-convex low-rank regularized term is used to replace the weighted nuclear norm in (3) which can improve the low-rank matrix approximation. Compared with the state-of-the-art RPCA approaches, the proposed efficient RPCA (eRPCA) algorithm are fast with better accuracy guarantees. The main contributions of this paper are as follows:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 312, + 492, + 547, + 647 + ], + "type": "list", + "angle": 0, + "index": 12, + "blocks": [ + { + "bbox": [ + 313, + 492, + 545, + 528 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 313, + 492, + 545, + 528 + ], + "spans": [ + { + "bbox": [ + 313, + 492, + 545, + 528 + ], + "type": "text", + "content": "1) An efficient rank estimation method based on Gerschgorin disks with block Krylov iteration is proposed to accelerate the rank estimate of low-rank matrices." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 312, + 528, + 547, + 563 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 528, + 547, + 563 + ], + "spans": [ + { + "bbox": [ + 312, + 528, + 547, + 563 + ], + "type": "text", + "content": "2) CUR decomposition is adopted to reduce the computation of SVD on a large-scale matrix in the update of the low-rank matrix." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 312, + 564, + 545, + 610 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 564, + 545, + 610 + ], + "spans": [ + { + "bbox": [ + 312, + 564, + 545, + 610 + ], + "type": "text", + "content": "3) An efficient non-convex RPCA method with a nonconvex weighted regularizer is proposed to achieve better recovery of the low-rank matrix and the sparse matrix." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 312, + 612, + 545, + 647 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 612, + 545, + 647 + ], + "spans": [ + { + "bbox": [ + 312, + 612, + 545, + 647 + ], + "type": "text", + "content": "4) The proposed eRPCA algorithm has been applied to various computer vision scenarios and outperforms the state-of-the-art methods on large-scale data." + } + ] + } + ], + "index": 11 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 304, + 653, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 653, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 304, + 653, + 545, + 712 + ], + "type": "text", + "content": "In the following section, the improved eRPCA method, which consists of efficient rank estimation and new weight is presented in Section 2. The experimental results are demonstrated in Section 3, and the conclusions are drawn in Section 4." + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "text", + "content": "1349" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 71, + 153, + 84 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 71, + 153, + 84 + ], + "spans": [ + { + "bbox": [ + 47, + 71, + 153, + 84 + ], + "type": "text", + "content": "2. Proposed Method" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 90, + 287, + 114 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 90, + 287, + 114 + ], + "spans": [ + { + "bbox": [ + 47, + 90, + 287, + 114 + ], + "type": "text", + "content": "2.1. Efficient Rank Estimation via Block Krylov Iteration" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 121, + 287, + 228 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 121, + 287, + 228 + ], + "spans": [ + { + "bbox": [ + 46, + 121, + 287, + 228 + ], + "type": "text", + "content": "In [26], GDE was used to estimate the rank of a low-rank matrix, which involves SVD and has the computational complexity " + }, + { + "bbox": [ + 46, + 121, + 287, + 228 + ], + "type": "inline_equation", + "content": "O\\left(\\left(d - 1\\right)^{3}\\right)" + }, + { + "bbox": [ + 46, + 121, + 287, + 228 + ], + "type": "text", + "content": " for a matrix " + }, + { + "bbox": [ + 46, + 121, + 287, + 228 + ], + "type": "inline_equation", + "content": "D \\in \\mathbb{R}^{n \\times d}" + }, + { + "bbox": [ + 46, + 121, + 287, + 228 + ], + "type": "text", + "content": ". Hence it is time-consuming to estimate the rank of large-scale matrix " + }, + { + "bbox": [ + 46, + 121, + 287, + 228 + ], + "type": "inline_equation", + "content": "D" + }, + { + "bbox": [ + 46, + 121, + 287, + 228 + ], + "type": "text", + "content": ". Recently it has been shown that block Krylov iteration (BKI) method [27] gives nearly optimal approximation of singular values and singular vectors with few interations. In this subsection, an efficient rank estimation is proposed by combining BKI and GDE, which is named as KGDE." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 229, + 287, + 266 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 229, + 287, + 266 + ], + "spans": [ + { + "bbox": [ + 46, + 229, + 287, + 266 + ], + "type": "text", + "content": "Now we give a brief review on the block Krylov iteration method. For a matrix " + }, + { + "bbox": [ + 46, + 229, + 287, + 266 + ], + "type": "inline_equation", + "content": "D \\in \\mathbb{R}^{n \\times d}" + }, + { + "bbox": [ + 46, + 229, + 287, + 266 + ], + "type": "text", + "content": ", the Krylov subspace is obtained by" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 97, + 276, + 287, + 289 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 97, + 276, + 287, + 289 + ], + "spans": [ + { + "bbox": [ + 97, + 276, + 287, + 289 + ], + "type": "interline_equation", + "content": "\\boldsymbol {K} := [ \\boldsymbol {v}, \\boldsymbol {D} \\boldsymbol {v}, \\boldsymbol {D} ^ {2} \\boldsymbol {v}, \\dots , \\boldsymbol {D} ^ {q - 1} \\boldsymbol {v} ] \\tag {4}", + "image_path": "d4302566f8f5bdd961e5c1d8d593651a432f4739d1f228add6077a181e9ac603.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 293, + 287, + 330 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 293, + 287, + 330 + ], + "spans": [ + { + "bbox": [ + 46, + 293, + 287, + 330 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 293, + 287, + 330 + ], + "type": "inline_equation", + "content": "\\pmb{v}" + }, + { + "bbox": [ + 46, + 293, + 287, + 330 + ], + "type": "text", + "content": " is a vector of unit norm, " + }, + { + "bbox": [ + 46, + 293, + 287, + 330 + ], + "type": "inline_equation", + "content": "\\| \\pmb {v}\\| = 1" + }, + { + "bbox": [ + 46, + 293, + 287, + 330 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 46, + 293, + 287, + 330 + ], + "type": "inline_equation", + "content": "q" + }, + { + "bbox": [ + 46, + 293, + 287, + 330 + ], + "type": "text", + "content": " is a scalar. In [28], the Krylov subspace was extended to randomized block Krylov subspace:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 90, + 340, + 287, + 354 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 90, + 340, + 287, + 354 + ], + "spans": [ + { + "bbox": [ + 90, + 340, + 287, + 354 + ], + "type": "interline_equation", + "content": "\\boldsymbol {K} := \\left[ \\boldsymbol {V}, \\boldsymbol {D V}, \\boldsymbol {D} ^ {2} \\boldsymbol {V}, \\dots , \\boldsymbol {D} ^ {q - 1} \\boldsymbol {V} \\right] \\tag {5}", + "image_path": "1ac79c64b305e9a9161638731b97c6126037bc85aa27bb186b16ab2da19f6618.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 358, + 287, + 381 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 358, + 287, + 381 + ], + "spans": [ + { + "bbox": [ + 46, + 358, + 287, + 381 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 358, + 287, + 381 + ], + "type": "inline_equation", + "content": "\\mathbf{V} = [\\pmb{v}_1, \\dots, \\pmb{v}_b] \\in \\mathbb{R}^{d \\times b}" + }, + { + "bbox": [ + 46, + 358, + 287, + 381 + ], + "type": "text", + "content": " is a block of " + }, + { + "bbox": [ + 46, + 358, + 287, + 381 + ], + "type": "inline_equation", + "content": "b" + }, + { + "bbox": [ + 46, + 358, + 287, + 381 + ], + "type": "text", + "content": " random vectors." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 383, + 287, + 466 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 383, + 287, + 466 + ], + "spans": [ + { + "bbox": [ + 46, + 383, + 287, + 466 + ], + "type": "text", + "content": "After constructing the block Krylov subspace, the Block Krylov Iteration (BKI) [27] can be used to generate closely approximate eigenpairs within fewer iterations by projecting the matrix onto the randomized block Krylov subspace. Its idea is to take a randomized starting matrix " + }, + { + "bbox": [ + 46, + 383, + 287, + 466 + ], + "type": "inline_equation", + "content": "V = D\\Omega" + }, + { + "bbox": [ + 46, + 383, + 287, + 466 + ], + "type": "text", + "content": " as the initial matrix, where " + }, + { + "bbox": [ + 46, + 383, + 287, + 466 + ], + "type": "inline_equation", + "content": "\\Omega" + }, + { + "bbox": [ + 46, + 383, + 287, + 466 + ], + "type": "text", + "content": " is a Gaussian random matrix. BKI captures an accurate range space:" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 124, + 467, + 287, + 483 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 124, + 467, + 287, + 483 + ], + "spans": [ + { + "bbox": [ + 124, + 467, + 287, + 483 + ], + "type": "interline_equation", + "content": "\\boldsymbol {K} := \\left(\\boldsymbol {D} \\boldsymbol {D} ^ {T}\\right) ^ {q} \\boldsymbol {D} \\boldsymbol {\\Omega} \\tag {6}", + "image_path": "5d872df8d6cf71a4b40da292f52f5b525131c65d7f2bc0cca4893e7616e07a0f.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 483, + 287, + 535 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 483, + 287, + 535 + ], + "spans": [ + { + "bbox": [ + 46, + 483, + 287, + 535 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 483, + 287, + 535 + ], + "type": "inline_equation", + "content": "q \\coloneqq \\Theta \\left( \\frac{\\log d}{\\sqrt{\\varepsilon}} \\right)" + }, + { + "bbox": [ + 46, + 483, + 287, + 535 + ], + "type": "text", + "content": ". Orthonormalize the columns of " + }, + { + "bbox": [ + 46, + 483, + 287, + 535 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 46, + 483, + 287, + 535 + ], + "type": "text", + "content": " to obtain " + }, + { + "bbox": [ + 46, + 483, + 287, + 535 + ], + "type": "inline_equation", + "content": "Q" + }, + { + "bbox": [ + 46, + 483, + 287, + 535 + ], + "type": "text", + "content": " then compute " + }, + { + "bbox": [ + 46, + 483, + 287, + 535 + ], + "type": "inline_equation", + "content": "M \\coloneqq Q^T D D^T Q" + }, + { + "bbox": [ + 46, + 483, + 287, + 535 + ], + "type": "text", + "content": ". Set " + }, + { + "bbox": [ + 46, + 483, + 287, + 535 + ], + "type": "inline_equation", + "content": "\\overline{U}_k" + }, + { + "bbox": [ + 46, + 483, + 287, + 535 + ], + "type": "text", + "content": " to the top " + }, + { + "bbox": [ + 46, + 483, + 287, + 535 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 483, + 287, + 535 + ], + "type": "text", + "content": " singular vectors of " + }, + { + "bbox": [ + 46, + 483, + 287, + 535 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 46, + 483, + 287, + 535 + ], + "type": "text", + "content": ". At last, return the low-dimension matrix " + }, + { + "bbox": [ + 46, + 483, + 287, + 535 + ], + "type": "inline_equation", + "content": "Z" + }, + { + "bbox": [ + 46, + 483, + 287, + 535 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 143, + 537, + 287, + 551 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 537, + 287, + 551 + ], + "spans": [ + { + "bbox": [ + 143, + 537, + 287, + 551 + ], + "type": "interline_equation", + "content": "\\boldsymbol {Z} = \\boldsymbol {Q} \\bar {\\boldsymbol {U}} _ {k} \\tag {7}", + "image_path": "83e0cbb4a1206ba7b24f3e824b61bc0f4c2cc336c1891de384714b3d4d1899b9.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 46, + 554, + 287, + 578 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 554, + 287, + 578 + ], + "spans": [ + { + "bbox": [ + 46, + 554, + 287, + 578 + ], + "type": "text", + "content": "The following theorem shows that the randomized BKI can get strong relative-error bound." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 47, + 585, + 287, + 648 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 585, + 287, + 648 + ], + "spans": [ + { + "bbox": [ + 47, + 585, + 287, + 648 + ], + "type": "text", + "content": "Theorem 1 [27] Given data matrix " + }, + { + "bbox": [ + 47, + 585, + 287, + 648 + ], + "type": "inline_equation", + "content": "\\pmb{D} \\in \\mathbb{R}^{n \\times d}" + }, + { + "bbox": [ + 47, + 585, + 287, + 648 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 585, + 287, + 648 + ], + "type": "inline_equation", + "content": "n < d" + }, + { + "bbox": [ + 47, + 585, + 287, + 648 + ], + "type": "text", + "content": " with eigenvalues " + }, + { + "bbox": [ + 47, + 585, + 287, + 648 + ], + "type": "inline_equation", + "content": "\\lambda_i, i = 1, 2, \\dots, n" + }, + { + "bbox": [ + 47, + 585, + 287, + 648 + ], + "type": "text", + "content": ". Let " + }, + { + "bbox": [ + 47, + 585, + 287, + 648 + ], + "type": "inline_equation", + "content": "\\{\\theta_i, \\varphi_i\\}_{i=1}^k" + }, + { + "bbox": [ + 47, + 585, + 287, + 648 + ], + "type": "text", + "content": " be the " + }, + { + "bbox": [ + 47, + 585, + 287, + 648 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 47, + 585, + 287, + 648 + ], + "type": "text", + "content": " eigenpair computed using " + }, + { + "bbox": [ + 47, + 585, + 287, + 648 + ], + "type": "inline_equation", + "content": "q" + }, + { + "bbox": [ + 47, + 585, + 287, + 648 + ], + "type": "text", + "content": " steps of Block Krylov Iteration (using the orthonormal basis of " + }, + { + "bbox": [ + 47, + 585, + 287, + 648 + ], + "type": "inline_equation", + "content": "\\pmb{K}" + }, + { + "bbox": [ + 47, + 585, + 287, + 648 + ], + "type": "text", + "content": " for " + }, + { + "bbox": [ + 47, + 585, + 287, + 648 + ], + "type": "inline_equation", + "content": "\\pmb{V} \\in \\mathbb{R}^{d \\times b}" + }, + { + "bbox": [ + 47, + 585, + 287, + 648 + ], + "type": "text", + "content": "). If " + }, + { + "bbox": [ + 47, + 585, + 287, + 648 + ], + "type": "inline_equation", + "content": "q = \\frac{\\log d}{\\sqrt{\\varepsilon}}" + }, + { + "bbox": [ + 47, + 585, + 287, + 648 + ], + "type": "text", + "content": " for some " + }, + { + "bbox": [ + 47, + 585, + 287, + 648 + ], + "type": "inline_equation", + "content": "0 < \\varepsilon < 1" + }, + { + "bbox": [ + 47, + 585, + 287, + 648 + ], + "type": "text", + "content": ", then have" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 100, + 648, + 234, + 661 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 100, + 648, + 234, + 661 + ], + "spans": [ + { + "bbox": [ + 100, + 648, + 234, + 661 + ], + "type": "interline_equation", + "content": "\\left| \\theta_ {i} - \\lambda_ {i} \\right| \\leq \\varepsilon \\lambda_ {k + 1}, i = 1, \\dots , k.", + "image_path": "ed2822e753471017f94382c4bddb255866ce9b8d502a644702ccfea585fc0d91.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "text", + "content": "In the rest of this subsection, we present a fast rank estimation of low-rank matrices based on the BKI and GDE. Given a low-rank matrix " + }, + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "inline_equation", + "content": "D \\in \\mathbb{R}^{n \\times d}" + }, + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "inline_equation", + "content": "n < d" + }, + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "text", + "content": " with rank " + }, + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "inline_equation", + "content": "r" + }, + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "text", + "content": ". The BKI algorithm outputs a low-dimension matrix" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 72, + 545, + 131 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 545, + 131 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 545, + 131 + ], + "type": "inline_equation", + "content": "Z \\in \\mathbb{R}^{n \\times k}" + }, + { + "bbox": [ + 305, + 72, + 545, + 131 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 305, + 72, + 545, + 131 + ], + "type": "inline_equation", + "content": "k < d" + }, + { + "bbox": [ + 305, + 72, + 545, + 131 + ], + "type": "text", + "content": ", which aligns well with the top " + }, + { + "bbox": [ + 305, + 72, + 545, + 131 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 305, + 72, + 545, + 131 + ], + "type": "text", + "content": " singular vectors of " + }, + { + "bbox": [ + 305, + 72, + 545, + 131 + ], + "type": "inline_equation", + "content": "D" + }, + { + "bbox": [ + 305, + 72, + 545, + 131 + ], + "type": "text", + "content": ". If " + }, + { + "bbox": [ + 305, + 72, + 545, + 131 + ], + "type": "inline_equation", + "content": "r \\leq k" + }, + { + "bbox": [ + 305, + 72, + 545, + 131 + ], + "type": "text", + "content": ", the ranks of " + }, + { + "bbox": [ + 305, + 72, + 545, + 131 + ], + "type": "inline_equation", + "content": "D" + }, + { + "bbox": [ + 305, + 72, + 545, + 131 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 72, + 545, + 131 + ], + "type": "inline_equation", + "content": "Z" + }, + { + "bbox": [ + 305, + 72, + 545, + 131 + ], + "type": "text", + "content": " are equal. Hence it reduces the computational complexity when GDE can also be applied to " + }, + { + "bbox": [ + 305, + 72, + 545, + 131 + ], + "type": "inline_equation", + "content": "Z" + }, + { + "bbox": [ + 305, + 72, + 545, + 131 + ], + "type": "text", + "content": " to estimate the rank instead of the large-scale matrix " + }, + { + "bbox": [ + 305, + 72, + 545, + 131 + ], + "type": "inline_equation", + "content": "D" + }, + { + "bbox": [ + 305, + 72, + 545, + 131 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 305, + 132, + 545, + 155 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 132, + 545, + 155 + ], + "spans": [ + { + "bbox": [ + 305, + 132, + 545, + 155 + ], + "type": "text", + "content": "The covariance matrix " + }, + { + "bbox": [ + 305, + 132, + 545, + 155 + ], + "type": "inline_equation", + "content": "\\mathbf{R}_{\\mathbf{Z}} \\in \\mathbb{R}^{k \\times k}" + }, + { + "bbox": [ + 305, + 132, + 545, + 155 + ], + "type": "text", + "content": " of the matrix " + }, + { + "bbox": [ + 305, + 132, + 545, + 155 + ], + "type": "inline_equation", + "content": "\\mathbf{Z}" + }, + { + "bbox": [ + 305, + 132, + 545, + 155 + ], + "type": "text", + "content": " with a rank " + }, + { + "bbox": [ + 305, + 132, + 545, + 155 + ], + "type": "inline_equation", + "content": "r" + }, + { + "bbox": [ + 305, + 132, + 545, + 155 + ], + "type": "text", + "content": " can be defined as:" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 398, + 157, + 545, + 171 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 398, + 157, + 545, + 171 + ], + "spans": [ + { + "bbox": [ + 398, + 157, + 545, + 171 + ], + "type": "interline_equation", + "content": "\\boldsymbol {R} _ {Z} = \\boldsymbol {Z} ^ {T} \\boldsymbol {Z} \\tag {8}", + "image_path": "e98ad534331ee6d2f28f2a950ba0c5ca4b681a57ee42af20a630f63301c512ac.jpg" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 317, + 174, + 538, + 186 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 174, + 538, + 186 + ], + "spans": [ + { + "bbox": [ + 317, + 174, + 538, + 186 + ], + "type": "text", + "content": "Then the eigenvalue decomposition of " + }, + { + "bbox": [ + 317, + 174, + 538, + 186 + ], + "type": "inline_equation", + "content": "R_Z" + }, + { + "bbox": [ + 317, + 174, + 538, + 186 + ], + "type": "text", + "content": " is given by" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 378, + 187, + 545, + 202 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 378, + 187, + 545, + 202 + ], + "spans": [ + { + "bbox": [ + 378, + 187, + 545, + 202 + ], + "type": "interline_equation", + "content": "R _ {Z} = U _ {R _ {Z}} \\Sigma_ {R _ {Z}} U _ {R _ {Z}} ^ {H} \\tag {9}", + "image_path": "b1b8cd87b08121e07f2a0c4985e3dc2c99058bd2037e35c2ada733f025bab01e.jpg" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 305, + 204, + 545, + 251 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 204, + 545, + 251 + ], + "spans": [ + { + "bbox": [ + 305, + 204, + 545, + 251 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 204, + 545, + 251 + ], + "type": "inline_equation", + "content": "U_{R_Z} = [u_1, u_2, \\dots, u_k]" + }, + { + "bbox": [ + 305, + 204, + 545, + 251 + ], + "type": "text", + "content": " is the eigenvector matrix, and " + }, + { + "bbox": [ + 305, + 204, + 545, + 251 + ], + "type": "inline_equation", + "content": "\\Sigma_{R_Z} = \\text{diag}(\\sigma_1, \\sigma_2, \\dots, \\sigma_k)" + }, + { + "bbox": [ + 305, + 204, + 545, + 251 + ], + "type": "text", + "content": " represents the eigenvalue matrix. According to the Gerschgorin disk theorem [29], " + }, + { + "bbox": [ + 305, + 204, + 545, + 251 + ], + "type": "inline_equation", + "content": "R_Z" + }, + { + "bbox": [ + 305, + 204, + 545, + 251 + ], + "type": "text", + "content": " can be transformed as follows:" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 311, + 253, + 545, + 319 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 311, + 253, + 545, + 319 + ], + "spans": [ + { + "bbox": [ + 311, + 253, + 545, + 319 + ], + "type": "interline_equation", + "content": "\\boldsymbol {R} _ {\\boldsymbol {Z}} = \\left[ \\begin{array}{c c c c} R _ {1 1} & R _ {1 2} & \\dots & R _ {1 k} \\\\ R _ {2 1} & R _ {2 2} & \\dots & R _ {2 k} \\\\ \\vdots & \\vdots & \\ddots & \\vdots \\\\ R _ {k 1} & R _ {k 2} & \\dots & R _ {k k} \\end{array} \\right] = \\left[ \\begin{array}{c c} \\boldsymbol {R} _ {\\boldsymbol {Z 1}} & \\boldsymbol {R} \\\\ \\boldsymbol {R} ^ {H} & R _ {k k} \\end{array} \\right] \\tag {10}", + "image_path": "0127d56c7e9268bc68fb4f907a7881be3b77806f1b3dd5bed8f42ba8a8433397.jpg" + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 305, + 319, + 545, + 367 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 319, + 545, + 367 + ], + "spans": [ + { + "bbox": [ + 305, + 319, + 545, + 367 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 319, + 545, + 367 + ], + "type": "inline_equation", + "content": "\\pmb{R}_{\\pmb{Z1}} \\in \\mathbb{R}^{(k-1) \\times (k-1)}" + }, + { + "bbox": [ + 305, + 319, + 545, + 367 + ], + "type": "text", + "content": " is the square matrix by the first " + }, + { + "bbox": [ + 305, + 319, + 545, + 367 + ], + "type": "inline_equation", + "content": "(k-1)" + }, + { + "bbox": [ + 305, + 319, + 545, + 367 + ], + "type": "text", + "content": " rows and the first " + }, + { + "bbox": [ + 305, + 319, + 545, + 367 + ], + "type": "inline_equation", + "content": "(k-1)" + }, + { + "bbox": [ + 305, + 319, + 545, + 367 + ], + "type": "text", + "content": " columns of " + }, + { + "bbox": [ + 305, + 319, + 545, + 367 + ], + "type": "inline_equation", + "content": "\\pmb{R}_{\\pmb{Z1}}" + }, + { + "bbox": [ + 305, + 319, + 545, + 367 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 305, + 319, + 545, + 367 + ], + "type": "inline_equation", + "content": "\\pmb{R} = [R_{1k}, R_{2k}, \\dots, R_{(k-1)k}]^T" + }, + { + "bbox": [ + 305, + 319, + 545, + 367 + ], + "type": "text", + "content": ". Then the eigenvalue decomposition on " + }, + { + "bbox": [ + 305, + 319, + 545, + 367 + ], + "type": "inline_equation", + "content": "\\pmb{R}_{\\pmb{Z1}}" + }, + { + "bbox": [ + 305, + 319, + 545, + 367 + ], + "type": "text", + "content": " is obtained as:" + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 381, + 369, + 545, + 383 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 381, + 369, + 545, + 383 + ], + "spans": [ + { + "bbox": [ + 381, + 369, + 545, + 383 + ], + "type": "interline_equation", + "content": "\\boldsymbol {R} _ {Z 1} = U _ {Z 1} \\boldsymbol {\\Sigma} _ {1} U _ {Z 1} ^ {H} \\tag {11}", + "image_path": "6716e6ecc7d4af8394a9130a84db2441e96afab945d2f45041c003c474bf02dc.jpg" + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 305, + 384, + 545, + 443 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 384, + 545, + 443 + ], + "spans": [ + { + "bbox": [ + 305, + 384, + 545, + 443 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 384, + 545, + 443 + ], + "type": "inline_equation", + "content": "U_{\\mathbf{Z1}} = [q_1', q_2', \\dots, q_{k-1}']" + }, + { + "bbox": [ + 305, + 384, + 545, + 443 + ], + "type": "text", + "content": " is an " + }, + { + "bbox": [ + 305, + 384, + 545, + 443 + ], + "type": "inline_equation", + "content": "(k-1) \\times (k-1)" + }, + { + "bbox": [ + 305, + 384, + 545, + 443 + ], + "type": "text", + "content": " unitary matrix composed of the eigenvectors of " + }, + { + "bbox": [ + 305, + 384, + 545, + 443 + ], + "type": "inline_equation", + "content": "\\mathbf{R}_{\\mathbf{Z1}}" + }, + { + "bbox": [ + 305, + 384, + 545, + 443 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 305, + 384, + 545, + 443 + ], + "type": "inline_equation", + "content": "\\pmb{\\Sigma}_{\\mathbf{1}} = \\text{diag}(\\sigma_1', \\sigma_2', \\dots, \\sigma_{k-1}')" + }, + { + "bbox": [ + 305, + 384, + 545, + 443 + ], + "type": "text", + "content": ". Similar to Eq. (10), a unitary transformed matrix " + }, + { + "bbox": [ + 305, + 384, + 545, + 443 + ], + "type": "inline_equation", + "content": "\\mathbf{U} \\in \\mathbb{R}^{k \\times k}(\\mathbf{U}\\mathbf{U}^H = \\mathbf{I})" + }, + { + "bbox": [ + 305, + 384, + 545, + 443 + ], + "type": "text", + "content": " is defined as:" + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 384, + 443, + 545, + 469 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 384, + 443, + 545, + 469 + ], + "spans": [ + { + "bbox": [ + 384, + 443, + 545, + 469 + ], + "type": "interline_equation", + "content": "\\boldsymbol {U} = \\left[ \\begin{array}{c c} U _ {Z 1} & \\mathbf {0} \\\\ \\mathbf {0} ^ {T} & \\mathbf {1} \\end{array} \\right] \\tag {12}", + "image_path": "20598bc9e2035fc1f0af96fb489eb3d7aa5a408ae0c1f57bdf5f6d799743fb0d.jpg" + } + ] + } + ], + "index": 26 + }, + { + "bbox": [ + 317, + 473, + 522, + 485 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 473, + 522, + 485 + ], + "spans": [ + { + "bbox": [ + 317, + 473, + 522, + 485 + ], + "type": "text", + "content": "The transformed covariance matrix is obtained by:" + } + ] + } + ], + "index": 27 + }, + { + "bbox": [ + 315, + 486, + 545, + 596 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 315, + 486, + 545, + 596 + ], + "spans": [ + { + "bbox": [ + 315, + 486, + 545, + 596 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\boldsymbol {R} _ {T} = \\boldsymbol {U} ^ {H} \\boldsymbol {R} _ {Z} \\boldsymbol {U} = \\left[ \\begin{array}{c c} \\boldsymbol {U} _ {Z 1} ^ {H} \\boldsymbol {R} _ {Z 1} \\boldsymbol {U} _ {Z 1} & \\boldsymbol {U} _ {Z 1} ^ {H} \\boldsymbol {R} \\\\ \\boldsymbol {R} ^ {H} \\boldsymbol {U} _ {Z 1} & R _ {k k} \\end{array} \\right] \\\\ = \\left[ \\begin{array}{c c c c c c} \\sigma_ {1} ^ {\\prime} & 0 & 0 & \\dots & 0 & \\rho_ {1} \\\\ 0 & \\sigma_ {2} ^ {\\prime} & 0 & \\dots & 0 & \\rho_ {2} \\\\ 0 & 0 & \\sigma_ {3} ^ {\\prime} & \\dots & 0 & \\rho_ {3} \\\\ \\vdots & \\vdots & \\vdots & \\ddots & \\vdots & \\vdots \\\\ 0 & 0 & 0 & \\dots & \\sigma_ {k - 1} ^ {\\prime} & \\rho_ {k - 1} \\\\ \\rho_ {1} ^ {*} & \\rho_ {2} ^ {*} & \\rho_ {3} ^ {*} & \\dots & \\rho_ {k - 1} ^ {*} & R _ {k k} \\end{array} \\right] \\tag {13} \\\\ \\end{array}", + "image_path": "3d4fc3b47b9b80b99c9362ce938fb88885735a01c3169938a5e7cb4b99abc009.jpg" + } + ] + } + ], + "index": 28 + }, + { + "bbox": [ + 305, + 598, + 545, + 645 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 598, + 545, + 645 + ], + "spans": [ + { + "bbox": [ + 305, + 598, + 545, + 645 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 598, + 545, + 645 + ], + "type": "inline_equation", + "content": "\\rho_{i} = \\pmb{q}_{i}^{\\prime H}\\pmb{R}" + }, + { + "bbox": [ + 305, + 598, + 545, + 645 + ], + "type": "text", + "content": ". The eigenvalues of " + }, + { + "bbox": [ + 305, + 598, + 545, + 645 + ], + "type": "inline_equation", + "content": "\\pmb{R}_{T}" + }, + { + "bbox": [ + 305, + 598, + 545, + 645 + ], + "type": "text", + "content": " can be estimated using the Gerschgorin disk theorem [29]. Then, the radii of the first " + }, + { + "bbox": [ + 305, + 598, + 545, + 645 + ], + "type": "inline_equation", + "content": "(k - 1)" + }, + { + "bbox": [ + 305, + 598, + 545, + 645 + ], + "type": "text", + "content": " Gerschgorin's disk can be written as:" + } + ] + } + ], + "index": 29 + }, + { + "bbox": [ + 384, + 645, + 545, + 661 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 384, + 645, + 545, + 661 + ], + "spans": [ + { + "bbox": [ + 384, + 645, + 545, + 661 + ], + "type": "interline_equation", + "content": "r _ {i} = \\left| \\rho_ {i} \\right| = \\left| \\boldsymbol {q} _ {i} ^ {\\prime H} \\boldsymbol {R} \\right| \\tag {14}", + "image_path": "8e45ca085e74b05d4c7481409280eb9c4bc63219cfbec209dbcea273fb52b55a.jpg" + } + ] + } + ], + "index": 30 + }, + { + "bbox": [ + 305, + 665, + 545, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 665, + 545, + 689 + ], + "spans": [ + { + "bbox": [ + 305, + 665, + 545, + 689 + ], + "type": "text", + "content": "where the radius " + }, + { + "bbox": [ + 305, + 665, + 545, + 689 + ], + "type": "inline_equation", + "content": "r_i" + }, + { + "bbox": [ + 305, + 665, + 545, + 689 + ], + "type": "text", + "content": " of the " + }, + { + "bbox": [ + 305, + 665, + 545, + 689 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 305, + 665, + 545, + 689 + ], + "type": "text", + "content": "th Gerschgorin's disk depends on the size of " + }, + { + "bbox": [ + 305, + 665, + 545, + 689 + ], + "type": "inline_equation", + "content": "\\pmb{q}_i^{\\prime H}\\pmb {R}" + } + ] + } + ], + "index": 31 + }, + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "type": "text", + "content": "To further improve the accuracy of the rank estimation, the radii of the Gerschgorin's disk are shrank in [26]. Then" + } + ] + } + ], + "index": 32 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "text", + "content": "1350" + } + ] + } + ], + "index": 33 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 72, + 132, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 72, + 132, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 72, + 132, + 83 + ], + "type": "text", + "content": "Algorithm 1 KGDE" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 88, + 286, + 115 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 88, + 286, + 115 + ], + "spans": [ + { + "bbox": [ + 47, + 88, + 286, + 115 + ], + "type": "text", + "content": "Input: " + }, + { + "bbox": [ + 47, + 88, + 286, + 115 + ], + "type": "inline_equation", + "content": "D\\in \\mathbb{R}^{n\\times d}" + }, + { + "bbox": [ + 47, + 88, + 286, + 115 + ], + "type": "text", + "content": ", error " + }, + { + "bbox": [ + 47, + 88, + 286, + 115 + ], + "type": "inline_equation", + "content": "\\varepsilon \\in (0,1)" + }, + { + "bbox": [ + 47, + 88, + 286, + 115 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 88, + 286, + 115 + ], + "type": "inline_equation", + "content": "k = 2" + }, + { + "bbox": [ + 47, + 88, + 286, + 115 + ], + "type": "text", + "content": ", the " + }, + { + "bbox": [ + 47, + 88, + 286, + 115 + ], + "type": "inline_equation", + "content": "(1 + \\varepsilon)" + }, + { + "bbox": [ + 47, + 88, + 286, + 115 + ], + "type": "text", + "content": " relative-error bound for BKI " + }, + { + "bbox": [ + 47, + 88, + 286, + 115 + ], + "type": "inline_equation", + "content": "q = \\frac{\\log d}{\\sqrt{\\varepsilon}}" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 48, + 115, + 157, + 125 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 115, + 157, + 125 + ], + "spans": [ + { + "bbox": [ + 48, + 115, + 157, + 125 + ], + "type": "text", + "content": "Output: Estimated rank " + }, + { + "bbox": [ + 48, + 115, + 157, + 125 + ], + "type": "inline_equation", + "content": "r" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 58, + 127, + 149, + 138 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 127, + 149, + 138 + ], + "spans": [ + { + "bbox": [ + 58, + 127, + 149, + 138 + ], + "type": "text", + "content": "Set " + }, + { + "bbox": [ + 58, + 127, + 149, + 138 + ], + "type": "inline_equation", + "content": "gde = \\text{zeros}(d, 1)" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 58, + 139, + 128, + 148 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 139, + 128, + 148 + ], + "spans": [ + { + "bbox": [ + 58, + 139, + 128, + 148 + ], + "type": "text", + "content": "for " + }, + { + "bbox": [ + 58, + 139, + 128, + 148 + ], + "type": "inline_equation", + "content": "t = 1" + }, + { + "bbox": [ + 58, + 139, + 128, + 148 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 58, + 139, + 128, + 148 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 58, + 139, + 128, + 148 + ], + "type": "text", + "content": " do" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 68, + 149, + 222, + 162 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 68, + 149, + 222, + 162 + ], + "spans": [ + { + "bbox": [ + 68, + 149, + 222, + 162 + ], + "type": "interline_equation", + "content": "\\boldsymbol {Z} \\in \\mathbb {R} ^ {n \\times k} \\leftarrow B K I (\\boldsymbol {D} \\in \\mathbb {R} ^ {n \\times d}, \\varepsilon , q)", + "image_path": "705acccd676c75a8776e3e64985238bffb525b7023fd487bbb4c75d8dc70a8d7.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 68, + 162, + 199, + 173 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 68, + 162, + 199, + 173 + ], + "spans": [ + { + "bbox": [ + 68, + 162, + 199, + 173 + ], + "type": "text", + "content": "Covariance matrix " + }, + { + "bbox": [ + 68, + 162, + 199, + 173 + ], + "type": "inline_equation", + "content": "\\mathbf{R}_{\\mathbf{Z}} = \\mathbf{Z}^{T}\\mathbf{Z}" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 68, + 175, + 287, + 198 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 68, + 175, + 287, + 198 + ], + "spans": [ + { + "bbox": [ + 68, + 175, + 287, + 198 + ], + "type": "text", + "content": "Obtain the transformed unitary matrix according to Eqs. (10)-(12)" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 68, + 198, + 287, + 221 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 68, + 198, + 287, + 221 + ], + "spans": [ + { + "bbox": [ + 68, + 198, + 287, + 221 + ], + "type": "text", + "content": "Calculate the radii " + }, + { + "bbox": [ + 68, + 198, + 287, + 221 + ], + "type": "inline_equation", + "content": "r_i" + }, + { + "bbox": [ + 68, + 198, + 287, + 221 + ], + "type": "text", + "content": " of the Gerschgorin's disk according to Eqs. (14)-(15)" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 68, + 222, + 248, + 234 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 68, + 222, + 248, + 234 + ], + "spans": [ + { + "bbox": [ + 68, + 222, + 248, + 234 + ], + "type": "text", + "content": "Calculate " + }, + { + "bbox": [ + 68, + 222, + 248, + 234 + ], + "type": "inline_equation", + "content": "gde(t)" + }, + { + "bbox": [ + 68, + 222, + 248, + 234 + ], + "type": "text", + "content": " according to Eqs. 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Thus, the new transformed matrix " + }, + { + "bbox": [ + 46, + 352, + 287, + 394 + ], + "type": "inline_equation", + "content": "\\pmb{R}_{\\pmb{T}\\pmb{\\Sigma}_{\\pmb{T}}}" + }, + { + "bbox": [ + 46, + 352, + 287, + 394 + ], + "type": "text", + "content": " is constructed as follows:" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 59, + 396, + 287, + 511 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 396, + 287, + 511 + ], + "spans": [ + { + "bbox": [ + 59, + 396, + 287, + 511 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\boldsymbol {R} _ {T \\Sigma_ {T}} = \\boldsymbol {\\Sigma} _ {T} \\boldsymbol {R} _ {T} \\boldsymbol {\\Sigma} _ {T} ^ {- 1} \\\\ = \\left[ \\begin{array}{c c c c c} \\sigma_ {1} ^ {\\prime} & 0 & \\dots & 0 & \\frac {\\sigma_ {1} ^ {\\prime}}{\\sigma_ {k} ^ {\\prime}} \\rho_ {1} \\\\ 0 & \\sigma_ {2} ^ {\\prime} & \\dots & 0 & \\frac {\\sigma_ {2}}{\\sigma_ {k} ^ {\\prime}} \\rho_ {2} \\\\ \\vdots & \\vdots & \\ddots & \\vdots & \\vdots \\\\ 0 & 0 & \\dots & \\sigma_ {k - 1} ^ {\\prime} & \\frac {\\sigma_ {k - 1} ^ {\\prime}}{\\sigma_ {k} ^ {\\prime}} \\rho_ {k - 1} \\\\ \\frac {\\sigma_ {1} ^ {\\prime}}{\\sigma_ {k} ^ {\\prime}} \\rho_ {1} ^ {*} & \\frac {\\sigma_ {2} ^ {\\prime}}{\\sigma_ {k} ^ {\\prime}} \\rho_ {2} ^ {*} & \\dots & \\frac {\\sigma_ {k - 1} ^ {\\prime}}{\\sigma_ {k} ^ {\\prime}} \\rho_ {k - 1} ^ {*} & R _ {k k} \\end{array} \\right] \\tag {15} \\\\ \\end{array}", + "image_path": "26bbebdcc9e988efcd14c499505637300c0c8e975443ddd940e0f62651b60d88.jpg" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 46, + 512, + 287, + 559 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 512, + 287, + 559 + ], + "spans": [ + { + "bbox": [ + 46, + 512, + 287, + 559 + ], + "type": "inline_equation", + "content": "R_{T\\Sigma_T}" + }, + { + "bbox": [ + 46, + 512, + 287, + 559 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 512, + 287, + 559 + ], + "type": "inline_equation", + "content": "R_{T}" + }, + { + "bbox": [ + 46, + 512, + 287, + 559 + ], + "type": "text", + "content": " are similar matrices and have the same eigenvalues. In Eq. (15), the radii are compressed to various degrees. Finally, the estimated rank is obtained by the improved heuristic decision rule:" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 52, + 563, + 287, + 599 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 52, + 563, + 287, + 599 + ], + "spans": [ + { + "bbox": [ + 52, + 563, + 287, + 599 + ], + "type": "interline_equation", + "content": "g d e (t) = \\frac {1}{\\sqrt {\\sum_ {i = 1} ^ {k - 1} \\sigma_ {i} ^ {\\prime 2}}} [ | \\sigma_ {t} ^ {\\prime} | r _ {t} - \\frac {H _ {D} ^ {(t)} (M)}{k - 1} \\sum_ {i = 1} ^ {k - 1} \\left| \\sigma_ {i} ^ {\\prime} \\right| r _ {i} ] \\tag {16}", + "image_path": "b0d2909e1e1f5cee3dc34e92483bfe0ab85ed1f59efcbfdd74faa717cfeda30c.jpg" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 46, + 602, + 287, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 602, + 287, + 628 + ], + "spans": [ + { + "bbox": [ + 46, + 602, + 287, + 628 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 602, + 287, + 628 + ], + "type": "inline_equation", + "content": "t = 1,2,\\dots ,k - 2" + }, + { + "bbox": [ + 46, + 602, + 287, + 628 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 602, + 287, + 628 + ], + "type": "inline_equation", + "content": "0 < H_D^{(t)}(M) < 1" + }, + { + "bbox": [ + 46, + 602, + 287, + 628 + ], + "type": "text", + "content": " is the adjustment factor:" + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 113, + 629, + 287, + 664 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 113, + 629, + 287, + 664 + ], + "spans": [ + { + "bbox": [ + 113, + 629, + 287, + 664 + ], + "type": "interline_equation", + "content": "H _ {D} ^ {(t)} (M) = \\frac {2 \\left| \\sigma_ {t + 1} ^ {\\prime} \\right|}{\\sqrt {\\sum_ {i = t} ^ {k - 1} \\sigma_ {i} ^ {\\prime 2}}} \\tag {17}", + "image_path": "146a9a518bf7c1a5d5e2e2f003db6f8e5f5feb8a2a5948c56ae3aae6f0a19b9e.jpg" + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 47, + 665, + 287, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 665, + 287, + 689 + ], + "spans": [ + { + "bbox": [ + 47, + 665, + 287, + 689 + ], + "type": "text", + "content": "As a result, the rank " + }, + { + "bbox": [ + 47, + 665, + 287, + 689 + ], + "type": "inline_equation", + "content": "r = t - 1" + }, + { + "bbox": [ + 47, + 665, + 287, + 689 + ], + "type": "text", + "content": " if the first negative value of (16) is reached at " + }, + { + "bbox": [ + 47, + 665, + 287, + 689 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 47, + 665, + 287, + 689 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "content": "When " + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "inline_equation", + "content": "r \\leq k" + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "inline_equation", + "content": "D" + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "content": " is transformed to " + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "inline_equation", + "content": "Z" + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "content": " by BKI, then the rank of " + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "inline_equation", + "content": "Z" + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "content": " is estimated by GDE. It is noted that while " + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "inline_equation", + "content": "r > k" + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "content": "," + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "text", + "content": "GDE can not estimate the true rank of " + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "inline_equation", + "content": "D" + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "text", + "content": " from " + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "inline_equation", + "content": "Z" + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "text", + "content": ". To adaptively determine an appropriate " + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "text", + "content": ", KGDE is proposed by adopting iteration, and GDE is served as a stopping criterion for such Krylov subspace approximation of " + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "inline_equation", + "content": "Z" + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "text", + "content": ". The KGDE for rank estimation based on BKI and GDE is summarized in Algorithm 1." + } + ] + } + ], + "index": 26 + }, + { + "bbox": [ + 304, + 144, + 545, + 243 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 144, + 545, + 243 + ], + "spans": [ + { + "bbox": [ + 304, + 144, + 545, + 243 + ], + "type": "text", + "content": "Remark 1: The computational cost of KGDE is related to BKI. If the estimated " + }, + { + "bbox": [ + 304, + 144, + 545, + 243 + ], + "type": "inline_equation", + "content": "r" + }, + { + "bbox": [ + 304, + 144, + 545, + 243 + ], + "type": "text", + "content": " of the input matrix " + }, + { + "bbox": [ + 304, + 144, + 545, + 243 + ], + "type": "inline_equation", + "content": "D \\in \\mathbb{R}^{n \\times d}" + }, + { + "bbox": [ + 304, + 144, + 545, + 243 + ], + "type": "text", + "content": " is exact, the computational complexity will be " + }, + { + "bbox": [ + 304, + 144, + 545, + 243 + ], + "type": "inline_equation", + "content": "O(ndrq + n(rq)^2)" + }, + { + "bbox": [ + 304, + 144, + 545, + 243 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 144, + 545, + 243 + ], + "type": "inline_equation", + "content": "n < d" + }, + { + "bbox": [ + 304, + 144, + 545, + 243 + ], + "type": "text", + "content": ". For sparse matrix, the computational cost of KGDE will be " + }, + { + "bbox": [ + 304, + 144, + 545, + 243 + ], + "type": "inline_equation", + "content": "O(nnz(D)rq + n(rq)^2)" + }, + { + "bbox": [ + 304, + 144, + 545, + 243 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 144, + 545, + 243 + ], + "type": "inline_equation", + "content": "nnz(D)" + }, + { + "bbox": [ + 304, + 144, + 545, + 243 + ], + "type": "text", + "content": " is the number of nonzeros in " + }, + { + "bbox": [ + 304, + 144, + 545, + 243 + ], + "type": "inline_equation", + "content": "D" + }, + { + "bbox": [ + 304, + 144, + 545, + 243 + ], + "type": "text", + "content": ". Since " + }, + { + "bbox": [ + 304, + 144, + 545, + 243 + ], + "type": "inline_equation", + "content": "r \\leq n" + }, + { + "bbox": [ + 304, + 144, + 545, + 243 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 144, + 545, + 243 + ], + "type": "inline_equation", + "content": "q = \\frac{\\log d}{\\sqrt{\\varepsilon}}" + }, + { + "bbox": [ + 304, + 144, + 545, + 243 + ], + "type": "text", + "content": " are small, the KGDE will be inexpensive, especially for sparse matrices." + } + ] + } + ], + "index": 27 + }, + { + "bbox": [ + 304, + 243, + 545, + 302 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 243, + 545, + 302 + ], + "spans": [ + { + "bbox": [ + 304, + 243, + 545, + 302 + ], + "type": "text", + "content": "Remark 2: The accuracy of the KGDE mainly depends on the BKI. In light of Theorem 1, " + }, + { + "bbox": [ + 304, + 243, + 545, + 302 + ], + "type": "inline_equation", + "content": "Z" + }, + { + "bbox": [ + 304, + 243, + 545, + 302 + ], + "type": "text", + "content": " is obtained within a high-quality principal components approximation of " + }, + { + "bbox": [ + 304, + 243, + 545, + 302 + ], + "type": "inline_equation", + "content": "D" + }, + { + "bbox": [ + 304, + 243, + 545, + 302 + ], + "type": "text", + "content": ", both its eigenvalues and eigenvectors are highly close to the actual ones of " + }, + { + "bbox": [ + 304, + 243, + 545, + 302 + ], + "type": "inline_equation", + "content": "D" + }, + { + "bbox": [ + 304, + 243, + 545, + 302 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 28 + }, + { + "bbox": [ + 306, + 312, + 545, + 337 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 312, + 545, + 337 + ], + "spans": [ + { + "bbox": [ + 306, + 312, + 545, + 337 + ], + "type": "text", + "content": "2.2. Efficient RPCA based on KGDE and CUR Decomposition" + } + ] + } + ], + "index": 29 + }, + { + "bbox": [ + 304, + 342, + 545, + 378 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 342, + 545, + 378 + ], + "spans": [ + { + "bbox": [ + 304, + 342, + 545, + 378 + ], + "type": "text", + "content": "In this subsection, an efficient RPCA based on the above rank estimation and CUR decomposition is proposed for solving the following optimization problem:" + } + ] + } + ], + "index": 30 + }, + { + "bbox": [ + 321, + 379, + 545, + 398 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 321, + 379, + 545, + 398 + ], + "spans": [ + { + "bbox": [ + 321, + 379, + 545, + 398 + ], + "type": "interline_equation", + "content": "\\min _ {\\boldsymbol {L}, \\boldsymbol {S}} \\| \\boldsymbol {D} - \\boldsymbol {L} - \\boldsymbol {S} \\| _ {F} ^ {2} + \\lambda \\| \\boldsymbol {L} \\| _ {\\gamma} \\quad s. t. \\| \\boldsymbol {S} \\| _ {0} \\leq s \\tag {18}", + "image_path": "f7be680af14df89393d165f4002ad723bea4d9936acc2b8f22dcd2d4362b600a.jpg" + } + ] + } + ], + "index": 31 + }, + { + "bbox": [ + 306, + 399, + 333, + 409 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 399, + 333, + 409 + ], + "spans": [ + { + "bbox": [ + 306, + 399, + 333, + 409 + ], + "type": "text", + "content": "where" + } + ] + } + ], + "index": 32 + }, + { + "bbox": [ + 362, + 409, + 488, + 453 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 362, + 409, + 488, + 453 + ], + "spans": [ + { + "bbox": [ + 362, + 409, + 488, + 453 + ], + "type": "interline_equation", + "content": "\\| \\boldsymbol {L}\\|_{\\gamma} = \\left\\{ \\begin{array}{l}\\sum_{i = 1}\\frac{e^{\\gamma}\\sigma_{i}}{\\gamma + \\sigma_{i}}, i\\leq r\\\\ 0 , i > r \\end{array} \\right.", + "image_path": "70b88225dbf2a2f4ae997961b1ea3b26aa2089dd95d1245c67b763690629db02.jpg" + } + ] + } + ], + "index": 33 + }, + { + "bbox": [ + 304, + 458, + 545, + 494 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 458, + 545, + 494 + ], + "spans": [ + { + "bbox": [ + 304, + 458, + 545, + 494 + ], + "type": "text", + "content": "and " + }, + { + "bbox": [ + 304, + 458, + 545, + 494 + ], + "type": "inline_equation", + "content": "\\sigma_{i}, i = 1,2,\\dots ,r" + }, + { + "bbox": [ + 304, + 458, + 545, + 494 + ], + "type": "text", + "content": ", is the singular value, " + }, + { + "bbox": [ + 304, + 458, + 545, + 494 + ], + "type": "inline_equation", + "content": "\\gamma >0" + }, + { + "bbox": [ + 304, + 458, + 545, + 494 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 304, + 458, + 545, + 494 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 304, + 458, + 545, + 494 + ], + "type": "text", + "content": " is the regularized parameter which provides a trade-off between the recovery of low-rank matrix and sparse matrix." + } + ] + } + ], + "index": 34 + }, + { + "bbox": [ + 304, + 495, + 545, + 542 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 495, + 545, + 542 + ], + "spans": [ + { + "bbox": [ + 304, + 495, + 545, + 542 + ], + "type": "text", + "content": "The optimization model (18) adds a new non-convex low-rank regularization term to Eq. (2), which adopts the estimated rank to achieve better recovery accuracy of the low-rank matrix than the weighted nuclear norm in (3)." + } + ] + } + ], + "index": 35 + }, + { + "bbox": [ + 304, + 543, + 545, + 567 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 543, + 545, + 567 + ], + "spans": [ + { + "bbox": [ + 304, + 543, + 545, + 567 + ], + "type": "text", + "content": "In this work, the alternating projection method is used to solve the following two sub-problems until convergence:" + } + ] + } + ], + "index": 36 + }, + { + "bbox": [ + 326, + 588, + 545, + 608 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 326, + 588, + 545, + 608 + ], + "spans": [ + { + "bbox": [ + 326, + 588, + 545, + 608 + ], + "type": "interline_equation", + "content": "\\boldsymbol {L} _ {\\ell + 1} = \\underset {\\boldsymbol {L}} {\\arg \\min } \\| \\boldsymbol {D} - \\boldsymbol {L} - \\boldsymbol {S} _ {\\ell} \\| _ {F} ^ {2} + \\lambda \\| \\boldsymbol {L} \\| _ {\\gamma} \\tag {19}", + "image_path": "aac0257eeb9d0a6afa9c50f5ad66a2369a7c2da472af0eb53c95d04ed83ba153.jpg" + } + ] + } + ], + "index": 37 + }, + { + "bbox": [ + 347, + 610, + 545, + 632 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 347, + 610, + 545, + 632 + ], + "spans": [ + { + "bbox": [ + 347, + 610, + 545, + 632 + ], + "type": "interline_equation", + "content": "\\boldsymbol {S} _ {\\ell + 1} = \\underset {\\boldsymbol {S}: \\| \\boldsymbol {S} \\| _ {0} \\leq s} {\\arg \\min } \\| \\boldsymbol {D} - \\boldsymbol {L} _ {\\ell + 1} - \\boldsymbol {S} \\| _ {F} ^ {2} \\tag {20}", + "image_path": "5e6d68a071e4e918e45c090040af498d7f16249523e1bab7945a036f5435dfcd.jpg" + } + ] + } + ], + "index": 38 + }, + { + "bbox": [ + 306, + 642, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 642, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 306, + 642, + 545, + 713 + ], + "type": "text", + "content": "Update for L: The traditional solution of (19) often involves SVD, which requires significant computational resource for a large-scale matrix. To efficiently solve the model (19), we replace SVD with CUR decomposition [30], which has been proven to be efficient and effective in solving classical RPCA problem [31]. Mathematically, the CUR" + } + ] + } + ], + "index": 39 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 296, + 748, + 314, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 748, + 314, + 757 + ], + "spans": [ + { + "bbox": [ + 296, + 748, + 314, + 757 + ], + "type": "text", + "content": "1351" + } + ] + } + ], + "index": 40 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 55, + 53, + 167, + 153 + ], + "blocks": [ + { + "bbox": [ + 55, + 53, + 167, + 153 + ], + "lines": [ + { + "bbox": [ + 55, + 53, + 167, + 153 + ], + "spans": [ + { + "bbox": [ + 55, + 53, + 167, + 153 + ], + "type": "image", + "image_path": "449102a391a1ff7ed034b896a9956b319a0a3ad3bb58041afda27b734ffdb1cd.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 179, + 163, + 413, + 175 + ], + "lines": [ + { + "bbox": [ + 179, + 163, + 413, + 175 + ], + "spans": [ + { + "bbox": [ + 179, + 163, + 413, + 175 + ], + "type": "text", + "content": "Figure 1. The numerical rank estimation of sparse data matrices." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 179, + 53, + 291, + 153 + ], + "blocks": [ + { + "bbox": [ + 179, + 53, + 291, + 153 + ], + "lines": [ + { + "bbox": [ + 179, + 53, + 291, + 153 + ], + "spans": [ + { + "bbox": [ + 179, + 53, + 291, + 153 + ], + "type": "image", + "image_path": "4574448e17edbfe350785fc482ce96c5f9ab580a8dda0f69355c52e6f79f1a92.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 302, + 53, + 414, + 153 + ], + "blocks": [ + { + "bbox": [ + 302, + 53, + 414, + 153 + ], + "lines": [ + { + "bbox": [ + 302, + 53, + 414, + 153 + ], + "spans": [ + { + "bbox": [ + 302, + 53, + 414, + 153 + ], + "type": "image", + "image_path": "3d39cfbde76e612f32f4b5f76c67bebeaf0f64d0ba8f32c6b5c1831f77a59209.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 425, + 53, + 538, + 153 + ], + "blocks": [ + { + "bbox": [ + 425, + 53, + 538, + 153 + ], + "lines": [ + { + "bbox": [ + 425, + 53, + 538, + 153 + ], + "spans": [ + { + "bbox": [ + 425, + 53, + 538, + 153 + ], + "type": "image", + "image_path": "62bacbecab044961e7183415c4bc2d11e34f8712604e7447e1bed2f28997fd20.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 182, + 251, + 194 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 182, + 251, + 194 + ], + "spans": [ + { + "bbox": [ + 47, + 182, + 251, + 194 + ], + "type": "text", + "content": "decomposition of (19) can be rewritten as follows:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 52, + 201, + 287, + 223 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 52, + 201, + 287, + 223 + ], + "spans": [ + { + "bbox": [ + 52, + 201, + 287, + 223 + ], + "type": "interline_equation", + "content": "\\boldsymbol {C} _ {\\ell + 1} = \\underset {\\boldsymbol {L} _ {:, \\mathcal {J}}} {\\arg \\min } \\| [ \\boldsymbol {D} - \\boldsymbol {L} - \\boldsymbol {S} _ {\\ell} ] _ {:, \\mathcal {J}} \\| _ {F} ^ {2} + \\lambda \\| \\boldsymbol {L} _ {:, \\mathcal {J}} \\| _ {\\gamma} \\tag {21}", + "image_path": "8b19d4320ac8d7d85c3c6de27599ac32771f8773597dfde39e7ef295925248e5.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 100, + 226, + 287, + 240 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 100, + 226, + 287, + 240 + ], + "spans": [ + { + "bbox": [ + 100, + 226, + 287, + 240 + ], + "type": "interline_equation", + "content": "\\boldsymbol {U} _ {\\ell + 1} = \\mathcal {T} \\boldsymbol {S} ([ \\boldsymbol {D} - \\boldsymbol {L} - \\boldsymbol {S} _ {\\ell} ] _ {\\mathcal {I}, \\mathcal {J}}) \\tag {22}", + "image_path": "d18d319ec18cb3182d9dab1bd53c18c2aebcdfec2c4992f9e12537957b4c74c1.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 55, + 242, + 287, + 263 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 55, + 242, + 287, + 263 + ], + "spans": [ + { + "bbox": [ + 55, + 242, + 287, + 263 + ], + "type": "interline_equation", + "content": "\\boldsymbol {R} _ {\\ell + 1} = \\underset {\\boldsymbol {L} _ {\\mathcal {I},:}} {\\arg \\min } \\| [ \\boldsymbol {D} - \\boldsymbol {L} - \\boldsymbol {S} _ {\\ell} ] _ {\\mathcal {I},:} \\| _ {F} ^ {2} + \\lambda \\| \\boldsymbol {L} _ {\\mathcal {I},:} \\| _ {\\gamma} \\tag {23}", + "image_path": "acdaf658f0f83c5c2f75dfba21bf34e6ae7ccacaedc4b399c91ed155fc0a63dd.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 274, + 287, + 321 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 274, + 287, + 321 + ], + "spans": [ + { + "bbox": [ + 47, + 274, + 287, + 321 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 274, + 287, + 321 + ], + "type": "inline_equation", + "content": "C_{\\ell +1}\\in \\mathbb{R}^{n\\times \\mathcal{I}}" + }, + { + "bbox": [ + 47, + 274, + 287, + 321 + ], + "type": "text", + "content": " is " + }, + { + "bbox": [ + 47, + 274, + 287, + 321 + ], + "type": "inline_equation", + "content": "\\mathcal{I}" + }, + { + "bbox": [ + 47, + 274, + 287, + 321 + ], + "type": "text", + "content": " columns of (19) via uniform sampling, " + }, + { + "bbox": [ + 47, + 274, + 287, + 321 + ], + "type": "inline_equation", + "content": "R_{\\ell +1}\\in \\mathbb{R}^{\\mathcal{I}\\times d}" + }, + { + "bbox": [ + 47, + 274, + 287, + 321 + ], + "type": "text", + "content": " is " + }, + { + "bbox": [ + 47, + 274, + 287, + 321 + ], + "type": "inline_equation", + "content": "\\mathcal{J}" + }, + { + "bbox": [ + 47, + 274, + 287, + 321 + ], + "type": "text", + "content": " rows of (19) in the same way, " + }, + { + "bbox": [ + 47, + 274, + 287, + 321 + ], + "type": "inline_equation", + "content": "U_{\\ell +1}\\in \\mathbb{R}^{\\mathcal{I}\\times \\mathcal{I}}" + }, + { + "bbox": [ + 47, + 274, + 287, + 321 + ], + "type": "text", + "content": " is the overlap of the column and row indices of " + }, + { + "bbox": [ + 47, + 274, + 287, + 321 + ], + "type": "inline_equation", + "content": "C_{\\ell +1}" + }, + { + "bbox": [ + 47, + 274, + 287, + 321 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 274, + 287, + 321 + ], + "type": "inline_equation", + "content": "R_{\\ell +1}" + }, + { + "bbox": [ + 47, + 274, + 287, + 321 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 47, + 274, + 287, + 321 + ], + "type": "inline_equation", + "content": "\\mathcal{T}S(\\cdot)" + }, + { + "bbox": [ + 47, + 274, + 287, + 321 + ], + "type": "text", + "content": " denotes the truncated SVD." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 322, + 287, + 357 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 322, + 287, + 357 + ], + "spans": [ + { + "bbox": [ + 46, + 322, + 287, + 357 + ], + "type": "text", + "content": "In addition, the rank value " + }, + { + "bbox": [ + 46, + 322, + 287, + 357 + ], + "type": "inline_equation", + "content": "r" + }, + { + "bbox": [ + 46, + 322, + 287, + 357 + ], + "type": "text", + "content": " is needed for " + }, + { + "bbox": [ + 46, + 322, + 287, + 357 + ], + "type": "inline_equation", + "content": "\\mathcal{T}S(\\cdot)" + }, + { + "bbox": [ + 46, + 322, + 287, + 357 + ], + "type": "text", + "content": " and CUR decomposition, which can be exactly estimated by our proposed KGDE method." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 357, + 287, + 405 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 357, + 287, + 405 + ], + "spans": [ + { + "bbox": [ + 46, + 357, + 287, + 405 + ], + "type": "text", + "content": "As Eqs. (21) and (23) are the combination of concave and convex functions, the Difference of Convex programming [32] is used to solve these problems. 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thresholding value. The hard thresholding is employed for projections on to " + }, + { + "bbox": [ + 306, + 495, + 544, + 519 + ], + "type": "inline_equation", + "content": "(D - L_{\\ell})" + }, + { + "bbox": [ + 306, + 495, + 544, + 519 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 43 + }, + { + "bbox": [ + 318, + 521, + 451, + 530 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 318, + 521, + 451, + 530 + ], + "spans": [ + { + "bbox": [ + 318, + 521, + 451, + 530 + ], + "type": "text", + "content": "The iteration is terminated when" + } + ] + } + ], + "index": 44 + }, + { + "bbox": [ + 319, + 531, + 545, + 567 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 319, + 531, + 545, + 567 + ], + "spans": [ + { + "bbox": [ + 319, + 531, + 545, + 567 + ], + "type": "interline_equation", + "content": "\\frac {\\left\\| \\left[ \\boldsymbol {D} - \\boldsymbol {L} _ {\\ell} - \\boldsymbol {S} _ {\\ell} \\right] _ {: , \\mathcal {I}} \\right\\| _ {F} + \\left\\| \\left[ \\boldsymbol {D} - \\boldsymbol {L} _ {\\ell} - \\boldsymbol {S} _ {\\ell} \\right] _ {\\mathcal {I} , :} \\right\\| _ {F}}{\\left\\| \\boldsymbol {D} _ {: , \\mathcal {I}} \\right\\| _ {F} + \\left\\| \\boldsymbol {D} _ {\\mathcal {I} , :} \\right\\| _ {F}} < \\delta \\tag {31}", + "image_path": "a89a7dd6f8f52203b194f45578194bd87afd56dfeb92436fa3380007c5b3c624.jpg" + } + ] + } + ], + "index": 45 + }, + { + "bbox": [ + 306, + 568, + 544, + 592 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 568, + 544, + 592 + ], + "spans": [ + { + "bbox": [ + 306, + 568, + 544, + 592 + ], + "type": "text", + "content": "The entire procedure to solve the problem (18) is summarized in Algorithm 2." + } + ] + } + ], + "index": 46 + }, + { + "bbox": [ + 304, + 592, + 545, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 592, + 545, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 592, + 545, + 715 + ], + "type": "text", + "content": "Remark 3: The computational complexity of " + }, + { + "bbox": [ + 304, + 592, + 545, + 715 + ], + "type": "inline_equation", + "content": "U" + }, + { + "bbox": [ + 304, + 592, + 545, + 715 + ], + "type": "text", + "content": " in CUR decomposition is " + }, + { + "bbox": [ + 304, + 592, + 545, + 715 + ], + "type": "inline_equation", + "content": "O(r^3)" + }, + { + "bbox": [ + 304, + 592, + 545, + 715 + ], + "type": "text", + "content": ". Since the sampling numbers of rows and columns are " + }, + { + "bbox": [ + 304, + 592, + 545, + 715 + ], + "type": "inline_equation", + "content": "|\\mathcal{I}| = O(r)" + }, + { + "bbox": [ + 304, + 592, + 545, + 715 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 592, + 545, + 715 + ], + "type": "inline_equation", + "content": "|\\mathcal{J}| = O(r)" + }, + { + "bbox": [ + 304, + 592, + 545, + 715 + ], + "type": "text", + "content": ", respectively, updating " + }, + { + "bbox": [ + 304, + 592, + 545, + 715 + ], + "type": "inline_equation", + "content": "L" + }, + { + "bbox": [ + 304, + 592, + 545, + 715 + ], + "type": "text", + "content": " requires " + }, + { + "bbox": [ + 304, + 592, + 545, + 715 + ], + "type": "inline_equation", + "content": "O(r^{2}n)" + }, + { + "bbox": [ + 304, + 592, + 545, + 715 + ], + "type": "text", + "content": " flops per iteration. In contrast, computing the SVD usually requires " + }, + { + "bbox": [ + 304, + 592, + 545, + 715 + ], + "type": "inline_equation", + "content": "O(rnd)" + }, + { + "bbox": [ + 304, + 592, + 545, + 715 + ], + "type": "text", + "content": ". In addition, the runtime of updating " + }, + { + "bbox": [ + 304, + 592, + 545, + 715 + ], + "type": "inline_equation", + "content": "S" + }, + { + "bbox": [ + 304, + 592, + 545, + 715 + ], + "type": "text", + "content": " is actually a simple projection, whose computational complexity is further less than that of " + }, + { + "bbox": [ + 304, + 592, + 545, + 715 + ], + "type": "inline_equation", + "content": "L" + }, + { + "bbox": [ + 304, + 592, + 545, + 715 + ], + "type": "text", + "content": ". Thus, the computational complexity of the alternating projection procedure is " + }, + { + "bbox": [ + 304, + 592, + 545, + 715 + ], + "type": "inline_equation", + "content": "O\\left(\\frac{d^2r}{\\epsilon} + d \\cdot \\text{poly}(r, \\log(r / \\epsilon), 1 / \\epsilon)\\right)" + }, + { + "bbox": [ + 304, + 592, + 545, + 715 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 592, + 545, + 715 + ], + "type": "inline_equation", + "content": "0 < \\epsilon < 1" + }, + { + "bbox": [ + 304, + 592, + 545, + 715 + ], + "type": "text", + "content": " is an" + } + ] + } + ], + "index": 47 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "text", + "content": "1352" + } + ] + } + ], + "index": 48 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 53, + 64, + 164, + 160 + ], + "blocks": [ + { + "bbox": [ + 53, + 64, + 164, + 160 + ], + "lines": [ + { + "bbox": [ + 53, + 64, + 164, + 160 + ], + "spans": [ + { + "bbox": [ + 53, + 64, + 164, + 160 + ], + "type": "image", + "image_path": "ae35347ff9ab07ed21ffb218540d74c34b6798bc25172e17bb58f491841068f0.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 50, + 171, + 282, + 182 + ], + "lines": [ + { + "bbox": [ + 50, + 171, + 282, + 182 + ], + "spans": [ + { + "bbox": [ + 50, + 171, + 282, + 182 + ], + "type": "text", + "content": "Figure 2. The numerical rank estimation of video data matrices." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 173, + 64, + 275, + 160 + ], + "blocks": [ + { + "bbox": [ + 173, + 64, + 275, + 160 + ], + "lines": [ + { + "bbox": [ + 173, + 64, + 275, + 160 + ], + "spans": [ + { + "bbox": [ + 173, + 64, + 275, + 160 + ], + "type": "image", + "image_path": "7a563cf6a4ef7bf765d8e28c102129d2ad4ffc4bce8da79c9e680ecba716517c.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 190, + 129, + 201 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 190, + 129, + 201 + ], + "spans": [ + { + "bbox": [ + 47, + 190, + 129, + 201 + ], + "type": "text", + "content": "accuracy parameter." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 213, + 172, + 225 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 213, + 172, + 225 + ], + "spans": [ + { + "bbox": [ + 47, + 213, + 172, + 225 + ], + "type": "text", + "content": "3. Experimental Results" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 232, + 287, + 340 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 232, + 287, + 340 + ], + "spans": [ + { + "bbox": [ + 47, + 232, + 287, + 340 + ], + "type": "text", + "content": "This section reports the experimental results of our proposed eRPCA and compares it with state-of-the-art algorithms on synthetic datasets and two practical computer vision scenarios. The parameters in our method are listed as follows: " + }, + { + "bbox": [ + 47, + 232, + 287, + 340 + ], + "type": "inline_equation", + "content": "\\gamma = 0.02" + }, + { + "bbox": [ + 47, + 232, + 287, + 340 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 232, + 287, + 340 + ], + "type": "inline_equation", + "content": "\\delta = 10^{-7}" + }, + { + "bbox": [ + 47, + 232, + 287, + 340 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 232, + 287, + 340 + ], + "type": "inline_equation", + "content": "\\lambda = 10^{-3}" + }, + { + "bbox": [ + 47, + 232, + 287, + 340 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 232, + 287, + 340 + ], + "type": "inline_equation", + "content": "\\mu = \\frac{1}{2}" + }, + { + "bbox": [ + 47, + 232, + 287, + 340 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 232, + 287, + 340 + ], + "type": "inline_equation", + "content": "\\zeta_0 = \\max(|D|)" + }, + { + "bbox": [ + 47, + 232, + 287, + 340 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 47, + 232, + 287, + 340 + ], + "type": "inline_equation", + "content": "\\varepsilon = 0.05" + }, + { + "bbox": [ + 47, + 232, + 287, + 340 + ], + "type": "text", + "content": ". The parameters in other methods use their default settings. All the experiments are conducted on a laptop with MATLAB 2019 equipped with Windows 10 based on AMD Ryzen 5 CPU with 32G RAM." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 348, + 272, + 360 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 348, + 272, + 360 + ], + "spans": [ + { + "bbox": [ + 47, + 348, + 272, + 360 + ], + "type": "text", + "content": "3.1. The Validation of Rank Estimation Method" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 366, + 163, + 377 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 366, + 163, + 377 + ], + "spans": [ + { + "bbox": [ + 47, + 366, + 163, + 377 + ], + "type": "text", + "content": "3.1.1 Public real datasets" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 385, + 287, + 479 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 385, + 287, + 479 + ], + "spans": [ + { + "bbox": [ + 47, + 385, + 287, + 479 + ], + "type": "text", + "content": "To validate the efficiency and accuracy of KGDE, the general data matrices are tested to estimate the rank. SuiteSparse Database1 [34] provides general data matrices with low numerical rank, whose Gaussian-type distribution assumptions for the data and noise may not hold. In addition, the video datasets from Scene Background Initialization (SBI) dataset2 [35], which are converted to the full matrix are also tested." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 481, + 287, + 577 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 481, + 287, + 577 + ], + "spans": [ + { + "bbox": [ + 46, + 481, + 287, + 577 + ], + "type": "text", + "content": "Fig.1 shows the numerical rank estimation for the SVD curve of sparse data matrices. The singular values of Fig.1(a) and Fig.1(b) have apparent distribution, and KGDE and GDE obtain the exact rank estimation. The singular values of Fig.1(c) and Fig.1(d) are very close, it is therefore hard to bind the rank. The result of Fig.1(c) is the same, and the one of Fig.1(d) is slightly different, while the gap can be ignored in practice." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 578, + 287, + 625 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 578, + 287, + 625 + ], + "spans": [ + { + "bbox": [ + 47, + 578, + 287, + 625 + ], + "type": "text", + "content": "Fig.2 shows the rank estimation results of video data matrices. The video datasets have a stable low-rank, and the rank is usually equal to 1. Thus, the distribution of their singular values has a noticeable gap." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 47, + 625, + 287, + 685 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 625, + 287, + 685 + ], + "spans": [ + { + "bbox": [ + 47, + 625, + 287, + 685 + ], + "type": "text", + "content": "The comparisons of runtime and estimated rank for different matrices are shown in Table 1. When the matrix scale is small, the execution time is close, but KGDE is still faster than GDE. When the matrix becomes more extensive, the efficiency of KGDE performs better than GDE. Because the" + } + ] + } + ], + "index": 11 + }, + { + "type": "image", + "bbox": [ + 309, + 56, + 539, + 119 + ], + "blocks": [ + { + "bbox": [ + 309, + 56, + 539, + 119 + ], + "lines": [ + { + "bbox": [ + 309, + 56, + 539, + 119 + ], + "spans": [ + { + "bbox": [ + 309, + 56, + 539, + 119 + ], + "type": "image", + "image_path": "a5249b0c51468920d4d5eb4a2c69235f8a8ba00c25f3147e0efd780ad59a3744.jpg" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 126, + 545, + 148 + ], + "lines": [ + { + "bbox": [ + 305, + 126, + 545, + 148 + ], + "spans": [ + { + "bbox": [ + 305, + 126, + 545, + 148 + ], + "type": "text", + "content": "Figure 3. The comparison of the average runtime between different algorithms." + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_caption" + } + ], + "index": 12 + }, + { + "type": "table", + "bbox": [ + 307, + 175, + 545, + 284 + ], + "blocks": [ + { + "bbox": [ + 306, + 153, + 545, + 174 + ], + "lines": [ + { + "bbox": [ + 306, + 153, + 545, + 174 + ], + "spans": [ + { + "bbox": [ + 306, + 153, + 545, + 174 + ], + "type": "text", + "content": "Table 1. The results of runtime and estimated rank using GDE and KGDE" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 307, + 175, + 545, + 284 + ], + "lines": [ + { + "bbox": [ + 307, + 175, + 545, + 284 + ], + "spans": [ + { + "bbox": [ + 307, + 175, + 545, + 284 + ], + "type": "table", + "html": "
DatasetGDEKGDE
Runtime(s)RankRuntime(s)Rank
lp Blend0.15630.0943
lp_pilot41.48830.2503
Ipi bgdbg10.27460.2666
Ipi_ceria3d91.18050.2343
IBMtest20.17610.1341
CAVIAR12.23510.7571
", + "image_path": "4cadb674c50bb5a9b0c2502dc4973f43048b5a1a4f5dbdf3385c561031c06173.jpg" + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "table_body" + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 292, + 545, + 327 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 292, + 545, + 327 + ], + "spans": [ + { + "bbox": [ + 305, + 292, + 545, + 327 + ], + "type": "text", + "content": "computational complexity of KGDE is not too much related to the dimension of the matrix, KGDE can maintain a fast result." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 345, + 417, + 357 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 345, + 417, + 357 + ], + "spans": [ + { + "bbox": [ + 306, + 345, + 417, + 357 + ], + "type": "text", + "content": "3.1.2 Synthetic Datasets" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 305, + 364, + 545, + 400 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 364, + 545, + 400 + ], + "spans": [ + { + "bbox": [ + 305, + 364, + 545, + 400 + ], + "type": "text", + "content": "For synthetic datasets, our algorithm was compared with the state-of-the-art RPCA-based approaches: RPCA [1], PSSV [36], WNNM [37], and ARE-RPCA [26]." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 305, + 401, + 545, + 497 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 401, + 545, + 497 + ], + "spans": [ + { + "bbox": [ + 305, + 401, + 545, + 497 + ], + "type": "text", + "content": "The recovery ability and execution time of the algorithms are investigated. The input matrix " + }, + { + "bbox": [ + 305, + 401, + 545, + 497 + ], + "type": "inline_equation", + "content": "D \\in \\mathbb{R}^{n \\times d}" + }, + { + "bbox": [ + 305, + 401, + 545, + 497 + ], + "type": "text", + "content": " is corrupted by sparse noise with the corruption rate " + }, + { + "bbox": [ + 305, + 401, + 545, + 497 + ], + "type": "inline_equation", + "content": "\\alpha = \\{0.1, 0.3, 0.5, 0.7\\}" + }, + { + "bbox": [ + 305, + 401, + 545, + 497 + ], + "type": "text", + "content": ". The parameters are set: " + }, + { + "bbox": [ + 305, + 401, + 545, + 497 + ], + "type": "inline_equation", + "content": "d = 10000" + }, + { + "bbox": [ + 305, + 401, + 545, + 497 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 305, + 401, + 545, + 497 + ], + "type": "inline_equation", + "content": "n = \\{20, 100, 500\\}" + }, + { + "bbox": [ + 305, + 401, + 545, + 497 + ], + "type": "text", + "content": " and different ranks " + }, + { + "bbox": [ + 305, + 401, + 545, + 497 + ], + "type": "inline_equation", + "content": "r = \\{1, 3, 5\\}" + }, + { + "bbox": [ + 305, + 401, + 545, + 497 + ], + "type": "text", + "content": ". The iteration stop criterion is " + }, + { + "bbox": [ + 305, + 401, + 545, + 497 + ], + "type": "inline_equation", + "content": "10^{-7}" + }, + { + "bbox": [ + 305, + 401, + 545, + 497 + ], + "type": "text", + "content": ". Let " + }, + { + "bbox": [ + 305, + 401, + 545, + 497 + ], + "type": "inline_equation", + "content": "L_{sol}" + }, + { + "bbox": [ + 305, + 401, + 545, + 497 + ], + "type": "text", + "content": " be the reconstruction of " + }, + { + "bbox": [ + 305, + 401, + 545, + 497 + ], + "type": "inline_equation", + "content": "L" + }, + { + "bbox": [ + 305, + 401, + 545, + 497 + ], + "type": "text", + "content": " and the reconstruction error is defined as " + }, + { + "bbox": [ + 305, + 401, + 545, + 497 + ], + "type": "inline_equation", + "content": "\\| L_{sol} - L \\|_F / \\| L \\|_F" + }, + { + "bbox": [ + 305, + 401, + 545, + 497 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 497, + 545, + 556 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 497, + 545, + 556 + ], + "spans": [ + { + "bbox": [ + 304, + 497, + 545, + 556 + ], + "type": "text", + "content": "The comparisons of the average runtime with different ranks " + }, + { + "bbox": [ + 304, + 497, + 545, + 556 + ], + "type": "inline_equation", + "content": "r" + }, + { + "bbox": [ + 304, + 497, + 545, + 556 + ], + "type": "text", + "content": " and dimensions " + }, + { + "bbox": [ + 304, + 497, + 545, + 556 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 304, + 497, + 545, + 556 + ], + "type": "text", + "content": " are shown in Fig.3. The eRPCA is faster than others for the average runtime in Fig.3. When the input matrix has a larger scale or rank, the time gap between our method and others is more prominent." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 304, + 557, + 545, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 557, + 545, + 628 + ], + "spans": [ + { + "bbox": [ + 304, + 557, + 545, + 628 + ], + "type": "text", + "content": "The simulation results are shown in Fig.4. It can be seen that eRPCA algorithm is stubborn when the corruption rate is low and has similar results with other algorithms. When the corruption rate rises, the reconstruction error of eRPCA algorithm is larger. eRPCA performs worse when the corruption rate is 0.7 with a large rank." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 304, + 629, + 545, + 700 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 629, + 545, + 700 + ], + "spans": [ + { + "bbox": [ + 304, + 629, + 545, + 700 + ], + "type": "text", + "content": "Table 2 shows the desired rank of the low-rank matrix decomposed by different algorithms under different corruption rates. It can be observed that the proposed eRPCA can obtain correct ranks of low-rank matrices in all cases. Other algorithms can get the desired rank correctly only if the corruption rate is low." + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 318, + 701, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 318, + 701, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 318, + 701, + 545, + 713 + ], + "type": "text", + "content": "According to the above analysis, it is observed that eR-" + } + ] + } + ], + "index": 23 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 58, + 693, + 141, + 703 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 693, + 141, + 703 + ], + "spans": [ + { + "bbox": [ + 58, + 693, + 141, + 703 + ], + "type": "text", + "content": "1https://sparse.tamu.edu/" + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 58, + 703, + 212, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 703, + 212, + 712 + ], + "spans": [ + { + "bbox": [ + 58, + 703, + 212, + 712 + ], + "type": "inline_equation", + "content": "^{2}" + }, + { + "bbox": [ + 58, + 703, + 212, + 712 + ], + "type": "text", + "content": "https://sbmi2015.na.icar.cnr.it/SBIdataset.html" + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "text", + "content": "1353" + } + ] + } + ], + "index": 27 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 115, + 71, + 229, + 168 + ], + "blocks": [ + { + "bbox": [ + 115, + 71, + 229, + 168 + ], + "lines": [ + { + "bbox": [ + 115, + 71, + 229, + 168 + ], + "spans": [ + { + "bbox": [ + 115, + 71, + 229, + 168 + ], + "type": "image", + "image_path": "1128a80c9adfbdd6dbe4ad41a0d998905993d0e20473f32beb4d885e47fb25a5.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 236, + 72, + 351, + 168 + ], + "blocks": [ + { + "bbox": [ + 236, + 72, + 351, + 168 + ], + "lines": [ + { + "bbox": [ + 236, + 72, + 351, + 168 + ], + "spans": [ + { + "bbox": [ + 236, + 72, + 351, + 168 + ], + "type": "image", + "image_path": "3868c151360f7336ffee565a181cb89f91d8a3684fd3663eee0e9f6fa8fb8009.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 360, + 72, + 472, + 168 + ], + "blocks": [ + { + "bbox": [ + 360, + 72, + 472, + 168 + ], + "lines": [ + { + "bbox": [ + 360, + 72, + 472, + 168 + ], + "spans": [ + { + "bbox": [ + 360, + 72, + 472, + 168 + ], + "type": "image", + "image_path": "94a1debc227dad820f2144c8f56bd850804f85c61be6621f905588c729c3a971.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 115, + 169, + 228, + 265 + ], + "blocks": [ + { + "bbox": [ + 115, + 169, + 228, + 265 + ], + "lines": [ + { + "bbox": [ + 115, + 169, + 228, + 265 + ], + "spans": [ + { + "bbox": [ + 115, + 169, + 228, + 265 + ], + "type": "image", + "image_path": "4c59e566e933216d645521e6e2900bb6b27c48fb375583898a62b40094f6a011.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + } + ], + "index": 3 + }, + { + "type": "image", + "bbox": [ + 238, + 169, + 351, + 265 + ], + "blocks": [ + { + "bbox": [ + 238, + 169, + 351, + 265 + ], + "lines": [ + { + "bbox": [ + 238, + 169, + 351, + 265 + ], + "spans": [ + { + "bbox": [ + 238, + 169, + 351, + 265 + ], + "type": "image", + "image_path": "64e5245212bbe5551cdf9697b43e963330d16b6f11c0967c75fe5bb8e0495245.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + } + ], + "index": 4 + }, + { + "type": "image", + "bbox": [ + 360, + 169, + 472, + 265 + ], + "blocks": [ + { + "bbox": [ + 360, + 169, + 472, + 265 + ], + "lines": [ + { + "bbox": [ + 360, + 169, + 472, + 265 + ], + "spans": [ + { + "bbox": [ + 360, + 169, + 472, + 265 + ], + "type": "image", + "image_path": "30b17348bd204304021979b2ec7f48b80297e6853a83c03d5f3b33551fa9c051.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_body" + } + ], + "index": 5 + }, + { + "type": "image", + "bbox": [ + 115, + 266, + 228, + 363 + ], + "blocks": [ + { + "bbox": [ + 115, + 266, + 228, + 363 + ], + "lines": [ + { + "bbox": [ + 115, + 266, + 228, + 363 + ], + "spans": [ + { + "bbox": [ + 115, + 266, + 228, + 363 + ], + "type": "image", + "image_path": "23174bc418f4f11341c652a282066900aa1872bbd1dea2dae534945ef2afc38d.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 93, + 371, + 499, + 383 + ], + "lines": [ + { + "bbox": [ + 93, + 371, + 499, + 383 + ], + "spans": [ + { + "bbox": [ + 93, + 371, + 499, + 383 + ], + "type": "text", + "content": "Figure 4. Comparison of various algorithms with different dimensions " + }, + { + "bbox": [ + 93, + 371, + 499, + 383 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 93, + 371, + 499, + 383 + ], + "type": "text", + "content": ", matrix ranks " + }, + { + "bbox": [ + 93, + 371, + 499, + 383 + ], + "type": "inline_equation", + "content": "r" + }, + { + "bbox": [ + 93, + 371, + 499, + 383 + ], + "type": "text", + "content": ", and corruption rates " + }, + { + "bbox": [ + 93, + 371, + 499, + 383 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 93, + 371, + 499, + 383 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 238, + 266, + 351, + 363 + ], + "blocks": [ + { + "bbox": [ + 238, + 266, + 351, + 363 + ], + "lines": [ + { + "bbox": [ + 238, + 266, + 351, + 363 + ], + "spans": [ + { + "bbox": [ + 238, + 266, + 351, + 363 + ], + "type": "image", + "image_path": "7279b9371cf4a6321eee50277c775258059ea506006125fa4b3e15609d7c9ca9.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_body" + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 360, + 266, + 472, + 363 + ], + "blocks": [ + { + "bbox": [ + 360, + 266, + 472, + 363 + ], + "lines": [ + { + "bbox": [ + 360, + 266, + 472, + 363 + ], + "spans": [ + { + "bbox": [ + 360, + 266, + 472, + 363 + ], + "type": "image", + "image_path": "df7d04f3f12663de7310d5317b0f240f1883b3667996f90b6ea72b1123af1eea.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + } + ], + "index": 8 + }, + { + "type": "table", + "bbox": [ + 52, + 417, + 542, + 579 + ], + "blocks": [ + { + "bbox": [ + 46, + 394, + 546, + 415 + ], + "lines": [ + { + "bbox": [ + 46, + 394, + 546, + 415 + ], + "spans": [ + { + "bbox": [ + 46, + 394, + 546, + 415 + ], + "type": "text", + "content": "Table 2. The desired rank of low-rank matrix decomposed by different algorithms in different corruption rates and dimensions with different ranks" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 52, + 417, + 542, + 579 + ], + "lines": [ + { + "bbox": [ + 52, + 417, + 542, + 579 + ], + "spans": [ + { + "bbox": [ + 52, + 417, + 542, + 579 + ], + "type": "table", + "html": "
AlgorithmDimensionr=1r=3r=5
α=0.1α=0.3α=0.5α=0.7α=0.1α=0.3α=0.5α=0.7α=0.1α=0.3α=0.5α=0.7
RPCAn=20116648655656
n=10011123335555552
n=50011173331255516
PSSVn=20111233515551519
n=100111133335558
n=50011163331055513
ARE-RPCAn=20111133355555
n=100111133335555
n=500111133375555
WNNMn=20111133511551520
n=1001111333100555100
n=5001111333500555500
eRPCAn=20111133335555
n=100111133335555
n=500111133335555
", + "image_path": "a6cfbce333d338d050e9530f5b5f7678178e5ec6e743536e6b3e6790a4e15610.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "table_body" + } + ], + "index": 11 + }, + { + "bbox": [ + 46, + 585, + 287, + 608 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 585, + 287, + 608 + ], + "spans": [ + { + "bbox": [ + 46, + 585, + 287, + 608 + ], + "type": "text", + "content": "PCA has excellent robustness and the fastest execution time." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 47, + 628, + 241, + 641 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 628, + 241, + 641 + ], + "spans": [ + { + "bbox": [ + 47, + 628, + 241, + 641 + ], + "type": "text", + "content": "3.2. Foreground-Background Separation" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 46, + 650, + 287, + 685 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 650, + 287, + 685 + ], + "spans": [ + { + "bbox": [ + 46, + 650, + 287, + 685 + ], + "type": "text", + "content": "In this subsection, we evaluate the proposed eRPCA with the following approaches: ARE-RPCA [26], IRCUR [25], PETRELS [38], and ADW-RPCA [39]." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "text", + "content": "Foreground-background separation is an important application of RPCA. Scene Background Initialization (SBI)" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 585, + 545, + 681 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 585, + 545, + 681 + ], + "spans": [ + { + "bbox": [ + 304, + 585, + 545, + 681 + ], + "type": "text", + "content": "dataset3 [35] is considered. The visual comparisons of the sub-dataset CAVIAR1 are shown in Fig.5, containing 610 frames with size " + }, + { + "bbox": [ + 304, + 585, + 545, + 681 + ], + "type": "inline_equation", + "content": "384 \\times 256" + }, + { + "bbox": [ + 304, + 585, + 545, + 681 + ], + "type": "text", + "content": ". The dataset can be represented by a matrix, where each column is a vectorized video frame. Then each algorithm can be applied to decompose the matrix into low-rank parts and sparse ones; that is, this scene can be separated from the moving foreground object from the static background." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 317, + 681, + 545, + 694 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 681, + 545, + 694 + ], + "spans": [ + { + "bbox": [ + 317, + 681, + 545, + 694 + ], + "type": "text", + "content": "There are five frames selected in Fig.5, and the upper and" + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 317, + 702, + 471, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 702, + 471, + 712 + ], + "spans": [ + { + "bbox": [ + 317, + 702, + 471, + 712 + ], + "type": "text", + "content": "3https://sbmi2015.na.icar.cnr.it/SBIdataset.html" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "text", + "content": "1354" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 49, + 61, + 287, + 327 + ], + "blocks": [ + { + "bbox": [ + 49, + 61, + 287, + 327 + ], + "lines": [ + { + "bbox": [ + 49, + 61, + 287, + 327 + ], + "spans": [ + { + "bbox": [ + 49, + 61, + 287, + 327 + ], + "type": "image", + "image_path": "8f25d0552f440415af5d345500dc32ec85ed24edf98ae7cc8def0545566ebd01.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 47, + 338, + 287, + 361 + ], + "lines": [ + { + "bbox": [ + 47, + 338, + 287, + 361 + ], + "spans": [ + { + "bbox": [ + 47, + 338, + 287, + 361 + ], + "type": "text", + "content": "Figure 5. The comparison of visual results on CAVIAR1 between different algorithms." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 49, + 387, + 288, + 440 + ], + "blocks": [ + { + "bbox": [ + 47, + 364, + 287, + 385 + ], + "lines": [ + { + "bbox": [ + 47, + 364, + 287, + 385 + ], + "spans": [ + { + "bbox": [ + 47, + 364, + 287, + 385 + ], + "type": "text", + "content": "Table 3. Performance of one frame from CAVIAR1 dataset among different algorithms" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 49, + 387, + 288, + 440 + ], + "lines": [ + { + "bbox": [ + 49, + 387, + 288, + 440 + ], + "spans": [ + { + "bbox": [ + 49, + 387, + 288, + 440 + ], + "type": "table", + "html": "
AGEpEPs%pCEPS%MSSSIMPSNRCQMTIME(s)
ARE-RPCA5.26374.07413.48710.856425.441424.787610.78593
IRCUR3.14890.28280.18210.991734.468933.27140.007564
PETRELS4.99725.01614.02220.932929.801729.07731.14708
ADW-RPCA2.640.34990.24820.990534.485333.34026.356669
eRPCA2.63940.26860.16890.991734.862633.57250.034198
", + "image_path": "3ba8f610150dfed3d93429e44ef2dbe71a80299f489fd29847ade1250de82d79.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 460, + 287, + 508 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 460, + 287, + 508 + ], + "spans": [ + { + "bbox": [ + 46, + 460, + 287, + 508 + ], + "type": "text", + "content": "lower parts represent the background and foreground. It can be shown that ARE-RPCA and PETRELS yield artifacts in some backgrounds. IRCUR, ADW-RPCA, and eRPCA obtain more distinctive visual results." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 508, + 287, + 663 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 508, + 287, + 663 + ], + "spans": [ + { + "bbox": [ + 46, + 508, + 287, + 663 + ], + "type": "text", + "content": "In addition, objective evaluations, i.e. AGE, pEP, pCEP, PSNR, MS-SSIM, CQM, are performed on SBI database where the smaller the first three values, the better the separation results, and the last three ones and vice versa. Table 3 shows the performance evaluation of the above six metrics and runtime. For the first six metrics, eRPCA algorithm obtains better results. Due to the time of estimating the rank, eRPCA algorithm is slower than IRCUR for each frame. However, IRCUR needs to determine the rank in advance, leading to its results being slightly inferior to ours. Moreover, only ARE-RPCA and eRPCA algorithm can obtain the rank prior, but ours are better than ARE-RPCA in all aspects." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 671, + 237, + 685 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 671, + 237, + 685 + ], + "spans": [ + { + "bbox": [ + 47, + 671, + 237, + 685 + ], + "type": "text", + "content": "3.3. Shadow Removal from Face Images" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 689, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 715 + ], + "type": "text", + "content": "Face images taken under different lighting conditions always introduce errors, for example, uneven lighting," + } + ] + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 307, + 70, + 547, + 167 + ], + "blocks": [ + { + "bbox": [ + 307, + 70, + 547, + 167 + ], + "lines": [ + { + "bbox": [ + 307, + 70, + 547, + 167 + ], + "spans": [ + { + "bbox": [ + 307, + 70, + 547, + 167 + ], + "type": "image", + "image_path": "6d782ff7971e33f8949dad73d5d7357695115e4c47639627c8a5c395754f4c28.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 307, + 178, + 544, + 190 + ], + "lines": [ + { + "bbox": [ + 307, + 178, + 544, + 190 + ], + "spans": [ + { + "bbox": [ + 307, + 178, + 544, + 190 + ], + "type": "text", + "content": "Figure 6. The comparison of different algorithms on two images." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "type": "table", + "bbox": [ + 309, + 208, + 543, + 250 + ], + "blocks": [ + { + "bbox": [ + 307, + 196, + 545, + 207 + ], + "lines": [ + { + "bbox": [ + 307, + 196, + 545, + 207 + ], + "spans": [ + { + "bbox": [ + 307, + 196, + 545, + 207 + ], + "type": "text", + "content": "Table 4. The comparison of runtime between different algorithms" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 309, + 208, + 543, + 250 + ], + "lines": [ + { + "bbox": [ + 309, + 208, + 543, + 250 + ], + "spans": [ + { + "bbox": [ + 309, + 208, + 543, + 250 + ], + "type": "table", + "html": "
RPCAPSSVWNNMARE-RPCAeRPCA
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", + "image_path": "e71f99c651c2f9046fd5657eceeb814f918a5726e4a453448c9a1587614ff582.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "table_body" + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 258, + 545, + 365 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 258, + 545, + 365 + ], + "spans": [ + { + "bbox": [ + 304, + 258, + 545, + 365 + ], + "type": "text", + "content": "shadow etc, which yields challenge for face recognition. Fig.6 (first column) shows two typical examples with size " + }, + { + "bbox": [ + 304, + 258, + 545, + 365 + ], + "type": "inline_equation", + "content": "192 \\times 168" + }, + { + "bbox": [ + 304, + 258, + 545, + 365 + ], + "type": "text", + "content": " from the Extended Yale B database[40], a benchmark database in face recognition. Each image is converted to a column vector. The comparisons of these methods are given: RPCA [1], PSSV [36], WNNM [37], and ARE-RPCA [26]. In addition, since the images are aligned, the rank is set to 1, and ARE-RPCA and eRPCA can adaptively estimate the rank." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 366, + 545, + 425 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 366, + 545, + 425 + ], + "spans": [ + { + "bbox": [ + 304, + 366, + 545, + 425 + ], + "type": "text", + "content": "Fig.6 shows the shadow removal results of different algorithms. In the visual aspect, the proposed eRPCA algorithm removes the shadow well and does not need to determine the rank. The runtime of different algorithms is shown in Table 4 and ours is the fastest." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 427, + 545, + 452 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 427, + 545, + 452 + ], + "spans": [ + { + "bbox": [ + 305, + 427, + 545, + 452 + ], + "type": "text", + "content": "Due to the space limitation, more experimental results are shown in the Supplementary Material." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 465, + 378, + 478 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 465, + 378, + 478 + ], + "spans": [ + { + "bbox": [ + 306, + 465, + 378, + 478 + ], + "type": "text", + "content": "4. Conclusion" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 486, + 545, + 617 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 486, + 545, + 617 + ], + "spans": [ + { + "bbox": [ + 304, + 486, + 545, + 617 + ], + "type": "text", + "content": "In this paper, an efficient non-convex RPCA method is proposed for recovering a low-rank matrix and a sparse matrix, especially with large sizes. Specifically, a fast rank estimation method KGDE has been proposed by using Gerschgorin disk theorem with the block Krylov iteration. Based on the estimated rank, a new non-convex regularizer is proposed to achieve better recovery of the low-rank matrices with less computation due to CUR decomposition involved in the iterations. Experimental results demonstrate that the proposed eRPCA algorithm outperforms state-of-the-art algorithms in various vision applications." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 619, + 545, + 691 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 619, + 545, + 691 + ], + "spans": [ + { + "bbox": [ + 304, + 619, + 545, + 691 + ], + "type": "text", + "content": "In future, our algorithm will be extended in other applications, such as image recovery and video denoising. However, the accuracy of eRPCA for high corruption rate is still a big challenge. Therefore, we will devote ourselves to improving the robustness of the algorithm. Meanwhile, the parameter adaptability is considered in our future work." + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 315, + 702, + 520, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 315, + 702, + 520, + 712 + ], + "spans": [ + { + "bbox": [ + 315, + 702, + 520, + 712 + ], + "type": "text", + "content": "4http://vision.ucsd.edu/leekc/ExtYaleDatabase/ExtYaleB.html" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "text", + "content": "1355" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 107, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 107, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 107, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 288, + 712 + ], + "type": "list", + "angle": 0, + "index": 14, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 124 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 124 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 124 + ], + "type": "text", + "content": "[1] Emmanuel J Candès, Xiaodong Li, Yi Ma, and John Wright. 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IEEE Transactions on pattern analysis and machine intelligence, 27(5):684-698, 2005. 8" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "text", + "content": "1357" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 9 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Efficient Scale-Invariant Generator With Column-Row Entangled Pixel Synthesis/e82bfa76-118c-45c9-a6c3-50265e9de1a3_content_list.json b/2023/Efficient Scale-Invariant Generator With Column-Row Entangled Pixel Synthesis/e82bfa76-118c-45c9-a6c3-50265e9de1a3_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..1659ef5f0ffd266b5d7e9051c350237e2dbd9330 --- /dev/null +++ b/2023/Efficient Scale-Invariant Generator With Column-Row Entangled Pixel Synthesis/e82bfa76-118c-45c9-a6c3-50265e9de1a3_content_list.json @@ -0,0 +1,1485 @@ +[ + { + "type": "text", + "text": "Efficient Scale-Invariant Generator with Column-Row Entangled Pixel Synthesis", + "text_level": 1, + "bbox": [ + 78, + 130, + 890, + 151 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Thuan Hoang Nguyen* Thanh Van Le* Anh Tran VinAI Research, Hanoi, Vietnam", + "bbox": [ + 269, + 180, + 697, + 215 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "{v.thuannh5,v.thanhlv19,v.anhtt152}@vinai.io", + "bbox": [ + 287, + 218, + 676, + 233 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 268, + 313, + 282 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Any-scale image synthesis offers an efficient and scalable solution to synthesize photo-realistic images at any scale, even going beyond $2K$ resolution. However, existing GAN-based solutions depend excessively on convolutions and a hierarchical architecture, which introduce inconsistency and the \"texture sticking\" issue when scaling the output resolution. From another perspective, INR-based generators are scale-equivariant by design, but their huge memory footprint and slow inference hinder these networks from being adopted in large-scale or real-time systems. In this work, we propose Column-Row Entangled Pixel Synthesis (CREPS), a new generative model that is both efficient and scale-equivariant without using any spatial convolutions or coarse-to-fine design. To save memory footprint and make the system scalable, we employ a novel bi-line representation that decomposes layer-wise feature maps into separate \"thick\" column and row encodings. Experiments on various datasets, including FFHQ, LSUN-Church, MetFaces, and Flickr-Scenery, confirm CREPS' ability to synthesize scale-consistent and alias-free images at any arbitrary resolution with proper training and inference speed. Code is available at https://github.com/VinAIResearch/CREPS.", + "bbox": [ + 75, + 301, + 473, + 648 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 680, + 209, + 696 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Generative Adversarial Networks (GANs) [8] are one of the most widely used structures for image generation and manipulation [2, 28]. Previously, a GAN model could only generate images with a fixed scale and layout as defined in the training dataset. However, natural images come with varying resolutions and contain unstructured objects at diverse poses. Therefore, designing a generative model that can handle more flexible geometric configurations is gaining more attention in the machine-learning community. StyleGAN3 [13] already supports out-of-the-box translation and rotation with consistent and artifact-free outputs.", + "bbox": [ + 75, + 705, + 468, + 875 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/bd42e72e533db1418f6ecc5be53c18b7b781baddc447cb5f519b2087d695d56e.jpg", + "image_caption": [ + "Figure 1. Previous any-scale image synthesis networks, including AnyresGAN [4] and ScaleParty [18], produce inconsistent image details when changing the output scale (see zoomed-in patches). In contrast, our proposed network can produce the same details but sharper when increasing the scale. Check the supplemental video for a clearer comparison." + ], + "image_footnote": [], + "bbox": [ + 500, + 266, + 633, + 489 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/4253c8e00e4c3d264c3ae87d891e846b3575bab2a0057a6586aa8d40652dcdb7.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 651, + 266, + 759, + 491 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/4ab75ebd8221edc2e6b85b0b093a9d295be5df37aa7a5012b12354fdd7b016af.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 782, + 266, + 890, + 491 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Any-scale synthesis, however, remains under-explored.", + "bbox": [ + 500, + 595, + 864, + 609 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "In this paper, we are interested in the task of arbitrary-scale image synthesis where a single generator can effortlessly synthesize images at many different scales while strongly preserving detail consistency. Such a model can be a promising research direction and bring many benefits. It enables synthesizing a high-resolution image from a lower-resolution training dataset. Hence, it eliminates the need for collecting and training models on high-resolution images, which is costly in storage, time, and computation resources. The output resolution can be ultra-high, e.g., $2048 \\times 2048$ , which is impossible for standard GAN models due to the limit of GPU memory. Any-scale image synthesis also allows geometric interactions like zooming in and out. Despite promising results, previous works on this topic, such as AnyresGAN [4] and ScaleParty [18], show strong inconsistency when scaling the output resolution (see Fig. 1).", + "bbox": [ + 496, + 611, + 892, + 852 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "We investigate the GAN structures to find the potential cause of the inconsistency at image scaling. Traditional GAN models are based on convolutional generators", + "bbox": [ + 498, + 854, + 890, + 900 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Equal contribution.", + "bbox": [ + 101, + 887, + 210, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "22408", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "[3,15,20], which introduce an implicit spatial bias that helps the model to produce high-quality images. Recently, Xu et al. [29] and Karras et al. [13] discovered that these positional priors can hamper the model's consistency when applying translations, rotations, or scalings. In order to combat this issue, many works introduce non-trivial changes such as sophisticated architecture re-design [13] or opt for a better training strategy and input positional encoding [4,18]. However, these are only partial remedies as the output pixels still depend on their surroundings, making it impossible for these models to produce consistent attributes of an object regardless of positions and scales.", + "bbox": [ + 75, + 90, + 472, + 272 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In contrast to the traditional GANs, some recent methods are based on Implicit Neural Representation (INR) [1, 23]. By predicting the color of each pixel separately, INR-based GANs can, in theory, synthesize objects in a spatial-arbitrary manner and still achieve comparable quality at small to medium resolution compared to convolution-based approach. However, these models' memory usage grows quadratically with the input resolution since all pixels have to be queried. Thus, there has been no existing work that can efficiently scale INR-GANs to resolutions higher than 1024. To reduce training complexity, Anokhin et al. [1] employs a simple patch-based strategy where only a portion of pixels is generated and passed through the discriminator at a time. However, this approach unsurprisingly leads to poor results and inconsistency between patches.", + "bbox": [ + 75, + 275, + 472, + 501 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Inspired by the latter approach, we aim to tackle the task of scale-consistent image generation with essential changes to StyleGAN2 [15]. Similar to Anokhin et al. [1], we change the $3 \\times 3$ convolutions to $1 \\times 1$ ones and add a Fourier feature embedding [25] at the input layer. Although these two changes alone already achieve our goal, it is still expensive to train in high-resolution settings. Thus, instead of using dense 2D features, our model relies on a novel thick biline representation, which largely reduces the training and inference complexity by using two low-rank features for row and column. Our network first regresses these row and column embeddings, then composes layer-wise intermediate 2D features, and finally fuses these maps to produce the final output. We name this novel structure Column-Row Entangled Pixel Synthesis, or CREPS for short.", + "bbox": [ + 75, + 505, + 472, + 731 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "We run a series of experiments on four datasets, including FFHQ, MetFaces, LSUN-Church, and Flickr-Scenery, to confirm the effectiveness of our proposed CREPS structure. Our model can synthesize images with quality comparable to the previous generative models like CIPS or StyleGAN2. While CIPS has trouble in training on images of resolutions more than $256 \\times 256$ , CREPS can sufficiently handle training data at resolutions $512 \\times 512$ and $1024 \\times 1024$ . CREPS produces scale-equivariant images and keeps the object details unchanged when scaling the output resolution, unlike previous any-scale GANs such as AnyresGAN", + "bbox": [ + 75, + 734, + 472, + 902 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "and ScaleParty. Using a CREPS model trained on $512 \\times 512$ images, we still can generate near-realistic images at higher resolution. Finally, we demonstrate CREPS's ability to synthesize images with complex geometric transformations and distortions while preserving attribute consistency.", + "bbox": [ + 496, + 90, + 893, + 167 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To summarize our contributions:", + "bbox": [ + 517, + 167, + 736, + 181 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- We propose a simple and elegant network equipped with only modulated linear layers and no upsampling layers in-between. It supports scale-consistent outputs for any-scale image synthesis.", + "- To further improve efficiency, we introduce a thick bi-line representation, which decomposes 2D network features into two light-weight row and column embeddings. It significantly saves memory and computation costs compared with the full 2D-feature counterparts.", + "- We demonstrate competitive results for unconditional image synthesis on the FFHQ, LSUN-Church, Met-Faces, and Flickr-Scenery datasets, along with the ability to generate each image at arbitrary scales with consistent details.", + "- Our CREPS models support complex geometric transformations and distortions." + ], + "bbox": [ + 517, + 193, + 890, + 468 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 500, + 483, + 640, + 500 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Generative Adversarial Networks. Prior to denoising diffusion models [10, 24], GANs [8] hold state-of-the-art results for image synthesis tasks. The popular GAN models can generate realistic images at a high resolution, commonly up to $1024 \\times 1024$ [3, 12-15]. The promising results obtained by GANs have motivated several applications of computer graphics and visual content generation. However, these networks are only capable of generating images with same geometric configurations, e.g., center-located and face-forward objects. Recently, an exciting work StyleGAN3 [13] aimed to generalize GAN to arbitrary translation and rotation with consistent details, or Anycost GAN [16] with multi-resolution generation. In the same vein, ScaleParty [18] and AnyresGAN [4] extended StyleGAN2 and StyleGAN3 to support scaling and other geometric transformations by replacing learned input constant with suitable positional encoding and multi-scale training strategy. However, these works did not consider the scale consistency, and their images showed varied details as the output scale increases, illustrated in Fig. 1.", + "bbox": [ + 496, + 515, + 890, + 819 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Implicit Neural Representation. Typically, images are represented by a series of 2D arrays of values. However, it can be viewed as a continuous mapping from a 2D coordinate $(x,y) \\in \\mathbf{R}^2$ to the corresponding RGB value $(r,g,b) \\in \\mathbf{R}^3$ and the mapping can be parameterized as a", + "bbox": [ + 496, + 825, + 893, + 902 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "22409", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "black-box model. This coordinate-wise modeling has been used in a wide range of neural rendering tasks [5,17,22,26], where neural networks are used to provide an efficient and continuous representation of data compared with traditional methods. In the literature, implicit neural networks mainly utilize fully-connected layers as their building blocks. Unlike convolution or self-attention, such layers' receptive field size is exactly one; in other words, the output at every coordinate is independent of each other.", + "bbox": [ + 75, + 90, + 472, + 227 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "INR-based GANs. As the number of research increased, INR started to be used for generative tasks. These models soon inherited the success of GANs by employing the adversarial training manner. Generative radiance fields [6, 9, 19, 21] attempt to learn a view-consistent representation of 3D objects using implicit GAN. Despite all the success of INRs in 3D GANs, limited attention has been paid to utilizing the equivariance capability of fully-connected layers in 2D counterparts. The closest to our work are INRGAN [23] and CIPS [1]. Both these works use a grid of the target pixel coordinates as input for batch processing instead of passing each point individually. INR-GAN employs a multi-scale structure, which we will discuss later as a cause of scale inconsistency, while its uniform-scale versions have poor generation outputs. Meanwhile, CIPS does not need the multi-scale design thanks to its efficient weight modulation and expressive input embedding. The uniform-scale INR-GAN and CIPS disregard spatial convolutions in the generator and synthesize each pixel independently. However, their main goal is to investigate an alternative architecture that can compete with fully-convolutional GANs rather than paying attention to the equivariance characteristic of such models. They also struggle with expensive computation costs and memory usage using full-resolution 2D feature maps in processing.", + "bbox": [ + 75, + 234, + 472, + 612 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Proposed method", + "text_level": 1, + "bbox": [ + 76, + 628, + 246, + 643 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "This section describes our proposed CREPS structure. First, we recall the concept of any-scale image synthesis (Sec. 3.1). Then, we revise two existing GAN structures that support scale-equivariant image synthesis (Sec. 3.2). Next, we discuss how to reduce computation cost via the novel thick bi-line representation (Sec. 3.3). Finally, we describe the layer-wise feature composition scheme for improving the synthesis quality (Sec. 3.4).", + "bbox": [ + 75, + 654, + 468, + 776 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Any-scale image synthesis", + "text_level": 1, + "bbox": [ + 76, + 786, + 312, + 801 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In this section, we introduce any-scale image synthesis as the task of generating images while enforcing consistency at different scales given a single model. One way we naturally come up with is generating an image at many scales altogether. MSG-GAN [11] is one of the earliest works in this approach. Instead of producing single output,", + "bbox": [ + 75, + 810, + 468, + 902 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "MSG-GAN outputs an RGB image at each block of the generator, resulting in a mipmap representation [27]. However, this approach can only output pre-defined discrete scales, and there is no mechanism to guarantee scale consistency.", + "bbox": [ + 496, + 90, + 890, + 151 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "As such, we should consider injecting positional encoding $e$ as an additional input alongside the latent code into the generator. This approach is employed in some previous works [1, 4, 18, 23], in which $e$ is a 2D grid of normalized $(x,y)$ coordinates. If $e$ is a regular grid, we can decompose it into two vectors for the row and column coordinates denoted as $e^r$ and $e^c$ , respectively. The image generation process now becomes:", + "bbox": [ + 496, + 152, + 893, + 271 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nI = G \\left(z, e ^ {r}, e ^ {c}\\right), \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 635, + 282, + 890, + 299 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "with $G$ is the generative model and $z$ is the latent input. The decomposition from $e$ to $e^r$ and $e^c$ is more suitable to our thick bi-line representation, as later discussed. Doing so allows us to easily control the output's scale and other spatial properties via appropriate input encoding. However, naively adding positional input into an existing generator does not guarantee that the output image is equivariant to the change in the input coordinates. For example, when Karras et al. [13] replace the learnable constant in StyleGAN2's input layer with Fourier features (Config B), the \"texture sticking\" issue still occurs. Therefore, proper network design and training strategy should be examined to alleviate the output's geometric inconsistency.", + "bbox": [ + 496, + 309, + 890, + 506 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. Removing coarse-to-fine design and spatial convolution", + "text_level": 1, + "bbox": [ + 498, + 515, + 890, + 545 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We investigate two network structures that support any resolution image generation, including AnyresGAN [4] and CIPS [1], when keeping the same latent input but gradually increasing the output resolution. The former is built upon StyleGAN3 [13] with additional scale information concatenated with the latent code and a multi-scale training scheme. In contrast, the latter changes the 3x3 convolution of StyleGAN2 with a point-wise one and adds learnable Fourier features at the beginning. Both models are capable of multiscale generation, but they have different behaviors that we will discuss below.", + "bbox": [ + 496, + 553, + 890, + 717 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "As illustrated in Fig. 1, while having good photo-realism, AnyresGAN produces different image details at different scales. This can be explained by the fact that AnyresGAN, similar to most other GAN-based works, relies on spatial convolutions, such as 2D convolution with kernel size $3 \\times 3$ and upsample layers. When changing the output resolution, the neighbor pixels at each location change, greatly varying the output of this spatial-convolution-based network.", + "bbox": [ + 496, + 719, + 890, + 839 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "On the other hand, CIPS keeps the output image's details nearly the same regardless of resolution, thanks to its spatial-free building operators. CIPS, however, is very computationally expensive; this can be clearly shown in Tab. 1.", + "bbox": [ + 496, + 839, + 890, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "22410", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/98745f86b879f360b40f24a926f1c5ae118cf86e53e37867476b1334cfa2a051.jpg", + "image_caption": [ + "(a) Network structure", + "Figure 2. Our proposed CREPS structure" + ], + "image_footnote": [], + "bbox": [ + 130, + 90, + 500, + 380 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/08c8f57aa21075ae5fff4da4155d1094ecee81ec55ea4e319468330a7b339c19.jpg", + "image_caption": [ + "(b) Thick bi-line composition" + ], + "image_footnote": [], + "bbox": [ + 632, + 94, + 759, + 183 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/2371753f23e73f5dcf593c84b386f6593fd34c779afeebb33319e4d5cdfde3e4.jpg", + "image_caption": [ + "(c) Refinement block" + ], + "image_footnote": [], + "bbox": [ + 566, + 210, + 823, + 375 + ], + "page_idx": 3 + }, + { + "type": "table", + "img_path": "images/db97e28778a6e52338d722b979d256c562c129f36a6afc60ac3b3758a6ffecea.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
ResolutionBatch sizeMemory UsageRunning time
StyleGAN2CIPSOursStyleGAN2CIPSOurs
256 × 25611.5GB3.3GB2.3GB0.04s0.06s0.03s
42.5GB10.2GB5.2GB0.05s0.23s0.06s
512 × 51211.7GB10.4GB4.5GB0.04s0.21s0.05s
43.4GBOOM14.6GB0.06sOOM0.16s
", + "bbox": [ + 140, + 425, + 823, + 546 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Table 1. Memory usage and running time comparison between StyleGAN2, CIPS and our method. OOM means out-of-memory.", + "bbox": [ + 101, + 549, + 859, + 564 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "When measured on a single NVIDIA V100 GPU (32 GB) and all models have comparable number of parameters, it runs slower than StyleGAN2 as well as requires much more memory or even gets an out-of-memory (OOM) error when running at $512 \\times 512$ resolution. This makes CIPS inapplicable to use for learning fine details from high-resolution datasets. Moreover, it is worth noting that our method achieve the best trade-off between speed and memory.", + "bbox": [ + 75, + 575, + 468, + 696 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Based on the above observations, we implement CREPS without any spatial convolutions or coarse-to-fine design. Starting with StyleGAN2 [15], which consists of a mapping network and a generator, we remove all upsampling operators and replace all spatial convolutions with $1 \\times 1$ convolutions, which are equivalent to pixel-wise fully-connected layers. Next, we replace the constant in the first synthesis block with Fourier encodings of the input coordinate row and column $e^r$ and $e^c$ . This design is quite similar to CIPS, with only two minor differences. Firstly, the dense 2D grid input is now split into two vectors representing the row and column. Secondly, we do not combine learned input constant with the Fourier feature like CIPS did, making our", + "bbox": [ + 75, + 703, + 470, + 901 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "model simpler and more memory-friendly. While this initial network guarantees any-scale image synthesis with consistent image details, it faces the same memory issue as CIPS. We will discuss next how to solve this issue effectively.", + "bbox": [ + 496, + 575, + 890, + 637 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.3. Thick bi-line representation", + "text_level": 1, + "bbox": [ + 500, + 643, + 750, + 660 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Inspired by the tri-plane representation in [6], we propose to decompose each feature with 2D spatial dimensions into a column and a row embedding for a memory-efficient representation. For simplicity, let us drop the first two dimensions for the batch size $B$ and the number of channel $C$ , which are the same and element-wise processed for both the feature map and the mentioned embeddings. Let us denote the feature map as $F \\in \\mathbb{R}^{H \\times W}$ , with $H$ and $W$ as the height and width, respectively. We can decompose $F$ to a row embedding $f^r$ and a column embedding $f^c$ . In the simplest form, $f^r$ and $f^c$ are 1D vectors with the lengths $H$ and $W$ , respectively. Each pixel in the feature map $F_{ij}$ , with $i$ and $j$ as the row and the column indices, can be computed as the product of the corresponding elements in $f^r$ and $f^c$ :", + "bbox": [ + 496, + 667, + 890, + 878 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nF _ {i j} = f _ {i} ^ {r} f _ {j} ^ {c}. \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 651, + 885, + 890, + 902 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "22411", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/e66f352c0d2017d59ad5628ff9916cfdc0e01398c1d22fd6d0ad3345ad7aa1c0.jpg", + "image_caption": [ + "Figure 3. Fitting an input image to the thick bi-line representation in the image space." + ], + "image_footnote": [], + "bbox": [ + 78, + 88, + 468, + 180 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We call this representation \"bi-line\", which significantly reduces the memory usage and computation cost and allows the network to learn with high-resolution data. However, we found that this simple representation had a limited capacity and could not define complex structures. To enrich its representation power, we \"thicken\" the embeddings by adding an extra, short dimension. The revised $f^r$ and $f^c$ now have the shapes $H \\times D$ and $W \\times D$ , respectively, where $D \\ll \\min(H, W)$ is a uniform embedding \"thickness\". The composing feature element $F_{ij}$ is now the dot product of the corresponding elements in $f^r$ and $f^c$ :", + "bbox": [ + 75, + 224, + 473, + 393 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nF _ {i j} = f _ {i} ^ {r} \\cdot f _ {j} ^ {c} = \\sum_ {d = 1} ^ {D} f _ {i d} ^ {r} f _ {j d} ^ {c}. \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 178, + 404, + 468, + 446 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "This composition process is illustrated in Fig. 2b. In another perspective, this can be considered as a sum of $D$ different bi-line compositions. We call it \"thick bi-line\" representation.", + "bbox": [ + 75, + 455, + 468, + 503 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In Fig. 3, we provide a toy example illustrating the capacity of the proposed thick bi-line representation. Given an input image at resolution $512 \\times 512 \\times 3$ , we fit it into the proposed bi-line representation in the image space by optimizing a row and a column embedding of shape $512 \\times D \\times 3$ . Note that each channel is optimized independently. As can be seen, with the naive bi-linear composition ( $D = 1$ ), the reconstructed image is just a simple, incomprehensible grid. By adding just a small thickness $D = 8$ , we can capture the essential image content, recover the subject's identity, and reduce the MSE almost 6 times. When using $D = 32$ , we nearly recover the original image with only subtle pixel noise. Note that the row and column embeddings only take $1.56\\%$ of the original image size when $D = 8$ and $12.5\\%$ when $D = 32$ . This experiment confirms the efficacy of our proposed thick bi-line decomposition. Also, while this representation does not capture all details of the complex input image, it is more sufficient when modeling the overparameterized feature space.", + "bbox": [ + 75, + 503, + 473, + 792 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.4. Layer-wise feature composition", + "text_level": 1, + "bbox": [ + 76, + 801, + 354, + 816 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In CREPS, we assume the target output is square, i.e., $H = W$ . Hence, we can concatenate the row and column embeddings to a single tensor $f = [f^r, f^c] \\in \\mathbb{R}^{H \\times 2D}$ . Initially, we implement CREPS by revising StyleGAN2's code to predict $f$ from the latent input $w$ via $N$ synthesis blocks.", + "bbox": [ + 75, + 825, + 468, + 902 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The network then splits $f$ to get the row and column codes, perform the feature composition defined in Eq. (3) to get a feature map $F$ . This feature map will be passed to a simple refinement module (Fig. 2c) with 2 synthesis blocks to produce the output image. For efficient memory and computation cost, we only employ a small thickness value $D = 8$ .", + "bbox": [ + 496, + 90, + 890, + 181 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We found this initial design needed to be more efficient to catch up with the generation quality of StyleGAN and CIPS. It performed feature composition once near the end of the image synthesis process; thus, the model power was bounded by the capacity of the thick bi-line representation. Instead, we revise our solution by employing a layer-wise feature composition scheme. Specially, at each layer with index $l \\in [1..N]$ , we extract the intermediate row and column embedding $f^{(l)}$ . We can split $f^{(l)}$ and compose an intermediate feature map $F^{(l)}$ , following Eq. (3). Then, the intermediate maps across layers are fused to get the final map $F$ . This scheme enriches the representation power, similar to when increasing $D$ while using less memory.", + "bbox": [ + 496, + 181, + 892, + 378 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The fusion scheme is also important. Intuitively, we can set $F$ as the sum of the intermediate maps $\\{F^{(l)}\\}_{l = \\overline{1,N}}$ . However, this formulation treats the maps equally, and we find it undesirable. Let us call back the StyleGAN models' behavior. Thanks to the coarse-to-fine design, their early layers learn to capture the global shape, while the later layers learn to synthesize fine details. Since CREPS has no coarse-to-fine structure, it is hard to control which aspect of the output image each layer can learn. Hence, we propose adding asymmetry to the feature map fusion process: the feature maps at earlier layers are processed \"deeper\" than those at later layers. We hope it implicitly guides the layers to learn information from global to regional order, similar to StyleGAN. To do so, we introduce at each layer with index $l$ a narrow decoder, denoted as $\\pi^{(l)}$ . The process to fuse the intermediate maps $\\{F^{(l)}\\}_{l = \\overline{1,N}}$ is defined as following:", + "bbox": [ + 496, + 378, + 893, + 623 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nE ^ {(1)} \\quad = F ^ {(1)}, \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 517, + 641, + 890, + 659 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nE ^ {(l + 1)} = \\pi^ {(l)} \\left(E ^ {(l)}\\right) + F ^ {(l + 1)} \\quad \\forall l \\in [ 1, N - 1 ], \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 517, + 662, + 890, + 681 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nF \\quad = \\pi^ {N} \\left(E ^ {N}\\right), \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 517, + 684, + 890, + 702 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "with $E^{(l)}$ records the fused feature map at the $l^{th}$ layer. In our implementation, each decoder consists of pixelwise fully-connected layers with Leaky-RELU activations. Fig. 2a illustrates our proposed network structure, while Tab. 1 illustrates the efficiency of our proposed structure in memory usage and running time.", + "bbox": [ + 496, + 710, + 890, + 804 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 500, + 815, + 633, + 832 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.1. Experimental setup", + "text_level": 1, + "bbox": [ + 500, + 839, + 687, + 856 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Datasets. We conduct experiments on the common datasets when benchmarking CREPS, including FFHQ, MetFaces,", + "bbox": [ + 500, + 869, + 890, + 901 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "22412", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/dfd92940ee879e8774a5363b371738527084ae44a49173a38a7f08298a17a25a.jpg", + "image_caption": [ + "Figure 4. Sample images with our models trained on FFHQ (upper-left), LSUN-Church (upper-right), MetFace (bottom-left), and Flickr-Scenery (bottom-right)." + ], + "image_footnote": [], + "bbox": [ + 81, + 88, + 272, + 385 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/94f60fab2cc902e9b09c1c66ac5d30d119da998ac918b0c2f6680841000452a4.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 274, + 88, + 467, + 385 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "LSUN-Church, and Flickr-Scenery. FFHQ dataset contains 70k high-quality, diverse human faces collected from Flickr. We will use the FFHQ images with resolution $512 \\times 512$ . MetFaces is a small dataset of face drawings extracted from the collection of the Metropolitan Museum of Art, with a total of 1336 images at resolution $1024 \\times 1024$ . LSUN-Church consists of 126k outdoor photographs of churches at the resolution $256 \\times 256$ . Finally, Flickr-Scenery [7] is a landscape-centric dataset collected on Flickr with 50k images at resolution $256 \\times 256$ .", + "bbox": [ + 75, + 445, + 472, + 597 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Implementation. We use StyleGAN2 network design as a reference to implement CREPS. Except for the refinement module, our generator consists of 6 (for the target resolution 256) to 8 synthesis blocks (for the resolution 1024) and the same number of decoder blocks. We replace all modulated convolution layers in StyleGAN2 with modulated fully-connected ones. Unlike StyleGAN2, the output of each block is not an RGB image but a 32-channel bi-line feature with thickness $D = 8$ . Each decoder is a stack of $P = 4$ pixel-wise fully-connected layers, with the channel widths ranging from 32 to 128. This setting is applied for all experiments, except for our ablation study. Similar to StyleGAN3 and CIPS, we turn off style mixing regularization. Besides that, we kept most of the other components unchanged, including the mapping network, discriminator, path length regularization, and $R_{1}$ gradient penalty.", + "bbox": [ + 75, + 604, + 472, + 848 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Training. For FFHQ and LSUN-Church, our networks were trained from scratch until convergence. To verify the flexibility and scale consistency of CREPS on higher-", + "bbox": [ + 76, + 854, + 470, + 902 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "resolution image synthesis, we increase the length of its coordinate input to generate images at resolution $1024 \\times 1024$ on the FFHQ dataset. We also test the adaptability of our network on domain shift by applying transfer learning from the weights trained on FFHQ to MetFaces. Our networks were trained by Adam optimizer with learning rate $2 \\times 10^{-3}$ and hyperparameters $\\beta_0 = 0$ , $\\beta_1 = 0.99$ , and $\\epsilon = 10^{-8}$ . We use 4 NVIDIA A100 40GB GPUs for training all models.", + "bbox": [ + 496, + 90, + 893, + 213 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.2. Image generation", + "text_level": 1, + "bbox": [ + 500, + 222, + 671, + 238 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Tab. 2 compares the quality of images generated by our CREPS models with the standard spatial-convolution-based StyleGAN2 and the only scale-consistent any-scale image generation technique CIPS, using the Frechet Inception Distance (FID) score.", + "bbox": [ + 496, + 244, + 893, + 320 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "At resolution $512 \\times 512$ on FFHQ, our model achieves the FID score of 4.43, which is much better than the score from CIPS (6.18) and not far from StyleGAN2 (3.41). We can also use this model to generate images at resolution $1024 \\times 1024$ without retraining and achieve a better FID score (4.09). We found that CIPS cannot be trained for this resolution due to its expensive memory usage, even with training batch size 1, when using its official code. However, the authors provided a pretrained model for FFHQ-1024 using a progressive training scheme (no released code). This CIPS model has an FID score of 10.07, much worse than ours. This confirms the superiority of our method over its scale-consistent image generation counterpart.", + "bbox": [ + 496, + 321, + 893, + 518 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "On the MetFaces dataset, CREPS's FID score is 20.52, which is quite close to the score of StyleGAN2-Ada (18.22). As mentioned, CIPS fails to train on this $1024 \\times 1024$ resolution using its official code. It confirms that bi-line representation does not constrain the adaptability of our model.", + "bbox": [ + 496, + 518, + 893, + 594 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "On LSUN-Church and Flickr-Scenery, although the unstructured and diverse images in these datasets are intuitively adverse to column and row decomposition, CREPS obtains good results with only a small gap compared with StyleGAN2's ones. Note that CIPS achieves a surprisingly good result on LSUN-Church; it surpasses not only CREPS but also StyleGAN2 in this setting.", + "bbox": [ + 496, + 594, + 893, + 700 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Fig. 4 provides some samples synthesized by our networks on the benchmark datasets. As can be seen, CREPS produces highly realistic images in all cases.", + "bbox": [ + 496, + 700, + 893, + 746 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.3. Generate arbitrary-scale images", + "text_level": 1, + "bbox": [ + 498, + 756, + 784, + 772 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "While our models are trained on images with resolutions from $256 \\times 256$ to $1024 \\times 1024$ , they can generate images at any scale. One way is that we simply scale the length of $e^r$ and $e^c$ , and the output size is changed accordingly, thanks to our network design. With a V100 GPU (32GB), our models can generate an image up to resolution $3687 \\times 3687$ in a single run. Or we can generate an image patch-by-patch with suitable coordinate inputs, then combine them together into", + "bbox": [ + 496, + 779, + 893, + 902 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "22413", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/a8a71c4a7dcaa75f9b3e3ce8c497caa33723a61bf7069ad8e4ffb4716165d053.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
GeneratorFFHQ-512FFHQ-1024LSUN Church-256MetFaces-1024Scenery-256
StyleGANv23.412.843.8618.22*6.40
CIPS6.1810.07†2.92OOM8.49
CREPS (ours)4.434.09‡5.5020.527.21
", + "bbox": [ + 145, + 88, + 820, + 152 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/b31f68bd4a9adbe7e9700a4b4df21b1db24dc63df6843d1bc84f0cb22396408e.jpg", + "table_caption": [ + "Table 2. Comparison of our method against other works in FID metric. OOM means out-of-memory. \\*\\* means the result is taken from StyleGAN2-Ada paper [12]. $\\ddagger$ means the model is provided without releasing its progressive training code. $\\ddagger$ means the result is obtained by scaling the output resolution of the FFHQ-512 model." + ], + "table_footnote": [], + "table_body": "
PSNR ↑SSIM ↑LPIPS ↓
AnyresGAN24.190.730.07
ScaleParty24.500.700.08
CIPS33.330.930.05
CREPS34.650.960.01
", + "bbox": [ + 109, + 212, + 433, + 292 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/cc19668380b05f778c92502e1c7a778cf7311d8c1aa39778ce8f24ff595c6cca.jpg", + "image_caption": [ + "Figure 5. Qualitative results for the scale consistency experiment. For each method, we provide a sample generated $256 \\times 256$ image (top) and the magnified $(\\times 10)$ residual map between it and the $512 \\times 512$ rescaled version (bottom)." + ], + "image_footnote": [], + "bbox": [ + 83, + 335, + 465, + 494 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "a single gigantic image with no upper limit in the output size. We provide in the Supplementary some images generated at 6K resolution. While these images are not as sharp as real-world ultra-high-resolution images, they are much sharper than the ones generated at resolution $512 \\times 512$ and then upscaled with Lanczos resampling.", + "bbox": [ + 75, + 566, + 468, + 657 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.4. Image scaling consistency", + "text_level": 1, + "bbox": [ + 76, + 665, + 310, + 681 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "In this section, we evaluate the scale consistency of images produced by CREPS and other methods, including AnyresGAN [4], ScaleParty [18], and CIPS [1]. We run this experiment using models trained on the FFHQ dataset. For each model, we first randomly generate 10k images at resolution $256 \\times 256$ (first set). We then generate images with the same latent codes but at resolution $512 \\times 512$ and downsample them to $256 \\times 256$ (second set). The images in two sets are expected to be the same. Hence, we can compare two sets, with standard metrics such as PSNR, SSIM, and LPIPS, to measure each model's scale equivariance.", + "bbox": [ + 75, + 689, + 468, + 853 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Note that for ScaleParty and AnyresGAN, the pretrained weights are already trained with different resolutions at once, so we directly use their provided version. CIPS, how", + "bbox": [ + 75, + 854, + 468, + 900 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/36de59643cfd74353095ec6f664412abff7d75eabe92e80d5282a59031dd8390.jpg", + "table_caption": [ + "Table 3. Scale consistency comparison of our method against three other works on PSNR, SSIM and LPIP. The best scores are bold." + ], + "table_footnote": [], + "table_body": "
ConfigurationFIDMemoryTime
CREP-NB5.982.7GB0.13s
+ bi-line and d=111.371.5GB0.02s
+ bi-line and d=88.231.6GB0.03s
+ multiple decoders and d=46.461.6GB0.03s
+ multiple decoders and d=84.661.7GB0.04s
CIPS7.083.5GB0.05s
", + "bbox": [ + 501, + 212, + 897, + 323 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 4. Effects of the modifications of CREPS on the FFHQ dataset in terms of FID score, memory usage, and running time.", + "bbox": [ + 498, + 327, + 890, + 356 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "ever, is trained in a single-scale setting, so we use the available weights trained at the highest resolution $(1024 \\times 1024)$ but pass the input coordinate with size $512 \\times 512$ to synthesis image at resolution 512. As for CREPS, we simply use the weight trained at resolution $512 \\times 512$ .", + "bbox": [ + 498, + 380, + 890, + 455 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We report the qualitative and quantitative results in Fig. 5 and Tab. 3. As can be seen, it is clear that CREPS achieves the best scale consistency, while convolution-based models like ScaleParty and AnyresGAN perform poorly.", + "bbox": [ + 498, + 455, + 890, + 517 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.5. Ablation studies", + "text_level": 1, + "bbox": [ + 500, + 527, + 661, + 542 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "To better understand our proposed techniques, we analyze the effect of different parts of CREPS on the FFHQ datasets. We first consider a no-bi-line version of CREPS as a baseline (referred to as CREPS-NB), with dense 2D input and the decoder layers removed. We then apply bi-line decomposition but fuse the bi-line features only once at the end, with gradually increased thickness. Lastly, we add multiple decoders for layer-wise feature composition as introduced in Sec. 3.4. Because of limited time and computational resources, we only evaluate on $128 \\times 128$ resolution and all of our models were trained for maximum of 2 days.", + "bbox": [ + 496, + 551, + 890, + 718 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "As the results in Tab. 4 show, CIPS performs worst in all three aspects compared with most of our models. Simply adding the bi-line with a single decoder at the end nearly halves the memory costs, but the FID score is still behind CREPS-NB even when the thickness is increased to $d = 8$ . However, multiple decoders can help bring the image quality back to the level of CREPS-NB and even better with $d = 8$ . In all settings, it can be clearly seen that we easily boost the FID score when increasing the thickness. These observations prove the importance and effectiveness of our proposed techniques. Remarkably, while the decoders seem compute-intensive, they are actually lightweight due to their", + "bbox": [ + 496, + 719, + 892, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "22414", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/3f77bd13a279a27efdf02f49ee855f50fe39da7f0224b4d9f168849af722367d.jpg", + "image_caption": [ + "Figure 6. Geometric transformations on the same target image (FFHQ-512 model) by changing the input coordinates. We mark the original image boundary using a red rectangle." + ], + "image_footnote": [], + "bbox": [ + 78, + 87, + 468, + 161 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/5c2e38cd25cae7a40f75499f2e0e2f7660ac49426f87b5939fbfb5f240201e22.jpg", + "image_caption": [ + "Figure 7. Visualization of the feature maps extracted from our FFHQ-512 model. Each feature map is averaged over all channels." + ], + "image_footnote": [], + "bbox": [ + 78, + 220, + 468, + 305 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "narrow width compared with other layers, causing only small increases in memory and time.", + "bbox": [ + 76, + 364, + 468, + 395 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.6. Simple and complex geometric transformation", + "text_level": 1, + "bbox": [ + 76, + 416, + 468, + 431 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Our CREPS model can support various geometric transformations on the same target image by keeping the input latent code $z$ but changing the input coordinates $e^r$ and $e^c$ . We can translate the image by adding coordinate shifts $\\delta_y$ and $\\delta_x$ to the row and column input coordinates, respectively. We can also multiply these input coordinates by the same constant $s > 1$ for zooming out or divide them by $s$ for zooming in. As can be seen in the first three columns in Fig. 6, CREPS can perform those simple transformations with consistent details. Notably, CREPS can extrapolate the points outside the original image boundary, although it has never been trained on such input coordinates.", + "bbox": [ + 75, + 443, + 468, + 625 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "It is tricky for CREPS to handle complex transformations such as rotation or distortion since CREPS only takes in a row and a column coordinate input. Instead of producing the target image in one run, we can execute CREPS multiple times to generate different parts of the output image, then combine them. The simplest algorithm is to sample each target pixel per run by setting a single value for $e^r$ and $e^c$ . However, that algorithm is too slow, which requires 262k runs to produce a single $512 \\times 512$ image. A faster way is to sample the target image row-by-row. Assuming we need to generate an image $I$ with the input latent $z$ and the target pixels' normalized coordinates $\\{(r_{ij}, c_{ij})\\}_{i = \\overline{1,H}, j = \\overline{1,W}}$ . We can produce each row $I_i$ of the target image by generating an intermediate image $\\Gamma$ using the input coordinates $e^r = [r_{ij}]_{j = \\overline{1,W}}$ and $e^c = [c_{ij}]_{j = \\overline{1,W}}$ and sample its diagonal $I_i = \\text{diag}(I')$ . We provide two examples with rotation and elastic distortion in the last two columns of Fig. 6. Both images are correctly transformed with unchanged content.", + "bbox": [ + 75, + 628, + 470, + 901 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/94eb2199e186794db439e0125a038f740310a39b1f8fe1ada6b3676fc283a002.jpg", + "image_caption": [ + "Figure 8. Samples of the most common kinds of artifacts on different datasets. They are best described as repeating/wavy patterns, vertical symmetry, and glowing blobs. Left-most image is cropped and zoomed-in from a full-face image." + ], + "image_footnote": [], + "bbox": [ + 504, + 88, + 888, + 161 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.7. Feature analysis", + "text_level": 1, + "bbox": [ + 500, + 229, + 661, + 244 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We visualize the key feature maps inside our FFHQ-512 model when generating a facial image and provide them in Fig. 7. The maps include the layer-wise composed features $\\{F^{(l)}\\}_{l = \\overline{1,N}}$ , the corresponding layer-wise fused maps $\\{E^{(l)}\\}_{l = \\overline{1,N}}$ , and the final feature map $F$ (see Eq. 4-6). Thanks to the asymmetric fusion scheme, the model seems to synthesize the output in a coarse-to-fine manner. The early composed feature maps are smooth and focus on the global structure, while the later ones focus on sharp details. Although each composed feature map $F^{(l)}$ is quite simple, the network can represent complex content by fusion.", + "bbox": [ + 498, + 252, + 890, + 421 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.8. Limitation", + "text_level": 1, + "bbox": [ + 500, + 430, + 617, + 445 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Being a fully-connected generator, CREPS shares the same limitation with other similar work, which is the lack of spatial bias since each pixel is independently generated. Hence, some spatial-related artifacts occasionally occur in our generated images (Fig. 8). A potential cause is the sine activation at the beginning, producing repeating patterns and vertical symmetry of the output. We also note that some samples contain a noticeable blob that is completely out-of-domain. We found CIPS facing the same problem, and the root cause can be the missing spatial guidance from neighboring pixels and the effect of Leaky-RELU activations which strengthens the isolation of some pixel regions.", + "bbox": [ + 496, + 454, + 890, + 635 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 648, + 617, + 664 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this paper, we present a new architecture named CREPS, a cost-effective and scale-equivariant generator that can synthesize images with any target resolution. Our key contributions are an INR-based design, a thick biline representation, and a layer-wise feature composition scheme. While being more memory-efficient, our CREPS models can produce highly realistic images and surpass the INR-based model CIPS in most cases. CREPS also offers the best scale consistency by keeping image details unchanged when varying the output resolution. We conducted several experiments to explore some attractive properties of this fully-connected generator and discussed CREPS's applications in various scenarios. Future development of our approach can be eliminating artifacts mentioned in Sec. 4.8 and further improving the quality of our samples.", + "bbox": [ + 496, + 674, + 890, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "22415", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Ivan Anokhin, Kirill Demochkin, Taras Khakhulin, Gleb Sterkin, Victor Lempitsky, and Denis Korzhenkov. Image generators with conditionally-independent pixel synthesis. In IEEE/CVF Conference on Computer Vision and Pattern Recognition (CVPR), 2021. 2, 3, 7", + "[2] A.H. Bermano, R. Gal, Y. Alaluf, R. Mokady, Y. 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In IEEE/CVF Conference on Computer Vision and Pattern Recognition (CVPR), 2021. 2" + ], + "bbox": [ + 78, + 90, + 468, + 247 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "22417", + "bbox": [ + 478, + 945, + 517, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/Efficient Scale-Invariant Generator With Column-Row Entangled Pixel Synthesis/e82bfa76-118c-45c9-a6c3-50265e9de1a3_model.json b/2023/Efficient Scale-Invariant Generator With Column-Row Entangled Pixel Synthesis/e82bfa76-118c-45c9-a6c3-50265e9de1a3_model.json new file mode 100644 index 0000000000000000000000000000000000000000..3517e2303c3b2c80e00750c55e90156a419eeed9 --- /dev/null +++ b/2023/Efficient Scale-Invariant Generator With Column-Row Entangled Pixel Synthesis/e82bfa76-118c-45c9-a6c3-50265e9de1a3_model.json @@ -0,0 +1,1881 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.079, + 0.131, + 0.892, + 0.152 + ], + "angle": 0, + "content": "Efficient Scale-Invariant Generator with Column-Row Entangled Pixel Synthesis" + }, + { + "type": "text", + "bbox": [ + 0.27, + 0.181, + 0.699, + 0.216 + ], + "angle": 0, + "content": "Thuan Hoang Nguyen* Thanh Van Le* Anh Tran VinAI Research, Hanoi, Vietnam" + }, + { + "type": "text", + "bbox": [ + 0.289, + 0.219, + 0.678, + 0.234 + ], + "angle": 0, + "content": "{v.thuannh5,v.thanhlv19,v.anhtt152}@vinai.io" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.269, + 0.314, + 0.284 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.302, + 0.474, + 0.65 + ], + "angle": 0, + "content": "Any-scale image synthesis offers an efficient and scalable solution to synthesize photo-realistic images at any scale, even going beyond \\(2K\\) resolution. However, existing GAN-based solutions depend excessively on convolutions and a hierarchical architecture, which introduce inconsistency and the \"texture sticking\" issue when scaling the output resolution. From another perspective, INR-based generators are scale-equivariant by design, but their huge memory footprint and slow inference hinder these networks from being adopted in large-scale or real-time systems. In this work, we propose Column-Row Entangled Pixel Synthesis (CREPS), a new generative model that is both efficient and scale-equivariant without using any spatial convolutions or coarse-to-fine design. To save memory footprint and make the system scalable, we employ a novel bi-line representation that decomposes layer-wise feature maps into separate \"thick\" column and row encodings. Experiments on various datasets, including FFHQ, LSUN-Church, MetFaces, and Flickr-Scenery, confirm CREPS' ability to synthesize scale-consistent and alias-free images at any arbitrary resolution with proper training and inference speed. Code is available at https://github.com/VinAIResearch/CREPS." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.681, + 0.21, + 0.697 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.707, + 0.47, + 0.875 + ], + "angle": 0, + "content": "Generative Adversarial Networks (GANs) [8] are one of the most widely used structures for image generation and manipulation [2, 28]. Previously, a GAN model could only generate images with a fixed scale and layout as defined in the training dataset. However, natural images come with varying resolutions and contain unstructured objects at diverse poses. Therefore, designing a generative model that can handle more flexible geometric configurations is gaining more attention in the machine-learning community. StyleGAN3 [13] already supports out-of-the-box translation and rotation with consistent and artifact-free outputs." + }, + { + "type": "image", + "bbox": [ + 0.501, + 0.267, + 0.635, + 0.491 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.653, + 0.267, + 0.761, + 0.492 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.784, + 0.267, + 0.892, + 0.492 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.495, + 0.893, + 0.579 + ], + "angle": 0, + "content": "Figure 1. Previous any-scale image synthesis networks, including AnyresGAN [4] and ScaleParty [18], produce inconsistent image details when changing the output scale (see zoomed-in patches). In contrast, our proposed network can produce the same details but sharper when increasing the scale. Check the supplemental video for a clearer comparison." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.596, + 0.865, + 0.611 + ], + "angle": 0, + "content": "Any-scale synthesis, however, remains under-explored." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.612, + 0.893, + 0.853 + ], + "angle": 0, + "content": "In this paper, we are interested in the task of arbitrary-scale image synthesis where a single generator can effortlessly synthesize images at many different scales while strongly preserving detail consistency. Such a model can be a promising research direction and bring many benefits. It enables synthesizing a high-resolution image from a lower-resolution training dataset. Hence, it eliminates the need for collecting and training models on high-resolution images, which is costly in storage, time, and computation resources. The output resolution can be ultra-high, e.g., \\(2048 \\times 2048\\), which is impossible for standard GAN models due to the limit of GPU memory. Any-scale image synthesis also allows geometric interactions like zooming in and out. Despite promising results, previous works on this topic, such as AnyresGAN [4] and ScaleParty [18], show strong inconsistency when scaling the output resolution (see Fig. 1)." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.856, + 0.892, + 0.901 + ], + "angle": 0, + "content": "We investigate the GAN structures to find the potential cause of the inconsistency at image scaling. Traditional GAN models are based on convolutional generators" + }, + { + "type": "page_footnote", + "bbox": [ + 0.102, + 0.888, + 0.212, + 0.9 + ], + "angle": 0, + "content": "*Equal contribution." + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "22408" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.273 + ], + "angle": 0, + "content": "[3,15,20], which introduce an implicit spatial bias that helps the model to produce high-quality images. Recently, Xu et al. [29] and Karras et al. [13] discovered that these positional priors can hamper the model's consistency when applying translations, rotations, or scalings. In order to combat this issue, many works introduce non-trivial changes such as sophisticated architecture re-design [13] or opt for a better training strategy and input positional encoding [4,18]. However, these are only partial remedies as the output pixels still depend on their surroundings, making it impossible for these models to produce consistent attributes of an object regardless of positions and scales." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.276, + 0.473, + 0.502 + ], + "angle": 0, + "content": "In contrast to the traditional GANs, some recent methods are based on Implicit Neural Representation (INR) [1, 23]. By predicting the color of each pixel separately, INR-based GANs can, in theory, synthesize objects in a spatial-arbitrary manner and still achieve comparable quality at small to medium resolution compared to convolution-based approach. However, these models' memory usage grows quadratically with the input resolution since all pixels have to be queried. Thus, there has been no existing work that can efficiently scale INR-GANs to resolutions higher than 1024. To reduce training complexity, Anokhin et al. [1] employs a simple patch-based strategy where only a portion of pixels is generated and passed through the discriminator at a time. However, this approach unsurprisingly leads to poor results and inconsistency between patches." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.506, + 0.473, + 0.732 + ], + "angle": 0, + "content": "Inspired by the latter approach, we aim to tackle the task of scale-consistent image generation with essential changes to StyleGAN2 [15]. Similar to Anokhin et al. [1], we change the \\(3 \\times 3\\) convolutions to \\(1 \\times 1\\) ones and add a Fourier feature embedding [25] at the input layer. Although these two changes alone already achieve our goal, it is still expensive to train in high-resolution settings. Thus, instead of using dense 2D features, our model relies on a novel thick biline representation, which largely reduces the training and inference complexity by using two low-rank features for row and column. Our network first regresses these row and column embeddings, then composes layer-wise intermediate 2D features, and finally fuses these maps to produce the final output. We name this novel structure Column-Row Entangled Pixel Synthesis, or CREPS for short." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.735, + 0.473, + 0.903 + ], + "angle": 0, + "content": "We run a series of experiments on four datasets, including FFHQ, MetFaces, LSUN-Church, and Flickr-Scenery, to confirm the effectiveness of our proposed CREPS structure. Our model can synthesize images with quality comparable to the previous generative models like CIPS or StyleGAN2. While CIPS has trouble in training on images of resolutions more than \\(256 \\times 256\\), CREPS can sufficiently handle training data at resolutions \\(512 \\times 512\\) and \\(1024 \\times 1024\\). CREPS produces scale-equivariant images and keeps the object details unchanged when scaling the output resolution, unlike previous any-scale GANs such as AnyresGAN" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.895, + 0.168 + ], + "angle": 0, + "content": "and ScaleParty. Using a CREPS model trained on \\(512 \\times 512\\) images, we still can generate near-realistic images at higher resolution. Finally, we demonstrate CREPS's ability to synthesize images with complex geometric transformations and distortions while preserving attribute consistency." + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.168, + 0.738, + 0.182 + ], + "angle": 0, + "content": "To summarize our contributions:" + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.194, + 0.892, + 0.255 + ], + "angle": 0, + "content": "- We propose a simple and elegant network equipped with only modulated linear layers and no upsampling layers in-between. It supports scale-consistent outputs for any-scale image synthesis." + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.265, + 0.892, + 0.342 + ], + "angle": 0, + "content": "- To further improve efficiency, we introduce a thick bi-line representation, which decomposes 2D network features into two light-weight row and column embeddings. It significantly saves memory and computation costs compared with the full 2D-feature counterparts." + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.352, + 0.892, + 0.428 + ], + "angle": 0, + "content": "- We demonstrate competitive results for unconditional image synthesis on the FFHQ, LSUN-Church, Met-Faces, and Flickr-Scenery datasets, along with the ability to generate each image at arbitrary scales with consistent details." + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.439, + 0.892, + 0.469 + ], + "angle": 0, + "content": "- Our CREPS models support complex geometric transformations and distortions." + }, + { + "type": "list", + "bbox": [ + 0.519, + 0.194, + 0.892, + 0.469 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.484, + 0.642, + 0.5 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.516, + 0.892, + 0.82 + ], + "angle": 0, + "content": "Generative Adversarial Networks. Prior to denoising diffusion models [10, 24], GANs [8] hold state-of-the-art results for image synthesis tasks. The popular GAN models can generate realistic images at a high resolution, commonly up to \\(1024 \\times 1024\\) [3, 12-15]. The promising results obtained by GANs have motivated several applications of computer graphics and visual content generation. However, these networks are only capable of generating images with same geometric configurations, e.g., center-located and face-forward objects. Recently, an exciting work StyleGAN3 [13] aimed to generalize GAN to arbitrary translation and rotation with consistent details, or Anycost GAN [16] with multi-resolution generation. In the same vein, ScaleParty [18] and AnyresGAN [4] extended StyleGAN2 and StyleGAN3 to support scaling and other geometric transformations by replacing learned input constant with suitable positional encoding and multi-scale training strategy. However, these works did not consider the scale consistency, and their images showed varied details as the output scale increases, illustrated in Fig. 1." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.826, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Implicit Neural Representation. Typically, images are represented by a series of 2D arrays of values. However, it can be viewed as a continuous mapping from a 2D coordinate \\((x,y) \\in \\mathbf{R}^2\\) to the corresponding RGB value \\((r,g,b) \\in \\mathbf{R}^3\\) and the mapping can be parameterized as a" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "22409" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.228 + ], + "angle": 0, + "content": "black-box model. This coordinate-wise modeling has been used in a wide range of neural rendering tasks [5,17,22,26], where neural networks are used to provide an efficient and continuous representation of data compared with traditional methods. In the literature, implicit neural networks mainly utilize fully-connected layers as their building blocks. Unlike convolution or self-attention, such layers' receptive field size is exactly one; in other words, the output at every coordinate is independent of each other." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.235, + 0.473, + 0.613 + ], + "angle": 0, + "content": "INR-based GANs. As the number of research increased, INR started to be used for generative tasks. These models soon inherited the success of GANs by employing the adversarial training manner. Generative radiance fields [6, 9, 19, 21] attempt to learn a view-consistent representation of 3D objects using implicit GAN. Despite all the success of INRs in 3D GANs, limited attention has been paid to utilizing the equivariance capability of fully-connected layers in 2D counterparts. The closest to our work are INRGAN [23] and CIPS [1]. Both these works use a grid of the target pixel coordinates as input for batch processing instead of passing each point individually. INR-GAN employs a multi-scale structure, which we will discuss later as a cause of scale inconsistency, while its uniform-scale versions have poor generation outputs. Meanwhile, CIPS does not need the multi-scale design thanks to its efficient weight modulation and expressive input embedding. The uniform-scale INR-GAN and CIPS disregard spatial convolutions in the generator and synthesize each pixel independently. However, their main goal is to investigate an alternative architecture that can compete with fully-convolutional GANs rather than paying attention to the equivariance characteristic of such models. They also struggle with expensive computation costs and memory usage using full-resolution 2D feature maps in processing." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.629, + 0.248, + 0.645 + ], + "angle": 0, + "content": "3. Proposed method" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.655, + 0.47, + 0.777 + ], + "angle": 0, + "content": "This section describes our proposed CREPS structure. First, we recall the concept of any-scale image synthesis (Sec. 3.1). Then, we revise two existing GAN structures that support scale-equivariant image synthesis (Sec. 3.2). Next, we discuss how to reduce computation cost via the novel thick bi-line representation (Sec. 3.3). Finally, we describe the layer-wise feature composition scheme for improving the synthesis quality (Sec. 3.4)." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.787, + 0.313, + 0.803 + ], + "angle": 0, + "content": "3.1. Any-scale image synthesis" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.811, + 0.47, + 0.903 + ], + "angle": 0, + "content": "In this section, we introduce any-scale image synthesis as the task of generating images while enforcing consistency at different scales given a single model. One way we naturally come up with is generating an image at many scales altogether. MSG-GAN [11] is one of the earliest works in this approach. Instead of producing single output," + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.152 + ], + "angle": 0, + "content": "MSG-GAN outputs an RGB image at each block of the generator, resulting in a mipmap representation [27]. However, this approach can only output pre-defined discrete scales, and there is no mechanism to guarantee scale consistency." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.153, + 0.894, + 0.272 + ], + "angle": 0, + "content": "As such, we should consider injecting positional encoding \\( e \\) as an additional input alongside the latent code into the generator. This approach is employed in some previous works [1, 4, 18, 23], in which \\( e \\) is a 2D grid of normalized \\( (x,y) \\) coordinates. If \\( e \\) is a regular grid, we can decompose it into two vectors for the row and column coordinates denoted as \\( e^r \\) and \\( e^c \\), respectively. The image generation process now becomes:" + }, + { + "type": "equation", + "bbox": [ + 0.637, + 0.284, + 0.892, + 0.3 + ], + "angle": 0, + "content": "\\[\nI = G \\left(z, e ^ {r}, e ^ {c}\\right), \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.31, + 0.892, + 0.507 + ], + "angle": 0, + "content": "with \\( G \\) is the generative model and \\( z \\) is the latent input. The decomposition from \\( e \\) to \\( e^r \\) and \\( e^c \\) is more suitable to our thick bi-line representation, as later discussed. Doing so allows us to easily control the output's scale and other spatial properties via appropriate input encoding. However, naively adding positional input into an existing generator does not guarantee that the output image is equivariant to the change in the input coordinates. For example, when Karras et al. [13] replace the learnable constant in StyleGAN2's input layer with Fourier features (Config B), the \"texture sticking\" issue still occurs. Therefore, proper network design and training strategy should be examined to alleviate the output's geometric inconsistency." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.516, + 0.892, + 0.546 + ], + "angle": 0, + "content": "3.2. Removing coarse-to-fine design and spatial convolution" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.554, + 0.892, + 0.718 + ], + "angle": 0, + "content": "We investigate two network structures that support any resolution image generation, including AnyresGAN [4] and CIPS [1], when keeping the same latent input but gradually increasing the output resolution. The former is built upon StyleGAN3 [13] with additional scale information concatenated with the latent code and a multi-scale training scheme. In contrast, the latter changes the 3x3 convolution of StyleGAN2 with a point-wise one and adds learnable Fourier features at the beginning. Both models are capable of multiscale generation, but they have different behaviors that we will discuss below." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.892, + 0.84 + ], + "angle": 0, + "content": "As illustrated in Fig. 1, while having good photo-realism, AnyresGAN produces different image details at different scales. This can be explained by the fact that AnyresGAN, similar to most other GAN-based works, relies on spatial convolutions, such as 2D convolution with kernel size \\(3 \\times 3\\) and upsample layers. When changing the output resolution, the neighbor pixels at each location change, greatly varying the output of this spatial-convolution-based network." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.892, + 0.901 + ], + "angle": 0, + "content": "On the other hand, CIPS keeps the output image's details nearly the same regardless of resolution, thanks to its spatial-free building operators. CIPS, however, is very computationally expensive; this can be clearly shown in Tab. 1." + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "22410" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.132, + 0.092, + 0.501, + 0.381 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.258, + 0.384, + 0.373, + 0.395 + ], + "angle": 0, + "content": "(a) Network structure" + }, + { + "type": "image", + "bbox": [ + 0.633, + 0.095, + 0.761, + 0.184 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.617, + 0.186, + 0.774, + 0.199 + ], + "angle": 0, + "content": "(b) Thick bi-line composition" + }, + { + "type": "image", + "bbox": [ + 0.568, + 0.211, + 0.825, + 0.375 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.641, + 0.377, + 0.754, + 0.388 + ], + "angle": 0, + "content": "(c) Refinement block" + }, + { + "type": "image_caption", + "bbox": [ + 0.361, + 0.399, + 0.608, + 0.413 + ], + "angle": 0, + "content": "Figure 2. Our proposed CREPS structure" + }, + { + "type": "table", + "bbox": [ + 0.142, + 0.426, + 0.825, + 0.547 + ], + "angle": 0, + "content": "
ResolutionBatch sizeMemory UsageRunning time
StyleGAN2CIPSOursStyleGAN2CIPSOurs
256 × 25611.5GB3.3GB2.3GB0.04s0.06s0.03s
42.5GB10.2GB5.2GB0.05s0.23s0.06s
512 × 51211.7GB10.4GB4.5GB0.04s0.21s0.05s
43.4GBOOM14.6GB0.06sOOM0.16s
" + }, + { + "type": "table_caption", + "bbox": [ + 0.102, + 0.55, + 0.86, + 0.565 + ], + "angle": 0, + "content": "Table 1. Memory usage and running time comparison between StyleGAN2, CIPS and our method. OOM means out-of-memory." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.577, + 0.47, + 0.698 + ], + "angle": 0, + "content": "When measured on a single NVIDIA V100 GPU (32 GB) and all models have comparable number of parameters, it runs slower than StyleGAN2 as well as requires much more memory or even gets an out-of-memory (OOM) error when running at \\(512 \\times 512\\) resolution. This makes CIPS inapplicable to use for learning fine details from high-resolution datasets. Moreover, it is worth noting that our method achieve the best trade-off between speed and memory." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.704, + 0.471, + 0.902 + ], + "angle": 0, + "content": "Based on the above observations, we implement CREPS without any spatial convolutions or coarse-to-fine design. Starting with StyleGAN2 [15], which consists of a mapping network and a generator, we remove all upsampling operators and replace all spatial convolutions with \\( 1 \\times 1 \\) convolutions, which are equivalent to pixel-wise fully-connected layers. Next, we replace the constant in the first synthesis block with Fourier encodings of the input coordinate row and column \\( e^r \\) and \\( e^c \\). This design is quite similar to CIPS, with only two minor differences. Firstly, the dense 2D grid input is now split into two vectors representing the row and column. Secondly, we do not combine learned input constant with the Fourier feature like CIPS did, making our" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.577, + 0.892, + 0.638 + ], + "angle": 0, + "content": "model simpler and more memory-friendly. While this initial network guarantees any-scale image synthesis with consistent image details, it faces the same memory issue as CIPS. We will discuss next how to solve this issue effectively." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.644, + 0.75, + 0.661 + ], + "angle": 0, + "content": "3.3. Thick bi-line representation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.668, + 0.892, + 0.879 + ], + "angle": 0, + "content": "Inspired by the tri-plane representation in [6], we propose to decompose each feature with 2D spatial dimensions into a column and a row embedding for a memory-efficient representation. For simplicity, let us drop the first two dimensions for the batch size \\(B\\) and the number of channel \\(C\\), which are the same and element-wise processed for both the feature map and the mentioned embeddings. Let us denote the feature map as \\(F \\in \\mathbb{R}^{H \\times W}\\), with \\(H\\) and \\(W\\) as the height and width, respectively. We can decompose \\(F\\) to a row embedding \\(f^r\\) and a column embedding \\(f^c\\). In the simplest form, \\(f^r\\) and \\(f^c\\) are 1D vectors with the lengths \\(H\\) and \\(W\\), respectively. Each pixel in the feature map \\(F_{ij}\\), with \\(i\\) and \\(j\\) as the row and the column indices, can be computed as the product of the corresponding elements in \\(f^r\\) and \\(f^c\\):" + }, + { + "type": "equation", + "bbox": [ + 0.653, + 0.886, + 0.892, + 0.904 + ], + "angle": 0, + "content": "\\[\nF _ {i j} = f _ {i} ^ {r} f _ {j} ^ {c}. \\tag {2}\n\\]" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "22411" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.08, + 0.089, + 0.47, + 0.181 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.184, + 0.47, + 0.213 + ], + "angle": 0, + "content": "Figure 3. Fitting an input image to the thick bi-line representation in the image space." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.226, + 0.474, + 0.395 + ], + "angle": 0, + "content": "We call this representation \"bi-line\", which significantly reduces the memory usage and computation cost and allows the network to learn with high-resolution data. However, we found that this simple representation had a limited capacity and could not define complex structures. To enrich its representation power, we \"thicken\" the embeddings by adding an extra, short dimension. The revised \\( f^r \\) and \\( f^c \\) now have the shapes \\( H \\times D \\) and \\( W \\times D \\), respectively, where \\( D \\ll \\min(H, W) \\) is a uniform embedding \"thickness\". The composing feature element \\( F_{ij} \\) is now the dot product of the corresponding elements in \\( f^r \\) and \\( f^c \\):" + }, + { + "type": "equation", + "bbox": [ + 0.179, + 0.405, + 0.47, + 0.448 + ], + "angle": 0, + "content": "\\[\nF _ {i j} = f _ {i} ^ {r} \\cdot f _ {j} ^ {c} = \\sum_ {d = 1} ^ {D} f _ {i d} ^ {r} f _ {j d} ^ {c}. \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.457, + 0.47, + 0.504 + ], + "angle": 0, + "content": "This composition process is illustrated in Fig. 2b. In another perspective, this can be considered as a sum of \\( D \\) different bi-line compositions. We call it \"thick bi-line\" representation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.504, + 0.474, + 0.793 + ], + "angle": 0, + "content": "In Fig. 3, we provide a toy example illustrating the capacity of the proposed thick bi-line representation. Given an input image at resolution \\(512 \\times 512 \\times 3\\), we fit it into the proposed bi-line representation in the image space by optimizing a row and a column embedding of shape \\(512 \\times D \\times 3\\). Note that each channel is optimized independently. As can be seen, with the naive bi-linear composition (\\(D = 1\\)), the reconstructed image is just a simple, incomprehensible grid. By adding just a small thickness \\(D = 8\\), we can capture the essential image content, recover the subject's identity, and reduce the MSE almost 6 times. When using \\(D = 32\\), we nearly recover the original image with only subtle pixel noise. Note that the row and column embeddings only take \\(1.56\\%\\) of the original image size when \\(D = 8\\) and \\(12.5\\%\\) when \\(D = 32\\). This experiment confirms the efficacy of our proposed thick bi-line decomposition. Also, while this representation does not capture all details of the complex input image, it is more sufficient when modeling the overparameterized feature space." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.802, + 0.355, + 0.818 + ], + "angle": 0, + "content": "3.4. Layer-wise feature composition" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.826, + 0.47, + 0.903 + ], + "angle": 0, + "content": "In CREPS, we assume the target output is square, i.e., \\(H = W\\). Hence, we can concatenate the row and column embeddings to a single tensor \\(f = [f^r, f^c] \\in \\mathbb{R}^{H \\times 2D}\\). Initially, we implement CREPS by revising StyleGAN2's code to predict \\(f\\) from the latent input \\(w\\) via \\(N\\) synthesis blocks." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.182 + ], + "angle": 0, + "content": "The network then splits \\( f \\) to get the row and column codes, perform the feature composition defined in Eq. (3) to get a feature map \\( F \\). This feature map will be passed to a simple refinement module (Fig. 2c) with 2 synthesis blocks to produce the output image. For efficient memory and computation cost, we only employ a small thickness value \\( D = 8 \\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.183, + 0.893, + 0.379 + ], + "angle": 0, + "content": "We found this initial design needed to be more efficient to catch up with the generation quality of StyleGAN and CIPS. It performed feature composition once near the end of the image synthesis process; thus, the model power was bounded by the capacity of the thick bi-line representation. Instead, we revise our solution by employing a layer-wise feature composition scheme. Specially, at each layer with index \\( l \\in [1..N] \\), we extract the intermediate row and column embedding \\( f^{(l)} \\). We can split \\( f^{(l)} \\) and compose an intermediate feature map \\( F^{(l)} \\), following Eq. (3). Then, the intermediate maps across layers are fused to get the final map \\( F \\). This scheme enriches the representation power, similar to when increasing \\( D \\) while using less memory." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.379, + 0.895, + 0.624 + ], + "angle": 0, + "content": "The fusion scheme is also important. Intuitively, we can set \\(F\\) as the sum of the intermediate maps \\(\\{F^{(l)}\\}_{l = \\overline{1,N}}\\). However, this formulation treats the maps equally, and we find it undesirable. Let us call back the StyleGAN models' behavior. Thanks to the coarse-to-fine design, their early layers learn to capture the global shape, while the later layers learn to synthesize fine details. Since CREPS has no coarse-to-fine structure, it is hard to control which aspect of the output image each layer can learn. Hence, we propose adding asymmetry to the feature map fusion process: the feature maps at earlier layers are processed \"deeper\" than those at later layers. We hope it implicitly guides the layers to learn information from global to regional order, similar to StyleGAN. To do so, we introduce at each layer with index \\(l\\) a narrow decoder, denoted as \\(\\pi^{(l)}\\). The process to fuse the intermediate maps \\(\\{F^{(l)}\\}_{l = \\overline{1,N}}\\) is defined as following:" + }, + { + "type": "equation", + "bbox": [ + 0.518, + 0.642, + 0.892, + 0.66 + ], + "angle": 0, + "content": "\\[\nE ^ {(1)} \\quad = F ^ {(1)}, \\tag {4}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.519, + 0.663, + 0.892, + 0.682 + ], + "angle": 0, + "content": "\\[\nE ^ {(l + 1)} = \\pi^ {(l)} \\left(E ^ {(l)}\\right) + F ^ {(l + 1)} \\quad \\forall l \\in [ 1, N - 1 ], \\tag {5}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.519, + 0.685, + 0.892, + 0.703 + ], + "angle": 0, + "content": "\\[\nF \\quad = \\pi^ {N} \\left(E ^ {N}\\right), \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.712, + 0.892, + 0.805 + ], + "angle": 0, + "content": "with \\( E^{(l)} \\) records the fused feature map at the \\( l^{th} \\) layer. In our implementation, each decoder consists of pixelwise fully-connected layers with Leaky-RELU activations. Fig. 2a illustrates our proposed network structure, while Tab. 1 illustrates the efficiency of our proposed structure in memory usage and running time." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.816, + 0.634, + 0.833 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.84, + 0.688, + 0.857 + ], + "angle": 0, + "content": "4.1. Experimental setup" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.871, + 0.892, + 0.902 + ], + "angle": 0, + "content": "Datasets. We conduct experiments on the common datasets when benchmarking CREPS, including FFHQ, MetFaces," + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "22412" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.089, + 0.273, + 0.386 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.276, + 0.089, + 0.468, + 0.386 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.389, + 0.47, + 0.431 + ], + "angle": 0, + "content": "Figure 4. Sample images with our models trained on FFHQ (upper-left), LSUN-Church (upper-right), MetFace (bottom-left), and Flickr-Scenery (bottom-right)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.446, + 0.473, + 0.598 + ], + "angle": 0, + "content": "LSUN-Church, and Flickr-Scenery. FFHQ dataset contains 70k high-quality, diverse human faces collected from Flickr. We will use the FFHQ images with resolution \\(512 \\times 512\\). MetFaces is a small dataset of face drawings extracted from the collection of the Metropolitan Museum of Art, with a total of 1336 images at resolution \\(1024 \\times 1024\\). LSUN-Church consists of 126k outdoor photographs of churches at the resolution \\(256 \\times 256\\). Finally, Flickr-Scenery [7] is a landscape-centric dataset collected on Flickr with 50k images at resolution \\(256 \\times 256\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.606, + 0.473, + 0.849 + ], + "angle": 0, + "content": "Implementation. We use StyleGAN2 network design as a reference to implement CREPS. Except for the refinement module, our generator consists of 6 (for the target resolution 256) to 8 synthesis blocks (for the resolution 1024) and the same number of decoder blocks. We replace all modulated convolution layers in StyleGAN2 with modulated fully-connected ones. Unlike StyleGAN2, the output of each block is not an RGB image but a 32-channel bi-line feature with thickness \\( D = 8 \\). Each decoder is a stack of \\( P = 4 \\) pixel-wise fully-connected layers, with the channel widths ranging from 32 to 128. This setting is applied for all experiments, except for our ablation study. Similar to StyleGAN3 and CIPS, we turn off style mixing regularization. Besides that, we kept most of the other components unchanged, including the mapping network, discriminator, path length regularization, and \\( R_{1} \\) gradient penalty." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.856, + 0.472, + 0.903 + ], + "angle": 0, + "content": "Training. For FFHQ and LSUN-Church, our networks were trained from scratch until convergence. To verify the flexibility and scale consistency of CREPS on higher-" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.895, + 0.214 + ], + "angle": 0, + "content": "resolution image synthesis, we increase the length of its coordinate input to generate images at resolution \\(1024 \\times 1024\\) on the FFHQ dataset. We also test the adaptability of our network on domain shift by applying transfer learning from the weights trained on FFHQ to MetFaces. Our networks were trained by Adam optimizer with learning rate \\(2 \\times 10^{-3}\\) and hyperparameters \\(\\beta_0 = 0\\), \\(\\beta_1 = 0.99\\), and \\(\\epsilon = 10^{-8}\\). We use 4 NVIDIA A100 40GB GPUs for training all models." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.223, + 0.673, + 0.239 + ], + "angle": 0, + "content": "4.2. Image generation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.246, + 0.894, + 0.321 + ], + "angle": 0, + "content": "Tab. 2 compares the quality of images generated by our CREPS models with the standard spatial-convolution-based StyleGAN2 and the only scale-consistent any-scale image generation technique CIPS, using the Frechet Inception Distance (FID) score." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.322, + 0.895, + 0.519 + ], + "angle": 0, + "content": "At resolution \\(512 \\times 512\\) on FFHQ, our model achieves the FID score of 4.43, which is much better than the score from CIPS (6.18) and not far from StyleGAN2 (3.41). We can also use this model to generate images at resolution \\(1024 \\times 1024\\) without retraining and achieve a better FID score (4.09). We found that CIPS cannot be trained for this resolution due to its expensive memory usage, even with training batch size 1, when using its official code. However, the authors provided a pretrained model for FFHQ-1024 using a progressive training scheme (no released code). This CIPS model has an FID score of 10.07, much worse than ours. This confirms the superiority of our method over its scale-consistent image generation counterpart." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.519, + 0.895, + 0.595 + ], + "angle": 0, + "content": "On the MetFaces dataset, CREPS's FID score is 20.52, which is quite close to the score of StyleGAN2-Ada (18.22). As mentioned, CIPS fails to train on this \\(1024 \\times 1024\\) resolution using its official code. It confirms that bi-line representation does not constrain the adaptability of our model." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.595, + 0.895, + 0.701 + ], + "angle": 0, + "content": "On LSUN-Church and Flickr-Scenery, although the unstructured and diverse images in these datasets are intuitively adverse to column and row decomposition, CREPS obtains good results with only a small gap compared with StyleGAN2's ones. Note that CIPS achieves a surprisingly good result on LSUN-Church; it surpasses not only CREPS but also StyleGAN2 in this setting." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.701, + 0.895, + 0.747 + ], + "angle": 0, + "content": "Fig. 4 provides some samples synthesized by our networks on the benchmark datasets. As can be seen, CREPS produces highly realistic images in all cases." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.757, + 0.785, + 0.773 + ], + "angle": 0, + "content": "4.3. Generate arbitrary-scale images" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.895, + 0.903 + ], + "angle": 0, + "content": "While our models are trained on images with resolutions from \\(256 \\times 256\\) to \\(1024 \\times 1024\\), they can generate images at any scale. One way is that we simply scale the length of \\(e^r\\) and \\(e^c\\), and the output size is changed accordingly, thanks to our network design. With a V100 GPU (32GB), our models can generate an image up to resolution \\(3687 \\times 3687\\) in a single run. Or we can generate an image patch-by-patch with suitable coordinate inputs, then combine them together into" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "22413" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.147, + 0.089, + 0.821, + 0.154 + ], + "angle": 0, + "content": "
GeneratorFFHQ-512FFHQ-1024LSUN Church-256MetFaces-1024Scenery-256
StyleGANv23.412.843.8618.22*6.40
CIPS6.1810.07†2.92OOM8.49
CREPS (ours)4.434.09‡5.5020.527.21
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.158, + 0.894, + 0.201 + ], + "angle": 0, + "content": "Table 2. Comparison of our method against other works in FID metric. OOM means out-of-memory. \\*\\* means the result is taken from StyleGAN2-Ada paper [12]. \\(\\ddagger\\) means the model is provided without releasing its progressive training code. \\(\\ddagger\\) means the result is obtained by scaling the output resolution of the FFHQ-512 model." + }, + { + "type": "table", + "bbox": [ + 0.111, + 0.213, + 0.434, + 0.294 + ], + "angle": 0, + "content": "
PSNR ↑SSIM ↑LPIPS ↓
AnyresGAN24.190.730.07
ScaleParty24.500.700.08
CIPS33.330.930.05
CREPS34.650.960.01
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.298, + 0.47, + 0.326 + ], + "angle": 0, + "content": "Table 3. Scale consistency comparison of our method against three other works on PSNR, SSIM and LPIP. The best scores are bold." + }, + { + "type": "image", + "bbox": [ + 0.084, + 0.336, + 0.466, + 0.495 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.499, + 0.47, + 0.554 + ], + "angle": 0, + "content": "Figure 5. Qualitative results for the scale consistency experiment. For each method, we provide a sample generated \\(256 \\times 256\\) image (top) and the magnified \\((\\times 10)\\) residual map between it and the \\(512 \\times 512\\) rescaled version (bottom)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.567, + 0.47, + 0.658 + ], + "angle": 0, + "content": "a single gigantic image with no upper limit in the output size. We provide in the Supplementary some images generated at 6K resolution. While these images are not as sharp as real-world ultra-high-resolution images, they are much sharper than the ones generated at resolution \\(512 \\times 512\\) and then upscaled with Lanczos resampling." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.666, + 0.312, + 0.683 + ], + "angle": 0, + "content": "4.4. Image scaling consistency" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.69, + 0.469, + 0.854 + ], + "angle": 0, + "content": "In this section, we evaluate the scale consistency of images produced by CREPS and other methods, including AnyresGAN [4], ScaleParty [18], and CIPS [1]. We run this experiment using models trained on the FFHQ dataset. For each model, we first randomly generate 10k images at resolution \\(256 \\times 256\\) (first set). We then generate images with the same latent codes but at resolution \\(512 \\times 512\\) and downsample them to \\(256 \\times 256\\) (second set). The images in two sets are expected to be the same. Hence, we can compare two sets, with standard metrics such as PSNR, SSIM, and LPIPS, to measure each model's scale equivariance." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.47, + 0.901 + ], + "angle": 0, + "content": "Note that for ScaleParty and AnyresGAN, the pretrained weights are already trained with different resolutions at once, so we directly use their provided version. CIPS, how" + }, + { + "type": "table", + "bbox": [ + 0.502, + 0.213, + 0.898, + 0.324 + ], + "angle": 0, + "content": "
ConfigurationFIDMemoryTime
CREP-NB5.982.7GB0.13s
+ bi-line and d=111.371.5GB0.02s
+ bi-line and d=88.231.6GB0.03s
+ multiple decoders and d=46.461.6GB0.03s
+ multiple decoders and d=84.661.7GB0.04s
CIPS7.083.5GB0.05s
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.328, + 0.892, + 0.357 + ], + "angle": 0, + "content": "Table 4. Effects of the modifications of CREPS on the FFHQ dataset in terms of FID score, memory usage, and running time." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.381, + 0.892, + 0.456 + ], + "angle": 0, + "content": "ever, is trained in a single-scale setting, so we use the available weights trained at the highest resolution \\((1024 \\times 1024)\\) but pass the input coordinate with size \\(512 \\times 512\\) to synthesis image at resolution 512. As for CREPS, we simply use the weight trained at resolution \\(512 \\times 512\\)." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.457, + 0.892, + 0.518 + ], + "angle": 0, + "content": "We report the qualitative and quantitative results in Fig. 5 and Tab. 3. As can be seen, it is clear that CREPS achieves the best scale consistency, while convolution-based models like ScaleParty and AnyresGAN perform poorly." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.529, + 0.662, + 0.543 + ], + "angle": 0, + "content": "4.5. Ablation studies" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.553, + 0.892, + 0.719 + ], + "angle": 0, + "content": "To better understand our proposed techniques, we analyze the effect of different parts of CREPS on the FFHQ datasets. We first consider a no-bi-line version of CREPS as a baseline (referred to as CREPS-NB), with dense 2D input and the decoder layers removed. We then apply bi-line decomposition but fuse the bi-line features only once at the end, with gradually increased thickness. Lastly, we add multiple decoders for layer-wise feature composition as introduced in Sec. 3.4. Because of limited time and computational resources, we only evaluate on \\(128 \\times 128\\) resolution and all of our models were trained for maximum of 2 days." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.893, + 0.901 + ], + "angle": 0, + "content": "As the results in Tab. 4 show, CIPS performs worst in all three aspects compared with most of our models. Simply adding the bi-line with a single decoder at the end nearly halves the memory costs, but the FID score is still behind CREPS-NB even when the thickness is increased to \\( d = 8 \\). However, multiple decoders can help bring the image quality back to the level of CREPS-NB and even better with \\( d = 8 \\). In all settings, it can be clearly seen that we easily boost the FID score when increasing the thickness. These observations prove the importance and effectiveness of our proposed techniques. Remarkably, while the decoders seem compute-intensive, they are actually lightweight due to their" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "22414" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.08, + 0.088, + 0.47, + 0.162 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.166, + 0.47, + 0.208 + ], + "angle": 0, + "content": "Figure 6. Geometric transformations on the same target image (FFHQ-512 model) by changing the input coordinates. We mark the original image boundary using a red rectangle." + }, + { + "type": "image", + "bbox": [ + 0.079, + 0.221, + 0.47, + 0.306 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.309, + 0.469, + 0.339 + ], + "angle": 0, + "content": "Figure 7. Visualization of the feature maps extracted from our FFHQ-512 model. Each feature map is averaged over all channels." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.365, + 0.469, + 0.396 + ], + "angle": 0, + "content": "narrow width compared with other layers, causing only small increases in memory and time." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.417, + 0.469, + 0.433 + ], + "angle": 0, + "content": "4.6. Simple and complex geometric transformation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.444, + 0.47, + 0.626 + ], + "angle": 0, + "content": "Our CREPS model can support various geometric transformations on the same target image by keeping the input latent code \\( z \\) but changing the input coordinates \\( e^r \\) and \\( e^c \\). We can translate the image by adding coordinate shifts \\( \\delta_y \\) and \\( \\delta_x \\) to the row and column input coordinates, respectively. We can also multiply these input coordinates by the same constant \\( s > 1 \\) for zooming out or divide them by \\( s \\) for zooming in. As can be seen in the first three columns in Fig. 6, CREPS can perform those simple transformations with consistent details. Notably, CREPS can extrapolate the points outside the original image boundary, although it has never been trained on such input coordinates." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.629, + 0.471, + 0.902 + ], + "angle": 0, + "content": "It is tricky for CREPS to handle complex transformations such as rotation or distortion since CREPS only takes in a row and a column coordinate input. Instead of producing the target image in one run, we can execute CREPS multiple times to generate different parts of the output image, then combine them. The simplest algorithm is to sample each target pixel per run by setting a single value for \\( e^r \\) and \\( e^c \\). However, that algorithm is too slow, which requires 262k runs to produce a single \\( 512 \\times 512 \\) image. A faster way is to sample the target image row-by-row. Assuming we need to generate an image \\( I \\) with the input latent \\( z \\) and the target pixels' normalized coordinates \\( \\{(r_{ij}, c_{ij})\\}_{i = \\overline{1,H}, j = \\overline{1,W}} \\). We can produce each row \\( I_i \\) of the target image by generating an intermediate image \\( \\Gamma \\) using the input coordinates \\( e^r = [r_{ij}]_{j = \\overline{1,W}} \\) and \\( e^c = [c_{ij}]_{j = \\overline{1,W}} \\) and sample its diagonal \\( I_i = \\text{diag}(I') \\). We provide two examples with rotation and elastic distortion in the last two columns of Fig. 6. Both images are correctly transformed with unchanged content." + }, + { + "type": "image", + "bbox": [ + 0.505, + 0.089, + 0.89, + 0.162 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.166, + 0.892, + 0.221 + ], + "angle": 0, + "content": "Figure 8. Samples of the most common kinds of artifacts on different datasets. They are best described as repeating/wavy patterns, vertical symmetry, and glowing blobs. Left-most image is cropped and zoomed-in from a full-face image." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.23, + 0.663, + 0.245 + ], + "angle": 0, + "content": "4.7. Feature analysis" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.253, + 0.892, + 0.422 + ], + "angle": 0, + "content": "We visualize the key feature maps inside our FFHQ-512 model when generating a facial image and provide them in Fig. 7. The maps include the layer-wise composed features \\(\\{F^{(l)}\\}_{l = \\overline{1,N}}\\), the corresponding layer-wise fused maps \\(\\{E^{(l)}\\}_{l = \\overline{1,N}}\\), and the final feature map \\(F\\) (see Eq. 4-6). Thanks to the asymmetric fusion scheme, the model seems to synthesize the output in a coarse-to-fine manner. The early composed feature maps are smooth and focus on the global structure, while the later ones focus on sharp details. Although each composed feature map \\(F^{(l)}\\) is quite simple, the network can represent complex content by fusion." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.431, + 0.619, + 0.446 + ], + "angle": 0, + "content": "4.8. Limitation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.455, + 0.892, + 0.636 + ], + "angle": 0, + "content": "Being a fully-connected generator, CREPS shares the same limitation with other similar work, which is the lack of spatial bias since each pixel is independently generated. Hence, some spatial-related artifacts occasionally occur in our generated images (Fig. 8). A potential cause is the sine activation at the beginning, producing repeating patterns and vertical symmetry of the output. We also note that some samples contain a noticeable blob that is completely out-of-domain. We found CIPS facing the same problem, and the root cause can be the missing spatial guidance from neighboring pixels and the effect of Leaky-RELU activations which strengthens the isolation of some pixel regions." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.649, + 0.619, + 0.665 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.675, + 0.892, + 0.901 + ], + "angle": 0, + "content": "In this paper, we present a new architecture named CREPS, a cost-effective and scale-equivariant generator that can synthesize images with any target resolution. Our key contributions are an INR-based design, a thick biline representation, and a layer-wise feature composition scheme. While being more memory-efficient, our CREPS models can produce highly realistic images and surpass the INR-based model CIPS in most cases. CREPS also offers the best scale consistency by keeping image details unchanged when varying the output resolution. We conducted several experiments to explore some attractive properties of this fully-connected generator and discussed CREPS's applications in various scenarios. Future development of our approach can be eliminating artifacts mentioned in Sec. 4.8 and further improving the quality of our samples." + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "22415" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.115, + 0.47, + 0.184 + ], + "angle": 0, + "content": "[1] Ivan Anokhin, Kirill Demochkin, Taras Khakhulin, Gleb Sterkin, Victor Lempitsky, and Denis Korzhenkov. Image generators with conditionally-independent pixel synthesis. 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In IEEE/CVF Conference on Computer Vision and Pattern Recognition (CVPR), 2021. 2" + }, + { + "type": "list", + "bbox": [ + 0.08, + 0.092, + 0.47, + 0.248 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.946, + 0.519, + 0.957 + ], + "angle": 0, + "content": "22417" + } + ] +] \ No newline at end of file diff --git a/2023/Efficient Scale-Invariant Generator With Column-Row Entangled Pixel Synthesis/e82bfa76-118c-45c9-a6c3-50265e9de1a3_origin.pdf b/2023/Efficient Scale-Invariant Generator With Column-Row Entangled Pixel Synthesis/e82bfa76-118c-45c9-a6c3-50265e9de1a3_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..6455ca801cbcfb188d8aef3ac96953108a8115c3 --- /dev/null +++ b/2023/Efficient Scale-Invariant Generator With Column-Row Entangled Pixel Synthesis/e82bfa76-118c-45c9-a6c3-50265e9de1a3_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:371740b5a9c21158edaec73c78561650b656e5b6e5746b861499465388cd9569 +size 2099771 diff --git a/2023/Efficient Scale-Invariant Generator With Column-Row Entangled Pixel Synthesis/full.md b/2023/Efficient Scale-Invariant Generator With Column-Row Entangled Pixel Synthesis/full.md new file mode 100644 index 0000000000000000000000000000000000000000..52cce2727c0972bbd6fbd11d20395196a3e81d00 --- /dev/null +++ b/2023/Efficient Scale-Invariant Generator With Column-Row Entangled Pixel Synthesis/full.md @@ -0,0 +1,275 @@ +# Efficient Scale-Invariant Generator with Column-Row Entangled Pixel Synthesis + +Thuan Hoang Nguyen* Thanh Van Le* Anh Tran VinAI Research, Hanoi, Vietnam + +{v.thuannh5,v.thanhlv19,v.anhtt152}@vinai.io + +# Abstract + +Any-scale image synthesis offers an efficient and scalable solution to synthesize photo-realistic images at any scale, even going beyond $2K$ resolution. However, existing GAN-based solutions depend excessively on convolutions and a hierarchical architecture, which introduce inconsistency and the "texture sticking" issue when scaling the output resolution. From another perspective, INR-based generators are scale-equivariant by design, but their huge memory footprint and slow inference hinder these networks from being adopted in large-scale or real-time systems. In this work, we propose Column-Row Entangled Pixel Synthesis (CREPS), a new generative model that is both efficient and scale-equivariant without using any spatial convolutions or coarse-to-fine design. To save memory footprint and make the system scalable, we employ a novel bi-line representation that decomposes layer-wise feature maps into separate "thick" column and row encodings. Experiments on various datasets, including FFHQ, LSUN-Church, MetFaces, and Flickr-Scenery, confirm CREPS' ability to synthesize scale-consistent and alias-free images at any arbitrary resolution with proper training and inference speed. Code is available at https://github.com/VinAIResearch/CREPS. + +# 1. Introduction + +Generative Adversarial Networks (GANs) [8] are one of the most widely used structures for image generation and manipulation [2, 28]. Previously, a GAN model could only generate images with a fixed scale and layout as defined in the training dataset. However, natural images come with varying resolutions and contain unstructured objects at diverse poses. Therefore, designing a generative model that can handle more flexible geometric configurations is gaining more attention in the machine-learning community. StyleGAN3 [13] already supports out-of-the-box translation and rotation with consistent and artifact-free outputs. + +![](images/bd42e72e533db1418f6ecc5be53c18b7b781baddc447cb5f519b2087d695d56e.jpg) +Figure 1. Previous any-scale image synthesis networks, including AnyresGAN [4] and ScaleParty [18], produce inconsistent image details when changing the output scale (see zoomed-in patches). In contrast, our proposed network can produce the same details but sharper when increasing the scale. Check the supplemental video for a clearer comparison. + +![](images/4253c8e00e4c3d264c3ae87d891e846b3575bab2a0057a6586aa8d40652dcdb7.jpg) + +![](images/4ab75ebd8221edc2e6b85b0b093a9d295be5df37aa7a5012b12354fdd7b016af.jpg) + +Any-scale synthesis, however, remains under-explored. + +In this paper, we are interested in the task of arbitrary-scale image synthesis where a single generator can effortlessly synthesize images at many different scales while strongly preserving detail consistency. Such a model can be a promising research direction and bring many benefits. It enables synthesizing a high-resolution image from a lower-resolution training dataset. Hence, it eliminates the need for collecting and training models on high-resolution images, which is costly in storage, time, and computation resources. The output resolution can be ultra-high, e.g., $2048 \times 2048$ , which is impossible for standard GAN models due to the limit of GPU memory. Any-scale image synthesis also allows geometric interactions like zooming in and out. Despite promising results, previous works on this topic, such as AnyresGAN [4] and ScaleParty [18], show strong inconsistency when scaling the output resolution (see Fig. 1). + +We investigate the GAN structures to find the potential cause of the inconsistency at image scaling. Traditional GAN models are based on convolutional generators + +[3,15,20], which introduce an implicit spatial bias that helps the model to produce high-quality images. Recently, Xu et al. [29] and Karras et al. [13] discovered that these positional priors can hamper the model's consistency when applying translations, rotations, or scalings. In order to combat this issue, many works introduce non-trivial changes such as sophisticated architecture re-design [13] or opt for a better training strategy and input positional encoding [4,18]. However, these are only partial remedies as the output pixels still depend on their surroundings, making it impossible for these models to produce consistent attributes of an object regardless of positions and scales. + +In contrast to the traditional GANs, some recent methods are based on Implicit Neural Representation (INR) [1, 23]. By predicting the color of each pixel separately, INR-based GANs can, in theory, synthesize objects in a spatial-arbitrary manner and still achieve comparable quality at small to medium resolution compared to convolution-based approach. However, these models' memory usage grows quadratically with the input resolution since all pixels have to be queried. Thus, there has been no existing work that can efficiently scale INR-GANs to resolutions higher than 1024. To reduce training complexity, Anokhin et al. [1] employs a simple patch-based strategy where only a portion of pixels is generated and passed through the discriminator at a time. However, this approach unsurprisingly leads to poor results and inconsistency between patches. + +Inspired by the latter approach, we aim to tackle the task of scale-consistent image generation with essential changes to StyleGAN2 [15]. Similar to Anokhin et al. [1], we change the $3 \times 3$ convolutions to $1 \times 1$ ones and add a Fourier feature embedding [25] at the input layer. Although these two changes alone already achieve our goal, it is still expensive to train in high-resolution settings. Thus, instead of using dense 2D features, our model relies on a novel thick biline representation, which largely reduces the training and inference complexity by using two low-rank features for row and column. Our network first regresses these row and column embeddings, then composes layer-wise intermediate 2D features, and finally fuses these maps to produce the final output. We name this novel structure Column-Row Entangled Pixel Synthesis, or CREPS for short. + +We run a series of experiments on four datasets, including FFHQ, MetFaces, LSUN-Church, and Flickr-Scenery, to confirm the effectiveness of our proposed CREPS structure. Our model can synthesize images with quality comparable to the previous generative models like CIPS or StyleGAN2. While CIPS has trouble in training on images of resolutions more than $256 \times 256$ , CREPS can sufficiently handle training data at resolutions $512 \times 512$ and $1024 \times 1024$ . CREPS produces scale-equivariant images and keeps the object details unchanged when scaling the output resolution, unlike previous any-scale GANs such as AnyresGAN + +and ScaleParty. Using a CREPS model trained on $512 \times 512$ images, we still can generate near-realistic images at higher resolution. Finally, we demonstrate CREPS's ability to synthesize images with complex geometric transformations and distortions while preserving attribute consistency. + +To summarize our contributions: + +- We propose a simple and elegant network equipped with only modulated linear layers and no upsampling layers in-between. It supports scale-consistent outputs for any-scale image synthesis. +- To further improve efficiency, we introduce a thick bi-line representation, which decomposes 2D network features into two light-weight row and column embeddings. It significantly saves memory and computation costs compared with the full 2D-feature counterparts. +- We demonstrate competitive results for unconditional image synthesis on the FFHQ, LSUN-Church, Met-Faces, and Flickr-Scenery datasets, along with the ability to generate each image at arbitrary scales with consistent details. +- Our CREPS models support complex geometric transformations and distortions. + +# 2. Related Work + +Generative Adversarial Networks. Prior to denoising diffusion models [10, 24], GANs [8] hold state-of-the-art results for image synthesis tasks. The popular GAN models can generate realistic images at a high resolution, commonly up to $1024 \times 1024$ [3, 12-15]. The promising results obtained by GANs have motivated several applications of computer graphics and visual content generation. However, these networks are only capable of generating images with same geometric configurations, e.g., center-located and face-forward objects. Recently, an exciting work StyleGAN3 [13] aimed to generalize GAN to arbitrary translation and rotation with consistent details, or Anycost GAN [16] with multi-resolution generation. In the same vein, ScaleParty [18] and AnyresGAN [4] extended StyleGAN2 and StyleGAN3 to support scaling and other geometric transformations by replacing learned input constant with suitable positional encoding and multi-scale training strategy. However, these works did not consider the scale consistency, and their images showed varied details as the output scale increases, illustrated in Fig. 1. + +Implicit Neural Representation. Typically, images are represented by a series of 2D arrays of values. However, it can be viewed as a continuous mapping from a 2D coordinate $(x,y) \in \mathbf{R}^2$ to the corresponding RGB value $(r,g,b) \in \mathbf{R}^3$ and the mapping can be parameterized as a + +black-box model. This coordinate-wise modeling has been used in a wide range of neural rendering tasks [5,17,22,26], where neural networks are used to provide an efficient and continuous representation of data compared with traditional methods. In the literature, implicit neural networks mainly utilize fully-connected layers as their building blocks. Unlike convolution or self-attention, such layers' receptive field size is exactly one; in other words, the output at every coordinate is independent of each other. + +INR-based GANs. As the number of research increased, INR started to be used for generative tasks. These models soon inherited the success of GANs by employing the adversarial training manner. Generative radiance fields [6, 9, 19, 21] attempt to learn a view-consistent representation of 3D objects using implicit GAN. Despite all the success of INRs in 3D GANs, limited attention has been paid to utilizing the equivariance capability of fully-connected layers in 2D counterparts. The closest to our work are INRGAN [23] and CIPS [1]. Both these works use a grid of the target pixel coordinates as input for batch processing instead of passing each point individually. INR-GAN employs a multi-scale structure, which we will discuss later as a cause of scale inconsistency, while its uniform-scale versions have poor generation outputs. Meanwhile, CIPS does not need the multi-scale design thanks to its efficient weight modulation and expressive input embedding. The uniform-scale INR-GAN and CIPS disregard spatial convolutions in the generator and synthesize each pixel independently. However, their main goal is to investigate an alternative architecture that can compete with fully-convolutional GANs rather than paying attention to the equivariance characteristic of such models. They also struggle with expensive computation costs and memory usage using full-resolution 2D feature maps in processing. + +# 3. Proposed method + +This section describes our proposed CREPS structure. First, we recall the concept of any-scale image synthesis (Sec. 3.1). Then, we revise two existing GAN structures that support scale-equivariant image synthesis (Sec. 3.2). Next, we discuss how to reduce computation cost via the novel thick bi-line representation (Sec. 3.3). Finally, we describe the layer-wise feature composition scheme for improving the synthesis quality (Sec. 3.4). + +# 3.1. Any-scale image synthesis + +In this section, we introduce any-scale image synthesis as the task of generating images while enforcing consistency at different scales given a single model. One way we naturally come up with is generating an image at many scales altogether. MSG-GAN [11] is one of the earliest works in this approach. Instead of producing single output, + +MSG-GAN outputs an RGB image at each block of the generator, resulting in a mipmap representation [27]. However, this approach can only output pre-defined discrete scales, and there is no mechanism to guarantee scale consistency. + +As such, we should consider injecting positional encoding $e$ as an additional input alongside the latent code into the generator. This approach is employed in some previous works [1, 4, 18, 23], in which $e$ is a 2D grid of normalized $(x,y)$ coordinates. If $e$ is a regular grid, we can decompose it into two vectors for the row and column coordinates denoted as $e^r$ and $e^c$ , respectively. The image generation process now becomes: + +$$ +I = G \left(z, e ^ {r}, e ^ {c}\right), \tag {1} +$$ + +with $G$ is the generative model and $z$ is the latent input. The decomposition from $e$ to $e^r$ and $e^c$ is more suitable to our thick bi-line representation, as later discussed. Doing so allows us to easily control the output's scale and other spatial properties via appropriate input encoding. However, naively adding positional input into an existing generator does not guarantee that the output image is equivariant to the change in the input coordinates. For example, when Karras et al. [13] replace the learnable constant in StyleGAN2's input layer with Fourier features (Config B), the "texture sticking" issue still occurs. Therefore, proper network design and training strategy should be examined to alleviate the output's geometric inconsistency. + +# 3.2. Removing coarse-to-fine design and spatial convolution + +We investigate two network structures that support any resolution image generation, including AnyresGAN [4] and CIPS [1], when keeping the same latent input but gradually increasing the output resolution. The former is built upon StyleGAN3 [13] with additional scale information concatenated with the latent code and a multi-scale training scheme. In contrast, the latter changes the 3x3 convolution of StyleGAN2 with a point-wise one and adds learnable Fourier features at the beginning. Both models are capable of multiscale generation, but they have different behaviors that we will discuss below. + +As illustrated in Fig. 1, while having good photo-realism, AnyresGAN produces different image details at different scales. This can be explained by the fact that AnyresGAN, similar to most other GAN-based works, relies on spatial convolutions, such as 2D convolution with kernel size $3 \times 3$ and upsample layers. When changing the output resolution, the neighbor pixels at each location change, greatly varying the output of this spatial-convolution-based network. + +On the other hand, CIPS keeps the output image's details nearly the same regardless of resolution, thanks to its spatial-free building operators. CIPS, however, is very computationally expensive; this can be clearly shown in Tab. 1. + +![](images/98745f86b879f360b40f24a926f1c5ae118cf86e53e37867476b1334cfa2a051.jpg) +(a) Network structure +Figure 2. Our proposed CREPS structure + +![](images/08c8f57aa21075ae5fff4da4155d1094ecee81ec55ea4e319468330a7b339c19.jpg) +(b) Thick bi-line composition + +![](images/2371753f23e73f5dcf593c84b386f6593fd34c779afeebb33319e4d5cdfde3e4.jpg) +(c) Refinement block + +
ResolutionBatch sizeMemory UsageRunning time
StyleGAN2CIPSOursStyleGAN2CIPSOurs
256 × 25611.5GB3.3GB2.3GB0.04s0.06s0.03s
42.5GB10.2GB5.2GB0.05s0.23s0.06s
512 × 51211.7GB10.4GB4.5GB0.04s0.21s0.05s
43.4GBOOM14.6GB0.06sOOM0.16s
+ +Table 1. Memory usage and running time comparison between StyleGAN2, CIPS and our method. OOM means out-of-memory. + +When measured on a single NVIDIA V100 GPU (32 GB) and all models have comparable number of parameters, it runs slower than StyleGAN2 as well as requires much more memory or even gets an out-of-memory (OOM) error when running at $512 \times 512$ resolution. This makes CIPS inapplicable to use for learning fine details from high-resolution datasets. Moreover, it is worth noting that our method achieve the best trade-off between speed and memory. + +Based on the above observations, we implement CREPS without any spatial convolutions or coarse-to-fine design. Starting with StyleGAN2 [15], which consists of a mapping network and a generator, we remove all upsampling operators and replace all spatial convolutions with $1 \times 1$ convolutions, which are equivalent to pixel-wise fully-connected layers. Next, we replace the constant in the first synthesis block with Fourier encodings of the input coordinate row and column $e^r$ and $e^c$ . This design is quite similar to CIPS, with only two minor differences. Firstly, the dense 2D grid input is now split into two vectors representing the row and column. Secondly, we do not combine learned input constant with the Fourier feature like CIPS did, making our + +model simpler and more memory-friendly. While this initial network guarantees any-scale image synthesis with consistent image details, it faces the same memory issue as CIPS. We will discuss next how to solve this issue effectively. + +# 3.3. Thick bi-line representation + +Inspired by the tri-plane representation in [6], we propose to decompose each feature with 2D spatial dimensions into a column and a row embedding for a memory-efficient representation. For simplicity, let us drop the first two dimensions for the batch size $B$ and the number of channel $C$ , which are the same and element-wise processed for both the feature map and the mentioned embeddings. Let us denote the feature map as $F \in \mathbb{R}^{H \times W}$ , with $H$ and $W$ as the height and width, respectively. We can decompose $F$ to a row embedding $f^r$ and a column embedding $f^c$ . In the simplest form, $f^r$ and $f^c$ are 1D vectors with the lengths $H$ and $W$ , respectively. Each pixel in the feature map $F_{ij}$ , with $i$ and $j$ as the row and the column indices, can be computed as the product of the corresponding elements in $f^r$ and $f^c$ : + +$$ +F _ {i j} = f _ {i} ^ {r} f _ {j} ^ {c}. \tag {2} +$$ + +![](images/e66f352c0d2017d59ad5628ff9916cfdc0e01398c1d22fd6d0ad3345ad7aa1c0.jpg) +Figure 3. Fitting an input image to the thick bi-line representation in the image space. + +We call this representation "bi-line", which significantly reduces the memory usage and computation cost and allows the network to learn with high-resolution data. However, we found that this simple representation had a limited capacity and could not define complex structures. To enrich its representation power, we "thicken" the embeddings by adding an extra, short dimension. The revised $f^r$ and $f^c$ now have the shapes $H \times D$ and $W \times D$ , respectively, where $D \ll \min(H, W)$ is a uniform embedding "thickness". The composing feature element $F_{ij}$ is now the dot product of the corresponding elements in $f^r$ and $f^c$ : + +$$ +F _ {i j} = f _ {i} ^ {r} \cdot f _ {j} ^ {c} = \sum_ {d = 1} ^ {D} f _ {i d} ^ {r} f _ {j d} ^ {c}. \tag {3} +$$ + +This composition process is illustrated in Fig. 2b. In another perspective, this can be considered as a sum of $D$ different bi-line compositions. We call it "thick bi-line" representation. + +In Fig. 3, we provide a toy example illustrating the capacity of the proposed thick bi-line representation. Given an input image at resolution $512 \times 512 \times 3$ , we fit it into the proposed bi-line representation in the image space by optimizing a row and a column embedding of shape $512 \times D \times 3$ . Note that each channel is optimized independently. As can be seen, with the naive bi-linear composition ( $D = 1$ ), the reconstructed image is just a simple, incomprehensible grid. By adding just a small thickness $D = 8$ , we can capture the essential image content, recover the subject's identity, and reduce the MSE almost 6 times. When using $D = 32$ , we nearly recover the original image with only subtle pixel noise. Note that the row and column embeddings only take $1.56\%$ of the original image size when $D = 8$ and $12.5\%$ when $D = 32$ . This experiment confirms the efficacy of our proposed thick bi-line decomposition. Also, while this representation does not capture all details of the complex input image, it is more sufficient when modeling the overparameterized feature space. + +# 3.4. Layer-wise feature composition + +In CREPS, we assume the target output is square, i.e., $H = W$ . Hence, we can concatenate the row and column embeddings to a single tensor $f = [f^r, f^c] \in \mathbb{R}^{H \times 2D}$ . Initially, we implement CREPS by revising StyleGAN2's code to predict $f$ from the latent input $w$ via $N$ synthesis blocks. + +The network then splits $f$ to get the row and column codes, perform the feature composition defined in Eq. (3) to get a feature map $F$ . This feature map will be passed to a simple refinement module (Fig. 2c) with 2 synthesis blocks to produce the output image. For efficient memory and computation cost, we only employ a small thickness value $D = 8$ . + +We found this initial design needed to be more efficient to catch up with the generation quality of StyleGAN and CIPS. It performed feature composition once near the end of the image synthesis process; thus, the model power was bounded by the capacity of the thick bi-line representation. Instead, we revise our solution by employing a layer-wise feature composition scheme. Specially, at each layer with index $l \in [1..N]$ , we extract the intermediate row and column embedding $f^{(l)}$ . We can split $f^{(l)}$ and compose an intermediate feature map $F^{(l)}$ , following Eq. (3). Then, the intermediate maps across layers are fused to get the final map $F$ . This scheme enriches the representation power, similar to when increasing $D$ while using less memory. + +The fusion scheme is also important. Intuitively, we can set $F$ as the sum of the intermediate maps $\{F^{(l)}\}_{l = \overline{1,N}}$ . However, this formulation treats the maps equally, and we find it undesirable. Let us call back the StyleGAN models' behavior. Thanks to the coarse-to-fine design, their early layers learn to capture the global shape, while the later layers learn to synthesize fine details. Since CREPS has no coarse-to-fine structure, it is hard to control which aspect of the output image each layer can learn. Hence, we propose adding asymmetry to the feature map fusion process: the feature maps at earlier layers are processed "deeper" than those at later layers. We hope it implicitly guides the layers to learn information from global to regional order, similar to StyleGAN. To do so, we introduce at each layer with index $l$ a narrow decoder, denoted as $\pi^{(l)}$ . The process to fuse the intermediate maps $\{F^{(l)}\}_{l = \overline{1,N}}$ is defined as following: + +$$ +E ^ {(1)} \quad = F ^ {(1)}, \tag {4} +$$ + +$$ +E ^ {(l + 1)} = \pi^ {(l)} \left(E ^ {(l)}\right) + F ^ {(l + 1)} \quad \forall l \in [ 1, N - 1 ], \tag {5} +$$ + +$$ +F \quad = \pi^ {N} \left(E ^ {N}\right), \tag {6} +$$ + +with $E^{(l)}$ records the fused feature map at the $l^{th}$ layer. In our implementation, each decoder consists of pixelwise fully-connected layers with Leaky-RELU activations. Fig. 2a illustrates our proposed network structure, while Tab. 1 illustrates the efficiency of our proposed structure in memory usage and running time. + +# 4. Experiments + +# 4.1. Experimental setup + +Datasets. We conduct experiments on the common datasets when benchmarking CREPS, including FFHQ, MetFaces, + +![](images/dfd92940ee879e8774a5363b371738527084ae44a49173a38a7f08298a17a25a.jpg) +Figure 4. Sample images with our models trained on FFHQ (upper-left), LSUN-Church (upper-right), MetFace (bottom-left), and Flickr-Scenery (bottom-right). + +![](images/94f60fab2cc902e9b09c1c66ac5d30d119da998ac918b0c2f6680841000452a4.jpg) + +LSUN-Church, and Flickr-Scenery. FFHQ dataset contains 70k high-quality, diverse human faces collected from Flickr. We will use the FFHQ images with resolution $512 \times 512$ . MetFaces is a small dataset of face drawings extracted from the collection of the Metropolitan Museum of Art, with a total of 1336 images at resolution $1024 \times 1024$ . LSUN-Church consists of 126k outdoor photographs of churches at the resolution $256 \times 256$ . Finally, Flickr-Scenery [7] is a landscape-centric dataset collected on Flickr with 50k images at resolution $256 \times 256$ . + +Implementation. We use StyleGAN2 network design as a reference to implement CREPS. Except for the refinement module, our generator consists of 6 (for the target resolution 256) to 8 synthesis blocks (for the resolution 1024) and the same number of decoder blocks. We replace all modulated convolution layers in StyleGAN2 with modulated fully-connected ones. Unlike StyleGAN2, the output of each block is not an RGB image but a 32-channel bi-line feature with thickness $D = 8$ . Each decoder is a stack of $P = 4$ pixel-wise fully-connected layers, with the channel widths ranging from 32 to 128. This setting is applied for all experiments, except for our ablation study. Similar to StyleGAN3 and CIPS, we turn off style mixing regularization. Besides that, we kept most of the other components unchanged, including the mapping network, discriminator, path length regularization, and $R_{1}$ gradient penalty. + +Training. For FFHQ and LSUN-Church, our networks were trained from scratch until convergence. To verify the flexibility and scale consistency of CREPS on higher- + +resolution image synthesis, we increase the length of its coordinate input to generate images at resolution $1024 \times 1024$ on the FFHQ dataset. We also test the adaptability of our network on domain shift by applying transfer learning from the weights trained on FFHQ to MetFaces. Our networks were trained by Adam optimizer with learning rate $2 \times 10^{-3}$ and hyperparameters $\beta_0 = 0$ , $\beta_1 = 0.99$ , and $\epsilon = 10^{-8}$ . We use 4 NVIDIA A100 40GB GPUs for training all models. + +# 4.2. Image generation + +Tab. 2 compares the quality of images generated by our CREPS models with the standard spatial-convolution-based StyleGAN2 and the only scale-consistent any-scale image generation technique CIPS, using the Frechet Inception Distance (FID) score. + +At resolution $512 \times 512$ on FFHQ, our model achieves the FID score of 4.43, which is much better than the score from CIPS (6.18) and not far from StyleGAN2 (3.41). We can also use this model to generate images at resolution $1024 \times 1024$ without retraining and achieve a better FID score (4.09). We found that CIPS cannot be trained for this resolution due to its expensive memory usage, even with training batch size 1, when using its official code. However, the authors provided a pretrained model for FFHQ-1024 using a progressive training scheme (no released code). This CIPS model has an FID score of 10.07, much worse than ours. This confirms the superiority of our method over its scale-consistent image generation counterpart. + +On the MetFaces dataset, CREPS's FID score is 20.52, which is quite close to the score of StyleGAN2-Ada (18.22). As mentioned, CIPS fails to train on this $1024 \times 1024$ resolution using its official code. It confirms that bi-line representation does not constrain the adaptability of our model. + +On LSUN-Church and Flickr-Scenery, although the unstructured and diverse images in these datasets are intuitively adverse to column and row decomposition, CREPS obtains good results with only a small gap compared with StyleGAN2's ones. Note that CIPS achieves a surprisingly good result on LSUN-Church; it surpasses not only CREPS but also StyleGAN2 in this setting. + +Fig. 4 provides some samples synthesized by our networks on the benchmark datasets. As can be seen, CREPS produces highly realistic images in all cases. + +# 4.3. Generate arbitrary-scale images + +While our models are trained on images with resolutions from $256 \times 256$ to $1024 \times 1024$ , they can generate images at any scale. One way is that we simply scale the length of $e^r$ and $e^c$ , and the output size is changed accordingly, thanks to our network design. With a V100 GPU (32GB), our models can generate an image up to resolution $3687 \times 3687$ in a single run. Or we can generate an image patch-by-patch with suitable coordinate inputs, then combine them together into + +
GeneratorFFHQ-512FFHQ-1024LSUN Church-256MetFaces-1024Scenery-256
StyleGANv23.412.843.8618.22*6.40
CIPS6.1810.07†2.92OOM8.49
CREPS (ours)4.434.09‡5.5020.527.21
+ +Table 2. Comparison of our method against other works in FID metric. OOM means out-of-memory. \*\* means the result is taken from StyleGAN2-Ada paper [12]. $\ddagger$ means the model is provided without releasing its progressive training code. $\ddagger$ means the result is obtained by scaling the output resolution of the FFHQ-512 model. + +
PSNR ↑SSIM ↑LPIPS ↓
AnyresGAN24.190.730.07
ScaleParty24.500.700.08
CIPS33.330.930.05
CREPS34.650.960.01
+ +![](images/cc19668380b05f778c92502e1c7a778cf7311d8c1aa39778ce8f24ff595c6cca.jpg) +Figure 5. Qualitative results for the scale consistency experiment. For each method, we provide a sample generated $256 \times 256$ image (top) and the magnified $(\times 10)$ residual map between it and the $512 \times 512$ rescaled version (bottom). + +a single gigantic image with no upper limit in the output size. We provide in the Supplementary some images generated at 6K resolution. While these images are not as sharp as real-world ultra-high-resolution images, they are much sharper than the ones generated at resolution $512 \times 512$ and then upscaled with Lanczos resampling. + +# 4.4. Image scaling consistency + +In this section, we evaluate the scale consistency of images produced by CREPS and other methods, including AnyresGAN [4], ScaleParty [18], and CIPS [1]. We run this experiment using models trained on the FFHQ dataset. For each model, we first randomly generate 10k images at resolution $256 \times 256$ (first set). We then generate images with the same latent codes but at resolution $512 \times 512$ and downsample them to $256 \times 256$ (second set). The images in two sets are expected to be the same. Hence, we can compare two sets, with standard metrics such as PSNR, SSIM, and LPIPS, to measure each model's scale equivariance. + +Note that for ScaleParty and AnyresGAN, the pretrained weights are already trained with different resolutions at once, so we directly use their provided version. CIPS, how + +Table 3. Scale consistency comparison of our method against three other works on PSNR, SSIM and LPIP. The best scores are bold. + +
ConfigurationFIDMemoryTime
CREP-NB5.982.7GB0.13s
+ bi-line and d=111.371.5GB0.02s
+ bi-line and d=88.231.6GB0.03s
+ multiple decoders and d=46.461.6GB0.03s
+ multiple decoders and d=84.661.7GB0.04s
CIPS7.083.5GB0.05s
+ +Table 4. Effects of the modifications of CREPS on the FFHQ dataset in terms of FID score, memory usage, and running time. + +ever, is trained in a single-scale setting, so we use the available weights trained at the highest resolution $(1024 \times 1024)$ but pass the input coordinate with size $512 \times 512$ to synthesis image at resolution 512. As for CREPS, we simply use the weight trained at resolution $512 \times 512$ . + +We report the qualitative and quantitative results in Fig. 5 and Tab. 3. As can be seen, it is clear that CREPS achieves the best scale consistency, while convolution-based models like ScaleParty and AnyresGAN perform poorly. + +# 4.5. Ablation studies + +To better understand our proposed techniques, we analyze the effect of different parts of CREPS on the FFHQ datasets. We first consider a no-bi-line version of CREPS as a baseline (referred to as CREPS-NB), with dense 2D input and the decoder layers removed. We then apply bi-line decomposition but fuse the bi-line features only once at the end, with gradually increased thickness. Lastly, we add multiple decoders for layer-wise feature composition as introduced in Sec. 3.4. Because of limited time and computational resources, we only evaluate on $128 \times 128$ resolution and all of our models were trained for maximum of 2 days. + +As the results in Tab. 4 show, CIPS performs worst in all three aspects compared with most of our models. Simply adding the bi-line with a single decoder at the end nearly halves the memory costs, but the FID score is still behind CREPS-NB even when the thickness is increased to $d = 8$ . However, multiple decoders can help bring the image quality back to the level of CREPS-NB and even better with $d = 8$ . In all settings, it can be clearly seen that we easily boost the FID score when increasing the thickness. These observations prove the importance and effectiveness of our proposed techniques. Remarkably, while the decoders seem compute-intensive, they are actually lightweight due to their + +![](images/3f77bd13a279a27efdf02f49ee855f50fe39da7f0224b4d9f168849af722367d.jpg) +Figure 6. Geometric transformations on the same target image (FFHQ-512 model) by changing the input coordinates. We mark the original image boundary using a red rectangle. + +![](images/5c2e38cd25cae7a40f75499f2e0e2f7660ac49426f87b5939fbfb5f240201e22.jpg) +Figure 7. Visualization of the feature maps extracted from our FFHQ-512 model. Each feature map is averaged over all channels. + +narrow width compared with other layers, causing only small increases in memory and time. + +# 4.6. Simple and complex geometric transformation + +Our CREPS model can support various geometric transformations on the same target image by keeping the input latent code $z$ but changing the input coordinates $e^r$ and $e^c$ . We can translate the image by adding coordinate shifts $\delta_y$ and $\delta_x$ to the row and column input coordinates, respectively. We can also multiply these input coordinates by the same constant $s > 1$ for zooming out or divide them by $s$ for zooming in. As can be seen in the first three columns in Fig. 6, CREPS can perform those simple transformations with consistent details. Notably, CREPS can extrapolate the points outside the original image boundary, although it has never been trained on such input coordinates. + +It is tricky for CREPS to handle complex transformations such as rotation or distortion since CREPS only takes in a row and a column coordinate input. Instead of producing the target image in one run, we can execute CREPS multiple times to generate different parts of the output image, then combine them. The simplest algorithm is to sample each target pixel per run by setting a single value for $e^r$ and $e^c$ . However, that algorithm is too slow, which requires 262k runs to produce a single $512 \times 512$ image. A faster way is to sample the target image row-by-row. Assuming we need to generate an image $I$ with the input latent $z$ and the target pixels' normalized coordinates $\{(r_{ij}, c_{ij})\}_{i = \overline{1,H}, j = \overline{1,W}}$ . We can produce each row $I_i$ of the target image by generating an intermediate image $\Gamma$ using the input coordinates $e^r = [r_{ij}]_{j = \overline{1,W}}$ and $e^c = [c_{ij}]_{j = \overline{1,W}}$ and sample its diagonal $I_i = \text{diag}(I')$ . We provide two examples with rotation and elastic distortion in the last two columns of Fig. 6. Both images are correctly transformed with unchanged content. + +![](images/94eb2199e186794db439e0125a038f740310a39b1f8fe1ada6b3676fc283a002.jpg) +Figure 8. Samples of the most common kinds of artifacts on different datasets. They are best described as repeating/wavy patterns, vertical symmetry, and glowing blobs. Left-most image is cropped and zoomed-in from a full-face image. + +# 4.7. Feature analysis + +We visualize the key feature maps inside our FFHQ-512 model when generating a facial image and provide them in Fig. 7. The maps include the layer-wise composed features $\{F^{(l)}\}_{l = \overline{1,N}}$ , the corresponding layer-wise fused maps $\{E^{(l)}\}_{l = \overline{1,N}}$ , and the final feature map $F$ (see Eq. 4-6). Thanks to the asymmetric fusion scheme, the model seems to synthesize the output in a coarse-to-fine manner. The early composed feature maps are smooth and focus on the global structure, while the later ones focus on sharp details. Although each composed feature map $F^{(l)}$ is quite simple, the network can represent complex content by fusion. + +# 4.8. Limitation + +Being a fully-connected generator, CREPS shares the same limitation with other similar work, which is the lack of spatial bias since each pixel is independently generated. Hence, some spatial-related artifacts occasionally occur in our generated images (Fig. 8). A potential cause is the sine activation at the beginning, producing repeating patterns and vertical symmetry of the output. We also note that some samples contain a noticeable blob that is completely out-of-domain. We found CIPS facing the same problem, and the root cause can be the missing spatial guidance from neighboring pixels and the effect of Leaky-RELU activations which strengthens the isolation of some pixel regions. + +# 5. Conclusion + +In this paper, we present a new architecture named CREPS, a cost-effective and scale-equivariant generator that can synthesize images with any target resolution. Our key contributions are an INR-based design, a thick biline representation, and a layer-wise feature composition scheme. While being more memory-efficient, our CREPS models can produce highly realistic images and surpass the INR-based model CIPS in most cases. CREPS also offers the best scale consistency by keeping image details unchanged when varying the output resolution. We conducted several experiments to explore some attractive properties of this fully-connected generator and discussed CREPS's applications in various scenarios. Future development of our approach can be eliminating artifacts mentioned in Sec. 4.8 and further improving the quality of our samples. + +# References + +[1] Ivan Anokhin, Kirill Demochkin, Taras Khakhulin, Gleb Sterkin, Victor Lempitsky, and Denis Korzhenkov. Image generators with conditionally-independent pixel synthesis. In IEEE/CVF Conference on Computer Vision and Pattern Recognition (CVPR), 2021. 2, 3, 7 +[2] A.H. Bermano, R. Gal, Y. Alaluf, R. 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However, existing GAN-based solutions depend excessively on convolutions and a hierarchical architecture, which introduce inconsistency and the \"texture sticking\" issue when scaling the output resolution. From another perspective, INR-based generators are scale-equivariant by design, but their huge memory footprint and slow inference hinder these networks from being adopted in large-scale or real-time systems. In this work, we propose Column-Row Entangled Pixel Synthesis (CREPS), a new generative model that is both efficient and scale-equivariant without using any spatial convolutions or coarse-to-fine design. To save memory footprint and make the system scalable, we employ a novel bi-line representation that decomposes layer-wise feature maps into separate \"thick\" column and row encodings. Experiments on various datasets, including FFHQ, LSUN-Church, MetFaces, and Flickr-Scenery, confirm CREPS' ability to synthesize scale-consistent and alias-free images at any arbitrary resolution with proper training and inference speed. Code is available at https://github.com/VinAIResearch/CREPS." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 539, + 128, + 552 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 539, + 128, + 552 + ], + "spans": [ + { + "bbox": [ + 47, + 539, + 128, + 552 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 559, + 287, + 693 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 559, + 287, + 693 + ], + "spans": [ + { + "bbox": [ + 46, + 559, + 287, + 693 + ], + "type": "text", + "content": "Generative Adversarial Networks (GANs) [8] are one of the most widely used structures for image generation and manipulation [2, 28]. Previously, a GAN model could only generate images with a fixed scale and layout as defined in the training dataset. However, natural images come with varying resolutions and contain unstructured objects at diverse poses. Therefore, designing a generative model that can handle more flexible geometric configurations is gaining more attention in the machine-learning community. StyleGAN3 [13] already supports out-of-the-box translation and rotation with consistent and artifact-free outputs." + } + ] + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 306, + 211, + 388, + 388 + ], + "blocks": [ + { + "bbox": [ + 306, + 211, + 388, + 388 + ], + "lines": [ + { + "bbox": [ + 306, + 211, + 388, + 388 + ], + "spans": [ + { + "bbox": [ + 306, + 211, + 388, + 388 + ], + "type": "image", + "image_path": "bd42e72e533db1418f6ecc5be53c18b7b781baddc447cb5f519b2087d695d56e.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 392, + 546, + 458 + ], + "lines": [ + { + "bbox": [ + 305, + 392, + 546, + 458 + ], + "spans": [ + { + "bbox": [ + 305, + 392, + 546, + 458 + ], + "type": "text", + "content": "Figure 1. Previous any-scale image synthesis networks, including AnyresGAN [4] and ScaleParty [18], produce inconsistent image details when changing the output scale (see zoomed-in patches). In contrast, our proposed network can produce the same details but sharper when increasing the scale. Check the supplemental video for a clearer comparison." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 399, + 211, + 465, + 389 + ], + "blocks": [ + { + "bbox": [ + 399, + 211, + 465, + 389 + ], + "lines": [ + { + "bbox": [ + 399, + 211, + 465, + 389 + ], + "spans": [ + { + "bbox": [ + 399, + 211, + 465, + 389 + ], + "type": "image", + "image_path": "4253c8e00e4c3d264c3ae87d891e846b3575bab2a0057a6586aa8d40652dcdb7.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 479, + 211, + 545, + 389 + ], + "blocks": [ + { + "bbox": [ + 479, + 211, + 545, + 389 + ], + "lines": [ + { + "bbox": [ + 479, + 211, + 545, + 389 + ], + "spans": [ + { + "bbox": [ + 479, + 211, + 545, + 389 + ], + "type": "image", + "image_path": "4ab75ebd8221edc2e6b85b0b093a9d295be5df37aa7a5012b12354fdd7b016af.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 472, + 529, + 483 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 472, + 529, + 483 + ], + "spans": [ + { + "bbox": [ + 306, + 472, + 529, + 483 + ], + "type": "text", + "content": "Any-scale synthesis, however, remains under-explored." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 484, + 546, + 675 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 484, + 546, + 675 + ], + "spans": [ + { + "bbox": [ + 304, + 484, + 546, + 675 + ], + "type": "text", + "content": "In this paper, we are interested in the task of arbitrary-scale image synthesis where a single generator can effortlessly synthesize images at many different scales while strongly preserving detail consistency. Such a model can be a promising research direction and bring many benefits. It enables synthesizing a high-resolution image from a lower-resolution training dataset. Hence, it eliminates the need for collecting and training models on high-resolution images, which is costly in storage, time, and computation resources. The output resolution can be ultra-high, e.g., " + }, + { + "bbox": [ + 304, + 484, + 546, + 675 + ], + "type": "inline_equation", + "content": "2048 \\times 2048" + }, + { + "bbox": [ + 304, + 484, + 546, + 675 + ], + "type": "text", + "content": ", which is impossible for standard GAN models due to the limit of GPU memory. Any-scale image synthesis also allows geometric interactions like zooming in and out. Despite promising results, previous works on this topic, such as AnyresGAN [4] and ScaleParty [18], show strong inconsistency when scaling the output resolution (see Fig. 1)." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 677, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 677, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 677, + 545, + 713 + ], + "type": "text", + "content": "We investigate the GAN structures to find the potential cause of the inconsistency at image scaling. Traditional GAN models are based on convolutional generators" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 62, + 703, + 129, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 62, + 703, + 129, + 712 + ], + "spans": [ + { + "bbox": [ + 62, + 703, + 129, + 712 + ], + "type": "text", + "content": "*Equal contribution." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "22408" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 216 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 216 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 216 + ], + "type": "text", + "content": "[3,15,20], which introduce an implicit spatial bias that helps the model to produce high-quality images. Recently, Xu et al. [29] and Karras et al. [13] discovered that these positional priors can hamper the model's consistency when applying translations, rotations, or scalings. In order to combat this issue, many works introduce non-trivial changes such as sophisticated architecture re-design [13] or opt for a better training strategy and input positional encoding [4,18]. However, these are only partial remedies as the output pixels still depend on their surroundings, making it impossible for these models to produce consistent attributes of an object regardless of positions and scales." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 218, + 289, + 397 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 218, + 289, + 397 + ], + "spans": [ + { + "bbox": [ + 46, + 218, + 289, + 397 + ], + "type": "text", + "content": "In contrast to the traditional GANs, some recent methods are based on Implicit Neural Representation (INR) [1, 23]. By predicting the color of each pixel separately, INR-based GANs can, in theory, synthesize objects in a spatial-arbitrary manner and still achieve comparable quality at small to medium resolution compared to convolution-based approach. However, these models' memory usage grows quadratically with the input resolution since all pixels have to be queried. Thus, there has been no existing work that can efficiently scale INR-GANs to resolutions higher than 1024. To reduce training complexity, Anokhin et al. [1] employs a simple patch-based strategy where only a portion of pixels is generated and passed through the discriminator at a time. However, this approach unsurprisingly leads to poor results and inconsistency between patches." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 400, + 289, + 579 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 400, + 289, + 579 + ], + "spans": [ + { + "bbox": [ + 46, + 400, + 289, + 579 + ], + "type": "text", + "content": "Inspired by the latter approach, we aim to tackle the task of scale-consistent image generation with essential changes to StyleGAN2 [15]. Similar to Anokhin et al. [1], we change the " + }, + { + "bbox": [ + 46, + 400, + 289, + 579 + ], + "type": "inline_equation", + "content": "3 \\times 3" + }, + { + "bbox": [ + 46, + 400, + 289, + 579 + ], + "type": "text", + "content": " convolutions to " + }, + { + "bbox": [ + 46, + 400, + 289, + 579 + ], + "type": "inline_equation", + "content": "1 \\times 1" + }, + { + "bbox": [ + 46, + 400, + 289, + 579 + ], + "type": "text", + "content": " ones and add a Fourier feature embedding [25] at the input layer. Although these two changes alone already achieve our goal, it is still expensive to train in high-resolution settings. Thus, instead of using dense 2D features, our model relies on a novel thick biline representation, which largely reduces the training and inference complexity by using two low-rank features for row and column. Our network first regresses these row and column embeddings, then composes layer-wise intermediate 2D features, and finally fuses these maps to produce the final output. We name this novel structure Column-Row Entangled Pixel Synthesis, or CREPS for short." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "text", + "content": "We run a series of experiments on four datasets, including FFHQ, MetFaces, LSUN-Church, and Flickr-Scenery, to confirm the effectiveness of our proposed CREPS structure. Our model can synthesize images with quality comparable to the previous generative models like CIPS or StyleGAN2. While CIPS has trouble in training on images of resolutions more than " + }, + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "inline_equation", + "content": "256 \\times 256" + }, + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "text", + "content": ", CREPS can sufficiently handle training data at resolutions " + }, + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "inline_equation", + "content": "512 \\times 512" + }, + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "inline_equation", + "content": "1024 \\times 1024" + }, + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "text", + "content": ". CREPS produces scale-equivariant images and keeps the object details unchanged when scaling the output resolution, unlike previous any-scale GANs such as AnyresGAN" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 304, + 72, + 547, + 133 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 133 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 133 + ], + "type": "text", + "content": "and ScaleParty. Using a CREPS model trained on " + }, + { + "bbox": [ + 304, + 72, + 547, + 133 + ], + "type": "inline_equation", + "content": "512 \\times 512" + }, + { + "bbox": [ + 304, + 72, + 547, + 133 + ], + "type": "text", + "content": " images, we still can generate near-realistic images at higher resolution. Finally, we demonstrate CREPS's ability to synthesize images with complex geometric transformations and distortions while preserving attribute consistency." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 317, + 133, + 451, + 144 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 133, + 451, + 144 + ], + "spans": [ + { + "bbox": [ + 317, + 133, + 451, + 144 + ], + "type": "text", + "content": "To summarize our contributions:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 317, + 153, + 545, + 371 + ], + "type": "list", + "angle": 0, + "index": 10, + "blocks": [ + { + "bbox": [ + 317, + 153, + 545, + 201 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 153, + 545, + 201 + ], + "spans": [ + { + "bbox": [ + 317, + 153, + 545, + 201 + ], + "type": "text", + "content": "- We propose a simple and elegant network equipped with only modulated linear layers and no upsampling layers in-between. It supports scale-consistent outputs for any-scale image synthesis." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 317, + 209, + 545, + 270 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 209, + 545, + 270 + ], + "spans": [ + { + "bbox": [ + 317, + 209, + 545, + 270 + ], + "type": "text", + "content": "- To further improve efficiency, we introduce a thick bi-line representation, which decomposes 2D network features into two light-weight row and column embeddings. It significantly saves memory and computation costs compared with the full 2D-feature counterparts." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 317, + 278, + 545, + 338 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 278, + 545, + 338 + ], + "spans": [ + { + "bbox": [ + 317, + 278, + 545, + 338 + ], + "type": "text", + "content": "- We demonstrate competitive results for unconditional image synthesis on the FFHQ, LSUN-Church, Met-Faces, and Flickr-Scenery datasets, along with the ability to generate each image at arbitrary scales with consistent details." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 317, + 347, + 545, + 371 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 347, + 545, + 371 + ], + "spans": [ + { + "bbox": [ + 317, + 347, + 545, + 371 + ], + "type": "text", + "content": "- Our CREPS models support complex geometric transformations and distortions." + } + ] + } + ], + "index": 9 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 306, + 383, + 392, + 396 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 383, + 392, + 396 + ], + "spans": [ + { + "bbox": [ + 306, + 383, + 392, + 396 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 408, + 545, + 649 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 408, + 545, + 649 + ], + "spans": [ + { + "bbox": [ + 304, + 408, + 545, + 649 + ], + "type": "text", + "content": "Generative Adversarial Networks. Prior to denoising diffusion models [10, 24], GANs [8] hold state-of-the-art results for image synthesis tasks. The popular GAN models can generate realistic images at a high resolution, commonly up to " + }, + { + "bbox": [ + 304, + 408, + 545, + 649 + ], + "type": "inline_equation", + "content": "1024 \\times 1024" + }, + { + "bbox": [ + 304, + 408, + 545, + 649 + ], + "type": "text", + "content": " [3, 12-15]. The promising results obtained by GANs have motivated several applications of computer graphics and visual content generation. However, these networks are only capable of generating images with same geometric configurations, e.g., center-located and face-forward objects. Recently, an exciting work StyleGAN3 [13] aimed to generalize GAN to arbitrary translation and rotation with consistent details, or Anycost GAN [16] with multi-resolution generation. In the same vein, ScaleParty [18] and AnyresGAN [4] extended StyleGAN2 and StyleGAN3 to support scaling and other geometric transformations by replacing learned input constant with suitable positional encoding and multi-scale training strategy. However, these works did not consider the scale consistency, and their images showed varied details as the output scale increases, illustrated in Fig. 1." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 654, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 654, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 654, + 547, + 715 + ], + "type": "text", + "content": "Implicit Neural Representation. Typically, images are represented by a series of 2D arrays of values. However, it can be viewed as a continuous mapping from a 2D coordinate " + }, + { + "bbox": [ + 304, + 654, + 547, + 715 + ], + "type": "inline_equation", + "content": "(x,y) \\in \\mathbf{R}^2" + }, + { + "bbox": [ + 304, + 654, + 547, + 715 + ], + "type": "text", + "content": " to the corresponding RGB value " + }, + { + "bbox": [ + 304, + 654, + 547, + 715 + ], + "type": "inline_equation", + "content": "(r,g,b) \\in \\mathbf{R}^3" + }, + { + "bbox": [ + 304, + 654, + 547, + 715 + ], + "type": "text", + "content": " and the mapping can be parameterized as a" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "22409" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 180 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 180 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 180 + ], + "type": "text", + "content": "black-box model. This coordinate-wise modeling has been used in a wide range of neural rendering tasks [5,17,22,26], where neural networks are used to provide an efficient and continuous representation of data compared with traditional methods. In the literature, implicit neural networks mainly utilize fully-connected layers as their building blocks. Unlike convolution or self-attention, such layers' receptive field size is exactly one; in other words, the output at every coordinate is independent of each other." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 186, + 289, + 485 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 186, + 289, + 485 + ], + "spans": [ + { + "bbox": [ + 46, + 186, + 289, + 485 + ], + "type": "text", + "content": "INR-based GANs. As the number of research increased, INR started to be used for generative tasks. These models soon inherited the success of GANs by employing the adversarial training manner. Generative radiance fields [6, 9, 19, 21] attempt to learn a view-consistent representation of 3D objects using implicit GAN. Despite all the success of INRs in 3D GANs, limited attention has been paid to utilizing the equivariance capability of fully-connected layers in 2D counterparts. The closest to our work are INRGAN [23] and CIPS [1]. Both these works use a grid of the target pixel coordinates as input for batch processing instead of passing each point individually. INR-GAN employs a multi-scale structure, which we will discuss later as a cause of scale inconsistency, while its uniform-scale versions have poor generation outputs. Meanwhile, CIPS does not need the multi-scale design thanks to its efficient weight modulation and expressive input embedding. The uniform-scale INR-GAN and CIPS disregard spatial convolutions in the generator and synthesize each pixel independently. However, their main goal is to investigate an alternative architecture that can compete with fully-convolutional GANs rather than paying attention to the equivariance characteristic of such models. They also struggle with expensive computation costs and memory usage using full-resolution 2D feature maps in processing." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 498, + 151, + 510 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 498, + 151, + 510 + ], + "spans": [ + { + "bbox": [ + 47, + 498, + 151, + 510 + ], + "type": "text", + "content": "3. Proposed method" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 518, + 287, + 615 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 518, + 287, + 615 + ], + "spans": [ + { + "bbox": [ + 46, + 518, + 287, + 615 + ], + "type": "text", + "content": "This section describes our proposed CREPS structure. First, we recall the concept of any-scale image synthesis (Sec. 3.1). Then, we revise two existing GAN structures that support scale-equivariant image synthesis (Sec. 3.2). Next, we discuss how to reduce computation cost via the novel thick bi-line representation (Sec. 3.3). Finally, we describe the layer-wise feature composition scheme for improving the synthesis quality (Sec. 3.4)." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 623, + 191, + 635 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 623, + 191, + 635 + ], + "spans": [ + { + "bbox": [ + 47, + 623, + 191, + 635 + ], + "type": "text", + "content": "3.1. Any-scale image synthesis" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 642, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 642, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 642, + 287, + 715 + ], + "type": "text", + "content": "In this section, we introduce any-scale image synthesis as the task of generating images while enforcing consistency at different scales given a single model. One way we naturally come up with is generating an image at many scales altogether. MSG-GAN [11] is one of the earliest works in this approach. Instead of producing single output," + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "text", + "content": "MSG-GAN outputs an RGB image at each block of the generator, resulting in a mipmap representation [27]. However, this approach can only output pre-defined discrete scales, and there is no mechanism to guarantee scale consistency." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 121, + 547, + 215 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 121, + 547, + 215 + ], + "spans": [ + { + "bbox": [ + 304, + 121, + 547, + 215 + ], + "type": "text", + "content": "As such, we should consider injecting positional encoding " + }, + { + "bbox": [ + 304, + 121, + 547, + 215 + ], + "type": "inline_equation", + "content": "e" + }, + { + "bbox": [ + 304, + 121, + 547, + 215 + ], + "type": "text", + "content": " as an additional input alongside the latent code into the generator. This approach is employed in some previous works [1, 4, 18, 23], in which " + }, + { + "bbox": [ + 304, + 121, + 547, + 215 + ], + "type": "inline_equation", + "content": "e" + }, + { + "bbox": [ + 304, + 121, + 547, + 215 + ], + "type": "text", + "content": " is a 2D grid of normalized " + }, + { + "bbox": [ + 304, + 121, + 547, + 215 + ], + "type": "inline_equation", + "content": "(x,y)" + }, + { + "bbox": [ + 304, + 121, + 547, + 215 + ], + "type": "text", + "content": " coordinates. If " + }, + { + "bbox": [ + 304, + 121, + 547, + 215 + ], + "type": "inline_equation", + "content": "e" + }, + { + "bbox": [ + 304, + 121, + 547, + 215 + ], + "type": "text", + "content": " is a regular grid, we can decompose it into two vectors for the row and column coordinates denoted as " + }, + { + "bbox": [ + 304, + 121, + 547, + 215 + ], + "type": "inline_equation", + "content": "e^r" + }, + { + "bbox": [ + 304, + 121, + 547, + 215 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 121, + 547, + 215 + ], + "type": "inline_equation", + "content": "e^c" + }, + { + "bbox": [ + 304, + 121, + 547, + 215 + ], + "type": "text", + "content": ", respectively. The image generation process now becomes:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 389, + 224, + 545, + 237 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 389, + 224, + 545, + 237 + ], + "spans": [ + { + "bbox": [ + 389, + 224, + 545, + 237 + ], + "type": "interline_equation", + "content": "I = G \\left(z, e ^ {r}, e ^ {c}\\right), \\tag {1}", + "image_path": "2bbde4c7978ef246cb75bb2f159d12a36ff04599e691f08fed1f2ed7bf948854.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 245, + 545, + 401 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 245, + 545, + 401 + ], + "spans": [ + { + "bbox": [ + 304, + 245, + 545, + 401 + ], + "type": "text", + "content": "with " + }, + { + "bbox": [ + 304, + 245, + 545, + 401 + ], + "type": "inline_equation", + "content": "G" + }, + { + "bbox": [ + 304, + 245, + 545, + 401 + ], + "type": "text", + "content": " is the generative model and " + }, + { + "bbox": [ + 304, + 245, + 545, + 401 + ], + "type": "inline_equation", + "content": "z" + }, + { + "bbox": [ + 304, + 245, + 545, + 401 + ], + "type": "text", + "content": " is the latent input. The decomposition from " + }, + { + "bbox": [ + 304, + 245, + 545, + 401 + ], + "type": "inline_equation", + "content": "e" + }, + { + "bbox": [ + 304, + 245, + 545, + 401 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 304, + 245, + 545, + 401 + ], + "type": "inline_equation", + "content": "e^r" + }, + { + "bbox": [ + 304, + 245, + 545, + 401 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 245, + 545, + 401 + ], + "type": "inline_equation", + "content": "e^c" + }, + { + "bbox": [ + 304, + 245, + 545, + 401 + ], + "type": "text", + "content": " is more suitable to our thick bi-line representation, as later discussed. Doing so allows us to easily control the output's scale and other spatial properties via appropriate input encoding. However, naively adding positional input into an existing generator does not guarantee that the output image is equivariant to the change in the input coordinates. For example, when Karras et al. [13] replace the learnable constant in StyleGAN2's input layer with Fourier features (Config B), the \"texture sticking\" issue still occurs. Therefore, proper network design and training strategy should be examined to alleviate the output's geometric inconsistency." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 408, + 545, + 432 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 408, + 545, + 432 + ], + "spans": [ + { + "bbox": [ + 305, + 408, + 545, + 432 + ], + "type": "text", + "content": "3.2. Removing coarse-to-fine design and spatial convolution" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 438, + 545, + 568 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 438, + 545, + 568 + ], + "spans": [ + { + "bbox": [ + 304, + 438, + 545, + 568 + ], + "type": "text", + "content": "We investigate two network structures that support any resolution image generation, including AnyresGAN [4] and CIPS [1], when keeping the same latent input but gradually increasing the output resolution. The former is built upon StyleGAN3 [13] with additional scale information concatenated with the latent code and a multi-scale training scheme. In contrast, the latter changes the 3x3 convolution of StyleGAN2 with a point-wise one and adds learnable Fourier features at the beginning. Both models are capable of multiscale generation, but they have different behaviors that we will discuss below." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 570, + 545, + 665 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 545, + 665 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 545, + 665 + ], + "type": "text", + "content": "As illustrated in Fig. 1, while having good photo-realism, AnyresGAN produces different image details at different scales. This can be explained by the fact that AnyresGAN, similar to most other GAN-based works, relies on spatial convolutions, such as 2D convolution with kernel size " + }, + { + "bbox": [ + 304, + 570, + 545, + 665 + ], + "type": "inline_equation", + "content": "3 \\times 3" + }, + { + "bbox": [ + 304, + 570, + 545, + 665 + ], + "type": "text", + "content": " and upsample layers. When changing the output resolution, the neighbor pixels at each location change, greatly varying the output of this spatial-convolution-based network." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "content": "On the other hand, CIPS keeps the output image's details nearly the same regardless of resolution, thanks to its spatial-free building operators. CIPS, however, is very computationally expensive; this can be clearly shown in Tab. 1." + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "22410" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 80, + 72, + 306, + 301 + ], + "blocks": [ + { + "bbox": [ + 80, + 72, + 306, + 301 + ], + "lines": [ + { + "bbox": [ + 80, + 72, + 306, + 301 + ], + "spans": [ + { + "bbox": [ + 80, + 72, + 306, + 301 + ], + "type": "image", + "image_path": "98745f86b879f360b40f24a926f1c5ae118cf86e53e37867476b1334cfa2a051.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 157, + 304, + 228, + 312 + ], + "lines": [ + { + "bbox": [ + 157, + 304, + 228, + 312 + ], + "spans": [ + { + "bbox": [ + 157, + 304, + 228, + 312 + ], + "type": "text", + "content": "(a) Network structure" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 220, + 316, + 372, + 327 + ], + "lines": [ + { + "bbox": [ + 220, + 316, + 372, + 327 + ], + "spans": [ + { + "bbox": [ + 220, + 316, + 372, + 327 + ], + "type": "text", + "content": "Figure 2. Our proposed CREPS structure" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 387, + 75, + 465, + 145 + ], + "blocks": [ + { + "bbox": [ + 387, + 75, + 465, + 145 + ], + "lines": [ + { + "bbox": [ + 387, + 75, + 465, + 145 + ], + "spans": [ + { + "bbox": [ + 387, + 75, + 465, + 145 + ], + "type": "image", + "image_path": "08c8f57aa21075ae5fff4da4155d1094ecee81ec55ea4e319468330a7b339c19.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 377, + 147, + 473, + 157 + ], + "lines": [ + { + "bbox": [ + 377, + 147, + 473, + 157 + ], + "spans": [ + { + "bbox": [ + 377, + 147, + 473, + 157 + ], + "type": "text", + "content": "(b) Thick bi-line composition" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 347, + 167, + 504, + 297 + ], + "blocks": [ + { + "bbox": [ + 347, + 167, + 504, + 297 + ], + "lines": [ + { + "bbox": [ + 347, + 167, + 504, + 297 + ], + "spans": [ + { + "bbox": [ + 347, + 167, + 504, + 297 + ], + "type": "image", + "image_path": "2371753f23e73f5dcf593c84b386f6593fd34c779afeebb33319e4d5cdfde3e4.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 392, + 298, + 461, + 307 + ], + "lines": [ + { + "bbox": [ + 392, + 298, + 461, + 307 + ], + "spans": [ + { + "bbox": [ + 392, + 298, + 461, + 307 + ], + "type": "text", + "content": "(c) Refinement block" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "type": "table", + "bbox": [ + 86, + 337, + 504, + 433 + ], + "blocks": [ + { + "bbox": [ + 86, + 337, + 504, + 433 + ], + "lines": [ + { + "bbox": [ + 86, + 337, + 504, + 433 + ], + "spans": [ + { + "bbox": [ + 86, + 337, + 504, + 433 + ], + "type": "table", + "html": "
ResolutionBatch sizeMemory UsageRunning time
StyleGAN2CIPSOursStyleGAN2CIPSOurs
256 × 25611.5GB3.3GB2.3GB0.04s0.06s0.03s
42.5GB10.2GB5.2GB0.05s0.23s0.06s
512 × 51211.7GB10.4GB4.5GB0.04s0.21s0.05s
43.4GBOOM14.6GB0.06sOOM0.16s
", + "image_path": "db97e28778a6e52338d722b979d256c562c129f36a6afc60ac3b3758a6ffecea.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "table_body" + } + ], + "index": 7 + }, + { + "bbox": [ + 62, + 435, + 526, + 447 + ], + "lines": [ + { + "bbox": [ + 62, + 435, + 526, + 447 + ], + "spans": [ + { + "bbox": [ + 62, + 435, + 526, + 447 + ], + "type": "text", + "content": "Table 1. Memory usage and running time comparison between StyleGAN2, CIPS and our method. OOM means out-of-memory." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 456, + 287, + 552 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 456, + 287, + 552 + ], + "spans": [ + { + "bbox": [ + 46, + 456, + 287, + 552 + ], + "type": "text", + "content": "When measured on a single NVIDIA V100 GPU (32 GB) and all models have comparable number of parameters, it runs slower than StyleGAN2 as well as requires much more memory or even gets an out-of-memory (OOM) error when running at " + }, + { + "bbox": [ + 46, + 456, + 287, + 552 + ], + "type": "inline_equation", + "content": "512 \\times 512" + }, + { + "bbox": [ + 46, + 456, + 287, + 552 + ], + "type": "text", + "content": " resolution. This makes CIPS inapplicable to use for learning fine details from high-resolution datasets. Moreover, it is worth noting that our method achieve the best trade-off between speed and memory." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 557, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 557, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 557, + 288, + 714 + ], + "type": "text", + "content": "Based on the above observations, we implement CREPS without any spatial convolutions or coarse-to-fine design. Starting with StyleGAN2 [15], which consists of a mapping network and a generator, we remove all upsampling operators and replace all spatial convolutions with " + }, + { + "bbox": [ + 46, + 557, + 288, + 714 + ], + "type": "inline_equation", + "content": "1 \\times 1" + }, + { + "bbox": [ + 46, + 557, + 288, + 714 + ], + "type": "text", + "content": " convolutions, which are equivalent to pixel-wise fully-connected layers. Next, we replace the constant in the first synthesis block with Fourier encodings of the input coordinate row and column " + }, + { + "bbox": [ + 46, + 557, + 288, + 714 + ], + "type": "inline_equation", + "content": "e^r" + }, + { + "bbox": [ + 46, + 557, + 288, + 714 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 557, + 288, + 714 + ], + "type": "inline_equation", + "content": "e^c" + }, + { + "bbox": [ + 46, + 557, + 288, + 714 + ], + "type": "text", + "content": ". This design is quite similar to CIPS, with only two minor differences. Firstly, the dense 2D grid input is now split into two vectors representing the row and column. Secondly, we do not combine learned input constant with the Fourier feature like CIPS did, making our" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 456, + 545, + 505 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 456, + 545, + 505 + ], + "spans": [ + { + "bbox": [ + 304, + 456, + 545, + 505 + ], + "type": "text", + "content": "model simpler and more memory-friendly. While this initial network guarantees any-scale image synthesis with consistent image details, it faces the same memory issue as CIPS. We will discuss next how to solve this issue effectively." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 510, + 459, + 523 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 510, + 459, + 523 + ], + "spans": [ + { + "bbox": [ + 306, + 510, + 459, + 523 + ], + "type": "text", + "content": "3.3. Thick bi-line representation" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 529, + 545, + 696 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 529, + 545, + 696 + ], + "spans": [ + { + "bbox": [ + 304, + 529, + 545, + 696 + ], + "type": "text", + "content": "Inspired by the tri-plane representation in [6], we propose to decompose each feature with 2D spatial dimensions into a column and a row embedding for a memory-efficient representation. For simplicity, let us drop the first two dimensions for the batch size " + }, + { + "bbox": [ + 304, + 529, + 545, + 696 + ], + "type": "inline_equation", + "content": "B" + }, + { + "bbox": [ + 304, + 529, + 545, + 696 + ], + "type": "text", + "content": " and the number of channel " + }, + { + "bbox": [ + 304, + 529, + 545, + 696 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 304, + 529, + 545, + 696 + ], + "type": "text", + "content": ", which are the same and element-wise processed for both the feature map and the mentioned embeddings. Let us denote the feature map as " + }, + { + "bbox": [ + 304, + 529, + 545, + 696 + ], + "type": "inline_equation", + "content": "F \\in \\mathbb{R}^{H \\times W}" + }, + { + "bbox": [ + 304, + 529, + 545, + 696 + ], + "type": "text", + "content": ", with " + }, + { + "bbox": [ + 304, + 529, + 545, + 696 + ], + "type": "inline_equation", + "content": "H" + }, + { + "bbox": [ + 304, + 529, + 545, + 696 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 529, + 545, + 696 + ], + "type": "inline_equation", + "content": "W" + }, + { + "bbox": [ + 304, + 529, + 545, + 696 + ], + "type": "text", + "content": " as the height and width, respectively. We can decompose " + }, + { + "bbox": [ + 304, + 529, + 545, + 696 + ], + "type": "inline_equation", + "content": "F" + }, + { + "bbox": [ + 304, + 529, + 545, + 696 + ], + "type": "text", + "content": " to a row embedding " + }, + { + "bbox": [ + 304, + 529, + 545, + 696 + ], + "type": "inline_equation", + "content": "f^r" + }, + { + "bbox": [ + 304, + 529, + 545, + 696 + ], + "type": "text", + "content": " and a column embedding " + }, + { + "bbox": [ + 304, + 529, + 545, + 696 + ], + "type": "inline_equation", + "content": "f^c" + }, + { + "bbox": [ + 304, + 529, + 545, + 696 + ], + "type": "text", + "content": ". In the simplest form, " + }, + { + "bbox": [ + 304, + 529, + 545, + 696 + ], + "type": "inline_equation", + "content": "f^r" + }, + { + "bbox": [ + 304, + 529, + 545, + 696 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 529, + 545, + 696 + ], + "type": "inline_equation", + "content": "f^c" + }, + { + "bbox": [ + 304, + 529, + 545, + 696 + ], + "type": "text", + "content": " are 1D vectors with the lengths " + }, + { + "bbox": [ + 304, + 529, + 545, + 696 + ], + "type": "inline_equation", + "content": "H" + }, + { + "bbox": [ + 304, + 529, + 545, + 696 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 529, + 545, + 696 + ], + "type": "inline_equation", + "content": "W" + }, + { + "bbox": [ + 304, + 529, + 545, + 696 + ], + "type": "text", + "content": ", respectively. Each pixel in the feature map " + }, + { + "bbox": [ + 304, + 529, + 545, + 696 + ], + "type": "inline_equation", + "content": "F_{ij}" + }, + { + "bbox": [ + 304, + 529, + 545, + 696 + ], + "type": "text", + "content": ", with " + }, + { + "bbox": [ + 304, + 529, + 545, + 696 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 304, + 529, + 545, + 696 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 529, + 545, + 696 + ], + "type": "inline_equation", + "content": "j" + }, + { + "bbox": [ + 304, + 529, + 545, + 696 + ], + "type": "text", + "content": " as the row and the column indices, can be computed as the product of the corresponding elements in " + }, + { + "bbox": [ + 304, + 529, + 545, + 696 + ], + "type": "inline_equation", + "content": "f^r" + }, + { + "bbox": [ + 304, + 529, + 545, + 696 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 529, + 545, + 696 + ], + "type": "inline_equation", + "content": "f^c" + }, + { + "bbox": [ + 304, + 529, + 545, + 696 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 399, + 701, + 545, + 715 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 399, + 701, + 545, + 715 + ], + "spans": [ + { + "bbox": [ + 399, + 701, + 545, + 715 + ], + "type": "interline_equation", + "content": "F _ {i j} = f _ {i} ^ {r} f _ {j} ^ {c}. \\tag {2}", + "image_path": "7f0cc3022a07f3b6ef6d2eb81e36ce1f93fd5156f9f113bca81a3d23e09936c4.jpg" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "22411" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 48, + 70, + 287, + 143 + ], + "blocks": [ + { + "bbox": [ + 48, + 70, + 287, + 143 + ], + "lines": [ + { + "bbox": [ + 48, + 70, + 287, + 143 + ], + "spans": [ + { + "bbox": [ + 48, + 70, + 287, + 143 + ], + "type": "image", + "image_path": "e66f352c0d2017d59ad5628ff9916cfdc0e01398c1d22fd6d0ad3345ad7aa1c0.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 145, + 287, + 168 + ], + "lines": [ + { + "bbox": [ + 46, + 145, + 287, + 168 + ], + "spans": [ + { + "bbox": [ + 46, + 145, + 287, + 168 + ], + "type": "text", + "content": "Figure 3. Fitting an input image to the thick bi-line representation in the image space." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 178, + 290, + 312 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 178, + 290, + 312 + ], + "spans": [ + { + "bbox": [ + 46, + 178, + 290, + 312 + ], + "type": "text", + "content": "We call this representation \"bi-line\", which significantly reduces the memory usage and computation cost and allows the network to learn with high-resolution data. However, we found that this simple representation had a limited capacity and could not define complex structures. To enrich its representation power, we \"thicken\" the embeddings by adding an extra, short dimension. The revised " + }, + { + "bbox": [ + 46, + 178, + 290, + 312 + ], + "type": "inline_equation", + "content": "f^r" + }, + { + "bbox": [ + 46, + 178, + 290, + 312 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 178, + 290, + 312 + ], + "type": "inline_equation", + "content": "f^c" + }, + { + "bbox": [ + 46, + 178, + 290, + 312 + ], + "type": "text", + "content": " now have the shapes " + }, + { + "bbox": [ + 46, + 178, + 290, + 312 + ], + "type": "inline_equation", + "content": "H \\times D" + }, + { + "bbox": [ + 46, + 178, + 290, + 312 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 178, + 290, + 312 + ], + "type": "inline_equation", + "content": "W \\times D" + }, + { + "bbox": [ + 46, + 178, + 290, + 312 + ], + "type": "text", + "content": ", respectively, where " + }, + { + "bbox": [ + 46, + 178, + 290, + 312 + ], + "type": "inline_equation", + "content": "D \\ll \\min(H, W)" + }, + { + "bbox": [ + 46, + 178, + 290, + 312 + ], + "type": "text", + "content": " is a uniform embedding \"thickness\". The composing feature element " + }, + { + "bbox": [ + 46, + 178, + 290, + 312 + ], + "type": "inline_equation", + "content": "F_{ij}" + }, + { + "bbox": [ + 46, + 178, + 290, + 312 + ], + "type": "text", + "content": " is now the dot product of the corresponding elements in " + }, + { + "bbox": [ + 46, + 178, + 290, + 312 + ], + "type": "inline_equation", + "content": "f^r" + }, + { + "bbox": [ + 46, + 178, + 290, + 312 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 178, + 290, + 312 + ], + "type": "inline_equation", + "content": "f^c" + }, + { + "bbox": [ + 46, + 178, + 290, + 312 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 109, + 320, + 287, + 354 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 109, + 320, + 287, + 354 + ], + "spans": [ + { + "bbox": [ + 109, + 320, + 287, + 354 + ], + "type": "interline_equation", + "content": "F _ {i j} = f _ {i} ^ {r} \\cdot f _ {j} ^ {c} = \\sum_ {d = 1} ^ {D} f _ {i d} ^ {r} f _ {j d} ^ {c}. \\tag {3}", + "image_path": "4742d38f8731aee0ca59a899cf15a0f058590248926839186423010e8c7e4ae8.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 361, + 287, + 399 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 361, + 287, + 399 + ], + "spans": [ + { + "bbox": [ + 46, + 361, + 287, + 399 + ], + "type": "text", + "content": "This composition process is illustrated in Fig. 2b. In another perspective, this can be considered as a sum of " + }, + { + "bbox": [ + 46, + 361, + 287, + 399 + ], + "type": "inline_equation", + "content": "D" + }, + { + "bbox": [ + 46, + 361, + 287, + 399 + ], + "type": "text", + "content": " different bi-line compositions. We call it \"thick bi-line\" representation." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 399, + 290, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 399, + 290, + 628 + ], + "spans": [ + { + "bbox": [ + 46, + 399, + 290, + 628 + ], + "type": "text", + "content": "In Fig. 3, we provide a toy example illustrating the capacity of the proposed thick bi-line representation. Given an input image at resolution " + }, + { + "bbox": [ + 46, + 399, + 290, + 628 + ], + "type": "inline_equation", + "content": "512 \\times 512 \\times 3" + }, + { + "bbox": [ + 46, + 399, + 290, + 628 + ], + "type": "text", + "content": ", we fit it into the proposed bi-line representation in the image space by optimizing a row and a column embedding of shape " + }, + { + "bbox": [ + 46, + 399, + 290, + 628 + ], + "type": "inline_equation", + "content": "512 \\times D \\times 3" + }, + { + "bbox": [ + 46, + 399, + 290, + 628 + ], + "type": "text", + "content": ". Note that each channel is optimized independently. As can be seen, with the naive bi-linear composition (" + }, + { + "bbox": [ + 46, + 399, + 290, + 628 + ], + "type": "inline_equation", + "content": "D = 1" + }, + { + "bbox": [ + 46, + 399, + 290, + 628 + ], + "type": "text", + "content": "), the reconstructed image is just a simple, incomprehensible grid. By adding just a small thickness " + }, + { + "bbox": [ + 46, + 399, + 290, + 628 + ], + "type": "inline_equation", + "content": "D = 8" + }, + { + "bbox": [ + 46, + 399, + 290, + 628 + ], + "type": "text", + "content": ", we can capture the essential image content, recover the subject's identity, and reduce the MSE almost 6 times. When using " + }, + { + "bbox": [ + 46, + 399, + 290, + 628 + ], + "type": "inline_equation", + "content": "D = 32" + }, + { + "bbox": [ + 46, + 399, + 290, + 628 + ], + "type": "text", + "content": ", we nearly recover the original image with only subtle pixel noise. Note that the row and column embeddings only take " + }, + { + "bbox": [ + 46, + 399, + 290, + 628 + ], + "type": "inline_equation", + "content": "1.56\\%" + }, + { + "bbox": [ + 46, + 399, + 290, + 628 + ], + "type": "text", + "content": " of the original image size when " + }, + { + "bbox": [ + 46, + 399, + 290, + 628 + ], + "type": "inline_equation", + "content": "D = 8" + }, + { + "bbox": [ + 46, + 399, + 290, + 628 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 399, + 290, + 628 + ], + "type": "inline_equation", + "content": "12.5\\%" + }, + { + "bbox": [ + 46, + 399, + 290, + 628 + ], + "type": "text", + "content": " when " + }, + { + "bbox": [ + 46, + 399, + 290, + 628 + ], + "type": "inline_equation", + "content": "D = 32" + }, + { + "bbox": [ + 46, + 399, + 290, + 628 + ], + "type": "text", + "content": ". This experiment confirms the efficacy of our proposed thick bi-line decomposition. Also, while this representation does not capture all details of the complex input image, it is more sufficient when modeling the overparameterized feature space." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 635, + 217, + 647 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 635, + 217, + 647 + ], + "spans": [ + { + "bbox": [ + 47, + 635, + 217, + 647 + ], + "type": "text", + "content": "3.4. Layer-wise feature composition" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 654, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 654, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 654, + 287, + 715 + ], + "type": "text", + "content": "In CREPS, we assume the target output is square, i.e., " + }, + { + "bbox": [ + 46, + 654, + 287, + 715 + ], + "type": "inline_equation", + "content": "H = W" + }, + { + "bbox": [ + 46, + 654, + 287, + 715 + ], + "type": "text", + "content": ". Hence, we can concatenate the row and column embeddings to a single tensor " + }, + { + "bbox": [ + 46, + 654, + 287, + 715 + ], + "type": "inline_equation", + "content": "f = [f^r, f^c] \\in \\mathbb{R}^{H \\times 2D}" + }, + { + "bbox": [ + 46, + 654, + 287, + 715 + ], + "type": "text", + "content": ". Initially, we implement CREPS by revising StyleGAN2's code to predict " + }, + { + "bbox": [ + 46, + 654, + 287, + 715 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 46, + 654, + 287, + 715 + ], + "type": "text", + "content": " from the latent input " + }, + { + "bbox": [ + 46, + 654, + 287, + 715 + ], + "type": "inline_equation", + "content": "w" + }, + { + "bbox": [ + 46, + 654, + 287, + 715 + ], + "type": "text", + "content": " via " + }, + { + "bbox": [ + 46, + 654, + 287, + 715 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 654, + 287, + 715 + ], + "type": "text", + "content": " synthesis blocks." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "text", + "content": "The network then splits " + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "text", + "content": " to get the row and column codes, perform the feature composition defined in Eq. (3) to get a feature map " + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "inline_equation", + "content": "F" + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "text", + "content": ". This feature map will be passed to a simple refinement module (Fig. 2c) with 2 synthesis blocks to produce the output image. For efficient memory and computation cost, we only employ a small thickness value " + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "inline_equation", + "content": "D = 8" + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 144, + 546, + 300 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 144, + 546, + 300 + ], + "spans": [ + { + "bbox": [ + 304, + 144, + 546, + 300 + ], + "type": "text", + "content": "We found this initial design needed to be more efficient to catch up with the generation quality of StyleGAN and CIPS. It performed feature composition once near the end of the image synthesis process; thus, the model power was bounded by the capacity of the thick bi-line representation. Instead, we revise our solution by employing a layer-wise feature composition scheme. Specially, at each layer with index " + }, + { + "bbox": [ + 304, + 144, + 546, + 300 + ], + "type": "inline_equation", + "content": "l \\in [1..N]" + }, + { + "bbox": [ + 304, + 144, + 546, + 300 + ], + "type": "text", + "content": ", we extract the intermediate row and column embedding " + }, + { + "bbox": [ + 304, + 144, + 546, + 300 + ], + "type": "inline_equation", + "content": "f^{(l)}" + }, + { + "bbox": [ + 304, + 144, + 546, + 300 + ], + "type": "text", + "content": ". We can split " + }, + { + "bbox": [ + 304, + 144, + 546, + 300 + ], + "type": "inline_equation", + "content": "f^{(l)}" + }, + { + "bbox": [ + 304, + 144, + 546, + 300 + ], + "type": "text", + "content": " and compose an intermediate feature map " + }, + { + "bbox": [ + 304, + 144, + 546, + 300 + ], + "type": "inline_equation", + "content": "F^{(l)}" + }, + { + "bbox": [ + 304, + 144, + 546, + 300 + ], + "type": "text", + "content": ", following Eq. (3). Then, the intermediate maps across layers are fused to get the final map " + }, + { + "bbox": [ + 304, + 144, + 546, + 300 + ], + "type": "inline_equation", + "content": "F" + }, + { + "bbox": [ + 304, + 144, + 546, + 300 + ], + "type": "text", + "content": ". This scheme enriches the representation power, similar to when increasing " + }, + { + "bbox": [ + 304, + 144, + 546, + 300 + ], + "type": "inline_equation", + "content": "D" + }, + { + "bbox": [ + 304, + 144, + 546, + 300 + ], + "type": "text", + "content": " while using less memory." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 300, + 547, + 494 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 300, + 547, + 494 + ], + "spans": [ + { + "bbox": [ + 304, + 300, + 547, + 494 + ], + "type": "text", + "content": "The fusion scheme is also important. Intuitively, we can set " + }, + { + "bbox": [ + 304, + 300, + 547, + 494 + ], + "type": "inline_equation", + "content": "F" + }, + { + "bbox": [ + 304, + 300, + 547, + 494 + ], + "type": "text", + "content": " as the sum of the intermediate maps " + }, + { + "bbox": [ + 304, + 300, + 547, + 494 + ], + "type": "inline_equation", + "content": "\\{F^{(l)}\\}_{l = \\overline{1,N}}" + }, + { + "bbox": [ + 304, + 300, + 547, + 494 + ], + "type": "text", + "content": ". However, this formulation treats the maps equally, and we find it undesirable. Let us call back the StyleGAN models' behavior. Thanks to the coarse-to-fine design, their early layers learn to capture the global shape, while the later layers learn to synthesize fine details. Since CREPS has no coarse-to-fine structure, it is hard to control which aspect of the output image each layer can learn. Hence, we propose adding asymmetry to the feature map fusion process: the feature maps at earlier layers are processed \"deeper\" than those at later layers. We hope it implicitly guides the layers to learn information from global to regional order, similar to StyleGAN. To do so, we introduce at each layer with index " + }, + { + "bbox": [ + 304, + 300, + 547, + 494 + ], + "type": "inline_equation", + "content": "l" + }, + { + "bbox": [ + 304, + 300, + 547, + 494 + ], + "type": "text", + "content": " a narrow decoder, denoted as " + }, + { + "bbox": [ + 304, + 300, + 547, + 494 + ], + "type": "inline_equation", + "content": "\\pi^{(l)}" + }, + { + "bbox": [ + 304, + 300, + 547, + 494 + ], + "type": "text", + "content": ". The process to fuse the intermediate maps " + }, + { + "bbox": [ + 304, + 300, + 547, + 494 + ], + "type": "inline_equation", + "content": "\\{F^{(l)}\\}_{l = \\overline{1,N}}" + }, + { + "bbox": [ + 304, + 300, + 547, + 494 + ], + "type": "text", + "content": " is defined as following:" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 317, + 508, + 545, + 522 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 508, + 545, + 522 + ], + "spans": [ + { + "bbox": [ + 317, + 508, + 545, + 522 + ], + "type": "interline_equation", + "content": "E ^ {(1)} \\quad = F ^ {(1)}, \\tag {4}", + "image_path": "4bb1485a1b9c6de2d21fa4269fe1664558c0201c64598654e64f768c4bf93c8c.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 317, + 525, + 545, + 540 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 525, + 545, + 540 + ], + "spans": [ + { + "bbox": [ + 317, + 525, + 545, + 540 + ], + "type": "interline_equation", + "content": "E ^ {(l + 1)} = \\pi^ {(l)} \\left(E ^ {(l)}\\right) + F ^ {(l + 1)} \\quad \\forall l \\in [ 1, N - 1 ], \\tag {5}", + "image_path": "7ff91f73899fa209205a55d040cfb49e8c9282db80af29c37727c2f06eacd148.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 317, + 542, + 545, + 556 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 542, + 545, + 556 + ], + "spans": [ + { + "bbox": [ + 317, + 542, + 545, + 556 + ], + "type": "interline_equation", + "content": "F \\quad = \\pi^ {N} \\left(E ^ {N}\\right), \\tag {6}", + "image_path": "612776fa4c3e3260dd234577b142aa654a2a4b1ec7091a5963e0c72cf081bef7.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 563, + 545, + 637 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 563, + 545, + 637 + ], + "spans": [ + { + "bbox": [ + 304, + 563, + 545, + 637 + ], + "type": "text", + "content": "with " + }, + { + "bbox": [ + 304, + 563, + 545, + 637 + ], + "type": "inline_equation", + "content": "E^{(l)}" + }, + { + "bbox": [ + 304, + 563, + 545, + 637 + ], + "type": "text", + "content": " records the fused feature map at the " + }, + { + "bbox": [ + 304, + 563, + 545, + 637 + ], + "type": "inline_equation", + "content": "l^{th}" + }, + { + "bbox": [ + 304, + 563, + 545, + 637 + ], + "type": "text", + "content": " layer. In our implementation, each decoder consists of pixelwise fully-connected layers with Leaky-RELU activations. Fig. 2a illustrates our proposed network structure, while Tab. 1 illustrates the efficiency of our proposed structure in memory usage and running time." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 646, + 388, + 659 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 646, + 388, + 659 + ], + "spans": [ + { + "bbox": [ + 306, + 646, + 388, + 659 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 306, + 665, + 421, + 678 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 665, + 421, + 678 + ], + "spans": [ + { + "bbox": [ + 306, + 665, + 421, + 678 + ], + "type": "text", + "content": "4.1. Experimental setup" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 689, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 689, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 306, + 689, + 545, + 714 + ], + "type": "text", + "content": "Datasets. We conduct experiments on the common datasets when benchmarking CREPS, including FFHQ, MetFaces," + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "22412" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 50, + 70, + 167, + 305 + ], + "blocks": [ + { + "bbox": [ + 50, + 70, + 167, + 305 + ], + "lines": [ + { + "bbox": [ + 50, + 70, + 167, + 305 + ], + "spans": [ + { + "bbox": [ + 50, + 70, + 167, + 305 + ], + "type": "image", + "image_path": "dfd92940ee879e8774a5363b371738527084ae44a49173a38a7f08298a17a25a.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 47, + 308, + 287, + 341 + ], + "lines": [ + { + "bbox": [ + 47, + 308, + 287, + 341 + ], + "spans": [ + { + "bbox": [ + 47, + 308, + 287, + 341 + ], + "type": "text", + "content": "Figure 4. Sample images with our models trained on FFHQ (upper-left), LSUN-Church (upper-right), MetFace (bottom-left), and Flickr-Scenery (bottom-right)." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 168, + 70, + 286, + 305 + ], + "blocks": [ + { + "bbox": [ + 168, + 70, + 286, + 305 + ], + "lines": [ + { + "bbox": [ + 168, + 70, + 286, + 305 + ], + "spans": [ + { + "bbox": [ + 168, + 70, + 286, + 305 + ], + "type": "image", + "image_path": "94f60fab2cc902e9b09c1c66ac5d30d119da998ac918b0c2f6680841000452a4.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 353, + 289, + 473 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 353, + 289, + 473 + ], + "spans": [ + { + "bbox": [ + 46, + 353, + 289, + 473 + ], + "type": "text", + "content": "LSUN-Church, and Flickr-Scenery. FFHQ dataset contains 70k high-quality, diverse human faces collected from Flickr. We will use the FFHQ images with resolution " + }, + { + "bbox": [ + 46, + 353, + 289, + 473 + ], + "type": "inline_equation", + "content": "512 \\times 512" + }, + { + "bbox": [ + 46, + 353, + 289, + 473 + ], + "type": "text", + "content": ". MetFaces is a small dataset of face drawings extracted from the collection of the Metropolitan Museum of Art, with a total of 1336 images at resolution " + }, + { + "bbox": [ + 46, + 353, + 289, + 473 + ], + "type": "inline_equation", + "content": "1024 \\times 1024" + }, + { + "bbox": [ + 46, + 353, + 289, + 473 + ], + "type": "text", + "content": ". LSUN-Church consists of 126k outdoor photographs of churches at the resolution " + }, + { + "bbox": [ + 46, + 353, + 289, + 473 + ], + "type": "inline_equation", + "content": "256 \\times 256" + }, + { + "bbox": [ + 46, + 353, + 289, + 473 + ], + "type": "text", + "content": ". Finally, Flickr-Scenery [7] is a landscape-centric dataset collected on Flickr with 50k images at resolution " + }, + { + "bbox": [ + 46, + 353, + 289, + 473 + ], + "type": "inline_equation", + "content": "256 \\times 256" + }, + { + "bbox": [ + 46, + 353, + 289, + 473 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 479, + 289, + 672 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 479, + 289, + 672 + ], + "spans": [ + { + "bbox": [ + 46, + 479, + 289, + 672 + ], + "type": "text", + "content": "Implementation. We use StyleGAN2 network design as a reference to implement CREPS. Except for the refinement module, our generator consists of 6 (for the target resolution 256) to 8 synthesis blocks (for the resolution 1024) and the same number of decoder blocks. We replace all modulated convolution layers in StyleGAN2 with modulated fully-connected ones. Unlike StyleGAN2, the output of each block is not an RGB image but a 32-channel bi-line feature with thickness " + }, + { + "bbox": [ + 46, + 479, + 289, + 672 + ], + "type": "inline_equation", + "content": "D = 8" + }, + { + "bbox": [ + 46, + 479, + 289, + 672 + ], + "type": "text", + "content": ". Each decoder is a stack of " + }, + { + "bbox": [ + 46, + 479, + 289, + 672 + ], + "type": "inline_equation", + "content": "P = 4" + }, + { + "bbox": [ + 46, + 479, + 289, + 672 + ], + "type": "text", + "content": " pixel-wise fully-connected layers, with the channel widths ranging from 32 to 128. This setting is applied for all experiments, except for our ablation study. Similar to StyleGAN3 and CIPS, we turn off style mixing regularization. Besides that, we kept most of the other components unchanged, including the mapping network, discriminator, path length regularization, and " + }, + { + "bbox": [ + 46, + 479, + 289, + 672 + ], + "type": "inline_equation", + "content": "R_{1}" + }, + { + "bbox": [ + 46, + 479, + 289, + 672 + ], + "type": "text", + "content": " gradient penalty." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 677, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 677, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 47, + 677, + 288, + 715 + ], + "type": "text", + "content": "Training. For FFHQ and LSUN-Church, our networks were trained from scratch until convergence. To verify the flexibility and scale consistency of CREPS on higher-" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 72, + 547, + 169 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 169 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 169 + ], + "type": "text", + "content": "resolution image synthesis, we increase the length of its coordinate input to generate images at resolution " + }, + { + "bbox": [ + 304, + 72, + 547, + 169 + ], + "type": "inline_equation", + "content": "1024 \\times 1024" + }, + { + "bbox": [ + 304, + 72, + 547, + 169 + ], + "type": "text", + "content": " on the FFHQ dataset. We also test the adaptability of our network on domain shift by applying transfer learning from the weights trained on FFHQ to MetFaces. Our networks were trained by Adam optimizer with learning rate " + }, + { + "bbox": [ + 304, + 72, + 547, + 169 + ], + "type": "inline_equation", + "content": "2 \\times 10^{-3}" + }, + { + "bbox": [ + 304, + 72, + 547, + 169 + ], + "type": "text", + "content": " and hyperparameters " + }, + { + "bbox": [ + 304, + 72, + 547, + 169 + ], + "type": "inline_equation", + "content": "\\beta_0 = 0" + }, + { + "bbox": [ + 304, + 72, + 547, + 169 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 72, + 547, + 169 + ], + "type": "inline_equation", + "content": "\\beta_1 = 0.99" + }, + { + "bbox": [ + 304, + 72, + 547, + 169 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 304, + 72, + 547, + 169 + ], + "type": "inline_equation", + "content": "\\epsilon = 10^{-8}" + }, + { + "bbox": [ + 304, + 72, + 547, + 169 + ], + "type": "text", + "content": ". We use 4 NVIDIA A100 40GB GPUs for training all models." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 176, + 411, + 189 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 176, + 411, + 189 + ], + "spans": [ + { + "bbox": [ + 306, + 176, + 411, + 189 + ], + "type": "text", + "content": "4.2. Image generation" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 194, + 547, + 254 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 194, + 547, + 254 + ], + "spans": [ + { + "bbox": [ + 304, + 194, + 547, + 254 + ], + "type": "text", + "content": "Tab. 2 compares the quality of images generated by our CREPS models with the standard spatial-convolution-based StyleGAN2 and the only scale-consistent any-scale image generation technique CIPS, using the Frechet Inception Distance (FID) score." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 255, + 547, + 411 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 255, + 547, + 411 + ], + "spans": [ + { + "bbox": [ + 304, + 255, + 547, + 411 + ], + "type": "text", + "content": "At resolution " + }, + { + "bbox": [ + 304, + 255, + 547, + 411 + ], + "type": "inline_equation", + "content": "512 \\times 512" + }, + { + "bbox": [ + 304, + 255, + 547, + 411 + ], + "type": "text", + "content": " on FFHQ, our model achieves the FID score of 4.43, which is much better than the score from CIPS (6.18) and not far from StyleGAN2 (3.41). We can also use this model to generate images at resolution " + }, + { + "bbox": [ + 304, + 255, + 547, + 411 + ], + "type": "inline_equation", + "content": "1024 \\times 1024" + }, + { + "bbox": [ + 304, + 255, + 547, + 411 + ], + "type": "text", + "content": " without retraining and achieve a better FID score (4.09). We found that CIPS cannot be trained for this resolution due to its expensive memory usage, even with training batch size 1, when using its official code. However, the authors provided a pretrained model for FFHQ-1024 using a progressive training scheme (no released code). This CIPS model has an FID score of 10.07, much worse than ours. This confirms the superiority of our method over its scale-consistent image generation counterpart." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 411, + 547, + 471 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 411, + 547, + 471 + ], + "spans": [ + { + "bbox": [ + 304, + 411, + 547, + 471 + ], + "type": "text", + "content": "On the MetFaces dataset, CREPS's FID score is 20.52, which is quite close to the score of StyleGAN2-Ada (18.22). As mentioned, CIPS fails to train on this " + }, + { + "bbox": [ + 304, + 411, + 547, + 471 + ], + "type": "inline_equation", + "content": "1024 \\times 1024" + }, + { + "bbox": [ + 304, + 411, + 547, + 471 + ], + "type": "text", + "content": " resolution using its official code. It confirms that bi-line representation does not constrain the adaptability of our model." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 471, + 547, + 555 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 471, + 547, + 555 + ], + "spans": [ + { + "bbox": [ + 304, + 471, + 547, + 555 + ], + "type": "text", + "content": "On LSUN-Church and Flickr-Scenery, although the unstructured and diverse images in these datasets are intuitively adverse to column and row decomposition, CREPS obtains good results with only a small gap compared with StyleGAN2's ones. Note that CIPS achieves a surprisingly good result on LSUN-Church; it surpasses not only CREPS but also StyleGAN2 in this setting." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 555, + 547, + 591 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 555, + 547, + 591 + ], + "spans": [ + { + "bbox": [ + 304, + 555, + 547, + 591 + ], + "type": "text", + "content": "Fig. 4 provides some samples synthesized by our networks on the benchmark datasets. As can be seen, CREPS produces highly realistic images in all cases." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 599, + 480, + 612 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 599, + 480, + 612 + ], + "spans": [ + { + "bbox": [ + 305, + 599, + 480, + 612 + ], + "type": "text", + "content": "4.3. Generate arbitrary-scale images" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "type": "text", + "content": "While our models are trained on images with resolutions from " + }, + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "type": "inline_equation", + "content": "256 \\times 256" + }, + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "type": "inline_equation", + "content": "1024 \\times 1024" + }, + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "type": "text", + "content": ", they can generate images at any scale. One way is that we simply scale the length of " + }, + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "type": "inline_equation", + "content": "e^r" + }, + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "type": "inline_equation", + "content": "e^c" + }, + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "type": "text", + "content": ", and the output size is changed accordingly, thanks to our network design. With a V100 GPU (32GB), our models can generate an image up to resolution " + }, + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "type": "inline_equation", + "content": "3687 \\times 3687" + }, + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "type": "text", + "content": " in a single run. Or we can generate an image patch-by-patch with suitable coordinate inputs, then combine them together into" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "22413" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 89, + 70, + 502, + 121 + ], + "blocks": [ + { + "bbox": [ + 89, + 70, + 502, + 121 + ], + "lines": [ + { + "bbox": [ + 89, + 70, + 502, + 121 + ], + "spans": [ + { + "bbox": [ + 89, + 70, + 502, + 121 + ], + "type": "table", + "html": "
GeneratorFFHQ-512FFHQ-1024LSUN Church-256MetFaces-1024Scenery-256
StyleGANv23.412.843.8618.22*6.40
CIPS6.1810.07†2.92OOM8.49
CREPS (ours)4.434.09‡5.5020.527.21
", + "image_path": "a8a71c4a7dcaa75f9b3e3ce8c497caa33723a61bf7069ad8e4ffb4716165d053.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 67, + 168, + 265, + 232 + ], + "blocks": [ + { + "bbox": [ + 46, + 125, + 547, + 159 + ], + "lines": [ + { + "bbox": [ + 46, + 125, + 547, + 159 + ], + "spans": [ + { + "bbox": [ + 46, + 125, + 547, + 159 + ], + "type": "text", + "content": "Table 2. Comparison of our method against other works in FID metric. OOM means out-of-memory. \\*\\* means the result is taken from StyleGAN2-Ada paper [12]. " + }, + { + "bbox": [ + 46, + 125, + 547, + 159 + ], + "type": "inline_equation", + "content": "\\ddagger" + }, + { + "bbox": [ + 46, + 125, + 547, + 159 + ], + "type": "text", + "content": " means the model is provided without releasing its progressive training code. " + }, + { + "bbox": [ + 46, + 125, + 547, + 159 + ], + "type": "inline_equation", + "content": "\\ddagger" + }, + { + "bbox": [ + 46, + 125, + 547, + 159 + ], + "type": "text", + "content": " means the result is obtained by scaling the output resolution of the FFHQ-512 model." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 67, + 168, + 265, + 232 + ], + "lines": [ + { + "bbox": [ + 67, + 168, + 265, + 232 + ], + "spans": [ + { + "bbox": [ + 67, + 168, + 265, + 232 + ], + "type": "table", + "html": "
PSNR ↑SSIM ↑LPIPS ↓
AnyresGAN24.190.730.07
ScaleParty24.500.700.08
CIPS33.330.930.05
CREPS34.650.960.01
", + "image_path": "b31f68bd4a9adbe7e9700a4b4df21b1db24dc63df6843d1bc84f0cb22396408e.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 51, + 266, + 285, + 392 + ], + "blocks": [ + { + "bbox": [ + 51, + 266, + 285, + 392 + ], + "lines": [ + { + "bbox": [ + 51, + 266, + 285, + 392 + ], + "spans": [ + { + "bbox": [ + 51, + 266, + 285, + 392 + ], + "type": "image", + "image_path": "cc19668380b05f778c92502e1c7a778cf7311d8c1aa39778ce8f24ff595c6cca.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 395, + 287, + 438 + ], + "lines": [ + { + "bbox": [ + 46, + 395, + 287, + 438 + ], + "spans": [ + { + "bbox": [ + 46, + 395, + 287, + 438 + ], + "type": "text", + "content": "Figure 5. Qualitative results for the scale consistency experiment. For each method, we provide a sample generated " + }, + { + "bbox": [ + 46, + 395, + 287, + 438 + ], + "type": "inline_equation", + "content": "256 \\times 256" + }, + { + "bbox": [ + 46, + 395, + 287, + 438 + ], + "type": "text", + "content": " image (top) and the magnified " + }, + { + "bbox": [ + 46, + 395, + 287, + 438 + ], + "type": "inline_equation", + "content": "(\\times 10)" + }, + { + "bbox": [ + 46, + 395, + 287, + 438 + ], + "type": "text", + "content": " residual map between it and the " + }, + { + "bbox": [ + 46, + 395, + 287, + 438 + ], + "type": "inline_equation", + "content": "512 \\times 512" + }, + { + "bbox": [ + 46, + 395, + 287, + 438 + ], + "type": "text", + "content": " rescaled version (bottom)." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 449, + 287, + 521 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 449, + 287, + 521 + ], + "spans": [ + { + "bbox": [ + 46, + 449, + 287, + 521 + ], + "type": "text", + "content": "a single gigantic image with no upper limit in the output size. We provide in the Supplementary some images generated at 6K resolution. While these images are not as sharp as real-world ultra-high-resolution images, they are much sharper than the ones generated at resolution " + }, + { + "bbox": [ + 46, + 449, + 287, + 521 + ], + "type": "inline_equation", + "content": "512 \\times 512" + }, + { + "bbox": [ + 46, + 449, + 287, + 521 + ], + "type": "text", + "content": " and then upscaled with Lanczos resampling." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 527, + 190, + 540 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 527, + 190, + 540 + ], + "spans": [ + { + "bbox": [ + 47, + 527, + 190, + 540 + ], + "type": "text", + "content": "4.4. Image scaling consistency" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 546, + 287, + 676 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 546, + 287, + 676 + ], + "spans": [ + { + "bbox": [ + 46, + 546, + 287, + 676 + ], + "type": "text", + "content": "In this section, we evaluate the scale consistency of images produced by CREPS and other methods, including AnyresGAN [4], ScaleParty [18], and CIPS [1]. We run this experiment using models trained on the FFHQ dataset. For each model, we first randomly generate 10k images at resolution " + }, + { + "bbox": [ + 46, + 546, + 287, + 676 + ], + "type": "inline_equation", + "content": "256 \\times 256" + }, + { + "bbox": [ + 46, + 546, + 287, + 676 + ], + "type": "text", + "content": " (first set). We then generate images with the same latent codes but at resolution " + }, + { + "bbox": [ + 46, + 546, + 287, + 676 + ], + "type": "inline_equation", + "content": "512 \\times 512" + }, + { + "bbox": [ + 46, + 546, + 287, + 676 + ], + "type": "text", + "content": " and downsample them to " + }, + { + "bbox": [ + 46, + 546, + 287, + 676 + ], + "type": "inline_equation", + "content": "256 \\times 256" + }, + { + "bbox": [ + 46, + 546, + 287, + 676 + ], + "type": "text", + "content": " (second set). The images in two sets are expected to be the same. Hence, we can compare two sets, with standard metrics such as PSNR, SSIM, and LPIPS, to measure each model's scale equivariance." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "text", + "content": "Note that for ScaleParty and AnyresGAN, the pretrained weights are already trained with different resolutions at once, so we directly use their provided version. CIPS, how" + } + ] + } + ], + "index": 9 + }, + { + "type": "table", + "bbox": [ + 307, + 168, + 549, + 256 + ], + "blocks": [ + { + "bbox": [ + 47, + 236, + 287, + 258 + ], + "lines": [ + { + "bbox": [ + 47, + 236, + 287, + 258 + ], + "spans": [ + { + "bbox": [ + 47, + 236, + 287, + 258 + ], + "type": "text", + "content": "Table 3. Scale consistency comparison of our method against three other works on PSNR, SSIM and LPIP. The best scores are bold." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 307, + 168, + 549, + 256 + ], + "lines": [ + { + "bbox": [ + 307, + 168, + 549, + 256 + ], + "spans": [ + { + "bbox": [ + 307, + 168, + 549, + 256 + ], + "type": "table", + "html": "
ConfigurationFIDMemoryTime
CREP-NB5.982.7GB0.13s
+ bi-line and d=111.371.5GB0.02s
+ bi-line and d=88.231.6GB0.03s
+ multiple decoders and d=46.461.6GB0.03s
+ multiple decoders and d=84.661.7GB0.04s
CIPS7.083.5GB0.05s
", + "image_path": "36de59643cfd74353095ec6f664412abff7d75eabe92e80d5282a59031dd8390.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "table_body" + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 259, + 545, + 282 + ], + "lines": [ + { + "bbox": [ + 305, + 259, + 545, + 282 + ], + "spans": [ + { + "bbox": [ + 305, + 259, + 545, + 282 + ], + "type": "text", + "content": "Table 4. Effects of the modifications of CREPS on the FFHQ dataset in terms of FID score, memory usage, and running time." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 305, + 301, + 545, + 361 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 301, + 545, + 361 + ], + "spans": [ + { + "bbox": [ + 305, + 301, + 545, + 361 + ], + "type": "text", + "content": "ever, is trained in a single-scale setting, so we use the available weights trained at the highest resolution " + }, + { + "bbox": [ + 305, + 301, + 545, + 361 + ], + "type": "inline_equation", + "content": "(1024 \\times 1024)" + }, + { + "bbox": [ + 305, + 301, + 545, + 361 + ], + "type": "text", + "content": " but pass the input coordinate with size " + }, + { + "bbox": [ + 305, + 301, + 545, + 361 + ], + "type": "inline_equation", + "content": "512 \\times 512" + }, + { + "bbox": [ + 305, + 301, + 545, + 361 + ], + "type": "text", + "content": " to synthesis image at resolution 512. As for CREPS, we simply use the weight trained at resolution " + }, + { + "bbox": [ + 305, + 301, + 545, + 361 + ], + "type": "inline_equation", + "content": "512 \\times 512" + }, + { + "bbox": [ + 305, + 301, + 545, + 361 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 361, + 545, + 410 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 361, + 545, + 410 + ], + "spans": [ + { + "bbox": [ + 305, + 361, + 545, + 410 + ], + "type": "text", + "content": "We report the qualitative and quantitative results in Fig. 5 and Tab. 3. As can be seen, it is clear that CREPS achieves the best scale consistency, while convolution-based models like ScaleParty and AnyresGAN perform poorly." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 418, + 405, + 430 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 418, + 405, + 430 + ], + "spans": [ + { + "bbox": [ + 306, + 418, + 405, + 430 + ], + "type": "text", + "content": "4.5. Ablation studies" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 437, + 545, + 569 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 437, + 545, + 569 + ], + "spans": [ + { + "bbox": [ + 304, + 437, + 545, + 569 + ], + "type": "text", + "content": "To better understand our proposed techniques, we analyze the effect of different parts of CREPS on the FFHQ datasets. We first consider a no-bi-line version of CREPS as a baseline (referred to as CREPS-NB), with dense 2D input and the decoder layers removed. We then apply bi-line decomposition but fuse the bi-line features only once at the end, with gradually increased thickness. Lastly, we add multiple decoders for layer-wise feature composition as introduced in Sec. 3.4. Because of limited time and computational resources, we only evaluate on " + }, + { + "bbox": [ + 304, + 437, + 545, + 569 + ], + "type": "inline_equation", + "content": "128 \\times 128" + }, + { + "bbox": [ + 304, + 437, + 545, + 569 + ], + "type": "text", + "content": " resolution and all of our models were trained for maximum of 2 days." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 570, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 546, + 713 + ], + "type": "text", + "content": "As the results in Tab. 4 show, CIPS performs worst in all three aspects compared with most of our models. Simply adding the bi-line with a single decoder at the end nearly halves the memory costs, but the FID score is still behind CREPS-NB even when the thickness is increased to " + }, + { + "bbox": [ + 304, + 570, + 546, + 713 + ], + "type": "inline_equation", + "content": "d = 8" + }, + { + "bbox": [ + 304, + 570, + 546, + 713 + ], + "type": "text", + "content": ". However, multiple decoders can help bring the image quality back to the level of CREPS-NB and even better with " + }, + { + "bbox": [ + 304, + 570, + 546, + 713 + ], + "type": "inline_equation", + "content": "d = 8" + }, + { + "bbox": [ + 304, + 570, + 546, + 713 + ], + "type": "text", + "content": ". In all settings, it can be clearly seen that we easily boost the FID score when increasing the thickness. These observations prove the importance and effectiveness of our proposed techniques. Remarkably, while the decoders seem compute-intensive, they are actually lightweight due to their" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "22414" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 48, + 69, + 287, + 128 + ], + "blocks": [ + { + "bbox": [ + 48, + 69, + 287, + 128 + ], + "lines": [ + { + "bbox": [ + 48, + 69, + 287, + 128 + ], + "spans": [ + { + "bbox": [ + 48, + 69, + 287, + 128 + ], + "type": "image", + "image_path": "3f77bd13a279a27efdf02f49ee855f50fe39da7f0224b4d9f168849af722367d.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 47, + 131, + 287, + 164 + ], + "lines": [ + { + "bbox": [ + 47, + 131, + 287, + 164 + ], + "spans": [ + { + "bbox": [ + 47, + 131, + 287, + 164 + ], + "type": "text", + "content": "Figure 6. Geometric transformations on the same target image (FFHQ-512 model) by changing the input coordinates. We mark the original image boundary using a red rectangle." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 48, + 175, + 287, + 242 + ], + "blocks": [ + { + "bbox": [ + 48, + 175, + 287, + 242 + ], + "lines": [ + { + "bbox": [ + 48, + 175, + 287, + 242 + ], + "spans": [ + { + "bbox": [ + 48, + 175, + 287, + 242 + ], + "type": "image", + "image_path": "5c2e38cd25cae7a40f75499f2e0e2f7660ac49426f87b5939fbfb5f240201e22.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 47, + 244, + 287, + 268 + ], + "lines": [ + { + "bbox": [ + 47, + 244, + 287, + 268 + ], + "spans": [ + { + "bbox": [ + 47, + 244, + 287, + 268 + ], + "type": "text", + "content": "Figure 7. Visualization of the feature maps extracted from our FFHQ-512 model. Each feature map is averaged over all channels." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 289, + 287, + 313 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 289, + 287, + 313 + ], + "spans": [ + { + "bbox": [ + 47, + 289, + 287, + 313 + ], + "type": "text", + "content": "narrow width compared with other layers, causing only small increases in memory and time." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 330, + 287, + 342 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 330, + 287, + 342 + ], + "spans": [ + { + "bbox": [ + 47, + 330, + 287, + 342 + ], + "type": "text", + "content": "4.6. Simple and complex geometric transformation" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 351, + 287, + 495 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 351, + 287, + 495 + ], + "spans": [ + { + "bbox": [ + 46, + 351, + 287, + 495 + ], + "type": "text", + "content": "Our CREPS model can support various geometric transformations on the same target image by keeping the input latent code " + }, + { + "bbox": [ + 46, + 351, + 287, + 495 + ], + "type": "inline_equation", + "content": "z" + }, + { + "bbox": [ + 46, + 351, + 287, + 495 + ], + "type": "text", + "content": " but changing the input coordinates " + }, + { + "bbox": [ + 46, + 351, + 287, + 495 + ], + "type": "inline_equation", + "content": "e^r" + }, + { + "bbox": [ + 46, + 351, + 287, + 495 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 351, + 287, + 495 + ], + "type": "inline_equation", + "content": "e^c" + }, + { + "bbox": [ + 46, + 351, + 287, + 495 + ], + "type": "text", + "content": ". We can translate the image by adding coordinate shifts " + }, + { + "bbox": [ + 46, + 351, + 287, + 495 + ], + "type": "inline_equation", + "content": "\\delta_y" + }, + { + "bbox": [ + 46, + 351, + 287, + 495 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 351, + 287, + 495 + ], + "type": "inline_equation", + "content": "\\delta_x" + }, + { + "bbox": [ + 46, + 351, + 287, + 495 + ], + "type": "text", + "content": " to the row and column input coordinates, respectively. We can also multiply these input coordinates by the same constant " + }, + { + "bbox": [ + 46, + 351, + 287, + 495 + ], + "type": "inline_equation", + "content": "s > 1" + }, + { + "bbox": [ + 46, + 351, + 287, + 495 + ], + "type": "text", + "content": " for zooming out or divide them by " + }, + { + "bbox": [ + 46, + 351, + 287, + 495 + ], + "type": "inline_equation", + "content": "s" + }, + { + "bbox": [ + 46, + 351, + 287, + 495 + ], + "type": "text", + "content": " for zooming in. As can be seen in the first three columns in Fig. 6, CREPS can perform those simple transformations with consistent details. Notably, CREPS can extrapolate the points outside the original image boundary, although it has never been trained on such input coordinates." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 498, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 498, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 498, + 288, + 714 + ], + "type": "text", + "content": "It is tricky for CREPS to handle complex transformations such as rotation or distortion since CREPS only takes in a row and a column coordinate input. Instead of producing the target image in one run, we can execute CREPS multiple times to generate different parts of the output image, then combine them. The simplest algorithm is to sample each target pixel per run by setting a single value for " + }, + { + "bbox": [ + 46, + 498, + 288, + 714 + ], + "type": "inline_equation", + "content": "e^r" + }, + { + "bbox": [ + 46, + 498, + 288, + 714 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 498, + 288, + 714 + ], + "type": "inline_equation", + "content": "e^c" + }, + { + "bbox": [ + 46, + 498, + 288, + 714 + ], + "type": "text", + "content": ". However, that algorithm is too slow, which requires 262k runs to produce a single " + }, + { + "bbox": [ + 46, + 498, + 288, + 714 + ], + "type": "inline_equation", + "content": "512 \\times 512" + }, + { + "bbox": [ + 46, + 498, + 288, + 714 + ], + "type": "text", + "content": " image. A faster way is to sample the target image row-by-row. Assuming we need to generate an image " + }, + { + "bbox": [ + 46, + 498, + 288, + 714 + ], + "type": "inline_equation", + "content": "I" + }, + { + "bbox": [ + 46, + 498, + 288, + 714 + ], + "type": "text", + "content": " with the input latent " + }, + { + "bbox": [ + 46, + 498, + 288, + 714 + ], + "type": "inline_equation", + "content": "z" + }, + { + "bbox": [ + 46, + 498, + 288, + 714 + ], + "type": "text", + "content": " and the target pixels' normalized coordinates " + }, + { + "bbox": [ + 46, + 498, + 288, + 714 + ], + "type": "inline_equation", + "content": "\\{(r_{ij}, c_{ij})\\}_{i = \\overline{1,H}, j = \\overline{1,W}}" + }, + { + "bbox": [ + 46, + 498, + 288, + 714 + ], + "type": "text", + "content": ". We can produce each row " + }, + { + "bbox": [ + 46, + 498, + 288, + 714 + ], + "type": "inline_equation", + "content": "I_i" + }, + { + "bbox": [ + 46, + 498, + 288, + 714 + ], + "type": "text", + "content": " of the target image by generating an intermediate image " + }, + { + "bbox": [ + 46, + 498, + 288, + 714 + ], + "type": "inline_equation", + "content": "\\Gamma" + }, + { + "bbox": [ + 46, + 498, + 288, + 714 + ], + "type": "text", + "content": " using the input coordinates " + }, + { + "bbox": [ + 46, + 498, + 288, + 714 + ], + "type": "inline_equation", + "content": "e^r = [r_{ij}]_{j = \\overline{1,W}}" + }, + { + "bbox": [ + 46, + 498, + 288, + 714 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 498, + 288, + 714 + ], + "type": "inline_equation", + "content": "e^c = [c_{ij}]_{j = \\overline{1,W}}" + }, + { + "bbox": [ + 46, + 498, + 288, + 714 + ], + "type": "text", + "content": " and sample its diagonal " + }, + { + "bbox": [ + 46, + 498, + 288, + 714 + ], + "type": "inline_equation", + "content": "I_i = \\text{diag}(I')" + }, + { + "bbox": [ + 46, + 498, + 288, + 714 + ], + "type": "text", + "content": ". We provide two examples with rotation and elastic distortion in the last two columns of Fig. 6. Both images are correctly transformed with unchanged content." + } + ] + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 309, + 70, + 544, + 128 + ], + "blocks": [ + { + "bbox": [ + 309, + 70, + 544, + 128 + ], + "lines": [ + { + "bbox": [ + 309, + 70, + 544, + 128 + ], + "spans": [ + { + "bbox": [ + 309, + 70, + 544, + 128 + ], + "type": "image", + "image_path": "94eb2199e186794db439e0125a038f740310a39b1f8fe1ada6b3676fc283a002.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 131, + 545, + 175 + ], + "lines": [ + { + "bbox": [ + 305, + 131, + 545, + 175 + ], + "spans": [ + { + "bbox": [ + 305, + 131, + 545, + 175 + ], + "type": "text", + "content": "Figure 8. Samples of the most common kinds of artifacts on different datasets. They are best described as repeating/wavy patterns, vertical symmetry, and glowing blobs. Left-most image is cropped and zoomed-in from a full-face image." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 182, + 405, + 194 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 182, + 405, + 194 + ], + "spans": [ + { + "bbox": [ + 306, + 182, + 405, + 194 + ], + "type": "text", + "content": "4.7. Feature analysis" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 200, + 545, + 334 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 200, + 545, + 334 + ], + "spans": [ + { + "bbox": [ + 305, + 200, + 545, + 334 + ], + "type": "text", + "content": "We visualize the key feature maps inside our FFHQ-512 model when generating a facial image and provide them in Fig. 7. The maps include the layer-wise composed features " + }, + { + "bbox": [ + 305, + 200, + 545, + 334 + ], + "type": "inline_equation", + "content": "\\{F^{(l)}\\}_{l = \\overline{1,N}}" + }, + { + "bbox": [ + 305, + 200, + 545, + 334 + ], + "type": "text", + "content": ", the corresponding layer-wise fused maps " + }, + { + "bbox": [ + 305, + 200, + 545, + 334 + ], + "type": "inline_equation", + "content": "\\{E^{(l)}\\}_{l = \\overline{1,N}}" + }, + { + "bbox": [ + 305, + 200, + 545, + 334 + ], + "type": "text", + "content": ", and the final feature map " + }, + { + "bbox": [ + 305, + 200, + 545, + 334 + ], + "type": "inline_equation", + "content": "F" + }, + { + "bbox": [ + 305, + 200, + 545, + 334 + ], + "type": "text", + "content": " (see Eq. 4-6). Thanks to the asymmetric fusion scheme, the model seems to synthesize the output in a coarse-to-fine manner. The early composed feature maps are smooth and focus on the global structure, while the later ones focus on sharp details. Although each composed feature map " + }, + { + "bbox": [ + 305, + 200, + 545, + 334 + ], + "type": "inline_equation", + "content": "F^{(l)}" + }, + { + "bbox": [ + 305, + 200, + 545, + 334 + ], + "type": "text", + "content": " is quite simple, the network can represent complex content by fusion." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 341, + 378, + 353 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 341, + 378, + 353 + ], + "spans": [ + { + "bbox": [ + 306, + 341, + 378, + 353 + ], + "type": "text", + "content": "4.8. Limitation" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 360, + 545, + 503 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 360, + 545, + 503 + ], + "spans": [ + { + "bbox": [ + 304, + 360, + 545, + 503 + ], + "type": "text", + "content": "Being a fully-connected generator, CREPS shares the same limitation with other similar work, which is the lack of spatial bias since each pixel is independently generated. Hence, some spatial-related artifacts occasionally occur in our generated images (Fig. 8). A potential cause is the sine activation at the beginning, producing repeating patterns and vertical symmetry of the output. We also note that some samples contain a noticeable blob that is completely out-of-domain. We found CIPS facing the same problem, and the root cause can be the missing spatial guidance from neighboring pixels and the effect of Leaky-RELU activations which strengthens the isolation of some pixel regions." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 514, + 378, + 526 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 514, + 378, + 526 + ], + "spans": [ + { + "bbox": [ + 306, + 514, + 378, + 526 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 534, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 534, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 534, + 545, + 713 + ], + "type": "text", + "content": "In this paper, we present a new architecture named CREPS, a cost-effective and scale-equivariant generator that can synthesize images with any target resolution. Our key contributions are an INR-based design, a thick biline representation, and a layer-wise feature composition scheme. While being more memory-efficient, our CREPS models can produce highly realistic images and surpass the INR-based model CIPS in most cases. CREPS also offers the best scale consistency by keeping image details unchanged when varying the output resolution. We conducted several experiments to explore some attractive properties of this fully-connected generator and discussed CREPS's applications in various scenarios. Future development of our approach can be eliminating artifacts mentioned in Sec. 4.8 and further improving the quality of our samples." + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "22415" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 288, + 714 + ], + "type": "list", + "angle": 0, + "index": 14, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 145 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 145 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 145 + ], + "type": "text", + "content": "[1] Ivan Anokhin, Kirill Demochkin, Taras Khakhulin, Gleb Sterkin, Victor Lempitsky, and Denis Korzhenkov. 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In IEEE/CVF Conference on Computer Vision and Pattern Recognition (CVPR), 2021. 2" + } + ] + } + ], + "index": 2 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 749, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 749, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 749, + 317, + 757 + ], + "type": "text", + "content": "22417" + } + ] + } + ], + "index": 4 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 9 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Efficient Second-Order Plane Adjustment/0ca972fe-43f5-4fa8-bf07-17ebcd5d268a_content_list.json b/2023/Efficient Second-Order Plane Adjustment/0ca972fe-43f5-4fa8-bf07-17ebcd5d268a_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..5f8b20b2dc71dafdf359bc09c8131ef372d66871 --- /dev/null +++ b/2023/Efficient Second-Order Plane Adjustment/0ca972fe-43f5-4fa8-bf07-17ebcd5d268a_content_list.json @@ -0,0 +1,2045 @@ +[ + { + "type": "text", + "text": "Efficient Second-Order Plane Adjustment", + "text_level": 1, + "bbox": [ + 272, + 130, + 697, + 152 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Lipu Zhou Meituan, Beijing, China zhoulipu@meituan.com", + "bbox": [ + 388, + 181, + 581, + 233 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 268, + 313, + 284 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Planes are generally used in 3D reconstruction for depth sensors, such as RGB-D cameras and LiDARs. This paper focuses on the problem of estimating the optimal planes and sensor poses to minimize the point-to-plane distance. The resulting least-squares problem is referred to as plane adjustment (PA) in the literature, which is the counterpart of bundle adjustment (BA) in visual reconstruction. Iterative methods are adopted to solve these least-squares problems. Typically, Newton's method is rarely used for a large-scale least-squares problem, due to the high computational complexity of the Hessian matrix. Instead, methods using an approximation of the Hessian matrix, such as the Levenberg-Marquardt (LM) method, are generally adopted. This paper adopts the Newton's method to efficiently solve the PA problem. Specifically, given poses, the optimal plane have a close-form solution. Thus we can eliminate planes from the cost function, which significantly reduces the number of variables. Furthermore, as the optimal planes are functions of poses, this method actually ensures that the optimal planes for the current estimated poses can be obtained at each iteration, which benefits the convergence. The difficulty lies in how to efficiently compute the Hessian matrix and the gradient of the resulting cost. This paper provides an efficient solution. Empirical evaluation shows that our algorithm outperforms the state-of-the-art algorithms.", + "bbox": [ + 75, + 301, + 473, + 680 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 708, + 209, + 724 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Planes ubiquitously exist in man-made environments, as demonstrated in Fig. 1. Thus they are generally used in simultaneous localization and mapping (SLAM) systems for depth sensors, such as RGB-D cameras [6, 9, 12-14] and LiDARs [16, 21, 22, 24, 26]. Just as bundle adjustment (BA) [3, 8, 20, 25] is important for visual reconstruction [1, 5, 18, 19], jointly optimizing planes and depth sensor poses, which is called plane adjustment (PA) [24,26], is critical for 3D reconstruction using depth sensors. This paper focuses on efficiently solving the large-scale PA problem.", + "bbox": [ + 75, + 734, + 468, + 885 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "The BA and PA problems both involve jointly optimiz", + "bbox": [ + 96, + 885, + 468, + 901 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/9deb1687d382e0c43556b98b8b209c0391c0a1814a79c39e867c17c2fa22c858.jpg", + "image_caption": [ + "(a) Point cloud from perturbed poses" + ], + "image_footnote": [], + "bbox": [ + 527, + 271, + 867, + 388 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/37f2ef9a59f7a31f5dc58f03e53fd417b300370e284a02b070c728a8c916ab5b.jpg", + "image_caption": [ + "(b) Point cloud from our algorithm", + "Figure 1. We use Gaussian noises to perturb the poses of dataset D in Fig. 3. The standard deviations for rotation and translation are $3^{\\circ}$ and $0.3m$ , respectively. The resulting point cloud (a) is in a mess. Fig. (b) shows the result from our algorithm. Our algorithm can quickly align the planes, as shown in Fig. 5." + ], + "image_footnote": [], + "bbox": [ + 527, + 415, + 867, + 534 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "ing 3D structures and sensor poses. As the two problems are similar, it is straightforward to apply the well-studied solutions for BA to PA, as done in [23, 26]. However, planes in PA can be eliminated, so that the cost function of the PA problem only depends on sensor poses, which significantly reduces the number of variables. This property provides a promising direction to efficiently solve the PA problem. However, it is difficult to compute the Hessian matrix and the gradient vector of the resulting cost. Although this problem was studied in several previous works [10, 16], no efficient solution has been proposed. This paper seeks to solve this problem.", + "bbox": [ + 496, + 657, + 890, + 838 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "The main contribution of this paper is an efficient PA solution using Newton's method. We derive a closed-form solution for the Hessian matrix and the gradient vector for the PA problem whose computational complexity is inde", + "bbox": [ + 496, + 839, + 893, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "13113", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "pendent of the number of points on the planes. Our experimental results show that the proposed algorithm converges faster than the state-of-the-art algorithms.", + "bbox": [ + 75, + 90, + 468, + 137 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 76, + 150, + 218, + 166 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "The PA problem is closely related to the BA problem. In BA, points and camera poses are jointly optimized to minimize the reprojection error. Schur complement [3, 20, 25] or the square root method [7, 8] is generally used to solve the linear system of the iterative methods. The keypoint is to generate a reduced camera system (RCS) which only relates to camera poses.", + "bbox": [ + 75, + 175, + 467, + 281 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In PA, planes and poses are jointly optimized. Planes are the counterparts of points in BA. Thus, the well-known solutions for the BA problem can be applied to the PA problem [23, 24]. In the literature, two cost functions are used to formulate the PA problem. The first one is the plane-to-plane distance which measures the difference between two plane parameters [12, 13]. The value of the plane-to-plane distance is related to the choice of the global coordinate system, which means the selection of the global coordinate system will affect the accuracy of the results. The second one is the point-to-plane distance, whose value is invariant to the choice of the global coordinate system. The solutions of different choices of the global coordinate system are equivalent up to a rigid transformation. Zhou et al. [23] show that the point-to-plane distance can converge faster and lead to a more accurate result. But unlike BA where each 3D point has only one 2D observation at a pose, a plane can generate many points at a pose as demonstrated in Fig. 2. This means the point-to-plane distance probably leads to a very large-scale least-squares problem. Directly adopting the BA solutions is computationally infeasible for a large-scale PA problem. Zhou et al. [23] propose to use the QR decomposition to accelerate the computation.", + "bbox": [ + 75, + 281, + 467, + 628 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "For a general least-squares problem with $M$ variables, the computational complexity of the Hessian matrix is $O(M^2)$ . Thus, in the computer vision community, it is ingrained that Newton's method is infeasible for a large-scale optimization problem, as calculating the Hessian matrix is computationally demanding. Instead, Gauss-Newton-based iterative methods are generally adopted. Suppose that $\\mathbf{J}$ is the Jacobian matrix of the residuals. The Gauss-Newton method actually approximates the Hessian matrix by $\\mathbf{H} \\approx \\mathbf{J}^T\\mathbf{J}$ . In theory, Newton's method can lead to a better quadratic approximation to the original cost function, which means the Newton's step probably yields a better result. This in turn may reduce the number of iterations.", + "bbox": [ + 75, + 628, + 467, + 824 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "The PA problem has a special property that the optimal plane parameters are determined by the poses. That is to say the point-to-plane cost actually only depends on the poses. This property is attractive, as it significantly reduces the number of variables, which makes using the Newton's", + "bbox": [ + 75, + 825, + 467, + 900 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/2f6f9651529f33fdb7c651bb24179fca86e7565952419654e9fb8aa6534f7412.jpg", + "image_caption": [ + "(a) A PA problem with 3 poses and 4 planes" + ], + "image_footnote": [], + "bbox": [ + 506, + 92, + 709, + 204 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/9612a03506748a6aff89238dcf9ffb91e1fb6cd2f27eeadee99092a8811371ea.jpg", + "image_caption": [ + "(b) Plane Observation", + "Figure 2. A schematic of the PA problem and the planes detected in a LiDAR scan. Unlike BA where each 3D point only has one observation, many points can be captured from a plane in PA. Assume that $N$ points are captured from a plane. The computational complexity of the Hessian matrix related to these points using BALM [16] is $O(N^2)$ . Thus, this method is infeasible for a large-scale problem. In contrast, the computational complexity of our algorithm is independent of $N$ ." + ], + "image_footnote": [], + "bbox": [ + 725, + 95, + 885, + 200 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "method possible. In traditional iterative methods, the correlation between the plane parameters and the poses are ignored. Thus, after one iteration, there is no guarantee that the new plane parameters are optimal for the new poses. Using the property of the PA, it is possible to overcome this drawback, which may lead to faster convergence. Several previous works seek to exploit this property of PA. Ferrer [10] explored an algebraic point-to-plane distance and provided a closed-form gradient for the resulting cost. The algebraic cost may result in a suboptimal solution [4], and the first-order optimization generally leads to slow convergence [20]. Liu et al. [16] provided analytic forms of the Hessian matrix and the gradient of the genuine point-to-plane cost. Assume that $N$ points are captured from a plane. The computational complexity of the Hessian matrix related to these points is $O(N^2)$ . Since $N$ can be large as shown in Fig. 2, this algorithm is computationally demanding and infeasible for a large-scale problem.", + "bbox": [ + 496, + 369, + 890, + 642 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In summary, the potential benefits of the special property of the PA problem have not been manifested in previous works. The bottleneck is how to efficiently compute the Hessian matrix and the gradient vector. This paper focuses on solving this problem.", + "bbox": [ + 496, + 643, + 890, + 717 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "3. Problem Formulation", + "text_level": 1, + "bbox": [ + 500, + 733, + 705, + 750 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In this paper we use italic, boldfaced lowercase and bold-faced uppercase letters to represent scalars, vectors and matrices, respectively.", + "bbox": [ + 496, + 758, + 890, + 805 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "3.1. Notations", + "text_level": 1, + "bbox": [ + 500, + 816, + 609, + 830 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Planes and Poses A plane can be represented by a four-dimensional vector $\\pmb{\\pi} = [n;d]$ . We denote the rotational and translational components from a depth sensor coordinate system to the global coordinate system as $\\mathbf{R}\\in SO(3)$", + "bbox": [ + 496, + 840, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "13114", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "and $t \\in \\mathbb{R}^3$ , respectively. To simplify the notation in the following description, we also use the following two matrices to represent a pose:", + "bbox": [ + 75, + 90, + 468, + 137 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {X} = \\left[ \\begin{array}{l l} \\mathbf {R}, & t \\\\ \\mathbf {0}, & 1 \\end{array} \\right] \\in S E (3) \\text {a n d} \\mathbf {T} = \\left[ \\begin{array}{l l} \\mathbf {R}, & t \\end{array} \\right]. \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 125, + 148, + 468, + 184 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "As $\\mathbf{R} \\in SO(3)$ , a certain parameterization is usually adopted in the optimization [20]. In this paper, we use the Cayley-Gibbs-Rodriguez (CGR) parameterization [11] to represent $\\mathbf{R}$", + "bbox": [ + 76, + 196, + 468, + 258 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {R} = \\frac {\\bar {\\mathbf {R}}}{1 + \\boldsymbol {s} ^ {T} \\boldsymbol {s}}, \\bar {\\mathbf {R}} = \\left(1 - \\boldsymbol {s} ^ {T} \\boldsymbol {s}\\right) \\mathbf {I} _ {3} + 2 [ \\boldsymbol {s} ] _ {\\times} + 2 \\boldsymbol {s} \\boldsymbol {s} ^ {T}, \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 88, + 272, + 468, + 305 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $s = [s_1; s_2; s_3]$ is a three-dimensional vector. We adopt the CGR parameterization as it is a minimal representation for $\\mathbf{R}$ . Furthermore, unlike the angle-axis parameterization that is singular at $\\mathbf{I}_3$ , the CGR parameterization is well-defined at $\\mathbf{I}_3$ , and equals to $[0; 0; 0]$ which can accelerate the computation, as described in Section 4.3. We parameterize $\\mathbf{X}$ as a six-dimensional vector $x = [s; t]$ .", + "bbox": [ + 75, + 316, + 468, + 425 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Newton's method This paper adopts the damped Newton's method in the optimization. For a cost function $f(z)$ , the damped Newton's method seeks to find its minimizer from an initial point. Assume that $z_{n}$ is the solution at the $n$ th iteration. Given the Hessian matrix $\\mathbf{H}_f(z_n)$ and the gradient $g_{f}(z_{n})$ at $z_{n},z_{n}$ is updated by $z_{n + 1} = z_{n} + \\varDelta z$ . Here $\\varDelta z$ is from", + "bbox": [ + 75, + 425, + 468, + 530 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\left(\\mathbf {H} _ {f} \\left(\\boldsymbol {z} _ {n}\\right) + \\mu \\mathbf {I})\\right) \\Delta z = - \\boldsymbol {g} _ {f} \\left(\\boldsymbol {z} _ {n}\\right), \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 161, + 547, + 468, + 564 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\mu$ is adjusted at each iteration to make the value of $f(z)$ reduce, as done in the Levenberg-Marquardt (LM) algorithm [17].", + "bbox": [ + 76, + 578, + 468, + 625 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Matrix Calculus In the following derivation, we will use vector-by-vector, vector-by-scalar, scalar-by-vector derivatives. Here we provide their definitions.", + "bbox": [ + 75, + 625, + 468, + 670 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Assume $\\mathbf{a} = [a_1;\\dots ;a_N]\\in \\mathbb{R}^N$ is a vector function of $\\pmb {b} = [b_{1},\\dots ,b_{M}]\\in \\mathbb{R}^{M}$ . The first-order partial derivatives of vector-by-vector $\\frac{\\partial\\pmb{a}}{\\partial\\pmb{b}}$ , vector-by-scalar $\\frac{\\partial\\pmb{a}}{\\partial b_j}$ , and scalar-byvector $\\frac{\\partial a_i}{\\partial b}$ are defined as", + "bbox": [ + 76, + 671, + 468, + 739 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\frac {\\partial \\boldsymbol {a}}{\\partial \\boldsymbol {b}} = \\left[ \\begin{array}{c c c} \\frac {\\partial a _ {1}}{\\partial b _ {1}} & \\dots & \\frac {\\partial a _ {N}}{\\partial b _ {1}} \\\\ \\vdots & \\ddots & \\vdots \\\\ \\frac {\\partial a _ {1}}{\\partial b _ {M}} & \\dots & \\frac {\\partial a _ {N}}{\\partial b _ {M}} \\end{array} \\right], \\frac {\\partial \\boldsymbol {a}}{\\partial b _ {j}} = \\left[ \\begin{array}{c} \\frac {\\partial a _ {1}}{\\partial b _ {j}} \\\\ \\vdots \\\\ \\frac {\\partial a _ {N}}{\\partial b _ {j}} \\end{array} \\right], \\frac {\\partial a _ {i}}{\\partial \\boldsymbol {b}} = \\left[ \\begin{array}{c} \\frac {\\partial a _ {i}}{\\partial b _ {1}} \\\\ \\vdots \\\\ \\frac {\\partial a _ {i}}{\\partial b _ {M}} \\end{array} \\right] \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 76, + 752, + 480, + 827 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\frac{\\partial\\pmb{a}}{\\partial\\pmb{b}}$ is an $M\\times N$ matrix with $\\frac{\\partial a_j}{\\partial b_i}$ as the ith row jth column element, $\\frac{\\partial\\pmb{a}}{\\partial b_j}$ is an $N$ -dimensional vector whose ith term is $\\frac{\\partial a_i}{\\partial b_j}$ , and $\\frac{\\partial a_i}{\\partial\\pmb{b}}$ is an $M$ -dimensional vector whose ith term is $\\frac{\\partial a_i}{\\partial b_i}$ .", + "bbox": [ + 75, + 825, + 468, + 904 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. Optimal Plane Estimation", + "text_level": 1, + "bbox": [ + 500, + 90, + 735, + 107 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Given a set of $K$ points $\\{\\pmb{p}_i\\}$ , the optimal plane $\\hat{\\pi}$ can be estimated by minimizing the sum of squared point-to-plane distances", + "bbox": [ + 498, + 113, + 890, + 157 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {\\boldsymbol {\\pi}} = \\arg \\min _ {\\boldsymbol {\\pi}} \\sum_ {i} ^ {K} \\left(\\boldsymbol {n} ^ {T} \\boldsymbol {p} _ {i} + d\\right) ^ {2}, s. t. \\| \\boldsymbol {n} \\| _ {2} ^ {2} = 1. \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 524, + 164, + 890, + 204 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "There is a closed-form solution for $\\hat{\\pi}$ . Let us define", + "bbox": [ + 500, + 212, + 841, + 226 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {M} = \\sum_ {i = 1} ^ {K} \\left(\\boldsymbol {p} _ {i} - \\bar {\\boldsymbol {p}}\\right) \\left(\\boldsymbol {p} _ {i} - \\bar {\\boldsymbol {p}}\\right) ^ {T} = \\mathbf {S} - K \\bar {\\boldsymbol {p}} \\bar {\\boldsymbol {p}} ^ {T}, \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 555, + 232, + 890, + 268 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\mathbf{S} = \\sum_{i=1}^{K} \\pmb{p}_i \\pmb{p}_i^T$ and $\\bar{\\pmb{p}} = \\frac{1}{K} \\sum_{i}^{K} \\pmb{p}_i$ . Assume that $\\lambda_3(\\mathbf{M})$ and $\\xi_3(\\mathbf{M})$ are the smallest eigenvalue of $\\mathbf{M}$ and the corresponding eigenvector, respectively. Using these notations, we can write the optimal plane $\\hat{\\pmb{\\pi}} = [\\hat{\\pmb{n}}; \\hat{d}]$ as", + "bbox": [ + 498, + 275, + 890, + 339 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {\\boldsymbol {n}} = \\boldsymbol {\\xi} _ {3} (\\mathbf {M}), \\hat {d} = - \\hat {\\boldsymbol {n}} ^ {T} \\bar {\\boldsymbol {p}}. \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 607, + 347, + 890, + 364 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Furthermore, the cost of (5) at $\\hat{\\pi}$ equals to $\\lambda_3(\\mathbf{M})$ , i.e.,", + "bbox": [ + 500, + 372, + 861, + 388 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\lambda_ {3} (\\mathbf {M}) = \\sum_ {i = 1} ^ {K} \\left(\\hat {\\boldsymbol {n}} \\boldsymbol {p} _ {i} + \\hat {d}\\right) ^ {2} = \\min _ {\\pi} \\sum_ {i = 1} ^ {K} \\left(\\boldsymbol {n} \\boldsymbol {p} _ {i} + d\\right) ^ {2}. \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 514, + 396, + 890, + 438 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The above property will be used to eliminate planes in PA.", + "bbox": [ + 500, + 444, + 885, + 459 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.3. Plane Adjustment", + "text_level": 1, + "bbox": [ + 500, + 467, + 673, + 483 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Assume that there are $M$ planes and $N$ poses. According to section 3.1, the $i$ th plane can be represented by a four-dimensional vector $\\pmb{\\pi}_i = [n_i;d_i]$ . The $j$ th pose is denoted as $\\pmb{x}_j$ . The observation of $\\pmb{\\pi}_i$ at $\\pmb{x}_j$ is a set of $N_{ij}$ points $\\mathbb{Q}_{ij} = \\{\\pmb{p}_{ijk} \\in \\mathbb{R}^3\\}_{k=1}^{N_{ij}}$ . For a 3D point $\\pmb{p}_{ijk}$ , we use $\\tilde{\\pmb{p}}_{ijk} = [\\pmb{p}_{ijk};1]$ to represent the homogeneous coordinates of $\\pmb{p}_{ijk}$ . Then, the transformation from the local coordinate system at $\\pmb{x}_j$ to the global coordinate system can be represented as", + "bbox": [ + 498, + 489, + 890, + 628 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {p} _ {i j k} ^ {g} = \\mathbf {R} _ {j} \\boldsymbol {p} _ {i j k} + \\boldsymbol {t} _ {j} = \\mathbf {T} _ {j} \\tilde {\\boldsymbol {p}} _ {i j k}, \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 586, + 637, + 890, + 656 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\mathbf{T}_j$ is defined in (1). Then the distance $d_{ijk}$ from $\\pmb{p}_{ijk}$ to $\\pi_i$ has the form", + "bbox": [ + 498, + 662, + 888, + 691 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} d _ {i j k} \\left(\\boldsymbol {\\pi} _ {i}, \\mathbf {x} _ {j}\\right) = \\boldsymbol {n} _ {i} ^ {T} \\left(\\mathbf {R} _ {j} \\boldsymbol {p} _ {i j k} + \\boldsymbol {t} _ {j}\\right) + d _ {i} \\tag {10} \\\\ = \\boldsymbol {n} _ {i} ^ {T} \\mathbf {T} _ {j} \\tilde {\\boldsymbol {p}} _ {i j k} + d _ {j} = \\boldsymbol {\\pi} _ {i} ^ {T} \\tilde {\\boldsymbol {p}} _ {i j k} ^ {g}. \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 535, + 699, + 890, + 739 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The PA problem is to jointly adjust the $M$ planes $\\{\\pi_i\\}$ and the $N$ sensor poses $\\{\\pmb{x}_j\\}$ to minimize the sum of squared point-to-plane distances. Specifically, using (10), we can formulate the cost function of the PA problem as", + "bbox": [ + 498, + 746, + 890, + 806 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\min _ {\\left\\{\\boldsymbol {\\pi} _ {i} \\right\\}, \\left\\{\\mathbf {x} _ {j} \\right\\}} \\sum_ {i = 1} ^ {M} \\underbrace {\\sum_ {j \\in o b s \\left(\\boldsymbol {\\pi} _ {i}\\right)} \\sum_ {k = 1} ^ {N _ {i j}} d _ {i j k} ^ {2} \\left(\\boldsymbol {\\pi} _ {i} , \\mathbf {x} _ {j}\\right)} _ {C _ {i} \\left(\\boldsymbol {\\pi} _ {i}, \\mathbb {X} _ {i}\\right), \\mathbb {X} _ {i} = \\left\\{\\boldsymbol {x} _ {j} \\mid j \\in o b s \\left(\\boldsymbol {\\pi} _ {i}\\right) \\right\\}} = \\min _ {\\left\\{\\boldsymbol {\\pi} _ {i} \\right\\}, \\left\\{\\boldsymbol {x} _ {j} \\right\\}} \\sum_ {i = 1} ^ {M} C _ {i} \\left(\\boldsymbol {\\pi} _ {i}, \\mathbb {X} _ {i}\\right). \\tag {11}\n$$\n", + "text_format": "latex", + "bbox": [ + 501, + 825, + 934, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "13115", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $obs(\\pi_i)$ represents the indexes of poses where $\\pi_i$ can be observed, and $C_i(\\pi_i, \\mathbb{X}_i)$ accumulates the errors from $N_i = \\sum_{j \\in obs(\\pi_i)} N_{ij}$ points captured at the poses in $\\mathbb{X}_i$ . According to (6) and (9), we get", + "bbox": [ + 76, + 90, + 468, + 151 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {M} _ {i} \\left(\\mathbb {X} _ {i}\\right) = \\sum_ {j \\in o b s \\left(\\boldsymbol {\\pi} _ {i}\\right)} \\mathbf {S} _ {i j} - N _ {i} \\bar {\\boldsymbol {p}} _ {i} \\bar {\\boldsymbol {p}} _ {i} ^ {T}, \\tag {12}\n$$\n", + "text_format": "latex", + "bbox": [ + 158, + 161, + 468, + 191 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\bar{\\pmb{p}}_i = \\frac{1}{N_i}\\sum_{j\\in obs(\\pmb{\\pi}_i)}\\sum_{k = 1}^{N_{ij}}\\pmb{p}_{ijk}^g$ and $\\mathbf{S}_{ij} = \\sum_{k = 1}^{N_{ij}}\\pmb{p}_{ijk}^g\\left(\\pmb{p}_{ijk}^g\\right)^T$ . Here the elements in $\\mathbf{M}_i$ , $\\mathbf{S}_{ij}$ and $\\bar{\\pmb{p}}_i$ in (12) are all functions of the poses in $\\mathbb{X}_i$ . Substituting $\\pmb{p}_{ijk}^g$ in (9) into $\\mathbf{S}_{ij}$ and $\\bar{\\pmb{p}}_i$ in (12), we have", + "bbox": [ + 76, + 202, + 468, + 280 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\mathbf {S} _ {i j} = \\mathbf {T} _ {j} \\underbrace {\\sum_ {k = 1} ^ {N _ {i j}} \\tilde {\\boldsymbol {p}} _ {i j k} \\tilde {\\boldsymbol {p}} _ {i j k} ^ {T}} _ {\\mathbf {U} _ {i j}} \\mathbf {T} _ {j} ^ {T} = \\mathbf {T} _ {j} \\mathbf {U} _ {i j} \\mathbf {T} _ {j} ^ {T}, \\\\ \\bar {\\boldsymbol {p}} _ {i} = \\frac {1}{N _ {i}} \\sum_ {j \\in o b s (\\boldsymbol {\\pi} _ {i})} \\mathbf {T} _ {j} \\underbrace {\\sum_ {k = 1} ^ {N _ {i j}} \\tilde {\\boldsymbol {p}} _ {i j k}} _ {\\tilde {\\boldsymbol {p}} _ {i j}} = \\frac {1}{N _ {i}} \\sum_ {j \\in o b s (\\boldsymbol {\\pi} _ {i})} \\mathbf {T} _ {j} \\tilde {\\boldsymbol {p}} _ {i j}. \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 89, + 282, + 467, + 404 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Here $\\mathbf{U}_{ij}$ and $\\tilde{\\boldsymbol{p}}_{ij}$ in (13) are constants. We only need to compute them once, and reuse them in the iteration.", + "bbox": [ + 76, + 412, + 468, + 443 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "According to (7), given poses in $\\mathbb{X}_i$ , the optimal solution for $\\pi_i$ has a closed-form expression $\\hat{\\pi}_i = [\\hat{n}_i; \\hat{d}_i]$ , where $\\hat{n}_i = \\xi_3(\\mathbf{M}_i(\\mathbb{X}_i))$ and $\\hat{d}_i = -\\hat{n}\\bar{p}_i$ . As $\\mathbf{M}_i$ and $\\bar{p}_i$ are functions of the poses in $\\mathbb{X}_i$ , $\\hat{\\pi}_i$ is also a function of the poses in $\\mathbb{X}_i$ . That is to say $\\hat{\\pi}_i$ is completely determined by the poses in $\\mathbb{X}_i$ . To simplify the notation, let us define", + "bbox": [ + 76, + 444, + 468, + 535 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\lambda_ {i, 3} (\\mathbb {X} _ {i}) = \\lambda_ {3} \\left(\\mathbf {M} _ {i} (\\mathbb {X} _ {i})\\right), \\tag {14}\n$$\n", + "text_format": "latex", + "bbox": [ + 187, + 547, + 468, + 564 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "which represents the smallest eigenvalue of $\\mathbf{M}_i(\\mathbb{X}_i)$ .", + "bbox": [ + 76, + 575, + 424, + 590 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Substituting the optimal plane estimation $\\hat{\\pi}_i$ into $C_i(\\pi_i, \\mathbb{X}_i)$ in (11) and using (8), we have", + "bbox": [ + 76, + 592, + 468, + 622 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\lambda_ {i, 3} (\\mathbb {X} _ {i}) = C _ {i} \\left(\\hat {\\pi} _ {i}, \\mathbb {X} _ {i}\\right). \\tag {15}\n$$\n", + "text_format": "latex", + "bbox": [ + 191, + 633, + 468, + 651 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Using (15), we can formulate the PA problem in (11) as", + "bbox": [ + 76, + 662, + 444, + 678 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\left\\{\\hat {\\mathbf {x}} _ {j} \\right\\} = \\arg \\min _ {\\left\\{\\mathbf {X} _ {j} \\right\\}} \\boldsymbol {\\tau}, \\boldsymbol {\\tau} = \\sum_ {i = 1} ^ {M} \\lambda_ {i, 3} (\\mathbb {X} _ {i}). \\tag {16}\n$$\n", + "text_format": "latex", + "bbox": [ + 143, + 681, + 468, + 722 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Table 1 summarizes the notations for PA.", + "bbox": [ + 76, + 734, + 349, + 748 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The cost function (16) only depends on poses, which significantly reduces the number of variables. However, as it is the sum of squared point-to-plane distances, we cannot apply the Gauss-Newton-based methods to minimize it, where the Jacobian matrix of residuals are required. Here we adopt the Newton's method to solve it. The crux for applying the Newton's method to minimize (16) is how to compute the gradient and the Hessian matrix of (16) efficiently. In the following sections, we provide a closed-form solution for them. Note that we can assign a weight to each point to", + "bbox": [ + 75, + 750, + 468, + 900 + ], + "page_idx": 3 + }, + { + "type": "table", + "img_path": "images/112f1451ef0d645652ef80f3cb4f37e73f2fd5a13b569940bae9159cb67ff95a.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
NotationDescription
πiTheith plane.
obs(πi)The set of indexes of poses which can see πi.
XiThe set of poses which can see πi.
MiThe scatter matrix for πi.
λ3,iThe smallest eigenvalue ofMi.
xj, xkThe jth and kth poses.
xjm, xknThe mth and nth elements of xj and xk.
PjThe set of planes that are visible to xj.
PjkThe set of planes that are visible to xj and xk.
", + "bbox": [ + 500, + 89, + 890, + 256 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Table 1. Table of notations.", + "bbox": [ + 612, + 266, + 777, + 279 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "punish outliers, which also has a close-form solution for planes using the weighted PCA. Our algorithm can be extended to this situation. To simplify the notation, we omit the variables of functions in the following description (e.g., $\\lambda_{i,3}(\\mathbb{X}_i)\\to \\lambda_{i,3})$ .", + "bbox": [ + 498, + 305, + 890, + 381 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4. Newton's Iteration for Plane Adjustment", + "text_level": 1, + "bbox": [ + 498, + 393, + 864, + 410 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Let us denote the gradient and the Hessian matrix of $\\tau$ in (16) as $\\pmb{g}$ and $\\mathbf{H}$ , and denote the 6-dimensional gradient vector for $\\pmb{x}_j$ as $\\pmb{g}_j$ and the $6\\times 6$ Hessian matrix block for $\\pmb{x}_j$ and $\\pmb{x}_k$ as $\\mathbf{H}_{jk}$ (note that here $j$ can equal to $k$ ). Then $\\pmb{g}$ and $\\mathbf{H}$ can be written in the block form as $\\pmb{g} = (\\pmb{g}_j)\\in \\mathbb{R}^{6N}$ and $\\mathbf{H} = (\\mathbf{H}_{jk})\\in \\mathbb{R}^{6N\\times 6N}$ .", + "bbox": [ + 498, + 419, + 890, + 508 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The $i$ th plane $\\pi_i$ is observed by the poses in $\\mathbb{X}_i$ . Assume $\\boldsymbol{x}_j \\in \\mathbb{X}_i$ and $\\boldsymbol{x}_k \\in \\mathbb{X}_i$ . Let us define", + "bbox": [ + 498, + 508, + 890, + 541 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {g} _ {j} ^ {i} = \\frac {\\partial \\lambda_ {i , 3}}{\\partial \\boldsymbol {x} _ {j}}, \\mathbf {H} _ {j k} ^ {i} = \\frac {\\partial^ {2} \\lambda_ {i , 3}}{\\partial \\boldsymbol {x} _ {j} \\partial \\boldsymbol {x} _ {k}}. \\tag {17}\n$$\n", + "text_format": "latex", + "bbox": [ + 589, + 549, + 890, + 583 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "According to (16), we have", + "bbox": [ + 500, + 590, + 683, + 604 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {g} _ {j} = \\sum_ {i \\in \\mathbb {P} _ {j}} \\boldsymbol {g} _ {j} ^ {i}, \\quad \\mathrm {H} _ {j k} = \\sum_ {i \\in \\mathbb {P} _ {j k}} \\mathrm {H} _ {j k} ^ {i}, \\tag {18}\n$$\n", + "text_format": "latex", + "bbox": [ + 584, + 614, + 890, + 648 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\mathbb{P}_j$ is the set of planes observed by $\\pmb{x}_j$ , and $\\mathbb{P}_{jk}$ is the set of planes observed by $\\pmb{x}_j$ and $\\pmb{x}_k$ simultaneously. If $j = k$ , here $\\mathbb{P}_{jk}$ equals to $\\mathbb{P}_j$ . From (18), we know that the key point to get $\\pmb{g}$ and $\\mathbf{H}$ is to compute $\\pmb{g}_j^i$ and $\\mathbf{H}_{jk}^i$ in (17).", + "bbox": [ + 498, + 656, + 890, + 719 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4.1. Partial Derivatives of Eigenvalue", + "text_level": 1, + "bbox": [ + 500, + 724, + 785, + 739 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "According to (15), $\\lambda_{i,3}$ is a function of poses in $\\mathbb{X}_i$ . Assume that $x_{jm}$ and $x_{kn}$ are the $m$ th and $n$ th elements of $\\pmb{x}_j$ and $\\pmb{x}_k$ , respectively. We consider the first- and second-order partial derivation $\\frac{\\partial\\lambda_{i,3}}{\\partial x_{jm}}$ and $\\frac{\\partial^2\\lambda_{i,3}}{\\partial x_{jm}\\partial x_{kn}}$ , respectively.", + "bbox": [ + 498, + 748, + 890, + 815 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "$\\lambda_{i,3}$ is a root of the equation $|\\mathbf{M}_i(\\mathbb{X}_i) - \\lambda_i\\mathbf{I}_3| = 0$ where $|\\cdot |$ denotes the determinant of a matrix. Assume $m_{ef}$ is the $e$ th row $f$ th column term of $\\mathbf{M}_i(\\mathbb{X}_i)$ . $|\\mathbf{M}_i(\\mathbb{X}_i) - \\lambda_i\\mathbf{I}_3| = 0$ is a cubic equation with the following form", + "bbox": [ + 498, + 815, + 890, + 875 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n- \\lambda_ {i, 3} ^ {3} + a _ {i} \\lambda_ {i, 3} ^ {2} + b _ {i} \\lambda_ {i, 3} + c _ {i} = 0, \\tag {19}\n$$\n", + "text_format": "latex", + "bbox": [ + 581, + 883, + 890, + 902 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "13116", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $a_{i} = m_{11} + m_{22} + m_{33}, b_{i} = m_{12}^{2} + m_{13}^{2} + m_{23}^{2} - m_{11}m_{22} - m_{11}m_{33} - m_{22}m_{33}$ , and $c_{i} = -m_{33}m_{12}^{2} + 2m_{12}m_{13}m_{23} - m_{22}m_{13}^{2} - m_{11}m_{23}^{2} + m_{11}m_{22}m_{33}$ . Here $a_{i}, b_{i}$ and $c_{i}$ are all functions of the poses in $\\mathbb{X}_i$ . It is known that the root of a cubic equation has a closed form. One solution to compute $\\frac{\\partial\\lambda_{i,3}}{\\partial x_{jm}}$ and $\\frac{\\partial^2\\lambda_{i,3}}{\\partial x_{jm}\\partial x_{kn}}$ is to directly differentiate the root. However, the formula of the root is too complicated. Here we introduce a simple way to compute them. Briefly, we employ the implicit function theorem [15] to compute them. Let us define", + "bbox": [ + 76, + 89, + 472, + 247 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\chi_ {i} = \\left[ \\begin{array}{l} \\lambda_ {i, 3} ^ {2} \\\\ \\lambda_ {i, 3} \\\\ 1 \\end{array} \\right], \\eta_ {i} = \\left[ \\begin{array}{l} a _ {i} \\\\ b _ {i} \\\\ c _ {i} \\end{array} \\right] \\kappa_ {i} = \\left[ \\begin{array}{l} - 3 \\\\ 2 a _ {i} \\\\ b _ {i} \\end{array} \\right], \\delta_ {j m} ^ {i} = \\frac {\\partial \\eta_ {i}}{\\partial x _ {j m}}. \\tag {20}\n$$\n", + "text_format": "latex", + "bbox": [ + 88, + 253, + 468, + 316 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Using the above notations, we present $\\frac{\\partial\\lambda_{i,3}}{\\partial x_{jm}}$ and $\\frac{\\partial^2\\lambda_{i,3}}{\\partial x_{jm}\\partial x_{kn}}$ in Lemma 1 and 2. The proofs of the following lemmas and theorems are in the supplementary material.", + "bbox": [ + 76, + 316, + 468, + 367 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Lemma 1 Using the notations in (20), we have", + "bbox": [ + 76, + 375, + 393, + 390 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\frac {\\partial \\lambda_ {i , 3}}{\\partial x _ {j m}} = - \\varphi_ {i} \\boldsymbol {\\delta} _ {j m} ^ {i} \\cdot \\boldsymbol {\\chi} _ {i}, \\tag {21}\n$$\n", + "text_format": "latex", + "bbox": [ + 194, + 397, + 468, + 431 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\cdot$ represents the dot product and $\\varphi_{i} = (\\pmb{\\kappa}_{i}\\cdot \\pmb{\\chi}_{i})^{-1}$", + "bbox": [ + 76, + 440, + 452, + 458 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Lemma 2 Using the notations in (20) and (21), we have", + "bbox": [ + 76, + 465, + 452, + 481 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\frac {\\partial^ {2} \\lambda_ {i , 3}}{\\partial x _ {j m} \\partial x _ {k n}} = - \\varphi_ {i} \\left(\\boldsymbol {\\delta} _ {j m} ^ {i} \\cdot \\frac {\\partial \\boldsymbol {\\chi} _ {i}}{\\partial x _ {k n}} + \\boldsymbol {\\chi} _ {i} \\cdot \\frac {\\partial \\boldsymbol {\\delta} _ {j m} ^ {i}}{\\partial x _ {k n}} - \\frac {\\partial \\lambda_ {i , 3}}{\\partial x _ {j m}} \\frac {\\partial \\varphi_ {i} ^ {- 1}}{\\partial x _ {k n}}\\right). \\tag {22}\n$$\n", + "text_format": "latex", + "bbox": [ + 76, + 488, + 478, + 532 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Let us define", + "bbox": [ + 96, + 542, + 187, + 554 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {\\alpha} _ {j} ^ {i} = \\frac {\\partial a _ {i}}{\\partial \\boldsymbol {x} _ {j}}, \\beta_ {j} ^ {i} = \\frac {\\partial b _ {i}}{\\partial \\boldsymbol {x} _ {j}}, \\gamma_ {j} ^ {i} = \\frac {\\partial c _ {i}}{\\partial \\boldsymbol {x} _ {j}}, \\boldsymbol {\\Delta} _ {j} ^ {i} = [ \\boldsymbol {\\alpha} _ {j} ^ {i}, \\beta_ {j} ^ {i}, \\gamma_ {j} ^ {i} ],\n$$\n", + "text_format": "latex", + "bbox": [ + 84, + 560, + 424, + 589 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {\\alpha} _ {k} ^ {i} = \\frac {\\partial a _ {i}}{\\partial \\boldsymbol {x} _ {k}}, \\beta_ {k} ^ {i} = \\frac {\\partial b _ {i}}{\\partial \\boldsymbol {x} _ {k}}, \\gamma_ {k} ^ {i} = \\frac {\\partial c _ {i}}{\\partial \\boldsymbol {x} _ {k}}, \\boldsymbol {\\Delta} _ {k} ^ {i} = [ \\boldsymbol {\\alpha} _ {k} ^ {i}, \\boldsymbol {\\beta} _ {k} ^ {i}, \\boldsymbol {\\gamma} _ {k} ^ {i} ], \\tag {23}\n$$\n", + "text_format": "latex", + "bbox": [ + 84, + 590, + 468, + 619 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {H} _ {j k} ^ {a _ {i}} = \\frac {\\partial^ {2} a _ {i}}{\\partial \\boldsymbol {x} _ {j} \\partial \\boldsymbol {x} _ {k}}, \\mathbf {H} _ {j k} ^ {b _ {i}} = \\frac {\\partial^ {2} b _ {i}}{\\partial \\boldsymbol {x} _ {j} \\partial \\boldsymbol {x} _ {k}}, \\mathbf {H} _ {j k} ^ {c _ {i}} = \\frac {\\partial^ {2} c _ {i}}{\\partial \\boldsymbol {x} _ {j} \\partial \\boldsymbol {x} _ {k}}.\n$$\n", + "text_format": "latex", + "bbox": [ + 84, + 621, + 413, + 651 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Using the above lemmas and notations, we can derive $\\pmb{g}_j^i$ and $\\mathbf{H}_{jk}^i$ .", + "bbox": [ + 76, + 657, + 468, + 694 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Theorem 1 Using the notations in (20), (21) and (23), $\\pmb{g}_j^i$ and $\\mathbf{H}_{jk}^{i}$ have the forms", + "bbox": [ + 76, + 699, + 468, + 734 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {g} _ {j} ^ {i} = - \\varphi_ {i} \\boldsymbol {\\Delta} _ {j} ^ {i} \\chi_ {i},\n$$\n", + "text_format": "latex", + "bbox": [ + 107, + 743, + 223, + 762 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {H} _ {j k} ^ {i} = \\varphi_ {i} \\left(\\mathbf {K} _ {j k} ^ {i} - \\lambda_ {3, i} ^ {2} \\mathbf {H} _ {j k} ^ {a _ {i}} - \\lambda_ {3, i} \\mathbf {H} _ {j k} ^ {b _ {i}} - \\mathbf {H} _ {j k} ^ {c _ {i}}\\right), \\tag {24}\n$$\n", + "text_format": "latex", + "bbox": [ + 96, + 760, + 468, + 789 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\mathbf{K}_{jk}^{i} = \\pmb{g}_{j}^{i}\\pmb{u}^{T} - \\pmb{v}(\\pmb{g}_{k}^{i})^{T},\\pmb{u} = 2\\lambda_{i,3}\\pmb{\\alpha}_{k}^{i} + \\pmb{\\beta}_{k}^{i} + (2a - 6\\lambda_{i,3})\\pmb{g}_{k}^{i},$ and $\\pmb {v} = 2\\lambda_{i,3}\\pmb{\\alpha}_{j}^{i} + \\pmb{\\beta}_{j}^{i}$ , and similar to $\\pmb{g}_j^i,\\pmb{g}_k^i =$ $-\\varphi_i\\Delta_k^i\\chi_i$ is the gradient block for $\\pmb{x}_k$", + "bbox": [ + 76, + 796, + 468, + 848 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The formula of $\\mathbf{H}_{jk}^{i}$ in (24) is applicable to the case that $j = k$ . From Theorem 1, we know that the key point to get $\\pmb{g}_j^i$ and $\\mathbf{H}_{jk}^{i}$ is to get the derivatives of $a_{i}, b_{i}$ and $c_{i}$ in (23).", + "bbox": [ + 76, + 854, + 468, + 902 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.2. Partial Derivatives of $a_i$ , $b_i$ and $c_i$", + "text_level": 1, + "bbox": [ + 500, + 90, + 789, + 106 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "According to (19), $a_{i}, b_{i}$ and $c_{i}$ are functions of the elements in $\\mathbf{M}_i$ . Using this relationship, we can easily derive the partial derivatives in (23). For instance, as $a_{i} = m_{11} + m_{22} + m_{33}$ , we have", + "bbox": [ + 498, + 113, + 892, + 174 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\frac {\\partial a _ {i}}{\\partial \\boldsymbol {x} _ {j}} = \\frac {\\partial m _ {1 1}}{\\partial \\boldsymbol {x} _ {j}} + \\frac {\\partial m _ {2 2}}{\\partial \\boldsymbol {x} _ {j}} + \\frac {\\partial m _ {3 3}}{\\partial \\boldsymbol {x} _ {j}}. \\tag {25}\n$$\n", + "text_format": "latex", + "bbox": [ + 581, + 181, + 890, + 215 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Thus, to get the first- and second-order partial derivatives of $a_{i}, b_{i}$ and $c_{i}$ with respect to $\\pmb{x}_j$ and $\\pmb{x}_k$ in (23), we need to derive the form of $\\mathbf{M}_i$ with respect to $\\pmb{x}_j$ and $\\pmb{x}_k$ .", + "bbox": [ + 498, + 224, + 892, + 270 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Lemma 3 In terms of $\\pmb{x}_j$ and $\\pmb{x}_k$ , $\\bar{\\pmb{p}}_i$ in (13) has the form", + "bbox": [ + 500, + 281, + 879, + 297 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\bar {\\boldsymbol {p}} _ {i} \\left(\\boldsymbol {x} _ {j}, \\boldsymbol {x} _ {k}\\right) = \\mathbf {T} _ {j} \\boldsymbol {q} _ {i j} + \\mathbf {T} _ {k} \\boldsymbol {q} _ {i k} + \\boldsymbol {c} _ {i j k}, \\tag {26}\n$$\n", + "text_format": "latex", + "bbox": [ + 566, + 306, + 890, + 323 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\pmb{q}_{ij} = \\frac{1}{N_i}\\tilde{\\pmb{p}}_{ij},\\quad \\pmb{q}_{ik} = \\frac{1}{N_i}\\tilde{\\pmb{p}}_{ik},$ and $c_{ijk} = \\frac{1}{N_i}\\sum_{n\\in \\mathbb{O}_{jk}}\\mathbf{T}_n\\tilde{p}_{in}$ . Here $\\mathbb{O}_{jk} = \\mathrm{obs}(\\pi_i) - \\{j,k\\}$ represents the set of indexes of the poses that can observe $\\pi_i$ , excluding the $j$ th and $k$ th poses.", + "bbox": [ + 498, + 332, + 892, + 396 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In terms of $\\pmb{x}_j$ , $\\bar{\\pmb{p}}_i$ has the form", + "bbox": [ + 517, + 397, + 725, + 412 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\bar {\\boldsymbol {p}} _ {i} \\left(\\boldsymbol {x} _ {j}\\right) = \\mathbf {T} _ {j} \\mathbf {q} _ {i j} + \\boldsymbol {c} _ {i j}, \\tag {27}\n$$\n", + "text_format": "latex", + "bbox": [ + 614, + 422, + 890, + 439 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $c_{ij} = \\mathbf{T}_k\\mathbf{q}_{ik} + c_{ijk}$ .", + "bbox": [ + 500, + 449, + 683, + 465 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Using Lemma 3, we can have the following theorem for $\\mathbf{M}_i$ in (12).", + "bbox": [ + 500, + 474, + 890, + 505 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Theorem 2 In terms of $\\pmb{x}_j$ , $\\mathbf{M}_i$ in (12) can be written as", + "bbox": [ + 500, + 513, + 877, + 530 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {M} _ {i} \\left(\\boldsymbol {x} _ {j}\\right) = \\mathbf {T} _ {j} \\mathbf {Q} _ {j} ^ {i} \\mathbf {T} _ {j} ^ {T} + \\mathbf {T} _ {j} \\mathbf {K} _ {j} ^ {i} + \\left(\\mathbf {K} _ {j} ^ {i}\\right) ^ {T} \\mathbf {T} _ {j} ^ {T} + \\mathbf {C} _ {j} ^ {i}, \\tag {28}\n$$\n", + "text_format": "latex", + "bbox": [ + 511, + 539, + 890, + 559 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\mathbf{Q}_j^i = \\mathbf{U}_{ij} - N_j\\mathbf{q}_{ij}\\mathbf{q}_{ij}^T$ and $\\mathbf{K}_j^i = -N_i\\mathbf{q}_{ij}\\mathbf{c}_{ij}^T$ . Here $\\mathbf{U}_{ij}$ and $\\mathbf{q}_{ij}$ are defined in (13) and (26), respectively.", + "bbox": [ + 500, + 568, + 890, + 599 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In terms of $\\pmb{x}_j$ and $\\pmb{x}_k$ , $\\mathbf{M}_i$ can be written as", + "bbox": [ + 517, + 599, + 815, + 614 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {M} _ {i} \\left(\\boldsymbol {x} _ {j}, \\boldsymbol {x} _ {k}\\right) = \\mathbf {T} _ {j} \\mathbf {O} _ {j k} ^ {i} \\mathbf {T} _ {k} ^ {T} + \\mathbf {T} _ {k} \\left(\\mathbf {O} _ {j k} ^ {i}\\right) ^ {T} \\mathbf {T} _ {j} ^ {T} + \\mathbf {C} _ {j k} ^ {i}. \\tag {29}\n$$\n", + "text_format": "latex", + "bbox": [ + 509, + 625, + 890, + 647 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\mathbf{O}_{jk}^{i} = -N_{i}\\pmb{q}_{ij}\\pmb{q}_{ik}^{T}$ .", + "bbox": [ + 500, + 656, + 673, + 675 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Here we do not provide the detailed formulas for $\\mathbf{C}_j^i$ and $\\mathbf{C}_{jk}^{i}$ , as they will be eliminated in the partial derivative. Actually, only $\\mathbf{Q}_j^i$ , $\\mathbf{K}_j^i$ , and $\\mathbf{O}_{jk}^{i}$ are required to compute the partial derivatives in (23). Equation (28) is used to compute the first- and second-order partial derivatives of $a_i$ , $b_i$ and $c_i$ with respect to $\\pmb{x}_j$ . Equation (29) is used to compute the second-order partial derivatives of $a_i$ , $b_i$ and $c_i$ with respect to $\\pmb{x}_j$ and $\\pmb{x}_k$ .", + "bbox": [ + 498, + 683, + 890, + 808 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.3. Efficient Iteration", + "text_level": 1, + "bbox": [ + 500, + 816, + 673, + 830 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "From Theorem 2, we can easily derive the elements of $\\mathbf{M}_i(\\pmb{x}_j)$ and $\\mathbf{M}_i(\\pmb{x}_j,\\pmb{x}_i)$ . Assume $a(\\pmb{x}_j)$ and $b(\\pmb{x}_j,\\pmb{x}_k)$ are one of the elements in $\\mathbf{M}_i(\\pmb{x}_j)$ and $\\mathbf{M}_i(\\pmb{x}_j,\\pmb{x}_k)$ , respectively. Substituting $\\mathbf{T}_j$ and $\\mathbf{T}_k$ defined in (1) into (28) and", + "bbox": [ + 498, + 839, + 892, + 901 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "13117", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "(29) and expanding them, we can obtain that $a(\\pmb{x}_j)$ and $b(\\pmb{x}_j, \\pmb{x}_k)$ are second-order polynomials in terms of the elements in $\\mathbf{T}_j$ and $\\mathbf{T}_k$ . Using the CGB parameterization in (2), we can write $a(\\pmb{x}_j)$ and $b(\\pmb{x}_j, \\pmb{x}_k)$ as", + "bbox": [ + 75, + 90, + 468, + 154 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} a (\\boldsymbol {x} _ {j}) = \\boldsymbol {c} \\cdot \\boldsymbol {h} (\\boldsymbol {x} _ {j}) + c _ {0}, \\\\ b \\left(\\boldsymbol {x} _ {j}, \\boldsymbol {x} _ {k}\\right) = \\boldsymbol {d} \\cdot \\boldsymbol {g} \\left(\\boldsymbol {x} _ {j}, \\boldsymbol {x} _ {k}\\right) + d _ {0}, \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 165, + 164, + 380, + 200 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $\\pmb{c}$ is determined by $\\mathbf{Q}_j^i$ and $\\mathbf{K}_j^i$ in (28), $\\pmb{d}$ is determined by $\\mathbf{O}_{jk}^{i}$ in (29), $\\pmb{h}(\\pmb{x}_j)$ and $\\pmb{g}(\\pmb{x}_j, \\pmb{x}_k)$ are two vector functions, $c_0$ and $d_0$ are two scalars independent on $\\pmb{x}_j$ and $\\pmb{x}_k$ . Let us first consider the first-order partial derivative of $a(\\pmb{x}_j)$ with respect to $\\pmb{x}_j$ . It has the form", + "bbox": [ + 75, + 210, + 470, + 291 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\frac {\\partial a \\left(\\boldsymbol {x} _ {j}\\right)}{\\partial \\boldsymbol {x} _ {j}} = \\frac {\\partial h \\left(\\boldsymbol {x} _ {j}\\right)}{\\partial \\boldsymbol {x} _ {j}} c, \\tag {31}\n$$\n", + "text_format": "latex", + "bbox": [ + 199, + 300, + 468, + 335 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where the vector-by-vector derivative $\\frac{\\partial h(\\pmb{x}_j)}{\\partial\\pmb{x}_j}$ is defined in (4). To efficiently compute (31), we consider a special pose $\\mathbf{T}_0 = [\\mathbf{R}_0,t_0]$ where $\\mathbf{R}_0 = \\mathbf{I}_3$ and $t_0 = [0;0;0]$ . Let us denote the parameterization of $\\mathbf{T}_0$ as $\\pmb{x}_0$ . As the CGR parameterization for $\\mathbf{I}_3$ is $[0;0;0]$ , we have $\\pmb{x}_0 = [0;0;0;0;0;0]$ . For $\\pmb{x}_j = \\pmb{x}_0$ , the matrix $\\frac{\\partial h(\\mathbf{x}_j)}{\\partial\\mathbf{x}_j}$ can be easily computed. Similarly, the second-order partial derivatives of $\\pmb{h}(\\pmb{x}_j)$ and $\\pmb{g}(\\pmb{x}_j,\\pmb{x}_k)$ at $\\pmb{x}_j = \\pmb{x}_0$ and $\\pmb{x}_k = \\pmb{x}_0$ are also simple. As $\\pmb{h}(\\pmb{x}_j)$ and $\\pmb{g}(\\pmb{x}_j,\\pmb{x}_k)$ only depend on $\\pmb{x}_j$ and $\\pmb{x}_k$ , we can compute the partial derivatives at $\\pmb{x}_0$ once, and then reuse them in the following iterations. Here we introduce a method to make the iteration stay at $\\mathbf{x}_0$ for each pose.", + "bbox": [ + 75, + 345, + 468, + 536 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Assume that $\\{\\mathbf{X}_j^n\\}$ are the poses after the $n$ th iteration. Then we can update $\\mathbf{U}_{ij}$ and $\\tilde{p}_{ij}$ in (13) by", + "bbox": [ + 76, + 536, + 468, + 568 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {U} _ {i j} ^ {n + 1} = \\mathbf {X} _ {j} ^ {n} \\mathbf {U} _ {i j} \\left(\\mathbf {X} _ {j} ^ {n}\\right) ^ {T} \\text {a n d} \\tilde {\\boldsymbol {p}} _ {i j} ^ {n + 1} = \\mathbf {X} _ {j} ^ {n} \\tilde {\\boldsymbol {p}} _ {i j}. \\tag {32}\n$$\n", + "text_format": "latex", + "bbox": [ + 109, + 577, + 468, + 597 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Substituting $\\mathbf{U}_{ij}^{n + 1}$ and $\\tilde{\\pmb{p}}_{ij}^{n + 1}$ into (12), we get a new matrix $\\mathbf{M}_i(\\mathbb{X}_i)^{n + 1}$ , which can finally lead to a new cost $\\tau^{n + 1}$ in (16). As the points have been transformed by $\\{\\mathbf{X}_j^n\\}$ , each pose should start with $\\mathbf{X}_0$ for $\\tau^{n + 1}$ . Assume that $\\Delta \\pmb{x}_j^{n + 1}$ is the result from the $(n + 1)$ th iteration for the $j$ th pose. We can compute the corresponding transformation matrix $\\Delta \\mathbf{X}_j^{n + 1}$ using (1) and (2). Then we can update $\\mathbf{X}_j^n$ by", + "bbox": [ + 75, + 607, + 468, + 720 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {X} _ {j} ^ {n + 1} = \\Delta \\mathbf {X} _ {j} ^ {n + 1} \\mathbf {X} _ {j} ^ {n}. \\tag {33}\n$$\n", + "text_format": "latex", + "bbox": [ + 197, + 731, + 468, + 752 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Furthermore, the update steps in (32) will not introduce additional computation. This is because the damped Newton's method requires to compute the cost $\\tau$ in (16) to adjust $\\mu$ in (3) after each iteration, which requires to perform the computation in (32).", + "bbox": [ + 75, + 761, + 468, + 838 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.4. Algorithm Summary", + "text_level": 1, + "bbox": [ + 76, + 847, + 272, + 864 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We first construct $\\mathbf{H}$ and $\\pmb{g}$ . For each plane $\\pi_i$ , we solve the cubic equation (19), and select the smallest root $\\lambda_{i,3}$ .", + "bbox": [ + 75, + 869, + 468, + 901 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "For $\\boldsymbol{x}_j$ , we construct $\\mathbf{M}(\\boldsymbol{x}_j)$ in (28), and calculate the partial derivatives of $a_i$ , $b_i$ and $c_i$ with respect to $\\boldsymbol{x}_j$ in (23). Then, we use (24) to compute $g_j^i$ and $\\mathbf{H}_{jj}^i$ and use (18) to update $g_j$ and $\\mathbf{H}_{jj}$ . For $\\boldsymbol{x}_j$ and $\\boldsymbol{x}_k$ , $\\mathbf{M}_i(\\boldsymbol{x}_j, \\boldsymbol{x}_k)$ is generated, and then the partial derivatives of $a_i$ , $b_i$ and $c_i$ with respect to $\\boldsymbol{x}_j$ and $\\boldsymbol{x}_j$ in (23) are computed. Then, $\\mathbf{H}_{jk}^i$ can be easily obtained from (24), and $\\mathbf{H}_{jk}$ in (18) is computed accordingly. Using $\\mathbf{H}$ and $g$ , we conduct the damped Newton's step in (3). After each iteration, $\\mathbf{U}_{ij}$ and $\\tilde{\\boldsymbol{p}}_{ij}$ are updated by (32). The proposed algorithm is summarized in Algorithm 1. Let us denote the mean and variance of the number of observations per plane as $\\bar{K}$ and $\\sigma^2$ , respectively. According to [8], the computational complexity of the Hessian matrix is $O(M(\\bar{K}^2 + \\sigma^2))$ , which is of the same order as the Schur complement trick.", + "bbox": [ + 496, + 90, + 890, + 318 + ], + "page_idx": 5 + }, + { + "type": "code", + "sub_type": "algorithm", + "code_caption": [ + "Algorithm 1: Second-order plane adjustment for $N$ poses and $M$ planes" + ], + "code_body": "while not converge do $\\mathbf{H} = \\text{zeros}(6N, 6N), \\mathbf{g} = \\text{zeros}(6N, 1)$ ; for $i \\in [1, M]$ do \n\\[\n\\begin{aligned}\n& \\text{Compute } \\mathbf{g}\\text{ and the diagonal terms of } \\mathbf{H}. \\\\\n& \\text{for } j \\in \\text{obs}(\\pi_i) \\text{ do} \\\\\n& \\text{Compute } \\mathbf{M}_i(\\mathbf{x}_j) \\text{ using (28)}; \\\\\n& \\text{Compute } \\alpha_j^i, \\beta_j^i, \\gamma_j^i, \\mathbf{H}_{jj}^{a_i}, \\mathbf{H}_{jj}^{b_i}, \\mathbf{H}_{jj}^{c_i} \\text{ using (23)}; \\\\\n& \\text{Compute } \\mathbf{H}_{jj}^i \\text{ and } \\mathbf{g}_j^i \\text{ using (24)}; \\\\\n& \\text{H}_{jj} = \\mathbf{H}_{jj} + \\mathbf{H}_{jj}^i, \\mathbf{g}_j = \\mathbf{g}_j + \\mathbf{g}_j^i;\n\\end{aligned}\n\\] \n\\[\n\\begin{aligned}\n& \\text{for } j \\in \\text{obs}(\\pi_i) \\text{ do} \\\\\n& \\text{for } k \\in \\text{obs}(\\pi_i) \\text{ and } k > j \\text{ do} \\\\\n& \\text{Compute } \\mathbf{H}_{jk}^i \\text{ using (24)}; \\\\\n& \\text{H}_{jk} = \\mathbf{H}_{jk} + \\mathbf{H}_{jk}^i; \\\\\n& \\text{H}_{kj} = \\mathbf{H}_{kj} + (\\mathbf{H}_{jk}^i)^T;\n\\end{aligned}\n\\] \nConduct the damped Newton's step in (3); Update $\\mathbf{U}_{ij}$ and $\\tilde{\\boldsymbol{p}}_{ij}$ using (32);", + "bbox": [ + 519, + 368, + 867, + 680 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5. Experiments", + "text_level": 1, + "bbox": [ + 500, + 715, + 630, + 733 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5.1. Setup", + "text_level": 1, + "bbox": [ + 500, + 741, + 581, + 758 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "In this section, we compare our algorithm with EF [10], BALM [16] and the LM solution [23] with plane fitting after a successful LM step (named $\\mathbf{LM} + \\mathbf{PF}$ ). Our damped Newton's method was implemented according to the LM algorithm in Ceres [2]. The damped Newton's method and the LM algorithm are with the same parameters. Specifically, the initial value of the damping factor $\\mu$ in (3) is set to $10^{-4}$ . The early stopping tolerances (such as the cost value change and the norm of gradient) are set to $10^{-7}$ . The", + "bbox": [ + 496, + 763, + 890, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "13118", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/a69f873f088158572d06b5807a08fd71ea9af7c5667e475e004e8daffe7c2e3d.jpg", + "image_caption": [ + "(A)" + ], + "image_footnote": [], + "bbox": [ + 168, + 89, + 374, + 234 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/c7ef9988b38447e3aab215962fd24710d39910c4d7b0e5d54d73851ee5988afe.jpg", + "image_caption": [ + "(B)" + ], + "image_footnote": [], + "bbox": [ + 380, + 90, + 790, + 234 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/915bbd0b71fe635a3e032a744041326797493128d2790403932cb87d1144649f.jpg", + "image_caption": [ + "(C)" + ], + "image_footnote": [], + "bbox": [ + 166, + 253, + 375, + 402 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/424234a6cd6441bd86279b894d457ddd4f63fa4c2f2318a40f661acd9ef0d0d2.jpg", + "image_caption": [ + "(D)" + ], + "image_footnote": [], + "bbox": [ + 380, + 253, + 790, + 404 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/2a3f334e97d0b831aafbd009726f5ee56bf0636d24643818d62cd87d29565b3b.jpg", + "image_caption": [ + "Figure 3. The four datasets used in this paper. There are $4.5 \\times 10^{6}$ , $16.6 \\times 10^{6}$ , $16.7 \\times 10^{6}$ , and $10.5 \\times 10^{6}$ points in the 4 datasets. The 4 datasets have 339, 369, 856, and 589 planes, and 472, 1355, 1606, 1184 poses, respectively. Roofs are removed to show the trajectories." + ], + "image_footnote": [], + "bbox": [ + 81, + 484, + 181, + 555 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/1797e1f3cc2e9c6d579d0c4c92431899494c7c00e10169fcb627fecbf05c8f7f.jpg", + "image_caption": [ + "$\\sigma_{\\mathbf{R}} = 0.1^{\\circ}\\sigma_{t} = 0.01m$ $\\sigma_{\\mathbf{R}} = 1^{\\circ}\\sigma_{t} = 0.1m$" + ], + "image_footnote": [], + "bbox": [ + 181, + 484, + 276, + 555 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "$\\sigma_{\\mathbf{R}} = 1^{\\circ}\\sigma_{t} = 0.1m$", + "bbox": [ + 184, + 558, + 267, + 566 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/38490bd707da129099d0810b78c7adbe4157d1707659a845d3fe828948fdb519.jpg", + "image_caption": [ + "$\\sigma_{\\mathbf{R}} = 2^{\\circ}\\sigma_{t} = 0.2m$", + "Figure 4. The point clouds of dataset C after the poses were perturbs by the four noise levels." + ], + "image_footnote": [], + "bbox": [ + 277, + 484, + 370, + 555 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/10ff24e4a1465158846008776813eafbb4d1cd47fb489fa107df0a7684288448.jpg", + "image_caption": [ + "$\\sigma_{\\mathbf{R}} = 3^{\\circ}\\sigma_{t} = 0.3m$" + ], + "image_footnote": [], + "bbox": [ + 372, + 484, + 464, + 555 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "maximum number of iterations is set to 200 for our algorithm, BALM, and LM+PF, and $10^{5}$ for EF, as EF uses the first-order minimization which requires more iterations to converge. All the experiments were conducted on a desktop with an Intel i7 cpu and 64G memory.", + "bbox": [ + 75, + 636, + 467, + 712 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.2. Datasets", + "text_level": 1, + "bbox": [ + 76, + 724, + 179, + 739 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We collected four datasets using a VLP-16 LiDAR. We used the LiDAR SLAM algorithm [24] to detect the planes and establish the plane association. Fig. 3 shows the four datasets. Similar to the evaluation of BA algorithms [3,8,25], we perturb the pose, and compare the PA cost in (11) for different algorithms. Specifically, we directly add Gaussian noises to the translation, and randomly generate an angle-axis vector from a Gaussian distribution to perturb the rotation. After the poses are perturb, we use (7) to get the initial plane parameters for $\\mathrm{LM} + \\mathrm{PF}$ .", + "bbox": [ + 75, + 750, + 468, + 900 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We evaluate the performance of different algorithms under different noise levels. Let us denote the standard deviation (std) of the Gaussian noises for rotation and translation as $\\sigma_{\\mathbf{R}}$ and $\\sigma_t$ , respectively. We consider four noise levels: $\\sigma_{\\mathbf{R}} = 0.1^{\\circ}$ and $\\sigma_t = 0.01m$ , $\\sigma_{\\mathbf{R}} = 1^{\\circ}$ and $\\sigma_t = 0.1m$ , $\\sigma_{\\mathbf{R}} = 2^{\\circ}$ and $\\sigma_t = 0.2m$ , and $\\sigma_{\\mathbf{R}} = 3^{\\circ}$ and $\\sigma_t = 0.3m$ . Fig. 4 demonstrates the point clouds of dataset C after the poses are perturbed by the four noise levels. To evaluate the performance of different algorithms suffering from large measurement noises, we also test the case that additional Gaussian noises with the std $\\sigma_{pt} = 0.05m$ are added to the LiDAR point cloud, and the poses are perturbed by Gaussian noises with $\\sigma_{\\mathbf{R}} = 3^{\\circ}$ and $\\sigma_t = 0.3m$ .", + "bbox": [ + 496, + 486, + 890, + 681 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.3. Results", + "text_level": 1, + "bbox": [ + 500, + 695, + 591, + 709 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Fig. 5 and Fig. 6 illustrates the results. It is clear that our algorithm converges faster than other algorithms. LM+PF works well at small noises (such as $\\sigma_{\\mathbf{R}} = 0.1^{\\circ}$ and $\\sigma_t = 0.01m$ ). As the noise level increases, LM+PF tends to converge slower. Constructing H and g using BALM [16] is computationally demanding. For efficiency, BALM only keeps the centroid of each plane observation (i.e., only 1 point is kept), which results in bad performance. In Fig. 5 and Fig. 6, all points are used to compute the cost in (11) after an iteration of BALM. BALM generally converges slow, as it minimizes a reduced PA problem. EF [10] adopts the first-order optimization method as it only provides a method", + "bbox": [ + 496, + 719, + 890, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "13119", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/4fa1350a3cee5e97ba491459cf03ea026651cedda2181aa6f54b061cb335872d.jpg", + "image_caption": [ + "Figure 5. The results of different algorithms using different initial noise levels. It is clear that our algorithm converges significantly faster than other algorithms. The $y$ -axis represents the logarithmic scale of the cost in (11)." + ], + "image_footnote": [], + "bbox": [ + 109, + 88, + 861, + 535 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/b21bc28bd873f818d0c9d5a175517159a6153e323787c0cc1d30ffa9d3372f34.jpg", + "image_caption": [ + "Figure 6. The results of different algorithms for point clouds perturbed by Gaussian noise with std $\\sigma_{pt} = 0.05m$ . The rotations and translations of the poses are perturbed by Gaussian noise with std $\\sigma_{\\mathbf{R}} = 3^{\\circ}$ and $\\sigma_t = 0.3m$ , respectively." + ], + "image_footnote": [], + "bbox": [ + 112, + 593, + 859, + 705 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "to compute the gradient, which results in slow convergence.", + "bbox": [ + 76, + 771, + 470, + 787 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "6. Conclusion", + "text_level": 1, + "bbox": [ + 76, + 800, + 196, + 814 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In the computer vision community, Newton's method is generally considered too expensive for a large-scale least-squares problem. This paper adopts the Newton's method to efficiently solve the PA problem. Our algorithm takes advantage of the fact that the optimal planes are determined", + "bbox": [ + 75, + 825, + 470, + 902 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "by the poses, so that the number of unknowns can be significantly reduced. Furthermore, this property can ensure to obtain the optimal planes when we update the poses. The difficulty lies in how to efficiently compute the Hessian matrix and the gradient vector. The key contribution of this paper is to provide a closed-form solution for them. The experimental results show that our algorithm outperforms the state-of-the-art algorithms.", + "bbox": [ + 496, + 771, + 890, + 892 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "13120", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Sameer Agarwal, Yasutaka Furukawa, Noah Snavely, Ian Simon, Brian Curless, Steven M Seitz, and Richard Szeliski. Building rome in a day. Communications of the ACM, 54(10):105-112, 2011. 1", + "[2] Sameer Agarwal, Keir Mierle, and The Ceres Solver Team. Ceres Solver, 3 2022. 6", + "[3] Sameer Agarwal, Noah Snavely, Steven M Seitz, and Richard Szeliski. Bundle adjustment in the large. In European conference on computer vision, pages 29-42. Springer, 2010. 1, 2, 7", + "[4] Alex M Andrew. 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IEEE, 2021. 1" + ], + "bbox": [ + 501, + 92, + 890, + 729 + ], + "page_idx": 8 + }, + { + "type": "page_number", + "text": "13121", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 8 + } +] \ No newline at end of file diff --git a/2023/Efficient Second-Order Plane Adjustment/0ca972fe-43f5-4fa8-bf07-17ebcd5d268a_model.json b/2023/Efficient Second-Order Plane Adjustment/0ca972fe-43f5-4fa8-bf07-17ebcd5d268a_model.json new file mode 100644 index 0000000000000000000000000000000000000000..d8a08526faf860056099566dfdddf06cdbfe19ed --- /dev/null +++ b/2023/Efficient Second-Order Plane Adjustment/0ca972fe-43f5-4fa8-bf07-17ebcd5d268a_model.json @@ -0,0 +1,2396 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.274, + 0.131, + 0.698, + 0.154 + ], + "angle": 0, + "content": "Efficient Second-Order Plane Adjustment" + }, + { + "type": "text", + "bbox": [ + 0.389, + 0.182, + 0.582, + 0.234 + ], + "angle": 0, + "content": "Lipu Zhou Meituan, Beijing, China zhoulipu@meituan.com" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.269, + 0.314, + 0.285 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.302, + 0.474, + 0.681 + ], + "angle": 0, + "content": "Planes are generally used in 3D reconstruction for depth sensors, such as RGB-D cameras and LiDARs. This paper focuses on the problem of estimating the optimal planes and sensor poses to minimize the point-to-plane distance. The resulting least-squares problem is referred to as plane adjustment (PA) in the literature, which is the counterpart of bundle adjustment (BA) in visual reconstruction. Iterative methods are adopted to solve these least-squares problems. Typically, Newton's method is rarely used for a large-scale least-squares problem, due to the high computational complexity of the Hessian matrix. Instead, methods using an approximation of the Hessian matrix, such as the Levenberg-Marquardt (LM) method, are generally adopted. This paper adopts the Newton's method to efficiently solve the PA problem. Specifically, given poses, the optimal plane have a close-form solution. Thus we can eliminate planes from the cost function, which significantly reduces the number of variables. Furthermore, as the optimal planes are functions of poses, this method actually ensures that the optimal planes for the current estimated poses can be obtained at each iteration, which benefits the convergence. The difficulty lies in how to efficiently compute the Hessian matrix and the gradient of the resulting cost. This paper provides an efficient solution. Empirical evaluation shows that our algorithm outperforms the state-of-the-art algorithms." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.709, + 0.21, + 0.725 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.735, + 0.47, + 0.886 + ], + "angle": 0, + "content": "Planes ubiquitously exist in man-made environments, as demonstrated in Fig. 1. Thus they are generally used in simultaneous localization and mapping (SLAM) systems for depth sensors, such as RGB-D cameras [6, 9, 12-14] and LiDARs [16, 21, 22, 24, 26]. Just as bundle adjustment (BA) [3, 8, 20, 25] is important for visual reconstruction [1, 5, 18, 19], jointly optimizing planes and depth sensor poses, which is called plane adjustment (PA) [24,26], is critical for 3D reconstruction using depth sensors. This paper focuses on efficiently solving the large-scale PA problem." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.886, + 0.469, + 0.902 + ], + "angle": 0, + "content": "The BA and PA problems both involve jointly optimiz" + }, + { + "type": "image", + "bbox": [ + 0.529, + 0.272, + 0.869, + 0.39 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.589, + 0.392, + 0.796, + 0.406 + ], + "angle": 0, + "content": "(a) Point cloud from perturbed poses" + }, + { + "type": "image", + "bbox": [ + 0.529, + 0.416, + 0.869, + 0.535 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.603, + 0.537, + 0.797, + 0.55 + ], + "angle": 0, + "content": "(b) Point cloud from our algorithm" + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.561, + 0.895, + 0.632 + ], + "angle": 0, + "content": "Figure 1. We use Gaussian noises to perturb the poses of dataset D in Fig. 3. The standard deviations for rotation and translation are \\(3^{\\circ}\\) and \\(0.3m\\), respectively. The resulting point cloud (a) is in a mess. Fig. (b) shows the result from our algorithm. Our algorithm can quickly align the planes, as shown in Fig. 5." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.659, + 0.892, + 0.839 + ], + "angle": 0, + "content": "ing 3D structures and sensor poses. As the two problems are similar, it is straightforward to apply the well-studied solutions for BA to PA, as done in [23, 26]. However, planes in PA can be eliminated, so that the cost function of the PA problem only depends on sensor poses, which significantly reduces the number of variables. This property provides a promising direction to efficiently solve the PA problem. However, it is difficult to compute the Hessian matrix and the gradient vector of the resulting cost. Although this problem was studied in several previous works [10, 16], no efficient solution has been proposed. This paper seeks to solve this problem." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.895, + 0.903 + ], + "angle": 0, + "content": "The main contribution of this paper is an efficient PA solution using Newton's method. We derive a closed-form solution for the Hessian matrix and the gradient vector for the PA problem whose computational complexity is inde" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "13113" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.138 + ], + "angle": 0, + "content": "pendent of the number of points on the planes. Our experimental results show that the proposed algorithm converges faster than the state-of-the-art algorithms." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.151, + 0.22, + 0.167 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.176, + 0.468, + 0.282 + ], + "angle": 0, + "content": "The PA problem is closely related to the BA problem. In BA, points and camera poses are jointly optimized to minimize the reprojection error. Schur complement [3, 20, 25] or the square root method [7, 8] is generally used to solve the linear system of the iterative methods. The keypoint is to generate a reduced camera system (RCS) which only relates to camera poses." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.282, + 0.468, + 0.629 + ], + "angle": 0, + "content": "In PA, planes and poses are jointly optimized. Planes are the counterparts of points in BA. Thus, the well-known solutions for the BA problem can be applied to the PA problem [23, 24]. In the literature, two cost functions are used to formulate the PA problem. The first one is the plane-to-plane distance which measures the difference between two plane parameters [12, 13]. The value of the plane-to-plane distance is related to the choice of the global coordinate system, which means the selection of the global coordinate system will affect the accuracy of the results. The second one is the point-to-plane distance, whose value is invariant to the choice of the global coordinate system. The solutions of different choices of the global coordinate system are equivalent up to a rigid transformation. Zhou et al. [23] show that the point-to-plane distance can converge faster and lead to a more accurate result. But unlike BA where each 3D point has only one 2D observation at a pose, a plane can generate many points at a pose as demonstrated in Fig. 2. This means the point-to-plane distance probably leads to a very large-scale least-squares problem. Directly adopting the BA solutions is computationally infeasible for a large-scale PA problem. Zhou et al. [23] propose to use the QR decomposition to accelerate the computation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.63, + 0.468, + 0.825 + ], + "angle": 0, + "content": "For a general least-squares problem with \\(M\\) variables, the computational complexity of the Hessian matrix is \\(O(M^2)\\). Thus, in the computer vision community, it is ingrained that Newton's method is infeasible for a large-scale optimization problem, as calculating the Hessian matrix is computationally demanding. Instead, Gauss-Newton-based iterative methods are generally adopted. Suppose that \\(\\mathbf{J}\\) is the Jacobian matrix of the residuals. The Gauss-Newton method actually approximates the Hessian matrix by \\(\\mathbf{H} \\approx \\mathbf{J}^T\\mathbf{J}\\). In theory, Newton's method can lead to a better quadratic approximation to the original cost function, which means the Newton's step probably yields a better result. This in turn may reduce the number of iterations." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.826, + 0.468, + 0.901 + ], + "angle": 0, + "content": "The PA problem has a special property that the optimal plane parameters are determined by the poses. That is to say the point-to-plane cost actually only depends on the poses. This property is attractive, as it significantly reduces the number of variables, which makes using the Newton's" + }, + { + "type": "image", + "bbox": [ + 0.507, + 0.093, + 0.71, + 0.205 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.539, + 0.209, + 0.672, + 0.218 + ], + "angle": 0, + "content": "(a) A PA problem with 3 poses and 4 planes" + }, + { + "type": "image", + "bbox": [ + 0.727, + 0.097, + 0.887, + 0.201 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.783, + 0.209, + 0.851, + 0.216 + ], + "angle": 0, + "content": "(b) Plane Observation" + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.231, + 0.892, + 0.343 + ], + "angle": 0, + "content": "Figure 2. A schematic of the PA problem and the planes detected in a LiDAR scan. Unlike BA where each 3D point only has one observation, many points can be captured from a plane in PA. Assume that \\(N\\) points are captured from a plane. The computational complexity of the Hessian matrix related to these points using BALM [16] is \\(O(N^2)\\). Thus, this method is infeasible for a large-scale problem. In contrast, the computational complexity of our algorithm is independent of \\(N\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.371, + 0.892, + 0.643 + ], + "angle": 0, + "content": "method possible. In traditional iterative methods, the correlation between the plane parameters and the poses are ignored. Thus, after one iteration, there is no guarantee that the new plane parameters are optimal for the new poses. Using the property of the PA, it is possible to overcome this drawback, which may lead to faster convergence. Several previous works seek to exploit this property of PA. Ferrer [10] explored an algebraic point-to-plane distance and provided a closed-form gradient for the resulting cost. The algebraic cost may result in a suboptimal solution [4], and the first-order optimization generally leads to slow convergence [20]. Liu et al. [16] provided analytic forms of the Hessian matrix and the gradient of the genuine point-to-plane cost. Assume that \\(N\\) points are captured from a plane. The computational complexity of the Hessian matrix related to these points is \\(O(N^2)\\). Since \\(N\\) can be large as shown in Fig. 2, this algorithm is computationally demanding and infeasible for a large-scale problem." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.644, + 0.892, + 0.718 + ], + "angle": 0, + "content": "In summary, the potential benefits of the special property of the PA problem have not been manifested in previous works. The bottleneck is how to efficiently compute the Hessian matrix and the gradient vector. This paper focuses on solving this problem." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.734, + 0.706, + 0.75 + ], + "angle": 0, + "content": "3. Problem Formulation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.76, + 0.891, + 0.806 + ], + "angle": 0, + "content": "In this paper we use italic, boldfaced lowercase and bold-faced uppercase letters to represent scalars, vectors and matrices, respectively." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.817, + 0.611, + 0.832 + ], + "angle": 0, + "content": "3.1. Notations" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.841, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Planes and Poses A plane can be represented by a four-dimensional vector \\(\\pmb{\\pi} = [n;d]\\). We denote the rotational and translational components from a depth sensor coordinate system to the global coordinate system as \\(\\mathbf{R}\\in SO(3)\\)" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "13114" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.091, + 0.47, + 0.138 + ], + "angle": 0, + "content": "and \\( t \\in \\mathbb{R}^3 \\), respectively. To simplify the notation in the following description, we also use the following two matrices to represent a pose:" + }, + { + "type": "equation", + "bbox": [ + 0.126, + 0.15, + 0.47, + 0.185 + ], + "angle": 0, + "content": "\\[\n\\mathbf {X} = \\left[ \\begin{array}{l l} \\mathbf {R}, & t \\\\ \\mathbf {0}, & 1 \\end{array} \\right] \\in S E (3) \\text {a n d} \\mathbf {T} = \\left[ \\begin{array}{l l} \\mathbf {R}, & t \\end{array} \\right]. \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.198, + 0.469, + 0.259 + ], + "angle": 0, + "content": "As \\(\\mathbf{R} \\in SO(3)\\), a certain parameterization is usually adopted in the optimization [20]. In this paper, we use the Cayley-Gibbs-Rodriguez (CGR) parameterization [11] to represent \\(\\mathbf{R}\\)" + }, + { + "type": "equation", + "bbox": [ + 0.089, + 0.273, + 0.469, + 0.306 + ], + "angle": 0, + "content": "\\[\n\\mathbf {R} = \\frac {\\bar {\\mathbf {R}}}{1 + \\boldsymbol {s} ^ {T} \\boldsymbol {s}}, \\bar {\\mathbf {R}} = \\left(1 - \\boldsymbol {s} ^ {T} \\boldsymbol {s}\\right) \\mathbf {I} _ {3} + 2 [ \\boldsymbol {s} ] _ {\\times} + 2 \\boldsymbol {s} \\boldsymbol {s} ^ {T}, \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.318, + 0.469, + 0.426 + ], + "angle": 0, + "content": "where \\( s = [s_1; s_2; s_3] \\) is a three-dimensional vector. We adopt the CGR parameterization as it is a minimal representation for \\( \\mathbf{R} \\). Furthermore, unlike the angle-axis parameterization that is singular at \\( \\mathbf{I}_3 \\), the CGR parameterization is well-defined at \\( \\mathbf{I}_3 \\), and equals to \\( [0; 0; 0] \\) which can accelerate the computation, as described in Section 4.3. We parameterize \\( \\mathbf{X} \\) as a six-dimensional vector \\( x = [s; t] \\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.426, + 0.469, + 0.531 + ], + "angle": 0, + "content": "Newton's method This paper adopts the damped Newton's method in the optimization. For a cost function \\( f(z) \\), the damped Newton's method seeks to find its minimizer from an initial point. Assume that \\( z_{n} \\) is the solution at the \\( n \\)th iteration. Given the Hessian matrix \\( \\mathbf{H}_f(z_n) \\) and the gradient \\( g_{f}(z_{n}) \\) at \\( z_{n},z_{n} \\) is updated by \\( z_{n + 1} = z_{n} + \\varDelta z \\). Here \\( \\varDelta z \\) is from" + }, + { + "type": "equation", + "bbox": [ + 0.162, + 0.548, + 0.469, + 0.565 + ], + "angle": 0, + "content": "\\[\n\\left(\\mathbf {H} _ {f} \\left(\\boldsymbol {z} _ {n}\\right) + \\mu \\mathbf {I})\\right) \\Delta z = - \\boldsymbol {g} _ {f} \\left(\\boldsymbol {z} _ {n}\\right), \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.579, + 0.469, + 0.625 + ], + "angle": 0, + "content": "where \\(\\mu\\) is adjusted at each iteration to make the value of \\(f(z)\\) reduce, as done in the Levenberg-Marquardt (LM) algorithm [17]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.626, + 0.469, + 0.671 + ], + "angle": 0, + "content": "Matrix Calculus In the following derivation, we will use vector-by-vector, vector-by-scalar, scalar-by-vector derivatives. Here we provide their definitions." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.672, + 0.47, + 0.741 + ], + "angle": 0, + "content": "Assume \\(\\mathbf{a} = [a_1;\\dots ;a_N]\\in \\mathbb{R}^N\\) is a vector function of \\(\\pmb {b} = [b_{1},\\dots ,b_{M}]\\in \\mathbb{R}^{M}\\) . The first-order partial derivatives of vector-by-vector \\(\\frac{\\partial\\pmb{a}}{\\partial\\pmb{b}}\\) , vector-by-scalar \\(\\frac{\\partial\\pmb{a}}{\\partial b_j}\\) , and scalar-byvector \\(\\frac{\\partial a_i}{\\partial b}\\) are defined as" + }, + { + "type": "equation", + "bbox": [ + 0.078, + 0.753, + 0.481, + 0.828 + ], + "angle": 0, + "content": "\\[\n\\frac {\\partial \\boldsymbol {a}}{\\partial \\boldsymbol {b}} = \\left[ \\begin{array}{c c c} \\frac {\\partial a _ {1}}{\\partial b _ {1}} & \\dots & \\frac {\\partial a _ {N}}{\\partial b _ {1}} \\\\ \\vdots & \\ddots & \\vdots \\\\ \\frac {\\partial a _ {1}}{\\partial b _ {M}} & \\dots & \\frac {\\partial a _ {N}}{\\partial b _ {M}} \\end{array} \\right], \\frac {\\partial \\boldsymbol {a}}{\\partial b _ {j}} = \\left[ \\begin{array}{c} \\frac {\\partial a _ {1}}{\\partial b _ {j}} \\\\ \\vdots \\\\ \\frac {\\partial a _ {N}}{\\partial b _ {j}} \\end{array} \\right], \\frac {\\partial a _ {i}}{\\partial \\boldsymbol {b}} = \\left[ \\begin{array}{c} \\frac {\\partial a _ {i}}{\\partial b _ {1}} \\\\ \\vdots \\\\ \\frac {\\partial a _ {i}}{\\partial b _ {M}} \\end{array} \\right] \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.827, + 0.469, + 0.905 + ], + "angle": 0, + "content": "where \\(\\frac{\\partial\\pmb{a}}{\\partial\\pmb{b}}\\) is an \\(M\\times N\\) matrix with \\(\\frac{\\partial a_j}{\\partial b_i}\\) as the ith row jth column element, \\(\\frac{\\partial\\pmb{a}}{\\partial b_j}\\) is an \\(N\\) -dimensional vector whose ith term is \\(\\frac{\\partial a_i}{\\partial b_j}\\), and \\(\\frac{\\partial a_i}{\\partial\\pmb{b}}\\) is an \\(M\\) -dimensional vector whose ith term is \\(\\frac{\\partial a_i}{\\partial b_i}\\)." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.091, + 0.736, + 0.108 + ], + "angle": 0, + "content": "3.2. Optimal Plane Estimation" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.114, + 0.892, + 0.158 + ], + "angle": 0, + "content": "Given a set of \\(K\\) points \\(\\{\\pmb{p}_i\\}\\), the optimal plane \\(\\hat{\\pi}\\) can be estimated by minimizing the sum of squared point-to-plane distances" + }, + { + "type": "equation", + "bbox": [ + 0.525, + 0.165, + 0.892, + 0.205 + ], + "angle": 0, + "content": "\\[\n\\hat {\\boldsymbol {\\pi}} = \\arg \\min _ {\\boldsymbol {\\pi}} \\sum_ {i} ^ {K} \\left(\\boldsymbol {n} ^ {T} \\boldsymbol {p} _ {i} + d\\right) ^ {2}, s. t. \\| \\boldsymbol {n} \\| _ {2} ^ {2} = 1. \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.213, + 0.842, + 0.227 + ], + "angle": 0, + "content": "There is a closed-form solution for \\(\\hat{\\pi}\\). Let us define" + }, + { + "type": "equation", + "bbox": [ + 0.556, + 0.233, + 0.892, + 0.269 + ], + "angle": 0, + "content": "\\[\n\\mathbf {M} = \\sum_ {i = 1} ^ {K} \\left(\\boldsymbol {p} _ {i} - \\bar {\\boldsymbol {p}}\\right) \\left(\\boldsymbol {p} _ {i} - \\bar {\\boldsymbol {p}}\\right) ^ {T} = \\mathbf {S} - K \\bar {\\boldsymbol {p}} \\bar {\\boldsymbol {p}} ^ {T}, \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.276, + 0.892, + 0.34 + ], + "angle": 0, + "content": "where \\(\\mathbf{S} = \\sum_{i=1}^{K} \\pmb{p}_i \\pmb{p}_i^T\\) and \\(\\bar{\\pmb{p}} = \\frac{1}{K} \\sum_{i}^{K} \\pmb{p}_i\\). Assume that \\(\\lambda_3(\\mathbf{M})\\) and \\(\\xi_3(\\mathbf{M})\\) are the smallest eigenvalue of \\(\\mathbf{M}\\) and the corresponding eigenvector, respectively. Using these notations, we can write the optimal plane \\(\\hat{\\pmb{\\pi}} = [\\hat{\\pmb{n}}; \\hat{d}]\\) as" + }, + { + "type": "equation", + "bbox": [ + 0.608, + 0.348, + 0.892, + 0.366 + ], + "angle": 0, + "content": "\\[\n\\hat {\\boldsymbol {n}} = \\boldsymbol {\\xi} _ {3} (\\mathbf {M}), \\hat {d} = - \\hat {\\boldsymbol {n}} ^ {T} \\bar {\\boldsymbol {p}}. \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.373, + 0.862, + 0.389 + ], + "angle": 0, + "content": "Furthermore, the cost of (5) at \\(\\hat{\\pi}\\) equals to \\(\\lambda_3(\\mathbf{M})\\), i.e.," + }, + { + "type": "equation", + "bbox": [ + 0.515, + 0.397, + 0.891, + 0.439 + ], + "angle": 0, + "content": "\\[\n\\lambda_ {3} (\\mathbf {M}) = \\sum_ {i = 1} ^ {K} \\left(\\hat {\\boldsymbol {n}} \\boldsymbol {p} _ {i} + \\hat {d}\\right) ^ {2} = \\min _ {\\pi} \\sum_ {i = 1} ^ {K} \\left(\\boldsymbol {n} \\boldsymbol {p} _ {i} + d\\right) ^ {2}. \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.445, + 0.886, + 0.46 + ], + "angle": 0, + "content": "The above property will be used to eliminate planes in PA." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.468, + 0.674, + 0.484 + ], + "angle": 0, + "content": "3.3. Plane Adjustment" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.491, + 0.892, + 0.629 + ], + "angle": 0, + "content": "Assume that there are \\(M\\) planes and \\(N\\) poses. According to section 3.1, the \\(i\\)th plane can be represented by a four-dimensional vector \\(\\pmb{\\pi}_i = [n_i;d_i]\\). The \\(j\\)th pose is denoted as \\(\\pmb{x}_j\\). The observation of \\(\\pmb{\\pi}_i\\) at \\(\\pmb{x}_j\\) is a set of \\(N_{ij}\\) points \\(\\mathbb{Q}_{ij} = \\{\\pmb{p}_{ijk} \\in \\mathbb{R}^3\\}_{k=1}^{N_{ij}}\\). For a 3D point \\(\\pmb{p}_{ijk}\\), we use \\(\\tilde{\\pmb{p}}_{ijk} = [\\pmb{p}_{ijk};1]\\) to represent the homogeneous coordinates of \\(\\pmb{p}_{ijk}\\). Then, the transformation from the local coordinate system at \\(\\pmb{x}_j\\) to the global coordinate system can be represented as" + }, + { + "type": "equation", + "bbox": [ + 0.588, + 0.638, + 0.891, + 0.657 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {p} _ {i j k} ^ {g} = \\mathbf {R} _ {j} \\boldsymbol {p} _ {i j k} + \\boldsymbol {t} _ {j} = \\mathbf {T} _ {j} \\tilde {\\boldsymbol {p}} _ {i j k}, \\tag {9}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.663, + 0.89, + 0.693 + ], + "angle": 0, + "content": "where \\(\\mathbf{T}_j\\) is defined in (1). Then the distance \\(d_{ijk}\\) from \\(\\pmb{p}_{ijk}\\) to \\(\\pi_i\\) has the form" + }, + { + "type": "equation", + "bbox": [ + 0.537, + 0.7, + 0.891, + 0.741 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} d _ {i j k} \\left(\\boldsymbol {\\pi} _ {i}, \\mathbf {x} _ {j}\\right) = \\boldsymbol {n} _ {i} ^ {T} \\left(\\mathbf {R} _ {j} \\boldsymbol {p} _ {i j k} + \\boldsymbol {t} _ {j}\\right) + d _ {i} \\tag {10} \\\\ = \\boldsymbol {n} _ {i} ^ {T} \\mathbf {T} _ {j} \\tilde {\\boldsymbol {p}} _ {i j k} + d _ {j} = \\boldsymbol {\\pi} _ {i} ^ {T} \\tilde {\\boldsymbol {p}} _ {i j k} ^ {g}. \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.747, + 0.892, + 0.808 + ], + "angle": 0, + "content": "The PA problem is to jointly adjust the \\(M\\) planes \\(\\{\\pi_i\\}\\) and the \\(N\\) sensor poses \\(\\{\\pmb{x}_j\\}\\) to minimize the sum of squared point-to-plane distances. Specifically, using (10), we can formulate the cost function of the PA problem as" + }, + { + "type": "equation", + "bbox": [ + 0.503, + 0.827, + 0.935, + 0.901 + ], + "angle": 0, + "content": "\\[\n\\min _ {\\left\\{\\boldsymbol {\\pi} _ {i} \\right\\}, \\left\\{\\mathbf {x} _ {j} \\right\\}} \\sum_ {i = 1} ^ {M} \\underbrace {\\sum_ {j \\in o b s \\left(\\boldsymbol {\\pi} _ {i}\\right)} \\sum_ {k = 1} ^ {N _ {i j}} d _ {i j k} ^ {2} \\left(\\boldsymbol {\\pi} _ {i} , \\mathbf {x} _ {j}\\right)} _ {C _ {i} \\left(\\boldsymbol {\\pi} _ {i}, \\mathbb {X} _ {i}\\right), \\mathbb {X} _ {i} = \\left\\{\\boldsymbol {x} _ {j} \\mid j \\in o b s \\left(\\boldsymbol {\\pi} _ {i}\\right) \\right\\}} = \\min _ {\\left\\{\\boldsymbol {\\pi} _ {i} \\right\\}, \\left\\{\\boldsymbol {x} _ {j} \\right\\}} \\sum_ {i = 1} ^ {M} C _ {i} \\left(\\boldsymbol {\\pi} _ {i}, \\mathbb {X} _ {i}\\right). \\tag {11}\n\\]" + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "13115" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.47, + 0.152 + ], + "angle": 0, + "content": "where \\( obs(\\pi_i) \\) represents the indexes of poses where \\( \\pi_i \\) can be observed, and \\( C_i(\\pi_i, \\mathbb{X}_i) \\) accumulates the errors from \\( N_i = \\sum_{j \\in obs(\\pi_i)} N_{ij} \\) points captured at the poses in \\( \\mathbb{X}_i \\). According to (6) and (9), we get" + }, + { + "type": "equation", + "bbox": [ + 0.16, + 0.162, + 0.469, + 0.193 + ], + "angle": 0, + "content": "\\[\n\\mathbf {M} _ {i} \\left(\\mathbb {X} _ {i}\\right) = \\sum_ {j \\in o b s \\left(\\boldsymbol {\\pi} _ {i}\\right)} \\mathbf {S} _ {i j} - N _ {i} \\bar {\\boldsymbol {p}} _ {i} \\bar {\\boldsymbol {p}} _ {i} ^ {T}, \\tag {12}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.203, + 0.469, + 0.281 + ], + "angle": 0, + "content": "where \\(\\bar{\\pmb{p}}_i = \\frac{1}{N_i}\\sum_{j\\in obs(\\pmb{\\pi}_i)}\\sum_{k = 1}^{N_{ij}}\\pmb{p}_{ijk}^g\\) and \\(\\mathbf{S}_{ij} = \\sum_{k = 1}^{N_{ij}}\\pmb{p}_{ijk}^g\\left(\\pmb{p}_{ijk}^g\\right)^T\\). Here the elements in \\(\\mathbf{M}_i\\), \\(\\mathbf{S}_{ij}\\) and \\(\\bar{\\pmb{p}}_i\\) in (12) are all functions of the poses in \\(\\mathbb{X}_i\\). Substituting \\(\\pmb{p}_{ijk}^g\\) in (9) into \\(\\mathbf{S}_{ij}\\) and \\(\\bar{\\pmb{p}}_i\\) in (12), we have" + }, + { + "type": "equation", + "bbox": [ + 0.09, + 0.284, + 0.468, + 0.405 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\mathbf {S} _ {i j} = \\mathbf {T} _ {j} \\underbrace {\\sum_ {k = 1} ^ {N _ {i j}} \\tilde {\\boldsymbol {p}} _ {i j k} \\tilde {\\boldsymbol {p}} _ {i j k} ^ {T}} _ {\\mathbf {U} _ {i j}} \\mathbf {T} _ {j} ^ {T} = \\mathbf {T} _ {j} \\mathbf {U} _ {i j} \\mathbf {T} _ {j} ^ {T}, \\\\ \\bar {\\boldsymbol {p}} _ {i} = \\frac {1}{N _ {i}} \\sum_ {j \\in o b s (\\boldsymbol {\\pi} _ {i})} \\mathbf {T} _ {j} \\underbrace {\\sum_ {k = 1} ^ {N _ {i j}} \\tilde {\\boldsymbol {p}} _ {i j k}} _ {\\tilde {\\boldsymbol {p}} _ {i j}} = \\frac {1}{N _ {i}} \\sum_ {j \\in o b s (\\boldsymbol {\\pi} _ {i})} \\mathbf {T} _ {j} \\tilde {\\boldsymbol {p}} _ {i j}. \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.414, + 0.469, + 0.444 + ], + "angle": 0, + "content": "Here \\(\\mathbf{U}_{ij}\\) and \\(\\tilde{\\boldsymbol{p}}_{ij}\\) in (13) are constants. We only need to compute them once, and reuse them in the iteration." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.445, + 0.469, + 0.536 + ], + "angle": 0, + "content": "According to (7), given poses in \\(\\mathbb{X}_i\\), the optimal solution for \\(\\pi_i\\) has a closed-form expression \\(\\hat{\\pi}_i = [\\hat{n}_i; \\hat{d}_i]\\), where \\(\\hat{n}_i = \\xi_3(\\mathbf{M}_i(\\mathbb{X}_i))\\) and \\(\\hat{d}_i = -\\hat{n}\\bar{p}_i\\). As \\(\\mathbf{M}_i\\) and \\(\\bar{p}_i\\) are functions of the poses in \\(\\mathbb{X}_i\\), \\(\\hat{\\pi}_i\\) is also a function of the poses in \\(\\mathbb{X}_i\\). That is to say \\(\\hat{\\pi}_i\\) is completely determined by the poses in \\(\\mathbb{X}_i\\). To simplify the notation, let us define" + }, + { + "type": "equation", + "bbox": [ + 0.188, + 0.548, + 0.469, + 0.565 + ], + "angle": 0, + "content": "\\[\n\\lambda_ {i, 3} (\\mathbb {X} _ {i}) = \\lambda_ {3} \\left(\\mathbf {M} _ {i} (\\mathbb {X} _ {i})\\right), \\tag {14}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.577, + 0.426, + 0.592 + ], + "angle": 0, + "content": "which represents the smallest eigenvalue of \\(\\mathbf{M}_i(\\mathbb{X}_i)\\)." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.593, + 0.469, + 0.623 + ], + "angle": 0, + "content": "Substituting the optimal plane estimation \\(\\hat{\\pi}_i\\) into \\(C_i(\\pi_i, \\mathbb{X}_i)\\) in (11) and using (8), we have" + }, + { + "type": "equation", + "bbox": [ + 0.192, + 0.635, + 0.469, + 0.652 + ], + "angle": 0, + "content": "\\[\n\\lambda_ {i, 3} (\\mathbb {X} _ {i}) = C _ {i} \\left(\\hat {\\pi} _ {i}, \\mathbb {X} _ {i}\\right). \\tag {15}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.663, + 0.445, + 0.679 + ], + "angle": 0, + "content": "Using (15), we can formulate the PA problem in (11) as" + }, + { + "type": "equation", + "bbox": [ + 0.145, + 0.683, + 0.469, + 0.723 + ], + "angle": 0, + "content": "\\[\n\\left\\{\\hat {\\mathbf {x}} _ {j} \\right\\} = \\arg \\min _ {\\left\\{\\mathbf {X} _ {j} \\right\\}} \\boldsymbol {\\tau}, \\boldsymbol {\\tau} = \\sum_ {i = 1} ^ {M} \\lambda_ {i, 3} (\\mathbb {X} _ {i}). \\tag {16}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.735, + 0.35, + 0.749 + ], + "angle": 0, + "content": "Table 1 summarizes the notations for PA." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.75, + 0.469, + 0.901 + ], + "angle": 0, + "content": "The cost function (16) only depends on poses, which significantly reduces the number of variables. However, as it is the sum of squared point-to-plane distances, we cannot apply the Gauss-Newton-based methods to minimize it, where the Jacobian matrix of residuals are required. Here we adopt the Newton's method to solve it. The crux for applying the Newton's method to minimize (16) is how to compute the gradient and the Hessian matrix of (16) efficiently. In the following sections, we provide a closed-form solution for them. Note that we can assign a weight to each point to" + }, + { + "type": "table", + "bbox": [ + 0.501, + 0.09, + 0.892, + 0.257 + ], + "angle": 0, + "content": "
NotationDescription
πiTheith plane.
obs(πi)The set of indexes of poses which can see πi.
XiThe set of poses which can see πi.
MiThe scatter matrix for πi.
λ3,iThe smallest eigenvalue ofMi.
xj, xkThe jth and kth poses.
xjm, xknThe mth and nth elements of xj and xk.
PjThe set of planes that are visible to xj.
PjkThe set of planes that are visible to xj and xk.
" + }, + { + "type": "table_caption", + "bbox": [ + 0.613, + 0.267, + 0.778, + 0.28 + ], + "angle": 0, + "content": "Table 1. Table of notations." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.306, + 0.892, + 0.382 + ], + "angle": 0, + "content": "punish outliers, which also has a close-form solution for planes using the weighted PCA. Our algorithm can be extended to this situation. To simplify the notation, we omit the variables of functions in the following description (e.g., \\(\\lambda_{i,3}(\\mathbb{X}_i)\\to \\lambda_{i,3})\\)." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.394, + 0.866, + 0.411 + ], + "angle": 0, + "content": "4. Newton's Iteration for Plane Adjustment" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.42, + 0.892, + 0.51 + ], + "angle": 0, + "content": "Let us denote the gradient and the Hessian matrix of \\(\\tau\\) in (16) as \\(\\pmb{g}\\) and \\(\\mathbf{H}\\), and denote the 6-dimensional gradient vector for \\(\\pmb{x}_j\\) as \\(\\pmb{g}_j\\) and the \\(6\\times 6\\) Hessian matrix block for \\(\\pmb{x}_j\\) and \\(\\pmb{x}_k\\) as \\(\\mathbf{H}_{jk}\\) (note that here \\(j\\) can equal to \\(k\\)). Then \\(\\pmb{g}\\) and \\(\\mathbf{H}\\) can be written in the block form as \\(\\pmb{g} = (\\pmb{g}_j)\\in \\mathbb{R}^{6N}\\) and \\(\\mathbf{H} = (\\mathbf{H}_{jk})\\in \\mathbb{R}^{6N\\times 6N}\\)." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.51, + 0.892, + 0.542 + ], + "angle": 0, + "content": "The \\(i\\)th plane \\(\\pi_i\\) is observed by the poses in \\(\\mathbb{X}_i\\). Assume \\(\\boldsymbol{x}_j \\in \\mathbb{X}_i\\) and \\(\\boldsymbol{x}_k \\in \\mathbb{X}_i\\). Let us define" + }, + { + "type": "equation", + "bbox": [ + 0.591, + 0.55, + 0.891, + 0.584 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {g} _ {j} ^ {i} = \\frac {\\partial \\lambda_ {i , 3}}{\\partial \\boldsymbol {x} _ {j}}, \\mathbf {H} _ {j k} ^ {i} = \\frac {\\partial^ {2} \\lambda_ {i , 3}}{\\partial \\boldsymbol {x} _ {j} \\partial \\boldsymbol {x} _ {k}}. \\tag {17}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.591, + 0.684, + 0.606 + ], + "angle": 0, + "content": "According to (16), we have" + }, + { + "type": "equation", + "bbox": [ + 0.585, + 0.615, + 0.891, + 0.649 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {g} _ {j} = \\sum_ {i \\in \\mathbb {P} _ {j}} \\boldsymbol {g} _ {j} ^ {i}, \\quad \\mathrm {H} _ {j k} = \\sum_ {i \\in \\mathbb {P} _ {j k}} \\mathrm {H} _ {j k} ^ {i}, \\tag {18}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.657, + 0.892, + 0.72 + ], + "angle": 0, + "content": "where \\(\\mathbb{P}_j\\) is the set of planes observed by \\(\\pmb{x}_j\\), and \\(\\mathbb{P}_{jk}\\) is the set of planes observed by \\(\\pmb{x}_j\\) and \\(\\pmb{x}_k\\) simultaneously. If \\(j = k\\), here \\(\\mathbb{P}_{jk}\\) equals to \\(\\mathbb{P}_j\\). From (18), we know that the key point to get \\(\\pmb{g}\\) and \\(\\mathbf{H}\\) is to compute \\(\\pmb{g}_j^i\\) and \\(\\mathbf{H}_{jk}^i\\) in (17)." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.725, + 0.787, + 0.741 + ], + "angle": 0, + "content": "4.1. Partial Derivatives of Eigenvalue" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.749, + 0.892, + 0.816 + ], + "angle": 0, + "content": "According to (15), \\(\\lambda_{i,3}\\) is a function of poses in \\(\\mathbb{X}_i\\). Assume that \\(x_{jm}\\) and \\(x_{kn}\\) are the \\(m\\)th and \\(n\\)th elements of \\(\\pmb{x}_j\\) and \\(\\pmb{x}_k\\), respectively. We consider the first- and second-order partial derivation \\(\\frac{\\partial\\lambda_{i,3}}{\\partial x_{jm}}\\) and \\(\\frac{\\partial^2\\lambda_{i,3}}{\\partial x_{jm}\\partial x_{kn}}\\), respectively." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.816, + 0.892, + 0.876 + ], + "angle": 0, + "content": "\\(\\lambda_{i,3}\\) is a root of the equation \\(|\\mathbf{M}_i(\\mathbb{X}_i) - \\lambda_i\\mathbf{I}_3| = 0\\) where \\(|\\cdot |\\) denotes the determinant of a matrix. Assume \\(m_{ef}\\) is the \\(e\\)th row \\(f\\)th column term of \\(\\mathbf{M}_i(\\mathbb{X}_i)\\). \\(|\\mathbf{M}_i(\\mathbb{X}_i) - \\lambda_i\\mathbf{I}_3| = 0\\) is a cubic equation with the following form" + }, + { + "type": "equation", + "bbox": [ + 0.583, + 0.884, + 0.891, + 0.903 + ], + "angle": 0, + "content": "\\[\n- \\lambda_ {i, 3} ^ {3} + a _ {i} \\lambda_ {i, 3} ^ {2} + b _ {i} \\lambda_ {i, 3} + c _ {i} = 0, \\tag {19}\n\\]" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "13116" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.09, + 0.473, + 0.248 + ], + "angle": 0, + "content": "where \\(a_{i} = m_{11} + m_{22} + m_{33}, b_{i} = m_{12}^{2} + m_{13}^{2} + m_{23}^{2} - m_{11}m_{22} - m_{11}m_{33} - m_{22}m_{33}\\), and \\(c_{i} = -m_{33}m_{12}^{2} + 2m_{12}m_{13}m_{23} - m_{22}m_{13}^{2} - m_{11}m_{23}^{2} + m_{11}m_{22}m_{33}\\). Here \\(a_{i}, b_{i}\\) and \\(c_{i}\\) are all functions of the poses in \\(\\mathbb{X}_i\\). It is known that the root of a cubic equation has a closed form. One solution to compute \\(\\frac{\\partial\\lambda_{i,3}}{\\partial x_{jm}}\\) and \\(\\frac{\\partial^2\\lambda_{i,3}}{\\partial x_{jm}\\partial x_{kn}}\\) is to directly differentiate the root. However, the formula of the root is too complicated. Here we introduce a simple way to compute them. Briefly, we employ the implicit function theorem [15] to compute them. Let us define" + }, + { + "type": "equation", + "bbox": [ + 0.089, + 0.255, + 0.47, + 0.317 + ], + "angle": 0, + "content": "\\[\n\\chi_ {i} = \\left[ \\begin{array}{l} \\lambda_ {i, 3} ^ {2} \\\\ \\lambda_ {i, 3} \\\\ 1 \\end{array} \\right], \\eta_ {i} = \\left[ \\begin{array}{l} a _ {i} \\\\ b _ {i} \\\\ c _ {i} \\end{array} \\right] \\kappa_ {i} = \\left[ \\begin{array}{l} - 3 \\\\ 2 a _ {i} \\\\ b _ {i} \\end{array} \\right], \\delta_ {j m} ^ {i} = \\frac {\\partial \\eta_ {i}}{\\partial x _ {j m}}. \\tag {20}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.317, + 0.47, + 0.368 + ], + "angle": 0, + "content": "Using the above notations, we present \\(\\frac{\\partial\\lambda_{i,3}}{\\partial x_{jm}}\\) and \\(\\frac{\\partial^2\\lambda_{i,3}}{\\partial x_{jm}\\partial x_{kn}}\\) in Lemma 1 and 2. The proofs of the following lemmas and theorems are in the supplementary material." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.376, + 0.395, + 0.391 + ], + "angle": 0, + "content": "Lemma 1 Using the notations in (20), we have" + }, + { + "type": "equation", + "bbox": [ + 0.195, + 0.398, + 0.47, + 0.432 + ], + "angle": 0, + "content": "\\[\n\\frac {\\partial \\lambda_ {i , 3}}{\\partial x _ {j m}} = - \\varphi_ {i} \\boldsymbol {\\delta} _ {j m} ^ {i} \\cdot \\boldsymbol {\\chi} _ {i}, \\tag {21}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.441, + 0.453, + 0.459 + ], + "angle": 0, + "content": "where \\(\\cdot\\) represents the dot product and \\(\\varphi_{i} = (\\pmb{\\kappa}_{i}\\cdot \\pmb{\\chi}_{i})^{-1}\\)" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.467, + 0.454, + 0.482 + ], + "angle": 0, + "content": "Lemma 2 Using the notations in (20) and (21), we have" + }, + { + "type": "equation", + "bbox": [ + 0.078, + 0.489, + 0.48, + 0.533 + ], + "angle": 0, + "content": "\\[\n\\frac {\\partial^ {2} \\lambda_ {i , 3}}{\\partial x _ {j m} \\partial x _ {k n}} = - \\varphi_ {i} \\left(\\boldsymbol {\\delta} _ {j m} ^ {i} \\cdot \\frac {\\partial \\boldsymbol {\\chi} _ {i}}{\\partial x _ {k n}} + \\boldsymbol {\\chi} _ {i} \\cdot \\frac {\\partial \\boldsymbol {\\delta} _ {j m} ^ {i}}{\\partial x _ {k n}} - \\frac {\\partial \\lambda_ {i , 3}}{\\partial x _ {j m}} \\frac {\\partial \\varphi_ {i} ^ {- 1}}{\\partial x _ {k n}}\\right). \\tag {22}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.543, + 0.188, + 0.555 + ], + "angle": 0, + "content": "Let us define" + }, + { + "type": "equation", + "bbox": [ + 0.085, + 0.561, + 0.425, + 0.59 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {\\alpha} _ {j} ^ {i} = \\frac {\\partial a _ {i}}{\\partial \\boldsymbol {x} _ {j}}, \\beta_ {j} ^ {i} = \\frac {\\partial b _ {i}}{\\partial \\boldsymbol {x} _ {j}}, \\gamma_ {j} ^ {i} = \\frac {\\partial c _ {i}}{\\partial \\boldsymbol {x} _ {j}}, \\boldsymbol {\\Delta} _ {j} ^ {i} = [ \\boldsymbol {\\alpha} _ {j} ^ {i}, \\beta_ {j} ^ {i}, \\gamma_ {j} ^ {i} ],\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.086, + 0.592, + 0.469, + 0.62 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {\\alpha} _ {k} ^ {i} = \\frac {\\partial a _ {i}}{\\partial \\boldsymbol {x} _ {k}}, \\beta_ {k} ^ {i} = \\frac {\\partial b _ {i}}{\\partial \\boldsymbol {x} _ {k}}, \\gamma_ {k} ^ {i} = \\frac {\\partial c _ {i}}{\\partial \\boldsymbol {x} _ {k}}, \\boldsymbol {\\Delta} _ {k} ^ {i} = [ \\boldsymbol {\\alpha} _ {k} ^ {i}, \\boldsymbol {\\beta} _ {k} ^ {i}, \\boldsymbol {\\gamma} _ {k} ^ {i} ], \\tag {23}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.086, + 0.622, + 0.415, + 0.652 + ], + "angle": 0, + "content": "\\[\n\\mathbf {H} _ {j k} ^ {a _ {i}} = \\frac {\\partial^ {2} a _ {i}}{\\partial \\boldsymbol {x} _ {j} \\partial \\boldsymbol {x} _ {k}}, \\mathbf {H} _ {j k} ^ {b _ {i}} = \\frac {\\partial^ {2} b _ {i}}{\\partial \\boldsymbol {x} _ {j} \\partial \\boldsymbol {x} _ {k}}, \\mathbf {H} _ {j k} ^ {c _ {i}} = \\frac {\\partial^ {2} c _ {i}}{\\partial \\boldsymbol {x} _ {j} \\partial \\boldsymbol {x} _ {k}}.\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.659, + 0.469, + 0.695 + ], + "angle": 0, + "content": "Using the above lemmas and notations, we can derive \\( \\pmb{g}_j^i \\) and \\( \\mathbf{H}_{jk}^i \\)." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.7, + 0.469, + 0.736 + ], + "angle": 0, + "content": "Theorem 1 Using the notations in (20), (21) and (23), \\(\\pmb{g}_j^i\\) and \\(\\mathbf{H}_{jk}^{i}\\) have the forms" + }, + { + "type": "equation", + "bbox": [ + 0.109, + 0.744, + 0.225, + 0.763 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {g} _ {j} ^ {i} = - \\varphi_ {i} \\boldsymbol {\\Delta} _ {j} ^ {i} \\chi_ {i},\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.098, + 0.761, + 0.469, + 0.79 + ], + "angle": 0, + "content": "\\[\n\\mathbf {H} _ {j k} ^ {i} = \\varphi_ {i} \\left(\\mathbf {K} _ {j k} ^ {i} - \\lambda_ {3, i} ^ {2} \\mathbf {H} _ {j k} ^ {a _ {i}} - \\lambda_ {3, i} \\mathbf {H} _ {j k} ^ {b _ {i}} - \\mathbf {H} _ {j k} ^ {c _ {i}}\\right), \\tag {24}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.797, + 0.469, + 0.849 + ], + "angle": 0, + "content": "where \\(\\mathbf{K}_{jk}^{i} = \\pmb{g}_{j}^{i}\\pmb{u}^{T} - \\pmb{v}(\\pmb{g}_{k}^{i})^{T},\\pmb{u} = 2\\lambda_{i,3}\\pmb{\\alpha}_{k}^{i} + \\pmb{\\beta}_{k}^{i} + (2a - 6\\lambda_{i,3})\\pmb{g}_{k}^{i},\\) and \\(\\pmb {v} = 2\\lambda_{i,3}\\pmb{\\alpha}_{j}^{i} + \\pmb{\\beta}_{j}^{i}\\) , and similar to \\(\\pmb{g}_j^i,\\pmb{g}_k^i =\\) \\(-\\varphi_i\\Delta_k^i\\chi_i\\) is the gradient block for \\(\\pmb{x}_k\\)" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.855, + 0.47, + 0.904 + ], + "angle": 0, + "content": "The formula of \\(\\mathbf{H}_{jk}^{i}\\) in (24) is applicable to the case that \\(j = k\\). From Theorem 1, we know that the key point to get \\(\\pmb{g}_j^i\\) and \\(\\mathbf{H}_{jk}^{i}\\) is to get the derivatives of \\(a_{i}, b_{i}\\) and \\(c_{i}\\) in (23)." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.091, + 0.79, + 0.107 + ], + "angle": 0, + "content": "4.2. Partial Derivatives of \\(a_i\\), \\(b_i\\) and \\(c_i\\)" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.114, + 0.893, + 0.175 + ], + "angle": 0, + "content": "According to (19), \\(a_{i}, b_{i}\\) and \\(c_{i}\\) are functions of the elements in \\(\\mathbf{M}_i\\). Using this relationship, we can easily derive the partial derivatives in (23). For instance, as \\(a_{i} = m_{11} + m_{22} + m_{33}\\), we have" + }, + { + "type": "equation", + "bbox": [ + 0.583, + 0.183, + 0.891, + 0.217 + ], + "angle": 0, + "content": "\\[\n\\frac {\\partial a _ {i}}{\\partial \\boldsymbol {x} _ {j}} = \\frac {\\partial m _ {1 1}}{\\partial \\boldsymbol {x} _ {j}} + \\frac {\\partial m _ {2 2}}{\\partial \\boldsymbol {x} _ {j}} + \\frac {\\partial m _ {3 3}}{\\partial \\boldsymbol {x} _ {j}}. \\tag {25}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.225, + 0.893, + 0.271 + ], + "angle": 0, + "content": "Thus, to get the first- and second-order partial derivatives of \\(a_{i}, b_{i}\\) and \\(c_{i}\\) with respect to \\(\\pmb{x}_j\\) and \\(\\pmb{x}_k\\) in (23), we need to derive the form of \\(\\mathbf{M}_i\\) with respect to \\(\\pmb{x}_j\\) and \\(\\pmb{x}_k\\)." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.282, + 0.88, + 0.298 + ], + "angle": 0, + "content": "Lemma 3 In terms of \\( \\pmb{x}_j \\) and \\( \\pmb{x}_k \\), \\( \\bar{\\pmb{p}}_i \\) in (13) has the form" + }, + { + "type": "equation", + "bbox": [ + 0.568, + 0.308, + 0.891, + 0.324 + ], + "angle": 0, + "content": "\\[\n\\bar {\\boldsymbol {p}} _ {i} \\left(\\boldsymbol {x} _ {j}, \\boldsymbol {x} _ {k}\\right) = \\mathbf {T} _ {j} \\boldsymbol {q} _ {i j} + \\mathbf {T} _ {k} \\boldsymbol {q} _ {i k} + \\boldsymbol {c} _ {i j k}, \\tag {26}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.333, + 0.893, + 0.397 + ], + "angle": 0, + "content": "where \\(\\pmb{q}_{ij} = \\frac{1}{N_i}\\tilde{\\pmb{p}}_{ij},\\quad \\pmb{q}_{ik} = \\frac{1}{N_i}\\tilde{\\pmb{p}}_{ik},\\) and \\(c_{ijk} = \\frac{1}{N_i}\\sum_{n\\in \\mathbb{O}_{jk}}\\mathbf{T}_n\\tilde{p}_{in}\\). Here \\(\\mathbb{O}_{jk} = \\mathrm{obs}(\\pi_i) - \\{j,k\\}\\) represents the set of indexes of the poses that can observe \\(\\pi_i\\), excluding the \\(j\\)th and \\(k\\)th poses." + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.398, + 0.726, + 0.413 + ], + "angle": 0, + "content": "In terms of \\( \\pmb{x}_j \\), \\( \\bar{\\pmb{p}}_i \\) has the form" + }, + { + "type": "equation", + "bbox": [ + 0.616, + 0.424, + 0.891, + 0.44 + ], + "angle": 0, + "content": "\\[\n\\bar {\\boldsymbol {p}} _ {i} \\left(\\boldsymbol {x} _ {j}\\right) = \\mathbf {T} _ {j} \\mathbf {q} _ {i j} + \\boldsymbol {c} _ {i j}, \\tag {27}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.45, + 0.684, + 0.466 + ], + "angle": 0, + "content": "where \\( c_{ij} = \\mathbf{T}_k\\mathbf{q}_{ik} + c_{ijk} \\)." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.476, + 0.892, + 0.506 + ], + "angle": 0, + "content": "Using Lemma 3, we can have the following theorem for \\(\\mathbf{M}_i\\) in (12)." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.515, + 0.878, + 0.531 + ], + "angle": 0, + "content": "Theorem 2 In terms of \\( \\pmb{x}_j \\), \\( \\mathbf{M}_i \\) in (12) can be written as" + }, + { + "type": "equation", + "bbox": [ + 0.512, + 0.54, + 0.891, + 0.56 + ], + "angle": 0, + "content": "\\[\n\\mathbf {M} _ {i} \\left(\\boldsymbol {x} _ {j}\\right) = \\mathbf {T} _ {j} \\mathbf {Q} _ {j} ^ {i} \\mathbf {T} _ {j} ^ {T} + \\mathbf {T} _ {j} \\mathbf {K} _ {j} ^ {i} + \\left(\\mathbf {K} _ {j} ^ {i}\\right) ^ {T} \\mathbf {T} _ {j} ^ {T} + \\mathbf {C} _ {j} ^ {i}, \\tag {28}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.569, + 0.891, + 0.6 + ], + "angle": 0, + "content": "where \\(\\mathbf{Q}_j^i = \\mathbf{U}_{ij} - N_j\\mathbf{q}_{ij}\\mathbf{q}_{ij}^T\\) and \\(\\mathbf{K}_j^i = -N_i\\mathbf{q}_{ij}\\mathbf{c}_{ij}^T\\). Here \\(\\mathbf{U}_{ij}\\) and \\(\\mathbf{q}_{ij}\\) are defined in (13) and (26), respectively." + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.601, + 0.816, + 0.616 + ], + "angle": 0, + "content": "In terms of \\( \\pmb{x}_j \\) and \\( \\pmb{x}_k \\), \\( \\mathbf{M}_i \\) can be written as" + }, + { + "type": "equation", + "bbox": [ + 0.51, + 0.626, + 0.891, + 0.648 + ], + "angle": 0, + "content": "\\[\n\\mathbf {M} _ {i} \\left(\\boldsymbol {x} _ {j}, \\boldsymbol {x} _ {k}\\right) = \\mathbf {T} _ {j} \\mathbf {O} _ {j k} ^ {i} \\mathbf {T} _ {k} ^ {T} + \\mathbf {T} _ {k} \\left(\\mathbf {O} _ {j k} ^ {i}\\right) ^ {T} \\mathbf {T} _ {j} ^ {T} + \\mathbf {C} _ {j k} ^ {i}. \\tag {29}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.657, + 0.674, + 0.676 + ], + "angle": 0, + "content": "where \\(\\mathbf{O}_{jk}^{i} = -N_{i}\\pmb{q}_{ij}\\pmb{q}_{ik}^{T}\\)." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.684, + 0.892, + 0.809 + ], + "angle": 0, + "content": "Here we do not provide the detailed formulas for \\(\\mathbf{C}_j^i\\) and \\(\\mathbf{C}_{jk}^{i}\\), as they will be eliminated in the partial derivative. Actually, only \\(\\mathbf{Q}_j^i\\), \\(\\mathbf{K}_j^i\\), and \\(\\mathbf{O}_{jk}^{i}\\) are required to compute the partial derivatives in (23). Equation (28) is used to compute the first- and second-order partial derivatives of \\(a_i\\), \\(b_i\\) and \\(c_i\\) with respect to \\(\\pmb{x}_j\\). Equation (29) is used to compute the second-order partial derivatives of \\(a_i\\), \\(b_i\\) and \\(c_i\\) with respect to \\(\\pmb{x}_j\\) and \\(\\pmb{x}_k\\)." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.818, + 0.674, + 0.832 + ], + "angle": 0, + "content": "4.3. Efficient Iteration" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.84, + 0.893, + 0.902 + ], + "angle": 0, + "content": "From Theorem 2, we can easily derive the elements of \\(\\mathbf{M}_i(\\pmb{x}_j)\\) and \\(\\mathbf{M}_i(\\pmb{x}_j,\\pmb{x}_i)\\). Assume \\(a(\\pmb{x}_j)\\) and \\(b(\\pmb{x}_j,\\pmb{x}_k)\\) are one of the elements in \\(\\mathbf{M}_i(\\pmb{x}_j)\\) and \\(\\mathbf{M}_i(\\pmb{x}_j,\\pmb{x}_k)\\), respectively. Substituting \\(\\mathbf{T}_j\\) and \\(\\mathbf{T}_k\\) defined in (1) into (28) and" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "13117" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.091, + 0.47, + 0.155 + ], + "angle": 0, + "content": "(29) and expanding them, we can obtain that \\( a(\\pmb{x}_j) \\) and \\( b(\\pmb{x}_j, \\pmb{x}_k) \\) are second-order polynomials in terms of the elements in \\( \\mathbf{T}_j \\) and \\( \\mathbf{T}_k \\). Using the CGB parameterization in (2), we can write \\( a(\\pmb{x}_j) \\) and \\( b(\\pmb{x}_j, \\pmb{x}_k) \\) as" + }, + { + "type": "equation", + "bbox": [ + 0.166, + 0.165, + 0.382, + 0.201 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} a (\\boldsymbol {x} _ {j}) = \\boldsymbol {c} \\cdot \\boldsymbol {h} (\\boldsymbol {x} _ {j}) + c _ {0}, \\\\ b \\left(\\boldsymbol {x} _ {j}, \\boldsymbol {x} _ {k}\\right) = \\boldsymbol {d} \\cdot \\boldsymbol {g} \\left(\\boldsymbol {x} _ {j}, \\boldsymbol {x} _ {k}\\right) + d _ {0}, \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.212, + 0.471, + 0.292 + ], + "angle": 0, + "content": "where \\(\\pmb{c}\\) is determined by \\(\\mathbf{Q}_j^i\\) and \\(\\mathbf{K}_j^i\\) in (28), \\(\\pmb{d}\\) is determined by \\(\\mathbf{O}_{jk}^{i}\\) in (29), \\(\\pmb{h}(\\pmb{x}_j)\\) and \\(\\pmb{g}(\\pmb{x}_j, \\pmb{x}_k)\\) are two vector functions, \\(c_0\\) and \\(d_0\\) are two scalars independent on \\(\\pmb{x}_j\\) and \\(\\pmb{x}_k\\). Let us first consider the first-order partial derivative of \\(a(\\pmb{x}_j)\\) with respect to \\(\\pmb{x}_j\\). It has the form" + }, + { + "type": "equation", + "bbox": [ + 0.2, + 0.301, + 0.469, + 0.336 + ], + "angle": 0, + "content": "\\[\n\\frac {\\partial a \\left(\\boldsymbol {x} _ {j}\\right)}{\\partial \\boldsymbol {x} _ {j}} = \\frac {\\partial h \\left(\\boldsymbol {x} _ {j}\\right)}{\\partial \\boldsymbol {x} _ {j}} c, \\tag {31}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.347, + 0.47, + 0.537 + ], + "angle": 0, + "content": "where the vector-by-vector derivative \\(\\frac{\\partial h(\\pmb{x}_j)}{\\partial\\pmb{x}_j}\\) is defined in (4). To efficiently compute (31), we consider a special pose \\(\\mathbf{T}_0 = [\\mathbf{R}_0,t_0]\\) where \\(\\mathbf{R}_0 = \\mathbf{I}_3\\) and \\(t_0 = [0;0;0]\\). Let us denote the parameterization of \\(\\mathbf{T}_0\\) as \\(\\pmb{x}_0\\). As the CGR parameterization for \\(\\mathbf{I}_3\\) is \\([0;0;0]\\), we have \\(\\pmb{x}_0 = [0;0;0;0;0;0]\\). For \\(\\pmb{x}_j = \\pmb{x}_0\\), the matrix \\(\\frac{\\partial h(\\mathbf{x}_j)}{\\partial\\mathbf{x}_j}\\) can be easily computed. Similarly, the second-order partial derivatives of \\(\\pmb{h}(\\pmb{x}_j)\\) and \\(\\pmb{g}(\\pmb{x}_j,\\pmb{x}_k)\\) at \\(\\pmb{x}_j = \\pmb{x}_0\\) and \\(\\pmb{x}_k = \\pmb{x}_0\\) are also simple. As \\(\\pmb{h}(\\pmb{x}_j)\\) and \\(\\pmb{g}(\\pmb{x}_j,\\pmb{x}_k)\\) only depend on \\(\\pmb{x}_j\\) and \\(\\pmb{x}_k\\), we can compute the partial derivatives at \\(\\pmb{x}_0\\) once, and then reuse them in the following iterations. Here we introduce a method to make the iteration stay at \\(\\mathbf{x}_0\\) for each pose." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.537, + 0.469, + 0.569 + ], + "angle": 0, + "content": "Assume that \\(\\{\\mathbf{X}_j^n\\}\\) are the poses after the \\(n\\)th iteration. Then we can update \\(\\mathbf{U}_{ij}\\) and \\(\\tilde{p}_{ij}\\) in (13) by" + }, + { + "type": "equation", + "bbox": [ + 0.11, + 0.578, + 0.469, + 0.598 + ], + "angle": 0, + "content": "\\[\n\\mathbf {U} _ {i j} ^ {n + 1} = \\mathbf {X} _ {j} ^ {n} \\mathbf {U} _ {i j} \\left(\\mathbf {X} _ {j} ^ {n}\\right) ^ {T} \\text {a n d} \\tilde {\\boldsymbol {p}} _ {i j} ^ {n + 1} = \\mathbf {X} _ {j} ^ {n} \\tilde {\\boldsymbol {p}} _ {i j}. \\tag {32}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.608, + 0.469, + 0.722 + ], + "angle": 0, + "content": "Substituting \\(\\mathbf{U}_{ij}^{n + 1}\\) and \\(\\tilde{\\pmb{p}}_{ij}^{n + 1}\\) into (12), we get a new matrix \\(\\mathbf{M}_i(\\mathbb{X}_i)^{n + 1}\\), which can finally lead to a new cost \\(\\tau^{n + 1}\\) in (16). As the points have been transformed by \\(\\{\\mathbf{X}_j^n\\}\\), each pose should start with \\(\\mathbf{X}_0\\) for \\(\\tau^{n + 1}\\). Assume that \\(\\Delta \\pmb{x}_j^{n + 1}\\) is the result from the \\((n + 1)\\)th iteration for the \\(j\\)th pose. We can compute the corresponding transformation matrix \\(\\Delta \\mathbf{X}_j^{n + 1}\\) using (1) and (2). Then we can update \\(\\mathbf{X}_j^n\\) by" + }, + { + "type": "equation", + "bbox": [ + 0.199, + 0.732, + 0.469, + 0.753 + ], + "angle": 0, + "content": "\\[\n\\mathbf {X} _ {j} ^ {n + 1} = \\Delta \\mathbf {X} _ {j} ^ {n + 1} \\mathbf {X} _ {j} ^ {n}. \\tag {33}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.762, + 0.469, + 0.839 + ], + "angle": 0, + "content": "Furthermore, the update steps in (32) will not introduce additional computation. This is because the damped Newton's method requires to compute the cost \\(\\tau\\) in (16) to adjust \\(\\mu\\) in (3) after each iteration, which requires to perform the computation in (32)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.848, + 0.274, + 0.865 + ], + "angle": 0, + "content": "4.4. Algorithm Summary" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.871, + 0.469, + 0.902 + ], + "angle": 0, + "content": "We first construct \\(\\mathbf{H}\\) and \\(\\pmb{g}\\). For each plane \\(\\pi_i\\), we solve the cubic equation (19), and select the smallest root \\(\\lambda_{i,3}\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.091, + 0.892, + 0.319 + ], + "angle": 0, + "content": "For \\( \\boldsymbol{x}_j \\), we construct \\( \\mathbf{M}(\\boldsymbol{x}_j) \\) in (28), and calculate the partial derivatives of \\( a_i \\), \\( b_i \\) and \\( c_i \\) with respect to \\( \\boldsymbol{x}_j \\) in (23). Then, we use (24) to compute \\( g_j^i \\) and \\( \\mathbf{H}_{jj}^i \\) and use (18) to update \\( g_j \\) and \\( \\mathbf{H}_{jj} \\). For \\( \\boldsymbol{x}_j \\) and \\( \\boldsymbol{x}_k \\), \\( \\mathbf{M}_i(\\boldsymbol{x}_j, \\boldsymbol{x}_k) \\) is generated, and then the partial derivatives of \\( a_i \\), \\( b_i \\) and \\( c_i \\) with respect to \\( \\boldsymbol{x}_j \\) and \\( \\boldsymbol{x}_j \\) in (23) are computed. Then, \\( \\mathbf{H}_{jk}^i \\) can be easily obtained from (24), and \\( \\mathbf{H}_{jk} \\) in (18) is computed accordingly. Using \\( \\mathbf{H} \\) and \\( g \\), we conduct the damped Newton's step in (3). After each iteration, \\( \\mathbf{U}_{ij} \\) and \\( \\tilde{\\boldsymbol{p}}_{ij} \\) are updated by (32). The proposed algorithm is summarized in Algorithm 1. Let us denote the mean and variance of the number of observations per plane as \\( \\bar{K} \\) and \\( \\sigma^2 \\), respectively. According to [8], the computational complexity of the Hessian matrix is \\( O(M(\\bar{K}^2 + \\sigma^2)) \\), which is of the same order as the Schur complement trick." + }, + { + "type": "code_caption", + "bbox": [ + 0.51, + 0.335, + 0.848, + 0.365 + ], + "angle": 0, + "content": "Algorithm 1: Second-order plane adjustment for \\(N\\) poses and \\(M\\) planes" + }, + { + "type": "algorithm", + "bbox": [ + 0.52, + 0.369, + 0.868, + 0.681 + ], + "angle": 0, + "content": "while not converge do \\(\\mathbf{H} = \\text{zeros}(6N, 6N), \\mathbf{g} = \\text{zeros}(6N, 1)\\); for \\(i \\in [1, M]\\) do \n\\[\n\\begin{aligned}\n& \\text{Compute } \\mathbf{g}\\text{ and the diagonal terms of } \\mathbf{H}. \\\\\n& \\text{for } j \\in \\text{obs}(\\pi_i) \\text{ do} \\\\\n& \\text{Compute } \\mathbf{M}_i(\\mathbf{x}_j) \\text{ using (28)}; \\\\\n& \\text{Compute } \\alpha_j^i, \\beta_j^i, \\gamma_j^i, \\mathbf{H}_{jj}^{a_i}, \\mathbf{H}_{jj}^{b_i}, \\mathbf{H}_{jj}^{c_i} \\text{ using (23)}; \\\\\n& \\text{Compute } \\mathbf{H}_{jj}^i \\text{ and } \\mathbf{g}_j^i \\text{ using (24)}; \\\\\n& \\text{H}_{jj} = \\mathbf{H}_{jj} + \\mathbf{H}_{jj}^i, \\mathbf{g}_j = \\mathbf{g}_j + \\mathbf{g}_j^i;\n\\end{aligned}\n\\] \n\\[\n\\begin{aligned}\n& \\text{for } j \\in \\text{obs}(\\pi_i) \\text{ do} \\\\\n& \\text{for } k \\in \\text{obs}(\\pi_i) \\text{ and } k > j \\text{ do} \\\\\n& \\text{Compute } \\mathbf{H}_{jk}^i \\text{ using (24)}; \\\\\n& \\text{H}_{jk} = \\mathbf{H}_{jk} + \\mathbf{H}_{jk}^i; \\\\\n& \\text{H}_{kj} = \\mathbf{H}_{kj} + (\\mathbf{H}_{jk}^i)^T;\n\\end{aligned}\n\\] \nConduct the damped Newton's step in (3); Update \\(\\mathbf{U}_{ij}\\) and \\(\\tilde{\\boldsymbol{p}}_{ij}\\) using (32);" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.717, + 0.632, + 0.734 + ], + "angle": 0, + "content": "5. Experiments" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.742, + 0.582, + 0.759 + ], + "angle": 0, + "content": "5.1. Setup" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.892, + 0.901 + ], + "angle": 0, + "content": "In this section, we compare our algorithm with EF [10], BALM [16] and the LM solution [23] with plane fitting after a successful LM step (named \\(\\mathbf{LM} + \\mathbf{PF}\\)). Our damped Newton's method was implemented according to the LM algorithm in Ceres [2]. The damped Newton's method and the LM algorithm are with the same parameters. Specifically, the initial value of the damping factor \\(\\mu\\) in (3) is set to \\(10^{-4}\\). The early stopping tolerances (such as the cost value change and the norm of gradient) are set to \\(10^{-7}\\). The" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "13118" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.169, + 0.09, + 0.375, + 0.236 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.258, + 0.237, + 0.284, + 0.25 + ], + "angle": 0, + "content": "(A)" + }, + { + "type": "image", + "bbox": [ + 0.382, + 0.091, + 0.792, + 0.236 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.591, + 0.237, + 0.616, + 0.25 + ], + "angle": 0, + "content": "(B)" + }, + { + "type": "image", + "bbox": [ + 0.168, + 0.254, + 0.377, + 0.404 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.255, + 0.406, + 0.28, + 0.421 + ], + "angle": 0, + "content": "(C)" + }, + { + "type": "image", + "bbox": [ + 0.382, + 0.254, + 0.792, + 0.405 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.591, + 0.406, + 0.617, + 0.421 + ], + "angle": 0, + "content": "(D)" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.431, + 0.892, + 0.461 + ], + "angle": 0, + "content": "Figure 3. The four datasets used in this paper. There are \\(4.5 \\times 10^{6}\\), \\(16.6 \\times 10^{6}\\), \\(16.7 \\times 10^{6}\\), and \\(10.5 \\times 10^{6}\\) points in the 4 datasets. The 4 datasets have 339, 369, 856, and 589 planes, and 472, 1355, 1606, 1184 poses, respectively. Roofs are removed to show the trajectories." + }, + { + "type": "image", + "bbox": [ + 0.082, + 0.485, + 0.182, + 0.556 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.087, + 0.559, + 0.268, + 0.568 + ], + "angle": 0, + "content": "\\(\\sigma_{\\mathbf{R}} = 0.1^{\\circ}\\sigma_{t} = 0.01m\\) \\(\\sigma_{\\mathbf{R}} = 1^{\\circ}\\sigma_{t} = 0.1m\\)" + }, + { + "type": "image", + "bbox": [ + 0.182, + 0.485, + 0.277, + 0.556 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.186, + 0.559, + 0.268, + 0.568 + ], + "angle": 0, + "content": "\\(\\sigma_{\\mathbf{R}} = 1^{\\circ}\\sigma_{t} = 0.1m\\)" + }, + { + "type": "image", + "bbox": [ + 0.278, + 0.485, + 0.371, + 0.556 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.286, + 0.559, + 0.366, + 0.568 + ], + "angle": 0, + "content": "\\(\\sigma_{\\mathbf{R}} = 2^{\\circ}\\sigma_{t} = 0.2m\\)" + }, + { + "type": "image", + "bbox": [ + 0.373, + 0.485, + 0.465, + 0.556 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.379, + 0.559, + 0.459, + 0.568 + ], + "angle": 0, + "content": "\\(\\sigma_{\\mathbf{R}} = 3^{\\circ}\\sigma_{t} = 0.3m\\)" + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.58, + 0.468, + 0.607 + ], + "angle": 0, + "content": "Figure 4. The point clouds of dataset C after the poses were perturbs by the four noise levels." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.637, + 0.468, + 0.713 + ], + "angle": 0, + "content": "maximum number of iterations is set to 200 for our algorithm, BALM, and LM+PF, and \\(10^{5}\\) for EF, as EF uses the first-order minimization which requires more iterations to converge. All the experiments were conducted on a desktop with an Intel i7 cpu and 64G memory." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.726, + 0.18, + 0.74 + ], + "angle": 0, + "content": "5.2. Datasets" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.75, + 0.469, + 0.901 + ], + "angle": 0, + "content": "We collected four datasets using a VLP-16 LiDAR. We used the LiDAR SLAM algorithm [24] to detect the planes and establish the plane association. Fig. 3 shows the four datasets. Similar to the evaluation of BA algorithms [3,8,25], we perturb the pose, and compare the PA cost in (11) for different algorithms. Specifically, we directly add Gaussian noises to the translation, and randomly generate an angle-axis vector from a Gaussian distribution to perturb the rotation. After the poses are perturb, we use (7) to get the initial plane parameters for \\(\\mathrm{LM} + \\mathrm{PF}\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.487, + 0.892, + 0.683 + ], + "angle": 0, + "content": "We evaluate the performance of different algorithms under different noise levels. Let us denote the standard deviation (std) of the Gaussian noises for rotation and translation as \\(\\sigma_{\\mathbf{R}}\\) and \\(\\sigma_t\\), respectively. We consider four noise levels: \\(\\sigma_{\\mathbf{R}} = 0.1^{\\circ}\\) and \\(\\sigma_t = 0.01m\\), \\(\\sigma_{\\mathbf{R}} = 1^{\\circ}\\) and \\(\\sigma_t = 0.1m\\), \\(\\sigma_{\\mathbf{R}} = 2^{\\circ}\\) and \\(\\sigma_t = 0.2m\\), and \\(\\sigma_{\\mathbf{R}} = 3^{\\circ}\\) and \\(\\sigma_t = 0.3m\\). Fig. 4 demonstrates the point clouds of dataset C after the poses are perturbed by the four noise levels. To evaluate the performance of different algorithms suffering from large measurement noises, we also test the case that additional Gaussian noises with the std \\(\\sigma_{pt} = 0.05m\\) are added to the LiDAR point cloud, and the poses are perturbed by Gaussian noises with \\(\\sigma_{\\mathbf{R}} = 3^{\\circ}\\) and \\(\\sigma_t = 0.3m\\)." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.696, + 0.593, + 0.71 + ], + "angle": 0, + "content": "5.3. Results" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Fig. 5 and Fig. 6 illustrates the results. It is clear that our algorithm converges faster than other algorithms. LM+PF works well at small noises (such as \\(\\sigma_{\\mathbf{R}} = 0.1^{\\circ}\\) and \\(\\sigma_t = 0.01m\\)). As the noise level increases, LM+PF tends to converge slower. Constructing H and g using BALM [16] is computationally demanding. For efficiency, BALM only keeps the centroid of each plane observation (i.e., only 1 point is kept), which results in bad performance. In Fig. 5 and Fig. 6, all points are used to compute the cost in (11) after an iteration of BALM. BALM generally converges slow, as it minimizes a reduced PA problem. EF [10] adopts the first-order optimization method as it only provides a method" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "13119" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.11, + 0.089, + 0.862, + 0.536 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.548, + 0.895, + 0.577 + ], + "angle": 0, + "content": "Figure 5. The results of different algorithms using different initial noise levels. It is clear that our algorithm converges significantly faster than other algorithms. The \\(y\\)-axis represents the logarithmic scale of the cost in (11)." + }, + { + "type": "image", + "bbox": [ + 0.113, + 0.594, + 0.861, + 0.706 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.716, + 0.895, + 0.746 + ], + "angle": 0, + "content": "Figure 6. The results of different algorithms for point clouds perturbed by Gaussian noise with std \\(\\sigma_{pt} = 0.05m\\). The rotations and translations of the poses are perturbed by Gaussian noise with std \\(\\sigma_{\\mathbf{R}} = 3^{\\circ}\\) and \\(\\sigma_t = 0.3m\\), respectively." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.772, + 0.471, + 0.788 + ], + "angle": 0, + "content": "to compute the gradient, which results in slow convergence." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.801, + 0.197, + 0.815 + ], + "angle": 0, + "content": "6. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.826, + 0.471, + 0.903 + ], + "angle": 0, + "content": "In the computer vision community, Newton's method is generally considered too expensive for a large-scale least-squares problem. This paper adopts the Newton's method to efficiently solve the PA problem. Our algorithm takes advantage of the fact that the optimal planes are determined" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.772, + 0.892, + 0.893 + ], + "angle": 0, + "content": "by the poses, so that the number of unknowns can be significantly reduced. Furthermore, this property can ensure to obtain the optimal planes when we update the poses. The difficulty lies in how to efficiently compute the Hessian matrix and the gradient vector. The key contribution of this paper is to provide a closed-form solution for them. The experimental results show that our algorithm outperforms the state-of-the-art algorithms." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "13120" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.115, + 0.47, + 0.17 + ], + "angle": 0, + "content": "[1] Sameer Agarwal, Yasutaka Furukawa, Noah Snavely, Ian Simon, Brian Curless, Steven M Seitz, and Richard Szeliski. Building rome in a day. Communications of the ACM, 54(10):105-112, 2011. 1" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.171, + 0.468, + 0.198 + ], + "angle": 0, + "content": "[2] Sameer Agarwal, Keir Mierle, and The Ceres Solver Team. 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IEEE, 2021. 1" + }, + { + "type": "list", + "bbox": [ + 0.503, + 0.093, + 0.892, + 0.73 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "13121" + } + ] +] \ No newline at end of file diff --git a/2023/Efficient Second-Order Plane Adjustment/0ca972fe-43f5-4fa8-bf07-17ebcd5d268a_origin.pdf b/2023/Efficient Second-Order Plane Adjustment/0ca972fe-43f5-4fa8-bf07-17ebcd5d268a_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..9f23081a5bf6071965366bf22b2f0e32f92cd6ae --- /dev/null +++ b/2023/Efficient Second-Order Plane Adjustment/0ca972fe-43f5-4fa8-bf07-17ebcd5d268a_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:df1197673e7ce1a2347ac492665a599659e7736a5ebc04ed80702058f33b3557 +size 5627281 diff --git a/2023/Efficient Second-Order Plane Adjustment/full.md b/2023/Efficient Second-Order Plane Adjustment/full.md new file mode 100644 index 0000000000000000000000000000000000000000..b8219f5f1fc4b4ce565ce60b64e3e65a465a68b4 --- /dev/null +++ b/2023/Efficient Second-Order Plane Adjustment/full.md @@ -0,0 +1,455 @@ +# Efficient Second-Order Plane Adjustment + +Lipu Zhou Meituan, Beijing, China zhoulipu@meituan.com + +# Abstract + +Planes are generally used in 3D reconstruction for depth sensors, such as RGB-D cameras and LiDARs. This paper focuses on the problem of estimating the optimal planes and sensor poses to minimize the point-to-plane distance. The resulting least-squares problem is referred to as plane adjustment (PA) in the literature, which is the counterpart of bundle adjustment (BA) in visual reconstruction. Iterative methods are adopted to solve these least-squares problems. Typically, Newton's method is rarely used for a large-scale least-squares problem, due to the high computational complexity of the Hessian matrix. Instead, methods using an approximation of the Hessian matrix, such as the Levenberg-Marquardt (LM) method, are generally adopted. This paper adopts the Newton's method to efficiently solve the PA problem. Specifically, given poses, the optimal plane have a close-form solution. Thus we can eliminate planes from the cost function, which significantly reduces the number of variables. Furthermore, as the optimal planes are functions of poses, this method actually ensures that the optimal planes for the current estimated poses can be obtained at each iteration, which benefits the convergence. The difficulty lies in how to efficiently compute the Hessian matrix and the gradient of the resulting cost. This paper provides an efficient solution. Empirical evaluation shows that our algorithm outperforms the state-of-the-art algorithms. + +# 1. Introduction + +Planes ubiquitously exist in man-made environments, as demonstrated in Fig. 1. Thus they are generally used in simultaneous localization and mapping (SLAM) systems for depth sensors, such as RGB-D cameras [6, 9, 12-14] and LiDARs [16, 21, 22, 24, 26]. Just as bundle adjustment (BA) [3, 8, 20, 25] is important for visual reconstruction [1, 5, 18, 19], jointly optimizing planes and depth sensor poses, which is called plane adjustment (PA) [24,26], is critical for 3D reconstruction using depth sensors. This paper focuses on efficiently solving the large-scale PA problem. + +The BA and PA problems both involve jointly optimiz + +![](images/9deb1687d382e0c43556b98b8b209c0391c0a1814a79c39e867c17c2fa22c858.jpg) +(a) Point cloud from perturbed poses + +![](images/37f2ef9a59f7a31f5dc58f03e53fd417b300370e284a02b070c728a8c916ab5b.jpg) +(b) Point cloud from our algorithm +Figure 1. We use Gaussian noises to perturb the poses of dataset D in Fig. 3. The standard deviations for rotation and translation are $3^{\circ}$ and $0.3m$ , respectively. The resulting point cloud (a) is in a mess. Fig. (b) shows the result from our algorithm. Our algorithm can quickly align the planes, as shown in Fig. 5. + +ing 3D structures and sensor poses. As the two problems are similar, it is straightforward to apply the well-studied solutions for BA to PA, as done in [23, 26]. However, planes in PA can be eliminated, so that the cost function of the PA problem only depends on sensor poses, which significantly reduces the number of variables. This property provides a promising direction to efficiently solve the PA problem. However, it is difficult to compute the Hessian matrix and the gradient vector of the resulting cost. Although this problem was studied in several previous works [10, 16], no efficient solution has been proposed. This paper seeks to solve this problem. + +The main contribution of this paper is an efficient PA solution using Newton's method. We derive a closed-form solution for the Hessian matrix and the gradient vector for the PA problem whose computational complexity is inde + +pendent of the number of points on the planes. Our experimental results show that the proposed algorithm converges faster than the state-of-the-art algorithms. + +# 2. Related Work + +The PA problem is closely related to the BA problem. In BA, points and camera poses are jointly optimized to minimize the reprojection error. Schur complement [3, 20, 25] or the square root method [7, 8] is generally used to solve the linear system of the iterative methods. The keypoint is to generate a reduced camera system (RCS) which only relates to camera poses. + +In PA, planes and poses are jointly optimized. Planes are the counterparts of points in BA. Thus, the well-known solutions for the BA problem can be applied to the PA problem [23, 24]. In the literature, two cost functions are used to formulate the PA problem. The first one is the plane-to-plane distance which measures the difference between two plane parameters [12, 13]. The value of the plane-to-plane distance is related to the choice of the global coordinate system, which means the selection of the global coordinate system will affect the accuracy of the results. The second one is the point-to-plane distance, whose value is invariant to the choice of the global coordinate system. The solutions of different choices of the global coordinate system are equivalent up to a rigid transformation. Zhou et al. [23] show that the point-to-plane distance can converge faster and lead to a more accurate result. But unlike BA where each 3D point has only one 2D observation at a pose, a plane can generate many points at a pose as demonstrated in Fig. 2. This means the point-to-plane distance probably leads to a very large-scale least-squares problem. Directly adopting the BA solutions is computationally infeasible for a large-scale PA problem. Zhou et al. [23] propose to use the QR decomposition to accelerate the computation. + +For a general least-squares problem with $M$ variables, the computational complexity of the Hessian matrix is $O(M^2)$ . Thus, in the computer vision community, it is ingrained that Newton's method is infeasible for a large-scale optimization problem, as calculating the Hessian matrix is computationally demanding. Instead, Gauss-Newton-based iterative methods are generally adopted. Suppose that $\mathbf{J}$ is the Jacobian matrix of the residuals. The Gauss-Newton method actually approximates the Hessian matrix by $\mathbf{H} \approx \mathbf{J}^T\mathbf{J}$ . In theory, Newton's method can lead to a better quadratic approximation to the original cost function, which means the Newton's step probably yields a better result. This in turn may reduce the number of iterations. + +The PA problem has a special property that the optimal plane parameters are determined by the poses. That is to say the point-to-plane cost actually only depends on the poses. This property is attractive, as it significantly reduces the number of variables, which makes using the Newton's + +![](images/2f6f9651529f33fdb7c651bb24179fca86e7565952419654e9fb8aa6534f7412.jpg) +(a) A PA problem with 3 poses and 4 planes + +![](images/9612a03506748a6aff89238dcf9ffb91e1fb6cd2f27eeadee99092a8811371ea.jpg) +(b) Plane Observation +Figure 2. A schematic of the PA problem and the planes detected in a LiDAR scan. Unlike BA where each 3D point only has one observation, many points can be captured from a plane in PA. Assume that $N$ points are captured from a plane. The computational complexity of the Hessian matrix related to these points using BALM [16] is $O(N^2)$ . Thus, this method is infeasible for a large-scale problem. In contrast, the computational complexity of our algorithm is independent of $N$ . + +method possible. In traditional iterative methods, the correlation between the plane parameters and the poses are ignored. Thus, after one iteration, there is no guarantee that the new plane parameters are optimal for the new poses. Using the property of the PA, it is possible to overcome this drawback, which may lead to faster convergence. Several previous works seek to exploit this property of PA. Ferrer [10] explored an algebraic point-to-plane distance and provided a closed-form gradient for the resulting cost. The algebraic cost may result in a suboptimal solution [4], and the first-order optimization generally leads to slow convergence [20]. Liu et al. [16] provided analytic forms of the Hessian matrix and the gradient of the genuine point-to-plane cost. Assume that $N$ points are captured from a plane. The computational complexity of the Hessian matrix related to these points is $O(N^2)$ . Since $N$ can be large as shown in Fig. 2, this algorithm is computationally demanding and infeasible for a large-scale problem. + +In summary, the potential benefits of the special property of the PA problem have not been manifested in previous works. The bottleneck is how to efficiently compute the Hessian matrix and the gradient vector. This paper focuses on solving this problem. + +# 3. Problem Formulation + +In this paper we use italic, boldfaced lowercase and bold-faced uppercase letters to represent scalars, vectors and matrices, respectively. + +# 3.1. Notations + +Planes and Poses A plane can be represented by a four-dimensional vector $\pmb{\pi} = [n;d]$ . We denote the rotational and translational components from a depth sensor coordinate system to the global coordinate system as $\mathbf{R}\in SO(3)$ + +and $t \in \mathbb{R}^3$ , respectively. To simplify the notation in the following description, we also use the following two matrices to represent a pose: + +$$ +\mathbf {X} = \left[ \begin{array}{l l} \mathbf {R}, & t \\ \mathbf {0}, & 1 \end{array} \right] \in S E (3) \text {a n d} \mathbf {T} = \left[ \begin{array}{l l} \mathbf {R}, & t \end{array} \right]. \tag {1} +$$ + +As $\mathbf{R} \in SO(3)$ , a certain parameterization is usually adopted in the optimization [20]. In this paper, we use the Cayley-Gibbs-Rodriguez (CGR) parameterization [11] to represent $\mathbf{R}$ + +$$ +\mathbf {R} = \frac {\bar {\mathbf {R}}}{1 + \boldsymbol {s} ^ {T} \boldsymbol {s}}, \bar {\mathbf {R}} = \left(1 - \boldsymbol {s} ^ {T} \boldsymbol {s}\right) \mathbf {I} _ {3} + 2 [ \boldsymbol {s} ] _ {\times} + 2 \boldsymbol {s} \boldsymbol {s} ^ {T}, \tag {2} +$$ + +where $s = [s_1; s_2; s_3]$ is a three-dimensional vector. We adopt the CGR parameterization as it is a minimal representation for $\mathbf{R}$ . Furthermore, unlike the angle-axis parameterization that is singular at $\mathbf{I}_3$ , the CGR parameterization is well-defined at $\mathbf{I}_3$ , and equals to $[0; 0; 0]$ which can accelerate the computation, as described in Section 4.3. We parameterize $\mathbf{X}$ as a six-dimensional vector $x = [s; t]$ . + +Newton's method This paper adopts the damped Newton's method in the optimization. For a cost function $f(z)$ , the damped Newton's method seeks to find its minimizer from an initial point. Assume that $z_{n}$ is the solution at the $n$ th iteration. Given the Hessian matrix $\mathbf{H}_f(z_n)$ and the gradient $g_{f}(z_{n})$ at $z_{n},z_{n}$ is updated by $z_{n + 1} = z_{n} + \varDelta z$ . Here $\varDelta z$ is from + +$$ +\left(\mathbf {H} _ {f} \left(\boldsymbol {z} _ {n}\right) + \mu \mathbf {I})\right) \Delta z = - \boldsymbol {g} _ {f} \left(\boldsymbol {z} _ {n}\right), \tag {3} +$$ + +where $\mu$ is adjusted at each iteration to make the value of $f(z)$ reduce, as done in the Levenberg-Marquardt (LM) algorithm [17]. + +Matrix Calculus In the following derivation, we will use vector-by-vector, vector-by-scalar, scalar-by-vector derivatives. Here we provide their definitions. + +Assume $\mathbf{a} = [a_1;\dots ;a_N]\in \mathbb{R}^N$ is a vector function of $\pmb {b} = [b_{1},\dots ,b_{M}]\in \mathbb{R}^{M}$ . The first-order partial derivatives of vector-by-vector $\frac{\partial\pmb{a}}{\partial\pmb{b}}$ , vector-by-scalar $\frac{\partial\pmb{a}}{\partial b_j}$ , and scalar-byvector $\frac{\partial a_i}{\partial b}$ are defined as + +$$ +\frac {\partial \boldsymbol {a}}{\partial \boldsymbol {b}} = \left[ \begin{array}{c c c} \frac {\partial a _ {1}}{\partial b _ {1}} & \dots & \frac {\partial a _ {N}}{\partial b _ {1}} \\ \vdots & \ddots & \vdots \\ \frac {\partial a _ {1}}{\partial b _ {M}} & \dots & \frac {\partial a _ {N}}{\partial b _ {M}} \end{array} \right], \frac {\partial \boldsymbol {a}}{\partial b _ {j}} = \left[ \begin{array}{c} \frac {\partial a _ {1}}{\partial b _ {j}} \\ \vdots \\ \frac {\partial a _ {N}}{\partial b _ {j}} \end{array} \right], \frac {\partial a _ {i}}{\partial \boldsymbol {b}} = \left[ \begin{array}{c} \frac {\partial a _ {i}}{\partial b _ {1}} \\ \vdots \\ \frac {\partial a _ {i}}{\partial b _ {M}} \end{array} \right] \tag {4} +$$ + +where $\frac{\partial\pmb{a}}{\partial\pmb{b}}$ is an $M\times N$ matrix with $\frac{\partial a_j}{\partial b_i}$ as the ith row jth column element, $\frac{\partial\pmb{a}}{\partial b_j}$ is an $N$ -dimensional vector whose ith term is $\frac{\partial a_i}{\partial b_j}$ , and $\frac{\partial a_i}{\partial\pmb{b}}$ is an $M$ -dimensional vector whose ith term is $\frac{\partial a_i}{\partial b_i}$ . + +# 3.2. Optimal Plane Estimation + +Given a set of $K$ points $\{\pmb{p}_i\}$ , the optimal plane $\hat{\pi}$ can be estimated by minimizing the sum of squared point-to-plane distances + +$$ +\hat {\boldsymbol {\pi}} = \arg \min _ {\boldsymbol {\pi}} \sum_ {i} ^ {K} \left(\boldsymbol {n} ^ {T} \boldsymbol {p} _ {i} + d\right) ^ {2}, s. t. \| \boldsymbol {n} \| _ {2} ^ {2} = 1. \tag {5} +$$ + +There is a closed-form solution for $\hat{\pi}$ . Let us define + +$$ +\mathbf {M} = \sum_ {i = 1} ^ {K} \left(\boldsymbol {p} _ {i} - \bar {\boldsymbol {p}}\right) \left(\boldsymbol {p} _ {i} - \bar {\boldsymbol {p}}\right) ^ {T} = \mathbf {S} - K \bar {\boldsymbol {p}} \bar {\boldsymbol {p}} ^ {T}, \tag {6} +$$ + +where $\mathbf{S} = \sum_{i=1}^{K} \pmb{p}_i \pmb{p}_i^T$ and $\bar{\pmb{p}} = \frac{1}{K} \sum_{i}^{K} \pmb{p}_i$ . Assume that $\lambda_3(\mathbf{M})$ and $\xi_3(\mathbf{M})$ are the smallest eigenvalue of $\mathbf{M}$ and the corresponding eigenvector, respectively. Using these notations, we can write the optimal plane $\hat{\pmb{\pi}} = [\hat{\pmb{n}}; \hat{d}]$ as + +$$ +\hat {\boldsymbol {n}} = \boldsymbol {\xi} _ {3} (\mathbf {M}), \hat {d} = - \hat {\boldsymbol {n}} ^ {T} \bar {\boldsymbol {p}}. \tag {7} +$$ + +Furthermore, the cost of (5) at $\hat{\pi}$ equals to $\lambda_3(\mathbf{M})$ , i.e., + +$$ +\lambda_ {3} (\mathbf {M}) = \sum_ {i = 1} ^ {K} \left(\hat {\boldsymbol {n}} \boldsymbol {p} _ {i} + \hat {d}\right) ^ {2} = \min _ {\pi} \sum_ {i = 1} ^ {K} \left(\boldsymbol {n} \boldsymbol {p} _ {i} + d\right) ^ {2}. \tag {8} +$$ + +The above property will be used to eliminate planes in PA. + +# 3.3. Plane Adjustment + +Assume that there are $M$ planes and $N$ poses. According to section 3.1, the $i$ th plane can be represented by a four-dimensional vector $\pmb{\pi}_i = [n_i;d_i]$ . The $j$ th pose is denoted as $\pmb{x}_j$ . The observation of $\pmb{\pi}_i$ at $\pmb{x}_j$ is a set of $N_{ij}$ points $\mathbb{Q}_{ij} = \{\pmb{p}_{ijk} \in \mathbb{R}^3\}_{k=1}^{N_{ij}}$ . For a 3D point $\pmb{p}_{ijk}$ , we use $\tilde{\pmb{p}}_{ijk} = [\pmb{p}_{ijk};1]$ to represent the homogeneous coordinates of $\pmb{p}_{ijk}$ . Then, the transformation from the local coordinate system at $\pmb{x}_j$ to the global coordinate system can be represented as + +$$ +\boldsymbol {p} _ {i j k} ^ {g} = \mathbf {R} _ {j} \boldsymbol {p} _ {i j k} + \boldsymbol {t} _ {j} = \mathbf {T} _ {j} \tilde {\boldsymbol {p}} _ {i j k}, \tag {9} +$$ + +where $\mathbf{T}_j$ is defined in (1). Then the distance $d_{ijk}$ from $\pmb{p}_{ijk}$ to $\pi_i$ has the form + +$$ +\begin{array}{l} d _ {i j k} \left(\boldsymbol {\pi} _ {i}, \mathbf {x} _ {j}\right) = \boldsymbol {n} _ {i} ^ {T} \left(\mathbf {R} _ {j} \boldsymbol {p} _ {i j k} + \boldsymbol {t} _ {j}\right) + d _ {i} \tag {10} \\ = \boldsymbol {n} _ {i} ^ {T} \mathbf {T} _ {j} \tilde {\boldsymbol {p}} _ {i j k} + d _ {j} = \boldsymbol {\pi} _ {i} ^ {T} \tilde {\boldsymbol {p}} _ {i j k} ^ {g}. \\ \end{array} +$$ + +The PA problem is to jointly adjust the $M$ planes $\{\pi_i\}$ and the $N$ sensor poses $\{\pmb{x}_j\}$ to minimize the sum of squared point-to-plane distances. Specifically, using (10), we can formulate the cost function of the PA problem as + +$$ +\min _ {\left\{\boldsymbol {\pi} _ {i} \right\}, \left\{\mathbf {x} _ {j} \right\}} \sum_ {i = 1} ^ {M} \underbrace {\sum_ {j \in o b s \left(\boldsymbol {\pi} _ {i}\right)} \sum_ {k = 1} ^ {N _ {i j}} d _ {i j k} ^ {2} \left(\boldsymbol {\pi} _ {i} , \mathbf {x} _ {j}\right)} _ {C _ {i} \left(\boldsymbol {\pi} _ {i}, \mathbb {X} _ {i}\right), \mathbb {X} _ {i} = \left\{\boldsymbol {x} _ {j} \mid j \in o b s \left(\boldsymbol {\pi} _ {i}\right) \right\}} = \min _ {\left\{\boldsymbol {\pi} _ {i} \right\}, \left\{\boldsymbol {x} _ {j} \right\}} \sum_ {i = 1} ^ {M} C _ {i} \left(\boldsymbol {\pi} _ {i}, \mathbb {X} _ {i}\right). \tag {11} +$$ + +where $obs(\pi_i)$ represents the indexes of poses where $\pi_i$ can be observed, and $C_i(\pi_i, \mathbb{X}_i)$ accumulates the errors from $N_i = \sum_{j \in obs(\pi_i)} N_{ij}$ points captured at the poses in $\mathbb{X}_i$ . According to (6) and (9), we get + +$$ +\mathbf {M} _ {i} \left(\mathbb {X} _ {i}\right) = \sum_ {j \in o b s \left(\boldsymbol {\pi} _ {i}\right)} \mathbf {S} _ {i j} - N _ {i} \bar {\boldsymbol {p}} _ {i} \bar {\boldsymbol {p}} _ {i} ^ {T}, \tag {12} +$$ + +where $\bar{\pmb{p}}_i = \frac{1}{N_i}\sum_{j\in obs(\pmb{\pi}_i)}\sum_{k = 1}^{N_{ij}}\pmb{p}_{ijk}^g$ and $\mathbf{S}_{ij} = \sum_{k = 1}^{N_{ij}}\pmb{p}_{ijk}^g\left(\pmb{p}_{ijk}^g\right)^T$ . Here the elements in $\mathbf{M}_i$ , $\mathbf{S}_{ij}$ and $\bar{\pmb{p}}_i$ in (12) are all functions of the poses in $\mathbb{X}_i$ . Substituting $\pmb{p}_{ijk}^g$ in (9) into $\mathbf{S}_{ij}$ and $\bar{\pmb{p}}_i$ in (12), we have + +$$ +\begin{array}{l} \mathbf {S} _ {i j} = \mathbf {T} _ {j} \underbrace {\sum_ {k = 1} ^ {N _ {i j}} \tilde {\boldsymbol {p}} _ {i j k} \tilde {\boldsymbol {p}} _ {i j k} ^ {T}} _ {\mathbf {U} _ {i j}} \mathbf {T} _ {j} ^ {T} = \mathbf {T} _ {j} \mathbf {U} _ {i j} \mathbf {T} _ {j} ^ {T}, \\ \bar {\boldsymbol {p}} _ {i} = \frac {1}{N _ {i}} \sum_ {j \in o b s (\boldsymbol {\pi} _ {i})} \mathbf {T} _ {j} \underbrace {\sum_ {k = 1} ^ {N _ {i j}} \tilde {\boldsymbol {p}} _ {i j k}} _ {\tilde {\boldsymbol {p}} _ {i j}} = \frac {1}{N _ {i}} \sum_ {j \in o b s (\boldsymbol {\pi} _ {i})} \mathbf {T} _ {j} \tilde {\boldsymbol {p}} _ {i j}. \\ \end{array} +$$ + +Here $\mathbf{U}_{ij}$ and $\tilde{\boldsymbol{p}}_{ij}$ in (13) are constants. We only need to compute them once, and reuse them in the iteration. + +According to (7), given poses in $\mathbb{X}_i$ , the optimal solution for $\pi_i$ has a closed-form expression $\hat{\pi}_i = [\hat{n}_i; \hat{d}_i]$ , where $\hat{n}_i = \xi_3(\mathbf{M}_i(\mathbb{X}_i))$ and $\hat{d}_i = -\hat{n}\bar{p}_i$ . As $\mathbf{M}_i$ and $\bar{p}_i$ are functions of the poses in $\mathbb{X}_i$ , $\hat{\pi}_i$ is also a function of the poses in $\mathbb{X}_i$ . That is to say $\hat{\pi}_i$ is completely determined by the poses in $\mathbb{X}_i$ . To simplify the notation, let us define + +$$ +\lambda_ {i, 3} (\mathbb {X} _ {i}) = \lambda_ {3} \left(\mathbf {M} _ {i} (\mathbb {X} _ {i})\right), \tag {14} +$$ + +which represents the smallest eigenvalue of $\mathbf{M}_i(\mathbb{X}_i)$ . + +Substituting the optimal plane estimation $\hat{\pi}_i$ into $C_i(\pi_i, \mathbb{X}_i)$ in (11) and using (8), we have + +$$ +\lambda_ {i, 3} (\mathbb {X} _ {i}) = C _ {i} \left(\hat {\pi} _ {i}, \mathbb {X} _ {i}\right). \tag {15} +$$ + +Using (15), we can formulate the PA problem in (11) as + +$$ +\left\{\hat {\mathbf {x}} _ {j} \right\} = \arg \min _ {\left\{\mathbf {X} _ {j} \right\}} \boldsymbol {\tau}, \boldsymbol {\tau} = \sum_ {i = 1} ^ {M} \lambda_ {i, 3} (\mathbb {X} _ {i}). \tag {16} +$$ + +Table 1 summarizes the notations for PA. + +The cost function (16) only depends on poses, which significantly reduces the number of variables. However, as it is the sum of squared point-to-plane distances, we cannot apply the Gauss-Newton-based methods to minimize it, where the Jacobian matrix of residuals are required. Here we adopt the Newton's method to solve it. The crux for applying the Newton's method to minimize (16) is how to compute the gradient and the Hessian matrix of (16) efficiently. In the following sections, we provide a closed-form solution for them. Note that we can assign a weight to each point to + +
NotationDescription
πiTheith plane.
obs(πi)The set of indexes of poses which can see πi.
XiThe set of poses which can see πi.
MiThe scatter matrix for πi.
λ3,iThe smallest eigenvalue ofMi.
xj, xkThe jth and kth poses.
xjm, xknThe mth and nth elements of xj and xk.
PjThe set of planes that are visible to xj.
PjkThe set of planes that are visible to xj and xk.
+ +Table 1. Table of notations. + +punish outliers, which also has a close-form solution for planes using the weighted PCA. Our algorithm can be extended to this situation. To simplify the notation, we omit the variables of functions in the following description (e.g., $\lambda_{i,3}(\mathbb{X}_i)\to \lambda_{i,3})$ . + +# 4. Newton's Iteration for Plane Adjustment + +Let us denote the gradient and the Hessian matrix of $\tau$ in (16) as $\pmb{g}$ and $\mathbf{H}$ , and denote the 6-dimensional gradient vector for $\pmb{x}_j$ as $\pmb{g}_j$ and the $6\times 6$ Hessian matrix block for $\pmb{x}_j$ and $\pmb{x}_k$ as $\mathbf{H}_{jk}$ (note that here $j$ can equal to $k$ ). Then $\pmb{g}$ and $\mathbf{H}$ can be written in the block form as $\pmb{g} = (\pmb{g}_j)\in \mathbb{R}^{6N}$ and $\mathbf{H} = (\mathbf{H}_{jk})\in \mathbb{R}^{6N\times 6N}$ . + +The $i$ th plane $\pi_i$ is observed by the poses in $\mathbb{X}_i$ . Assume $\boldsymbol{x}_j \in \mathbb{X}_i$ and $\boldsymbol{x}_k \in \mathbb{X}_i$ . Let us define + +$$ +\boldsymbol {g} _ {j} ^ {i} = \frac {\partial \lambda_ {i , 3}}{\partial \boldsymbol {x} _ {j}}, \mathbf {H} _ {j k} ^ {i} = \frac {\partial^ {2} \lambda_ {i , 3}}{\partial \boldsymbol {x} _ {j} \partial \boldsymbol {x} _ {k}}. \tag {17} +$$ + +According to (16), we have + +$$ +\boldsymbol {g} _ {j} = \sum_ {i \in \mathbb {P} _ {j}} \boldsymbol {g} _ {j} ^ {i}, \quad \mathrm {H} _ {j k} = \sum_ {i \in \mathbb {P} _ {j k}} \mathrm {H} _ {j k} ^ {i}, \tag {18} +$$ + +where $\mathbb{P}_j$ is the set of planes observed by $\pmb{x}_j$ , and $\mathbb{P}_{jk}$ is the set of planes observed by $\pmb{x}_j$ and $\pmb{x}_k$ simultaneously. If $j = k$ , here $\mathbb{P}_{jk}$ equals to $\mathbb{P}_j$ . From (18), we know that the key point to get $\pmb{g}$ and $\mathbf{H}$ is to compute $\pmb{g}_j^i$ and $\mathbf{H}_{jk}^i$ in (17). + +# 4.1. Partial Derivatives of Eigenvalue + +According to (15), $\lambda_{i,3}$ is a function of poses in $\mathbb{X}_i$ . Assume that $x_{jm}$ and $x_{kn}$ are the $m$ th and $n$ th elements of $\pmb{x}_j$ and $\pmb{x}_k$ , respectively. We consider the first- and second-order partial derivation $\frac{\partial\lambda_{i,3}}{\partial x_{jm}}$ and $\frac{\partial^2\lambda_{i,3}}{\partial x_{jm}\partial x_{kn}}$ , respectively. + +$\lambda_{i,3}$ is a root of the equation $|\mathbf{M}_i(\mathbb{X}_i) - \lambda_i\mathbf{I}_3| = 0$ where $|\cdot |$ denotes the determinant of a matrix. Assume $m_{ef}$ is the $e$ th row $f$ th column term of $\mathbf{M}_i(\mathbb{X}_i)$ . $|\mathbf{M}_i(\mathbb{X}_i) - \lambda_i\mathbf{I}_3| = 0$ is a cubic equation with the following form + +$$ +- \lambda_ {i, 3} ^ {3} + a _ {i} \lambda_ {i, 3} ^ {2} + b _ {i} \lambda_ {i, 3} + c _ {i} = 0, \tag {19} +$$ + +where $a_{i} = m_{11} + m_{22} + m_{33}, b_{i} = m_{12}^{2} + m_{13}^{2} + m_{23}^{2} - m_{11}m_{22} - m_{11}m_{33} - m_{22}m_{33}$ , and $c_{i} = -m_{33}m_{12}^{2} + 2m_{12}m_{13}m_{23} - m_{22}m_{13}^{2} - m_{11}m_{23}^{2} + m_{11}m_{22}m_{33}$ . Here $a_{i}, b_{i}$ and $c_{i}$ are all functions of the poses in $\mathbb{X}_i$ . It is known that the root of a cubic equation has a closed form. One solution to compute $\frac{\partial\lambda_{i,3}}{\partial x_{jm}}$ and $\frac{\partial^2\lambda_{i,3}}{\partial x_{jm}\partial x_{kn}}$ is to directly differentiate the root. However, the formula of the root is too complicated. Here we introduce a simple way to compute them. Briefly, we employ the implicit function theorem [15] to compute them. Let us define + +$$ +\chi_ {i} = \left[ \begin{array}{l} \lambda_ {i, 3} ^ {2} \\ \lambda_ {i, 3} \\ 1 \end{array} \right], \eta_ {i} = \left[ \begin{array}{l} a _ {i} \\ b _ {i} \\ c _ {i} \end{array} \right] \kappa_ {i} = \left[ \begin{array}{l} - 3 \\ 2 a _ {i} \\ b _ {i} \end{array} \right], \delta_ {j m} ^ {i} = \frac {\partial \eta_ {i}}{\partial x _ {j m}}. \tag {20} +$$ + +Using the above notations, we present $\frac{\partial\lambda_{i,3}}{\partial x_{jm}}$ and $\frac{\partial^2\lambda_{i,3}}{\partial x_{jm}\partial x_{kn}}$ in Lemma 1 and 2. The proofs of the following lemmas and theorems are in the supplementary material. + +Lemma 1 Using the notations in (20), we have + +$$ +\frac {\partial \lambda_ {i , 3}}{\partial x _ {j m}} = - \varphi_ {i} \boldsymbol {\delta} _ {j m} ^ {i} \cdot \boldsymbol {\chi} _ {i}, \tag {21} +$$ + +where $\cdot$ represents the dot product and $\varphi_{i} = (\pmb{\kappa}_{i}\cdot \pmb{\chi}_{i})^{-1}$ + +Lemma 2 Using the notations in (20) and (21), we have + +$$ +\frac {\partial^ {2} \lambda_ {i , 3}}{\partial x _ {j m} \partial x _ {k n}} = - \varphi_ {i} \left(\boldsymbol {\delta} _ {j m} ^ {i} \cdot \frac {\partial \boldsymbol {\chi} _ {i}}{\partial x _ {k n}} + \boldsymbol {\chi} _ {i} \cdot \frac {\partial \boldsymbol {\delta} _ {j m} ^ {i}}{\partial x _ {k n}} - \frac {\partial \lambda_ {i , 3}}{\partial x _ {j m}} \frac {\partial \varphi_ {i} ^ {- 1}}{\partial x _ {k n}}\right). \tag {22} +$$ + +Let us define + +$$ +\boldsymbol {\alpha} _ {j} ^ {i} = \frac {\partial a _ {i}}{\partial \boldsymbol {x} _ {j}}, \beta_ {j} ^ {i} = \frac {\partial b _ {i}}{\partial \boldsymbol {x} _ {j}}, \gamma_ {j} ^ {i} = \frac {\partial c _ {i}}{\partial \boldsymbol {x} _ {j}}, \boldsymbol {\Delta} _ {j} ^ {i} = [ \boldsymbol {\alpha} _ {j} ^ {i}, \beta_ {j} ^ {i}, \gamma_ {j} ^ {i} ], +$$ + +$$ +\boldsymbol {\alpha} _ {k} ^ {i} = \frac {\partial a _ {i}}{\partial \boldsymbol {x} _ {k}}, \beta_ {k} ^ {i} = \frac {\partial b _ {i}}{\partial \boldsymbol {x} _ {k}}, \gamma_ {k} ^ {i} = \frac {\partial c _ {i}}{\partial \boldsymbol {x} _ {k}}, \boldsymbol {\Delta} _ {k} ^ {i} = [ \boldsymbol {\alpha} _ {k} ^ {i}, \boldsymbol {\beta} _ {k} ^ {i}, \boldsymbol {\gamma} _ {k} ^ {i} ], \tag {23} +$$ + +$$ +\mathbf {H} _ {j k} ^ {a _ {i}} = \frac {\partial^ {2} a _ {i}}{\partial \boldsymbol {x} _ {j} \partial \boldsymbol {x} _ {k}}, \mathbf {H} _ {j k} ^ {b _ {i}} = \frac {\partial^ {2} b _ {i}}{\partial \boldsymbol {x} _ {j} \partial \boldsymbol {x} _ {k}}, \mathbf {H} _ {j k} ^ {c _ {i}} = \frac {\partial^ {2} c _ {i}}{\partial \boldsymbol {x} _ {j} \partial \boldsymbol {x} _ {k}}. +$$ + +Using the above lemmas and notations, we can derive $\pmb{g}_j^i$ and $\mathbf{H}_{jk}^i$ . + +Theorem 1 Using the notations in (20), (21) and (23), $\pmb{g}_j^i$ and $\mathbf{H}_{jk}^{i}$ have the forms + +$$ +\boldsymbol {g} _ {j} ^ {i} = - \varphi_ {i} \boldsymbol {\Delta} _ {j} ^ {i} \chi_ {i}, +$$ + +$$ +\mathbf {H} _ {j k} ^ {i} = \varphi_ {i} \left(\mathbf {K} _ {j k} ^ {i} - \lambda_ {3, i} ^ {2} \mathbf {H} _ {j k} ^ {a _ {i}} - \lambda_ {3, i} \mathbf {H} _ {j k} ^ {b _ {i}} - \mathbf {H} _ {j k} ^ {c _ {i}}\right), \tag {24} +$$ + +where $\mathbf{K}_{jk}^{i} = \pmb{g}_{j}^{i}\pmb{u}^{T} - \pmb{v}(\pmb{g}_{k}^{i})^{T},\pmb{u} = 2\lambda_{i,3}\pmb{\alpha}_{k}^{i} + \pmb{\beta}_{k}^{i} + (2a - 6\lambda_{i,3})\pmb{g}_{k}^{i},$ and $\pmb {v} = 2\lambda_{i,3}\pmb{\alpha}_{j}^{i} + \pmb{\beta}_{j}^{i}$ , and similar to $\pmb{g}_j^i,\pmb{g}_k^i =$ $-\varphi_i\Delta_k^i\chi_i$ is the gradient block for $\pmb{x}_k$ + +The formula of $\mathbf{H}_{jk}^{i}$ in (24) is applicable to the case that $j = k$ . From Theorem 1, we know that the key point to get $\pmb{g}_j^i$ and $\mathbf{H}_{jk}^{i}$ is to get the derivatives of $a_{i}, b_{i}$ and $c_{i}$ in (23). + +# 4.2. Partial Derivatives of $a_i$ , $b_i$ and $c_i$ + +According to (19), $a_{i}, b_{i}$ and $c_{i}$ are functions of the elements in $\mathbf{M}_i$ . Using this relationship, we can easily derive the partial derivatives in (23). For instance, as $a_{i} = m_{11} + m_{22} + m_{33}$ , we have + +$$ +\frac {\partial a _ {i}}{\partial \boldsymbol {x} _ {j}} = \frac {\partial m _ {1 1}}{\partial \boldsymbol {x} _ {j}} + \frac {\partial m _ {2 2}}{\partial \boldsymbol {x} _ {j}} + \frac {\partial m _ {3 3}}{\partial \boldsymbol {x} _ {j}}. \tag {25} +$$ + +Thus, to get the first- and second-order partial derivatives of $a_{i}, b_{i}$ and $c_{i}$ with respect to $\pmb{x}_j$ and $\pmb{x}_k$ in (23), we need to derive the form of $\mathbf{M}_i$ with respect to $\pmb{x}_j$ and $\pmb{x}_k$ . + +Lemma 3 In terms of $\pmb{x}_j$ and $\pmb{x}_k$ , $\bar{\pmb{p}}_i$ in (13) has the form + +$$ +\bar {\boldsymbol {p}} _ {i} \left(\boldsymbol {x} _ {j}, \boldsymbol {x} _ {k}\right) = \mathbf {T} _ {j} \boldsymbol {q} _ {i j} + \mathbf {T} _ {k} \boldsymbol {q} _ {i k} + \boldsymbol {c} _ {i j k}, \tag {26} +$$ + +where $\pmb{q}_{ij} = \frac{1}{N_i}\tilde{\pmb{p}}_{ij},\quad \pmb{q}_{ik} = \frac{1}{N_i}\tilde{\pmb{p}}_{ik},$ and $c_{ijk} = \frac{1}{N_i}\sum_{n\in \mathbb{O}_{jk}}\mathbf{T}_n\tilde{p}_{in}$ . Here $\mathbb{O}_{jk} = \mathrm{obs}(\pi_i) - \{j,k\}$ represents the set of indexes of the poses that can observe $\pi_i$ , excluding the $j$ th and $k$ th poses. + +In terms of $\pmb{x}_j$ , $\bar{\pmb{p}}_i$ has the form + +$$ +\bar {\boldsymbol {p}} _ {i} \left(\boldsymbol {x} _ {j}\right) = \mathbf {T} _ {j} \mathbf {q} _ {i j} + \boldsymbol {c} _ {i j}, \tag {27} +$$ + +where $c_{ij} = \mathbf{T}_k\mathbf{q}_{ik} + c_{ijk}$ . + +Using Lemma 3, we can have the following theorem for $\mathbf{M}_i$ in (12). + +Theorem 2 In terms of $\pmb{x}_j$ , $\mathbf{M}_i$ in (12) can be written as + +$$ +\mathbf {M} _ {i} \left(\boldsymbol {x} _ {j}\right) = \mathbf {T} _ {j} \mathbf {Q} _ {j} ^ {i} \mathbf {T} _ {j} ^ {T} + \mathbf {T} _ {j} \mathbf {K} _ {j} ^ {i} + \left(\mathbf {K} _ {j} ^ {i}\right) ^ {T} \mathbf {T} _ {j} ^ {T} + \mathbf {C} _ {j} ^ {i}, \tag {28} +$$ + +where $\mathbf{Q}_j^i = \mathbf{U}_{ij} - N_j\mathbf{q}_{ij}\mathbf{q}_{ij}^T$ and $\mathbf{K}_j^i = -N_i\mathbf{q}_{ij}\mathbf{c}_{ij}^T$ . Here $\mathbf{U}_{ij}$ and $\mathbf{q}_{ij}$ are defined in (13) and (26), respectively. + +In terms of $\pmb{x}_j$ and $\pmb{x}_k$ , $\mathbf{M}_i$ can be written as + +$$ +\mathbf {M} _ {i} \left(\boldsymbol {x} _ {j}, \boldsymbol {x} _ {k}\right) = \mathbf {T} _ {j} \mathbf {O} _ {j k} ^ {i} \mathbf {T} _ {k} ^ {T} + \mathbf {T} _ {k} \left(\mathbf {O} _ {j k} ^ {i}\right) ^ {T} \mathbf {T} _ {j} ^ {T} + \mathbf {C} _ {j k} ^ {i}. \tag {29} +$$ + +where $\mathbf{O}_{jk}^{i} = -N_{i}\pmb{q}_{ij}\pmb{q}_{ik}^{T}$ . + +Here we do not provide the detailed formulas for $\mathbf{C}_j^i$ and $\mathbf{C}_{jk}^{i}$ , as they will be eliminated in the partial derivative. Actually, only $\mathbf{Q}_j^i$ , $\mathbf{K}_j^i$ , and $\mathbf{O}_{jk}^{i}$ are required to compute the partial derivatives in (23). Equation (28) is used to compute the first- and second-order partial derivatives of $a_i$ , $b_i$ and $c_i$ with respect to $\pmb{x}_j$ . Equation (29) is used to compute the second-order partial derivatives of $a_i$ , $b_i$ and $c_i$ with respect to $\pmb{x}_j$ and $\pmb{x}_k$ . + +# 4.3. Efficient Iteration + +From Theorem 2, we can easily derive the elements of $\mathbf{M}_i(\pmb{x}_j)$ and $\mathbf{M}_i(\pmb{x}_j,\pmb{x}_i)$ . Assume $a(\pmb{x}_j)$ and $b(\pmb{x}_j,\pmb{x}_k)$ are one of the elements in $\mathbf{M}_i(\pmb{x}_j)$ and $\mathbf{M}_i(\pmb{x}_j,\pmb{x}_k)$ , respectively. Substituting $\mathbf{T}_j$ and $\mathbf{T}_k$ defined in (1) into (28) and + +(29) and expanding them, we can obtain that $a(\pmb{x}_j)$ and $b(\pmb{x}_j, \pmb{x}_k)$ are second-order polynomials in terms of the elements in $\mathbf{T}_j$ and $\mathbf{T}_k$ . Using the CGB parameterization in (2), we can write $a(\pmb{x}_j)$ and $b(\pmb{x}_j, \pmb{x}_k)$ as + +$$ +\begin{array}{l} a (\boldsymbol {x} _ {j}) = \boldsymbol {c} \cdot \boldsymbol {h} (\boldsymbol {x} _ {j}) + c _ {0}, \\ b \left(\boldsymbol {x} _ {j}, \boldsymbol {x} _ {k}\right) = \boldsymbol {d} \cdot \boldsymbol {g} \left(\boldsymbol {x} _ {j}, \boldsymbol {x} _ {k}\right) + d _ {0}, \\ \end{array} +$$ + +where $\pmb{c}$ is determined by $\mathbf{Q}_j^i$ and $\mathbf{K}_j^i$ in (28), $\pmb{d}$ is determined by $\mathbf{O}_{jk}^{i}$ in (29), $\pmb{h}(\pmb{x}_j)$ and $\pmb{g}(\pmb{x}_j, \pmb{x}_k)$ are two vector functions, $c_0$ and $d_0$ are two scalars independent on $\pmb{x}_j$ and $\pmb{x}_k$ . Let us first consider the first-order partial derivative of $a(\pmb{x}_j)$ with respect to $\pmb{x}_j$ . It has the form + +$$ +\frac {\partial a \left(\boldsymbol {x} _ {j}\right)}{\partial \boldsymbol {x} _ {j}} = \frac {\partial h \left(\boldsymbol {x} _ {j}\right)}{\partial \boldsymbol {x} _ {j}} c, \tag {31} +$$ + +where the vector-by-vector derivative $\frac{\partial h(\pmb{x}_j)}{\partial\pmb{x}_j}$ is defined in (4). To efficiently compute (31), we consider a special pose $\mathbf{T}_0 = [\mathbf{R}_0,t_0]$ where $\mathbf{R}_0 = \mathbf{I}_3$ and $t_0 = [0;0;0]$ . Let us denote the parameterization of $\mathbf{T}_0$ as $\pmb{x}_0$ . As the CGR parameterization for $\mathbf{I}_3$ is $[0;0;0]$ , we have $\pmb{x}_0 = [0;0;0;0;0;0]$ . For $\pmb{x}_j = \pmb{x}_0$ , the matrix $\frac{\partial h(\mathbf{x}_j)}{\partial\mathbf{x}_j}$ can be easily computed. Similarly, the second-order partial derivatives of $\pmb{h}(\pmb{x}_j)$ and $\pmb{g}(\pmb{x}_j,\pmb{x}_k)$ at $\pmb{x}_j = \pmb{x}_0$ and $\pmb{x}_k = \pmb{x}_0$ are also simple. As $\pmb{h}(\pmb{x}_j)$ and $\pmb{g}(\pmb{x}_j,\pmb{x}_k)$ only depend on $\pmb{x}_j$ and $\pmb{x}_k$ , we can compute the partial derivatives at $\pmb{x}_0$ once, and then reuse them in the following iterations. Here we introduce a method to make the iteration stay at $\mathbf{x}_0$ for each pose. + +Assume that $\{\mathbf{X}_j^n\}$ are the poses after the $n$ th iteration. Then we can update $\mathbf{U}_{ij}$ and $\tilde{p}_{ij}$ in (13) by + +$$ +\mathbf {U} _ {i j} ^ {n + 1} = \mathbf {X} _ {j} ^ {n} \mathbf {U} _ {i j} \left(\mathbf {X} _ {j} ^ {n}\right) ^ {T} \text {a n d} \tilde {\boldsymbol {p}} _ {i j} ^ {n + 1} = \mathbf {X} _ {j} ^ {n} \tilde {\boldsymbol {p}} _ {i j}. \tag {32} +$$ + +Substituting $\mathbf{U}_{ij}^{n + 1}$ and $\tilde{\pmb{p}}_{ij}^{n + 1}$ into (12), we get a new matrix $\mathbf{M}_i(\mathbb{X}_i)^{n + 1}$ , which can finally lead to a new cost $\tau^{n + 1}$ in (16). As the points have been transformed by $\{\mathbf{X}_j^n\}$ , each pose should start with $\mathbf{X}_0$ for $\tau^{n + 1}$ . Assume that $\Delta \pmb{x}_j^{n + 1}$ is the result from the $(n + 1)$ th iteration for the $j$ th pose. We can compute the corresponding transformation matrix $\Delta \mathbf{X}_j^{n + 1}$ using (1) and (2). Then we can update $\mathbf{X}_j^n$ by + +$$ +\mathbf {X} _ {j} ^ {n + 1} = \Delta \mathbf {X} _ {j} ^ {n + 1} \mathbf {X} _ {j} ^ {n}. \tag {33} +$$ + +Furthermore, the update steps in (32) will not introduce additional computation. This is because the damped Newton's method requires to compute the cost $\tau$ in (16) to adjust $\mu$ in (3) after each iteration, which requires to perform the computation in (32). + +# 4.4. Algorithm Summary + +We first construct $\mathbf{H}$ and $\pmb{g}$ . For each plane $\pi_i$ , we solve the cubic equation (19), and select the smallest root $\lambda_{i,3}$ . + +For $\boldsymbol{x}_j$ , we construct $\mathbf{M}(\boldsymbol{x}_j)$ in (28), and calculate the partial derivatives of $a_i$ , $b_i$ and $c_i$ with respect to $\boldsymbol{x}_j$ in (23). Then, we use (24) to compute $g_j^i$ and $\mathbf{H}_{jj}^i$ and use (18) to update $g_j$ and $\mathbf{H}_{jj}$ . For $\boldsymbol{x}_j$ and $\boldsymbol{x}_k$ , $\mathbf{M}_i(\boldsymbol{x}_j, \boldsymbol{x}_k)$ is generated, and then the partial derivatives of $a_i$ , $b_i$ and $c_i$ with respect to $\boldsymbol{x}_j$ and $\boldsymbol{x}_j$ in (23) are computed. Then, $\mathbf{H}_{jk}^i$ can be easily obtained from (24), and $\mathbf{H}_{jk}$ in (18) is computed accordingly. Using $\mathbf{H}$ and $g$ , we conduct the damped Newton's step in (3). After each iteration, $\mathbf{U}_{ij}$ and $\tilde{\boldsymbol{p}}_{ij}$ are updated by (32). The proposed algorithm is summarized in Algorithm 1. Let us denote the mean and variance of the number of observations per plane as $\bar{K}$ and $\sigma^2$ , respectively. According to [8], the computational complexity of the Hessian matrix is $O(M(\bar{K}^2 + \sigma^2))$ , which is of the same order as the Schur complement trick. + +Algorithm 1: Second-order plane adjustment for $N$ poses and $M$ planes +while not converge do $\mathbf{H} = \text{zeros}(6N, 6N), \mathbf{g} = \text{zeros}(6N, 1)$ ; for $i \in [1, M]$ do +\[ +\begin{aligned} +& \text{Compute } \mathbf{g}\text{ and the diagonal terms of } \mathbf{H}. \\ +& \text{for } j \in \text{obs}(\pi_i) \text{ do} \\ +& \text{Compute } \mathbf{M}_i(\mathbf{x}_j) \text{ using (28)}; \\ +& \text{Compute } \alpha_j^i, \beta_j^i, \gamma_j^i, \mathbf{H}_{jj}^{a_i}, \mathbf{H}_{jj}^{b_i}, \mathbf{H}_{jj}^{c_i} \text{ using (23)}; \\ +& \text{Compute } \mathbf{H}_{jj}^i \text{ and } \mathbf{g}_j^i \text{ using (24)}; \\ +& \text{H}_{jj} = \mathbf{H}_{jj} + \mathbf{H}_{jj}^i, \mathbf{g}_j = \mathbf{g}_j + \mathbf{g}_j^i; +\end{aligned} +\] +\[ +\begin{aligned} +& \text{for } j \in \text{obs}(\pi_i) \text{ do} \\ +& \text{for } k \in \text{obs}(\pi_i) \text{ and } k > j \text{ do} \\ +& \text{Compute } \mathbf{H}_{jk}^i \text{ using (24)}; \\ +& \text{H}_{jk} = \mathbf{H}_{jk} + \mathbf{H}_{jk}^i; \\ +& \text{H}_{kj} = \mathbf{H}_{kj} + (\mathbf{H}_{jk}^i)^T; +\end{aligned} +\] +Conduct the damped Newton's step in (3); Update $\mathbf{U}_{ij}$ and $\tilde{\boldsymbol{p}}_{ij}$ using (32); + +# 5. Experiments + +# 5.1. Setup + +In this section, we compare our algorithm with EF [10], BALM [16] and the LM solution [23] with plane fitting after a successful LM step (named $\mathbf{LM} + \mathbf{PF}$ ). Our damped Newton's method was implemented according to the LM algorithm in Ceres [2]. The damped Newton's method and the LM algorithm are with the same parameters. Specifically, the initial value of the damping factor $\mu$ in (3) is set to $10^{-4}$ . The early stopping tolerances (such as the cost value change and the norm of gradient) are set to $10^{-7}$ . The + +![](images/a69f873f088158572d06b5807a08fd71ea9af7c5667e475e004e8daffe7c2e3d.jpg) +(A) + +![](images/c7ef9988b38447e3aab215962fd24710d39910c4d7b0e5d54d73851ee5988afe.jpg) +(B) + +![](images/915bbd0b71fe635a3e032a744041326797493128d2790403932cb87d1144649f.jpg) +(C) + +![](images/424234a6cd6441bd86279b894d457ddd4f63fa4c2f2318a40f661acd9ef0d0d2.jpg) +(D) + +![](images/2a3f334e97d0b831aafbd009726f5ee56bf0636d24643818d62cd87d29565b3b.jpg) +Figure 3. The four datasets used in this paper. There are $4.5 \times 10^{6}$ , $16.6 \times 10^{6}$ , $16.7 \times 10^{6}$ , and $10.5 \times 10^{6}$ points in the 4 datasets. The 4 datasets have 339, 369, 856, and 589 planes, and 472, 1355, 1606, 1184 poses, respectively. Roofs are removed to show the trajectories. + +![](images/1797e1f3cc2e9c6d579d0c4c92431899494c7c00e10169fcb627fecbf05c8f7f.jpg) +$\sigma_{\mathbf{R}} = 0.1^{\circ}\sigma_{t} = 0.01m$ $\sigma_{\mathbf{R}} = 1^{\circ}\sigma_{t} = 0.1m$ + +$\sigma_{\mathbf{R}} = 1^{\circ}\sigma_{t} = 0.1m$ + +![](images/38490bd707da129099d0810b78c7adbe4157d1707659a845d3fe828948fdb519.jpg) +$\sigma_{\mathbf{R}} = 2^{\circ}\sigma_{t} = 0.2m$ +Figure 4. The point clouds of dataset C after the poses were perturbs by the four noise levels. + +![](images/10ff24e4a1465158846008776813eafbb4d1cd47fb489fa107df0a7684288448.jpg) +$\sigma_{\mathbf{R}} = 3^{\circ}\sigma_{t} = 0.3m$ + +maximum number of iterations is set to 200 for our algorithm, BALM, and LM+PF, and $10^{5}$ for EF, as EF uses the first-order minimization which requires more iterations to converge. All the experiments were conducted on a desktop with an Intel i7 cpu and 64G memory. + +# 5.2. Datasets + +We collected four datasets using a VLP-16 LiDAR. We used the LiDAR SLAM algorithm [24] to detect the planes and establish the plane association. Fig. 3 shows the four datasets. Similar to the evaluation of BA algorithms [3,8,25], we perturb the pose, and compare the PA cost in (11) for different algorithms. Specifically, we directly add Gaussian noises to the translation, and randomly generate an angle-axis vector from a Gaussian distribution to perturb the rotation. After the poses are perturb, we use (7) to get the initial plane parameters for $\mathrm{LM} + \mathrm{PF}$ . + +We evaluate the performance of different algorithms under different noise levels. Let us denote the standard deviation (std) of the Gaussian noises for rotation and translation as $\sigma_{\mathbf{R}}$ and $\sigma_t$ , respectively. We consider four noise levels: $\sigma_{\mathbf{R}} = 0.1^{\circ}$ and $\sigma_t = 0.01m$ , $\sigma_{\mathbf{R}} = 1^{\circ}$ and $\sigma_t = 0.1m$ , $\sigma_{\mathbf{R}} = 2^{\circ}$ and $\sigma_t = 0.2m$ , and $\sigma_{\mathbf{R}} = 3^{\circ}$ and $\sigma_t = 0.3m$ . Fig. 4 demonstrates the point clouds of dataset C after the poses are perturbed by the four noise levels. To evaluate the performance of different algorithms suffering from large measurement noises, we also test the case that additional Gaussian noises with the std $\sigma_{pt} = 0.05m$ are added to the LiDAR point cloud, and the poses are perturbed by Gaussian noises with $\sigma_{\mathbf{R}} = 3^{\circ}$ and $\sigma_t = 0.3m$ . + +# 5.3. Results + +Fig. 5 and Fig. 6 illustrates the results. It is clear that our algorithm converges faster than other algorithms. LM+PF works well at small noises (such as $\sigma_{\mathbf{R}} = 0.1^{\circ}$ and $\sigma_t = 0.01m$ ). As the noise level increases, LM+PF tends to converge slower. Constructing H and g using BALM [16] is computationally demanding. For efficiency, BALM only keeps the centroid of each plane observation (i.e., only 1 point is kept), which results in bad performance. In Fig. 5 and Fig. 6, all points are used to compute the cost in (11) after an iteration of BALM. BALM generally converges slow, as it minimizes a reduced PA problem. EF [10] adopts the first-order optimization method as it only provides a method + +![](images/4fa1350a3cee5e97ba491459cf03ea026651cedda2181aa6f54b061cb335872d.jpg) +Figure 5. The results of different algorithms using different initial noise levels. It is clear that our algorithm converges significantly faster than other algorithms. The $y$ -axis represents the logarithmic scale of the cost in (11). + +![](images/b21bc28bd873f818d0c9d5a175517159a6153e323787c0cc1d30ffa9d3372f34.jpg) +Figure 6. The results of different algorithms for point clouds perturbed by Gaussian noise with std $\sigma_{pt} = 0.05m$ . The rotations and translations of the poses are perturbed by Gaussian noise with std $\sigma_{\mathbf{R}} = 3^{\circ}$ and $\sigma_t = 0.3m$ , respectively. + +to compute the gradient, which results in slow convergence. + +# 6. Conclusion + +In the computer vision community, Newton's method is generally considered too expensive for a large-scale least-squares problem. This paper adopts the Newton's method to efficiently solve the PA problem. Our algorithm takes advantage of the fact that the optimal planes are determined + +by the poses, so that the number of unknowns can be significantly reduced. Furthermore, this property can ensure to obtain the optimal planes when we update the poses. The difficulty lies in how to efficiently compute the Hessian matrix and the gradient vector. The key contribution of this paper is to provide a closed-form solution for them. The experimental results show that our algorithm outperforms the state-of-the-art algorithms. + +# References + +[1] Sameer Agarwal, Yasutaka Furukawa, Noah Snavely, Ian Simon, Brian Curless, Steven M Seitz, and Richard Szeliski. Building rome in a day. Communications of the ACM, 54(10):105-112, 2011. 1 +[2] Sameer Agarwal, Keir Mierle, and The Ceres Solver Team. Ceres Solver, 3 2022. 6 +[3] Sameer Agarwal, Noah Snavely, Steven M Seitz, and Richard Szeliski. Bundle adjustment in the large. In European conference on computer vision, pages 29-42. Springer, 2010. 1, 2, 7 +[4] Alex M Andrew. Multiple view geometry in computer vision. Kybernetes, 2001. 2 +[5] Carlos Campos, Richard Elvira, Juan J Gómez Rodríguez, José MM Montiel, and Juan D Tardós. Orb-slam3: An accurate open-source library for visual, visual-inertial, and multimap slam. IEEE Transactions on Robotics, 2021. 1 +[6] Danpeng Chen, Shuai Wang, Weijian Xie, Shangjin Zhai, Nan Wang, Hujun Bao, and Guofeng Zhang. Vip-slam: An efficient tightly-coupled rgb-d visual inertial planar slam. In 2022 International Conference on Robotics and Automation (ICRA), pages 5615-5621. IEEE, 2022. 1 +[7] Nikolaus Demmel, David Schubert, Christiane Sommer, Daniel Cremers, and Vladyslav Usenko. Square root marginalization for sliding-window bundle adjustment. In Proceedings of the IEEE/CVF International Conference on Computer Vision, pages 13260-13268, 2021. 2 +[8] Nikolaus Demmel, Christiane Sommer, Daniel Cremers, and Vladyslav Usenko. Square root bundle adjustment for large-scale reconstruction. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 11723-11732, 2021. 1, 2, 6, 7 +[9] Hakim Elchaoui Elghor, David Roussel, Fakhreddine Ababsa, and El Houssine Bouyakhf. Planes detection for robust localization and mapping in rgb-d slam systems. In 2015 International Conference on 3D Vision, pages 452-459. IEEE, 2015. 1 +[10] Gonzalo Ferrer. Eigen-factors: Plane estimation for multiframe and time-continuous point cloud alignment. In 2019 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), pages 1278–1284. IEEE, 2019. 1, 2, 6, 7 +[11] Joel A Hesch and Stergios I Roumeliotis. A direct least-squares (dls) method for pnp. In 2011 International Conference on Computer Vision, pages 383-390. IEEE, 2011. 3 +[12] Ming Hsiao, Eric Westman, Guofeng Zhang, and Michael Kaess. Keyframe-based dense planar slam. In 2017 IEEE International Conference on Robotics and Automation (ICRA), pages 5110-5117. IEEE, 2017. 1, 2 +[13] Michael Kaess. Simultaneous localization and mapping with infinite planes. In 2015 IEEE International Conference on Robotics and Automation (ICRA), pages 4605-4611. IEEE, 2015. 1, 2 +[14] Pyojin Kim, Brian Coltin, and H Jin Kim. Linear rgb-d slam for planar environments. In Proceedings of the European Conference on Computer Vision (ECCV), pages 333-348, 2018. 1 + +[15] Steven George Krantz and Harold R Parks. The implicit function theorem: history, theory, and applications. Springer Science & Business Media, 2002. 5 +[16] Zheng Liu and Fu Zhang. BALM: Bundle Adjustment for LiDAR Mapping. IEEE Robotics and Automation Letters, 6(2):3184-3191, 2021. 1, 2, 6, 7 +[17] Jorge J Moré. The levenberg-marquardt algorithm: implementation and theory. In Numerical analysis, pages 105-116. Springer, 1978. 3 +[18] Raul Mur-Artal, Jose Maria Martinez Montiel, and Juan D Tardos. Orb-slam: a versatile and accurate monocular slam system. IEEE transactions on robotics, 31(5):1147-1163, 2015. 1 +[19] Johannes L Schonberger and Jan-Michael Frahm. Structure-from-motion revisited. In Proceedings of the IEEE conference on computer vision and pattern recognition, pages 4104-4113, 2016. 1 +[20] Bill Triggs, Philip F McLauchlan, Richard I Hartley, and Andrew W Fitzgibbon. Bundle adjustment—a modern synthesis. In International workshop on vision algorithms, pages 298-372. Springer, 1999. 1, 2, 3 +[21] Ji Zhang and Sanjiv Singh. Loam: Lidar odometry and mapping in real-time. In Robotics: Science and Systems, volume 2, 2014. 1 +[22] Lipu Zhou, Guoquan Huang, Yinian Mao, Jincheng Yu, Shengze Wang, and Michael Kaess. Plc-lislam: Lidar slam with planes, lines and cylinders. IEEE Robotics and Automation Letters, 2022. 1 +[23] Lipu Zhou, Daniel Koppel, Hul Ju, Frank Steinbruecker, and Michael Kaess. An efficient planar bundle adjustment algorithm. In 2020 IEEE International Symposium on Mixed and Augmented Reality (ISMAR), pages 136-145, 2020. 1, 2, 6 +[24] Lipu Zhou, Daniel Koppel, and Michael Kaess. Lidar slam with plane adjustment for indoor environment. IEEE Robotics and Automation Letters, 6(4):7073-7080, 2021. 1, 2, 7 +[25] Lei Zhou, Zixin Luo, Mingmin Zhen, Tianwei Shen, Shiwei Li, Zhuofei Huang, Tian Fang, and Long Quan. Stochastic bundle adjustment for efficient and scalable 3d reconstruction. In European Conference on Computer Vision, pages 364-379. Springer, 2020. 1, 2, 7 +[26] Lipu Zhou, Shengze Wang, and Michael Kaess. $\pi$ -lsam: Lidar smoothing and mapping with planes. In 2021 IEEE International Conference on Robotics and Automation (ICRA), pages 5751-5757. IEEE, 2021. 1 \ No newline at end of file diff --git a/2023/Efficient Second-Order Plane Adjustment/images.zip b/2023/Efficient Second-Order Plane Adjustment/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..dbe34de428993dd7f13393579e1d285caa9ae006 --- /dev/null +++ b/2023/Efficient Second-Order Plane Adjustment/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:20b87324d82bb6593c47cde490ef911b382bc7db28213373f941c499520d2296 +size 726714 diff --git a/2023/Efficient Second-Order Plane Adjustment/layout.json b/2023/Efficient Second-Order Plane Adjustment/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..028c67b2ee0c57c31f5e3604e1041395ff97abaf --- /dev/null +++ b/2023/Efficient Second-Order Plane Adjustment/layout.json @@ -0,0 +1,14845 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 167, + 103, + 427, + 121 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 167, + 103, + 427, + 121 + ], + "spans": [ + { + "bbox": [ + 167, + 103, + 427, + 121 + ], + "type": "text", + "content": "Efficient Second-Order Plane Adjustment" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 238, + 144, + 356, + 185 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 238, + 144, + 356, + 185 + ], + "spans": [ + { + "bbox": [ + 238, + 144, + 356, + 185 + ], + "type": "text", + "content": "Lipu Zhou Meituan, Beijing, China zhoulipu@meituan.com" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 143, + 213, + 192, + 225 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 213, + 192, + 225 + ], + "spans": [ + { + "bbox": [ + 143, + 213, + 192, + 225 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 239, + 290, + 539 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 239, + 290, + 539 + ], + "spans": [ + { + "bbox": [ + 46, + 239, + 290, + 539 + ], + "type": "text", + "content": "Planes are generally used in 3D reconstruction for depth sensors, such as RGB-D cameras and LiDARs. This paper focuses on the problem of estimating the optimal planes and sensor poses to minimize the point-to-plane distance. The resulting least-squares problem is referred to as plane adjustment (PA) in the literature, which is the counterpart of bundle adjustment (BA) in visual reconstruction. Iterative methods are adopted to solve these least-squares problems. Typically, Newton's method is rarely used for a large-scale least-squares problem, due to the high computational complexity of the Hessian matrix. Instead, methods using an approximation of the Hessian matrix, such as the Levenberg-Marquardt (LM) method, are generally adopted. This paper adopts the Newton's method to efficiently solve the PA problem. Specifically, given poses, the optimal plane have a close-form solution. Thus we can eliminate planes from the cost function, which significantly reduces the number of variables. Furthermore, as the optimal planes are functions of poses, this method actually ensures that the optimal planes for the current estimated poses can be obtained at each iteration, which benefits the convergence. The difficulty lies in how to efficiently compute the Hessian matrix and the gradient of the resulting cost. This paper provides an efficient solution. Empirical evaluation shows that our algorithm outperforms the state-of-the-art algorithms." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 561, + 128, + 574 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 561, + 128, + 574 + ], + "spans": [ + { + "bbox": [ + 47, + 561, + 128, + 574 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 582, + 287, + 701 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 582, + 287, + 701 + ], + "spans": [ + { + "bbox": [ + 46, + 582, + 287, + 701 + ], + "type": "text", + "content": "Planes ubiquitously exist in man-made environments, as demonstrated in Fig. 1. Thus they are generally used in simultaneous localization and mapping (SLAM) systems for depth sensors, such as RGB-D cameras [6, 9, 12-14] and LiDARs [16, 21, 22, 24, 26]. Just as bundle adjustment (BA) [3, 8, 20, 25] is important for visual reconstruction [1, 5, 18, 19], jointly optimizing planes and depth sensor poses, which is called plane adjustment (PA) [24,26], is critical for 3D reconstruction using depth sensors. This paper focuses on efficiently solving the large-scale PA problem." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 59, + 701, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 701, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 59, + 701, + 287, + 714 + ], + "type": "text", + "content": "The BA and PA problems both involve jointly optimiz" + } + ] + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 323, + 215, + 531, + 308 + ], + "blocks": [ + { + "bbox": [ + 323, + 215, + 531, + 308 + ], + "lines": [ + { + "bbox": [ + 323, + 215, + 531, + 308 + ], + "spans": [ + { + "bbox": [ + 323, + 215, + 531, + 308 + ], + "type": "image", + "image_path": "9deb1687d382e0c43556b98b8b209c0391c0a1814a79c39e867c17c2fa22c858.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 360, + 310, + 487, + 321 + ], + "lines": [ + { + "bbox": [ + 360, + 310, + 487, + 321 + ], + "spans": [ + { + "bbox": [ + 360, + 310, + 487, + 321 + ], + "type": "text", + "content": "(a) Point cloud from perturbed poses" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 323, + 329, + 531, + 423 + ], + "blocks": [ + { + "bbox": [ + 323, + 329, + 531, + 423 + ], + "lines": [ + { + "bbox": [ + 323, + 329, + 531, + 423 + ], + "spans": [ + { + "bbox": [ + 323, + 329, + 531, + 423 + ], + "type": "image", + "image_path": "37f2ef9a59f7a31f5dc58f03e53fd417b300370e284a02b070c728a8c916ab5b.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 369, + 425, + 487, + 435 + ], + "lines": [ + { + "bbox": [ + 369, + 425, + 487, + 435 + ], + "spans": [ + { + "bbox": [ + 369, + 425, + 487, + 435 + ], + "type": "text", + "content": "(b) Point cloud from our algorithm" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 305, + 444, + 547, + 500 + ], + "lines": [ + { + "bbox": [ + 305, + 444, + 547, + 500 + ], + "spans": [ + { + "bbox": [ + 305, + 444, + 547, + 500 + ], + "type": "text", + "content": "Figure 1. We use Gaussian noises to perturb the poses of dataset D in Fig. 3. The standard deviations for rotation and translation are " + }, + { + "bbox": [ + 305, + 444, + 547, + 500 + ], + "type": "inline_equation", + "content": "3^{\\circ}" + }, + { + "bbox": [ + 305, + 444, + 547, + 500 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 444, + 547, + 500 + ], + "type": "inline_equation", + "content": "0.3m" + }, + { + "bbox": [ + 305, + 444, + 547, + 500 + ], + "type": "text", + "content": ", respectively. The resulting point cloud (a) is in a mess. Fig. (b) shows the result from our algorithm. Our algorithm can quickly align the planes, as shown in Fig. 5." + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_caption" + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 521, + 545, + 664 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 521, + 545, + 664 + ], + "spans": [ + { + "bbox": [ + 304, + 521, + 545, + 664 + ], + "type": "text", + "content": "ing 3D structures and sensor poses. As the two problems are similar, it is straightforward to apply the well-studied solutions for BA to PA, as done in [23, 26]. However, planes in PA can be eliminated, so that the cost function of the PA problem only depends on sensor poses, which significantly reduces the number of variables. This property provides a promising direction to efficiently solve the PA problem. However, it is difficult to compute the Hessian matrix and the gradient vector of the resulting cost. Although this problem was studied in several previous works [10, 16], no efficient solution has been proposed. This paper seeks to solve this problem." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 665, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 547, + 715 + ], + "type": "text", + "content": "The main contribution of this paper is an efficient PA solution using Newton's method. We derive a closed-form solution for the Hessian matrix and the gradient vector for the PA problem whose computational complexity is inde" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "13113" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 109 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 109 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 109 + ], + "type": "text", + "content": "pendent of the number of points on the planes. Our experimental results show that the proposed algorithm converges faster than the state-of-the-art algorithms." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 119, + 134, + 132 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 119, + 134, + 132 + ], + "spans": [ + { + "bbox": [ + 47, + 119, + 134, + 132 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 139, + 286, + 223 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 139, + 286, + 223 + ], + "spans": [ + { + "bbox": [ + 46, + 139, + 286, + 223 + ], + "type": "text", + "content": "The PA problem is closely related to the BA problem. In BA, points and camera poses are jointly optimized to minimize the reprojection error. Schur complement [3, 20, 25] or the square root method [7, 8] is generally used to solve the linear system of the iterative methods. The keypoint is to generate a reduced camera system (RCS) which only relates to camera poses." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 223, + 286, + 498 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 223, + 286, + 498 + ], + "spans": [ + { + "bbox": [ + 46, + 223, + 286, + 498 + ], + "type": "text", + "content": "In PA, planes and poses are jointly optimized. Planes are the counterparts of points in BA. Thus, the well-known solutions for the BA problem can be applied to the PA problem [23, 24]. In the literature, two cost functions are used to formulate the PA problem. The first one is the plane-to-plane distance which measures the difference between two plane parameters [12, 13]. The value of the plane-to-plane distance is related to the choice of the global coordinate system, which means the selection of the global coordinate system will affect the accuracy of the results. The second one is the point-to-plane distance, whose value is invariant to the choice of the global coordinate system. The solutions of different choices of the global coordinate system are equivalent up to a rigid transformation. Zhou et al. [23] show that the point-to-plane distance can converge faster and lead to a more accurate result. But unlike BA where each 3D point has only one 2D observation at a pose, a plane can generate many points at a pose as demonstrated in Fig. 2. This means the point-to-plane distance probably leads to a very large-scale least-squares problem. Directly adopting the BA solutions is computationally infeasible for a large-scale PA problem. Zhou et al. [23] propose to use the QR decomposition to accelerate the computation." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 498, + 286, + 653 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 498, + 286, + 653 + ], + "spans": [ + { + "bbox": [ + 46, + 498, + 286, + 653 + ], + "type": "text", + "content": "For a general least-squares problem with " + }, + { + "bbox": [ + 46, + 498, + 286, + 653 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 46, + 498, + 286, + 653 + ], + "type": "text", + "content": " variables, the computational complexity of the Hessian matrix is " + }, + { + "bbox": [ + 46, + 498, + 286, + 653 + ], + "type": "inline_equation", + "content": "O(M^2)" + }, + { + "bbox": [ + 46, + 498, + 286, + 653 + ], + "type": "text", + "content": ". Thus, in the computer vision community, it is ingrained that Newton's method is infeasible for a large-scale optimization problem, as calculating the Hessian matrix is computationally demanding. Instead, Gauss-Newton-based iterative methods are generally adopted. Suppose that " + }, + { + "bbox": [ + 46, + 498, + 286, + 653 + ], + "type": "inline_equation", + "content": "\\mathbf{J}" + }, + { + "bbox": [ + 46, + 498, + 286, + 653 + ], + "type": "text", + "content": " is the Jacobian matrix of the residuals. The Gauss-Newton method actually approximates the Hessian matrix by " + }, + { + "bbox": [ + 46, + 498, + 286, + 653 + ], + "type": "inline_equation", + "content": "\\mathbf{H} \\approx \\mathbf{J}^T\\mathbf{J}" + }, + { + "bbox": [ + 46, + 498, + 286, + 653 + ], + "type": "text", + "content": ". In theory, Newton's method can lead to a better quadratic approximation to the original cost function, which means the Newton's step probably yields a better result. This in turn may reduce the number of iterations." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 654, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 654, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 654, + 286, + 713 + ], + "type": "text", + "content": "The PA problem has a special property that the optimal plane parameters are determined by the poses. That is to say the point-to-plane cost actually only depends on the poses. This property is attractive, as it significantly reduces the number of variables, which makes using the Newton's" + } + ] + } + ], + "index": 5 + }, + { + "type": "image", + "bbox": [ + 310, + 73, + 434, + 162 + ], + "blocks": [ + { + "bbox": [ + 310, + 73, + 434, + 162 + ], + "lines": [ + { + "bbox": [ + 310, + 73, + 434, + 162 + ], + "spans": [ + { + "bbox": [ + 310, + 73, + 434, + 162 + ], + "type": "image", + "image_path": "2f6f9651529f33fdb7c651bb24179fca86e7565952419654e9fb8aa6534f7412.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 329, + 165, + 411, + 172 + ], + "lines": [ + { + "bbox": [ + 329, + 165, + 411, + 172 + ], + "spans": [ + { + "bbox": [ + 329, + 165, + 411, + 172 + ], + "type": "text", + "content": "(a) A PA problem with 3 poses and 4 planes" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_caption" + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 444, + 76, + 542, + 159 + ], + "blocks": [ + { + "bbox": [ + 444, + 76, + 542, + 159 + ], + "lines": [ + { + "bbox": [ + 444, + 76, + 542, + 159 + ], + "spans": [ + { + "bbox": [ + 444, + 76, + 542, + 159 + ], + "type": "image", + "image_path": "9612a03506748a6aff89238dcf9ffb91e1fb6cd2f27eeadee99092a8811371ea.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 479, + 165, + 520, + 171 + ], + "lines": [ + { + "bbox": [ + 479, + 165, + 520, + 171 + ], + "spans": [ + { + "bbox": [ + 479, + 165, + 520, + 171 + ], + "type": "text", + "content": "(b) Plane Observation" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 304, + 182, + 545, + 271 + ], + "lines": [ + { + "bbox": [ + 304, + 182, + 545, + 271 + ], + "spans": [ + { + "bbox": [ + 304, + 182, + 545, + 271 + ], + "type": "text", + "content": "Figure 2. A schematic of the PA problem and the planes detected in a LiDAR scan. Unlike BA where each 3D point only has one observation, many points can be captured from a plane in PA. Assume that " + }, + { + "bbox": [ + 304, + 182, + 545, + 271 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 304, + 182, + 545, + 271 + ], + "type": "text", + "content": " points are captured from a plane. The computational complexity of the Hessian matrix related to these points using BALM [16] is " + }, + { + "bbox": [ + 304, + 182, + 545, + 271 + ], + "type": "inline_equation", + "content": "O(N^2)" + }, + { + "bbox": [ + 304, + 182, + 545, + 271 + ], + "type": "text", + "content": ". Thus, this method is infeasible for a large-scale problem. In contrast, the computational complexity of our algorithm is independent of " + }, + { + "bbox": [ + 304, + 182, + 545, + 271 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 304, + 182, + 545, + 271 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 293, + 545, + 509 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 293, + 545, + 509 + ], + "spans": [ + { + "bbox": [ + 304, + 293, + 545, + 509 + ], + "type": "text", + "content": "method possible. In traditional iterative methods, the correlation between the plane parameters and the poses are ignored. Thus, after one iteration, there is no guarantee that the new plane parameters are optimal for the new poses. Using the property of the PA, it is possible to overcome this drawback, which may lead to faster convergence. Several previous works seek to exploit this property of PA. Ferrer [10] explored an algebraic point-to-plane distance and provided a closed-form gradient for the resulting cost. The algebraic cost may result in a suboptimal solution [4], and the first-order optimization generally leads to slow convergence [20]. Liu et al. [16] provided analytic forms of the Hessian matrix and the gradient of the genuine point-to-plane cost. Assume that " + }, + { + "bbox": [ + 304, + 293, + 545, + 509 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 304, + 293, + 545, + 509 + ], + "type": "text", + "content": " points are captured from a plane. The computational complexity of the Hessian matrix related to these points is " + }, + { + "bbox": [ + 304, + 293, + 545, + 509 + ], + "type": "inline_equation", + "content": "O(N^2)" + }, + { + "bbox": [ + 304, + 293, + 545, + 509 + ], + "type": "text", + "content": ". Since " + }, + { + "bbox": [ + 304, + 293, + 545, + 509 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 304, + 293, + 545, + 509 + ], + "type": "text", + "content": " can be large as shown in Fig. 2, this algorithm is computationally demanding and infeasible for a large-scale problem." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 510, + 545, + 568 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 510, + 545, + 568 + ], + "spans": [ + { + "bbox": [ + 304, + 510, + 545, + 568 + ], + "type": "text", + "content": "In summary, the potential benefits of the special property of the PA problem have not been manifested in previous works. The bottleneck is how to efficiently compute the Hessian matrix and the gradient vector. This paper focuses on solving this problem." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 581, + 432, + 594 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 581, + 432, + 594 + ], + "spans": [ + { + "bbox": [ + 306, + 581, + 432, + 594 + ], + "type": "text", + "content": "3. Problem Formulation" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 601, + 545, + 638 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 601, + 545, + 638 + ], + "spans": [ + { + "bbox": [ + 304, + 601, + 545, + 638 + ], + "type": "text", + "content": "In this paper we use italic, boldfaced lowercase and bold-faced uppercase letters to represent scalars, vectors and matrices, respectively." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 647, + 373, + 658 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 647, + 373, + 658 + ], + "spans": [ + { + "bbox": [ + 306, + 647, + 373, + 658 + ], + "type": "text", + "content": "3.1. Notations" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 666, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 666, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 666, + 545, + 713 + ], + "type": "text", + "content": "Planes and Poses A plane can be represented by a four-dimensional vector " + }, + { + "bbox": [ + 304, + 666, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\pmb{\\pi} = [n;d]" + }, + { + "bbox": [ + 304, + 666, + 545, + 713 + ], + "type": "text", + "content": ". We denote the rotational and translational components from a depth sensor coordinate system to the global coordinate system as " + }, + { + "bbox": [ + 304, + 666, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{R}\\in SO(3)" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "13114" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 109 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 109 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 109 + ], + "type": "text", + "content": "and " + }, + { + "bbox": [ + 46, + 72, + 287, + 109 + ], + "type": "inline_equation", + "content": "t \\in \\mathbb{R}^3" + }, + { + "bbox": [ + 46, + 72, + 287, + 109 + ], + "type": "text", + "content": ", respectively. To simplify the notation in the following description, we also use the following two matrices to represent a pose:" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 77, + 118, + 287, + 146 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 77, + 118, + 287, + 146 + ], + "spans": [ + { + "bbox": [ + 77, + 118, + 287, + 146 + ], + "type": "interline_equation", + "content": "\\mathbf {X} = \\left[ \\begin{array}{l l} \\mathbf {R}, & t \\\\ \\mathbf {0}, & 1 \\end{array} \\right] \\in S E (3) \\text {a n d} \\mathbf {T} = \\left[ \\begin{array}{l l} \\mathbf {R}, & t \\end{array} \\right]. \\tag {1}", + "image_path": "676d00fa9b956f78564243455102ef81b4e5e416d8f59e52769055ca3c23a9bd.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 156, + 287, + 205 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 156, + 287, + 205 + ], + "spans": [ + { + "bbox": [ + 47, + 156, + 287, + 205 + ], + "type": "text", + "content": "As " + }, + { + "bbox": [ + 47, + 156, + 287, + 205 + ], + "type": "inline_equation", + "content": "\\mathbf{R} \\in SO(3)" + }, + { + "bbox": [ + 47, + 156, + 287, + 205 + ], + "type": "text", + "content": ", a certain parameterization is usually adopted in the optimization [20]. In this paper, we use the Cayley-Gibbs-Rodriguez (CGR) parameterization [11] to represent " + }, + { + "bbox": [ + 47, + 156, + 287, + 205 + ], + "type": "inline_equation", + "content": "\\mathbf{R}" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 54, + 216, + 287, + 242 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 54, + 216, + 287, + 242 + ], + "spans": [ + { + "bbox": [ + 54, + 216, + 287, + 242 + ], + "type": "interline_equation", + "content": "\\mathbf {R} = \\frac {\\bar {\\mathbf {R}}}{1 + \\boldsymbol {s} ^ {T} \\boldsymbol {s}}, \\bar {\\mathbf {R}} = \\left(1 - \\boldsymbol {s} ^ {T} \\boldsymbol {s}\\right) \\mathbf {I} _ {3} + 2 [ \\boldsymbol {s} ] _ {\\times} + 2 \\boldsymbol {s} \\boldsymbol {s} ^ {T}, \\tag {2}", + "image_path": "93bdae7f80a1904e13af300b009566a9f588b2ce4d92373c6e998eeadfaa1f22.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 251, + 287, + 337 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 251, + 287, + 337 + ], + "spans": [ + { + "bbox": [ + 46, + 251, + 287, + 337 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 251, + 287, + 337 + ], + "type": "inline_equation", + "content": "s = [s_1; s_2; s_3]" + }, + { + "bbox": [ + 46, + 251, + 287, + 337 + ], + "type": "text", + "content": " is a three-dimensional vector. We adopt the CGR parameterization as it is a minimal representation for " + }, + { + "bbox": [ + 46, + 251, + 287, + 337 + ], + "type": "inline_equation", + "content": "\\mathbf{R}" + }, + { + "bbox": [ + 46, + 251, + 287, + 337 + ], + "type": "text", + "content": ". Furthermore, unlike the angle-axis parameterization that is singular at " + }, + { + "bbox": [ + 46, + 251, + 287, + 337 + ], + "type": "inline_equation", + "content": "\\mathbf{I}_3" + }, + { + "bbox": [ + 46, + 251, + 287, + 337 + ], + "type": "text", + "content": ", the CGR parameterization is well-defined at " + }, + { + "bbox": [ + 46, + 251, + 287, + 337 + ], + "type": "inline_equation", + "content": "\\mathbf{I}_3" + }, + { + "bbox": [ + 46, + 251, + 287, + 337 + ], + "type": "text", + "content": ", and equals to " + }, + { + "bbox": [ + 46, + 251, + 287, + 337 + ], + "type": "inline_equation", + "content": "[0; 0; 0]" + }, + { + "bbox": [ + 46, + 251, + 287, + 337 + ], + "type": "text", + "content": " which can accelerate the computation, as described in Section 4.3. We parameterize " + }, + { + "bbox": [ + 46, + 251, + 287, + 337 + ], + "type": "inline_equation", + "content": "\\mathbf{X}" + }, + { + "bbox": [ + 46, + 251, + 287, + 337 + ], + "type": "text", + "content": " as a six-dimensional vector " + }, + { + "bbox": [ + 46, + 251, + 287, + 337 + ], + "type": "inline_equation", + "content": "x = [s; t]" + }, + { + "bbox": [ + 46, + 251, + 287, + 337 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 337, + 287, + 420 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 337, + 287, + 420 + ], + "spans": [ + { + "bbox": [ + 46, + 337, + 287, + 420 + ], + "type": "text", + "content": "Newton's method This paper adopts the damped Newton's method in the optimization. For a cost function " + }, + { + "bbox": [ + 46, + 337, + 287, + 420 + ], + "type": "inline_equation", + "content": "f(z)" + }, + { + "bbox": [ + 46, + 337, + 287, + 420 + ], + "type": "text", + "content": ", the damped Newton's method seeks to find its minimizer from an initial point. Assume that " + }, + { + "bbox": [ + 46, + 337, + 287, + 420 + ], + "type": "inline_equation", + "content": "z_{n}" + }, + { + "bbox": [ + 46, + 337, + 287, + 420 + ], + "type": "text", + "content": " is the solution at the " + }, + { + "bbox": [ + 46, + 337, + 287, + 420 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 46, + 337, + 287, + 420 + ], + "type": "text", + "content": "th iteration. Given the Hessian matrix " + }, + { + "bbox": [ + 46, + 337, + 287, + 420 + ], + "type": "inline_equation", + "content": "\\mathbf{H}_f(z_n)" + }, + { + "bbox": [ + 46, + 337, + 287, + 420 + ], + "type": "text", + "content": " and the gradient " + }, + { + "bbox": [ + 46, + 337, + 287, + 420 + ], + "type": "inline_equation", + "content": "g_{f}(z_{n})" + }, + { + "bbox": [ + 46, + 337, + 287, + 420 + ], + "type": "text", + "content": " at " + }, + { + "bbox": [ + 46, + 337, + 287, + 420 + ], + "type": "inline_equation", + "content": "z_{n},z_{n}" + }, + { + "bbox": [ + 46, + 337, + 287, + 420 + ], + "type": "text", + "content": " is updated by " + }, + { + "bbox": [ + 46, + 337, + 287, + 420 + ], + "type": "inline_equation", + "content": "z_{n + 1} = z_{n} + \\varDelta z" + }, + { + "bbox": [ + 46, + 337, + 287, + 420 + ], + "type": "text", + "content": ". Here " + }, + { + "bbox": [ + 46, + 337, + 287, + 420 + ], + "type": "inline_equation", + "content": "\\varDelta z" + }, + { + "bbox": [ + 46, + 337, + 287, + 420 + ], + "type": "text", + "content": " is from" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 99, + 434, + 287, + 447 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 99, + 434, + 287, + 447 + ], + "spans": [ + { + "bbox": [ + 99, + 434, + 287, + 447 + ], + "type": "interline_equation", + "content": "\\left(\\mathbf {H} _ {f} \\left(\\boldsymbol {z} _ {n}\\right) + \\mu \\mathbf {I})\\right) \\Delta z = - \\boldsymbol {g} _ {f} \\left(\\boldsymbol {z} _ {n}\\right), \\tag {3}", + "image_path": "bd14b23f4cb5717c600eb75d7946d8bea8380beccb83bcb8840dbf4b6ef85898.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 458, + 287, + 495 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 458, + 287, + 495 + ], + "spans": [ + { + "bbox": [ + 47, + 458, + 287, + 495 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 458, + 287, + 495 + ], + "type": "inline_equation", + "content": "\\mu" + }, + { + "bbox": [ + 47, + 458, + 287, + 495 + ], + "type": "text", + "content": " is adjusted at each iteration to make the value of " + }, + { + "bbox": [ + 47, + 458, + 287, + 495 + ], + "type": "inline_equation", + "content": "f(z)" + }, + { + "bbox": [ + 47, + 458, + 287, + 495 + ], + "type": "text", + "content": " reduce, as done in the Levenberg-Marquardt (LM) algorithm [17]." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 495, + 287, + 531 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 495, + 287, + 531 + ], + "spans": [ + { + "bbox": [ + 46, + 495, + 287, + 531 + ], + "type": "text", + "content": "Matrix Calculus In the following derivation, we will use vector-by-vector, vector-by-scalar, scalar-by-vector derivatives. Here we provide their definitions." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 532, + 287, + 586 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 532, + 287, + 586 + ], + "spans": [ + { + "bbox": [ + 47, + 532, + 287, + 586 + ], + "type": "text", + "content": "Assume " + }, + { + "bbox": [ + 47, + 532, + 287, + 586 + ], + "type": "inline_equation", + "content": "\\mathbf{a} = [a_1;\\dots ;a_N]\\in \\mathbb{R}^N" + }, + { + "bbox": [ + 47, + 532, + 287, + 586 + ], + "type": "text", + "content": " is a vector function of " + }, + { + "bbox": [ + 47, + 532, + 287, + 586 + ], + "type": "inline_equation", + "content": "\\pmb {b} = [b_{1},\\dots ,b_{M}]\\in \\mathbb{R}^{M}" + }, + { + "bbox": [ + 47, + 532, + 287, + 586 + ], + "type": "text", + "content": " . The first-order partial derivatives of vector-by-vector " + }, + { + "bbox": [ + 47, + 532, + 287, + 586 + ], + "type": "inline_equation", + "content": "\\frac{\\partial\\pmb{a}}{\\partial\\pmb{b}}" + }, + { + "bbox": [ + 47, + 532, + 287, + 586 + ], + "type": "text", + "content": " , vector-by-scalar " + }, + { + "bbox": [ + 47, + 532, + 287, + 586 + ], + "type": "inline_equation", + "content": "\\frac{\\partial\\pmb{a}}{\\partial b_j}" + }, + { + "bbox": [ + 47, + 532, + 287, + 586 + ], + "type": "text", + "content": " , and scalar-byvector " + }, + { + "bbox": [ + 47, + 532, + 287, + 586 + ], + "type": "inline_equation", + "content": "\\frac{\\partial a_i}{\\partial b}" + }, + { + "bbox": [ + 47, + 532, + 287, + 586 + ], + "type": "text", + "content": " are defined as" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 596, + 294, + 655 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 596, + 294, + 655 + ], + "spans": [ + { + "bbox": [ + 47, + 596, + 294, + 655 + ], + "type": "interline_equation", + "content": "\\frac {\\partial \\boldsymbol {a}}{\\partial \\boldsymbol {b}} = \\left[ \\begin{array}{c c c} \\frac {\\partial a _ {1}}{\\partial b _ {1}} & \\dots & \\frac {\\partial a _ {N}}{\\partial b _ {1}} \\\\ \\vdots & \\ddots & \\vdots \\\\ \\frac {\\partial a _ {1}}{\\partial b _ {M}} & \\dots & \\frac {\\partial a _ {N}}{\\partial b _ {M}} \\end{array} \\right], \\frac {\\partial \\boldsymbol {a}}{\\partial b _ {j}} = \\left[ \\begin{array}{c} \\frac {\\partial a _ {1}}{\\partial b _ {j}} \\\\ \\vdots \\\\ \\frac {\\partial a _ {N}}{\\partial b _ {j}} \\end{array} \\right], \\frac {\\partial a _ {i}}{\\partial \\boldsymbol {b}} = \\left[ \\begin{array}{c} \\frac {\\partial a _ {i}}{\\partial b _ {1}} \\\\ \\vdots \\\\ \\frac {\\partial a _ {i}}{\\partial b _ {M}} \\end{array} \\right] \\tag {4}", + "image_path": "e89a8961f8c85fc5f89b17aee6291ec24591ac31dd0f6d833192c78d03cd9326.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 654, + 287, + 716 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 654, + 287, + 716 + ], + "spans": [ + { + "bbox": [ + 46, + 654, + 287, + 716 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 654, + 287, + 716 + ], + "type": "inline_equation", + "content": "\\frac{\\partial\\pmb{a}}{\\partial\\pmb{b}}" + }, + { + "bbox": [ + 46, + 654, + 287, + 716 + ], + "type": "text", + "content": " is an " + }, + { + "bbox": [ + 46, + 654, + 287, + 716 + ], + "type": "inline_equation", + "content": "M\\times N" + }, + { + "bbox": [ + 46, + 654, + 287, + 716 + ], + "type": "text", + "content": " matrix with " + }, + { + "bbox": [ + 46, + 654, + 287, + 716 + ], + "type": "inline_equation", + "content": "\\frac{\\partial a_j}{\\partial b_i}" + }, + { + "bbox": [ + 46, + 654, + 287, + 716 + ], + "type": "text", + "content": " as the ith row jth column element, " + }, + { + "bbox": [ + 46, + 654, + 287, + 716 + ], + "type": "inline_equation", + "content": "\\frac{\\partial\\pmb{a}}{\\partial b_j}" + }, + { + "bbox": [ + 46, + 654, + 287, + 716 + ], + "type": "text", + "content": " is an " + }, + { + "bbox": [ + 46, + 654, + 287, + 716 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 654, + 287, + 716 + ], + "type": "text", + "content": " -dimensional vector whose ith term is " + }, + { + "bbox": [ + 46, + 654, + 287, + 716 + ], + "type": "inline_equation", + "content": "\\frac{\\partial a_i}{\\partial b_j}" + }, + { + "bbox": [ + 46, + 654, + 287, + 716 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 46, + 654, + 287, + 716 + ], + "type": "inline_equation", + "content": "\\frac{\\partial a_i}{\\partial\\pmb{b}}" + }, + { + "bbox": [ + 46, + 654, + 287, + 716 + ], + "type": "text", + "content": " is an " + }, + { + "bbox": [ + 46, + 654, + 287, + 716 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 46, + 654, + 287, + 716 + ], + "type": "text", + "content": " -dimensional vector whose ith term is " + }, + { + "bbox": [ + 46, + 654, + 287, + 716 + ], + "type": "inline_equation", + "content": "\\frac{\\partial a_i}{\\partial b_i}" + }, + { + "bbox": [ + 46, + 654, + 287, + 716 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 72, + 450, + 85 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 72, + 450, + 85 + ], + "spans": [ + { + "bbox": [ + 306, + 72, + 450, + 85 + ], + "type": "text", + "content": "3.2. Optimal Plane Estimation" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 90, + 545, + 125 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 90, + 545, + 125 + ], + "spans": [ + { + "bbox": [ + 305, + 90, + 545, + 125 + ], + "type": "text", + "content": "Given a set of " + }, + { + "bbox": [ + 305, + 90, + 545, + 125 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 305, + 90, + 545, + 125 + ], + "type": "text", + "content": " points " + }, + { + "bbox": [ + 305, + 90, + 545, + 125 + ], + "type": "inline_equation", + "content": "\\{\\pmb{p}_i\\}" + }, + { + "bbox": [ + 305, + 90, + 545, + 125 + ], + "type": "text", + "content": ", the optimal plane " + }, + { + "bbox": [ + 305, + 90, + 545, + 125 + ], + "type": "inline_equation", + "content": "\\hat{\\pi}" + }, + { + "bbox": [ + 305, + 90, + 545, + 125 + ], + "type": "text", + "content": " can be estimated by minimizing the sum of squared point-to-plane distances" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 321, + 130, + 545, + 162 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 321, + 130, + 545, + 162 + ], + "spans": [ + { + "bbox": [ + 321, + 130, + 545, + 162 + ], + "type": "interline_equation", + "content": "\\hat {\\boldsymbol {\\pi}} = \\arg \\min _ {\\boldsymbol {\\pi}} \\sum_ {i} ^ {K} \\left(\\boldsymbol {n} ^ {T} \\boldsymbol {p} _ {i} + d\\right) ^ {2}, s. t. \\| \\boldsymbol {n} \\| _ {2} ^ {2} = 1. \\tag {5}", + "image_path": "18d8101a4722e6852a93edd1497fd2c7f88cf281b3cf78a37b6148f9a2188998.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 168, + 515, + 179 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 168, + 515, + 179 + ], + "spans": [ + { + "bbox": [ + 306, + 168, + 515, + 179 + ], + "type": "text", + "content": "There is a closed-form solution for " + }, + { + "bbox": [ + 306, + 168, + 515, + 179 + ], + "type": "inline_equation", + "content": "\\hat{\\pi}" + }, + { + "bbox": [ + 306, + 168, + 515, + 179 + ], + "type": "text", + "content": ". Let us define" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 340, + 184, + 545, + 213 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 340, + 184, + 545, + 213 + ], + "spans": [ + { + "bbox": [ + 340, + 184, + 545, + 213 + ], + "type": "interline_equation", + "content": "\\mathbf {M} = \\sum_ {i = 1} ^ {K} \\left(\\boldsymbol {p} _ {i} - \\bar {\\boldsymbol {p}}\\right) \\left(\\boldsymbol {p} _ {i} - \\bar {\\boldsymbol {p}}\\right) ^ {T} = \\mathbf {S} - K \\bar {\\boldsymbol {p}} \\bar {\\boldsymbol {p}} ^ {T}, \\tag {6}", + "image_path": "a256e54a9531271119b31d4fc881f8d515c1184c3eb23193b07920255346658d.jpg" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 305, + 218, + 545, + 269 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 218, + 545, + 269 + ], + "spans": [ + { + "bbox": [ + 305, + 218, + 545, + 269 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 218, + 545, + 269 + ], + "type": "inline_equation", + "content": "\\mathbf{S} = \\sum_{i=1}^{K} \\pmb{p}_i \\pmb{p}_i^T" + }, + { + "bbox": [ + 305, + 218, + 545, + 269 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 218, + 545, + 269 + ], + "type": "inline_equation", + "content": "\\bar{\\pmb{p}} = \\frac{1}{K} \\sum_{i}^{K} \\pmb{p}_i" + }, + { + "bbox": [ + 305, + 218, + 545, + 269 + ], + "type": "text", + "content": ". Assume that " + }, + { + "bbox": [ + 305, + 218, + 545, + 269 + ], + "type": "inline_equation", + "content": "\\lambda_3(\\mathbf{M})" + }, + { + "bbox": [ + 305, + 218, + 545, + 269 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 218, + 545, + 269 + ], + "type": "inline_equation", + "content": "\\xi_3(\\mathbf{M})" + }, + { + "bbox": [ + 305, + 218, + 545, + 269 + ], + "type": "text", + "content": " are the smallest eigenvalue of " + }, + { + "bbox": [ + 305, + 218, + 545, + 269 + ], + "type": "inline_equation", + "content": "\\mathbf{M}" + }, + { + "bbox": [ + 305, + 218, + 545, + 269 + ], + "type": "text", + "content": " and the corresponding eigenvector, respectively. Using these notations, we can write the optimal plane " + }, + { + "bbox": [ + 305, + 218, + 545, + 269 + ], + "type": "inline_equation", + "content": "\\hat{\\pmb{\\pi}} = [\\hat{\\pmb{n}}; \\hat{d}]" + }, + { + "bbox": [ + 305, + 218, + 545, + 269 + ], + "type": "text", + "content": " as" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 372, + 275, + 545, + 289 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 372, + 275, + 545, + 289 + ], + "spans": [ + { + "bbox": [ + 372, + 275, + 545, + 289 + ], + "type": "interline_equation", + "content": "\\hat {\\boldsymbol {n}} = \\boldsymbol {\\xi} _ {3} (\\mathbf {M}), \\hat {d} = - \\hat {\\boldsymbol {n}} ^ {T} \\bar {\\boldsymbol {p}}. \\tag {7}", + "image_path": "73260cb36a5be1ef151a734125cb84ebbcf26124fccd0d3f593abb4ac60141fe.jpg" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 306, + 295, + 527, + 308 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 295, + 527, + 308 + ], + "spans": [ + { + "bbox": [ + 306, + 295, + 527, + 308 + ], + "type": "text", + "content": "Furthermore, the cost of (5) at " + }, + { + "bbox": [ + 306, + 295, + 527, + 308 + ], + "type": "inline_equation", + "content": "\\hat{\\pi}" + }, + { + "bbox": [ + 306, + 295, + 527, + 308 + ], + "type": "text", + "content": " equals to " + }, + { + "bbox": [ + 306, + 295, + 527, + 308 + ], + "type": "inline_equation", + "content": "\\lambda_3(\\mathbf{M})" + }, + { + "bbox": [ + 306, + 295, + 527, + 308 + ], + "type": "text", + "content": ", i.e.," + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 315, + 314, + 545, + 347 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 315, + 314, + 545, + 347 + ], + "spans": [ + { + "bbox": [ + 315, + 314, + 545, + 347 + ], + "type": "interline_equation", + "content": "\\lambda_ {3} (\\mathbf {M}) = \\sum_ {i = 1} ^ {K} \\left(\\hat {\\boldsymbol {n}} \\boldsymbol {p} _ {i} + \\hat {d}\\right) ^ {2} = \\min _ {\\pi} \\sum_ {i = 1} ^ {K} \\left(\\boldsymbol {n} \\boldsymbol {p} _ {i} + d\\right) ^ {2}. \\tag {8}", + "image_path": "ca33749f4af9db15ae4b3b676986bc08c7e0819ddd0694a746b82048cc325fd9.jpg" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 306, + 352, + 542, + 364 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 352, + 542, + 364 + ], + "spans": [ + { + "bbox": [ + 306, + 352, + 542, + 364 + ], + "type": "text", + "content": "The above property will be used to eliminate planes in PA." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 306, + 370, + 412, + 383 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 370, + 412, + 383 + ], + "spans": [ + { + "bbox": [ + 306, + 370, + 412, + 383 + ], + "type": "text", + "content": "3.3. Plane Adjustment" + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 305, + 388, + 545, + 498 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 388, + 545, + 498 + ], + "spans": [ + { + "bbox": [ + 305, + 388, + 545, + 498 + ], + "type": "text", + "content": "Assume that there are " + }, + { + "bbox": [ + 305, + 388, + 545, + 498 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 305, + 388, + 545, + 498 + ], + "type": "text", + "content": " planes and " + }, + { + "bbox": [ + 305, + 388, + 545, + 498 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 305, + 388, + 545, + 498 + ], + "type": "text", + "content": " poses. According to section 3.1, the " + }, + { + "bbox": [ + 305, + 388, + 545, + 498 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 305, + 388, + 545, + 498 + ], + "type": "text", + "content": "th plane can be represented by a four-dimensional vector " + }, + { + "bbox": [ + 305, + 388, + 545, + 498 + ], + "type": "inline_equation", + "content": "\\pmb{\\pi}_i = [n_i;d_i]" + }, + { + "bbox": [ + 305, + 388, + 545, + 498 + ], + "type": "text", + "content": ". The " + }, + { + "bbox": [ + 305, + 388, + 545, + 498 + ], + "type": "inline_equation", + "content": "j" + }, + { + "bbox": [ + 305, + 388, + 545, + 498 + ], + "type": "text", + "content": "th pose is denoted as " + }, + { + "bbox": [ + 305, + 388, + 545, + 498 + ], + "type": "inline_equation", + "content": "\\pmb{x}_j" + }, + { + "bbox": [ + 305, + 388, + 545, + 498 + ], + "type": "text", + "content": ". The observation of " + }, + { + "bbox": [ + 305, + 388, + 545, + 498 + ], + "type": "inline_equation", + "content": "\\pmb{\\pi}_i" + }, + { + "bbox": [ + 305, + 388, + 545, + 498 + ], + "type": "text", + "content": " at " + }, + { + "bbox": [ + 305, + 388, + 545, + 498 + ], + "type": "inline_equation", + "content": "\\pmb{x}_j" + }, + { + "bbox": [ + 305, + 388, + 545, + 498 + ], + "type": "text", + "content": " is a set of " + }, + { + "bbox": [ + 305, + 388, + 545, + 498 + ], + "type": "inline_equation", + "content": "N_{ij}" + }, + { + "bbox": [ + 305, + 388, + 545, + 498 + ], + "type": "text", + "content": " points " + }, + { + "bbox": [ + 305, + 388, + 545, + 498 + ], + "type": "inline_equation", + "content": "\\mathbb{Q}_{ij} = \\{\\pmb{p}_{ijk} \\in \\mathbb{R}^3\\}_{k=1}^{N_{ij}}" + }, + { + "bbox": [ + 305, + 388, + 545, + 498 + ], + "type": "text", + "content": ". For a 3D point " + }, + { + "bbox": [ + 305, + 388, + 545, + 498 + ], + "type": "inline_equation", + "content": "\\pmb{p}_{ijk}" + }, + { + "bbox": [ + 305, + 388, + 545, + 498 + ], + "type": "text", + "content": ", we use " + }, + { + "bbox": [ + 305, + 388, + 545, + 498 + ], + "type": "inline_equation", + "content": "\\tilde{\\pmb{p}}_{ijk} = [\\pmb{p}_{ijk};1]" + }, + { + "bbox": [ + 305, + 388, + 545, + 498 + ], + "type": "text", + "content": " to represent the homogeneous coordinates of " + }, + { + "bbox": [ + 305, + 388, + 545, + 498 + ], + "type": "inline_equation", + "content": "\\pmb{p}_{ijk}" + }, + { + "bbox": [ + 305, + 388, + 545, + 498 + ], + "type": "text", + "content": ". Then, the transformation from the local coordinate system at " + }, + { + "bbox": [ + 305, + 388, + 545, + 498 + ], + "type": "inline_equation", + "content": "\\pmb{x}_j" + }, + { + "bbox": [ + 305, + 388, + 545, + 498 + ], + "type": "text", + "content": " to the global coordinate system can be represented as" + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 359, + 505, + 545, + 520 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 359, + 505, + 545, + 520 + ], + "spans": [ + { + "bbox": [ + 359, + 505, + 545, + 520 + ], + "type": "interline_equation", + "content": "\\boldsymbol {p} _ {i j k} ^ {g} = \\mathbf {R} _ {j} \\boldsymbol {p} _ {i j k} + \\boldsymbol {t} _ {j} = \\mathbf {T} _ {j} \\tilde {\\boldsymbol {p}} _ {i j k}, \\tag {9}", + "image_path": "171c7638ef705b2cbdf1185f52b70f0849006145951d2cccfc828bc7c012b35e.jpg" + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 305, + 525, + 544, + 548 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 525, + 544, + 548 + ], + "spans": [ + { + "bbox": [ + 305, + 525, + 544, + 548 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 525, + 544, + 548 + ], + "type": "inline_equation", + "content": "\\mathbf{T}_j" + }, + { + "bbox": [ + 305, + 525, + 544, + 548 + ], + "type": "text", + "content": " is defined in (1). Then the distance " + }, + { + "bbox": [ + 305, + 525, + 544, + 548 + ], + "type": "inline_equation", + "content": "d_{ijk}" + }, + { + "bbox": [ + 305, + 525, + 544, + 548 + ], + "type": "text", + "content": " from " + }, + { + "bbox": [ + 305, + 525, + 544, + 548 + ], + "type": "inline_equation", + "content": "\\pmb{p}_{ijk}" + }, + { + "bbox": [ + 305, + 525, + 544, + 548 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 305, + 525, + 544, + 548 + ], + "type": "inline_equation", + "content": "\\pi_i" + }, + { + "bbox": [ + 305, + 525, + 544, + 548 + ], + "type": "text", + "content": " has the form" + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 328, + 554, + 545, + 586 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 328, + 554, + 545, + 586 + ], + "spans": [ + { + "bbox": [ + 328, + 554, + 545, + 586 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} d _ {i j k} \\left(\\boldsymbol {\\pi} _ {i}, \\mathbf {x} _ {j}\\right) = \\boldsymbol {n} _ {i} ^ {T} \\left(\\mathbf {R} _ {j} \\boldsymbol {p} _ {i j k} + \\boldsymbol {t} _ {j}\\right) + d _ {i} \\tag {10} \\\\ = \\boldsymbol {n} _ {i} ^ {T} \\mathbf {T} _ {j} \\tilde {\\boldsymbol {p}} _ {i j k} + d _ {j} = \\boldsymbol {\\pi} _ {i} ^ {T} \\tilde {\\boldsymbol {p}} _ {i j k} ^ {g}. \\\\ \\end{array}", + "image_path": "7fdf534ca593827bb34f282c76f298b79b43ab63dc875facbb868697dadbd837.jpg" + } + ] + } + ], + "index": 26 + }, + { + "bbox": [ + 305, + 591, + 545, + 639 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 591, + 545, + 639 + ], + "spans": [ + { + "bbox": [ + 305, + 591, + 545, + 639 + ], + "type": "text", + "content": "The PA problem is to jointly adjust the " + }, + { + "bbox": [ + 305, + 591, + 545, + 639 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 305, + 591, + 545, + 639 + ], + "type": "text", + "content": " planes " + }, + { + "bbox": [ + 305, + 591, + 545, + 639 + ], + "type": "inline_equation", + "content": "\\{\\pi_i\\}" + }, + { + "bbox": [ + 305, + 591, + 545, + 639 + ], + "type": "text", + "content": " and the " + }, + { + "bbox": [ + 305, + 591, + 545, + 639 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 305, + 591, + 545, + 639 + ], + "type": "text", + "content": " sensor poses " + }, + { + "bbox": [ + 305, + 591, + 545, + 639 + ], + "type": "inline_equation", + "content": "\\{\\pmb{x}_j\\}" + }, + { + "bbox": [ + 305, + 591, + 545, + 639 + ], + "type": "text", + "content": " to minimize the sum of squared point-to-plane distances. Specifically, using (10), we can formulate the cost function of the PA problem as" + } + ] + } + ], + "index": 27 + }, + { + "bbox": [ + 307, + 654, + 572, + 713 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 307, + 654, + 572, + 713 + ], + "spans": [ + { + "bbox": [ + 307, + 654, + 572, + 713 + ], + "type": "interline_equation", + "content": "\\min _ {\\left\\{\\boldsymbol {\\pi} _ {i} \\right\\}, \\left\\{\\mathbf {x} _ {j} \\right\\}} \\sum_ {i = 1} ^ {M} \\underbrace {\\sum_ {j \\in o b s \\left(\\boldsymbol {\\pi} _ {i}\\right)} \\sum_ {k = 1} ^ {N _ {i j}} d _ {i j k} ^ {2} \\left(\\boldsymbol {\\pi} _ {i} , \\mathbf {x} _ {j}\\right)} _ {C _ {i} \\left(\\boldsymbol {\\pi} _ {i}, \\mathbb {X} _ {i}\\right), \\mathbb {X} _ {i} = \\left\\{\\boldsymbol {x} _ {j} \\mid j \\in o b s \\left(\\boldsymbol {\\pi} _ {i}\\right) \\right\\}} = \\min _ {\\left\\{\\boldsymbol {\\pi} _ {i} \\right\\}, \\left\\{\\boldsymbol {x} _ {j} \\right\\}} \\sum_ {i = 1} ^ {M} C _ {i} \\left(\\boldsymbol {\\pi} _ {i}, \\mathbb {X} _ {i}\\right). \\tag {11}", + "image_path": "88fc441c54266ab4afba69cc234859100e747580c5d92ed1452926a67c9e04c5.jpg" + } + ] + } + ], + "index": 28 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "13115" + } + ] + } + ], + "index": 29 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 287, + 120 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 287, + 120 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 287, + 120 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 72, + 287, + 120 + ], + "type": "inline_equation", + "content": "obs(\\pi_i)" + }, + { + "bbox": [ + 47, + 72, + 287, + 120 + ], + "type": "text", + "content": " represents the indexes of poses where " + }, + { + "bbox": [ + 47, + 72, + 287, + 120 + ], + "type": "inline_equation", + "content": "\\pi_i" + }, + { + "bbox": [ + 47, + 72, + 287, + 120 + ], + "type": "text", + "content": " can be observed, and " + }, + { + "bbox": [ + 47, + 72, + 287, + 120 + ], + "type": "inline_equation", + "content": "C_i(\\pi_i, \\mathbb{X}_i)" + }, + { + "bbox": [ + 47, + 72, + 287, + 120 + ], + "type": "text", + "content": " accumulates the errors from " + }, + { + "bbox": [ + 47, + 72, + 287, + 120 + ], + "type": "inline_equation", + "content": "N_i = \\sum_{j \\in obs(\\pi_i)} N_{ij}" + }, + { + "bbox": [ + 47, + 72, + 287, + 120 + ], + "type": "text", + "content": " points captured at the poses in " + }, + { + "bbox": [ + 47, + 72, + 287, + 120 + ], + "type": "inline_equation", + "content": "\\mathbb{X}_i" + }, + { + "bbox": [ + 47, + 72, + 287, + 120 + ], + "type": "text", + "content": ". According to (6) and (9), we get" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 97, + 128, + 287, + 152 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 97, + 128, + 287, + 152 + ], + "spans": [ + { + "bbox": [ + 97, + 128, + 287, + 152 + ], + "type": "interline_equation", + "content": "\\mathbf {M} _ {i} \\left(\\mathbb {X} _ {i}\\right) = \\sum_ {j \\in o b s \\left(\\boldsymbol {\\pi} _ {i}\\right)} \\mathbf {S} _ {i j} - N _ {i} \\bar {\\boldsymbol {p}} _ {i} \\bar {\\boldsymbol {p}} _ {i} ^ {T}, \\tag {12}", + "image_path": "7921fa33110a12e1aca841d3192b6ba89f7bb6e7ab95ab64fe1ced681c601b28.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 160, + 287, + 222 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 160, + 287, + 222 + ], + "spans": [ + { + "bbox": [ + 47, + 160, + 287, + 222 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 160, + 287, + 222 + ], + "type": "inline_equation", + "content": "\\bar{\\pmb{p}}_i = \\frac{1}{N_i}\\sum_{j\\in obs(\\pmb{\\pi}_i)}\\sum_{k = 1}^{N_{ij}}\\pmb{p}_{ijk}^g" + }, + { + "bbox": [ + 47, + 160, + 287, + 222 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 160, + 287, + 222 + ], + "type": "inline_equation", + "content": "\\mathbf{S}_{ij} = \\sum_{k = 1}^{N_{ij}}\\pmb{p}_{ijk}^g\\left(\\pmb{p}_{ijk}^g\\right)^T" + }, + { + "bbox": [ + 47, + 160, + 287, + 222 + ], + "type": "text", + "content": ". Here the elements in " + }, + { + "bbox": [ + 47, + 160, + 287, + 222 + ], + "type": "inline_equation", + "content": "\\mathbf{M}_i" + }, + { + "bbox": [ + 47, + 160, + 287, + 222 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 160, + 287, + 222 + ], + "type": "inline_equation", + "content": "\\mathbf{S}_{ij}" + }, + { + "bbox": [ + 47, + 160, + 287, + 222 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 160, + 287, + 222 + ], + "type": "inline_equation", + "content": "\\bar{\\pmb{p}}_i" + }, + { + "bbox": [ + 47, + 160, + 287, + 222 + ], + "type": "text", + "content": " in (12) are all functions of the poses in " + }, + { + "bbox": [ + 47, + 160, + 287, + 222 + ], + "type": "inline_equation", + "content": "\\mathbb{X}_i" + }, + { + "bbox": [ + 47, + 160, + 287, + 222 + ], + "type": "text", + "content": ". Substituting " + }, + { + "bbox": [ + 47, + 160, + 287, + 222 + ], + "type": "inline_equation", + "content": "\\pmb{p}_{ijk}^g" + }, + { + "bbox": [ + 47, + 160, + 287, + 222 + ], + "type": "text", + "content": " in (9) into " + }, + { + "bbox": [ + 47, + 160, + 287, + 222 + ], + "type": "inline_equation", + "content": "\\mathbf{S}_{ij}" + }, + { + "bbox": [ + 47, + 160, + 287, + 222 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 160, + 287, + 222 + ], + "type": "inline_equation", + "content": "\\bar{\\pmb{p}}_i" + }, + { + "bbox": [ + 47, + 160, + 287, + 222 + ], + "type": "text", + "content": " in (12), we have" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 55, + 224, + 286, + 320 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 55, + 224, + 286, + 320 + ], + "spans": [ + { + "bbox": [ + 55, + 224, + 286, + 320 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\mathbf {S} _ {i j} = \\mathbf {T} _ {j} \\underbrace {\\sum_ {k = 1} ^ {N _ {i j}} \\tilde {\\boldsymbol {p}} _ {i j k} \\tilde {\\boldsymbol {p}} _ {i j k} ^ {T}} _ {\\mathbf {U} _ {i j}} \\mathbf {T} _ {j} ^ {T} = \\mathbf {T} _ {j} \\mathbf {U} _ {i j} \\mathbf {T} _ {j} ^ {T}, \\\\ \\bar {\\boldsymbol {p}} _ {i} = \\frac {1}{N _ {i}} \\sum_ {j \\in o b s (\\boldsymbol {\\pi} _ {i})} \\mathbf {T} _ {j} \\underbrace {\\sum_ {k = 1} ^ {N _ {i j}} \\tilde {\\boldsymbol {p}} _ {i j k}} _ {\\tilde {\\boldsymbol {p}} _ {i j}} = \\frac {1}{N _ {i}} \\sum_ {j \\in o b s (\\boldsymbol {\\pi} _ {i})} \\mathbf {T} _ {j} \\tilde {\\boldsymbol {p}} _ {i j}. \\\\ \\end{array}", + "image_path": "0f6609012c2d5eacbd0e62c89a59286d860d060852e7a85393ec1526776c2a51.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 327, + 287, + 351 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 327, + 287, + 351 + ], + "spans": [ + { + "bbox": [ + 47, + 327, + 287, + 351 + ], + "type": "text", + "content": "Here " + }, + { + "bbox": [ + 47, + 327, + 287, + 351 + ], + "type": "inline_equation", + "content": "\\mathbf{U}_{ij}" + }, + { + "bbox": [ + 47, + 327, + 287, + 351 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 327, + 287, + 351 + ], + "type": "inline_equation", + "content": "\\tilde{\\boldsymbol{p}}_{ij}" + }, + { + "bbox": [ + 47, + 327, + 287, + 351 + ], + "type": "text", + "content": " in (13) are constants. We only need to compute them once, and reuse them in the iteration." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 352, + 287, + 424 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 352, + 287, + 424 + ], + "spans": [ + { + "bbox": [ + 47, + 352, + 287, + 424 + ], + "type": "text", + "content": "According to (7), given poses in " + }, + { + "bbox": [ + 47, + 352, + 287, + 424 + ], + "type": "inline_equation", + "content": "\\mathbb{X}_i" + }, + { + "bbox": [ + 47, + 352, + 287, + 424 + ], + "type": "text", + "content": ", the optimal solution for " + }, + { + "bbox": [ + 47, + 352, + 287, + 424 + ], + "type": "inline_equation", + "content": "\\pi_i" + }, + { + "bbox": [ + 47, + 352, + 287, + 424 + ], + "type": "text", + "content": " has a closed-form expression " + }, + { + "bbox": [ + 47, + 352, + 287, + 424 + ], + "type": "inline_equation", + "content": "\\hat{\\pi}_i = [\\hat{n}_i; \\hat{d}_i]" + }, + { + "bbox": [ + 47, + 352, + 287, + 424 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 47, + 352, + 287, + 424 + ], + "type": "inline_equation", + "content": "\\hat{n}_i = \\xi_3(\\mathbf{M}_i(\\mathbb{X}_i))" + }, + { + "bbox": [ + 47, + 352, + 287, + 424 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 352, + 287, + 424 + ], + "type": "inline_equation", + "content": "\\hat{d}_i = -\\hat{n}\\bar{p}_i" + }, + { + "bbox": [ + 47, + 352, + 287, + 424 + ], + "type": "text", + "content": ". As " + }, + { + "bbox": [ + 47, + 352, + 287, + 424 + ], + "type": "inline_equation", + "content": "\\mathbf{M}_i" + }, + { + "bbox": [ + 47, + 352, + 287, + 424 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 352, + 287, + 424 + ], + "type": "inline_equation", + "content": "\\bar{p}_i" + }, + { + "bbox": [ + 47, + 352, + 287, + 424 + ], + "type": "text", + "content": " are functions of the poses in " + }, + { + "bbox": [ + 47, + 352, + 287, + 424 + ], + "type": "inline_equation", + "content": "\\mathbb{X}_i" + }, + { + "bbox": [ + 47, + 352, + 287, + 424 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 352, + 287, + 424 + ], + "type": "inline_equation", + "content": "\\hat{\\pi}_i" + }, + { + "bbox": [ + 47, + 352, + 287, + 424 + ], + "type": "text", + "content": " is also a function of the poses in " + }, + { + "bbox": [ + 47, + 352, + 287, + 424 + ], + "type": "inline_equation", + "content": "\\mathbb{X}_i" + }, + { + "bbox": [ + 47, + 352, + 287, + 424 + ], + "type": "text", + "content": ". That is to say " + }, + { + "bbox": [ + 47, + 352, + 287, + 424 + ], + "type": "inline_equation", + "content": "\\hat{\\pi}_i" + }, + { + "bbox": [ + 47, + 352, + 287, + 424 + ], + "type": "text", + "content": " is completely determined by the poses in " + }, + { + "bbox": [ + 47, + 352, + 287, + 424 + ], + "type": "inline_equation", + "content": "\\mathbb{X}_i" + }, + { + "bbox": [ + 47, + 352, + 287, + 424 + ], + "type": "text", + "content": ". To simplify the notation, let us define" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 115, + 434, + 287, + 447 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 115, + 434, + 287, + 447 + ], + "spans": [ + { + "bbox": [ + 115, + 434, + 287, + 447 + ], + "type": "interline_equation", + "content": "\\lambda_ {i, 3} (\\mathbb {X} _ {i}) = \\lambda_ {3} \\left(\\mathbf {M} _ {i} (\\mathbb {X} _ {i})\\right), \\tag {14}", + "image_path": "4584d52a626db17d8c219d58b89df879035a4d79168e22b2842c21c2e6da38ae.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 456, + 260, + 468 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 456, + 260, + 468 + ], + "spans": [ + { + "bbox": [ + 47, + 456, + 260, + 468 + ], + "type": "text", + "content": "which represents the smallest eigenvalue of " + }, + { + "bbox": [ + 47, + 456, + 260, + 468 + ], + "type": "inline_equation", + "content": "\\mathbf{M}_i(\\mathbb{X}_i)" + }, + { + "bbox": [ + 47, + 456, + 260, + 468 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 469, + 287, + 493 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 469, + 287, + 493 + ], + "spans": [ + { + "bbox": [ + 47, + 469, + 287, + 493 + ], + "type": "text", + "content": "Substituting the optimal plane estimation " + }, + { + "bbox": [ + 47, + 469, + 287, + 493 + ], + "type": "inline_equation", + "content": "\\hat{\\pi}_i" + }, + { + "bbox": [ + 47, + 469, + 287, + 493 + ], + "type": "text", + "content": " into " + }, + { + "bbox": [ + 47, + 469, + 287, + 493 + ], + "type": "inline_equation", + "content": "C_i(\\pi_i, \\mathbb{X}_i)" + }, + { + "bbox": [ + 47, + 469, + 287, + 493 + ], + "type": "text", + "content": " in (11) and using (8), we have" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 117, + 502, + 287, + 516 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 117, + 502, + 287, + 516 + ], + "spans": [ + { + "bbox": [ + 117, + 502, + 287, + 516 + ], + "type": "interline_equation", + "content": "\\lambda_ {i, 3} (\\mathbb {X} _ {i}) = C _ {i} \\left(\\hat {\\pi} _ {i}, \\mathbb {X} _ {i}\\right). \\tag {15}", + "image_path": "6e4f4cba2585ba9dc38aac4f5ec74fbe80715c6ad232a9e02c08dd2d41cfbef3.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 525, + 272, + 537 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 525, + 272, + 537 + ], + "spans": [ + { + "bbox": [ + 47, + 525, + 272, + 537 + ], + "type": "text", + "content": "Using (15), we can formulate the PA problem in (11) as" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 88, + 540, + 287, + 572 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 88, + 540, + 287, + 572 + ], + "spans": [ + { + "bbox": [ + 88, + 540, + 287, + 572 + ], + "type": "interline_equation", + "content": "\\left\\{\\hat {\\mathbf {x}} _ {j} \\right\\} = \\arg \\min _ {\\left\\{\\mathbf {X} _ {j} \\right\\}} \\boldsymbol {\\tau}, \\boldsymbol {\\tau} = \\sum_ {i = 1} ^ {M} \\lambda_ {i, 3} (\\mathbb {X} _ {i}). \\tag {16}", + "image_path": "0c0720b28a668b5c06505f6f086a1d9624e35cc2e6f753874eedddbad2856800.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 47, + 582, + 214, + 593 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 582, + 214, + 593 + ], + "spans": [ + { + "bbox": [ + 47, + 582, + 214, + 593 + ], + "type": "text", + "content": "Table 1 summarizes the notations for PA." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 46, + 594, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 594, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 287, + 713 + ], + "type": "text", + "content": "The cost function (16) only depends on poses, which significantly reduces the number of variables. However, as it is the sum of squared point-to-plane distances, we cannot apply the Gauss-Newton-based methods to minimize it, where the Jacobian matrix of residuals are required. Here we adopt the Newton's method to solve it. The crux for applying the Newton's method to minimize (16) is how to compute the gradient and the Hessian matrix of (16) efficiently. In the following sections, we provide a closed-form solution for them. Note that we can assign a weight to each point to" + } + ] + } + ], + "index": 13 + }, + { + "type": "table", + "bbox": [ + 306, + 71, + 545, + 203 + ], + "blocks": [ + { + "bbox": [ + 306, + 71, + 545, + 203 + ], + "lines": [ + { + "bbox": [ + 306, + 71, + 545, + 203 + ], + "spans": [ + { + "bbox": [ + 306, + 71, + 545, + 203 + ], + "type": "table", + "html": "
NotationDescription
πiTheith plane.
obs(πi)The set of indexes of poses which can see πi.
XiThe set of poses which can see πi.
MiThe scatter matrix for πi.
λ3,iThe smallest eigenvalue ofMi.
xj, xkThe jth and kth poses.
xjm, xknThe mth and nth elements of xj and xk.
PjThe set of planes that are visible to xj.
PjkThe set of planes that are visible to xj and xk.
", + "image_path": "112f1451ef0d645652ef80f3cb4f37e73f2fd5a13b569940bae9159cb67ff95a.jpg" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "table_body" + } + ], + "index": 14 + }, + { + "bbox": [ + 375, + 211, + 476, + 221 + ], + "lines": [ + { + "bbox": [ + 375, + 211, + 476, + 221 + ], + "spans": [ + { + "bbox": [ + 375, + 211, + 476, + 221 + ], + "type": "text", + "content": "Table 1. Table of notations." + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 305, + 242, + 545, + 302 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 242, + 545, + 302 + ], + "spans": [ + { + "bbox": [ + 305, + 242, + 545, + 302 + ], + "type": "text", + "content": "punish outliers, which also has a close-form solution for planes using the weighted PCA. Our algorithm can be extended to this situation. To simplify the notation, we omit the variables of functions in the following description (e.g., " + }, + { + "bbox": [ + 305, + 242, + 545, + 302 + ], + "type": "inline_equation", + "content": "\\lambda_{i,3}(\\mathbb{X}_i)\\to \\lambda_{i,3})" + }, + { + "bbox": [ + 305, + 242, + 545, + 302 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 305, + 312, + 529, + 325 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 312, + 529, + 325 + ], + "spans": [ + { + "bbox": [ + 305, + 312, + 529, + 325 + ], + "type": "text", + "content": "4. Newton's Iteration for Plane Adjustment" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 305, + 332, + 545, + 403 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 332, + 545, + 403 + ], + "spans": [ + { + "bbox": [ + 305, + 332, + 545, + 403 + ], + "type": "text", + "content": "Let us denote the gradient and the Hessian matrix of " + }, + { + "bbox": [ + 305, + 332, + 545, + 403 + ], + "type": "inline_equation", + "content": "\\tau" + }, + { + "bbox": [ + 305, + 332, + 545, + 403 + ], + "type": "text", + "content": " in (16) as " + }, + { + "bbox": [ + 305, + 332, + 545, + 403 + ], + "type": "inline_equation", + "content": "\\pmb{g}" + }, + { + "bbox": [ + 305, + 332, + 545, + 403 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 332, + 545, + 403 + ], + "type": "inline_equation", + "content": "\\mathbf{H}" + }, + { + "bbox": [ + 305, + 332, + 545, + 403 + ], + "type": "text", + "content": ", and denote the 6-dimensional gradient vector for " + }, + { + "bbox": [ + 305, + 332, + 545, + 403 + ], + "type": "inline_equation", + "content": "\\pmb{x}_j" + }, + { + "bbox": [ + 305, + 332, + 545, + 403 + ], + "type": "text", + "content": " as " + }, + { + "bbox": [ + 305, + 332, + 545, + 403 + ], + "type": "inline_equation", + "content": "\\pmb{g}_j" + }, + { + "bbox": [ + 305, + 332, + 545, + 403 + ], + "type": "text", + "content": " and the " + }, + { + "bbox": [ + 305, + 332, + 545, + 403 + ], + "type": "inline_equation", + "content": "6\\times 6" + }, + { + "bbox": [ + 305, + 332, + 545, + 403 + ], + "type": "text", + "content": " Hessian matrix block for " + }, + { + "bbox": [ + 305, + 332, + 545, + 403 + ], + "type": "inline_equation", + "content": "\\pmb{x}_j" + }, + { + "bbox": [ + 305, + 332, + 545, + 403 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 332, + 545, + 403 + ], + "type": "inline_equation", + "content": "\\pmb{x}_k" + }, + { + "bbox": [ + 305, + 332, + 545, + 403 + ], + "type": "text", + "content": " as " + }, + { + "bbox": [ + 305, + 332, + 545, + 403 + ], + "type": "inline_equation", + "content": "\\mathbf{H}_{jk}" + }, + { + "bbox": [ + 305, + 332, + 545, + 403 + ], + "type": "text", + "content": " (note that here " + }, + { + "bbox": [ + 305, + 332, + 545, + 403 + ], + "type": "inline_equation", + "content": "j" + }, + { + "bbox": [ + 305, + 332, + 545, + 403 + ], + "type": "text", + "content": " can equal to " + }, + { + "bbox": [ + 305, + 332, + 545, + 403 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 305, + 332, + 545, + 403 + ], + "type": "text", + "content": "). Then " + }, + { + "bbox": [ + 305, + 332, + 545, + 403 + ], + "type": "inline_equation", + "content": "\\pmb{g}" + }, + { + "bbox": [ + 305, + 332, + 545, + 403 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 332, + 545, + 403 + ], + "type": "inline_equation", + "content": "\\mathbf{H}" + }, + { + "bbox": [ + 305, + 332, + 545, + 403 + ], + "type": "text", + "content": " can be written in the block form as " + }, + { + "bbox": [ + 305, + 332, + 545, + 403 + ], + "type": "inline_equation", + "content": "\\pmb{g} = (\\pmb{g}_j)\\in \\mathbb{R}^{6N}" + }, + { + "bbox": [ + 305, + 332, + 545, + 403 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 332, + 545, + 403 + ], + "type": "inline_equation", + "content": "\\mathbf{H} = (\\mathbf{H}_{jk})\\in \\mathbb{R}^{6N\\times 6N}" + }, + { + "bbox": [ + 305, + 332, + 545, + 403 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 305, + 403, + 545, + 429 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 403, + 545, + 429 + ], + "spans": [ + { + "bbox": [ + 305, + 403, + 545, + 429 + ], + "type": "text", + "content": "The " + }, + { + "bbox": [ + 305, + 403, + 545, + 429 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 305, + 403, + 545, + 429 + ], + "type": "text", + "content": "th plane " + }, + { + "bbox": [ + 305, + 403, + 545, + 429 + ], + "type": "inline_equation", + "content": "\\pi_i" + }, + { + "bbox": [ + 305, + 403, + 545, + 429 + ], + "type": "text", + "content": " is observed by the poses in " + }, + { + "bbox": [ + 305, + 403, + 545, + 429 + ], + "type": "inline_equation", + "content": "\\mathbb{X}_i" + }, + { + "bbox": [ + 305, + 403, + 545, + 429 + ], + "type": "text", + "content": ". Assume " + }, + { + "bbox": [ + 305, + 403, + 545, + 429 + ], + "type": "inline_equation", + "content": "\\boldsymbol{x}_j \\in \\mathbb{X}_i" + }, + { + "bbox": [ + 305, + 403, + 545, + 429 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 403, + 545, + 429 + ], + "type": "inline_equation", + "content": "\\boldsymbol{x}_k \\in \\mathbb{X}_i" + }, + { + "bbox": [ + 305, + 403, + 545, + 429 + ], + "type": "text", + "content": ". Let us define" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 361, + 435, + 545, + 462 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 361, + 435, + 545, + 462 + ], + "spans": [ + { + "bbox": [ + 361, + 435, + 545, + 462 + ], + "type": "interline_equation", + "content": "\\boldsymbol {g} _ {j} ^ {i} = \\frac {\\partial \\lambda_ {i , 3}}{\\partial \\boldsymbol {x} _ {j}}, \\mathbf {H} _ {j k} ^ {i} = \\frac {\\partial^ {2} \\lambda_ {i , 3}}{\\partial \\boldsymbol {x} _ {j} \\partial \\boldsymbol {x} _ {k}}. \\tag {17}", + "image_path": "e31af1300179263adf3ba00d3228c10a7b49df023bcb4ca5e714dd492621c1b5.jpg" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 306, + 468, + 418, + 479 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 468, + 418, + 479 + ], + "spans": [ + { + "bbox": [ + 306, + 468, + 418, + 479 + ], + "type": "text", + "content": "According to (16), we have" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 358, + 487, + 545, + 514 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 358, + 487, + 545, + 514 + ], + "spans": [ + { + "bbox": [ + 358, + 487, + 545, + 514 + ], + "type": "interline_equation", + "content": "\\boldsymbol {g} _ {j} = \\sum_ {i \\in \\mathbb {P} _ {j}} \\boldsymbol {g} _ {j} ^ {i}, \\quad \\mathrm {H} _ {j k} = \\sum_ {i \\in \\mathbb {P} _ {j k}} \\mathrm {H} _ {j k} ^ {i}, \\tag {18}", + "image_path": "ed8693395f39ba4ee2cefa426a771a1e31438b4c7b8323e30f4877aeb9816bd9.jpg" + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 305, + 520, + 545, + 570 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 520, + 545, + 570 + ], + "spans": [ + { + "bbox": [ + 305, + 520, + 545, + 570 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 520, + 545, + 570 + ], + "type": "inline_equation", + "content": "\\mathbb{P}_j" + }, + { + "bbox": [ + 305, + 520, + 545, + 570 + ], + "type": "text", + "content": " is the set of planes observed by " + }, + { + "bbox": [ + 305, + 520, + 545, + 570 + ], + "type": "inline_equation", + "content": "\\pmb{x}_j" + }, + { + "bbox": [ + 305, + 520, + 545, + 570 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 305, + 520, + 545, + 570 + ], + "type": "inline_equation", + "content": "\\mathbb{P}_{jk}" + }, + { + "bbox": [ + 305, + 520, + 545, + 570 + ], + "type": "text", + "content": " is the set of planes observed by " + }, + { + "bbox": [ + 305, + 520, + 545, + 570 + ], + "type": "inline_equation", + "content": "\\pmb{x}_j" + }, + { + "bbox": [ + 305, + 520, + 545, + 570 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 520, + 545, + 570 + ], + "type": "inline_equation", + "content": "\\pmb{x}_k" + }, + { + "bbox": [ + 305, + 520, + 545, + 570 + ], + "type": "text", + "content": " simultaneously. If " + }, + { + "bbox": [ + 305, + 520, + 545, + 570 + ], + "type": "inline_equation", + "content": "j = k" + }, + { + "bbox": [ + 305, + 520, + 545, + 570 + ], + "type": "text", + "content": ", here " + }, + { + "bbox": [ + 305, + 520, + 545, + 570 + ], + "type": "inline_equation", + "content": "\\mathbb{P}_{jk}" + }, + { + "bbox": [ + 305, + 520, + 545, + 570 + ], + "type": "text", + "content": " equals to " + }, + { + "bbox": [ + 305, + 520, + 545, + 570 + ], + "type": "inline_equation", + "content": "\\mathbb{P}_j" + }, + { + "bbox": [ + 305, + 520, + 545, + 570 + ], + "type": "text", + "content": ". From (18), we know that the key point to get " + }, + { + "bbox": [ + 305, + 520, + 545, + 570 + ], + "type": "inline_equation", + "content": "\\pmb{g}" + }, + { + "bbox": [ + 305, + 520, + 545, + 570 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 520, + 545, + 570 + ], + "type": "inline_equation", + "content": "\\mathbf{H}" + }, + { + "bbox": [ + 305, + 520, + 545, + 570 + ], + "type": "text", + "content": " is to compute " + }, + { + "bbox": [ + 305, + 520, + 545, + 570 + ], + "type": "inline_equation", + "content": "\\pmb{g}_j^i" + }, + { + "bbox": [ + 305, + 520, + 545, + 570 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 520, + 545, + 570 + ], + "type": "inline_equation", + "content": "\\mathbf{H}_{jk}^i" + }, + { + "bbox": [ + 305, + 520, + 545, + 570 + ], + "type": "text", + "content": " in (17)." + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 306, + 574, + 481, + 586 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 574, + 481, + 586 + ], + "spans": [ + { + "bbox": [ + 306, + 574, + 481, + 586 + ], + "type": "text", + "content": "4.1. Partial Derivatives of Eigenvalue" + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 305, + 593, + 545, + 646 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 593, + 545, + 646 + ], + "spans": [ + { + "bbox": [ + 305, + 593, + 545, + 646 + ], + "type": "text", + "content": "According to (15), " + }, + { + "bbox": [ + 305, + 593, + 545, + 646 + ], + "type": "inline_equation", + "content": "\\lambda_{i,3}" + }, + { + "bbox": [ + 305, + 593, + 545, + 646 + ], + "type": "text", + "content": " is a function of poses in " + }, + { + "bbox": [ + 305, + 593, + 545, + 646 + ], + "type": "inline_equation", + "content": "\\mathbb{X}_i" + }, + { + "bbox": [ + 305, + 593, + 545, + 646 + ], + "type": "text", + "content": ". Assume that " + }, + { + "bbox": [ + 305, + 593, + 545, + 646 + ], + "type": "inline_equation", + "content": "x_{jm}" + }, + { + "bbox": [ + 305, + 593, + 545, + 646 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 593, + 545, + 646 + ], + "type": "inline_equation", + "content": "x_{kn}" + }, + { + "bbox": [ + 305, + 593, + 545, + 646 + ], + "type": "text", + "content": " are the " + }, + { + "bbox": [ + 305, + 593, + 545, + 646 + ], + "type": "inline_equation", + "content": "m" + }, + { + "bbox": [ + 305, + 593, + 545, + 646 + ], + "type": "text", + "content": "th and " + }, + { + "bbox": [ + 305, + 593, + 545, + 646 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 305, + 593, + 545, + 646 + ], + "type": "text", + "content": "th elements of " + }, + { + "bbox": [ + 305, + 593, + 545, + 646 + ], + "type": "inline_equation", + "content": "\\pmb{x}_j" + }, + { + "bbox": [ + 305, + 593, + 545, + 646 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 593, + 545, + 646 + ], + "type": "inline_equation", + "content": "\\pmb{x}_k" + }, + { + "bbox": [ + 305, + 593, + 545, + 646 + ], + "type": "text", + "content": ", respectively. We consider the first- and second-order partial derivation " + }, + { + "bbox": [ + 305, + 593, + 545, + 646 + ], + "type": "inline_equation", + "content": "\\frac{\\partial\\lambda_{i,3}}{\\partial x_{jm}}" + }, + { + "bbox": [ + 305, + 593, + 545, + 646 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 593, + 545, + 646 + ], + "type": "inline_equation", + "content": "\\frac{\\partial^2\\lambda_{i,3}}{\\partial x_{jm}\\partial x_{kn}}" + }, + { + "bbox": [ + 305, + 593, + 545, + 646 + ], + "type": "text", + "content": ", respectively." + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 305, + 646, + 545, + 693 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 646, + 545, + 693 + ], + "spans": [ + { + "bbox": [ + 305, + 646, + 545, + 693 + ], + "type": "inline_equation", + "content": "\\lambda_{i,3}" + }, + { + "bbox": [ + 305, + 646, + 545, + 693 + ], + "type": "text", + "content": " is a root of the equation " + }, + { + "bbox": [ + 305, + 646, + 545, + 693 + ], + "type": "inline_equation", + "content": "|\\mathbf{M}_i(\\mathbb{X}_i) - \\lambda_i\\mathbf{I}_3| = 0" + }, + { + "bbox": [ + 305, + 646, + 545, + 693 + ], + "type": "text", + "content": " where " + }, + { + "bbox": [ + 305, + 646, + 545, + 693 + ], + "type": "inline_equation", + "content": "|\\cdot |" + }, + { + "bbox": [ + 305, + 646, + 545, + 693 + ], + "type": "text", + "content": " denotes the determinant of a matrix. Assume " + }, + { + "bbox": [ + 305, + 646, + 545, + 693 + ], + "type": "inline_equation", + "content": "m_{ef}" + }, + { + "bbox": [ + 305, + 646, + 545, + 693 + ], + "type": "text", + "content": " is the " + }, + { + "bbox": [ + 305, + 646, + 545, + 693 + ], + "type": "inline_equation", + "content": "e" + }, + { + "bbox": [ + 305, + 646, + 545, + 693 + ], + "type": "text", + "content": "th row " + }, + { + "bbox": [ + 305, + 646, + 545, + 693 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 305, + 646, + 545, + 693 + ], + "type": "text", + "content": "th column term of " + }, + { + "bbox": [ + 305, + 646, + 545, + 693 + ], + "type": "inline_equation", + "content": "\\mathbf{M}_i(\\mathbb{X}_i)" + }, + { + "bbox": [ + 305, + 646, + 545, + 693 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 305, + 646, + 545, + 693 + ], + "type": "inline_equation", + "content": "|\\mathbf{M}_i(\\mathbb{X}_i) - \\lambda_i\\mathbf{I}_3| = 0" + }, + { + "bbox": [ + 305, + 646, + 545, + 693 + ], + "type": "text", + "content": " is a cubic equation with the following form" + } + ] + } + ], + "index": 26 + }, + { + "bbox": [ + 356, + 700, + 545, + 715 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 356, + 700, + 545, + 715 + ], + "spans": [ + { + "bbox": [ + 356, + 700, + 545, + 715 + ], + "type": "interline_equation", + "content": "- \\lambda_ {i, 3} ^ {3} + a _ {i} \\lambda_ {i, 3} ^ {2} + b _ {i} \\lambda_ {i, 3} + c _ {i} = 0, \\tag {19}", + "image_path": "3744264c8193aeb8f82eed3d345e94628eb9298aaf8a74d40eba6e84976abce6.jpg" + } + ] + } + ], + "index": 27 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "13116" + } + ] + } + ], + "index": 28 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 71, + 289, + 196 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 71, + 289, + 196 + ], + "spans": [ + { + "bbox": [ + 47, + 71, + 289, + 196 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 71, + 289, + 196 + ], + "type": "inline_equation", + "content": "a_{i} = m_{11} + m_{22} + m_{33}, b_{i} = m_{12}^{2} + m_{13}^{2} + m_{23}^{2} - m_{11}m_{22} - m_{11}m_{33} - m_{22}m_{33}" + }, + { + "bbox": [ + 47, + 71, + 289, + 196 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 47, + 71, + 289, + 196 + ], + "type": "inline_equation", + "content": "c_{i} = -m_{33}m_{12}^{2} + 2m_{12}m_{13}m_{23} - m_{22}m_{13}^{2} - m_{11}m_{23}^{2} + m_{11}m_{22}m_{33}" + }, + { + "bbox": [ + 47, + 71, + 289, + 196 + ], + "type": "text", + "content": ". Here " + }, + { + "bbox": [ + 47, + 71, + 289, + 196 + ], + "type": "inline_equation", + "content": "a_{i}, b_{i}" + }, + { + "bbox": [ + 47, + 71, + 289, + 196 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 71, + 289, + 196 + ], + "type": "inline_equation", + "content": "c_{i}" + }, + { + "bbox": [ + 47, + 71, + 289, + 196 + ], + "type": "text", + "content": " are all functions of the poses in " + }, + { + "bbox": [ + 47, + 71, + 289, + 196 + ], + "type": "inline_equation", + "content": "\\mathbb{X}_i" + }, + { + "bbox": [ + 47, + 71, + 289, + 196 + ], + "type": "text", + "content": ". It is known that the root of a cubic equation has a closed form. One solution to compute " + }, + { + "bbox": [ + 47, + 71, + 289, + 196 + ], + "type": "inline_equation", + "content": "\\frac{\\partial\\lambda_{i,3}}{\\partial x_{jm}}" + }, + { + "bbox": [ + 47, + 71, + 289, + 196 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 71, + 289, + 196 + ], + "type": "inline_equation", + "content": "\\frac{\\partial^2\\lambda_{i,3}}{\\partial x_{jm}\\partial x_{kn}}" + }, + { + "bbox": [ + 47, + 71, + 289, + 196 + ], + "type": "text", + "content": " is to directly differentiate the root. However, the formula of the root is too complicated. Here we introduce a simple way to compute them. Briefly, we employ the implicit function theorem [15] to compute them. Let us define" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 54, + 201, + 287, + 251 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 54, + 201, + 287, + 251 + ], + "spans": [ + { + "bbox": [ + 54, + 201, + 287, + 251 + ], + "type": "interline_equation", + "content": "\\chi_ {i} = \\left[ \\begin{array}{l} \\lambda_ {i, 3} ^ {2} \\\\ \\lambda_ {i, 3} \\\\ 1 \\end{array} \\right], \\eta_ {i} = \\left[ \\begin{array}{l} a _ {i} \\\\ b _ {i} \\\\ c _ {i} \\end{array} \\right] \\kappa_ {i} = \\left[ \\begin{array}{l} - 3 \\\\ 2 a _ {i} \\\\ b _ {i} \\end{array} \\right], \\delta_ {j m} ^ {i} = \\frac {\\partial \\eta_ {i}}{\\partial x _ {j m}}. \\tag {20}", + "image_path": "16eb1aa4c3612ae9c3ce73d55ec939e38c8035690a0556d6d89e86e3c4d60c86.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 251, + 287, + 291 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 251, + 287, + 291 + ], + "spans": [ + { + "bbox": [ + 47, + 251, + 287, + 291 + ], + "type": "text", + "content": "Using the above notations, we present " + }, + { + "bbox": [ + 47, + 251, + 287, + 291 + ], + "type": "inline_equation", + "content": "\\frac{\\partial\\lambda_{i,3}}{\\partial x_{jm}}" + }, + { + "bbox": [ + 47, + 251, + 287, + 291 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 251, + 287, + 291 + ], + "type": "inline_equation", + "content": "\\frac{\\partial^2\\lambda_{i,3}}{\\partial x_{jm}\\partial x_{kn}}" + }, + { + "bbox": [ + 47, + 251, + 287, + 291 + ], + "type": "text", + "content": " in Lemma 1 and 2. The proofs of the following lemmas and theorems are in the supplementary material." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 297, + 241, + 309 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 297, + 241, + 309 + ], + "spans": [ + { + "bbox": [ + 47, + 297, + 241, + 309 + ], + "type": "text", + "content": "Lemma 1 Using the notations in (20), we have" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 119, + 315, + 287, + 342 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 119, + 315, + 287, + 342 + ], + "spans": [ + { + "bbox": [ + 119, + 315, + 287, + 342 + ], + "type": "interline_equation", + "content": "\\frac {\\partial \\lambda_ {i , 3}}{\\partial x _ {j m}} = - \\varphi_ {i} \\boldsymbol {\\delta} _ {j m} ^ {i} \\cdot \\boldsymbol {\\chi} _ {i}, \\tag {21}", + "image_path": "809826e06a7f91b11163d842f6f1bf248f386a05bfcdaea5ae778ccdce84e914.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 349, + 277, + 363 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 349, + 277, + 363 + ], + "spans": [ + { + "bbox": [ + 47, + 349, + 277, + 363 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 349, + 277, + 363 + ], + "type": "inline_equation", + "content": "\\cdot" + }, + { + "bbox": [ + 47, + 349, + 277, + 363 + ], + "type": "text", + "content": " represents the dot product and " + }, + { + "bbox": [ + 47, + 349, + 277, + 363 + ], + "type": "inline_equation", + "content": "\\varphi_{i} = (\\pmb{\\kappa}_{i}\\cdot \\pmb{\\chi}_{i})^{-1}" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 369, + 277, + 381 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 369, + 277, + 381 + ], + "spans": [ + { + "bbox": [ + 47, + 369, + 277, + 381 + ], + "type": "text", + "content": "Lemma 2 Using the notations in (20) and (21), we have" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 387, + 293, + 422 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 387, + 293, + 422 + ], + "spans": [ + { + "bbox": [ + 47, + 387, + 293, + 422 + ], + "type": "interline_equation", + "content": "\\frac {\\partial^ {2} \\lambda_ {i , 3}}{\\partial x _ {j m} \\partial x _ {k n}} = - \\varphi_ {i} \\left(\\boldsymbol {\\delta} _ {j m} ^ {i} \\cdot \\frac {\\partial \\boldsymbol {\\chi} _ {i}}{\\partial x _ {k n}} + \\boldsymbol {\\chi} _ {i} \\cdot \\frac {\\partial \\boldsymbol {\\delta} _ {j m} ^ {i}}{\\partial x _ {k n}} - \\frac {\\partial \\lambda_ {i , 3}}{\\partial x _ {j m}} \\frac {\\partial \\varphi_ {i} ^ {- 1}}{\\partial x _ {k n}}\\right). \\tag {22}", + "image_path": "508364e26d70fb19086498eb8a663120213803c49a81ae90d665025372895d8a.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 59, + 430, + 115, + 439 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 430, + 115, + 439 + ], + "spans": [ + { + "bbox": [ + 59, + 430, + 115, + 439 + ], + "type": "text", + "content": "Let us define" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 52, + 444, + 260, + 467 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 52, + 444, + 260, + 467 + ], + "spans": [ + { + "bbox": [ + 52, + 444, + 260, + 467 + ], + "type": "interline_equation", + "content": "\\boldsymbol {\\alpha} _ {j} ^ {i} = \\frac {\\partial a _ {i}}{\\partial \\boldsymbol {x} _ {j}}, \\beta_ {j} ^ {i} = \\frac {\\partial b _ {i}}{\\partial \\boldsymbol {x} _ {j}}, \\gamma_ {j} ^ {i} = \\frac {\\partial c _ {i}}{\\partial \\boldsymbol {x} _ {j}}, \\boldsymbol {\\Delta} _ {j} ^ {i} = [ \\boldsymbol {\\alpha} _ {j} ^ {i}, \\beta_ {j} ^ {i}, \\gamma_ {j} ^ {i} ],", + "image_path": "fe0036094c6321aae2619a182263375f3b1f6eacf64948b4e04b5faf63113c76.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 52, + 468, + 287, + 491 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 52, + 468, + 287, + 491 + ], + "spans": [ + { + "bbox": [ + 52, + 468, + 287, + 491 + ], + "type": "interline_equation", + "content": "\\boldsymbol {\\alpha} _ {k} ^ {i} = \\frac {\\partial a _ {i}}{\\partial \\boldsymbol {x} _ {k}}, \\beta_ {k} ^ {i} = \\frac {\\partial b _ {i}}{\\partial \\boldsymbol {x} _ {k}}, \\gamma_ {k} ^ {i} = \\frac {\\partial c _ {i}}{\\partial \\boldsymbol {x} _ {k}}, \\boldsymbol {\\Delta} _ {k} ^ {i} = [ \\boldsymbol {\\alpha} _ {k} ^ {i}, \\boldsymbol {\\beta} _ {k} ^ {i}, \\boldsymbol {\\gamma} _ {k} ^ {i} ], \\tag {23}", + "image_path": "026f5dc45ffccc4e1b874226a54316d70f2e63e6be82e43c4be38992b958fec3.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 52, + 492, + 253, + 516 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 52, + 492, + 253, + 516 + ], + "spans": [ + { + "bbox": [ + 52, + 492, + 253, + 516 + ], + "type": "interline_equation", + "content": "\\mathbf {H} _ {j k} ^ {a _ {i}} = \\frac {\\partial^ {2} a _ {i}}{\\partial \\boldsymbol {x} _ {j} \\partial \\boldsymbol {x} _ {k}}, \\mathbf {H} _ {j k} ^ {b _ {i}} = \\frac {\\partial^ {2} b _ {i}}{\\partial \\boldsymbol {x} _ {j} \\partial \\boldsymbol {x} _ {k}}, \\mathbf {H} _ {j k} ^ {c _ {i}} = \\frac {\\partial^ {2} c _ {i}}{\\partial \\boldsymbol {x} _ {j} \\partial \\boldsymbol {x} _ {k}}.", + "image_path": "6f6d080154df616f11e8ffc27a5b8279c46e573028d20ad0da43494af4c081f1.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 47, + 521, + 287, + 550 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 521, + 287, + 550 + ], + "spans": [ + { + "bbox": [ + 47, + 521, + 287, + 550 + ], + "type": "text", + "content": "Using the above lemmas and notations, we can derive " + }, + { + "bbox": [ + 47, + 521, + 287, + 550 + ], + "type": "inline_equation", + "content": "\\pmb{g}_j^i" + }, + { + "bbox": [ + 47, + 521, + 287, + 550 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 521, + 287, + 550 + ], + "type": "inline_equation", + "content": "\\mathbf{H}_{jk}^i" + }, + { + "bbox": [ + 47, + 521, + 287, + 550 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 47, + 554, + 287, + 582 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 554, + 287, + 582 + ], + "spans": [ + { + "bbox": [ + 47, + 554, + 287, + 582 + ], + "type": "text", + "content": "Theorem 1 Using the notations in (20), (21) and (23), " + }, + { + "bbox": [ + 47, + 554, + 287, + 582 + ], + "type": "inline_equation", + "content": "\\pmb{g}_j^i" + }, + { + "bbox": [ + 47, + 554, + 287, + 582 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 554, + 287, + 582 + ], + "type": "inline_equation", + "content": "\\mathbf{H}_{jk}^{i}" + }, + { + "bbox": [ + 47, + 554, + 287, + 582 + ], + "type": "text", + "content": " have the forms" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 66, + 589, + 137, + 604 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 66, + 589, + 137, + 604 + ], + "spans": [ + { + "bbox": [ + 66, + 589, + 137, + 604 + ], + "type": "interline_equation", + "content": "\\boldsymbol {g} _ {j} ^ {i} = - \\varphi_ {i} \\boldsymbol {\\Delta} _ {j} ^ {i} \\chi_ {i},", + "image_path": "15560223fc87a4699f448d9b9351854edd245a1ea835109d1a6dd900bb6cdfc7.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 59, + 602, + 287, + 625 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 602, + 287, + 625 + ], + "spans": [ + { + "bbox": [ + 59, + 602, + 287, + 625 + ], + "type": "interline_equation", + "content": "\\mathbf {H} _ {j k} ^ {i} = \\varphi_ {i} \\left(\\mathbf {K} _ {j k} ^ {i} - \\lambda_ {3, i} ^ {2} \\mathbf {H} _ {j k} ^ {a _ {i}} - \\lambda_ {3, i} \\mathbf {H} _ {j k} ^ {b _ {i}} - \\mathbf {H} _ {j k} ^ {c _ {i}}\\right), \\tag {24}", + "image_path": "e950182a91929a25c8b2dd4c325a74e763bfb286fa883c85b4d3c75344285e64.jpg" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 47, + 631, + 287, + 672 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 631, + 287, + 672 + ], + "spans": [ + { + "bbox": [ + 47, + 631, + 287, + 672 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 631, + 287, + 672 + ], + "type": "inline_equation", + "content": "\\mathbf{K}_{jk}^{i} = \\pmb{g}_{j}^{i}\\pmb{u}^{T} - \\pmb{v}(\\pmb{g}_{k}^{i})^{T},\\pmb{u} = 2\\lambda_{i,3}\\pmb{\\alpha}_{k}^{i} + \\pmb{\\beta}_{k}^{i} + (2a - 6\\lambda_{i,3})\\pmb{g}_{k}^{i}," + }, + { + "bbox": [ + 47, + 631, + 287, + 672 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 631, + 287, + 672 + ], + "type": "inline_equation", + "content": "\\pmb {v} = 2\\lambda_{i,3}\\pmb{\\alpha}_{j}^{i} + \\pmb{\\beta}_{j}^{i}" + }, + { + "bbox": [ + 47, + 631, + 287, + 672 + ], + "type": "text", + "content": " , and similar to " + }, + { + "bbox": [ + 47, + 631, + 287, + 672 + ], + "type": "inline_equation", + "content": "\\pmb{g}_j^i,\\pmb{g}_k^i =" + }, + { + "bbox": [ + 47, + 631, + 287, + 672 + ], + "type": "inline_equation", + "content": "-\\varphi_i\\Delta_k^i\\chi_i" + }, + { + "bbox": [ + 47, + 631, + 287, + 672 + ], + "type": "text", + "content": " is the gradient block for " + }, + { + "bbox": [ + 47, + 631, + 287, + 672 + ], + "type": "inline_equation", + "content": "\\pmb{x}_k" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 47, + 677, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 677, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 47, + 677, + 287, + 715 + ], + "type": "text", + "content": "The formula of " + }, + { + "bbox": [ + 47, + 677, + 287, + 715 + ], + "type": "inline_equation", + "content": "\\mathbf{H}_{jk}^{i}" + }, + { + "bbox": [ + 47, + 677, + 287, + 715 + ], + "type": "text", + "content": " in (24) is applicable to the case that " + }, + { + "bbox": [ + 47, + 677, + 287, + 715 + ], + "type": "inline_equation", + "content": "j = k" + }, + { + "bbox": [ + 47, + 677, + 287, + 715 + ], + "type": "text", + "content": ". From Theorem 1, we know that the key point to get " + }, + { + "bbox": [ + 47, + 677, + 287, + 715 + ], + "type": "inline_equation", + "content": "\\pmb{g}_j^i" + }, + { + "bbox": [ + 47, + 677, + 287, + 715 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 677, + 287, + 715 + ], + "type": "inline_equation", + "content": "\\mathbf{H}_{jk}^{i}" + }, + { + "bbox": [ + 47, + 677, + 287, + 715 + ], + "type": "text", + "content": " is to get the derivatives of " + }, + { + "bbox": [ + 47, + 677, + 287, + 715 + ], + "type": "inline_equation", + "content": "a_{i}, b_{i}" + }, + { + "bbox": [ + 47, + 677, + 287, + 715 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 677, + 287, + 715 + ], + "type": "inline_equation", + "content": "c_{i}" + }, + { + "bbox": [ + 47, + 677, + 287, + 715 + ], + "type": "text", + "content": " in (23)." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 306, + 72, + 483, + 84 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 72, + 483, + 84 + ], + "spans": [ + { + "bbox": [ + 306, + 72, + 483, + 84 + ], + "type": "text", + "content": "4.2. Partial Derivatives of " + }, + { + "bbox": [ + 306, + 72, + 483, + 84 + ], + "type": "inline_equation", + "content": "a_i" + }, + { + "bbox": [ + 306, + 72, + 483, + 84 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 306, + 72, + 483, + 84 + ], + "type": "inline_equation", + "content": "b_i" + }, + { + "bbox": [ + 306, + 72, + 483, + 84 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 306, + 72, + 483, + 84 + ], + "type": "inline_equation", + "content": "c_i" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 305, + 90, + 546, + 138 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 90, + 546, + 138 + ], + "spans": [ + { + "bbox": [ + 305, + 90, + 546, + 138 + ], + "type": "text", + "content": "According to (19), " + }, + { + "bbox": [ + 305, + 90, + 546, + 138 + ], + "type": "inline_equation", + "content": "a_{i}, b_{i}" + }, + { + "bbox": [ + 305, + 90, + 546, + 138 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 90, + 546, + 138 + ], + "type": "inline_equation", + "content": "c_{i}" + }, + { + "bbox": [ + 305, + 90, + 546, + 138 + ], + "type": "text", + "content": " are functions of the elements in " + }, + { + "bbox": [ + 305, + 90, + 546, + 138 + ], + "type": "inline_equation", + "content": "\\mathbf{M}_i" + }, + { + "bbox": [ + 305, + 90, + 546, + 138 + ], + "type": "text", + "content": ". Using this relationship, we can easily derive the partial derivatives in (23). For instance, as " + }, + { + "bbox": [ + 305, + 90, + 546, + 138 + ], + "type": "inline_equation", + "content": "a_{i} = m_{11} + m_{22} + m_{33}" + }, + { + "bbox": [ + 305, + 90, + 546, + 138 + ], + "type": "text", + "content": ", we have" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 356, + 144, + 545, + 171 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 356, + 144, + 545, + 171 + ], + "spans": [ + { + "bbox": [ + 356, + 144, + 545, + 171 + ], + "type": "interline_equation", + "content": "\\frac {\\partial a _ {i}}{\\partial \\boldsymbol {x} _ {j}} = \\frac {\\partial m _ {1 1}}{\\partial \\boldsymbol {x} _ {j}} + \\frac {\\partial m _ {2 2}}{\\partial \\boldsymbol {x} _ {j}} + \\frac {\\partial m _ {3 3}}{\\partial \\boldsymbol {x} _ {j}}. \\tag {25}", + "image_path": "b8b211c1532297abef19299ba25c08dde222771d8fb31c5c9214ea848397ca04.jpg" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 305, + 178, + 546, + 214 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 178, + 546, + 214 + ], + "spans": [ + { + "bbox": [ + 305, + 178, + 546, + 214 + ], + "type": "text", + "content": "Thus, to get the first- and second-order partial derivatives of " + }, + { + "bbox": [ + 305, + 178, + 546, + 214 + ], + "type": "inline_equation", + "content": "a_{i}, b_{i}" + }, + { + "bbox": [ + 305, + 178, + 546, + 214 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 178, + 546, + 214 + ], + "type": "inline_equation", + "content": "c_{i}" + }, + { + "bbox": [ + 305, + 178, + 546, + 214 + ], + "type": "text", + "content": " with respect to " + }, + { + "bbox": [ + 305, + 178, + 546, + 214 + ], + "type": "inline_equation", + "content": "\\pmb{x}_j" + }, + { + "bbox": [ + 305, + 178, + 546, + 214 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 178, + 546, + 214 + ], + "type": "inline_equation", + "content": "\\pmb{x}_k" + }, + { + "bbox": [ + 305, + 178, + 546, + 214 + ], + "type": "text", + "content": " in (23), we need to derive the form of " + }, + { + "bbox": [ + 305, + 178, + 546, + 214 + ], + "type": "inline_equation", + "content": "\\mathbf{M}_i" + }, + { + "bbox": [ + 305, + 178, + 546, + 214 + ], + "type": "text", + "content": " with respect to " + }, + { + "bbox": [ + 305, + 178, + 546, + 214 + ], + "type": "inline_equation", + "content": "\\pmb{x}_j" + }, + { + "bbox": [ + 305, + 178, + 546, + 214 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 178, + 546, + 214 + ], + "type": "inline_equation", + "content": "\\pmb{x}_k" + }, + { + "bbox": [ + 305, + 178, + 546, + 214 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 306, + 223, + 538, + 236 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 223, + 538, + 236 + ], + "spans": [ + { + "bbox": [ + 306, + 223, + 538, + 236 + ], + "type": "text", + "content": "Lemma 3 In terms of " + }, + { + "bbox": [ + 306, + 223, + 538, + 236 + ], + "type": "inline_equation", + "content": "\\pmb{x}_j" + }, + { + "bbox": [ + 306, + 223, + 538, + 236 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 306, + 223, + 538, + 236 + ], + "type": "inline_equation", + "content": "\\pmb{x}_k" + }, + { + "bbox": [ + 306, + 223, + 538, + 236 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 306, + 223, + 538, + 236 + ], + "type": "inline_equation", + "content": "\\bar{\\pmb{p}}_i" + }, + { + "bbox": [ + 306, + 223, + 538, + 236 + ], + "type": "text", + "content": " in (13) has the form" + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 347, + 243, + 545, + 256 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 347, + 243, + 545, + 256 + ], + "spans": [ + { + "bbox": [ + 347, + 243, + 545, + 256 + ], + "type": "interline_equation", + "content": "\\bar {\\boldsymbol {p}} _ {i} \\left(\\boldsymbol {x} _ {j}, \\boldsymbol {x} _ {k}\\right) = \\mathbf {T} _ {j} \\boldsymbol {q} _ {i j} + \\mathbf {T} _ {k} \\boldsymbol {q} _ {i k} + \\boldsymbol {c} _ {i j k}, \\tag {26}", + "image_path": "50abf10ed5ee6e7cdde14cb733d7d668c4eba8a35aa35dc2292f4c6c03daf97b.jpg" + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 305, + 263, + 546, + 314 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 263, + 546, + 314 + ], + "spans": [ + { + "bbox": [ + 305, + 263, + 546, + 314 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 263, + 546, + 314 + ], + "type": "inline_equation", + "content": "\\pmb{q}_{ij} = \\frac{1}{N_i}\\tilde{\\pmb{p}}_{ij},\\quad \\pmb{q}_{ik} = \\frac{1}{N_i}\\tilde{\\pmb{p}}_{ik}," + }, + { + "bbox": [ + 305, + 263, + 546, + 314 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 263, + 546, + 314 + ], + "type": "inline_equation", + "content": "c_{ijk} = \\frac{1}{N_i}\\sum_{n\\in \\mathbb{O}_{jk}}\\mathbf{T}_n\\tilde{p}_{in}" + }, + { + "bbox": [ + 305, + 263, + 546, + 314 + ], + "type": "text", + "content": ". Here " + }, + { + "bbox": [ + 305, + 263, + 546, + 314 + ], + "type": "inline_equation", + "content": "\\mathbb{O}_{jk} = \\mathrm{obs}(\\pi_i) - \\{j,k\\}" + }, + { + "bbox": [ + 305, + 263, + 546, + 314 + ], + "type": "text", + "content": " represents the set of indexes of the poses that can observe " + }, + { + "bbox": [ + 305, + 263, + 546, + 314 + ], + "type": "inline_equation", + "content": "\\pi_i" + }, + { + "bbox": [ + 305, + 263, + 546, + 314 + ], + "type": "text", + "content": ", excluding the " + }, + { + "bbox": [ + 305, + 263, + 546, + 314 + ], + "type": "inline_equation", + "content": "j" + }, + { + "bbox": [ + 305, + 263, + 546, + 314 + ], + "type": "text", + "content": "th and " + }, + { + "bbox": [ + 305, + 263, + 546, + 314 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 305, + 263, + 546, + 314 + ], + "type": "text", + "content": "th poses." + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 317, + 315, + 444, + 327 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 315, + 444, + 327 + ], + "spans": [ + { + "bbox": [ + 317, + 315, + 444, + 327 + ], + "type": "text", + "content": "In terms of " + }, + { + "bbox": [ + 317, + 315, + 444, + 327 + ], + "type": "inline_equation", + "content": "\\pmb{x}_j" + }, + { + "bbox": [ + 317, + 315, + 444, + 327 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 317, + 315, + 444, + 327 + ], + "type": "inline_equation", + "content": "\\bar{\\pmb{p}}_i" + }, + { + "bbox": [ + 317, + 315, + 444, + 327 + ], + "type": "text", + "content": " has the form" + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 376, + 335, + 545, + 348 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 376, + 335, + 545, + 348 + ], + "spans": [ + { + "bbox": [ + 376, + 335, + 545, + 348 + ], + "type": "interline_equation", + "content": "\\bar {\\boldsymbol {p}} _ {i} \\left(\\boldsymbol {x} _ {j}\\right) = \\mathbf {T} _ {j} \\mathbf {q} _ {i j} + \\boldsymbol {c} _ {i j}, \\tag {27}", + "image_path": "cc08336b67fccc185fe351a97d251000ad7b25cf0945f8f06113fff5c450f454.jpg" + } + ] + } + ], + "index": 26 + }, + { + "bbox": [ + 306, + 356, + 418, + 369 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 356, + 418, + 369 + ], + "spans": [ + { + "bbox": [ + 306, + 356, + 418, + 369 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 306, + 356, + 418, + 369 + ], + "type": "inline_equation", + "content": "c_{ij} = \\mathbf{T}_k\\mathbf{q}_{ik} + c_{ijk}" + }, + { + "bbox": [ + 306, + 356, + 418, + 369 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 27 + }, + { + "bbox": [ + 306, + 376, + 545, + 400 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 376, + 545, + 400 + ], + "spans": [ + { + "bbox": [ + 306, + 376, + 545, + 400 + ], + "type": "text", + "content": "Using Lemma 3, we can have the following theorem for " + }, + { + "bbox": [ + 306, + 376, + 545, + 400 + ], + "type": "inline_equation", + "content": "\\mathbf{M}_i" + }, + { + "bbox": [ + 306, + 376, + 545, + 400 + ], + "type": "text", + "content": " in (12)." + } + ] + } + ], + "index": 28 + }, + { + "bbox": [ + 306, + 407, + 537, + 420 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 407, + 537, + 420 + ], + "spans": [ + { + "bbox": [ + 306, + 407, + 537, + 420 + ], + "type": "text", + "content": "Theorem 2 In terms of " + }, + { + "bbox": [ + 306, + 407, + 537, + 420 + ], + "type": "inline_equation", + "content": "\\pmb{x}_j" + }, + { + "bbox": [ + 306, + 407, + 537, + 420 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 306, + 407, + 537, + 420 + ], + "type": "inline_equation", + "content": "\\mathbf{M}_i" + }, + { + "bbox": [ + 306, + 407, + 537, + 420 + ], + "type": "text", + "content": " in (12) can be written as" + } + ] + } + ], + "index": 29 + }, + { + "bbox": [ + 313, + 427, + 545, + 443 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 313, + 427, + 545, + 443 + ], + "spans": [ + { + "bbox": [ + 313, + 427, + 545, + 443 + ], + "type": "interline_equation", + "content": "\\mathbf {M} _ {i} \\left(\\boldsymbol {x} _ {j}\\right) = \\mathbf {T} _ {j} \\mathbf {Q} _ {j} ^ {i} \\mathbf {T} _ {j} ^ {T} + \\mathbf {T} _ {j} \\mathbf {K} _ {j} ^ {i} + \\left(\\mathbf {K} _ {j} ^ {i}\\right) ^ {T} \\mathbf {T} _ {j} ^ {T} + \\mathbf {C} _ {j} ^ {i}, \\tag {28}", + "image_path": "a567362337654a9d71e531cd3d87e50ecbf774891f6b7aa39dab0b280d7153a4.jpg" + } + ] + } + ], + "index": 30 + }, + { + "bbox": [ + 306, + 450, + 545, + 475 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 450, + 545, + 475 + ], + "spans": [ + { + "bbox": [ + 306, + 450, + 545, + 475 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 306, + 450, + 545, + 475 + ], + "type": "inline_equation", + "content": "\\mathbf{Q}_j^i = \\mathbf{U}_{ij} - N_j\\mathbf{q}_{ij}\\mathbf{q}_{ij}^T" + }, + { + "bbox": [ + 306, + 450, + 545, + 475 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 306, + 450, + 545, + 475 + ], + "type": "inline_equation", + "content": "\\mathbf{K}_j^i = -N_i\\mathbf{q}_{ij}\\mathbf{c}_{ij}^T" + }, + { + "bbox": [ + 306, + 450, + 545, + 475 + ], + "type": "text", + "content": ". Here " + }, + { + "bbox": [ + 306, + 450, + 545, + 475 + ], + "type": "inline_equation", + "content": "\\mathbf{U}_{ij}" + }, + { + "bbox": [ + 306, + 450, + 545, + 475 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 306, + 450, + 545, + 475 + ], + "type": "inline_equation", + "content": "\\mathbf{q}_{ij}" + }, + { + "bbox": [ + 306, + 450, + 545, + 475 + ], + "type": "text", + "content": " are defined in (13) and (26), respectively." + } + ] + } + ], + "index": 31 + }, + { + "bbox": [ + 317, + 475, + 499, + 487 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 475, + 499, + 487 + ], + "spans": [ + { + "bbox": [ + 317, + 475, + 499, + 487 + ], + "type": "text", + "content": "In terms of " + }, + { + "bbox": [ + 317, + 475, + 499, + 487 + ], + "type": "inline_equation", + "content": "\\pmb{x}_j" + }, + { + "bbox": [ + 317, + 475, + 499, + 487 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 317, + 475, + 499, + 487 + ], + "type": "inline_equation", + "content": "\\pmb{x}_k" + }, + { + "bbox": [ + 317, + 475, + 499, + 487 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 317, + 475, + 499, + 487 + ], + "type": "inline_equation", + "content": "\\mathbf{M}_i" + }, + { + "bbox": [ + 317, + 475, + 499, + 487 + ], + "type": "text", + "content": " can be written as" + } + ] + } + ], + "index": 32 + }, + { + "bbox": [ + 312, + 495, + 545, + 513 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 495, + 545, + 513 + ], + "spans": [ + { + "bbox": [ + 312, + 495, + 545, + 513 + ], + "type": "interline_equation", + "content": "\\mathbf {M} _ {i} \\left(\\boldsymbol {x} _ {j}, \\boldsymbol {x} _ {k}\\right) = \\mathbf {T} _ {j} \\mathbf {O} _ {j k} ^ {i} \\mathbf {T} _ {k} ^ {T} + \\mathbf {T} _ {k} \\left(\\mathbf {O} _ {j k} ^ {i}\\right) ^ {T} \\mathbf {T} _ {j} ^ {T} + \\mathbf {C} _ {j k} ^ {i}. \\tag {29}", + "image_path": "4fd5174cc30075aa1aaffc0f957e77e3afa08d2fc33ffaf05121e9effa66264e.jpg" + } + ] + } + ], + "index": 33 + }, + { + "bbox": [ + 306, + 520, + 412, + 535 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 520, + 412, + 535 + ], + "spans": [ + { + "bbox": [ + 306, + 520, + 412, + 535 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 306, + 520, + 412, + 535 + ], + "type": "inline_equation", + "content": "\\mathbf{O}_{jk}^{i} = -N_{i}\\pmb{q}_{ij}\\pmb{q}_{ik}^{T}" + }, + { + "bbox": [ + 306, + 520, + 412, + 535 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 34 + }, + { + "bbox": [ + 305, + 541, + 545, + 640 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 541, + 545, + 640 + ], + "spans": [ + { + "bbox": [ + 305, + 541, + 545, + 640 + ], + "type": "text", + "content": "Here we do not provide the detailed formulas for " + }, + { + "bbox": [ + 305, + 541, + 545, + 640 + ], + "type": "inline_equation", + "content": "\\mathbf{C}_j^i" + }, + { + "bbox": [ + 305, + 541, + 545, + 640 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 541, + 545, + 640 + ], + "type": "inline_equation", + "content": "\\mathbf{C}_{jk}^{i}" + }, + { + "bbox": [ + 305, + 541, + 545, + 640 + ], + "type": "text", + "content": ", as they will be eliminated in the partial derivative. Actually, only " + }, + { + "bbox": [ + 305, + 541, + 545, + 640 + ], + "type": "inline_equation", + "content": "\\mathbf{Q}_j^i" + }, + { + "bbox": [ + 305, + 541, + 545, + 640 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 305, + 541, + 545, + 640 + ], + "type": "inline_equation", + "content": "\\mathbf{K}_j^i" + }, + { + "bbox": [ + 305, + 541, + 545, + 640 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 305, + 541, + 545, + 640 + ], + "type": "inline_equation", + "content": "\\mathbf{O}_{jk}^{i}" + }, + { + "bbox": [ + 305, + 541, + 545, + 640 + ], + "type": "text", + "content": " are required to compute the partial derivatives in (23). Equation (28) is used to compute the first- and second-order partial derivatives of " + }, + { + "bbox": [ + 305, + 541, + 545, + 640 + ], + "type": "inline_equation", + "content": "a_i" + }, + { + "bbox": [ + 305, + 541, + 545, + 640 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 305, + 541, + 545, + 640 + ], + "type": "inline_equation", + "content": "b_i" + }, + { + "bbox": [ + 305, + 541, + 545, + 640 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 541, + 545, + 640 + ], + "type": "inline_equation", + "content": "c_i" + }, + { + "bbox": [ + 305, + 541, + 545, + 640 + ], + "type": "text", + "content": " with respect to " + }, + { + "bbox": [ + 305, + 541, + 545, + 640 + ], + "type": "inline_equation", + "content": "\\pmb{x}_j" + }, + { + "bbox": [ + 305, + 541, + 545, + 640 + ], + "type": "text", + "content": ". Equation (29) is used to compute the second-order partial derivatives of " + }, + { + "bbox": [ + 305, + 541, + 545, + 640 + ], + "type": "inline_equation", + "content": "a_i" + }, + { + "bbox": [ + 305, + 541, + 545, + 640 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 305, + 541, + 545, + 640 + ], + "type": "inline_equation", + "content": "b_i" + }, + { + "bbox": [ + 305, + 541, + 545, + 640 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 541, + 545, + 640 + ], + "type": "inline_equation", + "content": "c_i" + }, + { + "bbox": [ + 305, + 541, + 545, + 640 + ], + "type": "text", + "content": " with respect to " + }, + { + "bbox": [ + 305, + 541, + 545, + 640 + ], + "type": "inline_equation", + "content": "\\pmb{x}_j" + }, + { + "bbox": [ + 305, + 541, + 545, + 640 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 541, + 545, + 640 + ], + "type": "inline_equation", + "content": "\\pmb{x}_k" + }, + { + "bbox": [ + 305, + 541, + 545, + 640 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 35 + }, + { + "bbox": [ + 306, + 647, + 412, + 658 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 647, + 412, + 658 + ], + "spans": [ + { + "bbox": [ + 306, + 647, + 412, + 658 + ], + "type": "text", + "content": "4.3. Efficient Iteration" + } + ] + } + ], + "index": 36 + }, + { + "bbox": [ + 305, + 665, + 546, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 665, + 546, + 714 + ], + "spans": [ + { + "bbox": [ + 305, + 665, + 546, + 714 + ], + "type": "text", + "content": "From Theorem 2, we can easily derive the elements of " + }, + { + "bbox": [ + 305, + 665, + 546, + 714 + ], + "type": "inline_equation", + "content": "\\mathbf{M}_i(\\pmb{x}_j)" + }, + { + "bbox": [ + 305, + 665, + 546, + 714 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 665, + 546, + 714 + ], + "type": "inline_equation", + "content": "\\mathbf{M}_i(\\pmb{x}_j,\\pmb{x}_i)" + }, + { + "bbox": [ + 305, + 665, + 546, + 714 + ], + "type": "text", + "content": ". Assume " + }, + { + "bbox": [ + 305, + 665, + 546, + 714 + ], + "type": "inline_equation", + "content": "a(\\pmb{x}_j)" + }, + { + "bbox": [ + 305, + 665, + 546, + 714 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 665, + 546, + 714 + ], + "type": "inline_equation", + "content": "b(\\pmb{x}_j,\\pmb{x}_k)" + }, + { + "bbox": [ + 305, + 665, + 546, + 714 + ], + "type": "text", + "content": " are one of the elements in " + }, + { + "bbox": [ + 305, + 665, + 546, + 714 + ], + "type": "inline_equation", + "content": "\\mathbf{M}_i(\\pmb{x}_j)" + }, + { + "bbox": [ + 305, + 665, + 546, + 714 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 665, + 546, + 714 + ], + "type": "inline_equation", + "content": "\\mathbf{M}_i(\\pmb{x}_j,\\pmb{x}_k)" + }, + { + "bbox": [ + 305, + 665, + 546, + 714 + ], + "type": "text", + "content": ", respectively. Substituting " + }, + { + "bbox": [ + 305, + 665, + 546, + 714 + ], + "type": "inline_equation", + "content": "\\mathbf{T}_j" + }, + { + "bbox": [ + 305, + 665, + 546, + 714 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 665, + 546, + 714 + ], + "type": "inline_equation", + "content": "\\mathbf{T}_k" + }, + { + "bbox": [ + 305, + 665, + 546, + 714 + ], + "type": "text", + "content": " defined in (1) into (28) and" + } + ] + } + ], + "index": 37 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "13117" + } + ] + } + ], + "index": 38 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 122 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 122 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 122 + ], + "type": "text", + "content": "(29) and expanding them, we can obtain that " + }, + { + "bbox": [ + 46, + 72, + 287, + 122 + ], + "type": "inline_equation", + "content": "a(\\pmb{x}_j)" + }, + { + "bbox": [ + 46, + 72, + 287, + 122 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 72, + 287, + 122 + ], + "type": "inline_equation", + "content": "b(\\pmb{x}_j, \\pmb{x}_k)" + }, + { + "bbox": [ + 46, + 72, + 287, + 122 + ], + "type": "text", + "content": " are second-order polynomials in terms of the elements in " + }, + { + "bbox": [ + 46, + 72, + 287, + 122 + ], + "type": "inline_equation", + "content": "\\mathbf{T}_j" + }, + { + "bbox": [ + 46, + 72, + 287, + 122 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 72, + 287, + 122 + ], + "type": "inline_equation", + "content": "\\mathbf{T}_k" + }, + { + "bbox": [ + 46, + 72, + 287, + 122 + ], + "type": "text", + "content": ". Using the CGB parameterization in (2), we can write " + }, + { + "bbox": [ + 46, + 72, + 287, + 122 + ], + "type": "inline_equation", + "content": "a(\\pmb{x}_j)" + }, + { + "bbox": [ + 46, + 72, + 287, + 122 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 72, + 287, + 122 + ], + "type": "inline_equation", + "content": "b(\\pmb{x}_j, \\pmb{x}_k)" + }, + { + "bbox": [ + 46, + 72, + 287, + 122 + ], + "type": "text", + "content": " as" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 101, + 130, + 233, + 159 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 101, + 130, + 233, + 159 + ], + "spans": [ + { + "bbox": [ + 101, + 130, + 233, + 159 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} a (\\boldsymbol {x} _ {j}) = \\boldsymbol {c} \\cdot \\boldsymbol {h} (\\boldsymbol {x} _ {j}) + c _ {0}, \\\\ b \\left(\\boldsymbol {x} _ {j}, \\boldsymbol {x} _ {k}\\right) = \\boldsymbol {d} \\cdot \\boldsymbol {g} \\left(\\boldsymbol {x} _ {j}, \\boldsymbol {x} _ {k}\\right) + d _ {0}, \\\\ \\end{array}", + "image_path": "40fdb6fa886e5e566a1a9828214a0d35257dc8755ad83ce791ba2844eb2257eb.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 167, + 288, + 231 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 167, + 288, + 231 + ], + "spans": [ + { + "bbox": [ + 46, + 167, + 288, + 231 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 167, + 288, + 231 + ], + "type": "inline_equation", + "content": "\\pmb{c}" + }, + { + "bbox": [ + 46, + 167, + 288, + 231 + ], + "type": "text", + "content": " is determined by " + }, + { + "bbox": [ + 46, + 167, + 288, + 231 + ], + "type": "inline_equation", + "content": "\\mathbf{Q}_j^i" + }, + { + "bbox": [ + 46, + 167, + 288, + 231 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 167, + 288, + 231 + ], + "type": "inline_equation", + "content": "\\mathbf{K}_j^i" + }, + { + "bbox": [ + 46, + 167, + 288, + 231 + ], + "type": "text", + "content": " in (28), " + }, + { + "bbox": [ + 46, + 167, + 288, + 231 + ], + "type": "inline_equation", + "content": "\\pmb{d}" + }, + { + "bbox": [ + 46, + 167, + 288, + 231 + ], + "type": "text", + "content": " is determined by " + }, + { + "bbox": [ + 46, + 167, + 288, + 231 + ], + "type": "inline_equation", + "content": "\\mathbf{O}_{jk}^{i}" + }, + { + "bbox": [ + 46, + 167, + 288, + 231 + ], + "type": "text", + "content": " in (29), " + }, + { + "bbox": [ + 46, + 167, + 288, + 231 + ], + "type": "inline_equation", + "content": "\\pmb{h}(\\pmb{x}_j)" + }, + { + "bbox": [ + 46, + 167, + 288, + 231 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 167, + 288, + 231 + ], + "type": "inline_equation", + "content": "\\pmb{g}(\\pmb{x}_j, \\pmb{x}_k)" + }, + { + "bbox": [ + 46, + 167, + 288, + 231 + ], + "type": "text", + "content": " are two vector functions, " + }, + { + "bbox": [ + 46, + 167, + 288, + 231 + ], + "type": "inline_equation", + "content": "c_0" + }, + { + "bbox": [ + 46, + 167, + 288, + 231 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 167, + 288, + 231 + ], + "type": "inline_equation", + "content": "d_0" + }, + { + "bbox": [ + 46, + 167, + 288, + 231 + ], + "type": "text", + "content": " are two scalars independent on " + }, + { + "bbox": [ + 46, + 167, + 288, + 231 + ], + "type": "inline_equation", + "content": "\\pmb{x}_j" + }, + { + "bbox": [ + 46, + 167, + 288, + 231 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 167, + 288, + 231 + ], + "type": "inline_equation", + "content": "\\pmb{x}_k" + }, + { + "bbox": [ + 46, + 167, + 288, + 231 + ], + "type": "text", + "content": ". Let us first consider the first-order partial derivative of " + }, + { + "bbox": [ + 46, + 167, + 288, + 231 + ], + "type": "inline_equation", + "content": "a(\\pmb{x}_j)" + }, + { + "bbox": [ + 46, + 167, + 288, + 231 + ], + "type": "text", + "content": " with respect to " + }, + { + "bbox": [ + 46, + 167, + 288, + 231 + ], + "type": "inline_equation", + "content": "\\pmb{x}_j" + }, + { + "bbox": [ + 46, + 167, + 288, + 231 + ], + "type": "text", + "content": ". It has the form" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 122, + 238, + 287, + 266 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 122, + 238, + 287, + 266 + ], + "spans": [ + { + "bbox": [ + 122, + 238, + 287, + 266 + ], + "type": "interline_equation", + "content": "\\frac {\\partial a \\left(\\boldsymbol {x} _ {j}\\right)}{\\partial \\boldsymbol {x} _ {j}} = \\frac {\\partial h \\left(\\boldsymbol {x} _ {j}\\right)}{\\partial \\boldsymbol {x} _ {j}} c, \\tag {31}", + "image_path": "eaa5837af08609538722dcf16c07eb526eeb0d33266bf76d237e3188ad11e5e1.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 274, + 287, + 425 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 274, + 287, + 425 + ], + "spans": [ + { + "bbox": [ + 46, + 274, + 287, + 425 + ], + "type": "text", + "content": "where the vector-by-vector derivative " + }, + { + "bbox": [ + 46, + 274, + 287, + 425 + ], + "type": "inline_equation", + "content": "\\frac{\\partial h(\\pmb{x}_j)}{\\partial\\pmb{x}_j}" + }, + { + "bbox": [ + 46, + 274, + 287, + 425 + ], + "type": "text", + "content": " is defined in (4). To efficiently compute (31), we consider a special pose " + }, + { + "bbox": [ + 46, + 274, + 287, + 425 + ], + "type": "inline_equation", + "content": "\\mathbf{T}_0 = [\\mathbf{R}_0,t_0]" + }, + { + "bbox": [ + 46, + 274, + 287, + 425 + ], + "type": "text", + "content": " where " + }, + { + "bbox": [ + 46, + 274, + 287, + 425 + ], + "type": "inline_equation", + "content": "\\mathbf{R}_0 = \\mathbf{I}_3" + }, + { + "bbox": [ + 46, + 274, + 287, + 425 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 274, + 287, + 425 + ], + "type": "inline_equation", + "content": "t_0 = [0;0;0]" + }, + { + "bbox": [ + 46, + 274, + 287, + 425 + ], + "type": "text", + "content": ". Let us denote the parameterization of " + }, + { + "bbox": [ + 46, + 274, + 287, + 425 + ], + "type": "inline_equation", + "content": "\\mathbf{T}_0" + }, + { + "bbox": [ + 46, + 274, + 287, + 425 + ], + "type": "text", + "content": " as " + }, + { + "bbox": [ + 46, + 274, + 287, + 425 + ], + "type": "inline_equation", + "content": "\\pmb{x}_0" + }, + { + "bbox": [ + 46, + 274, + 287, + 425 + ], + "type": "text", + "content": ". As the CGR parameterization for " + }, + { + "bbox": [ + 46, + 274, + 287, + 425 + ], + "type": "inline_equation", + "content": "\\mathbf{I}_3" + }, + { + "bbox": [ + 46, + 274, + 287, + 425 + ], + "type": "text", + "content": " is " + }, + { + "bbox": [ + 46, + 274, + 287, + 425 + ], + "type": "inline_equation", + "content": "[0;0;0]" + }, + { + "bbox": [ + 46, + 274, + 287, + 425 + ], + "type": "text", + "content": ", we have " + }, + { + "bbox": [ + 46, + 274, + 287, + 425 + ], + "type": "inline_equation", + "content": "\\pmb{x}_0 = [0;0;0;0;0;0]" + }, + { + "bbox": [ + 46, + 274, + 287, + 425 + ], + "type": "text", + "content": ". For " + }, + { + "bbox": [ + 46, + 274, + 287, + 425 + ], + "type": "inline_equation", + "content": "\\pmb{x}_j = \\pmb{x}_0" + }, + { + "bbox": [ + 46, + 274, + 287, + 425 + ], + "type": "text", + "content": ", the matrix " + }, + { + "bbox": [ + 46, + 274, + 287, + 425 + ], + "type": "inline_equation", + "content": "\\frac{\\partial h(\\mathbf{x}_j)}{\\partial\\mathbf{x}_j}" + }, + { + "bbox": [ + 46, + 274, + 287, + 425 + ], + "type": "text", + "content": " can be easily computed. Similarly, the second-order partial derivatives of " + }, + { + "bbox": [ + 46, + 274, + 287, + 425 + ], + "type": "inline_equation", + "content": "\\pmb{h}(\\pmb{x}_j)" + }, + { + "bbox": [ + 46, + 274, + 287, + 425 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 274, + 287, + 425 + ], + "type": "inline_equation", + "content": "\\pmb{g}(\\pmb{x}_j,\\pmb{x}_k)" + }, + { + "bbox": [ + 46, + 274, + 287, + 425 + ], + "type": "text", + "content": " at " + }, + { + "bbox": [ + 46, + 274, + 287, + 425 + ], + "type": "inline_equation", + "content": "\\pmb{x}_j = \\pmb{x}_0" + }, + { + "bbox": [ + 46, + 274, + 287, + 425 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 274, + 287, + 425 + ], + "type": "inline_equation", + "content": "\\pmb{x}_k = \\pmb{x}_0" + }, + { + "bbox": [ + 46, + 274, + 287, + 425 + ], + "type": "text", + "content": " are also simple. As " + }, + { + "bbox": [ + 46, + 274, + 287, + 425 + ], + "type": "inline_equation", + "content": "\\pmb{h}(\\pmb{x}_j)" + }, + { + "bbox": [ + 46, + 274, + 287, + 425 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 274, + 287, + 425 + ], + "type": "inline_equation", + "content": "\\pmb{g}(\\pmb{x}_j,\\pmb{x}_k)" + }, + { + "bbox": [ + 46, + 274, + 287, + 425 + ], + "type": "text", + "content": " only depend on " + }, + { + "bbox": [ + 46, + 274, + 287, + 425 + ], + "type": "inline_equation", + "content": "\\pmb{x}_j" + }, + { + "bbox": [ + 46, + 274, + 287, + 425 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 274, + 287, + 425 + ], + "type": "inline_equation", + "content": "\\pmb{x}_k" + }, + { + "bbox": [ + 46, + 274, + 287, + 425 + ], + "type": "text", + "content": ", we can compute the partial derivatives at " + }, + { + "bbox": [ + 46, + 274, + 287, + 425 + ], + "type": "inline_equation", + "content": "\\pmb{x}_0" + }, + { + "bbox": [ + 46, + 274, + 287, + 425 + ], + "type": "text", + "content": " once, and then reuse them in the following iterations. Here we introduce a method to make the iteration stay at " + }, + { + "bbox": [ + 46, + 274, + 287, + 425 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_0" + }, + { + "bbox": [ + 46, + 274, + 287, + 425 + ], + "type": "text", + "content": " for each pose." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 425, + 287, + 450 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 425, + 287, + 450 + ], + "spans": [ + { + "bbox": [ + 47, + 425, + 287, + 450 + ], + "type": "text", + "content": "Assume that " + }, + { + "bbox": [ + 47, + 425, + 287, + 450 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{X}_j^n\\}" + }, + { + "bbox": [ + 47, + 425, + 287, + 450 + ], + "type": "text", + "content": " are the poses after the " + }, + { + "bbox": [ + 47, + 425, + 287, + 450 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 47, + 425, + 287, + 450 + ], + "type": "text", + "content": "th iteration. Then we can update " + }, + { + "bbox": [ + 47, + 425, + 287, + 450 + ], + "type": "inline_equation", + "content": "\\mathbf{U}_{ij}" + }, + { + "bbox": [ + 47, + 425, + 287, + 450 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 425, + 287, + 450 + ], + "type": "inline_equation", + "content": "\\tilde{p}_{ij}" + }, + { + "bbox": [ + 47, + 425, + 287, + 450 + ], + "type": "text", + "content": " in (13) by" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 67, + 457, + 287, + 473 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 67, + 457, + 287, + 473 + ], + "spans": [ + { + "bbox": [ + 67, + 457, + 287, + 473 + ], + "type": "interline_equation", + "content": "\\mathbf {U} _ {i j} ^ {n + 1} = \\mathbf {X} _ {j} ^ {n} \\mathbf {U} _ {i j} \\left(\\mathbf {X} _ {j} ^ {n}\\right) ^ {T} \\text {a n d} \\tilde {\\boldsymbol {p}} _ {i j} ^ {n + 1} = \\mathbf {X} _ {j} ^ {n} \\tilde {\\boldsymbol {p}} _ {i j}. \\tag {32}", + "image_path": "da9309f8a460485f35b5dee509ab2b5fd82f2b86bbb65a76596b5a0269066e52.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 481, + 287, + 571 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 481, + 287, + 571 + ], + "spans": [ + { + "bbox": [ + 46, + 481, + 287, + 571 + ], + "type": "text", + "content": "Substituting " + }, + { + "bbox": [ + 46, + 481, + 287, + 571 + ], + "type": "inline_equation", + "content": "\\mathbf{U}_{ij}^{n + 1}" + }, + { + "bbox": [ + 46, + 481, + 287, + 571 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 481, + 287, + 571 + ], + "type": "inline_equation", + "content": "\\tilde{\\pmb{p}}_{ij}^{n + 1}" + }, + { + "bbox": [ + 46, + 481, + 287, + 571 + ], + "type": "text", + "content": " into (12), we get a new matrix " + }, + { + "bbox": [ + 46, + 481, + 287, + 571 + ], + "type": "inline_equation", + "content": "\\mathbf{M}_i(\\mathbb{X}_i)^{n + 1}" + }, + { + "bbox": [ + 46, + 481, + 287, + 571 + ], + "type": "text", + "content": ", which can finally lead to a new cost " + }, + { + "bbox": [ + 46, + 481, + 287, + 571 + ], + "type": "inline_equation", + "content": "\\tau^{n + 1}" + }, + { + "bbox": [ + 46, + 481, + 287, + 571 + ], + "type": "text", + "content": " in (16). As the points have been transformed by " + }, + { + "bbox": [ + 46, + 481, + 287, + 571 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{X}_j^n\\}" + }, + { + "bbox": [ + 46, + 481, + 287, + 571 + ], + "type": "text", + "content": ", each pose should start with " + }, + { + "bbox": [ + 46, + 481, + 287, + 571 + ], + "type": "inline_equation", + "content": "\\mathbf{X}_0" + }, + { + "bbox": [ + 46, + 481, + 287, + 571 + ], + "type": "text", + "content": " for " + }, + { + "bbox": [ + 46, + 481, + 287, + 571 + ], + "type": "inline_equation", + "content": "\\tau^{n + 1}" + }, + { + "bbox": [ + 46, + 481, + 287, + 571 + ], + "type": "text", + "content": ". Assume that " + }, + { + "bbox": [ + 46, + 481, + 287, + 571 + ], + "type": "inline_equation", + "content": "\\Delta \\pmb{x}_j^{n + 1}" + }, + { + "bbox": [ + 46, + 481, + 287, + 571 + ], + "type": "text", + "content": " is the result from the " + }, + { + "bbox": [ + 46, + 481, + 287, + 571 + ], + "type": "inline_equation", + "content": "(n + 1)" + }, + { + "bbox": [ + 46, + 481, + 287, + 571 + ], + "type": "text", + "content": "th iteration for the " + }, + { + "bbox": [ + 46, + 481, + 287, + 571 + ], + "type": "inline_equation", + "content": "j" + }, + { + "bbox": [ + 46, + 481, + 287, + 571 + ], + "type": "text", + "content": "th pose. We can compute the corresponding transformation matrix " + }, + { + "bbox": [ + 46, + 481, + 287, + 571 + ], + "type": "inline_equation", + "content": "\\Delta \\mathbf{X}_j^{n + 1}" + }, + { + "bbox": [ + 46, + 481, + 287, + 571 + ], + "type": "text", + "content": " using (1) and (2). Then we can update " + }, + { + "bbox": [ + 46, + 481, + 287, + 571 + ], + "type": "inline_equation", + "content": "\\mathbf{X}_j^n" + }, + { + "bbox": [ + 46, + 481, + 287, + 571 + ], + "type": "text", + "content": " by" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 121, + 579, + 287, + 596 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 121, + 579, + 287, + 596 + ], + "spans": [ + { + "bbox": [ + 121, + 579, + 287, + 596 + ], + "type": "interline_equation", + "content": "\\mathbf {X} _ {j} ^ {n + 1} = \\Delta \\mathbf {X} _ {j} ^ {n + 1} \\mathbf {X} _ {j} ^ {n}. \\tag {33}", + "image_path": "87c6be55fd249694f3a55c87c5880e263083caf998e8ddaee7cd292c1cae58bf.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 603, + 287, + 664 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 603, + 287, + 664 + ], + "spans": [ + { + "bbox": [ + 46, + 603, + 287, + 664 + ], + "type": "text", + "content": "Furthermore, the update steps in (32) will not introduce additional computation. This is because the damped Newton's method requires to compute the cost " + }, + { + "bbox": [ + 46, + 603, + 287, + 664 + ], + "type": "inline_equation", + "content": "\\tau" + }, + { + "bbox": [ + 46, + 603, + 287, + 664 + ], + "type": "text", + "content": " in (16) to adjust " + }, + { + "bbox": [ + 46, + 603, + 287, + 664 + ], + "type": "inline_equation", + "content": "\\mu" + }, + { + "bbox": [ + 46, + 603, + 287, + 664 + ], + "type": "text", + "content": " in (3) after each iteration, which requires to perform the computation in (32)." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 671, + 167, + 685 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 671, + 167, + 685 + ], + "spans": [ + { + "bbox": [ + 47, + 671, + 167, + 685 + ], + "type": "text", + "content": "4.4. Algorithm Summary" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 689, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 689, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 689, + 287, + 714 + ], + "type": "text", + "content": "We first construct " + }, + { + "bbox": [ + 46, + 689, + 287, + 714 + ], + "type": "inline_equation", + "content": "\\mathbf{H}" + }, + { + "bbox": [ + 46, + 689, + 287, + 714 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 689, + 287, + 714 + ], + "type": "inline_equation", + "content": "\\pmb{g}" + }, + { + "bbox": [ + 46, + 689, + 287, + 714 + ], + "type": "text", + "content": ". For each plane " + }, + { + "bbox": [ + 46, + 689, + 287, + 714 + ], + "type": "inline_equation", + "content": "\\pi_i" + }, + { + "bbox": [ + 46, + 689, + 287, + 714 + ], + "type": "text", + "content": ", we solve the cubic equation (19), and select the smallest root " + }, + { + "bbox": [ + 46, + 689, + 287, + 714 + ], + "type": "inline_equation", + "content": "\\lambda_{i,3}" + }, + { + "bbox": [ + 46, + 689, + 287, + 714 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "text", + "content": "For " + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "inline_equation", + "content": "\\boldsymbol{x}_j" + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "text", + "content": ", we construct " + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "inline_equation", + "content": "\\mathbf{M}(\\boldsymbol{x}_j)" + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "text", + "content": " in (28), and calculate the partial derivatives of " + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "inline_equation", + "content": "a_i" + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "inline_equation", + "content": "b_i" + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "inline_equation", + "content": "c_i" + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "text", + "content": " with respect to " + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "inline_equation", + "content": "\\boldsymbol{x}_j" + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "text", + "content": " in (23). Then, we use (24) to compute " + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "inline_equation", + "content": "g_j^i" + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "inline_equation", + "content": "\\mathbf{H}_{jj}^i" + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "text", + "content": " and use (18) to update " + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "inline_equation", + "content": "g_j" + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "inline_equation", + "content": "\\mathbf{H}_{jj}" + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "text", + "content": ". For " + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "inline_equation", + "content": "\\boldsymbol{x}_j" + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "inline_equation", + "content": "\\boldsymbol{x}_k" + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "inline_equation", + "content": "\\mathbf{M}_i(\\boldsymbol{x}_j, \\boldsymbol{x}_k)" + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "text", + "content": " is generated, and then the partial derivatives of " + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "inline_equation", + "content": "a_i" + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "inline_equation", + "content": "b_i" + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "inline_equation", + "content": "c_i" + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "text", + "content": " with respect to " + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "inline_equation", + "content": "\\boldsymbol{x}_j" + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "inline_equation", + "content": "\\boldsymbol{x}_j" + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "text", + "content": " in (23) are computed. Then, " + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "inline_equation", + "content": "\\mathbf{H}_{jk}^i" + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "text", + "content": " can be easily obtained from (24), and " + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "inline_equation", + "content": "\\mathbf{H}_{jk}" + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "text", + "content": " in (18) is computed accordingly. Using " + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "inline_equation", + "content": "\\mathbf{H}" + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "inline_equation", + "content": "g" + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "text", + "content": ", we conduct the damped Newton's step in (3). After each iteration, " + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "inline_equation", + "content": "\\mathbf{U}_{ij}" + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "inline_equation", + "content": "\\tilde{\\boldsymbol{p}}_{ij}" + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "text", + "content": " are updated by (32). The proposed algorithm is summarized in Algorithm 1. Let us denote the mean and variance of the number of observations per plane as " + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "inline_equation", + "content": "\\bar{K}" + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "inline_equation", + "content": "\\sigma^2" + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "text", + "content": ", respectively. According to [8], the computational complexity of the Hessian matrix is " + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "inline_equation", + "content": "O(M(\\bar{K}^2 + \\sigma^2))" + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "text", + "content": ", which is of the same order as the Schur complement trick." + } + ] + } + ], + "index": 12 + }, + { + "type": "code", + "bbox": [ + 318, + 292, + 531, + 539 + ], + "blocks": [ + { + "bbox": [ + 312, + 265, + 518, + 289 + ], + "lines": [ + { + "bbox": [ + 312, + 265, + 518, + 289 + ], + "spans": [ + { + "bbox": [ + 312, + 265, + 518, + 289 + ], + "type": "text", + "content": "Algorithm 1: Second-order plane adjustment for " + }, + { + "bbox": [ + 312, + 265, + 518, + 289 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 312, + 265, + 518, + 289 + ], + "type": "text", + "content": " poses and " + }, + { + "bbox": [ + 312, + 265, + 518, + 289 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 312, + 265, + 518, + 289 + ], + "type": "text", + "content": " planes" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "code_caption" + }, + { + "bbox": [ + 318, + 292, + 531, + 539 + ], + "lines": [ + { + "bbox": [ + 318, + 292, + 531, + 539 + ], + "spans": [ + { + "bbox": [ + 318, + 292, + 531, + 539 + ], + "type": "text", + "content": "while not converge do " + }, + { + "bbox": [ + 318, + 292, + 531, + 539 + ], + "type": "inline_equation", + "content": "\\mathbf{H} = \\text{zeros}(6N, 6N), \\mathbf{g} = \\text{zeros}(6N, 1)" + }, + { + "bbox": [ + 318, + 292, + 531, + 539 + ], + "type": "text", + "content": "; for " + }, + { + "bbox": [ + 318, + 292, + 531, + 539 + ], + "type": "inline_equation", + "content": "i \\in [1, M]" + }, + { + "bbox": [ + 318, + 292, + 531, + 539 + ], + "type": "text", + "content": " do \n\\[\n\\begin{aligned}\n& \\text{Compute } \\mathbf{g}\\text{ and the diagonal terms of } \\mathbf{H}. \\\\\n& \\text{for } j \\in \\text{obs}(\\pi_i) \\text{ do} \\\\\n& \\text{Compute } \\mathbf{M}_i(\\mathbf{x}_j) \\text{ using (28)}; \\\\\n& \\text{Compute } \\alpha_j^i, \\beta_j^i, \\gamma_j^i, \\mathbf{H}_{jj}^{a_i}, \\mathbf{H}_{jj}^{b_i}, \\mathbf{H}_{jj}^{c_i} \\text{ using (23)}; \\\\\n& \\text{Compute } \\mathbf{H}_{jj}^i \\text{ and } \\mathbf{g}_j^i \\text{ using (24)}; \\\\\n& \\text{H}_{jj} = \\mathbf{H}_{jj} + \\mathbf{H}_{jj}^i, \\mathbf{g}_j = \\mathbf{g}_j + \\mathbf{g}_j^i;\n\\end{aligned}\n\\] \n\\[\n\\begin{aligned}\n& \\text{for } j \\in \\text{obs}(\\pi_i) \\text{ do} \\\\\n& \\text{for } k \\in \\text{obs}(\\pi_i) \\text{ and } k > j \\text{ do} \\\\\n& \\text{Compute } \\mathbf{H}_{jk}^i \\text{ using (24)}; \\\\\n& \\text{H}_{jk} = \\mathbf{H}_{jk} + \\mathbf{H}_{jk}^i; \\\\\n& \\text{H}_{kj} = \\mathbf{H}_{kj} + (\\mathbf{H}_{jk}^i)^T;\n\\end{aligned}\n\\] \nConduct the damped Newton's step in (3); Update " + }, + { + "bbox": [ + 318, + 292, + 531, + 539 + ], + "type": "inline_equation", + "content": "\\mathbf{U}_{ij}" + }, + { + "bbox": [ + 318, + 292, + 531, + 539 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 318, + 292, + 531, + 539 + ], + "type": "inline_equation", + "content": "\\tilde{\\boldsymbol{p}}_{ij}" + }, + { + "bbox": [ + 318, + 292, + 531, + 539 + ], + "type": "text", + "content": " using (32);" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "code_body" + } + ], + "index": 14, + "sub_type": "algorithm" + }, + { + "bbox": [ + 306, + 567, + 386, + 581 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 567, + 386, + 581 + ], + "spans": [ + { + "bbox": [ + 306, + 567, + 386, + 581 + ], + "type": "text", + "content": "5. Experiments" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 306, + 587, + 356, + 601 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 587, + 356, + 601 + ], + "spans": [ + { + "bbox": [ + 306, + 587, + 356, + 601 + ], + "type": "text", + "content": "5.1. Setup" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": "In this section, we compare our algorithm with EF [10], BALM [16] and the LM solution [23] with plane fitting after a successful LM step (named " + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{LM} + \\mathbf{PF}" + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": "). Our damped Newton's method was implemented according to the LM algorithm in Ceres [2]. The damped Newton's method and the LM algorithm are with the same parameters. Specifically, the initial value of the damping factor " + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mu" + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": " in (3) is set to " + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "inline_equation", + "content": "10^{-4}" + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": ". The early stopping tolerances (such as the cost value change and the norm of gradient) are set to " + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "inline_equation", + "content": "10^{-7}" + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": ". 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The four datasets used in this paper. There are " + }, + { + "bbox": [ + 46, + 341, + 545, + 365 + ], + "type": "inline_equation", + "content": "4.5 \\times 10^{6}" + }, + { + "bbox": [ + 46, + 341, + 545, + 365 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 341, + 545, + 365 + ], + "type": "inline_equation", + "content": "16.6 \\times 10^{6}" + }, + { + "bbox": [ + 46, + 341, + 545, + 365 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 341, + 545, + 365 + ], + "type": "inline_equation", + "content": "16.7 \\times 10^{6}" + }, + { + "bbox": [ + 46, + 341, + 545, + 365 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 46, + 341, + 545, + 365 + ], + "type": "inline_equation", + "content": "10.5 \\times 10^{6}" + }, + { + "bbox": [ + 46, + 341, + 545, + 365 + ], + "type": "text", + "content": " points in the 4 datasets. The 4 datasets have 339, 369, 856, and 589 planes, and 472, 1355, 1606, 1184 poses, respectively. Roofs are removed to show the trajectories." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 50, + 384, + 111, + 440 + ], + "lines": [ + { + "bbox": [ + 50, + 384, + 111, + 440 + ], + "spans": [ + { + "bbox": [ + 50, + 384, + 111, + 440 + ], + "type": "image", + "image_path": "2a3f334e97d0b831aafbd009726f5ee56bf0636d24643818d62cd87d29565b3b.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 111, + 384, + 169, + 440 + ], + "blocks": [ + { + "bbox": [ + 53, + 442, + 164, + 449 + ], + "lines": [ + { + "bbox": [ + 53, + 442, + 164, + 449 + ], + "spans": [ + { + "bbox": [ + 53, + 442, + 164, + 449 + ], + "type": "inline_equation", + "content": "\\sigma_{\\mathbf{R}} = 0.1^{\\circ}\\sigma_{t} = 0.01m" + }, + { + "bbox": [ + 53, + 442, + 164, + 449 + ], + "type": "inline_equation", + "content": "\\sigma_{\\mathbf{R}} = 1^{\\circ}\\sigma_{t} = 0.1m" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 111, + 384, + 169, + 440 + ], + "lines": [ + { + "bbox": [ + 111, + 384, + 169, + 440 + ], + "spans": [ + { + "bbox": [ + 111, + 384, + 169, + 440 + ], + "type": "image", + "image_path": "1797e1f3cc2e9c6d579d0c4c92431899494c7c00e10169fcb627fecbf05c8f7f.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + } + ], + "index": 11 + }, + { + "bbox": [ + 113, + 442, + 164, + 449 + ], + "angle": 0, + "lines": [ + { + "bbox": [ + 113, + 442, + 164, + 449 + ], + "spans": [ + { + "bbox": [ + 113, + 442, + 164, + 449 + ], + "type": "inline_equation", + "content": "\\sigma_{\\mathbf{R}} = 1^{\\circ}\\sigma_{t} = 0.1m" + } + ] + } + ], + "index": 12, + "type": "text" + }, + { + "type": "image", + "bbox": [ + 170, + 384, + 227, + 440 + ], + "blocks": [ + { + "bbox": [ + 170, + 384, + 227, + 440 + ], + "lines": [ + { + "bbox": [ + 170, + 384, + 227, + 440 + ], + "spans": [ + { + "bbox": [ + 170, + 384, + 227, + 440 + ], + "type": "image", + "image_path": "38490bd707da129099d0810b78c7adbe4157d1707659a845d3fe828948fdb519.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 175, + 442, + 223, + 449 + ], + "lines": [ + { + "bbox": [ + 175, + 442, + 223, + 449 + ], + "spans": [ + { + "bbox": [ + 175, + 442, + 223, + 449 + ], + "type": "inline_equation", + "content": "\\sigma_{\\mathbf{R}} = 2^{\\circ}\\sigma_{t} = 0.2m" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 47, + 459, + 286, + 480 + ], + "lines": [ + { + "bbox": [ + 47, + 459, + 286, + 480 + ], + "spans": [ + { + "bbox": [ + 47, + 459, + 286, + 480 + ], + "type": "text", + "content": "Figure 4. The point clouds of dataset C after the poses were perturbs by the four noise levels." + } + ] + } + ], + "index": 17, + "angle": 0, + "type": "image_caption" + } + ], + "index": 13 + }, + { + "type": "image", + "bbox": [ + 228, + 384, + 284, + 440 + ], + "blocks": [ + { + "bbox": [ + 228, + 384, + 284, + 440 + ], + "lines": [ + { + "bbox": [ + 228, + 384, + 284, + 440 + ], + "spans": [ + { + "bbox": [ + 228, + 384, + 284, + 440 + ], + "type": "image", + "image_path": "10ff24e4a1465158846008776813eafbb4d1cd47fb489fa107df0a7684288448.jpg" + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 231, + 442, + 280, + 449 + ], + "lines": [ + { + "bbox": [ + 231, + 442, + 280, + 449 + ], + "spans": [ + { + "bbox": [ + 231, + 442, + 280, + 449 + ], + "type": "inline_equation", + "content": "\\sigma_{\\mathbf{R}} = 3^{\\circ}\\sigma_{t} = 0.3m" + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "image_caption" + } + ], + "index": 15 + }, + { + "bbox": [ + 46, + 504, + 286, + 564 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 504, + 286, + 564 + ], + "spans": [ + { + "bbox": [ + 46, + 504, + 286, + 564 + ], + "type": "text", + "content": "maximum number of iterations is set to 200 for our algorithm, BALM, and LM+PF, and " + }, + { + "bbox": [ + 46, + 504, + 286, + 564 + ], + "type": "inline_equation", + "content": "10^{5}" + }, + { + "bbox": [ + 46, + 504, + 286, + 564 + ], + "type": "text", + "content": " for EF, as EF uses the first-order minimization which requires more iterations to converge. All the experiments were conducted on a desktop with an Intel i7 cpu and 64G memory." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 47, + 574, + 110, + 586 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 574, + 110, + 586 + ], + "spans": [ + { + "bbox": [ + 47, + 574, + 110, + 586 + ], + "type": "text", + "content": "5.2. Datasets" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 46, + 594, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 594, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 287, + 713 + ], + "type": "text", + "content": "We collected four datasets using a VLP-16 LiDAR. We used the LiDAR SLAM algorithm [24] to detect the planes and establish the plane association. Fig. 3 shows the four datasets. Similar to the evaluation of BA algorithms [3,8,25], we perturb the pose, and compare the PA cost in (11) for different algorithms. Specifically, we directly add Gaussian noises to the translation, and randomly generate an angle-axis vector from a Gaussian distribution to perturb the rotation. After the poses are perturb, we use (7) to get the initial plane parameters for " + }, + { + "bbox": [ + 46, + 594, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\mathrm{LM} + \\mathrm{PF}" + }, + { + "bbox": [ + 46, + 594, + 287, + 713 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 304, + 385, + 545, + 540 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 385, + 545, + 540 + ], + "spans": [ + { + "bbox": [ + 304, + 385, + 545, + 540 + ], + "type": "text", + "content": "We evaluate the performance of different algorithms under different noise levels. Let us denote the standard deviation (std) of the Gaussian noises for rotation and translation as " + }, + { + "bbox": [ + 304, + 385, + 545, + 540 + ], + "type": "inline_equation", + "content": "\\sigma_{\\mathbf{R}}" + }, + { + "bbox": [ + 304, + 385, + 545, + 540 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 385, + 545, + 540 + ], + "type": "inline_equation", + "content": "\\sigma_t" + }, + { + "bbox": [ + 304, + 385, + 545, + 540 + ], + "type": "text", + "content": ", respectively. We consider four noise levels: " + }, + { + "bbox": [ + 304, + 385, + 545, + 540 + ], + "type": "inline_equation", + "content": "\\sigma_{\\mathbf{R}} = 0.1^{\\circ}" + }, + { + "bbox": [ + 304, + 385, + 545, + 540 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 385, + 545, + 540 + ], + "type": "inline_equation", + "content": "\\sigma_t = 0.01m" + }, + { + "bbox": [ + 304, + 385, + 545, + 540 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 385, + 545, + 540 + ], + "type": "inline_equation", + "content": "\\sigma_{\\mathbf{R}} = 1^{\\circ}" + }, + { + "bbox": [ + 304, + 385, + 545, + 540 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 385, + 545, + 540 + ], + "type": "inline_equation", + "content": "\\sigma_t = 0.1m" + }, + { + "bbox": [ + 304, + 385, + 545, + 540 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 385, + 545, + 540 + ], + "type": "inline_equation", + "content": "\\sigma_{\\mathbf{R}} = 2^{\\circ}" + }, + { + "bbox": [ + 304, + 385, + 545, + 540 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 385, + 545, + 540 + ], + "type": "inline_equation", + "content": "\\sigma_t = 0.2m" + }, + { + "bbox": [ + 304, + 385, + 545, + 540 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 304, + 385, + 545, + 540 + ], + "type": "inline_equation", + "content": "\\sigma_{\\mathbf{R}} = 3^{\\circ}" + }, + { + "bbox": [ + 304, + 385, + 545, + 540 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 385, + 545, + 540 + ], + "type": "inline_equation", + "content": "\\sigma_t = 0.3m" + }, + { + "bbox": [ + 304, + 385, + 545, + 540 + ], + "type": "text", + "content": ". Fig. 4 demonstrates the point clouds of dataset C after the poses are perturbed by the four noise levels. To evaluate the performance of different algorithms suffering from large measurement noises, we also test the case that additional Gaussian noises with the std " + }, + { + "bbox": [ + 304, + 385, + 545, + 540 + ], + "type": "inline_equation", + "content": "\\sigma_{pt} = 0.05m" + }, + { + "bbox": [ + 304, + 385, + 545, + 540 + ], + "type": "text", + "content": " are added to the LiDAR point cloud, and the poses are perturbed by Gaussian noises with " + }, + { + "bbox": [ + 304, + 385, + 545, + 540 + ], + "type": "inline_equation", + "content": "\\sigma_{\\mathbf{R}} = 3^{\\circ}" + }, + { + "bbox": [ + 304, + 385, + 545, + 540 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 385, + 545, + 540 + ], + "type": "inline_equation", + "content": "\\sigma_t = 0.3m" + }, + { + "bbox": [ + 304, + 385, + 545, + 540 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 306, + 551, + 362, + 562 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 551, + 362, + 562 + ], + "spans": [ + { + "bbox": [ + 306, + 551, + 362, + 562 + ], + "type": "text", + "content": "5.3. Results" + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "content": "Fig. 5 and Fig. 6 illustrates the results. It is clear that our algorithm converges faster than other algorithms. LM+PF works well at small noises (such as " + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\sigma_{\\mathbf{R}} = 0.1^{\\circ}" + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\sigma_t = 0.01m" + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "content": "). As the noise level increases, LM+PF tends to converge slower. Constructing H and g using BALM [16] is computationally demanding. For efficiency, BALM only keeps the centroid of each plane observation (i.e., only 1 point is kept), which results in bad performance. In Fig. 5 and Fig. 6, all points are used to compute the cost in (11) after an iteration of BALM. BALM generally converges slow, as it minimizes a reduced PA problem. EF [10] adopts the first-order optimization method as it only provides a method" + } + ] + } + ], + "index": 23 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "13119" + } + ] + } + ], + "index": 24 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 67, + 70, + 527, + 424 + ], + "blocks": [ + { + "bbox": [ + 67, + 70, + 527, + 424 + ], + "lines": [ + { + "bbox": [ + 67, + 70, + 527, + 424 + ], + "spans": [ + { + "bbox": [ + 67, + 70, + 527, + 424 + ], + "type": "image", + "image_path": "4fa1350a3cee5e97ba491459cf03ea026651cedda2181aa6f54b061cb335872d.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 434, + 547, + 456 + ], + "lines": [ + { + "bbox": [ + 46, + 434, + 547, + 456 + ], + "spans": [ + { + "bbox": [ + 46, + 434, + 547, + 456 + ], + "type": "text", + "content": "Figure 5. The results of different algorithms using different initial noise levels. It is clear that our algorithm converges significantly faster than other algorithms. The " + }, + { + "bbox": [ + 46, + 434, + 547, + 456 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 46, + 434, + 547, + 456 + ], + "type": "text", + "content": "-axis represents the logarithmic scale of the cost in (11)." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 69, + 470, + 526, + 559 + ], + "blocks": [ + { + "bbox": [ + 69, + 470, + 526, + 559 + ], + "lines": [ + { + "bbox": [ + 69, + 470, + 526, + 559 + ], + "spans": [ + { + "bbox": [ + 69, + 470, + 526, + 559 + ], + "type": "image", + "image_path": "b21bc28bd873f818d0c9d5a175517159a6153e323787c0cc1d30ffa9d3372f34.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 567, + 547, + 590 + ], + "lines": [ + { + "bbox": [ + 46, + 567, + 547, + 590 + ], + "spans": [ + { + "bbox": [ + 46, + 567, + 547, + 590 + ], + "type": "text", + "content": "Figure 6. The results of different algorithms for point clouds perturbed by Gaussian noise with std " + }, + { + "bbox": [ + 46, + 567, + 547, + 590 + ], + "type": "inline_equation", + "content": "\\sigma_{pt} = 0.05m" + }, + { + "bbox": [ + 46, + 567, + 547, + 590 + ], + "type": "text", + "content": ". The rotations and translations of the poses are perturbed by Gaussian noise with std " + }, + { + "bbox": [ + 46, + 567, + 547, + 590 + ], + "type": "inline_equation", + "content": "\\sigma_{\\mathbf{R}} = 3^{\\circ}" + }, + { + "bbox": [ + 46, + 567, + 547, + 590 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 567, + 547, + 590 + ], + "type": "inline_equation", + "content": "\\sigma_t = 0.3m" + }, + { + "bbox": [ + 46, + 567, + 547, + 590 + ], + "type": "text", + "content": ", respectively." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 611, + 288, + 624 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 611, + 288, + 624 + ], + "spans": [ + { + "bbox": [ + 47, + 611, + 288, + 624 + ], + "type": "text", + "content": "to compute the gradient, which results in slow convergence." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 634, + 120, + 645 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 634, + 120, + 645 + ], + "spans": [ + { + "bbox": [ + 47, + 634, + 120, + 645 + ], + "type": "text", + "content": "6. Conclusion" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 654, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 654, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 654, + 288, + 715 + ], + "type": "text", + "content": "In the computer vision community, Newton's method is generally considered too expensive for a large-scale least-squares problem. This paper adopts the Newton's method to efficiently solve the PA problem. Our algorithm takes advantage of the fact that the optimal planes are determined" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 611, + 545, + 707 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 611, + 545, + 707 + ], + "spans": [ + { + "bbox": [ + 304, + 611, + 545, + 707 + ], + "type": "text", + "content": "by the poses, so that the number of unknowns can be significantly reduced. Furthermore, this property can ensure to obtain the optimal planes when we update the poses. The difficulty lies in how to efficiently compute the Hessian matrix and the gradient vector. The key contribution of this paper is to provide a closed-form solution for them. The experimental results show that our algorithm outperforms the state-of-the-art algorithms." + } + ] + } + ], + "index": 7 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "13120" + } + ] + } + ], + "index": 8 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 287, + 712 + ], + "type": "list", + "angle": 0, + "index": 15, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 134 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 134 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 134 + ], + "type": "text", + "content": "[1] Sameer Agarwal, Yasutaka Furukawa, Noah Snavely, Ian Simon, Brian Curless, Steven M Seitz, and Richard Szeliski. 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IEEE, 2021. 1" + } + ] + } + ], + "index": 27 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "13121" + } + ] + } + ], + "index": 29 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 8 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Efficient Semantic Segmentation by Altering Resolutions for Compressed Videos/7cf71203-1b67-4ff6-a186-04d01a4ea3fe_content_list.json b/2023/Efficient Semantic Segmentation by Altering Resolutions for Compressed Videos/7cf71203-1b67-4ff6-a186-04d01a4ea3fe_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..3427bf9e954a832a833d8dc60b3a9c2d806b3b26 --- /dev/null +++ b/2023/Efficient Semantic Segmentation by Altering Resolutions for Compressed Videos/7cf71203-1b67-4ff6-a186-04d01a4ea3fe_content_list.json @@ -0,0 +1,1447 @@ +[ + { + "type": "text", + "text": "Efficient Semantic Segmentation by Altering Resolutions for Compressed Videos", + "text_level": 1, + "bbox": [ + 80, + 130, + 888, + 152 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Yubin Hu $^{1}$ Yuze He $^{1}$ Yanghao Li $^{1}$ Jisheng Li $^{1}$ Yuxing Han $^{2}$ Jiangtao Wen $^{3}$ Yong-Jin Liu $^{1*}$ $^{1}$ BNRist, Department of Computer Science and Technology, Tsinghua University \n $^{2}$ Shenzhen International Graduate School, Tsinghua University \n $^{3}$ Eastern Institute for Advanced Study", + "bbox": [ + 106, + 179, + 869, + 252 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "{huyb20, hyz22, liyangha18}@mails.tsinghua.edu.cn, jas0nlee@icloud.com, yuxinghan@sz.tsinghua.edu.cn, jtwen@eias.ac.cn, liuyongjin@tsinghua.edu.cn", + "bbox": [ + 150, + 253, + 807, + 286 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 321, + 313, + 338 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Video semantic segmentation (VSS) is a computationally expensive task due to the per-frame prediction for videos of high frame rates. In recent work, compact models or adaptive network strategies have been proposed for efficient VSS. However, they did not consider a crucial factor that affects the computational cost from the input side: the input resolution. In this paper, we propose an altering resolution framework called AR-Seg for compressed videos to achieve efficient VSS. AR-Seg aims to reduce the computational cost by using low resolution for non-keyframes. To prevent the performance degradation caused by downsampling, we design a Cross Resolution Feature Fusion (CReFF) module, and supervise it with a novel Feature Similarity Training (FST) strategy. Specifically, CReFF first makes use of motion vectors stored in a compressed video to warp features from high-resolution keyframes to low-resolution non-keyframes for better spatial alignment, and then selectively aggregates the warped features with local attention mechanism. Furthermore, the proposed FST supervises the aggregated features with high-resolution features through an explicit similarity loss and an implicit constraint from the shared decoding layer. Extensive experiments on CamVid and Cityscapes show that AR-Seg achieves state-of-the-art performance and is compatible with different segmentation backbones. On CamVid, AR-Seg saves $67\\%$ computational cost (measured in GFLOPs) with the PSPNet18 backbone while maintaining high segmentation accuracy. Code: https://github.com/THU-LYJ-Lab/AR-Seg.", + "bbox": [ + 75, + 353, + 473, + 777 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 805, + 209, + 821 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Video semantic segmentation (VSS) aims to predict pixel-wise semantic labels for each frame in a video sequence. In contrast to a single image, a video sequence", + "bbox": [ + 75, + 830, + 468, + 878 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/a19c65e5563aed5e5e1aaf011244cad46bc64bf07f92e0f99beef46a717c6650.jpg", + "image_caption": [ + "(a)", + "Figure 1. Comparison of different VSS methods: (a) per-frame framework, (b) Accel [19] that alters the depth of models, and (c) our AR-Seg. AR-Seg reduces the computational cost for nonkeyframes by lowering the input resolution (depicted by narrow blocks), which is a dimension orthogonal to the depth of networks." + ], + "image_footnote": [], + "bbox": [ + 509, + 319, + 581, + 489 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/120c28654a5c1e738627652e955fb098b2fc38b0df3f86bef4abadf5d86ddbc9.jpg", + "image_caption": [ + "(b)" + ], + "image_footnote": [], + "bbox": [ + 593, + 319, + 736, + 489 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/a7dbec70155366bd182fbbeb651458745ca0977537f081ad81cbc229f9741477.jpg", + "image_caption": [ + "(c)" + ], + "image_footnote": [], + "bbox": [ + 748, + 319, + 890, + 489 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "is a series of consecutive image frames recorded at a certain frame rate (usually 25fps or higher). Applying image-based segmentation methods [6, 25, 48, 52, 55] to a video frame by frame consumes considerable computational resources. To improve the efficiency of VSS, existing methods mainly focus on the design of network architectures. A class of methods proposes compact and efficient image-based architectures to reduce the computational overhead per-frame [22, 23, 28, 49, 51, 52, 54]. Another class of methods applies a deep model to keyframes and a shallow network for non-keyframes to avoid the repetitive computation [19, 24, 27, 34] for videos.", + "bbox": [ + 496, + 609, + 892, + 792 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "The work presented in this paper is based on an important observation: the above existing works ignored a crucial factor that affects the computational cost from the input side: the input resolution. For image-related tasks, the input resolution directly determines the amount of computation, e.g., the computational cost of 2D convolution is proportional to the product of image width and height. Once we", + "bbox": [ + 496, + 795, + 893, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Corresponding author.", + "bbox": [ + 94, + 886, + 220, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "22627", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "downsample the input frame by $0.5 \\times 0.5$ , the computational overhead can be reduced by $75\\%$ . On the other hand, decreasing resolution often leads to worse segmentation accuracy due to the loss of information [43,54]. In this paper, we propose to prevent the accuracy degradation by using temporal correlation in the video. Since the contents of video frames are temporally correlated, the local features lacking in low-resolution (LR) frames can be inferred and enriched by finding correspondences in sparse high-resolution (HR) reference frames based on motion cues. In a compressed video, the motion vectors contain such motion cues and can be obtained along with the video frames from video decoding at almost no additional cost.", + "bbox": [ + 75, + 90, + 472, + 287 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Motivated by the above observation, we propose an altering resolution framework for compressed videos, named AR-Seg, to achieve efficient VSS. As shown in Figure 1(c), AR-Seg uses an HR branch to process keyframes at high resolution and an LR branch to process non-keyframes at low resolution. In particular, to prevent performance drop caused by downsampling, we insert a novel Cross Resolution Feature Fusion (CReFF) module into the LR branch and supervise the training with a Feature Similarity Training (FST) strategy to enrich local details in the LR features. CReFF fuses the HR keyframe features into LR nonkeyframe features in two steps: 1) Align the spatial structures of features from different frames by feature warping with motion vectors, which can be readily obtained from compressed videos at almost no additional cost; 2) Selectively aggregate the warped features (which may be noisy after warping) into LR features with the aid of local attention mechanism. Since local attention assigns different importance to each location in the neighborhood, it is an effective way to avoid misleading by noisy warped features.", + "bbox": [ + 75, + 289, + 472, + 592 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Furthermore, our proposed FST strategy guides the learning of the CReFF aggregated features. FST consists of an explicit similarity loss (between the aggregated features and HR features inferred from non-keyframes) and an implicit constraint from the shared decoding layer across the HR and LR branches. Such a training strategy helps the LR branch to learn from features extracted from the HR branch, which is reliable and effective. Integrated with CReFF and FST, AR-Seg efficiently compensates for the accuracy loss of LR frames. Overall, AR-Seg significantly reduces the computational cost of VSS by altering input resolutions, while maintaining high segmentation accuracy.", + "bbox": [ + 75, + 595, + 472, + 777 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To sum up, we make three contributions in this paper: 1) We propose an efficient framework for compressed videos, named AR-Seg, that uses altering input resolution for VSS and significantly reduces the computational cost without losing segmentation accuracy. 2) We design an efficient CReFF module to prevent the accuracy loss by aggregating HR keyframe features into LR non-keyframe features. 3) We propose a novel FST strategy that supervises the", + "bbox": [ + 75, + 779, + 472, + 902 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "LR branch to learn from the HR branch through both explicit and implicit constraints. Experiment results demonstrate the effectiveness of AR-Seg with different resolutions, backbones, and keyframe intervals. On both CamVid [3] and Cityscapes [9] datasets, compared to the constant-resolution baselines, AR-Seg reduces the computational cost by nearly $70\\%$ without compromising accuracy.", + "bbox": [ + 496, + 90, + 893, + 198 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Works", + "text_level": 1, + "bbox": [ + 498, + 210, + 650, + 226 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "As a fundamental task of scene understanding, semantic segmentation has been an active research area for many years [8, 13, 21, 41], which also attracts considerable attention in the study of deep neural networks, e.g., FCN [25], DeepLabs [4, 5] and PSPNet [55]. In order to obtain accurate results in real-time applications, several methods have been proposed to improve the efficiency of semantic segmentation, which we summarize as follows.", + "bbox": [ + 496, + 236, + 893, + 356 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Efficient Image Segmentation Methods. Many compact architectures have been proposed for efficient image segmentation. DFANet [22] adopted a lightweight backbone to reduce computational cost and designed cross-level aggregation for feature refinement. DFNet [23] utilized a partial order pruning algorithm to search segmentation models for a good trade-off between speed and accuracy. ICNet [54] used a cascade fusion module and transformed part of the computation from high-resolution to low-resolution. Wang et al. [43] designed superresolution learning to improve image segmentation performance. BiSeNets [11,51,52] used two-stream paths for low-level details and high-level context information, respectively. ESPNet [28] used an efficient spatial pyramid to accelerate the convolution computation. These efficient backbone networks reduce the computational burden of single-image segmentation, and can be applied to temporal or spatial frameworks in VSS.", + "bbox": [ + 496, + 357, + 895, + 628 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Temporally Correlated Video Segmentation. Another group of methods focus on utilizing temporal redundancy in videos. They proposed various mechanisms that propagate the deep features extracted from keyframes to reduce the computation for non-keyframes. Clockwork [36] directly reused the segmentation result from keyframes, while Mahasseni et al. [27] interpolated segmentation results in the neighborhood. Noticing the lack of information from non-keyframes, Li et al. [24] extracted shallow features from non-keyframes, and fused them into the propagated deep features by spatially variant convolution. To compensate for the spatial misalignment between video frames, Zhu et al. [56] and Xu et al. [50] warped the intermediate features from keyframes by optical flow to produce segmentation results for non-keyframes. Jain et al. [19] fused the shallow features of non-keyframe into the warped features, and decoded them into better results. With global attention mechanism, TD-Net [16] aggregated the features from different", + "bbox": [ + 496, + 628, + 895, + 901 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "22628", + "bbox": [ + 478, + 945, + 519, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "time stamps and replaced the deep model with several shallow models distributed across the timeline. All the above methods mainly reduced the depth of backbone networks, but neglected the factor of input resolution considered in this paper. Instead of processing the image frames as a whole, Verelst et al. [42] split the frame into blocks and chose to copy or process them by a policy network. This block-based method reduces computational overhead from the spatial dimension, but lacks global information on nonkeyframes. Kim et al. [20] attempted to improve efficiency by reducing resolution. But they directly used the LR segmentation results, thus suffering from severe performance degradation. Compared to these methods, our proposed AR-Seg keeps the global information of LR non-keyframes, and enhances LR frames by selectively aggregating intermediate features from HR keyframes.", + "bbox": [ + 75, + 90, + 472, + 332 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Compressed-Domain Video Analysis. Compressed video formats have been recently utilized in computer vision tasks. The motion vectors and residual maps are treated as additional modalities and directly fed into networks for video action recognition [1, 17, 37, 47] and semantic segmentation [39]. Such motion information also helps compensate for the spatial misalignment of features from different frames. Wang et al. [44] leveraged motion vectors to warp features in previous frames for object detection. Fan et al. [12] conditionally executed the backbone network for pose estimation depending on the residual values. For VSS, several methods have been proposed for efficient segmentation in the compressed domain. Jain et al. [18] warped the former and latter keyframe features using motion vectors, and predicted the non-keyframe features by interpolation. Tanujaya et al. [40] warped the results of keyframe segmentation for non-keyframes, and refined the warped segmentation by guided inpainting. Feng et al. [14] replaced a block of warped features with a local non-keyframe feature patch for further refinement. These methods reduced the computational cost of VSS, but suffered from performance degradation due to the limited capability of their feature refinement modules designed for non-keyframes. In our proposed AR-Seg, the warped features are refined by local attention mechanism according to the LR features of non-keyframes. Our attention-based refinement selectively aggregates the warped features and effectively suppresses the noise in motion vectors, achieving good segmentation accuracy with little computational overhead.", + "bbox": [ + 75, + 333, + 472, + 772 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Method", + "text_level": 1, + "bbox": [ + 76, + 784, + 169, + 800 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In order to achieve efficient VSS for compressed videos, we propose an altering resolution framework named AR-Seg (Section 3.1). AR-Seg uses two branches to process HR keyframes and LR non-keyframes in the video separately. To compensate for the information loss due to down-sampling the non-keyframes, we design a novel CReFF", + "bbox": [ + 75, + 809, + 472, + 902 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "module that aggregates HR keyframe features into LR nonkeyframe features (Section 3.2). To guide the learning of aggregated features, we further propose a novel feature similarity training (FST) strategy containing both explicit and implicit constraints (Section 3.3).", + "bbox": [ + 496, + 90, + 893, + 167 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. AR-Seg Framework", + "text_level": 1, + "bbox": [ + 498, + 176, + 692, + 191 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "For image/video semantic segmentation tasks, the input resolution directly determines the amount of computation, no matter what type of algorithms are applied, e.g., Conditional Random Fields, CNNs, and Transformers. Although reducing resolution has been studied in the context of video recognition [26, 29], altering resolution in dense prediction tasks like VSS remains unexplored. Based on this observation, we design the AR-Seg framework for VSS, which inputs video frames with altering resolutions; i.e., in AR-Seg, only a few keyframes are processed at high resolution to preserve fine details, while other non-keyframes are processed at low resolution to reduce the computational cost.", + "bbox": [ + 496, + 199, + 893, + 381 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "To identify the keyframes, we make use of the frame structure in a group of pictures (GOP) encoded in compressed videos [38, 46]. A GOP includes $L$ consecutive frames of three types: I frame, P frame, and B frame. I frames are encoded in intra mode, while P and B frames are encoded in inter mode that computes motion vectors for motion compensation. In each GOP, we treat the first I frame as a keyframe and process it at high resolution. The remaining $L - 1$ frames in GOP are non-keyframes and processed at low resolution. To simplify the description of our method, following the previous works [14, 47], we only consider the GOP structure without B frames in this section. The full treatment including B frames is presented in Appendix A4.", + "bbox": [ + 496, + 381, + 893, + 578 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Due to the domain gap between images with different resolutions, it is difficult for a single network to extract features suitable for both HR and LR resolution images. Thus we design two branches with shared backbone architecture in the model and train them separately for each resolution. Figure 1(c) summarizes the proposed AR-Seg framework. It consists of two branches: an HR branch for keyframes and an LR branch for non-keyframes.", + "bbox": [ + 496, + 578, + 893, + 699 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The HR branch adapts an image segmentation network, which consists of a feature sub-network $N_{feat}$ , a task subnetwork $N_{task}$ , and a final 1x1 convolutional layer1. It predicts segmentation results in high-resolution and simultaneously provides intermediate features before the final convolution as a reference for the LR branch. The LR branch is equipped with the same backbone network as the HR branch. To prevent performance degradation caused by downsampling, we design a CReFF module that aggregates HR features of the keyframe into the LR branch and place it before the final convolution layer of the backbone network.", + "bbox": [ + 496, + 699, + 893, + 866 + ], + "page_idx": 2 + }, + { + "type": "page_footnote", + "text": "1We follow the modular division of backbone networks in [19]. Two backbones are discussed and compared in Section 4.", + "bbox": [ + 500, + 875, + 890, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "22629", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/ec9230817086b2e542bd32614ab9b5fa9bcc243a2216af6299c71fffd6f663b9.jpg", + "image_caption": [ + "Figure 2. The CReFF module in the network architecture and feature similarity training (FST) strategy. CReFF consists of feature warping $\\mathcal{W}_{MV}$ and local-attention-based feature fusion $\\mathcal{F}_{LA}$ (Section 3.2). FST includes the explicit supervision by the feature similarity loss and the implicit supervision from shared convolution (Section 3.3). Parameters in gray blocks are fixed during the training of the LR branch." + ], + "image_footnote": [], + "bbox": [ + 98, + 85, + 877, + 378 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "CReFF aggregates the HR reference features into the extracted LR features, yielding estimated HR features for the non-keyframes, which are further converted into pixel-wise semantic labels by the final convolution layer.", + "bbox": [ + 75, + 444, + 468, + 503 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "As illustrated in Figure 1, different from the previous Accel framework [19], AR-Seg performs feature fusion before the last $1 \\times 1$ convolution layer, instead of before the task sub-network $N_{task}$ . The reason is twofold: 1) Since feature maps before the final convolution have basically the same spatial layout as the input images and segmentation outputs, we can utilize motion vectors to compensate for the spatial misalignment of features at such position; and 2) As the CReFF module actually upsamples the LR features, such a placement allows almost all convolution layers to benefit from the low resolution, thus reducing most of the computational cost.", + "bbox": [ + 75, + 505, + 470, + 686 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. CReFF: Cross Resolution Feature Fusion", + "text_level": 1, + "bbox": [ + 76, + 695, + 434, + 710 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In the AR-Seg framework, CReFF aims to prevent the performance degradation caused by the lack of fine local details in LR non-keyframes. Unlike a single image, video frames are intrinsically temporally correlated, so missing details in LR non-keyframes can be retrieved from the corresponding regions in HR keyframes according to motion cues. Motion vectors (MVs) in the compressed video exactly provide such motion cues at the block level, i.e., pixels inside a macroblock share the same motion vector. Almost all mainstream video compression standards use motion vectors for inter-prediction, including H.26x series [38, 46], AOMedia series [7] and AVS series [10, 15, 53]. Such block-", + "bbox": [ + 75, + 719, + 470, + 901 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "wise MVs are readily available in compressed videos and can be used to assist the LR branch.", + "bbox": [ + 496, + 444, + 890, + 472 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Specifically, as depicted in Figure 2, the HR branch of AR-Seg extracts the feature $F_{I} \\in \\mathcal{R}^{C \\times H \\times W}$ from an I frame, and the LR branch extracts the feature $f_{P} \\in \\mathcal{R}^{C \\times h \\times w}$ from a P frame. Although P frames are processed in low resolution, CReFF takes $F_{I}, M_{P},$ and $f_{P}$ as input to generate the aggregated feature $\\tilde{F}_{P}$ , where $M_{P} \\in \\mathcal{R}^{2 \\times H \\times W}$ denotes the MVs from P frame to I frame. The two channels of $M_{P}$ correspond to $x$ and $y$ dimensions of motion vectors, denoted by $c_{x}$ and $c_{y}$ . Inside the CReFF module, the MV-based feature warping operation $\\mathcal{W}_{MV}$ firstly warps $F_{I}$ to the spatial layout of the P frame, which can be formulated as per-pixel shifting:", + "bbox": [ + 496, + 474, + 892, + 656 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {F} _ {I} ^ {(x, y)} = F _ {I} ^ {\\left(x + M _ {P} ^ {\\left(c _ {x}, x, y\\right)}, y + M _ {P} ^ {\\left(c _ {y}, x, y\\right)}\\right)}, \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 571, + 666, + 890, + 691 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\hat{F}_I\\in \\mathcal{R}^{C\\times H\\times W}$ denotes the warped HR feature that will be further fused into LR features.", + "bbox": [ + 496, + 702, + 890, + 733 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Due to the coarse-grained MVs (block-level instead of pixel-level) and the varying occlusion relationships across video frames, the warped features $\\hat{F}_I$ are often noisy and misleading. Inspired by the success of non-local operation [45] and attention mechanism [16, 31, 33] in video-based applications, we propose to assign different fusion importance weights to the $(x,y)$ locations in noisy features $\\hat{F}_I$ by attention mechanism. Since $\\hat{F}_I$ is roughly spatially aligned to $f_{p}$ after warping, we use local attention to efficiently fuse the features as follows.", + "bbox": [ + 496, + 734, + 890, + 883 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In the local-attention-based feature fusion module $\\mathcal{F}_{LA}$", + "bbox": [ + 517, + 885, + 890, + 901 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "22630", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "we firstly generate the Value and Key feature maps from the warped HR features $\\hat{F}_I$ , and the Query maps from the upsampled LR features $\\bar{F}_P$ . The $3 \\times 3$ grouped convolution $\\mathbf{Conv}_g$ with groups $= C$ is selected to efficiently encode the feature maps into attention representations $V_I, K_I, Q_P \\in \\mathcal{R}^{C \\times H \\times W}$ . Note that attention representations share the same channel size as the intermediate features. Denote the $n \\times n$ neighborhood centered at $(x,y)$ as $Nbhd_{(x,y)}$ . Within $Nbhd_{(x,y)}$ , the output of local attention $A_P$ at the position $(x,y)$ is generated by", + "bbox": [ + 75, + 90, + 472, + 243 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nA _ {P} ^ {(x, y)} = \\overline {{V _ {I} ^ {N b h d _ {(x , y)}}}} \\mathcal {S} \\left(\\overline {{K _ {I} ^ {N b h d _ {(x , y)}}}}, Q _ {P} ^ {(x, y)}\\right), \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 101, + 250, + 468, + 268 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $A_{P}^{(x,y)}$ , $Q_{P}^{(x,y)} \\in \\mathcal{R}^{C \\times 1}$ denote the feature vectors at the position $(x,y)$ of $A_{P}$ and $Q_{P}$ respectively, and $\\overline{V_{I}^{Nbhd_{(x,y)}}}$ , $\\overline{K_{I}^{Nbhd_{(x,y)}}} \\in \\mathcal{R}^{C \\times n^{2}}$ are the re-arranged feature vectors within $Nbhd_{(x,y)}$ in $V_{I}$ and $K_{I}$ , respectively. The similarity operation $\\mathcal{S}(K,Q)$ is formulated as", + "bbox": [ + 76, + 273, + 468, + 354 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {S} (K, Q) = \\operatorname {S o f t m a x} \\left(\\frac {K ^ {T} Q}{\\sqrt {C}}\\right). \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 169, + 359, + 468, + 396 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Furthermore, the aggregated feature $\\tilde{F}_P$ for P frame is obtained in a residual fashion:", + "bbox": [ + 76, + 401, + 468, + 431 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\tilde {F} _ {P} = \\bar {F} _ {P} + A _ {P} = \\text {U p s a m p l e} \\left(f _ {P}\\right) + A _ {P}. \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 130, + 436, + 468, + 455 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In summary, using the CReFF module, the feature details from the I frame are firstly aligned to the P frame, and then aggregated into the LR branch according to the pixel-wise similarity between $Q_{P}$ and $K_{I}$ . The verification of the architecture design of CReFF is presented in Section 4.3. The reader is referred to Appendix A1 for more details on the visualization of attention weights in $\\mathcal{F}_{LA}$ .", + "bbox": [ + 75, + 460, + 468, + 568 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.3. FST: Feature Similarity Training", + "text_level": 1, + "bbox": [ + 76, + 574, + 372, + 590 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In order to effectively train the CReFF module, we propose a feature similarity training (FST) strategy. FST utilizes the HR features of P frame $F_{P}$ (extracted from the HR branch) to guide the learning of the aggregated features $\\tilde{F}_{P}$ in the LR branch. Since $F_{P}$ contains sufficient details to produce high-quality segmentation results, CReFF can learn how to aggregate $\\bar{F}_{P}$ and $\\hat{F}_{I}$ into effective HR features from it under the supervision of FST. Specifically, FST supervises the training process of the LR branch both explicitly and implicitly in the following ways.", + "bbox": [ + 75, + 598, + 468, + 748 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The explicit constraint is to use the feature similarity loss $\\mathcal{L}_{fs}$ . We use mean square error (MSE) to measure the difference between $\\tilde{F}_P$ and $F_{P}$ , which serves as an additional regularization for the LR model:", + "bbox": [ + 76, + 750, + 468, + 810 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} = \\mathcal {L} _ {s e g} + \\mathcal {L} _ {f s} = C E \\left(S _ {P}, G _ {P}\\right) + M S E \\left(\\tilde {F} _ {P}, F _ {P}\\right), \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 84, + 815, + 468, + 835 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $S_P \\in \\mathcal{R}^{C_{out} \\times H \\times W}$ denotes the segmentation result produced by LR branch, $G_P \\in \\mathcal{R}^{H \\times W}$ denotes the ground-truth segmentation of P frame and the segmentation loss $\\mathcal{L}_{seg}$ is the standard cross entropy loss $CE(S_P, G_P)$ .", + "bbox": [ + 76, + 838, + 468, + 901 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The implicit constraint of FST is the shared decoding layer of $\\tilde{F}_P$ and $F_{P}$ . In the segmentation backbone model trained on the HR images, the final convolution layer acts as the segmentation decoder, which contains deep semantic information about high-quality HR features. To utilize such information, we directly transfer the final $1\\times 1$ convolution layer of the HR branch to the LR branch with fixed parameters. Since the parameters are trained on HR features, they produce better segmentation results $S_P$ when $\\tilde{F}_{P}$ is closer to the HR feature $F_{P}$ .", + "bbox": [ + 496, + 90, + 890, + 241 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In summary, with the explicit and implicit constraints, FST effectively transfers the knowledge of HR features from the HR branch to the LR branch, enabling high-quality segmentation based on the aggregated features of CReFF. Figure 2 shows the overall training strategy for the LR branch. The HR I frame provides the features $F_{I}$ for feature fusion in CReFF, and the HR P frame provides the features $F_{P}$ for the explicit supervision in FST. Parameters of the LR branch are trained using the total loss $\\mathcal{L}$ via backpropagation, with fixed parameters of the HR branch and the shared final convolution layer.", + "bbox": [ + 496, + 243, + 890, + 409 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 500, + 426, + 633, + 444 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We evaluate the proposed AR-Seg framework on CamVid [3] and Cityscapes [9] datasets for street-view video semantic segmentation. Below we present experiments to demonstrate the efficiency of AR-Seg and its compatibility with different backbone models, resolutions, and video compression configurations.", + "bbox": [ + 496, + 453, + 890, + 544 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.1. Experimental Setup", + "text_level": 1, + "bbox": [ + 500, + 556, + 689, + 573 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Datasets & Pre-processing. The CamVid [3] dataset consists of 4 videos of $720 \\times 960$ resolution captured at 30 fps, with semantic annotations at 1Hz and, in part, 15Hz. The Cityscapes [9] dataset contains street view videos of $1024 \\times 2048$ resolution captured in 17 fps, from which 5,000 images are densely annotated. We use the official train/validation/test split for both datasets. Following the previous works [16, 51], we select 11 and 19 classes for training and evaluation on these two datasets, respectively.", + "bbox": [ + 496, + 580, + 890, + 717 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "To simulate a real video compressed scenario, we compress the videos at reasonable bit-rates of 3Mbps for CamVid and 5Mbps for Cityscapes with the HEVC/H.265 [38] standard. The reader is referred to Appendix A3.1 for the detailed pre-processing steps.", + "bbox": [ + 496, + 718, + 890, + 794 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Models & Baselines. To demonstrate the compatibility of AR-Seg with different backbones, we select two representative image segmentation models in our experiments: PSPNet [55] and BiseNet [52], which is similar to settings in the previous work [16]. The former is a widely used classical model, and the latter is a lightweight model that achieves state-of-the-art performance. We use $\\mathbf{A}\\mathbf{R}^{\\alpha}$ - as the prefix", + "bbox": [ + 496, + 795, + 890, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "22631", + "bbox": [ + 478, + 945, + 517, + 955 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "of AR-Seg with specified backbone networks, where $\\alpha$ denotes the downsample scale for the LR branch.", + "bbox": [ + 75, + 90, + 467, + 119 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Training & Evaluation Details. Given a GOP length $L$ , we train the LR branch with image pairs $(i, p)$ , where $p$ refers to the P frame with annotation and $i = p - (L - 1)$ refers to the I frame as a reference. We denote the distance between the annotated and the reference frames as $d$ , then $d = L - 1$ for the training pairs.", + "bbox": [ + 75, + 121, + 467, + 212 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "For evaluation, we test AR-Seg with different distances $d$ between the target frame $p$ and the reference keyframe $i$ . For $d = 0$ , we treat frame $p$ as the keyframe and process it by the HR branch. Otherwise, we feed frame $p$ into the LR branch for $d \\in (0, L - 1]$ . The average of $mIoU_{d}$ for each distance $d$ is reported as the mIoU result. We measure FLOPs by PyTorch-OpCounter [35] following the previous methods [30, 32]. All the comparisons are evaluated on the compressed videos. More training and evaluation details are presented in Appendix A3.2 and A3.3.", + "bbox": [ + 75, + 214, + 467, + 364 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.2. Experiment Results", + "text_level": 1, + "bbox": [ + 76, + 377, + 264, + 393 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Comparison with image-based methods. We first compare AR-Segs (with PSPNet [55] and BiseNet [52] as backbone) to their image-based counterparts of $1.0\\mathrm{x}$ resolution. As shown in Table 1, on both CamVid and Cityscapes datasets, the proposed $\\mathrm{AR^{0.5}}$ models achieve on-par or better performance than the $1.0\\mathrm{x}$ resolution baselines while saving $67\\%$ computational cost. Different from the low-resolution baselines that lead to significant performance degradation, AR-Seg successfully preserves the segmentation accuracy with the help of the CReFF module and the FST strategy. More comparisons between AR-Seg and the LR baselines under different resolutions are presented in Appendix A2.1. Furthermore, these experiment results with PSPNet and BiseNet also demonstrate the compatibility of AR-Seg for different backbone networks.", + "bbox": [ + 75, + 401, + 467, + 626 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Comparison with video-based methods. Taking temporal coherence into consideration, we compare AR-Seg with the recent state-of-the-art video-based methods for efficient VSS. Besides the accuracy and computational cost, we also follow the previous work [33] to report the relative changes compared to their single-frame backbone models. Specifically, $\\widetilde{\\Delta}\\mathrm{mIoU}$ denotes the relative change of mIoU, and $\\widetilde{\\Delta}\\mathrm{GFLOPs}$ denotes the relative change of GFLOPs. As shown in Table 2, existing video-based methods usually improve accuracy $(\\widetilde{\\Delta}\\mathrm{mIoU} > 0)$ at the cost of more computation $(\\widetilde{\\Delta}\\mathrm{GFLOPs} > 0)$ , e.g., TDNet [16] and Accel [19]. Other methods, including BlockCopy [42], TapLab [14] and Jain et al. [18], reduce the computational cost $(\\widetilde{\\Delta}\\mathrm{GFLOPs} < 0)$ but the accuracy also decreases $3\\% - 7\\%$ $(\\widetilde{\\Delta}\\mathrm{mIoU} < 0)$ . As a comparison, our proposed models $\\mathrm{AR^{0.6}}$ - can reduce the computational cost $(\\widetilde{\\Delta}\\mathrm{GFLOPs} < 0)$ by more than $55\\%$ and preserve the accuracy of single-frame backbone models $(\\widetilde{\\Delta}\\mathrm{mIoU} \\geq 0)$ . With the lightweight", + "bbox": [ + 75, + 628, + 467, + 900 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/9b8c50b213efd2148ee74c81a94a4299f978448bf8430a06465ad26122e68021.jpg", + "table_caption": [ + "Table 1. Comparison to the image-based methods on CamVid test set and Cityscapes valid set." + ], + "table_footnote": [], + "table_body": "
MethodPSPNet18 [55]BiseNet18 [52]
mIoU(%)↑GFLOPs ↓mIoU(%)↑GFLOPs ↓
CamVid1.0x69.43309.0271.5758.83
AR0.771.23169.8671.7831.89
AR0.670.82133.0971.6024.68
AR0.570.48101.9870.3818.96
Cityscapes1.0x69.00560.9770.09178.96
AR0.770.23302.9570.8697.10
AR0.669.45234.9170.7276.06
AR0.569.03177.4470.5757.00
", + "bbox": [ + 501, + 119, + 887, + 275 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/cd9f020ef2f717f40fe11560552ebd905d7bac4f5d17ab19e419a5643bd019c2.jpg", + "table_caption": [ + "Table 2. Comparison to the video-based methods on CamVid test set and Cityscapes valid set. $\\tilde{\\Delta} x = \\frac{\\Delta x}{|x|}$ denotes the relative change compared to their single-frame backbone models. The best results are bold and the second best results are underlined." + ], + "table_footnote": [], + "table_body": "
MethodmIoU↑GFLOPs↓ΔmIoU↑ΔGFLOPs↓
CamVidAccel-DL18 [19]66.15397.70+13.8%+61.9%
TD4-PSP18 [16]70.13363.70+1.0%+17.7%
BlockCopy [42]66.75107.52-5.2%-45.7%
TapLab-BL2 [14]67.57117.73-3.1%-50.2%
Jain et al. [18]67.61146.97-4.3%-53.8%
AR0.6-PSP1870.82101.98+2.0%-57.0%
AR0.6-Bise1871.6024.68+0.0%-58.0%
CityscapesAccel-DL18 [19]68.251011.75+18.4%+96.0%
TD4-PSP18 [16]70.11673.06+1.6%+20.0%
BlockCopy [42]67.69294.20-6.7%-41.2%
TapLab-BL2 [14]68.90237.29-4.1%-50.6%
Jain et al. [18]68.57342.67-5.1%-52.5%
AR0.6-PSP1869.45234.91+0.7%-58.1%
AR0.6-Bise1870.7276.06+0.9%-57.5%
", + "bbox": [ + 501, + 349, + 890, + 575 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "backbone model BiseNet, AR $^{0.6}$ -Bise18 achieves good performance in both accuracy and computational cost. More results of video-based methods and their single-frame backbone models are presented in Appendix A2.2.", + "bbox": [ + 498, + 592, + 890, + 654 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.3. Ablation Study", + "text_level": 1, + "bbox": [ + 500, + 664, + 653, + 681 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We perform ablation studies to show the importance of each component in CReFF and FST, as well as the location of CReFF. We also evaluate AR-Seg in terms of different resolutions and GOP lengths, which reflects the influence of hyper-parameters $\\alpha$ and $L$ , respectively. We conducted ablation studies on the 30fps CamVid dataset, and used PSPNet18 as the default backbone model, $L = 12$ as the default GOP length, and HEVC@3Mbps as the default codec.", + "bbox": [ + 496, + 688, + 890, + 808 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Architecture of CReFF. We first validate the necessity of $\\mathcal{W}_{MV}$ and $\\mathcal{F}_{LA}$ . The method without CReFF directly applies FST to the upsampled features $\\bar{F}_P$ and serves as a baseline. As shown in Table 3, simply warping the keyframe features $(+\\mathcal{W}_{MV})$ saves the most amount of computation by skipping processing non-keyframes with the", + "bbox": [ + 496, + 810, + 890, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "22632", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/844687012923341ca5ef9199a33873d1bf3ad665dfbbe5437e7dde33078d31ad.jpg", + "image_caption": [ + "Figure 3. Semantic segmentation on CamVid (top) and Cityscapes (bottom) with $d = 11$ . Note that AR0.5-PSP18 predicts more semantic details than the constant-resolution PSPNet18 working on 0.5x resolution. Compared to the 1.0x baseline, AR0.5-PSP18 generates similar segmentation results, but consumes only 33.0% computational cost (measured in GFLOPs)." + ], + "image_footnote": [], + "bbox": [ + 78, + 89, + 893, + 265 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "segmentation network, but receives poor accuracy. Directly fusing the keyframe features using local attention $(+ \\mathcal{F}_{LA})$ does not perform very well, because the feature maps are not well-aligned due to object motion in videos.", + "bbox": [ + 75, + 345, + 468, + 405 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We further evaluate the design of $\\mathcal{F}_{LA}$ by replacing $7\\times 7$ local attention $(LA)$ with other operations, including $LA$ with different neighborhood sizes, $LA$ with non-grouped convolution encoders $(\\mathcal{F}_{LA^*})$ , global attention $(\\mathcal{F}_{GA})$ and one-layer convolution $(\\mathcal{F}_{Conv})$ . For $\\mathcal{F}_{GA}$ , we downsample the Value and Key maps by $\\frac{1}{32}$ to save the computation. $\\mathcal{F}_{Conv}$ processes the concatenated feature $[\\hat{F}_I,\\bar{F}_P]$ with a $3\\times 3$ convolution. Due to the large channel number in deep layers, such an operation brings considerable computation overhead. Results in Table 3 show that $\\mathcal{F}_{LA}$ with a $7\\times 7$ neighborhood achieves a good balance between computation and accuracy. Other designs increase the computational cost without improving the accuracy. Furthermore, removing the direct connection (DC) path from CReFF reduces the mIoU to $69.14\\%$ . This result implies that CReFF is more likely to learn the residuals of HR features than the absolute values.", + "bbox": [ + 75, + 407, + 470, + 667 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Location of CReFF. As specified in Section 3.1, we place CReFF before the final $1 \\times 1$ convolution layer, which is different from the previous Accel framework [19]. To evaluate the influence of the split point location, we insert CReFF before different layers and evaluate the performance. Split points include the final convolution layer ( $C_{1 \\times 1}$ ), the task sub-network $N_{task}$ and the feature sub-network $N_{feat}$ . For the $N_{feat}$ case, we insert CReFF after the first convolution layer of ResNet. As shown in Table 3, placing CReFF before $C_{1 \\times 1}$ results in the best performance, which affirms our design in Section 3.1. We note that fusing features at an early stage does not improve accuracy, but rather considerably increases computational cost.", + "bbox": [ + 75, + 670, + 468, + 867 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Feature Similarity Training (FST). The proposed FST strategy consists of the MSE Loss and the shared final con", + "bbox": [ + 76, + 869, + 468, + 900 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/7895eb5dad6c0b7f1dc29089e91dd74fe90377eefcd34d8499ac10304801d821.jpg", + "table_caption": [ + "Table 3. Ablation experiments on CamVid dataset with PSPNet18. Settings used in our final model are underlined." + ], + "table_footnote": [], + "table_body": "
ExperimentMethodmIoU(%)GFLOPs
BaselinePSPNet18 (1.0x)69.43309.02
PSPNet18 (0.5x)66.5177.27
Architecture of CReFF+ WMV + FLA (7x7)70.48101.98
w/o CReFF67.1496.60
+ WMV57.6425.75
+ FLA (7x7)67.93101.98
+ WMV + FLA (3x3)70.3098.74
+ WMV + FLA* (11x11)70.48107.32
+ WMV + FLA* (7x7)69.99170.96
+ WMV + FGA (1/32)67.11113.58
+ WMV + FConv70.45143.63
+ CReFF w/o DC69.14101.98
Location of CReFFbefore C1×170.48101.98
before Ntask68.60214.76
before Nfeat68.31308.46
Feature Similarity+ MSE Loss + Shared C1×170.48101.98
w/o FST69.21101.98
Training (FST)+ Shared C1×169.57101.98
+ MSE Loss70.17101.98
+ KL Loss + Shared C1×168.91101.98
Keyframe IntervalAR0.5-PSP18, L=1270.48101.98
AR0.5-PSP18, L=1570.2897.88
AR0.5-PSP18, L=2070.2894.11
AR0.5-PSP18, L=3069.6790.34
", + "bbox": [ + 501, + 373, + 888, + 752 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "volution layer $C_{1\\times 1}$ . We train AR $^{0.5}$ -PSP18 with or without these components and report the results in Table 3. Both components improve the segmentation performance compared to the model trained without FST. We also replace the MSE Loss with the Kullback-Leibler (KL) Divergence Loss, but the resulting segmentation performance is poor.", + "bbox": [ + 496, + 775, + 890, + 867 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Resolution of LR Branch. By adjusting the resolution of the LR branch, AR-Seg can tailor the setting adaptive to", + "bbox": [ + 498, + 869, + 892, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "22633", + "bbox": [ + 478, + 945, + 517, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/441c89955f0eb3d5cff9182c5fdf7790b474f9a9b6763eb2de8dcce201210e50.jpg", + "image_caption": [ + "(a)" + ], + "image_footnote": [], + "bbox": [ + 78, + 88, + 308, + 200 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/3d81eac544980a27b9843fb620063f50117b8a1f1c120890a123f24bea38d930.jpg", + "image_caption": [ + "(b)", + "Figure 4. (a) Performance of AR-Seg with different resolutions for the LR branch. (b) $mIoU_{d}$ for annotated frames with different distances to key frame. Value intervals of $mIoU_{d}$ when $d$ varies from 1 to $L - 1$ are depicted as color bars in (a)." + ], + "image_footnote": [], + "bbox": [ + 316, + 88, + 468, + 202 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "different computational budgets. Here, we train and evaluate AR-Seg with different resolutions for the LR branch, ranging from 0.3x to 1.0x. We also train and evaluate the constant-resolution baselines of each resolution for comparison. As shown in Figure 4(a), AR-Seg improves both backbones under all resolutions, demonstrating the effectiveness of CReFF and FST. To quantify the average improvement, we utilize two metrics BD-FLOPs and BD-mIoU following the design of BD-Rate and BD-PSNR [2] in video compression. The results show that (1) with the same computational budget, AR-Seg improves the absolute accuracy for two backbones by $3.67\\%$ and $3.02\\%$ respectively, and (2) with the same accuracy, AR-Seg reduces the computational cost by $76.73\\%$ and $51.06\\%$ respectively. Both metrics are described in detail in Appendix A5.", + "bbox": [ + 75, + 292, + 468, + 518 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "The Temporal Gap. To investigate the influence of the distance $d$ to the keyframe, we plot the $mIoU_{d}$ results for $\\mathrm{AR}^{0.5}$ -PSP18 and the constant-resolution baselines in Figure 4(b). As $mIoU_{0}$ is determined by the HR branch, $\\mathrm{AR}^{0.5}$ -PSP18 shares the same point with PSPNet18(1.0x) at $d = 0$ . The $mIoU_{0}$ for PSPNet18(0.5x) is much lower due to downsampling. When $d > 0$ , the accuracy of PSPNet18(1.0x) decreases since the compression artifacts in P frames are more severe than those in I frames. As a comparison, the $\\mathrm{AR}^{0.5}$ -PSP18 benefits from the CReFF module and maintains high accuracy for all the $d$ values.", + "bbox": [ + 75, + 520, + 468, + 686 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Keyframe Intervals. To validate the long-range reference, we extend our evaluation to different keyframe intervals without re-training. As shown in Table 3, AR $^{0.5}$ -PSP18 trained with $L = 12$ maintains good performance with different GOP lengths. Moreover, even for $L = 30$ , which stands for 1s in 30fps videos and is larger than the discussion in previous works [19, 56], AR-Seg outperforms the 1.0x baseline using only $29.2\\%$ FLOPs.", + "bbox": [ + 75, + 686, + 468, + 808 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Video Compression Configurations. As shown in Table 4, we also train and evaluate our model with different realistic bit-rates (3Mbps and 1Mbps) and configurations for HEVC/H.265 encoders. We use x265-medium and x265-ultrafast to represent different presets for x265, which apply simplified motion search algorithms and larger macro", + "bbox": [ + 75, + 809, + 468, + 901 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/69854f9e09cec2fa77c99a7a0a25c1ba2d4c5fbaf9a6937ae8268298f5811707.jpg", + "table_caption": [ + "Table 4. Performance of AR-Seg on videos compressed by different codec's. AR-Seg achieves comparable or even better accuracy than its image-based constant-resolution counterparts." + ], + "table_footnote": [], + "table_body": "
CodecMethodmIoU(%)GFLOPs
HEVC@3MbpsPSPNet18(1.0x)69.43309.02
AR0.5-PSP1870.48101.98
HEVC@1MbpsPSPNet18(1.0x)65.76309.02
AR0.5-PSP1867.89101.98
x265-medium@3MbpsPSPNet18 (1.0x)68.19309.02
AR0.5-PSP1869.53101.98
x265-ultrafast@3MbpsPSPNet18 (1.0x)67.69309.02
AR0.5-PSP1868.78101.98
", + "bbox": [ + 501, + 133, + 890, + 273 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "blocks. These configurations are widely used in traditional video encoders. The results show that $\\mathrm{AR}^{0.5}$ -PSP18 consistently outperforms the $1.0\\mathrm{x}$ constant resolution counterpart using only $33\\%$ GFLOPs under different configurations.", + "bbox": [ + 496, + 292, + 890, + 354 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.4. Running Time", + "text_level": 1, + "bbox": [ + 500, + 362, + 648, + 378 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We measure the running time of AR-Seg with PSPNet18 on both CamVid and Cityscapes datasets, and the results are reported in Table 5. Our AR-Seg models run $2x - 3x$ times faster than the constant resolution counterparts. All tests are executed on a single GeForce RTX 3090 GPU.", + "bbox": [ + 496, + 385, + 890, + 460 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/b17158e060b8d007ce7a38e0f84a80cef3b601fb3bfde8a331f7616cd3d8a779.jpg", + "table_caption": [ + "Table 5. Running time of AR-PSP18 on 720x960 CamVid and 1024x2048 Cityscapes datasets." + ], + "table_footnote": [], + "table_body": "
Dataset1.0x baselineAR0.5AR0.3
CamVid31.2 ms (32fps)14.7 ms (68fps)9.0 ms (111fps)
Cityscapes95.4 ms (10fps)30.7 ms (33fps)19.9 ms (50fps)
", + "bbox": [ + 501, + 503, + 890, + 558 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 584, + 617, + 599 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this paper, we propose AR-Seg, an altering resolution framework for compressed video semantic segmentation, which innovatively improves the efficiency of video segmentation from the perspective of input resolution. By jointly considering the design of architecture and training strategy, our proposed CReFF module and FST strategy effectively prevent the accuracy loss caused by downsampling. Results evaluated on two widely used datasets show that AR-Seg can achieve competitive segmentation accuracy with a reduction of up to $67\\%$ computational cost. Our current study only uses two alternating resolutions (i.e., HR and LR). Future work that applies more complicated scheduling of multi-resolutions and keyframe gaps will be considered to further improve the VSS performance.", + "bbox": [ + 496, + 609, + 890, + 821 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgements: This work was partially supported by Beijing Natural Science Foundation (L222008), Tsinghua University Initiative Scientific Research Program, the Natural Science Foundation of China (61725204), BNRist, and MOE-Key Laboratory of Pervasive Computing.", + "bbox": [ + 496, + 824, + 890, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "22634", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Barak Battash, Haim Barad, Hanlin Tang, and Amit Blei-weiess. 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IEEE Computer Society, 2017. 2, 8" + ], + "bbox": [ + 501, + 92, + 890, + 654 + ], + "page_idx": 10 + }, + { + "type": "page_number", + "text": "22637", + "bbox": [ + 478, + 945, + 517, + 955 + ], + "page_idx": 10 + } +] \ No newline at end of file diff --git a/2023/Efficient Semantic Segmentation by Altering Resolutions for Compressed Videos/7cf71203-1b67-4ff6-a186-04d01a4ea3fe_model.json b/2023/Efficient Semantic Segmentation by Altering Resolutions for Compressed Videos/7cf71203-1b67-4ff6-a186-04d01a4ea3fe_model.json new file mode 100644 index 0000000000000000000000000000000000000000..5ec3f03dfd9b8cfbc4ac9e0fbde877572bdf14e0 --- /dev/null +++ b/2023/Efficient Semantic Segmentation by Altering Resolutions for Compressed Videos/7cf71203-1b67-4ff6-a186-04d01a4ea3fe_model.json @@ -0,0 +1,2136 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.081, + 0.131, + 0.89, + 0.153 + ], + "angle": 0, + "content": "Efficient Semantic Segmentation by Altering Resolutions for Compressed Videos" + }, + { + "type": "text", + "bbox": [ + 0.107, + 0.18, + 0.87, + 0.253 + ], + "angle": 0, + "content": "Yubin Hu\\(^{1}\\) Yuze He\\(^{1}\\) Yanghao Li\\(^{1}\\) Jisheng Li\\(^{1}\\) Yuxing Han\\(^{2}\\) Jiangtao Wen\\(^{3}\\) Yong-Jin Liu\\(^{1*}\\) \n\\(^{1}\\)BNRist, Department of Computer Science and Technology, Tsinghua University \n\\(^{2}\\)Shenzhen International Graduate School, Tsinghua University \n\\(^{3}\\)Eastern Institute for Advanced Study" + }, + { + "type": "text", + "bbox": [ + 0.151, + 0.255, + 0.808, + 0.287 + ], + "angle": 0, + "content": "{huyb20, hyz22, liyangha18}@mails.tsinghua.edu.cn, jas0nlee@icloud.com, yuxinghan@sz.tsinghua.edu.cn, jtwen@eias.ac.cn, liuyongjin@tsinghua.edu.cn" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.322, + 0.314, + 0.339 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.354, + 0.474, + 0.779 + ], + "angle": 0, + "content": "Video semantic segmentation (VSS) is a computationally expensive task due to the per-frame prediction for videos of high frame rates. In recent work, compact models or adaptive network strategies have been proposed for efficient VSS. However, they did not consider a crucial factor that affects the computational cost from the input side: the input resolution. In this paper, we propose an altering resolution framework called AR-Seg for compressed videos to achieve efficient VSS. AR-Seg aims to reduce the computational cost by using low resolution for non-keyframes. To prevent the performance degradation caused by downsampling, we design a Cross Resolution Feature Fusion (CReFF) module, and supervise it with a novel Feature Similarity Training (FST) strategy. Specifically, CReFF first makes use of motion vectors stored in a compressed video to warp features from high-resolution keyframes to low-resolution non-keyframes for better spatial alignment, and then selectively aggregates the warped features with local attention mechanism. Furthermore, the proposed FST supervises the aggregated features with high-resolution features through an explicit similarity loss and an implicit constraint from the shared decoding layer. Extensive experiments on CamVid and Cityscapes show that AR-Seg achieves state-of-the-art performance and is compatible with different segmentation backbones. On CamVid, AR-Seg saves \\(67\\%\\) computational cost (measured in GFLOPs) with the PSPNet18 backbone while maintaining high segmentation accuracy. Code: https://github.com/THU-LYJ-Lab/AR-Seg." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.806, + 0.21, + 0.822 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.832, + 0.47, + 0.879 + ], + "angle": 0, + "content": "Video semantic segmentation (VSS) aims to predict pixel-wise semantic labels for each frame in a video sequence. In contrast to a single image, a video sequence" + }, + { + "type": "image", + "bbox": [ + 0.51, + 0.32, + 0.583, + 0.491 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.538, + 0.495, + 0.555, + 0.507 + ], + "angle": 0, + "content": "(a)" + }, + { + "type": "image", + "bbox": [ + 0.594, + 0.32, + 0.738, + 0.491 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.659, + 0.495, + 0.677, + 0.507 + ], + "angle": 0, + "content": "(b)" + }, + { + "type": "image", + "bbox": [ + 0.749, + 0.32, + 0.891, + 0.491 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.81, + 0.495, + 0.828, + 0.507 + ], + "angle": 0, + "content": "(c)" + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.519, + 0.894, + 0.59 + ], + "angle": 0, + "content": "Figure 1. Comparison of different VSS methods: (a) per-frame framework, (b) Accel [19] that alters the depth of models, and (c) our AR-Seg. AR-Seg reduces the computational cost for nonkeyframes by lowering the input resolution (depicted by narrow blocks), which is a dimension orthogonal to the depth of networks." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.611, + 0.893, + 0.793 + ], + "angle": 0, + "content": "is a series of consecutive image frames recorded at a certain frame rate (usually 25fps or higher). Applying image-based segmentation methods [6, 25, 48, 52, 55] to a video frame by frame consumes considerable computational resources. To improve the efficiency of VSS, existing methods mainly focus on the design of network architectures. A class of methods proposes compact and efficient image-based architectures to reduce the computational overhead per-frame [22, 23, 28, 49, 51, 52, 54]. Another class of methods applies a deep model to keyframes and a shallow network for non-keyframes to avoid the repetitive computation [19, 24, 27, 34] for videos." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.796, + 0.895, + 0.903 + ], + "angle": 0, + "content": "The work presented in this paper is based on an important observation: the above existing works ignored a crucial factor that affects the computational cost from the input side: the input resolution. For image-related tasks, the input resolution directly determines the amount of computation, e.g., the computational cost of 2D convolution is proportional to the product of image width and height. Once we" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.887, + 0.222, + 0.9 + ], + "angle": 0, + "content": "*Corresponding author." + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "22627" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.288 + ], + "angle": 0, + "content": "downsample the input frame by \\(0.5 \\times 0.5\\), the computational overhead can be reduced by \\(75\\%\\). On the other hand, decreasing resolution often leads to worse segmentation accuracy due to the loss of information [43,54]. In this paper, we propose to prevent the accuracy degradation by using temporal correlation in the video. Since the contents of video frames are temporally correlated, the local features lacking in low-resolution (LR) frames can be inferred and enriched by finding correspondences in sparse high-resolution (HR) reference frames based on motion cues. In a compressed video, the motion vectors contain such motion cues and can be obtained along with the video frames from video decoding at almost no additional cost." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.29, + 0.473, + 0.593 + ], + "angle": 0, + "content": "Motivated by the above observation, we propose an altering resolution framework for compressed videos, named AR-Seg, to achieve efficient VSS. As shown in Figure 1(c), AR-Seg uses an HR branch to process keyframes at high resolution and an LR branch to process non-keyframes at low resolution. In particular, to prevent performance drop caused by downsampling, we insert a novel Cross Resolution Feature Fusion (CReFF) module into the LR branch and supervise the training with a Feature Similarity Training (FST) strategy to enrich local details in the LR features. CReFF fuses the HR keyframe features into LR nonkeyframe features in two steps: 1) Align the spatial structures of features from different frames by feature warping with motion vectors, which can be readily obtained from compressed videos at almost no additional cost; 2) Selectively aggregate the warped features (which may be noisy after warping) into LR features with the aid of local attention mechanism. Since local attention assigns different importance to each location in the neighborhood, it is an effective way to avoid misleading by noisy warped features." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.596, + 0.473, + 0.779 + ], + "angle": 0, + "content": "Furthermore, our proposed FST strategy guides the learning of the CReFF aggregated features. FST consists of an explicit similarity loss (between the aggregated features and HR features inferred from non-keyframes) and an implicit constraint from the shared decoding layer across the HR and LR branches. Such a training strategy helps the LR branch to learn from features extracted from the HR branch, which is reliable and effective. Integrated with CReFF and FST, AR-Seg efficiently compensates for the accuracy loss of LR frames. Overall, AR-Seg significantly reduces the computational cost of VSS by altering input resolutions, while maintaining high segmentation accuracy." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.78, + 0.473, + 0.903 + ], + "angle": 0, + "content": "To sum up, we make three contributions in this paper: 1) We propose an efficient framework for compressed videos, named AR-Seg, that uses altering input resolution for VSS and significantly reduces the computational cost without losing segmentation accuracy. 2) We design an efficient CReFF module to prevent the accuracy loss by aggregating HR keyframe features into LR non-keyframe features. 3) We propose a novel FST strategy that supervises the" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.895, + 0.199 + ], + "angle": 0, + "content": "LR branch to learn from the HR branch through both explicit and implicit constraints. Experiment results demonstrate the effectiveness of AR-Seg with different resolutions, backbones, and keyframe intervals. On both CamVid [3] and Cityscapes [9] datasets, compared to the constant-resolution baselines, AR-Seg reduces the computational cost by nearly \\(70\\%\\) without compromising accuracy." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.211, + 0.651, + 0.227 + ], + "angle": 0, + "content": "2. Related Works" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.237, + 0.895, + 0.357 + ], + "angle": 0, + "content": "As a fundamental task of scene understanding, semantic segmentation has been an active research area for many years [8, 13, 21, 41], which also attracts considerable attention in the study of deep neural networks, e.g., FCN [25], DeepLabs [4, 5] and PSPNet [55]. In order to obtain accurate results in real-time applications, several methods have been proposed to improve the efficiency of semantic segmentation, which we summarize as follows." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.358, + 0.896, + 0.629 + ], + "angle": 0, + "content": "Efficient Image Segmentation Methods. Many compact architectures have been proposed for efficient image segmentation. DFANet [22] adopted a lightweight backbone to reduce computational cost and designed cross-level aggregation for feature refinement. DFNet [23] utilized a partial order pruning algorithm to search segmentation models for a good trade-off between speed and accuracy. ICNet [54] used a cascade fusion module and transformed part of the computation from high-resolution to low-resolution. Wang et al. [43] designed superresolution learning to improve image segmentation performance. BiSeNets [11,51,52] used two-stream paths for low-level details and high-level context information, respectively. ESPNet [28] used an efficient spatial pyramid to accelerate the convolution computation. These efficient backbone networks reduce the computational burden of single-image segmentation, and can be applied to temporal or spatial frameworks in VSS." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.63, + 0.897, + 0.902 + ], + "angle": 0, + "content": "Temporally Correlated Video Segmentation. Another group of methods focus on utilizing temporal redundancy in videos. They proposed various mechanisms that propagate the deep features extracted from keyframes to reduce the computation for non-keyframes. Clockwork [36] directly reused the segmentation result from keyframes, while Mahasseni et al. [27] interpolated segmentation results in the neighborhood. Noticing the lack of information from non-keyframes, Li et al. [24] extracted shallow features from non-keyframes, and fused them into the propagated deep features by spatially variant convolution. To compensate for the spatial misalignment between video frames, Zhu et al. [56] and Xu et al. [50] warped the intermediate features from keyframes by optical flow to produce segmentation results for non-keyframes. Jain et al. [19] fused the shallow features of non-keyframe into the warped features, and decoded them into better results. With global attention mechanism, TD-Net [16] aggregated the features from different" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.946, + 0.521, + 0.957 + ], + "angle": 0, + "content": "22628" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.333 + ], + "angle": 0, + "content": "time stamps and replaced the deep model with several shallow models distributed across the timeline. All the above methods mainly reduced the depth of backbone networks, but neglected the factor of input resolution considered in this paper. Instead of processing the image frames as a whole, Verelst et al. [42] split the frame into blocks and chose to copy or process them by a policy network. This block-based method reduces computational overhead from the spatial dimension, but lacks global information on nonkeyframes. Kim et al. [20] attempted to improve efficiency by reducing resolution. But they directly used the LR segmentation results, thus suffering from severe performance degradation. Compared to these methods, our proposed AR-Seg keeps the global information of LR non-keyframes, and enhances LR frames by selectively aggregating intermediate features from HR keyframes." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.334, + 0.473, + 0.773 + ], + "angle": 0, + "content": "Compressed-Domain Video Analysis. Compressed video formats have been recently utilized in computer vision tasks. The motion vectors and residual maps are treated as additional modalities and directly fed into networks for video action recognition [1, 17, 37, 47] and semantic segmentation [39]. Such motion information also helps compensate for the spatial misalignment of features from different frames. Wang et al. [44] leveraged motion vectors to warp features in previous frames for object detection. Fan et al. [12] conditionally executed the backbone network for pose estimation depending on the residual values. For VSS, several methods have been proposed for efficient segmentation in the compressed domain. Jain et al. [18] warped the former and latter keyframe features using motion vectors, and predicted the non-keyframe features by interpolation. Tanujaya et al. [40] warped the results of keyframe segmentation for non-keyframes, and refined the warped segmentation by guided inpainting. Feng et al. [14] replaced a block of warped features with a local non-keyframe feature patch for further refinement. These methods reduced the computational cost of VSS, but suffered from performance degradation due to the limited capability of their feature refinement modules designed for non-keyframes. In our proposed AR-Seg, the warped features are refined by local attention mechanism according to the LR features of non-keyframes. Our attention-based refinement selectively aggregates the warped features and effectively suppresses the noise in motion vectors, achieving good segmentation accuracy with little computational overhead." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.785, + 0.17, + 0.801 + ], + "angle": 0, + "content": "3. Method" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.81, + 0.473, + 0.903 + ], + "angle": 0, + "content": "In order to achieve efficient VSS for compressed videos, we propose an altering resolution framework named AR-Seg (Section 3.1). AR-Seg uses two branches to process HR keyframes and LR non-keyframes in the video separately. To compensate for the information loss due to down-sampling the non-keyframes, we design a novel CReFF" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.895, + 0.168 + ], + "angle": 0, + "content": "module that aggregates HR keyframe features into LR nonkeyframe features (Section 3.2). To guide the learning of aggregated features, we further propose a novel feature similarity training (FST) strategy containing both explicit and implicit constraints (Section 3.3)." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.177, + 0.693, + 0.193 + ], + "angle": 0, + "content": "3.1. AR-Seg Framework" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.2, + 0.895, + 0.382 + ], + "angle": 0, + "content": "For image/video semantic segmentation tasks, the input resolution directly determines the amount of computation, no matter what type of algorithms are applied, e.g., Conditional Random Fields, CNNs, and Transformers. Although reducing resolution has been studied in the context of video recognition [26, 29], altering resolution in dense prediction tasks like VSS remains unexplored. Based on this observation, we design the AR-Seg framework for VSS, which inputs video frames with altering resolutions; i.e., in AR-Seg, only a few keyframes are processed at high resolution to preserve fine details, while other non-keyframes are processed at low resolution to reduce the computational cost." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.382, + 0.895, + 0.579 + ], + "angle": 0, + "content": "To identify the keyframes, we make use of the frame structure in a group of pictures (GOP) encoded in compressed videos [38, 46]. A GOP includes \\( L \\) consecutive frames of three types: I frame, P frame, and B frame. I frames are encoded in intra mode, while P and B frames are encoded in inter mode that computes motion vectors for motion compensation. In each GOP, we treat the first I frame as a keyframe and process it at high resolution. The remaining \\( L - 1 \\) frames in GOP are non-keyframes and processed at low resolution. To simplify the description of our method, following the previous works [14, 47], we only consider the GOP structure without B frames in this section. The full treatment including B frames is presented in Appendix A4." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.579, + 0.895, + 0.7 + ], + "angle": 0, + "content": "Due to the domain gap between images with different resolutions, it is difficult for a single network to extract features suitable for both HR and LR resolution images. Thus we design two branches with shared backbone architecture in the model and train them separately for each resolution. Figure 1(c) summarizes the proposed AR-Seg framework. It consists of two branches: an HR branch for keyframes and an LR branch for non-keyframes." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.7, + 0.895, + 0.867 + ], + "angle": 0, + "content": "The HR branch adapts an image segmentation network, which consists of a feature sub-network \\( N_{feat} \\), a task subnetwork \\( N_{task} \\), and a final 1x1 convolutional layer1. It predicts segmentation results in high-resolution and simultaneously provides intermediate features before the final convolution as a reference for the LR branch. The LR branch is equipped with the same backbone network as the HR branch. To prevent performance degradation caused by downsampling, we design a CReFF module that aggregates HR features of the keyframe into the LR branch and place it before the final convolution layer of the backbone network." + }, + { + "type": "page_footnote", + "bbox": [ + 0.5, + 0.875, + 0.892, + 0.901 + ], + "angle": 0, + "content": "1We follow the modular division of backbone networks in [19]. Two backbones are discussed and compared in Section 4." + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "22629" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.099, + 0.087, + 0.878, + 0.38 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.387, + 0.895, + 0.43 + ], + "angle": 0, + "content": "Figure 2. The CReFF module in the network architecture and feature similarity training (FST) strategy. CReFF consists of feature warping \\(\\mathcal{W}_{MV}\\) and local-attention-based feature fusion \\(\\mathcal{F}_{LA}\\) (Section 3.2). FST includes the explicit supervision by the feature similarity loss and the implicit supervision from shared convolution (Section 3.3). Parameters in gray blocks are fixed during the training of the LR branch." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.445, + 0.47, + 0.505 + ], + "angle": 0, + "content": "CReFF aggregates the HR reference features into the extracted LR features, yielding estimated HR features for the non-keyframes, which are further converted into pixel-wise semantic labels by the final convolution layer." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.506, + 0.471, + 0.688 + ], + "angle": 0, + "content": "As illustrated in Figure 1, different from the previous Accel framework [19], AR-Seg performs feature fusion before the last \\(1 \\times 1\\) convolution layer, instead of before the task sub-network \\(N_{task}\\). The reason is twofold: 1) Since feature maps before the final convolution have basically the same spatial layout as the input images and segmentation outputs, we can utilize motion vectors to compensate for the spatial misalignment of features at such position; and 2) As the CReFF module actually upsamples the LR features, such a placement allows almost all convolution layers to benefit from the low resolution, thus reducing most of the computational cost." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.696, + 0.436, + 0.712 + ], + "angle": 0, + "content": "3.2. CReFF: Cross Resolution Feature Fusion" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.72, + 0.471, + 0.902 + ], + "angle": 0, + "content": "In the AR-Seg framework, CReFF aims to prevent the performance degradation caused by the lack of fine local details in LR non-keyframes. Unlike a single image, video frames are intrinsically temporally correlated, so missing details in LR non-keyframes can be retrieved from the corresponding regions in HR keyframes according to motion cues. Motion vectors (MVs) in the compressed video exactly provide such motion cues at the block level, i.e., pixels inside a macroblock share the same motion vector. Almost all mainstream video compression standards use motion vectors for inter-prediction, including H.26x series [38, 46], AOMedia series [7] and AVS series [10, 15, 53]. Such block-" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.445, + 0.892, + 0.473 + ], + "angle": 0, + "content": "wise MVs are readily available in compressed videos and can be used to assist the LR branch." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.475, + 0.893, + 0.657 + ], + "angle": 0, + "content": "Specifically, as depicted in Figure 2, the HR branch of AR-Seg extracts the feature \\(F_{I} \\in \\mathcal{R}^{C \\times H \\times W}\\) from an I frame, and the LR branch extracts the feature \\(f_{P} \\in \\mathcal{R}^{C \\times h \\times w}\\) from a P frame. Although P frames are processed in low resolution, CReFF takes \\(F_{I}, M_{P},\\) and \\(f_{P}\\) as input to generate the aggregated feature \\(\\tilde{F}_{P}\\), where \\(M_{P} \\in \\mathcal{R}^{2 \\times H \\times W}\\) denotes the MVs from P frame to I frame. The two channels of \\(M_{P}\\) correspond to \\(x\\) and \\(y\\) dimensions of motion vectors, denoted by \\(c_{x}\\) and \\(c_{y}\\). Inside the CReFF module, the MV-based feature warping operation \\(\\mathcal{W}_{MV}\\) firstly warps \\(F_{I}\\) to the spatial layout of the P frame, which can be formulated as per-pixel shifting:" + }, + { + "type": "equation", + "bbox": [ + 0.572, + 0.667, + 0.892, + 0.693 + ], + "angle": 0, + "content": "\\[\n\\hat {F} _ {I} ^ {(x, y)} = F _ {I} ^ {\\left(x + M _ {P} ^ {\\left(c _ {x}, x, y\\right)}, y + M _ {P} ^ {\\left(c _ {y}, x, y\\right)}\\right)}, \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.703, + 0.891, + 0.734 + ], + "angle": 0, + "content": "where \\(\\hat{F}_I\\in \\mathcal{R}^{C\\times H\\times W}\\) denotes the warped HR feature that will be further fused into LR features." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.735, + 0.892, + 0.885 + ], + "angle": 0, + "content": "Due to the coarse-grained MVs (block-level instead of pixel-level) and the varying occlusion relationships across video frames, the warped features \\(\\hat{F}_I\\) are often noisy and misleading. Inspired by the success of non-local operation [45] and attention mechanism [16, 31, 33] in video-based applications, we propose to assign different fusion importance weights to the \\((x,y)\\) locations in noisy features \\(\\hat{F}_I\\) by attention mechanism. Since \\(\\hat{F}_I\\) is roughly spatially aligned to \\(f_{p}\\) after warping, we use local attention to efficiently fuse the features as follows." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.886, + 0.892, + 0.902 + ], + "angle": 0, + "content": "In the local-attention-based feature fusion module \\(\\mathcal{F}_{LA}\\)" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "22630" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.244 + ], + "angle": 0, + "content": "we firstly generate the Value and Key feature maps from the warped HR features \\(\\hat{F}_I\\), and the Query maps from the upsampled LR features \\(\\bar{F}_P\\). The \\(3 \\times 3\\) grouped convolution \\(\\mathbf{Conv}_g\\) with groups \\(= C\\) is selected to efficiently encode the feature maps into attention representations \\(V_I, K_I, Q_P \\in \\mathcal{R}^{C \\times H \\times W}\\). Note that attention representations share the same channel size as the intermediate features. Denote the \\(n \\times n\\) neighborhood centered at \\((x,y)\\) as \\(Nbhd_{(x,y)}\\). Within \\(Nbhd_{(x,y)}\\), the output of local attention \\(A_P\\) at the position \\((x,y)\\) is generated by" + }, + { + "type": "equation", + "bbox": [ + 0.102, + 0.25, + 0.47, + 0.27 + ], + "angle": 0, + "content": "\\[\nA _ {P} ^ {(x, y)} = \\overline {{V _ {I} ^ {N b h d _ {(x , y)}}}} \\mathcal {S} \\left(\\overline {{K _ {I} ^ {N b h d _ {(x , y)}}}}, Q _ {P} ^ {(x, y)}\\right), \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.275, + 0.47, + 0.356 + ], + "angle": 0, + "content": "where \\(A_{P}^{(x,y)}\\), \\(Q_{P}^{(x,y)} \\in \\mathcal{R}^{C \\times 1}\\) denote the feature vectors at the position \\((x,y)\\) of \\(A_{P}\\) and \\(Q_{P}\\) respectively, and \\(\\overline{V_{I}^{Nbhd_{(x,y)}}}\\), \\(\\overline{K_{I}^{Nbhd_{(x,y)}}} \\in \\mathcal{R}^{C \\times n^{2}}\\) are the re-arranged feature vectors within \\(Nbhd_{(x,y)}\\) in \\(V_{I}\\) and \\(K_{I}\\), respectively. The similarity operation \\(\\mathcal{S}(K,Q)\\) is formulated as" + }, + { + "type": "equation", + "bbox": [ + 0.17, + 0.361, + 0.469, + 0.397 + ], + "angle": 0, + "content": "\\[\n\\mathcal {S} (K, Q) = \\operatorname {S o f t m a x} \\left(\\frac {K ^ {T} Q}{\\sqrt {C}}\\right). \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.402, + 0.469, + 0.432 + ], + "angle": 0, + "content": "Furthermore, the aggregated feature \\(\\tilde{F}_P\\) for P frame is obtained in a residual fashion:" + }, + { + "type": "equation", + "bbox": [ + 0.132, + 0.438, + 0.469, + 0.457 + ], + "angle": 0, + "content": "\\[\n\\tilde {F} _ {P} = \\bar {F} _ {P} + A _ {P} = \\text {U p s a m p l e} \\left(f _ {P}\\right) + A _ {P}. \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.462, + 0.47, + 0.569 + ], + "angle": 0, + "content": "In summary, using the CReFF module, the feature details from the I frame are firstly aligned to the P frame, and then aggregated into the LR branch according to the pixel-wise similarity between \\( Q_{P} \\) and \\( K_{I} \\). The verification of the architecture design of CReFF is presented in Section 4.3. The reader is referred to Appendix A1 for more details on the visualization of attention weights in \\( \\mathcal{F}_{LA} \\)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.575, + 0.373, + 0.592 + ], + "angle": 0, + "content": "3.3. FST: Feature Similarity Training" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.599, + 0.469, + 0.749 + ], + "angle": 0, + "content": "In order to effectively train the CReFF module, we propose a feature similarity training (FST) strategy. FST utilizes the HR features of P frame \\( F_{P} \\) (extracted from the HR branch) to guide the learning of the aggregated features \\( \\tilde{F}_{P} \\) in the LR branch. Since \\( F_{P} \\) contains sufficient details to produce high-quality segmentation results, CReFF can learn how to aggregate \\( \\bar{F}_{P} \\) and \\( \\hat{F}_{I} \\) into effective HR features from it under the supervision of FST. Specifically, FST supervises the training process of the LR branch both explicitly and implicitly in the following ways." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.75, + 0.469, + 0.811 + ], + "angle": 0, + "content": "The explicit constraint is to use the feature similarity loss \\(\\mathcal{L}_{fs}\\). We use mean square error (MSE) to measure the difference between \\(\\tilde{F}_P\\) and \\(F_{P}\\), which serves as an additional regularization for the LR model:" + }, + { + "type": "equation", + "bbox": [ + 0.085, + 0.816, + 0.469, + 0.836 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} = \\mathcal {L} _ {s e g} + \\mathcal {L} _ {f s} = C E \\left(S _ {P}, G _ {P}\\right) + M S E \\left(\\tilde {F} _ {P}, F _ {P}\\right), \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.839, + 0.469, + 0.902 + ], + "angle": 0, + "content": "where \\(S_P \\in \\mathcal{R}^{C_{out} \\times H \\times W}\\) denotes the segmentation result produced by LR branch, \\(G_P \\in \\mathcal{R}^{H \\times W}\\) denotes the ground-truth segmentation of P frame and the segmentation loss \\(\\mathcal{L}_{seg}\\) is the standard cross entropy loss \\(CE(S_P, G_P)\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.242 + ], + "angle": 0, + "content": "The implicit constraint of FST is the shared decoding layer of \\(\\tilde{F}_P\\) and \\(F_{P}\\). In the segmentation backbone model trained on the HR images, the final convolution layer acts as the segmentation decoder, which contains deep semantic information about high-quality HR features. To utilize such information, we directly transfer the final \\(1\\times 1\\) convolution layer of the HR branch to the LR branch with fixed parameters. Since the parameters are trained on HR features, they produce better segmentation results \\(S_P\\) when \\(\\tilde{F}_{P}\\) is closer to the HR feature \\(F_{P}\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.244, + 0.892, + 0.41 + ], + "angle": 0, + "content": "In summary, with the explicit and implicit constraints, FST effectively transfers the knowledge of HR features from the HR branch to the LR branch, enabling high-quality segmentation based on the aggregated features of CReFF. Figure 2 shows the overall training strategy for the LR branch. The HR I frame provides the features \\(F_{I}\\) for feature fusion in CReFF, and the HR P frame provides the features \\(F_{P}\\) for the explicit supervision in FST. Parameters of the LR branch are trained using the total loss \\(\\mathcal{L}\\) via backpropagation, with fixed parameters of the HR branch and the shared final convolution layer." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.427, + 0.634, + 0.445 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.454, + 0.892, + 0.545 + ], + "angle": 0, + "content": "We evaluate the proposed AR-Seg framework on CamVid [3] and Cityscapes [9] datasets for street-view video semantic segmentation. Below we present experiments to demonstrate the efficiency of AR-Seg and its compatibility with different backbone models, resolutions, and video compression configurations." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.557, + 0.691, + 0.574 + ], + "angle": 0, + "content": "4.1. Experimental Setup" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.582, + 0.892, + 0.718 + ], + "angle": 0, + "content": "Datasets & Pre-processing. The CamVid [3] dataset consists of 4 videos of \\(720 \\times 960\\) resolution captured at 30 fps, with semantic annotations at 1Hz and, in part, 15Hz. The Cityscapes [9] dataset contains street view videos of \\(1024 \\times 2048\\) resolution captured in 17 fps, from which 5,000 images are densely annotated. We use the official train/validation/test split for both datasets. Following the previous works [16, 51], we select 11 and 19 classes for training and evaluation on these two datasets, respectively." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.719, + 0.892, + 0.795 + ], + "angle": 0, + "content": "To simulate a real video compressed scenario, we compress the videos at reasonable bit-rates of 3Mbps for CamVid and 5Mbps for Cityscapes with the HEVC/H.265 [38] standard. The reader is referred to Appendix A3.1 for the detailed pre-processing steps." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.796, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Models & Baselines. To demonstrate the compatibility of AR-Seg with different backbones, we select two representative image segmentation models in our experiments: PSPNet [55] and BiseNet [52], which is similar to settings in the previous work [16]. The former is a widely used classical model, and the latter is a lightweight model that achieves state-of-the-art performance. We use \\(\\mathbf{A}\\mathbf{R}^{\\alpha}\\) - as the prefix" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.946, + 0.518, + 0.957 + ], + "angle": 0, + "content": "22631" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.468, + 0.121 + ], + "angle": 0, + "content": "of AR-Seg with specified backbone networks, where \\(\\alpha\\) denotes the downsample scale for the LR branch." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.122, + 0.468, + 0.213 + ], + "angle": 0, + "content": "Training & Evaluation Details. Given a GOP length \\( L \\), we train the LR branch with image pairs \\( (i, p) \\), where \\( p \\) refers to the P frame with annotation and \\( i = p - (L - 1) \\) refers to the I frame as a reference. We denote the distance between the annotated and the reference frames as \\( d \\), then \\( d = L - 1 \\) for the training pairs." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.215, + 0.468, + 0.365 + ], + "angle": 0, + "content": "For evaluation, we test AR-Seg with different distances \\(d\\) between the target frame \\(p\\) and the reference keyframe \\(i\\). For \\(d = 0\\), we treat frame \\(p\\) as the keyframe and process it by the HR branch. Otherwise, we feed frame \\(p\\) into the LR branch for \\(d \\in (0, L - 1]\\). The average of \\(mIoU_{d}\\) for each distance \\(d\\) is reported as the mIoU result. We measure FLOPs by PyTorch-OpCounter [35] following the previous methods [30, 32]. All the comparisons are evaluated on the compressed videos. More training and evaluation details are presented in Appendix A3.2 and A3.3." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.378, + 0.265, + 0.394 + ], + "angle": 0, + "content": "4.2. Experiment Results" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.402, + 0.468, + 0.627 + ], + "angle": 0, + "content": "Comparison with image-based methods. We first compare AR-Segs (with PSPNet [55] and BiseNet [52] as backbone) to their image-based counterparts of \\(1.0\\mathrm{x}\\) resolution. As shown in Table 1, on both CamVid and Cityscapes datasets, the proposed \\(\\mathrm{AR^{0.5}}\\) models achieve on-par or better performance than the \\(1.0\\mathrm{x}\\) resolution baselines while saving \\(67\\%\\) computational cost. Different from the low-resolution baselines that lead to significant performance degradation, AR-Seg successfully preserves the segmentation accuracy with the help of the CReFF module and the FST strategy. More comparisons between AR-Seg and the LR baselines under different resolutions are presented in Appendix A2.1. Furthermore, these experiment results with PSPNet and BiseNet also demonstrate the compatibility of AR-Seg for different backbone networks." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.629, + 0.468, + 0.901 + ], + "angle": 0, + "content": "Comparison with video-based methods. Taking temporal coherence into consideration, we compare AR-Seg with the recent state-of-the-art video-based methods for efficient VSS. Besides the accuracy and computational cost, we also follow the previous work [33] to report the relative changes compared to their single-frame backbone models. Specifically, \\(\\widetilde{\\Delta}\\mathrm{mIoU}\\) denotes the relative change of mIoU, and \\(\\widetilde{\\Delta}\\mathrm{GFLOPs}\\) denotes the relative change of GFLOPs. As shown in Table 2, existing video-based methods usually improve accuracy \\((\\widetilde{\\Delta}\\mathrm{mIoU} > 0)\\) at the cost of more computation \\((\\widetilde{\\Delta}\\mathrm{GFLOPs} > 0)\\), e.g., TDNet [16] and Accel [19]. Other methods, including BlockCopy [42], TapLab [14] and Jain et al. [18], reduce the computational cost \\((\\widetilde{\\Delta}\\mathrm{GFLOPs} < 0)\\) but the accuracy also decreases \\(3\\% - 7\\%\\) \\((\\widetilde{\\Delta}\\mathrm{mIoU} < 0)\\). As a comparison, our proposed models \\(\\mathrm{AR^{0.6}}\\)- can reduce the computational cost \\((\\widetilde{\\Delta}\\mathrm{GFLOPs} < 0)\\) by more than \\(55\\%\\) and preserve the accuracy of single-frame backbone models \\((\\widetilde{\\Delta}\\mathrm{mIoU} \\geq 0)\\). With the lightweight" + }, + { + "type": "table_caption", + "bbox": [ + 0.5, + 0.09, + 0.892, + 0.117 + ], + "angle": 0, + "content": "Table 1. Comparison to the image-based methods on CamVid test set and Cityscapes valid set." + }, + { + "type": "table", + "bbox": [ + 0.502, + 0.12, + 0.888, + 0.276 + ], + "angle": 0, + "content": "
MethodPSPNet18 [55]BiseNet18 [52]
mIoU(%)↑GFLOPs ↓mIoU(%)↑GFLOPs ↓
CamVid1.0x69.43309.0271.5758.83
AR0.771.23169.8671.7831.89
AR0.670.82133.0971.6024.68
AR0.570.48101.9870.3818.96
Cityscapes1.0x69.00560.9770.09178.96
AR0.770.23302.9570.8697.10
AR0.669.45234.9170.7276.06
AR0.569.03177.4470.5757.00
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.292, + 0.892, + 0.348 + ], + "angle": 0, + "content": "Table 2. Comparison to the video-based methods on CamVid test set and Cityscapes valid set. \\(\\tilde{\\Delta} x = \\frac{\\Delta x}{|x|}\\) denotes the relative change compared to their single-frame backbone models. The best results are bold and the second best results are underlined." + }, + { + "type": "table", + "bbox": [ + 0.503, + 0.35, + 0.891, + 0.576 + ], + "angle": 0, + "content": "
MethodmIoU↑GFLOPs↓ΔmIoU↑ΔGFLOPs↓
CamVidAccel-DL18 [19]66.15397.70+13.8%+61.9%
TD4-PSP18 [16]70.13363.70+1.0%+17.7%
BlockCopy [42]66.75107.52-5.2%-45.7%
TapLab-BL2 [14]67.57117.73-3.1%-50.2%
Jain et al. [18]67.61146.97-4.3%-53.8%
AR0.6-PSP1870.82101.98+2.0%-57.0%
AR0.6-Bise1871.6024.68+0.0%-58.0%
CityscapesAccel-DL18 [19]68.251011.75+18.4%+96.0%
TD4-PSP18 [16]70.11673.06+1.6%+20.0%
BlockCopy [42]67.69294.20-6.7%-41.2%
TapLab-BL2 [14]68.90237.29-4.1%-50.6%
Jain et al. [18]68.57342.67-5.1%-52.5%
AR0.6-PSP1869.45234.91+0.7%-58.1%
AR0.6-Bise1870.7276.06+0.9%-57.5%
" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.593, + 0.891, + 0.655 + ], + "angle": 0, + "content": "backbone model BiseNet, AR\\(^{0.6}\\)-Bise18 achieves good performance in both accuracy and computational cost. More results of video-based methods and their single-frame backbone models are presented in Appendix A2.2." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.665, + 0.655, + 0.682 + ], + "angle": 0, + "content": "4.3. Ablation Study" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.689, + 0.892, + 0.809 + ], + "angle": 0, + "content": "We perform ablation studies to show the importance of each component in CReFF and FST, as well as the location of CReFF. We also evaluate AR-Seg in terms of different resolutions and GOP lengths, which reflects the influence of hyper-parameters \\(\\alpha\\) and \\(L\\), respectively. We conducted ablation studies on the 30fps CamVid dataset, and used PSPNet18 as the default backbone model, \\(L = 12\\) as the default GOP length, and HEVC@3Mbps as the default codec." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.811, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Architecture of CReFF. We first validate the necessity of \\(\\mathcal{W}_{MV}\\) and \\(\\mathcal{F}_{LA}\\). The method without CReFF directly applies FST to the upsampled features \\(\\bar{F}_P\\) and serves as a baseline. As shown in Table 3, simply warping the keyframe features \\((+\\mathcal{W}_{MV})\\) saves the most amount of computation by skipping processing non-keyframes with the" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "22632" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.08, + 0.09, + 0.894, + 0.266 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.277, + 0.893, + 0.32 + ], + "angle": 0, + "content": "Figure 3. Semantic segmentation on CamVid (top) and Cityscapes (bottom) with \\( d = 11 \\). Note that AR0.5-PSP18 predicts more semantic details than the constant-resolution PSPNet18 working on 0.5x resolution. Compared to the 1.0x baseline, AR0.5-PSP18 generates similar segmentation results, but consumes only 33.0% computational cost (measured in GFLOPs)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.346, + 0.47, + 0.406 + ], + "angle": 0, + "content": "segmentation network, but receives poor accuracy. Directly fusing the keyframe features using local attention \\((+ \\mathcal{F}_{LA})\\) does not perform very well, because the feature maps are not well-aligned due to object motion in videos." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.409, + 0.471, + 0.668 + ], + "angle": 0, + "content": "We further evaluate the design of \\(\\mathcal{F}_{LA}\\) by replacing \\(7\\times 7\\) local attention \\((LA)\\) with other operations, including \\(LA\\) with different neighborhood sizes, \\(LA\\) with non-grouped convolution encoders \\((\\mathcal{F}_{LA^*})\\), global attention \\((\\mathcal{F}_{GA})\\) and one-layer convolution \\((\\mathcal{F}_{Conv})\\). For \\(\\mathcal{F}_{GA}\\), we downsample the Value and Key maps by \\(\\frac{1}{32}\\) to save the computation. \\(\\mathcal{F}_{Conv}\\) processes the concatenated feature \\([\\hat{F}_I,\\bar{F}_P]\\) with a \\(3\\times 3\\) convolution. Due to the large channel number in deep layers, such an operation brings considerable computation overhead. Results in Table 3 show that \\(\\mathcal{F}_{LA}\\) with a \\(7\\times 7\\) neighborhood achieves a good balance between computation and accuracy. Other designs increase the computational cost without improving the accuracy. Furthermore, removing the direct connection (DC) path from CReFF reduces the mIoU to \\(69.14\\%\\). This result implies that CReFF is more likely to learn the residuals of HR features than the absolute values." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.671, + 0.47, + 0.868 + ], + "angle": 0, + "content": "Location of CReFF. As specified in Section 3.1, we place CReFF before the final \\(1 \\times 1\\) convolution layer, which is different from the previous Accel framework [19]. To evaluate the influence of the split point location, we insert CReFF before different layers and evaluate the performance. Split points include the final convolution layer (\\(C_{1 \\times 1}\\)), the task sub-network \\(N_{task}\\) and the feature sub-network \\(N_{feat}\\). For the \\(N_{feat}\\) case, we insert CReFF after the first convolution layer of ResNet. As shown in Table 3, placing CReFF before \\(C_{1 \\times 1}\\) results in the best performance, which affirms our design in Section 3.1. We note that fusing features at an early stage does not improve accuracy, but rather considerably increases computational cost." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.87, + 0.469, + 0.901 + ], + "angle": 0, + "content": "Feature Similarity Training (FST). The proposed FST strategy consists of the MSE Loss and the shared final con" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.344, + 0.89, + 0.371 + ], + "angle": 0, + "content": "Table 3. Ablation experiments on CamVid dataset with PSPNet18. Settings used in our final model are underlined." + }, + { + "type": "table", + "bbox": [ + 0.502, + 0.374, + 0.89, + 0.753 + ], + "angle": 0, + "content": "
ExperimentMethodmIoU(%)GFLOPs
BaselinePSPNet18 (1.0x)69.43309.02
PSPNet18 (0.5x)66.5177.27
Architecture of CReFF+ WMV + FLA (7x7)70.48101.98
w/o CReFF67.1496.60
+ WMV57.6425.75
+ FLA (7x7)67.93101.98
+ WMV + FLA (3x3)70.3098.74
+ WMV + FLA* (11x11)70.48107.32
+ WMV + FLA* (7x7)69.99170.96
+ WMV + FGA (1/32)67.11113.58
+ WMV + FConv70.45143.63
+ CReFF w/o DC69.14101.98
Location of CReFFbefore C1×170.48101.98
before Ntask68.60214.76
before Nfeat68.31308.46
Feature Similarity+ MSE Loss + Shared C1×170.48101.98
w/o FST69.21101.98
Training (FST)+ Shared C1×169.57101.98
+ MSE Loss70.17101.98
+ KL Loss + Shared C1×168.91101.98
Keyframe IntervalAR0.5-PSP18, L=1270.48101.98
AR0.5-PSP18, L=1570.2897.88
AR0.5-PSP18, L=2070.2894.11
AR0.5-PSP18, L=3069.6790.34
" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.776, + 0.892, + 0.868 + ], + "angle": 0, + "content": "volution layer \\( C_{1\\times 1} \\). We train AR\\(^{0.5}\\)-PSP18 with or without these components and report the results in Table 3. Both components improve the segmentation performance compared to the model trained without FST. We also replace the MSE Loss with the Kullback-Leibler (KL) Divergence Loss, but the resulting segmentation performance is poor." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.871, + 0.893, + 0.901 + ], + "angle": 0, + "content": "Resolution of LR Branch. By adjusting the resolution of the LR branch, AR-Seg can tailor the setting adaptive to" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.946, + 0.518, + 0.957 + ], + "angle": 0, + "content": "22633" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.08, + 0.089, + 0.309, + 0.202 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.187, + 0.206, + 0.205, + 0.217 + ], + "angle": 0, + "content": "(a)" + }, + { + "type": "image", + "bbox": [ + 0.318, + 0.089, + 0.47, + 0.203 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.383, + 0.206, + 0.401, + 0.217 + ], + "angle": 0, + "content": "(b)" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.22, + 0.47, + 0.275 + ], + "angle": 0, + "content": "Figure 4. (a) Performance of AR-Seg with different resolutions for the LR branch. (b) \\(mIoU_{d}\\) for annotated frames with different distances to key frame. Value intervals of \\(mIoU_{d}\\) when \\(d\\) varies from 1 to \\(L - 1\\) are depicted as color bars in (a)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.293, + 0.47, + 0.52 + ], + "angle": 0, + "content": "different computational budgets. Here, we train and evaluate AR-Seg with different resolutions for the LR branch, ranging from 0.3x to 1.0x. We also train and evaluate the constant-resolution baselines of each resolution for comparison. As shown in Figure 4(a), AR-Seg improves both backbones under all resolutions, demonstrating the effectiveness of CReFF and FST. To quantify the average improvement, we utilize two metrics BD-FLOPs and BD-mIoU following the design of BD-Rate and BD-PSNR [2] in video compression. The results show that (1) with the same computational budget, AR-Seg improves the absolute accuracy for two backbones by \\(3.67\\%\\) and \\(3.02\\%\\) respectively, and (2) with the same accuracy, AR-Seg reduces the computational cost by \\(76.73\\%\\) and \\(51.06\\%\\) respectively. Both metrics are described in detail in Appendix A5." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.521, + 0.47, + 0.687 + ], + "angle": 0, + "content": "The Temporal Gap. To investigate the influence of the distance \\(d\\) to the keyframe, we plot the \\(mIoU_{d}\\) results for \\(\\mathrm{AR}^{0.5}\\)-PSP18 and the constant-resolution baselines in Figure 4(b). As \\(mIoU_{0}\\) is determined by the HR branch, \\(\\mathrm{AR}^{0.5}\\)-PSP18 shares the same point with PSPNet18(1.0x) at \\(d = 0\\). The \\(mIoU_{0}\\) for PSPNet18(0.5x) is much lower due to downsampling. When \\(d > 0\\), the accuracy of PSPNet18(1.0x) decreases since the compression artifacts in P frames are more severe than those in I frames. As a comparison, the \\(\\mathrm{AR}^{0.5}\\)-PSP18 benefits from the CReFF module and maintains high accuracy for all the \\(d\\) values." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.688, + 0.47, + 0.809 + ], + "angle": 0, + "content": "Keyframe Intervals. To validate the long-range reference, we extend our evaluation to different keyframe intervals without re-training. As shown in Table 3, AR\\(^{0.5}\\)-PSP18 trained with \\( L = 12 \\) maintains good performance with different GOP lengths. Moreover, even for \\( L = 30 \\), which stands for 1s in 30fps videos and is larger than the discussion in previous works [19, 56], AR-Seg outperforms the 1.0x baseline using only \\( 29.2\\% \\) FLOPs." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.81, + 0.47, + 0.902 + ], + "angle": 0, + "content": "Video Compression Configurations. As shown in Table 4, we also train and evaluate our model with different realistic bit-rates (3Mbps and 1Mbps) and configurations for HEVC/H.265 encoders. We use x265-medium and x265-ultrafast to represent different presets for x265, which apply simplified motion search algorithms and larger macro" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.089, + 0.892, + 0.131 + ], + "angle": 0, + "content": "Table 4. Performance of AR-Seg on videos compressed by different codec's. AR-Seg achieves comparable or even better accuracy than its image-based constant-resolution counterparts." + }, + { + "type": "table", + "bbox": [ + 0.502, + 0.134, + 0.892, + 0.274 + ], + "angle": 0, + "content": "
CodecMethodmIoU(%)GFLOPs
HEVC@3MbpsPSPNet18(1.0x)69.43309.02
AR0.5-PSP1870.48101.98
HEVC@1MbpsPSPNet18(1.0x)65.76309.02
AR0.5-PSP1867.89101.98
x265-medium@3MbpsPSPNet18 (1.0x)68.19309.02
AR0.5-PSP1869.53101.98
x265-ultrafast@3MbpsPSPNet18 (1.0x)67.69309.02
AR0.5-PSP1868.78101.98
" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.294, + 0.892, + 0.356 + ], + "angle": 0, + "content": "blocks. These configurations are widely used in traditional video encoders. The results show that \\(\\mathrm{AR}^{0.5}\\)-PSP18 consistently outperforms the \\(1.0\\mathrm{x}\\) constant resolution counterpart using only \\(33\\%\\) GFLOPs under different configurations." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.363, + 0.649, + 0.379 + ], + "angle": 0, + "content": "4.4. Running Time" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.386, + 0.892, + 0.461 + ], + "angle": 0, + "content": "We measure the running time of AR-Seg with PSPNet18 on both CamVid and Cityscapes datasets, and the results are reported in Table 5. Our AR-Seg models run \\(2x - 3x\\) times faster than the constant resolution counterparts. All tests are executed on a single GeForce RTX 3090 GPU." + }, + { + "type": "table_caption", + "bbox": [ + 0.5, + 0.473, + 0.892, + 0.501 + ], + "angle": 0, + "content": "Table 5. Running time of AR-PSP18 on 720x960 CamVid and 1024x2048 Cityscapes datasets." + }, + { + "type": "table", + "bbox": [ + 0.502, + 0.504, + 0.892, + 0.559 + ], + "angle": 0, + "content": "
Dataset1.0x baselineAR0.5AR0.3
CamVid31.2 ms (32fps)14.7 ms (68fps)9.0 ms (111fps)
Cityscapes95.4 ms (10fps)30.7 ms (33fps)19.9 ms (50fps)
" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.585, + 0.619, + 0.601 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.61, + 0.892, + 0.822 + ], + "angle": 0, + "content": "In this paper, we propose AR-Seg, an altering resolution framework for compressed video semantic segmentation, which innovatively improves the efficiency of video segmentation from the perspective of input resolution. By jointly considering the design of architecture and training strategy, our proposed CReFF module and FST strategy effectively prevent the accuracy loss caused by downsampling. Results evaluated on two widely used datasets show that AR-Seg can achieve competitive segmentation accuracy with a reduction of up to \\(67\\%\\) computational cost. Our current study only uses two alternating resolutions (i.e., HR and LR). Future work that applies more complicated scheduling of multi-resolutions and keyframe gaps will be considered to further improve the VSS performance." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.825, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Acknowledgements: This work was partially supported by Beijing Natural Science Foundation (L222008), Tsinghua University Initiative Scientific Research Program, the Natural Science Foundation of China (61725204), BNRist, and MOE-Key Laboratory of Pervasive Computing." + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "22634" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.115, + 0.47, + 0.198 + ], + "angle": 0, + "content": "[1] Barak Battash, Haim Barad, Hanlin Tang, and Amit Blei-weiess. 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In recent work, compact models or adaptive network strategies have been proposed for efficient VSS. However, they did not consider a crucial factor that affects the computational cost from the input side: the input resolution. In this paper, we propose an altering resolution framework called AR-Seg for compressed videos to achieve efficient VSS. AR-Seg aims to reduce the computational cost by using low resolution for non-keyframes. To prevent the performance degradation caused by downsampling, we design a Cross Resolution Feature Fusion (CReFF) module, and supervise it with a novel Feature Similarity Training (FST) strategy. Specifically, CReFF first makes use of motion vectors stored in a compressed video to warp features from high-resolution keyframes to low-resolution non-keyframes for better spatial alignment, and then selectively aggregates the warped features with local attention mechanism. Furthermore, the proposed FST supervises the aggregated features with high-resolution features through an explicit similarity loss and an implicit constraint from the shared decoding layer. Extensive experiments on CamVid and Cityscapes show that AR-Seg achieves state-of-the-art performance and is compatible with different segmentation backbones. On CamVid, AR-Seg saves $67\%$ computational cost (measured in GFLOPs) with the PSPNet18 backbone while maintaining high segmentation accuracy. Code: https://github.com/THU-LYJ-Lab/AR-Seg. + +# 1. Introduction + +Video semantic segmentation (VSS) aims to predict pixel-wise semantic labels for each frame in a video sequence. In contrast to a single image, a video sequence + +![](images/a19c65e5563aed5e5e1aaf011244cad46bc64bf07f92e0f99beef46a717c6650.jpg) +(a) +Figure 1. Comparison of different VSS methods: (a) per-frame framework, (b) Accel [19] that alters the depth of models, and (c) our AR-Seg. AR-Seg reduces the computational cost for nonkeyframes by lowering the input resolution (depicted by narrow blocks), which is a dimension orthogonal to the depth of networks. + +![](images/120c28654a5c1e738627652e955fb098b2fc38b0df3f86bef4abadf5d86ddbc9.jpg) +(b) + +![](images/a7dbec70155366bd182fbbeb651458745ca0977537f081ad81cbc229f9741477.jpg) +(c) + +is a series of consecutive image frames recorded at a certain frame rate (usually 25fps or higher). Applying image-based segmentation methods [6, 25, 48, 52, 55] to a video frame by frame consumes considerable computational resources. To improve the efficiency of VSS, existing methods mainly focus on the design of network architectures. A class of methods proposes compact and efficient image-based architectures to reduce the computational overhead per-frame [22, 23, 28, 49, 51, 52, 54]. Another class of methods applies a deep model to keyframes and a shallow network for non-keyframes to avoid the repetitive computation [19, 24, 27, 34] for videos. + +The work presented in this paper is based on an important observation: the above existing works ignored a crucial factor that affects the computational cost from the input side: the input resolution. For image-related tasks, the input resolution directly determines the amount of computation, e.g., the computational cost of 2D convolution is proportional to the product of image width and height. Once we + +downsample the input frame by $0.5 \times 0.5$ , the computational overhead can be reduced by $75\%$ . On the other hand, decreasing resolution often leads to worse segmentation accuracy due to the loss of information [43,54]. In this paper, we propose to prevent the accuracy degradation by using temporal correlation in the video. Since the contents of video frames are temporally correlated, the local features lacking in low-resolution (LR) frames can be inferred and enriched by finding correspondences in sparse high-resolution (HR) reference frames based on motion cues. In a compressed video, the motion vectors contain such motion cues and can be obtained along with the video frames from video decoding at almost no additional cost. + +Motivated by the above observation, we propose an altering resolution framework for compressed videos, named AR-Seg, to achieve efficient VSS. As shown in Figure 1(c), AR-Seg uses an HR branch to process keyframes at high resolution and an LR branch to process non-keyframes at low resolution. In particular, to prevent performance drop caused by downsampling, we insert a novel Cross Resolution Feature Fusion (CReFF) module into the LR branch and supervise the training with a Feature Similarity Training (FST) strategy to enrich local details in the LR features. CReFF fuses the HR keyframe features into LR nonkeyframe features in two steps: 1) Align the spatial structures of features from different frames by feature warping with motion vectors, which can be readily obtained from compressed videos at almost no additional cost; 2) Selectively aggregate the warped features (which may be noisy after warping) into LR features with the aid of local attention mechanism. Since local attention assigns different importance to each location in the neighborhood, it is an effective way to avoid misleading by noisy warped features. + +Furthermore, our proposed FST strategy guides the learning of the CReFF aggregated features. FST consists of an explicit similarity loss (between the aggregated features and HR features inferred from non-keyframes) and an implicit constraint from the shared decoding layer across the HR and LR branches. Such a training strategy helps the LR branch to learn from features extracted from the HR branch, which is reliable and effective. Integrated with CReFF and FST, AR-Seg efficiently compensates for the accuracy loss of LR frames. Overall, AR-Seg significantly reduces the computational cost of VSS by altering input resolutions, while maintaining high segmentation accuracy. + +To sum up, we make three contributions in this paper: 1) We propose an efficient framework for compressed videos, named AR-Seg, that uses altering input resolution for VSS and significantly reduces the computational cost without losing segmentation accuracy. 2) We design an efficient CReFF module to prevent the accuracy loss by aggregating HR keyframe features into LR non-keyframe features. 3) We propose a novel FST strategy that supervises the + +LR branch to learn from the HR branch through both explicit and implicit constraints. Experiment results demonstrate the effectiveness of AR-Seg with different resolutions, backbones, and keyframe intervals. On both CamVid [3] and Cityscapes [9] datasets, compared to the constant-resolution baselines, AR-Seg reduces the computational cost by nearly $70\%$ without compromising accuracy. + +# 2. Related Works + +As a fundamental task of scene understanding, semantic segmentation has been an active research area for many years [8, 13, 21, 41], which also attracts considerable attention in the study of deep neural networks, e.g., FCN [25], DeepLabs [4, 5] and PSPNet [55]. In order to obtain accurate results in real-time applications, several methods have been proposed to improve the efficiency of semantic segmentation, which we summarize as follows. + +Efficient Image Segmentation Methods. Many compact architectures have been proposed for efficient image segmentation. DFANet [22] adopted a lightweight backbone to reduce computational cost and designed cross-level aggregation for feature refinement. DFNet [23] utilized a partial order pruning algorithm to search segmentation models for a good trade-off between speed and accuracy. ICNet [54] used a cascade fusion module and transformed part of the computation from high-resolution to low-resolution. Wang et al. [43] designed superresolution learning to improve image segmentation performance. BiSeNets [11,51,52] used two-stream paths for low-level details and high-level context information, respectively. ESPNet [28] used an efficient spatial pyramid to accelerate the convolution computation. These efficient backbone networks reduce the computational burden of single-image segmentation, and can be applied to temporal or spatial frameworks in VSS. + +Temporally Correlated Video Segmentation. Another group of methods focus on utilizing temporal redundancy in videos. They proposed various mechanisms that propagate the deep features extracted from keyframes to reduce the computation for non-keyframes. Clockwork [36] directly reused the segmentation result from keyframes, while Mahasseni et al. [27] interpolated segmentation results in the neighborhood. Noticing the lack of information from non-keyframes, Li et al. [24] extracted shallow features from non-keyframes, and fused them into the propagated deep features by spatially variant convolution. To compensate for the spatial misalignment between video frames, Zhu et al. [56] and Xu et al. [50] warped the intermediate features from keyframes by optical flow to produce segmentation results for non-keyframes. Jain et al. [19] fused the shallow features of non-keyframe into the warped features, and decoded them into better results. With global attention mechanism, TD-Net [16] aggregated the features from different + +time stamps and replaced the deep model with several shallow models distributed across the timeline. All the above methods mainly reduced the depth of backbone networks, but neglected the factor of input resolution considered in this paper. Instead of processing the image frames as a whole, Verelst et al. [42] split the frame into blocks and chose to copy or process them by a policy network. This block-based method reduces computational overhead from the spatial dimension, but lacks global information on nonkeyframes. Kim et al. [20] attempted to improve efficiency by reducing resolution. But they directly used the LR segmentation results, thus suffering from severe performance degradation. Compared to these methods, our proposed AR-Seg keeps the global information of LR non-keyframes, and enhances LR frames by selectively aggregating intermediate features from HR keyframes. + +Compressed-Domain Video Analysis. Compressed video formats have been recently utilized in computer vision tasks. The motion vectors and residual maps are treated as additional modalities and directly fed into networks for video action recognition [1, 17, 37, 47] and semantic segmentation [39]. Such motion information also helps compensate for the spatial misalignment of features from different frames. Wang et al. [44] leveraged motion vectors to warp features in previous frames for object detection. Fan et al. [12] conditionally executed the backbone network for pose estimation depending on the residual values. For VSS, several methods have been proposed for efficient segmentation in the compressed domain. Jain et al. [18] warped the former and latter keyframe features using motion vectors, and predicted the non-keyframe features by interpolation. Tanujaya et al. [40] warped the results of keyframe segmentation for non-keyframes, and refined the warped segmentation by guided inpainting. Feng et al. [14] replaced a block of warped features with a local non-keyframe feature patch for further refinement. These methods reduced the computational cost of VSS, but suffered from performance degradation due to the limited capability of their feature refinement modules designed for non-keyframes. In our proposed AR-Seg, the warped features are refined by local attention mechanism according to the LR features of non-keyframes. Our attention-based refinement selectively aggregates the warped features and effectively suppresses the noise in motion vectors, achieving good segmentation accuracy with little computational overhead. + +# 3. Method + +In order to achieve efficient VSS for compressed videos, we propose an altering resolution framework named AR-Seg (Section 3.1). AR-Seg uses two branches to process HR keyframes and LR non-keyframes in the video separately. To compensate for the information loss due to down-sampling the non-keyframes, we design a novel CReFF + +module that aggregates HR keyframe features into LR nonkeyframe features (Section 3.2). To guide the learning of aggregated features, we further propose a novel feature similarity training (FST) strategy containing both explicit and implicit constraints (Section 3.3). + +# 3.1. AR-Seg Framework + +For image/video semantic segmentation tasks, the input resolution directly determines the amount of computation, no matter what type of algorithms are applied, e.g., Conditional Random Fields, CNNs, and Transformers. Although reducing resolution has been studied in the context of video recognition [26, 29], altering resolution in dense prediction tasks like VSS remains unexplored. Based on this observation, we design the AR-Seg framework for VSS, which inputs video frames with altering resolutions; i.e., in AR-Seg, only a few keyframes are processed at high resolution to preserve fine details, while other non-keyframes are processed at low resolution to reduce the computational cost. + +To identify the keyframes, we make use of the frame structure in a group of pictures (GOP) encoded in compressed videos [38, 46]. A GOP includes $L$ consecutive frames of three types: I frame, P frame, and B frame. I frames are encoded in intra mode, while P and B frames are encoded in inter mode that computes motion vectors for motion compensation. In each GOP, we treat the first I frame as a keyframe and process it at high resolution. The remaining $L - 1$ frames in GOP are non-keyframes and processed at low resolution. To simplify the description of our method, following the previous works [14, 47], we only consider the GOP structure without B frames in this section. The full treatment including B frames is presented in Appendix A4. + +Due to the domain gap between images with different resolutions, it is difficult for a single network to extract features suitable for both HR and LR resolution images. Thus we design two branches with shared backbone architecture in the model and train them separately for each resolution. Figure 1(c) summarizes the proposed AR-Seg framework. It consists of two branches: an HR branch for keyframes and an LR branch for non-keyframes. + +The HR branch adapts an image segmentation network, which consists of a feature sub-network $N_{feat}$ , a task subnetwork $N_{task}$ , and a final 1x1 convolutional layer1. It predicts segmentation results in high-resolution and simultaneously provides intermediate features before the final convolution as a reference for the LR branch. The LR branch is equipped with the same backbone network as the HR branch. To prevent performance degradation caused by downsampling, we design a CReFF module that aggregates HR features of the keyframe into the LR branch and place it before the final convolution layer of the backbone network. + +![](images/ec9230817086b2e542bd32614ab9b5fa9bcc243a2216af6299c71fffd6f663b9.jpg) +Figure 2. The CReFF module in the network architecture and feature similarity training (FST) strategy. CReFF consists of feature warping $\mathcal{W}_{MV}$ and local-attention-based feature fusion $\mathcal{F}_{LA}$ (Section 3.2). FST includes the explicit supervision by the feature similarity loss and the implicit supervision from shared convolution (Section 3.3). Parameters in gray blocks are fixed during the training of the LR branch. + +CReFF aggregates the HR reference features into the extracted LR features, yielding estimated HR features for the non-keyframes, which are further converted into pixel-wise semantic labels by the final convolution layer. + +As illustrated in Figure 1, different from the previous Accel framework [19], AR-Seg performs feature fusion before the last $1 \times 1$ convolution layer, instead of before the task sub-network $N_{task}$ . The reason is twofold: 1) Since feature maps before the final convolution have basically the same spatial layout as the input images and segmentation outputs, we can utilize motion vectors to compensate for the spatial misalignment of features at such position; and 2) As the CReFF module actually upsamples the LR features, such a placement allows almost all convolution layers to benefit from the low resolution, thus reducing most of the computational cost. + +# 3.2. CReFF: Cross Resolution Feature Fusion + +In the AR-Seg framework, CReFF aims to prevent the performance degradation caused by the lack of fine local details in LR non-keyframes. Unlike a single image, video frames are intrinsically temporally correlated, so missing details in LR non-keyframes can be retrieved from the corresponding regions in HR keyframes according to motion cues. Motion vectors (MVs) in the compressed video exactly provide such motion cues at the block level, i.e., pixels inside a macroblock share the same motion vector. Almost all mainstream video compression standards use motion vectors for inter-prediction, including H.26x series [38, 46], AOMedia series [7] and AVS series [10, 15, 53]. Such block- + +wise MVs are readily available in compressed videos and can be used to assist the LR branch. + +Specifically, as depicted in Figure 2, the HR branch of AR-Seg extracts the feature $F_{I} \in \mathcal{R}^{C \times H \times W}$ from an I frame, and the LR branch extracts the feature $f_{P} \in \mathcal{R}^{C \times h \times w}$ from a P frame. Although P frames are processed in low resolution, CReFF takes $F_{I}, M_{P},$ and $f_{P}$ as input to generate the aggregated feature $\tilde{F}_{P}$ , where $M_{P} \in \mathcal{R}^{2 \times H \times W}$ denotes the MVs from P frame to I frame. The two channels of $M_{P}$ correspond to $x$ and $y$ dimensions of motion vectors, denoted by $c_{x}$ and $c_{y}$ . Inside the CReFF module, the MV-based feature warping operation $\mathcal{W}_{MV}$ firstly warps $F_{I}$ to the spatial layout of the P frame, which can be formulated as per-pixel shifting: + +$$ +\hat {F} _ {I} ^ {(x, y)} = F _ {I} ^ {\left(x + M _ {P} ^ {\left(c _ {x}, x, y\right)}, y + M _ {P} ^ {\left(c _ {y}, x, y\right)}\right)}, \tag {1} +$$ + +where $\hat{F}_I\in \mathcal{R}^{C\times H\times W}$ denotes the warped HR feature that will be further fused into LR features. + +Due to the coarse-grained MVs (block-level instead of pixel-level) and the varying occlusion relationships across video frames, the warped features $\hat{F}_I$ are often noisy and misleading. Inspired by the success of non-local operation [45] and attention mechanism [16, 31, 33] in video-based applications, we propose to assign different fusion importance weights to the $(x,y)$ locations in noisy features $\hat{F}_I$ by attention mechanism. Since $\hat{F}_I$ is roughly spatially aligned to $f_{p}$ after warping, we use local attention to efficiently fuse the features as follows. + +In the local-attention-based feature fusion module $\mathcal{F}_{LA}$ + +we firstly generate the Value and Key feature maps from the warped HR features $\hat{F}_I$ , and the Query maps from the upsampled LR features $\bar{F}_P$ . The $3 \times 3$ grouped convolution $\mathbf{Conv}_g$ with groups $= C$ is selected to efficiently encode the feature maps into attention representations $V_I, K_I, Q_P \in \mathcal{R}^{C \times H \times W}$ . Note that attention representations share the same channel size as the intermediate features. Denote the $n \times n$ neighborhood centered at $(x,y)$ as $Nbhd_{(x,y)}$ . Within $Nbhd_{(x,y)}$ , the output of local attention $A_P$ at the position $(x,y)$ is generated by + +$$ +A _ {P} ^ {(x, y)} = \overline {{V _ {I} ^ {N b h d _ {(x , y)}}}} \mathcal {S} \left(\overline {{K _ {I} ^ {N b h d _ {(x , y)}}}}, Q _ {P} ^ {(x, y)}\right), \tag {2} +$$ + +where $A_{P}^{(x,y)}$ , $Q_{P}^{(x,y)} \in \mathcal{R}^{C \times 1}$ denote the feature vectors at the position $(x,y)$ of $A_{P}$ and $Q_{P}$ respectively, and $\overline{V_{I}^{Nbhd_{(x,y)}}}$ , $\overline{K_{I}^{Nbhd_{(x,y)}}} \in \mathcal{R}^{C \times n^{2}}$ are the re-arranged feature vectors within $Nbhd_{(x,y)}$ in $V_{I}$ and $K_{I}$ , respectively. The similarity operation $\mathcal{S}(K,Q)$ is formulated as + +$$ +\mathcal {S} (K, Q) = \operatorname {S o f t m a x} \left(\frac {K ^ {T} Q}{\sqrt {C}}\right). \tag {3} +$$ + +Furthermore, the aggregated feature $\tilde{F}_P$ for P frame is obtained in a residual fashion: + +$$ +\tilde {F} _ {P} = \bar {F} _ {P} + A _ {P} = \text {U p s a m p l e} \left(f _ {P}\right) + A _ {P}. \tag {4} +$$ + +In summary, using the CReFF module, the feature details from the I frame are firstly aligned to the P frame, and then aggregated into the LR branch according to the pixel-wise similarity between $Q_{P}$ and $K_{I}$ . The verification of the architecture design of CReFF is presented in Section 4.3. The reader is referred to Appendix A1 for more details on the visualization of attention weights in $\mathcal{F}_{LA}$ . + +# 3.3. FST: Feature Similarity Training + +In order to effectively train the CReFF module, we propose a feature similarity training (FST) strategy. FST utilizes the HR features of P frame $F_{P}$ (extracted from the HR branch) to guide the learning of the aggregated features $\tilde{F}_{P}$ in the LR branch. Since $F_{P}$ contains sufficient details to produce high-quality segmentation results, CReFF can learn how to aggregate $\bar{F}_{P}$ and $\hat{F}_{I}$ into effective HR features from it under the supervision of FST. Specifically, FST supervises the training process of the LR branch both explicitly and implicitly in the following ways. + +The explicit constraint is to use the feature similarity loss $\mathcal{L}_{fs}$ . We use mean square error (MSE) to measure the difference between $\tilde{F}_P$ and $F_{P}$ , which serves as an additional regularization for the LR model: + +$$ +\mathcal {L} = \mathcal {L} _ {s e g} + \mathcal {L} _ {f s} = C E \left(S _ {P}, G _ {P}\right) + M S E \left(\tilde {F} _ {P}, F _ {P}\right), \tag {5} +$$ + +where $S_P \in \mathcal{R}^{C_{out} \times H \times W}$ denotes the segmentation result produced by LR branch, $G_P \in \mathcal{R}^{H \times W}$ denotes the ground-truth segmentation of P frame and the segmentation loss $\mathcal{L}_{seg}$ is the standard cross entropy loss $CE(S_P, G_P)$ . + +The implicit constraint of FST is the shared decoding layer of $\tilde{F}_P$ and $F_{P}$ . In the segmentation backbone model trained on the HR images, the final convolution layer acts as the segmentation decoder, which contains deep semantic information about high-quality HR features. To utilize such information, we directly transfer the final $1\times 1$ convolution layer of the HR branch to the LR branch with fixed parameters. Since the parameters are trained on HR features, they produce better segmentation results $S_P$ when $\tilde{F}_{P}$ is closer to the HR feature $F_{P}$ . + +In summary, with the explicit and implicit constraints, FST effectively transfers the knowledge of HR features from the HR branch to the LR branch, enabling high-quality segmentation based on the aggregated features of CReFF. Figure 2 shows the overall training strategy for the LR branch. The HR I frame provides the features $F_{I}$ for feature fusion in CReFF, and the HR P frame provides the features $F_{P}$ for the explicit supervision in FST. Parameters of the LR branch are trained using the total loss $\mathcal{L}$ via backpropagation, with fixed parameters of the HR branch and the shared final convolution layer. + +# 4. Experiments + +We evaluate the proposed AR-Seg framework on CamVid [3] and Cityscapes [9] datasets for street-view video semantic segmentation. Below we present experiments to demonstrate the efficiency of AR-Seg and its compatibility with different backbone models, resolutions, and video compression configurations. + +# 4.1. Experimental Setup + +Datasets & Pre-processing. The CamVid [3] dataset consists of 4 videos of $720 \times 960$ resolution captured at 30 fps, with semantic annotations at 1Hz and, in part, 15Hz. The Cityscapes [9] dataset contains street view videos of $1024 \times 2048$ resolution captured in 17 fps, from which 5,000 images are densely annotated. We use the official train/validation/test split for both datasets. Following the previous works [16, 51], we select 11 and 19 classes for training and evaluation on these two datasets, respectively. + +To simulate a real video compressed scenario, we compress the videos at reasonable bit-rates of 3Mbps for CamVid and 5Mbps for Cityscapes with the HEVC/H.265 [38] standard. The reader is referred to Appendix A3.1 for the detailed pre-processing steps. + +Models & Baselines. To demonstrate the compatibility of AR-Seg with different backbones, we select two representative image segmentation models in our experiments: PSPNet [55] and BiseNet [52], which is similar to settings in the previous work [16]. The former is a widely used classical model, and the latter is a lightweight model that achieves state-of-the-art performance. We use $\mathbf{A}\mathbf{R}^{\alpha}$ - as the prefix + +of AR-Seg with specified backbone networks, where $\alpha$ denotes the downsample scale for the LR branch. + +Training & Evaluation Details. Given a GOP length $L$ , we train the LR branch with image pairs $(i, p)$ , where $p$ refers to the P frame with annotation and $i = p - (L - 1)$ refers to the I frame as a reference. We denote the distance between the annotated and the reference frames as $d$ , then $d = L - 1$ for the training pairs. + +For evaluation, we test AR-Seg with different distances $d$ between the target frame $p$ and the reference keyframe $i$ . For $d = 0$ , we treat frame $p$ as the keyframe and process it by the HR branch. Otherwise, we feed frame $p$ into the LR branch for $d \in (0, L - 1]$ . The average of $mIoU_{d}$ for each distance $d$ is reported as the mIoU result. We measure FLOPs by PyTorch-OpCounter [35] following the previous methods [30, 32]. All the comparisons are evaluated on the compressed videos. More training and evaluation details are presented in Appendix A3.2 and A3.3. + +# 4.2. Experiment Results + +Comparison with image-based methods. We first compare AR-Segs (with PSPNet [55] and BiseNet [52] as backbone) to their image-based counterparts of $1.0\mathrm{x}$ resolution. As shown in Table 1, on both CamVid and Cityscapes datasets, the proposed $\mathrm{AR^{0.5}}$ models achieve on-par or better performance than the $1.0\mathrm{x}$ resolution baselines while saving $67\%$ computational cost. Different from the low-resolution baselines that lead to significant performance degradation, AR-Seg successfully preserves the segmentation accuracy with the help of the CReFF module and the FST strategy. More comparisons between AR-Seg and the LR baselines under different resolutions are presented in Appendix A2.1. Furthermore, these experiment results with PSPNet and BiseNet also demonstrate the compatibility of AR-Seg for different backbone networks. + +Comparison with video-based methods. Taking temporal coherence into consideration, we compare AR-Seg with the recent state-of-the-art video-based methods for efficient VSS. Besides the accuracy and computational cost, we also follow the previous work [33] to report the relative changes compared to their single-frame backbone models. Specifically, $\widetilde{\Delta}\mathrm{mIoU}$ denotes the relative change of mIoU, and $\widetilde{\Delta}\mathrm{GFLOPs}$ denotes the relative change of GFLOPs. As shown in Table 2, existing video-based methods usually improve accuracy $(\widetilde{\Delta}\mathrm{mIoU} > 0)$ at the cost of more computation $(\widetilde{\Delta}\mathrm{GFLOPs} > 0)$ , e.g., TDNet [16] and Accel [19]. Other methods, including BlockCopy [42], TapLab [14] and Jain et al. [18], reduce the computational cost $(\widetilde{\Delta}\mathrm{GFLOPs} < 0)$ but the accuracy also decreases $3\% - 7\%$ $(\widetilde{\Delta}\mathrm{mIoU} < 0)$ . As a comparison, our proposed models $\mathrm{AR^{0.6}}$ - can reduce the computational cost $(\widetilde{\Delta}\mathrm{GFLOPs} < 0)$ by more than $55\%$ and preserve the accuracy of single-frame backbone models $(\widetilde{\Delta}\mathrm{mIoU} \geq 0)$ . With the lightweight + +Table 1. Comparison to the image-based methods on CamVid test set and Cityscapes valid set. + +
MethodPSPNet18 [55]BiseNet18 [52]
mIoU(%)↑GFLOPs ↓mIoU(%)↑GFLOPs ↓
CamVid1.0x69.43309.0271.5758.83
AR0.771.23169.8671.7831.89
AR0.670.82133.0971.6024.68
AR0.570.48101.9870.3818.96
Cityscapes1.0x69.00560.9770.09178.96
AR0.770.23302.9570.8697.10
AR0.669.45234.9170.7276.06
AR0.569.03177.4470.5757.00
+ +Table 2. Comparison to the video-based methods on CamVid test set and Cityscapes valid set. $\tilde{\Delta} x = \frac{\Delta x}{|x|}$ denotes the relative change compared to their single-frame backbone models. The best results are bold and the second best results are underlined. + +
MethodmIoU↑GFLOPs↓ΔmIoU↑ΔGFLOPs↓
CamVidAccel-DL18 [19]66.15397.70+13.8%+61.9%
TD4-PSP18 [16]70.13363.70+1.0%+17.7%
BlockCopy [42]66.75107.52-5.2%-45.7%
TapLab-BL2 [14]67.57117.73-3.1%-50.2%
Jain et al. [18]67.61146.97-4.3%-53.8%
AR0.6-PSP1870.82101.98+2.0%-57.0%
AR0.6-Bise1871.6024.68+0.0%-58.0%
CityscapesAccel-DL18 [19]68.251011.75+18.4%+96.0%
TD4-PSP18 [16]70.11673.06+1.6%+20.0%
BlockCopy [42]67.69294.20-6.7%-41.2%
TapLab-BL2 [14]68.90237.29-4.1%-50.6%
Jain et al. [18]68.57342.67-5.1%-52.5%
AR0.6-PSP1869.45234.91+0.7%-58.1%
AR0.6-Bise1870.7276.06+0.9%-57.5%
+ +backbone model BiseNet, AR $^{0.6}$ -Bise18 achieves good performance in both accuracy and computational cost. More results of video-based methods and their single-frame backbone models are presented in Appendix A2.2. + +# 4.3. Ablation Study + +We perform ablation studies to show the importance of each component in CReFF and FST, as well as the location of CReFF. We also evaluate AR-Seg in terms of different resolutions and GOP lengths, which reflects the influence of hyper-parameters $\alpha$ and $L$ , respectively. We conducted ablation studies on the 30fps CamVid dataset, and used PSPNet18 as the default backbone model, $L = 12$ as the default GOP length, and HEVC@3Mbps as the default codec. + +Architecture of CReFF. We first validate the necessity of $\mathcal{W}_{MV}$ and $\mathcal{F}_{LA}$ . The method without CReFF directly applies FST to the upsampled features $\bar{F}_P$ and serves as a baseline. As shown in Table 3, simply warping the keyframe features $(+\mathcal{W}_{MV})$ saves the most amount of computation by skipping processing non-keyframes with the + +![](images/844687012923341ca5ef9199a33873d1bf3ad665dfbbe5437e7dde33078d31ad.jpg) +Figure 3. Semantic segmentation on CamVid (top) and Cityscapes (bottom) with $d = 11$ . Note that AR0.5-PSP18 predicts more semantic details than the constant-resolution PSPNet18 working on 0.5x resolution. Compared to the 1.0x baseline, AR0.5-PSP18 generates similar segmentation results, but consumes only 33.0% computational cost (measured in GFLOPs). + +segmentation network, but receives poor accuracy. Directly fusing the keyframe features using local attention $(+ \mathcal{F}_{LA})$ does not perform very well, because the feature maps are not well-aligned due to object motion in videos. + +We further evaluate the design of $\mathcal{F}_{LA}$ by replacing $7\times 7$ local attention $(LA)$ with other operations, including $LA$ with different neighborhood sizes, $LA$ with non-grouped convolution encoders $(\mathcal{F}_{LA^*})$ , global attention $(\mathcal{F}_{GA})$ and one-layer convolution $(\mathcal{F}_{Conv})$ . For $\mathcal{F}_{GA}$ , we downsample the Value and Key maps by $\frac{1}{32}$ to save the computation. $\mathcal{F}_{Conv}$ processes the concatenated feature $[\hat{F}_I,\bar{F}_P]$ with a $3\times 3$ convolution. Due to the large channel number in deep layers, such an operation brings considerable computation overhead. Results in Table 3 show that $\mathcal{F}_{LA}$ with a $7\times 7$ neighborhood achieves a good balance between computation and accuracy. Other designs increase the computational cost without improving the accuracy. Furthermore, removing the direct connection (DC) path from CReFF reduces the mIoU to $69.14\%$ . This result implies that CReFF is more likely to learn the residuals of HR features than the absolute values. + +Location of CReFF. As specified in Section 3.1, we place CReFF before the final $1 \times 1$ convolution layer, which is different from the previous Accel framework [19]. To evaluate the influence of the split point location, we insert CReFF before different layers and evaluate the performance. Split points include the final convolution layer ( $C_{1 \times 1}$ ), the task sub-network $N_{task}$ and the feature sub-network $N_{feat}$ . For the $N_{feat}$ case, we insert CReFF after the first convolution layer of ResNet. As shown in Table 3, placing CReFF before $C_{1 \times 1}$ results in the best performance, which affirms our design in Section 3.1. We note that fusing features at an early stage does not improve accuracy, but rather considerably increases computational cost. + +Feature Similarity Training (FST). The proposed FST strategy consists of the MSE Loss and the shared final con + +Table 3. Ablation experiments on CamVid dataset with PSPNet18. Settings used in our final model are underlined. + +
ExperimentMethodmIoU(%)GFLOPs
BaselinePSPNet18 (1.0x)69.43309.02
PSPNet18 (0.5x)66.5177.27
Architecture of CReFF+ WMV + FLA (7x7)70.48101.98
w/o CReFF67.1496.60
+ WMV57.6425.75
+ FLA (7x7)67.93101.98
+ WMV + FLA (3x3)70.3098.74
+ WMV + FLA* (11x11)70.48107.32
+ WMV + FLA* (7x7)69.99170.96
+ WMV + FGA (1/32)67.11113.58
+ WMV + FConv70.45143.63
+ CReFF w/o DC69.14101.98
Location of CReFFbefore C1×170.48101.98
before Ntask68.60214.76
before Nfeat68.31308.46
Feature Similarity+ MSE Loss + Shared C1×170.48101.98
w/o FST69.21101.98
Training (FST)+ Shared C1×169.57101.98
+ MSE Loss70.17101.98
+ KL Loss + Shared C1×168.91101.98
Keyframe IntervalAR0.5-PSP18, L=1270.48101.98
AR0.5-PSP18, L=1570.2897.88
AR0.5-PSP18, L=2070.2894.11
AR0.5-PSP18, L=3069.6790.34
+ +volution layer $C_{1\times 1}$ . We train AR $^{0.5}$ -PSP18 with or without these components and report the results in Table 3. Both components improve the segmentation performance compared to the model trained without FST. We also replace the MSE Loss with the Kullback-Leibler (KL) Divergence Loss, but the resulting segmentation performance is poor. + +Resolution of LR Branch. By adjusting the resolution of the LR branch, AR-Seg can tailor the setting adaptive to + +![](images/441c89955f0eb3d5cff9182c5fdf7790b474f9a9b6763eb2de8dcce201210e50.jpg) +(a) + +![](images/3d81eac544980a27b9843fb620063f50117b8a1f1c120890a123f24bea38d930.jpg) +(b) +Figure 4. (a) Performance of AR-Seg with different resolutions for the LR branch. (b) $mIoU_{d}$ for annotated frames with different distances to key frame. Value intervals of $mIoU_{d}$ when $d$ varies from 1 to $L - 1$ are depicted as color bars in (a). + +different computational budgets. Here, we train and evaluate AR-Seg with different resolutions for the LR branch, ranging from 0.3x to 1.0x. We also train and evaluate the constant-resolution baselines of each resolution for comparison. As shown in Figure 4(a), AR-Seg improves both backbones under all resolutions, demonstrating the effectiveness of CReFF and FST. To quantify the average improvement, we utilize two metrics BD-FLOPs and BD-mIoU following the design of BD-Rate and BD-PSNR [2] in video compression. The results show that (1) with the same computational budget, AR-Seg improves the absolute accuracy for two backbones by $3.67\%$ and $3.02\%$ respectively, and (2) with the same accuracy, AR-Seg reduces the computational cost by $76.73\%$ and $51.06\%$ respectively. Both metrics are described in detail in Appendix A5. + +The Temporal Gap. To investigate the influence of the distance $d$ to the keyframe, we plot the $mIoU_{d}$ results for $\mathrm{AR}^{0.5}$ -PSP18 and the constant-resolution baselines in Figure 4(b). As $mIoU_{0}$ is determined by the HR branch, $\mathrm{AR}^{0.5}$ -PSP18 shares the same point with PSPNet18(1.0x) at $d = 0$ . The $mIoU_{0}$ for PSPNet18(0.5x) is much lower due to downsampling. When $d > 0$ , the accuracy of PSPNet18(1.0x) decreases since the compression artifacts in P frames are more severe than those in I frames. As a comparison, the $\mathrm{AR}^{0.5}$ -PSP18 benefits from the CReFF module and maintains high accuracy for all the $d$ values. + +Keyframe Intervals. To validate the long-range reference, we extend our evaluation to different keyframe intervals without re-training. As shown in Table 3, AR $^{0.5}$ -PSP18 trained with $L = 12$ maintains good performance with different GOP lengths. Moreover, even for $L = 30$ , which stands for 1s in 30fps videos and is larger than the discussion in previous works [19, 56], AR-Seg outperforms the 1.0x baseline using only $29.2\%$ FLOPs. + +Video Compression Configurations. As shown in Table 4, we also train and evaluate our model with different realistic bit-rates (3Mbps and 1Mbps) and configurations for HEVC/H.265 encoders. We use x265-medium and x265-ultrafast to represent different presets for x265, which apply simplified motion search algorithms and larger macro + +Table 4. Performance of AR-Seg on videos compressed by different codec's. AR-Seg achieves comparable or even better accuracy than its image-based constant-resolution counterparts. + +
CodecMethodmIoU(%)GFLOPs
HEVC@3MbpsPSPNet18(1.0x)69.43309.02
AR0.5-PSP1870.48101.98
HEVC@1MbpsPSPNet18(1.0x)65.76309.02
AR0.5-PSP1867.89101.98
x265-medium@3MbpsPSPNet18 (1.0x)68.19309.02
AR0.5-PSP1869.53101.98
x265-ultrafast@3MbpsPSPNet18 (1.0x)67.69309.02
AR0.5-PSP1868.78101.98
+ +blocks. These configurations are widely used in traditional video encoders. The results show that $\mathrm{AR}^{0.5}$ -PSP18 consistently outperforms the $1.0\mathrm{x}$ constant resolution counterpart using only $33\%$ GFLOPs under different configurations. + +# 4.4. Running Time + +We measure the running time of AR-Seg with PSPNet18 on both CamVid and Cityscapes datasets, and the results are reported in Table 5. Our AR-Seg models run $2x - 3x$ times faster than the constant resolution counterparts. All tests are executed on a single GeForce RTX 3090 GPU. + +Table 5. Running time of AR-PSP18 on 720x960 CamVid and 1024x2048 Cityscapes datasets. + +
Dataset1.0x baselineAR0.5AR0.3
CamVid31.2 ms (32fps)14.7 ms (68fps)9.0 ms (111fps)
Cityscapes95.4 ms (10fps)30.7 ms (33fps)19.9 ms (50fps)
+ +# 5. Conclusion + +In this paper, we propose AR-Seg, an altering resolution framework for compressed video semantic segmentation, which innovatively improves the efficiency of video segmentation from the perspective of input resolution. By jointly considering the design of architecture and training strategy, our proposed CReFF module and FST strategy effectively prevent the accuracy loss caused by downsampling. Results evaluated on two widely used datasets show that AR-Seg can achieve competitive segmentation accuracy with a reduction of up to $67\%$ computational cost. Our current study only uses two alternating resolutions (i.e., HR and LR). 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IEEE Computer Society, 2017. 2, 8 \ No newline at end of file diff --git a/2023/Efficient Semantic Segmentation by Altering Resolutions for Compressed Videos/images.zip b/2023/Efficient Semantic Segmentation by Altering Resolutions for Compressed Videos/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..572e8ada733d5a6504fb450131d06a8478902edf --- /dev/null +++ b/2023/Efficient Semantic Segmentation by Altering Resolutions for Compressed Videos/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:285169ee8a5d81a1bc3832477ad38f817fd54d866a553c01145745664f7c45fc +size 519070 diff --git a/2023/Efficient Semantic Segmentation by Altering Resolutions for Compressed Videos/layout.json b/2023/Efficient Semantic Segmentation by Altering Resolutions for Compressed Videos/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..90ab9f544bf3ca374ed434633329e82a2809b3d3 --- /dev/null +++ b/2023/Efficient Semantic Segmentation by Altering Resolutions for Compressed Videos/layout.json @@ -0,0 +1,10193 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 49, + 103, + 544, + 121 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 103, + 544, + 121 + ], + "spans": [ + { + "bbox": [ + 49, + 103, + 544, + 121 + ], + "type": "text", + "content": "Efficient Semantic Segmentation by Altering Resolutions for Compressed Videos" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 65, + 142, + 532, + 200 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 142, + 532, + 200 + ], + "spans": [ + { + "bbox": [ + 65, + 142, + 532, + 200 + ], + "type": "text", + "content": "Yubin Hu" + }, + { + "bbox": [ + 65, + 142, + 532, + 200 + ], + "type": "inline_equation", + "content": "^{1}" + }, + { + "bbox": [ + 65, + 142, + 532, + 200 + ], + "type": "text", + "content": " Yuze He" + }, + { + "bbox": [ + 65, + 142, + 532, + 200 + ], + "type": "inline_equation", + "content": "^{1}" + }, + { + "bbox": [ + 65, + 142, + 532, + 200 + ], + "type": "text", + "content": " Yanghao Li" + }, + { + "bbox": [ + 65, + 142, + 532, + 200 + ], + "type": "inline_equation", + "content": "^{1}" + }, + { + "bbox": [ + 65, + 142, + 532, + 200 + ], + "type": "text", + "content": " Jisheng Li" + }, + { + "bbox": [ + 65, + 142, + 532, + 200 + ], + "type": "inline_equation", + "content": "^{1}" + }, + { + "bbox": [ + 65, + 142, + 532, + 200 + ], + "type": "text", + "content": " Yuxing Han" + }, + { + "bbox": [ + 65, + 142, + 532, + 200 + ], + "type": "inline_equation", + "content": "^{2}" + }, + { + "bbox": [ + 65, + 142, + 532, + 200 + ], + "type": "text", + "content": " Jiangtao Wen" + }, + { + "bbox": [ + 65, + 142, + 532, + 200 + ], + "type": "inline_equation", + "content": "^{3}" + }, + { + "bbox": [ + 65, + 142, + 532, + 200 + ], + "type": "text", + "content": " Yong-Jin Liu" + }, + { + "bbox": [ + 65, + 142, + 532, + 200 + ], + "type": "inline_equation", + "content": "^{1*}" + }, + { + "bbox": [ + 65, + 142, + 532, + 200 + ], + "type": "inline_equation", + "content": "^{1}" + }, + { + "bbox": [ + 65, + 142, + 532, + 200 + ], + "type": "text", + "content": "BNRist, Department of Computer Science and Technology, Tsinghua University \n" + }, + { + "bbox": [ + 65, + 142, + 532, + 200 + ], + "type": "inline_equation", + "content": "^{2}" + }, + { + "bbox": [ + 65, + 142, + 532, + 200 + ], + "type": "text", + "content": "Shenzhen International Graduate School, Tsinghua University \n" + }, + { + "bbox": [ + 65, + 142, + 532, + 200 + ], + "type": "inline_equation", + "content": "^{3}" + }, + { + "bbox": [ + 65, + 142, + 532, + 200 + ], + "type": "text", + "content": "Eastern Institute for Advanced Study" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 92, + 201, + 494, + 227 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 92, + 201, + 494, + 227 + ], + "spans": [ + { + "bbox": [ + 92, + 201, + 494, + 227 + ], + "type": "text", + "content": "{huyb20, hyz22, liyangha18}@mails.tsinghua.edu.cn, jas0nlee@icloud.com, yuxinghan@sz.tsinghua.edu.cn, jtwen@eias.ac.cn, liuyongjin@tsinghua.edu.cn" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 143, + 255, + 192, + 268 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 255, + 192, + 268 + ], + "spans": [ + { + "bbox": [ + 143, + 255, + 192, + 268 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 280, + 290, + 616 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 280, + 290, + 616 + ], + "spans": [ + { + "bbox": [ + 46, + 280, + 290, + 616 + ], + "type": "text", + "content": "Video semantic segmentation (VSS) is a computationally expensive task due to the per-frame prediction for videos of high frame rates. In recent work, compact models or adaptive network strategies have been proposed for efficient VSS. However, they did not consider a crucial factor that affects the computational cost from the input side: the input resolution. In this paper, we propose an altering resolution framework called AR-Seg for compressed videos to achieve efficient VSS. AR-Seg aims to reduce the computational cost by using low resolution for non-keyframes. To prevent the performance degradation caused by downsampling, we design a Cross Resolution Feature Fusion (CReFF) module, and supervise it with a novel Feature Similarity Training (FST) strategy. Specifically, CReFF first makes use of motion vectors stored in a compressed video to warp features from high-resolution keyframes to low-resolution non-keyframes for better spatial alignment, and then selectively aggregates the warped features with local attention mechanism. Furthermore, the proposed FST supervises the aggregated features with high-resolution features through an explicit similarity loss and an implicit constraint from the shared decoding layer. Extensive experiments on CamVid and Cityscapes show that AR-Seg achieves state-of-the-art performance and is compatible with different segmentation backbones. On CamVid, AR-Seg saves " + }, + { + "bbox": [ + 46, + 280, + 290, + 616 + ], + "type": "inline_equation", + "content": "67\\%" + }, + { + "bbox": [ + 46, + 280, + 290, + 616 + ], + "type": "text", + "content": " computational cost (measured in GFLOPs) with the PSPNet18 backbone while maintaining high segmentation accuracy. Code: https://github.com/THU-LYJ-Lab/AR-Seg." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 638, + 128, + 651 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 638, + 128, + 651 + ], + "spans": [ + { + "bbox": [ + 47, + 638, + 128, + 651 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 658, + 287, + 696 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 658, + 287, + 696 + ], + "spans": [ + { + "bbox": [ + 46, + 658, + 287, + 696 + ], + "type": "text", + "content": "Video semantic segmentation (VSS) aims to predict pixel-wise semantic labels for each frame in a video sequence. In contrast to a single image, a video sequence" + } + ] + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 312, + 253, + 356, + 388 + ], + "blocks": [ + { + "bbox": [ + 312, + 253, + 356, + 388 + ], + "lines": [ + { + "bbox": [ + 312, + 253, + 356, + 388 + ], + "spans": [ + { + "bbox": [ + 312, + 253, + 356, + 388 + ], + "type": "image", + "image_path": "a19c65e5563aed5e5e1aaf011244cad46bc64bf07f92e0f99beef46a717c6650.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 329, + 392, + 339, + 401 + ], + "lines": [ + { + "bbox": [ + 329, + 392, + 339, + 401 + ], + "spans": [ + { + "bbox": [ + 329, + 392, + 339, + 401 + ], + "type": "text", + "content": "(a)" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 305, + 411, + 547, + 467 + ], + "lines": [ + { + "bbox": [ + 305, + 411, + 547, + 467 + ], + "spans": [ + { + "bbox": [ + 305, + 411, + 547, + 467 + ], + "type": "text", + "content": "Figure 1. Comparison of different VSS methods: (a) per-frame framework, (b) Accel [19] that alters the depth of models, and (c) our AR-Seg. AR-Seg reduces the computational cost for nonkeyframes by lowering the input resolution (depicted by narrow blocks), which is a dimension orthogonal to the depth of networks." + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 363, + 253, + 451, + 388 + ], + "blocks": [ + { + "bbox": [ + 363, + 253, + 451, + 388 + ], + "lines": [ + { + "bbox": [ + 363, + 253, + 451, + 388 + ], + "spans": [ + { + "bbox": [ + 363, + 253, + 451, + 388 + ], + "type": "image", + "image_path": "120c28654a5c1e738627652e955fb098b2fc38b0df3f86bef4abadf5d86ddbc9.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 403, + 392, + 414, + 401 + ], + "lines": [ + { + "bbox": [ + 403, + 392, + 414, + 401 + ], + "spans": [ + { + "bbox": [ + 403, + 392, + 414, + 401 + ], + "type": "text", + "content": "(b)" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 11 + }, + { + "type": "image", + "bbox": [ + 458, + 253, + 545, + 388 + ], + "blocks": [ + { + "bbox": [ + 458, + 253, + 545, + 388 + ], + "lines": [ + { + "bbox": [ + 458, + 253, + 545, + 388 + ], + "spans": [ + { + "bbox": [ + 458, + 253, + 545, + 388 + ], + "type": "image", + "image_path": "a7dbec70155366bd182fbbeb651458745ca0977537f081ad81cbc229f9741477.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 495, + 392, + 506, + 401 + ], + "lines": [ + { + "bbox": [ + 495, + 392, + 506, + 401 + ], + "spans": [ + { + "bbox": [ + 495, + 392, + 506, + 401 + ], + "type": "text", + "content": "(c)" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_caption" + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 483, + 546, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 483, + 546, + 628 + ], + "spans": [ + { + "bbox": [ + 304, + 483, + 546, + 628 + ], + "type": "text", + "content": "is a series of consecutive image frames recorded at a certain frame rate (usually 25fps or higher). Applying image-based segmentation methods [6, 25, 48, 52, 55] to a video frame by frame consumes considerable computational resources. To improve the efficiency of VSS, existing methods mainly focus on the design of network architectures. A class of methods proposes compact and efficient image-based architectures to reduce the computational overhead per-frame [22, 23, 28, 49, 51, 52, 54]. Another class of methods applies a deep model to keyframes and a shallow network for non-keyframes to avoid the repetitive computation [19, 24, 27, 34] for videos." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 630, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 630, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 630, + 547, + 715 + ], + "type": "text", + "content": "The work presented in this paper is based on an important observation: the above existing works ignored a crucial factor that affects the computational cost from the input side: the input resolution. For image-related tasks, the input resolution directly determines the amount of computation, e.g., the computational cost of 2D convolution is proportional to the product of image width and height. Once we" + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 702, + 135, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 702, + 135, + 712 + ], + "spans": [ + { + "bbox": [ + 58, + 702, + 135, + 712 + ], + "type": "text", + "content": "*Corresponding author." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "22627" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 228 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 228 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 228 + ], + "type": "text", + "content": "downsample the input frame by " + }, + { + "bbox": [ + 46, + 72, + 289, + 228 + ], + "type": "inline_equation", + "content": "0.5 \\times 0.5" + }, + { + "bbox": [ + 46, + 72, + 289, + 228 + ], + "type": "text", + "content": ", the computational overhead can be reduced by " + }, + { + "bbox": [ + 46, + 72, + 289, + 228 + ], + "type": "inline_equation", + "content": "75\\%" + }, + { + "bbox": [ + 46, + 72, + 289, + 228 + ], + "type": "text", + "content": ". On the other hand, decreasing resolution often leads to worse segmentation accuracy due to the loss of information [43,54]. In this paper, we propose to prevent the accuracy degradation by using temporal correlation in the video. Since the contents of video frames are temporally correlated, the local features lacking in low-resolution (LR) frames can be inferred and enriched by finding correspondences in sparse high-resolution (HR) reference frames based on motion cues. In a compressed video, the motion vectors contain such motion cues and can be obtained along with the video frames from video decoding at almost no additional cost." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 229, + 289, + 469 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 229, + 289, + 469 + ], + "spans": [ + { + "bbox": [ + 46, + 229, + 289, + 469 + ], + "type": "text", + "content": "Motivated by the above observation, we propose an altering resolution framework for compressed videos, named AR-Seg, to achieve efficient VSS. As shown in Figure 1(c), AR-Seg uses an HR branch to process keyframes at high resolution and an LR branch to process non-keyframes at low resolution. In particular, to prevent performance drop caused by downsampling, we insert a novel Cross Resolution Feature Fusion (CReFF) module into the LR branch and supervise the training with a Feature Similarity Training (FST) strategy to enrich local details in the LR features. CReFF fuses the HR keyframe features into LR nonkeyframe features in two steps: 1) Align the spatial structures of features from different frames by feature warping with motion vectors, which can be readily obtained from compressed videos at almost no additional cost; 2) Selectively aggregate the warped features (which may be noisy after warping) into LR features with the aid of local attention mechanism. Since local attention assigns different importance to each location in the neighborhood, it is an effective way to avoid misleading by noisy warped features." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 472, + 289, + 616 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 472, + 289, + 616 + ], + "spans": [ + { + "bbox": [ + 46, + 472, + 289, + 616 + ], + "type": "text", + "content": "Furthermore, our proposed FST strategy guides the learning of the CReFF aggregated features. FST consists of an explicit similarity loss (between the aggregated features and HR features inferred from non-keyframes) and an implicit constraint from the shared decoding layer across the HR and LR branches. Such a training strategy helps the LR branch to learn from features extracted from the HR branch, which is reliable and effective. Integrated with CReFF and FST, AR-Seg efficiently compensates for the accuracy loss of LR frames. Overall, AR-Seg significantly reduces the computational cost of VSS by altering input resolutions, while maintaining high segmentation accuracy." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 617, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 617, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 617, + 289, + 715 + ], + "type": "text", + "content": "To sum up, we make three contributions in this paper: 1) We propose an efficient framework for compressed videos, named AR-Seg, that uses altering input resolution for VSS and significantly reduces the computational cost without losing segmentation accuracy. 2) We design an efficient CReFF module to prevent the accuracy loss by aggregating HR keyframe features into LR non-keyframe features. 3) We propose a novel FST strategy that supervises the" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 304, + 72, + 547, + 157 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 157 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 157 + ], + "type": "text", + "content": "LR branch to learn from the HR branch through both explicit and implicit constraints. Experiment results demonstrate the effectiveness of AR-Seg with different resolutions, backbones, and keyframe intervals. On both CamVid [3] and Cityscapes [9] datasets, compared to the constant-resolution baselines, AR-Seg reduces the computational cost by nearly " + }, + { + "bbox": [ + 304, + 72, + 547, + 157 + ], + "type": "inline_equation", + "content": "70\\%" + }, + { + "bbox": [ + 304, + 72, + 547, + 157 + ], + "type": "text", + "content": " without compromising accuracy." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 305, + 167, + 398, + 179 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 167, + 398, + 179 + ], + "spans": [ + { + "bbox": [ + 305, + 167, + 398, + 179 + ], + "type": "text", + "content": "2. Related Works" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 187, + 547, + 282 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 187, + 547, + 282 + ], + "spans": [ + { + "bbox": [ + 304, + 187, + 547, + 282 + ], + "type": "text", + "content": "As a fundamental task of scene understanding, semantic segmentation has been an active research area for many years [8, 13, 21, 41], which also attracts considerable attention in the study of deep neural networks, e.g., FCN [25], DeepLabs [4, 5] and PSPNet [55]. In order to obtain accurate results in real-time applications, several methods have been proposed to improve the efficiency of semantic segmentation, which we summarize as follows." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 283, + 548, + 498 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 283, + 548, + 498 + ], + "spans": [ + { + "bbox": [ + 304, + 283, + 548, + 498 + ], + "type": "text", + "content": "Efficient Image Segmentation Methods. Many compact architectures have been proposed for efficient image segmentation. DFANet [22] adopted a lightweight backbone to reduce computational cost and designed cross-level aggregation for feature refinement. DFNet [23] utilized a partial order pruning algorithm to search segmentation models for a good trade-off between speed and accuracy. ICNet [54] used a cascade fusion module and transformed part of the computation from high-resolution to low-resolution. Wang et al. [43] designed superresolution learning to improve image segmentation performance. BiSeNets [11,51,52] used two-stream paths for low-level details and high-level context information, respectively. ESPNet [28] used an efficient spatial pyramid to accelerate the convolution computation. These efficient backbone networks reduce the computational burden of single-image segmentation, and can be applied to temporal or spatial frameworks in VSS." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 498, + 548, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 498, + 548, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 498, + 548, + 714 + ], + "type": "text", + "content": "Temporally Correlated Video Segmentation. Another group of methods focus on utilizing temporal redundancy in videos. They proposed various mechanisms that propagate the deep features extracted from keyframes to reduce the computation for non-keyframes. Clockwork [36] directly reused the segmentation result from keyframes, while Mahasseni et al. [27] interpolated segmentation results in the neighborhood. Noticing the lack of information from non-keyframes, Li et al. [24] extracted shallow features from non-keyframes, and fused them into the propagated deep features by spatially variant convolution. To compensate for the spatial misalignment between video frames, Zhu et al. [56] and Xu et al. [50] warped the intermediate features from keyframes by optical flow to produce segmentation results for non-keyframes. Jain et al. [19] fused the shallow features of non-keyframe into the warped features, and decoded them into better results. With global attention mechanism, TD-Net [16] aggregated the features from different" + } + ] + } + ], + "index": 8 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 749, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 749, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 749, + 318, + 757 + ], + "type": "text", + "content": "22628" + } + ] + } + ], + "index": 9 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 263 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 263 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 263 + ], + "type": "text", + "content": "time stamps and replaced the deep model with several shallow models distributed across the timeline. All the above methods mainly reduced the depth of backbone networks, but neglected the factor of input resolution considered in this paper. Instead of processing the image frames as a whole, Verelst et al. [42] split the frame into blocks and chose to copy or process them by a policy network. This block-based method reduces computational overhead from the spatial dimension, but lacks global information on nonkeyframes. Kim et al. [20] attempted to improve efficiency by reducing resolution. But they directly used the LR segmentation results, thus suffering from severe performance degradation. Compared to these methods, our proposed AR-Seg keeps the global information of LR non-keyframes, and enhances LR frames by selectively aggregating intermediate features from HR keyframes." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 264, + 289, + 612 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 264, + 289, + 612 + ], + "spans": [ + { + "bbox": [ + 46, + 264, + 289, + 612 + ], + "type": "text", + "content": "Compressed-Domain Video Analysis. Compressed video formats have been recently utilized in computer vision tasks. The motion vectors and residual maps are treated as additional modalities and directly fed into networks for video action recognition [1, 17, 37, 47] and semantic segmentation [39]. Such motion information also helps compensate for the spatial misalignment of features from different frames. Wang et al. [44] leveraged motion vectors to warp features in previous frames for object detection. Fan et al. [12] conditionally executed the backbone network for pose estimation depending on the residual values. For VSS, several methods have been proposed for efficient segmentation in the compressed domain. Jain et al. [18] warped the former and latter keyframe features using motion vectors, and predicted the non-keyframe features by interpolation. Tanujaya et al. [40] warped the results of keyframe segmentation for non-keyframes, and refined the warped segmentation by guided inpainting. Feng et al. [14] replaced a block of warped features with a local non-keyframe feature patch for further refinement. These methods reduced the computational cost of VSS, but suffered from performance degradation due to the limited capability of their feature refinement modules designed for non-keyframes. In our proposed AR-Seg, the warped features are refined by local attention mechanism according to the LR features of non-keyframes. Our attention-based refinement selectively aggregates the warped features and effectively suppresses the noise in motion vectors, achieving good segmentation accuracy with little computational overhead." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 621, + 104, + 634 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 621, + 104, + 634 + ], + "spans": [ + { + "bbox": [ + 47, + 621, + 104, + 634 + ], + "type": "text", + "content": "3. Method" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 641, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 641, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 641, + 289, + 715 + ], + "type": "text", + "content": "In order to achieve efficient VSS for compressed videos, we propose an altering resolution framework named AR-Seg (Section 3.1). AR-Seg uses two branches to process HR keyframes and LR non-keyframes in the video separately. To compensate for the information loss due to down-sampling the non-keyframes, we design a novel CReFF" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 304, + 72, + 547, + 133 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 133 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 133 + ], + "type": "text", + "content": "module that aggregates HR keyframe features into LR nonkeyframe features (Section 3.2). To guide the learning of aggregated features, we further propose a novel feature similarity training (FST) strategy containing both explicit and implicit constraints (Section 3.3)." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 305, + 140, + 424, + 152 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 140, + 424, + 152 + ], + "spans": [ + { + "bbox": [ + 305, + 140, + 424, + 152 + ], + "type": "text", + "content": "3.1. AR-Seg Framework" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 158, + 547, + 302 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 158, + 547, + 302 + ], + "spans": [ + { + "bbox": [ + 304, + 158, + 547, + 302 + ], + "type": "text", + "content": "For image/video semantic segmentation tasks, the input resolution directly determines the amount of computation, no matter what type of algorithms are applied, e.g., Conditional Random Fields, CNNs, and Transformers. Although reducing resolution has been studied in the context of video recognition [26, 29], altering resolution in dense prediction tasks like VSS remains unexplored. Based on this observation, we design the AR-Seg framework for VSS, which inputs video frames with altering resolutions; i.e., in AR-Seg, only a few keyframes are processed at high resolution to preserve fine details, while other non-keyframes are processed at low resolution to reduce the computational cost." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 302, + 547, + 458 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 302, + 547, + 458 + ], + "spans": [ + { + "bbox": [ + 304, + 302, + 547, + 458 + ], + "type": "text", + "content": "To identify the keyframes, we make use of the frame structure in a group of pictures (GOP) encoded in compressed videos [38, 46]. A GOP includes " + }, + { + "bbox": [ + 304, + 302, + 547, + 458 + ], + "type": "inline_equation", + "content": "L" + }, + { + "bbox": [ + 304, + 302, + 547, + 458 + ], + "type": "text", + "content": " consecutive frames of three types: I frame, P frame, and B frame. I frames are encoded in intra mode, while P and B frames are encoded in inter mode that computes motion vectors for motion compensation. In each GOP, we treat the first I frame as a keyframe and process it at high resolution. The remaining " + }, + { + "bbox": [ + 304, + 302, + 547, + 458 + ], + "type": "inline_equation", + "content": "L - 1" + }, + { + "bbox": [ + 304, + 302, + 547, + 458 + ], + "type": "text", + "content": " frames in GOP are non-keyframes and processed at low resolution. To simplify the description of our method, following the previous works [14, 47], we only consider the GOP structure without B frames in this section. The full treatment including B frames is presented in Appendix A4." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 458, + 547, + 554 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 458, + 547, + 554 + ], + "spans": [ + { + "bbox": [ + 304, + 458, + 547, + 554 + ], + "type": "text", + "content": "Due to the domain gap between images with different resolutions, it is difficult for a single network to extract features suitable for both HR and LR resolution images. Thus we design two branches with shared backbone architecture in the model and train them separately for each resolution. Figure 1(c) summarizes the proposed AR-Seg framework. It consists of two branches: an HR branch for keyframes and an LR branch for non-keyframes." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 554, + 547, + 686 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 554, + 547, + 686 + ], + "spans": [ + { + "bbox": [ + 304, + 554, + 547, + 686 + ], + "type": "text", + "content": "The HR branch adapts an image segmentation network, which consists of a feature sub-network " + }, + { + "bbox": [ + 304, + 554, + 547, + 686 + ], + "type": "inline_equation", + "content": "N_{feat}" + }, + { + "bbox": [ + 304, + 554, + 547, + 686 + ], + "type": "text", + "content": ", a task subnetwork " + }, + { + "bbox": [ + 304, + 554, + 547, + 686 + ], + "type": "inline_equation", + "content": "N_{task}" + }, + { + "bbox": [ + 304, + 554, + 547, + 686 + ], + "type": "text", + "content": ", and a final 1x1 convolutional layer1. It predicts segmentation results in high-resolution and simultaneously provides intermediate features before the final convolution as a reference for the LR branch. The LR branch is equipped with the same backbone network as the HR branch. To prevent performance degradation caused by downsampling, we design a CReFF module that aggregates HR features of the keyframe into the LR branch and place it before the final convolution layer of the backbone network." + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 306, + 693, + 545, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 693, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 306, + 693, + 545, + 713 + ], + "type": "text", + "content": "1We follow the modular division of backbone networks in [19]. Two backbones are discussed and compared in Section 4." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "22629" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 60, + 68, + 537, + 300 + ], + "blocks": [ + { + "bbox": [ + 60, + 68, + 537, + 300 + ], + "lines": [ + { + "bbox": [ + 60, + 68, + 537, + 300 + ], + "spans": [ + { + "bbox": [ + 60, + 68, + 537, + 300 + ], + "type": "image", + "image_path": "ec9230817086b2e542bd32614ab9b5fa9bcc243a2216af6299c71fffd6f663b9.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 306, + 547, + 340 + ], + "lines": [ + { + "bbox": [ + 46, + 306, + 547, + 340 + ], + "spans": [ + { + "bbox": [ + 46, + 306, + 547, + 340 + ], + "type": "text", + "content": "Figure 2. The CReFF module in the network architecture and feature similarity training (FST) strategy. CReFF consists of feature warping " + }, + { + "bbox": [ + 46, + 306, + 547, + 340 + ], + "type": "inline_equation", + "content": "\\mathcal{W}_{MV}" + }, + { + "bbox": [ + 46, + 306, + 547, + 340 + ], + "type": "text", + "content": " and local-attention-based feature fusion " + }, + { + "bbox": [ + 46, + 306, + 547, + 340 + ], + "type": "inline_equation", + "content": "\\mathcal{F}_{LA}" + }, + { + "bbox": [ + 46, + 306, + 547, + 340 + ], + "type": "text", + "content": " (Section 3.2). FST includes the explicit supervision by the feature similarity loss and the implicit supervision from shared convolution (Section 3.3). Parameters in gray blocks are fixed during the training of the LR branch." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 352, + 287, + 399 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 352, + 287, + 399 + ], + "spans": [ + { + "bbox": [ + 46, + 352, + 287, + 399 + ], + "type": "text", + "content": "CReFF aggregates the HR reference features into the extracted LR features, yielding estimated HR features for the non-keyframes, which are further converted into pixel-wise semantic labels by the final convolution layer." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 400, + 288, + 544 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 400, + 288, + 544 + ], + "spans": [ + { + "bbox": [ + 46, + 400, + 288, + 544 + ], + "type": "text", + "content": "As illustrated in Figure 1, different from the previous Accel framework [19], AR-Seg performs feature fusion before the last " + }, + { + "bbox": [ + 46, + 400, + 288, + 544 + ], + "type": "inline_equation", + "content": "1 \\times 1" + }, + { + "bbox": [ + 46, + 400, + 288, + 544 + ], + "type": "text", + "content": " convolution layer, instead of before the task sub-network " + }, + { + "bbox": [ + 46, + 400, + 288, + 544 + ], + "type": "inline_equation", + "content": "N_{task}" + }, + { + "bbox": [ + 46, + 400, + 288, + 544 + ], + "type": "text", + "content": ". The reason is twofold: 1) Since feature maps before the final convolution have basically the same spatial layout as the input images and segmentation outputs, we can utilize motion vectors to compensate for the spatial misalignment of features at such position; and 2) As the CReFF module actually upsamples the LR features, such a placement allows almost all convolution layers to benefit from the low resolution, thus reducing most of the computational cost." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 551, + 266, + 563 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 551, + 266, + 563 + ], + "spans": [ + { + "bbox": [ + 47, + 551, + 266, + 563 + ], + "type": "text", + "content": "3.2. CReFF: Cross Resolution Feature Fusion" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 570, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 570, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 570, + 288, + 714 + ], + "type": "text", + "content": "In the AR-Seg framework, CReFF aims to prevent the performance degradation caused by the lack of fine local details in LR non-keyframes. Unlike a single image, video frames are intrinsically temporally correlated, so missing details in LR non-keyframes can be retrieved from the corresponding regions in HR keyframes according to motion cues. Motion vectors (MVs) in the compressed video exactly provide such motion cues at the block level, i.e., pixels inside a macroblock share the same motion vector. Almost all mainstream video compression standards use motion vectors for inter-prediction, including H.26x series [38, 46], AOMedia series [7] and AVS series [10, 15, 53]. Such block-" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 352, + 545, + 374 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 352, + 545, + 374 + ], + "spans": [ + { + "bbox": [ + 304, + 352, + 545, + 374 + ], + "type": "text", + "content": "wise MVs are readily available in compressed videos and can be used to assist the LR branch." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 376, + 546, + 520 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 376, + 546, + 520 + ], + "spans": [ + { + "bbox": [ + 304, + 376, + 546, + 520 + ], + "type": "text", + "content": "Specifically, as depicted in Figure 2, the HR branch of AR-Seg extracts the feature " + }, + { + "bbox": [ + 304, + 376, + 546, + 520 + ], + "type": "inline_equation", + "content": "F_{I} \\in \\mathcal{R}^{C \\times H \\times W}" + }, + { + "bbox": [ + 304, + 376, + 546, + 520 + ], + "type": "text", + "content": " from an I frame, and the LR branch extracts the feature " + }, + { + "bbox": [ + 304, + 376, + 546, + 520 + ], + "type": "inline_equation", + "content": "f_{P} \\in \\mathcal{R}^{C \\times h \\times w}" + }, + { + "bbox": [ + 304, + 376, + 546, + 520 + ], + "type": "text", + "content": " from a P frame. Although P frames are processed in low resolution, CReFF takes " + }, + { + "bbox": [ + 304, + 376, + 546, + 520 + ], + "type": "inline_equation", + "content": "F_{I}, M_{P}," + }, + { + "bbox": [ + 304, + 376, + 546, + 520 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 376, + 546, + 520 + ], + "type": "inline_equation", + "content": "f_{P}" + }, + { + "bbox": [ + 304, + 376, + 546, + 520 + ], + "type": "text", + "content": " as input to generate the aggregated feature " + }, + { + "bbox": [ + 304, + 376, + 546, + 520 + ], + "type": "inline_equation", + "content": "\\tilde{F}_{P}" + }, + { + "bbox": [ + 304, + 376, + 546, + 520 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 376, + 546, + 520 + ], + "type": "inline_equation", + "content": "M_{P} \\in \\mathcal{R}^{2 \\times H \\times W}" + }, + { + "bbox": [ + 304, + 376, + 546, + 520 + ], + "type": "text", + "content": " denotes the MVs from P frame to I frame. The two channels of " + }, + { + "bbox": [ + 304, + 376, + 546, + 520 + ], + "type": "inline_equation", + "content": "M_{P}" + }, + { + "bbox": [ + 304, + 376, + 546, + 520 + ], + "type": "text", + "content": " correspond to " + }, + { + "bbox": [ + 304, + 376, + 546, + 520 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 304, + 376, + 546, + 520 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 376, + 546, + 520 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 304, + 376, + 546, + 520 + ], + "type": "text", + "content": " dimensions of motion vectors, denoted by " + }, + { + "bbox": [ + 304, + 376, + 546, + 520 + ], + "type": "inline_equation", + "content": "c_{x}" + }, + { + "bbox": [ + 304, + 376, + 546, + 520 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 376, + 546, + 520 + ], + "type": "inline_equation", + "content": "c_{y}" + }, + { + "bbox": [ + 304, + 376, + 546, + 520 + ], + "type": "text", + "content": ". Inside the CReFF module, the MV-based feature warping operation " + }, + { + "bbox": [ + 304, + 376, + 546, + 520 + ], + "type": "inline_equation", + "content": "\\mathcal{W}_{MV}" + }, + { + "bbox": [ + 304, + 376, + 546, + 520 + ], + "type": "text", + "content": " firstly warps " + }, + { + "bbox": [ + 304, + 376, + 546, + 520 + ], + "type": "inline_equation", + "content": "F_{I}" + }, + { + "bbox": [ + 304, + 376, + 546, + 520 + ], + "type": "text", + "content": " to the spatial layout of the P frame, which can be formulated as per-pixel shifting:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 350, + 528, + 545, + 548 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 350, + 528, + 545, + 548 + ], + "spans": [ + { + "bbox": [ + 350, + 528, + 545, + 548 + ], + "type": "interline_equation", + "content": "\\hat {F} _ {I} ^ {(x, y)} = F _ {I} ^ {\\left(x + M _ {P} ^ {\\left(c _ {x}, x, y\\right)}, y + M _ {P} ^ {\\left(c _ {y}, x, y\\right)}\\right)}, \\tag {1}", + "image_path": "95fbe0142975d843731adf1e89f399c0a70a731dd74e4d21943aad1d91ce08d4.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 556, + 545, + 581 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 556, + 545, + 581 + ], + "spans": [ + { + "bbox": [ + 304, + 556, + 545, + 581 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 556, + 545, + 581 + ], + "type": "inline_equation", + "content": "\\hat{F}_I\\in \\mathcal{R}^{C\\times H\\times W}" + }, + { + "bbox": [ + 304, + 556, + 545, + 581 + ], + "type": "text", + "content": " denotes the warped HR feature that will be further fused into LR features." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 582, + 545, + 700 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 545, + 700 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 545, + 700 + ], + "type": "text", + "content": "Due to the coarse-grained MVs (block-level instead of pixel-level) and the varying occlusion relationships across video frames, the warped features " + }, + { + "bbox": [ + 304, + 582, + 545, + 700 + ], + "type": "inline_equation", + "content": "\\hat{F}_I" + }, + { + "bbox": [ + 304, + 582, + 545, + 700 + ], + "type": "text", + "content": " are often noisy and misleading. Inspired by the success of non-local operation [45] and attention mechanism [16, 31, 33] in video-based applications, we propose to assign different fusion importance weights to the " + }, + { + "bbox": [ + 304, + 582, + 545, + 700 + ], + "type": "inline_equation", + "content": "(x,y)" + }, + { + "bbox": [ + 304, + 582, + 545, + 700 + ], + "type": "text", + "content": " locations in noisy features " + }, + { + "bbox": [ + 304, + 582, + 545, + 700 + ], + "type": "inline_equation", + "content": "\\hat{F}_I" + }, + { + "bbox": [ + 304, + 582, + 545, + 700 + ], + "type": "text", + "content": " by attention mechanism. Since " + }, + { + "bbox": [ + 304, + 582, + 545, + 700 + ], + "type": "inline_equation", + "content": "\\hat{F}_I" + }, + { + "bbox": [ + 304, + 582, + 545, + 700 + ], + "type": "text", + "content": " is roughly spatially aligned to " + }, + { + "bbox": [ + 304, + 582, + 545, + 700 + ], + "type": "inline_equation", + "content": "f_{p}" + }, + { + "bbox": [ + 304, + 582, + 545, + 700 + ], + "type": "text", + "content": " after warping, we use local attention to efficiently fuse the features as follows." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 317, + 701, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 701, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 317, + 701, + 545, + 714 + ], + "type": "text", + "content": "In the local-attention-based feature fusion module " + }, + { + "bbox": [ + 317, + 701, + 545, + 714 + ], + "type": "inline_equation", + "content": "\\mathcal{F}_{LA}" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "22630" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 193 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 193 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 193 + ], + "type": "text", + "content": "we firstly generate the Value and Key feature maps from the warped HR features " + }, + { + "bbox": [ + 46, + 72, + 289, + 193 + ], + "type": "inline_equation", + "content": "\\hat{F}_I" + }, + { + "bbox": [ + 46, + 72, + 289, + 193 + ], + "type": "text", + "content": ", and the Query maps from the upsampled LR features " + }, + { + "bbox": [ + 46, + 72, + 289, + 193 + ], + "type": "inline_equation", + "content": "\\bar{F}_P" + }, + { + "bbox": [ + 46, + 72, + 289, + 193 + ], + "type": "text", + "content": ". The " + }, + { + "bbox": [ + 46, + 72, + 289, + 193 + ], + "type": "inline_equation", + "content": "3 \\times 3" + }, + { + "bbox": [ + 46, + 72, + 289, + 193 + ], + "type": "text", + "content": " grouped convolution " + }, + { + "bbox": [ + 46, + 72, + 289, + 193 + ], + "type": "inline_equation", + "content": "\\mathbf{Conv}_g" + }, + { + "bbox": [ + 46, + 72, + 289, + 193 + ], + "type": "text", + "content": " with groups " + }, + { + "bbox": [ + 46, + 72, + 289, + 193 + ], + "type": "inline_equation", + "content": "= C" + }, + { + "bbox": [ + 46, + 72, + 289, + 193 + ], + "type": "text", + "content": " is selected to efficiently encode the feature maps into attention representations " + }, + { + "bbox": [ + 46, + 72, + 289, + 193 + ], + "type": "inline_equation", + "content": "V_I, K_I, Q_P \\in \\mathcal{R}^{C \\times H \\times W}" + }, + { + "bbox": [ + 46, + 72, + 289, + 193 + ], + "type": "text", + "content": ". Note that attention representations share the same channel size as the intermediate features. Denote the " + }, + { + "bbox": [ + 46, + 72, + 289, + 193 + ], + "type": "inline_equation", + "content": "n \\times n" + }, + { + "bbox": [ + 46, + 72, + 289, + 193 + ], + "type": "text", + "content": " neighborhood centered at " + }, + { + "bbox": [ + 46, + 72, + 289, + 193 + ], + "type": "inline_equation", + "content": "(x,y)" + }, + { + "bbox": [ + 46, + 72, + 289, + 193 + ], + "type": "text", + "content": " as " + }, + { + "bbox": [ + 46, + 72, + 289, + 193 + ], + "type": "inline_equation", + "content": "Nbhd_{(x,y)}" + }, + { + "bbox": [ + 46, + 72, + 289, + 193 + ], + "type": "text", + "content": ". Within " + }, + { + "bbox": [ + 46, + 72, + 289, + 193 + ], + "type": "inline_equation", + "content": "Nbhd_{(x,y)}" + }, + { + "bbox": [ + 46, + 72, + 289, + 193 + ], + "type": "text", + "content": ", the output of local attention " + }, + { + "bbox": [ + 46, + 72, + 289, + 193 + ], + "type": "inline_equation", + "content": "A_P" + }, + { + "bbox": [ + 46, + 72, + 289, + 193 + ], + "type": "text", + "content": " at the position " + }, + { + "bbox": [ + 46, + 72, + 289, + 193 + ], + "type": "inline_equation", + "content": "(x,y)" + }, + { + "bbox": [ + 46, + 72, + 289, + 193 + ], + "type": "text", + "content": " is generated by" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 62, + 198, + 287, + 213 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 62, + 198, + 287, + 213 + ], + "spans": [ + { + "bbox": [ + 62, + 198, + 287, + 213 + ], + "type": "interline_equation", + "content": "A _ {P} ^ {(x, y)} = \\overline {{V _ {I} ^ {N b h d _ {(x , y)}}}} \\mathcal {S} \\left(\\overline {{K _ {I} ^ {N b h d _ {(x , y)}}}}, Q _ {P} ^ {(x, y)}\\right), \\tag {2}", + "image_path": "873dfd605fa38023bd230ae56c00c30dee2777075f791ac120a863bd9bb9b51f.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 217, + 287, + 281 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 217, + 287, + 281 + ], + "spans": [ + { + "bbox": [ + 47, + 217, + 287, + 281 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 217, + 287, + 281 + ], + "type": "inline_equation", + "content": "A_{P}^{(x,y)}" + }, + { + "bbox": [ + 47, + 217, + 287, + 281 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 217, + 287, + 281 + ], + "type": "inline_equation", + "content": "Q_{P}^{(x,y)} \\in \\mathcal{R}^{C \\times 1}" + }, + { + "bbox": [ + 47, + 217, + 287, + 281 + ], + "type": "text", + "content": " denote the feature vectors at the position " + }, + { + "bbox": [ + 47, + 217, + 287, + 281 + ], + "type": "inline_equation", + "content": "(x,y)" + }, + { + "bbox": [ + 47, + 217, + 287, + 281 + ], + "type": "text", + "content": " of " + }, + { + "bbox": [ + 47, + 217, + 287, + 281 + ], + "type": "inline_equation", + "content": "A_{P}" + }, + { + "bbox": [ + 47, + 217, + 287, + 281 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 217, + 287, + 281 + ], + "type": "inline_equation", + "content": "Q_{P}" + }, + { + "bbox": [ + 47, + 217, + 287, + 281 + ], + "type": "text", + "content": " respectively, and " + }, + { + "bbox": [ + 47, + 217, + 287, + 281 + ], + "type": "inline_equation", + "content": "\\overline{V_{I}^{Nbhd_{(x,y)}}}" + }, + { + "bbox": [ + 47, + 217, + 287, + 281 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 217, + 287, + 281 + ], + "type": "inline_equation", + "content": "\\overline{K_{I}^{Nbhd_{(x,y)}}} \\in \\mathcal{R}^{C \\times n^{2}}" + }, + { + "bbox": [ + 47, + 217, + 287, + 281 + ], + "type": "text", + "content": " are the re-arranged feature vectors within " + }, + { + "bbox": [ + 47, + 217, + 287, + 281 + ], + "type": "inline_equation", + "content": "Nbhd_{(x,y)}" + }, + { + "bbox": [ + 47, + 217, + 287, + 281 + ], + "type": "text", + "content": " in " + }, + { + "bbox": [ + 47, + 217, + 287, + 281 + ], + "type": "inline_equation", + "content": "V_{I}" + }, + { + "bbox": [ + 47, + 217, + 287, + 281 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 217, + 287, + 281 + ], + "type": "inline_equation", + "content": "K_{I}" + }, + { + "bbox": [ + 47, + 217, + 287, + 281 + ], + "type": "text", + "content": ", respectively. The similarity operation " + }, + { + "bbox": [ + 47, + 217, + 287, + 281 + ], + "type": "inline_equation", + "content": "\\mathcal{S}(K,Q)" + }, + { + "bbox": [ + 47, + 217, + 287, + 281 + ], + "type": "text", + "content": " is formulated as" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 104, + 285, + 287, + 314 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 104, + 285, + 287, + 314 + ], + "spans": [ + { + "bbox": [ + 104, + 285, + 287, + 314 + ], + "type": "interline_equation", + "content": "\\mathcal {S} (K, Q) = \\operatorname {S o f t m a x} \\left(\\frac {K ^ {T} Q}{\\sqrt {C}}\\right). \\tag {3}", + "image_path": "5871cf7808f3a70b8bdff348542ce0ef989017f97cbc01b7fd093489b749170e.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 318, + 287, + 342 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 318, + 287, + 342 + ], + "spans": [ + { + "bbox": [ + 47, + 318, + 287, + 342 + ], + "type": "text", + "content": "Furthermore, the aggregated feature " + }, + { + "bbox": [ + 47, + 318, + 287, + 342 + ], + "type": "inline_equation", + "content": "\\tilde{F}_P" + }, + { + "bbox": [ + 47, + 318, + 287, + 342 + ], + "type": "text", + "content": " for P frame is obtained in a residual fashion:" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 80, + 346, + 287, + 361 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 80, + 346, + 287, + 361 + ], + "spans": [ + { + "bbox": [ + 80, + 346, + 287, + 361 + ], + "type": "interline_equation", + "content": "\\tilde {F} _ {P} = \\bar {F} _ {P} + A _ {P} = \\text {U p s a m p l e} \\left(f _ {P}\\right) + A _ {P}. \\tag {4}", + "image_path": "2234756c5b9b4981565bfa347f2c6356cf8ce70a14841fe12629312f0bd980de.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 365, + 287, + 450 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 365, + 287, + 450 + ], + "spans": [ + { + "bbox": [ + 46, + 365, + 287, + 450 + ], + "type": "text", + "content": "In summary, using the CReFF module, the feature details from the I frame are firstly aligned to the P frame, and then aggregated into the LR branch according to the pixel-wise similarity between " + }, + { + "bbox": [ + 46, + 365, + 287, + 450 + ], + "type": "inline_equation", + "content": "Q_{P}" + }, + { + "bbox": [ + 46, + 365, + 287, + 450 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 365, + 287, + 450 + ], + "type": "inline_equation", + "content": "K_{I}" + }, + { + "bbox": [ + 46, + 365, + 287, + 450 + ], + "type": "text", + "content": ". The verification of the architecture design of CReFF is presented in Section 4.3. The reader is referred to Appendix A1 for more details on the visualization of attention weights in " + }, + { + "bbox": [ + 46, + 365, + 287, + 450 + ], + "type": "inline_equation", + "content": "\\mathcal{F}_{LA}" + }, + { + "bbox": [ + 46, + 365, + 287, + 450 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 455, + 228, + 468 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 455, + 228, + 468 + ], + "spans": [ + { + "bbox": [ + 47, + 455, + 228, + 468 + ], + "type": "text", + "content": "3.3. FST: Feature Similarity Training" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 474, + 287, + 593 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 474, + 287, + 593 + ], + "spans": [ + { + "bbox": [ + 46, + 474, + 287, + 593 + ], + "type": "text", + "content": "In order to effectively train the CReFF module, we propose a feature similarity training (FST) strategy. FST utilizes the HR features of P frame " + }, + { + "bbox": [ + 46, + 474, + 287, + 593 + ], + "type": "inline_equation", + "content": "F_{P}" + }, + { + "bbox": [ + 46, + 474, + 287, + 593 + ], + "type": "text", + "content": " (extracted from the HR branch) to guide the learning of the aggregated features " + }, + { + "bbox": [ + 46, + 474, + 287, + 593 + ], + "type": "inline_equation", + "content": "\\tilde{F}_{P}" + }, + { + "bbox": [ + 46, + 474, + 287, + 593 + ], + "type": "text", + "content": " in the LR branch. Since " + }, + { + "bbox": [ + 46, + 474, + 287, + 593 + ], + "type": "inline_equation", + "content": "F_{P}" + }, + { + "bbox": [ + 46, + 474, + 287, + 593 + ], + "type": "text", + "content": " contains sufficient details to produce high-quality segmentation results, CReFF can learn how to aggregate " + }, + { + "bbox": [ + 46, + 474, + 287, + 593 + ], + "type": "inline_equation", + "content": "\\bar{F}_{P}" + }, + { + "bbox": [ + 46, + 474, + 287, + 593 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 474, + 287, + 593 + ], + "type": "inline_equation", + "content": "\\hat{F}_{I}" + }, + { + "bbox": [ + 46, + 474, + 287, + 593 + ], + "type": "text", + "content": " into effective HR features from it under the supervision of FST. Specifically, FST supervises the training process of the LR branch both explicitly and implicitly in the following ways." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 594, + 287, + 642 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 594, + 287, + 642 + ], + "spans": [ + { + "bbox": [ + 47, + 594, + 287, + 642 + ], + "type": "text", + "content": "The explicit constraint is to use the feature similarity loss " + }, + { + "bbox": [ + 47, + 594, + 287, + 642 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{fs}" + }, + { + "bbox": [ + 47, + 594, + 287, + 642 + ], + "type": "text", + "content": ". We use mean square error (MSE) to measure the difference between " + }, + { + "bbox": [ + 47, + 594, + 287, + 642 + ], + "type": "inline_equation", + "content": "\\tilde{F}_P" + }, + { + "bbox": [ + 47, + 594, + 287, + 642 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 594, + 287, + 642 + ], + "type": "inline_equation", + "content": "F_{P}" + }, + { + "bbox": [ + 47, + 594, + 287, + 642 + ], + "type": "text", + "content": ", which serves as an additional regularization for the LR model:" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 52, + 646, + 287, + 662 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 52, + 646, + 287, + 662 + ], + "spans": [ + { + "bbox": [ + 52, + 646, + 287, + 662 + ], + "type": "interline_equation", + "content": "\\mathcal {L} = \\mathcal {L} _ {s e g} + \\mathcal {L} _ {f s} = C E \\left(S _ {P}, G _ {P}\\right) + M S E \\left(\\tilde {F} _ {P}, F _ {P}\\right), \\tag {5}", + "image_path": "a6ca79bba29d437bca3a2258c7fca63748b4d870bafb467714c88ed3ebb5ed7b.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 47, + 664, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 664, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 47, + 664, + 287, + 714 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 664, + 287, + 714 + ], + "type": "inline_equation", + "content": "S_P \\in \\mathcal{R}^{C_{out} \\times H \\times W}" + }, + { + "bbox": [ + 47, + 664, + 287, + 714 + ], + "type": "text", + "content": " denotes the segmentation result produced by LR branch, " + }, + { + "bbox": [ + 47, + 664, + 287, + 714 + ], + "type": "inline_equation", + "content": "G_P \\in \\mathcal{R}^{H \\times W}" + }, + { + "bbox": [ + 47, + 664, + 287, + 714 + ], + "type": "text", + "content": " denotes the ground-truth segmentation of P frame and the segmentation loss " + }, + { + "bbox": [ + 47, + 664, + 287, + 714 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{seg}" + }, + { + "bbox": [ + 47, + 664, + 287, + 714 + ], + "type": "text", + "content": " is the standard cross entropy loss " + }, + { + "bbox": [ + 47, + 664, + 287, + 714 + ], + "type": "inline_equation", + "content": "CE(S_P, G_P)" + }, + { + "bbox": [ + 47, + 664, + 287, + 714 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 72, + 545, + 191 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 191 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 191 + ], + "type": "text", + "content": "The implicit constraint of FST is the shared decoding layer of " + }, + { + "bbox": [ + 304, + 72, + 545, + 191 + ], + "type": "inline_equation", + "content": "\\tilde{F}_P" + }, + { + "bbox": [ + 304, + 72, + 545, + 191 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 72, + 545, + 191 + ], + "type": "inline_equation", + "content": "F_{P}" + }, + { + "bbox": [ + 304, + 72, + 545, + 191 + ], + "type": "text", + "content": ". In the segmentation backbone model trained on the HR images, the final convolution layer acts as the segmentation decoder, which contains deep semantic information about high-quality HR features. To utilize such information, we directly transfer the final " + }, + { + "bbox": [ + 304, + 72, + 545, + 191 + ], + "type": "inline_equation", + "content": "1\\times 1" + }, + { + "bbox": [ + 304, + 72, + 545, + 191 + ], + "type": "text", + "content": " convolution layer of the HR branch to the LR branch with fixed parameters. Since the parameters are trained on HR features, they produce better segmentation results " + }, + { + "bbox": [ + 304, + 72, + 545, + 191 + ], + "type": "inline_equation", + "content": "S_P" + }, + { + "bbox": [ + 304, + 72, + 545, + 191 + ], + "type": "text", + "content": " when " + }, + { + "bbox": [ + 304, + 72, + 545, + 191 + ], + "type": "inline_equation", + "content": "\\tilde{F}_{P}" + }, + { + "bbox": [ + 304, + 72, + 545, + 191 + ], + "type": "text", + "content": " is closer to the HR feature " + }, + { + "bbox": [ + 304, + 72, + 545, + 191 + ], + "type": "inline_equation", + "content": "F_{P}" + }, + { + "bbox": [ + 304, + 72, + 545, + 191 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 193, + 545, + 324 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 193, + 545, + 324 + ], + "spans": [ + { + "bbox": [ + 304, + 193, + 545, + 324 + ], + "type": "text", + "content": "In summary, with the explicit and implicit constraints, FST effectively transfers the knowledge of HR features from the HR branch to the LR branch, enabling high-quality segmentation based on the aggregated features of CReFF. Figure 2 shows the overall training strategy for the LR branch. The HR I frame provides the features " + }, + { + "bbox": [ + 304, + 193, + 545, + 324 + ], + "type": "inline_equation", + "content": "F_{I}" + }, + { + "bbox": [ + 304, + 193, + 545, + 324 + ], + "type": "text", + "content": " for feature fusion in CReFF, and the HR P frame provides the features " + }, + { + "bbox": [ + 304, + 193, + 545, + 324 + ], + "type": "inline_equation", + "content": "F_{P}" + }, + { + "bbox": [ + 304, + 193, + 545, + 324 + ], + "type": "text", + "content": " for the explicit supervision in FST. Parameters of the LR branch are trained using the total loss " + }, + { + "bbox": [ + 304, + 193, + 545, + 324 + ], + "type": "inline_equation", + "content": "\\mathcal{L}" + }, + { + "bbox": [ + 304, + 193, + 545, + 324 + ], + "type": "text", + "content": " via backpropagation, with fixed parameters of the HR branch and the shared final convolution layer." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 338, + 388, + 352 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 338, + 388, + 352 + ], + "spans": [ + { + "bbox": [ + 306, + 338, + 388, + 352 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 359, + 545, + 431 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 359, + 545, + 431 + ], + "spans": [ + { + "bbox": [ + 304, + 359, + 545, + 431 + ], + "type": "text", + "content": "We evaluate the proposed AR-Seg framework on CamVid [3] and Cityscapes [9] datasets for street-view video semantic segmentation. Below we present experiments to demonstrate the efficiency of AR-Seg and its compatibility with different backbone models, resolutions, and video compression configurations." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 306, + 441, + 422, + 454 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 441, + 422, + 454 + ], + "spans": [ + { + "bbox": [ + 306, + 441, + 422, + 454 + ], + "type": "text", + "content": "4.1. Experimental Setup" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 460, + 545, + 568 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 460, + 545, + 568 + ], + "spans": [ + { + "bbox": [ + 304, + 460, + 545, + 568 + ], + "type": "text", + "content": "Datasets & Pre-processing. The CamVid [3] dataset consists of 4 videos of " + }, + { + "bbox": [ + 304, + 460, + 545, + 568 + ], + "type": "inline_equation", + "content": "720 \\times 960" + }, + { + "bbox": [ + 304, + 460, + 545, + 568 + ], + "type": "text", + "content": " resolution captured at 30 fps, with semantic annotations at 1Hz and, in part, 15Hz. The Cityscapes [9] dataset contains street view videos of " + }, + { + "bbox": [ + 304, + 460, + 545, + 568 + ], + "type": "inline_equation", + "content": "1024 \\times 2048" + }, + { + "bbox": [ + 304, + 460, + 545, + 568 + ], + "type": "text", + "content": " resolution captured in 17 fps, from which 5,000 images are densely annotated. We use the official train/validation/test split for both datasets. Following the previous works [16, 51], we select 11 and 19 classes for training and evaluation on these two datasets, respectively." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 569, + 545, + 629 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 569, + 545, + 629 + ], + "spans": [ + { + "bbox": [ + 304, + 569, + 545, + 629 + ], + "type": "text", + "content": "To simulate a real video compressed scenario, we compress the videos at reasonable bit-rates of 3Mbps for CamVid and 5Mbps for Cityscapes with the HEVC/H.265 [38] standard. The reader is referred to Appendix A3.1 for the detailed pre-processing steps." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "content": "Models & Baselines. To demonstrate the compatibility of AR-Seg with different backbones, we select two representative image segmentation models in our experiments: PSPNet [55] and BiseNet [52], which is similar to settings in the previous work [16]. The former is a widely used classical model, and the latter is a lightweight model that achieves state-of-the-art performance. We use " + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{A}\\mathbf{R}^{\\alpha}" + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "content": " - as the prefix" + } + ] + } + ], + "index": 19 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 749, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 749, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 749, + 317, + 757 + ], + "type": "text", + "content": "22631" + } + ] + } + ], + "index": 20 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 286, + 95 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 286, + 95 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 286, + 95 + ], + "type": "text", + "content": "of AR-Seg with specified backbone networks, where " + }, + { + "bbox": [ + 46, + 72, + 286, + 95 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 46, + 72, + 286, + 95 + ], + "type": "text", + "content": " denotes the downsample scale for the LR branch." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 96, + 286, + 168 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 96, + 286, + 168 + ], + "spans": [ + { + "bbox": [ + 46, + 96, + 286, + 168 + ], + "type": "text", + "content": "Training & Evaluation Details. Given a GOP length " + }, + { + "bbox": [ + 46, + 96, + 286, + 168 + ], + "type": "inline_equation", + "content": "L" + }, + { + "bbox": [ + 46, + 96, + 286, + 168 + ], + "type": "text", + "content": ", we train the LR branch with image pairs " + }, + { + "bbox": [ + 46, + 96, + 286, + 168 + ], + "type": "inline_equation", + "content": "(i, p)" + }, + { + "bbox": [ + 46, + 96, + 286, + 168 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 96, + 286, + 168 + ], + "type": "inline_equation", + "content": "p" + }, + { + "bbox": [ + 46, + 96, + 286, + 168 + ], + "type": "text", + "content": " refers to the P frame with annotation and " + }, + { + "bbox": [ + 46, + 96, + 286, + 168 + ], + "type": "inline_equation", + "content": "i = p - (L - 1)" + }, + { + "bbox": [ + 46, + 96, + 286, + 168 + ], + "type": "text", + "content": " refers to the I frame as a reference. We denote the distance between the annotated and the reference frames as " + }, + { + "bbox": [ + 46, + 96, + 286, + 168 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 46, + 96, + 286, + 168 + ], + "type": "text", + "content": ", then " + }, + { + "bbox": [ + 46, + 96, + 286, + 168 + ], + "type": "inline_equation", + "content": "d = L - 1" + }, + { + "bbox": [ + 46, + 96, + 286, + 168 + ], + "type": "text", + "content": " for the training pairs." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 170, + 286, + 289 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 170, + 286, + 289 + ], + "spans": [ + { + "bbox": [ + 46, + 170, + 286, + 289 + ], + "type": "text", + "content": "For evaluation, we test AR-Seg with different distances " + }, + { + "bbox": [ + 46, + 170, + 286, + 289 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 46, + 170, + 286, + 289 + ], + "type": "text", + "content": " between the target frame " + }, + { + "bbox": [ + 46, + 170, + 286, + 289 + ], + "type": "inline_equation", + "content": "p" + }, + { + "bbox": [ + 46, + 170, + 286, + 289 + ], + "type": "text", + "content": " and the reference keyframe " + }, + { + "bbox": [ + 46, + 170, + 286, + 289 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 170, + 286, + 289 + ], + "type": "text", + "content": ". For " + }, + { + "bbox": [ + 46, + 170, + 286, + 289 + ], + "type": "inline_equation", + "content": "d = 0" + }, + { + "bbox": [ + 46, + 170, + 286, + 289 + ], + "type": "text", + "content": ", we treat frame " + }, + { + "bbox": [ + 46, + 170, + 286, + 289 + ], + "type": "inline_equation", + "content": "p" + }, + { + "bbox": [ + 46, + 170, + 286, + 289 + ], + "type": "text", + "content": " as the keyframe and process it by the HR branch. Otherwise, we feed frame " + }, + { + "bbox": [ + 46, + 170, + 286, + 289 + ], + "type": "inline_equation", + "content": "p" + }, + { + "bbox": [ + 46, + 170, + 286, + 289 + ], + "type": "text", + "content": " into the LR branch for " + }, + { + "bbox": [ + 46, + 170, + 286, + 289 + ], + "type": "inline_equation", + "content": "d \\in (0, L - 1]" + }, + { + "bbox": [ + 46, + 170, + 286, + 289 + ], + "type": "text", + "content": ". The average of " + }, + { + "bbox": [ + 46, + 170, + 286, + 289 + ], + "type": "inline_equation", + "content": "mIoU_{d}" + }, + { + "bbox": [ + 46, + 170, + 286, + 289 + ], + "type": "text", + "content": " for each distance " + }, + { + "bbox": [ + 46, + 170, + 286, + 289 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 46, + 170, + 286, + 289 + ], + "type": "text", + "content": " is reported as the mIoU result. We measure FLOPs by PyTorch-OpCounter [35] following the previous methods [30, 32]. All the comparisons are evaluated on the compressed videos. More training and evaluation details are presented in Appendix A3.2 and A3.3." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 299, + 162, + 312 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 299, + 162, + 312 + ], + "spans": [ + { + "bbox": [ + 47, + 299, + 162, + 312 + ], + "type": "text", + "content": "4.2. Experiment Results" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 318, + 286, + 496 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 318, + 286, + 496 + ], + "spans": [ + { + "bbox": [ + 46, + 318, + 286, + 496 + ], + "type": "text", + "content": "Comparison with image-based methods. We first compare AR-Segs (with PSPNet [55] and BiseNet [52] as backbone) to their image-based counterparts of " + }, + { + "bbox": [ + 46, + 318, + 286, + 496 + ], + "type": "inline_equation", + "content": "1.0\\mathrm{x}" + }, + { + "bbox": [ + 46, + 318, + 286, + 496 + ], + "type": "text", + "content": " resolution. As shown in Table 1, on both CamVid and Cityscapes datasets, the proposed " + }, + { + "bbox": [ + 46, + 318, + 286, + 496 + ], + "type": "inline_equation", + "content": "\\mathrm{AR^{0.5}}" + }, + { + "bbox": [ + 46, + 318, + 286, + 496 + ], + "type": "text", + "content": " models achieve on-par or better performance than the " + }, + { + "bbox": [ + 46, + 318, + 286, + 496 + ], + "type": "inline_equation", + "content": "1.0\\mathrm{x}" + }, + { + "bbox": [ + 46, + 318, + 286, + 496 + ], + "type": "text", + "content": " resolution baselines while saving " + }, + { + "bbox": [ + 46, + 318, + 286, + 496 + ], + "type": "inline_equation", + "content": "67\\%" + }, + { + "bbox": [ + 46, + 318, + 286, + 496 + ], + "type": "text", + "content": " computational cost. Different from the low-resolution baselines that lead to significant performance degradation, AR-Seg successfully preserves the segmentation accuracy with the help of the CReFF module and the FST strategy. More comparisons between AR-Seg and the LR baselines under different resolutions are presented in Appendix A2.1. Furthermore, these experiment results with PSPNet and BiseNet also demonstrate the compatibility of AR-Seg for different backbone networks." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 498, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 498, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 498, + 286, + 713 + ], + "type": "text", + "content": "Comparison with video-based methods. Taking temporal coherence into consideration, we compare AR-Seg with the recent state-of-the-art video-based methods for efficient VSS. Besides the accuracy and computational cost, we also follow the previous work [33] to report the relative changes compared to their single-frame backbone models. Specifically, " + }, + { + "bbox": [ + 46, + 498, + 286, + 713 + ], + "type": "inline_equation", + "content": "\\widetilde{\\Delta}\\mathrm{mIoU}" + }, + { + "bbox": [ + 46, + 498, + 286, + 713 + ], + "type": "text", + "content": " denotes the relative change of mIoU, and " + }, + { + "bbox": [ + 46, + 498, + 286, + 713 + ], + "type": "inline_equation", + "content": "\\widetilde{\\Delta}\\mathrm{GFLOPs}" + }, + { + "bbox": [ + 46, + 498, + 286, + 713 + ], + "type": "text", + "content": " denotes the relative change of GFLOPs. As shown in Table 2, existing video-based methods usually improve accuracy " + }, + { + "bbox": [ + 46, + 498, + 286, + 713 + ], + "type": "inline_equation", + "content": "(\\widetilde{\\Delta}\\mathrm{mIoU} > 0)" + }, + { + "bbox": [ + 46, + 498, + 286, + 713 + ], + "type": "text", + "content": " at the cost of more computation " + }, + { + "bbox": [ + 46, + 498, + 286, + 713 + ], + "type": "inline_equation", + "content": "(\\widetilde{\\Delta}\\mathrm{GFLOPs} > 0)" + }, + { + "bbox": [ + 46, + 498, + 286, + 713 + ], + "type": "text", + "content": ", e.g., TDNet [16] and Accel [19]. Other methods, including BlockCopy [42], TapLab [14] and Jain et al. [18], reduce the computational cost " + }, + { + "bbox": [ + 46, + 498, + 286, + 713 + ], + "type": "inline_equation", + "content": "(\\widetilde{\\Delta}\\mathrm{GFLOPs} < 0)" + }, + { + "bbox": [ + 46, + 498, + 286, + 713 + ], + "type": "text", + "content": " but the accuracy also decreases " + }, + { + "bbox": [ + 46, + 498, + 286, + 713 + ], + "type": "inline_equation", + "content": "3\\% - 7\\%" + }, + { + "bbox": [ + 46, + 498, + 286, + 713 + ], + "type": "inline_equation", + "content": "(\\widetilde{\\Delta}\\mathrm{mIoU} < 0)" + }, + { + "bbox": [ + 46, + 498, + 286, + 713 + ], + "type": "text", + "content": ". As a comparison, our proposed models " + }, + { + "bbox": [ + 46, + 498, + 286, + 713 + ], + "type": "inline_equation", + "content": "\\mathrm{AR^{0.6}}" + }, + { + "bbox": [ + 46, + 498, + 286, + 713 + ], + "type": "text", + "content": "- can reduce the computational cost " + }, + { + "bbox": [ + 46, + 498, + 286, + 713 + ], + "type": "inline_equation", + "content": "(\\widetilde{\\Delta}\\mathrm{GFLOPs} < 0)" + }, + { + "bbox": [ + 46, + 498, + 286, + 713 + ], + "type": "text", + "content": " by more than " + }, + { + "bbox": [ + 46, + 498, + 286, + 713 + ], + "type": "inline_equation", + "content": "55\\%" + }, + { + "bbox": [ + 46, + 498, + 286, + 713 + ], + "type": "text", + "content": " and preserve the accuracy of single-frame backbone models " + }, + { + "bbox": [ + 46, + 498, + 286, + 713 + ], + "type": "inline_equation", + "content": "(\\widetilde{\\Delta}\\mathrm{mIoU} \\geq 0)" + }, + { + "bbox": [ + 46, + 498, + 286, + 713 + ], + "type": "text", + "content": ". With the lightweight" + } + ] + } + ], + "index": 5 + }, + { + "type": "table", + "bbox": [ + 307, + 95, + 543, + 218 + ], + "blocks": [ + { + "bbox": [ + 306, + 71, + 545, + 92 + ], + "lines": [ + { + "bbox": [ + 306, + 71, + 545, + 92 + ], + "spans": [ + { + "bbox": [ + 306, + 71, + 545, + 92 + ], + "type": "text", + "content": "Table 1. Comparison to the image-based methods on CamVid test set and Cityscapes valid set." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 307, + 95, + 543, + 218 + ], + "lines": [ + { + "bbox": [ + 307, + 95, + 543, + 218 + ], + "spans": [ + { + "bbox": [ + 307, + 95, + 543, + 218 + ], + "type": "table", + "html": "
MethodPSPNet18 [55]BiseNet18 [52]
mIoU(%)↑GFLOPs ↓mIoU(%)↑GFLOPs ↓
CamVid1.0x69.43309.0271.5758.83
AR0.771.23169.8671.7831.89
AR0.670.82133.0971.6024.68
AR0.570.48101.9870.3818.96
Cityscapes1.0x69.00560.9770.09178.96
AR0.770.23302.9570.8697.10
AR0.669.45234.9170.7276.06
AR0.569.03177.4470.5757.00
", + "image_path": "9b8c50b213efd2148ee74c81a94a4299f978448bf8430a06465ad26122e68021.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "table_body" + } + ], + "index": 7 + }, + { + "type": "table", + "bbox": [ + 307, + 277, + 545, + 456 + ], + "blocks": [ + { + "bbox": [ + 305, + 231, + 545, + 275 + ], + "lines": [ + { + "bbox": [ + 305, + 231, + 545, + 275 + ], + "spans": [ + { + "bbox": [ + 305, + 231, + 545, + 275 + ], + "type": "text", + "content": "Table 2. Comparison to the video-based methods on CamVid test set and Cityscapes valid set. " + }, + { + "bbox": [ + 305, + 231, + 545, + 275 + ], + "type": "inline_equation", + "content": "\\tilde{\\Delta} x = \\frac{\\Delta x}{|x|}" + }, + { + "bbox": [ + 305, + 231, + 545, + 275 + ], + "type": "text", + "content": " denotes the relative change compared to their single-frame backbone models. The best results are bold and the second best results are underlined." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 307, + 277, + 545, + 456 + ], + "lines": [ + { + "bbox": [ + 307, + 277, + 545, + 456 + ], + "spans": [ + { + "bbox": [ + 307, + 277, + 545, + 456 + ], + "type": "table", + "html": "
MethodmIoU↑GFLOPs↓ΔmIoU↑ΔGFLOPs↓
CamVidAccel-DL18 [19]66.15397.70+13.8%+61.9%
TD4-PSP18 [16]70.13363.70+1.0%+17.7%
BlockCopy [42]66.75107.52-5.2%-45.7%
TapLab-BL2 [14]67.57117.73-3.1%-50.2%
Jain et al. [18]67.61146.97-4.3%-53.8%
AR0.6-PSP1870.82101.98+2.0%-57.0%
AR0.6-Bise1871.6024.68+0.0%-58.0%
CityscapesAccel-DL18 [19]68.251011.75+18.4%+96.0%
TD4-PSP18 [16]70.11673.06+1.6%+20.0%
BlockCopy [42]67.69294.20-6.7%-41.2%
TapLab-BL2 [14]68.90237.29-4.1%-50.6%
Jain et al. [18]68.57342.67-5.1%-52.5%
AR0.6-PSP1869.45234.91+0.7%-58.1%
AR0.6-Bise1870.7276.06+0.9%-57.5%
", + "image_path": "cd9f020ef2f717f40fe11560552ebd905d7bac4f5d17ab19e419a5643bd019c2.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "table_body" + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 469, + 545, + 518 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 469, + 545, + 518 + ], + "spans": [ + { + "bbox": [ + 305, + 469, + 545, + 518 + ], + "type": "text", + "content": "backbone model BiseNet, AR" + }, + { + "bbox": [ + 305, + 469, + 545, + 518 + ], + "type": "inline_equation", + "content": "^{0.6}" + }, + { + "bbox": [ + 305, + 469, + 545, + 518 + ], + "type": "text", + "content": "-Bise18 achieves good performance in both accuracy and computational cost. More results of video-based methods and their single-frame backbone models are presented in Appendix A2.2." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 526, + 400, + 540 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 526, + 400, + 540 + ], + "spans": [ + { + "bbox": [ + 306, + 526, + 400, + 540 + ], + "type": "text", + "content": "4.3. Ablation Study" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 545, + 545, + 640 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 545, + 545, + 640 + ], + "spans": [ + { + "bbox": [ + 304, + 545, + 545, + 640 + ], + "type": "text", + "content": "We perform ablation studies to show the importance of each component in CReFF and FST, as well as the location of CReFF. We also evaluate AR-Seg in terms of different resolutions and GOP lengths, which reflects the influence of hyper-parameters " + }, + { + "bbox": [ + 304, + 545, + 545, + 640 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 304, + 545, + 545, + 640 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 545, + 545, + 640 + ], + "type": "inline_equation", + "content": "L" + }, + { + "bbox": [ + 304, + 545, + 545, + 640 + ], + "type": "text", + "content": ", respectively. We conducted ablation studies on the 30fps CamVid dataset, and used PSPNet18 as the default backbone model, " + }, + { + "bbox": [ + 304, + 545, + 545, + 640 + ], + "type": "inline_equation", + "content": "L = 12" + }, + { + "bbox": [ + 304, + 545, + 545, + 640 + ], + "type": "text", + "content": " as the default GOP length, and HEVC@3Mbps as the default codec." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 642, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 642, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 642, + 545, + 713 + ], + "type": "text", + "content": "Architecture of CReFF. We first validate the necessity of " + }, + { + "bbox": [ + 304, + 642, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{W}_{MV}" + }, + { + "bbox": [ + 304, + 642, + 545, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 642, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{F}_{LA}" + }, + { + "bbox": [ + 304, + 642, + 545, + 713 + ], + "type": "text", + "content": ". The method without CReFF directly applies FST to the upsampled features " + }, + { + "bbox": [ + 304, + 642, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\bar{F}_P" + }, + { + "bbox": [ + 304, + 642, + 545, + 713 + ], + "type": "text", + "content": " and serves as a baseline. As shown in Table 3, simply warping the keyframe features " + }, + { + "bbox": [ + 304, + 642, + 545, + 713 + ], + "type": "inline_equation", + "content": "(+\\mathcal{W}_{MV})" + }, + { + "bbox": [ + 304, + 642, + 545, + 713 + ], + "type": "text", + "content": " saves the most amount of computation by skipping processing non-keyframes with the" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "22632" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 48, + 71, + 547, + 210 + ], + "blocks": [ + { + "bbox": [ + 48, + 71, + 547, + 210 + ], + "lines": [ + { + "bbox": [ + 48, + 71, + 547, + 210 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 547, + 210 + ], + "type": "image", + "image_path": "844687012923341ca5ef9199a33873d1bf3ad665dfbbe5437e7dde33078d31ad.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 219, + 546, + 253 + ], + "lines": [ + { + "bbox": [ + 46, + 219, + 546, + 253 + ], + "spans": [ + { + "bbox": [ + 46, + 219, + 546, + 253 + ], + "type": "text", + "content": "Figure 3. Semantic segmentation on CamVid (top) and Cityscapes (bottom) with " + }, + { + "bbox": [ + 46, + 219, + 546, + 253 + ], + "type": "inline_equation", + "content": "d = 11" + }, + { + "bbox": [ + 46, + 219, + 546, + 253 + ], + "type": "text", + "content": ". Note that AR0.5-PSP18 predicts more semantic details than the constant-resolution PSPNet18 working on 0.5x resolution. Compared to the 1.0x baseline, AR0.5-PSP18 generates similar segmentation results, but consumes only 33.0% computational cost (measured in GFLOPs)." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 274, + 287, + 321 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 274, + 287, + 321 + ], + "spans": [ + { + "bbox": [ + 46, + 274, + 287, + 321 + ], + "type": "text", + "content": "segmentation network, but receives poor accuracy. Directly fusing the keyframe features using local attention " + }, + { + "bbox": [ + 46, + 274, + 287, + 321 + ], + "type": "inline_equation", + "content": "(+ \\mathcal{F}_{LA})" + }, + { + "bbox": [ + 46, + 274, + 287, + 321 + ], + "type": "text", + "content": " does not perform very well, because the feature maps are not well-aligned due to object motion in videos." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 323, + 288, + 529 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 323, + 288, + 529 + ], + "spans": [ + { + "bbox": [ + 46, + 323, + 288, + 529 + ], + "type": "text", + "content": "We further evaluate the design of " + }, + { + "bbox": [ + 46, + 323, + 288, + 529 + ], + "type": "inline_equation", + "content": "\\mathcal{F}_{LA}" + }, + { + "bbox": [ + 46, + 323, + 288, + 529 + ], + "type": "text", + "content": " by replacing " + }, + { + "bbox": [ + 46, + 323, + 288, + 529 + ], + "type": "inline_equation", + "content": "7\\times 7" + }, + { + "bbox": [ + 46, + 323, + 288, + 529 + ], + "type": "text", + "content": " local attention " + }, + { + "bbox": [ + 46, + 323, + 288, + 529 + ], + "type": "inline_equation", + "content": "(LA)" + }, + { + "bbox": [ + 46, + 323, + 288, + 529 + ], + "type": "text", + "content": " with other operations, including " + }, + { + "bbox": [ + 46, + 323, + 288, + 529 + ], + "type": "inline_equation", + "content": "LA" + }, + { + "bbox": [ + 46, + 323, + 288, + 529 + ], + "type": "text", + "content": " with different neighborhood sizes, " + }, + { + "bbox": [ + 46, + 323, + 288, + 529 + ], + "type": "inline_equation", + "content": "LA" + }, + { + "bbox": [ + 46, + 323, + 288, + 529 + ], + "type": "text", + "content": " with non-grouped convolution encoders " + }, + { + "bbox": [ + 46, + 323, + 288, + 529 + ], + "type": "inline_equation", + "content": "(\\mathcal{F}_{LA^*})" + }, + { + "bbox": [ + 46, + 323, + 288, + 529 + ], + "type": "text", + "content": ", global attention " + }, + { + "bbox": [ + 46, + 323, + 288, + 529 + ], + "type": "inline_equation", + "content": "(\\mathcal{F}_{GA})" + }, + { + "bbox": [ + 46, + 323, + 288, + 529 + ], + "type": "text", + "content": " and one-layer convolution " + }, + { + "bbox": [ + 46, + 323, + 288, + 529 + ], + "type": "inline_equation", + "content": "(\\mathcal{F}_{Conv})" + }, + { + "bbox": [ + 46, + 323, + 288, + 529 + ], + "type": "text", + "content": ". For " + }, + { + "bbox": [ + 46, + 323, + 288, + 529 + ], + "type": "inline_equation", + "content": "\\mathcal{F}_{GA}" + }, + { + "bbox": [ + 46, + 323, + 288, + 529 + ], + "type": "text", + "content": ", we downsample the Value and Key maps by " + }, + { + "bbox": [ + 46, + 323, + 288, + 529 + ], + "type": "inline_equation", + "content": "\\frac{1}{32}" + }, + { + "bbox": [ + 46, + 323, + 288, + 529 + ], + "type": "text", + "content": " to save the computation. " + }, + { + "bbox": [ + 46, + 323, + 288, + 529 + ], + "type": "inline_equation", + "content": "\\mathcal{F}_{Conv}" + }, + { + "bbox": [ + 46, + 323, + 288, + 529 + ], + "type": "text", + "content": " processes the concatenated feature " + }, + { + "bbox": [ + 46, + 323, + 288, + 529 + ], + "type": "inline_equation", + "content": "[\\hat{F}_I,\\bar{F}_P]" + }, + { + "bbox": [ + 46, + 323, + 288, + 529 + ], + "type": "text", + "content": " with a " + }, + { + "bbox": [ + 46, + 323, + 288, + 529 + ], + "type": "inline_equation", + "content": "3\\times 3" + }, + { + "bbox": [ + 46, + 323, + 288, + 529 + ], + "type": "text", + "content": " convolution. Due to the large channel number in deep layers, such an operation brings considerable computation overhead. Results in Table 3 show that " + }, + { + "bbox": [ + 46, + 323, + 288, + 529 + ], + "type": "inline_equation", + "content": "\\mathcal{F}_{LA}" + }, + { + "bbox": [ + 46, + 323, + 288, + 529 + ], + "type": "text", + "content": " with a " + }, + { + "bbox": [ + 46, + 323, + 288, + 529 + ], + "type": "inline_equation", + "content": "7\\times 7" + }, + { + "bbox": [ + 46, + 323, + 288, + 529 + ], + "type": "text", + "content": " neighborhood achieves a good balance between computation and accuracy. Other designs increase the computational cost without improving the accuracy. Furthermore, removing the direct connection (DC) path from CReFF reduces the mIoU to " + }, + { + "bbox": [ + 46, + 323, + 288, + 529 + ], + "type": "inline_equation", + "content": "69.14\\%" + }, + { + "bbox": [ + 46, + 323, + 288, + 529 + ], + "type": "text", + "content": ". This result implies that CReFF is more likely to learn the residuals of HR features than the absolute values." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 531, + 287, + 687 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 531, + 287, + 687 + ], + "spans": [ + { + "bbox": [ + 46, + 531, + 287, + 687 + ], + "type": "text", + "content": "Location of CReFF. As specified in Section 3.1, we place CReFF before the final " + }, + { + "bbox": [ + 46, + 531, + 287, + 687 + ], + "type": "inline_equation", + "content": "1 \\times 1" + }, + { + "bbox": [ + 46, + 531, + 287, + 687 + ], + "type": "text", + "content": " convolution layer, which is different from the previous Accel framework [19]. To evaluate the influence of the split point location, we insert CReFF before different layers and evaluate the performance. Split points include the final convolution layer (" + }, + { + "bbox": [ + 46, + 531, + 287, + 687 + ], + "type": "inline_equation", + "content": "C_{1 \\times 1}" + }, + { + "bbox": [ + 46, + 531, + 287, + 687 + ], + "type": "text", + "content": "), the task sub-network " + }, + { + "bbox": [ + 46, + 531, + 287, + 687 + ], + "type": "inline_equation", + "content": "N_{task}" + }, + { + "bbox": [ + 46, + 531, + 287, + 687 + ], + "type": "text", + "content": " and the feature sub-network " + }, + { + "bbox": [ + 46, + 531, + 287, + 687 + ], + "type": "inline_equation", + "content": "N_{feat}" + }, + { + "bbox": [ + 46, + 531, + 287, + 687 + ], + "type": "text", + "content": ". For the " + }, + { + "bbox": [ + 46, + 531, + 287, + 687 + ], + "type": "inline_equation", + "content": "N_{feat}" + }, + { + "bbox": [ + 46, + 531, + 287, + 687 + ], + "type": "text", + "content": " case, we insert CReFF after the first convolution layer of ResNet. As shown in Table 3, placing CReFF before " + }, + { + "bbox": [ + 46, + 531, + 287, + 687 + ], + "type": "inline_equation", + "content": "C_{1 \\times 1}" + }, + { + "bbox": [ + 46, + 531, + 287, + 687 + ], + "type": "text", + "content": " results in the best performance, which affirms our design in Section 3.1. We note that fusing features at an early stage does not improve accuracy, but rather considerably increases computational cost." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "content": "Feature Similarity Training (FST). The proposed FST strategy consists of the MSE Loss and the shared final con" + } + ] + } + ], + "index": 5 + }, + { + "type": "table", + "bbox": [ + 307, + 296, + 544, + 596 + ], + "blocks": [ + { + "bbox": [ + 305, + 272, + 544, + 293 + ], + "lines": [ + { + "bbox": [ + 305, + 272, + 544, + 293 + ], + "spans": [ + { + "bbox": [ + 305, + 272, + 544, + 293 + ], + "type": "text", + "content": "Table 3. Ablation experiments on CamVid dataset with PSPNet18. Settings used in our final model are underlined." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 307, + 296, + 544, + 596 + ], + "lines": [ + { + "bbox": [ + 307, + 296, + 544, + 596 + ], + "spans": [ + { + "bbox": [ + 307, + 296, + 544, + 596 + ], + "type": "table", + "html": "
ExperimentMethodmIoU(%)GFLOPs
BaselinePSPNet18 (1.0x)69.43309.02
PSPNet18 (0.5x)66.5177.27
Architecture of CReFF+ WMV + FLA (7x7)70.48101.98
w/o CReFF67.1496.60
+ WMV57.6425.75
+ FLA (7x7)67.93101.98
+ WMV + FLA (3x3)70.3098.74
+ WMV + FLA* (11x11)70.48107.32
+ WMV + FLA* (7x7)69.99170.96
+ WMV + FGA (1/32)67.11113.58
+ WMV + FConv70.45143.63
+ CReFF w/o DC69.14101.98
Location of CReFFbefore C1×170.48101.98
before Ntask68.60214.76
before Nfeat68.31308.46
Feature Similarity+ MSE Loss + Shared C1×170.48101.98
w/o FST69.21101.98
Training (FST)+ Shared C1×169.57101.98
+ MSE Loss70.17101.98
+ KL Loss + Shared C1×168.91101.98
Keyframe IntervalAR0.5-PSP18, L=1270.48101.98
AR0.5-PSP18, L=1570.2897.88
AR0.5-PSP18, L=2070.2894.11
AR0.5-PSP18, L=3069.6790.34
", + "image_path": "7895eb5dad6c0b7f1dc29089e91dd74fe90377eefcd34d8499ac10304801d821.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "table_body" + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 614, + 545, + 687 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 614, + 545, + 687 + ], + "spans": [ + { + "bbox": [ + 304, + 614, + 545, + 687 + ], + "type": "text", + "content": "volution layer " + }, + { + "bbox": [ + 304, + 614, + 545, + 687 + ], + "type": "inline_equation", + "content": "C_{1\\times 1}" + }, + { + "bbox": [ + 304, + 614, + 545, + 687 + ], + "type": "text", + "content": ". We train AR" + }, + { + "bbox": [ + 304, + 614, + 545, + 687 + ], + "type": "inline_equation", + "content": "^{0.5}" + }, + { + "bbox": [ + 304, + 614, + 545, + 687 + ], + "type": "text", + "content": "-PSP18 with or without these components and report the results in Table 3. Both components improve the segmentation performance compared to the model trained without FST. We also replace the MSE Loss with the Kullback-Leibler (KL) Divergence Loss, but the resulting segmentation performance is poor." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 689, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 689, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 689, + 546, + 713 + ], + "type": "text", + "content": "Resolution of LR Branch. By adjusting the resolution of the LR branch, AR-Seg can tailor the setting adaptive to" + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 749, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 749, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 749, + 317, + 757 + ], + "type": "text", + "content": "22633" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 48, + 70, + 189, + 159 + ], + "blocks": [ + { + "bbox": [ + 48, + 70, + 189, + 159 + ], + "lines": [ + { + "bbox": [ + 48, + 70, + 189, + 159 + ], + "spans": [ + { + "bbox": [ + 48, + 70, + 189, + 159 + ], + "type": "image", + "image_path": "441c89955f0eb3d5cff9182c5fdf7790b474f9a9b6763eb2de8dcce201210e50.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 114, + 163, + 125, + 171 + ], + "lines": [ + { + "bbox": [ + 114, + 163, + 125, + 171 + ], + "spans": [ + { + "bbox": [ + 114, + 163, + 125, + 171 + ], + "type": "text", + "content": "(a)" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 194, + 70, + 287, + 160 + ], + "blocks": [ + { + "bbox": [ + 194, + 70, + 287, + 160 + ], + "lines": [ + { + "bbox": [ + 194, + 70, + 287, + 160 + ], + "spans": [ + { + "bbox": [ + 194, + 70, + 287, + 160 + ], + "type": "image", + "image_path": "3d81eac544980a27b9843fb620063f50117b8a1f1c120890a123f24bea38d930.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 234, + 163, + 245, + 171 + ], + "lines": [ + { + "bbox": [ + 234, + 163, + 245, + 171 + ], + "spans": [ + { + "bbox": [ + 234, + 163, + 245, + 171 + ], + "type": "text", + "content": "(b)" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 46, + 174, + 287, + 217 + ], + "lines": [ + { + "bbox": [ + 46, + 174, + 287, + 217 + ], + "spans": [ + { + "bbox": [ + 46, + 174, + 287, + 217 + ], + "type": "text", + "content": "Figure 4. (a) Performance of AR-Seg with different resolutions for the LR branch. (b) " + }, + { + "bbox": [ + 46, + 174, + 287, + 217 + ], + "type": "inline_equation", + "content": "mIoU_{d}" + }, + { + "bbox": [ + 46, + 174, + 287, + 217 + ], + "type": "text", + "content": " for annotated frames with different distances to key frame. Value intervals of " + }, + { + "bbox": [ + 46, + 174, + 287, + 217 + ], + "type": "inline_equation", + "content": "mIoU_{d}" + }, + { + "bbox": [ + 46, + 174, + 287, + 217 + ], + "type": "text", + "content": " when " + }, + { + "bbox": [ + 46, + 174, + 287, + 217 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 46, + 174, + 287, + 217 + ], + "type": "text", + "content": " varies from 1 to " + }, + { + "bbox": [ + 46, + 174, + 287, + 217 + ], + "type": "inline_equation", + "content": "L - 1" + }, + { + "bbox": [ + 46, + 174, + 287, + 217 + ], + "type": "text", + "content": " are depicted as color bars in (a)." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 232, + 287, + 411 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 232, + 287, + 411 + ], + "spans": [ + { + "bbox": [ + 46, + 232, + 287, + 411 + ], + "type": "text", + "content": "different computational budgets. Here, we train and evaluate AR-Seg with different resolutions for the LR branch, ranging from 0.3x to 1.0x. We also train and evaluate the constant-resolution baselines of each resolution for comparison. As shown in Figure 4(a), AR-Seg improves both backbones under all resolutions, demonstrating the effectiveness of CReFF and FST. To quantify the average improvement, we utilize two metrics BD-FLOPs and BD-mIoU following the design of BD-Rate and BD-PSNR [2] in video compression. The results show that (1) with the same computational budget, AR-Seg improves the absolute accuracy for two backbones by " + }, + { + "bbox": [ + 46, + 232, + 287, + 411 + ], + "type": "inline_equation", + "content": "3.67\\%" + }, + { + "bbox": [ + 46, + 232, + 287, + 411 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 232, + 287, + 411 + ], + "type": "inline_equation", + "content": "3.02\\%" + }, + { + "bbox": [ + 46, + 232, + 287, + 411 + ], + "type": "text", + "content": " respectively, and (2) with the same accuracy, AR-Seg reduces the computational cost by " + }, + { + "bbox": [ + 46, + 232, + 287, + 411 + ], + "type": "inline_equation", + "content": "76.73\\%" + }, + { + "bbox": [ + 46, + 232, + 287, + 411 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 232, + 287, + 411 + ], + "type": "inline_equation", + "content": "51.06\\%" + }, + { + "bbox": [ + 46, + 232, + 287, + 411 + ], + "type": "text", + "content": " respectively. Both metrics are described in detail in Appendix A5." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 412, + 287, + 544 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 412, + 287, + 544 + ], + "spans": [ + { + "bbox": [ + 46, + 412, + 287, + 544 + ], + "type": "text", + "content": "The Temporal Gap. To investigate the influence of the distance " + }, + { + "bbox": [ + 46, + 412, + 287, + 544 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 46, + 412, + 287, + 544 + ], + "type": "text", + "content": " to the keyframe, we plot the " + }, + { + "bbox": [ + 46, + 412, + 287, + 544 + ], + "type": "inline_equation", + "content": "mIoU_{d}" + }, + { + "bbox": [ + 46, + 412, + 287, + 544 + ], + "type": "text", + "content": " results for " + }, + { + "bbox": [ + 46, + 412, + 287, + 544 + ], + "type": "inline_equation", + "content": "\\mathrm{AR}^{0.5}" + }, + { + "bbox": [ + 46, + 412, + 287, + 544 + ], + "type": "text", + "content": "-PSP18 and the constant-resolution baselines in Figure 4(b). As " + }, + { + "bbox": [ + 46, + 412, + 287, + 544 + ], + "type": "inline_equation", + "content": "mIoU_{0}" + }, + { + "bbox": [ + 46, + 412, + 287, + 544 + ], + "type": "text", + "content": " is determined by the HR branch, " + }, + { + "bbox": [ + 46, + 412, + 287, + 544 + ], + "type": "inline_equation", + "content": "\\mathrm{AR}^{0.5}" + }, + { + "bbox": [ + 46, + 412, + 287, + 544 + ], + "type": "text", + "content": "-PSP18 shares the same point with PSPNet18(1.0x) at " + }, + { + "bbox": [ + 46, + 412, + 287, + 544 + ], + "type": "inline_equation", + "content": "d = 0" + }, + { + "bbox": [ + 46, + 412, + 287, + 544 + ], + "type": "text", + "content": ". The " + }, + { + "bbox": [ + 46, + 412, + 287, + 544 + ], + "type": "inline_equation", + "content": "mIoU_{0}" + }, + { + "bbox": [ + 46, + 412, + 287, + 544 + ], + "type": "text", + "content": " for PSPNet18(0.5x) is much lower due to downsampling. When " + }, + { + "bbox": [ + 46, + 412, + 287, + 544 + ], + "type": "inline_equation", + "content": "d > 0" + }, + { + "bbox": [ + 46, + 412, + 287, + 544 + ], + "type": "text", + "content": ", the accuracy of PSPNet18(1.0x) decreases since the compression artifacts in P frames are more severe than those in I frames. As a comparison, the " + }, + { + "bbox": [ + 46, + 412, + 287, + 544 + ], + "type": "inline_equation", + "content": "\\mathrm{AR}^{0.5}" + }, + { + "bbox": [ + 46, + 412, + 287, + 544 + ], + "type": "text", + "content": "-PSP18 benefits from the CReFF module and maintains high accuracy for all the " + }, + { + "bbox": [ + 46, + 412, + 287, + 544 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 46, + 412, + 287, + 544 + ], + "type": "text", + "content": " values." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 544, + 287, + 640 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 544, + 287, + 640 + ], + "spans": [ + { + "bbox": [ + 46, + 544, + 287, + 640 + ], + "type": "text", + "content": "Keyframe Intervals. To validate the long-range reference, we extend our evaluation to different keyframe intervals without re-training. As shown in Table 3, AR" + }, + { + "bbox": [ + 46, + 544, + 287, + 640 + ], + "type": "inline_equation", + "content": "^{0.5}" + }, + { + "bbox": [ + 46, + 544, + 287, + 640 + ], + "type": "text", + "content": "-PSP18 trained with " + }, + { + "bbox": [ + 46, + 544, + 287, + 640 + ], + "type": "inline_equation", + "content": "L = 12" + }, + { + "bbox": [ + 46, + 544, + 287, + 640 + ], + "type": "text", + "content": " maintains good performance with different GOP lengths. Moreover, even for " + }, + { + "bbox": [ + 46, + 544, + 287, + 640 + ], + "type": "inline_equation", + "content": "L = 30" + }, + { + "bbox": [ + 46, + 544, + 287, + 640 + ], + "type": "text", + "content": ", which stands for 1s in 30fps videos and is larger than the discussion in previous works [19, 56], AR-Seg outperforms the 1.0x baseline using only " + }, + { + "bbox": [ + 46, + 544, + 287, + 640 + ], + "type": "inline_equation", + "content": "29.2\\%" + }, + { + "bbox": [ + 46, + 544, + 287, + 640 + ], + "type": "text", + "content": " FLOPs." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 641, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 641, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 641, + 287, + 714 + ], + "type": "text", + "content": "Video Compression Configurations. As shown in Table 4, we also train and evaluate our model with different realistic bit-rates (3Mbps and 1Mbps) and configurations for HEVC/H.265 encoders. We use x265-medium and x265-ultrafast to represent different presets for x265, which apply simplified motion search algorithms and larger macro" + } + ] + } + ], + "index": 8 + }, + { + "type": "table", + "bbox": [ + 307, + 106, + 545, + 217 + ], + "blocks": [ + { + "bbox": [ + 305, + 70, + 545, + 103 + ], + "lines": [ + { + "bbox": [ + 305, + 70, + 545, + 103 + ], + "spans": [ + { + "bbox": [ + 305, + 70, + 545, + 103 + ], + "type": "text", + "content": "Table 4. Performance of AR-Seg on videos compressed by different codec's. AR-Seg achieves comparable or even better accuracy than its image-based constant-resolution counterparts." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 307, + 106, + 545, + 217 + ], + "lines": [ + { + "bbox": [ + 307, + 106, + 545, + 217 + ], + "spans": [ + { + "bbox": [ + 307, + 106, + 545, + 217 + ], + "type": "table", + "html": "
CodecMethodmIoU(%)GFLOPs
HEVC@3MbpsPSPNet18(1.0x)69.43309.02
AR0.5-PSP1870.48101.98
HEVC@1MbpsPSPNet18(1.0x)65.76309.02
AR0.5-PSP1867.89101.98
x265-medium@3MbpsPSPNet18 (1.0x)68.19309.02
AR0.5-PSP1869.53101.98
x265-ultrafast@3MbpsPSPNet18 (1.0x)67.69309.02
AR0.5-PSP1868.78101.98
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Dataset1.0x baselineAR0.5AR0.3
CamVid31.2 ms (32fps)14.7 ms (68fps)9.0 ms (111fps)
Cityscapes95.4 ms (10fps)30.7 ms (33fps)19.9 ms (50fps)
", + "image_path": "b17158e060b8d007ce7a38e0f84a80cef3b601fb3bfde8a331f7616cd3d8a779.jpg" + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "table_body" + } + ], + "index": 15 + }, + { + "bbox": [ + 306, + 463, + 378, + 475 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 463, + 378, + 475 + ], + "spans": [ + { + "bbox": [ + 306, + 463, + 378, + 475 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 483, + 545, + 651 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 483, + 545, + 651 + ], + "spans": [ + { + "bbox": [ + 304, + 483, + 545, + 651 + ], + "type": "text", + "content": "In this paper, we propose AR-Seg, an altering resolution framework for compressed video semantic segmentation, which innovatively improves the efficiency of video segmentation from the perspective of input resolution. By jointly considering the design of architecture and training strategy, our proposed CReFF module and FST strategy effectively prevent the accuracy loss caused by downsampling. Results evaluated on two widely used datasets show that AR-Seg can achieve competitive segmentation accuracy with a reduction of up to " + }, + { + "bbox": [ + 304, + 483, + 545, + 651 + ], + "type": "inline_equation", + "content": "67\\%" + }, + { + "bbox": [ + 304, + 483, + 545, + 651 + ], + "type": "text", + "content": " computational cost. Our current study only uses two alternating resolutions (i.e., HR and LR). Future work that applies more complicated scheduling of multi-resolutions and keyframe gaps will be considered to further improve the VSS performance." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 653, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 653, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 653, + 545, + 713 + ], + "type": "text", + "content": "Acknowledgements: This work was partially supported by Beijing Natural Science Foundation (L222008), Tsinghua University Initiative Scientific Research Program, the Natural Science Foundation of China (61725204), BNRist, and MOE-Key Laboratory of Pervasive Computing." + } + ] + } + ], + "index": 18 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "22634" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 287, + 713 + ], + "type": "list", + "angle": 0, + "index": 11, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 156 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 156 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 156 + ], + "type": "text", + "content": "[1] Barak Battash, Haim Barad, Hanlin Tang, and Amit Blei-weiess. 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IEEE Computer Society, 2017. 2, 8" + } + ] + } + ], + "index": 17 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 749, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 749, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 749, + 317, + 757 + ], + "type": "text", + "content": "22637" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 10 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Efficient Verification of Neural Networks Against LVM-Based Specifications/f017e278-be6a-4fc6-a7c8-64ae1c47c99f_content_list.json b/2023/Efficient Verification of Neural Networks Against LVM-Based Specifications/f017e278-be6a-4fc6-a7c8-64ae1c47c99f_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..fa791d8a65c6ebbde2ea2063e32aabeb9bf47940 --- /dev/null +++ b/2023/Efficient Verification of Neural Networks Against LVM-Based Specifications/f017e278-be6a-4fc6-a7c8-64ae1c47c99f_content_list.json @@ -0,0 +1,1620 @@ +[ + { + "type": "text", + "text": "Efficient Verification of Neural Networks against LVM-based Specifications", + "text_level": 1, + "bbox": [ + 106, + 128, + 864, + 152 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Harleen Hanspal \nImperial College London & Safe Intelligence \nLondon, United Kingdom", + "bbox": [ + 158, + 181, + 517, + 233 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "h.hanspal21@imperial.ac.uk", + "bbox": [ + 220, + 237, + 455, + 250 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Alessio Lomuscio \nSafe Intelligence \nLondon, United Kingdom", + "bbox": [ + 589, + 181, + 790, + 233 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "alessio@safeintelligence.ai", + "bbox": [ + 563, + 237, + 803, + 250 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 286, + 313, + 301 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "The deployment of perception systems based on neural networks in safety critical applications requires assurance on their robustness. Deterministic guarantees on network robustness require formal verification. Standard approaches for verifying robustness analyse invariance to analytically defined transformations, but not the diverse and ubiquitous changes involving object pose, scene viewpoint, occlusions, etc. To this end, we present an efficient approach for verifying specifications definable using Latent Variable Models that capture such diverse changes. The approach involves adding an invertible encoding head to the network to be verified, enabling the verification of latent space sets with minimal reconstruction overhead. We report verification experiments for three classes of proposed latent space specifications, each capturing different types of realistic input variations. Differently from previous work in this area, the proposed approach is relatively independent of input dimensionality and scales to a broad class of deep networks and real-world datasets by mitigating the inefficiency and decoder expressivity dependence in the present state-of-the-art.", + "bbox": [ + 75, + 316, + 473, + 633 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 662, + 209, + 679 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "The deployment of perception systems based on neural networks in safety-critical applications requires assurance on their performance, notably accuracy and robustness. Formal verification contributes to this requirement by providing provable and deterministic guarantees that a network meets a given specification. Typically, specifications are mathematically expressed constraints on the network's intended input/output and may encode desirable properties, such as robustness to noise (including adversarial attacks) [35], geometric changes [1,2], bias-field changes [14] and beyond.", + "bbox": [ + 75, + 688, + 468, + 854 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "While the above is useful, practical applications require robustness against diverse changes in a scene, including changes in the pose of objects, viewpoints, occlusions, etc.", + "bbox": [ + 75, + 854, + 468, + 900 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Such changes cannot be efficiently mathematically defined, but may be encoded from data by using generative models. For instance, [11, 12, 28, 34] use generative models to generate novel in-domain images for data augmentation, adversarial training or evaluating network generalisation; [34] additionally derives formal conditions for a latent space set to necessarily contain sufficient perturbations for it to be trusted for adversarial training and robustness checks. All these approaches either provide statistical robustness measures, or generate attacks based on gradient-search, which is not guaranteed to find an attack if one exists.", + "bbox": [ + 496, + 287, + 893, + 454 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Popular for network robustification and empirical evaluation, latent space sets are seldom used as inputs for verification due to the valid concern over the lack of mathematical guarantees on the completeness of the specifications they encode. Therefore, we reiterate that this work is most useful for changes that are difficult to mathematically define. We additionally argue that formal verification of latent space-based specifications can be more valuable than their empirical evaluation. This is because the latent space is a continuous domain and countably infinite number of inputs can be mapped to and reconstructed from a latent space set. Therefore, no amount of testing, or search in the latent space can provide guarantees against all the variations encoded in it. To the best of our knowledge, only [20, 27] encode specifications in a latent space and propose architectures to verify them.", + "bbox": [ + 496, + 455, + 893, + 696 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "There are, however, two difficulties with verification in the latent space. The first concerns the scalability of verification methods; the second relates to the quality of reconstructions affecting the verification outcomes. In this paper, we focus on alleviating these two concerns. Specifically, we propose a novel, invertible encoder-based pipeline for verifying latent space sets, that lends two key benefits of:", + "bbox": [ + 496, + 699, + 893, + 806 + ], + "page_idx": 0 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- Computational efficiency and relative independence to input dimensionality,", + "- Verification outcomes' independence to reconstructions, and precise counterexamples with high recall." + ], + "bbox": [ + 500, + 808, + 890, + 868 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "We focus our analysis on pose and attribute variations in vision inference tasks, but the approach is likely extendable", + "bbox": [ + 500, + 869, + 890, + 900 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "3894", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "to other variations, domains and tasks. Next, we recall key notions for network verification and discuss the existing relevant work, before presenting and validating our method in subsequent sections.", + "bbox": [ + 75, + 90, + 468, + 151 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Background and Related Work", + "text_level": 1, + "bbox": [ + 76, + 165, + 362, + 181 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Neural network verification. Given a network $N$ and an input-output specification $(X_{\\mathrm{des}},Y_{\\mathrm{des}})$ , the network verification problem is the decision problem of determining whether", + "bbox": [ + 75, + 191, + 468, + 250 + ], + "page_idx": 1 + }, + { + "type": "equation", + "text": "\n$$\nN (x) \\in Y _ {\\mathrm {d e s}}, \\forall x \\in X _ {\\mathrm {d e s}}.\n$$\n", + "text_format": "latex", + "bbox": [ + 189, + 253, + 356, + 268 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Verification methods, such as those based on SMT [19], MILP [4, 10, 22], Interval Propagation [15, 16, 32, 33], SDP [3, 29] or Lipschitz analysis [39], propagate a set $X_{\\mathrm{des}}$ in a single forward pass through $N$ and determine whether or not the output set of $N$ for $X_{\\mathrm{des}}$ lies in $Y_{\\mathrm{des}}$ . These methods mostly support input specifications defined in:", + "bbox": [ + 75, + 273, + 468, + 363 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- Data space, such that $X_{\\mathrm{des}}$ is a norm ball around an input $x$ , i.e., $\\mathcal{B}_{\\epsilon}(x) = \\{x' \\mid \\| x' - x \\| < \\epsilon\\}$ . The norm is defined in metric spaces such as $\\ell_p$ [2,16,19] or Wasserstein [36], and the $\\epsilon$ is adequately set to include intended photometric and geometric variations, albeit along with considerable unrealistic instances in case of large variations.", + "- Parameter space, such that, given an input $x$ and a set of transformations $T$ , $X_{\\mathrm{des}}$ is defined by prepending parametric transform layers $N_T(\\alpha)$ , where $\\alpha$ determines the transformation extent, to the network; $X_{\\mathrm{des}} = N_T(\\alpha)(x)$ . This definition is more precise in capturing planar geometric changes [26] and photometric changes, such as smooth illumination variations [14], in an input." + ], + "bbox": [ + 78, + 364, + 468, + 561 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "While these specifications are important, they do not efficiently capture non-planar and semantic transformations.", + "bbox": [ + 75, + 563, + 468, + 592 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "LVM-based specifications. Latent Variable Models (LVMs) for data generation map a typically lower-dimensional, continuous latent distribution to the input space. This mapping and its converse is learnt by LVM's decoder-encoder pair. Additionally, conditional training can disentangle latent dimensions to precisely capture specific dataset features and variations [5, 7, 23]. We refer to specifications which use LVM encoders to map input variations and define query input sets as LVM-based specifications.", + "bbox": [ + 75, + 593, + 468, + 728 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Related work. As mentioned in Section 1, most formal verification approaches do not use generative models. Only [20, 27] use an autoencoder in a verification setup to prove whether or not the output of a network $N$ is consistent for the image set produced by an independent autoencoder $(e,d)$ from the interpolations in its latent space. Formally, [27] establishes whether", + "bbox": [ + 75, + 729, + 468, + 834 + ], + "page_idx": 1 + }, + { + "type": "equation", + "text": "\n$$\n(N \\circ d) \\circ e (x) \\in Y _ {\\mathrm {d e s}}, \\forall x \\in \\{X \\mid e (X) \\in Z _ {\\mathrm {d e s}} \\},\n$$\n", + "text_format": "latex", + "bbox": [ + 109, + 844, + 434, + 861 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "where $Z_{\\mathrm{des}} \\in \\mathbb{R}^{\\mathrm{latent\\_dim}}$ is a segment joining latent encodings of samples in $X_{\\mathrm{des}}$ . Since propagating $Z_{\\mathrm{des}}$ through", + "bbox": [ + 76, + 869, + 468, + 900 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "a useful decoder is computationally expensive, deterministic verification using this approach is reported to not scale beyond small networks. To overcome this, the authors a) heuristically subsume and approximate line segments by axes-aligned boxes, and b) turn specifications into probabilistic statements that determine whether a vector sampled uniformly from $Z_{\\mathrm{des}}$ generates a correctly classified image.", + "bbox": [ + 496, + 90, + 890, + 196 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "The general approach of prepending a generative model as an independent input set generator for verifying a network, which we henceforth refer to as the Encoder-Decoder-Network (EDN) approach, suffers from the following limitations:", + "bbox": [ + 496, + 198, + 890, + 272 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "1. The network is verified only against images appropriately mapped by the encoder, but the encoding could be loose $(z \\in Z_{\\mathrm{des}} \\Rightarrow e^{-1}(z) \\in X_{\\mathrm{des}})$ and incomplete $(x \\in X_{\\mathrm{des}} \\Rightarrow e(x) \\in Z_{\\mathrm{des}})$ .", + "2. The network is verified against reconstructions of the decoder which may not have the same quality as the dataset images in terms of sharpness and diversity. If the decoder does not reconstruct an intended attribute's variations, either because all variations of that attribute are encoded to the same latent vector, or because it is not expressive enough, verification may incorrectly suggest that the network is invariant to that attribute.", + "3. The input set $Z_{\\mathrm{des}}$ is propagated through both the decoder and the network to be verified, thereby resulting in considerable computational cost." + ], + "bbox": [ + 503, + 273, + 890, + 503 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In the rest of the paper, we propose a pipeline for verifying LVM-based specifications in a computationally lighter manner, and alleviate the last two shortcomings by construction. We do not solve the first limitation; but in Section 5.4, we present metrics to quantify the precision of the proposed specifications in terms of how well they capture the desired variations.", + "bbox": [ + 496, + 503, + 890, + 609 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "3. Efficient Verification in Latent Space", + "text_level": 1, + "bbox": [ + 498, + 627, + 831, + 643 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In this section we present an efficient approach to verify the robustness of neural networks against specifications capturing diverse and realistic input variations. Formally, given a network $N$ and a variation $v$ , we define the Semantic Verification Problem (SVP) as the network verification problem where $X_{\\mathrm{des}}$ is the preimage of a set $Z_{\\mathrm{des}}$ under a partially invertible encoder $e$ :", + "bbox": [ + 496, + 654, + 890, + 758 + ], + "page_idx": 1 + }, + { + "type": "equation", + "text": "\n$$\nN (x) \\in Y _ {\\mathrm {d e s}}, \\forall x \\in \\{X \\mid e (X) = Z _ {\\mathrm {d e s}} \\}.\n$$\n", + "text_format": "latex", + "bbox": [ + 560, + 768, + 826, + 784 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Here, $Z_{\\mathrm{des}}$ is a set in the encoder's output space that captures $v$ and the input-output specification set is $(Z_{\\mathrm{des}}, Y_{\\mathrm{des}})$ . In the following, we study the Semantic Robustness Verification Problem (SRVP), which is an instance of SVP that checks for network robustness, i.e., $Y_{\\mathrm{des}}$ is a singleton. To solve SRVP, we propose the multi-head architecture shown in Figure 1.", + "bbox": [ + 496, + 794, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "3895", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/2b0f102aa84cb435a76a7f512d541566301ed3768cb68d0f83c13f67b173657c.jpg", + "image_caption": [ + "Figure 1. The proposed pipeline consists of an LVM, built around the network to be verified, that takes the network's intermediate features as its input. The LVM encoder is invertible and maps its input feature set to a spatially coherent latent manifold, where the input specification is defined." + ], + "image_footnote": [], + "bbox": [ + 80, + 87, + 486, + 255 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Verification pipeline. The network $N$ to be verified is divided into a Feature Detection Network (FDN), consisting of $N$ 's initial layers, and a task head, e.g., a classification or regression head. In our implementation, $N$ is a classifier, but the approach applies similarly for other learning tasks. To define the specification, we add an LVM after the FDN. The encoder of this LVM is invertible and maps the intermediate features, output by FDN, to its latent space where the input specification is defined. Unlike the feature space, this latent space is queryable by using the decoder and can be made approximately bounded.", + "bbox": [ + 75, + 352, + 468, + 518 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The verification path with this pipeline is limited to the inverse of LVM's encoding head and $N$ 's task head (green region in Figure 1). Differently from previous work, the decoder here is only used for training the LVM and as a counterexample generator to provide semantically meaningful counterexamples when verification outcomes are negative.", + "bbox": [ + 75, + 520, + 468, + 611 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Specification inputs in latent space. We consider specifications focused on encoding the network's invariance to changes in an object-of-interest in the input. These changes include non-planar transformations, specific semantic changes of the object or its arbitrary task-orthogonal variations commonly occurring in the dataset. The learning tasks and datasets where the objects-of-interest and their variations are discernible against unimportant content in the input are well suited for such specifications.", + "bbox": [ + 75, + 611, + 468, + 747 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We now describe the definitions we consider for the local latent space set $Z_{\\mathrm{des}}$ against which the network is verified.", + "bbox": [ + 76, + 748, + 468, + 777 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "- Segment. We define $Z_{\\mathrm{des}}$ to be a path connecting the encodings of two images $\\{x_1, x_2\\}$ that differ in the intended attributes or transforms (e.g., images of an object with different poses or backgrounds). Multiple definitions for $Z_{\\mathrm{des}}$ are possible based on the traversal between the pair encodings, such as the maximum likelihood-based traversal [24], splines using multiple intermediate encodings, etc. With the Shortest Length Path", + "bbox": [ + 86, + 780, + 470, + 901 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "(SLP), we get", + "bbox": [ + 524, + 90, + 622, + 106 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nZ _ {\\mathrm {d e s}} = e \\left(x _ {1}\\right) + \\alpha \\left(e \\left(x _ {2}\\right) - e \\left(x _ {1}\\right)\\right), \\alpha \\in [ 0, 1 ] ^ {\\text {l a t e n t , d i m}}.\n$$\n", + "text_format": "latex", + "bbox": [ + 529, + 109, + 883, + 128 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "This $Z_{\\mathrm{des}}$ is highly expressive since, in general, the image pair can be of any two images whose semantic interpolations should be consistently predicted by a network.", + "bbox": [ + 524, + 132, + 890, + 176 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "- Axis. We define $Z_{\\mathrm{des}}$ to be the set generated by varying an encoding's disentangled dimensions, such as those trained to capture variations of a specific attribute or a single degree of freedom for pose change. For example, we may consider", + "bbox": [ + 509, + 179, + 890, + 253 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nZ _ {\\mathrm {d e s}} = \\left[ \\max \\{z _ {\\mathrm {l}}, e (x) _ {i} - \\epsilon \\}, \\min \\{e (x) _ {i} + \\epsilon , z _ {\\mathrm {u}} \\} \\right], i \\in I _ {C}\n$$\n", + "text_format": "latex", + "bbox": [ + 524, + 258, + 890, + 277 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $I_{C}$ is the set of conditional dimension indices and $[z_{\\mathrm{l}}, z_{\\mathrm{u}}]$ are the limits containing a significant percentile of the distribution along these dimensions.", + "bbox": [ + 522, + 279, + 890, + 325 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Given conditional training, this $Z_{\\mathrm{des}}$ can capture all variations of an image generated by an attribute or transform change, even when this image has no similar variations present in the dataset.", + "bbox": [ + 522, + 325, + 890, + 385 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "- Region. We define $Z_{\\mathrm{des}}$ as a $\\ell_{\\infty}$ -norm ball around an image encoding, i.e., $\\mathcal{B}_{\\epsilon}(z) = \\{z' \\mid ||z' - e(x)||_{\\infty} < \\epsilon \\}$ . Given a spatially coherent manifold, $Z_{\\mathrm{des}}$ should capture the commonly occurring variations of an image.", + "bbox": [ + 509, + 387, + 890, + 446 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The rest of our method is independent of the choice of $Z_{\\mathrm{des}}$ .", + "bbox": [ + 500, + 446, + 890, + 462 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Note again that since the specifications cannot be guaranteed to be complete by construction, we empirically ascertain $Z_{\\mathrm{des}}$ to be sufficiently capturing the intended variations using metrics presented in Section 5.4. Also note that [34] gives theoretical guarantees that local epsilon balls in a sufficiently trained Conditional VAE's latent space, necessarily generate sufficient instances of local input perturbations. This further validates the use of Axis and Region queries for formal robustness checks and the use of VAEs as the LVM in our pipeline (details in the next section). The specifications can also be systematically inspected by means of sample reconstructions, representative results for which are shown in Figure 2.", + "bbox": [ + 496, + 463, + 890, + 657 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Verification. Having formally defined $Z_{\\mathrm{des}}$ to capture a variation $v$ , the SRVP becomes a standard verification problem for a network composed of the inverted encoding head and the original network's task head. This problem can be solved by any standard NN verifier; we use VeriNet [15, 17], an open-source linear programming-based verification toolkit. The invertibility of the encoding head is necessary to guarantee that the feature vectors that map to $Z_{\\mathrm{des}}$ are contained in the bounds of feature space set obtained during verification. In our queries, the output constraints $Y_{\\mathrm{des}}$ encode invariance of $N$ to $v$ . When the query outcome is negative, the verifier provides a counterexample in $Z_{\\mathrm{des}}$ which is then mapped to a counterexample in input space using the decoder. This ideally gives an instance of $v$ against which the network is incorrect (see Section 5.3 for details).", + "bbox": [ + 496, + 659, + 892, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "3896", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/ff28e75b368ba842a065c55960648e6cf549fb225cbbd83335b29b64c9d17795.jpg", + "image_caption": [ + "(b)", + "Figure 2. Reconstructed by our LVMs for Region specifications in (a), Segment specifications in (b) and Axis specifications in (c). (a) shows variations sampled from $\\epsilon$ -balls around an image encoding; notice how a larger $\\epsilon$ captures more varied changes of the input. The middle columns in (b) show reconstructions of samples from a segment joining the encodings of the dataset images in outer columns. In (c), all images are reconstructions and can be seen undergoing changes as specified conditional dimensions are varied." + ], + "image_footnote": [], + "bbox": [ + 116, + 95, + 387, + 366 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/89c97ade108ecdd1e2fb39c38125b774db3b0775021ab9cde2e50f7e6e128c10.jpg", + "image_caption": [ + "(c)" + ], + "image_footnote": [], + "bbox": [ + 413, + 87, + 854, + 366 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Discussion. We evaluate the approach experimentally in Section 5; below we analyse it against the last two shortcomings of the EDN approach discussed in Section 2.", + "bbox": [ + 76, + 450, + 468, + 496 + ], + "page_idx": 3 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "1. Observe that this approach directly verifies network features corresponding to latent space sets defined by mappings of the original images, rather than the reconstructed images. Thus, the pipeline ensures that the network is tested against at least the original image(s) that form the basis of a specification. Notice from Eq. 2, that this is not the case with the EDN approach if the decoder is not the exact inverse of the encoder. Moreover, since the encoding head is invertible, variations of an image mapping onto the same latent vector directly implies the stability of the network against these variations. Therefore, a many-to-one mapping is not a barrier for our approach, whereas it leads to insufficiently diverse input specifications with the EDN approach.", + "2. The proposed approach employs shorter paths for verification than the EDN approach. Since the encoding head is invertible, a latent space set need not be passed through the decoder and original network to obtain its corresponding feature set, and since most verification methods have an exponential complexity dependence on the number of unstable activations, the exclusion of the high-dimensional decoder and initial network layers from the verification path allows this approach to scale more favourably than the EDN approach." + ], + "bbox": [ + 86, + 500, + 470, + 864 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "A concern over the proposed approach could be that the network to be verified is partly used to define the input spec", + "bbox": [ + 76, + 869, + 468, + 900 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "ification that it is verified for. However, consider the FDN-encoding head pair as an independent encoder, and the encoding head inverse as a compute efficient analogue of the decoder-FDN pair in the EDN pipeline. From this perspective, the proposed approach is identical to the traditional EDN-based approaches for robustness validation. Additionally, the proposed approach benefits from:", + "bbox": [ + 496, + 450, + 890, + 556 + ], + "page_idx": 3 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- Added flexibility to use a deep decoder for manifold learning and sharper counterexample generation without impacting verification outcomes. Verification also ensures maximal recall in finding counterexamples as opposed to a gradient search-based approach.", + "- Relative flexibility in choosing the network layer after which the encoding head is added and thereby, how many of the network's posterior layers feature in the verification path. This decision can depend on the scalability and implementation support of the chosen verification backend or the feasibility of learning a latent space of given dimensionality (see Section 5.2).", + "- Independence with respect to the FDN architecture's depth and type (residual, recurrent, non-standard convolutional, etc.), and possibly to input dimensionality1, leading to an easier extension of the verification approach to newer architectures." + ], + "bbox": [ + 509, + 556, + 890, + 816 + ], + "page_idx": 3 + }, + { + "type": "page_footnote", + "text": "1Independence to input dimensionality is conditional on the nature of the FDN and its last layer being fully-connected (fc); however, since most vision inference tasks, such as classification, regression and detection, involve dimensionality reduction and network's posterior layers are usually fc, the specification input dimensionality can almost always be made lower than that of input data.", + "bbox": [ + 500, + 827, + 893, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "3897", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4. Implementation", + "text_level": 1, + "bbox": [ + 76, + 90, + 235, + 107 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In this section we describe our implementation of the proposed verification pipeline [13].", + "bbox": [ + 76, + 114, + 468, + 145 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Encoding head. In terms of design choices, all common LVMs for data generation, including VAEs, Normalising Flows (NFs) and GANs, can be used in the pipeline if the following holds:", + "bbox": [ + 75, + 145, + 468, + 205 + ], + "page_idx": 4 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- The FDN of the network to be verified can serve as the backbone of the LVM encoder (e.g., if the FDN involves a dimensionality change then NFs cannot serve as the LVM).", + "- The verification backend can verify the inverted encoding head of the pipeline." + ], + "bbox": [ + 71, + 205, + 467, + 280 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Given any LVM, $Z_{\\mathrm{des}}$ is defined in the output space of the LVM encoding head in ways described in Section 3. A VAE fits the pipeline particularly well given the backing of the theoretical analysis in [34], and as it regularises the underlying latent space to resemble a prior. This prior (normal, von Mises-Fisher distribution in $\\mathcal{N}$ -VAE [21], S-VAE [8] resp.) is light-tailed, so the latent space can be approximately bounded or truncated, and the epsilons in our specifications have bounded domain. Note that the latent variable $z$ in a VAE is not the output of the encoder but a random variable conditioned on its outputs $(\\mu, \\sigma \\in \\mathbb{R}^{\\mathrm{latent.dim}})$ by reparameterisation [21]. Since reparameterisation cannot be inverted, $Z_{\\mathrm{des}}$ is defined using the vector $[\\mu, \\sigma]$ instead of $z$ , albeit with no change in $Z_{\\mathrm{des}}$ .", + "bbox": [ + 75, + 281, + 468, + 492 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In contrast, GANs do not use an encoder to learn a latent distribution and instead take a prior distribution as input. However, when using a GAN as the LVM, we still add an encoding head after the FDN to transform the unconstrained FDN output to a desired prior for the GAN and define input-parameterized local specifications.", + "bbox": [ + 75, + 492, + 468, + 582 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "LVM design. As discussed previously, our pipeline features an encoding head after the FDN of the network to be analysed. Since the encoding head must not undergo dimensionality change, the dimension of the flattened FDN output is the dimension of the encoding head layers and the latent space where the input specification is defined. Typically, a shorter FDN implies larger latent space dimensionality and verification involves more network layers.", + "bbox": [ + 75, + 583, + 468, + 703 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We use two types of feed-forward encoding heads: one consists of pairs of an invertible activation and fully-connected (FC) layers; the other consists of alternating affine-coupling layers [9]. The former is easier to train and supported by most NN verifiers, but its invertibility to sufficient precision needs to be validated by checking the singular values of the individual layers' weight matrices. Affine-coupling layer is invertible-by-construction but not supported by standard NN verifiers. To support its verification, we replace its typically input dependent scaling and translation unit with an input independent learnt vector and an FC layer respectively. This modified affine-coupling layer is equivalent to an FC layer in expressiveness, but is", + "bbox": [ + 75, + 704, + 468, + 900 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "more challenging to train.", + "bbox": [ + 500, + 90, + 671, + 106 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "One can increase the encoding head depth with the pairs described above until the LVM is adequately trained; in our experience, a single layered encoding head sufficed for good reconstructions. The decoder is always a deep upscaling network mirroring the pipeline encoder.", + "bbox": [ + 496, + 106, + 890, + 181 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "LVM training. In addition to the negative log likelihood or GAN loss, we conditionally train latent dimensions [5, 23] for Axis specifications. We use Cross-Entropy (CE) loss for discrete attributes. For instance, we train one dimension with binary CE loss so that $[0,1]$ for this dimension corresponds to variations from no attribute to complete attribute. Note that we cannot use the common conditional generation approach of augmenting encodings with attribute labels [31] because the entire encoding must be inferred from the FDN output for invertibility. Therefore, differently from usual practice, our VAEs for conditional generation do not take attributes as priors to condition on but rather learn them with supervision from data.", + "bbox": [ + 496, + 181, + 890, + 377 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Continuum in transformations is important when verifying against pose changes, which CE loss may not provide. Therefore, dimensions capturing continuous changes are trained as graphics code as per the procedure in [23].", + "bbox": [ + 496, + 378, + 890, + 438 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Note that it may not be possible to train an LVM by adding an encoding head to the extreme end of every network, as network's task-agnostic information may be lost till that layer. However, if an LVM can be trained by adding an encoding head after the $K^{th}$ network layer, it is inexpensive to train a new LVM from after the $(K - k)^{th}, k > 0$ , layer, with the frozen original network.", + "bbox": [ + 496, + 439, + 890, + 542 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Datasets preparation. To train the LVMs for our experiments, we used public datasets with customdataloading to have attribute and transform labels for every input. We only used datasets for which realistic variations can be produced with labels, as it is required for conditional training and forming precise queries for pipeline evaluation (see Section 5.4). We worked with five datasets: CelebA [25], Traffic Signs Recognition (TSRD), 3D Objects (3DOD), (Fashion)MNIST [38]. For TSRD, we took traffic signs and city scene crops, apply planar (rotation, scale, photometric) and spatial (perspective) transformations on the former and blend them into the latter during dataloading. For 3DOD, we took 3D models from ModelNet10 dataset [37] and render their images from different distances, azimuth and elevation angles in Blender [6]. For all trainings, the dataset was balanced such that every class had adequate samples of the variation being verified against.", + "bbox": [ + 496, + 544, + 890, + 800 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "5. Experimental Analysis", + "text_level": 1, + "bbox": [ + 500, + 814, + 714, + 832 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We report on our experiments to validate the proposed approach, with focus on answering three key questions:", + "bbox": [ + 500, + 839, + 890, + 869 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Q1. Can an LVM added to a classifier generate an appropriate latent manifold and good reconstructions?", + "bbox": [ + 500, + 869, + 890, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "3898", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 4 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "Q2. Can the proposed pipeline efficiently verify deep networks?", + "Q3. Can the specifications, discussed in Section 3, encode intended input variations?" + ], + "bbox": [ + 76, + 90, + 467, + 151 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "To assess Q1, we refer to the reconstructions presented in Figure 2 and the low values of mean reconstruction error and FID score [18] reported in Table 1. To assess Q2, we refer to the verification outcomes for deep networks of different architectures reported in Sections 5.1, 5.2. To assess Q3, we refer to the values of metrics quantifying the precision of a specification in capturing intended variations, discussed in Section 5.4. With this overview, we now discuss the experiments in greater detail.", + "bbox": [ + 75, + 152, + 467, + 287 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5.1. Verifying segments joining input encodings", + "text_level": 1, + "bbox": [ + 76, + 297, + 442, + 313 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "To verify robustness against variations reflected in an image pair, we generated Segment specifications capturing object pose and viewpoint changes. For CelebA, we also verify specifications capturing the classifier's invariance to task-orthogonal attributes. These queries are similar to the queries in [27] which uses the EDN approach and reports successful deterministic verification of $23.8\\%$ queries for a ConvMed model with 64k activations. Based on the classifier layer separating the FDN and task head, multiple verification pipelines were trained for each classifier. The verification outcomes for all queries and pipelines are reported in Table 1, from which the following observations can be drawn:", + "bbox": [ + 75, + 320, + 467, + 515 + ], + "page_idx": 5 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- The mean reconstruction errors and FID scores for the multiple SRVP pipelines per classifier are low with consistent verification outcomes, indicating that latent spaces of a considerable range of dimensionality can be successfully learnt and verified against.", + "- The SRVP pipelines require an order of magnitude less time than the EDN pipelines to solve safe queries, and produce fewer trivial output bounds or undecided cases. This remains the case with the inclusion of more network layers in the verification path.", + "- The verified robust accuracy tightly lower bounds the adversarial accuracy computed against gradient-ascent-based latent space interpolation attacks [28]." + ], + "bbox": [ + 86, + 517, + 467, + 715 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5.2. Verifying along latent dimensions", + "text_level": 1, + "bbox": [ + 76, + 726, + 369, + 742 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "As discussed in Section 3, Axis specifications can be used to verify an input against the entire range of a task-orthogonal change (e.g., style, or pose). Figure 3 shows representative results for verifying these specifications where the local input set is increased for individual latent dimensions of an encoding. For many inputs, conditional dimensions were verifiably robust for almost their entire range, while dimensions without conditional training were found to be robust for much smaller epsilons. Decoded samples from latent dimensions in Figure 4 corroborate these", + "bbox": [ + 75, + 750, + 467, + 900 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "outcomes. The object class change was not observed for all non-conditional dimensions, but conditional dimensions were more consistent in preserving the object class. However, with increase in latent dimensionality, as with a shorter FDN, it became harder to balance the conditional and standard LVM training to achieve both good reconstructions and distinct attribute changes with class consistency. This explains the reduced transform detections for higher dimensional manifolds reported in Figure 3. In Section 5.4, we present a validity metric to assess the success of conditional manifold training and in turn, derive expectation on the usefulness of Axis specifications defined in the manifold.", + "bbox": [ + 496, + 90, + 890, + 272 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/1433487e700bfc05e973a71bb44f777d23bd0fad9ac7f8cda1b62ccc808a4c21.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 539, + 277, + 851, + 417 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/0ae5792338b1e49efed07ce0003867e1f56cc2d805d2014bc0649c4588cc6dad.jpg", + "image_caption": [ + "Figure 3. Both graphs show mean percentage of Axis queries verified as safe (out of 200 tested) for local intervals of $\\pm \\epsilon$ for LVMs of different latent dimensionality. The percentage of reconstructions of samples along the conditional axes, around the $\\epsilon$ s reported on the x-axis, in which a learnt transform detector detects the intended transform, is also plotted. The axes were trained with (B)CE loss with 0,1 mapping to the base and the attribute added image resp." + ], + "image_footnote": [], + "bbox": [ + 539, + 421, + 851, + 561 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/c81b55cfa9669c84d663e796bdf8ab6f3efe7cdd3a29cfbab0b65ea642205da1.jpg", + "image_caption": [ + "Figure 4. All images above are generated by an LVM from a single image per dataset. The columns feature samples along non-conditional dimensions, and each row has a constant conditional axis value which enforces rendering of the specified transform in all its reconstructions." + ], + "image_footnote": [], + "bbox": [ + 513, + 676, + 851, + 803 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "In case of Region specifications, where the local ep", + "bbox": [ + 517, + 885, + 890, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "3899", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/801356e8ae7c67e5432a8ce82ec52540a00a9f59a028c1d81b1f7f079f4ae96c.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
Dataset (size)Verifying inv. to *NetworkAccuracies*Pipeline**Verification outcomes (100 std.safe queries)Recons.outcomes
Std.Adv.Type #Ver.actv.layers (actvs.)Safe(s†)Unsafe(s)Undec.(s)Rob.accRMSSrr*FIDscore
Runs for efficiency comparison of EDNs (with decoders of different depths) vs. SRVPs (with encoding heads after different n/w layers).
CelebA64.2%EDtinyN-328 (5k)61 (6.8)39 (3.94)056%0.064218.61
65%EDdeepN-329 (27k)64 (22.3)29 (31.6)7 (64)59%0.053107.42
(64x64)ConvSmall (6k ReLUs)92%69%EDresnet18N-3211 (0.2M)042 (370)58 (802)0%0.05189.62
91%SRVP Lin1-321 (64)99 (0.4)1 (0.01)091%0.058114
89%SRVP Lin1-642 (192)94 (0.5)6 (0.02)085.5%0.042112
Head Flip (gender cla.)87%SRVP Lin1-1923 (576)88 (1.1)12 (0.08)081%0.035105
89%SRVP Lin1-3924 (1.3k)91 (2.7)9 (0.11)084%0.031102
74%EDtinyN-328 (86k)59 (32.8)41 (20)056.6%0.07264
81%EDdeepN-329 (0.1M)66 (35.3)22 (23.5)12 (64)63%0.06223
(128x128)ConvBig (72k ReLUs)96%77%EDresnet18N-3211 (475k)021 (410)79 (816)0%0.06124
93%SRVP Lin1-641 (64)95 (0.4)5 (0.07)091%0.23252
95%SRVP Lin1-1922 (256)96 (0.8)4 (0.09)092%0.15225
94%SRVP Lin1-3923 (648)96 (1.9)4 (0.11)092%0.04202
", + "bbox": [ + 89, + 89, + 879, + 306 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/657f6bce7de264fa1f19f4ea886ab71044a1e7a2ab85d659549d366bd430b51d.jpg", + "table_caption": [], + "table_footnote": [ + "* Std. and Adv. accuracy are the network's accuracy against clean, augmented data and latent-space PGD attacks [28] ( $\\alpha = 2\\mathrm{e} - 3$ , #iters=2000) resp. The PGD attacks are found for $N \\circ d(z)$ in EDN pipelines and $e^{-1} \\circ N_{\\mathrm{head}}(z)$ in SRVP pipelines for $z \\in Z_{\\mathrm{segment}}$ .", + "** The suffixed integer in the pipeline type is the dimensionality of its latent space and is equal to its verification input. Higher dimensions for a SRVP pipeline for the same network indicate an earlier split and the inclusion of more layers in the verification path.", + "$\\dagger$ Seconds (s) reported are the mean query solving time. All queries were run on a 24 core, 256GB CPU with timeout of 60 or 800 seconds.", + "$\\star$ The reconstruction error is per-pixel for normalised float [-1,1] images. The FID score is computed by using pytorch-fid package [30].", + "All pipelines for the same network were trained until comparable reconstruction outcomes, were tested for the same queries using the same backend and use $\\mathcal{N}$ -VAE as the LVM so that all of them have an approximately normal latent manifold distribution." + ], + "table_body": "
SRVP runs with encoding heads of different dimensions for different n/w architectures and datasets
(64x64)ResNet1884%82%SRVP Lin1-2561 (512)95 (2.6)5 (0.1)080%0.022104
TRDS (64x64)Planar Pose (sign cla.)ResNet1892.5%SRVP Lin1-2562 (1k)96 (2.1)4 (0.21)089%0.03116
89%SRVP Lin1-10242 (1.5k)94 (3.8)6 (0.46)087%0.03106
MobileNetv282%78%SRVP Lin1-6401 (640)93 (2.1)7 (0.42)076%0.09133
3DOD (64x64)Spatial Pose (obj cla.)ResNet1897%SRVP Lin1-2562 (1k)94 (1.9)6 (0.2)091%0.04106
90%SRVP Lin1-10242 (1.5k)92 (4.7)8 (0.45)089%0.0298
", + "bbox": [ + 89, + 306, + 879, + 405 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 1. Verification results for Segment queries; representative specification inputs for the above are shown in Figure 2b.", + "bbox": [ + 125, + 516, + 841, + 531 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "silon ball is increased uniformly in all latent dimensions, we could verify robustness for a maximum $\\epsilon = 0.01$ (for $< 10\\%$ queries) for SRVP Lin-32 pipelines.", + "bbox": [ + 76, + 556, + 468, + 603 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.3. Counterexamples analysis", + "text_level": 1, + "bbox": [ + 76, + 616, + 313, + 633 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Counterexamples are instances of the input specification set that falsify the robustness property under investigation. In our approach, the verifier finds a latent space counterexample $z^{*} \\in Z_{\\mathrm{des}}$ for every unsafe query such that $N_{\\mathrm{head}} \\circ e^{-1}(z^{*})$ demonstrates non-robustness. However, since the LVM decoder is not the exact inverse of its encoder, the decoded counterexample could be spurious, i.e., $N \\circ d(z^{*})$ may not be a counterexample. Therefore, we decode every $z^{*}$ and label it a valid counterexample iff its reconstruction is also a counterexample for the network.", + "bbox": [ + 75, + 642, + 468, + 792 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Similar to [16], in the case of a spurious counterexample $z^{*}$ , we run a local gradient search for a valid one, taking $z^{*}$ as the starting point. In comparison to starting from a mapped vector, this local gradient-based search around $z^{*}$ takes much fewer iterations to reach a valid counterexample in most cases, and results in high precision in finding valid and in-domain counterexamples (see Figure 5).", + "bbox": [ + 75, + 795, + 470, + 902 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/6284998916bc17bf7e2e4aece6bc3d55c3093e03de0af06718daa4cf8c003e4b.jpg", + "image_caption": [ + "Figure 5. The table reports the mean ratios of valid counterexamples (ceg.) to all cegs found by SRVP pipelines for network $N_{\\mathrm{head}} \\circ e^{-1}$ through verification of 100 Segment queries, with and without PGD-based search in the second and third column resp. The full search and refinement iterations are median PGD iterations of step-size 1e-3 for success in the latent/attribute space attack [28] and in the local search for a valid ceg around a verification-returned spurious ceg resp. Rows in the figure below show reconstructions for some unsafe Segment and Axis queries with their valid cegs in the rightmost column." + ], + "image_footnote": [], + "bbox": [ + 501, + 554, + 874, + 767 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Male (Female)", + "bbox": [ + 810, + 638, + 885, + 652 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Chair (Table)", + "bbox": [ + 810, + 666, + 877, + 676 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "No right", + "bbox": [ + 810, + 686, + 856, + 698 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "(No U-turn)", + "bbox": [ + 810, + 699, + 870, + 709 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Old (Young)", + "bbox": [ + 810, + 718, + 874, + 728 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Change: Glasses", + "bbox": [ + 810, + 729, + 888, + 738 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Male (Female)", + "bbox": [ + 810, + 744, + 885, + 753 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Change:Gender", + "bbox": [ + 810, + 753, + 887, + 762 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "3900", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.4. Validating the LVM based pipeline", + "text_level": 1, + "bbox": [ + 76, + 90, + 379, + 107 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Having assessed the capabilities of our approach in terms of scaling to deep networks and the fidelity of returned counterexamples, we now evaluate its precision in sufficiently capturing the intended variations in the proposed specifications. For this, we consider two latent space-based validity metrics as described below.", + "bbox": [ + 75, + 114, + 467, + 204 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "The assumption behind Segment specifications is that the in-domain interpolations of an image pair map to the interpolations of its encoding pair. To validate this, we measure the distance of the encodings of the desired interpolations of an image pair to the path joining its encoding pair. In practice, for validating pose invariance queries, we generate images with varying extents of a transform, construct a path between the encodings of the image pair with the most extreme mutual transform, and compute the distance between the encodings of the intermediate transforms and their projection on this path. This distance is divided by square-root of latent dimensionality to generalise across manifolds of different dimensions. We compute this metric for the following pairs of encoding paths and VAE manifolds used in our pipelines, and report its mean value distribution below.", + "bbox": [ + 75, + 205, + 467, + 431 + ], + "page_idx": 7 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "1. Shortest Length Path (SLP) + untrained normal distribution manifold (baseline),", + "2. $\\mathrm{SLP} + \\mathcal{N}$ -VAE,", + "3. $\\mathrm{SLP} + \\mathcal{N}$ -VAE trained with a latent space-based cycle consistency loss that encourages its encoder-decoder to be an inverse pair,", + "4. Real-vs-fake discriminator-guided path $+\\mathcal{N}$ -VAE." + ], + "bbox": [ + 81, + 431, + 467, + 545 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/86dad0c44704e25fe40867b839d28ab5da2b911fe27bb7b29d90f6eac1e89d9f.jpg", + "image_caption": [ + "Normalised histogram of distances of intermediate transform encodings to $Z_{\\mathrm{des}}$ , i.e., $\\mathbf{d}(e(x_i), \\text{proj}_{Z_{\\mathrm{des}}} e(x_i)) / \\sqrt{m}$ , $e(.) \\in \\mathbb{R}^m$ ." + ], + "image_footnote": [], + "bbox": [ + 55, + 547, + 459, + 680 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In comparison to the primitive baseline, the metric values with $\\mathcal{N}$ -VAEs are low for most queries as desired, and further reduce on incentivising consistency in their mappings, as in 3., and making the encoding traversals more precise and segmented, as in 4. Although we do not observe notable changes in the verification outcomes with different $\\mathcal{N}$ -VAEs, this metric could be used to guide the construction of input specifications. Notice that this metric is the latent space-based analogue of the pixel space distance used to define input specifications and evaluate generators for EDN-based verification [20].", + "bbox": [ + 75, + 718, + 467, + 883 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "The motivation behind Axis specifications is the disen", + "bbox": [ + 96, + 885, + 467, + 900 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "tanglement of conditional dimensions in capturing specified variations. To assess disentanglement, we compute the ratio of the highest value among the incorrect conditional dimensions to the value of the correct conditional dimension of an encoding for a discrete attribute. For the continuous transforms encoded as graphics code [23], an equivalent metric is the ratio of the maximum variance among the incorrect conditional dimensions to the variance in the correct conditional dimension, computed for a batch of encodings. Below we report the mean value distribution of this metric for normally and conditionally trained $\\mathcal{N}$ -VAEs. As expected, conditional training results in low metric values as desired, while normal training results in similar values for most dimensions and metric values closer to unity.", + "bbox": [ + 496, + 90, + 890, + 301 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/03ff1b40bb2f46c75760f5af0c59b401f4cba20579025afe10c0d1a1075e8be8.jpg", + "image_caption": [ + "Normalised histogram of maximum incorrect-to-correct dimension ratios for conditionally trained LVMs." + ], + "image_footnote": [ + "Numbers in the legend entries denote manifold dimensionality." + ], + "bbox": [ + 485, + 306, + 880, + 436 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "These latent space-based metrics are more relevant to our approach than the pixel space-based or the attribute detection-based analyses relevant to the EDN approach. This is because the effectiveness of verification with our approach depends more on the spatial coherence and precision of the LVM encodings, than its reconstruction capabilities.", + "bbox": [ + 496, + 483, + 890, + 574 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "6. Conclusions", + "text_level": 1, + "bbox": [ + 500, + 588, + 625, + 603 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this work we introduced an efficient and precise approach for verifying specifications in the latent space. By means of the proposed approach, we could effectively assess and verify deep networks against pose changes, and provide counterexamples that inform of their fragilities.", + "bbox": [ + 496, + 613, + 890, + 688 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In terms of limitations, we discussed that the ease of learning a conditional latent manifold, and the computational gains of our verification approach can be affected by the increase of layers in the network head of our pipeline. However, since the largest activation layers can be excluded from the verification path with our approach, it still fares better than the existing approach. A general limitation of latent-space based verification approaches is their necessity for an adequate LVM, which, as discussed for our approach, may require the original network to be trained as part of the proposed pipeline. While we did not find these limitations to hinder the application of our approach to the practical usecases demonstrated in this work, further experiments should be conducted to better assess its generality.", + "bbox": [ + 496, + 689, + 890, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "3901", + "bbox": [ + 482, + 944, + 513, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] M. Akintunde, A. Lomuscio, L. Maganti, and E. Pirovano. Reachability analysis for neural agent-environment systems. In Proceedings of the 16th International Conference on Principles of Knowledge Representation and Reasoning (KR18), pages 184–193. AAAI Press, 2018. 1", + "[2] M. Balunovic, M. Baader, G. Singh, T. Gehr, and M. Vechev. Certifying geometric robustness of neural networks. 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Proceedings of the AAAI Conference on Artificial Intelligence (AAAI19), 33(01):5757-5764, Jul. 2019. 2" + ], + "bbox": [ + 78, + 92, + 468, + 825 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "3903", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/Efficient Verification of Neural Networks Against LVM-Based Specifications/f017e278-be6a-4fc6-a7c8-64ae1c47c99f_model.json b/2023/Efficient Verification of Neural Networks Against LVM-Based Specifications/f017e278-be6a-4fc6-a7c8-64ae1c47c99f_model.json new file mode 100644 index 0000000000000000000000000000000000000000..8dee7f014fb3e37d9deb79bc08cdc1cfd46b7624 --- /dev/null +++ b/2023/Efficient Verification of Neural Networks Against LVM-Based Specifications/f017e278-be6a-4fc6-a7c8-64ae1c47c99f_model.json @@ -0,0 +1,2365 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.107, + 0.13, + 0.865, + 0.154 + ], + "angle": 0, + "content": "Efficient Verification of Neural Networks against LVM-based Specifications" + }, + { + "type": "text", + "bbox": [ + 0.159, + 0.182, + 0.518, + 0.234 + ], + "angle": 0, + "content": "Harleen Hanspal \nImperial College London & Safe Intelligence \nLondon, United Kingdom" + }, + { + "type": "text", + "bbox": [ + 0.222, + 0.238, + 0.456, + 0.251 + ], + "angle": 0, + "content": "h.hanspal21@imperial.ac.uk" + }, + { + "type": "text", + "bbox": [ + 0.59, + 0.182, + 0.792, + 0.234 + ], + "angle": 0, + "content": "Alessio Lomuscio \nSafe Intelligence \nLondon, United Kingdom" + }, + { + "type": "text", + "bbox": [ + 0.565, + 0.238, + 0.804, + 0.251 + ], + "angle": 0, + "content": "alessio@safeintelligence.ai" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.287, + 0.314, + 0.303 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.318, + 0.474, + 0.635 + ], + "angle": 0, + "content": "The deployment of perception systems based on neural networks in safety critical applications requires assurance on their robustness. Deterministic guarantees on network robustness require formal verification. Standard approaches for verifying robustness analyse invariance to analytically defined transformations, but not the diverse and ubiquitous changes involving object pose, scene viewpoint, occlusions, etc. To this end, we present an efficient approach for verifying specifications definable using Latent Variable Models that capture such diverse changes. The approach involves adding an invertible encoding head to the network to be verified, enabling the verification of latent space sets with minimal reconstruction overhead. We report verification experiments for three classes of proposed latent space specifications, each capturing different types of realistic input variations. Differently from previous work in this area, the proposed approach is relatively independent of input dimensionality and scales to a broad class of deep networks and real-world datasets by mitigating the inefficiency and decoder expressivity dependence in the present state-of-the-art." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.664, + 0.21, + 0.68 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.689, + 0.47, + 0.856 + ], + "angle": 0, + "content": "The deployment of perception systems based on neural networks in safety-critical applications requires assurance on their performance, notably accuracy and robustness. Formal verification contributes to this requirement by providing provable and deterministic guarantees that a network meets a given specification. Typically, specifications are mathematically expressed constraints on the network's intended input/output and may encode desirable properties, such as robustness to noise (including adversarial attacks) [35], geometric changes [1,2], bias-field changes [14] and beyond." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.47, + 0.901 + ], + "angle": 0, + "content": "While the above is useful, practical applications require robustness against diverse changes in a scene, including changes in the pose of objects, viewpoints, occlusions, etc." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.288, + 0.895, + 0.455 + ], + "angle": 0, + "content": "Such changes cannot be efficiently mathematically defined, but may be encoded from data by using generative models. For instance, [11, 12, 28, 34] use generative models to generate novel in-domain images for data augmentation, adversarial training or evaluating network generalisation; [34] additionally derives formal conditions for a latent space set to necessarily contain sufficient perturbations for it to be trusted for adversarial training and robustness checks. All these approaches either provide statistical robustness measures, or generate attacks based on gradient-search, which is not guaranteed to find an attack if one exists." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.456, + 0.895, + 0.698 + ], + "angle": 0, + "content": "Popular for network robustification and empirical evaluation, latent space sets are seldom used as inputs for verification due to the valid concern over the lack of mathematical guarantees on the completeness of the specifications they encode. Therefore, we reiterate that this work is most useful for changes that are difficult to mathematically define. We additionally argue that formal verification of latent space-based specifications can be more valuable than their empirical evaluation. This is because the latent space is a continuous domain and countably infinite number of inputs can be mapped to and reconstructed from a latent space set. Therefore, no amount of testing, or search in the latent space can provide guarantees against all the variations encoded in it. To the best of our knowledge, only [20, 27] encode specifications in a latent space and propose architectures to verify them." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.7, + 0.895, + 0.807 + ], + "angle": 0, + "content": "There are, however, two difficulties with verification in the latent space. The first concerns the scalability of verification methods; the second relates to the quality of reconstructions affecting the verification outcomes. In this paper, we focus on alleviating these two concerns. Specifically, we propose a novel, invertible encoder-based pipeline for verifying latent space sets, that lends two key benefits of:" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.809, + 0.891, + 0.838 + ], + "angle": 0, + "content": "- Computational efficiency and relative independence to input dimensionality," + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.839, + 0.89, + 0.869 + ], + "angle": 0, + "content": "- Verification outcomes' independence to reconstructions, and precise counterexamples with high recall." + }, + { + "type": "list", + "bbox": [ + 0.5, + 0.809, + 0.891, + 0.869 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.871, + 0.892, + 0.901 + ], + "angle": 0, + "content": "We focus our analysis on pose and attribute variations in vision inference tasks, but the approach is likely extendable" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "3894" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.152 + ], + "angle": 0, + "content": "to other variations, domains and tasks. Next, we recall key notions for network verification and discuss the existing relevant work, before presenting and validating our method in subsequent sections." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.166, + 0.364, + 0.183 + ], + "angle": 0, + "content": "2. Background and Related Work" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.192, + 0.47, + 0.25 + ], + "angle": 0, + "content": "Neural network verification. Given a network \\(N\\) and an input-output specification \\((X_{\\mathrm{des}},Y_{\\mathrm{des}})\\), the network verification problem is the decision problem of determining whether" + }, + { + "type": "equation", + "bbox": [ + 0.19, + 0.254, + 0.357, + 0.269 + ], + "angle": 0, + "content": "\\[\nN (x) \\in Y _ {\\mathrm {d e s}}, \\forall x \\in X _ {\\mathrm {d e s}}.\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.274, + 0.469, + 0.364 + ], + "angle": 0, + "content": "Verification methods, such as those based on SMT [19], MILP [4, 10, 22], Interval Propagation [15, 16, 32, 33], SDP [3, 29] or Lipschitz analysis [39], propagate a set \\( X_{\\mathrm{des}} \\) in a single forward pass through \\( N \\) and determine whether or not the output set of \\( N \\) for \\( X_{\\mathrm{des}} \\) lies in \\( Y_{\\mathrm{des}} \\). These methods mostly support input specifications defined in:" + }, + { + "type": "text", + "bbox": [ + 0.08, + 0.365, + 0.469, + 0.456 + ], + "angle": 0, + "content": "- Data space, such that \\( X_{\\mathrm{des}} \\) is a norm ball around an input \\( x \\), i.e., \\( \\mathcal{B}_{\\epsilon}(x) = \\{x' \\mid \\| x' - x \\| < \\epsilon\\} \\). The norm is defined in metric spaces such as \\( \\ell_p \\) [2,16,19] or Wasserstein [36], and the \\( \\epsilon \\) is adequately set to include intended photometric and geometric variations, albeit along with considerable unrealistic instances in case of large variations." + }, + { + "type": "text", + "bbox": [ + 0.08, + 0.457, + 0.469, + 0.563 + ], + "angle": 0, + "content": "- Parameter space, such that, given an input \\( x \\) and a set of transformations \\( T \\), \\( X_{\\mathrm{des}} \\) is defined by prepending parametric transform layers \\( N_T(\\alpha) \\), where \\( \\alpha \\) determines the transformation extent, to the network; \\( X_{\\mathrm{des}} = N_T(\\alpha)(x) \\). This definition is more precise in capturing planar geometric changes [26] and photometric changes, such as smooth illumination variations [14], in an input." + }, + { + "type": "list", + "bbox": [ + 0.08, + 0.365, + 0.469, + 0.563 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.564, + 0.469, + 0.593 + ], + "angle": 0, + "content": "While these specifications are important, they do not efficiently capture non-planar and semantic transformations." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.594, + 0.469, + 0.729 + ], + "angle": 0, + "content": "LVM-based specifications. Latent Variable Models (LVMs) for data generation map a typically lower-dimensional, continuous latent distribution to the input space. This mapping and its converse is learnt by LVM's decoder-encoder pair. Additionally, conditional training can disentangle latent dimensions to precisely capture specific dataset features and variations [5, 7, 23]. We refer to specifications which use LVM encoders to map input variations and define query input sets as LVM-based specifications." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.73, + 0.469, + 0.835 + ], + "angle": 0, + "content": "Related work. As mentioned in Section 1, most formal verification approaches do not use generative models. Only [20, 27] use an autoencoder in a verification setup to prove whether or not the output of a network \\(N\\) is consistent for the image set produced by an independent autoencoder \\((e,d)\\) from the interpolations in its latent space. Formally, [27] establishes whether" + }, + { + "type": "equation", + "bbox": [ + 0.11, + 0.845, + 0.435, + 0.862 + ], + "angle": 0, + "content": "\\[\n(N \\circ d) \\circ e (x) \\in Y _ {\\mathrm {d e s}}, \\forall x \\in \\{X \\mid e (X) \\in Z _ {\\mathrm {d e s}} \\},\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.87, + 0.469, + 0.901 + ], + "angle": 0, + "content": "where \\(Z_{\\mathrm{des}} \\in \\mathbb{R}^{\\mathrm{latent\\_dim}}\\) is a segment joining latent encodings of samples in \\(X_{\\mathrm{des}}\\). Since propagating \\(Z_{\\mathrm{des}}\\) through" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.198 + ], + "angle": 0, + "content": "a useful decoder is computationally expensive, deterministic verification using this approach is reported to not scale beyond small networks. To overcome this, the authors a) heuristically subsume and approximate line segments by axes-aligned boxes, and b) turn specifications into probabilistic statements that determine whether a vector sampled uniformly from \\( Z_{\\mathrm{des}} \\) generates a correctly classified image." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.199, + 0.892, + 0.273 + ], + "angle": 0, + "content": "The general approach of prepending a generative model as an independent input set generator for verifying a network, which we henceforth refer to as the Encoder-Decoder-Network (EDN) approach, suffers from the following limitations:" + }, + { + "type": "text", + "bbox": [ + 0.505, + 0.275, + 0.892, + 0.336 + ], + "angle": 0, + "content": "1. The network is verified only against images appropriately mapped by the encoder, but the encoding could be loose \\((z \\in Z_{\\mathrm{des}} \\Rightarrow e^{-1}(z) \\in X_{\\mathrm{des}})\\) and incomplete \\((x \\in X_{\\mathrm{des}} \\Rightarrow e(x) \\in Z_{\\mathrm{des}})\\)." + }, + { + "type": "text", + "bbox": [ + 0.505, + 0.337, + 0.892, + 0.456 + ], + "angle": 0, + "content": "2. The network is verified against reconstructions of the decoder which may not have the same quality as the dataset images in terms of sharpness and diversity. If the decoder does not reconstruct an intended attribute's variations, either because all variations of that attribute are encoded to the same latent vector, or because it is not expressive enough, verification may incorrectly suggest that the network is invariant to that attribute." + }, + { + "type": "text", + "bbox": [ + 0.504, + 0.459, + 0.892, + 0.504 + ], + "angle": 0, + "content": "3. The input set \\( Z_{\\mathrm{des}} \\) is propagated through both the decoder and the network to be verified, thereby resulting in considerable computational cost." + }, + { + "type": "list", + "bbox": [ + 0.504, + 0.275, + 0.892, + 0.504 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.505, + 0.892, + 0.61 + ], + "angle": 0, + "content": "In the rest of the paper, we propose a pipeline for verifying LVM-based specifications in a computationally lighter manner, and alleviate the last two shortcomings by construction. We do not solve the first limitation; but in Section 5.4, we present metrics to quantify the precision of the proposed specifications in terms of how well they capture the desired variations." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.628, + 0.833, + 0.645 + ], + "angle": 0, + "content": "3. Efficient Verification in Latent Space" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.655, + 0.892, + 0.76 + ], + "angle": 0, + "content": "In this section we present an efficient approach to verify the robustness of neural networks against specifications capturing diverse and realistic input variations. Formally, given a network \\(N\\) and a variation \\(v\\), we define the Semantic Verification Problem (SVP) as the network verification problem where \\(X_{\\mathrm{des}}\\) is the preimage of a set \\(Z_{\\mathrm{des}}\\) under a partially invertible encoder \\(e\\):" + }, + { + "type": "equation", + "bbox": [ + 0.562, + 0.769, + 0.828, + 0.785 + ], + "angle": 0, + "content": "\\[\nN (x) \\in Y _ {\\mathrm {d e s}}, \\forall x \\in \\{X \\mid e (X) = Z _ {\\mathrm {d e s}} \\}.\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.795, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Here, \\( Z_{\\mathrm{des}} \\) is a set in the encoder's output space that captures \\( v \\) and the input-output specification set is \\( (Z_{\\mathrm{des}}, Y_{\\mathrm{des}}) \\). In the following, we study the Semantic Robustness Verification Problem (SRVP), which is an instance of SVP that checks for network robustness, i.e., \\( Y_{\\mathrm{des}} \\) is a singleton. To solve SRVP, we propose the multi-head architecture shown in Figure 1." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "3895" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.081, + 0.088, + 0.487, + 0.256 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.266, + 0.471, + 0.336 + ], + "angle": 0, + "content": "Figure 1. The proposed pipeline consists of an LVM, built around the network to be verified, that takes the network's intermediate features as its input. The LVM encoder is invertible and maps its input feature set to a spatially coherent latent manifold, where the input specification is defined." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.353, + 0.47, + 0.519 + ], + "angle": 0, + "content": "Verification pipeline. The network \\( N \\) to be verified is divided into a Feature Detection Network (FDN), consisting of \\( N \\)'s initial layers, and a task head, e.g., a classification or regression head. In our implementation, \\( N \\) is a classifier, but the approach applies similarly for other learning tasks. To define the specification, we add an LVM after the FDN. The encoder of this LVM is invertible and maps the intermediate features, output by FDN, to its latent space where the input specification is defined. Unlike the feature space, this latent space is queryable by using the decoder and can be made approximately bounded." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.521, + 0.47, + 0.612 + ], + "angle": 0, + "content": "The verification path with this pipeline is limited to the inverse of LVM's encoding head and \\( N \\)'s task head (green region in Figure 1). Differently from previous work, the decoder here is only used for training the LVM and as a counterexample generator to provide semantically meaningful counterexamples when verification outcomes are negative." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.612, + 0.47, + 0.748 + ], + "angle": 0, + "content": "Specification inputs in latent space. We consider specifications focused on encoding the network's invariance to changes in an object-of-interest in the input. These changes include non-planar transformations, specific semantic changes of the object or its arbitrary task-orthogonal variations commonly occurring in the dataset. The learning tasks and datasets where the objects-of-interest and their variations are discernible against unimportant content in the input are well suited for such specifications." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.749, + 0.47, + 0.779 + ], + "angle": 0, + "content": "We now describe the definitions we consider for the local latent space set \\( Z_{\\mathrm{des}} \\) against which the network is verified." + }, + { + "type": "text", + "bbox": [ + 0.087, + 0.781, + 0.471, + 0.902 + ], + "angle": 0, + "content": "- Segment. We define \\( Z_{\\mathrm{des}} \\) to be a path connecting the encodings of two images \\( \\{x_1, x_2\\} \\) that differ in the intended attributes or transforms (e.g., images of an object with different poses or backgrounds). Multiple definitions for \\( Z_{\\mathrm{des}} \\) are possible based on the traversal between the pair encodings, such as the maximum likelihood-based traversal [24], splines using multiple intermediate encodings, etc. With the Shortest Length Path" + }, + { + "type": "text", + "bbox": [ + 0.525, + 0.092, + 0.623, + 0.107 + ], + "angle": 0, + "content": "(SLP), we get" + }, + { + "type": "equation", + "bbox": [ + 0.531, + 0.11, + 0.885, + 0.129 + ], + "angle": 0, + "content": "\\[\nZ _ {\\mathrm {d e s}} = e \\left(x _ {1}\\right) + \\alpha \\left(e \\left(x _ {2}\\right) - e \\left(x _ {1}\\right)\\right), \\alpha \\in [ 0, 1 ] ^ {\\text {l a t e n t , d i m}}.\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.525, + 0.133, + 0.892, + 0.178 + ], + "angle": 0, + "content": "This \\( Z_{\\mathrm{des}} \\) is highly expressive since, in general, the image pair can be of any two images whose semantic interpolations should be consistently predicted by a network." + }, + { + "type": "text", + "bbox": [ + 0.511, + 0.18, + 0.892, + 0.255 + ], + "angle": 0, + "content": "- Axis. We define \\( Z_{\\mathrm{des}} \\) to be the set generated by varying an encoding's disentangled dimensions, such as those trained to capture variations of a specific attribute or a single degree of freedom for pose change. For example, we may consider" + }, + { + "type": "equation", + "bbox": [ + 0.525, + 0.259, + 0.892, + 0.278 + ], + "angle": 0, + "content": "\\[\nZ _ {\\mathrm {d e s}} = \\left[ \\max \\{z _ {\\mathrm {l}}, e (x) _ {i} - \\epsilon \\}, \\min \\{e (x) _ {i} + \\epsilon , z _ {\\mathrm {u}} \\} \\right], i \\in I _ {C}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.523, + 0.28, + 0.892, + 0.326 + ], + "angle": 0, + "content": "where \\( I_{C} \\) is the set of conditional dimension indices and \\( [z_{\\mathrm{l}}, z_{\\mathrm{u}}] \\) are the limits containing a significant percentile of the distribution along these dimensions." + }, + { + "type": "text", + "bbox": [ + 0.523, + 0.326, + 0.892, + 0.386 + ], + "angle": 0, + "content": "Given conditional training, this \\( Z_{\\mathrm{des}} \\) can capture all variations of an image generated by an attribute or transform change, even when this image has no similar variations present in the dataset." + }, + { + "type": "text", + "bbox": [ + 0.51, + 0.388, + 0.892, + 0.448 + ], + "angle": 0, + "content": "- Region. We define \\( Z_{\\mathrm{des}} \\) as a \\( \\ell_{\\infty} \\)-norm ball around an image encoding, i.e., \\( \\mathcal{B}_{\\epsilon}(z) = \\{z' \\mid ||z' - e(x)||_{\\infty} < \\epsilon \\} \\). Given a spatially coherent manifold, \\( Z_{\\mathrm{des}} \\) should capture the commonly occurring variations of an image." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.448, + 0.892, + 0.463 + ], + "angle": 0, + "content": "The rest of our method is independent of the choice of \\( Z_{\\mathrm{des}} \\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.464, + 0.892, + 0.659 + ], + "angle": 0, + "content": "Note again that since the specifications cannot be guaranteed to be complete by construction, we empirically ascertain \\( Z_{\\mathrm{des}} \\) to be sufficiently capturing the intended variations using metrics presented in Section 5.4. Also note that [34] gives theoretical guarantees that local epsilon balls in a sufficiently trained Conditional VAE's latent space, necessarily generate sufficient instances of local input perturbations. This further validates the use of Axis and Region queries for formal robustness checks and the use of VAEs as the LVM in our pipeline (details in the next section). The specifications can also be systematically inspected by means of sample reconstructions, representative results for which are shown in Figure 2." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.66, + 0.893, + 0.901 + ], + "angle": 0, + "content": "Verification. Having formally defined \\( Z_{\\mathrm{des}} \\) to capture a variation \\( v \\), the SRVP becomes a standard verification problem for a network composed of the inverted encoding head and the original network's task head. This problem can be solved by any standard NN verifier; we use VeriNet [15, 17], an open-source linear programming-based verification toolkit. The invertibility of the encoding head is necessary to guarantee that the feature vectors that map to \\( Z_{\\mathrm{des}} \\) are contained in the bounds of feature space set obtained during verification. In our queries, the output constraints \\( Y_{\\mathrm{des}} \\) encode invariance of \\( N \\) to \\( v \\). When the query outcome is negative, the verifier provides a counterexample in \\( Z_{\\mathrm{des}} \\) which is then mapped to a counterexample in input space using the decoder. This ideally gives an instance of \\( v \\) against which the network is incorrect (see Section 5.3 for details)." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "3896" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.117, + 0.096, + 0.388, + 0.367 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.242, + 0.369, + 0.258, + 0.378 + ], + "angle": 0, + "content": "(b)" + }, + { + "type": "image", + "bbox": [ + 0.414, + 0.088, + 0.856, + 0.367 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.626, + 0.369, + 0.641, + 0.378 + ], + "angle": 0, + "content": "(c)" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.383, + 0.892, + 0.44 + ], + "angle": 0, + "content": "Figure 2. Reconstructed by our LVMs for Region specifications in (a), Segment specifications in (b) and Axis specifications in (c). (a) shows variations sampled from \\(\\epsilon\\)-balls around an image encoding; notice how a larger \\(\\epsilon\\) captures more varied changes of the input. The middle columns in (b) show reconstructions of samples from a segment joining the encodings of the dataset images in outer columns. In (c), all images are reconstructions and can be seen undergoing changes as specified conditional dimensions are varied." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.452, + 0.47, + 0.497 + ], + "angle": 0, + "content": "Discussion. We evaluate the approach experimentally in Section 5; below we analyse it against the last two shortcomings of the EDN approach discussed in Section 2." + }, + { + "type": "text", + "bbox": [ + 0.088, + 0.501, + 0.47, + 0.713 + ], + "angle": 0, + "content": "1. Observe that this approach directly verifies network features corresponding to latent space sets defined by mappings of the original images, rather than the reconstructed images. Thus, the pipeline ensures that the network is tested against at least the original image(s) that form the basis of a specification. Notice from Eq. 2, that this is not the case with the EDN approach if the decoder is not the exact inverse of the encoder. Moreover, since the encoding head is invertible, variations of an image mapping onto the same latent vector directly implies the stability of the network against these variations. Therefore, a many-to-one mapping is not a barrier for our approach, whereas it leads to insufficiently diverse input specifications with the EDN approach." + }, + { + "type": "text", + "bbox": [ + 0.087, + 0.716, + 0.471, + 0.866 + ], + "angle": 0, + "content": "2. The proposed approach employs shorter paths for verification than the EDN approach. Since the encoding head is invertible, a latent space set need not be passed through the decoder and original network to obtain its corresponding feature set, and since most verification methods have an exponential complexity dependence on the number of unstable activations, the exclusion of the high-dimensional decoder and initial network layers from the verification path allows this approach to scale more favourably than the EDN approach." + }, + { + "type": "list", + "bbox": [ + 0.087, + 0.501, + 0.471, + 0.866 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.871, + 0.47, + 0.901 + ], + "angle": 0, + "content": "A concern over the proposed approach could be that the network to be verified is partly used to define the input spec" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.451, + 0.892, + 0.557 + ], + "angle": 0, + "content": "ification that it is verified for. However, consider the FDN-encoding head pair as an independent encoder, and the encoding head inverse as a compute efficient analogue of the decoder-FDN pair in the EDN pipeline. From this perspective, the proposed approach is identical to the traditional EDN-based approaches for robustness validation. Additionally, the proposed approach benefits from:" + }, + { + "type": "text", + "bbox": [ + 0.511, + 0.558, + 0.892, + 0.634 + ], + "angle": 0, + "content": "- Added flexibility to use a deep decoder for manifold learning and sharper counterexample generation without impacting verification outcomes. Verification also ensures maximal recall in finding counterexamples as opposed to a gradient search-based approach." + }, + { + "type": "text", + "bbox": [ + 0.511, + 0.635, + 0.892, + 0.74 + ], + "angle": 0, + "content": "- Relative flexibility in choosing the network layer after which the encoding head is added and thereby, how many of the network's posterior layers feature in the verification path. This decision can depend on the scalability and implementation support of the chosen verification backend or the feasibility of learning a latent space of given dimensionality (see Section 5.2)." + }, + { + "type": "text", + "bbox": [ + 0.511, + 0.741, + 0.892, + 0.817 + ], + "angle": 0, + "content": "- Independence with respect to the FDN architecture's depth and type (residual, recurrent, non-standard convolutional, etc.), and possibly to input dimensionality1, leading to an easier extension of the verification approach to newer architectures." + }, + { + "type": "list", + "bbox": [ + 0.511, + 0.558, + 0.892, + 0.817 + ], + "angle": 0, + "content": null + }, + { + "type": "page_footnote", + "bbox": [ + 0.5, + 0.828, + 0.894, + 0.901 + ], + "angle": 0, + "content": "1Independence to input dimensionality is conditional on the nature of the FDN and its last layer being fully-connected (fc); however, since most vision inference tasks, such as classification, regression and detection, involve dimensionality reduction and network's posterior layers are usually fc, the specification input dimensionality can almost always be made lower than that of input data." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "3897" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.078, + 0.091, + 0.236, + 0.108 + ], + "angle": 0, + "content": "4. Implementation" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.115, + 0.469, + 0.146 + ], + "angle": 0, + "content": "In this section we describe our implementation of the proposed verification pipeline [13]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.146, + 0.469, + 0.207 + ], + "angle": 0, + "content": "Encoding head. In terms of design choices, all common LVMs for data generation, including VAEs, Normalising Flows (NFs) and GANs, can be used in the pipeline if the following holds:" + }, + { + "type": "text", + "bbox": [ + 0.072, + 0.207, + 0.468, + 0.251 + ], + "angle": 0, + "content": "- The FDN of the network to be verified can serve as the backbone of the LVM encoder (e.g., if the FDN involves a dimensionality change then NFs cannot serve as the LVM)." + }, + { + "type": "text", + "bbox": [ + 0.072, + 0.252, + 0.468, + 0.281 + ], + "angle": 0, + "content": "- The verification backend can verify the inverted encoding head of the pipeline." + }, + { + "type": "list", + "bbox": [ + 0.072, + 0.207, + 0.468, + 0.281 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.282, + 0.469, + 0.493 + ], + "angle": 0, + "content": "Given any LVM, \\( Z_{\\mathrm{des}} \\) is defined in the output space of the LVM encoding head in ways described in Section 3. A VAE fits the pipeline particularly well given the backing of the theoretical analysis in [34], and as it regularises the underlying latent space to resemble a prior. This prior (normal, von Mises-Fisher distribution in \\( \\mathcal{N} \\)-VAE [21], S-VAE [8] resp.) is light-tailed, so the latent space can be approximately bounded or truncated, and the epsilons in our specifications have bounded domain. Note that the latent variable \\( z \\) in a VAE is not the output of the encoder but a random variable conditioned on its outputs \\( (\\mu, \\sigma \\in \\mathbb{R}^{\\mathrm{latent.dim}}) \\) by reparameterisation [21]. Since reparameterisation cannot be inverted, \\( Z_{\\mathrm{des}} \\) is defined using the vector \\( [\\mu, \\sigma] \\) instead of \\( z \\), albeit with no change in \\( Z_{\\mathrm{des}} \\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.493, + 0.469, + 0.583 + ], + "angle": 0, + "content": "In contrast, GANs do not use an encoder to learn a latent distribution and instead take a prior distribution as input. However, when using a GAN as the LVM, we still add an encoding head after the FDN to transform the unconstrained FDN output to a desired prior for the GAN and define input-parameterized local specifications." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.584, + 0.469, + 0.704 + ], + "angle": 0, + "content": "LVM design. As discussed previously, our pipeline features an encoding head after the FDN of the network to be analysed. Since the encoding head must not undergo dimensionality change, the dimension of the flattened FDN output is the dimension of the encoding head layers and the latent space where the input specification is defined. Typically, a shorter FDN implies larger latent space dimensionality and verification involves more network layers." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.705, + 0.469, + 0.901 + ], + "angle": 0, + "content": "We use two types of feed-forward encoding heads: one consists of pairs of an invertible activation and fully-connected (FC) layers; the other consists of alternating affine-coupling layers [9]. The former is easier to train and supported by most NN verifiers, but its invertibility to sufficient precision needs to be validated by checking the singular values of the individual layers' weight matrices. Affine-coupling layer is invertible-by-construction but not supported by standard NN verifiers. To support its verification, we replace its typically input dependent scaling and translation unit with an input independent learnt vector and an FC layer respectively. This modified affine-coupling layer is equivalent to an FC layer in expressiveness, but is" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.092, + 0.673, + 0.107 + ], + "angle": 0, + "content": "more challenging to train." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.107, + 0.892, + 0.182 + ], + "angle": 0, + "content": "One can increase the encoding head depth with the pairs described above until the LVM is adequately trained; in our experience, a single layered encoding head sufficed for good reconstructions. The decoder is always a deep upscaling network mirroring the pipeline encoder." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.182, + 0.892, + 0.378 + ], + "angle": 0, + "content": "LVM training. In addition to the negative log likelihood or GAN loss, we conditionally train latent dimensions [5, 23] for Axis specifications. We use Cross-Entropy (CE) loss for discrete attributes. For instance, we train one dimension with binary CE loss so that \\([0,1]\\) for this dimension corresponds to variations from no attribute to complete attribute. Note that we cannot use the common conditional generation approach of augmenting encodings with attribute labels [31] because the entire encoding must be inferred from the FDN output for invertibility. Therefore, differently from usual practice, our VAEs for conditional generation do not take attributes as priors to condition on but rather learn them with supervision from data." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.379, + 0.892, + 0.439 + ], + "angle": 0, + "content": "Continuum in transformations is important when verifying against pose changes, which CE loss may not provide. Therefore, dimensions capturing continuous changes are trained as graphics code as per the procedure in [23]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.44, + 0.892, + 0.544 + ], + "angle": 0, + "content": "Note that it may not be possible to train an LVM by adding an encoding head to the extreme end of every network, as network's task-agnostic information may be lost till that layer. However, if an LVM can be trained by adding an encoding head after the \\( K^{th} \\) network layer, it is inexpensive to train a new LVM from after the \\( (K - k)^{th}, k > 0 \\), layer, with the frozen original network." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.545, + 0.892, + 0.801 + ], + "angle": 0, + "content": "Datasets preparation. To train the LVMs for our experiments, we used public datasets with customdataloading to have attribute and transform labels for every input. We only used datasets for which realistic variations can be produced with labels, as it is required for conditional training and forming precise queries for pipeline evaluation (see Section 5.4). We worked with five datasets: CelebA [25], Traffic Signs Recognition (TSRD), 3D Objects (3DOD), (Fashion)MNIST [38]. For TSRD, we took traffic signs and city scene crops, apply planar (rotation, scale, photometric) and spatial (perspective) transformations on the former and blend them into the latter during dataloading. For 3DOD, we took 3D models from ModelNet10 dataset [37] and render their images from different distances, azimuth and elevation angles in Blender [6]. For all trainings, the dataset was balanced such that every class had adequate samples of the variation being verified against." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.815, + 0.715, + 0.833 + ], + "angle": 0, + "content": "5. Experimental Analysis" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.84, + 0.892, + 0.871 + ], + "angle": 0, + "content": "We report on our experiments to validate the proposed approach, with focus on answering three key questions:" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.871, + 0.891, + 0.901 + ], + "angle": 0, + "content": "Q1. Can an LVM added to a classifier generate an appropriate latent manifold and good reconstructions?" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "3898" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.078, + 0.092, + 0.468, + 0.12 + ], + "angle": 0, + "content": "Q2. Can the proposed pipeline efficiently verify deep networks?" + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.121, + 0.468, + 0.152 + ], + "angle": 0, + "content": "Q3. Can the specifications, discussed in Section 3, encode intended input variations?" + }, + { + "type": "list", + "bbox": [ + 0.078, + 0.092, + 0.468, + 0.152 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.153, + 0.468, + 0.288 + ], + "angle": 0, + "content": "To assess Q1, we refer to the reconstructions presented in Figure 2 and the low values of mean reconstruction error and FID score [18] reported in Table 1. To assess Q2, we refer to the verification outcomes for deep networks of different architectures reported in Sections 5.1, 5.2. To assess Q3, we refer to the values of metrics quantifying the precision of a specification in capturing intended variations, discussed in Section 5.4. With this overview, we now discuss the experiments in greater detail." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.298, + 0.443, + 0.314 + ], + "angle": 0, + "content": "5.1. Verifying segments joining input encodings" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.321, + 0.468, + 0.516 + ], + "angle": 0, + "content": "To verify robustness against variations reflected in an image pair, we generated Segment specifications capturing object pose and viewpoint changes. For CelebA, we also verify specifications capturing the classifier's invariance to task-orthogonal attributes. These queries are similar to the queries in [27] which uses the EDN approach and reports successful deterministic verification of \\(23.8\\%\\) queries for a ConvMed model with 64k activations. Based on the classifier layer separating the FDN and task head, multiple verification pipelines were trained for each classifier. The verification outcomes for all queries and pipelines are reported in Table 1, from which the following observations can be drawn:" + }, + { + "type": "text", + "bbox": [ + 0.088, + 0.518, + 0.468, + 0.593 + ], + "angle": 0, + "content": "- The mean reconstruction errors and FID scores for the multiple SRVP pipelines per classifier are low with consistent verification outcomes, indicating that latent spaces of a considerable range of dimensionality can be successfully learnt and verified against." + }, + { + "type": "text", + "bbox": [ + 0.088, + 0.595, + 0.468, + 0.67 + ], + "angle": 0, + "content": "- The SRVP pipelines require an order of magnitude less time than the EDN pipelines to solve safe queries, and produce fewer trivial output bounds or undecided cases. This remains the case with the inclusion of more network layers in the verification path." + }, + { + "type": "text", + "bbox": [ + 0.088, + 0.672, + 0.468, + 0.717 + ], + "angle": 0, + "content": "- The verified robust accuracy tightly lower bounds the adversarial accuracy computed against gradient-ascent-based latent space interpolation attacks [28]." + }, + { + "type": "list", + "bbox": [ + 0.088, + 0.518, + 0.468, + 0.717 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.727, + 0.37, + 0.743 + ], + "angle": 0, + "content": "5.2. Verifying along latent dimensions" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.75, + 0.468, + 0.901 + ], + "angle": 0, + "content": "As discussed in Section 3, Axis specifications can be used to verify an input against the entire range of a task-orthogonal change (e.g., style, or pose). Figure 3 shows representative results for verifying these specifications where the local input set is increased for individual latent dimensions of an encoding. For many inputs, conditional dimensions were verifiably robust for almost their entire range, while dimensions without conditional training were found to be robust for much smaller epsilons. Decoded samples from latent dimensions in Figure 4 corroborate these" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.273 + ], + "angle": 0, + "content": "outcomes. The object class change was not observed for all non-conditional dimensions, but conditional dimensions were more consistent in preserving the object class. However, with increase in latent dimensionality, as with a shorter FDN, it became harder to balance the conditional and standard LVM training to achieve both good reconstructions and distinct attribute changes with class consistency. This explains the reduced transform detections for higher dimensional manifolds reported in Figure 3. In Section 5.4, we present a validity metric to assess the success of conditional manifold training and in turn, derive expectation on the usefulness of Axis specifications defined in the manifold." + }, + { + "type": "image", + "bbox": [ + 0.54, + 0.279, + 0.852, + 0.419 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.54, + 0.422, + 0.852, + 0.562 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.566, + 0.892, + 0.663 + ], + "angle": 0, + "content": "Figure 3. Both graphs show mean percentage of Axis queries verified as safe (out of 200 tested) for local intervals of \\(\\pm \\epsilon\\) for LVMs of different latent dimensionality. The percentage of reconstructions of samples along the conditional axes, around the \\(\\epsilon\\)s reported on the x-axis, in which a learnt transform detector detects the intended transform, is also plotted. The axes were trained with (B)CE loss with 0,1 mapping to the base and the attribute added image resp." + }, + { + "type": "image", + "bbox": [ + 0.514, + 0.677, + 0.852, + 0.804 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.811, + 0.892, + 0.879 + ], + "angle": 0, + "content": "Figure 4. All images above are generated by an LVM from a single image per dataset. The columns feature samples along non-conditional dimensions, and each row has a constant conditional axis value which enforces rendering of the specified transform in all its reconstructions." + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.886, + 0.891, + 0.901 + ], + "angle": 0, + "content": "In case of Region specifications, where the local ep" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "3899" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.091, + 0.09, + 0.88, + 0.307 + ], + "angle": 0, + "content": "
Dataset (size)Verifying inv. to *NetworkAccuracies*Pipeline**Verification outcomes (100 std.safe queries)Recons.outcomes
Std.Adv.Type #Ver.actv.layers (actvs.)Safe(s†)Unsafe(s)Undec.(s)Rob.accRMSSrr*FIDscore
Runs for efficiency comparison of EDNs (with decoders of different depths) vs. SRVPs (with encoding heads after different n/w layers).
CelebA64.2%EDtinyN-328 (5k)61 (6.8)39 (3.94)056%0.064218.61
65%EDdeepN-329 (27k)64 (22.3)29 (31.6)7 (64)59%0.053107.42
(64x64)ConvSmall (6k ReLUs)92%69%EDresnet18N-3211 (0.2M)042 (370)58 (802)0%0.05189.62
91%SRVP Lin1-321 (64)99 (0.4)1 (0.01)091%0.058114
89%SRVP Lin1-642 (192)94 (0.5)6 (0.02)085.5%0.042112
Head Flip (gender cla.)87%SRVP Lin1-1923 (576)88 (1.1)12 (0.08)081%0.035105
89%SRVP Lin1-3924 (1.3k)91 (2.7)9 (0.11)084%0.031102
74%EDtinyN-328 (86k)59 (32.8)41 (20)056.6%0.07264
81%EDdeepN-329 (0.1M)66 (35.3)22 (23.5)12 (64)63%0.06223
(128x128)ConvBig (72k ReLUs)96%77%EDresnet18N-3211 (475k)021 (410)79 (816)0%0.06124
93%SRVP Lin1-641 (64)95 (0.4)5 (0.07)091%0.23252
95%SRVP Lin1-1922 (256)96 (0.8)4 (0.09)092%0.15225
94%SRVP Lin1-3923 (648)96 (1.9)4 (0.11)092%0.04202
" + }, + { + "type": "table", + "bbox": [ + 0.09, + 0.308, + 0.88, + 0.406 + ], + "angle": 0, + "content": "
SRVP runs with encoding heads of different dimensions for different n/w architectures and datasets
(64x64)ResNet1884%82%SRVP Lin1-2561 (512)95 (2.6)5 (0.1)080%0.022104
TRDS (64x64)Planar Pose (sign cla.)ResNet1892.5%SRVP Lin1-2562 (1k)96 (2.1)4 (0.21)089%0.03116
89%SRVP Lin1-10242 (1.5k)94 (3.8)6 (0.46)087%0.03106
MobileNetv282%78%SRVP Lin1-6401 (640)93 (2.1)7 (0.42)076%0.09133
3DOD (64x64)Spatial Pose (obj cla.)ResNet1897%SRVP Lin1-2562 (1k)94 (1.9)6 (0.2)091%0.04106
90%SRVP Lin1-10242 (1.5k)92 (4.7)8 (0.45)089%0.0298
" + }, + { + "type": "table_footnote", + "bbox": [ + 0.077, + 0.408, + 0.892, + 0.435 + ], + "angle": 0, + "content": "* Std. and Adv. accuracy are the network's accuracy against clean, augmented data and latent-space PGD attacks [28] (\\( \\alpha = 2\\mathrm{e} - 3 \\), #iters=2000) resp. The PGD attacks are found for \\( N \\circ d(z) \\) in EDN pipelines and \\( e^{-1} \\circ N_{\\mathrm{head}}(z) \\) in SRVP pipelines for \\( z \\in Z_{\\mathrm{segment}} \\)." + }, + { + "type": "table_footnote", + "bbox": [ + 0.078, + 0.434, + 0.891, + 0.459 + ], + "angle": 0, + "content": "** The suffixed integer in the pipeline type is the dimensionality of its latent space and is equal to its verification input. Higher dimensions for a SRVP pipeline for the same network indicate an earlier split and the inclusion of more layers in the verification path." + }, + { + "type": "table_footnote", + "bbox": [ + 0.08, + 0.458, + 0.89, + 0.472 + ], + "angle": 0, + "content": "\\(\\dagger\\) Seconds (s) reported are the mean query solving time. All queries were run on a 24 core, 256GB CPU with timeout of 60 or 800 seconds." + }, + { + "type": "table_footnote", + "bbox": [ + 0.08, + 0.471, + 0.884, + 0.485 + ], + "angle": 0, + "content": "\\(\\star\\) The reconstruction error is per-pixel for normalised float [-1,1] images. The FID score is computed by using pytorch-fid package [30]." + }, + { + "type": "table_footnote", + "bbox": [ + 0.079, + 0.484, + 0.891, + 0.509 + ], + "angle": 0, + "content": "All pipelines for the same network were trained until comparable reconstruction outcomes, were tested for the same queries using the same backend and use \\(\\mathcal{N}\\)-VAE as the LVM so that all of them have an approximately normal latent manifold distribution." + }, + { + "type": "list", + "bbox": [ + 0.077, + 0.408, + 0.892, + 0.509 + ], + "angle": 0, + "content": null + }, + { + "type": "table_caption", + "bbox": [ + 0.126, + 0.517, + 0.842, + 0.532 + ], + "angle": 0, + "content": "Table 1. Verification results for Segment queries; representative specification inputs for the above are shown in Figure 2b." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.557, + 0.47, + 0.604 + ], + "angle": 0, + "content": "silon ball is increased uniformly in all latent dimensions, we could verify robustness for a maximum \\(\\epsilon = 0.01\\) (for \\(< 10\\%\\) queries) for SRVP Lin-32 pipelines." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.617, + 0.314, + 0.634 + ], + "angle": 0, + "content": "5.3. Counterexamples analysis" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.643, + 0.47, + 0.793 + ], + "angle": 0, + "content": "Counterexamples are instances of the input specification set that falsify the robustness property under investigation. In our approach, the verifier finds a latent space counterexample \\( z^{*} \\in Z_{\\mathrm{des}} \\) for every unsafe query such that \\( N_{\\mathrm{head}} \\circ e^{-1}(z^{*}) \\) demonstrates non-robustness. However, since the LVM decoder is not the exact inverse of its encoder, the decoded counterexample could be spurious, i.e., \\( N \\circ d(z^{*}) \\) may not be a counterexample. Therefore, we decode every \\( z^{*} \\) and label it a valid counterexample iff its reconstruction is also a counterexample for the network." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.796, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Similar to [16], in the case of a spurious counterexample \\( z^{*} \\), we run a local gradient search for a valid one, taking \\( z^{*} \\) as the starting point. In comparison to starting from a mapped vector, this local gradient-based search around \\( z^{*} \\) takes much fewer iterations to reach a valid counterexample in most cases, and results in high precision in finding valid and in-domain counterexamples (see Figure 5)." + }, + { + "type": "image", + "bbox": [ + 0.502, + 0.555, + 0.875, + 0.768 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.812, + 0.64, + 0.886, + 0.653 + ], + "angle": 0, + "content": "Male (Female)" + }, + { + "type": "text", + "bbox": [ + 0.812, + 0.667, + 0.879, + 0.678 + ], + "angle": 0, + "content": "Chair (Table)" + }, + { + "type": "text", + "bbox": [ + 0.812, + 0.688, + 0.857, + 0.699 + ], + "angle": 0, + "content": "No right" + }, + { + "type": "text", + "bbox": [ + 0.812, + 0.7, + 0.871, + 0.71 + ], + "angle": 0, + "content": "(No U-turn)" + }, + { + "type": "text", + "bbox": [ + 0.812, + 0.719, + 0.875, + 0.729 + ], + "angle": 0, + "content": "Old (Young)" + }, + { + "type": "text", + "bbox": [ + 0.812, + 0.73, + 0.889, + 0.739 + ], + "angle": 0, + "content": "Change: Glasses" + }, + { + "type": "text", + "bbox": [ + 0.812, + 0.745, + 0.886, + 0.755 + ], + "angle": 0, + "content": "Male (Female)" + }, + { + "type": "text", + "bbox": [ + 0.812, + 0.754, + 0.888, + 0.763 + ], + "angle": 0, + "content": "Change:Gender" + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.77, + 0.892, + 0.909 + ], + "angle": 0, + "content": "Figure 5. The table reports the mean ratios of valid counterexamples (ceg.) to all cegs found by SRVP pipelines for network \\( N_{\\mathrm{head}} \\circ e^{-1} \\) through verification of 100 Segment queries, with and without PGD-based search in the second and third column resp. The full search and refinement iterations are median PGD iterations of step-size 1e-3 for success in the latent/attribute space attack [28] and in the local search for a valid ceg around a verification-returned spurious ceg resp. Rows in the figure below show reconstructions for some unsafe Segment and Axis queries with their valid cegs in the rightmost column." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "3900" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.077, + 0.091, + 0.38, + 0.108 + ], + "angle": 0, + "content": "5.4. Validating the LVM based pipeline" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.115, + 0.468, + 0.205 + ], + "angle": 0, + "content": "Having assessed the capabilities of our approach in terms of scaling to deep networks and the fidelity of returned counterexamples, we now evaluate its precision in sufficiently capturing the intended variations in the proposed specifications. For this, we consider two latent space-based validity metrics as described below." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.206, + 0.468, + 0.432 + ], + "angle": 0, + "content": "The assumption behind Segment specifications is that the in-domain interpolations of an image pair map to the interpolations of its encoding pair. To validate this, we measure the distance of the encodings of the desired interpolations of an image pair to the path joining its encoding pair. In practice, for validating pose invariance queries, we generate images with varying extents of a transform, construct a path between the encodings of the image pair with the most extreme mutual transform, and compute the distance between the encodings of the intermediate transforms and their projection on this path. This distance is divided by square-root of latent dimensionality to generalise across manifolds of different dimensions. We compute this metric for the following pairs of encoding paths and VAE manifolds used in our pipelines, and report its mean value distribution below." + }, + { + "type": "text", + "bbox": [ + 0.082, + 0.433, + 0.468, + 0.463 + ], + "angle": 0, + "content": "1. Shortest Length Path (SLP) + untrained normal distribution manifold (baseline)," + }, + { + "type": "text", + "bbox": [ + 0.082, + 0.466, + 0.21, + 0.48 + ], + "angle": 0, + "content": "2. \\(\\mathrm{SLP} + \\mathcal{N}\\) -VAE," + }, + { + "type": "text", + "bbox": [ + 0.082, + 0.482, + 0.468, + 0.528 + ], + "angle": 0, + "content": "3. \\(\\mathrm{SLP} + \\mathcal{N}\\)-VAE trained with a latent space-based cycle consistency loss that encourages its encoder-decoder to be an inverse pair," + }, + { + "type": "text", + "bbox": [ + 0.082, + 0.53, + 0.435, + 0.546 + ], + "angle": 0, + "content": "4. Real-vs-fake discriminator-guided path \\(+\\mathcal{N}\\) -VAE." + }, + { + "type": "list", + "bbox": [ + 0.082, + 0.433, + 0.468, + 0.546 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.057, + 0.549, + 0.46, + 0.681 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.088, + 0.683, + 0.454, + 0.71 + ], + "angle": 0, + "content": "Normalised histogram of distances of intermediate transform encodings to \\(Z_{\\mathrm{des}}\\), i.e., \\(\\mathbf{d}(e(x_i), \\text{proj}_{Z_{\\mathrm{des}}} e(x_i)) / \\sqrt{m}\\), \\(e(.) \\in \\mathbb{R}^m\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.719, + 0.468, + 0.884 + ], + "angle": 0, + "content": "In comparison to the primitive baseline, the metric values with \\(\\mathcal{N}\\)-VAEs are low for most queries as desired, and further reduce on incentivising consistency in their mappings, as in 3., and making the encoding traversals more precise and segmented, as in 4. Although we do not observe notable changes in the verification outcomes with different \\(\\mathcal{N}\\)-VAEs, this metric could be used to guide the construction of input specifications. Notice that this metric is the latent space-based analogue of the pixel space distance used to define input specifications and evaluate generators for EDN-based verification [20]." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.886, + 0.468, + 0.901 + ], + "angle": 0, + "content": "The motivation behind Axis specifications is the disen" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.303 + ], + "angle": 0, + "content": "tanglement of conditional dimensions in capturing specified variations. To assess disentanglement, we compute the ratio of the highest value among the incorrect conditional dimensions to the value of the correct conditional dimension of an encoding for a discrete attribute. For the continuous transforms encoded as graphics code [23], an equivalent metric is the ratio of the maximum variance among the incorrect conditional dimensions to the variance in the correct conditional dimension, computed for a batch of encodings. Below we report the mean value distribution of this metric for normally and conditionally trained \\(\\mathcal{N}\\)-VAEs. As expected, conditional training results in low metric values as desired, while normal training results in similar values for most dimensions and metric values closer to unity." + }, + { + "type": "image", + "bbox": [ + 0.486, + 0.307, + 0.882, + 0.437 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.526, + 0.44, + 0.862, + 0.465 + ], + "angle": 0, + "content": "Normalised histogram of maximum incorrect-to-correct dimension ratios for conditionally trained LVMs." + }, + { + "type": "image_footnote", + "bbox": [ + 0.52, + 0.465, + 0.867, + 0.478 + ], + "angle": 0, + "content": "Numbers in the legend entries denote manifold dimensionality." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.484, + 0.892, + 0.575 + ], + "angle": 0, + "content": "These latent space-based metrics are more relevant to our approach than the pixel space-based or the attribute detection-based analyses relevant to the EDN approach. This is because the effectiveness of verification with our approach depends more on the spatial coherence and precision of the LVM encodings, than its reconstruction capabilities." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.589, + 0.627, + 0.604 + ], + "angle": 0, + "content": "6. Conclusions" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.614, + 0.892, + 0.689 + ], + "angle": 0, + "content": "In this work we introduced an efficient and precise approach for verifying specifications in the latent space. By means of the proposed approach, we could effectively assess and verify deep networks against pose changes, and provide counterexamples that inform of their fragilities." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.69, + 0.892, + 0.901 + ], + "angle": 0, + "content": "In terms of limitations, we discussed that the ease of learning a conditional latent manifold, and the computational gains of our verification approach can be affected by the increase of layers in the network head of our pipeline. However, since the largest activation layers can be excluded from the verification path with our approach, it still fares better than the existing approach. A general limitation of latent-space based verification approaches is their necessity for an adequate LVM, which, as discussed for our approach, may require the original network to be trained as part of the proposed pipeline. 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Proceedings of the AAAI Conference on Artificial Intelligence (AAAI19), 33(01):5757-5764, Jul. 2019. 2" + }, + { + "type": "list", + "bbox": [ + 0.08, + 0.093, + 0.47, + 0.826 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "3903" + } + ] +] \ No newline at end of file diff --git a/2023/Efficient Verification of Neural Networks Against LVM-Based Specifications/f017e278-be6a-4fc6-a7c8-64ae1c47c99f_origin.pdf b/2023/Efficient Verification of Neural Networks Against LVM-Based Specifications/f017e278-be6a-4fc6-a7c8-64ae1c47c99f_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..3babf1dbb5cc8c228d6159fcfd3b25a20cf90d7d --- /dev/null +++ b/2023/Efficient Verification of Neural Networks Against LVM-Based Specifications/f017e278-be6a-4fc6-a7c8-64ae1c47c99f_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:7d88ba28e9f670de497018baac22472848318a66fabdcb0b102eda90a9a55822 +size 1700980 diff --git a/2023/Efficient Verification of Neural Networks Against LVM-Based Specifications/full.md b/2023/Efficient Verification of Neural Networks Against LVM-Based Specifications/full.md new file mode 100644 index 0000000000000000000000000000000000000000..b35cfb2495cb0e6aa83e4480f49ad42e72ceb9e2 --- /dev/null +++ b/2023/Efficient Verification of Neural Networks Against LVM-Based Specifications/full.md @@ -0,0 +1,321 @@ +# Efficient Verification of Neural Networks against LVM-based Specifications + +Harleen Hanspal +Imperial College London & Safe Intelligence +London, United Kingdom + +h.hanspal21@imperial.ac.uk + +Alessio Lomuscio +Safe Intelligence +London, United Kingdom + +alessio@safeintelligence.ai + +# Abstract + +The deployment of perception systems based on neural networks in safety critical applications requires assurance on their robustness. Deterministic guarantees on network robustness require formal verification. Standard approaches for verifying robustness analyse invariance to analytically defined transformations, but not the diverse and ubiquitous changes involving object pose, scene viewpoint, occlusions, etc. To this end, we present an efficient approach for verifying specifications definable using Latent Variable Models that capture such diverse changes. The approach involves adding an invertible encoding head to the network to be verified, enabling the verification of latent space sets with minimal reconstruction overhead. We report verification experiments for three classes of proposed latent space specifications, each capturing different types of realistic input variations. Differently from previous work in this area, the proposed approach is relatively independent of input dimensionality and scales to a broad class of deep networks and real-world datasets by mitigating the inefficiency and decoder expressivity dependence in the present state-of-the-art. + +# 1. Introduction + +The deployment of perception systems based on neural networks in safety-critical applications requires assurance on their performance, notably accuracy and robustness. Formal verification contributes to this requirement by providing provable and deterministic guarantees that a network meets a given specification. Typically, specifications are mathematically expressed constraints on the network's intended input/output and may encode desirable properties, such as robustness to noise (including adversarial attacks) [35], geometric changes [1,2], bias-field changes [14] and beyond. + +While the above is useful, practical applications require robustness against diverse changes in a scene, including changes in the pose of objects, viewpoints, occlusions, etc. + +Such changes cannot be efficiently mathematically defined, but may be encoded from data by using generative models. For instance, [11, 12, 28, 34] use generative models to generate novel in-domain images for data augmentation, adversarial training or evaluating network generalisation; [34] additionally derives formal conditions for a latent space set to necessarily contain sufficient perturbations for it to be trusted for adversarial training and robustness checks. All these approaches either provide statistical robustness measures, or generate attacks based on gradient-search, which is not guaranteed to find an attack if one exists. + +Popular for network robustification and empirical evaluation, latent space sets are seldom used as inputs for verification due to the valid concern over the lack of mathematical guarantees on the completeness of the specifications they encode. Therefore, we reiterate that this work is most useful for changes that are difficult to mathematically define. We additionally argue that formal verification of latent space-based specifications can be more valuable than their empirical evaluation. This is because the latent space is a continuous domain and countably infinite number of inputs can be mapped to and reconstructed from a latent space set. Therefore, no amount of testing, or search in the latent space can provide guarantees against all the variations encoded in it. To the best of our knowledge, only [20, 27] encode specifications in a latent space and propose architectures to verify them. + +There are, however, two difficulties with verification in the latent space. The first concerns the scalability of verification methods; the second relates to the quality of reconstructions affecting the verification outcomes. In this paper, we focus on alleviating these two concerns. Specifically, we propose a novel, invertible encoder-based pipeline for verifying latent space sets, that lends two key benefits of: + +- Computational efficiency and relative independence to input dimensionality, +- Verification outcomes' independence to reconstructions, and precise counterexamples with high recall. + +We focus our analysis on pose and attribute variations in vision inference tasks, but the approach is likely extendable + +to other variations, domains and tasks. Next, we recall key notions for network verification and discuss the existing relevant work, before presenting and validating our method in subsequent sections. + +# 2. Background and Related Work + +Neural network verification. Given a network $N$ and an input-output specification $(X_{\mathrm{des}},Y_{\mathrm{des}})$ , the network verification problem is the decision problem of determining whether + +$$ +N (x) \in Y _ {\mathrm {d e s}}, \forall x \in X _ {\mathrm {d e s}}. +$$ + +Verification methods, such as those based on SMT [19], MILP [4, 10, 22], Interval Propagation [15, 16, 32, 33], SDP [3, 29] or Lipschitz analysis [39], propagate a set $X_{\mathrm{des}}$ in a single forward pass through $N$ and determine whether or not the output set of $N$ for $X_{\mathrm{des}}$ lies in $Y_{\mathrm{des}}$ . These methods mostly support input specifications defined in: + +- Data space, such that $X_{\mathrm{des}}$ is a norm ball around an input $x$ , i.e., $\mathcal{B}_{\epsilon}(x) = \{x' \mid \| x' - x \| < \epsilon\}$ . The norm is defined in metric spaces such as $\ell_p$ [2,16,19] or Wasserstein [36], and the $\epsilon$ is adequately set to include intended photometric and geometric variations, albeit along with considerable unrealistic instances in case of large variations. +- Parameter space, such that, given an input $x$ and a set of transformations $T$ , $X_{\mathrm{des}}$ is defined by prepending parametric transform layers $N_T(\alpha)$ , where $\alpha$ determines the transformation extent, to the network; $X_{\mathrm{des}} = N_T(\alpha)(x)$ . This definition is more precise in capturing planar geometric changes [26] and photometric changes, such as smooth illumination variations [14], in an input. + +While these specifications are important, they do not efficiently capture non-planar and semantic transformations. + +LVM-based specifications. Latent Variable Models (LVMs) for data generation map a typically lower-dimensional, continuous latent distribution to the input space. This mapping and its converse is learnt by LVM's decoder-encoder pair. Additionally, conditional training can disentangle latent dimensions to precisely capture specific dataset features and variations [5, 7, 23]. We refer to specifications which use LVM encoders to map input variations and define query input sets as LVM-based specifications. + +Related work. As mentioned in Section 1, most formal verification approaches do not use generative models. Only [20, 27] use an autoencoder in a verification setup to prove whether or not the output of a network $N$ is consistent for the image set produced by an independent autoencoder $(e,d)$ from the interpolations in its latent space. Formally, [27] establishes whether + +$$ +(N \circ d) \circ e (x) \in Y _ {\mathrm {d e s}}, \forall x \in \{X \mid e (X) \in Z _ {\mathrm {d e s}} \}, +$$ + +where $Z_{\mathrm{des}} \in \mathbb{R}^{\mathrm{latent\_dim}}$ is a segment joining latent encodings of samples in $X_{\mathrm{des}}$ . Since propagating $Z_{\mathrm{des}}$ through + +a useful decoder is computationally expensive, deterministic verification using this approach is reported to not scale beyond small networks. To overcome this, the authors a) heuristically subsume and approximate line segments by axes-aligned boxes, and b) turn specifications into probabilistic statements that determine whether a vector sampled uniformly from $Z_{\mathrm{des}}$ generates a correctly classified image. + +The general approach of prepending a generative model as an independent input set generator for verifying a network, which we henceforth refer to as the Encoder-Decoder-Network (EDN) approach, suffers from the following limitations: + +1. The network is verified only against images appropriately mapped by the encoder, but the encoding could be loose $(z \in Z_{\mathrm{des}} \Rightarrow e^{-1}(z) \in X_{\mathrm{des}})$ and incomplete $(x \in X_{\mathrm{des}} \Rightarrow e(x) \in Z_{\mathrm{des}})$ . +2. The network is verified against reconstructions of the decoder which may not have the same quality as the dataset images in terms of sharpness and diversity. If the decoder does not reconstruct an intended attribute's variations, either because all variations of that attribute are encoded to the same latent vector, or because it is not expressive enough, verification may incorrectly suggest that the network is invariant to that attribute. +3. The input set $Z_{\mathrm{des}}$ is propagated through both the decoder and the network to be verified, thereby resulting in considerable computational cost. + +In the rest of the paper, we propose a pipeline for verifying LVM-based specifications in a computationally lighter manner, and alleviate the last two shortcomings by construction. We do not solve the first limitation; but in Section 5.4, we present metrics to quantify the precision of the proposed specifications in terms of how well they capture the desired variations. + +# 3. Efficient Verification in Latent Space + +In this section we present an efficient approach to verify the robustness of neural networks against specifications capturing diverse and realistic input variations. Formally, given a network $N$ and a variation $v$ , we define the Semantic Verification Problem (SVP) as the network verification problem where $X_{\mathrm{des}}$ is the preimage of a set $Z_{\mathrm{des}}$ under a partially invertible encoder $e$ : + +$$ +N (x) \in Y _ {\mathrm {d e s}}, \forall x \in \{X \mid e (X) = Z _ {\mathrm {d e s}} \}. +$$ + +Here, $Z_{\mathrm{des}}$ is a set in the encoder's output space that captures $v$ and the input-output specification set is $(Z_{\mathrm{des}}, Y_{\mathrm{des}})$ . In the following, we study the Semantic Robustness Verification Problem (SRVP), which is an instance of SVP that checks for network robustness, i.e., $Y_{\mathrm{des}}$ is a singleton. To solve SRVP, we propose the multi-head architecture shown in Figure 1. + +![](images/2b0f102aa84cb435a76a7f512d541566301ed3768cb68d0f83c13f67b173657c.jpg) +Figure 1. The proposed pipeline consists of an LVM, built around the network to be verified, that takes the network's intermediate features as its input. The LVM encoder is invertible and maps its input feature set to a spatially coherent latent manifold, where the input specification is defined. + +Verification pipeline. The network $N$ to be verified is divided into a Feature Detection Network (FDN), consisting of $N$ 's initial layers, and a task head, e.g., a classification or regression head. In our implementation, $N$ is a classifier, but the approach applies similarly for other learning tasks. To define the specification, we add an LVM after the FDN. The encoder of this LVM is invertible and maps the intermediate features, output by FDN, to its latent space where the input specification is defined. Unlike the feature space, this latent space is queryable by using the decoder and can be made approximately bounded. + +The verification path with this pipeline is limited to the inverse of LVM's encoding head and $N$ 's task head (green region in Figure 1). Differently from previous work, the decoder here is only used for training the LVM and as a counterexample generator to provide semantically meaningful counterexamples when verification outcomes are negative. + +Specification inputs in latent space. We consider specifications focused on encoding the network's invariance to changes in an object-of-interest in the input. These changes include non-planar transformations, specific semantic changes of the object or its arbitrary task-orthogonal variations commonly occurring in the dataset. The learning tasks and datasets where the objects-of-interest and their variations are discernible against unimportant content in the input are well suited for such specifications. + +We now describe the definitions we consider for the local latent space set $Z_{\mathrm{des}}$ against which the network is verified. + +- Segment. We define $Z_{\mathrm{des}}$ to be a path connecting the encodings of two images $\{x_1, x_2\}$ that differ in the intended attributes or transforms (e.g., images of an object with different poses or backgrounds). Multiple definitions for $Z_{\mathrm{des}}$ are possible based on the traversal between the pair encodings, such as the maximum likelihood-based traversal [24], splines using multiple intermediate encodings, etc. With the Shortest Length Path + +(SLP), we get + +$$ +Z _ {\mathrm {d e s}} = e \left(x _ {1}\right) + \alpha \left(e \left(x _ {2}\right) - e \left(x _ {1}\right)\right), \alpha \in [ 0, 1 ] ^ {\text {l a t e n t , d i m}}. +$$ + +This $Z_{\mathrm{des}}$ is highly expressive since, in general, the image pair can be of any two images whose semantic interpolations should be consistently predicted by a network. + +- Axis. We define $Z_{\mathrm{des}}$ to be the set generated by varying an encoding's disentangled dimensions, such as those trained to capture variations of a specific attribute or a single degree of freedom for pose change. For example, we may consider + +$$ +Z _ {\mathrm {d e s}} = \left[ \max \{z _ {\mathrm {l}}, e (x) _ {i} - \epsilon \}, \min \{e (x) _ {i} + \epsilon , z _ {\mathrm {u}} \} \right], i \in I _ {C} +$$ + +where $I_{C}$ is the set of conditional dimension indices and $[z_{\mathrm{l}}, z_{\mathrm{u}}]$ are the limits containing a significant percentile of the distribution along these dimensions. + +Given conditional training, this $Z_{\mathrm{des}}$ can capture all variations of an image generated by an attribute or transform change, even when this image has no similar variations present in the dataset. + +- Region. We define $Z_{\mathrm{des}}$ as a $\ell_{\infty}$ -norm ball around an image encoding, i.e., $\mathcal{B}_{\epsilon}(z) = \{z' \mid ||z' - e(x)||_{\infty} < \epsilon \}$ . Given a spatially coherent manifold, $Z_{\mathrm{des}}$ should capture the commonly occurring variations of an image. + +The rest of our method is independent of the choice of $Z_{\mathrm{des}}$ . + +Note again that since the specifications cannot be guaranteed to be complete by construction, we empirically ascertain $Z_{\mathrm{des}}$ to be sufficiently capturing the intended variations using metrics presented in Section 5.4. Also note that [34] gives theoretical guarantees that local epsilon balls in a sufficiently trained Conditional VAE's latent space, necessarily generate sufficient instances of local input perturbations. This further validates the use of Axis and Region queries for formal robustness checks and the use of VAEs as the LVM in our pipeline (details in the next section). The specifications can also be systematically inspected by means of sample reconstructions, representative results for which are shown in Figure 2. + +Verification. Having formally defined $Z_{\mathrm{des}}$ to capture a variation $v$ , the SRVP becomes a standard verification problem for a network composed of the inverted encoding head and the original network's task head. This problem can be solved by any standard NN verifier; we use VeriNet [15, 17], an open-source linear programming-based verification toolkit. The invertibility of the encoding head is necessary to guarantee that the feature vectors that map to $Z_{\mathrm{des}}$ are contained in the bounds of feature space set obtained during verification. In our queries, the output constraints $Y_{\mathrm{des}}$ encode invariance of $N$ to $v$ . When the query outcome is negative, the verifier provides a counterexample in $Z_{\mathrm{des}}$ which is then mapped to a counterexample in input space using the decoder. This ideally gives an instance of $v$ against which the network is incorrect (see Section 5.3 for details). + +![](images/ff28e75b368ba842a065c55960648e6cf549fb225cbbd83335b29b64c9d17795.jpg) +(b) +Figure 2. Reconstructed by our LVMs for Region specifications in (a), Segment specifications in (b) and Axis specifications in (c). (a) shows variations sampled from $\epsilon$ -balls around an image encoding; notice how a larger $\epsilon$ captures more varied changes of the input. The middle columns in (b) show reconstructions of samples from a segment joining the encodings of the dataset images in outer columns. In (c), all images are reconstructions and can be seen undergoing changes as specified conditional dimensions are varied. + +![](images/89c97ade108ecdd1e2fb39c38125b774db3b0775021ab9cde2e50f7e6e128c10.jpg) +(c) + +Discussion. We evaluate the approach experimentally in Section 5; below we analyse it against the last two shortcomings of the EDN approach discussed in Section 2. + +1. Observe that this approach directly verifies network features corresponding to latent space sets defined by mappings of the original images, rather than the reconstructed images. Thus, the pipeline ensures that the network is tested against at least the original image(s) that form the basis of a specification. Notice from Eq. 2, that this is not the case with the EDN approach if the decoder is not the exact inverse of the encoder. Moreover, since the encoding head is invertible, variations of an image mapping onto the same latent vector directly implies the stability of the network against these variations. Therefore, a many-to-one mapping is not a barrier for our approach, whereas it leads to insufficiently diverse input specifications with the EDN approach. +2. The proposed approach employs shorter paths for verification than the EDN approach. Since the encoding head is invertible, a latent space set need not be passed through the decoder and original network to obtain its corresponding feature set, and since most verification methods have an exponential complexity dependence on the number of unstable activations, the exclusion of the high-dimensional decoder and initial network layers from the verification path allows this approach to scale more favourably than the EDN approach. + +A concern over the proposed approach could be that the network to be verified is partly used to define the input spec + +ification that it is verified for. However, consider the FDN-encoding head pair as an independent encoder, and the encoding head inverse as a compute efficient analogue of the decoder-FDN pair in the EDN pipeline. From this perspective, the proposed approach is identical to the traditional EDN-based approaches for robustness validation. Additionally, the proposed approach benefits from: + +- Added flexibility to use a deep decoder for manifold learning and sharper counterexample generation without impacting verification outcomes. Verification also ensures maximal recall in finding counterexamples as opposed to a gradient search-based approach. +- Relative flexibility in choosing the network layer after which the encoding head is added and thereby, how many of the network's posterior layers feature in the verification path. This decision can depend on the scalability and implementation support of the chosen verification backend or the feasibility of learning a latent space of given dimensionality (see Section 5.2). +- Independence with respect to the FDN architecture's depth and type (residual, recurrent, non-standard convolutional, etc.), and possibly to input dimensionality1, leading to an easier extension of the verification approach to newer architectures. + +# 4. Implementation + +In this section we describe our implementation of the proposed verification pipeline [13]. + +Encoding head. In terms of design choices, all common LVMs for data generation, including VAEs, Normalising Flows (NFs) and GANs, can be used in the pipeline if the following holds: + +- The FDN of the network to be verified can serve as the backbone of the LVM encoder (e.g., if the FDN involves a dimensionality change then NFs cannot serve as the LVM). +- The verification backend can verify the inverted encoding head of the pipeline. + +Given any LVM, $Z_{\mathrm{des}}$ is defined in the output space of the LVM encoding head in ways described in Section 3. A VAE fits the pipeline particularly well given the backing of the theoretical analysis in [34], and as it regularises the underlying latent space to resemble a prior. This prior (normal, von Mises-Fisher distribution in $\mathcal{N}$ -VAE [21], S-VAE [8] resp.) is light-tailed, so the latent space can be approximately bounded or truncated, and the epsilons in our specifications have bounded domain. Note that the latent variable $z$ in a VAE is not the output of the encoder but a random variable conditioned on its outputs $(\mu, \sigma \in \mathbb{R}^{\mathrm{latent.dim}})$ by reparameterisation [21]. Since reparameterisation cannot be inverted, $Z_{\mathrm{des}}$ is defined using the vector $[\mu, \sigma]$ instead of $z$ , albeit with no change in $Z_{\mathrm{des}}$ . + +In contrast, GANs do not use an encoder to learn a latent distribution and instead take a prior distribution as input. However, when using a GAN as the LVM, we still add an encoding head after the FDN to transform the unconstrained FDN output to a desired prior for the GAN and define input-parameterized local specifications. + +LVM design. As discussed previously, our pipeline features an encoding head after the FDN of the network to be analysed. Since the encoding head must not undergo dimensionality change, the dimension of the flattened FDN output is the dimension of the encoding head layers and the latent space where the input specification is defined. Typically, a shorter FDN implies larger latent space dimensionality and verification involves more network layers. + +We use two types of feed-forward encoding heads: one consists of pairs of an invertible activation and fully-connected (FC) layers; the other consists of alternating affine-coupling layers [9]. The former is easier to train and supported by most NN verifiers, but its invertibility to sufficient precision needs to be validated by checking the singular values of the individual layers' weight matrices. Affine-coupling layer is invertible-by-construction but not supported by standard NN verifiers. To support its verification, we replace its typically input dependent scaling and translation unit with an input independent learnt vector and an FC layer respectively. This modified affine-coupling layer is equivalent to an FC layer in expressiveness, but is + +more challenging to train. + +One can increase the encoding head depth with the pairs described above until the LVM is adequately trained; in our experience, a single layered encoding head sufficed for good reconstructions. The decoder is always a deep upscaling network mirroring the pipeline encoder. + +LVM training. In addition to the negative log likelihood or GAN loss, we conditionally train latent dimensions [5, 23] for Axis specifications. We use Cross-Entropy (CE) loss for discrete attributes. For instance, we train one dimension with binary CE loss so that $[0,1]$ for this dimension corresponds to variations from no attribute to complete attribute. Note that we cannot use the common conditional generation approach of augmenting encodings with attribute labels [31] because the entire encoding must be inferred from the FDN output for invertibility. Therefore, differently from usual practice, our VAEs for conditional generation do not take attributes as priors to condition on but rather learn them with supervision from data. + +Continuum in transformations is important when verifying against pose changes, which CE loss may not provide. Therefore, dimensions capturing continuous changes are trained as graphics code as per the procedure in [23]. + +Note that it may not be possible to train an LVM by adding an encoding head to the extreme end of every network, as network's task-agnostic information may be lost till that layer. However, if an LVM can be trained by adding an encoding head after the $K^{th}$ network layer, it is inexpensive to train a new LVM from after the $(K - k)^{th}, k > 0$ , layer, with the frozen original network. + +Datasets preparation. To train the LVMs for our experiments, we used public datasets with customdataloading to have attribute and transform labels for every input. We only used datasets for which realistic variations can be produced with labels, as it is required for conditional training and forming precise queries for pipeline evaluation (see Section 5.4). We worked with five datasets: CelebA [25], Traffic Signs Recognition (TSRD), 3D Objects (3DOD), (Fashion)MNIST [38]. For TSRD, we took traffic signs and city scene crops, apply planar (rotation, scale, photometric) and spatial (perspective) transformations on the former and blend them into the latter during dataloading. For 3DOD, we took 3D models from ModelNet10 dataset [37] and render their images from different distances, azimuth and elevation angles in Blender [6]. For all trainings, the dataset was balanced such that every class had adequate samples of the variation being verified against. + +# 5. Experimental Analysis + +We report on our experiments to validate the proposed approach, with focus on answering three key questions: + +Q1. Can an LVM added to a classifier generate an appropriate latent manifold and good reconstructions? + +Q2. Can the proposed pipeline efficiently verify deep networks? +Q3. Can the specifications, discussed in Section 3, encode intended input variations? + +To assess Q1, we refer to the reconstructions presented in Figure 2 and the low values of mean reconstruction error and FID score [18] reported in Table 1. To assess Q2, we refer to the verification outcomes for deep networks of different architectures reported in Sections 5.1, 5.2. To assess Q3, we refer to the values of metrics quantifying the precision of a specification in capturing intended variations, discussed in Section 5.4. With this overview, we now discuss the experiments in greater detail. + +# 5.1. Verifying segments joining input encodings + +To verify robustness against variations reflected in an image pair, we generated Segment specifications capturing object pose and viewpoint changes. For CelebA, we also verify specifications capturing the classifier's invariance to task-orthogonal attributes. These queries are similar to the queries in [27] which uses the EDN approach and reports successful deterministic verification of $23.8\%$ queries for a ConvMed model with 64k activations. Based on the classifier layer separating the FDN and task head, multiple verification pipelines were trained for each classifier. The verification outcomes for all queries and pipelines are reported in Table 1, from which the following observations can be drawn: + +- The mean reconstruction errors and FID scores for the multiple SRVP pipelines per classifier are low with consistent verification outcomes, indicating that latent spaces of a considerable range of dimensionality can be successfully learnt and verified against. +- The SRVP pipelines require an order of magnitude less time than the EDN pipelines to solve safe queries, and produce fewer trivial output bounds or undecided cases. This remains the case with the inclusion of more network layers in the verification path. +- The verified robust accuracy tightly lower bounds the adversarial accuracy computed against gradient-ascent-based latent space interpolation attacks [28]. + +# 5.2. Verifying along latent dimensions + +As discussed in Section 3, Axis specifications can be used to verify an input against the entire range of a task-orthogonal change (e.g., style, or pose). Figure 3 shows representative results for verifying these specifications where the local input set is increased for individual latent dimensions of an encoding. For many inputs, conditional dimensions were verifiably robust for almost their entire range, while dimensions without conditional training were found to be robust for much smaller epsilons. Decoded samples from latent dimensions in Figure 4 corroborate these + +outcomes. The object class change was not observed for all non-conditional dimensions, but conditional dimensions were more consistent in preserving the object class. However, with increase in latent dimensionality, as with a shorter FDN, it became harder to balance the conditional and standard LVM training to achieve both good reconstructions and distinct attribute changes with class consistency. This explains the reduced transform detections for higher dimensional manifolds reported in Figure 3. In Section 5.4, we present a validity metric to assess the success of conditional manifold training and in turn, derive expectation on the usefulness of Axis specifications defined in the manifold. + +![](images/1433487e700bfc05e973a71bb44f777d23bd0fad9ac7f8cda1b62ccc808a4c21.jpg) + +![](images/0ae5792338b1e49efed07ce0003867e1f56cc2d805d2014bc0649c4588cc6dad.jpg) +Figure 3. Both graphs show mean percentage of Axis queries verified as safe (out of 200 tested) for local intervals of $\pm \epsilon$ for LVMs of different latent dimensionality. The percentage of reconstructions of samples along the conditional axes, around the $\epsilon$ s reported on the x-axis, in which a learnt transform detector detects the intended transform, is also plotted. The axes were trained with (B)CE loss with 0,1 mapping to the base and the attribute added image resp. + +![](images/c81b55cfa9669c84d663e796bdf8ab6f3efe7cdd3a29cfbab0b65ea642205da1.jpg) +Figure 4. All images above are generated by an LVM from a single image per dataset. The columns feature samples along non-conditional dimensions, and each row has a constant conditional axis value which enforces rendering of the specified transform in all its reconstructions. + +In case of Region specifications, where the local ep + +
Dataset (size)Verifying inv. to *NetworkAccuracies*Pipeline**Verification outcomes (100 std.safe queries)Recons.outcomes
Std.Adv.Type #Ver.actv.layers (actvs.)Safe(s†)Unsafe(s)Undec.(s)Rob.accRMSSrr*FIDscore
Runs for efficiency comparison of EDNs (with decoders of different depths) vs. SRVPs (with encoding heads after different n/w layers).
CelebA64.2%EDtinyN-328 (5k)61 (6.8)39 (3.94)056%0.064218.61
65%EDdeepN-329 (27k)64 (22.3)29 (31.6)7 (64)59%0.053107.42
(64x64)ConvSmall (6k ReLUs)92%69%EDresnet18N-3211 (0.2M)042 (370)58 (802)0%0.05189.62
91%SRVP Lin1-321 (64)99 (0.4)1 (0.01)091%0.058114
89%SRVP Lin1-642 (192)94 (0.5)6 (0.02)085.5%0.042112
Head Flip (gender cla.)87%SRVP Lin1-1923 (576)88 (1.1)12 (0.08)081%0.035105
89%SRVP Lin1-3924 (1.3k)91 (2.7)9 (0.11)084%0.031102
74%EDtinyN-328 (86k)59 (32.8)41 (20)056.6%0.07264
81%EDdeepN-329 (0.1M)66 (35.3)22 (23.5)12 (64)63%0.06223
(128x128)ConvBig (72k ReLUs)96%77%EDresnet18N-3211 (475k)021 (410)79 (816)0%0.06124
93%SRVP Lin1-641 (64)95 (0.4)5 (0.07)091%0.23252
95%SRVP Lin1-1922 (256)96 (0.8)4 (0.09)092%0.15225
94%SRVP Lin1-3923 (648)96 (1.9)4 (0.11)092%0.04202
+ +
SRVP runs with encoding heads of different dimensions for different n/w architectures and datasets
(64x64)ResNet1884%82%SRVP Lin1-2561 (512)95 (2.6)5 (0.1)080%0.022104
TRDS (64x64)Planar Pose (sign cla.)ResNet1892.5%SRVP Lin1-2562 (1k)96 (2.1)4 (0.21)089%0.03116
89%SRVP Lin1-10242 (1.5k)94 (3.8)6 (0.46)087%0.03106
MobileNetv282%78%SRVP Lin1-6401 (640)93 (2.1)7 (0.42)076%0.09133
3DOD (64x64)Spatial Pose (obj cla.)ResNet1897%SRVP Lin1-2562 (1k)94 (1.9)6 (0.2)091%0.04106
90%SRVP Lin1-10242 (1.5k)92 (4.7)8 (0.45)089%0.0298
+ +* Std. and Adv. accuracy are the network's accuracy against clean, augmented data and latent-space PGD attacks [28] ( $\alpha = 2\mathrm{e} - 3$ , #iters=2000) resp. The PGD attacks are found for $N \circ d(z)$ in EDN pipelines and $e^{-1} \circ N_{\mathrm{head}}(z)$ in SRVP pipelines for $z \in Z_{\mathrm{segment}}$ . +** The suffixed integer in the pipeline type is the dimensionality of its latent space and is equal to its verification input. Higher dimensions for a SRVP pipeline for the same network indicate an earlier split and the inclusion of more layers in the verification path. +$\dagger$ Seconds (s) reported are the mean query solving time. All queries were run on a 24 core, 256GB CPU with timeout of 60 or 800 seconds. +$\star$ The reconstruction error is per-pixel for normalised float [-1,1] images. The FID score is computed by using pytorch-fid package [30]. +All pipelines for the same network were trained until comparable reconstruction outcomes, were tested for the same queries using the same backend and use $\mathcal{N}$ -VAE as the LVM so that all of them have an approximately normal latent manifold distribution. + +Table 1. Verification results for Segment queries; representative specification inputs for the above are shown in Figure 2b. + +silon ball is increased uniformly in all latent dimensions, we could verify robustness for a maximum $\epsilon = 0.01$ (for $< 10\%$ queries) for SRVP Lin-32 pipelines. + +# 5.3. Counterexamples analysis + +Counterexamples are instances of the input specification set that falsify the robustness property under investigation. In our approach, the verifier finds a latent space counterexample $z^{*} \in Z_{\mathrm{des}}$ for every unsafe query such that $N_{\mathrm{head}} \circ e^{-1}(z^{*})$ demonstrates non-robustness. However, since the LVM decoder is not the exact inverse of its encoder, the decoded counterexample could be spurious, i.e., $N \circ d(z^{*})$ may not be a counterexample. Therefore, we decode every $z^{*}$ and label it a valid counterexample iff its reconstruction is also a counterexample for the network. + +Similar to [16], in the case of a spurious counterexample $z^{*}$ , we run a local gradient search for a valid one, taking $z^{*}$ as the starting point. In comparison to starting from a mapped vector, this local gradient-based search around $z^{*}$ takes much fewer iterations to reach a valid counterexample in most cases, and results in high precision in finding valid and in-domain counterexamples (see Figure 5). + +![](images/6284998916bc17bf7e2e4aece6bc3d55c3093e03de0af06718daa4cf8c003e4b.jpg) +Figure 5. The table reports the mean ratios of valid counterexamples (ceg.) to all cegs found by SRVP pipelines for network $N_{\mathrm{head}} \circ e^{-1}$ through verification of 100 Segment queries, with and without PGD-based search in the second and third column resp. The full search and refinement iterations are median PGD iterations of step-size 1e-3 for success in the latent/attribute space attack [28] and in the local search for a valid ceg around a verification-returned spurious ceg resp. Rows in the figure below show reconstructions for some unsafe Segment and Axis queries with their valid cegs in the rightmost column. + +Male (Female) + +Chair (Table) + +No right + +(No U-turn) + +Old (Young) + +Change: Glasses + +Male (Female) + +Change:Gender + +# 5.4. Validating the LVM based pipeline + +Having assessed the capabilities of our approach in terms of scaling to deep networks and the fidelity of returned counterexamples, we now evaluate its precision in sufficiently capturing the intended variations in the proposed specifications. For this, we consider two latent space-based validity metrics as described below. + +The assumption behind Segment specifications is that the in-domain interpolations of an image pair map to the interpolations of its encoding pair. To validate this, we measure the distance of the encodings of the desired interpolations of an image pair to the path joining its encoding pair. In practice, for validating pose invariance queries, we generate images with varying extents of a transform, construct a path between the encodings of the image pair with the most extreme mutual transform, and compute the distance between the encodings of the intermediate transforms and their projection on this path. This distance is divided by square-root of latent dimensionality to generalise across manifolds of different dimensions. We compute this metric for the following pairs of encoding paths and VAE manifolds used in our pipelines, and report its mean value distribution below. + +1. Shortest Length Path (SLP) + untrained normal distribution manifold (baseline), +2. $\mathrm{SLP} + \mathcal{N}$ -VAE, +3. $\mathrm{SLP} + \mathcal{N}$ -VAE trained with a latent space-based cycle consistency loss that encourages its encoder-decoder to be an inverse pair, +4. Real-vs-fake discriminator-guided path $+\mathcal{N}$ -VAE. + +![](images/86dad0c44704e25fe40867b839d28ab5da2b911fe27bb7b29d90f6eac1e89d9f.jpg) +Normalised histogram of distances of intermediate transform encodings to $Z_{\mathrm{des}}$ , i.e., $\mathbf{d}(e(x_i), \text{proj}_{Z_{\mathrm{des}}} e(x_i)) / \sqrt{m}$ , $e(.) \in \mathbb{R}^m$ . + +In comparison to the primitive baseline, the metric values with $\mathcal{N}$ -VAEs are low for most queries as desired, and further reduce on incentivising consistency in their mappings, as in 3., and making the encoding traversals more precise and segmented, as in 4. Although we do not observe notable changes in the verification outcomes with different $\mathcal{N}$ -VAEs, this metric could be used to guide the construction of input specifications. Notice that this metric is the latent space-based analogue of the pixel space distance used to define input specifications and evaluate generators for EDN-based verification [20]. + +The motivation behind Axis specifications is the disen + +tanglement of conditional dimensions in capturing specified variations. To assess disentanglement, we compute the ratio of the highest value among the incorrect conditional dimensions to the value of the correct conditional dimension of an encoding for a discrete attribute. For the continuous transforms encoded as graphics code [23], an equivalent metric is the ratio of the maximum variance among the incorrect conditional dimensions to the variance in the correct conditional dimension, computed for a batch of encodings. Below we report the mean value distribution of this metric for normally and conditionally trained $\mathcal{N}$ -VAEs. As expected, conditional training results in low metric values as desired, while normal training results in similar values for most dimensions and metric values closer to unity. + +Normalised histogram of maximum incorrect-to-correct dimension ratios for conditionally trained LVMs. +![](images/03ff1b40bb2f46c75760f5af0c59b401f4cba20579025afe10c0d1a1075e8be8.jpg) +Numbers in the legend entries denote manifold dimensionality. + +These latent space-based metrics are more relevant to our approach than the pixel space-based or the attribute detection-based analyses relevant to the EDN approach. This is because the effectiveness of verification with our approach depends more on the spatial coherence and precision of the LVM encodings, than its reconstruction capabilities. + +# 6. Conclusions + +In this work we introduced an efficient and precise approach for verifying specifications in the latent space. By means of the proposed approach, we could effectively assess and verify deep networks against pose changes, and provide counterexamples that inform of their fragilities. + +In terms of limitations, we discussed that the ease of learning a conditional latent manifold, and the computational gains of our verification approach can be affected by the increase of layers in the network head of our pipeline. However, since the largest activation layers can be excluded from the verification path with our approach, it still fares better than the existing approach. A general limitation of latent-space based verification approaches is their necessity for an adequate LVM, which, as discussed for our approach, may require the original network to be trained as part of the proposed pipeline. While we did not find these limitations to hinder the application of our approach to the practical usecases demonstrated in this work, further experiments should be conducted to better assess its generality. + +# References + +[1] M. Akintunde, A. Lomuscio, L. Maganti, and E. Pirovano. Reachability analysis for neural agent-environment systems. In Proceedings of the 16th International Conference on Principles of Knowledge Representation and Reasoning (KR18), pages 184–193. AAAI Press, 2018. 1 +[2] M. Balunovic, M. Baader, G. Singh, T. Gehr, and M. Vechev. Certifying geometric robustness of neural networks. In Advances in Neural Information Processing Systems (NeurIPS19), pages 15313-15323. Curran Associates, Inc., 2019. 1, 2 +[3] B. Batten, P. Kouvaros, A. Lomuscio, and Y. Zheng. Efficient neural network verification via layer-based semidefinite relaxations and linear cuts. 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Seitzer. pytorch-fid: FID Score for PyTorch. github.com/mseitzer/pytorch-fid, August 2020. Version 0.2.1.7 +[31] K. Sohn, H. Lee, and X. Yan. Learning structured output representation using deep conditional generative models. In Proceedings of the 29th International Conference on Neural Information Processing Systems (NIPS15), volume 28. Curran Associates, Inc., 2015. 5 +[32] S. Wang, K. Pei, J. Whitehouse, J. Yang, and S. Jana. Formal security analysis of neural networks using symbolic intervals. In Proceedings of the 27th USENIX Security Symposium (USENIX18), 2018. 2 +[33] S. Wang, H. Zhang, K. Xu, X. Lin, S. Jana, C. Hsieh, and J. Kolter. Beta-crown: Efficient bound propagation with perneuron split constraints for complete and incomplete neural network verification. arXiv preprint arXiv:2103.06624, 2021. 2 +[34] E. Wong and J. Zico Kolter. Learning perturbation sets for robust machine learning. CoRR, abs/2007.08450, 2020. 1, 3, 5 +[35] E. Wong and Z. Kolter. Provable defenses against adversarial examples via the convex outer adversarial polytope. In Proceedings of the 35th International Conference on Machine Learning (ICML18), pages 5286-5295. PMLR, 2018. 1 +[36] E. Wong, F. Schmidt, and Z. Kolter. Wasserstein adversarial examples via projected Sinkhorn iterations. In Proceedings of the 36th International Conference on Machine Learning, volume 97, pages 6808-6817. PMLR, 2019. 2 +[37] Z. Wu, S. Song, A. Khosla, F. Yu, L. Zhang, X. Tang, and J. Xiao. 3d shapenets: A deep representation for volumetric shapes. In IEEE/CVF Conference on Computer Vision and Pattern Recognition (CVPR15), pages 1912-1920. IEEE Computer Society, 2015. 5 +[38] H. Xiao, K. Rasul, and R. Vollgraf. Fashion-mnist: a novel image dataset for benchmarking machine learning algorithms. CoRR, abs/1708.07747, 2017. 5 +[39] H. Zhang, P. Zhang, and C. Hsieh. Recurjac: An efficient recursive algorithm for bounding jacobian matrix of neural networks and its applications. Proceedings of the AAAI Conference on Artificial Intelligence (AAAI19), 33(01):5757-5764, Jul. 2019. 2 \ No newline at end of file diff --git a/2023/Efficient Verification of Neural Networks Against LVM-Based Specifications/images.zip b/2023/Efficient Verification of Neural Networks Against LVM-Based Specifications/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..1d5aada04e157fc6c552b10abe73516d37b1f875 --- /dev/null +++ b/2023/Efficient Verification of Neural Networks Against LVM-Based Specifications/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:3fbd6cbc5c4cedd1eef7eaba0ed75256deed455b3aed9c8a5f8c3daa877ef815 +size 549559 diff --git a/2023/Efficient Verification of Neural Networks Against LVM-Based Specifications/layout.json b/2023/Efficient Verification of Neural Networks Against LVM-Based Specifications/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..db04e60249ada96c6f35b1f957cbcb8071919f5a --- /dev/null +++ b/2023/Efficient Verification of Neural Networks Against LVM-Based Specifications/layout.json @@ -0,0 +1,9103 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 65, + 102, + 529, + 121 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 102, + 529, + 121 + ], + "spans": [ + { + "bbox": [ + 65, + 102, + 529, + 121 + ], + "type": "text", + "content": "Efficient Verification of Neural Networks against LVM-based Specifications" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 97, + 144, + 317, + 185 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 97, + 144, + 317, + 185 + ], + "spans": [ + { + "bbox": [ + 97, + 144, + 317, + 185 + ], + "type": "text", + "content": "Harleen Hanspal \nImperial College London & Safe Intelligence \nLondon, United Kingdom" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 135, + 188, + 279, + 198 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 135, + 188, + 279, + 198 + ], + "spans": [ + { + "bbox": [ + 135, + 188, + 279, + 198 + ], + "type": "text", + "content": "h.hanspal21@imperial.ac.uk" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 361, + 144, + 484, + 185 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 361, + 144, + 484, + 185 + ], + "spans": [ + { + "bbox": [ + 361, + 144, + 484, + 185 + ], + "type": "text", + "content": "Alessio Lomuscio \nSafe Intelligence \nLondon, United Kingdom" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 345, + 188, + 492, + 198 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 345, + 188, + 492, + 198 + ], + "spans": [ + { + "bbox": [ + 345, + 188, + 492, + 198 + ], + "type": "text", + "content": "alessio@safeintelligence.ai" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 143, + 227, + 192, + 239 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 227, + 192, + 239 + ], + "spans": [ + { + "bbox": [ + 143, + 227, + 192, + 239 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 251, + 290, + 502 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 251, + 290, + 502 + ], + "spans": [ + { + "bbox": [ + 46, + 251, + 290, + 502 + ], + "type": "text", + "content": "The deployment of perception systems based on neural networks in safety critical applications requires assurance on their robustness. Deterministic guarantees on network robustness require formal verification. Standard approaches for verifying robustness analyse invariance to analytically defined transformations, but not the diverse and ubiquitous changes involving object pose, scene viewpoint, occlusions, etc. To this end, we present an efficient approach for verifying specifications definable using Latent Variable Models that capture such diverse changes. The approach involves adding an invertible encoding head to the network to be verified, enabling the verification of latent space sets with minimal reconstruction overhead. We report verification experiments for three classes of proposed latent space specifications, each capturing different types of realistic input variations. Differently from previous work in this area, the proposed approach is relatively independent of input dimensionality and scales to a broad class of deep networks and real-world datasets by mitigating the inefficiency and decoder expressivity dependence in the present state-of-the-art." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 525, + 128, + 538 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 525, + 128, + 538 + ], + "spans": [ + { + "bbox": [ + 47, + 525, + 128, + 538 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 545, + 287, + 677 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 545, + 287, + 677 + ], + "spans": [ + { + "bbox": [ + 46, + 545, + 287, + 677 + ], + "type": "text", + "content": "The deployment of perception systems based on neural networks in safety-critical applications requires assurance on their performance, notably accuracy and robustness. Formal verification contributes to this requirement by providing provable and deterministic guarantees that a network meets a given specification. Typically, specifications are mathematically expressed constraints on the network's intended input/output and may encode desirable properties, such as robustness to noise (including adversarial attacks) [35], geometric changes [1,2], bias-field changes [14] and beyond." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "text", + "content": "While the above is useful, practical applications require robustness against diverse changes in a scene, including changes in the pose of objects, viewpoints, occlusions, etc." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 228, + 547, + 360 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 228, + 547, + 360 + ], + "spans": [ + { + "bbox": [ + 304, + 228, + 547, + 360 + ], + "type": "text", + "content": "Such changes cannot be efficiently mathematically defined, but may be encoded from data by using generative models. For instance, [11, 12, 28, 34] use generative models to generate novel in-domain images for data augmentation, adversarial training or evaluating network generalisation; [34] additionally derives formal conditions for a latent space set to necessarily contain sufficient perturbations for it to be trusted for adversarial training and robustness checks. All these approaches either provide statistical robustness measures, or generate attacks based on gradient-search, which is not guaranteed to find an attack if one exists." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 361, + 547, + 552 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 361, + 547, + 552 + ], + "spans": [ + { + "bbox": [ + 304, + 361, + 547, + 552 + ], + "type": "text", + "content": "Popular for network robustification and empirical evaluation, latent space sets are seldom used as inputs for verification due to the valid concern over the lack of mathematical guarantees on the completeness of the specifications they encode. Therefore, we reiterate that this work is most useful for changes that are difficult to mathematically define. We additionally argue that formal verification of latent space-based specifications can be more valuable than their empirical evaluation. This is because the latent space is a continuous domain and countably infinite number of inputs can be mapped to and reconstructed from a latent space set. Therefore, no amount of testing, or search in the latent space can provide guarantees against all the variations encoded in it. To the best of our knowledge, only [20, 27] encode specifications in a latent space and propose architectures to verify them." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 554, + 547, + 639 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 554, + 547, + 639 + ], + "spans": [ + { + "bbox": [ + 304, + 554, + 547, + 639 + ], + "type": "text", + "content": "There are, however, two difficulties with verification in the latent space. The first concerns the scalability of verification methods; the second relates to the quality of reconstructions affecting the verification outcomes. In this paper, we focus on alleviating these two concerns. Specifically, we propose a novel, invertible encoder-based pipeline for verifying latent space sets, that lends two key benefits of:" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 640, + 545, + 688 + ], + "type": "list", + "angle": 0, + "index": 17, + "blocks": [ + { + "bbox": [ + 306, + 640, + 545, + 663 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 640, + 545, + 663 + ], + "spans": [ + { + "bbox": [ + 306, + 640, + 545, + 663 + ], + "type": "text", + "content": "- Computational efficiency and relative independence to input dimensionality," + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 306, + 664, + 544, + 688 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 664, + 544, + 688 + ], + "spans": [ + { + "bbox": [ + 306, + 664, + 544, + 688 + ], + "type": "text", + "content": "- Verification outcomes' independence to reconstructions, and precise counterexamples with high recall." + } + ] + } + ], + "index": 16 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "text", + "content": "We focus our analysis on pose and attribute variations in vision inference tasks, but the approach is likely extendable" + } + ] + } + ], + "index": 18 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "3894" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 120 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 120 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 120 + ], + "type": "text", + "content": "to other variations, domains and tasks. Next, we recall key notions for network verification and discuss the existing relevant work, before presenting and validating our method in subsequent sections." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 131, + 222, + 144 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 131, + 222, + 144 + ], + "spans": [ + { + "bbox": [ + 47, + 131, + 222, + 144 + ], + "type": "text", + "content": "2. Background and Related Work" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 152, + 287, + 198 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 152, + 287, + 198 + ], + "spans": [ + { + "bbox": [ + 46, + 152, + 287, + 198 + ], + "type": "text", + "content": "Neural network verification. Given a network " + }, + { + "bbox": [ + 46, + 152, + 287, + 198 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 152, + 287, + 198 + ], + "type": "text", + "content": " and an input-output specification " + }, + { + "bbox": [ + 46, + 152, + 287, + 198 + ], + "type": "inline_equation", + "content": "(X_{\\mathrm{des}},Y_{\\mathrm{des}})" + }, + { + "bbox": [ + 46, + 152, + 287, + 198 + ], + "type": "text", + "content": ", the network verification problem is the decision problem of determining whether" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 116, + 201, + 218, + 213 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 116, + 201, + 218, + 213 + ], + "spans": [ + { + "bbox": [ + 116, + 201, + 218, + 213 + ], + "type": "interline_equation", + "content": "N (x) \\in Y _ {\\mathrm {d e s}}, \\forall x \\in X _ {\\mathrm {d e s}}.", + "image_path": "9c096937e700c9718b6692458d0041b3640e405a5860aeb9fb150c3fb892965c.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 217, + 287, + 288 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 217, + 287, + 288 + ], + "spans": [ + { + "bbox": [ + 46, + 217, + 287, + 288 + ], + "type": "text", + "content": "Verification methods, such as those based on SMT [19], MILP [4, 10, 22], Interval Propagation [15, 16, 32, 33], SDP [3, 29] or Lipschitz analysis [39], propagate a set " + }, + { + "bbox": [ + 46, + 217, + 287, + 288 + ], + "type": "inline_equation", + "content": "X_{\\mathrm{des}}" + }, + { + "bbox": [ + 46, + 217, + 287, + 288 + ], + "type": "text", + "content": " in a single forward pass through " + }, + { + "bbox": [ + 46, + 217, + 287, + 288 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 217, + 287, + 288 + ], + "type": "text", + "content": " and determine whether or not the output set of " + }, + { + "bbox": [ + 46, + 217, + 287, + 288 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 217, + 287, + 288 + ], + "type": "text", + "content": " for " + }, + { + "bbox": [ + 46, + 217, + 287, + 288 + ], + "type": "inline_equation", + "content": "X_{\\mathrm{des}}" + }, + { + "bbox": [ + 46, + 217, + 287, + 288 + ], + "type": "text", + "content": " lies in " + }, + { + "bbox": [ + 46, + 217, + 287, + 288 + ], + "type": "inline_equation", + "content": "Y_{\\mathrm{des}}" + }, + { + "bbox": [ + 46, + 217, + 287, + 288 + ], + "type": "text", + "content": ". These methods mostly support input specifications defined in:" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 48, + 289, + 287, + 445 + ], + "type": "list", + "angle": 0, + "index": 7, + "blocks": [ + { + "bbox": [ + 48, + 289, + 287, + 361 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 289, + 287, + 361 + ], + "spans": [ + { + "bbox": [ + 48, + 289, + 287, + 361 + ], + "type": "text", + "content": "- Data space, such that " + }, + { + "bbox": [ + 48, + 289, + 287, + 361 + ], + "type": "inline_equation", + "content": "X_{\\mathrm{des}}" + }, + { + "bbox": [ + 48, + 289, + 287, + 361 + ], + "type": "text", + "content": " is a norm ball around an input " + }, + { + "bbox": [ + 48, + 289, + 287, + 361 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 48, + 289, + 287, + 361 + ], + "type": "text", + "content": ", i.e., " + }, + { + "bbox": [ + 48, + 289, + 287, + 361 + ], + "type": "inline_equation", + "content": "\\mathcal{B}_{\\epsilon}(x) = \\{x' \\mid \\| x' - x \\| < \\epsilon\\}" + }, + { + "bbox": [ + 48, + 289, + 287, + 361 + ], + "type": "text", + "content": ". The norm is defined in metric spaces such as " + }, + { + "bbox": [ + 48, + 289, + 287, + 361 + ], + "type": "inline_equation", + "content": "\\ell_p" + }, + { + "bbox": [ + 48, + 289, + 287, + 361 + ], + "type": "text", + "content": " [2,16,19] or Wasserstein [36], and the " + }, + { + "bbox": [ + 48, + 289, + 287, + 361 + ], + "type": "inline_equation", + "content": "\\epsilon" + }, + { + "bbox": [ + 48, + 289, + 287, + 361 + ], + "type": "text", + "content": " is adequately set to include intended photometric and geometric variations, albeit along with considerable unrealistic instances in case of large variations." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 48, + 361, + 287, + 445 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 361, + 287, + 445 + ], + "spans": [ + { + "bbox": [ + 48, + 361, + 287, + 445 + ], + "type": "text", + "content": "- Parameter space, such that, given an input " + }, + { + "bbox": [ + 48, + 361, + 287, + 445 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 48, + 361, + 287, + 445 + ], + "type": "text", + "content": " and a set of transformations " + }, + { + "bbox": [ + 48, + 361, + 287, + 445 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 48, + 361, + 287, + 445 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 48, + 361, + 287, + 445 + ], + "type": "inline_equation", + "content": "X_{\\mathrm{des}}" + }, + { + "bbox": [ + 48, + 361, + 287, + 445 + ], + "type": "text", + "content": " is defined by prepending parametric transform layers " + }, + { + "bbox": [ + 48, + 361, + 287, + 445 + ], + "type": "inline_equation", + "content": "N_T(\\alpha)" + }, + { + "bbox": [ + 48, + 361, + 287, + 445 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 48, + 361, + 287, + 445 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 48, + 361, + 287, + 445 + ], + "type": "text", + "content": " determines the transformation extent, to the network; " + }, + { + "bbox": [ + 48, + 361, + 287, + 445 + ], + "type": "inline_equation", + "content": "X_{\\mathrm{des}} = N_T(\\alpha)(x)" + }, + { + "bbox": [ + 48, + 361, + 287, + 445 + ], + "type": "text", + "content": ". This definition is more precise in capturing planar geometric changes [26] and photometric changes, such as smooth illumination variations [14], in an input." + } + ] + } + ], + "index": 6 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 46, + 446, + 287, + 469 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 446, + 287, + 469 + ], + "spans": [ + { + "bbox": [ + 46, + 446, + 287, + 469 + ], + "type": "text", + "content": "While these specifications are important, they do not efficiently capture non-planar and semantic transformations." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 470, + 287, + 577 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 470, + 287, + 577 + ], + "spans": [ + { + "bbox": [ + 46, + 470, + 287, + 577 + ], + "type": "text", + "content": "LVM-based specifications. Latent Variable Models (LVMs) for data generation map a typically lower-dimensional, continuous latent distribution to the input space. This mapping and its converse is learnt by LVM's decoder-encoder pair. Additionally, conditional training can disentangle latent dimensions to precisely capture specific dataset features and variations [5, 7, 23]. We refer to specifications which use LVM encoders to map input variations and define query input sets as LVM-based specifications." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 578, + 287, + 661 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 578, + 287, + 661 + ], + "spans": [ + { + "bbox": [ + 46, + 578, + 287, + 661 + ], + "type": "text", + "content": "Related work. As mentioned in Section 1, most formal verification approaches do not use generative models. Only [20, 27] use an autoencoder in a verification setup to prove whether or not the output of a network " + }, + { + "bbox": [ + 46, + 578, + 287, + 661 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 578, + 287, + 661 + ], + "type": "text", + "content": " is consistent for the image set produced by an independent autoencoder " + }, + { + "bbox": [ + 46, + 578, + 287, + 661 + ], + "type": "inline_equation", + "content": "(e,d)" + }, + { + "bbox": [ + 46, + 578, + 287, + 661 + ], + "type": "text", + "content": " from the interpolations in its latent space. Formally, [27] establishes whether" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 67, + 669, + 266, + 682 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 67, + 669, + 266, + 682 + ], + "spans": [ + { + "bbox": [ + 67, + 669, + 266, + 682 + ], + "type": "interline_equation", + "content": "(N \\circ d) \\circ e (x) \\in Y _ {\\mathrm {d e s}}, \\forall x \\in \\{X \\mid e (X) \\in Z _ {\\mathrm {d e s}} \\},", + "image_path": "069183b4fb28160265bacfb6d45aefeb0d4a6dcd339589243609f2dfb3e14975.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "inline_equation", + "content": "Z_{\\mathrm{des}} \\in \\mathbb{R}^{\\mathrm{latent\\_dim}}" + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "content": " is a segment joining latent encodings of samples in " + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "inline_equation", + "content": "X_{\\mathrm{des}}" + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "content": ". Since propagating " + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "inline_equation", + "content": "Z_{\\mathrm{des}}" + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "content": " through" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 72, + 545, + 156 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 156 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 156 + ], + "type": "text", + "content": "a useful decoder is computationally expensive, deterministic verification using this approach is reported to not scale beyond small networks. To overcome this, the authors a) heuristically subsume and approximate line segments by axes-aligned boxes, and b) turn specifications into probabilistic statements that determine whether a vector sampled uniformly from " + }, + { + "bbox": [ + 304, + 72, + 545, + 156 + ], + "type": "inline_equation", + "content": "Z_{\\mathrm{des}}" + }, + { + "bbox": [ + 304, + 72, + 545, + 156 + ], + "type": "text", + "content": " generates a correctly classified image." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 157, + 545, + 216 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 157, + 545, + 216 + ], + "spans": [ + { + "bbox": [ + 304, + 157, + 545, + 216 + ], + "type": "text", + "content": "The general approach of prepending a generative model as an independent input set generator for verifying a network, which we henceforth refer to as the Encoder-Decoder-Network (EDN) approach, suffers from the following limitations:" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 308, + 217, + 545, + 399 + ], + "type": "list", + "angle": 0, + "index": 18, + "blocks": [ + { + "bbox": [ + 309, + 217, + 545, + 266 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 309, + 217, + 545, + 266 + ], + "spans": [ + { + "bbox": [ + 309, + 217, + 545, + 266 + ], + "type": "text", + "content": "1. The network is verified only against images appropriately mapped by the encoder, but the encoding could be loose " + }, + { + "bbox": [ + 309, + 217, + 545, + 266 + ], + "type": "inline_equation", + "content": "(z \\in Z_{\\mathrm{des}} \\Rightarrow e^{-1}(z) \\in X_{\\mathrm{des}})" + }, + { + "bbox": [ + 309, + 217, + 545, + 266 + ], + "type": "text", + "content": " and incomplete " + }, + { + "bbox": [ + 309, + 217, + 545, + 266 + ], + "type": "inline_equation", + "content": "(x \\in X_{\\mathrm{des}} \\Rightarrow e(x) \\in Z_{\\mathrm{des}})" + }, + { + "bbox": [ + 309, + 217, + 545, + 266 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 309, + 266, + 545, + 361 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 309, + 266, + 545, + 361 + ], + "spans": [ + { + "bbox": [ + 309, + 266, + 545, + 361 + ], + "type": "text", + "content": "2. The network is verified against reconstructions of the decoder which may not have the same quality as the dataset images in terms of sharpness and diversity. If the decoder does not reconstruct an intended attribute's variations, either because all variations of that attribute are encoded to the same latent vector, or because it is not expressive enough, verification may incorrectly suggest that the network is invariant to that attribute." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 308, + 363, + 545, + 399 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 363, + 545, + 399 + ], + "spans": [ + { + "bbox": [ + 308, + 363, + 545, + 399 + ], + "type": "text", + "content": "3. The input set " + }, + { + "bbox": [ + 308, + 363, + 545, + 399 + ], + "type": "inline_equation", + "content": "Z_{\\mathrm{des}}" + }, + { + "bbox": [ + 308, + 363, + 545, + 399 + ], + "type": "text", + "content": " is propagated through both the decoder and the network to be verified, thereby resulting in considerable computational cost." + } + ] + } + ], + "index": 17 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 304, + 399, + 545, + 483 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 399, + 545, + 483 + ], + "spans": [ + { + "bbox": [ + 304, + 399, + 545, + 483 + ], + "type": "text", + "content": "In the rest of the paper, we propose a pipeline for verifying LVM-based specifications in a computationally lighter manner, and alleviate the last two shortcomings by construction. We do not solve the first limitation; but in Section 5.4, we present metrics to quantify the precision of the proposed specifications in terms of how well they capture the desired variations." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 305, + 497, + 509, + 510 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 497, + 509, + 510 + ], + "spans": [ + { + "bbox": [ + 305, + 497, + 509, + 510 + ], + "type": "text", + "content": "3. Efficient Verification in Latent Space" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 304, + 518, + 545, + 601 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 518, + 545, + 601 + ], + "spans": [ + { + "bbox": [ + 304, + 518, + 545, + 601 + ], + "type": "text", + "content": "In this section we present an efficient approach to verify the robustness of neural networks against specifications capturing diverse and realistic input variations. Formally, given a network " + }, + { + "bbox": [ + 304, + 518, + 545, + 601 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 304, + 518, + 545, + 601 + ], + "type": "text", + "content": " and a variation " + }, + { + "bbox": [ + 304, + 518, + 545, + 601 + ], + "type": "inline_equation", + "content": "v" + }, + { + "bbox": [ + 304, + 518, + 545, + 601 + ], + "type": "text", + "content": ", we define the Semantic Verification Problem (SVP) as the network verification problem where " + }, + { + "bbox": [ + 304, + 518, + 545, + 601 + ], + "type": "inline_equation", + "content": "X_{\\mathrm{des}}" + }, + { + "bbox": [ + 304, + 518, + 545, + 601 + ], + "type": "text", + "content": " is the preimage of a set " + }, + { + "bbox": [ + 304, + 518, + 545, + 601 + ], + "type": "inline_equation", + "content": "Z_{\\mathrm{des}}" + }, + { + "bbox": [ + 304, + 518, + 545, + 601 + ], + "type": "text", + "content": " under a partially invertible encoder " + }, + { + "bbox": [ + 304, + 518, + 545, + 601 + ], + "type": "inline_equation", + "content": "e" + }, + { + "bbox": [ + 304, + 518, + 545, + 601 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 343, + 609, + 506, + 621 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 343, + 609, + 506, + 621 + ], + "spans": [ + { + "bbox": [ + 343, + 609, + 506, + 621 + ], + "type": "interline_equation", + "content": "N (x) \\in Y _ {\\mathrm {d e s}}, \\forall x \\in \\{X \\mid e (X) = Z _ {\\mathrm {d e s}} \\}.", + "image_path": "61cb187e7f0f3a6a67b667aab18e4c9a19ab03a817841df6b98a0053af5bb4b2.jpg" + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 304, + 629, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 629, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 629, + 545, + 713 + ], + "type": "text", + "content": "Here, " + }, + { + "bbox": [ + 304, + 629, + 545, + 713 + ], + "type": "inline_equation", + "content": "Z_{\\mathrm{des}}" + }, + { + "bbox": [ + 304, + 629, + 545, + 713 + ], + "type": "text", + "content": " is a set in the encoder's output space that captures " + }, + { + "bbox": [ + 304, + 629, + 545, + 713 + ], + "type": "inline_equation", + "content": "v" + }, + { + "bbox": [ + 304, + 629, + 545, + 713 + ], + "type": "text", + "content": " and the input-output specification set is " + }, + { + "bbox": [ + 304, + 629, + 545, + 713 + ], + "type": "inline_equation", + "content": "(Z_{\\mathrm{des}}, Y_{\\mathrm{des}})" + }, + { + "bbox": [ + 304, + 629, + 545, + 713 + ], + "type": "text", + "content": ". In the following, we study the Semantic Robustness Verification Problem (SRVP), which is an instance of SVP that checks for network robustness, i.e., " + }, + { + "bbox": [ + 304, + 629, + 545, + 713 + ], + "type": "inline_equation", + "content": "Y_{\\mathrm{des}}" + }, + { + "bbox": [ + 304, + 629, + 545, + 713 + ], + "type": "text", + "content": " is a singleton. To solve SRVP, we propose the multi-head architecture shown in Figure 1." + } + ] + } + ], + "index": 23 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "3895" + } + ] + } + ], + "index": 24 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 49, + 69, + 298, + 202 + ], + "blocks": [ + { + "bbox": [ + 49, + 69, + 298, + 202 + ], + "lines": [ + { + "bbox": [ + 49, + 69, + 298, + 202 + ], + "spans": [ + { + "bbox": [ + 49, + 69, + 298, + 202 + ], + "type": "image", + "image_path": "2b0f102aa84cb435a76a7f512d541566301ed3768cb68d0f83c13f67b173657c.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 210, + 288, + 266 + ], + "lines": [ + { + "bbox": [ + 46, + 210, + 288, + 266 + ], + "spans": [ + { + "bbox": [ + 46, + 210, + 288, + 266 + ], + "type": "text", + "content": "Figure 1. The proposed pipeline consists of an LVM, built around the network to be verified, that takes the network's intermediate features as its input. The LVM encoder is invertible and maps its input feature set to a spatially coherent latent manifold, where the input specification is defined." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 279, + 287, + 411 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 279, + 287, + 411 + ], + "spans": [ + { + "bbox": [ + 46, + 279, + 287, + 411 + ], + "type": "text", + "content": "Verification pipeline. The network " + }, + { + "bbox": [ + 46, + 279, + 287, + 411 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 279, + 287, + 411 + ], + "type": "text", + "content": " to be verified is divided into a Feature Detection Network (FDN), consisting of " + }, + { + "bbox": [ + 46, + 279, + 287, + 411 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 279, + 287, + 411 + ], + "type": "text", + "content": "'s initial layers, and a task head, e.g., a classification or regression head. In our implementation, " + }, + { + "bbox": [ + 46, + 279, + 287, + 411 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 279, + 287, + 411 + ], + "type": "text", + "content": " is a classifier, but the approach applies similarly for other learning tasks. To define the specification, we add an LVM after the FDN. The encoder of this LVM is invertible and maps the intermediate features, output by FDN, to its latent space where the input specification is defined. Unlike the feature space, this latent space is queryable by using the decoder and can be made approximately bounded." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 412, + 287, + 484 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 412, + 287, + 484 + ], + "spans": [ + { + "bbox": [ + 46, + 412, + 287, + 484 + ], + "type": "text", + "content": "The verification path with this pipeline is limited to the inverse of LVM's encoding head and " + }, + { + "bbox": [ + 46, + 412, + 287, + 484 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 412, + 287, + 484 + ], + "type": "text", + "content": "'s task head (green region in Figure 1). Differently from previous work, the decoder here is only used for training the LVM and as a counterexample generator to provide semantically meaningful counterexamples when verification outcomes are negative." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 484, + 287, + 592 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 484, + 287, + 592 + ], + "spans": [ + { + "bbox": [ + 46, + 484, + 287, + 592 + ], + "type": "text", + "content": "Specification inputs in latent space. We consider specifications focused on encoding the network's invariance to changes in an object-of-interest in the input. These changes include non-planar transformations, specific semantic changes of the object or its arbitrary task-orthogonal variations commonly occurring in the dataset. The learning tasks and datasets where the objects-of-interest and their variations are discernible against unimportant content in the input are well suited for such specifications." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 593, + 287, + 616 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 593, + 287, + 616 + ], + "spans": [ + { + "bbox": [ + 47, + 593, + 287, + 616 + ], + "type": "text", + "content": "We now describe the definitions we consider for the local latent space set " + }, + { + "bbox": [ + 47, + 593, + 287, + 616 + ], + "type": "inline_equation", + "content": "Z_{\\mathrm{des}}" + }, + { + "bbox": [ + 47, + 593, + 287, + 616 + ], + "type": "text", + "content": " against which the network is verified." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 53, + 618, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 618, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 53, + 618, + 288, + 714 + ], + "type": "text", + "content": "- Segment. We define " + }, + { + "bbox": [ + 53, + 618, + 288, + 714 + ], + "type": "inline_equation", + "content": "Z_{\\mathrm{des}}" + }, + { + "bbox": [ + 53, + 618, + 288, + 714 + ], + "type": "text", + "content": " to be a path connecting the encodings of two images " + }, + { + "bbox": [ + 53, + 618, + 288, + 714 + ], + "type": "inline_equation", + "content": "\\{x_1, x_2\\}" + }, + { + "bbox": [ + 53, + 618, + 288, + 714 + ], + "type": "text", + "content": " that differ in the intended attributes or transforms (e.g., images of an object with different poses or backgrounds). Multiple definitions for " + }, + { + "bbox": [ + 53, + 618, + 288, + 714 + ], + "type": "inline_equation", + "content": "Z_{\\mathrm{des}}" + }, + { + "bbox": [ + 53, + 618, + 288, + 714 + ], + "type": "text", + "content": " are possible based on the traversal between the pair encodings, such as the maximum likelihood-based traversal [24], splines using multiple intermediate encodings, etc. With the Shortest Length Path" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 321, + 72, + 381, + 84 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 321, + 72, + 381, + 84 + ], + "spans": [ + { + "bbox": [ + 321, + 72, + 381, + 84 + ], + "type": "text", + "content": "(SLP), we get" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 324, + 87, + 541, + 102 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 324, + 87, + 541, + 102 + ], + "spans": [ + { + "bbox": [ + 324, + 87, + 541, + 102 + ], + "type": "interline_equation", + "content": "Z _ {\\mathrm {d e s}} = e \\left(x _ {1}\\right) + \\alpha \\left(e \\left(x _ {2}\\right) - e \\left(x _ {1}\\right)\\right), \\alpha \\in [ 0, 1 ] ^ {\\text {l a t e n t , d i m}}.", + "image_path": "3dc3a9c35cfed00bf2d0194a4029b2c4b74817f59319aff32408941644aa79e2.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 321, + 105, + 545, + 140 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 321, + 105, + 545, + 140 + ], + "spans": [ + { + "bbox": [ + 321, + 105, + 545, + 140 + ], + "type": "text", + "content": "This " + }, + { + "bbox": [ + 321, + 105, + 545, + 140 + ], + "type": "inline_equation", + "content": "Z_{\\mathrm{des}}" + }, + { + "bbox": [ + 321, + 105, + 545, + 140 + ], + "type": "text", + "content": " is highly expressive since, in general, the image pair can be of any two images whose semantic interpolations should be consistently predicted by a network." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 312, + 142, + 545, + 201 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 142, + 545, + 201 + ], + "spans": [ + { + "bbox": [ + 312, + 142, + 545, + 201 + ], + "type": "text", + "content": "- Axis. We define " + }, + { + "bbox": [ + 312, + 142, + 545, + 201 + ], + "type": "inline_equation", + "content": "Z_{\\mathrm{des}}" + }, + { + "bbox": [ + 312, + 142, + 545, + 201 + ], + "type": "text", + "content": " to be the set generated by varying an encoding's disentangled dimensions, such as those trained to capture variations of a specific attribute or a single degree of freedom for pose change. For example, we may consider" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 321, + 205, + 545, + 220 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 321, + 205, + 545, + 220 + ], + "spans": [ + { + "bbox": [ + 321, + 205, + 545, + 220 + ], + "type": "interline_equation", + "content": "Z _ {\\mathrm {d e s}} = \\left[ \\max \\{z _ {\\mathrm {l}}, e (x) _ {i} - \\epsilon \\}, \\min \\{e (x) _ {i} + \\epsilon , z _ {\\mathrm {u}} \\} \\right], i \\in I _ {C}", + "image_path": "86d1299e9d96617dd52c1c33b53298cea6e18b370a41d8f82620ce1372831f77.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 320, + 221, + 545, + 258 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 320, + 221, + 545, + 258 + ], + "spans": [ + { + "bbox": [ + 320, + 221, + 545, + 258 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 320, + 221, + 545, + 258 + ], + "type": "inline_equation", + "content": "I_{C}" + }, + { + "bbox": [ + 320, + 221, + 545, + 258 + ], + "type": "text", + "content": " is the set of conditional dimension indices and " + }, + { + "bbox": [ + 320, + 221, + 545, + 258 + ], + "type": "inline_equation", + "content": "[z_{\\mathrm{l}}, z_{\\mathrm{u}}]" + }, + { + "bbox": [ + 320, + 221, + 545, + 258 + ], + "type": "text", + "content": " are the limits containing a significant percentile of the distribution along these dimensions." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 320, + 258, + 545, + 305 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 320, + 258, + 545, + 305 + ], + "spans": [ + { + "bbox": [ + 320, + 258, + 545, + 305 + ], + "type": "text", + "content": "Given conditional training, this " + }, + { + "bbox": [ + 320, + 258, + 545, + 305 + ], + "type": "inline_equation", + "content": "Z_{\\mathrm{des}}" + }, + { + "bbox": [ + 320, + 258, + 545, + 305 + ], + "type": "text", + "content": " can capture all variations of an image generated by an attribute or transform change, even when this image has no similar variations present in the dataset." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 312, + 307, + 545, + 354 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 307, + 545, + 354 + ], + "spans": [ + { + "bbox": [ + 312, + 307, + 545, + 354 + ], + "type": "text", + "content": "- Region. We define " + }, + { + "bbox": [ + 312, + 307, + 545, + 354 + ], + "type": "inline_equation", + "content": "Z_{\\mathrm{des}}" + }, + { + "bbox": [ + 312, + 307, + 545, + 354 + ], + "type": "text", + "content": " as a " + }, + { + "bbox": [ + 312, + 307, + 545, + 354 + ], + "type": "inline_equation", + "content": "\\ell_{\\infty}" + }, + { + "bbox": [ + 312, + 307, + 545, + 354 + ], + "type": "text", + "content": "-norm ball around an image encoding, i.e., " + }, + { + "bbox": [ + 312, + 307, + 545, + 354 + ], + "type": "inline_equation", + "content": "\\mathcal{B}_{\\epsilon}(z) = \\{z' \\mid ||z' - e(x)||_{\\infty} < \\epsilon \\}" + }, + { + "bbox": [ + 312, + 307, + 545, + 354 + ], + "type": "text", + "content": ". Given a spatially coherent manifold, " + }, + { + "bbox": [ + 312, + 307, + 545, + 354 + ], + "type": "inline_equation", + "content": "Z_{\\mathrm{des}}" + }, + { + "bbox": [ + 312, + 307, + 545, + 354 + ], + "type": "text", + "content": " should capture the commonly occurring variations of an image." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 354, + 545, + 366 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 354, + 545, + 366 + ], + "spans": [ + { + "bbox": [ + 306, + 354, + 545, + 366 + ], + "type": "text", + "content": "The rest of our method is independent of the choice of " + }, + { + "bbox": [ + 306, + 354, + 545, + 366 + ], + "type": "inline_equation", + "content": "Z_{\\mathrm{des}}" + }, + { + "bbox": [ + 306, + 354, + 545, + 366 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 367, + 545, + 521 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 367, + 545, + 521 + ], + "spans": [ + { + "bbox": [ + 304, + 367, + 545, + 521 + ], + "type": "text", + "content": "Note again that since the specifications cannot be guaranteed to be complete by construction, we empirically ascertain " + }, + { + "bbox": [ + 304, + 367, + 545, + 521 + ], + "type": "inline_equation", + "content": "Z_{\\mathrm{des}}" + }, + { + "bbox": [ + 304, + 367, + 545, + 521 + ], + "type": "text", + "content": " to be sufficiently capturing the intended variations using metrics presented in Section 5.4. Also note that [34] gives theoretical guarantees that local epsilon balls in a sufficiently trained Conditional VAE's latent space, necessarily generate sufficient instances of local input perturbations. This further validates the use of Axis and Region queries for formal robustness checks and the use of VAEs as the LVM in our pipeline (details in the next section). The specifications can also be systematically inspected by means of sample reconstructions, representative results for which are shown in Figure 2." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "type": "text", + "content": "Verification. Having formally defined " + }, + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "type": "inline_equation", + "content": "Z_{\\mathrm{des}}" + }, + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "type": "text", + "content": " to capture a variation " + }, + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "type": "inline_equation", + "content": "v" + }, + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "type": "text", + "content": ", the SRVP becomes a standard verification problem for a network composed of the inverted encoding head and the original network's task head. This problem can be solved by any standard NN verifier; we use VeriNet [15, 17], an open-source linear programming-based verification toolkit. The invertibility of the encoding head is necessary to guarantee that the feature vectors that map to " + }, + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "type": "inline_equation", + "content": "Z_{\\mathrm{des}}" + }, + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "type": "text", + "content": " are contained in the bounds of feature space set obtained during verification. In our queries, the output constraints " + }, + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "type": "inline_equation", + "content": "Y_{\\mathrm{des}}" + }, + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "type": "text", + "content": " encode invariance of " + }, + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "type": "inline_equation", + "content": "v" + }, + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "type": "text", + "content": ". When the query outcome is negative, the verifier provides a counterexample in " + }, + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "type": "inline_equation", + "content": "Z_{\\mathrm{des}}" + }, + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "type": "text", + "content": " which is then mapped to a counterexample in input space using the decoder. This ideally gives an instance of " + }, + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "type": "inline_equation", + "content": "v" + }, + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "type": "text", + "content": " against which the network is incorrect (see Section 5.3 for details)." + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "3896" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 71, + 76, + 237, + 290 + ], + "blocks": [ + { + "bbox": [ + 71, + 76, + 237, + 290 + ], + "lines": [ + { + "bbox": [ + 71, + 76, + 237, + 290 + ], + "spans": [ + { + "bbox": [ + 71, + 76, + 237, + 290 + ], + "type": "image", + "image_path": "ff28e75b368ba842a065c55960648e6cf549fb225cbbd83335b29b64c9d17795.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 148, + 292, + 157, + 299 + ], + "lines": [ + { + "bbox": [ + 148, + 292, + 157, + 299 + ], + "spans": [ + { + "bbox": [ + 148, + 292, + 157, + 299 + ], + "type": "text", + "content": "(b)" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 46, + 303, + 545, + 348 + ], + "lines": [ + { + "bbox": [ + 46, + 303, + 545, + 348 + ], + "spans": [ + { + "bbox": [ + 46, + 303, + 545, + 348 + ], + "type": "text", + "content": "Figure 2. Reconstructed by our LVMs for Region specifications in (a), Segment specifications in (b) and Axis specifications in (c). (a) shows variations sampled from " + }, + { + "bbox": [ + 46, + 303, + 545, + 348 + ], + "type": "inline_equation", + "content": "\\epsilon" + }, + { + "bbox": [ + 46, + 303, + 545, + 348 + ], + "type": "text", + "content": "-balls around an image encoding; notice how a larger " + }, + { + "bbox": [ + 46, + 303, + 545, + 348 + ], + "type": "inline_equation", + "content": "\\epsilon" + }, + { + "bbox": [ + 46, + 303, + 545, + 348 + ], + "type": "text", + "content": " captures more varied changes of the input. The middle columns in (b) show reconstructions of samples from a segment joining the encodings of the dataset images in outer columns. In (c), all images are reconstructions and can be seen undergoing changes as specified conditional dimensions are varied." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 253, + 69, + 523, + 290 + ], + "blocks": [ + { + "bbox": [ + 253, + 69, + 523, + 290 + ], + "lines": [ + { + "bbox": [ + 253, + 69, + 523, + 290 + ], + "spans": [ + { + "bbox": [ + 253, + 69, + 523, + 290 + ], + "type": "image", + "image_path": "89c97ade108ecdd1e2fb39c38125b774db3b0775021ab9cde2e50f7e6e128c10.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 383, + 292, + 392, + 299 + ], + "lines": [ + { + "bbox": [ + 383, + 292, + 392, + 299 + ], + "spans": [ + { + "bbox": [ + 383, + 292, + 392, + 299 + ], + "type": "text", + "content": "(c)" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 357, + 287, + 393 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 357, + 287, + 393 + ], + "spans": [ + { + "bbox": [ + 47, + 357, + 287, + 393 + ], + "type": "text", + "content": "Discussion. We evaluate the approach experimentally in Section 5; below we analyse it against the last two shortcomings of the EDN approach discussed in Section 2." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 53, + 396, + 288, + 685 + ], + "type": "list", + "angle": 0, + "index": 8, + "blocks": [ + { + "bbox": [ + 53, + 396, + 287, + 564 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 396, + 287, + 564 + ], + "spans": [ + { + "bbox": [ + 53, + 396, + 287, + 564 + ], + "type": "text", + "content": "1. Observe that this approach directly verifies network features corresponding to latent space sets defined by mappings of the original images, rather than the reconstructed images. Thus, the pipeline ensures that the network is tested against at least the original image(s) that form the basis of a specification. Notice from Eq. 2, that this is not the case with the EDN approach if the decoder is not the exact inverse of the encoder. Moreover, since the encoding head is invertible, variations of an image mapping onto the same latent vector directly implies the stability of the network against these variations. Therefore, a many-to-one mapping is not a barrier for our approach, whereas it leads to insufficiently diverse input specifications with the EDN approach." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 53, + 567, + 288, + 685 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 567, + 288, + 685 + ], + "spans": [ + { + "bbox": [ + 53, + 567, + 288, + 685 + ], + "type": "text", + "content": "2. The proposed approach employs shorter paths for verification than the EDN approach. Since the encoding head is invertible, a latent space set need not be passed through the decoder and original network to obtain its corresponding feature set, and since most verification methods have an exponential complexity dependence on the number of unstable activations, the exclusion of the high-dimensional decoder and initial network layers from the verification path allows this approach to scale more favourably than the EDN approach." + } + ] + } + ], + "index": 7 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "content": "A concern over the proposed approach could be that the network to be verified is partly used to define the input spec" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 357, + 545, + 441 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 357, + 545, + 441 + ], + "spans": [ + { + "bbox": [ + 304, + 357, + 545, + 441 + ], + "type": "text", + "content": "ification that it is verified for. However, consider the FDN-encoding head pair as an independent encoder, and the encoding head inverse as a compute efficient analogue of the decoder-FDN pair in the EDN pipeline. From this perspective, the proposed approach is identical to the traditional EDN-based approaches for robustness validation. Additionally, the proposed approach benefits from:" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 312, + 441, + 545, + 647 + ], + "type": "list", + "angle": 0, + "index": 14, + "blocks": [ + { + "bbox": [ + 312, + 441, + 545, + 502 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 441, + 545, + 502 + ], + "spans": [ + { + "bbox": [ + 312, + 441, + 545, + 502 + ], + "type": "text", + "content": "- Added flexibility to use a deep decoder for manifold learning and sharper counterexample generation without impacting verification outcomes. Verification also ensures maximal recall in finding counterexamples as opposed to a gradient search-based approach." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 312, + 502, + 545, + 586 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 502, + 545, + 586 + ], + "spans": [ + { + "bbox": [ + 312, + 502, + 545, + 586 + ], + "type": "text", + "content": "- Relative flexibility in choosing the network layer after which the encoding head is added and thereby, how many of the network's posterior layers feature in the verification path. This decision can depend on the scalability and implementation support of the chosen verification backend or the feasibility of learning a latent space of given dimensionality (see Section 5.2)." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 312, + 586, + 545, + 647 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 586, + 545, + 647 + ], + "spans": [ + { + "bbox": [ + 312, + 586, + 545, + 647 + ], + "type": "text", + "content": "- Independence with respect to the FDN architecture's depth and type (residual, recurrent, non-standard convolutional, etc.), and possibly to input dimensionality1, leading to an easier extension of the verification approach to newer architectures." + } + ] + } + ], + "index": 13 + } + ], + "sub_type": "text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 306, + 655, + 547, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 655, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 306, + 655, + 547, + 713 + ], + "type": "text", + "content": "1Independence to input dimensionality is conditional on the nature of the FDN and its last layer being fully-connected (fc); however, since most vision inference tasks, such as classification, regression and detection, involve dimensionality reduction and network's posterior layers are usually fc, the specification input dimensionality can almost always be made lower than that of input data." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "3897" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 144, + 85 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 144, + 85 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 144, + 85 + ], + "type": "text", + "content": "4. Implementation" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 91, + 287, + 115 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 91, + 287, + 115 + ], + "spans": [ + { + "bbox": [ + 47, + 91, + 287, + 115 + ], + "type": "text", + "content": "In this section we describe our implementation of the proposed verification pipeline [13]." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 115, + 287, + 163 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 115, + 287, + 163 + ], + "spans": [ + { + "bbox": [ + 46, + 115, + 287, + 163 + ], + "type": "text", + "content": "Encoding head. In terms of design choices, all common LVMs for data generation, including VAEs, Normalising Flows (NFs) and GANs, can be used in the pipeline if the following holds:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 44, + 163, + 286, + 222 + ], + "type": "list", + "angle": 0, + "index": 5, + "blocks": [ + { + "bbox": [ + 44, + 163, + 286, + 198 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 44, + 163, + 286, + 198 + ], + "spans": [ + { + "bbox": [ + 44, + 163, + 286, + 198 + ], + "type": "text", + "content": "- The FDN of the network to be verified can serve as the backbone of the LVM encoder (e.g., if the FDN involves a dimensionality change then NFs cannot serve as the LVM)." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 44, + 199, + 286, + 222 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 44, + 199, + 286, + 222 + ], + "spans": [ + { + "bbox": [ + 44, + 199, + 286, + 222 + ], + "type": "text", + "content": "- The verification backend can verify the inverted encoding head of the pipeline." + } + ] + } + ], + "index": 4 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 46, + 223, + 287, + 390 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 223, + 287, + 390 + ], + "spans": [ + { + "bbox": [ + 46, + 223, + 287, + 390 + ], + "type": "text", + "content": "Given any LVM, " + }, + { + "bbox": [ + 46, + 223, + 287, + 390 + ], + "type": "inline_equation", + "content": "Z_{\\mathrm{des}}" + }, + { + "bbox": [ + 46, + 223, + 287, + 390 + ], + "type": "text", + "content": " is defined in the output space of the LVM encoding head in ways described in Section 3. A VAE fits the pipeline particularly well given the backing of the theoretical analysis in [34], and as it regularises the underlying latent space to resemble a prior. This prior (normal, von Mises-Fisher distribution in " + }, + { + "bbox": [ + 46, + 223, + 287, + 390 + ], + "type": "inline_equation", + "content": "\\mathcal{N}" + }, + { + "bbox": [ + 46, + 223, + 287, + 390 + ], + "type": "text", + "content": "-VAE [21], S-VAE [8] resp.) is light-tailed, so the latent space can be approximately bounded or truncated, and the epsilons in our specifications have bounded domain. Note that the latent variable " + }, + { + "bbox": [ + 46, + 223, + 287, + 390 + ], + "type": "inline_equation", + "content": "z" + }, + { + "bbox": [ + 46, + 223, + 287, + 390 + ], + "type": "text", + "content": " in a VAE is not the output of the encoder but a random variable conditioned on its outputs " + }, + { + "bbox": [ + 46, + 223, + 287, + 390 + ], + "type": "inline_equation", + "content": "(\\mu, \\sigma \\in \\mathbb{R}^{\\mathrm{latent.dim}})" + }, + { + "bbox": [ + 46, + 223, + 287, + 390 + ], + "type": "text", + "content": " by reparameterisation [21]. Since reparameterisation cannot be inverted, " + }, + { + "bbox": [ + 46, + 223, + 287, + 390 + ], + "type": "inline_equation", + "content": "Z_{\\mathrm{des}}" + }, + { + "bbox": [ + 46, + 223, + 287, + 390 + ], + "type": "text", + "content": " is defined using the vector " + }, + { + "bbox": [ + 46, + 223, + 287, + 390 + ], + "type": "inline_equation", + "content": "[\\mu, \\sigma]" + }, + { + "bbox": [ + 46, + 223, + 287, + 390 + ], + "type": "text", + "content": " instead of " + }, + { + "bbox": [ + 46, + 223, + 287, + 390 + ], + "type": "inline_equation", + "content": "z" + }, + { + "bbox": [ + 46, + 223, + 287, + 390 + ], + "type": "text", + "content": ", albeit with no change in " + }, + { + "bbox": [ + 46, + 223, + 287, + 390 + ], + "type": "inline_equation", + "content": "Z_{\\mathrm{des}}" + }, + { + "bbox": [ + 46, + 223, + 287, + 390 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 390, + 287, + 461 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 390, + 287, + 461 + ], + "spans": [ + { + "bbox": [ + 46, + 390, + 287, + 461 + ], + "type": "text", + "content": "In contrast, GANs do not use an encoder to learn a latent distribution and instead take a prior distribution as input. However, when using a GAN as the LVM, we still add an encoding head after the FDN to transform the unconstrained FDN output to a desired prior for the GAN and define input-parameterized local specifications." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 462, + 287, + 557 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 462, + 287, + 557 + ], + "spans": [ + { + "bbox": [ + 46, + 462, + 287, + 557 + ], + "type": "text", + "content": "LVM design. As discussed previously, our pipeline features an encoding head after the FDN of the network to be analysed. Since the encoding head must not undergo dimensionality change, the dimension of the flattened FDN output is the dimension of the encoding head layers and the latent space where the input specification is defined. Typically, a shorter FDN implies larger latent space dimensionality and verification involves more network layers." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 558, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 558, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 558, + 287, + 713 + ], + "type": "text", + "content": "We use two types of feed-forward encoding heads: one consists of pairs of an invertible activation and fully-connected (FC) layers; the other consists of alternating affine-coupling layers [9]. The former is easier to train and supported by most NN verifiers, but its invertibility to sufficient precision needs to be validated by checking the singular values of the individual layers' weight matrices. Affine-coupling layer is invertible-by-construction but not supported by standard NN verifiers. To support its verification, we replace its typically input dependent scaling and translation unit with an input independent learnt vector and an FC layer respectively. This modified affine-coupling layer is equivalent to an FC layer in expressiveness, but is" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 72, + 411, + 84 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 72, + 411, + 84 + ], + "spans": [ + { + "bbox": [ + 306, + 72, + 411, + 84 + ], + "type": "text", + "content": "more challenging to train." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 84, + 545, + 144 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 84, + 545, + 144 + ], + "spans": [ + { + "bbox": [ + 304, + 84, + 545, + 144 + ], + "type": "text", + "content": "One can increase the encoding head depth with the pairs described above until the LVM is adequately trained; in our experience, a single layered encoding head sufficed for good reconstructions. The decoder is always a deep upscaling network mirroring the pipeline encoder." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 144, + 545, + 299 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 144, + 545, + 299 + ], + "spans": [ + { + "bbox": [ + 304, + 144, + 545, + 299 + ], + "type": "text", + "content": "LVM training. In addition to the negative log likelihood or GAN loss, we conditionally train latent dimensions [5, 23] for Axis specifications. We use Cross-Entropy (CE) loss for discrete attributes. For instance, we train one dimension with binary CE loss so that " + }, + { + "bbox": [ + 304, + 144, + 545, + 299 + ], + "type": "inline_equation", + "content": "[0,1]" + }, + { + "bbox": [ + 304, + 144, + 545, + 299 + ], + "type": "text", + "content": " for this dimension corresponds to variations from no attribute to complete attribute. Note that we cannot use the common conditional generation approach of augmenting encodings with attribute labels [31] because the entire encoding must be inferred from the FDN output for invertibility. Therefore, differently from usual practice, our VAEs for conditional generation do not take attributes as priors to condition on but rather learn them with supervision from data." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 300, + 545, + 347 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 300, + 545, + 347 + ], + "spans": [ + { + "bbox": [ + 304, + 300, + 545, + 347 + ], + "type": "text", + "content": "Continuum in transformations is important when verifying against pose changes, which CE loss may not provide. Therefore, dimensions capturing continuous changes are trained as graphics code as per the procedure in [23]." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 348, + 545, + 430 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 348, + 545, + 430 + ], + "spans": [ + { + "bbox": [ + 304, + 348, + 545, + 430 + ], + "type": "text", + "content": "Note that it may not be possible to train an LVM by adding an encoding head to the extreme end of every network, as network's task-agnostic information may be lost till that layer. However, if an LVM can be trained by adding an encoding head after the " + }, + { + "bbox": [ + 304, + 348, + 545, + 430 + ], + "type": "inline_equation", + "content": "K^{th}" + }, + { + "bbox": [ + 304, + 348, + 545, + 430 + ], + "type": "text", + "content": " network layer, it is inexpensive to train a new LVM from after the " + }, + { + "bbox": [ + 304, + 348, + 545, + 430 + ], + "type": "inline_equation", + "content": "(K - k)^{th}, k > 0" + }, + { + "bbox": [ + 304, + 348, + 545, + 430 + ], + "type": "text", + "content": ", layer, with the frozen original network." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 431, + 545, + 634 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 431, + 545, + 634 + ], + "spans": [ + { + "bbox": [ + 304, + 431, + 545, + 634 + ], + "type": "text", + "content": "Datasets preparation. To train the LVMs for our experiments, we used public datasets with customdataloading to have attribute and transform labels for every input. We only used datasets for which realistic variations can be produced with labels, as it is required for conditional training and forming precise queries for pipeline evaluation (see Section 5.4). We worked with five datasets: CelebA [25], Traffic Signs Recognition (TSRD), 3D Objects (3DOD), (Fashion)MNIST [38]. For TSRD, we took traffic signs and city scene crops, apply planar (rotation, scale, photometric) and spatial (perspective) transformations on the former and blend them into the latter during dataloading. For 3DOD, we took 3D models from ModelNet10 dataset [37] and render their images from different distances, azimuth and elevation angles in Blender [6]. For all trainings, the dataset was balanced such that every class had adequate samples of the variation being verified against." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 306, + 645, + 437, + 659 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 645, + 437, + 659 + ], + "spans": [ + { + "bbox": [ + 306, + 645, + 437, + 659 + ], + "type": "text", + "content": "5. Experimental Analysis" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 665, + 545, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 665, + 545, + 689 + ], + "spans": [ + { + "bbox": [ + 306, + 665, + 545, + 689 + ], + "type": "text", + "content": "We report on our experiments to validate the proposed approach, with focus on answering three key questions:" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "text", + "content": "Q1. Can an LVM added to a classifier generate an appropriate latent manifold and good reconstructions?" + } + ] + } + ], + "index": 18 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "3898" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 286, + 120 + ], + "type": "list", + "angle": 0, + "index": 2, + "blocks": [ + { + "bbox": [ + 47, + 72, + 286, + 95 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 286, + 95 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 286, + 95 + ], + "type": "text", + "content": "Q2. Can the proposed pipeline efficiently verify deep networks?" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 95, + 286, + 120 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 95, + 286, + 120 + ], + "spans": [ + { + "bbox": [ + 47, + 95, + 286, + 120 + ], + "type": "text", + "content": "Q3. Can the specifications, discussed in Section 3, encode intended input variations?" + } + ] + } + ], + "index": 1 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 46, + 121, + 286, + 228 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 121, + 286, + 228 + ], + "spans": [ + { + "bbox": [ + 46, + 121, + 286, + 228 + ], + "type": "text", + "content": "To assess Q1, we refer to the reconstructions presented in Figure 2 and the low values of mean reconstruction error and FID score [18] reported in Table 1. To assess Q2, we refer to the verification outcomes for deep networks of different architectures reported in Sections 5.1, 5.2. To assess Q3, we refer to the values of metrics quantifying the precision of a specification in capturing intended variations, discussed in Section 5.4. With this overview, we now discuss the experiments in greater detail." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 236, + 271, + 248 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 236, + 271, + 248 + ], + "spans": [ + { + "bbox": [ + 47, + 236, + 271, + 248 + ], + "type": "text", + "content": "5.1. Verifying segments joining input encodings" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 254, + 286, + 408 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 254, + 286, + 408 + ], + "spans": [ + { + "bbox": [ + 46, + 254, + 286, + 408 + ], + "type": "text", + "content": "To verify robustness against variations reflected in an image pair, we generated Segment specifications capturing object pose and viewpoint changes. For CelebA, we also verify specifications capturing the classifier's invariance to task-orthogonal attributes. These queries are similar to the queries in [27] which uses the EDN approach and reports successful deterministic verification of " + }, + { + "bbox": [ + 46, + 254, + 286, + 408 + ], + "type": "inline_equation", + "content": "23.8\\%" + }, + { + "bbox": [ + 46, + 254, + 286, + 408 + ], + "type": "text", + "content": " queries for a ConvMed model with 64k activations. Based on the classifier layer separating the FDN and task head, multiple verification pipelines were trained for each classifier. The verification outcomes for all queries and pipelines are reported in Table 1, from which the following observations can be drawn:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 53, + 410, + 286, + 567 + ], + "type": "list", + "angle": 0, + "index": 9, + "blocks": [ + { + "bbox": [ + 53, + 410, + 286, + 469 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 410, + 286, + 469 + ], + "spans": [ + { + "bbox": [ + 53, + 410, + 286, + 469 + ], + "type": "text", + "content": "- The mean reconstruction errors and FID scores for the multiple SRVP pipelines per classifier are low with consistent verification outcomes, indicating that latent spaces of a considerable range of dimensionality can be successfully learnt and verified against." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 53, + 471, + 286, + 530 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 471, + 286, + 530 + ], + "spans": [ + { + "bbox": [ + 53, + 471, + 286, + 530 + ], + "type": "text", + "content": "- The SRVP pipelines require an order of magnitude less time than the EDN pipelines to solve safe queries, and produce fewer trivial output bounds or undecided cases. This remains the case with the inclusion of more network layers in the verification path." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 53, + 532, + 286, + 567 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 532, + 286, + 567 + ], + "spans": [ + { + "bbox": [ + 53, + 532, + 286, + 567 + ], + "type": "text", + "content": "- The verified robust accuracy tightly lower bounds the adversarial accuracy computed against gradient-ascent-based latent space interpolation attacks [28]." + } + ] + } + ], + "index": 8 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 47, + 575, + 226, + 588 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 575, + 226, + 588 + ], + "spans": [ + { + "bbox": [ + 47, + 575, + 226, + 588 + ], + "type": "text", + "content": "5.2. Verifying along latent dimensions" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 594, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 594, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 286, + 713 + ], + "type": "text", + "content": "As discussed in Section 3, Axis specifications can be used to verify an input against the entire range of a task-orthogonal change (e.g., style, or pose). Figure 3 shows representative results for verifying these specifications where the local input set is increased for individual latent dimensions of an encoding. For many inputs, conditional dimensions were verifiably robust for almost their entire range, while dimensions without conditional training were found to be robust for much smaller epsilons. Decoded samples from latent dimensions in Figure 4 corroborate these" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 72, + 545, + 216 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 216 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 216 + ], + "type": "text", + "content": "outcomes. The object class change was not observed for all non-conditional dimensions, but conditional dimensions were more consistent in preserving the object class. However, with increase in latent dimensionality, as with a shorter FDN, it became harder to balance the conditional and standard LVM training to achieve both good reconstructions and distinct attribute changes with class consistency. This explains the reduced transform detections for higher dimensional manifolds reported in Figure 3. In Section 5.4, we present a validity metric to assess the success of conditional manifold training and in turn, derive expectation on the usefulness of Axis specifications defined in the manifold." + } + ] + } + ], + "index": 12 + }, + { + "type": "image", + "bbox": [ + 330, + 220, + 521, + 331 + ], + "blocks": [ + { + "bbox": [ + 330, + 220, + 521, + 331 + ], + "lines": [ + { + "bbox": [ + 330, + 220, + 521, + 331 + ], + "spans": [ + { + "bbox": [ + 330, + 220, + 521, + 331 + ], + "type": "image", + "image_path": "1433487e700bfc05e973a71bb44f777d23bd0fad9ac7f8cda1b62ccc808a4c21.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_body" + } + ], + "index": 13 + }, + { + "type": "image", + "bbox": [ + 330, + 334, + 521, + 445 + ], + "blocks": [ + { + "bbox": [ + 330, + 334, + 521, + 445 + ], + "lines": [ + { + "bbox": [ + 330, + 334, + 521, + 445 + ], + "spans": [ + { + "bbox": [ + 330, + 334, + 521, + 445 + ], + "type": "image", + "image_path": "0ae5792338b1e49efed07ce0003867e1f56cc2d805d2014bc0649c4588cc6dad.jpg" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 448, + 545, + 525 + ], + "lines": [ + { + "bbox": [ + 304, + 448, + 545, + 525 + ], + "spans": [ + { + "bbox": [ + 304, + 448, + 545, + 525 + ], + "type": "text", + "content": "Figure 3. Both graphs show mean percentage of Axis queries verified as safe (out of 200 tested) for local intervals of " + }, + { + "bbox": [ + 304, + 448, + 545, + 525 + ], + "type": "inline_equation", + "content": "\\pm \\epsilon" + }, + { + "bbox": [ + 304, + 448, + 545, + 525 + ], + "type": "text", + "content": " for LVMs of different latent dimensionality. The percentage of reconstructions of samples along the conditional axes, around the " + }, + { + "bbox": [ + 304, + 448, + 545, + 525 + ], + "type": "inline_equation", + "content": "\\epsilon" + }, + { + "bbox": [ + 304, + 448, + 545, + 525 + ], + "type": "text", + "content": "s reported on the x-axis, in which a learnt transform detector detects the intended transform, is also plotted. The axes were trained with (B)CE loss with 0,1 mapping to the base and the attribute added image resp." + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_caption" + } + ], + "index": 14 + }, + { + "type": "image", + "bbox": [ + 314, + 536, + 521, + 636 + ], + "blocks": [ + { + "bbox": [ + 314, + 536, + 521, + 636 + ], + "lines": [ + { + "bbox": [ + 314, + 536, + 521, + 636 + ], + "spans": [ + { + "bbox": [ + 314, + 536, + 521, + 636 + ], + "type": "image", + "image_path": "c81b55cfa9669c84d663e796bdf8ab6f3efe7cdd3a29cfbab0b65ea642205da1.jpg" + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 642, + 545, + 696 + ], + "lines": [ + { + "bbox": [ + 304, + 642, + 545, + 696 + ], + "spans": [ + { + "bbox": [ + 304, + 642, + 545, + 696 + ], + "type": "text", + "content": "Figure 4. All images above are generated by an LVM from a single image per dataset. The columns feature samples along non-conditional dimensions, and each row has a constant conditional axis value which enforces rendering of the specified transform in all its reconstructions." + } + ] + } + ], + "index": 17, + "angle": 0, + "type": "image_caption" + } + ], + "index": 16 + }, + { + "bbox": [ + 317, + 701, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 701, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 317, + 701, + 545, + 713 + ], + "type": "text", + "content": "In case of Region specifications, where the local ep" + } + ] + } + ], + "index": 18 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "3899" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 55, + 71, + 538, + 243 + ], + "blocks": [ + { + "bbox": [ + 55, + 71, + 538, + 243 + ], + "lines": [ + { + "bbox": [ + 55, + 71, + 538, + 243 + ], + "spans": [ + { + "bbox": [ + 55, + 71, + 538, + 243 + ], + "type": "table", + "html": "
Dataset (size)Verifying inv. to *NetworkAccuracies*Pipeline**Verification outcomes (100 std.safe queries)Recons.outcomes
Std.Adv.Type #Ver.actv.layers (actvs.)Safe(s†)Unsafe(s)Undec.(s)Rob.accRMSSrr*FIDscore
Runs for efficiency comparison of EDNs (with decoders of different depths) vs. SRVPs (with encoding heads after different n/w layers).
CelebA64.2%EDtinyN-328 (5k)61 (6.8)39 (3.94)056%0.064218.61
65%EDdeepN-329 (27k)64 (22.3)29 (31.6)7 (64)59%0.053107.42
(64x64)ConvSmall (6k ReLUs)92%69%EDresnet18N-3211 (0.2M)042 (370)58 (802)0%0.05189.62
91%SRVP Lin1-321 (64)99 (0.4)1 (0.01)091%0.058114
89%SRVP Lin1-642 (192)94 (0.5)6 (0.02)085.5%0.042112
Head Flip (gender cla.)87%SRVP Lin1-1923 (576)88 (1.1)12 (0.08)081%0.035105
89%SRVP Lin1-3924 (1.3k)91 (2.7)9 (0.11)084%0.031102
74%EDtinyN-328 (86k)59 (32.8)41 (20)056.6%0.07264
81%EDdeepN-329 (0.1M)66 (35.3)22 (23.5)12 (64)63%0.06223
(128x128)ConvBig (72k ReLUs)96%77%EDresnet18N-3211 (475k)021 (410)79 (816)0%0.06124
93%SRVP Lin1-641 (64)95 (0.4)5 (0.07)091%0.23252
95%SRVP Lin1-1922 (256)96 (0.8)4 (0.09)092%0.15225
94%SRVP Lin1-3923 (648)96 (1.9)4 (0.11)092%0.04202
", + "image_path": "801356e8ae7c67e5432a8ce82ec52540a00a9f59a028c1d81b1f7f079f4ae96c.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 55, + 243, + 538, + 321 + ], + "blocks": [ + { + "bbox": [ + 55, + 243, + 538, + 321 + ], + "lines": [ + { + "bbox": [ + 55, + 243, + 538, + 321 + ], + "spans": [ + { + "bbox": [ + 55, + 243, + 538, + 321 + ], + "type": "table", + "html": "
SRVP runs with encoding heads of different dimensions for different n/w architectures and datasets
(64x64)ResNet1884%82%SRVP Lin1-2561 (512)95 (2.6)5 (0.1)080%0.022104
TRDS (64x64)Planar Pose (sign cla.)ResNet1892.5%SRVP Lin1-2562 (1k)96 (2.1)4 (0.21)089%0.03116
89%SRVP Lin1-10242 (1.5k)94 (3.8)6 (0.46)087%0.03106
MobileNetv282%78%SRVP Lin1-6401 (640)93 (2.1)7 (0.42)076%0.09133
3DOD (64x64)Spatial Pose (obj cla.)ResNet1897%SRVP Lin1-2562 (1k)94 (1.9)6 (0.2)091%0.04106
90%SRVP Lin1-10242 (1.5k)92 (4.7)8 (0.45)089%0.0298
", + "image_path": "657f6bce7de264fa1f19f4ea886ab71044a1e7a2ab85d659549d366bd430b51d.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + }, + { + "bbox": [ + 47, + 323, + 545, + 344 + ], + "lines": [ + { + "bbox": [ + 47, + 323, + 545, + 344 + ], + "spans": [ + { + "bbox": [ + 47, + 323, + 545, + 344 + ], + "type": "text", + "content": "* Std. and Adv. accuracy are the network's accuracy against clean, augmented data and latent-space PGD attacks [28] (" + }, + { + "bbox": [ + 47, + 323, + 545, + 344 + ], + "type": "inline_equation", + "content": "\\alpha = 2\\mathrm{e} - 3" + }, + { + "bbox": [ + 47, + 323, + 545, + 344 + ], + "type": "text", + "content": ", #iters=2000) resp. The PGD attacks are found for " + }, + { + "bbox": [ + 47, + 323, + 545, + 344 + ], + "type": "inline_equation", + "content": "N \\circ d(z)" + }, + { + "bbox": [ + 47, + 323, + 545, + 344 + ], + "type": "text", + "content": " in EDN pipelines and " + }, + { + "bbox": [ + 47, + 323, + 545, + 344 + ], + "type": "inline_equation", + "content": "e^{-1} \\circ N_{\\mathrm{head}}(z)" + }, + { + "bbox": [ + 47, + 323, + 545, + 344 + ], + "type": "text", + "content": " in SRVP pipelines for " + }, + { + "bbox": [ + 47, + 323, + 545, + 344 + ], + "type": "inline_equation", + "content": "z \\in Z_{\\mathrm{segment}}" + }, + { + "bbox": [ + 47, + 323, + 545, + 344 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_footnote" + }, + { + "bbox": [ + 47, + 343, + 545, + 363 + ], + "lines": [ + { + "bbox": [ + 47, + 343, + 545, + 363 + ], + "spans": [ + { + "bbox": [ + 47, + 343, + 545, + 363 + ], + "type": "text", + "content": "** The suffixed integer in the pipeline type is the dimensionality of its latent space and is equal to its verification input. Higher dimensions for a SRVP pipeline for the same network indicate an earlier split and the inclusion of more layers in the verification path." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_footnote" + }, + { + "bbox": [ + 48, + 362, + 544, + 373 + ], + "lines": [ + { + "bbox": [ + 48, + 362, + 544, + 373 + ], + "spans": [ + { + "bbox": [ + 48, + 362, + 544, + 373 + ], + "type": "inline_equation", + "content": "\\dagger" + }, + { + "bbox": [ + 48, + 362, + 544, + 373 + ], + "type": "text", + "content": " Seconds (s) reported are the mean query solving time. All queries were run on a 24 core, 256GB CPU with timeout of 60 or 800 seconds." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_footnote" + }, + { + "bbox": [ + 48, + 373, + 541, + 384 + ], + "lines": [ + { + "bbox": [ + 48, + 373, + 541, + 384 + ], + "spans": [ + { + "bbox": [ + 48, + 373, + 541, + 384 + ], + "type": "inline_equation", + "content": "\\star" + }, + { + "bbox": [ + 48, + 373, + 541, + 384 + ], + "type": "text", + "content": " The reconstruction error is per-pixel for normalised float [-1,1] images. The FID score is computed by using pytorch-fid package [30]." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "table_footnote" + }, + { + "bbox": [ + 48, + 383, + 545, + 403 + ], + "lines": [ + { + "bbox": [ + 48, + 383, + 545, + 403 + ], + "spans": [ + { + "bbox": [ + 48, + 383, + 545, + 403 + ], + "type": "text", + "content": "All pipelines for the same network were trained until comparable reconstruction outcomes, were tested for the same queries using the same backend and use " + }, + { + "bbox": [ + 48, + 383, + 545, + 403 + ], + "type": "inline_equation", + "content": "\\mathcal{N}" + }, + { + "bbox": [ + 48, + 383, + 545, + 403 + ], + "type": "text", + "content": "-VAE as the LVM so that all of them have an approximately normal latent manifold distribution." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "table_footnote" + } + ], + "index": 1 + }, + { + "bbox": [ + 77, + 409, + 515, + 421 + ], + "lines": [ + { + "bbox": [ + 77, + 409, + 515, + 421 + ], + "spans": [ + { + "bbox": [ + 77, + 409, + 515, + 421 + ], + "type": "text", + "content": "Table 1. Verification results for Segment queries; representative specification inputs for the above are shown in Figure 2b." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 47, + 441, + 287, + 478 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 441, + 287, + 478 + ], + "spans": [ + { + "bbox": [ + 47, + 441, + 287, + 478 + ], + "type": "text", + "content": "silon ball is increased uniformly in all latent dimensions, we could verify robustness for a maximum " + }, + { + "bbox": [ + 47, + 441, + 287, + 478 + ], + "type": "inline_equation", + "content": "\\epsilon = 0.01" + }, + { + "bbox": [ + 47, + 441, + 287, + 478 + ], + "type": "text", + "content": " (for " + }, + { + "bbox": [ + 47, + 441, + 287, + 478 + ], + "type": "inline_equation", + "content": "< 10\\%" + }, + { + "bbox": [ + 47, + 441, + 287, + 478 + ], + "type": "text", + "content": " queries) for SRVP Lin-32 pipelines." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 488, + 192, + 502 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 488, + 192, + 502 + ], + "spans": [ + { + "bbox": [ + 47, + 488, + 192, + 502 + ], + "type": "text", + "content": "5.3. Counterexamples analysis" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 509, + 287, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 509, + 287, + 628 + ], + "spans": [ + { + "bbox": [ + 46, + 509, + 287, + 628 + ], + "type": "text", + "content": "Counterexamples are instances of the input specification set that falsify the robustness property under investigation. In our approach, the verifier finds a latent space counterexample " + }, + { + "bbox": [ + 46, + 509, + 287, + 628 + ], + "type": "inline_equation", + "content": "z^{*} \\in Z_{\\mathrm{des}}" + }, + { + "bbox": [ + 46, + 509, + 287, + 628 + ], + "type": "text", + "content": " for every unsafe query such that " + }, + { + "bbox": [ + 46, + 509, + 287, + 628 + ], + "type": "inline_equation", + "content": "N_{\\mathrm{head}} \\circ e^{-1}(z^{*})" + }, + { + "bbox": [ + 46, + 509, + 287, + 628 + ], + "type": "text", + "content": " demonstrates non-robustness. However, since the LVM decoder is not the exact inverse of its encoder, the decoded counterexample could be spurious, i.e., " + }, + { + "bbox": [ + 46, + 509, + 287, + 628 + ], + "type": "inline_equation", + "content": "N \\circ d(z^{*})" + }, + { + "bbox": [ + 46, + 509, + 287, + 628 + ], + "type": "text", + "content": " may not be a counterexample. Therefore, we decode every " + }, + { + "bbox": [ + 46, + 509, + 287, + 628 + ], + "type": "inline_equation", + "content": "z^{*}" + }, + { + "bbox": [ + 46, + 509, + 287, + 628 + ], + "type": "text", + "content": " and label it a valid counterexample iff its reconstruction is also a counterexample for the network." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 46, + 630, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 630, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 630, + 288, + 715 + ], + "type": "text", + "content": "Similar to [16], in the case of a spurious counterexample " + }, + { + "bbox": [ + 46, + 630, + 288, + 715 + ], + "type": "inline_equation", + "content": "z^{*}" + }, + { + "bbox": [ + 46, + 630, + 288, + 715 + ], + "type": "text", + "content": ", we run a local gradient search for a valid one, taking " + }, + { + "bbox": [ + 46, + 630, + 288, + 715 + ], + "type": "inline_equation", + "content": "z^{*}" + }, + { + "bbox": [ + 46, + 630, + 288, + 715 + ], + "type": "text", + "content": " as the starting point. In comparison to starting from a mapped vector, this local gradient-based search around " + }, + { + "bbox": [ + 46, + 630, + 288, + 715 + ], + "type": "inline_equation", + "content": "z^{*}" + }, + { + "bbox": [ + 46, + 630, + 288, + 715 + ], + "type": "text", + "content": " takes much fewer iterations to reach a valid counterexample in most cases, and results in high precision in finding valid and in-domain counterexamples (see Figure 5)." + } + ] + } + ], + "index": 12 + }, + { + "type": "image", + "bbox": [ + 307, + 439, + 535, + 608 + ], + "blocks": [ + { + "bbox": [ + 307, + 439, + 535, + 608 + ], + "lines": [ + { + "bbox": [ + 307, + 439, + 535, + 608 + ], + "spans": [ + { + "bbox": [ + 307, + 439, + 535, + 608 + ], + "type": "image", + "image_path": "6284998916bc17bf7e2e4aece6bc3d55c3093e03de0af06718daa4cf8c003e4b.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 609, + 545, + 719 + ], + "lines": [ + { + "bbox": [ + 304, + 609, + 545, + 719 + ], + "spans": [ + { + "bbox": [ + 304, + 609, + 545, + 719 + ], + "type": "text", + "content": "Figure 5. The table reports the mean ratios of valid counterexamples (ceg.) to all cegs found by SRVP pipelines for network " + }, + { + "bbox": [ + 304, + 609, + 545, + 719 + ], + "type": "inline_equation", + "content": "N_{\\mathrm{head}} \\circ e^{-1}" + }, + { + "bbox": [ + 304, + 609, + 545, + 719 + ], + "type": "text", + "content": " through verification of 100 Segment queries, with and without PGD-based search in the second and third column resp. The full search and refinement iterations are median PGD iterations of step-size 1e-3 for success in the latent/attribute space attack [28] and in the local search for a valid ceg around a verification-returned spurious ceg resp. Rows in the figure below show reconstructions for some unsafe Segment and Axis queries with their valid cegs in the rightmost column." + } + ] + } + ], + "index": 22, + "angle": 0, + "type": "image_caption" + } + ], + "index": 13 + }, + { + "bbox": [ + 496, + 506, + 542, + 517 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 496, + 506, + 542, + 517 + ], + "spans": [ + { + "bbox": [ + 496, + 506, + 542, + 517 + ], + "type": "text", + "content": "Male (Female)" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 496, + 528, + 537, + 536 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 496, + 528, + 537, + 536 + ], + "spans": [ + { + "bbox": [ + 496, + 528, + 537, + 536 + ], + "type": "text", + "content": "Chair (Table)" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 496, + 544, + 524, + 553 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 496, + 544, + 524, + 553 + ], + "spans": [ + { + "bbox": [ + 496, + 544, + 524, + 553 + ], + "type": "text", + "content": "No right" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 496, + 554, + 533, + 562 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 496, + 554, + 533, + 562 + ], + "spans": [ + { + "bbox": [ + 496, + 554, + 533, + 562 + ], + "type": "text", + "content": "(No U-turn)" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 496, + 569, + 535, + 577 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 496, + 569, + 535, + 577 + ], + "spans": [ + { + "bbox": [ + 496, + 569, + 535, + 577 + ], + "type": "text", + "content": "Old (Young)" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 496, + 578, + 544, + 585 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 496, + 578, + 544, + 585 + ], + "spans": [ + { + "bbox": [ + 496, + 578, + 544, + 585 + ], + "type": "text", + "content": "Change: Glasses" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 496, + 590, + 542, + 597 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 496, + 590, + 542, + 597 + ], + "spans": [ + { + "bbox": [ + 496, + 590, + 542, + 597 + ], + "type": "text", + "content": "Male (Female)" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 496, + 597, + 543, + 604 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 496, + 597, + 543, + 604 + ], + "spans": [ + { + "bbox": [ + 496, + 597, + 543, + 604 + ], + "type": "text", + "content": "Change:Gender" + } + ] + } + ], + "index": 21 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "3900" + } + ] + } + ], + "index": 23 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 232, + 85 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 232, + 85 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 232, + 85 + ], + "type": "text", + "content": "5.4. Validating the LVM based pipeline" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 91, + 286, + 162 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 91, + 286, + 162 + ], + "spans": [ + { + "bbox": [ + 46, + 91, + 286, + 162 + ], + "type": "text", + "content": "Having assessed the capabilities of our approach in terms of scaling to deep networks and the fidelity of returned counterexamples, we now evaluate its precision in sufficiently capturing the intended variations in the proposed specifications. For this, we consider two latent space-based validity metrics as described below." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 163, + 286, + 342 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 163, + 286, + 342 + ], + "spans": [ + { + "bbox": [ + 46, + 163, + 286, + 342 + ], + "type": "text", + "content": "The assumption behind Segment specifications is that the in-domain interpolations of an image pair map to the interpolations of its encoding pair. To validate this, we measure the distance of the encodings of the desired interpolations of an image pair to the path joining its encoding pair. In practice, for validating pose invariance queries, we generate images with varying extents of a transform, construct a path between the encodings of the image pair with the most extreme mutual transform, and compute the distance between the encodings of the intermediate transforms and their projection on this path. This distance is divided by square-root of latent dimensionality to generalise across manifolds of different dimensions. We compute this metric for the following pairs of encoding paths and VAE manifolds used in our pipelines, and report its mean value distribution below." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 50, + 342, + 286, + 432 + ], + "type": "list", + "angle": 0, + "index": 7, + "blocks": [ + { + "bbox": [ + 50, + 342, + 286, + 366 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 50, + 342, + 286, + 366 + ], + "spans": [ + { + "bbox": [ + 50, + 342, + 286, + 366 + ], + "type": "text", + "content": "1. Shortest Length Path (SLP) + untrained normal distribution manifold (baseline)," + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 50, + 369, + 128, + 380 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 50, + 369, + 128, + 380 + ], + "spans": [ + { + "bbox": [ + 50, + 369, + 128, + 380 + ], + "type": "text", + "content": "2. " + }, + { + "bbox": [ + 50, + 369, + 128, + 380 + ], + "type": "inline_equation", + "content": "\\mathrm{SLP} + \\mathcal{N}" + }, + { + "bbox": [ + 50, + 369, + 128, + 380 + ], + "type": "text", + "content": " -VAE," + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 50, + 381, + 286, + 418 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 50, + 381, + 286, + 418 + ], + "spans": [ + { + "bbox": [ + 50, + 381, + 286, + 418 + ], + "type": "text", + "content": "3. " + }, + { + "bbox": [ + 50, + 381, + 286, + 418 + ], + "type": "inline_equation", + "content": "\\mathrm{SLP} + \\mathcal{N}" + }, + { + "bbox": [ + 50, + 381, + 286, + 418 + ], + "type": "text", + "content": "-VAE trained with a latent space-based cycle consistency loss that encourages its encoder-decoder to be an inverse pair," + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 50, + 419, + 266, + 432 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 50, + 419, + 266, + 432 + ], + "spans": [ + { + "bbox": [ + 50, + 419, + 266, + 432 + ], + "type": "text", + "content": "4. Real-vs-fake discriminator-guided path " + }, + { + "bbox": [ + 50, + 419, + 266, + 432 + ], + "type": "inline_equation", + "content": "+\\mathcal{N}" + }, + { + "bbox": [ + 50, + 419, + 266, + 432 + ], + "type": "text", + "content": " -VAE." + } + ] + } + ], + "index": 6 + } + ], + "sub_type": "text" + }, + { + "type": "image", + "bbox": [ + 34, + 434, + 281, + 539 + ], + "blocks": [ + { + "bbox": [ + 34, + 434, + 281, + 539 + ], + "lines": [ + { + "bbox": [ + 34, + 434, + 281, + 539 + ], + "spans": [ + { + "bbox": [ + 34, + 434, + 281, + 539 + ], + "type": "image", + "image_path": "86dad0c44704e25fe40867b839d28ab5da2b911fe27bb7b29d90f6eac1e89d9f.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 53, + 540, + 277, + 562 + ], + "lines": [ + { + "bbox": [ + 53, + 540, + 277, + 562 + ], + "spans": [ + { + "bbox": [ + 53, + 540, + 277, + 562 + ], + "type": "text", + "content": "Normalised histogram of distances of intermediate transform encodings to " + }, + { + "bbox": [ + 53, + 540, + 277, + 562 + ], + "type": "inline_equation", + "content": "Z_{\\mathrm{des}}" + }, + { + "bbox": [ + 53, + 540, + 277, + 562 + ], + "type": "text", + "content": ", i.e., " + }, + { + "bbox": [ + 53, + 540, + 277, + 562 + ], + "type": "inline_equation", + "content": "\\mathbf{d}(e(x_i), \\text{proj}_{Z_{\\mathrm{des}}} e(x_i)) / \\sqrt{m}" + }, + { + "bbox": [ + 53, + 540, + 277, + 562 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 53, + 540, + 277, + 562 + ], + "type": "inline_equation", + "content": "e(.) \\in \\mathbb{R}^m" + }, + { + "bbox": [ + 53, + 540, + 277, + 562 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 569, + 286, + 700 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 569, + 286, + 700 + ], + "spans": [ + { + "bbox": [ + 46, + 569, + 286, + 700 + ], + "type": "text", + "content": "In comparison to the primitive baseline, the metric values with " + }, + { + "bbox": [ + 46, + 569, + 286, + 700 + ], + "type": "inline_equation", + "content": "\\mathcal{N}" + }, + { + "bbox": [ + 46, + 569, + 286, + 700 + ], + "type": "text", + "content": "-VAEs are low for most queries as desired, and further reduce on incentivising consistency in their mappings, as in 3., and making the encoding traversals more precise and segmented, as in 4. Although we do not observe notable changes in the verification outcomes with different " + }, + { + "bbox": [ + 46, + 569, + 286, + 700 + ], + "type": "inline_equation", + "content": "\\mathcal{N}" + }, + { + "bbox": [ + 46, + 569, + 286, + 700 + ], + "type": "text", + "content": "-VAEs, this metric could be used to guide the construction of input specifications. Notice that this metric is the latent space-based analogue of the pixel space distance used to define input specifications and evaluate generators for EDN-based verification [20]." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 59, + 701, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 701, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 59, + 701, + 286, + 713 + ], + "type": "text", + "content": "The motivation behind Axis specifications is the disen" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 72, + 545, + 239 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 239 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 239 + ], + "type": "text", + "content": "tanglement of conditional dimensions in capturing specified variations. To assess disentanglement, we compute the ratio of the highest value among the incorrect conditional dimensions to the value of the correct conditional dimension of an encoding for a discrete attribute. For the continuous transforms encoded as graphics code [23], an equivalent metric is the ratio of the maximum variance among the incorrect conditional dimensions to the variance in the correct conditional dimension, computed for a batch of encodings. Below we report the mean value distribution of this metric for normally and conditionally trained " + }, + { + "bbox": [ + 304, + 72, + 545, + 239 + ], + "type": "inline_equation", + "content": "\\mathcal{N}" + }, + { + "bbox": [ + 304, + 72, + 545, + 239 + ], + "type": "text", + "content": "-VAEs. As expected, conditional training results in low metric values as desired, while normal training results in similar values for most dimensions and metric values closer to unity." + } + ] + } + ], + "index": 12 + }, + { + "type": "image", + "bbox": [ + 297, + 243, + 539, + 346 + ], + "blocks": [ + { + "bbox": [ + 297, + 243, + 539, + 346 + ], + "lines": [ + { + "bbox": [ + 297, + 243, + 539, + 346 + ], + "spans": [ + { + "bbox": [ + 297, + 243, + 539, + 346 + ], + "type": "image", + "image_path": "03ff1b40bb2f46c75760f5af0c59b401f4cba20579025afe10c0d1a1075e8be8.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 321, + 348, + 527, + 368 + ], + "lines": [ + { + "bbox": [ + 321, + 348, + 527, + 368 + ], + "spans": [ + { + "bbox": [ + 321, + 348, + 527, + 368 + ], + "type": "text", + "content": "Normalised histogram of maximum incorrect-to-correct dimension ratios for conditionally trained LVMs." + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 318, + 368, + 530, + 378 + ], + "lines": [ + { + "bbox": [ + 318, + 368, + 530, + 378 + ], + "spans": [ + { + "bbox": [ + 318, + 368, + 530, + 378 + ], + "type": "text", + "content": "Numbers in the legend entries denote manifold dimensionality." + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_footnote" + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 383, + 545, + 455 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 383, + 545, + 455 + ], + "spans": [ + { + "bbox": [ + 304, + 383, + 545, + 455 + ], + "type": "text", + "content": "These latent space-based metrics are more relevant to our approach than the pixel space-based or the attribute detection-based analyses relevant to the EDN approach. This is because the effectiveness of verification with our approach depends more on the spatial coherence and precision of the LVM encodings, than its reconstruction capabilities." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 466, + 383, + 478 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 466, + 383, + 478 + ], + "spans": [ + { + "bbox": [ + 306, + 466, + 383, + 478 + ], + "type": "text", + "content": "6. Conclusions" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 486, + 545, + 545 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 486, + 545, + 545 + ], + "spans": [ + { + "bbox": [ + 304, + 486, + 545, + 545 + ], + "type": "text", + "content": "In this work we introduced an efficient and precise approach for verifying specifications in the latent space. By means of the proposed approach, we could effectively assess and verify deep networks against pose changes, and provide counterexamples that inform of their fragilities." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 546, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 546, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 546, + 545, + 713 + ], + "type": "text", + "content": "In terms of limitations, we discussed that the ease of learning a conditional latent manifold, and the computational gains of our verification approach can be affected by the increase of layers in the network head of our pipeline. However, since the largest activation layers can be excluded from the verification path with our approach, it still fares better than the existing approach. A general limitation of latent-space based verification approaches is their necessity for an adequate LVM, which, as discussed for our approach, may require the original network to be trained as part of the proposed pipeline. While we did not find these limitations to hinder the application of our approach to the practical usecases demonstrated in this work, further experiments should be conducted to better assess its generality." + } + ] + } + ], + "index": 19 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "type": "text", + "content": "3901" + } + ] + } + ], + "index": 20 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 288, + 713 + ], + "type": "list", + "angle": 0, + "index": 14, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 147 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 147 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 147 + ], + "type": "text", + "content": "[1] M. 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In this work, we introduce the first 3D-based multi-frame denoising method that significantly outperforms its 2D-based counterparts with lower computational requirements. Our method extends the multiplane image (MPI) framework for novel view synthesis by introducing a learnable encoder-renderer pair manipulating multiplane representations in feature space. The encoder fuses information across views and operates in a depth-wise manner while the renderer fuses information across depths and operates in a view-wise manner. The two modules are trained end-to-end and learn to separate depths in an unsupervised way, giving rise to Multiplane Feature (MPF) representations. Experiments on the Spaces and Real Forward-Facing datasets as well as on raw burst data validate our approach for view synthesis, multi-frame denoising, and view synthesis under noisy conditions.", + "bbox": [ + 75, + 325, + 473, + 628 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 661, + 209, + 678 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Multi-frame denoising is a classical problem of computer vision where a noise process affecting a set of images must be inverted. The main challenge is to extract consistent information across images effectively and the current state of the art relies on optical flow-based 2D alignment [3,7,45]. Novel view synthesis, on the other hand, is a classical problem of computer graphics where a scene is viewed from one or more camera positions and the task is to predict novel views from target camera positions. This problem requires to reason about the 3D structure of the scene and is typically solved using some form of volumetric representation [28, 32, 55]. Although the two problems are traditionally considered distinct, some novel view synthesis approaches have recently been observed to handle noisy", + "bbox": [ + 75, + 688, + 470, + 902 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/d9336b458b51d07f33a7b19bee95e30bf383409c3a1c73fa220a5a647e57935f.jpg", + "image_caption": [ + "Figure 1. Top: Our Multiplane Features Encoder-Renderer (MPFER) reimagines the MPI pipeline by moving the multiplane representation to feature space. Bottom: MPFER significantly outperforms existing methods in multiple challenging scenarios, including here, novel view synthesis from 8 highly degraded inputs." + ], + "image_footnote": [], + "bbox": [ + 500, + 290, + 893, + 465 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "inputs well, and to have a denoising effect in synthesized views by discarding inconsistent information across input views [18,26]. This observation opens the door to 3D-based multi-frame denoising, by recasting the problem as a special case of novel view synthesis where the input views are noisy and the target views are the clean input views [26, 31].", + "bbox": [ + 496, + 566, + 890, + 657 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Recently, novel view synthesis has been approached as an encoding-rendering process where a scene representation is first encoded from a set of input images and an arbitrary number of novel views are then rendered from this scene representation. In the Neural Radiance Field (NeRF) framework for instance, the scene representation is a radiance field function encoded by training a neural network on the input views. Novel views are then rendered by querying and integrating this radiance field function over light rays originating from a target camera position [2, 24, 28]. In the Multiplane Image (MPI) framework on the other hand, the scene representation is a stack of semi-transparent colored layers arranged at various depths, encoded by feeding the input views to a neural network trained on a large number of scenes. Novel views are then rendered by warping and overcompositing the semi-transparent layers [8, 41, 55].", + "bbox": [ + 496, + 659, + 892, + 901 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "20898", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "In the present work, we adopt the MPI framework because it is much lighter than the NeRF framework computationally. The encoding stage only requires one inference pass on a network that generalizes to new scenes instead of training one neural network per-scene, and the rendering stage is essentially free instead of requiring a large number of inference passes. However, the standard MPI pipeline struggles to predict multiplane representations that are self-consistent across depths from multiple viewpoints. This problem can lead to depth-discretization artifacts in synthesized views [40] and has previously been addressed at the encoding stage using computationally expensive mechanisms and a large number of depth planes [8, 11, 27, 40]. Here, we propose to enforce cross-depth consistency at the rendering stage by replacing the fixed overcompositing operator with a learnable renderer. This change of approach has three important implications. First, the encoder module can now process depths independently from each other and focus on fusing information across views. This significantly reduces the computational load of the encoding stage. Second, the scene representation changes from a static MPI to Multiplane Features (MPF) rendered dynamically. This significantly increases the expressive power of the scene encoding. Finally, the framework's overall performance is greatly improved, making it suitable for novel scenarios including multi-frame denoising where it outperforms standard 2D-based approaches at a fraction of their computational cost. Our main contributions are as follow:", + "bbox": [ + 76, + 90, + 472, + 513 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- We solve the cross-depth consistency problem for multi-plane representations at the rendering stage, by introducing a learnable renderer.", + "- We introduce the Multiplane Feature (MPF) representation, a generalization of the multiplane image with higher representational power.", + "- We re-purpose the multiplane image framework originally developed for novel view synthesis to perform 3D-based multi-frame denoising.", + "- We validate the approach with experiments on 3 tasks and 3 datasets and significantly outperform existing 2D-based and 3D-based methods for multi-frame denoising." + ], + "bbox": [ + 76, + 515, + 468, + 696 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related work", + "text_level": 1, + "bbox": [ + 76, + 709, + 215, + 724 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Multi-frame denoising Multi-frame restoration methods are frequently divided into two categories, depending on the type of image alignment employed. Explicit alignment refers to the direct warping of images using optical flows predicted by a motion compensation module [4, 43, 44, 54]. In contrast, implicit alignment refers to local, data-driven deformations implemented using dynamic upsampling filters [16, 17], deformable convolutions [45, 49], kernel prediction networks [25] or their extension, basis prediction networks [53]. Explicit alignment is better at dealing with large motion while implicit alignment is better at deal", + "bbox": [ + 76, + 734, + 472, + 902 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "ing with residual motion, and state-of-the-art performance can be achieved by combining both in the form of flow-guided deformable convolutions [6, 7]. Another distinction between multi-frame restoration methods is the type of processing used. A common approach is to concatenate the input frames together along the channel dimension [4, 43, 44, 49, 54] but recurrent processing is more efficient [9, 10, 34, 42], especially when implemented in a bidirectional way [5, 7, 14]. Basic VSR++ achieves state-of-the-art performance by combining flow-guided deformable alignment with bidirectional recurrent processing iterated multiple times [7]. In a different spirit, the recent DeepRep method [3] introduces a deep reparameterization in feature space of the maximum a posteriori formulation of multiframe restoration. Similarly to the previous methods however, it still uses a form of explicit 2D alignment, and lacks any ability to reason about the 3D structure of the scene.", + "bbox": [ + 496, + 90, + 893, + 349 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "View synthesis The idea to decompose a scene into a set of semi-transparent planes can be traced back to the use of mattes and blue screens in special effects filmmaking [38, 47]. This scene representation was first applied to view interpolation in [41], and recently gained popularity under the name of Multiplane Image (MPI) [55]. It is particularly powerful to generate novel views from a small set of forward facing views [8, 27, 55], and can even be used to generate novels views from a single image [11, 20, 46]. The rendering of view dependent-effects and non-Lambertian surfaces is challenging due to the use of a single set of RGB $\\alpha$ images, and can be improved by predicting multiple MPIs combined as a weighted average of the distance from the input views [27], or as a set of basis components [51]. The simplicity of this representation is appealing, but it can still be computationally heavy when the number of depth planes grows [8, 51], and the rendered views can suffer from depth discretization artifacts [40]. A number of alternative layered scene representations exist, including the Layered Depth Image (LDI) consisting in one RGB image with an extra depth channel [36], and variants of MPIs and LDIs [13, 19, 21, 39]. So far however, all these methods use a fixed overcompositing operator at the rendering stage. The idea to perform view synthesis by applying 3D operations in the feature space of an encoder-decoder architecture was explored on simple geometries in [52], and used with success on a point-cloud scene representation for view synthesis from a single image in [50]. Recently, Neural Radiance Fields (NeRFs) have become highly popular for their ability to produce high quality renderings of complex scenes from arbitrary viewpoints [2, 24, 28-30]. However, they tend to be very heavy computationally, require a large number of input views, and lack the ability to generalize to novel scenes. IBRNet [48] improves generalizability by learning a generic view interpolation function, but the approach remains computationally heavy. The application of view syn", + "bbox": [ + 496, + 356, + 893, + 902 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "20899", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "thesis approaches to multi-frame restoration has been limited so far, and exclusively based on NeRF. RawNeRF [26] explores novel view synthesis in low-light conditions, and reports strong denoising effects in the synthesized views. Deblur-NeRF [22] augments the ability of NeRFs to deal with blur by including Deformable Sparse Kernels. Noise-aware-NeRFs [31] improves the IBRNet architecture to explicitly deal with noise. However, these different restoration approaches still suffer from the limitations affecting their underlying NeRF representations.", + "bbox": [ + 75, + 90, + 472, + 243 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Method", + "text_level": 1, + "bbox": [ + 76, + 256, + 168, + 272 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We start by describing the standard MPI processing pipeline, before discussing the cross-depth consistency problem. We then introduce our MPF Encoder-Renderer and its adaptation to multi-frame denoising.", + "bbox": [ + 75, + 282, + 468, + 343 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Standard MPI processing pipeline", + "text_level": 1, + "bbox": [ + 76, + 353, + 375, + 369 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The standard MPI processing pipeline turns a set of input views into an arbitrary set of rendered novel views by applying 4 main transformations: forward-warping, MPI prediction, backward-warping, overcompositing (See Figure 2a). We describe this pipeline in more details below.", + "bbox": [ + 75, + 377, + 468, + 452 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Input views The inputs of the pipeline are a set of $V$ views of a scene, consisting of images and camera parameters. The images are of height $H$ and width $W$ , with red-green-blue color channels, and can be stacked into a 4D tensor $\\boldsymbol{I} = \\{\\{\\{I_{vchw}\\}_{w=1}^{W}\\}_{h=1}^{H}\\}_{c=1}^{3}\\}_{v=1}^{V}$ . To simplify notations, we omit the dimensions $c, h, w$ and refer to an individual image as $\\boldsymbol{I}_v$ . The camera parameters consist of an intrinsic tensor $\\boldsymbol{K}$ of size $V \\times 3 \\times 3$ containing information about the focal lengths and principal point of the cameras, and an extrinsic tensor containing information about the camera orientations in the world coordinate system, that can be split into a rotation tensor $\\boldsymbol{R}$ of size $V \\times 3 \\times 3$ and a translation tensor $\\boldsymbol{t}$ of size $V \\times 3 \\times 1$ . A reference view $i$ is defined a priori, and the positions of all the cameras are assumed to be expressed relatively to it. The intrinsic matrix $\\boldsymbol{K}_i$ of the reference camera is defined such that the corresponding field of view covers the region of space visible to all the input views. Finally, a set of $D$ depth planes is distributed orthogonally to the reference viewing direction such that their normal is $\\boldsymbol{n} = (0,0,1)^{\\top}$ , and their distances $\\{a_d\\}_{d=1}^D$ from the reference camera center are sampled uniformly in disparity. The camera parameters and the depth planes are used to define a set of $D \\times V$ homography projections, represented by a tensor $\\boldsymbol{H}$ of size $D \\times V \\times 3 \\times 3$ . Each homography is between one of the input views and the reference view, and is induced by one of the depth planes, such that its matrix is expressed as [12]:", + "bbox": [ + 75, + 457, + 472, + 864 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {H} _ {d v} = \\boldsymbol {K} _ {v} \\left(\\boldsymbol {R} _ {v} - \\frac {\\boldsymbol {t} _ {v} \\boldsymbol {n} ^ {\\top}}{a _ {d}}\\right) \\boldsymbol {K} _ {i} ^ {- 1} \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 156, + 869, + 468, + 905 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/05c5183740a5ef516a1a6111974e4b17521f8ac9c0e7fb08be5fc47a5c26424b.jpg", + "image_caption": [ + "(a) Standard MPI processing pipeline." + ], + "image_footnote": [], + "bbox": [ + 501, + 88, + 893, + 156 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/4171f0d6022d2873f3481a5bcdcae794df4c8425eb6ad1f5f2cf326eee21c1d2.jpg", + "image_caption": [ + "(b) Our MPF Encoder-Encoder.", + "Figure 2. In the standard MPI processing pipeline, all the learning and most of the processing happens in the MPINet module. We propose to move the multiplane representation to feature space, by giving some processing power to the warping operators, and replacing the overcompositing operator with a learnable renderer." + ], + "image_footnote": [], + "bbox": [ + 501, + 186, + 893, + 256 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Plane Sweep Volumes The first transformation in the MPI pipeline is the computation of Plane Sweep Volumes (PSVs), obtained by forward-warping each input image $D$ times, according to the homography $\\pmb{H}_{dv}$ . The sampling rate of the warping operator $\\mathcal{W}$ is a hyperparameter that can be controlled using an up-scaling factor $s$ . Each transformation can thus be written as $\\pmb{X}_{dv} = \\mathcal{W}(\\pmb{I}_v, \\pmb{H}_{dv}, s)$ and the PSV tensor $\\pmb{X}$ is of size $D \\times V \\times 3 \\times sH \\times sW$ .", + "bbox": [ + 496, + 386, + 890, + 507 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Multiplane Image The main processing block of the pipeline is a neural network MPINet, turning the set of PSVs into a multiplane image representation of the scene $\\mathbf{Y} = \\mathrm{MPINet}(\\mathbf{X})$ where $\\mathbf{Y}$ is a set of $D$ semi-transparent RGB images of size $D \\times 4 \\times sH \\times sW$ , constrained to the [0,1] range by using a sigmoid activation function.", + "bbox": [ + 496, + 515, + 893, + 608 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Projected MPs The MPI is then backward-warped to a set of $R$ novel views, defined by an homography tensor $G$ of size $R \\times D \\times 3 \\times 3$ following Eq. (1) with the depth and view dimensions transposed. The backward-warping operation is defined as $Z_{rd} = \\mathcal{W}\\left(\\mathbf{Y}_d, \\mathbf{G}_{rd}^{-1}, 1 / s\\right)$ obtaining a tensor of projected MPs $Z$ of size $R \\times D \\times 4 \\times H \\times W$ .", + "bbox": [ + 496, + 614, + 893, + 705 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "**Rendered views** The projected MPs are finally collapsed into single RGB images by applying the overcompositing operator $\\mathcal{O}$ . This operator splits each RGB $\\alpha$ image $Z_{rd}$ into a colour component $C_{rd}$ and an alpha component $A_{rd}$ and computes $\\tilde{J}_r = \\sum_{d=1}^{D} \\left( C_{rd} A_{rd} \\prod_{k=d+1}^{D} (1 - A_{rk}) \\right)$ obtaining the rendered views $\\tilde{J}$ of size $R \\times 3 \\times H \\times W$ .", + "bbox": [ + 496, + 715, + 890, + 816 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Training The pipeline is typically trained end-to-end in a supervised way by minimizing a loss $\\mathcal{L}(\\tilde{\\boldsymbol{J}},\\boldsymbol {J})$ between the rendered views $\\tilde{\\boldsymbol{J}}$ and the corresponding ground-truth images $\\boldsymbol{J}$ . In practice, $\\mathcal{L}$ is often an $\\mathcal{L}_1$ loss applied to low level features of a VGG network [37].", + "bbox": [ + 496, + 824, + 893, + 900 + ], + "page_idx": 2 + }, + { + "type": "footer", + "text": "20900", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. Cross-depth consistency", + "text_level": 1, + "bbox": [ + 76, + 90, + 297, + 107 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The main and only learnable module of the standard MPI pipeline is the prediction network MPINet, transforming a 5D PSV tensor into a 4D MPI scene representation. Its task is challenging because multiplane images are hyperconstrained representations: their semi-transparent layers interact with each other in non-trivial and view-dependent ways, and missing or redundant information across layers can result in depth discretization artifacts after applying the overcompositing operator [40]. To perform well, MPINet requires a mechanism enforcing cross-depth consistency; and several approaches have been considered before.", + "bbox": [ + 75, + 114, + 468, + 281 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In the original case of stereo-magnification [55], there is one reference input and one secondary input which is turned into a single PSV. Both are concatenated along the channel dimension and fed to an MPINet module predicting the full MPI in one shot as a 3D tensor of size $(D \\times 4) \\times sH \\times sW$ , such that cross-depth consistency is enforced within the convolutional layers of MPINet. A similar solution can be used in the case of single-view synthesis [46], where there is a single reference input image and no PSV. In the general case with $V$ inputs, however, the PSV tensor $\\mathbf{X}$ becomes very large and there are two main ways to process it.", + "bbox": [ + 75, + 282, + 470, + 449 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Option 1 The first solution is to generalize the approach of [55] and concatenate $\\mathbf{X}$ across views and depths before feeding it to a network predicting the full MPI in one shot: $\\mathbf{Y} = \\mathrm{MPINet}\\Big(\\{\\{X_{dv}\\}_{v = 1}^{V}\\}_{d = 1}^{D}\\Big)$ .", + "bbox": [ + 76, + 450, + 468, + 518 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Option 2 The second solution is to concatenate $\\mathbf{X}$ across views, and process each depth separately—effectively running the MPINet block $D$ times in parallel: $\\mathbf{Y} = \\{\\mathrm{MPINet}\\big(\\{X_{dv}\\}_{v=1}^{V}\\big)\\}_{d=1}^{D}$ .", + "bbox": [ + 76, + 518, + 468, + 583 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Option 1 tends to work poorly in practice [8], as it requires to either use very large convolutional layers with intractable memory requirements, or discard most of the information contained in the input PSVs after the first convolutional layer. Option 2 is appealing as it fuses information across views more effectively, but the resulting MPI typically suffers from a lack of cross-depth consistency as each depth is processed separately. Most previous works adopt Option 2 as a starting point, and augment it with various mechanisms allowing some information to flow across depths. For instance, some methods implement MPINet with 3D convolutions [27, 40], such that each depth is treated semi-independently within a local depth neighborhood dependent on the size of the kernel, which is typically 3. By design however, this solution cannot handle interactions between distant depth planes. DeepView [8] proposes to solve the recursive cross-depth constraint by iteratively refining the prediction of the MPINet block, effectively performing a form of learned gradient descent. However, this solution requires to run the MPI network multiple times, which is computationally heavy. Finally, the method of [11] uses a feature", + "bbox": [ + 75, + 583, + 470, + 901 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "masking strategy to deal with inter-plane interactions explicitly. This solution is both complex (multiple networks are required to predict the masks) and rigid (the masking operations are fixed and still work on a per-depth basis).", + "bbox": [ + 496, + 90, + 890, + 152 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.3. Our MPF Encoder-Encoder", + "text_level": 1, + "bbox": [ + 498, + 162, + 759, + 176 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Here, we propose to solve the cross-depth consistency problem in a novel way, by addressing it at the rendering stage. Specifically, we replace the fixed overcompositing operator with a learnable renderer enforcing consistency directly at the output level on a per-view basis. This design change greatly simplifies the task of the multiplane representation encoder, which can now focus on fusing information across views in a depth-independent way. It also promotes the multiplane representation to feature space, by relaxing existing constraints on the number of channels and scaling in the [0,1] range. The four transformations of the pipeline are modified as follows (See Figure 2b).", + "bbox": [ + 496, + 185, + 890, + 367 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Plane Sweep Volumes To decrease the amount of information loss through image warping and promote the PSVs to feature space, we now apply a convolution to the images before warping them: $\\pmb{X}_{dv} = \\mathcal{W}(\\mathrm{Conv}(\\pmb{I}_v),\\pmb{H}_{dv},s)$ . The PSV tensor $\\pmb{X}$ is now of size $D\\times V\\times C_1\\times sH\\times sW$ where the number of channels $C_1$ is a hyperparameter.", + "bbox": [ + 496, + 371, + 890, + 463 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Multiplane Features We then replace the MPINet module with an encoder applied to each depth independently: $\\mathbf{Y} = \\{\\mathrm{Encoder}\\left(\\left\\{\\mathbf{X}_{dv}\\right\\}_{v=1}^{V}\\right)\\}_{d=1}^{D}$ . The multiplane representation $\\mathbf{Y}$ is now in feature space: its range is not constrained by a sigmoid function anymore and its size is $D \\times C_2 \\times sH \\times sW$ where the number of channels $C_2$ is a second hyperparameter.", + "bbox": [ + 496, + 465, + 890, + 575 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Projected MPFs The MPF is still backward-warped to a set of $R$ novel views defined by an homography tensor $\\pmb{G}$ , but this is now followed by a convolution collapsing the depth and channel dimensions into a single dimension: $\\mathbf{Z}_r = \\mathrm{Conv}\\Big(\\{\\mathcal{W}(\\mathbf{Y}_d,\\mathbf{G}_{dr}^{-1},1 / s)\\}_{d = 1}^D\\Big)$ . The tensor $\\pmb{Z}$ is of size $R\\times C_3\\times H\\times W$ where $C_3$ is a third hyperparameter.", + "bbox": [ + 496, + 580, + 890, + 678 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Rendered views Finally, the projected MPFs are turned into the final rendered views by a simple CNN renderer operating on each view separately: $\\tilde{J} = \\{\\mathrm{Renderer}(Z_r)\\}_{r=1}^R$ . The rendered views $\\tilde{J}$ are of size $R \\times 3 \\times H \\times W$ .", + "bbox": [ + 496, + 681, + 890, + 744 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Training The pipeline is still trained end-to-end by minimizing a loss $\\mathcal{L}(\\tilde{J}, J)$ between the rendered views $\\tilde{J}$ and the corresponding ground-truth images $J$ , but the renderer and the warping operators are now learnable. When the input views $I$ are noisy versions of ground-truth images $I^{*}$ , the pipeline can be turned into a multi-frame denoising method by using the input homographies $H$ during backward-warping, obtaining denoised outputs $\\tilde{I}$ , and by minimizing the loss $\\mathcal{L}(\\tilde{I}, I^{*})$ . There is then a one-to-one mapping between the input views and the rendered views,", + "bbox": [ + 496, + 750, + 890, + 901 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "20901", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/274977e804a5bde958c6e781ba13331b72a5e53c24b1f54dda6c2da36fc0a54f.jpg", + "image_caption": [ + "Figure 3. Our Multiplane Features Encoder-Encoder (MPFER). Input views are forward-warped into plane sweep volumes (PSVs) which are processed depthwise by the Encoder Unet64. The resulting multiplane feature representation (MPF) can then be back-projected to an arbitrary number of novel views, or to the same views as the inputs—allowing the integration of a skip connection (illustrated here). The Encoder Unet64 processes the projected MPFs on a per-view basis, producing the final synthesised or denoised outputs." + ], + "image_footnote": [], + "bbox": [ + 135, + 85, + 831, + 320 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "and it is possible to integrate a skip connection feeding the noisy inputs directly to the renderer to guide its final predictions. In all our experiments, we use Unets [33] with a base of 64 channels to implement both the encoder and the renderer. We set $C_1 = C$ , $C_2 = V \\times C$ and $C_3 = 64$ such that there is a single hyperparameter $C$ to vary. Our Multiplane Features Encoder-Render (MPFER) is illustrated in Figure 3 for 3 inputs views and 3 depth planes. A MindSpore [15] implementation of our method is available1.", + "bbox": [ + 75, + 412, + 472, + 549 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 76, + 561, + 209, + 579 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We first consider the Spaces dataset [8] and validate our approach on novel view synthesis. We then focus on a denoising setup and perform extensive comparisons to state-of-the-art 2D-based methods. Finally, we compare our approach to the 3D-based multi-frame denoising method of [31] by replicating their experimental setup on the Real Forward-Facing dataset. In all cases, our method outperforms competitors at a fraction of the computational cost.", + "bbox": [ + 75, + 587, + 468, + 708 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.1. Spaces", + "text_level": 1, + "bbox": [ + 76, + 715, + 166, + 732 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The Spaces dataset [8] consists of 100 indoor and outdoor scenes, captured 5 to 10 times each using a 16-camera rig placed at slightly different locations. 90 scenes are used for training and 10 scenes are held-out for evaluation. The resolution of the images is $480 \\times 800$ .", + "bbox": [ + 75, + 739, + 468, + 815 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Novel view synthesis We start by replicating the novel view synthesis setup of DeepView [8] with four scenarios: one with 12 input views and three with 4 input views. Similarly to DeepView, we use a VGG loss and train our models", + "bbox": [ + 75, + 818, + 468, + 878 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "for 100k steps using the Adam optimizer, with a learning rate of $1.5\\mathrm{e - }3$ . We reduce the learning rate to $1.5\\mathrm{e - }4$ after 80k steps, and use a batch size of 4. Memory usage was reported to be a major challenge in DeepView, and all our models are kept at a significantly smaller size to avoid this issue. While DeepView uses a sophisticated strategy to only generate enough of the MPI to render a $32\\times 32$ crop in the target image, we use a large patch size of 192 and only apply the loss on the region of the patch that contains more than $80\\%$ of the depths planes after backward warping. We compute all metrics by averaging over the validation scenes and target views of each setup, and after cropping a boundary of 16 pixels on all images as done in [8]. We compare to DeepView [8] and Soft3D [32] by using the synthesised images provided with the Spaces dataset. We also consider three variants of the standard MPI pipeline using the same Unet backbone as our MPFER method and trained in the same conditions, but processing the input PSV in different ways. MPINet implements Option 1 from Sec. 3.2. The views and depths dimensions of the PSV tensor are stacked along the channel dimension and fed to the Unet backbone to predict the output MPI in one shot. MPINet-dw implements Option 2 from Sec. 3.2. The Unet backbone runs depthwise on slices of the PSV to predict each depth plane of the MPI separately, without communication mechanism across depths. Finally, MPINet-dw-it implements a one-step version of the learned gradient descent algorithm of DeepView. A first estimate of the MPI is predicted by a Unet backbone running depthwise, and this estimate is fed to a second Unet backbone also running depthwise, along with the input PSV and gradient components (R), which are PSV-projected current estimates of the target views.", + "bbox": [ + 500, + 412, + 893, + 897 + ], + "page_idx": 4 + }, + { + "type": "page_footnote", + "text": "", + "bbox": [ + 94, + 886, + 450, + 901 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "20902", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/fe555aed21d8f9ec5727e740450c9f2fdcfc0135fc2524e7826295db142e70ad.jpg", + "image_caption": [ + "Figure 4. Qualitative evaluation for multi-frame denoising with Gain 20 (best viewed zoomed in). We compare MPFER to 2D-based methods on Spaces (top) and to 3D-based methods on the Real Forward-Facing dataset (bottom)." + ], + "image_footnote": [], + "bbox": [ + 76, + 85, + 893, + 429 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "For our MPFER method and the MPINet ablations, we use a number of depth planes $D = 64$ distributed between 100 and 0.5 meters away from the reference camera, placed at the average position of the input views. We use a number of channels $C = 8$ and a PSV/MPF upscaling factor $s = 1.5$ . Since the Unet backbone is not agnostic to the number of input views, we train one version of each model for the setup with 12 input views and one version for the three setups with 4 input views. The results are presented in Table 1. We observe a clear progression between the performances of MPINet, MPINet-dw and MPINet-dw-it, illustrating the benefit of each design change. Our MPFER method outperforms MPINet-dw-it by up to 4dBs in PSNR at a similar computational complexity, and outperforms DeepView by up to 1.8dB at a fraction of the complexity, clearly motivating the use of a learnt renderer for efficient depth fusion.", + "bbox": [ + 75, + 493, + 472, + 750 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Multi-frame denoising We now consider a different setup where the inputs are 16 views from one rig position with images degraded with noise, and the targets are the same 16 views denoised. Similarly to previous works [3, 25,31,53], we apply synthetic noise with a signal dependent Gaussian distribution $\\mathbf{I}_{vchw} \\sim \\mathcal{N}\\left(\\mathbf{I}_{vchw}^{*}, \\sigma_{r}^{2} + \\sigma_{s}\\mathbf{I}_{vchw}^{*}\\right)$ where $\\mathbf{I}$ is the tensor of noisy inputs, $\\mathbf{I}^{*}$ is the ground truth signal, and $\\sigma_r$ and $\\sigma_s$ are noise parameters that are fixed for each sequence. We focus in particular on challenging sce", + "bbox": [ + 75, + 763, + 472, + 902 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "narios with moderate to high gain levels [4, 8, 16, 20], corresponding to the $(\\log (\\sigma_r),\\log (\\sigma_s))$ values $[-1.44, - 1.84)$ $(-1.08, - 1.48)$ $(-0.72, - 1.12)$ $(-0.6, - 1.0)]$ respectively.", + "bbox": [ + 498, + 493, + 890, + 540 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We consider two patch-based approaches: VBM4D [23] and VNLB [1], as well as four state-of-the-art learning-based methods: BPN [53], BasicVSR [5] and its extension BasicVSR++ [7], and DeepRep [3]. To evaluate the influence of the model size and in particular the number of depth planes, we train three MPFER models: MPFER-16 with $(D,C,s) = (16,8,1.)$ , MPFER-32 with $(D,C,s) = (32,16,1.25)$ , and MPFER-64 with $(D,C,s) = (64,8,1.25)$ . MPFER-16 has the particularity of using the same number of depth planes as there are input images, meaning that the number of Unet passes per frame to denoise the sequence is $(D + V) / V = 2$ . This observation motivates us to perform a comparison with three other architectures, using a strict computational budget of 2 Unet passes per frame. Unet-SF (for Single-Frame) is constituted of two Unet blocks without temporal connection, therefore processing the sequence as a disjoint set of single frames. Unet-BR (for Bidirectional-Recurrent) is constituted of two Unet blocks with bidirectional recurrent connections: the lower Unet processes the sequence in a backward way, and the higher Unet processes the sequence in a feedforward way. Finally, Unet-BR-OF (for Bidirectional-Recurrent with Optical-Flow alignment) is constituted of two Unet", + "bbox": [ + 496, + 551, + 892, + 902 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "20903", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "blocks with bidirectional recurrent connections, and the recurrent hidden-state is aligned using a SpyNet module, as done in basicVSR [5]. We train all the models in the same conditions as for the novel view synthesis setup, except for the patch size which we increase to 256, and the loss which we replace with a simple L1 loss. During training, we vary the gain level randomly and concatenate an estimate of the standard deviation of the noise to the input, as in [25,31,53]. We evaluate on the first rig position of the 10 validation scenes of the Spaces dataset for the 4 gain levels without boundary-cropping, and present the results in Table 2. Each model receives 16 noisy images as input and produces 16 restored images as output, except for BPN and DeepRep which are burst processing methods and only produce one output. For these methods, we choose the view number 6 at the center of the camera rig as the target output, and compare the performances of all methods on this frame. Our MPFER method clearly outperforms all the other methods at a fraction of the computational cost. It performs particularly strongly at high noise levels, with improvements over other methods of more that 2dBs in PSNR. MPFER-16 also performs remarkably well, despite using only 16 depth planes. This suggests that the high representational power of multiplane features allows to significantly reduce the number of depth planes—and therefore the computational cost—compared to standard MPI approaches, which typically use a very high number of planes (80 in the case of DeepView [8], up to 192 in the case of NeX [51]). A qualitative evaluation is available in Figure 4 (top), and we observe that MPFER is able to reconstruct scenes with much better details. We also present a visualization of multiplane features in Figure 6, illustrating how the model learns to separate depths in an unsupervised way.", + "bbox": [ + 76, + 90, + 472, + 590 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.2. LLFF-N", + "text_level": 1, + "bbox": [ + 76, + 599, + 181, + 614 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "The LLFF-N dataset [31] is a variant of the Real Forward-Facing dataset [27] where images are linearized by applying inverse gamma correction and random inverse white balancing, and synthetic noise is applied following the same signal dependent Gaussian distribution as used in the previous section with the six gain levels [1, 2, 4, 8, 16, 20]. The dataset contains 35 scenes for training and 8 scenes for testing, and the resolution of the images is $756 \\times 1008$ .", + "bbox": [ + 76, + 623, + 468, + 744 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "**Denoising** In this setup, the model receives 8 frames in input: the target frame plus its 7 nearest neighbors in terms of camera distances. We train one MPFER model with $(D,C,s) = (64,8,1.25)$ , using an $\\mathcal{L}_1$ loss applied to the target frame. We evaluate on the 43 bursts used in [31] (every 8th frame of the test set) and present the results in the first half of Table 3. A qualitative evaluation is also available in Figure 4 (bottom). To assess the robustness of our method to noisy camera positions, we evaluate it using camera positions computed on clean images (MPFER-C) and", + "bbox": [ + 76, + 750, + 472, + 902 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "on noisy images (MPFER-N) using COLMAP [35]. Our method outperforms IBRNet-N and NAN in both scenarios by large margins, but the evaluation using clean camera poses performs significantly better at high noise levels.", + "bbox": [ + 496, + 90, + 893, + 152 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Synthesis under noisy conditions In this setup, the model receives as input the 8 nearest neighbors to a held-out target. Again, we train one MPFER model with $(D,C,s) = (64,8,1.25)$ , using an $\\mathcal{L}_1$ loss applied to the target frame. We evaluate on the same 43 bursts as before and report the results in the second half of Table 3. Our method performs on par with IBRNet and NAN at very low noise levels (close to a pure synthesis problem), and significantly outperforms the other methods at larger noise levels. MPFER only requires $D$ Unet passes to produce an MPF, and 1 Unet pass to render a novel view, which is significantly lighter than IBRNet and NAN. At inference time, the Unet pass requires 0.6 Mflops per pixel, compared to 45 Mflops for IBRNet [48]. A qualitative evaluation is available in Figure 1 for Gain 20.", + "bbox": [ + 496, + 155, + 893, + 368 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Low-Light Scenes Finally, we qualitatively evaluate our denoising model trained on LLFF-N on sequences with real noise captured with a Google Pixel 4 under low-light conditions. We use the sequences from [31] and estimate camera poses using COLMAP [35] on noisy images. We compare our results to those of [31]—downloaded from their project page where more baselines can be found—in Figure 5.", + "bbox": [ + 496, + 371, + 893, + 479 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/8975f5e6e4090028de873e302eb3a5acd82fa876d8f1f10232c355e44fb7523d.jpg", + "image_caption": [ + "Noisy input", + "Figure 5. Qualitative evaluation on sequences with real noise from [31], captured with a Google Pixel 4." + ], + "image_footnote": [], + "bbox": [ + 503, + 501, + 630, + 698 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/fff9bcf078fe527e3e4a5a7fe855444e6225faac1255396142cb8c25715e5e43.jpg", + "image_caption": [ + "NAN [31]" + ], + "image_footnote": [], + "bbox": [ + 632, + 501, + 759, + 698 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/194f6c8421dd993e1ebcfbbfdcd57f095f588a260f337cb0c334b8b5736f8cf7.jpg", + "image_caption": [ + "MPFER (Ours)" + ], + "image_footnote": [], + "bbox": [ + 763, + 501, + 890, + 698 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 767, + 619, + 782 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We proposed to approach multi-frame denoising as a view synthesis problem and argued in favor of using multi-plane representations for their low computational cost and generalizability. We introduced a powerful generalization of multiplane images to feature space, and demonstrated its effectiveness in multiple challenging scenarios.", + "bbox": [ + 496, + 792, + 893, + 885 + ], + "page_idx": 6 + }, + { + "type": "footer", + "text": "20904", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/dca7fc9a0337bb928e2850dee7ba5676e0bdf101479ee0fff3846eec717237c2.jpg", + "image_caption": [ + "Figure 6. Visualization of Multiplane Features for 3 scenes. We plot the first 3 channels of planes 1, 3, 5, 7, 9, 11, 13, 15 from MPFER-16. Our method learns to separate depths in an unsupervised way, in this case from a pure denoising problem." + ], + "image_footnote": [], + "bbox": [ + 76, + 85, + 890, + 229 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/5acf9577c989e585b8a4943e45bab1f2072c55cf95d2dfe98d518cdabab60229.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
12 input views (dense)4 input views (small)4 input views (medium)4 input views (large)GFlops@500×800
PSNR↑SSIM↑LPIPS↓PSNR↑SSIM↑LPIPS↓PSNR↑SSIM↑LPIPS↓PSNR↑SSIM↑LPIPS↓
Soft3D*31.930.9400.05230.290.9250.06430.840.9300.06030.570.9310.054n/a
DeepView*34.230.9650.01531.420.9540.02632.380.9570.02131.000.9520.02445800
MPINet27.430.9140.03527.000.9060.05426.160.8960.06224.930.8650.085450
MPINet-dw30.700.9630.02129.390.9510.02728.470.9480.03026.830.9370.0407890
MPINet-dw-it30.850.9660.01730.220.9550.02429.370.9530.02628.000.9430.03414800
MPFER-6435.730.9720.01233.200.9590.01833.470.9590.01832.380.9530.0218490
", + "bbox": [ + 76, + 271, + 890, + 393 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/62c59ad64ee758a8d5a81ec3a211d315c8efa379a08fd82f2a9c69a0368b221b.jpg", + "table_caption": [ + "Table 1. Novel view synthesis on Spaces. All metrics were computed on predicted images with a 16-pixel boundary cropped, as done in [8]. Stared methods were evaluated using the predicted images released with the Spaces dataset." + ], + "table_footnote": [], + "table_body": "
Gain 4Gain 8Gain 16Gain 20GFlops@500×800
PSNR↑SSIM↑LPIPS↓PSNR↑SSIM↑LPIPS↓PSNR↑SSIM↑LPIPS↓PSNR↑SSIM↑LPIPS↓
VBM4D32.000.9000.10829.940.8500.17227.480.7690.28026.550.7300.331n/a
VNLB33.410.9180.08930.300.8710.14425.740.7930.28323.510.7430.366n/a
BPN34.520.9340.04832.100.9000.08229.450.8460.14428.560.8240.168810
BasicVSR36.870.9590.02734.520.9370.04931.730.8980.09530.680.8790.1192090
BasicVSR++36.980.9590.02634.660.9380.04531.970.9020.08330.920.8830.1024300
DeepRep37.370.9630.02435.130.9430.04332.370.9060.08531.320.8880.1073230
UNet-SF35.100.9420.04332.620.9090.07529.810.8570.13428.810.8340.161440
UNet-BR35.190.9430.04032.670.9120.07029.900.8610.12428.940.8400.148470
UNet-BR-OF36.410.9560.02934.270.9360.04831.770.8990.08930.850.8820.110710
MPFER-1637.560.9680.02035.800.9550.03033.700.9330.05132.890.9210.063470
MPFER-3237.940.9700.01936.170.9580.02833.990.9360.04733.140.9240.0581210
MPFER-6438.000.9700.01836.250.9590.02734.080.9360.04733.230.9250.0571810
", + "bbox": [ + 76, + 433, + 890, + 643 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/45dba6e7e0ffdf2035b9ffcbb4cd9e0814be89ff7a375e3b58e8168c4788960e.jpg", + "table_caption": [ + "Table 2. Denoising on Spaces. All metrics were computed on frame 6, as BPN and DeepRep are burst-denoising methods producing only one output. For the other methods, average performances over the entire sequence are provided in Supplementary Material." + ], + "table_footnote": [], + "table_body": "
Gain 1Gain 2Gain 4Gain 8Gain 16Gain 20
PSNR↑SSIM↑LPIPS↓PSNR↑SSIM↑LPIPS↓PSNR↑SSIM↑LPIPS↓PSNR↑SSIM↑LPIPS↓PSNR↑SSIM↑LPIPS↓PSNR↑SSIM↑LPIPS↓
Denoising of Synthetic Noise
IBRNet-N*33.500.9150.03931.290.8770.07029.010.8220.12326.570.7410.21024.190.6340.33123.400.5910.380
NAN*35.840.9550.01833.670.9300.03431.260.8920.06828.640.8340.13225.950.7490.23125.070.7150.271
MPFER-N37.900.9690.01335.610.9510.02533.020.9210.04830.210.8720.09127.240.7970.16426.230.7650.198
MPFER-C38.060.9710.01135.950.9560.02033.650.9340.03631.210.8980.06528.610.8430.11527.710.8190.138
Novel View Synthesis Under Noisy Conditions
IBRNet*24.530.7740.13524.200.7300.15923.440.6530.21722.020.5360.32719.760.3770.49218.800.3190.553
IBRNet-N*23.860.7630.17023.730.7440.17823.380.7030.20822.680.6380.27521.670.5490.37721.290.5140.418
NAN*24.520.7990.13224.410.7870.14524.180.7650.17123.700.7260.22122.790.6660.30522.370.6410.342
MPFER24.520.7980.15724.510.7960.15824.470.7890.16424.330.7750.17823.940.7460.21223.720.7310.230
", + "bbox": [ + 76, + 683, + 890, + 851 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 3. LLFF-N. We consider the two scenarios introduced in [31]: Denoising of Synthetic Noise, where the noisy target is accessible, and Novel View Synthesis Under Noisy Conditions, where the noisy target is held-out. The numbers for the stared methods correspond to Figure 9 in [31], and were provided by the authors.", + "bbox": [ + 75, + 854, + 890, + 896 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "20905", + "bbox": [ + 478, + 945, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Pablo Arias and Jean-Michel Morel. Video denoising via empirical bayesian estimation of space-time patches. 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IJCV, 127(8):1106-1125, 2019. 2", + "[55] Tinghui Zhou, Richard Tucker, John Flynn, Graham Fyffe, and Noah Snavely. Stereo magnification: learning view synthesis using multiplane images. ACM TOG, 37(4):1-12, 2018. 1, 2, 4" + ], + "bbox": [ + 503, + 90, + 890, + 487 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "20907", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/Efficient View Synthesis and 3D-Based Multi-Frame Denoising With Multiplane Feature Representations/b6c4c560-21c7-4cb1-aa8c-86a25b81c853_model.json b/2023/Efficient View Synthesis and 3D-Based Multi-Frame Denoising With Multiplane Feature Representations/b6c4c560-21c7-4cb1-aa8c-86a25b81c853_model.json new file mode 100644 index 0000000000000000000000000000000000000000..feaee1fcd0767d93234fd74542ef1fa57234bf4f --- /dev/null +++ b/2023/Efficient View Synthesis and 3D-Based Multi-Frame Denoising With Multiplane Feature Representations/b6c4c560-21c7-4cb1-aa8c-86a25b81c853_model.json @@ -0,0 +1,1881 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.171, + 0.131, + 0.802, + 0.177 + ], + "angle": 0, + "content": "Efficient View Synthesis and 3D-based Multi-Frame Denoising with Multiplane Feature Representations" + }, + { + "type": "text", + "bbox": [ + 0.253, + 0.204, + 0.374, + 0.222 + ], + "angle": 0, + "content": "Thomas Tanay" + }, + { + "type": "text", + "bbox": [ + 0.413, + 0.205, + 0.536, + 0.222 + ], + "angle": 0, + "content": "Aleš Leonardis" + }, + { + "type": "text", + "bbox": [ + 0.577, + 0.205, + 0.715, + 0.222 + ], + "angle": 0, + "content": "Matteo Maggioni" + }, + { + "type": "text", + "bbox": [ + 0.388, + 0.223, + 0.583, + 0.238 + ], + "angle": 0, + "content": "Huawei Noah's Ark Lab" + }, + { + "type": "text", + "bbox": [ + 0.236, + 0.242, + 0.73, + 0.257 + ], + "angle": 0, + "content": "{thomas.tanay,ales.leonardis,matteo.maggioni}@huawei.com" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.292, + 0.314, + 0.308 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.326, + 0.474, + 0.629 + ], + "angle": 0, + "content": "While current multi-frame restoration methods combine information from multiple input images using 2D alignment techniques, recent advances in novel view synthesis are paving the way for a new paradigm relying on volumetric scene representations. In this work, we introduce the first 3D-based multi-frame denoising method that significantly outperforms its 2D-based counterparts with lower computational requirements. Our method extends the multiplane image (MPI) framework for novel view synthesis by introducing a learnable encoder-renderer pair manipulating multiplane representations in feature space. The encoder fuses information across views and operates in a depth-wise manner while the renderer fuses information across depths and operates in a view-wise manner. The two modules are trained end-to-end and learn to separate depths in an unsupervised way, giving rise to Multiplane Feature (MPF) representations. Experiments on the Spaces and Real Forward-Facing datasets as well as on raw burst data validate our approach for view synthesis, multi-frame denoising, and view synthesis under noisy conditions." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.662, + 0.21, + 0.679 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.689, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Multi-frame denoising is a classical problem of computer vision where a noise process affecting a set of images must be inverted. The main challenge is to extract consistent information across images effectively and the current state of the art relies on optical flow-based 2D alignment [3,7,45]. Novel view synthesis, on the other hand, is a classical problem of computer graphics where a scene is viewed from one or more camera positions and the task is to predict novel views from target camera positions. This problem requires to reason about the 3D structure of the scene and is typically solved using some form of volumetric representation [28, 32, 55]. Although the two problems are traditionally considered distinct, some novel view synthesis approaches have recently been observed to handle noisy" + }, + { + "type": "image", + "bbox": [ + 0.501, + 0.291, + 0.895, + 0.466 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.471, + 0.895, + 0.543 + ], + "angle": 0, + "content": "Figure 1. Top: Our Multiplane Features Encoder-Renderer (MPFER) reimagines the MPI pipeline by moving the multiplane representation to feature space. Bottom: MPFER significantly outperforms existing methods in multiple challenging scenarios, including here, novel view synthesis from 8 highly degraded inputs." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.568, + 0.892, + 0.659 + ], + "angle": 0, + "content": "inputs well, and to have a denoising effect in synthesized views by discarding inconsistent information across input views [18,26]. This observation opens the door to 3D-based multi-frame denoising, by recasting the problem as a special case of novel view synthesis where the input views are noisy and the target views are the clean input views [26, 31]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.66, + 0.893, + 0.902 + ], + "angle": 0, + "content": "Recently, novel view synthesis has been approached as an encoding-rendering process where a scene representation is first encoded from a set of input images and an arbitrary number of novel views are then rendered from this scene representation. In the Neural Radiance Field (NeRF) framework for instance, the scene representation is a radiance field function encoded by training a neural network on the input views. Novel views are then rendered by querying and integrating this radiance field function over light rays originating from a target camera position [2, 24, 28]. In the Multiplane Image (MPI) framework on the other hand, the scene representation is a stack of semi-transparent colored layers arranged at various depths, encoded by feeding the input views to a neural network trained on a large number of scenes. Novel views are then rendered by warping and overcompositing the semi-transparent layers [8, 41, 55]." + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "20898" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.473, + 0.514 + ], + "angle": 0, + "content": "In the present work, we adopt the MPI framework because it is much lighter than the NeRF framework computationally. The encoding stage only requires one inference pass on a network that generalizes to new scenes instead of training one neural network per-scene, and the rendering stage is essentially free instead of requiring a large number of inference passes. However, the standard MPI pipeline struggles to predict multiplane representations that are self-consistent across depths from multiple viewpoints. This problem can lead to depth-discretization artifacts in synthesized views [40] and has previously been addressed at the encoding stage using computationally expensive mechanisms and a large number of depth planes [8, 11, 27, 40]. Here, we propose to enforce cross-depth consistency at the rendering stage by replacing the fixed overcompositing operator with a learnable renderer. This change of approach has three important implications. First, the encoder module can now process depths independently from each other and focus on fusing information across views. This significantly reduces the computational load of the encoding stage. Second, the scene representation changes from a static MPI to Multiplane Features (MPF) rendered dynamically. This significantly increases the expressive power of the scene encoding. Finally, the framework's overall performance is greatly improved, making it suitable for novel scenarios including multi-frame denoising where it outperforms standard 2D-based approaches at a fraction of their computational cost. Our main contributions are as follow:" + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.516, + 0.47, + 0.56 + ], + "angle": 0, + "content": "- We solve the cross-depth consistency problem for multi-plane representations at the rendering stage, by introducing a learnable renderer." + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.562, + 0.47, + 0.607 + ], + "angle": 0, + "content": "- We introduce the Multiplane Feature (MPF) representation, a generalization of the multiplane image with higher representational power." + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.608, + 0.469, + 0.651 + ], + "angle": 0, + "content": "- We re-purpose the multiplane image framework originally developed for novel view synthesis to perform 3D-based multi-frame denoising." + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.652, + 0.469, + 0.697 + ], + "angle": 0, + "content": "- We validate the approach with experiments on 3 tasks and 3 datasets and significantly outperform existing 2D-based and 3D-based methods for multi-frame denoising." + }, + { + "type": "list", + "bbox": [ + 0.078, + 0.516, + 0.47, + 0.697 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.71, + 0.216, + 0.725 + ], + "angle": 0, + "content": "2. Related work" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.735, + 0.473, + 0.903 + ], + "angle": 0, + "content": "Multi-frame denoising Multi-frame restoration methods are frequently divided into two categories, depending on the type of image alignment employed. Explicit alignment refers to the direct warping of images using optical flows predicted by a motion compensation module [4, 43, 44, 54]. In contrast, implicit alignment refers to local, data-driven deformations implemented using dynamic upsampling filters [16, 17], deformable convolutions [45, 49], kernel prediction networks [25] or their extension, basis prediction networks [53]. Explicit alignment is better at dealing with large motion while implicit alignment is better at deal" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.895, + 0.351 + ], + "angle": 0, + "content": "ing with residual motion, and state-of-the-art performance can be achieved by combining both in the form of flow-guided deformable convolutions [6, 7]. Another distinction between multi-frame restoration methods is the type of processing used. A common approach is to concatenate the input frames together along the channel dimension [4, 43, 44, 49, 54] but recurrent processing is more efficient [9, 10, 34, 42], especially when implemented in a bidirectional way [5, 7, 14]. Basic VSR++ achieves state-of-the-art performance by combining flow-guided deformable alignment with bidirectional recurrent processing iterated multiple times [7]. In a different spirit, the recent DeepRep method [3] introduces a deep reparameterization in feature space of the maximum a posteriori formulation of multiframe restoration. Similarly to the previous methods however, it still uses a form of explicit 2D alignment, and lacks any ability to reason about the 3D structure of the scene." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.357, + 0.895, + 0.904 + ], + "angle": 0, + "content": "View synthesis The idea to decompose a scene into a set of semi-transparent planes can be traced back to the use of mattes and blue screens in special effects filmmaking [38, 47]. This scene representation was first applied to view interpolation in [41], and recently gained popularity under the name of Multiplane Image (MPI) [55]. It is particularly powerful to generate novel views from a small set of forward facing views [8, 27, 55], and can even be used to generate novels views from a single image [11, 20, 46]. The rendering of view dependent-effects and non-Lambertian surfaces is challenging due to the use of a single set of RGB\\(\\alpha\\) images, and can be improved by predicting multiple MPIs combined as a weighted average of the distance from the input views [27], or as a set of basis components [51]. The simplicity of this representation is appealing, but it can still be computationally heavy when the number of depth planes grows [8, 51], and the rendered views can suffer from depth discretization artifacts [40]. A number of alternative layered scene representations exist, including the Layered Depth Image (LDI) consisting in one RGB image with an extra depth channel [36], and variants of MPIs and LDIs [13, 19, 21, 39]. So far however, all these methods use a fixed overcompositing operator at the rendering stage. The idea to perform view synthesis by applying 3D operations in the feature space of an encoder-decoder architecture was explored on simple geometries in [52], and used with success on a point-cloud scene representation for view synthesis from a single image in [50]. Recently, Neural Radiance Fields (NeRFs) have become highly popular for their ability to produce high quality renderings of complex scenes from arbitrary viewpoints [2, 24, 28-30]. However, they tend to be very heavy computationally, require a large number of input views, and lack the ability to generalize to novel scenes. IBRNet [48] improves generalizability by learning a generic view interpolation function, but the approach remains computationally heavy. The application of view syn" + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "20899" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.244 + ], + "angle": 0, + "content": "thesis approaches to multi-frame restoration has been limited so far, and exclusively based on NeRF. RawNeRF [26] explores novel view synthesis in low-light conditions, and reports strong denoising effects in the synthesized views. Deblur-NeRF [22] augments the ability of NeRFs to deal with blur by including Deformable Sparse Kernels. Noise-aware-NeRFs [31] improves the IBRNet architecture to explicitly deal with noise. However, these different restoration approaches still suffer from the limitations affecting their underlying NeRF representations." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.257, + 0.169, + 0.273 + ], + "angle": 0, + "content": "3. Method" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.283, + 0.47, + 0.344 + ], + "angle": 0, + "content": "We start by describing the standard MPI processing pipeline, before discussing the cross-depth consistency problem. We then introduce our MPF Encoder-Renderer and its adaptation to multi-frame denoising." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.354, + 0.377, + 0.371 + ], + "angle": 0, + "content": "3.1. Standard MPI processing pipeline" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.378, + 0.47, + 0.453 + ], + "angle": 0, + "content": "The standard MPI processing pipeline turns a set of input views into an arbitrary set of rendered novel views by applying 4 main transformations: forward-warping, MPI prediction, backward-warping, overcompositing (See Figure 2a). We describe this pipeline in more details below." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.458, + 0.473, + 0.866 + ], + "angle": 0, + "content": "Input views The inputs of the pipeline are a set of \\(V\\) views of a scene, consisting of images and camera parameters. The images are of height \\(H\\) and width \\(W\\), with red-green-blue color channels, and can be stacked into a 4D tensor \\(\\boldsymbol{I} = \\{\\{\\{I_{vchw}\\}_{w=1}^{W}\\}_{h=1}^{H}\\}_{c=1}^{3}\\}_{v=1}^{V}\\). To simplify notations, we omit the dimensions \\(c, h, w\\) and refer to an individual image as \\(\\boldsymbol{I}_v\\). The camera parameters consist of an intrinsic tensor \\(\\boldsymbol{K}\\) of size \\(V \\times 3 \\times 3\\) containing information about the focal lengths and principal point of the cameras, and an extrinsic tensor containing information about the camera orientations in the world coordinate system, that can be split into a rotation tensor \\(\\boldsymbol{R}\\) of size \\(V \\times 3 \\times 3\\) and a translation tensor \\(\\boldsymbol{t}\\) of size \\(V \\times 3 \\times 1\\). A reference view \\(i\\) is defined a priori, and the positions of all the cameras are assumed to be expressed relatively to it. The intrinsic matrix \\(\\boldsymbol{K}_i\\) of the reference camera is defined such that the corresponding field of view covers the region of space visible to all the input views. Finally, a set of \\(D\\) depth planes is distributed orthogonally to the reference viewing direction such that their normal is \\(\\boldsymbol{n} = (0,0,1)^{\\top}\\), and their distances \\(\\{a_d\\}_{d=1}^D\\) from the reference camera center are sampled uniformly in disparity. The camera parameters and the depth planes are used to define a set of \\(D \\times V\\) homography projections, represented by a tensor \\(\\boldsymbol{H}\\) of size \\(D \\times V \\times 3 \\times 3\\). Each homography is between one of the input views and the reference view, and is induced by one of the depth planes, such that its matrix is expressed as [12]:" + }, + { + "type": "equation", + "bbox": [ + 0.157, + 0.87, + 0.47, + 0.906 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {H} _ {d v} = \\boldsymbol {K} _ {v} \\left(\\boldsymbol {R} _ {v} - \\frac {\\boldsymbol {t} _ {v} \\boldsymbol {n} ^ {\\top}}{a _ {d}}\\right) \\boldsymbol {K} _ {i} ^ {- 1} \\tag {1}\n\\]" + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.089, + 0.895, + 0.157 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.595, + 0.161, + 0.798, + 0.174 + ], + "angle": 0, + "content": "(a) Standard MPI processing pipeline." + }, + { + "type": "image", + "bbox": [ + 0.502, + 0.188, + 0.895, + 0.257 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.61, + 0.261, + 0.783, + 0.273 + ], + "angle": 0, + "content": "(b) Our MPF Encoder-Encoder." + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.285, + 0.894, + 0.356 + ], + "angle": 0, + "content": "Figure 2. In the standard MPI processing pipeline, all the learning and most of the processing happens in the MPINet module. We propose to move the multiplane representation to feature space, by giving some processing power to the warping operators, and replacing the overcompositing operator with a learnable renderer." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.387, + 0.892, + 0.508 + ], + "angle": 0, + "content": "Plane Sweep Volumes The first transformation in the MPI pipeline is the computation of Plane Sweep Volumes (PSVs), obtained by forward-warping each input image \\(D\\) times, according to the homography \\(\\pmb{H}_{dv}\\). The sampling rate of the warping operator \\(\\mathcal{W}\\) is a hyperparameter that can be controlled using an up-scaling factor \\(s\\). Each transformation can thus be written as \\(\\pmb{X}_{dv} = \\mathcal{W}(\\pmb{I}_v, \\pmb{H}_{dv}, s)\\) and the PSV tensor \\(\\pmb{X}\\) is of size \\(D \\times V \\times 3 \\times sH \\times sW\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.516, + 0.894, + 0.609 + ], + "angle": 0, + "content": "Multiplane Image The main processing block of the pipeline is a neural network MPINet, turning the set of PSVs into a multiplane image representation of the scene \\( \\mathbf{Y} = \\mathrm{MPINet}(\\mathbf{X}) \\) where \\( \\mathbf{Y} \\) is a set of \\( D \\) semi-transparent RGB images of size \\( D \\times 4 \\times sH \\times sW \\), constrained to the [0,1] range by using a sigmoid activation function." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.616, + 0.894, + 0.707 + ], + "angle": 0, + "content": "Projected MPs The MPI is then backward-warped to a set of \\( R \\) novel views, defined by an homography tensor \\( G \\) of size \\( R \\times D \\times 3 \\times 3 \\) following Eq. (1) with the depth and view dimensions transposed. The backward-warping operation is defined as \\( Z_{rd} = \\mathcal{W}\\left(\\mathbf{Y}_d, \\mathbf{G}_{rd}^{-1}, 1 / s\\right) \\) obtaining a tensor of projected MPs \\( Z \\) of size \\( R \\times D \\times 4 \\times H \\times W \\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.716, + 0.892, + 0.817 + ], + "angle": 0, + "content": "**Rendered views** The projected MPs are finally collapsed into single RGB images by applying the overcompositing operator \\(\\mathcal{O}\\). This operator splits each RGB\\(\\alpha\\) image \\(Z_{rd}\\) into a colour component \\(C_{rd}\\) and an alpha component \\(A_{rd}\\) and computes \\(\\tilde{J}_r = \\sum_{d=1}^{D} \\left( C_{rd} A_{rd} \\prod_{k=d+1}^{D} (1 - A_{rk}) \\right)\\) obtaining the rendered views \\(\\tilde{J}\\) of size \\(R \\times 3 \\times H \\times W\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.825, + 0.894, + 0.901 + ], + "angle": 0, + "content": "Training The pipeline is typically trained end-to-end in a supervised way by minimizing a loss \\(\\mathcal{L}(\\tilde{\\boldsymbol{J}},\\boldsymbol {J})\\) between the rendered views \\(\\tilde{\\boldsymbol{J}}\\) and the corresponding ground-truth images \\(\\boldsymbol{J}\\). In practice, \\(\\mathcal{L}\\) is often an \\(\\mathcal{L}_1\\) loss applied to low level features of a VGG network [37]." + }, + { + "type": "footer", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "20900" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.078, + 0.091, + 0.299, + 0.108 + ], + "angle": 0, + "content": "3.2. Cross-depth consistency" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.115, + 0.47, + 0.282 + ], + "angle": 0, + "content": "The main and only learnable module of the standard MPI pipeline is the prediction network MPINet, transforming a 5D PSV tensor into a 4D MPI scene representation. Its task is challenging because multiplane images are hyperconstrained representations: their semi-transparent layers interact with each other in non-trivial and view-dependent ways, and missing or redundant information across layers can result in depth discretization artifacts after applying the overcompositing operator [40]. To perform well, MPINet requires a mechanism enforcing cross-depth consistency; and several approaches have been considered before." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.283, + 0.471, + 0.45 + ], + "angle": 0, + "content": "In the original case of stereo-magnification [55], there is one reference input and one secondary input which is turned into a single PSV. Both are concatenated along the channel dimension and fed to an MPINet module predicting the full MPI in one shot as a 3D tensor of size \\((D \\times 4) \\times sH \\times sW\\), such that cross-depth consistency is enforced within the convolutional layers of MPINet. A similar solution can be used in the case of single-view synthesis [46], where there is a single reference input image and no PSV. In the general case with \\(V\\) inputs, however, the PSV tensor \\(\\mathbf{X}\\) becomes very large and there are two main ways to process it." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.452, + 0.47, + 0.519 + ], + "angle": 0, + "content": "Option 1 The first solution is to generalize the approach of [55] and concatenate \\(\\mathbf{X}\\) across views and depths before feeding it to a network predicting the full MPI in one shot: \\(\\mathbf{Y} = \\mathrm{MPINet}\\Big(\\{\\{X_{dv}\\}_{v = 1}^{V}\\}_{d = 1}^{D}\\Big)\\)." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.519, + 0.47, + 0.584 + ], + "angle": 0, + "content": "Option 2 The second solution is to concatenate \\(\\mathbf{X}\\) across views, and process each depth separately—effectively running the MPINet block \\(D\\) times in parallel: \\(\\mathbf{Y} = \\{\\mathrm{MPINet}\\big(\\{X_{dv}\\}_{v=1}^{V}\\big)\\}_{d=1}^{D}\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.584, + 0.471, + 0.902 + ], + "angle": 0, + "content": "Option 1 tends to work poorly in practice [8], as it requires to either use very large convolutional layers with intractable memory requirements, or discard most of the information contained in the input PSVs after the first convolutional layer. Option 2 is appealing as it fuses information across views more effectively, but the resulting MPI typically suffers from a lack of cross-depth consistency as each depth is processed separately. Most previous works adopt Option 2 as a starting point, and augment it with various mechanisms allowing some information to flow across depths. For instance, some methods implement MPINet with 3D convolutions [27, 40], such that each depth is treated semi-independently within a local depth neighborhood dependent on the size of the kernel, which is typically 3. By design however, this solution cannot handle interactions between distant depth planes. DeepView [8] proposes to solve the recursive cross-depth constraint by iteratively refining the prediction of the MPINet block, effectively performing a form of learned gradient descent. However, this solution requires to run the MPI network multiple times, which is computationally heavy. Finally, the method of [11] uses a feature" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.153 + ], + "angle": 0, + "content": "masking strategy to deal with inter-plane interactions explicitly. This solution is both complex (multiple networks are required to predict the masks) and rigid (the masking operations are fixed and still work on a per-depth basis)." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.163, + 0.76, + 0.178 + ], + "angle": 0, + "content": "3.3. Our MPF Encoder-Encoder" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.186, + 0.892, + 0.368 + ], + "angle": 0, + "content": "Here, we propose to solve the cross-depth consistency problem in a novel way, by addressing it at the rendering stage. Specifically, we replace the fixed overcompositing operator with a learnable renderer enforcing consistency directly at the output level on a per-view basis. This design change greatly simplifies the task of the multiplane representation encoder, which can now focus on fusing information across views in a depth-independent way. It also promotes the multiplane representation to feature space, by relaxing existing constraints on the number of channels and scaling in the [0,1] range. The four transformations of the pipeline are modified as follows (See Figure 2b)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.372, + 0.892, + 0.464 + ], + "angle": 0, + "content": "Plane Sweep Volumes To decrease the amount of information loss through image warping and promote the PSVs to feature space, we now apply a convolution to the images before warping them: \\( \\pmb{X}_{dv} = \\mathcal{W}(\\mathrm{Conv}(\\pmb{I}_v),\\pmb{H}_{dv},s) \\). The PSV tensor \\( \\pmb{X} \\) is now of size \\( D\\times V\\times C_1\\times sH\\times sW \\) where the number of channels \\( C_1 \\) is a hyperparameter." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.467, + 0.892, + 0.577 + ], + "angle": 0, + "content": "Multiplane Features We then replace the MPINet module with an encoder applied to each depth independently: \\(\\mathbf{Y} = \\{\\mathrm{Encoder}\\left(\\left\\{\\mathbf{X}_{dv}\\right\\}_{v=1}^{V}\\right)\\}_{d=1}^{D}\\). The multiplane representation \\(\\mathbf{Y}\\) is now in feature space: its range is not constrained by a sigmoid function anymore and its size is \\(D \\times C_2 \\times sH \\times sW\\) where the number of channels \\(C_2\\) is a second hyperparameter." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.581, + 0.892, + 0.679 + ], + "angle": 0, + "content": "Projected MPFs The MPF is still backward-warped to a set of \\(R\\) novel views defined by an homography tensor \\(\\pmb{G}\\), but this is now followed by a convolution collapsing the depth and channel dimensions into a single dimension: \\(\\mathbf{Z}_r = \\mathrm{Conv}\\Big(\\{\\mathcal{W}(\\mathbf{Y}_d,\\mathbf{G}_{dr}^{-1},1 / s)\\}_{d = 1}^D\\Big)\\). The tensor \\(\\pmb{Z}\\) is of size \\(R\\times C_3\\times H\\times W\\) where \\(C_3\\) is a third hyperparameter." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.683, + 0.892, + 0.745 + ], + "angle": 0, + "content": "Rendered views Finally, the projected MPFs are turned into the final rendered views by a simple CNN renderer operating on each view separately: \\(\\tilde{J} = \\{\\mathrm{Renderer}(Z_r)\\}_{r=1}^R\\). The rendered views \\(\\tilde{J}\\) are of size \\(R \\times 3 \\times H \\times W\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.75, + 0.892, + 0.902 + ], + "angle": 0, + "content": "Training The pipeline is still trained end-to-end by minimizing a loss \\(\\mathcal{L}(\\tilde{J}, J)\\) between the rendered views \\(\\tilde{J}\\) and the corresponding ground-truth images \\(J\\), but the renderer and the warping operators are now learnable. When the input views \\(I\\) are noisy versions of ground-truth images \\(I^{*}\\), the pipeline can be turned into a multi-frame denoising method by using the input homographies \\(H\\) during backward-warping, obtaining denoised outputs \\(\\tilde{I}\\), and by minimizing the loss \\(\\mathcal{L}(\\tilde{I}, I^{*})\\). There is then a one-to-one mapping between the input views and the rendered views," + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "20901" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.137, + 0.087, + 0.833, + 0.321 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.331, + 0.895, + 0.39 + ], + "angle": 0, + "content": "Figure 3. Our Multiplane Features Encoder-Encoder (MPFER). Input views are forward-warped into plane sweep volumes (PSVs) which are processed depthwise by the Encoder Unet64. The resulting multiplane feature representation (MPF) can then be back-projected to an arbitrary number of novel views, or to the same views as the inputs—allowing the integration of a skip connection (illustrated here). The Encoder Unet64 processes the projected MPFs on a per-view basis, producing the final synthesised or denoised outputs." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.414, + 0.473, + 0.55 + ], + "angle": 0, + "content": "and it is possible to integrate a skip connection feeding the noisy inputs directly to the renderer to guide its final predictions. In all our experiments, we use Unets [33] with a base of 64 channels to implement both the encoder and the renderer. We set \\( C_1 = C \\), \\( C_2 = V \\times C \\) and \\( C_3 = 64 \\) such that there is a single hyperparameter \\( C \\) to vary. Our Multiplane Features Encoder-Render (MPFER) is illustrated in Figure 3 for 3 inputs views and 3 depth planes. A MindSpore [15] implementation of our method is available1." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.562, + 0.21, + 0.58 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.588, + 0.47, + 0.709 + ], + "angle": 0, + "content": "We first consider the Spaces dataset [8] and validate our approach on novel view synthesis. We then focus on a denoising setup and perform extensive comparisons to state-of-the-art 2D-based methods. Finally, we compare our approach to the 3D-based multi-frame denoising method of [31] by replicating their experimental setup on the Real Forward-Facing dataset. In all cases, our method outperforms competitors at a fraction of the computational cost." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.717, + 0.168, + 0.733 + ], + "angle": 0, + "content": "4.1. Spaces" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.74, + 0.47, + 0.816 + ], + "angle": 0, + "content": "The Spaces dataset [8] consists of 100 indoor and outdoor scenes, captured 5 to 10 times each using a 16-camera rig placed at slightly different locations. 90 scenes are used for training and 10 scenes are held-out for evaluation. The resolution of the images is \\(480 \\times 800\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.819, + 0.47, + 0.88 + ], + "angle": 0, + "content": "Novel view synthesis We start by replicating the novel view synthesis setup of DeepView [8] with four scenarios: one with 12 input views and three with 4 input views. Similarly to DeepView, we use a VGG loss and train our models" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.414, + 0.895, + 0.898 + ], + "angle": 0, + "content": "for 100k steps using the Adam optimizer, with a learning rate of \\(1.5\\mathrm{e - }3\\). We reduce the learning rate to \\(1.5\\mathrm{e - }4\\) after 80k steps, and use a batch size of 4. Memory usage was reported to be a major challenge in DeepView, and all our models are kept at a significantly smaller size to avoid this issue. While DeepView uses a sophisticated strategy to only generate enough of the MPI to render a \\(32\\times 32\\) crop in the target image, we use a large patch size of 192 and only apply the loss on the region of the patch that contains more than \\(80\\%\\) of the depths planes after backward warping. We compute all metrics by averaging over the validation scenes and target views of each setup, and after cropping a boundary of 16 pixels on all images as done in [8]. We compare to DeepView [8] and Soft3D [32] by using the synthesised images provided with the Spaces dataset. We also consider three variants of the standard MPI pipeline using the same Unet backbone as our MPFER method and trained in the same conditions, but processing the input PSV in different ways. MPINet implements Option 1 from Sec. 3.2. The views and depths dimensions of the PSV tensor are stacked along the channel dimension and fed to the Unet backbone to predict the output MPI in one shot. MPINet-dw implements Option 2 from Sec. 3.2. The Unet backbone runs depthwise on slices of the PSV to predict each depth plane of the MPI separately, without communication mechanism across depths. Finally, MPINet-dw-it implements a one-step version of the learned gradient descent algorithm of DeepView. A first estimate of the MPI is predicted by a Unet backbone running depthwise, and this estimate is fed to a second Unet backbone also running depthwise, along with the input PSV and gradient components (R), which are PSV-projected current estimates of the target views." + }, + { + "type": "page_footnote", + "bbox": [ + 0.095, + 0.887, + 0.452, + 0.902 + ], + "angle": 0, + "content": "" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "20902" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.078, + 0.086, + 0.895, + 0.43 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.439, + 0.895, + 0.469 + ], + "angle": 0, + "content": "Figure 4. Qualitative evaluation for multi-frame denoising with Gain 20 (best viewed zoomed in). We compare MPFER to 2D-based methods on Spaces (top) and to 3D-based methods on the Real Forward-Facing dataset (bottom)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.494, + 0.473, + 0.751 + ], + "angle": 0, + "content": "For our MPFER method and the MPINet ablations, we use a number of depth planes \\( D = 64 \\) distributed between 100 and 0.5 meters away from the reference camera, placed at the average position of the input views. We use a number of channels \\( C = 8 \\) and a PSV/MPF upscaling factor \\( s = 1.5 \\). Since the Unet backbone is not agnostic to the number of input views, we train one version of each model for the setup with 12 input views and one version for the three setups with 4 input views. The results are presented in Table 1. We observe a clear progression between the performances of MPINet, MPINet-dw and MPINet-dw-it, illustrating the benefit of each design change. Our MPFER method outperforms MPINet-dw-it by up to 4dBs in PSNR at a similar computational complexity, and outperforms DeepView by up to 1.8dB at a fraction of the complexity, clearly motivating the use of a learnt renderer for efficient depth fusion." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.765, + 0.473, + 0.903 + ], + "angle": 0, + "content": "Multi-frame denoising We now consider a different setup where the inputs are 16 views from one rig position with images degraded with noise, and the targets are the same 16 views denoised. Similarly to previous works [3, 25,31,53], we apply synthetic noise with a signal dependent Gaussian distribution \\( \\mathbf{I}_{vchw} \\sim \\mathcal{N}\\left(\\mathbf{I}_{vchw}^{*}, \\sigma_{r}^{2} + \\sigma_{s}\\mathbf{I}_{vchw}^{*}\\right) \\) where \\( \\mathbf{I} \\) is the tensor of noisy inputs, \\( \\mathbf{I}^{*} \\) is the ground truth signal, and \\( \\sigma_r \\) and \\( \\sigma_s \\) are noise parameters that are fixed for each sequence. We focus in particular on challenging sce" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.494, + 0.892, + 0.541 + ], + "angle": 0, + "content": "narios with moderate to high gain levels [4, 8, 16, 20], corresponding to the \\((\\log (\\sigma_r),\\log (\\sigma_s))\\) values \\([-1.44, - 1.84)\\) \\((-1.08, - 1.48)\\) \\((-0.72, - 1.12)\\) \\((-0.6, - 1.0)]\\) respectively." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.553, + 0.893, + 0.903 + ], + "angle": 0, + "content": "We consider two patch-based approaches: VBM4D [23] and VNLB [1], as well as four state-of-the-art learning-based methods: BPN [53], BasicVSR [5] and its extension BasicVSR++ [7], and DeepRep [3]. To evaluate the influence of the model size and in particular the number of depth planes, we train three MPFER models: MPFER-16 with \\((D,C,s) = (16,8,1.)\\), MPFER-32 with \\((D,C,s) = (32,16,1.25)\\), and MPFER-64 with \\((D,C,s) = (64,8,1.25)\\). MPFER-16 has the particularity of using the same number of depth planes as there are input images, meaning that the number of Unet passes per frame to denoise the sequence is \\((D + V) / V = 2\\). This observation motivates us to perform a comparison with three other architectures, using a strict computational budget of 2 Unet passes per frame. Unet-SF (for Single-Frame) is constituted of two Unet blocks without temporal connection, therefore processing the sequence as a disjoint set of single frames. Unet-BR (for Bidirectional-Recurrent) is constituted of two Unet blocks with bidirectional recurrent connections: the lower Unet processes the sequence in a backward way, and the higher Unet processes the sequence in a feedforward way. Finally, Unet-BR-OF (for Bidirectional-Recurrent with Optical-Flow alignment) is constituted of two Unet" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "20903" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.473, + 0.591 + ], + "angle": 0, + "content": "blocks with bidirectional recurrent connections, and the recurrent hidden-state is aligned using a SpyNet module, as done in basicVSR [5]. We train all the models in the same conditions as for the novel view synthesis setup, except for the patch size which we increase to 256, and the loss which we replace with a simple L1 loss. During training, we vary the gain level randomly and concatenate an estimate of the standard deviation of the noise to the input, as in [25,31,53]. We evaluate on the first rig position of the 10 validation scenes of the Spaces dataset for the 4 gain levels without boundary-cropping, and present the results in Table 2. Each model receives 16 noisy images as input and produces 16 restored images as output, except for BPN and DeepRep which are burst processing methods and only produce one output. For these methods, we choose the view number 6 at the center of the camera rig as the target output, and compare the performances of all methods on this frame. Our MPFER method clearly outperforms all the other methods at a fraction of the computational cost. It performs particularly strongly at high noise levels, with improvements over other methods of more that 2dBs in PSNR. MPFER-16 also performs remarkably well, despite using only 16 depth planes. This suggests that the high representational power of multiplane features allows to significantly reduce the number of depth planes—and therefore the computational cost—compared to standard MPI approaches, which typically use a very high number of planes (80 in the case of DeepView [8], up to 192 in the case of NeX [51]). A qualitative evaluation is available in Figure 4 (top), and we observe that MPFER is able to reconstruct scenes with much better details. We also present a visualization of multiplane features in Figure 6, illustrating how the model learns to separate depths in an unsupervised way." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.6, + 0.182, + 0.615 + ], + "angle": 0, + "content": "4.2. LLFF-N" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.624, + 0.47, + 0.746 + ], + "angle": 0, + "content": "The LLFF-N dataset [31] is a variant of the Real Forward-Facing dataset [27] where images are linearized by applying inverse gamma correction and random inverse white balancing, and synthetic noise is applied following the same signal dependent Gaussian distribution as used in the previous section with the six gain levels [1, 2, 4, 8, 16, 20]. The dataset contains 35 scenes for training and 8 scenes for testing, and the resolution of the images is \\(756 \\times 1008\\)." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.75, + 0.473, + 0.903 + ], + "angle": 0, + "content": "**Denoising** In this setup, the model receives 8 frames in input: the target frame plus its 7 nearest neighbors in terms of camera distances. We train one MPFER model with \\((D,C,s) = (64,8,1.25)\\), using an \\(\\mathcal{L}_1\\) loss applied to the target frame. We evaluate on the 43 bursts used in [31] (every 8th frame of the test set) and present the results in the first half of Table 3. A qualitative evaluation is also available in Figure 4 (bottom). To assess the robustness of our method to noisy camera positions, we evaluate it using camera positions computed on clean images (MPFER-C) and" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.894, + 0.153 + ], + "angle": 0, + "content": "on noisy images (MPFER-N) using COLMAP [35]. Our method outperforms IBRNet-N and NAN in both scenarios by large margins, but the evaluation using clean camera poses performs significantly better at high noise levels." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.156, + 0.895, + 0.369 + ], + "angle": 0, + "content": "Synthesis under noisy conditions In this setup, the model receives as input the 8 nearest neighbors to a held-out target. Again, we train one MPFER model with \\((D,C,s) = (64,8,1.25)\\), using an \\(\\mathcal{L}_1\\) loss applied to the target frame. We evaluate on the same 43 bursts as before and report the results in the second half of Table 3. Our method performs on par with IBRNet and NAN at very low noise levels (close to a pure synthesis problem), and significantly outperforms the other methods at larger noise levels. MPFER only requires \\(D\\) Unet passes to produce an MPF, and 1 Unet pass to render a novel view, which is significantly lighter than IBRNet and NAN. At inference time, the Unet pass requires 0.6 Mflops per pixel, compared to 45 Mflops for IBRNet [48]. A qualitative evaluation is available in Figure 1 for Gain 20." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.372, + 0.895, + 0.48 + ], + "angle": 0, + "content": "Low-Light Scenes Finally, we qualitatively evaluate our denoising model trained on LLFF-N on sequences with real noise captured with a Google Pixel 4 under low-light conditions. We use the sequences from [31] and estimate camera poses using COLMAP [35] on noisy images. We compare our results to those of [31]—downloaded from their project page where more baselines can be found—in Figure 5." + }, + { + "type": "image_caption", + "bbox": [ + 0.533, + 0.489, + 0.6, + 0.502 + ], + "angle": 0, + "content": "Noisy input" + }, + { + "type": "image_caption", + "bbox": [ + 0.668, + 0.489, + 0.725, + 0.502 + ], + "angle": 0, + "content": "NAN [31]" + }, + { + "type": "image_caption", + "bbox": [ + 0.786, + 0.49, + 0.868, + 0.501 + ], + "angle": 0, + "content": "MPFER (Ours)" + }, + { + "type": "image", + "bbox": [ + 0.504, + 0.502, + 0.631, + 0.699 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.633, + 0.502, + 0.761, + 0.699 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.764, + 0.502, + 0.891, + 0.699 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.5, + 0.71, + 0.894, + 0.739 + ], + "angle": 0, + "content": "Figure 5. Qualitative evaluation on sequences with real noise from [31], captured with a Google Pixel 4." + }, + { + "type": "title", + "bbox": [ + 0.501, + 0.768, + 0.62, + 0.784 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.794, + 0.894, + 0.886 + ], + "angle": 0, + "content": "We proposed to approach multi-frame denoising as a view synthesis problem and argued in favor of using multi-plane representations for their low computational cost and generalizability. We introduced a powerful generalization of multiplane images to feature space, and demonstrated its effectiveness in multiple challenging scenarios." + }, + { + "type": "footer", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "20904" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.078, + 0.086, + 0.892, + 0.23 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.234, + 0.892, + 0.263 + ], + "angle": 0, + "content": "Figure 6. Visualization of Multiplane Features for 3 scenes. We plot the first 3 channels of planes 1, 3, 5, 7, 9, 11, 13, 15 from MPFER-16. Our method learns to separate depths in an unsupervised way, in this case from a pure denoising problem." + }, + { + "type": "table", + "bbox": [ + 0.078, + 0.272, + 0.892, + 0.394 + ], + "angle": 0, + "content": "
12 input views (dense)4 input views (small)4 input views (medium)4 input views (large)GFlops@500×800
PSNR↑SSIM↑LPIPS↓PSNR↑SSIM↑LPIPS↓PSNR↑SSIM↑LPIPS↓PSNR↑SSIM↑LPIPS↓
Soft3D*31.930.9400.05230.290.9250.06430.840.9300.06030.570.9310.054n/a
DeepView*34.230.9650.01531.420.9540.02632.380.9570.02131.000.9520.02445800
MPINet27.430.9140.03527.000.9060.05426.160.8960.06224.930.8650.085450
MPINet-dw30.700.9630.02129.390.9510.02728.470.9480.03026.830.9370.0407890
MPINet-dw-it30.850.9660.01730.220.9550.02429.370.9530.02628.000.9430.03414800
MPFER-6435.730.9720.01233.200.9590.01833.470.9590.01832.380.9530.0218490
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.397, + 0.892, + 0.424 + ], + "angle": 0, + "content": "Table 1. Novel view synthesis on Spaces. All metrics were computed on predicted images with a 16-pixel boundary cropped, as done in [8]. Stared methods were evaluated using the predicted images released with the Spaces dataset." + }, + { + "type": "table", + "bbox": [ + 0.078, + 0.434, + 0.892, + 0.645 + ], + "angle": 0, + "content": "
Gain 4Gain 8Gain 16Gain 20GFlops@500×800
PSNR↑SSIM↑LPIPS↓PSNR↑SSIM↑LPIPS↓PSNR↑SSIM↑LPIPS↓PSNR↑SSIM↑LPIPS↓
VBM4D32.000.9000.10829.940.8500.17227.480.7690.28026.550.7300.331n/a
VNLB33.410.9180.08930.300.8710.14425.740.7930.28323.510.7430.366n/a
BPN34.520.9340.04832.100.9000.08229.450.8460.14428.560.8240.168810
BasicVSR36.870.9590.02734.520.9370.04931.730.8980.09530.680.8790.1192090
BasicVSR++36.980.9590.02634.660.9380.04531.970.9020.08330.920.8830.1024300
DeepRep37.370.9630.02435.130.9430.04332.370.9060.08531.320.8880.1073230
UNet-SF35.100.9420.04332.620.9090.07529.810.8570.13428.810.8340.161440
UNet-BR35.190.9430.04032.670.9120.07029.900.8610.12428.940.8400.148470
UNet-BR-OF36.410.9560.02934.270.9360.04831.770.8990.08930.850.8820.110710
MPFER-1637.560.9680.02035.800.9550.03033.700.9330.05132.890.9210.063470
MPFER-3237.940.9700.01936.170.9580.02833.990.9360.04733.140.9240.0581210
MPFER-6438.000.9700.01836.250.9590.02734.080.9360.04733.230.9250.0571810
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.647, + 0.892, + 0.675 + ], + "angle": 0, + "content": "Table 2. Denoising on Spaces. All metrics were computed on frame 6, as BPN and DeepRep are burst-denoising methods producing only one output. For the other methods, average performances over the entire sequence are provided in Supplementary Material." + }, + { + "type": "table", + "bbox": [ + 0.078, + 0.684, + 0.892, + 0.852 + ], + "angle": 0, + "content": "
Gain 1Gain 2Gain 4Gain 8Gain 16Gain 20
PSNR↑SSIM↑LPIPS↓PSNR↑SSIM↑LPIPS↓PSNR↑SSIM↑LPIPS↓PSNR↑SSIM↑LPIPS↓PSNR↑SSIM↑LPIPS↓PSNR↑SSIM↑LPIPS↓
Denoising of Synthetic Noise
IBRNet-N*33.500.9150.03931.290.8770.07029.010.8220.12326.570.7410.21024.190.6340.33123.400.5910.380
NAN*35.840.9550.01833.670.9300.03431.260.8920.06828.640.8340.13225.950.7490.23125.070.7150.271
MPFER-N37.900.9690.01335.610.9510.02533.020.9210.04830.210.8720.09127.240.7970.16426.230.7650.198
MPFER-C38.060.9710.01135.950.9560.02033.650.9340.03631.210.8980.06528.610.8430.11527.710.8190.138
Novel View Synthesis Under Noisy Conditions
IBRNet*24.530.7740.13524.200.7300.15923.440.6530.21722.020.5360.32719.760.3770.49218.800.3190.553
IBRNet-N*23.860.7630.17023.730.7440.17823.380.7030.20822.680.6380.27521.670.5490.37721.290.5140.418
NAN*24.520.7990.13224.410.7870.14524.180.7650.17123.700.7260.22122.790.6660.30522.370.6410.342
MPFER24.520.7980.15724.510.7960.15824.470.7890.16424.330.7750.17823.940.7460.21223.720.7310.230
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.855, + 0.892, + 0.897 + ], + "angle": 0, + "content": "Table 3. LLFF-N. We consider the two scenarios introduced in [31]: Denoising of Synthetic Noise, where the noisy target is accessible, and Novel View Synthesis Under Noisy Conditions, where the noisy target is held-out. The numbers for the stared methods correspond to Figure 9 in [31], and were provided by the authors." + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.946, + 0.518, + 0.957 + ], + "angle": 0, + "content": "20905" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.115, + 0.47, + 0.157 + ], + "angle": 0, + "content": "[1] Pablo Arias and Jean-Michel Morel. Video denoising via empirical bayesian estimation of space-time patches. 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In this work, we introduce the first 3D-based multi-frame denoising method that significantly outperforms its 2D-based counterparts with lower computational requirements. Our method extends the multiplane image (MPI) framework for novel view synthesis by introducing a learnable encoder-renderer pair manipulating multiplane representations in feature space. The encoder fuses information across views and operates in a depth-wise manner while the renderer fuses information across depths and operates in a view-wise manner. The two modules are trained end-to-end and learn to separate depths in an unsupervised way, giving rise to Multiplane Feature (MPF) representations. Experiments on the Spaces and Real Forward-Facing datasets as well as on raw burst data validate our approach for view synthesis, multi-frame denoising, and view synthesis under noisy conditions. + +# 1. Introduction + +Multi-frame denoising is a classical problem of computer vision where a noise process affecting a set of images must be inverted. The main challenge is to extract consistent information across images effectively and the current state of the art relies on optical flow-based 2D alignment [3,7,45]. Novel view synthesis, on the other hand, is a classical problem of computer graphics where a scene is viewed from one or more camera positions and the task is to predict novel views from target camera positions. This problem requires to reason about the 3D structure of the scene and is typically solved using some form of volumetric representation [28, 32, 55]. Although the two problems are traditionally considered distinct, some novel view synthesis approaches have recently been observed to handle noisy + +![](images/d9336b458b51d07f33a7b19bee95e30bf383409c3a1c73fa220a5a647e57935f.jpg) +Figure 1. Top: Our Multiplane Features Encoder-Renderer (MPFER) reimagines the MPI pipeline by moving the multiplane representation to feature space. Bottom: MPFER significantly outperforms existing methods in multiple challenging scenarios, including here, novel view synthesis from 8 highly degraded inputs. + +inputs well, and to have a denoising effect in synthesized views by discarding inconsistent information across input views [18,26]. This observation opens the door to 3D-based multi-frame denoising, by recasting the problem as a special case of novel view synthesis where the input views are noisy and the target views are the clean input views [26, 31]. + +Recently, novel view synthesis has been approached as an encoding-rendering process where a scene representation is first encoded from a set of input images and an arbitrary number of novel views are then rendered from this scene representation. In the Neural Radiance Field (NeRF) framework for instance, the scene representation is a radiance field function encoded by training a neural network on the input views. Novel views are then rendered by querying and integrating this radiance field function over light rays originating from a target camera position [2, 24, 28]. In the Multiplane Image (MPI) framework on the other hand, the scene representation is a stack of semi-transparent colored layers arranged at various depths, encoded by feeding the input views to a neural network trained on a large number of scenes. Novel views are then rendered by warping and overcompositing the semi-transparent layers [8, 41, 55]. + +In the present work, we adopt the MPI framework because it is much lighter than the NeRF framework computationally. The encoding stage only requires one inference pass on a network that generalizes to new scenes instead of training one neural network per-scene, and the rendering stage is essentially free instead of requiring a large number of inference passes. However, the standard MPI pipeline struggles to predict multiplane representations that are self-consistent across depths from multiple viewpoints. This problem can lead to depth-discretization artifacts in synthesized views [40] and has previously been addressed at the encoding stage using computationally expensive mechanisms and a large number of depth planes [8, 11, 27, 40]. Here, we propose to enforce cross-depth consistency at the rendering stage by replacing the fixed overcompositing operator with a learnable renderer. This change of approach has three important implications. First, the encoder module can now process depths independently from each other and focus on fusing information across views. This significantly reduces the computational load of the encoding stage. Second, the scene representation changes from a static MPI to Multiplane Features (MPF) rendered dynamically. This significantly increases the expressive power of the scene encoding. Finally, the framework's overall performance is greatly improved, making it suitable for novel scenarios including multi-frame denoising where it outperforms standard 2D-based approaches at a fraction of their computational cost. Our main contributions are as follow: + +- We solve the cross-depth consistency problem for multi-plane representations at the rendering stage, by introducing a learnable renderer. +- We introduce the Multiplane Feature (MPF) representation, a generalization of the multiplane image with higher representational power. +- We re-purpose the multiplane image framework originally developed for novel view synthesis to perform 3D-based multi-frame denoising. +- We validate the approach with experiments on 3 tasks and 3 datasets and significantly outperform existing 2D-based and 3D-based methods for multi-frame denoising. + +# 2. Related work + +Multi-frame denoising Multi-frame restoration methods are frequently divided into two categories, depending on the type of image alignment employed. Explicit alignment refers to the direct warping of images using optical flows predicted by a motion compensation module [4, 43, 44, 54]. In contrast, implicit alignment refers to local, data-driven deformations implemented using dynamic upsampling filters [16, 17], deformable convolutions [45, 49], kernel prediction networks [25] or their extension, basis prediction networks [53]. Explicit alignment is better at dealing with large motion while implicit alignment is better at deal + +ing with residual motion, and state-of-the-art performance can be achieved by combining both in the form of flow-guided deformable convolutions [6, 7]. Another distinction between multi-frame restoration methods is the type of processing used. A common approach is to concatenate the input frames together along the channel dimension [4, 43, 44, 49, 54] but recurrent processing is more efficient [9, 10, 34, 42], especially when implemented in a bidirectional way [5, 7, 14]. Basic VSR++ achieves state-of-the-art performance by combining flow-guided deformable alignment with bidirectional recurrent processing iterated multiple times [7]. In a different spirit, the recent DeepRep method [3] introduces a deep reparameterization in feature space of the maximum a posteriori formulation of multiframe restoration. Similarly to the previous methods however, it still uses a form of explicit 2D alignment, and lacks any ability to reason about the 3D structure of the scene. + +View synthesis The idea to decompose a scene into a set of semi-transparent planes can be traced back to the use of mattes and blue screens in special effects filmmaking [38, 47]. This scene representation was first applied to view interpolation in [41], and recently gained popularity under the name of Multiplane Image (MPI) [55]. It is particularly powerful to generate novel views from a small set of forward facing views [8, 27, 55], and can even be used to generate novels views from a single image [11, 20, 46]. The rendering of view dependent-effects and non-Lambertian surfaces is challenging due to the use of a single set of RGB $\alpha$ images, and can be improved by predicting multiple MPIs combined as a weighted average of the distance from the input views [27], or as a set of basis components [51]. The simplicity of this representation is appealing, but it can still be computationally heavy when the number of depth planes grows [8, 51], and the rendered views can suffer from depth discretization artifacts [40]. A number of alternative layered scene representations exist, including the Layered Depth Image (LDI) consisting in one RGB image with an extra depth channel [36], and variants of MPIs and LDIs [13, 19, 21, 39]. So far however, all these methods use a fixed overcompositing operator at the rendering stage. The idea to perform view synthesis by applying 3D operations in the feature space of an encoder-decoder architecture was explored on simple geometries in [52], and used with success on a point-cloud scene representation for view synthesis from a single image in [50]. Recently, Neural Radiance Fields (NeRFs) have become highly popular for their ability to produce high quality renderings of complex scenes from arbitrary viewpoints [2, 24, 28-30]. However, they tend to be very heavy computationally, require a large number of input views, and lack the ability to generalize to novel scenes. IBRNet [48] improves generalizability by learning a generic view interpolation function, but the approach remains computationally heavy. The application of view syn + +thesis approaches to multi-frame restoration has been limited so far, and exclusively based on NeRF. RawNeRF [26] explores novel view synthesis in low-light conditions, and reports strong denoising effects in the synthesized views. Deblur-NeRF [22] augments the ability of NeRFs to deal with blur by including Deformable Sparse Kernels. Noise-aware-NeRFs [31] improves the IBRNet architecture to explicitly deal with noise. However, these different restoration approaches still suffer from the limitations affecting their underlying NeRF representations. + +# 3. Method + +We start by describing the standard MPI processing pipeline, before discussing the cross-depth consistency problem. We then introduce our MPF Encoder-Renderer and its adaptation to multi-frame denoising. + +# 3.1. Standard MPI processing pipeline + +The standard MPI processing pipeline turns a set of input views into an arbitrary set of rendered novel views by applying 4 main transformations: forward-warping, MPI prediction, backward-warping, overcompositing (See Figure 2a). We describe this pipeline in more details below. + +Input views The inputs of the pipeline are a set of $V$ views of a scene, consisting of images and camera parameters. The images are of height $H$ and width $W$ , with red-green-blue color channels, and can be stacked into a 4D tensor $\boldsymbol{I} = \{\{\{I_{vchw}\}_{w=1}^{W}\}_{h=1}^{H}\}_{c=1}^{3}\}_{v=1}^{V}$ . To simplify notations, we omit the dimensions $c, h, w$ and refer to an individual image as $\boldsymbol{I}_v$ . The camera parameters consist of an intrinsic tensor $\boldsymbol{K}$ of size $V \times 3 \times 3$ containing information about the focal lengths and principal point of the cameras, and an extrinsic tensor containing information about the camera orientations in the world coordinate system, that can be split into a rotation tensor $\boldsymbol{R}$ of size $V \times 3 \times 3$ and a translation tensor $\boldsymbol{t}$ of size $V \times 3 \times 1$ . A reference view $i$ is defined a priori, and the positions of all the cameras are assumed to be expressed relatively to it. The intrinsic matrix $\boldsymbol{K}_i$ of the reference camera is defined such that the corresponding field of view covers the region of space visible to all the input views. Finally, a set of $D$ depth planes is distributed orthogonally to the reference viewing direction such that their normal is $\boldsymbol{n} = (0,0,1)^{\top}$ , and their distances $\{a_d\}_{d=1}^D$ from the reference camera center are sampled uniformly in disparity. The camera parameters and the depth planes are used to define a set of $D \times V$ homography projections, represented by a tensor $\boldsymbol{H}$ of size $D \times V \times 3 \times 3$ . Each homography is between one of the input views and the reference view, and is induced by one of the depth planes, such that its matrix is expressed as [12]: + +$$ +\boldsymbol {H} _ {d v} = \boldsymbol {K} _ {v} \left(\boldsymbol {R} _ {v} - \frac {\boldsymbol {t} _ {v} \boldsymbol {n} ^ {\top}}{a _ {d}}\right) \boldsymbol {K} _ {i} ^ {- 1} \tag {1} +$$ + +![](images/05c5183740a5ef516a1a6111974e4b17521f8ac9c0e7fb08be5fc47a5c26424b.jpg) +(a) Standard MPI processing pipeline. + +![](images/4171f0d6022d2873f3481a5bcdcae794df4c8425eb6ad1f5f2cf326eee21c1d2.jpg) +(b) Our MPF Encoder-Encoder. +Figure 2. In the standard MPI processing pipeline, all the learning and most of the processing happens in the MPINet module. We propose to move the multiplane representation to feature space, by giving some processing power to the warping operators, and replacing the overcompositing operator with a learnable renderer. + +Plane Sweep Volumes The first transformation in the MPI pipeline is the computation of Plane Sweep Volumes (PSVs), obtained by forward-warping each input image $D$ times, according to the homography $\pmb{H}_{dv}$ . The sampling rate of the warping operator $\mathcal{W}$ is a hyperparameter that can be controlled using an up-scaling factor $s$ . Each transformation can thus be written as $\pmb{X}_{dv} = \mathcal{W}(\pmb{I}_v, \pmb{H}_{dv}, s)$ and the PSV tensor $\pmb{X}$ is of size $D \times V \times 3 \times sH \times sW$ . + +Multiplane Image The main processing block of the pipeline is a neural network MPINet, turning the set of PSVs into a multiplane image representation of the scene $\mathbf{Y} = \mathrm{MPINet}(\mathbf{X})$ where $\mathbf{Y}$ is a set of $D$ semi-transparent RGB images of size $D \times 4 \times sH \times sW$ , constrained to the [0,1] range by using a sigmoid activation function. + +Projected MPs The MPI is then backward-warped to a set of $R$ novel views, defined by an homography tensor $G$ of size $R \times D \times 3 \times 3$ following Eq. (1) with the depth and view dimensions transposed. The backward-warping operation is defined as $Z_{rd} = \mathcal{W}\left(\mathbf{Y}_d, \mathbf{G}_{rd}^{-1}, 1 / s\right)$ obtaining a tensor of projected MPs $Z$ of size $R \times D \times 4 \times H \times W$ . + +**Rendered views** The projected MPs are finally collapsed into single RGB images by applying the overcompositing operator $\mathcal{O}$ . This operator splits each RGB $\alpha$ image $Z_{rd}$ into a colour component $C_{rd}$ and an alpha component $A_{rd}$ and computes $\tilde{J}_r = \sum_{d=1}^{D} \left( C_{rd} A_{rd} \prod_{k=d+1}^{D} (1 - A_{rk}) \right)$ obtaining the rendered views $\tilde{J}$ of size $R \times 3 \times H \times W$ . + +Training The pipeline is typically trained end-to-end in a supervised way by minimizing a loss $\mathcal{L}(\tilde{\boldsymbol{J}},\boldsymbol {J})$ between the rendered views $\tilde{\boldsymbol{J}}$ and the corresponding ground-truth images $\boldsymbol{J}$ . In practice, $\mathcal{L}$ is often an $\mathcal{L}_1$ loss applied to low level features of a VGG network [37]. + +# 3.2. Cross-depth consistency + +The main and only learnable module of the standard MPI pipeline is the prediction network MPINet, transforming a 5D PSV tensor into a 4D MPI scene representation. Its task is challenging because multiplane images are hyperconstrained representations: their semi-transparent layers interact with each other in non-trivial and view-dependent ways, and missing or redundant information across layers can result in depth discretization artifacts after applying the overcompositing operator [40]. To perform well, MPINet requires a mechanism enforcing cross-depth consistency; and several approaches have been considered before. + +In the original case of stereo-magnification [55], there is one reference input and one secondary input which is turned into a single PSV. Both are concatenated along the channel dimension and fed to an MPINet module predicting the full MPI in one shot as a 3D tensor of size $(D \times 4) \times sH \times sW$ , such that cross-depth consistency is enforced within the convolutional layers of MPINet. A similar solution can be used in the case of single-view synthesis [46], where there is a single reference input image and no PSV. In the general case with $V$ inputs, however, the PSV tensor $\mathbf{X}$ becomes very large and there are two main ways to process it. + +Option 1 The first solution is to generalize the approach of [55] and concatenate $\mathbf{X}$ across views and depths before feeding it to a network predicting the full MPI in one shot: $\mathbf{Y} = \mathrm{MPINet}\Big(\{\{X_{dv}\}_{v = 1}^{V}\}_{d = 1}^{D}\Big)$ . + +Option 2 The second solution is to concatenate $\mathbf{X}$ across views, and process each depth separately—effectively running the MPINet block $D$ times in parallel: $\mathbf{Y} = \{\mathrm{MPINet}\big(\{X_{dv}\}_{v=1}^{V}\big)\}_{d=1}^{D}$ . + +Option 1 tends to work poorly in practice [8], as it requires to either use very large convolutional layers with intractable memory requirements, or discard most of the information contained in the input PSVs after the first convolutional layer. Option 2 is appealing as it fuses information across views more effectively, but the resulting MPI typically suffers from a lack of cross-depth consistency as each depth is processed separately. Most previous works adopt Option 2 as a starting point, and augment it with various mechanisms allowing some information to flow across depths. For instance, some methods implement MPINet with 3D convolutions [27, 40], such that each depth is treated semi-independently within a local depth neighborhood dependent on the size of the kernel, which is typically 3. By design however, this solution cannot handle interactions between distant depth planes. DeepView [8] proposes to solve the recursive cross-depth constraint by iteratively refining the prediction of the MPINet block, effectively performing a form of learned gradient descent. However, this solution requires to run the MPI network multiple times, which is computationally heavy. Finally, the method of [11] uses a feature + +masking strategy to deal with inter-plane interactions explicitly. This solution is both complex (multiple networks are required to predict the masks) and rigid (the masking operations are fixed and still work on a per-depth basis). + +# 3.3. Our MPF Encoder-Encoder + +Here, we propose to solve the cross-depth consistency problem in a novel way, by addressing it at the rendering stage. Specifically, we replace the fixed overcompositing operator with a learnable renderer enforcing consistency directly at the output level on a per-view basis. This design change greatly simplifies the task of the multiplane representation encoder, which can now focus on fusing information across views in a depth-independent way. It also promotes the multiplane representation to feature space, by relaxing existing constraints on the number of channels and scaling in the [0,1] range. The four transformations of the pipeline are modified as follows (See Figure 2b). + +Plane Sweep Volumes To decrease the amount of information loss through image warping and promote the PSVs to feature space, we now apply a convolution to the images before warping them: $\pmb{X}_{dv} = \mathcal{W}(\mathrm{Conv}(\pmb{I}_v),\pmb{H}_{dv},s)$ . The PSV tensor $\pmb{X}$ is now of size $D\times V\times C_1\times sH\times sW$ where the number of channels $C_1$ is a hyperparameter. + +Multiplane Features We then replace the MPINet module with an encoder applied to each depth independently: $\mathbf{Y} = \{\mathrm{Encoder}\left(\left\{\mathbf{X}_{dv}\right\}_{v=1}^{V}\right)\}_{d=1}^{D}$ . The multiplane representation $\mathbf{Y}$ is now in feature space: its range is not constrained by a sigmoid function anymore and its size is $D \times C_2 \times sH \times sW$ where the number of channels $C_2$ is a second hyperparameter. + +Projected MPFs The MPF is still backward-warped to a set of $R$ novel views defined by an homography tensor $\pmb{G}$ , but this is now followed by a convolution collapsing the depth and channel dimensions into a single dimension: $\mathbf{Z}_r = \mathrm{Conv}\Big(\{\mathcal{W}(\mathbf{Y}_d,\mathbf{G}_{dr}^{-1},1 / s)\}_{d = 1}^D\Big)$ . The tensor $\pmb{Z}$ is of size $R\times C_3\times H\times W$ where $C_3$ is a third hyperparameter. + +Rendered views Finally, the projected MPFs are turned into the final rendered views by a simple CNN renderer operating on each view separately: $\tilde{J} = \{\mathrm{Renderer}(Z_r)\}_{r=1}^R$ . The rendered views $\tilde{J}$ are of size $R \times 3 \times H \times W$ . + +Training The pipeline is still trained end-to-end by minimizing a loss $\mathcal{L}(\tilde{J}, J)$ between the rendered views $\tilde{J}$ and the corresponding ground-truth images $J$ , but the renderer and the warping operators are now learnable. When the input views $I$ are noisy versions of ground-truth images $I^{*}$ , the pipeline can be turned into a multi-frame denoising method by using the input homographies $H$ during backward-warping, obtaining denoised outputs $\tilde{I}$ , and by minimizing the loss $\mathcal{L}(\tilde{I}, I^{*})$ . There is then a one-to-one mapping between the input views and the rendered views, + +![](images/274977e804a5bde958c6e781ba13331b72a5e53c24b1f54dda6c2da36fc0a54f.jpg) +Figure 3. Our Multiplane Features Encoder-Encoder (MPFER). Input views are forward-warped into plane sweep volumes (PSVs) which are processed depthwise by the Encoder Unet64. The resulting multiplane feature representation (MPF) can then be back-projected to an arbitrary number of novel views, or to the same views as the inputs—allowing the integration of a skip connection (illustrated here). The Encoder Unet64 processes the projected MPFs on a per-view basis, producing the final synthesised or denoised outputs. + +and it is possible to integrate a skip connection feeding the noisy inputs directly to the renderer to guide its final predictions. In all our experiments, we use Unets [33] with a base of 64 channels to implement both the encoder and the renderer. We set $C_1 = C$ , $C_2 = V \times C$ and $C_3 = 64$ such that there is a single hyperparameter $C$ to vary. Our Multiplane Features Encoder-Render (MPFER) is illustrated in Figure 3 for 3 inputs views and 3 depth planes. A MindSpore [15] implementation of our method is available1. + +# 4. Experiments + +We first consider the Spaces dataset [8] and validate our approach on novel view synthesis. We then focus on a denoising setup and perform extensive comparisons to state-of-the-art 2D-based methods. Finally, we compare our approach to the 3D-based multi-frame denoising method of [31] by replicating their experimental setup on the Real Forward-Facing dataset. In all cases, our method outperforms competitors at a fraction of the computational cost. + +# 4.1. Spaces + +The Spaces dataset [8] consists of 100 indoor and outdoor scenes, captured 5 to 10 times each using a 16-camera rig placed at slightly different locations. 90 scenes are used for training and 10 scenes are held-out for evaluation. The resolution of the images is $480 \times 800$ . + +Novel view synthesis We start by replicating the novel view synthesis setup of DeepView [8] with four scenarios: one with 12 input views and three with 4 input views. Similarly to DeepView, we use a VGG loss and train our models + +for 100k steps using the Adam optimizer, with a learning rate of $1.5\mathrm{e - }3$ . We reduce the learning rate to $1.5\mathrm{e - }4$ after 80k steps, and use a batch size of 4. Memory usage was reported to be a major challenge in DeepView, and all our models are kept at a significantly smaller size to avoid this issue. While DeepView uses a sophisticated strategy to only generate enough of the MPI to render a $32\times 32$ crop in the target image, we use a large patch size of 192 and only apply the loss on the region of the patch that contains more than $80\%$ of the depths planes after backward warping. We compute all metrics by averaging over the validation scenes and target views of each setup, and after cropping a boundary of 16 pixels on all images as done in [8]. We compare to DeepView [8] and Soft3D [32] by using the synthesised images provided with the Spaces dataset. We also consider three variants of the standard MPI pipeline using the same Unet backbone as our MPFER method and trained in the same conditions, but processing the input PSV in different ways. MPINet implements Option 1 from Sec. 3.2. The views and depths dimensions of the PSV tensor are stacked along the channel dimension and fed to the Unet backbone to predict the output MPI in one shot. MPINet-dw implements Option 2 from Sec. 3.2. The Unet backbone runs depthwise on slices of the PSV to predict each depth plane of the MPI separately, without communication mechanism across depths. Finally, MPINet-dw-it implements a one-step version of the learned gradient descent algorithm of DeepView. A first estimate of the MPI is predicted by a Unet backbone running depthwise, and this estimate is fed to a second Unet backbone also running depthwise, along with the input PSV and gradient components (R), which are PSV-projected current estimates of the target views. + +![](images/fe555aed21d8f9ec5727e740450c9f2fdcfc0135fc2524e7826295db142e70ad.jpg) +Figure 4. Qualitative evaluation for multi-frame denoising with Gain 20 (best viewed zoomed in). We compare MPFER to 2D-based methods on Spaces (top) and to 3D-based methods on the Real Forward-Facing dataset (bottom). + +For our MPFER method and the MPINet ablations, we use a number of depth planes $D = 64$ distributed between 100 and 0.5 meters away from the reference camera, placed at the average position of the input views. We use a number of channels $C = 8$ and a PSV/MPF upscaling factor $s = 1.5$ . Since the Unet backbone is not agnostic to the number of input views, we train one version of each model for the setup with 12 input views and one version for the three setups with 4 input views. The results are presented in Table 1. We observe a clear progression between the performances of MPINet, MPINet-dw and MPINet-dw-it, illustrating the benefit of each design change. Our MPFER method outperforms MPINet-dw-it by up to 4dBs in PSNR at a similar computational complexity, and outperforms DeepView by up to 1.8dB at a fraction of the complexity, clearly motivating the use of a learnt renderer for efficient depth fusion. + +Multi-frame denoising We now consider a different setup where the inputs are 16 views from one rig position with images degraded with noise, and the targets are the same 16 views denoised. Similarly to previous works [3, 25,31,53], we apply synthetic noise with a signal dependent Gaussian distribution $\mathbf{I}_{vchw} \sim \mathcal{N}\left(\mathbf{I}_{vchw}^{*}, \sigma_{r}^{2} + \sigma_{s}\mathbf{I}_{vchw}^{*}\right)$ where $\mathbf{I}$ is the tensor of noisy inputs, $\mathbf{I}^{*}$ is the ground truth signal, and $\sigma_r$ and $\sigma_s$ are noise parameters that are fixed for each sequence. We focus in particular on challenging sce + +narios with moderate to high gain levels [4, 8, 16, 20], corresponding to the $(\log (\sigma_r),\log (\sigma_s))$ values $[-1.44, - 1.84)$ $(-1.08, - 1.48)$ $(-0.72, - 1.12)$ $(-0.6, - 1.0)]$ respectively. + +We consider two patch-based approaches: VBM4D [23] and VNLB [1], as well as four state-of-the-art learning-based methods: BPN [53], BasicVSR [5] and its extension BasicVSR++ [7], and DeepRep [3]. To evaluate the influence of the model size and in particular the number of depth planes, we train three MPFER models: MPFER-16 with $(D,C,s) = (16,8,1.)$ , MPFER-32 with $(D,C,s) = (32,16,1.25)$ , and MPFER-64 with $(D,C,s) = (64,8,1.25)$ . MPFER-16 has the particularity of using the same number of depth planes as there are input images, meaning that the number of Unet passes per frame to denoise the sequence is $(D + V) / V = 2$ . This observation motivates us to perform a comparison with three other architectures, using a strict computational budget of 2 Unet passes per frame. Unet-SF (for Single-Frame) is constituted of two Unet blocks without temporal connection, therefore processing the sequence as a disjoint set of single frames. Unet-BR (for Bidirectional-Recurrent) is constituted of two Unet blocks with bidirectional recurrent connections: the lower Unet processes the sequence in a backward way, and the higher Unet processes the sequence in a feedforward way. Finally, Unet-BR-OF (for Bidirectional-Recurrent with Optical-Flow alignment) is constituted of two Unet + +blocks with bidirectional recurrent connections, and the recurrent hidden-state is aligned using a SpyNet module, as done in basicVSR [5]. We train all the models in the same conditions as for the novel view synthesis setup, except for the patch size which we increase to 256, and the loss which we replace with a simple L1 loss. During training, we vary the gain level randomly and concatenate an estimate of the standard deviation of the noise to the input, as in [25,31,53]. We evaluate on the first rig position of the 10 validation scenes of the Spaces dataset for the 4 gain levels without boundary-cropping, and present the results in Table 2. Each model receives 16 noisy images as input and produces 16 restored images as output, except for BPN and DeepRep which are burst processing methods and only produce one output. For these methods, we choose the view number 6 at the center of the camera rig as the target output, and compare the performances of all methods on this frame. Our MPFER method clearly outperforms all the other methods at a fraction of the computational cost. It performs particularly strongly at high noise levels, with improvements over other methods of more that 2dBs in PSNR. MPFER-16 also performs remarkably well, despite using only 16 depth planes. This suggests that the high representational power of multiplane features allows to significantly reduce the number of depth planes—and therefore the computational cost—compared to standard MPI approaches, which typically use a very high number of planes (80 in the case of DeepView [8], up to 192 in the case of NeX [51]). A qualitative evaluation is available in Figure 4 (top), and we observe that MPFER is able to reconstruct scenes with much better details. We also present a visualization of multiplane features in Figure 6, illustrating how the model learns to separate depths in an unsupervised way. + +# 4.2. LLFF-N + +The LLFF-N dataset [31] is a variant of the Real Forward-Facing dataset [27] where images are linearized by applying inverse gamma correction and random inverse white balancing, and synthetic noise is applied following the same signal dependent Gaussian distribution as used in the previous section with the six gain levels [1, 2, 4, 8, 16, 20]. The dataset contains 35 scenes for training and 8 scenes for testing, and the resolution of the images is $756 \times 1008$ . + +**Denoising** In this setup, the model receives 8 frames in input: the target frame plus its 7 nearest neighbors in terms of camera distances. We train one MPFER model with $(D,C,s) = (64,8,1.25)$ , using an $\mathcal{L}_1$ loss applied to the target frame. We evaluate on the 43 bursts used in [31] (every 8th frame of the test set) and present the results in the first half of Table 3. A qualitative evaluation is also available in Figure 4 (bottom). To assess the robustness of our method to noisy camera positions, we evaluate it using camera positions computed on clean images (MPFER-C) and + +on noisy images (MPFER-N) using COLMAP [35]. Our method outperforms IBRNet-N and NAN in both scenarios by large margins, but the evaluation using clean camera poses performs significantly better at high noise levels. + +Synthesis under noisy conditions In this setup, the model receives as input the 8 nearest neighbors to a held-out target. Again, we train one MPFER model with $(D,C,s) = (64,8,1.25)$ , using an $\mathcal{L}_1$ loss applied to the target frame. We evaluate on the same 43 bursts as before and report the results in the second half of Table 3. Our method performs on par with IBRNet and NAN at very low noise levels (close to a pure synthesis problem), and significantly outperforms the other methods at larger noise levels. MPFER only requires $D$ Unet passes to produce an MPF, and 1 Unet pass to render a novel view, which is significantly lighter than IBRNet and NAN. At inference time, the Unet pass requires 0.6 Mflops per pixel, compared to 45 Mflops for IBRNet [48]. A qualitative evaluation is available in Figure 1 for Gain 20. + +Low-Light Scenes Finally, we qualitatively evaluate our denoising model trained on LLFF-N on sequences with real noise captured with a Google Pixel 4 under low-light conditions. We use the sequences from [31] and estimate camera poses using COLMAP [35] on noisy images. We compare our results to those of [31]—downloaded from their project page where more baselines can be found—in Figure 5. + +![](images/8975f5e6e4090028de873e302eb3a5acd82fa876d8f1f10232c355e44fb7523d.jpg) +Noisy input +Figure 5. Qualitative evaluation on sequences with real noise from [31], captured with a Google Pixel 4. + +![](images/fff9bcf078fe527e3e4a5a7fe855444e6225faac1255396142cb8c25715e5e43.jpg) +NAN [31] + +![](images/194f6c8421dd993e1ebcfbbfdcd57f095f588a260f337cb0c334b8b5736f8cf7.jpg) +MPFER (Ours) + +# 5. Conclusion + +We proposed to approach multi-frame denoising as a view synthesis problem and argued in favor of using multi-plane representations for their low computational cost and generalizability. We introduced a powerful generalization of multiplane images to feature space, and demonstrated its effectiveness in multiple challenging scenarios. + +![](images/dca7fc9a0337bb928e2850dee7ba5676e0bdf101479ee0fff3846eec717237c2.jpg) +Figure 6. Visualization of Multiplane Features for 3 scenes. We plot the first 3 channels of planes 1, 3, 5, 7, 9, 11, 13, 15 from MPFER-16. Our method learns to separate depths in an unsupervised way, in this case from a pure denoising problem. + +
12 input views (dense)4 input views (small)4 input views (medium)4 input views (large)GFlops@500×800
PSNR↑SSIM↑LPIPS↓PSNR↑SSIM↑LPIPS↓PSNR↑SSIM↑LPIPS↓PSNR↑SSIM↑LPIPS↓
Soft3D*31.930.9400.05230.290.9250.06430.840.9300.06030.570.9310.054n/a
DeepView*34.230.9650.01531.420.9540.02632.380.9570.02131.000.9520.02445800
MPINet27.430.9140.03527.000.9060.05426.160.8960.06224.930.8650.085450
MPINet-dw30.700.9630.02129.390.9510.02728.470.9480.03026.830.9370.0407890
MPINet-dw-it30.850.9660.01730.220.9550.02429.370.9530.02628.000.9430.03414800
MPFER-6435.730.9720.01233.200.9590.01833.470.9590.01832.380.9530.0218490
+ +Table 1. Novel view synthesis on Spaces. All metrics were computed on predicted images with a 16-pixel boundary cropped, as done in [8]. Stared methods were evaluated using the predicted images released with the Spaces dataset. + +
Gain 4Gain 8Gain 16Gain 20GFlops@500×800
PSNR↑SSIM↑LPIPS↓PSNR↑SSIM↑LPIPS↓PSNR↑SSIM↑LPIPS↓PSNR↑SSIM↑LPIPS↓
VBM4D32.000.9000.10829.940.8500.17227.480.7690.28026.550.7300.331n/a
VNLB33.410.9180.08930.300.8710.14425.740.7930.28323.510.7430.366n/a
BPN34.520.9340.04832.100.9000.08229.450.8460.14428.560.8240.168810
BasicVSR36.870.9590.02734.520.9370.04931.730.8980.09530.680.8790.1192090
BasicVSR++36.980.9590.02634.660.9380.04531.970.9020.08330.920.8830.1024300
DeepRep37.370.9630.02435.130.9430.04332.370.9060.08531.320.8880.1073230
UNet-SF35.100.9420.04332.620.9090.07529.810.8570.13428.810.8340.161440
UNet-BR35.190.9430.04032.670.9120.07029.900.8610.12428.940.8400.148470
UNet-BR-OF36.410.9560.02934.270.9360.04831.770.8990.08930.850.8820.110710
MPFER-1637.560.9680.02035.800.9550.03033.700.9330.05132.890.9210.063470
MPFER-3237.940.9700.01936.170.9580.02833.990.9360.04733.140.9240.0581210
MPFER-6438.000.9700.01836.250.9590.02734.080.9360.04733.230.9250.0571810
+ +Table 2. Denoising on Spaces. All metrics were computed on frame 6, as BPN and DeepRep are burst-denoising methods producing only one output. For the other methods, average performances over the entire sequence are provided in Supplementary Material. + +
Gain 1Gain 2Gain 4Gain 8Gain 16Gain 20
PSNR↑SSIM↑LPIPS↓PSNR↑SSIM↑LPIPS↓PSNR↑SSIM↑LPIPS↓PSNR↑SSIM↑LPIPS↓PSNR↑SSIM↑LPIPS↓PSNR↑SSIM↑LPIPS↓
Denoising of Synthetic Noise
IBRNet-N*33.500.9150.03931.290.8770.07029.010.8220.12326.570.7410.21024.190.6340.33123.400.5910.380
NAN*35.840.9550.01833.670.9300.03431.260.8920.06828.640.8340.13225.950.7490.23125.070.7150.271
MPFER-N37.900.9690.01335.610.9510.02533.020.9210.04830.210.8720.09127.240.7970.16426.230.7650.198
MPFER-C38.060.9710.01135.950.9560.02033.650.9340.03631.210.8980.06528.610.8430.11527.710.8190.138
Novel View Synthesis Under Noisy Conditions
IBRNet*24.530.7740.13524.200.7300.15923.440.6530.21722.020.5360.32719.760.3770.49218.800.3190.553
IBRNet-N*23.860.7630.17023.730.7440.17823.380.7030.20822.680.6380.27521.670.5490.37721.290.5140.418
NAN*24.520.7990.13224.410.7870.14524.180.7650.17123.700.7260.22122.790.6660.30522.370.6410.342
MPFER24.520.7980.15724.510.7960.15824.470.7890.16424.330.7750.17823.940.7460.21223.720.7310.230
+ +Table 3. LLFF-N. We consider the two scenarios introduced in [31]: Denoising of Synthetic Noise, where the noisy target is accessible, and Novel View Synthesis Under Noisy Conditions, where the noisy target is held-out. The numbers for the stared methods correspond to Figure 9 in [31], and were provided by the authors. + +# References + +[1] Pablo Arias and Jean-Michel Morel. Video denoising via empirical bayesian estimation of space-time patches. Journal of Mathematical Imaging and Vision, 60(1):70-93, 2018. 6 +[2] Jonathan T Barron, Ben Mildenhall, Matthew Tancik, Peter Hedman, Ricardo Martin-Brualla, and Pratul P Srinivasan. Mip-nerf: A multiscale representation for anti-aliasing neural radiance fields. In ICCV, pages 5855-5864, 2021. 1, 2 +[3] Goutam Bhat, Martin Danelljan, Fisher Yu, Luc Van Gool, and Radu Timofte. Deep reparametrization of multi-frame super-resolution and denoising. 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In this work, we introduce the first 3D-based multi-frame denoising method that significantly outperforms its 2D-based counterparts with lower computational requirements. Our method extends the multiplane image (MPI) framework for novel view synthesis by introducing a learnable encoder-renderer pair manipulating multiplane representations in feature space. The encoder fuses information across views and operates in a depth-wise manner while the renderer fuses information across depths and operates in a view-wise manner. The two modules are trained end-to-end and learn to separate depths in an unsupervised way, giving rise to Multiplane Feature (MPF) representations. Experiments on the Spaces and Real Forward-Facing datasets as well as on raw burst data validate our approach for view synthesis, multi-frame denoising, and view synthesis under noisy conditions." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 524, + 128, + 537 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 524, + 128, + 537 + ], + "spans": [ + { + "bbox": [ + 47, + 524, + 128, + 537 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 545, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 545, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 545, + 288, + 715 + ], + "type": "text", + "content": "Multi-frame denoising is a classical problem of computer vision where a noise process affecting a set of images must be inverted. The main challenge is to extract consistent information across images effectively and the current state of the art relies on optical flow-based 2D alignment [3,7,45]. Novel view synthesis, on the other hand, is a classical problem of computer graphics where a scene is viewed from one or more camera positions and the task is to predict novel views from target camera positions. This problem requires to reason about the 3D structure of the scene and is typically solved using some form of volumetric representation [28, 32, 55]. Although the two problems are traditionally considered distinct, some novel view synthesis approaches have recently been observed to handle noisy" + } + ] + } + ], + "index": 11 + }, + { + "type": "image", + "bbox": [ + 306, + 230, + 547, + 369 + ], + "blocks": [ + { + "bbox": [ + 306, + 230, + 547, + 369 + ], + "lines": [ + { + "bbox": [ + 306, + 230, + 547, + 369 + ], + "spans": [ + { + "bbox": [ + 306, + 230, + 547, + 369 + ], + "type": "image", + "image_path": "d9336b458b51d07f33a7b19bee95e30bf383409c3a1c73fa220a5a647e57935f.jpg" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 373, + 547, + 430 + ], + "lines": [ + { + "bbox": [ + 305, + 373, + 547, + 430 + ], + "spans": [ + { + "bbox": [ + 305, + 373, + 547, + 430 + ], + "type": "text", + "content": "Figure 1. Top: Our Multiplane Features Encoder-Renderer (MPFER) reimagines the MPI pipeline by moving the multiplane representation to feature space. Bottom: MPFER significantly outperforms existing methods in multiple challenging scenarios, including here, novel view synthesis from 8 highly degraded inputs." + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_caption" + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 449, + 545, + 521 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 449, + 545, + 521 + ], + "spans": [ + { + "bbox": [ + 304, + 449, + 545, + 521 + ], + "type": "text", + "content": "inputs well, and to have a denoising effect in synthesized views by discarding inconsistent information across input views [18,26]. This observation opens the door to 3D-based multi-frame denoising, by recasting the problem as a special case of novel view synthesis where the input views are noisy and the target views are the clean input views [26, 31]." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 522, + 546, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 522, + 546, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 522, + 546, + 714 + ], + "type": "text", + "content": "Recently, novel view synthesis has been approached as an encoding-rendering process where a scene representation is first encoded from a set of input images and an arbitrary number of novel views are then rendered from this scene representation. In the Neural Radiance Field (NeRF) framework for instance, the scene representation is a radiance field function encoded by training a neural network on the input views. Novel views are then rendered by querying and integrating this radiance field function over light rays originating from a target camera position [2, 24, 28]. In the Multiplane Image (MPI) framework on the other hand, the scene representation is a stack of semi-transparent colored layers arranged at various depths, encoded by feeding the input views to a neural network trained on a large number of scenes. Novel views are then rendered by warping and overcompositing the semi-transparent layers [8, 41, 55]." + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "20898" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 289, + 407 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 289, + 407 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 289, + 407 + ], + "type": "text", + "content": "In the present work, we adopt the MPI framework because it is much lighter than the NeRF framework computationally. The encoding stage only requires one inference pass on a network that generalizes to new scenes instead of training one neural network per-scene, and the rendering stage is essentially free instead of requiring a large number of inference passes. However, the standard MPI pipeline struggles to predict multiplane representations that are self-consistent across depths from multiple viewpoints. This problem can lead to depth-discretization artifacts in synthesized views [40] and has previously been addressed at the encoding stage using computationally expensive mechanisms and a large number of depth planes [8, 11, 27, 40]. Here, we propose to enforce cross-depth consistency at the rendering stage by replacing the fixed overcompositing operator with a learnable renderer. This change of approach has three important implications. First, the encoder module can now process depths independently from each other and focus on fusing information across views. This significantly reduces the computational load of the encoding stage. Second, the scene representation changes from a static MPI to Multiplane Features (MPF) rendered dynamically. This significantly increases the expressive power of the scene encoding. Finally, the framework's overall performance is greatly improved, making it suitable for novel scenarios including multi-frame denoising where it outperforms standard 2D-based approaches at a fraction of their computational cost. Our main contributions are as follow:" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 408, + 287, + 552 + ], + "type": "list", + "angle": 0, + "index": 5, + "blocks": [ + { + "bbox": [ + 47, + 408, + 287, + 443 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 408, + 287, + 443 + ], + "spans": [ + { + "bbox": [ + 47, + 408, + 287, + 443 + ], + "type": "text", + "content": "- We solve the cross-depth consistency problem for multi-plane representations at the rendering stage, by introducing a learnable renderer." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 445, + 287, + 480 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 445, + 287, + 480 + ], + "spans": [ + { + "bbox": [ + 47, + 445, + 287, + 480 + ], + "type": "text", + "content": "- We introduce the Multiplane Feature (MPF) representation, a generalization of the multiplane image with higher representational power." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 481, + 287, + 515 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 481, + 287, + 515 + ], + "spans": [ + { + "bbox": [ + 47, + 481, + 287, + 515 + ], + "type": "text", + "content": "- We re-purpose the multiplane image framework originally developed for novel view synthesis to perform 3D-based multi-frame denoising." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 516, + 287, + 552 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 516, + 287, + 552 + ], + "spans": [ + { + "bbox": [ + 47, + 516, + 287, + 552 + ], + "type": "text", + "content": "- We validate the approach with experiments on 3 tasks and 3 datasets and significantly outperform existing 2D-based and 3D-based methods for multi-frame denoising." + } + ] + } + ], + "index": 4 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 47, + 562, + 132, + 574 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 562, + 132, + 574 + ], + "spans": [ + { + "bbox": [ + 47, + 562, + 132, + 574 + ], + "type": "text", + "content": "2. Related work" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 582, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 582, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 47, + 582, + 289, + 715 + ], + "type": "text", + "content": "Multi-frame denoising Multi-frame restoration methods are frequently divided into two categories, depending on the type of image alignment employed. Explicit alignment refers to the direct warping of images using optical flows predicted by a motion compensation module [4, 43, 44, 54]. In contrast, implicit alignment refers to local, data-driven deformations implemented using dynamic upsampling filters [16, 17], deformable convolutions [45, 49], kernel prediction networks [25] or their extension, basis prediction networks [53]. Explicit alignment is better at dealing with large motion while implicit alignment is better at deal" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 72, + 547, + 277 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 277 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 277 + ], + "type": "text", + "content": "ing with residual motion, and state-of-the-art performance can be achieved by combining both in the form of flow-guided deformable convolutions [6, 7]. Another distinction between multi-frame restoration methods is the type of processing used. A common approach is to concatenate the input frames together along the channel dimension [4, 43, 44, 49, 54] but recurrent processing is more efficient [9, 10, 34, 42], especially when implemented in a bidirectional way [5, 7, 14]. Basic VSR++ achieves state-of-the-art performance by combining flow-guided deformable alignment with bidirectional recurrent processing iterated multiple times [7]. In a different spirit, the recent DeepRep method [3] introduces a deep reparameterization in feature space of the maximum a posteriori formulation of multiframe restoration. Similarly to the previous methods however, it still uses a form of explicit 2D alignment, and lacks any ability to reason about the 3D structure of the scene." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 282, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 282, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 282, + 547, + 715 + ], + "type": "text", + "content": "View synthesis The idea to decompose a scene into a set of semi-transparent planes can be traced back to the use of mattes and blue screens in special effects filmmaking [38, 47]. This scene representation was first applied to view interpolation in [41], and recently gained popularity under the name of Multiplane Image (MPI) [55]. It is particularly powerful to generate novel views from a small set of forward facing views [8, 27, 55], and can even be used to generate novels views from a single image [11, 20, 46]. The rendering of view dependent-effects and non-Lambertian surfaces is challenging due to the use of a single set of RGB" + }, + { + "bbox": [ + 304, + 282, + 547, + 715 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 304, + 282, + 547, + 715 + ], + "type": "text", + "content": " images, and can be improved by predicting multiple MPIs combined as a weighted average of the distance from the input views [27], or as a set of basis components [51]. The simplicity of this representation is appealing, but it can still be computationally heavy when the number of depth planes grows [8, 51], and the rendered views can suffer from depth discretization artifacts [40]. A number of alternative layered scene representations exist, including the Layered Depth Image (LDI) consisting in one RGB image with an extra depth channel [36], and variants of MPIs and LDIs [13, 19, 21, 39]. So far however, all these methods use a fixed overcompositing operator at the rendering stage. The idea to perform view synthesis by applying 3D operations in the feature space of an encoder-decoder architecture was explored on simple geometries in [52], and used with success on a point-cloud scene representation for view synthesis from a single image in [50]. Recently, Neural Radiance Fields (NeRFs) have become highly popular for their ability to produce high quality renderings of complex scenes from arbitrary viewpoints [2, 24, 28-30]. However, they tend to be very heavy computationally, require a large number of input views, and lack the ability to generalize to novel scenes. IBRNet [48] improves generalizability by learning a generic view interpolation function, but the approach remains computationally heavy. The application of view syn" + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "20899" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 193 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 193 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 193 + ], + "type": "text", + "content": "thesis approaches to multi-frame restoration has been limited so far, and exclusively based on NeRF. RawNeRF [26] explores novel view synthesis in low-light conditions, and reports strong denoising effects in the synthesized views. Deblur-NeRF [22] augments the ability of NeRFs to deal with blur by including Deformable Sparse Kernels. Noise-aware-NeRFs [31] improves the IBRNet architecture to explicitly deal with noise. However, these different restoration approaches still suffer from the limitations affecting their underlying NeRF representations." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 203, + 103, + 216 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 203, + 103, + 216 + ], + "spans": [ + { + "bbox": [ + 47, + 203, + 103, + 216 + ], + "type": "text", + "content": "3. Method" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 224, + 287, + 272 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 224, + 287, + 272 + ], + "spans": [ + { + "bbox": [ + 46, + 224, + 287, + 272 + ], + "type": "text", + "content": "We start by describing the standard MPI processing pipeline, before discussing the cross-depth consistency problem. We then introduce our MPF Encoder-Renderer and its adaptation to multi-frame denoising." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 280, + 230, + 293 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 280, + 230, + 293 + ], + "spans": [ + { + "bbox": [ + 47, + 280, + 230, + 293 + ], + "type": "text", + "content": "3.1. Standard MPI processing pipeline" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 299, + 287, + 358 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 299, + 287, + 358 + ], + "spans": [ + { + "bbox": [ + 46, + 299, + 287, + 358 + ], + "type": "text", + "content": "The standard MPI processing pipeline turns a set of input views into an arbitrary set of rendered novel views by applying 4 main transformations: forward-warping, MPI prediction, backward-warping, overcompositing (See Figure 2a). We describe this pipeline in more details below." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 362, + 289, + 685 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 362, + 289, + 685 + ], + "spans": [ + { + "bbox": [ + 46, + 362, + 289, + 685 + ], + "type": "text", + "content": "Input views The inputs of the pipeline are a set of " + }, + { + "bbox": [ + 46, + 362, + 289, + 685 + ], + "type": "inline_equation", + "content": "V" + }, + { + "bbox": [ + 46, + 362, + 289, + 685 + ], + "type": "text", + "content": " views of a scene, consisting of images and camera parameters. The images are of height " + }, + { + "bbox": [ + 46, + 362, + 289, + 685 + ], + "type": "inline_equation", + "content": "H" + }, + { + "bbox": [ + 46, + 362, + 289, + 685 + ], + "type": "text", + "content": " and width " + }, + { + "bbox": [ + 46, + 362, + 289, + 685 + ], + "type": "inline_equation", + "content": "W" + }, + { + "bbox": [ + 46, + 362, + 289, + 685 + ], + "type": "text", + "content": ", with red-green-blue color channels, and can be stacked into a 4D tensor " + }, + { + "bbox": [ + 46, + 362, + 289, + 685 + ], + "type": "inline_equation", + "content": "\\boldsymbol{I} = \\{\\{\\{I_{vchw}\\}_{w=1}^{W}\\}_{h=1}^{H}\\}_{c=1}^{3}\\}_{v=1}^{V}" + }, + { + "bbox": [ + 46, + 362, + 289, + 685 + ], + "type": "text", + "content": ". To simplify notations, we omit the dimensions " + }, + { + "bbox": [ + 46, + 362, + 289, + 685 + ], + "type": "inline_equation", + "content": "c, h, w" + }, + { + "bbox": [ + 46, + 362, + 289, + 685 + ], + "type": "text", + "content": " and refer to an individual image as " + }, + { + "bbox": [ + 46, + 362, + 289, + 685 + ], + "type": "inline_equation", + "content": "\\boldsymbol{I}_v" + }, + { + "bbox": [ + 46, + 362, + 289, + 685 + ], + "type": "text", + "content": ". The camera parameters consist of an intrinsic tensor " + }, + { + "bbox": [ + 46, + 362, + 289, + 685 + ], + "type": "inline_equation", + "content": "\\boldsymbol{K}" + }, + { + "bbox": [ + 46, + 362, + 289, + 685 + ], + "type": "text", + "content": " of size " + }, + { + "bbox": [ + 46, + 362, + 289, + 685 + ], + "type": "inline_equation", + "content": "V \\times 3 \\times 3" + }, + { + "bbox": [ + 46, + 362, + 289, + 685 + ], + "type": "text", + "content": " containing information about the focal lengths and principal point of the cameras, and an extrinsic tensor containing information about the camera orientations in the world coordinate system, that can be split into a rotation tensor " + }, + { + "bbox": [ + 46, + 362, + 289, + 685 + ], + "type": "inline_equation", + "content": "\\boldsymbol{R}" + }, + { + "bbox": [ + 46, + 362, + 289, + 685 + ], + "type": "text", + "content": " of size " + }, + { + "bbox": [ + 46, + 362, + 289, + 685 + ], + "type": "inline_equation", + "content": "V \\times 3 \\times 3" + }, + { + "bbox": [ + 46, + 362, + 289, + 685 + ], + "type": "text", + "content": " and a translation tensor " + }, + { + "bbox": [ + 46, + 362, + 289, + 685 + ], + "type": "inline_equation", + "content": "\\boldsymbol{t}" + }, + { + "bbox": [ + 46, + 362, + 289, + 685 + ], + "type": "text", + "content": " of size " + }, + { + "bbox": [ + 46, + 362, + 289, + 685 + ], + "type": "inline_equation", + "content": "V \\times 3 \\times 1" + }, + { + "bbox": [ + 46, + 362, + 289, + 685 + ], + "type": "text", + "content": ". A reference view " + }, + { + "bbox": [ + 46, + 362, + 289, + 685 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 362, + 289, + 685 + ], + "type": "text", + "content": " is defined a priori, and the positions of all the cameras are assumed to be expressed relatively to it. The intrinsic matrix " + }, + { + "bbox": [ + 46, + 362, + 289, + 685 + ], + "type": "inline_equation", + "content": "\\boldsymbol{K}_i" + }, + { + "bbox": [ + 46, + 362, + 289, + 685 + ], + "type": "text", + "content": " of the reference camera is defined such that the corresponding field of view covers the region of space visible to all the input views. Finally, a set of " + }, + { + "bbox": [ + 46, + 362, + 289, + 685 + ], + "type": "inline_equation", + "content": "D" + }, + { + "bbox": [ + 46, + 362, + 289, + 685 + ], + "type": "text", + "content": " depth planes is distributed orthogonally to the reference viewing direction such that their normal is " + }, + { + "bbox": [ + 46, + 362, + 289, + 685 + ], + "type": "inline_equation", + "content": "\\boldsymbol{n} = (0,0,1)^{\\top}" + }, + { + "bbox": [ + 46, + 362, + 289, + 685 + ], + "type": "text", + "content": ", and their distances " + }, + { + "bbox": [ + 46, + 362, + 289, + 685 + ], + "type": "inline_equation", + "content": "\\{a_d\\}_{d=1}^D" + }, + { + "bbox": [ + 46, + 362, + 289, + 685 + ], + "type": "text", + "content": " from the reference camera center are sampled uniformly in disparity. The camera parameters and the depth planes are used to define a set of " + }, + { + "bbox": [ + 46, + 362, + 289, + 685 + ], + "type": "inline_equation", + "content": "D \\times V" + }, + { + "bbox": [ + 46, + 362, + 289, + 685 + ], + "type": "text", + "content": " homography projections, represented by a tensor " + }, + { + "bbox": [ + 46, + 362, + 289, + 685 + ], + "type": "inline_equation", + "content": "\\boldsymbol{H}" + }, + { + "bbox": [ + 46, + 362, + 289, + 685 + ], + "type": "text", + "content": " of size " + }, + { + "bbox": [ + 46, + 362, + 289, + 685 + ], + "type": "inline_equation", + "content": "D \\times V \\times 3 \\times 3" + }, + { + "bbox": [ + 46, + 362, + 289, + 685 + ], + "type": "text", + "content": ". Each homography is between one of the input views and the reference view, and is induced by one of the depth planes, such that its matrix is expressed as [12]:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 96, + 689, + 287, + 717 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 96, + 689, + 287, + 717 + ], + "spans": [ + { + "bbox": [ + 96, + 689, + 287, + 717 + ], + "type": "interline_equation", + "content": "\\boldsymbol {H} _ {d v} = \\boldsymbol {K} _ {v} \\left(\\boldsymbol {R} _ {v} - \\frac {\\boldsymbol {t} _ {v} \\boldsymbol {n} ^ {\\top}}{a _ {d}}\\right) \\boldsymbol {K} _ {i} ^ {- 1} \\tag {1}", + "image_path": "fb788a3739d4e08dcd07291eeafdee4ffd93ffbb7ea37a460921e54fbfc5122b.jpg" + } + ] + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 307, + 70, + 547, + 124 + ], + "blocks": [ + { + "bbox": [ + 307, + 70, + 547, + 124 + ], + "lines": [ + { + "bbox": [ + 307, + 70, + 547, + 124 + ], + "spans": [ + { + "bbox": [ + 307, + 70, + 547, + 124 + ], + "type": "image", + "image_path": "05c5183740a5ef516a1a6111974e4b17521f8ac9c0e7fb08be5fc47a5c26424b.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 364, + 127, + 488, + 137 + ], + "lines": [ + { + "bbox": [ + 364, + 127, + 488, + 137 + ], + "spans": [ + { + "bbox": [ + 364, + 127, + 488, + 137 + ], + "type": "text", + "content": "(a) Standard MPI processing pipeline." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_caption" + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 307, + 148, + 547, + 203 + ], + "blocks": [ + { + "bbox": [ + 307, + 148, + 547, + 203 + ], + "lines": [ + { + "bbox": [ + 307, + 148, + 547, + 203 + ], + "spans": [ + { + "bbox": [ + 307, + 148, + 547, + 203 + ], + "type": "image", + "image_path": "4171f0d6022d2873f3481a5bcdcae794df4c8425eb6ad1f5f2cf326eee21c1d2.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 373, + 206, + 479, + 216 + ], + "lines": [ + { + "bbox": [ + 373, + 206, + 479, + 216 + ], + "spans": [ + { + "bbox": [ + 373, + 206, + 479, + 216 + ], + "type": "text", + "content": "(b) Our MPF Encoder-Encoder." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 304, + 225, + 547, + 281 + ], + "lines": [ + { + "bbox": [ + 304, + 225, + 547, + 281 + ], + "spans": [ + { + "bbox": [ + 304, + 225, + 547, + 281 + ], + "type": "text", + "content": "Figure 2. In the standard MPI processing pipeline, all the learning and most of the processing happens in the MPINet module. We propose to move the multiplane representation to feature space, by giving some processing power to the warping operators, and replacing the overcompositing operator with a learnable renderer." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 306, + 545, + 402 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 306, + 545, + 402 + ], + "spans": [ + { + "bbox": [ + 304, + 306, + 545, + 402 + ], + "type": "text", + "content": "Plane Sweep Volumes The first transformation in the MPI pipeline is the computation of Plane Sweep Volumes (PSVs), obtained by forward-warping each input image " + }, + { + "bbox": [ + 304, + 306, + 545, + 402 + ], + "type": "inline_equation", + "content": "D" + }, + { + "bbox": [ + 304, + 306, + 545, + 402 + ], + "type": "text", + "content": " times, according to the homography " + }, + { + "bbox": [ + 304, + 306, + 545, + 402 + ], + "type": "inline_equation", + "content": "\\pmb{H}_{dv}" + }, + { + "bbox": [ + 304, + 306, + 545, + 402 + ], + "type": "text", + "content": ". The sampling rate of the warping operator " + }, + { + "bbox": [ + 304, + 306, + 545, + 402 + ], + "type": "inline_equation", + "content": "\\mathcal{W}" + }, + { + "bbox": [ + 304, + 306, + 545, + 402 + ], + "type": "text", + "content": " is a hyperparameter that can be controlled using an up-scaling factor " + }, + { + "bbox": [ + 304, + 306, + 545, + 402 + ], + "type": "inline_equation", + "content": "s" + }, + { + "bbox": [ + 304, + 306, + 545, + 402 + ], + "type": "text", + "content": ". Each transformation can thus be written as " + }, + { + "bbox": [ + 304, + 306, + 545, + 402 + ], + "type": "inline_equation", + "content": "\\pmb{X}_{dv} = \\mathcal{W}(\\pmb{I}_v, \\pmb{H}_{dv}, s)" + }, + { + "bbox": [ + 304, + 306, + 545, + 402 + ], + "type": "text", + "content": " and the PSV tensor " + }, + { + "bbox": [ + 304, + 306, + 545, + 402 + ], + "type": "inline_equation", + "content": "\\pmb{X}" + }, + { + "bbox": [ + 304, + 306, + 545, + 402 + ], + "type": "text", + "content": " is of size " + }, + { + "bbox": [ + 304, + 306, + 545, + 402 + ], + "type": "inline_equation", + "content": "D \\times V \\times 3 \\times sH \\times sW" + }, + { + "bbox": [ + 304, + 306, + 545, + 402 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 408, + 547, + 482 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 408, + 547, + 482 + ], + "spans": [ + { + "bbox": [ + 304, + 408, + 547, + 482 + ], + "type": "text", + "content": "Multiplane Image The main processing block of the pipeline is a neural network MPINet, turning the set of PSVs into a multiplane image representation of the scene " + }, + { + "bbox": [ + 304, + 408, + 547, + 482 + ], + "type": "inline_equation", + "content": "\\mathbf{Y} = \\mathrm{MPINet}(\\mathbf{X})" + }, + { + "bbox": [ + 304, + 408, + 547, + 482 + ], + "type": "text", + "content": " where " + }, + { + "bbox": [ + 304, + 408, + 547, + 482 + ], + "type": "inline_equation", + "content": "\\mathbf{Y}" + }, + { + "bbox": [ + 304, + 408, + 547, + 482 + ], + "type": "text", + "content": " is a set of " + }, + { + "bbox": [ + 304, + 408, + 547, + 482 + ], + "type": "inline_equation", + "content": "D" + }, + { + "bbox": [ + 304, + 408, + 547, + 482 + ], + "type": "text", + "content": " semi-transparent RGB images of size " + }, + { + "bbox": [ + 304, + 408, + 547, + 482 + ], + "type": "inline_equation", + "content": "D \\times 4 \\times sH \\times sW" + }, + { + "bbox": [ + 304, + 408, + 547, + 482 + ], + "type": "text", + "content": ", constrained to the [0,1] range by using a sigmoid activation function." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 487, + 547, + 559 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 487, + 547, + 559 + ], + "spans": [ + { + "bbox": [ + 304, + 487, + 547, + 559 + ], + "type": "text", + "content": "Projected MPs The MPI is then backward-warped to a set of " + }, + { + "bbox": [ + 304, + 487, + 547, + 559 + ], + "type": "inline_equation", + "content": "R" + }, + { + "bbox": [ + 304, + 487, + 547, + 559 + ], + "type": "text", + "content": " novel views, defined by an homography tensor " + }, + { + "bbox": [ + 304, + 487, + 547, + 559 + ], + "type": "inline_equation", + "content": "G" + }, + { + "bbox": [ + 304, + 487, + 547, + 559 + ], + "type": "text", + "content": " of size " + }, + { + "bbox": [ + 304, + 487, + 547, + 559 + ], + "type": "inline_equation", + "content": "R \\times D \\times 3 \\times 3" + }, + { + "bbox": [ + 304, + 487, + 547, + 559 + ], + "type": "text", + "content": " following Eq. (1) with the depth and view dimensions transposed. The backward-warping operation is defined as " + }, + { + "bbox": [ + 304, + 487, + 547, + 559 + ], + "type": "inline_equation", + "content": "Z_{rd} = \\mathcal{W}\\left(\\mathbf{Y}_d, \\mathbf{G}_{rd}^{-1}, 1 / s\\right)" + }, + { + "bbox": [ + 304, + 487, + 547, + 559 + ], + "type": "text", + "content": " obtaining a tensor of projected MPs " + }, + { + "bbox": [ + 304, + 487, + 547, + 559 + ], + "type": "inline_equation", + "content": "Z" + }, + { + "bbox": [ + 304, + 487, + 547, + 559 + ], + "type": "text", + "content": " of size " + }, + { + "bbox": [ + 304, + 487, + 547, + 559 + ], + "type": "inline_equation", + "content": "R \\times D \\times 4 \\times H \\times W" + }, + { + "bbox": [ + 304, + 487, + 547, + 559 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 567, + 545, + 647 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 567, + 545, + 647 + ], + "spans": [ + { + "bbox": [ + 304, + 567, + 545, + 647 + ], + "type": "text", + "content": "**Rendered views** The projected MPs are finally collapsed into single RGB images by applying the overcompositing operator " + }, + { + "bbox": [ + 304, + 567, + 545, + 647 + ], + "type": "inline_equation", + "content": "\\mathcal{O}" + }, + { + "bbox": [ + 304, + 567, + 545, + 647 + ], + "type": "text", + "content": ". This operator splits each RGB" + }, + { + "bbox": [ + 304, + 567, + 545, + 647 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 304, + 567, + 545, + 647 + ], + "type": "text", + "content": " image " + }, + { + "bbox": [ + 304, + 567, + 545, + 647 + ], + "type": "inline_equation", + "content": "Z_{rd}" + }, + { + "bbox": [ + 304, + 567, + 545, + 647 + ], + "type": "text", + "content": " into a colour component " + }, + { + "bbox": [ + 304, + 567, + 545, + 647 + ], + "type": "inline_equation", + "content": "C_{rd}" + }, + { + "bbox": [ + 304, + 567, + 545, + 647 + ], + "type": "text", + "content": " and an alpha component " + }, + { + "bbox": [ + 304, + 567, + 545, + 647 + ], + "type": "inline_equation", + "content": "A_{rd}" + }, + { + "bbox": [ + 304, + 567, + 545, + 647 + ], + "type": "text", + "content": " and computes " + }, + { + "bbox": [ + 304, + 567, + 545, + 647 + ], + "type": "inline_equation", + "content": "\\tilde{J}_r = \\sum_{d=1}^{D} \\left( C_{rd} A_{rd} \\prod_{k=d+1}^{D} (1 - A_{rk}) \\right)" + }, + { + "bbox": [ + 304, + 567, + 545, + 647 + ], + "type": "text", + "content": " obtaining the rendered views " + }, + { + "bbox": [ + 304, + 567, + 545, + 647 + ], + "type": "inline_equation", + "content": "\\tilde{J}" + }, + { + "bbox": [ + 304, + 567, + 545, + 647 + ], + "type": "text", + "content": " of size " + }, + { + "bbox": [ + 304, + 567, + 545, + 647 + ], + "type": "inline_equation", + "content": "R \\times 3 \\times H \\times W" + }, + { + "bbox": [ + 304, + 567, + 545, + 647 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 653, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 653, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 653, + 547, + 713 + ], + "type": "text", + "content": "Training The pipeline is typically trained end-to-end in a supervised way by minimizing a loss " + }, + { + "bbox": [ + 304, + 653, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{L}(\\tilde{\\boldsymbol{J}},\\boldsymbol {J})" + }, + { + "bbox": [ + 304, + 653, + 547, + 713 + ], + "type": "text", + "content": " between the rendered views " + }, + { + "bbox": [ + 304, + 653, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\tilde{\\boldsymbol{J}}" + }, + { + "bbox": [ + 304, + 653, + 547, + 713 + ], + "type": "text", + "content": " and the corresponding ground-truth images " + }, + { + "bbox": [ + 304, + 653, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\boldsymbol{J}" + }, + { + "bbox": [ + 304, + 653, + 547, + 713 + ], + "type": "text", + "content": ". In practice, " + }, + { + "bbox": [ + 304, + 653, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{L}" + }, + { + "bbox": [ + 304, + 653, + 547, + 713 + ], + "type": "text", + "content": " is often an " + }, + { + "bbox": [ + 304, + 653, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_1" + }, + { + "bbox": [ + 304, + 653, + 547, + 713 + ], + "type": "text", + "content": " loss applied to low level features of a VGG network [37]." + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "footer", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "20900" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 182, + 85 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 182, + 85 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 182, + 85 + ], + "type": "text", + "content": "3.2. Cross-depth consistency" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 91, + 287, + 223 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 91, + 287, + 223 + ], + "spans": [ + { + "bbox": [ + 46, + 91, + 287, + 223 + ], + "type": "text", + "content": "The main and only learnable module of the standard MPI pipeline is the prediction network MPINet, transforming a 5D PSV tensor into a 4D MPI scene representation. Its task is challenging because multiplane images are hyperconstrained representations: their semi-transparent layers interact with each other in non-trivial and view-dependent ways, and missing or redundant information across layers can result in depth discretization artifacts after applying the overcompositing operator [40]. To perform well, MPINet requires a mechanism enforcing cross-depth consistency; and several approaches have been considered before." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 224, + 288, + 356 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 224, + 288, + 356 + ], + "spans": [ + { + "bbox": [ + 46, + 224, + 288, + 356 + ], + "type": "text", + "content": "In the original case of stereo-magnification [55], there is one reference input and one secondary input which is turned into a single PSV. Both are concatenated along the channel dimension and fed to an MPINet module predicting the full MPI in one shot as a 3D tensor of size " + }, + { + "bbox": [ + 46, + 224, + 288, + 356 + ], + "type": "inline_equation", + "content": "(D \\times 4) \\times sH \\times sW" + }, + { + "bbox": [ + 46, + 224, + 288, + 356 + ], + "type": "text", + "content": ", such that cross-depth consistency is enforced within the convolutional layers of MPINet. A similar solution can be used in the case of single-view synthesis [46], where there is a single reference input image and no PSV. In the general case with " + }, + { + "bbox": [ + 46, + 224, + 288, + 356 + ], + "type": "inline_equation", + "content": "V" + }, + { + "bbox": [ + 46, + 224, + 288, + 356 + ], + "type": "text", + "content": " inputs, however, the PSV tensor " + }, + { + "bbox": [ + 46, + 224, + 288, + 356 + ], + "type": "inline_equation", + "content": "\\mathbf{X}" + }, + { + "bbox": [ + 46, + 224, + 288, + 356 + ], + "type": "text", + "content": " becomes very large and there are two main ways to process it." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 357, + 287, + 411 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 357, + 287, + 411 + ], + "spans": [ + { + "bbox": [ + 47, + 357, + 287, + 411 + ], + "type": "text", + "content": "Option 1 The first solution is to generalize the approach of [55] and concatenate " + }, + { + "bbox": [ + 47, + 357, + 287, + 411 + ], + "type": "inline_equation", + "content": "\\mathbf{X}" + }, + { + "bbox": [ + 47, + 357, + 287, + 411 + ], + "type": "text", + "content": " across views and depths before feeding it to a network predicting the full MPI in one shot: " + }, + { + "bbox": [ + 47, + 357, + 287, + 411 + ], + "type": "inline_equation", + "content": "\\mathbf{Y} = \\mathrm{MPINet}\\Big(\\{\\{X_{dv}\\}_{v = 1}^{V}\\}_{d = 1}^{D}\\Big)" + }, + { + "bbox": [ + 47, + 357, + 287, + 411 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 411, + 287, + 462 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 411, + 287, + 462 + ], + "spans": [ + { + "bbox": [ + 47, + 411, + 287, + 462 + ], + "type": "text", + "content": "Option 2 The second solution is to concatenate " + }, + { + "bbox": [ + 47, + 411, + 287, + 462 + ], + "type": "inline_equation", + "content": "\\mathbf{X}" + }, + { + "bbox": [ + 47, + 411, + 287, + 462 + ], + "type": "text", + "content": " across views, and process each depth separately—effectively running the MPINet block " + }, + { + "bbox": [ + 47, + 411, + 287, + 462 + ], + "type": "inline_equation", + "content": "D" + }, + { + "bbox": [ + 47, + 411, + 287, + 462 + ], + "type": "text", + "content": " times in parallel: " + }, + { + "bbox": [ + 47, + 411, + 287, + 462 + ], + "type": "inline_equation", + "content": "\\mathbf{Y} = \\{\\mathrm{MPINet}\\big(\\{X_{dv}\\}_{v=1}^{V}\\big)\\}_{d=1}^{D}" + }, + { + "bbox": [ + 47, + 411, + 287, + 462 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 462, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 462, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 462, + 288, + 714 + ], + "type": "text", + "content": "Option 1 tends to work poorly in practice [8], as it requires to either use very large convolutional layers with intractable memory requirements, or discard most of the information contained in the input PSVs after the first convolutional layer. Option 2 is appealing as it fuses information across views more effectively, but the resulting MPI typically suffers from a lack of cross-depth consistency as each depth is processed separately. Most previous works adopt Option 2 as a starting point, and augment it with various mechanisms allowing some information to flow across depths. For instance, some methods implement MPINet with 3D convolutions [27, 40], such that each depth is treated semi-independently within a local depth neighborhood dependent on the size of the kernel, which is typically 3. By design however, this solution cannot handle interactions between distant depth planes. DeepView [8] proposes to solve the recursive cross-depth constraint by iteratively refining the prediction of the MPINet block, effectively performing a form of learned gradient descent. However, this solution requires to run the MPI network multiple times, which is computationally heavy. Finally, the method of [11] uses a feature" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 72, + 545, + 121 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 121 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 121 + ], + "type": "text", + "content": "masking strategy to deal with inter-plane interactions explicitly. This solution is both complex (multiple networks are required to predict the masks) and rigid (the masking operations are fixed and still work on a per-depth basis)." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 305, + 129, + 465, + 140 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 129, + 465, + 140 + ], + "spans": [ + { + "bbox": [ + 305, + 129, + 465, + 140 + ], + "type": "text", + "content": "3.3. Our MPF Encoder-Encoder" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 147, + 545, + 291 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 147, + 545, + 291 + ], + "spans": [ + { + "bbox": [ + 304, + 147, + 545, + 291 + ], + "type": "text", + "content": "Here, we propose to solve the cross-depth consistency problem in a novel way, by addressing it at the rendering stage. Specifically, we replace the fixed overcompositing operator with a learnable renderer enforcing consistency directly at the output level on a per-view basis. This design change greatly simplifies the task of the multiplane representation encoder, which can now focus on fusing information across views in a depth-independent way. It also promotes the multiplane representation to feature space, by relaxing existing constraints on the number of channels and scaling in the [0,1] range. The four transformations of the pipeline are modified as follows (See Figure 2b)." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 294, + 545, + 367 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 294, + 545, + 367 + ], + "spans": [ + { + "bbox": [ + 304, + 294, + 545, + 367 + ], + "type": "text", + "content": "Plane Sweep Volumes To decrease the amount of information loss through image warping and promote the PSVs to feature space, we now apply a convolution to the images before warping them: " + }, + { + "bbox": [ + 304, + 294, + 545, + 367 + ], + "type": "inline_equation", + "content": "\\pmb{X}_{dv} = \\mathcal{W}(\\mathrm{Conv}(\\pmb{I}_v),\\pmb{H}_{dv},s)" + }, + { + "bbox": [ + 304, + 294, + 545, + 367 + ], + "type": "text", + "content": ". The PSV tensor " + }, + { + "bbox": [ + 304, + 294, + 545, + 367 + ], + "type": "inline_equation", + "content": "\\pmb{X}" + }, + { + "bbox": [ + 304, + 294, + 545, + 367 + ], + "type": "text", + "content": " is now of size " + }, + { + "bbox": [ + 304, + 294, + 545, + 367 + ], + "type": "inline_equation", + "content": "D\\times V\\times C_1\\times sH\\times sW" + }, + { + "bbox": [ + 304, + 294, + 545, + 367 + ], + "type": "text", + "content": " where the number of channels " + }, + { + "bbox": [ + 304, + 294, + 545, + 367 + ], + "type": "inline_equation", + "content": "C_1" + }, + { + "bbox": [ + 304, + 294, + 545, + 367 + ], + "type": "text", + "content": " is a hyperparameter." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 369, + 545, + 456 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 369, + 545, + 456 + ], + "spans": [ + { + "bbox": [ + 304, + 369, + 545, + 456 + ], + "type": "text", + "content": "Multiplane Features We then replace the MPINet module with an encoder applied to each depth independently: " + }, + { + "bbox": [ + 304, + 369, + 545, + 456 + ], + "type": "inline_equation", + "content": "\\mathbf{Y} = \\{\\mathrm{Encoder}\\left(\\left\\{\\mathbf{X}_{dv}\\right\\}_{v=1}^{V}\\right)\\}_{d=1}^{D}" + }, + { + "bbox": [ + 304, + 369, + 545, + 456 + ], + "type": "text", + "content": ". The multiplane representation " + }, + { + "bbox": [ + 304, + 369, + 545, + 456 + ], + "type": "inline_equation", + "content": "\\mathbf{Y}" + }, + { + "bbox": [ + 304, + 369, + 545, + 456 + ], + "type": "text", + "content": " is now in feature space: its range is not constrained by a sigmoid function anymore and its size is " + }, + { + "bbox": [ + 304, + 369, + 545, + 456 + ], + "type": "inline_equation", + "content": "D \\times C_2 \\times sH \\times sW" + }, + { + "bbox": [ + 304, + 369, + 545, + 456 + ], + "type": "text", + "content": " where the number of channels " + }, + { + "bbox": [ + 304, + 369, + 545, + 456 + ], + "type": "inline_equation", + "content": "C_2" + }, + { + "bbox": [ + 304, + 369, + 545, + 456 + ], + "type": "text", + "content": " is a second hyperparameter." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 460, + 545, + 537 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 460, + 545, + 537 + ], + "spans": [ + { + "bbox": [ + 304, + 460, + 545, + 537 + ], + "type": "text", + "content": "Projected MPFs The MPF is still backward-warped to a set of " + }, + { + "bbox": [ + 304, + 460, + 545, + 537 + ], + "type": "inline_equation", + "content": "R" + }, + { + "bbox": [ + 304, + 460, + 545, + 537 + ], + "type": "text", + "content": " novel views defined by an homography tensor " + }, + { + "bbox": [ + 304, + 460, + 545, + 537 + ], + "type": "inline_equation", + "content": "\\pmb{G}" + }, + { + "bbox": [ + 304, + 460, + 545, + 537 + ], + "type": "text", + "content": ", but this is now followed by a convolution collapsing the depth and channel dimensions into a single dimension: " + }, + { + "bbox": [ + 304, + 460, + 545, + 537 + ], + "type": "inline_equation", + "content": "\\mathbf{Z}_r = \\mathrm{Conv}\\Big(\\{\\mathcal{W}(\\mathbf{Y}_d,\\mathbf{G}_{dr}^{-1},1 / s)\\}_{d = 1}^D\\Big)" + }, + { + "bbox": [ + 304, + 460, + 545, + 537 + ], + "type": "text", + "content": ". The tensor " + }, + { + "bbox": [ + 304, + 460, + 545, + 537 + ], + "type": "inline_equation", + "content": "\\pmb{Z}" + }, + { + "bbox": [ + 304, + 460, + 545, + 537 + ], + "type": "text", + "content": " is of size " + }, + { + "bbox": [ + 304, + 460, + 545, + 537 + ], + "type": "inline_equation", + "content": "R\\times C_3\\times H\\times W" + }, + { + "bbox": [ + 304, + 460, + 545, + 537 + ], + "type": "text", + "content": " where " + }, + { + "bbox": [ + 304, + 460, + 545, + 537 + ], + "type": "inline_equation", + "content": "C_3" + }, + { + "bbox": [ + 304, + 460, + 545, + 537 + ], + "type": "text", + "content": " is a third hyperparameter." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 540, + 545, + 590 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 540, + 545, + 590 + ], + "spans": [ + { + "bbox": [ + 304, + 540, + 545, + 590 + ], + "type": "text", + "content": "Rendered views Finally, the projected MPFs are turned into the final rendered views by a simple CNN renderer operating on each view separately: " + }, + { + "bbox": [ + 304, + 540, + 545, + 590 + ], + "type": "inline_equation", + "content": "\\tilde{J} = \\{\\mathrm{Renderer}(Z_r)\\}_{r=1}^R" + }, + { + "bbox": [ + 304, + 540, + 545, + 590 + ], + "type": "text", + "content": ". The rendered views " + }, + { + "bbox": [ + 304, + 540, + 545, + 590 + ], + "type": "inline_equation", + "content": "\\tilde{J}" + }, + { + "bbox": [ + 304, + 540, + 545, + 590 + ], + "type": "text", + "content": " are of size " + }, + { + "bbox": [ + 304, + 540, + 545, + 590 + ], + "type": "inline_equation", + "content": "R \\times 3 \\times H \\times W" + }, + { + "bbox": [ + 304, + 540, + 545, + 590 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 594, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 594, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 594, + 545, + 714 + ], + "type": "text", + "content": "Training The pipeline is still trained end-to-end by minimizing a loss " + }, + { + "bbox": [ + 304, + 594, + 545, + 714 + ], + "type": "inline_equation", + "content": "\\mathcal{L}(\\tilde{J}, J)" + }, + { + "bbox": [ + 304, + 594, + 545, + 714 + ], + "type": "text", + "content": " between the rendered views " + }, + { + "bbox": [ + 304, + 594, + 545, + 714 + ], + "type": "inline_equation", + "content": "\\tilde{J}" + }, + { + "bbox": [ + 304, + 594, + 545, + 714 + ], + "type": "text", + "content": " and the corresponding ground-truth images " + }, + { + "bbox": [ + 304, + 594, + 545, + 714 + ], + "type": "inline_equation", + "content": "J" + }, + { + "bbox": [ + 304, + 594, + 545, + 714 + ], + "type": "text", + "content": ", but the renderer and the warping operators are now learnable. When the input views " + }, + { + "bbox": [ + 304, + 594, + 545, + 714 + ], + "type": "inline_equation", + "content": "I" + }, + { + "bbox": [ + 304, + 594, + 545, + 714 + ], + "type": "text", + "content": " are noisy versions of ground-truth images " + }, + { + "bbox": [ + 304, + 594, + 545, + 714 + ], + "type": "inline_equation", + "content": "I^{*}" + }, + { + "bbox": [ + 304, + 594, + 545, + 714 + ], + "type": "text", + "content": ", the pipeline can be turned into a multi-frame denoising method by using the input homographies " + }, + { + "bbox": [ + 304, + 594, + 545, + 714 + ], + "type": "inline_equation", + "content": "H" + }, + { + "bbox": [ + 304, + 594, + 545, + 714 + ], + "type": "text", + "content": " during backward-warping, obtaining denoised outputs " + }, + { + "bbox": [ + 304, + 594, + 545, + 714 + ], + "type": "inline_equation", + "content": "\\tilde{I}" + }, + { + "bbox": [ + 304, + 594, + 545, + 714 + ], + "type": "text", + "content": ", and by minimizing the loss " + }, + { + "bbox": [ + 304, + 594, + 545, + 714 + ], + "type": "inline_equation", + "content": "\\mathcal{L}(\\tilde{I}, I^{*})" + }, + { + "bbox": [ + 304, + 594, + 545, + 714 + ], + "type": "text", + "content": ". There is then a one-to-one mapping between the input views and the rendered views," + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "20901" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 83, + 68, + 509, + 254 + ], + "blocks": [ + { + "bbox": [ + 83, + 68, + 509, + 254 + ], + "lines": [ + { + "bbox": [ + 83, + 68, + 509, + 254 + ], + "spans": [ + { + "bbox": [ + 83, + 68, + 509, + 254 + ], + "type": "image", + "image_path": "274977e804a5bde958c6e781ba13331b72a5e53c24b1f54dda6c2da36fc0a54f.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 262, + 547, + 308 + ], + "lines": [ + { + "bbox": [ + 46, + 262, + 547, + 308 + ], + "spans": [ + { + "bbox": [ + 46, + 262, + 547, + 308 + ], + "type": "text", + "content": "Figure 3. Our Multiplane Features Encoder-Encoder (MPFER). Input views are forward-warped into plane sweep volumes (PSVs) which are processed depthwise by the Encoder Unet64. The resulting multiplane feature representation (MPF) can then be back-projected to an arbitrary number of novel views, or to the same views as the inputs—allowing the integration of a skip connection (illustrated here). The Encoder Unet64 processes the projected MPFs on a per-view basis, producing the final synthesised or denoised outputs." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 327, + 289, + 435 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 327, + 289, + 435 + ], + "spans": [ + { + "bbox": [ + 46, + 327, + 289, + 435 + ], + "type": "text", + "content": "and it is possible to integrate a skip connection feeding the noisy inputs directly to the renderer to guide its final predictions. In all our experiments, we use Unets [33] with a base of 64 channels to implement both the encoder and the renderer. We set " + }, + { + "bbox": [ + 46, + 327, + 289, + 435 + ], + "type": "inline_equation", + "content": "C_1 = C" + }, + { + "bbox": [ + 46, + 327, + 289, + 435 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 327, + 289, + 435 + ], + "type": "inline_equation", + "content": "C_2 = V \\times C" + }, + { + "bbox": [ + 46, + 327, + 289, + 435 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 327, + 289, + 435 + ], + "type": "inline_equation", + "content": "C_3 = 64" + }, + { + "bbox": [ + 46, + 327, + 289, + 435 + ], + "type": "text", + "content": " such that there is a single hyperparameter " + }, + { + "bbox": [ + 46, + 327, + 289, + 435 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 46, + 327, + 289, + 435 + ], + "type": "text", + "content": " to vary. Our Multiplane Features Encoder-Render (MPFER) is illustrated in Figure 3 for 3 inputs views and 3 depth planes. A MindSpore [15] implementation of our method is available1." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 445, + 128, + 459 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 445, + 128, + 459 + ], + "spans": [ + { + "bbox": [ + 47, + 445, + 128, + 459 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 465, + 287, + 561 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 465, + 287, + 561 + ], + "spans": [ + { + "bbox": [ + 46, + 465, + 287, + 561 + ], + "type": "text", + "content": "We first consider the Spaces dataset [8] and validate our approach on novel view synthesis. We then focus on a denoising setup and perform extensive comparisons to state-of-the-art 2D-based methods. Finally, we compare our approach to the 3D-based multi-frame denoising method of [31] by replicating their experimental setup on the Real Forward-Facing dataset. In all cases, our method outperforms competitors at a fraction of the computational cost." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 567, + 102, + 580 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 567, + 102, + 580 + ], + "spans": [ + { + "bbox": [ + 47, + 567, + 102, + 580 + ], + "type": "text", + "content": "4.1. Spaces" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 586, + 287, + 646 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 586, + 287, + 646 + ], + "spans": [ + { + "bbox": [ + 46, + 586, + 287, + 646 + ], + "type": "text", + "content": "The Spaces dataset [8] consists of 100 indoor and outdoor scenes, captured 5 to 10 times each using a 16-camera rig placed at slightly different locations. 90 scenes are used for training and 10 scenes are held-out for evaluation. The resolution of the images is " + }, + { + "bbox": [ + 46, + 586, + 287, + 646 + ], + "type": "inline_equation", + "content": "480 \\times 800" + }, + { + "bbox": [ + 46, + 586, + 287, + 646 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 648, + 287, + 696 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 648, + 287, + 696 + ], + "spans": [ + { + "bbox": [ + 46, + 648, + 287, + 696 + ], + "type": "text", + "content": "Novel view synthesis We start by replicating the novel view synthesis setup of DeepView [8] with four scenarios: one with 12 input views and three with 4 input views. Similarly to DeepView, we use a VGG loss and train our models" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 327, + 547, + 711 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 327, + 547, + 711 + ], + "spans": [ + { + "bbox": [ + 306, + 327, + 547, + 711 + ], + "type": "text", + "content": "for 100k steps using the Adam optimizer, with a learning rate of " + }, + { + "bbox": [ + 306, + 327, + 547, + 711 + ], + "type": "inline_equation", + "content": "1.5\\mathrm{e - }3" + }, + { + "bbox": [ + 306, + 327, + 547, + 711 + ], + "type": "text", + "content": ". We reduce the learning rate to " + }, + { + "bbox": [ + 306, + 327, + 547, + 711 + ], + "type": "inline_equation", + "content": "1.5\\mathrm{e - }4" + }, + { + "bbox": [ + 306, + 327, + 547, + 711 + ], + "type": "text", + "content": " after 80k steps, and use a batch size of 4. Memory usage was reported to be a major challenge in DeepView, and all our models are kept at a significantly smaller size to avoid this issue. While DeepView uses a sophisticated strategy to only generate enough of the MPI to render a " + }, + { + "bbox": [ + 306, + 327, + 547, + 711 + ], + "type": "inline_equation", + "content": "32\\times 32" + }, + { + "bbox": [ + 306, + 327, + 547, + 711 + ], + "type": "text", + "content": " crop in the target image, we use a large patch size of 192 and only apply the loss on the region of the patch that contains more than " + }, + { + "bbox": [ + 306, + 327, + 547, + 711 + ], + "type": "inline_equation", + "content": "80\\%" + }, + { + "bbox": [ + 306, + 327, + 547, + 711 + ], + "type": "text", + "content": " of the depths planes after backward warping. We compute all metrics by averaging over the validation scenes and target views of each setup, and after cropping a boundary of 16 pixels on all images as done in [8]. We compare to DeepView [8] and Soft3D [32] by using the synthesised images provided with the Spaces dataset. We also consider three variants of the standard MPI pipeline using the same Unet backbone as our MPFER method and trained in the same conditions, but processing the input PSV in different ways. MPINet implements Option 1 from Sec. 3.2. The views and depths dimensions of the PSV tensor are stacked along the channel dimension and fed to the Unet backbone to predict the output MPI in one shot. MPINet-dw implements Option 2 from Sec. 3.2. The Unet backbone runs depthwise on slices of the PSV to predict each depth plane of the MPI separately, without communication mechanism across depths. Finally, MPINet-dw-it implements a one-step version of the learned gradient descent algorithm of DeepView. A first estimate of the MPI is predicted by a Unet backbone running depthwise, and this estimate is fed to a second Unet backbone also running depthwise, along with the input PSV and gradient components (R), which are PSV-projected current estimates of the target views." + } + ] + } + ], + "index": 8 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 58, + 702, + 276, + 714 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 702, + 276, + 714 + ], + "spans": [ + { + "bbox": [ + 58, + 702, + 276, + 714 + ], + "type": "text", + "content": "" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "20902" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 47, + 68, + 547, + 340 + ], + "blocks": [ + { + "bbox": [ + 47, + 68, + 547, + 340 + ], + "lines": [ + { + "bbox": [ + 47, + 68, + 547, + 340 + ], + "spans": [ + { + "bbox": [ + 47, + 68, + 547, + 340 + ], + "type": "image", + "image_path": "fe555aed21d8f9ec5727e740450c9f2fdcfc0135fc2524e7826295db142e70ad.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 347, + 547, + 371 + ], + "lines": [ + { + "bbox": [ + 46, + 347, + 547, + 371 + ], + "spans": [ + { + "bbox": [ + 46, + 347, + 547, + 371 + ], + "type": "text", + "content": "Figure 4. Qualitative evaluation for multi-frame denoising with Gain 20 (best viewed zoomed in). We compare MPFER to 2D-based methods on Spaces (top) and to 3D-based methods on the Real Forward-Facing dataset (bottom)." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 391, + 289, + 594 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 391, + 289, + 594 + ], + "spans": [ + { + "bbox": [ + 46, + 391, + 289, + 594 + ], + "type": "text", + "content": "For our MPFER method and the MPINet ablations, we use a number of depth planes " + }, + { + "bbox": [ + 46, + 391, + 289, + 594 + ], + "type": "inline_equation", + "content": "D = 64" + }, + { + "bbox": [ + 46, + 391, + 289, + 594 + ], + "type": "text", + "content": " distributed between 100 and 0.5 meters away from the reference camera, placed at the average position of the input views. We use a number of channels " + }, + { + "bbox": [ + 46, + 391, + 289, + 594 + ], + "type": "inline_equation", + "content": "C = 8" + }, + { + "bbox": [ + 46, + 391, + 289, + 594 + ], + "type": "text", + "content": " and a PSV/MPF upscaling factor " + }, + { + "bbox": [ + 46, + 391, + 289, + 594 + ], + "type": "inline_equation", + "content": "s = 1.5" + }, + { + "bbox": [ + 46, + 391, + 289, + 594 + ], + "type": "text", + "content": ". Since the Unet backbone is not agnostic to the number of input views, we train one version of each model for the setup with 12 input views and one version for the three setups with 4 input views. The results are presented in Table 1. We observe a clear progression between the performances of MPINet, MPINet-dw and MPINet-dw-it, illustrating the benefit of each design change. Our MPFER method outperforms MPINet-dw-it by up to 4dBs in PSNR at a similar computational complexity, and outperforms DeepView by up to 1.8dB at a fraction of the complexity, clearly motivating the use of a learnt renderer for efficient depth fusion." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 605, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 605, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 605, + 289, + 715 + ], + "type": "text", + "content": "Multi-frame denoising We now consider a different setup where the inputs are 16 views from one rig position with images degraded with noise, and the targets are the same 16 views denoised. Similarly to previous works [3, 25,31,53], we apply synthetic noise with a signal dependent Gaussian distribution " + }, + { + "bbox": [ + 46, + 605, + 289, + 715 + ], + "type": "inline_equation", + "content": "\\mathbf{I}_{vchw} \\sim \\mathcal{N}\\left(\\mathbf{I}_{vchw}^{*}, \\sigma_{r}^{2} + \\sigma_{s}\\mathbf{I}_{vchw}^{*}\\right)" + }, + { + "bbox": [ + 46, + 605, + 289, + 715 + ], + "type": "text", + "content": " where " + }, + { + "bbox": [ + 46, + 605, + 289, + 715 + ], + "type": "inline_equation", + "content": "\\mathbf{I}" + }, + { + "bbox": [ + 46, + 605, + 289, + 715 + ], + "type": "text", + "content": " is the tensor of noisy inputs, " + }, + { + "bbox": [ + 46, + 605, + 289, + 715 + ], + "type": "inline_equation", + "content": "\\mathbf{I}^{*}" + }, + { + "bbox": [ + 46, + 605, + 289, + 715 + ], + "type": "text", + "content": " is the ground truth signal, and " + }, + { + "bbox": [ + 46, + 605, + 289, + 715 + ], + "type": "inline_equation", + "content": "\\sigma_r" + }, + { + "bbox": [ + 46, + 605, + 289, + 715 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 605, + 289, + 715 + ], + "type": "inline_equation", + "content": "\\sigma_s" + }, + { + "bbox": [ + 46, + 605, + 289, + 715 + ], + "type": "text", + "content": " are noise parameters that are fixed for each sequence. We focus in particular on challenging sce" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 305, + 391, + 545, + 428 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 391, + 545, + 428 + ], + "spans": [ + { + "bbox": [ + 305, + 391, + 545, + 428 + ], + "type": "text", + "content": "narios with moderate to high gain levels [4, 8, 16, 20], corresponding to the " + }, + { + "bbox": [ + 305, + 391, + 545, + 428 + ], + "type": "inline_equation", + "content": "(\\log (\\sigma_r),\\log (\\sigma_s))" + }, + { + "bbox": [ + 305, + 391, + 545, + 428 + ], + "type": "text", + "content": " values " + }, + { + "bbox": [ + 305, + 391, + 545, + 428 + ], + "type": "inline_equation", + "content": "[-1.44, - 1.84)" + }, + { + "bbox": [ + 305, + 391, + 545, + 428 + ], + "type": "inline_equation", + "content": "(-1.08, - 1.48)" + }, + { + "bbox": [ + 305, + 391, + 545, + 428 + ], + "type": "inline_equation", + "content": "(-0.72, - 1.12)" + }, + { + "bbox": [ + 305, + 391, + 545, + 428 + ], + "type": "inline_equation", + "content": "(-0.6, - 1.0)]" + }, + { + "bbox": [ + 305, + 391, + 545, + 428 + ], + "type": "text", + "content": " respectively." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 437, + 546, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 437, + 546, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 437, + 546, + 715 + ], + "type": "text", + "content": "We consider two patch-based approaches: VBM4D [23] and VNLB [1], as well as four state-of-the-art learning-based methods: BPN [53], BasicVSR [5] and its extension BasicVSR++ [7], and DeepRep [3]. To evaluate the influence of the model size and in particular the number of depth planes, we train three MPFER models: MPFER-16 with " + }, + { + "bbox": [ + 304, + 437, + 546, + 715 + ], + "type": "inline_equation", + "content": "(D,C,s) = (16,8,1.)" + }, + { + "bbox": [ + 304, + 437, + 546, + 715 + ], + "type": "text", + "content": ", MPFER-32 with " + }, + { + "bbox": [ + 304, + 437, + 546, + 715 + ], + "type": "inline_equation", + "content": "(D,C,s) = (32,16,1.25)" + }, + { + "bbox": [ + 304, + 437, + 546, + 715 + ], + "type": "text", + "content": ", and MPFER-64 with " + }, + { + "bbox": [ + 304, + 437, + 546, + 715 + ], + "type": "inline_equation", + "content": "(D,C,s) = (64,8,1.25)" + }, + { + "bbox": [ + 304, + 437, + 546, + 715 + ], + "type": "text", + "content": ". MPFER-16 has the particularity of using the same number of depth planes as there are input images, meaning that the number of Unet passes per frame to denoise the sequence is " + }, + { + "bbox": [ + 304, + 437, + 546, + 715 + ], + "type": "inline_equation", + "content": "(D + V) / V = 2" + }, + { + "bbox": [ + 304, + 437, + 546, + 715 + ], + "type": "text", + "content": ". This observation motivates us to perform a comparison with three other architectures, using a strict computational budget of 2 Unet passes per frame. Unet-SF (for Single-Frame) is constituted of two Unet blocks without temporal connection, therefore processing the sequence as a disjoint set of single frames. Unet-BR (for Bidirectional-Recurrent) is constituted of two Unet blocks with bidirectional recurrent connections: the lower Unet processes the sequence in a backward way, and the higher Unet processes the sequence in a feedforward way. Finally, Unet-BR-OF (for Bidirectional-Recurrent with Optical-Flow alignment) is constituted of two Unet" + } + ] + } + ], + "index": 5 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "20903" + } + ] + } + ], + "index": 6 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 289, + 468 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 289, + 468 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 289, + 468 + ], + "type": "text", + "content": "blocks with bidirectional recurrent connections, and the recurrent hidden-state is aligned using a SpyNet module, as done in basicVSR [5]. We train all the models in the same conditions as for the novel view synthesis setup, except for the patch size which we increase to 256, and the loss which we replace with a simple L1 loss. During training, we vary the gain level randomly and concatenate an estimate of the standard deviation of the noise to the input, as in [25,31,53]. We evaluate on the first rig position of the 10 validation scenes of the Spaces dataset for the 4 gain levels without boundary-cropping, and present the results in Table 2. Each model receives 16 noisy images as input and produces 16 restored images as output, except for BPN and DeepRep which are burst processing methods and only produce one output. For these methods, we choose the view number 6 at the center of the camera rig as the target output, and compare the performances of all methods on this frame. Our MPFER method clearly outperforms all the other methods at a fraction of the computational cost. It performs particularly strongly at high noise levels, with improvements over other methods of more that 2dBs in PSNR. MPFER-16 also performs remarkably well, despite using only 16 depth planes. This suggests that the high representational power of multiplane features allows to significantly reduce the number of depth planes—and therefore the computational cost—compared to standard MPI approaches, which typically use a very high number of planes (80 in the case of DeepView [8], up to 192 in the case of NeX [51]). A qualitative evaluation is available in Figure 4 (top), and we observe that MPFER is able to reconstruct scenes with much better details. We also present a visualization of multiplane features in Figure 6, illustrating how the model learns to separate depths in an unsupervised way." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 475, + 111, + 487 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 475, + 111, + 487 + ], + "spans": [ + { + "bbox": [ + 47, + 475, + 111, + 487 + ], + "type": "text", + "content": "4.2. LLFF-N" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 494, + 287, + 590 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 494, + 287, + 590 + ], + "spans": [ + { + "bbox": [ + 47, + 494, + 287, + 590 + ], + "type": "text", + "content": "The LLFF-N dataset [31] is a variant of the Real Forward-Facing dataset [27] where images are linearized by applying inverse gamma correction and random inverse white balancing, and synthetic noise is applied following the same signal dependent Gaussian distribution as used in the previous section with the six gain levels [1, 2, 4, 8, 16, 20]. The dataset contains 35 scenes for training and 8 scenes for testing, and the resolution of the images is " + }, + { + "bbox": [ + 47, + 494, + 287, + 590 + ], + "type": "inline_equation", + "content": "756 \\times 1008" + }, + { + "bbox": [ + 47, + 494, + 287, + 590 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 594, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 594, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 47, + 594, + 289, + 715 + ], + "type": "text", + "content": "**Denoising** In this setup, the model receives 8 frames in input: the target frame plus its 7 nearest neighbors in terms of camera distances. We train one MPFER model with " + }, + { + "bbox": [ + 47, + 594, + 289, + 715 + ], + "type": "inline_equation", + "content": "(D,C,s) = (64,8,1.25)" + }, + { + "bbox": [ + 47, + 594, + 289, + 715 + ], + "type": "text", + "content": ", using an " + }, + { + "bbox": [ + 47, + 594, + 289, + 715 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_1" + }, + { + "bbox": [ + 47, + 594, + 289, + 715 + ], + "type": "text", + "content": " loss applied to the target frame. We evaluate on the 43 bursts used in [31] (every 8th frame of the test set) and present the results in the first half of Table 3. A qualitative evaluation is also available in Figure 4 (bottom). To assess the robustness of our method to noisy camera positions, we evaluate it using camera positions computed on clean images (MPFER-C) and" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 304, + 72, + 547, + 121 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 121 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 121 + ], + "type": "text", + "content": "on noisy images (MPFER-N) using COLMAP [35]. Our method outperforms IBRNet-N and NAN in both scenarios by large margins, but the evaluation using clean camera poses performs significantly better at high noise levels." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 123, + 547, + 292 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 123, + 547, + 292 + ], + "spans": [ + { + "bbox": [ + 304, + 123, + 547, + 292 + ], + "type": "text", + "content": "Synthesis under noisy conditions In this setup, the model receives as input the 8 nearest neighbors to a held-out target. Again, we train one MPFER model with " + }, + { + "bbox": [ + 304, + 123, + 547, + 292 + ], + "type": "inline_equation", + "content": "(D,C,s) = (64,8,1.25)" + }, + { + "bbox": [ + 304, + 123, + 547, + 292 + ], + "type": "text", + "content": ", using an " + }, + { + "bbox": [ + 304, + 123, + 547, + 292 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_1" + }, + { + "bbox": [ + 304, + 123, + 547, + 292 + ], + "type": "text", + "content": " loss applied to the target frame. We evaluate on the same 43 bursts as before and report the results in the second half of Table 3. Our method performs on par with IBRNet and NAN at very low noise levels (close to a pure synthesis problem), and significantly outperforms the other methods at larger noise levels. MPFER only requires " + }, + { + "bbox": [ + 304, + 123, + 547, + 292 + ], + "type": "inline_equation", + "content": "D" + }, + { + "bbox": [ + 304, + 123, + 547, + 292 + ], + "type": "text", + "content": " Unet passes to produce an MPF, and 1 Unet pass to render a novel view, which is significantly lighter than IBRNet and NAN. At inference time, the Unet pass requires 0.6 Mflops per pixel, compared to 45 Mflops for IBRNet [48]. A qualitative evaluation is available in Figure 1 for Gain 20." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 294, + 547, + 380 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 294, + 547, + 380 + ], + "spans": [ + { + "bbox": [ + 304, + 294, + 547, + 380 + ], + "type": "text", + "content": "Low-Light Scenes Finally, we qualitatively evaluate our denoising model trained on LLFF-N on sequences with real noise captured with a Google Pixel 4 under low-light conditions. We use the sequences from [31] and estimate camera poses using COLMAP [35] on noisy images. We compare our results to those of [31]—downloaded from their project page where more baselines can be found—in Figure 5." + } + ] + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 308, + 397, + 386, + 553 + ], + "blocks": [ + { + "bbox": [ + 326, + 387, + 367, + 397 + ], + "lines": [ + { + "bbox": [ + 326, + 387, + 367, + 397 + ], + "spans": [ + { + "bbox": [ + 326, + 387, + 367, + 397 + ], + "type": "text", + "content": "Noisy input" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 308, + 397, + 386, + 553 + ], + "lines": [ + { + "bbox": [ + 308, + 397, + 386, + 553 + ], + "spans": [ + { + "bbox": [ + 308, + 397, + 386, + 553 + ], + "type": "image", + "image_path": "8975f5e6e4090028de873e302eb3a5acd82fa876d8f1f10232c355e44fb7523d.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 306, + 562, + 547, + 585 + ], + "lines": [ + { + "bbox": [ + 306, + 562, + 547, + 585 + ], + "spans": [ + { + "bbox": [ + 306, + 562, + 547, + 585 + ], + "type": "text", + "content": "Figure 5. Qualitative evaluation on sequences with real noise from [31], captured with a Google Pixel 4." + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 387, + 397, + 465, + 553 + ], + "blocks": [ + { + "bbox": [ + 408, + 387, + 443, + 397 + ], + "lines": [ + { + "bbox": [ + 408, + 387, + 443, + 397 + ], + "spans": [ + { + "bbox": [ + 408, + 387, + 443, + 397 + ], + "type": "text", + "content": "NAN [31]" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 387, + 397, + 465, + 553 + ], + "lines": [ + { + "bbox": [ + 387, + 397, + 465, + 553 + ], + "spans": [ + { + "bbox": [ + 387, + 397, + 465, + 553 + ], + "type": "image", + "image_path": "fff9bcf078fe527e3e4a5a7fe855444e6225faac1255396142cb8c25715e5e43.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + } + ], + "index": 11 + }, + { + "type": "image", + "bbox": [ + 467, + 397, + 545, + 553 + ], + "blocks": [ + { + "bbox": [ + 481, + 388, + 531, + 396 + ], + "lines": [ + { + "bbox": [ + 481, + 388, + 531, + 396 + ], + "spans": [ + { + "bbox": [ + 481, + 388, + 531, + 396 + ], + "type": "text", + "content": "MPFER (Ours)" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 467, + 397, + 545, + 553 + ], + "lines": [ + { + "bbox": [ + 467, + 397, + 545, + 553 + ], + "spans": [ + { + "bbox": [ + 467, + 397, + 545, + 553 + ], + "type": "image", + "image_path": "194f6c8421dd993e1ebcfbbfdcd57f095f588a260f337cb0c334b8b5736f8cf7.jpg" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_body" + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 608, + 379, + 620 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 608, + 379, + 620 + ], + "spans": [ + { + "bbox": [ + 306, + 608, + 379, + 620 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 628, + 547, + 701 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 628, + 547, + 701 + ], + "spans": [ + { + "bbox": [ + 304, + 628, + 547, + 701 + ], + "type": "text", + "content": "We proposed to approach multi-frame denoising as a view synthesis problem and argued in favor of using multi-plane representations for their low computational cost and generalizability. We introduced a powerful generalization of multiplane images to feature space, and demonstrated its effectiveness in multiple challenging scenarios." + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "footer", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "20904" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 47, + 68, + 545, + 182 + ], + "blocks": [ + { + "bbox": [ + 47, + 68, + 545, + 182 + ], + "lines": [ + { + "bbox": [ + 47, + 68, + 545, + 182 + ], + "spans": [ + { + "bbox": [ + 47, + 68, + 545, + 182 + ], + "type": "image", + "image_path": "dca7fc9a0337bb928e2850dee7ba5676e0bdf101479ee0fff3846eec717237c2.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 47, + 185, + 545, + 208 + ], + "lines": [ + { + "bbox": [ + 47, + 185, + 545, + 208 + ], + "spans": [ + { + "bbox": [ + 47, + 185, + 545, + 208 + ], + "type": "text", + "content": "Figure 6. Visualization of Multiplane Features for 3 scenes. We plot the first 3 channels of planes 1, 3, 5, 7, 9, 11, 13, 15 from MPFER-16. Our method learns to separate depths in an unsupervised way, in this case from a pure denoising problem." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 47, + 215, + 545, + 312 + ], + "blocks": [ + { + "bbox": [ + 47, + 215, + 545, + 312 + ], + "lines": [ + { + "bbox": [ + 47, + 215, + 545, + 312 + ], + "spans": [ + { + "bbox": [ + 47, + 215, + 545, + 312 + ], + "type": "table", + "html": "
12 input views (dense)4 input views (small)4 input views (medium)4 input views (large)GFlops@500×800
PSNR↑SSIM↑LPIPS↓PSNR↑SSIM↑LPIPS↓PSNR↑SSIM↑LPIPS↓PSNR↑SSIM↑LPIPS↓
Soft3D*31.930.9400.05230.290.9250.06430.840.9300.06030.570.9310.054n/a
DeepView*34.230.9650.01531.420.9540.02632.380.9570.02131.000.9520.02445800
MPINet27.430.9140.03527.000.9060.05426.160.8960.06224.930.8650.085450
MPINet-dw30.700.9630.02129.390.9510.02728.470.9480.03026.830.9370.0407890
MPINet-dw-it30.850.9660.01730.220.9550.02429.370.9530.02628.000.9430.03414800
MPFER-6435.730.9720.01233.200.9590.01833.470.9590.01832.380.9530.0218490
", + "image_path": "5acf9577c989e585b8a4943e45bab1f2072c55cf95d2dfe98d518cdabab60229.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "type": "table", + "bbox": [ + 47, + 343, + 545, + 510 + ], + "blocks": [ + { + "bbox": [ + 47, + 314, + 545, + 335 + ], + "lines": [ + { + "bbox": [ + 47, + 314, + 545, + 335 + ], + "spans": [ + { + "bbox": [ + 47, + 314, + 545, + 335 + ], + "type": "text", + "content": "Table 1. Novel view synthesis on Spaces. All metrics were computed on predicted images with a 16-pixel boundary cropped, as done in [8]. Stared methods were evaluated using the predicted images released with the Spaces dataset." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 47, + 343, + 545, + 510 + ], + "lines": [ + { + "bbox": [ + 47, + 343, + 545, + 510 + ], + "spans": [ + { + "bbox": [ + 47, + 343, + 545, + 510 + ], + "type": "table", + "html": "
Gain 4Gain 8Gain 16Gain 20GFlops@500×800
PSNR↑SSIM↑LPIPS↓PSNR↑SSIM↑LPIPS↓PSNR↑SSIM↑LPIPS↓PSNR↑SSIM↑LPIPS↓
VBM4D32.000.9000.10829.940.8500.17227.480.7690.28026.550.7300.331n/a
VNLB33.410.9180.08930.300.8710.14425.740.7930.28323.510.7430.366n/a
BPN34.520.9340.04832.100.9000.08229.450.8460.14428.560.8240.168810
BasicVSR36.870.9590.02734.520.9370.04931.730.8980.09530.680.8790.1192090
BasicVSR++36.980.9590.02634.660.9380.04531.970.9020.08330.920.8830.1024300
DeepRep37.370.9630.02435.130.9430.04332.370.9060.08531.320.8880.1073230
UNet-SF35.100.9420.04332.620.9090.07529.810.8570.13428.810.8340.161440
UNet-BR35.190.9430.04032.670.9120.07029.900.8610.12428.940.8400.148470
UNet-BR-OF36.410.9560.02934.270.9360.04831.770.8990.08930.850.8820.110710
MPFER-1637.560.9680.02035.800.9550.03033.700.9330.05132.890.9210.063470
MPFER-3237.940.9700.01936.170.9580.02833.990.9360.04733.140.9240.0581210
MPFER-6438.000.9700.01836.250.9590.02734.080.9360.04733.230.9250.0571810
", + "image_path": "62c59ad64ee758a8d5a81ec3a211d315c8efa379a08fd82f2a9c69a0368b221b.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_body" + } + ], + "index": 4 + }, + { + "type": "table", + "bbox": [ + 47, + 541, + 545, + 674 + ], + "blocks": [ + { + "bbox": [ + 47, + 512, + 545, + 534 + ], + "lines": [ + { + "bbox": [ + 47, + 512, + 545, + 534 + ], + "spans": [ + { + "bbox": [ + 47, + 512, + 545, + 534 + ], + "type": "text", + "content": "Table 2. Denoising on Spaces. All metrics were computed on frame 6, as BPN and DeepRep are burst-denoising methods producing only one output. For the other methods, average performances over the entire sequence are provided in Supplementary Material." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 47, + 541, + 545, + 674 + ], + "lines": [ + { + "bbox": [ + 47, + 541, + 545, + 674 + ], + "spans": [ + { + "bbox": [ + 47, + 541, + 545, + 674 + ], + "type": "table", + "html": "
Gain 1Gain 2Gain 4Gain 8Gain 16Gain 20
PSNR↑SSIM↑LPIPS↓PSNR↑SSIM↑LPIPS↓PSNR↑SSIM↑LPIPS↓PSNR↑SSIM↑LPIPS↓PSNR↑SSIM↑LPIPS↓PSNR↑SSIM↑LPIPS↓
Denoising of Synthetic Noise
IBRNet-N*33.500.9150.03931.290.8770.07029.010.8220.12326.570.7410.21024.190.6340.33123.400.5910.380
NAN*35.840.9550.01833.670.9300.03431.260.8920.06828.640.8340.13225.950.7490.23125.070.7150.271
MPFER-N37.900.9690.01335.610.9510.02533.020.9210.04830.210.8720.09127.240.7970.16426.230.7650.198
MPFER-C38.060.9710.01135.950.9560.02033.650.9340.03631.210.8980.06528.610.8430.11527.710.8190.138
Novel View Synthesis Under Noisy Conditions
IBRNet*24.530.7740.13524.200.7300.15923.440.6530.21722.020.5360.32719.760.3770.49218.800.3190.553
IBRNet-N*23.860.7630.17023.730.7440.17823.380.7030.20822.680.6380.27521.670.5490.37721.290.5140.418
NAN*24.520.7990.13224.410.7870.14524.180.7650.17123.700.7260.22122.790.6660.30522.370.6410.342
MPFER24.520.7980.15724.510.7960.15824.470.7890.16424.330.7750.17823.940.7460.21223.720.7310.230
", + "image_path": "45dba6e7e0ffdf2035b9ffcbb4cd9e0814be89ff7a375e3b58e8168c4788960e.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "table_body" + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 677, + 545, + 710 + ], + "lines": [ + { + "bbox": [ + 46, + 677, + 545, + 710 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 545, + 710 + ], + "type": "text", + "content": "Table 3. LLFF-N. We consider the two scenarios introduced in [31]: Denoising of Synthetic Noise, where the noisy target is accessible, and Novel View Synthesis Under Noisy Conditions, where the noisy target is held-out. The numbers for the stared methods correspond to Figure 9 in [31], and were provided by the authors." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 749, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 749, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 749, + 317, + 757 + ], + "type": "text", + "content": "20905" + } + ] + } + ], + "index": 8 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 288, + 714 + ], + "type": "list", + "angle": 0, + "index": 18, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 124 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 124 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 124 + ], + "type": "text", + "content": "[1] Pablo Arias and Jean-Michel Morel. 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ACM TOG, 37(4):1-12, 2018. 1, 2, 4" + } + ] + } + ], + "index": 26 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "20907" + } + ] + } + ], + "index": 28 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 9 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Efficient and Explicit Modelling of Image Hierarchies for Image Restoration/61b7e2ab-0381-45d6-b5b0-549e3c623e77_content_list.json b/2023/Efficient and Explicit Modelling of Image Hierarchies for Image Restoration/61b7e2ab-0381-45d6-b5b0-549e3c623e77_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..19c0147ecce8ff497203c3426c4cecaf526bdfd4 --- /dev/null +++ b/2023/Efficient and Explicit Modelling of Image Hierarchies for Image Restoration/61b7e2ab-0381-45d6-b5b0-549e3c623e77_content_list.json @@ -0,0 +1,1750 @@ +[ + { + "type": "text", + "text": "Efficient and Explicit Modelling of Image Hierarchies for Image Restoration", + "text_level": 1, + "bbox": [ + 99, + 130, + 869, + 151 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Yawei Li1 Yuchen Fan2 Xiaoyu Xiang2 Denis Demandolx2", + "bbox": [ + 225, + 179, + 750, + 198 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Rakesh Ranjan $^{2}$ Radu Timofte $^{1,3}$ Luc Van Gool $^{1,4}$", + "bbox": [ + 272, + 198, + 705, + 215 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1Computer Vision Lab, ETH Zürich 2Meta Reality Labs 3University of Würzburg 4KU Leuven", + "bbox": [ + 88, + 215, + 893, + 234 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 268, + 313, + 284 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "The aim of this paper is to propose a mechanism to efficiently and explicitly model image hierarchies in the global, regional, and local range for image restoration. To achieve that, we start by analyzing two important properties of natural images including cross-scale similarity and anisotropic image features. Inspired by that, we propose the anchored stripe self-attention which achieves a good balance between the space and time complexity of self-attention and the modelling capacity beyond the regional range. Then we propose a new network architecture dubbed GRL to explicitly model image hierarchies in the Global, Regional, and Local range via anchored stripe self-attention, window self-attention, and channel attention enhanced convolution. Finally, the proposed network is applied to 7 image restoration types, covering both real and synthetic settings. The proposed method sets the new state-of-the-art for several of those. Code will be available at https://github.com/ofsoundof/GRL-Image-Restoration.git.", + "bbox": [ + 75, + 300, + 473, + 589 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 617, + 209, + 633 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Image restoration aims at recovering high-quality images from low-quality ones, resulting from an image degradation processes such as blurring, sub-sampling, noise corruption, and JPEG compression. Image restoration is an ill-posed inverse problem since important content information about the image is missing during the image degradation processes. Thus, in order to recover a high-quality image, the rich information exhibited in the degraded image should be fully exploited.", + "bbox": [ + 75, + 643, + 468, + 779 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Natural images contain a hierarchy of features at global, regional, and local ranges which could be used by deep neural networks for image restoration. First, the local range covers a span of several pixels and typical features are edges and local colors. To model such local features, convolutional neural networks (CNNs) with small kernels (e.g. $3 \\times 3$ ) are utilized. Second, the regional range is characterized by a window with tens of pixels. This range of pix", + "bbox": [ + 75, + 779, + 468, + 902 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/ecbcec5227d0dc7456f5ede5d3de3a19989cbf063fc1d23baa28da0b7c72b020.jpg", + "image_caption": [ + "(a) bridge from ICB, $2749\\times 4049$" + ], + "image_footnote": [], + "bbox": [ + 501, + 267, + 704, + 494 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/f07e5edd31683e40fccf7ac488ca0122dc610b128acb455401a31cd8dfd72536.jpg", + "image_caption": [ + "(b) $0848x4$ from DIV2K, $1020 \\times 768$" + ], + "image_footnote": [], + "bbox": [ + 705, + 267, + 890, + 375 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/74081cd07c48d14bb1648cb98a2239a864aa8bb452efd783d2c2d7ba3c88d23e.jpg", + "image_caption": [ + "(c) 073 from Urban100, $1024 \\times 765$", + "Figure 1. Natural images show a hierarchy of features in a global, regional, and local range. The local (edges, colors) and regional features (the pink squares) could be well modelled by CNNs and window self-attention. By contrast, it is difficult to efficiently and explicitly model the rich global features (cyan rectangles)." + ], + "image_footnote": [], + "bbox": [ + 705, + 388, + 890, + 494 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "els can cover small objects and components of large objects (pink squares in Fig. 1). Due to the larger range, modelling the regional features (consistency, similarity) explicitly with large-kernel CNNs would be inefficient in both parameters and computation. Instead, transformers with a window attention mechanism are well suited for this task. Third, beyond local and regional, some features have a global span (cyan rectangles in Fig. 1), incl. but not limited to symmetry, multi-scale pattern repetition (Fig. 1a), same scale texture similarity (Fig. 1b), and structural similarity and consistency in large objects and content (Fig. 1c). To model features at this range, global image understanding is needed.", + "bbox": [ + 496, + 593, + 892, + 776 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Different from the local and regional range features, there are two major challenges to model the global range features. Firstly, existing image restoration networks based on convolutions and window attention could not capture long-range dependencies explicitly by using a single computational module. Although non-local operations are used in some works, they are either used sparsely in the network or applied to small image crops. Thus, global image under", + "bbox": [ + 496, + 779, + 893, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 807, + 44 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "18278", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/4fde8b78e8ba6c9af11c8f71a9614873d91aceaf93c71263ec3fcc4bc974c9a0.jpg", + "image_caption": [ + "Figure 2. The proposed GRL achieves state-of-the-art performances on various image restoration tasks. Details provided in Sec. 5." + ], + "image_footnote": [], + "bbox": [ + 80, + 97, + 883, + 176 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "standing still mainly happens via progressive propagation of features through repeated computational modules. Secondly, the increasing resolution of today's images poses a challenge for long-range dependency modelling. High image resolution leads to a computational burden associated with pairwise pixel comparisons and similarity searches.", + "bbox": [ + 75, + 200, + 467, + 290 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "The aforementioned discussion leads to a series of research questions: 1) how to efficiently model global range features in high-dimensional images for image restoration; 2) how to model image hierarchies (local, regional, global) explicitly by a single computational module for high-dimensional image restoration; 3) and how can this joint modelling lead to a uniform performance improvement for different image restoration tasks. The paper tries to answer these questions in Sec. 3, Sec. 4, and Sec. 5, resp.", + "bbox": [ + 75, + 292, + 467, + 428 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "First, we propose anchored stripe self-attention for efficient dependency modelling beyond the regional range. The proposed self-attention is inspired by two properties of natural images including cross-scale similarity and anisotropic image features. Cross-scale similarity means that structures in a natural image are replicated at different scales. Inspired by that, we propose to use anchors as an intermediate to approximate the exact attention map between queries and keys in self-attention. Since the anchors summarize image information into a lower-dimensional space, the space and time complexity of self-attention can be significantly reduced. In addition, based on the observation of anisotropic image features, we propose to conduct anchored self-attention within vertical and horizontal stripes. Due to the anisotropic shrinkage of the attention range, a further reduction of complexity is achieved. And the combination of axial stripes also ensures a global view of the image content. When equipped with the stripe shift operation, the four stripe self-attention modes (horizontal, vertical, shifted horizontal, shifted vertical) achieves a good balance between computational complexity and the capacity of global range dependency modelling. Furthermore, the proposed anchored stripe self-attention is analyzed from the perspective of low-rankness and similarity propagation.", + "bbox": [ + 75, + 431, + 467, + 792 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Secondly, a new transformer network is proposed to explicitly model global, regional, and local range dependencies in a single computational module. The hierarchical modelling of images is achieved by the parallel computation of the proposed anchored stripe self-attention, window self-attention, and channel-attention enhanced convolution. And the transformer architecture is dubbed GRL.", + "bbox": [ + 75, + 795, + 467, + 898 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Thirdly, the proposed GRL transformer is applied to various image restoration tasks. Those tasks could be classified into three settings based on the availability of data including real image restoration, synthetic image restoration, and data synthesis based real image restoration. In total, seven tasks are explored for the proposed network including image super-resolution, image denoising, JPEG compression artifacts removal, demosaicking, real image superresolution, single image motion deblurring, and defocus deblurring. As shown in Fig. 2, the proposed network shows promising results on the investigated tasks.", + "bbox": [ + 496, + 200, + 890, + 366 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Works", + "text_level": 1, + "bbox": [ + 500, + 385, + 648, + 400 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Convolution for local range modelling. One of the basic assumptions for example and learning-based image restoration is that repetitive patterns could exist in either the same or different images [17] and that the redundant information they carry could help to restore the local patches. Thus, it helps if repetitive patterns could be detected and modelled [13, 33, 44, 61]. This intuition matches the computational procedure of convolution well, which slides the kernel across the image and detects local patterns similar to the learnable kernels. By stacking multiple convolutional layers, the receptive field of a CNN gets progressively enlarged and rich image features are captured. Since the advent of deep learning, great efforts have been made to design CNNs for image restoration [26, 39, 71, 72, 86].", + "bbox": [ + 496, + 412, + 890, + 623 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Non-local and global priors. Besides the local features, it is also important to model the non-local and global image priors. The early work of non-local means serves this purpose, which computes an output pixel as the weighted sum of all the pixels within the image [4]. Inspired by that, later works have been developed to utilize the repetitive patterns in a non-local range for image denoising [10] and superresolution [22]. Apart from the traditional methods, nonlocal operations are also introduced into deep neural networks for video classification [70] and image SR [45, 85].", + "bbox": [ + 496, + 625, + 890, + 776 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Besides the non-local operations, self-attention has been developed to model the global range dependencies [12, 68]. However, the computational complexity of global self-attention grows quadratically with the number of tokens. Thus, the increase in efficiency of global self-attention is investigated by several works [7, 9, 31, 35, 69].", + "bbox": [ + 496, + 777, + 890, + 868 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Regional self-attention. Among the methods for accelerating transformers, regional self-attention appears to", + "bbox": [ + 500, + 869, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "18279", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "be promising. The idea is proposed in the pioneering works [54, 56] and improved as shifted window attention [47, 48]. Inspired by the success of shifted window attention for visual recognition and perception, this method is also used for image restoration [6, 42, 43]. Despite the good performance of the window attention mechanism, it is pointed out in recent works that a wider range of pixel involvement could lead to better image restoration [6, 23]. Thus, in this paper, we try to propose a method that efficiently brings the modelling capacity of self-attention beyond the regional range.", + "bbox": [ + 75, + 90, + 472, + 257 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Motivation", + "text_level": 1, + "bbox": [ + 76, + 268, + 194, + 284 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Self-attention for dependency modelling", + "text_level": 1, + "bbox": [ + 76, + 292, + 419, + 310 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Self-attention is good at modelling long-range dependencies explicitly and it facilitates the propagation of information across the modelled dependencies. This operation allows a token to be compared with all the other tokens. The output token is computed as a weighted sum of all the tokens based on a similarity comparison, i.e.,", + "bbox": [ + 75, + 316, + 468, + 407 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {Y} = \\operatorname {S o f t m a x} \\left(\\mathbf {Q} \\cdot \\mathbf {K} ^ {T} / \\sqrt {d}\\right) \\cdot \\mathbf {V}, \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 153, + 415, + 468, + 440 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\mathbf{Q} = \\mathbf{X}\\cdot \\mathbf{W}_Q$ , $\\mathbf{K} = \\mathbf{X}\\cdot \\mathbf{W}_K$ , $\\mathbf{V} = \\mathbf{X}\\cdot \\mathbf{W}_V$ , $\\mathbf{W}_Q, \\mathbf{W}_K, \\mathbf{W}_V \\in \\mathbb{R}^{d\\times d}$ , and $\\mathbf{X}, \\mathbf{Y} \\in \\mathbb{R}^{N\\times d}$ . $N$ and $d$ denote the number of tokens and the dimension of one token, respectively. Additionally, $\\mathbf{M}$ denotes the attention map, i.e. $\\mathbf{M} = \\mathrm{Softmax}(\\mathbf{Q}\\cdot \\mathbf{K}^T / \\sqrt{d})$ .", + "bbox": [ + 75, + 446, + 468, + 521 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The time complexity of self-attention is $\\mathcal{O}(N^2 d)$ and the space complexity is dominated by the term $\\mathcal{O}(N^2)$ of the attention map $\\mathbf{M}$ . The computational complexity and memory footprint of self-attention grow quadratically with the number of tokens. Thus, self-attention can easily become a computation bottleneck for images where the number of tokens is the multiplication of the two dimensions of the feature map. To overcome this problem, it is proposed to apply self-attention within a window. In this way, the number of tokens that participate in self-attention is significantly reduced and the computational burden is also lifted.", + "bbox": [ + 75, + 521, + 468, + 686 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The problem of window self-attention is that the modelling capacity of the operation is limited to a regional range due to the small window size $(8\\times 8$ [43]). On the other hand, it is shown in recent works [6,23] that even a slight increase in window size can lead to better image restoration. Thus, it can be conjectured that modelling dependencies beyond the regional range is still important for image restoration. Hence, it remained to be investigated how to maintain the ability for long-range dependency modelling under a controlled computational budget.", + "bbox": [ + 75, + 688, + 468, + 839 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. Motivation I: cross-scale similarity", + "text_level": 1, + "bbox": [ + 76, + 847, + 377, + 862 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The attention map $\\mathbf{M}$ plays an essential role in selfattention as it captures the similarity between every paired", + "bbox": [ + 76, + 869, + 468, + 900 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/c72472b6788e684f2b194108e6a409a526d7c9b9794ab8a0e2d92dc451ec4930.jpg", + "image_caption": [ + "Figure 3. Cross-scale similarity. (c) and (d) shows the attention map between the selected pixels and the example high-resolution image. Although the cyan pixel in (a) and the red pixel in (b) are from images with different resolutions, their attention map with respect to the high-resolution image shows very similar structures." + ], + "image_footnote": [], + "bbox": [ + 511, + 88, + 883, + 195 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "pixels in the image. Thus, improving the efficiency of the self-attention in Eq. (1) needs one to analyze the property of the attention map. And we are inspired by a property of images, i.e. cross-scale similarity. That is, the basic structure such as lines and edges of an image is kept in the different versions of the image with different scaling factors. In Fig. 3, the attention map between pixels in an image is shown. Particularly, the attention map between a pixel and the whole image is visualized as a gray-scale heat map. As shown, no matter whether the pixel comes from the high-resolution image or the down-scaled version, the heat map between the pixel and the high-resolution image shows the basic structure of the image. And the heat maps in Fig. 3(c) and Fig. 3(d) are very similar to each other.", + "bbox": [ + 496, + 287, + 890, + 497 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Anchored self-attention. Inspired by the cross-scale similarity shown in Fig. 3, we try to reduce the complexity of the global self-attention in Eq. (1) by operating on images with different resolutions and manipulating the number of tokens, i.e. the $N^2$ term in $\\mathcal{O}(N^2 d)$ . To achieve that, we introduce an additional concept named anchors besides the triplets of queries, keys, and values. The set of anchors is a summary of the information in the image feature map and has a lower dimensionality. Instead of conducting the similarity comparison between the queries and keys directly, the anchors act as an intermediate for the similarity comparison. Formally, the anchored self-attention is proposed as in the following equation", + "bbox": [ + 496, + 500, + 890, + 695 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {Y} = \\mathbf {M} _ {e} \\cdot \\mathbf {Z} = \\mathbf {M} _ {e} \\cdot \\left(\\mathbf {M} _ {d} \\cdot \\mathbf {V}\\right), \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 589, + 705, + 890, + 722 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {M} _ {d} = \\operatorname {S o f t m a x} \\left(\\mathbf {A} \\cdot \\mathbf {K} ^ {T} / \\sqrt {d}\\right), \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 580, + 726, + 890, + 744 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {M} _ {e} = \\operatorname {S o f t m a x} \\left(\\mathbf {Q} \\cdot \\mathbf {A} ^ {T} / \\sqrt {d}\\right), \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 581, + 748, + 890, + 766 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $M \\ll N$ , $\\mathbf{A} \\in \\mathbb{R}^{M \\times d}$ is the anchor, $\\mathbf{M}_e \\in \\mathcal{R}^{N \\times M}$ and $\\mathbf{M}_d \\in \\mathcal{R}^{M \\times N}$ denotes the attention map between the query-anchor pair and anchor-key pair. The choice of the operations to derive the anchors is investigated in the implementation details of the ablation study of the paper.", + "bbox": [ + 496, + 777, + 890, + 854 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Since the number of anchors is much smaller than the number of the other tokens, the size of the resulting two attention maps $\\mathbf{M}_e$ and $\\mathbf{M}_d$ are much smaller than the orig", + "bbox": [ + 496, + 854, + 890, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "18280", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/aa64f8a27a81c585982e02934d681ba022d48f1c9a918907f89f653edfd9502c.jpg", + "image_caption": [ + "(a)" + ], + "image_footnote": [], + "bbox": [ + 89, + 88, + 181, + 157 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/a08c323f933f9eb792953af3edac8de14b4bdf9a57d0c9276818f7be1c0e9281.jpg", + "image_caption": [ + "(b)" + ], + "image_footnote": [], + "bbox": [ + 181, + 88, + 272, + 157 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/6a09d43d95a02fa59a6ed816ef2fbe25fc3c7d0812bc1df440d32744007052d6.jpg", + "image_caption": [ + "(c)" + ], + "image_footnote": [], + "bbox": [ + 274, + 88, + 364, + 157 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/99858ec5a3d4e561f21052374422e329dc090b705ae56074671c337e8662b2d9.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 366, + 89, + 455, + 157 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/5e83a2bcf6df1186ea8dc08d2069d287aacac32e3b4417e7a7c4950e62cfda3d.jpg", + "image_caption": [ + "(e)" + ], + "image_footnote": [], + "bbox": [ + 91, + 169, + 181, + 237 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/3a7365b3e9f81a481384db8e5910305d107bb71223166a6437f71bc5611e2c80.jpg", + "image_caption": [ + "(f)" + ], + "image_footnote": [], + "bbox": [ + 181, + 169, + 272, + 238 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/f12da035661fac66ca2e6db7d2e51dd7c277907bc41998187f4efff4711fc6c2.jpg", + "image_caption": [ + "(g)", + "Figure 4. The image features in natural images are anisotropic. Thus, it is not always necessary to employ the uniform global range attention in all parts of the image." + ], + "image_footnote": [], + "bbox": [ + 274, + 169, + 364, + 238 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/2cb0a1f5fb88335fa634389ffe8bab8869e74f13aae0e1f4ab92badd3640bfbf.jpg", + "image_caption": [ + "(h)" + ], + "image_footnote": [], + "bbox": [ + 366, + 169, + 455, + 238 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "inal attention map $\\mathbf{M}$ in Eq. (1). Then the matrix multiplication in Eq. (2) is computed from the right hand. The self-attention is first done for the anchors and keys. The attention map $\\mathbf{M}_d$ distills the tokens $\\mathbf{V}$ into an intermediate feature $\\mathbf{Z}$ . Then the self-attention is done between the queries and the anchors. The second attention map $\\mathbf{M}_e$ expands the size of the feature $\\mathbf{Z}$ and recovers the information in $\\mathbf{V}$ . The computational complexity of the anchored self-attention is reduced to $\\mathcal{O}(NMd)$ . And the space complexity is reduced to $\\mathcal{O}(NM)$ .", + "bbox": [ + 75, + 301, + 467, + 452 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.3. Motivation II: anisotropic image features", + "text_level": 1, + "bbox": [ + 76, + 465, + 428, + 482 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The anchored self-attention could reduce the space and time complexity of the self-attention in Eq. (1) significantly by removing the quadratic term $N^2$ . Yet, for image restoration tasks, the remaining term $N$ is the multiplication of the width and height of the image. Thus, the complexity of the anchored self-attention in Eq. (2) could still be unaffordable due to the large term $N$ . Thus, it is desirable to further reduce the complexity of the anchored self-attention.", + "bbox": [ + 75, + 489, + 467, + 609 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "To achieve that goal, we resort to another characteristic of natural images, i.e., the anisotropic image features. As shown in Fig. 4, the natural image features such as the single object in Fig. 4(c)&(d), the multi-scale similarity in Fig. 4(h), symmetry in Fig. 4(e)&(g) span in an anisotropic manner. Thus, isotropic global range attention across the entire image is redundant to capture the anisotropic image features. And in response to that, we propose to conduct attention within the anisotropic stripes shown in Fig. 4.", + "bbox": [ + 75, + 612, + 467, + 748 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Stripe attention mechanism. The proposed stripe attention mechanism consists of four modes including the horizontal stripe, the vertical stripe, the shifted horizontal stripe, and the shifted vertical stripe. The horizontal and vertical stripe attention mechanisms could be employed alternately across a transformer network. In this way, a trade-off is made between maintaining the global range modelling capacity and controlling the computation complexity of global self-attention. Thus, in combination with the concept of anchors, we propose the anchored stripe self-attention.", + "bbox": [ + 75, + 750, + 467, + 900 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/216eea99595506323707652d41af117b8d27dbb1e6a3cadb12ed9b373c111268.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 535, + 88, + 643, + 174 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/ae83d6c7609bbf801189fc3451a3ac4c0aca0b943dc45c3ebf183904c5ce3bde.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 656, + 114, + 712, + 157 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/f3d0ac7b181fc358cfafd18ecd7ea47e0f3d4f18ef199aea4d13277254872fb9.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 723, + 88, + 833, + 174 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/210d501e35ca59f61b09847af5f42c2968f11652ccda9f10eddaf1acaa1caeb7.jpg", + "image_caption": [ + "(a) Query", + "(b) Anchor", + "(d) Attention map via anchors", + "Figure 5. The visualization of the (a) queries, (b) anchors, and (c) keys from the different layers of the proposed network. (d) shows the attention map approximated by Eq. (2), i.e. $\\mathbf{M}_e\\cdot \\mathbf{M}_d$ (e) shows the exact attention map $\\mathbf{M}$ computed in Eq. (1)." + ], + "image_footnote": [], + "bbox": [ + 521, + 189, + 661, + 291 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/04b96cb264b3595d4423e928e081b471b49eb8870ccbc1b13545438c7ed4093a.jpg", + "image_caption": [ + "(c) Key", + "(e) Direct attention map" + ], + "image_footnote": [], + "bbox": [ + 661, + 189, + 864, + 291 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "For this attention mechanism, efficient self-attention is conducted inside the vertical and horizontal stripes with the help of the introduced anchors.", + "bbox": [ + 496, + 369, + 890, + 414 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.4. Discussion", + "text_level": 1, + "bbox": [ + 500, + 424, + 617, + 438 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The proposed anchored stripe self-attention mechanism is closely related to two other concepts including low-rankness and similarity propagation. And we detail the relationship in this subsection as follows.", + "bbox": [ + 496, + 446, + 890, + 507 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Low-rankness of attention map. By comparing the self-attention mechanisms in Eq. (1) and Eq. (2), we can easily found out that the original attention map $\\mathbf{M}$ is decomposed into small attention maps $\\mathbf{M}_d$ and $\\mathbf{M}_e$ whose rank is no larger than $M$ . And the essence here is to provide the low-rank approximation without calculating the original attention map first. For the success of the anchored self-attention, it is important to ensure that with the anchors as the intermediate, the approximated attention map is similar to the original attention map. Thus, an additional analysis is provided in Fig. 5.", + "bbox": [ + 496, + 508, + 890, + 672 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "First, by observing the queries, anchors, and keys, we can conclude that the anchors have a very similar structure to the query and key. Thus, the anchors are a good summary of the information in the queries and keys. And approximating self-attention with anchors as intermediate seems to be plausible. Additionally, the approximate attention map $\\mathbf{M}_e\\cdot \\mathbf{M}_d$ and the exact attention map $\\mathbf{M}$ are also compared in Fig. 5. As shown, the approximate attention map keeps the major structure in the exact attention map, which is confirmed by the large Pearson correlation coefficients (0.9505) between the two attention maps. Thus, the quality of the anchored self-attention is guaranteed.", + "bbox": [ + 496, + 674, + 890, + 853 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Metric and similarity propagation. From another perspective, in the proposed anchored self-attention, the queries and keys are first compared with the anchors and", + "bbox": [ + 496, + 854, + 890, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "18281", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/52b52556b2feb4068d1cb83f06e815391d7caa4416ada74daf6717728696eefa.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 91, + 88, + 870, + 252 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/809201fc804abe1d93233a4b79616569de5cbb11f0c47706e5c2fe2cbebb0f0a.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 94, + 255, + 395, + 435 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/0e4121212154a51327a5d66840e814fcec4f299440fb31c1e1da8199f00f3b03.jpg", + "image_caption": [ + "Figure 6. Network architecture. (a) The representation learning module contains stages of transformer layers. (b) The transformer layer is equipped with global, regional, and local modelling blocks. (c) The anchored stripe attention helps to attend beyond regional ranges." + ], + "image_footnote": [], + "bbox": [ + 426, + 255, + 867, + 436 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "then the query-key similarity is computed. Thus, this computation procedure needs to propagate the query-anchor and key-anchor similarity to the query-key pair. And similarity propagation is related to the triangle inequality in a metric space [19, 27, 73]. A mathematical metric needs to satisfy several conditions including the essential triangle inequality, $d(\\mathbf{q}, \\mathbf{k}) \\leq d(\\mathbf{a}, \\mathbf{q}) + d(\\mathbf{a}, \\mathbf{k})$ , where $d(\\cdot, \\cdot)$ defines a metric between two entities. Thus, the $\\mathbf{q} / \\mathbf{k}$ distance is upper-bounded by the sum of the $\\mathbf{a} / \\mathbf{q}$ distance and the $\\mathbf{a} / \\mathbf{k}$ distance. This implies that if $\\mathbf{a}$ is similar (close) to both $\\mathbf{q}$ and $\\mathbf{k}$ , then $\\mathbf{q}$ and $\\mathbf{k}$ should also be similar (close) to each other. Yet, the similarity measure in Eq. (1) and Eq. (2) is defined by the dot product instead of the distance between tokens, which does not satisfy the triangle inequality. Thus, similarity propagation could not be theoretically guaranteed. To study the influence of the similarity measure, an ablation study is conducted and the results are shown in Sec. 5. Dot product and distance are compared as a similarity measure. According to the results, although the dot product does not strictly obey the triangle inequality, it still guarantees better image restoration results. Thus, we can conclude empirically that the dot product is enough for similarity propagation.", + "bbox": [ + 75, + 470, + 472, + 819 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Modelling Image Hierarchies", + "text_level": 1, + "bbox": [ + 76, + 829, + 346, + 847 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In this section, we answer the second research question described in the introduction, that is, how to explicitly model image hierarchies by a single computational module.", + "bbox": [ + 76, + 854, + 468, + 902 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In response to that, we propose the GRL network architecture that incorporates global range, regional range, and local range image modelling capacities.", + "bbox": [ + 496, + 470, + 890, + 516 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Network architecture. The overall architecture of the proposed network is shown in Fig. 6. The network takes a degraded low-quality image as input, processes the image inside the network, and outputs a recovered high-quality image. In detail, the network contains three parts. 1) The feature extraction layer is implemented as a simple convolution and converts the input image into feature maps. 2) The representation learning component enriches the information extracted in the previous operation. The transformer stage consists of several transformer layers and ends with a convolution layer. The dimension of the feature map is maintained across the whole representation learning module. Skip connection is applied to both the transformer stage and the representation learning module. 3) The image reconstruction module takes the rich features calculated by the previous operations and estimates a recovered image.", + "bbox": [ + 496, + 518, + 892, + 761 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Transformer Layer. This layer in Fig. 6b is the key component that provides the hierarchical image modelling capacity in the global, regional, and local range. This layer first processes the input feature map by the parallel self-attention module and channel attention enhanced convolutions. The convolution branch serves to capture local structures in the input feature map. On the other hand, the self-attention module contains the window attention proposed in Swin transformer V2 [47] and the anchored stripe attenuation", + "bbox": [ + 496, + 763, + 893, + 902 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "18282", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/4cd06dd0a8049d04ef20e9c1b61b2cbfa6f659e566c7c973aac26f92f1f2759e.jpg", + "table_caption": [ + "Table 1. Defocus deblurring results. S: single-image defocus deblurring. D: dual-pixel defocus deblurring." + ], + "table_footnote": [], + "table_body": "
MethodIndoor ScenesOutdoor ScenesCombined
PSNR↑SSIM↑MAE↓LPIPS↓PSNR↑SSIM↑MAE↓LPIPS↓PSNR↑SSIM↑MAE↓LPIPS↓
EBDBS[30]25.770.7720.0400.29721.250.5990.0580.37323.450.6830.0490.336
DMENetS[40]25.500.7880.0380.29821.430.6440.0630.39723.410.7140.0510.349
JNBs[60]26.730.8280.0310.27321.100.6080.0640.35523.840.7150.0480.315
DPDNetS[1]26.540.8160.0310.23922.250.6820.0560.31324.340.7470.0440.277
KPACS[62]27.970.8520.0260.18222.620.7010.0530.26925.220.7740.0400.227
IFANs[41]28.110.8610.0260.17922.760.7200.0520.25425.370.7890.0390.217
RestormerS[76]28.870.8820.0250.14523.240.7430.0500.20925.980.8110.0380.178
GRLS-B29.060.8860.0240.13923.450.7610.0490.19626.180.8220.0370.168
DPDNetD[1]27.480.8490.0290.18922.900.7260.0520.25525.130.7860.0410.223
RDPD2[2]28.100.8430.0270.21022.820.7040.0530.29825.390.7720.0400.255
UformerD[74]28.230.8600.0260.19923.100.7280.0510.28525.650.7950.0390.243
IFAND[41]28.660.8680.0250.17223.460.7430.0490.24025.990.8040.0370.207
RestormerD[76]29.480.8950.0230.13423.970.7730.0470.17526.660.8330.0350.155
GRLD-B29.830.9030.0220.11424.390.7950.0450.15027.040.8470.0340.133
", + "bbox": [ + 215, + 104, + 759, + 290 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/38e9712f868d1aee568fdd79378135b1fef44fa8b0a8b3c5d90c9f5a66c46b28.jpg", + "table_caption": [ + "Table 2. Single-image motion deblurring results. GoPro dataset [51] is used for training." + ], + "table_footnote": [], + "table_body": "
MethodGoPro [51]HIDE [59]Average
PSNR↑ / SSIM↑PSNR↑ / SSIM↑PSNR↑ / SSIM↑
DeblurGAN [37]28.70 / 0.85824.51 / 0.87126.61 / 0.865
Nah et al. [51]29.08 / 0.91425.73 / 0.87427.41 / 0.894
DeblurGAN-v2 [38]29.55 / 0.93426.61 / 0.87528.08 / 0.905
SRN [64]30.26 / 0.93428.36 / 0.91529.31 / 0.925
Gao et al. [20]30.90 / 0.93529.11 / 0.91330.01 / 0.924
DBGAN [81]31.10 / 0.94228.94 / 0.91530.02 / 0.929
MT-RNN [53]31.15 / 0.94529.15 / 0.91830.15 / 0.932
DMPHN [79]31.20 / 0.94029.09 / 0.92430.15 / 0.932
Suin et al. [63]31.85 / 0.94829.98 / 0.93030.92 / 0.939
SPAIR [55]32.06 / 0.95330.29 / 0.93131.18 / 0.942
MIMO-UNet+ [8]32.45 / 0.95729.99 / 0.93031.22 / 0.944
IPT [5]32.52 / -- / -- / -
MPRNet [77]32.66 / 0.95930.96 / 0.93931.81 / 0.949
Restormer [76]32.92 / 0.96131.22 / 0.94232.07 / 0.952
GRL-B (ours)33.93 / 0.96831.65 / 0.94732.79 / 0.958
", + "bbox": [ + 102, + 327, + 441, + 516 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/4d0376b83fd6c7aab63b2cba3b3271dc52bac37b215e60fcb48c322275475e92.jpg", + "table_caption": [ + "Table 3. Single-image motion deblurring results on RealBlur [57] dataset. The networks are trained and tested on RealBlur dataset." + ], + "table_footnote": [], + "table_body": "
MethodRealBlur-R [57]RealBlur-J [57]Average
PSNR↑ / SSIM↑PSNR↑ / SSIM↑PSNR↑ / SSIM↑
DeblurGAN-v2 [38]36.44 / 0.93529.69 / 0.87033.07 / 0.903
SRN [64]38.65 / 0.96531.38 / 0.90935.02 / 0.937
MPRNet [77]39.31 / 0.97231.76 / 0.92235.54 / 0.947
MIMO-UNet+ [8]- / -32.05 / 0.921- / -
MAXIM-3S [67]39.45 / 0.96232.84 / 0.93536.15 / 0.949
BANet [66]39.55 / 0.97132.00 / 0.92335.78 / 0.947
MSSNet [34]39.76 / 0.97232.10 / 0.92835.93 / 0.950
Stripformer [65]39.84 / 0.97432.48 / 0.92936.16 / 0.952
GRL-B (ours)40.20 / 0.97432.82 / 0.93236.51 / 0.953
", + "bbox": [ + 102, + 547, + 442, + 675 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "tion proposed in this paper. The feature map is split equally along the channel dimension and concatenated along the channel dimension again after the parallel processing within the two attention modules. The window attention provides the mechanism to capture the regional range dependencies. Then the feature maps outputted by the convolution module and the attention module are added to the input feature map, which is processed by the following MLP module.", + "bbox": [ + 75, + 688, + 467, + 808 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Anchored stripe self-attention. The operation of the proposed anchored stripe attention is conducted according to Eq. (2) and visualized in Fig. 6c. The dimension of different features is also shown. The triplet of $\\mathbf{Q},\\mathbf{K},\\mathbf{V}$ is derived by plain linear projections. To summarize the information into anchors, the anchor projection is implemented as an", + "bbox": [ + 75, + 810, + 467, + 900 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "average pooling layer followed by a linear projection. After the anchor projection, the resolution of the image feature map is down-scaled by a factor of $s$ along both directions. As shown in Fig. 6, the two attention maps $\\mathbf{M}_d$ and $\\mathbf{M}_e$ play a similar role as the original attention map $\\mathbf{M}$ but with less space and time complexity.", + "bbox": [ + 496, + 300, + 890, + 391 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5. Experimental Results", + "text_level": 1, + "bbox": [ + 500, + 404, + 705, + 422 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "The experimental results are shown in this section. We answer the third research question raised in the introduction by investigating the performance of the proposed network on different image restoration tasks. Based on the data type, the investigated tasks are classified into three commonly used settings including 1) real image restoration (single-image motion deblurring, defocus deblurring), 2) image restoration based on synthetic data (image denoising, single image SR, JPEG compression artifact removal, demosaicking), and 3) real image restoration based on data synthesis. We provide three networks with different model sizes including the tiny, small, and base versions (GRL-T, GRL-S, GRL-B). For real and synthetic image restoration, Adam optimizer and $L_{1}$ loss are used to train the network with an initial learning rate $2 \\times 10^{-4}$ . More details about the training dataset, training protocols, and additional visual results are shown in the supplementary material.", + "bbox": [ + 496, + 429, + 890, + 686 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5.1. Image deblurring", + "text_level": 1, + "bbox": [ + 500, + 696, + 671, + 712 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We first investigate the performance of the proposed network on two real image restoration tasks including single-image motion deblurring, and motion deblurring.", + "bbox": [ + 496, + 719, + 890, + 762 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Single image motion deblurring. Tab. 2 and Tab. 3 show the experimental results for single image motion deblurring on synthetic datasets (GoPro [51], HIDE [59]) and real dataset (RealBlur-R [57]), respectively. Compared with the previous state-of-the-art Restormer [76], the proposed GRL achieves significant PSNR improvement of $1.01\\mathrm{dB}$ on the GoPro dataset. On the HIDE dataset, the PSNR improvement is $0.43\\mathrm{dB}$ . Please note that the improvement is achieved under fewer parameter budget. As shown in Tab. 4,", + "bbox": [ + 496, + 763, + 890, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "18283", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/ce1a6297d4087333ed2a72f620bb5ad65d04b0d7e15d302f8aad6d45a94d1ee2.jpg", + "table_caption": [ + "Table 4. Color and grayscale image denoising results. Model complexity and prediction accuracy are shown for better comparison." + ], + "table_footnote": [], + "table_body": "
Method# Params [M]ColorGrayscale
CBSD68 [49]σ=15 σ=25 σ=50Kodak24 [16]σ=15 σ=25 σ=50McMaster [83]σ=15 σ=25 σ=50Urban100 [28]σ=15 σ=25 σ=50Set12 [82]σ=15 σ=25 σ=50BSD68 [49]σ=15 σ=25 σ=50Urban100 [28]σ=15 σ=25 σ=50
DnCNN [32]0.5633.9031.2427.9534.6032.1428.9533.4531.5228.6232.9830.8127.5932.8630.4427.1831.7329.2326.2332.6429.9526.26
RNAN [85]8.96--28.27--29.58--29.72--29.08--27.70--26.48--27.65
IPT [5]115.33--28.39--29.64--29.98--29.71---------
EDT-B [42]11.4834.3931.7628.5635.3732.9429.8735.6133.3430.2535.2233.0730.16---------
DRUNet [80]32.6434.3031.6928.5135.3132.8929.8635.4033.1430.0834.8132.6029.6133.2530.9427.9031.9129.4826.5933.4431.1127.96
SwinIR [43]11.7534.4231.7828.5635.3432.8929.7935.6133.2030.2235.1332.9029.8233.3631.0127.9131.9729.5026.5833.7031.3027.98
Restormer [76]26.1334.4031.7928.6035.4733.0430.0135.6133.3430.3035.1332.9630.0233.4231.0828.0031.9629.5226.6233.7931.4628.29
GRL-T0.8834.3031.6628.4535.2432.7829.6735.4933.1830.0635.0832.8429.7833.2930.9227.7831.9029.4326.4933.6631.2327.89
GRL-S3.1234.3631.7228.5135.3232.8829.7735.5933.2930.1835.2433.0730.0933.3631.0227.9131.9329.4726.5433.8431.4928.24
GRL-B19.8134.4531.8228.6235.4333.0229.9335.7333.4630.3635.5433.3530.4633.4731.1228.0332.0029.5426.6034.0931.8028.59
", + "bbox": [ + 86, + 104, + 885, + 253 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/62d48bf477dc3d8d911947e81905db4966e27444a806f2981199e5cbd5ef6180.jpg", + "table_caption": [ + "Table 5. Classical image SR results. Results of both lightweight models and accurate models are summarized." + ], + "table_footnote": [], + "table_body": "
MethodScale# Params [M]Set5 [3]Set14 [78]BSD100 [49]Urban100 [28]Manga109 [50]
PSNR↑SSIM↑PSNR↑SSIM↑PSNR↑SSIM↑PSNR↑SSIM↑PSNR↑SSIM↑
RCAN [84]×215.4438.270.961434.120.921632.410.902733.340.938439.440.9786
SAN [11]×215.7138.310.962034.070.921332.420.902833.100.937039.320.9792
HAN [52]×263.6138.270.961434.160.921732.410.902733.350.938539.460.9785
IPT [5]×2115.4838.37-34.43-32.48-33.76---
SwinIR [43]×20.8838.140.961133.860.920632.310.901232.760.934039.120.9783
SwinIR [43]×211.7538.420.962334.460.925032.530.904133.810.942739.920.9797
EDT [42]×20.9238.230.961533.990.920932.370.902132.980.936239.450.9789
EDT [42]×211.4838.630.963234.800.927332.620.905234.270.945640.370.9811
GRL-T (ours)×20.8938.270.962734.210.925832.420.905633.600.941139.610.9790
GRL-S (ours)×23.3438.370.963234.640.928032.520.906934.360.946339.840.9793
GRL-B (ours)×220.0538.670.964735.080.930332.670.908735.060.950540.670.9818
RCAN [84]×415.5932.630.900228.870.788927.770.743626.820.808731.220.9173
SAN [11]×415.8632.640.900328.920.788827.780.743626.790.806831.180.9169
HAN [52]×464.2032.640.900228.900.789027.800.744226.850.809431.420.9177
IPT [5]×4115.6332.64-29.01-27.82-27.26---
SwinIR [43]×40.9032.440.897628.770.785827.690.740626.470.798030.920.9151
SwinIR [43]×411.9032.920.904429.090.795027.920.748927.450.825432.030.9260
EDT [42]×40.9232.530.899128.880.788227.760.743326.710.805131.350.9180
EDT [42]×411.6333.060.905529.230.797127.990.751027.750.831732.390.9283
GRL-T (ours)×40.9132.560.902928.930.796127.770.752327.150.818531.570.9219
GRL-S (ours)×43.4932.760.905829.100.800727.900.756827.900.835732.110.9267
GRL-B (ours)×420.2033.100.909429.370.805828.010.761128.530.850432.770.9325
", + "bbox": [ + 102, + 282, + 867, + 547 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "GRL-B saves $24\\%$ parameters compared with Restormer. As shown in Tab. 3, GRL-B sets the new state-of-the-art performance of 40.20 PSNR on RealBlur-R dataset.", + "bbox": [ + 75, + 559, + 468, + 604 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Defocus deblurring. Tab. 1 shows the experimental results for defocus deblurring using single image and dual-pixel images. Our GRL outperforms the previous methods for all three scene types. Compared with Restormer on the combined scenes, our GRL achieves an elegant performance boost of $0.20\\mathrm{dB}$ and $0.38\\mathrm{dB}$ for single and dual-pixel defocus deblurring. Compared with Uformer [74] and IFAN [41], GRL achieves PSNR gain of $1.39\\mathrm{dB}$ and $1.05\\mathrm{dB}$ for the dual-pixel setting.", + "bbox": [ + 75, + 604, + 468, + 742 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.2. Image restoration based on synthetic data", + "text_level": 1, + "bbox": [ + 76, + 753, + 433, + 771 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Investigating image restoration with synthetic data is also valuable to reveal the network capacity of restoration methods. Besides the experiments on the real data, we also study the performance of the network on synthetic data.", + "bbox": [ + 75, + 777, + 468, + 840 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Image denoising. First, the experimental results on Gaussian image denoising are shown in Tab. 4. For a fair comparison between different models, both the network complexity and accuracy are shown in the table. And several key find", + "bbox": [ + 75, + 840, + 468, + 900 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "ings are observed. I. The tiny version GRL-T is extremely efficient, reducing model complexity by two orders of magnitude (only $0.76\\%$ of [5] and $2.7\\%$ of DRUNet [80]) while not sacrificing network accuracy. II. The small version GRL-S performs competitive with the previous state-of-the-art SwinIR [43] and Restormer [76]. III. On Urban100, the base version outperforms Restormer by a large margin (e.g. 0.44dB PSNR gain for color image and noise level 50).", + "bbox": [ + 496, + 559, + 890, + 679 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Image SR. Experimental results for classical images are shown in Tab. 5. Both lightweight models and accurate SR models are summarized. A similar conclusion could be drawn from the results. I. Among the lightweight networks, GRL-T outperforms both convolution and self-attention-based networks including DBPN [25], SwinIR [43] and EDT [42]. Compared with EDT, Significant improvements are obtained on Urban100 and Manga109 datasets (0.44 dB and 0.22 dB for $\\times 4$ SR). II. GRL-B sets the new state-of-the-art for accurate image SR. III. GRL-S achieves a good balance between network complexity and SR image quality.", + "bbox": [ + 496, + 684, + 890, + 851 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "JPEG compression artifact removal. The experimental results for color and grayscale images are shown in Tab. 6. Four image quality factors ranging from 10 to 40 for JPEG", + "bbox": [ + 496, + 854, + 890, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "18284", + "bbox": [ + 480, + 945, + 517, + 955 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/d7cab793658685bef00d4ce113dd3b032e0bee68d0e84bd47e88631a93e62fc2.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
SetQFJPEG PSNR SSIMDnCNN [82] PSNR SSIMDCSC [18] PSNR SSIMQGAC [14] PSNR SSIMMWCNN [46] PSNR SSIMFBCNN [29] PSNR SSIMGRL-S PSNR SSIM
Classic5 [15]1027.82 0.76029.40 0.80329.62 0.81029.84 0.81230.01 0.82030.12 0.82230.20 0.829
2030.12 0.83431.63 0.86131.81 0.86431.98 0.86932.16 0.87032.31 0.87232.49 0.878
3031.48 0.86732.91 0.88633.06 0.88833.22 0.89233.43 0.89333.54 0.89433.72 0.899
4032.43 0.88533.77 0.90033.87 0.90234.05 0.90534.27 0.90634.35 0.90734.53 0.911
BSD500 [49]1027.80 0.76829.21 0.80929.32 0.81329.46 0.82129.61 0.82029.67 0.82129.74 0.823
2030.05 0.84931.53 0.87831.63 0.88031.73 0.88431.92 0.88532.00 0.88532.05 0.885
3031.37 0.88432.90 0.90732.99 0.90833.07 0.91233.30 0.91233.37 0.91333.43 0.912
4032.30 0.90333.85 0.92333.92 0.92434.01 0.92734.27 0.92834.33 0.92834.38 0.928
", + "bbox": [ + 81, + 119, + 586, + 241 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/ff02f7f24d15665c09a22e67aa1b5ca8fc15466120c5eb7deb6e4914de788aab.jpg", + "table_caption": [ + "Table 6. Grayscale image JPEG compression artifact removal results. As a compar- Table 7. Color image JPEG compression artifact ison metric, the parameter count of FBCNN [29] GRL-S are 71.92M and 3.12M. removal results." + ], + "table_footnote": [], + "table_body": "
SetQFJPEG PSNR SSIMQGAC [14] PSNR SSIMFBCNN [29] PSNR SSIMGRL-S PSNR SSIM
LIVE1 [58]1025.69 0.74327.62 0.80427.77 0.80328.13 0.814
2028.06 0.82629.88 0.86830.11 0.86830.49 0.878
3029.37 0.86131.17 0.89631.43 0.89731.85 0.905
4030.28 0.88232.05 0.91232.34 0.91332.79 0.920
BSD500 [49]1025.84 0.74127.74 0.80227.85 0.79928.26 0.808
2028.21 0.82730.01 0.86930.14 0.86730.57 0.875
3029.57 0.86531.33 0.89831.45 0.89731.92 0.903
4030.52 0.88732.25 0.91532.36 0.91332.86 0.919
", + "bbox": [ + 589, + 118, + 893, + 241 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/eb07d4696a7a0c29f3f0a6200724ade114c99a778fa8c24bf8b7a7a3f0c8dacb.jpg", + "table_caption": [ + "Table 8. Image demosaicking results." + ], + "table_footnote": [], + "table_body": "
DatasetsMatlabDDR [75]DeepJoint [21]MMNet [36]RLDD [24]RNAN [85]DRUNet [80]GRL-S (ours)
Kodak [16]35.7841.1142.0040.1942.4943.1642.6843.57
McMaster [83]34.4337.1239.1437.0939.2539.7039.3940.22
", + "bbox": [ + 81, + 268, + 470, + 319 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/73f89d3c33902e560790816e0067283be68bcec4b80d23ec03d9ebb1fee8aba6.jpg", + "image_caption": [ + "Figure 7. Visual results for real-world image SR." + ], + "image_footnote": [], + "bbox": [ + 83, + 330, + 465, + 484 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "compression are studied. As shown in the table, the proposed GRL-S network outperforms the previous state-of-the-art method elegantly across different datasets and quality factors. Notably, GRL-S has a much smaller model complexity than FBCNN.", + "bbox": [ + 76, + 515, + 468, + 589 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Demosaicking. Results for image demosaicking is shown in Tab. 8. The proposed method outperforms the previous methods RNAN [85] and DRUNet [80] significantly.", + "bbox": [ + 76, + 590, + 468, + 636 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5.3. Real image restoration based on data synthesis", + "text_level": 1, + "bbox": [ + 76, + 646, + 468, + 662 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Finally, we also investigate the performance of the network for real-world image restoration. The aim is to superresolve a low-quality image by an upscaling factor of 4. Since there are no ground-truth images for this task, only the visual comparison is given in Fig. 7. Compared with the other methods, the proposed GRL is able to remove more artifacts in the low-resolution images.", + "bbox": [ + 76, + 670, + 468, + 775 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5.4. Ablation study", + "text_level": 1, + "bbox": [ + 76, + 786, + 225, + 801 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Influence of the similarity comparison method. As mentioned in Sec. 3.4, for theoretical guarantee of similarity propagation, a mathematical metric rather than a dot product should be used. To study the difference between, image restoration with the two operations are compared and the results are shown in Tab. 9. As revealed by the table, the dot", + "bbox": [ + 76, + 809, + 468, + 898 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/61ef5b00a55d3f38282ceef226873aa922e9b33a27cb7ad9c486524fa8427a74.jpg", + "table_caption": [ + "Table 9. Ablation study on similarity comparison operation." + ], + "table_footnote": [], + "table_body": "
Test setMetricColor DNGray DNImage SR
σ15σ25σ50σ15σ25σ50×2×3×4
BSD68 or BSD100Euclidean35.0232.5629.4231.8429.3626.4332.3029.1927.67
Dot product35.1032.6429.5431.8529.3926.4432.3329.2227.70
Urban100Euclidean34.6332.2828.9433.2530.6427.1732.7628.6226.50
Dot product34.7732.4129.1933.2830.7527.2632.8828.7826.67
", + "bbox": [ + 506, + 267, + 883, + 343 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/3a0489343083f820008b7d884ad4b0e5d130452976ca900f82879fdeb4676120.jpg", + "table_caption": [ + "Table 10. Ablation study on anchor projection operation." + ], + "table_footnote": [], + "table_body": "
Anchor projection operation# Params [m]PSNR on Set 5
Depthwise Conv3.1735.03
Conv4.1935.03
Patch merging3.5334.98
Maxpool + Linear Projection3.1235.02
Avgpool + Linear Projection3.1235.03
", + "bbox": [ + 555, + 373, + 834, + 449 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "product is very competitive compared with a metric and it outperforms a distance metric for a couple of settings. Considering this, the dot product is still used.", + "bbox": [ + 498, + 465, + 890, + 510 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Influence of the anchor projections. The anchor projection operation helps to summarize the information in the feature map. The ablation study is shown in Tab. 10. Considering both the accuracy performance and parameter budget, Avgpool followed by linear projection is finally used.", + "bbox": [ + 498, + 513, + 890, + 589 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "6. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 625, + 617, + 638 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this paper, we proposed GRL, a network with efficient and explicit hierarchical modelling capacities for image restoration. The proposed network was mainly inspired by two image properties including cross-scale similarity and anisotropic image features. Based on that, we proposed the efficient anchored stripe self-attention module for long-range dependency modelling. Then a versatile network architecture was proposed for image restoration. The proposed network can model image hierarchies in the global, regional, and local ranges. Owing to the advanced computational mechanism, the proposed network architecture achieves state-of-the-art performances for various image restoration tasks.", + "bbox": [ + 496, + 652, + 890, + 848 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgements. This work was partly supported by ETH Zürich General Fund (OK), Meta Reality Labs and the Alexander von Humboldt Foundation.", + "bbox": [ + 498, + 854, + 890, + 898 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "18285", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Abdullah Abuolaim and Michael S Brown. Defocus deblurring using dual-pixel data. In European Conference on Computer Vision, pages 111-126. Springer, 2020. 6", + "[2] Abdullah Abuolaim, Mauricio Delbracio, Damien Kelly, Michael S. Brown, and Peyman Milanfar. Learning to reduce defocus blur by realistically modeling dual-pixel data. In ICCV, 2021. 6", + "[3] Marco Bevilacqua, Aline Roumy, Christine Guillemot, and Marie Line Alberi-Morel. 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In Proceedings of the IEEE Conference on Computer Vision and Pattern Recognition, 2018. 2" + ], + "bbox": [ + 78, + 90, + 468, + 191 + ], + "page_idx": 11 + }, + { + "type": "page_number", + "text": "18289", + "bbox": [ + 480, + 945, + 517, + 955 + ], + "page_idx": 11 + } +] \ No newline at end of file diff --git a/2023/Efficient and Explicit Modelling of Image Hierarchies for Image Restoration/61b7e2ab-0381-45d6-b5b0-549e3c623e77_model.json b/2023/Efficient and Explicit Modelling of Image Hierarchies for Image Restoration/61b7e2ab-0381-45d6-b5b0-549e3c623e77_model.json new file mode 100644 index 0000000000000000000000000000000000000000..fb59b2d47dce945ca96d6250e3c492058253e841 --- /dev/null +++ b/2023/Efficient and Explicit Modelling of Image Hierarchies for Image Restoration/61b7e2ab-0381-45d6-b5b0-549e3c623e77_model.json @@ -0,0 +1,2820 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.001, + 0.808, + 0.045 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.101, + 0.131, + 0.87, + 0.152 + ], + "angle": 0, + "content": "Efficient and Explicit Modelling of Image Hierarchies for Image Restoration" + }, + { + "type": "text", + "bbox": [ + 0.227, + 0.18, + 0.751, + 0.199 + ], + "angle": 0, + "content": "Yawei Li1 Yuchen Fan2 Xiaoyu Xiang2 Denis Demandolx2" + }, + { + "type": "text", + "bbox": [ + 0.273, + 0.199, + 0.707, + 0.216 + ], + "angle": 0, + "content": "Rakesh Ranjan\\(^{2}\\) Radu Timofte\\(^{1,3}\\) Luc Van Gool\\(^{1,4}\\)" + }, + { + "type": "text", + "bbox": [ + 0.089, + 0.216, + 0.894, + 0.235 + ], + "angle": 0, + "content": "1Computer Vision Lab, ETH Zürich 2Meta Reality Labs 3University of Würzburg 4KU Leuven" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.269, + 0.314, + 0.285 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.301, + 0.474, + 0.59 + ], + "angle": 0, + "content": "The aim of this paper is to propose a mechanism to efficiently and explicitly model image hierarchies in the global, regional, and local range for image restoration. To achieve that, we start by analyzing two important properties of natural images including cross-scale similarity and anisotropic image features. Inspired by that, we propose the anchored stripe self-attention which achieves a good balance between the space and time complexity of self-attention and the modelling capacity beyond the regional range. Then we propose a new network architecture dubbed GRL to explicitly model image hierarchies in the Global, Regional, and Local range via anchored stripe self-attention, window self-attention, and channel attention enhanced convolution. Finally, the proposed network is applied to 7 image restoration types, covering both real and synthetic settings. The proposed method sets the new state-of-the-art for several of those. Code will be available at https://github.com/ofsoundof/GRL-Image-Restoration.git." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.618, + 0.21, + 0.634 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.644, + 0.47, + 0.78 + ], + "angle": 0, + "content": "Image restoration aims at recovering high-quality images from low-quality ones, resulting from an image degradation processes such as blurring, sub-sampling, noise corruption, and JPEG compression. Image restoration is an ill-posed inverse problem since important content information about the image is missing during the image degradation processes. Thus, in order to recover a high-quality image, the rich information exhibited in the degraded image should be fully exploited." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.78, + 0.47, + 0.903 + ], + "angle": 0, + "content": "Natural images contain a hierarchy of features at global, regional, and local ranges which could be used by deep neural networks for image restoration. First, the local range covers a span of several pixels and typical features are edges and local colors. To model such local features, convolutional neural networks (CNNs) with small kernels (e.g. \\(3 \\times 3\\)) are utilized. Second, the regional range is characterized by a window with tens of pixels. This range of pix" + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.268, + 0.705, + 0.496 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.503, + 0.497, + 0.671, + 0.507 + ], + "angle": 0, + "content": "(a) bridge from ICB, \\(2749\\times 4049\\)" + }, + { + "type": "image", + "bbox": [ + 0.706, + 0.268, + 0.892, + 0.376 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.708, + 0.377, + 0.888, + 0.388 + ], + "angle": 0, + "content": "(b) \\(0848x4\\) from DIV2K, \\(1020 \\times 768\\)" + }, + { + "type": "image", + "bbox": [ + 0.706, + 0.389, + 0.892, + 0.496 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.707, + 0.497, + 0.883, + 0.507 + ], + "angle": 0, + "content": "(c) 073 from Urban100, \\(1024 \\times 765\\)" + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.51, + 0.894, + 0.58 + ], + "angle": 0, + "content": "Figure 1. Natural images show a hierarchy of features in a global, regional, and local range. The local (edges, colors) and regional features (the pink squares) could be well modelled by CNNs and window self-attention. By contrast, it is difficult to efficiently and explicitly model the rich global features (cyan rectangles)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.594, + 0.893, + 0.777 + ], + "angle": 0, + "content": "els can cover small objects and components of large objects (pink squares in Fig. 1). Due to the larger range, modelling the regional features (consistency, similarity) explicitly with large-kernel CNNs would be inefficient in both parameters and computation. Instead, transformers with a window attention mechanism are well suited for this task. Third, beyond local and regional, some features have a global span (cyan rectangles in Fig. 1), incl. but not limited to symmetry, multi-scale pattern repetition (Fig. 1a), same scale texture similarity (Fig. 1b), and structural similarity and consistency in large objects and content (Fig. 1c). To model features at this range, global image understanding is needed." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Different from the local and regional range features, there are two major challenges to model the global range features. Firstly, existing image restoration networks based on convolutions and window attention could not capture long-range dependencies explicitly by using a single computational module. Although non-local operations are used in some works, they are either used sparsely in the network or applied to small image crops. Thus, global image under" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "18278" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.081, + 0.098, + 0.884, + 0.177 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.098, + 0.182, + 0.87, + 0.195 + ], + "angle": 0, + "content": "Figure 2. The proposed GRL achieves state-of-the-art performances on various image restoration tasks. Details provided in Sec. 5." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.201, + 0.468, + 0.291 + ], + "angle": 0, + "content": "standing still mainly happens via progressive propagation of features through repeated computational modules. Secondly, the increasing resolution of today's images poses a challenge for long-range dependency modelling. High image resolution leads to a computational burden associated with pairwise pixel comparisons and similarity searches." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.293, + 0.468, + 0.429 + ], + "angle": 0, + "content": "The aforementioned discussion leads to a series of research questions: 1) how to efficiently model global range features in high-dimensional images for image restoration; 2) how to model image hierarchies (local, regional, global) explicitly by a single computational module for high-dimensional image restoration; 3) and how can this joint modelling lead to a uniform performance improvement for different image restoration tasks. The paper tries to answer these questions in Sec. 3, Sec. 4, and Sec. 5, resp." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.432, + 0.468, + 0.793 + ], + "angle": 0, + "content": "First, we propose anchored stripe self-attention for efficient dependency modelling beyond the regional range. The proposed self-attention is inspired by two properties of natural images including cross-scale similarity and anisotropic image features. Cross-scale similarity means that structures in a natural image are replicated at different scales. Inspired by that, we propose to use anchors as an intermediate to approximate the exact attention map between queries and keys in self-attention. Since the anchors summarize image information into a lower-dimensional space, the space and time complexity of self-attention can be significantly reduced. In addition, based on the observation of anisotropic image features, we propose to conduct anchored self-attention within vertical and horizontal stripes. Due to the anisotropic shrinkage of the attention range, a further reduction of complexity is achieved. And the combination of axial stripes also ensures a global view of the image content. When equipped with the stripe shift operation, the four stripe self-attention modes (horizontal, vertical, shifted horizontal, shifted vertical) achieves a good balance between computational complexity and the capacity of global range dependency modelling. Furthermore, the proposed anchored stripe self-attention is analyzed from the perspective of low-rankness and similarity propagation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.796, + 0.468, + 0.9 + ], + "angle": 0, + "content": "Secondly, a new transformer network is proposed to explicitly model global, regional, and local range dependencies in a single computational module. The hierarchical modelling of images is achieved by the parallel computation of the proposed anchored stripe self-attention, window self-attention, and channel-attention enhanced convolution. And the transformer architecture is dubbed GRL." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.201, + 0.892, + 0.367 + ], + "angle": 0, + "content": "Thirdly, the proposed GRL transformer is applied to various image restoration tasks. Those tasks could be classified into three settings based on the availability of data including real image restoration, synthetic image restoration, and data synthesis based real image restoration. In total, seven tasks are explored for the proposed network including image super-resolution, image denoising, JPEG compression artifacts removal, demosaicking, real image superresolution, single image motion deblurring, and defocus deblurring. As shown in Fig. 2, the proposed network shows promising results on the investigated tasks." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.386, + 0.65, + 0.401 + ], + "angle": 0, + "content": "2. Related Works" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.413, + 0.892, + 0.624 + ], + "angle": 0, + "content": "Convolution for local range modelling. One of the basic assumptions for example and learning-based image restoration is that repetitive patterns could exist in either the same or different images [17] and that the redundant information they carry could help to restore the local patches. Thus, it helps if repetitive patterns could be detected and modelled [13, 33, 44, 61]. This intuition matches the computational procedure of convolution well, which slides the kernel across the image and detects local patterns similar to the learnable kernels. By stacking multiple convolutional layers, the receptive field of a CNN gets progressively enlarged and rich image features are captured. Since the advent of deep learning, great efforts have been made to design CNNs for image restoration [26, 39, 71, 72, 86]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.626, + 0.892, + 0.777 + ], + "angle": 0, + "content": "Non-local and global priors. Besides the local features, it is also important to model the non-local and global image priors. The early work of non-local means serves this purpose, which computes an output pixel as the weighted sum of all the pixels within the image [4]. Inspired by that, later works have been developed to utilize the repetitive patterns in a non-local range for image denoising [10] and superresolution [22]. Apart from the traditional methods, nonlocal operations are also introduced into deep neural networks for video classification [70] and image SR [45, 85]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.779, + 0.892, + 0.869 + ], + "angle": 0, + "content": "Besides the non-local operations, self-attention has been developed to model the global range dependencies [12, 68]. However, the computational complexity of global self-attention grows quadratically with the number of tokens. Thus, the increase in efficiency of global self-attention is investigated by several works [7, 9, 31, 35, 69]." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.871, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Regional self-attention. Among the methods for accelerating transformers, regional self-attention appears to" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "18279" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.258 + ], + "angle": 0, + "content": "be promising. The idea is proposed in the pioneering works [54, 56] and improved as shifted window attention [47, 48]. Inspired by the success of shifted window attention for visual recognition and perception, this method is also used for image restoration [6, 42, 43]. Despite the good performance of the window attention mechanism, it is pointed out in recent works that a wider range of pixel involvement could lead to better image restoration [6, 23]. Thus, in this paper, we try to propose a method that efficiently brings the modelling capacity of self-attention beyond the regional range." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.27, + 0.195, + 0.285 + ], + "angle": 0, + "content": "3. Motivation" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.294, + 0.421, + 0.311 + ], + "angle": 0, + "content": "3.1. Self-attention for dependency modelling" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.318, + 0.469, + 0.409 + ], + "angle": 0, + "content": "Self-attention is good at modelling long-range dependencies explicitly and it facilitates the propagation of information across the modelled dependencies. This operation allows a token to be compared with all the other tokens. The output token is computed as a weighted sum of all the tokens based on a similarity comparison, i.e.," + }, + { + "type": "equation", + "bbox": [ + 0.155, + 0.416, + 0.469, + 0.441 + ], + "angle": 0, + "content": "\\[\n\\mathbf {Y} = \\operatorname {S o f t m a x} \\left(\\mathbf {Q} \\cdot \\mathbf {K} ^ {T} / \\sqrt {d}\\right) \\cdot \\mathbf {V}, \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.447, + 0.469, + 0.522 + ], + "angle": 0, + "content": "where \\(\\mathbf{Q} = \\mathbf{X}\\cdot \\mathbf{W}_Q\\), \\(\\mathbf{K} = \\mathbf{X}\\cdot \\mathbf{W}_K\\), \\(\\mathbf{V} = \\mathbf{X}\\cdot \\mathbf{W}_V\\), \\(\\mathbf{W}_Q, \\mathbf{W}_K, \\mathbf{W}_V \\in \\mathbb{R}^{d\\times d}\\), and \\(\\mathbf{X}, \\mathbf{Y} \\in \\mathbb{R}^{N\\times d}\\). \\(N\\) and \\(d\\) denote the number of tokens and the dimension of one token, respectively. Additionally, \\(\\mathbf{M}\\) denotes the attention map, i.e. \\(\\mathbf{M} = \\mathrm{Softmax}(\\mathbf{Q}\\cdot \\mathbf{K}^T / \\sqrt{d})\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.522, + 0.469, + 0.688 + ], + "angle": 0, + "content": "The time complexity of self-attention is \\(\\mathcal{O}(N^2 d)\\) and the space complexity is dominated by the term \\(\\mathcal{O}(N^2)\\) of the attention map \\(\\mathbf{M}\\). The computational complexity and memory footprint of self-attention grow quadratically with the number of tokens. Thus, self-attention can easily become a computation bottleneck for images where the number of tokens is the multiplication of the two dimensions of the feature map. To overcome this problem, it is proposed to apply self-attention within a window. In this way, the number of tokens that participate in self-attention is significantly reduced and the computational burden is also lifted." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.689, + 0.469, + 0.84 + ], + "angle": 0, + "content": "The problem of window self-attention is that the modelling capacity of the operation is limited to a regional range due to the small window size \\((8\\times 8\\) [43]). On the other hand, it is shown in recent works [6,23] that even a slight increase in window size can lead to better image restoration. Thus, it can be conjectured that modelling dependencies beyond the regional range is still important for image restoration. Hence, it remained to be investigated how to maintain the ability for long-range dependency modelling under a controlled computational budget." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.848, + 0.379, + 0.863 + ], + "angle": 0, + "content": "3.2. Motivation I: cross-scale similarity" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.469, + 0.901 + ], + "angle": 0, + "content": "The attention map \\(\\mathbf{M}\\) plays an essential role in selfattention as it captures the similarity between every paired" + }, + { + "type": "image", + "bbox": [ + 0.513, + 0.089, + 0.885, + 0.196 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.204, + 0.892, + 0.274 + ], + "angle": 0, + "content": "Figure 3. Cross-scale similarity. (c) and (d) shows the attention map between the selected pixels and the example high-resolution image. Although the cyan pixel in (a) and the red pixel in (b) are from images with different resolutions, their attention map with respect to the high-resolution image shows very similar structures." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.288, + 0.892, + 0.498 + ], + "angle": 0, + "content": "pixels in the image. Thus, improving the efficiency of the self-attention in Eq. (1) needs one to analyze the property of the attention map. And we are inspired by a property of images, i.e. cross-scale similarity. That is, the basic structure such as lines and edges of an image is kept in the different versions of the image with different scaling factors. In Fig. 3, the attention map between pixels in an image is shown. Particularly, the attention map between a pixel and the whole image is visualized as a gray-scale heat map. As shown, no matter whether the pixel comes from the high-resolution image or the down-scaled version, the heat map between the pixel and the high-resolution image shows the basic structure of the image. And the heat maps in Fig. 3(c) and Fig. 3(d) are very similar to each other." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.5, + 0.892, + 0.696 + ], + "angle": 0, + "content": "Anchored self-attention. Inspired by the cross-scale similarity shown in Fig. 3, we try to reduce the complexity of the global self-attention in Eq. (1) by operating on images with different resolutions and manipulating the number of tokens, i.e. the \\( N^2 \\) term in \\( \\mathcal{O}(N^2 d) \\). To achieve that, we introduce an additional concept named anchors besides the triplets of queries, keys, and values. The set of anchors is a summary of the information in the image feature map and has a lower dimensionality. Instead of conducting the similarity comparison between the queries and keys directly, the anchors act as an intermediate for the similarity comparison. Formally, the anchored self-attention is proposed as in the following equation" + }, + { + "type": "equation", + "bbox": [ + 0.591, + 0.707, + 0.891, + 0.723 + ], + "angle": 0, + "content": "\\[\n\\mathbf {Y} = \\mathbf {M} _ {e} \\cdot \\mathbf {Z} = \\mathbf {M} _ {e} \\cdot \\left(\\mathbf {M} _ {d} \\cdot \\mathbf {V}\\right), \\tag {2}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.581, + 0.727, + 0.891, + 0.745 + ], + "angle": 0, + "content": "\\[\n\\mathbf {M} _ {d} = \\operatorname {S o f t m a x} \\left(\\mathbf {A} \\cdot \\mathbf {K} ^ {T} / \\sqrt {d}\\right), \\tag {3}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.582, + 0.749, + 0.891, + 0.767 + ], + "angle": 0, + "content": "\\[\n\\mathbf {M} _ {e} = \\operatorname {S o f t m a x} \\left(\\mathbf {Q} \\cdot \\mathbf {A} ^ {T} / \\sqrt {d}\\right), \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.779, + 0.891, + 0.855 + ], + "angle": 0, + "content": "where \\(M \\ll N\\), \\(\\mathbf{A} \\in \\mathbb{R}^{M \\times d}\\) is the anchor, \\(\\mathbf{M}_e \\in \\mathcal{R}^{N \\times M}\\) and \\(\\mathbf{M}_d \\in \\mathcal{R}^{M \\times N}\\) denotes the attention map between the query-anchor pair and anchor-key pair. The choice of the operations to derive the anchors is investigated in the implementation details of the ablation study of the paper." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.856, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Since the number of anchors is much smaller than the number of the other tokens, the size of the resulting two attention maps \\(\\mathbf{M}_e\\) and \\(\\mathbf{M}_d\\) are much smaller than the orig" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "18280" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.091, + 0.089, + 0.182, + 0.158 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.133, + 0.161, + 0.148, + 0.169 + ], + "angle": 0, + "content": "(a)" + }, + { + "type": "image", + "bbox": [ + 0.182, + 0.089, + 0.273, + 0.158 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.221, + 0.16, + 0.236, + 0.169 + ], + "angle": 0, + "content": "(b)" + }, + { + "type": "image", + "bbox": [ + 0.275, + 0.089, + 0.366, + 0.158 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.367, + 0.09, + 0.456, + 0.158 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.313, + 0.161, + 0.327, + 0.169 + ], + "angle": 0, + "content": "(c)" + }, + { + "type": "image", + "bbox": [ + 0.092, + 0.17, + 0.182, + 0.238 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.133, + 0.24, + 0.148, + 0.249 + ], + "angle": 0, + "content": "(e)" + }, + { + "type": "image", + "bbox": [ + 0.182, + 0.17, + 0.274, + 0.239 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.222, + 0.24, + 0.236, + 0.249 + ], + "angle": 0, + "content": "(f)" + }, + { + "type": "image", + "bbox": [ + 0.275, + 0.17, + 0.366, + 0.239 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.313, + 0.24, + 0.328, + 0.249 + ], + "angle": 0, + "content": "(g)" + }, + { + "type": "image", + "bbox": [ + 0.367, + 0.17, + 0.457, + 0.239 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.405, + 0.24, + 0.419, + 0.249 + ], + "angle": 0, + "content": "(h)" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.253, + 0.468, + 0.295 + ], + "angle": 0, + "content": "Figure 4. The image features in natural images are anisotropic. Thus, it is not always necessary to employ the uniform global range attention in all parts of the image." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.302, + 0.468, + 0.453 + ], + "angle": 0, + "content": "inal attention map \\(\\mathbf{M}\\) in Eq. (1). Then the matrix multiplication in Eq. (2) is computed from the right hand. The self-attention is first done for the anchors and keys. The attention map \\(\\mathbf{M}_d\\) distills the tokens \\(\\mathbf{V}\\) into an intermediate feature \\(\\mathbf{Z}\\). Then the self-attention is done between the queries and the anchors. The second attention map \\(\\mathbf{M}_e\\) expands the size of the feature \\(\\mathbf{Z}\\) and recovers the information in \\(\\mathbf{V}\\). The computational complexity of the anchored self-attention is reduced to \\(\\mathcal{O}(NMd)\\). And the space complexity is reduced to \\(\\mathcal{O}(NM)\\)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.467, + 0.429, + 0.483 + ], + "angle": 0, + "content": "3.3. Motivation II: anisotropic image features" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.491, + 0.468, + 0.611 + ], + "angle": 0, + "content": "The anchored self-attention could reduce the space and time complexity of the self-attention in Eq. (1) significantly by removing the quadratic term \\( N^2 \\). Yet, for image restoration tasks, the remaining term \\( N \\) is the multiplication of the width and height of the image. Thus, the complexity of the anchored self-attention in Eq. (2) could still be unaffordable due to the large term \\( N \\). Thus, it is desirable to further reduce the complexity of the anchored self-attention." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.613, + 0.468, + 0.749 + ], + "angle": 0, + "content": "To achieve that goal, we resort to another characteristic of natural images, i.e., the anisotropic image features. As shown in Fig. 4, the natural image features such as the single object in Fig. 4(c)&(d), the multi-scale similarity in Fig. 4(h), symmetry in Fig. 4(e)&(g) span in an anisotropic manner. Thus, isotropic global range attention across the entire image is redundant to capture the anisotropic image features. And in response to that, we propose to conduct attention within the anisotropic stripes shown in Fig. 4." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.75, + 0.468, + 0.901 + ], + "angle": 0, + "content": "Stripe attention mechanism. The proposed stripe attention mechanism consists of four modes including the horizontal stripe, the vertical stripe, the shifted horizontal stripe, and the shifted vertical stripe. The horizontal and vertical stripe attention mechanisms could be employed alternately across a transformer network. In this way, a trade-off is made between maintaining the global range modelling capacity and controlling the computation complexity of global self-attention. Thus, in combination with the concept of anchors, we propose the anchored stripe self-attention." + }, + { + "type": "image", + "bbox": [ + 0.536, + 0.089, + 0.645, + 0.175 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.563, + 0.179, + 0.606, + 0.189 + ], + "angle": 0, + "content": "(a) Query" + }, + { + "type": "image", + "bbox": [ + 0.657, + 0.115, + 0.713, + 0.158 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.661, + 0.179, + 0.71, + 0.188 + ], + "angle": 0, + "content": "(b) Anchor" + }, + { + "type": "image", + "bbox": [ + 0.725, + 0.089, + 0.834, + 0.175 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.757, + 0.179, + 0.791, + 0.188 + ], + "angle": 0, + "content": "(c) Key" + }, + { + "type": "image", + "bbox": [ + 0.522, + 0.19, + 0.663, + 0.292 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.541, + 0.298, + 0.672, + 0.308 + ], + "angle": 0, + "content": "(d) Attention map via anchors" + }, + { + "type": "image", + "bbox": [ + 0.663, + 0.19, + 0.865, + 0.292 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.724, + 0.298, + 0.829, + 0.308 + ], + "angle": 0, + "content": "(e) Direct attention map" + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.31, + 0.892, + 0.366 + ], + "angle": 0, + "content": "Figure 5. The visualization of the (a) queries, (b) anchors, and (c) keys from the different layers of the proposed network. (d) shows the attention map approximated by Eq. (2), i.e. \\(\\mathbf{M}_e\\cdot \\mathbf{M}_d\\) (e) shows the exact attention map \\(\\mathbf{M}\\) computed in Eq. (1)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.371, + 0.892, + 0.415 + ], + "angle": 0, + "content": "For this attention mechanism, efficient self-attention is conducted inside the vertical and horizontal stripes with the help of the introduced anchors." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.425, + 0.618, + 0.439 + ], + "angle": 0, + "content": "3.4. Discussion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.448, + 0.892, + 0.508 + ], + "angle": 0, + "content": "The proposed anchored stripe self-attention mechanism is closely related to two other concepts including low-rankness and similarity propagation. And we detail the relationship in this subsection as follows." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.509, + 0.892, + 0.674 + ], + "angle": 0, + "content": "Low-rankness of attention map. By comparing the self-attention mechanisms in Eq. (1) and Eq. (2), we can easily found out that the original attention map \\(\\mathbf{M}\\) is decomposed into small attention maps \\(\\mathbf{M}_d\\) and \\(\\mathbf{M}_e\\) whose rank is no larger than \\(M\\). And the essence here is to provide the low-rank approximation without calculating the original attention map first. For the success of the anchored self-attention, it is important to ensure that with the anchors as the intermediate, the approximated attention map is similar to the original attention map. Thus, an additional analysis is provided in Fig. 5." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.675, + 0.892, + 0.854 + ], + "angle": 0, + "content": "First, by observing the queries, anchors, and keys, we can conclude that the anchors have a very similar structure to the query and key. Thus, the anchors are a good summary of the information in the queries and keys. And approximating self-attention with anchors as intermediate seems to be plausible. Additionally, the approximate attention map \\(\\mathbf{M}_e\\cdot \\mathbf{M}_d\\) and the exact attention map \\(\\mathbf{M}\\) are also compared in Fig. 5. As shown, the approximate attention map keeps the major structure in the exact attention map, which is confirmed by the large Pearson correlation coefficients (0.9505) between the two attention maps. Thus, the quality of the anchored self-attention is guaranteed." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.856, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Metric and similarity propagation. From another perspective, in the proposed anchored self-attention, the queries and keys are first compared with the anchors and" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "18281" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.092, + 0.089, + 0.872, + 0.253 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.096, + 0.256, + 0.396, + 0.436 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.427, + 0.256, + 0.868, + 0.437 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.438, + 0.892, + 0.467 + ], + "angle": 0, + "content": "Figure 6. Network architecture. (a) The representation learning module contains stages of transformer layers. (b) The transformer layer is equipped with global, regional, and local modelling blocks. (c) The anchored stripe attention helps to attend beyond regional ranges." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.471, + 0.473, + 0.82 + ], + "angle": 0, + "content": "then the query-key similarity is computed. Thus, this computation procedure needs to propagate the query-anchor and key-anchor similarity to the query-key pair. And similarity propagation is related to the triangle inequality in a metric space [19, 27, 73]. A mathematical metric needs to satisfy several conditions including the essential triangle inequality, \\( d(\\mathbf{q}, \\mathbf{k}) \\leq d(\\mathbf{a}, \\mathbf{q}) + d(\\mathbf{a}, \\mathbf{k}) \\), where \\( d(\\cdot, \\cdot) \\) defines a metric between two entities. Thus, the \\( \\mathbf{q} / \\mathbf{k} \\) distance is upper-bounded by the sum of the \\( \\mathbf{a} / \\mathbf{q} \\) distance and the \\( \\mathbf{a} / \\mathbf{k} \\) distance. This implies that if \\( \\mathbf{a} \\) is similar (close) to both \\( \\mathbf{q} \\) and \\( \\mathbf{k} \\), then \\( \\mathbf{q} \\) and \\( \\mathbf{k} \\) should also be similar (close) to each other. Yet, the similarity measure in Eq. (1) and Eq. (2) is defined by the dot product instead of the distance between tokens, which does not satisfy the triangle inequality. Thus, similarity propagation could not be theoretically guaranteed. To study the influence of the similarity measure, an ablation study is conducted and the results are shown in Sec. 5. Dot product and distance are compared as a similarity measure. According to the results, although the dot product does not strictly obey the triangle inequality, it still guarantees better image restoration results. Thus, we can conclude empirically that the dot product is enough for similarity propagation." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.83, + 0.347, + 0.848 + ], + "angle": 0, + "content": "4. Modelling Image Hierarchies" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.856, + 0.47, + 0.903 + ], + "angle": 0, + "content": "In this section, we answer the second research question described in the introduction, that is, how to explicitly model image hierarchies by a single computational module." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.471, + 0.892, + 0.517 + ], + "angle": 0, + "content": "In response to that, we propose the GRL network architecture that incorporates global range, regional range, and local range image modelling capacities." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.52, + 0.893, + 0.762 + ], + "angle": 0, + "content": "Network architecture. The overall architecture of the proposed network is shown in Fig. 6. The network takes a degraded low-quality image as input, processes the image inside the network, and outputs a recovered high-quality image. In detail, the network contains three parts. 1) The feature extraction layer is implemented as a simple convolution and converts the input image into feature maps. 2) The representation learning component enriches the information extracted in the previous operation. The transformer stage consists of several transformer layers and ends with a convolution layer. The dimension of the feature map is maintained across the whole representation learning module. Skip connection is applied to both the transformer stage and the representation learning module. 3) The image reconstruction module takes the rich features calculated by the previous operations and estimates a recovered image." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Transformer Layer. This layer in Fig. 6b is the key component that provides the hierarchical image modelling capacity in the global, regional, and local range. This layer first processes the input feature map by the parallel self-attention module and channel attention enhanced convolutions. The convolution branch serves to capture local structures in the input feature map. On the other hand, the self-attention module contains the window attention proposed in Swin transformer V2 [47] and the anchored stripe attenuation" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "18282" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.168, + 0.089, + 0.8, + 0.104 + ], + "angle": 0, + "content": "Table 1. Defocus deblurring results. S: single-image defocus deblurring. D: dual-pixel defocus deblurring." + }, + { + "type": "table", + "bbox": [ + 0.216, + 0.106, + 0.761, + 0.291 + ], + "angle": 0, + "content": "
MethodIndoor ScenesOutdoor ScenesCombined
PSNR↑SSIM↑MAE↓LPIPS↓PSNR↑SSIM↑MAE↓LPIPS↓PSNR↑SSIM↑MAE↓LPIPS↓
EBDBS[30]25.770.7720.0400.29721.250.5990.0580.37323.450.6830.0490.336
DMENetS[40]25.500.7880.0380.29821.430.6440.0630.39723.410.7140.0510.349
JNBs[60]26.730.8280.0310.27321.100.6080.0640.35523.840.7150.0480.315
DPDNetS[1]26.540.8160.0310.23922.250.6820.0560.31324.340.7470.0440.277
KPACS[62]27.970.8520.0260.18222.620.7010.0530.26925.220.7740.0400.227
IFANs[41]28.110.8610.0260.17922.760.7200.0520.25425.370.7890.0390.217
RestormerS[76]28.870.8820.0250.14523.240.7430.0500.20925.980.8110.0380.178
GRLS-B29.060.8860.0240.13923.450.7610.0490.19626.180.8220.0370.168
DPDNetD[1]27.480.8490.0290.18922.900.7260.0520.25525.130.7860.0410.223
RDPD2[2]28.100.8430.0270.21022.820.7040.0530.29825.390.7720.0400.255
UformerD[74]28.230.8600.0260.19923.100.7280.0510.28525.650.7950.0390.243
IFAND[41]28.660.8680.0250.17223.460.7430.0490.24025.990.8040.0370.207
RestormerD[76]29.480.8950.0230.13423.970.7730.0470.17526.660.8330.0350.155
GRLD-B29.830.9030.0220.11424.390.7950.0450.15027.040.8470.0340.133
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.299, + 0.47, + 0.327 + ], + "angle": 0, + "content": "Table 2. Single-image motion deblurring results. GoPro dataset [51] is used for training." + }, + { + "type": "table", + "bbox": [ + 0.104, + 0.328, + 0.442, + 0.517 + ], + "angle": 0, + "content": "
MethodGoPro [51]HIDE [59]Average
PSNR↑ / SSIM↑PSNR↑ / SSIM↑PSNR↑ / SSIM↑
DeblurGAN [37]28.70 / 0.85824.51 / 0.87126.61 / 0.865
Nah et al. [51]29.08 / 0.91425.73 / 0.87427.41 / 0.894
DeblurGAN-v2 [38]29.55 / 0.93426.61 / 0.87528.08 / 0.905
SRN [64]30.26 / 0.93428.36 / 0.91529.31 / 0.925
Gao et al. [20]30.90 / 0.93529.11 / 0.91330.01 / 0.924
DBGAN [81]31.10 / 0.94228.94 / 0.91530.02 / 0.929
MT-RNN [53]31.15 / 0.94529.15 / 0.91830.15 / 0.932
DMPHN [79]31.20 / 0.94029.09 / 0.92430.15 / 0.932
Suin et al. [63]31.85 / 0.94829.98 / 0.93030.92 / 0.939
SPAIR [55]32.06 / 0.95330.29 / 0.93131.18 / 0.942
MIMO-UNet+ [8]32.45 / 0.95729.99 / 0.93031.22 / 0.944
IPT [5]32.52 / -- / -- / -
MPRNet [77]32.66 / 0.95930.96 / 0.93931.81 / 0.949
Restormer [76]32.92 / 0.96131.22 / 0.94232.07 / 0.952
GRL-B (ours)33.93 / 0.96831.65 / 0.94732.79 / 0.958
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.519, + 0.468, + 0.546 + ], + "angle": 0, + "content": "Table 3. Single-image motion deblurring results on RealBlur [57] dataset. The networks are trained and tested on RealBlur dataset." + }, + { + "type": "table", + "bbox": [ + 0.104, + 0.548, + 0.444, + 0.676 + ], + "angle": 0, + "content": "
MethodRealBlur-R [57]RealBlur-J [57]Average
PSNR↑ / SSIM↑PSNR↑ / SSIM↑PSNR↑ / SSIM↑
DeblurGAN-v2 [38]36.44 / 0.93529.69 / 0.87033.07 / 0.903
SRN [64]38.65 / 0.96531.38 / 0.90935.02 / 0.937
MPRNet [77]39.31 / 0.97231.76 / 0.92235.54 / 0.947
MIMO-UNet+ [8]- / -32.05 / 0.921- / -
MAXIM-3S [67]39.45 / 0.96232.84 / 0.93536.15 / 0.949
BANet [66]39.55 / 0.97132.00 / 0.92335.78 / 0.947
MSSNet [34]39.76 / 0.97232.10 / 0.92835.93 / 0.950
Stripformer [65]39.84 / 0.97432.48 / 0.92936.16 / 0.952
GRL-B (ours)40.20 / 0.97432.82 / 0.93236.51 / 0.953
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.689, + 0.468, + 0.809 + ], + "angle": 0, + "content": "tion proposed in this paper. The feature map is split equally along the channel dimension and concatenated along the channel dimension again after the parallel processing within the two attention modules. The window attention provides the mechanism to capture the regional range dependencies. Then the feature maps outputted by the convolution module and the attention module are added to the input feature map, which is processed by the following MLP module." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.811, + 0.468, + 0.901 + ], + "angle": 0, + "content": "Anchored stripe self-attention. The operation of the proposed anchored stripe attention is conducted according to Eq. (2) and visualized in Fig. 6c. The dimension of different features is also shown. The triplet of \\(\\mathbf{Q},\\mathbf{K},\\mathbf{V}\\) is derived by plain linear projections. To summarize the information into anchors, the anchor projection is implemented as an" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.301, + 0.892, + 0.392 + ], + "angle": 0, + "content": "average pooling layer followed by a linear projection. After the anchor projection, the resolution of the image feature map is down-scaled by a factor of \\(s\\) along both directions. As shown in Fig. 6, the two attention maps \\(\\mathbf{M}_d\\) and \\(\\mathbf{M}_e\\) play a similar role as the original attention map \\(\\mathbf{M}\\) but with less space and time complexity." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.405, + 0.706, + 0.423 + ], + "angle": 0, + "content": "5. Experimental Results" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.43, + 0.892, + 0.688 + ], + "angle": 0, + "content": "The experimental results are shown in this section. We answer the third research question raised in the introduction by investigating the performance of the proposed network on different image restoration tasks. Based on the data type, the investigated tasks are classified into three commonly used settings including 1) real image restoration (single-image motion deblurring, defocus deblurring), 2) image restoration based on synthetic data (image denoising, single image SR, JPEG compression artifact removal, demosaicking), and 3) real image restoration based on data synthesis. We provide three networks with different model sizes including the tiny, small, and base versions (GRL-T, GRL-S, GRL-B). For real and synthetic image restoration, Adam optimizer and \\( L_{1} \\) loss are used to train the network with an initial learning rate \\( 2 \\times 10^{-4} \\). More details about the training dataset, training protocols, and additional visual results are shown in the supplementary material." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.697, + 0.673, + 0.713 + ], + "angle": 0, + "content": "5.1. Image deblurring" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.891, + 0.763 + ], + "angle": 0, + "content": "We first investigate the performance of the proposed network on two real image restoration tasks including single-image motion deblurring, and motion deblurring." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Single image motion deblurring. Tab. 2 and Tab. 3 show the experimental results for single image motion deblurring on synthetic datasets (GoPro [51], HIDE [59]) and real dataset (RealBlur-R [57]), respectively. Compared with the previous state-of-the-art Restormer [76], the proposed GRL achieves significant PSNR improvement of \\(1.01\\mathrm{dB}\\) on the GoPro dataset. On the HIDE dataset, the PSNR improvement is \\(0.43\\mathrm{dB}\\). Please note that the improvement is achieved under fewer parameter budget. As shown in Tab. 4," + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.956 + ], + "angle": 0, + "content": "18283" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.096, + 0.09, + 0.873, + 0.104 + ], + "angle": 0, + "content": "Table 4. Color and grayscale image denoising results. Model complexity and prediction accuracy are shown for better comparison." + }, + { + "type": "table", + "bbox": [ + 0.087, + 0.105, + 0.887, + 0.255 + ], + "angle": 0, + "content": "
Method# Params [M]ColorGrayscale
CBSD68 [49]σ=15 σ=25 σ=50Kodak24 [16]σ=15 σ=25 σ=50McMaster [83]σ=15 σ=25 σ=50Urban100 [28]σ=15 σ=25 σ=50Set12 [82]σ=15 σ=25 σ=50BSD68 [49]σ=15 σ=25 σ=50Urban100 [28]σ=15 σ=25 σ=50
DnCNN [32]0.5633.9031.2427.9534.6032.1428.9533.4531.5228.6232.9830.8127.5932.8630.4427.1831.7329.2326.2332.6429.9526.26
RNAN [85]8.96--28.27--29.58--29.72--29.08--27.70--26.48--27.65
IPT [5]115.33--28.39--29.64--29.98--29.71---------
EDT-B [42]11.4834.3931.7628.5635.3732.9429.8735.6133.3430.2535.2233.0730.16---------
DRUNet [80]32.6434.3031.6928.5135.3132.8929.8635.4033.1430.0834.8132.6029.6133.2530.9427.9031.9129.4826.5933.4431.1127.96
SwinIR [43]11.7534.4231.7828.5635.3432.8929.7935.6133.2030.2235.1332.9029.8233.3631.0127.9131.9729.5026.5833.7031.3027.98
Restormer [76]26.1334.4031.7928.6035.4733.0430.0135.6133.3430.3035.1332.9630.0233.4231.0828.0031.9629.5226.6233.7931.4628.29
GRL-T0.8834.3031.6628.4535.2432.7829.6735.4933.1830.0635.0832.8429.7833.2930.9227.7831.9029.4326.4933.6631.2327.89
GRL-S3.1234.3631.7228.5135.3232.8829.7735.5933.2930.1835.2433.0730.0933.3631.0227.9131.9329.4726.5433.8431.4928.24
GRL-B19.8134.4531.8228.6235.4333.0229.9335.7333.4630.3635.5433.3530.4633.4731.1228.0332.0029.5426.6034.0931.8028.59
" + }, + { + "type": "table_caption", + "bbox": [ + 0.159, + 0.268, + 0.81, + 0.282 + ], + "angle": 0, + "content": "Table 5. Classical image SR results. Results of both lightweight models and accurate models are summarized." + }, + { + "type": "table", + "bbox": [ + 0.104, + 0.284, + 0.869, + 0.548 + ], + "angle": 0, + "content": "
MethodScale# Params [M]Set5 [3]Set14 [78]BSD100 [49]Urban100 [28]Manga109 [50]
PSNR↑SSIM↑PSNR↑SSIM↑PSNR↑SSIM↑PSNR↑SSIM↑PSNR↑SSIM↑
RCAN [84]×215.4438.270.961434.120.921632.410.902733.340.938439.440.9786
SAN [11]×215.7138.310.962034.070.921332.420.902833.100.937039.320.9792
HAN [52]×263.6138.270.961434.160.921732.410.902733.350.938539.460.9785
IPT [5]×2115.4838.37-34.43-32.48-33.76---
SwinIR [43]×20.8838.140.961133.860.920632.310.901232.760.934039.120.9783
SwinIR [43]×211.7538.420.962334.460.925032.530.904133.810.942739.920.9797
EDT [42]×20.9238.230.961533.990.920932.370.902132.980.936239.450.9789
EDT [42]×211.4838.630.963234.800.927332.620.905234.270.945640.370.9811
GRL-T (ours)×20.8938.270.962734.210.925832.420.905633.600.941139.610.9790
GRL-S (ours)×23.3438.370.963234.640.928032.520.906934.360.946339.840.9793
GRL-B (ours)×220.0538.670.964735.080.930332.670.908735.060.950540.670.9818
RCAN [84]×415.5932.630.900228.870.788927.770.743626.820.808731.220.9173
SAN [11]×415.8632.640.900328.920.788827.780.743626.790.806831.180.9169
HAN [52]×464.2032.640.900228.900.789027.800.744226.850.809431.420.9177
IPT [5]×4115.6332.64-29.01-27.82-27.26---
SwinIR [43]×40.9032.440.897628.770.785827.690.740626.470.798030.920.9151
SwinIR [43]×411.9032.920.904429.090.795027.920.748927.450.825432.030.9260
EDT [42]×40.9232.530.899128.880.788227.760.743326.710.805131.350.9180
EDT [42]×411.6333.060.905529.230.797127.990.751027.750.831732.390.9283
GRL-T (ours)×40.9132.560.902928.930.796127.770.752327.150.818531.570.9219
GRL-S (ours)×43.4932.760.905829.100.800727.900.756827.900.835732.110.9267
GRL-B (ours)×420.2033.100.909429.370.805828.010.761128.530.850432.770.9325
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.56, + 0.47, + 0.605 + ], + "angle": 0, + "content": "GRL-B saves \\(24\\%\\) parameters compared with Restormer. As shown in Tab. 3, GRL-B sets the new state-of-the-art performance of 40.20 PSNR on RealBlur-R dataset." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.606, + 0.47, + 0.743 + ], + "angle": 0, + "content": "Defocus deblurring. Tab. 1 shows the experimental results for defocus deblurring using single image and dual-pixel images. Our GRL outperforms the previous methods for all three scene types. Compared with Restormer on the combined scenes, our GRL achieves an elegant performance boost of \\(0.20\\mathrm{dB}\\) and \\(0.38\\mathrm{dB}\\) for single and dual-pixel defocus deblurring. Compared with Uformer [74] and IFAN [41], GRL achieves PSNR gain of \\(1.39\\mathrm{dB}\\) and \\(1.05\\mathrm{dB}\\) for the dual-pixel setting." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.755, + 0.434, + 0.772 + ], + "angle": 0, + "content": "5.2. Image restoration based on synthetic data" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.779, + 0.469, + 0.841 + ], + "angle": 0, + "content": "Investigating image restoration with synthetic data is also valuable to reveal the network capacity of restoration methods. Besides the experiments on the real data, we also study the performance of the network on synthetic data." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.841, + 0.469, + 0.901 + ], + "angle": 0, + "content": "Image denoising. First, the experimental results on Gaussian image denoising are shown in Tab. 4. For a fair comparison between different models, both the network complexity and accuracy are shown in the table. And several key find" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.56, + 0.892, + 0.68 + ], + "angle": 0, + "content": "ings are observed. I. The tiny version GRL-T is extremely efficient, reducing model complexity by two orders of magnitude (only \\(0.76\\%\\) of [5] and \\(2.7\\%\\) of DRUNet [80]) while not sacrificing network accuracy. II. The small version GRL-S performs competitive with the previous state-of-the-art SwinIR [43] and Restormer [76]. III. On Urban100, the base version outperforms Restormer by a large margin (e.g. 0.44dB PSNR gain for color image and noise level 50)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.685, + 0.892, + 0.852 + ], + "angle": 0, + "content": "Image SR. Experimental results for classical images are shown in Tab. 5. Both lightweight models and accurate SR models are summarized. A similar conclusion could be drawn from the results. I. Among the lightweight networks, GRL-T outperforms both convolution and self-attention-based networks including DBPN [25], SwinIR [43] and EDT [42]. Compared with EDT, Significant improvements are obtained on Urban100 and Manga109 datasets (0.44 dB and 0.22 dB for \\(\\times 4\\) SR). II. GRL-B sets the new state-of-the-art for accurate image SR. III. GRL-S achieves a good balance between network complexity and SR image quality." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.856, + 0.892, + 0.901 + ], + "angle": 0, + "content": "JPEG compression artifact removal. The experimental results for color and grayscale images are shown in Tab. 6. Four image quality factors ranging from 10 to 40 for JPEG" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.946, + 0.519, + 0.957 + ], + "angle": 0, + "content": "18284" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.089, + 0.897, + 0.117 + ], + "angle": 0, + "content": "Table 6. Grayscale image JPEG compression artifact removal results. As a compar- Table 7. Color image JPEG compression artifact ison metric, the parameter count of FBCNN [29] GRL-S are 71.92M and 3.12M. removal results." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.12, + 0.587, + 0.242 + ], + "angle": 0, + "content": "
SetQFJPEG PSNR SSIMDnCNN [82] PSNR SSIMDCSC [18] PSNR SSIMQGAC [14] PSNR SSIMMWCNN [46] PSNR SSIMFBCNN [29] PSNR SSIMGRL-S PSNR SSIM
Classic5 [15]1027.82 0.76029.40 0.80329.62 0.81029.84 0.81230.01 0.82030.12 0.82230.20 0.829
2030.12 0.83431.63 0.86131.81 0.86431.98 0.86932.16 0.87032.31 0.87232.49 0.878
3031.48 0.86732.91 0.88633.06 0.88833.22 0.89233.43 0.89333.54 0.89433.72 0.899
4032.43 0.88533.77 0.90033.87 0.90234.05 0.90534.27 0.90634.35 0.90734.53 0.911
BSD500 [49]1027.80 0.76829.21 0.80929.32 0.81329.46 0.82129.61 0.82029.67 0.82129.74 0.823
2030.05 0.84931.53 0.87831.63 0.88031.73 0.88431.92 0.88532.00 0.88532.05 0.885
3031.37 0.88432.90 0.90732.99 0.90833.07 0.91233.30 0.91233.37 0.91333.43 0.912
4032.30 0.90333.85 0.92333.92 0.92434.01 0.92734.27 0.92834.33 0.92834.38 0.928
" + }, + { + "type": "table", + "bbox": [ + 0.59, + 0.119, + 0.895, + 0.242 + ], + "angle": 0, + "content": "
SetQFJPEG PSNR SSIMQGAC [14] PSNR SSIMFBCNN [29] PSNR SSIMGRL-S PSNR SSIM
LIVE1 [58]1025.69 0.74327.62 0.80427.77 0.80328.13 0.814
2028.06 0.82629.88 0.86830.11 0.86830.49 0.878
3029.37 0.86131.17 0.89631.43 0.89731.85 0.905
4030.28 0.88232.05 0.91232.34 0.91332.79 0.920
BSD500 [49]1025.84 0.74127.74 0.80227.85 0.79928.26 0.808
2028.21 0.82730.01 0.86930.14 0.86730.57 0.875
3029.57 0.86531.33 0.89831.45 0.89731.92 0.903
4030.52 0.88732.25 0.91532.36 0.91332.86 0.919
" + }, + { + "type": "table_caption", + "bbox": [ + 0.16, + 0.253, + 0.386, + 0.266 + ], + "angle": 0, + "content": "Table 8. Image demosaicking results." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.269, + 0.472, + 0.32 + ], + "angle": 0, + "content": "
DatasetsMatlabDDR [75]DeepJoint [21]MMNet [36]RLDD [24]RNAN [85]DRUNet [80]GRL-S (ours)
Kodak [16]35.7841.1142.0040.1942.4943.1642.6843.57
McMaster [83]34.4337.1239.1437.0939.2539.7039.3940.22
" + }, + { + "type": "image", + "bbox": [ + 0.084, + 0.331, + 0.467, + 0.485 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.127, + 0.496, + 0.419, + 0.51 + ], + "angle": 0, + "content": "Figure 7. Visual results for real-world image SR." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.516, + 0.469, + 0.59 + ], + "angle": 0, + "content": "compression are studied. As shown in the table, the proposed GRL-S network outperforms the previous state-of-the-art method elegantly across different datasets and quality factors. Notably, GRL-S has a much smaller model complexity than FBCNN." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.592, + 0.469, + 0.637 + ], + "angle": 0, + "content": "Demosaicking. Results for image demosaicking is shown in Tab. 8. The proposed method outperforms the previous methods RNAN [85] and DRUNet [80] significantly." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.647, + 0.469, + 0.663 + ], + "angle": 0, + "content": "5.3. Real image restoration based on data synthesis" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.671, + 0.469, + 0.776 + ], + "angle": 0, + "content": "Finally, we also investigate the performance of the network for real-world image restoration. The aim is to superresolve a low-quality image by an upscaling factor of 4. Since there are no ground-truth images for this task, only the visual comparison is given in Fig. 7. Compared with the other methods, the proposed GRL is able to remove more artifacts in the low-resolution images." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.787, + 0.227, + 0.803 + ], + "angle": 0, + "content": "5.4. Ablation study" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.81, + 0.469, + 0.9 + ], + "angle": 0, + "content": "Influence of the similarity comparison method. As mentioned in Sec. 3.4, for theoretical guarantee of similarity propagation, a mathematical metric rather than a dot product should be used. To study the difference between, image restoration with the two operations are compared and the results are shown in Tab. 9. As revealed by the table, the dot" + }, + { + "type": "table_caption", + "bbox": [ + 0.518, + 0.253, + 0.874, + 0.267 + ], + "angle": 0, + "content": "Table 9. Ablation study on similarity comparison operation." + }, + { + "type": "table", + "bbox": [ + 0.508, + 0.268, + 0.885, + 0.344 + ], + "angle": 0, + "content": "
Test setMetricColor DNGray DNImage SR
σ15σ25σ50σ15σ25σ50×2×3×4
BSD68 or BSD100Euclidean35.0232.5629.4231.8429.3626.4332.3029.1927.67
Dot product35.1032.6429.5431.8529.3926.4432.3329.2227.70
Urban100Euclidean34.6332.2828.9433.2530.6427.1732.7628.6226.50
Dot product34.7732.4129.1933.2830.7527.2632.8828.7826.67
" + }, + { + "type": "table_caption", + "bbox": [ + 0.527, + 0.348, + 0.865, + 0.362 + ], + "angle": 0, + "content": "Table 10. Ablation study on anchor projection operation." + }, + { + "type": "table", + "bbox": [ + 0.557, + 0.374, + 0.836, + 0.45 + ], + "angle": 0, + "content": "
Anchor projection operation# Params [m]PSNR on Set 5
Depthwise Conv3.1735.03
Conv4.1935.03
Patch merging3.5334.98
Maxpool + Linear Projection3.1235.02
Avgpool + Linear Projection3.1235.03
" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.466, + 0.892, + 0.511 + ], + "angle": 0, + "content": "product is very competitive compared with a metric and it outperforms a distance metric for a couple of settings. Considering this, the dot product is still used." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.514, + 0.892, + 0.59 + ], + "angle": 0, + "content": "Influence of the anchor projections. The anchor projection operation helps to summarize the information in the feature map. The ablation study is shown in Tab. 10. Considering both the accuracy performance and parameter budget, Avgpool followed by linear projection is finally used." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.626, + 0.619, + 0.64 + ], + "angle": 0, + "content": "6. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.653, + 0.892, + 0.849 + ], + "angle": 0, + "content": "In this paper, we proposed GRL, a network with efficient and explicit hierarchical modelling capacities for image restoration. The proposed network was mainly inspired by two image properties including cross-scale similarity and anisotropic image features. Based on that, we proposed the efficient anchored stripe self-attention module for long-range dependency modelling. Then a versatile network architecture was proposed for image restoration. The proposed network can model image hierarchies in the global, regional, and local ranges. Owing to the advanced computational mechanism, the proposed network architecture achieves state-of-the-art performances for various image restoration tasks." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.856, + 0.892, + 0.9 + ], + "angle": 0, + "content": "Acknowledgements. This work was partly supported by ETH Zürich General Fund (OK), Meta Reality Labs and the Alexander von Humboldt Foundation." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.956 + ], + "angle": 0, + "content": "18285" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.116, + 0.469, + 0.158 + ], + "angle": 0, + "content": "[1] Abdullah Abuolaim and Michael S Brown. Defocus deblurring using dual-pixel data. In European Conference on Computer Vision, pages 111-126. Springer, 2020. 6" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.16, + 0.469, + 0.213 + ], + "angle": 0, + "content": "[2] Abdullah Abuolaim, Mauricio Delbracio, Damien Kelly, Michael S. Brown, and Peyman Milanfar. Learning to reduce defocus blur by realistically modeling dual-pixel data. 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To achieve that, we start by analyzing two important properties of natural images including cross-scale similarity and anisotropic image features. Inspired by that, we propose the anchored stripe self-attention which achieves a good balance between the space and time complexity of self-attention and the modelling capacity beyond the regional range. Then we propose a new network architecture dubbed GRL to explicitly model image hierarchies in the Global, Regional, and Local range via anchored stripe self-attention, window self-attention, and channel attention enhanced convolution. Finally, the proposed network is applied to 7 image restoration types, covering both real and synthetic settings. The proposed method sets the new state-of-the-art for several of those. Code will be available at https://github.com/ofsoundof/GRL-Image-Restoration.git. + +# 1. Introduction + +Image restoration aims at recovering high-quality images from low-quality ones, resulting from an image degradation processes such as blurring, sub-sampling, noise corruption, and JPEG compression. Image restoration is an ill-posed inverse problem since important content information about the image is missing during the image degradation processes. Thus, in order to recover a high-quality image, the rich information exhibited in the degraded image should be fully exploited. + +Natural images contain a hierarchy of features at global, regional, and local ranges which could be used by deep neural networks for image restoration. First, the local range covers a span of several pixels and typical features are edges and local colors. To model such local features, convolutional neural networks (CNNs) with small kernels (e.g. $3 \times 3$ ) are utilized. Second, the regional range is characterized by a window with tens of pixels. This range of pix + +![](images/ecbcec5227d0dc7456f5ede5d3de3a19989cbf063fc1d23baa28da0b7c72b020.jpg) +(a) bridge from ICB, $2749\times 4049$ + +![](images/f07e5edd31683e40fccf7ac488ca0122dc610b128acb455401a31cd8dfd72536.jpg) +(b) $0848x4$ from DIV2K, $1020 \times 768$ + +![](images/74081cd07c48d14bb1648cb98a2239a864aa8bb452efd783d2c2d7ba3c88d23e.jpg) +(c) 073 from Urban100, $1024 \times 765$ +Figure 1. Natural images show a hierarchy of features in a global, regional, and local range. The local (edges, colors) and regional features (the pink squares) could be well modelled by CNNs and window self-attention. By contrast, it is difficult to efficiently and explicitly model the rich global features (cyan rectangles). + +els can cover small objects and components of large objects (pink squares in Fig. 1). Due to the larger range, modelling the regional features (consistency, similarity) explicitly with large-kernel CNNs would be inefficient in both parameters and computation. Instead, transformers with a window attention mechanism are well suited for this task. Third, beyond local and regional, some features have a global span (cyan rectangles in Fig. 1), incl. but not limited to symmetry, multi-scale pattern repetition (Fig. 1a), same scale texture similarity (Fig. 1b), and structural similarity and consistency in large objects and content (Fig. 1c). To model features at this range, global image understanding is needed. + +Different from the local and regional range features, there are two major challenges to model the global range features. Firstly, existing image restoration networks based on convolutions and window attention could not capture long-range dependencies explicitly by using a single computational module. Although non-local operations are used in some works, they are either used sparsely in the network or applied to small image crops. Thus, global image under + +![](images/4fde8b78e8ba6c9af11c8f71a9614873d91aceaf93c71263ec3fcc4bc974c9a0.jpg) +Figure 2. The proposed GRL achieves state-of-the-art performances on various image restoration tasks. Details provided in Sec. 5. + +standing still mainly happens via progressive propagation of features through repeated computational modules. Secondly, the increasing resolution of today's images poses a challenge for long-range dependency modelling. High image resolution leads to a computational burden associated with pairwise pixel comparisons and similarity searches. + +The aforementioned discussion leads to a series of research questions: 1) how to efficiently model global range features in high-dimensional images for image restoration; 2) how to model image hierarchies (local, regional, global) explicitly by a single computational module for high-dimensional image restoration; 3) and how can this joint modelling lead to a uniform performance improvement for different image restoration tasks. The paper tries to answer these questions in Sec. 3, Sec. 4, and Sec. 5, resp. + +First, we propose anchored stripe self-attention for efficient dependency modelling beyond the regional range. The proposed self-attention is inspired by two properties of natural images including cross-scale similarity and anisotropic image features. Cross-scale similarity means that structures in a natural image are replicated at different scales. Inspired by that, we propose to use anchors as an intermediate to approximate the exact attention map between queries and keys in self-attention. Since the anchors summarize image information into a lower-dimensional space, the space and time complexity of self-attention can be significantly reduced. In addition, based on the observation of anisotropic image features, we propose to conduct anchored self-attention within vertical and horizontal stripes. Due to the anisotropic shrinkage of the attention range, a further reduction of complexity is achieved. And the combination of axial stripes also ensures a global view of the image content. When equipped with the stripe shift operation, the four stripe self-attention modes (horizontal, vertical, shifted horizontal, shifted vertical) achieves a good balance between computational complexity and the capacity of global range dependency modelling. Furthermore, the proposed anchored stripe self-attention is analyzed from the perspective of low-rankness and similarity propagation. + +Secondly, a new transformer network is proposed to explicitly model global, regional, and local range dependencies in a single computational module. The hierarchical modelling of images is achieved by the parallel computation of the proposed anchored stripe self-attention, window self-attention, and channel-attention enhanced convolution. And the transformer architecture is dubbed GRL. + +Thirdly, the proposed GRL transformer is applied to various image restoration tasks. Those tasks could be classified into three settings based on the availability of data including real image restoration, synthetic image restoration, and data synthesis based real image restoration. In total, seven tasks are explored for the proposed network including image super-resolution, image denoising, JPEG compression artifacts removal, demosaicking, real image superresolution, single image motion deblurring, and defocus deblurring. As shown in Fig. 2, the proposed network shows promising results on the investigated tasks. + +# 2. Related Works + +Convolution for local range modelling. One of the basic assumptions for example and learning-based image restoration is that repetitive patterns could exist in either the same or different images [17] and that the redundant information they carry could help to restore the local patches. Thus, it helps if repetitive patterns could be detected and modelled [13, 33, 44, 61]. This intuition matches the computational procedure of convolution well, which slides the kernel across the image and detects local patterns similar to the learnable kernels. By stacking multiple convolutional layers, the receptive field of a CNN gets progressively enlarged and rich image features are captured. Since the advent of deep learning, great efforts have been made to design CNNs for image restoration [26, 39, 71, 72, 86]. + +Non-local and global priors. Besides the local features, it is also important to model the non-local and global image priors. The early work of non-local means serves this purpose, which computes an output pixel as the weighted sum of all the pixels within the image [4]. Inspired by that, later works have been developed to utilize the repetitive patterns in a non-local range for image denoising [10] and superresolution [22]. Apart from the traditional methods, nonlocal operations are also introduced into deep neural networks for video classification [70] and image SR [45, 85]. + +Besides the non-local operations, self-attention has been developed to model the global range dependencies [12, 68]. However, the computational complexity of global self-attention grows quadratically with the number of tokens. Thus, the increase in efficiency of global self-attention is investigated by several works [7, 9, 31, 35, 69]. + +Regional self-attention. Among the methods for accelerating transformers, regional self-attention appears to + +be promising. The idea is proposed in the pioneering works [54, 56] and improved as shifted window attention [47, 48]. Inspired by the success of shifted window attention for visual recognition and perception, this method is also used for image restoration [6, 42, 43]. Despite the good performance of the window attention mechanism, it is pointed out in recent works that a wider range of pixel involvement could lead to better image restoration [6, 23]. Thus, in this paper, we try to propose a method that efficiently brings the modelling capacity of self-attention beyond the regional range. + +# 3. Motivation + +# 3.1. Self-attention for dependency modelling + +Self-attention is good at modelling long-range dependencies explicitly and it facilitates the propagation of information across the modelled dependencies. This operation allows a token to be compared with all the other tokens. The output token is computed as a weighted sum of all the tokens based on a similarity comparison, i.e., + +$$ +\mathbf {Y} = \operatorname {S o f t m a x} \left(\mathbf {Q} \cdot \mathbf {K} ^ {T} / \sqrt {d}\right) \cdot \mathbf {V}, \tag {1} +$$ + +where $\mathbf{Q} = \mathbf{X}\cdot \mathbf{W}_Q$ , $\mathbf{K} = \mathbf{X}\cdot \mathbf{W}_K$ , $\mathbf{V} = \mathbf{X}\cdot \mathbf{W}_V$ , $\mathbf{W}_Q, \mathbf{W}_K, \mathbf{W}_V \in \mathbb{R}^{d\times d}$ , and $\mathbf{X}, \mathbf{Y} \in \mathbb{R}^{N\times d}$ . $N$ and $d$ denote the number of tokens and the dimension of one token, respectively. Additionally, $\mathbf{M}$ denotes the attention map, i.e. $\mathbf{M} = \mathrm{Softmax}(\mathbf{Q}\cdot \mathbf{K}^T / \sqrt{d})$ . + +The time complexity of self-attention is $\mathcal{O}(N^2 d)$ and the space complexity is dominated by the term $\mathcal{O}(N^2)$ of the attention map $\mathbf{M}$ . The computational complexity and memory footprint of self-attention grow quadratically with the number of tokens. Thus, self-attention can easily become a computation bottleneck for images where the number of tokens is the multiplication of the two dimensions of the feature map. To overcome this problem, it is proposed to apply self-attention within a window. In this way, the number of tokens that participate in self-attention is significantly reduced and the computational burden is also lifted. + +The problem of window self-attention is that the modelling capacity of the operation is limited to a regional range due to the small window size $(8\times 8$ [43]). On the other hand, it is shown in recent works [6,23] that even a slight increase in window size can lead to better image restoration. Thus, it can be conjectured that modelling dependencies beyond the regional range is still important for image restoration. Hence, it remained to be investigated how to maintain the ability for long-range dependency modelling under a controlled computational budget. + +# 3.2. Motivation I: cross-scale similarity + +The attention map $\mathbf{M}$ plays an essential role in selfattention as it captures the similarity between every paired + +![](images/c72472b6788e684f2b194108e6a409a526d7c9b9794ab8a0e2d92dc451ec4930.jpg) +Figure 3. Cross-scale similarity. (c) and (d) shows the attention map between the selected pixels and the example high-resolution image. Although the cyan pixel in (a) and the red pixel in (b) are from images with different resolutions, their attention map with respect to the high-resolution image shows very similar structures. + +pixels in the image. Thus, improving the efficiency of the self-attention in Eq. (1) needs one to analyze the property of the attention map. And we are inspired by a property of images, i.e. cross-scale similarity. That is, the basic structure such as lines and edges of an image is kept in the different versions of the image with different scaling factors. In Fig. 3, the attention map between pixels in an image is shown. Particularly, the attention map between a pixel and the whole image is visualized as a gray-scale heat map. As shown, no matter whether the pixel comes from the high-resolution image or the down-scaled version, the heat map between the pixel and the high-resolution image shows the basic structure of the image. And the heat maps in Fig. 3(c) and Fig. 3(d) are very similar to each other. + +Anchored self-attention. Inspired by the cross-scale similarity shown in Fig. 3, we try to reduce the complexity of the global self-attention in Eq. (1) by operating on images with different resolutions and manipulating the number of tokens, i.e. the $N^2$ term in $\mathcal{O}(N^2 d)$ . To achieve that, we introduce an additional concept named anchors besides the triplets of queries, keys, and values. The set of anchors is a summary of the information in the image feature map and has a lower dimensionality. Instead of conducting the similarity comparison between the queries and keys directly, the anchors act as an intermediate for the similarity comparison. Formally, the anchored self-attention is proposed as in the following equation + +$$ +\mathbf {Y} = \mathbf {M} _ {e} \cdot \mathbf {Z} = \mathbf {M} _ {e} \cdot \left(\mathbf {M} _ {d} \cdot \mathbf {V}\right), \tag {2} +$$ + +$$ +\mathbf {M} _ {d} = \operatorname {S o f t m a x} \left(\mathbf {A} \cdot \mathbf {K} ^ {T} / \sqrt {d}\right), \tag {3} +$$ + +$$ +\mathbf {M} _ {e} = \operatorname {S o f t m a x} \left(\mathbf {Q} \cdot \mathbf {A} ^ {T} / \sqrt {d}\right), \tag {4} +$$ + +where $M \ll N$ , $\mathbf{A} \in \mathbb{R}^{M \times d}$ is the anchor, $\mathbf{M}_e \in \mathcal{R}^{N \times M}$ and $\mathbf{M}_d \in \mathcal{R}^{M \times N}$ denotes the attention map between the query-anchor pair and anchor-key pair. The choice of the operations to derive the anchors is investigated in the implementation details of the ablation study of the paper. + +Since the number of anchors is much smaller than the number of the other tokens, the size of the resulting two attention maps $\mathbf{M}_e$ and $\mathbf{M}_d$ are much smaller than the orig + +![](images/aa64f8a27a81c585982e02934d681ba022d48f1c9a918907f89f653edfd9502c.jpg) +(a) + +![](images/a08c323f933f9eb792953af3edac8de14b4bdf9a57d0c9276818f7be1c0e9281.jpg) +(b) + +![](images/6a09d43d95a02fa59a6ed816ef2fbe25fc3c7d0812bc1df440d32744007052d6.jpg) +(c) + +![](images/99858ec5a3d4e561f21052374422e329dc090b705ae56074671c337e8662b2d9.jpg) + +![](images/5e83a2bcf6df1186ea8dc08d2069d287aacac32e3b4417e7a7c4950e62cfda3d.jpg) +(e) + +![](images/3a7365b3e9f81a481384db8e5910305d107bb71223166a6437f71bc5611e2c80.jpg) +(f) + +![](images/f12da035661fac66ca2e6db7d2e51dd7c277907bc41998187f4efff4711fc6c2.jpg) +(g) +Figure 4. The image features in natural images are anisotropic. Thus, it is not always necessary to employ the uniform global range attention in all parts of the image. + +![](images/2cb0a1f5fb88335fa634389ffe8bab8869e74f13aae0e1f4ab92badd3640bfbf.jpg) +(h) + +inal attention map $\mathbf{M}$ in Eq. (1). Then the matrix multiplication in Eq. (2) is computed from the right hand. The self-attention is first done for the anchors and keys. The attention map $\mathbf{M}_d$ distills the tokens $\mathbf{V}$ into an intermediate feature $\mathbf{Z}$ . Then the self-attention is done between the queries and the anchors. The second attention map $\mathbf{M}_e$ expands the size of the feature $\mathbf{Z}$ and recovers the information in $\mathbf{V}$ . The computational complexity of the anchored self-attention is reduced to $\mathcal{O}(NMd)$ . And the space complexity is reduced to $\mathcal{O}(NM)$ . + +# 3.3. Motivation II: anisotropic image features + +The anchored self-attention could reduce the space and time complexity of the self-attention in Eq. (1) significantly by removing the quadratic term $N^2$ . Yet, for image restoration tasks, the remaining term $N$ is the multiplication of the width and height of the image. Thus, the complexity of the anchored self-attention in Eq. (2) could still be unaffordable due to the large term $N$ . Thus, it is desirable to further reduce the complexity of the anchored self-attention. + +To achieve that goal, we resort to another characteristic of natural images, i.e., the anisotropic image features. As shown in Fig. 4, the natural image features such as the single object in Fig. 4(c)&(d), the multi-scale similarity in Fig. 4(h), symmetry in Fig. 4(e)&(g) span in an anisotropic manner. Thus, isotropic global range attention across the entire image is redundant to capture the anisotropic image features. And in response to that, we propose to conduct attention within the anisotropic stripes shown in Fig. 4. + +Stripe attention mechanism. The proposed stripe attention mechanism consists of four modes including the horizontal stripe, the vertical stripe, the shifted horizontal stripe, and the shifted vertical stripe. The horizontal and vertical stripe attention mechanisms could be employed alternately across a transformer network. In this way, a trade-off is made between maintaining the global range modelling capacity and controlling the computation complexity of global self-attention. Thus, in combination with the concept of anchors, we propose the anchored stripe self-attention. + +![](images/216eea99595506323707652d41af117b8d27dbb1e6a3cadb12ed9b373c111268.jpg) + +![](images/ae83d6c7609bbf801189fc3451a3ac4c0aca0b943dc45c3ebf183904c5ce3bde.jpg) + +![](images/f3d0ac7b181fc358cfafd18ecd7ea47e0f3d4f18ef199aea4d13277254872fb9.jpg) + +![](images/210d501e35ca59f61b09847af5f42c2968f11652ccda9f10eddaf1acaa1caeb7.jpg) +(a) Query +(b) Anchor +(d) Attention map via anchors +Figure 5. The visualization of the (a) queries, (b) anchors, and (c) keys from the different layers of the proposed network. (d) shows the attention map approximated by Eq. (2), i.e. $\mathbf{M}_e\cdot \mathbf{M}_d$ (e) shows the exact attention map $\mathbf{M}$ computed in Eq. (1). + +![](images/04b96cb264b3595d4423e928e081b471b49eb8870ccbc1b13545438c7ed4093a.jpg) +(c) Key +(e) Direct attention map + +For this attention mechanism, efficient self-attention is conducted inside the vertical and horizontal stripes with the help of the introduced anchors. + +# 3.4. Discussion + +The proposed anchored stripe self-attention mechanism is closely related to two other concepts including low-rankness and similarity propagation. And we detail the relationship in this subsection as follows. + +Low-rankness of attention map. By comparing the self-attention mechanisms in Eq. (1) and Eq. (2), we can easily found out that the original attention map $\mathbf{M}$ is decomposed into small attention maps $\mathbf{M}_d$ and $\mathbf{M}_e$ whose rank is no larger than $M$ . And the essence here is to provide the low-rank approximation without calculating the original attention map first. For the success of the anchored self-attention, it is important to ensure that with the anchors as the intermediate, the approximated attention map is similar to the original attention map. Thus, an additional analysis is provided in Fig. 5. + +First, by observing the queries, anchors, and keys, we can conclude that the anchors have a very similar structure to the query and key. Thus, the anchors are a good summary of the information in the queries and keys. And approximating self-attention with anchors as intermediate seems to be plausible. Additionally, the approximate attention map $\mathbf{M}_e\cdot \mathbf{M}_d$ and the exact attention map $\mathbf{M}$ are also compared in Fig. 5. As shown, the approximate attention map keeps the major structure in the exact attention map, which is confirmed by the large Pearson correlation coefficients (0.9505) between the two attention maps. Thus, the quality of the anchored self-attention is guaranteed. + +Metric and similarity propagation. From another perspective, in the proposed anchored self-attention, the queries and keys are first compared with the anchors and + +![](images/52b52556b2feb4068d1cb83f06e815391d7caa4416ada74daf6717728696eefa.jpg) + +![](images/809201fc804abe1d93233a4b79616569de5cbb11f0c47706e5c2fe2cbebb0f0a.jpg) + +![](images/0e4121212154a51327a5d66840e814fcec4f299440fb31c1e1da8199f00f3b03.jpg) +Figure 6. Network architecture. (a) The representation learning module contains stages of transformer layers. (b) The transformer layer is equipped with global, regional, and local modelling blocks. (c) The anchored stripe attention helps to attend beyond regional ranges. + +then the query-key similarity is computed. Thus, this computation procedure needs to propagate the query-anchor and key-anchor similarity to the query-key pair. And similarity propagation is related to the triangle inequality in a metric space [19, 27, 73]. A mathematical metric needs to satisfy several conditions including the essential triangle inequality, $d(\mathbf{q}, \mathbf{k}) \leq d(\mathbf{a}, \mathbf{q}) + d(\mathbf{a}, \mathbf{k})$ , where $d(\cdot, \cdot)$ defines a metric between two entities. Thus, the $\mathbf{q} / \mathbf{k}$ distance is upper-bounded by the sum of the $\mathbf{a} / \mathbf{q}$ distance and the $\mathbf{a} / \mathbf{k}$ distance. This implies that if $\mathbf{a}$ is similar (close) to both $\mathbf{q}$ and $\mathbf{k}$ , then $\mathbf{q}$ and $\mathbf{k}$ should also be similar (close) to each other. Yet, the similarity measure in Eq. (1) and Eq. (2) is defined by the dot product instead of the distance between tokens, which does not satisfy the triangle inequality. Thus, similarity propagation could not be theoretically guaranteed. To study the influence of the similarity measure, an ablation study is conducted and the results are shown in Sec. 5. Dot product and distance are compared as a similarity measure. According to the results, although the dot product does not strictly obey the triangle inequality, it still guarantees better image restoration results. Thus, we can conclude empirically that the dot product is enough for similarity propagation. + +# 4. Modelling Image Hierarchies + +In this section, we answer the second research question described in the introduction, that is, how to explicitly model image hierarchies by a single computational module. + +In response to that, we propose the GRL network architecture that incorporates global range, regional range, and local range image modelling capacities. + +Network architecture. The overall architecture of the proposed network is shown in Fig. 6. The network takes a degraded low-quality image as input, processes the image inside the network, and outputs a recovered high-quality image. In detail, the network contains three parts. 1) The feature extraction layer is implemented as a simple convolution and converts the input image into feature maps. 2) The representation learning component enriches the information extracted in the previous operation. The transformer stage consists of several transformer layers and ends with a convolution layer. The dimension of the feature map is maintained across the whole representation learning module. Skip connection is applied to both the transformer stage and the representation learning module. 3) The image reconstruction module takes the rich features calculated by the previous operations and estimates a recovered image. + +Transformer Layer. This layer in Fig. 6b is the key component that provides the hierarchical image modelling capacity in the global, regional, and local range. This layer first processes the input feature map by the parallel self-attention module and channel attention enhanced convolutions. The convolution branch serves to capture local structures in the input feature map. On the other hand, the self-attention module contains the window attention proposed in Swin transformer V2 [47] and the anchored stripe attenuation + +Table 1. Defocus deblurring results. S: single-image defocus deblurring. D: dual-pixel defocus deblurring. + +
MethodIndoor ScenesOutdoor ScenesCombined
PSNR↑SSIM↑MAE↓LPIPS↓PSNR↑SSIM↑MAE↓LPIPS↓PSNR↑SSIM↑MAE↓LPIPS↓
EBDBS[30]25.770.7720.0400.29721.250.5990.0580.37323.450.6830.0490.336
DMENetS[40]25.500.7880.0380.29821.430.6440.0630.39723.410.7140.0510.349
JNBs[60]26.730.8280.0310.27321.100.6080.0640.35523.840.7150.0480.315
DPDNetS[1]26.540.8160.0310.23922.250.6820.0560.31324.340.7470.0440.277
KPACS[62]27.970.8520.0260.18222.620.7010.0530.26925.220.7740.0400.227
IFANs[41]28.110.8610.0260.17922.760.7200.0520.25425.370.7890.0390.217
RestormerS[76]28.870.8820.0250.14523.240.7430.0500.20925.980.8110.0380.178
GRLS-B29.060.8860.0240.13923.450.7610.0490.19626.180.8220.0370.168
DPDNetD[1]27.480.8490.0290.18922.900.7260.0520.25525.130.7860.0410.223
RDPD2[2]28.100.8430.0270.21022.820.7040.0530.29825.390.7720.0400.255
UformerD[74]28.230.8600.0260.19923.100.7280.0510.28525.650.7950.0390.243
IFAND[41]28.660.8680.0250.17223.460.7430.0490.24025.990.8040.0370.207
RestormerD[76]29.480.8950.0230.13423.970.7730.0470.17526.660.8330.0350.155
GRLD-B29.830.9030.0220.11424.390.7950.0450.15027.040.8470.0340.133
+ +Table 2. Single-image motion deblurring results. GoPro dataset [51] is used for training. + +
MethodGoPro [51]HIDE [59]Average
PSNR↑ / SSIM↑PSNR↑ / SSIM↑PSNR↑ / SSIM↑
DeblurGAN [37]28.70 / 0.85824.51 / 0.87126.61 / 0.865
Nah et al. [51]29.08 / 0.91425.73 / 0.87427.41 / 0.894
DeblurGAN-v2 [38]29.55 / 0.93426.61 / 0.87528.08 / 0.905
SRN [64]30.26 / 0.93428.36 / 0.91529.31 / 0.925
Gao et al. [20]30.90 / 0.93529.11 / 0.91330.01 / 0.924
DBGAN [81]31.10 / 0.94228.94 / 0.91530.02 / 0.929
MT-RNN [53]31.15 / 0.94529.15 / 0.91830.15 / 0.932
DMPHN [79]31.20 / 0.94029.09 / 0.92430.15 / 0.932
Suin et al. [63]31.85 / 0.94829.98 / 0.93030.92 / 0.939
SPAIR [55]32.06 / 0.95330.29 / 0.93131.18 / 0.942
MIMO-UNet+ [8]32.45 / 0.95729.99 / 0.93031.22 / 0.944
IPT [5]32.52 / -- / -- / -
MPRNet [77]32.66 / 0.95930.96 / 0.93931.81 / 0.949
Restormer [76]32.92 / 0.96131.22 / 0.94232.07 / 0.952
GRL-B (ours)33.93 / 0.96831.65 / 0.94732.79 / 0.958
+ +Table 3. Single-image motion deblurring results on RealBlur [57] dataset. The networks are trained and tested on RealBlur dataset. + +
MethodRealBlur-R [57]RealBlur-J [57]Average
PSNR↑ / SSIM↑PSNR↑ / SSIM↑PSNR↑ / SSIM↑
DeblurGAN-v2 [38]36.44 / 0.93529.69 / 0.87033.07 / 0.903
SRN [64]38.65 / 0.96531.38 / 0.90935.02 / 0.937
MPRNet [77]39.31 / 0.97231.76 / 0.92235.54 / 0.947
MIMO-UNet+ [8]- / -32.05 / 0.921- / -
MAXIM-3S [67]39.45 / 0.96232.84 / 0.93536.15 / 0.949
BANet [66]39.55 / 0.97132.00 / 0.92335.78 / 0.947
MSSNet [34]39.76 / 0.97232.10 / 0.92835.93 / 0.950
Stripformer [65]39.84 / 0.97432.48 / 0.92936.16 / 0.952
GRL-B (ours)40.20 / 0.97432.82 / 0.93236.51 / 0.953
+ +tion proposed in this paper. The feature map is split equally along the channel dimension and concatenated along the channel dimension again after the parallel processing within the two attention modules. The window attention provides the mechanism to capture the regional range dependencies. Then the feature maps outputted by the convolution module and the attention module are added to the input feature map, which is processed by the following MLP module. + +Anchored stripe self-attention. The operation of the proposed anchored stripe attention is conducted according to Eq. (2) and visualized in Fig. 6c. The dimension of different features is also shown. The triplet of $\mathbf{Q},\mathbf{K},\mathbf{V}$ is derived by plain linear projections. To summarize the information into anchors, the anchor projection is implemented as an + +average pooling layer followed by a linear projection. After the anchor projection, the resolution of the image feature map is down-scaled by a factor of $s$ along both directions. As shown in Fig. 6, the two attention maps $\mathbf{M}_d$ and $\mathbf{M}_e$ play a similar role as the original attention map $\mathbf{M}$ but with less space and time complexity. + +# 5. Experimental Results + +The experimental results are shown in this section. We answer the third research question raised in the introduction by investigating the performance of the proposed network on different image restoration tasks. Based on the data type, the investigated tasks are classified into three commonly used settings including 1) real image restoration (single-image motion deblurring, defocus deblurring), 2) image restoration based on synthetic data (image denoising, single image SR, JPEG compression artifact removal, demosaicking), and 3) real image restoration based on data synthesis. We provide three networks with different model sizes including the tiny, small, and base versions (GRL-T, GRL-S, GRL-B). For real and synthetic image restoration, Adam optimizer and $L_{1}$ loss are used to train the network with an initial learning rate $2 \times 10^{-4}$ . More details about the training dataset, training protocols, and additional visual results are shown in the supplementary material. + +# 5.1. Image deblurring + +We first investigate the performance of the proposed network on two real image restoration tasks including single-image motion deblurring, and motion deblurring. + +Single image motion deblurring. Tab. 2 and Tab. 3 show the experimental results for single image motion deblurring on synthetic datasets (GoPro [51], HIDE [59]) and real dataset (RealBlur-R [57]), respectively. Compared with the previous state-of-the-art Restormer [76], the proposed GRL achieves significant PSNR improvement of $1.01\mathrm{dB}$ on the GoPro dataset. On the HIDE dataset, the PSNR improvement is $0.43\mathrm{dB}$ . Please note that the improvement is achieved under fewer parameter budget. As shown in Tab. 4, + +Table 4. Color and grayscale image denoising results. Model complexity and prediction accuracy are shown for better comparison. + +
Method# Params [M]ColorGrayscale
CBSD68 [49]σ=15 σ=25 σ=50Kodak24 [16]σ=15 σ=25 σ=50McMaster [83]σ=15 σ=25 σ=50Urban100 [28]σ=15 σ=25 σ=50Set12 [82]σ=15 σ=25 σ=50BSD68 [49]σ=15 σ=25 σ=50Urban100 [28]σ=15 σ=25 σ=50
DnCNN [32]0.5633.9031.2427.9534.6032.1428.9533.4531.5228.6232.9830.8127.5932.8630.4427.1831.7329.2326.2332.6429.9526.26
RNAN [85]8.96--28.27--29.58--29.72--29.08--27.70--26.48--27.65
IPT [5]115.33--28.39--29.64--29.98--29.71---------
EDT-B [42]11.4834.3931.7628.5635.3732.9429.8735.6133.3430.2535.2233.0730.16---------
DRUNet [80]32.6434.3031.6928.5135.3132.8929.8635.4033.1430.0834.8132.6029.6133.2530.9427.9031.9129.4826.5933.4431.1127.96
SwinIR [43]11.7534.4231.7828.5635.3432.8929.7935.6133.2030.2235.1332.9029.8233.3631.0127.9131.9729.5026.5833.7031.3027.98
Restormer [76]26.1334.4031.7928.6035.4733.0430.0135.6133.3430.3035.1332.9630.0233.4231.0828.0031.9629.5226.6233.7931.4628.29
GRL-T0.8834.3031.6628.4535.2432.7829.6735.4933.1830.0635.0832.8429.7833.2930.9227.7831.9029.4326.4933.6631.2327.89
GRL-S3.1234.3631.7228.5135.3232.8829.7735.5933.2930.1835.2433.0730.0933.3631.0227.9131.9329.4726.5433.8431.4928.24
GRL-B19.8134.4531.8228.6235.4333.0229.9335.7333.4630.3635.5433.3530.4633.4731.1228.0332.0029.5426.6034.0931.8028.59
+ +Table 5. Classical image SR results. Results of both lightweight models and accurate models are summarized. + +
MethodScale# Params [M]Set5 [3]Set14 [78]BSD100 [49]Urban100 [28]Manga109 [50]
PSNR↑SSIM↑PSNR↑SSIM↑PSNR↑SSIM↑PSNR↑SSIM↑PSNR↑SSIM↑
RCAN [84]×215.4438.270.961434.120.921632.410.902733.340.938439.440.9786
SAN [11]×215.7138.310.962034.070.921332.420.902833.100.937039.320.9792
HAN [52]×263.6138.270.961434.160.921732.410.902733.350.938539.460.9785
IPT [5]×2115.4838.37-34.43-32.48-33.76---
SwinIR [43]×20.8838.140.961133.860.920632.310.901232.760.934039.120.9783
SwinIR [43]×211.7538.420.962334.460.925032.530.904133.810.942739.920.9797
EDT [42]×20.9238.230.961533.990.920932.370.902132.980.936239.450.9789
EDT [42]×211.4838.630.963234.800.927332.620.905234.270.945640.370.9811
GRL-T (ours)×20.8938.270.962734.210.925832.420.905633.600.941139.610.9790
GRL-S (ours)×23.3438.370.963234.640.928032.520.906934.360.946339.840.9793
GRL-B (ours)×220.0538.670.964735.080.930332.670.908735.060.950540.670.9818
RCAN [84]×415.5932.630.900228.870.788927.770.743626.820.808731.220.9173
SAN [11]×415.8632.640.900328.920.788827.780.743626.790.806831.180.9169
HAN [52]×464.2032.640.900228.900.789027.800.744226.850.809431.420.9177
IPT [5]×4115.6332.64-29.01-27.82-27.26---
SwinIR [43]×40.9032.440.897628.770.785827.690.740626.470.798030.920.9151
SwinIR [43]×411.9032.920.904429.090.795027.920.748927.450.825432.030.9260
EDT [42]×40.9232.530.899128.880.788227.760.743326.710.805131.350.9180
EDT [42]×411.6333.060.905529.230.797127.990.751027.750.831732.390.9283
GRL-T (ours)×40.9132.560.902928.930.796127.770.752327.150.818531.570.9219
GRL-S (ours)×43.4932.760.905829.100.800727.900.756827.900.835732.110.9267
GRL-B (ours)×420.2033.100.909429.370.805828.010.761128.530.850432.770.9325
+ +GRL-B saves $24\%$ parameters compared with Restormer. As shown in Tab. 3, GRL-B sets the new state-of-the-art performance of 40.20 PSNR on RealBlur-R dataset. + +Defocus deblurring. Tab. 1 shows the experimental results for defocus deblurring using single image and dual-pixel images. Our GRL outperforms the previous methods for all three scene types. Compared with Restormer on the combined scenes, our GRL achieves an elegant performance boost of $0.20\mathrm{dB}$ and $0.38\mathrm{dB}$ for single and dual-pixel defocus deblurring. Compared with Uformer [74] and IFAN [41], GRL achieves PSNR gain of $1.39\mathrm{dB}$ and $1.05\mathrm{dB}$ for the dual-pixel setting. + +# 5.2. Image restoration based on synthetic data + +Investigating image restoration with synthetic data is also valuable to reveal the network capacity of restoration methods. Besides the experiments on the real data, we also study the performance of the network on synthetic data. + +Image denoising. First, the experimental results on Gaussian image denoising are shown in Tab. 4. For a fair comparison between different models, both the network complexity and accuracy are shown in the table. And several key find + +ings are observed. I. The tiny version GRL-T is extremely efficient, reducing model complexity by two orders of magnitude (only $0.76\%$ of [5] and $2.7\%$ of DRUNet [80]) while not sacrificing network accuracy. II. The small version GRL-S performs competitive with the previous state-of-the-art SwinIR [43] and Restormer [76]. III. On Urban100, the base version outperforms Restormer by a large margin (e.g. 0.44dB PSNR gain for color image and noise level 50). + +Image SR. Experimental results for classical images are shown in Tab. 5. Both lightweight models and accurate SR models are summarized. A similar conclusion could be drawn from the results. I. Among the lightweight networks, GRL-T outperforms both convolution and self-attention-based networks including DBPN [25], SwinIR [43] and EDT [42]. Compared with EDT, Significant improvements are obtained on Urban100 and Manga109 datasets (0.44 dB and 0.22 dB for $\times 4$ SR). II. GRL-B sets the new state-of-the-art for accurate image SR. III. GRL-S achieves a good balance between network complexity and SR image quality. + +JPEG compression artifact removal. The experimental results for color and grayscale images are shown in Tab. 6. Four image quality factors ranging from 10 to 40 for JPEG + +
SetQFJPEG PSNR SSIMDnCNN [82] PSNR SSIMDCSC [18] PSNR SSIMQGAC [14] PSNR SSIMMWCNN [46] PSNR SSIMFBCNN [29] PSNR SSIMGRL-S PSNR SSIM
Classic5 [15]1027.82 0.76029.40 0.80329.62 0.81029.84 0.81230.01 0.82030.12 0.82230.20 0.829
2030.12 0.83431.63 0.86131.81 0.86431.98 0.86932.16 0.87032.31 0.87232.49 0.878
3031.48 0.86732.91 0.88633.06 0.88833.22 0.89233.43 0.89333.54 0.89433.72 0.899
4032.43 0.88533.77 0.90033.87 0.90234.05 0.90534.27 0.90634.35 0.90734.53 0.911
BSD500 [49]1027.80 0.76829.21 0.80929.32 0.81329.46 0.82129.61 0.82029.67 0.82129.74 0.823
2030.05 0.84931.53 0.87831.63 0.88031.73 0.88431.92 0.88532.00 0.88532.05 0.885
3031.37 0.88432.90 0.90732.99 0.90833.07 0.91233.30 0.91233.37 0.91333.43 0.912
4032.30 0.90333.85 0.92333.92 0.92434.01 0.92734.27 0.92834.33 0.92834.38 0.928
+ +Table 6. Grayscale image JPEG compression artifact removal results. As a compar- Table 7. Color image JPEG compression artifact ison metric, the parameter count of FBCNN [29] GRL-S are 71.92M and 3.12M. removal results. + +
SetQFJPEG PSNR SSIMQGAC [14] PSNR SSIMFBCNN [29] PSNR SSIMGRL-S PSNR SSIM
LIVE1 [58]1025.69 0.74327.62 0.80427.77 0.80328.13 0.814
2028.06 0.82629.88 0.86830.11 0.86830.49 0.878
3029.37 0.86131.17 0.89631.43 0.89731.85 0.905
4030.28 0.88232.05 0.91232.34 0.91332.79 0.920
BSD500 [49]1025.84 0.74127.74 0.80227.85 0.79928.26 0.808
2028.21 0.82730.01 0.86930.14 0.86730.57 0.875
3029.57 0.86531.33 0.89831.45 0.89731.92 0.903
4030.52 0.88732.25 0.91532.36 0.91332.86 0.919
+ +Table 8. Image demosaicking results. + +
DatasetsMatlabDDR [75]DeepJoint [21]MMNet [36]RLDD [24]RNAN [85]DRUNet [80]GRL-S (ours)
Kodak [16]35.7841.1142.0040.1942.4943.1642.6843.57
McMaster [83]34.4337.1239.1437.0939.2539.7039.3940.22
+ +![](images/73f89d3c33902e560790816e0067283be68bcec4b80d23ec03d9ebb1fee8aba6.jpg) +Figure 7. Visual results for real-world image SR. + +compression are studied. As shown in the table, the proposed GRL-S network outperforms the previous state-of-the-art method elegantly across different datasets and quality factors. Notably, GRL-S has a much smaller model complexity than FBCNN. + +Demosaicking. Results for image demosaicking is shown in Tab. 8. The proposed method outperforms the previous methods RNAN [85] and DRUNet [80] significantly. + +# 5.3. Real image restoration based on data synthesis + +Finally, we also investigate the performance of the network for real-world image restoration. The aim is to superresolve a low-quality image by an upscaling factor of 4. Since there are no ground-truth images for this task, only the visual comparison is given in Fig. 7. Compared with the other methods, the proposed GRL is able to remove more artifacts in the low-resolution images. + +# 5.4. Ablation study + +Influence of the similarity comparison method. As mentioned in Sec. 3.4, for theoretical guarantee of similarity propagation, a mathematical metric rather than a dot product should be used. To study the difference between, image restoration with the two operations are compared and the results are shown in Tab. 9. As revealed by the table, the dot + +Table 9. Ablation study on similarity comparison operation. + +
Test setMetricColor DNGray DNImage SR
σ15σ25σ50σ15σ25σ50×2×3×4
BSD68 or BSD100Euclidean35.0232.5629.4231.8429.3626.4332.3029.1927.67
Dot product35.1032.6429.5431.8529.3926.4432.3329.2227.70
Urban100Euclidean34.6332.2828.9433.2530.6427.1732.7628.6226.50
Dot product34.7732.4129.1933.2830.7527.2632.8828.7826.67
+ +Table 10. Ablation study on anchor projection operation. + +
Anchor projection operation# Params [m]PSNR on Set 5
Depthwise Conv3.1735.03
Conv4.1935.03
Patch merging3.5334.98
Maxpool + Linear Projection3.1235.02
Avgpool + Linear Projection3.1235.03
+ +product is very competitive compared with a metric and it outperforms a distance metric for a couple of settings. Considering this, the dot product is still used. + +Influence of the anchor projections. The anchor projection operation helps to summarize the information in the feature map. The ablation study is shown in Tab. 10. Considering both the accuracy performance and parameter budget, Avgpool followed by linear projection is finally used. + +# 6. Conclusion + +In this paper, we proposed GRL, a network with efficient and explicit hierarchical modelling capacities for image restoration. The proposed network was mainly inspired by two image properties including cross-scale similarity and anisotropic image features. Based on that, we proposed the efficient anchored stripe self-attention module for long-range dependency modelling. Then a versatile network architecture was proposed for image restoration. 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In Proceedings of the IEEE Conference on Computer Vision and Pattern Recognition, 2018. 2 \ No newline at end of file diff --git a/2023/Efficient and Explicit Modelling of Image Hierarchies for Image Restoration/images.zip b/2023/Efficient and Explicit Modelling of Image Hierarchies for Image Restoration/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..1587ff4d997ac407061543b6cef17f2faf5d995c --- /dev/null +++ b/2023/Efficient and Explicit Modelling of Image Hierarchies for Image Restoration/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:a1a02ab111d0cbb62f7ed65b6d7def92377c2e238edec78edddd3fe3f8c0f18d +size 1143259 diff --git a/2023/Efficient and Explicit Modelling of Image Hierarchies for Image Restoration/layout.json b/2023/Efficient and Explicit Modelling of Image Hierarchies for Image Restoration/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..725cf57043ba0ddc27d3bf10e7d7fab30fb945a1 --- /dev/null +++ b/2023/Efficient and Explicit Modelling of Image Hierarchies for Image Restoration/layout.json @@ -0,0 +1,10285 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 61, + 103, + 532, + 120 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 61, + 103, + 532, + 120 + ], + "spans": [ + { + "bbox": [ + 61, + 103, + 532, + 120 + ], + "type": "text", + "content": "Efficient and Explicit Modelling of Image Hierarchies for Image Restoration" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 138, + 142, + 459, + 157 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 138, + 142, + 459, + 157 + ], + "spans": [ + { + "bbox": [ + 138, + 142, + 459, + 157 + ], + "type": "text", + "content": "Yawei Li1 Yuchen Fan2 Xiaoyu Xiang2 Denis Demandolx2" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 167, + 157, + 432, + 171 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 167, + 157, + 432, + 171 + ], + "spans": [ + { + "bbox": [ + 167, + 157, + 432, + 171 + ], + "type": "text", + "content": "Rakesh Ranjan" + }, + { + "bbox": [ + 167, + 157, + 432, + 171 + ], + "type": "inline_equation", + "content": "^{2}" + }, + { + "bbox": [ + 167, + 157, + 432, + 171 + ], + "type": "text", + "content": " Radu Timofte" + }, + { + "bbox": [ + 167, + 157, + 432, + 171 + ], + "type": "inline_equation", + "content": "^{1,3}" + }, + { + "bbox": [ + 167, + 157, + 432, + 171 + ], + "type": "text", + "content": " Luc Van Gool" + }, + { + "bbox": [ + 167, + 157, + 432, + 171 + ], + "type": "inline_equation", + "content": "^{1,4}" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 54, + 171, + 547, + 186 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 54, + 171, + 547, + 186 + ], + "spans": [ + { + "bbox": [ + 54, + 171, + 547, + 186 + ], + "type": "text", + "content": "1Computer Vision Lab, ETH Zürich 2Meta Reality Labs 3University of Würzburg 4KU Leuven" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 143, + 213, + 192, + 225 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 213, + 192, + 225 + ], + "spans": [ + { + "bbox": [ + 143, + 213, + 192, + 225 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 238, + 290, + 467 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 238, + 290, + 467 + ], + "spans": [ + { + "bbox": [ + 46, + 238, + 290, + 467 + ], + "type": "text", + "content": "The aim of this paper is to propose a mechanism to efficiently and explicitly model image hierarchies in the global, regional, and local range for image restoration. To achieve that, we start by analyzing two important properties of natural images including cross-scale similarity and anisotropic image features. Inspired by that, we propose the anchored stripe self-attention which achieves a good balance between the space and time complexity of self-attention and the modelling capacity beyond the regional range. Then we propose a new network architecture dubbed GRL to explicitly model image hierarchies in the Global, Regional, and Local range via anchored stripe self-attention, window self-attention, and channel attention enhanced convolution. Finally, the proposed network is applied to 7 image restoration types, covering both real and synthetic settings. The proposed method sets the new state-of-the-art for several of those. 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Thus, in order to recover a high-quality image, the rich information exhibited in the degraded image should be fully exploited." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 617, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 617, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 617, + 287, + 715 + ], + "type": "text", + "content": "Natural images contain a hierarchy of features at global, regional, and local ranges which could be used by deep neural networks for image restoration. First, the local range covers a span of several pixels and typical features are edges and local colors. To model such local features, convolutional neural networks (CNNs) with small kernels (e.g. " + }, + { + "bbox": [ + 46, + 617, + 287, + 715 + ], + "type": "inline_equation", + "content": "3 \\times 3" + }, + { + "bbox": [ + 46, + 617, + 287, + 715 + ], + "type": "text", + "content": ") are utilized. 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Natural images show a hierarchy of features in a global, regional, and local range. The local (edges, colors) and regional features (the pink squares) could be well modelled by CNNs and window self-attention. By contrast, it is difficult to efficiently and explicitly model the rich global features (cyan rectangles)." + } + ] + } + ], + "index": 17, + "angle": 0, + "type": "image_caption" + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 470, + 546, + 615 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 470, + 546, + 615 + ], + "spans": [ + { + "bbox": [ + 304, + 470, + 546, + 615 + ], + "type": "text", + "content": "els can cover small objects and components of large objects (pink squares in Fig. 1). Due to the larger range, modelling the regional features (consistency, similarity) explicitly with large-kernel CNNs would be inefficient in both parameters and computation. Instead, transformers with a window attention mechanism are well suited for this task. Third, beyond local and regional, some features have a global span (cyan rectangles in Fig. 1), incl. but not limited to symmetry, multi-scale pattern repetition (Fig. 1a), same scale texture similarity (Fig. 1b), and structural similarity and consistency in large objects and content (Fig. 1c). To model features at this range, global image understanding is needed." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "type": "text", + "content": "Different from the local and regional range features, there are two major challenges to model the global range features. Firstly, existing image restoration networks based on convolutions and window attention could not capture long-range dependencies explicitly by using a single computational module. Although non-local operations are used in some works, they are either used sparsely in the network or applied to small image crops. Thus, global image under" + } + ] + } + ], + "index": 19 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 494, + 35 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 494, + 35 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 494, + 35 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "18278" + } + ] + } + ], + "index": 20 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 49, + 77, + 541, + 140 + ], + "blocks": [ + { + "bbox": [ + 49, + 77, + 541, + 140 + ], + "lines": [ + { + "bbox": [ + 49, + 77, + 541, + 140 + ], + "spans": [ + { + "bbox": [ + 49, + 77, + 541, + 140 + ], + "type": "image", + "image_path": "4fde8b78e8ba6c9af11c8f71a9614873d91aceaf93c71263ec3fcc4bc974c9a0.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 59, + 144, + 532, + 154 + ], + "lines": [ + { + "bbox": [ + 59, + 144, + 532, + 154 + ], + "spans": [ + { + "bbox": [ + 59, + 144, + 532, + 154 + ], + "type": "text", + "content": "Figure 2. The proposed GRL achieves state-of-the-art performances on various image restoration tasks. Details provided in Sec. 5." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 159, + 286, + 230 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 159, + 286, + 230 + ], + "spans": [ + { + "bbox": [ + 46, + 159, + 286, + 230 + ], + "type": "text", + "content": "standing still mainly happens via progressive propagation of features through repeated computational modules. Secondly, the increasing resolution of today's images poses a challenge for long-range dependency modelling. High image resolution leads to a computational burden associated with pairwise pixel comparisons and similarity searches." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 232, + 286, + 339 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 232, + 286, + 339 + ], + "spans": [ + { + "bbox": [ + 46, + 232, + 286, + 339 + ], + "type": "text", + "content": "The aforementioned discussion leads to a series of research questions: 1) how to efficiently model global range features in high-dimensional images for image restoration; 2) how to model image hierarchies (local, regional, global) explicitly by a single computational module for high-dimensional image restoration; 3) and how can this joint modelling lead to a uniform performance improvement for different image restoration tasks. The paper tries to answer these questions in Sec. 3, Sec. 4, and Sec. 5, resp." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 342, + 286, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 342, + 286, + 628 + ], + "spans": [ + { + "bbox": [ + 46, + 342, + 286, + 628 + ], + "type": "text", + "content": "First, we propose anchored stripe self-attention for efficient dependency modelling beyond the regional range. The proposed self-attention is inspired by two properties of natural images including cross-scale similarity and anisotropic image features. Cross-scale similarity means that structures in a natural image are replicated at different scales. Inspired by that, we propose to use anchors as an intermediate to approximate the exact attention map between queries and keys in self-attention. Since the anchors summarize image information into a lower-dimensional space, the space and time complexity of self-attention can be significantly reduced. In addition, based on the observation of anisotropic image features, we propose to conduct anchored self-attention within vertical and horizontal stripes. Due to the anisotropic shrinkage of the attention range, a further reduction of complexity is achieved. And the combination of axial stripes also ensures a global view of the image content. When equipped with the stripe shift operation, the four stripe self-attention modes (horizontal, vertical, shifted horizontal, shifted vertical) achieves a good balance between computational complexity and the capacity of global range dependency modelling. Furthermore, the proposed anchored stripe self-attention is analyzed from the perspective of low-rankness and similarity propagation." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 630, + 286, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 630, + 286, + 712 + ], + "spans": [ + { + "bbox": [ + 46, + 630, + 286, + 712 + ], + "type": "text", + "content": "Secondly, a new transformer network is proposed to explicitly model global, regional, and local range dependencies in a single computational module. The hierarchical modelling of images is achieved by the parallel computation of the proposed anchored stripe self-attention, window self-attention, and channel-attention enhanced convolution. And the transformer architecture is dubbed GRL." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 159, + 545, + 290 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 159, + 545, + 290 + ], + "spans": [ + { + "bbox": [ + 304, + 159, + 545, + 290 + ], + "type": "text", + "content": "Thirdly, the proposed GRL transformer is applied to various image restoration tasks. Those tasks could be classified into three settings based on the availability of data including real image restoration, synthetic image restoration, and data synthesis based real image restoration. In total, seven tasks are explored for the proposed network including image super-resolution, image denoising, JPEG compression artifacts removal, demosaicking, real image superresolution, single image motion deblurring, and defocus deblurring. As shown in Fig. 2, the proposed network shows promising results on the investigated tasks." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 305, + 397, + 317 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 305, + 397, + 317 + ], + "spans": [ + { + "bbox": [ + 306, + 305, + 397, + 317 + ], + "type": "text", + "content": "2. Related Works" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 327, + 545, + 494 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 327, + 545, + 494 + ], + "spans": [ + { + "bbox": [ + 304, + 327, + 545, + 494 + ], + "type": "text", + "content": "Convolution for local range modelling. One of the basic assumptions for example and learning-based image restoration is that repetitive patterns could exist in either the same or different images [17] and that the redundant information they carry could help to restore the local patches. Thus, it helps if repetitive patterns could be detected and modelled [13, 33, 44, 61]. This intuition matches the computational procedure of convolution well, which slides the kernel across the image and detects local patterns similar to the learnable kernels. By stacking multiple convolutional layers, the receptive field of a CNN gets progressively enlarged and rich image features are captured. Since the advent of deep learning, great efforts have been made to design CNNs for image restoration [26, 39, 71, 72, 86]." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 495, + 545, + 615 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 495, + 545, + 615 + ], + "spans": [ + { + "bbox": [ + 304, + 495, + 545, + 615 + ], + "type": "text", + "content": "Non-local and global priors. Besides the local features, it is also important to model the non-local and global image priors. The early work of non-local means serves this purpose, which computes an output pixel as the weighted sum of all the pixels within the image [4]. Inspired by that, later works have been developed to utilize the repetitive patterns in a non-local range for image denoising [10] and superresolution [22]. Apart from the traditional methods, nonlocal operations are also introduced into deep neural networks for video classification [70] and image SR [45, 85]." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 616, + 545, + 688 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 616, + 545, + 688 + ], + "spans": [ + { + "bbox": [ + 304, + 616, + 545, + 688 + ], + "type": "text", + "content": "Besides the non-local operations, self-attention has been developed to model the global range dependencies [12, 68]. However, the computational complexity of global self-attention grows quadratically with the number of tokens. Thus, the increase in efficiency of global self-attention is investigated by several works [7, 9, 31, 35, 69]." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "text", + "content": "Regional self-attention. Among the methods for accelerating transformers, regional self-attention appears to" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "18279" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "text", + "content": "be promising. The idea is proposed in the pioneering works [54, 56] and improved as shifted window attention [47, 48]. Inspired by the success of shifted window attention for visual recognition and perception, this method is also used for image restoration [6, 42, 43]. Despite the good performance of the window attention mechanism, it is pointed out in recent works that a wider range of pixel involvement could lead to better image restoration [6, 23]. Thus, in this paper, we try to propose a method that efficiently brings the modelling capacity of self-attention beyond the regional range." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 213, + 119, + 225 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 213, + 119, + 225 + ], + "spans": [ + { + "bbox": [ + 47, + 213, + 119, + 225 + ], + "type": "text", + "content": "3. Motivation" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 232, + 257, + 246 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 232, + 257, + 246 + ], + "spans": [ + { + "bbox": [ + 47, + 232, + 257, + 246 + ], + "type": "text", + "content": "3.1. Self-attention for dependency modelling" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 251, + 287, + 323 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 251, + 287, + 323 + ], + "spans": [ + { + "bbox": [ + 46, + 251, + 287, + 323 + ], + "type": "text", + "content": "Self-attention is good at modelling long-range dependencies explicitly and it facilitates the propagation of information across the modelled dependencies. This operation allows a token to be compared with all the other tokens. The output token is computed as a weighted sum of all the tokens based on a similarity comparison, i.e.," + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 94, + 329, + 287, + 349 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 94, + 329, + 287, + 349 + ], + "spans": [ + { + "bbox": [ + 94, + 329, + 287, + 349 + ], + "type": "interline_equation", + "content": "\\mathbf {Y} = \\operatorname {S o f t m a x} \\left(\\mathbf {Q} \\cdot \\mathbf {K} ^ {T} / \\sqrt {d}\\right) \\cdot \\mathbf {V}, \\tag {1}", + "image_path": "599bd1507dfac1993c29f1b46a252b3e66c531e4b22dedbbacad3fc74d37e825.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 354, + 287, + 413 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 354, + 287, + 413 + ], + "spans": [ + { + "bbox": [ + 46, + 354, + 287, + 413 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 354, + 287, + 413 + ], + "type": "inline_equation", + "content": "\\mathbf{Q} = \\mathbf{X}\\cdot \\mathbf{W}_Q" + }, + { + "bbox": [ + 46, + 354, + 287, + 413 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 354, + 287, + 413 + ], + "type": "inline_equation", + "content": "\\mathbf{K} = \\mathbf{X}\\cdot \\mathbf{W}_K" + }, + { + "bbox": [ + 46, + 354, + 287, + 413 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 354, + 287, + 413 + ], + "type": "inline_equation", + "content": "\\mathbf{V} = \\mathbf{X}\\cdot \\mathbf{W}_V" + }, + { + "bbox": [ + 46, + 354, + 287, + 413 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 354, + 287, + 413 + ], + "type": "inline_equation", + "content": "\\mathbf{W}_Q, \\mathbf{W}_K, \\mathbf{W}_V \\in \\mathbb{R}^{d\\times d}" + }, + { + "bbox": [ + 46, + 354, + 287, + 413 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 46, + 354, + 287, + 413 + ], + "type": "inline_equation", + "content": "\\mathbf{X}, \\mathbf{Y} \\in \\mathbb{R}^{N\\times d}" + }, + { + "bbox": [ + 46, + 354, + 287, + 413 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 46, + 354, + 287, + 413 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 354, + 287, + 413 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 354, + 287, + 413 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 46, + 354, + 287, + 413 + ], + "type": "text", + "content": " denote the number of tokens and the dimension of one token, respectively. Additionally, " + }, + { + "bbox": [ + 46, + 354, + 287, + 413 + ], + "type": "inline_equation", + "content": "\\mathbf{M}" + }, + { + "bbox": [ + 46, + 354, + 287, + 413 + ], + "type": "text", + "content": " denotes the attention map, i.e. " + }, + { + "bbox": [ + 46, + 354, + 287, + 413 + ], + "type": "inline_equation", + "content": "\\mathbf{M} = \\mathrm{Softmax}(\\mathbf{Q}\\cdot \\mathbf{K}^T / \\sqrt{d})" + }, + { + "bbox": [ + 46, + 354, + 287, + 413 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 413, + 287, + 544 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 413, + 287, + 544 + ], + "spans": [ + { + "bbox": [ + 46, + 413, + 287, + 544 + ], + "type": "text", + "content": "The time complexity of self-attention is " + }, + { + "bbox": [ + 46, + 413, + 287, + 544 + ], + "type": "inline_equation", + "content": "\\mathcal{O}(N^2 d)" + }, + { + "bbox": [ + 46, + 413, + 287, + 544 + ], + "type": "text", + "content": " and the space complexity is dominated by the term " + }, + { + "bbox": [ + 46, + 413, + 287, + 544 + ], + "type": "inline_equation", + "content": "\\mathcal{O}(N^2)" + }, + { + "bbox": [ + 46, + 413, + 287, + 544 + ], + "type": "text", + "content": " of the attention map " + }, + { + "bbox": [ + 46, + 413, + 287, + 544 + ], + "type": "inline_equation", + "content": "\\mathbf{M}" + }, + { + "bbox": [ + 46, + 413, + 287, + 544 + ], + "type": "text", + "content": ". The computational complexity and memory footprint of self-attention grow quadratically with the number of tokens. Thus, self-attention can easily become a computation bottleneck for images where the number of tokens is the multiplication of the two dimensions of the feature map. To overcome this problem, it is proposed to apply self-attention within a window. In this way, the number of tokens that participate in self-attention is significantly reduced and the computational burden is also lifted." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 545, + 287, + 665 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 545, + 287, + 665 + ], + "spans": [ + { + "bbox": [ + 46, + 545, + 287, + 665 + ], + "type": "text", + "content": "The problem of window self-attention is that the modelling capacity of the operation is limited to a regional range due to the small window size " + }, + { + "bbox": [ + 46, + 545, + 287, + 665 + ], + "type": "inline_equation", + "content": "(8\\times 8" + }, + { + "bbox": [ + 46, + 545, + 287, + 665 + ], + "type": "text", + "content": " [43]). On the other hand, it is shown in recent works [6,23] that even a slight increase in window size can lead to better image restoration. Thus, it can be conjectured that modelling dependencies beyond the regional range is still important for image restoration. Hence, it remained to be investigated how to maintain the ability for long-range dependency modelling under a controlled computational budget." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 671, + 231, + 683 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 671, + 231, + 683 + ], + "spans": [ + { + "bbox": [ + 47, + 671, + 231, + 683 + ], + "type": "text", + "content": "3.2. Motivation I: cross-scale similarity" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "content": "The attention map " + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{M}" + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "content": " plays an essential role in selfattention as it captures the similarity between every paired" + } + ] + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 313, + 70, + 541, + 155 + ], + "blocks": [ + { + "bbox": [ + 313, + 70, + 541, + 155 + ], + "lines": [ + { + "bbox": [ + 313, + 70, + 541, + 155 + ], + "spans": [ + { + "bbox": [ + 313, + 70, + 541, + 155 + ], + "type": "image", + "image_path": "c72472b6788e684f2b194108e6a409a526d7c9b9794ab8a0e2d92dc451ec4930.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 161, + 545, + 217 + ], + "lines": [ + { + "bbox": [ + 304, + 161, + 545, + 217 + ], + "spans": [ + { + "bbox": [ + 304, + 161, + 545, + 217 + ], + "type": "text", + "content": "Figure 3. Cross-scale similarity. (c) and (d) shows the attention map between the selected pixels and the example high-resolution image. Although the cyan pixel in (a) and the red pixel in (b) are from images with different resolutions, their attention map with respect to the high-resolution image shows very similar structures." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 228, + 545, + 394 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 228, + 545, + 394 + ], + "spans": [ + { + "bbox": [ + 304, + 228, + 545, + 394 + ], + "type": "text", + "content": "pixels in the image. Thus, improving the efficiency of the self-attention in Eq. (1) needs one to analyze the property of the attention map. And we are inspired by a property of images, i.e. cross-scale similarity. That is, the basic structure such as lines and edges of an image is kept in the different versions of the image with different scaling factors. In Fig. 3, the attention map between pixels in an image is shown. Particularly, the attention map between a pixel and the whole image is visualized as a gray-scale heat map. As shown, no matter whether the pixel comes from the high-resolution image or the down-scaled version, the heat map between the pixel and the high-resolution image shows the basic structure of the image. And the heat maps in Fig. 3(c) and Fig. 3(d) are very similar to each other." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 396, + 545, + 551 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 396, + 545, + 551 + ], + "spans": [ + { + "bbox": [ + 304, + 396, + 545, + 551 + ], + "type": "text", + "content": "Anchored self-attention. Inspired by the cross-scale similarity shown in Fig. 3, we try to reduce the complexity of the global self-attention in Eq. (1) by operating on images with different resolutions and manipulating the number of tokens, i.e. the " + }, + { + "bbox": [ + 304, + 396, + 545, + 551 + ], + "type": "inline_equation", + "content": "N^2" + }, + { + "bbox": [ + 304, + 396, + 545, + 551 + ], + "type": "text", + "content": " term in " + }, + { + "bbox": [ + 304, + 396, + 545, + 551 + ], + "type": "inline_equation", + "content": "\\mathcal{O}(N^2 d)" + }, + { + "bbox": [ + 304, + 396, + 545, + 551 + ], + "type": "text", + "content": ". To achieve that, we introduce an additional concept named anchors besides the triplets of queries, keys, and values. The set of anchors is a summary of the information in the image feature map and has a lower dimensionality. Instead of conducting the similarity comparison between the queries and keys directly, the anchors act as an intermediate for the similarity comparison. Formally, the anchored self-attention is proposed as in the following equation" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 361, + 559, + 545, + 572 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 361, + 559, + 545, + 572 + ], + "spans": [ + { + "bbox": [ + 361, + 559, + 545, + 572 + ], + "type": "interline_equation", + "content": "\\mathbf {Y} = \\mathbf {M} _ {e} \\cdot \\mathbf {Z} = \\mathbf {M} _ {e} \\cdot \\left(\\mathbf {M} _ {d} \\cdot \\mathbf {V}\\right), \\tag {2}", + "image_path": "7d6b87b643e55dcd1e2ca6f7f968f283fcccdc629e9a38ff5d95cb00d0864a98.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 355, + 575, + 545, + 590 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 355, + 575, + 545, + 590 + ], + "spans": [ + { + "bbox": [ + 355, + 575, + 545, + 590 + ], + "type": "interline_equation", + "content": "\\mathbf {M} _ {d} = \\operatorname {S o f t m a x} \\left(\\mathbf {A} \\cdot \\mathbf {K} ^ {T} / \\sqrt {d}\\right), \\tag {3}", + "image_path": "0748161121ba52dcd27b5c1c3496ac0efb485ad1876939d00f5bfc8984be9163.jpg" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 356, + 593, + 545, + 607 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 356, + 593, + 545, + 607 + ], + "spans": [ + { + "bbox": [ + 356, + 593, + 545, + 607 + ], + "type": "interline_equation", + "content": "\\mathbf {M} _ {e} = \\operatorname {S o f t m a x} \\left(\\mathbf {Q} \\cdot \\mathbf {A} ^ {T} / \\sqrt {d}\\right), \\tag {4}", + "image_path": "0453da19ffbca8704038861108f7a18ef3e42472e4bd28e560b2bdfb6ace76da.jpg" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 616, + 545, + 677 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 616, + 545, + 677 + ], + "spans": [ + { + "bbox": [ + 304, + 616, + 545, + 677 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 616, + 545, + 677 + ], + "type": "inline_equation", + "content": "M \\ll N" + }, + { + "bbox": [ + 304, + 616, + 545, + 677 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 616, + 545, + 677 + ], + "type": "inline_equation", + "content": "\\mathbf{A} \\in \\mathbb{R}^{M \\times d}" + }, + { + "bbox": [ + 304, + 616, + 545, + 677 + ], + "type": "text", + "content": " is the anchor, " + }, + { + "bbox": [ + 304, + 616, + 545, + 677 + ], + "type": "inline_equation", + "content": "\\mathbf{M}_e \\in \\mathcal{R}^{N \\times M}" + }, + { + "bbox": [ + 304, + 616, + 545, + 677 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 616, + 545, + 677 + ], + "type": "inline_equation", + "content": "\\mathbf{M}_d \\in \\mathcal{R}^{M \\times N}" + }, + { + "bbox": [ + 304, + 616, + 545, + 677 + ], + "type": "text", + "content": " denotes the attention map between the query-anchor pair and anchor-key pair. The choice of the operations to derive the anchors is investigated in the implementation details of the ablation study of the paper." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "text", + "content": "Since the number of anchors is much smaller than the number of the other tokens, the size of the resulting two attention maps " + }, + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{M}_e" + }, + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{M}_d" + }, + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "text", + "content": " are much smaller than the orig" + } + ] + } + ], + "index": 18 + } + 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The image features in natural images are anisotropic. Thus, it is not always necessary to employ the uniform global range attention in all parts of the image." + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_caption" + } + ], + "index": 11 + }, + { + "type": "image", + "bbox": [ + 224, + 134, + 279, + 189 + ], + "blocks": [ + { + "bbox": [ + 224, + 134, + 279, + 189 + ], + "lines": [ + { + "bbox": [ + 224, + 134, + 279, + 189 + ], + "spans": [ + { + "bbox": [ + 224, + 134, + 279, + 189 + ], + "type": "image", + "image_path": "2cb0a1f5fb88335fa634389ffe8bab8869e74f13aae0e1f4ab92badd3640bfbf.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 247, + 190, + 256, + 197 + ], + "lines": [ + { + "bbox": [ + 247, + 190, + 256, + 197 + ], + "spans": [ + { + "bbox": [ + 247, + 190, + 256, + 197 + ], + "type": "text", + "content": "(h)" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_caption" + } + ], + "index": 13 + }, + { + "bbox": [ + 46, + 239, + 286, + 358 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 239, + 286, + 358 + ], + "spans": [ + { + "bbox": [ + 46, + 239, + 286, + 358 + ], + "type": "text", + "content": "inal attention map " + }, + { + "bbox": [ + 46, + 239, + 286, + 358 + ], + "type": "inline_equation", + "content": "\\mathbf{M}" + }, + { + "bbox": [ + 46, + 239, + 286, + 358 + ], + "type": "text", + "content": " in Eq. (1). Then the matrix multiplication in Eq. (2) is computed from the right hand. The self-attention is first done for the anchors and keys. The attention map " + }, + { + "bbox": [ + 46, + 239, + 286, + 358 + ], + "type": "inline_equation", + "content": "\\mathbf{M}_d" + }, + { + "bbox": [ + 46, + 239, + 286, + 358 + ], + "type": "text", + "content": " distills the tokens " + }, + { + "bbox": [ + 46, + 239, + 286, + 358 + ], + "type": "inline_equation", + "content": "\\mathbf{V}" + }, + { + "bbox": [ + 46, + 239, + 286, + 358 + ], + "type": "text", + "content": " into an intermediate feature " + }, + { + "bbox": [ + 46, + 239, + 286, + 358 + ], + "type": "inline_equation", + "content": "\\mathbf{Z}" + }, + { + "bbox": [ + 46, + 239, + 286, + 358 + ], + "type": "text", + "content": ". Then the self-attention is done between the queries and the anchors. The second attention map " + }, + { + "bbox": [ + 46, + 239, + 286, + 358 + ], + "type": "inline_equation", + "content": "\\mathbf{M}_e" + }, + { + "bbox": [ + 46, + 239, + 286, + 358 + ], + "type": "text", + "content": " expands the size of the feature " + }, + { + "bbox": [ + 46, + 239, + 286, + 358 + ], + "type": "inline_equation", + "content": "\\mathbf{Z}" + }, + { + "bbox": [ + 46, + 239, + 286, + 358 + ], + "type": "text", + "content": " and recovers the information in " + }, + { + "bbox": [ + 46, + 239, + 286, + 358 + ], + "type": "inline_equation", + "content": "\\mathbf{V}" + }, + { + "bbox": [ + 46, + 239, + 286, + 358 + ], + "type": "text", + "content": ". The computational complexity of the anchored self-attention is reduced to " + }, + { + "bbox": [ + 46, + 239, + 286, + 358 + ], + "type": "inline_equation", + "content": "\\mathcal{O}(NMd)" + }, + { + "bbox": [ + 46, + 239, + 286, + 358 + ], + "type": "text", + "content": ". And the space complexity is reduced to " + }, + { + "bbox": [ + 46, + 239, + 286, + 358 + ], + "type": "inline_equation", + "content": "\\mathcal{O}(NM)" + }, + { + "bbox": [ + 46, + 239, + 286, + 358 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 47, + 369, + 262, + 382 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 369, + 262, + 382 + ], + "spans": [ + { + "bbox": [ + 47, + 369, + 262, + 382 + ], + "type": "text", + "content": "3.3. Motivation II: anisotropic image features" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 46, + 388, + 286, + 483 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 388, + 286, + 483 + ], + "spans": [ + { + "bbox": [ + 46, + 388, + 286, + 483 + ], + "type": "text", + "content": "The anchored self-attention could reduce the space and time complexity of the self-attention in Eq. (1) significantly by removing the quadratic term " + }, + { + "bbox": [ + 46, + 388, + 286, + 483 + ], + "type": "inline_equation", + "content": "N^2" + }, + { + "bbox": [ + 46, + 388, + 286, + 483 + ], + "type": "text", + "content": ". Yet, for image restoration tasks, the remaining term " + }, + { + "bbox": [ + 46, + 388, + 286, + 483 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 388, + 286, + 483 + ], + "type": "text", + "content": " is the multiplication of the width and height of the image. Thus, the complexity of the anchored self-attention in Eq. (2) could still be unaffordable due to the large term " + }, + { + "bbox": [ + 46, + 388, + 286, + 483 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 388, + 286, + 483 + ], + "type": "text", + "content": ". Thus, it is desirable to further reduce the complexity of the anchored self-attention." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 46, + 485, + 286, + 593 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 485, + 286, + 593 + ], + "spans": [ + { + "bbox": [ + 46, + 485, + 286, + 593 + ], + "type": "text", + "content": "To achieve that goal, we resort to another characteristic of natural images, i.e., the anisotropic image features. As shown in Fig. 4, the natural image features such as the single object in Fig. 4(c)&(d), the multi-scale similarity in Fig. 4(h), symmetry in Fig. 4(e)&(g) span in an anisotropic manner. Thus, isotropic global range attention across the entire image is redundant to capture the anisotropic image features. And in response to that, we propose to conduct attention within the anisotropic stripes shown in Fig. 4." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 46, + 594, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 594, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 286, + 713 + ], + "type": "text", + "content": "Stripe attention mechanism. The proposed stripe attention mechanism consists of four modes including the horizontal stripe, the vertical stripe, the shifted horizontal stripe, and the shifted vertical stripe. The horizontal and vertical stripe attention mechanisms could be employed alternately across a transformer network. In this way, a trade-off is made between maintaining the global range modelling capacity and controlling the computation complexity of global self-attention. Thus, in combination with the concept of anchors, we propose the anchored stripe self-attention." + } + ] + } + ], + "index": 20 + }, + { + "type": "image", + "bbox": [ + 328, + 70, + 394, + 138 + ], + "blocks": [ + { + "bbox": [ + 328, + 70, + 394, + 138 + ], + "lines": [ + { + "bbox": [ + 328, + 70, + 394, + 138 + ], + "spans": [ + { + "bbox": [ + 328, + 70, + 394, + 138 + ], + "type": "image", + "image_path": "216eea99595506323707652d41af117b8d27dbb1e6a3cadb12ed9b373c111268.jpg" + } + ] + } + ], + "index": 21, + "angle": 0, + "type": "image_body" + } + ], + "index": 21 + }, + { + "type": "image", + "bbox": [ + 402, + 91, + 436, + 125 + ], + "blocks": [ + { + "bbox": [ + 402, + 91, + 436, + 125 + ], + "lines": [ + { + "bbox": [ + 402, + 91, + 436, + 125 + ], + "spans": [ + { + "bbox": [ + 402, + 91, + 436, + 125 + ], + "type": "image", + "image_path": "ae83d6c7609bbf801189fc3451a3ac4c0aca0b943dc45c3ebf183904c5ce3bde.jpg" + } + ] + } + ], + "index": 23, + "angle": 0, + "type": "image_body" + } + ], + "index": 23 + }, + { + "type": "image", + "bbox": [ + 443, + 70, + 510, + 138 + ], + "blocks": [ + { + "bbox": [ + 443, + 70, + 510, + 138 + ], + "lines": [ + { + "bbox": [ + 443, + 70, + 510, + 138 + ], + "spans": [ + { + "bbox": [ + 443, + 70, + 510, + 138 + ], + "type": "image", + "image_path": "f3d0ac7b181fc358cfafd18ecd7ea47e0f3d4f18ef199aea4d13277254872fb9.jpg" + } + ] + } + ], + "index": 25, + "angle": 0, + "type": "image_body" + } + ], + "index": 25 + }, + { + "type": "image", + "bbox": [ + 319, + 150, + 405, + 231 + ], + "blocks": [ + { + "bbox": [ + 344, + 141, + 370, + 149 + ], + "lines": [ + { + "bbox": [ + 344, + 141, + 370, + 149 + ], + "spans": [ + { + "bbox": [ + 344, + 141, + 370, + 149 + ], + "type": "text", + "content": "(a) Query" + } + ] + } + ], + "index": 22, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 404, + 141, + 434, + 148 + ], + "lines": [ + { + "bbox": [ + 404, + 141, + 434, + 148 + ], + "spans": [ + { + "bbox": [ + 404, + 141, + 434, + 148 + ], + "type": "text", + "content": "(b) Anchor" + } + ] + } + ], + "index": 24, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 319, + 150, + 405, + 231 + ], + "lines": [ + { + "bbox": [ + 319, + 150, + 405, + 231 + ], + "spans": [ + { + "bbox": [ + 319, + 150, + 405, + 231 + ], + "type": "image", + "image_path": "210d501e35ca59f61b09847af5f42c2968f11652ccda9f10eddaf1acaa1caeb7.jpg" + } + ] + } + ], + "index": 27, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 331, + 236, + 411, + 243 + ], + "lines": [ + { + "bbox": [ + 331, + 236, + 411, + 243 + ], + "spans": [ + { + "bbox": [ + 331, + 236, + 411, + 243 + ], + "type": "text", + "content": "(d) Attention map via anchors" + } + ] + } + ], + "index": 28, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 304, + 245, + 545, + 289 + ], + "lines": [ + { + "bbox": [ + 304, + 245, + 545, + 289 + ], + "spans": [ + { + "bbox": [ + 304, + 245, + 545, + 289 + ], + "type": "text", + "content": "Figure 5. The visualization of the (a) queries, (b) anchors, and (c) keys from the different layers of the proposed network. (d) shows the attention map approximated by Eq. (2), i.e. " + }, + { + "bbox": [ + 304, + 245, + 545, + 289 + ], + "type": "inline_equation", + "content": "\\mathbf{M}_e\\cdot \\mathbf{M}_d" + }, + { + "bbox": [ + 304, + 245, + 545, + 289 + ], + "type": "text", + "content": " (e) shows the exact attention map " + }, + { + "bbox": [ + 304, + 245, + 545, + 289 + ], + "type": "inline_equation", + "content": "\\mathbf{M}" + }, + { + "bbox": [ + 304, + 245, + 545, + 289 + ], + "type": "text", + "content": " computed in Eq. (1)." + } + ] + } + ], + "index": 31, + "angle": 0, + "type": "image_caption" + } + ], + "index": 27 + }, + { + "type": "image", + "bbox": [ + 405, + 150, + 529, + 231 + ], + "blocks": [ + { + "bbox": [ + 463, + 141, + 484, + 148 + ], + "lines": [ + { + "bbox": [ + 463, + 141, + 484, + 148 + ], + "spans": [ + { + "bbox": [ + 463, + 141, + 484, + 148 + ], + "type": "text", + "content": "(c) Key" + } + ] + } + ], + "index": 26, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 405, + 150, + 529, + 231 + ], + "lines": [ + { + "bbox": [ + 405, + 150, + 529, + 231 + ], + "spans": [ + { + "bbox": [ + 405, + 150, + 529, + 231 + ], + "type": "image", + "image_path": "04b96cb264b3595d4423e928e081b471b49eb8870ccbc1b13545438c7ed4093a.jpg" + } + ] + } + ], + "index": 29, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 443, + 236, + 507, + 243 + ], + "lines": [ + { + "bbox": [ + 443, + 236, + 507, + 243 + ], + "spans": [ + { + "bbox": [ + 443, + 236, + 507, + 243 + ], + "type": "text", + "content": "(e) Direct attention map" + } + ] + } + ], + "index": 30, + "angle": 0, + "type": "image_caption" + } + ], + "index": 29 + }, + { + "bbox": [ + 304, + 293, + 545, + 328 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 293, + 545, + 328 + ], + "spans": [ + { + "bbox": [ + 304, + 293, + 545, + 328 + ], + "type": "text", + "content": "For this attention mechanism, efficient self-attention is conducted inside the vertical and horizontal stripes with the help of the introduced anchors." + } + ] + } + ], + "index": 32 + }, + { + "bbox": [ + 306, + 336, + 378, + 347 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 336, + 378, + 347 + ], + "spans": [ + { + "bbox": [ + 306, + 336, + 378, + 347 + ], + "type": "text", + "content": "3.4. Discussion" + } + ] + } + ], + "index": 33 + }, + { + "bbox": [ + 304, + 354, + 545, + 402 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 354, + 545, + 402 + ], + "spans": [ + { + "bbox": [ + 304, + 354, + 545, + 402 + ], + "type": "text", + "content": "The proposed anchored stripe self-attention mechanism is closely related to two other concepts including low-rankness and similarity propagation. And we detail the relationship in this subsection as follows." + } + ] + } + ], + "index": 34 + }, + { + "bbox": [ + 304, + 403, + 545, + 533 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 403, + 545, + 533 + ], + "spans": [ + { + "bbox": [ + 304, + 403, + 545, + 533 + ], + "type": "text", + "content": "Low-rankness of attention map. By comparing the self-attention mechanisms in Eq. (1) and Eq. (2), we can easily found out that the original attention map " + }, + { + "bbox": [ + 304, + 403, + 545, + 533 + ], + "type": "inline_equation", + "content": "\\mathbf{M}" + }, + { + "bbox": [ + 304, + 403, + 545, + 533 + ], + "type": "text", + "content": " is decomposed into small attention maps " + }, + { + "bbox": [ + 304, + 403, + 545, + 533 + ], + "type": "inline_equation", + "content": "\\mathbf{M}_d" + }, + { + "bbox": [ + 304, + 403, + 545, + 533 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 403, + 545, + 533 + ], + "type": "inline_equation", + "content": "\\mathbf{M}_e" + }, + { + "bbox": [ + 304, + 403, + 545, + 533 + ], + "type": "text", + "content": " whose rank is no larger than " + }, + { + "bbox": [ + 304, + 403, + 545, + 533 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 304, + 403, + 545, + 533 + ], + "type": "text", + "content": ". And the essence here is to provide the low-rank approximation without calculating the original attention map first. For the success of the anchored self-attention, it is important to ensure that with the anchors as the intermediate, the approximated attention map is similar to the original attention map. Thus, an additional analysis is provided in Fig. 5." + } + ] + } + ], + "index": 35 + }, + { + "bbox": [ + 304, + 534, + 545, + 676 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 534, + 545, + 676 + ], + "spans": [ + { + "bbox": [ + 304, + 534, + 545, + 676 + ], + "type": "text", + "content": "First, by observing the queries, anchors, and keys, we can conclude that the anchors have a very similar structure to the query and key. Thus, the anchors are a good summary of the information in the queries and keys. And approximating self-attention with anchors as intermediate seems to be plausible. Additionally, the approximate attention map " + }, + { + "bbox": [ + 304, + 534, + 545, + 676 + ], + "type": "inline_equation", + "content": "\\mathbf{M}_e\\cdot \\mathbf{M}_d" + }, + { + "bbox": [ + 304, + 534, + 545, + 676 + ], + "type": "text", + "content": " and the exact attention map " + }, + { + "bbox": [ + 304, + 534, + 545, + 676 + ], + "type": "inline_equation", + "content": "\\mathbf{M}" + }, + { + "bbox": [ + 304, + 534, + 545, + 676 + ], + "type": "text", + "content": " are also compared in Fig. 5. As shown, the approximate attention map keeps the major structure in the exact attention map, which is confirmed by the large Pearson correlation coefficients (0.9505) between the two attention maps. Thus, the quality of the anchored self-attention is guaranteed." + } + ] + } + ], + "index": 36 + }, + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "text", + "content": "Metric and similarity propagation. From another perspective, in the proposed anchored self-attention, the queries and keys are first compared with the anchors and" + } + ] + } + ], + "index": 37 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "18281" + } + ] + } + ], + "index": 38 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 56, + 70, + 533, + 200 + ], + "blocks": [ + { + "bbox": [ + 56, + 70, + 533, + 200 + ], + "lines": [ + { + "bbox": [ + 56, + 70, + 533, + 200 + ], + "spans": [ + { + "bbox": [ + 56, + 70, + 533, + 200 + ], + "type": "image", + "image_path": "52b52556b2feb4068d1cb83f06e815391d7caa4416ada74daf6717728696eefa.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 58, + 202, + 242, + 345 + ], + "blocks": [ + { + "bbox": [ + 58, + 202, + 242, + 345 + ], + "lines": [ + { + "bbox": [ + 58, + 202, + 242, + 345 + ], + "spans": [ + { + "bbox": [ + 58, + 202, + 242, + 345 + ], + "type": "image", + "image_path": "809201fc804abe1d93233a4b79616569de5cbb11f0c47706e5c2fe2cbebb0f0a.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 261, + 202, + 531, + 346 + ], + "blocks": [ + { + "bbox": [ + 261, + 202, + 531, + 346 + ], + "lines": [ + { + "bbox": [ + 261, + 202, + 531, + 346 + ], + "spans": [ + { + "bbox": [ + 261, + 202, + 531, + 346 + ], + "type": "image", + "image_path": "0e4121212154a51327a5d66840e814fcec4f299440fb31c1e1da8199f00f3b03.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 346, + 545, + 369 + ], + "lines": [ + { + "bbox": [ + 46, + 346, + 545, + 369 + ], + "spans": [ + { + "bbox": [ + 46, + 346, + 545, + 369 + ], + "type": "text", + "content": "Figure 6. Network architecture. (a) The representation learning module contains stages of transformer layers. (b) The transformer layer is equipped with global, regional, and local modelling blocks. (c) The anchored stripe attention helps to attend beyond regional ranges." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 373, + 289, + 649 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 373, + 289, + 649 + ], + "spans": [ + { + "bbox": [ + 46, + 373, + 289, + 649 + ], + "type": "text", + "content": "then the query-key similarity is computed. Thus, this computation procedure needs to propagate the query-anchor and key-anchor similarity to the query-key pair. And similarity propagation is related to the triangle inequality in a metric space [19, 27, 73]. A mathematical metric needs to satisfy several conditions including the essential triangle inequality, " + }, + { + "bbox": [ + 46, + 373, + 289, + 649 + ], + "type": "inline_equation", + "content": "d(\\mathbf{q}, \\mathbf{k}) \\leq d(\\mathbf{a}, \\mathbf{q}) + d(\\mathbf{a}, \\mathbf{k})" + }, + { + "bbox": [ + 46, + 373, + 289, + 649 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 373, + 289, + 649 + ], + "type": "inline_equation", + "content": "d(\\cdot, \\cdot)" + }, + { + "bbox": [ + 46, + 373, + 289, + 649 + ], + "type": "text", + "content": " defines a metric between two entities. Thus, the " + }, + { + "bbox": [ + 46, + 373, + 289, + 649 + ], + "type": "inline_equation", + "content": "\\mathbf{q} / \\mathbf{k}" + }, + { + "bbox": [ + 46, + 373, + 289, + 649 + ], + "type": "text", + "content": " distance is upper-bounded by the sum of the " + }, + { + "bbox": [ + 46, + 373, + 289, + 649 + ], + "type": "inline_equation", + "content": "\\mathbf{a} / \\mathbf{q}" + }, + { + "bbox": [ + 46, + 373, + 289, + 649 + ], + "type": "text", + "content": " distance and the " + }, + { + "bbox": [ + 46, + 373, + 289, + 649 + ], + "type": "inline_equation", + "content": "\\mathbf{a} / \\mathbf{k}" + }, + { + "bbox": [ + 46, + 373, + 289, + 649 + ], + "type": "text", + "content": " distance. This implies that if " + }, + { + "bbox": [ + 46, + 373, + 289, + 649 + ], + "type": "inline_equation", + "content": "\\mathbf{a}" + }, + { + "bbox": [ + 46, + 373, + 289, + 649 + ], + "type": "text", + "content": " is similar (close) to both " + }, + { + "bbox": [ + 46, + 373, + 289, + 649 + ], + "type": "inline_equation", + "content": "\\mathbf{q}" + }, + { + "bbox": [ + 46, + 373, + 289, + 649 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 373, + 289, + 649 + ], + "type": "inline_equation", + "content": "\\mathbf{k}" + }, + { + "bbox": [ + 46, + 373, + 289, + 649 + ], + "type": "text", + "content": ", then " + }, + { + "bbox": [ + 46, + 373, + 289, + 649 + ], + "type": "inline_equation", + "content": "\\mathbf{q}" + }, + { + "bbox": [ + 46, + 373, + 289, + 649 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 373, + 289, + 649 + ], + "type": "inline_equation", + "content": "\\mathbf{k}" + }, + { + "bbox": [ + 46, + 373, + 289, + 649 + ], + "type": "text", + "content": " should also be similar (close) to each other. Yet, the similarity measure in Eq. (1) and Eq. (2) is defined by the dot product instead of the distance between tokens, which does not satisfy the triangle inequality. Thus, similarity propagation could not be theoretically guaranteed. To study the influence of the similarity measure, an ablation study is conducted and the results are shown in Sec. 5. Dot product and distance are compared as a similarity measure. According to the results, although the dot product does not strictly obey the triangle inequality, it still guarantees better image restoration results. Thus, we can conclude empirically that the dot product is enough for similarity propagation." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 657, + 212, + 671 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 657, + 212, + 671 + ], + "spans": [ + { + "bbox": [ + 47, + 657, + 212, + 671 + ], + "type": "text", + "content": "4. Modelling Image Hierarchies" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 677, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 677, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 47, + 677, + 287, + 715 + ], + "type": "text", + "content": "In this section, we answer the second research question described in the introduction, that is, how to explicitly model image hierarchies by a single computational module." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 373, + 545, + 409 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 373, + 545, + 409 + ], + "spans": [ + { + "bbox": [ + 304, + 373, + 545, + 409 + ], + "type": "text", + "content": "In response to that, we propose the GRL network architecture that incorporates global range, regional range, and local range image modelling capacities." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 411, + 546, + 603 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 411, + 546, + 603 + ], + "spans": [ + { + "bbox": [ + 304, + 411, + 546, + 603 + ], + "type": "text", + "content": "Network architecture. The overall architecture of the proposed network is shown in Fig. 6. The network takes a degraded low-quality image as input, processes the image inside the network, and outputs a recovered high-quality image. In detail, the network contains three parts. 1) The feature extraction layer is implemented as a simple convolution and converts the input image into feature maps. 2) The representation learning component enriches the information extracted in the previous operation. The transformer stage consists of several transformer layers and ends with a convolution layer. The dimension of the feature map is maintained across the whole representation learning module. Skip connection is applied to both the transformer stage and the representation learning module. 3) The image reconstruction module takes the rich features calculated by the previous operations and estimates a recovered image." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 605, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 547, + 715 + ], + "type": "text", + "content": "Transformer Layer. This layer in Fig. 6b is the key component that provides the hierarchical image modelling capacity in the global, regional, and local range. This layer first processes the input feature map by the parallel self-attention module and channel attention enhanced convolutions. The convolution branch serves to capture local structures in the input feature map. On the other hand, the self-attention module contains the window attention proposed in Swin transformer V2 [47] and the anchored stripe attenuation" + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "18282" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 132, + 83, + 465, + 230 + ], + "blocks": [ + { + "bbox": [ + 102, + 70, + 489, + 82 + ], + "lines": [ + { + "bbox": [ + 102, + 70, + 489, + 82 + ], + "spans": [ + { + "bbox": [ + 102, + 70, + 489, + 82 + ], + "type": "text", + "content": "Table 1. Defocus deblurring results. S: single-image defocus deblurring. D: dual-pixel defocus deblurring." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 132, + 83, + 465, + 230 + ], + "lines": [ + { + "bbox": [ + 132, + 83, + 465, + 230 + ], + "spans": [ + { + "bbox": [ + 132, + 83, + 465, + 230 + ], + "type": "table", + "html": "
MethodIndoor ScenesOutdoor ScenesCombined
PSNR↑SSIM↑MAE↓LPIPS↓PSNR↑SSIM↑MAE↓LPIPS↓PSNR↑SSIM↑MAE↓LPIPS↓
EBDBS[30]25.770.7720.0400.29721.250.5990.0580.37323.450.6830.0490.336
DMENetS[40]25.500.7880.0380.29821.430.6440.0630.39723.410.7140.0510.349
JNBs[60]26.730.8280.0310.27321.100.6080.0640.35523.840.7150.0480.315
DPDNetS[1]26.540.8160.0310.23922.250.6820.0560.31324.340.7470.0440.277
KPACS[62]27.970.8520.0260.18222.620.7010.0530.26925.220.7740.0400.227
IFANs[41]28.110.8610.0260.17922.760.7200.0520.25425.370.7890.0390.217
RestormerS[76]28.870.8820.0250.14523.240.7430.0500.20925.980.8110.0380.178
GRLS-B29.060.8860.0240.13923.450.7610.0490.19626.180.8220.0370.168
DPDNetD[1]27.480.8490.0290.18922.900.7260.0520.25525.130.7860.0410.223
RDPD2[2]28.100.8430.0270.21022.820.7040.0530.29825.390.7720.0400.255
UformerD[74]28.230.8600.0260.19923.100.7280.0510.28525.650.7950.0390.243
IFAND[41]28.660.8680.0250.17223.460.7430.0490.24025.990.8040.0370.207
RestormerD[76]29.480.8950.0230.13423.970.7730.0470.17526.660.8330.0350.155
GRLD-B29.830.9030.0220.11424.390.7950.0450.15027.040.8470.0340.133
", + "image_path": "4cd06dd0a8049d04ef20e9c1b61b2cbfa6f659e566c7c973aac26f92f1f2759e.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "type": "table", + "bbox": [ + 63, + 259, + 270, + 409 + ], + "blocks": [ + { + "bbox": [ + 47, + 236, + 287, + 258 + ], + "lines": [ + { + "bbox": [ + 47, + 236, + 287, + 258 + ], + "spans": [ + { + "bbox": [ + 47, + 236, + 287, + 258 + ], + "type": "text", + "content": "Table 2. Single-image motion deblurring results. GoPro dataset [51] is used for training." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 63, + 259, + 270, + 409 + ], + "lines": [ + { + "bbox": [ + 63, + 259, + 270, + 409 + ], + "spans": [ + { + "bbox": [ + 63, + 259, + 270, + 409 + ], + "type": "table", + "html": "
MethodGoPro [51]HIDE [59]Average
PSNR↑ / SSIM↑PSNR↑ / SSIM↑PSNR↑ / SSIM↑
DeblurGAN [37]28.70 / 0.85824.51 / 0.87126.61 / 0.865
Nah et al. [51]29.08 / 0.91425.73 / 0.87427.41 / 0.894
DeblurGAN-v2 [38]29.55 / 0.93426.61 / 0.87528.08 / 0.905
SRN [64]30.26 / 0.93428.36 / 0.91529.31 / 0.925
Gao et al. [20]30.90 / 0.93529.11 / 0.91330.01 / 0.924
DBGAN [81]31.10 / 0.94228.94 / 0.91530.02 / 0.929
MT-RNN [53]31.15 / 0.94529.15 / 0.91830.15 / 0.932
DMPHN [79]31.20 / 0.94029.09 / 0.92430.15 / 0.932
Suin et al. [63]31.85 / 0.94829.98 / 0.93030.92 / 0.939
SPAIR [55]32.06 / 0.95330.29 / 0.93131.18 / 0.942
MIMO-UNet+ [8]32.45 / 0.95729.99 / 0.93031.22 / 0.944
IPT [5]32.52 / -- / -- / -
MPRNet [77]32.66 / 0.95930.96 / 0.93931.81 / 0.949
Restormer [76]32.92 / 0.96131.22 / 0.94232.07 / 0.952
GRL-B (ours)33.93 / 0.96831.65 / 0.94732.79 / 0.958
", + "image_path": "38e9712f868d1aee568fdd79378135b1fef44fa8b0a8b3c5d90c9f5a66c46b28.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "type": "table", + "bbox": [ + 63, + 434, + 271, + 535 + ], + "blocks": [ + { + "bbox": [ + 47, + 411, + 286, + 432 + ], + "lines": [ + { + "bbox": [ + 47, + 411, + 286, + 432 + ], + "spans": [ + { + "bbox": [ + 47, + 411, + 286, + 432 + ], + "type": "text", + "content": "Table 3. Single-image motion deblurring results on RealBlur [57] dataset. The networks are trained and tested on RealBlur dataset." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 63, + 434, + 271, + 535 + ], + "lines": [ + { + "bbox": [ + 63, + 434, + 271, + 535 + ], + "spans": [ + { + "bbox": [ + 63, + 434, + 271, + 535 + ], + "type": "table", + "html": "
MethodRealBlur-R [57]RealBlur-J [57]Average
PSNR↑ / SSIM↑PSNR↑ / SSIM↑PSNR↑ / SSIM↑
DeblurGAN-v2 [38]36.44 / 0.93529.69 / 0.87033.07 / 0.903
SRN [64]38.65 / 0.96531.38 / 0.90935.02 / 0.937
MPRNet [77]39.31 / 0.97231.76 / 0.92235.54 / 0.947
MIMO-UNet+ [8]- / -32.05 / 0.921- / -
MAXIM-3S [67]39.45 / 0.96232.84 / 0.93536.15 / 0.949
BANet [66]39.55 / 0.97132.00 / 0.92335.78 / 0.947
MSSNet [34]39.76 / 0.97232.10 / 0.92835.93 / 0.950
Stripformer [65]39.84 / 0.97432.48 / 0.92936.16 / 0.952
GRL-B (ours)40.20 / 0.97432.82 / 0.93236.51 / 0.953
", + "image_path": "4d0376b83fd6c7aab63b2cba3b3271dc52bac37b215e60fcb48c322275475e92.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "table_body" + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 545, + 286, + 640 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 545, + 286, + 640 + ], + "spans": [ + { + "bbox": [ + 46, + 545, + 286, + 640 + ], + "type": "text", + "content": "tion proposed in this paper. The feature map is split equally along the channel dimension and concatenated along the channel dimension again after the parallel processing within the two attention modules. The window attention provides the mechanism to capture the regional range dependencies. Then the feature maps outputted by the convolution module and the attention module are added to the input feature map, which is processed by the following MLP module." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 642, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 642, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 642, + 286, + 713 + ], + "type": "text", + "content": "Anchored stripe self-attention. The operation of the proposed anchored stripe attention is conducted according to Eq. (2) and visualized in Fig. 6c. The dimension of different features is also shown. The triplet of " + }, + { + "bbox": [ + 46, + 642, + 286, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{Q},\\mathbf{K},\\mathbf{V}" + }, + { + "bbox": [ + 46, + 642, + 286, + 713 + ], + "type": "text", + "content": " is derived by plain linear projections. To summarize the information into anchors, the anchor projection is implemented as an" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 238, + 545, + 310 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 238, + 545, + 310 + ], + "spans": [ + { + "bbox": [ + 304, + 238, + 545, + 310 + ], + "type": "text", + "content": "average pooling layer followed by a linear projection. After the anchor projection, the resolution of the image feature map is down-scaled by a factor of " + }, + { + "bbox": [ + 304, + 238, + 545, + 310 + ], + "type": "inline_equation", + "content": "s" + }, + { + "bbox": [ + 304, + 238, + 545, + 310 + ], + "type": "text", + "content": " along both directions. As shown in Fig. 6, the two attention maps " + }, + { + "bbox": [ + 304, + 238, + 545, + 310 + ], + "type": "inline_equation", + "content": "\\mathbf{M}_d" + }, + { + "bbox": [ + 304, + 238, + 545, + 310 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 238, + 545, + 310 + ], + "type": "inline_equation", + "content": "\\mathbf{M}_e" + }, + { + "bbox": [ + 304, + 238, + 545, + 310 + ], + "type": "text", + "content": " play a similar role as the original attention map " + }, + { + "bbox": [ + 304, + 238, + 545, + 310 + ], + "type": "inline_equation", + "content": "\\mathbf{M}" + }, + { + "bbox": [ + 304, + 238, + 545, + 310 + ], + "type": "text", + "content": " but with less space and time complexity." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 320, + 432, + 335 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 320, + 432, + 335 + ], + "spans": [ + { + "bbox": [ + 306, + 320, + 432, + 335 + ], + "type": "text", + "content": "5. Experimental Results" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 340, + 545, + 544 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 340, + 545, + 544 + ], + "spans": [ + { + "bbox": [ + 304, + 340, + 545, + 544 + ], + "type": "text", + "content": "The experimental results are shown in this section. We answer the third research question raised in the introduction by investigating the performance of the proposed network on different image restoration tasks. Based on the data type, the investigated tasks are classified into three commonly used settings including 1) real image restoration (single-image motion deblurring, defocus deblurring), 2) image restoration based on synthetic data (image denoising, single image SR, JPEG compression artifact removal, demosaicking), and 3) real image restoration based on data synthesis. We provide three networks with different model sizes including the tiny, small, and base versions (GRL-T, GRL-S, GRL-B). For real and synthetic image restoration, Adam optimizer and " + }, + { + "bbox": [ + 304, + 340, + 545, + 544 + ], + "type": "inline_equation", + "content": "L_{1}" + }, + { + "bbox": [ + 304, + 340, + 545, + 544 + ], + "type": "text", + "content": " loss are used to train the network with an initial learning rate " + }, + { + "bbox": [ + 304, + 340, + 545, + 544 + ], + "type": "inline_equation", + "content": "2 \\times 10^{-4}" + }, + { + "bbox": [ + 304, + 340, + 545, + 544 + ], + "type": "text", + "content": ". More details about the training dataset, training protocols, and additional visual results are shown in the supplementary material." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 552, + 411, + 564 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 552, + 411, + 564 + ], + "spans": [ + { + "bbox": [ + 306, + 552, + 411, + 564 + ], + "type": "text", + "content": "5.1. Image deblurring" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 570, + 545, + 604 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 545, + 604 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 545, + 604 + ], + "type": "text", + "content": "We first investigate the performance of the proposed network on two real image restoration tasks including single-image motion deblurring, and motion deblurring." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": "Single image motion deblurring. Tab. 2 and Tab. 3 show the experimental results for single image motion deblurring on synthetic datasets (GoPro [51], HIDE [59]) and real dataset (RealBlur-R [57]), respectively. Compared with the previous state-of-the-art Restormer [76], the proposed GRL achieves significant PSNR improvement of " + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "inline_equation", + "content": "1.01\\mathrm{dB}" + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": " on the GoPro dataset. On the HIDE dataset, the PSNR improvement is " + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "inline_equation", + "content": "0.43\\mathrm{dB}" + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": ". Please note that the improvement is achieved under fewer parameter budget. As shown in Tab. 4," + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "18283" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 53, + 83, + 542, + 201 + ], + "blocks": [ + { + "bbox": [ + 58, + 71, + 534, + 82 + ], + "lines": [ + { + "bbox": [ + 58, + 71, + 534, + 82 + ], + "spans": [ + { + "bbox": [ + 58, + 71, + 534, + 82 + ], + "type": "text", + "content": "Table 4. Color and grayscale image denoising results. Model complexity and prediction accuracy are shown for better comparison." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 53, + 83, + 542, + 201 + ], + "lines": [ + { + "bbox": [ + 53, + 83, + 542, + 201 + ], + "spans": [ + { + "bbox": [ + 53, + 83, + 542, + 201 + ], + "type": "table", + "html": "
Method# Params [M]ColorGrayscale
CBSD68 [49]σ=15 σ=25 σ=50Kodak24 [16]σ=15 σ=25 σ=50McMaster [83]σ=15 σ=25 σ=50Urban100 [28]σ=15 σ=25 σ=50Set12 [82]σ=15 σ=25 σ=50BSD68 [49]σ=15 σ=25 σ=50Urban100 [28]σ=15 σ=25 σ=50
DnCNN [32]0.5633.9031.2427.9534.6032.1428.9533.4531.5228.6232.9830.8127.5932.8630.4427.1831.7329.2326.2332.6429.9526.26
RNAN [85]8.96--28.27--29.58--29.72--29.08--27.70--26.48--27.65
IPT [5]115.33--28.39--29.64--29.98--29.71---------
EDT-B [42]11.4834.3931.7628.5635.3732.9429.8735.6133.3430.2535.2233.0730.16---------
DRUNet [80]32.6434.3031.6928.5135.3132.8929.8635.4033.1430.0834.8132.6029.6133.2530.9427.9031.9129.4826.5933.4431.1127.96
SwinIR [43]11.7534.4231.7828.5635.3432.8929.7935.6133.2030.2235.1332.9029.8233.3631.0127.9131.9729.5026.5833.7031.3027.98
Restormer [76]26.1334.4031.7928.6035.4733.0430.0135.6133.3430.3035.1332.9630.0233.4231.0828.0031.9629.5226.6233.7931.4628.29
GRL-T0.8834.3031.6628.4535.2432.7829.6735.4933.1830.0635.0832.8429.7833.2930.9227.7831.9029.4326.4933.6631.2327.89
GRL-S3.1234.3631.7228.5135.3232.8829.7735.5933.2930.1835.2433.0730.0933.3631.0227.9131.9329.4726.5433.8431.4928.24
GRL-B19.8134.4531.8228.6235.4333.0229.9335.7333.4630.3635.5433.3530.4633.4731.1228.0332.0029.5426.6034.0931.8028.59
", + "image_path": "ce1a6297d4087333ed2a72f620bb5ad65d04b0d7e15d302f8aad6d45a94d1ee2.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "type": "table", + "bbox": [ + 63, + 224, + 531, + 434 + ], + "blocks": [ + { + "bbox": [ + 97, + 212, + 495, + 223 + ], + "lines": [ + { + "bbox": [ + 97, + 212, + 495, + 223 + ], + "spans": [ + { + "bbox": [ + 97, + 212, + 495, + 223 + ], + "type": "text", + "content": "Table 5. Classical image SR results. Results of both lightweight models and accurate models are summarized." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 63, + 224, + 531, + 434 + ], + "lines": [ + { + "bbox": [ + 63, + 224, + 531, + 434 + ], + "spans": [ + { + "bbox": [ + 63, + 224, + 531, + 434 + ], + "type": "table", + "html": "
MethodScale# Params [M]Set5 [3]Set14 [78]BSD100 [49]Urban100 [28]Manga109 [50]
PSNR↑SSIM↑PSNR↑SSIM↑PSNR↑SSIM↑PSNR↑SSIM↑PSNR↑SSIM↑
RCAN [84]×215.4438.270.961434.120.921632.410.902733.340.938439.440.9786
SAN [11]×215.7138.310.962034.070.921332.420.902833.100.937039.320.9792
HAN [52]×263.6138.270.961434.160.921732.410.902733.350.938539.460.9785
IPT [5]×2115.4838.37-34.43-32.48-33.76---
SwinIR [43]×20.8838.140.961133.860.920632.310.901232.760.934039.120.9783
SwinIR [43]×211.7538.420.962334.460.925032.530.904133.810.942739.920.9797
EDT [42]×20.9238.230.961533.990.920932.370.902132.980.936239.450.9789
EDT [42]×211.4838.630.963234.800.927332.620.905234.270.945640.370.9811
GRL-T (ours)×20.8938.270.962734.210.925832.420.905633.600.941139.610.9790
GRL-S (ours)×23.3438.370.963234.640.928032.520.906934.360.946339.840.9793
GRL-B (ours)×220.0538.670.964735.080.930332.670.908735.060.950540.670.9818
RCAN [84]×415.5932.630.900228.870.788927.770.743626.820.808731.220.9173
SAN [11]×415.8632.640.900328.920.788827.780.743626.790.806831.180.9169
HAN [52]×464.2032.640.900228.900.789027.800.744226.850.809431.420.9177
IPT [5]×4115.6332.64-29.01-27.82-27.26---
SwinIR [43]×40.9032.440.897628.770.785827.690.740626.470.798030.920.9151
SwinIR [43]×411.9032.920.904429.090.795027.920.748927.450.825432.030.9260
EDT [42]×40.9232.530.899128.880.788227.760.743326.710.805131.350.9180
EDT [42]×411.6333.060.905529.230.797127.990.751027.750.831732.390.9283
GRL-T (ours)×40.9132.560.902928.930.796127.770.752327.150.818531.570.9219
GRL-S (ours)×43.4932.760.905829.100.800727.900.756827.900.835732.110.9267
GRL-B (ours)×420.2033.100.909429.370.805828.010.761128.530.850432.770.9325
", + "image_path": "62d48bf477dc3d8d911947e81905db4966e27444a806f2981199e5cbd5ef6180.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 443, + 287, + 479 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 443, + 287, + 479 + ], + "spans": [ + { + "bbox": [ + 46, + 443, + 287, + 479 + ], + "type": "text", + "content": "GRL-B saves " + }, + { + "bbox": [ + 46, + 443, + 287, + 479 + ], + "type": "inline_equation", + "content": "24\\%" + }, + { + "bbox": [ + 46, + 443, + 287, + 479 + ], + "type": "text", + "content": " parameters compared with Restormer. As shown in Tab. 3, GRL-B sets the new state-of-the-art performance of 40.20 PSNR on RealBlur-R dataset." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 479, + 287, + 588 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 479, + 287, + 588 + ], + "spans": [ + { + "bbox": [ + 46, + 479, + 287, + 588 + ], + "type": "text", + "content": "Defocus deblurring. Tab. 1 shows the experimental results for defocus deblurring using single image and dual-pixel images. Our GRL outperforms the previous methods for all three scene types. Compared with Restormer on the combined scenes, our GRL achieves an elegant performance boost of " + }, + { + "bbox": [ + 46, + 479, + 287, + 588 + ], + "type": "inline_equation", + "content": "0.20\\mathrm{dB}" + }, + { + "bbox": [ + 46, + 479, + 287, + 588 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 479, + 287, + 588 + ], + "type": "inline_equation", + "content": "0.38\\mathrm{dB}" + }, + { + "bbox": [ + 46, + 479, + 287, + 588 + ], + "type": "text", + "content": " for single and dual-pixel defocus deblurring. Compared with Uformer [74] and IFAN [41], GRL achieves PSNR gain of " + }, + { + "bbox": [ + 46, + 479, + 287, + 588 + ], + "type": "inline_equation", + "content": "1.39\\mathrm{dB}" + }, + { + "bbox": [ + 46, + 479, + 287, + 588 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 479, + 287, + 588 + ], + "type": "inline_equation", + "content": "1.05\\mathrm{dB}" + }, + { + "bbox": [ + 46, + 479, + 287, + 588 + ], + "type": "text", + "content": " for the dual-pixel setting." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 597, + 265, + 611 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 597, + 265, + 611 + ], + "spans": [ + { + "bbox": [ + 47, + 597, + 265, + 611 + ], + "type": "text", + "content": "5.2. Image restoration based on synthetic data" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 616, + 287, + 666 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 616, + 287, + 666 + ], + "spans": [ + { + "bbox": [ + 46, + 616, + 287, + 666 + ], + "type": "text", + "content": "Investigating image restoration with synthetic data is also valuable to reveal the network capacity of restoration methods. Besides the experiments on the real data, we also study the performance of the network on synthetic data." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 666, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 666, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 666, + 287, + 713 + ], + "type": "text", + "content": "Image denoising. First, the experimental results on Gaussian image denoising are shown in Tab. 4. For a fair comparison between different models, both the network complexity and accuracy are shown in the table. And several key find" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 443, + 545, + 538 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 443, + 545, + 538 + ], + "spans": [ + { + "bbox": [ + 304, + 443, + 545, + 538 + ], + "type": "text", + "content": "ings are observed. I. The tiny version GRL-T is extremely efficient, reducing model complexity by two orders of magnitude (only " + }, + { + "bbox": [ + 304, + 443, + 545, + 538 + ], + "type": "inline_equation", + "content": "0.76\\%" + }, + { + "bbox": [ + 304, + 443, + 545, + 538 + ], + "type": "text", + "content": " of [5] and " + }, + { + "bbox": [ + 304, + 443, + 545, + 538 + ], + "type": "inline_equation", + "content": "2.7\\%" + }, + { + "bbox": [ + 304, + 443, + 545, + 538 + ], + "type": "text", + "content": " of DRUNet [80]) while not sacrificing network accuracy. II. The small version GRL-S performs competitive with the previous state-of-the-art SwinIR [43] and Restormer [76]. III. On Urban100, the base version outperforms Restormer by a large margin (e.g. 0.44dB PSNR gain for color image and noise level 50)." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 542, + 545, + 674 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 542, + 545, + 674 + ], + "spans": [ + { + "bbox": [ + 304, + 542, + 545, + 674 + ], + "type": "text", + "content": "Image SR. Experimental results for classical images are shown in Tab. 5. Both lightweight models and accurate SR models are summarized. A similar conclusion could be drawn from the results. I. Among the lightweight networks, GRL-T outperforms both convolution and self-attention-based networks including DBPN [25], SwinIR [43] and EDT [42]. Compared with EDT, Significant improvements are obtained on Urban100 and Manga109 datasets (0.44 dB and 0.22 dB for " + }, + { + "bbox": [ + 304, + 542, + 545, + 674 + ], + "type": "inline_equation", + "content": "\\times 4" + }, + { + "bbox": [ + 304, + 542, + 545, + 674 + ], + "type": "text", + "content": " SR). II. GRL-B sets the new state-of-the-art for accurate image SR. III. GRL-S achieves a good balance between network complexity and SR image quality." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "text", + "content": "JPEG compression artifact removal. The experimental results for color and grayscale images are shown in Tab. 6. Four image quality factors ranging from 10 to 40 for JPEG" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "type": "text", + "content": "18284" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 50, + 95, + 359, + 191 + ], + "blocks": [ + { + "bbox": [ + 50, + 95, + 359, + 191 + ], + "lines": [ + { + "bbox": [ + 50, + 95, + 359, + 191 + ], + "spans": [ + { + "bbox": [ + 50, + 95, + 359, + 191 + ], + "type": "table", + "html": "
SetQFJPEG PSNR SSIMDnCNN [82] PSNR SSIMDCSC [18] PSNR SSIMQGAC [14] PSNR SSIMMWCNN [46] PSNR SSIMFBCNN [29] PSNR SSIMGRL-S PSNR SSIM
Classic5 [15]1027.82 0.76029.40 0.80329.62 0.81029.84 0.81230.01 0.82030.12 0.82230.20 0.829
2030.12 0.83431.63 0.86131.81 0.86431.98 0.86932.16 0.87032.31 0.87232.49 0.878
3031.48 0.86732.91 0.88633.06 0.88833.22 0.89233.43 0.89333.54 0.89433.72 0.899
4032.43 0.88533.77 0.90033.87 0.90234.05 0.90534.27 0.90634.35 0.90734.53 0.911
BSD500 [49]1027.80 0.76829.21 0.80929.32 0.81329.46 0.82129.61 0.82029.67 0.82129.74 0.823
2030.05 0.84931.53 0.87831.63 0.88031.73 0.88431.92 0.88532.00 0.88532.05 0.885
3031.37 0.88432.90 0.90732.99 0.90833.07 0.91233.30 0.91233.37 0.91333.43 0.912
4032.30 0.90333.85 0.92333.92 0.92434.01 0.92734.27 0.92834.33 0.92834.38 0.928
", + "image_path": "d7cab793658685bef00d4ce113dd3b032e0bee68d0e84bd47e88631a93e62fc2.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "type": "table", + "bbox": [ + 361, + 94, + 547, + 191 + ], + "blocks": [ + { + "bbox": [ + 47, + 70, + 548, + 92 + ], + "lines": [ + { + "bbox": [ + 47, + 70, + 548, + 92 + ], + "spans": [ + { + "bbox": [ + 47, + 70, + 548, + 92 + ], + "type": "text", + "content": "Table 6. Grayscale image JPEG compression artifact removal results. As a compar- Table 7. Color image JPEG compression artifact ison metric, the parameter count of FBCNN [29] GRL-S are 71.92M and 3.12M. removal results." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 361, + 94, + 547, + 191 + ], + "lines": [ + { + "bbox": [ + 361, + 94, + 547, + 191 + ], + "spans": [ + { + "bbox": [ + 361, + 94, + 547, + 191 + ], + "type": "table", + "html": "
SetQFJPEG PSNR SSIMQGAC [14] PSNR SSIMFBCNN [29] PSNR SSIMGRL-S PSNR SSIM
LIVE1 [58]1025.69 0.74327.62 0.80427.77 0.80328.13 0.814
2028.06 0.82629.88 0.86830.11 0.86830.49 0.878
3029.37 0.86131.17 0.89631.43 0.89731.85 0.905
4030.28 0.88232.05 0.91232.34 0.91332.79 0.920
BSD500 [49]1025.84 0.74127.74 0.80227.85 0.79928.26 0.808
2028.21 0.82730.01 0.86930.14 0.86730.57 0.875
3029.57 0.86531.33 0.89831.45 0.89731.92 0.903
4030.52 0.88732.25 0.91532.36 0.91332.86 0.919
", + "image_path": "ff02f7f24d15665c09a22e67aa1b5ca8fc15466120c5eb7deb6e4914de788aab.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "type": "table", + "bbox": [ + 50, + 213, + 288, + 253 + ], + "blocks": [ + { + "bbox": [ + 97, + 200, + 236, + 210 + ], + "lines": [ + { + "bbox": [ + 97, + 200, + 236, + 210 + ], + "spans": [ + { + "bbox": [ + 97, + 200, + 236, + 210 + ], + "type": "text", + "content": "Table 8. Image demosaicking results." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 50, + 213, + 288, + 253 + ], + "lines": [ + { + "bbox": [ + 50, + 213, + 288, + 253 + ], + "spans": [ + { + "bbox": [ + 50, + 213, + 288, + 253 + ], + "type": "table", + "html": "
DatasetsMatlabDDR [75]DeepJoint [21]MMNet [36]RLDD [24]RNAN [85]DRUNet [80]GRL-S (ours)
Kodak [16]35.7841.1142.0040.1942.4943.1642.6843.57
McMaster [83]34.4337.1239.1437.0939.2539.7039.3940.22
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Test setMetricColor DNGray DNImage SR
σ15σ25σ50σ15σ25σ50×2×3×4
BSD68 or BSD100Euclidean35.0232.5629.4231.8429.3626.4332.3029.1927.67
Dot product35.1032.6429.5431.8529.3926.4432.3329.2227.70
Urban100Euclidean34.6332.2828.9433.2530.6427.1732.7628.6226.50
Dot product34.7732.4129.1933.2830.7527.2632.8828.7826.67
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Anchor projection operation# Params [m]PSNR on Set 5
Depthwise Conv3.1735.03
Conv4.1935.03
Patch merging3.5334.98
Maxpool + Linear Projection3.1235.02
Avgpool + Linear Projection3.1235.03
", + "image_path": "3a0489343083f820008b7d884ad4b0e5d130452976ca900f82879fdeb4676120.jpg" + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "table_body" + } + ], + "index": 16 + }, + { + "bbox": [ + 305, + 369, + 545, + 404 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 369, + 545, + 404 + ], + "spans": [ + { + "bbox": [ + 305, + 369, + 545, + 404 + ], + "type": "text", + "content": "product is very competitive compared with a metric and it outperforms a distance metric for a couple of settings. Considering this, the dot product is still used." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 305, + 407, + 545, + 467 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 407, + 545, + 467 + ], + "spans": [ + { + "bbox": [ + 305, + 407, + 545, + 467 + ], + "type": "text", + "content": "Influence of the anchor projections. The anchor projection operation helps to summarize the information in the feature map. The ablation study is shown in Tab. 10. Considering both the accuracy performance and parameter budget, Avgpool followed by linear projection is finally used." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 306, + 495, + 378, + 506 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 495, + 378, + 506 + ], + "spans": [ + { + "bbox": [ + 306, + 495, + 378, + 506 + ], + "type": "text", + "content": "6. Conclusion" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 517, + 545, + 672 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 517, + 545, + 672 + ], + "spans": [ + { + "bbox": [ + 304, + 517, + 545, + 672 + ], + "type": "text", + "content": "In this paper, we proposed GRL, a network with efficient and explicit hierarchical modelling capacities for image restoration. The proposed network was mainly inspired by two image properties including cross-scale similarity and anisotropic image features. Based on that, we proposed the efficient anchored stripe self-attention module for long-range dependency modelling. Then a versatile network architecture was proposed for image restoration. The proposed network can model image hierarchies in the global, regional, and local ranges. Owing to the advanced computational mechanism, the proposed network architecture achieves state-of-the-art performances for various image restoration tasks." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 305, + 677, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 677, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 305, + 677, + 545, + 712 + ], + "type": "text", + "content": "Acknowledgements. 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In Proceedings of the IEEE Conference on Computer Vision and Pattern Recognition, 2018. 2" + } + ] + } + ], + "index": 1 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "type": "text", + "content": "18289" + } + ] + } + ], + "index": 3 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 11 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/EfficientSCI_ Densely Connected Network With Space-Time Factorization for Large-Scale Video Snapshot Compressive Imaging/ba9925d6-1c9f-468a-bc9d-dc4b6c4a5ca6_content_list.json b/2023/EfficientSCI_ Densely Connected Network With Space-Time Factorization for Large-Scale Video Snapshot Compressive Imaging/ba9925d6-1c9f-468a-bc9d-dc4b6c4a5ca6_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..3a1584f237797d8050aac200a24165f3b89214c8 --- /dev/null +++ b/2023/EfficientSCI_ Densely Connected Network With Space-Time Factorization for Large-Scale Video Snapshot Compressive Imaging/ba9925d6-1c9f-468a-bc9d-dc4b6c4a5ca6_content_list.json @@ -0,0 +1,1526 @@ +[ + { + "type": "text", + "text": "EfficientSCI: Densely Connected Network with Space-time Factorization for Large-scale Video Snapshot Compressive Imaging", + "text_level": 1, + "bbox": [ + 101, + 128, + 869, + 176 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Lishun Wang $^{1,2,*}$ , Miao Cao $^{3,4,*}$ , and Xin Yuan $^{3,\\dagger}$", + "bbox": [ + 277, + 202, + 686, + 220 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1 Chengdu Institute of Computer Application Chinese Academy of Sciences,", + "bbox": [ + 179, + 220, + 787, + 239 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "$^{2}$ University of Chinese Academy of Sciences, $^{3}$ Westlake University, $^{4}$ Zhejiang University", + "bbox": [ + 120, + 239, + 841, + 257 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 291, + 313, + 306 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Video snapshot compressive imaging (SCI) uses a two-dimensional detector to capture consecutive video frames during a single exposure time. Following this, an efficient reconstruction algorithm needs to be designed to reconstruct the desired video frames. Although recent deep learning-based state-of-the-art (SOTA) reconstruction algorithms have achieved good results in most tasks, they still face the following challenges due to excessive model complexity and GPU memory limitations: 1) these models need high computational cost, and 2) they are usually unable to reconstruct large-scale video frames at high compression ratios. To address these issues, we develop an efficient network for video SCI by using dense connections and space-time factorization mechanism within a single residual block, dubbed EfficientSCI. The EfficientSCI network can well establish spatial-temporal correlation by using convolution in the spatial domain and Transformer in the temporal domain, respectively. We are the first time to show that an UHD color video with high compression ratio can be reconstructed from a snapshot 2D measurement using a single end-to-end deep learning model with PSNR above 32 dB. Extensive results on both simulation and real data show that our method significantly outperforms all previous SOTA algorithms with better real-time performance. The code is at https://github.com/ucaswangls/EfficientSCI.git.", + "bbox": [ + 75, + 323, + 473, + 717 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 744, + 209, + 760 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Traditional high-speed camera imaging methods usually suffer from high hardware and storage transmission cost. Inspired by compressed sensing (CS) [5, 9], video snapshot compressive imaging (SCI) [45] provides an elegant solution. As shown in Fig. 2, video SCI consists of a hardware encoder and a software decoder. In the encoder part, multiple raw video frames are modulated by different masks and", + "bbox": [ + 75, + 771, + 468, + 878 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/6e028b4c59a14fe49510021b749e66600621c5fb1d7da19aafd0841c9305a420.jpg", + "image_caption": [ + "Figure 1. Comparison of reconstruction quality (average PSNR in dB on 6 benchmark grayscale datasets) and testing time of several SOTA deep learning based algorithms. Our proposed EfficientSCI achieves higher reconstruction quality with fewer parameters and shorter testing time." + ], + "image_footnote": [], + "bbox": [ + 501, + 289, + 893, + 518 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "then integrated by the camera to get a compressed measurement, giving low-speed cameras the ability to capture high-speed scenes. For the decoding part, the desired high-speed video is retrieved by the reconstruction algorithm using the captured measurement and masks.", + "bbox": [ + 496, + 606, + 893, + 681 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "So far, many mature SCI imaging systems [14, 24, 31] have been built, but for the decoding part, there are still many challenges. In particular, although the model-based methods [21, 43, 44] have good flexibility and can reconstruct videos with different resolutions and compression rates, they require long reconstruction time and can only achieve poor reconstruction quality. In order to improve the reconstruction quality and running speed, PnP-FFDNet [46] and PnP-FastDVDnet [47] integrate the pre-trained denoising network into an iterative optimization algorithm. However, they still need a long reconstruction time on large-scale datasets, e.g., PnP-FastDVDNet takes hours to reconstruct a UHD video from a single measurement.", + "bbox": [ + 496, + 685, + 893, + 882 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "By contrast, deep learning based methods [28,30,35,40]", + "bbox": [ + 517, + 885, + 890, + 901 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 810, + 44 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Equal Contribution, † Corresponding Author", + "bbox": [ + 94, + 886, + 339, + 900 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "18477", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/b80883aba0a14977c145c065f39cef9aaa16162d90a875481c4752be480d5808.jpg", + "image_caption": [ + "Figure 2. Schematic diagram of grayscale and color video SCI." + ], + "image_footnote": [], + "bbox": [ + 81, + 88, + 467, + 238 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "have better real-time performance and higher reconstruction quality. For example, BIRNAT [8] uses bidirectional recurrent neural network and generative adversarial method to surpass model-based method DeSCI [21] for the first time. MetaSCI [39] has made some explorations for the model to adapt to different masks, which reduces the model training time. DUN-3DUnet [40] and ELP-Unfolding [42] combine iterative optimization ideas with deep learning models to further improve reconstruction quality. However, due to the high model complexity and insufficient GPU memory, most existing deep learning algorithms cannot train the models required for reconstructing HD or large-scale videos. RevSCI [7] uses a reversible mechanism [2] to reduce the memory used for model training, and can reconstruct HD video with a compression rate up to 24, but the model training time increases exponentially. In addition, the current reconstruction algorithms generally use convolution to establish spatial-temporal correlation. Due to the local connection of convolution, long-term dependencies cannot be well established, and the model cannot reconstruct data with high compression rates.", + "bbox": [ + 76, + 271, + 468, + 588 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In summary, model-based methods usually require long reconstruction time and can only achieve poor reconstruction quality. Learning-based methods have high model complexity but cannot be well applied to large-scale color video reconstruction. To address these challenges, we develop an efficient network for video SCI by using dense connections and space-time factorization mechanism. As shown in Fig. 1, our proposed method dramatically outperforms all previous deep learning based reconstruction algorithms in terms of reconstruction quality and running speed with fewer parameters. Our main contributions can be summarized as follows:", + "bbox": [ + 76, + 588, + 468, + 770 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- An efficient end-to-end network, dubbed EfficientSCI, is proposed for reconstructing high quality video frames from a snapshot SCI measurement.", + "- By building hierarchical dense connections within a single residual block, we devise a novel ResDNet block to effectively reduces model computational complexity but enhance the learning ability of the model." + ], + "bbox": [ + 94, + 782, + 467, + 900 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- Based on the space-time factorization mechanism, a Convolution and Transformer hybrid block (CFormer) is built, which can efficiently establish space-time correlation by using convolution in the spatial domain and Transformer in the temporal domain, respectively.", + "- Experimental results on a large number of simulated and real datasets demonstrate that our proposed method achieves state-of-the-art (SOTA) results and better real-time performance." + ], + "bbox": [ + 517, + 90, + 890, + 239 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 500, + 253, + 640, + 270 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "CNN and Variants: In the past ten years, models with convolutional neural networks (CNN) as the backbone [13,15,20] have achieved excellent results on multiple computer vision tasks [20, 25, 32]. Among them, ResNeXt [41] and Res2Net [11] effectively increases model capacity without increasing model complexity by using grouped convolutions inside residual blocks. DenseNet [15] and CSPNet [34] achieve feature reuse by taking all previous feature maps as input. In video-related tasks, 3D convolution can establish good spatial-temporal correlation and has been widely used in action recognition [18], video superresolution [26], video inpainting [6] and so on. In previous video SCI reconstruction, RevSCI and DUN-3DUnet greatly improve the reconstruction quality of benchmark grayscale datasets by integrating 3D convolution into the network. However, in complex high-speed scenarios (e.g., crash), since they cannot effectively establish long-term temporal dependencies, the reconstruction quality is still lower than $30\\mathrm{dB}$ . In addition, the excessive use of 3D convolution increases the amount of model parameters, which is not conducive to the application of large-scale and high compression ratio data.", + "bbox": [ + 496, + 280, + 890, + 611 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Vision Transformers: Most recently, Vision Transformer (ViT) [10] and its variants [4, 12, 37, 50] have achieved competitive results in computer vision. However, the high computational complexity limits its application in video-related tasks. TimeSformer [3] performs self-attention calculations in time and space respectively, which reduces model complexity and improves model accuracy, but the computational complexity still increases quadratically with the image size. The Video Swin Transformer [23] limits self-attention calculations to local windows but cannot effectively establish long-term temporal dependencies. In addition, a large number of experimental results show that Transformer has higher memory consumption than CNN, and using Transformer in space is not conducive to large-scale video SCI reconstruction. Therefore, through space-time factorization mechanism, using Transformer only in time domain can not only effectively utilize its ability to establish long-term time series dependencies, but also reduce model complexity and memory consumption.", + "bbox": [ + 496, + 613, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "18478", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/029625615612b212673c7634f8bfc935ed2da89d5a0ae3cd563220b48f108e05.jpg", + "image_caption": [ + "Figure 3. Architecture of the proposed EfficientSCI network and the overall process of color or grayscale video reconstruction. The measurement $(\\mathbf{Y})$ and masks $(\\mathbf{M})$ are pre-processed by the estimation module to obtain an estimated $\\mathbf{X}_e$ , and then feed $\\mathbf{X}_e$ into EfficientSCI network to get the desired reconstruction result. (a) ResDNet module with $N$ residual style units. (b) ResDNet block. Inside a residual block, the input features are divided into $S$ parts by the channel split. Each part uses CFormer to efficiently extract spatial-temporal correlation, and employs dense connections to further improve model capacity. For convenience, only the case of $S = 4$ is shown here." + ], + "image_footnote": [], + "bbox": [ + 98, + 85, + 869, + 273 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Mathematical Model of Video SCI", + "text_level": 1, + "bbox": [ + 76, + 351, + 390, + 368 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Fig. 2 briefly describes the flow chart of video SCI. For grayscale video SCI system, the original $B$ -frame (grayscale) input video $\\{\\mathbf{X}_m\\}_{m=1}^B \\in \\mathbb{R}^{n_x \\times n_y}$ is modulated by pre-defined masks $\\{\\mathbf{M}\\}_{m=1}^B \\in \\mathbb{R}^{n_x \\times n_y}$ . Then, by compressing across time, the camera sensor captures a compressed measurement $\\mathbf{Y} \\in \\mathbb{R}^{n_x \\times n_y}$ . The whole process can be expressed as:", + "bbox": [ + 75, + 376, + 470, + 482 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {Y} = \\sum_ {m = 1} ^ {B} \\mathbf {X} _ {m} \\odot \\mathbf {M} _ {m} + \\mathbf {Z}, \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 169, + 489, + 468, + 512 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\odot$ denotes the Hadamard (element-wise) multiplication, and $\\mathbf{Z} \\in \\mathbb{R}^{n_x \\times n_y}$ denotes the measurement noise. Eq. (1) can also be represented by a vectorized formulation. Firstly, we vectorize $\\pmb{y} = \\operatorname{vec}(\\mathbf{Y}) \\in \\mathbb{R}^{n_x n_y}$ , $\\pmb{z} = \\operatorname{vec}(\\mathbf{Z}) \\in \\mathbb{R}^{n_x n_y}$ , $\\pmb{x} = [\\pmb{x}_1^\\top, \\dots, \\pmb{x}_B^\\top]^\\top \\in \\mathbb{R}^{n_x n_y B}$ , where $\\pmb{x}_m = \\operatorname{vec}(\\mathbf{X}_m)$ . Then, sensing matrix generated by masks can be defined as:", + "bbox": [ + 75, + 520, + 468, + 628 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {H} = \\left[ \\mathbf {D} _ {1}, \\dots , \\mathbf {D} _ {B} \\right] \\in \\mathbb {R} ^ {n _ {x} n _ {y} \\times n _ {x} n _ {y} B}, \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 145, + 637, + 468, + 656 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\mathbf{D}_m = \\mathrm{Diag}(\\mathrm{vec}(\\mathbf{M}))\\in \\mathbb{R}^{n_xn_y\\times n_xn_y}$ is a diagonal matrix and its diagonal elements is filled by $\\operatorname {vec}(\\mathbf{M})$ Finally, the vectorized expression of Eq. (1) is", + "bbox": [ + 75, + 664, + 468, + 712 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {y} = \\mathbf {H} \\boldsymbol {x} + \\boldsymbol {z}. \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 223, + 722, + 468, + 738 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "For color video SCI system, we use the Bayer pattern filter sensor, where each pixel captures only red (R), blue (B) or green (G) channel of the raw data in a spatial layout such as 'RGGB'. Since adjacent pixels are different color components, we divide the original measurement $\\mathbf{Y}$ into four sub-measurements $\\{\\mathbf{Y}^r,\\mathbf{Y}^{g1},\\mathbf{Y}^{g2},\\mathbf{Y}^b\\} \\in \\mathbb{R}^{\\frac{n_x}{2}\\times \\frac{n_y}{2}}$ according to the Bayer filter pattern. For color video reconstruction, most of the previous algorithms [46, 48] reconstruct each sub-measurement independently, and then use off-the-shelf demosaic algorithms to get the final RGB color", + "bbox": [ + 75, + 748, + 470, + 901 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "videos. These methods are usually inefficient and have poor reconstruction quality. In this paper, we feed the four submeasurements simultaneously into the reconstruction network to directly obtain the final desired color video.", + "bbox": [ + 496, + 352, + 892, + 414 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "4. The Proposed Network", + "text_level": 1, + "bbox": [ + 498, + 424, + 718, + 441 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "As shown in Fig. 3, in the pre-processing stage of EfficientSCI, inspired by [7, 8], we use the estimation module to pre-process measurement $(\\mathbf{Y})$ and masks $(\\mathbf{M})$ as follows:", + "bbox": [ + 496, + 450, + 892, + 494 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\overline {{\\mathbf {Y}}} = \\mathbf {Y} \\oslash \\sum_ {m = 1} ^ {B} \\mathbf {M} _ {m}, \\quad \\mathbf {X} _ {e} = \\overline {{\\mathbf {Y}}} \\odot \\mathbf {M} + \\overline {{\\mathbf {Y}}}, \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 539, + 498, + 890, + 518 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\varnothing$ represents Hadamard (element-wise) division, $\\overline{\\mathbf{Y}}\\in \\mathbb{R}^{n_x\\times n_y}$ is the normalized measurement, which preserves a certain background and motion trajectory information, and $\\mathbf{X}_e\\in \\mathbb{R}^{n_x\\times n_y\\times B}$ represents the coarse estimate of the desired video. We then take $\\mathbf{X}_e$ as the input of the EfficientSCI network to get the final reconstruction result.", + "bbox": [ + 496, + 523, + 890, + 613 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "EfficientSCI network is mainly composed of three parts: i) feature extraction module, ii) ResDNet module and iii) video reconstruction module. The feature extraction module is mainly composed of three 3D convolutional layers with kernel sizes of $3 \\times 7 \\times 7$ , $3 \\times 3 \\times 3$ and $3 \\times 3 \\times 3$ respectively. Among them, each 3D convolution is followed by a LeakyReLU activation function [27], and the spatial stride step size of the final 3D convolution is 2. The spatial resolution of the final output feature map is reduced to half of the input. The feature extraction module effectively maps the input image space to the high-dimensional feature space. The ResDNet module is composed of $N$ ResDNet block (described in Sec. 4.1), which can efficiently explore spatial-temporal correlation. The video reconstruction module is composed of pixelshuffle [33] (mainly restore spatial resolution to input network input size) and three 3D convolution layers (kernel sizes are $3 \\times 3 \\times 3$ , $1 \\times 1 \\times 1$ and $3 \\times 3 \\times 3$ respectively), and conducts video reconstruction on the features output by the ResDNet blocks.", + "bbox": [ + 496, + 613, + 892, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "18479", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "4.1. ResDNet Block", + "text_level": 1, + "bbox": [ + 76, + 90, + 230, + 104 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Dense connection is an effective way to increase model capacity. Unlike DenseNet, which spans multiple layers, we build a more efficient dense connection within a single residual block. As shown in Fig. 3(b), the input features of the ResDNet block are first divided into $S$ parts along the feature channel dimension. Then, for each part $i = 1,\\dots ,S$ , we use CFormer (described in Section 4.2) to efficiently establish the spatial-temporal correlation. Specifically, for the input of the $i^{th}$ CFormer, we concatenate all the CFormer output features before the $i^{th}$ part with the input features of the $i^{th}$ part and then use a $1\\times 1\\times 1$ convolution to reduce the dimension of the feature channel, which can further reduce the computational complexity. Next, we concatenate all CFormer output features along the feature channel dimension and use a $1\\times 1\\times 1$ convolution to better fuse each part of the information. Given an input $\\mathbf{X}_r\\in \\mathbb{R}^{T\\times H\\times W\\times C}$ , ResDNet block can be expressed as:", + "bbox": [ + 75, + 113, + 473, + 371 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {X} _ {1}, \\dots , \\mathbf {X} _ {S} = \\operatorname {S p l i t} (\\mathbf {X} _ {r}),\n$$\n", + "text_format": "latex", + "bbox": [ + 76, + 380, + 261, + 398 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {Y} _ {1} = \\operatorname {C F o r m e r} _ {1} (\\mathbf {X} _ {1}),\n$$\n", + "text_format": "latex", + "bbox": [ + 80, + 400, + 233, + 416 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {Y} _ {2} = \\operatorname {C F o r m e r} _ {2} (\\operatorname {C o n v} _ {1} (\\operatorname {C o n c a t} ([ \\mathbf {Y} _ {1}, \\mathbf {X} _ {2} ]))),\n$$\n", + "text_format": "latex", + "bbox": [ + 80, + 419, + 392, + 436 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": ":", + "bbox": [ + 143, + 445, + 153, + 460 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {Y} _ {S} = \\operatorname {C F o r m e r} _ {\\mathrm {S}} \\left(\\operatorname {C o n v} _ {1} \\left(\\operatorname {C o n c a t} \\left([ \\mathbf {Y} _ {1}, \\dots , \\mathbf {Y} _ {S - 1}, \\mathbf {X} _ {S} ]\\right)\\right)\\right),\n$$\n", + "text_format": "latex", + "bbox": [ + 76, + 465, + 475, + 483 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {\\mathbf {Y}} _ {r} = \\operatorname {C o n c a t} ([ \\mathbf {Y} _ {1}, \\dots , \\mathbf {Y} _ {S} ]),\n$$\n", + "text_format": "latex", + "bbox": [ + 78, + 486, + 287, + 503 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {\\mathbf {X}} _ {r} = \\operatorname {C o n v} _ {1} \\left(\\hat {\\mathbf {Y}} _ {\\mathrm {r}}\\right) + \\mathbf {X} _ {r}, \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 76, + 508, + 468, + 526 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where 'Split' represents division along the channel, 'Conv1' represents a $1 \\times 1 \\times 1$ convolution operation, 'Concat' represents concatenate along the channel and $\\hat{\\mathbf{X}}_r \\in \\mathbb{R}^{T \\times H \\times W \\times C}$ represents the output of the ResDNet block. This design has two advantages: i) the features of different levels are aggregated at a more granular level, which improves the representation ability of the model; ii) the model complexity is reduced (shown in Table 6).", + "bbox": [ + 76, + 536, + 468, + 657 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4.2. CFormer Block", + "text_level": 1, + "bbox": [ + 76, + 665, + 233, + 680 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "As shown in Fig. 4, the CFormer block includes three parts: Spatial Convolution Branch (SCB), Temporal Self-Attention Branch (TSAB) and Feed Forward Network (FFN). Based on the space-time factorization mechanism, SCB is used to extract spatial local information, TSAB is used to calculate temporal attention of the feature points at the same spatial position in each frame. After that, FFN is used to further integrate spatial-temporal information.", + "bbox": [ + 75, + 688, + 468, + 809 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "It is worth noting that in order to make the model flexible to different compression ratios, we introduce zero padding position encoding [17] into CFormer block, instead of the absolute position encoding [10] or relative position encoding [22]. Specifically, we modified the first linear transformation layer in the traditional FFN to a $3 \\times 3 \\times 3$ convolution", + "bbox": [ + 75, + 810, + 470, + 901 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/a0822b709a03dae7cb6ac7dfd2c12207b9245dd4f13c2622be6834ba2a6470d3.jpg", + "image_caption": [ + "Figure 4. The CFormer block is composed of Spatial Convolution Branch (SCB), Temporal Self-Attention Branch (TSAB) and Feed Forward Network (FFN). For ease of presentation, only the head $N = 1$ scenario is described in the TSAB." + ], + "image_footnote": [], + "bbox": [ + 501, + 89, + 893, + 268 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "with padding size of 1.", + "bbox": [ + 500, + 340, + 653, + 354 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Spatial Convolution Branch: 2D convolution can well exploit spatial local correlation and reconstructs more detailed information, and it also enjoys efficient memory consumption and higher operating efficiency, which is suitable for large-scale video reconstruction. Therefore, We only use two $3 \\times 3$ 2D convolutions to reconstruct spatial local details in SCB as shown in Fig. 4.", + "bbox": [ + 496, + 354, + 890, + 460 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Temporal Self-attention Branch: The local receptive field of convolution makes it difficult to establish long-term dependencies. The global perception ability of Transformer can mitigate this issue. However, the time and memory complexity of traditional Transformers increase quadratically with the image size. To alleviate this problem, following [3, 35], we propose TSAB (shown in Fig. 4), which restricts the self-attention computation to the temporal domain, and its complexity only increases linearly with the image/video size.", + "bbox": [ + 496, + 460, + 892, + 611 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In particular, we first reshape the input $\\mathbf{X}_{st} \\in \\mathbb{R}^{T \\times H \\times W \\times \\frac{C}{S}}$ to $\\mathbf{X}_t \\in \\mathbb{R}^{HW \\times T \\times \\frac{C}{S}}$ , and then obtain query $(\\mathbf{Q} \\in \\mathbb{R}^{HW \\times T \\times \\frac{C}{2S}})$ , key $(\\mathbf{K} \\in \\mathbb{R}^{HW \\times T \\times \\frac{C}{2S}})$ and value $(\\mathbf{V} \\in \\mathbb{R}^{HW \\times T \\times \\frac{C}{2S}})$ by linearly mapping $\\mathbf{X}_t$ :", + "bbox": [ + 498, + 612, + 893, + 675 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {Q} = \\mathbf {X} _ {t} \\mathbf {W} ^ {Q}, \\quad \\mathbf {K} = \\mathbf {X} _ {t} \\mathbf {W} ^ {K}, \\quad \\mathbf {V} = \\mathbf {X} _ {t} \\mathbf {W} ^ {V}, \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 542, + 681, + 890, + 700 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\{\\mathbf{W}^Q,\\mathbf{W}^K,\\mathbf{W}^V\\} \\in \\mathbb{R}_{\\overline{S}}^{C\\times \\frac{C}{2S}}$ are projection matrices.", + "bbox": [ + 496, + 707, + 890, + 738 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "It is worth noting that the output dimension of the projection matrix is reduced to half of the input dimension, further decreasing the computational complexity of TSAB. Then, we respectively divide $\\mathbf{Q}$ , $\\mathbf{K}$ , $\\mathbf{V}$ into $N$ heads along the feature channel: $\\mathbf{Q} = \\{\\mathbf{Q}_j\\}_{1}^{N}$ , $\\mathbf{K} = \\{\\mathbf{K}_j\\}_{1}^{N}$ , $\\mathbf{V} = \\{\\mathbf{V}_j\\}_{1}^{N} \\in \\mathbb{R}^{HW \\times T \\times \\frac{C}{2SN}}$ . For each head $j = 1, \\dots, N$ , the attention can be calculated as:", + "bbox": [ + 496, + 739, + 890, + 847 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\operatorname {h e a d} _ {j} = \\mathbf {A} _ {j} * \\mathbf {V} _ {j}, \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 629, + 857, + 890, + 875 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\mathbf{A}_j = \\text{softmax}(\\mathbf{Q}_j\\mathbf{K}_j^T / \\sqrt{d}) \\in \\mathbb{R}^{HW \\times T \\times T}$ repre", + "bbox": [ + 500, + 883, + 890, + 902 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "18480", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "sents an attention map, $\\mathbf{K}_j^T$ represents the transposed matrix of $\\mathbf{K}_j$ and $d = \\frac{C}{2SN}$ is a scaling parameter. Then, we concatenate the outputs of $N$ heads along the feature channel dimension and perform a linear mapping to obtain the final output $\\hat{\\mathbf{X}}_t\\in \\mathbb{R}^{T\\times H\\times W\\times \\frac{C}{S}}$ of TSAB:", + "bbox": [ + 75, + 90, + 468, + 167 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {\\mathbf {X}} _ {t} = \\mathbf {R} \\left(\\mathbf {W} ^ {P} \\left(\\operatorname {C o n c a t} \\left[ h e a d _ {1}, \\dots , h e a d _ {N} \\right]\\right)\\right), \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 102, + 176, + 468, + 194 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\mathbf{W}^P\\in \\mathbb{R}^{\\frac{C}{2S}\\times \\frac{C}{S}}$ represents projection matrices, and $\\mathbf{R}$ is the reshape operator.", + "bbox": [ + 76, + 200, + 468, + 233 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/ff463ca59205c496ebfe285d817416e4fb875fe2cbb5c391aac7d12b0aa87241.jpg", + "table_caption": [ + "Table 1. Computational complexity of several SOTA methods." + ], + "table_footnote": [], + "table_body": "
MethodComputational Complexity
SCB3D1/2HWTK3C2
G-MSAHWTC2+(HWT)2C
TS-MSA2HWTC2+T(HW)2C+HWT2C
SCB1/2HWTK2C2
TSAB1/2HWTC2+1/2HWT2C
", + "bbox": [ + 127, + 263, + 410, + 359 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We further analyze the computational complexity of SCB and TSAB, and compare them with 3D convolution and several classic Multi-head Self-Attention (MSA) mechanisms. The results are shown in Table 1, where 'SCB3D' represents the replacement of 2D convolution in SCB with 3D convolution and $K$ represents the kernel size, 'G-MSA' represents the original global MSA [10], and 'TS-MSA' represents the MSA in TimeSformer [3]. It can be observed that the computational complexity of our proposed SCB and TSAB grows linearly with the spatial size $HW$ , the computational cost is much less than 'TS-MSA' and 'G-MSA' (grow quadratically with $HW$ ). Compared with 3D convolution, since $T$ is generally smaller than $C$ , 'SCB' and 'TSAB' still need less computational cost.", + "bbox": [ + 75, + 364, + 468, + 575 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Feed Forward Network: The feed forward network of traditional Transformer usually uses two linear layers and a nonlinear activation function to learn more abstract feature representations. However, in the whole FFN, there is no interaction between the feature points. In order to better integrate the spatial-temporal information and position coding information, we replace the first linear transformation layer in the traditional FFN with a $3 \\times 3 \\times 3$ convolution.", + "bbox": [ + 75, + 575, + 468, + 696 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Given $\\mathbf{X}_f\\in \\mathbb{R}^{T\\times H\\times W\\times \\frac{C}{2}}$ , FFN can be expressed as:", + "bbox": [ + 96, + 696, + 452, + 712 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {\\mathbf {X}} _ {f} = \\mathbf {X} _ {f} + \\mathbf {W} _ {1} \\left(\\phi \\left(\\mathbf {W} _ {2} \\left(\\mathbf {X} _ {f}\\right)\\right)\\right), \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 161, + 720, + 468, + 739 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\mathbf{W}_1, \\mathbf{W}_2$ represent $1 \\times 1 \\times 1$ convolution and $3 \\times 3 \\times 3$ convolution operations respectively, $\\phi$ denotes the LeakyReLU non-linearity activation, and $\\hat{\\mathbf{X}}_f \\in \\mathbb{R}^{T \\times H \\times W \\times \\frac{C}{2}}$ is the output of the FFN.", + "bbox": [ + 76, + 747, + 468, + 809 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "It should be noted that in the whole CFormer block, we do not use any regularization layers, such as Layer Normalization [1] and Batch Normalization [16]. The experimental results show that removing the regularization layer will not reduce the quality of model reconstruction and can further improve the efficiency of the model.", + "bbox": [ + 75, + 810, + 468, + 900 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/b97cd128071263344403babfc1cc3b5276b1cf90a6cbc1b3691ad9dece141532.jpg", + "table_caption": [ + "Table 2. Reconstruction quality and test time (s) using EfficientSCI with different number of channels and blocks." + ], + "table_footnote": [], + "table_body": "
ModelChannelBlockPSNRSSIMTest time(s)
EfficientSCI-T64834.220.9610.07
EfficientSCI-S128835.510.9700.15
EfficientSCI-B256836.480.9750.31
EfficientSCI-L2561236.920.9770.45
", + "bbox": [ + 532, + 117, + 856, + 190 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/23c017ad2553a2766391b68ba070fbc5ab0bf717e44e76ae838a45f8cfd911ca.jpg", + "table_caption": [ + "Table 3. Computational complexity and reconstruction quality of several SOTA algorithms on 6 grayscale benchmark datasets." + ], + "table_footnote": [], + "table_body": "
MethodParams (M)FLOPs (G)PSNRSSIM
BIRNAT4.13390.5633.310.951
RevSCI5.66766.9533.920.956
DUN-3DUnet61.913975.8335.260.968
ELP-Unfolding565.734634.9435.410.969
EfficientSCI-T0.95142.1834.220.961
EfficientSCI-S3.78563.8735.510.970
EfficientSCI-B8.821426.3836.480.975
EfficientSCI-L12.391893.7236.920.977
", + "bbox": [ + 550, + 226, + 834, + 342 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Network Variants: To balance speed and performance of the proposed network, we introduce four different versions of EfficientSCI network, dubbed as EfficientSCI-T, EfficientSCI-S, EfficientSCI-B and EfficientSCI-L standing for Tiny, Small, Base and Large networks, respectively. The network hyper-parameters are shown in Table 2, in which we mainly changed the the number of ResD-Net blocks and the number of channels. As shown in Table 3, we also compare model parameters and computational complexity (FLOPs) with several advanced methods. The complexity of our proposed EfficientSCI-T is smaller than that of BIRNAT and RevSCI, and EfficientSCI-L is smaller than that of DUN-3DUnet and ELP-Unfolding.", + "bbox": [ + 496, + 352, + 890, + 549 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "5. Experiment Results", + "text_level": 1, + "bbox": [ + 500, + 563, + 689, + 580 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "5.1. Datasets", + "text_level": 1, + "bbox": [ + 500, + 588, + 601, + 602 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Following BIRNAT [8], we use DAVIS2017 [29] with resolution $480 \\times 894$ (480p) as the model training dataset. To verify model performance, we first test the EfficientSCI network on several simulated datasets, including six benchmark grayscale datasets (Kobe, Traffic, Runner, Drop, Crash and Aerial with a size of $256 \\times 256 \\times 8$ ), six benchmark mid-scale color datasets (Beauty, Bosphorus, Jockey, Runner, ShakeNDry and Traffic with a size of $512 \\times 512 \\times 3 \\times 8$ ), and four large-scale datasets (Messi, Hummingbird, Swinger and Football with different sizes and compression ratios). Then we test our model on some real data (including Duomino, Water Balloon) captured by a real SCI system [30].", + "bbox": [ + 496, + 609, + 890, + 821 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "5.2. Implementation Details", + "text_level": 1, + "bbox": [ + 500, + 832, + 717, + 847 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We use PyTorch framework with 4 NVIDIA RTX 3090 GPUs for training with random cropping, random scaling, and random flipping for data augmentation, and use", + "bbox": [ + 496, + 854, + 890, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "18481", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/fe3a163dbdaec1bb433c3a29f32bd34deffda629d3e95a463fd73a7d49a79a05.jpg", + "table_caption": [ + "Table 4. The average PSNR in dB (left entry) and SSIM (right entry) and running time per measurement of different algorithms on 6 benchmark grayscale datasets. The best results are shown in bold and the second-best results are underlined." + ], + "table_footnote": [], + "table_body": "
MethodKobeTrafficRunnerDropCrashAerialAverageTest time(s)
GAP-TV26.46, 0.88520.89, 0.71528.52, 0.90934.63, 0.97024.82, 0.83825.05, 0.82826.73, 0.8584.2 (CPU)
PnP-FFDNet30.50, 0.92624.18, 0.82832.15, 0.93340.70, 0.98925.42, 0.84925.27, 0.82929.70, 0.8923.0 (GPU)
PnP-FastDVDnet32.73, 0.94727.95, 0.93236.29, 0.96241.82, 0.98927.32, 0.92527.98, 0.89732.35, 0.9426.0 (GPU)
DeSCI33.25, 0.95228.71, 0.92538.48, 0.96943.10, 0.99327.04, 0.90925.33, 0.86032.65, 0.9356180 (CPU)
BIRNAT32.71, 0.95029.33, 0.94238.70, 0.97642.28, 0.99227.84, 0.92728.99, 0.91733.31, 0.9510.10 (GPU)
RevSCI33.72, 0.95730.02, 0.94939.40, 0.97742.93, 0.99228.12, 0.93729.35, 0.92433.92, 0.9560.19 (GPU)
GAP-CCoT32.58, 0.94929.03, 0.93839.12, 0.98042.54, 0.99228.52, 0.94129.40, 0.92333.53, 0.9580.08 (GPU)
DUN-3DUnet35.00, 0.96931.76, 0.96640.03, 0.98044.96, 0.99529.33, 0.95630.46, 0.94335.26, 0.9680.58 (GPU)
ELP-Unfolding34.41, 0.96631.58, 0.96241,16, 0.98644.99, 0.99529.65, 0.95930.68, 0.94435.41, 0.9690.34 (GPU)
EfficientSCI-T33.45, 0.96029.20, 0.94239.51, 0.98143.56, 0.99329.27, 0.95430.32, 0.93734.22, 0.9610.07 (GPU)
EfficientSCI-S34.79, 0.96831.21, 0.96141.34, 0.98644.61, 0.99430.34, 0.96530.78, 0.94535.51, 0.9700.15 (GPU)
EfficientSCI-B35.76, 0.97432.30, 0.96843.05, 0.98845.18, 0.99531.13, 0.97131.50, 0.95336.48, 0.9750.31 (GPU)
EfficientSCI-L36.27, 0.97632.83, 0.97143.79, 0.99145.46, 0.99531.52, 0.97431.64, 0.95536.92, 0.9770.45 (GPU)
", + "bbox": [ + 83, + 118, + 883, + 318 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/10f5dbc5f4fdf5b517365203a522ccd68a97a42925a72fd1833f862f976beb51.jpg", + "image_caption": [ + "Figure 5. Selected reconstruction frames of simulated grayscale data. Zoom in for better view." + ], + "image_footnote": [], + "bbox": [ + 81, + 327, + 467, + 547 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Adam [19] to optimize the model with the initial learning rate 0.0001. After iterating for 300 epochs, we adjusted the learning rate to 0.00001 and continued to iterate for 40 epochs to get the final model parameters. The peak-signal-to-noise-ratio (PSNR) and structured similarity index metrics (SSIM) [38] are used as the performance indicators of reconstruction quality.", + "bbox": [ + 75, + 585, + 470, + 691 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5.3. Results on Simulation Datasets", + "text_level": 1, + "bbox": [ + 76, + 700, + 349, + 717 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5.3.1 Grayscale Simulation Video", + "text_level": 1, + "bbox": [ + 76, + 724, + 326, + 739 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We compare our method with SOTA model-based methods (GAP-TV [44], PnP-FFDNet [46], PnP-FastDVDnet [47], DeSCI [21]) and deep learning-based methods (BIR-NAT [8], RevSCI [7], GAP-CCoT [36], DUN-3DUnet [40], ELP-Unfolding [42]) on simulated grayscale datasets. Table 4 shows the quantitative comparison results, it can be observed that our proposed EfficientSCI-L can achieve the highest reconstruction quality and has good real-time performance. In particular, the PSNR value of our method surpasses the existing best method ELP-Unfolding by 1.46", + "bbox": [ + 75, + 750, + 470, + 902 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "dB on average. In addition, our proposed EfficientSCIT achieves high reconstruction quality while achieving the best real-time performance. It is worth noting that, for a fair comparison, we uniformly test the running time of all deep learning based methods on the same NVIDIA RTX 3090 GPU. Fig. 5 shows the visual reconstruction results of some data. By zooming in some local areas, we can observe that our method can recover sharper edges and more detailed information compared to previous SOTA methods. The mid-scale color results are shown in the SM due to space limitation and our method outperforms previous SOTA by 2.02 dB in PSNR on the benchmark dataset [47].", + "bbox": [ + 496, + 330, + 893, + 512 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5.3.2 Large-scale Color Simulation Video", + "text_level": 1, + "bbox": [ + 498, + 530, + 803, + 545 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Most deep learning based methods, such as BIRNAT [8], DUN-3DUnet [40], cannot be applied to large-scale data reconstruction due to excessive model complexity and GPU memory constraints. RevSCI [7] uses a reversible mechanism and can reconstruct a 24 frames RGB color video with size of $1080 \\times 1920 \\times 3$ , but training the model is extremely slow. GAP-CCoT [36] and ELP-Unfolding [42] only use 2D convolution for reconstruction and thus cannot handle color video data well. Therefore, we only compare with several SOTA model-based methods (GAP-TV [44], PnP-FFDNet-color [46], PnP-FastDVDnet-color [47]) on large-scale color data. Table 5 shows the comparisons between our proposed method and several model-based methods on PSNR, SSIM and test time (in minutes). It can be observed that model-based methods either have long reconstruction time (PnP-FFDNet-color, PnP-FastDVDnet-color) or low reconstruction quality (GAP-TV). Our proposed EfficientSCI-S can achieve higher reconstruction quality and running speed. Especially on UHD color video football $(1644 \\times 3840 \\times 3 \\times 40)$ , the PSNR value of our method is 2.5 dB higher than PnP-FastDVDnet-color, and the reconstruction time is only $0.5\\%$ of it. Fig. 6 shows some visual reconstruction results. By zooming", + "bbox": [ + 496, + 551, + 890, + 902 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "18482", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/f7578abf2d7174cd0feb84037cd84fa81896f69277b64cb44d570cbdff57e983.jpg", + "table_caption": [ + "Table 5. The average PSNR in dB (left entry) and SSIM (middle entry) and test time (minutes) per measurement (right entry) of different algorithms on 4 benchmark large-scale datasets. Best results are in bold." + ], + "table_footnote": [], + "table_body": "
DatasetPixel resolutionGAP-TVPnP-FFDNet-colorPnP-FastDVDnet-colorEfficientSCI-S
Messi1080 × 1920 × 3 × 825.20, 0.874, 0.6634.28, 0.968, 14.9334.34, 0.970, 15.9434.41, 0.973, 0.09
Hummingbird1080 × 1920 × 3 × 3025.10, 0.750, 20.328.79, 0.665, 61.2031.17, 0.916, 54.0035.56, 0.952, 0.39
Swinger2160 × 3840 × 3 × 1522.68, 0.769, 39.229.30, 0.934, 138.830.57, 0.949, 138.431.05, 0.951, 0.62
Football1644 × 3840 × 3 × 4026.19, 0.858, 83.032.70, 0.951, 308.832.31, 0.947, 298.134.81, 0.964, 1.52
", + "bbox": [ + 86, + 128, + 879, + 212 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/d17274b01809fdeea6cfc85ca178d50b6190ef28083d9a2c8ba399f8da85c83c.jpg", + "image_caption": [ + "Figure 6. Comparison of reconstruction results of different algorithms on several benchmark large-scale color video simulation datasets." + ], + "image_footnote": [], + "bbox": [ + 86, + 222, + 879, + 569 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/aa88788552c191bfde1524a8d9791ac8bc906306a3546dcddfbaa14622a37abe.jpg", + "image_caption": [ + "Figure 7. Reconstruction quality (PSNR in dB, higher is better) of different reconstruction algorithms, with varying compression rates $B$ from 8 to 48." + ], + "image_footnote": [], + "bbox": [ + 84, + 602, + 459, + 765 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "in local areas, we can observe that the reconstruction results of our method are closer to the real value. In addition, our proposed model enjoys high flexibility for different compression ratios, that is, the model trained on low compression ratio data can be directly used for high com", + "bbox": [ + 75, + 825, + 470, + 902 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "pression ratio video reconstruction task. To verify this, we test hummingbird data with different compression ratios $B = 8, 16, 24, 32, 40, 48$ , and the reconstruction results are shown in Fig. 7. We can observe that our method can be applied to video data with different compression ratios, even when the compression ratio $B$ grows to 48, the PSNR value of EfficientSCI-T model can still reach more than 32 dB. Moreover, our proposed approach surpasses other reconstruction algorithms at all compression ratios.", + "bbox": [ + 496, + 606, + 893, + 743 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.3.3 Ablation Study", + "text_level": 1, + "bbox": [ + 500, + 768, + 660, + 784 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "To verify the performance of the proposed ResDNet block and CFormer block on the impact of the reconstruction quality, we conduct some ablation experiments. The results are shown in Table 6 and Table 7, we not only compare the reconstruction quality of different models, but also analyze the model parameters and FLOPs. All experiments are conducted on the 6 grayscale benchmark datasets.", + "bbox": [ + 496, + 794, + 893, + 902 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "18483", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/a1067afe16e95ce228ed332898d092f799a2e0bf257f34d01e67a216ebbc1451.jpg", + "table_caption": [ + "Table 6. Ablation study on the ResDNet block without dense connections (left entry) and with dense connections (right entry)." + ], + "table_footnote": [], + "table_body": "
GNParamsFLOPsPSNRSSIM
127.40, 27.403860.94, 3860.9435.17, 35.170.967, 0.967
214.82, 15.082211.77, 2246.3935.09, 36.020.966, 0.974
48.53, 8.821387.33, 1426.3835.02, 36.480.966, 0.975
85.38, 5.65975.39, 1013.4534.31, 35.680.961, 0.971
", + "bbox": [ + 81, + 114, + 467, + 186 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/a0b1e1f03ef1255e0640026d69fa791ce30b9aaf5aabe8203bec504b1a9743af.jpg", + "table_caption": [ + "Table 7. Ablation study on the CFormer block." + ], + "table_footnote": [], + "table_body": "
SCBTSABSwinS2-3DParams (M)FLOPs (G)PSNRSSIM
✓✓2.88471.0334.990.967
✓6.93999.3134.930.966
✓✓3.78563.8735.510.970
", + "bbox": [ + 81, + 214, + 465, + 270 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "ResDNet Block: We verify the effect of different group numbers (GN) (corresponding to $S$ in Eq. 5) and dense connections on the reconstruction quality. As shown in Table 6, the model complexity decreases gradually with the increase of GN, but the reconstruction quality greatly decreases when there are no dense connections in the ResDNet block. By introducing dense connections in the ResDNet block, the reconstruction quality of our proposed method is greatly improved, and a gain of $1.46\\mathrm{dB}$ can be obtained when GN is 4.", + "bbox": [ + 75, + 291, + 467, + 440 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "CFormer Block: In the CFormer block, we first replace SCB with Swin Transformer (Swin) to verify its effectiveness. Then, we replace SCB and TSAB with two stacked 3D convolutions (S2-3D) to verify the effectiveness of TSAB. As shown in Table 7, compared with Swin Transformer, SCB can bring a $0.52\\mathrm{dB}$ gain. Although the number of parameters and FLOPs have increased, the experimental results show that SCB takes up less memory than the Swin Transformer, which is very important for large-scale and high compression ratio data. Please refer to more detailed analysis in SM. Compared with SCB and TSAB, S2-3D not only increases model parameters and FLOPs by $83\\%$ and $77\\%$ respectively, but also reduces the PSNR value by 0.58 dB, which verifies the necessity of using space-time factorization and TSAB.", + "bbox": [ + 75, + 441, + 467, + 667 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Number of Channels and Blocks: Table 2 shows that the quality of model reconstruction increases with the number of channels and blocks. However, the amount of parameters and FLOPs also increase (see Table 3), resulting in a degradation in the real-time performance of the model.", + "bbox": [ + 75, + 669, + 467, + 744 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5.4. Results on Real Video SCI Data", + "text_level": 1, + "bbox": [ + 76, + 756, + 356, + 770 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We further test our method on real data. Fig. 8 and Fig. 9 show the reconstruction results of multiple algorithms on two public data (Duomino, Water Ballon), we can see that our method can reconstruct clearer details and edges. Specifically, we can clearly recognize the letters on the Duomino. Even with a high compression ratio $(B = 50)$ , our proposed method can still reconstruct clear foreground and background information (shown in Fig. 9).", + "bbox": [ + 75, + 779, + 467, + 900 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/b086261c597715f90d12709648405d9000afb9b96062e7d12afcbc57c4292949.jpg", + "image_caption": [ + "Figure 8. Reconstruction results of different algorithms on Duomino real data with compression rate $B = 10$ ." + ], + "image_footnote": [], + "bbox": [ + 501, + 88, + 890, + 303 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/6440a8697529966d1698e0d40cc006be5cfaef126a45224c11dc9031daa0ebb0.jpg", + "image_caption": [ + "Figure 9. Reconstruction results of different algorithms on Water Ballon real data with compression rate $B = 50$ ." + ], + "image_footnote": [], + "bbox": [ + 501, + 359, + 890, + 536 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "6. Conclusions and Future Work", + "text_level": 1, + "bbox": [ + 500, + 585, + 774, + 599 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "This paper proposes an efficient end-to-end video SCI reconstruction network, dubbed EfficientSCI, which achieves the state-of-the-art performance on simulated data and real data, significantly surpassing the previous best reconstruction algorithms with high real-time performance. In addition, we show for the first time that an UHD color video with high compression rate can be reconstructed using a deep learning based method. For future work, we consider applying EfficientSCI Network to more SCI reconstruction tasks, such as spectral SCI [4, 49].", + "bbox": [ + 496, + 613, + 890, + 765 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgements", + "text_level": 1, + "bbox": [ + 500, + 789, + 666, + 806 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "This work was supported by the National Natural Science Foundation of China [62271414], Zhejiang Provincial Natural Science Foundation of China [LR23F010001]. We would like to thank Research Center for Industries of the Future (RCIF) at Westlake University and the funding from Lochn Optics.", + "bbox": [ + 496, + 816, + 890, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "18484", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Jimmy Lei Ba, Jamie Ryan Kiros, and Geoffrey E Hinton. Layer normalization. arXiv preprint arXiv:1607.06450, 2016. 5", + "[2] Jens Behrmann, Will Grathwohl, Ricky TQ Chen, David Duvenaud, and Jorn-Henrik Jacobsen. Invertible residual networks. In International Conference on Machine Learning, pages 573-582. PMLR, 2019. 2", + "[3] Gedas Bertasius, Heng Wang, and Lorenzo Torresani. Is space-time attention all you need for video understanding? 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In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 5728-5739, 2022. 2" + ], + "bbox": [ + 501, + 92, + 890, + 738 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "18486", + "bbox": [ + 480, + 945, + 519, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/EfficientSCI_ Densely Connected Network With Space-Time Factorization for Large-Scale Video Snapshot Compressive Imaging/ba9925d6-1c9f-468a-bc9d-dc4b6c4a5ca6_model.json b/2023/EfficientSCI_ Densely Connected Network With Space-Time Factorization for Large-Scale Video Snapshot Compressive Imaging/ba9925d6-1c9f-468a-bc9d-dc4b6c4a5ca6_model.json new file mode 100644 index 0000000000000000000000000000000000000000..ba3698f444077c610ea496f0f4b0879ebe3e9fdc --- /dev/null +++ b/2023/EfficientSCI_ Densely Connected Network With Space-Time Factorization for Large-Scale Video Snapshot Compressive Imaging/ba9925d6-1c9f-468a-bc9d-dc4b6c4a5ca6_model.json @@ -0,0 +1,2156 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.0, + 0.812, + 0.045 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.102, + 0.13, + 0.87, + 0.177 + ], + "angle": 0, + "content": "EfficientSCI: Densely Connected Network with Space-time Factorization for Large-scale Video Snapshot Compressive Imaging" + }, + { + "type": "text", + "bbox": [ + 0.279, + 0.203, + 0.687, + 0.221 + ], + "angle": 0, + "content": "Lishun Wang \\(^{1,2,*}\\), Miao Cao \\(^{3,4,*}\\), and Xin Yuan \\(^{3,\\dagger}\\)" + }, + { + "type": "text", + "bbox": [ + 0.18, + 0.221, + 0.788, + 0.24 + ], + "angle": 0, + "content": "1 Chengdu Institute of Computer Application Chinese Academy of Sciences," + }, + { + "type": "text", + "bbox": [ + 0.122, + 0.24, + 0.842, + 0.258 + ], + "angle": 0, + "content": "\\(^{2}\\) University of Chinese Academy of Sciences, \\(^{3}\\) Westlake University, \\(^{4}\\) Zhejiang University" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.292, + 0.314, + 0.308 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.324, + 0.474, + 0.718 + ], + "angle": 0, + "content": "Video snapshot compressive imaging (SCI) uses a two-dimensional detector to capture consecutive video frames during a single exposure time. Following this, an efficient reconstruction algorithm needs to be designed to reconstruct the desired video frames. Although recent deep learning-based state-of-the-art (SOTA) reconstruction algorithms have achieved good results in most tasks, they still face the following challenges due to excessive model complexity and GPU memory limitations: 1) these models need high computational cost, and 2) they are usually unable to reconstruct large-scale video frames at high compression ratios. To address these issues, we develop an efficient network for video SCI by using dense connections and space-time factorization mechanism within a single residual block, dubbed EfficientSCI. The EfficientSCI network can well establish spatial-temporal correlation by using convolution in the spatial domain and Transformer in the temporal domain, respectively. We are the first time to show that an UHD color video with high compression ratio can be reconstructed from a snapshot 2D measurement using a single end-to-end deep learning model with PSNR above 32 dB. Extensive results on both simulation and real data show that our method significantly outperforms all previous SOTA algorithms with better real-time performance. The code is at https://github.com/ucaswangls/EfficientSCI.git." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.746, + 0.21, + 0.761 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.772, + 0.47, + 0.879 + ], + "angle": 0, + "content": "Traditional high-speed camera imaging methods usually suffer from high hardware and storage transmission cost. Inspired by compressed sensing (CS) [5, 9], video snapshot compressive imaging (SCI) [45] provides an elegant solution. As shown in Fig. 2, video SCI consists of a hardware encoder and a software decoder. In the encoder part, multiple raw video frames are modulated by different masks and" + }, + { + "type": "image", + "bbox": [ + 0.502, + 0.29, + 0.895, + 0.519 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.525, + 0.895, + 0.596 + ], + "angle": 0, + "content": "Figure 1. Comparison of reconstruction quality (average PSNR in dB on 6 benchmark grayscale datasets) and testing time of several SOTA deep learning based algorithms. Our proposed EfficientSCI achieves higher reconstruction quality with fewer parameters and shorter testing time." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.607, + 0.894, + 0.682 + ], + "angle": 0, + "content": "then integrated by the camera to get a compressed measurement, giving low-speed cameras the ability to capture high-speed scenes. For the decoding part, the desired high-speed video is retrieved by the reconstruction algorithm using the captured measurement and masks." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.686, + 0.895, + 0.883 + ], + "angle": 0, + "content": "So far, many mature SCI imaging systems [14, 24, 31] have been built, but for the decoding part, there are still many challenges. In particular, although the model-based methods [21, 43, 44] have good flexibility and can reconstruct videos with different resolutions and compression rates, they require long reconstruction time and can only achieve poor reconstruction quality. In order to improve the reconstruction quality and running speed, PnP-FFDNet [46] and PnP-FastDVDnet [47] integrate the pre-trained denoising network into an iterative optimization algorithm. However, they still need a long reconstruction time on large-scale datasets, e.g., PnP-FastDVDNet takes hours to reconstruct a UHD video from a single measurement." + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.886, + 0.892, + 0.902 + ], + "angle": 0, + "content": "By contrast, deep learning based methods [28,30,35,40]" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.887, + 0.341, + 0.901 + ], + "angle": 0, + "content": "*Equal Contribution, † Corresponding Author" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "18477" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.089, + 0.468, + 0.239 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.081, + 0.247, + 0.458, + 0.262 + ], + "angle": 0, + "content": "Figure 2. Schematic diagram of grayscale and color video SCI." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.272, + 0.47, + 0.589 + ], + "angle": 0, + "content": "have better real-time performance and higher reconstruction quality. For example, BIRNAT [8] uses bidirectional recurrent neural network and generative adversarial method to surpass model-based method DeSCI [21] for the first time. MetaSCI [39] has made some explorations for the model to adapt to different masks, which reduces the model training time. DUN-3DUnet [40] and ELP-Unfolding [42] combine iterative optimization ideas with deep learning models to further improve reconstruction quality. However, due to the high model complexity and insufficient GPU memory, most existing deep learning algorithms cannot train the models required for reconstructing HD or large-scale videos. RevSCI [7] uses a reversible mechanism [2] to reduce the memory used for model training, and can reconstruct HD video with a compression rate up to 24, but the model training time increases exponentially. In addition, the current reconstruction algorithms generally use convolution to establish spatial-temporal correlation. Due to the local connection of convolution, long-term dependencies cannot be well established, and the model cannot reconstruct data with high compression rates." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.589, + 0.47, + 0.771 + ], + "angle": 0, + "content": "In summary, model-based methods usually require long reconstruction time and can only achieve poor reconstruction quality. Learning-based methods have high model complexity but cannot be well applied to large-scale color video reconstruction. To address these challenges, we develop an efficient network for video SCI by using dense connections and space-time factorization mechanism. As shown in Fig. 1, our proposed method dramatically outperforms all previous deep learning based reconstruction algorithms in terms of reconstruction quality and running speed with fewer parameters. Our main contributions can be summarized as follows:" + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.783, + 0.468, + 0.827 + ], + "angle": 0, + "content": "- An efficient end-to-end network, dubbed EfficientSCI, is proposed for reconstructing high quality video frames from a snapshot SCI measurement." + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.84, + 0.468, + 0.901 + ], + "angle": 0, + "content": "- By building hierarchical dense connections within a single residual block, we devise a novel ResDNet block to effectively reduces model computational complexity but enhance the learning ability of the model." + }, + { + "type": "list", + "bbox": [ + 0.096, + 0.783, + 0.468, + 0.901 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.092, + 0.892, + 0.168 + ], + "angle": 0, + "content": "- Based on the space-time factorization mechanism, a Convolution and Transformer hybrid block (CFormer) is built, which can efficiently establish space-time correlation by using convolution in the spatial domain and Transformer in the temporal domain, respectively." + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.18, + 0.892, + 0.24 + ], + "angle": 0, + "content": "- Experimental results on a large number of simulated and real datasets demonstrate that our proposed method achieves state-of-the-art (SOTA) results and better real-time performance." + }, + { + "type": "list", + "bbox": [ + 0.518, + 0.092, + 0.892, + 0.24 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.255, + 0.642, + 0.271 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.281, + 0.892, + 0.612 + ], + "angle": 0, + "content": "CNN and Variants: In the past ten years, models with convolutional neural networks (CNN) as the backbone [13,15,20] have achieved excellent results on multiple computer vision tasks [20, 25, 32]. Among them, ResNeXt [41] and Res2Net [11] effectively increases model capacity without increasing model complexity by using grouped convolutions inside residual blocks. DenseNet [15] and CSPNet [34] achieve feature reuse by taking all previous feature maps as input. In video-related tasks, 3D convolution can establish good spatial-temporal correlation and has been widely used in action recognition [18], video superresolution [26], video inpainting [6] and so on. In previous video SCI reconstruction, RevSCI and DUN-3DUnet greatly improve the reconstruction quality of benchmark grayscale datasets by integrating 3D convolution into the network. However, in complex high-speed scenarios (e.g., crash), since they cannot effectively establish long-term temporal dependencies, the reconstruction quality is still lower than \\(30\\mathrm{dB}\\). In addition, the excessive use of 3D convolution increases the amount of model parameters, which is not conducive to the application of large-scale and high compression ratio data." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.614, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Vision Transformers: Most recently, Vision Transformer (ViT) [10] and its variants [4, 12, 37, 50] have achieved competitive results in computer vision. However, the high computational complexity limits its application in video-related tasks. TimeSformer [3] performs self-attention calculations in time and space respectively, which reduces model complexity and improves model accuracy, but the computational complexity still increases quadratically with the image size. The Video Swin Transformer [23] limits self-attention calculations to local windows but cannot effectively establish long-term temporal dependencies. In addition, a large number of experimental results show that Transformer has higher memory consumption than CNN, and using Transformer in space is not conducive to large-scale video SCI reconstruction. Therefore, through space-time factorization mechanism, using Transformer only in time domain can not only effectively utilize its ability to establish long-term time series dependencies, but also reduce model complexity and memory consumption." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.956 + ], + "angle": 0, + "content": "18478" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.099, + 0.087, + 0.87, + 0.274 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.276, + 0.894, + 0.346 + ], + "angle": 0, + "content": "Figure 3. Architecture of the proposed EfficientSCI network and the overall process of color or grayscale video reconstruction. The measurement \\((\\mathbf{Y})\\) and masks \\((\\mathbf{M})\\) are pre-processed by the estimation module to obtain an estimated \\(\\mathbf{X}_e\\), and then feed \\(\\mathbf{X}_e\\) into EfficientSCI network to get the desired reconstruction result. (a) ResDNet module with \\(N\\) residual style units. (b) ResDNet block. Inside a residual block, the input features are divided into \\(S\\) parts by the channel split. Each part uses CFormer to efficiently extract spatial-temporal correlation, and employs dense connections to further improve model capacity. For convenience, only the case of \\(S = 4\\) is shown here." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.352, + 0.391, + 0.369 + ], + "angle": 0, + "content": "3. Mathematical Model of Video SCI" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.377, + 0.471, + 0.483 + ], + "angle": 0, + "content": "Fig. 2 briefly describes the flow chart of video SCI. For grayscale video SCI system, the original \\(B\\)-frame (grayscale) input video \\(\\{\\mathbf{X}_m\\}_{m=1}^B \\in \\mathbb{R}^{n_x \\times n_y}\\) is modulated by pre-defined masks \\(\\{\\mathbf{M}\\}_{m=1}^B \\in \\mathbb{R}^{n_x \\times n_y}\\). Then, by compressing across time, the camera sensor captures a compressed measurement \\(\\mathbf{Y} \\in \\mathbb{R}^{n_x \\times n_y}\\). The whole process can be expressed as:" + }, + { + "type": "equation", + "bbox": [ + 0.171, + 0.491, + 0.47, + 0.513 + ], + "angle": 0, + "content": "\\[\n\\mathbf {Y} = \\sum_ {m = 1} ^ {B} \\mathbf {X} _ {m} \\odot \\mathbf {M} _ {m} + \\mathbf {Z}, \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.521, + 0.47, + 0.629 + ], + "angle": 0, + "content": "where \\(\\odot\\) denotes the Hadamard (element-wise) multiplication, and \\(\\mathbf{Z} \\in \\mathbb{R}^{n_x \\times n_y}\\) denotes the measurement noise. Eq. (1) can also be represented by a vectorized formulation. Firstly, we vectorize \\(\\pmb{y} = \\operatorname{vec}(\\mathbf{Y}) \\in \\mathbb{R}^{n_x n_y}\\), \\(\\pmb{z} = \\operatorname{vec}(\\mathbf{Z}) \\in \\mathbb{R}^{n_x n_y}\\), \\(\\pmb{x} = [\\pmb{x}_1^\\top, \\dots, \\pmb{x}_B^\\top]^\\top \\in \\mathbb{R}^{n_x n_y B}\\), where \\(\\pmb{x}_m = \\operatorname{vec}(\\mathbf{X}_m)\\). Then, sensing matrix generated by masks can be defined as:" + }, + { + "type": "equation", + "bbox": [ + 0.146, + 0.638, + 0.47, + 0.657 + ], + "angle": 0, + "content": "\\[\n\\mathbf {H} = \\left[ \\mathbf {D} _ {1}, \\dots , \\mathbf {D} _ {B} \\right] \\in \\mathbb {R} ^ {n _ {x} n _ {y} \\times n _ {x} n _ {y} B}, \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.665, + 0.469, + 0.713 + ], + "angle": 0, + "content": "where \\(\\mathbf{D}_m = \\mathrm{Diag}(\\mathrm{vec}(\\mathbf{M}))\\in \\mathbb{R}^{n_xn_y\\times n_xn_y}\\) is a diagonal matrix and its diagonal elements is filled by \\(\\operatorname {vec}(\\mathbf{M})\\) Finally, the vectorized expression of Eq. (1) is" + }, + { + "type": "equation", + "bbox": [ + 0.224, + 0.723, + 0.47, + 0.739 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {y} = \\mathbf {H} \\boldsymbol {x} + \\boldsymbol {z}. \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.749, + 0.471, + 0.902 + ], + "angle": 0, + "content": "For color video SCI system, we use the Bayer pattern filter sensor, where each pixel captures only red (R), blue (B) or green (G) channel of the raw data in a spatial layout such as 'RGGB'. Since adjacent pixels are different color components, we divide the original measurement \\(\\mathbf{Y}\\) into four sub-measurements \\(\\{\\mathbf{Y}^r,\\mathbf{Y}^{g1},\\mathbf{Y}^{g2},\\mathbf{Y}^b\\} \\in \\mathbb{R}^{\\frac{n_x}{2}\\times \\frac{n_y}{2}}\\) according to the Bayer filter pattern. For color video reconstruction, most of the previous algorithms [46, 48] reconstruct each sub-measurement independently, and then use off-the-shelf demosaic algorithms to get the final RGB color" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.353, + 0.893, + 0.415 + ], + "angle": 0, + "content": "videos. These methods are usually inefficient and have poor reconstruction quality. In this paper, we feed the four submeasurements simultaneously into the reconstruction network to directly obtain the final desired color video." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.425, + 0.72, + 0.443 + ], + "angle": 0, + "content": "4. The Proposed Network" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.451, + 0.893, + 0.496 + ], + "angle": 0, + "content": "As shown in Fig. 3, in the pre-processing stage of EfficientSCI, inspired by [7, 8], we use the estimation module to pre-process measurement \\((\\mathbf{Y})\\) and masks \\((\\mathbf{M})\\) as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.54, + 0.499, + 0.892, + 0.52 + ], + "angle": 0, + "content": "\\[\n\\overline {{\\mathbf {Y}}} = \\mathbf {Y} \\oslash \\sum_ {m = 1} ^ {B} \\mathbf {M} _ {m}, \\quad \\mathbf {X} _ {e} = \\overline {{\\mathbf {Y}}} \\odot \\mathbf {M} + \\overline {{\\mathbf {Y}}}, \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.524, + 0.892, + 0.614 + ], + "angle": 0, + "content": "where \\(\\varnothing\\) represents Hadamard (element-wise) division, \\(\\overline{\\mathbf{Y}}\\in \\mathbb{R}^{n_x\\times n_y}\\) is the normalized measurement, which preserves a certain background and motion trajectory information, and \\(\\mathbf{X}_e\\in \\mathbb{R}^{n_x\\times n_y\\times B}\\) represents the coarse estimate of the desired video. We then take \\(\\mathbf{X}_e\\) as the input of the EfficientSCI network to get the final reconstruction result." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.614, + 0.893, + 0.901 + ], + "angle": 0, + "content": "EfficientSCI network is mainly composed of three parts: i) feature extraction module, ii) ResDNet module and iii) video reconstruction module. The feature extraction module is mainly composed of three 3D convolutional layers with kernel sizes of \\(3 \\times 7 \\times 7\\), \\(3 \\times 3 \\times 3\\) and \\(3 \\times 3 \\times 3\\) respectively. Among them, each 3D convolution is followed by a LeakyReLU activation function [27], and the spatial stride step size of the final 3D convolution is 2. The spatial resolution of the final output feature map is reduced to half of the input. The feature extraction module effectively maps the input image space to the high-dimensional feature space. The ResDNet module is composed of \\(N\\) ResDNet block (described in Sec. 4.1), which can efficiently explore spatial-temporal correlation. The video reconstruction module is composed of pixelshuffle [33] (mainly restore spatial resolution to input network input size) and three 3D convolution layers (kernel sizes are \\(3 \\times 3 \\times 3\\), \\(1 \\times 1 \\times 1\\) and \\(3 \\times 3 \\times 3\\) respectively), and conducts video reconstruction on the features output by the ResDNet blocks." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "18479" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.077, + 0.091, + 0.232, + 0.105 + ], + "angle": 0, + "content": "4.1. ResDNet Block" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.114, + 0.474, + 0.372 + ], + "angle": 0, + "content": "Dense connection is an effective way to increase model capacity. Unlike DenseNet, which spans multiple layers, we build a more efficient dense connection within a single residual block. As shown in Fig. 3(b), the input features of the ResDNet block are first divided into \\(S\\) parts along the feature channel dimension. Then, for each part \\(i = 1,\\dots ,S\\), we use CFormer (described in Section 4.2) to efficiently establish the spatial-temporal correlation. Specifically, for the input of the \\(i^{th}\\) CFormer, we concatenate all the CFormer output features before the \\(i^{th}\\) part with the input features of the \\(i^{th}\\) part and then use a \\(1\\times 1\\times 1\\) convolution to reduce the dimension of the feature channel, which can further reduce the computational complexity. Next, we concatenate all CFormer output features along the feature channel dimension and use a \\(1\\times 1\\times 1\\) convolution to better fuse each part of the information. Given an input \\(\\mathbf{X}_r\\in \\mathbb{R}^{T\\times H\\times W\\times C}\\), ResDNet block can be expressed as:" + }, + { + "type": "equation", + "bbox": [ + 0.077, + 0.381, + 0.262, + 0.399 + ], + "angle": 0, + "content": "\\[\n\\mathbf {X} _ {1}, \\dots , \\mathbf {X} _ {S} = \\operatorname {S p l i t} (\\mathbf {X} _ {r}),\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.081, + 0.401, + 0.235, + 0.417 + ], + "angle": 0, + "content": "\\[\n\\mathbf {Y} _ {1} = \\operatorname {C F o r m e r} _ {1} (\\mathbf {X} _ {1}),\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.081, + 0.42, + 0.393, + 0.437 + ], + "angle": 0, + "content": "\\[\n\\mathbf {Y} _ {2} = \\operatorname {C F o r m e r} _ {2} (\\operatorname {C o n v} _ {1} (\\operatorname {C o n c a t} ([ \\mathbf {Y} _ {1}, \\mathbf {X} _ {2} ]))),\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.144, + 0.446, + 0.154, + 0.461 + ], + "angle": 0, + "content": ":" + }, + { + "type": "equation", + "bbox": [ + 0.077, + 0.466, + 0.477, + 0.484 + ], + "angle": 0, + "content": "\\[\n\\mathbf {Y} _ {S} = \\operatorname {C F o r m e r} _ {\\mathrm {S}} \\left(\\operatorname {C o n v} _ {1} \\left(\\operatorname {C o n c a t} \\left([ \\mathbf {Y} _ {1}, \\dots , \\mathbf {Y} _ {S - 1}, \\mathbf {X} _ {S} ]\\right)\\right)\\right),\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.079, + 0.487, + 0.288, + 0.505 + ], + "angle": 0, + "content": "\\[\n\\hat {\\mathbf {Y}} _ {r} = \\operatorname {C o n c a t} ([ \\mathbf {Y} _ {1}, \\dots , \\mathbf {Y} _ {S} ]),\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.078, + 0.509, + 0.47, + 0.527 + ], + "angle": 0, + "content": "\\[\n\\hat {\\mathbf {X}} _ {r} = \\operatorname {C o n v} _ {1} \\left(\\hat {\\mathbf {Y}} _ {\\mathrm {r}}\\right) + \\mathbf {X} _ {r}, \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.537, + 0.47, + 0.658 + ], + "angle": 0, + "content": "where 'Split' represents division along the channel, 'Conv1' represents a \\(1 \\times 1 \\times 1\\) convolution operation, 'Concat' represents concatenate along the channel and \\(\\hat{\\mathbf{X}}_r \\in \\mathbb{R}^{T \\times H \\times W \\times C}\\) represents the output of the ResDNet block. This design has two advantages: i) the features of different levels are aggregated at a more granular level, which improves the representation ability of the model; ii) the model complexity is reduced (shown in Table 6)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.666, + 0.235, + 0.681 + ], + "angle": 0, + "content": "4.2. CFormer Block" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.689, + 0.47, + 0.81 + ], + "angle": 0, + "content": "As shown in Fig. 4, the CFormer block includes three parts: Spatial Convolution Branch (SCB), Temporal Self-Attention Branch (TSAB) and Feed Forward Network (FFN). Based on the space-time factorization mechanism, SCB is used to extract spatial local information, TSAB is used to calculate temporal attention of the feature points at the same spatial position in each frame. After that, FFN is used to further integrate spatial-temporal information." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.811, + 0.471, + 0.902 + ], + "angle": 0, + "content": "It is worth noting that in order to make the model flexible to different compression ratios, we introduce zero padding position encoding [17] into CFormer block, instead of the absolute position encoding [10] or relative position encoding [22]. Specifically, we modified the first linear transformation layer in the traditional FFN to a \\(3 \\times 3 \\times 3\\) convolution" + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.09, + 0.895, + 0.269 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.278, + 0.894, + 0.334 + ], + "angle": 0, + "content": "Figure 4. The CFormer block is composed of Spatial Convolution Branch (SCB), Temporal Self-Attention Branch (TSAB) and Feed Forward Network (FFN). For ease of presentation, only the head \\( N = 1 \\) scenario is described in the TSAB." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.341, + 0.655, + 0.355 + ], + "angle": 0, + "content": "with padding size of 1." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.356, + 0.892, + 0.461 + ], + "angle": 0, + "content": "Spatial Convolution Branch: 2D convolution can well exploit spatial local correlation and reconstructs more detailed information, and it also enjoys efficient memory consumption and higher operating efficiency, which is suitable for large-scale video reconstruction. Therefore, We only use two \\(3 \\times 3\\) 2D convolutions to reconstruct spatial local details in SCB as shown in Fig. 4." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.462, + 0.893, + 0.612 + ], + "angle": 0, + "content": "Temporal Self-attention Branch: The local receptive field of convolution makes it difficult to establish long-term dependencies. The global perception ability of Transformer can mitigate this issue. However, the time and memory complexity of traditional Transformers increase quadratically with the image size. To alleviate this problem, following [3, 35], we propose TSAB (shown in Fig. 4), which restricts the self-attention computation to the temporal domain, and its complexity only increases linearly with the image/video size." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.613, + 0.894, + 0.676 + ], + "angle": 0, + "content": "In particular, we first reshape the input \\(\\mathbf{X}_{st} \\in \\mathbb{R}^{T \\times H \\times W \\times \\frac{C}{S}}\\) to \\(\\mathbf{X}_t \\in \\mathbb{R}^{HW \\times T \\times \\frac{C}{S}}\\), and then obtain query \\((\\mathbf{Q} \\in \\mathbb{R}^{HW \\times T \\times \\frac{C}{2S}})\\), key \\((\\mathbf{K} \\in \\mathbb{R}^{HW \\times T \\times \\frac{C}{2S}})\\) and value \\((\\mathbf{V} \\in \\mathbb{R}^{HW \\times T \\times \\frac{C}{2S}})\\) by linearly mapping \\(\\mathbf{X}_t\\):" + }, + { + "type": "equation", + "bbox": [ + 0.544, + 0.683, + 0.892, + 0.701 + ], + "angle": 0, + "content": "\\[\n\\mathbf {Q} = \\mathbf {X} _ {t} \\mathbf {W} ^ {Q}, \\quad \\mathbf {K} = \\mathbf {X} _ {t} \\mathbf {W} ^ {K}, \\quad \\mathbf {V} = \\mathbf {X} _ {t} \\mathbf {W} ^ {V}, \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.708, + 0.892, + 0.739 + ], + "angle": 0, + "content": "where \\(\\{\\mathbf{W}^Q,\\mathbf{W}^K,\\mathbf{W}^V\\} \\in \\mathbb{R}_{\\overline{S}}^{C\\times \\frac{C}{2S}}\\) are projection matrices." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.741, + 0.892, + 0.848 + ], + "angle": 0, + "content": "It is worth noting that the output dimension of the projection matrix is reduced to half of the input dimension, further decreasing the computational complexity of TSAB. Then, we respectively divide \\(\\mathbf{Q}\\), \\(\\mathbf{K}\\), \\(\\mathbf{V}\\) into \\(N\\) heads along the feature channel: \\(\\mathbf{Q} = \\{\\mathbf{Q}_j\\}_{1}^{N}\\), \\(\\mathbf{K} = \\{\\mathbf{K}_j\\}_{1}^{N}\\), \\(\\mathbf{V} = \\{\\mathbf{V}_j\\}_{1}^{N} \\in \\mathbb{R}^{HW \\times T \\times \\frac{C}{2SN}}\\). For each head \\(j = 1, \\dots, N\\), the attention can be calculated as:" + }, + { + "type": "equation", + "bbox": [ + 0.63, + 0.858, + 0.892, + 0.876 + ], + "angle": 0, + "content": "\\[\n\\operatorname {h e a d} _ {j} = \\mathbf {A} _ {j} * \\mathbf {V} _ {j}, \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.884, + 0.892, + 0.903 + ], + "angle": 0, + "content": "where \\(\\mathbf{A}_j = \\text{softmax}(\\mathbf{Q}_j\\mathbf{K}_j^T / \\sqrt{d}) \\in \\mathbb{R}^{HW \\times T \\times T}\\) repre" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "18480" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.091, + 0.47, + 0.169 + ], + "angle": 0, + "content": "sents an attention map, \\(\\mathbf{K}_j^T\\) represents the transposed matrix of \\(\\mathbf{K}_j\\) and \\(d = \\frac{C}{2SN}\\) is a scaling parameter. Then, we concatenate the outputs of \\(N\\) heads along the feature channel dimension and perform a linear mapping to obtain the final output \\(\\hat{\\mathbf{X}}_t\\in \\mathbb{R}^{T\\times H\\times W\\times \\frac{C}{S}}\\) of TSAB:" + }, + { + "type": "equation", + "bbox": [ + 0.104, + 0.177, + 0.469, + 0.195 + ], + "angle": 0, + "content": "\\[\n\\hat {\\mathbf {X}} _ {t} = \\mathbf {R} \\left(\\mathbf {W} ^ {P} \\left(\\operatorname {C o n c a t} \\left[ h e a d _ {1}, \\dots , h e a d _ {N} \\right]\\right)\\right), \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.202, + 0.469, + 0.234 + ], + "angle": 0, + "content": "where \\(\\mathbf{W}^P\\in \\mathbb{R}^{\\frac{C}{2S}\\times \\frac{C}{S}}\\) represents projection matrices, and \\(\\mathbf{R}\\) is the reshape operator." + }, + { + "type": "table_caption", + "bbox": [ + 0.088, + 0.246, + 0.458, + 0.26 + ], + "angle": 0, + "content": "Table 1. Computational complexity of several SOTA methods." + }, + { + "type": "table", + "bbox": [ + 0.129, + 0.264, + 0.411, + 0.36 + ], + "angle": 0, + "content": "
MethodComputational Complexity
SCB3D1/2HWTK3C2
G-MSAHWTC2+(HWT)2C
TS-MSA2HWTC2+T(HW)2C+HWT2C
SCB1/2HWTK2C2
TSAB1/2HWTC2+1/2HWT2C
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.366, + 0.47, + 0.576 + ], + "angle": 0, + "content": "We further analyze the computational complexity of SCB and TSAB, and compare them with 3D convolution and several classic Multi-head Self-Attention (MSA) mechanisms. The results are shown in Table 1, where 'SCB3D' represents the replacement of 2D convolution in SCB with 3D convolution and \\( K \\) represents the kernel size, 'G-MSA' represents the original global MSA [10], and 'TS-MSA' represents the MSA in TimeSformer [3]. It can be observed that the computational complexity of our proposed SCB and TSAB grows linearly with the spatial size \\( HW \\), the computational cost is much less than 'TS-MSA' and 'G-MSA' (grow quadratically with \\( HW \\)). Compared with 3D convolution, since \\( T \\) is generally smaller than \\( C \\), 'SCB' and 'TSAB' still need less computational cost." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.577, + 0.47, + 0.697 + ], + "angle": 0, + "content": "Feed Forward Network: The feed forward network of traditional Transformer usually uses two linear layers and a nonlinear activation function to learn more abstract feature representations. However, in the whole FFN, there is no interaction between the feature points. In order to better integrate the spatial-temporal information and position coding information, we replace the first linear transformation layer in the traditional FFN with a \\(3 \\times 3 \\times 3\\) convolution." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.697, + 0.454, + 0.713 + ], + "angle": 0, + "content": "Given \\(\\mathbf{X}_f\\in \\mathbb{R}^{T\\times H\\times W\\times \\frac{C}{2}}\\) , FFN can be expressed as:" + }, + { + "type": "equation", + "bbox": [ + 0.163, + 0.722, + 0.469, + 0.74 + ], + "angle": 0, + "content": "\\[\n\\hat {\\mathbf {X}} _ {f} = \\mathbf {X} _ {f} + \\mathbf {W} _ {1} \\left(\\phi \\left(\\mathbf {W} _ {2} \\left(\\mathbf {X} _ {f}\\right)\\right)\\right), \\tag {9}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.748, + 0.469, + 0.81 + ], + "angle": 0, + "content": "where \\(\\mathbf{W}_1, \\mathbf{W}_2\\) represent \\(1 \\times 1 \\times 1\\) convolution and \\(3 \\times 3 \\times 3\\) convolution operations respectively, \\(\\phi\\) denotes the LeakyReLU non-linearity activation, and \\(\\hat{\\mathbf{X}}_f \\in \\mathbb{R}^{T \\times H \\times W \\times \\frac{C}{2}}\\) is the output of the FFN." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.811, + 0.469, + 0.901 + ], + "angle": 0, + "content": "It should be noted that in the whole CFormer block, we do not use any regularization layers, such as Layer Normalization [1] and Batch Normalization [16]. The experimental results show that removing the regularization layer will not reduce the quality of model reconstruction and can further improve the efficiency of the model." + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.09, + 0.892, + 0.116 + ], + "angle": 0, + "content": "Table 2. Reconstruction quality and test time (s) using EfficientSCI with different number of channels and blocks." + }, + { + "type": "table", + "bbox": [ + 0.534, + 0.118, + 0.857, + 0.191 + ], + "angle": 0, + "content": "
ModelChannelBlockPSNRSSIMTest time(s)
EfficientSCI-T64834.220.9610.07
EfficientSCI-S128835.510.9700.15
EfficientSCI-B256836.480.9750.31
EfficientSCI-L2561236.920.9770.45
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.197, + 0.894, + 0.225 + ], + "angle": 0, + "content": "Table 3. Computational complexity and reconstruction quality of several SOTA algorithms on 6 grayscale benchmark datasets." + }, + { + "type": "table", + "bbox": [ + 0.552, + 0.227, + 0.835, + 0.343 + ], + "angle": 0, + "content": "
MethodParams (M)FLOPs (G)PSNRSSIM
BIRNAT4.13390.5633.310.951
RevSCI5.66766.9533.920.956
DUN-3DUnet61.913975.8335.260.968
ELP-Unfolding565.734634.9435.410.969
EfficientSCI-T0.95142.1834.220.961
EfficientSCI-S3.78563.8735.510.970
EfficientSCI-B8.821426.3836.480.975
EfficientSCI-L12.391893.7236.920.977
" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.353, + 0.892, + 0.55 + ], + "angle": 0, + "content": "Network Variants: To balance speed and performance of the proposed network, we introduce four different versions of EfficientSCI network, dubbed as EfficientSCI-T, EfficientSCI-S, EfficientSCI-B and EfficientSCI-L standing for Tiny, Small, Base and Large networks, respectively. The network hyper-parameters are shown in Table 2, in which we mainly changed the the number of ResD-Net blocks and the number of channels. As shown in Table 3, we also compare model parameters and computational complexity (FLOPs) with several advanced methods. The complexity of our proposed EfficientSCI-T is smaller than that of BIRNAT and RevSCI, and EfficientSCI-L is smaller than that of DUN-3DUnet and ELP-Unfolding." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.564, + 0.69, + 0.581 + ], + "angle": 0, + "content": "5. Experiment Results" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.589, + 0.602, + 0.603 + ], + "angle": 0, + "content": "5.1. Datasets" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.611, + 0.892, + 0.822 + ], + "angle": 0, + "content": "Following BIRNAT [8], we use DAVIS2017 [29] with resolution \\(480 \\times 894\\) (480p) as the model training dataset. To verify model performance, we first test the EfficientSCI network on several simulated datasets, including six benchmark grayscale datasets (Kobe, Traffic, Runner, Drop, Crash and Aerial with a size of \\(256 \\times 256 \\times 8\\)), six benchmark mid-scale color datasets (Beauty, Bosphorus, Jockey, Runner, ShakeNDry and Traffic with a size of \\(512 \\times 512 \\times 3 \\times 8\\)), and four large-scale datasets (Messi, Hummingbird, Swinger and Football with different sizes and compression ratios). Then we test our model on some real data (including Duomino, Water Balloon) captured by a real SCI system [30]." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.833, + 0.718, + 0.848 + ], + "angle": 0, + "content": "5.2. Implementation Details" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.856, + 0.892, + 0.901 + ], + "angle": 0, + "content": "We use PyTorch framework with 4 NVIDIA RTX 3090 GPUs for training with random cropping, random scaling, and random flipping for data augmentation, and use" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "18481" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.089, + 0.894, + 0.117 + ], + "angle": 0, + "content": "Table 4. The average PSNR in dB (left entry) and SSIM (right entry) and running time per measurement of different algorithms on 6 benchmark grayscale datasets. The best results are shown in bold and the second-best results are underlined." + }, + { + "type": "table", + "bbox": [ + 0.084, + 0.119, + 0.885, + 0.319 + ], + "angle": 0, + "content": "
MethodKobeTrafficRunnerDropCrashAerialAverageTest time(s)
GAP-TV26.46, 0.88520.89, 0.71528.52, 0.90934.63, 0.97024.82, 0.83825.05, 0.82826.73, 0.8584.2 (CPU)
PnP-FFDNet30.50, 0.92624.18, 0.82832.15, 0.93340.70, 0.98925.42, 0.84925.27, 0.82929.70, 0.8923.0 (GPU)
PnP-FastDVDnet32.73, 0.94727.95, 0.93236.29, 0.96241.82, 0.98927.32, 0.92527.98, 0.89732.35, 0.9426.0 (GPU)
DeSCI33.25, 0.95228.71, 0.92538.48, 0.96943.10, 0.99327.04, 0.90925.33, 0.86032.65, 0.9356180 (CPU)
BIRNAT32.71, 0.95029.33, 0.94238.70, 0.97642.28, 0.99227.84, 0.92728.99, 0.91733.31, 0.9510.10 (GPU)
RevSCI33.72, 0.95730.02, 0.94939.40, 0.97742.93, 0.99228.12, 0.93729.35, 0.92433.92, 0.9560.19 (GPU)
GAP-CCoT32.58, 0.94929.03, 0.93839.12, 0.98042.54, 0.99228.52, 0.94129.40, 0.92333.53, 0.9580.08 (GPU)
DUN-3DUnet35.00, 0.96931.76, 0.96640.03, 0.98044.96, 0.99529.33, 0.95630.46, 0.94335.26, 0.9680.58 (GPU)
ELP-Unfolding34.41, 0.96631.58, 0.96241,16, 0.98644.99, 0.99529.65, 0.95930.68, 0.94435.41, 0.9690.34 (GPU)
EfficientSCI-T33.45, 0.96029.20, 0.94239.51, 0.98143.56, 0.99329.27, 0.95430.32, 0.93734.22, 0.9610.07 (GPU)
EfficientSCI-S34.79, 0.96831.21, 0.96141.34, 0.98644.61, 0.99430.34, 0.96530.78, 0.94535.51, 0.9700.15 (GPU)
EfficientSCI-B35.76, 0.97432.30, 0.96843.05, 0.98845.18, 0.99531.13, 0.97131.50, 0.95336.48, 0.9750.31 (GPU)
EfficientSCI-L36.27, 0.97632.83, 0.97143.79, 0.99145.46, 0.99531.52, 0.97431.64, 0.95536.92, 0.9770.45 (GPU)
" + }, + { + "type": "image", + "bbox": [ + 0.082, + 0.328, + 0.468, + 0.548 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.553, + 0.47, + 0.581 + ], + "angle": 0, + "content": "Figure 5. Selected reconstruction frames of simulated grayscale data. Zoom in for better view." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.587, + 0.471, + 0.693 + ], + "angle": 0, + "content": "Adam [19] to optimize the model with the initial learning rate 0.0001. After iterating for 300 epochs, we adjusted the learning rate to 0.00001 and continued to iterate for 40 epochs to get the final model parameters. The peak-signal-to-noise-ratio (PSNR) and structured similarity index metrics (SSIM) [38] are used as the performance indicators of reconstruction quality." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.702, + 0.351, + 0.718 + ], + "angle": 0, + "content": "5.3. Results on Simulation Datasets" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.726, + 0.327, + 0.741 + ], + "angle": 0, + "content": "5.3.1 Grayscale Simulation Video" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.75, + 0.471, + 0.903 + ], + "angle": 0, + "content": "We compare our method with SOTA model-based methods (GAP-TV [44], PnP-FFDNet [46], PnP-FastDVDnet [47], DeSCI [21]) and deep learning-based methods (BIR-NAT [8], RevSCI [7], GAP-CCoT [36], DUN-3DUnet [40], ELP-Unfolding [42]) on simulated grayscale datasets. Table 4 shows the quantitative comparison results, it can be observed that our proposed EfficientSCI-L can achieve the highest reconstruction quality and has good real-time performance. In particular, the PSNR value of our method surpasses the existing best method ELP-Unfolding by 1.46" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.332, + 0.895, + 0.513 + ], + "angle": 0, + "content": "dB on average. In addition, our proposed EfficientSCIT achieves high reconstruction quality while achieving the best real-time performance. It is worth noting that, for a fair comparison, we uniformly test the running time of all deep learning based methods on the same NVIDIA RTX 3090 GPU. Fig. 5 shows the visual reconstruction results of some data. By zooming in some local areas, we can observe that our method can recover sharper edges and more detailed information compared to previous SOTA methods. The mid-scale color results are shown in the SM due to space limitation and our method outperforms previous SOTA by 2.02 dB in PSNR on the benchmark dataset [47]." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.531, + 0.804, + 0.546 + ], + "angle": 0, + "content": "5.3.2 Large-scale Color Simulation Video" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.553, + 0.892, + 0.903 + ], + "angle": 0, + "content": "Most deep learning based methods, such as BIRNAT [8], DUN-3DUnet [40], cannot be applied to large-scale data reconstruction due to excessive model complexity and GPU memory constraints. RevSCI [7] uses a reversible mechanism and can reconstruct a 24 frames RGB color video with size of \\(1080 \\times 1920 \\times 3\\), but training the model is extremely slow. GAP-CCoT [36] and ELP-Unfolding [42] only use 2D convolution for reconstruction and thus cannot handle color video data well. Therefore, we only compare with several SOTA model-based methods (GAP-TV [44], PnP-FFDNet-color [46], PnP-FastDVDnet-color [47]) on large-scale color data. Table 5 shows the comparisons between our proposed method and several model-based methods on PSNR, SSIM and test time (in minutes). It can be observed that model-based methods either have long reconstruction time (PnP-FFDNet-color, PnP-FastDVDnet-color) or low reconstruction quality (GAP-TV). Our proposed EfficientSCI-S can achieve higher reconstruction quality and running speed. Especially on UHD color video football \\((1644 \\times 3840 \\times 3 \\times 40)\\), the PSNR value of our method is 2.5 dB higher than PnP-FastDVDnet-color, and the reconstruction time is only \\(0.5\\%\\) of it. Fig. 6 shows some visual reconstruction results. By zooming" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "18482" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.089, + 0.895, + 0.119 + ], + "angle": 0, + "content": "Table 5. The average PSNR in dB (left entry) and SSIM (middle entry) and test time (minutes) per measurement (right entry) of different algorithms on 4 benchmark large-scale datasets. Best results are in bold." + }, + { + "type": "table", + "bbox": [ + 0.088, + 0.129, + 0.88, + 0.213 + ], + "angle": 0, + "content": "
DatasetPixel resolutionGAP-TVPnP-FFDNet-colorPnP-FastDVDnet-colorEfficientSCI-S
Messi1080 × 1920 × 3 × 825.20, 0.874, 0.6634.28, 0.968, 14.9334.34, 0.970, 15.9434.41, 0.973, 0.09
Hummingbird1080 × 1920 × 3 × 3025.10, 0.750, 20.328.79, 0.665, 61.2031.17, 0.916, 54.0035.56, 0.952, 0.39
Swinger2160 × 3840 × 3 × 1522.68, 0.769, 39.229.30, 0.934, 138.830.57, 0.949, 138.431.05, 0.951, 0.62
Football1644 × 3840 × 3 × 4026.19, 0.858, 83.032.70, 0.951, 308.832.31, 0.947, 298.134.81, 0.964, 1.52
" + }, + { + "type": "image", + "bbox": [ + 0.087, + 0.223, + 0.88, + 0.57 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.08, + 0.573, + 0.885, + 0.588 + ], + "angle": 0, + "content": "Figure 6. Comparison of reconstruction results of different algorithms on several benchmark large-scale color video simulation datasets." + }, + { + "type": "image", + "bbox": [ + 0.085, + 0.603, + 0.46, + 0.766 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.767, + 0.471, + 0.809 + ], + "angle": 0, + "content": "Figure 7. Reconstruction quality (PSNR in dB, higher is better) of different reconstruction algorithms, with varying compression rates \\( B \\) from 8 to 48." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.826, + 0.471, + 0.903 + ], + "angle": 0, + "content": "in local areas, we can observe that the reconstruction results of our method are closer to the real value. In addition, our proposed model enjoys high flexibility for different compression ratios, that is, the model trained on low compression ratio data can be directly used for high com" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.607, + 0.895, + 0.744 + ], + "angle": 0, + "content": "pression ratio video reconstruction task. To verify this, we test hummingbird data with different compression ratios \\( B = 8, 16, 24, 32, 40, 48 \\), and the reconstruction results are shown in Fig. 7. We can observe that our method can be applied to video data with different compression ratios, even when the compression ratio \\( B \\) grows to 48, the PSNR value of EfficientSCI-T model can still reach more than 32 dB. Moreover, our proposed approach surpasses other reconstruction algorithms at all compression ratios." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.769, + 0.661, + 0.785 + ], + "angle": 0, + "content": "5.3.3 Ablation Study" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.795, + 0.895, + 0.903 + ], + "angle": 0, + "content": "To verify the performance of the proposed ResDNet block and CFormer block on the impact of the reconstruction quality, we conduct some ablation experiments. The results are shown in Table 6 and Table 7, we not only compare the reconstruction quality of different models, but also analyze the model parameters and FLOPs. All experiments are conducted on the 6 grayscale benchmark datasets." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "18483" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.078, + 0.083, + 0.468, + 0.11 + ], + "angle": 0, + "content": "Table 6. Ablation study on the ResDNet block without dense connections (left entry) and with dense connections (right entry)." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.115, + 0.468, + 0.188 + ], + "angle": 0, + "content": "
GNParamsFLOPsPSNRSSIM
127.40, 27.403860.94, 3860.9435.17, 35.170.967, 0.967
214.82, 15.082211.77, 2246.3935.09, 36.020.966, 0.974
48.53, 8.821387.33, 1426.3835.02, 36.480.966, 0.975
85.38, 5.65975.39, 1013.4534.31, 35.680.961, 0.971
" + }, + { + "type": "table_caption", + "bbox": [ + 0.134, + 0.197, + 0.411, + 0.21 + ], + "angle": 0, + "content": "Table 7. Ablation study on the CFormer block." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.215, + 0.467, + 0.271 + ], + "angle": 0, + "content": "
SCBTSABSwinS2-3DParams (M)FLOPs (G)PSNRSSIM
✓✓2.88471.0334.990.967
✓6.93999.3134.930.966
✓✓3.78563.8735.510.970
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.292, + 0.468, + 0.441 + ], + "angle": 0, + "content": "ResDNet Block: We verify the effect of different group numbers (GN) (corresponding to \\( S \\) in Eq. 5) and dense connections on the reconstruction quality. As shown in Table 6, the model complexity decreases gradually with the increase of GN, but the reconstruction quality greatly decreases when there are no dense connections in the ResDNet block. By introducing dense connections in the ResDNet block, the reconstruction quality of our proposed method is greatly improved, and a gain of \\( 1.46\\mathrm{dB} \\) can be obtained when GN is 4." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.443, + 0.468, + 0.669 + ], + "angle": 0, + "content": "CFormer Block: In the CFormer block, we first replace SCB with Swin Transformer (Swin) to verify its effectiveness. Then, we replace SCB and TSAB with two stacked 3D convolutions (S2-3D) to verify the effectiveness of TSAB. As shown in Table 7, compared with Swin Transformer, SCB can bring a \\(0.52\\mathrm{dB}\\) gain. Although the number of parameters and FLOPs have increased, the experimental results show that SCB takes up less memory than the Swin Transformer, which is very important for large-scale and high compression ratio data. Please refer to more detailed analysis in SM. Compared with SCB and TSAB, S2-3D not only increases model parameters and FLOPs by \\(83\\%\\) and \\(77\\%\\) respectively, but also reduces the PSNR value by 0.58 dB, which verifies the necessity of using space-time factorization and TSAB." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.67, + 0.468, + 0.745 + ], + "angle": 0, + "content": "Number of Channels and Blocks: Table 2 shows that the quality of model reconstruction increases with the number of channels and blocks. However, the amount of parameters and FLOPs also increase (see Table 3), resulting in a degradation in the real-time performance of the model." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.757, + 0.357, + 0.771 + ], + "angle": 0, + "content": "5.4. Results on Real Video SCI Data" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.78, + 0.468, + 0.901 + ], + "angle": 0, + "content": "We further test our method on real data. Fig. 8 and Fig. 9 show the reconstruction results of multiple algorithms on two public data (Duomino, Water Ballon), we can see that our method can reconstruct clearer details and edges. Specifically, we can clearly recognize the letters on the Duomino. Even with a high compression ratio \\((B = 50)\\), our proposed method can still reconstruct clear foreground and background information (shown in Fig. 9)." + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.089, + 0.892, + 0.304 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.5, + 0.312, + 0.892, + 0.34 + ], + "angle": 0, + "content": "Figure 8. Reconstruction results of different algorithms on Duomino real data with compression rate \\( B = 10 \\)." + }, + { + "type": "image", + "bbox": [ + 0.502, + 0.361, + 0.892, + 0.537 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.5, + 0.544, + 0.89, + 0.571 + ], + "angle": 0, + "content": "Figure 9. Reconstruction results of different algorithms on Water Ballon real data with compression rate \\( B = 50 \\)." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.586, + 0.776, + 0.601 + ], + "angle": 0, + "content": "6. Conclusions and Future Work" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.614, + 0.892, + 0.766 + ], + "angle": 0, + "content": "This paper proposes an efficient end-to-end video SCI reconstruction network, dubbed EfficientSCI, which achieves the state-of-the-art performance on simulated data and real data, significantly surpassing the previous best reconstruction algorithms with high real-time performance. In addition, we show for the first time that an UHD color video with high compression rate can be reconstructed using a deep learning based method. For future work, we consider applying EfficientSCI Network to more SCI reconstruction tasks, such as spectral SCI [4, 49]." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.79, + 0.667, + 0.807 + ], + "angle": 0, + "content": "Acknowledgements" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.817, + 0.892, + 0.901 + ], + "angle": 0, + "content": "This work was supported by the National Natural Science Foundation of China [62271414], Zhejiang Provincial Natural Science Foundation of China [LR23F010001]. We would like to thank Research Center for Industries of the Future (RCIF) at Westlake University and the funding from Lochn Optics." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.956 + ], + "angle": 0, + "content": "18484" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.116, + 0.47, + 0.156 + ], + "angle": 0, + "content": "[1] Jimmy Lei Ba, Jamie Ryan Kiros, and Geoffrey E Hinton. Layer normalization. arXiv preprint arXiv:1607.06450, 2016. 5" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.16, + 0.47, + 0.215 + ], + "angle": 0, + "content": "[2] Jens Behrmann, Will Grathwohl, Ricky TQ Chen, David Duvenaud, and Jorn-Henrik Jacobsen. Invertible residual networks. In International Conference on Machine Learning, pages 573-582. 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In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 5728-5739, 2022. 2" + }, + { + "type": "list", + "bbox": [ + 0.503, + 0.093, + 0.892, + 0.739 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.946, + 0.52, + 0.957 + ], + "angle": 0, + "content": "18486" + } + ] +] \ No newline at end of file diff --git a/2023/EfficientSCI_ Densely Connected Network With Space-Time Factorization for Large-Scale Video Snapshot Compressive Imaging/ba9925d6-1c9f-468a-bc9d-dc4b6c4a5ca6_origin.pdf b/2023/EfficientSCI_ Densely Connected Network With Space-Time Factorization for Large-Scale Video Snapshot Compressive Imaging/ba9925d6-1c9f-468a-bc9d-dc4b6c4a5ca6_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..69e0078beeef4d80c6e1f3a3d7ef82279e3c8e66 --- /dev/null +++ b/2023/EfficientSCI_ Densely Connected Network With Space-Time Factorization for Large-Scale Video Snapshot Compressive Imaging/ba9925d6-1c9f-468a-bc9d-dc4b6c4a5ca6_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:502e1a1c1d1e27358105364d947e8ad783572fdad74167b3a129e025125aa50a +size 8511202 diff --git a/2023/EfficientSCI_ Densely Connected Network With Space-Time Factorization for Large-Scale Video Snapshot Compressive Imaging/full.md b/2023/EfficientSCI_ Densely Connected Network With Space-Time Factorization for Large-Scale Video Snapshot Compressive Imaging/full.md new file mode 100644 index 0000000000000000000000000000000000000000..d784a16d797792fcd4bac89ccb55f01163d10fdd --- /dev/null +++ b/2023/EfficientSCI_ Densely Connected Network With Space-Time Factorization for Large-Scale Video Snapshot Compressive Imaging/full.md @@ -0,0 +1,319 @@ +# EfficientSCI: Densely Connected Network with Space-time Factorization for Large-scale Video Snapshot Compressive Imaging + +Lishun Wang $^{1,2,*}$ , Miao Cao $^{3,4,*}$ , and Xin Yuan $^{3,\dagger}$ + +1 Chengdu Institute of Computer Application Chinese Academy of Sciences, + +$^{2}$ University of Chinese Academy of Sciences, $^{3}$ Westlake University, $^{4}$ Zhejiang University + +# Abstract + +Video snapshot compressive imaging (SCI) uses a two-dimensional detector to capture consecutive video frames during a single exposure time. Following this, an efficient reconstruction algorithm needs to be designed to reconstruct the desired video frames. Although recent deep learning-based state-of-the-art (SOTA) reconstruction algorithms have achieved good results in most tasks, they still face the following challenges due to excessive model complexity and GPU memory limitations: 1) these models need high computational cost, and 2) they are usually unable to reconstruct large-scale video frames at high compression ratios. To address these issues, we develop an efficient network for video SCI by using dense connections and space-time factorization mechanism within a single residual block, dubbed EfficientSCI. The EfficientSCI network can well establish spatial-temporal correlation by using convolution in the spatial domain and Transformer in the temporal domain, respectively. We are the first time to show that an UHD color video with high compression ratio can be reconstructed from a snapshot 2D measurement using a single end-to-end deep learning model with PSNR above 32 dB. Extensive results on both simulation and real data show that our method significantly outperforms all previous SOTA algorithms with better real-time performance. The code is at https://github.com/ucaswangls/EfficientSCI.git. + +# 1. Introduction + +Traditional high-speed camera imaging methods usually suffer from high hardware and storage transmission cost. Inspired by compressed sensing (CS) [5, 9], video snapshot compressive imaging (SCI) [45] provides an elegant solution. As shown in Fig. 2, video SCI consists of a hardware encoder and a software decoder. In the encoder part, multiple raw video frames are modulated by different masks and + +![](images/6e028b4c59a14fe49510021b749e66600621c5fb1d7da19aafd0841c9305a420.jpg) +Figure 1. Comparison of reconstruction quality (average PSNR in dB on 6 benchmark grayscale datasets) and testing time of several SOTA deep learning based algorithms. Our proposed EfficientSCI achieves higher reconstruction quality with fewer parameters and shorter testing time. + +then integrated by the camera to get a compressed measurement, giving low-speed cameras the ability to capture high-speed scenes. For the decoding part, the desired high-speed video is retrieved by the reconstruction algorithm using the captured measurement and masks. + +So far, many mature SCI imaging systems [14, 24, 31] have been built, but for the decoding part, there are still many challenges. In particular, although the model-based methods [21, 43, 44] have good flexibility and can reconstruct videos with different resolutions and compression rates, they require long reconstruction time and can only achieve poor reconstruction quality. In order to improve the reconstruction quality and running speed, PnP-FFDNet [46] and PnP-FastDVDnet [47] integrate the pre-trained denoising network into an iterative optimization algorithm. However, they still need a long reconstruction time on large-scale datasets, e.g., PnP-FastDVDNet takes hours to reconstruct a UHD video from a single measurement. + +By contrast, deep learning based methods [28,30,35,40] + +![](images/b80883aba0a14977c145c065f39cef9aaa16162d90a875481c4752be480d5808.jpg) +Figure 2. Schematic diagram of grayscale and color video SCI. + +have better real-time performance and higher reconstruction quality. For example, BIRNAT [8] uses bidirectional recurrent neural network and generative adversarial method to surpass model-based method DeSCI [21] for the first time. MetaSCI [39] has made some explorations for the model to adapt to different masks, which reduces the model training time. DUN-3DUnet [40] and ELP-Unfolding [42] combine iterative optimization ideas with deep learning models to further improve reconstruction quality. However, due to the high model complexity and insufficient GPU memory, most existing deep learning algorithms cannot train the models required for reconstructing HD or large-scale videos. RevSCI [7] uses a reversible mechanism [2] to reduce the memory used for model training, and can reconstruct HD video with a compression rate up to 24, but the model training time increases exponentially. In addition, the current reconstruction algorithms generally use convolution to establish spatial-temporal correlation. Due to the local connection of convolution, long-term dependencies cannot be well established, and the model cannot reconstruct data with high compression rates. + +In summary, model-based methods usually require long reconstruction time and can only achieve poor reconstruction quality. Learning-based methods have high model complexity but cannot be well applied to large-scale color video reconstruction. To address these challenges, we develop an efficient network for video SCI by using dense connections and space-time factorization mechanism. As shown in Fig. 1, our proposed method dramatically outperforms all previous deep learning based reconstruction algorithms in terms of reconstruction quality and running speed with fewer parameters. Our main contributions can be summarized as follows: + +- An efficient end-to-end network, dubbed EfficientSCI, is proposed for reconstructing high quality video frames from a snapshot SCI measurement. +- By building hierarchical dense connections within a single residual block, we devise a novel ResDNet block to effectively reduces model computational complexity but enhance the learning ability of the model. + +- Based on the space-time factorization mechanism, a Convolution and Transformer hybrid block (CFormer) is built, which can efficiently establish space-time correlation by using convolution in the spatial domain and Transformer in the temporal domain, respectively. +- Experimental results on a large number of simulated and real datasets demonstrate that our proposed method achieves state-of-the-art (SOTA) results and better real-time performance. + +# 2. Related Work + +CNN and Variants: In the past ten years, models with convolutional neural networks (CNN) as the backbone [13,15,20] have achieved excellent results on multiple computer vision tasks [20, 25, 32]. Among them, ResNeXt [41] and Res2Net [11] effectively increases model capacity without increasing model complexity by using grouped convolutions inside residual blocks. DenseNet [15] and CSPNet [34] achieve feature reuse by taking all previous feature maps as input. In video-related tasks, 3D convolution can establish good spatial-temporal correlation and has been widely used in action recognition [18], video superresolution [26], video inpainting [6] and so on. In previous video SCI reconstruction, RevSCI and DUN-3DUnet greatly improve the reconstruction quality of benchmark grayscale datasets by integrating 3D convolution into the network. However, in complex high-speed scenarios (e.g., crash), since they cannot effectively establish long-term temporal dependencies, the reconstruction quality is still lower than $30\mathrm{dB}$ . In addition, the excessive use of 3D convolution increases the amount of model parameters, which is not conducive to the application of large-scale and high compression ratio data. + +Vision Transformers: Most recently, Vision Transformer (ViT) [10] and its variants [4, 12, 37, 50] have achieved competitive results in computer vision. However, the high computational complexity limits its application in video-related tasks. TimeSformer [3] performs self-attention calculations in time and space respectively, which reduces model complexity and improves model accuracy, but the computational complexity still increases quadratically with the image size. The Video Swin Transformer [23] limits self-attention calculations to local windows but cannot effectively establish long-term temporal dependencies. In addition, a large number of experimental results show that Transformer has higher memory consumption than CNN, and using Transformer in space is not conducive to large-scale video SCI reconstruction. Therefore, through space-time factorization mechanism, using Transformer only in time domain can not only effectively utilize its ability to establish long-term time series dependencies, but also reduce model complexity and memory consumption. + +![](images/029625615612b212673c7634f8bfc935ed2da89d5a0ae3cd563220b48f108e05.jpg) +Figure 3. Architecture of the proposed EfficientSCI network and the overall process of color or grayscale video reconstruction. The measurement $(\mathbf{Y})$ and masks $(\mathbf{M})$ are pre-processed by the estimation module to obtain an estimated $\mathbf{X}_e$ , and then feed $\mathbf{X}_e$ into EfficientSCI network to get the desired reconstruction result. (a) ResDNet module with $N$ residual style units. (b) ResDNet block. Inside a residual block, the input features are divided into $S$ parts by the channel split. Each part uses CFormer to efficiently extract spatial-temporal correlation, and employs dense connections to further improve model capacity. For convenience, only the case of $S = 4$ is shown here. + +# 3. Mathematical Model of Video SCI + +Fig. 2 briefly describes the flow chart of video SCI. For grayscale video SCI system, the original $B$ -frame (grayscale) input video $\{\mathbf{X}_m\}_{m=1}^B \in \mathbb{R}^{n_x \times n_y}$ is modulated by pre-defined masks $\{\mathbf{M}\}_{m=1}^B \in \mathbb{R}^{n_x \times n_y}$ . Then, by compressing across time, the camera sensor captures a compressed measurement $\mathbf{Y} \in \mathbb{R}^{n_x \times n_y}$ . The whole process can be expressed as: + +$$ +\mathbf {Y} = \sum_ {m = 1} ^ {B} \mathbf {X} _ {m} \odot \mathbf {M} _ {m} + \mathbf {Z}, \tag {1} +$$ + +where $\odot$ denotes the Hadamard (element-wise) multiplication, and $\mathbf{Z} \in \mathbb{R}^{n_x \times n_y}$ denotes the measurement noise. Eq. (1) can also be represented by a vectorized formulation. Firstly, we vectorize $\pmb{y} = \operatorname{vec}(\mathbf{Y}) \in \mathbb{R}^{n_x n_y}$ , $\pmb{z} = \operatorname{vec}(\mathbf{Z}) \in \mathbb{R}^{n_x n_y}$ , $\pmb{x} = [\pmb{x}_1^\top, \dots, \pmb{x}_B^\top]^\top \in \mathbb{R}^{n_x n_y B}$ , where $\pmb{x}_m = \operatorname{vec}(\mathbf{X}_m)$ . Then, sensing matrix generated by masks can be defined as: + +$$ +\mathbf {H} = \left[ \mathbf {D} _ {1}, \dots , \mathbf {D} _ {B} \right] \in \mathbb {R} ^ {n _ {x} n _ {y} \times n _ {x} n _ {y} B}, \tag {2} +$$ + +where $\mathbf{D}_m = \mathrm{Diag}(\mathrm{vec}(\mathbf{M}))\in \mathbb{R}^{n_xn_y\times n_xn_y}$ is a diagonal matrix and its diagonal elements is filled by $\operatorname {vec}(\mathbf{M})$ Finally, the vectorized expression of Eq. (1) is + +$$ +\boldsymbol {y} = \mathbf {H} \boldsymbol {x} + \boldsymbol {z}. \tag {3} +$$ + +For color video SCI system, we use the Bayer pattern filter sensor, where each pixel captures only red (R), blue (B) or green (G) channel of the raw data in a spatial layout such as 'RGGB'. Since adjacent pixels are different color components, we divide the original measurement $\mathbf{Y}$ into four sub-measurements $\{\mathbf{Y}^r,\mathbf{Y}^{g1},\mathbf{Y}^{g2},\mathbf{Y}^b\} \in \mathbb{R}^{\frac{n_x}{2}\times \frac{n_y}{2}}$ according to the Bayer filter pattern. For color video reconstruction, most of the previous algorithms [46, 48] reconstruct each sub-measurement independently, and then use off-the-shelf demosaic algorithms to get the final RGB color + +videos. These methods are usually inefficient and have poor reconstruction quality. In this paper, we feed the four submeasurements simultaneously into the reconstruction network to directly obtain the final desired color video. + +# 4. The Proposed Network + +As shown in Fig. 3, in the pre-processing stage of EfficientSCI, inspired by [7, 8], we use the estimation module to pre-process measurement $(\mathbf{Y})$ and masks $(\mathbf{M})$ as follows: + +$$ +\overline {{\mathbf {Y}}} = \mathbf {Y} \oslash \sum_ {m = 1} ^ {B} \mathbf {M} _ {m}, \quad \mathbf {X} _ {e} = \overline {{\mathbf {Y}}} \odot \mathbf {M} + \overline {{\mathbf {Y}}}, \tag {4} +$$ + +where $\varnothing$ represents Hadamard (element-wise) division, $\overline{\mathbf{Y}}\in \mathbb{R}^{n_x\times n_y}$ is the normalized measurement, which preserves a certain background and motion trajectory information, and $\mathbf{X}_e\in \mathbb{R}^{n_x\times n_y\times B}$ represents the coarse estimate of the desired video. We then take $\mathbf{X}_e$ as the input of the EfficientSCI network to get the final reconstruction result. + +EfficientSCI network is mainly composed of three parts: i) feature extraction module, ii) ResDNet module and iii) video reconstruction module. The feature extraction module is mainly composed of three 3D convolutional layers with kernel sizes of $3 \times 7 \times 7$ , $3 \times 3 \times 3$ and $3 \times 3 \times 3$ respectively. Among them, each 3D convolution is followed by a LeakyReLU activation function [27], and the spatial stride step size of the final 3D convolution is 2. The spatial resolution of the final output feature map is reduced to half of the input. The feature extraction module effectively maps the input image space to the high-dimensional feature space. The ResDNet module is composed of $N$ ResDNet block (described in Sec. 4.1), which can efficiently explore spatial-temporal correlation. The video reconstruction module is composed of pixelshuffle [33] (mainly restore spatial resolution to input network input size) and three 3D convolution layers (kernel sizes are $3 \times 3 \times 3$ , $1 \times 1 \times 1$ and $3 \times 3 \times 3$ respectively), and conducts video reconstruction on the features output by the ResDNet blocks. + +# 4.1. ResDNet Block + +Dense connection is an effective way to increase model capacity. Unlike DenseNet, which spans multiple layers, we build a more efficient dense connection within a single residual block. As shown in Fig. 3(b), the input features of the ResDNet block are first divided into $S$ parts along the feature channel dimension. Then, for each part $i = 1,\dots ,S$ , we use CFormer (described in Section 4.2) to efficiently establish the spatial-temporal correlation. Specifically, for the input of the $i^{th}$ CFormer, we concatenate all the CFormer output features before the $i^{th}$ part with the input features of the $i^{th}$ part and then use a $1\times 1\times 1$ convolution to reduce the dimension of the feature channel, which can further reduce the computational complexity. Next, we concatenate all CFormer output features along the feature channel dimension and use a $1\times 1\times 1$ convolution to better fuse each part of the information. Given an input $\mathbf{X}_r\in \mathbb{R}^{T\times H\times W\times C}$ , ResDNet block can be expressed as: + +$$ +\mathbf {X} _ {1}, \dots , \mathbf {X} _ {S} = \operatorname {S p l i t} (\mathbf {X} _ {r}), +$$ + +$$ +\mathbf {Y} _ {1} = \operatorname {C F o r m e r} _ {1} (\mathbf {X} _ {1}), +$$ + +$$ +\mathbf {Y} _ {2} = \operatorname {C F o r m e r} _ {2} (\operatorname {C o n v} _ {1} (\operatorname {C o n c a t} ([ \mathbf {Y} _ {1}, \mathbf {X} _ {2} ]))), +$$ + +: + +$$ +\mathbf {Y} _ {S} = \operatorname {C F o r m e r} _ {\mathrm {S}} \left(\operatorname {C o n v} _ {1} \left(\operatorname {C o n c a t} \left([ \mathbf {Y} _ {1}, \dots , \mathbf {Y} _ {S - 1}, \mathbf {X} _ {S} ]\right)\right)\right), +$$ + +$$ +\hat {\mathbf {Y}} _ {r} = \operatorname {C o n c a t} ([ \mathbf {Y} _ {1}, \dots , \mathbf {Y} _ {S} ]), +$$ + +$$ +\hat {\mathbf {X}} _ {r} = \operatorname {C o n v} _ {1} \left(\hat {\mathbf {Y}} _ {\mathrm {r}}\right) + \mathbf {X} _ {r}, \tag {5} +$$ + +where 'Split' represents division along the channel, 'Conv1' represents a $1 \times 1 \times 1$ convolution operation, 'Concat' represents concatenate along the channel and $\hat{\mathbf{X}}_r \in \mathbb{R}^{T \times H \times W \times C}$ represents the output of the ResDNet block. This design has two advantages: i) the features of different levels are aggregated at a more granular level, which improves the representation ability of the model; ii) the model complexity is reduced (shown in Table 6). + +# 4.2. CFormer Block + +As shown in Fig. 4, the CFormer block includes three parts: Spatial Convolution Branch (SCB), Temporal Self-Attention Branch (TSAB) and Feed Forward Network (FFN). Based on the space-time factorization mechanism, SCB is used to extract spatial local information, TSAB is used to calculate temporal attention of the feature points at the same spatial position in each frame. After that, FFN is used to further integrate spatial-temporal information. + +It is worth noting that in order to make the model flexible to different compression ratios, we introduce zero padding position encoding [17] into CFormer block, instead of the absolute position encoding [10] or relative position encoding [22]. Specifically, we modified the first linear transformation layer in the traditional FFN to a $3 \times 3 \times 3$ convolution + +![](images/a0822b709a03dae7cb6ac7dfd2c12207b9245dd4f13c2622be6834ba2a6470d3.jpg) +Figure 4. The CFormer block is composed of Spatial Convolution Branch (SCB), Temporal Self-Attention Branch (TSAB) and Feed Forward Network (FFN). For ease of presentation, only the head $N = 1$ scenario is described in the TSAB. + +with padding size of 1. + +Spatial Convolution Branch: 2D convolution can well exploit spatial local correlation and reconstructs more detailed information, and it also enjoys efficient memory consumption and higher operating efficiency, which is suitable for large-scale video reconstruction. Therefore, We only use two $3 \times 3$ 2D convolutions to reconstruct spatial local details in SCB as shown in Fig. 4. + +Temporal Self-attention Branch: The local receptive field of convolution makes it difficult to establish long-term dependencies. The global perception ability of Transformer can mitigate this issue. However, the time and memory complexity of traditional Transformers increase quadratically with the image size. To alleviate this problem, following [3, 35], we propose TSAB (shown in Fig. 4), which restricts the self-attention computation to the temporal domain, and its complexity only increases linearly with the image/video size. + +In particular, we first reshape the input $\mathbf{X}_{st} \in \mathbb{R}^{T \times H \times W \times \frac{C}{S}}$ to $\mathbf{X}_t \in \mathbb{R}^{HW \times T \times \frac{C}{S}}$ , and then obtain query $(\mathbf{Q} \in \mathbb{R}^{HW \times T \times \frac{C}{2S}})$ , key $(\mathbf{K} \in \mathbb{R}^{HW \times T \times \frac{C}{2S}})$ and value $(\mathbf{V} \in \mathbb{R}^{HW \times T \times \frac{C}{2S}})$ by linearly mapping $\mathbf{X}_t$ : + +$$ +\mathbf {Q} = \mathbf {X} _ {t} \mathbf {W} ^ {Q}, \quad \mathbf {K} = \mathbf {X} _ {t} \mathbf {W} ^ {K}, \quad \mathbf {V} = \mathbf {X} _ {t} \mathbf {W} ^ {V}, \tag {6} +$$ + +where $\{\mathbf{W}^Q,\mathbf{W}^K,\mathbf{W}^V\} \in \mathbb{R}_{\overline{S}}^{C\times \frac{C}{2S}}$ are projection matrices. + +It is worth noting that the output dimension of the projection matrix is reduced to half of the input dimension, further decreasing the computational complexity of TSAB. Then, we respectively divide $\mathbf{Q}$ , $\mathbf{K}$ , $\mathbf{V}$ into $N$ heads along the feature channel: $\mathbf{Q} = \{\mathbf{Q}_j\}_{1}^{N}$ , $\mathbf{K} = \{\mathbf{K}_j\}_{1}^{N}$ , $\mathbf{V} = \{\mathbf{V}_j\}_{1}^{N} \in \mathbb{R}^{HW \times T \times \frac{C}{2SN}}$ . For each head $j = 1, \dots, N$ , the attention can be calculated as: + +$$ +\operatorname {h e a d} _ {j} = \mathbf {A} _ {j} * \mathbf {V} _ {j}, \tag {7} +$$ + +where $\mathbf{A}_j = \text{softmax}(\mathbf{Q}_j\mathbf{K}_j^T / \sqrt{d}) \in \mathbb{R}^{HW \times T \times T}$ repre + +sents an attention map, $\mathbf{K}_j^T$ represents the transposed matrix of $\mathbf{K}_j$ and $d = \frac{C}{2SN}$ is a scaling parameter. Then, we concatenate the outputs of $N$ heads along the feature channel dimension and perform a linear mapping to obtain the final output $\hat{\mathbf{X}}_t\in \mathbb{R}^{T\times H\times W\times \frac{C}{S}}$ of TSAB: + +$$ +\hat {\mathbf {X}} _ {t} = \mathbf {R} \left(\mathbf {W} ^ {P} \left(\operatorname {C o n c a t} \left[ h e a d _ {1}, \dots , h e a d _ {N} \right]\right)\right), \tag {8} +$$ + +where $\mathbf{W}^P\in \mathbb{R}^{\frac{C}{2S}\times \frac{C}{S}}$ represents projection matrices, and $\mathbf{R}$ is the reshape operator. + +Table 1. Computational complexity of several SOTA methods. + +
MethodComputational Complexity
SCB3D1/2HWTK3C2
G-MSAHWTC2+(HWT)2C
TS-MSA2HWTC2+T(HW)2C+HWT2C
SCB1/2HWTK2C2
TSAB1/2HWTC2+1/2HWT2C
+ +We further analyze the computational complexity of SCB and TSAB, and compare them with 3D convolution and several classic Multi-head Self-Attention (MSA) mechanisms. The results are shown in Table 1, where 'SCB3D' represents the replacement of 2D convolution in SCB with 3D convolution and $K$ represents the kernel size, 'G-MSA' represents the original global MSA [10], and 'TS-MSA' represents the MSA in TimeSformer [3]. It can be observed that the computational complexity of our proposed SCB and TSAB grows linearly with the spatial size $HW$ , the computational cost is much less than 'TS-MSA' and 'G-MSA' (grow quadratically with $HW$ ). Compared with 3D convolution, since $T$ is generally smaller than $C$ , 'SCB' and 'TSAB' still need less computational cost. + +Feed Forward Network: The feed forward network of traditional Transformer usually uses two linear layers and a nonlinear activation function to learn more abstract feature representations. However, in the whole FFN, there is no interaction between the feature points. In order to better integrate the spatial-temporal information and position coding information, we replace the first linear transformation layer in the traditional FFN with a $3 \times 3 \times 3$ convolution. + +Given $\mathbf{X}_f\in \mathbb{R}^{T\times H\times W\times \frac{C}{2}}$ , FFN can be expressed as: + +$$ +\hat {\mathbf {X}} _ {f} = \mathbf {X} _ {f} + \mathbf {W} _ {1} \left(\phi \left(\mathbf {W} _ {2} \left(\mathbf {X} _ {f}\right)\right)\right), \tag {9} +$$ + +where $\mathbf{W}_1, \mathbf{W}_2$ represent $1 \times 1 \times 1$ convolution and $3 \times 3 \times 3$ convolution operations respectively, $\phi$ denotes the LeakyReLU non-linearity activation, and $\hat{\mathbf{X}}_f \in \mathbb{R}^{T \times H \times W \times \frac{C}{2}}$ is the output of the FFN. + +It should be noted that in the whole CFormer block, we do not use any regularization layers, such as Layer Normalization [1] and Batch Normalization [16]. The experimental results show that removing the regularization layer will not reduce the quality of model reconstruction and can further improve the efficiency of the model. + +Table 2. Reconstruction quality and test time (s) using EfficientSCI with different number of channels and blocks. + +
ModelChannelBlockPSNRSSIMTest time(s)
EfficientSCI-T64834.220.9610.07
EfficientSCI-S128835.510.9700.15
EfficientSCI-B256836.480.9750.31
EfficientSCI-L2561236.920.9770.45
+ +Table 3. Computational complexity and reconstruction quality of several SOTA algorithms on 6 grayscale benchmark datasets. + +
MethodParams (M)FLOPs (G)PSNRSSIM
BIRNAT4.13390.5633.310.951
RevSCI5.66766.9533.920.956
DUN-3DUnet61.913975.8335.260.968
ELP-Unfolding565.734634.9435.410.969
EfficientSCI-T0.95142.1834.220.961
EfficientSCI-S3.78563.8735.510.970
EfficientSCI-B8.821426.3836.480.975
EfficientSCI-L12.391893.7236.920.977
+ +Network Variants: To balance speed and performance of the proposed network, we introduce four different versions of EfficientSCI network, dubbed as EfficientSCI-T, EfficientSCI-S, EfficientSCI-B and EfficientSCI-L standing for Tiny, Small, Base and Large networks, respectively. The network hyper-parameters are shown in Table 2, in which we mainly changed the the number of ResD-Net blocks and the number of channels. As shown in Table 3, we also compare model parameters and computational complexity (FLOPs) with several advanced methods. The complexity of our proposed EfficientSCI-T is smaller than that of BIRNAT and RevSCI, and EfficientSCI-L is smaller than that of DUN-3DUnet and ELP-Unfolding. + +# 5. Experiment Results + +# 5.1. Datasets + +Following BIRNAT [8], we use DAVIS2017 [29] with resolution $480 \times 894$ (480p) as the model training dataset. To verify model performance, we first test the EfficientSCI network on several simulated datasets, including six benchmark grayscale datasets (Kobe, Traffic, Runner, Drop, Crash and Aerial with a size of $256 \times 256 \times 8$ ), six benchmark mid-scale color datasets (Beauty, Bosphorus, Jockey, Runner, ShakeNDry and Traffic with a size of $512 \times 512 \times 3 \times 8$ ), and four large-scale datasets (Messi, Hummingbird, Swinger and Football with different sizes and compression ratios). Then we test our model on some real data (including Duomino, Water Balloon) captured by a real SCI system [30]. + +# 5.2. Implementation Details + +We use PyTorch framework with 4 NVIDIA RTX 3090 GPUs for training with random cropping, random scaling, and random flipping for data augmentation, and use + +Table 4. The average PSNR in dB (left entry) and SSIM (right entry) and running time per measurement of different algorithms on 6 benchmark grayscale datasets. The best results are shown in bold and the second-best results are underlined. + +
MethodKobeTrafficRunnerDropCrashAerialAverageTest time(s)
GAP-TV26.46, 0.88520.89, 0.71528.52, 0.90934.63, 0.97024.82, 0.83825.05, 0.82826.73, 0.8584.2 (CPU)
PnP-FFDNet30.50, 0.92624.18, 0.82832.15, 0.93340.70, 0.98925.42, 0.84925.27, 0.82929.70, 0.8923.0 (GPU)
PnP-FastDVDnet32.73, 0.94727.95, 0.93236.29, 0.96241.82, 0.98927.32, 0.92527.98, 0.89732.35, 0.9426.0 (GPU)
DeSCI33.25, 0.95228.71, 0.92538.48, 0.96943.10, 0.99327.04, 0.90925.33, 0.86032.65, 0.9356180 (CPU)
BIRNAT32.71, 0.95029.33, 0.94238.70, 0.97642.28, 0.99227.84, 0.92728.99, 0.91733.31, 0.9510.10 (GPU)
RevSCI33.72, 0.95730.02, 0.94939.40, 0.97742.93, 0.99228.12, 0.93729.35, 0.92433.92, 0.9560.19 (GPU)
GAP-CCoT32.58, 0.94929.03, 0.93839.12, 0.98042.54, 0.99228.52, 0.94129.40, 0.92333.53, 0.9580.08 (GPU)
DUN-3DUnet35.00, 0.96931.76, 0.96640.03, 0.98044.96, 0.99529.33, 0.95630.46, 0.94335.26, 0.9680.58 (GPU)
ELP-Unfolding34.41, 0.96631.58, 0.96241,16, 0.98644.99, 0.99529.65, 0.95930.68, 0.94435.41, 0.9690.34 (GPU)
EfficientSCI-T33.45, 0.96029.20, 0.94239.51, 0.98143.56, 0.99329.27, 0.95430.32, 0.93734.22, 0.9610.07 (GPU)
EfficientSCI-S34.79, 0.96831.21, 0.96141.34, 0.98644.61, 0.99430.34, 0.96530.78, 0.94535.51, 0.9700.15 (GPU)
EfficientSCI-B35.76, 0.97432.30, 0.96843.05, 0.98845.18, 0.99531.13, 0.97131.50, 0.95336.48, 0.9750.31 (GPU)
EfficientSCI-L36.27, 0.97632.83, 0.97143.79, 0.99145.46, 0.99531.52, 0.97431.64, 0.95536.92, 0.9770.45 (GPU)
+ +![](images/10f5dbc5f4fdf5b517365203a522ccd68a97a42925a72fd1833f862f976beb51.jpg) +Figure 5. Selected reconstruction frames of simulated grayscale data. Zoom in for better view. + +Adam [19] to optimize the model with the initial learning rate 0.0001. After iterating for 300 epochs, we adjusted the learning rate to 0.00001 and continued to iterate for 40 epochs to get the final model parameters. The peak-signal-to-noise-ratio (PSNR) and structured similarity index metrics (SSIM) [38] are used as the performance indicators of reconstruction quality. + +# 5.3. Results on Simulation Datasets + +# 5.3.1 Grayscale Simulation Video + +We compare our method with SOTA model-based methods (GAP-TV [44], PnP-FFDNet [46], PnP-FastDVDnet [47], DeSCI [21]) and deep learning-based methods (BIR-NAT [8], RevSCI [7], GAP-CCoT [36], DUN-3DUnet [40], ELP-Unfolding [42]) on simulated grayscale datasets. Table 4 shows the quantitative comparison results, it can be observed that our proposed EfficientSCI-L can achieve the highest reconstruction quality and has good real-time performance. In particular, the PSNR value of our method surpasses the existing best method ELP-Unfolding by 1.46 + +dB on average. In addition, our proposed EfficientSCIT achieves high reconstruction quality while achieving the best real-time performance. It is worth noting that, for a fair comparison, we uniformly test the running time of all deep learning based methods on the same NVIDIA RTX 3090 GPU. Fig. 5 shows the visual reconstruction results of some data. By zooming in some local areas, we can observe that our method can recover sharper edges and more detailed information compared to previous SOTA methods. The mid-scale color results are shown in the SM due to space limitation and our method outperforms previous SOTA by 2.02 dB in PSNR on the benchmark dataset [47]. + +# 5.3.2 Large-scale Color Simulation Video + +Most deep learning based methods, such as BIRNAT [8], DUN-3DUnet [40], cannot be applied to large-scale data reconstruction due to excessive model complexity and GPU memory constraints. RevSCI [7] uses a reversible mechanism and can reconstruct a 24 frames RGB color video with size of $1080 \times 1920 \times 3$ , but training the model is extremely slow. GAP-CCoT [36] and ELP-Unfolding [42] only use 2D convolution for reconstruction and thus cannot handle color video data well. Therefore, we only compare with several SOTA model-based methods (GAP-TV [44], PnP-FFDNet-color [46], PnP-FastDVDnet-color [47]) on large-scale color data. Table 5 shows the comparisons between our proposed method and several model-based methods on PSNR, SSIM and test time (in minutes). It can be observed that model-based methods either have long reconstruction time (PnP-FFDNet-color, PnP-FastDVDnet-color) or low reconstruction quality (GAP-TV). Our proposed EfficientSCI-S can achieve higher reconstruction quality and running speed. Especially on UHD color video football $(1644 \times 3840 \times 3 \times 40)$ , the PSNR value of our method is 2.5 dB higher than PnP-FastDVDnet-color, and the reconstruction time is only $0.5\%$ of it. Fig. 6 shows some visual reconstruction results. By zooming + +Table 5. The average PSNR in dB (left entry) and SSIM (middle entry) and test time (minutes) per measurement (right entry) of different algorithms on 4 benchmark large-scale datasets. Best results are in bold. + +
DatasetPixel resolutionGAP-TVPnP-FFDNet-colorPnP-FastDVDnet-colorEfficientSCI-S
Messi1080 × 1920 × 3 × 825.20, 0.874, 0.6634.28, 0.968, 14.9334.34, 0.970, 15.9434.41, 0.973, 0.09
Hummingbird1080 × 1920 × 3 × 3025.10, 0.750, 20.328.79, 0.665, 61.2031.17, 0.916, 54.0035.56, 0.952, 0.39
Swinger2160 × 3840 × 3 × 1522.68, 0.769, 39.229.30, 0.934, 138.830.57, 0.949, 138.431.05, 0.951, 0.62
Football1644 × 3840 × 3 × 4026.19, 0.858, 83.032.70, 0.951, 308.832.31, 0.947, 298.134.81, 0.964, 1.52
+ +![](images/d17274b01809fdeea6cfc85ca178d50b6190ef28083d9a2c8ba399f8da85c83c.jpg) +Figure 6. Comparison of reconstruction results of different algorithms on several benchmark large-scale color video simulation datasets. + +![](images/aa88788552c191bfde1524a8d9791ac8bc906306a3546dcddfbaa14622a37abe.jpg) +Figure 7. Reconstruction quality (PSNR in dB, higher is better) of different reconstruction algorithms, with varying compression rates $B$ from 8 to 48. + +in local areas, we can observe that the reconstruction results of our method are closer to the real value. In addition, our proposed model enjoys high flexibility for different compression ratios, that is, the model trained on low compression ratio data can be directly used for high com + +pression ratio video reconstruction task. To verify this, we test hummingbird data with different compression ratios $B = 8, 16, 24, 32, 40, 48$ , and the reconstruction results are shown in Fig. 7. We can observe that our method can be applied to video data with different compression ratios, even when the compression ratio $B$ grows to 48, the PSNR value of EfficientSCI-T model can still reach more than 32 dB. Moreover, our proposed approach surpasses other reconstruction algorithms at all compression ratios. + +# 5.3.3 Ablation Study + +To verify the performance of the proposed ResDNet block and CFormer block on the impact of the reconstruction quality, we conduct some ablation experiments. The results are shown in Table 6 and Table 7, we not only compare the reconstruction quality of different models, but also analyze the model parameters and FLOPs. All experiments are conducted on the 6 grayscale benchmark datasets. + +Table 6. Ablation study on the ResDNet block without dense connections (left entry) and with dense connections (right entry). + +
GNParamsFLOPsPSNRSSIM
127.40, 27.403860.94, 3860.9435.17, 35.170.967, 0.967
214.82, 15.082211.77, 2246.3935.09, 36.020.966, 0.974
48.53, 8.821387.33, 1426.3835.02, 36.480.966, 0.975
85.38, 5.65975.39, 1013.4534.31, 35.680.961, 0.971
+ +Table 7. Ablation study on the CFormer block. + +
SCBTSABSwinS2-3DParams (M)FLOPs (G)PSNRSSIM
✓✓2.88471.0334.990.967
✓6.93999.3134.930.966
✓✓3.78563.8735.510.970
+ +ResDNet Block: We verify the effect of different group numbers (GN) (corresponding to $S$ in Eq. 5) and dense connections on the reconstruction quality. As shown in Table 6, the model complexity decreases gradually with the increase of GN, but the reconstruction quality greatly decreases when there are no dense connections in the ResDNet block. By introducing dense connections in the ResDNet block, the reconstruction quality of our proposed method is greatly improved, and a gain of $1.46\mathrm{dB}$ can be obtained when GN is 4. + +CFormer Block: In the CFormer block, we first replace SCB with Swin Transformer (Swin) to verify its effectiveness. Then, we replace SCB and TSAB with two stacked 3D convolutions (S2-3D) to verify the effectiveness of TSAB. As shown in Table 7, compared with Swin Transformer, SCB can bring a $0.52\mathrm{dB}$ gain. Although the number of parameters and FLOPs have increased, the experimental results show that SCB takes up less memory than the Swin Transformer, which is very important for large-scale and high compression ratio data. Please refer to more detailed analysis in SM. Compared with SCB and TSAB, S2-3D not only increases model parameters and FLOPs by $83\%$ and $77\%$ respectively, but also reduces the PSNR value by 0.58 dB, which verifies the necessity of using space-time factorization and TSAB. + +Number of Channels and Blocks: Table 2 shows that the quality of model reconstruction increases with the number of channels and blocks. However, the amount of parameters and FLOPs also increase (see Table 3), resulting in a degradation in the real-time performance of the model. + +# 5.4. Results on Real Video SCI Data + +We further test our method on real data. Fig. 8 and Fig. 9 show the reconstruction results of multiple algorithms on two public data (Duomino, Water Ballon), we can see that our method can reconstruct clearer details and edges. Specifically, we can clearly recognize the letters on the Duomino. Even with a high compression ratio $(B = 50)$ , our proposed method can still reconstruct clear foreground and background information (shown in Fig. 9). + +![](images/b086261c597715f90d12709648405d9000afb9b96062e7d12afcbc57c4292949.jpg) +Figure 8. Reconstruction results of different algorithms on Duomino real data with compression rate $B = 10$ . + +![](images/6440a8697529966d1698e0d40cc006be5cfaef126a45224c11dc9031daa0ebb0.jpg) +Figure 9. Reconstruction results of different algorithms on Water Ballon real data with compression rate $B = 50$ . + +# 6. Conclusions and Future Work + +This paper proposes an efficient end-to-end video SCI reconstruction network, dubbed EfficientSCI, which achieves the state-of-the-art performance on simulated data and real data, significantly surpassing the previous best reconstruction algorithms with high real-time performance. In addition, we show for the first time that an UHD color video with high compression rate can be reconstructed using a deep learning based method. For future work, we consider applying EfficientSCI Network to more SCI reconstruction tasks, such as spectral SCI [4, 49]. + +# Acknowledgements + +This work was supported by the National Natural Science Foundation of China [62271414], Zhejiang Provincial Natural Science Foundation of China [LR23F010001]. We would like to thank Research Center for Industries of the Future (RCIF) at Westlake University and the funding from Lochn Optics. + +# References + +[1] Jimmy Lei Ba, Jamie Ryan Kiros, and Geoffrey E Hinton. 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In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 5728-5739, 2022. 2 \ No newline at end of file diff --git a/2023/EfficientSCI_ Densely Connected Network With Space-Time Factorization for Large-Scale Video Snapshot Compressive Imaging/images.zip b/2023/EfficientSCI_ Densely Connected Network With Space-Time Factorization for Large-Scale Video Snapshot Compressive Imaging/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..47fa7353eb75044bbca5a2a0a43c4451b39dce5c --- /dev/null +++ b/2023/EfficientSCI_ Densely Connected Network With Space-Time Factorization for Large-Scale Video Snapshot Compressive Imaging/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:1957df035d4a583ae7887df6573da4246d8bd62d49e622118909c5b284941a61 +size 928549 diff --git a/2023/EfficientSCI_ Densely Connected Network With Space-Time Factorization for Large-Scale Video Snapshot Compressive Imaging/layout.json b/2023/EfficientSCI_ Densely Connected Network With Space-Time Factorization for Large-Scale Video Snapshot Compressive Imaging/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..0ca6099759d011aeb86a948e466d71c62f5a437a --- /dev/null +++ b/2023/EfficientSCI_ Densely Connected Network With Space-Time Factorization for Large-Scale Video Snapshot Compressive Imaging/layout.json @@ -0,0 +1,8717 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 62, + 102, + 532, + 140 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 62, + 102, + 532, + 140 + ], + "spans": [ + { + "bbox": [ + 62, + 102, + 532, + 140 + ], + "type": "text", + "content": "EfficientSCI: Densely Connected Network with Space-time Factorization for Large-scale Video Snapshot Compressive Imaging" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 170, + 160, + 420, + 175 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 170, + 160, + 420, + 175 + ], + "spans": [ + { + "bbox": [ + 170, + 160, + 420, + 175 + ], + "type": "text", + "content": "Lishun Wang " + }, + { + "bbox": [ + 170, + 160, + 420, + 175 + ], + "type": "inline_equation", + "content": "^{1,2,*}" + }, + { + "bbox": [ + 170, + 160, + 420, + 175 + ], + "type": "text", + "content": ", Miao Cao " + }, + { + "bbox": [ + 170, + 160, + 420, + 175 + ], + "type": "inline_equation", + "content": "^{3,4,*}" + }, + { + "bbox": [ + 170, + 160, + 420, + 175 + ], + "type": "text", + "content": ", and Xin Yuan " + }, + { + "bbox": [ + 170, + 160, + 420, + 175 + ], + "type": "inline_equation", + "content": "^{3,\\dagger}" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 110, + 175, + 482, + 190 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 110, + 175, + 482, + 190 + ], + "spans": [ + { + "bbox": [ + 110, + 175, + 482, + 190 + ], + "type": "text", + "content": "1 Chengdu Institute of Computer Application Chinese Academy of Sciences," + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 74, + 190, + 515, + 204 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 74, + 190, + 515, + 204 + ], + "spans": [ + { + "bbox": [ + 74, + 190, + 515, + 204 + ], + "type": "inline_equation", + "content": "^{2}" + }, + { + "bbox": [ + 74, + 190, + 515, + 204 + ], + "type": "text", + "content": " University of Chinese Academy of Sciences, " + }, + { + "bbox": [ + 74, + 190, + 515, + 204 + ], + "type": "inline_equation", + "content": "^{3}" + }, + { + "bbox": [ + 74, + 190, + 515, + 204 + ], + "type": "text", + "content": " Westlake University, " + }, + { + "bbox": [ + 74, + 190, + 515, + 204 + ], + "type": "inline_equation", + "content": "^{4}" + }, + { + "bbox": [ + 74, + 190, + 515, + 204 + ], + "type": "text", + "content": " Zhejiang University" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 143, + 231, + 192, + 243 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 231, + 192, + 243 + ], + "spans": [ + { + "bbox": [ + 143, + 231, + 192, + 243 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 256, + 290, + 568 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 256, + 290, + 568 + ], + "spans": [ + { + "bbox": [ + 46, + 256, + 290, + 568 + ], + "type": "text", + "content": "Video snapshot compressive imaging (SCI) uses a two-dimensional detector to capture consecutive video frames during a single exposure time. Following this, an efficient reconstruction algorithm needs to be designed to reconstruct the desired video frames. Although recent deep learning-based state-of-the-art (SOTA) reconstruction algorithms have achieved good results in most tasks, they still face the following challenges due to excessive model complexity and GPU memory limitations: 1) these models need high computational cost, and 2) they are usually unable to reconstruct large-scale video frames at high compression ratios. To address these issues, we develop an efficient network for video SCI by using dense connections and space-time factorization mechanism within a single residual block, dubbed EfficientSCI. The EfficientSCI network can well establish spatial-temporal correlation by using convolution in the spatial domain and Transformer in the temporal domain, respectively. We are the first time to show that an UHD color video with high compression ratio can be reconstructed from a snapshot 2D measurement using a single end-to-end deep learning model with PSNR above 32 dB. Extensive results on both simulation and real data show that our method significantly outperforms all previous SOTA algorithms with better real-time performance. The code is at https://github.com/ucaswangls/EfficientSCI.git." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 590, + 128, + 602 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 590, + 128, + 602 + ], + "spans": [ + { + "bbox": [ + 47, + 590, + 128, + 602 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 611, + 287, + 696 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 611, + 287, + 696 + ], + "spans": [ + { + "bbox": [ + 46, + 611, + 287, + 696 + ], + "type": "text", + "content": "Traditional high-speed camera imaging methods usually suffer from high hardware and storage transmission cost. Inspired by compressed sensing (CS) [5, 9], video snapshot compressive imaging (SCI) [45] provides an elegant solution. As shown in Fig. 2, video SCI consists of a hardware encoder and a software decoder. In the encoder part, multiple raw video frames are modulated by different masks and" + } + ] + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 307, + 229, + 547, + 411 + ], + "blocks": [ + { + "bbox": [ + 307, + 229, + 547, + 411 + ], + "lines": [ + { + "bbox": [ + 307, + 229, + 547, + 411 + ], + "spans": [ + { + "bbox": [ + 307, + 229, + 547, + 411 + ], + "type": "image", + "image_path": "6e028b4c59a14fe49510021b749e66600621c5fb1d7da19aafd0841c9305a420.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 415, + 547, + 472 + ], + "lines": [ + { + "bbox": [ + 304, + 415, + 547, + 472 + ], + "spans": [ + { + "bbox": [ + 304, + 415, + 547, + 472 + ], + "type": "text", + "content": "Figure 1. Comparison of reconstruction quality (average PSNR in dB on 6 benchmark grayscale datasets) and testing time of several SOTA deep learning based algorithms. Our proposed EfficientSCI achieves higher reconstruction quality with fewer parameters and shorter testing time." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 480, + 547, + 540 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 480, + 547, + 540 + ], + "spans": [ + { + "bbox": [ + 304, + 480, + 547, + 540 + ], + "type": "text", + "content": "then integrated by the camera to get a compressed measurement, giving low-speed cameras the ability to capture high-speed scenes. For the decoding part, the desired high-speed video is retrieved by the reconstruction algorithm using the captured measurement and masks." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 543, + 547, + 699 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 543, + 547, + 699 + ], + "spans": [ + { + "bbox": [ + 304, + 543, + 547, + 699 + ], + "type": "text", + "content": "So far, many mature SCI imaging systems [14, 24, 31] have been built, but for the decoding part, there are still many challenges. In particular, although the model-based methods [21, 43, 44] have good flexibility and can reconstruct videos with different resolutions and compression rates, they require long reconstruction time and can only achieve poor reconstruction quality. In order to improve the reconstruction quality and running speed, PnP-FFDNet [46] and PnP-FastDVDnet [47] integrate the pre-trained denoising network into an iterative optimization algorithm. However, they still need a long reconstruction time on large-scale datasets, e.g., PnP-FastDVDNet takes hours to reconstruct a UHD video from a single measurement." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 317, + 701, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 701, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 317, + 701, + 545, + 714 + ], + "type": "text", + "content": "By contrast, deep learning based methods [28,30,35,40]" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 496, + 35 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 496, + 35 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 496, + 35 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 702, + 208, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 702, + 208, + 713 + ], + "spans": [ + { + "bbox": [ + 58, + 702, + 208, + 713 + ], + "type": "text", + "content": "*Equal Contribution, † Corresponding Author" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "18477" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 50, + 70, + 286, + 189 + ], + "blocks": [ + { + "bbox": [ + 50, + 70, + 286, + 189 + ], + "lines": [ + { + "bbox": [ + 50, + 70, + 286, + 189 + ], + "spans": [ + { + "bbox": [ + 50, + 70, + 286, + 189 + ], + "type": "image", + "image_path": "b80883aba0a14977c145c065f39cef9aaa16162d90a875481c4752be480d5808.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 49, + 195, + 280, + 207 + ], + "lines": [ + { + "bbox": [ + 49, + 195, + 280, + 207 + ], + "spans": [ + { + "bbox": [ + 49, + 195, + 280, + 207 + ], + "type": "text", + "content": "Figure 2. Schematic diagram of grayscale and color video SCI." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 215, + 287, + 466 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 215, + 287, + 466 + ], + "spans": [ + { + "bbox": [ + 47, + 215, + 287, + 466 + ], + "type": "text", + "content": "have better real-time performance and higher reconstruction quality. For example, BIRNAT [8] uses bidirectional recurrent neural network and generative adversarial method to surpass model-based method DeSCI [21] for the first time. MetaSCI [39] has made some explorations for the model to adapt to different masks, which reduces the model training time. DUN-3DUnet [40] and ELP-Unfolding [42] combine iterative optimization ideas with deep learning models to further improve reconstruction quality. However, due to the high model complexity and insufficient GPU memory, most existing deep learning algorithms cannot train the models required for reconstructing HD or large-scale videos. RevSCI [7] uses a reversible mechanism [2] to reduce the memory used for model training, and can reconstruct HD video with a compression rate up to 24, but the model training time increases exponentially. In addition, the current reconstruction algorithms generally use convolution to establish spatial-temporal correlation. Due to the local connection of convolution, long-term dependencies cannot be well established, and the model cannot reconstruct data with high compression rates." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 466, + 287, + 610 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 466, + 287, + 610 + ], + "spans": [ + { + "bbox": [ + 47, + 466, + 287, + 610 + ], + "type": "text", + "content": "In summary, model-based methods usually require long reconstruction time and can only achieve poor reconstruction quality. Learning-based methods have high model complexity but cannot be well applied to large-scale color video reconstruction. To address these challenges, we develop an efficient network for video SCI by using dense connections and space-time factorization mechanism. As shown in Fig. 1, our proposed method dramatically outperforms all previous deep learning based reconstruction algorithms in terms of reconstruction quality and running speed with fewer parameters. Our main contributions can be summarized as follows:" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 58, + 620, + 286, + 713 + ], + "type": "list", + "angle": 0, + "index": 6, + "blocks": [ + { + "bbox": [ + 59, + 620, + 286, + 654 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 620, + 286, + 654 + ], + "spans": [ + { + "bbox": [ + 59, + 620, + 286, + 654 + ], + "type": "text", + "content": "- An efficient end-to-end network, dubbed EfficientSCI, is proposed for reconstructing high quality video frames from a snapshot SCI measurement." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 58, + 665, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 665, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 58, + 665, + 286, + 713 + ], + "type": "text", + "content": "- By building hierarchical dense connections within a single residual block, we devise a novel ResDNet block to effectively reduces model computational complexity but enhance the learning ability of the model." + } + ] + } + ], + "index": 5 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 317, + 72, + 545, + 190 + ], + "type": "list", + "angle": 0, + "index": 9, + "blocks": [ + { + "bbox": [ + 317, + 72, + 545, + 133 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 72, + 545, + 133 + ], + "spans": [ + { + "bbox": [ + 317, + 72, + 545, + 133 + ], + "type": "text", + "content": "- Based on the space-time factorization mechanism, a Convolution and Transformer hybrid block (CFormer) is built, which can efficiently establish space-time correlation by using convolution in the spatial domain and Transformer in the temporal domain, respectively." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 317, + 142, + 545, + 190 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 142, + 545, + 190 + ], + "spans": [ + { + "bbox": [ + 317, + 142, + 545, + 190 + ], + "type": "text", + "content": "- Experimental results on a large number of simulated and real datasets demonstrate that our proposed method achieves state-of-the-art (SOTA) results and better real-time performance." + } + ] + } + ], + "index": 8 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 306, + 201, + 392, + 214 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 201, + 392, + 214 + ], + "spans": [ + { + "bbox": [ + 306, + 201, + 392, + 214 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 222, + 545, + 484 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 222, + 545, + 484 + ], + "spans": [ + { + "bbox": [ + 304, + 222, + 545, + 484 + ], + "type": "text", + "content": "CNN and Variants: In the past ten years, models with convolutional neural networks (CNN) as the backbone [13,15,20] have achieved excellent results on multiple computer vision tasks [20, 25, 32]. Among them, ResNeXt [41] and Res2Net [11] effectively increases model capacity without increasing model complexity by using grouped convolutions inside residual blocks. DenseNet [15] and CSPNet [34] achieve feature reuse by taking all previous feature maps as input. In video-related tasks, 3D convolution can establish good spatial-temporal correlation and has been widely used in action recognition [18], video superresolution [26], video inpainting [6] and so on. In previous video SCI reconstruction, RevSCI and DUN-3DUnet greatly improve the reconstruction quality of benchmark grayscale datasets by integrating 3D convolution into the network. However, in complex high-speed scenarios (e.g., crash), since they cannot effectively establish long-term temporal dependencies, the reconstruction quality is still lower than " + }, + { + "bbox": [ + 304, + 222, + 545, + 484 + ], + "type": "inline_equation", + "content": "30\\mathrm{dB}" + }, + { + "bbox": [ + 304, + 222, + 545, + 484 + ], + "type": "text", + "content": ". In addition, the excessive use of 3D convolution increases the amount of model parameters, which is not conducive to the application of large-scale and high compression ratio data." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 486, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 486, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 486, + 545, + 713 + ], + "type": "text", + "content": "Vision Transformers: Most recently, Vision Transformer (ViT) [10] and its variants [4, 12, 37, 50] have achieved competitive results in computer vision. However, the high computational complexity limits its application in video-related tasks. TimeSformer [3] performs self-attention calculations in time and space respectively, which reduces model complexity and improves model accuracy, but the computational complexity still increases quadratically with the image size. The Video Swin Transformer [23] limits self-attention calculations to local windows but cannot effectively establish long-term temporal dependencies. In addition, a large number of experimental results show that Transformer has higher memory consumption than CNN, and using Transformer in space is not conducive to large-scale video SCI reconstruction. Therefore, through space-time factorization mechanism, using Transformer only in time domain can not only effectively utilize its ability to establish long-term time series dependencies, but also reduce model complexity and memory consumption." + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "18478" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 60, + 68, + 532, + 217 + ], + "blocks": [ + { + "bbox": [ + 60, + 68, + 532, + 217 + ], + "lines": [ + { + "bbox": [ + 60, + 68, + 532, + 217 + ], + "spans": [ + { + "bbox": [ + 60, + 68, + 532, + 217 + ], + "type": "image", + "image_path": "029625615612b212673c7634f8bfc935ed2da89d5a0ae3cd563220b48f108e05.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 218, + 547, + 274 + ], + "lines": [ + { + "bbox": [ + 46, + 218, + 547, + 274 + ], + "spans": [ + { + "bbox": [ + 46, + 218, + 547, + 274 + ], + "type": "text", + "content": "Figure 3. Architecture of the proposed EfficientSCI network and the overall process of color or grayscale video reconstruction. The measurement " + }, + { + "bbox": [ + 46, + 218, + 547, + 274 + ], + "type": "inline_equation", + "content": "(\\mathbf{Y})" + }, + { + "bbox": [ + 46, + 218, + 547, + 274 + ], + "type": "text", + "content": " and masks " + }, + { + "bbox": [ + 46, + 218, + 547, + 274 + ], + "type": "inline_equation", + "content": "(\\mathbf{M})" + }, + { + "bbox": [ + 46, + 218, + 547, + 274 + ], + "type": "text", + "content": " are pre-processed by the estimation module to obtain an estimated " + }, + { + "bbox": [ + 46, + 218, + 547, + 274 + ], + "type": "inline_equation", + "content": "\\mathbf{X}_e" + }, + { + "bbox": [ + 46, + 218, + 547, + 274 + ], + "type": "text", + "content": ", and then feed " + }, + { + "bbox": [ + 46, + 218, + 547, + 274 + ], + "type": "inline_equation", + "content": "\\mathbf{X}_e" + }, + { + "bbox": [ + 46, + 218, + 547, + 274 + ], + "type": "text", + "content": " into EfficientSCI network to get the desired reconstruction result. (a) ResDNet module with " + }, + { + "bbox": [ + 46, + 218, + 547, + 274 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 218, + 547, + 274 + ], + "type": "text", + "content": " residual style units. (b) ResDNet block. Inside a residual block, the input features are divided into " + }, + { + "bbox": [ + 46, + 218, + 547, + 274 + ], + "type": "inline_equation", + "content": "S" + }, + { + "bbox": [ + 46, + 218, + 547, + 274 + ], + "type": "text", + "content": " parts by the channel split. Each part uses CFormer to efficiently extract spatial-temporal correlation, and employs dense connections to further improve model capacity. For convenience, only the case of " + }, + { + "bbox": [ + 46, + 218, + 547, + 274 + ], + "type": "inline_equation", + "content": "S = 4" + }, + { + "bbox": [ + 46, + 218, + 547, + 274 + ], + "type": "text", + "content": " is shown here." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 278, + 239, + 292 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 278, + 239, + 292 + ], + "spans": [ + { + "bbox": [ + 47, + 278, + 239, + 292 + ], + "type": "text", + "content": "3. Mathematical Model of Video SCI" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 298, + 288, + 382 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 298, + 288, + 382 + ], + "spans": [ + { + "bbox": [ + 46, + 298, + 288, + 382 + ], + "type": "text", + "content": "Fig. 2 briefly describes the flow chart of video SCI. For grayscale video SCI system, the original " + }, + { + "bbox": [ + 46, + 298, + 288, + 382 + ], + "type": "inline_equation", + "content": "B" + }, + { + "bbox": [ + 46, + 298, + 288, + 382 + ], + "type": "text", + "content": "-frame (grayscale) input video " + }, + { + "bbox": [ + 46, + 298, + 288, + 382 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{X}_m\\}_{m=1}^B \\in \\mathbb{R}^{n_x \\times n_y}" + }, + { + "bbox": [ + 46, + 298, + 288, + 382 + ], + "type": "text", + "content": " is modulated by pre-defined masks " + }, + { + "bbox": [ + 46, + 298, + 288, + 382 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{M}\\}_{m=1}^B \\in \\mathbb{R}^{n_x \\times n_y}" + }, + { + "bbox": [ + 46, + 298, + 288, + 382 + ], + "type": "text", + "content": ". Then, by compressing across time, the camera sensor captures a compressed measurement " + }, + { + "bbox": [ + 46, + 298, + 288, + 382 + ], + "type": "inline_equation", + "content": "\\mathbf{Y} \\in \\mathbb{R}^{n_x \\times n_y}" + }, + { + "bbox": [ + 46, + 298, + 288, + 382 + ], + "type": "text", + "content": ". The whole process can be expressed as:" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 104, + 388, + 287, + 406 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 104, + 388, + 287, + 406 + ], + "spans": [ + { + "bbox": [ + 104, + 388, + 287, + 406 + ], + "type": "interline_equation", + "content": "\\mathbf {Y} = \\sum_ {m = 1} ^ {B} \\mathbf {X} _ {m} \\odot \\mathbf {M} _ {m} + \\mathbf {Z}, \\tag {1}", + "image_path": "d86d49e7f98f9bc25124b82ab8e83dabac13b2a705c75ef1ef4237e912f6feaf.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 412, + 287, + 498 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 412, + 287, + 498 + ], + "spans": [ + { + "bbox": [ + 46, + 412, + 287, + 498 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 412, + 287, + 498 + ], + "type": "inline_equation", + "content": "\\odot" + }, + { + "bbox": [ + 46, + 412, + 287, + 498 + ], + "type": "text", + "content": " denotes the Hadamard (element-wise) multiplication, and " + }, + { + "bbox": [ + 46, + 412, + 287, + 498 + ], + "type": "inline_equation", + "content": "\\mathbf{Z} \\in \\mathbb{R}^{n_x \\times n_y}" + }, + { + "bbox": [ + 46, + 412, + 287, + 498 + ], + "type": "text", + "content": " denotes the measurement noise. Eq. (1) can also be represented by a vectorized formulation. Firstly, we vectorize " + }, + { + "bbox": [ + 46, + 412, + 287, + 498 + ], + "type": "inline_equation", + "content": "\\pmb{y} = \\operatorname{vec}(\\mathbf{Y}) \\in \\mathbb{R}^{n_x n_y}" + }, + { + "bbox": [ + 46, + 412, + 287, + 498 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 412, + 287, + 498 + ], + "type": "inline_equation", + "content": "\\pmb{z} = \\operatorname{vec}(\\mathbf{Z}) \\in \\mathbb{R}^{n_x n_y}" + }, + { + "bbox": [ + 46, + 412, + 287, + 498 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 412, + 287, + 498 + ], + "type": "inline_equation", + "content": "\\pmb{x} = [\\pmb{x}_1^\\top, \\dots, \\pmb{x}_B^\\top]^\\top \\in \\mathbb{R}^{n_x n_y B}" + }, + { + "bbox": [ + 46, + 412, + 287, + 498 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 412, + 287, + 498 + ], + "type": "inline_equation", + "content": "\\pmb{x}_m = \\operatorname{vec}(\\mathbf{X}_m)" + }, + { + "bbox": [ + 46, + 412, + 287, + 498 + ], + "type": "text", + "content": ". Then, sensing matrix generated by masks can be defined as:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 89, + 505, + 287, + 520 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 89, + 505, + 287, + 520 + ], + "spans": [ + { + "bbox": [ + 89, + 505, + 287, + 520 + ], + "type": "interline_equation", + "content": "\\mathbf {H} = \\left[ \\mathbf {D} _ {1}, \\dots , \\mathbf {D} _ {B} \\right] \\in \\mathbb {R} ^ {n _ {x} n _ {y} \\times n _ {x} n _ {y} B}, \\tag {2}", + "image_path": "e1e2a915a586a51c5a52e52e94e081c97075e31dd20c16a67e0f78360ca8a8aa.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 526, + 287, + 564 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 526, + 287, + 564 + ], + "spans": [ + { + "bbox": [ + 46, + 526, + 287, + 564 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 526, + 287, + 564 + ], + "type": "inline_equation", + "content": "\\mathbf{D}_m = \\mathrm{Diag}(\\mathrm{vec}(\\mathbf{M}))\\in \\mathbb{R}^{n_xn_y\\times n_xn_y}" + }, + { + "bbox": [ + 46, + 526, + 287, + 564 + ], + "type": "text", + "content": " is a diagonal matrix and its diagonal elements is filled by " + }, + { + "bbox": [ + 46, + 526, + 287, + 564 + ], + "type": "inline_equation", + "content": "\\operatorname {vec}(\\mathbf{M})" + }, + { + "bbox": [ + 46, + 526, + 287, + 564 + ], + "type": "text", + "content": " Finally, the vectorized expression of Eq. (1) is" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 137, + 572, + 287, + 585 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 137, + 572, + 287, + 585 + ], + "spans": [ + { + "bbox": [ + 137, + 572, + 287, + 585 + ], + "type": "interline_equation", + "content": "\\boldsymbol {y} = \\mathbf {H} \\boldsymbol {x} + \\boldsymbol {z}. \\tag {3}", + "image_path": "35a3b7bcff415068ce9233d942bbe066c74a11667852ab77c0d71c4ae886bad5.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 593, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 593, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 593, + 288, + 714 + ], + "type": "text", + "content": "For color video SCI system, we use the Bayer pattern filter sensor, where each pixel captures only red (R), blue (B) or green (G) channel of the raw data in a spatial layout such as 'RGGB'. Since adjacent pixels are different color components, we divide the original measurement " + }, + { + "bbox": [ + 46, + 593, + 288, + 714 + ], + "type": "inline_equation", + "content": "\\mathbf{Y}" + }, + { + "bbox": [ + 46, + 593, + 288, + 714 + ], + "type": "text", + "content": " into four sub-measurements " + }, + { + "bbox": [ + 46, + 593, + 288, + 714 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{Y}^r,\\mathbf{Y}^{g1},\\mathbf{Y}^{g2},\\mathbf{Y}^b\\} \\in \\mathbb{R}^{\\frac{n_x}{2}\\times \\frac{n_y}{2}}" + }, + { + "bbox": [ + 46, + 593, + 288, + 714 + ], + "type": "text", + "content": " according to the Bayer filter pattern. For color video reconstruction, most of the previous algorithms [46, 48] reconstruct each sub-measurement independently, and then use off-the-shelf demosaic algorithms to get the final RGB color" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 279, + 546, + 328 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 279, + 546, + 328 + ], + "spans": [ + { + "bbox": [ + 304, + 279, + 546, + 328 + ], + "type": "text", + "content": "videos. These methods are usually inefficient and have poor reconstruction quality. In this paper, we feed the four submeasurements simultaneously into the reconstruction network to directly obtain the final desired color video." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 336, + 440, + 350 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 336, + 440, + 350 + ], + "spans": [ + { + "bbox": [ + 305, + 336, + 440, + 350 + ], + "type": "text", + "content": "4. The Proposed Network" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 357, + 546, + 392 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 357, + 546, + 392 + ], + "spans": [ + { + "bbox": [ + 304, + 357, + 546, + 392 + ], + "type": "text", + "content": "As shown in Fig. 3, in the pre-processing stage of EfficientSCI, inspired by [7, 8], we use the estimation module to pre-process measurement " + }, + { + "bbox": [ + 304, + 357, + 546, + 392 + ], + "type": "inline_equation", + "content": "(\\mathbf{Y})" + }, + { + "bbox": [ + 304, + 357, + 546, + 392 + ], + "type": "text", + "content": " and masks " + }, + { + "bbox": [ + 304, + 357, + 546, + 392 + ], + "type": "inline_equation", + "content": "(\\mathbf{M})" + }, + { + "bbox": [ + 304, + 357, + 546, + 392 + ], + "type": "text", + "content": " as follows:" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 330, + 395, + 545, + 411 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 330, + 395, + 545, + 411 + ], + "spans": [ + { + "bbox": [ + 330, + 395, + 545, + 411 + ], + "type": "interline_equation", + "content": "\\overline {{\\mathbf {Y}}} = \\mathbf {Y} \\oslash \\sum_ {m = 1} ^ {B} \\mathbf {M} _ {m}, \\quad \\mathbf {X} _ {e} = \\overline {{\\mathbf {Y}}} \\odot \\mathbf {M} + \\overline {{\\mathbf {Y}}}, \\tag {4}", + "image_path": "75d3b2a6b1488215be23decc57ca7419deaacdb86d7eeaf124a7cc0df76adf34.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 415, + 545, + 486 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 415, + 545, + 486 + ], + "spans": [ + { + "bbox": [ + 304, + 415, + 545, + 486 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 415, + 545, + 486 + ], + "type": "inline_equation", + "content": "\\varnothing" + }, + { + "bbox": [ + 304, + 415, + 545, + 486 + ], + "type": "text", + "content": " represents Hadamard (element-wise) division, " + }, + { + "bbox": [ + 304, + 415, + 545, + 486 + ], + "type": "inline_equation", + "content": "\\overline{\\mathbf{Y}}\\in \\mathbb{R}^{n_x\\times n_y}" + }, + { + "bbox": [ + 304, + 415, + 545, + 486 + ], + "type": "text", + "content": " is the normalized measurement, which preserves a certain background and motion trajectory information, and " + }, + { + "bbox": [ + 304, + 415, + 545, + 486 + ], + "type": "inline_equation", + "content": "\\mathbf{X}_e\\in \\mathbb{R}^{n_x\\times n_y\\times B}" + }, + { + "bbox": [ + 304, + 415, + 545, + 486 + ], + "type": "text", + "content": " represents the coarse estimate of the desired video. We then take " + }, + { + "bbox": [ + 304, + 415, + 545, + 486 + ], + "type": "inline_equation", + "content": "\\mathbf{X}_e" + }, + { + "bbox": [ + 304, + 415, + 545, + 486 + ], + "type": "text", + "content": " as the input of the EfficientSCI network to get the final reconstruction result." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 486, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 486, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 486, + 546, + 713 + ], + "type": "text", + "content": "EfficientSCI network is mainly composed of three parts: i) feature extraction module, ii) ResDNet module and iii) video reconstruction module. The feature extraction module is mainly composed of three 3D convolutional layers with kernel sizes of " + }, + { + "bbox": [ + 304, + 486, + 546, + 713 + ], + "type": "inline_equation", + "content": "3 \\times 7 \\times 7" + }, + { + "bbox": [ + 304, + 486, + 546, + 713 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 486, + 546, + 713 + ], + "type": "inline_equation", + "content": "3 \\times 3 \\times 3" + }, + { + "bbox": [ + 304, + 486, + 546, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 486, + 546, + 713 + ], + "type": "inline_equation", + "content": "3 \\times 3 \\times 3" + }, + { + "bbox": [ + 304, + 486, + 546, + 713 + ], + "type": "text", + "content": " respectively. Among them, each 3D convolution is followed by a LeakyReLU activation function [27], and the spatial stride step size of the final 3D convolution is 2. The spatial resolution of the final output feature map is reduced to half of the input. The feature extraction module effectively maps the input image space to the high-dimensional feature space. The ResDNet module is composed of " + }, + { + "bbox": [ + 304, + 486, + 546, + 713 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 304, + 486, + 546, + 713 + ], + "type": "text", + "content": " ResDNet block (described in Sec. 4.1), which can efficiently explore spatial-temporal correlation. The video reconstruction module is composed of pixelshuffle [33] (mainly restore spatial resolution to input network input size) and three 3D convolution layers (kernel sizes are " + }, + { + "bbox": [ + 304, + 486, + 546, + 713 + ], + "type": "inline_equation", + "content": "3 \\times 3 \\times 3" + }, + { + "bbox": [ + 304, + 486, + 546, + 713 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 486, + 546, + 713 + ], + "type": "inline_equation", + "content": "1 \\times 1 \\times 1" + }, + { + "bbox": [ + 304, + 486, + 546, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 486, + 546, + 713 + ], + "type": "inline_equation", + "content": "3 \\times 3 \\times 3" + }, + { + "bbox": [ + 304, + 486, + 546, + 713 + ], + "type": "text", + "content": " respectively), and conducts video reconstruction on the features output by the ResDNet blocks." + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "18479" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 141, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 141, + 83 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 141, + 83 + ], + "type": "text", + "content": "4.1. ResDNet Block" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 90, + 290, + 294 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 90, + 290, + 294 + ], + "spans": [ + { + "bbox": [ + 46, + 90, + 290, + 294 + ], + "type": "text", + "content": "Dense connection is an effective way to increase model capacity. Unlike DenseNet, which spans multiple layers, we build a more efficient dense connection within a single residual block. As shown in Fig. 3(b), the input features of the ResDNet block are first divided into " + }, + { + "bbox": [ + 46, + 90, + 290, + 294 + ], + "type": "inline_equation", + "content": "S" + }, + { + "bbox": [ + 46, + 90, + 290, + 294 + ], + "type": "text", + "content": " parts along the feature channel dimension. Then, for each part " + }, + { + "bbox": [ + 46, + 90, + 290, + 294 + ], + "type": "inline_equation", + "content": "i = 1,\\dots ,S" + }, + { + "bbox": [ + 46, + 90, + 290, + 294 + ], + "type": "text", + "content": ", we use CFormer (described in Section 4.2) to efficiently establish the spatial-temporal correlation. Specifically, for the input of the " + }, + { + "bbox": [ + 46, + 90, + 290, + 294 + ], + "type": "inline_equation", + "content": "i^{th}" + }, + { + "bbox": [ + 46, + 90, + 290, + 294 + ], + "type": "text", + "content": " CFormer, we concatenate all the CFormer output features before the " + }, + { + "bbox": [ + 46, + 90, + 290, + 294 + ], + "type": "inline_equation", + "content": "i^{th}" + }, + { + "bbox": [ + 46, + 90, + 290, + 294 + ], + "type": "text", + "content": " part with the input features of the " + }, + { + "bbox": [ + 46, + 90, + 290, + 294 + ], + "type": "inline_equation", + "content": "i^{th}" + }, + { + "bbox": [ + 46, + 90, + 290, + 294 + ], + "type": "text", + "content": " part and then use a " + }, + { + "bbox": [ + 46, + 90, + 290, + 294 + ], + "type": "inline_equation", + "content": "1\\times 1\\times 1" + }, + { + "bbox": [ + 46, + 90, + 290, + 294 + ], + "type": "text", + "content": " convolution to reduce the dimension of the feature channel, which can further reduce the computational complexity. Next, we concatenate all CFormer output features along the feature channel dimension and use a " + }, + { + "bbox": [ + 46, + 90, + 290, + 294 + ], + "type": "inline_equation", + "content": "1\\times 1\\times 1" + }, + { + "bbox": [ + 46, + 90, + 290, + 294 + ], + "type": "text", + "content": " convolution to better fuse each part of the information. Given an input " + }, + { + "bbox": [ + 46, + 90, + 290, + 294 + ], + "type": "inline_equation", + "content": "\\mathbf{X}_r\\in \\mathbb{R}^{T\\times H\\times W\\times C}" + }, + { + "bbox": [ + 46, + 90, + 290, + 294 + ], + "type": "text", + "content": ", ResDNet block can be expressed as:" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 301, + 160, + 316 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 301, + 160, + 316 + ], + "spans": [ + { + "bbox": [ + 47, + 301, + 160, + 316 + ], + "type": "interline_equation", + "content": "\\mathbf {X} _ {1}, \\dots , \\mathbf {X} _ {S} = \\operatorname {S p l i t} (\\mathbf {X} _ {r}),", + "image_path": "8b89cf28926fb215da943e8f9e9bb770ba22a16d6858b54b1ede0c8cedf9a9c9.jpg" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 49, + 317, + 143, + 330 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 317, + 143, + 330 + ], + "spans": [ + { + "bbox": [ + 49, + 317, + 143, + 330 + ], + "type": "interline_equation", + "content": "\\mathbf {Y} _ {1} = \\operatorname {C F o r m e r} _ {1} (\\mathbf {X} _ {1}),", + "image_path": "12c8035ae24a1cb34584303f7888942804e752f7f591512e87544ff33cbe2fba.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 49, + 332, + 240, + 346 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 332, + 240, + 346 + ], + "spans": [ + { + "bbox": [ + 49, + 332, + 240, + 346 + ], + "type": "interline_equation", + "content": "\\mathbf {Y} _ {2} = \\operatorname {C F o r m e r} _ {2} (\\operatorname {C o n v} _ {1} (\\operatorname {C o n c a t} ([ \\mathbf {Y} _ {1}, \\mathbf {X} _ {2} ]))),", + "image_path": "7b57220cb4bbc2389dbb1c98770fdd0c6502267b2cc046b96fc7db5424a34c8d.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 88, + 353, + 94, + 365 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 88, + 353, + 94, + 365 + ], + "spans": [ + { + "bbox": [ + 88, + 353, + 94, + 365 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 369, + 291, + 383 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 369, + 291, + 383 + ], + "spans": [ + { + "bbox": [ + 47, + 369, + 291, + 383 + ], + "type": "interline_equation", + "content": "\\mathbf {Y} _ {S} = \\operatorname {C F o r m e r} _ {\\mathrm {S}} \\left(\\operatorname {C o n v} _ {1} \\left(\\operatorname {C o n c a t} \\left([ \\mathbf {Y} _ {1}, \\dots , \\mathbf {Y} _ {S - 1}, \\mathbf {X} _ {S} ]\\right)\\right)\\right),", + "image_path": "079ba28e9d0436fed303a705a3c26e939a467aec100b85e804ecf4b74e432b74.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 48, + 385, + 176, + 399 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 385, + 176, + 399 + ], + "spans": [ + { + "bbox": [ + 48, + 385, + 176, + 399 + ], + "type": "interline_equation", + "content": "\\hat {\\mathbf {Y}} _ {r} = \\operatorname {C o n c a t} ([ \\mathbf {Y} _ {1}, \\dots , \\mathbf {Y} _ {S} ]),", + "image_path": "f85d467c40bc3e4a58b103e7f7103144d03f85c0dc727f4dec28711d582a3670.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 403, + 287, + 417 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 403, + 287, + 417 + ], + "spans": [ + { + "bbox": [ + 47, + 403, + 287, + 417 + ], + "type": "interline_equation", + "content": "\\hat {\\mathbf {X}} _ {r} = \\operatorname {C o n v} _ {1} \\left(\\hat {\\mathbf {Y}} _ {\\mathrm {r}}\\right) + \\mathbf {X} _ {r}, \\tag {5}", + "image_path": "7e568c34a2c78ee62c7945702f12e7772ce75340bf0fde1d3502cd2b66708b97.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 425, + 287, + 521 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 425, + 287, + 521 + ], + "spans": [ + { + "bbox": [ + 47, + 425, + 287, + 521 + ], + "type": "text", + "content": "where 'Split' represents division along the channel, 'Conv1' represents a " + }, + { + "bbox": [ + 47, + 425, + 287, + 521 + ], + "type": "inline_equation", + "content": "1 \\times 1 \\times 1" + }, + { + "bbox": [ + 47, + 425, + 287, + 521 + ], + "type": "text", + "content": " convolution operation, 'Concat' represents concatenate along the channel and " + }, + { + "bbox": [ + 47, + 425, + 287, + 521 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{X}}_r \\in \\mathbb{R}^{T \\times H \\times W \\times C}" + }, + { + "bbox": [ + 47, + 425, + 287, + 521 + ], + "type": "text", + "content": " represents the output of the ResDNet block. This design has two advantages: i) the features of different levels are aggregated at a more granular level, which improves the representation ability of the model; ii) the model complexity is reduced (shown in Table 6)." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 527, + 143, + 539 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 527, + 143, + 539 + ], + "spans": [ + { + "bbox": [ + 47, + 527, + 143, + 539 + ], + "type": "text", + "content": "4.2. CFormer Block" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 545, + 287, + 641 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 545, + 287, + 641 + ], + "spans": [ + { + "bbox": [ + 46, + 545, + 287, + 641 + ], + "type": "text", + "content": "As shown in Fig. 4, the CFormer block includes three parts: Spatial Convolution Branch (SCB), Temporal Self-Attention Branch (TSAB) and Feed Forward Network (FFN). Based on the space-time factorization mechanism, SCB is used to extract spatial local information, TSAB is used to calculate temporal attention of the feature points at the same spatial position in each frame. After that, FFN is used to further integrate spatial-temporal information." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 46, + 642, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 642, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 642, + 288, + 714 + ], + "type": "text", + "content": "It is worth noting that in order to make the model flexible to different compression ratios, we introduce zero padding position encoding [17] into CFormer block, instead of the absolute position encoding [10] or relative position encoding [22]. Specifically, we modified the first linear transformation layer in the traditional FFN to a " + }, + { + "bbox": [ + 46, + 642, + 288, + 714 + ], + "type": "inline_equation", + "content": "3 \\times 3 \\times 3" + }, + { + "bbox": [ + 46, + 642, + 288, + 714 + ], + "type": "text", + "content": " convolution" + } + ] + } + ], + "index": 12 + }, + { + "type": "image", + "bbox": [ + 307, + 71, + 547, + 213 + ], + "blocks": [ + { + "bbox": [ + 307, + 71, + 547, + 213 + ], + "lines": [ + { + "bbox": [ + 307, + 71, + 547, + 213 + ], + "spans": [ + { + "bbox": [ + 307, + 71, + 547, + 213 + ], + "type": "image", + "image_path": "a0822b709a03dae7cb6ac7dfd2c12207b9245dd4f13c2622be6834ba2a6470d3.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 220, + 547, + 264 + ], + "lines": [ + { + "bbox": [ + 305, + 220, + 547, + 264 + ], + "spans": [ + { + "bbox": [ + 305, + 220, + 547, + 264 + ], + "type": "text", + "content": "Figure 4. The CFormer block is composed of Spatial Convolution Branch (SCB), Temporal Self-Attention Branch (TSAB) and Feed Forward Network (FFN). For ease of presentation, only the head " + }, + { + "bbox": [ + 305, + 220, + 547, + 264 + ], + "type": "inline_equation", + "content": "N = 1" + }, + { + "bbox": [ + 305, + 220, + 547, + 264 + ], + "type": "text", + "content": " scenario is described in the TSAB." + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_caption" + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 270, + 400, + 281 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 270, + 400, + 281 + ], + "spans": [ + { + "bbox": [ + 306, + 270, + 400, + 281 + ], + "type": "text", + "content": "with padding size of 1." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 281, + 545, + 365 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 281, + 545, + 365 + ], + "spans": [ + { + "bbox": [ + 304, + 281, + 545, + 365 + ], + "type": "text", + "content": "Spatial Convolution Branch: 2D convolution can well exploit spatial local correlation and reconstructs more detailed information, and it also enjoys efficient memory consumption and higher operating efficiency, which is suitable for large-scale video reconstruction. Therefore, We only use two " + }, + { + "bbox": [ + 304, + 281, + 545, + 365 + ], + "type": "inline_equation", + "content": "3 \\times 3" + }, + { + "bbox": [ + 304, + 281, + 545, + 365 + ], + "type": "text", + "content": " 2D convolutions to reconstruct spatial local details in SCB as shown in Fig. 4." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 365, + 546, + 484 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 365, + 546, + 484 + ], + "spans": [ + { + "bbox": [ + 304, + 365, + 546, + 484 + ], + "type": "text", + "content": "Temporal Self-attention Branch: The local receptive field of convolution makes it difficult to establish long-term dependencies. The global perception ability of Transformer can mitigate this issue. However, the time and memory complexity of traditional Transformers increase quadratically with the image size. To alleviate this problem, following [3, 35], we propose TSAB (shown in Fig. 4), which restricts the self-attention computation to the temporal domain, and its complexity only increases linearly with the image/video size." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 305, + 485, + 547, + 535 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 485, + 547, + 535 + ], + "spans": [ + { + "bbox": [ + 305, + 485, + 547, + 535 + ], + "type": "text", + "content": "In particular, we first reshape the input " + }, + { + "bbox": [ + 305, + 485, + 547, + 535 + ], + "type": "inline_equation", + "content": "\\mathbf{X}_{st} \\in \\mathbb{R}^{T \\times H \\times W \\times \\frac{C}{S}}" + }, + { + "bbox": [ + 305, + 485, + 547, + 535 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 305, + 485, + 547, + 535 + ], + "type": "inline_equation", + "content": "\\mathbf{X}_t \\in \\mathbb{R}^{HW \\times T \\times \\frac{C}{S}}" + }, + { + "bbox": [ + 305, + 485, + 547, + 535 + ], + "type": "text", + "content": ", and then obtain query " + }, + { + "bbox": [ + 305, + 485, + 547, + 535 + ], + "type": "inline_equation", + "content": "(\\mathbf{Q} \\in \\mathbb{R}^{HW \\times T \\times \\frac{C}{2S}})" + }, + { + "bbox": [ + 305, + 485, + 547, + 535 + ], + "type": "text", + "content": ", key " + }, + { + "bbox": [ + 305, + 485, + 547, + 535 + ], + "type": "inline_equation", + "content": "(\\mathbf{K} \\in \\mathbb{R}^{HW \\times T \\times \\frac{C}{2S}})" + }, + { + "bbox": [ + 305, + 485, + 547, + 535 + ], + "type": "text", + "content": " and value " + }, + { + "bbox": [ + 305, + 485, + 547, + 535 + ], + "type": "inline_equation", + "content": "(\\mathbf{V} \\in \\mathbb{R}^{HW \\times T \\times \\frac{C}{2S}})" + }, + { + "bbox": [ + 305, + 485, + 547, + 535 + ], + "type": "text", + "content": " by linearly mapping " + }, + { + "bbox": [ + 305, + 485, + 547, + 535 + ], + "type": "inline_equation", + "content": "\\mathbf{X}_t" + }, + { + "bbox": [ + 305, + 485, + 547, + 535 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 332, + 540, + 545, + 555 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 332, + 540, + 545, + 555 + ], + "spans": [ + { + "bbox": [ + 332, + 540, + 545, + 555 + ], + "type": "interline_equation", + "content": "\\mathbf {Q} = \\mathbf {X} _ {t} \\mathbf {W} ^ {Q}, \\quad \\mathbf {K} = \\mathbf {X} _ {t} \\mathbf {W} ^ {K}, \\quad \\mathbf {V} = \\mathbf {X} _ {t} \\mathbf {W} ^ {V}, \\tag {6}", + "image_path": "e0d6ee2c7aac8d113bba900c5d22e4ee649fce6c1ff361be4edf1664878c992e.jpg" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 560, + 545, + 585 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 560, + 545, + 585 + ], + "spans": [ + { + "bbox": [ + 304, + 560, + 545, + 585 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 560, + 545, + 585 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{W}^Q,\\mathbf{W}^K,\\mathbf{W}^V\\} \\in \\mathbb{R}_{\\overline{S}}^{C\\times \\frac{C}{2S}}" + }, + { + "bbox": [ + 304, + 560, + 545, + 585 + ], + "type": "text", + "content": " are projection matrices." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 304, + 586, + 545, + 671 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 586, + 545, + 671 + ], + "spans": [ + { + "bbox": [ + 304, + 586, + 545, + 671 + ], + "type": "text", + "content": "It is worth noting that the output dimension of the projection matrix is reduced to half of the input dimension, further decreasing the computational complexity of TSAB. Then, we respectively divide " + }, + { + "bbox": [ + 304, + 586, + 545, + 671 + ], + "type": "inline_equation", + "content": "\\mathbf{Q}" + }, + { + "bbox": [ + 304, + 586, + 545, + 671 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 586, + 545, + 671 + ], + "type": "inline_equation", + "content": "\\mathbf{K}" + }, + { + "bbox": [ + 304, + 586, + 545, + 671 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 586, + 545, + 671 + ], + "type": "inline_equation", + "content": "\\mathbf{V}" + }, + { + "bbox": [ + 304, + 586, + 545, + 671 + ], + "type": "text", + "content": " into " + }, + { + "bbox": [ + 304, + 586, + 545, + 671 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 304, + 586, + 545, + 671 + ], + "type": "text", + "content": " heads along the feature channel: " + }, + { + "bbox": [ + 304, + 586, + 545, + 671 + ], + "type": "inline_equation", + "content": "\\mathbf{Q} = \\{\\mathbf{Q}_j\\}_{1}^{N}" + }, + { + "bbox": [ + 304, + 586, + 545, + 671 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 586, + 545, + 671 + ], + "type": "inline_equation", + "content": "\\mathbf{K} = \\{\\mathbf{K}_j\\}_{1}^{N}" + }, + { + "bbox": [ + 304, + 586, + 545, + 671 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 586, + 545, + 671 + ], + "type": "inline_equation", + "content": "\\mathbf{V} = \\{\\mathbf{V}_j\\}_{1}^{N} \\in \\mathbb{R}^{HW \\times T \\times \\frac{C}{2SN}}" + }, + { + "bbox": [ + 304, + 586, + 545, + 671 + ], + "type": "text", + "content": ". For each head " + }, + { + "bbox": [ + 304, + 586, + 545, + 671 + ], + "type": "inline_equation", + "content": "j = 1, \\dots, N" + }, + { + "bbox": [ + 304, + 586, + 545, + 671 + ], + "type": "text", + "content": ", the attention can be calculated as:" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 385, + 679, + 545, + 693 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 385, + 679, + 545, + 693 + ], + "spans": [ + { + "bbox": [ + 385, + 679, + 545, + 693 + ], + "type": "interline_equation", + "content": "\\operatorname {h e a d} _ {j} = \\mathbf {A} _ {j} * \\mathbf {V} _ {j}, \\tag {7}", + "image_path": "2f03995f08a50e349f1c1070474ab1c29db06784957d2880b8434e6979820e32.jpg" + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 306, + 700, + 545, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 700, + 545, + 715 + ], + "spans": [ + { + "bbox": [ + 306, + 700, + 545, + 715 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 306, + 700, + 545, + 715 + ], + "type": "inline_equation", + "content": "\\mathbf{A}_j = \\text{softmax}(\\mathbf{Q}_j\\mathbf{K}_j^T / \\sqrt{d}) \\in \\mathbb{R}^{HW \\times T \\times T}" + }, + { + "bbox": [ + 306, + 700, + 545, + 715 + ], + "type": "text", + "content": " repre" + } + ] + } + ], + "index": 23 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "18480" + } + ] + } + ], + "index": 24 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 133 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 133 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 133 + ], + "type": "text", + "content": "sents an attention map, " + }, + { + "bbox": [ + 46, + 72, + 287, + 133 + ], + "type": "inline_equation", + "content": "\\mathbf{K}_j^T" + }, + { + "bbox": [ + 46, + 72, + 287, + 133 + ], + "type": "text", + "content": " represents the transposed matrix of " + }, + { + "bbox": [ + 46, + 72, + 287, + 133 + ], + "type": "inline_equation", + "content": "\\mathbf{K}_j" + }, + { + "bbox": [ + 46, + 72, + 287, + 133 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 72, + 287, + 133 + ], + "type": "inline_equation", + "content": "d = \\frac{C}{2SN}" + }, + { + "bbox": [ + 46, + 72, + 287, + 133 + ], + "type": "text", + "content": " is a scaling parameter. Then, we concatenate the outputs of " + }, + { + "bbox": [ + 46, + 72, + 287, + 133 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 72, + 287, + 133 + ], + "type": "text", + "content": " heads along the feature channel dimension and perform a linear mapping to obtain the final output " + }, + { + "bbox": [ + 46, + 72, + 287, + 133 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{X}}_t\\in \\mathbb{R}^{T\\times H\\times W\\times \\frac{C}{S}}" + }, + { + "bbox": [ + 46, + 72, + 287, + 133 + ], + "type": "text", + "content": " of TSAB:" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 63, + 140, + 287, + 154 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 63, + 140, + 287, + 154 + ], + "spans": [ + { + "bbox": [ + 63, + 140, + 287, + 154 + ], + "type": "interline_equation", + "content": "\\hat {\\mathbf {X}} _ {t} = \\mathbf {R} \\left(\\mathbf {W} ^ {P} \\left(\\operatorname {C o n c a t} \\left[ h e a d _ {1}, \\dots , h e a d _ {N} \\right]\\right)\\right), \\tag {8}", + "image_path": "d5fc1542b547844e7b6c31c87f7fff7c8d5acaab7335813d5d477aedbd309314.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 159, + 287, + 185 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 159, + 287, + 185 + ], + "spans": [ + { + "bbox": [ + 47, + 159, + 287, + 185 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 159, + 287, + 185 + ], + "type": "inline_equation", + "content": "\\mathbf{W}^P\\in \\mathbb{R}^{\\frac{C}{2S}\\times \\frac{C}{S}}" + }, + { + "bbox": [ + 47, + 159, + 287, + 185 + ], + "type": "text", + "content": " represents projection matrices, and " + }, + { + "bbox": [ + 47, + 159, + 287, + 185 + ], + "type": "inline_equation", + "content": "\\mathbf{R}" + }, + { + "bbox": [ + 47, + 159, + 287, + 185 + ], + "type": "text", + "content": " is the reshape operator." + } + ] + } + ], + "index": 2 + }, + { + "type": "table", + "bbox": [ + 78, + 209, + 251, + 285 + ], + "blocks": [ + { + "bbox": [ + 53, + 194, + 280, + 205 + ], + "lines": [ + { + "bbox": [ + 53, + 194, + 280, + 205 + ], + "spans": [ + { + "bbox": [ + 53, + 194, + 280, + 205 + ], + "type": "text", + "content": "Table 1. Computational complexity of several SOTA methods." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 78, + 209, + 251, + 285 + ], + "lines": [ + { + "bbox": [ + 78, + 209, + 251, + 285 + ], + "spans": [ + { + "bbox": [ + 78, + 209, + 251, + 285 + ], + "type": "table", + "html": "
MethodComputational Complexity
SCB3D1/2HWTK3C2
G-MSAHWTC2+(HWT)2C
TS-MSA2HWTC2+T(HW)2C+HWT2C
SCB1/2HWTK2C2
TSAB1/2HWTC2+1/2HWT2C
", + "image_path": "ff463ca59205c496ebfe285d817416e4fb875fe2cbb5c391aac7d12b0aa87241.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_body" + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 289, + 287, + 456 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 289, + 287, + 456 + ], + "spans": [ + { + "bbox": [ + 46, + 289, + 287, + 456 + ], + "type": "text", + "content": "We further analyze the computational complexity of SCB and TSAB, and compare them with 3D convolution and several classic Multi-head Self-Attention (MSA) mechanisms. The results are shown in Table 1, where 'SCB3D' represents the replacement of 2D convolution in SCB with 3D convolution and " + }, + { + "bbox": [ + 46, + 289, + 287, + 456 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 46, + 289, + 287, + 456 + ], + "type": "text", + "content": " represents the kernel size, 'G-MSA' represents the original global MSA [10], and 'TS-MSA' represents the MSA in TimeSformer [3]. It can be observed that the computational complexity of our proposed SCB and TSAB grows linearly with the spatial size " + }, + { + "bbox": [ + 46, + 289, + 287, + 456 + ], + "type": "inline_equation", + "content": "HW" + }, + { + "bbox": [ + 46, + 289, + 287, + 456 + ], + "type": "text", + "content": ", the computational cost is much less than 'TS-MSA' and 'G-MSA' (grow quadratically with " + }, + { + "bbox": [ + 46, + 289, + 287, + 456 + ], + "type": "inline_equation", + "content": "HW" + }, + { + "bbox": [ + 46, + 289, + 287, + 456 + ], + "type": "text", + "content": "). Compared with 3D convolution, since " + }, + { + "bbox": [ + 46, + 289, + 287, + 456 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 46, + 289, + 287, + 456 + ], + "type": "text", + "content": " is generally smaller than " + }, + { + "bbox": [ + 46, + 289, + 287, + 456 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 46, + 289, + 287, + 456 + ], + "type": "text", + "content": ", 'SCB' and 'TSAB' still need less computational cost." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 456, + 287, + 552 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 456, + 287, + 552 + ], + "spans": [ + { + "bbox": [ + 46, + 456, + 287, + 552 + ], + "type": "text", + "content": "Feed Forward Network: The feed forward network of traditional Transformer usually uses two linear layers and a nonlinear activation function to learn more abstract feature representations. However, in the whole FFN, there is no interaction between the feature points. In order to better integrate the spatial-temporal information and position coding information, we replace the first linear transformation layer in the traditional FFN with a " + }, + { + "bbox": [ + 46, + 456, + 287, + 552 + ], + "type": "inline_equation", + "content": "3 \\times 3 \\times 3" + }, + { + "bbox": [ + 46, + 456, + 287, + 552 + ], + "type": "text", + "content": " convolution." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 59, + 552, + 277, + 564 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 552, + 277, + 564 + ], + "spans": [ + { + "bbox": [ + 59, + 552, + 277, + 564 + ], + "type": "text", + "content": "Given " + }, + { + "bbox": [ + 59, + 552, + 277, + 564 + ], + "type": "inline_equation", + "content": "\\mathbf{X}_f\\in \\mathbb{R}^{T\\times H\\times W\\times \\frac{C}{2}}" + }, + { + "bbox": [ + 59, + 552, + 277, + 564 + ], + "type": "text", + "content": " , FFN can be expressed as:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 99, + 571, + 287, + 586 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 99, + 571, + 287, + 586 + ], + "spans": [ + { + "bbox": [ + 99, + 571, + 287, + 586 + ], + "type": "interline_equation", + "content": "\\hat {\\mathbf {X}} _ {f} = \\mathbf {X} _ {f} + \\mathbf {W} _ {1} \\left(\\phi \\left(\\mathbf {W} _ {2} \\left(\\mathbf {X} _ {f}\\right)\\right)\\right), \\tag {9}", + "image_path": "800ebf29bab4f63bbbe9200ef3c0590aca789229ded78af7ca45dd20dd564833.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 592, + 287, + 641 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 592, + 287, + 641 + ], + "spans": [ + { + "bbox": [ + 47, + 592, + 287, + 641 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 592, + 287, + 641 + ], + "type": "inline_equation", + "content": "\\mathbf{W}_1, \\mathbf{W}_2" + }, + { + "bbox": [ + 47, + 592, + 287, + 641 + ], + "type": "text", + "content": " represent " + }, + { + "bbox": [ + 47, + 592, + 287, + 641 + ], + "type": "inline_equation", + "content": "1 \\times 1 \\times 1" + }, + { + "bbox": [ + 47, + 592, + 287, + 641 + ], + "type": "text", + "content": " convolution and " + }, + { + "bbox": [ + 47, + 592, + 287, + 641 + ], + "type": "inline_equation", + "content": "3 \\times 3 \\times 3" + }, + { + "bbox": [ + 47, + 592, + 287, + 641 + ], + "type": "text", + "content": " convolution operations respectively, " + }, + { + "bbox": [ + 47, + 592, + 287, + 641 + ], + "type": "inline_equation", + "content": "\\phi" + }, + { + "bbox": [ + 47, + 592, + 287, + 641 + ], + "type": "text", + "content": " denotes the LeakyReLU non-linearity activation, and " + }, + { + "bbox": [ + 47, + 592, + 287, + 641 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{X}}_f \\in \\mathbb{R}^{T \\times H \\times W \\times \\frac{C}{2}}" + }, + { + "bbox": [ + 47, + 592, + 287, + 641 + ], + "type": "text", + "content": " is the output of the FFN." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 642, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 642, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 642, + 287, + 713 + ], + "type": "text", + "content": "It should be noted that in the whole CFormer block, we do not use any regularization layers, such as Layer Normalization [1] and Batch Normalization [16]. The experimental results show that removing the regularization layer will not reduce the quality of model reconstruction and can further improve the efficiency of the model." + } + ] + } + ], + "index": 10 + }, + { + "type": "table", + "bbox": [ + 326, + 93, + 524, + 151 + ], + "blocks": [ + { + "bbox": [ + 305, + 71, + 545, + 91 + ], + "lines": [ + { + "bbox": [ + 305, + 71, + 545, + 91 + ], + "spans": [ + { + "bbox": [ + 305, + 71, + 545, + 91 + ], + "type": "text", + "content": "Table 2. Reconstruction quality and test time (s) using EfficientSCI with different number of channels and blocks." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 326, + 93, + 524, + 151 + ], + "lines": [ + { + "bbox": [ + 326, + 93, + 524, + 151 + ], + "spans": [ + { + "bbox": [ + 326, + 93, + 524, + 151 + ], + "type": "table", + "html": "
ModelChannelBlockPSNRSSIMTest time(s)
EfficientSCI-T64834.220.9610.07
EfficientSCI-S128835.510.9700.15
EfficientSCI-B256836.480.9750.31
EfficientSCI-L2561236.920.9770.45
", + "image_path": "b97cd128071263344403babfc1cc3b5276b1cf90a6cbc1b3691ad9dece141532.jpg" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "table_body" + } + ], + "index": 12 + }, + { + "type": "table", + "bbox": [ + 337, + 179, + 511, + 271 + ], + "blocks": [ + { + "bbox": [ + 305, + 156, + 547, + 178 + ], + "lines": [ + { + "bbox": [ + 305, + 156, + 547, + 178 + ], + "spans": [ + { + "bbox": [ + 305, + 156, + 547, + 178 + ], + "type": "text", + "content": "Table 3. Computational complexity and reconstruction quality of several SOTA algorithms on 6 grayscale benchmark datasets." + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 337, + 179, + 511, + 271 + ], + "lines": [ + { + "bbox": [ + 337, + 179, + 511, + 271 + ], + "spans": [ + { + "bbox": [ + 337, + 179, + 511, + 271 + ], + "type": "table", + "html": "
MethodParams (M)FLOPs (G)PSNRSSIM
BIRNAT4.13390.5633.310.951
RevSCI5.66766.9533.920.956
DUN-3DUnet61.913975.8335.260.968
ELP-Unfolding565.734634.9435.410.969
EfficientSCI-T0.95142.1834.220.961
EfficientSCI-S3.78563.8735.510.970
EfficientSCI-B8.821426.3836.480.975
EfficientSCI-L12.391893.7236.920.977
", + "image_path": "23c017ad2553a2766391b68ba070fbc5ab0bf717e44e76ae838a45f8cfd911ca.jpg" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "table_body" + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 279, + 545, + 435 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 279, + 545, + 435 + ], + "spans": [ + { + "bbox": [ + 304, + 279, + 545, + 435 + ], + "type": "text", + "content": "Network Variants: To balance speed and performance of the proposed network, we introduce four different versions of EfficientSCI network, dubbed as EfficientSCI-T, EfficientSCI-S, EfficientSCI-B and EfficientSCI-L standing for Tiny, Small, Base and Large networks, respectively. The network hyper-parameters are shown in Table 2, in which we mainly changed the the number of ResD-Net blocks and the number of channels. As shown in Table 3, we also compare model parameters and computational complexity (FLOPs) with several advanced methods. The complexity of our proposed EfficientSCI-T is smaller than that of BIRNAT and RevSCI, and EfficientSCI-L is smaller than that of DUN-3DUnet and ELP-Unfolding." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 306, + 446, + 422, + 460 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 446, + 422, + 460 + ], + "spans": [ + { + "bbox": [ + 306, + 446, + 422, + 460 + ], + "type": "text", + "content": "5. Experiment Results" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 466, + 368, + 477 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 466, + 368, + 477 + ], + "spans": [ + { + "bbox": [ + 306, + 466, + 368, + 477 + ], + "type": "text", + "content": "5.1. Datasets" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 483, + 545, + 651 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 483, + 545, + 651 + ], + "spans": [ + { + "bbox": [ + 304, + 483, + 545, + 651 + ], + "type": "text", + "content": "Following BIRNAT [8], we use DAVIS2017 [29] with resolution " + }, + { + "bbox": [ + 304, + 483, + 545, + 651 + ], + "type": "inline_equation", + "content": "480 \\times 894" + }, + { + "bbox": [ + 304, + 483, + 545, + 651 + ], + "type": "text", + "content": " (480p) as the model training dataset. To verify model performance, we first test the EfficientSCI network on several simulated datasets, including six benchmark grayscale datasets (Kobe, Traffic, Runner, Drop, Crash and Aerial with a size of " + }, + { + "bbox": [ + 304, + 483, + 545, + 651 + ], + "type": "inline_equation", + "content": "256 \\times 256 \\times 8" + }, + { + "bbox": [ + 304, + 483, + 545, + 651 + ], + "type": "text", + "content": "), six benchmark mid-scale color datasets (Beauty, Bosphorus, Jockey, Runner, ShakeNDry and Traffic with a size of " + }, + { + "bbox": [ + 304, + 483, + 545, + 651 + ], + "type": "inline_equation", + "content": "512 \\times 512 \\times 3 \\times 8" + }, + { + "bbox": [ + 304, + 483, + 545, + 651 + ], + "type": "text", + "content": "), and four large-scale datasets (Messi, Hummingbird, Swinger and Football with different sizes and compression ratios). Then we test our model on some real data (including Duomino, Water Balloon) captured by a real SCI system [30]." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 306, + 659, + 439, + 671 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 659, + 439, + 671 + ], + "spans": [ + { + "bbox": [ + 306, + 659, + 439, + 671 + ], + "type": "text", + "content": "5.2. Implementation Details" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "text", + "content": "We use PyTorch framework with 4 NVIDIA RTX 3090 GPUs for training with random cropping, random scaling, and random flipping for data augmentation, and use" + } + ] + } + ], + "index": 20 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "18481" + } + ] + } + ], + "index": 21 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 51, + 94, + 541, + 252 + ], + "blocks": [ + { + "bbox": [ + 47, + 70, + 547, + 92 + ], + "lines": [ + { + "bbox": [ + 47, + 70, + 547, + 92 + ], + "spans": [ + { + "bbox": [ + 47, + 70, + 547, + 92 + ], + "type": "text", + "content": "Table 4. The average PSNR in dB (left entry) and SSIM (right entry) and running time per measurement of different algorithms on 6 benchmark grayscale datasets. The best results are shown in bold and the second-best results are underlined." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 51, + 94, + 541, + 252 + ], + "lines": [ + { + "bbox": [ + 51, + 94, + 541, + 252 + ], + "spans": [ + { + "bbox": [ + 51, + 94, + 541, + 252 + ], + "type": "table", + "html": "
MethodKobeTrafficRunnerDropCrashAerialAverageTest time(s)
GAP-TV26.46, 0.88520.89, 0.71528.52, 0.90934.63, 0.97024.82, 0.83825.05, 0.82826.73, 0.8584.2 (CPU)
PnP-FFDNet30.50, 0.92624.18, 0.82832.15, 0.93340.70, 0.98925.42, 0.84925.27, 0.82929.70, 0.8923.0 (GPU)
PnP-FastDVDnet32.73, 0.94727.95, 0.93236.29, 0.96241.82, 0.98927.32, 0.92527.98, 0.89732.35, 0.9426.0 (GPU)
DeSCI33.25, 0.95228.71, 0.92538.48, 0.96943.10, 0.99327.04, 0.90925.33, 0.86032.65, 0.9356180 (CPU)
BIRNAT32.71, 0.95029.33, 0.94238.70, 0.97642.28, 0.99227.84, 0.92728.99, 0.91733.31, 0.9510.10 (GPU)
RevSCI33.72, 0.95730.02, 0.94939.40, 0.97742.93, 0.99228.12, 0.93729.35, 0.92433.92, 0.9560.19 (GPU)
GAP-CCoT32.58, 0.94929.03, 0.93839.12, 0.98042.54, 0.99228.52, 0.94129.40, 0.92333.53, 0.9580.08 (GPU)
DUN-3DUnet35.00, 0.96931.76, 0.96640.03, 0.98044.96, 0.99529.33, 0.95630.46, 0.94335.26, 0.9680.58 (GPU)
ELP-Unfolding34.41, 0.96631.58, 0.96241,16, 0.98644.99, 0.99529.65, 0.95930.68, 0.94435.41, 0.9690.34 (GPU)
EfficientSCI-T33.45, 0.96029.20, 0.94239.51, 0.98143.56, 0.99329.27, 0.95430.32, 0.93734.22, 0.9610.07 (GPU)
EfficientSCI-S34.79, 0.96831.21, 0.96141.34, 0.98644.61, 0.99430.34, 0.96530.78, 0.94535.51, 0.9700.15 (GPU)
EfficientSCI-B35.76, 0.97432.30, 0.96843.05, 0.98845.18, 0.99531.13, 0.97131.50, 0.95336.48, 0.9750.31 (GPU)
EfficientSCI-L36.27, 0.97632.83, 0.97143.79, 0.99145.46, 0.99531.52, 0.97431.64, 0.95536.92, 0.9770.45 (GPU)
", + "image_path": "fe3a163dbdaec1bb433c3a29f32bd34deffda629d3e95a463fd73a7d49a79a05.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 50, + 259, + 286, + 434 + ], + "blocks": [ + { + "bbox": [ + 50, + 259, + 286, + 434 + ], + "lines": [ + { + "bbox": [ + 50, + 259, + 286, + 434 + ], + "spans": [ + { + "bbox": [ + 50, + 259, + 286, + 434 + ], + "type": "image", + "image_path": "10f5dbc5f4fdf5b517365203a522ccd68a97a42925a72fd1833f862f976beb51.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 437, + 287, + 460 + ], + "lines": [ + { + "bbox": [ + 46, + 437, + 287, + 460 + ], + "spans": [ + { + "bbox": [ + 46, + 437, + 287, + 460 + ], + "type": "text", + "content": "Figure 5. Selected reconstruction frames of simulated grayscale data. Zoom in for better view." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 464, + 288, + 548 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 464, + 288, + 548 + ], + "spans": [ + { + "bbox": [ + 46, + 464, + 288, + 548 + ], + "type": "text", + "content": "Adam [19] to optimize the model with the initial learning rate 0.0001. After iterating for 300 epochs, we adjusted the learning rate to 0.00001 and continued to iterate for 40 epochs to get the final model parameters. The peak-signal-to-noise-ratio (PSNR) and structured similarity index metrics (SSIM) [38] are used as the performance indicators of reconstruction quality." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 555, + 214, + 568 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 555, + 214, + 568 + ], + "spans": [ + { + "bbox": [ + 47, + 555, + 214, + 568 + ], + "type": "text", + "content": "5.3. Results on Simulation Datasets" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 574, + 200, + 586 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 574, + 200, + 586 + ], + "spans": [ + { + "bbox": [ + 47, + 574, + 200, + 586 + ], + "type": "text", + "content": "5.3.1 Grayscale Simulation Video" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 594, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 594, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 288, + 715 + ], + "type": "text", + "content": "We compare our method with SOTA model-based methods (GAP-TV [44], PnP-FFDNet [46], PnP-FastDVDnet [47], DeSCI [21]) and deep learning-based methods (BIR-NAT [8], RevSCI [7], GAP-CCoT [36], DUN-3DUnet [40], ELP-Unfolding [42]) on simulated grayscale datasets. Table 4 shows the quantitative comparison results, it can be observed that our proposed EfficientSCI-L can achieve the highest reconstruction quality and has good real-time performance. In particular, the PSNR value of our method surpasses the existing best method ELP-Unfolding by 1.46" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 262, + 547, + 406 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 262, + 547, + 406 + ], + "spans": [ + { + "bbox": [ + 304, + 262, + 547, + 406 + ], + "type": "text", + "content": "dB on average. In addition, our proposed EfficientSCIT achieves high reconstruction quality while achieving the best real-time performance. It is worth noting that, for a fair comparison, we uniformly test the running time of all deep learning based methods on the same NVIDIA RTX 3090 GPU. Fig. 5 shows the visual reconstruction results of some data. By zooming in some local areas, we can observe that our method can recover sharper edges and more detailed information compared to previous SOTA methods. The mid-scale color results are shown in the SM due to space limitation and our method outperforms previous SOTA by 2.02 dB in PSNR on the benchmark dataset [47]." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 420, + 492, + 432 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 420, + 492, + 432 + ], + "spans": [ + { + "bbox": [ + 305, + 420, + 492, + 432 + ], + "type": "text", + "content": "5.3.2 Large-scale Color Simulation Video" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 437, + 545, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 437, + 545, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 437, + 545, + 715 + ], + "type": "text", + "content": "Most deep learning based methods, such as BIRNAT [8], DUN-3DUnet [40], cannot be applied to large-scale data reconstruction due to excessive model complexity and GPU memory constraints. RevSCI [7] uses a reversible mechanism and can reconstruct a 24 frames RGB color video with size of " + }, + { + "bbox": [ + 304, + 437, + 545, + 715 + ], + "type": "inline_equation", + "content": "1080 \\times 1920 \\times 3" + }, + { + "bbox": [ + 304, + 437, + 545, + 715 + ], + "type": "text", + "content": ", but training the model is extremely slow. GAP-CCoT [36] and ELP-Unfolding [42] only use 2D convolution for reconstruction and thus cannot handle color video data well. Therefore, we only compare with several SOTA model-based methods (GAP-TV [44], PnP-FFDNet-color [46], PnP-FastDVDnet-color [47]) on large-scale color data. Table 5 shows the comparisons between our proposed method and several model-based methods on PSNR, SSIM and test time (in minutes). It can be observed that model-based methods either have long reconstruction time (PnP-FFDNet-color, PnP-FastDVDnet-color) or low reconstruction quality (GAP-TV). Our proposed EfficientSCI-S can achieve higher reconstruction quality and running speed. Especially on UHD color video football " + }, + { + "bbox": [ + 304, + 437, + 545, + 715 + ], + "type": "inline_equation", + "content": "(1644 \\times 3840 \\times 3 \\times 40)" + }, + { + "bbox": [ + 304, + 437, + 545, + 715 + ], + "type": "text", + "content": ", the PSNR value of our method is 2.5 dB higher than PnP-FastDVDnet-color, and the reconstruction time is only " + }, + { + "bbox": [ + 304, + 437, + 545, + 715 + ], + "type": "inline_equation", + "content": "0.5\\%" + }, + { + "bbox": [ + 304, + 437, + 545, + 715 + ], + "type": "text", + "content": " of it. Fig. 6 shows some visual reconstruction results. By zooming" + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "18482" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 53, + 102, + 538, + 168 + ], + "blocks": [ + { + "bbox": [ + 47, + 70, + 547, + 94 + ], + "lines": [ + { + "bbox": [ + 47, + 70, + 547, + 94 + ], + "spans": [ + { + "bbox": [ + 47, + 70, + 547, + 94 + ], + "type": "text", + "content": "Table 5. The average PSNR in dB (left entry) and SSIM (middle entry) and test time (minutes) per measurement (right entry) of different algorithms on 4 benchmark large-scale datasets. Best results are in bold." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 53, + 102, + 538, + 168 + ], + "lines": [ + { + "bbox": [ + 53, + 102, + 538, + 168 + ], + "spans": [ + { + "bbox": [ + 53, + 102, + 538, + 168 + ], + "type": "table", + "html": "
DatasetPixel resolutionGAP-TVPnP-FFDNet-colorPnP-FastDVDnet-colorEfficientSCI-S
Messi1080 × 1920 × 3 × 825.20, 0.874, 0.6634.28, 0.968, 14.9334.34, 0.970, 15.9434.41, 0.973, 0.09
Hummingbird1080 × 1920 × 3 × 3025.10, 0.750, 20.328.79, 0.665, 61.2031.17, 0.916, 54.0035.56, 0.952, 0.39
Swinger2160 × 3840 × 3 × 1522.68, 0.769, 39.229.30, 0.934, 138.830.57, 0.949, 138.431.05, 0.951, 0.62
Football1644 × 3840 × 3 × 4026.19, 0.858, 83.032.70, 0.951, 308.832.31, 0.947, 298.134.81, 0.964, 1.52
", + "image_path": "f7578abf2d7174cd0feb84037cd84fa81896f69277b64cb44d570cbdff57e983.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 53, + 176, + 538, + 451 + ], + "blocks": [ + { + "bbox": [ + 53, + 176, + 538, + 451 + ], + "lines": [ + { + "bbox": [ + 53, + 176, + 538, + 451 + ], + "spans": [ + { + "bbox": [ + 53, + 176, + 538, + 451 + ], + "type": "image", + "image_path": "d17274b01809fdeea6cfc85ca178d50b6190ef28083d9a2c8ba399f8da85c83c.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 48, + 453, + 541, + 465 + ], + "lines": [ + { + "bbox": [ + 48, + 453, + 541, + 465 + ], + "spans": [ + { + "bbox": [ + 48, + 453, + 541, + 465 + ], + "type": "text", + "content": "Figure 6. Comparison of reconstruction results of different algorithms on several benchmark large-scale color video simulation datasets." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 52, + 477, + 281, + 606 + ], + "blocks": [ + { + "bbox": [ + 52, + 477, + 281, + 606 + ], + "lines": [ + { + "bbox": [ + 52, + 477, + 281, + 606 + ], + "spans": [ + { + "bbox": [ + 52, + 477, + 281, + 606 + ], + "type": "image", + "image_path": "aa88788552c191bfde1524a8d9791ac8bc906306a3546dcddfbaa14622a37abe.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 607, + 288, + 640 + ], + "lines": [ + { + "bbox": [ + 46, + 607, + 288, + 640 + ], + "spans": [ + { + "bbox": [ + 46, + 607, + 288, + 640 + ], + "type": "text", + "content": "Figure 7. Reconstruction quality (PSNR in dB, higher is better) of different reconstruction algorithms, with varying compression rates " + }, + { + "bbox": [ + 46, + 607, + 288, + 640 + ], + "type": "inline_equation", + "content": "B" + }, + { + "bbox": [ + 46, + 607, + 288, + 640 + ], + "type": "text", + "content": " from 8 to 48." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 654, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 654, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 654, + 288, + 715 + ], + "type": "text", + "content": "in local areas, we can observe that the reconstruction results of our method are closer to the real value. In addition, our proposed model enjoys high flexibility for different compression ratios, that is, the model trained on low compression ratio data can be directly used for high com" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 480, + 547, + 589 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 480, + 547, + 589 + ], + "spans": [ + { + "bbox": [ + 304, + 480, + 547, + 589 + ], + "type": "text", + "content": "pression ratio video reconstruction task. To verify this, we test hummingbird data with different compression ratios " + }, + { + "bbox": [ + 304, + 480, + 547, + 589 + ], + "type": "inline_equation", + "content": "B = 8, 16, 24, 32, 40, 48" + }, + { + "bbox": [ + 304, + 480, + 547, + 589 + ], + "type": "text", + "content": ", and the reconstruction results are shown in Fig. 7. We can observe that our method can be applied to video data with different compression ratios, even when the compression ratio " + }, + { + "bbox": [ + 304, + 480, + 547, + 589 + ], + "type": "inline_equation", + "content": "B" + }, + { + "bbox": [ + 304, + 480, + 547, + 589 + ], + "type": "text", + "content": " grows to 48, the PSNR value of EfficientSCI-T model can still reach more than 32 dB. Moreover, our proposed approach surpasses other reconstruction algorithms at all compression ratios." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 609, + 404, + 621 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 609, + 404, + 621 + ], + "spans": [ + { + "bbox": [ + 306, + 609, + 404, + 621 + ], + "type": "text", + "content": "5.3.3 Ablation Study" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 629, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 629, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 629, + 547, + 715 + ], + "type": "text", + "content": "To verify the performance of the proposed ResDNet block and CFormer block on the impact of the reconstruction quality, we conduct some ablation experiments. The results are shown in Table 6 and Table 7, we not only compare the reconstruction quality of different models, but also analyze the model parameters and FLOPs. All experiments are conducted on the 6 grayscale benchmark datasets." + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "18483" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 50, + 91, + 286, + 148 + ], + "blocks": [ + { + "bbox": [ + 47, + 65, + 286, + 87 + ], + "lines": [ + { + "bbox": [ + 47, + 65, + 286, + 87 + ], + "spans": [ + { + "bbox": [ + 47, + 65, + 286, + 87 + ], + "type": "text", + "content": "Table 6. Ablation study on the ResDNet block without dense connections (left entry) and with dense connections (right entry)." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 50, + 91, + 286, + 148 + ], + "lines": [ + { + "bbox": [ + 50, + 91, + 286, + 148 + ], + "spans": [ + { + "bbox": [ + 50, + 91, + 286, + 148 + ], + "type": "table", + "html": "
GNParamsFLOPsPSNRSSIM
127.40, 27.403860.94, 3860.9435.17, 35.170.967, 0.967
214.82, 15.082211.77, 2246.3935.09, 36.020.966, 0.974
48.53, 8.821387.33, 1426.3835.02, 36.480.966, 0.975
85.38, 5.65975.39, 1013.4534.31, 35.680.961, 0.971
", + "image_path": "a1067afe16e95ce228ed332898d092f799a2e0bf257f34d01e67a216ebbc1451.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "type": "table", + "bbox": [ + 50, + 170, + 285, + 214 + ], + "blocks": [ + { + "bbox": [ + 82, + 156, + 251, + 166 + ], + "lines": [ + { + "bbox": [ + 82, + 156, + 251, + 166 + ], + "spans": [ + { + "bbox": [ + 82, + 156, + 251, + 166 + ], + "type": "text", + "content": "Table 7. Ablation study on the CFormer block." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 50, + 170, + 285, + 214 + ], + "lines": [ + { + "bbox": [ + 50, + 170, + 285, + 214 + ], + "spans": [ + { + "bbox": [ + 50, + 170, + 285, + 214 + ], + "type": "table", + "html": "
SCBTSABSwinS2-3DParams (M)FLOPs (G)PSNRSSIM
✓✓2.88471.0334.990.967
✓6.93999.3134.930.966
✓✓3.78563.8735.510.970
", + "image_path": "a0b1e1f03ef1255e0640026d69fa791ce30b9aaf5aabe8203bec504b1a9743af.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 231, + 286, + 349 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 231, + 286, + 349 + ], + "spans": [ + { + "bbox": [ + 46, + 231, + 286, + 349 + ], + "type": "text", + "content": "ResDNet Block: We verify the effect of different group numbers (GN) (corresponding to " + }, + { + "bbox": [ + 46, + 231, + 286, + 349 + ], + "type": "inline_equation", + "content": "S" + }, + { + "bbox": [ + 46, + 231, + 286, + 349 + ], + "type": "text", + "content": " in Eq. 5) and dense connections on the reconstruction quality. As shown in Table 6, the model complexity decreases gradually with the increase of GN, but the reconstruction quality greatly decreases when there are no dense connections in the ResDNet block. By introducing dense connections in the ResDNet block, the reconstruction quality of our proposed method is greatly improved, and a gain of " + }, + { + "bbox": [ + 46, + 231, + 286, + 349 + ], + "type": "inline_equation", + "content": "1.46\\mathrm{dB}" + }, + { + "bbox": [ + 46, + 231, + 286, + 349 + ], + "type": "text", + "content": " can be obtained when GN is 4." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 350, + 286, + 529 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 350, + 286, + 529 + ], + "spans": [ + { + "bbox": [ + 46, + 350, + 286, + 529 + ], + "type": "text", + "content": "CFormer Block: In the CFormer block, we first replace SCB with Swin Transformer (Swin) to verify its effectiveness. Then, we replace SCB and TSAB with two stacked 3D convolutions (S2-3D) to verify the effectiveness of TSAB. As shown in Table 7, compared with Swin Transformer, SCB can bring a " + }, + { + "bbox": [ + 46, + 350, + 286, + 529 + ], + "type": "inline_equation", + "content": "0.52\\mathrm{dB}" + }, + { + "bbox": [ + 46, + 350, + 286, + 529 + ], + "type": "text", + "content": " gain. Although the number of parameters and FLOPs have increased, the experimental results show that SCB takes up less memory than the Swin Transformer, which is very important for large-scale and high compression ratio data. Please refer to more detailed analysis in SM. Compared with SCB and TSAB, S2-3D not only increases model parameters and FLOPs by " + }, + { + "bbox": [ + 46, + 350, + 286, + 529 + ], + "type": "inline_equation", + "content": "83\\%" + }, + { + "bbox": [ + 46, + 350, + 286, + 529 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 350, + 286, + 529 + ], + "type": "inline_equation", + "content": "77\\%" + }, + { + "bbox": [ + 46, + 350, + 286, + 529 + ], + "type": "text", + "content": " respectively, but also reduces the PSNR value by 0.58 dB, which verifies the necessity of using space-time factorization and TSAB." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 530, + 286, + 590 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 530, + 286, + 590 + ], + "spans": [ + { + "bbox": [ + 46, + 530, + 286, + 590 + ], + "type": "text", + "content": "Number of Channels and Blocks: Table 2 shows that the quality of model reconstruction increases with the number of channels and blocks. However, the amount of parameters and FLOPs also increase (see Table 3), resulting in a degradation in the real-time performance of the model." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 599, + 218, + 610 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 599, + 218, + 610 + ], + "spans": [ + { + "bbox": [ + 47, + 599, + 218, + 610 + ], + "type": "text", + "content": "5.4. Results on Real Video SCI Data" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 617, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 617, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 617, + 286, + 713 + ], + "type": "text", + "content": "We further test our method on real data. Fig. 8 and Fig. 9 show the reconstruction results of multiple algorithms on two public data (Duomino, Water Ballon), we can see that our method can reconstruct clearer details and edges. Specifically, we can clearly recognize the letters on the Duomino. Even with a high compression ratio " + }, + { + "bbox": [ + 46, + 617, + 286, + 713 + ], + "type": "inline_equation", + "content": "(B = 50)" + }, + { + "bbox": [ + 46, + 617, + 286, + 713 + ], + "type": "text", + "content": ", our proposed method can still reconstruct clear foreground and background information (shown in Fig. 9)." + } + ] + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 307, + 70, + 545, + 240 + ], + "blocks": [ + { + "bbox": [ + 307, + 70, + 545, + 240 + ], + "lines": [ + { + "bbox": [ + 307, + 70, + 545, + 240 + ], + "spans": [ + { + "bbox": [ + 307, + 70, + 545, + 240 + ], + "type": "image", + "image_path": "b086261c597715f90d12709648405d9000afb9b96062e7d12afcbc57c4292949.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 306, + 247, + 545, + 269 + ], + "lines": [ + { + "bbox": [ + 306, + 247, + 545, + 269 + ], + "spans": [ + { + "bbox": [ + 306, + 247, + 545, + 269 + ], + "type": "text", + "content": "Figure 8. Reconstruction results of different algorithms on Duomino real data with compression rate " + }, + { + "bbox": [ + 306, + 247, + 545, + 269 + ], + "type": "inline_equation", + "content": "B = 10" + }, + { + "bbox": [ + 306, + 247, + 545, + 269 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 307, + 285, + 545, + 425 + ], + "blocks": [ + { + "bbox": [ + 307, + 285, + 545, + 425 + ], + "lines": [ + { + "bbox": [ + 307, + 285, + 545, + 425 + ], + "spans": [ + { + "bbox": [ + 307, + 285, + 545, + 425 + ], + "type": "image", + "image_path": "6440a8697529966d1698e0d40cc006be5cfaef126a45224c11dc9031daa0ebb0.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 306, + 430, + 544, + 452 + ], + "lines": [ + { + "bbox": [ + 306, + 430, + 544, + 452 + ], + "spans": [ + { + "bbox": [ + 306, + 430, + 544, + 452 + ], + "type": "text", + "content": "Figure 9. Reconstruction results of different algorithms on Water Ballon real data with compression rate " + }, + { + "bbox": [ + 306, + 430, + 544, + 452 + ], + "type": "inline_equation", + "content": "B = 50" + }, + { + "bbox": [ + 306, + 430, + 544, + 452 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 464, + 474, + 475 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 464, + 474, + 475 + ], + "spans": [ + { + "bbox": [ + 306, + 464, + 474, + 475 + ], + "type": "text", + "content": "6. Conclusions and Future Work" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 486, + 545, + 606 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 486, + 545, + 606 + ], + "spans": [ + { + "bbox": [ + 304, + 486, + 545, + 606 + ], + "type": "text", + "content": "This paper proposes an efficient end-to-end video SCI reconstruction network, dubbed EfficientSCI, which achieves the state-of-the-art performance on simulated data and real data, significantly surpassing the previous best reconstruction algorithms with high real-time performance. In addition, we show for the first time that an UHD color video with high compression rate can be reconstructed using a deep learning based method. For future work, we consider applying EfficientSCI Network to more SCI reconstruction tasks, such as spectral SCI [4, 49]." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 625, + 408, + 639 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 625, + 408, + 639 + ], + "spans": [ + { + "bbox": [ + 306, + 625, + 408, + 639 + ], + "type": "text", + "content": "Acknowledgements" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 647, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 647, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 647, + 545, + 713 + ], + "type": "text", + "content": "This work was supported by the National Natural Science Foundation of China [62271414], Zhejiang Provincial Natural Science Foundation of China [LR23F010001]. 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However, their remarkable performance is accompanied by heavy computation costs, which makes them unsuitable for real-time applications. In this paper, we propose a family of high-speed vision transformers named EfficientViT. We find that the speed of existing transformer models is commonly bounded by memory inefficient operations, especially the tensor reshaping and element-wise functions in MHSA. Therefore, we design a new building block with a sandwich layout, i.e., using a single memory-bound MHSA between efficient FFN layers, which improves memory efficiency while enhancing channel communication. Moreover, we discover that the attention maps share high similarities across heads, leading to computational redundancy. To address this, we present a cascaded group attention module feeding attention heads with different splits of the full feature, which not only saves computation cost but also improves attention diversity. Comprehensive experiments demonstrate EfficientViT outperforms existing efficient models, striking a good trade-off between speed and accuracy. For instance, our EfficientViT-M5 surpasses MobileNetV3-Large by $1.9\\%$ in accuracy, while getting $40.4\\%$ and $45.2\\%$ higher throughput on Nvidia V100 GPU and Intel Xeon CPU, respectively. Compared to the recent efficient model MobileViT-XXS, EfficientViT-M2 achieves $1.8\\%$ superior accuracy, while running $5.8 \\times / 3.7 \\times$ faster on the GPU/CPU, and $7.4 \\times$ faster when converted to ONNX format. Code and models are available at here.", + "bbox": [ + 75, + 313, + 472, + 736 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 750, + 209, + 763 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Vision Transformers (ViTs) have taken computer vision domain by storm due to their high model capabilities and superior performance [18,44,69]. However, the constantly improved accuracy comes at the cost of increasing model sizes and computation overhead. For example, SwinV2 [43] uses 3.0B parameters, while V-MoE [62] taking 14.7B parameters, to achieve state-of-the-art performance on Ima", + "bbox": [ + 75, + 768, + 468, + 877 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/b8fceb61ddd0ee7e9f113af2288b31dec9923c12b1740b9f87114187be953262.jpg", + "image_caption": [ + "Figure 1. Speed and accuracy comparisons between EfficientViT (Ours) and other efficient CNN and ViT models tested on an Nvidia V100 GPU with ImageNet-1K dataset [17]." + ], + "image_footnote": [], + "bbox": [ + 540, + 282, + 846, + 445 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "geNet [17]. Such large model sizes and the accompanying heavy computational costs make these models unsuitable for applications with real-time requirements [40, 78, 86].", + "bbox": [ + 496, + 492, + 892, + 537 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "There are several recent works designing light and efficient vision transformer models [9, 19, 29, 49, 50, 56, 79, 81]. Unfortunately, most of these methods aim to reduce model parameters or Flops, which are indirect metrics for speed and do not reflect the actual inference throughput of models. For example, MobileViT-XS [50] using 700M Flops runs much slower than DeiT-T [69] with 1,220M Flops on an Nvidia V100 GPU. Although these methods have achieved good performance with fewer Flops or parameters, many of them do not show significant wall-clock speedup against standard isomorphic or hierarchical transformers, e.g., DeiT [69] and Swin [44], and have not gained wide adoption.", + "bbox": [ + 496, + 537, + 893, + 719 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "To address this issue, in this paper, we explore how to go faster with vision transformers, seeking to find principles for designing efficient transformer architectures. Based on the prevailing vision transformers DeiT [69] and Swin [44], we systematically analyze three main factors that affect model inference speed, including memory access, computation redundancy, and parameter usage. In particular, we find that the speed of transformer models is commonly memory-bound. In other words, memory accessing delay prohibits the full utilization of the computing power in GPU/CPUs [21, 32, 72], leading to a critically negative impact on the runtime speed of transformers [15, 31]. The", + "bbox": [ + 496, + 719, + 895, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 810, + 44 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Work done when Xinyu was an intern of Microsoft Research.", + "bbox": [ + 99, + 886, + 433, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "14420", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "most memory-inefficient operations are the frequent tensor reshaping and element-wise functions in multi-head self-attention (MHSA). We observe that through an appropriate adjustment of the ratio between MHSA and FFN (feedforward network) layers, the memory access time can be reduced significantly without compromising the performance. Moreover, we find that some attention heads tend to learn similar linear projections, resulting in redundancy in attention maps. The analysis shows that explicitly decomposing the computation of each head by feeding them with diverse features can mitigate this issue while improving computation efficiency. In addition, the parameter allocation in different modules is often overlooked by existing lightweight models, as they mainly follow the configurations in standard transformer models [44,69]. To improve parameter efficiency, we use structured pruning [45] to identify the most important network components, and summarize empirical guidance of parameter reallocation for model acceleration.", + "bbox": [ + 75, + 90, + 472, + 363 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Based upon the analysis and findings, we propose a new family of memory efficient transformer models named EfficientViT. Specifically, we design a new block with a sandwich layout to build up the model. The sandwich layout block applies a single memory-bound MHSA layer between FFN layers. It reduces the time cost caused by memory-bound operations in MHSA, and applies more FFN layers to allow communication between different channels, which is more memory efficient. Then, we propose a new cascaded group attention (CGA) module to improve computation efficiency. The core idea is to enhance the diversity of the features fed into the attention heads. In contrast to prior self-attention using the same feature for all heads, CGA feeds each head with different input splits and cascades the output features across heads. This module not only reduces the computation redundancy in multi-head attention, but also elevates model capacity by increasing network depth. Last but not least, we redistribute parameters through expanding the channel width of critical network components such as value projections, while shrinking the ones with lower importance like hidden dimensions in FFNs. This reallocation finally promotes model parameter efficiency.", + "bbox": [ + 75, + 367, + 472, + 700 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Experiments demonstrate that our models achieve clear improvements over existing efficient CNN and ViT models in terms of both speed and accuracy, as shown in Fig. 1. For instance, our EfficientViT-M5 gets $77.1\\%$ top-1 accuracy on ImageNet with throughput of 10,621 images/s on an Nvidia V100 GPU and 56.8 images/s on an Intel Xeon E5-2690 v4 CPU @ 2.60GHz, outperforming MobileNetV3-Large [26] by $1.9\\%$ in accuracy, $40.4\\%$ in GPU inference speed, and $45.2\\%$ in CPU speed. Moreover, EfficientViTM2 gets $70.8\\%$ accuracy, surpassing MobileViT-XXS [50] by $1.8\\%$ , while running $5.8 \\times / 3.7 \\times$ faster on the GPU/CPU, and $7.4 \\times$ faster when converted to ONNX [3] format. When deployed on the mobile chipset, i.e., Apple A13 Bionic chip", + "bbox": [ + 75, + 704, + 472, + 902 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/544c2b317b436b9974bef96ad7da65cabc5d5665652df3322c8867d911e0acf5.jpg", + "image_caption": [ + "Figure 2. Runtime profiling on two standard vision transformers Swin-T and DeiT-T. Red text denotes memory-bound operations, i.e., the time taken by the operation is mainly determined by memory accesses, while time spent in computation is much smaller." + ], + "image_footnote": [], + "bbox": [ + 527, + 75, + 658, + 186 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/53d1435c2cbdca9f0236c1f53b980dd492a99f30c1af19a0d8fee42ab3141bd9.jpg", + "image_caption": [], + "image_footnote": [ + "Tensor Multiplication Reshape Normalization Copy Addition Others" + ], + "bbox": [ + 663, + 75, + 795, + 186 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "in iPhone 11, EfficientViT-M2 model runs $2.3 \\times$ faster than MobileViT-XXS [50] using the CoreML [1].", + "bbox": [ + 496, + 253, + 890, + 282 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In summary, the contributions of this work are two-fold:", + "bbox": [ + 517, + 284, + 888, + 297 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- We present a systematic analysis on the factors that affect the inference speed of vision transformers, deriving a set of guidelines for efficient model design.", + "- We design a new family of vision transformer models, which strike a good trade-off between efficiency and accuracy. The models also demonstrate good transfer ability on a variety of downstream tasks." + ], + "bbox": [ + 517, + 299, + 890, + 406 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Going Faster with Vision Transformers", + "text_level": 1, + "bbox": [ + 498, + 414, + 852, + 430 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In this section, we explore how to improve the efficiency of vision transformers from three perspectives: memory access, computation redundancy, and parameter usage. We seek to identify the underlying speed bottlenecks through empirical studies, and summarize useful design guidelines.", + "bbox": [ + 496, + 435, + 890, + 511 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.1. Memory Efficiency", + "text_level": 1, + "bbox": [ + 498, + 518, + 683, + 535 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Memory access overhead is a critical factor affecting model speed [15,28,31,65]. Many operators in transformer [71], such as frequent reshaping, element-wise addition, and normalization are memory inefficient, requiring time-consuming access across different memory units, as shown in Fig. 2. Although there are some methods proposed to address this issue by simplifying the computation of standard softmax self-attention, e.g., sparse attention [34,57,61,75] and low-rank approximation [11,51,74], they often come at the cost of accuracy degradation and limited acceleration.", + "bbox": [ + 496, + 537, + 890, + 688 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In this work, we turn to save memory access cost by reducing memory-inefficient layers. Recent studies reveal that memory-inefficient operations are mainly located in MHSA rather than FFN layers [31, 33]. However, most existing ViTs [18, 44, 69] use an equivalent number of these two layers, which may not achieve the optimal efficiency. We thereby explore the optimal allocation of MHSA and FFN layers in small models with fast inference. Specifically, we scale down Swin-T [44] and DeiT-T [69] to several small subnetworks with $1.25 \\times$ and $1.5 \\times$ higher inference throughput, and compare the performance of subnetworks with different proportions of MHSA layers. As shown in Fig. 3, subnetworks with $20\\% - 40\\%$ MHSA layers tend to get better accuracy. Such ratios are much smaller than the", + "bbox": [ + 496, + 689, + 892, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "14421", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/9b6c96320c6ac8bd76c81eaaf1b8c3d1019c0312dcaec7c35b2b6b9b76bbbe00.jpg", + "image_caption": [ + "Figure 3. The accuracy of downscaled baseline models with different MHSA layer proportions, where the dots on each line represent subnetworks with similar throughput. Left: Swin-T as the baseline. Right: DeiT-T as the baseline. The $1.25 \\times 1.5 \\times$ denote accelerating the baseline models by 1.25/1.5 times, respectively." + ], + "image_footnote": [], + "bbox": [ + 101, + 79, + 271, + 193 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/65c10f493d8f0d2071970e226d4269ec2e18842b47ace7afc3361cbac6bbc6b1.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 274, + 79, + 441, + 193 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "typical ViTs that adopt $50\\%$ MHSA layers. Furthermore, we measure the time consumption on memory-bound operations to compare memory access efficiency, including reshaping, element-wise addition, copying, and normalization. Memory-bound operations is reduced to $44.26\\%$ of the total runtime in Swin-T-1.25× that has $20\\%$ MHSA layers. The observation also generalizes to DeiT and smaller models with $1.5\\times$ speed-up. It is demonstrated that reducing MHSA layer utilization ratio appropriately can enhance memory efficiency while improving model performance.", + "bbox": [ + 75, + 268, + 468, + 421 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "2.2. Computation Efficiency", + "text_level": 1, + "bbox": [ + 76, + 428, + 294, + 444 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "MHSA embeds the input sequence into multiple subspaces (heads) and computes attention maps separately, which has been proven effective in improving performance [18, 69, 71]. However, attention maps are computationally expensive, and studies have shown that a number of them are not of vital importance [52, 73]. To save computation cost, we explore how to reduce redundant attention in small ViT models. We train width downscaled Swin-T [44] and DeiT [69] models with $1.25 \\times$ inference speed-up, and measure the maximum cosine similarity of each head and the remaining heads within each block. From Fig. 4, we observe there exists high similarities between attention heads, especially in the last blocks. The phenomenon suggests that many heads learn similar projections of the same full feature and incur computation redundancy. To explicitly encourage the heads to learn different patterns, we apply an intuitive solution by feeding each head with only a split of the full feature, which is similar to the idea of group convolution in [10, 87]. We train the variants of downscaled models with the modified MHSA, and also compute the attention similarities in Fig. 4. It is shown that using different channel-wise splits of the feature in different heads, instead of using the same full feature for all heads as MHSA, could effectively mitigate attention computation redundancy.", + "bbox": [ + 75, + 449, + 470, + 811 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "2.3. Parameter Efficiency", + "text_level": 1, + "bbox": [ + 76, + 819, + 274, + 835 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Typical ViTs mainly inherit the design strategies from NLP transformer [71], e.g., using an equivalent width for $Q, K, V$ projections, increasing heads over stages, and setting the expansion ratio to 4 in FFN. For lightweight mod", + "bbox": [ + 75, + 839, + 468, + 901 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/ba13c9b27405e85559599ff09a1eb315a0e999245dc7d9d3670d305c0be893f8.jpg", + "image_caption": [ + "Figure 4. The average maximum cosine similarity of each head in different blocks. Left: downscaled Swin-T models. Right: downscaled DeiT-T models. Blue lines denote Swin-T-1.25×/DeiT-T-1.25× model, while darkblue lines denote the variants that feed each head with only a split of the full feature." + ], + "image_footnote": [], + "bbox": [ + 524, + 77, + 694, + 193 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/ebbd6c782e99ca4b3eb212632c46e4496c1ad7e60a52dd8beba8750619cd66ed.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 702, + 80, + 864, + 193 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/331e779be23bf82137a11dff3fbbf9d93bfbffab83d14f594ab9a36791e4b2e8.jpg", + "image_caption": [ + "Figure 5. The ratio of the channels to the input embeddings before and after pruning Swin-T. Baseline accuracy: $79.1\\%$ ; pruned accuracy: $76.5\\%$ . Results for DeiT-T are given in the supplementary." + ], + "image_footnote": [], + "bbox": [ + 524, + 268, + 864, + 381 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "els, the configurations of these components need to be carefully re-designed [7, 8, 39]. Inspired by [45, 82], we adopt Taylor structured pruning [53] to automatically find the important components in Swin-T and DeiT-T, and explore the underlying principles of parameter allocation. The pruning method removes unimportant channels under a certain resource constraint and keeps the most critical ones to best preserve the accuracy. It uses the multiplication of gradient and weight as channel importance, which approximates the loss fluctuation when removing channels [38].", + "bbox": [ + 496, + 439, + 890, + 590 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The ratio between the remaining output channels to the input channels is plotted in Fig. 5, and the original ratios in the unpruned model are also given for reference. It is observed that: 1) The first two stages preserve more dimensions, while the last stage keeps much less; 2) The $Q, K$ and FFN dimensions are largely trimmed, whereas the dimension of $V$ is almost preserved and diminishes only at the last few blocks. These phenomena show that 1) the typical channel configuration, that doubles the channel after each stage [44] or use equivalent channels for all blocks [69], may produce substantial redundancy in last few blocks; 2) The redundancy in $Q, K$ is much larger than $V$ when they have the same dimensions. $V$ prefers a relative large channels, being close to the input embedding dimension.", + "bbox": [ + 496, + 595, + 892, + 806 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Efficient Vision Transformer", + "text_level": 1, + "bbox": [ + 500, + 825, + 764, + 842 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Based upon the above analysis, in this section, we propose a new hierarchical model with fast inference named EfficientViT. The architecture overview is shown in Fig. 6.", + "bbox": [ + 498, + 853, + 890, + 898 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "14422", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/c37d84c7fb2098ae31f4f984cc68eca0ae171dc409c5370ae2486d34015be964.jpg", + "image_caption": [ + "Figure 6. Overview of EfficientViT. (a) Architecture of EfficientViT; (b) Sandwich Layout block; (c) Cascaded Group Attention." + ], + "image_footnote": [], + "bbox": [ + 156, + 74, + 816, + 422 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.1. EfficientViT Building Blocks", + "text_level": 1, + "bbox": [ + 76, + 455, + 331, + 470 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We propose a new efficient building block for vision transformer, as shown in Fig. 6 (b). It is composed of a memory-efficient sandwich layout, a cascaded group attention module, and a parameter reallocation strategy, which focus on improving model efficiency in terms of memory, computation, and parameter, respectively.", + "bbox": [ + 75, + 479, + 467, + 569 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Sandwich Layout. To build up a memory-efficient block, we propose a sandwich layout that employs less memory-bound self-attention layers and more memory-efficient FFN layers for channel communication. Specifically, it applies a single self-attention layer $\\Phi_i^{\\mathrm{A}}$ for spatial mixing, which is sandwiched between FFN layers $\\Phi_i^{\\mathrm{F}}$ . The computation can be formulated as:", + "bbox": [ + 75, + 569, + 467, + 671 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nX _ {i + 1} = \\prod^ {\\mathcal {N}} \\Phi_ {i} ^ {\\mathrm {F}} \\left(\\Phi_ {i} ^ {\\mathrm {A}} \\left(\\prod^ {\\mathcal {N}} \\Phi_ {i} ^ {\\mathrm {F}} \\left(X _ {i}\\right)\\right)\\right), \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 155, + 670, + 468, + 703 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $X_{i}$ is the full input feature for the $i$ -th block. The block transforms $X_{i}$ into $X_{i+1}$ with $\\mathcal{N}$ FFNs before and after the single self-attention layer. This design reduces the memory time consumption caused by self-attention layers in the model, and applies more FFN layers to allow communication between different feature channels efficiently. We also apply an extra token interaction layer before each FFN using a depthwise convolution (DWConv) [27]. It introduces inductive bias of the local structural information to enhance model capability [14].", + "bbox": [ + 75, + 703, + 467, + 854 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Cascaded Group Attention. Attention head redundancy is a severe issue in MHSA, which causes computation inefficiency. Inspired by group convolutions in efficient CNNs", + "bbox": [ + 75, + 854, + 467, + 900 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "[10, 37, 64, 87], we propose a new attention module named cascaded group attention (CGA) for vision transformers. It feeds each head with different splits of the full features, thus explicitly decomposing the attention computation across heads. Formally, this attention can be formulated as:", + "bbox": [ + 496, + 455, + 890, + 531 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\tilde {X} _ {i j} = \\operatorname {A t t n} \\left(X _ {i j} W _ {i j} ^ {\\mathrm {Q}}, X _ {i j} W _ {i j} ^ {\\mathrm {K}}, X _ {i j} W _ {i j} ^ {\\mathrm {V}}\\right), \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 560, + 534, + 890, + 561 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\tilde {X} _ {i + 1} = \\operatorname {C o n c a t} \\left[ \\tilde {X} _ {i j} \\right] _ {j = 1: h} W _ {i} ^ {\\mathrm {P}},\n$$\n", + "text_format": "latex", + "bbox": [ + 553, + 556, + 764, + 575 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where the $j$ -th head computes the self-attention over $X_{ij}$ , which is the $j$ -th split of the input feature $X_{i}$ , i.e., $X_{i} = [X_{i1}, X_{i2}, \\ldots, X_{ih}]$ and $1 \\leq j \\leq h$ . $h$ is the total number of heads, $W_{ij}^{\\mathrm{Q}}, W_{ij}^{\\mathrm{K}}$ , and $W_{ij}^{\\mathrm{V}}$ are projection layers mapping the input feature split into different subspaces, and $W_{i}^{\\mathrm{P}}$ is a linear layer that projects the concatenated output features back to the dimension consistent with the input.", + "bbox": [ + 496, + 579, + 890, + 686 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Although using feature splits instead of the full features for each head is more efficient and saves computation overhead, we continue to improve its capacity, by encouraging the $Q$ , $K$ , $V$ layers to learn projections on features with richer information. We compute the attention map of each head in a cascaded manner, as illustrated in Fig. 6 (c), which adds the output of each head to the subsequent head to refine the feature representations progressively:", + "bbox": [ + 496, + 688, + 890, + 809 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nX _ {i j} ^ {\\prime} = X _ {i j} + \\widetilde {X} _ {i (j - 1)}, \\quad 1 < j \\leq h, \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 571, + 813, + 890, + 833 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $X_{ij}^{\\prime}$ is the addition of the $j$ -th input split $X_{ij}$ and the $(j-1)$ -th head output $\\widetilde{X}_{i(j-1)}$ calculated by Eq. (2). It replaces $X_{ij}$ to serve as the new input feature for the $j$ -th head when calculating the self-attention. Besides, another token", + "bbox": [ + 496, + 835, + 890, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "14423", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 3 + }, + { + "type": "table", + "img_path": "images/082ed267043fe1cd08a942f0a442ae51a7fb54373ea2e225213933d425f9a630.jpg", + "table_caption": [ + "Table 1. Architecture details of EfficientViT model variants." + ], + "table_footnote": [], + "table_body": "
Model{C1,C2,C3}{L1,L2,L3}{H1,H2,H3}
EfficientViT-M0{64,128,192}{1,2,3}{4,4,4}
EfficientViT-M1{128,144,192}{1,2,3}{2,3,3}
EfficientViT-M2{128,192,224}{1,2,3}{4,3,2}
EfficientViT-M3{128,240,320}{1,2,3}{4,3,4}
EfficientViT-M4{128,256,384}{1,2,3}{4,4,4}
EfficientViT-M5{192,288,384}{1,3,4}{3,3,4}
", + "bbox": [ + 96, + 93, + 446, + 196 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "interaction layer is applied after the $Q$ projection, which enables the self-attention to jointly capture local and global relations and further enhances the feature representation.", + "bbox": [ + 75, + 200, + 468, + 247 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Such a cascaded design enjoys two advantages. First, feeding each head with different feature splits could improve the diversity of attention maps, as validated in Sec. 2.2. Similar to group convolutions [10, 87], the cascaded group attention could save the Flops and parameters by $h \\times$ , since the input and output channels in the QKV layers are reduced by $h \\times$ . Second, cascading the attention heads allows for an increase of network depth, thus further elevating the model capacity without introducing any extra parameters. It only incurs minor latency overhead since the attention map computation in each head uses smaller QK channel dimensions.", + "bbox": [ + 75, + 248, + 467, + 428 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Parameter Reallocation. To improve parameter efficiency, we reallocate the parameters in the network by expanding the channel width of critical modules while shrinking the unimportant ones. Specifically, based on the Taylor importance analysis in Sec. 2.3, we set small channel dimensions for $Q$ and $K$ projections in each head for all stages. For the $V$ projection, we allow it to have the same dimension as the input embedding. The expansion ratio in FFN is also reduced from 4 to 2 due to its parameter redundancy. With the proposed reallocation strategy, the important modules have larger number of channels to learn representations in a high dimensional space, which prevent the loss of feature information. Meanwhile, the redundant parameters in unimportant modules are removed to speed up inference and enhance the model efficiency.", + "bbox": [ + 75, + 430, + 467, + 656 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.2. EfficientViT Network Architectures", + "text_level": 1, + "bbox": [ + 76, + 667, + 387, + 681 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The overall architecture of our EfficientViT is presented in Fig. 6 (a). Concretely, we introduce overlapping patch embedding [20, 80] to embed $16 \\times 16$ patches into tokens with $C_1$ dimension, which enhances the model capacity in low-level visual representation learning. The architecture contains three stages. Each stage stacks the proposed EfficientViT building blocks and the number of tokens is reduced by $4 \\times$ at each subsampling layer ( $2 \\times$ subsampling of the resolution). To achieve efficient subsampling, we propose an EfficientViT subsample block which also has the sandwich layout, except that the self-attention layer is replaced by an inverted residual block to reduce the information loss during subsampling [26, 63]. It is worth noting that we adopt BatchNorm (BN) [30] instead of Layer", + "bbox": [ + 75, + 688, + 467, + 900 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Norm (LN) [2] throughout the model, as BN can be folded into the preceding convolution or linear layers, which is a runtime advantage over LN. We also use ReLU [54] as the activation function, as the commonly used GELU [25] or HardSwish [26] are much slower, and sometimes not well-supported by certain inference deployment platforms [1, 3].", + "bbox": [ + 496, + 90, + 890, + 181 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We build our model family with six different width and depth scales, and set different number of heads for each stage. We use fewer blocks in early stages than late stages similar to MobileNetV3 [26] and LeViT [20], since that the processing on early stages with larger resolutions is more time consuming. We increase the width over stages with a small factor $(\\leq 2)$ to alleviate redundancy in later stages, as analyzed in Sec. 2.3. The architecture details of our model family are presented in Tab. 1. $C_i$ , $L_i$ , and $H_i$ refer to the width, depth, and number of heads in the $i$ -th stage.", + "bbox": [ + 496, + 181, + 890, + 332 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 498, + 340, + 633, + 357 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.1. Implementation Details", + "text_level": 1, + "bbox": [ + 500, + 364, + 718, + 381 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We conduct image classification experiments on ImageNet-1K [17]. The models are built with PyTorch 1.11.0 [59] and Timm 0.5.4 [77], and trained from scratch for 300 epochs on 8 Nvidia V100 GPUs using AdamW [46] optimizer and cosine learning rate scheduler. We set the total batchsize as 2,048. The input images are resized and randomly cropped into $224 \\times 224$ . The initial learning rate is $1 \\times 10^{-3}$ with weight decay of $2.5 \\times 10^{-2}$ . We use the same data augmentation as [69], including Mixup [85], auto-augmentation [13], and random erasing [88]. In addition, we provide throughput evaluation on different hardware. For GPU, we measure the throughput on an Nvidia V100, with the maximum power-of-two batchsize that fits in memory following [20, 69]. For CPU and ONNX, we measure the runtime on an Intel Xeon E5-2690 v4 @ 2.60 GHz processor, with batchsize 16 and run the model in a single thread following [20]. We also test the transferability of EfficientViT on downstream tasks. For the experiments on downstream image classification, we finetune the models for 300 epochs following [86], using AdamW [46] with batchsize 256, learning rate $1 \\times 10^{-3}$ and weight-decay $1 \\times 10^{-8}$ . We use RetinaNet [41] for object detection on COCO [42], and train the models for 12 epochs ( $1 \\times$ schedule) with the same settings as [44] on mmdetection [6]. For instance segmentation, please refer to the supplementary.", + "bbox": [ + 496, + 386, + 890, + 763 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.2. Results on ImageNet", + "text_level": 1, + "bbox": [ + 500, + 773, + 694, + 789 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We compare EfficientViT with prevailing efficient CNN and ViT models on ImageNet [17], and report the results in Tab. 2 and Fig. 1. The results show that, in most cases, our EfficientViT achieves the best accuracy and speed trade-off across different evaluation settings.", + "bbox": [ + 496, + 794, + 890, + 869 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Comparisons with efficient CNNs. We first compare EfficientViT with vanilla CNN models, such as MobileNets", + "bbox": [ + 500, + 869, + 890, + 898 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "14424", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/666b002b6cf6fe0d3d85d30f81a5584a910b9b097c0974b12f05976e16b49e5d.jpg", + "table_caption": [ + "Table 2. EfficientViT image classification performance on ImageNet-1K [17] with comparisons to state-of-the-art efficient CNN and ViT models trained without extra data. Throughput is tested on Nvidia V100 for GPU and Intel Xeon E5-2690 v4 @ 2.60 GHz processor for CPU and ONNX, where larger throughput means faster inference speed. ↑: finetune with higher resolution." + ], + "table_footnote": [], + "table_body": "
ModelTop-1 (%)Top-5 (%)Throughput (images/s)Flops (M)Params (M)InputEpochs
GPUCPUONNX
EfficientViT-M063.285.427644228.4340.1792.3224300
MobileNetV3-Small [26]67.4-19738156.5231.7572.5224600
EfficientViT-M168.488.720093126.9215.91673.0224300
Mobile-Former-52M [9]68.7-314132.821.5523.5224450
MobileViT-XXS [50]69.0-445629.441.74101.3256300
ShuffleNetV2 1.0× [48]69.488.913301106.7177.01462.3224300
MobileViTV2-0.5 [51]70.2-514234.444.94661.4256300
EfficientViT-M270.890.218218121.2158.72014.2224300
MobileOne-S0 [70]71.4-1132067.4128.62742.1224300
MobileNetV2 1.0× [63]72.091.0653432.580.43003.4224300
EfficientViT-M373.491.41664496.4120.82636.9224300
GhostNet 1.0× [23]73.991.4738257.377.01415.2224300
NASNet-A-Mobile [89]74.1-262319.825.55645.3224300
EfficientViT-M474.391.81591488.5108.62998.8224300
EdgeViT-XXS [56]74.4-363828.229.65564.1224300
MobileViT-XS [50]74.7-334411.120.59862.3256300
ShuffleNetV2 2.0× [48]74.992.4696237.952.35917.4224300
MobileNetV3-Large [26]75.2-756039.170.52175.4224600
MobileViTV2-0.75 [51]75.6-335016.022.710302.9256300
MobileOne-S1 [70]75.9-666330.751.18254.8224300
GLiT-Tiny [5]76.4-351617.515.713337.3224300
EfficientNet-B0 [67]77.193.3453230.229.53905.3224350
EfficientViT-M577.193.41062156.862.552212.4224300
EfficientViT-M4↑38479.895.0398615.822.6148612.4384330
EfficientViT-M5↑51280.895.523138.310.5267012.4512360
", + "bbox": [ + 142, + 125, + 826, + 547 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "[26, 63] and EfficientNet [67]. Specifically, compared to MobileNetV2 $1.0 \\times$ [63], EfficientViT-M3 obtains $1.4\\%$ better top-1 accuracy, while running at $2.5 \\times$ and $3.0 \\times$ faster speed on V100 GPU and Intel CPU, respectively. Compared to the state-of-the-art MobileNetV3-Large [26], EfficientViT-M5 achieves $1.9\\%$ higher accuracy yet runs much faster, e.g., $40.5\\%$ faster on the V100 GPU and $45.2\\%$ faster on the Intel CPU but is $11.5\\%$ slower as ONNX models. This may because reshaping is slower in ONNX implementation, which is inevitable in computing self-attention. Moreover, EfficientViT-M5 achieves comparable accuracy with the searched model EfficientNet-B0 [67], while runs $2.3 \\times / 1.9 \\times$ faster on the V100 GPU/Intel CPU, and $2.1 \\times$ faster as ONNX models. Although our model uses more parameters, it reduces memory-inefficient operations that affect the inference speed and achieves higher throughput.", + "bbox": [ + 75, + 565, + 472, + 808 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Comparisons with efficient ViTs. We also compare our models with recent efficient vision transformers [5, 9, 50, 51, 56] in Tab. 2. In particular, when getting similar performance on ImageNet-1K [17], our EfficientViT-M4 runs $4.4 \\times$ and $3.0 \\times$ faster than the recent EdgeViT-XXS [56] on the tested CPU and GPU devices. Even converted to ONNX", + "bbox": [ + 75, + 810, + 470, + 901 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "runtime format, our model still gets $3.7 \\times$ higher speed. Compared to the state-of-the-art MobileViTV2-0.5 [51], our EfficientViT-M2 achieves slightly better performance with higher throughput, e.g., $3.4 \\times$ and $3.5 \\times$ higher throughput tested on the GPU and CPU devices, respectively. Furthermore, we compare with tiny variants of state-of-the-art large ViTs in Tab. 3. PoolFormer-12S [83] has comparable accuracy with EfficientViT-M5 yet runs $3.0 \\times$ slower on the V100 GPU. Compared to Swin-T [44], EfficientViT-M5 is $4.1\\%$ inferior in accuracy yet is $12.3 \\times$ faster on the Intel CPU, demonstrating the efficiency of the proposed design. In addition, we present the speed evaluation and comparison on mobile chipsets in the supplementary material.", + "bbox": [ + 496, + 565, + 890, + 762 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Finetune with higher resolutions. Recent works on ViTs have demonstrated that finetuning with higher resolutions can further improve the capacity of the models. We also finetune our largest model EfficientViT-M5 to higher resolutions. EfficientViT-M5↑384 reaches 79.8% top-1 accuracy with throughput of 3,986 images/s on the V100 GPU, and EfficientViT-M5↑512 further improves the top-1 accuracy to 80.8%, demonstrating the efficiency on processing images with larger resolutions and the good model capacity.", + "bbox": [ + 496, + 763, + 893, + 902 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "14425", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/fad66f880e1da229fe3bf5341377c57387728ebe5bd34c74df6e20dd4c1b576b.jpg", + "table_caption": [ + "Table 3. Comparison with the tiny variants of state-of-the-art large-scale ViTs on ImageNet-1K [17]." + ], + "table_footnote": [], + "table_body": "
ModelTop-1 (%)Throughput (imgs/s)Flops (G)Params (M)
GPUCPUONNX
PVTV2-B0 [76]70.5350712.718.50.61.4
T2T-ViT-7 [84]71.7115622.516.11.14.3
DeiT-T [69]72.2463126.025.11.35.9
PoolFormer-12S [83]77.2353410.414.61.912.0
EffFormer-L1 [40]79.2446512.921.21.312.3
Swin-T [44]81.213934.66.44.529.0
EfficientViT-M577.11062156.862.50.512.4
", + "bbox": [ + 84, + 111, + 459, + 227 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/578ea6dbe8887b254b2c1729b81ec3873940ce54c2a2533713c08583f110ea57.jpg", + "table_caption": [ + "Table 4. Results of EfficientViT and other efficient models on downstream image classification datasets." + ], + "table_footnote": [], + "table_body": "
ModelThroughputImageNetCIFAR10CIFAR100CarsFlowersPets
MobileNetV1 [27]854370.696.182.391.496.789.9
MobileNetV2 [63]653472.995.780.891.096.690.5
MobileNetV3 [26]756075.297.685.591.297.090.1
NASNet-A-M [89]262374.196.883.988.596.889.4
ViT-S/16 [18]213581.497.685.7-86.490.4
EfficientViT-M51062177.198.086.489.797.192.0
", + "bbox": [ + 84, + 260, + 460, + 381 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.3. Transfer Learning Results", + "text_level": 1, + "bbox": [ + 76, + 388, + 316, + 404 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "To further evaluate the transfer ability, we apply EfficientViT on various downstream tasks.", + "bbox": [ + 76, + 410, + 467, + 439 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Downstream Image Classification. We transfer EfficientViT to downstream image classification datasets to test its generalization ability: 1) CIFAR-10 and CIFAR-100 [36]; 2) fine-grained classification: Flowers [55], Stanford Cars [35], and Oxford-IIIT Pets [58]. We report the results in Tab. 4. Compared to existing efficient models [18, 26, 27, 63, 89], our EfficientViT-M5 achieves comparable or slightly better accuracy across all datasets with much higher throughput. An exception lies in Cars, where our model is slightly inferior in accuracy. This may because the subtle differences between classes lie more in local details thus is more feasible to be captured with convolution.", + "bbox": [ + 75, + 441, + 467, + 621 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Object Detection. We compare EfficientViT-M4 with efficient models [12, 22, 26, 63, 66, 68] on the COCO [42] object detection task, and present the results in Tab. 5. Specifically, EfficientViT-M4 surpasses MobileNetV2 [63] by $4.4\\%$ AP with comparable Flops. Compared to the searched method SPOS [22], our EfficientViT-M4 uses $18.1\\%$ fewer Flops while achieving $2.0\\%$ higher AP, demonstrating its capacity and generalization ability in different vision tasks.", + "bbox": [ + 75, + 623, + 467, + 743 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.4. Ablation Study", + "text_level": 1, + "bbox": [ + 76, + 755, + 228, + 771 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "In this section, we ablate important design elements in the proposed EfficientViT on ImageNet-1K [17]. All models are trained for 100 epochs to magnify the differences and reduce training time [20]. Tab. 6 reports the results.", + "bbox": [ + 75, + 777, + 467, + 839 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Impact of the sandwich layout block. We first present an ablation study to verify the efficiency of the proposed sandwich layout design, by replacing the sandwich layout block with the original Swin block [44]. The depth is adjusted to", + "bbox": [ + 75, + 840, + 467, + 900 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/725a9b2d64e70a4a7e54004a3ef9bf830485ce4fcdecc6d3ace598b78ab8ad3e.jpg", + "table_caption": [ + "Table 5. EfficientViT object detection performance on COCOval2017 [42] with comparisons to other efficient models." + ], + "table_footnote": [], + "table_body": "
ModelRetinaNet 1×FlopsParams
APAP50AP75APsAPmAPl(M)(M)
MobileNetV2 [63]28.346.729.314.830.738.13003.4
MobileNetV3 [26]29.949.330.814.933.341.12175.4
SPOS [22]30.749.832.215.433.941.63654.3
MNASNet-A2 [66]30.550.232.016.634.141.13404.8
FairNAS-C [12]31.250.832.716.334.442.33255.6
MixNet-M [68]31.351.732.417.035.041.93605.0
EfficientViT-M432.752.234.117.635.346.02998.8
", + "bbox": [ + 511, + 111, + 879, + 231 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/9d4a5202a81b5c8e45680da248eb0c63fc7eb31cccfcc3efb4e695819eff22b8.jpg", + "table_caption": [ + "Table 6. Ablation for EfficientViT-M4 on ImageNet-1K [17] dataset. Top-1 accuracy, GPU and ONNX throughput are reported." + ], + "table_footnote": [], + "table_body": "
#AblationTop-1 (%)Throughput (imgs/s)
GPUONNX
1EfficientViT-M471.315914108.6
2Sandwich → Swin [44]68.315804114.5
3N = 1 → 270.214977112.3
4N = 1 → 365.715856139.7
5CGA → MHSA [18]70.216243102.2
6Cascade → None69.816411111.0
7QKV allocation → None69.915132103.1
8FFN ratio 2 → 469.815310112.4
9DWConv → None69.916325110.4
10BN → LN [2]70.415463103.6
11ReLU → HSwish [26]72.21588787.5
", + "bbox": [ + 517, + 267, + 874, + 454 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "$\\{2, 2, 3\\}$ to guarantee similar throughput with EfficientViTM4 for a fair comparison. The top-1 accuracy degrades by $3.0\\%$ at a similar speed, verifying that applying more FFNs instead of memory-bound MHSA is more effective for small models. Furthermore, to analyze the impact of the number of FFNs $\\mathcal{N}$ before and after self-attention, we change the number from 1 to 2 and 3. The number of blocks is reduced accordingly to maintain similar throughput. As presented in Tab. 6 (#3 and #4), further increasing the number of FFNs is not effective due to the lack of long-range spatial relation and $\\mathcal{N} = 1$ achieves the best efficiency.", + "bbox": [ + 496, + 459, + 890, + 625 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Impact of the cascaded group attention. We have proposed CGA to improve the computation efficiency of MHSA. As shown in Tab. 6 (#5 and #6), replacing CGA with MHSA decreases the accuracy by $1.1\\%$ and ONNX speed by $5.9\\%$ , suggesting that addressing head redundancy improves the model efficiency. For the model without the cascade operation, its performance is comparable with MHSA but worse than CGA, demonstrating the efficacy of enhancing the feature representations of each head.", + "bbox": [ + 496, + 627, + 890, + 762 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Impact of the parameter reallocation. Our EfficientViTM4 yields $1.4\\% / 1.5\\%$ higher top-1 accuracy, $4.9\\% / 3.8\\%$ higher GPU throughput than the models without QKV channel dimension reallocation or FFN ratio reduction, respectively, indicating the effectiveness of parameter reallocation (#1 vs. #7, #8). Moreover, we study the choices of QK dimension in each head and the ratio of V dimension to the input embedding in Fig. 7. It is shown that the performance is improved gradually as QK dimension increases", + "bbox": [ + 496, + 763, + 890, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "14426", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/bbee4e0d10b96b38229df9201d691613ae7bd043ed548cbc27fc9c71640491c8.jpg", + "table_caption": [ + "Table 7. Performance comparison on ImageNet-1K [17] and ImageNet-ReaL [4]. Results with $\\dagger$ are trained with 1,000 epochs and knowledge distillation following LeViT [20]." + ], + "table_footnote": [], + "table_body": "
ModelImageNet (%)Throughput (imgs/s)Flops Params
Top-1Top-1†RealL†GPUCPUONNX(M)(M)
LeViT-128S [20]73.676.682.61445782.380.93057.8
EfficientViT-M474.377.183.61591488.5108.62998.8
", + "bbox": [ + 84, + 121, + 460, + 183 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "from 4 to 16, while further increasing it gives inferior performance. Besides, the performance improves from $70.3\\%$ to $71.3\\%$ when increasing the ratio between $V$ dimension and input embedding from 0.4 to 1.0. When further enlarging the ratio to 1.2, it only gets $0.1\\%$ improvements. Therefore, setting the channels of $V$ close to the input embedding achieves the best parameter efficiency, which meets our analysis in Sec. 2.3 and design strategy.", + "bbox": [ + 75, + 190, + 467, + 310 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Impact of other components. We ablate the impact of using DWConv for token interaction, the normalization layer, and the activation function, as presented in Tab. 6 (#9, #10, and #11). With DWConv, the accuracy improves by $1.4\\%$ with a minor latency overhead, demonstrating the effectiveness of introducing local structural information. Replacing BN with LN decreases accuracy by $0.9\\%$ and GPU speed by $2.9\\%$ . Using HardSwish instead of ReLU improves accuracy by $0.9\\%$ but leads to a large drop of $20.0\\%$ ONNX speed. The activation functions are element-wise operations that occupy a considerable amount of processing time on GPU/CPU [15,48,72], thus utilizing ReLU instead of more complicated activation functions is of better efficiency.", + "bbox": [ + 75, + 311, + 467, + 505 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Results of 1,000 training epochs and distillation. Tab. 7 shows the results with 1,000 training epochs and knowledge distillation using RegNetY-16GF [60] as the teacher model following [20] on ImageNet-1K [17] and ImageNet-ReaL [4]. Compared to LeViT-128S [20], EfficientViT-M4 surpasses it by $0.5\\%$ on ImageNet-1K and $1.0\\%$ on ImageNet-ReaL, respectively. For the inference speed, our model has $34.2\\%$ higher throughput on ONNX and also shows superiority on other settings. The results demonstrate that the strong capability and generalization ability of EfficientViT can be further explored with longer training schedules.", + "bbox": [ + 75, + 507, + 467, + 674 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Related Work", + "text_level": 1, + "bbox": [ + 76, + 681, + 218, + 696 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Efficient CNNs. With the demand of deploying CNNs on resource-constrained scenarios, efficient CNNs have been intensively studied in literature [23, 24, 26, 48, 63, 67, 87]. Xception [10] proposes an architecture built with depthwise separable convolutions. MobileNetV2 [63] builds an inverted residual structure which expands the input to a higher dimension. MobileNetV3 [26] and EfficientNet [67] resort to neural architecture search techniques to design compact models. To boost the actual speed on hardware, ShuffleNetV2 [48] introduces channel split and shuffle operations to improve the information communication among channel groups. However, the spatial locality of convolutional kernels hampers CNN models from capturing long-", + "bbox": [ + 75, + 703, + 467, + 900 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/833cbf3b725904c503508d22147a1f2f3ebc5e510ea444b2f53e572a84af25e0.jpg", + "image_caption": [ + "Figure 7. Ablation on the $QK$ dimension of each head and the ratio of $V$ dimension to the input embedding." + ], + "image_footnote": [], + "bbox": [ + 504, + 75, + 689, + 138 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/c9dcaaafbbbf228bb114b6f8d0699435b8898f89702b5ed6531a072e6168023e.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 691, + 75, + 882, + 138 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "range dependencies, thus limiting their model capacity.", + "bbox": [ + 500, + 174, + 862, + 189 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Efficient ViTs. ViT and its variants [18, 44, 69, 76] have achieved success on various vision tasks. Despite the superior performance, most of them are inferior to typical CNNs in inference speed. Some efficient transformers have been proposed recently and they fall into two camps: 1) efficient self-attention; and 2) efficient architecture design. Efficient self-attention methods reduce the cost of softmax attention via sparse attention [34, 57, 61, 75] or low-rank approximation [11, 51, 74]. However, they suffer from performance degradation with negligible or moderate inference acceleration over softmax attention [71]. Another line of work combines ViTs with lightweight CNNs to build efficient architectures [9, 47, 49, 50, 81]. LVT [81] proposes enhanced attention mechanisms with dilated convolution to improve the model performance and efficiency. Mobile-Former [9] designs a parallel CNN-transformer block to encode both local features and global interaction. However, most of them target at minimizing Flops and parameters [16], which could have low correlations with actual inference latency [70] and still inferior to efficient CNNs in speed. Different from them, we explore models with fast inference by directly optimizing their throughput on different hardware and deployment settings, and design a family of hierarchical models with a good trade-off between speed and accuracy.", + "bbox": [ + 496, + 190, + 890, + 551 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "6. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 561, + 617, + 575 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this paper, we have presented a systematic analysis on the factors that affect the inference speed of vision transformers, and proposed a new family of fast vision transformers with memory-efficient operations and cascaded group attention, named EfficientViT. Extensive experiments have demonstrated the efficacy and high speed of EfficientViT, and also show its superiority on various downstream benchmarks.", + "bbox": [ + 496, + 582, + 890, + 700 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Limitations. One limitation of EfficientViT is that, despite its high inference speed, the model size is slightly larger compared to state-of-the-art efficient CNN [26] due to the extra FFNs in the introduced sandwich layout. Besides, our models are designed manually based on the derived guidelines on building efficient vision transformers. In future work, we are interested in reducing the model size and incorporating automatic search techniques to further enhance the model capacity and efficiency.", + "bbox": [ + 496, + 703, + 890, + 839 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgement. Prof. Yuan was partially supported by Hong Kong Research Grants Council (RGC) General Research Fund 11211221, and Innovation and Technology Commission-Innovation and Technology Fund ITS/100/20.", + "bbox": [ + 496, + 839, + 890, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "14427", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Apple. Coremltools: Use coremltools to convert machine learning models from third-party libraries to the core ml format, 2021. 2, 5", + "[2] Jimmy Lei Ba, Jamie Ryan Kiros, and Geoffrey E Hinton. Layer normalization. arXiv, 2016. 5, 7", + "[3] Junjie Bai, Fang Lu, Ke Zhang, et al. 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In CVPR, pages 8697-8710, 2018. 6, 7" + ], + "bbox": [ + 501, + 90, + 890, + 376 + ], + "page_idx": 10 + }, + { + "type": "page_number", + "text": "14430", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 10 + } +] \ No newline at end of file diff --git a/2023/EfficientViT_ Memory Efficient Vision Transformer With Cascaded Group Attention/351f9dba-430a-462e-86ab-2879d7f983dd_model.json b/2023/EfficientViT_ Memory Efficient Vision Transformer With Cascaded Group Attention/351f9dba-430a-462e-86ab-2879d7f983dd_model.json new file mode 100644 index 0000000000000000000000000000000000000000..fe05af0c1d10891ca38c1c105d9ec76f8dc48909 --- /dev/null +++ b/2023/EfficientViT_ Memory Efficient Vision Transformer With Cascaded Group Attention/351f9dba-430a-462e-86ab-2879d7f983dd_model.json @@ -0,0 +1,2532 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.0, + 0.812, + 0.045 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.202, + 0.131, + 0.773, + 0.177 + ], + "angle": 0, + "content": "EfficientViT: Memory Efficient Vision Transformer with Cascaded Group Attention" + }, + { + "type": "text", + "bbox": [ + 0.139, + 0.203, + 0.828, + 0.24 + ], + "angle": 0, + "content": "Xinyu Liu\\(^{1,\\ast}\\), Houwen Peng\\(^{2}\\), Ningxin Zheng\\(^{2}\\), Yuqing Yang\\(^{2}\\), Han Hu\\(^{2}\\), Yixuan Yuan\\(^{1}\\) \n\\(^{1}\\) The Chinese University of Hong Kong, \\(^{2}\\) Microsoft Research" + }, + { + "type": "text", + "bbox": [ + 0.105, + 0.242, + 0.86, + 0.258 + ], + "angle": 0, + "content": "1155195604@link.cuhk.edu.hk, {houwen.peng, ningxin.zheng, yuqing.yang, hanhu} @microsoft.com, yxyuan@ee.cuhk.edu.hk" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.292, + 0.314, + 0.308 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.314, + 0.473, + 0.737 + ], + "angle": 0, + "content": "Vision transformers have shown great success due to their high model capabilities. However, their remarkable performance is accompanied by heavy computation costs, which makes them unsuitable for real-time applications. In this paper, we propose a family of high-speed vision transformers named EfficientViT. We find that the speed of existing transformer models is commonly bounded by memory inefficient operations, especially the tensor reshaping and element-wise functions in MHSA. Therefore, we design a new building block with a sandwich layout, i.e., using a single memory-bound MHSA between efficient FFN layers, which improves memory efficiency while enhancing channel communication. Moreover, we discover that the attention maps share high similarities across heads, leading to computational redundancy. To address this, we present a cascaded group attention module feeding attention heads with different splits of the full feature, which not only saves computation cost but also improves attention diversity. Comprehensive experiments demonstrate EfficientViT outperforms existing efficient models, striking a good trade-off between speed and accuracy. For instance, our EfficientViT-M5 surpasses MobileNetV3-Large by \\(1.9\\%\\) in accuracy, while getting \\(40.4\\%\\) and \\(45.2\\%\\) higher throughput on Nvidia V100 GPU and Intel Xeon CPU, respectively. Compared to the recent efficient model MobileViT-XXS, EfficientViT-M2 achieves \\(1.8\\%\\) superior accuracy, while running \\(5.8 \\times / 3.7 \\times\\) faster on the GPU/CPU, and \\(7.4 \\times\\) faster when converted to ONNX format. Code and models are available at here." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.75, + 0.21, + 0.765 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.77, + 0.47, + 0.878 + ], + "angle": 0, + "content": "Vision Transformers (ViTs) have taken computer vision domain by storm due to their high model capabilities and superior performance [18,44,69]. However, the constantly improved accuracy comes at the cost of increasing model sizes and computation overhead. For example, SwinV2 [43] uses 3.0B parameters, while V-MoE [62] taking 14.7B parameters, to achieve state-of-the-art performance on Ima" + }, + { + "type": "image", + "bbox": [ + 0.541, + 0.283, + 0.847, + 0.446 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.447, + 0.895, + 0.49 + ], + "angle": 0, + "content": "Figure 1. Speed and accuracy comparisons between EfficientViT (Ours) and other efficient CNN and ViT models tested on an Nvidia V100 GPU with ImageNet-1K dataset [17]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.493, + 0.893, + 0.539 + ], + "angle": 0, + "content": "geNet [17]. Such large model sizes and the accompanying heavy computational costs make these models unsuitable for applications with real-time requirements [40, 78, 86]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.539, + 0.895, + 0.72 + ], + "angle": 0, + "content": "There are several recent works designing light and efficient vision transformer models [9, 19, 29, 49, 50, 56, 79, 81]. Unfortunately, most of these methods aim to reduce model parameters or Flops, which are indirect metrics for speed and do not reflect the actual inference throughput of models. For example, MobileViT-XS [50] using 700M Flops runs much slower than DeiT-T [69] with 1,220M Flops on an Nvidia V100 GPU. Although these methods have achieved good performance with fewer Flops or parameters, many of them do not show significant wall-clock speedup against standard isomorphic or hierarchical transformers, e.g., DeiT [69] and Swin [44], and have not gained wide adoption." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.896, + 0.903 + ], + "angle": 0, + "content": "To address this issue, in this paper, we explore how to go faster with vision transformers, seeking to find principles for designing efficient transformer architectures. Based on the prevailing vision transformers DeiT [69] and Swin [44], we systematically analyze three main factors that affect model inference speed, including memory access, computation redundancy, and parameter usage. In particular, we find that the speed of transformer models is commonly memory-bound. In other words, memory accessing delay prohibits the full utilization of the computing power in GPU/CPUs [21, 32, 72], leading to a critically negative impact on the runtime speed of transformers [15, 31]. The" + }, + { + "type": "page_footnote", + "bbox": [ + 0.101, + 0.887, + 0.434, + 0.9 + ], + "angle": 0, + "content": "*Work done when Xinyu was an intern of Microsoft Research." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "14420" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.364 + ], + "angle": 0, + "content": "most memory-inefficient operations are the frequent tensor reshaping and element-wise functions in multi-head self-attention (MHSA). We observe that through an appropriate adjustment of the ratio between MHSA and FFN (feedforward network) layers, the memory access time can be reduced significantly without compromising the performance. Moreover, we find that some attention heads tend to learn similar linear projections, resulting in redundancy in attention maps. The analysis shows that explicitly decomposing the computation of each head by feeding them with diverse features can mitigate this issue while improving computation efficiency. In addition, the parameter allocation in different modules is often overlooked by existing lightweight models, as they mainly follow the configurations in standard transformer models [44,69]. To improve parameter efficiency, we use structured pruning [45] to identify the most important network components, and summarize empirical guidance of parameter reallocation for model acceleration." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.368, + 0.473, + 0.702 + ], + "angle": 0, + "content": "Based upon the analysis and findings, we propose a new family of memory efficient transformer models named EfficientViT. Specifically, we design a new block with a sandwich layout to build up the model. The sandwich layout block applies a single memory-bound MHSA layer between FFN layers. It reduces the time cost caused by memory-bound operations in MHSA, and applies more FFN layers to allow communication between different channels, which is more memory efficient. Then, we propose a new cascaded group attention (CGA) module to improve computation efficiency. The core idea is to enhance the diversity of the features fed into the attention heads. In contrast to prior self-attention using the same feature for all heads, CGA feeds each head with different input splits and cascades the output features across heads. This module not only reduces the computation redundancy in multi-head attention, but also elevates model capacity by increasing network depth. Last but not least, we redistribute parameters through expanding the channel width of critical network components such as value projections, while shrinking the ones with lower importance like hidden dimensions in FFNs. This reallocation finally promotes model parameter efficiency." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.705, + 0.473, + 0.904 + ], + "angle": 0, + "content": "Experiments demonstrate that our models achieve clear improvements over existing efficient CNN and ViT models in terms of both speed and accuracy, as shown in Fig. 1. For instance, our EfficientViT-M5 gets \\(77.1\\%\\) top-1 accuracy on ImageNet with throughput of 10,621 images/s on an Nvidia V100 GPU and 56.8 images/s on an Intel Xeon E5-2690 v4 CPU @ 2.60GHz, outperforming MobileNetV3-Large [26] by \\(1.9\\%\\) in accuracy, \\(40.4\\%\\) in GPU inference speed, and \\(45.2\\%\\) in CPU speed. Moreover, EfficientViTM2 gets \\(70.8\\%\\) accuracy, surpassing MobileViT-XXS [50] by \\(1.8\\%\\), while running \\(5.8 \\times / 3.7 \\times\\) faster on the GPU/CPU, and \\(7.4 \\times\\) faster when converted to ONNX [3] format. When deployed on the mobile chipset, i.e., Apple A13 Bionic chip" + }, + { + "type": "image", + "bbox": [ + 0.529, + 0.077, + 0.66, + 0.188 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.665, + 0.077, + 0.797, + 0.188 + ], + "angle": 0, + "content": null + }, + { + "type": "image_footnote", + "bbox": [ + 0.803, + 0.099, + 0.867, + 0.166 + ], + "angle": 0, + "content": "Tensor Multiplication Reshape Normalization Copy Addition Others" + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.191, + 0.895, + 0.248 + ], + "angle": 0, + "content": "Figure 2. Runtime profiling on two standard vision transformers Swin-T and DeiT-T. Red text denotes memory-bound operations, i.e., the time taken by the operation is mainly determined by memory accesses, while time spent in computation is much smaller." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.254, + 0.892, + 0.284 + ], + "angle": 0, + "content": "in iPhone 11, EfficientViT-M2 model runs \\(2.3 \\times\\) faster than MobileViT-XXS [50] using the CoreML [1]." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.285, + 0.89, + 0.299 + ], + "angle": 0, + "content": "In summary, the contributions of this work are two-fold:" + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.3, + 0.891, + 0.345 + ], + "angle": 0, + "content": "- We present a systematic analysis on the factors that affect the inference speed of vision transformers, deriving a set of guidelines for efficient model design." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.347, + 0.892, + 0.407 + ], + "angle": 0, + "content": "- We design a new family of vision transformer models, which strike a good trade-off between efficiency and accuracy. The models also demonstrate good transfer ability on a variety of downstream tasks." + }, + { + "type": "list", + "bbox": [ + 0.518, + 0.3, + 0.892, + 0.407 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.415, + 0.854, + 0.431 + ], + "angle": 0, + "content": "2. Going Faster with Vision Transformers" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.436, + 0.892, + 0.512 + ], + "angle": 0, + "content": "In this section, we explore how to improve the efficiency of vision transformers from three perspectives: memory access, computation redundancy, and parameter usage. We seek to identify the underlying speed bottlenecks through empirical studies, and summarize useful design guidelines." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.52, + 0.684, + 0.536 + ], + "angle": 0, + "content": "2.1. Memory Efficiency" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.539, + 0.892, + 0.689 + ], + "angle": 0, + "content": "Memory access overhead is a critical factor affecting model speed [15,28,31,65]. Many operators in transformer [71], such as frequent reshaping, element-wise addition, and normalization are memory inefficient, requiring time-consuming access across different memory units, as shown in Fig. 2. Although there are some methods proposed to address this issue by simplifying the computation of standard softmax self-attention, e.g., sparse attention [34,57,61,75] and low-rank approximation [11,51,74], they often come at the cost of accuracy degradation and limited acceleration." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.69, + 0.893, + 0.901 + ], + "angle": 0, + "content": "In this work, we turn to save memory access cost by reducing memory-inefficient layers. Recent studies reveal that memory-inefficient operations are mainly located in MHSA rather than FFN layers [31, 33]. However, most existing ViTs [18, 44, 69] use an equivalent number of these two layers, which may not achieve the optimal efficiency. We thereby explore the optimal allocation of MHSA and FFN layers in small models with fast inference. Specifically, we scale down Swin-T [44] and DeiT-T [69] to several small subnetworks with \\(1.25 \\times\\) and \\(1.5 \\times\\) higher inference throughput, and compare the performance of subnetworks with different proportions of MHSA layers. As shown in Fig. 3, subnetworks with \\(20\\% - 40\\%\\) MHSA layers tend to get better accuracy. Such ratios are much smaller than the" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "14421" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.102, + 0.08, + 0.272, + 0.194 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.276, + 0.08, + 0.442, + 0.194 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.195, + 0.47, + 0.265 + ], + "angle": 0, + "content": "Figure 3. The accuracy of downscaled baseline models with different MHSA layer proportions, where the dots on each line represent subnetworks with similar throughput. Left: Swin-T as the baseline. Right: DeiT-T as the baseline. The \\(1.25 \\times 1.5 \\times\\) denote accelerating the baseline models by 1.25/1.5 times, respectively." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.27, + 0.47, + 0.422 + ], + "angle": 0, + "content": "typical ViTs that adopt \\(50\\%\\) MHSA layers. Furthermore, we measure the time consumption on memory-bound operations to compare memory access efficiency, including reshaping, element-wise addition, copying, and normalization. Memory-bound operations is reduced to \\(44.26\\%\\) of the total runtime in Swin-T-1.25× that has \\(20\\%\\) MHSA layers. The observation also generalizes to DeiT and smaller models with \\(1.5\\times\\) speed-up. It is demonstrated that reducing MHSA layer utilization ratio appropriately can enhance memory efficiency while improving model performance." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.429, + 0.295, + 0.445 + ], + "angle": 0, + "content": "2.2. Computation Efficiency" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.45, + 0.471, + 0.813 + ], + "angle": 0, + "content": "MHSA embeds the input sequence into multiple subspaces (heads) and computes attention maps separately, which has been proven effective in improving performance [18, 69, 71]. However, attention maps are computationally expensive, and studies have shown that a number of them are not of vital importance [52, 73]. To save computation cost, we explore how to reduce redundant attention in small ViT models. We train width downscaled Swin-T [44] and DeiT [69] models with \\(1.25 \\times\\) inference speed-up, and measure the maximum cosine similarity of each head and the remaining heads within each block. From Fig. 4, we observe there exists high similarities between attention heads, especially in the last blocks. The phenomenon suggests that many heads learn similar projections of the same full feature and incur computation redundancy. To explicitly encourage the heads to learn different patterns, we apply an intuitive solution by feeding each head with only a split of the full feature, which is similar to the idea of group convolution in [10, 87]. We train the variants of downscaled models with the modified MHSA, and also compute the attention similarities in Fig. 4. It is shown that using different channel-wise splits of the feature in different heads, instead of using the same full feature for all heads as MHSA, could effectively mitigate attention computation redundancy." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.82, + 0.276, + 0.836 + ], + "angle": 0, + "content": "2.3. Parameter Efficiency" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.469, + 0.902 + ], + "angle": 0, + "content": "Typical ViTs mainly inherit the design strategies from NLP transformer [71], e.g., using an equivalent width for \\( Q, K, V \\) projections, increasing heads over stages, and setting the expansion ratio to 4 in FFN. For lightweight mod" + }, + { + "type": "image", + "bbox": [ + 0.526, + 0.078, + 0.696, + 0.194 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.704, + 0.081, + 0.865, + 0.194 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.195, + 0.892, + 0.263 + ], + "angle": 0, + "content": "Figure 4. The average maximum cosine similarity of each head in different blocks. Left: downscaled Swin-T models. Right: downscaled DeiT-T models. Blue lines denote Swin-T-1.25×/DeiT-T-1.25× model, while darkblue lines denote the variants that feed each head with only a split of the full feature." + }, + { + "type": "image", + "bbox": [ + 0.526, + 0.27, + 0.865, + 0.382 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.383, + 0.892, + 0.424 + ], + "angle": 0, + "content": "Figure 5. The ratio of the channels to the input embeddings before and after pruning Swin-T. Baseline accuracy: \\(79.1\\%\\); pruned accuracy: \\(76.5\\%\\). Results for DeiT-T are given in the supplementary." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.44, + 0.892, + 0.592 + ], + "angle": 0, + "content": "els, the configurations of these components need to be carefully re-designed [7, 8, 39]. Inspired by [45, 82], we adopt Taylor structured pruning [53] to automatically find the important components in Swin-T and DeiT-T, and explore the underlying principles of parameter allocation. The pruning method removes unimportant channels under a certain resource constraint and keeps the most critical ones to best preserve the accuracy. It uses the multiplication of gradient and weight as channel importance, which approximates the loss fluctuation when removing channels [38]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.596, + 0.893, + 0.807 + ], + "angle": 0, + "content": "The ratio between the remaining output channels to the input channels is plotted in Fig. 5, and the original ratios in the unpruned model are also given for reference. It is observed that: 1) The first two stages preserve more dimensions, while the last stage keeps much less; 2) The \\( Q, K \\) and FFN dimensions are largely trimmed, whereas the dimension of \\( V \\) is almost preserved and diminishes only at the last few blocks. These phenomena show that 1) the typical channel configuration, that doubles the channel after each stage [44] or use equivalent channels for all blocks [69], may produce substantial redundancy in last few blocks; 2) The redundancy in \\( Q, K \\) is much larger than \\( V \\) when they have the same dimensions. \\( V \\) prefers a relative large channels, being close to the input embedding dimension." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.827, + 0.765, + 0.843 + ], + "angle": 0, + "content": "3. Efficient Vision Transformer" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.854, + 0.892, + 0.9 + ], + "angle": 0, + "content": "Based upon the above analysis, in this section, we propose a new hierarchical model with fast inference named EfficientViT. The architecture overview is shown in Fig. 6." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "14422" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.157, + 0.075, + 0.818, + 0.423 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.104, + 0.426, + 0.863, + 0.44 + ], + "angle": 0, + "content": "Figure 6. Overview of EfficientViT. (a) Architecture of EfficientViT; (b) Sandwich Layout block; (c) Cascaded Group Attention." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.456, + 0.333, + 0.472 + ], + "angle": 0, + "content": "3.1. EfficientViT Building Blocks" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.48, + 0.468, + 0.57 + ], + "angle": 0, + "content": "We propose a new efficient building block for vision transformer, as shown in Fig. 6 (b). It is composed of a memory-efficient sandwich layout, a cascaded group attention module, and a parameter reallocation strategy, which focus on improving model efficiency in terms of memory, computation, and parameter, respectively." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.57, + 0.468, + 0.672 + ], + "angle": 0, + "content": "Sandwich Layout. To build up a memory-efficient block, we propose a sandwich layout that employs less memory-bound self-attention layers and more memory-efficient FFN layers for channel communication. Specifically, it applies a single self-attention layer \\(\\Phi_i^{\\mathrm{A}}\\) for spatial mixing, which is sandwiched between FFN layers \\(\\Phi_i^{\\mathrm{F}}\\). The computation can be formulated as:" + }, + { + "type": "equation", + "bbox": [ + 0.156, + 0.671, + 0.469, + 0.704 + ], + "angle": 0, + "content": "\\[\nX _ {i + 1} = \\prod^ {\\mathcal {N}} \\Phi_ {i} ^ {\\mathrm {F}} \\left(\\Phi_ {i} ^ {\\mathrm {A}} \\left(\\prod^ {\\mathcal {N}} \\Phi_ {i} ^ {\\mathrm {F}} \\left(X _ {i}\\right)\\right)\\right), \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.704, + 0.468, + 0.856 + ], + "angle": 0, + "content": "where \\( X_{i} \\) is the full input feature for the \\( i \\)-th block. The block transforms \\( X_{i} \\) into \\( X_{i+1} \\) with \\( \\mathcal{N} \\) FFNs before and after the single self-attention layer. This design reduces the memory time consumption caused by self-attention layers in the model, and applies more FFN layers to allow communication between different feature channels efficiently. We also apply an extra token interaction layer before each FFN using a depthwise convolution (DWConv) [27]. It introduces inductive bias of the local structural information to enhance model capability [14]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.468, + 0.901 + ], + "angle": 0, + "content": "Cascaded Group Attention. Attention head redundancy is a severe issue in MHSA, which causes computation inefficiency. Inspired by group convolutions in efficient CNNs" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.456, + 0.892, + 0.532 + ], + "angle": 0, + "content": "[10, 37, 64, 87], we propose a new attention module named cascaded group attention (CGA) for vision transformers. It feeds each head with different splits of the full features, thus explicitly decomposing the attention computation across heads. Formally, this attention can be formulated as:" + }, + { + "type": "equation", + "bbox": [ + 0.561, + 0.535, + 0.892, + 0.562 + ], + "angle": 0, + "content": "\\[\n\\tilde {X} _ {i j} = \\operatorname {A t t n} \\left(X _ {i j} W _ {i j} ^ {\\mathrm {Q}}, X _ {i j} W _ {i j} ^ {\\mathrm {K}}, X _ {i j} W _ {i j} ^ {\\mathrm {V}}\\right), \\tag {2}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.555, + 0.558, + 0.766, + 0.577 + ], + "angle": 0, + "content": "\\[\n\\tilde {X} _ {i + 1} = \\operatorname {C o n c a t} \\left[ \\tilde {X} _ {i j} \\right] _ {j = 1: h} W _ {i} ^ {\\mathrm {P}},\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.58, + 0.892, + 0.688 + ], + "angle": 0, + "content": "where the \\(j\\)-th head computes the self-attention over \\(X_{ij}\\), which is the \\(j\\)-th split of the input feature \\(X_{i}\\), i.e., \\(X_{i} = [X_{i1}, X_{i2}, \\ldots, X_{ih}]\\) and \\(1 \\leq j \\leq h\\). \\(h\\) is the total number of heads, \\(W_{ij}^{\\mathrm{Q}}, W_{ij}^{\\mathrm{K}}\\), and \\(W_{ij}^{\\mathrm{V}}\\) are projection layers mapping the input feature split into different subspaces, and \\(W_{i}^{\\mathrm{P}}\\) is a linear layer that projects the concatenated output features back to the dimension consistent with the input." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.689, + 0.892, + 0.81 + ], + "angle": 0, + "content": "Although using feature splits instead of the full features for each head is more efficient and saves computation overhead, we continue to improve its capacity, by encouraging the \\( Q \\), \\( K \\), \\( V \\) layers to learn projections on features with richer information. We compute the attention map of each head in a cascaded manner, as illustrated in Fig. 6 (c), which adds the output of each head to the subsequent head to refine the feature representations progressively:" + }, + { + "type": "equation", + "bbox": [ + 0.573, + 0.814, + 0.891, + 0.834 + ], + "angle": 0, + "content": "\\[\nX _ {i j} ^ {\\prime} = X _ {i j} + \\widetilde {X} _ {i (j - 1)}, \\quad 1 < j \\leq h, \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.836, + 0.892, + 0.901 + ], + "angle": 0, + "content": "where \\(X_{ij}^{\\prime}\\) is the addition of the \\(j\\)-th input split \\(X_{ij}\\) and the \\((j-1)\\)-th head output \\(\\widetilde{X}_{i(j-1)}\\) calculated by Eq. (2). It replaces \\(X_{ij}\\) to serve as the new input feature for the \\(j\\)-th head when calculating the self-attention. Besides, another token" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "14423" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.095, + 0.08, + 0.451, + 0.093 + ], + "angle": 0, + "content": "Table 1. Architecture details of EfficientViT model variants." + }, + { + "type": "table", + "bbox": [ + 0.097, + 0.094, + 0.447, + 0.197 + ], + "angle": 0, + "content": "
Model{C1,C2,C3}{L1,L2,L3}{H1,H2,H3}
EfficientViT-M0{64,128,192}{1,2,3}{4,4,4}
EfficientViT-M1{128,144,192}{1,2,3}{2,3,3}
EfficientViT-M2{128,192,224}{1,2,3}{4,3,2}
EfficientViT-M3{128,240,320}{1,2,3}{4,3,4}
EfficientViT-M4{128,256,384}{1,2,3}{4,4,4}
EfficientViT-M5{192,288,384}{1,3,4}{3,3,4}
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.202, + 0.47, + 0.248 + ], + "angle": 0, + "content": "interaction layer is applied after the \\(Q\\) projection, which enables the self-attention to jointly capture local and global relations and further enhances the feature representation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.249, + 0.468, + 0.429 + ], + "angle": 0, + "content": "Such a cascaded design enjoys two advantages. First, feeding each head with different feature splits could improve the diversity of attention maps, as validated in Sec. 2.2. Similar to group convolutions [10, 87], the cascaded group attention could save the Flops and parameters by \\( h \\times \\), since the input and output channels in the QKV layers are reduced by \\( h \\times \\). Second, cascading the attention heads allows for an increase of network depth, thus further elevating the model capacity without introducing any extra parameters. It only incurs minor latency overhead since the attention map computation in each head uses smaller QK channel dimensions." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.431, + 0.468, + 0.657 + ], + "angle": 0, + "content": "Parameter Reallocation. To improve parameter efficiency, we reallocate the parameters in the network by expanding the channel width of critical modules while shrinking the unimportant ones. Specifically, based on the Taylor importance analysis in Sec. 2.3, we set small channel dimensions for \\( Q \\) and \\( K \\) projections in each head for all stages. For the \\( V \\) projection, we allow it to have the same dimension as the input embedding. The expansion ratio in FFN is also reduced from 4 to 2 due to its parameter redundancy. With the proposed reallocation strategy, the important modules have larger number of channels to learn representations in a high dimensional space, which prevent the loss of feature information. Meanwhile, the redundant parameters in unimportant modules are removed to speed up inference and enhance the model efficiency." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.668, + 0.388, + 0.683 + ], + "angle": 0, + "content": "3.2. EfficientViT Network Architectures" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.689, + 0.468, + 0.901 + ], + "angle": 0, + "content": "The overall architecture of our EfficientViT is presented in Fig. 6 (a). Concretely, we introduce overlapping patch embedding [20, 80] to embed \\(16 \\times 16\\) patches into tokens with \\(C_1\\) dimension, which enhances the model capacity in low-level visual representation learning. The architecture contains three stages. Each stage stacks the proposed EfficientViT building blocks and the number of tokens is reduced by \\(4 \\times\\) at each subsampling layer (\\(2 \\times\\) subsampling of the resolution). To achieve efficient subsampling, we propose an EfficientViT subsample block which also has the sandwich layout, except that the self-attention layer is replaced by an inverted residual block to reduce the information loss during subsampling [26, 63]. It is worth noting that we adopt BatchNorm (BN) [30] instead of Layer" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.182 + ], + "angle": 0, + "content": "Norm (LN) [2] throughout the model, as BN can be folded into the preceding convolution or linear layers, which is a runtime advantage over LN. We also use ReLU [54] as the activation function, as the commonly used GELU [25] or HardSwish [26] are much slower, and sometimes not well-supported by certain inference deployment platforms [1, 3]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.183, + 0.892, + 0.333 + ], + "angle": 0, + "content": "We build our model family with six different width and depth scales, and set different number of heads for each stage. We use fewer blocks in early stages than late stages similar to MobileNetV3 [26] and LeViT [20], since that the processing on early stages with larger resolutions is more time consuming. We increase the width over stages with a small factor \\((\\leq 2)\\) to alleviate redundancy in later stages, as analyzed in Sec. 2.3. The architecture details of our model family are presented in Tab. 1. \\(C_i\\), \\(L_i\\), and \\(H_i\\) refer to the width, depth, and number of heads in the \\(i\\)-th stage." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.341, + 0.634, + 0.358 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.366, + 0.719, + 0.382 + ], + "angle": 0, + "content": "4.1. Implementation Details" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.387, + 0.892, + 0.765 + ], + "angle": 0, + "content": "We conduct image classification experiments on ImageNet-1K [17]. The models are built with PyTorch 1.11.0 [59] and Timm 0.5.4 [77], and trained from scratch for 300 epochs on 8 Nvidia V100 GPUs using AdamW [46] optimizer and cosine learning rate scheduler. We set the total batchsize as 2,048. The input images are resized and randomly cropped into \\(224 \\times 224\\). The initial learning rate is \\(1 \\times 10^{-3}\\) with weight decay of \\(2.5 \\times 10^{-2}\\). We use the same data augmentation as [69], including Mixup [85], auto-augmentation [13], and random erasing [88]. In addition, we provide throughput evaluation on different hardware. For GPU, we measure the throughput on an Nvidia V100, with the maximum power-of-two batchsize that fits in memory following [20, 69]. For CPU and ONNX, we measure the runtime on an Intel Xeon E5-2690 v4 @ 2.60 GHz processor, with batchsize 16 and run the model in a single thread following [20]. We also test the transferability of EfficientViT on downstream tasks. For the experiments on downstream image classification, we finetune the models for 300 epochs following [86], using AdamW [46] with batchsize 256, learning rate \\(1 \\times 10^{-3}\\) and weight-decay \\(1 \\times 10^{-8}\\). We use RetinaNet [41] for object detection on COCO [42], and train the models for 12 epochs (\\(1 \\times\\) schedule) with the same settings as [44] on mmdetection [6]. For instance segmentation, please refer to the supplementary." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.775, + 0.696, + 0.79 + ], + "angle": 0, + "content": "4.2. Results on ImageNet" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.795, + 0.892, + 0.87 + ], + "angle": 0, + "content": "We compare EfficientViT with prevailing efficient CNN and ViT models on ImageNet [17], and report the results in Tab. 2 and Fig. 1. The results show that, in most cases, our EfficientViT achieves the best accuracy and speed trade-off across different evaluation settings." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.871, + 0.892, + 0.9 + ], + "angle": 0, + "content": "Comparisons with efficient CNNs. We first compare EfficientViT with vanilla CNN models, such as MobileNets" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "14424" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.082, + 0.894, + 0.125 + ], + "angle": 0, + "content": "Table 2. EfficientViT image classification performance on ImageNet-1K [17] with comparisons to state-of-the-art efficient CNN and ViT models trained without extra data. Throughput is tested on Nvidia V100 for GPU and Intel Xeon E5-2690 v4 @ 2.60 GHz processor for CPU and ONNX, where larger throughput means faster inference speed. ↑: finetune with higher resolution." + }, + { + "type": "table", + "bbox": [ + 0.143, + 0.125, + 0.828, + 0.548 + ], + "angle": 0, + "content": "
ModelTop-1 (%)Top-5 (%)Throughput (images/s)Flops (M)Params (M)InputEpochs
GPUCPUONNX
EfficientViT-M063.285.427644228.4340.1792.3224300
MobileNetV3-Small [26]67.4-19738156.5231.7572.5224600
EfficientViT-M168.488.720093126.9215.91673.0224300
Mobile-Former-52M [9]68.7-314132.821.5523.5224450
MobileViT-XXS [50]69.0-445629.441.74101.3256300
ShuffleNetV2 1.0× [48]69.488.913301106.7177.01462.3224300
MobileViTV2-0.5 [51]70.2-514234.444.94661.4256300
EfficientViT-M270.890.218218121.2158.72014.2224300
MobileOne-S0 [70]71.4-1132067.4128.62742.1224300
MobileNetV2 1.0× [63]72.091.0653432.580.43003.4224300
EfficientViT-M373.491.41664496.4120.82636.9224300
GhostNet 1.0× [23]73.991.4738257.377.01415.2224300
NASNet-A-Mobile [89]74.1-262319.825.55645.3224300
EfficientViT-M474.391.81591488.5108.62998.8224300
EdgeViT-XXS [56]74.4-363828.229.65564.1224300
MobileViT-XS [50]74.7-334411.120.59862.3256300
ShuffleNetV2 2.0× [48]74.992.4696237.952.35917.4224300
MobileNetV3-Large [26]75.2-756039.170.52175.4224600
MobileViTV2-0.75 [51]75.6-335016.022.710302.9256300
MobileOne-S1 [70]75.9-666330.751.18254.8224300
GLiT-Tiny [5]76.4-351617.515.713337.3224300
EfficientNet-B0 [67]77.193.3453230.229.53905.3224350
EfficientViT-M577.193.41062156.862.552212.4224300
EfficientViT-M4↑38479.895.0398615.822.6148612.4384330
EfficientViT-M5↑51280.895.523138.310.5267012.4512360
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.566, + 0.473, + 0.809 + ], + "angle": 0, + "content": "[26, 63] and EfficientNet [67]. Specifically, compared to MobileNetV2 \\(1.0 \\times\\) [63], EfficientViT-M3 obtains \\(1.4\\%\\) better top-1 accuracy, while running at \\(2.5 \\times\\) and \\(3.0 \\times\\) faster speed on V100 GPU and Intel CPU, respectively. Compared to the state-of-the-art MobileNetV3-Large [26], EfficientViT-M5 achieves \\(1.9\\%\\) higher accuracy yet runs much faster, e.g., \\(40.5\\%\\) faster on the V100 GPU and \\(45.2\\%\\) faster on the Intel CPU but is \\(11.5\\%\\) slower as ONNX models. This may because reshaping is slower in ONNX implementation, which is inevitable in computing self-attention. Moreover, EfficientViT-M5 achieves comparable accuracy with the searched model EfficientNet-B0 [67], while runs \\(2.3 \\times / 1.9 \\times\\) faster on the V100 GPU/Intel CPU, and \\(2.1 \\times\\) faster as ONNX models. Although our model uses more parameters, it reduces memory-inefficient operations that affect the inference speed and achieves higher throughput." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.811, + 0.472, + 0.902 + ], + "angle": 0, + "content": "Comparisons with efficient ViTs. We also compare our models with recent efficient vision transformers [5, 9, 50, 51, 56] in Tab. 2. In particular, when getting similar performance on ImageNet-1K [17], our EfficientViT-M4 runs \\(4.4 \\times\\) and \\(3.0 \\times\\) faster than the recent EdgeViT-XXS [56] on the tested CPU and GPU devices. Even converted to ONNX" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.566, + 0.892, + 0.763 + ], + "angle": 0, + "content": "runtime format, our model still gets \\(3.7 \\times\\) higher speed. Compared to the state-of-the-art MobileViTV2-0.5 [51], our EfficientViT-M2 achieves slightly better performance with higher throughput, e.g., \\(3.4 \\times\\) and \\(3.5 \\times\\) higher throughput tested on the GPU and CPU devices, respectively. Furthermore, we compare with tiny variants of state-of-the-art large ViTs in Tab. 3. PoolFormer-12S [83] has comparable accuracy with EfficientViT-M5 yet runs \\(3.0 \\times\\) slower on the V100 GPU. Compared to Swin-T [44], EfficientViT-M5 is \\(4.1\\%\\) inferior in accuracy yet is \\(12.3 \\times\\) faster on the Intel CPU, demonstrating the efficiency of the proposed design. In addition, we present the speed evaluation and comparison on mobile chipsets in the supplementary material." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Finetune with higher resolutions. Recent works on ViTs have demonstrated that finetuning with higher resolutions can further improve the capacity of the models. We also finetune our largest model EfficientViT-M5 to higher resolutions. EfficientViT-M5↑384 reaches 79.8% top-1 accuracy with throughput of 3,986 images/s on the V100 GPU, and EfficientViT-M5↑512 further improves the top-1 accuracy to 80.8%, demonstrating the efficiency on processing images with larger resolutions and the good model capacity." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "14425" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.082, + 0.47, + 0.11 + ], + "angle": 0, + "content": "Table 3. Comparison with the tiny variants of state-of-the-art large-scale ViTs on ImageNet-1K [17]." + }, + { + "type": "table", + "bbox": [ + 0.086, + 0.112, + 0.46, + 0.228 + ], + "angle": 0, + "content": "
ModelTop-1 (%)Throughput (imgs/s)Flops (G)Params (M)
GPUCPUONNX
PVTV2-B0 [76]70.5350712.718.50.61.4
T2T-ViT-7 [84]71.7115622.516.11.14.3
DeiT-T [69]72.2463126.025.11.35.9
PoolFormer-12S [83]77.2353410.414.61.912.0
EffFormer-L1 [40]79.2446512.921.21.312.3
Swin-T [44]81.213934.66.44.529.0
EfficientViT-M577.11062156.862.50.512.4
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.232, + 0.468, + 0.258 + ], + "angle": 0, + "content": "Table 4. Results of EfficientViT and other efficient models on downstream image classification datasets." + }, + { + "type": "table", + "bbox": [ + 0.086, + 0.261, + 0.462, + 0.382 + ], + "angle": 0, + "content": "
ModelThroughputImageNetCIFAR10CIFAR100CarsFlowersPets
MobileNetV1 [27]854370.696.182.391.496.789.9
MobileNetV2 [63]653472.995.780.891.096.690.5
MobileNetV3 [26]756075.297.685.591.297.090.1
NASNet-A-M [89]262374.196.883.988.596.889.4
ViT-S/16 [18]213581.497.685.7-86.490.4
EfficientViT-M51062177.198.086.489.797.192.0
" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.39, + 0.317, + 0.405 + ], + "angle": 0, + "content": "4.3. Transfer Learning Results" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.411, + 0.468, + 0.44 + ], + "angle": 0, + "content": "To further evaluate the transfer ability, we apply EfficientViT on various downstream tasks." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.442, + 0.468, + 0.622 + ], + "angle": 0, + "content": "Downstream Image Classification. We transfer EfficientViT to downstream image classification datasets to test its generalization ability: 1) CIFAR-10 and CIFAR-100 [36]; 2) fine-grained classification: Flowers [55], Stanford Cars [35], and Oxford-IIIT Pets [58]. We report the results in Tab. 4. Compared to existing efficient models [18, 26, 27, 63, 89], our EfficientViT-M5 achieves comparable or slightly better accuracy across all datasets with much higher throughput. An exception lies in Cars, where our model is slightly inferior in accuracy. This may because the subtle differences between classes lie more in local details thus is more feasible to be captured with convolution." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.624, + 0.468, + 0.744 + ], + "angle": 0, + "content": "Object Detection. We compare EfficientViT-M4 with efficient models [12, 22, 26, 63, 66, 68] on the COCO [42] object detection task, and present the results in Tab. 5. Specifically, EfficientViT-M4 surpasses MobileNetV2 [63] by \\(4.4\\%\\) AP with comparable Flops. Compared to the searched method SPOS [22], our EfficientViT-M4 uses \\(18.1\\%\\) fewer Flops while achieving \\(2.0\\%\\) higher AP, demonstrating its capacity and generalization ability in different vision tasks." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.756, + 0.229, + 0.772 + ], + "angle": 0, + "content": "4.4. Ablation Study" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.779, + 0.468, + 0.84 + ], + "angle": 0, + "content": "In this section, we ablate important design elements in the proposed EfficientViT on ImageNet-1K [17]. All models are trained for 100 epochs to magnify the differences and reduce training time [20]. Tab. 6 reports the results." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.841, + 0.468, + 0.901 + ], + "angle": 0, + "content": "Impact of the sandwich layout block. We first present an ablation study to verify the efficiency of the proposed sandwich layout design, by replacing the sandwich layout block with the original Swin block [44]. The depth is adjusted to" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.082, + 0.892, + 0.11 + ], + "angle": 0, + "content": "Table 5. EfficientViT object detection performance on COCOval2017 [42] with comparisons to other efficient models." + }, + { + "type": "table", + "bbox": [ + 0.513, + 0.112, + 0.88, + 0.232 + ], + "angle": 0, + "content": "
ModelRetinaNet 1×FlopsParams
APAP50AP75APsAPmAPl(M)(M)
MobileNetV2 [63]28.346.729.314.830.738.13003.4
MobileNetV3 [26]29.949.330.814.933.341.12175.4
SPOS [22]30.749.832.215.433.941.63654.3
MNASNet-A2 [66]30.550.232.016.634.141.13404.8
FairNAS-C [12]31.250.832.716.334.442.33255.6
MixNet-M [68]31.351.732.417.035.041.93605.0
EfficientViT-M432.752.234.117.635.346.02998.8
" + }, + { + "type": "table_caption", + "bbox": [ + 0.5, + 0.236, + 0.892, + 0.265 + ], + "angle": 0, + "content": "Table 6. Ablation for EfficientViT-M4 on ImageNet-1K [17] dataset. Top-1 accuracy, GPU and ONNX throughput are reported." + }, + { + "type": "table", + "bbox": [ + 0.519, + 0.268, + 0.875, + 0.455 + ], + "angle": 0, + "content": "
#AblationTop-1 (%)Throughput (imgs/s)
GPUONNX
1EfficientViT-M471.315914108.6
2Sandwich → Swin [44]68.315804114.5
3N = 1 → 270.214977112.3
4N = 1 → 365.715856139.7
5CGA → MHSA [18]70.216243102.2
6Cascade → None69.816411111.0
7QKV allocation → None69.915132103.1
8FFN ratio 2 → 469.815310112.4
9DWConv → None69.916325110.4
10BN → LN [2]70.415463103.6
11ReLU → HSwish [26]72.21588787.5
" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.46, + 0.892, + 0.626 + ], + "angle": 0, + "content": "\\(\\{2, 2, 3\\}\\) to guarantee similar throughput with EfficientViTM4 for a fair comparison. The top-1 accuracy degrades by \\(3.0\\%\\) at a similar speed, verifying that applying more FFNs instead of memory-bound MHSA is more effective for small models. Furthermore, to analyze the impact of the number of FFNs \\(\\mathcal{N}\\) before and after self-attention, we change the number from 1 to 2 and 3. The number of blocks is reduced accordingly to maintain similar throughput. As presented in Tab. 6 (#3 and #4), further increasing the number of FFNs is not effective due to the lack of long-range spatial relation and \\(\\mathcal{N} = 1\\) achieves the best efficiency." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.628, + 0.892, + 0.763 + ], + "angle": 0, + "content": "Impact of the cascaded group attention. We have proposed CGA to improve the computation efficiency of MHSA. As shown in Tab. 6 (#5 and #6), replacing CGA with MHSA decreases the accuracy by \\(1.1\\%\\) and ONNX speed by \\(5.9\\%\\), suggesting that addressing head redundancy improves the model efficiency. For the model without the cascade operation, its performance is comparable with MHSA but worse than CGA, demonstrating the efficacy of enhancing the feature representations of each head." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Impact of the parameter reallocation. Our EfficientViTM4 yields \\(1.4\\% / 1.5\\%\\) higher top-1 accuracy, \\(4.9\\% / 3.8\\%\\) higher GPU throughput than the models without QKV channel dimension reallocation or FFN ratio reduction, respectively, indicating the effectiveness of parameter reallocation (#1 vs. #7, #8). Moreover, we study the choices of QK dimension in each head and the ratio of V dimension to the input embedding in Fig. 7. It is shown that the performance is improved gradually as QK dimension increases" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "14426" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.081, + 0.47, + 0.121 + ], + "angle": 0, + "content": "Table 7. Performance comparison on ImageNet-1K [17] and ImageNet-ReaL [4]. Results with \\(\\dagger\\) are trained with 1,000 epochs and knowledge distillation following LeViT [20]." + }, + { + "type": "table", + "bbox": [ + 0.085, + 0.122, + 0.462, + 0.184 + ], + "angle": 0, + "content": "
ModelImageNet (%)Throughput (imgs/s)Flops Params
Top-1Top-1†RealL†GPUCPUONNX(M)(M)
LeViT-128S [20]73.676.682.61445782.380.93057.8
EfficientViT-M474.377.183.61591488.5108.62998.8
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.191, + 0.468, + 0.311 + ], + "angle": 0, + "content": "from 4 to 16, while further increasing it gives inferior performance. Besides, the performance improves from \\(70.3\\%\\) to \\(71.3\\%\\) when increasing the ratio between \\(V\\) dimension and input embedding from 0.4 to 1.0. When further enlarging the ratio to 1.2, it only gets \\(0.1\\%\\) improvements. Therefore, setting the channels of \\(V\\) close to the input embedding achieves the best parameter efficiency, which meets our analysis in Sec. 2.3 and design strategy." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.312, + 0.468, + 0.506 + ], + "angle": 0, + "content": "Impact of other components. We ablate the impact of using DWConv for token interaction, the normalization layer, and the activation function, as presented in Tab. 6 (#9, #10, and #11). With DWConv, the accuracy improves by \\(1.4\\%\\) with a minor latency overhead, demonstrating the effectiveness of introducing local structural information. Replacing BN with LN decreases accuracy by \\(0.9\\%\\) and GPU speed by \\(2.9\\%\\). Using HardSwish instead of ReLU improves accuracy by \\(0.9\\%\\) but leads to a large drop of \\(20.0\\%\\) ONNX speed. The activation functions are element-wise operations that occupy a considerable amount of processing time on GPU/CPU [15,48,72], thus utilizing ReLU instead of more complicated activation functions is of better efficiency." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.508, + 0.468, + 0.675 + ], + "angle": 0, + "content": "Results of 1,000 training epochs and distillation. Tab. 7 shows the results with 1,000 training epochs and knowledge distillation using RegNetY-16GF [60] as the teacher model following [20] on ImageNet-1K [17] and ImageNet-ReaL [4]. Compared to LeViT-128S [20], EfficientViT-M4 surpasses it by \\(0.5\\%\\) on ImageNet-1K and \\(1.0\\%\\) on ImageNet-ReaL, respectively. For the inference speed, our model has \\(34.2\\%\\) higher throughput on ONNX and also shows superiority on other settings. The results demonstrate that the strong capability and generalization ability of EfficientViT can be further explored with longer training schedules." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.682, + 0.219, + 0.697 + ], + "angle": 0, + "content": "5. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.704, + 0.468, + 0.901 + ], + "angle": 0, + "content": "Efficient CNNs. With the demand of deploying CNNs on resource-constrained scenarios, efficient CNNs have been intensively studied in literature [23, 24, 26, 48, 63, 67, 87]. Xception [10] proposes an architecture built with depthwise separable convolutions. MobileNetV2 [63] builds an inverted residual structure which expands the input to a higher dimension. MobileNetV3 [26] and EfficientNet [67] resort to neural architecture search techniques to design compact models. To boost the actual speed on hardware, ShuffleNetV2 [48] introduces channel split and shuffle operations to improve the information communication among channel groups. However, the spatial locality of convolutional kernels hampers CNN models from capturing long-" + }, + { + "type": "image", + "bbox": [ + 0.505, + 0.077, + 0.69, + 0.139 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.692, + 0.077, + 0.883, + 0.14 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.5, + 0.14, + 0.892, + 0.167 + ], + "angle": 0, + "content": "Figure 7. Ablation on the \\( QK \\) dimension of each head and the ratio of \\( V \\) dimension to the input embedding." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.175, + 0.864, + 0.19 + ], + "angle": 0, + "content": "range dependencies, thus limiting their model capacity." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.191, + 0.892, + 0.553 + ], + "angle": 0, + "content": "Efficient ViTs. ViT and its variants [18, 44, 69, 76] have achieved success on various vision tasks. Despite the superior performance, most of them are inferior to typical CNNs in inference speed. Some efficient transformers have been proposed recently and they fall into two camps: 1) efficient self-attention; and 2) efficient architecture design. Efficient self-attention methods reduce the cost of softmax attention via sparse attention [34, 57, 61, 75] or low-rank approximation [11, 51, 74]. However, they suffer from performance degradation with negligible or moderate inference acceleration over softmax attention [71]. Another line of work combines ViTs with lightweight CNNs to build efficient architectures [9, 47, 49, 50, 81]. LVT [81] proposes enhanced attention mechanisms with dilated convolution to improve the model performance and efficiency. Mobile-Former [9] designs a parallel CNN-transformer block to encode both local features and global interaction. However, most of them target at minimizing Flops and parameters [16], which could have low correlations with actual inference latency [70] and still inferior to efficient CNNs in speed. Different from them, we explore models with fast inference by directly optimizing their throughput on different hardware and deployment settings, and design a family of hierarchical models with a good trade-off between speed and accuracy." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.562, + 0.619, + 0.577 + ], + "angle": 0, + "content": "6. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.583, + 0.891, + 0.701 + ], + "angle": 0, + "content": "In this paper, we have presented a systematic analysis on the factors that affect the inference speed of vision transformers, and proposed a new family of fast vision transformers with memory-efficient operations and cascaded group attention, named EfficientViT. Extensive experiments have demonstrated the efficacy and high speed of EfficientViT, and also show its superiority on various downstream benchmarks." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.704, + 0.892, + 0.84 + ], + "angle": 0, + "content": "Limitations. One limitation of EfficientViT is that, despite its high inference speed, the model size is slightly larger compared to state-of-the-art efficient CNN [26] due to the extra FFNs in the introduced sandwich layout. Besides, our models are designed manually based on the derived guidelines on building efficient vision transformers. In future work, we are interested in reducing the model size and incorporating automatic search techniques to further enhance the model capacity and efficiency." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Acknowledgement. Prof. Yuan was partially supported by Hong Kong Research Grants Council (RGC) General Research Fund 11211221, and Innovation and Technology Commission-Innovation and Technology Fund ITS/100/20." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "14427" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.115, + 0.468, + 0.155 + ], + "angle": 0, + "content": "[1] Apple. Coremltools: Use coremltools to convert machine learning models from third-party libraries to the core ml format, 2021. 2, 5" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.157, + 0.468, + 0.185 + ], + "angle": 0, + "content": "[2] Jimmy Lei Ba, Jamie Ryan Kiros, and Geoffrey E Hinton. 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In CVPR, pages 8697-8710, 2018. 6, 7" + }, + { + "type": "list", + "bbox": [ + 0.503, + 0.092, + 0.892, + 0.377 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "14430" + } + ] +] \ No newline at end of file diff --git a/2023/EfficientViT_ Memory Efficient Vision Transformer With Cascaded Group Attention/351f9dba-430a-462e-86ab-2879d7f983dd_origin.pdf b/2023/EfficientViT_ Memory Efficient Vision Transformer With Cascaded Group Attention/351f9dba-430a-462e-86ab-2879d7f983dd_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..d25cbfa839b2dbe48beda804ef298a416f905ca8 --- /dev/null +++ b/2023/EfficientViT_ Memory Efficient Vision Transformer With Cascaded Group Attention/351f9dba-430a-462e-86ab-2879d7f983dd_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:55ca27bec7d805cac60cce92f868a22214c18fe12342cc4750c78644e8c59554 +size 5514245 diff --git a/2023/EfficientViT_ Memory Efficient Vision Transformer With Cascaded Group Attention/full.md b/2023/EfficientViT_ Memory Efficient Vision Transformer With Cascaded Group Attention/full.md new file mode 100644 index 0000000000000000000000000000000000000000..94060ff748d9317ea0d7bcdf6178be96e3e5b4a7 --- /dev/null +++ b/2023/EfficientViT_ Memory Efficient Vision Transformer With Cascaded Group Attention/full.md @@ -0,0 +1,327 @@ +# EfficientViT: Memory Efficient Vision Transformer with Cascaded Group Attention + +Xinyu Liu $^{1,\ast}$ , Houwen Peng $^{2}$ , Ningxin Zheng $^{2}$ , Yuqing Yang $^{2}$ , Han Hu $^{2}$ , Yixuan Yuan $^{1}$ $^{1}$ The Chinese University of Hong Kong, $^{2}$ Microsoft Research + +1155195604@link.cuhk.edu.hk, {houwen.peng, ningxin.zheng, yuqing.yang, hanhu} @microsoft.com, yxyuan@ee.cuhk.edu.hk + +# Abstract + +Vision transformers have shown great success due to their high model capabilities. However, their remarkable performance is accompanied by heavy computation costs, which makes them unsuitable for real-time applications. In this paper, we propose a family of high-speed vision transformers named EfficientViT. We find that the speed of existing transformer models is commonly bounded by memory inefficient operations, especially the tensor reshaping and element-wise functions in MHSA. Therefore, we design a new building block with a sandwich layout, i.e., using a single memory-bound MHSA between efficient FFN layers, which improves memory efficiency while enhancing channel communication. Moreover, we discover that the attention maps share high similarities across heads, leading to computational redundancy. To address this, we present a cascaded group attention module feeding attention heads with different splits of the full feature, which not only saves computation cost but also improves attention diversity. Comprehensive experiments demonstrate EfficientViT outperforms existing efficient models, striking a good trade-off between speed and accuracy. For instance, our EfficientViT-M5 surpasses MobileNetV3-Large by $1.9\%$ in accuracy, while getting $40.4\%$ and $45.2\%$ higher throughput on Nvidia V100 GPU and Intel Xeon CPU, respectively. Compared to the recent efficient model MobileViT-XXS, EfficientViT-M2 achieves $1.8\%$ superior accuracy, while running $5.8 \times / 3.7 \times$ faster on the GPU/CPU, and $7.4 \times$ faster when converted to ONNX format. Code and models are available at here. + +# 1. Introduction + +Vision Transformers (ViTs) have taken computer vision domain by storm due to their high model capabilities and superior performance [18,44,69]. However, the constantly improved accuracy comes at the cost of increasing model sizes and computation overhead. For example, SwinV2 [43] uses 3.0B parameters, while V-MoE [62] taking 14.7B parameters, to achieve state-of-the-art performance on Ima + +![](images/b8fceb61ddd0ee7e9f113af2288b31dec9923c12b1740b9f87114187be953262.jpg) +Figure 1. Speed and accuracy comparisons between EfficientViT (Ours) and other efficient CNN and ViT models tested on an Nvidia V100 GPU with ImageNet-1K dataset [17]. + +geNet [17]. Such large model sizes and the accompanying heavy computational costs make these models unsuitable for applications with real-time requirements [40, 78, 86]. + +There are several recent works designing light and efficient vision transformer models [9, 19, 29, 49, 50, 56, 79, 81]. Unfortunately, most of these methods aim to reduce model parameters or Flops, which are indirect metrics for speed and do not reflect the actual inference throughput of models. For example, MobileViT-XS [50] using 700M Flops runs much slower than DeiT-T [69] with 1,220M Flops on an Nvidia V100 GPU. Although these methods have achieved good performance with fewer Flops or parameters, many of them do not show significant wall-clock speedup against standard isomorphic or hierarchical transformers, e.g., DeiT [69] and Swin [44], and have not gained wide adoption. + +To address this issue, in this paper, we explore how to go faster with vision transformers, seeking to find principles for designing efficient transformer architectures. Based on the prevailing vision transformers DeiT [69] and Swin [44], we systematically analyze three main factors that affect model inference speed, including memory access, computation redundancy, and parameter usage. In particular, we find that the speed of transformer models is commonly memory-bound. In other words, memory accessing delay prohibits the full utilization of the computing power in GPU/CPUs [21, 32, 72], leading to a critically negative impact on the runtime speed of transformers [15, 31]. The + +most memory-inefficient operations are the frequent tensor reshaping and element-wise functions in multi-head self-attention (MHSA). We observe that through an appropriate adjustment of the ratio between MHSA and FFN (feedforward network) layers, the memory access time can be reduced significantly without compromising the performance. Moreover, we find that some attention heads tend to learn similar linear projections, resulting in redundancy in attention maps. The analysis shows that explicitly decomposing the computation of each head by feeding them with diverse features can mitigate this issue while improving computation efficiency. In addition, the parameter allocation in different modules is often overlooked by existing lightweight models, as they mainly follow the configurations in standard transformer models [44,69]. To improve parameter efficiency, we use structured pruning [45] to identify the most important network components, and summarize empirical guidance of parameter reallocation for model acceleration. + +Based upon the analysis and findings, we propose a new family of memory efficient transformer models named EfficientViT. Specifically, we design a new block with a sandwich layout to build up the model. The sandwich layout block applies a single memory-bound MHSA layer between FFN layers. It reduces the time cost caused by memory-bound operations in MHSA, and applies more FFN layers to allow communication between different channels, which is more memory efficient. Then, we propose a new cascaded group attention (CGA) module to improve computation efficiency. The core idea is to enhance the diversity of the features fed into the attention heads. In contrast to prior self-attention using the same feature for all heads, CGA feeds each head with different input splits and cascades the output features across heads. This module not only reduces the computation redundancy in multi-head attention, but also elevates model capacity by increasing network depth. Last but not least, we redistribute parameters through expanding the channel width of critical network components such as value projections, while shrinking the ones with lower importance like hidden dimensions in FFNs. This reallocation finally promotes model parameter efficiency. + +Experiments demonstrate that our models achieve clear improvements over existing efficient CNN and ViT models in terms of both speed and accuracy, as shown in Fig. 1. For instance, our EfficientViT-M5 gets $77.1\%$ top-1 accuracy on ImageNet with throughput of 10,621 images/s on an Nvidia V100 GPU and 56.8 images/s on an Intel Xeon E5-2690 v4 CPU @ 2.60GHz, outperforming MobileNetV3-Large [26] by $1.9\%$ in accuracy, $40.4\%$ in GPU inference speed, and $45.2\%$ in CPU speed. Moreover, EfficientViTM2 gets $70.8\%$ accuracy, surpassing MobileViT-XXS [50] by $1.8\%$ , while running $5.8 \times / 3.7 \times$ faster on the GPU/CPU, and $7.4 \times$ faster when converted to ONNX [3] format. When deployed on the mobile chipset, i.e., Apple A13 Bionic chip + +![](images/544c2b317b436b9974bef96ad7da65cabc5d5665652df3322c8867d911e0acf5.jpg) +Figure 2. Runtime profiling on two standard vision transformers Swin-T and DeiT-T. Red text denotes memory-bound operations, i.e., the time taken by the operation is mainly determined by memory accesses, while time spent in computation is much smaller. + +![](images/53d1435c2cbdca9f0236c1f53b980dd492a99f30c1af19a0d8fee42ab3141bd9.jpg) +Tensor Multiplication Reshape Normalization Copy Addition Others + +in iPhone 11, EfficientViT-M2 model runs $2.3 \times$ faster than MobileViT-XXS [50] using the CoreML [1]. + +In summary, the contributions of this work are two-fold: + +- We present a systematic analysis on the factors that affect the inference speed of vision transformers, deriving a set of guidelines for efficient model design. +- We design a new family of vision transformer models, which strike a good trade-off between efficiency and accuracy. The models also demonstrate good transfer ability on a variety of downstream tasks. + +# 2. Going Faster with Vision Transformers + +In this section, we explore how to improve the efficiency of vision transformers from three perspectives: memory access, computation redundancy, and parameter usage. We seek to identify the underlying speed bottlenecks through empirical studies, and summarize useful design guidelines. + +# 2.1. Memory Efficiency + +Memory access overhead is a critical factor affecting model speed [15,28,31,65]. Many operators in transformer [71], such as frequent reshaping, element-wise addition, and normalization are memory inefficient, requiring time-consuming access across different memory units, as shown in Fig. 2. Although there are some methods proposed to address this issue by simplifying the computation of standard softmax self-attention, e.g., sparse attention [34,57,61,75] and low-rank approximation [11,51,74], they often come at the cost of accuracy degradation and limited acceleration. + +In this work, we turn to save memory access cost by reducing memory-inefficient layers. Recent studies reveal that memory-inefficient operations are mainly located in MHSA rather than FFN layers [31, 33]. However, most existing ViTs [18, 44, 69] use an equivalent number of these two layers, which may not achieve the optimal efficiency. We thereby explore the optimal allocation of MHSA and FFN layers in small models with fast inference. Specifically, we scale down Swin-T [44] and DeiT-T [69] to several small subnetworks with $1.25 \times$ and $1.5 \times$ higher inference throughput, and compare the performance of subnetworks with different proportions of MHSA layers. As shown in Fig. 3, subnetworks with $20\% - 40\%$ MHSA layers tend to get better accuracy. Such ratios are much smaller than the + +![](images/9b6c96320c6ac8bd76c81eaaf1b8c3d1019c0312dcaec7c35b2b6b9b76bbbe00.jpg) +Figure 3. The accuracy of downscaled baseline models with different MHSA layer proportions, where the dots on each line represent subnetworks with similar throughput. Left: Swin-T as the baseline. Right: DeiT-T as the baseline. The $1.25 \times 1.5 \times$ denote accelerating the baseline models by 1.25/1.5 times, respectively. + +![](images/65c10f493d8f0d2071970e226d4269ec2e18842b47ace7afc3361cbac6bbc6b1.jpg) + +typical ViTs that adopt $50\%$ MHSA layers. Furthermore, we measure the time consumption on memory-bound operations to compare memory access efficiency, including reshaping, element-wise addition, copying, and normalization. Memory-bound operations is reduced to $44.26\%$ of the total runtime in Swin-T-1.25× that has $20\%$ MHSA layers. The observation also generalizes to DeiT and smaller models with $1.5\times$ speed-up. It is demonstrated that reducing MHSA layer utilization ratio appropriately can enhance memory efficiency while improving model performance. + +# 2.2. Computation Efficiency + +MHSA embeds the input sequence into multiple subspaces (heads) and computes attention maps separately, which has been proven effective in improving performance [18, 69, 71]. However, attention maps are computationally expensive, and studies have shown that a number of them are not of vital importance [52, 73]. To save computation cost, we explore how to reduce redundant attention in small ViT models. We train width downscaled Swin-T [44] and DeiT [69] models with $1.25 \times$ inference speed-up, and measure the maximum cosine similarity of each head and the remaining heads within each block. From Fig. 4, we observe there exists high similarities between attention heads, especially in the last blocks. The phenomenon suggests that many heads learn similar projections of the same full feature and incur computation redundancy. To explicitly encourage the heads to learn different patterns, we apply an intuitive solution by feeding each head with only a split of the full feature, which is similar to the idea of group convolution in [10, 87]. We train the variants of downscaled models with the modified MHSA, and also compute the attention similarities in Fig. 4. It is shown that using different channel-wise splits of the feature in different heads, instead of using the same full feature for all heads as MHSA, could effectively mitigate attention computation redundancy. + +# 2.3. Parameter Efficiency + +Typical ViTs mainly inherit the design strategies from NLP transformer [71], e.g., using an equivalent width for $Q, K, V$ projections, increasing heads over stages, and setting the expansion ratio to 4 in FFN. For lightweight mod + +![](images/ba13c9b27405e85559599ff09a1eb315a0e999245dc7d9d3670d305c0be893f8.jpg) +Figure 4. The average maximum cosine similarity of each head in different blocks. Left: downscaled Swin-T models. Right: downscaled DeiT-T models. Blue lines denote Swin-T-1.25×/DeiT-T-1.25× model, while darkblue lines denote the variants that feed each head with only a split of the full feature. + +![](images/ebbd6c782e99ca4b3eb212632c46e4496c1ad7e60a52dd8beba8750619cd66ed.jpg) + +![](images/331e779be23bf82137a11dff3fbbf9d93bfbffab83d14f594ab9a36791e4b2e8.jpg) +Figure 5. The ratio of the channels to the input embeddings before and after pruning Swin-T. Baseline accuracy: $79.1\%$ ; pruned accuracy: $76.5\%$ . Results for DeiT-T are given in the supplementary. + +els, the configurations of these components need to be carefully re-designed [7, 8, 39]. Inspired by [45, 82], we adopt Taylor structured pruning [53] to automatically find the important components in Swin-T and DeiT-T, and explore the underlying principles of parameter allocation. The pruning method removes unimportant channels under a certain resource constraint and keeps the most critical ones to best preserve the accuracy. It uses the multiplication of gradient and weight as channel importance, which approximates the loss fluctuation when removing channels [38]. + +The ratio between the remaining output channels to the input channels is plotted in Fig. 5, and the original ratios in the unpruned model are also given for reference. It is observed that: 1) The first two stages preserve more dimensions, while the last stage keeps much less; 2) The $Q, K$ and FFN dimensions are largely trimmed, whereas the dimension of $V$ is almost preserved and diminishes only at the last few blocks. These phenomena show that 1) the typical channel configuration, that doubles the channel after each stage [44] or use equivalent channels for all blocks [69], may produce substantial redundancy in last few blocks; 2) The redundancy in $Q, K$ is much larger than $V$ when they have the same dimensions. $V$ prefers a relative large channels, being close to the input embedding dimension. + +# 3. Efficient Vision Transformer + +Based upon the above analysis, in this section, we propose a new hierarchical model with fast inference named EfficientViT. The architecture overview is shown in Fig. 6. + +![](images/c37d84c7fb2098ae31f4f984cc68eca0ae171dc409c5370ae2486d34015be964.jpg) +Figure 6. Overview of EfficientViT. (a) Architecture of EfficientViT; (b) Sandwich Layout block; (c) Cascaded Group Attention. + +# 3.1. EfficientViT Building Blocks + +We propose a new efficient building block for vision transformer, as shown in Fig. 6 (b). It is composed of a memory-efficient sandwich layout, a cascaded group attention module, and a parameter reallocation strategy, which focus on improving model efficiency in terms of memory, computation, and parameter, respectively. + +Sandwich Layout. To build up a memory-efficient block, we propose a sandwich layout that employs less memory-bound self-attention layers and more memory-efficient FFN layers for channel communication. Specifically, it applies a single self-attention layer $\Phi_i^{\mathrm{A}}$ for spatial mixing, which is sandwiched between FFN layers $\Phi_i^{\mathrm{F}}$ . The computation can be formulated as: + +$$ +X _ {i + 1} = \prod^ {\mathcal {N}} \Phi_ {i} ^ {\mathrm {F}} \left(\Phi_ {i} ^ {\mathrm {A}} \left(\prod^ {\mathcal {N}} \Phi_ {i} ^ {\mathrm {F}} \left(X _ {i}\right)\right)\right), \tag {1} +$$ + +where $X_{i}$ is the full input feature for the $i$ -th block. The block transforms $X_{i}$ into $X_{i+1}$ with $\mathcal{N}$ FFNs before and after the single self-attention layer. This design reduces the memory time consumption caused by self-attention layers in the model, and applies more FFN layers to allow communication between different feature channels efficiently. We also apply an extra token interaction layer before each FFN using a depthwise convolution (DWConv) [27]. It introduces inductive bias of the local structural information to enhance model capability [14]. + +Cascaded Group Attention. Attention head redundancy is a severe issue in MHSA, which causes computation inefficiency. Inspired by group convolutions in efficient CNNs + +[10, 37, 64, 87], we propose a new attention module named cascaded group attention (CGA) for vision transformers. It feeds each head with different splits of the full features, thus explicitly decomposing the attention computation across heads. Formally, this attention can be formulated as: + +$$ +\tilde {X} _ {i j} = \operatorname {A t t n} \left(X _ {i j} W _ {i j} ^ {\mathrm {Q}}, X _ {i j} W _ {i j} ^ {\mathrm {K}}, X _ {i j} W _ {i j} ^ {\mathrm {V}}\right), \tag {2} +$$ + +$$ +\tilde {X} _ {i + 1} = \operatorname {C o n c a t} \left[ \tilde {X} _ {i j} \right] _ {j = 1: h} W _ {i} ^ {\mathrm {P}}, +$$ + +where the $j$ -th head computes the self-attention over $X_{ij}$ , which is the $j$ -th split of the input feature $X_{i}$ , i.e., $X_{i} = [X_{i1}, X_{i2}, \ldots, X_{ih}]$ and $1 \leq j \leq h$ . $h$ is the total number of heads, $W_{ij}^{\mathrm{Q}}, W_{ij}^{\mathrm{K}}$ , and $W_{ij}^{\mathrm{V}}$ are projection layers mapping the input feature split into different subspaces, and $W_{i}^{\mathrm{P}}$ is a linear layer that projects the concatenated output features back to the dimension consistent with the input. + +Although using feature splits instead of the full features for each head is more efficient and saves computation overhead, we continue to improve its capacity, by encouraging the $Q$ , $K$ , $V$ layers to learn projections on features with richer information. We compute the attention map of each head in a cascaded manner, as illustrated in Fig. 6 (c), which adds the output of each head to the subsequent head to refine the feature representations progressively: + +$$ +X _ {i j} ^ {\prime} = X _ {i j} + \widetilde {X} _ {i (j - 1)}, \quad 1 < j \leq h, \tag {3} +$$ + +where $X_{ij}^{\prime}$ is the addition of the $j$ -th input split $X_{ij}$ and the $(j-1)$ -th head output $\widetilde{X}_{i(j-1)}$ calculated by Eq. (2). It replaces $X_{ij}$ to serve as the new input feature for the $j$ -th head when calculating the self-attention. Besides, another token + +Table 1. Architecture details of EfficientViT model variants. + +
Model{C1,C2,C3}{L1,L2,L3}{H1,H2,H3}
EfficientViT-M0{64,128,192}{1,2,3}{4,4,4}
EfficientViT-M1{128,144,192}{1,2,3}{2,3,3}
EfficientViT-M2{128,192,224}{1,2,3}{4,3,2}
EfficientViT-M3{128,240,320}{1,2,3}{4,3,4}
EfficientViT-M4{128,256,384}{1,2,3}{4,4,4}
EfficientViT-M5{192,288,384}{1,3,4}{3,3,4}
+ +interaction layer is applied after the $Q$ projection, which enables the self-attention to jointly capture local and global relations and further enhances the feature representation. + +Such a cascaded design enjoys two advantages. First, feeding each head with different feature splits could improve the diversity of attention maps, as validated in Sec. 2.2. Similar to group convolutions [10, 87], the cascaded group attention could save the Flops and parameters by $h \times$ , since the input and output channels in the QKV layers are reduced by $h \times$ . Second, cascading the attention heads allows for an increase of network depth, thus further elevating the model capacity without introducing any extra parameters. It only incurs minor latency overhead since the attention map computation in each head uses smaller QK channel dimensions. + +Parameter Reallocation. To improve parameter efficiency, we reallocate the parameters in the network by expanding the channel width of critical modules while shrinking the unimportant ones. Specifically, based on the Taylor importance analysis in Sec. 2.3, we set small channel dimensions for $Q$ and $K$ projections in each head for all stages. For the $V$ projection, we allow it to have the same dimension as the input embedding. The expansion ratio in FFN is also reduced from 4 to 2 due to its parameter redundancy. With the proposed reallocation strategy, the important modules have larger number of channels to learn representations in a high dimensional space, which prevent the loss of feature information. Meanwhile, the redundant parameters in unimportant modules are removed to speed up inference and enhance the model efficiency. + +# 3.2. EfficientViT Network Architectures + +The overall architecture of our EfficientViT is presented in Fig. 6 (a). Concretely, we introduce overlapping patch embedding [20, 80] to embed $16 \times 16$ patches into tokens with $C_1$ dimension, which enhances the model capacity in low-level visual representation learning. The architecture contains three stages. Each stage stacks the proposed EfficientViT building blocks and the number of tokens is reduced by $4 \times$ at each subsampling layer ( $2 \times$ subsampling of the resolution). To achieve efficient subsampling, we propose an EfficientViT subsample block which also has the sandwich layout, except that the self-attention layer is replaced by an inverted residual block to reduce the information loss during subsampling [26, 63]. It is worth noting that we adopt BatchNorm (BN) [30] instead of Layer + +Norm (LN) [2] throughout the model, as BN can be folded into the preceding convolution or linear layers, which is a runtime advantage over LN. We also use ReLU [54] as the activation function, as the commonly used GELU [25] or HardSwish [26] are much slower, and sometimes not well-supported by certain inference deployment platforms [1, 3]. + +We build our model family with six different width and depth scales, and set different number of heads for each stage. We use fewer blocks in early stages than late stages similar to MobileNetV3 [26] and LeViT [20], since that the processing on early stages with larger resolutions is more time consuming. We increase the width over stages with a small factor $(\leq 2)$ to alleviate redundancy in later stages, as analyzed in Sec. 2.3. The architecture details of our model family are presented in Tab. 1. $C_i$ , $L_i$ , and $H_i$ refer to the width, depth, and number of heads in the $i$ -th stage. + +# 4. Experiments + +# 4.1. Implementation Details + +We conduct image classification experiments on ImageNet-1K [17]. The models are built with PyTorch 1.11.0 [59] and Timm 0.5.4 [77], and trained from scratch for 300 epochs on 8 Nvidia V100 GPUs using AdamW [46] optimizer and cosine learning rate scheduler. We set the total batchsize as 2,048. The input images are resized and randomly cropped into $224 \times 224$ . The initial learning rate is $1 \times 10^{-3}$ with weight decay of $2.5 \times 10^{-2}$ . We use the same data augmentation as [69], including Mixup [85], auto-augmentation [13], and random erasing [88]. In addition, we provide throughput evaluation on different hardware. For GPU, we measure the throughput on an Nvidia V100, with the maximum power-of-two batchsize that fits in memory following [20, 69]. For CPU and ONNX, we measure the runtime on an Intel Xeon E5-2690 v4 @ 2.60 GHz processor, with batchsize 16 and run the model in a single thread following [20]. We also test the transferability of EfficientViT on downstream tasks. For the experiments on downstream image classification, we finetune the models for 300 epochs following [86], using AdamW [46] with batchsize 256, learning rate $1 \times 10^{-3}$ and weight-decay $1 \times 10^{-8}$ . We use RetinaNet [41] for object detection on COCO [42], and train the models for 12 epochs ( $1 \times$ schedule) with the same settings as [44] on mmdetection [6]. For instance segmentation, please refer to the supplementary. + +# 4.2. Results on ImageNet + +We compare EfficientViT with prevailing efficient CNN and ViT models on ImageNet [17], and report the results in Tab. 2 and Fig. 1. The results show that, in most cases, our EfficientViT achieves the best accuracy and speed trade-off across different evaluation settings. + +Comparisons with efficient CNNs. We first compare EfficientViT with vanilla CNN models, such as MobileNets + +Table 2. EfficientViT image classification performance on ImageNet-1K [17] with comparisons to state-of-the-art efficient CNN and ViT models trained without extra data. Throughput is tested on Nvidia V100 for GPU and Intel Xeon E5-2690 v4 @ 2.60 GHz processor for CPU and ONNX, where larger throughput means faster inference speed. ↑: finetune with higher resolution. + +
ModelTop-1 (%)Top-5 (%)Throughput (images/s)Flops (M)Params (M)InputEpochs
GPUCPUONNX
EfficientViT-M063.285.427644228.4340.1792.3224300
MobileNetV3-Small [26]67.4-19738156.5231.7572.5224600
EfficientViT-M168.488.720093126.9215.91673.0224300
Mobile-Former-52M [9]68.7-314132.821.5523.5224450
MobileViT-XXS [50]69.0-445629.441.74101.3256300
ShuffleNetV2 1.0× [48]69.488.913301106.7177.01462.3224300
MobileViTV2-0.5 [51]70.2-514234.444.94661.4256300
EfficientViT-M270.890.218218121.2158.72014.2224300
MobileOne-S0 [70]71.4-1132067.4128.62742.1224300
MobileNetV2 1.0× [63]72.091.0653432.580.43003.4224300
EfficientViT-M373.491.41664496.4120.82636.9224300
GhostNet 1.0× [23]73.991.4738257.377.01415.2224300
NASNet-A-Mobile [89]74.1-262319.825.55645.3224300
EfficientViT-M474.391.81591488.5108.62998.8224300
EdgeViT-XXS [56]74.4-363828.229.65564.1224300
MobileViT-XS [50]74.7-334411.120.59862.3256300
ShuffleNetV2 2.0× [48]74.992.4696237.952.35917.4224300
MobileNetV3-Large [26]75.2-756039.170.52175.4224600
MobileViTV2-0.75 [51]75.6-335016.022.710302.9256300
MobileOne-S1 [70]75.9-666330.751.18254.8224300
GLiT-Tiny [5]76.4-351617.515.713337.3224300
EfficientNet-B0 [67]77.193.3453230.229.53905.3224350
EfficientViT-M577.193.41062156.862.552212.4224300
EfficientViT-M4↑38479.895.0398615.822.6148612.4384330
EfficientViT-M5↑51280.895.523138.310.5267012.4512360
+ +[26, 63] and EfficientNet [67]. Specifically, compared to MobileNetV2 $1.0 \times$ [63], EfficientViT-M3 obtains $1.4\%$ better top-1 accuracy, while running at $2.5 \times$ and $3.0 \times$ faster speed on V100 GPU and Intel CPU, respectively. Compared to the state-of-the-art MobileNetV3-Large [26], EfficientViT-M5 achieves $1.9\%$ higher accuracy yet runs much faster, e.g., $40.5\%$ faster on the V100 GPU and $45.2\%$ faster on the Intel CPU but is $11.5\%$ slower as ONNX models. This may because reshaping is slower in ONNX implementation, which is inevitable in computing self-attention. Moreover, EfficientViT-M5 achieves comparable accuracy with the searched model EfficientNet-B0 [67], while runs $2.3 \times / 1.9 \times$ faster on the V100 GPU/Intel CPU, and $2.1 \times$ faster as ONNX models. Although our model uses more parameters, it reduces memory-inefficient operations that affect the inference speed and achieves higher throughput. + +Comparisons with efficient ViTs. We also compare our models with recent efficient vision transformers [5, 9, 50, 51, 56] in Tab. 2. In particular, when getting similar performance on ImageNet-1K [17], our EfficientViT-M4 runs $4.4 \times$ and $3.0 \times$ faster than the recent EdgeViT-XXS [56] on the tested CPU and GPU devices. Even converted to ONNX + +runtime format, our model still gets $3.7 \times$ higher speed. Compared to the state-of-the-art MobileViTV2-0.5 [51], our EfficientViT-M2 achieves slightly better performance with higher throughput, e.g., $3.4 \times$ and $3.5 \times$ higher throughput tested on the GPU and CPU devices, respectively. Furthermore, we compare with tiny variants of state-of-the-art large ViTs in Tab. 3. PoolFormer-12S [83] has comparable accuracy with EfficientViT-M5 yet runs $3.0 \times$ slower on the V100 GPU. Compared to Swin-T [44], EfficientViT-M5 is $4.1\%$ inferior in accuracy yet is $12.3 \times$ faster on the Intel CPU, demonstrating the efficiency of the proposed design. In addition, we present the speed evaluation and comparison on mobile chipsets in the supplementary material. + +Finetune with higher resolutions. Recent works on ViTs have demonstrated that finetuning with higher resolutions can further improve the capacity of the models. We also finetune our largest model EfficientViT-M5 to higher resolutions. EfficientViT-M5↑384 reaches 79.8% top-1 accuracy with throughput of 3,986 images/s on the V100 GPU, and EfficientViT-M5↑512 further improves the top-1 accuracy to 80.8%, demonstrating the efficiency on processing images with larger resolutions and the good model capacity. + +Table 3. Comparison with the tiny variants of state-of-the-art large-scale ViTs on ImageNet-1K [17]. + +
ModelTop-1 (%)Throughput (imgs/s)Flops (G)Params (M)
GPUCPUONNX
PVTV2-B0 [76]70.5350712.718.50.61.4
T2T-ViT-7 [84]71.7115622.516.11.14.3
DeiT-T [69]72.2463126.025.11.35.9
PoolFormer-12S [83]77.2353410.414.61.912.0
EffFormer-L1 [40]79.2446512.921.21.312.3
Swin-T [44]81.213934.66.44.529.0
EfficientViT-M577.11062156.862.50.512.4
+ +Table 4. Results of EfficientViT and other efficient models on downstream image classification datasets. + +
ModelThroughputImageNetCIFAR10CIFAR100CarsFlowersPets
MobileNetV1 [27]854370.696.182.391.496.789.9
MobileNetV2 [63]653472.995.780.891.096.690.5
MobileNetV3 [26]756075.297.685.591.297.090.1
NASNet-A-M [89]262374.196.883.988.596.889.4
ViT-S/16 [18]213581.497.685.7-86.490.4
EfficientViT-M51062177.198.086.489.797.192.0
+ +# 4.3. Transfer Learning Results + +To further evaluate the transfer ability, we apply EfficientViT on various downstream tasks. + +Downstream Image Classification. We transfer EfficientViT to downstream image classification datasets to test its generalization ability: 1) CIFAR-10 and CIFAR-100 [36]; 2) fine-grained classification: Flowers [55], Stanford Cars [35], and Oxford-IIIT Pets [58]. We report the results in Tab. 4. Compared to existing efficient models [18, 26, 27, 63, 89], our EfficientViT-M5 achieves comparable or slightly better accuracy across all datasets with much higher throughput. An exception lies in Cars, where our model is slightly inferior in accuracy. This may because the subtle differences between classes lie more in local details thus is more feasible to be captured with convolution. + +Object Detection. We compare EfficientViT-M4 with efficient models [12, 22, 26, 63, 66, 68] on the COCO [42] object detection task, and present the results in Tab. 5. Specifically, EfficientViT-M4 surpasses MobileNetV2 [63] by $4.4\%$ AP with comparable Flops. Compared to the searched method SPOS [22], our EfficientViT-M4 uses $18.1\%$ fewer Flops while achieving $2.0\%$ higher AP, demonstrating its capacity and generalization ability in different vision tasks. + +# 4.4. Ablation Study + +In this section, we ablate important design elements in the proposed EfficientViT on ImageNet-1K [17]. All models are trained for 100 epochs to magnify the differences and reduce training time [20]. Tab. 6 reports the results. + +Impact of the sandwich layout block. We first present an ablation study to verify the efficiency of the proposed sandwich layout design, by replacing the sandwich layout block with the original Swin block [44]. The depth is adjusted to + +Table 5. EfficientViT object detection performance on COCOval2017 [42] with comparisons to other efficient models. + +
ModelRetinaNet 1×FlopsParams
APAP50AP75APsAPmAPl(M)(M)
MobileNetV2 [63]28.346.729.314.830.738.13003.4
MobileNetV3 [26]29.949.330.814.933.341.12175.4
SPOS [22]30.749.832.215.433.941.63654.3
MNASNet-A2 [66]30.550.232.016.634.141.13404.8
FairNAS-C [12]31.250.832.716.334.442.33255.6
MixNet-M [68]31.351.732.417.035.041.93605.0
EfficientViT-M432.752.234.117.635.346.02998.8
+ +Table 6. Ablation for EfficientViT-M4 on ImageNet-1K [17] dataset. Top-1 accuracy, GPU and ONNX throughput are reported. + +
#AblationTop-1 (%)Throughput (imgs/s)
GPUONNX
1EfficientViT-M471.315914108.6
2Sandwich → Swin [44]68.315804114.5
3N = 1 → 270.214977112.3
4N = 1 → 365.715856139.7
5CGA → MHSA [18]70.216243102.2
6Cascade → None69.816411111.0
7QKV allocation → None69.915132103.1
8FFN ratio 2 → 469.815310112.4
9DWConv → None69.916325110.4
10BN → LN [2]70.415463103.6
11ReLU → HSwish [26]72.21588787.5
+ +$\{2, 2, 3\}$ to guarantee similar throughput with EfficientViTM4 for a fair comparison. The top-1 accuracy degrades by $3.0\%$ at a similar speed, verifying that applying more FFNs instead of memory-bound MHSA is more effective for small models. Furthermore, to analyze the impact of the number of FFNs $\mathcal{N}$ before and after self-attention, we change the number from 1 to 2 and 3. The number of blocks is reduced accordingly to maintain similar throughput. As presented in Tab. 6 (#3 and #4), further increasing the number of FFNs is not effective due to the lack of long-range spatial relation and $\mathcal{N} = 1$ achieves the best efficiency. + +Impact of the cascaded group attention. We have proposed CGA to improve the computation efficiency of MHSA. As shown in Tab. 6 (#5 and #6), replacing CGA with MHSA decreases the accuracy by $1.1\%$ and ONNX speed by $5.9\%$ , suggesting that addressing head redundancy improves the model efficiency. For the model without the cascade operation, its performance is comparable with MHSA but worse than CGA, demonstrating the efficacy of enhancing the feature representations of each head. + +Impact of the parameter reallocation. Our EfficientViTM4 yields $1.4\% / 1.5\%$ higher top-1 accuracy, $4.9\% / 3.8\%$ higher GPU throughput than the models without QKV channel dimension reallocation or FFN ratio reduction, respectively, indicating the effectiveness of parameter reallocation (#1 vs. #7, #8). Moreover, we study the choices of QK dimension in each head and the ratio of V dimension to the input embedding in Fig. 7. It is shown that the performance is improved gradually as QK dimension increases + +Table 7. Performance comparison on ImageNet-1K [17] and ImageNet-ReaL [4]. Results with $\dagger$ are trained with 1,000 epochs and knowledge distillation following LeViT [20]. + +
ModelImageNet (%)Throughput (imgs/s)Flops Params
Top-1Top-1†RealL†GPUCPUONNX(M)(M)
LeViT-128S [20]73.676.682.61445782.380.93057.8
EfficientViT-M474.377.183.61591488.5108.62998.8
+ +from 4 to 16, while further increasing it gives inferior performance. Besides, the performance improves from $70.3\%$ to $71.3\%$ when increasing the ratio between $V$ dimension and input embedding from 0.4 to 1.0. When further enlarging the ratio to 1.2, it only gets $0.1\%$ improvements. Therefore, setting the channels of $V$ close to the input embedding achieves the best parameter efficiency, which meets our analysis in Sec. 2.3 and design strategy. + +Impact of other components. We ablate the impact of using DWConv for token interaction, the normalization layer, and the activation function, as presented in Tab. 6 (#9, #10, and #11). With DWConv, the accuracy improves by $1.4\%$ with a minor latency overhead, demonstrating the effectiveness of introducing local structural information. Replacing BN with LN decreases accuracy by $0.9\%$ and GPU speed by $2.9\%$ . Using HardSwish instead of ReLU improves accuracy by $0.9\%$ but leads to a large drop of $20.0\%$ ONNX speed. The activation functions are element-wise operations that occupy a considerable amount of processing time on GPU/CPU [15,48,72], thus utilizing ReLU instead of more complicated activation functions is of better efficiency. + +Results of 1,000 training epochs and distillation. Tab. 7 shows the results with 1,000 training epochs and knowledge distillation using RegNetY-16GF [60] as the teacher model following [20] on ImageNet-1K [17] and ImageNet-ReaL [4]. Compared to LeViT-128S [20], EfficientViT-M4 surpasses it by $0.5\%$ on ImageNet-1K and $1.0\%$ on ImageNet-ReaL, respectively. For the inference speed, our model has $34.2\%$ higher throughput on ONNX and also shows superiority on other settings. The results demonstrate that the strong capability and generalization ability of EfficientViT can be further explored with longer training schedules. + +# 5. Related Work + +Efficient CNNs. With the demand of deploying CNNs on resource-constrained scenarios, efficient CNNs have been intensively studied in literature [23, 24, 26, 48, 63, 67, 87]. Xception [10] proposes an architecture built with depthwise separable convolutions. MobileNetV2 [63] builds an inverted residual structure which expands the input to a higher dimension. MobileNetV3 [26] and EfficientNet [67] resort to neural architecture search techniques to design compact models. To boost the actual speed on hardware, ShuffleNetV2 [48] introduces channel split and shuffle operations to improve the information communication among channel groups. However, the spatial locality of convolutional kernels hampers CNN models from capturing long- + +![](images/833cbf3b725904c503508d22147a1f2f3ebc5e510ea444b2f53e572a84af25e0.jpg) +Figure 7. Ablation on the $QK$ dimension of each head and the ratio of $V$ dimension to the input embedding. + +![](images/c9dcaaafbbbf228bb114b6f8d0699435b8898f89702b5ed6531a072e6168023e.jpg) + +range dependencies, thus limiting their model capacity. + +Efficient ViTs. ViT and its variants [18, 44, 69, 76] have achieved success on various vision tasks. Despite the superior performance, most of them are inferior to typical CNNs in inference speed. Some efficient transformers have been proposed recently and they fall into two camps: 1) efficient self-attention; and 2) efficient architecture design. Efficient self-attention methods reduce the cost of softmax attention via sparse attention [34, 57, 61, 75] or low-rank approximation [11, 51, 74]. However, they suffer from performance degradation with negligible or moderate inference acceleration over softmax attention [71]. Another line of work combines ViTs with lightweight CNNs to build efficient architectures [9, 47, 49, 50, 81]. LVT [81] proposes enhanced attention mechanisms with dilated convolution to improve the model performance and efficiency. Mobile-Former [9] designs a parallel CNN-transformer block to encode both local features and global interaction. However, most of them target at minimizing Flops and parameters [16], which could have low correlations with actual inference latency [70] and still inferior to efficient CNNs in speed. Different from them, we explore models with fast inference by directly optimizing their throughput on different hardware and deployment settings, and design a family of hierarchical models with a good trade-off between speed and accuracy. + +# 6. Conclusion + +In this paper, we have presented a systematic analysis on the factors that affect the inference speed of vision transformers, and proposed a new family of fast vision transformers with memory-efficient operations and cascaded group attention, named EfficientViT. Extensive experiments have demonstrated the efficacy and high speed of EfficientViT, and also show its superiority on various downstream benchmarks. + +Limitations. One limitation of EfficientViT is that, despite its high inference speed, the model size is slightly larger compared to state-of-the-art efficient CNN [26] due to the extra FFNs in the introduced sandwich layout. Besides, our models are designed manually based on the derived guidelines on building efficient vision transformers. In future work, we are interested in reducing the model size and incorporating automatic search techniques to further enhance the model capacity and efficiency. + +Acknowledgement. Prof. Yuan was partially supported by Hong Kong Research Grants Council (RGC) General Research Fund 11211221, and Innovation and Technology Commission-Innovation and Technology Fund ITS/100/20. + +# References + +[1] Apple. 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Pytorch image models, 2019. 5 +[78] Kan Wu, Jinnian Zhang, Houwen Peng, Mengchen Liu, Bin Xiao, Jianlong Fu, and Lu Yuan. Tinyvit: Fast pretraining distillation for small vision transformers. In ECCV, 2022. 1 +[79] Sitong Wu, Tianyi Wu, Haoru Tan, and Guodong Guo. Pale transformer: A general vision transformer backbone with pale-shaped attention. In AAAI, 2022. 1 +[80] Tete Xiao, Piotr Dollar, Mannat Singh, Eric Mintun, Trevor Darrell, and Ross Girshick. Early convolutions help transformers see better. NeurIPS, 2021. 5 +[81] Chenglin Yang, Yilin Wang, Jianming Zhang, He Zhang, Zijun Wei, Zhe Lin, and Alan Yuille. Lite vision transformer with enhanced self-attention. In CVPR, pages 11998–12008, 2022. 1, 8 +[82] Huanrui Yang, Hongxu Yin, Pavlo Molchanov, Hai Li, and Jan Kautz. Nvit: Vision transformer compression and parameter redistribution. arXiv preprint arXiv:2110.04869, 2021.3 +[83] Weihao Yu, Mi Luo, Pan Zhou, Chenyang Si, Yichen Zhou, Xinchao Wang, Jiashi Feng, and Shuicheng Yan. Metaformer is actually what you need for vision. In CVPR, pages 10819-10829, 2022. 6, 7 + +[84] Li Yuan, Yunpeng Chen, Tao Wang, Weihao Yu, Yujun Shi, Francis EH Tay, Jiashi Feng, and Shuicheng Yan. Token-to-token vit: Training vision transformers from scratch onImagenet. ICCV, 2021. 7 +[85] Hongyi Zhang, Moustapha Cisse, Yann N Dauphin, and David Lopez-Paz. mixup: Beyond empirical risk minimization. In ICLR, 2018. 5 +[86] Jinnian Zhang, Houwen Peng, Kan Wu, Mengchen Liu, Bin Xiao, Jianlong Fu, and Lu Yuan. Minivit: Compressing vision transformers with weight multiplexing. In CVPR, 2022, 1, 5 +[87] Xiangyu Zhang, Xinyu Zhou, Mengxiao Lin, and Jian Sun. Shufflenet: An extremely efficient convolutional neural network for mobile devices. In CVPR, 2018. 3, 4, 5, 8 +[88] Zhun Zhong, Liang Zheng, Guoliang Kang, Shaozi Li, and Yi Yang. Random erasing data augmentation. In AAAI, 2020. 5 +[89] Barret Zoph, Vijay Vasudevan, Jonathon Shlens, and Quoc V Le. Learning transferable architectures for scalable image recognition. 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However, their remarkable performance is accompanied by heavy computation costs, which makes them unsuitable for real-time applications. In this paper, we propose a family of high-speed vision transformers named EfficientViT. We find that the speed of existing transformer models is commonly bounded by memory inefficient operations, especially the tensor reshaping and element-wise functions in MHSA. Therefore, we design a new building block with a sandwich layout, i.e., using a single memory-bound MHSA between efficient FFN layers, which improves memory efficiency while enhancing channel communication. Moreover, we discover that the attention maps share high similarities across heads, leading to computational redundancy. To address this, we present a cascaded group attention module feeding attention heads with different splits of the full feature, which not only saves computation cost but also improves attention diversity. Comprehensive experiments demonstrate EfficientViT outperforms existing efficient models, striking a good trade-off between speed and accuracy. For instance, our EfficientViT-M5 surpasses MobileNetV3-Large by " + }, + { + "bbox": [ + 46, + 248, + 289, + 583 + ], + "type": "inline_equation", + "content": "1.9\\%" + }, + { + "bbox": [ + 46, + 248, + 289, + 583 + ], + "type": "text", + "content": " in accuracy, while getting " + }, + { + "bbox": [ + 46, + 248, + 289, + 583 + ], + "type": "inline_equation", + "content": "40.4\\%" + }, + { + "bbox": [ + 46, + 248, + 289, + 583 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 248, + 289, + 583 + ], + "type": "inline_equation", + "content": "45.2\\%" + }, + { + "bbox": [ + 46, + 248, + 289, + 583 + ], + "type": "text", + "content": " higher throughput on Nvidia V100 GPU and Intel Xeon CPU, respectively. Compared to the recent efficient model MobileViT-XXS, EfficientViT-M2 achieves " + }, + { + "bbox": [ + 46, + 248, + 289, + 583 + ], + "type": "inline_equation", + "content": "1.8\\%" + }, + { + "bbox": [ + 46, + 248, + 289, + 583 + ], + "type": "text", + "content": " superior accuracy, while running " + }, + { + "bbox": [ + 46, + 248, + 289, + 583 + ], + "type": "inline_equation", + "content": "5.8 \\times / 3.7 \\times" + }, + { + "bbox": [ + 46, + 248, + 289, + 583 + ], + "type": "text", + "content": " faster on the GPU/CPU, and " + }, + { + "bbox": [ + 46, + 248, + 289, + 583 + ], + "type": "inline_equation", + "content": "7.4 \\times" + }, + { + "bbox": [ + 46, + 248, + 289, + 583 + ], + "type": "text", + "content": " faster when converted to ONNX format. Code and models are available at here." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 594, + 128, + 605 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 594, + 128, + 605 + ], + "spans": [ + { + "bbox": [ + 47, + 594, + 128, + 605 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 609, + 287, + 695 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 609, + 287, + 695 + ], + "spans": [ + { + "bbox": [ + 46, + 609, + 287, + 695 + ], + "type": "text", + "content": "Vision Transformers (ViTs) have taken computer vision domain by storm due to their high model capabilities and superior performance [18,44,69]. However, the constantly improved accuracy comes at the cost of increasing model sizes and computation overhead. For example, SwinV2 [43] uses 3.0B parameters, while V-MoE [62] taking 14.7B parameters, to achieve state-of-the-art performance on Ima" + } + ] + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 331, + 224, + 518, + 353 + ], + "blocks": [ + { + "bbox": [ + 331, + 224, + 518, + 353 + ], + "lines": [ + { + "bbox": [ + 331, + 224, + 518, + 353 + ], + "spans": [ + { + "bbox": [ + 331, + 224, + 518, + 353 + ], + "type": "image", + "image_path": "b8fceb61ddd0ee7e9f113af2288b31dec9923c12b1740b9f87114187be953262.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 354, + 547, + 388 + ], + "lines": [ + { + "bbox": [ + 305, + 354, + 547, + 388 + ], + "spans": [ + { + "bbox": [ + 305, + 354, + 547, + 388 + ], + "type": "text", + "content": "Figure 1. Speed and accuracy comparisons between EfficientViT (Ours) and other efficient CNN and ViT models tested on an Nvidia V100 GPU with ImageNet-1K dataset [17]." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 390, + 546, + 426 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 390, + 546, + 426 + ], + "spans": [ + { + "bbox": [ + 304, + 390, + 546, + 426 + ], + "type": "text", + "content": "geNet [17]. Such large model sizes and the accompanying heavy computational costs make these models unsuitable for applications with real-time requirements [40, 78, 86]." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 426, + 547, + 570 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 426, + 547, + 570 + ], + "spans": [ + { + "bbox": [ + 304, + 426, + 547, + 570 + ], + "type": "text", + "content": "There are several recent works designing light and efficient vision transformer models [9, 19, 29, 49, 50, 56, 79, 81]. Unfortunately, most of these methods aim to reduce model parameters or Flops, which are indirect metrics for speed and do not reflect the actual inference throughput of models. For example, MobileViT-XS [50] using 700M Flops runs much slower than DeiT-T [69] with 1,220M Flops on an Nvidia V100 GPU. Although these methods have achieved good performance with fewer Flops or parameters, many of them do not show significant wall-clock speedup against standard isomorphic or hierarchical transformers, e.g., DeiT [69] and Swin [44], and have not gained wide adoption." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 570, + 548, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 548, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 548, + 715 + ], + "type": "text", + "content": "To address this issue, in this paper, we explore how to go faster with vision transformers, seeking to find principles for designing efficient transformer architectures. Based on the prevailing vision transformers DeiT [69] and Swin [44], we systematically analyze three main factors that affect model inference speed, including memory access, computation redundancy, and parameter usage. In particular, we find that the speed of transformer models is commonly memory-bound. In other words, memory accessing delay prohibits the full utilization of the computing power in GPU/CPUs [21, 32, 72], leading to a critically negative impact on the runtime speed of transformers [15, 31]. The" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 496, + 35 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 496, + 35 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 496, + 35 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 61, + 702, + 265, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 61, + 702, + 265, + 712 + ], + "spans": [ + { + "bbox": [ + 61, + 702, + 265, + 712 + ], + "type": "text", + "content": "*Work done when Xinyu was an intern of Microsoft Research." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "14420" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 288 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 288 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 288 + ], + "type": "text", + "content": "most memory-inefficient operations are the frequent tensor reshaping and element-wise functions in multi-head self-attention (MHSA). We observe that through an appropriate adjustment of the ratio between MHSA and FFN (feedforward network) layers, the memory access time can be reduced significantly without compromising the performance. Moreover, we find that some attention heads tend to learn similar linear projections, resulting in redundancy in attention maps. The analysis shows that explicitly decomposing the computation of each head by feeding them with diverse features can mitigate this issue while improving computation efficiency. In addition, the parameter allocation in different modules is often overlooked by existing lightweight models, as they mainly follow the configurations in standard transformer models [44,69]. To improve parameter efficiency, we use structured pruning [45] to identify the most important network components, and summarize empirical guidance of parameter reallocation for model acceleration." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 291, + 289, + 555 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 291, + 289, + 555 + ], + "spans": [ + { + "bbox": [ + 46, + 291, + 289, + 555 + ], + "type": "text", + "content": "Based upon the analysis and findings, we propose a new family of memory efficient transformer models named EfficientViT. Specifically, we design a new block with a sandwich layout to build up the model. The sandwich layout block applies a single memory-bound MHSA layer between FFN layers. It reduces the time cost caused by memory-bound operations in MHSA, and applies more FFN layers to allow communication between different channels, which is more memory efficient. Then, we propose a new cascaded group attention (CGA) module to improve computation efficiency. The core idea is to enhance the diversity of the features fed into the attention heads. In contrast to prior self-attention using the same feature for all heads, CGA feeds each head with different input splits and cascades the output features across heads. This module not only reduces the computation redundancy in multi-head attention, but also elevates model capacity by increasing network depth. Last but not least, we redistribute parameters through expanding the channel width of critical network components such as value projections, while shrinking the ones with lower importance like hidden dimensions in FFNs. This reallocation finally promotes model parameter efficiency." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 558, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 558, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 558, + 289, + 715 + ], + "type": "text", + "content": "Experiments demonstrate that our models achieve clear improvements over existing efficient CNN and ViT models in terms of both speed and accuracy, as shown in Fig. 1. For instance, our EfficientViT-M5 gets " + }, + { + "bbox": [ + 46, + 558, + 289, + 715 + ], + "type": "inline_equation", + "content": "77.1\\%" + }, + { + "bbox": [ + 46, + 558, + 289, + 715 + ], + "type": "text", + "content": " top-1 accuracy on ImageNet with throughput of 10,621 images/s on an Nvidia V100 GPU and 56.8 images/s on an Intel Xeon E5-2690 v4 CPU @ 2.60GHz, outperforming MobileNetV3-Large [26] by " + }, + { + "bbox": [ + 46, + 558, + 289, + 715 + ], + "type": "inline_equation", + "content": "1.9\\%" + }, + { + "bbox": [ + 46, + 558, + 289, + 715 + ], + "type": "text", + "content": " in accuracy, " + }, + { + "bbox": [ + 46, + 558, + 289, + 715 + ], + "type": "inline_equation", + "content": "40.4\\%" + }, + { + "bbox": [ + 46, + 558, + 289, + 715 + ], + "type": "text", + "content": " in GPU inference speed, and " + }, + { + "bbox": [ + 46, + 558, + 289, + 715 + ], + "type": "inline_equation", + "content": "45.2\\%" + }, + { + "bbox": [ + 46, + 558, + 289, + 715 + ], + "type": "text", + "content": " in CPU speed. Moreover, EfficientViTM2 gets " + }, + { + "bbox": [ + 46, + 558, + 289, + 715 + ], + "type": "inline_equation", + "content": "70.8\\%" + }, + { + "bbox": [ + 46, + 558, + 289, + 715 + ], + "type": "text", + "content": " accuracy, surpassing MobileViT-XXS [50] by " + }, + { + "bbox": [ + 46, + 558, + 289, + 715 + ], + "type": "inline_equation", + "content": "1.8\\%" + }, + { + "bbox": [ + 46, + 558, + 289, + 715 + ], + "type": "text", + "content": ", while running " + }, + { + "bbox": [ + 46, + 558, + 289, + 715 + ], + "type": "inline_equation", + "content": "5.8 \\times / 3.7 \\times" + }, + { + "bbox": [ + 46, + 558, + 289, + 715 + ], + "type": "text", + "content": " faster on the GPU/CPU, and " + }, + { + "bbox": [ + 46, + 558, + 289, + 715 + ], + "type": "inline_equation", + "content": "7.4 \\times" + }, + { + "bbox": [ + 46, + 558, + 289, + 715 + ], + "type": "text", + "content": " faster when converted to ONNX [3] format. When deployed on the mobile chipset, i.e., Apple A13 Bionic chip" + } + ] + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 323, + 60, + 403, + 148 + ], + "blocks": [ + { + "bbox": [ + 323, + 60, + 403, + 148 + ], + "lines": [ + { + "bbox": [ + 323, + 60, + 403, + 148 + ], + "spans": [ + { + "bbox": [ + 323, + 60, + 403, + 148 + ], + "type": "image", + "image_path": "544c2b317b436b9974bef96ad7da65cabc5d5665652df3322c8867d911e0acf5.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 151, + 547, + 196 + ], + "lines": [ + { + "bbox": [ + 304, + 151, + 547, + 196 + ], + "spans": [ + { + "bbox": [ + 304, + 151, + 547, + 196 + ], + "type": "text", + "content": "Figure 2. Runtime profiling on two standard vision transformers Swin-T and DeiT-T. Red text denotes memory-bound operations, i.e., the time taken by the operation is mainly determined by memory accesses, while time spent in computation is much smaller." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_caption" + } + ], + "index": 3 + }, + { + "type": "image", + "bbox": [ + 406, + 60, + 487, + 148 + ], + "blocks": [ + { + "bbox": [ + 406, + 60, + 487, + 148 + ], + "lines": [ + { + "bbox": [ + 406, + 60, + 487, + 148 + ], + "spans": [ + { + "bbox": [ + 406, + 60, + 487, + 148 + ], + "type": "image", + "image_path": "53d1435c2cbdca9f0236c1f53b980dd492a99f30c1af19a0d8fee42ab3141bd9.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 491, + 78, + 530, + 131 + ], + "lines": [ + { + "bbox": [ + 491, + 78, + 530, + 131 + ], + "spans": [ + { + "bbox": [ + 491, + 78, + 530, + 131 + ], + "type": "text", + "content": "Tensor Multiplication Reshape Normalization Copy Addition Others" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_footnote" + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 201, + 545, + 224 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 201, + 545, + 224 + ], + "spans": [ + { + "bbox": [ + 304, + 201, + 545, + 224 + ], + "type": "text", + "content": "in iPhone 11, EfficientViT-M2 model runs " + }, + { + "bbox": [ + 304, + 201, + 545, + 224 + ], + "type": "inline_equation", + "content": "2.3 \\times" + }, + { + "bbox": [ + 304, + 201, + 545, + 224 + ], + "type": "text", + "content": " faster than MobileViT-XXS [50] using the CoreML [1]." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 317, + 225, + 544, + 236 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 225, + 544, + 236 + ], + "spans": [ + { + "bbox": [ + 317, + 225, + 544, + 236 + ], + "type": "text", + "content": "In summary, the contributions of this work are two-fold:" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 317, + 237, + 545, + 322 + ], + "type": "list", + "angle": 0, + "index": 11, + "blocks": [ + { + "bbox": [ + 317, + 237, + 545, + 273 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 237, + 545, + 273 + ], + "spans": [ + { + "bbox": [ + 317, + 237, + 545, + 273 + ], + "type": "text", + "content": "- We present a systematic analysis on the factors that affect the inference speed of vision transformers, deriving a set of guidelines for efficient model design." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 317, + 274, + 545, + 322 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 274, + 545, + 322 + ], + "spans": [ + { + "bbox": [ + 317, + 274, + 545, + 322 + ], + "type": "text", + "content": "- We design a new family of vision transformer models, which strike a good trade-off between efficiency and accuracy. The models also demonstrate good transfer ability on a variety of downstream tasks." + } + ] + } + ], + "index": 10 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 305, + 328, + 522, + 341 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 328, + 522, + 341 + ], + "spans": [ + { + "bbox": [ + 305, + 328, + 522, + 341 + ], + "type": "text", + "content": "2. Going Faster with Vision Transformers" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 345, + 545, + 405 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 345, + 545, + 405 + ], + "spans": [ + { + "bbox": [ + 304, + 345, + 545, + 405 + ], + "type": "text", + "content": "In this section, we explore how to improve the efficiency of vision transformers from three perspectives: memory access, computation redundancy, and parameter usage. We seek to identify the underlying speed bottlenecks through empirical studies, and summarize useful design guidelines." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 411, + 418, + 424 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 411, + 418, + 424 + ], + "spans": [ + { + "bbox": [ + 305, + 411, + 418, + 424 + ], + "type": "text", + "content": "2.1. Memory Efficiency" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 426, + 545, + 545 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 426, + 545, + 545 + ], + "spans": [ + { + "bbox": [ + 304, + 426, + 545, + 545 + ], + "type": "text", + "content": "Memory access overhead is a critical factor affecting model speed [15,28,31,65]. Many operators in transformer [71], such as frequent reshaping, element-wise addition, and normalization are memory inefficient, requiring time-consuming access across different memory units, as shown in Fig. 2. Although there are some methods proposed to address this issue by simplifying the computation of standard softmax self-attention, e.g., sparse attention [34,57,61,75] and low-rank approximation [11,51,74], they often come at the cost of accuracy degradation and limited acceleration." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 546, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 546, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 546, + 546, + 713 + ], + "type": "text", + "content": "In this work, we turn to save memory access cost by reducing memory-inefficient layers. Recent studies reveal that memory-inefficient operations are mainly located in MHSA rather than FFN layers [31, 33]. However, most existing ViTs [18, 44, 69] use an equivalent number of these two layers, which may not achieve the optimal efficiency. We thereby explore the optimal allocation of MHSA and FFN layers in small models with fast inference. Specifically, we scale down Swin-T [44] and DeiT-T [69] to several small subnetworks with " + }, + { + "bbox": [ + 304, + 546, + 546, + 713 + ], + "type": "inline_equation", + "content": "1.25 \\times" + }, + { + "bbox": [ + 304, + 546, + 546, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 546, + 546, + 713 + ], + "type": "inline_equation", + "content": "1.5 \\times" + }, + { + "bbox": [ + 304, + 546, + 546, + 713 + ], + "type": "text", + "content": " higher inference throughput, and compare the performance of subnetworks with different proportions of MHSA layers. As shown in Fig. 3, subnetworks with " + }, + { + "bbox": [ + 304, + 546, + 546, + 713 + ], + "type": "inline_equation", + "content": "20\\% - 40\\%" + }, + { + "bbox": [ + 304, + 546, + 546, + 713 + ], + "type": "text", + "content": " MHSA layers tend to get better accuracy. Such ratios are much smaller than the" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "14421" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 62, + 63, + 166, + 153 + ], + "blocks": [ + { + "bbox": [ + 62, + 63, + 166, + 153 + ], + "lines": [ + { + "bbox": [ + 62, + 63, + 166, + 153 + ], + "spans": [ + { + "bbox": [ + 62, + 63, + 166, + 153 + ], + "type": "image", + "image_path": "9b6c96320c6ac8bd76c81eaaf1b8c3d1019c0312dcaec7c35b2b6b9b76bbbe00.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 154, + 287, + 209 + ], + "lines": [ + { + "bbox": [ + 46, + 154, + 287, + 209 + ], + "spans": [ + { + "bbox": [ + 46, + 154, + 287, + 209 + ], + "type": "text", + "content": "Figure 3. The accuracy of downscaled baseline models with different MHSA layer proportions, where the dots on each line represent subnetworks with similar throughput. Left: Swin-T as the baseline. Right: DeiT-T as the baseline. The " + }, + { + "bbox": [ + 46, + 154, + 287, + 209 + ], + "type": "inline_equation", + "content": "1.25 \\times 1.5 \\times" + }, + { + "bbox": [ + 46, + 154, + 287, + 209 + ], + "type": "text", + "content": " denote accelerating the baseline models by 1.25/1.5 times, respectively." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 168, + 63, + 270, + 153 + ], + "blocks": [ + { + "bbox": [ + 168, + 63, + 270, + 153 + ], + "lines": [ + { + "bbox": [ + 168, + 63, + 270, + 153 + ], + "spans": [ + { + "bbox": [ + 168, + 63, + 270, + 153 + ], + "type": "image", + "image_path": "65c10f493d8f0d2071970e226d4269ec2e18842b47ace7afc3361cbac6bbc6b1.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 213, + 287, + 334 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 213, + 287, + 334 + ], + "spans": [ + { + "bbox": [ + 46, + 213, + 287, + 334 + ], + "type": "text", + "content": "typical ViTs that adopt " + }, + { + "bbox": [ + 46, + 213, + 287, + 334 + ], + "type": "inline_equation", + "content": "50\\%" + }, + { + "bbox": [ + 46, + 213, + 287, + 334 + ], + "type": "text", + "content": " MHSA layers. Furthermore, we measure the time consumption on memory-bound operations to compare memory access efficiency, including reshaping, element-wise addition, copying, and normalization. Memory-bound operations is reduced to " + }, + { + "bbox": [ + 46, + 213, + 287, + 334 + ], + "type": "inline_equation", + "content": "44.26\\%" + }, + { + "bbox": [ + 46, + 213, + 287, + 334 + ], + "type": "text", + "content": " of the total runtime in Swin-T-1.25× that has " + }, + { + "bbox": [ + 46, + 213, + 287, + 334 + ], + "type": "inline_equation", + "content": "20\\%" + }, + { + "bbox": [ + 46, + 213, + 287, + 334 + ], + "type": "text", + "content": " MHSA layers. The observation also generalizes to DeiT and smaller models with " + }, + { + "bbox": [ + 46, + 213, + 287, + 334 + ], + "type": "inline_equation", + "content": "1.5\\times" + }, + { + "bbox": [ + 46, + 213, + 287, + 334 + ], + "type": "text", + "content": " speed-up. It is demonstrated that reducing MHSA layer utilization ratio appropriately can enhance memory efficiency while improving model performance." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 339, + 180, + 352 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 339, + 180, + 352 + ], + "spans": [ + { + "bbox": [ + 47, + 339, + 180, + 352 + ], + "type": "text", + "content": "2.2. Computation Efficiency" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 356, + 288, + 643 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 356, + 288, + 643 + ], + "spans": [ + { + "bbox": [ + 46, + 356, + 288, + 643 + ], + "type": "text", + "content": "MHSA embeds the input sequence into multiple subspaces (heads) and computes attention maps separately, which has been proven effective in improving performance [18, 69, 71]. However, attention maps are computationally expensive, and studies have shown that a number of them are not of vital importance [52, 73]. To save computation cost, we explore how to reduce redundant attention in small ViT models. We train width downscaled Swin-T [44] and DeiT [69] models with " + }, + { + "bbox": [ + 46, + 356, + 288, + 643 + ], + "type": "inline_equation", + "content": "1.25 \\times" + }, + { + "bbox": [ + 46, + 356, + 288, + 643 + ], + "type": "text", + "content": " inference speed-up, and measure the maximum cosine similarity of each head and the remaining heads within each block. From Fig. 4, we observe there exists high similarities between attention heads, especially in the last blocks. The phenomenon suggests that many heads learn similar projections of the same full feature and incur computation redundancy. To explicitly encourage the heads to learn different patterns, we apply an intuitive solution by feeding each head with only a split of the full feature, which is similar to the idea of group convolution in [10, 87]. We train the variants of downscaled models with the modified MHSA, and also compute the attention similarities in Fig. 4. It is shown that using different channel-wise splits of the feature in different heads, instead of using the same full feature for all heads as MHSA, could effectively mitigate attention computation redundancy." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 649, + 168, + 662 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 649, + 168, + 662 + ], + "spans": [ + { + "bbox": [ + 47, + 649, + 168, + 662 + ], + "type": "text", + "content": "2.3. Parameter Efficiency" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "text", + "content": "Typical ViTs mainly inherit the design strategies from NLP transformer [71], e.g., using an equivalent width for " + }, + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "inline_equation", + "content": "Q, K, V" + }, + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "text", + "content": " projections, increasing heads over stages, and setting the expansion ratio to 4 in FFN. For lightweight mod" + } + ] + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 321, + 61, + 425, + 153 + ], + "blocks": [ + { + "bbox": [ + 321, + 61, + 425, + 153 + ], + "lines": [ + { + "bbox": [ + 321, + 61, + 425, + 153 + ], + "spans": [ + { + "bbox": [ + 321, + 61, + 425, + 153 + ], + "type": "image", + "image_path": "ba13c9b27405e85559599ff09a1eb315a0e999245dc7d9d3670d305c0be893f8.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 154, + 545, + 208 + ], + "lines": [ + { + "bbox": [ + 305, + 154, + 545, + 208 + ], + "spans": [ + { + "bbox": [ + 305, + 154, + 545, + 208 + ], + "type": "text", + "content": "Figure 4. The average maximum cosine similarity of each head in different blocks. Left: downscaled Swin-T models. Right: downscaled DeiT-T models. Blue lines denote Swin-T-1.25×/DeiT-T-1.25× model, while darkblue lines denote the variants that feed each head with only a split of the full feature." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 430, + 64, + 529, + 153 + ], + "blocks": [ + { + "bbox": [ + 430, + 64, + 529, + 153 + ], + "lines": [ + { + "bbox": [ + 430, + 64, + 529, + 153 + ], + "spans": [ + { + "bbox": [ + 430, + 64, + 529, + 153 + ], + "type": "image", + "image_path": "ebbd6c782e99ca4b3eb212632c46e4496c1ad7e60a52dd8beba8750619cd66ed.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 321, + 213, + 529, + 302 + ], + "blocks": [ + { + "bbox": [ + 321, + 213, + 529, + 302 + ], + "lines": [ + { + "bbox": [ + 321, + 213, + 529, + 302 + ], + "spans": [ + { + "bbox": [ + 321, + 213, + 529, + 302 + ], + "type": "image", + "image_path": "331e779be23bf82137a11dff3fbbf9d93bfbffab83d14f594ab9a36791e4b2e8.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 303, + 545, + 335 + ], + "lines": [ + { + "bbox": [ + 305, + 303, + 545, + 335 + ], + "spans": [ + { + "bbox": [ + 305, + 303, + 545, + 335 + ], + "type": "text", + "content": "Figure 5. The ratio of the channels to the input embeddings before and after pruning Swin-T. Baseline accuracy: " + }, + { + "bbox": [ + 305, + 303, + 545, + 335 + ], + "type": "inline_equation", + "content": "79.1\\%" + }, + { + "bbox": [ + 305, + 303, + 545, + 335 + ], + "type": "text", + "content": "; pruned accuracy: " + }, + { + "bbox": [ + 305, + 303, + 545, + 335 + ], + "type": "inline_equation", + "content": "76.5\\%" + }, + { + "bbox": [ + 305, + 303, + 545, + 335 + ], + "type": "text", + "content": ". Results for DeiT-T are given in the supplementary." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 348, + 545, + 468 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 348, + 545, + 468 + ], + "spans": [ + { + "bbox": [ + 304, + 348, + 545, + 468 + ], + "type": "text", + "content": "els, the configurations of these components need to be carefully re-designed [7, 8, 39]. Inspired by [45, 82], we adopt Taylor structured pruning [53] to automatically find the important components in Swin-T and DeiT-T, and explore the underlying principles of parameter allocation. The pruning method removes unimportant channels under a certain resource constraint and keeps the most critical ones to best preserve the accuracy. It uses the multiplication of gradient and weight as channel importance, which approximates the loss fluctuation when removing channels [38]." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 472, + 546, + 639 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 472, + 546, + 639 + ], + "spans": [ + { + "bbox": [ + 304, + 472, + 546, + 639 + ], + "type": "text", + "content": "The ratio between the remaining output channels to the input channels is plotted in Fig. 5, and the original ratios in the unpruned model are also given for reference. It is observed that: 1) The first two stages preserve more dimensions, while the last stage keeps much less; 2) The " + }, + { + "bbox": [ + 304, + 472, + 546, + 639 + ], + "type": "inline_equation", + "content": "Q, K" + }, + { + "bbox": [ + 304, + 472, + 546, + 639 + ], + "type": "text", + "content": " and FFN dimensions are largely trimmed, whereas the dimension of " + }, + { + "bbox": [ + 304, + 472, + 546, + 639 + ], + "type": "inline_equation", + "content": "V" + }, + { + "bbox": [ + 304, + 472, + 546, + 639 + ], + "type": "text", + "content": " is almost preserved and diminishes only at the last few blocks. These phenomena show that 1) the typical channel configuration, that doubles the channel after each stage [44] or use equivalent channels for all blocks [69], may produce substantial redundancy in last few blocks; 2) The redundancy in " + }, + { + "bbox": [ + 304, + 472, + 546, + 639 + ], + "type": "inline_equation", + "content": "Q, K" + }, + { + "bbox": [ + 304, + 472, + 546, + 639 + ], + "type": "text", + "content": " is much larger than " + }, + { + "bbox": [ + 304, + 472, + 546, + 639 + ], + "type": "inline_equation", + "content": "V" + }, + { + "bbox": [ + 304, + 472, + 546, + 639 + ], + "type": "text", + "content": " when they have the same dimensions. " + }, + { + "bbox": [ + 304, + 472, + 546, + 639 + ], + "type": "inline_equation", + "content": "V" + }, + { + "bbox": [ + 304, + 472, + 546, + 639 + ], + "type": "text", + "content": " prefers a relative large channels, being close to the input embedding dimension." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 654, + 468, + 667 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 654, + 468, + 667 + ], + "spans": [ + { + "bbox": [ + 306, + 654, + 468, + 667 + ], + "type": "text", + "content": "3. Efficient Vision Transformer" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 676, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 676, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 305, + 676, + 545, + 712 + ], + "type": "text", + "content": "Based upon the above analysis, in this section, we propose a new hierarchical model with fast inference named EfficientViT. The architecture overview is shown in Fig. 6." + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "14422" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 96, + 59, + 500, + 335 + ], + "blocks": [ + { + "bbox": [ + 96, + 59, + 500, + 335 + ], + "lines": [ + { + "bbox": [ + 96, + 59, + 500, + 335 + ], + "spans": [ + { + "bbox": [ + 96, + 59, + 500, + 335 + ], + "type": "image", + "image_path": "c37d84c7fb2098ae31f4f984cc68eca0ae171dc409c5370ae2486d34015be964.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 63, + 337, + 528, + 348 + ], + "lines": [ + { + "bbox": [ + 63, + 337, + 528, + 348 + ], + "spans": [ + { + "bbox": [ + 63, + 337, + 528, + 348 + ], + "type": "text", + "content": "Figure 6. Overview of EfficientViT. (a) Architecture of EfficientViT; (b) Sandwich Layout block; (c) Cascaded Group Attention." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 361, + 203, + 373 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 361, + 203, + 373 + ], + "spans": [ + { + "bbox": [ + 47, + 361, + 203, + 373 + ], + "type": "text", + "content": "3.1. EfficientViT Building Blocks" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 380, + 286, + 451 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 380, + 286, + 451 + ], + "spans": [ + { + "bbox": [ + 46, + 380, + 286, + 451 + ], + "type": "text", + "content": "We propose a new efficient building block for vision transformer, as shown in Fig. 6 (b). It is composed of a memory-efficient sandwich layout, a cascaded group attention module, and a parameter reallocation strategy, which focus on improving model efficiency in terms of memory, computation, and parameter, respectively." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 451, + 286, + 532 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 451, + 286, + 532 + ], + "spans": [ + { + "bbox": [ + 46, + 451, + 286, + 532 + ], + "type": "text", + "content": "Sandwich Layout. To build up a memory-efficient block, we propose a sandwich layout that employs less memory-bound self-attention layers and more memory-efficient FFN layers for channel communication. Specifically, it applies a single self-attention layer " + }, + { + "bbox": [ + 46, + 451, + 286, + 532 + ], + "type": "inline_equation", + "content": "\\Phi_i^{\\mathrm{A}}" + }, + { + "bbox": [ + 46, + 451, + 286, + 532 + ], + "type": "text", + "content": " for spatial mixing, which is sandwiched between FFN layers " + }, + { + "bbox": [ + 46, + 451, + 286, + 532 + ], + "type": "inline_equation", + "content": "\\Phi_i^{\\mathrm{F}}" + }, + { + "bbox": [ + 46, + 451, + 286, + 532 + ], + "type": "text", + "content": ". The computation can be formulated as:" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 95, + 531, + 287, + 557 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 95, + 531, + 287, + 557 + ], + "spans": [ + { + "bbox": [ + 95, + 531, + 287, + 557 + ], + "type": "interline_equation", + "content": "X _ {i + 1} = \\prod^ {\\mathcal {N}} \\Phi_ {i} ^ {\\mathrm {F}} \\left(\\Phi_ {i} ^ {\\mathrm {A}} \\left(\\prod^ {\\mathcal {N}} \\Phi_ {i} ^ {\\mathrm {F}} \\left(X _ {i}\\right)\\right)\\right), \\tag {1}", + "image_path": "116088307368a6a23c8f5131b85a301525ecd57e298bccd6937113de7be206a2.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 557, + 286, + 677 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 557, + 286, + 677 + ], + "spans": [ + { + "bbox": [ + 46, + 557, + 286, + 677 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 557, + 286, + 677 + ], + "type": "inline_equation", + "content": "X_{i}" + }, + { + "bbox": [ + 46, + 557, + 286, + 677 + ], + "type": "text", + "content": " is the full input feature for the " + }, + { + "bbox": [ + 46, + 557, + 286, + 677 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 557, + 286, + 677 + ], + "type": "text", + "content": "-th block. The block transforms " + }, + { + "bbox": [ + 46, + 557, + 286, + 677 + ], + "type": "inline_equation", + "content": "X_{i}" + }, + { + "bbox": [ + 46, + 557, + 286, + 677 + ], + "type": "text", + "content": " into " + }, + { + "bbox": [ + 46, + 557, + 286, + 677 + ], + "type": "inline_equation", + "content": "X_{i+1}" + }, + { + "bbox": [ + 46, + 557, + 286, + 677 + ], + "type": "text", + "content": " with " + }, + { + "bbox": [ + 46, + 557, + 286, + 677 + ], + "type": "inline_equation", + "content": "\\mathcal{N}" + }, + { + "bbox": [ + 46, + 557, + 286, + 677 + ], + "type": "text", + "content": " FFNs before and after the single self-attention layer. This design reduces the memory time consumption caused by self-attention layers in the model, and applies more FFN layers to allow communication between different feature channels efficiently. We also apply an extra token interaction layer before each FFN using a depthwise convolution (DWConv) [27]. It introduces inductive bias of the local structural information to enhance model capability [14]." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 677, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 286, + 713 + ], + "type": "text", + "content": "Cascaded Group Attention. Attention head redundancy is a severe issue in MHSA, which causes computation inefficiency. Inspired by group convolutions in efficient CNNs" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 361, + 545, + 421 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 361, + 545, + 421 + ], + "spans": [ + { + "bbox": [ + 304, + 361, + 545, + 421 + ], + "type": "text", + "content": "[10, 37, 64, 87], we propose a new attention module named cascaded group attention (CGA) for vision transformers. It feeds each head with different splits of the full features, thus explicitly decomposing the attention computation across heads. Formally, this attention can be formulated as:" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 343, + 423, + 545, + 445 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 343, + 423, + 545, + 445 + ], + "spans": [ + { + "bbox": [ + 343, + 423, + 545, + 445 + ], + "type": "interline_equation", + "content": "\\tilde {X} _ {i j} = \\operatorname {A t t n} \\left(X _ {i j} W _ {i j} ^ {\\mathrm {Q}}, X _ {i j} W _ {i j} ^ {\\mathrm {K}}, X _ {i j} W _ {i j} ^ {\\mathrm {V}}\\right), \\tag {2}", + "image_path": "b1164f3ea246ce14f61f7572749b03176610982ffebfba36c980156b21381be5.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 339, + 441, + 468, + 456 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 339, + 441, + 468, + 456 + ], + "spans": [ + { + "bbox": [ + 339, + 441, + 468, + 456 + ], + "type": "interline_equation", + "content": "\\tilde {X} _ {i + 1} = \\operatorname {C o n c a t} \\left[ \\tilde {X} _ {i j} \\right] _ {j = 1: h} W _ {i} ^ {\\mathrm {P}},", + "image_path": "05577af609e4a91b02e3c353816d1f0be62427e6eaa81abc787c876de6725ae4.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 459, + 545, + 544 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 459, + 545, + 544 + ], + "spans": [ + { + "bbox": [ + 304, + 459, + 545, + 544 + ], + "type": "text", + "content": "where the " + }, + { + "bbox": [ + 304, + 459, + 545, + 544 + ], + "type": "inline_equation", + "content": "j" + }, + { + "bbox": [ + 304, + 459, + 545, + 544 + ], + "type": "text", + "content": "-th head computes the self-attention over " + }, + { + "bbox": [ + 304, + 459, + 545, + 544 + ], + "type": "inline_equation", + "content": "X_{ij}" + }, + { + "bbox": [ + 304, + 459, + 545, + 544 + ], + "type": "text", + "content": ", which is the " + }, + { + "bbox": [ + 304, + 459, + 545, + 544 + ], + "type": "inline_equation", + "content": "j" + }, + { + "bbox": [ + 304, + 459, + 545, + 544 + ], + "type": "text", + "content": "-th split of the input feature " + }, + { + "bbox": [ + 304, + 459, + 545, + 544 + ], + "type": "inline_equation", + "content": "X_{i}" + }, + { + "bbox": [ + 304, + 459, + 545, + 544 + ], + "type": "text", + "content": ", i.e., " + }, + { + "bbox": [ + 304, + 459, + 545, + 544 + ], + "type": "inline_equation", + "content": "X_{i} = [X_{i1}, X_{i2}, \\ldots, X_{ih}]" + }, + { + "bbox": [ + 304, + 459, + 545, + 544 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 459, + 545, + 544 + ], + "type": "inline_equation", + "content": "1 \\leq j \\leq h" + }, + { + "bbox": [ + 304, + 459, + 545, + 544 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 304, + 459, + 545, + 544 + ], + "type": "inline_equation", + "content": "h" + }, + { + "bbox": [ + 304, + 459, + 545, + 544 + ], + "type": "text", + "content": " is the total number of heads, " + }, + { + "bbox": [ + 304, + 459, + 545, + 544 + ], + "type": "inline_equation", + "content": "W_{ij}^{\\mathrm{Q}}, W_{ij}^{\\mathrm{K}}" + }, + { + "bbox": [ + 304, + 459, + 545, + 544 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 304, + 459, + 545, + 544 + ], + "type": "inline_equation", + "content": "W_{ij}^{\\mathrm{V}}" + }, + { + "bbox": [ + 304, + 459, + 545, + 544 + ], + "type": "text", + "content": " are projection layers mapping the input feature split into different subspaces, and " + }, + { + "bbox": [ + 304, + 459, + 545, + 544 + ], + "type": "inline_equation", + "content": "W_{i}^{\\mathrm{P}}" + }, + { + "bbox": [ + 304, + 459, + 545, + 544 + ], + "type": "text", + "content": " is a linear layer that projects the concatenated output features back to the dimension consistent with the input." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 545, + 545, + 641 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 545, + 545, + 641 + ], + "spans": [ + { + "bbox": [ + 304, + 545, + 545, + 641 + ], + "type": "text", + "content": "Although using feature splits instead of the full features for each head is more efficient and saves computation overhead, we continue to improve its capacity, by encouraging the " + }, + { + "bbox": [ + 304, + 545, + 545, + 641 + ], + "type": "inline_equation", + "content": "Q" + }, + { + "bbox": [ + 304, + 545, + 545, + 641 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 545, + 545, + 641 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 304, + 545, + 545, + 641 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 545, + 545, + 641 + ], + "type": "inline_equation", + "content": "V" + }, + { + "bbox": [ + 304, + 545, + 545, + 641 + ], + "type": "text", + "content": " layers to learn projections on features with richer information. We compute the attention map of each head in a cascaded manner, as illustrated in Fig. 6 (c), which adds the output of each head to the subsequent head to refine the feature representations progressively:" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 350, + 644, + 545, + 660 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 350, + 644, + 545, + 660 + ], + "spans": [ + { + "bbox": [ + 350, + 644, + 545, + 660 + ], + "type": "interline_equation", + "content": "X _ {i j} ^ {\\prime} = X _ {i j} + \\widetilde {X} _ {i (j - 1)}, \\quad 1 < j \\leq h, \\tag {3}", + "image_path": "5819dae9b7f031ccfad3a8a8b68cc55478d24e6315e5330bda3698003448abcc.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 662, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 662, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 662, + 545, + 713 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 662, + 545, + 713 + ], + "type": "inline_equation", + "content": "X_{ij}^{\\prime}" + }, + { + "bbox": [ + 304, + 662, + 545, + 713 + ], + "type": "text", + "content": " is the addition of the " + }, + { + "bbox": [ + 304, + 662, + 545, + 713 + ], + "type": "inline_equation", + "content": "j" + }, + { + "bbox": [ + 304, + 662, + 545, + 713 + ], + "type": "text", + "content": "-th input split " + }, + { + "bbox": [ + 304, + 662, + 545, + 713 + ], + "type": "inline_equation", + "content": "X_{ij}" + }, + { + "bbox": [ + 304, + 662, + 545, + 713 + ], + "type": "text", + "content": " and the " + }, + { + "bbox": [ + 304, + 662, + 545, + 713 + ], + "type": "inline_equation", + "content": "(j-1)" + }, + { + "bbox": [ + 304, + 662, + 545, + 713 + ], + "type": "text", + "content": "-th head output " + }, + { + "bbox": [ + 304, + 662, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\widetilde{X}_{i(j-1)}" + }, + { + "bbox": [ + 304, + 662, + 545, + 713 + ], + "type": "text", + "content": " calculated by Eq. (2). It replaces " + }, + { + "bbox": [ + 304, + 662, + 545, + 713 + ], + "type": "inline_equation", + "content": "X_{ij}" + }, + { + "bbox": [ + 304, + 662, + 545, + 713 + ], + "type": "text", + "content": " to serve as the new input feature for the " + }, + { + "bbox": [ + 304, + 662, + 545, + 713 + ], + "type": "inline_equation", + "content": "j" + }, + { + "bbox": [ + 304, + 662, + 545, + 713 + ], + "type": "text", + "content": "-th head when calculating the self-attention. Besides, another token" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "14423" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 59, + 74, + 273, + 156 + ], + "blocks": [ + { + "bbox": [ + 58, + 63, + 276, + 73 + ], + "lines": [ + { + "bbox": [ + 58, + 63, + 276, + 73 + ], + "spans": [ + { + "bbox": [ + 58, + 63, + 276, + 73 + ], + "type": "text", + "content": "Table 1. Architecture details of EfficientViT model variants." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 59, + 74, + 273, + 156 + ], + "lines": [ + { + "bbox": [ + 59, + 74, + 273, + 156 + ], + "spans": [ + { + "bbox": [ + 59, + 74, + 273, + 156 + ], + "type": "table", + "html": "
Model{C1,C2,C3}{L1,L2,L3}{H1,H2,H3}
EfficientViT-M0{64,128,192}{1,2,3}{4,4,4}
EfficientViT-M1{128,144,192}{1,2,3}{2,3,3}
EfficientViT-M2{128,192,224}{1,2,3}{4,3,2}
EfficientViT-M3{128,240,320}{1,2,3}{4,3,4}
EfficientViT-M4{128,256,384}{1,2,3}{4,4,4}
EfficientViT-M5{192,288,384}{1,3,4}{3,3,4}
", + "image_path": "082ed267043fe1cd08a942f0a442ae51a7fb54373ea2e225213933d425f9a630.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 159, + 287, + 196 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 159, + 287, + 196 + ], + "spans": [ + { + "bbox": [ + 46, + 159, + 287, + 196 + ], + "type": "text", + "content": "interaction layer is applied after the " + }, + { + "bbox": [ + 46, + 159, + 287, + 196 + ], + "type": "inline_equation", + "content": "Q" + }, + { + "bbox": [ + 46, + 159, + 287, + 196 + ], + "type": "text", + "content": " projection, which enables the self-attention to jointly capture local and global relations and further enhances the feature representation." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 197, + 286, + 339 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 197, + 286, + 339 + ], + "spans": [ + { + "bbox": [ + 46, + 197, + 286, + 339 + ], + "type": "text", + "content": "Such a cascaded design enjoys two advantages. First, feeding each head with different feature splits could improve the diversity of attention maps, as validated in Sec. 2.2. Similar to group convolutions [10, 87], the cascaded group attention could save the Flops and parameters by " + }, + { + "bbox": [ + 46, + 197, + 286, + 339 + ], + "type": "inline_equation", + "content": "h \\times" + }, + { + "bbox": [ + 46, + 197, + 286, + 339 + ], + "type": "text", + "content": ", since the input and output channels in the QKV layers are reduced by " + }, + { + "bbox": [ + 46, + 197, + 286, + 339 + ], + "type": "inline_equation", + "content": "h \\times" + }, + { + "bbox": [ + 46, + 197, + 286, + 339 + ], + "type": "text", + "content": ". Second, cascading the attention heads allows for an increase of network depth, thus further elevating the model capacity without introducing any extra parameters. It only incurs minor latency overhead since the attention map computation in each head uses smaller QK channel dimensions." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 341, + 286, + 520 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 341, + 286, + 520 + ], + "spans": [ + { + "bbox": [ + 46, + 341, + 286, + 520 + ], + "type": "text", + "content": "Parameter Reallocation. To improve parameter efficiency, we reallocate the parameters in the network by expanding the channel width of critical modules while shrinking the unimportant ones. Specifically, based on the Taylor importance analysis in Sec. 2.3, we set small channel dimensions for " + }, + { + "bbox": [ + 46, + 341, + 286, + 520 + ], + "type": "inline_equation", + "content": "Q" + }, + { + "bbox": [ + 46, + 341, + 286, + 520 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 341, + 286, + 520 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 46, + 341, + 286, + 520 + ], + "type": "text", + "content": " projections in each head for all stages. For the " + }, + { + "bbox": [ + 46, + 341, + 286, + 520 + ], + "type": "inline_equation", + "content": "V" + }, + { + "bbox": [ + 46, + 341, + 286, + 520 + ], + "type": "text", + "content": " projection, we allow it to have the same dimension as the input embedding. The expansion ratio in FFN is also reduced from 4 to 2 due to its parameter redundancy. With the proposed reallocation strategy, the important modules have larger number of channels to learn representations in a high dimensional space, which prevent the loss of feature information. Meanwhile, the redundant parameters in unimportant modules are removed to speed up inference and enhance the model efficiency." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 529, + 237, + 540 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 529, + 237, + 540 + ], + "spans": [ + { + "bbox": [ + 47, + 529, + 237, + 540 + ], + "type": "text", + "content": "3.2. EfficientViT Network Architectures" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 545, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 545, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 545, + 286, + 713 + ], + "type": "text", + "content": "The overall architecture of our EfficientViT is presented in Fig. 6 (a). Concretely, we introduce overlapping patch embedding [20, 80] to embed " + }, + { + "bbox": [ + 46, + 545, + 286, + 713 + ], + "type": "inline_equation", + "content": "16 \\times 16" + }, + { + "bbox": [ + 46, + 545, + 286, + 713 + ], + "type": "text", + "content": " patches into tokens with " + }, + { + "bbox": [ + 46, + 545, + 286, + 713 + ], + "type": "inline_equation", + "content": "C_1" + }, + { + "bbox": [ + 46, + 545, + 286, + 713 + ], + "type": "text", + "content": " dimension, which enhances the model capacity in low-level visual representation learning. The architecture contains three stages. Each stage stacks the proposed EfficientViT building blocks and the number of tokens is reduced by " + }, + { + "bbox": [ + 46, + 545, + 286, + 713 + ], + "type": "inline_equation", + "content": "4 \\times" + }, + { + "bbox": [ + 46, + 545, + 286, + 713 + ], + "type": "text", + "content": " at each subsampling layer (" + }, + { + "bbox": [ + 46, + 545, + 286, + 713 + ], + "type": "inline_equation", + "content": "2 \\times" + }, + { + "bbox": [ + 46, + 545, + 286, + 713 + ], + "type": "text", + "content": " subsampling of the resolution). To achieve efficient subsampling, we propose an EfficientViT subsample block which also has the sandwich layout, except that the self-attention layer is replaced by an inverted residual block to reduce the information loss during subsampling [26, 63]. It is worth noting that we adopt BatchNorm (BN) [30] instead of Layer" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "text", + "content": "Norm (LN) [2] throughout the model, as BN can be folded into the preceding convolution or linear layers, which is a runtime advantage over LN. We also use ReLU [54] as the activation function, as the commonly used GELU [25] or HardSwish [26] are much slower, and sometimes not well-supported by certain inference deployment platforms [1, 3]." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 144, + 545, + 263 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 144, + 545, + 263 + ], + "spans": [ + { + "bbox": [ + 304, + 144, + 545, + 263 + ], + "type": "text", + "content": "We build our model family with six different width and depth scales, and set different number of heads for each stage. We use fewer blocks in early stages than late stages similar to MobileNetV3 [26] and LeViT [20], since that the processing on early stages with larger resolutions is more time consuming. We increase the width over stages with a small factor " + }, + { + "bbox": [ + 304, + 144, + 545, + 263 + ], + "type": "inline_equation", + "content": "(\\leq 2)" + }, + { + "bbox": [ + 304, + 144, + 545, + 263 + ], + "type": "text", + "content": " to alleviate redundancy in later stages, as analyzed in Sec. 2.3. The architecture details of our model family are presented in Tab. 1. " + }, + { + "bbox": [ + 304, + 144, + 545, + 263 + ], + "type": "inline_equation", + "content": "C_i" + }, + { + "bbox": [ + 304, + 144, + 545, + 263 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 144, + 545, + 263 + ], + "type": "inline_equation", + "content": "L_i" + }, + { + "bbox": [ + 304, + 144, + 545, + 263 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 304, + 144, + 545, + 263 + ], + "type": "inline_equation", + "content": "H_i" + }, + { + "bbox": [ + 304, + 144, + 545, + 263 + ], + "type": "text", + "content": " refer to the width, depth, and number of heads in the " + }, + { + "bbox": [ + 304, + 144, + 545, + 263 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 304, + 144, + 545, + 263 + ], + "type": "text", + "content": "-th stage." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 270, + 388, + 283 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 270, + 388, + 283 + ], + "spans": [ + { + "bbox": [ + 305, + 270, + 388, + 283 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 289, + 440, + 302 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 289, + 440, + 302 + ], + "spans": [ + { + "bbox": [ + 306, + 289, + 440, + 302 + ], + "type": "text", + "content": "4.1. Implementation Details" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 306, + 545, + 605 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 306, + 545, + 605 + ], + "spans": [ + { + "bbox": [ + 304, + 306, + 545, + 605 + ], + "type": "text", + "content": "We conduct image classification experiments on ImageNet-1K [17]. The models are built with PyTorch 1.11.0 [59] and Timm 0.5.4 [77], and trained from scratch for 300 epochs on 8 Nvidia V100 GPUs using AdamW [46] optimizer and cosine learning rate scheduler. We set the total batchsize as 2,048. The input images are resized and randomly cropped into " + }, + { + "bbox": [ + 304, + 306, + 545, + 605 + ], + "type": "inline_equation", + "content": "224 \\times 224" + }, + { + "bbox": [ + 304, + 306, + 545, + 605 + ], + "type": "text", + "content": ". The initial learning rate is " + }, + { + "bbox": [ + 304, + 306, + 545, + 605 + ], + "type": "inline_equation", + "content": "1 \\times 10^{-3}" + }, + { + "bbox": [ + 304, + 306, + 545, + 605 + ], + "type": "text", + "content": " with weight decay of " + }, + { + "bbox": [ + 304, + 306, + 545, + 605 + ], + "type": "inline_equation", + "content": "2.5 \\times 10^{-2}" + }, + { + "bbox": [ + 304, + 306, + 545, + 605 + ], + "type": "text", + "content": ". We use the same data augmentation as [69], including Mixup [85], auto-augmentation [13], and random erasing [88]. In addition, we provide throughput evaluation on different hardware. For GPU, we measure the throughput on an Nvidia V100, with the maximum power-of-two batchsize that fits in memory following [20, 69]. For CPU and ONNX, we measure the runtime on an Intel Xeon E5-2690 v4 @ 2.60 GHz processor, with batchsize 16 and run the model in a single thread following [20]. We also test the transferability of EfficientViT on downstream tasks. For the experiments on downstream image classification, we finetune the models for 300 epochs following [86], using AdamW [46] with batchsize 256, learning rate " + }, + { + "bbox": [ + 304, + 306, + 545, + 605 + ], + "type": "inline_equation", + "content": "1 \\times 10^{-3}" + }, + { + "bbox": [ + 304, + 306, + 545, + 605 + ], + "type": "text", + "content": " and weight-decay " + }, + { + "bbox": [ + 304, + 306, + 545, + 605 + ], + "type": "inline_equation", + "content": "1 \\times 10^{-8}" + }, + { + "bbox": [ + 304, + 306, + 545, + 605 + ], + "type": "text", + "content": ". We use RetinaNet [41] for object detection on COCO [42], and train the models for 12 epochs (" + }, + { + "bbox": [ + 304, + 306, + 545, + 605 + ], + "type": "inline_equation", + "content": "1 \\times" + }, + { + "bbox": [ + 304, + 306, + 545, + 605 + ], + "type": "text", + "content": " schedule) with the same settings as [44] on mmdetection [6]. For instance segmentation, please refer to the supplementary." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 613, + 425, + 625 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 613, + 425, + 625 + ], + "spans": [ + { + "bbox": [ + 306, + 613, + 425, + 625 + ], + "type": "text", + "content": "4.2. Results on ImageNet" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 629, + 545, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 629, + 545, + 689 + ], + "spans": [ + { + "bbox": [ + 304, + 629, + 545, + 689 + ], + "type": "text", + "content": "We compare EfficientViT with prevailing efficient CNN and ViT models on ImageNet [17], and report the results in Tab. 2 and Fig. 1. The results show that, in most cases, our EfficientViT achieves the best accuracy and speed trade-off across different evaluation settings." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 689, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 689, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 306, + 689, + 545, + 712 + ], + "type": "text", + "content": "Comparisons with efficient CNNs. We first compare EfficientViT with vanilla CNN models, such as MobileNets" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "14424" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 87, + 99, + 506, + 434 + ], + "blocks": [ + { + "bbox": [ + 46, + 64, + 547, + 99 + ], + "lines": [ + { + "bbox": [ + 46, + 64, + 547, + 99 + ], + "spans": [ + { + "bbox": [ + 46, + 64, + 547, + 99 + ], + "type": "text", + "content": "Table 2. EfficientViT image classification performance on ImageNet-1K [17] with comparisons to state-of-the-art efficient CNN and ViT models trained without extra data. Throughput is tested on Nvidia V100 for GPU and Intel Xeon E5-2690 v4 @ 2.60 GHz processor for CPU and ONNX, where larger throughput means faster inference speed. ↑: finetune with higher resolution." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 87, + 99, + 506, + 434 + ], + "lines": [ + { + "bbox": [ + 87, + 99, + 506, + 434 + ], + "spans": [ + { + "bbox": [ + 87, + 99, + 506, + 434 + ], + "type": "table", + "html": "
ModelTop-1 (%)Top-5 (%)Throughput (images/s)Flops (M)Params (M)InputEpochs
GPUCPUONNX
EfficientViT-M063.285.427644228.4340.1792.3224300
MobileNetV3-Small [26]67.4-19738156.5231.7572.5224600
EfficientViT-M168.488.720093126.9215.91673.0224300
Mobile-Former-52M [9]68.7-314132.821.5523.5224450
MobileViT-XXS [50]69.0-445629.441.74101.3256300
ShuffleNetV2 1.0× [48]69.488.913301106.7177.01462.3224300
MobileViTV2-0.5 [51]70.2-514234.444.94661.4256300
EfficientViT-M270.890.218218121.2158.72014.2224300
MobileOne-S0 [70]71.4-1132067.4128.62742.1224300
MobileNetV2 1.0× [63]72.091.0653432.580.43003.4224300
EfficientViT-M373.491.41664496.4120.82636.9224300
GhostNet 1.0× [23]73.991.4738257.377.01415.2224300
NASNet-A-Mobile [89]74.1-262319.825.55645.3224300
EfficientViT-M474.391.81591488.5108.62998.8224300
EdgeViT-XXS [56]74.4-363828.229.65564.1224300
MobileViT-XS [50]74.7-334411.120.59862.3256300
ShuffleNetV2 2.0× [48]74.992.4696237.952.35917.4224300
MobileNetV3-Large [26]75.2-756039.170.52175.4224600
MobileViTV2-0.75 [51]75.6-335016.022.710302.9256300
MobileOne-S1 [70]75.9-666330.751.18254.8224300
GLiT-Tiny [5]76.4-351617.515.713337.3224300
EfficientNet-B0 [67]77.193.3453230.229.53905.3224350
EfficientViT-M577.193.41062156.862.552212.4224300
EfficientViT-M4↑38479.895.0398615.822.6148612.4384330
EfficientViT-M5↑51280.895.523138.310.5267012.4512360
", + "image_path": "666b002b6cf6fe0d3d85d30f81a5584a910b9b097c0974b12f05976e16b49e5d.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 448, + 289, + 640 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 448, + 289, + 640 + ], + "spans": [ + { + "bbox": [ + 46, + 448, + 289, + 640 + ], + "type": "text", + "content": "[26, 63] and EfficientNet [67]. Specifically, compared to MobileNetV2 " + }, + { + "bbox": [ + 46, + 448, + 289, + 640 + ], + "type": "inline_equation", + "content": "1.0 \\times" + }, + { + "bbox": [ + 46, + 448, + 289, + 640 + ], + "type": "text", + "content": " [63], EfficientViT-M3 obtains " + }, + { + "bbox": [ + 46, + 448, + 289, + 640 + ], + "type": "inline_equation", + "content": "1.4\\%" + }, + { + "bbox": [ + 46, + 448, + 289, + 640 + ], + "type": "text", + "content": " better top-1 accuracy, while running at " + }, + { + "bbox": [ + 46, + 448, + 289, + 640 + ], + "type": "inline_equation", + "content": "2.5 \\times" + }, + { + "bbox": [ + 46, + 448, + 289, + 640 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 448, + 289, + 640 + ], + "type": "inline_equation", + "content": "3.0 \\times" + }, + { + "bbox": [ + 46, + 448, + 289, + 640 + ], + "type": "text", + "content": " faster speed on V100 GPU and Intel CPU, respectively. Compared to the state-of-the-art MobileNetV3-Large [26], EfficientViT-M5 achieves " + }, + { + "bbox": [ + 46, + 448, + 289, + 640 + ], + "type": "inline_equation", + "content": "1.9\\%" + }, + { + "bbox": [ + 46, + 448, + 289, + 640 + ], + "type": "text", + "content": " higher accuracy yet runs much faster, e.g., " + }, + { + "bbox": [ + 46, + 448, + 289, + 640 + ], + "type": "inline_equation", + "content": "40.5\\%" + }, + { + "bbox": [ + 46, + 448, + 289, + 640 + ], + "type": "text", + "content": " faster on the V100 GPU and " + }, + { + "bbox": [ + 46, + 448, + 289, + 640 + ], + "type": "inline_equation", + "content": "45.2\\%" + }, + { + "bbox": [ + 46, + 448, + 289, + 640 + ], + "type": "text", + "content": " faster on the Intel CPU but is " + }, + { + "bbox": [ + 46, + 448, + 289, + 640 + ], + "type": "inline_equation", + "content": "11.5\\%" + }, + { + "bbox": [ + 46, + 448, + 289, + 640 + ], + "type": "text", + "content": " slower as ONNX models. This may because reshaping is slower in ONNX implementation, which is inevitable in computing self-attention. Moreover, EfficientViT-M5 achieves comparable accuracy with the searched model EfficientNet-B0 [67], while runs " + }, + { + "bbox": [ + 46, + 448, + 289, + 640 + ], + "type": "inline_equation", + "content": "2.3 \\times / 1.9 \\times" + }, + { + "bbox": [ + 46, + 448, + 289, + 640 + ], + "type": "text", + "content": " faster on the V100 GPU/Intel CPU, and " + }, + { + "bbox": [ + 46, + 448, + 289, + 640 + ], + "type": "inline_equation", + "content": "2.1 \\times" + }, + { + "bbox": [ + 46, + 448, + 289, + 640 + ], + "type": "text", + "content": " faster as ONNX models. Although our model uses more parameters, it reduces memory-inefficient operations that affect the inference speed and achieves higher throughput." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 642, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 642, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 642, + 288, + 714 + ], + "type": "text", + "content": "Comparisons with efficient ViTs. We also compare our models with recent efficient vision transformers [5, 9, 50, 51, 56] in Tab. 2. In particular, when getting similar performance on ImageNet-1K [17], our EfficientViT-M4 runs " + }, + { + "bbox": [ + 46, + 642, + 288, + 714 + ], + "type": "inline_equation", + "content": "4.4 \\times" + }, + { + "bbox": [ + 46, + 642, + 288, + 714 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 642, + 288, + 714 + ], + "type": "inline_equation", + "content": "3.0 \\times" + }, + { + "bbox": [ + 46, + 642, + 288, + 714 + ], + "type": "text", + "content": " faster than the recent EdgeViT-XXS [56] on the tested CPU and GPU devices. Even converted to ONNX" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 304, + 448, + 545, + 604 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 448, + 545, + 604 + ], + "spans": [ + { + "bbox": [ + 304, + 448, + 545, + 604 + ], + "type": "text", + "content": "runtime format, our model still gets " + }, + { + "bbox": [ + 304, + 448, + 545, + 604 + ], + "type": "inline_equation", + "content": "3.7 \\times" + }, + { + "bbox": [ + 304, + 448, + 545, + 604 + ], + "type": "text", + "content": " higher speed. Compared to the state-of-the-art MobileViTV2-0.5 [51], our EfficientViT-M2 achieves slightly better performance with higher throughput, e.g., " + }, + { + "bbox": [ + 304, + 448, + 545, + 604 + ], + "type": "inline_equation", + "content": "3.4 \\times" + }, + { + "bbox": [ + 304, + 448, + 545, + 604 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 448, + 545, + 604 + ], + "type": "inline_equation", + "content": "3.5 \\times" + }, + { + "bbox": [ + 304, + 448, + 545, + 604 + ], + "type": "text", + "content": " higher throughput tested on the GPU and CPU devices, respectively. Furthermore, we compare with tiny variants of state-of-the-art large ViTs in Tab. 3. PoolFormer-12S [83] has comparable accuracy with EfficientViT-M5 yet runs " + }, + { + "bbox": [ + 304, + 448, + 545, + 604 + ], + "type": "inline_equation", + "content": "3.0 \\times" + }, + { + "bbox": [ + 304, + 448, + 545, + 604 + ], + "type": "text", + "content": " slower on the V100 GPU. Compared to Swin-T [44], EfficientViT-M5 is " + }, + { + "bbox": [ + 304, + 448, + 545, + 604 + ], + "type": "inline_equation", + "content": "4.1\\%" + }, + { + "bbox": [ + 304, + 448, + 545, + 604 + ], + "type": "text", + "content": " inferior in accuracy yet is " + }, + { + "bbox": [ + 304, + 448, + 545, + 604 + ], + "type": "inline_equation", + "content": "12.3 \\times" + }, + { + "bbox": [ + 304, + 448, + 545, + 604 + ], + "type": "text", + "content": " faster on the Intel CPU, demonstrating the efficiency of the proposed design. In addition, we present the speed evaluation and comparison on mobile chipsets in the supplementary material." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 605, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 547, + 715 + ], + "type": "text", + "content": "Finetune with higher resolutions. Recent works on ViTs have demonstrated that finetuning with higher resolutions can further improve the capacity of the models. We also finetune our largest model EfficientViT-M5 to higher resolutions. EfficientViT-M5↑384 reaches 79.8% top-1 accuracy with throughput of 3,986 images/s on the V100 GPU, and EfficientViT-M5↑512 further improves the top-1 accuracy to 80.8%, demonstrating the efficiency on processing images with larger resolutions and the good model capacity." + } + ] + } + ], + "index": 5 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "14425" + } + ] + } + ], + "index": 6 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 52, + 88, + 281, + 180 + ], + "blocks": [ + { + "bbox": [ + 47, + 64, + 287, + 87 + ], + "lines": [ + { + "bbox": [ + 47, + 64, + 287, + 87 + ], + "spans": [ + { + "bbox": [ + 47, + 64, + 287, + 87 + ], + "type": "text", + "content": "Table 3. Comparison with the tiny variants of state-of-the-art large-scale ViTs on ImageNet-1K [17]." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 52, + 88, + 281, + 180 + ], + "lines": [ + { + "bbox": [ + 52, + 88, + 281, + 180 + ], + "spans": [ + { + "bbox": [ + 52, + 88, + 281, + 180 + ], + "type": "table", + "html": "
ModelTop-1 (%)Throughput (imgs/s)Flops (G)Params (M)
GPUCPUONNX
PVTV2-B0 [76]70.5350712.718.50.61.4
T2T-ViT-7 [84]71.7115622.516.11.14.3
DeiT-T [69]72.2463126.025.11.35.9
PoolFormer-12S [83]77.2353410.414.61.912.0
EffFormer-L1 [40]79.2446512.921.21.312.3
Swin-T [44]81.213934.66.44.529.0
EfficientViT-M577.11062156.862.50.512.4
", + "image_path": "fad66f880e1da229fe3bf5341377c57387728ebe5bd34c74df6e20dd4c1b576b.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "type": "table", + "bbox": [ + 52, + 206, + 282, + 302 + ], + "blocks": [ + { + "bbox": [ + 47, + 183, + 286, + 204 + ], + "lines": [ + { + "bbox": [ + 47, + 183, + 286, + 204 + ], + "spans": [ + { + "bbox": [ + 47, + 183, + 286, + 204 + ], + "type": "text", + "content": "Table 4. Results of EfficientViT and other efficient models on downstream image classification datasets." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 52, + 206, + 282, + 302 + ], + "lines": [ + { + "bbox": [ + 52, + 206, + 282, + 302 + ], + "spans": [ + { + "bbox": [ + 52, + 206, + 282, + 302 + ], + "type": "table", + "html": "
ModelThroughputImageNetCIFAR10CIFAR100CarsFlowersPets
MobileNetV1 [27]854370.696.182.391.496.789.9
MobileNetV2 [63]653472.995.780.891.096.690.5
MobileNetV3 [26]756075.297.685.591.297.090.1
NASNet-A-M [89]262374.196.883.988.596.889.4
ViT-S/16 [18]213581.497.685.7-86.490.4
EfficientViT-M51062177.198.086.489.797.192.0
", + "image_path": "578ea6dbe8887b254b2c1729b81ec3873940ce54c2a2533713c08583f110ea57.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 308, + 194, + 320 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 308, + 194, + 320 + ], + "spans": [ + { + "bbox": [ + 47, + 308, + 194, + 320 + ], + "type": "text", + "content": "4.3. Transfer Learning Results" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 325, + 286, + 348 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 325, + 286, + 348 + ], + "spans": [ + { + "bbox": [ + 47, + 325, + 286, + 348 + ], + "type": "text", + "content": "To further evaluate the transfer ability, we apply EfficientViT on various downstream tasks." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 350, + 286, + 492 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 350, + 286, + 492 + ], + "spans": [ + { + "bbox": [ + 46, + 350, + 286, + 492 + ], + "type": "text", + "content": "Downstream Image Classification. We transfer EfficientViT to downstream image classification datasets to test its generalization ability: 1) CIFAR-10 and CIFAR-100 [36]; 2) fine-grained classification: Flowers [55], Stanford Cars [35], and Oxford-IIIT Pets [58]. We report the results in Tab. 4. Compared to existing efficient models [18, 26, 27, 63, 89], our EfficientViT-M5 achieves comparable or slightly better accuracy across all datasets with much higher throughput. An exception lies in Cars, where our model is slightly inferior in accuracy. This may because the subtle differences between classes lie more in local details thus is more feasible to be captured with convolution." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 494, + 286, + 589 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 494, + 286, + 589 + ], + "spans": [ + { + "bbox": [ + 46, + 494, + 286, + 589 + ], + "type": "text", + "content": "Object Detection. We compare EfficientViT-M4 with efficient models [12, 22, 26, 63, 66, 68] on the COCO [42] object detection task, and present the results in Tab. 5. Specifically, EfficientViT-M4 surpasses MobileNetV2 [63] by " + }, + { + "bbox": [ + 46, + 494, + 286, + 589 + ], + "type": "inline_equation", + "content": "4.4\\%" + }, + { + "bbox": [ + 46, + 494, + 286, + 589 + ], + "type": "text", + "content": " AP with comparable Flops. Compared to the searched method SPOS [22], our EfficientViT-M4 uses " + }, + { + "bbox": [ + 46, + 494, + 286, + 589 + ], + "type": "inline_equation", + "content": "18.1\\%" + }, + { + "bbox": [ + 46, + 494, + 286, + 589 + ], + "type": "text", + "content": " fewer Flops while achieving " + }, + { + "bbox": [ + 46, + 494, + 286, + 589 + ], + "type": "inline_equation", + "content": "2.0\\%" + }, + { + "bbox": [ + 46, + 494, + 286, + 589 + ], + "type": "text", + "content": " higher AP, demonstrating its capacity and generalization ability in different vision tasks." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 598, + 140, + 611 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 598, + 140, + 611 + ], + "spans": [ + { + "bbox": [ + 47, + 598, + 140, + 611 + ], + "type": "text", + "content": "4.4. Ablation Study" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 616, + 286, + 665 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 616, + 286, + 665 + ], + "spans": [ + { + "bbox": [ + 46, + 616, + 286, + 665 + ], + "type": "text", + "content": "In this section, we ablate important design elements in the proposed EfficientViT on ImageNet-1K [17]. All models are trained for 100 epochs to magnify the differences and reduce training time [20]. Tab. 6 reports the results." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 666, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 666, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 666, + 286, + 713 + ], + "type": "text", + "content": "Impact of the sandwich layout block. We first present an ablation study to verify the efficiency of the proposed sandwich layout design, by replacing the sandwich layout block with the original Swin block [44]. The depth is adjusted to" + } + ] + } + ], + "index": 10 + }, + { + "type": "table", + "bbox": [ + 313, + 88, + 538, + 183 + ], + "blocks": [ + { + "bbox": [ + 305, + 64, + 545, + 87 + ], + "lines": [ + { + "bbox": [ + 305, + 64, + 545, + 87 + ], + "spans": [ + { + "bbox": [ + 305, + 64, + 545, + 87 + ], + "type": "text", + "content": "Table 5. EfficientViT object detection performance on COCOval2017 [42] with comparisons to other efficient models." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 313, + 88, + 538, + 183 + ], + "lines": [ + { + "bbox": [ + 313, + 88, + 538, + 183 + ], + "spans": [ + { + "bbox": [ + 313, + 88, + 538, + 183 + ], + "type": "table", + "html": "
ModelRetinaNet 1×FlopsParams
APAP50AP75APsAPmAPl(M)(M)
MobileNetV2 [63]28.346.729.314.830.738.13003.4
MobileNetV3 [26]29.949.330.814.933.341.12175.4
SPOS [22]30.749.832.215.433.941.63654.3
MNASNet-A2 [66]30.550.232.016.634.141.13404.8
FairNAS-C [12]31.250.832.716.334.442.33255.6
MixNet-M [68]31.351.732.417.035.041.93605.0
EfficientViT-M432.752.234.117.635.346.02998.8
", + "image_path": "725a9b2d64e70a4a7e54004a3ef9bf830485ce4fcdecc6d3ace598b78ab8ad3e.jpg" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "table_body" + } + ], + "index": 12 + }, + { + "type": "table", + "bbox": [ + 317, + 212, + 535, + 360 + ], + "blocks": [ + { + "bbox": [ + 306, + 186, + 545, + 209 + ], + "lines": [ + { + "bbox": [ + 306, + 186, + 545, + 209 + ], + "spans": [ + { + "bbox": [ + 306, + 186, + 545, + 209 + ], + "type": "text", + "content": "Table 6. Ablation for EfficientViT-M4 on ImageNet-1K [17] dataset. Top-1 accuracy, GPU and ONNX throughput are reported." + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 317, + 212, + 535, + 360 + ], + "lines": [ + { + "bbox": [ + 317, + 212, + 535, + 360 + ], + "spans": [ + { + "bbox": [ + 317, + 212, + 535, + 360 + ], + "type": "table", + "html": "
#AblationTop-1 (%)Throughput (imgs/s)
GPUONNX
1EfficientViT-M471.315914108.6
2Sandwich → Swin [44]68.315804114.5
3N = 1 → 270.214977112.3
4N = 1 → 365.715856139.7
5CGA → MHSA [18]70.216243102.2
6Cascade → None69.816411111.0
7QKV allocation → None69.915132103.1
8FFN ratio 2 → 469.815310112.4
9DWConv → None69.916325110.4
10BN → LN [2]70.415463103.6
11ReLU → HSwish [26]72.21588787.5
", + "image_path": "9d4a5202a81b5c8e45680da248eb0c63fc7eb31cccfcc3efb4e695819eff22b8.jpg" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "table_body" + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 364, + 545, + 495 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 364, + 545, + 495 + ], + "spans": [ + { + "bbox": [ + 304, + 364, + 545, + 495 + ], + "type": "inline_equation", + "content": "\\{2, 2, 3\\}" + }, + { + "bbox": [ + 304, + 364, + 545, + 495 + ], + "type": "text", + "content": " to guarantee similar throughput with EfficientViTM4 for a fair comparison. The top-1 accuracy degrades by " + }, + { + "bbox": [ + 304, + 364, + 545, + 495 + ], + "type": "inline_equation", + "content": "3.0\\%" + }, + { + "bbox": [ + 304, + 364, + 545, + 495 + ], + "type": "text", + "content": " at a similar speed, verifying that applying more FFNs instead of memory-bound MHSA is more effective for small models. Furthermore, to analyze the impact of the number of FFNs " + }, + { + "bbox": [ + 304, + 364, + 545, + 495 + ], + "type": "inline_equation", + "content": "\\mathcal{N}" + }, + { + "bbox": [ + 304, + 364, + 545, + 495 + ], + "type": "text", + "content": " before and after self-attention, we change the number from 1 to 2 and 3. The number of blocks is reduced accordingly to maintain similar throughput. As presented in Tab. 6 (#3 and #4), further increasing the number of FFNs is not effective due to the lack of long-range spatial relation and " + }, + { + "bbox": [ + 304, + 364, + 545, + 495 + ], + "type": "inline_equation", + "content": "\\mathcal{N} = 1" + }, + { + "bbox": [ + 304, + 364, + 545, + 495 + ], + "type": "text", + "content": " achieves the best efficiency." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 497, + 545, + 604 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 497, + 545, + 604 + ], + "spans": [ + { + "bbox": [ + 304, + 497, + 545, + 604 + ], + "type": "text", + "content": "Impact of the cascaded group attention. We have proposed CGA to improve the computation efficiency of MHSA. As shown in Tab. 6 (#5 and #6), replacing CGA with MHSA decreases the accuracy by " + }, + { + "bbox": [ + 304, + 497, + 545, + 604 + ], + "type": "inline_equation", + "content": "1.1\\%" + }, + { + "bbox": [ + 304, + 497, + 545, + 604 + ], + "type": "text", + "content": " and ONNX speed by " + }, + { + "bbox": [ + 304, + 497, + 545, + 604 + ], + "type": "inline_equation", + "content": "5.9\\%" + }, + { + "bbox": [ + 304, + 497, + 545, + 604 + ], + "type": "text", + "content": ", suggesting that addressing head redundancy improves the model efficiency. For the model without the cascade operation, its performance is comparable with MHSA but worse than CGA, demonstrating the efficacy of enhancing the feature representations of each head." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": "Impact of the parameter reallocation. Our EfficientViTM4 yields " + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "inline_equation", + "content": "1.4\\% / 1.5\\%" + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": " higher top-1 accuracy, " + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "inline_equation", + "content": "4.9\\% / 3.8\\%" + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": " higher GPU throughput than the models without QKV channel dimension reallocation or FFN ratio reduction, respectively, indicating the effectiveness of parameter reallocation (#1 vs. #7, #8). Moreover, we study the choices of QK dimension in each head and the ratio of V dimension to the input embedding in Fig. 7. It is shown that the performance is improved gradually as QK dimension increases" + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "14426" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 52, + 96, + 282, + 145 + ], + "blocks": [ + { + "bbox": [ + 47, + 64, + 287, + 95 + ], + "lines": [ + { + "bbox": [ + 47, + 64, + 287, + 95 + ], + "spans": [ + { + "bbox": [ + 47, + 64, + 287, + 95 + ], + "type": "text", + "content": "Table 7. Performance comparison on ImageNet-1K [17] and ImageNet-ReaL [4]. Results with " + }, + { + "bbox": [ + 47, + 64, + 287, + 95 + ], + "type": "inline_equation", + "content": "\\dagger" + }, + { + "bbox": [ + 47, + 64, + 287, + 95 + ], + "type": "text", + "content": " are trained with 1,000 epochs and knowledge distillation following LeViT [20]." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 52, + 96, + 282, + 145 + ], + "lines": [ + { + "bbox": [ + 52, + 96, + 282, + 145 + ], + "spans": [ + { + "bbox": [ + 52, + 96, + 282, + 145 + ], + "type": "table", + "html": "
ModelImageNet (%)Throughput (imgs/s)Flops Params
Top-1Top-1†RealL†GPUCPUONNX(M)(M)
LeViT-128S [20]73.676.682.61445782.380.93057.8
EfficientViT-M474.377.183.61591488.5108.62998.8
", + "image_path": "bbee4e0d10b96b38229df9201d691613ae7bd043ed548cbc27fc9c71640491c8.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 151, + 286, + 246 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 151, + 286, + 246 + ], + "spans": [ + { + "bbox": [ + 46, + 151, + 286, + 246 + ], + "type": "text", + "content": "from 4 to 16, while further increasing it gives inferior performance. Besides, the performance improves from " + }, + { + "bbox": [ + 46, + 151, + 286, + 246 + ], + "type": "inline_equation", + "content": "70.3\\%" + }, + { + "bbox": [ + 46, + 151, + 286, + 246 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 46, + 151, + 286, + 246 + ], + "type": "inline_equation", + "content": "71.3\\%" + }, + { + "bbox": [ + 46, + 151, + 286, + 246 + ], + "type": "text", + "content": " when increasing the ratio between " + }, + { + "bbox": [ + 46, + 151, + 286, + 246 + ], + "type": "inline_equation", + "content": "V" + }, + { + "bbox": [ + 46, + 151, + 286, + 246 + ], + "type": "text", + "content": " dimension and input embedding from 0.4 to 1.0. When further enlarging the ratio to 1.2, it only gets " + }, + { + "bbox": [ + 46, + 151, + 286, + 246 + ], + "type": "inline_equation", + "content": "0.1\\%" + }, + { + "bbox": [ + 46, + 151, + 286, + 246 + ], + "type": "text", + "content": " improvements. Therefore, setting the channels of " + }, + { + "bbox": [ + 46, + 151, + 286, + 246 + ], + "type": "inline_equation", + "content": "V" + }, + { + "bbox": [ + 46, + 151, + 286, + 246 + ], + "type": "text", + "content": " close to the input embedding achieves the best parameter efficiency, which meets our analysis in Sec. 2.3 and design strategy." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 247, + 286, + 400 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 247, + 286, + 400 + ], + "spans": [ + { + "bbox": [ + 46, + 247, + 286, + 400 + ], + "type": "text", + "content": "Impact of other components. We ablate the impact of using DWConv for token interaction, the normalization layer, and the activation function, as presented in Tab. 6 (#9, #10, and #11). With DWConv, the accuracy improves by " + }, + { + "bbox": [ + 46, + 247, + 286, + 400 + ], + "type": "inline_equation", + "content": "1.4\\%" + }, + { + "bbox": [ + 46, + 247, + 286, + 400 + ], + "type": "text", + "content": " with a minor latency overhead, demonstrating the effectiveness of introducing local structural information. Replacing BN with LN decreases accuracy by " + }, + { + "bbox": [ + 46, + 247, + 286, + 400 + ], + "type": "inline_equation", + "content": "0.9\\%" + }, + { + "bbox": [ + 46, + 247, + 286, + 400 + ], + "type": "text", + "content": " and GPU speed by " + }, + { + "bbox": [ + 46, + 247, + 286, + 400 + ], + "type": "inline_equation", + "content": "2.9\\%" + }, + { + "bbox": [ + 46, + 247, + 286, + 400 + ], + "type": "text", + "content": ". Using HardSwish instead of ReLU improves accuracy by " + }, + { + "bbox": [ + 46, + 247, + 286, + 400 + ], + "type": "inline_equation", + "content": "0.9\\%" + }, + { + "bbox": [ + 46, + 247, + 286, + 400 + ], + "type": "text", + "content": " but leads to a large drop of " + }, + { + "bbox": [ + 46, + 247, + 286, + 400 + ], + "type": "inline_equation", + "content": "20.0\\%" + }, + { + "bbox": [ + 46, + 247, + 286, + 400 + ], + "type": "text", + "content": " ONNX speed. The activation functions are element-wise operations that occupy a considerable amount of processing time on GPU/CPU [15,48,72], thus utilizing ReLU instead of more complicated activation functions is of better efficiency." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 402, + 286, + 534 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 402, + 286, + 534 + ], + "spans": [ + { + "bbox": [ + 46, + 402, + 286, + 534 + ], + "type": "text", + "content": "Results of 1,000 training epochs and distillation. Tab. 7 shows the results with 1,000 training epochs and knowledge distillation using RegNetY-16GF [60] as the teacher model following [20] on ImageNet-1K [17] and ImageNet-ReaL [4]. Compared to LeViT-128S [20], EfficientViT-M4 surpasses it by " + }, + { + "bbox": [ + 46, + 402, + 286, + 534 + ], + "type": "inline_equation", + "content": "0.5\\%" + }, + { + "bbox": [ + 46, + 402, + 286, + 534 + ], + "type": "text", + "content": " on ImageNet-1K and " + }, + { + "bbox": [ + 46, + 402, + 286, + 534 + ], + "type": "inline_equation", + "content": "1.0\\%" + }, + { + "bbox": [ + 46, + 402, + 286, + 534 + ], + "type": "text", + "content": " on ImageNet-ReaL, respectively. For the inference speed, our model has " + }, + { + "bbox": [ + 46, + 402, + 286, + 534 + ], + "type": "inline_equation", + "content": "34.2\\%" + }, + { + "bbox": [ + 46, + 402, + 286, + 534 + ], + "type": "text", + "content": " higher throughput on ONNX and also shows superiority on other settings. The results demonstrate that the strong capability and generalization ability of EfficientViT can be further explored with longer training schedules." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 540, + 134, + 552 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 540, + 134, + 552 + ], + "spans": [ + { + "bbox": [ + 47, + 540, + 134, + 552 + ], + "type": "text", + "content": "5. Related Work" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 557, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 557, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 557, + 286, + 713 + ], + "type": "text", + "content": "Efficient CNNs. With the demand of deploying CNNs on resource-constrained scenarios, efficient CNNs have been intensively studied in literature [23, 24, 26, 48, 63, 67, 87]. Xception [10] proposes an architecture built with depthwise separable convolutions. MobileNetV2 [63] builds an inverted residual structure which expands the input to a higher dimension. MobileNetV3 [26] and EfficientNet [67] resort to neural architecture search techniques to design compact models. To boost the actual speed on hardware, ShuffleNetV2 [48] introduces channel split and shuffle operations to improve the information communication among channel groups. However, the spatial locality of convolutional kernels hampers CNN models from capturing long-" + } + ] + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 309, + 60, + 422, + 110 + ], + "blocks": [ + { + "bbox": [ + 309, + 60, + 422, + 110 + ], + "lines": [ + { + "bbox": [ + 309, + 60, + 422, + 110 + ], + "spans": [ + { + "bbox": [ + 309, + 60, + 422, + 110 + ], + "type": "image", + "image_path": "833cbf3b725904c503508d22147a1f2f3ebc5e510ea444b2f53e572a84af25e0.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 306, + 110, + 545, + 132 + ], + "lines": [ + { + "bbox": [ + 306, + 110, + 545, + 132 + ], + "spans": [ + { + "bbox": [ + 306, + 110, + 545, + 132 + ], + "type": "text", + "content": "Figure 7. Ablation on the " + }, + { + "bbox": [ + 306, + 110, + 545, + 132 + ], + "type": "inline_equation", + "content": "QK" + }, + { + "bbox": [ + 306, + 110, + 545, + 132 + ], + "type": "text", + "content": " dimension of each head and the ratio of " + }, + { + "bbox": [ + 306, + 110, + 545, + 132 + ], + "type": "inline_equation", + "content": "V" + }, + { + "bbox": [ + 306, + 110, + 545, + 132 + ], + "type": "text", + "content": " dimension to the input embedding." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 423, + 60, + 540, + 110 + ], + "blocks": [ + { + "bbox": [ + 423, + 60, + 540, + 110 + ], + "lines": [ + { + "bbox": [ + 423, + 60, + 540, + 110 + ], + "spans": [ + { + "bbox": [ + 423, + 60, + 540, + 110 + ], + "type": "image", + "image_path": "c9dcaaafbbbf228bb114b6f8d0699435b8898f89702b5ed6531a072e6168023e.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 138, + 528, + 150 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 138, + 528, + 150 + ], + "spans": [ + { + "bbox": [ + 306, + 138, + 528, + 150 + ], + "type": "text", + "content": "range dependencies, thus limiting their model capacity." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 151, + 545, + 437 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 151, + 545, + 437 + ], + "spans": [ + { + "bbox": [ + 304, + 151, + 545, + 437 + ], + "type": "text", + "content": "Efficient ViTs. ViT and its variants [18, 44, 69, 76] have achieved success on various vision tasks. Despite the superior performance, most of them are inferior to typical CNNs in inference speed. Some efficient transformers have been proposed recently and they fall into two camps: 1) efficient self-attention; and 2) efficient architecture design. Efficient self-attention methods reduce the cost of softmax attention via sparse attention [34, 57, 61, 75] or low-rank approximation [11, 51, 74]. However, they suffer from performance degradation with negligible or moderate inference acceleration over softmax attention [71]. Another line of work combines ViTs with lightweight CNNs to build efficient architectures [9, 47, 49, 50, 81]. LVT [81] proposes enhanced attention mechanisms with dilated convolution to improve the model performance and efficiency. Mobile-Former [9] designs a parallel CNN-transformer block to encode both local features and global interaction. However, most of them target at minimizing Flops and parameters [16], which could have low correlations with actual inference latency [70] and still inferior to efficient CNNs in speed. Different from them, we explore models with fast inference by directly optimizing their throughput on different hardware and deployment settings, and design a family of hierarchical models with a good trade-off between speed and accuracy." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 445, + 378, + 456 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 445, + 378, + 456 + ], + "spans": [ + { + "bbox": [ + 306, + 445, + 378, + 456 + ], + "type": "text", + "content": "6. Conclusion" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 461, + 545, + 555 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 461, + 545, + 555 + ], + "spans": [ + { + "bbox": [ + 304, + 461, + 545, + 555 + ], + "type": "text", + "content": "In this paper, we have presented a systematic analysis on the factors that affect the inference speed of vision transformers, and proposed a new family of fast vision transformers with memory-efficient operations and cascaded group attention, named EfficientViT. Extensive experiments have demonstrated the efficacy and high speed of EfficientViT, and also show its superiority on various downstream benchmarks." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 557, + 545, + 665 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 557, + 545, + 665 + ], + "spans": [ + { + "bbox": [ + 304, + 557, + 545, + 665 + ], + "type": "text", + "content": "Limitations. One limitation of EfficientViT is that, despite its high inference speed, the model size is slightly larger compared to state-of-the-art efficient CNN [26] due to the extra FFNs in the introduced sandwich layout. Besides, our models are designed manually based on the derived guidelines on building efficient vision transformers. In future work, we are interested in reducing the model size and incorporating automatic search techniques to further enhance the model capacity and efficiency." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "content": "Acknowledgement. Prof. Yuan was partially supported by Hong Kong Research Grants Council (RGC) General Research Fund 11211221, and Innovation and Technology Commission-Innovation and Technology Fund ITS/100/20." + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "14427" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 286, + 712 + ], + "type": "list", + "angle": 0, + "index": 18, + "blocks": [ + { + "bbox": [ + 53, + 91, + 286, + 122 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 286, + 122 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 286, + 122 + ], + "type": "text", + "content": "[1] Apple. 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Karen Liu† Jiajun Wu† \nStanford University", + "bbox": [ + 307, + 180, + 666, + 217 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "{jiamanli,karenliu, jiajunwu}@cs.stanford.edu", + "bbox": [ + 287, + 219, + 676, + 233 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/5629dcdc91b252f9c4b0bcc955e4cd5b3ed7301ac758604421c115a37b0da9b6.jpg", + "image_caption": [ + "(a) Egocentric Video" + ], + "image_footnote": [], + "bbox": [ + 84, + 250, + 333, + 321 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/d4c5cc31c0b93522ff2b1a585517c5d051d249e4f91da194e66b0f090a99800c.jpg", + "image_caption": [ + "(b) Head Pose Estimation" + ], + "image_footnote": [], + "bbox": [ + 101, + 351, + 321, + 503 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/504783766255b4ad7ed39040cceffb8dc4b6c2024c1a334b3a14b0f538994d12.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 338, + 251, + 888, + 372 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/ab131e744c7762baa1c28e8a3d9a5091fbebde23d2465c1ee937571094a633e4.jpg", + "image_caption": [ + "(c) Full-Body Human Motion Generation", + "Figure 1. Taking egocentric video (a) as input, our approach first predicts head pose (b); it then estimates multiple plausible full-body human motions (c) from the predicted head pose. This motion sequence shows a human kicking and jumping in place. Please refer to the supplementary video on our project page for a complete motion sequence visualization." + ], + "image_footnote": [], + "bbox": [ + 338, + 373, + 888, + 503 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 583, + 313, + 598 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Estimating 3D human motion from an egocentric video sequence plays a critical role in human behavior understanding and has various applications in VR/AR. However, naively learning a mapping between egocentric videos and human motions is challenging, because the user's body is often unobserved by the front-facing camera placed on the head of the user. In addition, collecting large-scale, high-quality datasets with paired egocentric videos and 3D human motions requires accurate motion capture devices, which often limit the variety of scenes in the videos to lab-like environments. To eliminate the need for paired egocentric video and human motions, we propose a new method, Ego-Body Pose Estimation via Ego-Head Pose Estimation (EgoEgo), which decomposes the problem into two stages, connected by the head motion as an intermediate representation. EgoEgo first integrates SLAM and a learning approach to estimate accurate head motion. Subsequently, leveraging the estimated head pose as input, EgoEgo utilizes conditional diffusion", + "bbox": [ + 75, + 601, + 473, + 875 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "to generate multiple plausible full-body motions. This disentanglement of head and body pose eliminates the need for training datasets with paired egocentric videos and 3D human motion, enabling us to leverage large-scale egocentric video datasets and motion capture datasets separately. Moreover, for systematic benchmarking, we develop a synthetic dataset, AMASS-Replica-Ego-Syn (ARES), with paired egocentric videos and human motion. On both AREs and real data, our EgoEgo model performs significantly better than the current state-of-the-art methods.", + "bbox": [ + 496, + 584, + 895, + 736 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 500, + 744, + 632, + 758 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Estimating 3D human motion from an egocentric video, which records the environment viewed from the first-person perspective with a front-facing monocular camera, is critical to applications in VR/AR. However, naively learning a mapping between egocentric videos and full-body human motions is challenging for two reasons. First, modeling this complex relationship is difficult; unlike reconstruction motion from third-person videos, the human body is often out of view of an egocentric video. Second, learning this", + "bbox": [ + 496, + 765, + 893, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 810, + 44 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "$\\dagger$ indicates equal contribution.", + "bbox": [ + 99, + 887, + 261, + 901 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "17142", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "mapping requires a large-scale, diverse dataset containing paired egocentric videos and the corresponding 3D human poses. Creating such a dataset requires meticulous instrumentation for data acquisition, and unfortunately, such a dataset does not currently exist. As such, existing works have only worked on small-scale datasets with limited motion and scene diversity [22, 47, 48].", + "bbox": [ + 75, + 90, + 470, + 196 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "We introduce a generalized and robust method, EgoEgo, to estimate full-body human motions from only egocentric video for diverse scenarios. Our key idea is to use head motion as an intermediate representation to decompose the problem into two stages: head motion estimation from the input egocentric video and full-body motion estimation from the estimated head motion. For most day-to-day activities, humans have an extraordinary ability to stabilize the head such that it aligns with the center of mass of the body [13], which makes head motion an excellent feature for full-body motion estimation. More importantly, the decomposition of our method removes the need to learn from paired egocentric videos and human poses, enabling learning from a combination of large-scale, single-modality datasets (e.g., datasets with egocentric videos or 3D human poses only), which are commonly and readily available.", + "bbox": [ + 75, + 199, + 470, + 441 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "The first stage, estimating the head pose from an egocentric video, resembles the localization problem. However, directly applying the state-of-the-art monocular SLAM methods [33] yields unsatisfactory results, due to the unknown gravity direction and the scaling difference between the estimated space and the real 3D world. We propose a hybrid solution that leverages SLAM and learned transformer-based models to achieve significantly more accurate head motion estimation from egocentric video. In the second stage, we generate the full-body motion based on a diffusion model conditioned on the predicted head pose. Finally, to evaluate our method and train other baselines, we build a large-scale synthetic dataset with paired egocentric videos and 3D human motions, which can also be useful for future work on visuomotor skill learning and sim-to-real transfer.", + "bbox": [ + 75, + 444, + 470, + 671 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Our work makes four main contributions. First, we propose a decomposition paradigm, EgoEgo, to decouple the problem of motion estimation from egocentric video into two stages: ego-head pose estimation, and ego-body pose estimation conditioned on the head pose. The decomposition lets us learn each component separately, eliminating the need for a large-scale dataset with two paired modalities. Second, we develop a hybrid approach for ego-head pose estimation, integrating the results of monocular SLAM and learning. Third, we propose a conditional diffusion model to generate full-body poses conditioned on the head pose. Finally, we contribute a large-scale synthetic dataset with both egocentric videos and 3D human motions as a test bed to benchmark different approaches and showcase that our method outperforms the baselines by a large margin.", + "bbox": [ + 75, + 674, + 470, + 902 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 500, + 89, + 640, + 106 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Motion Estimation from Third-person Video. 3D pose estimation from images and videos in third-person view has been extensively studied in recent years. There are mainly two typical categories in this direction. One is to regress joint positions directly from images and videos [25, 28, 36, 52]. The other adopts parametric human body model [20] to estimate body model parameters from images or videos [3, 12, 15-18, 21]. And recently, learned motion prior is applied to address the issues of jitters, lack of global trajectory, and missing joints or frames [19, 29, 46]. Moreover, physical constraints are enforced in motion estimation from videos [41, 49]. In contrast to third-person videos, where the full body can be seen, body joints are mostly not visible in an egocentric video, which poses a significant challenge for the problem. Although the body joints are unobserved from egocentric views, the visual information of how the environment changes provides a strong signal to infer how the head moves. In this work, we propose to use the head pose as an intermediate representation to bridge the egocentric video and full-body motions.", + "bbox": [ + 496, + 114, + 893, + 419 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Motion Estimation from Egocentric Video. Growing attention is received in pose estimation from egocentric videos. Special hardware like the fisheye camera is deployed to predict full body pose from captured images [9, 35, 38, 42]. While body joints are usually visible in images captured with a fisheye camera, the distortion of images poses a significant challenge. Jiang et al. [8] deploy a standard camera to a human chest and propose an implicit motion graph matching approach to predict full body motions from the input video. You2Me [26] predicts full body motions by observing the interaction pose of the second-person in the camera view. Towards a goal of estimating and forecasting physically plausible motions from a head-mounted camera, EgoPose [47, 48] develop a Deep-RL framework to learn a control policy to estimate current poses and forecast future poses. Follow-up work Kinpoly [22] integrates kinematics and dynamics to predict physically plausible motions interacting with known objects. While their method achieves impressive results in their collected dataset, it cannot handle scenes and motions out of their data distribution. This work aims to establish a more generalized and robust framework to infer full-body motions from egocentric video only. To validate the effectiveness in more generalized scenes and motions, we also introduce an approach of synthesizing egocentric video corresponding to mocap data in diverse 3D scenes for quantitative evaluation.", + "bbox": [ + 496, + 425, + 893, + 818 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Motion Estimation from Sparse Sensors. Instead of estimating motion from videos, some work explored reconstructing human motions from sparse sensor input. TransPose [45] proposes a real-time pipeline to predict full body motions from 6 IMU sensors, including head, torso, left/right arms,", + "bbox": [ + 496, + 825, + 893, + 902 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "17143", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "and left/right lower legs. Follow-up work PIP [44] further includes a PD controller on top of the kinematic estimator to introduce physics constraints during reconstruction. TIP [11] follows the same sensor setting and deploys a transformer-based model to leverage IMU sequential information effectively. Fewer sensors are investigated in LoBSTr [43]. Given tracker information from 4 joints (head, left/right hands, torso), they present an RNN-based model to infer lower-body motions from past upper-body joint signals. Recent advances [1,4,10,40] further relax the input constraints to head and hand signals only. In this work, we do not rely on any observations from inertial sensors. Instead, we aim to develop a solution with egocentric video input only.", + "bbox": [ + 75, + 90, + 472, + 287 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Method", + "text_level": 1, + "bbox": [ + 76, + 303, + 168, + 318 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Our method, EgoEgo, estimates 3D human motion from a monocular egocentric video sequence. As shown in Figure 2, our key idea is to leverage head motion: first estimating head motion from egocentric video, and then estimating full body motion from head motion. We show that head motion is an excellent feature for full-body motion estimation and a compact, intermediate representation that reduces the challenge into two much simpler sub-problems. Such a disentanglement also allows us to leverage a large-scale egocentric video dataset with head motion (but no full body motion) in stage one, and a separate 3D human motion dataset (but no egocentric videos) in stage two.", + "bbox": [ + 75, + 329, + 472, + 511 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Notations. We denote full body motion as $\\mathbf{X} \\in \\mathbb{R}^{T \\times D}$ and egocentric images captured from a front-facing, head-mounted camera as $\\mathbf{I} \\in \\mathbb{R}^{T \\times h \\times w \\times 3}$ , where $T$ is the sequence length, $D$ is the dimension of the pose state, and $h \\times w$ is the size of an image. We introduce head motion $\\mathbf{H} \\in \\mathbb{R}^{T \\times D'}$ as an intermediate representation to bridge the input egocentric video and the output human motions, where $D'$ is the dimension of the head pose.", + "bbox": [ + 76, + 516, + 472, + 638 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Head Pose Estimation from Egocentric Video", + "text_level": 1, + "bbox": [ + 76, + 648, + 460, + 666 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Estimating the head motion from an egocentric video can be viewed as a camera localization problem. However, we observed three issues that prevent us from directly applying the state-of-the-art monocular SLAM method [33] to our problem. First, the gravity direction of the estimated head pose is unknown. Thus, the results cannot be directly fed to the full-body motion estimator, since it expects the head pose expressed in a coordinate frame where the gravity direction is $[0, 0, -1]^T$ . Second, the estimated translation by monocular SLAM is not to scale when compared with the distance in the real world. Third, monocular SLAM tends to be less accurate in estimating relative head rotation than translation.", + "bbox": [ + 75, + 672, + 468, + 854 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Based on these observations, we propose a hybrid method that leverages SLAM and learned models to achieve more accurate head pose estimation than the state-of-the-art SLAM", + "bbox": [ + 75, + 854, + 472, + 900 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "alone. First, we develop a transformer-based model GravityNet to estimate the gravity direction from the rotation and the translation trajectories computed by SLAM. We rotate the SLAM translation by aligning the estimated gravity direction with the real gravity direction $[0, 0, -1]^T$ in the 3D world. Moreover, from the optical flow features extracted from the egocentric video, our method learns a model, HeadNet, to estimate head rotations and translation distance. The predicted translation distance of HeadNet is used to re-scale the translation estimated by SLAM. The predicted head rotation by HeadNet is directly used to replace the rotation estimated by SLAM. Figure 2 summarizes our process to generate head poses.", + "bbox": [ + 496, + 90, + 893, + 287 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Monocular SLAM. We adopt DROID-SLAM [33] to estimate camera trajectory from egocentric videos. DROID-SLAM [33] is a learning-based method to estimate camera pose trajectory and reconstruct the 3D map of the environment simultaneously. By a design of recurrent iterative updates to camera pose and depth, it showcases superior and more robust results compared to prior SLAM systems [2]. For more details, please refer to [33].", + "bbox": [ + 496, + 294, + 895, + 417 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Gravity Direction Estimation. We introduce GravityNet to predict gravity direction $\\pmb{g} \\in \\mathbb{R}^3$ from a sequence of head poses $\\hat{h}_1, \\hat{h}_2, \\dots, \\hat{h}_T$ . The gravity direction $\\pmb{g}$ is represented by a unit vector. The head poses input $\\hat{h}_t$ consists of a 3D head translation, a head rotation represented by a continuous 6D rotation vector [53], head translation difference, and head rotation difference computed by $O_{t-1}^{-1}O_t$ where $O_t$ denotes the head rotation matrix at time step $t$ . We adopt a transformer-based architecture [37] consisting of two self-attention blocks, each of which has a multi-head attention layer followed by a position-wise feed-forward layer. We take the first output of the transformer and feed it to an MLP to predict the gravity direction $\\pmb{g}$ . We train our GravityNet on the large-scale motion capture dataset AMASS [23]. However, the motion sequences in AMASS have the correct gravity direction $\\pmb{g}_c = [0,0,-1]^T$ . To emulate the distribution of the predicted head poses from monocular SLAM, we apply a random scale and a random rotation to the head poses in each AMASS sequence to generate our training data for gravity estimation. $L_1$ loss for the gravity vector is used during training. Based on the prediction of GravityNet, we compute the rotation matrix $R_g$ to align the prediction $\\pmb{g}$ and $\\pmb{g}_c$ . Then we apply $R_g$ to the SLAM translation denoted as $\\hat{P}_1, \\hat{P}_2, \\dots, \\hat{P}_T$ and get $P_1, P_2, \\dots, P_T$ , where $P_t = R_g\\hat{P}_t$ .", + "bbox": [ + 496, + 422, + 895, + 787 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Head Pose Estimation. We propose HeadNet to predict a sequence of distance $d_{1}, d_{2}, \\ldots, d_{T}$ and head rotations $R_{1}, \\ldots, R_{T}$ from a sequence of optical flow features $o_{1}, \\ldots, o_{T}$ . The optical flow features are extracted by a pretrained ResNet-18 [6]. We deploy the same model architecture as GravityNet. Since the scale from the monocular SLAM system may not be consistent with the real", + "bbox": [ + 496, + 794, + 895, + 902 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "17144", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/93b4443eb4e1aeffd9adf927845425932d7028ee5ba1e5f1bd1ca5e5b6f90562.jpg", + "image_caption": [ + "Figure 2. Overview of EgoEgo. The model first takes an egocentric video as input and predicts the head pose with a hybrid approach that combines monocular SLAM and the learned GravityNet and HeadNet. The predicted head pose is then fed to a conditional diffusion model to generate the full-body pose." + ], + "image_footnote": [], + "bbox": [ + 81, + 77, + 885, + 344 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/aefa011ffac48f22583e5352dedc737a7b8af70a263c903320b8206e72bd4b66.jpg", + "image_caption": [ + "Figure 3. Model architecture of the denoising network in a single step of the reverse diffusion process." + ], + "image_footnote": [], + "bbox": [ + 91, + 411, + 447, + 611 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3D world where human moves, we use HeadNet to predict the vector norm of the translation difference between consecutive time steps denoted as $d_1, \\ldots, d_T$ , where $d_t$ represents a scalar value. For each camera translation sequence produced by monocular SLAM and rotated by aligning gravity direction, given the camera translation trajectory $P \\in \\mathbb{R}^{T \\times 3}$ , we calculate the distance $d_t^s$ between $P_t$ and $P_{t+1}$ as $d_t^s = ||P_{t+1} - P_t||_2$ . We take the mean value for the sequence of distances as $d^s = \\frac{1}{T}\\sum_{t=1}^{T}d_t^s$ . Similarly, we compute the mean of the predicted distance sequence $d = \\frac{1}{T}\\sum_{t=1}^{T}d_t$ . The scale is calculated as $s = \\frac{d}{d^s}$ . We multiply scale $s$ to the predicted translation $P$ and use $sP$ as our global head translation results.", + "bbox": [ + 75, + 656, + 468, + 853 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The network also predicts the head angular velocity, $\\omega_{1},\\ldots ,\\omega_{T}$ , in the head frame. We integrate predicted angular velocity to generate corresponding rotations $R_{1},\\ldots ,R_{T}$", + "bbox": [ + 75, + 854, + 472, + 902 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "During inference, we assume that the first head orientation is given and integrate the predicted head angular velocity to estimate the subsequent head orientations.", + "bbox": [ + 496, + 416, + 890, + 460 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The training loss of the HeadNet is defined as: $\\mathcal{L} = \\mathcal{L}_{dist} + \\mathcal{L}_{vel} + \\mathcal{L}_{rot}$ . $\\mathcal{L}_{dist}$ represents the $L1$ loss for translation distance. $\\mathcal{L}_{vel}$ represents the $L1$ loss for angular velocity. $\\mathcal{L}_{rot}$ denotes the rotation loss $\\mathcal{L}_{rot} = ||\\pmb{R}_{pred}\\pmb{R}_{gt}^T - \\pmb{I}||_1$ where $\\pmb{R}_{pred}$ represents the integrated rotation using predicted angular velocity, $\\pmb{R}_{gt}$ represents the ground truth rotation matrix and $\\pmb{I}$ represents the identity matrix.", + "bbox": [ + 496, + 460, + 893, + 568 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. Full-Body Pose Estimation from Head Pose", + "text_level": 1, + "bbox": [ + 500, + 574, + 867, + 590 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Predicting full-body pose from head pose is not a one-to-one mapping problem as different full-body motions may have the same head pose. Thus, we formulate the task using a conditional generative model. Inspired by the recent success of the diffusion model in image generation [30], we deploy a diffusion model to generate full-body poses conditioned on head poses. We use the formulation proposed in the denoising diffusion probabilistic model (DDPM) [7], which has also been applied in some concurrent work [14, 34, 50] for motion generation and motion interpolation tasks. We will first introduce our data representation and then detail the conditional diffusion model formulation.", + "bbox": [ + 496, + 598, + 892, + 777 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "A body pose $\\mathbf{X}_t \\in \\mathbb{R}^D$ at time $t$ consists of the global joint position $(\\mathbb{R}^{J \\times 3})$ and global joint rotations $(\\mathbb{R}^{J \\times 6})$ . We adopt the widely used SMPL model [20] as our skeleton, and the number of joints $J$ is 22. For the convenience of notation in the diffusion model, we use $x_n$ to denote a sequence of body poses $\\mathbf{X}_1^n, \\mathbf{X}_2^n, \\dots, \\mathbf{X}_T^n$ at noise level $n$ .", + "bbox": [ + 496, + 779, + 890, + 869 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The high-level idea of the diffusion model is to design a forward diffusion process to add Gaussian noises to the", + "bbox": [ + 500, + 869, + 890, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "17145", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "original data with a known variance schedule and learn a denoising model to gradually denoise $N$ steps given a sampled $\\pmb{x}_N$ from a normal distribution to generate $\\pmb{x}_0$ .", + "bbox": [ + 76, + 90, + 468, + 136 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Specifically, diffusion models consist of a forward diffusion process and a reverse diffusion process. The forward diffusion process gradually adds Gaussian noise to the original data $\\boldsymbol{x}_0$ . And it is formulated using a Markov chain of $N$ steps as shown in Equation 1:", + "bbox": [ + 76, + 136, + 470, + 212 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nq \\left(\\boldsymbol {x} _ {1: N} \\mid \\boldsymbol {x} _ {0}\\right) := \\prod_ {n = 1} ^ {N} q \\left(\\boldsymbol {x} _ {n} \\mid \\boldsymbol {x} _ {n - 1}\\right). \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 161, + 222, + 468, + 263 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Each step is decided by a variance schedule using $\\beta_{n}$ and is defined as", + "bbox": [ + 76, + 272, + 468, + 301 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nq \\left(\\boldsymbol {x} _ {n} \\mid \\boldsymbol {x} _ {n - 1}\\right) := \\mathcal {N} \\left(\\boldsymbol {x} _ {n}; \\sqrt {1 - \\beta_ {n}} \\boldsymbol {x} _ {n - 1}, \\beta_ {n} \\boldsymbol {I}\\right). \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 119, + 311, + 468, + 330 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "To generate full-body motion conditioned on the head pose, we need to reverse the diffusion process. The reverse process can be approximated as a Markov chain with a learned mean and fixed variance:", + "bbox": [ + 76, + 340, + 468, + 400 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\np _ {\\theta} \\left(\\boldsymbol {x} _ {n - 1} \\mid \\boldsymbol {x} _ {n}, c\\right) := \\mathcal {N} \\left(\\boldsymbol {x} _ {n - 1}; \\boldsymbol {\\mu} _ {\\theta} \\left(\\boldsymbol {x} _ {n}, n, c\\right), \\sigma_ {n} ^ {2} \\boldsymbol {I}\\right). \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 98, + 412, + 468, + 429 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\pmb{\\theta}$ represents the parameters of a neural network, $c$ is the head conditions. The learned mean $\\pmb{\\mu}_{\\theta}(\\pmb{x}_n,n,c)$ (we use $\\pmb{\\mu}_{\\theta}$ in the equation for brevity) can be represented as follows where $\\alpha_{n}$ and $\\bar{\\alpha}_{n}$ are fixed parameters, $\\hat{\\pmb{x}}_{\\theta}(\\pmb{x}_n,n,c)$ is the prediction of $\\pmb{x}_0$ :", + "bbox": [ + 76, + 440, + 468, + 515 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {\\mu} _ {\\theta} = \\frac {\\sqrt {\\alpha_ {n}} (1 - \\bar {\\alpha} _ {n - 1}) \\boldsymbol {x} _ {n} + \\sqrt {\\bar {\\alpha} _ {n - 1}} (1 - \\alpha_ {n}) \\hat {\\boldsymbol {x}} _ {\\theta} (\\boldsymbol {x} _ {n} , n , c)}{1 - \\bar {\\alpha} _ {n}} \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 76, + 523, + 467, + 568 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Learning the mean can be reparameterized as learning to predict the original data $\\pmb{x}_0$ . The training loss is defined as a reconstruction loss of $\\pmb{x}_0$ :", + "bbox": [ + 76, + 570, + 468, + 614 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} = \\mathbb {E} _ {\\boldsymbol {x} _ {0}, n} \\| \\hat {\\boldsymbol {x}} _ {\\theta} (\\boldsymbol {x} _ {n}, n, c) - \\boldsymbol {x} _ {0} \\| _ {1} \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 161, + 626, + 468, + 642 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "As shown in Figure 3, in denoising step $n$ , we concatenate head pose condition $c_{1},\\ldots ,c_{T}$ with body pose representation $X_{1}^{n},\\ldots ,X_{T}^{n}$ at noise level $n$ , combined with noise embedding as input to a transformer model, and estimate $x_0$ .", + "bbox": [ + 76, + 652, + 468, + 713 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.3. Synthetic Data Generation", + "text_level": 1, + "bbox": [ + 76, + 722, + 316, + 738 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Our method does not need paired training data. Still, for benchmarking purposes, we develop a way to automatically synthesize a large-scale dataset with various paired egocentric videos and human motions.", + "bbox": [ + 76, + 744, + 468, + 805 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Generate Motions in 3D Scenes. To generate a dataset with both egocentric video and ground truth human motions, we use a large-scale motion capture dataset AMASS [23] and a 3D scene dataset Replica [31]. We convert the scene mesh from Replica to the signed distance field (SDF) for the penetration calculation. We divide each sequence of", + "bbox": [ + 76, + 809, + 468, + 900 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "AMASS [23] into sub-sequences with 150 frames. For each sub-sequence, based on the semantic annotation provided by Replica [31], we place the first pose in a random location with the feet in contact with the floor. Then we calculate penetration loss following Wang et al. [39] for each pose in this sequence. We empirically set the threshold to 2 and only keep the poses with penetration loss less than the threshold. Specifically, for human mesh $M_{t}$ at time $t$ represented by a parameterized human model [20, 27], we denote $d_{i}$ as the signed distance of vertex $i$ . The penetration loss is then defined as $L_{pen}^{t} = \\sum_{d_{i} < 0} ||d_{i}||$ .", + "bbox": [ + 496, + 90, + 890, + 258 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Synthesize Realistic Egocentric Images. The motion sequences produced by detecting penetration with 3D scenes provide the camera pose trajectories to render synthetic egocentric videos. AI Habitat [24,32] is a platform for embodied agent research that supports fast rendering given a camera trajectory and a 3D scene. We feed the head pose trajectories to the platform and synthesize realistic images in the egocentric view. We generate 1,664,616 frames with 30 fps, approximately 15 hours of motion in 18 scenes. We name the synthetic dataset AMASS-Replica-Ego-Syn (ARES) and show some examples from our synthetic dataset in Figure 4.", + "bbox": [ + 496, + 260, + 893, + 426 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 500, + 438, + 630, + 455 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We evaluate and compare our method to baselines on five commonly used metrics for human motion reconstruction, in addition to the human perception studies. We also conduct ablation studies to analyze the performance of each stage of our method, as well as the design choices in our model.", + "bbox": [ + 496, + 463, + 890, + 537 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.1. Datasets and Evaluation Metrics", + "text_level": 1, + "bbox": [ + 500, + 546, + 785, + 561 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "AMASS-Replica-Ego-Syn (ARES) is our synthetic dataset which contains synthetic egocentric videos and ground truth motions. ARES contains about 15 hours of motion across 18 scenes. We remove 5 scenes from training as unseen scenes. The training dataset consists of about $1.2\\mathrm{M}$ frames in 13 different scenes. The testing dataset contains 34,850 frames from 5 unseen scenes.", + "bbox": [ + 496, + 568, + 890, + 672 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "AMASS [23] is a large-scale motion capture dataset with about 45 hours of diverse motions. We split training and testing data following HuMoR [29].", + "bbox": [ + 496, + 678, + 890, + 723 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Kinpoly-MoCap [22] consists of egocentric videos captured using a head-mounted camera and corresponding 3D motions captured with motion capture devices. The total motion is about 80 minutes long. Since it uses motion capture devices, the egocentric video is constrained to a single lab scene.", + "bbox": [ + 496, + 726, + 890, + 801 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Kinpoly-RealWorld [22] contains paired egocentric videos and head poses captured using iPhone ARKit. Unlike Kinpoly-MoCap which is captured in a lab scene, Kinpoly-RealWorld provides in-the-wild egocentric videos.", + "bbox": [ + 496, + 806, + 890, + 866 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "GIMO [51] consists of egocentric video, eye gaze, 3D motions, and scanned 3D scenes. This dataset is collected using", + "bbox": [ + 496, + 869, + 890, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "17146", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/05d883d87448c3362c04ef6cd27ff5d0c674bc6798fc1114cdce8d186f015436.jpg", + "image_caption": [ + "Figure 4. Illustration of our ARES Dataset. \"Ego-View\" represents the synthetic egocentric images using our proposed data generation pipeline. We also provide a third-person view reference in the second row. The left and right show two sequences from different scenes." + ], + "image_footnote": [], + "bbox": [ + 80, + 89, + 893, + 212 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/9a7f0dde4eb0648759275b4cf1d4b7e2c97f0bbbc656dac51162a81ed9429c50.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodARESKinpoly-MoCap [22]GIMO [51]
OheadTheadMPJPEAccelFSOheadTheadMPJPEAccelFSOheadTheadMPJPEAccelFS
PoseReg [48]0.77354.7147.7127.687.11.051943.9160.461.810.81.511528.6189.371.514.2
Kinpoly-OF [22]0.62323.4141.67.34.21.332475.5230.516.415.81.521739.3404.221.914.4
EgoEgo (ours)0.20148.0121.16.22.70.58505.1125.98.01.60.67356.8152.110.41.9
", + "bbox": [ + 81, + 250, + 890, + 333 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 1. Full-body motion estimation from egocentric video on ARES, Kinpoly-MoCap [22], and GIMO [51].", + "bbox": [ + 156, + 338, + 810, + 353 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Hololens, iPhone 12, and IMU-based motion capture suits to study motion prediction tasks guided by eye gaze. We use 15 scenes for training and 4 scenes for testing.", + "bbox": [ + 76, + 364, + 470, + 411 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Evaluation Metrics.", + "text_level": 1, + "bbox": [ + 76, + 415, + 220, + 429 + ], + "page_idx": 5 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- Head Orientation Error $(\\mathbf{O}_{head})$ computes the Frobenius norm of the difference between the $3 \\times 3$ rotation matrix $||\\pmb{R}_{pred}\\pmb{R}_{gt}^{-1} - \\pmb{I}||_2$ , where $\\pmb{R}_{pred}$ is the predicted head rotation matrix and $\\pmb{R}_{gt}$ is the ground truth head rotation matrix.", + "- Head Translation Error $\\left(\\mathbf{T}_{\\text {head }}\\right)$ is computed by taking the mean Euclidean distance of two trajectories. We use this metric to measure the head joint translation errors in millimeters (mm).", + "- MPJPE represents mean per-joint position errors in millimeters (mm).", + "- Accel represents the difference of acceleration between predicted joint positions and ground truth joint positions measured in $(mm / s^2)$ .", + "- FS represents foot skating metric and is computed following NeMF [5]. Specifically, we first project the toe and ankle joints' velocity to the $xy$ plane and compute the $L1$ norm of the projected velocities in each step denoted as $v_{t}$ . We only accumulate the horizontal translation for those steps that have a height $h_t$ lower than a specified threshold $H$ . And the metric is calculated as a mean of weighted values $v_{t}(2 - 2^{\\frac{h_{t}}{H}})$ across the sequence and is measured in $(mm)$ ." + ], + "bbox": [ + 94, + 434, + 473, + 801 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.2. Body Pose Estimation from Egocentric Video", + "text_level": 1, + "bbox": [ + 76, + 820, + 460, + 835 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Training Data. We train our HeadNet using paired egocentric videos and head poses provided by ARES, KinplyRealWorld, and GIMO. Note that the body motion in these datasets is not used for training HeadNet. Our GravityNet", + "bbox": [ + 75, + 839, + 472, + 902 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "and the conditional diffusion model are both trained on AMASS. For the baselines below, we train them using paired egocentric videos and ground truth motions in ARES.", + "bbox": [ + 496, + 364, + 892, + 411 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Baselines. We compare our approach with two baselines PoseReg [48] and Kinpoly [22]. PoseReg [48] takes a sequence of optical flow features as input and uses an LSTM model to predict the pose state at each time step. The pose state consists of root translation, root orientation, joint rotations, and corresponding velocities including root linear velocity and angular velocities of all the joints. Kinpoly-OF [22] proposes a per-step regression model to estimate full body motion from optical flow features. Because our problem only allows for egocentric video as input, we choose the option of Kinpoly which only has optical flow features as input, without relying on ground truth head poses and action labels that depend on additional knowledge.", + "bbox": [ + 496, + 420, + 893, + 618 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Results. We compare the complete pipeline of EgoEgo with baseline methods PoseReg [48] and Kinpoly-OF [22] on ARES, Kinpoly-MoCap [22] and GIMO [51], as shown in Table 1. We show that our EgoEgo outperforms all the baselines by a large margin on all three datasets. We show qualitative results in Figure 5. Our generated motions better preserve the root trajectories. And our approach can also generate more dynamic and realistic motions compared to the baselines.", + "bbox": [ + 496, + 625, + 893, + 760 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.3. Head Pose Estimation from Egocentric Video", + "text_level": 1, + "bbox": [ + 498, + 773, + 883, + 789 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Baselines. We compare our hybrid approach with the prediction results of DROID-SLAM [33]. For a fair comparison, we apply a rotation to the SLAM trajectory by aligning the first predicted head pose of SLAM with the ground truth head pose. We train our GravityNet on AMASS training split. As for HeadNet, we train on ARES, Kinpoly-RealWorld, and GIMO separately for the evaluation of different datasets.", + "bbox": [ + 496, + 794, + 893, + 902 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "17147", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/e25c16503b42b0127d25c61ccf099b5c3c06bea3ea56441f21c453ef11155e0a.jpg", + "image_caption": [ + "(a) Example 1", + "Figure 5. Qualitative results comparisons. We show the results of two egocentric videos from different scenes." + ], + "image_footnote": [], + "bbox": [ + 76, + 112, + 893, + 569 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Results. We evaluate the head pose estimation on the three datasets as shown in Table 2. We show more accurate head rotation prediction results on ARES and comparable results on real-captured data. As the real-captured data is limited in scale (Kinpoly-RealWorld contains 20 minutes of training videos and GIMO contains 30 minutes of training videos), we believe the head rotation prediction can be further improved by future developments of large-scale real-captured datasets with head poses. Overall, our hybrid approach combines the accurate rotation prediction from HeadNet and re-scaled translation of gravity-aligned SLAM results, and produces more accurate head pose estimation results as input to the second stage.", + "bbox": [ + 75, + 607, + 470, + 803 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.4. Body Pose Estimation from the Head Pose", + "text_level": 1, + "bbox": [ + 76, + 818, + 434, + 834 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Baselines. We compare our conditional diffusion model for full-body pose estimation with two baselines AvatarPoser [10] and Kinpoly-Head [22]. AvatarPoser [10] takes both head and hand pose as input to predict full body motion.", + "bbox": [ + 75, + 839, + 470, + 902 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/9777fcdcfe73ab41c791bfaf02ba5463d8694bbd4e61a8f14e8622c60c39ab25.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
DROID-SLAM [33]Ours
OheadThedOheadThed
ARES0.62411.30.23176.5
Kinpoly-MoCap0.551290.80.58487.8
GIMO0.67865.40.68304.7
", + "bbox": [ + 506, + 603, + 883, + 696 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 2. Head pose estimation on test sets.", + "bbox": [ + 566, + 699, + 821, + 713 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We remove the hand poses from the input and modified it to a setting with head pose input only. Kinpoly-Head [22] is our modified variant of the Kinpoly model that only takes the head pose as input. Both the baselines and our method are trained on the training split of AMASS with high-quality motion capture data.", + "bbox": [ + 496, + 727, + 890, + 818 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Results. We evaluate the baselines and our method on the AMASS test set, as shown in Table 3. Since our model is generative, there are multiple plausible predictions from the same head pose input. For a quantitative comparison, we generate 200 samples for each head pose input and use the", + "bbox": [ + 496, + 824, + 892, + 902 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "17148", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/779a5ebaebe5b2e7b8ca1b2d5def2b782a2b4c31791cd7cbd075f6f0135063f0.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodOheadTheadMPJPEAccelFS
AvatarPoser [10]0.1928.6124.716.118.8
Kinpoly-Head [22]0.1987.8110.911.411.2
Diffusion Model (ours)0.0436.7109.010.54.4
", + "bbox": [ + 78, + 89, + 470, + 154 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/710407e7a5239a55b46d0d16e769ab7688a3bfd5e3dd85b9d46cc83e65fae1db.jpg", + "table_caption": [ + "Table 3. Full-body motion estimation from GT head pose on AMASS testing dataset [22]." + ], + "table_footnote": [], + "table_body": "
ARESKinpoly-MoCapGIMO
OheadThedOheadThedOheadThed
SLAM0.62411.330.551290.820.67865.41
SLAM+S0.62325.950.55643.450.67569.48
SLAM+S+G0.62176.540.55487.770.67304.74
Full model0.23176.540.58487.770.68304.74
", + "bbox": [ + 78, + 191, + 468, + 296 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "one with the smallest MPJPE as our result.", + "bbox": [ + 76, + 358, + 359, + 372 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.5. Ablation Studies", + "text_level": 1, + "bbox": [ + 76, + 383, + 241, + 398 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Effects of Components in Head Pose Estimation. We study the effects of each component in head pose estimation in Table 4. We showcase that the rotation for aligning gravity direction and the learned scale are both effective to improve head translation results.", + "bbox": [ + 76, + 404, + 468, + 479 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Effects of Head Pose in Full-Body Pose Estimation. We compare the full-body pose estimation results that take our predicted head poses and the ground truth head poses as input. Table 5 shows that the ground truth head poses significantly improve the full body pose estimation, indicating that by developing methods that predict more accurate head pose, the full body pose estimation can be further improved.", + "bbox": [ + 76, + 487, + 470, + 594 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.6. Human Perceptual Study", + "text_level": 1, + "bbox": [ + 76, + 604, + 307, + 619 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We also conduct two human perceptual studies as part of the evaluation. The first is to evaluate the quality of predicted full-body motion from egocentric video, the second is to evaluate the quality of predicted full-body motion from ground truth head poses. In both studies, we compare four types of motion: results from our EgoEgo and from two baselines, as well as the ground truth. For the first human study, each time, users are presented with two motions and an egocentric video, and asked to select which one is more plausible. For the second human study, users are presented with two motions and asked to select which one looks more natural and realistic. Because there are 10 examples and the two motions can be from four sources, we have 60 questions for each study. Each question was answered by 20 Amazon Mechanical Turk workers.", + "bbox": [ + 75, + 628, + 468, + 853 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "As shown in Figure 6(a), for full-body estimation from egocentric video, our results are preferred by $98\\%$ and $69\\%$ of workers when compared to the baselines. Also, when", + "bbox": [ + 76, + 854, + 470, + 900 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/e06c6f822040a8af489ec5e4170a23d01078b14fe6325af5bc1913db3a493f3a.jpg", + "table_caption": [ + "Table 4. Ablation study for the components in head pose estimation. S represents the scale predicted by HeadNet, and G represents GravityNet." + ], + "table_footnote": [], + "table_body": "
ARESKinpoly-MoCapGIMO
EEEE w/ GTEEEE w/ GTEEEE w/ GT
Ohead0.200.040.580.030.670.06
Thead148.029.1505.160.7356.866.0
MPJPE121.1105.6125.976.0152.1125.7
Accel6.26.38.07.210.410.2
FS2.73.01.62.51.91.7
", + "bbox": [ + 500, + 88, + 888, + 207 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 5. Ablation study for the effects of head pose to full-body pose estimation. EE represents EgoEgo. GT represents ground truth head poses.", + "bbox": [ + 498, + 210, + 890, + 253 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/49a7561fb578c848fd9a51e49a58cf85400232b9c31172feb6f3879751eae323.jpg", + "image_caption": [ + "Figure 6. Results of human perceptual studies. The numbers shown in the chart represent $\\%$" + ], + "image_footnote": [], + "bbox": [ + 501, + 262, + 890, + 416 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "compared with the ground truth, $34\\%$ of the responses prefer our results (note that a perfect output would achieve $50\\%$ ), suggesting that people cannot easily distinguish our results from ground truth motions. As shown in Figure 6(b), for full-body estimation from head poses, our results are preferred by $88\\%$ and $79\\%$ of workers when compared to the baselines.", + "bbox": [ + 498, + 460, + 893, + 551 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 559, + 617, + 575 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We presented a generalized framework to estimate full-body motions from egocentric video. The key is to decompose the problem into two stages. We predicted the head pose from an egocentric video and fed the output from the first stage to estimate full-body motions in the second stage. In addition, we developed a hybrid solution to produce more accurate head poses on top of monocular SLAM. We also proposed a conditional diffusion model to generate diverse high-quality full-body motions from predicted head poses. To benchmark different methods in a large-scale dataset, we proposed a data generation pipeline to synthesize a largescale dataset with paired egocentric videos and 3D human motions. We showcased superior results on both the synthetic and the real-captured dataset compared to prior work.", + "bbox": [ + 496, + 587, + 893, + 799 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgement. We thank Zhengfei Kuang for the help with visualizations and Jonathan Tseng for discussions about the diffusion model. This work is in part supported by ONR MURI N00014-22-1-2740, NSF CCRI 2120095, the Toyota Research Institute (TRI), the Stanford Institute for Human-Centered AI (HAI), Innopeak, Meta, and Samsung.", + "bbox": [ + 496, + 809, + 893, + 902 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "17149", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 174, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Sadegh Aliakbarian, Pashmina Cameron, Federica Bogo, Andrew Fitzgibbon, and Thomas J Cashman. FLAG: Flow-based 3D avatar generation from sparse observations. In CVPR, 2022. 3", + "[2] Carlos Campos, Richard Elvira, Juan J Gomez Rodríguez, José MM Montiel, and Juan D Tardós. ORB-SLAM3: An accurate open-source library for visual, visual-inertial, and multimap SLAM. 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In CVPR, 2019. 3" + ], + "bbox": [ + 501, + 92, + 893, + 345 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "17151", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/Ego-Body Pose Estimation via Ego-Head Pose Estimation/efdf65a4-1b22-494a-ba23-4617e8cb1fe5_model.json b/2023/Ego-Body Pose Estimation via Ego-Head Pose Estimation/efdf65a4-1b22-494a-ba23-4617e8cb1fe5_model.json new file mode 100644 index 0000000000000000000000000000000000000000..98959ac92ca1feaf53de212a15c01be62a30e1f3 --- /dev/null +++ b/2023/Ego-Body Pose Estimation via Ego-Head Pose Estimation/efdf65a4-1b22-494a-ba23-4617e8cb1fe5_model.json @@ -0,0 +1,2145 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.0, + 0.812, + 0.045 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.196, + 0.131, + 0.776, + 0.154 + ], + "angle": 0, + "content": "Ego-Body Pose Estimation via Ego-Head Pose Estimation" + }, + { + "type": "text", + "bbox": [ + 0.308, + 0.181, + 0.668, + 0.218 + ], + "angle": 0, + "content": "Jiaman Li C. Karen Liu† Jiajun Wu† \nStanford University" + }, + { + "type": "text", + "bbox": [ + 0.289, + 0.22, + 0.677, + 0.234 + ], + "angle": 0, + "content": "{jiamanli,karenliu, jiajunwu}@cs.stanford.edu" + }, + { + "type": "image", + "bbox": [ + 0.086, + 0.251, + 0.334, + 0.322 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.137, + 0.333, + 0.277, + 0.347 + ], + "angle": 0, + "content": "(a) Egocentric Video" + }, + { + "type": "image", + "bbox": [ + 0.102, + 0.352, + 0.323, + 0.505 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.123, + 0.509, + 0.295, + 0.523 + ], + "angle": 0, + "content": "(b) Head Pose Estimation" + }, + { + "type": "image", + "bbox": [ + 0.339, + 0.252, + 0.889, + 0.373 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.339, + 0.374, + 0.889, + 0.505 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.47, + 0.508, + 0.746, + 0.523 + ], + "angle": 0, + "content": "(c) Full-Body Human Motion Generation" + }, + { + "type": "image_caption", + "bbox": [ + 0.075, + 0.527, + 0.895, + 0.571 + ], + "angle": 0, + "content": "Figure 1. Taking egocentric video (a) as input, our approach first predicts head pose (b); it then estimates multiple plausible full-body human motions (c) from the predicted head pose. This motion sequence shows a human kicking and jumping in place. Please refer to the supplementary video on our project page for a complete motion sequence visualization." + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.584, + 0.314, + 0.599 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.602, + 0.474, + 0.875 + ], + "angle": 0, + "content": "Estimating 3D human motion from an egocentric video sequence plays a critical role in human behavior understanding and has various applications in VR/AR. However, naively learning a mapping between egocentric videos and human motions is challenging, because the user's body is often unobserved by the front-facing camera placed on the head of the user. In addition, collecting large-scale, high-quality datasets with paired egocentric videos and 3D human motions requires accurate motion capture devices, which often limit the variety of scenes in the videos to lab-like environments. To eliminate the need for paired egocentric video and human motions, we propose a new method, Ego-Body Pose Estimation via Ego-Head Pose Estimation (EgoEgo), which decomposes the problem into two stages, connected by the head motion as an intermediate representation. EgoEgo first integrates SLAM and a learning approach to estimate accurate head motion. Subsequently, leveraging the estimated head pose as input, EgoEgo utilizes conditional diffusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.585, + 0.896, + 0.737 + ], + "angle": 0, + "content": "to generate multiple plausible full-body motions. This disentanglement of head and body pose eliminates the need for training datasets with paired egocentric videos and 3D human motion, enabling us to leverage large-scale egocentric video datasets and motion capture datasets separately. Moreover, for systematic benchmarking, we develop a synthetic dataset, AMASS-Replica-Ego-Syn (ARES), with paired egocentric videos and human motion. On both AREs and real data, our EgoEgo model performs significantly better than the current state-of-the-art methods." + }, + { + "type": "title", + "bbox": [ + 0.501, + 0.745, + 0.633, + 0.76 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.766, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Estimating 3D human motion from an egocentric video, which records the environment viewed from the first-person perspective with a front-facing monocular camera, is critical to applications in VR/AR. However, naively learning a mapping between egocentric videos and full-body human motions is challenging for two reasons. First, modeling this complex relationship is difficult; unlike reconstruction motion from third-person videos, the human body is often out of view of an egocentric video. Second, learning this" + }, + { + "type": "page_footnote", + "bbox": [ + 0.101, + 0.888, + 0.263, + 0.902 + ], + "angle": 0, + "content": "\\( \\dagger \\) indicates equal contribution." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "17142" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.471, + 0.198 + ], + "angle": 0, + "content": "mapping requires a large-scale, diverse dataset containing paired egocentric videos and the corresponding 3D human poses. Creating such a dataset requires meticulous instrumentation for data acquisition, and unfortunately, such a dataset does not currently exist. As such, existing works have only worked on small-scale datasets with limited motion and scene diversity [22, 47, 48]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.2, + 0.471, + 0.442 + ], + "angle": 0, + "content": "We introduce a generalized and robust method, EgoEgo, to estimate full-body human motions from only egocentric video for diverse scenarios. Our key idea is to use head motion as an intermediate representation to decompose the problem into two stages: head motion estimation from the input egocentric video and full-body motion estimation from the estimated head motion. For most day-to-day activities, humans have an extraordinary ability to stabilize the head such that it aligns with the center of mass of the body [13], which makes head motion an excellent feature for full-body motion estimation. More importantly, the decomposition of our method removes the need to learn from paired egocentric videos and human poses, enabling learning from a combination of large-scale, single-modality datasets (e.g., datasets with egocentric videos or 3D human poses only), which are commonly and readily available." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.445, + 0.471, + 0.672 + ], + "angle": 0, + "content": "The first stage, estimating the head pose from an egocentric video, resembles the localization problem. However, directly applying the state-of-the-art monocular SLAM methods [33] yields unsatisfactory results, due to the unknown gravity direction and the scaling difference between the estimated space and the real 3D world. We propose a hybrid solution that leverages SLAM and learned transformer-based models to achieve significantly more accurate head motion estimation from egocentric video. In the second stage, we generate the full-body motion based on a diffusion model conditioned on the predicted head pose. Finally, to evaluate our method and train other baselines, we build a large-scale synthetic dataset with paired egocentric videos and 3D human motions, which can also be useful for future work on visuomotor skill learning and sim-to-real transfer." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.675, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Our work makes four main contributions. First, we propose a decomposition paradigm, EgoEgo, to decouple the problem of motion estimation from egocentric video into two stages: ego-head pose estimation, and ego-body pose estimation conditioned on the head pose. The decomposition lets us learn each component separately, eliminating the need for a large-scale dataset with two paired modalities. Second, we develop a hybrid approach for ego-head pose estimation, integrating the results of monocular SLAM and learning. Third, we propose a conditional diffusion model to generate full-body poses conditioned on the head pose. Finally, we contribute a large-scale synthetic dataset with both egocentric videos and 3D human motions as a test bed to benchmark different approaches and showcase that our method outperforms the baselines by a large margin." + }, + { + "type": "title", + "bbox": [ + 0.501, + 0.09, + 0.642, + 0.107 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.116, + 0.895, + 0.42 + ], + "angle": 0, + "content": "Motion Estimation from Third-person Video. 3D pose estimation from images and videos in third-person view has been extensively studied in recent years. There are mainly two typical categories in this direction. One is to regress joint positions directly from images and videos [25, 28, 36, 52]. The other adopts parametric human body model [20] to estimate body model parameters from images or videos [3, 12, 15-18, 21]. And recently, learned motion prior is applied to address the issues of jitters, lack of global trajectory, and missing joints or frames [19, 29, 46]. Moreover, physical constraints are enforced in motion estimation from videos [41, 49]. In contrast to third-person videos, where the full body can be seen, body joints are mostly not visible in an egocentric video, which poses a significant challenge for the problem. Although the body joints are unobserved from egocentric views, the visual information of how the environment changes provides a strong signal to infer how the head moves. In this work, we propose to use the head pose as an intermediate representation to bridge the egocentric video and full-body motions." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.426, + 0.895, + 0.819 + ], + "angle": 0, + "content": "Motion Estimation from Egocentric Video. Growing attention is received in pose estimation from egocentric videos. Special hardware like the fisheye camera is deployed to predict full body pose from captured images [9, 35, 38, 42]. While body joints are usually visible in images captured with a fisheye camera, the distortion of images poses a significant challenge. Jiang et al. [8] deploy a standard camera to a human chest and propose an implicit motion graph matching approach to predict full body motions from the input video. You2Me [26] predicts full body motions by observing the interaction pose of the second-person in the camera view. Towards a goal of estimating and forecasting physically plausible motions from a head-mounted camera, EgoPose [47, 48] develop a Deep-RL framework to learn a control policy to estimate current poses and forecast future poses. Follow-up work Kinpoly [22] integrates kinematics and dynamics to predict physically plausible motions interacting with known objects. While their method achieves impressive results in their collected dataset, it cannot handle scenes and motions out of their data distribution. This work aims to establish a more generalized and robust framework to infer full-body motions from egocentric video only. To validate the effectiveness in more generalized scenes and motions, we also introduce an approach of synthesizing egocentric video corresponding to mocap data in diverse 3D scenes for quantitative evaluation." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.826, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Motion Estimation from Sparse Sensors. Instead of estimating motion from videos, some work explored reconstructing human motions from sparse sensor input. TransPose [45] proposes a real-time pipeline to predict full body motions from 6 IMU sensors, including head, torso, left/right arms," + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "17143" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.289 + ], + "angle": 0, + "content": "and left/right lower legs. Follow-up work PIP [44] further includes a PD controller on top of the kinematic estimator to introduce physics constraints during reconstruction. TIP [11] follows the same sensor setting and deploys a transformer-based model to leverage IMU sequential information effectively. Fewer sensors are investigated in LoBSTr [43]. Given tracker information from 4 joints (head, left/right hands, torso), they present an RNN-based model to infer lower-body motions from past upper-body joint signals. Recent advances [1,4,10,40] further relax the input constraints to head and hand signals only. In this work, we do not rely on any observations from inertial sensors. Instead, we aim to develop a solution with egocentric video input only." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.304, + 0.169, + 0.319 + ], + "angle": 0, + "content": "3. Method" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.33, + 0.473, + 0.512 + ], + "angle": 0, + "content": "Our method, EgoEgo, estimates 3D human motion from a monocular egocentric video sequence. As shown in Figure 2, our key idea is to leverage head motion: first estimating head motion from egocentric video, and then estimating full body motion from head motion. We show that head motion is an excellent feature for full-body motion estimation and a compact, intermediate representation that reduces the challenge into two much simpler sub-problems. Such a disentanglement also allows us to leverage a large-scale egocentric video dataset with head motion (but no full body motion) in stage one, and a separate 3D human motion dataset (but no egocentric videos) in stage two." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.517, + 0.473, + 0.64 + ], + "angle": 0, + "content": "Notations. We denote full body motion as \\( \\mathbf{X} \\in \\mathbb{R}^{T \\times D} \\) and egocentric images captured from a front-facing, head-mounted camera as \\( \\mathbf{I} \\in \\mathbb{R}^{T \\times h \\times w \\times 3} \\), where \\( T \\) is the sequence length, \\( D \\) is the dimension of the pose state, and \\( h \\times w \\) is the size of an image. We introduce head motion \\( \\mathbf{H} \\in \\mathbb{R}^{T \\times D'} \\) as an intermediate representation to bridge the input egocentric video and the output human motions, where \\( D' \\) is the dimension of the head pose." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.65, + 0.462, + 0.667 + ], + "angle": 0, + "content": "3.1. Head Pose Estimation from Egocentric Video" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.674, + 0.47, + 0.856 + ], + "angle": 0, + "content": "Estimating the head motion from an egocentric video can be viewed as a camera localization problem. However, we observed three issues that prevent us from directly applying the state-of-the-art monocular SLAM method [33] to our problem. First, the gravity direction of the estimated head pose is unknown. Thus, the results cannot be directly fed to the full-body motion estimator, since it expects the head pose expressed in a coordinate frame where the gravity direction is \\([0, 0, -1]^T\\). Second, the estimated translation by monocular SLAM is not to scale when compared with the distance in the real world. Third, monocular SLAM tends to be less accurate in estimating relative head rotation than translation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.473, + 0.901 + ], + "angle": 0, + "content": "Based on these observations, we propose a hybrid method that leverages SLAM and learned models to achieve more accurate head pose estimation than the state-of-the-art SLAM" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.895, + 0.289 + ], + "angle": 0, + "content": "alone. First, we develop a transformer-based model GravityNet to estimate the gravity direction from the rotation and the translation trajectories computed by SLAM. We rotate the SLAM translation by aligning the estimated gravity direction with the real gravity direction \\([0, 0, -1]^T\\) in the 3D world. Moreover, from the optical flow features extracted from the egocentric video, our method learns a model, HeadNet, to estimate head rotations and translation distance. The predicted translation distance of HeadNet is used to re-scale the translation estimated by SLAM. The predicted head rotation by HeadNet is directly used to replace the rotation estimated by SLAM. Figure 2 summarizes our process to generate head poses." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.295, + 0.897, + 0.418 + ], + "angle": 0, + "content": "Monocular SLAM. We adopt DROID-SLAM [33] to estimate camera trajectory from egocentric videos. DROID-SLAM [33] is a learning-based method to estimate camera pose trajectory and reconstruct the 3D map of the environment simultaneously. By a design of recurrent iterative updates to camera pose and depth, it showcases superior and more robust results compared to prior SLAM systems [2]. For more details, please refer to [33]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.424, + 0.897, + 0.789 + ], + "angle": 0, + "content": "Gravity Direction Estimation. We introduce GravityNet to predict gravity direction \\( \\pmb{g} \\in \\mathbb{R}^3 \\) from a sequence of head poses \\( \\hat{h}_1, \\hat{h}_2, \\dots, \\hat{h}_T \\). The gravity direction \\( \\pmb{g} \\) is represented by a unit vector. The head poses input \\( \\hat{h}_t \\) consists of a 3D head translation, a head rotation represented by a continuous 6D rotation vector [53], head translation difference, and head rotation difference computed by \\( O_{t-1}^{-1}O_t \\) where \\( O_t \\) denotes the head rotation matrix at time step \\( t \\). We adopt a transformer-based architecture [37] consisting of two self-attention blocks, each of which has a multi-head attention layer followed by a position-wise feed-forward layer. We take the first output of the transformer and feed it to an MLP to predict the gravity direction \\( \\pmb{g} \\). We train our GravityNet on the large-scale motion capture dataset AMASS [23]. However, the motion sequences in AMASS have the correct gravity direction \\( \\pmb{g}_c = [0,0,-1]^T \\). To emulate the distribution of the predicted head poses from monocular SLAM, we apply a random scale and a random rotation to the head poses in each AMASS sequence to generate our training data for gravity estimation. \\( L_1 \\) loss for the gravity vector is used during training. Based on the prediction of GravityNet, we compute the rotation matrix \\( R_g \\) to align the prediction \\( \\pmb{g} \\) and \\( \\pmb{g}_c \\). Then we apply \\( R_g \\) to the SLAM translation denoted as \\( \\hat{P}_1, \\hat{P}_2, \\dots, \\hat{P}_T \\) and get \\( P_1, P_2, \\dots, P_T \\), where \\( P_t = R_g\\hat{P}_t \\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.795, + 0.897, + 0.903 + ], + "angle": 0, + "content": "Head Pose Estimation. We propose HeadNet to predict a sequence of distance \\( d_{1}, d_{2}, \\ldots, d_{T} \\) and head rotations \\( R_{1}, \\ldots, R_{T} \\) from a sequence of optical flow features \\( o_{1}, \\ldots, o_{T} \\). The optical flow features are extracted by a pretrained ResNet-18 [6]. We deploy the same model architecture as GravityNet. Since the scale from the monocular SLAM system may not be consistent with the real" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "17144" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.078, + 0.887, + 0.345 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.352, + 0.895, + 0.396 + ], + "angle": 0, + "content": "Figure 2. Overview of EgoEgo. The model first takes an egocentric video as input and predicts the head pose with a hybrid approach that combines monocular SLAM and the learned GravityNet and HeadNet. The predicted head pose is then fed to a conditional diffusion model to generate the full-body pose." + }, + { + "type": "image", + "bbox": [ + 0.093, + 0.412, + 0.449, + 0.612 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.616, + 0.471, + 0.645 + ], + "angle": 0, + "content": "Figure 3. Model architecture of the denoising network in a single step of the reverse diffusion process." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.657, + 0.47, + 0.854 + ], + "angle": 0, + "content": "3D world where human moves, we use HeadNet to predict the vector norm of the translation difference between consecutive time steps denoted as \\( d_1, \\ldots, d_T \\), where \\( d_t \\) represents a scalar value. For each camera translation sequence produced by monocular SLAM and rotated by aligning gravity direction, given the camera translation trajectory \\( P \\in \\mathbb{R}^{T \\times 3} \\), we calculate the distance \\( d_t^s \\) between \\( P_t \\) and \\( P_{t+1} \\) as \\( d_t^s = ||P_{t+1} - P_t||_2 \\). We take the mean value for the sequence of distances as \\( d^s = \\frac{1}{T}\\sum_{t=1}^{T}d_t^s \\). Similarly, we compute the mean of the predicted distance sequence \\( d = \\frac{1}{T}\\sum_{t=1}^{T}d_t \\). The scale is calculated as \\( s = \\frac{d}{d^s} \\). We multiply scale \\( s \\) to the predicted translation \\( P \\) and use \\( sP \\) as our global head translation results." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.473, + 0.903 + ], + "angle": 0, + "content": "The network also predicts the head angular velocity, \\(\\omega_{1},\\ldots ,\\omega_{T}\\) , in the head frame. We integrate predicted angular velocity to generate corresponding rotations \\(R_{1},\\ldots ,R_{T}\\)" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.417, + 0.892, + 0.461 + ], + "angle": 0, + "content": "During inference, we assume that the first head orientation is given and integrate the predicted head angular velocity to estimate the subsequent head orientations." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.462, + 0.895, + 0.569 + ], + "angle": 0, + "content": "The training loss of the HeadNet is defined as: \\(\\mathcal{L} = \\mathcal{L}_{dist} + \\mathcal{L}_{vel} + \\mathcal{L}_{rot}\\). \\(\\mathcal{L}_{dist}\\) represents the \\(L1\\) loss for translation distance. \\(\\mathcal{L}_{vel}\\) represents the \\(L1\\) loss for angular velocity. \\(\\mathcal{L}_{rot}\\) denotes the rotation loss \\(\\mathcal{L}_{rot} = ||\\pmb{R}_{pred}\\pmb{R}_{gt}^T - \\pmb{I}||_1\\) where \\(\\pmb{R}_{pred}\\) represents the integrated rotation using predicted angular velocity, \\(\\pmb{R}_{gt}\\) represents the ground truth rotation matrix and \\(\\pmb{I}\\) represents the identity matrix." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.575, + 0.868, + 0.592 + ], + "angle": 0, + "content": "3.2. Full-Body Pose Estimation from Head Pose" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.599, + 0.893, + 0.779 + ], + "angle": 0, + "content": "Predicting full-body pose from head pose is not a one-to-one mapping problem as different full-body motions may have the same head pose. Thus, we formulate the task using a conditional generative model. Inspired by the recent success of the diffusion model in image generation [30], we deploy a diffusion model to generate full-body poses conditioned on head poses. We use the formulation proposed in the denoising diffusion probabilistic model (DDPM) [7], which has also been applied in some concurrent work [14, 34, 50] for motion generation and motion interpolation tasks. We will first introduce our data representation and then detail the conditional diffusion model formulation." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.892, + 0.871 + ], + "angle": 0, + "content": "A body pose \\( \\mathbf{X}_t \\in \\mathbb{R}^D \\) at time \\( t \\) consists of the global joint position \\( (\\mathbb{R}^{J \\times 3}) \\) and global joint rotations \\( (\\mathbb{R}^{J \\times 6}) \\). We adopt the widely used SMPL model [20] as our skeleton, and the number of joints \\( J \\) is 22. For the convenience of notation in the diffusion model, we use \\( x_n \\) to denote a sequence of body poses \\( \\mathbf{X}_1^n, \\mathbf{X}_2^n, \\dots, \\mathbf{X}_T^n \\) at noise level \\( n \\)." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.871, + 0.892, + 0.901 + ], + "angle": 0, + "content": "The high-level idea of the diffusion model is to design a forward diffusion process to add Gaussian noises to the" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "17145" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.47, + 0.137 + ], + "angle": 0, + "content": "original data with a known variance schedule and learn a denoising model to gradually denoise \\(N\\) steps given a sampled \\(\\pmb{x}_N\\) from a normal distribution to generate \\(\\pmb{x}_0\\)." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.137, + 0.471, + 0.213 + ], + "angle": 0, + "content": "Specifically, diffusion models consist of a forward diffusion process and a reverse diffusion process. The forward diffusion process gradually adds Gaussian noise to the original data \\( \\boldsymbol{x}_0 \\). And it is formulated using a Markov chain of \\( N \\) steps as shown in Equation 1:" + }, + { + "type": "equation", + "bbox": [ + 0.162, + 0.223, + 0.469, + 0.264 + ], + "angle": 0, + "content": "\\[\nq \\left(\\boldsymbol {x} _ {1: N} \\mid \\boldsymbol {x} _ {0}\\right) := \\prod_ {n = 1} ^ {N} q \\left(\\boldsymbol {x} _ {n} \\mid \\boldsymbol {x} _ {n - 1}\\right). \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.273, + 0.469, + 0.303 + ], + "angle": 0, + "content": "Each step is decided by a variance schedule using \\(\\beta_{n}\\) and is defined as" + }, + { + "type": "equation", + "bbox": [ + 0.12, + 0.313, + 0.469, + 0.332 + ], + "angle": 0, + "content": "\\[\nq \\left(\\boldsymbol {x} _ {n} \\mid \\boldsymbol {x} _ {n - 1}\\right) := \\mathcal {N} \\left(\\boldsymbol {x} _ {n}; \\sqrt {1 - \\beta_ {n}} \\boldsymbol {x} _ {n - 1}, \\beta_ {n} \\boldsymbol {I}\\right). \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.342, + 0.469, + 0.401 + ], + "angle": 0, + "content": "To generate full-body motion conditioned on the head pose, we need to reverse the diffusion process. The reverse process can be approximated as a Markov chain with a learned mean and fixed variance:" + }, + { + "type": "equation", + "bbox": [ + 0.099, + 0.413, + 0.469, + 0.43 + ], + "angle": 0, + "content": "\\[\np _ {\\theta} \\left(\\boldsymbol {x} _ {n - 1} \\mid \\boldsymbol {x} _ {n}, c\\right) := \\mathcal {N} \\left(\\boldsymbol {x} _ {n - 1}; \\boldsymbol {\\mu} _ {\\theta} \\left(\\boldsymbol {x} _ {n}, n, c\\right), \\sigma_ {n} ^ {2} \\boldsymbol {I}\\right). \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.441, + 0.469, + 0.516 + ], + "angle": 0, + "content": "where \\(\\pmb{\\theta}\\) represents the parameters of a neural network, \\(c\\) is the head conditions. The learned mean \\(\\pmb{\\mu}_{\\theta}(\\pmb{x}_n,n,c)\\) (we use \\(\\pmb{\\mu}_{\\theta}\\) in the equation for brevity) can be represented as follows where \\(\\alpha_{n}\\) and \\(\\bar{\\alpha}_{n}\\) are fixed parameters, \\(\\hat{\\pmb{x}}_{\\theta}(\\pmb{x}_n,n,c)\\) is the prediction of \\(\\pmb{x}_0\\):" + }, + { + "type": "equation", + "bbox": [ + 0.078, + 0.525, + 0.468, + 0.569 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {\\mu} _ {\\theta} = \\frac {\\sqrt {\\alpha_ {n}} (1 - \\bar {\\alpha} _ {n - 1}) \\boldsymbol {x} _ {n} + \\sqrt {\\bar {\\alpha} _ {n - 1}} (1 - \\alpha_ {n}) \\hat {\\boldsymbol {x}} _ {\\theta} (\\boldsymbol {x} _ {n} , n , c)}{1 - \\bar {\\alpha} _ {n}} \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.571, + 0.469, + 0.615 + ], + "angle": 0, + "content": "Learning the mean can be reparameterized as learning to predict the original data \\( \\pmb{x}_0 \\). The training loss is defined as a reconstruction loss of \\( \\pmb{x}_0 \\):" + }, + { + "type": "equation", + "bbox": [ + 0.163, + 0.627, + 0.469, + 0.643 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} = \\mathbb {E} _ {\\boldsymbol {x} _ {0}, n} \\| \\hat {\\boldsymbol {x}} _ {\\theta} (\\boldsymbol {x} _ {n}, n, c) - \\boldsymbol {x} _ {0} \\| _ {1} \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.654, + 0.469, + 0.714 + ], + "angle": 0, + "content": "As shown in Figure 3, in denoising step \\( n \\), we concatenate head pose condition \\( c_{1},\\ldots ,c_{T} \\) with body pose representation \\( X_{1}^{n},\\ldots ,X_{T}^{n} \\) at noise level \\( n \\), combined with noise embedding as input to a transformer model, and estimate \\( x_0 \\)." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.723, + 0.318, + 0.739 + ], + "angle": 0, + "content": "3.3. Synthetic Data Generation" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.746, + 0.47, + 0.806 + ], + "angle": 0, + "content": "Our method does not need paired training data. Still, for benchmarking purposes, we develop a way to automatically synthesize a large-scale dataset with various paired egocentric videos and human motions." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.81, + 0.469, + 0.901 + ], + "angle": 0, + "content": "Generate Motions in 3D Scenes. To generate a dataset with both egocentric video and ground truth human motions, we use a large-scale motion capture dataset AMASS [23] and a 3D scene dataset Replica [31]. We convert the scene mesh from Replica to the signed distance field (SDF) for the penetration calculation. We divide each sequence of" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.26 + ], + "angle": 0, + "content": "AMASS [23] into sub-sequences with 150 frames. For each sub-sequence, based on the semantic annotation provided by Replica [31], we place the first pose in a random location with the feet in contact with the floor. Then we calculate penetration loss following Wang et al. [39] for each pose in this sequence. We empirically set the threshold to 2 and only keep the poses with penetration loss less than the threshold. Specifically, for human mesh \\( M_{t} \\) at time \\( t \\) represented by a parameterized human model [20, 27], we denote \\( d_{i} \\) as the signed distance of vertex \\( i \\). The penetration loss is then defined as \\( L_{pen}^{t} = \\sum_{d_{i} < 0} ||d_{i}|| \\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.261, + 0.894, + 0.427 + ], + "angle": 0, + "content": "Synthesize Realistic Egocentric Images. The motion sequences produced by detecting penetration with 3D scenes provide the camera pose trajectories to render synthetic egocentric videos. AI Habitat [24,32] is a platform for embodied agent research that supports fast rendering given a camera trajectory and a 3D scene. We feed the head pose trajectories to the platform and synthesize realistic images in the egocentric view. We generate 1,664,616 frames with 30 fps, approximately 15 hours of motion in 18 scenes. We name the synthetic dataset AMASS-Replica-Ego-Syn (ARES) and show some examples from our synthetic dataset in Figure 4." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.439, + 0.632, + 0.456 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.464, + 0.892, + 0.539 + ], + "angle": 0, + "content": "We evaluate and compare our method to baselines on five commonly used metrics for human motion reconstruction, in addition to the human perception studies. We also conduct ablation studies to analyze the performance of each stage of our method, as well as the design choices in our model." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.547, + 0.787, + 0.562 + ], + "angle": 0, + "content": "4.1. Datasets and Evaluation Metrics" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.569, + 0.892, + 0.674 + ], + "angle": 0, + "content": "AMASS-Replica-Ego-Syn (ARES) is our synthetic dataset which contains synthetic egocentric videos and ground truth motions. ARES contains about 15 hours of motion across 18 scenes. We remove 5 scenes from training as unseen scenes. The training dataset consists of about \\(1.2\\mathrm{M}\\) frames in 13 different scenes. The testing dataset contains 34,850 frames from 5 unseen scenes." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.679, + 0.891, + 0.724 + ], + "angle": 0, + "content": "AMASS [23] is a large-scale motion capture dataset with about 45 hours of diverse motions. We split training and testing data following HuMoR [29]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.727, + 0.892, + 0.803 + ], + "angle": 0, + "content": "Kinpoly-MoCap [22] consists of egocentric videos captured using a head-mounted camera and corresponding 3D motions captured with motion capture devices. The total motion is about 80 minutes long. Since it uses motion capture devices, the egocentric video is constrained to a single lab scene." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.807, + 0.892, + 0.867 + ], + "angle": 0, + "content": "Kinpoly-RealWorld [22] contains paired egocentric videos and head poses captured using iPhone ARKit. Unlike Kinpoly-MoCap which is captured in a lab scene, Kinpoly-RealWorld provides in-the-wild egocentric videos." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.871, + 0.892, + 0.901 + ], + "angle": 0, + "content": "GIMO [51] consists of egocentric video, eye gaze, 3D motions, and scanned 3D scenes. This dataset is collected using" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "17146" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.081, + 0.09, + 0.894, + 0.213 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.216, + 0.893, + 0.245 + ], + "angle": 0, + "content": "Figure 4. Illustration of our ARES Dataset. \"Ego-View\" represents the synthetic egocentric images using our proposed data generation pipeline. We also provide a third-person view reference in the second row. The left and right show two sequences from different scenes." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.25, + 0.891, + 0.334 + ], + "angle": 0, + "content": "
MethodARESKinpoly-MoCap [22]GIMO [51]
OheadTheadMPJPEAccelFSOheadTheadMPJPEAccelFSOheadTheadMPJPEAccelFS
PoseReg [48]0.77354.7147.7127.687.11.051943.9160.461.810.81.511528.6189.371.514.2
Kinpoly-OF [22]0.62323.4141.67.34.21.332475.5230.516.415.81.521739.3404.221.914.4
EgoEgo (ours)0.20148.0121.16.22.70.58505.1125.98.01.60.67356.8152.110.41.9
" + }, + { + "type": "table_caption", + "bbox": [ + 0.158, + 0.339, + 0.812, + 0.354 + ], + "angle": 0, + "content": "Table 1. Full-body motion estimation from egocentric video on ARES, Kinpoly-MoCap [22], and GIMO [51]." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.365, + 0.471, + 0.412 + ], + "angle": 0, + "content": "Hololens, iPhone 12, and IMU-based motion capture suits to study motion prediction tasks guided by eye gaze. We use 15 scenes for training and 4 scenes for testing." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.416, + 0.221, + 0.43 + ], + "angle": 0, + "content": "Evaluation Metrics." + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.435, + 0.474, + 0.51 + ], + "angle": 0, + "content": "- Head Orientation Error \\((\\mathbf{O}_{head})\\) computes the Frobenius norm of the difference between the \\(3 \\times 3\\) rotation matrix \\(||\\pmb{R}_{pred}\\pmb{R}_{gt}^{-1} - \\pmb{I}||_2\\), where \\(\\pmb{R}_{pred}\\) is the predicted head rotation matrix and \\(\\pmb{R}_{gt}\\) is the ground truth head rotation matrix." + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.514, + 0.474, + 0.576 + ], + "angle": 0, + "content": "- Head Translation Error \\(\\left(\\mathbf{T}_{\\text {head }}\\right)\\) is computed by taking the mean Euclidean distance of two trajectories. We use this metric to measure the head joint translation errors in millimeters (mm)." + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.579, + 0.473, + 0.61 + ], + "angle": 0, + "content": "- MPJPE represents mean per-joint position errors in millimeters (mm)." + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.613, + 0.473, + 0.659 + ], + "angle": 0, + "content": "- Accel represents the difference of acceleration between predicted joint positions and ground truth joint positions measured in \\((mm / s^2)\\)." + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.662, + 0.474, + 0.802 + ], + "angle": 0, + "content": "- FS represents foot skating metric and is computed following NeMF [5]. Specifically, we first project the toe and ankle joints' velocity to the \\(xy\\) plane and compute the \\(L1\\) norm of the projected velocities in each step denoted as \\(v_{t}\\). We only accumulate the horizontal translation for those steps that have a height \\(h_t\\) lower than a specified threshold \\(H\\). And the metric is calculated as a mean of weighted values \\(v_{t}(2 - 2^{\\frac{h_{t}}{H}})\\) across the sequence and is measured in \\((mm)\\)." + }, + { + "type": "list", + "bbox": [ + 0.096, + 0.435, + 0.474, + 0.802 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.821, + 0.461, + 0.837 + ], + "angle": 0, + "content": "4.2. Body Pose Estimation from Egocentric Video" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.473, + 0.903 + ], + "angle": 0, + "content": "Training Data. We train our HeadNet using paired egocentric videos and head poses provided by ARES, KinplyRealWorld, and GIMO. Note that the body motion in these datasets is not used for training HeadNet. Our GravityNet" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.365, + 0.893, + 0.412 + ], + "angle": 0, + "content": "and the conditional diffusion model are both trained on AMASS. For the baselines below, we train them using paired egocentric videos and ground truth motions in ARES." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.421, + 0.895, + 0.619 + ], + "angle": 0, + "content": "Baselines. We compare our approach with two baselines PoseReg [48] and Kinpoly [22]. PoseReg [48] takes a sequence of optical flow features as input and uses an LSTM model to predict the pose state at each time step. The pose state consists of root translation, root orientation, joint rotations, and corresponding velocities including root linear velocity and angular velocities of all the joints. Kinpoly-OF [22] proposes a per-step regression model to estimate full body motion from optical flow features. Because our problem only allows for egocentric video as input, we choose the option of Kinpoly which only has optical flow features as input, without relying on ground truth head poses and action labels that depend on additional knowledge." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.625, + 0.894, + 0.761 + ], + "angle": 0, + "content": "Results. We compare the complete pipeline of EgoEgo with baseline methods PoseReg [48] and Kinpoly-OF [22] on ARES, Kinpoly-MoCap [22] and GIMO [51], as shown in Table 1. We show that our EgoEgo outperforms all the baselines by a large margin on all three datasets. We show qualitative results in Figure 5. Our generated motions better preserve the root trajectories. And our approach can also generate more dynamic and realistic motions compared to the baselines." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.774, + 0.884, + 0.79 + ], + "angle": 0, + "content": "4.3. Head Pose Estimation from Egocentric Video" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.795, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Baselines. We compare our hybrid approach with the prediction results of DROID-SLAM [33]. For a fair comparison, we apply a rotation to the SLAM trajectory by aligning the first predicted head pose of SLAM with the ground truth head pose. We train our GravityNet on AMASS training split. As for HeadNet, we train on ARES, Kinpoly-RealWorld, and GIMO separately for the evaluation of different datasets." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "17147" + } + ], + [ + { + "type": "image_caption", + "bbox": [ + 0.437, + 0.097, + 0.532, + 0.111 + ], + "angle": 0, + "content": "(a) Example 1" + }, + { + "type": "image", + "bbox": [ + 0.078, + 0.113, + 0.895, + 0.57 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.158, + 0.574, + 0.812, + 0.588 + ], + "angle": 0, + "content": "Figure 5. Qualitative results comparisons. We show the results of two egocentric videos from different scenes." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.608, + 0.471, + 0.804 + ], + "angle": 0, + "content": "Results. We evaluate the head pose estimation on the three datasets as shown in Table 2. We show more accurate head rotation prediction results on ARES and comparable results on real-captured data. As the real-captured data is limited in scale (Kinpoly-RealWorld contains 20 minutes of training videos and GIMO contains 30 minutes of training videos), we believe the head rotation prediction can be further improved by future developments of large-scale real-captured datasets with head poses. Overall, our hybrid approach combines the accurate rotation prediction from HeadNet and re-scaled translation of gravity-aligned SLAM results, and produces more accurate head pose estimation results as input to the second stage." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.819, + 0.436, + 0.835 + ], + "angle": 0, + "content": "4.4. Body Pose Estimation from the Head Pose" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.472, + 0.903 + ], + "angle": 0, + "content": "Baselines. We compare our conditional diffusion model for full-body pose estimation with two baselines AvatarPoser [10] and Kinpoly-Head [22]. AvatarPoser [10] takes both head and hand pose as input to predict full body motion." + }, + { + "type": "table", + "bbox": [ + 0.507, + 0.604, + 0.884, + 0.698 + ], + "angle": 0, + "content": "
DROID-SLAM [33]Ours
OheadThedOheadThed
ARES0.62411.30.23176.5
Kinpoly-MoCap0.551290.80.58487.8
GIMO0.67865.40.68304.7
" + }, + { + "type": "table_caption", + "bbox": [ + 0.568, + 0.7, + 0.822, + 0.714 + ], + "angle": 0, + "content": "Table 2. Head pose estimation on test sets." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.728, + 0.892, + 0.819 + ], + "angle": 0, + "content": "We remove the hand poses from the input and modified it to a setting with head pose input only. Kinpoly-Head [22] is our modified variant of the Kinpoly model that only takes the head pose as input. Both the baselines and our method are trained on the training split of AMASS with high-quality motion capture data." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.825, + 0.893, + 0.903 + ], + "angle": 0, + "content": "Results. We evaluate the baselines and our method on the AMASS test set, as shown in Table 3. Since our model is generative, there are multiple plausible predictions from the same head pose input. For a quantitative comparison, we generate 200 samples for each head pose input and use the" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "17148" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.079, + 0.09, + 0.472, + 0.155 + ], + "angle": 0, + "content": "
MethodOheadTheadMPJPEAccelFS
AvatarPoser [10]0.1928.6124.716.118.8
Kinpoly-Head [22]0.1987.8110.911.411.2
Diffusion Model (ours)0.0436.7109.010.54.4
" + }, + { + "type": "table_caption", + "bbox": [ + 0.078, + 0.157, + 0.47, + 0.185 + ], + "angle": 0, + "content": "Table 3. Full-body motion estimation from GT head pose on AMASS testing dataset [22]." + }, + { + "type": "table", + "bbox": [ + 0.08, + 0.192, + 0.47, + 0.297 + ], + "angle": 0, + "content": "
ARESKinpoly-MoCapGIMO
OheadThedOheadThedOheadThed
SLAM0.62411.330.551290.820.67865.41
SLAM+S0.62325.950.55643.450.67569.48
SLAM+S+G0.62176.540.55487.770.67304.74
Full model0.23176.540.58487.770.68304.74
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.303, + 0.471, + 0.346 + ], + "angle": 0, + "content": "Table 4. Ablation study for the components in head pose estimation. S represents the scale predicted by HeadNet, and G represents GravityNet." + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.359, + 0.361, + 0.373 + ], + "angle": 0, + "content": "one with the smallest MPJPE as our result." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.385, + 0.242, + 0.4 + ], + "angle": 0, + "content": "4.5. Ablation Studies" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.405, + 0.47, + 0.48 + ], + "angle": 0, + "content": "Effects of Components in Head Pose Estimation. We study the effects of each component in head pose estimation in Table 4. We showcase that the rotation for aligning gravity direction and the learned scale are both effective to improve head translation results." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.488, + 0.471, + 0.595 + ], + "angle": 0, + "content": "Effects of Head Pose in Full-Body Pose Estimation. We compare the full-body pose estimation results that take our predicted head poses and the ground truth head poses as input. Table 5 shows that the ground truth head poses significantly improve the full body pose estimation, indicating that by developing methods that predict more accurate head pose, the full body pose estimation can be further improved." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.605, + 0.308, + 0.621 + ], + "angle": 0, + "content": "4.6. Human Perceptual Study" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.629, + 0.47, + 0.854 + ], + "angle": 0, + "content": "We also conduct two human perceptual studies as part of the evaluation. The first is to evaluate the quality of predicted full-body motion from egocentric video, the second is to evaluate the quality of predicted full-body motion from ground truth head poses. In both studies, we compare four types of motion: results from our EgoEgo and from two baselines, as well as the ground truth. For the first human study, each time, users are presented with two motions and an egocentric video, and asked to select which one is more plausible. For the second human study, users are presented with two motions and asked to select which one looks more natural and realistic. Because there are 10 examples and the two motions can be from four sources, we have 60 questions for each study. Each question was answered by 20 Amazon Mechanical Turk workers." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.856, + 0.471, + 0.901 + ], + "angle": 0, + "content": "As shown in Figure 6(a), for full-body estimation from egocentric video, our results are preferred by \\(98\\%\\) and \\(69\\%\\) of workers when compared to the baselines. Also, when" + }, + { + "type": "table", + "bbox": [ + 0.501, + 0.089, + 0.89, + 0.208 + ], + "angle": 0, + "content": "
ARESKinpoly-MoCapGIMO
EEEE w/ GTEEEE w/ GTEEEE w/ GT
Ohead0.200.040.580.030.670.06
Thead148.029.1505.160.7356.866.0
MPJPE121.1105.6125.976.0152.1125.7
Accel6.26.38.07.210.410.2
FS2.73.01.62.51.91.7
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.212, + 0.892, + 0.254 + ], + "angle": 0, + "content": "Table 5. Ablation study for the effects of head pose to full-body pose estimation. EE represents EgoEgo. GT represents ground truth head poses." + }, + { + "type": "image", + "bbox": [ + 0.502, + 0.263, + 0.891, + 0.417 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.5, + 0.42, + 0.892, + 0.448 + ], + "angle": 0, + "content": "Figure 6. Results of human perceptual studies. The numbers shown in the chart represent \\(\\%\\)" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.461, + 0.894, + 0.552 + ], + "angle": 0, + "content": "compared with the ground truth, \\(34\\%\\) of the responses prefer our results (note that a perfect output would achieve \\(50\\%\\)), suggesting that people cannot easily distinguish our results from ground truth motions. As shown in Figure 6(b), for full-body estimation from head poses, our results are preferred by \\(88\\%\\) and \\(79\\%\\) of workers when compared to the baselines." + }, + { + "type": "title", + "bbox": [ + 0.501, + 0.56, + 0.619, + 0.576 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.588, + 0.895, + 0.8 + ], + "angle": 0, + "content": "We presented a generalized framework to estimate full-body motions from egocentric video. The key is to decompose the problem into two stages. We predicted the head pose from an egocentric video and fed the output from the first stage to estimate full-body motions in the second stage. In addition, we developed a hybrid solution to produce more accurate head poses on top of monocular SLAM. We also proposed a conditional diffusion model to generate diverse high-quality full-body motions from predicted head poses. To benchmark different methods in a large-scale dataset, we proposed a data generation pipeline to synthesize a largescale dataset with paired egocentric videos and 3D human motions. We showcased superior results on both the synthetic and the real-captured dataset compared to prior work." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.81, + 0.894, + 0.903 + ], + "angle": 0, + "content": "Acknowledgement. We thank Zhengfei Kuang for the help with visualizations and Jonathan Tseng for discussions about the diffusion model. This work is in part supported by ONR MURI N00014-22-1-2740, NSF CCRI 2120095, the Toyota Research Institute (TRI), the Stanford Institute for Human-Centered AI (HAI), Innopeak, Meta, and Samsung." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "17149" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.175, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.116, + 0.472, + 0.169 + ], + "angle": 0, + "content": "[1] Sadegh Aliakbarian, Pashmina Cameron, Federica Bogo, Andrew Fitzgibbon, and Thomas J Cashman. FLAG: Flow-based 3D avatar generation from sparse observations. In CVPR, 2022. 3" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.173, + 0.473, + 0.241 + ], + "angle": 0, + "content": "[2] Carlos Campos, Richard Elvira, Juan J Gomez Rodríguez, José MM Montiel, and Juan D Tardós. 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In CVPR, 2019. 3" + }, + { + "type": "list", + "bbox": [ + 0.503, + 0.093, + 0.894, + 0.346 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "17151" + } + ] +] \ No newline at end of file diff --git a/2023/Ego-Body Pose Estimation via Ego-Head Pose Estimation/efdf65a4-1b22-494a-ba23-4617e8cb1fe5_origin.pdf b/2023/Ego-Body Pose Estimation via Ego-Head Pose Estimation/efdf65a4-1b22-494a-ba23-4617e8cb1fe5_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..76b270d6f5b6105096e2453f28c5900837d5cafb --- /dev/null +++ b/2023/Ego-Body Pose Estimation via Ego-Head Pose Estimation/efdf65a4-1b22-494a-ba23-4617e8cb1fe5_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:1e4a6ef01eda228cb66cf4d635b981fd2171b3b92ecb74992b35a0d5c1b0aab1 +size 3643356 diff --git a/2023/Ego-Body Pose Estimation via Ego-Head Pose Estimation/full.md b/2023/Ego-Body Pose Estimation via Ego-Head Pose Estimation/full.md new file mode 100644 index 0000000000000000000000000000000000000000..591beca1e65bf7566e9851840d3923e5920cdbaa --- /dev/null +++ b/2023/Ego-Body Pose Estimation via Ego-Head Pose Estimation/full.md @@ -0,0 +1,295 @@ +# Ego-Body Pose Estimation via Ego-Head Pose Estimation + +Jiaman Li C. Karen Liu† Jiajun Wu† +Stanford University + +{jiamanli,karenliu, jiajunwu}@cs.stanford.edu + +![](images/5629dcdc91b252f9c4b0bcc955e4cd5b3ed7301ac758604421c115a37b0da9b6.jpg) +(a) Egocentric Video + +![](images/d4c5cc31c0b93522ff2b1a585517c5d051d249e4f91da194e66b0f090a99800c.jpg) +(b) Head Pose Estimation + +![](images/504783766255b4ad7ed39040cceffb8dc4b6c2024c1a334b3a14b0f538994d12.jpg) + +![](images/ab131e744c7762baa1c28e8a3d9a5091fbebde23d2465c1ee937571094a633e4.jpg) +(c) Full-Body Human Motion Generation +Figure 1. Taking egocentric video (a) as input, our approach first predicts head pose (b); it then estimates multiple plausible full-body human motions (c) from the predicted head pose. This motion sequence shows a human kicking and jumping in place. Please refer to the supplementary video on our project page for a complete motion sequence visualization. + +# Abstract + +Estimating 3D human motion from an egocentric video sequence plays a critical role in human behavior understanding and has various applications in VR/AR. However, naively learning a mapping between egocentric videos and human motions is challenging, because the user's body is often unobserved by the front-facing camera placed on the head of the user. In addition, collecting large-scale, high-quality datasets with paired egocentric videos and 3D human motions requires accurate motion capture devices, which often limit the variety of scenes in the videos to lab-like environments. To eliminate the need for paired egocentric video and human motions, we propose a new method, Ego-Body Pose Estimation via Ego-Head Pose Estimation (EgoEgo), which decomposes the problem into two stages, connected by the head motion as an intermediate representation. EgoEgo first integrates SLAM and a learning approach to estimate accurate head motion. Subsequently, leveraging the estimated head pose as input, EgoEgo utilizes conditional diffusion + +to generate multiple plausible full-body motions. This disentanglement of head and body pose eliminates the need for training datasets with paired egocentric videos and 3D human motion, enabling us to leverage large-scale egocentric video datasets and motion capture datasets separately. Moreover, for systematic benchmarking, we develop a synthetic dataset, AMASS-Replica-Ego-Syn (ARES), with paired egocentric videos and human motion. On both AREs and real data, our EgoEgo model performs significantly better than the current state-of-the-art methods. + +# 1. Introduction + +Estimating 3D human motion from an egocentric video, which records the environment viewed from the first-person perspective with a front-facing monocular camera, is critical to applications in VR/AR. However, naively learning a mapping between egocentric videos and full-body human motions is challenging for two reasons. First, modeling this complex relationship is difficult; unlike reconstruction motion from third-person videos, the human body is often out of view of an egocentric video. Second, learning this + +mapping requires a large-scale, diverse dataset containing paired egocentric videos and the corresponding 3D human poses. Creating such a dataset requires meticulous instrumentation for data acquisition, and unfortunately, such a dataset does not currently exist. As such, existing works have only worked on small-scale datasets with limited motion and scene diversity [22, 47, 48]. + +We introduce a generalized and robust method, EgoEgo, to estimate full-body human motions from only egocentric video for diverse scenarios. Our key idea is to use head motion as an intermediate representation to decompose the problem into two stages: head motion estimation from the input egocentric video and full-body motion estimation from the estimated head motion. For most day-to-day activities, humans have an extraordinary ability to stabilize the head such that it aligns with the center of mass of the body [13], which makes head motion an excellent feature for full-body motion estimation. More importantly, the decomposition of our method removes the need to learn from paired egocentric videos and human poses, enabling learning from a combination of large-scale, single-modality datasets (e.g., datasets with egocentric videos or 3D human poses only), which are commonly and readily available. + +The first stage, estimating the head pose from an egocentric video, resembles the localization problem. However, directly applying the state-of-the-art monocular SLAM methods [33] yields unsatisfactory results, due to the unknown gravity direction and the scaling difference between the estimated space and the real 3D world. We propose a hybrid solution that leverages SLAM and learned transformer-based models to achieve significantly more accurate head motion estimation from egocentric video. In the second stage, we generate the full-body motion based on a diffusion model conditioned on the predicted head pose. Finally, to evaluate our method and train other baselines, we build a large-scale synthetic dataset with paired egocentric videos and 3D human motions, which can also be useful for future work on visuomotor skill learning and sim-to-real transfer. + +Our work makes four main contributions. First, we propose a decomposition paradigm, EgoEgo, to decouple the problem of motion estimation from egocentric video into two stages: ego-head pose estimation, and ego-body pose estimation conditioned on the head pose. The decomposition lets us learn each component separately, eliminating the need for a large-scale dataset with two paired modalities. Second, we develop a hybrid approach for ego-head pose estimation, integrating the results of monocular SLAM and learning. Third, we propose a conditional diffusion model to generate full-body poses conditioned on the head pose. Finally, we contribute a large-scale synthetic dataset with both egocentric videos and 3D human motions as a test bed to benchmark different approaches and showcase that our method outperforms the baselines by a large margin. + +# 2. Related Work + +Motion Estimation from Third-person Video. 3D pose estimation from images and videos in third-person view has been extensively studied in recent years. There are mainly two typical categories in this direction. One is to regress joint positions directly from images and videos [25, 28, 36, 52]. The other adopts parametric human body model [20] to estimate body model parameters from images or videos [3, 12, 15-18, 21]. And recently, learned motion prior is applied to address the issues of jitters, lack of global trajectory, and missing joints or frames [19, 29, 46]. Moreover, physical constraints are enforced in motion estimation from videos [41, 49]. In contrast to third-person videos, where the full body can be seen, body joints are mostly not visible in an egocentric video, which poses a significant challenge for the problem. Although the body joints are unobserved from egocentric views, the visual information of how the environment changes provides a strong signal to infer how the head moves. In this work, we propose to use the head pose as an intermediate representation to bridge the egocentric video and full-body motions. + +Motion Estimation from Egocentric Video. Growing attention is received in pose estimation from egocentric videos. Special hardware like the fisheye camera is deployed to predict full body pose from captured images [9, 35, 38, 42]. While body joints are usually visible in images captured with a fisheye camera, the distortion of images poses a significant challenge. Jiang et al. [8] deploy a standard camera to a human chest and propose an implicit motion graph matching approach to predict full body motions from the input video. You2Me [26] predicts full body motions by observing the interaction pose of the second-person in the camera view. Towards a goal of estimating and forecasting physically plausible motions from a head-mounted camera, EgoPose [47, 48] develop a Deep-RL framework to learn a control policy to estimate current poses and forecast future poses. Follow-up work Kinpoly [22] integrates kinematics and dynamics to predict physically plausible motions interacting with known objects. While their method achieves impressive results in their collected dataset, it cannot handle scenes and motions out of their data distribution. This work aims to establish a more generalized and robust framework to infer full-body motions from egocentric video only. To validate the effectiveness in more generalized scenes and motions, we also introduce an approach of synthesizing egocentric video corresponding to mocap data in diverse 3D scenes for quantitative evaluation. + +Motion Estimation from Sparse Sensors. Instead of estimating motion from videos, some work explored reconstructing human motions from sparse sensor input. TransPose [45] proposes a real-time pipeline to predict full body motions from 6 IMU sensors, including head, torso, left/right arms, + +and left/right lower legs. Follow-up work PIP [44] further includes a PD controller on top of the kinematic estimator to introduce physics constraints during reconstruction. TIP [11] follows the same sensor setting and deploys a transformer-based model to leverage IMU sequential information effectively. Fewer sensors are investigated in LoBSTr [43]. Given tracker information from 4 joints (head, left/right hands, torso), they present an RNN-based model to infer lower-body motions from past upper-body joint signals. Recent advances [1,4,10,40] further relax the input constraints to head and hand signals only. In this work, we do not rely on any observations from inertial sensors. Instead, we aim to develop a solution with egocentric video input only. + +# 3. Method + +Our method, EgoEgo, estimates 3D human motion from a monocular egocentric video sequence. As shown in Figure 2, our key idea is to leverage head motion: first estimating head motion from egocentric video, and then estimating full body motion from head motion. We show that head motion is an excellent feature for full-body motion estimation and a compact, intermediate representation that reduces the challenge into two much simpler sub-problems. Such a disentanglement also allows us to leverage a large-scale egocentric video dataset with head motion (but no full body motion) in stage one, and a separate 3D human motion dataset (but no egocentric videos) in stage two. + +Notations. We denote full body motion as $\mathbf{X} \in \mathbb{R}^{T \times D}$ and egocentric images captured from a front-facing, head-mounted camera as $\mathbf{I} \in \mathbb{R}^{T \times h \times w \times 3}$ , where $T$ is the sequence length, $D$ is the dimension of the pose state, and $h \times w$ is the size of an image. We introduce head motion $\mathbf{H} \in \mathbb{R}^{T \times D'}$ as an intermediate representation to bridge the input egocentric video and the output human motions, where $D'$ is the dimension of the head pose. + +# 3.1. Head Pose Estimation from Egocentric Video + +Estimating the head motion from an egocentric video can be viewed as a camera localization problem. However, we observed three issues that prevent us from directly applying the state-of-the-art monocular SLAM method [33] to our problem. First, the gravity direction of the estimated head pose is unknown. Thus, the results cannot be directly fed to the full-body motion estimator, since it expects the head pose expressed in a coordinate frame where the gravity direction is $[0, 0, -1]^T$ . Second, the estimated translation by monocular SLAM is not to scale when compared with the distance in the real world. Third, monocular SLAM tends to be less accurate in estimating relative head rotation than translation. + +Based on these observations, we propose a hybrid method that leverages SLAM and learned models to achieve more accurate head pose estimation than the state-of-the-art SLAM + +alone. First, we develop a transformer-based model GravityNet to estimate the gravity direction from the rotation and the translation trajectories computed by SLAM. We rotate the SLAM translation by aligning the estimated gravity direction with the real gravity direction $[0, 0, -1]^T$ in the 3D world. Moreover, from the optical flow features extracted from the egocentric video, our method learns a model, HeadNet, to estimate head rotations and translation distance. The predicted translation distance of HeadNet is used to re-scale the translation estimated by SLAM. The predicted head rotation by HeadNet is directly used to replace the rotation estimated by SLAM. Figure 2 summarizes our process to generate head poses. + +Monocular SLAM. We adopt DROID-SLAM [33] to estimate camera trajectory from egocentric videos. DROID-SLAM [33] is a learning-based method to estimate camera pose trajectory and reconstruct the 3D map of the environment simultaneously. By a design of recurrent iterative updates to camera pose and depth, it showcases superior and more robust results compared to prior SLAM systems [2]. For more details, please refer to [33]. + +Gravity Direction Estimation. We introduce GravityNet to predict gravity direction $\pmb{g} \in \mathbb{R}^3$ from a sequence of head poses $\hat{h}_1, \hat{h}_2, \dots, \hat{h}_T$ . The gravity direction $\pmb{g}$ is represented by a unit vector. The head poses input $\hat{h}_t$ consists of a 3D head translation, a head rotation represented by a continuous 6D rotation vector [53], head translation difference, and head rotation difference computed by $O_{t-1}^{-1}O_t$ where $O_t$ denotes the head rotation matrix at time step $t$ . We adopt a transformer-based architecture [37] consisting of two self-attention blocks, each of which has a multi-head attention layer followed by a position-wise feed-forward layer. We take the first output of the transformer and feed it to an MLP to predict the gravity direction $\pmb{g}$ . We train our GravityNet on the large-scale motion capture dataset AMASS [23]. However, the motion sequences in AMASS have the correct gravity direction $\pmb{g}_c = [0,0,-1]^T$ . To emulate the distribution of the predicted head poses from monocular SLAM, we apply a random scale and a random rotation to the head poses in each AMASS sequence to generate our training data for gravity estimation. $L_1$ loss for the gravity vector is used during training. Based on the prediction of GravityNet, we compute the rotation matrix $R_g$ to align the prediction $\pmb{g}$ and $\pmb{g}_c$ . Then we apply $R_g$ to the SLAM translation denoted as $\hat{P}_1, \hat{P}_2, \dots, \hat{P}_T$ and get $P_1, P_2, \dots, P_T$ , where $P_t = R_g\hat{P}_t$ . + +Head Pose Estimation. We propose HeadNet to predict a sequence of distance $d_{1}, d_{2}, \ldots, d_{T}$ and head rotations $R_{1}, \ldots, R_{T}$ from a sequence of optical flow features $o_{1}, \ldots, o_{T}$ . The optical flow features are extracted by a pretrained ResNet-18 [6]. We deploy the same model architecture as GravityNet. Since the scale from the monocular SLAM system may not be consistent with the real + +![](images/93b4443eb4e1aeffd9adf927845425932d7028ee5ba1e5f1bd1ca5e5b6f90562.jpg) +Figure 2. Overview of EgoEgo. The model first takes an egocentric video as input and predicts the head pose with a hybrid approach that combines monocular SLAM and the learned GravityNet and HeadNet. The predicted head pose is then fed to a conditional diffusion model to generate the full-body pose. + +![](images/aefa011ffac48f22583e5352dedc737a7b8af70a263c903320b8206e72bd4b66.jpg) +Figure 3. Model architecture of the denoising network in a single step of the reverse diffusion process. + +3D world where human moves, we use HeadNet to predict the vector norm of the translation difference between consecutive time steps denoted as $d_1, \ldots, d_T$ , where $d_t$ represents a scalar value. For each camera translation sequence produced by monocular SLAM and rotated by aligning gravity direction, given the camera translation trajectory $P \in \mathbb{R}^{T \times 3}$ , we calculate the distance $d_t^s$ between $P_t$ and $P_{t+1}$ as $d_t^s = ||P_{t+1} - P_t||_2$ . We take the mean value for the sequence of distances as $d^s = \frac{1}{T}\sum_{t=1}^{T}d_t^s$ . Similarly, we compute the mean of the predicted distance sequence $d = \frac{1}{T}\sum_{t=1}^{T}d_t$ . The scale is calculated as $s = \frac{d}{d^s}$ . We multiply scale $s$ to the predicted translation $P$ and use $sP$ as our global head translation results. + +The network also predicts the head angular velocity, $\omega_{1},\ldots ,\omega_{T}$ , in the head frame. We integrate predicted angular velocity to generate corresponding rotations $R_{1},\ldots ,R_{T}$ + +During inference, we assume that the first head orientation is given and integrate the predicted head angular velocity to estimate the subsequent head orientations. + +The training loss of the HeadNet is defined as: $\mathcal{L} = \mathcal{L}_{dist} + \mathcal{L}_{vel} + \mathcal{L}_{rot}$ . $\mathcal{L}_{dist}$ represents the $L1$ loss for translation distance. $\mathcal{L}_{vel}$ represents the $L1$ loss for angular velocity. $\mathcal{L}_{rot}$ denotes the rotation loss $\mathcal{L}_{rot} = ||\pmb{R}_{pred}\pmb{R}_{gt}^T - \pmb{I}||_1$ where $\pmb{R}_{pred}$ represents the integrated rotation using predicted angular velocity, $\pmb{R}_{gt}$ represents the ground truth rotation matrix and $\pmb{I}$ represents the identity matrix. + +# 3.2. Full-Body Pose Estimation from Head Pose + +Predicting full-body pose from head pose is not a one-to-one mapping problem as different full-body motions may have the same head pose. Thus, we formulate the task using a conditional generative model. Inspired by the recent success of the diffusion model in image generation [30], we deploy a diffusion model to generate full-body poses conditioned on head poses. We use the formulation proposed in the denoising diffusion probabilistic model (DDPM) [7], which has also been applied in some concurrent work [14, 34, 50] for motion generation and motion interpolation tasks. We will first introduce our data representation and then detail the conditional diffusion model formulation. + +A body pose $\mathbf{X}_t \in \mathbb{R}^D$ at time $t$ consists of the global joint position $(\mathbb{R}^{J \times 3})$ and global joint rotations $(\mathbb{R}^{J \times 6})$ . We adopt the widely used SMPL model [20] as our skeleton, and the number of joints $J$ is 22. For the convenience of notation in the diffusion model, we use $x_n$ to denote a sequence of body poses $\mathbf{X}_1^n, \mathbf{X}_2^n, \dots, \mathbf{X}_T^n$ at noise level $n$ . + +The high-level idea of the diffusion model is to design a forward diffusion process to add Gaussian noises to the + +original data with a known variance schedule and learn a denoising model to gradually denoise $N$ steps given a sampled $\pmb{x}_N$ from a normal distribution to generate $\pmb{x}_0$ . + +Specifically, diffusion models consist of a forward diffusion process and a reverse diffusion process. The forward diffusion process gradually adds Gaussian noise to the original data $\boldsymbol{x}_0$ . And it is formulated using a Markov chain of $N$ steps as shown in Equation 1: + +$$ +q \left(\boldsymbol {x} _ {1: N} \mid \boldsymbol {x} _ {0}\right) := \prod_ {n = 1} ^ {N} q \left(\boldsymbol {x} _ {n} \mid \boldsymbol {x} _ {n - 1}\right). \tag {1} +$$ + +Each step is decided by a variance schedule using $\beta_{n}$ and is defined as + +$$ +q \left(\boldsymbol {x} _ {n} \mid \boldsymbol {x} _ {n - 1}\right) := \mathcal {N} \left(\boldsymbol {x} _ {n}; \sqrt {1 - \beta_ {n}} \boldsymbol {x} _ {n - 1}, \beta_ {n} \boldsymbol {I}\right). \tag {2} +$$ + +To generate full-body motion conditioned on the head pose, we need to reverse the diffusion process. The reverse process can be approximated as a Markov chain with a learned mean and fixed variance: + +$$ +p _ {\theta} \left(\boldsymbol {x} _ {n - 1} \mid \boldsymbol {x} _ {n}, c\right) := \mathcal {N} \left(\boldsymbol {x} _ {n - 1}; \boldsymbol {\mu} _ {\theta} \left(\boldsymbol {x} _ {n}, n, c\right), \sigma_ {n} ^ {2} \boldsymbol {I}\right). \tag {3} +$$ + +where $\pmb{\theta}$ represents the parameters of a neural network, $c$ is the head conditions. The learned mean $\pmb{\mu}_{\theta}(\pmb{x}_n,n,c)$ (we use $\pmb{\mu}_{\theta}$ in the equation for brevity) can be represented as follows where $\alpha_{n}$ and $\bar{\alpha}_{n}$ are fixed parameters, $\hat{\pmb{x}}_{\theta}(\pmb{x}_n,n,c)$ is the prediction of $\pmb{x}_0$ : + +$$ +\boldsymbol {\mu} _ {\theta} = \frac {\sqrt {\alpha_ {n}} (1 - \bar {\alpha} _ {n - 1}) \boldsymbol {x} _ {n} + \sqrt {\bar {\alpha} _ {n - 1}} (1 - \alpha_ {n}) \hat {\boldsymbol {x}} _ {\theta} (\boldsymbol {x} _ {n} , n , c)}{1 - \bar {\alpha} _ {n}} \tag {4} +$$ + +Learning the mean can be reparameterized as learning to predict the original data $\pmb{x}_0$ . The training loss is defined as a reconstruction loss of $\pmb{x}_0$ : + +$$ +\mathcal {L} = \mathbb {E} _ {\boldsymbol {x} _ {0}, n} \| \hat {\boldsymbol {x}} _ {\theta} (\boldsymbol {x} _ {n}, n, c) - \boldsymbol {x} _ {0} \| _ {1} \tag {5} +$$ + +As shown in Figure 3, in denoising step $n$ , we concatenate head pose condition $c_{1},\ldots ,c_{T}$ with body pose representation $X_{1}^{n},\ldots ,X_{T}^{n}$ at noise level $n$ , combined with noise embedding as input to a transformer model, and estimate $x_0$ . + +# 3.3. Synthetic Data Generation + +Our method does not need paired training data. Still, for benchmarking purposes, we develop a way to automatically synthesize a large-scale dataset with various paired egocentric videos and human motions. + +Generate Motions in 3D Scenes. To generate a dataset with both egocentric video and ground truth human motions, we use a large-scale motion capture dataset AMASS [23] and a 3D scene dataset Replica [31]. We convert the scene mesh from Replica to the signed distance field (SDF) for the penetration calculation. We divide each sequence of + +AMASS [23] into sub-sequences with 150 frames. For each sub-sequence, based on the semantic annotation provided by Replica [31], we place the first pose in a random location with the feet in contact with the floor. Then we calculate penetration loss following Wang et al. [39] for each pose in this sequence. We empirically set the threshold to 2 and only keep the poses with penetration loss less than the threshold. Specifically, for human mesh $M_{t}$ at time $t$ represented by a parameterized human model [20, 27], we denote $d_{i}$ as the signed distance of vertex $i$ . The penetration loss is then defined as $L_{pen}^{t} = \sum_{d_{i} < 0} ||d_{i}||$ . + +Synthesize Realistic Egocentric Images. The motion sequences produced by detecting penetration with 3D scenes provide the camera pose trajectories to render synthetic egocentric videos. AI Habitat [24,32] is a platform for embodied agent research that supports fast rendering given a camera trajectory and a 3D scene. We feed the head pose trajectories to the platform and synthesize realistic images in the egocentric view. We generate 1,664,616 frames with 30 fps, approximately 15 hours of motion in 18 scenes. We name the synthetic dataset AMASS-Replica-Ego-Syn (ARES) and show some examples from our synthetic dataset in Figure 4. + +# 4. Experiments + +We evaluate and compare our method to baselines on five commonly used metrics for human motion reconstruction, in addition to the human perception studies. We also conduct ablation studies to analyze the performance of each stage of our method, as well as the design choices in our model. + +# 4.1. Datasets and Evaluation Metrics + +AMASS-Replica-Ego-Syn (ARES) is our synthetic dataset which contains synthetic egocentric videos and ground truth motions. ARES contains about 15 hours of motion across 18 scenes. We remove 5 scenes from training as unseen scenes. The training dataset consists of about $1.2\mathrm{M}$ frames in 13 different scenes. The testing dataset contains 34,850 frames from 5 unseen scenes. + +AMASS [23] is a large-scale motion capture dataset with about 45 hours of diverse motions. We split training and testing data following HuMoR [29]. + +Kinpoly-MoCap [22] consists of egocentric videos captured using a head-mounted camera and corresponding 3D motions captured with motion capture devices. The total motion is about 80 minutes long. Since it uses motion capture devices, the egocentric video is constrained to a single lab scene. + +Kinpoly-RealWorld [22] contains paired egocentric videos and head poses captured using iPhone ARKit. Unlike Kinpoly-MoCap which is captured in a lab scene, Kinpoly-RealWorld provides in-the-wild egocentric videos. + +GIMO [51] consists of egocentric video, eye gaze, 3D motions, and scanned 3D scenes. This dataset is collected using + +![](images/05d883d87448c3362c04ef6cd27ff5d0c674bc6798fc1114cdce8d186f015436.jpg) +Figure 4. Illustration of our ARES Dataset. "Ego-View" represents the synthetic egocentric images using our proposed data generation pipeline. We also provide a third-person view reference in the second row. The left and right show two sequences from different scenes. + +
MethodARESKinpoly-MoCap [22]GIMO [51]
OheadTheadMPJPEAccelFSOheadTheadMPJPEAccelFSOheadTheadMPJPEAccelFS
PoseReg [48]0.77354.7147.7127.687.11.051943.9160.461.810.81.511528.6189.371.514.2
Kinpoly-OF [22]0.62323.4141.67.34.21.332475.5230.516.415.81.521739.3404.221.914.4
EgoEgo (ours)0.20148.0121.16.22.70.58505.1125.98.01.60.67356.8152.110.41.9
+ +Table 1. Full-body motion estimation from egocentric video on ARES, Kinpoly-MoCap [22], and GIMO [51]. + +Hololens, iPhone 12, and IMU-based motion capture suits to study motion prediction tasks guided by eye gaze. We use 15 scenes for training and 4 scenes for testing. + +# Evaluation Metrics. + +- Head Orientation Error $(\mathbf{O}_{head})$ computes the Frobenius norm of the difference between the $3 \times 3$ rotation matrix $||\pmb{R}_{pred}\pmb{R}_{gt}^{-1} - \pmb{I}||_2$ , where $\pmb{R}_{pred}$ is the predicted head rotation matrix and $\pmb{R}_{gt}$ is the ground truth head rotation matrix. +- Head Translation Error $\left(\mathbf{T}_{\text {head }}\right)$ is computed by taking the mean Euclidean distance of two trajectories. We use this metric to measure the head joint translation errors in millimeters (mm). +- MPJPE represents mean per-joint position errors in millimeters (mm). +- Accel represents the difference of acceleration between predicted joint positions and ground truth joint positions measured in $(mm / s^2)$ . +- FS represents foot skating metric and is computed following NeMF [5]. Specifically, we first project the toe and ankle joints' velocity to the $xy$ plane and compute the $L1$ norm of the projected velocities in each step denoted as $v_{t}$ . We only accumulate the horizontal translation for those steps that have a height $h_t$ lower than a specified threshold $H$ . And the metric is calculated as a mean of weighted values $v_{t}(2 - 2^{\frac{h_{t}}{H}})$ across the sequence and is measured in $(mm)$ . + +# 4.2. Body Pose Estimation from Egocentric Video + +Training Data. We train our HeadNet using paired egocentric videos and head poses provided by ARES, KinplyRealWorld, and GIMO. Note that the body motion in these datasets is not used for training HeadNet. Our GravityNet + +and the conditional diffusion model are both trained on AMASS. For the baselines below, we train them using paired egocentric videos and ground truth motions in ARES. + +Baselines. We compare our approach with two baselines PoseReg [48] and Kinpoly [22]. PoseReg [48] takes a sequence of optical flow features as input and uses an LSTM model to predict the pose state at each time step. The pose state consists of root translation, root orientation, joint rotations, and corresponding velocities including root linear velocity and angular velocities of all the joints. Kinpoly-OF [22] proposes a per-step regression model to estimate full body motion from optical flow features. Because our problem only allows for egocentric video as input, we choose the option of Kinpoly which only has optical flow features as input, without relying on ground truth head poses and action labels that depend on additional knowledge. + +Results. We compare the complete pipeline of EgoEgo with baseline methods PoseReg [48] and Kinpoly-OF [22] on ARES, Kinpoly-MoCap [22] and GIMO [51], as shown in Table 1. We show that our EgoEgo outperforms all the baselines by a large margin on all three datasets. We show qualitative results in Figure 5. Our generated motions better preserve the root trajectories. And our approach can also generate more dynamic and realistic motions compared to the baselines. + +# 4.3. Head Pose Estimation from Egocentric Video + +Baselines. We compare our hybrid approach with the prediction results of DROID-SLAM [33]. For a fair comparison, we apply a rotation to the SLAM trajectory by aligning the first predicted head pose of SLAM with the ground truth head pose. We train our GravityNet on AMASS training split. As for HeadNet, we train on ARES, Kinpoly-RealWorld, and GIMO separately for the evaluation of different datasets. + +![](images/e25c16503b42b0127d25c61ccf099b5c3c06bea3ea56441f21c453ef11155e0a.jpg) +(a) Example 1 +Figure 5. Qualitative results comparisons. We show the results of two egocentric videos from different scenes. + +Results. We evaluate the head pose estimation on the three datasets as shown in Table 2. We show more accurate head rotation prediction results on ARES and comparable results on real-captured data. As the real-captured data is limited in scale (Kinpoly-RealWorld contains 20 minutes of training videos and GIMO contains 30 minutes of training videos), we believe the head rotation prediction can be further improved by future developments of large-scale real-captured datasets with head poses. Overall, our hybrid approach combines the accurate rotation prediction from HeadNet and re-scaled translation of gravity-aligned SLAM results, and produces more accurate head pose estimation results as input to the second stage. + +# 4.4. Body Pose Estimation from the Head Pose + +Baselines. We compare our conditional diffusion model for full-body pose estimation with two baselines AvatarPoser [10] and Kinpoly-Head [22]. AvatarPoser [10] takes both head and hand pose as input to predict full body motion. + +
DROID-SLAM [33]Ours
OheadThedOheadThed
ARES0.62411.30.23176.5
Kinpoly-MoCap0.551290.80.58487.8
GIMO0.67865.40.68304.7
+ +Table 2. Head pose estimation on test sets. + +We remove the hand poses from the input and modified it to a setting with head pose input only. Kinpoly-Head [22] is our modified variant of the Kinpoly model that only takes the head pose as input. Both the baselines and our method are trained on the training split of AMASS with high-quality motion capture data. + +Results. We evaluate the baselines and our method on the AMASS test set, as shown in Table 3. Since our model is generative, there are multiple plausible predictions from the same head pose input. For a quantitative comparison, we generate 200 samples for each head pose input and use the + +
MethodOheadTheadMPJPEAccelFS
AvatarPoser [10]0.1928.6124.716.118.8
Kinpoly-Head [22]0.1987.8110.911.411.2
Diffusion Model (ours)0.0436.7109.010.54.4
+ +Table 3. Full-body motion estimation from GT head pose on AMASS testing dataset [22]. + +
ARESKinpoly-MoCapGIMO
OheadThedOheadThedOheadThed
SLAM0.62411.330.551290.820.67865.41
SLAM+S0.62325.950.55643.450.67569.48
SLAM+S+G0.62176.540.55487.770.67304.74
Full model0.23176.540.58487.770.68304.74
+ +one with the smallest MPJPE as our result. + +# 4.5. Ablation Studies + +Effects of Components in Head Pose Estimation. We study the effects of each component in head pose estimation in Table 4. We showcase that the rotation for aligning gravity direction and the learned scale are both effective to improve head translation results. + +Effects of Head Pose in Full-Body Pose Estimation. We compare the full-body pose estimation results that take our predicted head poses and the ground truth head poses as input. Table 5 shows that the ground truth head poses significantly improve the full body pose estimation, indicating that by developing methods that predict more accurate head pose, the full body pose estimation can be further improved. + +# 4.6. Human Perceptual Study + +We also conduct two human perceptual studies as part of the evaluation. The first is to evaluate the quality of predicted full-body motion from egocentric video, the second is to evaluate the quality of predicted full-body motion from ground truth head poses. In both studies, we compare four types of motion: results from our EgoEgo and from two baselines, as well as the ground truth. For the first human study, each time, users are presented with two motions and an egocentric video, and asked to select which one is more plausible. For the second human study, users are presented with two motions and asked to select which one looks more natural and realistic. Because there are 10 examples and the two motions can be from four sources, we have 60 questions for each study. Each question was answered by 20 Amazon Mechanical Turk workers. + +As shown in Figure 6(a), for full-body estimation from egocentric video, our results are preferred by $98\%$ and $69\%$ of workers when compared to the baselines. Also, when + +Table 4. Ablation study for the components in head pose estimation. S represents the scale predicted by HeadNet, and G represents GravityNet. + +
ARESKinpoly-MoCapGIMO
EEEE w/ GTEEEE w/ GTEEEE w/ GT
Ohead0.200.040.580.030.670.06
Thead148.029.1505.160.7356.866.0
MPJPE121.1105.6125.976.0152.1125.7
Accel6.26.38.07.210.410.2
FS2.73.01.62.51.91.7
+ +Table 5. Ablation study for the effects of head pose to full-body pose estimation. EE represents EgoEgo. GT represents ground truth head poses. + +![](images/49a7561fb578c848fd9a51e49a58cf85400232b9c31172feb6f3879751eae323.jpg) +Figure 6. Results of human perceptual studies. The numbers shown in the chart represent $\%$ + +compared with the ground truth, $34\%$ of the responses prefer our results (note that a perfect output would achieve $50\%$ ), suggesting that people cannot easily distinguish our results from ground truth motions. As shown in Figure 6(b), for full-body estimation from head poses, our results are preferred by $88\%$ and $79\%$ of workers when compared to the baselines. + +# 5. Conclusion + +We presented a generalized framework to estimate full-body motions from egocentric video. The key is to decompose the problem into two stages. We predicted the head pose from an egocentric video and fed the output from the first stage to estimate full-body motions in the second stage. In addition, we developed a hybrid solution to produce more accurate head poses on top of monocular SLAM. We also proposed a conditional diffusion model to generate diverse high-quality full-body motions from predicted head poses. To benchmark different methods in a large-scale dataset, we proposed a data generation pipeline to synthesize a largescale dataset with paired egocentric videos and 3D human motions. We showcased superior results on both the synthetic and the real-captured dataset compared to prior work. + +Acknowledgement. We thank Zhengfei Kuang for the help with visualizations and Jonathan Tseng for discussions about the diffusion model. 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Taking egocentric video (a) as input, our approach first predicts head pose (b); it then estimates multiple plausible full-body human motions (c) from the predicted head pose. This motion sequence shows a human kicking and jumping in place. Please refer to the supplementary video on our project page for a complete motion sequence visualization." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "bbox": [ + 143, + 462, + 192, + 474 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 462, + 192, + 474 + ], + "spans": [ + { + "bbox": [ + 143, + 462, + 192, + 474 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 46, + 476, + 290, + 693 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 476, + 290, + 693 + ], + "spans": [ + { + "bbox": [ + 46, + 476, + 290, + 693 + ], + "type": "text", + "content": "Estimating 3D human motion from an egocentric video sequence plays a critical role in human behavior understanding and has various applications in VR/AR. However, naively learning a mapping between egocentric videos and human motions is challenging, because the user's body is often unobserved by the front-facing camera placed on the head of the user. In addition, collecting large-scale, high-quality datasets with paired egocentric videos and 3D human motions requires accurate motion capture devices, which often limit the variety of scenes in the videos to lab-like environments. To eliminate the need for paired egocentric video and human motions, we propose a new method, Ego-Body Pose Estimation via Ego-Head Pose Estimation (EgoEgo), which decomposes the problem into two stages, connected by the head motion as an intermediate representation. EgoEgo first integrates SLAM and a learning approach to estimate accurate head motion. Subsequently, leveraging the estimated head pose as input, EgoEgo utilizes conditional diffusion" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 463, + 548, + 583 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 463, + 548, + 583 + ], + "spans": [ + { + "bbox": [ + 304, + 463, + 548, + 583 + ], + "type": "text", + "content": "to generate multiple plausible full-body motions. This disentanglement of head and body pose eliminates the need for training datasets with paired egocentric videos and 3D human motion, enabling us to leverage large-scale egocentric video datasets and motion capture datasets separately. Moreover, for systematic benchmarking, we develop a synthetic dataset, AMASS-Replica-Ego-Syn (ARES), with paired egocentric videos and human motion. On both AREs and real data, our EgoEgo model performs significantly better than the current state-of-the-art methods." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 306, + 590, + 387, + 601 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 590, + 387, + 601 + ], + "spans": [ + { + "bbox": [ + 306, + 590, + 387, + 601 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 606, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 606, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 606, + 547, + 715 + ], + "type": "text", + "content": "Estimating 3D human motion from an egocentric video, which records the environment viewed from the first-person perspective with a front-facing monocular camera, is critical to applications in VR/AR. However, naively learning a mapping between egocentric videos and full-body human motions is challenging for two reasons. First, modeling this complex relationship is difficult; unlike reconstruction motion from third-person videos, the human body is often out of view of an egocentric video. Second, learning this" + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 496, + 35 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 496, + 35 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 496, + 35 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 61, + 703, + 160, + 714 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 61, + 703, + 160, + 714 + ], + "spans": [ + { + "bbox": [ + 61, + 703, + 160, + 714 + ], + "type": "inline_equation", + "content": "\\dagger" + }, + { + "bbox": [ + 61, + 703, + 160, + 714 + ], + "type": "text", + "content": " indicates equal contribution." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "17142" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 288, + 156 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 288, + 156 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 288, + 156 + ], + "type": "text", + "content": "mapping requires a large-scale, diverse dataset containing paired egocentric videos and the corresponding 3D human poses. Creating such a dataset requires meticulous instrumentation for data acquisition, and unfortunately, such a dataset does not currently exist. As such, existing works have only worked on small-scale datasets with limited motion and scene diversity [22, 47, 48]." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 158, + 288, + 350 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 158, + 288, + 350 + ], + "spans": [ + { + "bbox": [ + 46, + 158, + 288, + 350 + ], + "type": "text", + "content": "We introduce a generalized and robust method, EgoEgo, to estimate full-body human motions from only egocentric video for diverse scenarios. Our key idea is to use head motion as an intermediate representation to decompose the problem into two stages: head motion estimation from the input egocentric video and full-body motion estimation from the estimated head motion. For most day-to-day activities, humans have an extraordinary ability to stabilize the head such that it aligns with the center of mass of the body [13], which makes head motion an excellent feature for full-body motion estimation. More importantly, the decomposition of our method removes the need to learn from paired egocentric videos and human poses, enabling learning from a combination of large-scale, single-modality datasets (e.g., datasets with egocentric videos or 3D human poses only), which are commonly and readily available." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 352, + 288, + 532 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 352, + 288, + 532 + ], + "spans": [ + { + "bbox": [ + 46, + 352, + 288, + 532 + ], + "type": "text", + "content": "The first stage, estimating the head pose from an egocentric video, resembles the localization problem. However, directly applying the state-of-the-art monocular SLAM methods [33] yields unsatisfactory results, due to the unknown gravity direction and the scaling difference between the estimated space and the real 3D world. We propose a hybrid solution that leverages SLAM and learned transformer-based models to achieve significantly more accurate head motion estimation from egocentric video. In the second stage, we generate the full-body motion based on a diffusion model conditioned on the predicted head pose. Finally, to evaluate our method and train other baselines, we build a large-scale synthetic dataset with paired egocentric videos and 3D human motions, which can also be useful for future work on visuomotor skill learning and sim-to-real transfer." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 534, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 534, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 534, + 288, + 715 + ], + "type": "text", + "content": "Our work makes four main contributions. First, we propose a decomposition paradigm, EgoEgo, to decouple the problem of motion estimation from egocentric video into two stages: ego-head pose estimation, and ego-body pose estimation conditioned on the head pose. The decomposition lets us learn each component separately, eliminating the need for a large-scale dataset with two paired modalities. Second, we develop a hybrid approach for ego-head pose estimation, integrating the results of monocular SLAM and learning. Third, we propose a conditional diffusion model to generate full-body poses conditioned on the head pose. Finally, we contribute a large-scale synthetic dataset with both egocentric videos and 3D human motions as a test bed to benchmark different approaches and showcase that our method outperforms the baselines by a large margin." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 306, + 71, + 392, + 84 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 71, + 392, + 84 + ], + "spans": [ + { + "bbox": [ + 306, + 71, + 392, + 84 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 91, + 547, + 332 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 91, + 547, + 332 + ], + "spans": [ + { + "bbox": [ + 304, + 91, + 547, + 332 + ], + "type": "text", + "content": "Motion Estimation from Third-person Video. 3D pose estimation from images and videos in third-person view has been extensively studied in recent years. There are mainly two typical categories in this direction. One is to regress joint positions directly from images and videos [25, 28, 36, 52]. The other adopts parametric human body model [20] to estimate body model parameters from images or videos [3, 12, 15-18, 21]. And recently, learned motion prior is applied to address the issues of jitters, lack of global trajectory, and missing joints or frames [19, 29, 46]. Moreover, physical constraints are enforced in motion estimation from videos [41, 49]. In contrast to third-person videos, where the full body can be seen, body joints are mostly not visible in an egocentric video, which poses a significant challenge for the problem. Although the body joints are unobserved from egocentric views, the visual information of how the environment changes provides a strong signal to infer how the head moves. In this work, we propose to use the head pose as an intermediate representation to bridge the egocentric video and full-body motions." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 337, + 547, + 648 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 337, + 547, + 648 + ], + "spans": [ + { + "bbox": [ + 304, + 337, + 547, + 648 + ], + "type": "text", + "content": "Motion Estimation from Egocentric Video. Growing attention is received in pose estimation from egocentric videos. Special hardware like the fisheye camera is deployed to predict full body pose from captured images [9, 35, 38, 42]. While body joints are usually visible in images captured with a fisheye camera, the distortion of images poses a significant challenge. Jiang et al. [8] deploy a standard camera to a human chest and propose an implicit motion graph matching approach to predict full body motions from the input video. You2Me [26] predicts full body motions by observing the interaction pose of the second-person in the camera view. Towards a goal of estimating and forecasting physically plausible motions from a head-mounted camera, EgoPose [47, 48] develop a Deep-RL framework to learn a control policy to estimate current poses and forecast future poses. Follow-up work Kinpoly [22] integrates kinematics and dynamics to predict physically plausible motions interacting with known objects. While their method achieves impressive results in their collected dataset, it cannot handle scenes and motions out of their data distribution. This work aims to establish a more generalized and robust framework to infer full-body motions from egocentric video only. To validate the effectiveness in more generalized scenes and motions, we also introduce an approach of synthesizing egocentric video corresponding to mocap data in diverse 3D scenes for quantitative evaluation." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 654, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 654, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 654, + 547, + 715 + ], + "type": "text", + "content": "Motion Estimation from Sparse Sensors. Instead of estimating motion from videos, some work explored reconstructing human motions from sparse sensor input. TransPose [45] proposes a real-time pipeline to predict full body motions from 6 IMU sensors, including head, torso, left/right arms," + } + ] + } + ], + "index": 7 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "17143" + } + ] + } + ], + "index": 8 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 228 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 228 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 228 + ], + "type": "text", + "content": "and left/right lower legs. Follow-up work PIP [44] further includes a PD controller on top of the kinematic estimator to introduce physics constraints during reconstruction. TIP [11] follows the same sensor setting and deploys a transformer-based model to leverage IMU sequential information effectively. Fewer sensors are investigated in LoBSTr [43]. Given tracker information from 4 joints (head, left/right hands, torso), they present an RNN-based model to infer lower-body motions from past upper-body joint signals. Recent advances [1,4,10,40] further relax the input constraints to head and hand signals only. In this work, we do not rely on any observations from inertial sensors. Instead, we aim to develop a solution with egocentric video input only." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 240, + 103, + 252 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 240, + 103, + 252 + ], + "spans": [ + { + "bbox": [ + 47, + 240, + 103, + 252 + ], + "type": "text", + "content": "3. Method" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 261, + 289, + 405 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 261, + 289, + 405 + ], + "spans": [ + { + "bbox": [ + 46, + 261, + 289, + 405 + ], + "type": "text", + "content": "Our method, EgoEgo, estimates 3D human motion from a monocular egocentric video sequence. As shown in Figure 2, our key idea is to leverage head motion: first estimating head motion from egocentric video, and then estimating full body motion from head motion. We show that head motion is an excellent feature for full-body motion estimation and a compact, intermediate representation that reduces the challenge into two much simpler sub-problems. Such a disentanglement also allows us to leverage a large-scale egocentric video dataset with head motion (but no full body motion) in stage one, and a separate 3D human motion dataset (but no egocentric videos) in stage two." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 409, + 289, + 506 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 409, + 289, + 506 + ], + "spans": [ + { + "bbox": [ + 47, + 409, + 289, + 506 + ], + "type": "text", + "content": "Notations. We denote full body motion as " + }, + { + "bbox": [ + 47, + 409, + 289, + 506 + ], + "type": "inline_equation", + "content": "\\mathbf{X} \\in \\mathbb{R}^{T \\times D}" + }, + { + "bbox": [ + 47, + 409, + 289, + 506 + ], + "type": "text", + "content": " and egocentric images captured from a front-facing, head-mounted camera as " + }, + { + "bbox": [ + 47, + 409, + 289, + 506 + ], + "type": "inline_equation", + "content": "\\mathbf{I} \\in \\mathbb{R}^{T \\times h \\times w \\times 3}" + }, + { + "bbox": [ + 47, + 409, + 289, + 506 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 47, + 409, + 289, + 506 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 47, + 409, + 289, + 506 + ], + "type": "text", + "content": " is the sequence length, " + }, + { + "bbox": [ + 47, + 409, + 289, + 506 + ], + "type": "inline_equation", + "content": "D" + }, + { + "bbox": [ + 47, + 409, + 289, + 506 + ], + "type": "text", + "content": " is the dimension of the pose state, and " + }, + { + "bbox": [ + 47, + 409, + 289, + 506 + ], + "type": "inline_equation", + "content": "h \\times w" + }, + { + "bbox": [ + 47, + 409, + 289, + 506 + ], + "type": "text", + "content": " is the size of an image. We introduce head motion " + }, + { + "bbox": [ + 47, + 409, + 289, + 506 + ], + "type": "inline_equation", + "content": "\\mathbf{H} \\in \\mathbb{R}^{T \\times D'}" + }, + { + "bbox": [ + 47, + 409, + 289, + 506 + ], + "type": "text", + "content": " as an intermediate representation to bridge the input egocentric video and the output human motions, where " + }, + { + "bbox": [ + 47, + 409, + 289, + 506 + ], + "type": "inline_equation", + "content": "D'" + }, + { + "bbox": [ + 47, + 409, + 289, + 506 + ], + "type": "text", + "content": " is the dimension of the head pose." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 514, + 282, + 528 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 514, + 282, + 528 + ], + "spans": [ + { + "bbox": [ + 47, + 514, + 282, + 528 + ], + "type": "text", + "content": "3.1. Head Pose Estimation from Egocentric Video" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 533, + 287, + 677 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 533, + 287, + 677 + ], + "spans": [ + { + "bbox": [ + 46, + 533, + 287, + 677 + ], + "type": "text", + "content": "Estimating the head motion from an egocentric video can be viewed as a camera localization problem. However, we observed three issues that prevent us from directly applying the state-of-the-art monocular SLAM method [33] to our problem. First, the gravity direction of the estimated head pose is unknown. Thus, the results cannot be directly fed to the full-body motion estimator, since it expects the head pose expressed in a coordinate frame where the gravity direction is " + }, + { + "bbox": [ + 46, + 533, + 287, + 677 + ], + "type": "inline_equation", + "content": "[0, 0, -1]^T" + }, + { + "bbox": [ + 46, + 533, + 287, + 677 + ], + "type": "text", + "content": ". Second, the estimated translation by monocular SLAM is not to scale when compared with the distance in the real world. Third, monocular SLAM tends to be less accurate in estimating relative head rotation than translation." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 677, + 289, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 289, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 289, + 713 + ], + "type": "text", + "content": "Based on these observations, we propose a hybrid method that leverages SLAM and learned models to achieve more accurate head pose estimation than the state-of-the-art SLAM" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 72, + 547, + 228 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 228 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 228 + ], + "type": "text", + "content": "alone. First, we develop a transformer-based model GravityNet to estimate the gravity direction from the rotation and the translation trajectories computed by SLAM. We rotate the SLAM translation by aligning the estimated gravity direction with the real gravity direction " + }, + { + "bbox": [ + 304, + 72, + 547, + 228 + ], + "type": "inline_equation", + "content": "[0, 0, -1]^T" + }, + { + "bbox": [ + 304, + 72, + 547, + 228 + ], + "type": "text", + "content": " in the 3D world. Moreover, from the optical flow features extracted from the egocentric video, our method learns a model, HeadNet, to estimate head rotations and translation distance. The predicted translation distance of HeadNet is used to re-scale the translation estimated by SLAM. The predicted head rotation by HeadNet is directly used to replace the rotation estimated by SLAM. Figure 2 summarizes our process to generate head poses." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 233, + 548, + 331 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 233, + 548, + 331 + ], + "spans": [ + { + "bbox": [ + 304, + 233, + 548, + 331 + ], + "type": "text", + "content": "Monocular SLAM. We adopt DROID-SLAM [33] to estimate camera trajectory from egocentric videos. DROID-SLAM [33] is a learning-based method to estimate camera pose trajectory and reconstruct the 3D map of the environment simultaneously. By a design of recurrent iterative updates to camera pose and depth, it showcases superior and more robust results compared to prior SLAM systems [2]. For more details, please refer to [33]." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 335, + 548, + 624 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 335, + 548, + 624 + ], + "spans": [ + { + "bbox": [ + 304, + 335, + 548, + 624 + ], + "type": "text", + "content": "Gravity Direction Estimation. We introduce GravityNet to predict gravity direction " + }, + { + "bbox": [ + 304, + 335, + 548, + 624 + ], + "type": "inline_equation", + "content": "\\pmb{g} \\in \\mathbb{R}^3" + }, + { + "bbox": [ + 304, + 335, + 548, + 624 + ], + "type": "text", + "content": " from a sequence of head poses " + }, + { + "bbox": [ + 304, + 335, + 548, + 624 + ], + "type": "inline_equation", + "content": "\\hat{h}_1, \\hat{h}_2, \\dots, \\hat{h}_T" + }, + { + "bbox": [ + 304, + 335, + 548, + 624 + ], + "type": "text", + "content": ". The gravity direction " + }, + { + "bbox": [ + 304, + 335, + 548, + 624 + ], + "type": "inline_equation", + "content": "\\pmb{g}" + }, + { + "bbox": [ + 304, + 335, + 548, + 624 + ], + "type": "text", + "content": " is represented by a unit vector. The head poses input " + }, + { + "bbox": [ + 304, + 335, + 548, + 624 + ], + "type": "inline_equation", + "content": "\\hat{h}_t" + }, + { + "bbox": [ + 304, + 335, + 548, + 624 + ], + "type": "text", + "content": " consists of a 3D head translation, a head rotation represented by a continuous 6D rotation vector [53], head translation difference, and head rotation difference computed by " + }, + { + "bbox": [ + 304, + 335, + 548, + 624 + ], + "type": "inline_equation", + "content": "O_{t-1}^{-1}O_t" + }, + { + "bbox": [ + 304, + 335, + 548, + 624 + ], + "type": "text", + "content": " where " + }, + { + "bbox": [ + 304, + 335, + 548, + 624 + ], + "type": "inline_equation", + "content": "O_t" + }, + { + "bbox": [ + 304, + 335, + 548, + 624 + ], + "type": "text", + "content": " denotes the head rotation matrix at time step " + }, + { + "bbox": [ + 304, + 335, + 548, + 624 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 335, + 548, + 624 + ], + "type": "text", + "content": ". We adopt a transformer-based architecture [37] consisting of two self-attention blocks, each of which has a multi-head attention layer followed by a position-wise feed-forward layer. We take the first output of the transformer and feed it to an MLP to predict the gravity direction " + }, + { + "bbox": [ + 304, + 335, + 548, + 624 + ], + "type": "inline_equation", + "content": "\\pmb{g}" + }, + { + "bbox": [ + 304, + 335, + 548, + 624 + ], + "type": "text", + "content": ". We train our GravityNet on the large-scale motion capture dataset AMASS [23]. However, the motion sequences in AMASS have the correct gravity direction " + }, + { + "bbox": [ + 304, + 335, + 548, + 624 + ], + "type": "inline_equation", + "content": "\\pmb{g}_c = [0,0,-1]^T" + }, + { + "bbox": [ + 304, + 335, + 548, + 624 + ], + "type": "text", + "content": ". To emulate the distribution of the predicted head poses from monocular SLAM, we apply a random scale and a random rotation to the head poses in each AMASS sequence to generate our training data for gravity estimation. " + }, + { + "bbox": [ + 304, + 335, + 548, + 624 + ], + "type": "inline_equation", + "content": "L_1" + }, + { + "bbox": [ + 304, + 335, + 548, + 624 + ], + "type": "text", + "content": " loss for the gravity vector is used during training. Based on the prediction of GravityNet, we compute the rotation matrix " + }, + { + "bbox": [ + 304, + 335, + 548, + 624 + ], + "type": "inline_equation", + "content": "R_g" + }, + { + "bbox": [ + 304, + 335, + 548, + 624 + ], + "type": "text", + "content": " to align the prediction " + }, + { + "bbox": [ + 304, + 335, + 548, + 624 + ], + "type": "inline_equation", + "content": "\\pmb{g}" + }, + { + "bbox": [ + 304, + 335, + 548, + 624 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 335, + 548, + 624 + ], + "type": "inline_equation", + "content": "\\pmb{g}_c" + }, + { + "bbox": [ + 304, + 335, + 548, + 624 + ], + "type": "text", + "content": ". Then we apply " + }, + { + "bbox": [ + 304, + 335, + 548, + 624 + ], + "type": "inline_equation", + "content": "R_g" + }, + { + "bbox": [ + 304, + 335, + 548, + 624 + ], + "type": "text", + "content": " to the SLAM translation denoted as " + }, + { + "bbox": [ + 304, + 335, + 548, + 624 + ], + "type": "inline_equation", + "content": "\\hat{P}_1, \\hat{P}_2, \\dots, \\hat{P}_T" + }, + { + "bbox": [ + 304, + 335, + 548, + 624 + ], + "type": "text", + "content": " and get " + }, + { + "bbox": [ + 304, + 335, + 548, + 624 + ], + "type": "inline_equation", + "content": "P_1, P_2, \\dots, P_T" + }, + { + "bbox": [ + 304, + 335, + 548, + 624 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 335, + 548, + 624 + ], + "type": "inline_equation", + "content": "P_t = R_g\\hat{P}_t" + }, + { + "bbox": [ + 304, + 335, + 548, + 624 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 629, + 548, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 629, + 548, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 629, + 548, + 715 + ], + "type": "text", + "content": "Head Pose Estimation. We propose HeadNet to predict a sequence of distance " + }, + { + "bbox": [ + 304, + 629, + 548, + 715 + ], + "type": "inline_equation", + "content": "d_{1}, d_{2}, \\ldots, d_{T}" + }, + { + "bbox": [ + 304, + 629, + 548, + 715 + ], + "type": "text", + "content": " and head rotations " + }, + { + "bbox": [ + 304, + 629, + 548, + 715 + ], + "type": "inline_equation", + "content": "R_{1}, \\ldots, R_{T}" + }, + { + "bbox": [ + 304, + 629, + 548, + 715 + ], + "type": "text", + "content": " from a sequence of optical flow features " + }, + { + "bbox": [ + 304, + 629, + 548, + 715 + ], + "type": "inline_equation", + "content": "o_{1}, \\ldots, o_{T}" + }, + { + "bbox": [ + 304, + 629, + 548, + 715 + ], + "type": "text", + "content": ". The optical flow features are extracted by a pretrained ResNet-18 [6]. We deploy the same model architecture as GravityNet. Since the scale from the monocular SLAM system may not be consistent with the real" + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "17144" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 50, + 61, + 542, + 273 + ], + "blocks": [ + { + "bbox": [ + 50, + 61, + 542, + 273 + ], + "lines": [ + { + "bbox": [ + 50, + 61, + 542, + 273 + ], + "spans": [ + { + "bbox": [ + 50, + 61, + 542, + 273 + ], + "type": "image", + "image_path": "93b4443eb4e1aeffd9adf927845425932d7028ee5ba1e5f1bd1ca5e5b6f90562.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 278, + 547, + 313 + ], + "lines": [ + { + "bbox": [ + 46, + 278, + 547, + 313 + ], + "spans": [ + { + "bbox": [ + 46, + 278, + 547, + 313 + ], + "type": "text", + "content": "Figure 2. Overview of EgoEgo. The model first takes an egocentric video as input and predicts the head pose with a hybrid approach that combines monocular SLAM and the learned GravityNet and HeadNet. The predicted head pose is then fed to a conditional diffusion model to generate the full-body pose." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 56, + 326, + 274, + 484 + ], + "blocks": [ + { + "bbox": [ + 56, + 326, + 274, + 484 + ], + "lines": [ + { + "bbox": [ + 56, + 326, + 274, + 484 + ], + "spans": [ + { + "bbox": [ + 56, + 326, + 274, + 484 + ], + "type": "image", + "image_path": "aefa011ffac48f22583e5352dedc737a7b8af70a263c903320b8206e72bd4b66.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 47, + 487, + 288, + 510 + ], + "lines": [ + { + "bbox": [ + 47, + 487, + 288, + 510 + ], + "spans": [ + { + "bbox": [ + 47, + 487, + 288, + 510 + ], + "type": "text", + "content": "Figure 3. Model architecture of the denoising network in a single step of the reverse diffusion process." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 520, + 287, + 676 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 520, + 287, + 676 + ], + "spans": [ + { + "bbox": [ + 46, + 520, + 287, + 676 + ], + "type": "text", + "content": "3D world where human moves, we use HeadNet to predict the vector norm of the translation difference between consecutive time steps denoted as " + }, + { + "bbox": [ + 46, + 520, + 287, + 676 + ], + "type": "inline_equation", + "content": "d_1, \\ldots, d_T" + }, + { + "bbox": [ + 46, + 520, + 287, + 676 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 520, + 287, + 676 + ], + "type": "inline_equation", + "content": "d_t" + }, + { + "bbox": [ + 46, + 520, + 287, + 676 + ], + "type": "text", + "content": " represents a scalar value. For each camera translation sequence produced by monocular SLAM and rotated by aligning gravity direction, given the camera translation trajectory " + }, + { + "bbox": [ + 46, + 520, + 287, + 676 + ], + "type": "inline_equation", + "content": "P \\in \\mathbb{R}^{T \\times 3}" + }, + { + "bbox": [ + 46, + 520, + 287, + 676 + ], + "type": "text", + "content": ", we calculate the distance " + }, + { + "bbox": [ + 46, + 520, + 287, + 676 + ], + "type": "inline_equation", + "content": "d_t^s" + }, + { + "bbox": [ + 46, + 520, + 287, + 676 + ], + "type": "text", + "content": " between " + }, + { + "bbox": [ + 46, + 520, + 287, + 676 + ], + "type": "inline_equation", + "content": "P_t" + }, + { + "bbox": [ + 46, + 520, + 287, + 676 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 520, + 287, + 676 + ], + "type": "inline_equation", + "content": "P_{t+1}" + }, + { + "bbox": [ + 46, + 520, + 287, + 676 + ], + "type": "text", + "content": " as " + }, + { + "bbox": [ + 46, + 520, + 287, + 676 + ], + "type": "inline_equation", + "content": "d_t^s = ||P_{t+1} - P_t||_2" + }, + { + "bbox": [ + 46, + 520, + 287, + 676 + ], + "type": "text", + "content": ". We take the mean value for the sequence of distances as " + }, + { + "bbox": [ + 46, + 520, + 287, + 676 + ], + "type": "inline_equation", + "content": "d^s = \\frac{1}{T}\\sum_{t=1}^{T}d_t^s" + }, + { + "bbox": [ + 46, + 520, + 287, + 676 + ], + "type": "text", + "content": ". Similarly, we compute the mean of the predicted distance sequence " + }, + { + "bbox": [ + 46, + 520, + 287, + 676 + ], + "type": "inline_equation", + "content": "d = \\frac{1}{T}\\sum_{t=1}^{T}d_t" + }, + { + "bbox": [ + 46, + 520, + 287, + 676 + ], + "type": "text", + "content": ". The scale is calculated as " + }, + { + "bbox": [ + 46, + 520, + 287, + 676 + ], + "type": "inline_equation", + "content": "s = \\frac{d}{d^s}" + }, + { + "bbox": [ + 46, + 520, + 287, + 676 + ], + "type": "text", + "content": ". We multiply scale " + }, + { + "bbox": [ + 46, + 520, + 287, + 676 + ], + "type": "inline_equation", + "content": "s" + }, + { + "bbox": [ + 46, + 520, + 287, + 676 + ], + "type": "text", + "content": " to the predicted translation " + }, + { + "bbox": [ + 46, + 520, + 287, + 676 + ], + "type": "inline_equation", + "content": "P" + }, + { + "bbox": [ + 46, + 520, + 287, + 676 + ], + "type": "text", + "content": " and use " + }, + { + "bbox": [ + 46, + 520, + 287, + 676 + ], + "type": "inline_equation", + "content": "sP" + }, + { + "bbox": [ + 46, + 520, + 287, + 676 + ], + "type": "text", + "content": " as our global head translation results." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 677, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 289, + 715 + ], + "type": "text", + "content": "The network also predicts the head angular velocity, " + }, + { + "bbox": [ + 46, + 677, + 289, + 715 + ], + "type": "inline_equation", + "content": "\\omega_{1},\\ldots ,\\omega_{T}" + }, + { + "bbox": [ + 46, + 677, + 289, + 715 + ], + "type": "text", + "content": " , in the head frame. We integrate predicted angular velocity to generate corresponding rotations " + }, + { + "bbox": [ + 46, + 677, + 289, + 715 + ], + "type": "inline_equation", + "content": "R_{1},\\ldots ,R_{T}" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 330, + 545, + 365 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 330, + 545, + 365 + ], + "spans": [ + { + "bbox": [ + 304, + 330, + 545, + 365 + ], + "type": "text", + "content": "During inference, we assume that the first head orientation is given and integrate the predicted head angular velocity to estimate the subsequent head orientations." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 365, + 547, + 450 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 365, + 547, + 450 + ], + "spans": [ + { + "bbox": [ + 304, + 365, + 547, + 450 + ], + "type": "text", + "content": "The training loss of the HeadNet is defined as: " + }, + { + "bbox": [ + 304, + 365, + 547, + 450 + ], + "type": "inline_equation", + "content": "\\mathcal{L} = \\mathcal{L}_{dist} + \\mathcal{L}_{vel} + \\mathcal{L}_{rot}" + }, + { + "bbox": [ + 304, + 365, + 547, + 450 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 304, + 365, + 547, + 450 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{dist}" + }, + { + "bbox": [ + 304, + 365, + 547, + 450 + ], + "type": "text", + "content": " represents the " + }, + { + "bbox": [ + 304, + 365, + 547, + 450 + ], + "type": "inline_equation", + "content": "L1" + }, + { + "bbox": [ + 304, + 365, + 547, + 450 + ], + "type": "text", + "content": " loss for translation distance. " + }, + { + "bbox": [ + 304, + 365, + 547, + 450 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{vel}" + }, + { + "bbox": [ + 304, + 365, + 547, + 450 + ], + "type": "text", + "content": " represents the " + }, + { + "bbox": [ + 304, + 365, + 547, + 450 + ], + "type": "inline_equation", + "content": "L1" + }, + { + "bbox": [ + 304, + 365, + 547, + 450 + ], + "type": "text", + "content": " loss for angular velocity. " + }, + { + "bbox": [ + 304, + 365, + 547, + 450 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{rot}" + }, + { + "bbox": [ + 304, + 365, + 547, + 450 + ], + "type": "text", + "content": " denotes the rotation loss " + }, + { + "bbox": [ + 304, + 365, + 547, + 450 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{rot} = ||\\pmb{R}_{pred}\\pmb{R}_{gt}^T - \\pmb{I}||_1" + }, + { + "bbox": [ + 304, + 365, + 547, + 450 + ], + "type": "text", + "content": " where " + }, + { + "bbox": [ + 304, + 365, + 547, + 450 + ], + "type": "inline_equation", + "content": "\\pmb{R}_{pred}" + }, + { + "bbox": [ + 304, + 365, + 547, + 450 + ], + "type": "text", + "content": " represents the integrated rotation using predicted angular velocity, " + }, + { + "bbox": [ + 304, + 365, + 547, + 450 + ], + "type": "inline_equation", + "content": "\\pmb{R}_{gt}" + }, + { + "bbox": [ + 304, + 365, + 547, + 450 + ], + "type": "text", + "content": " represents the ground truth rotation matrix and " + }, + { + "bbox": [ + 304, + 365, + 547, + 450 + ], + "type": "inline_equation", + "content": "\\pmb{I}" + }, + { + "bbox": [ + 304, + 365, + 547, + 450 + ], + "type": "text", + "content": " represents the identity matrix." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 455, + 531, + 468 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 455, + 531, + 468 + ], + "spans": [ + { + "bbox": [ + 306, + 455, + 531, + 468 + ], + "type": "text", + "content": "3.2. Full-Body Pose Estimation from Head Pose" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 474, + 546, + 616 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 474, + 546, + 616 + ], + "spans": [ + { + "bbox": [ + 304, + 474, + 546, + 616 + ], + "type": "text", + "content": "Predicting full-body pose from head pose is not a one-to-one mapping problem as different full-body motions may have the same head pose. Thus, we formulate the task using a conditional generative model. Inspired by the recent success of the diffusion model in image generation [30], we deploy a diffusion model to generate full-body poses conditioned on head poses. We use the formulation proposed in the denoising diffusion probabilistic model (DDPM) [7], which has also been applied in some concurrent work [14, 34, 50] for motion generation and motion interpolation tasks. We will first introduce our data representation and then detail the conditional diffusion model formulation." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 617, + 545, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 545, + 689 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 545, + 689 + ], + "type": "text", + "content": "A body pose " + }, + { + "bbox": [ + 304, + 617, + 545, + 689 + ], + "type": "inline_equation", + "content": "\\mathbf{X}_t \\in \\mathbb{R}^D" + }, + { + "bbox": [ + 304, + 617, + 545, + 689 + ], + "type": "text", + "content": " at time " + }, + { + "bbox": [ + 304, + 617, + 545, + 689 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 617, + 545, + 689 + ], + "type": "text", + "content": " consists of the global joint position " + }, + { + "bbox": [ + 304, + 617, + 545, + 689 + ], + "type": "inline_equation", + "content": "(\\mathbb{R}^{J \\times 3})" + }, + { + "bbox": [ + 304, + 617, + 545, + 689 + ], + "type": "text", + "content": " and global joint rotations " + }, + { + "bbox": [ + 304, + 617, + 545, + 689 + ], + "type": "inline_equation", + "content": "(\\mathbb{R}^{J \\times 6})" + }, + { + "bbox": [ + 304, + 617, + 545, + 689 + ], + "type": "text", + "content": ". We adopt the widely used SMPL model [20] as our skeleton, and the number of joints " + }, + { + "bbox": [ + 304, + 617, + 545, + 689 + ], + "type": "inline_equation", + "content": "J" + }, + { + "bbox": [ + 304, + 617, + 545, + 689 + ], + "type": "text", + "content": " is 22. For the convenience of notation in the diffusion model, we use " + }, + { + "bbox": [ + 304, + 617, + 545, + 689 + ], + "type": "inline_equation", + "content": "x_n" + }, + { + "bbox": [ + 304, + 617, + 545, + 689 + ], + "type": "text", + "content": " to denote a sequence of body poses " + }, + { + "bbox": [ + 304, + 617, + 545, + 689 + ], + "type": "inline_equation", + "content": "\\mathbf{X}_1^n, \\mathbf{X}_2^n, \\dots, \\mathbf{X}_T^n" + }, + { + "bbox": [ + 304, + 617, + 545, + 689 + ], + "type": "text", + "content": " at noise level " + }, + { + "bbox": [ + 304, + 617, + 545, + 689 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 304, + 617, + 545, + 689 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "text", + "content": "The high-level idea of the diffusion model is to design a forward diffusion process to add Gaussian noises to the" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "17145" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 287, + 108 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 287, + 108 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 287, + 108 + ], + "type": "text", + "content": "original data with a known variance schedule and learn a denoising model to gradually denoise " + }, + { + "bbox": [ + 47, + 72, + 287, + 108 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 47, + 72, + 287, + 108 + ], + "type": "text", + "content": " steps given a sampled " + }, + { + "bbox": [ + 47, + 72, + 287, + 108 + ], + "type": "inline_equation", + "content": "\\pmb{x}_N" + }, + { + "bbox": [ + 47, + 72, + 287, + 108 + ], + "type": "text", + "content": " from a normal distribution to generate " + }, + { + "bbox": [ + 47, + 72, + 287, + 108 + ], + "type": "inline_equation", + "content": "\\pmb{x}_0" + }, + { + "bbox": [ + 47, + 72, + 287, + 108 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 108, + 288, + 168 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 108, + 288, + 168 + ], + "spans": [ + { + "bbox": [ + 47, + 108, + 288, + 168 + ], + "type": "text", + "content": "Specifically, diffusion models consist of a forward diffusion process and a reverse diffusion process. The forward diffusion process gradually adds Gaussian noise to the original data " + }, + { + "bbox": [ + 47, + 108, + 288, + 168 + ], + "type": "inline_equation", + "content": "\\boldsymbol{x}_0" + }, + { + "bbox": [ + 47, + 108, + 288, + 168 + ], + "type": "text", + "content": ". And it is formulated using a Markov chain of " + }, + { + "bbox": [ + 47, + 108, + 288, + 168 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 47, + 108, + 288, + 168 + ], + "type": "text", + "content": " steps as shown in Equation 1:" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 99, + 176, + 287, + 209 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 99, + 176, + 287, + 209 + ], + "spans": [ + { + "bbox": [ + 99, + 176, + 287, + 209 + ], + "type": "interline_equation", + "content": "q \\left(\\boldsymbol {x} _ {1: N} \\mid \\boldsymbol {x} _ {0}\\right) := \\prod_ {n = 1} ^ {N} q \\left(\\boldsymbol {x} _ {n} \\mid \\boldsymbol {x} _ {n - 1}\\right). \\tag {1}", + "image_path": "f66ff24cee478cb2955a242bf06e2a9199b95190325175eacd042ba0cf6c2401.jpg" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 216, + 287, + 239 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 216, + 287, + 239 + ], + "spans": [ + { + "bbox": [ + 47, + 216, + 287, + 239 + ], + "type": "text", + "content": "Each step is decided by a variance schedule using " + }, + { + "bbox": [ + 47, + 216, + 287, + 239 + ], + "type": "inline_equation", + "content": "\\beta_{n}" + }, + { + "bbox": [ + 47, + 216, + 287, + 239 + ], + "type": "text", + "content": " and is defined as" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 73, + 247, + 287, + 262 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 73, + 247, + 287, + 262 + ], + "spans": [ + { + "bbox": [ + 73, + 247, + 287, + 262 + ], + "type": "interline_equation", + "content": "q \\left(\\boldsymbol {x} _ {n} \\mid \\boldsymbol {x} _ {n - 1}\\right) := \\mathcal {N} \\left(\\boldsymbol {x} _ {n}; \\sqrt {1 - \\beta_ {n}} \\boldsymbol {x} _ {n - 1}, \\beta_ {n} \\boldsymbol {I}\\right). \\tag {2}", + "image_path": "b46dd13f9d19f2a9e2f0a60241a985d954c1ac99043677809db8dd13066c8ab4.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 270, + 287, + 317 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 270, + 287, + 317 + ], + "spans": [ + { + "bbox": [ + 47, + 270, + 287, + 317 + ], + "type": "text", + "content": "To generate full-body motion conditioned on the head pose, we need to reverse the diffusion process. The reverse process can be approximated as a Markov chain with a learned mean and fixed variance:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 60, + 327, + 287, + 340 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 60, + 327, + 287, + 340 + ], + "spans": [ + { + "bbox": [ + 60, + 327, + 287, + 340 + ], + "type": "interline_equation", + "content": "p _ {\\theta} \\left(\\boldsymbol {x} _ {n - 1} \\mid \\boldsymbol {x} _ {n}, c\\right) := \\mathcal {N} \\left(\\boldsymbol {x} _ {n - 1}; \\boldsymbol {\\mu} _ {\\theta} \\left(\\boldsymbol {x} _ {n}, n, c\\right), \\sigma_ {n} ^ {2} \\boldsymbol {I}\\right). \\tag {3}", + "image_path": "589ce279986c021229037eac98cb6a2ad4ee5dd5a40b18662395700b1560b034.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 349, + 287, + 408 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 349, + 287, + 408 + ], + "spans": [ + { + "bbox": [ + 47, + 349, + 287, + 408 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 349, + 287, + 408 + ], + "type": "inline_equation", + "content": "\\pmb{\\theta}" + }, + { + "bbox": [ + 47, + 349, + 287, + 408 + ], + "type": "text", + "content": " represents the parameters of a neural network, " + }, + { + "bbox": [ + 47, + 349, + 287, + 408 + ], + "type": "inline_equation", + "content": "c" + }, + { + "bbox": [ + 47, + 349, + 287, + 408 + ], + "type": "text", + "content": " is the head conditions. The learned mean " + }, + { + "bbox": [ + 47, + 349, + 287, + 408 + ], + "type": "inline_equation", + "content": "\\pmb{\\mu}_{\\theta}(\\pmb{x}_n,n,c)" + }, + { + "bbox": [ + 47, + 349, + 287, + 408 + ], + "type": "text", + "content": " (we use " + }, + { + "bbox": [ + 47, + 349, + 287, + 408 + ], + "type": "inline_equation", + "content": "\\pmb{\\mu}_{\\theta}" + }, + { + "bbox": [ + 47, + 349, + 287, + 408 + ], + "type": "text", + "content": " in the equation for brevity) can be represented as follows where " + }, + { + "bbox": [ + 47, + 349, + 287, + 408 + ], + "type": "inline_equation", + "content": "\\alpha_{n}" + }, + { + "bbox": [ + 47, + 349, + 287, + 408 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 349, + 287, + 408 + ], + "type": "inline_equation", + "content": "\\bar{\\alpha}_{n}" + }, + { + "bbox": [ + 47, + 349, + 287, + 408 + ], + "type": "text", + "content": " are fixed parameters, " + }, + { + "bbox": [ + 47, + 349, + 287, + 408 + ], + "type": "inline_equation", + "content": "\\hat{\\pmb{x}}_{\\theta}(\\pmb{x}_n,n,c)" + }, + { + "bbox": [ + 47, + 349, + 287, + 408 + ], + "type": "text", + "content": " is the prediction of " + }, + { + "bbox": [ + 47, + 349, + 287, + 408 + ], + "type": "inline_equation", + "content": "\\pmb{x}_0" + }, + { + "bbox": [ + 47, + 349, + 287, + 408 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 415, + 286, + 450 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 415, + 286, + 450 + ], + "spans": [ + { + "bbox": [ + 47, + 415, + 286, + 450 + ], + "type": "interline_equation", + "content": "\\boldsymbol {\\mu} _ {\\theta} = \\frac {\\sqrt {\\alpha_ {n}} (1 - \\bar {\\alpha} _ {n - 1}) \\boldsymbol {x} _ {n} + \\sqrt {\\bar {\\alpha} _ {n - 1}} (1 - \\alpha_ {n}) \\hat {\\boldsymbol {x}} _ {\\theta} (\\boldsymbol {x} _ {n} , n , c)}{1 - \\bar {\\alpha} _ {n}} \\tag {4}", + "image_path": "abba94b2a737d9cd420f90db67af5051ef39225c7baf04f7a991515823eae8d7.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 452, + 287, + 487 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 452, + 287, + 487 + ], + "spans": [ + { + "bbox": [ + 47, + 452, + 287, + 487 + ], + "type": "text", + "content": "Learning the mean can be reparameterized as learning to predict the original data " + }, + { + "bbox": [ + 47, + 452, + 287, + 487 + ], + "type": "inline_equation", + "content": "\\pmb{x}_0" + }, + { + "bbox": [ + 47, + 452, + 287, + 487 + ], + "type": "text", + "content": ". The training loss is defined as a reconstruction loss of " + }, + { + "bbox": [ + 47, + 452, + 287, + 487 + ], + "type": "inline_equation", + "content": "\\pmb{x}_0" + }, + { + "bbox": [ + 47, + 452, + 287, + 487 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 99, + 496, + 287, + 509 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 99, + 496, + 287, + 509 + ], + "spans": [ + { + "bbox": [ + 99, + 496, + 287, + 509 + ], + "type": "interline_equation", + "content": "\\mathcal {L} = \\mathbb {E} _ {\\boldsymbol {x} _ {0}, n} \\| \\hat {\\boldsymbol {x}} _ {\\theta} (\\boldsymbol {x} _ {n}, n, c) - \\boldsymbol {x} _ {0} \\| _ {1} \\tag {5}", + "image_path": "1f4385e6110d0fccefe3a970014e8587c6e663915e8016ade270b9dbb9bc4654.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 47, + 517, + 287, + 565 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 517, + 287, + 565 + ], + "spans": [ + { + "bbox": [ + 47, + 517, + 287, + 565 + ], + "type": "text", + "content": "As shown in Figure 3, in denoising step " + }, + { + "bbox": [ + 47, + 517, + 287, + 565 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 47, + 517, + 287, + 565 + ], + "type": "text", + "content": ", we concatenate head pose condition " + }, + { + "bbox": [ + 47, + 517, + 287, + 565 + ], + "type": "inline_equation", + "content": "c_{1},\\ldots ,c_{T}" + }, + { + "bbox": [ + 47, + 517, + 287, + 565 + ], + "type": "text", + "content": " with body pose representation " + }, + { + "bbox": [ + 47, + 517, + 287, + 565 + ], + "type": "inline_equation", + "content": "X_{1}^{n},\\ldots ,X_{T}^{n}" + }, + { + "bbox": [ + 47, + 517, + 287, + 565 + ], + "type": "text", + "content": " at noise level " + }, + { + "bbox": [ + 47, + 517, + 287, + 565 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 47, + 517, + 287, + 565 + ], + "type": "text", + "content": ", combined with noise embedding as input to a transformer model, and estimate " + }, + { + "bbox": [ + 47, + 517, + 287, + 565 + ], + "type": "inline_equation", + "content": "x_0" + }, + { + "bbox": [ + 47, + 517, + 287, + 565 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 47, + 572, + 194, + 585 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 572, + 194, + 585 + ], + "spans": [ + { + "bbox": [ + 47, + 572, + 194, + 585 + ], + "type": "text", + "content": "3.3. Synthetic Data Generation" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 47, + 590, + 287, + 638 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 590, + 287, + 638 + ], + "spans": [ + { + "bbox": [ + 47, + 590, + 287, + 638 + ], + "type": "text", + "content": "Our method does not need paired training data. Still, for benchmarking purposes, we develop a way to automatically synthesize a large-scale dataset with various paired egocentric videos and human motions." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 47, + 641, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 641, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 641, + 287, + 713 + ], + "type": "text", + "content": "Generate Motions in 3D Scenes. To generate a dataset with both egocentric video and ground truth human motions, we use a large-scale motion capture dataset AMASS [23] and a 3D scene dataset Replica [31]. We convert the scene mesh from Replica to the signed distance field (SDF) for the penetration calculation. We divide each sequence of" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 72, + 545, + 205 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 205 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 205 + ], + "type": "text", + "content": "AMASS [23] into sub-sequences with 150 frames. For each sub-sequence, based on the semantic annotation provided by Replica [31], we place the first pose in a random location with the feet in contact with the floor. Then we calculate penetration loss following Wang et al. [39] for each pose in this sequence. We empirically set the threshold to 2 and only keep the poses with penetration loss less than the threshold. Specifically, for human mesh " + }, + { + "bbox": [ + 304, + 72, + 545, + 205 + ], + "type": "inline_equation", + "content": "M_{t}" + }, + { + "bbox": [ + 304, + 72, + 545, + 205 + ], + "type": "text", + "content": " at time " + }, + { + "bbox": [ + 304, + 72, + 545, + 205 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 72, + 545, + 205 + ], + "type": "text", + "content": " represented by a parameterized human model [20, 27], we denote " + }, + { + "bbox": [ + 304, + 72, + 545, + 205 + ], + "type": "inline_equation", + "content": "d_{i}" + }, + { + "bbox": [ + 304, + 72, + 545, + 205 + ], + "type": "text", + "content": " as the signed distance of vertex " + }, + { + "bbox": [ + 304, + 72, + 545, + 205 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 304, + 72, + 545, + 205 + ], + "type": "text", + "content": ". The penetration loss is then defined as " + }, + { + "bbox": [ + 304, + 72, + 545, + 205 + ], + "type": "inline_equation", + "content": "L_{pen}^{t} = \\sum_{d_{i} < 0} ||d_{i}||" + }, + { + "bbox": [ + 304, + 72, + 545, + 205 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 206, + 547, + 338 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 206, + 547, + 338 + ], + "spans": [ + { + "bbox": [ + 304, + 206, + 547, + 338 + ], + "type": "text", + "content": "Synthesize Realistic Egocentric Images. The motion sequences produced by detecting penetration with 3D scenes provide the camera pose trajectories to render synthetic egocentric videos. AI Habitat [24,32] is a platform for embodied agent research that supports fast rendering given a camera trajectory and a 3D scene. We feed the head pose trajectories to the platform and synthesize realistic images in the egocentric view. We generate 1,664,616 frames with 30 fps, approximately 15 hours of motion in 18 scenes. We name the synthetic dataset AMASS-Replica-Ego-Syn (ARES) and show some examples from our synthetic dataset in Figure 4." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 347, + 386, + 361 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 347, + 386, + 361 + ], + "spans": [ + { + "bbox": [ + 306, + 347, + 386, + 361 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 367, + 545, + 426 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 367, + 545, + 426 + ], + "spans": [ + { + "bbox": [ + 304, + 367, + 545, + 426 + ], + "type": "text", + "content": "We evaluate and compare our method to baselines on five commonly used metrics for human motion reconstruction, in addition to the human perception studies. We also conduct ablation studies to analyze the performance of each stage of our method, as well as the design choices in our model." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 306, + 433, + 481, + 445 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 433, + 481, + 445 + ], + "spans": [ + { + "bbox": [ + 306, + 433, + 481, + 445 + ], + "type": "text", + "content": "4.1. Datasets and Evaluation Metrics" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 450, + 545, + 533 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 450, + 545, + 533 + ], + "spans": [ + { + "bbox": [ + 304, + 450, + 545, + 533 + ], + "type": "text", + "content": "AMASS-Replica-Ego-Syn (ARES) is our synthetic dataset which contains synthetic egocentric videos and ground truth motions. ARES contains about 15 hours of motion across 18 scenes. We remove 5 scenes from training as unseen scenes. The training dataset consists of about " + }, + { + "bbox": [ + 304, + 450, + 545, + 533 + ], + "type": "inline_equation", + "content": "1.2\\mathrm{M}" + }, + { + "bbox": [ + 304, + 450, + 545, + 533 + ], + "type": "text", + "content": " frames in 13 different scenes. The testing dataset contains 34,850 frames from 5 unseen scenes." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 304, + 537, + 545, + 573 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 537, + 545, + 573 + ], + "spans": [ + { + "bbox": [ + 304, + 537, + 545, + 573 + ], + "type": "text", + "content": "AMASS [23] is a large-scale motion capture dataset with about 45 hours of diverse motions. We split training and testing data following HuMoR [29]." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 304, + 575, + 545, + 635 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 575, + 545, + 635 + ], + "spans": [ + { + "bbox": [ + 304, + 575, + 545, + 635 + ], + "type": "text", + "content": "Kinpoly-MoCap [22] consists of egocentric videos captured using a head-mounted camera and corresponding 3D motions captured with motion capture devices. The total motion is about 80 minutes long. Since it uses motion capture devices, the egocentric video is constrained to a single lab scene." + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 304, + 639, + 545, + 686 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 639, + 545, + 686 + ], + "spans": [ + { + "bbox": [ + 304, + 639, + 545, + 686 + ], + "type": "text", + "content": "Kinpoly-RealWorld [22] contains paired egocentric videos and head poses captured using iPhone ARKit. Unlike Kinpoly-MoCap which is captured in a lab scene, Kinpoly-RealWorld provides in-the-wild egocentric videos." + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 304, + 689, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 689, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 689, + 545, + 713 + ], + "type": "text", + "content": "GIMO [51] consists of egocentric video, eye gaze, 3D motions, and scanned 3D scenes. This dataset is collected using" + } + ] + } + ], + "index": 24 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "17146" + } + ] + } + ], + "index": 25 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 49, + 71, + 547, + 168 + ], + "blocks": [ + { + "bbox": [ + 49, + 71, + 547, + 168 + ], + "lines": [ + { + "bbox": [ + 49, + 71, + 547, + 168 + ], + "spans": [ + { + "bbox": [ + 49, + 71, + 547, + 168 + ], + "type": "image", + "image_path": "05d883d87448c3362c04ef6cd27ff5d0c674bc6798fc1114cdce8d186f015436.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 47, + 171, + 546, + 194 + ], + "lines": [ + { + "bbox": [ + 47, + 171, + 546, + 194 + ], + "spans": [ + { + "bbox": [ + 47, + 171, + 546, + 194 + ], + "type": "text", + "content": "Figure 4. Illustration of our ARES Dataset. \"Ego-View\" represents the synthetic egocentric images using our proposed data generation pipeline. We also provide a third-person view reference in the second row. The left and right show two sequences from different scenes." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 50, + 198, + 545, + 264 + ], + "blocks": [ + { + "bbox": [ + 50, + 198, + 545, + 264 + ], + "lines": [ + { + "bbox": [ + 50, + 198, + 545, + 264 + ], + "spans": [ + { + "bbox": [ + 50, + 198, + 545, + 264 + ], + "type": "table", + "html": "
MethodARESKinpoly-MoCap [22]GIMO [51]
OheadTheadMPJPEAccelFSOheadTheadMPJPEAccelFSOheadTheadMPJPEAccelFS
PoseReg [48]0.77354.7147.7127.687.11.051943.9160.461.810.81.511528.6189.371.514.2
Kinpoly-OF [22]0.62323.4141.67.34.21.332475.5230.516.415.81.521739.3404.221.914.4
EgoEgo (ours)0.20148.0121.16.22.70.58505.1125.98.01.60.67356.8152.110.41.9
", + "image_path": "9a7f0dde4eb0648759275b4cf1d4b7e2c97f0bbbc656dac51162a81ed9429c50.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 96, + 268, + 496, + 280 + ], + "lines": [ + { + "bbox": [ + 96, + 268, + 496, + 280 + ], + "spans": [ + { + "bbox": [ + 96, + 268, + 496, + 280 + ], + "type": "text", + "content": "Table 1. Full-body motion estimation from egocentric video on ARES, Kinpoly-MoCap [22], and GIMO [51]." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 47, + 289, + 288, + 326 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 289, + 288, + 326 + ], + "spans": [ + { + "bbox": [ + 47, + 289, + 288, + 326 + ], + "type": "text", + "content": "Hololens, iPhone 12, and IMU-based motion capture suits to study motion prediction tasks guided by eye gaze. We use 15 scenes for training and 4 scenes for testing." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 329, + 135, + 340 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 329, + 135, + 340 + ], + "spans": [ + { + "bbox": [ + 47, + 329, + 135, + 340 + ], + "type": "text", + "content": "Evaluation Metrics." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 58, + 344, + 290, + 635 + ], + "type": "list", + "angle": 0, + "index": 11, + "blocks": [ + { + "bbox": [ + 58, + 344, + 290, + 403 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 344, + 290, + 403 + ], + "spans": [ + { + "bbox": [ + 58, + 344, + 290, + 403 + ], + "type": "text", + "content": "- Head Orientation Error " + }, + { + "bbox": [ + 58, + 344, + 290, + 403 + ], + "type": "inline_equation", + "content": "(\\mathbf{O}_{head})" + }, + { + "bbox": [ + 58, + 344, + 290, + 403 + ], + "type": "text", + "content": " computes the Frobenius norm of the difference between the " + }, + { + "bbox": [ + 58, + 344, + 290, + 403 + ], + "type": "inline_equation", + "content": "3 \\times 3" + }, + { + "bbox": [ + 58, + 344, + 290, + 403 + ], + "type": "text", + "content": " rotation matrix " + }, + { + "bbox": [ + 58, + 344, + 290, + 403 + ], + "type": "inline_equation", + "content": "||\\pmb{R}_{pred}\\pmb{R}_{gt}^{-1} - \\pmb{I}||_2" + }, + { + "bbox": [ + 58, + 344, + 290, + 403 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 58, + 344, + 290, + 403 + ], + "type": "inline_equation", + "content": "\\pmb{R}_{pred}" + }, + { + "bbox": [ + 58, + 344, + 290, + 403 + ], + "type": "text", + "content": " is the predicted head rotation matrix and " + }, + { + "bbox": [ + 58, + 344, + 290, + 403 + ], + "type": "inline_equation", + "content": "\\pmb{R}_{gt}" + }, + { + "bbox": [ + 58, + 344, + 290, + 403 + ], + "type": "text", + "content": " is the ground truth head rotation matrix." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 58, + 407, + 290, + 456 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 407, + 290, + 456 + ], + "spans": [ + { + "bbox": [ + 58, + 407, + 290, + 456 + ], + "type": "text", + "content": "- Head Translation Error " + }, + { + "bbox": [ + 58, + 407, + 290, + 456 + ], + "type": "inline_equation", + "content": "\\left(\\mathbf{T}_{\\text {head }}\\right)" + }, + { + "bbox": [ + 58, + 407, + 290, + 456 + ], + "type": "text", + "content": " is computed by taking the mean Euclidean distance of two trajectories. We use this metric to measure the head joint translation errors in millimeters (mm)." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 58, + 458, + 289, + 483 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 458, + 289, + 483 + ], + "spans": [ + { + "bbox": [ + 58, + 458, + 289, + 483 + ], + "type": "text", + "content": "- MPJPE represents mean per-joint position errors in millimeters (mm)." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 58, + 485, + 289, + 521 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 485, + 289, + 521 + ], + "spans": [ + { + "bbox": [ + 58, + 485, + 289, + 521 + ], + "type": "text", + "content": "- Accel represents the difference of acceleration between predicted joint positions and ground truth joint positions measured in " + }, + { + "bbox": [ + 58, + 485, + 289, + 521 + ], + "type": "inline_equation", + "content": "(mm / s^2)" + }, + { + "bbox": [ + 58, + 485, + 289, + 521 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 58, + 524, + 290, + 635 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 524, + 290, + 635 + ], + "spans": [ + { + "bbox": [ + 58, + 524, + 290, + 635 + ], + "type": "text", + "content": "- FS represents foot skating metric and is computed following NeMF [5]. Specifically, we first project the toe and ankle joints' velocity to the " + }, + { + "bbox": [ + 58, + 524, + 290, + 635 + ], + "type": "inline_equation", + "content": "xy" + }, + { + "bbox": [ + 58, + 524, + 290, + 635 + ], + "type": "text", + "content": " plane and compute the " + }, + { + "bbox": [ + 58, + 524, + 290, + 635 + ], + "type": "inline_equation", + "content": "L1" + }, + { + "bbox": [ + 58, + 524, + 290, + 635 + ], + "type": "text", + "content": " norm of the projected velocities in each step denoted as " + }, + { + "bbox": [ + 58, + 524, + 290, + 635 + ], + "type": "inline_equation", + "content": "v_{t}" + }, + { + "bbox": [ + 58, + 524, + 290, + 635 + ], + "type": "text", + "content": ". We only accumulate the horizontal translation for those steps that have a height " + }, + { + "bbox": [ + 58, + 524, + 290, + 635 + ], + "type": "inline_equation", + "content": "h_t" + }, + { + "bbox": [ + 58, + 524, + 290, + 635 + ], + "type": "text", + "content": " lower than a specified threshold " + }, + { + "bbox": [ + 58, + 524, + 290, + 635 + ], + "type": "inline_equation", + "content": "H" + }, + { + "bbox": [ + 58, + 524, + 290, + 635 + ], + "type": "text", + "content": ". And the metric is calculated as a mean of weighted values " + }, + { + "bbox": [ + 58, + 524, + 290, + 635 + ], + "type": "inline_equation", + "content": "v_{t}(2 - 2^{\\frac{h_{t}}{H}})" + }, + { + "bbox": [ + 58, + 524, + 290, + 635 + ], + "type": "text", + "content": " across the sequence and is measured in " + }, + { + "bbox": [ + 58, + 524, + 290, + 635 + ], + "type": "inline_equation", + "content": "(mm)" + }, + { + "bbox": [ + 58, + 524, + 290, + 635 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 10 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 47, + 650, + 282, + 662 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 650, + 282, + 662 + ], + "spans": [ + { + "bbox": [ + 47, + 650, + 282, + 662 + ], + "type": "text", + "content": "4.2. Body Pose Estimation from Egocentric Video" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 46, + 665, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 289, + 715 + ], + "type": "text", + "content": "Training Data. We train our HeadNet using paired egocentric videos and head poses provided by ARES, KinplyRealWorld, and GIMO. Note that the body motion in these datasets is not used for training HeadNet. Our GravityNet" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 289, + 546, + 326 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 289, + 546, + 326 + ], + "spans": [ + { + "bbox": [ + 304, + 289, + 546, + 326 + ], + "type": "text", + "content": "and the conditional diffusion model are both trained on AMASS. For the baselines below, we train them using paired egocentric videos and ground truth motions in ARES." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 333, + 547, + 490 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 333, + 547, + 490 + ], + "spans": [ + { + "bbox": [ + 304, + 333, + 547, + 490 + ], + "type": "text", + "content": "Baselines. We compare our approach with two baselines PoseReg [48] and Kinpoly [22]. PoseReg [48] takes a sequence of optical flow features as input and uses an LSTM model to predict the pose state at each time step. The pose state consists of root translation, root orientation, joint rotations, and corresponding velocities including root linear velocity and angular velocities of all the joints. Kinpoly-OF [22] proposes a per-step regression model to estimate full body motion from optical flow features. Because our problem only allows for egocentric video as input, we choose the option of Kinpoly which only has optical flow features as input, without relying on ground truth head poses and action labels that depend on additional knowledge." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 495, + 547, + 602 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 495, + 547, + 602 + ], + "spans": [ + { + "bbox": [ + 304, + 495, + 547, + 602 + ], + "type": "text", + "content": "Results. We compare the complete pipeline of EgoEgo with baseline methods PoseReg [48] and Kinpoly-OF [22] on ARES, Kinpoly-MoCap [22] and GIMO [51], as shown in Table 1. We show that our EgoEgo outperforms all the baselines by a large margin on all three datasets. We show qualitative results in Figure 5. Our generated motions better preserve the root trajectories. And our approach can also generate more dynamic and realistic motions compared to the baselines." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 305, + 613, + 541, + 625 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 613, + 541, + 625 + ], + "spans": [ + { + "bbox": [ + 305, + 613, + 541, + 625 + ], + "type": "text", + "content": "4.3. Head Pose Estimation from Egocentric Video" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 629, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 629, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 629, + 547, + 715 + ], + "type": "text", + "content": "Baselines. We compare our hybrid approach with the prediction results of DROID-SLAM [33]. For a fair comparison, we apply a rotation to the SLAM trajectory by aligning the first predicted head pose of SLAM with the ground truth head pose. We train our GravityNet on AMASS training split. As for HeadNet, we train on ARES, Kinpoly-RealWorld, and GIMO separately for the evaluation of different datasets." + } + ] + } + ], + "index": 18 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "17147" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 47, + 89, + 547, + 451 + ], + "blocks": [ + { + "bbox": [ + 267, + 76, + 325, + 87 + ], + "lines": [ + { + "bbox": [ + 267, + 76, + 325, + 87 + ], + "spans": [ + { + "bbox": [ + 267, + 76, + 325, + 87 + ], + "type": "text", + "content": "(a) Example 1" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 47, + 89, + 547, + 451 + ], + "lines": [ + { + "bbox": [ + 47, + 89, + 547, + 451 + ], + "spans": [ + { + "bbox": [ + 47, + 89, + 547, + 451 + ], + "type": "image", + "image_path": "e25c16503b42b0127d25c61ccf099b5c3c06bea3ea56441f21c453ef11155e0a.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 96, + 454, + 496, + 465 + ], + "lines": [ + { + "bbox": [ + 96, + 454, + 496, + 465 + ], + "spans": [ + { + "bbox": [ + 96, + 454, + 496, + 465 + ], + "type": "text", + "content": "Figure 5. Qualitative results comparisons. We show the results of two egocentric videos from different scenes." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_caption" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 481, + 288, + 636 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 481, + 288, + 636 + ], + "spans": [ + { + "bbox": [ + 46, + 481, + 288, + 636 + ], + "type": "text", + "content": "Results. We evaluate the head pose estimation on the three datasets as shown in Table 2. We show more accurate head rotation prediction results on ARES and comparable results on real-captured data. As the real-captured data is limited in scale (Kinpoly-RealWorld contains 20 minutes of training videos and GIMO contains 30 minutes of training videos), we believe the head rotation prediction can be further improved by future developments of large-scale real-captured datasets with head poses. Overall, our hybrid approach combines the accurate rotation prediction from HeadNet and re-scaled translation of gravity-aligned SLAM results, and produces more accurate head pose estimation results as input to the second stage." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 648, + 266, + 661 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 648, + 266, + 661 + ], + "spans": [ + { + "bbox": [ + 47, + 648, + 266, + 661 + ], + "type": "text", + "content": "4.4. Body Pose Estimation from the Head Pose" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "text", + "content": "Baselines. We compare our conditional diffusion model for full-body pose estimation with two baselines AvatarPoser [10] and Kinpoly-Head [22]. AvatarPoser [10] takes both head and hand pose as input to predict full body motion." + } + ] + } + ], + "index": 5 + }, + { + "type": "table", + "bbox": [ + 310, + 478, + 541, + 552 + ], + "blocks": [ + { + "bbox": [ + 310, + 478, + 541, + 552 + ], + "lines": [ + { + "bbox": [ + 310, + 478, + 541, + 552 + ], + "spans": [ + { + "bbox": [ + 310, + 478, + 541, + 552 + ], + "type": "table", + "html": "
DROID-SLAM [33]Ours
OheadThedOheadThed
ARES0.62411.30.23176.5
Kinpoly-MoCap0.551290.80.58487.8
GIMO0.67865.40.68304.7
", + "image_path": "9777fcdcfe73ab41c791bfaf02ba5463d8694bbd4e61a8f14e8622c60c39ab25.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "table_body" + } + ], + "index": 6 + }, + { + "bbox": [ + 347, + 554, + 503, + 565 + ], + "lines": [ + { + "bbox": [ + 347, + 554, + 503, + 565 + ], + "spans": [ + { + "bbox": [ + 347, + 554, + 503, + 565 + ], + "type": "text", + "content": "Table 2. Head pose estimation on test sets." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 304, + 576, + 545, + 648 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 576, + 545, + 648 + ], + "spans": [ + { + "bbox": [ + 304, + 576, + 545, + 648 + ], + "type": "text", + "content": "We remove the hand poses from the input and modified it to a setting with head pose input only. Kinpoly-Head [22] is our modified variant of the Kinpoly model that only takes the head pose as input. Both the baselines and our method are trained on the training split of AMASS with high-quality motion capture data." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 653, + 546, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 653, + 546, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 653, + 546, + 715 + ], + "type": "text", + "content": "Results. We evaluate the baselines and our method on the AMASS test set, as shown in Table 3. Since our model is generative, there are multiple plausible predictions from the same head pose input. For a quantitative comparison, we generate 200 samples for each head pose input and use the" + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "17148" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 48, + 71, + 288, + 122 + ], + "blocks": [ + { + "bbox": [ + 48, + 71, + 288, + 122 + ], + "lines": [ + { + "bbox": [ + 48, + 71, + 288, + 122 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 288, + 122 + ], + "type": "table", + "html": "
MethodOheadTheadMPJPEAccelFS
AvatarPoser [10]0.1928.6124.716.118.8
Kinpoly-Head [22]0.1987.8110.911.411.2
Diffusion Model (ours)0.0436.7109.010.54.4
", + "image_path": "779a5ebaebe5b2e7b8ca1b2d5def2b782a2b4c31791cd7cbd075f6f0135063f0.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 48, + 152, + 287, + 235 + ], + "blocks": [ + { + "bbox": [ + 47, + 124, + 287, + 146 + ], + "lines": [ + { + "bbox": [ + 47, + 124, + 287, + 146 + ], + "spans": [ + { + "bbox": [ + 47, + 124, + 287, + 146 + ], + "type": "text", + "content": "Table 3. Full-body motion estimation from GT head pose on AMASS testing dataset [22]." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 48, + 152, + 287, + 235 + ], + "lines": [ + { + "bbox": [ + 48, + 152, + 287, + 235 + ], + "spans": [ + { + "bbox": [ + 48, + 152, + 287, + 235 + ], + "type": "table", + "html": "
ARESKinpoly-MoCapGIMO
OheadThedOheadThedOheadThed
SLAM0.62411.330.551290.820.67865.41
SLAM+S0.62325.950.55643.450.67569.48
SLAM+S+G0.62176.540.55487.770.67304.74
Full model0.23176.540.58487.770.68304.74
", + "image_path": "710407e7a5239a55b46d0d16e769ab7688a3bfd5e3dd85b9d46cc83e65fae1db.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 284, + 220, + 295 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 284, + 220, + 295 + ], + "spans": [ + { + "bbox": [ + 47, + 284, + 220, + 295 + ], + "type": "text", + "content": "one with the smallest MPJPE as our result." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 304, + 148, + 316 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 304, + 148, + 316 + ], + "spans": [ + { + "bbox": [ + 47, + 304, + 148, + 316 + ], + "type": "text", + "content": "4.5. Ablation Studies" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 320, + 287, + 380 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 320, + 287, + 380 + ], + "spans": [ + { + "bbox": [ + 47, + 320, + 287, + 380 + ], + "type": "text", + "content": "Effects of Components in Head Pose Estimation. We study the effects of each component in head pose estimation in Table 4. We showcase that the rotation for aligning gravity direction and the learned scale are both effective to improve head translation results." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 386, + 288, + 471 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 386, + 288, + 471 + ], + "spans": [ + { + "bbox": [ + 47, + 386, + 288, + 471 + ], + "type": "text", + "content": "Effects of Head Pose in Full-Body Pose Estimation. We compare the full-body pose estimation results that take our predicted head poses and the ground truth head poses as input. Table 5 shows that the ground truth head poses significantly improve the full body pose estimation, indicating that by developing methods that predict more accurate head pose, the full body pose estimation can be further improved." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 479, + 188, + 491 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 479, + 188, + 491 + ], + "spans": [ + { + "bbox": [ + 47, + 479, + 188, + 491 + ], + "type": "text", + "content": "4.6. Human Perceptual Study" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 498, + 287, + 676 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 498, + 287, + 676 + ], + "spans": [ + { + "bbox": [ + 46, + 498, + 287, + 676 + ], + "type": "text", + "content": "We also conduct two human perceptual studies as part of the evaluation. The first is to evaluate the quality of predicted full-body motion from egocentric video, the second is to evaluate the quality of predicted full-body motion from ground truth head poses. In both studies, we compare four types of motion: results from our EgoEgo and from two baselines, as well as the ground truth. For the first human study, each time, users are presented with two motions and an egocentric video, and asked to select which one is more plausible. For the second human study, users are presented with two motions and asked to select which one looks more natural and realistic. Because there are 10 examples and the two motions can be from four sources, we have 60 questions for each study. Each question was answered by 20 Amazon Mechanical Turk workers." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 677, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 677, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 677, + 288, + 713 + ], + "type": "text", + "content": "As shown in Figure 6(a), for full-body estimation from egocentric video, our results are preferred by " + }, + { + "bbox": [ + 47, + 677, + 288, + 713 + ], + "type": "inline_equation", + "content": "98\\%" + }, + { + "bbox": [ + 47, + 677, + 288, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 677, + 288, + 713 + ], + "type": "inline_equation", + "content": "69\\%" + }, + { + "bbox": [ + 47, + 677, + 288, + 713 + ], + "type": "text", + "content": " of workers when compared to the baselines. Also, when" + } + ] + } + ], + "index": 10 + }, + { + "type": "table", + "bbox": [ + 306, + 70, + 544, + 164 + ], + "blocks": [ + { + "bbox": [ + 47, + 239, + 288, + 274 + ], + "lines": [ + { + "bbox": [ + 47, + 239, + 288, + 274 + ], + "spans": [ + { + "bbox": [ + 47, + 239, + 288, + 274 + ], + "type": "text", + "content": "Table 4. Ablation study for the components in head pose estimation. S represents the scale predicted by HeadNet, and G represents GravityNet." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 306, + 70, + 544, + 164 + ], + "lines": [ + { + "bbox": [ + 306, + 70, + 544, + 164 + ], + "spans": [ + { + "bbox": [ + 306, + 70, + 544, + 164 + ], + "type": "table", + "html": "
ARESKinpoly-MoCapGIMO
EEEE w/ GTEEEE w/ GTEEEE w/ GT
Ohead0.200.040.580.030.670.06
Thead148.029.1505.160.7356.866.0
MPJPE121.1105.6125.976.0152.1125.7
Accel6.26.38.07.210.410.2
FS2.73.01.62.51.91.7
", + "image_path": "e06c6f822040a8af489ec5e4170a23d01078b14fe6325af5bc1913db3a493f3a.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "table_body" + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 167, + 545, + 201 + ], + "lines": [ + { + "bbox": [ + 305, + 167, + 545, + 201 + ], + "spans": [ + { + "bbox": [ + 305, + 167, + 545, + 201 + ], + "type": "text", + "content": "Table 5. Ablation study for the effects of head pose to full-body pose estimation. EE represents EgoEgo. GT represents ground truth head poses." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "text" + }, + { + "type": "image", + "bbox": [ + 307, + 208, + 545, + 330 + ], + "blocks": [ + { + "bbox": [ + 307, + 208, + 545, + 330 + ], + "lines": [ + { + "bbox": [ + 307, + 208, + 545, + 330 + ], + "spans": [ + { + "bbox": [ + 307, + 208, + 545, + 330 + ], + "type": "image", + "image_path": "49a7561fb578c848fd9a51e49a58cf85400232b9c31172feb6f3879751eae323.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 306, + 332, + 545, + 354 + ], + "lines": [ + { + "bbox": [ + 306, + 332, + 545, + 354 + ], + "spans": [ + { + "bbox": [ + 306, + 332, + 545, + 354 + ], + "type": "text", + "content": "Figure 6. Results of human perceptual studies. The numbers shown in the chart represent " + }, + { + "bbox": [ + 306, + 332, + 545, + 354 + ], + "type": "inline_equation", + "content": "\\%" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_caption" + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 365, + 547, + 437 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 365, + 547, + 437 + ], + "spans": [ + { + "bbox": [ + 305, + 365, + 547, + 437 + ], + "type": "text", + "content": "compared with the ground truth, " + }, + { + "bbox": [ + 305, + 365, + 547, + 437 + ], + "type": "inline_equation", + "content": "34\\%" + }, + { + "bbox": [ + 305, + 365, + 547, + 437 + ], + "type": "text", + "content": " of the responses prefer our results (note that a perfect output would achieve " + }, + { + "bbox": [ + 305, + 365, + 547, + 437 + ], + "type": "inline_equation", + "content": "50\\%" + }, + { + "bbox": [ + 305, + 365, + 547, + 437 + ], + "type": "text", + "content": "), suggesting that people cannot easily distinguish our results from ground truth motions. As shown in Figure 6(b), for full-body estimation from head poses, our results are preferred by " + }, + { + "bbox": [ + 305, + 365, + 547, + 437 + ], + "type": "inline_equation", + "content": "88\\%" + }, + { + "bbox": [ + 305, + 365, + 547, + 437 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 365, + 547, + 437 + ], + "type": "inline_equation", + "content": "79\\%" + }, + { + "bbox": [ + 305, + 365, + 547, + 437 + ], + "type": "text", + "content": " of workers when compared to the baselines." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 306, + 443, + 378, + 456 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 443, + 378, + 456 + ], + "spans": [ + { + "bbox": [ + 306, + 443, + 378, + 456 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 465, + 547, + 633 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 465, + 547, + 633 + ], + "spans": [ + { + "bbox": [ + 304, + 465, + 547, + 633 + ], + "type": "text", + "content": "We presented a generalized framework to estimate full-body motions from egocentric video. The key is to decompose the problem into two stages. We predicted the head pose from an egocentric video and fed the output from the first stage to estimate full-body motions in the second stage. In addition, we developed a hybrid solution to produce more accurate head poses on top of monocular SLAM. We also proposed a conditional diffusion model to generate diverse high-quality full-body motions from predicted head poses. To benchmark different methods in a large-scale dataset, we proposed a data generation pipeline to synthesize a largescale dataset with paired egocentric videos and 3D human motions. We showcased superior results on both the synthetic and the real-captured dataset compared to prior work." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 641, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 641, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 641, + 547, + 715 + ], + "type": "text", + "content": "Acknowledgement. We thank Zhengfei Kuang for the help with visualizations and Jonathan Tseng for discussions about the diffusion model. This work is in part supported by ONR MURI N00014-22-1-2740, NSF CCRI 2120095, the Toyota Research Institute (TRI), the Stanford Institute for Human-Centered AI (HAI), Innopeak, Meta, and Samsung." + } + ] + } + ], + "index": 18 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "17149" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 107, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 107, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 107, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 289, + 713 + ], + "type": "list", + "angle": 0, + "index": 18, + "blocks": [ + { + "bbox": [ + 53, + 91, + 288, + 133 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 288, + 133 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 288, + 133 + ], + "type": "text", + "content": "[1] Sadegh Aliakbarian, Pashmina Cameron, Federica Bogo, Andrew Fitzgibbon, and Thomas J Cashman. 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Likewise, machines are advanced to approach human intelligence by learning with multisensory inputs from an egocentric perspective. In this paper, we explore the challenging egocentric audio-visual object localization task and observe that 1) egomotion commonly exists in first-person recordings, even within a short duration; 2) The out-of-view sound components can be created when wearers shift their attention. To address the first problem, we propose a geometry-aware temporal aggregation module that handles the egomotion explicitly. The effect of egomotion is mitigated by estimating the temporal geometry transformation and exploiting it to update visual representations. Moreover, we propose a cascaded feature enhancement module to overcome the second issue. It improves cross-modal localization robustness by disentangling visually-indicated audio representation. During training, we take advantage of the naturally occurring audio-visual temporal synchronization as the \"free\" self-supervision to avoid costly labeling. We also annotate and create the Epic Sounding Object dataset for evaluation purposes. Extensive experiments show that our method achieves state-of-the-art localization performance in egocentric videos and can be generalized to diverse audio-visual scenes. Code is available at https://github.com/WikiChao/Ego-AV-Loc.", + "bbox": [ + 75, + 301, + 473, + 694 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 723, + 207, + 738 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "The emergence of wearable devices has drawn the attention of the research community to egocentric videos, the significance of which can be seen from egocentric research in a variety of applications such as robotics [32,34,48], augmented/virtual reality [31,61,75], and healthcare [53,66]. In recent years, the computer vision community has made substantial efforts to build benchmarks [12, 13, 15, 40, 57, 69], establish new tasks [17, 36, 37, 39, 60], and develop frameworks [33,41,54,82] for egocentric video understanding.", + "bbox": [ + 75, + 750, + 468, + 885 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "While existing works achieve promising results in the", + "bbox": [ + 96, + 885, + 468, + 900 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/3719b6f38374c3c1571081325abefaa481fd944ba0f6e9b33211f0b2afa03920.jpg", + "image_caption": [ + "Figure 1. Sounding object localization in egocentric videos. Due to the wearer's egomotion, the viewpoint changes continuously across time. Consequently, audio-visual relations are dynamically changing in egocentric videos. Our approach tackles challenges in the egocentric audio-visual sounding object task and learns audio-visual associations from first-person videos." + ], + "image_footnote": [], + "bbox": [ + 504, + 267, + 890, + 421 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "egocentric domain, it still remains an interesting but challenging topic to perform fine-grained egocentric video understanding. For instance, understanding which object is emitting sound in a first-person recording is difficult for machines. As shown in Fig. 1, the wearer moves his/her head to put down the bottle. The frying pot which emits sound subsequently suffers deformation and occlusion due to the wearer's egomotion. Human speech outside the wearer's view also affects the machine's understanding of the current scene. This example reveals two significant challenges for designing powerful and robust egocentric video understanding systems: First, people with wearable devices usually record videos in naturalistic surroundings, where a variety of illumination conditions, object appearance, and motion patterns are shown. The dynamic visual variations introduce difficulties in accurate visual perception. Second, egocentric scenes are often perceived within a limited field of view (FoV). The common body and head movements cause frequent view changes (see Fig. 1), which brings object deformation and creates dynamic out-of-view content.", + "bbox": [ + 496, + 523, + 892, + 824 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Although a visual-only system may struggle to fully decode the surrounding information and perceive scenes in egocentric videos, audio provides stable and persistent signals associated with the depicted events. Instead of purely visual perception, numerous psychological and cognitive", + "bbox": [ + 496, + 825, + 893, + 900 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "22910", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "studies [6, 29, 67, 73] show that integration of auditory and visual signals is significant in human perception. Audio, as an essential but less focused modality, often provides synchronized and complementary information with the video stream. In contrast to the variability of first-person visual footage, sound describes the underlying scenes consistently. These natural characteristics make audio another indispensable ingredient for egocentric video understanding.", + "bbox": [ + 75, + 90, + 468, + 210 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To effectively leverage audio and visual information in egocentric videos, a pivotal problem is to analyze the fine-grained audio-visual association, specifically identifying which objects are emitting sounds in the scene. In this paper, we explore a novel egocentric audio-visual object localization task, which aims to associate audio with dynamic visual scenes and localize sounding objects in egocentric videos. Given the dynamic nature of egocentric videos, it is exceedingly challenging to link visual content from various viewpoints with audio captured from the entire space. Hence, we develop a new framework to model the distinct characteristics of egocentric videos by integrating audio. In the framework, we propose a geometry-aware temporal module to handle egomotion explicitly. Our approach mitigates the impact of egomotion by performing geometric transformations in the embedding space and aligning visual features from different frames. We further use the aligned features to leverage temporal contexts across frames to learn discriminative cues for localization. Additionally, we introduce a cascaded feature enhancement module to handle out-of-view sounds. The module helps mitigate audio noises and improves cross-modal localization robustness.", + "bbox": [ + 75, + 212, + 470, + 542 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Due to the dynamic nature of egocentric videos, it is hard and costly to label sounding objects for supervised training. To avoid tedious labeling, we formulate this task in a self-supervised manner, and our framework is trained with audio-visual temporal synchronization. Since there are no publicly available egocentric sounding object localization datasets, we annotate an Epic Sounding dataset to facilitate research in this field. Experimental results demonstrate that modeling egomotion and mitigating out-of-view sound can improve egocentric audio-visual localization performance.", + "bbox": [ + 75, + 544, + 468, + 694 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In summary, our contributions are: (1) the first systematic study on egocentric audio-visual sounding object localization; (2) an effective geometry-aware temporal aggregation approach to deal with unique egomotion; (3) a novel cascaded feature enhancement module to progressively inject localization cues; and (4) an Epic Sounding Object dataset with sounding object annotations to benchmark the localization performance in egocentric videos.", + "bbox": [ + 75, + 696, + 468, + 815 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 76, + 829, + 218, + 845 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Audio-visual learning in third-person view videos. Taking the natural audio-visual synchronization in videos, a large number of studies in the past few years have proposed", + "bbox": [ + 75, + 854, + 468, + 902 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "to jointly learn from both auditory and visual modalities. We have seen a spectrum of new audio-visual problems and applications, including visually guided sound source separation [16,20-23,63,76,87,88], audio-visual representation learning [2,3,5,26,35,58,59], audio-visual event localization [44,78,79,84], audio-visual video parsing [77,83], and sounding object visual localization [4, 11, 27, 28, 38, 51, 52, 62, 65, 71]. Most previous approaches learn audio-visual correlations from third-person videos, while the distinct challenges of audio-visual learning in egocentric videos are underexplored. Different from existing works, we propose an audio-visual learning framework to explicitly solve egomotion and out-of-view audio issues in egocentric videos.", + "bbox": [ + 496, + 90, + 890, + 286 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Egocentric video understanding. In the last decade, video scene understanding techniques thrived because of the well-defined third-person video datasets [7, 9, 49, 72]. Nevertheless, most of the algorithms are developed to tackle videos curated by human photographers. The natural characteristics of egocentric video data, e.g., view changes, large motions, and visual deformation, are not well-explored. To bridge this gap, multiple egocentric datasets [12, 13, 24, 36, 69, 74] have been collected. These datasets have significantly advanced investigations on egocentric video understanding problems, including activity recognition [33, 41, 89], human(hand)-object interaction [8, 14, 55, 68], anticipation [1, 19, 45, 70], and human body pose inferring [30, 56]. However, only a handful of audio-visual works [10, 33, 50, 85] is presented for egocentric video understanding. Among those, Kazakos et al. [33] proposed an audio-visual fusion network for action recognition, while Mittal et al. [50] used audible interactions as cues to learn state-aware visual representations in egocentric videos. There are limited studies in explicit egomotion mitigation and fine-grained audio-visual association learning in egocentric videos. Unlike past works, we tackle challenges in egocentric audio-visual data and propose a robust sounding object localization framework. To enable the research, we propose Epic Sounding Object dataset based on Epic-Kitchens [12, 13].", + "bbox": [ + 496, + 287, + 890, + 680 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "3. Method", + "text_level": 1, + "bbox": [ + 500, + 691, + 589, + 708 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Our goal is to localize sounding objects in egocentric videos visually. We start by formulating our egocentric audio-visual object localization task in Sec. 3.1. Our proposed method includes a feature extraction process (described in Sec. 3.2), a two-stage cascaded feature enhancement pipeline (in Sec. 3.3), and a geometry-aware temporal aggregation module (explained in Sec. 3.4). Finally, we summarize the overall training objective in Sec. 3.5.", + "bbox": [ + 496, + 717, + 890, + 839 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "3.1. Problem Formulation and Method Overview", + "text_level": 1, + "bbox": [ + 500, + 847, + 877, + 862 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Given an egocentric video clip $V = \\{I_i\\}_{i=1}^T$ in $T$ frames and its corresponding sound stream $s$ , sounding object vi", + "bbox": [ + 500, + 869, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "22911", + "bbox": [ + 478, + 944, + 517, + 957 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/cba04654b8493f0991bd560f67b906f1d9de82f6b9779af9697eff747dd03de6.jpg", + "image_caption": [ + "Figure 2. An overview of our egocentric audio-visual object localization framework. In the beginning, our model extracts deep features from the video and audio streams. Then, the audio and visual features are fed into the cascaded feature enhancement module to inject localization cues for both branches. Such a module is additionally trained with \"mix-and-separation\" strategy. Next, our geometric-aware temporal modeling block leverages the relative geometric information between visual frames and performs temporal context aggregation to get the final visual features for localization." + ], + "image_footnote": [], + "bbox": [ + 158, + 88, + 816, + 340 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "sual localization aims at predicting location maps $\\mathcal{O} = \\{O_i\\}_{i=1}^T$ that represent sounding objects in the egocentric video. Specifically, $O_i(x,y) \\in \\{0,1\\}$ and positive visual regions indicate locations of sounding objects. In real-world scenarios, the captured sound can be a mixture of multiple sound sources $s = \\sum_{n=1}^{N} s_n$ , where $s_n$ is the $n$ -th sound source and it could be out of view. For the visual input, the video frames may be captured from different viewpoints. To design a robust and effective egocentric audio-visual sounding object localization system, we should consider the above issues in egocentric audio and visual data and answer two key questions: (Q1) how to associate visual content with audio representations while out-of-view sounds may exist; (Q2) how to persistently associate audio features with visual content that are captured under different viewpoints.", + "bbox": [ + 75, + 430, + 472, + 657 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Due to the dynamic nature of egocentric videos, it is difficult and costly to annotate sounding objects for supervised training. To bypass the tedious labeling, we solve the egocentric audio-visual object localization task in a self-supervised manner. The proposed framework is shown in Fig. 2. Our model first extracts representations from the audio $s$ and video clip $V$ . In order to handle Q1, we develop a cascaded feature enhancement module to disentangle visually indicated sound sources and attend to visual regions that correspond to the visible sound sources. To enable the disentanglement, we use on-screen sound separation task as the proxy and adopt a multi-task learning objective to train our model where the localization task is solved along with a sound-separation task. To deal with the egomotion in egocentric videos (Q2), we design a geometry-aware temporal modeling approach to mitigate the feature distortion", + "bbox": [ + 75, + 659, + 472, + 902 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "brought by viewpoint changes and aggregate the visual features temporally. We take the audio-visual temporal synchronization as the supervision signal and estimate the localization map $\\tilde{O}_i$ .", + "bbox": [ + 496, + 430, + 893, + 491 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. Feature Extraction", + "text_level": 1, + "bbox": [ + 500, + 498, + 683, + 513 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Visual representation. We use a visual encoder network $E_{v}$ to extract visual feature maps from each input frame $I_{i}$ . In our implementation, a pre-trained Dilated ResNet [86] model is adopted by removing the final fully-connected layer. We can subsequently obtain a group of feature maps $v_{i} = E_{v}(I_{i})$ , where $v_{i} \\in \\mathbb{R}^{c \\times h_{v} \\times w_{v}}$ . Here $c$ is the number of channels, and $h_{v} \\times w_{v}$ denotes the spatial size.", + "bbox": [ + 496, + 522, + 890, + 627 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Audio representation. To extract audio representations from the input raw waveform, we first transform audio stream $s$ into a magnitude spectrogram $X$ with the short-time Fourier transform (STFT). Then, we extract audio features $a = E_{a}(X), a \\in \\mathbb{R}^{c \\times h_{a} \\times w_{a}}$ by means of a CNN encoder $E_{a}$ in the Time-Frequency (T-F) space.", + "bbox": [ + 496, + 628, + 890, + 719 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.3. Cascaded Feature Enhancement", + "text_level": 1, + "bbox": [ + 500, + 726, + 784, + 741 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "As discussed in Sec. 3.1, a sound source $s_n$ in the mixture $s$ could be out of view due to constant view changes in egocentric videos and the limited FoV. This poses challenges in visually localizing sound sources and performance can degrade when the audio-visual associations are not precise. To address this, we update the features in a cascaded fashion. We first force the network to learn disentangled audio representations from the mixture using visual guidance. Then we utilize the disentangled audio representations to inject the visual features with more localization cues.", + "bbox": [ + 496, + 750, + 893, + 902 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "22912", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Disentanglement through sound source separation. Sound source localization objective can implicitly guide the system to learn disentangled audio features as the network will try to precisely localize the sound, and in turn, the on-screen sound will get disentangled from the rest. However, we formulate our problem in an unsupervised setting where labels for such localization objective are not available.", + "bbox": [ + 75, + 90, + 467, + 196 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Audio-visual sound separation task [23, 87] uses visual information as guidance to learn to separate individual sounds from a mixture. Given the visual guidance, it is expected that the learned representations primarily encode information from visually indicated sound sources. Hence we argue for a multi-task learning approach to solve our primary task. Along with the audio-visual sounding object localization task, the network also learns to disentangle visible audio representations from the mixture through a source separation task.", + "bbox": [ + 75, + 198, + 467, + 348 + ], + "page_idx": 3 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- Training. We adopt the commonly used \"mix-and-separate\" strategy [23,87] for audio-visual sound separation. Given the current audio $s^{(1)}$ , we randomly sample another audio stream $s^{(2)}$ from a different video and mix them together to generate input audio mixture $\\tilde{s} = s^{(1)} + s^{(2)}$ . We then obtain magnitude spectrograms $\\tilde{X}, X^{(1)}, X^{(2)}$ for $\\tilde{s}, s^{(1)}$ and $s^{(2)}$ respectively. The audio features is then modified as $a = E_a(\\tilde{X})$ .", + "- Inference. During inference, we take the original audio stream as input: $s = s^{(1)}$ and $X = X^{(1)}$ to extract visually correlated audio representations. Note that the audio features is $a = E_{a}(X)$ ." + ], + "bbox": [ + 96, + 362, + 467, + 554 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We define the audio disentanglement network as a network $f(\\cdot)$ , which produces the disentangled audio features $\\hat{a} \\in \\mathbb{R}^{c \\times h_a \\times w_a}$ . In this network, we want to associate the visual content with the audio representations to perform disentanglement in the embedding space. Concretely, we first apply spatial average pooling on each $v_i$ and temporal max pooling along the time axis to obtain a visual feature vector $g_v \\in \\mathbb{R}^c$ . Then we replicate the visual feature vector $h_a \\times w_a$ times and tile them to match the size of $a$ . We concatenate the visual and audio feature maps along the channel dimension and feed them into the network. Therefore, the audio feature disentanglement can be formulated as:", + "bbox": [ + 75, + 566, + 467, + 748 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {a} = f \\left(\\operatorname {C O N C A T} [ a, \\operatorname {T I L E} \\left(g _ {v}\\right) ]\\right). \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 158, + 763, + 467, + 780 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In practice, we implement the disentanglement network $f$ using two 1x1 convolution layers. The audio feature $\\hat{a}$ will be used for both separation mask and sounding object localization map generation.", + "bbox": [ + 75, + 792, + 467, + 853 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "To separate visible sounds, we add an audio decoder $D_{a}$ following the disentanglement network to output a binary mask $M_{pred} = D_{a}(\\hat{a})$ (at the bottom of Fig. 2). U-Net", + "bbox": [ + 75, + 854, + 467, + 901 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/4e6ae599120192a1f2f9884117b6944e2743f3b24b13a7bbdc1df5055a4b5ee4.jpg", + "image_caption": [ + "Figure 3. Overview of our proposed geometry-aware modeling approach. The visual features $\\hat{v}_j$ are warped to viewpoint $i$ by homography transformation." + ], + "image_footnote": [], + "bbox": [ + 514, + 90, + 879, + 232 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "architectures [23] are used in the audio encoder $E_{a}$ and decoder $D_{a}$ . We implement the $E_{a}$ and $D_{a}$ in five convolution and up-convolution layers, respectively. Details of the network architectures are provided in the Appendix. The ground truth separation mask $M_{gt}$ can be calculated by determining whether the original input sound is dominant at locations $(u,v)$ in the T-F space:", + "bbox": [ + 496, + 295, + 890, + 402 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nM _ {g t} (u, v) = \\left[ X ^ {(1)} (u, v) \\geq \\tilde {X} (u, v) \\right]. \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 570, + 407, + 890, + 426 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "To train the sound separator, we minimize the $\\ell_2$ distance between the predicted and ground-truth masks as the disentanglement learning objective:", + "bbox": [ + 496, + 434, + 890, + 479 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {d i s} = \\left| \\left| M _ {p r e d} - M _ {g t} \\right| \\right| _ {2} ^ {2}. \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 606, + 486, + 890, + 503 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Soft localization. Similar to the out-of-view sounds, the visual frames may contain sound-irrelevant regions. In order to learn more precise audio-visual associations, we propose to highlight the spatial regions that are more likely to be correlated with the on-screen sounds by computing audio-visual attention. The attention map will indicate the correlation between audio and visual representations at different spatial locations. Given the output $\\hat{a}$ from disentanglement network $f(\\cdot)$ , we apply max pooling on its time and frequency dimensions, obtaining an audio feature vector $g_{\\hat{a}}$ . Then at each spatial position (x,y) of visual feature $v_{i}$ , we compute the cosine similarity between audio and visual feature vectors:", + "bbox": [ + 496, + 511, + 890, + 705 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nS _ {i}: S _ {i} (x, y) = \\operatorname {C O S I N E S I M} \\left(v _ {i} (x, y), g _ {\\hat {a}}\\right). \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 553, + 715, + 890, + 732 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "SOFTMAX is then used on $S_{i}$ to generate a soft mask that represents the audio-visual correspondence. Hence, each $v_{i}$ can be attended with the calculated weights:", + "bbox": [ + 496, + 739, + 890, + 785 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {v} _ {i} = \\operatorname {S O F T M A X} \\left(S _ {i}\\right) \\cdot v _ {i}. \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 611, + 792, + 890, + 809 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.4. Geometry-Aware Temporal Modeling", + "text_level": 1, + "bbox": [ + 500, + 816, + 823, + 833 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Given the temporal nature of sounds and the persistence of audio-visual associations, we incorporate temporal information from neighboring frames to learn sounding object features. However, temporal modeling is a challenging", + "bbox": [ + 496, + 840, + 890, + 901 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "22913", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "problem for egocentric videos due to widespread egomotion and object-appearance deformations.", + "bbox": [ + 75, + 90, + 468, + 119 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Although visual objects are dynamically changing, the surrounding physical environment is persistent. Hence, temporal variations in egocentric videos reveal rich 3D geometric cues that can recover the surrounding scene from changing viewpoints. Prior works have shown that given a sequence of frames, one can reconstruct the underlying 3D scene from the 2D observations [64,81]. In our work, rather than reconstructing the 3D structures, we estimate the relative geometric transformation between frames to alleviate egomotion. Specifically, we apply the transformation at the feature level to perform geometry-aware temporal aggregation. Given $\\{I_i\\}_{i=1}^T$ and their features $\\{\\hat{v}_i\\}_{i=1}^T$ , we take $\\hat{v}_i$ as a query at a time and use the other features from neighboring frames as support features to aggregate temporal contexts. For clarity, we decompose the geometry-aware temporal aggregation into two parts: geometry modeling and temporal aggregation.", + "bbox": [ + 75, + 121, + 470, + 378 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Geometry modeling. This step aims to compute the geometric transformation that represents the egomotion between frames (see Fig. 3). We found that homography estimation, which can align images taken from different perspectives, can serve as a way to measure geometric transformation. We adopt SIFT [46] + RANSAC [18] to solve homography. To be specific, a homography is a $3 \\times 3$ matrix that consists of 8 degree of freedom (DOF) for scale, translation, rotation, and perspective respectively. Given the query frame $I_{i}$ and a supporting frame $I_{j}$ , we use $h(\\cdot)$ to denote the computation process:", + "bbox": [ + 75, + 378, + 470, + 544 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {H} _ {j i} = h \\left(I _ {j}, I _ {i}\\right) _ {j \\rightarrow i}, \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 200, + 554, + 468, + 571 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\mathcal{H}_{ji}$ represents the homography transformation from frame $I_{j}$ to $I_{i}$ . With the computed homography transformation, we can then apply it at the feature level to transform visual features $\\hat{v}_j$ to $\\hat{v}_{ji}$ . The $\\hat{v}_{ji}$ is egomotion-free under the viewpoint of $I_{i}$ . Since the resolution of feature maps is scaled down compared to the raw frame size, the homography matrix $\\mathcal{H}$ should also be downsampled using the same scaling factor. The feature transformation can be written as:", + "bbox": [ + 75, + 580, + 468, + 702 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {v} _ {j i} = \\mathcal {H} _ {j i} \\otimes \\hat {v} _ {j}, \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 217, + 715, + 468, + 733 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\otimes$ represents the warping operation.", + "bbox": [ + 75, + 738, + 359, + 752 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Temporal aggregation. For the query feature $\\hat{v}_i$ , we end up with set of aligned features $\\{\\hat{v}_{ji}\\}_{j=1}^{T}$ corresponding to each frame viewpoint. To aggregate the temporal contexts, we propose to compute the correlation between features from different frames at the same locations (see Fig. 4). The aggregation process can be formulated as:", + "bbox": [ + 75, + 752, + 468, + 844 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nz _ {i} (x, y) = \\hat {v} _ {i} (x, y) + \\operatorname {S O F T M A X} \\left(\\frac {\\hat {v} _ {i} (x , y) \\hat {\\boldsymbol {v}} (x , y) ^ {T}}{\\sqrt {d}}\\right) \\hat {\\boldsymbol {v}} (x, y), \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 76, + 852, + 468, + 901 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/040729c88d40b05b44f5ec95699dcd9bdd09cebd9cc8aafa20d089d931a93bba.jpg", + "image_caption": [ + "Figure 4. Illustration on the temporal context aggregation process for query feature $\\hat{v}_i$ and neighboring frame features $\\hat{v}_{i-1}$ and $\\hat{v}_{i+1}$ , which is performed independently at each spatial location." + ], + "image_footnote": [], + "bbox": [ + 532, + 90, + 859, + 186 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\hat{\\pmb{v}} = [\\hat{v}_{1i};\\dots;\\hat{v}_{Ti}]$ is the concatenation of frame features; the scaling factor $d$ is equal to the feature dimension; and $(\\cdot)^T$ represents the transpose operation [80]. The aggregation operation is applied at all spatial locations $(x,y)$ to generate the updated visual features $z_{i}$ .", + "bbox": [ + 498, + 252, + 890, + 329 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.5. Training Objective", + "text_level": 1, + "bbox": [ + 500, + 337, + 681, + 353 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We take audio-visual synchronization as the \"free\" supervision and solve the task in a self-supervised manner using contrastive learning [2,4,11,65].", + "bbox": [ + 498, + 359, + 890, + 406 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "With the audio feature vector $g_{\\hat{a}}$ and the visual features $\\{z_i\\}_{i=1}^T$ , we can compute an audio-visual attention map $S_i$ in Eq. 4 for each frame $I_i$ . The training objective should optimize the network such that only the sounding regions have a high response in $S_i$ . Since the ground-truth sounding map is unknown, we apply differential thresholding on $S_i$ to predict sounding objectness map $O_i = sigmoid((S_i - \\epsilon) / \\tau)$ [11], where $\\epsilon$ is the threshold, and $\\tau$ denotes the temperature that controls the sharpness.", + "bbox": [ + 498, + 406, + 890, + 541 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In an egocentric video clip, a visual scene is usually temporally dynamic. Sometimes a single audio-visual pair $(I_i,s)$ may not be audio-visually correlated. To this end, we solve the localization task in the Multiple-Instance Learning (MIL) [47] setting to improve robustness. Concretely, we use a soft MIL pooling function to aggregate the concatenated attention maps $S = [S_1;\\dots;S_T]$ by assigning different weights to $S_{t}$ at different time steps:", + "bbox": [ + 498, + 542, + 890, + 662 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\bar {S} = \\sum_ {t = 1} ^ {T} \\left(W _ {t} \\cdot \\boldsymbol {S}\\right) [:,:, t ], \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 612, + 674, + 890, + 714 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $W_{t}[x,y,:] = \\mathrm{SOFTMAX}(S[x,y,:])$ , $x$ and $y$ are the indices on spatial dimensions. Subsequently, an aggregated sounding objectness map $\\overline{O}$ is calculated from $\\overline{S}$ . In this way, for each video clip $V$ in the batch, we can define its positive and negative training signals as:", + "bbox": [ + 498, + 724, + 890, + 801 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nP = \\frac {1}{| \\bar {O} |} \\langle \\bar {O}, \\bar {S} \\rangle , \\quad N = \\frac {1}{h w} \\langle \\mathbf {1}, S _ {n e g} \\rangle , \\tag {10}\n$$\n", + "text_format": "latex", + "bbox": [ + 565, + 811, + 890, + 844 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\langle \\cdot ,\\cdot \\rangle$ is the Frobenius inner product.", + "bbox": [ + 500, + 854, + 781, + 869 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We obtain negative audio-visual attention maps $S_{\\text{neg}}$ by associating the current visual inputs $I$ with audio from other", + "bbox": [ + 500, + 869, + 890, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "22914", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/16f4c347bd6d5688c50d38ce7f65a9dd4e3908b56547207cb9965ddb6abba32a.jpg", + "image_caption": [ + "Squeeze packaging" + ], + "image_footnote": [], + "bbox": [ + 83, + 88, + 276, + 118 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/e78fd755ee6a7f2fe90c76c15c53a9bffdcb7976593f60deabb8eda79aa2982a.jpg", + "image_caption": [ + "Take out bottle" + ], + "image_footnote": [], + "bbox": [ + 84, + 126, + 276, + 154 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/fbf7288017d472bdd0f25c052e95b1a202e01172eb86345efad36918ff63b3e5.jpg", + "image_caption": [ + "Put pot", + "(a) Epic Sounding Object Dataset examples", + "Figure 5. Illustration of the Epic Sounding Object dataset statistics. (a) Example of our video frames and sounding object annotations. Class diversity (squeeze packaging, close trash can, put the pot, etc.) (b): The distribution of untrimmed video duration. (c): The number of videos that are annotated as containing out-of-view sounds. (d): Distribution of bounding box areas in Epic Sounding Object dataset, the majority of boxes cover less than $20\\%$ of the image area, demonstrating the difficulty of this task." + ], + "image_footnote": [], + "bbox": [ + 84, + 161, + 277, + 189 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/f21d3b0b2243e3ae50866820ed6666506885c7f7085448dba0abf91426c98546.jpg", + "image_caption": [ + "Stir meat" + ], + "image_footnote": [], + "bbox": [ + 277, + 88, + 472, + 118 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/39544f331674d69926cf69c46cc1d6d9b4a1f932f7ece2fd65ae211f2cbbe01a.jpg", + "image_caption": [ + "Close trash can" + ], + "image_footnote": [], + "bbox": [ + 279, + 125, + 470, + 154 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/bdf62fe0aeef2d8919389b0961bc77abdfeaa80c6fde8c0a0f3301c23d2cb460.jpg", + "image_caption": [ + "Wash spoon", + "(b) Duration of videos" + ], + "image_footnote": [], + "bbox": [ + 279, + 161, + 470, + 189 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/e2109ce2de80cfd4ca14ce9e80cf56452808140a63775fd712532aa4db7ab9af.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 490, + 103, + 589, + 181 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/86d877af01a069604f7117b97b50b6014c20b8a6fa057b8a8ed15703e8f24ee6.jpg", + "image_caption": [ + "(c) Num of out-of-view sounds" + ], + "image_footnote": [], + "bbox": [ + 601, + 104, + 720, + 181 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/1c22b4f33df9a18a90e2f63f07488d07bdd9774f2f0b6106ae4c5f0a663de38a.jpg", + "image_caption": [ + "(d) Sounding object area" + ], + "image_footnote": [], + "bbox": [ + 738, + 94, + 882, + 181 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "video clips. 1 denotes an all ones tensor with shape $h \\times w$ . Therefore, the localization optimization objective is:", + "bbox": [ + 76, + 306, + 467, + 338 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {l o c} = - \\frac {1}{N} \\sum_ {k = 1} ^ {N} \\left[ \\log \\frac {\\exp \\left(P _ {k}\\right)}{\\exp \\left(P _ {k}\\right) + \\exp \\left(N _ {k}\\right)} \\right], \\tag {11}\n$$\n", + "text_format": "latex", + "bbox": [ + 114, + 345, + 468, + 386 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $k$ is the video sample index in a training batch. The overall objective is $\\mathcal{L} = \\mathcal{L}_{loc} + \\lambda \\mathcal{L}_{dis}$ , where we empirically set $\\lambda = 5$ in our experiments.", + "bbox": [ + 76, + 393, + 468, + 441 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4. The Epic Sounding Object Dataset", + "text_level": 1, + "bbox": [ + 76, + 452, + 390, + 470 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Existing sound source visual localization evaluation datasets, such as SoundNet-Flickr [65], VGG-Sound Source [11], only contain third-person recordings. To the best of our knowledge, there is no existing dataset that is suitable for evaluating our model. Thus, we introduce an Epic Sounding Object Dataset for egocentric audio-visual sounding object localization. Built upon the well-known Epic-Kitchens [13] dataset, we collect sounding object annotations on its action recognition test set.", + "bbox": [ + 75, + 477, + 468, + 613 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Data preparation. We select 13k test videos from the Epic-Kitchens action recognition benchmark as our source data. Since these videos are not originally collected for audiovisual analysis, they vary in length, and not all of them contain meaningful sounds. To verify the videos for annotations, we conduct a two-step process: We first determine if a video is silent by checking its sound-level in decibels relative to full scale. Consequently, silent videos are filtered out to provide a meaningful data source. Second, we bin the videos by their duration and show the statistics in Fig. 5 (b). The majority last less than 2 seconds, and hence we choose to trim the center 1-second clip from each video.", + "bbox": [ + 75, + 613, + 468, + 794 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "After pre-processing, we obtain 5,089 videos in total for annotation. For each video, we uniformly select three frames and annotate sounding objects in the frames. We follow previous works [11,76] to use bounding boxes to annotate the objects that emit sounds. To obtain proposals of potential sounding objects automatically, we follow EpicKitchens [13] to use a Mask R-CNN object detector [25]", + "bbox": [ + 75, + 795, + 468, + 901 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/947cef83410e70948945c6fa33151d026489a7cb1119c88bd7229b50cc7ad09f.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
Before votingAfter voting
VideoFramesVideoFramesClasses
5,08915,2673,1729,19630
", + "bbox": [ + 519, + 304, + 874, + 364 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 1. Statistics of the Epic Sounding Object dataset.", + "bbox": [ + 531, + 376, + 857, + 390 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "trained on MS-COCO [43] and a hand-objects detector [68] that is pretrained with 42K egocentric images [13,42,69].", + "bbox": [ + 496, + 402, + 890, + 431 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Annotation collection. Given the pre-processed data, we then annotate the sounding objects manually. Unlike third-person view videos, the object-sound associations in the egocentric domain are more complicated. There are two main challenges: (i) Numerous egocentric videos record wearer-environment interaction (e.g., a human places a dish on the table). The object-sound associations could be dynamic, and sometimes it is hard to determine what objects are emitting sounds; and (ii) the objects in egocentric videos are often missing from the screen, resulting in variations in scale (see Fig. 5 (c)). We address the above issues by taking advantage of human commonsense knowledge. We ask three or more annotators from the Amazon Mechanic Turk to annotate the same video (frames). Concretely, they do this by first watching the 1-second video with three annotated frames to confirm what objects make sounds in the video. During the annotation course, they are asked to answer two questions: (1) Does the video contain out-of-view sounds? (2) Which bounding boxes correspond to the sounding objects? We collect the annotations in multiple rounds until each video has at least three or more valid annotations from the Amazon annotators. Finally, we conduct an annotation verification by voting on all videos. If at least two annotators agree on the same answer, it will be considered as a correct annotation; If not, we will simply omit the video. The annotation statistics after voting are shown in Tab. 1. We obtain 30 classes of sounds by counting the noun (object) classes. The annotations are evenly split into two sets for validation and testing. The examples and statistics in Fig. 5 illustrate the diverse and complicated nature of egocentric audio-visual scenes.", + "bbox": [ + 496, + 433, + 892, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "22915", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/6e5e8c9971c634038c219afcaf7fca327c471303b1df78a7847c11c2f96551ba.jpg", + "image_caption": [ + "Figure 6. Qualitative comparison on Epic Sounding Object dataset. We show diverse sounding objects in the kitchen scenes in the first column, sounding objects are annotated in red boxes. Our method outperforms all the compared works." + ], + "image_footnote": [], + "bbox": [ + 81, + 89, + 460, + 339 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5. Experiment", + "text_level": 1, + "bbox": [ + 76, + 417, + 200, + 435 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Datasets. In our experiments, we use two egocentric datasets. (1) Epic-Kitchens [13]: The dataset consists of 100 hours of egocentric recordings from 45 kitchen scenes. Thus, diverse kitchen-relevant events and sounds are in the dataset. We follow the same data split released in their action recognition benchmark and select 62,413 training videos. We then filter out the silent videos by measuring the Decibels relative to full scale. This results in 47,214 training videos in total. For evaluation, we use our annotated Epic Sounding Object dataset to report the results; (2) Ego4D [24]: Ego4D is the most recent large-scale egocentric video dataset. Besides kitchen scenes, it includes diverse daily life scenarios. Specifically, it consists of different subsets serving different benchmarks. We select the \"Bristol\" subset as it contains diverse scenarios (e.g., entertainment, sports, commuting, and more) to test our method. We randomly sample and trim 50,000 1-second videos from this subset and use $90\\% / 10\\%$ as the train/test split. A similar filtering strategy is applied to obtain 26,858 videos for training. We conduct experiments in Sec. 5.1.3 on this dataset to showcase the generalization ability of our method.", + "bbox": [ + 75, + 446, + 468, + 763 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Evaluation metric. We follow the prior works [11, 28, 38] and adopt the pixel-level measurement for evaluating localization performance. Given the ground truth sounding object bounding boxes, we compute the Consensus Intersection over Union (CIoU) and Area Under Curve (AUC) between the predicted localization map and ground truth boxes. We report CIoU over a range of thresholds to expose the finer aspects of comparison.", + "bbox": [ + 75, + 763, + 467, + 885 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Implementation details. To facilitate the training, we cut", + "bbox": [ + 76, + 885, + 467, + 900 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/bfce1e5baa325b1f17b6974425ba0b972881fb7e0f9ce4a7150d50892da25666.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
CIoUAUC
@0.2@0.3@0.4
Attention [65]7.12--6.42
STM [38]12.107.644.018.87
Hardway [11]24.5113.556.1013.38
SSPL [71]13.628.104.459.56
Mix [28]26.0115.259.9015.39
Our38.7119.4210.5118.38
", + "bbox": [ + 517, + 88, + 870, + 224 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 2. Quantitative comparison of localization results on Epic Sounding Object dataset. All methods are re-trained on EpicKitchen. The results of metrics CIoU@{0.2, 0.3, 0.4} and AUC are reported. The top-1 results are highlighted.", + "bbox": [ + 498, + 229, + 890, + 285 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "a 1-second long video around the center of each raw video. We select the middle frame from the video clip and its four neighboring frames with an interval of 2 between frames. Consequently, we get $T = 5$ frames as visual input. During training, the frames are first resized to $256 \\times 256$ and then randomly cropped to $224 \\times 224$ . During inference, all the frames are directly resized to the desired size without cropping. For the audio stream, we extract the corresponding 1-second audio clip to create the audio-visual pairs. The audio waveform is sub-sampled at $11\\mathrm{kHz}$ and transformed into a spectrogram with a Hann window of size 254 and a hop length of 64. The obtained spectrogram is subsequently resampled to $128 \\times 128$ to feed into the audio network. We set the number of audio and visual feature channels as 512 and choose $\\epsilon = 0.5$ and $\\tau = 0.03$ . All models are trained with the Adam optimizer, with a learning rate of $10^{-4}$ on the visual encoder and temporal network, while using a learning rate of $10^{-2}$ for updating the audio encoder.", + "bbox": [ + 496, + 299, + 890, + 571 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.1. Results", + "text_level": 1, + "bbox": [ + 500, + 583, + 591, + 598 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.1.1 Experimental Comparison", + "text_level": 1, + "bbox": [ + 500, + 607, + 738, + 623 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "To validate the effectiveness of our framework, we compare it with recent audio-visual localization methods: Attention [65], STM [38], Hardway [11], SSPL [71] and Mix [28]. Among all the comparative methods, STM [38] utilizes weak labels for the training, while the other methods are trained with self-supervision. We hence adjust STM [38] with our self-supervised localization loss. As all the methods are developed for third-person view videos, we retrain their methods on our training data for a fair comparison. The quantitative results are shown in Tab. 2. We can find that our method outperforms all the compared approaches by a large margin in all metrics, indicating the benefits of mitigating out-of-view sounds and explicitly modeling egomotion in learning egocentric audio-visual localization. Moreover, we provide a qualitative comparison to visually showcase our localization results. In Fig. 6, we can see that our model produces localization results that are tight around the ground truth sounding objects.", + "bbox": [ + 496, + 632, + 890, + 904 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "22916", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/8227cf81531c31f827340514e2ddb6cc89b6ecedffbbefd34c93cd7fab7b595c.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
ModelTMSLLdisCIoU@0.2AUC
AvgMaxGA
a27.4115.36
b✓31.8415.79
c✓33.2916.10
d✓37.3816.59
f✓✓38.2117.92
g✓✓✓38.7118.38
", + "bbox": [ + 86, + 88, + 459, + 224 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 3. Ablations on GATM, SL, and audio disentanglement module. The top-1 result in each column is highlighted.", + "bbox": [ + 76, + 229, + 468, + 258 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5.1.2 Ablation Study", + "text_level": 1, + "bbox": [ + 76, + 271, + 236, + 286 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We conduct an ablation study to illustrate how each module affects localization performance. As shown in Tab. 3, we compare our full model with different baselines — model a: we remove all the modules and only use the features from the visual and audio encoders to compute the localization map; model b-d: we insert Average, Max, and Geometry-Aware Temporal modeling approaches separately in the framework; in model f, we incorporate the soft localization (SL) into the pipeline; and in model g, we employ the audio disentanglement module and train the model with $L_{dis}$ . By comparing a and b-c, we found that it's crucial to aggregate temporal context, while d emphasizes the importance of GATM in mitigating the egomotion in egocentric videos. model d vs. f shows that SL slightly enhances the performance since some of the unrelated visual content can be reweighted. The comparison between f and g demonstrates that by incorporating audio feature disentanglement, the localization performance can be further boosted because it can handle the out-of-view sounds in videos.", + "bbox": [ + 75, + 287, + 468, + 574 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Naive baseline. To assess the difficulty of the task, we provide a center box method that predicts a gaussian heatmap around the center. This results in a naive baseline of 16.51 compared to 27.41 (model a) from Tab. 3, showing that there are various challenging scenarios apart from the object being in the center that this naive baseline cannot capture.", + "bbox": [ + 75, + 575, + 468, + 667 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5.1.3 Generalization to More Scenarios", + "text_level": 1, + "bbox": [ + 76, + 678, + 366, + 691 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "The experiments on Epic Sounding Object dataset demonstrate the effectiveness of our method in localizing sounding objects in the egocentric videos. To further validate the generalization ability of our method, we train our audio-visual sounding object localization network on Ego4D [24] and qualitatively showcase the localization results in Fig. 7. The examples are all selected from the Ego4D test set. We can see that our model can learn audio-visual associations and localize the sounding objects in diverse scenes.", + "bbox": [ + 75, + 695, + 468, + 830 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "6. Discussions and Conclusions", + "text_level": 1, + "bbox": [ + 76, + 845, + 346, + 861 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this work, we tackle a fundamental task: egocentric audio-visual localization to promote the field of study in", + "bbox": [ + 76, + 869, + 468, + 901 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/6589a18f80e29947fd2bef09a8dc15113f80c27a08f4144175035b96a15b15ca.jpg", + "image_caption": [ + "Figure 7. Localization results on diverse scenarios in Ego4D [24]. Ref.: Sounding objects; Pred.: predicted localization results." + ], + "image_footnote": [], + "bbox": [ + 506, + 90, + 887, + 251 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "egocentric audio-visual video understanding. The uniqueness of egocentric videos, such as egomotions and out-of-view sounds pose significant challenges to learning fine-grained audio-visual associations. To address these problems, we propose a new framework with a cascaded feature enhancement module to disentangle visually indicated audio representations and a geometry-aware temporal modeling module to mitigate egomotion. Extensive experiments on our annotated Epic Sounding Object dataset underpin the findings that explicitly mitigating out-of-view sounds and egomotion can boost localization performance and learn the better audio-visual association for egocentric videos.", + "bbox": [ + 496, + 316, + 890, + 498 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Limitations. The proposed geometry-aware temporal modeling approach requires geometric transformation computation. For certain visual scenes with severe illumination changes or drastic motions, the homography estimation may fail. Then, our GATM will degrade to a vanilla temporal modeling approach. To mitigate the issue, we can consider designing a more robust geometric estimation approach.", + "bbox": [ + 496, + 500, + 890, + 604 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Potential Applications. Our work offers potential for several applications: (a) Audio-visual episodic memory. As egocentric video records what and where of an individual's daily life experience, it would be interesting to build an intelligent AR assistant to localize the object (\"where did I use it?\") by processing an audio query, e.g., an audio clip of \"vacuum cleaner\"; (b) Audio-visual object state recognition. In egocentric research, it is important to know the state of objects that human is interacting with, while the human-object interaction often makes a sound. Therefore, localizing objects by sounds provides a new angle in recognizing an object state; (c) Audio-visual future anticipation: following the audio-visual object state recognition task, it's natural to predict the trajectory of a sounding object by analyzing the most recent audio-visual clips.", + "bbox": [ + 496, + 604, + 892, + 832 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 500, + 847, + 596, + 862 + ], + "page_idx": 7 + }, + { + "type": "ref_text", + "text": "[1] Yazan Abu Farha, Alexander Richard, and Juergen Gall. When will you do what?-anticipating temporal occurrences", + "bbox": [ + 506, + 872, + 890, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "22917", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "of activities. 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In Proceedings of the IEEE International Conference on Computer Vision, pages 4498-4506, 2015. 2" + ], + "bbox": [ + 78, + 90, + 468, + 500 + ], + "page_idx": 11 + }, + { + "type": "page_number", + "text": "22921", + "bbox": [ + 478, + 945, + 517, + 955 + ], + "page_idx": 11 + } +] \ No newline at end of file diff --git a/2023/Egocentric Audio-Visual Object Localization/ba22c8dd-0e4e-4696-a837-4a7f7a179a45_model.json b/2023/Egocentric Audio-Visual Object Localization/ba22c8dd-0e4e-4696-a837-4a7f7a179a45_model.json new file mode 100644 index 0000000000000000000000000000000000000000..8560fed7a4be9ccedd52d722804acaaf3d212a07 --- /dev/null +++ b/2023/Egocentric Audio-Visual Object Localization/ba22c8dd-0e4e-4696-a837-4a7f7a179a45_model.json @@ -0,0 +1,2732 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.259, + 0.131, + 0.711, + 0.153 + ], + "angle": 0, + "content": "Egocentric Audio-Visual Object Localization" + }, + { + "type": "text", + "bbox": [ + 0.24, + 0.18, + 0.728, + 0.217 + ], + "angle": 0, + "content": "Chao Huang\\(^{1}\\), Yapeng Tian\\(^{1}\\), Anurag Kumar\\(^{2}\\), Chenliang Xu\\(^{1}\\) \n\\(^{1}\\)University of Rochester, \\(^{2}\\)Meta Reality Labs Research" + }, + { + "type": "text", + "bbox": [ + 0.168, + 0.22, + 0.802, + 0.234 + ], + "angle": 0, + "content": "{chaohuang, yapengtian, chenliang.xu}@rochester.edu, anuragkr90@meta.com" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.269, + 0.314, + 0.285 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.302, + 0.474, + 0.695 + ], + "angle": 0, + "content": "Humans naturally perceive surrounding scenes by unifying sound and sight from a first-person view. Likewise, machines are advanced to approach human intelligence by learning with multisensory inputs from an egocentric perspective. In this paper, we explore the challenging egocentric audio-visual object localization task and observe that 1) egomotion commonly exists in first-person recordings, even within a short duration; 2) The out-of-view sound components can be created when wearers shift their attention. To address the first problem, we propose a geometry-aware temporal aggregation module that handles the egomotion explicitly. The effect of egomotion is mitigated by estimating the temporal geometry transformation and exploiting it to update visual representations. Moreover, we propose a cascaded feature enhancement module to overcome the second issue. It improves cross-modal localization robustness by disentangling visually-indicated audio representation. During training, we take advantage of the naturally occurring audio-visual temporal synchronization as the \"free\" self-supervision to avoid costly labeling. We also annotate and create the Epic Sounding Object dataset for evaluation purposes. Extensive experiments show that our method achieves state-of-the-art localization performance in egocentric videos and can be generalized to diverse audio-visual scenes. Code is available at https://github.com/WikiChao/Ego-AV-Loc." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.724, + 0.208, + 0.739 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.75, + 0.47, + 0.886 + ], + "angle": 0, + "content": "The emergence of wearable devices has drawn the attention of the research community to egocentric videos, the significance of which can be seen from egocentric research in a variety of applications such as robotics [32,34,48], augmented/virtual reality [31,61,75], and healthcare [53,66]. In recent years, the computer vision community has made substantial efforts to build benchmarks [12, 13, 15, 40, 57, 69], establish new tasks [17, 36, 37, 39, 60], and develop frameworks [33,41,54,82] for egocentric video understanding." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.886, + 0.47, + 0.901 + ], + "angle": 0, + "content": "While existing works achieve promising results in the" + }, + { + "type": "image", + "bbox": [ + 0.505, + 0.268, + 0.891, + 0.422 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.431, + 0.893, + 0.515 + ], + "angle": 0, + "content": "Figure 1. Sounding object localization in egocentric videos. Due to the wearer's egomotion, the viewpoint changes continuously across time. Consequently, audio-visual relations are dynamically changing in egocentric videos. Our approach tackles challenges in the egocentric audio-visual sounding object task and learns audio-visual associations from first-person videos." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.524, + 0.893, + 0.825 + ], + "angle": 0, + "content": "egocentric domain, it still remains an interesting but challenging topic to perform fine-grained egocentric video understanding. For instance, understanding which object is emitting sound in a first-person recording is difficult for machines. As shown in Fig. 1, the wearer moves his/her head to put down the bottle. The frying pot which emits sound subsequently suffers deformation and occlusion due to the wearer's egomotion. Human speech outside the wearer's view also affects the machine's understanding of the current scene. This example reveals two significant challenges for designing powerful and robust egocentric video understanding systems: First, people with wearable devices usually record videos in naturalistic surroundings, where a variety of illumination conditions, object appearance, and motion patterns are shown. The dynamic visual variations introduce difficulties in accurate visual perception. Second, egocentric scenes are often perceived within a limited field of view (FoV). The common body and head movements cause frequent view changes (see Fig. 1), which brings object deformation and creates dynamic out-of-view content." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.826, + 0.894, + 0.901 + ], + "angle": 0, + "content": "Although a visual-only system may struggle to fully decode the surrounding information and perceive scenes in egocentric videos, audio provides stable and persistent signals associated with the depicted events. Instead of purely visual perception, numerous psychological and cognitive" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "22910" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.212 + ], + "angle": 0, + "content": "studies [6, 29, 67, 73] show that integration of auditory and visual signals is significant in human perception. Audio, as an essential but less focused modality, often provides synchronized and complementary information with the video stream. In contrast to the variability of first-person visual footage, sound describes the underlying scenes consistently. These natural characteristics make audio another indispensable ingredient for egocentric video understanding." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.213, + 0.471, + 0.544 + ], + "angle": 0, + "content": "To effectively leverage audio and visual information in egocentric videos, a pivotal problem is to analyze the fine-grained audio-visual association, specifically identifying which objects are emitting sounds in the scene. In this paper, we explore a novel egocentric audio-visual object localization task, which aims to associate audio with dynamic visual scenes and localize sounding objects in egocentric videos. Given the dynamic nature of egocentric videos, it is exceedingly challenging to link visual content from various viewpoints with audio captured from the entire space. Hence, we develop a new framework to model the distinct characteristics of egocentric videos by integrating audio. In the framework, we propose a geometry-aware temporal module to handle egomotion explicitly. Our approach mitigates the impact of egomotion by performing geometric transformations in the embedding space and aligning visual features from different frames. We further use the aligned features to leverage temporal contexts across frames to learn discriminative cues for localization. Additionally, we introduce a cascaded feature enhancement module to handle out-of-view sounds. The module helps mitigate audio noises and improves cross-modal localization robustness." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.545, + 0.47, + 0.695 + ], + "angle": 0, + "content": "Due to the dynamic nature of egocentric videos, it is hard and costly to label sounding objects for supervised training. To avoid tedious labeling, we formulate this task in a self-supervised manner, and our framework is trained with audio-visual temporal synchronization. Since there are no publicly available egocentric sounding object localization datasets, we annotate an Epic Sounding dataset to facilitate research in this field. Experimental results demonstrate that modeling egomotion and mitigating out-of-view sound can improve egocentric audio-visual localization performance." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.697, + 0.47, + 0.816 + ], + "angle": 0, + "content": "In summary, our contributions are: (1) the first systematic study on egocentric audio-visual sounding object localization; (2) an effective geometry-aware temporal aggregation approach to deal with unique egomotion; (3) a novel cascaded feature enhancement module to progressively inject localization cues; and (4) an Epic Sounding Object dataset with sounding object annotations to benchmark the localization performance in egocentric videos." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.83, + 0.22, + 0.846 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.47, + 0.903 + ], + "angle": 0, + "content": "Audio-visual learning in third-person view videos. Taking the natural audio-visual synchronization in videos, a large number of studies in the past few years have proposed" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.287 + ], + "angle": 0, + "content": "to jointly learn from both auditory and visual modalities. We have seen a spectrum of new audio-visual problems and applications, including visually guided sound source separation [16,20-23,63,76,87,88], audio-visual representation learning [2,3,5,26,35,58,59], audio-visual event localization [44,78,79,84], audio-visual video parsing [77,83], and sounding object visual localization [4, 11, 27, 28, 38, 51, 52, 62, 65, 71]. Most previous approaches learn audio-visual correlations from third-person videos, while the distinct challenges of audio-visual learning in egocentric videos are underexplored. Different from existing works, we propose an audio-visual learning framework to explicitly solve egomotion and out-of-view audio issues in egocentric videos." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.289, + 0.892, + 0.681 + ], + "angle": 0, + "content": "Egocentric video understanding. In the last decade, video scene understanding techniques thrived because of the well-defined third-person video datasets [7, 9, 49, 72]. Nevertheless, most of the algorithms are developed to tackle videos curated by human photographers. The natural characteristics of egocentric video data, e.g., view changes, large motions, and visual deformation, are not well-explored. To bridge this gap, multiple egocentric datasets [12, 13, 24, 36, 69, 74] have been collected. These datasets have significantly advanced investigations on egocentric video understanding problems, including activity recognition [33, 41, 89], human(hand)-object interaction [8, 14, 55, 68], anticipation [1, 19, 45, 70], and human body pose inferring [30, 56]. However, only a handful of audio-visual works [10, 33, 50, 85] is presented for egocentric video understanding. Among those, Kazakos et al. [33] proposed an audio-visual fusion network for action recognition, while Mittal et al. [50] used audible interactions as cues to learn state-aware visual representations in egocentric videos. There are limited studies in explicit egomotion mitigation and fine-grained audio-visual association learning in egocentric videos. Unlike past works, we tackle challenges in egocentric audio-visual data and propose a robust sounding object localization framework. To enable the research, we propose Epic Sounding Object dataset based on Epic-Kitchens [12, 13]." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.693, + 0.591, + 0.709 + ], + "angle": 0, + "content": "3. Method" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.718, + 0.892, + 0.84 + ], + "angle": 0, + "content": "Our goal is to localize sounding objects in egocentric videos visually. We start by formulating our egocentric audio-visual object localization task in Sec. 3.1. Our proposed method includes a feature extraction process (described in Sec. 3.2), a two-stage cascaded feature enhancement pipeline (in Sec. 3.3), and a geometry-aware temporal aggregation module (explained in Sec. 3.4). Finally, we summarize the overall training objective in Sec. 3.5." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.848, + 0.878, + 0.863 + ], + "angle": 0, + "content": "3.1. Problem Formulation and Method Overview" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.87, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Given an egocentric video clip \\( V = \\{I_i\\}_{i=1}^T \\) in \\( T \\) frames and its corresponding sound stream \\( s \\), sounding object vi" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.518, + 0.958 + ], + "angle": 0, + "content": "22911" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.159, + 0.089, + 0.817, + 0.341 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.349, + 0.896, + 0.42 + ], + "angle": 0, + "content": "Figure 2. An overview of our egocentric audio-visual object localization framework. In the beginning, our model extracts deep features from the video and audio streams. Then, the audio and visual features are fed into the cascaded feature enhancement module to inject localization cues for both branches. Such a module is additionally trained with \"mix-and-separation\" strategy. Next, our geometric-aware temporal modeling block leverages the relative geometric information between visual frames and performs temporal context aggregation to get the final visual features for localization." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.431, + 0.473, + 0.658 + ], + "angle": 0, + "content": "sual localization aims at predicting location maps \\(\\mathcal{O} = \\{O_i\\}_{i=1}^T\\) that represent sounding objects in the egocentric video. Specifically, \\(O_i(x,y) \\in \\{0,1\\}\\) and positive visual regions indicate locations of sounding objects. In real-world scenarios, the captured sound can be a mixture of multiple sound sources \\(s = \\sum_{n=1}^{N} s_n\\), where \\(s_n\\) is the \\(n\\)-th sound source and it could be out of view. For the visual input, the video frames may be captured from different viewpoints. To design a robust and effective egocentric audio-visual sounding object localization system, we should consider the above issues in egocentric audio and visual data and answer two key questions: (Q1) how to associate visual content with audio representations while out-of-view sounds may exist; (Q2) how to persistently associate audio features with visual content that are captured under different viewpoints." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.66, + 0.473, + 0.903 + ], + "angle": 0, + "content": "Due to the dynamic nature of egocentric videos, it is difficult and costly to annotate sounding objects for supervised training. To bypass the tedious labeling, we solve the egocentric audio-visual object localization task in a self-supervised manner. The proposed framework is shown in Fig. 2. Our model first extracts representations from the audio \\( s \\) and video clip \\( V \\). In order to handle Q1, we develop a cascaded feature enhancement module to disentangle visually indicated sound sources and attend to visual regions that correspond to the visible sound sources. To enable the disentanglement, we use on-screen sound separation task as the proxy and adopt a multi-task learning objective to train our model where the localization task is solved along with a sound-separation task. To deal with the egomotion in egocentric videos (Q2), we design a geometry-aware temporal modeling approach to mitigate the feature distortion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.431, + 0.895, + 0.492 + ], + "angle": 0, + "content": "brought by viewpoint changes and aggregate the visual features temporally. We take the audio-visual temporal synchronization as the supervision signal and estimate the localization map \\(\\tilde{O}_i\\)." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.499, + 0.684, + 0.515 + ], + "angle": 0, + "content": "3.2. Feature Extraction" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.523, + 0.892, + 0.628 + ], + "angle": 0, + "content": "Visual representation. We use a visual encoder network \\( E_{v} \\) to extract visual feature maps from each input frame \\( I_{i} \\). In our implementation, a pre-trained Dilated ResNet [86] model is adopted by removing the final fully-connected layer. We can subsequently obtain a group of feature maps \\( v_{i} = E_{v}(I_{i}) \\), where \\( v_{i} \\in \\mathbb{R}^{c \\times h_{v} \\times w_{v}} \\). Here \\( c \\) is the number of channels, and \\( h_{v} \\times w_{v} \\) denotes the spatial size." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.629, + 0.892, + 0.72 + ], + "angle": 0, + "content": "Audio representation. To extract audio representations from the input raw waveform, we first transform audio stream \\( s \\) into a magnitude spectrogram \\( X \\) with the short-time Fourier transform (STFT). Then, we extract audio features \\( a = E_{a}(X), a \\in \\mathbb{R}^{c \\times h_{a} \\times w_{a}} \\) by means of a CNN encoder \\( E_{a} \\) in the Time-Frequency (T-F) space." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.727, + 0.785, + 0.742 + ], + "angle": 0, + "content": "3.3. Cascaded Feature Enhancement" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.75, + 0.895, + 0.903 + ], + "angle": 0, + "content": "As discussed in Sec. 3.1, a sound source \\( s_n \\) in the mixture \\( s \\) could be out of view due to constant view changes in egocentric videos and the limited FoV. This poses challenges in visually localizing sound sources and performance can degrade when the audio-visual associations are not precise. To address this, we update the features in a cascaded fashion. We first force the network to learn disentangled audio representations from the mixture using visual guidance. Then we utilize the disentangled audio representations to inject the visual features with more localization cues." + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "22912" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.468, + 0.197 + ], + "angle": 0, + "content": "Disentanglement through sound source separation. Sound source localization objective can implicitly guide the system to learn disentangled audio features as the network will try to precisely localize the sound, and in turn, the on-screen sound will get disentangled from the rest. However, we formulate our problem in an unsupervised setting where labels for such localization objective are not available." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.199, + 0.468, + 0.349 + ], + "angle": 0, + "content": "Audio-visual sound separation task [23, 87] uses visual information as guidance to learn to separate individual sounds from a mixture. Given the visual guidance, it is expected that the learned representations primarily encode information from visually indicated sound sources. Hence we argue for a multi-task learning approach to solve our primary task. Along with the audio-visual sounding object localization task, the network also learns to disentangle visible audio representations from the mixture through a source separation task." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.363, + 0.468, + 0.484 + ], + "angle": 0, + "content": "- Training. We adopt the commonly used \"mix-and-separate\" strategy [23,87] for audio-visual sound separation. Given the current audio \\( s^{(1)} \\), we randomly sample another audio stream \\( s^{(2)} \\) from a different video and mix them together to generate input audio mixture \\( \\tilde{s} = s^{(1)} + s^{(2)} \\). We then obtain magnitude spectrograms \\( \\tilde{X}, X^{(1)}, X^{(2)} \\) for \\( \\tilde{s}, s^{(1)} \\) and \\( s^{(2)} \\) respectively. The audio features is then modified as \\( a = E_a(\\tilde{X}) \\)." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.495, + 0.468, + 0.555 + ], + "angle": 0, + "content": "- Inference. During inference, we take the original audio stream as input: \\( s = s^{(1)} \\) and \\( X = X^{(1)} \\) to extract visually correlated audio representations. Note that the audio features is \\( a = E_{a}(X) \\)." + }, + { + "type": "list", + "bbox": [ + 0.097, + 0.363, + 0.468, + 0.555 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.568, + 0.468, + 0.749 + ], + "angle": 0, + "content": "We define the audio disentanglement network as a network \\( f(\\cdot) \\), which produces the disentangled audio features \\( \\hat{a} \\in \\mathbb{R}^{c \\times h_a \\times w_a} \\). In this network, we want to associate the visual content with the audio representations to perform disentanglement in the embedding space. Concretely, we first apply spatial average pooling on each \\( v_i \\) and temporal max pooling along the time axis to obtain a visual feature vector \\( g_v \\in \\mathbb{R}^c \\). Then we replicate the visual feature vector \\( h_a \\times w_a \\) times and tile them to match the size of \\( a \\). We concatenate the visual and audio feature maps along the channel dimension and feed them into the network. Therefore, the audio feature disentanglement can be formulated as:" + }, + { + "type": "equation", + "bbox": [ + 0.16, + 0.764, + 0.468, + 0.781 + ], + "angle": 0, + "content": "\\[\n\\hat {a} = f \\left(\\operatorname {C O N C A T} [ a, \\operatorname {T I L E} \\left(g _ {v}\\right) ]\\right). \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.794, + 0.468, + 0.854 + ], + "angle": 0, + "content": "In practice, we implement the disentanglement network \\( f \\) using two 1x1 convolution layers. The audio feature \\( \\hat{a} \\) will be used for both separation mask and sounding object localization map generation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.468, + 0.902 + ], + "angle": 0, + "content": "To separate visible sounds, we add an audio decoder \\( D_{a} \\) following the disentanglement network to output a binary mask \\( M_{pred} = D_{a}(\\hat{a}) \\) (at the bottom of Fig. 2). U-Net" + }, + { + "type": "image", + "bbox": [ + 0.515, + 0.091, + 0.88, + 0.233 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.246, + 0.892, + 0.288 + ], + "angle": 0, + "content": "Figure 3. Overview of our proposed geometry-aware modeling approach. The visual features \\(\\hat{v}_j\\) are warped to viewpoint \\(i\\) by homography transformation." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.296, + 0.892, + 0.403 + ], + "angle": 0, + "content": "architectures [23] are used in the audio encoder \\( E_{a} \\) and decoder \\( D_{a} \\). We implement the \\( E_{a} \\) and \\( D_{a} \\) in five convolution and up-convolution layers, respectively. Details of the network architectures are provided in the Appendix. The ground truth separation mask \\( M_{gt} \\) can be calculated by determining whether the original input sound is dominant at locations \\( (u,v) \\) in the T-F space:" + }, + { + "type": "equation", + "bbox": [ + 0.571, + 0.409, + 0.891, + 0.427 + ], + "angle": 0, + "content": "\\[\nM _ {g t} (u, v) = \\left[ X ^ {(1)} (u, v) \\geq \\tilde {X} (u, v) \\right]. \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.435, + 0.891, + 0.48 + ], + "angle": 0, + "content": "To train the sound separator, we minimize the \\(\\ell_2\\) distance between the predicted and ground-truth masks as the disentanglement learning objective:" + }, + { + "type": "equation", + "bbox": [ + 0.607, + 0.487, + 0.891, + 0.505 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {d i s} = \\left| \\left| M _ {p r e d} - M _ {g t} \\right| \\right| _ {2} ^ {2}. \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.512, + 0.892, + 0.706 + ], + "angle": 0, + "content": "Soft localization. Similar to the out-of-view sounds, the visual frames may contain sound-irrelevant regions. In order to learn more precise audio-visual associations, we propose to highlight the spatial regions that are more likely to be correlated with the on-screen sounds by computing audio-visual attention. The attention map will indicate the correlation between audio and visual representations at different spatial locations. Given the output \\(\\hat{a}\\) from disentanglement network \\(f(\\cdot)\\), we apply max pooling on its time and frequency dimensions, obtaining an audio feature vector \\(g_{\\hat{a}}\\). Then at each spatial position (x,y) of visual feature \\(v_{i}\\), we compute the cosine similarity between audio and visual feature vectors:" + }, + { + "type": "equation", + "bbox": [ + 0.555, + 0.716, + 0.891, + 0.733 + ], + "angle": 0, + "content": "\\[\nS _ {i}: S _ {i} (x, y) = \\operatorname {C O S I N E S I M} \\left(v _ {i} (x, y), g _ {\\hat {a}}\\right). \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.74, + 0.891, + 0.786 + ], + "angle": 0, + "content": "SOFTMAX is then used on \\( S_{i} \\) to generate a soft mask that represents the audio-visual correspondence. Hence, each \\( v_{i} \\) can be attended with the calculated weights:" + }, + { + "type": "equation", + "bbox": [ + 0.612, + 0.794, + 0.891, + 0.81 + ], + "angle": 0, + "content": "\\[\n\\hat {v} _ {i} = \\operatorname {S O F T M A X} \\left(S _ {i}\\right) \\cdot v _ {i}. \\tag {5}\n\\]" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.818, + 0.824, + 0.834 + ], + "angle": 0, + "content": "3.4. Geometry-Aware Temporal Modeling" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.841, + 0.892, + 0.902 + ], + "angle": 0, + "content": "Given the temporal nature of sounds and the persistence of audio-visual associations, we incorporate temporal information from neighboring frames to learn sounding object features. However, temporal modeling is a challenging" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "22913" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.121 + ], + "angle": 0, + "content": "problem for egocentric videos due to widespread egomotion and object-appearance deformations." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.122, + 0.471, + 0.379 + ], + "angle": 0, + "content": "Although visual objects are dynamically changing, the surrounding physical environment is persistent. Hence, temporal variations in egocentric videos reveal rich 3D geometric cues that can recover the surrounding scene from changing viewpoints. Prior works have shown that given a sequence of frames, one can reconstruct the underlying 3D scene from the 2D observations [64,81]. In our work, rather than reconstructing the 3D structures, we estimate the relative geometric transformation between frames to alleviate egomotion. Specifically, we apply the transformation at the feature level to perform geometry-aware temporal aggregation. Given \\(\\{I_i\\}_{i=1}^T\\) and their features \\(\\{\\hat{v}_i\\}_{i=1}^T\\), we take \\(\\hat{v}_i\\) as a query at a time and use the other features from neighboring frames as support features to aggregate temporal contexts. For clarity, we decompose the geometry-aware temporal aggregation into two parts: geometry modeling and temporal aggregation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.379, + 0.471, + 0.545 + ], + "angle": 0, + "content": "Geometry modeling. This step aims to compute the geometric transformation that represents the egomotion between frames (see Fig. 3). We found that homography estimation, which can align images taken from different perspectives, can serve as a way to measure geometric transformation. We adopt SIFT [46] + RANSAC [18] to solve homography. To be specific, a homography is a \\(3 \\times 3\\) matrix that consists of 8 degree of freedom (DOF) for scale, translation, rotation, and perspective respectively. Given the query frame \\(I_{i}\\) and a supporting frame \\(I_{j}\\), we use \\(h(\\cdot)\\) to denote the computation process:" + }, + { + "type": "equation", + "bbox": [ + 0.202, + 0.555, + 0.47, + 0.573 + ], + "angle": 0, + "content": "\\[\n\\mathcal {H} _ {j i} = h \\left(I _ {j}, I _ {i}\\right) _ {j \\rightarrow i}, \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.581, + 0.47, + 0.703 + ], + "angle": 0, + "content": "where \\(\\mathcal{H}_{ji}\\) represents the homography transformation from frame \\(I_{j}\\) to \\(I_{i}\\). With the computed homography transformation, we can then apply it at the feature level to transform visual features \\(\\hat{v}_j\\) to \\(\\hat{v}_{ji}\\). The \\(\\hat{v}_{ji}\\) is egomotion-free under the viewpoint of \\(I_{i}\\). Since the resolution of feature maps is scaled down compared to the raw frame size, the homography matrix \\(\\mathcal{H}\\) should also be downsampled using the same scaling factor. The feature transformation can be written as:" + }, + { + "type": "equation", + "bbox": [ + 0.218, + 0.717, + 0.469, + 0.734 + ], + "angle": 0, + "content": "\\[\n\\hat {v} _ {j i} = \\mathcal {H} _ {j i} \\otimes \\hat {v} _ {j}, \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.739, + 0.36, + 0.753 + ], + "angle": 0, + "content": "where \\(\\otimes\\) represents the warping operation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.753, + 0.469, + 0.845 + ], + "angle": 0, + "content": "Temporal aggregation. For the query feature \\(\\hat{v}_i\\), we end up with set of aligned features \\(\\{\\hat{v}_{ji}\\}_{j=1}^{T}\\) corresponding to each frame viewpoint. To aggregate the temporal contexts, we propose to compute the correlation between features from different frames at the same locations (see Fig. 4). The aggregation process can be formulated as:" + }, + { + "type": "equation", + "bbox": [ + 0.078, + 0.853, + 0.47, + 0.902 + ], + "angle": 0, + "content": "\\[\nz _ {i} (x, y) = \\hat {v} _ {i} (x, y) + \\operatorname {S O F T M A X} \\left(\\frac {\\hat {v} _ {i} (x , y) \\hat {\\boldsymbol {v}} (x , y) ^ {T}}{\\sqrt {d}}\\right) \\hat {\\boldsymbol {v}} (x, y), \\tag {8}\n\\]" + }, + { + "type": "image", + "bbox": [ + 0.534, + 0.092, + 0.861, + 0.188 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.197, + 0.892, + 0.24 + ], + "angle": 0, + "content": "Figure 4. Illustration on the temporal context aggregation process for query feature \\(\\hat{v}_i\\) and neighboring frame features \\(\\hat{v}_{i-1}\\) and \\(\\hat{v}_{i+1}\\), which is performed independently at each spatial location." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.253, + 0.892, + 0.33 + ], + "angle": 0, + "content": "where \\(\\hat{\\pmb{v}} = [\\hat{v}_{1i};\\dots;\\hat{v}_{Ti}]\\) is the concatenation of frame features; the scaling factor \\(d\\) is equal to the feature dimension; and \\((\\cdot)^T\\) represents the transpose operation [80]. The aggregation operation is applied at all spatial locations \\((x,y)\\) to generate the updated visual features \\(z_{i}\\)." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.338, + 0.682, + 0.354 + ], + "angle": 0, + "content": "3.5. Training Objective" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.361, + 0.892, + 0.407 + ], + "angle": 0, + "content": "We take audio-visual synchronization as the \"free\" supervision and solve the task in a self-supervised manner using contrastive learning [2,4,11,65]." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.407, + 0.892, + 0.542 + ], + "angle": 0, + "content": "With the audio feature vector \\( g_{\\hat{a}} \\) and the visual features \\( \\{z_i\\}_{i=1}^T \\), we can compute an audio-visual attention map \\( S_i \\) in Eq. 4 for each frame \\( I_i \\). The training objective should optimize the network such that only the sounding regions have a high response in \\( S_i \\). Since the ground-truth sounding map is unknown, we apply differential thresholding on \\( S_i \\) to predict sounding objectness map \\( O_i = sigmoid((S_i - \\epsilon) / \\tau) \\) [11], where \\( \\epsilon \\) is the threshold, and \\( \\tau \\) denotes the temperature that controls the sharpness." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.543, + 0.892, + 0.664 + ], + "angle": 0, + "content": "In an egocentric video clip, a visual scene is usually temporally dynamic. Sometimes a single audio-visual pair \\((I_i,s)\\) may not be audio-visually correlated. To this end, we solve the localization task in the Multiple-Instance Learning (MIL) [47] setting to improve robustness. Concretely, we use a soft MIL pooling function to aggregate the concatenated attention maps \\(S = [S_1;\\dots;S_T]\\) by assigning different weights to \\(S_{t}\\) at different time steps:" + }, + { + "type": "equation", + "bbox": [ + 0.614, + 0.675, + 0.892, + 0.715 + ], + "angle": 0, + "content": "\\[\n\\bar {S} = \\sum_ {t = 1} ^ {T} \\left(W _ {t} \\cdot \\boldsymbol {S}\\right) [:,:, t ], \\tag {9}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.726, + 0.892, + 0.803 + ], + "angle": 0, + "content": "where \\( W_{t}[x,y,:] = \\mathrm{SOFTMAX}(S[x,y,:]) \\), \\( x \\) and \\( y \\) are the indices on spatial dimensions. Subsequently, an aggregated sounding objectness map \\( \\overline{O} \\) is calculated from \\( \\overline{S} \\). In this way, for each video clip \\( V \\) in the batch, we can define its positive and negative training signals as:" + }, + { + "type": "equation", + "bbox": [ + 0.566, + 0.812, + 0.892, + 0.845 + ], + "angle": 0, + "content": "\\[\nP = \\frac {1}{| \\bar {O} |} \\langle \\bar {O}, \\bar {S} \\rangle , \\quad N = \\frac {1}{h w} \\langle \\mathbf {1}, S _ {n e g} \\rangle , \\tag {10}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.856, + 0.782, + 0.871 + ], + "angle": 0, + "content": "where \\(\\langle \\cdot ,\\cdot \\rangle\\) is the Frobenius inner product." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.871, + 0.892, + 0.901 + ], + "angle": 0, + "content": "We obtain negative audio-visual attention maps \\( S_{\\text{neg}} \\) by associating the current visual inputs \\( I \\) with audio from other" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "22914" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.084, + 0.089, + 0.277, + 0.119 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.087, + 0.119, + 0.155, + 0.126 + ], + "angle": 0, + "content": "Squeeze packaging" + }, + { + "type": "image", + "bbox": [ + 0.085, + 0.127, + 0.277, + 0.155 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.088, + 0.155, + 0.142, + 0.161 + ], + "angle": 0, + "content": "Take out bottle" + }, + { + "type": "image", + "bbox": [ + 0.086, + 0.162, + 0.278, + 0.19 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.088, + 0.19, + 0.116, + 0.197 + ], + "angle": 0, + "content": "Put pot" + }, + { + "type": "image", + "bbox": [ + 0.278, + 0.089, + 0.473, + 0.119 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.281, + 0.119, + 0.315, + 0.125 + ], + "angle": 0, + "content": "Stir meat" + }, + { + "type": "image", + "bbox": [ + 0.28, + 0.126, + 0.472, + 0.155 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.28, + 0.155, + 0.336, + 0.161 + ], + "angle": 0, + "content": "Close trash can" + }, + { + "type": "image", + "bbox": [ + 0.28, + 0.162, + 0.472, + 0.19 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.282, + 0.19, + 0.326, + 0.197 + ], + "angle": 0, + "content": "Wash spoon" + }, + { + "type": "image_caption", + "bbox": [ + 0.18, + 0.208, + 0.372, + 0.219 + ], + "angle": 0, + "content": "(a) Epic Sounding Object Dataset examples" + }, + { + "type": "image", + "bbox": [ + 0.491, + 0.104, + 0.591, + 0.182 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.485, + 0.208, + 0.585, + 0.219 + ], + "angle": 0, + "content": "(b) Duration of videos" + }, + { + "type": "image", + "bbox": [ + 0.602, + 0.105, + 0.721, + 0.182 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.607, + 0.208, + 0.745, + 0.219 + ], + "angle": 0, + "content": "(c) Num of out-of-view sounds" + }, + { + "type": "image", + "bbox": [ + 0.739, + 0.095, + 0.883, + 0.182 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.757, + 0.208, + 0.868, + 0.219 + ], + "angle": 0, + "content": "(d) Sounding object area" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.224, + 0.894, + 0.281 + ], + "angle": 0, + "content": "Figure 5. Illustration of the Epic Sounding Object dataset statistics. (a) Example of our video frames and sounding object annotations. Class diversity (squeeze packaging, close trash can, put the pot, etc.) (b): The distribution of untrimmed video duration. (c): The number of videos that are annotated as containing out-of-view sounds. (d): Distribution of bounding box areas in Epic Sounding Object dataset, the majority of boxes cover less than \\(20\\%\\) of the image area, demonstrating the difficulty of this task." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.307, + 0.468, + 0.339 + ], + "angle": 0, + "content": "video clips. 1 denotes an all ones tensor with shape \\( h \\times w \\). Therefore, the localization optimization objective is:" + }, + { + "type": "equation", + "bbox": [ + 0.115, + 0.346, + 0.469, + 0.387 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {l o c} = - \\frac {1}{N} \\sum_ {k = 1} ^ {N} \\left[ \\log \\frac {\\exp \\left(P _ {k}\\right)}{\\exp \\left(P _ {k}\\right) + \\exp \\left(N _ {k}\\right)} \\right], \\tag {11}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.395, + 0.47, + 0.442 + ], + "angle": 0, + "content": "where \\( k \\) is the video sample index in a training batch. The overall objective is \\( \\mathcal{L} = \\mathcal{L}_{loc} + \\lambda \\mathcal{L}_{dis} \\), where we empirically set \\( \\lambda = 5 \\) in our experiments." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.453, + 0.391, + 0.471 + ], + "angle": 0, + "content": "4. The Epic Sounding Object Dataset" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.478, + 0.469, + 0.614 + ], + "angle": 0, + "content": "Existing sound source visual localization evaluation datasets, such as SoundNet-Flickr [65], VGG-Sound Source [11], only contain third-person recordings. To the best of our knowledge, there is no existing dataset that is suitable for evaluating our model. Thus, we introduce an Epic Sounding Object Dataset for egocentric audio-visual sounding object localization. Built upon the well-known Epic-Kitchens [13] dataset, we collect sounding object annotations on its action recognition test set." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.614, + 0.469, + 0.795 + ], + "angle": 0, + "content": "Data preparation. We select 13k test videos from the Epic-Kitchens action recognition benchmark as our source data. Since these videos are not originally collected for audiovisual analysis, they vary in length, and not all of them contain meaningful sounds. To verify the videos for annotations, we conduct a two-step process: We first determine if a video is silent by checking its sound-level in decibels relative to full scale. Consequently, silent videos are filtered out to provide a meaningful data source. Second, we bin the videos by their duration and show the statistics in Fig. 5 (b). The majority last less than 2 seconds, and hence we choose to trim the center 1-second clip from each video." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.796, + 0.469, + 0.902 + ], + "angle": 0, + "content": "After pre-processing, we obtain 5,089 videos in total for annotation. For each video, we uniformly select three frames and annotate sounding objects in the frames. We follow previous works [11,76] to use bounding boxes to annotate the objects that emit sounds. To obtain proposals of potential sounding objects automatically, we follow EpicKitchens [13] to use a Mask R-CNN object detector [25]" + }, + { + "type": "table", + "bbox": [ + 0.52, + 0.305, + 0.875, + 0.366 + ], + "angle": 0, + "content": "
Before votingAfter voting
VideoFramesVideoFramesClasses
5,08915,2673,1729,19630
" + }, + { + "type": "table_caption", + "bbox": [ + 0.532, + 0.377, + 0.859, + 0.391 + ], + "angle": 0, + "content": "Table 1. Statistics of the Epic Sounding Object dataset." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.403, + 0.892, + 0.433 + ], + "angle": 0, + "content": "trained on MS-COCO [43] and a hand-objects detector [68] that is pretrained with 42K egocentric images [13,42,69]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.434, + 0.893, + 0.901 + ], + "angle": 0, + "content": "Annotation collection. Given the pre-processed data, we then annotate the sounding objects manually. Unlike third-person view videos, the object-sound associations in the egocentric domain are more complicated. There are two main challenges: (i) Numerous egocentric videos record wearer-environment interaction (e.g., a human places a dish on the table). The object-sound associations could be dynamic, and sometimes it is hard to determine what objects are emitting sounds; and (ii) the objects in egocentric videos are often missing from the screen, resulting in variations in scale (see Fig. 5 (c)). We address the above issues by taking advantage of human commonsense knowledge. We ask three or more annotators from the Amazon Mechanic Turk to annotate the same video (frames). Concretely, they do this by first watching the 1-second video with three annotated frames to confirm what objects make sounds in the video. During the annotation course, they are asked to answer two questions: (1) Does the video contain out-of-view sounds? (2) Which bounding boxes correspond to the sounding objects? We collect the annotations in multiple rounds until each video has at least three or more valid annotations from the Amazon annotators. Finally, we conduct an annotation verification by voting on all videos. If at least two annotators agree on the same answer, it will be considered as a correct annotation; If not, we will simply omit the video. The annotation statistics after voting are shown in Tab. 1. We obtain 30 classes of sounds by counting the noun (object) classes. The annotations are evenly split into two sets for validation and testing. The examples and statistics in Fig. 5 illustrate the diverse and complicated nature of egocentric audio-visual scenes." + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "22915" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.09, + 0.462, + 0.34 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.344, + 0.47, + 0.4 + ], + "angle": 0, + "content": "Figure 6. Qualitative comparison on Epic Sounding Object dataset. We show diverse sounding objects in the kitchen scenes in the first column, sounding objects are annotated in red boxes. Our method outperforms all the compared works." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.418, + 0.201, + 0.436 + ], + "angle": 0, + "content": "5. Experiment" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.448, + 0.47, + 0.765 + ], + "angle": 0, + "content": "Datasets. In our experiments, we use two egocentric datasets. (1) Epic-Kitchens [13]: The dataset consists of 100 hours of egocentric recordings from 45 kitchen scenes. Thus, diverse kitchen-relevant events and sounds are in the dataset. We follow the same data split released in their action recognition benchmark and select 62,413 training videos. We then filter out the silent videos by measuring the Decibels relative to full scale. This results in 47,214 training videos in total. For evaluation, we use our annotated Epic Sounding Object dataset to report the results; (2) Ego4D [24]: Ego4D is the most recent large-scale egocentric video dataset. Besides kitchen scenes, it includes diverse daily life scenarios. Specifically, it consists of different subsets serving different benchmarks. We select the \"Bristol\" subset as it contains diverse scenarios (e.g., entertainment, sports, commuting, and more) to test our method. We randomly sample and trim 50,000 1-second videos from this subset and use \\(90\\% / 10\\%\\) as the train/test split. A similar filtering strategy is applied to obtain 26,858 videos for training. We conduct experiments in Sec. 5.1.3 on this dataset to showcase the generalization ability of our method." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.765, + 0.468, + 0.886 + ], + "angle": 0, + "content": "Evaluation metric. We follow the prior works [11, 28, 38] and adopt the pixel-level measurement for evaluating localization performance. Given the ground truth sounding object bounding boxes, we compute the Consensus Intersection over Union (CIoU) and Area Under Curve (AUC) between the predicted localization map and ground truth boxes. We report CIoU over a range of thresholds to expose the finer aspects of comparison." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.886, + 0.468, + 0.901 + ], + "angle": 0, + "content": "Implementation details. To facilitate the training, we cut" + }, + { + "type": "table", + "bbox": [ + 0.518, + 0.089, + 0.872, + 0.226 + ], + "angle": 0, + "content": "
CIoUAUC
@0.2@0.3@0.4
Attention [65]7.12--6.42
STM [38]12.107.644.018.87
Hardway [11]24.5113.556.1013.38
SSPL [71]13.628.104.459.56
Mix [28]26.0115.259.9015.39
Our38.7119.4210.5118.38
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.23, + 0.892, + 0.286 + ], + "angle": 0, + "content": "Table 2. Quantitative comparison of localization results on Epic Sounding Object dataset. All methods are re-trained on EpicKitchen. The results of metrics CIoU@{0.2, 0.3, 0.4} and AUC are reported. The top-1 results are highlighted." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.3, + 0.892, + 0.572 + ], + "angle": 0, + "content": "a 1-second long video around the center of each raw video. We select the middle frame from the video clip and its four neighboring frames with an interval of 2 between frames. Consequently, we get \\( T = 5 \\) frames as visual input. During training, the frames are first resized to \\( 256 \\times 256 \\) and then randomly cropped to \\( 224 \\times 224 \\). During inference, all the frames are directly resized to the desired size without cropping. For the audio stream, we extract the corresponding 1-second audio clip to create the audio-visual pairs. The audio waveform is sub-sampled at \\( 11\\mathrm{kHz} \\) and transformed into a spectrogram with a Hann window of size 254 and a hop length of 64. The obtained spectrogram is subsequently resampled to \\( 128 \\times 128 \\) to feed into the audio network. We set the number of audio and visual feature channels as 512 and choose \\( \\epsilon = 0.5 \\) and \\( \\tau = 0.03 \\). All models are trained with the Adam optimizer, with a learning rate of \\( 10^{-4} \\) on the visual encoder and temporal network, while using a learning rate of \\( 10^{-2} \\) for updating the audio encoder." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.584, + 0.593, + 0.599 + ], + "angle": 0, + "content": "5.1. Results" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.608, + 0.74, + 0.624 + ], + "angle": 0, + "content": "5.1.1 Experimental Comparison" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.633, + 0.892, + 0.905 + ], + "angle": 0, + "content": "To validate the effectiveness of our framework, we compare it with recent audio-visual localization methods: Attention [65], STM [38], Hardway [11], SSPL [71] and Mix [28]. Among all the comparative methods, STM [38] utilizes weak labels for the training, while the other methods are trained with self-supervision. We hence adjust STM [38] with our self-supervised localization loss. As all the methods are developed for third-person view videos, we retrain their methods on our training data for a fair comparison. The quantitative results are shown in Tab. 2. We can find that our method outperforms all the compared approaches by a large margin in all metrics, indicating the benefits of mitigating out-of-view sounds and explicitly modeling egomotion in learning egocentric audio-visual localization. Moreover, we provide a qualitative comparison to visually showcase our localization results. In Fig. 6, we can see that our model produces localization results that are tight around the ground truth sounding objects." + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "22916" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.088, + 0.089, + 0.46, + 0.226 + ], + "angle": 0, + "content": "
ModelTMSLLdisCIoU@0.2AUC
AvgMaxGA
a27.4115.36
b✓31.8415.79
c✓33.2916.10
d✓37.3816.59
f✓✓38.2117.92
g✓✓✓38.7118.38
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.23, + 0.47, + 0.259 + ], + "angle": 0, + "content": "Table 3. Ablations on GATM, SL, and audio disentanglement module. The top-1 result in each column is highlighted." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.272, + 0.238, + 0.287 + ], + "angle": 0, + "content": "5.1.2 Ablation Study" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.289, + 0.47, + 0.575 + ], + "angle": 0, + "content": "We conduct an ablation study to illustrate how each module affects localization performance. As shown in Tab. 3, we compare our full model with different baselines — model a: we remove all the modules and only use the features from the visual and audio encoders to compute the localization map; model b-d: we insert Average, Max, and Geometry-Aware Temporal modeling approaches separately in the framework; in model f, we incorporate the soft localization (SL) into the pipeline; and in model g, we employ the audio disentanglement module and train the model with \\( L_{dis} \\). By comparing a and b-c, we found that it's crucial to aggregate temporal context, while d emphasizes the importance of GATM in mitigating the egomotion in egocentric videos. model d vs. f shows that SL slightly enhances the performance since some of the unrelated visual content can be reweighted. The comparison between f and g demonstrates that by incorporating audio feature disentanglement, the localization performance can be further boosted because it can handle the out-of-view sounds in videos." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.577, + 0.469, + 0.668 + ], + "angle": 0, + "content": "Naive baseline. To assess the difficulty of the task, we provide a center box method that predicts a gaussian heatmap around the center. This results in a naive baseline of 16.51 compared to 27.41 (model a) from Tab. 3, showing that there are various challenging scenarios apart from the object being in the center that this naive baseline cannot capture." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.679, + 0.367, + 0.693 + ], + "angle": 0, + "content": "5.1.3 Generalization to More Scenarios" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.696, + 0.469, + 0.831 + ], + "angle": 0, + "content": "The experiments on Epic Sounding Object dataset demonstrate the effectiveness of our method in localizing sounding objects in the egocentric videos. To further validate the generalization ability of our method, we train our audio-visual sounding object localization network on Ego4D [24] and qualitatively showcase the localization results in Fig. 7. The examples are all selected from the Ego4D test set. We can see that our model can learn audio-visual associations and localize the sounding objects in diverse scenes." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.846, + 0.347, + 0.862 + ], + "angle": 0, + "content": "6. Discussions and Conclusions" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.469, + 0.902 + ], + "angle": 0, + "content": "In this work, we tackle a fundamental task: egocentric audio-visual localization to promote the field of study in" + }, + { + "type": "image", + "bbox": [ + 0.508, + 0.091, + 0.888, + 0.252 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.5, + 0.263, + 0.892, + 0.291 + ], + "angle": 0, + "content": "Figure 7. Localization results on diverse scenarios in Ego4D [24]. Ref.: Sounding objects; Pred.: predicted localization results." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.318, + 0.892, + 0.499 + ], + "angle": 0, + "content": "egocentric audio-visual video understanding. The uniqueness of egocentric videos, such as egomotions and out-of-view sounds pose significant challenges to learning fine-grained audio-visual associations. To address these problems, we propose a new framework with a cascaded feature enhancement module to disentangle visually indicated audio representations and a geometry-aware temporal modeling module to mitigate egomotion. Extensive experiments on our annotated Epic Sounding Object dataset underpin the findings that explicitly mitigating out-of-view sounds and egomotion can boost localization performance and learn the better audio-visual association for egocentric videos." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.5, + 0.892, + 0.606 + ], + "angle": 0, + "content": "Limitations. The proposed geometry-aware temporal modeling approach requires geometric transformation computation. For certain visual scenes with severe illumination changes or drastic motions, the homography estimation may fail. Then, our GATM will degrade to a vanilla temporal modeling approach. To mitigate the issue, we can consider designing a more robust geometric estimation approach." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.606, + 0.893, + 0.833 + ], + "angle": 0, + "content": "Potential Applications. Our work offers potential for several applications: (a) Audio-visual episodic memory. As egocentric video records what and where of an individual's daily life experience, it would be interesting to build an intelligent AR assistant to localize the object (\"where did I use it?\") by processing an audio query, e.g., an audio clip of \"vacuum cleaner\"; (b) Audio-visual object state recognition. In egocentric research, it is important to know the state of objects that human is interacting with, while the human-object interaction often makes a sound. Therefore, localizing objects by sounds provides a new angle in recognizing an object state; (c) Audio-visual future anticipation: following the audio-visual object state recognition task, it's natural to predict the trajectory of a sounding object by analyzing the most recent audio-visual clips." + }, + { + "type": "title", + "bbox": [ + 0.501, + 0.848, + 0.597, + 0.863 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.508, + 0.873, + 0.892, + 0.901 + ], + "angle": 0, + "content": "[1] Yazan Abu Farha, Alexander Richard, and Juergen Gall. When will you do what?-anticipating temporal occurrences" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "22917" + } + ], + [ + { + "type": "ref_text", + "bbox": [ + 0.108, + 0.092, + 0.47, + 0.133 + ], + "angle": 0, + "content": "of activities. 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In Proceedings of the IEEE International Conference on Computer Vision, pages 4498-4506, 2015. 2" + }, + { + "type": "list", + "bbox": [ + 0.08, + 0.092, + 0.47, + 0.501 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.946, + 0.518, + 0.957 + ], + "angle": 0, + "content": "22921" + } + ] +] \ No newline at end of file diff --git a/2023/Egocentric Audio-Visual Object Localization/ba22c8dd-0e4e-4696-a837-4a7f7a179a45_origin.pdf b/2023/Egocentric Audio-Visual Object Localization/ba22c8dd-0e4e-4696-a837-4a7f7a179a45_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..a257fea093ae07d9f30780f9cbc94c29ebc340be --- /dev/null +++ b/2023/Egocentric Audio-Visual Object Localization/ba22c8dd-0e4e-4696-a837-4a7f7a179a45_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:978a5d377dc6df6fa5e06173b418c80d12065d7cd16d38ec96d242e8ce2b3245 +size 9656145 diff --git a/2023/Egocentric Audio-Visual Object Localization/full.md b/2023/Egocentric Audio-Visual Object Localization/full.md new file mode 100644 index 0000000000000000000000000000000000000000..aeae3cac746cc4b03c1b372941eb5f710d7f2ca8 --- /dev/null +++ b/2023/Egocentric Audio-Visual Object Localization/full.md @@ -0,0 +1,368 @@ +# Egocentric Audio-Visual Object Localization + +Chao Huang $^{1}$ , Yapeng Tian $^{1}$ , Anurag Kumar $^{2}$ , Chenliang Xu $^{1}$ $^{1}$ University of Rochester, $^{2}$ Meta Reality Labs Research + +{chaohuang, yapengtian, chenliang.xu}@rochester.edu, anuragkr90@meta.com + +# Abstract + +Humans naturally perceive surrounding scenes by unifying sound and sight from a first-person view. Likewise, machines are advanced to approach human intelligence by learning with multisensory inputs from an egocentric perspective. In this paper, we explore the challenging egocentric audio-visual object localization task and observe that 1) egomotion commonly exists in first-person recordings, even within a short duration; 2) The out-of-view sound components can be created when wearers shift their attention. To address the first problem, we propose a geometry-aware temporal aggregation module that handles the egomotion explicitly. The effect of egomotion is mitigated by estimating the temporal geometry transformation and exploiting it to update visual representations. Moreover, we propose a cascaded feature enhancement module to overcome the second issue. It improves cross-modal localization robustness by disentangling visually-indicated audio representation. During training, we take advantage of the naturally occurring audio-visual temporal synchronization as the "free" self-supervision to avoid costly labeling. We also annotate and create the Epic Sounding Object dataset for evaluation purposes. Extensive experiments show that our method achieves state-of-the-art localization performance in egocentric videos and can be generalized to diverse audio-visual scenes. Code is available at https://github.com/WikiChao/Ego-AV-Loc. + +# 1. Introduction + +The emergence of wearable devices has drawn the attention of the research community to egocentric videos, the significance of which can be seen from egocentric research in a variety of applications such as robotics [32,34,48], augmented/virtual reality [31,61,75], and healthcare [53,66]. In recent years, the computer vision community has made substantial efforts to build benchmarks [12, 13, 15, 40, 57, 69], establish new tasks [17, 36, 37, 39, 60], and develop frameworks [33,41,54,82] for egocentric video understanding. + +While existing works achieve promising results in the + +![](images/3719b6f38374c3c1571081325abefaa481fd944ba0f6e9b33211f0b2afa03920.jpg) +Figure 1. Sounding object localization in egocentric videos. Due to the wearer's egomotion, the viewpoint changes continuously across time. Consequently, audio-visual relations are dynamically changing in egocentric videos. Our approach tackles challenges in the egocentric audio-visual sounding object task and learns audio-visual associations from first-person videos. + +egocentric domain, it still remains an interesting but challenging topic to perform fine-grained egocentric video understanding. For instance, understanding which object is emitting sound in a first-person recording is difficult for machines. As shown in Fig. 1, the wearer moves his/her head to put down the bottle. The frying pot which emits sound subsequently suffers deformation and occlusion due to the wearer's egomotion. Human speech outside the wearer's view also affects the machine's understanding of the current scene. This example reveals two significant challenges for designing powerful and robust egocentric video understanding systems: First, people with wearable devices usually record videos in naturalistic surroundings, where a variety of illumination conditions, object appearance, and motion patterns are shown. The dynamic visual variations introduce difficulties in accurate visual perception. Second, egocentric scenes are often perceived within a limited field of view (FoV). The common body and head movements cause frequent view changes (see Fig. 1), which brings object deformation and creates dynamic out-of-view content. + +Although a visual-only system may struggle to fully decode the surrounding information and perceive scenes in egocentric videos, audio provides stable and persistent signals associated with the depicted events. Instead of purely visual perception, numerous psychological and cognitive + +studies [6, 29, 67, 73] show that integration of auditory and visual signals is significant in human perception. Audio, as an essential but less focused modality, often provides synchronized and complementary information with the video stream. In contrast to the variability of first-person visual footage, sound describes the underlying scenes consistently. These natural characteristics make audio another indispensable ingredient for egocentric video understanding. + +To effectively leverage audio and visual information in egocentric videos, a pivotal problem is to analyze the fine-grained audio-visual association, specifically identifying which objects are emitting sounds in the scene. In this paper, we explore a novel egocentric audio-visual object localization task, which aims to associate audio with dynamic visual scenes and localize sounding objects in egocentric videos. Given the dynamic nature of egocentric videos, it is exceedingly challenging to link visual content from various viewpoints with audio captured from the entire space. Hence, we develop a new framework to model the distinct characteristics of egocentric videos by integrating audio. In the framework, we propose a geometry-aware temporal module to handle egomotion explicitly. Our approach mitigates the impact of egomotion by performing geometric transformations in the embedding space and aligning visual features from different frames. We further use the aligned features to leverage temporal contexts across frames to learn discriminative cues for localization. Additionally, we introduce a cascaded feature enhancement module to handle out-of-view sounds. The module helps mitigate audio noises and improves cross-modal localization robustness. + +Due to the dynamic nature of egocentric videos, it is hard and costly to label sounding objects for supervised training. To avoid tedious labeling, we formulate this task in a self-supervised manner, and our framework is trained with audio-visual temporal synchronization. Since there are no publicly available egocentric sounding object localization datasets, we annotate an Epic Sounding dataset to facilitate research in this field. Experimental results demonstrate that modeling egomotion and mitigating out-of-view sound can improve egocentric audio-visual localization performance. + +In summary, our contributions are: (1) the first systematic study on egocentric audio-visual sounding object localization; (2) an effective geometry-aware temporal aggregation approach to deal with unique egomotion; (3) a novel cascaded feature enhancement module to progressively inject localization cues; and (4) an Epic Sounding Object dataset with sounding object annotations to benchmark the localization performance in egocentric videos. + +# 2. Related Work + +Audio-visual learning in third-person view videos. Taking the natural audio-visual synchronization in videos, a large number of studies in the past few years have proposed + +to jointly learn from both auditory and visual modalities. We have seen a spectrum of new audio-visual problems and applications, including visually guided sound source separation [16,20-23,63,76,87,88], audio-visual representation learning [2,3,5,26,35,58,59], audio-visual event localization [44,78,79,84], audio-visual video parsing [77,83], and sounding object visual localization [4, 11, 27, 28, 38, 51, 52, 62, 65, 71]. Most previous approaches learn audio-visual correlations from third-person videos, while the distinct challenges of audio-visual learning in egocentric videos are underexplored. Different from existing works, we propose an audio-visual learning framework to explicitly solve egomotion and out-of-view audio issues in egocentric videos. + +Egocentric video understanding. In the last decade, video scene understanding techniques thrived because of the well-defined third-person video datasets [7, 9, 49, 72]. Nevertheless, most of the algorithms are developed to tackle videos curated by human photographers. The natural characteristics of egocentric video data, e.g., view changes, large motions, and visual deformation, are not well-explored. To bridge this gap, multiple egocentric datasets [12, 13, 24, 36, 69, 74] have been collected. These datasets have significantly advanced investigations on egocentric video understanding problems, including activity recognition [33, 41, 89], human(hand)-object interaction [8, 14, 55, 68], anticipation [1, 19, 45, 70], and human body pose inferring [30, 56]. However, only a handful of audio-visual works [10, 33, 50, 85] is presented for egocentric video understanding. Among those, Kazakos et al. [33] proposed an audio-visual fusion network for action recognition, while Mittal et al. [50] used audible interactions as cues to learn state-aware visual representations in egocentric videos. There are limited studies in explicit egomotion mitigation and fine-grained audio-visual association learning in egocentric videos. Unlike past works, we tackle challenges in egocentric audio-visual data and propose a robust sounding object localization framework. To enable the research, we propose Epic Sounding Object dataset based on Epic-Kitchens [12, 13]. + +# 3. Method + +Our goal is to localize sounding objects in egocentric videos visually. We start by formulating our egocentric audio-visual object localization task in Sec. 3.1. Our proposed method includes a feature extraction process (described in Sec. 3.2), a two-stage cascaded feature enhancement pipeline (in Sec. 3.3), and a geometry-aware temporal aggregation module (explained in Sec. 3.4). Finally, we summarize the overall training objective in Sec. 3.5. + +# 3.1. Problem Formulation and Method Overview + +Given an egocentric video clip $V = \{I_i\}_{i=1}^T$ in $T$ frames and its corresponding sound stream $s$ , sounding object vi + +![](images/cba04654b8493f0991bd560f67b906f1d9de82f6b9779af9697eff747dd03de6.jpg) +Figure 2. An overview of our egocentric audio-visual object localization framework. In the beginning, our model extracts deep features from the video and audio streams. Then, the audio and visual features are fed into the cascaded feature enhancement module to inject localization cues for both branches. Such a module is additionally trained with "mix-and-separation" strategy. Next, our geometric-aware temporal modeling block leverages the relative geometric information between visual frames and performs temporal context aggregation to get the final visual features for localization. + +sual localization aims at predicting location maps $\mathcal{O} = \{O_i\}_{i=1}^T$ that represent sounding objects in the egocentric video. Specifically, $O_i(x,y) \in \{0,1\}$ and positive visual regions indicate locations of sounding objects. In real-world scenarios, the captured sound can be a mixture of multiple sound sources $s = \sum_{n=1}^{N} s_n$ , where $s_n$ is the $n$ -th sound source and it could be out of view. For the visual input, the video frames may be captured from different viewpoints. To design a robust and effective egocentric audio-visual sounding object localization system, we should consider the above issues in egocentric audio and visual data and answer two key questions: (Q1) how to associate visual content with audio representations while out-of-view sounds may exist; (Q2) how to persistently associate audio features with visual content that are captured under different viewpoints. + +Due to the dynamic nature of egocentric videos, it is difficult and costly to annotate sounding objects for supervised training. To bypass the tedious labeling, we solve the egocentric audio-visual object localization task in a self-supervised manner. The proposed framework is shown in Fig. 2. Our model first extracts representations from the audio $s$ and video clip $V$ . In order to handle Q1, we develop a cascaded feature enhancement module to disentangle visually indicated sound sources and attend to visual regions that correspond to the visible sound sources. To enable the disentanglement, we use on-screen sound separation task as the proxy and adopt a multi-task learning objective to train our model where the localization task is solved along with a sound-separation task. To deal with the egomotion in egocentric videos (Q2), we design a geometry-aware temporal modeling approach to mitigate the feature distortion + +brought by viewpoint changes and aggregate the visual features temporally. We take the audio-visual temporal synchronization as the supervision signal and estimate the localization map $\tilde{O}_i$ . + +# 3.2. Feature Extraction + +Visual representation. We use a visual encoder network $E_{v}$ to extract visual feature maps from each input frame $I_{i}$ . In our implementation, a pre-trained Dilated ResNet [86] model is adopted by removing the final fully-connected layer. We can subsequently obtain a group of feature maps $v_{i} = E_{v}(I_{i})$ , where $v_{i} \in \mathbb{R}^{c \times h_{v} \times w_{v}}$ . Here $c$ is the number of channels, and $h_{v} \times w_{v}$ denotes the spatial size. + +Audio representation. To extract audio representations from the input raw waveform, we first transform audio stream $s$ into a magnitude spectrogram $X$ with the short-time Fourier transform (STFT). Then, we extract audio features $a = E_{a}(X), a \in \mathbb{R}^{c \times h_{a} \times w_{a}}$ by means of a CNN encoder $E_{a}$ in the Time-Frequency (T-F) space. + +# 3.3. Cascaded Feature Enhancement + +As discussed in Sec. 3.1, a sound source $s_n$ in the mixture $s$ could be out of view due to constant view changes in egocentric videos and the limited FoV. This poses challenges in visually localizing sound sources and performance can degrade when the audio-visual associations are not precise. To address this, we update the features in a cascaded fashion. We first force the network to learn disentangled audio representations from the mixture using visual guidance. Then we utilize the disentangled audio representations to inject the visual features with more localization cues. + +Disentanglement through sound source separation. Sound source localization objective can implicitly guide the system to learn disentangled audio features as the network will try to precisely localize the sound, and in turn, the on-screen sound will get disentangled from the rest. However, we formulate our problem in an unsupervised setting where labels for such localization objective are not available. + +Audio-visual sound separation task [23, 87] uses visual information as guidance to learn to separate individual sounds from a mixture. Given the visual guidance, it is expected that the learned representations primarily encode information from visually indicated sound sources. Hence we argue for a multi-task learning approach to solve our primary task. Along with the audio-visual sounding object localization task, the network also learns to disentangle visible audio representations from the mixture through a source separation task. + +- Training. We adopt the commonly used "mix-and-separate" strategy [23,87] for audio-visual sound separation. Given the current audio $s^{(1)}$ , we randomly sample another audio stream $s^{(2)}$ from a different video and mix them together to generate input audio mixture $\tilde{s} = s^{(1)} + s^{(2)}$ . We then obtain magnitude spectrograms $\tilde{X}, X^{(1)}, X^{(2)}$ for $\tilde{s}, s^{(1)}$ and $s^{(2)}$ respectively. The audio features is then modified as $a = E_a(\tilde{X})$ . +- Inference. During inference, we take the original audio stream as input: $s = s^{(1)}$ and $X = X^{(1)}$ to extract visually correlated audio representations. Note that the audio features is $a = E_{a}(X)$ . + +We define the audio disentanglement network as a network $f(\cdot)$ , which produces the disentangled audio features $\hat{a} \in \mathbb{R}^{c \times h_a \times w_a}$ . In this network, we want to associate the visual content with the audio representations to perform disentanglement in the embedding space. Concretely, we first apply spatial average pooling on each $v_i$ and temporal max pooling along the time axis to obtain a visual feature vector $g_v \in \mathbb{R}^c$ . Then we replicate the visual feature vector $h_a \times w_a$ times and tile them to match the size of $a$ . We concatenate the visual and audio feature maps along the channel dimension and feed them into the network. Therefore, the audio feature disentanglement can be formulated as: + +$$ +\hat {a} = f \left(\operatorname {C O N C A T} [ a, \operatorname {T I L E} \left(g _ {v}\right) ]\right). \tag {1} +$$ + +In practice, we implement the disentanglement network $f$ using two 1x1 convolution layers. The audio feature $\hat{a}$ will be used for both separation mask and sounding object localization map generation. + +To separate visible sounds, we add an audio decoder $D_{a}$ following the disentanglement network to output a binary mask $M_{pred} = D_{a}(\hat{a})$ (at the bottom of Fig. 2). U-Net + +![](images/4e6ae599120192a1f2f9884117b6944e2743f3b24b13a7bbdc1df5055a4b5ee4.jpg) +Figure 3. Overview of our proposed geometry-aware modeling approach. The visual features $\hat{v}_j$ are warped to viewpoint $i$ by homography transformation. + +architectures [23] are used in the audio encoder $E_{a}$ and decoder $D_{a}$ . We implement the $E_{a}$ and $D_{a}$ in five convolution and up-convolution layers, respectively. Details of the network architectures are provided in the Appendix. The ground truth separation mask $M_{gt}$ can be calculated by determining whether the original input sound is dominant at locations $(u,v)$ in the T-F space: + +$$ +M _ {g t} (u, v) = \left[ X ^ {(1)} (u, v) \geq \tilde {X} (u, v) \right]. \tag {2} +$$ + +To train the sound separator, we minimize the $\ell_2$ distance between the predicted and ground-truth masks as the disentanglement learning objective: + +$$ +\mathcal {L} _ {d i s} = \left| \left| M _ {p r e d} - M _ {g t} \right| \right| _ {2} ^ {2}. \tag {3} +$$ + +Soft localization. Similar to the out-of-view sounds, the visual frames may contain sound-irrelevant regions. In order to learn more precise audio-visual associations, we propose to highlight the spatial regions that are more likely to be correlated with the on-screen sounds by computing audio-visual attention. The attention map will indicate the correlation between audio and visual representations at different spatial locations. Given the output $\hat{a}$ from disentanglement network $f(\cdot)$ , we apply max pooling on its time and frequency dimensions, obtaining an audio feature vector $g_{\hat{a}}$ . Then at each spatial position (x,y) of visual feature $v_{i}$ , we compute the cosine similarity between audio and visual feature vectors: + +$$ +S _ {i}: S _ {i} (x, y) = \operatorname {C O S I N E S I M} \left(v _ {i} (x, y), g _ {\hat {a}}\right). \tag {4} +$$ + +SOFTMAX is then used on $S_{i}$ to generate a soft mask that represents the audio-visual correspondence. Hence, each $v_{i}$ can be attended with the calculated weights: + +$$ +\hat {v} _ {i} = \operatorname {S O F T M A X} \left(S _ {i}\right) \cdot v _ {i}. \tag {5} +$$ + +# 3.4. Geometry-Aware Temporal Modeling + +Given the temporal nature of sounds and the persistence of audio-visual associations, we incorporate temporal information from neighboring frames to learn sounding object features. However, temporal modeling is a challenging + +problem for egocentric videos due to widespread egomotion and object-appearance deformations. + +Although visual objects are dynamically changing, the surrounding physical environment is persistent. Hence, temporal variations in egocentric videos reveal rich 3D geometric cues that can recover the surrounding scene from changing viewpoints. Prior works have shown that given a sequence of frames, one can reconstruct the underlying 3D scene from the 2D observations [64,81]. In our work, rather than reconstructing the 3D structures, we estimate the relative geometric transformation between frames to alleviate egomotion. Specifically, we apply the transformation at the feature level to perform geometry-aware temporal aggregation. Given $\{I_i\}_{i=1}^T$ and their features $\{\hat{v}_i\}_{i=1}^T$ , we take $\hat{v}_i$ as a query at a time and use the other features from neighboring frames as support features to aggregate temporal contexts. For clarity, we decompose the geometry-aware temporal aggregation into two parts: geometry modeling and temporal aggregation. + +Geometry modeling. This step aims to compute the geometric transformation that represents the egomotion between frames (see Fig. 3). We found that homography estimation, which can align images taken from different perspectives, can serve as a way to measure geometric transformation. We adopt SIFT [46] + RANSAC [18] to solve homography. To be specific, a homography is a $3 \times 3$ matrix that consists of 8 degree of freedom (DOF) for scale, translation, rotation, and perspective respectively. Given the query frame $I_{i}$ and a supporting frame $I_{j}$ , we use $h(\cdot)$ to denote the computation process: + +$$ +\mathcal {H} _ {j i} = h \left(I _ {j}, I _ {i}\right) _ {j \rightarrow i}, \tag {6} +$$ + +where $\mathcal{H}_{ji}$ represents the homography transformation from frame $I_{j}$ to $I_{i}$ . With the computed homography transformation, we can then apply it at the feature level to transform visual features $\hat{v}_j$ to $\hat{v}_{ji}$ . The $\hat{v}_{ji}$ is egomotion-free under the viewpoint of $I_{i}$ . Since the resolution of feature maps is scaled down compared to the raw frame size, the homography matrix $\mathcal{H}$ should also be downsampled using the same scaling factor. The feature transformation can be written as: + +$$ +\hat {v} _ {j i} = \mathcal {H} _ {j i} \otimes \hat {v} _ {j}, \tag {7} +$$ + +where $\otimes$ represents the warping operation. + +Temporal aggregation. For the query feature $\hat{v}_i$ , we end up with set of aligned features $\{\hat{v}_{ji}\}_{j=1}^{T}$ corresponding to each frame viewpoint. To aggregate the temporal contexts, we propose to compute the correlation between features from different frames at the same locations (see Fig. 4). The aggregation process can be formulated as: + +$$ +z _ {i} (x, y) = \hat {v} _ {i} (x, y) + \operatorname {S O F T M A X} \left(\frac {\hat {v} _ {i} (x , y) \hat {\boldsymbol {v}} (x , y) ^ {T}}{\sqrt {d}}\right) \hat {\boldsymbol {v}} (x, y), \tag {8} +$$ + +![](images/040729c88d40b05b44f5ec95699dcd9bdd09cebd9cc8aafa20d089d931a93bba.jpg) +Figure 4. Illustration on the temporal context aggregation process for query feature $\hat{v}_i$ and neighboring frame features $\hat{v}_{i-1}$ and $\hat{v}_{i+1}$ , which is performed independently at each spatial location. + +where $\hat{\pmb{v}} = [\hat{v}_{1i};\dots;\hat{v}_{Ti}]$ is the concatenation of frame features; the scaling factor $d$ is equal to the feature dimension; and $(\cdot)^T$ represents the transpose operation [80]. The aggregation operation is applied at all spatial locations $(x,y)$ to generate the updated visual features $z_{i}$ . + +# 3.5. Training Objective + +We take audio-visual synchronization as the "free" supervision and solve the task in a self-supervised manner using contrastive learning [2,4,11,65]. + +With the audio feature vector $g_{\hat{a}}$ and the visual features $\{z_i\}_{i=1}^T$ , we can compute an audio-visual attention map $S_i$ in Eq. 4 for each frame $I_i$ . The training objective should optimize the network such that only the sounding regions have a high response in $S_i$ . Since the ground-truth sounding map is unknown, we apply differential thresholding on $S_i$ to predict sounding objectness map $O_i = sigmoid((S_i - \epsilon) / \tau)$ [11], where $\epsilon$ is the threshold, and $\tau$ denotes the temperature that controls the sharpness. + +In an egocentric video clip, a visual scene is usually temporally dynamic. Sometimes a single audio-visual pair $(I_i,s)$ may not be audio-visually correlated. To this end, we solve the localization task in the Multiple-Instance Learning (MIL) [47] setting to improve robustness. Concretely, we use a soft MIL pooling function to aggregate the concatenated attention maps $S = [S_1;\dots;S_T]$ by assigning different weights to $S_{t}$ at different time steps: + +$$ +\bar {S} = \sum_ {t = 1} ^ {T} \left(W _ {t} \cdot \boldsymbol {S}\right) [:,:, t ], \tag {9} +$$ + +where $W_{t}[x,y,:] = \mathrm{SOFTMAX}(S[x,y,:])$ , $x$ and $y$ are the indices on spatial dimensions. Subsequently, an aggregated sounding objectness map $\overline{O}$ is calculated from $\overline{S}$ . In this way, for each video clip $V$ in the batch, we can define its positive and negative training signals as: + +$$ +P = \frac {1}{| \bar {O} |} \langle \bar {O}, \bar {S} \rangle , \quad N = \frac {1}{h w} \langle \mathbf {1}, S _ {n e g} \rangle , \tag {10} +$$ + +where $\langle \cdot ,\cdot \rangle$ is the Frobenius inner product. + +We obtain negative audio-visual attention maps $S_{\text{neg}}$ by associating the current visual inputs $I$ with audio from other + +![](images/16f4c347bd6d5688c50d38ce7f65a9dd4e3908b56547207cb9965ddb6abba32a.jpg) +Squeeze packaging + +![](images/e78fd755ee6a7f2fe90c76c15c53a9bffdcb7976593f60deabb8eda79aa2982a.jpg) +Take out bottle + +![](images/fbf7288017d472bdd0f25c052e95b1a202e01172eb86345efad36918ff63b3e5.jpg) +Put pot +(a) Epic Sounding Object Dataset examples +Figure 5. Illustration of the Epic Sounding Object dataset statistics. (a) Example of our video frames and sounding object annotations. Class diversity (squeeze packaging, close trash can, put the pot, etc.) (b): The distribution of untrimmed video duration. (c): The number of videos that are annotated as containing out-of-view sounds. (d): Distribution of bounding box areas in Epic Sounding Object dataset, the majority of boxes cover less than $20\%$ of the image area, demonstrating the difficulty of this task. + +![](images/f21d3b0b2243e3ae50866820ed6666506885c7f7085448dba0abf91426c98546.jpg) +Stir meat + +![](images/39544f331674d69926cf69c46cc1d6d9b4a1f932f7ece2fd65ae211f2cbbe01a.jpg) +Close trash can + +![](images/bdf62fe0aeef2d8919389b0961bc77abdfeaa80c6fde8c0a0f3301c23d2cb460.jpg) +Wash spoon +(b) Duration of videos + +![](images/e2109ce2de80cfd4ca14ce9e80cf56452808140a63775fd712532aa4db7ab9af.jpg) + +![](images/86d877af01a069604f7117b97b50b6014c20b8a6fa057b8a8ed15703e8f24ee6.jpg) +(c) Num of out-of-view sounds + +![](images/1c22b4f33df9a18a90e2f63f07488d07bdd9774f2f0b6106ae4c5f0a663de38a.jpg) +(d) Sounding object area + +video clips. 1 denotes an all ones tensor with shape $h \times w$ . Therefore, the localization optimization objective is: + +$$ +\mathcal {L} _ {l o c} = - \frac {1}{N} \sum_ {k = 1} ^ {N} \left[ \log \frac {\exp \left(P _ {k}\right)}{\exp \left(P _ {k}\right) + \exp \left(N _ {k}\right)} \right], \tag {11} +$$ + +where $k$ is the video sample index in a training batch. The overall objective is $\mathcal{L} = \mathcal{L}_{loc} + \lambda \mathcal{L}_{dis}$ , where we empirically set $\lambda = 5$ in our experiments. + +# 4. The Epic Sounding Object Dataset + +Existing sound source visual localization evaluation datasets, such as SoundNet-Flickr [65], VGG-Sound Source [11], only contain third-person recordings. To the best of our knowledge, there is no existing dataset that is suitable for evaluating our model. Thus, we introduce an Epic Sounding Object Dataset for egocentric audio-visual sounding object localization. Built upon the well-known Epic-Kitchens [13] dataset, we collect sounding object annotations on its action recognition test set. + +Data preparation. We select 13k test videos from the Epic-Kitchens action recognition benchmark as our source data. Since these videos are not originally collected for audiovisual analysis, they vary in length, and not all of them contain meaningful sounds. To verify the videos for annotations, we conduct a two-step process: We first determine if a video is silent by checking its sound-level in decibels relative to full scale. Consequently, silent videos are filtered out to provide a meaningful data source. Second, we bin the videos by their duration and show the statistics in Fig. 5 (b). The majority last less than 2 seconds, and hence we choose to trim the center 1-second clip from each video. + +After pre-processing, we obtain 5,089 videos in total for annotation. For each video, we uniformly select three frames and annotate sounding objects in the frames. We follow previous works [11,76] to use bounding boxes to annotate the objects that emit sounds. To obtain proposals of potential sounding objects automatically, we follow EpicKitchens [13] to use a Mask R-CNN object detector [25] + +
Before votingAfter voting
VideoFramesVideoFramesClasses
5,08915,2673,1729,19630
+ +Table 1. Statistics of the Epic Sounding Object dataset. + +trained on MS-COCO [43] and a hand-objects detector [68] that is pretrained with 42K egocentric images [13,42,69]. + +Annotation collection. Given the pre-processed data, we then annotate the sounding objects manually. Unlike third-person view videos, the object-sound associations in the egocentric domain are more complicated. There are two main challenges: (i) Numerous egocentric videos record wearer-environment interaction (e.g., a human places a dish on the table). The object-sound associations could be dynamic, and sometimes it is hard to determine what objects are emitting sounds; and (ii) the objects in egocentric videos are often missing from the screen, resulting in variations in scale (see Fig. 5 (c)). We address the above issues by taking advantage of human commonsense knowledge. We ask three or more annotators from the Amazon Mechanic Turk to annotate the same video (frames). Concretely, they do this by first watching the 1-second video with three annotated frames to confirm what objects make sounds in the video. During the annotation course, they are asked to answer two questions: (1) Does the video contain out-of-view sounds? (2) Which bounding boxes correspond to the sounding objects? We collect the annotations in multiple rounds until each video has at least three or more valid annotations from the Amazon annotators. Finally, we conduct an annotation verification by voting on all videos. If at least two annotators agree on the same answer, it will be considered as a correct annotation; If not, we will simply omit the video. The annotation statistics after voting are shown in Tab. 1. We obtain 30 classes of sounds by counting the noun (object) classes. The annotations are evenly split into two sets for validation and testing. The examples and statistics in Fig. 5 illustrate the diverse and complicated nature of egocentric audio-visual scenes. + +![](images/6e5e8c9971c634038c219afcaf7fca327c471303b1df78a7847c11c2f96551ba.jpg) +Figure 6. Qualitative comparison on Epic Sounding Object dataset. We show diverse sounding objects in the kitchen scenes in the first column, sounding objects are annotated in red boxes. Our method outperforms all the compared works. + +# 5. Experiment + +Datasets. In our experiments, we use two egocentric datasets. (1) Epic-Kitchens [13]: The dataset consists of 100 hours of egocentric recordings from 45 kitchen scenes. Thus, diverse kitchen-relevant events and sounds are in the dataset. We follow the same data split released in their action recognition benchmark and select 62,413 training videos. We then filter out the silent videos by measuring the Decibels relative to full scale. This results in 47,214 training videos in total. For evaluation, we use our annotated Epic Sounding Object dataset to report the results; (2) Ego4D [24]: Ego4D is the most recent large-scale egocentric video dataset. Besides kitchen scenes, it includes diverse daily life scenarios. Specifically, it consists of different subsets serving different benchmarks. We select the "Bristol" subset as it contains diverse scenarios (e.g., entertainment, sports, commuting, and more) to test our method. We randomly sample and trim 50,000 1-second videos from this subset and use $90\% / 10\%$ as the train/test split. A similar filtering strategy is applied to obtain 26,858 videos for training. We conduct experiments in Sec. 5.1.3 on this dataset to showcase the generalization ability of our method. + +Evaluation metric. We follow the prior works [11, 28, 38] and adopt the pixel-level measurement for evaluating localization performance. Given the ground truth sounding object bounding boxes, we compute the Consensus Intersection over Union (CIoU) and Area Under Curve (AUC) between the predicted localization map and ground truth boxes. We report CIoU over a range of thresholds to expose the finer aspects of comparison. + +Implementation details. To facilitate the training, we cut + +
CIoUAUC
@0.2@0.3@0.4
Attention [65]7.12--6.42
STM [38]12.107.644.018.87
Hardway [11]24.5113.556.1013.38
SSPL [71]13.628.104.459.56
Mix [28]26.0115.259.9015.39
Our38.7119.4210.5118.38
+ +Table 2. Quantitative comparison of localization results on Epic Sounding Object dataset. All methods are re-trained on EpicKitchen. The results of metrics CIoU@{0.2, 0.3, 0.4} and AUC are reported. The top-1 results are highlighted. + +a 1-second long video around the center of each raw video. We select the middle frame from the video clip and its four neighboring frames with an interval of 2 between frames. Consequently, we get $T = 5$ frames as visual input. During training, the frames are first resized to $256 \times 256$ and then randomly cropped to $224 \times 224$ . During inference, all the frames are directly resized to the desired size without cropping. For the audio stream, we extract the corresponding 1-second audio clip to create the audio-visual pairs. The audio waveform is sub-sampled at $11\mathrm{kHz}$ and transformed into a spectrogram with a Hann window of size 254 and a hop length of 64. The obtained spectrogram is subsequently resampled to $128 \times 128$ to feed into the audio network. We set the number of audio and visual feature channels as 512 and choose $\epsilon = 0.5$ and $\tau = 0.03$ . All models are trained with the Adam optimizer, with a learning rate of $10^{-4}$ on the visual encoder and temporal network, while using a learning rate of $10^{-2}$ for updating the audio encoder. + +# 5.1. Results + +# 5.1.1 Experimental Comparison + +To validate the effectiveness of our framework, we compare it with recent audio-visual localization methods: Attention [65], STM [38], Hardway [11], SSPL [71] and Mix [28]. Among all the comparative methods, STM [38] utilizes weak labels for the training, while the other methods are trained with self-supervision. We hence adjust STM [38] with our self-supervised localization loss. As all the methods are developed for third-person view videos, we retrain their methods on our training data for a fair comparison. The quantitative results are shown in Tab. 2. We can find that our method outperforms all the compared approaches by a large margin in all metrics, indicating the benefits of mitigating out-of-view sounds and explicitly modeling egomotion in learning egocentric audio-visual localization. Moreover, we provide a qualitative comparison to visually showcase our localization results. In Fig. 6, we can see that our model produces localization results that are tight around the ground truth sounding objects. + +
ModelTMSLLdisCIoU@0.2AUC
AvgMaxGA
a27.4115.36
b✓31.8415.79
c✓33.2916.10
d✓37.3816.59
f✓✓38.2117.92
g✓✓✓38.7118.38
+ +Table 3. Ablations on GATM, SL, and audio disentanglement module. The top-1 result in each column is highlighted. + +# 5.1.2 Ablation Study + +We conduct an ablation study to illustrate how each module affects localization performance. As shown in Tab. 3, we compare our full model with different baselines — model a: we remove all the modules and only use the features from the visual and audio encoders to compute the localization map; model b-d: we insert Average, Max, and Geometry-Aware Temporal modeling approaches separately in the framework; in model f, we incorporate the soft localization (SL) into the pipeline; and in model g, we employ the audio disentanglement module and train the model with $L_{dis}$ . By comparing a and b-c, we found that it's crucial to aggregate temporal context, while d emphasizes the importance of GATM in mitigating the egomotion in egocentric videos. model d vs. f shows that SL slightly enhances the performance since some of the unrelated visual content can be reweighted. The comparison between f and g demonstrates that by incorporating audio feature disentanglement, the localization performance can be further boosted because it can handle the out-of-view sounds in videos. + +Naive baseline. To assess the difficulty of the task, we provide a center box method that predicts a gaussian heatmap around the center. This results in a naive baseline of 16.51 compared to 27.41 (model a) from Tab. 3, showing that there are various challenging scenarios apart from the object being in the center that this naive baseline cannot capture. + +# 5.1.3 Generalization to More Scenarios + +The experiments on Epic Sounding Object dataset demonstrate the effectiveness of our method in localizing sounding objects in the egocentric videos. To further validate the generalization ability of our method, we train our audio-visual sounding object localization network on Ego4D [24] and qualitatively showcase the localization results in Fig. 7. The examples are all selected from the Ego4D test set. We can see that our model can learn audio-visual associations and localize the sounding objects in diverse scenes. + +# 6. Discussions and Conclusions + +In this work, we tackle a fundamental task: egocentric audio-visual localization to promote the field of study in + +![](images/6589a18f80e29947fd2bef09a8dc15113f80c27a08f4144175035b96a15b15ca.jpg) +Figure 7. Localization results on diverse scenarios in Ego4D [24]. Ref.: Sounding objects; Pred.: predicted localization results. + +egocentric audio-visual video understanding. The uniqueness of egocentric videos, such as egomotions and out-of-view sounds pose significant challenges to learning fine-grained audio-visual associations. To address these problems, we propose a new framework with a cascaded feature enhancement module to disentangle visually indicated audio representations and a geometry-aware temporal modeling module to mitigate egomotion. Extensive experiments on our annotated Epic Sounding Object dataset underpin the findings that explicitly mitigating out-of-view sounds and egomotion can boost localization performance and learn the better audio-visual association for egocentric videos. + +Limitations. The proposed geometry-aware temporal modeling approach requires geometric transformation computation. For certain visual scenes with severe illumination changes or drastic motions, the homography estimation may fail. Then, our GATM will degrade to a vanilla temporal modeling approach. To mitigate the issue, we can consider designing a more robust geometric estimation approach. + +Potential Applications. Our work offers potential for several applications: (a) Audio-visual episodic memory. As egocentric video records what and where of an individual's daily life experience, it would be interesting to build an intelligent AR assistant to localize the object ("where did I use it?") by processing an audio query, e.g., an audio clip of "vacuum cleaner"; (b) Audio-visual object state recognition. In egocentric research, it is important to know the state of objects that human is interacting with, while the human-object interaction often makes a sound. Therefore, localizing objects by sounds provides a new angle in recognizing an object state; (c) Audio-visual future anticipation: following the audio-visual object state recognition task, it's natural to predict the trajectory of a sounding object by analyzing the most recent audio-visual clips. + +# References + +[1] Yazan Abu Farha, Alexander Richard, and Juergen Gall. When will you do what?-anticipating temporal occurrences + +of activities. 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Likewise, machines are advanced to approach human intelligence by learning with multisensory inputs from an egocentric perspective. In this paper, we explore the challenging egocentric audio-visual object localization task and observe that 1) egomotion commonly exists in first-person recordings, even within a short duration; 2) The out-of-view sound components can be created when wearers shift their attention. To address the first problem, we propose a geometry-aware temporal aggregation module that handles the egomotion explicitly. The effect of egomotion is mitigated by estimating the temporal geometry transformation and exploiting it to update visual representations. Moreover, we propose a cascaded feature enhancement module to overcome the second issue. It improves cross-modal localization robustness by disentangling visually-indicated audio representation. During training, we take advantage of the naturally occurring audio-visual temporal synchronization as the \"free\" self-supervision to avoid costly labeling. We also annotate and create the Epic Sounding Object dataset for evaluation purposes. Extensive experiments show that our method achieves state-of-the-art localization performance in egocentric videos and can be generalized to diverse audio-visual scenes. Code is available at https://github.com/WikiChao/Ego-AV-Loc." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 573, + 127, + 585 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 573, + 127, + 585 + ], + "spans": [ + { + "bbox": [ + 47, + 573, + 127, + 585 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 594, + 287, + 701 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 594, + 287, + 701 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 287, + 701 + ], + "type": "text", + "content": "The emergence of wearable devices has drawn the attention of the research community to egocentric videos, the significance of which can be seen from egocentric research in a variety of applications such as robotics [32,34,48], augmented/virtual reality [31,61,75], and healthcare [53,66]. In recent years, the computer vision community has made substantial efforts to build benchmarks [12, 13, 15, 40, 57, 69], establish new tasks [17, 36, 37, 39, 60], and develop frameworks [33,41,54,82] for egocentric video understanding." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 59, + 701, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 701, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 59, + 701, + 287, + 713 + ], + "type": "text", + "content": "While existing works achieve promising results in the" + } + ] + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 309, + 212, + 545, + 334 + ], + "blocks": [ + { + "bbox": [ + 309, + 212, + 545, + 334 + ], + "lines": [ + { + "bbox": [ + 309, + 212, + 545, + 334 + ], + "spans": [ + { + "bbox": [ + 309, + 212, + 545, + 334 + ], + "type": "image", + "image_path": "3719b6f38374c3c1571081325abefaa481fd944ba0f6e9b33211f0b2afa03920.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 341, + 546, + 407 + ], + "lines": [ + { + "bbox": [ + 304, + 341, + 546, + 407 + ], + "spans": [ + { + "bbox": [ + 304, + 341, + 546, + 407 + ], + "type": "text", + "content": "Figure 1. Sounding object localization in egocentric videos. Due to the wearer's egomotion, the viewpoint changes continuously across time. Consequently, audio-visual relations are dynamically changing in egocentric videos. Our approach tackles challenges in the egocentric audio-visual sounding object task and learns audio-visual associations from first-person videos." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 415, + 546, + 653 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 415, + 546, + 653 + ], + "spans": [ + { + "bbox": [ + 304, + 415, + 546, + 653 + ], + "type": "text", + "content": "egocentric domain, it still remains an interesting but challenging topic to perform fine-grained egocentric video understanding. For instance, understanding which object is emitting sound in a first-person recording is difficult for machines. As shown in Fig. 1, the wearer moves his/her head to put down the bottle. The frying pot which emits sound subsequently suffers deformation and occlusion due to the wearer's egomotion. Human speech outside the wearer's view also affects the machine's understanding of the current scene. This example reveals two significant challenges for designing powerful and robust egocentric video understanding systems: First, people with wearable devices usually record videos in naturalistic surroundings, where a variety of illumination conditions, object appearance, and motion patterns are shown. The dynamic visual variations introduce difficulties in accurate visual perception. Second, egocentric scenes are often perceived within a limited field of view (FoV). The common body and head movements cause frequent view changes (see Fig. 1), which brings object deformation and creates dynamic out-of-view content." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 654, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 654, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 654, + 547, + 713 + ], + "type": "text", + "content": "Although a visual-only system may struggle to fully decode the surrounding information and perceive scenes in egocentric videos, audio provides stable and persistent signals associated with the depicted events. Instead of purely visual perception, numerous psychological and cognitive" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "22910" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 167 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 167 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 167 + ], + "type": "text", + "content": "studies [6, 29, 67, 73] show that integration of auditory and visual signals is significant in human perception. Audio, as an essential but less focused modality, often provides synchronized and complementary information with the video stream. In contrast to the variability of first-person visual footage, sound describes the underlying scenes consistently. These natural characteristics make audio another indispensable ingredient for egocentric video understanding." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 168, + 288, + 430 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 168, + 288, + 430 + ], + "spans": [ + { + "bbox": [ + 46, + 168, + 288, + 430 + ], + "type": "text", + "content": "To effectively leverage audio and visual information in egocentric videos, a pivotal problem is to analyze the fine-grained audio-visual association, specifically identifying which objects are emitting sounds in the scene. In this paper, we explore a novel egocentric audio-visual object localization task, which aims to associate audio with dynamic visual scenes and localize sounding objects in egocentric videos. Given the dynamic nature of egocentric videos, it is exceedingly challenging to link visual content from various viewpoints with audio captured from the entire space. Hence, we develop a new framework to model the distinct characteristics of egocentric videos by integrating audio. In the framework, we propose a geometry-aware temporal module to handle egomotion explicitly. Our approach mitigates the impact of egomotion by performing geometric transformations in the embedding space and aligning visual features from different frames. We further use the aligned features to leverage temporal contexts across frames to learn discriminative cues for localization. Additionally, we introduce a cascaded feature enhancement module to handle out-of-view sounds. The module helps mitigate audio noises and improves cross-modal localization robustness." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 431, + 287, + 550 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 431, + 287, + 550 + ], + "spans": [ + { + "bbox": [ + 46, + 431, + 287, + 550 + ], + "type": "text", + "content": "Due to the dynamic nature of egocentric videos, it is hard and costly to label sounding objects for supervised training. To avoid tedious labeling, we formulate this task in a self-supervised manner, and our framework is trained with audio-visual temporal synchronization. Since there are no publicly available egocentric sounding object localization datasets, we annotate an Epic Sounding dataset to facilitate research in this field. Experimental results demonstrate that modeling egomotion and mitigating out-of-view sound can improve egocentric audio-visual localization performance." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 552, + 287, + 646 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 552, + 287, + 646 + ], + "spans": [ + { + "bbox": [ + 46, + 552, + 287, + 646 + ], + "type": "text", + "content": "In summary, our contributions are: (1) the first systematic study on egocentric audio-visual sounding object localization; (2) an effective geometry-aware temporal aggregation approach to deal with unique egomotion; (3) a novel cascaded feature enhancement module to progressively inject localization cues; and (4) an Epic Sounding Object dataset with sounding object annotations to benchmark the localization performance in egocentric videos." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 657, + 134, + 670 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 657, + 134, + 670 + ], + "spans": [ + { + "bbox": [ + 47, + 657, + 134, + 670 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 677, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 287, + 715 + ], + "type": "text", + "content": "Audio-visual learning in third-person view videos. Taking the natural audio-visual synchronization in videos, a large number of studies in the past few years have proposed" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 72, + 545, + 227 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 227 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 227 + ], + "type": "text", + "content": "to jointly learn from both auditory and visual modalities. We have seen a spectrum of new audio-visual problems and applications, including visually guided sound source separation [16,20-23,63,76,87,88], audio-visual representation learning [2,3,5,26,35,58,59], audio-visual event localization [44,78,79,84], audio-visual video parsing [77,83], and sounding object visual localization [4, 11, 27, 28, 38, 51, 52, 62, 65, 71]. Most previous approaches learn audio-visual correlations from third-person videos, while the distinct challenges of audio-visual learning in egocentric videos are underexplored. Different from existing works, we propose an audio-visual learning framework to explicitly solve egomotion and out-of-view audio issues in egocentric videos." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 228, + 545, + 539 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 228, + 545, + 539 + ], + "spans": [ + { + "bbox": [ + 304, + 228, + 545, + 539 + ], + "type": "text", + "content": "Egocentric video understanding. In the last decade, video scene understanding techniques thrived because of the well-defined third-person video datasets [7, 9, 49, 72]. Nevertheless, most of the algorithms are developed to tackle videos curated by human photographers. The natural characteristics of egocentric video data, e.g., view changes, large motions, and visual deformation, are not well-explored. To bridge this gap, multiple egocentric datasets [12, 13, 24, 36, 69, 74] have been collected. These datasets have significantly advanced investigations on egocentric video understanding problems, including activity recognition [33, 41, 89], human(hand)-object interaction [8, 14, 55, 68], anticipation [1, 19, 45, 70], and human body pose inferring [30, 56]. However, only a handful of audio-visual works [10, 33, 50, 85] is presented for egocentric video understanding. Among those, Kazakos et al. [33] proposed an audio-visual fusion network for action recognition, while Mittal et al. [50] used audible interactions as cues to learn state-aware visual representations in egocentric videos. There are limited studies in explicit egomotion mitigation and fine-grained audio-visual association learning in egocentric videos. Unlike past works, we tackle challenges in egocentric audio-visual data and propose a robust sounding object localization framework. To enable the research, we propose Epic Sounding Object dataset based on Epic-Kitchens [12, 13]." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 548, + 361, + 561 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 548, + 361, + 561 + ], + "spans": [ + { + "bbox": [ + 306, + 548, + 361, + 561 + ], + "type": "text", + "content": "3. Method" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 568, + 545, + 665 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 568, + 545, + 665 + ], + "spans": [ + { + "bbox": [ + 304, + 568, + 545, + 665 + ], + "type": "text", + "content": "Our goal is to localize sounding objects in egocentric videos visually. We start by formulating our egocentric audio-visual object localization task in Sec. 3.1. Our proposed method includes a feature extraction process (described in Sec. 3.2), a two-stage cascaded feature enhancement pipeline (in Sec. 3.3), and a geometry-aware temporal aggregation module (explained in Sec. 3.4). Finally, we summarize the overall training objective in Sec. 3.5." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 671, + 537, + 683 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 671, + 537, + 683 + ], + "spans": [ + { + "bbox": [ + 306, + 671, + 537, + 683 + ], + "type": "text", + "content": "3.1. Problem Formulation and Method Overview" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "text", + "content": "Given an egocentric video clip " + }, + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "inline_equation", + "content": "V = \\{I_i\\}_{i=1}^T" + }, + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "text", + "content": " in " + }, + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "text", + "content": " frames and its corresponding sound stream " + }, + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "inline_equation", + "content": "s" + }, + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "text", + "content": ", sounding object vi" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 758 + ], + "type": "text", + "content": "22911" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 97, + 70, + 500, + 270 + ], + "blocks": [ + { + "bbox": [ + 97, + 70, + 500, + 270 + ], + "lines": [ + { + "bbox": [ + 97, + 70, + 500, + 270 + ], + "spans": [ + { + "bbox": [ + 97, + 70, + 500, + 270 + ], + "type": "image", + "image_path": "cba04654b8493f0991bd560f67b906f1d9de82f6b9779af9697eff747dd03de6.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 276, + 548, + 332 + ], + "lines": [ + { + "bbox": [ + 46, + 276, + 548, + 332 + ], + "spans": [ + { + "bbox": [ + 46, + 276, + 548, + 332 + ], + "type": "text", + "content": "Figure 2. An overview of our egocentric audio-visual object localization framework. In the beginning, our model extracts deep features from the video and audio streams. Then, the audio and visual features are fed into the cascaded feature enhancement module to inject localization cues for both branches. Such a module is additionally trained with \"mix-and-separation\" strategy. Next, our geometric-aware temporal modeling block leverages the relative geometric information between visual frames and performs temporal context aggregation to get the final visual features for localization." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 341, + 289, + 521 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 341, + 289, + 521 + ], + "spans": [ + { + "bbox": [ + 46, + 341, + 289, + 521 + ], + "type": "text", + "content": "sual localization aims at predicting location maps " + }, + { + "bbox": [ + 46, + 341, + 289, + 521 + ], + "type": "inline_equation", + "content": "\\mathcal{O} = \\{O_i\\}_{i=1}^T" + }, + { + "bbox": [ + 46, + 341, + 289, + 521 + ], + "type": "text", + "content": " that represent sounding objects in the egocentric video. Specifically, " + }, + { + "bbox": [ + 46, + 341, + 289, + 521 + ], + "type": "inline_equation", + "content": "O_i(x,y) \\in \\{0,1\\}" + }, + { + "bbox": [ + 46, + 341, + 289, + 521 + ], + "type": "text", + "content": " and positive visual regions indicate locations of sounding objects. In real-world scenarios, the captured sound can be a mixture of multiple sound sources " + }, + { + "bbox": [ + 46, + 341, + 289, + 521 + ], + "type": "inline_equation", + "content": "s = \\sum_{n=1}^{N} s_n" + }, + { + "bbox": [ + 46, + 341, + 289, + 521 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 341, + 289, + 521 + ], + "type": "inline_equation", + "content": "s_n" + }, + { + "bbox": [ + 46, + 341, + 289, + 521 + ], + "type": "text", + "content": " is the " + }, + { + "bbox": [ + 46, + 341, + 289, + 521 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 46, + 341, + 289, + 521 + ], + "type": "text", + "content": "-th sound source and it could be out of view. For the visual input, the video frames may be captured from different viewpoints. To design a robust and effective egocentric audio-visual sounding object localization system, we should consider the above issues in egocentric audio and visual data and answer two key questions: (Q1) how to associate visual content with audio representations while out-of-view sounds may exist; (Q2) how to persistently associate audio features with visual content that are captured under different viewpoints." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 522, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 522, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 522, + 289, + 715 + ], + "type": "text", + "content": "Due to the dynamic nature of egocentric videos, it is difficult and costly to annotate sounding objects for supervised training. To bypass the tedious labeling, we solve the egocentric audio-visual object localization task in a self-supervised manner. The proposed framework is shown in Fig. 2. Our model first extracts representations from the audio " + }, + { + "bbox": [ + 46, + 522, + 289, + 715 + ], + "type": "inline_equation", + "content": "s" + }, + { + "bbox": [ + 46, + 522, + 289, + 715 + ], + "type": "text", + "content": " and video clip " + }, + { + "bbox": [ + 46, + 522, + 289, + 715 + ], + "type": "inline_equation", + "content": "V" + }, + { + "bbox": [ + 46, + 522, + 289, + 715 + ], + "type": "text", + "content": ". In order to handle Q1, we develop a cascaded feature enhancement module to disentangle visually indicated sound sources and attend to visual regions that correspond to the visible sound sources. To enable the disentanglement, we use on-screen sound separation task as the proxy and adopt a multi-task learning objective to train our model where the localization task is solved along with a sound-separation task. To deal with the egomotion in egocentric videos (Q2), we design a geometry-aware temporal modeling approach to mitigate the feature distortion" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 304, + 341, + 547, + 389 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 341, + 547, + 389 + ], + "spans": [ + { + "bbox": [ + 304, + 341, + 547, + 389 + ], + "type": "text", + "content": "brought by viewpoint changes and aggregate the visual features temporally. We take the audio-visual temporal synchronization as the supervision signal and estimate the localization map " + }, + { + "bbox": [ + 304, + 341, + 547, + 389 + ], + "type": "inline_equation", + "content": "\\tilde{O}_i" + }, + { + "bbox": [ + 304, + 341, + 547, + 389 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 306, + 395, + 418, + 407 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 395, + 418, + 407 + ], + "spans": [ + { + "bbox": [ + 306, + 395, + 418, + 407 + ], + "type": "text", + "content": "3.2. Feature Extraction" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 414, + 545, + 497 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 414, + 545, + 497 + ], + "spans": [ + { + "bbox": [ + 304, + 414, + 545, + 497 + ], + "type": "text", + "content": "Visual representation. We use a visual encoder network " + }, + { + "bbox": [ + 304, + 414, + 545, + 497 + ], + "type": "inline_equation", + "content": "E_{v}" + }, + { + "bbox": [ + 304, + 414, + 545, + 497 + ], + "type": "text", + "content": " to extract visual feature maps from each input frame " + }, + { + "bbox": [ + 304, + 414, + 545, + 497 + ], + "type": "inline_equation", + "content": "I_{i}" + }, + { + "bbox": [ + 304, + 414, + 545, + 497 + ], + "type": "text", + "content": ". In our implementation, a pre-trained Dilated ResNet [86] model is adopted by removing the final fully-connected layer. We can subsequently obtain a group of feature maps " + }, + { + "bbox": [ + 304, + 414, + 545, + 497 + ], + "type": "inline_equation", + "content": "v_{i} = E_{v}(I_{i})" + }, + { + "bbox": [ + 304, + 414, + 545, + 497 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 414, + 545, + 497 + ], + "type": "inline_equation", + "content": "v_{i} \\in \\mathbb{R}^{c \\times h_{v} \\times w_{v}}" + }, + { + "bbox": [ + 304, + 414, + 545, + 497 + ], + "type": "text", + "content": ". Here " + }, + { + "bbox": [ + 304, + 414, + 545, + 497 + ], + "type": "inline_equation", + "content": "c" + }, + { + "bbox": [ + 304, + 414, + 545, + 497 + ], + "type": "text", + "content": " is the number of channels, and " + }, + { + "bbox": [ + 304, + 414, + 545, + 497 + ], + "type": "inline_equation", + "content": "h_{v} \\times w_{v}" + }, + { + "bbox": [ + 304, + 414, + 545, + 497 + ], + "type": "text", + "content": " denotes the spatial size." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 498, + 545, + 570 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 498, + 545, + 570 + ], + "spans": [ + { + "bbox": [ + 304, + 498, + 545, + 570 + ], + "type": "text", + "content": "Audio representation. To extract audio representations from the input raw waveform, we first transform audio stream " + }, + { + "bbox": [ + 304, + 498, + 545, + 570 + ], + "type": "inline_equation", + "content": "s" + }, + { + "bbox": [ + 304, + 498, + 545, + 570 + ], + "type": "text", + "content": " into a magnitude spectrogram " + }, + { + "bbox": [ + 304, + 498, + 545, + 570 + ], + "type": "inline_equation", + "content": "X" + }, + { + "bbox": [ + 304, + 498, + 545, + 570 + ], + "type": "text", + "content": " with the short-time Fourier transform (STFT). Then, we extract audio features " + }, + { + "bbox": [ + 304, + 498, + 545, + 570 + ], + "type": "inline_equation", + "content": "a = E_{a}(X), a \\in \\mathbb{R}^{c \\times h_{a} \\times w_{a}}" + }, + { + "bbox": [ + 304, + 498, + 545, + 570 + ], + "type": "text", + "content": " by means of a CNN encoder " + }, + { + "bbox": [ + 304, + 498, + 545, + 570 + ], + "type": "inline_equation", + "content": "E_{a}" + }, + { + "bbox": [ + 304, + 498, + 545, + 570 + ], + "type": "text", + "content": " in the Time-Frequency (T-F) space." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 575, + 480, + 587 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 575, + 480, + 587 + ], + "spans": [ + { + "bbox": [ + 306, + 575, + 480, + 587 + ], + "type": "text", + "content": "3.3. Cascaded Feature Enhancement" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 594, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 594, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 594, + 547, + 715 + ], + "type": "text", + "content": "As discussed in Sec. 3.1, a sound source " + }, + { + "bbox": [ + 304, + 594, + 547, + 715 + ], + "type": "inline_equation", + "content": "s_n" + }, + { + "bbox": [ + 304, + 594, + 547, + 715 + ], + "type": "text", + "content": " in the mixture " + }, + { + "bbox": [ + 304, + 594, + 547, + 715 + ], + "type": "inline_equation", + "content": "s" + }, + { + "bbox": [ + 304, + 594, + 547, + 715 + ], + "type": "text", + "content": " could be out of view due to constant view changes in egocentric videos and the limited FoV. This poses challenges in visually localizing sound sources and performance can degrade when the audio-visual associations are not precise. To address this, we update the features in a cascaded fashion. We first force the network to learn disentangled audio representations from the mixture using visual guidance. Then we utilize the disentangled audio representations to inject the visual features with more localization cues." + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "22912" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 286, + 156 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 286, + 156 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 286, + 156 + ], + "type": "text", + "content": "Disentanglement through sound source separation. Sound source localization objective can implicitly guide the system to learn disentangled audio features as the network will try to precisely localize the sound, and in turn, the on-screen sound will get disentangled from the rest. However, we formulate our problem in an unsupervised setting where labels for such localization objective are not available." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 157, + 286, + 276 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 157, + 286, + 276 + ], + "spans": [ + { + "bbox": [ + 46, + 157, + 286, + 276 + ], + "type": "text", + "content": "Audio-visual sound separation task [23, 87] uses visual information as guidance to learn to separate individual sounds from a mixture. Given the visual guidance, it is expected that the learned representations primarily encode information from visually indicated sound sources. Hence we argue for a multi-task learning approach to solve our primary task. Along with the audio-visual sounding object localization task, the network also learns to disentangle visible audio representations from the mixture through a source separation task." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 59, + 287, + 286, + 439 + ], + "type": "list", + "angle": 0, + "index": 4, + "blocks": [ + { + "bbox": [ + 59, + 287, + 286, + 383 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 287, + 286, + 383 + ], + "spans": [ + { + "bbox": [ + 59, + 287, + 286, + 383 + ], + "type": "text", + "content": "- Training. We adopt the commonly used \"mix-and-separate\" strategy [23,87] for audio-visual sound separation. Given the current audio " + }, + { + "bbox": [ + 59, + 287, + 286, + 383 + ], + "type": "inline_equation", + "content": "s^{(1)}" + }, + { + "bbox": [ + 59, + 287, + 286, + 383 + ], + "type": "text", + "content": ", we randomly sample another audio stream " + }, + { + "bbox": [ + 59, + 287, + 286, + 383 + ], + "type": "inline_equation", + "content": "s^{(2)}" + }, + { + "bbox": [ + 59, + 287, + 286, + 383 + ], + "type": "text", + "content": " from a different video and mix them together to generate input audio mixture " + }, + { + "bbox": [ + 59, + 287, + 286, + 383 + ], + "type": "inline_equation", + "content": "\\tilde{s} = s^{(1)} + s^{(2)}" + }, + { + "bbox": [ + 59, + 287, + 286, + 383 + ], + "type": "text", + "content": ". We then obtain magnitude spectrograms " + }, + { + "bbox": [ + 59, + 287, + 286, + 383 + ], + "type": "inline_equation", + "content": "\\tilde{X}, X^{(1)}, X^{(2)}" + }, + { + "bbox": [ + 59, + 287, + 286, + 383 + ], + "type": "text", + "content": " for " + }, + { + "bbox": [ + 59, + 287, + 286, + 383 + ], + "type": "inline_equation", + "content": "\\tilde{s}, s^{(1)}" + }, + { + "bbox": [ + 59, + 287, + 286, + 383 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 59, + 287, + 286, + 383 + ], + "type": "inline_equation", + "content": "s^{(2)}" + }, + { + "bbox": [ + 59, + 287, + 286, + 383 + ], + "type": "text", + "content": " respectively. The audio features is then modified as " + }, + { + "bbox": [ + 59, + 287, + 286, + 383 + ], + "type": "inline_equation", + "content": "a = E_a(\\tilde{X})" + }, + { + "bbox": [ + 59, + 287, + 286, + 383 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 59, + 392, + 286, + 439 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 392, + 286, + 439 + ], + "spans": [ + { + "bbox": [ + 59, + 392, + 286, + 439 + ], + "type": "text", + "content": "- Inference. During inference, we take the original audio stream as input: " + }, + { + "bbox": [ + 59, + 392, + 286, + 439 + ], + "type": "inline_equation", + "content": "s = s^{(1)}" + }, + { + "bbox": [ + 59, + 392, + 286, + 439 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 59, + 392, + 286, + 439 + ], + "type": "inline_equation", + "content": "X = X^{(1)}" + }, + { + "bbox": [ + 59, + 392, + 286, + 439 + ], + "type": "text", + "content": " to extract visually correlated audio representations. Note that the audio features is " + }, + { + "bbox": [ + 59, + 392, + 286, + 439 + ], + "type": "inline_equation", + "content": "a = E_{a}(X)" + }, + { + "bbox": [ + 59, + 392, + 286, + 439 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 3 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 46, + 449, + 286, + 593 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 449, + 286, + 593 + ], + "spans": [ + { + "bbox": [ + 46, + 449, + 286, + 593 + ], + "type": "text", + "content": "We define the audio disentanglement network as a network " + }, + { + "bbox": [ + 46, + 449, + 286, + 593 + ], + "type": "inline_equation", + "content": "f(\\cdot)" + }, + { + "bbox": [ + 46, + 449, + 286, + 593 + ], + "type": "text", + "content": ", which produces the disentangled audio features " + }, + { + "bbox": [ + 46, + 449, + 286, + 593 + ], + "type": "inline_equation", + "content": "\\hat{a} \\in \\mathbb{R}^{c \\times h_a \\times w_a}" + }, + { + "bbox": [ + 46, + 449, + 286, + 593 + ], + "type": "text", + "content": ". In this network, we want to associate the visual content with the audio representations to perform disentanglement in the embedding space. Concretely, we first apply spatial average pooling on each " + }, + { + "bbox": [ + 46, + 449, + 286, + 593 + ], + "type": "inline_equation", + "content": "v_i" + }, + { + "bbox": [ + 46, + 449, + 286, + 593 + ], + "type": "text", + "content": " and temporal max pooling along the time axis to obtain a visual feature vector " + }, + { + "bbox": [ + 46, + 449, + 286, + 593 + ], + "type": "inline_equation", + "content": "g_v \\in \\mathbb{R}^c" + }, + { + "bbox": [ + 46, + 449, + 286, + 593 + ], + "type": "text", + "content": ". Then we replicate the visual feature vector " + }, + { + "bbox": [ + 46, + 449, + 286, + 593 + ], + "type": "inline_equation", + "content": "h_a \\times w_a" + }, + { + "bbox": [ + 46, + 449, + 286, + 593 + ], + "type": "text", + "content": " times and tile them to match the size of " + }, + { + "bbox": [ + 46, + 449, + 286, + 593 + ], + "type": "inline_equation", + "content": "a" + }, + { + "bbox": [ + 46, + 449, + 286, + 593 + ], + "type": "text", + "content": ". We concatenate the visual and audio feature maps along the channel dimension and feed them into the network. Therefore, the audio feature disentanglement can be formulated as:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 97, + 605, + 286, + 618 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 97, + 605, + 286, + 618 + ], + "spans": [ + { + "bbox": [ + 97, + 605, + 286, + 618 + ], + "type": "interline_equation", + "content": "\\hat {a} = f \\left(\\operatorname {C O N C A T} [ a, \\operatorname {T I L E} \\left(g _ {v}\\right) ]\\right). \\tag {1}", + "image_path": "f6a1eb90d7a54b6a74657b2fab87267b080c84a4001828ca8f91c1e519c006dd.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 628, + 286, + 676 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 628, + 286, + 676 + ], + "spans": [ + { + "bbox": [ + 46, + 628, + 286, + 676 + ], + "type": "text", + "content": "In practice, we implement the disentanglement network " + }, + { + "bbox": [ + 46, + 628, + 286, + 676 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 46, + 628, + 286, + 676 + ], + "type": "text", + "content": " using two 1x1 convolution layers. The audio feature " + }, + { + "bbox": [ + 46, + 628, + 286, + 676 + ], + "type": "inline_equation", + "content": "\\hat{a}" + }, + { + "bbox": [ + 46, + 628, + 286, + 676 + ], + "type": "text", + "content": " will be used for both separation mask and sounding object localization map generation." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 677, + 286, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 286, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 286, + 714 + ], + "type": "text", + "content": "To separate visible sounds, we add an audio decoder " + }, + { + "bbox": [ + 46, + 677, + 286, + 714 + ], + "type": "inline_equation", + "content": "D_{a}" + }, + { + "bbox": [ + 46, + 677, + 286, + 714 + ], + "type": "text", + "content": " following the disentanglement network to output a binary mask " + }, + { + "bbox": [ + 46, + 677, + 286, + 714 + ], + "type": "inline_equation", + "content": "M_{pred} = D_{a}(\\hat{a})" + }, + { + "bbox": [ + 46, + 677, + 286, + 714 + ], + "type": "text", + "content": " (at the bottom of Fig. 2). U-Net" + } + ] + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 315, + 72, + 538, + 184 + ], + "blocks": [ + { + "bbox": [ + 315, + 72, + 538, + 184 + ], + "lines": [ + { + "bbox": [ + 315, + 72, + 538, + 184 + ], + "spans": [ + { + "bbox": [ + 315, + 72, + 538, + 184 + ], + "type": "image", + "image_path": "4e6ae599120192a1f2f9884117b6944e2743f3b24b13a7bbdc1df5055a4b5ee4.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 194, + 545, + 228 + ], + "lines": [ + { + "bbox": [ + 304, + 194, + 545, + 228 + ], + "spans": [ + { + "bbox": [ + 304, + 194, + 545, + 228 + ], + "type": "text", + "content": "Figure 3. Overview of our proposed geometry-aware modeling approach. The visual features " + }, + { + "bbox": [ + 304, + 194, + 545, + 228 + ], + "type": "inline_equation", + "content": "\\hat{v}_j" + }, + { + "bbox": [ + 304, + 194, + 545, + 228 + ], + "type": "text", + "content": " are warped to viewpoint " + }, + { + "bbox": [ + 304, + 194, + 545, + 228 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 304, + 194, + 545, + 228 + ], + "type": "text", + "content": " by homography transformation." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 234, + 545, + 319 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 234, + 545, + 319 + ], + "spans": [ + { + "bbox": [ + 304, + 234, + 545, + 319 + ], + "type": "text", + "content": "architectures [23] are used in the audio encoder " + }, + { + "bbox": [ + 304, + 234, + 545, + 319 + ], + "type": "inline_equation", + "content": "E_{a}" + }, + { + "bbox": [ + 304, + 234, + 545, + 319 + ], + "type": "text", + "content": " and decoder " + }, + { + "bbox": [ + 304, + 234, + 545, + 319 + ], + "type": "inline_equation", + "content": "D_{a}" + }, + { + "bbox": [ + 304, + 234, + 545, + 319 + ], + "type": "text", + "content": ". We implement the " + }, + { + "bbox": [ + 304, + 234, + 545, + 319 + ], + "type": "inline_equation", + "content": "E_{a}" + }, + { + "bbox": [ + 304, + 234, + 545, + 319 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 234, + 545, + 319 + ], + "type": "inline_equation", + "content": "D_{a}" + }, + { + "bbox": [ + 304, + 234, + 545, + 319 + ], + "type": "text", + "content": " in five convolution and up-convolution layers, respectively. Details of the network architectures are provided in the Appendix. The ground truth separation mask " + }, + { + "bbox": [ + 304, + 234, + 545, + 319 + ], + "type": "inline_equation", + "content": "M_{gt}" + }, + { + "bbox": [ + 304, + 234, + 545, + 319 + ], + "type": "text", + "content": " can be calculated by determining whether the original input sound is dominant at locations " + }, + { + "bbox": [ + 304, + 234, + 545, + 319 + ], + "type": "inline_equation", + "content": "(u,v)" + }, + { + "bbox": [ + 304, + 234, + 545, + 319 + ], + "type": "text", + "content": " in the T-F space:" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 349, + 323, + 545, + 338 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 349, + 323, + 545, + 338 + ], + "spans": [ + { + "bbox": [ + 349, + 323, + 545, + 338 + ], + "type": "interline_equation", + "content": "M _ {g t} (u, v) = \\left[ X ^ {(1)} (u, v) \\geq \\tilde {X} (u, v) \\right]. \\tag {2}", + "image_path": "292b564ad6c3f7d4188d2079e05be68f7e8edabbc7b236558f86ac84dcfd4d46.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 344, + 545, + 380 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 344, + 545, + 380 + ], + "spans": [ + { + "bbox": [ + 304, + 344, + 545, + 380 + ], + "type": "text", + "content": "To train the sound separator, we minimize the " + }, + { + "bbox": [ + 304, + 344, + 545, + 380 + ], + "type": "inline_equation", + "content": "\\ell_2" + }, + { + "bbox": [ + 304, + 344, + 545, + 380 + ], + "type": "text", + "content": " distance between the predicted and ground-truth masks as the disentanglement learning objective:" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 371, + 385, + 545, + 399 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 371, + 385, + 545, + 399 + ], + "spans": [ + { + "bbox": [ + 371, + 385, + 545, + 399 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {d i s} = \\left| \\left| M _ {p r e d} - M _ {g t} \\right| \\right| _ {2} ^ {2}. \\tag {3}", + "image_path": "2b5ec7e4d4c4d303435184678f1ea6c5eb86c32f8d5051b60ba4dee456261a36.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 405, + 545, + 559 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 405, + 545, + 559 + ], + "spans": [ + { + "bbox": [ + 304, + 405, + 545, + 559 + ], + "type": "text", + "content": "Soft localization. Similar to the out-of-view sounds, the visual frames may contain sound-irrelevant regions. In order to learn more precise audio-visual associations, we propose to highlight the spatial regions that are more likely to be correlated with the on-screen sounds by computing audio-visual attention. The attention map will indicate the correlation between audio and visual representations at different spatial locations. Given the output " + }, + { + "bbox": [ + 304, + 405, + 545, + 559 + ], + "type": "inline_equation", + "content": "\\hat{a}" + }, + { + "bbox": [ + 304, + 405, + 545, + 559 + ], + "type": "text", + "content": " from disentanglement network " + }, + { + "bbox": [ + 304, + 405, + 545, + 559 + ], + "type": "inline_equation", + "content": "f(\\cdot)" + }, + { + "bbox": [ + 304, + 405, + 545, + 559 + ], + "type": "text", + "content": ", we apply max pooling on its time and frequency dimensions, obtaining an audio feature vector " + }, + { + "bbox": [ + 304, + 405, + 545, + 559 + ], + "type": "inline_equation", + "content": "g_{\\hat{a}}" + }, + { + "bbox": [ + 304, + 405, + 545, + 559 + ], + "type": "text", + "content": ". Then at each spatial position (x,y) of visual feature " + }, + { + "bbox": [ + 304, + 405, + 545, + 559 + ], + "type": "inline_equation", + "content": "v_{i}" + }, + { + "bbox": [ + 304, + 405, + 545, + 559 + ], + "type": "text", + "content": ", we compute the cosine similarity between audio and visual feature vectors:" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 339, + 567, + 545, + 580 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 339, + 567, + 545, + 580 + ], + "spans": [ + { + "bbox": [ + 339, + 567, + 545, + 580 + ], + "type": "interline_equation", + "content": "S _ {i}: S _ {i} (x, y) = \\operatorname {C O S I N E S I M} \\left(v _ {i} (x, y), g _ {\\hat {a}}\\right). \\tag {4}", + "image_path": "8c17454c6c73e77fce4e61cdc80670d04c139604f52904c0101e412172644581.jpg" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 586, + 545, + 622 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 586, + 545, + 622 + ], + "spans": [ + { + "bbox": [ + 304, + 586, + 545, + 622 + ], + "type": "text", + "content": "SOFTMAX is then used on " + }, + { + "bbox": [ + 304, + 586, + 545, + 622 + ], + "type": "inline_equation", + "content": "S_{i}" + }, + { + "bbox": [ + 304, + 586, + 545, + 622 + ], + "type": "text", + "content": " to generate a soft mask that represents the audio-visual correspondence. Hence, each " + }, + { + "bbox": [ + 304, + 586, + 545, + 622 + ], + "type": "inline_equation", + "content": "v_{i}" + }, + { + "bbox": [ + 304, + 586, + 545, + 622 + ], + "type": "text", + "content": " can be attended with the calculated weights:" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 374, + 628, + 545, + 641 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 374, + 628, + 545, + 641 + ], + "spans": [ + { + "bbox": [ + 374, + 628, + 545, + 641 + ], + "type": "interline_equation", + "content": "\\hat {v} _ {i} = \\operatorname {S O F T M A X} \\left(S _ {i}\\right) \\cdot v _ {i}. \\tag {5}", + "image_path": "3c0a2158dc2a30e4f8ff601254f544af780dbef01b12fbeeec56dd84e71f7dc4.jpg" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 306, + 647, + 504, + 660 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 647, + 504, + 660 + ], + "spans": [ + { + "bbox": [ + 306, + 647, + 504, + 660 + ], + "type": "text", + "content": "3.4. Geometry-Aware Temporal Modeling" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 666, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 666, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 666, + 545, + 714 + ], + "type": "text", + "content": "Given the temporal nature of sounds and the persistence of audio-visual associations, we incorporate temporal information from neighboring frames to learn sounding object features. However, temporal modeling is a challenging" + } + ] + } + ], + "index": 20 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "22913" + } + ] + } + ], + "index": 21 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 95 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 95 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 95 + ], + "type": "text", + "content": "problem for egocentric videos due to widespread egomotion and object-appearance deformations." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 96, + 288, + 300 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 96, + 288, + 300 + ], + "spans": [ + { + "bbox": [ + 46, + 96, + 288, + 300 + ], + "type": "text", + "content": "Although visual objects are dynamically changing, the surrounding physical environment is persistent. Hence, temporal variations in egocentric videos reveal rich 3D geometric cues that can recover the surrounding scene from changing viewpoints. Prior works have shown that given a sequence of frames, one can reconstruct the underlying 3D scene from the 2D observations [64,81]. In our work, rather than reconstructing the 3D structures, we estimate the relative geometric transformation between frames to alleviate egomotion. Specifically, we apply the transformation at the feature level to perform geometry-aware temporal aggregation. Given " + }, + { + "bbox": [ + 46, + 96, + 288, + 300 + ], + "type": "inline_equation", + "content": "\\{I_i\\}_{i=1}^T" + }, + { + "bbox": [ + 46, + 96, + 288, + 300 + ], + "type": "text", + "content": " and their features " + }, + { + "bbox": [ + 46, + 96, + 288, + 300 + ], + "type": "inline_equation", + "content": "\\{\\hat{v}_i\\}_{i=1}^T" + }, + { + "bbox": [ + 46, + 96, + 288, + 300 + ], + "type": "text", + "content": ", we take " + }, + { + "bbox": [ + 46, + 96, + 288, + 300 + ], + "type": "inline_equation", + "content": "\\hat{v}_i" + }, + { + "bbox": [ + 46, + 96, + 288, + 300 + ], + "type": "text", + "content": " as a query at a time and use the other features from neighboring frames as support features to aggregate temporal contexts. For clarity, we decompose the geometry-aware temporal aggregation into two parts: geometry modeling and temporal aggregation." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 300, + 288, + 431 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 300, + 288, + 431 + ], + "spans": [ + { + "bbox": [ + 46, + 300, + 288, + 431 + ], + "type": "text", + "content": "Geometry modeling. This step aims to compute the geometric transformation that represents the egomotion between frames (see Fig. 3). We found that homography estimation, which can align images taken from different perspectives, can serve as a way to measure geometric transformation. We adopt SIFT [46] + RANSAC [18] to solve homography. To be specific, a homography is a " + }, + { + "bbox": [ + 46, + 300, + 288, + 431 + ], + "type": "inline_equation", + "content": "3 \\times 3" + }, + { + "bbox": [ + 46, + 300, + 288, + 431 + ], + "type": "text", + "content": " matrix that consists of 8 degree of freedom (DOF) for scale, translation, rotation, and perspective respectively. Given the query frame " + }, + { + "bbox": [ + 46, + 300, + 288, + 431 + ], + "type": "inline_equation", + "content": "I_{i}" + }, + { + "bbox": [ + 46, + 300, + 288, + 431 + ], + "type": "text", + "content": " and a supporting frame " + }, + { + "bbox": [ + 46, + 300, + 288, + 431 + ], + "type": "inline_equation", + "content": "I_{j}" + }, + { + "bbox": [ + 46, + 300, + 288, + 431 + ], + "type": "text", + "content": ", we use " + }, + { + "bbox": [ + 46, + 300, + 288, + 431 + ], + "type": "inline_equation", + "content": "h(\\cdot)" + }, + { + "bbox": [ + 46, + 300, + 288, + 431 + ], + "type": "text", + "content": " to denote the computation process:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 123, + 439, + 287, + 453 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 123, + 439, + 287, + 453 + ], + "spans": [ + { + "bbox": [ + 123, + 439, + 287, + 453 + ], + "type": "interline_equation", + "content": "\\mathcal {H} _ {j i} = h \\left(I _ {j}, I _ {i}\\right) _ {j \\rightarrow i}, \\tag {6}", + "image_path": "6df4f63f4abbba6e80657ac4f7974e0c4774f307fa385fba8f7bf93a5ed565d3.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 460, + 287, + 556 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 460, + 287, + 556 + ], + "spans": [ + { + "bbox": [ + 46, + 460, + 287, + 556 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 460, + 287, + 556 + ], + "type": "inline_equation", + "content": "\\mathcal{H}_{ji}" + }, + { + "bbox": [ + 46, + 460, + 287, + 556 + ], + "type": "text", + "content": " represents the homography transformation from frame " + }, + { + "bbox": [ + 46, + 460, + 287, + 556 + ], + "type": "inline_equation", + "content": "I_{j}" + }, + { + "bbox": [ + 46, + 460, + 287, + 556 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 46, + 460, + 287, + 556 + ], + "type": "inline_equation", + "content": "I_{i}" + }, + { + "bbox": [ + 46, + 460, + 287, + 556 + ], + "type": "text", + "content": ". With the computed homography transformation, we can then apply it at the feature level to transform visual features " + }, + { + "bbox": [ + 46, + 460, + 287, + 556 + ], + "type": "inline_equation", + "content": "\\hat{v}_j" + }, + { + "bbox": [ + 46, + 460, + 287, + 556 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 46, + 460, + 287, + 556 + ], + "type": "inline_equation", + "content": "\\hat{v}_{ji}" + }, + { + "bbox": [ + 46, + 460, + 287, + 556 + ], + "type": "text", + "content": ". The " + }, + { + "bbox": [ + 46, + 460, + 287, + 556 + ], + "type": "inline_equation", + "content": "\\hat{v}_{ji}" + }, + { + "bbox": [ + 46, + 460, + 287, + 556 + ], + "type": "text", + "content": " is egomotion-free under the viewpoint of " + }, + { + "bbox": [ + 46, + 460, + 287, + 556 + ], + "type": "inline_equation", + "content": "I_{i}" + }, + { + "bbox": [ + 46, + 460, + 287, + 556 + ], + "type": "text", + "content": ". Since the resolution of feature maps is scaled down compared to the raw frame size, the homography matrix " + }, + { + "bbox": [ + 46, + 460, + 287, + 556 + ], + "type": "inline_equation", + "content": "\\mathcal{H}" + }, + { + "bbox": [ + 46, + 460, + 287, + 556 + ], + "type": "text", + "content": " should also be downsampled using the same scaling factor. The feature transformation can be written as:" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 133, + 567, + 287, + 581 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 133, + 567, + 287, + 581 + ], + "spans": [ + { + "bbox": [ + 133, + 567, + 287, + 581 + ], + "type": "interline_equation", + "content": "\\hat {v} _ {j i} = \\mathcal {H} _ {j i} \\otimes \\hat {v} _ {j}, \\tag {7}", + "image_path": "6ad3742cd6735aea42b97ab09bcef1415e6c8c5f7f6fc77f6badb1958ad4baff.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 585, + 220, + 596 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 585, + 220, + 596 + ], + "spans": [ + { + "bbox": [ + 46, + 585, + 220, + 596 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 585, + 220, + 596 + ], + "type": "inline_equation", + "content": "\\otimes" + }, + { + "bbox": [ + 46, + 585, + 220, + 596 + ], + "type": "text", + "content": " represents the warping operation." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 596, + 287, + 669 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 596, + 287, + 669 + ], + "spans": [ + { + "bbox": [ + 46, + 596, + 287, + 669 + ], + "type": "text", + "content": "Temporal aggregation. For the query feature " + }, + { + "bbox": [ + 46, + 596, + 287, + 669 + ], + "type": "inline_equation", + "content": "\\hat{v}_i" + }, + { + "bbox": [ + 46, + 596, + 287, + 669 + ], + "type": "text", + "content": ", we end up with set of aligned features " + }, + { + "bbox": [ + 46, + 596, + 287, + 669 + ], + "type": "inline_equation", + "content": "\\{\\hat{v}_{ji}\\}_{j=1}^{T}" + }, + { + "bbox": [ + 46, + 596, + 287, + 669 + ], + "type": "text", + "content": " corresponding to each frame viewpoint. To aggregate the temporal contexts, we propose to compute the correlation between features from different frames at the same locations (see Fig. 4). The aggregation process can be formulated as:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 675, + 287, + 714 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 675, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 47, + 675, + 287, + 714 + ], + "type": "interline_equation", + "content": "z _ {i} (x, y) = \\hat {v} _ {i} (x, y) + \\operatorname {S O F T M A X} \\left(\\frac {\\hat {v} _ {i} (x , y) \\hat {\\boldsymbol {v}} (x , y) ^ {T}}{\\sqrt {d}}\\right) \\hat {\\boldsymbol {v}} (x, y), \\tag {8}", + "image_path": "f5c46ccacd4032896edb091c7261fbcd4df6bdeaf130b10a443f2d741a16d436.jpg" + } + ] + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 326, + 72, + 526, + 148 + ], + "blocks": [ + { + "bbox": [ + 326, + 72, + 526, + 148 + ], + "lines": [ + { + "bbox": [ + 326, + 72, + 526, + 148 + ], + "spans": [ + { + "bbox": [ + 326, + 72, + 526, + 148 + ], + "type": "image", + "image_path": "040729c88d40b05b44f5ec95699dcd9bdd09cebd9cc8aafa20d089d931a93bba.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 156, + 545, + 190 + ], + "lines": [ + { + "bbox": [ + 305, + 156, + 545, + 190 + ], + "spans": [ + { + "bbox": [ + 305, + 156, + 545, + 190 + ], + "type": "text", + "content": "Figure 4. Illustration on the temporal context aggregation process for query feature " + }, + { + "bbox": [ + 305, + 156, + 545, + 190 + ], + "type": "inline_equation", + "content": "\\hat{v}_i" + }, + { + "bbox": [ + 305, + 156, + 545, + 190 + ], + "type": "text", + "content": " and neighboring frame features " + }, + { + "bbox": [ + 305, + 156, + 545, + 190 + ], + "type": "inline_equation", + "content": "\\hat{v}_{i-1}" + }, + { + "bbox": [ + 305, + 156, + 545, + 190 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 156, + 545, + 190 + ], + "type": "inline_equation", + "content": "\\hat{v}_{i+1}" + }, + { + "bbox": [ + 305, + 156, + 545, + 190 + ], + "type": "text", + "content": ", which is performed independently at each spatial location." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 200, + 545, + 261 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 200, + 545, + 261 + ], + "spans": [ + { + "bbox": [ + 305, + 200, + 545, + 261 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 200, + 545, + 261 + ], + "type": "inline_equation", + "content": "\\hat{\\pmb{v}} = [\\hat{v}_{1i};\\dots;\\hat{v}_{Ti}]" + }, + { + "bbox": [ + 305, + 200, + 545, + 261 + ], + "type": "text", + "content": " is the concatenation of frame features; the scaling factor " + }, + { + "bbox": [ + 305, + 200, + 545, + 261 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 305, + 200, + 545, + 261 + ], + "type": "text", + "content": " is equal to the feature dimension; and " + }, + { + "bbox": [ + 305, + 200, + 545, + 261 + ], + "type": "inline_equation", + "content": "(\\cdot)^T" + }, + { + "bbox": [ + 305, + 200, + 545, + 261 + ], + "type": "text", + "content": " represents the transpose operation [80]. The aggregation operation is applied at all spatial locations " + }, + { + "bbox": [ + 305, + 200, + 545, + 261 + ], + "type": "inline_equation", + "content": "(x,y)" + }, + { + "bbox": [ + 305, + 200, + 545, + 261 + ], + "type": "text", + "content": " to generate the updated visual features " + }, + { + "bbox": [ + 305, + 200, + 545, + 261 + ], + "type": "inline_equation", + "content": "z_{i}" + }, + { + "bbox": [ + 305, + 200, + 545, + 261 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 267, + 417, + 280 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 267, + 417, + 280 + ], + "spans": [ + { + "bbox": [ + 306, + 267, + 417, + 280 + ], + "type": "text", + "content": "3.5. Training Objective" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 285, + 545, + 322 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 285, + 545, + 322 + ], + "spans": [ + { + "bbox": [ + 305, + 285, + 545, + 322 + ], + "type": "text", + "content": "We take audio-visual synchronization as the \"free\" supervision and solve the task in a self-supervised manner using contrastive learning [2,4,11,65]." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 322, + 545, + 429 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 322, + 545, + 429 + ], + "spans": [ + { + "bbox": [ + 305, + 322, + 545, + 429 + ], + "type": "text", + "content": "With the audio feature vector " + }, + { + "bbox": [ + 305, + 322, + 545, + 429 + ], + "type": "inline_equation", + "content": "g_{\\hat{a}}" + }, + { + "bbox": [ + 305, + 322, + 545, + 429 + ], + "type": "text", + "content": " and the visual features " + }, + { + "bbox": [ + 305, + 322, + 545, + 429 + ], + "type": "inline_equation", + "content": "\\{z_i\\}_{i=1}^T" + }, + { + "bbox": [ + 305, + 322, + 545, + 429 + ], + "type": "text", + "content": ", we can compute an audio-visual attention map " + }, + { + "bbox": [ + 305, + 322, + 545, + 429 + ], + "type": "inline_equation", + "content": "S_i" + }, + { + "bbox": [ + 305, + 322, + 545, + 429 + ], + "type": "text", + "content": " in Eq. 4 for each frame " + }, + { + "bbox": [ + 305, + 322, + 545, + 429 + ], + "type": "inline_equation", + "content": "I_i" + }, + { + "bbox": [ + 305, + 322, + 545, + 429 + ], + "type": "text", + "content": ". The training objective should optimize the network such that only the sounding regions have a high response in " + }, + { + "bbox": [ + 305, + 322, + 545, + 429 + ], + "type": "inline_equation", + "content": "S_i" + }, + { + "bbox": [ + 305, + 322, + 545, + 429 + ], + "type": "text", + "content": ". Since the ground-truth sounding map is unknown, we apply differential thresholding on " + }, + { + "bbox": [ + 305, + 322, + 545, + 429 + ], + "type": "inline_equation", + "content": "S_i" + }, + { + "bbox": [ + 305, + 322, + 545, + 429 + ], + "type": "text", + "content": " to predict sounding objectness map " + }, + { + "bbox": [ + 305, + 322, + 545, + 429 + ], + "type": "inline_equation", + "content": "O_i = sigmoid((S_i - \\epsilon) / \\tau)" + }, + { + "bbox": [ + 305, + 322, + 545, + 429 + ], + "type": "text", + "content": " [11], where " + }, + { + "bbox": [ + 305, + 322, + 545, + 429 + ], + "type": "inline_equation", + "content": "\\epsilon" + }, + { + "bbox": [ + 305, + 322, + 545, + 429 + ], + "type": "text", + "content": " is the threshold, and " + }, + { + "bbox": [ + 305, + 322, + 545, + 429 + ], + "type": "inline_equation", + "content": "\\tau" + }, + { + "bbox": [ + 305, + 322, + 545, + 429 + ], + "type": "text", + "content": " denotes the temperature that controls the sharpness." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 430, + 545, + 525 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 430, + 545, + 525 + ], + "spans": [ + { + "bbox": [ + 305, + 430, + 545, + 525 + ], + "type": "text", + "content": "In an egocentric video clip, a visual scene is usually temporally dynamic. Sometimes a single audio-visual pair " + }, + { + "bbox": [ + 305, + 430, + 545, + 525 + ], + "type": "inline_equation", + "content": "(I_i,s)" + }, + { + "bbox": [ + 305, + 430, + 545, + 525 + ], + "type": "text", + "content": " may not be audio-visually correlated. To this end, we solve the localization task in the Multiple-Instance Learning (MIL) [47] setting to improve robustness. Concretely, we use a soft MIL pooling function to aggregate the concatenated attention maps " + }, + { + "bbox": [ + 305, + 430, + 545, + 525 + ], + "type": "inline_equation", + "content": "S = [S_1;\\dots;S_T]" + }, + { + "bbox": [ + 305, + 430, + 545, + 525 + ], + "type": "text", + "content": " by assigning different weights to " + }, + { + "bbox": [ + 305, + 430, + 545, + 525 + ], + "type": "inline_equation", + "content": "S_{t}" + }, + { + "bbox": [ + 305, + 430, + 545, + 525 + ], + "type": "text", + "content": " at different time steps:" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 375, + 534, + 545, + 566 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 375, + 534, + 545, + 566 + ], + "spans": [ + { + "bbox": [ + 375, + 534, + 545, + 566 + ], + "type": "interline_equation", + "content": "\\bar {S} = \\sum_ {t = 1} ^ {T} \\left(W _ {t} \\cdot \\boldsymbol {S}\\right) [:,:, t ], \\tag {9}", + "image_path": "d0f34d2b07f2b538613c75ffbbbba95ca0dcc8607dc98bb1f647dff5ae32cd3b.jpg" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 305, + 574, + 545, + 635 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 574, + 545, + 635 + ], + "spans": [ + { + "bbox": [ + 305, + 574, + 545, + 635 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 574, + 545, + 635 + ], + "type": "inline_equation", + "content": "W_{t}[x,y,:] = \\mathrm{SOFTMAX}(S[x,y,:])" + }, + { + "bbox": [ + 305, + 574, + 545, + 635 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 305, + 574, + 545, + 635 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 305, + 574, + 545, + 635 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 574, + 545, + 635 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 305, + 574, + 545, + 635 + ], + "type": "text", + "content": " are the indices on spatial dimensions. Subsequently, an aggregated sounding objectness map " + }, + { + "bbox": [ + 305, + 574, + 545, + 635 + ], + "type": "inline_equation", + "content": "\\overline{O}" + }, + { + "bbox": [ + 305, + 574, + 545, + 635 + ], + "type": "text", + "content": " is calculated from " + }, + { + "bbox": [ + 305, + 574, + 545, + 635 + ], + "type": "inline_equation", + "content": "\\overline{S}" + }, + { + "bbox": [ + 305, + 574, + 545, + 635 + ], + "type": "text", + "content": ". In this way, for each video clip " + }, + { + "bbox": [ + 305, + 574, + 545, + 635 + ], + "type": "inline_equation", + "content": "V" + }, + { + "bbox": [ + 305, + 574, + 545, + 635 + ], + "type": "text", + "content": " in the batch, we can define its positive and negative training signals as:" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 346, + 643, + 545, + 669 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 346, + 643, + 545, + 669 + ], + "spans": [ + { + "bbox": [ + 346, + 643, + 545, + 669 + ], + "type": "interline_equation", + "content": "P = \\frac {1}{| \\bar {O} |} \\langle \\bar {O}, \\bar {S} \\rangle , \\quad N = \\frac {1}{h w} \\langle \\mathbf {1}, S _ {n e g} \\rangle , \\tag {10}", + "image_path": "c6fa5a9743dce84ee8522e2c8e66cf7ee5f2aec1b50355964891c7233d40dec9.jpg" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 306, + 677, + 478, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 677, + 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] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 46, + 177, + 547, + 222 + ], + "lines": [ + { + "bbox": [ + 46, + 177, + 547, + 222 + ], + "spans": [ + { + "bbox": [ + 46, + 177, + 547, + 222 + ], + "type": "text", + "content": "Figure 5. Illustration of the Epic Sounding Object dataset statistics. (a) Example of our video frames and sounding object annotations. Class diversity (squeeze packaging, close trash can, put the pot, etc.) (b): The distribution of untrimmed video duration. (c): The number of videos that are annotated as containing out-of-view sounds. (d): Distribution of bounding box areas in Epic Sounding Object dataset, the majority of boxes cover less than " + }, + { + "bbox": [ + 46, + 177, + 547, + 222 + ], + "type": "inline_equation", + "content": "20\\%" + }, + { + "bbox": [ + 46, + 177, + 547, + 222 + ], + "type": "text", + "content": " of the image area, demonstrating the difficulty of this task." + } + ] + } + ], + "index": 19, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "type": "image", + "bbox": [ + 170, + 70, + 289, + 94 + ], + "blocks": [ + { + "bbox": [ + 170, + 70, + 289, + 94 + ], + "lines": [ + { + "bbox": [ + 170, + 70, + 289, + 94 + ], + "spans": [ + { + "bbox": [ + 170, + 70, + 289, + 94 + ], + "type": "image", + "image_path": "f21d3b0b2243e3ae50866820ed6666506885c7f7085448dba0abf91426c98546.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 171, + 94, + 192, + 99 + ], + "lines": [ + { + "bbox": [ + 171, + 94, + 192, + 99 + ], + "spans": [ + { + "bbox": [ + 171, + 94, + 192, + 99 + ], + "type": "text", + "content": "Stir meat" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_caption" + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 171, + 99, + 288, + 122 + ], + "blocks": [ + { + "bbox": [ + 171, + 99, + 288, + 122 + ], + "lines": [ + { + "bbox": [ + 171, + 99, + 288, + 122 + ], + "spans": [ + { + "bbox": [ + 171, + 99, + 288, + 122 + ], + "type": "image", + "image_path": "39544f331674d69926cf69c46cc1d6d9b4a1f932f7ece2fd65ae211f2cbbe01a.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 171, + 122, + 205, + 127 + ], + "lines": [ + { + "bbox": [ + 171, + 122, + 205, + 127 + ], + "spans": [ + { + "bbox": [ + 171, + 122, + 205, + 127 + ], + "type": "text", + "content": "Close trash can" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 171, + 128, + 288, + 150 + ], + 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"type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 243, + 286, + 268 + ], + "spans": [ + { + "bbox": [ + 47, + 243, + 286, + 268 + ], + "type": "text", + "content": "video clips. 1 denotes an all ones tensor with shape " + }, + { + "bbox": [ + 47, + 243, + 286, + 268 + ], + "type": "inline_equation", + "content": "h \\times w" + }, + { + "bbox": [ + 47, + 243, + 286, + 268 + ], + "type": "text", + "content": ". Therefore, the localization optimization objective is:" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 70, + 274, + 287, + 306 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 70, + 274, + 287, + 306 + ], + "spans": [ + { + "bbox": [ + 70, + 274, + 287, + 306 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {l o c} = - \\frac {1}{N} \\sum_ {k = 1} ^ {N} \\left[ \\log \\frac {\\exp \\left(P _ {k}\\right)}{\\exp \\left(P _ {k}\\right) + \\exp \\left(N _ {k}\\right)} \\right], \\tag {11}", + "image_path": "4f936e08c837be8bd1680b2242c1b8d0e24f7b6826ebab6ae353c3e5fd1268b8.jpg" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 47, + 312, + 287, + 350 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 312, + 287, + 350 + ], + "spans": [ + { + "bbox": [ + 47, + 312, + 287, + 350 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 312, + 287, + 350 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 47, + 312, + 287, + 350 + ], + "type": "text", + "content": " is the video sample index in a training batch. The overall objective is " + }, + { + "bbox": [ + 47, + 312, + 287, + 350 + ], + "type": "inline_equation", + "content": "\\mathcal{L} = \\mathcal{L}_{loc} + \\lambda \\mathcal{L}_{dis}" + }, + { + "bbox": [ + 47, + 312, + 287, + 350 + ], + "type": "text", + "content": ", where we empirically set " + }, + { + "bbox": [ + 47, + 312, + 287, + 350 + ], + "type": "inline_equation", + "content": "\\lambda = 5" + }, + { + "bbox": [ + 47, + 312, + 287, + 350 + ], + "type": "text", + "content": " in our experiments." + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 47, + 358, + 239, + 373 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 358, + 239, + 373 + ], + "spans": [ + { + "bbox": [ + 47, + 358, + 239, + 373 + ], + "type": "text", + "content": "4. The Epic Sounding Object Dataset" + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 46, + 378, + 287, + 486 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 378, + 287, + 486 + ], + "spans": [ + { + "bbox": [ + 46, + 378, + 287, + 486 + ], + "type": "text", + "content": "Existing sound source visual localization evaluation datasets, such as SoundNet-Flickr [65], VGG-Sound Source [11], only contain third-person recordings. To the best of our knowledge, there is no existing dataset that is suitable for evaluating our model. Thus, we introduce an Epic Sounding Object Dataset for egocentric audio-visual sounding object localization. Built upon the well-known Epic-Kitchens [13] dataset, we collect sounding object annotations on its action recognition test set." + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 46, + 486, + 287, + 629 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 486, + 287, + 629 + ], + "spans": [ + { + "bbox": [ + 46, + 486, + 287, + 629 + ], + "type": "text", + "content": "Data preparation. We select 13k test videos from the Epic-Kitchens action recognition benchmark as our source data. Since these videos are not originally collected for audiovisual analysis, they vary in length, and not all of them contain meaningful sounds. To verify the videos for annotations, we conduct a two-step process: We first determine if a video is silent by checking its sound-level in decibels relative to full scale. Consequently, silent videos are filtered out to provide a meaningful data source. Second, we bin the videos by their duration and show the statistics in Fig. 5 (b). The majority last less than 2 seconds, and hence we choose to trim the center 1-second clip from each video." + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 46, + 630, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 630, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 630, + 287, + 714 + ], + "type": "text", + "content": "After pre-processing, we obtain 5,089 videos in total for annotation. For each video, we uniformly select three frames and annotate sounding objects in the frames. We follow previous works [11,76] to use bounding boxes to annotate the objects that emit sounds. To obtain proposals of potential sounding objects automatically, we follow EpicKitchens [13] to use a Mask R-CNN object detector [25]" + } + ] + } + ], + "index": 26 + }, + { + "type": "table", + "bbox": [ + 318, + 241, + 535, + 289 + ], + "blocks": [ + { + "bbox": [ + 318, + 241, + 535, + 289 + ], + "lines": [ + { + "bbox": [ + 318, + 241, + 535, + 289 + ], + "spans": [ + { + "bbox": [ + 318, + 241, + 535, + 289 + ], + "type": "table", + "html": "
Before votingAfter voting
VideoFramesVideoFramesClasses
5,08915,2673,1729,19630
", + "image_path": "947cef83410e70948945c6fa33151d026489a7cb1119c88bd7229b50cc7ad09f.jpg" + } + ] + } + ], + "index": 27, + "angle": 0, + "type": "table_body" + } + ], + "index": 27 + }, + { + "bbox": [ + 325, + 298, + 525, + 309 + ], + "lines": [ + { + "bbox": [ + 325, + 298, + 525, + 309 + ], + "spans": [ + { + "bbox": [ + 325, + 298, + 525, + 309 + ], + "type": "text", + "content": "Table 1. Statistics of the Epic Sounding Object dataset." + } + ] + } + ], + "index": 28, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 304, + 319, + 545, + 342 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 319, + 545, + 342 + ], + "spans": [ + { + "bbox": [ + 304, + 319, + 545, + 342 + ], + "type": "text", + "content": "trained on MS-COCO [43] and a hand-objects detector [68] that is pretrained with 42K egocentric images [13,42,69]." + } + ] + } + ], + "index": 29 + }, + { + "bbox": [ + 304, + 343, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 343, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 343, + 546, + 713 + ], + "type": "text", + "content": "Annotation collection. Given the pre-processed data, we then annotate the sounding objects manually. Unlike third-person view videos, the object-sound associations in the egocentric domain are more complicated. There are two main challenges: (i) Numerous egocentric videos record wearer-environment interaction (e.g., a human places a dish on the table). The object-sound associations could be dynamic, and sometimes it is hard to determine what objects are emitting sounds; and (ii) the objects in egocentric videos are often missing from the screen, resulting in variations in scale (see Fig. 5 (c)). We address the above issues by taking advantage of human commonsense knowledge. We ask three or more annotators from the Amazon Mechanic Turk to annotate the same video (frames). Concretely, they do this by first watching the 1-second video with three annotated frames to confirm what objects make sounds in the video. During the annotation course, they are asked to answer two questions: (1) Does the video contain out-of-view sounds? (2) Which bounding boxes correspond to the sounding objects? We collect the annotations in multiple rounds until each video has at least three or more valid annotations from the Amazon annotators. Finally, we conduct an annotation verification by voting on all videos. If at least two annotators agree on the same answer, it will be considered as a correct annotation; If not, we will simply omit the video. The annotation statistics after voting are shown in Tab. 1. We obtain 30 classes of sounds by counting the noun (object) classes. The annotations are evenly split into two sets for validation and testing. The examples and statistics in Fig. 5 illustrate the diverse and complicated nature of egocentric audio-visual scenes." + } + ] + } + ], + "index": 30 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "22915" + } + ] + } + ], + "index": 31 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 50, + 71, + 282, + 269 + ], + "blocks": [ + { + "bbox": [ + 50, + 71, + 282, + 269 + ], + "lines": [ + { + "bbox": [ + 50, + 71, + 282, + 269 + ], + "spans": [ + { + "bbox": [ + 50, + 71, + 282, + 269 + ], + "type": "image", + "image_path": "6e5e8c9971c634038c219afcaf7fca327c471303b1df78a7847c11c2f96551ba.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 272, + 287, + 316 + ], + "lines": [ + { + "bbox": [ + 46, + 272, + 287, + 316 + ], + "spans": [ + { + "bbox": [ + 46, + 272, + 287, + 316 + ], + "type": "text", + "content": "Figure 6. Qualitative comparison on Epic Sounding Object dataset. We show diverse sounding objects in the kitchen scenes in the first column, sounding objects are annotated in red boxes. Our method outperforms all the compared works." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 331, + 123, + 345 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 331, + 123, + 345 + ], + "spans": [ + { + "bbox": [ + 47, + 331, + 123, + 345 + ], + "type": "text", + "content": "5. Experiment" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 354, + 287, + 605 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 354, + 287, + 605 + ], + "spans": [ + { + "bbox": [ + 46, + 354, + 287, + 605 + ], + "type": "text", + "content": "Datasets. In our experiments, we use two egocentric datasets. (1) Epic-Kitchens [13]: The dataset consists of 100 hours of egocentric recordings from 45 kitchen scenes. Thus, diverse kitchen-relevant events and sounds are in the dataset. We follow the same data split released in their action recognition benchmark and select 62,413 training videos. We then filter out the silent videos by measuring the Decibels relative to full scale. This results in 47,214 training videos in total. For evaluation, we use our annotated Epic Sounding Object dataset to report the results; (2) Ego4D [24]: Ego4D is the most recent large-scale egocentric video dataset. Besides kitchen scenes, it includes diverse daily life scenarios. Specifically, it consists of different subsets serving different benchmarks. We select the \"Bristol\" subset as it contains diverse scenarios (e.g., entertainment, sports, commuting, and more) to test our method. We randomly sample and trim 50,000 1-second videos from this subset and use " + }, + { + "bbox": [ + 46, + 354, + 287, + 605 + ], + "type": "inline_equation", + "content": "90\\% / 10\\%" + }, + { + "bbox": [ + 46, + 354, + 287, + 605 + ], + "type": "text", + "content": " as the train/test split. A similar filtering strategy is applied to obtain 26,858 videos for training. We conduct experiments in Sec. 5.1.3 on this dataset to showcase the generalization ability of our method." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 605, + 286, + 701 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 605, + 286, + 701 + ], + "spans": [ + { + "bbox": [ + 46, + 605, + 286, + 701 + ], + "type": "text", + "content": "Evaluation metric. We follow the prior works [11, 28, 38] and adopt the pixel-level measurement for evaluating localization performance. Given the ground truth sounding object bounding boxes, we compute the Consensus Intersection over Union (CIoU) and Area Under Curve (AUC) between the predicted localization map and ground truth boxes. We report CIoU over a range of thresholds to expose the finer aspects of comparison." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 701, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 701, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 701, + 286, + 713 + ], + "type": "text", + "content": "Implementation details. To facilitate the training, we cut" + } + ] + } + ], + "index": 5 + }, + { + "type": "table", + "bbox": [ + 317, + 70, + 533, + 178 + ], + "blocks": [ + { + "bbox": [ + 317, + 70, + 533, + 178 + ], + "lines": [ + { + "bbox": [ + 317, + 70, + 533, + 178 + ], + "spans": [ + { + "bbox": [ + 317, + 70, + 533, + 178 + ], + "type": "table", + "html": "
CIoUAUC
@0.2@0.3@0.4
Attention [65]7.12--6.42
STM [38]12.107.644.018.87
Hardway [11]24.5113.556.1013.38
SSPL [71]13.628.104.459.56
Mix [28]26.0115.259.9015.39
Our38.7119.4210.5118.38
", + "image_path": "bfce1e5baa325b1f17b6974425ba0b972881fb7e0f9ce4a7150d50892da25666.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "table_body" + } + ], + "index": 6 + }, + { + "bbox": [ + 305, + 182, + 545, + 226 + ], + "lines": [ + { + "bbox": [ + 305, + 182, + 545, + 226 + ], + "spans": [ + { + "bbox": [ + 305, + 182, + 545, + 226 + ], + "type": "text", + "content": "Table 2. Quantitative comparison of localization results on Epic Sounding Object dataset. All methods are re-trained on EpicKitchen. The results of metrics CIoU@{0.2, 0.3, 0.4} and AUC are reported. The top-1 results are highlighted." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 304, + 237, + 545, + 453 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 237, + 545, + 453 + ], + "spans": [ + { + "bbox": [ + 304, + 237, + 545, + 453 + ], + "type": "text", + "content": "a 1-second long video around the center of each raw video. We select the middle frame from the video clip and its four neighboring frames with an interval of 2 between frames. Consequently, we get " + }, + { + "bbox": [ + 304, + 237, + 545, + 453 + ], + "type": "inline_equation", + "content": "T = 5" + }, + { + "bbox": [ + 304, + 237, + 545, + 453 + ], + "type": "text", + "content": " frames as visual input. During training, the frames are first resized to " + }, + { + "bbox": [ + 304, + 237, + 545, + 453 + ], + "type": "inline_equation", + "content": "256 \\times 256" + }, + { + "bbox": [ + 304, + 237, + 545, + 453 + ], + "type": "text", + "content": " and then randomly cropped to " + }, + { + "bbox": [ + 304, + 237, + 545, + 453 + ], + "type": "inline_equation", + "content": "224 \\times 224" + }, + { + "bbox": [ + 304, + 237, + 545, + 453 + ], + "type": "text", + "content": ". During inference, all the frames are directly resized to the desired size without cropping. For the audio stream, we extract the corresponding 1-second audio clip to create the audio-visual pairs. The audio waveform is sub-sampled at " + }, + { + "bbox": [ + 304, + 237, + 545, + 453 + ], + "type": "inline_equation", + "content": "11\\mathrm{kHz}" + }, + { + "bbox": [ + 304, + 237, + 545, + 453 + ], + "type": "text", + "content": " and transformed into a spectrogram with a Hann window of size 254 and a hop length of 64. The obtained spectrogram is subsequently resampled to " + }, + { + "bbox": [ + 304, + 237, + 545, + 453 + ], + "type": "inline_equation", + "content": "128 \\times 128" + }, + { + "bbox": [ + 304, + 237, + 545, + 453 + ], + "type": "text", + "content": " to feed into the audio network. We set the number of audio and visual feature channels as 512 and choose " + }, + { + "bbox": [ + 304, + 237, + 545, + 453 + ], + "type": "inline_equation", + "content": "\\epsilon = 0.5" + }, + { + "bbox": [ + 304, + 237, + 545, + 453 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 237, + 545, + 453 + ], + "type": "inline_equation", + "content": "\\tau = 0.03" + }, + { + "bbox": [ + 304, + 237, + 545, + 453 + ], + "type": "text", + "content": ". All models are trained with the Adam optimizer, with a learning rate of " + }, + { + "bbox": [ + 304, + 237, + 545, + 453 + ], + "type": "inline_equation", + "content": "10^{-4}" + }, + { + "bbox": [ + 304, + 237, + 545, + 453 + ], + "type": "text", + "content": " on the visual encoder and temporal network, while using a learning rate of " + }, + { + "bbox": [ + 304, + 237, + 545, + 453 + ], + "type": "inline_equation", + "content": "10^{-2}" + }, + { + "bbox": [ + 304, + 237, + 545, + 453 + ], + "type": "text", + "content": " for updating the audio encoder." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 462, + 362, + 474 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 462, + 362, + 474 + ], + "spans": [ + { + "bbox": [ + 306, + 462, + 362, + 474 + ], + "type": "text", + "content": "5.1. Results" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 481, + 452, + 494 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 481, + 452, + 494 + ], + "spans": [ + { + "bbox": [ + 306, + 481, + 452, + 494 + ], + "type": "text", + "content": "5.1.1 Experimental Comparison" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 501, + 545, + 716 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 501, + 545, + 716 + ], + "spans": [ + { + "bbox": [ + 304, + 501, + 545, + 716 + ], + "type": "text", + "content": "To validate the effectiveness of our framework, we compare it with recent audio-visual localization methods: Attention [65], STM [38], Hardway [11], SSPL [71] and Mix [28]. Among all the comparative methods, STM [38] utilizes weak labels for the training, while the other methods are trained with self-supervision. We hence adjust STM [38] with our self-supervised localization loss. As all the methods are developed for third-person view videos, we retrain their methods on our training data for a fair comparison. The quantitative results are shown in Tab. 2. We can find that our method outperforms all the compared approaches by a large margin in all metrics, indicating the benefits of mitigating out-of-view sounds and explicitly modeling egomotion in learning egocentric audio-visual localization. Moreover, we provide a qualitative comparison to visually showcase our localization results. In Fig. 6, we can see that our model produces localization results that are tight around the ground truth sounding objects." + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "22916" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 53, + 70, + 281, + 178 + ], + "blocks": [ + { + "bbox": [ + 53, + 70, + 281, + 178 + ], + "lines": [ + { + "bbox": [ + 53, + 70, + 281, + 178 + ], + "spans": [ + { + "bbox": [ + 53, + 70, + 281, + 178 + ], + "type": "table", + "html": "
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", + "image_path": "8227cf81531c31f827340514e2ddb6cc89b6ecedffbbefd34c93cd7fab7b595c.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 182, + 287, + 205 + ], + "lines": [ + { + "bbox": [ + 47, + 182, + 287, + 205 + ], + "spans": [ + { + "bbox": [ + 47, + 182, + 287, + 205 + ], + "type": "text", + "content": "Table 3. Ablations on GATM, SL, and audio disentanglement module. The top-1 result in each column is highlighted." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 47, + 215, + 145, + 227 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 215, + 145, + 227 + ], + "spans": [ + { + "bbox": [ + 47, + 215, + 145, + 227 + ], + "type": "text", + "content": "5.1.2 Ablation Study" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 228, + 287, + 455 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 228, + 287, + 455 + ], + "spans": [ + { + "bbox": [ + 46, + 228, + 287, + 455 + ], + "type": "text", + "content": "We conduct an ablation study to illustrate how each module affects localization performance. As shown in Tab. 3, we compare our full model with different baselines — model a: we remove all the modules and only use the features from the visual and audio encoders to compute the localization map; model b-d: we insert Average, Max, and Geometry-Aware Temporal modeling approaches separately in the framework; in model f, we incorporate the soft localization (SL) into the pipeline; and in model g, we employ the audio disentanglement module and train the model with " + }, + { + "bbox": [ + 46, + 228, + 287, + 455 + ], + "type": "inline_equation", + "content": "L_{dis}" + }, + { + "bbox": [ + 46, + 228, + 287, + 455 + ], + "type": "text", + "content": ". By comparing a and b-c, we found that it's crucial to aggregate temporal context, while d emphasizes the importance of GATM in mitigating the egomotion in egocentric videos. model d vs. f shows that SL slightly enhances the performance since some of the unrelated visual content can be reweighted. The comparison between f and g demonstrates that by incorporating audio feature disentanglement, the localization performance can be further boosted because it can handle the out-of-view sounds in videos." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 456, + 287, + 529 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 456, + 287, + 529 + ], + "spans": [ + { + "bbox": [ + 46, + 456, + 287, + 529 + ], + "type": "text", + "content": "Naive baseline. To assess the difficulty of the task, we provide a center box method that predicts a gaussian heatmap around the center. This results in a naive baseline of 16.51 compared to 27.41 (model a) from Tab. 3, showing that there are various challenging scenarios apart from the object being in the center that this naive baseline cannot capture." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 537, + 224, + 548 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 537, + 224, + 548 + ], + "spans": [ + { + "bbox": [ + 47, + 537, + 224, + 548 + ], + "type": "text", + "content": "5.1.3 Generalization to More Scenarios" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 551, + 287, + 658 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 551, + 287, + 658 + ], + "spans": [ + { + "bbox": [ + 46, + 551, + 287, + 658 + ], + "type": "text", + "content": "The experiments on Epic Sounding Object dataset demonstrate the effectiveness of our method in localizing sounding objects in the egocentric videos. To further validate the generalization ability of our method, we train our audio-visual sounding object localization network on Ego4D [24] and qualitatively showcase the localization results in Fig. 7. The examples are all selected from the Ego4D test set. We can see that our model can learn audio-visual associations and localize the sounding objects in diverse scenes." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 670, + 212, + 682 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 670, + 212, + 682 + ], + "spans": [ + { + "bbox": [ + 47, + 670, + 212, + 682 + ], + "type": "text", + "content": "6. Discussions and Conclusions" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "text", + "content": "In this work, we tackle a fundamental task: egocentric audio-visual localization to promote the field of study in" + } + ] + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 310, + 72, + 543, + 199 + ], + "blocks": [ + { + "bbox": [ + 310, + 72, + 543, + 199 + ], + "lines": [ + { + "bbox": [ + 310, + 72, + 543, + 199 + ], + "spans": [ + { + "bbox": [ + 310, + 72, + 543, + 199 + ], + "type": "image", + "image_path": "6589a18f80e29947fd2bef09a8dc15113f80c27a08f4144175035b96a15b15ca.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 306, + 208, + 545, + 230 + ], + "lines": [ + { + "bbox": [ + 306, + 208, + 545, + 230 + ], + "spans": [ + { + "bbox": [ + 306, + 208, + 545, + 230 + ], + "type": "text", + "content": "Figure 7. Localization results on diverse scenarios in Ego4D [24]. Ref.: Sounding objects; Pred.: predicted localization results." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 251, + 545, + 395 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 251, + 545, + 395 + ], + "spans": [ + { + "bbox": [ + 304, + 251, + 545, + 395 + ], + "type": "text", + "content": "egocentric audio-visual video understanding. The uniqueness of egocentric videos, such as egomotions and out-of-view sounds pose significant challenges to learning fine-grained audio-visual associations. To address these problems, we propose a new framework with a cascaded feature enhancement module to disentangle visually indicated audio representations and a geometry-aware temporal modeling module to mitigate egomotion. Extensive experiments on our annotated Epic Sounding Object dataset underpin the findings that explicitly mitigating out-of-view sounds and egomotion can boost localization performance and learn the better audio-visual association for egocentric videos." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 396, + 545, + 479 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 396, + 545, + 479 + ], + "spans": [ + { + "bbox": [ + 304, + 396, + 545, + 479 + ], + "type": "text", + "content": "Limitations. The proposed geometry-aware temporal modeling approach requires geometric transformation computation. For certain visual scenes with severe illumination changes or drastic motions, the homography estimation may fail. Then, our GATM will degrade to a vanilla temporal modeling approach. To mitigate the issue, we can consider designing a more robust geometric estimation approach." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 479, + 546, + 659 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 479, + 546, + 659 + ], + "spans": [ + { + "bbox": [ + 304, + 479, + 546, + 659 + ], + "type": "text", + "content": "Potential Applications. Our work offers potential for several applications: (a) Audio-visual episodic memory. As egocentric video records what and where of an individual's daily life experience, it would be interesting to build an intelligent AR assistant to localize the object (\"where did I use it?\") by processing an audio query, e.g., an audio clip of \"vacuum cleaner\"; (b) Audio-visual object state recognition. In egocentric research, it is important to know the state of objects that human is interacting with, while the human-object interaction often makes a sound. Therefore, localizing objects by sounds provides a new angle in recognizing an object state; (c) Audio-visual future anticipation: following the audio-visual object state recognition task, it's natural to predict the trajectory of a sounding object by analyzing the most recent audio-visual clips." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 671, + 365, + 683 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 671, + 365, + 683 + ], + "spans": [ + { + "bbox": [ + 306, + 671, + 365, + 683 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 310, + 691, + 545, + 713 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 310, + 691, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 310, + 691, + 545, + 713 + ], + "type": "text", + "content": "[1] Yazan Abu Farha, Alexander Richard, and Juergen Gall. 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Rehg $^{1,2}$ , Vamsi Krishna Ithapu $^{2}$ , Georgia Institute of Technology $^{1}$ , Meta Reality Labs Research $^{2}$", + "bbox": [ + 133, + 179, + 833, + 215 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "{fkryan, rehg}@gatech.edu, {haojiang, ithapu}@meta.com, abhinav.shukla.research@gmail.com", + "bbox": [ + 91, + 218, + 877, + 234 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 282, + 313, + 300 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "In a noisy conversation environment such as a dinner party, people often exhibit selective auditory attention, or the ability to focus on a particular speaker while tuning out others. Recognizing who somebody is listening to in a conversation is essential for developing technologies that can understand social behavior and devices that can augment human hearing by amplifying particular sound sources. The computer vision and audio research communities have made great strides towards recognizing sound sources and speakers in scenes. In this work, we take a step further by focusing on the problem of localizing auditory attention targets in egocentric video, or detecting who in a camera wearer's field of view they are listening to. To tackle the new and challenging Selective Auditory Attention Localization problem, we propose an end-to-end deep learning approach that uses egocentric video and multichannel audio to predict the heatmap of the camera wearer's auditory attention. Our approach leverages spatiotemporal audiovisual features and holistic reasoning about the scene to make predictions, and outperforms a set of baselines on a challenging multi-speaker conversation dataset. Project page: https://fkryan.github.io/saal", + "bbox": [ + 76, + 316, + 473, + 648 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 667, + 209, + 681 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "One of the primary goals of wearable computing devices like augmented reality (AR) glasses is to enhance human perceptual and cognitive capabilities. This includes helping people have natural conversations in settings with high noise level (e.g. coffee shops, restaurants, etc.) by selectively amplifying certain speakers while suppressing noise and the voices of background speakers. This desired effect mirrors selective auditory attention (SAA), or humans' ability to intentionally focus on certain sounds while tuning out others. People exercise SAA in everyday conversational settings; at restaurants people tune out the voices at adjacent tables, and in group social settings, such as dining at", + "bbox": [ + 75, + 693, + 470, + 875 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/dc50728007db9a2c06fbdced454a87284060a7f9f00cabe76ed51e7869048f51.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 503, + 267, + 696, + 409 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/b0ca4af14948e8e82fd315ac94952aa707920746bf8bfa1758ab0e3b92dc063e.jpg", + "image_caption": [ + "Figure 1. We address the novel task of Selective Auditory Attention Localization in multi-speaker environments: given egocentric video and multichannel audio, we predict which people, if any, the camera wearer is listening to. We show our model's predicted heatmaps, with red bounding boxes denoting ground truth auditory attention targets and white boxes denoting non-attended speakers." + ], + "image_footnote": [], + "bbox": [ + 503, + 410, + 696, + 551 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/e970668b335822d8fff9d60241336f873e689f29f5e022a0906c4d8b78027e1d.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 697, + 268, + 890, + 409 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/558ca4087a8cd6dadf824971563e78dc1567f5d61d35775e3a80981ee09cbf20.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 697, + 410, + 890, + 551 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "a large table or socializing at a party, people often engage in conversations with smaller subsets of people while others converse in close proximity. Being able to determine which speaker(s) a person is selectively listening to is important for developing systems that can aid communication in noisy environments and assist people with hearing loss.", + "bbox": [ + 496, + 669, + 890, + 760 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "While the computer vision community has made strides towards understanding conversational dynamics with largescale datasets like Ego4D [37], AVA-ActiveSpeaker [78], VoxConverse [24], and AMI [57], the problem of modeling selective listening behavior has not yet been addressed. In fact, determining auditory attention among competing sound signals has traditionally been approached using neurophysiological sensing [11, 50]. These approaches involve a controlled listening task, where competing audio signals", + "bbox": [ + 496, + 763, + 892, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 810, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Work done during internship at Meta.", + "bbox": [ + 99, + 887, + 307, + 900 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "14663", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "are played simultaneously and a listener selectively listens to one. Statistical models are then used to correlate brain activity and the attended sound signal. However, the sensing approach is obtrusive and currently not feasible for use in realistic conversational settings in daily life.", + "bbox": [ + 75, + 90, + 468, + 167 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In this work, we approach modeling SAA from an egocentric audiovisual perspective. The egocentric setting provides a compelling lens to study social conversational dynamics, as it captures both the audio and visual stimuli present in a scene and how the camera wearer orients their view in response to them. We hypothesize that the behavior of the wearer that is implicitly captured in the egocentric video and multichannel audio can facilitate the prediction of auditory attention targets. To this end, we introduce and formulate the novel task of Selective Auditory Attention Localization (SAAL), which uses egocentric video and multichannel audio to localize the target of auditory attention in egocentric video. We specifically target multi-speaker conversation scenarios where the camera wearer must selectively attend to certain speaker(s) while tuning out others. This challenging setting is representative of everyday noisy conversation environments and highlights the complexity of modeling auditory attention in naturalistic settings.", + "bbox": [ + 75, + 167, + 472, + 438 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "We propose a deep audiovisual video network for SAAL that leverages both appearance-based features from the ego-centric video stream and spatial audio information from multichannel audio. Our key insight is to extract a spatiotemporal feature representation from each modality and use a transformer on the fused features to reason holistically about the scene. Our contributions are:", + "bbox": [ + 75, + 438, + 468, + 542 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- We introduce the novel problem of Selective Auditory Attention Localization (SAAL) as an egocentric multimodal learning task.", + "- We propose a new architecture for SAAL. Our model extracts spatiotemporal video and audio features and uses a transformer to refine selection of an attention target by reasoning globally about the scene.", + "- We evaluate our approach on a challenging multispeaker conversation dataset and demonstrate our model's superiority over intuitive baselines and approaches based on Active Speaker Localization (ASL).", + "- We conduct thorough experiments to give insight into our multimodal architecture design, effective multichannel audio and visual input representations, and the relationship between SAAL and ASL." + ], + "bbox": [ + 96, + 546, + 467, + 782 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 76, + 800, + 217, + 814 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Computational Models for Auditory Attention Attention is typically categorized into two types: bottom-up, where a stimulus is likely to cause attention due to inherent salient properties, and top-down, where a person intentionally focuses on a certain stimulus. Top-down, or selective auditory", + "bbox": [ + 75, + 825, + 467, + 900 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "attention has been studied by correlating the attended sound signal with the neural response measured by EEG / MEG using statistical models [4,17-19,27,33,38,40,65,67,71,74, 89], and more recently deep neural networks [36, 58]. This is done in a controlled listening scenario where competing sounds, such as audio books, are played at once and a participant is instructed to listen to a particular sound. Models are used to predict which sound source is attended and/or decode the attended signal. The sources may be combined into a single channel or played in separate ears, as in the dichotic listening task paradigm [20]. Some works have used acoustic simulation methods to reflect more realistic multispeaker environments [17, 33, 89]. However, these studies have not addressed modeling SAA in in-the-wild social conversation scenarios. Beyond using brain activity to predict auditory attention, Lu et al. develop a head movement-based approach for predicting the attended speaker in a conversation [64]. However, this work focuses on single group conversations where there is typically only one speaker.", + "bbox": [ + 496, + 90, + 890, + 378 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "A smaller body of work focuses on modeling bottom-up auditory attention, or the qualities of a sound signal that make it likely to be attended to. Works in this domain construct representations of audio signals and evaluate their ability to reflect human judgment of saliency [30, 49, 51, 52, 56, 85, 86], distinguish between changes in perceptual qualities of sound [48], or perform on a downstream speech recognition task [47]. In this work, we focus on top-down, or selective auditory attention.", + "bbox": [ + 496, + 380, + 890, + 516 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Active Speaker Detection & Localization Our task builds upon a rich foundation of work on Active Speaker Detection (ASD) and Active Speaker Localization (ASL). Recognizing speech activity is an established problem in computer vision, with early approaches correlating video and audio streams [25], or using purely visual features [31, 39, 79] to determine if a person is speaking. The AVA-ActiveSpeaker dataset [78] has accelerated deep learning approaches for ASD by providing a large-scale dataset and a benchmark. Methods use deep learning to extract visual features from a head bounding box track and combine them with features from monoaural scene audio to classify the person as speaking and audible, speaking and inaudible, or not speaking in each frame [8-10, 26, 54, 66, 82, 95]. Some approaches additionally explicitly model the relationships between multiple people within a scene to refine classification of speakers [8, 54, 66]. Xiong et al. [93] develop an architecture to jointly perform ASD and speech enhancement.", + "bbox": [ + 496, + 518, + 890, + 792 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Other methods approach the task of ASL, which seeks to localize speakers spatially within the scene rather than classifying bounding box tracks [6, 15, 22, 34, 35, 76, 92, 94]. Several use multichannel audio to incorporate directional audio information [6, 15, 22, 34, 35, 92, 94]. Recently, Jiang et al. [46] expanded upon these approaches by developing a deep model that also leverages multichannel audio to lo", + "bbox": [ + 496, + 795, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "14664", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/c51d3794c3f6837f31275d3b0a0f50c6ece9d16146504e80cec32a14feb30366.jpg", + "image_caption": [ + "Figure 2. Our architecture for predicting auditory attention heatmaps from egocentric video and multichannel audio: the Video Encoder and Audio Encoder embed spatiotemporal features from the video and spatial audio modalities respectively. The audio and visual features are fused and passed to the Scene Relation Transformer, which models the relationships between different regions of the scene. Finally, the features are passed to the convolutional Decoder, which produces the predicted attention heatmaps for the input video frames." + ], + "image_footnote": [], + "bbox": [ + 89, + 85, + 883, + 329 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "calize speakers in the challenging egocentric setting, which contains motion blur and rapid changes of field of view (FOV), using the EasyCom dataset [28]. Our problem setting is different from ASD and ASL in that we seek to determine which of the speakers the camera wearer is listening to using egocentric audiovisual cues. Importantly, active speakers are not necessarily auditorily attended; they can be background people or nearby people engaged in a different conversation. Thus, SAAL demands a novel approach.", + "bbox": [ + 75, + 416, + 468, + 551 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Modeling of Conversation Dynamics and Social Interactions SAAL is also related to work on modeling social interactions and conversational dynamics. Prior works have explored detecting social interactions in egocentric video [2, 16, 32]. The recent Ego4D dataset and benchmark suite [37] introduces the \"Talking to Me\" task for identifying which people are speaking to the camera wearer in egocentric video. This task is closely related to SAAL in that it models dyadic conversational behavior between the camera wearer and people in their FOV. However our task differs by modeling egocentric listening behavior, particularly in the presence of multiple speakers. Researchers have also explored modeling conversational turn taking behaviors [88] as well as predicting listener motion in dyadic conversations [70]. To our knowledge, we are the first to address the problem of modeling auditory attention using egocentric video, wearable audio, or both modalities together.", + "bbox": [ + 75, + 551, + 468, + 809 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Egocentric Visual Attention Prediction Our problem also relates to egocentric visual attention prediction, which regresses a heatmap localizing the target of visual attention in egocentric video. Approaches for this task use eye tracking data as ground truth for attention targets and develop models to predict the attention location from video. Re", + "bbox": [ + 75, + 810, + 468, + 902 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "searchers have proposed several vision models for this task [5,44,59,61,83], including some that jointly model gaze and action [43,62] or gaze and IMU [84]. Importantly, visual attention and auditory attention are not the same; people will generally not always look at the person they are conversing with. Rather, SAAL can be considered as an auditory variant of egocentric visual attention prediction, and SAAL additionally demands the use of audio cues.", + "bbox": [ + 496, + 416, + 890, + 536 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Audiovisual Representation Learning Our work relates to a larger body of research on learning effective audiovisual feature representations [3,7,12,45,55,69,72,73,75] and localizing sound sources in video [1, 13, 23, 41, 42, 63, 68, 77, 80, 81]. These methods learn semantic correspondences between visual and audio features, typically using contrastive training paradigms. In contrast to these approaches, we leverage multichannel audio and employ a fusion mechanism that enforces spatial alignment between the visual and spatial audio domains, allowing us to reason globally about the audiovisual content in different regions of the scene.", + "bbox": [ + 496, + 537, + 892, + 703 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Method", + "text_level": 1, + "bbox": [ + 500, + 715, + 591, + 732 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Problem Definition", + "text_level": 1, + "bbox": [ + 500, + 741, + 683, + 756 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "At each time $t$ , we predict an auditory attention heatmap $\\mathcal{H}_t$ , given the raw audiovisual input $\\{I_n, a_n | n = 0 \\dots t\\}$ where $I_n$ is an egocentric video frame at time $n$ and $a_n$ is a multi-channel audio segment aligned with the video frame $I_n$ . Each pixel $\\mathcal{H}_t(i, j)$ has a value in (0,1) and indicates the probability of the camera wearer's auditory attention. Video $I$ captures the movement of both the camera wearer and the other people in the scene, as well as information about their head and body poses, facial expression, mouth", + "bbox": [ + 496, + 763, + 890, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "14665", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "movement, and overall scene layout. Multichannel audio $a$ , from a microphone array, captures people's speech as well as other spatialized sound sources. We use video from a 180-degree fish-eye camera with resolution $200 \\times 212$ and audio from a 6-channel microphone array. In this paper, we demonstrate how to use $\\{I, a\\}$ to infer $\\mathcal{H}$ , where we construct $\\mathcal{H}_{\\mathrm{label}}$ by setting all pixels within the head bounding box of an attended speaker in a frame as 1.", + "bbox": [ + 75, + 90, + 472, + 212 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. Model", + "text_level": 1, + "bbox": [ + 76, + 224, + 163, + 239 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "SAAL is a complex task that involves understanding both the camera wearer's behavior and the activity of the people in the scene. We design a deep multimodal model for this task to have 4 key abilities: (1) It extracts relevant visual features such as lip movement, the relative positions and orientations of heads, and social body language like when a person looks at the camera wearer. (2) It leverages multichannel audio to construct a spatial representation of voice activity occurring around the camera wearer. (3) It encodes temporal information like how the wearer moves their head in response to stimuli as well as the movement of people in the scene and pattern of voice activity. (4) It reasons globally about the audiovisual content of scene as a whole to select an attention target; while an active speaker detector identifies all speakers in a scene, determining attention demands holistic reasoning about different potential attention targets in a scene to select the most likely one(s).", + "bbox": [ + 75, + 248, + 472, + 505 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "To this end, our method consists of 4 main components as shown in Figure 2: the Visual Encoder and Audio Encoder to extract spatiotemporal features from the video and multichannel audio inputs respectively, the Scene Relation Transformer to refine attention localization by modeling the relationships between audiovisual features in different spatial regions of the scene, and a convolutional Decoder to produce an auditory attention heatmap for each input frame.", + "bbox": [ + 75, + 507, + 472, + 628 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Visual Encoder The Visual Encoder $\\mathcal{V}$ takes the visual input $X^V$ as a stack of $200 \\times 212$ frames over a time interval $T$ and extracts appearance-based features about the scene. We construct $X^V$ by cropping the people's heads in the raw grayscale video frames and filling the background with black. This representation leverages 1) our focus on conversational attention, and 2) the effectiveness of face detection methods. The input is a 3D video tensor of head tubes that represents not only how the people in the scene move, how they are laid out in space, where they look, their facial expression, mouth movement, and who they talk to, but also the head movement of the wearer over time. In our experiments, we compare this representation to using the raw image as well as a binary map of the bounding boxes. We find that this representation improves performance by removing background distractions while retaining appearance-based facial features. Additionally, this representation makes the model more generalizable to different scenes. We use a 3D", + "bbox": [ + 75, + 628, + 472, + 901 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "ResNet-18 network [87] as our backbone, which uses 3D convolutions to capture both spatial and temporal features. The result of $\\mathcal{V}(X^V)$ is a spatiotemporal visual feature map $\\mathcal{Z}^V$ of dimension $512 \\times 1 \\times 13 \\times 14$ , where 512 is the channel dimension, 1 is the temporal dimension, and 13 and 14 correspond to the height and width. We use 8 frames as input with temporal stride 3, so each input $X^V$ spans a 24 frame window, which is 0.8 seconds in 30fps video.", + "bbox": [ + 496, + 90, + 890, + 212 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Audio Encoder The Audio Encoder $\\mathcal{A}$ extracts spatial audio features from the multichannel audio in the input clip to encode information about the conversational speech patterns and spatially localize speakers. We process the audio into 2000 sample $\\times 6$ channel frames corresponding to each frame in the video input clip. We construct input features $X^A$ by calculating the complex spectogram with 201 frequency bins, window length 20, and hop length 10 and stacking these vertically for the 6 channels. We found this performs slightly better than concatenating along the channel dimension. We additionally construct a feature representation of the cross correlation between all pairs of channels as used in Jiang et al. [46] and stack the real and complex parts of the spectogram and the channel correlation features along the channel dimension. We then resize the audio features to $200\\times 212$ spatially in order to extract feature maps that align with the visual domain. Due to the importance of capturing dense temporal audio features to predict auditory attention, such as the pattern of speech, we pass all 24 audio frames in the clip to $\\mathcal{A}$ , which uses another 3D ResNet-18 backbone. The resultant feature map $\\mathcal{Z}^A$ is of size $512\\times 3\\times 13\\times 14$ . We average pool the temporal dimension to 1 to match the dimension of $\\mathcal{Z}^V$ .", + "bbox": [ + 496, + 214, + 892, + 561 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Scene Relation Transformer From $\\mathcal{A}$ and $\\nu$ , we extract visual and spatial audio features maps $\\mathcal{Z}^V$ and $\\mathcal{Z}^A$ , which we concatenate along the channel dimension to form $\\mathcal{Z}^{AV} \\in 1024 \\times 1 \\times 13 \\times 14$ . We choose to concatenate the features along the channel dimension because our approach importantly leverages multichannel audio, which can extract a spatial representation of voice activity in the scene so that the visual and audio domains can be spatially aligned.", + "bbox": [ + 496, + 565, + 890, + 686 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We use a transformer $\\mathcal{T}$ to further refine this fused multimodal feature map by modeling correlations between the features in different regions of the scene to holistically select a likely attention target. As in the transformer literature [14, 29], we treat each spatial location $Z_{1,h,w}^{AV}$ as a spatiotemporal patch of embedded dimension $D = 512$ , and flatten the feature map into a sequence of length $L = 1 \\times 13 \\times 14 = 182$ . A learnable position embedding $E \\in \\mathbb{R}^{L \\times D}$ is added to preserve absolute and relative positional information, which is particularly important for the egocentric setting where the camera wearer orients their view of the scene in response to stimuli. The transformer consists of 12 transformer blocks [90] where each computes self-attention on the audiovisual feature map as Softmax $(QK^T / \\sqrt{D})V$", + "bbox": [ + 496, + 688, + 893, + 902 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "14666", + "bbox": [ + 480, + 945, + 519, + 955 + ], + "page_idx": 3 + }, + { + "type": "table", + "img_path": "images/3d53a2526a4b4f7e72390c035f3be0d78cc98d85a631b89eebdc373b07deaf3d.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
SplitTotal framesFrames with 1+ attention targetAvg. heads per frameAvg. speakers per frame
Train1,416,262881,9313.051.43
Test571,027367,5363.061.45
", + "bbox": [ + 163, + 88, + 803, + 147 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Table 1. Dataset statistics: our evaluation dataset of multi-speaker conversations is representative of challenging conversation environments where several people and speakers are present. Note that we use $\\frac{1}{3}$ of these frames for training and evaluation with temporal stride 3.", + "bbox": [ + 75, + 157, + 888, + 186 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/102ff4ef94df725f83d35d16d54005fefee386b19f8d41d8edb523515773243a.jpg", + "image_caption": [ + "Figure 3. In our multi-speaker evaluation dataset, participants are divided into 2 subgroups that converse simultaneously. A person is labeled as being an auditory attention target if they are both speaking and within the camera wearer's conversation group." + ], + "image_footnote": [], + "bbox": [ + 107, + 204, + 279, + 328 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/66602d8c4b0a440855bbc8ff6b3d8ced100059fca8d1ad0c5c3d91818fdc4caf.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 282, + 215, + 439, + 316 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $Q$ , $K$ , and $V$ are learned linear projections on the multimodal spatiotemporal patches. In this way, the model learns correlations between audiovisual features occurring in different regions of the scene and can suppress or enhance values accordingly to refine attention prediction.", + "bbox": [ + 75, + 410, + 467, + 484 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Decoder A decoder consisting of 4 3D transpose convolutions and 1 final convolutional classifier layer upsamples the resulting feature map $\\mathcal{T}(\\mathcal{Z}^{AV})$ to produce the attention class heatmap $\\mathcal{H}_{\\mathrm{pred}}$ of size $2\\times T\\times H\\times W$ . The 2 channels reflect the not attended and attended classes.", + "bbox": [ + 75, + 486, + 467, + 560 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.3. Implementation & Model Training", + "text_level": 1, + "bbox": [ + 76, + 571, + 379, + 588 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We train end-to-end with pixel-wise cross entropy loss. We initialize $\\mathcal{V}$ and $\\mathcal{A}$ with pretrained weights on Kinetics 400 [21]. The transformer consists of 12 transformer blocks using multi-head self-attention with 8 heads [90]. We use the Adam optimizer [53] and learning rate 1e-4. The training procedure converges quickly in less than 10 epochs.", + "bbox": [ + 75, + 595, + 467, + 686 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Experimental Results", + "text_level": 1, + "bbox": [ + 76, + 700, + 281, + 717 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.1. Evaluation Dataset & Criteria", + "text_level": 1, + "bbox": [ + 76, + 726, + 344, + 739 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "To our knowledge there is no existing dataset with associated labels suited to our task. While egocentric AV datasets like Ego4D [37] and EasyCom [28] capture egocentric conversations, they have few situations with multiple people speaking at the same time, with the result that SAAL reduces to ASL. To evaluate our approach, we collected a dataset of complex multi-speaker conversations, where groups converse in close proximity. The dataset consists of 50 participants conversing in groups of 5, where each person wears a headset with a camera and microphone", + "bbox": [ + 75, + 750, + 467, + 898 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "array. In total, there are $\\sim 20$ hours of egocentric video.", + "bbox": [ + 500, + 205, + 862, + 220 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In each 10-minute recording, a group of 5 people sits at a table in a meeting room and is partitioned into two conversational groups. Participants are instructed to only listen to and engage in conversations with their own group. In this way, we design a naturalistic social version of traditional dichotic listening tasks, where participants intentionally focus on certain speakers while tuning out others. By splitting the group into smaller groups, we simulate conversational layouts that may occur at a large dinner table, coffee shop, restaurant, or party, where groups of people converse in close proximity with others. As illustrated in Figure 3, we construct ground truth auditory attention labels by determining that the camera wearer is listening to a given person if they are both speaking and in the wearer's conversation group. The dataset was collected under an approved IRB.", + "bbox": [ + 496, + 226, + 890, + 452 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Each participant wears a headset that includes an Intel SLAM camera and a 6-microphone array. We record the fish-eye grayscale video and the audio from the 6 microphones simultaneously for all the wearers in each session. We generate speaker activity and head bounding box annotations automatically by using person tracking and wearer speech detection algorithms, and leveraging synchronization between each person's egocentric audio and video in each session. We obtain active speaker labels for each person by using their own headset's microphone array to determine if they are speaking, using a deep model adapted from [46] trained on synthetic data for the headset's microphone array configuration. We then use a 3D tracking-by-detection method that uses camera pose from the SLAM camera to annotate head bounding boxes and identities for each person in each egocentric FOV. From these person tracking results and speaker activity labels for each person, we have a set of visible head bounding boxes for each egocentric frame along with a label for each box indicating if that person is speaking. We then use the identity tracking and known conversation group assignments to label if each person is auditorily attended to by the camera wearer.", + "bbox": [ + 496, + 457, + 890, + 789 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Due to the wide 180-degree FOV of the camera, the auditorily attended person is almost always in the FOV, so we constrain our modeling approach to this scenario. Additionally, by design of the dataset, there are typically several people and often multiple speakers within FOV, as shown in Table 1. Along with the inherent challenges of motion blur and rapid head movements in the egocentric modality, this", + "bbox": [ + 496, + 795, + 890, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "14667", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "makes our dataset a rich means for studying auditory attention in complex and naturalistic conversation environments.", + "bbox": [ + 76, + 90, + 467, + 119 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We evaluate the result of auditory attention localization using mean average precision (mAP) on the task of classifying each person in the FOV as being a target of auditory attention or not. From the output heatmap $\\mathcal{H}_{\\mathrm{pred}}$ , we calculate the auditory attention score for each person by taking the maximum value of Softmax $(\\mathcal{H}_{\\mathrm{pred}})$ in channel 1 (the attended class) in the region of their head bounding box. We split our data and use $70\\%$ data for training and $30\\%$ for testing, with no overlapping participants between splits.", + "bbox": [ + 75, + 122, + 467, + 258 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.2. Competing methods", + "text_level": 1, + "bbox": [ + 76, + 270, + 267, + 286 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Because SAAL is a new problem, there are no previous methods that can be used directly to solve this problem. We therefore compare our approach to several naive baseline methods as well as a set of baselines that adapt Jiang et al.'s multichannel audiovisual ASL architecture (MAVASL) [46] for our task. The methods we compare are the following:", + "bbox": [ + 75, + 294, + 467, + 385 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "(1) Our proposed method with different audio and visual input representations: In our experiments, we label variations of our method as \"Ours - [visual] & [audio]\", where [visual] is the visual input representation type and [audio] is the audio input representation type. The visual input representations we consider are Image (the raw image), Bbox (a binary map of the bounding boxes), and Heads (the cropped heads from the raw image on a black background). The audio representations are Channel Corr (the channel correlation features as described in Section 3.2), Channel Corr + Spectogram (the channel correlation features concatenated with the real and complex parts of the multichannel spectrogram), and ASL (active speaker localization output maps from MAVASL). We report two different training strategies for using MAVASL to generate ASL maps for our dataset: $\\mathrm{ASL}_{\\mathrm{synthetic}}$ , which trains the ASL model on synthetic data created from VTCK [91] and EasyCom, and $\\mathrm{ASL}_{\\mathrm{real}}$ , which directly trains the ASL model on our dataset using the active speaker labels. In this way, we compare using audio features constructed from the raw multichannel audio with using ASL maps generated from an existing model, both with and without the advantage of tuning to our dataset.", + "bbox": [ + 75, + 386, + 467, + 717 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "(2) Naive baselines using ground truth ASL labels and heuristic strategies: We first report the SAAL mAP from simply selecting all active speakers as being attended using the ground truth ASL labels (Perfect ASL). We also report 2 baselines that use the center prior, which is the intuition that the attended person is likely near the center of the FOV because people often face the speaker they are paying attention to. Similar center prior baselines are used in the egocentric visual attention literature. We construct 2 center prior baselines: CP-I finds the head bounding box nearest to the center of FOV and selects it as the attention target if they are speaking, and otherwise predicts that there is no at", + "bbox": [ + 75, + 719, + 467, + 900 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "tention in the frame. CP-II selects the speaking person closest to the center of the FOV as the target of attention. We also construct 2 baselines that select the \"closest\" speaker based on the size of their bounding box. We can reason that the person with the largest head bounding box area is likely the closest to the camera wearer, and if speaking, likely appears the loudest. We consider 2 baselines based on this strategy: CS-I selects the \"closest\" person only if they are speaking, and CS-II selects the \"closest\" speaker. We note that because these methods depend on the dataset's ground truth ASL labels, they are not realistic results, and are not a fair comparison to our method. However, we report them to demonstrate that Perfect ASL and heuristic strategies perform poorly on our evaluation dataset. This clearly implies that SAAL is a complicated task that demands a novel approach, and that our evaluation dataset is rich enough to demonstrate the complexity of this task.", + "bbox": [ + 496, + 90, + 890, + 347 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "(4) Networks adapted from MAVASL: The first adaption (MAVASL-I) is to directly use MAVASL to localize active speakers and use this as the auditory attention heatmap. The second adaptation (MAVASL-II) directly trains the network for the task of SAAL instead of ASL. The third adaptation (MAVASL-III) is similar to (MAVASL-II) but uses a multiframe video input (3-frame) to the AV network to further incorporate temporal information. MAVASL consists of an Audio Network, which predicts a coarse spatial voice activity map from multichannel audio, and an AV Network, which uses this voice activity map and the image to predict a final ASL map. For MAVASL-II and III, we achieve best results by supervising the audio network in MAVASL using the ASL labels from our dataset and the AV network with the auditory attention labels. We use Heads as the visual input representation. Because MAVASL is a frame-based network, we additionally apply temporal smoothing with a window size of 10 frames as in the original method.", + "bbox": [ + 496, + 348, + 890, + 621 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.3. Comparison results", + "text_level": 1, + "bbox": [ + 500, + 633, + 686, + 648 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "As shown in Table 2, our proposed method outperforms the baselines on mAP, including baselines that leverage ground truth active speaker labels. We observe that the Perfect ASL and naive baselines perform poorly on our dataset, illustrating that reducing the problem of SAAL to ASL is not viable in complex and challenging conversation environments with multiple speakers. The highest mAP achieved from adapting Jiang et al.'s ASL architecture is MAVASL-II, which obtains $75.20\\%$ mAP. However, our best approach achieves a gain of $7.74\\%$ mAP over this baseline, demonstrating that the task of SAAL demands a novel architecture design. We qualitatively compare our results against these baselines in Figure 4.", + "bbox": [ + 496, + 657, + 890, + 853 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "From our experiments investigating different combinations of audio and visual input representations, we observe that the combination of Heads and Channel Corr + Spec", + "bbox": [ + 496, + 854, + 890, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "14668", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/46cd6f0eb0d2254129ca2cee0350240995fd302fd403a4d085c46f25a396f627.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodmAP (%)
Perfect ASL*47.99
CP-I*63.55
CP-II*51.48
CS-I*53.86
CS-II*49.47
MAVASL-I59.11
MAVASL-II75.20
MAVASL-III72.90
Ours-Bbox & ASLsynthetic75.93
Ours-Bbox & ASL_real74.97
Ours-Bbox & Channel Corr80.41
Ours-Bbox & Channel Corr + Spectogram80.31
Ours-Image & ASLsynthetic72.20
Ours-Image & ASL_real70.04
Ours-Image & Channel Corr76.52
Ours-Image & Channel Corr + Spectogram76.95
Ours-Heads & ASLsynthetic76.72
Ours-Heads & ASL_real77.11
Ours-Heads & Channel Corr82.35
Ours-Heads & Channel Corr + Spectogram82.94
", + "bbox": [ + 93, + 88, + 452, + 397 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "togram produces the best results. In fact, we observe that Bbox, the binary bounding box location map, performs better as an input representation than the raw image. We can interpret this result as showing the importance of relative position and sizes of heads to the problem of SAAL. Channel Corr and Channel Corr + Spectogram, which contain information from the raw multichannel audio signal, generally perform better as the spatial audio input representation than the pre-computed ASL maps, both real and synthetically trained. We hypothesize that this is because the role of audio features in determining auditory attention is greater than just localizing active speakers; SAAL additionally involves correlating different speech signals with the camera wearer's egocentric movement, using the wearer's own voice activity as an indicator of conversational turn taking behavior (e.g. whether they are speaking or listening), and reasoning about the relative volume of different speech signals. Notably, the pre-computed ASL maps have the advantage of being spatially aligned with the visual modality, which the spectograms and channel correlation features do not have. The performance gains from using Channel Corr and Channel Corr + Spectogram indicate that our Audio Encoder is able to learn this alignment and construct a spatial representation of audio activity from these features.", + "bbox": [ + 75, + 459, + 470, + 823 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.4. Analysis", + "text_level": 1, + "bbox": [ + 76, + 830, + 181, + 847 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Model ablation We further investigate the contribution of each component of our best model to its overall performance in Table 3. We observe that the visual modality", + "bbox": [ + 75, + 854, + 470, + 902 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/a484be7900772b1665deebd843f3ab7a851f5308ae032935bcd4a60611f64d37.jpg", + "table_caption": [ + "Table 2. Comparison results on the multi-speaker conversation dataset. (*) denotes methods that use ground truth ASL, which is not given to our model." + ], + "table_footnote": [], + "table_body": "
MethodmAP (%)
Visual only56.81
Visual only + Transformer57.70
Audio only76.30
Audio only + Transformer75.84
Audiovisual80.10
Audiovisual1-channel + Transformer71.47
Audiovisual2-channel + Transformer76.73
Audiovisual4-channel + Transformer80.99
Audiovisual + Transformer82.94
", + "bbox": [ + 555, + 88, + 838, + 244 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/d4c6cd3bfc430faeef34010e67b0e932e0ec4daeba938d4e36b11fd695c8144d.jpg", + "table_caption": [ + "Table 3. Model ablation: All studies use Heads as the visual input and Channel Corr + Spectogram as the audio input." + ], + "table_footnote": [], + "table_body": "
MethodmAP (%)
Audiovisual + Transformer (no spatial alignment)80.57
Audiovisual + Transformer (spatial alignment)82.94
", + "bbox": [ + 509, + 297, + 883, + 357 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 4. Spatial modality alignment in the transformer.", + "bbox": [ + 531, + 367, + 859, + 382 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "alone is much weaker than the spatial audio modality, and that clearly audio plays an important role. We also ablate the number of audio channels used, observing that removing the spatial component of the audio (Audiovisual $_{1}$ -channel + Transformer) significantly reduces performance of our overall model. We see that spatial audio is an important cue for this task, but using slightly less channels can still achieve effective performance. Adding the transformer to the audiovisual features results in a gain of $2.84\\mathrm{mAP}$ , demonstrating that the transformer improves performance by refining the embedded audiovisual feature maps through modeling relationships across spatial regions of the scene.", + "bbox": [ + 496, + 398, + 890, + 580 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Results on Unseen Environment We additionally test our model's ability to generalize to unseen environments by evaluating our best model on a subset of data collected in a room with different acoustic and visual properties. The data follows the same structure as the main evaluation dataset, with 5 participants split into 2 conversation subgroups, and is $\\sim 49$ minutes. Further details are provided in the supplement. On this unseen environment, our best model achieves $80.43\\%$ mAP, demonstrating scene generalizability.", + "bbox": [ + 496, + 582, + 890, + 718 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Spatial Modality Alignment in Self-Attention A key feature of our approach is leveraging multichannel audio to learn a spatial feature representation of voice activity in the scene, which we align with the visual representation by concatenating along the channel dimension. In our transformer design, therefore, each spatiotemporal patch of $\\mathcal{Z}^{AV}$ contains the visual and audio features for that region. We validate this choice by designing an additional experiment where the modalities are not fused before the transformer, like in VisualBERT [60]. Rather than concatenating $\\mathcal{Z}^A$ and $\\mathcal{Z}^V$ before flattening them into a sequence of tokens to pass to $\\mathcal{T}$ , we separately create a sequence of 182 tokens each", + "bbox": [ + 496, + 719, + 890, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "14669", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/9740bb2f053e985e9557544d544c04ac075f20813f89e36f151779c10d30f03e.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 138, + 88, + 277, + 188 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/d2313bd74ae25add2f1988c5fa734b99face845d517eb7e46e9754033bfa2ac1.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 138, + 188, + 276, + 286 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/cce581b4204d1af81eedff750f995a6aeb8bf0d1006b8fab9a9bd668f84c332e.jpg", + "image_caption": [ + "Ground truth" + ], + "image_footnote": [], + "bbox": [ + 138, + 286, + 276, + 386 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/076df813a0469629b4d8d8e9b6a9554de97a294b6fc002eff91204fd1c8730cc.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 285, + 88, + 421, + 188 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/697dac345412e6fb320b8c9e31da17232943a9de856d9e197491d24d50fe5a5c.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 285, + 188, + 421, + 286 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/1a44a95fb86a90633342df6586587569a30fae443f8c8b821b66accbdda68e24.jpg", + "image_caption": [ + "Ours" + ], + "image_footnote": [], + "bbox": [ + 285, + 286, + 421, + 386 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/584d455ae728dcdc0baf889e3a6139d89883ccc15569fa084179ff9797b02aa8.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 421, + 88, + 557, + 188 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/b3774a142f8cfb8bd6fa037befcf8549a02c05f3ce069d1bebf66d210f0509db.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 421, + 188, + 557, + 286 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/42b4e254883c4821ccc5747d739a7fecf9a5db58215a710ae9d6bb387f94eefe.jpg", + "image_caption": [ + "MAVASL-II" + ], + "image_footnote": [], + "bbox": [ + 421, + 286, + 557, + 386 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/a46b681c0b05e3348396cbbd0f593d9fef3547f2ddd1663fd002b815459c277a.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 557, + 88, + 692, + 188 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/a5ed135b234088f9057205fa2c414fe8f915970a6b000070e891d59af51635af.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 557, + 188, + 692, + 286 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/8f81c53a857e6c7709fe3aaab9b0838c168bb8be69c58051b0b2fbe91a45f2dc.jpg", + "image_caption": [ + "Perfect ASL" + ], + "image_footnote": [], + "bbox": [ + 557, + 286, + 692, + 386 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/9614f3a4ff5b9cdd47fa13f0bb9088646d9e97c0e19cf29f286d504e0c8fca76.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 694, + 88, + 830, + 188 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/eee9713d2dcef838f7f9f11e2a5031587d040e677c225cc38a3fd9c097bbdee3.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 694, + 188, + 828, + 286 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/a746d9c637f9933a0868a3b5096b50dc56a3ba20d925c5e185249ff2143c97db.jpg", + "image_caption": [ + "CP-I - Perfect ASL" + ], + "image_footnote": [], + "bbox": [ + 694, + 286, + 828, + 386 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/4f61cb04c5bff466a2a027b51b1f43d5eb6ebf444f3c0422cfdcb16be997a583.jpg", + "image_caption": [ + "Figure 4. We compare our output heatmaps to competing methods on challenging cases with multiple speakers, the attended speaker being far from the center, or no auditory attention. Our method performs well in these scenarios and more consistently identifies who is and isn't attended than MAVASL-II. Perfect ASL is prone to false positives by selecting all speakers and CPI is prone to false negatives by only considering the person closest to the center, demonstrating that ASL is not enough to solve SAAL. (Best viewed in color).", + "Figure 5. Decoupling SAAL & ASL: Without the responsibility for learning ASL, our model learns to segment the people within the camera wearer's conversation group." + ], + "image_footnote": [], + "bbox": [ + 135, + 474, + 411, + 574 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "from $\\mathcal{Z}^V$ and $\\mathcal{Z}^A$ and pass these 364 total tokens of dimension 512 to $\\mathcal{T}$ . We concatenate the modalities afterwards. In this case, the self-attention mechanism is left to discover alignment between the modalities itself by comparing all tokens across both modalities. We observe a decrease in performance, indicating that our choice to explicitly align the visual and audio modalities spatially contributes to our model's ability to use both modalities together successfully. This result suggests utility in incorporating inductive bias about the spatial alignment of visual and multichannel audio modalities into token design for transformer architectures.", + "bbox": [ + 75, + 638, + 468, + 805 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Decoupling SAAL & ASL By nature of our dataset design, we train our model to predict auditory attention as the intersection of active speakers and people in the camera wearer's conversation group. To investigate the relationship between SAAL and ASL, we train a model by modulating our model's heatmap for the attended class", + "bbox": [ + 75, + 809, + 470, + 901 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "with the ground truth ASL labels before calculating loss and performing backpropagation. The loss is calculated as $\\mathcal{L}_{CE}(\\mathcal{H}_{\\mathrm{pred}}*\\mathrm{ASL}_{\\mathrm{label}},\\mathcal{H}_{\\mathrm{label}})$ . In this way we eliminate the responsibility for ASL from our model. The model achieves $92.67\\%$ mAP on SAAL, however, this is a purely theoretical upper bound that relies on perfect ASL. We visualize $\\mathcal{H}_{\\mathrm{pred}}$ for our model before it is modulated by ASL label in Figure 5. We observe that our model learns to more generally segment the camera wearer's conversation group regardless of speaking activity, and likely relies on ASL label to constrain the heatmaps to the exact bounding box region.", + "bbox": [ + 496, + 476, + 893, + 643 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 657, + 619, + 672 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We introduce the novel problem of Selective Auditory Attention Localization (SAAL) and demonstrate that a deep model is able to perform this task on a challenging multispeaker conversation dataset. We propose a multimodal modeling approach that uses egocentric video and multichannel audio to predict a person's target of auditory attention, combining spatial and temporal features from both modalities and using a transformer to reason holistically about the scene. We believe our work is an important step towards selective sound source enhancement and AR devices that can help people converse in noisy environments.", + "bbox": [ + 496, + 681, + 890, + 849 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgments: We thank Jacob Donley and Christi Miller for facilitating data collection, and Calvin Murdock and Ishwarya Ananthabhotla for valuable discussions.", + "bbox": [ + 496, + 854, + 890, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "14670", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Triantafyllos Afouras, Andrew Owens, Joon Son Chung, and Andrew Zisserman. Self-supervised learning of audio-visual objects from video. In European Conference on Computer Vision, pages 208–224. 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Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.179, + 0.131, + 0.795, + 0.154 + ], + "angle": 0, + "content": "Egocentric Auditory Attention Localization in Conversations" + }, + { + "type": "text", + "bbox": [ + 0.135, + 0.18, + 0.834, + 0.217 + ], + "angle": 0, + "content": "Fiona Ryan\\(^{1,2*}\\), Hao Jiang\\(^{2}\\), Abhinav Shukla\\(^{2}\\), James M. Rehg\\(^{1,2}\\), Vamsi Krishna Ithapu\\(^{2}\\), Georgia Institute of Technology\\(^{1}\\), Meta Reality Labs Research\\(^{2}\\)" + }, + { + "type": "text", + "bbox": [ + 0.093, + 0.219, + 0.878, + 0.235 + ], + "angle": 0, + "content": "{fkryan, rehg}@gatech.edu, {haojiang, ithapu}@meta.com, abhinav.shukla.research@gmail.com" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.284, + 0.314, + 0.301 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.317, + 0.474, + 0.649 + ], + "angle": 0, + "content": "In a noisy conversation environment such as a dinner party, people often exhibit selective auditory attention, or the ability to focus on a particular speaker while tuning out others. Recognizing who somebody is listening to in a conversation is essential for developing technologies that can understand social behavior and devices that can augment human hearing by amplifying particular sound sources. The computer vision and audio research communities have made great strides towards recognizing sound sources and speakers in scenes. In this work, we take a step further by focusing on the problem of localizing auditory attention targets in egocentric video, or detecting who in a camera wearer's field of view they are listening to. To tackle the new and challenging Selective Auditory Attention Localization problem, we propose an end-to-end deep learning approach that uses egocentric video and multichannel audio to predict the heatmap of the camera wearer's auditory attention. Our approach leverages spatiotemporal audiovisual features and holistic reasoning about the scene to make predictions, and outperforms a set of baselines on a challenging multi-speaker conversation dataset. Project page: https://fkryan.github.io/saal" + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.668, + 0.21, + 0.683 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.694, + 0.471, + 0.876 + ], + "angle": 0, + "content": "One of the primary goals of wearable computing devices like augmented reality (AR) glasses is to enhance human perceptual and cognitive capabilities. This includes helping people have natural conversations in settings with high noise level (e.g. coffee shops, restaurants, etc.) by selectively amplifying certain speakers while suppressing noise and the voices of background speakers. This desired effect mirrors selective auditory attention (SAA), or humans' ability to intentionally focus on certain sounds while tuning out others. People exercise SAA in everyday conversational settings; at restaurants people tune out the voices at adjacent tables, and in group social settings, such as dining at" + }, + { + "type": "image", + "bbox": [ + 0.504, + 0.268, + 0.697, + 0.41 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.504, + 0.411, + 0.697, + 0.552 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.698, + 0.269, + 0.892, + 0.41 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.698, + 0.411, + 0.892, + 0.552 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.563, + 0.894, + 0.648 + ], + "angle": 0, + "content": "Figure 1. We address the novel task of Selective Auditory Attention Localization in multi-speaker environments: given egocentric video and multichannel audio, we predict which people, if any, the camera wearer is listening to. We show our model's predicted heatmaps, with red bounding boxes denoting ground truth auditory attention targets and white boxes denoting non-attended speakers." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.67, + 0.892, + 0.761 + ], + "angle": 0, + "content": "a large table or socializing at a party, people often engage in conversations with smaller subsets of people while others converse in close proximity. Being able to determine which speaker(s) a person is selectively listening to is important for developing systems that can aid communication in noisy environments and assist people with hearing loss." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.893, + 0.903 + ], + "angle": 0, + "content": "While the computer vision community has made strides towards understanding conversational dynamics with largescale datasets like Ego4D [37], AVA-ActiveSpeaker [78], VoxConverse [24], and AMI [57], the problem of modeling selective listening behavior has not yet been addressed. In fact, determining auditory attention among competing sound signals has traditionally been approached using neurophysiological sensing [11, 50]. These approaches involve a controlled listening task, where competing audio signals" + }, + { + "type": "page_footnote", + "bbox": [ + 0.101, + 0.888, + 0.308, + 0.901 + ], + "angle": 0, + "content": "*Work done during internship at Meta." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "14663" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.168 + ], + "angle": 0, + "content": "are played simultaneously and a listener selectively listens to one. Statistical models are then used to correlate brain activity and the attended sound signal. However, the sensing approach is obtrusive and currently not feasible for use in realistic conversational settings in daily life." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.168, + 0.473, + 0.439 + ], + "angle": 0, + "content": "In this work, we approach modeling SAA from an egocentric audiovisual perspective. The egocentric setting provides a compelling lens to study social conversational dynamics, as it captures both the audio and visual stimuli present in a scene and how the camera wearer orients their view in response to them. We hypothesize that the behavior of the wearer that is implicitly captured in the egocentric video and multichannel audio can facilitate the prediction of auditory attention targets. To this end, we introduce and formulate the novel task of Selective Auditory Attention Localization (SAAL), which uses egocentric video and multichannel audio to localize the target of auditory attention in egocentric video. We specifically target multi-speaker conversation scenarios where the camera wearer must selectively attend to certain speaker(s) while tuning out others. This challenging setting is representative of everyday noisy conversation environments and highlights the complexity of modeling auditory attention in naturalistic settings." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.439, + 0.47, + 0.543 + ], + "angle": 0, + "content": "We propose a deep audiovisual video network for SAAL that leverages both appearance-based features from the ego-centric video stream and spatial audio information from multichannel audio. Our key insight is to extract a spatiotemporal feature representation from each modality and use a transformer on the fused features to reason holistically about the scene. Our contributions are:" + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.547, + 0.468, + 0.591 + ], + "angle": 0, + "content": "- We introduce the novel problem of Selective Auditory Attention Localization (SAAL) as an egocentric multimodal learning task." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.597, + 0.468, + 0.655 + ], + "angle": 0, + "content": "- We propose a new architecture for SAAL. Our model extracts spatiotemporal video and audio features and uses a transformer to refine selection of an attention target by reasoning globally about the scene." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.661, + 0.468, + 0.72 + ], + "angle": 0, + "content": "- We evaluate our approach on a challenging multispeaker conversation dataset and demonstrate our model's superiority over intuitive baselines and approaches based on Active Speaker Localization (ASL)." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.726, + 0.468, + 0.784 + ], + "angle": 0, + "content": "- We conduct thorough experiments to give insight into our multimodal architecture design, effective multichannel audio and visual input representations, and the relationship between SAAL and ASL." + }, + { + "type": "list", + "bbox": [ + 0.097, + 0.547, + 0.468, + 0.784 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.801, + 0.218, + 0.815 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.826, + 0.468, + 0.901 + ], + "angle": 0, + "content": "Computational Models for Auditory Attention Attention is typically categorized into two types: bottom-up, where a stimulus is likely to cause attention due to inherent salient properties, and top-down, where a person intentionally focuses on a certain stimulus. Top-down, or selective auditory" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.379 + ], + "angle": 0, + "content": "attention has been studied by correlating the attended sound signal with the neural response measured by EEG / MEG using statistical models [4,17-19,27,33,38,40,65,67,71,74, 89], and more recently deep neural networks [36, 58]. This is done in a controlled listening scenario where competing sounds, such as audio books, are played at once and a participant is instructed to listen to a particular sound. Models are used to predict which sound source is attended and/or decode the attended signal. The sources may be combined into a single channel or played in separate ears, as in the dichotic listening task paradigm [20]. Some works have used acoustic simulation methods to reflect more realistic multispeaker environments [17, 33, 89]. However, these studies have not addressed modeling SAA in in-the-wild social conversation scenarios. Beyond using brain activity to predict auditory attention, Lu et al. develop a head movement-based approach for predicting the attended speaker in a conversation [64]. However, this work focuses on single group conversations where there is typically only one speaker." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.381, + 0.892, + 0.517 + ], + "angle": 0, + "content": "A smaller body of work focuses on modeling bottom-up auditory attention, or the qualities of a sound signal that make it likely to be attended to. Works in this domain construct representations of audio signals and evaluate their ability to reflect human judgment of saliency [30, 49, 51, 52, 56, 85, 86], distinguish between changes in perceptual qualities of sound [48], or perform on a downstream speech recognition task [47]. In this work, we focus on top-down, or selective auditory attention." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.52, + 0.892, + 0.793 + ], + "angle": 0, + "content": "Active Speaker Detection & Localization Our task builds upon a rich foundation of work on Active Speaker Detection (ASD) and Active Speaker Localization (ASL). Recognizing speech activity is an established problem in computer vision, with early approaches correlating video and audio streams [25], or using purely visual features [31, 39, 79] to determine if a person is speaking. The AVA-ActiveSpeaker dataset [78] has accelerated deep learning approaches for ASD by providing a large-scale dataset and a benchmark. Methods use deep learning to extract visual features from a head bounding box track and combine them with features from monoaural scene audio to classify the person as speaking and audible, speaking and inaudible, or not speaking in each frame [8-10, 26, 54, 66, 82, 95]. Some approaches additionally explicitly model the relationships between multiple people within a scene to refine classification of speakers [8, 54, 66]. Xiong et al. [93] develop an architecture to jointly perform ASD and speech enhancement." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.796, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Other methods approach the task of ASL, which seeks to localize speakers spatially within the scene rather than classifying bounding box tracks [6, 15, 22, 34, 35, 76, 92, 94]. Several use multichannel audio to incorporate directional audio information [6, 15, 22, 34, 35, 92, 94]. Recently, Jiang et al. [46] expanded upon these approaches by developing a deep model that also leverages multichannel audio to lo" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "14664" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.09, + 0.086, + 0.885, + 0.33 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.341, + 0.896, + 0.398 + ], + "angle": 0, + "content": "Figure 2. Our architecture for predicting auditory attention heatmaps from egocentric video and multichannel audio: the Video Encoder and Audio Encoder embed spatiotemporal features from the video and spatial audio modalities respectively. The audio and visual features are fused and passed to the Scene Relation Transformer, which models the relationships between different regions of the scene. Finally, the features are passed to the convolutional Decoder, which produces the predicted attention heatmaps for the input video frames." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.417, + 0.47, + 0.553 + ], + "angle": 0, + "content": "calize speakers in the challenging egocentric setting, which contains motion blur and rapid changes of field of view (FOV), using the EasyCom dataset [28]. Our problem setting is different from ASD and ASL in that we seek to determine which of the speakers the camera wearer is listening to using egocentric audiovisual cues. Importantly, active speakers are not necessarily auditorily attended; they can be background people or nearby people engaged in a different conversation. Thus, SAAL demands a novel approach." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.553, + 0.47, + 0.81 + ], + "angle": 0, + "content": "Modeling of Conversation Dynamics and Social Interactions SAAL is also related to work on modeling social interactions and conversational dynamics. Prior works have explored detecting social interactions in egocentric video [2, 16, 32]. The recent Ego4D dataset and benchmark suite [37] introduces the \"Talking to Me\" task for identifying which people are speaking to the camera wearer in egocentric video. This task is closely related to SAAL in that it models dyadic conversational behavior between the camera wearer and people in their FOV. However our task differs by modeling egocentric listening behavior, particularly in the presence of multiple speakers. Researchers have also explored modeling conversational turn taking behaviors [88] as well as predicting listener motion in dyadic conversations [70]. To our knowledge, we are the first to address the problem of modeling auditory attention using egocentric video, wearable audio, or both modalities together." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.811, + 0.47, + 0.903 + ], + "angle": 0, + "content": "Egocentric Visual Attention Prediction Our problem also relates to egocentric visual attention prediction, which regresses a heatmap localizing the target of visual attention in egocentric video. Approaches for this task use eye tracking data as ground truth for attention targets and develop models to predict the attention location from video. Re" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.417, + 0.892, + 0.537 + ], + "angle": 0, + "content": "searchers have proposed several vision models for this task [5,44,59,61,83], including some that jointly model gaze and action [43,62] or gaze and IMU [84]. Importantly, visual attention and auditory attention are not the same; people will generally not always look at the person they are conversing with. Rather, SAAL can be considered as an auditory variant of egocentric visual attention prediction, and SAAL additionally demands the use of audio cues." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.538, + 0.893, + 0.704 + ], + "angle": 0, + "content": "Audiovisual Representation Learning Our work relates to a larger body of research on learning effective audiovisual feature representations [3,7,12,45,55,69,72,73,75] and localizing sound sources in video [1, 13, 23, 41, 42, 63, 68, 77, 80, 81]. These methods learn semantic correspondences between visual and audio features, typically using contrastive training paradigms. In contrast to these approaches, we leverage multichannel audio and employ a fusion mechanism that enforces spatial alignment between the visual and spatial audio domains, allowing us to reason globally about the audiovisual content in different regions of the scene." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.717, + 0.593, + 0.733 + ], + "angle": 0, + "content": "3. Method" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.742, + 0.684, + 0.757 + ], + "angle": 0, + "content": "3.1. Problem Definition" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.892, + 0.901 + ], + "angle": 0, + "content": "At each time \\( t \\), we predict an auditory attention heatmap \\( \\mathcal{H}_t \\), given the raw audiovisual input \\( \\{I_n, a_n | n = 0 \\dots t\\} \\) where \\( I_n \\) is an egocentric video frame at time \\( n \\) and \\( a_n \\) is a multi-channel audio segment aligned with the video frame \\( I_n \\). Each pixel \\( \\mathcal{H}_t(i, j) \\) has a value in (0,1) and indicates the probability of the camera wearer's auditory attention. Video \\( I \\) captures the movement of both the camera wearer and the other people in the scene, as well as information about their head and body poses, facial expression, mouth" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "14665" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.213 + ], + "angle": 0, + "content": "movement, and overall scene layout. Multichannel audio \\( a \\), from a microphone array, captures people's speech as well as other spatialized sound sources. We use video from a 180-degree fish-eye camera with resolution \\( 200 \\times 212 \\) and audio from a 6-channel microphone array. In this paper, we demonstrate how to use \\( \\{I, a\\} \\) to infer \\( \\mathcal{H} \\), where we construct \\( \\mathcal{H}_{\\mathrm{label}} \\) by setting all pixels within the head bounding box of an attended speaker in a frame as 1." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.225, + 0.165, + 0.24 + ], + "angle": 0, + "content": "3.2. Model" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.249, + 0.473, + 0.506 + ], + "angle": 0, + "content": "SAAL is a complex task that involves understanding both the camera wearer's behavior and the activity of the people in the scene. We design a deep multimodal model for this task to have 4 key abilities: (1) It extracts relevant visual features such as lip movement, the relative positions and orientations of heads, and social body language like when a person looks at the camera wearer. (2) It leverages multichannel audio to construct a spatial representation of voice activity occurring around the camera wearer. (3) It encodes temporal information like how the wearer moves their head in response to stimuli as well as the movement of people in the scene and pattern of voice activity. (4) It reasons globally about the audiovisual content of scene as a whole to select an attention target; while an active speaker detector identifies all speakers in a scene, determining attention demands holistic reasoning about different potential attention targets in a scene to select the most likely one(s)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.508, + 0.473, + 0.629 + ], + "angle": 0, + "content": "To this end, our method consists of 4 main components as shown in Figure 2: the Visual Encoder and Audio Encoder to extract spatiotemporal features from the video and multichannel audio inputs respectively, the Scene Relation Transformer to refine attention localization by modeling the relationships between audiovisual features in different spatial regions of the scene, and a convolutional Decoder to produce an auditory attention heatmap for each input frame." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.63, + 0.473, + 0.902 + ], + "angle": 0, + "content": "Visual Encoder The Visual Encoder \\(\\mathcal{V}\\) takes the visual input \\(X^V\\) as a stack of \\(200 \\times 212\\) frames over a time interval \\(T\\) and extracts appearance-based features about the scene. We construct \\(X^V\\) by cropping the people's heads in the raw grayscale video frames and filling the background with black. This representation leverages 1) our focus on conversational attention, and 2) the effectiveness of face detection methods. The input is a 3D video tensor of head tubes that represents not only how the people in the scene move, how they are laid out in space, where they look, their facial expression, mouth movement, and who they talk to, but also the head movement of the wearer over time. In our experiments, we compare this representation to using the raw image as well as a binary map of the bounding boxes. We find that this representation improves performance by removing background distractions while retaining appearance-based facial features. Additionally, this representation makes the model more generalizable to different scenes. We use a 3D" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.213 + ], + "angle": 0, + "content": "ResNet-18 network [87] as our backbone, which uses 3D convolutions to capture both spatial and temporal features. The result of \\(\\mathcal{V}(X^V)\\) is a spatiotemporal visual feature map \\(\\mathcal{Z}^V\\) of dimension \\(512 \\times 1 \\times 13 \\times 14\\), where 512 is the channel dimension, 1 is the temporal dimension, and 13 and 14 correspond to the height and width. We use 8 frames as input with temporal stride 3, so each input \\(X^V\\) spans a 24 frame window, which is 0.8 seconds in 30fps video." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.215, + 0.893, + 0.562 + ], + "angle": 0, + "content": "Audio Encoder The Audio Encoder \\(\\mathcal{A}\\) extracts spatial audio features from the multichannel audio in the input clip to encode information about the conversational speech patterns and spatially localize speakers. We process the audio into 2000 sample \\(\\times 6\\) channel frames corresponding to each frame in the video input clip. We construct input features \\(X^A\\) by calculating the complex spectogram with 201 frequency bins, window length 20, and hop length 10 and stacking these vertically for the 6 channels. We found this performs slightly better than concatenating along the channel dimension. We additionally construct a feature representation of the cross correlation between all pairs of channels as used in Jiang et al. [46] and stack the real and complex parts of the spectogram and the channel correlation features along the channel dimension. We then resize the audio features to \\(200\\times 212\\) spatially in order to extract feature maps that align with the visual domain. Due to the importance of capturing dense temporal audio features to predict auditory attention, such as the pattern of speech, we pass all 24 audio frames in the clip to \\(\\mathcal{A}\\), which uses another 3D ResNet-18 backbone. The resultant feature map \\(\\mathcal{Z}^A\\) is of size \\(512\\times 3\\times 13\\times 14\\). We average pool the temporal dimension to 1 to match the dimension of \\(\\mathcal{Z}^V\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.566, + 0.892, + 0.687 + ], + "angle": 0, + "content": "Scene Relation Transformer From \\(\\mathcal{A}\\) and \\(\\nu\\), we extract visual and spatial audio features maps \\(\\mathcal{Z}^V\\) and \\(\\mathcal{Z}^A\\), which we concatenate along the channel dimension to form \\(\\mathcal{Z}^{AV} \\in 1024 \\times 1 \\times 13 \\times 14\\). We choose to concatenate the features along the channel dimension because our approach importantly leverages multichannel audio, which can extract a spatial representation of voice activity in the scene so that the visual and audio domains can be spatially aligned." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.689, + 0.895, + 0.903 + ], + "angle": 0, + "content": "We use a transformer \\(\\mathcal{T}\\) to further refine this fused multimodal feature map by modeling correlations between the features in different regions of the scene to holistically select a likely attention target. As in the transformer literature [14, 29], we treat each spatial location \\(Z_{1,h,w}^{AV}\\) as a spatiotemporal patch of embedded dimension \\(D = 512\\), and flatten the feature map into a sequence of length \\(L = 1 \\times 13 \\times 14 = 182\\). A learnable position embedding \\(E \\in \\mathbb{R}^{L \\times D}\\) is added to preserve absolute and relative positional information, which is particularly important for the egocentric setting where the camera wearer orients their view of the scene in response to stimuli. The transformer consists of 12 transformer blocks [90] where each computes self-attention on the audiovisual feature map as Softmax \\((QK^T / \\sqrt{D})V\\)" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.946, + 0.521, + 0.957 + ], + "angle": 0, + "content": "14666" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.164, + 0.089, + 0.805, + 0.148 + ], + "angle": 0, + "content": "
SplitTotal framesFrames with 1+ attention targetAvg. heads per frameAvg. speakers per frame
Train1,416,262881,9313.051.43
Test571,027367,5363.061.45
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.158, + 0.89, + 0.187 + ], + "angle": 0, + "content": "Table 1. Dataset statistics: our evaluation dataset of multi-speaker conversations is representative of challenging conversation environments where several people and speakers are present. Note that we use \\( \\frac{1}{3} \\) of these frames for training and evaluation with temporal stride 3." + }, + { + "type": "image", + "bbox": [ + 0.109, + 0.205, + 0.28, + 0.329 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.283, + 0.217, + 0.44, + 0.317 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.34, + 0.468, + 0.396 + ], + "angle": 0, + "content": "Figure 3. In our multi-speaker evaluation dataset, participants are divided into 2 subgroups that converse simultaneously. A person is labeled as being an auditory attention target if they are both speaking and within the camera wearer's conversation group." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.411, + 0.468, + 0.486 + ], + "angle": 0, + "content": "where \\( Q \\), \\( K \\), and \\( V \\) are learned linear projections on the multimodal spatiotemporal patches. In this way, the model learns correlations between audiovisual features occurring in different regions of the scene and can suppress or enhance values accordingly to refine attention prediction." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.487, + 0.468, + 0.561 + ], + "angle": 0, + "content": "Decoder A decoder consisting of 4 3D transpose convolutions and 1 final convolutional classifier layer upsamples the resulting feature map \\(\\mathcal{T}(\\mathcal{Z}^{AV})\\) to produce the attention class heatmap \\(\\mathcal{H}_{\\mathrm{pred}}\\) of size \\(2\\times T\\times H\\times W\\). The 2 channels reflect the not attended and attended classes." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.572, + 0.38, + 0.589 + ], + "angle": 0, + "content": "3.3. Implementation & Model Training" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.597, + 0.468, + 0.687 + ], + "angle": 0, + "content": "We train end-to-end with pixel-wise cross entropy loss. We initialize \\(\\mathcal{V}\\) and \\(\\mathcal{A}\\) with pretrained weights on Kinetics 400 [21]. The transformer consists of 12 transformer blocks using multi-head self-attention with 8 heads [90]. We use the Adam optimizer [53] and learning rate 1e-4. The training procedure converges quickly in less than 10 epochs." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.701, + 0.282, + 0.718 + ], + "angle": 0, + "content": "4. Experimental Results" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.727, + 0.345, + 0.741 + ], + "angle": 0, + "content": "4.1. Evaluation Dataset & Criteria" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.75, + 0.468, + 0.9 + ], + "angle": 0, + "content": "To our knowledge there is no existing dataset with associated labels suited to our task. While egocentric AV datasets like Ego4D [37] and EasyCom [28] capture egocentric conversations, they have few situations with multiple people speaking at the same time, with the result that SAAL reduces to ASL. To evaluate our approach, we collected a dataset of complex multi-speaker conversations, where groups converse in close proximity. The dataset consists of 50 participants conversing in groups of 5, where each person wears a headset with a camera and microphone" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.207, + 0.864, + 0.222 + ], + "angle": 0, + "content": "array. In total, there are \\(\\sim 20\\) hours of egocentric video." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.227, + 0.892, + 0.453 + ], + "angle": 0, + "content": "In each 10-minute recording, a group of 5 people sits at a table in a meeting room and is partitioned into two conversational groups. Participants are instructed to only listen to and engage in conversations with their own group. In this way, we design a naturalistic social version of traditional dichotic listening tasks, where participants intentionally focus on certain speakers while tuning out others. By splitting the group into smaller groups, we simulate conversational layouts that may occur at a large dinner table, coffee shop, restaurant, or party, where groups of people converse in close proximity with others. As illustrated in Figure 3, we construct ground truth auditory attention labels by determining that the camera wearer is listening to a given person if they are both speaking and in the wearer's conversation group. The dataset was collected under an approved IRB." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.458, + 0.892, + 0.79 + ], + "angle": 0, + "content": "Each participant wears a headset that includes an Intel SLAM camera and a 6-microphone array. We record the fish-eye grayscale video and the audio from the 6 microphones simultaneously for all the wearers in each session. We generate speaker activity and head bounding box annotations automatically by using person tracking and wearer speech detection algorithms, and leveraging synchronization between each person's egocentric audio and video in each session. We obtain active speaker labels for each person by using their own headset's microphone array to determine if they are speaking, using a deep model adapted from [46] trained on synthetic data for the headset's microphone array configuration. We then use a 3D tracking-by-detection method that uses camera pose from the SLAM camera to annotate head bounding boxes and identities for each person in each egocentric FOV. From these person tracking results and speaker activity labels for each person, we have a set of visible head bounding boxes for each egocentric frame along with a label for each box indicating if that person is speaking. We then use the identity tracking and known conversation group assignments to label if each person is auditorily attended to by the camera wearer." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.796, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Due to the wide 180-degree FOV of the camera, the auditorily attended person is almost always in the FOV, so we constrain our modeling approach to this scenario. Additionally, by design of the dataset, there are typically several people and often multiple speakers within FOV, as shown in Table 1. Along with the inherent challenges of motion blur and rapid head movements in the egocentric modality, this" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.956 + ], + "angle": 0, + "content": "14667" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.468, + 0.121 + ], + "angle": 0, + "content": "makes our dataset a rich means for studying auditory attention in complex and naturalistic conversation environments." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.123, + 0.468, + 0.259 + ], + "angle": 0, + "content": "We evaluate the result of auditory attention localization using mean average precision (mAP) on the task of classifying each person in the FOV as being a target of auditory attention or not. From the output heatmap \\(\\mathcal{H}_{\\mathrm{pred}}\\), we calculate the auditory attention score for each person by taking the maximum value of Softmax \\((\\mathcal{H}_{\\mathrm{pred}})\\) in channel 1 (the attended class) in the region of their head bounding box. We split our data and use \\(70\\%\\) data for training and \\(30\\%\\) for testing, with no overlapping participants between splits." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.271, + 0.268, + 0.287 + ], + "angle": 0, + "content": "4.2. Competing methods" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.295, + 0.468, + 0.386 + ], + "angle": 0, + "content": "Because SAAL is a new problem, there are no previous methods that can be used directly to solve this problem. We therefore compare our approach to several naive baseline methods as well as a set of baselines that adapt Jiang et al.'s multichannel audiovisual ASL architecture (MAVASL) [46] for our task. The methods we compare are the following:" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.387, + 0.468, + 0.718 + ], + "angle": 0, + "content": "(1) Our proposed method with different audio and visual input representations: In our experiments, we label variations of our method as \"Ours - [visual] & [audio]\", where [visual] is the visual input representation type and [audio] is the audio input representation type. The visual input representations we consider are Image (the raw image), Bbox (a binary map of the bounding boxes), and Heads (the cropped heads from the raw image on a black background). The audio representations are Channel Corr (the channel correlation features as described in Section 3.2), Channel Corr + Spectogram (the channel correlation features concatenated with the real and complex parts of the multichannel spectrogram), and ASL (active speaker localization output maps from MAVASL). We report two different training strategies for using MAVASL to generate ASL maps for our dataset: \\(\\mathrm{ASL}_{\\mathrm{synthetic}}\\), which trains the ASL model on synthetic data created from VTCK [91] and EasyCom, and \\(\\mathrm{ASL}_{\\mathrm{real}}\\), which directly trains the ASL model on our dataset using the active speaker labels. In this way, we compare using audio features constructed from the raw multichannel audio with using ASL maps generated from an existing model, both with and without the advantage of tuning to our dataset." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.72, + 0.468, + 0.901 + ], + "angle": 0, + "content": "(2) Naive baselines using ground truth ASL labels and heuristic strategies: We first report the SAAL mAP from simply selecting all active speakers as being attended using the ground truth ASL labels (Perfect ASL). We also report 2 baselines that use the center prior, which is the intuition that the attended person is likely near the center of the FOV because people often face the speaker they are paying attention to. Similar center prior baselines are used in the egocentric visual attention literature. We construct 2 center prior baselines: CP-I finds the head bounding box nearest to the center of FOV and selects it as the attention target if they are speaking, and otherwise predicts that there is no at" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.348 + ], + "angle": 0, + "content": "tention in the frame. CP-II selects the speaking person closest to the center of the FOV as the target of attention. We also construct 2 baselines that select the \"closest\" speaker based on the size of their bounding box. We can reason that the person with the largest head bounding box area is likely the closest to the camera wearer, and if speaking, likely appears the loudest. We consider 2 baselines based on this strategy: CS-I selects the \"closest\" person only if they are speaking, and CS-II selects the \"closest\" speaker. We note that because these methods depend on the dataset's ground truth ASL labels, they are not realistic results, and are not a fair comparison to our method. However, we report them to demonstrate that Perfect ASL and heuristic strategies perform poorly on our evaluation dataset. This clearly implies that SAAL is a complicated task that demands a novel approach, and that our evaluation dataset is rich enough to demonstrate the complexity of this task." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.349, + 0.892, + 0.622 + ], + "angle": 0, + "content": "(4) Networks adapted from MAVASL: The first adaption (MAVASL-I) is to directly use MAVASL to localize active speakers and use this as the auditory attention heatmap. The second adaptation (MAVASL-II) directly trains the network for the task of SAAL instead of ASL. The third adaptation (MAVASL-III) is similar to (MAVASL-II) but uses a multiframe video input (3-frame) to the AV network to further incorporate temporal information. MAVASL consists of an Audio Network, which predicts a coarse spatial voice activity map from multichannel audio, and an AV Network, which uses this voice activity map and the image to predict a final ASL map. For MAVASL-II and III, we achieve best results by supervising the audio network in MAVASL using the ASL labels from our dataset and the AV network with the auditory attention labels. We use Heads as the visual input representation. Because MAVASL is a frame-based network, we additionally apply temporal smoothing with a window size of 10 frames as in the original method." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.634, + 0.687, + 0.65 + ], + "angle": 0, + "content": "4.3. Comparison results" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.658, + 0.892, + 0.854 + ], + "angle": 0, + "content": "As shown in Table 2, our proposed method outperforms the baselines on mAP, including baselines that leverage ground truth active speaker labels. We observe that the Perfect ASL and naive baselines perform poorly on our dataset, illustrating that reducing the problem of SAAL to ASL is not viable in complex and challenging conversation environments with multiple speakers. The highest mAP achieved from adapting Jiang et al.'s ASL architecture is MAVASL-II, which obtains \\(75.20\\%\\) mAP. However, our best approach achieves a gain of \\(7.74\\%\\) mAP over this baseline, demonstrating that the task of SAAL demands a novel architecture design. We qualitatively compare our results against these baselines in Figure 4." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.856, + 0.892, + 0.901 + ], + "angle": 0, + "content": "From our experiments investigating different combinations of audio and visual input representations, we observe that the combination of Heads and Channel Corr + Spec" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.956 + ], + "angle": 0, + "content": "14668" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.094, + 0.089, + 0.454, + 0.398 + ], + "angle": 0, + "content": "
MethodmAP (%)
Perfect ASL*47.99
CP-I*63.55
CP-II*51.48
CS-I*53.86
CS-II*49.47
MAVASL-I59.11
MAVASL-II75.20
MAVASL-III72.90
Ours-Bbox & ASLsynthetic75.93
Ours-Bbox & ASL_real74.97
Ours-Bbox & Channel Corr80.41
Ours-Bbox & Channel Corr + Spectogram80.31
Ours-Image & ASLsynthetic72.20
Ours-Image & ASL_real70.04
Ours-Image & Channel Corr76.52
Ours-Image & Channel Corr + Spectogram76.95
Ours-Heads & ASLsynthetic76.72
Ours-Heads & ASL_real77.11
Ours-Heads & Channel Corr82.35
Ours-Heads & Channel Corr + Spectogram82.94
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.408, + 0.472, + 0.45 + ], + "angle": 0, + "content": "Table 2. Comparison results on the multi-speaker conversation dataset. (*) denotes methods that use ground truth ASL, which is not given to our model." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.46, + 0.472, + 0.824 + ], + "angle": 0, + "content": "togram produces the best results. In fact, we observe that Bbox, the binary bounding box location map, performs better as an input representation than the raw image. We can interpret this result as showing the importance of relative position and sizes of heads to the problem of SAAL. Channel Corr and Channel Corr + Spectogram, which contain information from the raw multichannel audio signal, generally perform better as the spatial audio input representation than the pre-computed ASL maps, both real and synthetically trained. We hypothesize that this is because the role of audio features in determining auditory attention is greater than just localizing active speakers; SAAL additionally involves correlating different speech signals with the camera wearer's egocentric movement, using the wearer's own voice activity as an indicator of conversational turn taking behavior (e.g. whether they are speaking or listening), and reasoning about the relative volume of different speech signals. Notably, the pre-computed ASL maps have the advantage of being spatially aligned with the visual modality, which the spectograms and channel correlation features do not have. The performance gains from using Channel Corr and Channel Corr + Spectogram indicate that our Audio Encoder is able to learn this alignment and construct a spatial representation of audio activity from these features." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.832, + 0.182, + 0.848 + ], + "angle": 0, + "content": "4.4. Analysis" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Model ablation We further investigate the contribution of each component of our best model to its overall performance in Table 3. We observe that the visual modality" + }, + { + "type": "table", + "bbox": [ + 0.557, + 0.089, + 0.839, + 0.245 + ], + "angle": 0, + "content": "
MethodmAP (%)
Visual only56.81
Visual only + Transformer57.70
Audio only76.30
Audio only + Transformer75.84
Audiovisual80.10
Audiovisual1-channel + Transformer71.47
Audiovisual2-channel + Transformer76.73
Audiovisual4-channel + Transformer80.99
Audiovisual + Transformer82.94
" + }, + { + "type": "table_caption", + "bbox": [ + 0.5, + 0.254, + 0.892, + 0.283 + ], + "angle": 0, + "content": "Table 3. Model ablation: All studies use Heads as the visual input and Channel Corr + Spectogram as the audio input." + }, + { + "type": "table", + "bbox": [ + 0.511, + 0.298, + 0.885, + 0.358 + ], + "angle": 0, + "content": "
MethodmAP (%)
Audiovisual + Transformer (no spatial alignment)80.57
Audiovisual + Transformer (spatial alignment)82.94
" + }, + { + "type": "table_caption", + "bbox": [ + 0.532, + 0.368, + 0.86, + 0.383 + ], + "angle": 0, + "content": "Table 4. Spatial modality alignment in the transformer." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.4, + 0.892, + 0.581 + ], + "angle": 0, + "content": "alone is much weaker than the spatial audio modality, and that clearly audio plays an important role. We also ablate the number of audio channels used, observing that removing the spatial component of the audio (Audiovisual\\(_{1}\\)-channel + Transformer) significantly reduces performance of our overall model. We see that spatial audio is an important cue for this task, but using slightly less channels can still achieve effective performance. Adding the transformer to the audiovisual features results in a gain of \\(2.84\\mathrm{mAP}\\), demonstrating that the transformer improves performance by refining the embedded audiovisual feature maps through modeling relationships across spatial regions of the scene." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.583, + 0.892, + 0.719 + ], + "angle": 0, + "content": "Results on Unseen Environment We additionally test our model's ability to generalize to unseen environments by evaluating our best model on a subset of data collected in a room with different acoustic and visual properties. The data follows the same structure as the main evaluation dataset, with 5 participants split into 2 conversation subgroups, and is \\(\\sim 49\\) minutes. Further details are provided in the supplement. On this unseen environment, our best model achieves \\(80.43\\%\\) mAP, demonstrating scene generalizability." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Spatial Modality Alignment in Self-Attention A key feature of our approach is leveraging multichannel audio to learn a spatial feature representation of voice activity in the scene, which we align with the visual representation by concatenating along the channel dimension. In our transformer design, therefore, each spatiotemporal patch of \\(\\mathcal{Z}^{AV}\\) contains the visual and audio features for that region. We validate this choice by designing an additional experiment where the modalities are not fused before the transformer, like in VisualBERT [60]. Rather than concatenating \\(\\mathcal{Z}^A\\) and \\(\\mathcal{Z}^V\\) before flattening them into a sequence of tokens to pass to \\(\\mathcal{T}\\), we separately create a sequence of 182 tokens each" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "14669" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.14, + 0.089, + 0.278, + 0.189 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.14, + 0.189, + 0.277, + 0.287 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.14, + 0.287, + 0.277, + 0.387 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.182, + 0.388, + 0.237, + 0.396 + ], + "angle": 0, + "content": "Ground truth" + }, + { + "type": "image", + "bbox": [ + 0.286, + 0.089, + 0.422, + 0.189 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.286, + 0.189, + 0.422, + 0.287 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.286, + 0.287, + 0.422, + 0.387 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.344, + 0.388, + 0.366, + 0.395 + ], + "angle": 0, + "content": "Ours" + }, + { + "type": "image", + "bbox": [ + 0.422, + 0.089, + 0.558, + 0.189 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.422, + 0.189, + 0.558, + 0.287 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.422, + 0.287, + 0.558, + 0.387 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.465, + 0.388, + 0.515, + 0.396 + ], + "angle": 0, + "content": "MAVASL-II" + }, + { + "type": "image", + "bbox": [ + 0.558, + 0.089, + 0.694, + 0.189 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.558, + 0.189, + 0.694, + 0.287 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.558, + 0.287, + 0.694, + 0.387 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.599, + 0.388, + 0.652, + 0.396 + ], + "angle": 0, + "content": "Perfect ASL" + }, + { + "type": "image", + "bbox": [ + 0.695, + 0.089, + 0.831, + 0.189 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.695, + 0.189, + 0.83, + 0.287 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.695, + 0.287, + 0.83, + 0.387 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.721, + 0.388, + 0.802, + 0.396 + ], + "angle": 0, + "content": "CP-I - Perfect ASL" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.407, + 0.895, + 0.464 + ], + "angle": 0, + "content": "Figure 4. We compare our output heatmaps to competing methods on challenging cases with multiple speakers, the attended speaker being far from the center, or no auditory attention. Our method performs well in these scenarios and more consistently identifies who is and isn't attended than MAVASL-II. Perfect ASL is prone to false positives by selecting all speakers and CPI is prone to false negatives by only considering the person closest to the center, demonstrating that ASL is not enough to solve SAAL. (Best viewed in color)." + }, + { + "type": "image", + "bbox": [ + 0.137, + 0.475, + 0.412, + 0.575 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.586, + 0.471, + 0.629 + ], + "angle": 0, + "content": "Figure 5. Decoupling SAAL & ASL: Without the responsibility for learning ASL, our model learns to segment the people within the camera wearer's conversation group." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.639, + 0.47, + 0.806 + ], + "angle": 0, + "content": "from \\(\\mathcal{Z}^V\\) and \\(\\mathcal{Z}^A\\) and pass these 364 total tokens of dimension 512 to \\(\\mathcal{T}\\). We concatenate the modalities afterwards. In this case, the self-attention mechanism is left to discover alignment between the modalities itself by comparing all tokens across both modalities. We observe a decrease in performance, indicating that our choice to explicitly align the visual and audio modalities spatially contributes to our model's ability to use both modalities together successfully. This result suggests utility in incorporating inductive bias about the spatial alignment of visual and multichannel audio modalities into token design for transformer architectures." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.81, + 0.471, + 0.902 + ], + "angle": 0, + "content": "Decoupling SAAL & ASL By nature of our dataset design, we train our model to predict auditory attention as the intersection of active speakers and people in the camera wearer's conversation group. To investigate the relationship between SAAL and ASL, we train a model by modulating our model's heatmap for the attended class" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.477, + 0.895, + 0.645 + ], + "angle": 0, + "content": "with the ground truth ASL labels before calculating loss and performing backpropagation. The loss is calculated as \\(\\mathcal{L}_{CE}(\\mathcal{H}_{\\mathrm{pred}}*\\mathrm{ASL}_{\\mathrm{label}},\\mathcal{H}_{\\mathrm{label}})\\). In this way we eliminate the responsibility for ASL from our model. The model achieves \\(92.67\\%\\) mAP on SAAL, however, this is a purely theoretical upper bound that relies on perfect ASL. We visualize \\(\\mathcal{H}_{\\mathrm{pred}}\\) for our model before it is modulated by ASL label in Figure 5. We observe that our model learns to more generally segment the camera wearer's conversation group regardless of speaking activity, and likely relies on ASL label to constrain the heatmaps to the exact bounding box region." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.658, + 0.62, + 0.673 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.683, + 0.892, + 0.85 + ], + "angle": 0, + "content": "We introduce the novel problem of Selective Auditory Attention Localization (SAAL) and demonstrate that a deep model is able to perform this task on a challenging multispeaker conversation dataset. We propose a multimodal modeling approach that uses egocentric video and multichannel audio to predict a person's target of auditory attention, combining spatial and temporal features from both modalities and using a transformer to reason holistically about the scene. We believe our work is an important step towards selective sound source enhancement and AR devices that can help people converse in noisy environments." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.856, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Acknowledgments: We thank Jacob Donley and Christi Miller for facilitating data collection, and Calvin Murdock and Ishwarya Ananthabhotla for valuable discussions." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "14670" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.117, + 0.47, + 0.173 + ], + "angle": 0, + "content": "[1] Triantafyllos Afouras, Andrew Owens, Joon Son Chung, and Andrew Zisserman. Self-supervised learning of audio-visual objects from video. In European Conference on Computer Vision, pages 208–224. 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The ActivityNet Large-Scale Activity Recognition Challenge, pages 1–4, 2019. 2" + }, + { + "type": "list", + "bbox": [ + 0.503, + 0.093, + 0.892, + 0.712 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.946, + 0.519, + 0.957 + ], + "angle": 0, + "content": "14674" + } + ] +] \ No newline at end of file diff --git a/2023/Egocentric Auditory Attention Localization in Conversations/89830ac3-80bf-409b-844e-adf1daa6e387_origin.pdf b/2023/Egocentric Auditory Attention Localization in Conversations/89830ac3-80bf-409b-844e-adf1daa6e387_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..846c6aee9ea6cf5a689724555a5b2f5c57c9774a --- /dev/null +++ b/2023/Egocentric Auditory Attention Localization in Conversations/89830ac3-80bf-409b-844e-adf1daa6e387_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:f41eab6d6d7012ec44f42e9273a5e6caf03e547a3d666df7f228c9a36a4447a0 +size 1951272 diff --git a/2023/Egocentric Auditory Attention Localization in Conversations/full.md b/2023/Egocentric Auditory Attention Localization in Conversations/full.md new file mode 100644 index 0000000000000000000000000000000000000000..99a46c7f7c2c79a866985e498f953a8ef2bcd78c --- /dev/null +++ b/2023/Egocentric Auditory Attention Localization in Conversations/full.md @@ -0,0 +1,323 @@ +# Egocentric Auditory Attention Localization in Conversations + +Fiona Ryan $^{1,2*}$ , Hao Jiang $^{2}$ , Abhinav Shukla $^{2}$ , James M. Rehg $^{1,2}$ , Vamsi Krishna Ithapu $^{2}$ , Georgia Institute of Technology $^{1}$ , Meta Reality Labs Research $^{2}$ + +{fkryan, rehg}@gatech.edu, {haojiang, ithapu}@meta.com, abhinav.shukla.research@gmail.com + +# Abstract + +In a noisy conversation environment such as a dinner party, people often exhibit selective auditory attention, or the ability to focus on a particular speaker while tuning out others. Recognizing who somebody is listening to in a conversation is essential for developing technologies that can understand social behavior and devices that can augment human hearing by amplifying particular sound sources. The computer vision and audio research communities have made great strides towards recognizing sound sources and speakers in scenes. In this work, we take a step further by focusing on the problem of localizing auditory attention targets in egocentric video, or detecting who in a camera wearer's field of view they are listening to. To tackle the new and challenging Selective Auditory Attention Localization problem, we propose an end-to-end deep learning approach that uses egocentric video and multichannel audio to predict the heatmap of the camera wearer's auditory attention. Our approach leverages spatiotemporal audiovisual features and holistic reasoning about the scene to make predictions, and outperforms a set of baselines on a challenging multi-speaker conversation dataset. Project page: https://fkryan.github.io/saal + +# 1. Introduction + +One of the primary goals of wearable computing devices like augmented reality (AR) glasses is to enhance human perceptual and cognitive capabilities. This includes helping people have natural conversations in settings with high noise level (e.g. coffee shops, restaurants, etc.) by selectively amplifying certain speakers while suppressing noise and the voices of background speakers. This desired effect mirrors selective auditory attention (SAA), or humans' ability to intentionally focus on certain sounds while tuning out others. People exercise SAA in everyday conversational settings; at restaurants people tune out the voices at adjacent tables, and in group social settings, such as dining at + +![](images/dc50728007db9a2c06fbdced454a87284060a7f9f00cabe76ed51e7869048f51.jpg) + +![](images/b0ca4af14948e8e82fd315ac94952aa707920746bf8bfa1758ab0e3b92dc063e.jpg) +Figure 1. We address the novel task of Selective Auditory Attention Localization in multi-speaker environments: given egocentric video and multichannel audio, we predict which people, if any, the camera wearer is listening to. We show our model's predicted heatmaps, with red bounding boxes denoting ground truth auditory attention targets and white boxes denoting non-attended speakers. + +![](images/e970668b335822d8fff9d60241336f873e689f29f5e022a0906c4d8b78027e1d.jpg) + +![](images/558ca4087a8cd6dadf824971563e78dc1567f5d61d35775e3a80981ee09cbf20.jpg) + +a large table or socializing at a party, people often engage in conversations with smaller subsets of people while others converse in close proximity. Being able to determine which speaker(s) a person is selectively listening to is important for developing systems that can aid communication in noisy environments and assist people with hearing loss. + +While the computer vision community has made strides towards understanding conversational dynamics with largescale datasets like Ego4D [37], AVA-ActiveSpeaker [78], VoxConverse [24], and AMI [57], the problem of modeling selective listening behavior has not yet been addressed. In fact, determining auditory attention among competing sound signals has traditionally been approached using neurophysiological sensing [11, 50]. These approaches involve a controlled listening task, where competing audio signals + +are played simultaneously and a listener selectively listens to one. Statistical models are then used to correlate brain activity and the attended sound signal. However, the sensing approach is obtrusive and currently not feasible for use in realistic conversational settings in daily life. + +In this work, we approach modeling SAA from an egocentric audiovisual perspective. The egocentric setting provides a compelling lens to study social conversational dynamics, as it captures both the audio and visual stimuli present in a scene and how the camera wearer orients their view in response to them. We hypothesize that the behavior of the wearer that is implicitly captured in the egocentric video and multichannel audio can facilitate the prediction of auditory attention targets. To this end, we introduce and formulate the novel task of Selective Auditory Attention Localization (SAAL), which uses egocentric video and multichannel audio to localize the target of auditory attention in egocentric video. We specifically target multi-speaker conversation scenarios where the camera wearer must selectively attend to certain speaker(s) while tuning out others. This challenging setting is representative of everyday noisy conversation environments and highlights the complexity of modeling auditory attention in naturalistic settings. + +We propose a deep audiovisual video network for SAAL that leverages both appearance-based features from the ego-centric video stream and spatial audio information from multichannel audio. Our key insight is to extract a spatiotemporal feature representation from each modality and use a transformer on the fused features to reason holistically about the scene. Our contributions are: + +- We introduce the novel problem of Selective Auditory Attention Localization (SAAL) as an egocentric multimodal learning task. +- We propose a new architecture for SAAL. Our model extracts spatiotemporal video and audio features and uses a transformer to refine selection of an attention target by reasoning globally about the scene. +- We evaluate our approach on a challenging multispeaker conversation dataset and demonstrate our model's superiority over intuitive baselines and approaches based on Active Speaker Localization (ASL). +- We conduct thorough experiments to give insight into our multimodal architecture design, effective multichannel audio and visual input representations, and the relationship between SAAL and ASL. + +# 2. Related Work + +Computational Models for Auditory Attention Attention is typically categorized into two types: bottom-up, where a stimulus is likely to cause attention due to inherent salient properties, and top-down, where a person intentionally focuses on a certain stimulus. Top-down, or selective auditory + +attention has been studied by correlating the attended sound signal with the neural response measured by EEG / MEG using statistical models [4,17-19,27,33,38,40,65,67,71,74, 89], and more recently deep neural networks [36, 58]. This is done in a controlled listening scenario where competing sounds, such as audio books, are played at once and a participant is instructed to listen to a particular sound. Models are used to predict which sound source is attended and/or decode the attended signal. The sources may be combined into a single channel or played in separate ears, as in the dichotic listening task paradigm [20]. Some works have used acoustic simulation methods to reflect more realistic multispeaker environments [17, 33, 89]. However, these studies have not addressed modeling SAA in in-the-wild social conversation scenarios. Beyond using brain activity to predict auditory attention, Lu et al. develop a head movement-based approach for predicting the attended speaker in a conversation [64]. However, this work focuses on single group conversations where there is typically only one speaker. + +A smaller body of work focuses on modeling bottom-up auditory attention, or the qualities of a sound signal that make it likely to be attended to. Works in this domain construct representations of audio signals and evaluate their ability to reflect human judgment of saliency [30, 49, 51, 52, 56, 85, 86], distinguish between changes in perceptual qualities of sound [48], or perform on a downstream speech recognition task [47]. In this work, we focus on top-down, or selective auditory attention. + +Active Speaker Detection & Localization Our task builds upon a rich foundation of work on Active Speaker Detection (ASD) and Active Speaker Localization (ASL). Recognizing speech activity is an established problem in computer vision, with early approaches correlating video and audio streams [25], or using purely visual features [31, 39, 79] to determine if a person is speaking. The AVA-ActiveSpeaker dataset [78] has accelerated deep learning approaches for ASD by providing a large-scale dataset and a benchmark. Methods use deep learning to extract visual features from a head bounding box track and combine them with features from monoaural scene audio to classify the person as speaking and audible, speaking and inaudible, or not speaking in each frame [8-10, 26, 54, 66, 82, 95]. Some approaches additionally explicitly model the relationships between multiple people within a scene to refine classification of speakers [8, 54, 66]. Xiong et al. [93] develop an architecture to jointly perform ASD and speech enhancement. + +Other methods approach the task of ASL, which seeks to localize speakers spatially within the scene rather than classifying bounding box tracks [6, 15, 22, 34, 35, 76, 92, 94]. Several use multichannel audio to incorporate directional audio information [6, 15, 22, 34, 35, 92, 94]. Recently, Jiang et al. [46] expanded upon these approaches by developing a deep model that also leverages multichannel audio to lo + +![](images/c51d3794c3f6837f31275d3b0a0f50c6ece9d16146504e80cec32a14feb30366.jpg) +Figure 2. Our architecture for predicting auditory attention heatmaps from egocentric video and multichannel audio: the Video Encoder and Audio Encoder embed spatiotemporal features from the video and spatial audio modalities respectively. The audio and visual features are fused and passed to the Scene Relation Transformer, which models the relationships between different regions of the scene. Finally, the features are passed to the convolutional Decoder, which produces the predicted attention heatmaps for the input video frames. + +calize speakers in the challenging egocentric setting, which contains motion blur and rapid changes of field of view (FOV), using the EasyCom dataset [28]. Our problem setting is different from ASD and ASL in that we seek to determine which of the speakers the camera wearer is listening to using egocentric audiovisual cues. Importantly, active speakers are not necessarily auditorily attended; they can be background people or nearby people engaged in a different conversation. Thus, SAAL demands a novel approach. + +Modeling of Conversation Dynamics and Social Interactions SAAL is also related to work on modeling social interactions and conversational dynamics. Prior works have explored detecting social interactions in egocentric video [2, 16, 32]. The recent Ego4D dataset and benchmark suite [37] introduces the "Talking to Me" task for identifying which people are speaking to the camera wearer in egocentric video. This task is closely related to SAAL in that it models dyadic conversational behavior between the camera wearer and people in their FOV. However our task differs by modeling egocentric listening behavior, particularly in the presence of multiple speakers. Researchers have also explored modeling conversational turn taking behaviors [88] as well as predicting listener motion in dyadic conversations [70]. To our knowledge, we are the first to address the problem of modeling auditory attention using egocentric video, wearable audio, or both modalities together. + +Egocentric Visual Attention Prediction Our problem also relates to egocentric visual attention prediction, which regresses a heatmap localizing the target of visual attention in egocentric video. Approaches for this task use eye tracking data as ground truth for attention targets and develop models to predict the attention location from video. Re + +searchers have proposed several vision models for this task [5,44,59,61,83], including some that jointly model gaze and action [43,62] or gaze and IMU [84]. Importantly, visual attention and auditory attention are not the same; people will generally not always look at the person they are conversing with. Rather, SAAL can be considered as an auditory variant of egocentric visual attention prediction, and SAAL additionally demands the use of audio cues. + +Audiovisual Representation Learning Our work relates to a larger body of research on learning effective audiovisual feature representations [3,7,12,45,55,69,72,73,75] and localizing sound sources in video [1, 13, 23, 41, 42, 63, 68, 77, 80, 81]. These methods learn semantic correspondences between visual and audio features, typically using contrastive training paradigms. In contrast to these approaches, we leverage multichannel audio and employ a fusion mechanism that enforces spatial alignment between the visual and spatial audio domains, allowing us to reason globally about the audiovisual content in different regions of the scene. + +# 3. Method + +# 3.1. Problem Definition + +At each time $t$ , we predict an auditory attention heatmap $\mathcal{H}_t$ , given the raw audiovisual input $\{I_n, a_n | n = 0 \dots t\}$ where $I_n$ is an egocentric video frame at time $n$ and $a_n$ is a multi-channel audio segment aligned with the video frame $I_n$ . Each pixel $\mathcal{H}_t(i, j)$ has a value in (0,1) and indicates the probability of the camera wearer's auditory attention. Video $I$ captures the movement of both the camera wearer and the other people in the scene, as well as information about their head and body poses, facial expression, mouth + +movement, and overall scene layout. Multichannel audio $a$ , from a microphone array, captures people's speech as well as other spatialized sound sources. We use video from a 180-degree fish-eye camera with resolution $200 \times 212$ and audio from a 6-channel microphone array. In this paper, we demonstrate how to use $\{I, a\}$ to infer $\mathcal{H}$ , where we construct $\mathcal{H}_{\mathrm{label}}$ by setting all pixels within the head bounding box of an attended speaker in a frame as 1. + +# 3.2. Model + +SAAL is a complex task that involves understanding both the camera wearer's behavior and the activity of the people in the scene. We design a deep multimodal model for this task to have 4 key abilities: (1) It extracts relevant visual features such as lip movement, the relative positions and orientations of heads, and social body language like when a person looks at the camera wearer. (2) It leverages multichannel audio to construct a spatial representation of voice activity occurring around the camera wearer. (3) It encodes temporal information like how the wearer moves their head in response to stimuli as well as the movement of people in the scene and pattern of voice activity. (4) It reasons globally about the audiovisual content of scene as a whole to select an attention target; while an active speaker detector identifies all speakers in a scene, determining attention demands holistic reasoning about different potential attention targets in a scene to select the most likely one(s). + +To this end, our method consists of 4 main components as shown in Figure 2: the Visual Encoder and Audio Encoder to extract spatiotemporal features from the video and multichannel audio inputs respectively, the Scene Relation Transformer to refine attention localization by modeling the relationships between audiovisual features in different spatial regions of the scene, and a convolutional Decoder to produce an auditory attention heatmap for each input frame. + +Visual Encoder The Visual Encoder $\mathcal{V}$ takes the visual input $X^V$ as a stack of $200 \times 212$ frames over a time interval $T$ and extracts appearance-based features about the scene. We construct $X^V$ by cropping the people's heads in the raw grayscale video frames and filling the background with black. This representation leverages 1) our focus on conversational attention, and 2) the effectiveness of face detection methods. The input is a 3D video tensor of head tubes that represents not only how the people in the scene move, how they are laid out in space, where they look, their facial expression, mouth movement, and who they talk to, but also the head movement of the wearer over time. In our experiments, we compare this representation to using the raw image as well as a binary map of the bounding boxes. We find that this representation improves performance by removing background distractions while retaining appearance-based facial features. Additionally, this representation makes the model more generalizable to different scenes. We use a 3D + +ResNet-18 network [87] as our backbone, which uses 3D convolutions to capture both spatial and temporal features. The result of $\mathcal{V}(X^V)$ is a spatiotemporal visual feature map $\mathcal{Z}^V$ of dimension $512 \times 1 \times 13 \times 14$ , where 512 is the channel dimension, 1 is the temporal dimension, and 13 and 14 correspond to the height and width. We use 8 frames as input with temporal stride 3, so each input $X^V$ spans a 24 frame window, which is 0.8 seconds in 30fps video. + +Audio Encoder The Audio Encoder $\mathcal{A}$ extracts spatial audio features from the multichannel audio in the input clip to encode information about the conversational speech patterns and spatially localize speakers. We process the audio into 2000 sample $\times 6$ channel frames corresponding to each frame in the video input clip. We construct input features $X^A$ by calculating the complex spectogram with 201 frequency bins, window length 20, and hop length 10 and stacking these vertically for the 6 channels. We found this performs slightly better than concatenating along the channel dimension. We additionally construct a feature representation of the cross correlation between all pairs of channels as used in Jiang et al. [46] and stack the real and complex parts of the spectogram and the channel correlation features along the channel dimension. We then resize the audio features to $200\times 212$ spatially in order to extract feature maps that align with the visual domain. Due to the importance of capturing dense temporal audio features to predict auditory attention, such as the pattern of speech, we pass all 24 audio frames in the clip to $\mathcal{A}$ , which uses another 3D ResNet-18 backbone. The resultant feature map $\mathcal{Z}^A$ is of size $512\times 3\times 13\times 14$ . We average pool the temporal dimension to 1 to match the dimension of $\mathcal{Z}^V$ . + +Scene Relation Transformer From $\mathcal{A}$ and $\nu$ , we extract visual and spatial audio features maps $\mathcal{Z}^V$ and $\mathcal{Z}^A$ , which we concatenate along the channel dimension to form $\mathcal{Z}^{AV} \in 1024 \times 1 \times 13 \times 14$ . We choose to concatenate the features along the channel dimension because our approach importantly leverages multichannel audio, which can extract a spatial representation of voice activity in the scene so that the visual and audio domains can be spatially aligned. + +We use a transformer $\mathcal{T}$ to further refine this fused multimodal feature map by modeling correlations between the features in different regions of the scene to holistically select a likely attention target. As in the transformer literature [14, 29], we treat each spatial location $Z_{1,h,w}^{AV}$ as a spatiotemporal patch of embedded dimension $D = 512$ , and flatten the feature map into a sequence of length $L = 1 \times 13 \times 14 = 182$ . A learnable position embedding $E \in \mathbb{R}^{L \times D}$ is added to preserve absolute and relative positional information, which is particularly important for the egocentric setting where the camera wearer orients their view of the scene in response to stimuli. The transformer consists of 12 transformer blocks [90] where each computes self-attention on the audiovisual feature map as Softmax $(QK^T / \sqrt{D})V$ + +
SplitTotal framesFrames with 1+ attention targetAvg. heads per frameAvg. speakers per frame
Train1,416,262881,9313.051.43
Test571,027367,5363.061.45
+ +Table 1. Dataset statistics: our evaluation dataset of multi-speaker conversations is representative of challenging conversation environments where several people and speakers are present. Note that we use $\frac{1}{3}$ of these frames for training and evaluation with temporal stride 3. + +![](images/102ff4ef94df725f83d35d16d54005fefee386b19f8d41d8edb523515773243a.jpg) +Figure 3. In our multi-speaker evaluation dataset, participants are divided into 2 subgroups that converse simultaneously. A person is labeled as being an auditory attention target if they are both speaking and within the camera wearer's conversation group. + +![](images/66602d8c4b0a440855bbc8ff6b3d8ced100059fca8d1ad0c5c3d91818fdc4caf.jpg) + +where $Q$ , $K$ , and $V$ are learned linear projections on the multimodal spatiotemporal patches. In this way, the model learns correlations between audiovisual features occurring in different regions of the scene and can suppress or enhance values accordingly to refine attention prediction. + +Decoder A decoder consisting of 4 3D transpose convolutions and 1 final convolutional classifier layer upsamples the resulting feature map $\mathcal{T}(\mathcal{Z}^{AV})$ to produce the attention class heatmap $\mathcal{H}_{\mathrm{pred}}$ of size $2\times T\times H\times W$ . The 2 channels reflect the not attended and attended classes. + +# 3.3. Implementation & Model Training + +We train end-to-end with pixel-wise cross entropy loss. We initialize $\mathcal{V}$ and $\mathcal{A}$ with pretrained weights on Kinetics 400 [21]. The transformer consists of 12 transformer blocks using multi-head self-attention with 8 heads [90]. We use the Adam optimizer [53] and learning rate 1e-4. The training procedure converges quickly in less than 10 epochs. + +# 4. Experimental Results + +# 4.1. Evaluation Dataset & Criteria + +To our knowledge there is no existing dataset with associated labels suited to our task. While egocentric AV datasets like Ego4D [37] and EasyCom [28] capture egocentric conversations, they have few situations with multiple people speaking at the same time, with the result that SAAL reduces to ASL. To evaluate our approach, we collected a dataset of complex multi-speaker conversations, where groups converse in close proximity. The dataset consists of 50 participants conversing in groups of 5, where each person wears a headset with a camera and microphone + +array. In total, there are $\sim 20$ hours of egocentric video. + +In each 10-minute recording, a group of 5 people sits at a table in a meeting room and is partitioned into two conversational groups. Participants are instructed to only listen to and engage in conversations with their own group. In this way, we design a naturalistic social version of traditional dichotic listening tasks, where participants intentionally focus on certain speakers while tuning out others. By splitting the group into smaller groups, we simulate conversational layouts that may occur at a large dinner table, coffee shop, restaurant, or party, where groups of people converse in close proximity with others. As illustrated in Figure 3, we construct ground truth auditory attention labels by determining that the camera wearer is listening to a given person if they are both speaking and in the wearer's conversation group. The dataset was collected under an approved IRB. + +Each participant wears a headset that includes an Intel SLAM camera and a 6-microphone array. We record the fish-eye grayscale video and the audio from the 6 microphones simultaneously for all the wearers in each session. We generate speaker activity and head bounding box annotations automatically by using person tracking and wearer speech detection algorithms, and leveraging synchronization between each person's egocentric audio and video in each session. We obtain active speaker labels for each person by using their own headset's microphone array to determine if they are speaking, using a deep model adapted from [46] trained on synthetic data for the headset's microphone array configuration. We then use a 3D tracking-by-detection method that uses camera pose from the SLAM camera to annotate head bounding boxes and identities for each person in each egocentric FOV. From these person tracking results and speaker activity labels for each person, we have a set of visible head bounding boxes for each egocentric frame along with a label for each box indicating if that person is speaking. We then use the identity tracking and known conversation group assignments to label if each person is auditorily attended to by the camera wearer. + +Due to the wide 180-degree FOV of the camera, the auditorily attended person is almost always in the FOV, so we constrain our modeling approach to this scenario. Additionally, by design of the dataset, there are typically several people and often multiple speakers within FOV, as shown in Table 1. Along with the inherent challenges of motion blur and rapid head movements in the egocentric modality, this + +makes our dataset a rich means for studying auditory attention in complex and naturalistic conversation environments. + +We evaluate the result of auditory attention localization using mean average precision (mAP) on the task of classifying each person in the FOV as being a target of auditory attention or not. From the output heatmap $\mathcal{H}_{\mathrm{pred}}$ , we calculate the auditory attention score for each person by taking the maximum value of Softmax $(\mathcal{H}_{\mathrm{pred}})$ in channel 1 (the attended class) in the region of their head bounding box. We split our data and use $70\%$ data for training and $30\%$ for testing, with no overlapping participants between splits. + +# 4.2. Competing methods + +Because SAAL is a new problem, there are no previous methods that can be used directly to solve this problem. We therefore compare our approach to several naive baseline methods as well as a set of baselines that adapt Jiang et al.'s multichannel audiovisual ASL architecture (MAVASL) [46] for our task. The methods we compare are the following: + +(1) Our proposed method with different audio and visual input representations: In our experiments, we label variations of our method as "Ours - [visual] & [audio]", where [visual] is the visual input representation type and [audio] is the audio input representation type. The visual input representations we consider are Image (the raw image), Bbox (a binary map of the bounding boxes), and Heads (the cropped heads from the raw image on a black background). The audio representations are Channel Corr (the channel correlation features as described in Section 3.2), Channel Corr + Spectogram (the channel correlation features concatenated with the real and complex parts of the multichannel spectrogram), and ASL (active speaker localization output maps from MAVASL). We report two different training strategies for using MAVASL to generate ASL maps for our dataset: $\mathrm{ASL}_{\mathrm{synthetic}}$ , which trains the ASL model on synthetic data created from VTCK [91] and EasyCom, and $\mathrm{ASL}_{\mathrm{real}}$ , which directly trains the ASL model on our dataset using the active speaker labels. In this way, we compare using audio features constructed from the raw multichannel audio with using ASL maps generated from an existing model, both with and without the advantage of tuning to our dataset. + +(2) Naive baselines using ground truth ASL labels and heuristic strategies: We first report the SAAL mAP from simply selecting all active speakers as being attended using the ground truth ASL labels (Perfect ASL). We also report 2 baselines that use the center prior, which is the intuition that the attended person is likely near the center of the FOV because people often face the speaker they are paying attention to. Similar center prior baselines are used in the egocentric visual attention literature. We construct 2 center prior baselines: CP-I finds the head bounding box nearest to the center of FOV and selects it as the attention target if they are speaking, and otherwise predicts that there is no at + +tention in the frame. CP-II selects the speaking person closest to the center of the FOV as the target of attention. We also construct 2 baselines that select the "closest" speaker based on the size of their bounding box. We can reason that the person with the largest head bounding box area is likely the closest to the camera wearer, and if speaking, likely appears the loudest. We consider 2 baselines based on this strategy: CS-I selects the "closest" person only if they are speaking, and CS-II selects the "closest" speaker. We note that because these methods depend on the dataset's ground truth ASL labels, they are not realistic results, and are not a fair comparison to our method. However, we report them to demonstrate that Perfect ASL and heuristic strategies perform poorly on our evaluation dataset. This clearly implies that SAAL is a complicated task that demands a novel approach, and that our evaluation dataset is rich enough to demonstrate the complexity of this task. + +(4) Networks adapted from MAVASL: The first adaption (MAVASL-I) is to directly use MAVASL to localize active speakers and use this as the auditory attention heatmap. The second adaptation (MAVASL-II) directly trains the network for the task of SAAL instead of ASL. The third adaptation (MAVASL-III) is similar to (MAVASL-II) but uses a multiframe video input (3-frame) to the AV network to further incorporate temporal information. MAVASL consists of an Audio Network, which predicts a coarse spatial voice activity map from multichannel audio, and an AV Network, which uses this voice activity map and the image to predict a final ASL map. For MAVASL-II and III, we achieve best results by supervising the audio network in MAVASL using the ASL labels from our dataset and the AV network with the auditory attention labels. We use Heads as the visual input representation. Because MAVASL is a frame-based network, we additionally apply temporal smoothing with a window size of 10 frames as in the original method. + +# 4.3. Comparison results + +As shown in Table 2, our proposed method outperforms the baselines on mAP, including baselines that leverage ground truth active speaker labels. We observe that the Perfect ASL and naive baselines perform poorly on our dataset, illustrating that reducing the problem of SAAL to ASL is not viable in complex and challenging conversation environments with multiple speakers. The highest mAP achieved from adapting Jiang et al.'s ASL architecture is MAVASL-II, which obtains $75.20\%$ mAP. However, our best approach achieves a gain of $7.74\%$ mAP over this baseline, demonstrating that the task of SAAL demands a novel architecture design. We qualitatively compare our results against these baselines in Figure 4. + +From our experiments investigating different combinations of audio and visual input representations, we observe that the combination of Heads and Channel Corr + Spec + +
MethodmAP (%)
Perfect ASL*47.99
CP-I*63.55
CP-II*51.48
CS-I*53.86
CS-II*49.47
MAVASL-I59.11
MAVASL-II75.20
MAVASL-III72.90
Ours-Bbox & ASLsynthetic75.93
Ours-Bbox & ASL_real74.97
Ours-Bbox & Channel Corr80.41
Ours-Bbox & Channel Corr + Spectogram80.31
Ours-Image & ASLsynthetic72.20
Ours-Image & ASL_real70.04
Ours-Image & Channel Corr76.52
Ours-Image & Channel Corr + Spectogram76.95
Ours-Heads & ASLsynthetic76.72
Ours-Heads & ASL_real77.11
Ours-Heads & Channel Corr82.35
Ours-Heads & Channel Corr + Spectogram82.94
+ +togram produces the best results. In fact, we observe that Bbox, the binary bounding box location map, performs better as an input representation than the raw image. We can interpret this result as showing the importance of relative position and sizes of heads to the problem of SAAL. Channel Corr and Channel Corr + Spectogram, which contain information from the raw multichannel audio signal, generally perform better as the spatial audio input representation than the pre-computed ASL maps, both real and synthetically trained. We hypothesize that this is because the role of audio features in determining auditory attention is greater than just localizing active speakers; SAAL additionally involves correlating different speech signals with the camera wearer's egocentric movement, using the wearer's own voice activity as an indicator of conversational turn taking behavior (e.g. whether they are speaking or listening), and reasoning about the relative volume of different speech signals. Notably, the pre-computed ASL maps have the advantage of being spatially aligned with the visual modality, which the spectograms and channel correlation features do not have. The performance gains from using Channel Corr and Channel Corr + Spectogram indicate that our Audio Encoder is able to learn this alignment and construct a spatial representation of audio activity from these features. + +# 4.4. Analysis + +Model ablation We further investigate the contribution of each component of our best model to its overall performance in Table 3. We observe that the visual modality + +Table 2. Comparison results on the multi-speaker conversation dataset. (*) denotes methods that use ground truth ASL, which is not given to our model. + +
MethodmAP (%)
Visual only56.81
Visual only + Transformer57.70
Audio only76.30
Audio only + Transformer75.84
Audiovisual80.10
Audiovisual1-channel + Transformer71.47
Audiovisual2-channel + Transformer76.73
Audiovisual4-channel + Transformer80.99
Audiovisual + Transformer82.94
+ +Table 3. Model ablation: All studies use Heads as the visual input and Channel Corr + Spectogram as the audio input. + +
MethodmAP (%)
Audiovisual + Transformer (no spatial alignment)80.57
Audiovisual + Transformer (spatial alignment)82.94
+ +Table 4. Spatial modality alignment in the transformer. + +alone is much weaker than the spatial audio modality, and that clearly audio plays an important role. We also ablate the number of audio channels used, observing that removing the spatial component of the audio (Audiovisual $_{1}$ -channel + Transformer) significantly reduces performance of our overall model. We see that spatial audio is an important cue for this task, but using slightly less channels can still achieve effective performance. Adding the transformer to the audiovisual features results in a gain of $2.84\mathrm{mAP}$ , demonstrating that the transformer improves performance by refining the embedded audiovisual feature maps through modeling relationships across spatial regions of the scene. + +Results on Unseen Environment We additionally test our model's ability to generalize to unseen environments by evaluating our best model on a subset of data collected in a room with different acoustic and visual properties. The data follows the same structure as the main evaluation dataset, with 5 participants split into 2 conversation subgroups, and is $\sim 49$ minutes. Further details are provided in the supplement. On this unseen environment, our best model achieves $80.43\%$ mAP, demonstrating scene generalizability. + +Spatial Modality Alignment in Self-Attention A key feature of our approach is leveraging multichannel audio to learn a spatial feature representation of voice activity in the scene, which we align with the visual representation by concatenating along the channel dimension. In our transformer design, therefore, each spatiotemporal patch of $\mathcal{Z}^{AV}$ contains the visual and audio features for that region. We validate this choice by designing an additional experiment where the modalities are not fused before the transformer, like in VisualBERT [60]. Rather than concatenating $\mathcal{Z}^A$ and $\mathcal{Z}^V$ before flattening them into a sequence of tokens to pass to $\mathcal{T}$ , we separately create a sequence of 182 tokens each + +![](images/9740bb2f053e985e9557544d544c04ac075f20813f89e36f151779c10d30f03e.jpg) + +![](images/d2313bd74ae25add2f1988c5fa734b99face845d517eb7e46e9754033bfa2ac1.jpg) + +![](images/cce581b4204d1af81eedff750f995a6aeb8bf0d1006b8fab9a9bd668f84c332e.jpg) +Ground truth + +![](images/076df813a0469629b4d8d8e9b6a9554de97a294b6fc002eff91204fd1c8730cc.jpg) + +![](images/697dac345412e6fb320b8c9e31da17232943a9de856d9e197491d24d50fe5a5c.jpg) + +![](images/1a44a95fb86a90633342df6586587569a30fae443f8c8b821b66accbdda68e24.jpg) +Ours + +![](images/584d455ae728dcdc0baf889e3a6139d89883ccc15569fa084179ff9797b02aa8.jpg) + +![](images/b3774a142f8cfb8bd6fa037befcf8549a02c05f3ce069d1bebf66d210f0509db.jpg) + +![](images/42b4e254883c4821ccc5747d739a7fecf9a5db58215a710ae9d6bb387f94eefe.jpg) +MAVASL-II + +![](images/a46b681c0b05e3348396cbbd0f593d9fef3547f2ddd1663fd002b815459c277a.jpg) + +![](images/a5ed135b234088f9057205fa2c414fe8f915970a6b000070e891d59af51635af.jpg) + +![](images/8f81c53a857e6c7709fe3aaab9b0838c168bb8be69c58051b0b2fbe91a45f2dc.jpg) +Perfect ASL + +![](images/9614f3a4ff5b9cdd47fa13f0bb9088646d9e97c0e19cf29f286d504e0c8fca76.jpg) + +![](images/eee9713d2dcef838f7f9f11e2a5031587d040e677c225cc38a3fd9c097bbdee3.jpg) + +![](images/a746d9c637f9933a0868a3b5096b50dc56a3ba20d925c5e185249ff2143c97db.jpg) +CP-I - Perfect ASL + +![](images/4f61cb04c5bff466a2a027b51b1f43d5eb6ebf444f3c0422cfdcb16be997a583.jpg) +Figure 4. We compare our output heatmaps to competing methods on challenging cases with multiple speakers, the attended speaker being far from the center, or no auditory attention. Our method performs well in these scenarios and more consistently identifies who is and isn't attended than MAVASL-II. Perfect ASL is prone to false positives by selecting all speakers and CPI is prone to false negatives by only considering the person closest to the center, demonstrating that ASL is not enough to solve SAAL. (Best viewed in color). +Figure 5. Decoupling SAAL & ASL: Without the responsibility for learning ASL, our model learns to segment the people within the camera wearer's conversation group. + +from $\mathcal{Z}^V$ and $\mathcal{Z}^A$ and pass these 364 total tokens of dimension 512 to $\mathcal{T}$ . We concatenate the modalities afterwards. In this case, the self-attention mechanism is left to discover alignment between the modalities itself by comparing all tokens across both modalities. We observe a decrease in performance, indicating that our choice to explicitly align the visual and audio modalities spatially contributes to our model's ability to use both modalities together successfully. This result suggests utility in incorporating inductive bias about the spatial alignment of visual and multichannel audio modalities into token design for transformer architectures. + +Decoupling SAAL & ASL By nature of our dataset design, we train our model to predict auditory attention as the intersection of active speakers and people in the camera wearer's conversation group. To investigate the relationship between SAAL and ASL, we train a model by modulating our model's heatmap for the attended class + +with the ground truth ASL labels before calculating loss and performing backpropagation. The loss is calculated as $\mathcal{L}_{CE}(\mathcal{H}_{\mathrm{pred}}*\mathrm{ASL}_{\mathrm{label}},\mathcal{H}_{\mathrm{label}})$ . In this way we eliminate the responsibility for ASL from our model. The model achieves $92.67\%$ mAP on SAAL, however, this is a purely theoretical upper bound that relies on perfect ASL. We visualize $\mathcal{H}_{\mathrm{pred}}$ for our model before it is modulated by ASL label in Figure 5. We observe that our model learns to more generally segment the camera wearer's conversation group regardless of speaking activity, and likely relies on ASL label to constrain the heatmaps to the exact bounding box region. + +# 5. Conclusion + +We introduce the novel problem of Selective Auditory Attention Localization (SAAL) and demonstrate that a deep model is able to perform this task on a challenging multispeaker conversation dataset. 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Recognizing who somebody is listening to in a conversation is essential for developing technologies that can understand social behavior and devices that can augment human hearing by amplifying particular sound sources. The computer vision and audio research communities have made great strides towards recognizing sound sources and speakers in scenes. In this work, we take a step further by focusing on the problem of localizing auditory attention targets in egocentric video, or detecting who in a camera wearer's field of view they are listening to. To tackle the new and challenging Selective Auditory Attention Localization problem, we propose an end-to-end deep learning approach that uses egocentric video and multichannel audio to predict the heatmap of the camera wearer's auditory attention. 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This includes helping people have natural conversations in settings with high noise level (e.g. coffee shops, restaurants, etc.) by selectively amplifying certain speakers while suppressing noise and the voices of background speakers. This desired effect mirrors selective auditory attention (SAA), or humans' ability to intentionally focus on certain sounds while tuning out others. 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We address the novel task of Selective Auditory Attention Localization in multi-speaker environments: given egocentric video and multichannel audio, we predict which people, if any, the camera wearer is listening to. We show our model's predicted heatmaps, with red bounding boxes denoting ground truth auditory attention targets and white boxes denoting non-attended speakers." + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 427, + 213, + 545, + 324 + ], + "blocks": [ + { + "bbox": [ + 427, + 213, + 545, + 324 + ], + "lines": [ + { + "bbox": [ + 427, + 213, + 545, + 324 + ], + "spans": [ + { + "bbox": [ + 427, + 213, + 545, + 324 + ], + "type": "image", + "image_path": "e970668b335822d8fff9d60241336f873e689f29f5e022a0906c4d8b78027e1d.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + } + ], + "index": 11 + }, + { + "type": "image", + "bbox": [ + 427, + 325, + 545, + 437 + ], + "blocks": [ + { + "bbox": [ + 427, + 325, + 545, + 437 + ], + "lines": [ + { + "bbox": [ + 427, + 325, + 545, + 437 + ], + "spans": [ + { + "bbox": [ + 427, + 325, + 545, + 437 + ], + "type": "image", + "image_path": "558ca4087a8cd6dadf824971563e78dc1567f5d61d35775e3a80981ee09cbf20.jpg" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_body" + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 530, + 545, + 602 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 530, + 545, + 602 + ], + "spans": [ + { + "bbox": [ + 304, + 530, + 545, + 602 + ], + "type": "text", + "content": "a large table or socializing at a party, people often engage in conversations with smaller subsets of people while others converse in close proximity. Being able to determine which speaker(s) a person is selectively listening to is important for developing systems that can aid communication in noisy environments and assist people with hearing loss." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 605, + 546, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 546, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 546, + 715 + ], + "type": "text", + "content": "While the computer vision community has made strides towards understanding conversational dynamics with largescale datasets like Ego4D [37], AVA-ActiveSpeaker [78], VoxConverse [24], and AMI [57], the problem of modeling selective listening behavior has not yet been addressed. In fact, determining auditory attention among competing sound signals has traditionally been approached using neurophysiological sensing [11, 50]. These approaches involve a controlled listening task, where competing audio signals" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 61, + 703, + 188, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 61, + 703, + 188, + 713 + ], + "spans": [ + { + "bbox": [ + 61, + 703, + 188, + 713 + ], + "type": "text", + "content": "*Work done during internship at Meta." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "14663" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 133 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 133 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 133 + ], + "type": "text", + "content": "are played simultaneously and a listener selectively listens to one. Statistical models are then used to correlate brain activity and the attended sound signal. However, the sensing approach is obtrusive and currently not feasible for use in realistic conversational settings in daily life." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 133, + 289, + 347 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 133, + 289, + 347 + ], + "spans": [ + { + "bbox": [ + 46, + 133, + 289, + 347 + ], + "type": "text", + "content": "In this work, we approach modeling SAA from an egocentric audiovisual perspective. The egocentric setting provides a compelling lens to study social conversational dynamics, as it captures both the audio and visual stimuli present in a scene and how the camera wearer orients their view in response to them. We hypothesize that the behavior of the wearer that is implicitly captured in the egocentric video and multichannel audio can facilitate the prediction of auditory attention targets. To this end, we introduce and formulate the novel task of Selective Auditory Attention Localization (SAAL), which uses egocentric video and multichannel audio to localize the target of auditory attention in egocentric video. We specifically target multi-speaker conversation scenarios where the camera wearer must selectively attend to certain speaker(s) while tuning out others. This challenging setting is representative of everyday noisy conversation environments and highlights the complexity of modeling auditory attention in naturalistic settings." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 347, + 287, + 430 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 347, + 287, + 430 + ], + "spans": [ + { + "bbox": [ + 46, + 347, + 287, + 430 + ], + "type": "text", + "content": "We propose a deep audiovisual video network for SAAL that leverages both appearance-based features from the ego-centric video stream and spatial audio information from multichannel audio. Our key insight is to extract a spatiotemporal feature representation from each modality and use a transformer on the fused features to reason holistically about the scene. Our contributions are:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 59, + 433, + 286, + 620 + ], + "type": "list", + "angle": 0, + "index": 7, + "blocks": [ + { + "bbox": [ + 59, + 433, + 286, + 468 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 433, + 286, + 468 + ], + "spans": [ + { + "bbox": [ + 59, + 433, + 286, + 468 + ], + "type": "text", + "content": "- We introduce the novel problem of Selective Auditory Attention Localization (SAAL) as an egocentric multimodal learning task." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 59, + 472, + 286, + 518 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 472, + 286, + 518 + ], + "spans": [ + { + "bbox": [ + 59, + 472, + 286, + 518 + ], + "type": "text", + "content": "- We propose a new architecture for SAAL. Our model extracts spatiotemporal video and audio features and uses a transformer to refine selection of an attention target by reasoning globally about the scene." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 59, + 523, + 286, + 570 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 523, + 286, + 570 + ], + "spans": [ + { + "bbox": [ + 59, + 523, + 286, + 570 + ], + "type": "text", + "content": "- We evaluate our approach on a challenging multispeaker conversation dataset and demonstrate our model's superiority over intuitive baselines and approaches based on Active Speaker Localization (ASL)." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 59, + 574, + 286, + 620 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 574, + 286, + 620 + ], + "spans": [ + { + "bbox": [ + 59, + 574, + 286, + 620 + ], + "type": "text", + "content": "- We conduct thorough experiments to give insight into our multimodal architecture design, effective multichannel audio and visual input representations, and the relationship between SAAL and ASL." + } + ] + } + ], + "index": 6 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 47, + 634, + 133, + 645 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 634, + 133, + 645 + ], + "spans": [ + { + "bbox": [ + 47, + 634, + 133, + 645 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 654, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 654, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 654, + 286, + 713 + ], + "type": "text", + "content": "Computational Models for Auditory Attention Attention is typically categorized into two types: bottom-up, where a stimulus is likely to cause attention due to inherent salient properties, and top-down, where a person intentionally focuses on a certain stimulus. Top-down, or selective auditory" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 72, + 545, + 300 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 300 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 300 + ], + "type": "text", + "content": "attention has been studied by correlating the attended sound signal with the neural response measured by EEG / MEG using statistical models [4,17-19,27,33,38,40,65,67,71,74, 89], and more recently deep neural networks [36, 58]. This is done in a controlled listening scenario where competing sounds, such as audio books, are played at once and a participant is instructed to listen to a particular sound. Models are used to predict which sound source is attended and/or decode the attended signal. The sources may be combined into a single channel or played in separate ears, as in the dichotic listening task paradigm [20]. Some works have used acoustic simulation methods to reflect more realistic multispeaker environments [17, 33, 89]. However, these studies have not addressed modeling SAA in in-the-wild social conversation scenarios. Beyond using brain activity to predict auditory attention, Lu et al. develop a head movement-based approach for predicting the attended speaker in a conversation [64]. However, this work focuses on single group conversations where there is typically only one speaker." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 301, + 545, + 409 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 301, + 545, + 409 + ], + "spans": [ + { + "bbox": [ + 304, + 301, + 545, + 409 + ], + "type": "text", + "content": "A smaller body of work focuses on modeling bottom-up auditory attention, or the qualities of a sound signal that make it likely to be attended to. Works in this domain construct representations of audio signals and evaluate their ability to reflect human judgment of saliency [30, 49, 51, 52, 56, 85, 86], distinguish between changes in perceptual qualities of sound [48], or perform on a downstream speech recognition task [47]. In this work, we focus on top-down, or selective auditory attention." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 411, + 545, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 411, + 545, + 628 + ], + "spans": [ + { + "bbox": [ + 304, + 411, + 545, + 628 + ], + "type": "text", + "content": "Active Speaker Detection & Localization Our task builds upon a rich foundation of work on Active Speaker Detection (ASD) and Active Speaker Localization (ASL). Recognizing speech activity is an established problem in computer vision, with early approaches correlating video and audio streams [25], or using purely visual features [31, 39, 79] to determine if a person is speaking. The AVA-ActiveSpeaker dataset [78] has accelerated deep learning approaches for ASD by providing a large-scale dataset and a benchmark. Methods use deep learning to extract visual features from a head bounding box track and combine them with features from monoaural scene audio to classify the person as speaking and audible, speaking and inaudible, or not speaking in each frame [8-10, 26, 54, 66, 82, 95]. Some approaches additionally explicitly model the relationships between multiple people within a scene to refine classification of speakers [8, 54, 66]. Xiong et al. [93] develop an architecture to jointly perform ASD and speech enhancement." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "content": "Other methods approach the task of ASL, which seeks to localize speakers spatially within the scene rather than classifying bounding box tracks [6, 15, 22, 34, 35, 76, 92, 94]. Several use multichannel audio to incorporate directional audio information [6, 15, 22, 34, 35, 92, 94]. Recently, Jiang et al. [46] expanded upon these approaches by developing a deep model that also leverages multichannel audio to lo" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "14664" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 55, + 68, + 541, + 261 + ], + "blocks": [ + { + "bbox": [ + 55, + 68, + 541, + 261 + ], + "lines": [ + { + "bbox": [ + 55, + 68, + 541, + 261 + ], + "spans": [ + { + "bbox": [ + 55, + 68, + 541, + 261 + ], + "type": "image", + "image_path": "c51d3794c3f6837f31275d3b0a0f50c6ece9d16146504e80cec32a14feb30366.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 270, + 548, + 315 + ], + "lines": [ + { + "bbox": [ + 46, + 270, + 548, + 315 + ], + "spans": [ + { + "bbox": [ + 46, + 270, + 548, + 315 + ], + "type": "text", + "content": "Figure 2. Our architecture for predicting auditory attention heatmaps from egocentric video and multichannel audio: the Video Encoder and Audio Encoder embed spatiotemporal features from the video and spatial audio modalities respectively. The audio and visual features are fused and passed to the Scene Relation Transformer, which models the relationships between different regions of the scene. Finally, the features are passed to the convolutional Decoder, which produces the predicted attention heatmaps for the input video frames." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 330, + 287, + 437 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 330, + 287, + 437 + ], + "spans": [ + { + "bbox": [ + 46, + 330, + 287, + 437 + ], + "type": "text", + "content": "calize speakers in the challenging egocentric setting, which contains motion blur and rapid changes of field of view (FOV), using the EasyCom dataset [28]. Our problem setting is different from ASD and ASL in that we seek to determine which of the speakers the camera wearer is listening to using egocentric audiovisual cues. Importantly, active speakers are not necessarily auditorily attended; they can be background people or nearby people engaged in a different conversation. Thus, SAAL demands a novel approach." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 437, + 287, + 641 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 437, + 287, + 641 + ], + "spans": [ + { + "bbox": [ + 46, + 437, + 287, + 641 + ], + "type": "text", + "content": "Modeling of Conversation Dynamics and Social Interactions SAAL is also related to work on modeling social interactions and conversational dynamics. Prior works have explored detecting social interactions in egocentric video [2, 16, 32]. The recent Ego4D dataset and benchmark suite [37] introduces the \"Talking to Me\" task for identifying which people are speaking to the camera wearer in egocentric video. This task is closely related to SAAL in that it models dyadic conversational behavior between the camera wearer and people in their FOV. However our task differs by modeling egocentric listening behavior, particularly in the presence of multiple speakers. Researchers have also explored modeling conversational turn taking behaviors [88] as well as predicting listener motion in dyadic conversations [70]. To our knowledge, we are the first to address the problem of modeling auditory attention using egocentric video, wearable audio, or both modalities together." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 642, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 642, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 642, + 287, + 715 + ], + "type": "text", + "content": "Egocentric Visual Attention Prediction Our problem also relates to egocentric visual attention prediction, which regresses a heatmap localizing the target of visual attention in egocentric video. Approaches for this task use eye tracking data as ground truth for attention targets and develop models to predict the attention location from video. Re" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 330, + 545, + 425 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 330, + 545, + 425 + ], + "spans": [ + { + "bbox": [ + 304, + 330, + 545, + 425 + ], + "type": "text", + "content": "searchers have proposed several vision models for this task [5,44,59,61,83], including some that jointly model gaze and action [43,62] or gaze and IMU [84]. Importantly, visual attention and auditory attention are not the same; people will generally not always look at the person they are conversing with. Rather, SAAL can be considered as an auditory variant of egocentric visual attention prediction, and SAAL additionally demands the use of audio cues." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 426, + 546, + 557 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 426, + 546, + 557 + ], + "spans": [ + { + "bbox": [ + 304, + 426, + 546, + 557 + ], + "type": "text", + "content": "Audiovisual Representation Learning Our work relates to a larger body of research on learning effective audiovisual feature representations [3,7,12,45,55,69,72,73,75] and localizing sound sources in video [1, 13, 23, 41, 42, 63, 68, 77, 80, 81]. These methods learn semantic correspondences between visual and audio features, typically using contrastive training paradigms. In contrast to these approaches, we leverage multichannel audio and employ a fusion mechanism that enforces spatial alignment between the visual and spatial audio domains, allowing us to reason globally about the audiovisual content in different regions of the scene." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 567, + 362, + 580 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 567, + 362, + 580 + ], + "spans": [ + { + "bbox": [ + 306, + 567, + 362, + 580 + ], + "type": "text", + "content": "3. Method" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 587, + 418, + 599 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 587, + 418, + 599 + ], + "spans": [ + { + "bbox": [ + 306, + 587, + 418, + 599 + ], + "type": "text", + "content": "3.1. Problem Definition" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": "At each time " + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": ", we predict an auditory attention heatmap " + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{H}_t" + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": ", given the raw audiovisual input " + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\{I_n, a_n | n = 0 \\dots t\\}" + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": " where " + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "inline_equation", + "content": "I_n" + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": " is an egocentric video frame at time " + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "inline_equation", + "content": "a_n" + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": " is a multi-channel audio segment aligned with the video frame " + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "inline_equation", + "content": "I_n" + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": ". Each pixel " + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{H}_t(i, j)" + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": " has a value in (0,1) and indicates the probability of the camera wearer's auditory attention. Video " + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "inline_equation", + "content": "I" + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": " captures the movement of both the camera wearer and the other people in the scene, as well as information about their head and body poses, facial expression, mouth" + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "14665" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 168 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 168 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 168 + ], + "type": "text", + "content": "movement, and overall scene layout. Multichannel audio " + }, + { + "bbox": [ + 46, + 72, + 289, + 168 + ], + "type": "inline_equation", + "content": "a" + }, + { + "bbox": [ + 46, + 72, + 289, + 168 + ], + "type": "text", + "content": ", from a microphone array, captures people's speech as well as other spatialized sound sources. We use video from a 180-degree fish-eye camera with resolution " + }, + { + "bbox": [ + 46, + 72, + 289, + 168 + ], + "type": "inline_equation", + "content": "200 \\times 212" + }, + { + "bbox": [ + 46, + 72, + 289, + 168 + ], + "type": "text", + "content": " and audio from a 6-channel microphone array. In this paper, we demonstrate how to use " + }, + { + "bbox": [ + 46, + 72, + 289, + 168 + ], + "type": "inline_equation", + "content": "\\{I, a\\}" + }, + { + "bbox": [ + 46, + 72, + 289, + 168 + ], + "type": "text", + "content": " to infer " + }, + { + "bbox": [ + 46, + 72, + 289, + 168 + ], + "type": "inline_equation", + "content": "\\mathcal{H}" + }, + { + "bbox": [ + 46, + 72, + 289, + 168 + ], + "type": "text", + "content": ", where we construct " + }, + { + "bbox": [ + 46, + 72, + 289, + 168 + ], + "type": "inline_equation", + "content": "\\mathcal{H}_{\\mathrm{label}}" + }, + { + "bbox": [ + 46, + 72, + 289, + 168 + ], + "type": "text", + "content": " by setting all pixels within the head bounding box of an attended speaker in a frame as 1." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 178, + 100, + 190 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 178, + 100, + 190 + ], + "spans": [ + { + "bbox": [ + 47, + 178, + 100, + 190 + ], + "type": "text", + "content": "3.2. Model" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 197, + 289, + 400 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 197, + 289, + 400 + ], + "spans": [ + { + "bbox": [ + 46, + 197, + 289, + 400 + ], + "type": "text", + "content": "SAAL is a complex task that involves understanding both the camera wearer's behavior and the activity of the people in the scene. We design a deep multimodal model for this task to have 4 key abilities: (1) It extracts relevant visual features such as lip movement, the relative positions and orientations of heads, and social body language like when a person looks at the camera wearer. (2) It leverages multichannel audio to construct a spatial representation of voice activity occurring around the camera wearer. (3) It encodes temporal information like how the wearer moves their head in response to stimuli as well as the movement of people in the scene and pattern of voice activity. (4) It reasons globally about the audiovisual content of scene as a whole to select an attention target; while an active speaker detector identifies all speakers in a scene, determining attention demands holistic reasoning about different potential attention targets in a scene to select the most likely one(s)." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 402, + 289, + 498 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 402, + 289, + 498 + ], + "spans": [ + { + "bbox": [ + 46, + 402, + 289, + 498 + ], + "type": "text", + "content": "To this end, our method consists of 4 main components as shown in Figure 2: the Visual Encoder and Audio Encoder to extract spatiotemporal features from the video and multichannel audio inputs respectively, the Scene Relation Transformer to refine attention localization by modeling the relationships between audiovisual features in different spatial regions of the scene, and a convolutional Decoder to produce an auditory attention heatmap for each input frame." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 498, + 289, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 498, + 289, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 498, + 289, + 714 + ], + "type": "text", + "content": "Visual Encoder The Visual Encoder " + }, + { + "bbox": [ + 46, + 498, + 289, + 714 + ], + "type": "inline_equation", + "content": "\\mathcal{V}" + }, + { + "bbox": [ + 46, + 498, + 289, + 714 + ], + "type": "text", + "content": " takes the visual input " + }, + { + "bbox": [ + 46, + 498, + 289, + 714 + ], + "type": "inline_equation", + "content": "X^V" + }, + { + "bbox": [ + 46, + 498, + 289, + 714 + ], + "type": "text", + "content": " as a stack of " + }, + { + "bbox": [ + 46, + 498, + 289, + 714 + ], + "type": "inline_equation", + "content": "200 \\times 212" + }, + { + "bbox": [ + 46, + 498, + 289, + 714 + ], + "type": "text", + "content": " frames over a time interval " + }, + { + "bbox": [ + 46, + 498, + 289, + 714 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 46, + 498, + 289, + 714 + ], + "type": "text", + "content": " and extracts appearance-based features about the scene. We construct " + }, + { + "bbox": [ + 46, + 498, + 289, + 714 + ], + "type": "inline_equation", + "content": "X^V" + }, + { + "bbox": [ + 46, + 498, + 289, + 714 + ], + "type": "text", + "content": " by cropping the people's heads in the raw grayscale video frames and filling the background with black. This representation leverages 1) our focus on conversational attention, and 2) the effectiveness of face detection methods. The input is a 3D video tensor of head tubes that represents not only how the people in the scene move, how they are laid out in space, where they look, their facial expression, mouth movement, and who they talk to, but also the head movement of the wearer over time. In our experiments, we compare this representation to using the raw image as well as a binary map of the bounding boxes. We find that this representation improves performance by removing background distractions while retaining appearance-based facial features. Additionally, this representation makes the model more generalizable to different scenes. We use a 3D" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 72, + 545, + 168 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 168 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 168 + ], + "type": "text", + "content": "ResNet-18 network [87] as our backbone, which uses 3D convolutions to capture both spatial and temporal features. The result of " + }, + { + "bbox": [ + 304, + 72, + 545, + 168 + ], + "type": "inline_equation", + "content": "\\mathcal{V}(X^V)" + }, + { + "bbox": [ + 304, + 72, + 545, + 168 + ], + "type": "text", + "content": " is a spatiotemporal visual feature map " + }, + { + "bbox": [ + 304, + 72, + 545, + 168 + ], + "type": "inline_equation", + "content": "\\mathcal{Z}^V" + }, + { + "bbox": [ + 304, + 72, + 545, + 168 + ], + "type": "text", + "content": " of dimension " + }, + { + "bbox": [ + 304, + 72, + 545, + 168 + ], + "type": "inline_equation", + "content": "512 \\times 1 \\times 13 \\times 14" + }, + { + "bbox": [ + 304, + 72, + 545, + 168 + ], + "type": "text", + "content": ", where 512 is the channel dimension, 1 is the temporal dimension, and 13 and 14 correspond to the height and width. We use 8 frames as input with temporal stride 3, so each input " + }, + { + "bbox": [ + 304, + 72, + 545, + 168 + ], + "type": "inline_equation", + "content": "X^V" + }, + { + "bbox": [ + 304, + 72, + 545, + 168 + ], + "type": "text", + "content": " spans a 24 frame window, which is 0.8 seconds in 30fps video." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 170, + 546, + 445 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 170, + 546, + 445 + ], + "spans": [ + { + "bbox": [ + 304, + 170, + 546, + 445 + ], + "type": "text", + "content": "Audio Encoder The Audio Encoder " + }, + { + "bbox": [ + 304, + 170, + 546, + 445 + ], + "type": "inline_equation", + "content": "\\mathcal{A}" + }, + { + "bbox": [ + 304, + 170, + 546, + 445 + ], + "type": "text", + "content": " extracts spatial audio features from the multichannel audio in the input clip to encode information about the conversational speech patterns and spatially localize speakers. We process the audio into 2000 sample " + }, + { + "bbox": [ + 304, + 170, + 546, + 445 + ], + "type": "inline_equation", + "content": "\\times 6" + }, + { + "bbox": [ + 304, + 170, + 546, + 445 + ], + "type": "text", + "content": " channel frames corresponding to each frame in the video input clip. We construct input features " + }, + { + "bbox": [ + 304, + 170, + 546, + 445 + ], + "type": "inline_equation", + "content": "X^A" + }, + { + "bbox": [ + 304, + 170, + 546, + 445 + ], + "type": "text", + "content": " by calculating the complex spectogram with 201 frequency bins, window length 20, and hop length 10 and stacking these vertically for the 6 channels. We found this performs slightly better than concatenating along the channel dimension. We additionally construct a feature representation of the cross correlation between all pairs of channels as used in Jiang et al. [46] and stack the real and complex parts of the spectogram and the channel correlation features along the channel dimension. We then resize the audio features to " + }, + { + "bbox": [ + 304, + 170, + 546, + 445 + ], + "type": "inline_equation", + "content": "200\\times 212" + }, + { + "bbox": [ + 304, + 170, + 546, + 445 + ], + "type": "text", + "content": " spatially in order to extract feature maps that align with the visual domain. Due to the importance of capturing dense temporal audio features to predict auditory attention, such as the pattern of speech, we pass all 24 audio frames in the clip to " + }, + { + "bbox": [ + 304, + 170, + 546, + 445 + ], + "type": "inline_equation", + "content": "\\mathcal{A}" + }, + { + "bbox": [ + 304, + 170, + 546, + 445 + ], + "type": "text", + "content": ", which uses another 3D ResNet-18 backbone. The resultant feature map " + }, + { + "bbox": [ + 304, + 170, + 546, + 445 + ], + "type": "inline_equation", + "content": "\\mathcal{Z}^A" + }, + { + "bbox": [ + 304, + 170, + 546, + 445 + ], + "type": "text", + "content": " is of size " + }, + { + "bbox": [ + 304, + 170, + 546, + 445 + ], + "type": "inline_equation", + "content": "512\\times 3\\times 13\\times 14" + }, + { + "bbox": [ + 304, + 170, + 546, + 445 + ], + "type": "text", + "content": ". We average pool the temporal dimension to 1 to match the dimension of " + }, + { + "bbox": [ + 304, + 170, + 546, + 445 + ], + "type": "inline_equation", + "content": "\\mathcal{Z}^V" + }, + { + "bbox": [ + 304, + 170, + 546, + 445 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 448, + 545, + 544 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 448, + 545, + 544 + ], + "spans": [ + { + "bbox": [ + 304, + 448, + 545, + 544 + ], + "type": "text", + "content": "Scene Relation Transformer From " + }, + { + "bbox": [ + 304, + 448, + 545, + 544 + ], + "type": "inline_equation", + "content": "\\mathcal{A}" + }, + { + "bbox": [ + 304, + 448, + 545, + 544 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 448, + 545, + 544 + ], + "type": "inline_equation", + "content": "\\nu" + }, + { + "bbox": [ + 304, + 448, + 545, + 544 + ], + "type": "text", + "content": ", we extract visual and spatial audio features maps " + }, + { + "bbox": [ + 304, + 448, + 545, + 544 + ], + "type": "inline_equation", + "content": "\\mathcal{Z}^V" + }, + { + "bbox": [ + 304, + 448, + 545, + 544 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 448, + 545, + 544 + ], + "type": "inline_equation", + "content": "\\mathcal{Z}^A" + }, + { + "bbox": [ + 304, + 448, + 545, + 544 + ], + "type": "text", + "content": ", which we concatenate along the channel dimension to form " + }, + { + "bbox": [ + 304, + 448, + 545, + 544 + ], + "type": "inline_equation", + "content": "\\mathcal{Z}^{AV} \\in 1024 \\times 1 \\times 13 \\times 14" + }, + { + "bbox": [ + 304, + 448, + 545, + 544 + ], + "type": "text", + "content": ". We choose to concatenate the features along the channel dimension because our approach importantly leverages multichannel audio, which can extract a spatial representation of voice activity in the scene so that the visual and audio domains can be spatially aligned." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 545, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 545, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 545, + 547, + 715 + ], + "type": "text", + "content": "We use a transformer " + }, + { + "bbox": [ + 304, + 545, + 547, + 715 + ], + "type": "inline_equation", + "content": "\\mathcal{T}" + }, + { + "bbox": [ + 304, + 545, + 547, + 715 + ], + "type": "text", + "content": " to further refine this fused multimodal feature map by modeling correlations between the features in different regions of the scene to holistically select a likely attention target. As in the transformer literature [14, 29], we treat each spatial location " + }, + { + "bbox": [ + 304, + 545, + 547, + 715 + ], + "type": "inline_equation", + "content": "Z_{1,h,w}^{AV}" + }, + { + "bbox": [ + 304, + 545, + 547, + 715 + ], + "type": "text", + "content": " as a spatiotemporal patch of embedded dimension " + }, + { + "bbox": [ + 304, + 545, + 547, + 715 + ], + "type": "inline_equation", + "content": "D = 512" + }, + { + "bbox": [ + 304, + 545, + 547, + 715 + ], + "type": "text", + "content": ", and flatten the feature map into a sequence of length " + }, + { + "bbox": [ + 304, + 545, + 547, + 715 + ], + "type": "inline_equation", + "content": "L = 1 \\times 13 \\times 14 = 182" + }, + { + "bbox": [ + 304, + 545, + 547, + 715 + ], + "type": "text", + "content": ". A learnable position embedding " + }, + { + "bbox": [ + 304, + 545, + 547, + 715 + ], + "type": "inline_equation", + "content": "E \\in \\mathbb{R}^{L \\times D}" + }, + { + "bbox": [ + 304, + 545, + 547, + 715 + ], + "type": "text", + "content": " is added to preserve absolute and relative positional information, which is particularly important for the egocentric setting where the camera wearer orients their view of the scene in response to stimuli. The transformer consists of 12 transformer blocks [90] where each computes self-attention on the audiovisual feature map as Softmax " + }, + { + "bbox": [ + 304, + 545, + 547, + 715 + ], + "type": "inline_equation", + "content": "(QK^T / \\sqrt{D})V" + } + ] + } + ], + "index": 8 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 749, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 749, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 749, + 318, + 757 + ], + "type": "text", + "content": "14666" + } + ] + } + ], + "index": 9 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 100, + 70, + 492, + 117 + ], + "blocks": [ + { + "bbox": [ + 100, + 70, + 492, + 117 + ], + "lines": [ + { + "bbox": [ + 100, + 70, + 492, + 117 + ], + "spans": [ + { + "bbox": [ + 100, + 70, + 492, + 117 + ], + "type": "table", + "html": "
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", + "image_path": "3d53a2526a4b4f7e72390c035f3be0d78cc98d85a631b89eebdc373b07deaf3d.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 125, + 544, + 148 + ], + "lines": [ + { + "bbox": [ + 46, + 125, + 544, + 148 + ], + "spans": [ + { + "bbox": [ + 46, + 125, + 544, + 148 + ], + "type": "text", + "content": "Table 1. Dataset statistics: our evaluation dataset of multi-speaker conversations is representative of challenging conversation environments where several people and speakers are present. Note that we use " + }, + { + "bbox": [ + 46, + 125, + 544, + 148 + ], + "type": "inline_equation", + "content": "\\frac{1}{3}" + }, + { + "bbox": [ + 46, + 125, + 544, + 148 + ], + "type": "text", + "content": " of these frames for training and evaluation with temporal stride 3." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "text" + }, + { + "type": "image", + "bbox": [ + 66, + 162, + 171, + 260 + ], + "blocks": [ + { + "bbox": [ + 66, + 162, + 171, + 260 + ], + "lines": [ + { + "bbox": [ + 66, + 162, + 171, + 260 + ], + "spans": [ + { + "bbox": [ + 66, + 162, + 171, + 260 + ], + "type": "image", + "image_path": "102ff4ef94df725f83d35d16d54005fefee386b19f8d41d8edb523515773243a.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 269, + 286, + 313 + ], + "lines": [ + { + "bbox": [ + 46, + 269, + 286, + 313 + ], + "spans": [ + { + "bbox": [ + 46, + 269, + 286, + 313 + ], + "type": "text", + "content": "Figure 3. In our multi-speaker evaluation dataset, participants are divided into 2 subgroups that converse simultaneously. A person is labeled as being an auditory attention target if they are both speaking and within the camera wearer's conversation group." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 173, + 171, + 269, + 251 + ], + "blocks": [ + { + "bbox": [ + 173, + 171, + 269, + 251 + ], + "lines": [ + { + "bbox": [ + 173, + 171, + 269, + 251 + ], + "spans": [ + { + "bbox": [ + 173, + 171, + 269, + 251 + ], + "type": "image", + "image_path": "66602d8c4b0a440855bbc8ff6b3d8ced100059fca8d1ad0c5c3d91818fdc4caf.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 325, + 286, + 384 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 325, + 286, + 384 + ], + "spans": [ + { + "bbox": [ + 46, + 325, + 286, + 384 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 325, + 286, + 384 + ], + "type": "inline_equation", + "content": "Q" + }, + { + "bbox": [ + 46, + 325, + 286, + 384 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 325, + 286, + 384 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 46, + 325, + 286, + 384 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 46, + 325, + 286, + 384 + ], + "type": "inline_equation", + "content": "V" + }, + { + "bbox": [ + 46, + 325, + 286, + 384 + ], + "type": "text", + "content": " are learned linear projections on the multimodal spatiotemporal patches. In this way, the model learns correlations between audiovisual features occurring in different regions of the scene and can suppress or enhance values accordingly to refine attention prediction." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 385, + 286, + 444 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 385, + 286, + 444 + ], + "spans": [ + { + "bbox": [ + 46, + 385, + 286, + 444 + ], + "type": "text", + "content": "Decoder A decoder consisting of 4 3D transpose convolutions and 1 final convolutional classifier layer upsamples the resulting feature map " + }, + { + "bbox": [ + 46, + 385, + 286, + 444 + ], + "type": "inline_equation", + "content": "\\mathcal{T}(\\mathcal{Z}^{AV})" + }, + { + "bbox": [ + 46, + 385, + 286, + 444 + ], + "type": "text", + "content": " to produce the attention class heatmap " + }, + { + "bbox": [ + 46, + 385, + 286, + 444 + ], + "type": "inline_equation", + "content": "\\mathcal{H}_{\\mathrm{pred}}" + }, + { + "bbox": [ + 46, + 385, + 286, + 444 + ], + "type": "text", + "content": " of size " + }, + { + "bbox": [ + 46, + 385, + 286, + 444 + ], + "type": "inline_equation", + "content": "2\\times T\\times H\\times W" + }, + { + "bbox": [ + 46, + 385, + 286, + 444 + ], + "type": "text", + "content": ". The 2 channels reflect the not attended and attended classes." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 453, + 232, + 466 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 453, + 232, + 466 + ], + "spans": [ + { + "bbox": [ + 47, + 453, + 232, + 466 + ], + "type": "text", + "content": "3.3. Implementation & Model Training" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 472, + 286, + 544 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 472, + 286, + 544 + ], + "spans": [ + { + "bbox": [ + 46, + 472, + 286, + 544 + ], + "type": "text", + "content": "We train end-to-end with pixel-wise cross entropy loss. We initialize " + }, + { + "bbox": [ + 46, + 472, + 286, + 544 + ], + "type": "inline_equation", + "content": "\\mathcal{V}" + }, + { + "bbox": [ + 46, + 472, + 286, + 544 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 472, + 286, + 544 + ], + "type": "inline_equation", + "content": "\\mathcal{A}" + }, + { + "bbox": [ + 46, + 472, + 286, + 544 + ], + "type": "text", + "content": " with pretrained weights on Kinetics 400 [21]. The transformer consists of 12 transformer blocks using multi-head self-attention with 8 heads [90]. We use the Adam optimizer [53] and learning rate 1e-4. The training procedure converges quickly in less than 10 epochs." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 555, + 172, + 568 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 555, + 172, + 568 + ], + "spans": [ + { + "bbox": [ + 47, + 555, + 172, + 568 + ], + "type": "text", + "content": "4. Experimental Results" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 575, + 211, + 586 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 575, + 211, + 586 + ], + "spans": [ + { + "bbox": [ + 47, + 575, + 211, + 586 + ], + "type": "text", + "content": "4.1. Evaluation Dataset & Criteria" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 594, + 286, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 594, + 286, + 712 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 286, + 712 + ], + "type": "text", + "content": "To our knowledge there is no existing dataset with associated labels suited to our task. While egocentric AV datasets like Ego4D [37] and EasyCom [28] capture egocentric conversations, they have few situations with multiple people speaking at the same time, with the result that SAAL reduces to ASL. To evaluate our approach, we collected a dataset of complex multi-speaker conversations, where groups converse in close proximity. The dataset consists of 50 participants conversing in groups of 5, where each person wears a headset with a camera and microphone" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 163, + 528, + 175 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 163, + 528, + 175 + ], + "spans": [ + { + "bbox": [ + 306, + 163, + 528, + 175 + ], + "type": "text", + "content": "array. In total, there are " + }, + { + "bbox": [ + 306, + 163, + 528, + 175 + ], + "type": "inline_equation", + "content": "\\sim 20" + }, + { + "bbox": [ + 306, + 163, + 528, + 175 + ], + "type": "text", + "content": " hours of egocentric video." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 179, + 545, + 358 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 179, + 545, + 358 + ], + "spans": [ + { + "bbox": [ + 304, + 179, + 545, + 358 + ], + "type": "text", + "content": "In each 10-minute recording, a group of 5 people sits at a table in a meeting room and is partitioned into two conversational groups. Participants are instructed to only listen to and engage in conversations with their own group. In this way, we design a naturalistic social version of traditional dichotic listening tasks, where participants intentionally focus on certain speakers while tuning out others. By splitting the group into smaller groups, we simulate conversational layouts that may occur at a large dinner table, coffee shop, restaurant, or party, where groups of people converse in close proximity with others. As illustrated in Figure 3, we construct ground truth auditory attention labels by determining that the camera wearer is listening to a given person if they are both speaking and in the wearer's conversation group. The dataset was collected under an approved IRB." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 362, + 545, + 625 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 362, + 545, + 625 + ], + "spans": [ + { + "bbox": [ + 304, + 362, + 545, + 625 + ], + "type": "text", + "content": "Each participant wears a headset that includes an Intel SLAM camera and a 6-microphone array. We record the fish-eye grayscale video and the audio from the 6 microphones simultaneously for all the wearers in each session. We generate speaker activity and head bounding box annotations automatically by using person tracking and wearer speech detection algorithms, and leveraging synchronization between each person's egocentric audio and video in each session. We obtain active speaker labels for each person by using their own headset's microphone array to determine if they are speaking, using a deep model adapted from [46] trained on synthetic data for the headset's microphone array configuration. We then use a 3D tracking-by-detection method that uses camera pose from the SLAM camera to annotate head bounding boxes and identities for each person in each egocentric FOV. From these person tracking results and speaker activity labels for each person, we have a set of visible head bounding boxes for each egocentric frame along with a label for each box indicating if that person is speaking. We then use the identity tracking and known conversation group assignments to label if each person is auditorily attended to by the camera wearer." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "content": "Due to the wide 180-degree FOV of the camera, the auditorily attended person is almost always in the FOV, so we constrain our modeling approach to this scenario. Additionally, by design of the dataset, there are typically several people and often multiple speakers within FOV, as shown in Table 1. Along with the inherent challenges of motion blur and rapid head movements in the egocentric modality, this" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "14667" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 286, + 95 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 286, + 95 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 286, + 95 + ], + "type": "text", + "content": "makes our dataset a rich means for studying auditory attention in complex and naturalistic conversation environments." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 97, + 286, + 205 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 97, + 286, + 205 + ], + "spans": [ + { + "bbox": [ + 46, + 97, + 286, + 205 + ], + "type": "text", + "content": "We evaluate the result of auditory attention localization using mean average precision (mAP) on the task of classifying each person in the FOV as being a target of auditory attention or not. From the output heatmap " + }, + { + "bbox": [ + 46, + 97, + 286, + 205 + ], + "type": "inline_equation", + "content": "\\mathcal{H}_{\\mathrm{pred}}" + }, + { + "bbox": [ + 46, + 97, + 286, + 205 + ], + "type": "text", + "content": ", we calculate the auditory attention score for each person by taking the maximum value of Softmax " + }, + { + "bbox": [ + 46, + 97, + 286, + 205 + ], + "type": "inline_equation", + "content": "(\\mathcal{H}_{\\mathrm{pred}})" + }, + { + "bbox": [ + 46, + 97, + 286, + 205 + ], + "type": "text", + "content": " in channel 1 (the attended class) in the region of their head bounding box. We split our data and use " + }, + { + "bbox": [ + 46, + 97, + 286, + 205 + ], + "type": "inline_equation", + "content": "70\\%" + }, + { + "bbox": [ + 46, + 97, + 286, + 205 + ], + "type": "text", + "content": " data for training and " + }, + { + "bbox": [ + 46, + 97, + 286, + 205 + ], + "type": "inline_equation", + "content": "30\\%" + }, + { + "bbox": [ + 46, + 97, + 286, + 205 + ], + "type": "text", + "content": " for testing, with no overlapping participants between splits." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 214, + 164, + 227 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 214, + 164, + 227 + ], + "spans": [ + { + "bbox": [ + 47, + 214, + 164, + 227 + ], + "type": "text", + "content": "4.2. Competing methods" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 233, + 286, + 305 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 233, + 286, + 305 + ], + "spans": [ + { + "bbox": [ + 46, + 233, + 286, + 305 + ], + "type": "text", + "content": "Because SAAL is a new problem, there are no previous methods that can be used directly to solve this problem. We therefore compare our approach to several naive baseline methods as well as a set of baselines that adapt Jiang et al.'s multichannel audiovisual ASL architecture (MAVASL) [46] for our task. The methods we compare are the following:" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 306, + 286, + 568 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 306, + 286, + 568 + ], + "spans": [ + { + "bbox": [ + 46, + 306, + 286, + 568 + ], + "type": "text", + "content": "(1) Our proposed method with different audio and visual input representations: In our experiments, we label variations of our method as \"Ours - [visual] & [audio]\", where [visual] is the visual input representation type and [audio] is the audio input representation type. The visual input representations we consider are Image (the raw image), Bbox (a binary map of the bounding boxes), and Heads (the cropped heads from the raw image on a black background). The audio representations are Channel Corr (the channel correlation features as described in Section 3.2), Channel Corr + Spectogram (the channel correlation features concatenated with the real and complex parts of the multichannel spectrogram), and ASL (active speaker localization output maps from MAVASL). We report two different training strategies for using MAVASL to generate ASL maps for our dataset: " + }, + { + "bbox": [ + 46, + 306, + 286, + 568 + ], + "type": "inline_equation", + "content": "\\mathrm{ASL}_{\\mathrm{synthetic}}" + }, + { + "bbox": [ + 46, + 306, + 286, + 568 + ], + "type": "text", + "content": ", which trains the ASL model on synthetic data created from VTCK [91] and EasyCom, and " + }, + { + "bbox": [ + 46, + 306, + 286, + 568 + ], + "type": "inline_equation", + "content": "\\mathrm{ASL}_{\\mathrm{real}}" + }, + { + "bbox": [ + 46, + 306, + 286, + 568 + ], + "type": "text", + "content": ", which directly trains the ASL model on our dataset using the active speaker labels. In this way, we compare using audio features constructed from the raw multichannel audio with using ASL maps generated from an existing model, both with and without the advantage of tuning to our dataset." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 570, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 570, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 570, + 286, + 713 + ], + "type": "text", + "content": "(2) Naive baselines using ground truth ASL labels and heuristic strategies: We first report the SAAL mAP from simply selecting all active speakers as being attended using the ground truth ASL labels (Perfect ASL). We also report 2 baselines that use the center prior, which is the intuition that the attended person is likely near the center of the FOV because people often face the speaker they are paying attention to. Similar center prior baselines are used in the egocentric visual attention literature. We construct 2 center prior baselines: CP-I finds the head bounding box nearest to the center of FOV and selects it as the attention target if they are speaking, and otherwise predicts that there is no at" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 72, + 545, + 275 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 275 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 275 + ], + "type": "text", + "content": "tention in the frame. CP-II selects the speaking person closest to the center of the FOV as the target of attention. We also construct 2 baselines that select the \"closest\" speaker based on the size of their bounding box. We can reason that the person with the largest head bounding box area is likely the closest to the camera wearer, and if speaking, likely appears the loudest. We consider 2 baselines based on this strategy: CS-I selects the \"closest\" person only if they are speaking, and CS-II selects the \"closest\" speaker. We note that because these methods depend on the dataset's ground truth ASL labels, they are not realistic results, and are not a fair comparison to our method. However, we report them to demonstrate that Perfect ASL and heuristic strategies perform poorly on our evaluation dataset. This clearly implies that SAAL is a complicated task that demands a novel approach, and that our evaluation dataset is rich enough to demonstrate the complexity of this task." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 276, + 545, + 492 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 276, + 545, + 492 + ], + "spans": [ + { + "bbox": [ + 304, + 276, + 545, + 492 + ], + "type": "text", + "content": "(4) Networks adapted from MAVASL: The first adaption (MAVASL-I) is to directly use MAVASL to localize active speakers and use this as the auditory attention heatmap. The second adaptation (MAVASL-II) directly trains the network for the task of SAAL instead of ASL. The third adaptation (MAVASL-III) is similar to (MAVASL-II) but uses a multiframe video input (3-frame) to the AV network to further incorporate temporal information. MAVASL consists of an Audio Network, which predicts a coarse spatial voice activity map from multichannel audio, and an AV Network, which uses this voice activity map and the image to predict a final ASL map. For MAVASL-II and III, we achieve best results by supervising the audio network in MAVASL using the ASL labels from our dataset and the AV network with the auditory attention labels. We use Heads as the visual input representation. Because MAVASL is a frame-based network, we additionally apply temporal smoothing with a window size of 10 frames as in the original method." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 502, + 420, + 514 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 502, + 420, + 514 + ], + "spans": [ + { + "bbox": [ + 306, + 502, + 420, + 514 + ], + "type": "text", + "content": "4.3. Comparison results" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 521, + 545, + 676 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 521, + 545, + 676 + ], + "spans": [ + { + "bbox": [ + 304, + 521, + 545, + 676 + ], + "type": "text", + "content": "As shown in Table 2, our proposed method outperforms the baselines on mAP, including baselines that leverage ground truth active speaker labels. We observe that the Perfect ASL and naive baselines perform poorly on our dataset, illustrating that reducing the problem of SAAL to ASL is not viable in complex and challenging conversation environments with multiple speakers. The highest mAP achieved from adapting Jiang et al.'s ASL architecture is MAVASL-II, which obtains " + }, + { + "bbox": [ + 304, + 521, + 545, + 676 + ], + "type": "inline_equation", + "content": "75.20\\%" + }, + { + "bbox": [ + 304, + 521, + 545, + 676 + ], + "type": "text", + "content": " mAP. However, our best approach achieves a gain of " + }, + { + "bbox": [ + 304, + 521, + 545, + 676 + ], + "type": "inline_equation", + "content": "7.74\\%" + }, + { + "bbox": [ + 304, + 521, + 545, + 676 + ], + "type": "text", + "content": " mAP over this baseline, demonstrating that the task of SAAL demands a novel architecture design. We qualitatively compare our results against these baselines in Figure 4." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "text", + "content": "From our experiments investigating different combinations of audio and visual input representations, we observe that the combination of Heads and Channel Corr + Spec" + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "14668" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 57, + 70, + 277, + 315 + ], + "blocks": [ + { + "bbox": [ + 57, + 70, + 277, + 315 + ], + "lines": [ + { + "bbox": [ + 57, + 70, + 277, + 315 + ], + "spans": [ + { + "bbox": [ + 57, + 70, + 277, + 315 + ], + "type": "table", + "html": "
MethodmAP (%)
Perfect ASL*47.99
CP-I*63.55
CP-II*51.48
CS-I*53.86
CS-II*49.47
MAVASL-I59.11
MAVASL-II75.20
MAVASL-III72.90
Ours-Bbox & ASLsynthetic75.93
Ours-Bbox & ASL_real74.97
Ours-Bbox & Channel Corr80.41
Ours-Bbox & Channel Corr + Spectogram80.31
Ours-Image & ASLsynthetic72.20
Ours-Image & ASL_real70.04
Ours-Image & Channel Corr76.52
Ours-Image & Channel Corr + Spectogram76.95
Ours-Heads & ASLsynthetic76.72
Ours-Heads & ASL_real77.11
Ours-Heads & Channel Corr82.35
Ours-Heads & Channel Corr + Spectogram82.94
", + "image_path": "46cd6f0eb0d2254129ca2cee0350240995fd302fd403a4d085c46f25a396f627.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 364, + 288, + 652 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 364, + 288, + 652 + ], + "spans": [ + { + "bbox": [ + 46, + 364, + 288, + 652 + ], + "type": "text", + "content": "togram produces the best results. In fact, we observe that Bbox, the binary bounding box location map, performs better as an input representation than the raw image. We can interpret this result as showing the importance of relative position and sizes of heads to the problem of SAAL. Channel Corr and Channel Corr + Spectogram, which contain information from the raw multichannel audio signal, generally perform better as the spatial audio input representation than the pre-computed ASL maps, both real and synthetically trained. We hypothesize that this is because the role of audio features in determining auditory attention is greater than just localizing active speakers; SAAL additionally involves correlating different speech signals with the camera wearer's egocentric movement, using the wearer's own voice activity as an indicator of conversational turn taking behavior (e.g. whether they are speaking or listening), and reasoning about the relative volume of different speech signals. Notably, the pre-computed ASL maps have the advantage of being spatially aligned with the visual modality, which the spectograms and channel correlation features do not have. The performance gains from using Channel Corr and Channel Corr + Spectogram indicate that our Audio Encoder is able to learn this alignment and construct a spatial representation of audio activity from these features." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 658, + 111, + 671 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 658, + 111, + 671 + ], + "spans": [ + { + "bbox": [ + 47, + 658, + 111, + 671 + ], + "type": "text", + "content": "4.4. Analysis" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 677, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 288, + 715 + ], + "type": "text", + "content": "Model ablation We further investigate the contribution of each component of our best model to its overall performance in Table 3. We observe that the visual modality" + } + ] + } + ], + "index": 4 + }, + { + "type": "table", + "bbox": [ + 340, + 70, + 513, + 194 + ], + "blocks": [ + { + "bbox": [ + 46, + 323, + 288, + 356 + ], + "lines": [ + { + "bbox": [ + 46, + 323, + 288, + 356 + ], + "spans": [ + { + "bbox": [ + 46, + 323, + 288, + 356 + ], + "type": "text", + "content": "Table 2. Comparison results on the multi-speaker conversation dataset. (*) denotes methods that use ground truth ASL, which is not given to our model." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 340, + 70, + 513, + 194 + ], + "lines": [ + { + "bbox": [ + 340, + 70, + 513, + 194 + ], + "spans": [ + { + "bbox": [ + 340, + 70, + 513, + 194 + ], + "type": "table", + "html": "
MethodmAP (%)
Visual only56.81
Visual only + Transformer57.70
Audio only76.30
Audio only + Transformer75.84
Audiovisual80.10
Audiovisual1-channel + Transformer71.47
Audiovisual2-channel + Transformer76.73
Audiovisual4-channel + Transformer80.99
Audiovisual + Transformer82.94
", + "image_path": "a484be7900772b1665deebd843f3ab7a851f5308ae032935bcd4a60611f64d37.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "table_body" + } + ], + "index": 5 + }, + { + "type": "table", + "bbox": [ + 312, + 236, + 541, + 283 + ], + "blocks": [ + { + "bbox": [ + 306, + 201, + 545, + 224 + ], + "lines": [ + { + "bbox": [ + 306, + 201, + 545, + 224 + ], + "spans": [ + { + "bbox": [ + 306, + 201, + 545, + 224 + ], + "type": "text", + "content": "Table 3. Model ablation: All studies use Heads as the visual input and Channel Corr + Spectogram as the audio input." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 312, + 236, + 541, + 283 + ], + "lines": [ + { + "bbox": [ + 312, + 236, + 541, + 283 + ], + "spans": [ + { + "bbox": [ + 312, + 236, + 541, + 283 + ], + "type": "table", + "html": "
MethodmAP (%)
Audiovisual + Transformer (no spatial alignment)80.57
Audiovisual + Transformer (spatial alignment)82.94
", + "image_path": "d4c6cd3bfc430faeef34010e67b0e932e0ec4daeba938d4e36b11fd695c8144d.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "table_body" + } + ], + "index": 7 + }, + { + "bbox": [ + 325, + 291, + 526, + 303 + ], + "lines": [ + { + "bbox": [ + 325, + 291, + 526, + 303 + ], + "spans": [ + { + "bbox": [ + 325, + 291, + 526, + 303 + ], + "type": "text", + "content": "Table 4. Spatial modality alignment in the transformer." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 304, + 316, + 545, + 460 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 316, + 545, + 460 + ], + "spans": [ + { + "bbox": [ + 304, + 316, + 545, + 460 + ], + "type": "text", + "content": "alone is much weaker than the spatial audio modality, and that clearly audio plays an important role. We also ablate the number of audio channels used, observing that removing the spatial component of the audio (Audiovisual" + }, + { + "bbox": [ + 304, + 316, + 545, + 460 + ], + "type": "inline_equation", + "content": "_{1}" + }, + { + "bbox": [ + 304, + 316, + 545, + 460 + ], + "type": "text", + "content": "-channel + Transformer) significantly reduces performance of our overall model. We see that spatial audio is an important cue for this task, but using slightly less channels can still achieve effective performance. Adding the transformer to the audiovisual features results in a gain of " + }, + { + "bbox": [ + 304, + 316, + 545, + 460 + ], + "type": "inline_equation", + "content": "2.84\\mathrm{mAP}" + }, + { + "bbox": [ + 304, + 316, + 545, + 460 + ], + "type": "text", + "content": ", demonstrating that the transformer improves performance by refining the embedded audiovisual feature maps through modeling relationships across spatial regions of the scene." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 461, + 545, + 569 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 461, + 545, + 569 + ], + "spans": [ + { + "bbox": [ + 304, + 461, + 545, + 569 + ], + "type": "text", + "content": "Results on Unseen Environment We additionally test our model's ability to generalize to unseen environments by evaluating our best model on a subset of data collected in a room with different acoustic and visual properties. The data follows the same structure as the main evaluation dataset, with 5 participants split into 2 conversation subgroups, and is " + }, + { + "bbox": [ + 304, + 461, + 545, + 569 + ], + "type": "inline_equation", + "content": "\\sim 49" + }, + { + "bbox": [ + 304, + 461, + 545, + 569 + ], + "type": "text", + "content": " minutes. Further details are provided in the supplement. On this unseen environment, our best model achieves " + }, + { + "bbox": [ + 304, + 461, + 545, + 569 + ], + "type": "inline_equation", + "content": "80.43\\%" + }, + { + "bbox": [ + 304, + 461, + 545, + 569 + ], + "type": "text", + "content": " mAP, demonstrating scene generalizability." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "content": "Spatial Modality Alignment in Self-Attention A key feature of our approach is leveraging multichannel audio to learn a spatial feature representation of voice activity in the scene, which we align with the visual representation by concatenating along the channel dimension. In our transformer design, therefore, each spatiotemporal patch of " + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{Z}^{AV}" + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "content": " contains the visual and audio features for that region. We validate this choice by designing an additional experiment where the modalities are not fused before the transformer, like in VisualBERT [60]. Rather than concatenating " + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{Z}^A" + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{Z}^V" + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "content": " before flattening them into a sequence of tokens to pass to " + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{T}" + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "content": ", we separately create a sequence of 182 tokens each" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 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We compare our output heatmaps to competing methods on challenging cases with multiple speakers, the attended speaker being far from the center, or no auditory attention. Our method performs well in these scenarios and more consistently identifies who is and isn't attended than MAVASL-II. Perfect ASL is prone to false positives by selecting all speakers and CPI is prone to false negatives by only considering the person closest to the center, demonstrating that ASL is not enough to solve SAAL. (Best viewed in color)." + } + ] + } + ], + "index": 20, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 83, + 376, + 252, + 455 + ], + "lines": [ + { + "bbox": [ + 83, + 376, + 252, + 455 + ], + "spans": [ + { + "bbox": [ + 83, + 376, + 252, + 455 + ], + "type": "image", + "image_path": "4f61cb04c5bff466a2a027b51b1f43d5eb6ebf444f3c0422cfdcb16be997a583.jpg" + } + ] + } + ], + "index": 21, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 464, + 288, + 498 + ], + "lines": [ + { + "bbox": [ + 46, + 464, + 288, + 498 + ], + "spans": [ + { + "bbox": [ + 46, + 464, + 288, + 498 + ], + "type": "text", + "content": "Figure 5. Decoupling SAAL & ASL: Without the responsibility for learning ASL, our model learns to segment the people within the camera wearer's conversation group." + } + ] + } + ], + "index": 22, + "angle": 0, + "type": "image_caption" + } + ], + "index": 21 + }, + { + "bbox": [ + 46, + 506, + 287, + 638 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 506, + 287, + 638 + ], + "spans": [ + { + "bbox": [ + 46, + 506, + 287, + 638 + ], + "type": "text", + "content": "from " + }, + { + "bbox": [ + 46, + 506, + 287, + 638 + ], + "type": "inline_equation", + "content": "\\mathcal{Z}^V" + }, + { + "bbox": [ + 46, + 506, + 287, + 638 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 506, + 287, + 638 + ], + "type": "inline_equation", + "content": "\\mathcal{Z}^A" + }, + { + "bbox": [ + 46, + 506, + 287, + 638 + ], + "type": "text", + "content": " and pass these 364 total tokens of dimension 512 to " + }, + { + "bbox": [ + 46, + 506, + 287, + 638 + ], + "type": "inline_equation", + "content": "\\mathcal{T}" + }, + { + "bbox": [ + 46, + 506, + 287, + 638 + ], + "type": "text", + "content": ". We concatenate the modalities afterwards. In this case, the self-attention mechanism is left to discover alignment between the modalities itself by comparing all tokens across both modalities. We observe a decrease in performance, indicating that our choice to explicitly align the visual and audio modalities spatially contributes to our model's ability to use both modalities together successfully. This result suggests utility in incorporating inductive bias about the spatial alignment of visual and multichannel audio modalities into token design for transformer architectures." + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 46, + 641, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 641, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 641, + 288, + 714 + ], + "type": "text", + "content": "Decoupling SAAL & ASL By nature of our dataset design, we train our model to predict auditory attention as the intersection of active speakers and people in the camera wearer's conversation group. To investigate the relationship between SAAL and ASL, we train a model by modulating our model's heatmap for the attended class" + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 304, + 377, + 547, + 510 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 377, + 547, + 510 + ], + "spans": [ + { + "bbox": [ + 304, + 377, + 547, + 510 + ], + "type": "text", + "content": "with the ground truth ASL labels before calculating loss and performing backpropagation. The loss is calculated as " + }, + { + "bbox": [ + 304, + 377, + 547, + 510 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{CE}(\\mathcal{H}_{\\mathrm{pred}}*\\mathrm{ASL}_{\\mathrm{label}},\\mathcal{H}_{\\mathrm{label}})" + }, + { + "bbox": [ + 304, + 377, + 547, + 510 + ], + "type": "text", + "content": ". In this way we eliminate the responsibility for ASL from our model. The model achieves " + }, + { + "bbox": [ + 304, + 377, + 547, + 510 + ], + "type": "inline_equation", + "content": "92.67\\%" + }, + { + "bbox": [ + 304, + 377, + 547, + 510 + ], + "type": "text", + "content": " mAP on SAAL, however, this is a purely theoretical upper bound that relies on perfect ASL. We visualize " + }, + { + "bbox": [ + 304, + 377, + 547, + 510 + ], + "type": "inline_equation", + "content": "\\mathcal{H}_{\\mathrm{pred}}" + }, + { + "bbox": [ + 304, + 377, + 547, + 510 + ], + "type": "text", + "content": " for our model before it is modulated by ASL label in Figure 5. We observe that our model learns to more generally segment the camera wearer's conversation group regardless of speaking activity, and likely relies on ASL label to constrain the heatmaps to the exact bounding box region." + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 306, + 521, + 379, + 533 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 521, + 379, + 533 + ], + "spans": [ + { + "bbox": [ + 306, + 521, + 379, + 533 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 26 + }, + { + "bbox": [ + 304, + 540, + 545, + 673 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 540, + 545, + 673 + ], + "spans": [ + { + "bbox": [ + 304, + 540, + 545, + 673 + ], + "type": "text", + "content": "We introduce the novel problem of Selective Auditory Attention Localization (SAAL) and demonstrate that a deep model is able to perform this task on a challenging multispeaker conversation dataset. We propose a multimodal modeling approach that uses egocentric video and multichannel audio to predict a person's target of auditory attention, combining spatial and temporal features from both modalities and using a transformer to reason holistically about the scene. We believe our work is an important step towards selective sound source enhancement and AR devices that can help people converse in noisy environments." + } + ] + } + ], + "index": 27 + }, + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "text", + "content": "Acknowledgments: We thank Jacob Donley and Christi Miller for facilitating data collection, and Calvin Murdock and Ishwarya Ananthabhotla for valuable discussions." + } + ] + } + ], + "index": 28 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "14670" + } + ] + } + ], + "index": 29 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 92, + 288, + 712 + ], + "type": "list", + "angle": 0, + "index": 13, + "blocks": [ + { + "bbox": [ + 53, + 92, + 287, + 137 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 92, + 287, + 137 + ], + "spans": [ + { + "bbox": [ + 53, + 92, + 287, + 137 + ], + "type": "text", + "content": "[1] Triantafyllos Afouras, Andrew Owens, Joon Son Chung, and Andrew Zisserman. 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The ActivityNet Large-Scale Activity Recognition Challenge, pages 1–4, 2019. 2" + } + ] + } + ], + "index": 21 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "type": "text", + "content": "14674" + } + ] + } + ], + "index": 23 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 11 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Egocentric Video Task Translation/4f7e3293-877b-4c9b-8bc7-d95d33f4f800_content_list.json b/2023/Egocentric Video Task Translation/4f7e3293-877b-4c9b-8bc7-d95d33f4f800_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..143c22d9a2668b12881b6b68c54d43a25c3b9d5d --- /dev/null +++ b/2023/Egocentric Video Task Translation/4f7e3293-877b-4c9b-8bc7-d95d33f4f800_content_list.json @@ -0,0 +1,1495 @@ +[ + { + "type": "text", + "text": "Egocentric Video Task Translation", + "text_level": 1, + "bbox": [ + 308, + 130, + 658, + 152 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Zihui Xue $^{1,2*}$ Yale Song $^{2}$ Kristen Grauman $^{1,2}$ Lorenzo Torresani $^{2}$ $^{1}$ The University of Texas at Austin $\\mathbf{\\Pi}^{2}$ FAIR, Meta AI", + "bbox": [ + 200, + 179, + 767, + 215 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 251, + 313, + 266 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Different video understanding tasks are typically treated in isolation, and even with distinct types of curated data (e.g., classifying sports in one dataset, tracking animals in another). However, in wearable cameras, the immersive egocentric perspective of a person engaging with the world around them presents an interconnected web of video understanding tasks—hand-object manipulations, navigation in the space, or human-human interactions—that unfold continuously, driven by the person's goals. We argue that this calls for a much more unified approach. We propose EgoTask Translation (EgoT2), which takes a collection of models optimized on separate tasks and learns to translate their outputs for improved performance on any or all of them at once. Unlike traditional transfer or multitask learning, EgoT2's \"flipped design\" entails separate task-specific backbones and a task translator shared across all tasks, which captures synergies between even heterogeneous tasks and mitigates task competition. Demonstrating our model on a wide array of video tasks from Ego4D, we show its advantages over existing transfer paradigms and achieve top-ranked results on four of the Ego4D 2022 benchmark challenges.1", + "bbox": [ + 75, + 282, + 473, + 616 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 645, + 209, + 660 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "In recent years, the introduction of large-scale video datasets (e.g., Kinetics [6, 33] and Something-Something [22]) have enabled the application of powerful deep learning models to video understanding and have led to dramatic advances. These third-person datasets, however, have overwhelmingly focused on the single task of action recognition in trimmed clips [12, 36, 47, 64]. Unlike curated third-person videos, our daily life involves frequent and heterogeneous interactions with other humans, objects, and environments in the wild. First-person videos from wearable cameras capture the observer's perspective and attention as a continuous stream. As such,", + "bbox": [ + 75, + 671, + 468, + 853 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/b5b271b132e591b377d1e8cc3c22c24ae475f355ff3d4581540b36981925e3ca.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 504, + 250, + 890, + 373 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/2b89278c26fb7be9e5a83545df086154e56792574874c72d9ffa99da633a80c2.jpg", + "image_caption": [ + "Figure 1. Given a set of diverse egocentric video tasks, the proposed EgoT2 leverages synergies among the tasks to improve each individual task performance. The attention maps produced by EgoT2 offer good interpretability on inherent task relations." + ], + "image_footnote": [], + "bbox": [ + 519, + 382, + 883, + 500 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "they are better equipped to reveal these multi-faceted, spontaneous interactions. Indeed egocentric datasets, such as EPIC-Kitchens [9] and Ego4D [23], provide suites of tasks associated with varied interactions. However, while these benchmarks have promoted a broader and more heterogeneous view of video understanding, they risk perpetuating the fragmented development of models specialized for each individual task.", + "bbox": [ + 496, + 598, + 890, + 717 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "In this work, we argue that the egocentric perspective offers an opportunity for holistic perception that can beneficially leverage synergies among video tasks to solve all problems in a unified manner. See Figure 1.", + "bbox": [ + 496, + 719, + 890, + 779 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Imagine a cooking scenario where the camera wearer actively interacts with objects and other people in an environment while preparing dinner. These interactions relate to each other: a hand grasping a knife suggests the upcoming action of cutting; the view of a tomato on a cutting board suggests that the object is likely to undergo a state transition from whole to chopped; the conversation may further reveal the camera wearer's ongoing and planned actions.", + "bbox": [ + 496, + 780, + 892, + 900 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 810, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Work done during an internship at FAIR, Meta AI.", + "bbox": [ + 94, + 862, + 369, + 875 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "1Project webpage: https://vision.cs.utexas.edu/ ojects/egot2/.", + "bbox": [ + 96, + 875, + 467, + 900 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "2310", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Apart from the natural relation among these tasks, egocentric video's partial observability (i.e., the camera wearer is largely out of the field of view) further motivates us to seek synergistic, comprehensive video understanding to leverage complementary cues among multiple tasks.", + "bbox": [ + 75, + 90, + 468, + 167 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Our goal presents several technical challenges for conventional transfer learning (TL) [65] and multi-task learning (MTL) [63]. First, MTL requires training sets where each sample includes annotations for all tasks [15, 24, 48, 53, 55, 62], which is often impractical. Second, egocentric video tasks are heterogeneous in nature, requiring different modalities (audio, visual, motion), diverse labels (e.g., temporal, spatial or semantic), and different temporal granularities (e.g., action anticipation requires long-term observations, but object state recognition operates at a few sparsely sampled frames)—all of which makes a unified model design problematic and fosters specialization. Finally, while existing work advocates the use of a shared encoder across tasks to learn general representations [3, 18, 26, 32, 39, 44, 45, 51], the diverse span of egocentric tasks poses a hazard to parameter sharing which can lead to negative transfer [21, 24, 38, 53].", + "bbox": [ + 75, + 169, + 470, + 425 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To address the above limitations, we propose EgoTask Translation (EgoT2), a unified learning framework to address a diverse set of egocentric video tasks together. EgoT2 is flexible and general in that it can handle separate datasets for the different tasks; it takes video heterogeneity into account; and it mitigates negative transfer when tasks are not strongly related. To be specific, EgoT2 consists of specialized models developed for individual tasks and a task translator that explicitly models inter-task and inter-frame relations. We propose two distinct designs: (1) task-specific EgoT2 (EgoT2-s) optimizes a given primary task with the assistance of auxiliary tasks (Figure 2(c)) while (2) task-general EgoT2 (EgoT2-g) supports task translation for multiple tasks at the same time (Figure 2(d)).", + "bbox": [ + 75, + 428, + 468, + 638 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Compared with a unified backbone across tasks [62], adopting task-specific backbones preserves peculiarities of each task (e.g. different temporal granularities) and mitigates negative transfer since each backbone is optimized on one task. Furthermore, unlike traditional parameter sharing [51], the proposed task translator learns to \"translate\" all task features into predictions for the target task by selectively activating useful features and discarding irrelevant ones. The task translator also facilitates interpretability by explicitly revealing which temporal segments and which subsets of tasks contribute to improving a given task.", + "bbox": [ + 75, + 642, + 470, + 808 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "We evaluate EgoT2 on a diverse set of 7 egocentric perception tasks from the world's largest egocentric video benchmark, Ego4D [23]. Its heterogeneous tasks extend beyond mere action recognition to speaker/listener identification, keyframe localization, object state change classification, long-term action anticipation, and others, and pro", + "bbox": [ + 75, + 810, + 468, + 901 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/795fb7c3cf184832889bd4d85e9379d7b306cd8cd8a9817e67265ad08bf37fa0.jpg", + "image_caption": [ + "(a) conventional TL" + ], + "image_footnote": [], + "bbox": [ + 501, + 90, + 691, + 179 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/4a9b3708210c51290713fbe12e55f29e0a7b46733115a0b574700a9632dbc3f0.jpg", + "image_caption": [ + "(b) conventional MTL" + ], + "image_footnote": [], + "bbox": [ + 723, + 90, + 870, + 179 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/b157b4abb82ebc039fd5b25df5b1b776e6146a898172c763c14fa18a297cefcc.jpg", + "image_caption": [ + "(c) EgoT2-s" + ], + "image_footnote": [], + "bbox": [ + 501, + 205, + 687, + 299 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/7280d445f79bf6066aaae22514df428038a731ff1074d7f9dcbed2a4e729beb5.jpg", + "image_caption": [ + "(d) EgoT2-g", + "Figure 2. (a) Conventional TL uses a backbone pretrained on the source task followed by a head transferring supervision to the target task; (b) Traditional MTL consists of a shared backbone and several task-specific heads; (c) EgoT2-s adopts task-specific backbones and optimizes the task translator for a given primary task; (d) EgoT2-g jointly optimizes the task translator for all tasks." + ], + "image_footnote": [], + "bbox": [ + 705, + 205, + 892, + 299 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "vide a perfect fit for our study. Our results reveal inherent task synergies, demonstrate consistent performance improvement across tasks, and offer good interpretability in task translation. Among all four Ego4D challenges involved in our task setup, EgoT2 outperforms all submissions to three Ego4D-CVPR'22 challenges and achieves state-of-the-art performance in one Ego4D-ECCV'22 challenge.", + "bbox": [ + 496, + 436, + 890, + 542 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 500, + 556, + 640, + 571 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Transfer Learning. TL [65] aims at transferring knowledge from a source domain to improve the performance in a target domain. The most widely adopted approach is to pretrain a model on a source task then finetune on the target task, as shown in Figure 2(a). Following this paradigm, many video classification models [1, 5, 42, 59] are initialized from models pretrained on ImageNet [11]. In addition, many works propose to transfer knowledge from a large-scale video dataset (e.g., Kinetics [6, 33]) to benefit action recognition in smaller-scale datasets [54] such as UCF-101 [52] and HMDB-51 [37] or to improve other video tasks, such as spatiotemporal action localization [2, 17, 19, 27, 49] and video anomaly detection [25, 41]. While this technique is ubiquitous in video understanding, prior approaches only consider the transfer from one single source task (dataset) and are thus unable to model the relations among multiple video tasks simultaneously.", + "bbox": [ + 496, + 582, + 890, + 839 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Taskonomy [62] presents task transfer with a thorough analysis on the structure of multiple visual tasks. Many works [15, 48, 53, 61] continue along this direction and explore visual task relations, yet they limit the discussion to", + "bbox": [ + 496, + 839, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "2311", + "bbox": [ + 482, + 944, + 513, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "static images and generally require a unified design across all tasks. In contrast, we consider a diverse set of egocentric video tasks, which are addressed with a heterogeneous set of task-specific video architectures (e.g., accommodating different time, space, or multimodality). Clearly, forcing the same network architecture across all tasks can be suboptimal for each individual task. This motivates our proposed EgoT2-s (Figure 2(c)), where we preserve the heterogeneous backbones developed for each task and build a task translator on top of the task-specific models.", + "bbox": [ + 75, + 90, + 472, + 241 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Multi-task Learning. In MTL [63], a single model is trained to address multiple tasks simultaneously in order to capture synergistic supervision across tasks. As depicted in Figure 2(b), hard parameter sharing [51] (i.e., sharing a backbone among tasks and keeping one separate head for each task) is the most commonly used technique within this genre. Although MTL has shown to be beneficial of video analysis [3, 18, 26, 32, 39, 44, 45], there is ongoing debate about the best strategies to determine what parameters to share across which tasks [7, 24, 31, 53, 55]. As pointed out in [34], when MTL is achieved by means of a single common backbone, the performance tends to decrease when the number of tasks grows beyond a certain point. Furthermore, many works [21, 24, 38, 53] observe that over-sharing a network across unrelated tasks causes negative transfer and hinders individual task performance. While soft parameter sharing [14, 60] mitigates this by retaining distinct copies of parameters, it still requires adopting the same identical architecture and \"similar\" weight values across all tasks.", + "bbox": [ + 75, + 241, + 472, + 527 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In the video domain, several works utilize synergies between related tasks (e.g., action recognition with gaze prediction [18, 26, 39] or body pose estimation [44]). However, when selected tasks are not strongly related, prior approaches that split the learning capacity of a shared backbone over multiple tasks can suffer from task competition and inferior performance. In the image domain, with the great advancement of transformers [58], training with multiple datasets together for a generalist model is gaining popularity. Recent work [8, 20, 29, 30, 35, 43] investigates a unified transformer architecture across a diverse set of tasks. Our variant EgoT2-g (Figure 2(d)) is motivated by the desiderata of shared knowledge encapsulated by MTL and of a generalist model. Unlike previous learning paradigms, we adopt a \"flipped design\" involving separate task-specific backbones and a task translator shared across all tasks. This effectively mitigates task competition and achieves task translation for all tasks simultaneously.", + "bbox": [ + 75, + 529, + 472, + 801 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Approach", + "text_level": 1, + "bbox": [ + 76, + 815, + 186, + 832 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We are given $K$ video tasks, $\\mathcal{T}_k$ for $k = 1,\\dots ,K$ . We note that our approach does not require a common training set with annotations for all tasks. Let the dataset for task $\\mathcal{T}_k$ be $\\mathcal{D}^{\\mathcal{T}_k} = \\{(\\mathbf{x}_i^{\\mathcal{T}_k},y_i^{\\mathcal{T}_k})\\}_{i = 1}^{N_k}$ , where $(\\mathbf{x}_i^{\\mathcal{T}_k},y_i^{\\mathcal{T}_k})$ denotes the", + "bbox": [ + 75, + 839, + 470, + 902 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "$i$ -th pair of (input video, output label) and $N_{k}$ represents the number of given examples. Note that \"labels\" $y_{i}^{\\mathcal{T}_{k}}$ can be a variety of output types, and are not limited to category labels. For simplicity we omit the subscript $i$ hereafter.", + "bbox": [ + 496, + 90, + 890, + 151 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We consider two formulations with distinct advantages: (1) task-specific translation, where we partition the tasks into one primary task $\\mathcal{T}_p$ and $K - 1$ auxiliary tasks, and optimize the objective to improve performance on $\\mathcal{T}_p$ with the assistance of the auxiliary tasks (EgoT2-s, Sec. 3.1); (2) task-general translation, where we treat all $K$ tasks equally, and the goal is to maximize the collective performance of all the tasks (EgoT2-g, Sec. 3.2). As demonstrated in our experiments, objective (1) leads to the strongest performance on the primary task, while objective (2) offers the benefit of a single unified model addressing all tasks at once.", + "bbox": [ + 496, + 152, + 893, + 318 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Task-Specific Translation: EgoT2-s", + "text_level": 1, + "bbox": [ + 498, + 325, + 807, + 340 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The training of EgoT2-s is split over two stages.", + "bbox": [ + 517, + 348, + 838, + 363 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Stage I: Individual-Task Training. We train a separate model $f_{k}$ on each individual task dataset $\\mathcal{D}^{\\mathcal{T}_k}$ , obtaining $K$ task-specific models $\\{f_k\\}_{k = 1}^K$ . We do not place any restrictions on the task-specific model designs, nor do we require a unified design (i.e., identical encoder-decoder architecture) across tasks. Therefore, any available model checkpoint developed for task $\\mathcal{T}_k$ can be adopted as $f_{k}$ within our framework, offering maximum flexibility.", + "bbox": [ + 496, + 363, + 890, + 484 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Stage II: Task-Specific Translation. We train a task translator that takes features produced by task-specific models as input and outputs predictions for the primary task. Formally, let $\\mathbf{h}_k\\in \\mathbb{R}^{T_k\\times D_k}$ be features produced by the $k$ -th task-specific model $f_{k}$ , where $T_{k}$ is the temporal dimension and $D_{k}$ is the per-frame feature dimension for model $f_{k}$ . Following the feature extraction step, we design a projection layer $\\mathbf{P}_k\\in \\mathbb{R}^{D_k\\times D}$ for each $f_{k}$ to map task-specific features to a shared latent feature space. This yields a temporal sequence of task-specific tokens $\\tilde{\\mathbf{h}}_k\\in \\mathbb{R}^{T_k\\times D}$ .", + "bbox": [ + 496, + 484, + 890, + 635 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We process this collection of task-specific temporal sequences using a transformer encoder [58] of $L$ layers to capture both inter-frame and inter-task dependencies. We denote the propagation rule of layer $l$ by $\\mathbf{z}^{l + 1} = \\text{Encoder}^l (\\mathbf{z}^l)$ . Finally, we adopt a decoder head $\\text{Decoder}^{\\mathcal{T}_p}$ to obtain predictions for the primary task $\\mathcal{T}_p$ .", + "bbox": [ + 496, + 635, + 890, + 727 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In all, this stage has four major steps: (1) feature extraction; (2) feature projection; (3) transformer fusion; and (4) feature decoding. The procedure is summarized below:", + "bbox": [ + 496, + 726, + 890, + 771 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {h} _ {k} = f _ {k} \\left(\\mathbf {x} ^ {\\mathcal {T} _ {p}}\\right), \\quad \\forall k \\in \\{1, 2, \\dots , K \\} \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 553, + 792, + 890, + 810 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\tilde {\\mathbf {h}} _ {k} = \\mathbf {P} _ {k} \\mathbf {h} _ {k}, \\quad \\forall k \\in \\{1, 2, \\dots , K \\} \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 555, + 813, + 890, + 830 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {z} ^ {0} = \\left[ \\tilde {\\mathbf {h}} _ {1}, \\tilde {\\mathbf {h}} _ {2}, \\dots , \\tilde {\\mathbf {h}} _ {K} \\right] \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 558, + 835, + 890, + 861 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {z} ^ {l + 1} = \\operatorname {E n c o d e r} ^ {l} \\left(\\mathbf {z} ^ {l}\\right), \\forall l \\in \\{0, 1, \\dots , L - 1 \\} \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 544, + 854, + 890, + 873 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\ny _ {p r e d} ^ {\\mathcal {T} _ {p}} = \\operatorname {D e c o d e r} ^ {\\mathcal {T} _ {p}} \\left(\\mathbf {z} ^ {L}\\right) \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 539, + 876, + 890, + 898 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "2312", + "bbox": [ + 480, + 944, + 514, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/f1ad90441deaf649ac36d57c76df4e8d7b6767f2fdea9f6041ce6237ef1ae94a.jpg", + "image_caption": [ + "Figure 3. An illustration of EgoT2-s (left) and EgoT2-g (right) on three candidate tasks. The left figure illustrates EgoT2-s on three social interaction tasks, where the input to each model is unimodal (i.e., video) or multimodal (i.e., video and audio). The right figure shows the design of EgoT2-g on three example tasks that focus on different aspects of human-object interactions (i.e., localization, object state change classification, and action recognition). EgoT2-s learns to \"translate\" auxiliary task features into predictions for the primary task and EgoT2-g conducts task translation conditioned on the task of interest." + ], + "image_footnote": [], + "bbox": [ + 76, + 88, + 444, + 364 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/72c9c09502c2b197044bee2c885e8554fcb91928d1c7ff2c8b1ef97ba9a9fd50.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 452, + 88, + 861, + 367 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $y_{pred}^{\\mathcal{T}_p}$ denotes the prediction given by EgoT2-s. During the second stage of training, we freeze the task-specific models and optimize the task translator with respect to the primary task dataset $\\mathcal{D}^{\\mathcal{T}_p}$ .", + "bbox": [ + 75, + 472, + 468, + 535 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Figure 3 (left) illustrates the design of EgoT2-s using three social interaction tasks from Ego4D [23] as an example. EgoT2-s allows heterogeneity in the task-specific models (i.e., $f_{1}$ is unimodal while $f_{2}$ and $f_{3}$ are multimodal; also the three task-specific models can be associated with different frame rates and temporal durations) and utilizes a transformer encoder to model inter-frame and inter-task relations. The resulting EgoT2-s learns to adaptively utilize auxiliary task features for the primary task prediction.", + "bbox": [ + 75, + 536, + 470, + 674 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. Task-General Translation: EgoT2-g", + "text_level": 1, + "bbox": [ + 76, + 680, + 390, + 698 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "EgoT2-s optimizes performance for a single primary task. Therefore, in the event all $K$ tasks must be addressed, it requires $K$ separate training runs and $K$ distinct translators. This motivates us to extend EgoT2-s to perform task translation for all $K$ tasks at once. In EgoT2-g, the task translator processes features from all $K$ tasks and learns to \"translate\" features conditioned on the task of interest.", + "bbox": [ + 75, + 703, + 468, + 809 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The first stage of EgoT2-g is identical to EgoT2-s. For the second stage, we propose two main modifications. First, we replace the task-specific decoder in EgoT2-s with a \"generalist\" decoder that outputs predictions conditioned on the task of interest. Natural language provides us with a flexible scheme to specify all tasks as a sequence of sym", + "bbox": [ + 75, + 810, + 470, + 902 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "bols. Inspired by [8], we tokenize all task outputs and replace the original task-specific decoder with a sequence decoder [50] for a unified interface. Specifically, we first transform the original label $y^{\\mathcal{T}_k}$ to a target output sequence $\\mathbf{y}_{seq}^{\\mathcal{T}_k} \\in \\mathbb{R}^M$ , where $M$ is the target sequence length. For the task translator to produce task-dependent outputs, we preprocess a task prompt token $\\mathbf{y}_{prompt}$ to the target output, i.e., $\\mathbf{y}_{seq_1}^{\\mathcal{T}_k} = \\mathbf{y}_{prompt}$ . We then let the sequence decoder generate a sentence answering the requested task. Figure 3 (right) illustrates how we express task outputs as sequences of discrete tokens and attach task prompts.", + "bbox": [ + 496, + 474, + 890, + 642 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "With the transformed output, we treat the problem as a language modeling task and train the task translator to predict subsequent tokens (one token at a time) conditioned on the input video and its preceding tokens. The training objective is $\\mathcal{L}^{\\mathcal{T}_k} = \\sum_{j=1}^{M} \\mathbf{w}_j \\log P(\\mathbf{y}_{seq_j}^{\\mathcal{T}_k} | \\mathbf{x}^{\\mathcal{T}_k}, \\mathbf{y}_{seq_{1:j-1}}^{\\mathcal{T}_k})$ . Note that the maximum likelihood loss is weighted to mask the loss corresponding to the task prompt token: $\\mathbf{w}_j$ is set to 0 for $j = 1$ , and to 1 for any other $j$ . During inference, the task prompt is prepended, and the task translator predicts the remaining output tokens. We use argmax sampling (i.e., take the token with the largest likelihood) to sample tokens from the model likelihood and transform the output tokens back to the original label space. Detokenization is easy as we simply reverse the tokenization process.", + "bbox": [ + 496, + 642, + 892, + 853 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The second modification lies in the training strategy. While EgoT2-s adopts the primary task dataset for training, EgoT2-g requires joint training on all $K$ task datasets. Sim", + "bbox": [ + 498, + 854, + 890, + 902 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "2313", + "bbox": [ + 482, + 944, + 514, + 957 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "ilar to the training strategy in [8,20], we sample one batch from each task, compute the task loss, aggregate the $K$ gradients, and perform model updates in one training iteration. The final training objective is $\\mathcal{L} = \\sum_{k=1}^{K} \\mathcal{L}^{\\mathcal{T}_k}$ .", + "bbox": [ + 75, + 90, + 468, + 151 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Figure 3 contrasts the design of EgoT2-s and EgoT2-g. They both provide a flexible framework that can incorporate multiple heterogeneous task-specific models (e.g., the three example tasks we give here focus on different aspects of human-object interactions). With a design and an optimization that are specialized to a single primary task, EgoT2-s is expected to lead to superior individual task performance while EgoT2-g brings the efficiency and compactness benefits of a single translator addressing all tasks.", + "bbox": [ + 75, + 152, + 470, + 287 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 76, + 301, + 209, + 319 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.1. Experimental Setup", + "text_level": 1, + "bbox": [ + 76, + 327, + 266, + 343 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Dataset and Tasks. We evaluate on Ego4D [23], the world's largest egocentric dataset with 3,670 hours of videos spanning hundreds of scenarios (e.g., household, outdoor, leisure). It offers five benchmarks: episodic memory (EM), hands and objects (HO), audio-visual diarization (AV), social interactions (Social) and forecasting. For our study, we select 7 tasks spanning 4 benchmarks, representing a variety of tasks in egocentric perception, as illustrated in Figure 4. The 7 tasks fall into two broad clusters: (a) human-object interactions and (b) human-human interactions. Table 1 summarizes our task setup. For each cluster, we use tasks from the same benchmark as well as tasks across benchmarks, in an attempt to reveal connections among seemingly unrelated tasks. The 7 candidate tasks are heterogeneous in nature as they are defined on videos of varying duration, adopt different video models as backbones, and process unimodal (i.e., video) or multimodal (i.e., video and audio) input, offering a diverse task setup for our study. See Appendix A.2.1 for more details.", + "bbox": [ + 75, + 349, + 468, + 637 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Models and Baselines. For each task, we adopt for consistency the baseline models introduced with the Ego4D dataset $^2$ as the task-specific (TS) models in EgoT2. For task-specific translation (Sec. 4.2), we train one task translator for each primary task and use all the other tasks in the same cluster (either human-object interactions or human-human interactions) as auxiliary tasks. We compare EgoT2-s with two representative transfer learning approaches: (1) Transfer [62] denotes finetuning a transfer function on top of features produced by the auxiliary task models (Figure 2(a)). (2) Late Fusion [45] (LF) concatenates auxiliary task features along with primary task features, and finetunes a few layers that receive the concatenated features as input for the final prediction. Furthermore, to gauge possible improvements over TS by increasing capacity, we consider a", + "bbox": [ + 75, + 638, + 470, + 864 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/ab8ce47a51b3bafe298cd6dbb23551881273556c5100cfb5f8be2c9b7f94fbb0.jpg", + "image_caption": [ + "Figure 4. Task Setup. We select a broad set of egocentric video tasks that focus on (a) human-object interactions and (b) human-human interactions from Ego4D benchmarks." + ], + "image_footnote": [], + "bbox": [ + 542, + 90, + 846, + 243 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/e071d4258890b77a02ce81b6293412265469de22daed7d880436a5a4f700d2e5.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
TaskBenchmarkMod.Duration (seconds)Model backbone
(a)PNRHOV8.0I3D RN-50 [6]
OSCCHOV8.0I3D RN-50 [6]
ARForecastingV8.0SlowFast [19]
LTAForecastingV16.0SlowFast [19]
(b)LAMSocialV0.23D RN-18 [57]
TTMSocialA&V2.73D RN-18 [57]
ASDAVA&V3.7TalkNet [56]
", + "bbox": [ + 529, + 301, + 864, + 417 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Table 1. Task Descriptions. 'Mod.' is short for modality; 'A' and 'V' denote audio and video, respectively.", + "bbox": [ + 500, + 428, + 890, + 455 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Finetuning [13] baseline, which finetunes a few layers on top of the features produced by the primary task model. In order to make a fair comparison, the first-stage training of these baselines is identical to that of EgoT2, and the number of parameters in the second stage of training is set to match that of EgoT2-s as closely as possible.", + "bbox": [ + 496, + 484, + 890, + 575 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "For task-general translation (Sec. 4.3), the task translator is jointly optimized for all tasks within a cluster $^{3}$ , thus we have one task translator for human-object interactions that attends to all tasks simultaneously and one translator that performs three human-human interaction tasks at the same time. For comparison with EgoT2-g, we implement the most widely adopted multi-task learning approach, hard parameter sharing [51] (Figure 2(b)).", + "bbox": [ + 496, + 575, + 890, + 696 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Implementation Details. There is one video preprocessing step before the feature extraction step in Equation (1), where we transform the original video input from $\\mathbf{x}^{T_p}$ to match the input format of the $k$ -th task-specific model $f_k$ . In particular, $\\mathbf{x}^{T_p}$ is first upsampled or downsampled to match the frame rates required by $f_k$ . Next, if the temporal span of the auxiliary task is smaller than that of the primary task, we slide $f_k$ in a moving window to extract a sequence of features, where the window length is the temporal span required by $f_k$ , and stride size is a hyperparameter. Conversely, if $f_k$ requires video inputs of a longer temporal span", + "bbox": [ + 496, + 696, + 890, + 864 + ], + "page_idx": 4 + }, + { + "type": "page_footnote", + "text": "2We use model checkpoints provided on the Ego4D website: https://github.com/EGO4D.", + "bbox": [ + 76, + 875, + 467, + 898 + ], + "page_idx": 4 + }, + { + "type": "page_footnote", + "text": "3There is a significant domain gap between human-human and human-object interaction videos. See Appendix A.3 for cross-cluster EgoT2-g.", + "bbox": [ + 500, + 875, + 890, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "2314", + "bbox": [ + 480, + 944, + 514, + 955 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/9856ffd9fea1640031a8d582396d2dbddbbb07583ac3d5af0cb9222b157c3c66.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
\\( \\mathcal{T}_{p}\\text{ is PNR} \\)\\( \\mathcal{T}_{p}\\text{ is OSCC} \\)\\( \\mathcal{T}_{p}\\text{ is AR} \\)\\( \\mathcal{T}_{p}\\text{ is LTA} \\)
# Params \\( \\cdot 10^{6} \\) Trainable (All)Error (s) ↓# Params \\( \\cdot 10^{6} \\) Trainable (All)Acc. (%) ↑# Params \\( \\cdot 10^{6} \\) Trainable (All)Acc. (%) Verb(%) ↑ Noun# Params \\( \\cdot 10^{6} \\) Trainable (All)ED@20 ↓ VerbNoun
TS model [23]32.2 (32.2)0.61532.2 (32.2)68.2263.3 (63.3)22.1821.55180 (242)0.7460.789
Finetuning [13]8.4 (40.6)0.6118.4 (40.6)67.934.9 (66.8)21.6422.8448.6 (266)0.7440.787
Transfer [62] (PNR)N/AN/A8.4 (40.6)66.804.9 (37.1)19.985.4465.4 (97.6)0.7780.902
Transfer [62] (OSCC)8.4 (40.6)0.611N/AN/A4.9 (37.1)20.009.6165.4 (97.6)0.7740.899
Transfer [62] (AR)9.5 (71.4)0.6139.4 (71.4)70.98N/AN/AN/A53.3 (115)0.7450.806
LF [45] (All Tasks)9.6 (135)0.6109.6 (135)72.105.2 (131)21.1119.2483.6 (427)0.7440.788
EgoT2-s (All Tasks)6.4 (132)0.6107.4 (133)72.694.3 (130)23.0423.2841.8 (348)0.7310.769
", + "bbox": [ + 98, + 88, + 874, + 227 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/947252044b69f388b7e0a49224b54f86ce71187a3a85dece2a67ef4351b299d6.jpg", + "table_caption": [ + "Table 2. Results of EgoT2-s as we vary the primary human-object interaction task $\\mathcal{T}_p$ . First row records performance of the task-specific (TS) model we obtain in the first-stage training; we compare EgoT2-s with other baseline methods in the second-stage training. We list the number of trainable parameters for each separate stage as well as the total (i.e., trainable parameters plus parameters of frozen TS models) in parentheses. Following [23], the evaluation metric is temporal localization error (unit: seconds) for PNR, accuracy for OSCC and AR, and edit distance at future 20 time stamps (i.e., ED@20) for LTA. For localization error and ED@20, lower is better. EgoT2-s reliably adapts the auxiliary tasks to suit the target task." + ], + "table_footnote": [], + "table_body": "
\\( \\mathcal{T}_{p} \\) is TTM\\( \\mathcal{T}_{p} \\) is ASD
# Params \\( \\cdot 10^{6} \\) Trainable (All)mAP (%)↑# Params \\( \\cdot 10^{6} \\) Trainable (All)mAP (%)↑
TS model [23]20.2 (20.2)58.9115.7 (15.7)79.05
Finetuning [13]0.8 (20.8)59.671.1 (16.8)78.62
Transfer [62] (LAM)0.8 (15.4)63.591.6 (16.2)66.40
Transfer [62] (TTM)N/AN/A1.6 (21.6)71.06
Transfer [62] (ASD)0.8 (16.5)62.31N/AN/A
LF [45] (All Tasks)1.2 (51.5)64.291.6 (51.9)77.54
EgoT2-s (All Tasks)0.7 (51.1)66.541.5 (51.9)79.38
", + "bbox": [ + 81, + 345, + 464, + 478 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 3. Results of EgoT2-s as we vary the primary human-human interaction task $\\mathcal{T}_p$ . EgoT2-s consistently improves the TS model.", + "bbox": [ + 76, + 489, + 468, + 518 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "than $\\mathbf{x}^{\\mathcal{T}_p}$ , we exclude task $k$ from auxiliary task candidates to avoid providing potential advantages of a longer observation window to our framework as otherwise we need to expand video length of $\\mathbf{x}^{\\mathcal{T}_p}$ to match the requirement of $f_{k}$ . Moreover, if the auxiliary task dataset is multimodal (i.e., video and audio) and the primary task involves only video, we apply the unimodal video pathway of $f_{k}$ to obtain features; if the primary task is multimodal, we provide all task-specific features that are computable from these modalities. See Appendix A.2.2 for more implementation details.", + "bbox": [ + 75, + 544, + 468, + 696 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.2. Evaluation of Task-Specific Translation", + "text_level": 1, + "bbox": [ + 76, + 707, + 413, + 722 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Results. We conduct experiments with EgoT2-s for each task being the primary task4 and summarize the results for human-object interactions and human-human interactions in Table 2 and 3, respectively.", + "bbox": [ + 75, + 729, + 468, + 792 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "From the two tables, we observe uneven performance by the baseline methods. Transfer and Late Fusion sometimes outperform the dedicated TS model and sometimes underperform it. When tasks do not exhibit a strong transfer rela", + "bbox": [ + 75, + 792, + 468, + 852 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "tion, reusing the backbone of the auxiliary task for the primary task leads to negative transfer and performance degradation. For instance, in Table 2, when $\\mathcal{T}_p$ is AR, Transfer (OSCC) and Late Fusion both downgrade noun prediction accuracy, suggesting object state change is more dependent on verbs and unrelated to noun prediction tasks in AR.", + "bbox": [ + 504, + 348, + 890, + 439 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "On the contrary, our proposed EgoT2-s learns to adaptively utilize task-specific features and effectively mitigates negative transfer, demonstrating consistent improvement over the TS model for all 6 cases. For instance, in Table 3, when $\\mathcal{T}_p$ is ASD, Late Fusion indicates there is a deleterious relation from LAM and TTM to ASD, as it suffers from an accuracy degradation of $1.51\\%$ over TS, yet EgoT2-s still obtains slightly better performance compared to TS (i.e., $79.38\\%$ v.s. $79.05\\%$ ). Moreover, when auxiliary tasks are beneficial for the primary task, EgoT2-s outperforms all baselines with fewer trainable parameters. For example, when $\\mathcal{T}_p$ is TTM, it achieves a $+7.63\\%$ mAP improvement over the original TS model by training a lightweight task translator with only 0.7M parameters on top of it (TS is kept frozen). These results across different primary and auxiliary task combinations help demonstrate the generalizability of EgoT2-s. See Appendix A.3 for experiments using a subset of auxiliary tasks rather than all tasks.", + "bbox": [ + 496, + 443, + 890, + 715 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Ablation Study. In Table 4, we ablate three different design choices of EgoT2-s using TTM as the primary task: (a) We replace the LAM and ASD TS models in EgoT2-s with two TTM models with different parameters. This yields a task fusion transformer that is architecturally identical to EgoT2-s but takes only TTM tokens as input; (b) We pass features produced by TS models after temporal pooling as the input of our task fusion transformer; (c) We do not freeze TS models in our second-stage training. By comparing (a) with our default configuration (d), we see that EgoT2-s indeed benefits from the introduction of auxiliary tasks. Although equipped with three different TTM models", + "bbox": [ + 496, + 719, + 890, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_footnote", + "text": "4Following the time-span guidelines in Sec. 4.1, LAM is not considered as the primary task and LTA is not adopted as an auxiliary task. Nonetheless, Appendix A.3 shows some special cases for completeness.", + "bbox": [ + 75, + 862, + 468, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "2315", + "bbox": [ + 480, + 944, + 514, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/e6591334d2ac9661ecde70c9cdf7f946fb4d6c089d770fd8f55f1362577e60a8.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
# Params ·106Trainable (All)Auxiliary TasksTemporal InformationFrozen TS modelmAP (%)↑
(a)0.7 (60.8)✓✓63.40
(b)0.7 (51.1)✓✓65.47
(c)51.1 (51.1)✓✓66.00
(d)0.7 (51.1)✓✓✓66.54
", + "bbox": [ + 83, + 88, + 464, + 172 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/1d81b9492068f48a48835bd8bd072246fb3507fb6fbaa1e7f3884e3902b6f734.jpg", + "table_caption": [ + "Table 4. Ablation study of EgoT2-s $\\left( {\\mathcal{T}}_{p}\\right.$ is TTM)." + ], + "table_footnote": [], + "table_body": "
(a)# Params TrainablePNR ↓OSCC ↑AR Verb ↑AR Noun ↑LTA Verb ↑LTA Noun ↑
TS model [23]N/A0.61568.222.1821.5520.8221.80
Multi-task [51]32.20.61766.0N/AN/AN/AN/A
EgoT2-g (P & O)5.90.61268.6N/AN/AN/AN/A
EgoT2-g (All)34.50.61171.721.9322.7321.9123.61
", + "bbox": [ + 81, + 215, + 465, + 299 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/8c4fa0404de23e36d7829cf3f21bcd1350ac8a874d740839d77c39ccdc5a8c4f.jpg", + "table_caption": [], + "table_footnote": [ + "Table 5. EgoT2-g for (a) human-object interaction and (b) human-human interaction tasks. The evaluation metric is error (seconds) for PNR (P) and accuracy (\\%) for OSCC (O), AR and LTA. We report the number of trainable parameters required for each method in the second-stage training (unit: million). Our model is flexible, accurate, and avoids negative transfer." + ], + "table_body": "
(b)# Params TrainableLAM mAP (%) ↑TTM mAP (%) ↑ASD Acc.(%) ↑
TS model [23]N/A77.7958.9179.05
Multi-task [51]20.260.5361.91N/A
EgoT2-g1.477.6364.4979.06
", + "bbox": [ + 81, + 319, + 465, + 393 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "and a larger model size (the total number of parameters of three TTM models is larger than the sum of three TS models), variant (a) does not bring as much performance gain as EgoT2-s (d). Also, preserving the temporal information of task-specific tokens further boosts performance, as can be seen in the comparison of EgoT2-s (b) with EgoT2-s (d). Finally, not freezing TS (c) greatly increases the training cost yet brings no performance gain. These results validate the design of our proposed EgoT2-s.", + "bbox": [ + 75, + 516, + 467, + 652 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.3. Evaluation of Task-General Translation", + "text_level": 1, + "bbox": [ + 76, + 664, + 416, + 679 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Results. Table 5 provides results of EgoT2-g. Since the TTM and LAM baseline models use identical video backbones (i.e., 3D ResNet-18), the hard parameter sharing multi-task baseline [51] can jointly learn TTM and LAM. Yet this model design is unable to solve the ASD task without further modifications to the ASD backbone model. In contrast, our EgoT2-g provides a flexible solution that can incorporate a heterogeneous mix of pretrained models. Similarly, we apply the multi-task baseline to PNR and OSCC, as they use the same video backbone (i.e., I3D ResNet-50). Compared with dedicated TS models, our proposed EgoT2-g performs task translation for all tasks at the same time and achieves on parallel or better performance for all tasks. For instance, it achieves $+5.58\\%$ mAP im", + "bbox": [ + 75, + 688, + 467, + 898 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/d374cc75b79c68941d4401e0c35ab29474e4c16f39a078883d8ddfd5b47830e4.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
TTM ChallengemAP↑
Random Guess [23]0.50
3D ResNet-18 Bi-LSTM [23]0.54
EgoT2-g (3D ResNet-18)0.58
EgoT2-s (3D ResNet-18)0.58
PNR ChallengeError (s)↓
Always Center Frame [23]1.01
CNN LSTM [23]0.76
EgoVLP [40]0.67
Video Swin Transformer [16]0.66
SViT [4]0.66
EgoT2-s (I3D ResNet-50)0.66
OSCC ChallengeAcc. ↑
Always Positive [23]0.48
I3D ResNet-50 [23]0.68
Video Swin Transformer [16]0.68
Divided ST Attention [28]0.72
EgoVLP [40]0.74
EgoT2-g (I3D ResNet-50)0.70
EgoT2-s (I3D ResNet-50)0.71
EgoT2-s (EgoVLP)0.75
LTA ChallengeED@20↓
VerbNounAction
SlowFast + Transformer [23]0.740.780.94
Video + CLIP [10]0.740.770.94
Hierarchical MLP Mixer [46]0.740.740.93
EgoT2-s (SlowFast)0.720.760.93
", + "bbox": [ + 540, + 88, + 851, + 439 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 6. Comparison of EgoT2 with SOTA approaches on four Ego4D challenges (test set). We list the TS model architecture of EgoT2 in parentheses. Our model improves the state of the art.", + "bbox": [ + 498, + 450, + 890, + 492 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "provement for TTM and $3.5\\%$ accuracy gain for OSCC. Notably, on ASD, it retains the top-performance of the original TS models when the other two auxiliary tasks do not help. In contrast, we observe task competition for the multi-task baseline: the improvement for TTM (i.e., $+3.0\\%$ mAP) is at the cost of significantly downgraded LAM performance (i.e., $-17.26\\%$ mAP). Similarly, sharing an encoder for PNR and OSCC also leads to task competition and suboptimal performance for the multi-task baseline. For a side-by-side comparison, we also implement EgoT2-g that performs task translation for PNR and OSCC only and observe its advantages over the multi-task baseline in terms of both performance and trainable parameters. As EgoT2-g does not require re-training of the backbone, we can integrate any available model checkpoint developed for each individual task into our framework and train a lightweight task-general translator to further boost performance in the second stage.", + "bbox": [ + 496, + 522, + 890, + 777 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Comparison with SOTA Approaches. To further demonstrate the efficacy of both EgoT2-s and EgoT2-g, we submit our model to the EvalAI server to compare it with winning submissions to Ego4D-CVPR'22 and Ego4D-ECCV'22 challenges on the withheld test set. Table 6 shows the results.5 EgoT2-s achieves top performance for all 4 chal", + "bbox": [ + 496, + 780, + 890, + 871 + ], + "page_idx": 6 + }, + { + "type": "page_footnote", + "text": "ASD & AR are not applicable since they are not Ego4D challenges.", + "bbox": [ + 514, + 886, + 888, + 898 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "2316", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "lenges. By only incorporating basic video backbones (e.g., 3D ResNet-18 and SlowFast) as the task-specific model, EgoT2-s achieves similar or better performance than works that adopt more powerful, novel architectures such as Video Swin Transformer. Moreover, the benefits of our approach are orthogonal to such architecture improvements: e.g., for the OSCC challenge, replacing the I3D ResNet-50 backbone with the one used in EgoVLP [40] can further elevate the accuracy of EgoVLP by $1\\%$ . This indicates the success of EgoT2 stems from its effective use of task synergies.", + "bbox": [ + 75, + 90, + 472, + 241 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "While EgoT2-g is a strong performer that surpasses or matches TS across all tasks, if we compare its results with those of EgoT2-s, we observe that EgoT2-s demonstrates superior performance. This is understandable given that EgoT2-s is individually optimized for each primary task and employs a specialized translator. On the other hand, EgoT2-g provides a favorable unified framework that performs task translation for all tasks simultaneously via the design of a task-general translator. Thus, EgoT2-s serves as the framework of choice for top performance while EgoT2-g provides added flexibility. See Appendix A.3 for a detailed comparison of the performance and efficiency of these two variants.", + "bbox": [ + 75, + 242, + 472, + 422 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.4. Visualization of Uncovered Task Relations", + "text_level": 1, + "bbox": [ + 76, + 431, + 437, + 448 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Our proposed EgoT2 explicitly models task relations via a task translator and offers good interpretability on task relations. For EgoT2-s, Figure 5 shows the attention weights of task tokens when the primary task is LTA and the auxiliary task is AR. Given two adjacent input video clips, the goal of LTA is to predict the next action (e.g., put container and turn off nozzle for the two examples here). In the upper example, there is a scene change from the first clip (the temporal segment corresponding to put wheel) to the second clip (the clip corresponding to take container). The attention weights of AR tokens are small for the first clip and large for the second clip. Clearly, the future action to predict is more closely related to the second temporal segment due to similarities in the scene and objects. In the lower example, the AR tokens have large attention weights, as the video is temporally similar and the previous two actions are indicative of the next action. These results show how EgoT2-s accurately characterizes temporal and auxiliary task information to improve the primary task. More visualizations are in Appendix A.4.", + "bbox": [ + 75, + 455, + 472, + 742 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Similarly, for EgoT2-g, we visualize its encoder-decoder attention weights from the last layer transformer in Figure 6. Given the same video clip as input, feature tokens are activated differently when EgoT2-g is given different task prompts, demonstrating that EgoT2-g learns to perform task translation conditioned on the task of interest. As it assigns small weights to task features that are not beneficial for the task of interest (e.g., PNR features to noun prediction tasks), EgoT2-g discards non-relevant task features to", + "bbox": [ + 75, + 742, + 472, + 878 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/b829f891dbb03b2a701e6f428f3778642ced2e999762364fa3a299fc06929b30.jpg", + "image_caption": [ + "Figure 5. Attention weights of EgoT2-s when $\\mathcal{T}_p$ is LTA. EgoT2-s learns to utilize tokens from relevant temporal segments and tasks. The attention weights of AR tokens are large when the current action is indicative of future action." + ], + "image_footnote": [], + "bbox": [ + 506, + 90, + 893, + 247 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/16f622391e69b04c03db4202704d36c390297a2f2ec98a1eb6178e415964433c.jpg", + "image_caption": [ + "Figure 6. Attention weights of EgoT2-g. Given the same video and different task prompts, EgoT2-g assigns different weights to different task tokens. See text." + ], + "image_footnote": [], + "bbox": [ + 501, + 327, + 883, + 465 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "mitigate task competition. We also observe temporal differences of attention weights from same task features, indicating that EgoT2-g captures both inter-frame and inter-task dependencies to improve the task of interest. Finally, recall that in Figure 1, we derive task relations for 4 human-object interaction tasks via attention weights provided by EgoT2-g. The attention weights are temporally pooled and averaged over all validation data, revealing task relations from a global perspective. Results for human-human interaction tasks are presented in Appendix A.4. In all, EgoT2 provides good interpretability patterns on (1) which subset of tasks (2) which time segments lead to the final prediction.", + "bbox": [ + 496, + 542, + 893, + 726 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 738, + 619, + 753 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "As a step towards unified egocentric perception, we propose EgoT2, a general and flexible design for task translation. EgoT2 consists of heterogeneous video models optimized for each individual task and a transformer-based task translator that captures inter-frame and inter-task relations. We propose EgoT2-s to improve one primary task and EgoT2-g to conduct task translation for all tasks simultaneously. Results on 7 diverse egocentric video tasks reveal valuable task relations and validate the proposed design.", + "bbox": [ + 496, + 763, + 893, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_footnote", + "text": "Results of EgoT2-g for PNR & LTA are unavailable (see Appendix A.2.2).", + "bbox": [ + 76, + 886, + 470, + 901 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "2317", + "bbox": [ + 482, + 944, + 516, + 957 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Anurag Arnab, Mostafa Dehghani, Georg Heigold, Chen Sun, Mario Lucic, and Cordelia Schmid. Vivit: A video vision transformer. 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A comprehensive survey on transfer learning. Proceedings of the IEEE, 109(1):43-76, 2020. 2", + "bbox": [ + 501, + 90, + 893, + 147 + ], + "page_idx": 10 + }, + { + "type": "page_number", + "text": "2320", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 10 + } +] \ No newline at end of file diff --git a/2023/Egocentric Video Task Translation/4f7e3293-877b-4c9b-8bc7-d95d33f4f800_model.json b/2023/Egocentric Video Task Translation/4f7e3293-877b-4c9b-8bc7-d95d33f4f800_model.json new file mode 100644 index 0000000000000000000000000000000000000000..65731eec685b43e10084484a9e442d7735a6556a --- /dev/null +++ b/2023/Egocentric Video Task Translation/4f7e3293-877b-4c9b-8bc7-d95d33f4f800_model.json @@ -0,0 +1,2224 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.001, + 0.812, + 0.047 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.31, + 0.131, + 0.66, + 0.153 + ], + "angle": 0, + "content": "Egocentric Video Task Translation" + }, + { + "type": "text", + "bbox": [ + 0.202, + 0.18, + 0.768, + 0.217 + ], + "angle": 0, + "content": "Zihui Xue\\(^{1,2*}\\) Yale Song\\(^{2}\\) Kristen Grauman\\(^{1,2}\\) Lorenzo Torresani\\(^{2}\\) \n\\(^{1}\\)The University of Texas at Austin \\(\\mathbf{\\Pi}^{2}\\)FAIR, Meta AI" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.252, + 0.314, + 0.267 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.284, + 0.474, + 0.617 + ], + "angle": 0, + "content": "Different video understanding tasks are typically treated in isolation, and even with distinct types of curated data (e.g., classifying sports in one dataset, tracking animals in another). However, in wearable cameras, the immersive egocentric perspective of a person engaging with the world around them presents an interconnected web of video understanding tasks—hand-object manipulations, navigation in the space, or human-human interactions—that unfold continuously, driven by the person's goals. We argue that this calls for a much more unified approach. We propose EgoTask Translation (EgoT2), which takes a collection of models optimized on separate tasks and learns to translate their outputs for improved performance on any or all of them at once. Unlike traditional transfer or multitask learning, EgoT2's \"flipped design\" entails separate task-specific backbones and a task translator shared across all tasks, which captures synergies between even heterogeneous tasks and mitigates task competition. Demonstrating our model on a wide array of video tasks from Ego4D, we show its advantages over existing transfer paradigms and achieve top-ranked results on four of the Ego4D 2022 benchmark challenges.1" + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.646, + 0.21, + 0.661 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.672, + 0.47, + 0.854 + ], + "angle": 0, + "content": "In recent years, the introduction of large-scale video datasets (e.g., Kinetics [6, 33] and Something-Something [22]) have enabled the application of powerful deep learning models to video understanding and have led to dramatic advances. These third-person datasets, however, have overwhelmingly focused on the single task of action recognition in trimmed clips [12, 36, 47, 64]. Unlike curated third-person videos, our daily life involves frequent and heterogeneous interactions with other humans, objects, and environments in the wild. First-person videos from wearable cameras capture the observer's perspective and attention as a continuous stream. As such," + }, + { + "type": "image", + "bbox": [ + 0.505, + 0.25, + 0.891, + 0.374 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.52, + 0.383, + 0.885, + 0.5 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.515, + 0.894, + 0.572 + ], + "angle": 0, + "content": "Figure 1. Given a set of diverse egocentric video tasks, the proposed EgoT2 leverages synergies among the tasks to improve each individual task performance. The attention maps produced by EgoT2 offer good interpretability on inherent task relations." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.599, + 0.892, + 0.718 + ], + "angle": 0, + "content": "they are better equipped to reveal these multi-faceted, spontaneous interactions. Indeed egocentric datasets, such as EPIC-Kitchens [9] and Ego4D [23], provide suites of tasks associated with varied interactions. However, while these benchmarks have promoted a broader and more heterogeneous view of video understanding, they risk perpetuating the fragmented development of models specialized for each individual task." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.892, + 0.78 + ], + "angle": 0, + "content": "In this work, we argue that the egocentric perspective offers an opportunity for holistic perception that can beneficially leverage synergies among video tasks to solve all problems in a unified manner. See Figure 1." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.781, + 0.893, + 0.901 + ], + "angle": 0, + "content": "Imagine a cooking scenario where the camera wearer actively interacts with objects and other people in an environment while preparing dinner. These interactions relate to each other: a hand grasping a knife suggests the upcoming action of cutting; the view of a tomato on a cutting board suggests that the object is likely to undergo a state transition from whole to chopped; the conversation may further reveal the camera wearer's ongoing and planned actions." + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.863, + 0.37, + 0.876 + ], + "angle": 0, + "content": "*Work done during an internship at FAIR, Meta AI." + }, + { + "type": "page_footnote", + "bbox": [ + 0.097, + 0.876, + 0.468, + 0.901 + ], + "angle": 0, + "content": "1Project webpage: https://vision.cs.utexas.edu/ ojects/egot2/." + }, + { + "type": "list", + "bbox": [ + 0.096, + 0.863, + 0.468, + 0.901 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "2310" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.168 + ], + "angle": 0, + "content": "Apart from the natural relation among these tasks, egocentric video's partial observability (i.e., the camera wearer is largely out of the field of view) further motivates us to seek synergistic, comprehensive video understanding to leverage complementary cues among multiple tasks." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.17, + 0.471, + 0.426 + ], + "angle": 0, + "content": "Our goal presents several technical challenges for conventional transfer learning (TL) [65] and multi-task learning (MTL) [63]. First, MTL requires training sets where each sample includes annotations for all tasks [15, 24, 48, 53, 55, 62], which is often impractical. Second, egocentric video tasks are heterogeneous in nature, requiring different modalities (audio, visual, motion), diverse labels (e.g., temporal, spatial or semantic), and different temporal granularities (e.g., action anticipation requires long-term observations, but object state recognition operates at a few sparsely sampled frames)—all of which makes a unified model design problematic and fosters specialization. Finally, while existing work advocates the use of a shared encoder across tasks to learn general representations [3, 18, 26, 32, 39, 44, 45, 51], the diverse span of egocentric tasks poses a hazard to parameter sharing which can lead to negative transfer [21, 24, 38, 53]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.429, + 0.47, + 0.64 + ], + "angle": 0, + "content": "To address the above limitations, we propose EgoTask Translation (EgoT2), a unified learning framework to address a diverse set of egocentric video tasks together. EgoT2 is flexible and general in that it can handle separate datasets for the different tasks; it takes video heterogeneity into account; and it mitigates negative transfer when tasks are not strongly related. To be specific, EgoT2 consists of specialized models developed for individual tasks and a task translator that explicitly models inter-task and inter-frame relations. We propose two distinct designs: (1) task-specific EgoT2 (EgoT2-s) optimizes a given primary task with the assistance of auxiliary tasks (Figure 2(c)) while (2) task-general EgoT2 (EgoT2-g) supports task translation for multiple tasks at the same time (Figure 2(d))." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.643, + 0.471, + 0.809 + ], + "angle": 0, + "content": "Compared with a unified backbone across tasks [62], adopting task-specific backbones preserves peculiarities of each task (e.g. different temporal granularities) and mitigates negative transfer since each backbone is optimized on one task. Furthermore, unlike traditional parameter sharing [51], the proposed task translator learns to \"translate\" all task features into predictions for the target task by selectively activating useful features and discarding irrelevant ones. The task translator also facilitates interpretability by explicitly revealing which temporal segments and which subsets of tasks contribute to improving a given task." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.811, + 0.47, + 0.902 + ], + "angle": 0, + "content": "We evaluate EgoT2 on a diverse set of 7 egocentric perception tasks from the world's largest egocentric video benchmark, Ego4D [23]. Its heterogeneous tasks extend beyond mere action recognition to speaker/listener identification, keyframe localization, object state change classification, long-term action anticipation, and others, and pro" + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.092, + 0.692, + 0.18 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.544, + 0.185, + 0.645, + 0.196 + ], + "angle": 0, + "content": "(a) conventional TL" + }, + { + "type": "image", + "bbox": [ + 0.724, + 0.091, + 0.871, + 0.18 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.741, + 0.185, + 0.853, + 0.196 + ], + "angle": 0, + "content": "(b) conventional MTL" + }, + { + "type": "image", + "bbox": [ + 0.502, + 0.206, + 0.688, + 0.3 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.562, + 0.304, + 0.623, + 0.315 + ], + "angle": 0, + "content": "(c) EgoT2-s" + }, + { + "type": "image", + "bbox": [ + 0.706, + 0.206, + 0.893, + 0.3 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.769, + 0.304, + 0.832, + 0.315 + ], + "angle": 0, + "content": "(d) EgoT2-g" + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.326, + 0.893, + 0.411 + ], + "angle": 0, + "content": "Figure 2. (a) Conventional TL uses a backbone pretrained on the source task followed by a head transferring supervision to the target task; (b) Traditional MTL consists of a shared backbone and several task-specific heads; (c) EgoT2-s adopts task-specific backbones and optimizes the task translator for a given primary task; (d) EgoT2-g jointly optimizes the task translator for all tasks." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.437, + 0.892, + 0.543 + ], + "angle": 0, + "content": "vide a perfect fit for our study. Our results reveal inherent task synergies, demonstrate consistent performance improvement across tasks, and offer good interpretability in task translation. Among all four Ego4D challenges involved in our task setup, EgoT2 outperforms all submissions to three Ego4D-CVPR'22 challenges and achieves state-of-the-art performance in one Ego4D-ECCV'22 challenge." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.558, + 0.642, + 0.573 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.583, + 0.892, + 0.84 + ], + "angle": 0, + "content": "Transfer Learning. TL [65] aims at transferring knowledge from a source domain to improve the performance in a target domain. The most widely adopted approach is to pretrain a model on a source task then finetune on the target task, as shown in Figure 2(a). Following this paradigm, many video classification models [1, 5, 42, 59] are initialized from models pretrained on ImageNet [11]. In addition, many works propose to transfer knowledge from a large-scale video dataset (e.g., Kinetics [6, 33]) to benefit action recognition in smaller-scale datasets [54] such as UCF-101 [52] and HMDB-51 [37] or to improve other video tasks, such as spatiotemporal action localization [2, 17, 19, 27, 49] and video anomaly detection [25, 41]. While this technique is ubiquitous in video understanding, prior approaches only consider the transfer from one single source task (dataset) and are thus unable to model the relations among multiple video tasks simultaneously." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Taskonomy [62] presents task transfer with a thorough analysis on the structure of multiple visual tasks. Many works [15, 48, 53, 61] continue along this direction and explore visual task relations, yet they limit the discussion to" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.514, + 0.957 + ], + "angle": 0, + "content": "2311" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.242 + ], + "angle": 0, + "content": "static images and generally require a unified design across all tasks. In contrast, we consider a diverse set of egocentric video tasks, which are addressed with a heterogeneous set of task-specific video architectures (e.g., accommodating different time, space, or multimodality). Clearly, forcing the same network architecture across all tasks can be suboptimal for each individual task. This motivates our proposed EgoT2-s (Figure 2(c)), where we preserve the heterogeneous backbones developed for each task and build a task translator on top of the task-specific models." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.242, + 0.473, + 0.529 + ], + "angle": 0, + "content": "Multi-task Learning. In MTL [63], a single model is trained to address multiple tasks simultaneously in order to capture synergistic supervision across tasks. As depicted in Figure 2(b), hard parameter sharing [51] (i.e., sharing a backbone among tasks and keeping one separate head for each task) is the most commonly used technique within this genre. Although MTL has shown to be beneficial of video analysis [3, 18, 26, 32, 39, 44, 45], there is ongoing debate about the best strategies to determine what parameters to share across which tasks [7, 24, 31, 53, 55]. As pointed out in [34], when MTL is achieved by means of a single common backbone, the performance tends to decrease when the number of tasks grows beyond a certain point. Furthermore, many works [21, 24, 38, 53] observe that over-sharing a network across unrelated tasks causes negative transfer and hinders individual task performance. While soft parameter sharing [14, 60] mitigates this by retaining distinct copies of parameters, it still requires adopting the same identical architecture and \"similar\" weight values across all tasks." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.53, + 0.473, + 0.803 + ], + "angle": 0, + "content": "In the video domain, several works utilize synergies between related tasks (e.g., action recognition with gaze prediction [18, 26, 39] or body pose estimation [44]). However, when selected tasks are not strongly related, prior approaches that split the learning capacity of a shared backbone over multiple tasks can suffer from task competition and inferior performance. In the image domain, with the great advancement of transformers [58], training with multiple datasets together for a generalist model is gaining popularity. Recent work [8, 20, 29, 30, 35, 43] investigates a unified transformer architecture across a diverse set of tasks. Our variant EgoT2-g (Figure 2(d)) is motivated by the desiderata of shared knowledge encapsulated by MTL and of a generalist model. Unlike previous learning paradigms, we adopt a \"flipped design\" involving separate task-specific backbones and a task translator shared across all tasks. This effectively mitigates task competition and achieves task translation for all tasks simultaneously." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.816, + 0.187, + 0.833 + ], + "angle": 0, + "content": "3. Approach" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.472, + 0.903 + ], + "angle": 0, + "content": "We are given \\(K\\) video tasks, \\(\\mathcal{T}_k\\) for \\(k = 1,\\dots ,K\\). We note that our approach does not require a common training set with annotations for all tasks. Let the dataset for task \\(\\mathcal{T}_k\\) be \\(\\mathcal{D}^{\\mathcal{T}_k} = \\{(\\mathbf{x}_i^{\\mathcal{T}_k},y_i^{\\mathcal{T}_k})\\}_{i = 1}^{N_k}\\), where \\((\\mathbf{x}_i^{\\mathcal{T}_k},y_i^{\\mathcal{T}_k})\\) denotes the" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.152 + ], + "angle": 0, + "content": "\\(i\\)-th pair of (input video, output label) and \\(N_{k}\\) represents the number of given examples. Note that \"labels\" \\(y_{i}^{\\mathcal{T}_{k}}\\) can be a variety of output types, and are not limited to category labels. For simplicity we omit the subscript \\(i\\) hereafter." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.153, + 0.895, + 0.319 + ], + "angle": 0, + "content": "We consider two formulations with distinct advantages: (1) task-specific translation, where we partition the tasks into one primary task \\(\\mathcal{T}_p\\) and \\(K - 1\\) auxiliary tasks, and optimize the objective to improve performance on \\(\\mathcal{T}_p\\) with the assistance of the auxiliary tasks (EgoT2-s, Sec. 3.1); (2) task-general translation, where we treat all \\(K\\) tasks equally, and the goal is to maximize the collective performance of all the tasks (EgoT2-g, Sec. 3.2). As demonstrated in our experiments, objective (1) leads to the strongest performance on the primary task, while objective (2) offers the benefit of a single unified model addressing all tasks at once." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.326, + 0.808, + 0.342 + ], + "angle": 0, + "content": "3.1. Task-Specific Translation: EgoT2-s" + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.349, + 0.839, + 0.364 + ], + "angle": 0, + "content": "The training of EgoT2-s is split over two stages." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.364, + 0.892, + 0.485 + ], + "angle": 0, + "content": "Stage I: Individual-Task Training. We train a separate model \\( f_{k} \\) on each individual task dataset \\( \\mathcal{D}^{\\mathcal{T}_k} \\), obtaining \\( K \\) task-specific models \\( \\{f_k\\}_{k = 1}^K \\). We do not place any restrictions on the task-specific model designs, nor do we require a unified design (i.e., identical encoder-decoder architecture) across tasks. Therefore, any available model checkpoint developed for task \\( \\mathcal{T}_k \\) can be adopted as \\( f_{k} \\) within our framework, offering maximum flexibility." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.485, + 0.892, + 0.636 + ], + "angle": 0, + "content": "Stage II: Task-Specific Translation. We train a task translator that takes features produced by task-specific models as input and outputs predictions for the primary task. Formally, let \\(\\mathbf{h}_k\\in \\mathbb{R}^{T_k\\times D_k}\\) be features produced by the \\(k\\) -th task-specific model \\(f_{k}\\), where \\(T_{k}\\) is the temporal dimension and \\(D_{k}\\) is the per-frame feature dimension for model \\(f_{k}\\). Following the feature extraction step, we design a projection layer \\(\\mathbf{P}_k\\in \\mathbb{R}^{D_k\\times D}\\) for each \\(f_{k}\\) to map task-specific features to a shared latent feature space. This yields a temporal sequence of task-specific tokens \\(\\tilde{\\mathbf{h}}_k\\in \\mathbb{R}^{T_k\\times D}\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.636, + 0.892, + 0.728 + ], + "angle": 0, + "content": "We process this collection of task-specific temporal sequences using a transformer encoder [58] of \\(L\\) layers to capture both inter-frame and inter-task dependencies. We denote the propagation rule of layer \\(l\\) by \\(\\mathbf{z}^{l + 1} = \\text{Encoder}^l (\\mathbf{z}^l)\\). Finally, we adopt a decoder head \\(\\text{Decoder}^{\\mathcal{T}_p}\\) to obtain predictions for the primary task \\(\\mathcal{T}_p\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.727, + 0.892, + 0.772 + ], + "angle": 0, + "content": "In all, this stage has four major steps: (1) feature extraction; (2) feature projection; (3) transformer fusion; and (4) feature decoding. The procedure is summarized below:" + }, + { + "type": "equation", + "bbox": [ + 0.554, + 0.793, + 0.891, + 0.811 + ], + "angle": 0, + "content": "\\[\n\\mathbf {h} _ {k} = f _ {k} \\left(\\mathbf {x} ^ {\\mathcal {T} _ {p}}\\right), \\quad \\forall k \\in \\{1, 2, \\dots , K \\} \\tag {1}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.556, + 0.814, + 0.891, + 0.832 + ], + "angle": 0, + "content": "\\[\n\\tilde {\\mathbf {h}} _ {k} = \\mathbf {P} _ {k} \\mathbf {h} _ {k}, \\quad \\forall k \\in \\{1, 2, \\dots , K \\} \\tag {2}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.559, + 0.836, + 0.891, + 0.862 + ], + "angle": 0, + "content": "\\[\n\\mathbf {z} ^ {0} = \\left[ \\tilde {\\mathbf {h}} _ {1}, \\tilde {\\mathbf {h}} _ {2}, \\dots , \\tilde {\\mathbf {h}} _ {K} \\right] \\tag {3}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.545, + 0.856, + 0.891, + 0.874 + ], + "angle": 0, + "content": "\\[\n\\mathbf {z} ^ {l + 1} = \\operatorname {E n c o d e r} ^ {l} \\left(\\mathbf {z} ^ {l}\\right), \\forall l \\in \\{0, 1, \\dots , L - 1 \\} \\tag {5}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.54, + 0.877, + 0.891, + 0.899 + ], + "angle": 0, + "content": "\\[\ny _ {p r e d} ^ {\\mathcal {T} _ {p}} = \\operatorname {D e c o d e r} ^ {\\mathcal {T} _ {p}} \\left(\\mathbf {z} ^ {L}\\right) \\tag {4}\n\\]" + }, + { + "type": "page_number", + "bbox": [ + 0.482, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "2312" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.078, + 0.089, + 0.446, + 0.365 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.453, + 0.089, + 0.862, + 0.368 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.38, + 0.895, + 0.451 + ], + "angle": 0, + "content": "Figure 3. An illustration of EgoT2-s (left) and EgoT2-g (right) on three candidate tasks. The left figure illustrates EgoT2-s on three social interaction tasks, where the input to each model is unimodal (i.e., video) or multimodal (i.e., video and audio). The right figure shows the design of EgoT2-g on three example tasks that focus on different aspects of human-object interactions (i.e., localization, object state change classification, and action recognition). EgoT2-s learns to \"translate\" auxiliary task features into predictions for the primary task and EgoT2-g conducts task translation conditioned on the task of interest." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.473, + 0.47, + 0.536 + ], + "angle": 0, + "content": "where \\( y_{pred}^{\\mathcal{T}_p} \\) denotes the prediction given by EgoT2-s. During the second stage of training, we freeze the task-specific models and optimize the task translator with respect to the primary task dataset \\( \\mathcal{D}^{\\mathcal{T}_p} \\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.537, + 0.471, + 0.675 + ], + "angle": 0, + "content": "Figure 3 (left) illustrates the design of EgoT2-s using three social interaction tasks from Ego4D [23] as an example. EgoT2-s allows heterogeneity in the task-specific models (i.e., \\( f_{1} \\) is unimodal while \\( f_{2} \\) and \\( f_{3} \\) are multimodal; also the three task-specific models can be associated with different frame rates and temporal durations) and utilizes a transformer encoder to model inter-frame and inter-task relations. The resulting EgoT2-s learns to adaptively utilize auxiliary task features for the primary task prediction." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.681, + 0.391, + 0.699 + ], + "angle": 0, + "content": "3.2. Task-General Translation: EgoT2-g" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.704, + 0.47, + 0.81 + ], + "angle": 0, + "content": "EgoT2-s optimizes performance for a single primary task. Therefore, in the event all \\( K \\) tasks must be addressed, it requires \\( K \\) separate training runs and \\( K \\) distinct translators. This motivates us to extend EgoT2-s to perform task translation for all \\( K \\) tasks at once. In EgoT2-g, the task translator processes features from all \\( K \\) tasks and learns to \"translate\" features conditioned on the task of interest." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.811, + 0.471, + 0.903 + ], + "angle": 0, + "content": "The first stage of EgoT2-g is identical to EgoT2-s. For the second stage, we propose two main modifications. First, we replace the task-specific decoder in EgoT2-s with a \"generalist\" decoder that outputs predictions conditioned on the task of interest. Natural language provides us with a flexible scheme to specify all tasks as a sequence of sym" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.476, + 0.892, + 0.643 + ], + "angle": 0, + "content": "bols. Inspired by [8], we tokenize all task outputs and replace the original task-specific decoder with a sequence decoder [50] for a unified interface. Specifically, we first transform the original label \\( y^{\\mathcal{T}_k} \\) to a target output sequence \\( \\mathbf{y}_{seq}^{\\mathcal{T}_k} \\in \\mathbb{R}^M \\), where \\( M \\) is the target sequence length. For the task translator to produce task-dependent outputs, we preprocess a task prompt token \\( \\mathbf{y}_{prompt} \\) to the target output, i.e., \\( \\mathbf{y}_{seq_1}^{\\mathcal{T}_k} = \\mathbf{y}_{prompt} \\). We then let the sequence decoder generate a sentence answering the requested task. Figure 3 (right) illustrates how we express task outputs as sequences of discrete tokens and attach task prompts." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.643, + 0.893, + 0.854 + ], + "angle": 0, + "content": "With the transformed output, we treat the problem as a language modeling task and train the task translator to predict subsequent tokens (one token at a time) conditioned on the input video and its preceding tokens. The training objective is \\(\\mathcal{L}^{\\mathcal{T}_k} = \\sum_{j=1}^{M} \\mathbf{w}_j \\log P(\\mathbf{y}_{seq_j}^{\\mathcal{T}_k} | \\mathbf{x}^{\\mathcal{T}_k}, \\mathbf{y}_{seq_{1:j-1}}^{\\mathcal{T}_k})\\). Note that the maximum likelihood loss is weighted to mask the loss corresponding to the task prompt token: \\(\\mathbf{w}_j\\) is set to 0 for \\(j = 1\\), and to 1 for any other \\(j\\). During inference, the task prompt is prepended, and the task translator predicts the remaining output tokens. We use argmax sampling (i.e., take the token with the largest likelihood) to sample tokens from the model likelihood and transform the output tokens back to the original label space. Detokenization is easy as we simply reverse the tokenization process." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.856, + 0.892, + 0.903 + ], + "angle": 0, + "content": "The second modification lies in the training strategy. While EgoT2-s adopts the primary task dataset for training, EgoT2-g requires joint training on all \\(K\\) task datasets. Sim" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.958 + ], + "angle": 0, + "content": "2313" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.152 + ], + "angle": 0, + "content": "ilar to the training strategy in [8,20], we sample one batch from each task, compute the task loss, aggregate the \\(K\\) gradients, and perform model updates in one training iteration. The final training objective is \\(\\mathcal{L} = \\sum_{k=1}^{K} \\mathcal{L}^{\\mathcal{T}_k}\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.153, + 0.471, + 0.289 + ], + "angle": 0, + "content": "Figure 3 contrasts the design of EgoT2-s and EgoT2-g. They both provide a flexible framework that can incorporate multiple heterogeneous task-specific models (e.g., the three example tasks we give here focus on different aspects of human-object interactions). With a design and an optimization that are specialized to a single primary task, EgoT2-s is expected to lead to superior individual task performance while EgoT2-g brings the efficiency and compactness benefits of a single translator addressing all tasks." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.303, + 0.21, + 0.32 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.328, + 0.267, + 0.344 + ], + "angle": 0, + "content": "4.1. Experimental Setup" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.351, + 0.47, + 0.638 + ], + "angle": 0, + "content": "Dataset and Tasks. We evaluate on Ego4D [23], the world's largest egocentric dataset with 3,670 hours of videos spanning hundreds of scenarios (e.g., household, outdoor, leisure). It offers five benchmarks: episodic memory (EM), hands and objects (HO), audio-visual diarization (AV), social interactions (Social) and forecasting. For our study, we select 7 tasks spanning 4 benchmarks, representing a variety of tasks in egocentric perception, as illustrated in Figure 4. The 7 tasks fall into two broad clusters: (a) human-object interactions and (b) human-human interactions. Table 1 summarizes our task setup. For each cluster, we use tasks from the same benchmark as well as tasks across benchmarks, in an attempt to reveal connections among seemingly unrelated tasks. The 7 candidate tasks are heterogeneous in nature as they are defined on videos of varying duration, adopt different video models as backbones, and process unimodal (i.e., video) or multimodal (i.e., video and audio) input, offering a diverse task setup for our study. See Appendix A.2.1 for more details." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.639, + 0.471, + 0.866 + ], + "angle": 0, + "content": "Models and Baselines. For each task, we adopt for consistency the baseline models introduced with the Ego4D dataset\\(^2\\) as the task-specific (TS) models in EgoT2. For task-specific translation (Sec. 4.2), we train one task translator for each primary task and use all the other tasks in the same cluster (either human-object interactions or human-human interactions) as auxiliary tasks. We compare EgoT2-s with two representative transfer learning approaches: (1) Transfer [62] denotes finetuning a transfer function on top of features produced by the auxiliary task models (Figure 2(a)). (2) Late Fusion [45] (LF) concatenates auxiliary task features along with primary task features, and finetunes a few layers that receive the concatenated features as input for the final prediction. Furthermore, to gauge possible improvements over TS by increasing capacity, we consider a" + }, + { + "type": "image", + "bbox": [ + 0.544, + 0.092, + 0.848, + 0.244 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.245, + 0.892, + 0.287 + ], + "angle": 0, + "content": "Figure 4. Task Setup. We select a broad set of egocentric video tasks that focus on (a) human-object interactions and (b) human-human interactions from Ego4D benchmarks." + }, + { + "type": "table", + "bbox": [ + 0.531, + 0.302, + 0.866, + 0.419 + ], + "angle": 0, + "content": "
TaskBenchmarkMod.Duration (seconds)Model backbone
(a)PNRHOV8.0I3D RN-50 [6]
OSCCHOV8.0I3D RN-50 [6]
ARForecastingV8.0SlowFast [19]
LTAForecastingV16.0SlowFast [19]
(b)LAMSocialV0.23D RN-18 [57]
TTMSocialA&V2.73D RN-18 [57]
ASDAVA&V3.7TalkNet [56]
" + }, + { + "type": "table_caption", + "bbox": [ + 0.5, + 0.429, + 0.892, + 0.457 + ], + "angle": 0, + "content": "Table 1. Task Descriptions. 'Mod.' is short for modality; 'A' and 'V' denote audio and video, respectively." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.485, + 0.892, + 0.576 + ], + "angle": 0, + "content": "Finetuning [13] baseline, which finetunes a few layers on top of the features produced by the primary task model. In order to make a fair comparison, the first-stage training of these baselines is identical to that of EgoT2, and the number of parameters in the second stage of training is set to match that of EgoT2-s as closely as possible." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.577, + 0.892, + 0.698 + ], + "angle": 0, + "content": "For task-general translation (Sec. 4.3), the task translator is jointly optimized for all tasks within a cluster\\(^{3}\\), thus we have one task translator for human-object interactions that attends to all tasks simultaneously and one translator that performs three human-human interaction tasks at the same time. For comparison with EgoT2-g, we implement the most widely adopted multi-task learning approach, hard parameter sharing [51] (Figure 2(b))." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.698, + 0.892, + 0.865 + ], + "angle": 0, + "content": "Implementation Details. There is one video preprocessing step before the feature extraction step in Equation (1), where we transform the original video input from \\(\\mathbf{x}^{T_p}\\) to match the input format of the \\(k\\)-th task-specific model \\(f_k\\). In particular, \\(\\mathbf{x}^{T_p}\\) is first upsampled or downsampled to match the frame rates required by \\(f_k\\). Next, if the temporal span of the auxiliary task is smaller than that of the primary task, we slide \\(f_k\\) in a moving window to extract a sequence of features, where the window length is the temporal span required by \\(f_k\\), and stride size is a hyperparameter. Conversely, if \\(f_k\\) requires video inputs of a longer temporal span" + }, + { + "type": "page_footnote", + "bbox": [ + 0.078, + 0.875, + 0.468, + 0.9 + ], + "angle": 0, + "content": "2We use model checkpoints provided on the Ego4D website: https://github.com/EGO4D." + }, + { + "type": "page_footnote", + "bbox": [ + 0.5, + 0.875, + 0.892, + 0.901 + ], + "angle": 0, + "content": "3There is a significant domain gap between human-human and human-object interaction videos. See Appendix A.3 for cross-cluster EgoT2-g." + }, + { + "type": "page_number", + "bbox": [ + 0.482, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "2314" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.099, + 0.089, + 0.875, + 0.228 + ], + "angle": 0, + "content": "
\\( \\mathcal{T}_{p}\\text{ is PNR} \\)\\( \\mathcal{T}_{p}\\text{ is OSCC} \\)\\( \\mathcal{T}_{p}\\text{ is AR} \\)\\( \\mathcal{T}_{p}\\text{ is LTA} \\)
# Params \\( \\cdot 10^{6} \\) Trainable (All)Error (s) ↓# Params \\( \\cdot 10^{6} \\) Trainable (All)Acc. (%) ↑# Params \\( \\cdot 10^{6} \\) Trainable (All)Acc. (%) Verb(%) ↑ Noun# Params \\( \\cdot 10^{6} \\) Trainable (All)ED@20 ↓ VerbNoun
TS model [23]32.2 (32.2)0.61532.2 (32.2)68.2263.3 (63.3)22.1821.55180 (242)0.7460.789
Finetuning [13]8.4 (40.6)0.6118.4 (40.6)67.934.9 (66.8)21.6422.8448.6 (266)0.7440.787
Transfer [62] (PNR)N/AN/A8.4 (40.6)66.804.9 (37.1)19.985.4465.4 (97.6)0.7780.902
Transfer [62] (OSCC)8.4 (40.6)0.611N/AN/A4.9 (37.1)20.009.6165.4 (97.6)0.7740.899
Transfer [62] (AR)9.5 (71.4)0.6139.4 (71.4)70.98N/AN/AN/A53.3 (115)0.7450.806
LF [45] (All Tasks)9.6 (135)0.6109.6 (135)72.105.2 (131)21.1119.2483.6 (427)0.7440.788
EgoT2-s (All Tasks)6.4 (132)0.6107.4 (133)72.694.3 (130)23.0423.2841.8 (348)0.7310.769
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.239, + 0.892, + 0.324 + ], + "angle": 0, + "content": "Table 2. Results of EgoT2-s as we vary the primary human-object interaction task \\(\\mathcal{T}_p\\). First row records performance of the task-specific (TS) model we obtain in the first-stage training; we compare EgoT2-s with other baseline methods in the second-stage training. We list the number of trainable parameters for each separate stage as well as the total (i.e., trainable parameters plus parameters of frozen TS models) in parentheses. Following [23], the evaluation metric is temporal localization error (unit: seconds) for PNR, accuracy for OSCC and AR, and edit distance at future 20 time stamps (i.e., ED@20) for LTA. For localization error and ED@20, lower is better. EgoT2-s reliably adapts the auxiliary tasks to suit the target task." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.347, + 0.465, + 0.479 + ], + "angle": 0, + "content": "
\\( \\mathcal{T}_{p} \\) is TTM\\( \\mathcal{T}_{p} \\) is ASD
# Params \\( \\cdot 10^{6} \\) Trainable (All)mAP (%)↑# Params \\( \\cdot 10^{6} \\) Trainable (All)mAP (%)↑
TS model [23]20.2 (20.2)58.9115.7 (15.7)79.05
Finetuning [13]0.8 (20.8)59.671.1 (16.8)78.62
Transfer [62] (LAM)0.8 (15.4)63.591.6 (16.2)66.40
Transfer [62] (TTM)N/AN/A1.6 (21.6)71.06
Transfer [62] (ASD)0.8 (16.5)62.31N/AN/A
LF [45] (All Tasks)1.2 (51.5)64.291.6 (51.9)77.54
EgoT2-s (All Tasks)0.7 (51.1)66.541.5 (51.9)79.38
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.49, + 0.469, + 0.519 + ], + "angle": 0, + "content": "Table 3. Results of EgoT2-s as we vary the primary human-human interaction task \\(\\mathcal{T}_p\\). EgoT2-s consistently improves the TS model." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.545, + 0.469, + 0.697 + ], + "angle": 0, + "content": "than \\(\\mathbf{x}^{\\mathcal{T}_p}\\), we exclude task \\(k\\) from auxiliary task candidates to avoid providing potential advantages of a longer observation window to our framework as otherwise we need to expand video length of \\(\\mathbf{x}^{\\mathcal{T}_p}\\) to match the requirement of \\(f_{k}\\). Moreover, if the auxiliary task dataset is multimodal (i.e., video and audio) and the primary task involves only video, we apply the unimodal video pathway of \\(f_{k}\\) to obtain features; if the primary task is multimodal, we provide all task-specific features that are computable from these modalities. See Appendix A.2.2 for more implementation details." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.708, + 0.415, + 0.723 + ], + "angle": 0, + "content": "4.2. Evaluation of Task-Specific Translation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.731, + 0.469, + 0.793 + ], + "angle": 0, + "content": "Results. We conduct experiments with EgoT2-s for each task being the primary task4 and summarize the results for human-object interactions and human-human interactions in Table 2 and 3, respectively." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.793, + 0.469, + 0.853 + ], + "angle": 0, + "content": "From the two tables, we observe uneven performance by the baseline methods. Transfer and Late Fusion sometimes outperform the dedicated TS model and sometimes underperform it. When tasks do not exhibit a strong transfer rela" + }, + { + "type": "text", + "bbox": [ + 0.506, + 0.349, + 0.891, + 0.44 + ], + "angle": 0, + "content": "tion, reusing the backbone of the auxiliary task for the primary task leads to negative transfer and performance degradation. For instance, in Table 2, when \\(\\mathcal{T}_p\\) is AR, Transfer (OSCC) and Late Fusion both downgrade noun prediction accuracy, suggesting object state change is more dependent on verbs and unrelated to noun prediction tasks in AR." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.444, + 0.892, + 0.716 + ], + "angle": 0, + "content": "On the contrary, our proposed EgoT2-s learns to adaptively utilize task-specific features and effectively mitigates negative transfer, demonstrating consistent improvement over the TS model for all 6 cases. For instance, in Table 3, when \\(\\mathcal{T}_p\\) is ASD, Late Fusion indicates there is a deleterious relation from LAM and TTM to ASD, as it suffers from an accuracy degradation of \\(1.51\\%\\) over TS, yet EgoT2-s still obtains slightly better performance compared to TS (i.e., \\(79.38\\%\\) v.s. \\(79.05\\%\\)). Moreover, when auxiliary tasks are beneficial for the primary task, EgoT2-s outperforms all baselines with fewer trainable parameters. For example, when \\(\\mathcal{T}_p\\) is TTM, it achieves a \\(+7.63\\%\\) mAP improvement over the original TS model by training a lightweight task translator with only 0.7M parameters on top of it (TS is kept frozen). These results across different primary and auxiliary task combinations help demonstrate the generalizability of EgoT2-s. See Appendix A.3 for experiments using a subset of auxiliary tasks rather than all tasks." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Ablation Study. In Table 4, we ablate three different design choices of EgoT2-s using TTM as the primary task: (a) We replace the LAM and ASD TS models in EgoT2-s with two TTM models with different parameters. This yields a task fusion transformer that is architecturally identical to EgoT2-s but takes only TTM tokens as input; (b) We pass features produced by TS models after temporal pooling as the input of our task fusion transformer; (c) We do not freeze TS models in our second-stage training. By comparing (a) with our default configuration (d), we see that EgoT2-s indeed benefits from the introduction of auxiliary tasks. Although equipped with three different TTM models" + }, + { + "type": "page_footnote", + "bbox": [ + 0.076, + 0.863, + 0.469, + 0.901 + ], + "angle": 0, + "content": "4Following the time-span guidelines in Sec. 4.1, LAM is not considered as the primary task and LTA is not adopted as an auxiliary task. Nonetheless, Appendix A.3 shows some special cases for completeness." + }, + { + "type": "page_number", + "bbox": [ + 0.482, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "2315" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.084, + 0.089, + 0.465, + 0.174 + ], + "angle": 0, + "content": "
# Params ·106Trainable (All)Auxiliary TasksTemporal InformationFrozen TS modelmAP (%)↑
(a)0.7 (60.8)✓✓63.40
(b)0.7 (51.1)✓✓65.47
(c)51.1 (51.1)✓✓66.00
(d)0.7 (51.1)✓✓✓66.54
" + }, + { + "type": "table_caption", + "bbox": [ + 0.127, + 0.186, + 0.419, + 0.201 + ], + "angle": 0, + "content": "Table 4. Ablation study of EgoT2-s \\( \\left( {\\mathcal{T}}_{p}\\right. \\) is TTM)." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.216, + 0.467, + 0.3 + ], + "angle": 0, + "content": "
(a)# Params TrainablePNR ↓OSCC ↑AR Verb ↑AR Noun ↑LTA Verb ↑LTA Noun ↑
TS model [23]N/A0.61568.222.1821.5520.8221.80
Multi-task [51]32.20.61766.0N/AN/AN/AN/A
EgoT2-g (P & O)5.90.61268.6N/AN/AN/AN/A
EgoT2-g (All)34.50.61171.721.9322.7321.9123.61
" + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.32, + 0.466, + 0.394 + ], + "angle": 0, + "content": "
(b)# Params TrainableLAM mAP (%) ↑TTM mAP (%) ↑ASD Acc.(%) ↑
TS model [23]N/A77.7958.9179.05
Multi-task [51]20.260.5361.91N/A
EgoT2-g1.477.6364.4979.06
" + }, + { + "type": "table_footnote", + "bbox": [ + 0.076, + 0.405, + 0.468, + 0.488 + ], + "angle": 0, + "content": "Table 5. EgoT2-g for (a) human-object interaction and (b) human-human interaction tasks. The evaluation metric is error (seconds) for PNR (P) and accuracy (\\%) for OSCC (O), AR and LTA. We report the number of trainable parameters required for each method in the second-stage training (unit: million). Our model is flexible, accurate, and avoids negative transfer." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.517, + 0.468, + 0.653 + ], + "angle": 0, + "content": "and a larger model size (the total number of parameters of three TTM models is larger than the sum of three TS models), variant (a) does not bring as much performance gain as EgoT2-s (d). Also, preserving the temporal information of task-specific tokens further boosts performance, as can be seen in the comparison of EgoT2-s (b) with EgoT2-s (d). Finally, not freezing TS (c) greatly increases the training cost yet brings no performance gain. These results validate the design of our proposed EgoT2-s." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.665, + 0.418, + 0.68 + ], + "angle": 0, + "content": "4.3. Evaluation of Task-General Translation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.689, + 0.468, + 0.9 + ], + "angle": 0, + "content": "Results. Table 5 provides results of EgoT2-g. Since the TTM and LAM baseline models use identical video backbones (i.e., 3D ResNet-18), the hard parameter sharing multi-task baseline [51] can jointly learn TTM and LAM. Yet this model design is unable to solve the ASD task without further modifications to the ASD backbone model. In contrast, our EgoT2-g provides a flexible solution that can incorporate a heterogeneous mix of pretrained models. Similarly, we apply the multi-task baseline to PNR and OSCC, as they use the same video backbone (i.e., I3D ResNet-50). Compared with dedicated TS models, our proposed EgoT2-g performs task translation for all tasks at the same time and achieves on parallel or better performance for all tasks. For instance, it achieves \\(+5.58\\%\\) mAP im" + }, + { + "type": "table", + "bbox": [ + 0.541, + 0.089, + 0.852, + 0.44 + ], + "angle": 0, + "content": "
TTM ChallengemAP↑
Random Guess [23]0.50
3D ResNet-18 Bi-LSTM [23]0.54
EgoT2-g (3D ResNet-18)0.58
EgoT2-s (3D ResNet-18)0.58
PNR ChallengeError (s)↓
Always Center Frame [23]1.01
CNN LSTM [23]0.76
EgoVLP [40]0.67
Video Swin Transformer [16]0.66
SViT [4]0.66
EgoT2-s (I3D ResNet-50)0.66
OSCC ChallengeAcc. ↑
Always Positive [23]0.48
I3D ResNet-50 [23]0.68
Video Swin Transformer [16]0.68
Divided ST Attention [28]0.72
EgoVLP [40]0.74
EgoT2-g (I3D ResNet-50)0.70
EgoT2-s (I3D ResNet-50)0.71
EgoT2-s (EgoVLP)0.75
LTA ChallengeED@20↓
VerbNounAction
SlowFast + Transformer [23]0.740.780.94
Video + CLIP [10]0.740.770.94
Hierarchical MLP Mixer [46]0.740.740.93
EgoT2-s (SlowFast)0.720.760.93
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.451, + 0.892, + 0.493 + ], + "angle": 0, + "content": "Table 6. Comparison of EgoT2 with SOTA approaches on four Ego4D challenges (test set). We list the TS model architecture of EgoT2 in parentheses. Our model improves the state of the art." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.523, + 0.892, + 0.779 + ], + "angle": 0, + "content": "provement for TTM and \\(3.5\\%\\) accuracy gain for OSCC. Notably, on ASD, it retains the top-performance of the original TS models when the other two auxiliary tasks do not help. In contrast, we observe task competition for the multi-task baseline: the improvement for TTM (i.e., \\(+3.0\\%\\) mAP) is at the cost of significantly downgraded LAM performance (i.e., \\(-17.26\\%\\) mAP). Similarly, sharing an encoder for PNR and OSCC also leads to task competition and suboptimal performance for the multi-task baseline. For a side-by-side comparison, we also implement EgoT2-g that performs task translation for PNR and OSCC only and observe its advantages over the multi-task baseline in terms of both performance and trainable parameters. As EgoT2-g does not require re-training of the backbone, we can integrate any available model checkpoint developed for each individual task into our framework and train a lightweight task-general translator to further boost performance in the second stage." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.781, + 0.892, + 0.872 + ], + "angle": 0, + "content": "Comparison with SOTA Approaches. To further demonstrate the efficacy of both EgoT2-s and EgoT2-g, we submit our model to the EvalAI server to compare it with winning submissions to Ego4D-CVPR'22 and Ego4D-ECCV'22 challenges on the withheld test set. Table 6 shows the results.5 EgoT2-s achieves top performance for all 4 chal" + }, + { + "type": "page_footnote", + "bbox": [ + 0.516, + 0.887, + 0.89, + 0.9 + ], + "angle": 0, + "content": "ASD & AR are not applicable since they are not Ego4D challenges." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "2316" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.242 + ], + "angle": 0, + "content": "lenges. By only incorporating basic video backbones (e.g., 3D ResNet-18 and SlowFast) as the task-specific model, EgoT2-s achieves similar or better performance than works that adopt more powerful, novel architectures such as Video Swin Transformer. Moreover, the benefits of our approach are orthogonal to such architecture improvements: e.g., for the OSCC challenge, replacing the I3D ResNet-50 backbone with the one used in EgoVLP [40] can further elevate the accuracy of EgoVLP by \\(1\\%\\). This indicates the success of EgoT2 stems from its effective use of task synergies." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.243, + 0.473, + 0.424 + ], + "angle": 0, + "content": "While EgoT2-g is a strong performer that surpasses or matches TS across all tasks, if we compare its results with those of EgoT2-s, we observe that EgoT2-s demonstrates superior performance. This is understandable given that EgoT2-s is individually optimized for each primary task and employs a specialized translator. On the other hand, EgoT2-g provides a favorable unified framework that performs task translation for all tasks simultaneously via the design of a task-general translator. Thus, EgoT2-s serves as the framework of choice for top performance while EgoT2-g provides added flexibility. See Appendix A.3 for a detailed comparison of the performance and efficiency of these two variants." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.433, + 0.439, + 0.449 + ], + "angle": 0, + "content": "4.4. Visualization of Uncovered Task Relations" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.456, + 0.473, + 0.743 + ], + "angle": 0, + "content": "Our proposed EgoT2 explicitly models task relations via a task translator and offers good interpretability on task relations. For EgoT2-s, Figure 5 shows the attention weights of task tokens when the primary task is LTA and the auxiliary task is AR. Given two adjacent input video clips, the goal of LTA is to predict the next action (e.g., put container and turn off nozzle for the two examples here). In the upper example, there is a scene change from the first clip (the temporal segment corresponding to put wheel) to the second clip (the clip corresponding to take container). The attention weights of AR tokens are small for the first clip and large for the second clip. Clearly, the future action to predict is more closely related to the second temporal segment due to similarities in the scene and objects. In the lower example, the AR tokens have large attention weights, as the video is temporally similar and the previous two actions are indicative of the next action. These results show how EgoT2-s accurately characterizes temporal and auxiliary task information to improve the primary task. More visualizations are in Appendix A.4." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.743, + 0.473, + 0.879 + ], + "angle": 0, + "content": "Similarly, for EgoT2-g, we visualize its encoder-decoder attention weights from the last layer transformer in Figure 6. Given the same video clip as input, feature tokens are activated differently when EgoT2-g is given different task prompts, demonstrating that EgoT2-g learns to perform task translation conditioned on the task of interest. As it assigns small weights to task features that are not beneficial for the task of interest (e.g., PNR features to noun prediction tasks), EgoT2-g discards non-relevant task features to" + }, + { + "type": "image", + "bbox": [ + 0.507, + 0.092, + 0.895, + 0.248 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.259, + 0.895, + 0.316 + ], + "angle": 0, + "content": "Figure 5. Attention weights of EgoT2-s when \\(\\mathcal{T}_p\\) is LTA. EgoT2-s learns to utilize tokens from relevant temporal segments and tasks. The attention weights of AR tokens are large when the current action is indicative of future action." + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.328, + 0.885, + 0.466 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.475, + 0.895, + 0.517 + ], + "angle": 0, + "content": "Figure 6. Attention weights of EgoT2-g. Given the same video and different task prompts, EgoT2-g assigns different weights to different task tokens. See text." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.543, + 0.895, + 0.727 + ], + "angle": 0, + "content": "mitigate task competition. We also observe temporal differences of attention weights from same task features, indicating that EgoT2-g captures both inter-frame and inter-task dependencies to improve the task of interest. Finally, recall that in Figure 1, we derive task relations for 4 human-object interaction tasks via attention weights provided by EgoT2-g. The attention weights are temporally pooled and averaged over all validation data, revealing task relations from a global perspective. Results for human-human interaction tasks are presented in Appendix A.4. In all, EgoT2 provides good interpretability patterns on (1) which subset of tasks (2) which time segments lead to the final prediction." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.739, + 0.62, + 0.755 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.764, + 0.895, + 0.901 + ], + "angle": 0, + "content": "As a step towards unified egocentric perception, we propose EgoT2, a general and flexible design for task translation. EgoT2 consists of heterogeneous video models optimized for each individual task and a transformer-based task translator that captures inter-frame and inter-task relations. We propose EgoT2-s to improve one primary task and EgoT2-g to conduct task translation for all tasks simultaneously. Results on 7 diverse egocentric video tasks reveal valuable task relations and validate the proposed design." + }, + { + "type": "page_footnote", + "bbox": [ + 0.077, + 0.887, + 0.471, + 0.902 + ], + "angle": 0, + "content": "Results of EgoT2-g for PNR & LTA are unavailable (see Appendix A.2.2)." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.517, + 0.958 + ], + "angle": 0, + "content": "2317" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.116, + 0.47, + 0.184 + ], + "angle": 0, + "content": "[1] Anurag Arnab, Mostafa Dehghani, Georg Heigold, Chen Sun, Mario Lucic, and Cordelia Schmid. Vivit: A video vision transformer. 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Proceedings of the IEEE, 109(1):43-76, 2020. 2" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.956 + ], + "angle": 0, + "content": "2320" + } + ] +] \ No newline at end of file diff --git a/2023/Egocentric Video Task Translation/4f7e3293-877b-4c9b-8bc7-d95d33f4f800_origin.pdf b/2023/Egocentric Video Task Translation/4f7e3293-877b-4c9b-8bc7-d95d33f4f800_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..e7b5dee75a052e61ff401c06545d8a8d0297c560 --- /dev/null +++ b/2023/Egocentric Video Task Translation/4f7e3293-877b-4c9b-8bc7-d95d33f4f800_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:092c688743a25379401350307139e30e079d24ad5eeb9203c5244ab2d4f669b2 +size 9255352 diff --git a/2023/Egocentric Video Task Translation/full.md b/2023/Egocentric Video Task Translation/full.md new file mode 100644 index 0000000000000000000000000000000000000000..e79215cb018661603ccc4a827aa5b22487409ef9 --- /dev/null +++ b/2023/Egocentric Video Task Translation/full.md @@ -0,0 +1,287 @@ +# Egocentric Video Task Translation + +Zihui Xue $^{1,2*}$ Yale Song $^{2}$ Kristen Grauman $^{1,2}$ Lorenzo Torresani $^{2}$ $^{1}$ The University of Texas at Austin $\mathbf{\Pi}^{2}$ FAIR, Meta AI + +# Abstract + +Different video understanding tasks are typically treated in isolation, and even with distinct types of curated data (e.g., classifying sports in one dataset, tracking animals in another). However, in wearable cameras, the immersive egocentric perspective of a person engaging with the world around them presents an interconnected web of video understanding tasks—hand-object manipulations, navigation in the space, or human-human interactions—that unfold continuously, driven by the person's goals. We argue that this calls for a much more unified approach. We propose EgoTask Translation (EgoT2), which takes a collection of models optimized on separate tasks and learns to translate their outputs for improved performance on any or all of them at once. Unlike traditional transfer or multitask learning, EgoT2's "flipped design" entails separate task-specific backbones and a task translator shared across all tasks, which captures synergies between even heterogeneous tasks and mitigates task competition. Demonstrating our model on a wide array of video tasks from Ego4D, we show its advantages over existing transfer paradigms and achieve top-ranked results on four of the Ego4D 2022 benchmark challenges.1 + +# 1. Introduction + +In recent years, the introduction of large-scale video datasets (e.g., Kinetics [6, 33] and Something-Something [22]) have enabled the application of powerful deep learning models to video understanding and have led to dramatic advances. These third-person datasets, however, have overwhelmingly focused on the single task of action recognition in trimmed clips [12, 36, 47, 64]. Unlike curated third-person videos, our daily life involves frequent and heterogeneous interactions with other humans, objects, and environments in the wild. First-person videos from wearable cameras capture the observer's perspective and attention as a continuous stream. As such, + +![](images/b5b271b132e591b377d1e8cc3c22c24ae475f355ff3d4581540b36981925e3ca.jpg) + +![](images/2b89278c26fb7be9e5a83545df086154e56792574874c72d9ffa99da633a80c2.jpg) +Figure 1. Given a set of diverse egocentric video tasks, the proposed EgoT2 leverages synergies among the tasks to improve each individual task performance. The attention maps produced by EgoT2 offer good interpretability on inherent task relations. + +they are better equipped to reveal these multi-faceted, spontaneous interactions. Indeed egocentric datasets, such as EPIC-Kitchens [9] and Ego4D [23], provide suites of tasks associated with varied interactions. However, while these benchmarks have promoted a broader and more heterogeneous view of video understanding, they risk perpetuating the fragmented development of models specialized for each individual task. + +In this work, we argue that the egocentric perspective offers an opportunity for holistic perception that can beneficially leverage synergies among video tasks to solve all problems in a unified manner. See Figure 1. + +Imagine a cooking scenario where the camera wearer actively interacts with objects and other people in an environment while preparing dinner. These interactions relate to each other: a hand grasping a knife suggests the upcoming action of cutting; the view of a tomato on a cutting board suggests that the object is likely to undergo a state transition from whole to chopped; the conversation may further reveal the camera wearer's ongoing and planned actions. + +Apart from the natural relation among these tasks, egocentric video's partial observability (i.e., the camera wearer is largely out of the field of view) further motivates us to seek synergistic, comprehensive video understanding to leverage complementary cues among multiple tasks. + +Our goal presents several technical challenges for conventional transfer learning (TL) [65] and multi-task learning (MTL) [63]. First, MTL requires training sets where each sample includes annotations for all tasks [15, 24, 48, 53, 55, 62], which is often impractical. Second, egocentric video tasks are heterogeneous in nature, requiring different modalities (audio, visual, motion), diverse labels (e.g., temporal, spatial or semantic), and different temporal granularities (e.g., action anticipation requires long-term observations, but object state recognition operates at a few sparsely sampled frames)—all of which makes a unified model design problematic and fosters specialization. Finally, while existing work advocates the use of a shared encoder across tasks to learn general representations [3, 18, 26, 32, 39, 44, 45, 51], the diverse span of egocentric tasks poses a hazard to parameter sharing which can lead to negative transfer [21, 24, 38, 53]. + +To address the above limitations, we propose EgoTask Translation (EgoT2), a unified learning framework to address a diverse set of egocentric video tasks together. EgoT2 is flexible and general in that it can handle separate datasets for the different tasks; it takes video heterogeneity into account; and it mitigates negative transfer when tasks are not strongly related. To be specific, EgoT2 consists of specialized models developed for individual tasks and a task translator that explicitly models inter-task and inter-frame relations. We propose two distinct designs: (1) task-specific EgoT2 (EgoT2-s) optimizes a given primary task with the assistance of auxiliary tasks (Figure 2(c)) while (2) task-general EgoT2 (EgoT2-g) supports task translation for multiple tasks at the same time (Figure 2(d)). + +Compared with a unified backbone across tasks [62], adopting task-specific backbones preserves peculiarities of each task (e.g. different temporal granularities) and mitigates negative transfer since each backbone is optimized on one task. Furthermore, unlike traditional parameter sharing [51], the proposed task translator learns to "translate" all task features into predictions for the target task by selectively activating useful features and discarding irrelevant ones. The task translator also facilitates interpretability by explicitly revealing which temporal segments and which subsets of tasks contribute to improving a given task. + +We evaluate EgoT2 on a diverse set of 7 egocentric perception tasks from the world's largest egocentric video benchmark, Ego4D [23]. Its heterogeneous tasks extend beyond mere action recognition to speaker/listener identification, keyframe localization, object state change classification, long-term action anticipation, and others, and pro + +![](images/795fb7c3cf184832889bd4d85e9379d7b306cd8cd8a9817e67265ad08bf37fa0.jpg) +(a) conventional TL + +![](images/4a9b3708210c51290713fbe12e55f29e0a7b46733115a0b574700a9632dbc3f0.jpg) +(b) conventional MTL + +![](images/b157b4abb82ebc039fd5b25df5b1b776e6146a898172c763c14fa18a297cefcc.jpg) +(c) EgoT2-s + +![](images/7280d445f79bf6066aaae22514df428038a731ff1074d7f9dcbed2a4e729beb5.jpg) +(d) EgoT2-g +Figure 2. (a) Conventional TL uses a backbone pretrained on the source task followed by a head transferring supervision to the target task; (b) Traditional MTL consists of a shared backbone and several task-specific heads; (c) EgoT2-s adopts task-specific backbones and optimizes the task translator for a given primary task; (d) EgoT2-g jointly optimizes the task translator for all tasks. + +vide a perfect fit for our study. Our results reveal inherent task synergies, demonstrate consistent performance improvement across tasks, and offer good interpretability in task translation. Among all four Ego4D challenges involved in our task setup, EgoT2 outperforms all submissions to three Ego4D-CVPR'22 challenges and achieves state-of-the-art performance in one Ego4D-ECCV'22 challenge. + +# 2. Related Work + +Transfer Learning. TL [65] aims at transferring knowledge from a source domain to improve the performance in a target domain. The most widely adopted approach is to pretrain a model on a source task then finetune on the target task, as shown in Figure 2(a). Following this paradigm, many video classification models [1, 5, 42, 59] are initialized from models pretrained on ImageNet [11]. In addition, many works propose to transfer knowledge from a large-scale video dataset (e.g., Kinetics [6, 33]) to benefit action recognition in smaller-scale datasets [54] such as UCF-101 [52] and HMDB-51 [37] or to improve other video tasks, such as spatiotemporal action localization [2, 17, 19, 27, 49] and video anomaly detection [25, 41]. While this technique is ubiquitous in video understanding, prior approaches only consider the transfer from one single source task (dataset) and are thus unable to model the relations among multiple video tasks simultaneously. + +Taskonomy [62] presents task transfer with a thorough analysis on the structure of multiple visual tasks. Many works [15, 48, 53, 61] continue along this direction and explore visual task relations, yet they limit the discussion to + +static images and generally require a unified design across all tasks. In contrast, we consider a diverse set of egocentric video tasks, which are addressed with a heterogeneous set of task-specific video architectures (e.g., accommodating different time, space, or multimodality). Clearly, forcing the same network architecture across all tasks can be suboptimal for each individual task. This motivates our proposed EgoT2-s (Figure 2(c)), where we preserve the heterogeneous backbones developed for each task and build a task translator on top of the task-specific models. + +Multi-task Learning. In MTL [63], a single model is trained to address multiple tasks simultaneously in order to capture synergistic supervision across tasks. As depicted in Figure 2(b), hard parameter sharing [51] (i.e., sharing a backbone among tasks and keeping one separate head for each task) is the most commonly used technique within this genre. Although MTL has shown to be beneficial of video analysis [3, 18, 26, 32, 39, 44, 45], there is ongoing debate about the best strategies to determine what parameters to share across which tasks [7, 24, 31, 53, 55]. As pointed out in [34], when MTL is achieved by means of a single common backbone, the performance tends to decrease when the number of tasks grows beyond a certain point. Furthermore, many works [21, 24, 38, 53] observe that over-sharing a network across unrelated tasks causes negative transfer and hinders individual task performance. While soft parameter sharing [14, 60] mitigates this by retaining distinct copies of parameters, it still requires adopting the same identical architecture and "similar" weight values across all tasks. + +In the video domain, several works utilize synergies between related tasks (e.g., action recognition with gaze prediction [18, 26, 39] or body pose estimation [44]). However, when selected tasks are not strongly related, prior approaches that split the learning capacity of a shared backbone over multiple tasks can suffer from task competition and inferior performance. In the image domain, with the great advancement of transformers [58], training with multiple datasets together for a generalist model is gaining popularity. Recent work [8, 20, 29, 30, 35, 43] investigates a unified transformer architecture across a diverse set of tasks. Our variant EgoT2-g (Figure 2(d)) is motivated by the desiderata of shared knowledge encapsulated by MTL and of a generalist model. Unlike previous learning paradigms, we adopt a "flipped design" involving separate task-specific backbones and a task translator shared across all tasks. This effectively mitigates task competition and achieves task translation for all tasks simultaneously. + +# 3. Approach + +We are given $K$ video tasks, $\mathcal{T}_k$ for $k = 1,\dots ,K$ . We note that our approach does not require a common training set with annotations for all tasks. Let the dataset for task $\mathcal{T}_k$ be $\mathcal{D}^{\mathcal{T}_k} = \{(\mathbf{x}_i^{\mathcal{T}_k},y_i^{\mathcal{T}_k})\}_{i = 1}^{N_k}$ , where $(\mathbf{x}_i^{\mathcal{T}_k},y_i^{\mathcal{T}_k})$ denotes the + +$i$ -th pair of (input video, output label) and $N_{k}$ represents the number of given examples. Note that "labels" $y_{i}^{\mathcal{T}_{k}}$ can be a variety of output types, and are not limited to category labels. For simplicity we omit the subscript $i$ hereafter. + +We consider two formulations with distinct advantages: (1) task-specific translation, where we partition the tasks into one primary task $\mathcal{T}_p$ and $K - 1$ auxiliary tasks, and optimize the objective to improve performance on $\mathcal{T}_p$ with the assistance of the auxiliary tasks (EgoT2-s, Sec. 3.1); (2) task-general translation, where we treat all $K$ tasks equally, and the goal is to maximize the collective performance of all the tasks (EgoT2-g, Sec. 3.2). As demonstrated in our experiments, objective (1) leads to the strongest performance on the primary task, while objective (2) offers the benefit of a single unified model addressing all tasks at once. + +# 3.1. Task-Specific Translation: EgoT2-s + +The training of EgoT2-s is split over two stages. + +Stage I: Individual-Task Training. We train a separate model $f_{k}$ on each individual task dataset $\mathcal{D}^{\mathcal{T}_k}$ , obtaining $K$ task-specific models $\{f_k\}_{k = 1}^K$ . We do not place any restrictions on the task-specific model designs, nor do we require a unified design (i.e., identical encoder-decoder architecture) across tasks. Therefore, any available model checkpoint developed for task $\mathcal{T}_k$ can be adopted as $f_{k}$ within our framework, offering maximum flexibility. + +Stage II: Task-Specific Translation. We train a task translator that takes features produced by task-specific models as input and outputs predictions for the primary task. Formally, let $\mathbf{h}_k\in \mathbb{R}^{T_k\times D_k}$ be features produced by the $k$ -th task-specific model $f_{k}$ , where $T_{k}$ is the temporal dimension and $D_{k}$ is the per-frame feature dimension for model $f_{k}$ . Following the feature extraction step, we design a projection layer $\mathbf{P}_k\in \mathbb{R}^{D_k\times D}$ for each $f_{k}$ to map task-specific features to a shared latent feature space. This yields a temporal sequence of task-specific tokens $\tilde{\mathbf{h}}_k\in \mathbb{R}^{T_k\times D}$ . + +We process this collection of task-specific temporal sequences using a transformer encoder [58] of $L$ layers to capture both inter-frame and inter-task dependencies. We denote the propagation rule of layer $l$ by $\mathbf{z}^{l + 1} = \text{Encoder}^l (\mathbf{z}^l)$ . Finally, we adopt a decoder head $\text{Decoder}^{\mathcal{T}_p}$ to obtain predictions for the primary task $\mathcal{T}_p$ . + +In all, this stage has four major steps: (1) feature extraction; (2) feature projection; (3) transformer fusion; and (4) feature decoding. The procedure is summarized below: + +$$ +\mathbf {h} _ {k} = f _ {k} \left(\mathbf {x} ^ {\mathcal {T} _ {p}}\right), \quad \forall k \in \{1, 2, \dots , K \} \tag {1} +$$ + +$$ +\tilde {\mathbf {h}} _ {k} = \mathbf {P} _ {k} \mathbf {h} _ {k}, \quad \forall k \in \{1, 2, \dots , K \} \tag {2} +$$ + +$$ +\mathbf {z} ^ {0} = \left[ \tilde {\mathbf {h}} _ {1}, \tilde {\mathbf {h}} _ {2}, \dots , \tilde {\mathbf {h}} _ {K} \right] \tag {3} +$$ + +$$ +\mathbf {z} ^ {l + 1} = \operatorname {E n c o d e r} ^ {l} \left(\mathbf {z} ^ {l}\right), \forall l \in \{0, 1, \dots , L - 1 \} \tag {5} +$$ + +$$ +y _ {p r e d} ^ {\mathcal {T} _ {p}} = \operatorname {D e c o d e r} ^ {\mathcal {T} _ {p}} \left(\mathbf {z} ^ {L}\right) \tag {4} +$$ + +![](images/f1ad90441deaf649ac36d57c76df4e8d7b6767f2fdea9f6041ce6237ef1ae94a.jpg) +Figure 3. An illustration of EgoT2-s (left) and EgoT2-g (right) on three candidate tasks. The left figure illustrates EgoT2-s on three social interaction tasks, where the input to each model is unimodal (i.e., video) or multimodal (i.e., video and audio). The right figure shows the design of EgoT2-g on three example tasks that focus on different aspects of human-object interactions (i.e., localization, object state change classification, and action recognition). EgoT2-s learns to "translate" auxiliary task features into predictions for the primary task and EgoT2-g conducts task translation conditioned on the task of interest. + +![](images/72c9c09502c2b197044bee2c885e8554fcb91928d1c7ff2c8b1ef97ba9a9fd50.jpg) + +where $y_{pred}^{\mathcal{T}_p}$ denotes the prediction given by EgoT2-s. During the second stage of training, we freeze the task-specific models and optimize the task translator with respect to the primary task dataset $\mathcal{D}^{\mathcal{T}_p}$ . + +Figure 3 (left) illustrates the design of EgoT2-s using three social interaction tasks from Ego4D [23] as an example. EgoT2-s allows heterogeneity in the task-specific models (i.e., $f_{1}$ is unimodal while $f_{2}$ and $f_{3}$ are multimodal; also the three task-specific models can be associated with different frame rates and temporal durations) and utilizes a transformer encoder to model inter-frame and inter-task relations. The resulting EgoT2-s learns to adaptively utilize auxiliary task features for the primary task prediction. + +# 3.2. Task-General Translation: EgoT2-g + +EgoT2-s optimizes performance for a single primary task. Therefore, in the event all $K$ tasks must be addressed, it requires $K$ separate training runs and $K$ distinct translators. This motivates us to extend EgoT2-s to perform task translation for all $K$ tasks at once. In EgoT2-g, the task translator processes features from all $K$ tasks and learns to "translate" features conditioned on the task of interest. + +The first stage of EgoT2-g is identical to EgoT2-s. For the second stage, we propose two main modifications. First, we replace the task-specific decoder in EgoT2-s with a "generalist" decoder that outputs predictions conditioned on the task of interest. Natural language provides us with a flexible scheme to specify all tasks as a sequence of sym + +bols. Inspired by [8], we tokenize all task outputs and replace the original task-specific decoder with a sequence decoder [50] for a unified interface. Specifically, we first transform the original label $y^{\mathcal{T}_k}$ to a target output sequence $\mathbf{y}_{seq}^{\mathcal{T}_k} \in \mathbb{R}^M$ , where $M$ is the target sequence length. For the task translator to produce task-dependent outputs, we preprocess a task prompt token $\mathbf{y}_{prompt}$ to the target output, i.e., $\mathbf{y}_{seq_1}^{\mathcal{T}_k} = \mathbf{y}_{prompt}$ . We then let the sequence decoder generate a sentence answering the requested task. Figure 3 (right) illustrates how we express task outputs as sequences of discrete tokens and attach task prompts. + +With the transformed output, we treat the problem as a language modeling task and train the task translator to predict subsequent tokens (one token at a time) conditioned on the input video and its preceding tokens. The training objective is $\mathcal{L}^{\mathcal{T}_k} = \sum_{j=1}^{M} \mathbf{w}_j \log P(\mathbf{y}_{seq_j}^{\mathcal{T}_k} | \mathbf{x}^{\mathcal{T}_k}, \mathbf{y}_{seq_{1:j-1}}^{\mathcal{T}_k})$ . Note that the maximum likelihood loss is weighted to mask the loss corresponding to the task prompt token: $\mathbf{w}_j$ is set to 0 for $j = 1$ , and to 1 for any other $j$ . During inference, the task prompt is prepended, and the task translator predicts the remaining output tokens. We use argmax sampling (i.e., take the token with the largest likelihood) to sample tokens from the model likelihood and transform the output tokens back to the original label space. Detokenization is easy as we simply reverse the tokenization process. + +The second modification lies in the training strategy. While EgoT2-s adopts the primary task dataset for training, EgoT2-g requires joint training on all $K$ task datasets. Sim + +ilar to the training strategy in [8,20], we sample one batch from each task, compute the task loss, aggregate the $K$ gradients, and perform model updates in one training iteration. The final training objective is $\mathcal{L} = \sum_{k=1}^{K} \mathcal{L}^{\mathcal{T}_k}$ . + +Figure 3 contrasts the design of EgoT2-s and EgoT2-g. They both provide a flexible framework that can incorporate multiple heterogeneous task-specific models (e.g., the three example tasks we give here focus on different aspects of human-object interactions). With a design and an optimization that are specialized to a single primary task, EgoT2-s is expected to lead to superior individual task performance while EgoT2-g brings the efficiency and compactness benefits of a single translator addressing all tasks. + +# 4. Experiments + +# 4.1. Experimental Setup + +Dataset and Tasks. We evaluate on Ego4D [23], the world's largest egocentric dataset with 3,670 hours of videos spanning hundreds of scenarios (e.g., household, outdoor, leisure). It offers five benchmarks: episodic memory (EM), hands and objects (HO), audio-visual diarization (AV), social interactions (Social) and forecasting. For our study, we select 7 tasks spanning 4 benchmarks, representing a variety of tasks in egocentric perception, as illustrated in Figure 4. The 7 tasks fall into two broad clusters: (a) human-object interactions and (b) human-human interactions. Table 1 summarizes our task setup. For each cluster, we use tasks from the same benchmark as well as tasks across benchmarks, in an attempt to reveal connections among seemingly unrelated tasks. The 7 candidate tasks are heterogeneous in nature as they are defined on videos of varying duration, adopt different video models as backbones, and process unimodal (i.e., video) or multimodal (i.e., video and audio) input, offering a diverse task setup for our study. See Appendix A.2.1 for more details. + +Models and Baselines. For each task, we adopt for consistency the baseline models introduced with the Ego4D dataset $^2$ as the task-specific (TS) models in EgoT2. For task-specific translation (Sec. 4.2), we train one task translator for each primary task and use all the other tasks in the same cluster (either human-object interactions or human-human interactions) as auxiliary tasks. We compare EgoT2-s with two representative transfer learning approaches: (1) Transfer [62] denotes finetuning a transfer function on top of features produced by the auxiliary task models (Figure 2(a)). (2) Late Fusion [45] (LF) concatenates auxiliary task features along with primary task features, and finetunes a few layers that receive the concatenated features as input for the final prediction. Furthermore, to gauge possible improvements over TS by increasing capacity, we consider a + +![](images/ab8ce47a51b3bafe298cd6dbb23551881273556c5100cfb5f8be2c9b7f94fbb0.jpg) +Figure 4. Task Setup. We select a broad set of egocentric video tasks that focus on (a) human-object interactions and (b) human-human interactions from Ego4D benchmarks. + +
TaskBenchmarkMod.Duration (seconds)Model backbone
(a)PNRHOV8.0I3D RN-50 [6]
OSCCHOV8.0I3D RN-50 [6]
ARForecastingV8.0SlowFast [19]
LTAForecastingV16.0SlowFast [19]
(b)LAMSocialV0.23D RN-18 [57]
TTMSocialA&V2.73D RN-18 [57]
ASDAVA&V3.7TalkNet [56]
+ +Table 1. Task Descriptions. 'Mod.' is short for modality; 'A' and 'V' denote audio and video, respectively. + +Finetuning [13] baseline, which finetunes a few layers on top of the features produced by the primary task model. In order to make a fair comparison, the first-stage training of these baselines is identical to that of EgoT2, and the number of parameters in the second stage of training is set to match that of EgoT2-s as closely as possible. + +For task-general translation (Sec. 4.3), the task translator is jointly optimized for all tasks within a cluster $^{3}$ , thus we have one task translator for human-object interactions that attends to all tasks simultaneously and one translator that performs three human-human interaction tasks at the same time. For comparison with EgoT2-g, we implement the most widely adopted multi-task learning approach, hard parameter sharing [51] (Figure 2(b)). + +Implementation Details. There is one video preprocessing step before the feature extraction step in Equation (1), where we transform the original video input from $\mathbf{x}^{T_p}$ to match the input format of the $k$ -th task-specific model $f_k$ . In particular, $\mathbf{x}^{T_p}$ is first upsampled or downsampled to match the frame rates required by $f_k$ . Next, if the temporal span of the auxiliary task is smaller than that of the primary task, we slide $f_k$ in a moving window to extract a sequence of features, where the window length is the temporal span required by $f_k$ , and stride size is a hyperparameter. Conversely, if $f_k$ requires video inputs of a longer temporal span + +
\( \mathcal{T}_{p}\text{ is PNR} \)\( \mathcal{T}_{p}\text{ is OSCC} \)\( \mathcal{T}_{p}\text{ is AR} \)\( \mathcal{T}_{p}\text{ is LTA} \)
# Params \( \cdot 10^{6} \) Trainable (All)Error (s) ↓# Params \( \cdot 10^{6} \) Trainable (All)Acc. (%) ↑# Params \( \cdot 10^{6} \) Trainable (All)Acc. (%) Verb(%) ↑ Noun# Params \( \cdot 10^{6} \) Trainable (All)ED@20 ↓ VerbNoun
TS model [23]32.2 (32.2)0.61532.2 (32.2)68.2263.3 (63.3)22.1821.55180 (242)0.7460.789
Finetuning [13]8.4 (40.6)0.6118.4 (40.6)67.934.9 (66.8)21.6422.8448.6 (266)0.7440.787
Transfer [62] (PNR)N/AN/A8.4 (40.6)66.804.9 (37.1)19.985.4465.4 (97.6)0.7780.902
Transfer [62] (OSCC)8.4 (40.6)0.611N/AN/A4.9 (37.1)20.009.6165.4 (97.6)0.7740.899
Transfer [62] (AR)9.5 (71.4)0.6139.4 (71.4)70.98N/AN/AN/A53.3 (115)0.7450.806
LF [45] (All Tasks)9.6 (135)0.6109.6 (135)72.105.2 (131)21.1119.2483.6 (427)0.7440.788
EgoT2-s (All Tasks)6.4 (132)0.6107.4 (133)72.694.3 (130)23.0423.2841.8 (348)0.7310.769
+ +Table 2. Results of EgoT2-s as we vary the primary human-object interaction task $\mathcal{T}_p$ . First row records performance of the task-specific (TS) model we obtain in the first-stage training; we compare EgoT2-s with other baseline methods in the second-stage training. We list the number of trainable parameters for each separate stage as well as the total (i.e., trainable parameters plus parameters of frozen TS models) in parentheses. Following [23], the evaluation metric is temporal localization error (unit: seconds) for PNR, accuracy for OSCC and AR, and edit distance at future 20 time stamps (i.e., ED@20) for LTA. For localization error and ED@20, lower is better. EgoT2-s reliably adapts the auxiliary tasks to suit the target task. + +
\( \mathcal{T}_{p} \) is TTM\( \mathcal{T}_{p} \) is ASD
# Params \( \cdot 10^{6} \) Trainable (All)mAP (%)↑# Params \( \cdot 10^{6} \) Trainable (All)mAP (%)↑
TS model [23]20.2 (20.2)58.9115.7 (15.7)79.05
Finetuning [13]0.8 (20.8)59.671.1 (16.8)78.62
Transfer [62] (LAM)0.8 (15.4)63.591.6 (16.2)66.40
Transfer [62] (TTM)N/AN/A1.6 (21.6)71.06
Transfer [62] (ASD)0.8 (16.5)62.31N/AN/A
LF [45] (All Tasks)1.2 (51.5)64.291.6 (51.9)77.54
EgoT2-s (All Tasks)0.7 (51.1)66.541.5 (51.9)79.38
+ +Table 3. Results of EgoT2-s as we vary the primary human-human interaction task $\mathcal{T}_p$ . EgoT2-s consistently improves the TS model. + +than $\mathbf{x}^{\mathcal{T}_p}$ , we exclude task $k$ from auxiliary task candidates to avoid providing potential advantages of a longer observation window to our framework as otherwise we need to expand video length of $\mathbf{x}^{\mathcal{T}_p}$ to match the requirement of $f_{k}$ . Moreover, if the auxiliary task dataset is multimodal (i.e., video and audio) and the primary task involves only video, we apply the unimodal video pathway of $f_{k}$ to obtain features; if the primary task is multimodal, we provide all task-specific features that are computable from these modalities. See Appendix A.2.2 for more implementation details. + +# 4.2. Evaluation of Task-Specific Translation + +Results. We conduct experiments with EgoT2-s for each task being the primary task4 and summarize the results for human-object interactions and human-human interactions in Table 2 and 3, respectively. + +From the two tables, we observe uneven performance by the baseline methods. Transfer and Late Fusion sometimes outperform the dedicated TS model and sometimes underperform it. When tasks do not exhibit a strong transfer rela + +tion, reusing the backbone of the auxiliary task for the primary task leads to negative transfer and performance degradation. For instance, in Table 2, when $\mathcal{T}_p$ is AR, Transfer (OSCC) and Late Fusion both downgrade noun prediction accuracy, suggesting object state change is more dependent on verbs and unrelated to noun prediction tasks in AR. + +On the contrary, our proposed EgoT2-s learns to adaptively utilize task-specific features and effectively mitigates negative transfer, demonstrating consistent improvement over the TS model for all 6 cases. For instance, in Table 3, when $\mathcal{T}_p$ is ASD, Late Fusion indicates there is a deleterious relation from LAM and TTM to ASD, as it suffers from an accuracy degradation of $1.51\%$ over TS, yet EgoT2-s still obtains slightly better performance compared to TS (i.e., $79.38\%$ v.s. $79.05\%$ ). Moreover, when auxiliary tasks are beneficial for the primary task, EgoT2-s outperforms all baselines with fewer trainable parameters. For example, when $\mathcal{T}_p$ is TTM, it achieves a $+7.63\%$ mAP improvement over the original TS model by training a lightweight task translator with only 0.7M parameters on top of it (TS is kept frozen). These results across different primary and auxiliary task combinations help demonstrate the generalizability of EgoT2-s. See Appendix A.3 for experiments using a subset of auxiliary tasks rather than all tasks. + +Ablation Study. In Table 4, we ablate three different design choices of EgoT2-s using TTM as the primary task: (a) We replace the LAM and ASD TS models in EgoT2-s with two TTM models with different parameters. This yields a task fusion transformer that is architecturally identical to EgoT2-s but takes only TTM tokens as input; (b) We pass features produced by TS models after temporal pooling as the input of our task fusion transformer; (c) We do not freeze TS models in our second-stage training. By comparing (a) with our default configuration (d), we see that EgoT2-s indeed benefits from the introduction of auxiliary tasks. Although equipped with three different TTM models + +
# Params ·106Trainable (All)Auxiliary TasksTemporal InformationFrozen TS modelmAP (%)↑
(a)0.7 (60.8)✓✓63.40
(b)0.7 (51.1)✓✓65.47
(c)51.1 (51.1)✓✓66.00
(d)0.7 (51.1)✓✓✓66.54
+ +Table 4. Ablation study of EgoT2-s $\left( {\mathcal{T}}_{p}\right.$ is TTM). + +
(a)# Params TrainablePNR ↓OSCC ↑AR Verb ↑AR Noun ↑LTA Verb ↑LTA Noun ↑
TS model [23]N/A0.61568.222.1821.5520.8221.80
Multi-task [51]32.20.61766.0N/AN/AN/AN/A
EgoT2-g (P & O)5.90.61268.6N/AN/AN/AN/A
EgoT2-g (All)34.50.61171.721.9322.7321.9123.61
+ +
(b)# Params TrainableLAM mAP (%) ↑TTM mAP (%) ↑ASD Acc.(%) ↑
TS model [23]N/A77.7958.9179.05
Multi-task [51]20.260.5361.91N/A
EgoT2-g1.477.6364.4979.06
+ +Table 5. EgoT2-g for (a) human-object interaction and (b) human-human interaction tasks. The evaluation metric is error (seconds) for PNR (P) and accuracy (\%) for OSCC (O), AR and LTA. We report the number of trainable parameters required for each method in the second-stage training (unit: million). Our model is flexible, accurate, and avoids negative transfer. + +and a larger model size (the total number of parameters of three TTM models is larger than the sum of three TS models), variant (a) does not bring as much performance gain as EgoT2-s (d). Also, preserving the temporal information of task-specific tokens further boosts performance, as can be seen in the comparison of EgoT2-s (b) with EgoT2-s (d). Finally, not freezing TS (c) greatly increases the training cost yet brings no performance gain. These results validate the design of our proposed EgoT2-s. + +# 4.3. Evaluation of Task-General Translation + +Results. Table 5 provides results of EgoT2-g. Since the TTM and LAM baseline models use identical video backbones (i.e., 3D ResNet-18), the hard parameter sharing multi-task baseline [51] can jointly learn TTM and LAM. Yet this model design is unable to solve the ASD task without further modifications to the ASD backbone model. In contrast, our EgoT2-g provides a flexible solution that can incorporate a heterogeneous mix of pretrained models. Similarly, we apply the multi-task baseline to PNR and OSCC, as they use the same video backbone (i.e., I3D ResNet-50). Compared with dedicated TS models, our proposed EgoT2-g performs task translation for all tasks at the same time and achieves on parallel or better performance for all tasks. For instance, it achieves $+5.58\%$ mAP im + +
TTM ChallengemAP↑
Random Guess [23]0.50
3D ResNet-18 Bi-LSTM [23]0.54
EgoT2-g (3D ResNet-18)0.58
EgoT2-s (3D ResNet-18)0.58
PNR ChallengeError (s)↓
Always Center Frame [23]1.01
CNN LSTM [23]0.76
EgoVLP [40]0.67
Video Swin Transformer [16]0.66
SViT [4]0.66
EgoT2-s (I3D ResNet-50)0.66
OSCC ChallengeAcc. ↑
Always Positive [23]0.48
I3D ResNet-50 [23]0.68
Video Swin Transformer [16]0.68
Divided ST Attention [28]0.72
EgoVLP [40]0.74
EgoT2-g (I3D ResNet-50)0.70
EgoT2-s (I3D ResNet-50)0.71
EgoT2-s (EgoVLP)0.75
LTA ChallengeED@20↓
VerbNounAction
SlowFast + Transformer [23]0.740.780.94
Video + CLIP [10]0.740.770.94
Hierarchical MLP Mixer [46]0.740.740.93
EgoT2-s (SlowFast)0.720.760.93
+ +Table 6. Comparison of EgoT2 with SOTA approaches on four Ego4D challenges (test set). We list the TS model architecture of EgoT2 in parentheses. Our model improves the state of the art. + +provement for TTM and $3.5\%$ accuracy gain for OSCC. Notably, on ASD, it retains the top-performance of the original TS models when the other two auxiliary tasks do not help. In contrast, we observe task competition for the multi-task baseline: the improvement for TTM (i.e., $+3.0\%$ mAP) is at the cost of significantly downgraded LAM performance (i.e., $-17.26\%$ mAP). Similarly, sharing an encoder for PNR and OSCC also leads to task competition and suboptimal performance for the multi-task baseline. For a side-by-side comparison, we also implement EgoT2-g that performs task translation for PNR and OSCC only and observe its advantages over the multi-task baseline in terms of both performance and trainable parameters. As EgoT2-g does not require re-training of the backbone, we can integrate any available model checkpoint developed for each individual task into our framework and train a lightweight task-general translator to further boost performance in the second stage. + +Comparison with SOTA Approaches. To further demonstrate the efficacy of both EgoT2-s and EgoT2-g, we submit our model to the EvalAI server to compare it with winning submissions to Ego4D-CVPR'22 and Ego4D-ECCV'22 challenges on the withheld test set. Table 6 shows the results.5 EgoT2-s achieves top performance for all 4 chal + +lenges. By only incorporating basic video backbones (e.g., 3D ResNet-18 and SlowFast) as the task-specific model, EgoT2-s achieves similar or better performance than works that adopt more powerful, novel architectures such as Video Swin Transformer. Moreover, the benefits of our approach are orthogonal to such architecture improvements: e.g., for the OSCC challenge, replacing the I3D ResNet-50 backbone with the one used in EgoVLP [40] can further elevate the accuracy of EgoVLP by $1\%$ . This indicates the success of EgoT2 stems from its effective use of task synergies. + +While EgoT2-g is a strong performer that surpasses or matches TS across all tasks, if we compare its results with those of EgoT2-s, we observe that EgoT2-s demonstrates superior performance. This is understandable given that EgoT2-s is individually optimized for each primary task and employs a specialized translator. On the other hand, EgoT2-g provides a favorable unified framework that performs task translation for all tasks simultaneously via the design of a task-general translator. Thus, EgoT2-s serves as the framework of choice for top performance while EgoT2-g provides added flexibility. See Appendix A.3 for a detailed comparison of the performance and efficiency of these two variants. + +# 4.4. Visualization of Uncovered Task Relations + +Our proposed EgoT2 explicitly models task relations via a task translator and offers good interpretability on task relations. For EgoT2-s, Figure 5 shows the attention weights of task tokens when the primary task is LTA and the auxiliary task is AR. Given two adjacent input video clips, the goal of LTA is to predict the next action (e.g., put container and turn off nozzle for the two examples here). In the upper example, there is a scene change from the first clip (the temporal segment corresponding to put wheel) to the second clip (the clip corresponding to take container). The attention weights of AR tokens are small for the first clip and large for the second clip. Clearly, the future action to predict is more closely related to the second temporal segment due to similarities in the scene and objects. In the lower example, the AR tokens have large attention weights, as the video is temporally similar and the previous two actions are indicative of the next action. These results show how EgoT2-s accurately characterizes temporal and auxiliary task information to improve the primary task. More visualizations are in Appendix A.4. + +Similarly, for EgoT2-g, we visualize its encoder-decoder attention weights from the last layer transformer in Figure 6. Given the same video clip as input, feature tokens are activated differently when EgoT2-g is given different task prompts, demonstrating that EgoT2-g learns to perform task translation conditioned on the task of interest. As it assigns small weights to task features that are not beneficial for the task of interest (e.g., PNR features to noun prediction tasks), EgoT2-g discards non-relevant task features to + +![](images/b829f891dbb03b2a701e6f428f3778642ced2e999762364fa3a299fc06929b30.jpg) +Figure 5. Attention weights of EgoT2-s when $\mathcal{T}_p$ is LTA. EgoT2-s learns to utilize tokens from relevant temporal segments and tasks. The attention weights of AR tokens are large when the current action is indicative of future action. + +![](images/16f622391e69b04c03db4202704d36c390297a2f2ec98a1eb6178e415964433c.jpg) +Figure 6. Attention weights of EgoT2-g. Given the same video and different task prompts, EgoT2-g assigns different weights to different task tokens. See text. + +mitigate task competition. We also observe temporal differences of attention weights from same task features, indicating that EgoT2-g captures both inter-frame and inter-task dependencies to improve the task of interest. Finally, recall that in Figure 1, we derive task relations for 4 human-object interaction tasks via attention weights provided by EgoT2-g. The attention weights are temporally pooled and averaged over all validation data, revealing task relations from a global perspective. Results for human-human interaction tasks are presented in Appendix A.4. In all, EgoT2 provides good interpretability patterns on (1) which subset of tasks (2) which time segments lead to the final prediction. + +# 5. Conclusion + +As a step towards unified egocentric perception, we propose EgoT2, a general and flexible design for task translation. EgoT2 consists of heterogeneous video models optimized for each individual task and a transformer-based task translator that captures inter-frame and inter-task relations. We propose EgoT2-s to improve one primary task and EgoT2-g to conduct task translation for all tasks simultaneously. Results on 7 diverse egocentric video tasks reveal valuable task relations and validate the proposed design. + +# References + +[1] Anurag Arnab, Mostafa Dehghani, Georg Heigold, Chen Sun, Mario Lucic, and Cordelia Schmid. Vivit: A video vision transformer. 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However, in wearable cameras, the immersive egocentric perspective of a person engaging with the world around them presents an interconnected web of video understanding tasks—hand-object manipulations, navigation in the space, or human-human interactions—that unfold continuously, driven by the person's goals. We argue that this calls for a much more unified approach. We propose EgoTask Translation (EgoT2), which takes a collection of models optimized on separate tasks and learns to translate their outputs for improved performance on any or all of them at once. Unlike traditional transfer or multitask learning, EgoT2's \"flipped design\" entails separate task-specific backbones and a task translator shared across all tasks, which captures synergies between even heterogeneous tasks and mitigates task competition. Demonstrating our model on a wide array of video tasks from Ego4D, we show its advantages over existing transfer paradigms and achieve top-ranked results on four of the Ego4D 2022 benchmark challenges.1" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 511, + 128, + 523 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 511, + 128, + 523 + ], + "spans": [ + { + "bbox": [ + 47, + 511, + 128, + 523 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 532, + 287, + 676 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 532, + 287, + 676 + ], + "spans": [ + { + "bbox": [ + 46, + 532, + 287, + 676 + ], + "type": "text", + "content": "In recent years, the introduction of large-scale video datasets (e.g., Kinetics [6, 33] and Something-Something [22]) have enabled the application of powerful deep learning models to video understanding and have led to dramatic advances. These third-person datasets, however, have overwhelmingly focused on the single task of action recognition in trimmed clips [12, 36, 47, 64]. Unlike curated third-person videos, our daily life involves frequent and heterogeneous interactions with other humans, objects, and environments in the wild. First-person videos from wearable cameras capture the observer's perspective and attention as a continuous stream. As such," + } + ] + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 309, + 198, + 545, + 296 + ], + "blocks": [ + { + "bbox": [ + 309, + 198, + 545, + 296 + ], + "lines": [ + { + "bbox": [ + 309, + 198, + 545, + 296 + ], + "spans": [ + { + "bbox": [ + 309, + 198, + 545, + 296 + ], + "type": "image", + "image_path": "b5b271b132e591b377d1e8cc3c22c24ae475f355ff3d4581540b36981925e3ca.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 318, + 303, + 541, + 396 + ], + "blocks": [ + { + "bbox": [ + 318, + 303, + 541, + 396 + ], + "lines": [ + { + "bbox": [ + 318, + 303, + 541, + 396 + ], + "spans": [ + { + "bbox": [ + 318, + 303, + 541, + 396 + ], + "type": "image", + "image_path": "2b89278c26fb7be9e5a83545df086154e56792574874c72d9ffa99da633a80c2.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 407, + 547, + 453 + ], + "lines": [ + { + "bbox": [ + 305, + 407, + 547, + 453 + ], + "spans": [ + { + "bbox": [ + 305, + 407, + 547, + 453 + ], + "type": "text", + "content": "Figure 1. Given a set of diverse egocentric video tasks, the proposed EgoT2 leverages synergies among the tasks to improve each individual task performance. The attention maps produced by EgoT2 offer good interpretability on inherent task relations." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 474, + 545, + 568 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 474, + 545, + 568 + ], + "spans": [ + { + "bbox": [ + 304, + 474, + 545, + 568 + ], + "type": "text", + "content": "they are better equipped to reveal these multi-faceted, spontaneous interactions. Indeed egocentric datasets, such as EPIC-Kitchens [9] and Ego4D [23], provide suites of tasks associated with varied interactions. However, while these benchmarks have promoted a broader and more heterogeneous view of video understanding, they risk perpetuating the fragmented development of models specialized for each individual task." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 570, + 545, + 617 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 545, + 617 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 545, + 617 + ], + "type": "text", + "content": "In this work, we argue that the egocentric perspective offers an opportunity for holistic perception that can beneficially leverage synergies among video tasks to solve all problems in a unified manner. See Figure 1." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 618, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 618, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 618, + 546, + 713 + ], + "type": "text", + "content": "Imagine a cooking scenario where the camera wearer actively interacts with objects and other people in an environment while preparing dinner. These interactions relate to each other: a hand grasping a knife suggests the upcoming action of cutting; the view of a tomato on a cutting board suggests that the object is likely to undergo a state transition from whole to chopped; the conversation may further reveal the camera wearer's ongoing and planned actions." + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 683, + 226, + 693 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 683, + 226, + 693 + ], + "spans": [ + { + "bbox": [ + 58, + 683, + 226, + 693 + ], + "type": "text", + "content": "*Work done during an internship at FAIR, Meta AI." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 59, + 693, + 286, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 693, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 59, + 693, + 286, + 713 + ], + "type": "text", + "content": "1Project webpage: https://vision.cs.utexas.edu/ ojects/egot2/." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "2310" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 133 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 133 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 133 + ], + "type": "text", + "content": "Apart from the natural relation among these tasks, egocentric video's partial observability (i.e., the camera wearer is largely out of the field of view) further motivates us to seek synergistic, comprehensive video understanding to leverage complementary cues among multiple tasks." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 134, + 288, + 337 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 134, + 288, + 337 + ], + "spans": [ + { + "bbox": [ + 46, + 134, + 288, + 337 + ], + "type": "text", + "content": "Our goal presents several technical challenges for conventional transfer learning (TL) [65] and multi-task learning (MTL) [63]. First, MTL requires training sets where each sample includes annotations for all tasks [15, 24, 48, 53, 55, 62], which is often impractical. Second, egocentric video tasks are heterogeneous in nature, requiring different modalities (audio, visual, motion), diverse labels (e.g., temporal, spatial or semantic), and different temporal granularities (e.g., action anticipation requires long-term observations, but object state recognition operates at a few sparsely sampled frames)—all of which makes a unified model design problematic and fosters specialization. Finally, while existing work advocates the use of a shared encoder across tasks to learn general representations [3, 18, 26, 32, 39, 44, 45, 51], the diverse span of egocentric tasks poses a hazard to parameter sharing which can lead to negative transfer [21, 24, 38, 53]." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 339, + 287, + 506 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 339, + 287, + 506 + ], + "spans": [ + { + "bbox": [ + 46, + 339, + 287, + 506 + ], + "type": "text", + "content": "To address the above limitations, we propose EgoTask Translation (EgoT2), a unified learning framework to address a diverse set of egocentric video tasks together. EgoT2 is flexible and general in that it can handle separate datasets for the different tasks; it takes video heterogeneity into account; and it mitigates negative transfer when tasks are not strongly related. To be specific, EgoT2 consists of specialized models developed for individual tasks and a task translator that explicitly models inter-task and inter-frame relations. We propose two distinct designs: (1) task-specific EgoT2 (EgoT2-s) optimizes a given primary task with the assistance of auxiliary tasks (Figure 2(c)) while (2) task-general EgoT2 (EgoT2-g) supports task translation for multiple tasks at the same time (Figure 2(d))." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 509, + 288, + 640 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 509, + 288, + 640 + ], + "spans": [ + { + "bbox": [ + 46, + 509, + 288, + 640 + ], + "type": "text", + "content": "Compared with a unified backbone across tasks [62], adopting task-specific backbones preserves peculiarities of each task (e.g. different temporal granularities) and mitigates negative transfer since each backbone is optimized on one task. Furthermore, unlike traditional parameter sharing [51], the proposed task translator learns to \"translate\" all task features into predictions for the target task by selectively activating useful features and discarding irrelevant ones. The task translator also facilitates interpretability by explicitly revealing which temporal segments and which subsets of tasks contribute to improving a given task." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 642, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 642, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 642, + 287, + 714 + ], + "type": "text", + "content": "We evaluate EgoT2 on a diverse set of 7 egocentric perception tasks from the world's largest egocentric video benchmark, Ego4D [23]. Its heterogeneous tasks extend beyond mere action recognition to speaker/listener identification, keyframe localization, object state change classification, long-term action anticipation, and others, and pro" + } + ] + } + ], + "index": 4 + }, + { + "type": "image", + "bbox": [ + 307, + 72, + 423, + 142 + ], + "blocks": [ + { + "bbox": [ + 307, + 72, + 423, + 142 + ], + "lines": [ + { + "bbox": [ + 307, + 72, + 423, + 142 + ], + "spans": [ + { + "bbox": [ + 307, + 72, + 423, + 142 + ], + "type": "image", + "image_path": "795fb7c3cf184832889bd4d85e9379d7b306cd8cd8a9817e67265ad08bf37fa0.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 332, + 146, + 394, + 155 + ], + "lines": [ + { + "bbox": [ + 332, + 146, + 394, + 155 + ], + "spans": [ + { + "bbox": [ + 332, + 146, + 394, + 155 + ], + "type": "text", + "content": "(a) conventional TL" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_caption" + } + ], + "index": 5 + }, + { + "type": "image", + "bbox": [ + 443, + 72, + 533, + 142 + ], + "blocks": [ + { + "bbox": [ + 443, + 72, + 533, + 142 + ], + "lines": [ + { + "bbox": [ + 443, + 72, + 533, + 142 + ], + "spans": [ + { + "bbox": [ + 443, + 72, + 533, + 142 + ], + "type": "image", + "image_path": "4a9b3708210c51290713fbe12e55f29e0a7b46733115a0b574700a9632dbc3f0.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 453, + 146, + 522, + 155 + ], + "lines": [ + { + "bbox": [ + 453, + 146, + 522, + 155 + ], + "spans": [ + { + "bbox": [ + 453, + 146, + 522, + 155 + ], + "type": "text", + "content": "(b) conventional MTL" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_caption" + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 307, + 163, + 421, + 237 + ], + "blocks": [ + { + "bbox": [ + 307, + 163, + 421, + 237 + ], + "lines": [ + { + "bbox": [ + 307, + 163, + 421, + 237 + ], + "spans": [ + { + "bbox": [ + 307, + 163, + 421, + 237 + ], + "type": "image", + "image_path": "b157b4abb82ebc039fd5b25df5b1b776e6146a898172c763c14fa18a297cefcc.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 343, + 240, + 381, + 249 + ], + "lines": [ + { + "bbox": [ + 343, + 240, + 381, + 249 + ], + "spans": [ + { + "bbox": [ + 343, + 240, + 381, + 249 + ], + "type": "text", + "content": "(c) EgoT2-s" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 432, + 163, + 546, + 237 + ], + "blocks": [ + { + "bbox": [ + 432, + 163, + 546, + 237 + ], + "lines": [ + { + "bbox": [ + 432, + 163, + 546, + 237 + ], + "spans": [ + { + "bbox": [ + 432, + 163, + 546, + 237 + ], + "type": "image", + "image_path": "7280d445f79bf6066aaae22514df428038a731ff1074d7f9dcbed2a4e729beb5.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 470, + 240, + 509, + 249 + ], + "lines": [ + { + "bbox": [ + 470, + 240, + 509, + 249 + ], + "spans": [ + { + "bbox": [ + 470, + 240, + 509, + 249 + ], + "type": "text", + "content": "(d) EgoT2-g" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 304, + 258, + 546, + 325 + ], + "lines": [ + { + "bbox": [ + 304, + 258, + 546, + 325 + ], + "spans": [ + { + "bbox": [ + 304, + 258, + 546, + 325 + ], + "type": "text", + "content": "Figure 2. (a) Conventional TL uses a backbone pretrained on the source task followed by a head transferring supervision to the target task; (b) Traditional MTL consists of a shared backbone and several task-specific heads; (c) EgoT2-s adopts task-specific backbones and optimizes the task translator for a given primary task; (d) EgoT2-g jointly optimizes the task translator for all tasks." + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_caption" + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 346, + 545, + 430 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 346, + 545, + 430 + ], + "spans": [ + { + "bbox": [ + 304, + 346, + 545, + 430 + ], + "type": "text", + "content": "vide a perfect fit for our study. Our results reveal inherent task synergies, demonstrate consistent performance improvement across tasks, and offer good interpretability in task translation. Among all four Ego4D challenges involved in our task setup, EgoT2 outperforms all submissions to three Ego4D-CVPR'22 challenges and achieves state-of-the-art performance in one Ego4D-ECCV'22 challenge." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 441, + 392, + 453 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 441, + 392, + 453 + ], + "spans": [ + { + "bbox": [ + 306, + 441, + 392, + 453 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 461, + 545, + 665 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 461, + 545, + 665 + ], + "spans": [ + { + "bbox": [ + 304, + 461, + 545, + 665 + ], + "type": "text", + "content": "Transfer Learning. TL [65] aims at transferring knowledge from a source domain to improve the performance in a target domain. The most widely adopted approach is to pretrain a model on a source task then finetune on the target task, as shown in Figure 2(a). Following this paradigm, many video classification models [1, 5, 42, 59] are initialized from models pretrained on ImageNet [11]. In addition, many works propose to transfer knowledge from a large-scale video dataset (e.g., Kinetics [6, 33]) to benefit action recognition in smaller-scale datasets [54] such as UCF-101 [52] and HMDB-51 [37] or to improve other video tasks, such as spatiotemporal action localization [2, 17, 19, 27, 49] and video anomaly detection [25, 41]. While this technique is ubiquitous in video understanding, prior approaches only consider the transfer from one single source task (dataset) and are thus unable to model the relations among multiple video tasks simultaneously." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "content": "Taskonomy [62] presents task transfer with a thorough analysis on the structure of multiple visual tasks. Many works [15, 48, 53, 61] continue along this direction and explore visual task relations, yet they limit the discussion to" + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "type": "text", + "content": "2311" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 191 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 191 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 191 + ], + "type": "text", + "content": "static images and generally require a unified design across all tasks. In contrast, we consider a diverse set of egocentric video tasks, which are addressed with a heterogeneous set of task-specific video architectures (e.g., accommodating different time, space, or multimodality). Clearly, forcing the same network architecture across all tasks can be suboptimal for each individual task. This motivates our proposed EgoT2-s (Figure 2(c)), where we preserve the heterogeneous backbones developed for each task and build a task translator on top of the task-specific models." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 191, + 289, + 418 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 191, + 289, + 418 + ], + "spans": [ + { + "bbox": [ + 46, + 191, + 289, + 418 + ], + "type": "text", + "content": "Multi-task Learning. In MTL [63], a single model is trained to address multiple tasks simultaneously in order to capture synergistic supervision across tasks. As depicted in Figure 2(b), hard parameter sharing [51] (i.e., sharing a backbone among tasks and keeping one separate head for each task) is the most commonly used technique within this genre. Although MTL has shown to be beneficial of video analysis [3, 18, 26, 32, 39, 44, 45], there is ongoing debate about the best strategies to determine what parameters to share across which tasks [7, 24, 31, 53, 55]. As pointed out in [34], when MTL is achieved by means of a single common backbone, the performance tends to decrease when the number of tasks grows beyond a certain point. Furthermore, many works [21, 24, 38, 53] observe that over-sharing a network across unrelated tasks causes negative transfer and hinders individual task performance. While soft parameter sharing [14, 60] mitigates this by retaining distinct copies of parameters, it still requires adopting the same identical architecture and \"similar\" weight values across all tasks." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 419, + 289, + 635 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 419, + 289, + 635 + ], + "spans": [ + { + "bbox": [ + 46, + 419, + 289, + 635 + ], + "type": "text", + "content": "In the video domain, several works utilize synergies between related tasks (e.g., action recognition with gaze prediction [18, 26, 39] or body pose estimation [44]). However, when selected tasks are not strongly related, prior approaches that split the learning capacity of a shared backbone over multiple tasks can suffer from task competition and inferior performance. In the image domain, with the great advancement of transformers [58], training with multiple datasets together for a generalist model is gaining popularity. Recent work [8, 20, 29, 30, 35, 43] investigates a unified transformer architecture across a diverse set of tasks. Our variant EgoT2-g (Figure 2(d)) is motivated by the desiderata of shared knowledge encapsulated by MTL and of a generalist model. Unlike previous learning paradigms, we adopt a \"flipped design\" involving separate task-specific backbones and a task translator shared across all tasks. This effectively mitigates task competition and achieves task translation for all tasks simultaneously." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 646, + 114, + 659 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 646, + 114, + 659 + ], + "spans": [ + { + "bbox": [ + 47, + 646, + 114, + 659 + ], + "type": "text", + "content": "3. Approach" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "text", + "content": "We are given " + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "text", + "content": " video tasks, " + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\mathcal{T}_k" + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "text", + "content": " for " + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "inline_equation", + "content": "k = 1,\\dots ,K" + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "text", + "content": ". We note that our approach does not require a common training set with annotations for all tasks. Let the dataset for task " + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\mathcal{T}_k" + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "text", + "content": " be " + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\mathcal{D}^{\\mathcal{T}_k} = \\{(\\mathbf{x}_i^{\\mathcal{T}_k},y_i^{\\mathcal{T}_k})\\}_{i = 1}^{N_k}" + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "inline_equation", + "content": "(\\mathbf{x}_i^{\\mathcal{T}_k},y_i^{\\mathcal{T}_k})" + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "text", + "content": " denotes the" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "text", + "content": "-th pair of (input video, output label) and " + }, + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "inline_equation", + "content": "N_{k}" + }, + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "text", + "content": " represents the number of given examples. Note that \"labels\" " + }, + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "inline_equation", + "content": "y_{i}^{\\mathcal{T}_{k}}" + }, + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "text", + "content": " can be a variety of output types, and are not limited to category labels. For simplicity we omit the subscript " + }, + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "text", + "content": " hereafter." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 121, + 547, + 252 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 121, + 547, + 252 + ], + "spans": [ + { + "bbox": [ + 304, + 121, + 547, + 252 + ], + "type": "text", + "content": "We consider two formulations with distinct advantages: (1) task-specific translation, where we partition the tasks into one primary task " + }, + { + "bbox": [ + 304, + 121, + 547, + 252 + ], + "type": "inline_equation", + "content": "\\mathcal{T}_p" + }, + { + "bbox": [ + 304, + 121, + 547, + 252 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 121, + 547, + 252 + ], + "type": "inline_equation", + "content": "K - 1" + }, + { + "bbox": [ + 304, + 121, + 547, + 252 + ], + "type": "text", + "content": " auxiliary tasks, and optimize the objective to improve performance on " + }, + { + "bbox": [ + 304, + 121, + 547, + 252 + ], + "type": "inline_equation", + "content": "\\mathcal{T}_p" + }, + { + "bbox": [ + 304, + 121, + 547, + 252 + ], + "type": "text", + "content": " with the assistance of the auxiliary tasks (EgoT2-s, Sec. 3.1); (2) task-general translation, where we treat all " + }, + { + "bbox": [ + 304, + 121, + 547, + 252 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 304, + 121, + 547, + 252 + ], + "type": "text", + "content": " tasks equally, and the goal is to maximize the collective performance of all the tasks (EgoT2-g, Sec. 3.2). As demonstrated in our experiments, objective (1) leads to the strongest performance on the primary task, while objective (2) offers the benefit of a single unified model addressing all tasks at once." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 305, + 258, + 494, + 270 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 258, + 494, + 270 + ], + "spans": [ + { + "bbox": [ + 305, + 258, + 494, + 270 + ], + "type": "text", + "content": "3.1. Task-Specific Translation: EgoT2-s" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 317, + 276, + 513, + 288 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 276, + 513, + 288 + ], + "spans": [ + { + "bbox": [ + 317, + 276, + 513, + 288 + ], + "type": "text", + "content": "The training of EgoT2-s is split over two stages." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 288, + 545, + 384 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 288, + 545, + 384 + ], + "spans": [ + { + "bbox": [ + 304, + 288, + 545, + 384 + ], + "type": "text", + "content": "Stage I: Individual-Task Training. We train a separate model " + }, + { + "bbox": [ + 304, + 288, + 545, + 384 + ], + "type": "inline_equation", + "content": "f_{k}" + }, + { + "bbox": [ + 304, + 288, + 545, + 384 + ], + "type": "text", + "content": " on each individual task dataset " + }, + { + "bbox": [ + 304, + 288, + 545, + 384 + ], + "type": "inline_equation", + "content": "\\mathcal{D}^{\\mathcal{T}_k}" + }, + { + "bbox": [ + 304, + 288, + 545, + 384 + ], + "type": "text", + "content": ", obtaining " + }, + { + "bbox": [ + 304, + 288, + 545, + 384 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 304, + 288, + 545, + 384 + ], + "type": "text", + "content": " task-specific models " + }, + { + "bbox": [ + 304, + 288, + 545, + 384 + ], + "type": "inline_equation", + "content": "\\{f_k\\}_{k = 1}^K" + }, + { + "bbox": [ + 304, + 288, + 545, + 384 + ], + "type": "text", + "content": ". We do not place any restrictions on the task-specific model designs, nor do we require a unified design (i.e., identical encoder-decoder architecture) across tasks. Therefore, any available model checkpoint developed for task " + }, + { + "bbox": [ + 304, + 288, + 545, + 384 + ], + "type": "inline_equation", + "content": "\\mathcal{T}_k" + }, + { + "bbox": [ + 304, + 288, + 545, + 384 + ], + "type": "text", + "content": " can be adopted as " + }, + { + "bbox": [ + 304, + 288, + 545, + 384 + ], + "type": "inline_equation", + "content": "f_{k}" + }, + { + "bbox": [ + 304, + 288, + 545, + 384 + ], + "type": "text", + "content": " within our framework, offering maximum flexibility." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 384, + 545, + 503 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 384, + 545, + 503 + ], + "spans": [ + { + "bbox": [ + 304, + 384, + 545, + 503 + ], + "type": "text", + "content": "Stage II: Task-Specific Translation. We train a task translator that takes features produced by task-specific models as input and outputs predictions for the primary task. Formally, let " + }, + { + "bbox": [ + 304, + 384, + 545, + 503 + ], + "type": "inline_equation", + "content": "\\mathbf{h}_k\\in \\mathbb{R}^{T_k\\times D_k}" + }, + { + "bbox": [ + 304, + 384, + 545, + 503 + ], + "type": "text", + "content": " be features produced by the " + }, + { + "bbox": [ + 304, + 384, + 545, + 503 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 304, + 384, + 545, + 503 + ], + "type": "text", + "content": " -th task-specific model " + }, + { + "bbox": [ + 304, + 384, + 545, + 503 + ], + "type": "inline_equation", + "content": "f_{k}" + }, + { + "bbox": [ + 304, + 384, + 545, + 503 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 384, + 545, + 503 + ], + "type": "inline_equation", + "content": "T_{k}" + }, + { + "bbox": [ + 304, + 384, + 545, + 503 + ], + "type": "text", + "content": " is the temporal dimension and " + }, + { + "bbox": [ + 304, + 384, + 545, + 503 + ], + "type": "inline_equation", + "content": "D_{k}" + }, + { + "bbox": [ + 304, + 384, + 545, + 503 + ], + "type": "text", + "content": " is the per-frame feature dimension for model " + }, + { + "bbox": [ + 304, + 384, + 545, + 503 + ], + "type": "inline_equation", + "content": "f_{k}" + }, + { + "bbox": [ + 304, + 384, + 545, + 503 + ], + "type": "text", + "content": ". Following the feature extraction step, we design a projection layer " + }, + { + "bbox": [ + 304, + 384, + 545, + 503 + ], + "type": "inline_equation", + "content": "\\mathbf{P}_k\\in \\mathbb{R}^{D_k\\times D}" + }, + { + "bbox": [ + 304, + 384, + 545, + 503 + ], + "type": "text", + "content": " for each " + }, + { + "bbox": [ + 304, + 384, + 545, + 503 + ], + "type": "inline_equation", + "content": "f_{k}" + }, + { + "bbox": [ + 304, + 384, + 545, + 503 + ], + "type": "text", + "content": " to map task-specific features to a shared latent feature space. This yields a temporal sequence of task-specific tokens " + }, + { + "bbox": [ + 304, + 384, + 545, + 503 + ], + "type": "inline_equation", + "content": "\\tilde{\\mathbf{h}}_k\\in \\mathbb{R}^{T_k\\times D}" + }, + { + "bbox": [ + 304, + 384, + 545, + 503 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 503, + 545, + 576 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 503, + 545, + 576 + ], + "spans": [ + { + "bbox": [ + 304, + 503, + 545, + 576 + ], + "type": "text", + "content": "We process this collection of task-specific temporal sequences using a transformer encoder [58] of " + }, + { + "bbox": [ + 304, + 503, + 545, + 576 + ], + "type": "inline_equation", + "content": "L" + }, + { + "bbox": [ + 304, + 503, + 545, + 576 + ], + "type": "text", + "content": " layers to capture both inter-frame and inter-task dependencies. We denote the propagation rule of layer " + }, + { + "bbox": [ + 304, + 503, + 545, + 576 + ], + "type": "inline_equation", + "content": "l" + }, + { + "bbox": [ + 304, + 503, + 545, + 576 + ], + "type": "text", + "content": " by " + }, + { + "bbox": [ + 304, + 503, + 545, + 576 + ], + "type": "inline_equation", + "content": "\\mathbf{z}^{l + 1} = \\text{Encoder}^l (\\mathbf{z}^l)" + }, + { + "bbox": [ + 304, + 503, + 545, + 576 + ], + "type": "text", + "content": ". Finally, we adopt a decoder head " + }, + { + "bbox": [ + 304, + 503, + 545, + 576 + ], + "type": "inline_equation", + "content": "\\text{Decoder}^{\\mathcal{T}_p}" + }, + { + "bbox": [ + 304, + 503, + 545, + 576 + ], + "type": "text", + "content": " to obtain predictions for the primary task " + }, + { + "bbox": [ + 304, + 503, + 545, + 576 + ], + "type": "inline_equation", + "content": "\\mathcal{T}_p" + }, + { + "bbox": [ + 304, + 503, + 545, + 576 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 575, + 545, + 611 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 575, + 545, + 611 + ], + "spans": [ + { + "bbox": [ + 304, + 575, + 545, + 611 + ], + "type": "text", + "content": "In all, this stage has four major steps: (1) feature extraction; (2) feature projection; (3) transformer fusion; and (4) feature decoding. The procedure is summarized below:" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 339, + 628, + 545, + 642 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 339, + 628, + 545, + 642 + ], + "spans": [ + { + "bbox": [ + 339, + 628, + 545, + 642 + ], + "type": "interline_equation", + "content": "\\mathbf {h} _ {k} = f _ {k} \\left(\\mathbf {x} ^ {\\mathcal {T} _ {p}}\\right), \\quad \\forall k \\in \\{1, 2, \\dots , K \\} \\tag {1}", + "image_path": "294a7247029acb2799115253acefc39972d0c48b88af4196b34d63be17cc9e07.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 340, + 644, + 545, + 658 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 340, + 644, + 545, + 658 + ], + "spans": [ + { + "bbox": [ + 340, + 644, + 545, + 658 + ], + "type": "interline_equation", + "content": "\\tilde {\\mathbf {h}} _ {k} = \\mathbf {P} _ {k} \\mathbf {h} _ {k}, \\quad \\forall k \\in \\{1, 2, \\dots , K \\} \\tag {2}", + "image_path": "250987483b43ede28e87147f574b0d63969d5e4569d4f2448a590c08e53b5d07.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 342, + 662, + 545, + 682 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 342, + 662, + 545, + 682 + ], + "spans": [ + { + "bbox": [ + 342, + 662, + 545, + 682 + ], + "type": "interline_equation", + "content": "\\mathbf {z} ^ {0} = \\left[ \\tilde {\\mathbf {h}} _ {1}, \\tilde {\\mathbf {h}} _ {2}, \\dots , \\tilde {\\mathbf {h}} _ {K} \\right] \\tag {3}", + "image_path": "00e99569d6a9535244c1a775c67f30d313eb3e759e08534703cb959a686655ea.jpg" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 333, + 677, + 545, + 692 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 333, + 677, + 545, + 692 + ], + "spans": [ + { + "bbox": [ + 333, + 677, + 545, + 692 + ], + "type": "interline_equation", + "content": "\\mathbf {z} ^ {l + 1} = \\operatorname {E n c o d e r} ^ {l} \\left(\\mathbf {z} ^ {l}\\right), \\forall l \\in \\{0, 1, \\dots , L - 1 \\} \\tag {5}", + "image_path": "2af03a705677d5cf66a905d76adca58ae4d81e24eb2d672f3ec3645aff672571.jpg" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 330, + 694, + 545, + 712 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 330, + 694, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 330, + 694, + 545, + 712 + ], + "type": "interline_equation", + "content": "y _ {p r e d} ^ {\\mathcal {T} _ {p}} = \\operatorname {D e c o d e r} ^ {\\mathcal {T} _ {p}} \\left(\\mathbf {z} ^ {L}\\right) \\tag {4}", + "image_path": "15de620721380e17e442d047f610558ad0dab657683084f07fa34cf28d35baf3.jpg" + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "text", + "content": "2312" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 47, + 70, + 272, + 289 + ], + "blocks": [ + { + "bbox": [ + 47, + 70, + 272, + 289 + ], + "lines": [ + { + "bbox": [ + 47, + 70, + 272, + 289 + ], + "spans": [ + { + "bbox": [ + 47, + 70, + 272, + 289 + ], + "type": "image", + "image_path": "f1ad90441deaf649ac36d57c76df4e8d7b6767f2fdea9f6041ce6237ef1ae94a.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 300, + 547, + 357 + ], + "lines": [ + { + "bbox": [ + 46, + 300, + 547, + 357 + ], + "spans": [ + { + "bbox": [ + 46, + 300, + 547, + 357 + ], + "type": "text", + "content": "Figure 3. An illustration of EgoT2-s (left) and EgoT2-g (right) on three candidate tasks. The left figure illustrates EgoT2-s on three social interaction tasks, where the input to each model is unimodal (i.e., video) or multimodal (i.e., video and audio). The right figure shows the design of EgoT2-g on three example tasks that focus on different aspects of human-object interactions (i.e., localization, object state change classification, and action recognition). EgoT2-s learns to \"translate\" auxiliary task features into predictions for the primary task and EgoT2-g conducts task translation conditioned on the task of interest." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 277, + 70, + 527, + 291 + ], + "blocks": [ + { + "bbox": [ + 277, + 70, + 527, + 291 + ], + "lines": [ + { + "bbox": [ + 277, + 70, + 527, + 291 + ], + "spans": [ + { + "bbox": [ + 277, + 70, + 527, + 291 + ], + "type": "image", + "image_path": "72c9c09502c2b197044bee2c885e8554fcb91928d1c7ff2c8b1ef97ba9a9fd50.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 374, + 287, + 424 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 374, + 287, + 424 + ], + "spans": [ + { + "bbox": [ + 46, + 374, + 287, + 424 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 374, + 287, + 424 + ], + "type": "inline_equation", + "content": "y_{pred}^{\\mathcal{T}_p}" + }, + { + "bbox": [ + 46, + 374, + 287, + 424 + ], + "type": "text", + "content": " denotes the prediction given by EgoT2-s. During the second stage of training, we freeze the task-specific models and optimize the task translator with respect to the primary task dataset " + }, + { + "bbox": [ + 46, + 374, + 287, + 424 + ], + "type": "inline_equation", + "content": "\\mathcal{D}^{\\mathcal{T}_p}" + }, + { + "bbox": [ + 46, + 374, + 287, + 424 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 425, + 288, + 534 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 425, + 288, + 534 + ], + "spans": [ + { + "bbox": [ + 46, + 425, + 288, + 534 + ], + "type": "text", + "content": "Figure 3 (left) illustrates the design of EgoT2-s using three social interaction tasks from Ego4D [23] as an example. EgoT2-s allows heterogeneity in the task-specific models (i.e., " + }, + { + "bbox": [ + 46, + 425, + 288, + 534 + ], + "type": "inline_equation", + "content": "f_{1}" + }, + { + "bbox": [ + 46, + 425, + 288, + 534 + ], + "type": "text", + "content": " is unimodal while " + }, + { + "bbox": [ + 46, + 425, + 288, + 534 + ], + "type": "inline_equation", + "content": "f_{2}" + }, + { + "bbox": [ + 46, + 425, + 288, + 534 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 425, + 288, + 534 + ], + "type": "inline_equation", + "content": "f_{3}" + }, + { + "bbox": [ + 46, + 425, + 288, + 534 + ], + "type": "text", + "content": " are multimodal; also the three task-specific models can be associated with different frame rates and temporal durations) and utilizes a transformer encoder to model inter-frame and inter-task relations. The resulting EgoT2-s learns to adaptively utilize auxiliary task features for the primary task prediction." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 539, + 239, + 553 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 539, + 239, + 553 + ], + "spans": [ + { + "bbox": [ + 47, + 539, + 239, + 553 + ], + "type": "text", + "content": "3.2. Task-General Translation: EgoT2-g" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 557, + 287, + 641 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 557, + 287, + 641 + ], + "spans": [ + { + "bbox": [ + 46, + 557, + 287, + 641 + ], + "type": "text", + "content": "EgoT2-s optimizes performance for a single primary task. Therefore, in the event all " + }, + { + "bbox": [ + 46, + 557, + 287, + 641 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 46, + 557, + 287, + 641 + ], + "type": "text", + "content": " tasks must be addressed, it requires " + }, + { + "bbox": [ + 46, + 557, + 287, + 641 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 46, + 557, + 287, + 641 + ], + "type": "text", + "content": " separate training runs and " + }, + { + "bbox": [ + 46, + 557, + 287, + 641 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 46, + 557, + 287, + 641 + ], + "type": "text", + "content": " distinct translators. This motivates us to extend EgoT2-s to perform task translation for all " + }, + { + "bbox": [ + 46, + 557, + 287, + 641 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 46, + 557, + 287, + 641 + ], + "type": "text", + "content": " tasks at once. In EgoT2-g, the task translator processes features from all " + }, + { + "bbox": [ + 46, + 557, + 287, + 641 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 46, + 557, + 287, + 641 + ], + "type": "text", + "content": " tasks and learns to \"translate\" features conditioned on the task of interest." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 642, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 642, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 642, + 288, + 715 + ], + "type": "text", + "content": "The first stage of EgoT2-g is identical to EgoT2-s. For the second stage, we propose two main modifications. First, we replace the task-specific decoder in EgoT2-s with a \"generalist\" decoder that outputs predictions conditioned on the task of interest. Natural language provides us with a flexible scheme to specify all tasks as a sequence of sym" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 376, + 545, + 509 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 376, + 545, + 509 + ], + "spans": [ + { + "bbox": [ + 304, + 376, + 545, + 509 + ], + "type": "text", + "content": "bols. Inspired by [8], we tokenize all task outputs and replace the original task-specific decoder with a sequence decoder [50] for a unified interface. Specifically, we first transform the original label " + }, + { + "bbox": [ + 304, + 376, + 545, + 509 + ], + "type": "inline_equation", + "content": "y^{\\mathcal{T}_k}" + }, + { + "bbox": [ + 304, + 376, + 545, + 509 + ], + "type": "text", + "content": " to a target output sequence " + }, + { + "bbox": [ + 304, + 376, + 545, + 509 + ], + "type": "inline_equation", + "content": "\\mathbf{y}_{seq}^{\\mathcal{T}_k} \\in \\mathbb{R}^M" + }, + { + "bbox": [ + 304, + 376, + 545, + 509 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 376, + 545, + 509 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 304, + 376, + 545, + 509 + ], + "type": "text", + "content": " is the target sequence length. For the task translator to produce task-dependent outputs, we preprocess a task prompt token " + }, + { + "bbox": [ + 304, + 376, + 545, + 509 + ], + "type": "inline_equation", + "content": "\\mathbf{y}_{prompt}" + }, + { + "bbox": [ + 304, + 376, + 545, + 509 + ], + "type": "text", + "content": " to the target output, i.e., " + }, + { + "bbox": [ + 304, + 376, + 545, + 509 + ], + "type": "inline_equation", + "content": "\\mathbf{y}_{seq_1}^{\\mathcal{T}_k} = \\mathbf{y}_{prompt}" + }, + { + "bbox": [ + 304, + 376, + 545, + 509 + ], + "type": "text", + "content": ". We then let the sequence decoder generate a sentence answering the requested task. Figure 3 (right) illustrates how we express task outputs as sequences of discrete tokens and attach task prompts." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 509, + 546, + 676 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 509, + 546, + 676 + ], + "spans": [ + { + "bbox": [ + 304, + 509, + 546, + 676 + ], + "type": "text", + "content": "With the transformed output, we treat the problem as a language modeling task and train the task translator to predict subsequent tokens (one token at a time) conditioned on the input video and its preceding tokens. The training objective is " + }, + { + "bbox": [ + 304, + 509, + 546, + 676 + ], + "type": "inline_equation", + "content": "\\mathcal{L}^{\\mathcal{T}_k} = \\sum_{j=1}^{M} \\mathbf{w}_j \\log P(\\mathbf{y}_{seq_j}^{\\mathcal{T}_k} | \\mathbf{x}^{\\mathcal{T}_k}, \\mathbf{y}_{seq_{1:j-1}}^{\\mathcal{T}_k})" + }, + { + "bbox": [ + 304, + 509, + 546, + 676 + ], + "type": "text", + "content": ". Note that the maximum likelihood loss is weighted to mask the loss corresponding to the task prompt token: " + }, + { + "bbox": [ + 304, + 509, + 546, + 676 + ], + "type": "inline_equation", + "content": "\\mathbf{w}_j" + }, + { + "bbox": [ + 304, + 509, + 546, + 676 + ], + "type": "text", + "content": " is set to 0 for " + }, + { + "bbox": [ + 304, + 509, + 546, + 676 + ], + "type": "inline_equation", + "content": "j = 1" + }, + { + "bbox": [ + 304, + 509, + 546, + 676 + ], + "type": "text", + "content": ", and to 1 for any other " + }, + { + "bbox": [ + 304, + 509, + 546, + 676 + ], + "type": "inline_equation", + "content": "j" + }, + { + "bbox": [ + 304, + 509, + 546, + 676 + ], + "type": "text", + "content": ". During inference, the task prompt is prepended, and the task translator predicts the remaining output tokens. We use argmax sampling (i.e., take the token with the largest likelihood) to sample tokens from the model likelihood and transform the output tokens back to the original label space. Detokenization is easy as we simply reverse the tokenization process." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 677, + 545, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 677, + 545, + 715 + ], + "spans": [ + { + "bbox": [ + 305, + 677, + 545, + 715 + ], + "type": "text", + "content": "The second modification lies in the training strategy. While EgoT2-s adopts the primary task dataset for training, EgoT2-g requires joint training on all " + }, + { + "bbox": [ + 305, + 677, + 545, + 715 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 305, + 677, + 545, + 715 + ], + "type": "text", + "content": " task datasets. Sim" + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 758 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 758 + ], + "type": "text", + "content": "2313" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 120 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 120 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 120 + ], + "type": "text", + "content": "ilar to the training strategy in [8,20], we sample one batch from each task, compute the task loss, aggregate the " + }, + { + "bbox": [ + 46, + 72, + 287, + 120 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 46, + 72, + 287, + 120 + ], + "type": "text", + "content": " gradients, and perform model updates in one training iteration. The final training objective is " + }, + { + "bbox": [ + 46, + 72, + 287, + 120 + ], + "type": "inline_equation", + "content": "\\mathcal{L} = \\sum_{k=1}^{K} \\mathcal{L}^{\\mathcal{T}_k}" + }, + { + "bbox": [ + 46, + 72, + 287, + 120 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 121, + 288, + 228 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 121, + 288, + 228 + ], + "spans": [ + { + "bbox": [ + 46, + 121, + 288, + 228 + ], + "type": "text", + "content": "Figure 3 contrasts the design of EgoT2-s and EgoT2-g. They both provide a flexible framework that can incorporate multiple heterogeneous task-specific models (e.g., the three example tasks we give here focus on different aspects of human-object interactions). With a design and an optimization that are specialized to a single primary task, EgoT2-s is expected to lead to superior individual task performance while EgoT2-g brings the efficiency and compactness benefits of a single translator addressing all tasks." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 239, + 128, + 253 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 239, + 128, + 253 + ], + "spans": [ + { + "bbox": [ + 47, + 239, + 128, + 253 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 259, + 163, + 272 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 259, + 163, + 272 + ], + "spans": [ + { + "bbox": [ + 47, + 259, + 163, + 272 + ], + "type": "text", + "content": "4.1. Experimental Setup" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 277, + 287, + 505 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 277, + 287, + 505 + ], + "spans": [ + { + "bbox": [ + 46, + 277, + 287, + 505 + ], + "type": "text", + "content": "Dataset and Tasks. We evaluate on Ego4D [23], the world's largest egocentric dataset with 3,670 hours of videos spanning hundreds of scenarios (e.g., household, outdoor, leisure). It offers five benchmarks: episodic memory (EM), hands and objects (HO), audio-visual diarization (AV), social interactions (Social) and forecasting. For our study, we select 7 tasks spanning 4 benchmarks, representing a variety of tasks in egocentric perception, as illustrated in Figure 4. The 7 tasks fall into two broad clusters: (a) human-object interactions and (b) human-human interactions. Table 1 summarizes our task setup. For each cluster, we use tasks from the same benchmark as well as tasks across benchmarks, in an attempt to reveal connections among seemingly unrelated tasks. The 7 candidate tasks are heterogeneous in nature as they are defined on videos of varying duration, adopt different video models as backbones, and process unimodal (i.e., video) or multimodal (i.e., video and audio) input, offering a diverse task setup for our study. See Appendix A.2.1 for more details." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 506, + 288, + 685 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 506, + 288, + 685 + ], + "spans": [ + { + "bbox": [ + 46, + 506, + 288, + 685 + ], + "type": "text", + "content": "Models and Baselines. For each task, we adopt for consistency the baseline models introduced with the Ego4D dataset" + }, + { + "bbox": [ + 46, + 506, + 288, + 685 + ], + "type": "inline_equation", + "content": "^2" + }, + { + "bbox": [ + 46, + 506, + 288, + 685 + ], + "type": "text", + "content": " as the task-specific (TS) models in EgoT2. For task-specific translation (Sec. 4.2), we train one task translator for each primary task and use all the other tasks in the same cluster (either human-object interactions or human-human interactions) as auxiliary tasks. We compare EgoT2-s with two representative transfer learning approaches: (1) Transfer [62] denotes finetuning a transfer function on top of features produced by the auxiliary task models (Figure 2(a)). (2) Late Fusion [45] (LF) concatenates auxiliary task features along with primary task features, and finetunes a few layers that receive the concatenated features as input for the final prediction. Furthermore, to gauge possible improvements over TS by increasing capacity, we consider a" + } + ] + } + ], + "index": 5 + }, + { + "type": "image", + "bbox": [ + 332, + 72, + 518, + 193 + ], + "blocks": [ + { + "bbox": [ + 332, + 72, + 518, + 193 + ], + "lines": [ + { + "bbox": [ + 332, + 72, + 518, + 193 + ], + "spans": [ + { + "bbox": [ + 332, + 72, + 518, + 193 + ], + "type": "image", + "image_path": "ab8ce47a51b3bafe298cd6dbb23551881273556c5100cfb5f8be2c9b7f94fbb0.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 194, + 545, + 227 + ], + "lines": [ + { + "bbox": [ + 305, + 194, + 545, + 227 + ], + "spans": [ + { + "bbox": [ + 305, + 194, + 545, + 227 + ], + "type": "text", + "content": "Figure 4. Task Setup. We select a broad set of egocentric video tasks that focus on (a) human-object interactions and (b) human-human interactions from Ego4D benchmarks." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_caption" + } + ], + "index": 6 + }, + { + "type": "table", + "bbox": [ + 324, + 239, + 529, + 331 + ], + "blocks": [ + { + "bbox": [ + 324, + 239, + 529, + 331 + ], + "lines": [ + { + "bbox": [ + 324, + 239, + 529, + 331 + ], + "spans": [ + { + "bbox": [ + 324, + 239, + 529, + 331 + ], + "type": "table", + "html": "
TaskBenchmarkMod.Duration (seconds)Model backbone
(a)PNRHOV8.0I3D RN-50 [6]
OSCCHOV8.0I3D RN-50 [6]
ARForecastingV8.0SlowFast [19]
LTAForecastingV16.0SlowFast [19]
(b)LAMSocialV0.23D RN-18 [57]
TTMSocialA&V2.73D RN-18 [57]
ASDAVA&V3.7TalkNet [56]
", + "image_path": "e071d4258890b77a02ce81b6293412265469de22daed7d880436a5a4f700d2e5.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "table_body" + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 339, + 545, + 361 + ], + "lines": [ + { + "bbox": [ + 306, + 339, + 545, + 361 + ], + "spans": [ + { + "bbox": [ + 306, + 339, + 545, + 361 + ], + "type": "text", + "content": "Table 1. Task Descriptions. 'Mod.' is short for modality; 'A' and 'V' denote audio and video, respectively." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 304, + 384, + 545, + 456 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 384, + 545, + 456 + ], + "spans": [ + { + "bbox": [ + 304, + 384, + 545, + 456 + ], + "type": "text", + "content": "Finetuning [13] baseline, which finetunes a few layers on top of the features produced by the primary task model. In order to make a fair comparison, the first-stage training of these baselines is identical to that of EgoT2, and the number of parameters in the second stage of training is set to match that of EgoT2-s as closely as possible." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 456, + 545, + 552 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 456, + 545, + 552 + ], + "spans": [ + { + "bbox": [ + 304, + 456, + 545, + 552 + ], + "type": "text", + "content": "For task-general translation (Sec. 4.3), the task translator is jointly optimized for all tasks within a cluster" + }, + { + "bbox": [ + 304, + 456, + 545, + 552 + ], + "type": "inline_equation", + "content": "^{3}" + }, + { + "bbox": [ + 304, + 456, + 545, + 552 + ], + "type": "text", + "content": ", thus we have one task translator for human-object interactions that attends to all tasks simultaneously and one translator that performs three human-human interaction tasks at the same time. For comparison with EgoT2-g, we implement the most widely adopted multi-task learning approach, hard parameter sharing [51] (Figure 2(b))." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 552, + 545, + 685 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 552, + 545, + 685 + ], + "spans": [ + { + "bbox": [ + 304, + 552, + 545, + 685 + ], + "type": "text", + "content": "Implementation Details. There is one video preprocessing step before the feature extraction step in Equation (1), where we transform the original video input from " + }, + { + "bbox": [ + 304, + 552, + 545, + 685 + ], + "type": "inline_equation", + "content": "\\mathbf{x}^{T_p}" + }, + { + "bbox": [ + 304, + 552, + 545, + 685 + ], + "type": "text", + "content": " to match the input format of the " + }, + { + "bbox": [ + 304, + 552, + 545, + 685 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 304, + 552, + 545, + 685 + ], + "type": "text", + "content": "-th task-specific model " + }, + { + "bbox": [ + 304, + 552, + 545, + 685 + ], + "type": "inline_equation", + "content": "f_k" + }, + { + "bbox": [ + 304, + 552, + 545, + 685 + ], + "type": "text", + "content": ". In particular, " + }, + { + "bbox": [ + 304, + 552, + 545, + 685 + ], + "type": "inline_equation", + "content": "\\mathbf{x}^{T_p}" + }, + { + "bbox": [ + 304, + 552, + 545, + 685 + ], + "type": "text", + "content": " is first upsampled or downsampled to match the frame rates required by " + }, + { + "bbox": [ + 304, + 552, + 545, + 685 + ], + "type": "inline_equation", + "content": "f_k" + }, + { + "bbox": [ + 304, + 552, + 545, + 685 + ], + "type": "text", + "content": ". Next, if the temporal span of the auxiliary task is smaller than that of the primary task, we slide " + }, + { + "bbox": [ + 304, + 552, + 545, + 685 + ], + "type": "inline_equation", + "content": "f_k" + }, + { + "bbox": [ + 304, + 552, + 545, + 685 + ], + "type": "text", + "content": " in a moving window to extract a sequence of features, where the window length is the temporal span required by " + }, + { + "bbox": [ + 304, + 552, + 545, + 685 + ], + "type": "inline_equation", + "content": "f_k" + }, + { + "bbox": [ + 304, + 552, + 545, + 685 + ], + "type": "text", + "content": ", and stride size is a hyperparameter. Conversely, if " + }, + { + "bbox": [ + 304, + 552, + 545, + 685 + ], + "type": "inline_equation", + "content": "f_k" + }, + { + "bbox": [ + 304, + 552, + 545, + 685 + ], + "type": "text", + "content": " requires video inputs of a longer temporal span" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 47, + 693, + 286, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 693, + 286, + 712 + ], + "spans": [ + { + "bbox": [ + 47, + 693, + 286, + 712 + ], + "type": "text", + "content": "2We use model checkpoints provided on the Ego4D website: https://github.com/EGO4D." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 693, + 545, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 693, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 306, + 693, + 545, + 713 + ], + "type": "text", + "content": "3There is a significant domain gap between human-human and human-object interaction videos. See Appendix A.3 for cross-cluster EgoT2-g." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "text", + "content": "2314" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 60, + 70, + 535, + 180 + ], + "blocks": [ + { + "bbox": [ + 60, + 70, + 535, + 180 + ], + "lines": [ + { + "bbox": [ + 60, + 70, + 535, + 180 + ], + "spans": [ + { + "bbox": [ + 60, + 70, + 535, + 180 + ], + "type": "table", + "html": "
\\( \\mathcal{T}_{p}\\text{ is PNR} \\)\\( \\mathcal{T}_{p}\\text{ is OSCC} \\)\\( \\mathcal{T}_{p}\\text{ is AR} \\)\\( \\mathcal{T}_{p}\\text{ is LTA} \\)
# Params \\( \\cdot 10^{6} \\) Trainable (All)Error (s) ↓# Params \\( \\cdot 10^{6} \\) Trainable (All)Acc. (%) ↑# Params \\( \\cdot 10^{6} \\) Trainable (All)Acc. (%) Verb(%) ↑ Noun# Params \\( \\cdot 10^{6} \\) Trainable (All)ED@20 ↓ VerbNoun
TS model [23]32.2 (32.2)0.61532.2 (32.2)68.2263.3 (63.3)22.1821.55180 (242)0.7460.789
Finetuning [13]8.4 (40.6)0.6118.4 (40.6)67.934.9 (66.8)21.6422.8448.6 (266)0.7440.787
Transfer [62] (PNR)N/AN/A8.4 (40.6)66.804.9 (37.1)19.985.4465.4 (97.6)0.7780.902
Transfer [62] (OSCC)8.4 (40.6)0.611N/AN/A4.9 (37.1)20.009.6165.4 (97.6)0.7740.899
Transfer [62] (AR)9.5 (71.4)0.6139.4 (71.4)70.98N/AN/AN/A53.3 (115)0.7450.806
LF [45] (All Tasks)9.6 (135)0.6109.6 (135)72.105.2 (131)21.1119.2483.6 (427)0.7440.788
EgoT2-s (All Tasks)6.4 (132)0.6107.4 (133)72.694.3 (130)23.0423.2841.8 (348)0.7310.769
", + "image_path": "9856ffd9fea1640031a8d582396d2dbddbbb07583ac3d5af0cb9222b157c3c66.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 50, + 274, + 284, + 379 + ], + "blocks": [ + { + "bbox": [ + 46, + 189, + 545, + 256 + ], + "lines": [ + { + "bbox": [ + 46, + 189, + 545, + 256 + ], + "spans": [ + { + "bbox": [ + 46, + 189, + 545, + 256 + ], + "type": "text", + "content": "Table 2. Results of EgoT2-s as we vary the primary human-object interaction task " + }, + { + "bbox": [ + 46, + 189, + 545, + 256 + ], + "type": "inline_equation", + "content": "\\mathcal{T}_p" + }, + { + "bbox": [ + 46, + 189, + 545, + 256 + ], + "type": "text", + "content": ". First row records performance of the task-specific (TS) model we obtain in the first-stage training; we compare EgoT2-s with other baseline methods in the second-stage training. We list the number of trainable parameters for each separate stage as well as the total (i.e., trainable parameters plus parameters of frozen TS models) in parentheses. Following [23], the evaluation metric is temporal localization error (unit: seconds) for PNR, accuracy for OSCC and AR, and edit distance at future 20 time stamps (i.e., ED@20) for LTA. For localization error and ED@20, lower is better. EgoT2-s reliably adapts the auxiliary tasks to suit the target task." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 50, + 274, + 284, + 379 + ], + "lines": [ + { + "bbox": [ + 50, + 274, + 284, + 379 + ], + "spans": [ + { + "bbox": [ + 50, + 274, + 284, + 379 + ], + "type": "table", + "html": "
\\( \\mathcal{T}_{p} \\) is TTM\\( \\mathcal{T}_{p} \\) is ASD
# Params \\( \\cdot 10^{6} \\) Trainable (All)mAP (%)↑# Params \\( \\cdot 10^{6} \\) Trainable (All)mAP (%)↑
TS model [23]20.2 (20.2)58.9115.7 (15.7)79.05
Finetuning [13]0.8 (20.8)59.671.1 (16.8)78.62
Transfer [62] (LAM)0.8 (15.4)63.591.6 (16.2)66.40
Transfer [62] (TTM)N/AN/A1.6 (21.6)71.06
Transfer [62] (ASD)0.8 (16.5)62.31N/AN/A
LF [45] (All Tasks)1.2 (51.5)64.291.6 (51.9)77.54
EgoT2-s (All Tasks)0.7 (51.1)66.541.5 (51.9)79.38
", + "image_path": "947252044b69f388b7e0a49224b54f86ce71187a3a85dece2a67ef4351b299d6.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 388, + 287, + 411 + ], + "lines": [ + { + "bbox": [ + 47, + 388, + 287, + 411 + ], + "spans": [ + { + "bbox": [ + 47, + 388, + 287, + 411 + ], + "type": "text", + "content": "Table 3. Results of EgoT2-s as we vary the primary human-human interaction task " + }, + { + "bbox": [ + 47, + 388, + 287, + 411 + ], + "type": "inline_equation", + "content": "\\mathcal{T}_p" + }, + { + "bbox": [ + 47, + 388, + 287, + 411 + ], + "type": "text", + "content": ". EgoT2-s consistently improves the TS model." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 431, + 287, + 552 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 431, + 287, + 552 + ], + "spans": [ + { + "bbox": [ + 46, + 431, + 287, + 552 + ], + "type": "text", + "content": "than " + }, + { + "bbox": [ + 46, + 431, + 287, + 552 + ], + "type": "inline_equation", + "content": "\\mathbf{x}^{\\mathcal{T}_p}" + }, + { + "bbox": [ + 46, + 431, + 287, + 552 + ], + "type": "text", + "content": ", we exclude task " + }, + { + "bbox": [ + 46, + 431, + 287, + 552 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 431, + 287, + 552 + ], + "type": "text", + "content": " from auxiliary task candidates to avoid providing potential advantages of a longer observation window to our framework as otherwise we need to expand video length of " + }, + { + "bbox": [ + 46, + 431, + 287, + 552 + ], + "type": "inline_equation", + "content": "\\mathbf{x}^{\\mathcal{T}_p}" + }, + { + "bbox": [ + 46, + 431, + 287, + 552 + ], + "type": "text", + "content": " to match the requirement of " + }, + { + "bbox": [ + 46, + 431, + 287, + 552 + ], + "type": "inline_equation", + "content": "f_{k}" + }, + { + "bbox": [ + 46, + 431, + 287, + 552 + ], + "type": "text", + "content": ". Moreover, if the auxiliary task dataset is multimodal (i.e., video and audio) and the primary task involves only video, we apply the unimodal video pathway of " + }, + { + "bbox": [ + 46, + 431, + 287, + 552 + ], + "type": "inline_equation", + "content": "f_{k}" + }, + { + "bbox": [ + 46, + 431, + 287, + 552 + ], + "type": "text", + "content": " to obtain features; if the primary task is multimodal, we provide all task-specific features that are computable from these modalities. See Appendix A.2.2 for more implementation details." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 560, + 253, + 572 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 560, + 253, + 572 + ], + "spans": [ + { + "bbox": [ + 47, + 560, + 253, + 572 + ], + "type": "text", + "content": "4.2. Evaluation of Task-Specific Translation" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 578, + 287, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 578, + 287, + 628 + ], + "spans": [ + { + "bbox": [ + 46, + 578, + 287, + 628 + ], + "type": "text", + "content": "Results. We conduct experiments with EgoT2-s for each task being the primary task4 and summarize the results for human-object interactions and human-human interactions in Table 2 and 3, respectively." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 628, + 287, + 675 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 628, + 287, + 675 + ], + "spans": [ + { + "bbox": [ + 46, + 628, + 287, + 675 + ], + "type": "text", + "content": "From the two tables, we observe uneven performance by the baseline methods. Transfer and Late Fusion sometimes outperform the dedicated TS model and sometimes underperform it. When tasks do not exhibit a strong transfer rela" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 309, + 276, + 545, + 348 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 309, + 276, + 545, + 348 + ], + "spans": [ + { + "bbox": [ + 309, + 276, + 545, + 348 + ], + "type": "text", + "content": "tion, reusing the backbone of the auxiliary task for the primary task leads to negative transfer and performance degradation. For instance, in Table 2, when " + }, + { + "bbox": [ + 309, + 276, + 545, + 348 + ], + "type": "inline_equation", + "content": "\\mathcal{T}_p" + }, + { + "bbox": [ + 309, + 276, + 545, + 348 + ], + "type": "text", + "content": " is AR, Transfer (OSCC) and Late Fusion both downgrade noun prediction accuracy, suggesting object state change is more dependent on verbs and unrelated to noun prediction tasks in AR." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 351, + 545, + 567 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 351, + 545, + 567 + ], + "spans": [ + { + "bbox": [ + 304, + 351, + 545, + 567 + ], + "type": "text", + "content": "On the contrary, our proposed EgoT2-s learns to adaptively utilize task-specific features and effectively mitigates negative transfer, demonstrating consistent improvement over the TS model for all 6 cases. For instance, in Table 3, when " + }, + { + "bbox": [ + 304, + 351, + 545, + 567 + ], + "type": "inline_equation", + "content": "\\mathcal{T}_p" + }, + { + "bbox": [ + 304, + 351, + 545, + 567 + ], + "type": "text", + "content": " is ASD, Late Fusion indicates there is a deleterious relation from LAM and TTM to ASD, as it suffers from an accuracy degradation of " + }, + { + "bbox": [ + 304, + 351, + 545, + 567 + ], + "type": "inline_equation", + "content": "1.51\\%" + }, + { + "bbox": [ + 304, + 351, + 545, + 567 + ], + "type": "text", + "content": " over TS, yet EgoT2-s still obtains slightly better performance compared to TS (i.e., " + }, + { + "bbox": [ + 304, + 351, + 545, + 567 + ], + "type": "inline_equation", + "content": "79.38\\%" + }, + { + "bbox": [ + 304, + 351, + 545, + 567 + ], + "type": "text", + "content": " v.s. " + }, + { + "bbox": [ + 304, + 351, + 545, + 567 + ], + "type": "inline_equation", + "content": "79.05\\%" + }, + { + "bbox": [ + 304, + 351, + 545, + 567 + ], + "type": "text", + "content": "). Moreover, when auxiliary tasks are beneficial for the primary task, EgoT2-s outperforms all baselines with fewer trainable parameters. For example, when " + }, + { + "bbox": [ + 304, + 351, + 545, + 567 + ], + "type": "inline_equation", + "content": "\\mathcal{T}_p" + }, + { + "bbox": [ + 304, + 351, + 545, + 567 + ], + "type": "text", + "content": " is TTM, it achieves a " + }, + { + "bbox": [ + 304, + 351, + 545, + 567 + ], + "type": "inline_equation", + "content": "+7.63\\%" + }, + { + "bbox": [ + 304, + 351, + 545, + 567 + ], + "type": "text", + "content": " mAP improvement over the original TS model by training a lightweight task translator with only 0.7M parameters on top of it (TS is kept frozen). These results across different primary and auxiliary task combinations help demonstrate the generalizability of EgoT2-s. See Appendix A.3 for experiments using a subset of auxiliary tasks rather than all tasks." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "content": "Ablation Study. In Table 4, we ablate three different design choices of EgoT2-s using TTM as the primary task: (a) We replace the LAM and ASD TS models in EgoT2-s with two TTM models with different parameters. This yields a task fusion transformer that is architecturally identical to EgoT2-s but takes only TTM tokens as input; (b) We pass features produced by TS models after temporal pooling as the input of our task fusion transformer; (c) We do not freeze TS models in our second-stage training. By comparing (a) with our default configuration (d), we see that EgoT2-s indeed benefits from the introduction of auxiliary tasks. Although equipped with three different TTM models" + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 46, + 683, + 287, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 683, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 683, + 287, + 713 + ], + "type": "text", + "content": "4Following the time-span guidelines in Sec. 4.1, LAM is not considered as the primary task and LTA is not adopted as an auxiliary task. Nonetheless, Appendix A.3 shows some special cases for completeness." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "text", + "content": "2315" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 51, + 70, + 284, + 137 + ], + "blocks": [ + { + "bbox": [ + 51, + 70, + 284, + 137 + ], + "lines": [ + { + "bbox": [ + 51, + 70, + 284, + 137 + ], + "spans": [ + { + "bbox": [ + 51, + 70, + 284, + 137 + ], + "type": "table", + "html": "
# Params ·106Trainable (All)Auxiliary TasksTemporal InformationFrozen TS modelmAP (%)↑
(a)0.7 (60.8)✓✓63.40
(b)0.7 (51.1)✓✓65.47
(c)51.1 (51.1)✓✓66.00
(d)0.7 (51.1)✓✓✓66.54
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(a)# Params TrainablePNR ↓OSCC ↑AR Verb ↑AR Noun ↑LTA Verb ↑LTA Noun ↑
TS model [23]N/A0.61568.222.1821.5520.8221.80
Multi-task [51]32.20.61766.0N/AN/AN/AN/A
EgoT2-g (P & O)5.90.61268.6N/AN/AN/AN/A
EgoT2-g (All)34.50.61171.721.9322.7321.9123.61
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(b)# Params TrainableLAM mAP (%) ↑TTM mAP (%) ↑ASD Acc.(%) ↑
TS model [23]N/A77.7958.9179.05
Multi-task [51]20.260.5361.91N/A
EgoT2-g1.477.6364.4979.06
", + "image_path": "8c4fa0404de23e36d7829cf3f21bcd1350ac8a874d740839d77c39ccdc5a8c4f.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + }, + { + "bbox": [ + 46, + 320, + 286, + 386 + ], + "lines": [ + { + "bbox": [ + 46, + 320, + 286, + 386 + ], + "spans": [ + { + "bbox": [ + 46, + 320, + 286, + 386 + ], + "type": "text", + "content": "Table 5. EgoT2-g for (a) human-object interaction and (b) human-human interaction tasks. The evaluation metric is error (seconds) for PNR (P) and accuracy (\\%) for OSCC (O), AR and LTA. We report the number of trainable parameters required for each method in the second-stage training (unit: million). Our model is flexible, accurate, and avoids negative transfer." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_footnote" + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 409, + 286, + 517 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 409, + 286, + 517 + ], + "spans": [ + { + "bbox": [ + 46, + 409, + 286, + 517 + ], + "type": "text", + "content": "and a larger model size (the total number of parameters of three TTM models is larger than the sum of three TS models), variant (a) does not bring as much performance gain as EgoT2-s (d). Also, preserving the temporal information of task-specific tokens further boosts performance, as can be seen in the comparison of EgoT2-s (b) with EgoT2-s (d). Finally, not freezing TS (c) greatly increases the training cost yet brings no performance gain. These results validate the design of our proposed EgoT2-s." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 526, + 255, + 538 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 526, + 255, + 538 + ], + "spans": [ + { + "bbox": [ + 47, + 526, + 255, + 538 + ], + "type": "text", + "content": "4.3. Evaluation of Task-General Translation" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 545, + 286, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 545, + 286, + 712 + ], + "spans": [ + { + "bbox": [ + 46, + 545, + 286, + 712 + ], + "type": "text", + "content": "Results. Table 5 provides results of EgoT2-g. Since the TTM and LAM baseline models use identical video backbones (i.e., 3D ResNet-18), the hard parameter sharing multi-task baseline [51] can jointly learn TTM and LAM. Yet this model design is unable to solve the ASD task without further modifications to the ASD backbone model. In contrast, our EgoT2-g provides a flexible solution that can incorporate a heterogeneous mix of pretrained models. Similarly, we apply the multi-task baseline to PNR and OSCC, as they use the same video backbone (i.e., I3D ResNet-50). Compared with dedicated TS models, our proposed EgoT2-g performs task translation for all tasks at the same time and achieves on parallel or better performance for all tasks. For instance, it achieves " + }, + { + "bbox": [ + 46, + 545, + 286, + 712 + ], + "type": "inline_equation", + "content": "+5.58\\%" + }, + { + "bbox": [ + 46, + 545, + 286, + 712 + ], + "type": "text", + "content": " mAP im" + } + ] + } + ], + "index": 7 + }, + { + "type": "table", + "bbox": [ + 331, + 70, + 521, + 348 + ], + "blocks": [ + { + "bbox": [ + 331, + 70, + 521, + 348 + ], + "lines": [ + { + "bbox": [ + 331, + 70, + 521, + 348 + ], + "spans": [ + { + "bbox": [ + 331, + 70, + 521, + 348 + ], + "type": "table", + "html": "
TTM ChallengemAP↑
Random Guess [23]0.50
3D ResNet-18 Bi-LSTM [23]0.54
EgoT2-g (3D ResNet-18)0.58
EgoT2-s (3D ResNet-18)0.58
PNR ChallengeError (s)↓
Always Center Frame [23]1.01
CNN LSTM [23]0.76
EgoVLP [40]0.67
Video Swin Transformer [16]0.66
SViT [4]0.66
EgoT2-s (I3D ResNet-50)0.66
OSCC ChallengeAcc. ↑
Always Positive [23]0.48
I3D ResNet-50 [23]0.68
Video Swin Transformer [16]0.68
Divided ST Attention [28]0.72
EgoVLP [40]0.74
EgoT2-g (I3D ResNet-50)0.70
EgoT2-s (I3D ResNet-50)0.71
EgoT2-s (EgoVLP)0.75
LTA ChallengeED@20↓
VerbNounAction
SlowFast + Transformer [23]0.740.780.94
Video + CLIP [10]0.740.770.94
Hierarchical MLP Mixer [46]0.740.740.93
EgoT2-s (SlowFast)0.720.760.93
", + "image_path": "d374cc75b79c68941d4401e0c35ab29474e4c16f39a078883d8ddfd5b47830e4.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "table_body" + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 357, + 545, + 390 + ], + "lines": [ + { + "bbox": [ + 305, + 357, + 545, + 390 + ], + "spans": [ + { + "bbox": [ + 305, + 357, + 545, + 390 + ], + "type": "text", + "content": "Table 6. Comparison of EgoT2 with SOTA approaches on four Ego4D challenges (test set). We list the TS model architecture of EgoT2 in parentheses. Our model improves the state of the art." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 304, + 414, + 545, + 616 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 414, + 545, + 616 + ], + "spans": [ + { + "bbox": [ + 304, + 414, + 545, + 616 + ], + "type": "text", + "content": "provement for TTM and " + }, + { + "bbox": [ + 304, + 414, + 545, + 616 + ], + "type": "inline_equation", + "content": "3.5\\%" + }, + { + "bbox": [ + 304, + 414, + 545, + 616 + ], + "type": "text", + "content": " accuracy gain for OSCC. Notably, on ASD, it retains the top-performance of the original TS models when the other two auxiliary tasks do not help. In contrast, we observe task competition for the multi-task baseline: the improvement for TTM (i.e., " + }, + { + "bbox": [ + 304, + 414, + 545, + 616 + ], + "type": "inline_equation", + "content": "+3.0\\%" + }, + { + "bbox": [ + 304, + 414, + 545, + 616 + ], + "type": "text", + "content": " mAP) is at the cost of significantly downgraded LAM performance (i.e., " + }, + { + "bbox": [ + 304, + 414, + 545, + 616 + ], + "type": "inline_equation", + "content": "-17.26\\%" + }, + { + "bbox": [ + 304, + 414, + 545, + 616 + ], + "type": "text", + "content": " mAP). Similarly, sharing an encoder for PNR and OSCC also leads to task competition and suboptimal performance for the multi-task baseline. For a side-by-side comparison, we also implement EgoT2-g that performs task translation for PNR and OSCC only and observe its advantages over the multi-task baseline in terms of both performance and trainable parameters. As EgoT2-g does not require re-training of the backbone, we can integrate any available model checkpoint developed for each individual task into our framework and train a lightweight task-general translator to further boost performance in the second stage." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 618, + 545, + 690 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 618, + 545, + 690 + ], + "spans": [ + { + "bbox": [ + 304, + 618, + 545, + 690 + ], + "type": "text", + "content": "Comparison with SOTA Approaches. To further demonstrate the efficacy of both EgoT2-s and EgoT2-g, we submit our model to the EvalAI server to compare it with winning submissions to Ego4D-CVPR'22 and Ego4D-ECCV'22 challenges on the withheld test set. Table 6 shows the results.5 EgoT2-s achieves top performance for all 4 chal" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 315, + 702, + 544, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 315, + 702, + 544, + 712 + ], + "spans": [ + { + "bbox": [ + 315, + 702, + 544, + 712 + ], + "type": "text", + "content": "ASD & AR are not applicable since they are not Ego4D challenges." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "2316" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 191 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 191 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 191 + ], + "type": "text", + "content": "lenges. By only incorporating basic video backbones (e.g., 3D ResNet-18 and SlowFast) as the task-specific model, EgoT2-s achieves similar or better performance than works that adopt more powerful, novel architectures such as Video Swin Transformer. Moreover, the benefits of our approach are orthogonal to such architecture improvements: e.g., for the OSCC challenge, replacing the I3D ResNet-50 backbone with the one used in EgoVLP [40] can further elevate the accuracy of EgoVLP by " + }, + { + "bbox": [ + 46, + 72, + 289, + 191 + ], + "type": "inline_equation", + "content": "1\\%" + }, + { + "bbox": [ + 46, + 72, + 289, + 191 + ], + "type": "text", + "content": ". This indicates the success of EgoT2 stems from its effective use of task synergies." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 192, + 289, + 335 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 192, + 289, + 335 + ], + "spans": [ + { + "bbox": [ + 46, + 192, + 289, + 335 + ], + "type": "text", + "content": "While EgoT2-g is a strong performer that surpasses or matches TS across all tasks, if we compare its results with those of EgoT2-s, we observe that EgoT2-s demonstrates superior performance. This is understandable given that EgoT2-s is individually optimized for each primary task and employs a specialized translator. On the other hand, EgoT2-g provides a favorable unified framework that performs task translation for all tasks simultaneously via the design of a task-general translator. Thus, EgoT2-s serves as the framework of choice for top performance while EgoT2-g provides added flexibility. See Appendix A.3 for a detailed comparison of the performance and efficiency of these two variants." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 342, + 268, + 355 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 342, + 268, + 355 + ], + "spans": [ + { + "bbox": [ + 47, + 342, + 268, + 355 + ], + "type": "text", + "content": "4.4. Visualization of Uncovered Task Relations" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 361, + 289, + 588 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 361, + 289, + 588 + ], + "spans": [ + { + "bbox": [ + 46, + 361, + 289, + 588 + ], + "type": "text", + "content": "Our proposed EgoT2 explicitly models task relations via a task translator and offers good interpretability on task relations. For EgoT2-s, Figure 5 shows the attention weights of task tokens when the primary task is LTA and the auxiliary task is AR. Given two adjacent input video clips, the goal of LTA is to predict the next action (e.g., put container and turn off nozzle for the two examples here). In the upper example, there is a scene change from the first clip (the temporal segment corresponding to put wheel) to the second clip (the clip corresponding to take container). The attention weights of AR tokens are small for the first clip and large for the second clip. Clearly, the future action to predict is more closely related to the second temporal segment due to similarities in the scene and objects. In the lower example, the AR tokens have large attention weights, as the video is temporally similar and the previous two actions are indicative of the next action. These results show how EgoT2-s accurately characterizes temporal and auxiliary task information to improve the primary task. More visualizations are in Appendix A.4." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 588, + 289, + 696 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 588, + 289, + 696 + ], + "spans": [ + { + "bbox": [ + 46, + 588, + 289, + 696 + ], + "type": "text", + "content": "Similarly, for EgoT2-g, we visualize its encoder-decoder attention weights from the last layer transformer in Figure 6. Given the same video clip as input, feature tokens are activated differently when EgoT2-g is given different task prompts, demonstrating that EgoT2-g learns to perform task translation conditioned on the task of interest. As it assigns small weights to task features that are not beneficial for the task of interest (e.g., PNR features to noun prediction tasks), EgoT2-g discards non-relevant task features to" + } + ] + } + ], + "index": 4 + }, + { + "type": "image", + "bbox": [ + 310, + 72, + 547, + 196 + ], + "blocks": [ + { + "bbox": [ + 310, + 72, + 547, + 196 + ], + "lines": [ + { + "bbox": [ + 310, + 72, + 547, + 196 + ], + "spans": [ + { + "bbox": [ + 310, + 72, + 547, + 196 + ], + "type": "image", + "image_path": "b829f891dbb03b2a701e6f428f3778642ced2e999762364fa3a299fc06929b30.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 205, + 547, + 250 + ], + "lines": [ + { + "bbox": [ + 305, + 205, + 547, + 250 + ], + "spans": [ + { + "bbox": [ + 305, + 205, + 547, + 250 + ], + "type": "text", + "content": "Figure 5. Attention weights of EgoT2-s when " + }, + { + "bbox": [ + 305, + 205, + 547, + 250 + ], + "type": "inline_equation", + "content": "\\mathcal{T}_p" + }, + { + "bbox": [ + 305, + 205, + 547, + 250 + ], + "type": "text", + "content": " is LTA. EgoT2-s learns to utilize tokens from relevant temporal segments and tasks. The attention weights of AR tokens are large when the current action is indicative of future action." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_caption" + } + ], + "index": 5 + }, + { + "type": "image", + "bbox": [ + 307, + 259, + 541, + 369 + ], + "blocks": [ + { + "bbox": [ + 307, + 259, + 541, + 369 + ], + "lines": [ + { + "bbox": [ + 307, + 259, + 541, + 369 + ], + "spans": [ + { + "bbox": [ + 307, + 259, + 541, + 369 + ], + "type": "image", + "image_path": "16f622391e69b04c03db4202704d36c390297a2f2ec98a1eb6178e415964433c.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 376, + 547, + 409 + ], + "lines": [ + { + "bbox": [ + 305, + 376, + 547, + 409 + ], + "spans": [ + { + "bbox": [ + 305, + 376, + 547, + 409 + ], + "type": "text", + "content": "Figure 6. Attention weights of EgoT2-g. Given the same video and different task prompts, EgoT2-g assigns different weights to different task tokens. See text." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_caption" + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 430, + 547, + 575 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 430, + 547, + 575 + ], + "spans": [ + { + "bbox": [ + 304, + 430, + 547, + 575 + ], + "type": "text", + "content": "mitigate task competition. We also observe temporal differences of attention weights from same task features, indicating that EgoT2-g captures both inter-frame and inter-task dependencies to improve the task of interest. Finally, recall that in Figure 1, we derive task relations for 4 human-object interaction tasks via attention weights provided by EgoT2-g. The attention weights are temporally pooled and averaged over all validation data, revealing task relations from a global perspective. Results for human-human interaction tasks are presented in Appendix A.4. In all, EgoT2 provides good interpretability patterns on (1) which subset of tasks (2) which time segments lead to the final prediction." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 585, + 379, + 597 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 585, + 379, + 597 + ], + "spans": [ + { + "bbox": [ + 306, + 585, + 379, + 597 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 605, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 547, + 713 + ], + "type": "text", + "content": "As a step towards unified egocentric perception, we propose EgoT2, a general and flexible design for task translation. EgoT2 consists of heterogeneous video models optimized for each individual task and a transformer-based task translator that captures inter-frame and inter-task relations. We propose EgoT2-s to improve one primary task and EgoT2-g to conduct task translation for all tasks simultaneously. Results on 7 diverse egocentric video tasks reveal valuable task relations and validate the proposed design." + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 47, + 702, + 288, + 714 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 702, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 47, + 702, + 288, + 714 + ], + "type": "text", + "content": "Results of EgoT2-g for PNR & LTA are unavailable (see Appendix A.2.2)." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 295, + 748, + 316, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 316, + 758 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 316, + 758 + ], + "type": "text", + "content": "2317" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 288, + 712 + ], + "type": "list", + "angle": 0, + "index": 14, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 145 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 145 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 145 + ], + "type": "text", + "content": "[1] Anurag Arnab, Mostafa Dehghani, Georg Heigold, Chen Sun, Mario Lucic, and Cordelia Schmid. 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Proceedings of the IEEE, 109(1):43-76, 2020. 2" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "2320" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 10 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Elastic Aggregation for Federated Optimization/aa6cbfa9-0a85-4695-927f-135bdd87fa31_content_list.json b/2023/Elastic Aggregation for Federated Optimization/aa6cbfa9-0a85-4695-927f-135bdd87fa31_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..856d1fc79c2e6c471f8adf6b8fe8a88017f2de2d --- /dev/null +++ b/2023/Elastic Aggregation for Federated Optimization/aa6cbfa9-0a85-4695-927f-135bdd87fa31_content_list.json @@ -0,0 +1,1487 @@ +[ + { + "type": "text", + "text": "Elastic Aggregation for Federated Optimization", + "text_level": 1, + "bbox": [ + 243, + 130, + 725, + 152 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Dengsheng Chen $^{1*}$ , Jie Hu $^{2,3*}$ , Vince Junkai Tan $^{4}$ , Xiaoming Wei $^{1}$ , Enhua Wu $^{2,3,5\\dagger}$", + "bbox": [ + 143, + 179, + 828, + 198 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "$^{1}$ Meituan $^{2}$ State Key Laboratory of Computer Science, ISCAS", + "bbox": [ + 207, + 198, + 761, + 215 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "3 University of Chinese Academy of Sciences 4 Bytedance Inc. 5 University of Macau", + "bbox": [ + 117, + 215, + 849, + 233 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "{chendengsheng,weixiaoming}@meituan.com,hujie@ios.ac.cn,vince.tan.jun.kai@gmail.com,ehwu@um.edu.m0", + "bbox": [ + 93, + 236, + 872, + 250 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 286, + 313, + 301 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Federated learning enables the privacy-preserving training of neural network models using real-world data across distributed clients. FedAvg has become the preferred optimizer for federated learning because of its simplicity and effectiveness. FedAvg uses naive aggregation to update the server model, interpolating client models based on the number of instances used in their training. However, naive aggregation suffers from client drift when the data is heterogeneous (non-IID), leading to unstable and slow convergence. In this work, we propose a novel aggregation approach, elastic aggregation, to overcome these issues. Elastic aggregation interpolates client models adaptively according to parameter sensitivity, which is measured by computing how much the overall prediction function output changes when each parameter is changed. This measurement is performed in an unsupervised and online manner. Elastic aggregation reduces the magnitudes of updates to the more sensitive parameters so as to prevent the server model from drifting to any one client distribution, and conversely boosts updates to the less sensitive parameters to better explore different client distributions. Empirical results on real and synthetic data as well as analytical results show that elastic aggregation leads to efficient training in both convex and non-convex settings while being fully agnostic to client heterogeneity and robust to large numbers of clients, partial participation, and imbalanced data. Finally, elastic aggregation works well with other federated optimizers and achieves significant improvements across the board.", + "bbox": [ + 76, + 316, + 473, + 741 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 768, + 209, + 784 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Unlike traditional centralized learning in which models are trained using large datasets stored in a central server [15], federated learning - first proposed in [40] - leverages data spread across many clients to learn classification tasks dis", + "bbox": [ + 75, + 792, + 470, + 854 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "tributively without explicitly sharing data [22, 26, 27, 42], thereby ensuring a basic level of privacy. Federated learning is characterized by four key features:", + "bbox": [ + 500, + 287, + 892, + 333 + ], + "page_idx": 0 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- Unreliable links: The links connecting the server and clients can be unreliable, and only a small subset of clients may be active at any given time.", + "- Massive distribution: The number of clients is typically high, but the amount of data per client is relatively small.", + "- Substantial heterogeneity: Client data is heterogeneous and non-IID [26], meaning that data across different clients can be sampled from varying regions of the sampling space.", + "- Imbalanced data: There can be significant imbalances in the amount of data available per client." + ], + "bbox": [ + 517, + 337, + 892, + 532 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "The most popular algorithm for federated learning is FedAvg [40], which tackles the communication bottleneck by performing multiple local updates on the available clients before communicating the overall change to the server. FedAvg uses naive aggregation to interpolate client models and has shown success in certain applications. However, its performance on heterogeneous data is still an active area of research [16, 25, 33]. According to [25], training models on local data that minimize local empirical loss appears to be meaningful, but yet, doing so is fundamentally inconsistent with minimizing the global empirical loss. Client updates drive the server model away from the ideal distribution, a phenomenon known as 'client drift'. Naive aggregation [40] is efficient in aggregating client models but does not account for distribution inconsistencies across client data or the consequent objective inconsistency. In other words, with naive aggregation, the server model risks converging to a stationary point of a mismatched objective function which can be arbitrarily different from the true objective [53].", + "bbox": [ + 496, + 537, + 893, + 824 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Prior works [24, 40, 48] attempt to overcome this issue by running fewer epochs or iterations of SGD on the devices or by stabilizing server-side updates so that the resulting models correspond to inexact minimizations and keep globally desirable properties. In this work, we propose a novel aggregation", + "bbox": [ + 496, + 825, + 893, + 901 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Equal contribution.", + "bbox": [ + 94, + 863, + 205, + 875 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "†Corresponding author. This work is supported in part by NSFC Grants (62072449).", + "bbox": [ + 76, + 875, + 468, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "12187", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/1b9104cfda764cfca9722821c68ff6d2c890367eb096c1b8787b813f85780d34.jpg", + "image_caption": [ + "Figure 1. Illustration of naive aggregation and elastic aggregation. The local updates of client A and client B drive the server model $\\theta$ towards their individual minima (black dots in plot). Naive aggregation simply averages the received model from clients A and B, yielding $\\theta'$ as the new server model. Although $\\theta'$ minimizes the local empirical loss of clients A and B, $\\theta'$ drifts from ideal distribution for the server model. Elastic aggregation adjusts gradient with respect to parameter sensitivity. Parameter $\\theta_x$ is more sensitive (has a larger gradient norm), and is restricted with $\\zeta_x < 1$ to reduce the magnitude of its update. Parameter $\\theta_y$ is less sensitive (has a smaller gradient norm), and is correspondingly boosted with $\\zeta_y > 1$ to better explore the parameter space. This minimizes the loss for clients A and B, while not causing the server model to drift from its ideal distribution. Hence, elastic aggregation results in a better update $\\theta''$ ." + ], + "image_footnote": [ + "Minima point", + "Low empirical loss for client A", + "Low empirical loss for client B", + "Low empirical loss for server", + "Naïve aggregation", + "Elastic aggregation", + "Client update" + ], + "bbox": [ + 158, + 87, + 472, + 330 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "approach, elastic aggregation, to overcome client drift. We measure parameter sensitivity using unlabeled samples of client data, by computing the changes to the overall function output for a given change to the parameter in question, without relying on the loss. This allows our method to not only avoid requiring labeled data but importantly also pre-empt complications that could otherwise arise from the loss being at a local minimum with gradients close to zero. During the aggregation of client models, updates to the more sensitive parameters can then be reduced in magnitude, preventing the server model from drifting to any client distribution. Conversely, updates to the less sensitive parameters can be boosted to better explore different client distributions.", + "bbox": [ + 75, + 467, + 472, + 662 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Contributions. Elastic aggregation tackles distribution inconsistency across client data using the concept of parameter sensitivity and is simple to implement, requiring little hyperparameter tuning. Furthermore, parameter sensitivity is computed in an online and unsupervised manner, and thus better utilizes the unlabeled data generated by the client during runtime. Elastic aggregation is easily integrated into different federated optimizers, achieving substantial improvements over naïve aggregation. The empirical results on real and synthetic data and analytical results show that elastic aggregation leads to efficient training in both convex and non-convex settings, across all four federated learning scenarios (unreliable links, massive distribution, substantial heterogeneity, and imbalanced data).", + "bbox": [ + 75, + 688, + 468, + 900 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related work", + "text_level": 1, + "bbox": [ + 500, + 465, + 635, + 479 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Federated learning is a fast-evolving topic. The general setup involves server and client updates; each of these updates is associated with minimizing some local loss function. The server model then benefits from all client data and achieves superior performance, for tasks such as next word prediction [17, 56], emoji prediction [45], decoder models [8], vocabulary estimation [7], low latency vehicle-to-vehicle communication [49] and predictive models in health [6]. Nevertheless, federated learning raises several issues and has been the topic of much research effort, focusing on the issues of generalization and fairness [33, 42], the design of more efficient communication strategies [4,24,26,27,51,52], the study of lower bounds [55], differential privacy guarantees [2], security [5], etc [22]. We focus here on relevant work that specifically addresses the four federated learning characteristics noted above - massive distribution, heterogeneity, unreliable links, and imbalanced data.", + "bbox": [ + 496, + 491, + 893, + 762 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Much of earlier work in this context proposes optimizing for the local risk objective with SGD [51] over mini-batches of client data, analogous to the centralized scenario, with the server then averages the received models. FedAvg [40] is a generalization of local SGD, proposing a larger number of local SGD steps per round. In the case of identical clients, it reduces to parallel SGD for which asymptotic convergence has been proven [51, 62]; more recently, [25, 43] analyzed the same method under the name of local SGD, also for", + "bbox": [ + 496, + 763, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "12188", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "identical functions. FedAvg in exactly solves client-side optimization, requiring the tuning of the number of epochs and the learning rate hyper-parameters in order to achieve a good accuracy-communication trade-off [30,40].", + "bbox": [ + 75, + 90, + 470, + 151 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Despite the strong empirical performance of FedAvg in IID settings, performance degrades in non-IID scenarios [61]. The analysis of FedAvg for heterogeneous clients is more delicate, due to the aforementioned client drift, first empirically observed by [61]. Several analyses bound this drift by assuming bounded gradients [54, 57], viewing it as additional noise [25], or assuming that the client optima are $\\epsilon$ -close [16,33]. [36] proposes using variance reduction to deal with client heterogeneity but achieved slower convergence rates than SGD. Other variants include using a decreasing learning rate [30], modifying client empirical loss dynamically [1,31], adding regularizers on local updates [23,24,50], or modifying the server side updates [21,48]. While these works do recognize the incompatibility of local and global stationary points, their proposed fixes are based on inexact minimization. Additionally, in order to establish convergence for non-IID situations, these works impose additional constraints.", + "bbox": [ + 75, + 160, + 473, + 431 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Another class of work that extend the analysis of SGD-type methods to federated learning settings specifically addresses the special case of full client participation [9, 14, 26, 34-36, 38, 44, 50, 58]. For example, FedSVRG [26] and DANE [50] need gradient information from all clients each round and are as such not directly applicable to partial federated learning settings. Furthermore, it may not be trivial to extend these works to overcome the deficiency. For example, FedDANE [32] is a version of DANE that works with partial participation. However, with partial participation, FedDANE empirically performs worse than FedAvg [33]. Similar to these works, FedPD [60] proposes distributed optimization with a different notion of 'participation'. FedPD activates either all clients or no clients per round, which again fails to satisfy the partial participation condition.", + "bbox": [ + 75, + 440, + 470, + 667 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Finally, there have been earlier works aiming to decrease communication costs by compressing the transmitted models [3, 12, 41], decreasing the bit-rate of the transmission. These ideas are complementary to our work and can work together with our approach.", + "bbox": [ + 75, + 676, + 470, + 752 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Method", + "text_level": 1, + "bbox": [ + 76, + 790, + 166, + 806 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In this section, we focus on the introduction of parameter sensitivity in process of federated learning, which is our main innovation. The proof of convergence is provided in the technical part of supplementary materials.", + "bbox": [ + 75, + 825, + 470, + 886 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Federated Learning with Naïve Aggregation", + "text_level": 1, + "bbox": [ + 500, + 90, + 874, + 107 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In federated learning, we solve an optimization problem of the form:", + "bbox": [ + 498, + 113, + 890, + 142 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\arg \\min _ {\\theta \\in \\mathbb {R} ^ {n}} [ \\ell (\\theta) \\triangleq \\frac {1}{m} \\sum_ {k = 1} ^ {m} L _ {k} (\\theta) ], \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 586, + 150, + 890, + 189 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $L_{k}(\\theta)\\triangleq \\mathbb{E}_{(x,y)\\sim \\mathcal{P}_{k}}[\\ell_{k}(\\theta ;(x,y))]$ is the empirical loss of the $k^{th}$ client, $\\mathcal{P}_k$ is the data distribution for the $k^{th}$ client across $K$ clients.", + "bbox": [ + 496, + 200, + 890, + 247 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "FedAvg. A common approach to solving Eq. 1 in federated settings is FedAvg [40]. At each round, a subset of clients is selected (typically randomly) and the server broadcasts its model to each client. In parallel, the clients run SGD on their own loss function $\\ell_{k}$ and then send their updated models to the server. The server then updates its model to be the average of these client models.", + "bbox": [ + 496, + 266, + 890, + 371 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Suppose that at the $r^{th}$ round, the server has model $\\theta$ and samples a client set $S$ . Here we use a standard gradient descent form to update parameters:", + "bbox": [ + 496, + 372, + 890, + 417 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\theta \\leftarrow \\theta - \\eta \\Delta , \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 648, + 428, + 890, + 444 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\Delta$ is the aggregated clients' gradients and $\\eta$ is the learning rate of the server, which is typically 1.0. FedAvg uses naive aggregation to compute $\\Delta$ .", + "bbox": [ + 496, + 454, + 890, + 500 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Naive aggregation. We can write naive aggregation as:", + "bbox": [ + 500, + 517, + 879, + 532 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\Delta = \\sum_ {k \\in \\mathcal {S}} \\left(w _ {k} \\cdot \\Delta_ {k}\\right), \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 627, + 541, + 890, + 574 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\Delta_{k} = \\theta -\\theta_{k}$ is the accumulated gradients within a training round of the $k^{th}$ client, and $w_{k} = |D_{k}| / \\sum_{k\\in S}|D_{k}|$ is the aggregated weight of the $k^{th}$ client across the activated clients $\\mathcal{S}$ . $D_{k},\\theta_{k}$ are the training dataset and trained parameters on the $k^{th}$ client, respectively.", + "bbox": [ + 496, + 583, + 893, + 660 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. Exploring parameter sensitivity", + "text_level": 1, + "bbox": [ + 500, + 681, + 779, + 698 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Due to the non-IID-ness (heterogeneity) across different clients, $\\mathcal{P}$ can vary substantially across different clients. Thus, the simple and efficient way to aggregate client models described in Eq. 3 cannot solve client drift and cause oscillation as well as slow convergence. We explore parameter sensitivity as an approach to overcoming these issues.", + "bbox": [ + 496, + 704, + 893, + 795 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The main idea we are proposing is that less sensitive parameters can be freely updated to minimize the loss for individual clients in $S$ without causing the server to drift; by the same reasoning, parameters that are more sensitive should not be updated as much. This is illustrated in Fig. 1.", + "bbox": [ + 496, + 796, + 893, + 869 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "At the $r^{th}$ round, the active clients receive the server model $\\theta_r$ , which parameterizes the approximation function", + "bbox": [ + 500, + 869, + 890, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "12189", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 2 + }, + { + "type": "code", + "sub_type": "algorithm", + "code_caption": [ + "Algorithm 1: Elastic aggregation within a single layer" + ], + "code_body": "A variable with a superscript $i$ indicates the $i^{th}$ element of the variable. A variable with a subscript $k$ indicates the variable from $k^{th}$ client. $\\eta, \\eta'$ are learning rates of server and clients respectively. $\\mu, \\tau$ are the hyper-parameters. $\\theta, \\theta_k \\in \\mathbb{R}^n$ are the server's and the $k^{th}$ client's parameters respectively. $\\Omega \\in \\mathbb{R}^n$ is the aggregated parameter sensitivity. $\\Omega_k \\in \\mathbb{R}^n$ is the parameter sensitivity on the $k^{th}$ client.", + "bbox": [ + 96, + 127, + 447, + 263 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Initialize $\\theta$", + "bbox": [ + 98, + 265, + 171, + 277 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "$B_{k}\\gets$ Sample a subset of training data $D_{k}$", + "bbox": [ + 99, + 280, + 383, + 294 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "$D_{k}\\gets$ Drop the samples of $B_{k}$ from $D_{k}$", + "bbox": [ + 99, + 295, + 367, + 310 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "for each round do", + "bbox": [ + 99, + 311, + 220, + 323 + ], + "page_idx": 3 + }, + { + "type": "code", + "sub_type": "algorithm", + "code_caption": [], + "code_body": "for each activated client $k$ do Initialize $\\Omega_{k}$ as zeros. \nfor each batch data $x\\in B_k$ do $\\begin{array}{l}g = \\nabla ||F(\\theta ;x)||_2^2\\\\ \\mathbf{for}i\\in [1,\\dots ,n]\\mathbf{do}\\\\ \\big{\\lfloor}\\Omega_k^i\\gets \\mu \\Omega_k^i +(1 - \\mu)|g^i |\\\\ \\theta_k\\gets \\theta \\\\ \\mathbf{for}$ each epoch do for each batch data $x\\in D_k$ do $\\begin{array}{r}\\Big{\\lfloor}\\theta_{k}\\leftarrow \\theta_{k} - \\eta^{\\prime}\\nabla \\ell_{k}(F(\\theta_{k};x))\\\\ \\Delta_{k} = \\theta_{k} - \\theta \\end{array}$ $w_{k}\\gets |D_{k}| / \\sum_{k}|D_{k}|;\\Omega = \\sum_{k}(w_{k}\\cdot \\Omega_{k});$ $\\Omega^{\\prime} = \\max (\\Omega)$ \nfor $i\\in [1,\\dots ,n]$ do $\\zeta^i = 1 + \\tau -\\Omega^i /\\Omega '$ $\\Delta^i = \\zeta^i\\cdot \\sum_k(w_k\\cdot \\Delta_k^i)$ $\\theta^i\\gets \\theta^i -\\eta \\cdot \\Delta^i$", + "bbox": [ + 122, + 325, + 408, + 594 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "$F$ of the true function $\\bar{F}$ . $F$ maps the input $x$ to the output $y$ , and our goal is to largely maintain the same output $y$ for the observed $x$ while learning additional training instances $(x,y) \\sim P_k$ . To this end, we measure how sensitive the output of function $F$ is to changes in the network parameters. To reduce confusion, we ignore the symbols denoting the round $r$ and the client $k$ for all variables and only discuss parameter sensitivity locally.", + "bbox": [ + 75, + 633, + 468, + 755 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "For a given data point $x$ , the output of the network is $F(\\theta; x)$ . A small perturbation $\\delta$ in the parameters $\\theta$ results in a change in the function output that can be approximated by:", + "bbox": [ + 75, + 756, + 468, + 815 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nF (\\theta + \\delta ; x) - F (\\theta ; x) \\approx g (\\theta ; x) \\delta , \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 156, + 816, + 468, + 832 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $g(\\theta ;x) = \\frac{\\partial F(\\theta;x)}{\\partial\\theta}$ is the gradient of the learned function with respect to the parameter $\\theta$ evaluated at the data point $x$ . Our goal is to maintain the output of the network (the learned function $F$ ) for each observed data point and", + "bbox": [ + 75, + 837, + 470, + 900 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "thus we reduce the magnitudes of the updates to the parameters that are more sensitive for the data point. Conversely, we boost the updates to the less sensitive parameters to better-fit client distributions.", + "bbox": [ + 496, + 90, + 893, + 150 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Based on equation 4, and assuming a small constant change $\\delta$ , we can measure the sensitivity of a parameter by the magnitude of the gradient $g(\\theta; x)$ , i.e., how much does a small perturbation to that parameter change the output of the learned function for data point $x$ . There are many ways to measure the sensitivity of a parameter by the magnitude of the gradient, such as a fishing matrix. However, in federated learning, we have to take the computation ability of each client into account, which is only with limited computation ability. Therefore, we use the exponentially-decayed moving average1 to obtain sensitivity $\\Omega^i$ for $i^{th}$ parameter $\\theta^i$ :", + "bbox": [ + 496, + 151, + 892, + 318 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\Omega^ {i} \\leftarrow \\mu \\Omega^ {i} + (1 - \\mu) | g \\left(\\theta^ {i}; x\\right) |, \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 589, + 325, + 890, + 344 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\mu$ is momentum and we empirically set it to 0.9.", + "bbox": [ + 498, + 353, + 861, + 367 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "When the output function $F$ is multi-dimensional, as is the case for most neural networks, equation 5 involves computing the gradients for each output, which requires as many backward passes as the dimensionality of the output. As a more efficient alternative, we propose to use the gradients of the squared $L^2$ norm of the learned function output, i.e. $g(\\theta ;x) = \\nabla ||F(\\theta ;x)||_2^2$ . Hence, we only need to compute one backward pass in order to estimate the parameters' sensitivity.", + "bbox": [ + 496, + 368, + 893, + 503 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.3. Elastic aggregation with respect to parameter sensitivity", + "text_level": 1, + "bbox": [ + 500, + 523, + 890, + 556 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The elastic aggregation for $i^{th}$ parameter can be written as:", + "bbox": [ + 500, + 561, + 890, + 590 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\Delta^ {i} = \\zeta^ {i} \\cdot \\sum_ {k \\in \\mathcal {S}} \\left(w _ {k} \\cdot \\Delta_ {k} ^ {i}\\right), \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 612, + 590, + 890, + 622 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\zeta^i$ is the adaptive coefficient with respect to the parameter sensitivity. The definition of $\\zeta^i$ is:", + "bbox": [ + 498, + 627, + 893, + 657 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\zeta^ {i} = 1 + \\tau - \\Omega^ {i} / \\Omega^ {\\prime}, \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 622, + 667, + 890, + 685 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\Omega' = \\max(\\Omega)$ is the maximum of parameter sensitivities in each layer, and $\\Omega^i = \\sum_{k \\in S} (w_k \\cdot \\Omega_k^i)$ is the aggregated sensitivity of $i^{th}$ parameter across activated clients. The server is able to boost updates ( $\\zeta^i > 1.0$ ) to parameters that have low sensitivity (low $\\Omega^i$ ). Meanwhile, sensitive parameters (high $\\Omega^i$ ) have their updates restricted with a penalty ( $\\zeta^i < 1.0$ ). $\\tau$ is a hyper-parameter determining the ratio of boosted or restricted parameters. FedAvg with elastic aggregation is formalized in Algorithm 1.", + "bbox": [ + 496, + 693, + 893, + 830 + ], + "page_idx": 3 + }, + { + "type": "page_footnote", + "text": "1While a Polyak-style average has more theoretical guarantees for accumulating $\\Omega$ over batches, our results match the claim that \"an exponentially-decayed moving average typically works much better in practice\" [39]. Thus, we use the exponentially-decayed moving average to accumulate $\\Omega$ over batches. Refer to supplementary materials for more discussion.", + "bbox": [ + 496, + 838, + 893, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "12190", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Discussion on $\\tau$ . In Eq. 6, $\\zeta^i \\in (1, 1 + \\tau]$ is applied to the less sensitive parameters, and $\\zeta^i \\in [\\tau, 1)$ is applied to the more sensitive parameters. Thus, $\\tau$ determines the portion of the parameter to be restricted or boosted. Generally, a larger $\\tau$ indicates that a larger proportion of parameters will be boosted, as shown in Tab. 1, and vice versa.", + "bbox": [ + 75, + 90, + 470, + 181 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "If a large proportion of parameters is restricted ( $\\tau$ is small, such as 0.1), the server model will not be updated much, and exiting local minima becomes difficult. However, with a large $\\tau$ such as 0.9, optimization of the server model becomes unstable, and this also causes performance degradation. It is therefore critical to maintain a balance between these extremes with a suitable $\\tau$ and we find that $\\tau = 0.5$ generalizes well to various experiments. At this value of $\\tau$ , roughly three-quarters of the parameters are boosted.", + "bbox": [ + 75, + 181, + 473, + 319 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Experiments settings", + "text_level": 1, + "bbox": [ + 76, + 337, + 277, + 356 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Inconsistent usage of models, datasets, and non-IID partition methods makes it difficult to compare the performances of federated learning algorithms fairly. To enforce fair comparison, we explicitly specify the combinations of datasets, models, and non-IID partition methods to be used for experiments, which mostly consist of those used in existing work published at top-tier machine learning venues [18]. Note that although the reported precisions are state-of-the-art for the models we have chosen, higher-capacity models can achieve higher performances on these datasets. Therefore, we compare the relative performance of elastic aggregation against naive aggregation for various federated learning scenarios.", + "bbox": [ + 75, + 363, + 472, + 544 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.1. Implementation", + "text_level": 1, + "bbox": [ + 76, + 560, + 238, + 575 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We measure our algorithm against the most comprehensive and representative suite of federated datasets and modeling tasks to date. For this purpose, we carry out simulations on five diverse and representative experiments on several datasets. In order to facilitate the experiments, we use the cosine annealing scheduler [37] for the client learning rate $\\eta_r^\\prime$ at the $r^{th}$ round, which is given by $\\eta_r^\\prime = (1 + \\cos (\\frac{r}{R}\\pi))\\eta^\\prime$ . For all tasks, we measure the performance on the entire test set throughout training. Clients are sampled uniformly at random, without replacement within a given round, but with replacement across rounds. There are a variety of federated optimizers that improve the performance of federated learning. Here, we use the most basic and widely used federated optimization algorithm, i.e., FedAvg [40], as the default baseline in our experiments. With reference to [46], we implement all experiments with two important characteristics. First, instead of doing $K$ training steps per client, we do $E$ epochs of training over each client's data. Second, to account for varying numbers of gradient steps per client, we weigh the average of the client outputs $\\Delta_t^k$ by the number of training samples. This also follows the approach of", + "bbox": [ + 75, + 583, + 472, + 902 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "[40] and often outperforms uniform weighting [47]. We set $\\mu = 0.95$ for the accumulation of the parameter sensitivity over batches in each client. $\\tau = 0.5, \\eta = 1.0$ is used for all experiments. While computing Eq. 7, we normalize the parameter sensitivity layer by layer, which means that the parameter sensitivity is divided by the maximum value within the same layer. Aside from experiments 5.1, we set $E = 1$ for each client for all experiments.", + "bbox": [ + 496, + 90, + 893, + 212 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.2. Generate synthetic federated datasets.", + "text_level": 1, + "bbox": [ + 498, + 229, + 828, + 244 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Differences in distribution have an enormous influence on the performance of federated optimization. The Dirichlet distribution is used on the label ratios to ensure uneven label distributions among clients for non-IID splits, as in [59]. To generate imbalanced data, we sample the number of data points from a log-normal distribution. The degree of imbalance depends on the variance of the log-normal distribution, which is controlled by the hyper-parameter $\\alpha$ . A smaller $\\alpha$ indicates a stronger non-IID-ness in partitions, as shown in Fig. 2.", + "bbox": [ + 496, + 253, + 893, + 405 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "5. Experiments", + "text_level": 1, + "bbox": [ + 498, + 425, + 633, + 443 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Under all experiments, the samples used for computing parameter sensitivities at each client will be randomly sampled training data, and these sampled data will not be used for supervised training anymore. For a fair comparison, these sampled data will not be used in the baseline methods either.", + "bbox": [ + 496, + 450, + 893, + 527 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "5.1. Comparison with naive aggregation", + "text_level": 1, + "bbox": [ + 498, + 553, + 810, + 570 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "MNIST. As our baseline, we conduct a convex optimization experiment on MNIST [29] with logistic regression [31, 33, 40]. In this experiment, we generate a synthetic federated dataset of MNIST with $\\alpha = 100.0$ and split the dataset into 1000 partitions. At each round of training, we randomly choose 100 clients without repeating the partition. As shown in Tab. 2, the elastic aggregation has a large advantage over naive aggregation even with a large number of participating clients.", + "bbox": [ + 496, + 577, + 893, + 714 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Federated EMNIST. Due to resource constraints of edge devices, existing works commonly use shallow neural networks for experiments. Similarly, we include Federated EMNIST [46] with a shallow neural network consisting of two convolution layers followed by two linear layers [46]. Notably, Fed-EMNIST [46] has a natural client partitioning that is highly representative of real-world federated learning problems. It contains 3,400 users (clients) and 62 label classes. The dataset is split into 671,585 training examples and 77,483 testing examples. Rather than holding out specific users, we split each user's examples across the train", + "bbox": [ + 496, + 734, + 895, + 902 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "12191", + "bbox": [ + 480, + 944, + 517, + 957 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/e773dec5da96cced1bd5a49a0c5da321880ca5698f21654cbf2bf790ff765bf4.jpg", + "image_caption": [ + "Figure 2. Performances across different partitioning distributions, participation rates and numbers of local epochs. Compared with naive aggregation, elastic aggregation achieves significant improvements across these settings." + ], + "image_footnote": [], + "bbox": [ + 84, + 89, + 890, + 628 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/83c075ffa22a38c8c89c3786be3459b092112dfc6bd6b5703be923cec1047cb9.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
τNaïve0.00.10.20.30.40.50.60.70.80.91.0
Train Acc.(%)58.3657.2158.3358.7660.6660.4761.4460.6660.5561.0159.2758.96
Test Acc.(%)60.7458.3059.7661.1761.9163.3962.7463.3963.2363.2260.8361.37
Boosted(%)-0.011.4527.2443.7559.7474.4384.5789.9393.5396.2697.38
", + "bbox": [ + 102, + 689, + 870, + 760 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 1. The effect of $\\tau$ . Using an unsuitable $\\tau$ for elastic aggregation with cause it to even under-perform naïve aggregation. The last row shows the percentage of parameters that are boosted for different $\\tau$ .", + "bbox": [ + 75, + 768, + 893, + 797 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "and test so that all users have at least one example in the train and one example in the test. Users with fewer than 2 examples are excluded from the data set. As shown in Tab. 2, elastic aggregation generalizes well to real-world federated learning problems.", + "bbox": [ + 75, + 823, + 472, + 898 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "CIFAR-100. In this experiment, we conduct a balanced but non-IID partition on Fed-CIFAR $^{100}$ ², which was introduced by TensorFlow Federated [20] with ResNet-20 [19]", + "bbox": [ + 498, + 823, + 895, + 869 + ], + "page_idx": 5 + }, + { + "type": "page_footnote", + "text": "2https://github.com/tensorflow/federated", + "bbox": [ + 514, + 886, + 736, + 901 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "12192", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/929765a29705e852c78253a24b730eb841bcae96542e0fbb242b12ed8e9682c7.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
DatasetRounds(Epochs)TotalSampledBatchInit. LRModelNaïve(%)Elastic(%)
Balanced data across clients
CIFAR-1004000(~80)50010100.05ResNet-2032.3156.64
Unbalanced data across clients
MNIST20(~2)10001001000.1Logistic Regression70.1473.64
EMNIST1000(~2.5)3400101000.12Conv+2Linear88.7189.82
CIFAR-104000(~40)100010100.05ResNet-2066.8468.74
CINIC-10200(~20)1000100100.05ResNet-2035.8136.29
CINIC-104000(~40)100010100.05ResNet-2068.6869.25
", + "bbox": [ + 122, + 87, + 848, + 227 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/e4a9335965d8fd4ee056370f20f29020451593755d84b82f8d417219ce715118.jpg", + "table_caption": [ + "Table 2. Test accuracies for various datasets. Along with rounds, we list a more intuitive measure, i.e., epochs, to better reflect the total training computation." + ], + "table_footnote": [], + "table_body": "
OptimizerFedAvgFedAvgMFedProxSCAFFOLDAdaOptPFNMPer-FedAvgpFedMe
w/o Elastic.49.3462.5251.5272.1078.0071.2350.4483.20
w/ Elastic.52.3764.4853.6475.4280.3473.6453.2485.63
Improvement.3.031.962.123.322.342.412.802.43
", + "bbox": [ + 142, + 285, + 831, + 349 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 3. Elastic aggregation can be easily integrated with different federated optimizers, achieving performance improvements. (Notes that the comparison across different federated optimizers is meaningless since they are under different experiment settings.)", + "bbox": [ + 75, + 359, + 892, + 390 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "as the baseline model. As shown in Tab. 2, elastic aggregation significantly speeds up training. Furthermore, the final accuracy is improved by over $20\\%$ compared with the naïve baseline, which demonstrates the effectiveness of elastic aggregation.", + "bbox": [ + 75, + 415, + 470, + 491 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "CIFAR-10 and CINIC-10. To further demonstrate the performance improvement resulting from elastic aggregation, we generate two synthetic federated datasets for CIFAR-10 [20] and CINIC-10 [10] with $\\alpha = 100.0$ . CINIC-10 extends CIFAR-10 with the addition of down-sampled ImageNet images, making for a more challenging dataset. This also enables measuring the performance of models trained on CIFAR images on ImageNet images for the same classes. As shown in Tab. 2, elastic aggregation achieves superior performances on both the CIFAR-10 and the more difficult CINIC-10 datasets, confirming that our method generalizes well to large scale datasets.", + "bbox": [ + 75, + 527, + 470, + 712 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Natural Language Processing on Shakespeare dataset.", + "text_level": 1, + "bbox": [ + 75, + 750, + 470, + 763 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We maintain the same experimental setup as [40] on the most commonly used natural language processing tasks: Shakespeare LSTM. The epoch in each round is 1, the batch size is 10 and both elastic and naive aggregation are trained for 2k rounds. We get the final accuracy as $62.14\\%$ for naive aggregation and $64.73\\%$ for elastic aggregation. The results show that elastic aggregation not only has a significant improvement in CV related tasks, but also has an positive effect on NLP related tasks.", + "bbox": [ + 75, + 763, + 470, + 900 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Imbalanced and non-IID. We are also interested in understanding how parameter sensitivity can help improve convergence, particularly in cross-device and non-IID scenarios. Given the resource constraints of edge devices, large DNN models are usually trained under the cross-organization (also known as cross-silo) federated learning settings. Across the following experiments, we use CIFAR10 [28] with ResNet-20 [19]. We study three different parameters here: non-IID-ness, participation rate, and number of epochs. We explore the effects of varying non-IID-ness with $\\alpha = 100.0, 50.0, 10.0, 1.0, 0.5$ across 1000 partitions. For participation rate, we test sampling $5\\%$ , $10\\%$ , $20\\%$ , $40\\%$ of the clients at each round. Finally, we test having 1, 5 epochs of local updates, to better show the robustness of elastic aggregation. As shown in Fig. 2, elastic aggregation is especially superior for situations with massive distribution, substantial heterogeneity, and imbalanced data.", + "bbox": [ + 496, + 414, + 893, + 672 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.2. Integration with modern optimizer", + "text_level": 1, + "bbox": [ + 498, + 694, + 805, + 710 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Federated optimizer with elastic aggregation. To illustrate the generalizability of elastic aggregation, we integrate elastic aggregation into FedAvg [40], FedAvgM [46] and FedProx [31]. FedAvgM is an enhancement of FedAvg on the server-side, making use of the momentum strategy to update the server model. FedProx is an enhancement of FedAvg on the client-side, adding a penalty to the client updates. We have presented the details of FedAvg with elastic aggregation in Algorithm 1. Please refer to supplementary materials for more details about the other federated optimizers with elastic aggregation. As shown in the left part of Tab. 3, elastic aggregation works well with other com", + "bbox": [ + 496, + 719, + 895, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "12193", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/e9f6b8691d01618f2a02fbdd8ecff9dfcada6e137cf7affcea0e7d0dc1941b6d.jpg", + "image_caption": [ + "Figure 3. Convergence speeds on different datasets." + ], + "image_footnote": [], + "bbox": [ + 83, + 89, + 883, + 487 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "plementary approaches whether designed for client-side or server-side. In order to further verify the generality of elastic aggregation, we did further experiments on the stat-of-the-art methods in FL, i.e. SCAFFOLD [23], AdaOpt [46] and PFNM [59]. Since these methods target on different aspect of federated learning, we conducted experiments based on their original experimental settings. As shown in middle part of Tab. 3, elastic aggregation plays a positive effect in most federated optimizers.", + "bbox": [ + 75, + 541, + 472, + 676 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Influence on personalization. Personalization in federated learning is also a topic of great concern. Specifically, we equipped Per-FedAvg [13], pFedMe [11] – both focus on the model personalization (local model performance) in federated learning with elastic aggregation and found that elastic aggregation is also a favour in learning a better personalized model, as shown in the right part of Tab. 3.", + "bbox": [ + 75, + 696, + 470, + 803 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5.3. Limitations", + "text_level": 1, + "bbox": [ + 76, + 830, + 204, + 845 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In Fig. 3, we compare testing curves on various datasets and observe that elastic aggregation outperforms naive aggregation by converging faster. Nevertheless, using elas", + "bbox": [ + 75, + 854, + 470, + 902 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "tic aggregation results in additional computational burden and communication costs, which may affect the overall performance of federated learning scenarios. For a more detailed analysis of the computational overhead, please refer to the supplementary materials. Despite these challenges, we firmly believe that the significant performance improvements associated with elastic aggregation warrant its use over naive aggregation.", + "bbox": [ + 496, + 541, + 893, + 662 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "6. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 678, + 617, + 693 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Our work delves into the impact of heterogeneity on optimization methods for federated learning. We proposed a novel aggregation method, elastic aggregation, which utilizes parameter sensitivity to overcome gradient dissimilarity. To the best of our knowledge, we are the pioneers in utilizing unlabeled client data to enhance federated learning performances. Empirical evaluations across various federated datasets validate the theoretical analysis and reveal that elastic aggregation can significantly enhance the convergence behavior of federated learning in realistic heterogeneous scenarios. Future directions may include expanding the elastic aggregation approach to adaptive optimization methods or gossip-based training techniques.", + "bbox": [ + 496, + 704, + 893, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "12194", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Durmus Alp Emre Acar, Yue Zhao, Ramon Matas Navarro, Matthew Mattina, Paul N Whatmough, and Venkatesh Saligrama. Federated learning based on dynamic regularization. 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CiteSeer, 2010." + ], + "bbox": [ + 501, + 90, + 893, + 344 + ], + "page_idx": 10 + }, + { + "type": "page_number", + "text": "12197", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 10 + } +] \ No newline at end of file diff --git a/2023/Elastic Aggregation for Federated Optimization/aa6cbfa9-0a85-4695-927f-135bdd87fa31_model.json b/2023/Elastic Aggregation for Federated Optimization/aa6cbfa9-0a85-4695-927f-135bdd87fa31_model.json new file mode 100644 index 0000000000000000000000000000000000000000..1539a1919a717d5e3455cd178a50eb31232231ac --- /dev/null +++ b/2023/Elastic Aggregation for Federated Optimization/aa6cbfa9-0a85-4695-927f-135bdd87fa31_model.json @@ -0,0 +1,2257 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.244, + 0.131, + 0.726, + 0.154 + ], + "angle": 0, + "content": "Elastic Aggregation for Federated Optimization" + }, + { + "type": "text", + "bbox": [ + 0.145, + 0.18, + 0.83, + 0.199 + ], + "angle": 0, + "content": "Dengsheng Chen\\(^{1*}\\), Jie Hu\\(^{2,3*}\\), Vince Junkai Tan\\(^{4}\\), Xiaoming Wei\\(^{1}\\), Enhua Wu\\(^{2,3,5\\dagger}\\)" + }, + { + "type": "text", + "bbox": [ + 0.209, + 0.199, + 0.762, + 0.216 + ], + "angle": 0, + "content": "\\(^{1}\\) Meituan \\(^{2}\\) State Key Laboratory of Computer Science, ISCAS" + }, + { + "type": "text", + "bbox": [ + 0.119, + 0.216, + 0.851, + 0.234 + ], + "angle": 0, + "content": "3 University of Chinese Academy of Sciences 4 Bytedance Inc. 5 University of Macau" + }, + { + "type": "text", + "bbox": [ + 0.094, + 0.237, + 0.873, + 0.251 + ], + "angle": 0, + "content": "{chendengsheng,weixiaoming}@meituan.com,hujie@ios.ac.cn,vince.tan.jun.kai@gmail.com,ehwu@um.edu.m0" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.287, + 0.314, + 0.303 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.318, + 0.474, + 0.742 + ], + "angle": 0, + "content": "Federated learning enables the privacy-preserving training of neural network models using real-world data across distributed clients. FedAvg has become the preferred optimizer for federated learning because of its simplicity and effectiveness. FedAvg uses naive aggregation to update the server model, interpolating client models based on the number of instances used in their training. However, naive aggregation suffers from client drift when the data is heterogeneous (non-IID), leading to unstable and slow convergence. In this work, we propose a novel aggregation approach, elastic aggregation, to overcome these issues. Elastic aggregation interpolates client models adaptively according to parameter sensitivity, which is measured by computing how much the overall prediction function output changes when each parameter is changed. This measurement is performed in an unsupervised and online manner. Elastic aggregation reduces the magnitudes of updates to the more sensitive parameters so as to prevent the server model from drifting to any one client distribution, and conversely boosts updates to the less sensitive parameters to better explore different client distributions. Empirical results on real and synthetic data as well as analytical results show that elastic aggregation leads to efficient training in both convex and non-convex settings while being fully agnostic to client heterogeneity and robust to large numbers of clients, partial participation, and imbalanced data. Finally, elastic aggregation works well with other federated optimizers and achieves significant improvements across the board." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.769, + 0.21, + 0.785 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.794, + 0.471, + 0.855 + ], + "angle": 0, + "content": "Unlike traditional centralized learning in which models are trained using large datasets stored in a central server [15], federated learning - first proposed in [40] - leverages data spread across many clients to learn classification tasks dis" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.288, + 0.893, + 0.334 + ], + "angle": 0, + "content": "tributively without explicitly sharing data [22, 26, 27, 42], thereby ensuring a basic level of privacy. Federated learning is characterized by four key features:" + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.338, + 0.893, + 0.383 + ], + "angle": 0, + "content": "- Unreliable links: The links connecting the server and clients can be unreliable, and only a small subset of clients may be active at any given time." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.388, + 0.892, + 0.433 + ], + "angle": 0, + "content": "- Massive distribution: The number of clients is typically high, but the amount of data per client is relatively small." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.439, + 0.892, + 0.499 + ], + "angle": 0, + "content": "- Substantial heterogeneity: Client data is heterogeneous and non-IID [26], meaning that data across different clients can be sampled from varying regions of the sampling space." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.504, + 0.892, + 0.534 + ], + "angle": 0, + "content": "- Imbalanced data: There can be significant imbalances in the amount of data available per client." + }, + { + "type": "list", + "bbox": [ + 0.518, + 0.338, + 0.893, + 0.534 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.538, + 0.895, + 0.825 + ], + "angle": 0, + "content": "The most popular algorithm for federated learning is FedAvg [40], which tackles the communication bottleneck by performing multiple local updates on the available clients before communicating the overall change to the server. FedAvg uses naive aggregation to interpolate client models and has shown success in certain applications. However, its performance on heterogeneous data is still an active area of research [16, 25, 33]. According to [25], training models on local data that minimize local empirical loss appears to be meaningful, but yet, doing so is fundamentally inconsistent with minimizing the global empirical loss. Client updates drive the server model away from the ideal distribution, a phenomenon known as 'client drift'. Naive aggregation [40] is efficient in aggregating client models but does not account for distribution inconsistencies across client data or the consequent objective inconsistency. In other words, with naive aggregation, the server model risks converging to a stationary point of a mismatched objective function which can be arbitrarily different from the true objective [53]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.826, + 0.895, + 0.902 + ], + "angle": 0, + "content": "Prior works [24, 40, 48] attempt to overcome this issue by running fewer epochs or iterations of SGD on the devices or by stabilizing server-side updates so that the resulting models correspond to inexact minimizations and keep globally desirable properties. In this work, we propose a novel aggregation" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.864, + 0.207, + 0.876 + ], + "angle": 0, + "content": "*Equal contribution." + }, + { + "type": "page_footnote", + "bbox": [ + 0.078, + 0.876, + 0.469, + 0.9 + ], + "angle": 0, + "content": "†Corresponding author. This work is supported in part by NSFC Grants (62072449)." + }, + { + "type": "list", + "bbox": [ + 0.078, + 0.864, + 0.469, + 0.9 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "12187" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.16, + 0.088, + 0.473, + 0.332 + ], + "angle": 0, + "content": null + }, + { + "type": "image_footnote", + "bbox": [ + 0.562, + 0.124, + 0.687, + 0.138 + ], + "angle": 0, + "content": "Minima point" + }, + { + "type": "image_footnote", + "bbox": [ + 0.558, + 0.15, + 0.8, + 0.163 + ], + "angle": 0, + "content": "Low empirical loss for client A" + }, + { + "type": "image_footnote", + "bbox": [ + 0.558, + 0.177, + 0.799, + 0.19 + ], + "angle": 0, + "content": "Low empirical loss for client B" + }, + { + "type": "image_footnote", + "bbox": [ + 0.558, + 0.203, + 0.792, + 0.216 + ], + "angle": 0, + "content": "Low empirical loss for server" + }, + { + "type": "image_footnote", + "bbox": [ + 0.558, + 0.23, + 0.723, + 0.244 + ], + "angle": 0, + "content": "Naïve aggregation" + }, + { + "type": "image_footnote", + "bbox": [ + 0.558, + 0.257, + 0.728, + 0.271 + ], + "angle": 0, + "content": "Elastic aggregation" + }, + { + "type": "image_footnote", + "bbox": [ + 0.56, + 0.278, + 0.689, + 0.292 + ], + "angle": 0, + "content": "Client update" + }, + { + "type": "list", + "bbox": [ + 0.558, + 0.124, + 0.8, + 0.292 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.343, + 0.892, + 0.442 + ], + "angle": 0, + "content": "Figure 1. Illustration of naive aggregation and elastic aggregation. The local updates of client A and client B drive the server model \\(\\theta\\) towards their individual minima (black dots in plot). Naive aggregation simply averages the received model from clients A and B, yielding \\(\\theta'\\) as the new server model. Although \\(\\theta'\\) minimizes the local empirical loss of clients A and B, \\(\\theta'\\) drifts from ideal distribution for the server model. Elastic aggregation adjusts gradient with respect to parameter sensitivity. Parameter \\(\\theta_x\\) is more sensitive (has a larger gradient norm), and is restricted with \\(\\zeta_x < 1\\) to reduce the magnitude of its update. Parameter \\(\\theta_y\\) is less sensitive (has a smaller gradient norm), and is correspondingly boosted with \\(\\zeta_y > 1\\) to better explore the parameter space. This minimizes the loss for clients A and B, while not causing the server model to drift from its ideal distribution. Hence, elastic aggregation results in a better update \\(\\theta''\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.468, + 0.473, + 0.664 + ], + "angle": 0, + "content": "approach, elastic aggregation, to overcome client drift. We measure parameter sensitivity using unlabeled samples of client data, by computing the changes to the overall function output for a given change to the parameter in question, without relying on the loss. This allows our method to not only avoid requiring labeled data but importantly also pre-empt complications that could otherwise arise from the loss being at a local minimum with gradients close to zero. During the aggregation of client models, updates to the more sensitive parameters can then be reduced in magnitude, preventing the server model from drifting to any client distribution. Conversely, updates to the less sensitive parameters can be boosted to better explore different client distributions." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.689, + 0.47, + 0.901 + ], + "angle": 0, + "content": "Contributions. Elastic aggregation tackles distribution inconsistency across client data using the concept of parameter sensitivity and is simple to implement, requiring little hyperparameter tuning. Furthermore, parameter sensitivity is computed in an online and unsupervised manner, and thus better utilizes the unlabeled data generated by the client during runtime. Elastic aggregation is easily integrated into different federated optimizers, achieving substantial improvements over naïve aggregation. The empirical results on real and synthetic data and analytical results show that elastic aggregation leads to efficient training in both convex and non-convex settings, across all four federated learning scenarios (unreliable links, massive distribution, substantial heterogeneity, and imbalanced data)." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.466, + 0.637, + 0.481 + ], + "angle": 0, + "content": "2. Related work" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.492, + 0.895, + 0.763 + ], + "angle": 0, + "content": "Federated learning is a fast-evolving topic. The general setup involves server and client updates; each of these updates is associated with minimizing some local loss function. The server model then benefits from all client data and achieves superior performance, for tasks such as next word prediction [17, 56], emoji prediction [45], decoder models [8], vocabulary estimation [7], low latency vehicle-to-vehicle communication [49] and predictive models in health [6]. Nevertheless, federated learning raises several issues and has been the topic of much research effort, focusing on the issues of generalization and fairness [33, 42], the design of more efficient communication strategies [4,24,26,27,51,52], the study of lower bounds [55], differential privacy guarantees [2], security [5], etc [22]. We focus here on relevant work that specifically addresses the four federated learning characteristics noted above - massive distribution, heterogeneity, unreliable links, and imbalanced data." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Much of earlier work in this context proposes optimizing for the local risk objective with SGD [51] over mini-batches of client data, analogous to the centralized scenario, with the server then averages the received models. FedAvg [40] is a generalization of local SGD, proposing a larger number of local SGD steps per round. In the case of identical clients, it reduces to parallel SGD for which asymptotic convergence has been proven [51, 62]; more recently, [25, 43] analyzed the same method under the name of local SGD, also for" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "12188" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.471, + 0.152 + ], + "angle": 0, + "content": "identical functions. FedAvg in exactly solves client-side optimization, requiring the tuning of the number of epochs and the learning rate hyper-parameters in order to achieve a good accuracy-communication trade-off [30,40]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.161, + 0.474, + 0.432 + ], + "angle": 0, + "content": "Despite the strong empirical performance of FedAvg in IID settings, performance degrades in non-IID scenarios [61]. The analysis of FedAvg for heterogeneous clients is more delicate, due to the aforementioned client drift, first empirically observed by [61]. Several analyses bound this drift by assuming bounded gradients [54, 57], viewing it as additional noise [25], or assuming that the client optima are \\(\\epsilon\\)-close [16,33]. [36] proposes using variance reduction to deal with client heterogeneity but achieved slower convergence rates than SGD. Other variants include using a decreasing learning rate [30], modifying client empirical loss dynamically [1,31], adding regularizers on local updates [23,24,50], or modifying the server side updates [21,48]. While these works do recognize the incompatibility of local and global stationary points, their proposed fixes are based on inexact minimization. Additionally, in order to establish convergence for non-IID situations, these works impose additional constraints." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.441, + 0.472, + 0.669 + ], + "angle": 0, + "content": "Another class of work that extend the analysis of SGD-type methods to federated learning settings specifically addresses the special case of full client participation [9, 14, 26, 34-36, 38, 44, 50, 58]. For example, FedSVRG [26] and DANE [50] need gradient information from all clients each round and are as such not directly applicable to partial federated learning settings. Furthermore, it may not be trivial to extend these works to overcome the deficiency. For example, FedDANE [32] is a version of DANE that works with partial participation. However, with partial participation, FedDANE empirically performs worse than FedAvg [33]. Similar to these works, FedPD [60] proposes distributed optimization with a different notion of 'participation'. FedPD activates either all clients or no clients per round, which again fails to satisfy the partial participation condition." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.677, + 0.472, + 0.753 + ], + "angle": 0, + "content": "Finally, there have been earlier works aiming to decrease communication costs by compressing the transmitted models [3, 12, 41], decreasing the bit-rate of the transmission. These ideas are complementary to our work and can work together with our approach." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.791, + 0.168, + 0.807 + ], + "angle": 0, + "content": "3. Method" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.826, + 0.471, + 0.887 + ], + "angle": 0, + "content": "In this section, we focus on the introduction of parameter sensitivity in process of federated learning, which is our main innovation. The proof of convergence is provided in the technical part of supplementary materials." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.091, + 0.875, + 0.108 + ], + "angle": 0, + "content": "3.1. Federated Learning with Naïve Aggregation" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.114, + 0.892, + 0.143 + ], + "angle": 0, + "content": "In federated learning, we solve an optimization problem of the form:" + }, + { + "type": "equation", + "bbox": [ + 0.588, + 0.151, + 0.892, + 0.19 + ], + "angle": 0, + "content": "\\[\n\\arg \\min _ {\\theta \\in \\mathbb {R} ^ {n}} [ \\ell (\\theta) \\triangleq \\frac {1}{m} \\sum_ {k = 1} ^ {m} L _ {k} (\\theta) ], \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.201, + 0.892, + 0.248 + ], + "angle": 0, + "content": "where \\(L_{k}(\\theta)\\triangleq \\mathbb{E}_{(x,y)\\sim \\mathcal{P}_{k}}[\\ell_{k}(\\theta ;(x,y))]\\) is the empirical loss of the \\(k^{th}\\) client, \\(\\mathcal{P}_k\\) is the data distribution for the \\(k^{th}\\) client across \\(K\\) clients." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.267, + 0.892, + 0.372 + ], + "angle": 0, + "content": "FedAvg. A common approach to solving Eq. 1 in federated settings is FedAvg [40]. At each round, a subset of clients is selected (typically randomly) and the server broadcasts its model to each client. In parallel, the clients run SGD on their own loss function \\(\\ell_{k}\\) and then send their updated models to the server. The server then updates its model to be the average of these client models." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.373, + 0.892, + 0.418 + ], + "angle": 0, + "content": "Suppose that at the \\( r^{th} \\) round, the server has model \\( \\theta \\) and samples a client set \\( S \\). Here we use a standard gradient descent form to update parameters:" + }, + { + "type": "equation", + "bbox": [ + 0.649, + 0.429, + 0.892, + 0.445 + ], + "angle": 0, + "content": "\\[\n\\theta \\leftarrow \\theta - \\eta \\Delta , \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.455, + 0.892, + 0.501 + ], + "angle": 0, + "content": "where \\(\\Delta\\) is the aggregated clients' gradients and \\(\\eta\\) is the learning rate of the server, which is typically 1.0. FedAvg uses naive aggregation to compute \\(\\Delta\\)." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.518, + 0.88, + 0.534 + ], + "angle": 0, + "content": "Naive aggregation. We can write naive aggregation as:" + }, + { + "type": "equation", + "bbox": [ + 0.628, + 0.542, + 0.892, + 0.575 + ], + "angle": 0, + "content": "\\[\n\\Delta = \\sum_ {k \\in \\mathcal {S}} \\left(w _ {k} \\cdot \\Delta_ {k}\\right), \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.584, + 0.894, + 0.661 + ], + "angle": 0, + "content": "where \\(\\Delta_{k} = \\theta -\\theta_{k}\\) is the accumulated gradients within a training round of the \\(k^{th}\\) client, and \\(w_{k} = |D_{k}| / \\sum_{k\\in S}|D_{k}|\\) is the aggregated weight of the \\(k^{th}\\) client across the activated clients \\(\\mathcal{S}\\). \\(D_{k},\\theta_{k}\\) are the training dataset and trained parameters on the \\(k^{th}\\) client, respectively." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.682, + 0.78, + 0.699 + ], + "angle": 0, + "content": "3.2. Exploring parameter sensitivity" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.705, + 0.894, + 0.796 + ], + "angle": 0, + "content": "Due to the non-IID-ness (heterogeneity) across different clients, \\(\\mathcal{P}\\) can vary substantially across different clients. Thus, the simple and efficient way to aggregate client models described in Eq. 3 cannot solve client drift and cause oscillation as well as slow convergence. We explore parameter sensitivity as an approach to overcoming these issues." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.797, + 0.894, + 0.871 + ], + "angle": 0, + "content": "The main idea we are proposing is that less sensitive parameters can be freely updated to minimize the loss for individual clients in \\( S \\) without causing the server to drift; by the same reasoning, parameters that are more sensitive should not be updated as much. This is illustrated in Fig. 1." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.871, + 0.892, + 0.901 + ], + "angle": 0, + "content": "At the \\(r^{th}\\) round, the active clients receive the server model \\(\\theta_r\\), which parameterizes the approximation function" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "12189" + } + ], + [ + { + "type": "code_caption", + "bbox": [ + 0.087, + 0.095, + 0.427, + 0.125 + ], + "angle": 0, + "content": "Algorithm 1: Elastic aggregation within a single layer" + }, + { + "type": "algorithm", + "bbox": [ + 0.097, + 0.128, + 0.449, + 0.264 + ], + "angle": 0, + "content": "A variable with a superscript \\(i\\) indicates the \\(i^{th}\\) element of the variable. A variable with a subscript \\(k\\) indicates the variable from \\(k^{th}\\) client. \\(\\eta, \\eta'\\) are learning rates of server and clients respectively. \\(\\mu, \\tau\\) are the hyper-parameters. \\(\\theta, \\theta_k \\in \\mathbb{R}^n\\) are the server's and the \\(k^{th}\\) client's parameters respectively. \\(\\Omega \\in \\mathbb{R}^n\\) is the aggregated parameter sensitivity. \\(\\Omega_k \\in \\mathbb{R}^n\\) is the parameter sensitivity on the \\(k^{th}\\) client." + }, + { + "type": "text", + "bbox": [ + 0.099, + 0.266, + 0.172, + 0.278 + ], + "angle": 0, + "content": "Initialize \\(\\theta\\)" + }, + { + "type": "text", + "bbox": [ + 0.1, + 0.281, + 0.384, + 0.295 + ], + "angle": 0, + "content": "\\(B_{k}\\gets\\) Sample a subset of training data \\(D_{k}\\)" + }, + { + "type": "text", + "bbox": [ + 0.1, + 0.296, + 0.369, + 0.311 + ], + "angle": 0, + "content": "\\(D_{k}\\gets\\) Drop the samples of \\(B_{k}\\) from \\(D_{k}\\)" + }, + { + "type": "text", + "bbox": [ + 0.1, + 0.312, + 0.221, + 0.324 + ], + "angle": 0, + "content": "for each round do" + }, + { + "type": "algorithm", + "bbox": [ + 0.124, + 0.327, + 0.409, + 0.595 + ], + "angle": 0, + "content": "for each activated client \\(k\\) do Initialize \\(\\Omega_{k}\\) as zeros. \nfor each batch data \\(x\\in B_k\\) do \\(\\begin{array}{l}g = \\nabla ||F(\\theta ;x)||_2^2\\\\ \\mathbf{for}i\\in [1,\\dots ,n]\\mathbf{do}\\\\ \\big{\\lfloor}\\Omega_k^i\\gets \\mu \\Omega_k^i +(1 - \\mu)|g^i |\\\\ \\theta_k\\gets \\theta \\\\ \\mathbf{for}\\) each epoch do for each batch data \\(x\\in D_k\\) do \\(\\begin{array}{r}\\Big{\\lfloor}\\theta_{k}\\leftarrow \\theta_{k} - \\eta^{\\prime}\\nabla \\ell_{k}(F(\\theta_{k};x))\\\\ \\Delta_{k} = \\theta_{k} - \\theta \\end{array}\\) \n\\(w_{k}\\gets |D_{k}| / \\sum_{k}|D_{k}|;\\Omega = \\sum_{k}(w_{k}\\cdot \\Omega_{k});\\) \\(\\Omega^{\\prime} = \\max (\\Omega)\\) \nfor \\(i\\in [1,\\dots ,n]\\) do \\(\\zeta^i = 1 + \\tau -\\Omega^i /\\Omega '\\) \\(\\Delta^i = \\zeta^i\\cdot \\sum_k(w_k\\cdot \\Delta_k^i)\\) \\(\\theta^i\\gets \\theta^i -\\eta \\cdot \\Delta^i\\)" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.635, + 0.47, + 0.756 + ], + "angle": 0, + "content": "\\(F\\) of the true function \\(\\bar{F}\\). \\(F\\) maps the input \\(x\\) to the output \\(y\\), and our goal is to largely maintain the same output \\(y\\) for the observed \\(x\\) while learning additional training instances \\((x,y) \\sim P_k\\). To this end, we measure how sensitive the output of function \\(F\\) is to changes in the network parameters. To reduce confusion, we ignore the symbols denoting the round \\(r\\) and the client \\(k\\) for all variables and only discuss parameter sensitivity locally." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.757, + 0.47, + 0.816 + ], + "angle": 0, + "content": "For a given data point \\( x \\), the output of the network is \\( F(\\theta; x) \\). A small perturbation \\( \\delta \\) in the parameters \\( \\theta \\) results in a change in the function output that can be approximated by:" + }, + { + "type": "equation", + "bbox": [ + 0.158, + 0.817, + 0.469, + 0.833 + ], + "angle": 0, + "content": "\\[\nF (\\theta + \\delta ; x) - F (\\theta ; x) \\approx g (\\theta ; x) \\delta , \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.838, + 0.471, + 0.901 + ], + "angle": 0, + "content": "where \\( g(\\theta ;x) = \\frac{\\partial F(\\theta;x)}{\\partial\\theta} \\) is the gradient of the learned function with respect to the parameter \\( \\theta \\) evaluated at the data point \\( x \\). Our goal is to maintain the output of the network (the learned function \\( F \\)) for each observed data point and" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.894, + 0.151 + ], + "angle": 0, + "content": "thus we reduce the magnitudes of the updates to the parameters that are more sensitive for the data point. Conversely, we boost the updates to the less sensitive parameters to better-fit client distributions." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.152, + 0.893, + 0.319 + ], + "angle": 0, + "content": "Based on equation 4, and assuming a small constant change \\(\\delta\\), we can measure the sensitivity of a parameter by the magnitude of the gradient \\(g(\\theta; x)\\), i.e., how much does a small perturbation to that parameter change the output of the learned function for data point \\(x\\). There are many ways to measure the sensitivity of a parameter by the magnitude of the gradient, such as a fishing matrix. However, in federated learning, we have to take the computation ability of each client into account, which is only with limited computation ability. Therefore, we use the exponentially-decayed moving average1 to obtain sensitivity \\(\\Omega^i\\) for \\(i^{th}\\) parameter \\(\\theta^i\\):" + }, + { + "type": "equation", + "bbox": [ + 0.59, + 0.327, + 0.892, + 0.345 + ], + "angle": 0, + "content": "\\[\n\\Omega^ {i} \\leftarrow \\mu \\Omega^ {i} + (1 - \\mu) | g \\left(\\theta^ {i}; x\\right) |, \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.354, + 0.862, + 0.368 + ], + "angle": 0, + "content": "where \\(\\mu\\) is momentum and we empirically set it to 0.9." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.369, + 0.894, + 0.504 + ], + "angle": 0, + "content": "When the output function \\(F\\) is multi-dimensional, as is the case for most neural networks, equation 5 involves computing the gradients for each output, which requires as many backward passes as the dimensionality of the output. As a more efficient alternative, we propose to use the gradients of the squared \\(L^2\\) norm of the learned function output, i.e. \\(g(\\theta ;x) = \\nabla ||F(\\theta ;x)||_2^2\\). Hence, we only need to compute one backward pass in order to estimate the parameters' sensitivity." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.525, + 0.892, + 0.557 + ], + "angle": 0, + "content": "3.3. Elastic aggregation with respect to parameter sensitivity" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.563, + 0.892, + 0.592 + ], + "angle": 0, + "content": "The elastic aggregation for \\( i^{th} \\) parameter can be written as:" + }, + { + "type": "equation", + "bbox": [ + 0.614, + 0.592, + 0.891, + 0.623 + ], + "angle": 0, + "content": "\\[\n\\Delta^ {i} = \\zeta^ {i} \\cdot \\sum_ {k \\in \\mathcal {S}} \\left(w _ {k} \\cdot \\Delta_ {k} ^ {i}\\right), \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.628, + 0.894, + 0.659 + ], + "angle": 0, + "content": "where \\(\\zeta^i\\) is the adaptive coefficient with respect to the parameter sensitivity. The definition of \\(\\zeta^i\\) is:" + }, + { + "type": "equation", + "bbox": [ + 0.624, + 0.668, + 0.891, + 0.686 + ], + "angle": 0, + "content": "\\[\n\\zeta^ {i} = 1 + \\tau - \\Omega^ {i} / \\Omega^ {\\prime}, \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.694, + 0.894, + 0.832 + ], + "angle": 0, + "content": "where \\(\\Omega' = \\max(\\Omega)\\) is the maximum of parameter sensitivities in each layer, and \\(\\Omega^i = \\sum_{k \\in S} (w_k \\cdot \\Omega_k^i)\\) is the aggregated sensitivity of \\(i^{th}\\) parameter across activated clients. The server is able to boost updates (\\(\\zeta^i > 1.0\\)) to parameters that have low sensitivity (low \\(\\Omega^i\\)). Meanwhile, sensitive parameters (high \\(\\Omega^i\\)) have their updates restricted with a penalty (\\(\\zeta^i < 1.0\\)). \\(\\tau\\) is a hyper-parameter determining the ratio of boosted or restricted parameters. FedAvg with elastic aggregation is formalized in Algorithm 1." + }, + { + "type": "page_footnote", + "bbox": [ + 0.498, + 0.839, + 0.894, + 0.901 + ], + "angle": 0, + "content": "1While a Polyak-style average has more theoretical guarantees for accumulating \\(\\Omega\\) over batches, our results match the claim that \"an exponentially-decayed moving average typically works much better in practice\" [39]. Thus, we use the exponentially-decayed moving average to accumulate \\(\\Omega\\) over batches. Refer to supplementary materials for more discussion." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "12190" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.091, + 0.471, + 0.182 + ], + "angle": 0, + "content": "Discussion on \\(\\tau\\). In Eq. 6, \\(\\zeta^i \\in (1, 1 + \\tau]\\) is applied to the less sensitive parameters, and \\(\\zeta^i \\in [\\tau, 1)\\) is applied to the more sensitive parameters. Thus, \\(\\tau\\) determines the portion of the parameter to be restricted or boosted. Generally, a larger \\(\\tau\\) indicates that a larger proportion of parameters will be boosted, as shown in Tab. 1, and vice versa." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.183, + 0.474, + 0.32 + ], + "angle": 0, + "content": "If a large proportion of parameters is restricted (\\(\\tau\\) is small, such as 0.1), the server model will not be updated much, and exiting local minima becomes difficult. However, with a large \\(\\tau\\) such as 0.9, optimization of the server model becomes unstable, and this also causes performance degradation. It is therefore critical to maintain a balance between these extremes with a suitable \\(\\tau\\) and we find that \\(\\tau = 0.5\\) generalizes well to various experiments. At this value of \\(\\tau\\), roughly three-quarters of the parameters are boosted." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.338, + 0.279, + 0.357 + ], + "angle": 0, + "content": "4. Experiments settings" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.364, + 0.473, + 0.545 + ], + "angle": 0, + "content": "Inconsistent usage of models, datasets, and non-IID partition methods makes it difficult to compare the performances of federated learning algorithms fairly. To enforce fair comparison, we explicitly specify the combinations of datasets, models, and non-IID partition methods to be used for experiments, which mostly consist of those used in existing work published at top-tier machine learning venues [18]. Note that although the reported precisions are state-of-the-art for the models we have chosen, higher-capacity models can achieve higher performances on these datasets. Therefore, we compare the relative performance of elastic aggregation against naive aggregation for various federated learning scenarios." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.561, + 0.24, + 0.577 + ], + "angle": 0, + "content": "4.1. Implementation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.584, + 0.473, + 0.903 + ], + "angle": 0, + "content": "We measure our algorithm against the most comprehensive and representative suite of federated datasets and modeling tasks to date. For this purpose, we carry out simulations on five diverse and representative experiments on several datasets. In order to facilitate the experiments, we use the cosine annealing scheduler [37] for the client learning rate \\(\\eta_r^\\prime\\) at the \\(r^{th}\\) round, which is given by \\(\\eta_r^\\prime = (1 + \\cos (\\frac{r}{R}\\pi))\\eta^\\prime\\). For all tasks, we measure the performance on the entire test set throughout training. Clients are sampled uniformly at random, without replacement within a given round, but with replacement across rounds. There are a variety of federated optimizers that improve the performance of federated learning. Here, we use the most basic and widely used federated optimization algorithm, i.e., FedAvg [40], as the default baseline in our experiments. With reference to [46], we implement all experiments with two important characteristics. First, instead of doing \\(K\\) training steps per client, we do \\(E\\) epochs of training over each client's data. Second, to account for varying numbers of gradient steps per client, we weigh the average of the client outputs \\(\\Delta_t^k\\) by the number of training samples. This also follows the approach of" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.091, + 0.895, + 0.213 + ], + "angle": 0, + "content": "[40] and often outperforms uniform weighting [47]. We set \\(\\mu = 0.95\\) for the accumulation of the parameter sensitivity over batches in each client. \\(\\tau = 0.5, \\eta = 1.0\\) is used for all experiments. While computing Eq. 7, we normalize the parameter sensitivity layer by layer, which means that the parameter sensitivity is divided by the maximum value within the same layer. Aside from experiments 5.1, we set \\(E = 1\\) for each client for all experiments." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.23, + 0.83, + 0.246 + ], + "angle": 0, + "content": "4.2. Generate synthetic federated datasets." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.254, + 0.895, + 0.406 + ], + "angle": 0, + "content": "Differences in distribution have an enormous influence on the performance of federated optimization. The Dirichlet distribution is used on the label ratios to ensure uneven label distributions among clients for non-IID splits, as in [59]. To generate imbalanced data, we sample the number of data points from a log-normal distribution. The degree of imbalance depends on the variance of the log-normal distribution, which is controlled by the hyper-parameter \\(\\alpha\\). A smaller \\(\\alpha\\) indicates a stronger non-IID-ness in partitions, as shown in Fig. 2." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.426, + 0.634, + 0.444 + ], + "angle": 0, + "content": "5. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.452, + 0.895, + 0.529 + ], + "angle": 0, + "content": "Under all experiments, the samples used for computing parameter sensitivities at each client will be randomly sampled training data, and these sampled data will not be used for supervised training anymore. For a fair comparison, these sampled data will not be used in the baseline methods either." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.554, + 0.812, + 0.571 + ], + "angle": 0, + "content": "5.1. Comparison with naive aggregation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.578, + 0.895, + 0.715 + ], + "angle": 0, + "content": "MNIST. As our baseline, we conduct a convex optimization experiment on MNIST [29] with logistic regression [31, 33, 40]. In this experiment, we generate a synthetic federated dataset of MNIST with \\(\\alpha = 100.0\\) and split the dataset into 1000 partitions. At each round of training, we randomly choose 100 clients without repeating the partition. As shown in Tab. 2, the elastic aggregation has a large advantage over naive aggregation even with a large number of participating clients." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.735, + 0.897, + 0.903 + ], + "angle": 0, + "content": "Federated EMNIST. Due to resource constraints of edge devices, existing works commonly use shallow neural networks for experiments. Similarly, we include Federated EMNIST [46] with a shallow neural network consisting of two convolution layers followed by two linear layers [46]. Notably, Fed-EMNIST [46] has a natural client partitioning that is highly representative of real-world federated learning problems. It contains 3,400 users (clients) and 62 label classes. The dataset is split into 671,585 training examples and 77,483 testing examples. Rather than holding out specific users, we split each user's examples across the train" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.958 + ], + "angle": 0, + "content": "12191" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.086, + 0.09, + 0.891, + 0.63 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.643, + 0.895, + 0.677 + ], + "angle": 0, + "content": "Figure 2. Performances across different partitioning distributions, participation rates and numbers of local epochs. Compared with naive aggregation, elastic aggregation achieves significant improvements across these settings." + }, + { + "type": "table", + "bbox": [ + 0.103, + 0.69, + 0.871, + 0.761 + ], + "angle": 0, + "content": "
τNaïve0.00.10.20.30.40.50.60.70.80.91.0
Train Acc.(%)58.3657.2158.3358.7660.6660.4761.4460.6660.5561.0159.2758.96
Test Acc.(%)60.7458.3059.7661.1761.9163.3962.7463.3963.2363.2260.8361.37
Boosted(%)-0.011.4527.2443.7559.7474.4384.5789.9393.5396.2697.38
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.769, + 0.895, + 0.799 + ], + "angle": 0, + "content": "Table 1. The effect of \\( \\tau \\). Using an unsuitable \\( \\tau \\) for elastic aggregation with cause it to even under-perform naïve aggregation. The last row shows the percentage of parameters that are boosted for different \\( \\tau \\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.824, + 0.473, + 0.9 + ], + "angle": 0, + "content": "and test so that all users have at least one example in the train and one example in the test. Users with fewer than 2 examples are excluded from the data set. As shown in Tab. 2, elastic aggregation generalizes well to real-world federated learning problems." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.824, + 0.896, + 0.871 + ], + "angle": 0, + "content": "CIFAR-100. In this experiment, we conduct a balanced but non-IID partition on Fed-CIFAR\\(^{100}\\)², which was introduced by TensorFlow Federated [20] with ResNet-20 [19]" + }, + { + "type": "page_footnote", + "bbox": [ + 0.516, + 0.887, + 0.737, + 0.902 + ], + "angle": 0, + "content": "2https://github.com/tensorflow/federated" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "12192" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.123, + 0.088, + 0.849, + 0.228 + ], + "angle": 0, + "content": "
DatasetRounds(Epochs)TotalSampledBatchInit. LRModelNaïve(%)Elastic(%)
Balanced data across clients
CIFAR-1004000(~80)50010100.05ResNet-2032.3156.64
Unbalanced data across clients
MNIST20(~2)10001001000.1Logistic Regression70.1473.64
EMNIST1000(~2.5)3400101000.12Conv+2Linear88.7189.82
CIFAR-104000(~40)100010100.05ResNet-2066.8468.74
CINIC-10200(~20)1000100100.05ResNet-2035.8136.29
CINIC-104000(~40)100010100.05ResNet-2068.6869.25
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.238, + 0.895, + 0.268 + ], + "angle": 0, + "content": "Table 2. Test accuracies for various datasets. Along with rounds, we list a more intuitive measure, i.e., epochs, to better reflect the total training computation." + }, + { + "type": "table", + "bbox": [ + 0.143, + 0.286, + 0.832, + 0.351 + ], + "angle": 0, + "content": "
OptimizerFedAvgFedAvgMFedProxSCAFFOLDAdaOptPFNMPer-FedAvgpFedMe
w/o Elastic.49.3462.5251.5272.1078.0071.2350.4483.20
w/ Elastic.52.3764.4853.6475.4280.3473.6453.2485.63
Improvement.3.031.962.123.322.342.412.802.43
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.361, + 0.893, + 0.391 + ], + "angle": 0, + "content": "Table 3. Elastic aggregation can be easily integrated with different federated optimizers, achieving performance improvements. (Notes that the comparison across different federated optimizers is meaningless since they are under different experiment settings.)" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.416, + 0.472, + 0.492 + ], + "angle": 0, + "content": "as the baseline model. As shown in Tab. 2, elastic aggregation significantly speeds up training. Furthermore, the final accuracy is improved by over \\(20\\%\\) compared with the naïve baseline, which demonstrates the effectiveness of elastic aggregation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.529, + 0.472, + 0.713 + ], + "angle": 0, + "content": "CIFAR-10 and CINIC-10. To further demonstrate the performance improvement resulting from elastic aggregation, we generate two synthetic federated datasets for CIFAR-10 [20] and CINIC-10 [10] with \\(\\alpha = 100.0\\). CINIC-10 extends CIFAR-10 with the addition of down-sampled ImageNet images, making for a more challenging dataset. This also enables measuring the performance of models trained on CIFAR images on ImageNet images for the same classes. As shown in Tab. 2, elastic aggregation achieves superior performances on both the CIFAR-10 and the more difficult CINIC-10 datasets, confirming that our method generalizes well to large scale datasets." + }, + { + "type": "title", + "bbox": [ + 0.076, + 0.75, + 0.472, + 0.765 + ], + "angle": 0, + "content": "Natural Language Processing on Shakespeare dataset." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.765, + 0.472, + 0.901 + ], + "angle": 0, + "content": "We maintain the same experimental setup as [40] on the most commonly used natural language processing tasks: Shakespeare LSTM. The epoch in each round is 1, the batch size is 10 and both elastic and naive aggregation are trained for 2k rounds. We get the final accuracy as \\(62.14\\%\\) for naive aggregation and \\(64.73\\%\\) for elastic aggregation. The results show that elastic aggregation not only has a significant improvement in CV related tasks, but also has an positive effect on NLP related tasks." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.415, + 0.895, + 0.673 + ], + "angle": 0, + "content": "Imbalanced and non-IID. We are also interested in understanding how parameter sensitivity can help improve convergence, particularly in cross-device and non-IID scenarios. Given the resource constraints of edge devices, large DNN models are usually trained under the cross-organization (also known as cross-silo) federated learning settings. Across the following experiments, we use CIFAR10 [28] with ResNet-20 [19]. We study three different parameters here: non-IID-ness, participation rate, and number of epochs. We explore the effects of varying non-IID-ness with \\(\\alpha = 100.0, 50.0, 10.0, 1.0, 0.5\\) across 1000 partitions. For participation rate, we test sampling \\(5\\%\\), \\(10\\%\\), \\(20\\%\\), \\(40\\%\\) of the clients at each round. Finally, we test having 1, 5 epochs of local updates, to better show the robustness of elastic aggregation. As shown in Fig. 2, elastic aggregation is especially superior for situations with massive distribution, substantial heterogeneity, and imbalanced data." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.695, + 0.807, + 0.712 + ], + "angle": 0, + "content": "5.2. Integration with modern optimizer" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.897, + 0.901 + ], + "angle": 0, + "content": "Federated optimizer with elastic aggregation. To illustrate the generalizability of elastic aggregation, we integrate elastic aggregation into FedAvg [40], FedAvgM [46] and FedProx [31]. FedAvgM is an enhancement of FedAvg on the server-side, making use of the momentum strategy to update the server model. FedProx is an enhancement of FedAvg on the client-side, adding a penalty to the client updates. We have presented the details of FedAvg with elastic aggregation in Algorithm 1. Please refer to supplementary materials for more details about the other federated optimizers with elastic aggregation. As shown in the left part of Tab. 3, elastic aggregation works well with other com" + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "12193" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.084, + 0.09, + 0.885, + 0.488 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.33, + 0.501, + 0.638, + 0.516 + ], + "angle": 0, + "content": "Figure 3. Convergence speeds on different datasets." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.542, + 0.473, + 0.678 + ], + "angle": 0, + "content": "plementary approaches whether designed for client-side or server-side. In order to further verify the generality of elastic aggregation, we did further experiments on the stat-of-the-art methods in FL, i.e. SCAFFOLD [23], AdaOpt [46] and PFNM [59]. Since these methods target on different aspect of federated learning, we conducted experiments based on their original experimental settings. As shown in middle part of Tab. 3, elastic aggregation plays a positive effect in most federated optimizers." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.697, + 0.471, + 0.804 + ], + "angle": 0, + "content": "Influence on personalization. Personalization in federated learning is also a topic of great concern. Specifically, we equipped Per-FedAvg [13], pFedMe [11] – both focus on the model personalization (local model performance) in federated learning with elastic aggregation and found that elastic aggregation is also a favour in learning a better personalized model, as shown in the right part of Tab. 3." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.832, + 0.205, + 0.847 + ], + "angle": 0, + "content": "5.3. Limitations" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.472, + 0.903 + ], + "angle": 0, + "content": "In Fig. 3, we compare testing curves on various datasets and observe that elastic aggregation outperforms naive aggregation by converging faster. Nevertheless, using elas" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.542, + 0.895, + 0.663 + ], + "angle": 0, + "content": "tic aggregation results in additional computational burden and communication costs, which may affect the overall performance of federated learning scenarios. For a more detailed analysis of the computational overhead, please refer to the supplementary materials. Despite these challenges, we firmly believe that the significant performance improvements associated with elastic aggregation warrant its use over naive aggregation." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.679, + 0.618, + 0.694 + ], + "angle": 0, + "content": "6. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.705, + 0.895, + 0.901 + ], + "angle": 0, + "content": "Our work delves into the impact of heterogeneity on optimization methods for federated learning. We proposed a novel aggregation method, elastic aggregation, which utilizes parameter sensitivity to overcome gradient dissimilarity. To the best of our knowledge, we are the pioneers in utilizing unlabeled client data to enhance federated learning performances. Empirical evaluations across various federated datasets validate the theoretical analysis and reveal that elastic aggregation can significantly enhance the convergence behavior of federated learning in realistic heterogeneous scenarios. Future directions may include expanding the elastic aggregation approach to adaptive optimization methods or gossip-based training techniques." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "12194" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.088, + 0.117, + 0.47, + 0.193 + ], + "angle": 0, + "content": "[1] Durmus Alp Emre Acar, Yue Zhao, Ramon Matas Navarro, Matthew Mattina, Paul N Whatmough, and Venkatesh Saligrama. Federated learning based on dynamic regularization. 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CiteSeer, 2010." + }, + { + "type": "list", + "bbox": [ + 0.503, + 0.092, + 0.894, + 0.345 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "12197" + } + ] +] \ No newline at end of file diff --git a/2023/Elastic Aggregation for Federated Optimization/aa6cbfa9-0a85-4695-927f-135bdd87fa31_origin.pdf b/2023/Elastic Aggregation for Federated Optimization/aa6cbfa9-0a85-4695-927f-135bdd87fa31_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..daa94cc44db8ae9ad3289263ec933444a6edae80 --- /dev/null +++ b/2023/Elastic Aggregation for Federated Optimization/aa6cbfa9-0a85-4695-927f-135bdd87fa31_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:608db6891e51e4a7e5c20e7556e02543e35c8ed1207ecc0b85104e27c1b6c76f +size 533384 diff --git a/2023/Elastic Aggregation for Federated Optimization/full.md b/2023/Elastic Aggregation for Federated Optimization/full.md new file mode 100644 index 0000000000000000000000000000000000000000..7da1e30f611b9080c6b91eeb23f50ca0562d1aac --- /dev/null +++ b/2023/Elastic Aggregation for Federated Optimization/full.md @@ -0,0 +1,298 @@ +# Elastic Aggregation for Federated Optimization + +Dengsheng Chen $^{1*}$ , Jie Hu $^{2,3*}$ , Vince Junkai Tan $^{4}$ , Xiaoming Wei $^{1}$ , Enhua Wu $^{2,3,5\dagger}$ + +$^{1}$ Meituan $^{2}$ State Key Laboratory of Computer Science, ISCAS + +3 University of Chinese Academy of Sciences 4 Bytedance Inc. 5 University of Macau + +{chendengsheng,weixiaoming}@meituan.com,hujie@ios.ac.cn,vince.tan.jun.kai@gmail.com,ehwu@um.edu.m0 + +# Abstract + +Federated learning enables the privacy-preserving training of neural network models using real-world data across distributed clients. FedAvg has become the preferred optimizer for federated learning because of its simplicity and effectiveness. FedAvg uses naive aggregation to update the server model, interpolating client models based on the number of instances used in their training. However, naive aggregation suffers from client drift when the data is heterogeneous (non-IID), leading to unstable and slow convergence. In this work, we propose a novel aggregation approach, elastic aggregation, to overcome these issues. Elastic aggregation interpolates client models adaptively according to parameter sensitivity, which is measured by computing how much the overall prediction function output changes when each parameter is changed. This measurement is performed in an unsupervised and online manner. Elastic aggregation reduces the magnitudes of updates to the more sensitive parameters so as to prevent the server model from drifting to any one client distribution, and conversely boosts updates to the less sensitive parameters to better explore different client distributions. Empirical results on real and synthetic data as well as analytical results show that elastic aggregation leads to efficient training in both convex and non-convex settings while being fully agnostic to client heterogeneity and robust to large numbers of clients, partial participation, and imbalanced data. Finally, elastic aggregation works well with other federated optimizers and achieves significant improvements across the board. + +# 1. Introduction + +Unlike traditional centralized learning in which models are trained using large datasets stored in a central server [15], federated learning - first proposed in [40] - leverages data spread across many clients to learn classification tasks dis + +tributively without explicitly sharing data [22, 26, 27, 42], thereby ensuring a basic level of privacy. Federated learning is characterized by four key features: + +- Unreliable links: The links connecting the server and clients can be unreliable, and only a small subset of clients may be active at any given time. +- Massive distribution: The number of clients is typically high, but the amount of data per client is relatively small. +- Substantial heterogeneity: Client data is heterogeneous and non-IID [26], meaning that data across different clients can be sampled from varying regions of the sampling space. +- Imbalanced data: There can be significant imbalances in the amount of data available per client. + +The most popular algorithm for federated learning is FedAvg [40], which tackles the communication bottleneck by performing multiple local updates on the available clients before communicating the overall change to the server. FedAvg uses naive aggregation to interpolate client models and has shown success in certain applications. However, its performance on heterogeneous data is still an active area of research [16, 25, 33]. According to [25], training models on local data that minimize local empirical loss appears to be meaningful, but yet, doing so is fundamentally inconsistent with minimizing the global empirical loss. Client updates drive the server model away from the ideal distribution, a phenomenon known as 'client drift'. Naive aggregation [40] is efficient in aggregating client models but does not account for distribution inconsistencies across client data or the consequent objective inconsistency. In other words, with naive aggregation, the server model risks converging to a stationary point of a mismatched objective function which can be arbitrarily different from the true objective [53]. + +Prior works [24, 40, 48] attempt to overcome this issue by running fewer epochs or iterations of SGD on the devices or by stabilizing server-side updates so that the resulting models correspond to inexact minimizations and keep globally desirable properties. In this work, we propose a novel aggregation + +Figure 1. Illustration of naive aggregation and elastic aggregation. The local updates of client A and client B drive the server model $\theta$ towards their individual minima (black dots in plot). Naive aggregation simply averages the received model from clients A and B, yielding $\theta'$ as the new server model. Although $\theta'$ minimizes the local empirical loss of clients A and B, $\theta'$ drifts from ideal distribution for the server model. Elastic aggregation adjusts gradient with respect to parameter sensitivity. Parameter $\theta_x$ is more sensitive (has a larger gradient norm), and is restricted with $\zeta_x < 1$ to reduce the magnitude of its update. Parameter $\theta_y$ is less sensitive (has a smaller gradient norm), and is correspondingly boosted with $\zeta_y > 1$ to better explore the parameter space. This minimizes the loss for clients A and B, while not causing the server model to drift from its ideal distribution. Hence, elastic aggregation results in a better update $\theta''$ . +![](images/1b9104cfda764cfca9722821c68ff6d2c890367eb096c1b8787b813f85780d34.jpg) +Minima point +Low empirical loss for client A +Low empirical loss for client B +Low empirical loss for server +Naïve aggregation +Elastic aggregation +Client update + +approach, elastic aggregation, to overcome client drift. We measure parameter sensitivity using unlabeled samples of client data, by computing the changes to the overall function output for a given change to the parameter in question, without relying on the loss. This allows our method to not only avoid requiring labeled data but importantly also pre-empt complications that could otherwise arise from the loss being at a local minimum with gradients close to zero. During the aggregation of client models, updates to the more sensitive parameters can then be reduced in magnitude, preventing the server model from drifting to any client distribution. Conversely, updates to the less sensitive parameters can be boosted to better explore different client distributions. + +Contributions. Elastic aggregation tackles distribution inconsistency across client data using the concept of parameter sensitivity and is simple to implement, requiring little hyperparameter tuning. Furthermore, parameter sensitivity is computed in an online and unsupervised manner, and thus better utilizes the unlabeled data generated by the client during runtime. Elastic aggregation is easily integrated into different federated optimizers, achieving substantial improvements over naïve aggregation. The empirical results on real and synthetic data and analytical results show that elastic aggregation leads to efficient training in both convex and non-convex settings, across all four federated learning scenarios (unreliable links, massive distribution, substantial heterogeneity, and imbalanced data). + +# 2. Related work + +Federated learning is a fast-evolving topic. The general setup involves server and client updates; each of these updates is associated with minimizing some local loss function. The server model then benefits from all client data and achieves superior performance, for tasks such as next word prediction [17, 56], emoji prediction [45], decoder models [8], vocabulary estimation [7], low latency vehicle-to-vehicle communication [49] and predictive models in health [6]. Nevertheless, federated learning raises several issues and has been the topic of much research effort, focusing on the issues of generalization and fairness [33, 42], the design of more efficient communication strategies [4,24,26,27,51,52], the study of lower bounds [55], differential privacy guarantees [2], security [5], etc [22]. We focus here on relevant work that specifically addresses the four federated learning characteristics noted above - massive distribution, heterogeneity, unreliable links, and imbalanced data. + +Much of earlier work in this context proposes optimizing for the local risk objective with SGD [51] over mini-batches of client data, analogous to the centralized scenario, with the server then averages the received models. FedAvg [40] is a generalization of local SGD, proposing a larger number of local SGD steps per round. In the case of identical clients, it reduces to parallel SGD for which asymptotic convergence has been proven [51, 62]; more recently, [25, 43] analyzed the same method under the name of local SGD, also for + +identical functions. FedAvg in exactly solves client-side optimization, requiring the tuning of the number of epochs and the learning rate hyper-parameters in order to achieve a good accuracy-communication trade-off [30,40]. + +Despite the strong empirical performance of FedAvg in IID settings, performance degrades in non-IID scenarios [61]. The analysis of FedAvg for heterogeneous clients is more delicate, due to the aforementioned client drift, first empirically observed by [61]. Several analyses bound this drift by assuming bounded gradients [54, 57], viewing it as additional noise [25], or assuming that the client optima are $\epsilon$ -close [16,33]. [36] proposes using variance reduction to deal with client heterogeneity but achieved slower convergence rates than SGD. Other variants include using a decreasing learning rate [30], modifying client empirical loss dynamically [1,31], adding regularizers on local updates [23,24,50], or modifying the server side updates [21,48]. While these works do recognize the incompatibility of local and global stationary points, their proposed fixes are based on inexact minimization. Additionally, in order to establish convergence for non-IID situations, these works impose additional constraints. + +Another class of work that extend the analysis of SGD-type methods to federated learning settings specifically addresses the special case of full client participation [9, 14, 26, 34-36, 38, 44, 50, 58]. For example, FedSVRG [26] and DANE [50] need gradient information from all clients each round and are as such not directly applicable to partial federated learning settings. Furthermore, it may not be trivial to extend these works to overcome the deficiency. For example, FedDANE [32] is a version of DANE that works with partial participation. However, with partial participation, FedDANE empirically performs worse than FedAvg [33]. Similar to these works, FedPD [60] proposes distributed optimization with a different notion of 'participation'. FedPD activates either all clients or no clients per round, which again fails to satisfy the partial participation condition. + +Finally, there have been earlier works aiming to decrease communication costs by compressing the transmitted models [3, 12, 41], decreasing the bit-rate of the transmission. These ideas are complementary to our work and can work together with our approach. + +# 3. Method + +In this section, we focus on the introduction of parameter sensitivity in process of federated learning, which is our main innovation. The proof of convergence is provided in the technical part of supplementary materials. + +# 3.1. Federated Learning with Naïve Aggregation + +In federated learning, we solve an optimization problem of the form: + +$$ +\arg \min _ {\theta \in \mathbb {R} ^ {n}} [ \ell (\theta) \triangleq \frac {1}{m} \sum_ {k = 1} ^ {m} L _ {k} (\theta) ], \tag {1} +$$ + +where $L_{k}(\theta)\triangleq \mathbb{E}_{(x,y)\sim \mathcal{P}_{k}}[\ell_{k}(\theta ;(x,y))]$ is the empirical loss of the $k^{th}$ client, $\mathcal{P}_k$ is the data distribution for the $k^{th}$ client across $K$ clients. + +FedAvg. A common approach to solving Eq. 1 in federated settings is FedAvg [40]. At each round, a subset of clients is selected (typically randomly) and the server broadcasts its model to each client. In parallel, the clients run SGD on their own loss function $\ell_{k}$ and then send their updated models to the server. The server then updates its model to be the average of these client models. + +Suppose that at the $r^{th}$ round, the server has model $\theta$ and samples a client set $S$ . Here we use a standard gradient descent form to update parameters: + +$$ +\theta \leftarrow \theta - \eta \Delta , \tag {2} +$$ + +where $\Delta$ is the aggregated clients' gradients and $\eta$ is the learning rate of the server, which is typically 1.0. FedAvg uses naive aggregation to compute $\Delta$ . + +Naive aggregation. We can write naive aggregation as: + +$$ +\Delta = \sum_ {k \in \mathcal {S}} \left(w _ {k} \cdot \Delta_ {k}\right), \tag {3} +$$ + +where $\Delta_{k} = \theta -\theta_{k}$ is the accumulated gradients within a training round of the $k^{th}$ client, and $w_{k} = |D_{k}| / \sum_{k\in S}|D_{k}|$ is the aggregated weight of the $k^{th}$ client across the activated clients $\mathcal{S}$ . $D_{k},\theta_{k}$ are the training dataset and trained parameters on the $k^{th}$ client, respectively. + +# 3.2. Exploring parameter sensitivity + +Due to the non-IID-ness (heterogeneity) across different clients, $\mathcal{P}$ can vary substantially across different clients. Thus, the simple and efficient way to aggregate client models described in Eq. 3 cannot solve client drift and cause oscillation as well as slow convergence. We explore parameter sensitivity as an approach to overcoming these issues. + +The main idea we are proposing is that less sensitive parameters can be freely updated to minimize the loss for individual clients in $S$ without causing the server to drift; by the same reasoning, parameters that are more sensitive should not be updated as much. This is illustrated in Fig. 1. + +At the $r^{th}$ round, the active clients receive the server model $\theta_r$ , which parameterizes the approximation function + +Algorithm 1: Elastic aggregation within a single layer +A variable with a superscript $i$ indicates the $i^{th}$ element of the variable. A variable with a subscript $k$ indicates the variable from $k^{th}$ client. $\eta, \eta'$ are learning rates of server and clients respectively. $\mu, \tau$ are the hyper-parameters. $\theta, \theta_k \in \mathbb{R}^n$ are the server's and the $k^{th}$ client's parameters respectively. $\Omega \in \mathbb{R}^n$ is the aggregated parameter sensitivity. $\Omega_k \in \mathbb{R}^n$ is the parameter sensitivity on the $k^{th}$ client. + +Initialize $\theta$ + +$B_{k}\gets$ Sample a subset of training data $D_{k}$ + +$D_{k}\gets$ Drop the samples of $B_{k}$ from $D_{k}$ + +for each round do + +for each activated client $k$ do Initialize $\Omega_{k}$ as zeros. +for each batch data $x\in B_k$ do $\begin{array}{l}g = \nabla ||F(\theta ;x)||_2^2\\ \mathbf{for}i\in [1,\dots ,n]\mathbf{do}\\ \big{\lfloor}\Omega_k^i\gets \mu \Omega_k^i +(1 - \mu)|g^i |\\ \theta_k\gets \theta \\ \mathbf{for}$ each epoch do for each batch data $x\in D_k$ do $\begin{array}{r}\Big{\lfloor}\theta_{k}\leftarrow \theta_{k} - \eta^{\prime}\nabla \ell_{k}(F(\theta_{k};x))\\ \Delta_{k} = \theta_{k} - \theta \end{array}$ $w_{k}\gets |D_{k}| / \sum_{k}|D_{k}|;\Omega = \sum_{k}(w_{k}\cdot \Omega_{k});$ $\Omega^{\prime} = \max (\Omega)$ +for $i\in [1,\dots ,n]$ do $\zeta^i = 1 + \tau -\Omega^i /\Omega '$ $\Delta^i = \zeta^i\cdot \sum_k(w_k\cdot \Delta_k^i)$ $\theta^i\gets \theta^i -\eta \cdot \Delta^i$ + +$F$ of the true function $\bar{F}$ . $F$ maps the input $x$ to the output $y$ , and our goal is to largely maintain the same output $y$ for the observed $x$ while learning additional training instances $(x,y) \sim P_k$ . To this end, we measure how sensitive the output of function $F$ is to changes in the network parameters. To reduce confusion, we ignore the symbols denoting the round $r$ and the client $k$ for all variables and only discuss parameter sensitivity locally. + +For a given data point $x$ , the output of the network is $F(\theta; x)$ . A small perturbation $\delta$ in the parameters $\theta$ results in a change in the function output that can be approximated by: + +$$ +F (\theta + \delta ; x) - F (\theta ; x) \approx g (\theta ; x) \delta , \tag {4} +$$ + +where $g(\theta ;x) = \frac{\partial F(\theta;x)}{\partial\theta}$ is the gradient of the learned function with respect to the parameter $\theta$ evaluated at the data point $x$ . Our goal is to maintain the output of the network (the learned function $F$ ) for each observed data point and + +thus we reduce the magnitudes of the updates to the parameters that are more sensitive for the data point. Conversely, we boost the updates to the less sensitive parameters to better-fit client distributions. + +Based on equation 4, and assuming a small constant change $\delta$ , we can measure the sensitivity of a parameter by the magnitude of the gradient $g(\theta; x)$ , i.e., how much does a small perturbation to that parameter change the output of the learned function for data point $x$ . There are many ways to measure the sensitivity of a parameter by the magnitude of the gradient, such as a fishing matrix. However, in federated learning, we have to take the computation ability of each client into account, which is only with limited computation ability. Therefore, we use the exponentially-decayed moving average1 to obtain sensitivity $\Omega^i$ for $i^{th}$ parameter $\theta^i$ : + +$$ +\Omega^ {i} \leftarrow \mu \Omega^ {i} + (1 - \mu) | g \left(\theta^ {i}; x\right) |, \tag {5} +$$ + +where $\mu$ is momentum and we empirically set it to 0.9. + +When the output function $F$ is multi-dimensional, as is the case for most neural networks, equation 5 involves computing the gradients for each output, which requires as many backward passes as the dimensionality of the output. As a more efficient alternative, we propose to use the gradients of the squared $L^2$ norm of the learned function output, i.e. $g(\theta ;x) = \nabla ||F(\theta ;x)||_2^2$ . Hence, we only need to compute one backward pass in order to estimate the parameters' sensitivity. + +# 3.3. Elastic aggregation with respect to parameter sensitivity + +The elastic aggregation for $i^{th}$ parameter can be written as: + +$$ +\Delta^ {i} = \zeta^ {i} \cdot \sum_ {k \in \mathcal {S}} \left(w _ {k} \cdot \Delta_ {k} ^ {i}\right), \tag {6} +$$ + +where $\zeta^i$ is the adaptive coefficient with respect to the parameter sensitivity. The definition of $\zeta^i$ is: + +$$ +\zeta^ {i} = 1 + \tau - \Omega^ {i} / \Omega^ {\prime}, \tag {7} +$$ + +where $\Omega' = \max(\Omega)$ is the maximum of parameter sensitivities in each layer, and $\Omega^i = \sum_{k \in S} (w_k \cdot \Omega_k^i)$ is the aggregated sensitivity of $i^{th}$ parameter across activated clients. The server is able to boost updates ( $\zeta^i > 1.0$ ) to parameters that have low sensitivity (low $\Omega^i$ ). Meanwhile, sensitive parameters (high $\Omega^i$ ) have their updates restricted with a penalty ( $\zeta^i < 1.0$ ). $\tau$ is a hyper-parameter determining the ratio of boosted or restricted parameters. FedAvg with elastic aggregation is formalized in Algorithm 1. + +Discussion on $\tau$ . In Eq. 6, $\zeta^i \in (1, 1 + \tau]$ is applied to the less sensitive parameters, and $\zeta^i \in [\tau, 1)$ is applied to the more sensitive parameters. Thus, $\tau$ determines the portion of the parameter to be restricted or boosted. Generally, a larger $\tau$ indicates that a larger proportion of parameters will be boosted, as shown in Tab. 1, and vice versa. + +If a large proportion of parameters is restricted ( $\tau$ is small, such as 0.1), the server model will not be updated much, and exiting local minima becomes difficult. However, with a large $\tau$ such as 0.9, optimization of the server model becomes unstable, and this also causes performance degradation. It is therefore critical to maintain a balance between these extremes with a suitable $\tau$ and we find that $\tau = 0.5$ generalizes well to various experiments. At this value of $\tau$ , roughly three-quarters of the parameters are boosted. + +# 4. Experiments settings + +Inconsistent usage of models, datasets, and non-IID partition methods makes it difficult to compare the performances of federated learning algorithms fairly. To enforce fair comparison, we explicitly specify the combinations of datasets, models, and non-IID partition methods to be used for experiments, which mostly consist of those used in existing work published at top-tier machine learning venues [18]. Note that although the reported precisions are state-of-the-art for the models we have chosen, higher-capacity models can achieve higher performances on these datasets. Therefore, we compare the relative performance of elastic aggregation against naive aggregation for various federated learning scenarios. + +# 4.1. Implementation + +We measure our algorithm against the most comprehensive and representative suite of federated datasets and modeling tasks to date. For this purpose, we carry out simulations on five diverse and representative experiments on several datasets. In order to facilitate the experiments, we use the cosine annealing scheduler [37] for the client learning rate $\eta_r^\prime$ at the $r^{th}$ round, which is given by $\eta_r^\prime = (1 + \cos (\frac{r}{R}\pi))\eta^\prime$ . For all tasks, we measure the performance on the entire test set throughout training. Clients are sampled uniformly at random, without replacement within a given round, but with replacement across rounds. There are a variety of federated optimizers that improve the performance of federated learning. Here, we use the most basic and widely used federated optimization algorithm, i.e., FedAvg [40], as the default baseline in our experiments. With reference to [46], we implement all experiments with two important characteristics. First, instead of doing $K$ training steps per client, we do $E$ epochs of training over each client's data. Second, to account for varying numbers of gradient steps per client, we weigh the average of the client outputs $\Delta_t^k$ by the number of training samples. This also follows the approach of + +[40] and often outperforms uniform weighting [47]. We set $\mu = 0.95$ for the accumulation of the parameter sensitivity over batches in each client. $\tau = 0.5, \eta = 1.0$ is used for all experiments. While computing Eq. 7, we normalize the parameter sensitivity layer by layer, which means that the parameter sensitivity is divided by the maximum value within the same layer. Aside from experiments 5.1, we set $E = 1$ for each client for all experiments. + +# 4.2. Generate synthetic federated datasets. + +Differences in distribution have an enormous influence on the performance of federated optimization. The Dirichlet distribution is used on the label ratios to ensure uneven label distributions among clients for non-IID splits, as in [59]. To generate imbalanced data, we sample the number of data points from a log-normal distribution. The degree of imbalance depends on the variance of the log-normal distribution, which is controlled by the hyper-parameter $\alpha$ . A smaller $\alpha$ indicates a stronger non-IID-ness in partitions, as shown in Fig. 2. + +# 5. Experiments + +Under all experiments, the samples used for computing parameter sensitivities at each client will be randomly sampled training data, and these sampled data will not be used for supervised training anymore. For a fair comparison, these sampled data will not be used in the baseline methods either. + +# 5.1. Comparison with naive aggregation + +MNIST. As our baseline, we conduct a convex optimization experiment on MNIST [29] with logistic regression [31, 33, 40]. In this experiment, we generate a synthetic federated dataset of MNIST with $\alpha = 100.0$ and split the dataset into 1000 partitions. At each round of training, we randomly choose 100 clients without repeating the partition. As shown in Tab. 2, the elastic aggregation has a large advantage over naive aggregation even with a large number of participating clients. + +Federated EMNIST. Due to resource constraints of edge devices, existing works commonly use shallow neural networks for experiments. Similarly, we include Federated EMNIST [46] with a shallow neural network consisting of two convolution layers followed by two linear layers [46]. Notably, Fed-EMNIST [46] has a natural client partitioning that is highly representative of real-world federated learning problems. It contains 3,400 users (clients) and 62 label classes. The dataset is split into 671,585 training examples and 77,483 testing examples. Rather than holding out specific users, we split each user's examples across the train + +![](images/e773dec5da96cced1bd5a49a0c5da321880ca5698f21654cbf2bf790ff765bf4.jpg) +Figure 2. Performances across different partitioning distributions, participation rates and numbers of local epochs. Compared with naive aggregation, elastic aggregation achieves significant improvements across these settings. + +
τNaïve0.00.10.20.30.40.50.60.70.80.91.0
Train Acc.(%)58.3657.2158.3358.7660.6660.4761.4460.6660.5561.0159.2758.96
Test Acc.(%)60.7458.3059.7661.1761.9163.3962.7463.3963.2363.2260.8361.37
Boosted(%)-0.011.4527.2443.7559.7474.4384.5789.9393.5396.2697.38
+ +Table 1. The effect of $\tau$ . Using an unsuitable $\tau$ for elastic aggregation with cause it to even under-perform naïve aggregation. The last row shows the percentage of parameters that are boosted for different $\tau$ . + +and test so that all users have at least one example in the train and one example in the test. Users with fewer than 2 examples are excluded from the data set. As shown in Tab. 2, elastic aggregation generalizes well to real-world federated learning problems. + +CIFAR-100. In this experiment, we conduct a balanced but non-IID partition on Fed-CIFAR $^{100}$ ², which was introduced by TensorFlow Federated [20] with ResNet-20 [19] + +
DatasetRounds(Epochs)TotalSampledBatchInit. LRModelNaïve(%)Elastic(%)
Balanced data across clients
CIFAR-1004000(~80)50010100.05ResNet-2032.3156.64
Unbalanced data across clients
MNIST20(~2)10001001000.1Logistic Regression70.1473.64
EMNIST1000(~2.5)3400101000.12Conv+2Linear88.7189.82
CIFAR-104000(~40)100010100.05ResNet-2066.8468.74
CINIC-10200(~20)1000100100.05ResNet-2035.8136.29
CINIC-104000(~40)100010100.05ResNet-2068.6869.25
+ +Table 2. Test accuracies for various datasets. Along with rounds, we list a more intuitive measure, i.e., epochs, to better reflect the total training computation. + +
OptimizerFedAvgFedAvgMFedProxSCAFFOLDAdaOptPFNMPer-FedAvgpFedMe
w/o Elastic.49.3462.5251.5272.1078.0071.2350.4483.20
w/ Elastic.52.3764.4853.6475.4280.3473.6453.2485.63
Improvement.3.031.962.123.322.342.412.802.43
+ +Table 3. Elastic aggregation can be easily integrated with different federated optimizers, achieving performance improvements. (Notes that the comparison across different federated optimizers is meaningless since they are under different experiment settings.) + +as the baseline model. As shown in Tab. 2, elastic aggregation significantly speeds up training. Furthermore, the final accuracy is improved by over $20\%$ compared with the naïve baseline, which demonstrates the effectiveness of elastic aggregation. + +CIFAR-10 and CINIC-10. To further demonstrate the performance improvement resulting from elastic aggregation, we generate two synthetic federated datasets for CIFAR-10 [20] and CINIC-10 [10] with $\alpha = 100.0$ . CINIC-10 extends CIFAR-10 with the addition of down-sampled ImageNet images, making for a more challenging dataset. This also enables measuring the performance of models trained on CIFAR images on ImageNet images for the same classes. As shown in Tab. 2, elastic aggregation achieves superior performances on both the CIFAR-10 and the more difficult CINIC-10 datasets, confirming that our method generalizes well to large scale datasets. + +# Natural Language Processing on Shakespeare dataset. + +We maintain the same experimental setup as [40] on the most commonly used natural language processing tasks: Shakespeare LSTM. The epoch in each round is 1, the batch size is 10 and both elastic and naive aggregation are trained for 2k rounds. We get the final accuracy as $62.14\%$ for naive aggregation and $64.73\%$ for elastic aggregation. The results show that elastic aggregation not only has a significant improvement in CV related tasks, but also has an positive effect on NLP related tasks. + +Imbalanced and non-IID. We are also interested in understanding how parameter sensitivity can help improve convergence, particularly in cross-device and non-IID scenarios. Given the resource constraints of edge devices, large DNN models are usually trained under the cross-organization (also known as cross-silo) federated learning settings. Across the following experiments, we use CIFAR10 [28] with ResNet-20 [19]. We study three different parameters here: non-IID-ness, participation rate, and number of epochs. We explore the effects of varying non-IID-ness with $\alpha = 100.0, 50.0, 10.0, 1.0, 0.5$ across 1000 partitions. For participation rate, we test sampling $5\%$ , $10\%$ , $20\%$ , $40\%$ of the clients at each round. Finally, we test having 1, 5 epochs of local updates, to better show the robustness of elastic aggregation. As shown in Fig. 2, elastic aggregation is especially superior for situations with massive distribution, substantial heterogeneity, and imbalanced data. + +# 5.2. Integration with modern optimizer + +Federated optimizer with elastic aggregation. To illustrate the generalizability of elastic aggregation, we integrate elastic aggregation into FedAvg [40], FedAvgM [46] and FedProx [31]. FedAvgM is an enhancement of FedAvg on the server-side, making use of the momentum strategy to update the server model. FedProx is an enhancement of FedAvg on the client-side, adding a penalty to the client updates. We have presented the details of FedAvg with elastic aggregation in Algorithm 1. Please refer to supplementary materials for more details about the other federated optimizers with elastic aggregation. As shown in the left part of Tab. 3, elastic aggregation works well with other com + +![](images/e9f6b8691d01618f2a02fbdd8ecff9dfcada6e137cf7affcea0e7d0dc1941b6d.jpg) +Figure 3. Convergence speeds on different datasets. + +plementary approaches whether designed for client-side or server-side. In order to further verify the generality of elastic aggregation, we did further experiments on the stat-of-the-art methods in FL, i.e. SCAFFOLD [23], AdaOpt [46] and PFNM [59]. Since these methods target on different aspect of federated learning, we conducted experiments based on their original experimental settings. As shown in middle part of Tab. 3, elastic aggregation plays a positive effect in most federated optimizers. + +Influence on personalization. Personalization in federated learning is also a topic of great concern. Specifically, we equipped Per-FedAvg [13], pFedMe [11] – both focus on the model personalization (local model performance) in federated learning with elastic aggregation and found that elastic aggregation is also a favour in learning a better personalized model, as shown in the right part of Tab. 3. + +# 5.3. Limitations + +In Fig. 3, we compare testing curves on various datasets and observe that elastic aggregation outperforms naive aggregation by converging faster. Nevertheless, using elas + +tic aggregation results in additional computational burden and communication costs, which may affect the overall performance of federated learning scenarios. For a more detailed analysis of the computational overhead, please refer to the supplementary materials. Despite these challenges, we firmly believe that the significant performance improvements associated with elastic aggregation warrant its use over naive aggregation. + +# 6. Conclusion + +Our work delves into the impact of heterogeneity on optimization methods for federated learning. We proposed a novel aggregation method, elastic aggregation, which utilizes parameter sensitivity to overcome gradient dissimilarity. To the best of our knowledge, we are the pioneers in utilizing unlabeled client data to enhance federated learning performances. 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FedAvg has become the preferred optimizer for federated learning because of its simplicity and effectiveness. FedAvg uses naive aggregation to update the server model, interpolating client models based on the number of instances used in their training. However, naive aggregation suffers from client drift when the data is heterogeneous (non-IID), leading to unstable and slow convergence. In this work, we propose a novel aggregation approach, elastic aggregation, to overcome these issues. Elastic aggregation interpolates client models adaptively according to parameter sensitivity, which is measured by computing how much the overall prediction function output changes when each parameter is changed. This measurement is performed in an unsupervised and online manner. Elastic aggregation reduces the magnitudes of updates to the more sensitive parameters so as to prevent the server model from drifting to any one client distribution, and conversely boosts updates to the less sensitive parameters to better explore different client distributions. Empirical results on real and synthetic data as well as analytical results show that elastic aggregation leads to efficient training in both convex and non-convex settings while being fully agnostic to client heterogeneity and robust to large numbers of clients, partial participation, and imbalanced data. Finally, elastic aggregation works well with other federated optimizers and achieves significant improvements across the board." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 609, + 128, + 621 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 609, + 128, + 621 + ], + "spans": [ + { + "bbox": [ + 47, + 609, + 128, + 621 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 628, + 288, + 677 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 628, + 288, + 677 + ], + "spans": [ + { + "bbox": [ + 46, + 628, + 288, + 677 + ], + "type": "text", + "content": "Unlike traditional centralized learning in which models are trained using large datasets stored in a central server [15], federated learning - first proposed in [40] - leverages data spread across many clients to learn classification tasks dis" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 228, + 546, + 264 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 228, + 546, + 264 + ], + "spans": [ + { + "bbox": [ + 306, + 228, + 546, + 264 + ], + "type": "text", + "content": "tributively without explicitly sharing data [22, 26, 27, 42], thereby ensuring a basic level of privacy. Federated learning is characterized by four key features:" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 317, + 267, + 546, + 422 + ], + "type": "list", + "angle": 0, + "index": 16, + "blocks": [ + { + "bbox": [ + 317, + 267, + 546, + 303 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 267, + 546, + 303 + ], + "spans": [ + { + "bbox": [ + 317, + 267, + 546, + 303 + ], + "type": "text", + "content": "- Unreliable links: The links connecting the server and clients can be unreliable, and only a small subset of clients may be active at any given time." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 317, + 307, + 545, + 342 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 307, + 545, + 342 + ], + "spans": [ + { + "bbox": [ + 317, + 307, + 545, + 342 + ], + "type": "text", + "content": "- Massive distribution: The number of clients is typically high, but the amount of data per client is relatively small." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 317, + 347, + 545, + 395 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 347, + 545, + 395 + ], + "spans": [ + { + "bbox": [ + 317, + 347, + 545, + 395 + ], + "type": "text", + "content": "- Substantial heterogeneity: Client data is heterogeneous and non-IID [26], meaning that data across different clients can be sampled from varying regions of the sampling space." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 317, + 399, + 545, + 422 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 399, + 545, + 422 + ], + "spans": [ + { + "bbox": [ + 317, + 399, + 545, + 422 + ], + "type": "text", + "content": "- Imbalanced data: There can be significant imbalances in the amount of data available per client." + } + ] + } + ], + "index": 15 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 304, + 426, + 547, + 653 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 426, + 547, + 653 + ], + "spans": [ + { + "bbox": [ + 304, + 426, + 547, + 653 + ], + "type": "text", + "content": "The most popular algorithm for federated learning is FedAvg [40], which tackles the communication bottleneck by performing multiple local updates on the available clients before communicating the overall change to the server. FedAvg uses naive aggregation to interpolate client models and has shown success in certain applications. However, its performance on heterogeneous data is still an active area of research [16, 25, 33]. According to [25], training models on local data that minimize local empirical loss appears to be meaningful, but yet, doing so is fundamentally inconsistent with minimizing the global empirical loss. Client updates drive the server model away from the ideal distribution, a phenomenon known as 'client drift'. Naive aggregation [40] is efficient in aggregating client models but does not account for distribution inconsistencies across client data or the consequent objective inconsistency. In other words, with naive aggregation, the server model risks converging to a stationary point of a mismatched objective function which can be arbitrarily different from the true objective [53]." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 654, + 547, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 654, + 547, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 654, + 547, + 714 + ], + "type": "text", + "content": "Prior works [24, 40, 48] attempt to overcome this issue by running fewer epochs or iterations of SGD on the devices or by stabilizing server-side updates so that the resulting models correspond to inexact minimizations and keep globally desirable properties. In this work, we propose a novel aggregation" + } + ] + } + ], + "index": 18 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 684, + 126, + 693 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 684, + 126, + 693 + ], + "spans": [ + { + "bbox": [ + 58, + 684, + 126, + 693 + ], + "type": "text", + "content": "*Equal contribution." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 47, + 693, + 287, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 693, + 287, + 712 + ], + "spans": [ + { + "bbox": [ + 47, + 693, + 287, + 712 + ], + "type": "text", + "content": "†Corresponding author. 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Illustration of naive aggregation and elastic aggregation. The local updates of client A and client B drive the server model " + }, + { + "bbox": [ + 46, + 271, + 545, + 350 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 46, + 271, + 545, + 350 + ], + "type": "text", + "content": " towards their individual minima (black dots in plot). Naive aggregation simply averages the received model from clients A and B, yielding " + }, + { + "bbox": [ + 46, + 271, + 545, + 350 + ], + "type": "inline_equation", + "content": "\\theta'" + }, + { + "bbox": [ + 46, + 271, + 545, + 350 + ], + "type": "text", + "content": " as the new server model. Although " + }, + { + "bbox": [ + 46, + 271, + 545, + 350 + ], + "type": "inline_equation", + "content": "\\theta'" + }, + { + "bbox": [ + 46, + 271, + 545, + 350 + ], + "type": "text", + "content": " minimizes the local empirical loss of clients A and B, " + }, + { + "bbox": [ + 46, + 271, + 545, + 350 + ], + "type": "inline_equation", + "content": "\\theta'" + }, + { + "bbox": [ + 46, + 271, + 545, + 350 + ], + "type": "text", + "content": " drifts from ideal distribution for the server model. Elastic aggregation adjusts gradient with respect to parameter sensitivity. Parameter " + }, + { + "bbox": [ + 46, + 271, + 545, + 350 + ], + "type": "inline_equation", + "content": "\\theta_x" + }, + { + "bbox": [ + 46, + 271, + 545, + 350 + ], + "type": "text", + "content": " is more sensitive (has a larger gradient norm), and is restricted with " + }, + { + "bbox": [ + 46, + 271, + 545, + 350 + ], + "type": "inline_equation", + "content": "\\zeta_x < 1" + }, + { + "bbox": [ + 46, + 271, + 545, + 350 + ], + "type": "text", + "content": " to reduce the magnitude of its update. Parameter " + }, + { + "bbox": [ + 46, + 271, + 545, + 350 + ], + "type": "inline_equation", + "content": "\\theta_y" + }, + { + "bbox": [ + 46, + 271, + 545, + 350 + ], + "type": "text", + "content": " is less sensitive (has a smaller gradient norm), and is correspondingly boosted with " + }, + { + "bbox": [ + 46, + 271, + 545, + 350 + ], + "type": "inline_equation", + "content": "\\zeta_y > 1" + }, + { + "bbox": [ + 46, + 271, + 545, + 350 + ], + "type": "text", + "content": " to better explore the parameter space. This minimizes the loss for clients A and B, while not causing the server model to drift from its ideal distribution. Hence, elastic aggregation results in a better update " + }, + { + "bbox": [ + 46, + 271, + 545, + 350 + ], + "type": "inline_equation", + "content": "\\theta''" + }, + { + "bbox": [ + 46, + 271, + 545, + 350 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 370, + 289, + 525 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 370, + 289, + 525 + ], + "spans": [ + { + "bbox": [ + 46, + 370, + 289, + 525 + ], + "type": "text", + "content": "approach, elastic aggregation, to overcome client drift. We measure parameter sensitivity using unlabeled samples of client data, by computing the changes to the overall function output for a given change to the parameter in question, without relying on the loss. This allows our method to not only avoid requiring labeled data but importantly also pre-empt complications that could otherwise arise from the loss being at a local minimum with gradients close to zero. During the aggregation of client models, updates to the more sensitive parameters can then be reduced in magnitude, preventing the server model from drifting to any client distribution. Conversely, updates to the less sensitive parameters can be boosted to better explore different client distributions." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 545, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 545, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 545, + 287, + 713 + ], + "type": "text", + "content": "Contributions. Elastic aggregation tackles distribution inconsistency across client data using the concept of parameter sensitivity and is simple to implement, requiring little hyperparameter tuning. Furthermore, parameter sensitivity is computed in an online and unsupervised manner, and thus better utilizes the unlabeled data generated by the client during runtime. Elastic aggregation is easily integrated into different federated optimizers, achieving substantial improvements over naïve aggregation. The empirical results on real and synthetic data and analytical results show that elastic aggregation leads to efficient training in both convex and non-convex settings, across all four federated learning scenarios (unreliable links, massive distribution, substantial heterogeneity, and imbalanced data)." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 369, + 389, + 380 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 369, + 389, + 380 + ], + "spans": [ + { + "bbox": [ + 306, + 369, + 389, + 380 + ], + "type": "text", + "content": "2. Related work" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 389, + 547, + 604 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 389, + 547, + 604 + ], + "spans": [ + { + "bbox": [ + 304, + 389, + 547, + 604 + ], + "type": "text", + "content": "Federated learning is a fast-evolving topic. The general setup involves server and client updates; each of these updates is associated with minimizing some local loss function. The server model then benefits from all client data and achieves superior performance, for tasks such as next word prediction [17, 56], emoji prediction [45], decoder models [8], vocabulary estimation [7], low latency vehicle-to-vehicle communication [49] and predictive models in health [6]. Nevertheless, federated learning raises several issues and has been the topic of much research effort, focusing on the issues of generalization and fairness [33, 42], the design of more efficient communication strategies [4,24,26,27,51,52], the study of lower bounds [55], differential privacy guarantees [2], security [5], etc [22]. We focus here on relevant work that specifically addresses the four federated learning characteristics noted above - massive distribution, heterogeneity, unreliable links, and imbalanced data." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": "Much of earlier work in this context proposes optimizing for the local risk objective with SGD [51] over mini-batches of client data, analogous to the centralized scenario, with the server then averages the received models. FedAvg [40] is a generalization of local SGD, proposing a larger number of local SGD steps per round. In the case of identical clients, it reduces to parallel SGD for which asymptotic convergence has been proven [51, 62]; more recently, [25, 43] analyzed the same method under the name of local SGD, also for" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "12188" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 288, + 120 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 288, + 120 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 288, + 120 + ], + "type": "text", + "content": "identical functions. FedAvg in exactly solves client-side optimization, requiring the tuning of the number of epochs and the learning rate hyper-parameters in order to achieve a good accuracy-communication trade-off [30,40]." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 127, + 290, + 342 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 127, + 290, + 342 + ], + "spans": [ + { + "bbox": [ + 46, + 127, + 290, + 342 + ], + "type": "text", + "content": "Despite the strong empirical performance of FedAvg in IID settings, performance degrades in non-IID scenarios [61]. The analysis of FedAvg for heterogeneous clients is more delicate, due to the aforementioned client drift, first empirically observed by [61]. Several analyses bound this drift by assuming bounded gradients [54, 57], viewing it as additional noise [25], or assuming that the client optima are " + }, + { + "bbox": [ + 46, + 127, + 290, + 342 + ], + "type": "inline_equation", + "content": "\\epsilon" + }, + { + "bbox": [ + 46, + 127, + 290, + 342 + ], + "type": "text", + "content": "-close [16,33]. [36] proposes using variance reduction to deal with client heterogeneity but achieved slower convergence rates than SGD. Other variants include using a decreasing learning rate [30], modifying client empirical loss dynamically [1,31], adding regularizers on local updates [23,24,50], or modifying the server side updates [21,48]. While these works do recognize the incompatibility of local and global stationary points, their proposed fixes are based on inexact minimization. Additionally, in order to establish convergence for non-IID situations, these works impose additional constraints." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 349, + 288, + 529 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 349, + 288, + 529 + ], + "spans": [ + { + "bbox": [ + 46, + 349, + 288, + 529 + ], + "type": "text", + "content": "Another class of work that extend the analysis of SGD-type methods to federated learning settings specifically addresses the special case of full client participation [9, 14, 26, 34-36, 38, 44, 50, 58]. For example, FedSVRG [26] and DANE [50] need gradient information from all clients each round and are as such not directly applicable to partial federated learning settings. Furthermore, it may not be trivial to extend these works to overcome the deficiency. For example, FedDANE [32] is a version of DANE that works with partial participation. However, with partial participation, FedDANE empirically performs worse than FedAvg [33]. Similar to these works, FedPD [60] proposes distributed optimization with a different notion of 'participation'. FedPD activates either all clients or no clients per round, which again fails to satisfy the partial participation condition." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 536, + 288, + 596 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 536, + 288, + 596 + ], + "spans": [ + { + "bbox": [ + 46, + 536, + 288, + 596 + ], + "type": "text", + "content": "Finally, there have been earlier works aiming to decrease communication costs by compressing the transmitted models [3, 12, 41], decreasing the bit-rate of the transmission. These ideas are complementary to our work and can work together with our approach." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 626, + 102, + 639 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 626, + 102, + 639 + ], + "spans": [ + { + "bbox": [ + 47, + 626, + 102, + 639 + ], + "type": "text", + "content": "3. Method" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 654, + 288, + 702 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 654, + 288, + 702 + ], + "spans": [ + { + "bbox": [ + 46, + 654, + 288, + 702 + ], + "type": "text", + "content": "In this section, we focus on the introduction of parameter sensitivity in process of federated learning, which is our main innovation. The proof of convergence is provided in the technical part of supplementary materials." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 306, + 72, + 535, + 85 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 72, + 535, + 85 + ], + "spans": [ + { + "bbox": [ + 306, + 72, + 535, + 85 + ], + "type": "text", + "content": "3.1. Federated Learning with Naïve Aggregation" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 305, + 90, + 545, + 113 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 90, + 545, + 113 + ], + "spans": [ + { + "bbox": [ + 305, + 90, + 545, + 113 + ], + "type": "text", + "content": "In federated learning, we solve an optimization problem of the form:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 359, + 119, + 545, + 150 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 359, + 119, + 545, + 150 + ], + "spans": [ + { + "bbox": [ + 359, + 119, + 545, + 150 + ], + "type": "interline_equation", + "content": "\\arg \\min _ {\\theta \\in \\mathbb {R} ^ {n}} [ \\ell (\\theta) \\triangleq \\frac {1}{m} \\sum_ {k = 1} ^ {m} L _ {k} (\\theta) ], \\tag {1}", + "image_path": "ca9dd89e485ecc17b3dbe83f0199a2ec376245f6b7f376b044f956b0f561f9bd.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 159, + 545, + 196 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 159, + 545, + 196 + ], + "spans": [ + { + "bbox": [ + 304, + 159, + 545, + 196 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 159, + 545, + 196 + ], + "type": "inline_equation", + "content": "L_{k}(\\theta)\\triangleq \\mathbb{E}_{(x,y)\\sim \\mathcal{P}_{k}}[\\ell_{k}(\\theta ;(x,y))]" + }, + { + "bbox": [ + 304, + 159, + 545, + 196 + ], + "type": "text", + "content": " is the empirical loss of the " + }, + { + "bbox": [ + 304, + 159, + 545, + 196 + ], + "type": "inline_equation", + "content": "k^{th}" + }, + { + "bbox": [ + 304, + 159, + 545, + 196 + ], + "type": "text", + "content": " client, " + }, + { + "bbox": [ + 304, + 159, + 545, + 196 + ], + "type": "inline_equation", + "content": "\\mathcal{P}_k" + }, + { + "bbox": [ + 304, + 159, + 545, + 196 + ], + "type": "text", + "content": " is the data distribution for the " + }, + { + "bbox": [ + 304, + 159, + 545, + 196 + ], + "type": "inline_equation", + "content": "k^{th}" + }, + { + "bbox": [ + 304, + 159, + 545, + 196 + ], + "type": "text", + "content": " client across " + }, + { + "bbox": [ + 304, + 159, + 545, + 196 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 304, + 159, + 545, + 196 + ], + "type": "text", + "content": " clients." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 211, + 545, + 294 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 211, + 545, + 294 + ], + "spans": [ + { + "bbox": [ + 304, + 211, + 545, + 294 + ], + "type": "text", + "content": "FedAvg. A common approach to solving Eq. 1 in federated settings is FedAvg [40]. At each round, a subset of clients is selected (typically randomly) and the server broadcasts its model to each client. In parallel, the clients run SGD on their own loss function " + }, + { + "bbox": [ + 304, + 211, + 545, + 294 + ], + "type": "inline_equation", + "content": "\\ell_{k}" + }, + { + "bbox": [ + 304, + 211, + 545, + 294 + ], + "type": "text", + "content": " and then send their updated models to the server. The server then updates its model to be the average of these client models." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 295, + 545, + 331 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 295, + 545, + 331 + ], + "spans": [ + { + "bbox": [ + 304, + 295, + 545, + 331 + ], + "type": "text", + "content": "Suppose that at the " + }, + { + "bbox": [ + 304, + 295, + 545, + 331 + ], + "type": "inline_equation", + "content": "r^{th}" + }, + { + "bbox": [ + 304, + 295, + 545, + 331 + ], + "type": "text", + "content": " round, the server has model " + }, + { + "bbox": [ + 304, + 295, + 545, + 331 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 304, + 295, + 545, + 331 + ], + "type": "text", + "content": " and samples a client set " + }, + { + "bbox": [ + 304, + 295, + 545, + 331 + ], + "type": "inline_equation", + "content": "S" + }, + { + "bbox": [ + 304, + 295, + 545, + 331 + ], + "type": "text", + "content": ". Here we use a standard gradient descent form to update parameters:" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 397, + 339, + 545, + 352 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 397, + 339, + 545, + 352 + ], + "spans": [ + { + "bbox": [ + 397, + 339, + 545, + 352 + ], + "type": "interline_equation", + "content": "\\theta \\leftarrow \\theta - \\eta \\Delta , \\tag {2}", + "image_path": "589c7c3c7af4f59a31a361d9c195cc262b699eae8b23feff17659cb1a9e73dc8.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 360, + 545, + 396 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 360, + 545, + 396 + ], + "spans": [ + { + "bbox": [ + 304, + 360, + 545, + 396 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 360, + 545, + 396 + ], + "type": "inline_equation", + "content": "\\Delta" + }, + { + "bbox": [ + 304, + 360, + 545, + 396 + ], + "type": "text", + "content": " is the aggregated clients' gradients and " + }, + { + "bbox": [ + 304, + 360, + 545, + 396 + ], + "type": "inline_equation", + "content": "\\eta" + }, + { + "bbox": [ + 304, + 360, + 545, + 396 + ], + "type": "text", + "content": " is the learning rate of the server, which is typically 1.0. FedAvg uses naive aggregation to compute " + }, + { + "bbox": [ + 304, + 360, + 545, + 396 + ], + "type": "inline_equation", + "content": "\\Delta" + }, + { + "bbox": [ + 304, + 360, + 545, + 396 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 410, + 538, + 422 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 410, + 538, + 422 + ], + "spans": [ + { + "bbox": [ + 306, + 410, + 538, + 422 + ], + "type": "text", + "content": "Naive aggregation. We can write naive aggregation as:" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 384, + 429, + 545, + 455 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 384, + 429, + 545, + 455 + ], + "spans": [ + { + "bbox": [ + 384, + 429, + 545, + 455 + ], + "type": "interline_equation", + "content": "\\Delta = \\sum_ {k \\in \\mathcal {S}} \\left(w _ {k} \\cdot \\Delta_ {k}\\right), \\tag {3}", + "image_path": "7d35514ae362ebfd7f994b91e837e74157bb88b4afb03c297c7d05944e574911.jpg" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 462, + 547, + 523 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 462, + 547, + 523 + ], + "spans": [ + { + "bbox": [ + 304, + 462, + 547, + 523 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 462, + 547, + 523 + ], + "type": "inline_equation", + "content": "\\Delta_{k} = \\theta -\\theta_{k}" + }, + { + "bbox": [ + 304, + 462, + 547, + 523 + ], + "type": "text", + "content": " is the accumulated gradients within a training round of the " + }, + { + "bbox": [ + 304, + 462, + 547, + 523 + ], + "type": "inline_equation", + "content": "k^{th}" + }, + { + "bbox": [ + 304, + 462, + 547, + 523 + ], + "type": "text", + "content": " client, and " + }, + { + "bbox": [ + 304, + 462, + 547, + 523 + ], + "type": "inline_equation", + "content": "w_{k} = |D_{k}| / \\sum_{k\\in S}|D_{k}|" + }, + { + "bbox": [ + 304, + 462, + 547, + 523 + ], + "type": "text", + "content": " is the aggregated weight of the " + }, + { + "bbox": [ + 304, + 462, + 547, + 523 + ], + "type": "inline_equation", + "content": "k^{th}" + }, + { + "bbox": [ + 304, + 462, + 547, + 523 + ], + "type": "text", + "content": " client across the activated clients " + }, + { + "bbox": [ + 304, + 462, + 547, + 523 + ], + "type": "inline_equation", + "content": "\\mathcal{S}" + }, + { + "bbox": [ + 304, + 462, + 547, + 523 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 304, + 462, + 547, + 523 + ], + "type": "inline_equation", + "content": "D_{k},\\theta_{k}" + }, + { + "bbox": [ + 304, + 462, + 547, + 523 + ], + "type": "text", + "content": " are the training dataset and trained parameters on the " + }, + { + "bbox": [ + 304, + 462, + 547, + 523 + ], + "type": "inline_equation", + "content": "k^{th}" + }, + { + "bbox": [ + 304, + 462, + 547, + 523 + ], + "type": "text", + "content": " client, respectively." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 540, + 477, + 553 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 540, + 477, + 553 + ], + "spans": [ + { + "bbox": [ + 306, + 540, + 477, + 553 + ], + "type": "text", + "content": "3.2. Exploring parameter sensitivity" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 558, + 547, + 630 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 558, + 547, + 630 + ], + "spans": [ + { + "bbox": [ + 304, + 558, + 547, + 630 + ], + "type": "text", + "content": "Due to the non-IID-ness (heterogeneity) across different clients, " + }, + { + "bbox": [ + 304, + 558, + 547, + 630 + ], + "type": "inline_equation", + "content": "\\mathcal{P}" + }, + { + "bbox": [ + 304, + 558, + 547, + 630 + ], + "type": "text", + "content": " can vary substantially across different clients. Thus, the simple and efficient way to aggregate client models described in Eq. 3 cannot solve client drift and cause oscillation as well as slow convergence. We explore parameter sensitivity as an approach to overcoming these issues." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 631, + 547, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 631, + 547, + 689 + ], + "spans": [ + { + "bbox": [ + 304, + 631, + 547, + 689 + ], + "type": "text", + "content": "The main idea we are proposing is that less sensitive parameters can be freely updated to minimize the loss for individual clients in " + }, + { + "bbox": [ + 304, + 631, + 547, + 689 + ], + "type": "inline_equation", + "content": "S" + }, + { + "bbox": [ + 304, + 631, + 547, + 689 + ], + "type": "text", + "content": " without causing the server to drift; by the same reasoning, parameters that are more sensitive should not be updated as much. This is illustrated in Fig. 1." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "text", + "content": "At the " + }, + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "inline_equation", + "content": "r^{th}" + }, + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "text", + "content": " round, the active clients receive the server model " + }, + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\theta_r" + }, + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "text", + "content": ", which parameterizes the approximation function" + } + ] + } + ], + "index": 20 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "12189" + } + ] + } + ], + "index": 21 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "code", + "bbox": [ + 59, + 101, + 274, + 209 + ], + "blocks": [ + { + "bbox": [ + 53, + 75, + 261, + 99 + ], + "lines": [ + { + "bbox": [ + 53, + 75, + 261, + 99 + ], + "spans": [ + { + "bbox": [ + 53, + 75, + 261, + 99 + ], + "type": "text", + "content": "Algorithm 1: Elastic aggregation within a single layer" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "code_caption" + }, + { + "bbox": [ + 59, + 101, + 274, + 209 + ], + "lines": [ + { + "bbox": [ + 59, + 101, + 274, + 209 + ], + "spans": [ + { + "bbox": [ + 59, + 101, + 274, + 209 + ], + "type": "text", + "content": "A variable with a superscript " + }, + { + "bbox": [ + 59, + 101, + 274, + 209 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 59, + 101, + 274, + 209 + ], + "type": "text", + "content": " indicates the " + }, + { + "bbox": [ + 59, + 101, + 274, + 209 + ], + "type": "inline_equation", + "content": "i^{th}" + }, + { + "bbox": [ + 59, + 101, + 274, + 209 + ], + "type": "text", + "content": " element of the variable. A variable with a subscript " + }, + { + "bbox": [ + 59, + 101, + 274, + 209 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 59, + 101, + 274, + 209 + ], + "type": "text", + "content": " indicates the variable from " + }, + { + "bbox": [ + 59, + 101, + 274, + 209 + ], + "type": "inline_equation", + "content": "k^{th}" + }, + { + "bbox": [ + 59, + 101, + 274, + 209 + ], + "type": "text", + "content": " client. " + }, + { + "bbox": [ + 59, + 101, + 274, + 209 + ], + "type": "inline_equation", + "content": "\\eta, \\eta'" + }, + { + "bbox": [ + 59, + 101, + 274, + 209 + ], + "type": "text", + "content": " are learning rates of server and clients respectively. " + }, + { + "bbox": [ + 59, + 101, + 274, + 209 + ], + "type": "inline_equation", + "content": "\\mu, \\tau" + }, + { + "bbox": [ + 59, + 101, + 274, + 209 + ], + "type": "text", + "content": " are the hyper-parameters. " + }, + { + "bbox": [ + 59, + 101, + 274, + 209 + ], + "type": "inline_equation", + "content": "\\theta, \\theta_k \\in \\mathbb{R}^n" + }, + { + "bbox": [ + 59, + 101, + 274, + 209 + ], + "type": "text", + "content": " are the server's and the " + }, + { + "bbox": [ + 59, + 101, + 274, + 209 + ], + "type": "inline_equation", + "content": "k^{th}" + }, + { + "bbox": [ + 59, + 101, + 274, + 209 + ], + "type": "text", + "content": " client's parameters respectively. " + }, + { + "bbox": [ + 59, + 101, + 274, + 209 + ], + "type": "inline_equation", + "content": "\\Omega \\in \\mathbb{R}^n" + }, + { + "bbox": [ + 59, + 101, + 274, + 209 + ], + "type": "text", + "content": " is the aggregated parameter sensitivity. " + }, + { + "bbox": [ + 59, + 101, + 274, + 209 + ], + "type": "inline_equation", + "content": "\\Omega_k \\in \\mathbb{R}^n" + }, + { + "bbox": [ + 59, + 101, + 274, + 209 + ], + "type": "text", + "content": " is the parameter sensitivity on the " + }, + { + "bbox": [ + 59, + 101, + 274, + 209 + ], + "type": "inline_equation", + "content": "k^{th}" + }, + { + "bbox": [ + 59, + 101, + 274, + 209 + ], + "type": "text", + "content": " client." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "code_body" + } + ], + "index": 1, + "sub_type": "algorithm" + }, + { + "bbox": [ + 60, + 210, + 105, + 220 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 60, + 210, + 105, + 220 + ], + "spans": [ + { + "bbox": [ + 60, + 210, + 105, + 220 + ], + "type": "text", + "content": "Initialize " + }, + { + "bbox": [ + 60, + 210, + 105, + 220 + ], + "type": "inline_equation", + "content": "\\theta" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 61, + 222, + 235, + 233 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 61, + 222, + 235, + 233 + ], + "spans": [ + { + "bbox": [ + 61, + 222, + 235, + 233 + ], + "type": "inline_equation", + "content": "B_{k}\\gets" + }, + { + "bbox": [ + 61, + 222, + 235, + 233 + ], + "type": "text", + "content": " Sample a subset of training data " + }, + { + "bbox": [ + 61, + 222, + 235, + 233 + ], + "type": "inline_equation", + "content": "D_{k}" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 61, + 234, + 225, + 246 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 61, + 234, + 225, + 246 + ], + "spans": [ + { + "bbox": [ + 61, + 234, + 225, + 246 + ], + "type": "inline_equation", + "content": "D_{k}\\gets" + }, + { + "bbox": [ + 61, + 234, + 225, + 246 + ], + "type": "text", + "content": " Drop the samples of " + }, + { + "bbox": [ + 61, + 234, + 225, + 246 + ], + "type": "inline_equation", + "content": "B_{k}" + }, + { + "bbox": [ + 61, + 234, + 225, + 246 + ], + "type": "text", + "content": " from " + }, + { + "bbox": [ + 61, + 234, + 225, + 246 + ], + "type": "inline_equation", + "content": "D_{k}" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 61, + 247, + 135, + 256 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 61, + 247, + 135, + 256 + ], + "spans": [ + { + "bbox": [ + 61, + 247, + 135, + 256 + ], + "type": "text", + "content": "for each round do" + } + ] + } + ], + "index": 5 + }, + { + "type": "code", + "bbox": [ + 75, + 258, + 250, + 471 + ], + "blocks": [ + { + "bbox": [ + 75, + 258, + 250, + 471 + ], + "lines": [ + { + "bbox": [ + 75, + 258, + 250, + 471 + ], + "spans": [ + { + "bbox": [ + 75, + 258, + 250, + 471 + ], + "type": "text", + "content": "for each activated client " + }, + { + "bbox": [ + 75, + 258, + 250, + 471 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 75, + 258, + 250, + 471 + ], + "type": "text", + "content": " do Initialize " + }, + { + "bbox": [ + 75, + 258, + 250, + 471 + ], + "type": "inline_equation", + "content": "\\Omega_{k}" + }, + { + "bbox": [ + 75, + 258, + 250, + 471 + ], + "type": "text", + "content": " as zeros. \nfor each batch data " + }, + { + "bbox": [ + 75, + 258, + 250, + 471 + ], + "type": "inline_equation", + "content": "x\\in B_k" + }, + { + "bbox": [ + 75, + 258, + 250, + 471 + ], + "type": "text", + "content": " do " + }, + { + "bbox": [ + 75, + 258, + 250, + 471 + ], + "type": "inline_equation", + "content": "\\begin{array}{l}g = \\nabla ||F(\\theta ;x)||_2^2\\\\ \\mathbf{for}i\\in [1,\\dots ,n]\\mathbf{do}\\\\ \\big{\\lfloor}\\Omega_k^i\\gets \\mu \\Omega_k^i +(1 - \\mu)|g^i |\\\\ \\theta_k\\gets \\theta \\\\ \\mathbf{for}" + }, + { + "bbox": [ + 75, + 258, + 250, + 471 + ], + "type": "text", + "content": " each epoch do for each batch data " + }, + { + "bbox": [ + 75, + 258, + 250, + 471 + ], + "type": "inline_equation", + "content": "x\\in D_k" + }, + { + "bbox": [ + 75, + 258, + 250, + 471 + ], + "type": "text", + "content": " do " + }, + { + "bbox": [ + 75, + 258, + 250, + 471 + ], + "type": "inline_equation", + "content": "\\begin{array}{r}\\Big{\\lfloor}\\theta_{k}\\leftarrow \\theta_{k} - \\eta^{\\prime}\\nabla \\ell_{k}(F(\\theta_{k};x))\\\\ \\Delta_{k} = \\theta_{k} - \\theta \\end{array}" + }, + { + "bbox": [ + 75, + 258, + 250, + 471 + ], + "type": "inline_equation", + "content": "w_{k}\\gets |D_{k}| / \\sum_{k}|D_{k}|;\\Omega = \\sum_{k}(w_{k}\\cdot \\Omega_{k});" + }, + { + "bbox": [ + 75, + 258, + 250, + 471 + ], + "type": "inline_equation", + "content": "\\Omega^{\\prime} = \\max (\\Omega)" + }, + { + "bbox": [ + 75, + 258, + 250, + 471 + ], + "type": "text", + "content": " \nfor " + }, + { + "bbox": [ + 75, + 258, + 250, + 471 + ], + "type": "inline_equation", + "content": "i\\in [1,\\dots ,n]" + }, + { + "bbox": [ + 75, + 258, + 250, + 471 + ], + "type": "text", + "content": " do " + }, + { + "bbox": [ + 75, + 258, + 250, + 471 + ], + "type": "inline_equation", + "content": "\\zeta^i = 1 + \\tau -\\Omega^i /\\Omega '" + }, + { + "bbox": [ + 75, + 258, + 250, + 471 + ], + "type": "inline_equation", + "content": "\\Delta^i = \\zeta^i\\cdot \\sum_k(w_k\\cdot \\Delta_k^i)" + }, + { + "bbox": [ + 75, + 258, + 250, + 471 + ], + "type": "inline_equation", + "content": "\\theta^i\\gets \\theta^i -\\eta \\cdot \\Delta^i" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "code_body" + } + ], + "index": 6, + "sub_type": "algorithm" + }, + { + "bbox": [ + 46, + 502, + 287, + 598 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 502, + 287, + 598 + ], + "spans": [ + { + "bbox": [ + 46, + 502, + 287, + 598 + ], + "type": "inline_equation", + "content": "F" + }, + { + "bbox": [ + 46, + 502, + 287, + 598 + ], + "type": "text", + "content": " of the true function " + }, + { + "bbox": [ + 46, + 502, + 287, + 598 + ], + "type": "inline_equation", + "content": "\\bar{F}" + }, + { + "bbox": [ + 46, + 502, + 287, + 598 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 46, + 502, + 287, + 598 + ], + "type": "inline_equation", + "content": "F" + }, + { + "bbox": [ + 46, + 502, + 287, + 598 + ], + "type": "text", + "content": " maps the input " + }, + { + "bbox": [ + 46, + 502, + 287, + 598 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 46, + 502, + 287, + 598 + ], + "type": "text", + "content": " to the output " + }, + { + "bbox": [ + 46, + 502, + 287, + 598 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 46, + 502, + 287, + 598 + ], + "type": "text", + "content": ", and our goal is to largely maintain the same output " + }, + { + "bbox": [ + 46, + 502, + 287, + 598 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 46, + 502, + 287, + 598 + ], + "type": "text", + "content": " for the observed " + }, + { + "bbox": [ + 46, + 502, + 287, + 598 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 46, + 502, + 287, + 598 + ], + "type": "text", + "content": " while learning additional training instances " + }, + { + "bbox": [ + 46, + 502, + 287, + 598 + ], + "type": "inline_equation", + "content": "(x,y) \\sim P_k" + }, + { + "bbox": [ + 46, + 502, + 287, + 598 + ], + "type": "text", + "content": ". To this end, we measure how sensitive the output of function " + }, + { + "bbox": [ + 46, + 502, + 287, + 598 + ], + "type": "inline_equation", + "content": "F" + }, + { + "bbox": [ + 46, + 502, + 287, + 598 + ], + "type": "text", + "content": " is to changes in the network parameters. To reduce confusion, we ignore the symbols denoting the round " + }, + { + "bbox": [ + 46, + 502, + 287, + 598 + ], + "type": "inline_equation", + "content": "r" + }, + { + "bbox": [ + 46, + 502, + 287, + 598 + ], + "type": "text", + "content": " and the client " + }, + { + "bbox": [ + 46, + 502, + 287, + 598 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 502, + 287, + 598 + ], + "type": "text", + "content": " for all variables and only discuss parameter sensitivity locally." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 599, + 287, + 646 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 599, + 287, + 646 + ], + "spans": [ + { + "bbox": [ + 46, + 599, + 287, + 646 + ], + "type": "text", + "content": "For a given data point " + }, + { + "bbox": [ + 46, + 599, + 287, + 646 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 46, + 599, + 287, + 646 + ], + "type": "text", + "content": ", the output of the network is " + }, + { + "bbox": [ + 46, + 599, + 287, + 646 + ], + "type": "inline_equation", + "content": "F(\\theta; x)" + }, + { + "bbox": [ + 46, + 599, + 287, + 646 + ], + "type": "text", + "content": ". A small perturbation " + }, + { + "bbox": [ + 46, + 599, + 287, + 646 + ], + "type": "inline_equation", + "content": "\\delta" + }, + { + "bbox": [ + 46, + 599, + 287, + 646 + ], + "type": "text", + "content": " in the parameters " + }, + { + "bbox": [ + 46, + 599, + 287, + 646 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 46, + 599, + 287, + 646 + ], + "type": "text", + "content": " results in a change in the function output that can be approximated by:" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 96, + 647, + 287, + 659 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 96, + 647, + 287, + 659 + ], + "spans": [ + { + "bbox": [ + 96, + 647, + 287, + 659 + ], + "type": "interline_equation", + "content": "F (\\theta + \\delta ; x) - F (\\theta ; x) \\approx g (\\theta ; x) \\delta , \\tag {4}", + "image_path": "aa5366f11c29243718087fca2bb64efea5402036c0cce30f6a6492a0708c6c82.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 663, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 663, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 663, + 288, + 713 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 663, + 288, + 713 + ], + "type": "inline_equation", + "content": "g(\\theta ;x) = \\frac{\\partial F(\\theta;x)}{\\partial\\theta}" + }, + { + "bbox": [ + 46, + 663, + 288, + 713 + ], + "type": "text", + "content": " is the gradient of the learned function with respect to the parameter " + }, + { + "bbox": [ + 46, + 663, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 46, + 663, + 288, + 713 + ], + "type": "text", + "content": " evaluated at the data point " + }, + { + "bbox": [ + 46, + 663, + 288, + 713 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 46, + 663, + 288, + 713 + ], + "type": "text", + "content": ". Our goal is to maintain the output of the network (the learned function " + }, + { + "bbox": [ + 46, + 663, + 288, + 713 + ], + "type": "inline_equation", + "content": "F" + }, + { + "bbox": [ + 46, + 663, + 288, + 713 + ], + "type": "text", + "content": ") for each observed data point and" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 72, + 547, + 119 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 119 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 119 + ], + "type": "text", + "content": "thus we reduce the magnitudes of the updates to the parameters that are more sensitive for the data point. Conversely, we boost the updates to the less sensitive parameters to better-fit client distributions." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 120, + 546, + 252 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 120, + 546, + 252 + ], + "spans": [ + { + "bbox": [ + 304, + 120, + 546, + 252 + ], + "type": "text", + "content": "Based on equation 4, and assuming a small constant change " + }, + { + "bbox": [ + 304, + 120, + 546, + 252 + ], + "type": "inline_equation", + "content": "\\delta" + }, + { + "bbox": [ + 304, + 120, + 546, + 252 + ], + "type": "text", + "content": ", we can measure the sensitivity of a parameter by the magnitude of the gradient " + }, + { + "bbox": [ + 304, + 120, + 546, + 252 + ], + "type": "inline_equation", + "content": "g(\\theta; x)" + }, + { + "bbox": [ + 304, + 120, + 546, + 252 + ], + "type": "text", + "content": ", i.e., how much does a small perturbation to that parameter change the output of the learned function for data point " + }, + { + "bbox": [ + 304, + 120, + 546, + 252 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 304, + 120, + 546, + 252 + ], + "type": "text", + "content": ". There are many ways to measure the sensitivity of a parameter by the magnitude of the gradient, such as a fishing matrix. However, in federated learning, we have to take the computation ability of each client into account, which is only with limited computation ability. Therefore, we use the exponentially-decayed moving average1 to obtain sensitivity " + }, + { + "bbox": [ + 304, + 120, + 546, + 252 + ], + "type": "inline_equation", + "content": "\\Omega^i" + }, + { + "bbox": [ + 304, + 120, + 546, + 252 + ], + "type": "text", + "content": " for " + }, + { + "bbox": [ + 304, + 120, + 546, + 252 + ], + "type": "inline_equation", + "content": "i^{th}" + }, + { + "bbox": [ + 304, + 120, + 546, + 252 + ], + "type": "text", + "content": " parameter " + }, + { + "bbox": [ + 304, + 120, + 546, + 252 + ], + "type": "inline_equation", + "content": "\\theta^i" + }, + { + "bbox": [ + 304, + 120, + 546, + 252 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 361, + 258, + 545, + 273 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 361, + 258, + 545, + 273 + ], + "spans": [ + { + "bbox": [ + 361, + 258, + 545, + 273 + ], + "type": "interline_equation", + "content": "\\Omega^ {i} \\leftarrow \\mu \\Omega^ {i} + (1 - \\mu) | g \\left(\\theta^ {i}; x\\right) |, \\tag {5}", + "image_path": "fbafed194813c692c0daf1f2f3949c550e43524d368b737a51fc9300dfc3b7b5.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 280, + 527, + 291 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 280, + 527, + 291 + ], + "spans": [ + { + "bbox": [ + 305, + 280, + 527, + 291 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 280, + 527, + 291 + ], + "type": "inline_equation", + "content": "\\mu" + }, + { + "bbox": [ + 305, + 280, + 527, + 291 + ], + "type": "text", + "content": " is momentum and we empirically set it to 0.9." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 292, + 547, + 399 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 292, + 547, + 399 + ], + "spans": [ + { + "bbox": [ + 304, + 292, + 547, + 399 + ], + "type": "text", + "content": "When the output function " + }, + { + "bbox": [ + 304, + 292, + 547, + 399 + ], + "type": "inline_equation", + "content": "F" + }, + { + "bbox": [ + 304, + 292, + 547, + 399 + ], + "type": "text", + "content": " is multi-dimensional, as is the case for most neural networks, equation 5 involves computing the gradients for each output, which requires as many backward passes as the dimensionality of the output. As a more efficient alternative, we propose to use the gradients of the squared " + }, + { + "bbox": [ + 304, + 292, + 547, + 399 + ], + "type": "inline_equation", + "content": "L^2" + }, + { + "bbox": [ + 304, + 292, + 547, + 399 + ], + "type": "text", + "content": " norm of the learned function output, i.e. " + }, + { + "bbox": [ + 304, + 292, + 547, + 399 + ], + "type": "inline_equation", + "content": "g(\\theta ;x) = \\nabla ||F(\\theta ;x)||_2^2" + }, + { + "bbox": [ + 304, + 292, + 547, + 399 + ], + "type": "text", + "content": ". Hence, we only need to compute one backward pass in order to estimate the parameters' sensitivity." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 306, + 415, + 545, + 441 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 415, + 545, + 441 + ], + "spans": [ + { + "bbox": [ + 306, + 415, + 545, + 441 + ], + "type": "text", + "content": "3.3. Elastic aggregation with respect to parameter sensitivity" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 445, + 545, + 468 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 445, + 545, + 468 + ], + "spans": [ + { + "bbox": [ + 306, + 445, + 545, + 468 + ], + "type": "text", + "content": "The elastic aggregation for " + }, + { + "bbox": [ + 306, + 445, + 545, + 468 + ], + "type": "inline_equation", + "content": "i^{th}" + }, + { + "bbox": [ + 306, + 445, + 545, + 468 + ], + "type": "text", + "content": " parameter can be written as:" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 375, + 468, + 545, + 493 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 375, + 468, + 545, + 493 + ], + "spans": [ + { + "bbox": [ + 375, + 468, + 545, + 493 + ], + "type": "interline_equation", + "content": "\\Delta^ {i} = \\zeta^ {i} \\cdot \\sum_ {k \\in \\mathcal {S}} \\left(w _ {k} \\cdot \\Delta_ {k} ^ {i}\\right), \\tag {6}", + "image_path": "e46e51fb194098383d041cfd3ed46bea072286f4122198700a257f19bb293ec1.jpg" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 305, + 497, + 547, + 521 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 497, + 547, + 521 + ], + "spans": [ + { + "bbox": [ + 305, + 497, + 547, + 521 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 497, + 547, + 521 + ], + "type": "inline_equation", + "content": "\\zeta^i" + }, + { + "bbox": [ + 305, + 497, + 547, + 521 + ], + "type": "text", + "content": " is the adaptive coefficient with respect to the parameter sensitivity. The definition of " + }, + { + "bbox": [ + 305, + 497, + 547, + 521 + ], + "type": "inline_equation", + "content": "\\zeta^i" + }, + { + "bbox": [ + 305, + 497, + 547, + 521 + ], + "type": "text", + "content": " is:" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 381, + 529, + 545, + 543 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 381, + 529, + 545, + 543 + ], + "spans": [ + { + "bbox": [ + 381, + 529, + 545, + 543 + ], + "type": "interline_equation", + "content": "\\zeta^ {i} = 1 + \\tau - \\Omega^ {i} / \\Omega^ {\\prime}, \\tag {7}", + "image_path": "c8b5d400b1d20f347456cbb90d6df065ff0b84c8a5a97c9c2980fe1714914fc1.jpg" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 304, + 549, + 547, + 658 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 549, + 547, + 658 + ], + "spans": [ + { + "bbox": [ + 304, + 549, + 547, + 658 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 549, + 547, + 658 + ], + "type": "inline_equation", + "content": "\\Omega' = \\max(\\Omega)" + }, + { + "bbox": [ + 304, + 549, + 547, + 658 + ], + "type": "text", + "content": " is the maximum of parameter sensitivities in each layer, and " + }, + { + "bbox": [ + 304, + 549, + 547, + 658 + ], + "type": "inline_equation", + "content": "\\Omega^i = \\sum_{k \\in S} (w_k \\cdot \\Omega_k^i)" + }, + { + "bbox": [ + 304, + 549, + 547, + 658 + ], + "type": "text", + "content": " is the aggregated sensitivity of " + }, + { + "bbox": [ + 304, + 549, + 547, + 658 + ], + "type": "inline_equation", + "content": "i^{th}" + }, + { + "bbox": [ + 304, + 549, + 547, + 658 + ], + "type": "text", + "content": " parameter across activated clients. The server is able to boost updates (" + }, + { + "bbox": [ + 304, + 549, + 547, + 658 + ], + "type": "inline_equation", + "content": "\\zeta^i > 1.0" + }, + { + "bbox": [ + 304, + 549, + 547, + 658 + ], + "type": "text", + "content": ") to parameters that have low sensitivity (low " + }, + { + "bbox": [ + 304, + 549, + 547, + 658 + ], + "type": "inline_equation", + "content": "\\Omega^i" + }, + { + "bbox": [ + 304, + 549, + 547, + 658 + ], + "type": "text", + "content": "). Meanwhile, sensitive parameters (high " + }, + { + "bbox": [ + 304, + 549, + 547, + 658 + ], + "type": "inline_equation", + "content": "\\Omega^i" + }, + { + "bbox": [ + 304, + 549, + 547, + 658 + ], + "type": "text", + "content": ") have their updates restricted with a penalty (" + }, + { + "bbox": [ + 304, + 549, + 547, + 658 + ], + "type": "inline_equation", + "content": "\\zeta^i < 1.0" + }, + { + "bbox": [ + 304, + 549, + 547, + 658 + ], + "type": "text", + "content": "). " + }, + { + "bbox": [ + 304, + 549, + 547, + 658 + ], + "type": "inline_equation", + "content": "\\tau" + }, + { + "bbox": [ + 304, + 549, + 547, + 658 + ], + "type": "text", + "content": " is a hyper-parameter determining the ratio of boosted or restricted parameters. FedAvg with elastic aggregation is formalized in Algorithm 1." + } + ] + } + ], + "index": 21 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 304, + 664, + 547, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 664, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 664, + 547, + 713 + ], + "type": "text", + "content": "1While a Polyak-style average has more theoretical guarantees for accumulating " + }, + { + "bbox": [ + 304, + 664, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\Omega" + }, + { + "bbox": [ + 304, + 664, + 547, + 713 + ], + "type": "text", + "content": " over batches, our results match the claim that \"an exponentially-decayed moving average typically works much better in practice\" [39]. Thus, we use the exponentially-decayed moving average to accumulate " + }, + { + "bbox": [ + 304, + 664, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\Omega" + }, + { + "bbox": [ + 304, + 664, + 547, + 713 + ], + "type": "text", + "content": " over batches. Refer to supplementary materials for more discussion." + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "12190" + } + ] + } + ], + "index": 23 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 288, + 144 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 288, + 144 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 288, + 144 + ], + "type": "text", + "content": "Discussion on " + }, + { + "bbox": [ + 46, + 72, + 288, + 144 + ], + "type": "inline_equation", + "content": "\\tau" + }, + { + "bbox": [ + 46, + 72, + 288, + 144 + ], + "type": "text", + "content": ". In Eq. 6, " + }, + { + "bbox": [ + 46, + 72, + 288, + 144 + ], + "type": "inline_equation", + "content": "\\zeta^i \\in (1, 1 + \\tau]" + }, + { + "bbox": [ + 46, + 72, + 288, + 144 + ], + "type": "text", + "content": " is applied to the less sensitive parameters, and " + }, + { + "bbox": [ + 46, + 72, + 288, + 144 + ], + "type": "inline_equation", + "content": "\\zeta^i \\in [\\tau, 1)" + }, + { + "bbox": [ + 46, + 72, + 288, + 144 + ], + "type": "text", + "content": " is applied to the more sensitive parameters. Thus, " + }, + { + "bbox": [ + 46, + 72, + 288, + 144 + ], + "type": "inline_equation", + "content": "\\tau" + }, + { + "bbox": [ + 46, + 72, + 288, + 144 + ], + "type": "text", + "content": " determines the portion of the parameter to be restricted or boosted. Generally, a larger " + }, + { + "bbox": [ + 46, + 72, + 288, + 144 + ], + "type": "inline_equation", + "content": "\\tau" + }, + { + "bbox": [ + 46, + 72, + 288, + 144 + ], + "type": "text", + "content": " indicates that a larger proportion of parameters will be boosted, as shown in Tab. 1, and vice versa." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 144, + 290, + 253 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 144, + 290, + 253 + ], + "spans": [ + { + "bbox": [ + 46, + 144, + 290, + 253 + ], + "type": "text", + "content": "If a large proportion of parameters is restricted (" + }, + { + "bbox": [ + 46, + 144, + 290, + 253 + ], + "type": "inline_equation", + "content": "\\tau" + }, + { + "bbox": [ + 46, + 144, + 290, + 253 + ], + "type": "text", + "content": " is small, such as 0.1), the server model will not be updated much, and exiting local minima becomes difficult. However, with a large " + }, + { + "bbox": [ + 46, + 144, + 290, + 253 + ], + "type": "inline_equation", + "content": "\\tau" + }, + { + "bbox": [ + 46, + 144, + 290, + 253 + ], + "type": "text", + "content": " such as 0.9, optimization of the server model becomes unstable, and this also causes performance degradation. It is therefore critical to maintain a balance between these extremes with a suitable " + }, + { + "bbox": [ + 46, + 144, + 290, + 253 + ], + "type": "inline_equation", + "content": "\\tau" + }, + { + "bbox": [ + 46, + 144, + 290, + 253 + ], + "type": "text", + "content": " and we find that " + }, + { + "bbox": [ + 46, + 144, + 290, + 253 + ], + "type": "inline_equation", + "content": "\\tau = 0.5" + }, + { + "bbox": [ + 46, + 144, + 290, + 253 + ], + "type": "text", + "content": " generalizes well to various experiments. At this value of " + }, + { + "bbox": [ + 46, + 144, + 290, + 253 + ], + "type": "inline_equation", + "content": "\\tau" + }, + { + "bbox": [ + 46, + 144, + 290, + 253 + ], + "type": "text", + "content": ", roughly three-quarters of the parameters are boosted." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 267, + 170, + 282 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 267, + 170, + 282 + ], + "spans": [ + { + "bbox": [ + 47, + 267, + 170, + 282 + ], + "type": "text", + "content": "4. Experiments settings" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 288, + 289, + 431 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 288, + 289, + 431 + ], + "spans": [ + { + "bbox": [ + 46, + 288, + 289, + 431 + ], + "type": "text", + "content": "Inconsistent usage of models, datasets, and non-IID partition methods makes it difficult to compare the performances of federated learning algorithms fairly. To enforce fair comparison, we explicitly specify the combinations of datasets, models, and non-IID partition methods to be used for experiments, which mostly consist of those used in existing work published at top-tier machine learning venues [18]. Note that although the reported precisions are state-of-the-art for the models we have chosen, higher-capacity models can achieve higher performances on these datasets. Therefore, we compare the relative performance of elastic aggregation against naive aggregation for various federated learning scenarios." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 444, + 146, + 456 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 444, + 146, + 456 + ], + "spans": [ + { + "bbox": [ + 47, + 444, + 146, + 456 + ], + "type": "text", + "content": "4.1. Implementation" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 462, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 462, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 462, + 289, + 715 + ], + "type": "text", + "content": "We measure our algorithm against the most comprehensive and representative suite of federated datasets and modeling tasks to date. For this purpose, we carry out simulations on five diverse and representative experiments on several datasets. In order to facilitate the experiments, we use the cosine annealing scheduler [37] for the client learning rate " + }, + { + "bbox": [ + 46, + 462, + 289, + 715 + ], + "type": "inline_equation", + "content": "\\eta_r^\\prime" + }, + { + "bbox": [ + 46, + 462, + 289, + 715 + ], + "type": "text", + "content": " at the " + }, + { + "bbox": [ + 46, + 462, + 289, + 715 + ], + "type": "inline_equation", + "content": "r^{th}" + }, + { + "bbox": [ + 46, + 462, + 289, + 715 + ], + "type": "text", + "content": " round, which is given by " + }, + { + "bbox": [ + 46, + 462, + 289, + 715 + ], + "type": "inline_equation", + "content": "\\eta_r^\\prime = (1 + \\cos (\\frac{r}{R}\\pi))\\eta^\\prime" + }, + { + "bbox": [ + 46, + 462, + 289, + 715 + ], + "type": "text", + "content": ". For all tasks, we measure the performance on the entire test set throughout training. Clients are sampled uniformly at random, without replacement within a given round, but with replacement across rounds. There are a variety of federated optimizers that improve the performance of federated learning. Here, we use the most basic and widely used federated optimization algorithm, i.e., FedAvg [40], as the default baseline in our experiments. With reference to [46], we implement all experiments with two important characteristics. First, instead of doing " + }, + { + "bbox": [ + 46, + 462, + 289, + 715 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 46, + 462, + 289, + 715 + ], + "type": "text", + "content": " training steps per client, we do " + }, + { + "bbox": [ + 46, + 462, + 289, + 715 + ], + "type": "inline_equation", + "content": "E" + }, + { + "bbox": [ + 46, + 462, + 289, + 715 + ], + "type": "text", + "content": " epochs of training over each client's data. Second, to account for varying numbers of gradient steps per client, we weigh the average of the client outputs " + }, + { + "bbox": [ + 46, + 462, + 289, + 715 + ], + "type": "inline_equation", + "content": "\\Delta_t^k" + }, + { + "bbox": [ + 46, + 462, + 289, + 715 + ], + "type": "text", + "content": " by the number of training samples. This also follows the approach of" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 72, + 547, + 168 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 168 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 168 + ], + "type": "text", + "content": "[40] and often outperforms uniform weighting [47]. We set " + }, + { + "bbox": [ + 304, + 72, + 547, + 168 + ], + "type": "inline_equation", + "content": "\\mu = 0.95" + }, + { + "bbox": [ + 304, + 72, + 547, + 168 + ], + "type": "text", + "content": " for the accumulation of the parameter sensitivity over batches in each client. " + }, + { + "bbox": [ + 304, + 72, + 547, + 168 + ], + "type": "inline_equation", + "content": "\\tau = 0.5, \\eta = 1.0" + }, + { + "bbox": [ + 304, + 72, + 547, + 168 + ], + "type": "text", + "content": " is used for all experiments. While computing Eq. 7, we normalize the parameter sensitivity layer by layer, which means that the parameter sensitivity is divided by the maximum value within the same layer. Aside from experiments 5.1, we set " + }, + { + "bbox": [ + 304, + 72, + 547, + 168 + ], + "type": "inline_equation", + "content": "E = 1" + }, + { + "bbox": [ + 304, + 72, + 547, + 168 + ], + "type": "text", + "content": " for each client for all experiments." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 305, + 182, + 507, + 194 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 182, + 507, + 194 + ], + "spans": [ + { + "bbox": [ + 305, + 182, + 507, + 194 + ], + "type": "text", + "content": "4.2. Generate synthetic federated datasets." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 201, + 547, + 321 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 201, + 547, + 321 + ], + "spans": [ + { + "bbox": [ + 304, + 201, + 547, + 321 + ], + "type": "text", + "content": "Differences in distribution have an enormous influence on the performance of federated optimization. The Dirichlet distribution is used on the label ratios to ensure uneven label distributions among clients for non-IID splits, as in [59]. To generate imbalanced data, we sample the number of data points from a log-normal distribution. The degree of imbalance depends on the variance of the log-normal distribution, which is controlled by the hyper-parameter " + }, + { + "bbox": [ + 304, + 201, + 547, + 321 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 304, + 201, + 547, + 321 + ], + "type": "text", + "content": ". A smaller " + }, + { + "bbox": [ + 304, + 201, + 547, + 321 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 304, + 201, + 547, + 321 + ], + "type": "text", + "content": " indicates a stronger non-IID-ness in partitions, as shown in Fig. 2." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 337, + 388, + 351 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 337, + 388, + 351 + ], + "spans": [ + { + "bbox": [ + 305, + 337, + 388, + 351 + ], + "type": "text", + "content": "5. Experiments" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 357, + 547, + 418 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 357, + 547, + 418 + ], + "spans": [ + { + "bbox": [ + 304, + 357, + 547, + 418 + ], + "type": "text", + "content": "Under all experiments, the samples used for computing parameter sensitivities at each client will be randomly sampled training data, and these sampled data will not be used for supervised training anymore. For a fair comparison, these sampled data will not be used in the baseline methods either." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 438, + 496, + 452 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 438, + 496, + 452 + ], + "spans": [ + { + "bbox": [ + 305, + 438, + 496, + 452 + ], + "type": "text", + "content": "5.1. Comparison with naive aggregation" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 457, + 547, + 566 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 457, + 547, + 566 + ], + "spans": [ + { + "bbox": [ + 304, + 457, + 547, + 566 + ], + "type": "text", + "content": "MNIST. As our baseline, we conduct a convex optimization experiment on MNIST [29] with logistic regression [31, 33, 40]. In this experiment, we generate a synthetic federated dataset of MNIST with " + }, + { + "bbox": [ + 304, + 457, + 547, + 566 + ], + "type": "inline_equation", + "content": "\\alpha = 100.0" + }, + { + "bbox": [ + 304, + 457, + 547, + 566 + ], + "type": "text", + "content": " and split the dataset into 1000 partitions. At each round of training, we randomly choose 100 clients without repeating the partition. As shown in Tab. 2, the elastic aggregation has a large advantage over naive aggregation even with a large number of participating clients." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 582, + 548, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 548, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 548, + 715 + ], + "type": "text", + "content": "Federated EMNIST. Due to resource constraints of edge devices, existing works commonly use shallow neural networks for experiments. Similarly, we include Federated EMNIST [46] with a shallow neural network consisting of two convolution layers followed by two linear layers [46]. Notably, Fed-EMNIST [46] has a natural client partitioning that is highly representative of real-world federated learning problems. It contains 3,400 users (clients) and 62 label classes. The dataset is split into 671,585 training examples and 77,483 testing examples. Rather than holding out specific users, we split each user's examples across the train" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 758 + ], + "type": "text", + "content": "12191" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 52, + 71, + 545, + 498 + ], + "blocks": [ + { + "bbox": [ + 52, + 71, + 545, + 498 + ], + "lines": [ + { + "bbox": [ + 52, + 71, + 545, + 498 + ], + "spans": [ + { + "bbox": [ + 52, + 71, + 545, + 498 + ], + "type": "image", + "image_path": "e773dec5da96cced1bd5a49a0c5da321880ca5698f21654cbf2bf790ff765bf4.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 509, + 547, + 536 + ], + "lines": [ + { + "bbox": [ + 46, + 509, + 547, + 536 + ], + "spans": [ + { + "bbox": [ + 46, + 509, + 547, + 536 + ], + "type": "text", + "content": "Figure 2. Performances across different partitioning distributions, participation rates and numbers of local epochs. Compared with naive aggregation, elastic aggregation achieves significant improvements across these settings." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 63, + 546, + 533, + 602 + ], + "blocks": [ + { + "bbox": [ + 63, + 546, + 533, + 602 + ], + "lines": [ + { + "bbox": [ + 63, + 546, + 533, + 602 + ], + "spans": [ + { + "bbox": [ + 63, + 546, + 533, + 602 + ], + "type": "table", + "html": "
τNaïve0.00.10.20.30.40.50.60.70.80.91.0
Train Acc.(%)58.3657.2158.3358.7660.6660.4761.4460.6660.5561.0159.2758.96
Test Acc.(%)60.7458.3059.7661.1761.9163.3962.7463.3963.2363.2260.8361.37
Boosted(%)-0.011.4527.2443.7559.7474.4384.5789.9393.5396.2697.38
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DatasetRounds(Epochs)TotalSampledBatchInit. LRModelNaïve(%)Elastic(%)
Balanced data across clients
CIFAR-1004000(~80)50010100.05ResNet-2032.3156.64
Unbalanced data across clients
MNIST20(~2)10001001000.1Logistic Regression70.1473.64
EMNIST1000(~2.5)3400101000.12Conv+2Linear88.7189.82
CIFAR-104000(~40)100010100.05ResNet-2066.8468.74
CINIC-10200(~20)1000100100.05ResNet-2035.8136.29
CINIC-104000(~40)100010100.05ResNet-2068.6869.25
", + "image_path": "929765a29705e852c78253a24b730eb841bcae96542e0fbb242b12ed8e9682c7.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 87, + 226, + 509, + 277 + ], + "blocks": [ + { + "bbox": [ + 46, + 188, + 547, + 212 + ], + "lines": [ + { + "bbox": [ + 46, + 188, + 547, + 212 + ], + "spans": [ + { + "bbox": [ + 46, + 188, + 547, + 212 + ], + "type": "text", + "content": "Table 2. Test accuracies for various datasets. Along with rounds, we list a more intuitive measure, i.e., epochs, to better reflect the total training computation." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 87, + 226, + 509, + 277 + ], + "lines": [ + { + "bbox": [ + 87, + 226, + 509, + 277 + ], + "spans": [ + { + "bbox": [ + 87, + 226, + 509, + 277 + ], + "type": "table", + "html": "
OptimizerFedAvgFedAvgMFedProxSCAFFOLDAdaOptPFNMPer-FedAvgpFedMe
w/o Elastic.49.3462.5251.5272.1078.0071.2350.4483.20
w/ Elastic.52.3764.4853.6475.4280.3473.6453.2485.63
Improvement.3.031.962.123.322.342.412.802.43
", + "image_path": "e4a9335965d8fd4ee056370f20f29020451593755d84b82f8d417219ce715118.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 285, + 546, + 309 + ], + "lines": [ + { + "bbox": [ + 46, + 285, + 546, + 309 + ], + "spans": [ + { + "bbox": [ + 46, + 285, + 546, + 309 + ], + "type": "text", + "content": "Table 3. Elastic aggregation can be easily integrated with different federated optimizers, achieving performance improvements. (Notes that the comparison across different federated optimizers is meaningless since they are under different experiment settings.)" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 329, + 288, + 389 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 329, + 288, + 389 + ], + "spans": [ + { + "bbox": [ + 46, + 329, + 288, + 389 + ], + "type": "text", + "content": "as the baseline model. As shown in Tab. 2, elastic aggregation significantly speeds up training. Furthermore, the final accuracy is improved by over " + }, + { + "bbox": [ + 46, + 329, + 288, + 389 + ], + "type": "inline_equation", + "content": "20\\%" + }, + { + "bbox": [ + 46, + 329, + 288, + 389 + ], + "type": "text", + "content": " compared with the naïve baseline, which demonstrates the effectiveness of elastic aggregation." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 418, + 288, + 564 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 418, + 288, + 564 + ], + "spans": [ + { + "bbox": [ + 46, + 418, + 288, + 564 + ], + "type": "text", + "content": "CIFAR-10 and CINIC-10. To further demonstrate the performance improvement resulting from elastic aggregation, we generate two synthetic federated datasets for CIFAR-10 [20] and CINIC-10 [10] with " + }, + { + "bbox": [ + 46, + 418, + 288, + 564 + ], + "type": "inline_equation", + "content": "\\alpha = 100.0" + }, + { + "bbox": [ + 46, + 418, + 288, + 564 + ], + "type": "text", + "content": ". CINIC-10 extends CIFAR-10 with the addition of down-sampled ImageNet images, making for a more challenging dataset. This also enables measuring the performance of models trained on CIFAR images on ImageNet images for the same classes. As shown in Tab. 2, elastic aggregation achieves superior performances on both the CIFAR-10 and the more difficult CINIC-10 datasets, confirming that our method generalizes well to large scale datasets." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 594, + 288, + 605 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 594, + 288, + 605 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 288, + 605 + ], + "type": "text", + "content": "Natural Language Processing on Shakespeare dataset." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 605, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 605, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 605, + 288, + 713 + ], + "type": "text", + "content": "We maintain the same experimental setup as [40] on the most commonly used natural language processing tasks: Shakespeare LSTM. The epoch in each round is 1, the batch size is 10 and both elastic and naive aggregation are trained for 2k rounds. We get the final accuracy as " + }, + { + "bbox": [ + 46, + 605, + 288, + 713 + ], + "type": "inline_equation", + "content": "62.14\\%" + }, + { + "bbox": [ + 46, + 605, + 288, + 713 + ], + "type": "text", + "content": " for naive aggregation and " + }, + { + "bbox": [ + 46, + 605, + 288, + 713 + ], + "type": "inline_equation", + "content": "64.73\\%" + }, + { + "bbox": [ + 46, + 605, + 288, + 713 + ], + "type": "text", + "content": " for elastic aggregation. The results show that elastic aggregation not only has a significant improvement in CV related tasks, but also has an positive effect on NLP related tasks." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 328, + 547, + 533 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 328, + 547, + 533 + ], + "spans": [ + { + "bbox": [ + 304, + 328, + 547, + 533 + ], + "type": "text", + "content": "Imbalanced and non-IID. We are also interested in understanding how parameter sensitivity can help improve convergence, particularly in cross-device and non-IID scenarios. Given the resource constraints of edge devices, large DNN models are usually trained under the cross-organization (also known as cross-silo) federated learning settings. Across the following experiments, we use CIFAR10 [28] with ResNet-20 [19]. We study three different parameters here: non-IID-ness, participation rate, and number of epochs. We explore the effects of varying non-IID-ness with " + }, + { + "bbox": [ + 304, + 328, + 547, + 533 + ], + "type": "inline_equation", + "content": "\\alpha = 100.0, 50.0, 10.0, 1.0, 0.5" + }, + { + "bbox": [ + 304, + 328, + 547, + 533 + ], + "type": "text", + "content": " across 1000 partitions. For participation rate, we test sampling " + }, + { + "bbox": [ + 304, + 328, + 547, + 533 + ], + "type": "inline_equation", + "content": "5\\%" + }, + { + "bbox": [ + 304, + 328, + 547, + 533 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 328, + 547, + 533 + ], + "type": "inline_equation", + "content": "10\\%" + }, + { + "bbox": [ + 304, + 328, + 547, + 533 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 328, + 547, + 533 + ], + "type": "inline_equation", + "content": "20\\%" + }, + { + "bbox": [ + 304, + 328, + 547, + 533 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 328, + 547, + 533 + ], + "type": "inline_equation", + "content": "40\\%" + }, + { + "bbox": [ + 304, + 328, + 547, + 533 + ], + "type": "text", + "content": " of the clients at each round. Finally, we test having 1, 5 epochs of local updates, to better show the robustness of elastic aggregation. As shown in Fig. 2, elastic aggregation is especially superior for situations with massive distribution, substantial heterogeneity, and imbalanced data." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 550, + 493, + 563 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 550, + 493, + 563 + ], + "spans": [ + { + "bbox": [ + 305, + 550, + 493, + 563 + ], + "type": "text", + "content": "5.2. Integration with modern optimizer" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 570, + 548, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 548, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 548, + 713 + ], + "type": "text", + "content": "Federated optimizer with elastic aggregation. To illustrate the generalizability of elastic aggregation, we integrate elastic aggregation into FedAvg [40], FedAvgM [46] and FedProx [31]. FedAvgM is an enhancement of FedAvg on the server-side, making use of the momentum strategy to update the server model. FedProx is an enhancement of FedAvg on the client-side, adding a penalty to the client updates. We have presented the details of FedAvg with elastic aggregation in Algorithm 1. Please refer to supplementary materials for more details about the other federated optimizers with elastic aggregation. As shown in the left part of Tab. 3, elastic aggregation works well with other com" + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "12193" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 51, + 71, + 541, + 386 + ], + "blocks": [ + { + "bbox": [ + 51, + 71, + 541, + 386 + ], + "lines": [ + { + "bbox": [ + 51, + 71, + 541, + 386 + ], + "spans": [ + { + "bbox": [ + 51, + 71, + 541, + 386 + ], + "type": "image", + "image_path": "e9f6b8691d01618f2a02fbdd8ecff9dfcada6e137cf7affcea0e7d0dc1941b6d.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 201, + 396, + 390, + 408 + ], + "lines": [ + { + "bbox": [ + 201, + 396, + 390, + 408 + ], + "spans": [ + { + "bbox": [ + 201, + 396, + 390, + 408 + ], + "type": "text", + "content": "Figure 3. Convergence speeds on different datasets." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 429, + 289, + 536 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 429, + 289, + 536 + ], + "spans": [ + { + "bbox": [ + 46, + 429, + 289, + 536 + ], + "type": "text", + "content": "plementary approaches whether designed for client-side or server-side. In order to further verify the generality of elastic aggregation, we did further experiments on the stat-of-the-art methods in FL, i.e. SCAFFOLD [23], AdaOpt [46] and PFNM [59]. Since these methods target on different aspect of federated learning, we conducted experiments based on their original experimental settings. As shown in middle part of Tab. 3, elastic aggregation plays a positive effect in most federated optimizers." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 552, + 288, + 636 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 552, + 288, + 636 + ], + "spans": [ + { + "bbox": [ + 46, + 552, + 288, + 636 + ], + "type": "text", + "content": "Influence on personalization. Personalization in federated learning is also a topic of great concern. Specifically, we equipped Per-FedAvg [13], pFedMe [11] – both focus on the model personalization (local model performance) in federated learning with elastic aggregation and found that elastic aggregation is also a favour in learning a better personalized model, as shown in the right part of Tab. 3." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 658, + 125, + 670 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 658, + 125, + 670 + ], + "spans": [ + { + "bbox": [ + 47, + 658, + 125, + 670 + ], + "type": "text", + "content": "5.3. Limitations" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 677, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 288, + 715 + ], + "type": "text", + "content": "In Fig. 3, we compare testing curves on various datasets and observe that elastic aggregation outperforms naive aggregation by converging faster. Nevertheless, using elas" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 429, + 547, + 525 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 429, + 547, + 525 + ], + "spans": [ + { + "bbox": [ + 304, + 429, + 547, + 525 + ], + "type": "text", + "content": "tic aggregation results in additional computational burden and communication costs, which may affect the overall performance of federated learning scenarios. For a more detailed analysis of the computational overhead, please refer to the supplementary materials. Despite these challenges, we firmly believe that the significant performance improvements associated with elastic aggregation warrant its use over naive aggregation." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 537, + 378, + 549 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 537, + 378, + 549 + ], + "spans": [ + { + "bbox": [ + 306, + 537, + 378, + 549 + ], + "type": "text", + "content": "6. Conclusion" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 558, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 558, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 558, + 547, + 713 + ], + "type": "text", + "content": "Our work delves into the impact of heterogeneity on optimization methods for federated learning. We proposed a novel aggregation method, elastic aggregation, which utilizes parameter sensitivity to overcome gradient dissimilarity. To the best of our knowledge, we are the pioneers in utilizing unlabeled client data to enhance federated learning performances. Empirical evaluations across various federated datasets validate the theoretical analysis and reveal that elastic aggregation can significantly enhance the convergence behavior of federated learning in realistic heterogeneous scenarios. Future directions may include expanding the elastic aggregation approach to adaptive optimization methods or gossip-based training techniques." + } + ] + } + ], + "index": 8 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "12194" + } + ] + } + ], + "index": 9 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 92, + 289, + 714 + ], + "type": "list", + "angle": 0, + "index": 12, + "blocks": [ + { + "bbox": [ + 53, + 92, + 287, + 152 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 92, + 287, + 152 + ], + "spans": [ + { + "bbox": [ + 53, + 92, + 287, + 152 + ], + "type": "text", + "content": "[1] Durmus Alp Emre Acar, Yue Zhao, Ramon Matas Navarro, Matthew Mattina, Paul N Whatmough, and Venkatesh Saligrama. 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CiteSeer, 2010." + } + ] + } + ], + "index": 15 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "12197" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 10 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/End-to-End 3D Dense Captioning With Vote2Cap-DETR/b3b0c666-2a98-4d91-907b-4e3009df208c_content_list.json b/2023/End-to-End 3D Dense Captioning With Vote2Cap-DETR/b3b0c666-2a98-4d91-907b-4e3009df208c_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..c1d159bf9833228414922788d2a4f648f9eb3e1c --- /dev/null +++ b/2023/End-to-End 3D Dense Captioning With Vote2Cap-DETR/b3b0c666-2a98-4d91-907b-4e3009df208c_content_list.json @@ -0,0 +1,1691 @@ +[ + { + "type": "text", + "text": "End-to-End 3D Dense Captioning with Vote2Cap-DETR", + "text_level": 1, + "bbox": [ + 200, + 130, + 772, + 152 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Sijin Chen $^{1*}$", + "bbox": [ + 104, + 179, + 209, + 199 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Hongyuan Zhu", + "bbox": [ + 241, + 180, + 370, + 198 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Xin Chen", + "bbox": [ + 411, + 180, + 498, + 196 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Yinjie Lei", + "bbox": [ + 539, + 180, + 627, + 198 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Gang $\\mathrm{Yu}^3$", + "bbox": [ + 669, + 180, + 751, + 198 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Tao Chen $^{1\\dagger}$", + "bbox": [ + 795, + 180, + 890, + 196 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "$^{1}$ Fudan University $^{2}$ Institute for Infocomm Research (I $^{2}$ R) & Centre for Frontier AI Research (CFAR), A*STAR, Singapore $^{3}$ Tencent PCG $^{4}$ Sichuan University https://github.com/ch3cook-fdu/Vote2Cap-DETR", + "bbox": [ + 86, + 199, + 901, + 251 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 286, + 313, + 301 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "3D dense captioning aims to generate multiple captions localized with their associated object regions. Existing methods follow a sophisticated \"detect-then-describe\" pipeline equipped with numerous hand-crafted components. However, these hand-crafted components would yield suboptimal performance given cluttered object spatial and class distributions among different scenes. In this paper, we propose a simple-yet-effective transformer framework Vote2Cap-DETR based on recent popular DEetection Transformer (DETR). Compared with prior arts, our framework has several appealing advantages: 1) Without resorting to numerous hand-crafted components, our method is based on a full transformer encoder-decoder architecture with a learnable vote query driven object decoder, and a caption decoder that produces the dense captions in a set-prediction manner. 2) In contrast to the two-stage scheme, our method can perform detection and captioning in one-stage. 3) Without bells and whistles, extensive experiments on two commonly used datasets, ScanRefer and Nr3D, demonstrate that our Vote2Cap-DETR surpasses current state-of-the-arts by $11.13\\%$ and $7.11\\%$ in CIDEr@0.5IoU, respectively. Codes will be released soon.", + "bbox": [ + 75, + 316, + 473, + 650 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 678, + 209, + 694 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "In recent years, works on 3D learning has grown dramatically for various applications [10, 11, 21, 41, 42]. Among them, 3D dense captioning [7, 13] requires a system to localize all the objects in a 3D scene and generate descriptive sentences for each object. This problem is challenging, given 1) the sparsity of point clouds and 2) the cluttered distribution of objects.", + "bbox": [ + 75, + 703, + 468, + 809 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "3D dense captioning can be divided into two tasks, object detection, and object caption generation. Scan2Cap [13], MORE [20], and SpaCap3D [39] propose well-designed re", + "bbox": [ + 75, + 809, + 468, + 854 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/07449a239b3ac7eb9654da11b4f22bdc9e076b4a2fe3aa3d3a9580a9bc634ca7.jpg", + "image_caption": [ + "Figure 1. Illustration of existing two-stage 3D dense captioning method (upper) and our Vote2Cap-DETR (bottom). Existing methods adopt a two-stage pipeline that heavily depends on a detector's output. Therefore, we propose a transformer-based one-stage model, Vote2Cap-DETR, that frames 3D dense captioning as a set prediction problem." + ], + "image_footnote": [], + "bbox": [ + 503, + 287, + 893, + 488 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "lation reasoning modules to model relations among object proposals efficiently. [48] introduces contextual information from two branches to improve the caption. 3DJCG [4] and D3Net [7] study the correlation between 3D visual grounding and 3D dense captioning and point out that these two tasks promote each other. Additionally, $\\chi$ -Trans2Cap [43] discusses how to transfer knowledge from additional 2d information to boost 3d dense captioning.", + "bbox": [ + 496, + 595, + 893, + 717 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Among existing methods, they all adopt a two-stage \"detect-then-describe\" pipeline [4, 7, 13, 20, 39, 48] (Figure 1). This pipeline first generates a set of object proposals, then decodes each object by a caption generator with an explicit reasoning procedure. Though these methods have achieved remarkable performance, the \"detect-then-describe\" pipeline suffers from the following issues: 1) Because of the serial and explicit reasoning, the captioning performance highly depends on the object detection performance, which limits the mutual promotion of detection and captioning. 2) The heavy reliance on hand-crafted components, e.g., radii, 3D operators, the definition of pro", + "bbox": [ + 496, + 719, + 895, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 810, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Part of this work was accomplished under supervision by Dr. Hongyuan Zhu from A*STAR, Singapore. \n†Corresponding author.", + "bbox": [ + 76, + 862, + 468, + 900 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "11124", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "posal neighbors, and post-processing (non-maximum suppression [28]) introduces additional hyper-parameters, leading to a sub-optimal performance given the sparse object surfaces and cluttered object distributions among different indoor scenes. This inspires us to design a one-stage 3D dense captioning system.", + "bbox": [ + 75, + 90, + 468, + 181 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To address the above issues, we propose Vote2CapDETR, a full transformer encoder-decoder architecture for one-stage 3D dense captioning. Unlike traditional \"detect-then-describe\" pipelines, we directly feed the decoder's output into the localization head and caption head in parallel. By casting 3D dense captioning as a set-to-set problem, each target instance and its language annotation is matched with a query in a one-to-one correspondence manner, enabling a more discriminative feature representation for proposals to identify each distinctive object in a 3D scene. Additionally, we also propose a novel vote query driven decoder to introduce spatial bias for better localization of objects in a cluttered 3D scene.", + "bbox": [ + 75, + 181, + 470, + 378 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "With fully attentional design, we resolve 3D dense captioning with the following innovations: 1) Our method treats the 3D dense captioning task as a set prediction problem. The proposed Vote2Cap-DETR directly decodes the features into object sets with their locations and corresponding captions by applying two parallel prediction heads. 2) We propose a novel vote decoder by reformulating the object queries in 3DETR into the format of the vote query, which is a composition of the embeddings of the seeds point and the vote transformation with respect to the seeds. This indicates the connection between the vote query in Vote2Cap-DETR with the VoteNet, but with better localization and higher training efficiencies; 3) We develop a novel query driven caption head, which absorbs the relation and attribute modeling into self- and cross-attention, so that it can look into both local and global contexts for better scene description. Extensive experiments on two commonly used datasets, ScanRefer and Nr3D, demonstrate that our approach surpasses prior arts with many hand-crafted procedures by a large margin, which demonstrates the superiority that fully transformer architecture with sophisticated vote head and caption head can inspire many 3D vision and language tasks.", + "bbox": [ + 75, + 380, + 470, + 727 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To summarize, the main contributions of this work include:", + "bbox": [ + 76, + 728, + 468, + 758 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- We propose a novel one-stage and fully attention driven architecture for 3D dense captioning as a set-to-set prediction problem, which achieves object localization and caption generation in parallel.", + "- Extensive experiments show that our proposed Vote2Cap approach achieves a new state-of-the-art performance on both Nr3D [1] (45.53% C@0.5) and ScanRefer [13] (73.77% C@0.5)." + ], + "bbox": [ + 94, + 772, + 467, + 898 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 500, + 89, + 640, + 106 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "We briefly summarize works on 3D and video dense captioning, and DETR-based methods for images and 3D point clouds. Additionally, we also introduce some methods for image captioning, which are closely related to our work.", + "bbox": [ + 498, + 119, + 890, + 179 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "3D and Video Dense Captioning. 3D dense captioning, a task that requires translating 3D scene information to a set of bounding boxes and natural language descriptions, is challenging and has raised great interest among scholars recent years. Scan2Cap [13] and MORE [20] build graph on a detector's [19, 32] box estimations with handcrafted rules for complex relation reasoning among objects in a 3D scene. SpaCap3D [39] build a spatiality-guided transformer to model spatial relations among the detector's output. 3DJCG [4] and D3Net [7] study the joint promotion of 3D dense captioning and 3D visual grounding. $\\chi$ -Trans2Cap [43] introduces additional 2D prior to complement information for 3D dense captioning with knowledge transfer. Recently, [48] shifts attention to contextual information for the perception of non-object information. Though these approaches have made great attempts at 3D dense captioning, they all follow a \"detect-then-describe\" pipeline, which heavily depends on a detector's performance. Our proposed Vote2Cap-DETR differs from existing works in that our method is a one-stage model that detects and generates captions in parallel and treats 3D dense captioning as a set prediction problem. Video dense captioning requires a model to segment and describe video clips from an input video. [40, 49] propose transformer architecture for end-to-end video dense captioning. In this paper, we design elements specially for 3D dense captioning, such as vote queries for better localization in sparse 3D space and the utilization of local contextual information through cross attention for informative object description.", + "bbox": [ + 498, + 185, + 890, + 623 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "DETR: from 2D to 3D. DETection Transformer(DETR) [5] is a transformer [37] based architecture that treats object detection as a set prediction problem and does not require nonmaximum suppression [28] for post-processing. Though great results have been achieved, DETR suffers from slow convergence. Many follow-up works [9, 16, 18, 26, 44, 50] put efforts on speeding up DETR's training by introducing multi-scale features, cross attention designs, and label assignment techniques. Researchers also attempt to introduce transformer architectures to 3D object detection. GroupFree3D [24] learns proposal features from the whole point cloud through the transformer rather than grouping local points. 3DETR [27] analyzes the potential of the standard transformer model and generates proposals by uniformly sampling seed points from a 3D scene. In our work, we extend the DETR architecture for 3D dense captioning that makes caption generation and box localization fully interrelated with parallel decoding. Additionally, we propose", + "bbox": [ + 498, + 628, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "11125", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "vote query for better performance and faster convergence.", + "bbox": [ + 76, + 90, + 467, + 104 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Image Captioning. Image captioning requires a model to generate sentences describing key elements in an image, which has become a hot topic in computer vision. Existing image captioning works adopt an encoder-decoder architecture, where the decoder generates sentences from visual features extracted by the encoder. [2, 14, 17, 30] adopt a detector to extract region features as visual clues for the decoder, while [23, 46] extract grid features directly from an image. Additionally, [29] generates captions from both region and grid visual features. Though these methods are effective in image captioning, they cannot be directly applied to 3D dense captioning since it requires describing each 3D object in a scene with respect to its surroundings. In contrast, our proposed caption head sufficiently leverages the rich context information in a 3D point cloud, receives visual clues from both the object query and its local context, and fuses them to achieve effective 3D dense captioning.", + "bbox": [ + 75, + 107, + 468, + 364 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Method", + "text_level": 1, + "bbox": [ + 76, + 375, + 166, + 390 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "As shown in Fig. 2, given a 3D scene, our goal is to localize objects of interest and generate informative natural language descriptions for each object. The input of our model is a point cloud $PC = [p_{in};f_{in}]\\in \\mathbb{R}^{N\\times (3 + F)}$ representing an indoor 3D scene. Here, $p_{in}\\in \\mathbb{R}^{N\\times 3}$ is the absolute locations for each point, and $f_{in}\\in \\mathbb{R}^{N\\times F}$ is additional input feature for each point, such as color, normal, height, or multiview feature introduced by [6,13]. The expected output is a set of box-caption pairs $(\\hat{B},\\hat{C}) = \\{(\\hat{b}_1,\\hat{c}_1),\\dots ,(\\hat{b}_K,\\hat{c}_K)\\}$ , representing an estimation of $K$ distinctive objects in this 3D scene.", + "bbox": [ + 75, + 400, + 468, + 566 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Specifically, our system adopts 3DETR [27] encoder as our scene encoder and a transformer decoder to capture both object-object and object-scene interactions through the attention mechanism. Then, we feed the query feature to two parallel task-specific heads for object detection and caption generation.", + "bbox": [ + 75, + 568, + 468, + 657 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. 3DETR Encoder", + "text_level": 1, + "bbox": [ + 76, + 665, + 241, + 680 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Inspired by DETR [5], 3DETR [27] has made a successful attempt at bringing full transformer architecture to the 3D object detection task, which removes many hand-coded design decisions as the popular VoteNet and PointNet++ modules in most two-stage methods.", + "bbox": [ + 75, + 688, + 468, + 763 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In 3DETR encoder, the input $PC$ is first tokenized with a set-abstraction layer [33]. Then, point tokens are fed into a masked transformer encoder with a set-abstraction layer followed by another two encoder layers. We denote the encoded scene tokens as $[p_{enc};f_{enc}]\\in \\mathbb{R}^{1,024\\times (3 + 256)}$ .", + "bbox": [ + 75, + 763, + 468, + 840 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. Vote Query", + "text_level": 1, + "bbox": [ + 76, + 847, + 200, + 863 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Though 3DETR has achieved initial success in 3D object detection, it suffers from certain limitations. 3DETR", + "bbox": [ + 75, + 869, + 468, + 900 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "proposes box estimations around the query points (aka proposal centers) sampled from the scenes, which can make these predictions far away from real objects given the sparse object surfaces, resulting in slow convergence to capture discriminative object features with further miss detections.", + "bbox": [ + 496, + 90, + 890, + 165 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Prior works on fast convergence DETR models [12, 26, 45] show that injecting more structured bias to initialize object queries, such as anchor points or content-aware queries, accelerates training. Therefore, we propose the vote query, which introduces both 3D spatial bias and content-related information, for faster convergence and performance improvement.", + "bbox": [ + 496, + 166, + 890, + 271 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "More specifically, we reformulate the object queries in 3DETR into the format of vote query as a composition of the embedding of the reference points and vote transformation around them. This helps build the connection between the object query in 3DETR and the vote set prediction widely studied in VoteNet [32].", + "bbox": [ + 496, + 272, + 890, + 362 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The detailed structure is shown in Figure 3. Here, vote $\\Delta p_{vote}$ is predicted from encoded scene token feature $f_{enc}$ with a Feed Forward Network (FFN) $FFN_{vote}$ that learns to shift the encoded points to objects' centers spatially:", + "bbox": [ + 496, + 362, + 890, + 422 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\np _ {v o t e} = p _ {e n c} + \\Delta p _ {v o t e} = p _ {e n c} + F F N _ {v o t e} \\left(f _ {e n c}\\right). \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 513, + 435, + 890, + 452 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Then, we sample 256 points $p_{seed}$ from $p_{enc}$ with farthest point sampling and locate each point's offset estimation for $p_{vq} = p_{seed} + \\Delta p_{vote}$ . Finally, we gather features from $(p_{enc}, f_{enc})$ for $p_{vq}$ with a set-abstraction layer [33], to formulate the vote query feature $f_{vq} \\in \\mathbb{R}^{256 \\times 256}$ . We represent vote query as $(p_{vq}, f_{vq})$ .", + "bbox": [ + 496, + 462, + 890, + 553 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Following 3DETR [27], our model adopts an eight-layer transformer decoder, and the $i$ -th layer's input query feature $f_{query}^{i}$ is calculated through", + "bbox": [ + 496, + 554, + 890, + 601 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nf _ {q u e r y} ^ {i} = \\operatorname {L a y e r} _ {i - 1} \\left(f _ {q u e r y} ^ {i - 1} + F F N \\left(P E \\left(p _ {v q}\\right)\\right)\\right), \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 514, + 611, + 890, + 630 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $f_{query}^{0} = f_{vq}$ , and $PE(\\cdot)$ is the 3D Fourier positional encoding function [35]. Experiments in later sections demonstrate that: 1) Vote query injects additional spatial bias to object detection and boosts the detection performance. 2) Encoding features from the point cloud as initial queries accelerates convergence.", + "bbox": [ + 496, + 638, + 890, + 731 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.3. Parallel Decoding", + "text_level": 1, + "bbox": [ + 500, + 739, + 671, + 756 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We adopt two task-specific heads for simultaneous object detection and caption generation. The two task heads are agnostic to each other's output.", + "bbox": [ + 496, + 763, + 890, + 808 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Detection Head. Detecting objects in a 3D scene requires box corner estimation $\\hat{B}$ and class estimation $\\hat{S}$ (containing \"no object\" class) from each object query feature. Following 3DETR [27], box corner estimation is generated by learning spatial offset from a query point to an object's center and box size regression. All subtasks are implemented", + "bbox": [ + 496, + 809, + 890, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "11126", + "bbox": [ + 478, + 944, + 519, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/37b209ed6ca2864135c523d8cf2fe09e1f818b93f825c68fe8ee16396787b438.jpg", + "image_caption": [ + "Figure 2. Approach. Vote2Cap-DETR is a one-stage transformer model that takes a 3D point cloud as its input, and generates a set of box predictions and sentences localizing and describing each object in the point cloud. The scene encoder first generates encoded scene tokens $(p_{enc}, f_{enc})$ from the input point cloud. Then, we generate vote query $(p_{vq}, f_{vq})$ from the encoded scene tokens, which introduce both spatial bias $p_{vq}$ and content-aware feature $f_{vq}$ to initial object queries. The transformer decoder decodes each vote query with two parallel task heads for captioning and detection. We optimize Vote2Cap-DETR with a set loss." + ], + "image_footnote": [], + "bbox": [ + 80, + 77, + 377, + 347 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/bb0740e2ed932f39423205db07b664eb02d165c8b20ae85b9140146b0217bac1.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 383, + 78, + 645, + 347 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/3ea17e8bfdfd5eb2f57ce342a4f0195e6ddf39fd91bf15f18c0533ea1a50f37c.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 645, + 77, + 893, + 345 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/ba46b383ed21182412643127266501b8e266daecd41dd6cb69d258f7407e93e5.jpg", + "image_caption": [ + "Figure 3. Vote Query Generation. Vote query $p_{vq}$ contains spatial bias $(\\Delta p_{vote})$ to initial object queries $(p_{seed})$ , which are sampled from the scene with farthest point sampling (FPS) and gathered feature $f_{vq}$ from the point cloud for each query." + ], + "image_footnote": [], + "bbox": [ + 120, + 438, + 423, + 551 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "by FFNs. In practice, the object localization head is shared through different layers in the decoder, following all existing works on DETR [5, 12, 26, 27].", + "bbox": [ + 75, + 623, + 468, + 667 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Caption Head. 3D dense captioning requires attribute details on an object and its relation with its close surroundings. However, the vote query itself is agnostic to box predictions and fails to provide adequate attribute and spatial relations for informative caption generation. Therefore, the main difficulty is how to leverage sufficient surrounding contextual information without confusing the caption head.", + "bbox": [ + 75, + 671, + 468, + 777 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "To address the above issues, we propose Dual-Clued Captioner(DCC), a lightweight transformer decoder-based caption head, for 3D dense captioning. DCC consists of a stack of 2 identical transformer decoder blocks, sinusoid position embedding, and a linear classification head. To generate informative captions, DCC receives two streams of visual clue $\\mathcal{V} = (\\mathcal{V}^q,\\mathcal{V}^s)$ . Here, $\\mathcal{V}^q$ is the last decoder layer's output feature of a vote query, and $\\mathcal{V}^s$ is contextual", + "bbox": [ + 75, + 779, + 470, + 901 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/6764c5eb6eaf5a0a7e742b12fa983de332de13ac43c63dcf9f7ee89550868083.jpg", + "image_caption": [ + "Figure 4. Dual-Clued Captioner(DCC). DCC is a lightweight transformer based caption head that uses vote query feature $\\mathcal{V}_q$ as caption perfix to identify the region to be described, and contextual features $\\nu_{s}$ surrounding the vote query to complement with more surrounding information for descriptive caption generation." + ], + "image_footnote": [], + "bbox": [ + 517, + 434, + 870, + 551 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "information surrounding the absolute location of each vote query. When generating a caption for a proposal, we substitute the standard Start Of Sequenec( 'SOS') prefix with $\\nu^q$ to identify the object to be described following [39]. Since the vote query is agnostic of actual neighbor object proposals because of the parallel detection branch, we introduce the vote query's $k_{s}$ nearest local context token features as its local surroundings $\\nu^{s}$ as keys for cross attention. During inference, we generate captions through beam search with a beam size of 5.", + "bbox": [ + 496, + 633, + 892, + 785 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.4. Set prediction loss for 3D Dense Captioning", + "text_level": 1, + "bbox": [ + 500, + 797, + 870, + 815 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Our proposed Vote2Cap-DETR requires supervision for vote query $(\\mathcal{L}_{vq})$ , detection head $(\\mathcal{L}_{det})$ , and caption head $(\\mathcal{L}_{cap})$ .", + "bbox": [ + 496, + 821, + 892, + 868 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Vote Query Loss. We borrow vote loss from VoteNet [32] as $\\mathcal{L}_{vq}$ , to help the vote query generation module learn to", + "bbox": [ + 498, + 869, + 892, + 902 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "11127", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "shift points $p_{enc}$ to an object's center:", + "bbox": [ + 76, + 90, + 328, + 106 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {v q} = \\frac {1}{M} \\sum_ {i = 1} ^ {M} \\sum_ {j = 1} ^ {N _ {g t}} \\left\\| p _ {v o t e} ^ {i} - c n t _ {j} \\right\\| _ {1} \\cdot \\mathbb {I} \\left\\{p _ {e n c} ^ {i} \\in I _ {j} \\right\\}. \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 89, + 119, + 468, + 162 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Here, $\\mathbb{I}(\\cdot)$ is an indicator function that equals 1 when the condition meets and 0 otherwise, $N_{gt}$ is the number of instances in a 3D scene, $M$ is the size of $p_{vote}$ , and $cnt_j$ is the center of $j$ th instance $I_j$ .", + "bbox": [ + 76, + 175, + 468, + 236 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Detection Loss. Following 3DETR [27], we use the same Hungarian algorithm to assign each proposal with a ground truth label. Since 3D dense captioning cares much for the object localization ability, we apply a larger weight on the gIoU loss in set loss [27]:", + "bbox": [ + 76, + 238, + 468, + 313 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {s e t} = \\alpha_ {1} \\mathcal {L} _ {g i o u} + \\alpha_ {2} \\mathcal {L} _ {c l s} + \\alpha_ {3} \\mathcal {L} _ {\\text {c e n t e r - r e g}} + \\alpha_ {4} \\mathcal {L} _ {\\text {s i z e - r e g}}, \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 76, + 327, + 468, + 356 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\alpha_{1} = 10$ , $\\alpha_{2} = 1$ , $\\alpha_{3} = 5$ , $\\alpha_{4} = 1$ are set heuristically. The set loss $\\mathcal{L}_{set}$ is applied to all $n_{dec - layer}$ layers in the decoder for better convergence.", + "bbox": [ + 76, + 357, + 468, + 402 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Caption Loss. Following the standard practice of image captioning, we train our caption head first with standard cross-entropy loss (MLE training), and then fine-tune it with Self-Critical Sequence Training (SCST) [34]. During MLE training, the model is trained to predict the $(t + 1)$ th word $c_i^{t + 1}$ , given the first $t$ words $c_i^{[1:t]}$ and the visual clue $\\mathcal{V}$ . The loss function for a $T$ -length sentence is defined as:", + "bbox": [ + 76, + 404, + 468, + 512 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {c _ {i}} = \\sum_ {i = 1} ^ {T} \\mathcal {L} _ {c _ {i}} (t) = - \\sum_ {i = 1} ^ {T} \\log \\hat {P} \\left(c _ {i} ^ {t + 1} | \\mathcal {V}, c _ {i} ^ {[ 1: t ]}\\right). \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 98, + 525, + 468, + 566 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "After the caption head is trained under word-level supervision, we fine-tune it with SCST. During SCST, the model generates multiple captions $\\hat{c}_{1,\\dots,k}$ with a beam size of $k$ and another $\\hat{g}$ through greedy search as a baseline. The loss function for SCST is defined as:", + "bbox": [ + 76, + 578, + 468, + 652 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {c _ {i}} = - \\sum_ {i = 1} ^ {k} \\left(R \\left(\\hat {c} _ {i}\\right) - R (\\hat {g})\\right) \\cdot \\frac {1}{| \\hat {c} _ {i} |} \\log \\hat {P} (\\hat {c} _ {i} | \\mathcal {V}). \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 99, + 664, + 468, + 705 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Here, the reward function $R(\\cdot)$ is the CIDEr metric for caption evaluation, and the log probability of caption $\\hat{c}_i$ is normalized by caption length $|\\hat{c}_i|$ to encourage the model to treat captions in different length with equal importance.", + "bbox": [ + 76, + 717, + 468, + 777 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Set to Set Training for 3D Dense Captioning. We propose an easy-to-implement set-to-set training strategy for 3D dense captioning. Given a 3D scene, we randomly sample one sentence from the corpus for each annotated instance. Then, we assign language annotations to the corresponding number of proposals in the corresponding scene with the same Hungarian algorithm. During training, we average losses for captions $\\mathcal{L}_{c_i}$ on all annotated instances in", + "bbox": [ + 76, + 779, + 468, + 901 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "a batch to compute the caption loss $\\mathcal{L}_{cap}$ . To balance loss for different tasks, our loss function is defined as:", + "bbox": [ + 500, + 90, + 890, + 119 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} = \\beta_ {1} \\mathcal {L} _ {v q} + \\beta_ {2} \\sum_ {i = 1} ^ {n _ {\\text {d e c - l a y e r}}} \\mathcal {L} _ {\\text {s e t}} + \\beta_ {3} \\mathcal {L} _ {\\text {c a p}}, \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 552, + 128, + 890, + 169 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\beta_{1} = 10, \\beta_{2} = 1, \\beta_{3} = 5$ are set heuristically.", + "bbox": [ + 500, + 175, + 844, + 191 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 500, + 203, + 630, + 219 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We first present the datasets, metrics, and implementation details for 3D dense captioning (section 4.1). Then, we provide comparisons with all state-of-the-art methods (section 4.2). We also provide studies on the effectiveness of different parts in our model (section 4.3). Finally, we visualize several qualitative results to address the effectiveness of our method (section 4.4).", + "bbox": [ + 498, + 228, + 890, + 333 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.1. Datasets, Metrics, and Implementation Details", + "text_level": 1, + "bbox": [ + 500, + 342, + 890, + 357 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Datasets. We analyze performance on ScanRefer [6] and $\\mathrm{Nr3D}$ [1], both of which are built on 3D scenes from ScanNet [15]. ScanRefer/Nr3D contains 36,665/32,919 freeform language annotations describing 7,875/4,664 objects from 562/511 out of 1201 3D scenes in ScanNet for training and evaluates on 9,508/8,584 sentences for 2,068/1,214 objects from 141/130 out of 312 3D scenes in ScanNet.", + "bbox": [ + 498, + 366, + 890, + 470 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Evaluation Metrics. Following [4, 13, 20, 39], we first apply NMS on object proposals to drop duplicate object predictions. Each object proposal is a box-caption pair $(\\hat{b}_i, \\hat{c}_i)$ , containing box corner prediction $\\hat{b}_i$ and generated caption $\\hat{c}_i$ . Then, each annotated instance is assigned an object proposal with the largest IoU among the remaining proposals. Here, we use $(b_i, C_i)$ to represent an instance's label, where $b_i$ is an instance's box corner label, and $C_i$ is the corpus containing all caption annotations for this instance. To jointly evaluate the model's localization and caption generation capability, we adopt the $m@kIoU$ metric [13]:", + "bbox": [ + 498, + 473, + 890, + 641 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nm @ k I o U = \\frac {1}{N} \\sum_ {i = 1} ^ {N} m \\left(\\hat {c} _ {i}, C _ {i}\\right) \\cdot \\mathbb {I} \\left\\{I o U \\left(\\hat {b} _ {i}, b _ {i}\\right) \\geq k \\right\\}. \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 509, + 648, + 890, + 703 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Here, $N$ is the number of total annotated instances in the evaluation dataset, and $m$ could be any metric for natural language generation, such as CIDEr [38], METEOR [3], BLEU-4 [31], and ROUGE-L [22].", + "bbox": [ + 498, + 703, + 890, + 763 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Implementation Details. We offer implementation details of different baselines. \"w/o additional 2D\" means the input $\\mathcal{PC} \\in \\mathbb{R}^{40,000 \\times 10}$ contains absolute location as well as color, normal and height for 40,000 points representing a 3D scene. \"additional 2D\" means we replace color information with 128-dimensional multiview feature extracted by ENet [8] from 2D images following [13].", + "bbox": [ + 498, + 763, + 890, + 869 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We first pre-train the whole network without the caption head on ScanNet [15] for 1,080 epochs (163k iterations,", + "bbox": [ + 498, + 869, + 890, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "11128", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "$\\sim 34$ hours) using an AdamW optimizer [25] with a learning rate decaying from $5 \\times 10^{-4}$ to $10^{-6}$ by a cosine annealing scheduler, a weight decay of 0.1, a gradient clipping of 0.1, and a batch size of 8 following [27]. Then, we jointly train the full model from pre-trained weights with the MLE caption loss for another 720 epochs (51k/46k iterations for ScanRefer/Nr3D, $\\sim 11 / 10$ hours). To prevent overfitting, we fix the learning rate of the detector as $10^{-6}$ , and set that of the caption head decaying from $10^{-4}$ to $10^{-6}$ using another cosine annealing scheduler. During SCST, we tune the caption head with a batch size of 2 and freeze the detector for 180 epochs because of high memory cost (50k/46k iterations for ScanRefer/Nr3D, $\\sim 14 / 11$ hours) with a fixed learning rate of $10^{-6}$ . We evaluate the model every 2,000 iterations during training for consistency with existing works [13, 39], and all experiments mentioned above are conducted on a single RTX3090 GPU.", + "bbox": [ + 75, + 90, + 472, + 349 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.2. Comparison with Existing Methods", + "text_level": 1, + "bbox": [ + 76, + 359, + 387, + 378 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "In this section, we compare performance with existing works on metrics C, M, B-4, R as abbreviations for CIDEr [38], METEOR [3], BLEU-4 [31], Rouge-L [22] under IoU thresholds of 0.25, 0.5 for ScanRefer (Table 1) and 0.5 for Nr3D (Table 2). In both tables, “-” indicates that neither the original paper nor any follow-up works provide such results. We make separate comparisons for MLE training and SCST since different supervisions on the caption head have huge influence on the captioning performance. Among all the listed methods, experiments other than D3Net [7] and 3DJCG [4] utilize the standard VoteNet [32] detector. Meanwhile, D3Net adopts PointGroup [19], a 3D instance segmentation model, for better object detection. 3DJCG substitute the proposal head with an FCOS [36] head to improve VoteNet's localization performance. Additionally, 3DJCG and D3Net are trained on 3D dense captioning as well as 3D visual grounding to study the joint promotion of both tasks. Among methods listed under SCST, $\\chi$ -Trans2Cap [43] combines MLE training with standard SCST in an additive manner, while Scan2Cap and D3Net [7] adopt the same reward that combines CIDEr score with a listener's [47] grounding loss by weighted summation. Meanwhile, our method adopts the standard SCST with CIDEr reward.", + "bbox": [ + 75, + 385, + 472, + 746 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 1 reports comparisons on ScanRefer [6] validation dataset. Our Vote2Cap-DETR surpasses current state-of-the-art methods. Under MLE training with additional 2D inputs, Vote2Cap-DETR achieves $59.32\\%$ C@0.5 while 3DJCG [4] achieves $49.48\\%$ (9.84% C@0.5↑) with additional training data. Under SCST, our Vote2Cap-DETR achieves $70.63\\%$ C@0.5 comparing to $62.64\\%$ (7.99% C@0.5↑) for current state-of-the-art D3Net [7].", + "bbox": [ + 75, + 748, + 470, + 869 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "In Table 2, we list results on the Nr3D [1] dataset with additional 2D input following [39]. Since Scan2Cap [13]", + "bbox": [ + 76, + 869, + 470, + 902 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "has not reported results on $\\mathrm{Nr3D}$ , we adopt the best-reported result from [4]. Our Vote2Cap-DETR also surpasses current state-of-the-art methods (5.78%/7.11% C@0.5↑ for MLE training/SCST).", + "bbox": [ + 496, + 90, + 893, + 151 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.3. Ablation Study", + "text_level": 1, + "bbox": [ + 498, + 164, + 653, + 181 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Since 3D dense captioning concerns both localization and caption generation, we perform ablation studies to understand the effectiveness of different components.", + "bbox": [ + 496, + 189, + 893, + 234 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Does the vote query improve 3DETR? We performed ablation experiments in Table 3 and Figure 5 to see if the vote query can improve 3DETR's localization and convergence. We notice that introducing position features $p_{vq}$ alone helps improve detection performance (0.97% mAP50↑). However, it (green line in Figure 5) converges slower in the earlier training procedure than the 3DETR baseline (blue line in Figure 5), inferring the vote query generation module is not well learned to predict accurate spatial offset estimations at early training epochs. Introducing additional content feature $f_{vq}$ in vote query features results in another boost in both detection performance (2.98% mAP50↑) and training speed (red line in Figure 5). The overall localization performance of Vote2Cap-DETR is about 7.2% mAP higher than the popular VoteNet.", + "bbox": [ + 496, + 237, + 895, + 465 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/e3bc14e3aabed028ea7b167beee694bdf8b15030260d0563c9dd06fb4cf0aa48.jpg", + "image_caption": [ + "Figure 5. Vote query and convergence. We take out convergence study on a different combination of content feature $f_{vq}$ and position $p_{vq}$ in vote query. The baseline model $(p_{query}, f_{query}^{0}) = (p_{seed}, 0)$ downgrades to 3DETR. Introducing $p_{vq}$ boosts performance but decelerates training since $FFN_{vote}$ requires time to converge, and $f_{vq}$ accelerates training." + ], + "image_footnote": [], + "bbox": [ + 506, + 473, + 885, + 635 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Does 3D context feature help captioning? Since the performance of 3D dense captioning is affected by both localization and caption capability, we freeze all parameters other than the caption head and train with 3D only input and standard cross entropy loss (MLE training) for a fair evaluation. We use object-centric decoder [39] as our baseline, which is a decoder that generates captions with object feature as a caption's prefix. In Table 4, “-” refers to the object-centric decoder baseline, “global” means naively including all context tokens extracted from the scene encoder in the decoder, “local” is our proposed caption head that", + "bbox": [ + 496, + 734, + 895, + 902 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "11129", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/0f93ae867db503f9f9dc0b9dea29db3a458ec6cd2e64a2e5b069dfa5b73a8f4c.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodLdesw/o additional 2D inputw/ additional 2D input
IoU = 0.25IoU = 0.50IoU = 0.25IoU = 0.50
C↑B-4↑M↑R↑C↑B-4↑M↑R↑C↑B-4↑M↑R↑C↑B-4↑M↑R↑
Scan2Cap [13]53.7334.2526.1454.9535.2022.3621.4443.5756.8234.1826.2955.2739.0823.3221.9744.78
MORE [20]58.8935.4126.3655.4138.9823.0121.6544.3362.9136.2526.7556.3340.9422.9321.6644.42
SpaCap3d [39]58.0635.3026.1655.0342.7625.3822.8445.6663.3036.4626.7155.7144.0225.2622.3345.36
3DJCG [4]MLE60.8639.6727.4559.0247.6831.5324.2851.8064.7040.1727.6659.2349.4831.0324.2250.80
D3Net [7]------------46.0730.2924.3551.67
Ours71.4539.3428.2559.3361.8134.4626.2254.4072.7939.1728.0659.2359.3232.4225.2852.53
x-Trans2Cap [43]58.8134.1725.8154.1041.5223.8321.9044.9761.8335.6526.6154.7043.8725.0522.4645.28
Scan2Cap [13]------------48.3826.0922.1544.74
D3Net [7]SCST------------62.6435.6825.7253.90
Ours84.1542.5128.4759.2673.7738.2126.6454.7186.2842.6428.2759.0770.6335.6925.5152.28
", + "bbox": [ + 81, + 71, + 890, + 213 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/c56cb66ed0b76c505bc85ed59c055d50f14fca116d0188e3af4f33d8881fb312.jpg", + "table_caption": [ + "Table 1. Evaluating Vote2Cap-DETR on ScanRefer [6]. We compare Vote2Cap-DETR with all published state-of-the-art 3D dense caption methods on the ScanRefer dataset. Though our method does not depend on hand-crafted NMS [28] to drop overlapped boxes, we follow the standard evaluation protocol from [13] for fair comparison and provide evaluation without NMS in Table 7. Our proposed Vote2Cap-DETR achieves new state-of-the-art under both MLE training and SCST." + ], + "table_footnote": [], + "table_body": "
MethodLdesC@0.5↑B-4@0.5↑M@0.5↑R@0.5↑
Scan2Cap [13]27.4717.2421.8049.06
SpaCap3d [39]33.7119.9222.6150.50
D3Net [7]MLE33.8520.7023.1353.38
3DJCG [4]38.0622.8223.7752.99
Ours43.8426.6825.4154.43
x-Tran2Cap [43]33.6219.2922.2750.00
D3Net [7]SCST38.4222.2224.7454.37
Ours45.5326.8825.4354.76
", + "bbox": [ + 81, + 299, + 465, + 411 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/a47e30d72a6a7b5c3ef01a488fbcab1929cf6cb0ec17873e6fdac52d601d4208.jpg", + "table_caption": [ + "Table 2. Evaluating Vote2Cap-DETR on Nr3D [1]. Likewise, we perform the standard evaluation on the Nr3D dataset, and our proposed Vote2Cap-DETR surpasses prior arts." + ], + "table_footnote": [], + "table_body": "
\\( {p}_{query} \\)\\( {f}_{query}^{0} \\)IoU=0.25IoU=0.501st layer IoU=0.50
mAP↑AR↑mAP↑AR↑mAP↑AR↑
VoteNet Baseline63.4282.1844.9660.65--
\\( {p}_{seed} \\)067.2584.9148.1864.9834.8055.06
\\( {p}_{vq} \\)067.3385.6049.1566.3830.2358.44
\\( {p}_{vq} \\)\\( {f}_{vq} \\)69.6187.2052.1369.1246.5366.51
", + "bbox": [ + 80, + 470, + 465, + 540 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "includes a vote query's $k_{s}$ ( $k_{s} = 128$ empirically) nearest context tokens extracted from the scene encoder.", + "bbox": [ + 75, + 609, + 468, + 638 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Results show that the caption generation performance benefits from the introduction of additional contextual information. Additionally, compared with naively introducing contextual information from the whole scene, the introduction of local context could be more beneficial. This demonstrates our motivation that close surroundings matter when describing an object.", + "bbox": [ + 75, + 640, + 468, + 746 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/065065c84623174d3cd6defaa67e587e1dbcbb0008c50208d54e6139ff864545.jpg", + "table_caption": [ + "Table 3. Vote query and performance. We provide quantitative results for Figure 5. Introducing $p_{vq}$ as query positions improves detection, and gathering $f_{vq}$ from content further boosts performance." + ], + "table_footnote": [], + "table_body": "
keyIoU=0.25IoU=0.5
C↑B-4↑M↑R↑C↑B-4↑M↑R↑
-68.6238.6127.6758.4760.1534.0225.8053.82
global70.0539.2327.8458.4461.2034.6625.9353.79
local70.4239.9827.9958.8961.3935.2426.0254.12
", + "bbox": [ + 81, + 760, + 465, + 820 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Do set-to-set training benefit dense captioning? To analyze the effectiveness of set-to-set training, we use a smaller learning rate $(10^{-6})$ for all parameters other than the caption head and freeze these parameters during SCST. We name the traditional training strategy as \"Sentence Training\" adopted in previous works [13, 39], which traverses through all sentence annotations in the dataset. As is shown in Figure 7, our proposed \"Set-to-Set\" training achieves comparable results with the traditional strategy during MLE training and converges faster because of a bigger batch size on the caption head, which also benefits SCST.", + "bbox": [ + 496, + 301, + 890, + 468 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/336db4fd26647d45e218fa4ae16b4b3fe98279a80d7e0a1e8b404cb9b32f8859.jpg", + "table_caption": [ + "Table 4. Different keys for caption generation. We provide a comparison on different keys used in caption generation. Introducing contextual information relates to more informative captions generated. Since 3D dense captioning is more object-centric, introducing vote queries' local contextual feature is a better choice." + ], + "table_footnote": [], + "table_body": "
TrainingLdesC@0.5↑B-4@0.5↑M@0.5↑R@0.5↑
SentenceMLE61.2135.3526.1254.52
Set-to-Set61.8134.4626.2254.40
SentenceSCST71.3937.5726.0154.28
Set-to-Set73.7738.2126.6454.71
", + "bbox": [ + 504, + 481, + 887, + 554 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "End to end training from scratch. Our Vote2Cap-DETR also supports end-to-end training from scratch for 3D dense captioning. However, both ScanRefer and Nr3D are annotated on limited scenes (562/511 scenes) for training; thus, directly training Vote2Cap-DETR from scratch will underperform given to satisfy two objectives simultaneously. Experiments on Scanrefer in Table 6 show that the greedy strategy we choose by pre-training detection head as a good pre-requisite for captioning achieves better performance.", + "bbox": [ + 496, + 641, + 890, + 779 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/5994a25266fce0281976638bdcb026b2288dd0683575c302e199e23624804be2.jpg", + "table_caption": [ + "Table 5. Set to Set training and performance. We compare our proposed set-to-set training with traditional \"Sentence Training\", which traverses through all sentence annotations. We achieve comparable performance with MLE training, and $2.38\\%$ C@0.5 improvement with SCST." + ], + "table_footnote": [], + "table_body": "
pretrain/end2endC@0.5↑B-4@0.5↑M@0.5↑R@0.5↑AP@0.5↑AR@0.5↑
end2end52.1528.8724.6849.7646.6862.17
pretrain+end2end62.0334.9026.0654.3351.2667.57
", + "bbox": [ + 500, + 791, + 890, + 830 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 6. Ablation study for training strategies. The greedy strategy we choose by pre-training detection head as a good prerequisite for captioning achieves better performance than directly end to end training from scratch.", + "bbox": [ + 496, + 840, + 890, + 896 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "11130", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/03cb43e70539653fe553a620890c611add75e2d5f940a8524f601c949c007efc.jpg", + "image_caption": [ + "scene0011_00" + ], + "image_footnote": [], + "bbox": [ + 96, + 99, + 274, + 185 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/831e1c0ce41a1028e27e929c4f0222271f1a12c4f9964e11c203c5c0e810f8d4.jpg", + "image_caption": [ + "scene0015_00", + "3DJCG: This is a rectangular whiteboard. It is on the wall.", + "3DJCG: This is a brown table. It is in the middle of the room.", + "SpaCap3D: This is a wooden table. It is in the center of the room.", + "Ours: This is a wooden table. It is in the corner of the room." + ], + "image_footnote": [], + "bbox": [ + 295, + 101, + 473, + 185 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/c456dfcaa8143962bbae4175e7a69723a047d1d2944d8d6e9491371688506220.jpg", + "image_caption": [ + "scene0025_00", + "3DJCG: The is a small brown cabinet. It is to the right of the desk.", + "SpaCap3D: The cabinet is below the desk. It is to the left of the chair.", + "Ours: The tv is on the wall. It is to the right of the table.", + "Ours: This is a white cabinet. It is to the right of the table." + ], + "image_footnote": [], + "bbox": [ + 496, + 101, + 673, + 185 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/328921ee1bbcaf70805e923e55b2b870420b69908f8a8fe596a484864be2fae0.jpg", + "image_caption": [ + "scene0050_00", + "3DJCG: This is a brown table. It is in front of the couch.", + "SpaCap3D: This is a wooden coffee table. It is in front of the couch.", + "Ours: This is a brown ottoman. It is to the right of the chair.", + "GT: This is a brown ottoman. It is in front of a couch." + ], + "image_footnote": [], + "bbox": [ + 696, + 101, + 872, + 185 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/0c53d57d5bc9ca0e78c887611afbc6ea08a02364435a9e8a1fef9668d8ae224e.jpg", + "image_caption": [ + "SpaCap3D: The whiteboard is affixed to the wall. It is to the right of the window.", + "GT: This is a big black tv. It is above a thin table.", + "GT: This is a small table with a wood look. It is the table closest to the front of the room in the upper left corner.", + "GT: A white cabinet is sitting on the floor next to the wall. It is to the left of the couch.", + "Figure 6. Qualitative Comparisons. We compare qualitative results with two state-of-the-art \"detect-then-describe\" methods, 3DJCG [4] and SpaCap3D [39]. We underline phrases describing spatial locations, and mark correct attribute words in green and wrong description in red. Our Vote2Cap-DETR produces tight bounding boxes close to the ground truth and accurate descriptions.", + "Figure 7. Set-to-Set training and convergence. Convergence speed analysis of two different training strategies with MLE training as well as SCST. Set-to-Set training enables a larger batch size for the caption head and accelerates convergence." + ], + "image_footnote": [], + "bbox": [ + 84, + 435, + 460, + 612 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Is Vote2Cap-DETR robust to NMS? Similar to other DETR works, the set loss encourages the model to produce compact predictions. We compare performance on both 3D dense caption (C@0.5) and detection (mAP50, AR50) in Table 7. Since the $m@kIoU$ metric (Eq. 8) does not contain any penalties on redundant predictions, getting rid of NMS [28] results in performance growth in C@0.5. Results show that Vote2Cap-DETR is more stable compared to VoteNet based methods with the absence of NMS.", + "bbox": [ + 75, + 672, + 468, + 806 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/e336f7f759b1582cf233d5fa3baed24f83ae0e7252f1bcd42900160d5a76d5d9.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
Modelsw/NMSw/o NMS
C@0.5↑mAP50↑AR50↑C@0.5↑mAP50↑AR50↑
SpaCap3D43.9337.7753.9651.3523.3064.14
3DJCG50.2247.5862.1254.9430.0368.69
Vote2Cap-DETR70.6352.7966.0971.5752.8267.80
", + "bbox": [ + 81, + 806, + 465, + 863 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 7. Effect of NMS. We analyze whether the absence of NMS affects the 3D dense captioning performance (C@0.5) as well as detection performance (mAP50, AR50).", + "bbox": [ + 75, + 869, + 468, + 912 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.4. Qualitative Results", + "text_level": 1, + "bbox": [ + 500, + 431, + 681, + 446 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We compare qualitative results with two state-of-the-art models, SpaCap3D [39] and 3DJCG [4] in Figure 6. One can see that our method produces tight bounding boxes close to the ground truth as well as accurate descriptions of object attributes, classes, and spatial relationships.", + "bbox": [ + 496, + 448, + 890, + 523 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 531, + 617, + 545 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this work, we present Vote2Cap-DETR, a transformer based one-stage approach, for 3D dense captioning. The proposed Vote2Cap-DETR adopts a full transformer encoder-decoder architecture that decodes a set of vote queries to box predictions and captions in parallel. We show that by introducing spatial bias and content-aware features, vote query boosts both convergence and detection performance. Additionally, we develop a novel lightweight query-driven caption head for informative caption generation. Experiments on two widely used datasets for 3D dense captioning validate that our proposed one-stage Vote2Cap-DETR model surpasses prior works with heavy dependence on hand-crafted components by a large margin.", + "bbox": [ + 496, + 551, + 890, + 748 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "6. Acknowledgements", + "text_level": 1, + "bbox": [ + 500, + 753, + 687, + 771 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "This work is supported by National Natural Science Foundation of China (No. U1909207, 62071127, and 62276176), Shanghai Natural Science Foundation (No. 23ZR1402900), Zhejiang Lab Project (No. 2021KH0AB05), and in part by A*STAR AME Programmatic Funding A18A2b0046, RobotHTPO Seed Fund under Project C211518008, and EDB Space Technology Development Grant under Project S22-19016-STDP.", + "bbox": [ + 496, + 779, + 890, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "11131", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Panos Achlioptas, Ahmed Abdelreehm, Fei Xia, Mohamed Elhoseiny, and Leonidas Guibas. 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Deformable detr: Deformable transformers for end-to-end object detection. arXiv preprint arXiv:2010.04159, 2020. 2" + ], + "bbox": [ + 501, + 92, + 893, + 838 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "11133", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/End-to-End 3D Dense Captioning With Vote2Cap-DETR/b3b0c666-2a98-4d91-907b-4e3009df208c_model.json b/2023/End-to-End 3D Dense Captioning With Vote2Cap-DETR/b3b0c666-2a98-4d91-907b-4e3009df208c_model.json new file mode 100644 index 0000000000000000000000000000000000000000..3ec150c28f4440adfd46463a03e5ee5ccb3fcdcd --- /dev/null +++ b/2023/End-to-End 3D Dense Captioning With Vote2Cap-DETR/b3b0c666-2a98-4d91-907b-4e3009df208c_model.json @@ -0,0 +1,2486 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.044 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.001, + 0.812, + 0.047 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.201, + 0.131, + 0.773, + 0.154 + ], + "angle": 0, + "content": "End-to-End 3D Dense Captioning with Vote2Cap-DETR" + }, + { + "type": "text", + "bbox": [ + 0.106, + 0.18, + 0.21, + 0.2 + ], + "angle": 0, + "content": "Sijin Chen\\(^{1*}\\)" + }, + { + "type": "text", + "bbox": [ + 0.243, + 0.181, + 0.371, + 0.199 + ], + "angle": 0, + "content": "Hongyuan Zhu" + }, + { + "type": "text", + "bbox": [ + 0.412, + 0.181, + 0.499, + 0.198 + ], + "angle": 0, + "content": "Xin Chen" + }, + { + "type": "text", + "bbox": [ + 0.54, + 0.181, + 0.629, + 0.199 + ], + "angle": 0, + "content": "Yinjie Lei" + }, + { + "type": "text", + "bbox": [ + 0.67, + 0.181, + 0.753, + 0.199 + ], + "angle": 0, + "content": "Gang \\(\\mathrm{Yu}^3\\)" + }, + { + "type": "text", + "bbox": [ + 0.796, + 0.181, + 0.892, + 0.198 + ], + "angle": 0, + "content": "Tao Chen\\(^{1\\dagger}\\)" + }, + { + "type": "text", + "bbox": [ + 0.087, + 0.2, + 0.903, + 0.252 + ], + "angle": 0, + "content": "\\(^{1}\\)Fudan University \\(^{2}\\)Institute for Infocomm Research (I\\(^{2}\\)R) & Centre for Frontier AI Research (CFAR), A*STAR, Singapore \\(^{3}\\)Tencent PCG \\(^{4}\\)Sichuan University https://github.com/ch3cook-fdu/Vote2Cap-DETR" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.287, + 0.314, + 0.303 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.318, + 0.474, + 0.651 + ], + "angle": 0, + "content": "3D dense captioning aims to generate multiple captions localized with their associated object regions. Existing methods follow a sophisticated \"detect-then-describe\" pipeline equipped with numerous hand-crafted components. However, these hand-crafted components would yield suboptimal performance given cluttered object spatial and class distributions among different scenes. In this paper, we propose a simple-yet-effective transformer framework Vote2Cap-DETR based on recent popular DEetection Transformer (DETR). Compared with prior arts, our framework has several appealing advantages: 1) Without resorting to numerous hand-crafted components, our method is based on a full transformer encoder-decoder architecture with a learnable vote query driven object decoder, and a caption decoder that produces the dense captions in a set-prediction manner. 2) In contrast to the two-stage scheme, our method can perform detection and captioning in one-stage. 3) Without bells and whistles, extensive experiments on two commonly used datasets, ScanRefer and Nr3D, demonstrate that our Vote2Cap-DETR surpasses current state-of-the-arts by \\(11.13\\%\\) and \\(7.11\\%\\) in CIDEr@0.5IoU, respectively. Codes will be released soon." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.679, + 0.21, + 0.695 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.704, + 0.47, + 0.81 + ], + "angle": 0, + "content": "In recent years, works on 3D learning has grown dramatically for various applications [10, 11, 21, 41, 42]. Among them, 3D dense captioning [7, 13] requires a system to localize all the objects in a 3D scene and generate descriptive sentences for each object. This problem is challenging, given 1) the sparsity of point clouds and 2) the cluttered distribution of objects." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.81, + 0.47, + 0.856 + ], + "angle": 0, + "content": "3D dense captioning can be divided into two tasks, object detection, and object caption generation. Scan2Cap [13], MORE [20], and SpaCap3D [39] propose well-designed re" + }, + { + "type": "image", + "bbox": [ + 0.504, + 0.288, + 0.895, + 0.489 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.498, + 0.895, + 0.582 + ], + "angle": 0, + "content": "Figure 1. Illustration of existing two-stage 3D dense captioning method (upper) and our Vote2Cap-DETR (bottom). Existing methods adopt a two-stage pipeline that heavily depends on a detector's output. Therefore, we propose a transformer-based one-stage model, Vote2Cap-DETR, that frames 3D dense captioning as a set prediction problem." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.596, + 0.895, + 0.718 + ], + "angle": 0, + "content": "lation reasoning modules to model relations among object proposals efficiently. [48] introduces contextual information from two branches to improve the caption. 3DJCG [4] and D3Net [7] study the correlation between 3D visual grounding and 3D dense captioning and point out that these two tasks promote each other. Additionally, \\(\\chi\\)-Trans2Cap [43] discusses how to transfer knowledge from additional 2d information to boost 3d dense captioning." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.896, + 0.903 + ], + "angle": 0, + "content": "Among existing methods, they all adopt a two-stage \"detect-then-describe\" pipeline [4, 7, 13, 20, 39, 48] (Figure 1). This pipeline first generates a set of object proposals, then decodes each object by a caption generator with an explicit reasoning procedure. Though these methods have achieved remarkable performance, the \"detect-then-describe\" pipeline suffers from the following issues: 1) Because of the serial and explicit reasoning, the captioning performance highly depends on the object detection performance, which limits the mutual promotion of detection and captioning. 2) The heavy reliance on hand-crafted components, e.g., radii, 3D operators, the definition of pro" + }, + { + "type": "page_footnote", + "bbox": [ + 0.078, + 0.863, + 0.469, + 0.901 + ], + "angle": 0, + "content": "*Part of this work was accomplished under supervision by Dr. Hongyuan Zhu from A*STAR, Singapore. \n†Corresponding author." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "11124" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.182 + ], + "angle": 0, + "content": "posal neighbors, and post-processing (non-maximum suppression [28]) introduces additional hyper-parameters, leading to a sub-optimal performance given the sparse object surfaces and cluttered object distributions among different indoor scenes. This inspires us to design a one-stage 3D dense captioning system." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.183, + 0.471, + 0.379 + ], + "angle": 0, + "content": "To address the above issues, we propose Vote2CapDETR, a full transformer encoder-decoder architecture for one-stage 3D dense captioning. Unlike traditional \"detect-then-describe\" pipelines, we directly feed the decoder's output into the localization head and caption head in parallel. By casting 3D dense captioning as a set-to-set problem, each target instance and its language annotation is matched with a query in a one-to-one correspondence manner, enabling a more discriminative feature representation for proposals to identify each distinctive object in a 3D scene. Additionally, we also propose a novel vote query driven decoder to introduce spatial bias for better localization of objects in a cluttered 3D scene." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.381, + 0.471, + 0.728 + ], + "angle": 0, + "content": "With fully attentional design, we resolve 3D dense captioning with the following innovations: 1) Our method treats the 3D dense captioning task as a set prediction problem. The proposed Vote2Cap-DETR directly decodes the features into object sets with their locations and corresponding captions by applying two parallel prediction heads. 2) We propose a novel vote decoder by reformulating the object queries in 3DETR into the format of the vote query, which is a composition of the embeddings of the seeds point and the vote transformation with respect to the seeds. This indicates the connection between the vote query in Vote2Cap-DETR with the VoteNet, but with better localization and higher training efficiencies; 3) We develop a novel query driven caption head, which absorbs the relation and attribute modeling into self- and cross-attention, so that it can look into both local and global contexts for better scene description. Extensive experiments on two commonly used datasets, ScanRefer and Nr3D, demonstrate that our approach surpasses prior arts with many hand-crafted procedures by a large margin, which demonstrates the superiority that fully transformer architecture with sophisticated vote head and caption head can inspire many 3D vision and language tasks." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.729, + 0.47, + 0.759 + ], + "angle": 0, + "content": "To summarize, the main contributions of this work include:" + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.773, + 0.468, + 0.833 + ], + "angle": 0, + "content": "- We propose a novel one-stage and fully attention driven architecture for 3D dense captioning as a set-to-set prediction problem, which achieves object localization and caption generation in parallel." + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.841, + 0.468, + 0.9 + ], + "angle": 0, + "content": "- Extensive experiments show that our proposed Vote2Cap approach achieves a new state-of-the-art performance on both Nr3D [1] (45.53% C@0.5) and ScanRefer [13] (73.77% C@0.5)." + }, + { + "type": "list", + "bbox": [ + 0.096, + 0.773, + 0.468, + 0.9 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.501, + 0.09, + 0.642, + 0.107 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.12, + 0.892, + 0.18 + ], + "angle": 0, + "content": "We briefly summarize works on 3D and video dense captioning, and DETR-based methods for images and 3D point clouds. Additionally, we also introduce some methods for image captioning, which are closely related to our work." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.186, + 0.892, + 0.624 + ], + "angle": 0, + "content": "3D and Video Dense Captioning. 3D dense captioning, a task that requires translating 3D scene information to a set of bounding boxes and natural language descriptions, is challenging and has raised great interest among scholars recent years. Scan2Cap [13] and MORE [20] build graph on a detector's [19, 32] box estimations with handcrafted rules for complex relation reasoning among objects in a 3D scene. SpaCap3D [39] build a spatiality-guided transformer to model spatial relations among the detector's output. 3DJCG [4] and D3Net [7] study the joint promotion of 3D dense captioning and 3D visual grounding. \\(\\chi\\)-Trans2Cap [43] introduces additional 2D prior to complement information for 3D dense captioning with knowledge transfer. Recently, [48] shifts attention to contextual information for the perception of non-object information. Though these approaches have made great attempts at 3D dense captioning, they all follow a \"detect-then-describe\" pipeline, which heavily depends on a detector's performance. Our proposed Vote2Cap-DETR differs from existing works in that our method is a one-stage model that detects and generates captions in parallel and treats 3D dense captioning as a set prediction problem. Video dense captioning requires a model to segment and describe video clips from an input video. [40, 49] propose transformer architecture for end-to-end video dense captioning. In this paper, we design elements specially for 3D dense captioning, such as vote queries for better localization in sparse 3D space and the utilization of local contextual information through cross attention for informative object description." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.629, + 0.892, + 0.901 + ], + "angle": 0, + "content": "DETR: from 2D to 3D. DETection Transformer(DETR) [5] is a transformer [37] based architecture that treats object detection as a set prediction problem and does not require nonmaximum suppression [28] for post-processing. Though great results have been achieved, DETR suffers from slow convergence. Many follow-up works [9, 16, 18, 26, 44, 50] put efforts on speeding up DETR's training by introducing multi-scale features, cross attention designs, and label assignment techniques. Researchers also attempt to introduce transformer architectures to 3D object detection. GroupFree3D [24] learns proposal features from the whole point cloud through the transformer rather than grouping local points. 3DETR [27] analyzes the potential of the standard transformer model and generates proposals by uniformly sampling seed points from a 3D scene. In our work, we extend the DETR architecture for 3D dense captioning that makes caption generation and box localization fully interrelated with parallel decoding. Additionally, we propose" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "11125" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.468, + 0.106 + ], + "angle": 0, + "content": "vote query for better performance and faster convergence." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.108, + 0.47, + 0.365 + ], + "angle": 0, + "content": "Image Captioning. Image captioning requires a model to generate sentences describing key elements in an image, which has become a hot topic in computer vision. Existing image captioning works adopt an encoder-decoder architecture, where the decoder generates sentences from visual features extracted by the encoder. [2, 14, 17, 30] adopt a detector to extract region features as visual clues for the decoder, while [23, 46] extract grid features directly from an image. Additionally, [29] generates captions from both region and grid visual features. Though these methods are effective in image captioning, they cannot be directly applied to 3D dense captioning since it requires describing each 3D object in a scene with respect to its surroundings. In contrast, our proposed caption head sufficiently leverages the rich context information in a 3D point cloud, receives visual clues from both the object query and its local context, and fuses them to achieve effective 3D dense captioning." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.376, + 0.168, + 0.391 + ], + "angle": 0, + "content": "3. Method" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.401, + 0.47, + 0.568 + ], + "angle": 0, + "content": "As shown in Fig. 2, given a 3D scene, our goal is to localize objects of interest and generate informative natural language descriptions for each object. The input of our model is a point cloud \\(PC = [p_{in};f_{in}]\\in \\mathbb{R}^{N\\times (3 + F)}\\) representing an indoor 3D scene. Here, \\(p_{in}\\in \\mathbb{R}^{N\\times 3}\\) is the absolute locations for each point, and \\(f_{in}\\in \\mathbb{R}^{N\\times F}\\) is additional input feature for each point, such as color, normal, height, or multiview feature introduced by [6,13]. The expected output is a set of box-caption pairs \\((\\hat{B},\\hat{C}) = \\{(\\hat{b}_1,\\hat{c}_1),\\dots ,(\\hat{b}_K,\\hat{c}_K)\\}\\), representing an estimation of \\(K\\) distinctive objects in this 3D scene." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.569, + 0.47, + 0.659 + ], + "angle": 0, + "content": "Specifically, our system adopts 3DETR [27] encoder as our scene encoder and a transformer decoder to capture both object-object and object-scene interactions through the attention mechanism. Then, we feed the query feature to two parallel task-specific heads for object detection and caption generation." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.666, + 0.242, + 0.681 + ], + "angle": 0, + "content": "3.1. 3DETR Encoder" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.689, + 0.469, + 0.764 + ], + "angle": 0, + "content": "Inspired by DETR [5], 3DETR [27] has made a successful attempt at bringing full transformer architecture to the 3D object detection task, which removes many hand-coded design decisions as the popular VoteNet and PointNet++ modules in most two-stage methods." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.765, + 0.469, + 0.841 + ], + "angle": 0, + "content": "In 3DETR encoder, the input \\(PC\\) is first tokenized with a set-abstraction layer [33]. Then, point tokens are fed into a masked transformer encoder with a set-abstraction layer followed by another two encoder layers. We denote the encoded scene tokens as \\([p_{enc};f_{enc}]\\in \\mathbb{R}^{1,024\\times (3 + 256)}\\)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.848, + 0.202, + 0.864 + ], + "angle": 0, + "content": "3.2. Vote Query" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.871, + 0.469, + 0.901 + ], + "angle": 0, + "content": "Though 3DETR has achieved initial success in 3D object detection, it suffers from certain limitations. 3DETR" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.166 + ], + "angle": 0, + "content": "proposes box estimations around the query points (aka proposal centers) sampled from the scenes, which can make these predictions far away from real objects given the sparse object surfaces, resulting in slow convergence to capture discriminative object features with further miss detections." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.167, + 0.892, + 0.272 + ], + "angle": 0, + "content": "Prior works on fast convergence DETR models [12, 26, 45] show that injecting more structured bias to initialize object queries, such as anchor points or content-aware queries, accelerates training. Therefore, we propose the vote query, which introduces both 3D spatial bias and content-related information, for faster convergence and performance improvement." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.273, + 0.892, + 0.363 + ], + "angle": 0, + "content": "More specifically, we reformulate the object queries in 3DETR into the format of vote query as a composition of the embedding of the reference points and vote transformation around them. This helps build the connection between the object query in 3DETR and the vote set prediction widely studied in VoteNet [32]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.363, + 0.892, + 0.424 + ], + "angle": 0, + "content": "The detailed structure is shown in Figure 3. Here, vote \\(\\Delta p_{vote}\\) is predicted from encoded scene token feature \\(f_{enc}\\) with a Feed Forward Network (FFN) \\(FFN_{vote}\\) that learns to shift the encoded points to objects' centers spatially:" + }, + { + "type": "equation", + "bbox": [ + 0.514, + 0.436, + 0.892, + 0.453 + ], + "angle": 0, + "content": "\\[\np _ {v o t e} = p _ {e n c} + \\Delta p _ {v o t e} = p _ {e n c} + F F N _ {v o t e} \\left(f _ {e n c}\\right). \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.463, + 0.892, + 0.554 + ], + "angle": 0, + "content": "Then, we sample 256 points \\( p_{seed} \\) from \\( p_{enc} \\) with farthest point sampling and locate each point's offset estimation for \\( p_{vq} = p_{seed} + \\Delta p_{vote} \\). Finally, we gather features from \\( (p_{enc}, f_{enc}) \\) for \\( p_{vq} \\) with a set-abstraction layer [33], to formulate the vote query feature \\( f_{vq} \\in \\mathbb{R}^{256 \\times 256} \\). We represent vote query as \\( (p_{vq}, f_{vq}) \\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.555, + 0.892, + 0.602 + ], + "angle": 0, + "content": "Following 3DETR [27], our model adopts an eight-layer transformer decoder, and the \\(i\\)-th layer's input query feature \\(f_{query}^{i}\\) is calculated through" + }, + { + "type": "equation", + "bbox": [ + 0.515, + 0.612, + 0.892, + 0.631 + ], + "angle": 0, + "content": "\\[\nf _ {q u e r y} ^ {i} = \\operatorname {L a y e r} _ {i - 1} \\left(f _ {q u e r y} ^ {i - 1} + F F N \\left(P E \\left(p _ {v q}\\right)\\right)\\right), \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.64, + 0.892, + 0.732 + ], + "angle": 0, + "content": "where \\( f_{query}^{0} = f_{vq} \\), and \\( PE(\\cdot) \\) is the 3D Fourier positional encoding function [35]. Experiments in later sections demonstrate that: 1) Vote query injects additional spatial bias to object detection and boosts the detection performance. 2) Encoding features from the point cloud as initial queries accelerates convergence." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.741, + 0.673, + 0.757 + ], + "angle": 0, + "content": "3.3. Parallel Decoding" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.764, + 0.892, + 0.809 + ], + "angle": 0, + "content": "We adopt two task-specific heads for simultaneous object detection and caption generation. The two task heads are agnostic to each other's output." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.81, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Detection Head. Detecting objects in a 3D scene requires box corner estimation \\(\\hat{B}\\) and class estimation \\(\\hat{S}\\) (containing \"no object\" class) from each object query feature. Following 3DETR [27], box corner estimation is generated by learning spatial offset from a query point to an object's center and box size regression. All subtasks are implemented" + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "11126" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.081, + 0.078, + 0.379, + 0.348 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.384, + 0.079, + 0.646, + 0.348 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.647, + 0.078, + 0.895, + 0.346 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.35, + 0.895, + 0.421 + ], + "angle": 0, + "content": "Figure 2. Approach. Vote2Cap-DETR is a one-stage transformer model that takes a 3D point cloud as its input, and generates a set of box predictions and sentences localizing and describing each object in the point cloud. The scene encoder first generates encoded scene tokens \\((p_{enc}, f_{enc})\\) from the input point cloud. Then, we generate vote query \\((p_{vq}, f_{vq})\\) from the encoded scene tokens, which introduce both spatial bias \\(p_{vq}\\) and content-aware feature \\(f_{vq}\\) to initial object queries. The transformer decoder decodes each vote query with two parallel task heads for captioning and detection. We optimize Vote2Cap-DETR with a set loss." + }, + { + "type": "image", + "bbox": [ + 0.122, + 0.439, + 0.424, + 0.552 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.555, + 0.471, + 0.611 + ], + "angle": 0, + "content": "Figure 3. Vote Query Generation. Vote query \\( p_{vq} \\) contains spatial bias \\( (\\Delta p_{vote}) \\) to initial object queries \\( (p_{seed}) \\), which are sampled from the scene with farthest point sampling (FPS) and gathered feature \\( f_{vq} \\) from the point cloud for each query." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.624, + 0.47, + 0.669 + ], + "angle": 0, + "content": "by FFNs. In practice, the object localization head is shared through different layers in the decoder, following all existing works on DETR [5, 12, 26, 27]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.672, + 0.47, + 0.779 + ], + "angle": 0, + "content": "Caption Head. 3D dense captioning requires attribute details on an object and its relation with its close surroundings. However, the vote query itself is agnostic to box predictions and fails to provide adequate attribute and spatial relations for informative caption generation. Therefore, the main difficulty is how to leverage sufficient surrounding contextual information without confusing the caption head." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.78, + 0.471, + 0.902 + ], + "angle": 0, + "content": "To address the above issues, we propose Dual-Clued Captioner(DCC), a lightweight transformer decoder-based caption head, for 3D dense captioning. DCC consists of a stack of 2 identical transformer decoder blocks, sinusoid position embedding, and a linear classification head. To generate informative captions, DCC receives two streams of visual clue \\(\\mathcal{V} = (\\mathcal{V}^q,\\mathcal{V}^s)\\). Here, \\(\\mathcal{V}^q\\) is the last decoder layer's output feature of a vote query, and \\(\\mathcal{V}^s\\) is contextual" + }, + { + "type": "image", + "bbox": [ + 0.518, + 0.435, + 0.871, + 0.553 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.555, + 0.893, + 0.626 + ], + "angle": 0, + "content": "Figure 4. Dual-Clued Captioner(DCC). DCC is a lightweight transformer based caption head that uses vote query feature \\(\\mathcal{V}_q\\) as caption perfix to identify the region to be described, and contextual features \\(\\nu_{s}\\) surrounding the vote query to complement with more surrounding information for descriptive caption generation." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.635, + 0.893, + 0.786 + ], + "angle": 0, + "content": "information surrounding the absolute location of each vote query. When generating a caption for a proposal, we substitute the standard Start Of Sequenec( 'SOS') prefix with \\(\\nu^q\\) to identify the object to be described following [39]. Since the vote query is agnostic of actual neighbor object proposals because of the parallel detection branch, we introduce the vote query's \\(k_{s}\\) nearest local context token features as its local surroundings \\(\\nu^{s}\\) as keys for cross attention. During inference, we generate captions through beam search with a beam size of 5." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.799, + 0.871, + 0.816 + ], + "angle": 0, + "content": "3.4. Set prediction loss for 3D Dense Captioning" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.823, + 0.893, + 0.869 + ], + "angle": 0, + "content": "Our proposed Vote2Cap-DETR requires supervision for vote query \\((\\mathcal{L}_{vq})\\), detection head \\((\\mathcal{L}_{det})\\), and caption head \\((\\mathcal{L}_{cap})\\)." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.871, + 0.893, + 0.903 + ], + "angle": 0, + "content": "Vote Query Loss. We borrow vote loss from VoteNet [32] as \\(\\mathcal{L}_{vq}\\), to help the vote query generation module learn to" + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "11127" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.078, + 0.092, + 0.33, + 0.107 + ], + "angle": 0, + "content": "shift points \\( p_{enc} \\) to an object's center:" + }, + { + "type": "equation", + "bbox": [ + 0.09, + 0.12, + 0.47, + 0.164 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {v q} = \\frac {1}{M} \\sum_ {i = 1} ^ {M} \\sum_ {j = 1} ^ {N _ {g t}} \\left\\| p _ {v o t e} ^ {i} - c n t _ {j} \\right\\| _ {1} \\cdot \\mathbb {I} \\left\\{p _ {e n c} ^ {i} \\in I _ {j} \\right\\}. \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.176, + 0.469, + 0.237 + ], + "angle": 0, + "content": "Here, \\(\\mathbb{I}(\\cdot)\\) is an indicator function that equals 1 when the condition meets and 0 otherwise, \\(N_{gt}\\) is the number of instances in a 3D scene, \\(M\\) is the size of \\(p_{vote}\\), and \\(cnt_j\\) is the center of \\(j\\)th instance \\(I_j\\)." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.239, + 0.469, + 0.314 + ], + "angle": 0, + "content": "Detection Loss. Following 3DETR [27], we use the same Hungarian algorithm to assign each proposal with a ground truth label. Since 3D dense captioning cares much for the object localization ability, we apply a larger weight on the gIoU loss in set loss [27]:" + }, + { + "type": "equation", + "bbox": [ + 0.078, + 0.328, + 0.469, + 0.357 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {s e t} = \\alpha_ {1} \\mathcal {L} _ {g i o u} + \\alpha_ {2} \\mathcal {L} _ {c l s} + \\alpha_ {3} \\mathcal {L} _ {\\text {c e n t e r - r e g}} + \\alpha_ {4} \\mathcal {L} _ {\\text {s i z e - r e g}}, \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.358, + 0.469, + 0.403 + ], + "angle": 0, + "content": "where \\(\\alpha_{1} = 10\\), \\(\\alpha_{2} = 1\\), \\(\\alpha_{3} = 5\\), \\(\\alpha_{4} = 1\\) are set heuristically. The set loss \\(\\mathcal{L}_{set}\\) is applied to all \\(n_{dec - layer}\\) layers in the decoder for better convergence." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.405, + 0.469, + 0.513 + ], + "angle": 0, + "content": "Caption Loss. Following the standard practice of image captioning, we train our caption head first with standard cross-entropy loss (MLE training), and then fine-tune it with Self-Critical Sequence Training (SCST) [34]. During MLE training, the model is trained to predict the \\((t + 1)\\)th word \\(c_i^{t + 1}\\), given the first \\(t\\) words \\(c_i^{[1:t]}\\) and the visual clue \\(\\mathcal{V}\\). The loss function for a \\(T\\)-length sentence is defined as:" + }, + { + "type": "equation", + "bbox": [ + 0.099, + 0.526, + 0.469, + 0.567 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {c _ {i}} = \\sum_ {i = 1} ^ {T} \\mathcal {L} _ {c _ {i}} (t) = - \\sum_ {i = 1} ^ {T} \\log \\hat {P} \\left(c _ {i} ^ {t + 1} | \\mathcal {V}, c _ {i} ^ {[ 1: t ]}\\right). \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.579, + 0.469, + 0.653 + ], + "angle": 0, + "content": "After the caption head is trained under word-level supervision, we fine-tune it with SCST. During SCST, the model generates multiple captions \\(\\hat{c}_{1,\\dots,k}\\) with a beam size of \\(k\\) and another \\(\\hat{g}\\) through greedy search as a baseline. The loss function for SCST is defined as:" + }, + { + "type": "equation", + "bbox": [ + 0.1, + 0.665, + 0.469, + 0.706 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {c _ {i}} = - \\sum_ {i = 1} ^ {k} \\left(R \\left(\\hat {c} _ {i}\\right) - R (\\hat {g})\\right) \\cdot \\frac {1}{| \\hat {c} _ {i} |} \\log \\hat {P} (\\hat {c} _ {i} | \\mathcal {V}). \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.718, + 0.469, + 0.779 + ], + "angle": 0, + "content": "Here, the reward function \\( R(\\cdot) \\) is the CIDEr metric for caption evaluation, and the log probability of caption \\( \\hat{c}_i \\) is normalized by caption length \\( |\\hat{c}_i| \\) to encourage the model to treat captions in different length with equal importance." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.78, + 0.469, + 0.902 + ], + "angle": 0, + "content": "Set to Set Training for 3D Dense Captioning. We propose an easy-to-implement set-to-set training strategy for 3D dense captioning. Given a 3D scene, we randomly sample one sentence from the corpus for each annotated instance. Then, we assign language annotations to the corresponding number of proposals in the corresponding scene with the same Hungarian algorithm. During training, we average losses for captions \\(\\mathcal{L}_{c_i}\\) on all annotated instances in" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.092, + 0.892, + 0.121 + ], + "angle": 0, + "content": "a batch to compute the caption loss \\(\\mathcal{L}_{cap}\\). To balance loss for different tasks, our loss function is defined as:" + }, + { + "type": "equation", + "bbox": [ + 0.553, + 0.129, + 0.892, + 0.17 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} = \\beta_ {1} \\mathcal {L} _ {v q} + \\beta_ {2} \\sum_ {i = 1} ^ {n _ {\\text {d e c - l a y e r}}} \\mathcal {L} _ {\\text {s e t}} + \\beta_ {3} \\mathcal {L} _ {\\text {c a p}}, \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.176, + 0.846, + 0.192 + ], + "angle": 0, + "content": "where \\(\\beta_{1} = 10, \\beta_{2} = 1, \\beta_{3} = 5\\) are set heuristically." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.204, + 0.632, + 0.22 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.229, + 0.892, + 0.334 + ], + "angle": 0, + "content": "We first present the datasets, metrics, and implementation details for 3D dense captioning (section 4.1). Then, we provide comparisons with all state-of-the-art methods (section 4.2). We also provide studies on the effectiveness of different parts in our model (section 4.3). Finally, we visualize several qualitative results to address the effectiveness of our method (section 4.4)." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.343, + 0.892, + 0.358 + ], + "angle": 0, + "content": "4.1. Datasets, Metrics, and Implementation Details" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.367, + 0.892, + 0.472 + ], + "angle": 0, + "content": "Datasets. We analyze performance on ScanRefer [6] and \\(\\mathrm{Nr3D}\\) [1], both of which are built on 3D scenes from ScanNet [15]. ScanRefer/Nr3D contains 36,665/32,919 freeform language annotations describing 7,875/4,664 objects from 562/511 out of 1201 3D scenes in ScanNet for training and evaluates on 9,508/8,584 sentences for 2,068/1,214 objects from 141/130 out of 312 3D scenes in ScanNet." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.474, + 0.892, + 0.642 + ], + "angle": 0, + "content": "Evaluation Metrics. Following [4, 13, 20, 39], we first apply NMS on object proposals to drop duplicate object predictions. Each object proposal is a box-caption pair \\((\\hat{b}_i, \\hat{c}_i)\\), containing box corner prediction \\(\\hat{b}_i\\) and generated caption \\(\\hat{c}_i\\). Then, each annotated instance is assigned an object proposal with the largest IoU among the remaining proposals. Here, we use \\((b_i, C_i)\\) to represent an instance's label, where \\(b_i\\) is an instance's box corner label, and \\(C_i\\) is the corpus containing all caption annotations for this instance. To jointly evaluate the model's localization and caption generation capability, we adopt the \\(m@kIoU\\) metric [13]:" + }, + { + "type": "equation", + "bbox": [ + 0.51, + 0.649, + 0.891, + 0.704 + ], + "angle": 0, + "content": "\\[\nm @ k I o U = \\frac {1}{N} \\sum_ {i = 1} ^ {N} m \\left(\\hat {c} _ {i}, C _ {i}\\right) \\cdot \\mathbb {I} \\left\\{I o U \\left(\\hat {b} _ {i}, b _ {i}\\right) \\geq k \\right\\}. \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.704, + 0.892, + 0.764 + ], + "angle": 0, + "content": "Here, \\(N\\) is the number of total annotated instances in the evaluation dataset, and \\(m\\) could be any metric for natural language generation, such as CIDEr [38], METEOR [3], BLEU-4 [31], and ROUGE-L [22]." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.765, + 0.892, + 0.871 + ], + "angle": 0, + "content": "Implementation Details. We offer implementation details of different baselines. \"w/o additional 2D\" means the input \\(\\mathcal{PC} \\in \\mathbb{R}^{40,000 \\times 10}\\) contains absolute location as well as color, normal and height for 40,000 points representing a 3D scene. \"additional 2D\" means we replace color information with 128-dimensional multiview feature extracted by ENet [8] from 2D images following [13]." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.871, + 0.892, + 0.901 + ], + "angle": 0, + "content": "We first pre-train the whole network without the caption head on ScanNet [15] for 1,080 epochs (163k iterations," + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "11128" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.351 + ], + "angle": 0, + "content": "\\(\\sim 34\\) hours) using an AdamW optimizer [25] with a learning rate decaying from \\(5 \\times 10^{-4}\\) to \\(10^{-6}\\) by a cosine annealing scheduler, a weight decay of 0.1, a gradient clipping of 0.1, and a batch size of 8 following [27]. Then, we jointly train the full model from pre-trained weights with the MLE caption loss for another 720 epochs (51k/46k iterations for ScanRefer/Nr3D, \\(\\sim 11 / 10\\) hours). To prevent overfitting, we fix the learning rate of the detector as \\(10^{-6}\\), and set that of the caption head decaying from \\(10^{-4}\\) to \\(10^{-6}\\) using another cosine annealing scheduler. During SCST, we tune the caption head with a batch size of 2 and freeze the detector for 180 epochs because of high memory cost (50k/46k iterations for ScanRefer/Nr3D, \\(\\sim 14 / 11\\) hours) with a fixed learning rate of \\(10^{-6}\\). We evaluate the model every 2,000 iterations during training for consistency with existing works [13, 39], and all experiments mentioned above are conducted on a single RTX3090 GPU." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.361, + 0.388, + 0.379 + ], + "angle": 0, + "content": "4.2. Comparison with Existing Methods" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.386, + 0.473, + 0.747 + ], + "angle": 0, + "content": "In this section, we compare performance with existing works on metrics C, M, B-4, R as abbreviations for CIDEr [38], METEOR [3], BLEU-4 [31], Rouge-L [22] under IoU thresholds of 0.25, 0.5 for ScanRefer (Table 1) and 0.5 for Nr3D (Table 2). In both tables, “-” indicates that neither the original paper nor any follow-up works provide such results. We make separate comparisons for MLE training and SCST since different supervisions on the caption head have huge influence on the captioning performance. Among all the listed methods, experiments other than D3Net [7] and 3DJCG [4] utilize the standard VoteNet [32] detector. Meanwhile, D3Net adopts PointGroup [19], a 3D instance segmentation model, for better object detection. 3DJCG substitute the proposal head with an FCOS [36] head to improve VoteNet's localization performance. Additionally, 3DJCG and D3Net are trained on 3D dense captioning as well as 3D visual grounding to study the joint promotion of both tasks. Among methods listed under SCST, \\(\\chi\\)-Trans2Cap [43] combines MLE training with standard SCST in an additive manner, while Scan2Cap and D3Net [7] adopt the same reward that combines CIDEr score with a listener's [47] grounding loss by weighted summation. Meanwhile, our method adopts the standard SCST with CIDEr reward." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.749, + 0.472, + 0.87 + ], + "angle": 0, + "content": "Table 1 reports comparisons on ScanRefer [6] validation dataset. Our Vote2Cap-DETR surpasses current state-of-the-art methods. Under MLE training with additional 2D inputs, Vote2Cap-DETR achieves \\(59.32\\%\\) C@0.5 while 3DJCG [4] achieves \\(49.48\\%\\) (9.84% C@0.5↑) with additional training data. Under SCST, our Vote2Cap-DETR achieves \\(70.63\\%\\) C@0.5 comparing to \\(62.64\\%\\) (7.99% C@0.5↑) for current state-of-the-art D3Net [7]." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.472, + 0.903 + ], + "angle": 0, + "content": "In Table 2, we list results on the Nr3D [1] dataset with additional 2D input following [39]. Since Scan2Cap [13]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.895, + 0.152 + ], + "angle": 0, + "content": "has not reported results on \\(\\mathrm{Nr3D}\\), we adopt the best-reported result from [4]. Our Vote2Cap-DETR also surpasses current state-of-the-art methods (5.78%/7.11% C@0.5↑ for MLE training/SCST)." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.165, + 0.655, + 0.183 + ], + "angle": 0, + "content": "4.3. Ablation Study" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.19, + 0.895, + 0.235 + ], + "angle": 0, + "content": "Since 3D dense captioning concerns both localization and caption generation, we perform ablation studies to understand the effectiveness of different components." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.238, + 0.897, + 0.466 + ], + "angle": 0, + "content": "Does the vote query improve 3DETR? We performed ablation experiments in Table 3 and Figure 5 to see if the vote query can improve 3DETR's localization and convergence. We notice that introducing position features \\( p_{vq} \\) alone helps improve detection performance (0.97% mAP50↑). However, it (green line in Figure 5) converges slower in the earlier training procedure than the 3DETR baseline (blue line in Figure 5), inferring the vote query generation module is not well learned to predict accurate spatial offset estimations at early training epochs. Introducing additional content feature \\( f_{vq} \\) in vote query features results in another boost in both detection performance (2.98% mAP50↑) and training speed (red line in Figure 5). The overall localization performance of Vote2Cap-DETR is about 7.2% mAP higher than the popular VoteNet." + }, + { + "type": "image", + "bbox": [ + 0.508, + 0.474, + 0.887, + 0.636 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.641, + 0.895, + 0.727 + ], + "angle": 0, + "content": "Figure 5. Vote query and convergence. We take out convergence study on a different combination of content feature \\( f_{vq} \\) and position \\( p_{vq} \\) in vote query. The baseline model \\( (p_{query}, f_{query}^{0}) = (p_{seed}, 0) \\) downgrades to 3DETR. Introducing \\( p_{vq} \\) boosts performance but decelerates training since \\( FFN_{vote} \\) requires time to converge, and \\( f_{vq} \\) accelerates training." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.735, + 0.897, + 0.903 + ], + "angle": 0, + "content": "Does 3D context feature help captioning? Since the performance of 3D dense captioning is affected by both localization and caption capability, we freeze all parameters other than the caption head and train with 3D only input and standard cross entropy loss (MLE training) for a fair evaluation. We use object-centric decoder [39] as our baseline, which is a decoder that generates captions with object feature as a caption's prefix. In Table 4, “-” refers to the object-centric decoder baseline, “global” means naively including all context tokens extracted from the scene encoder in the decoder, “local” is our proposed caption head that" + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "11129" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.082, + 0.072, + 0.891, + 0.214 + ], + "angle": 0, + "content": "
MethodLdesw/o additional 2D inputw/ additional 2D input
IoU = 0.25IoU = 0.50IoU = 0.25IoU = 0.50
C↑B-4↑M↑R↑C↑B-4↑M↑R↑C↑B-4↑M↑R↑C↑B-4↑M↑R↑
Scan2Cap [13]53.7334.2526.1454.9535.2022.3621.4443.5756.8234.1826.2955.2739.0823.3221.9744.78
MORE [20]58.8935.4126.3655.4138.9823.0121.6544.3362.9136.2526.7556.3340.9422.9321.6644.42
SpaCap3d [39]58.0635.3026.1655.0342.7625.3822.8445.6663.3036.4626.7155.7144.0225.2622.3345.36
3DJCG [4]MLE60.8639.6727.4559.0247.6831.5324.2851.8064.7040.1727.6659.2349.4831.0324.2250.80
D3Net [7]------------46.0730.2924.3551.67
Ours71.4539.3428.2559.3361.8134.4626.2254.4072.7939.1728.0659.2359.3232.4225.2852.53
x-Trans2Cap [43]58.8134.1725.8154.1041.5223.8321.9044.9761.8335.6526.6154.7043.8725.0522.4645.28
Scan2Cap [13]------------48.3826.0922.1544.74
D3Net [7]SCST------------62.6435.6825.7253.90
Ours84.1542.5128.4759.2673.7738.2126.6454.7186.2842.6428.2759.0770.6335.6925.5152.28
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.22, + 0.893, + 0.277 + ], + "angle": 0, + "content": "Table 1. Evaluating Vote2Cap-DETR on ScanRefer [6]. We compare Vote2Cap-DETR with all published state-of-the-art 3D dense caption methods on the ScanRefer dataset. Though our method does not depend on hand-crafted NMS [28] to drop overlapped boxes, we follow the standard evaluation protocol from [13] for fair comparison and provide evaluation without NMS in Table 7. Our proposed Vote2Cap-DETR achieves new state-of-the-art under both MLE training and SCST." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.3, + 0.466, + 0.412 + ], + "angle": 0, + "content": "
MethodLdesC@0.5↑B-4@0.5↑M@0.5↑R@0.5↑
Scan2Cap [13]27.4717.2421.8049.06
SpaCap3d [39]33.7119.9222.6150.50
D3Net [7]MLE33.8520.7023.1353.38
3DJCG [4]38.0622.8223.7752.99
Ours43.8426.6825.4154.43
x-Tran2Cap [43]33.6219.2922.2750.00
D3Net [7]SCST38.4222.2224.7454.37
Ours45.5326.8825.4354.76
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.419, + 0.47, + 0.461 + ], + "angle": 0, + "content": "Table 2. Evaluating Vote2Cap-DETR on Nr3D [1]. Likewise, we perform the standard evaluation on the Nr3D dataset, and our proposed Vote2Cap-DETR surpasses prior arts." + }, + { + "type": "table", + "bbox": [ + 0.081, + 0.472, + 0.466, + 0.541 + ], + "angle": 0, + "content": "
\\( {p}_{query} \\)\\( {f}_{query}^{0} \\)IoU=0.25IoU=0.501st layer IoU=0.50
mAP↑AR↑mAP↑AR↑mAP↑AR↑
VoteNet Baseline63.4282.1844.9660.65--
\\( {p}_{seed} \\)067.2584.9148.1864.9834.8055.06
\\( {p}_{vq} \\)067.3385.6049.1566.3830.2358.44
\\( {p}_{vq} \\)\\( {f}_{vq} \\)69.6187.2052.1369.1246.5366.51
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.548, + 0.469, + 0.603 + ], + "angle": 0, + "content": "Table 3. Vote query and performance. We provide quantitative results for Figure 5. Introducing \\( p_{vq} \\) as query positions improves detection, and gathering \\( f_{vq} \\) from content further boosts performance." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.61, + 0.469, + 0.639 + ], + "angle": 0, + "content": "includes a vote query's \\( k_{s} \\) (\\( k_{s} = 128 \\) empirically) nearest context tokens extracted from the scene encoder." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.641, + 0.469, + 0.747 + ], + "angle": 0, + "content": "Results show that the caption generation performance benefits from the introduction of additional contextual information. Additionally, compared with naively introducing contextual information from the whole scene, the introduction of local context could be more beneficial. This demonstrates our motivation that close surroundings matter when describing an object." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.761, + 0.466, + 0.821 + ], + "angle": 0, + "content": "
keyIoU=0.25IoU=0.5
C↑B-4↑M↑R↑C↑B-4↑M↑R↑
-68.6238.6127.6758.4760.1534.0225.8053.82
global70.0539.2327.8458.4461.2034.6625.9353.79
local70.4239.9827.9958.8961.3935.2426.0254.12
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.827, + 0.469, + 0.897 + ], + "angle": 0, + "content": "Table 4. Different keys for caption generation. We provide a comparison on different keys used in caption generation. Introducing contextual information relates to more informative captions generated. Since 3D dense captioning is more object-centric, introducing vote queries' local contextual feature is a better choice." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.303, + 0.892, + 0.469 + ], + "angle": 0, + "content": "Do set-to-set training benefit dense captioning? To analyze the effectiveness of set-to-set training, we use a smaller learning rate \\((10^{-6})\\) for all parameters other than the caption head and freeze these parameters during SCST. We name the traditional training strategy as \"Sentence Training\" adopted in previous works [13, 39], which traverses through all sentence annotations in the dataset. As is shown in Figure 7, our proposed \"Set-to-Set\" training achieves comparable results with the traditional strategy during MLE training and converges faster because of a bigger batch size on the caption head, which also benefits SCST." + }, + { + "type": "table", + "bbox": [ + 0.505, + 0.482, + 0.888, + 0.555 + ], + "angle": 0, + "content": "
TrainingLdesC@0.5↑B-4@0.5↑M@0.5↑R@0.5↑
SentenceMLE61.2135.3526.1254.52
Set-to-Set61.8134.4626.2254.40
SentenceSCST71.3937.5726.0154.28
Set-to-Set73.7738.2126.6454.71
" + }, + { + "type": "table_caption", + "bbox": [ + 0.498, + 0.561, + 0.892, + 0.631 + ], + "angle": 0, + "content": "Table 5. Set to Set training and performance. We compare our proposed set-to-set training with traditional \"Sentence Training\", which traverses through all sentence annotations. We achieve comparable performance with MLE training, and \\(2.38\\%\\) C@0.5 improvement with SCST." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.642, + 0.892, + 0.78 + ], + "angle": 0, + "content": "End to end training from scratch. Our Vote2Cap-DETR also supports end-to-end training from scratch for 3D dense captioning. However, both ScanRefer and Nr3D are annotated on limited scenes (562/511 scenes) for training; thus, directly training Vote2Cap-DETR from scratch will underperform given to satisfy two objectives simultaneously. Experiments on Scanrefer in Table 6 show that the greedy strategy we choose by pre-training detection head as a good pre-requisite for captioning achieves better performance." + }, + { + "type": "table", + "bbox": [ + 0.501, + 0.792, + 0.892, + 0.831 + ], + "angle": 0, + "content": "
pretrain/end2endC@0.5↑B-4@0.5↑M@0.5↑R@0.5↑AP@0.5↑AR@0.5↑
end2end52.1528.8724.6849.7646.6862.17
pretrain+end2end62.0334.9026.0654.3351.2667.57
" + }, + { + "type": "table_caption", + "bbox": [ + 0.498, + 0.841, + 0.892, + 0.897 + ], + "angle": 0, + "content": "Table 6. Ablation study for training strategies. The greedy strategy we choose by pre-training detection head as a good prerequisite for captioning achieves better performance than directly end to end training from scratch." + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "11130" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.097, + 0.101, + 0.275, + 0.186 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.143, + 0.189, + 0.228, + 0.203 + ], + "angle": 0, + "content": "scene0011_00" + }, + { + "type": "image", + "bbox": [ + 0.296, + 0.102, + 0.475, + 0.186 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.342, + 0.189, + 0.428, + 0.202 + ], + "angle": 0, + "content": "scene0015_00" + }, + { + "type": "image", + "bbox": [ + 0.497, + 0.102, + 0.674, + 0.186 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.542, + 0.189, + 0.628, + 0.201 + ], + "angle": 0, + "content": "scene0025_00" + }, + { + "type": "image", + "bbox": [ + 0.697, + 0.102, + 0.874, + 0.186 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.743, + 0.189, + 0.828, + 0.201 + ], + "angle": 0, + "content": "scene0050_00" + }, + { + "type": "image_caption", + "bbox": [ + 0.099, + 0.215, + 0.246, + 0.237 + ], + "angle": 0, + "content": "3DJCG: This is a rectangular whiteboard. It is on the wall." + }, + { + "type": "image_caption", + "bbox": [ + 0.299, + 0.215, + 0.461, + 0.236 + ], + "angle": 0, + "content": "3DJCG: This is a brown table. It is in the middle of the room." + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.21, + 0.648, + 0.241 + ], + "angle": 0, + "content": "3DJCG: The is a small brown cabinet. It is to the right of the desk." + }, + { + "type": "image_caption", + "bbox": [ + 0.7, + 0.215, + 0.861, + 0.237 + ], + "angle": 0, + "content": "3DJCG: This is a brown table. It is in front of the couch." + }, + { + "type": "image_caption", + "bbox": [ + 0.099, + 0.25, + 0.269, + 0.282 + ], + "angle": 0, + "content": "SpaCap3D: The whiteboard is affixed to the wall. It is to the right of the window." + }, + { + "type": "image_caption", + "bbox": [ + 0.299, + 0.25, + 0.448, + 0.281 + ], + "angle": 0, + "content": "SpaCap3D: This is a wooden table. It is in the center of the room." + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.25, + 0.666, + 0.281 + ], + "angle": 0, + "content": "SpaCap3D: The cabinet is below the desk. It is to the left of the chair." + }, + { + "type": "image_caption", + "bbox": [ + 0.7, + 0.25, + 0.852, + 0.281 + ], + "angle": 0, + "content": "SpaCap3D: This is a wooden coffee table. It is in front of the couch." + }, + { + "type": "image_caption", + "bbox": [ + 0.099, + 0.295, + 0.269, + 0.317 + ], + "angle": 0, + "content": "Ours: The tv is on the wall. It is to the right of the table." + }, + { + "type": "image_caption", + "bbox": [ + 0.299, + 0.295, + 0.469, + 0.316 + ], + "angle": 0, + "content": "Ours: This is a wooden table. It is in the corner of the room." + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.295, + 0.667, + 0.316 + ], + "angle": 0, + "content": "Ours: This is a white cabinet. It is to the right of the table." + }, + { + "type": "image_caption", + "bbox": [ + 0.7, + 0.295, + 0.866, + 0.316 + ], + "angle": 0, + "content": "Ours: This is a brown ottoman. It is to the right of the chair." + }, + { + "type": "image_caption", + "bbox": [ + 0.099, + 0.34, + 0.248, + 0.361 + ], + "angle": 0, + "content": "GT: This is a big black tv. It is above a thin table." + }, + { + "type": "image_caption", + "bbox": [ + 0.299, + 0.33, + 0.461, + 0.372 + ], + "angle": 0, + "content": "GT: This is a small table with a wood look. It is the table closest to the front of the room in the upper left corner." + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.335, + 0.658, + 0.367 + ], + "angle": 0, + "content": "GT: A white cabinet is sitting on the floor next to the wall. It is to the left of the couch." + }, + { + "type": "image_caption", + "bbox": [ + 0.7, + 0.34, + 0.867, + 0.361 + ], + "angle": 0, + "content": "GT: This is a brown ottoman. It is in front of a couch." + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.382, + 0.894, + 0.424 + ], + "angle": 0, + "content": "Figure 6. Qualitative Comparisons. We compare qualitative results with two state-of-the-art \"detect-then-describe\" methods, 3DJCG [4] and SpaCap3D [39]. We underline phrases describing spatial locations, and mark correct attribute words in green and wrong description in red. Our Vote2Cap-DETR produces tight bounding boxes close to the ground truth and accurate descriptions." + }, + { + "type": "image", + "bbox": [ + 0.085, + 0.436, + 0.462, + 0.613 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.615, + 0.47, + 0.671 + ], + "angle": 0, + "content": "Figure 7. Set-to-Set training and convergence. Convergence speed analysis of two different training strategies with MLE training as well as SCST. Set-to-Set training enables a larger batch size for the caption head and accelerates convergence." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.673, + 0.47, + 0.807 + ], + "angle": 0, + "content": "Is Vote2Cap-DETR robust to NMS? Similar to other DETR works, the set loss encourages the model to produce compact predictions. We compare performance on both 3D dense caption (C@0.5) and detection (mAP50, AR50) in Table 7. Since the \\( m@kIoU \\) metric (Eq. 8) does not contain any penalties on redundant predictions, getting rid of NMS [28] results in performance growth in C@0.5. Results show that Vote2Cap-DETR is more stable compared to VoteNet based methods with the absence of NMS." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.808, + 0.467, + 0.864 + ], + "angle": 0, + "content": "
Modelsw/NMSw/o NMS
C@0.5↑mAP50↑AR50↑C@0.5↑mAP50↑AR50↑
SpaCap3D43.9337.7753.9651.3523.3064.14
3DJCG50.2247.5862.1254.9430.0368.69
Vote2Cap-DETR70.6352.7966.0971.5752.8267.80
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.871, + 0.469, + 0.913 + ], + "angle": 0, + "content": "Table 7. Effect of NMS. We analyze whether the absence of NMS affects the 3D dense captioning performance (C@0.5) as well as detection performance (mAP50, AR50)." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.432, + 0.683, + 0.447 + ], + "angle": 0, + "content": "4.4. Qualitative Results" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.449, + 0.892, + 0.525 + ], + "angle": 0, + "content": "We compare qualitative results with two state-of-the-art models, SpaCap3D [39] and 3DJCG [4] in Figure 6. One can see that our method produces tight bounding boxes close to the ground truth as well as accurate descriptions of object attributes, classes, and spatial relationships." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.532, + 0.619, + 0.546 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.552, + 0.892, + 0.749 + ], + "angle": 0, + "content": "In this work, we present Vote2Cap-DETR, a transformer based one-stage approach, for 3D dense captioning. The proposed Vote2Cap-DETR adopts a full transformer encoder-decoder architecture that decodes a set of vote queries to box predictions and captions in parallel. We show that by introducing spatial bias and content-aware features, vote query boosts both convergence and detection performance. Additionally, we develop a novel lightweight query-driven caption head for informative caption generation. Experiments on two widely used datasets for 3D dense captioning validate that our proposed one-stage Vote2Cap-DETR model surpasses prior works with heavy dependence on hand-crafted components by a large margin." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.755, + 0.688, + 0.772 + ], + "angle": 0, + "content": "6. Acknowledgements" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.892, + 0.901 + ], + "angle": 0, + "content": "This work is supported by National Natural Science Foundation of China (No. U1909207, 62071127, and 62276176), Shanghai Natural Science Foundation (No. 23ZR1402900), Zhejiang Lab Project (No. 2021KH0AB05), and in part by A*STAR AME Programmatic Funding A18A2b0046, RobotHTPO Seed Fund under Project C211518008, and EDB Space Technology Development Grant under Project S22-19016-STDP." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "11131" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.105 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.116, + 0.47, + 0.186 + ], + "angle": 0, + "content": "[1] Panos Achlioptas, Ahmed Abdelreehm, Fei Xia, Mohamed Elhoseiny, and Leonidas Guibas. 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Existing methods follow a sophisticated "detect-then-describe" pipeline equipped with numerous hand-crafted components. However, these hand-crafted components would yield suboptimal performance given cluttered object spatial and class distributions among different scenes. In this paper, we propose a simple-yet-effective transformer framework Vote2Cap-DETR based on recent popular DEetection Transformer (DETR). Compared with prior arts, our framework has several appealing advantages: 1) Without resorting to numerous hand-crafted components, our method is based on a full transformer encoder-decoder architecture with a learnable vote query driven object decoder, and a caption decoder that produces the dense captions in a set-prediction manner. 2) In contrast to the two-stage scheme, our method can perform detection and captioning in one-stage. 3) Without bells and whistles, extensive experiments on two commonly used datasets, ScanRefer and Nr3D, demonstrate that our Vote2Cap-DETR surpasses current state-of-the-arts by $11.13\%$ and $7.11\%$ in CIDEr@0.5IoU, respectively. Codes will be released soon. + +# 1. Introduction + +In recent years, works on 3D learning has grown dramatically for various applications [10, 11, 21, 41, 42]. Among them, 3D dense captioning [7, 13] requires a system to localize all the objects in a 3D scene and generate descriptive sentences for each object. This problem is challenging, given 1) the sparsity of point clouds and 2) the cluttered distribution of objects. + +3D dense captioning can be divided into two tasks, object detection, and object caption generation. Scan2Cap [13], MORE [20], and SpaCap3D [39] propose well-designed re + +![](images/07449a239b3ac7eb9654da11b4f22bdc9e076b4a2fe3aa3d3a9580a9bc634ca7.jpg) +Figure 1. Illustration of existing two-stage 3D dense captioning method (upper) and our Vote2Cap-DETR (bottom). Existing methods adopt a two-stage pipeline that heavily depends on a detector's output. Therefore, we propose a transformer-based one-stage model, Vote2Cap-DETR, that frames 3D dense captioning as a set prediction problem. + +lation reasoning modules to model relations among object proposals efficiently. [48] introduces contextual information from two branches to improve the caption. 3DJCG [4] and D3Net [7] study the correlation between 3D visual grounding and 3D dense captioning and point out that these two tasks promote each other. Additionally, $\chi$ -Trans2Cap [43] discusses how to transfer knowledge from additional 2d information to boost 3d dense captioning. + +Among existing methods, they all adopt a two-stage "detect-then-describe" pipeline [4, 7, 13, 20, 39, 48] (Figure 1). This pipeline first generates a set of object proposals, then decodes each object by a caption generator with an explicit reasoning procedure. Though these methods have achieved remarkable performance, the "detect-then-describe" pipeline suffers from the following issues: 1) Because of the serial and explicit reasoning, the captioning performance highly depends on the object detection performance, which limits the mutual promotion of detection and captioning. 2) The heavy reliance on hand-crafted components, e.g., radii, 3D operators, the definition of pro + +posal neighbors, and post-processing (non-maximum suppression [28]) introduces additional hyper-parameters, leading to a sub-optimal performance given the sparse object surfaces and cluttered object distributions among different indoor scenes. This inspires us to design a one-stage 3D dense captioning system. + +To address the above issues, we propose Vote2CapDETR, a full transformer encoder-decoder architecture for one-stage 3D dense captioning. Unlike traditional "detect-then-describe" pipelines, we directly feed the decoder's output into the localization head and caption head in parallel. By casting 3D dense captioning as a set-to-set problem, each target instance and its language annotation is matched with a query in a one-to-one correspondence manner, enabling a more discriminative feature representation for proposals to identify each distinctive object in a 3D scene. Additionally, we also propose a novel vote query driven decoder to introduce spatial bias for better localization of objects in a cluttered 3D scene. + +With fully attentional design, we resolve 3D dense captioning with the following innovations: 1) Our method treats the 3D dense captioning task as a set prediction problem. The proposed Vote2Cap-DETR directly decodes the features into object sets with their locations and corresponding captions by applying two parallel prediction heads. 2) We propose a novel vote decoder by reformulating the object queries in 3DETR into the format of the vote query, which is a composition of the embeddings of the seeds point and the vote transformation with respect to the seeds. This indicates the connection between the vote query in Vote2Cap-DETR with the VoteNet, but with better localization and higher training efficiencies; 3) We develop a novel query driven caption head, which absorbs the relation and attribute modeling into self- and cross-attention, so that it can look into both local and global contexts for better scene description. Extensive experiments on two commonly used datasets, ScanRefer and Nr3D, demonstrate that our approach surpasses prior arts with many hand-crafted procedures by a large margin, which demonstrates the superiority that fully transformer architecture with sophisticated vote head and caption head can inspire many 3D vision and language tasks. + +To summarize, the main contributions of this work include: + +- We propose a novel one-stage and fully attention driven architecture for 3D dense captioning as a set-to-set prediction problem, which achieves object localization and caption generation in parallel. +- Extensive experiments show that our proposed Vote2Cap approach achieves a new state-of-the-art performance on both Nr3D [1] (45.53% C@0.5) and ScanRefer [13] (73.77% C@0.5). + +# 2. Related Work + +We briefly summarize works on 3D and video dense captioning, and DETR-based methods for images and 3D point clouds. Additionally, we also introduce some methods for image captioning, which are closely related to our work. + +3D and Video Dense Captioning. 3D dense captioning, a task that requires translating 3D scene information to a set of bounding boxes and natural language descriptions, is challenging and has raised great interest among scholars recent years. Scan2Cap [13] and MORE [20] build graph on a detector's [19, 32] box estimations with handcrafted rules for complex relation reasoning among objects in a 3D scene. SpaCap3D [39] build a spatiality-guided transformer to model spatial relations among the detector's output. 3DJCG [4] and D3Net [7] study the joint promotion of 3D dense captioning and 3D visual grounding. $\chi$ -Trans2Cap [43] introduces additional 2D prior to complement information for 3D dense captioning with knowledge transfer. Recently, [48] shifts attention to contextual information for the perception of non-object information. Though these approaches have made great attempts at 3D dense captioning, they all follow a "detect-then-describe" pipeline, which heavily depends on a detector's performance. Our proposed Vote2Cap-DETR differs from existing works in that our method is a one-stage model that detects and generates captions in parallel and treats 3D dense captioning as a set prediction problem. Video dense captioning requires a model to segment and describe video clips from an input video. [40, 49] propose transformer architecture for end-to-end video dense captioning. In this paper, we design elements specially for 3D dense captioning, such as vote queries for better localization in sparse 3D space and the utilization of local contextual information through cross attention for informative object description. + +DETR: from 2D to 3D. DETection Transformer(DETR) [5] is a transformer [37] based architecture that treats object detection as a set prediction problem and does not require nonmaximum suppression [28] for post-processing. Though great results have been achieved, DETR suffers from slow convergence. Many follow-up works [9, 16, 18, 26, 44, 50] put efforts on speeding up DETR's training by introducing multi-scale features, cross attention designs, and label assignment techniques. Researchers also attempt to introduce transformer architectures to 3D object detection. GroupFree3D [24] learns proposal features from the whole point cloud through the transformer rather than grouping local points. 3DETR [27] analyzes the potential of the standard transformer model and generates proposals by uniformly sampling seed points from a 3D scene. In our work, we extend the DETR architecture for 3D dense captioning that makes caption generation and box localization fully interrelated with parallel decoding. Additionally, we propose + +vote query for better performance and faster convergence. + +Image Captioning. Image captioning requires a model to generate sentences describing key elements in an image, which has become a hot topic in computer vision. Existing image captioning works adopt an encoder-decoder architecture, where the decoder generates sentences from visual features extracted by the encoder. [2, 14, 17, 30] adopt a detector to extract region features as visual clues for the decoder, while [23, 46] extract grid features directly from an image. Additionally, [29] generates captions from both region and grid visual features. Though these methods are effective in image captioning, they cannot be directly applied to 3D dense captioning since it requires describing each 3D object in a scene with respect to its surroundings. In contrast, our proposed caption head sufficiently leverages the rich context information in a 3D point cloud, receives visual clues from both the object query and its local context, and fuses them to achieve effective 3D dense captioning. + +# 3. Method + +As shown in Fig. 2, given a 3D scene, our goal is to localize objects of interest and generate informative natural language descriptions for each object. The input of our model is a point cloud $PC = [p_{in};f_{in}]\in \mathbb{R}^{N\times (3 + F)}$ representing an indoor 3D scene. Here, $p_{in}\in \mathbb{R}^{N\times 3}$ is the absolute locations for each point, and $f_{in}\in \mathbb{R}^{N\times F}$ is additional input feature for each point, such as color, normal, height, or multiview feature introduced by [6,13]. The expected output is a set of box-caption pairs $(\hat{B},\hat{C}) = \{(\hat{b}_1,\hat{c}_1),\dots ,(\hat{b}_K,\hat{c}_K)\}$ , representing an estimation of $K$ distinctive objects in this 3D scene. + +Specifically, our system adopts 3DETR [27] encoder as our scene encoder and a transformer decoder to capture both object-object and object-scene interactions through the attention mechanism. Then, we feed the query feature to two parallel task-specific heads for object detection and caption generation. + +# 3.1. 3DETR Encoder + +Inspired by DETR [5], 3DETR [27] has made a successful attempt at bringing full transformer architecture to the 3D object detection task, which removes many hand-coded design decisions as the popular VoteNet and PointNet++ modules in most two-stage methods. + +In 3DETR encoder, the input $PC$ is first tokenized with a set-abstraction layer [33]. Then, point tokens are fed into a masked transformer encoder with a set-abstraction layer followed by another two encoder layers. We denote the encoded scene tokens as $[p_{enc};f_{enc}]\in \mathbb{R}^{1,024\times (3 + 256)}$ . + +# 3.2. Vote Query + +Though 3DETR has achieved initial success in 3D object detection, it suffers from certain limitations. 3DETR + +proposes box estimations around the query points (aka proposal centers) sampled from the scenes, which can make these predictions far away from real objects given the sparse object surfaces, resulting in slow convergence to capture discriminative object features with further miss detections. + +Prior works on fast convergence DETR models [12, 26, 45] show that injecting more structured bias to initialize object queries, such as anchor points or content-aware queries, accelerates training. Therefore, we propose the vote query, which introduces both 3D spatial bias and content-related information, for faster convergence and performance improvement. + +More specifically, we reformulate the object queries in 3DETR into the format of vote query as a composition of the embedding of the reference points and vote transformation around them. This helps build the connection between the object query in 3DETR and the vote set prediction widely studied in VoteNet [32]. + +The detailed structure is shown in Figure 3. Here, vote $\Delta p_{vote}$ is predicted from encoded scene token feature $f_{enc}$ with a Feed Forward Network (FFN) $FFN_{vote}$ that learns to shift the encoded points to objects' centers spatially: + +$$ +p _ {v o t e} = p _ {e n c} + \Delta p _ {v o t e} = p _ {e n c} + F F N _ {v o t e} \left(f _ {e n c}\right). \tag {1} +$$ + +Then, we sample 256 points $p_{seed}$ from $p_{enc}$ with farthest point sampling and locate each point's offset estimation for $p_{vq} = p_{seed} + \Delta p_{vote}$ . Finally, we gather features from $(p_{enc}, f_{enc})$ for $p_{vq}$ with a set-abstraction layer [33], to formulate the vote query feature $f_{vq} \in \mathbb{R}^{256 \times 256}$ . We represent vote query as $(p_{vq}, f_{vq})$ . + +Following 3DETR [27], our model adopts an eight-layer transformer decoder, and the $i$ -th layer's input query feature $f_{query}^{i}$ is calculated through + +$$ +f _ {q u e r y} ^ {i} = \operatorname {L a y e r} _ {i - 1} \left(f _ {q u e r y} ^ {i - 1} + F F N \left(P E \left(p _ {v q}\right)\right)\right), \tag {2} +$$ + +where $f_{query}^{0} = f_{vq}$ , and $PE(\cdot)$ is the 3D Fourier positional encoding function [35]. Experiments in later sections demonstrate that: 1) Vote query injects additional spatial bias to object detection and boosts the detection performance. 2) Encoding features from the point cloud as initial queries accelerates convergence. + +# 3.3. Parallel Decoding + +We adopt two task-specific heads for simultaneous object detection and caption generation. The two task heads are agnostic to each other's output. + +Detection Head. Detecting objects in a 3D scene requires box corner estimation $\hat{B}$ and class estimation $\hat{S}$ (containing "no object" class) from each object query feature. Following 3DETR [27], box corner estimation is generated by learning spatial offset from a query point to an object's center and box size regression. All subtasks are implemented + +![](images/37b209ed6ca2864135c523d8cf2fe09e1f818b93f825c68fe8ee16396787b438.jpg) +Figure 2. Approach. Vote2Cap-DETR is a one-stage transformer model that takes a 3D point cloud as its input, and generates a set of box predictions and sentences localizing and describing each object in the point cloud. The scene encoder first generates encoded scene tokens $(p_{enc}, f_{enc})$ from the input point cloud. Then, we generate vote query $(p_{vq}, f_{vq})$ from the encoded scene tokens, which introduce both spatial bias $p_{vq}$ and content-aware feature $f_{vq}$ to initial object queries. The transformer decoder decodes each vote query with two parallel task heads for captioning and detection. We optimize Vote2Cap-DETR with a set loss. + +![](images/bb0740e2ed932f39423205db07b664eb02d165c8b20ae85b9140146b0217bac1.jpg) + +![](images/3ea17e8bfdfd5eb2f57ce342a4f0195e6ddf39fd91bf15f18c0533ea1a50f37c.jpg) + +![](images/ba46b383ed21182412643127266501b8e266daecd41dd6cb69d258f7407e93e5.jpg) +Figure 3. Vote Query Generation. Vote query $p_{vq}$ contains spatial bias $(\Delta p_{vote})$ to initial object queries $(p_{seed})$ , which are sampled from the scene with farthest point sampling (FPS) and gathered feature $f_{vq}$ from the point cloud for each query. + +by FFNs. In practice, the object localization head is shared through different layers in the decoder, following all existing works on DETR [5, 12, 26, 27]. + +Caption Head. 3D dense captioning requires attribute details on an object and its relation with its close surroundings. However, the vote query itself is agnostic to box predictions and fails to provide adequate attribute and spatial relations for informative caption generation. Therefore, the main difficulty is how to leverage sufficient surrounding contextual information without confusing the caption head. + +To address the above issues, we propose Dual-Clued Captioner(DCC), a lightweight transformer decoder-based caption head, for 3D dense captioning. DCC consists of a stack of 2 identical transformer decoder blocks, sinusoid position embedding, and a linear classification head. To generate informative captions, DCC receives two streams of visual clue $\mathcal{V} = (\mathcal{V}^q,\mathcal{V}^s)$ . Here, $\mathcal{V}^q$ is the last decoder layer's output feature of a vote query, and $\mathcal{V}^s$ is contextual + +![](images/6764c5eb6eaf5a0a7e742b12fa983de332de13ac43c63dcf9f7ee89550868083.jpg) +Figure 4. Dual-Clued Captioner(DCC). DCC is a lightweight transformer based caption head that uses vote query feature $\mathcal{V}_q$ as caption perfix to identify the region to be described, and contextual features $\nu_{s}$ surrounding the vote query to complement with more surrounding information for descriptive caption generation. + +information surrounding the absolute location of each vote query. When generating a caption for a proposal, we substitute the standard Start Of Sequenec( 'SOS') prefix with $\nu^q$ to identify the object to be described following [39]. Since the vote query is agnostic of actual neighbor object proposals because of the parallel detection branch, we introduce the vote query's $k_{s}$ nearest local context token features as its local surroundings $\nu^{s}$ as keys for cross attention. During inference, we generate captions through beam search with a beam size of 5. + +# 3.4. Set prediction loss for 3D Dense Captioning + +Our proposed Vote2Cap-DETR requires supervision for vote query $(\mathcal{L}_{vq})$ , detection head $(\mathcal{L}_{det})$ , and caption head $(\mathcal{L}_{cap})$ . + +Vote Query Loss. We borrow vote loss from VoteNet [32] as $\mathcal{L}_{vq}$ , to help the vote query generation module learn to + +shift points $p_{enc}$ to an object's center: + +$$ +\mathcal {L} _ {v q} = \frac {1}{M} \sum_ {i = 1} ^ {M} \sum_ {j = 1} ^ {N _ {g t}} \left\| p _ {v o t e} ^ {i} - c n t _ {j} \right\| _ {1} \cdot \mathbb {I} \left\{p _ {e n c} ^ {i} \in I _ {j} \right\}. \tag {3} +$$ + +Here, $\mathbb{I}(\cdot)$ is an indicator function that equals 1 when the condition meets and 0 otherwise, $N_{gt}$ is the number of instances in a 3D scene, $M$ is the size of $p_{vote}$ , and $cnt_j$ is the center of $j$ th instance $I_j$ . + +Detection Loss. Following 3DETR [27], we use the same Hungarian algorithm to assign each proposal with a ground truth label. Since 3D dense captioning cares much for the object localization ability, we apply a larger weight on the gIoU loss in set loss [27]: + +$$ +\mathcal {L} _ {s e t} = \alpha_ {1} \mathcal {L} _ {g i o u} + \alpha_ {2} \mathcal {L} _ {c l s} + \alpha_ {3} \mathcal {L} _ {\text {c e n t e r - r e g}} + \alpha_ {4} \mathcal {L} _ {\text {s i z e - r e g}}, \tag {4} +$$ + +where $\alpha_{1} = 10$ , $\alpha_{2} = 1$ , $\alpha_{3} = 5$ , $\alpha_{4} = 1$ are set heuristically. The set loss $\mathcal{L}_{set}$ is applied to all $n_{dec - layer}$ layers in the decoder for better convergence. + +Caption Loss. Following the standard practice of image captioning, we train our caption head first with standard cross-entropy loss (MLE training), and then fine-tune it with Self-Critical Sequence Training (SCST) [34]. During MLE training, the model is trained to predict the $(t + 1)$ th word $c_i^{t + 1}$ , given the first $t$ words $c_i^{[1:t]}$ and the visual clue $\mathcal{V}$ . The loss function for a $T$ -length sentence is defined as: + +$$ +\mathcal {L} _ {c _ {i}} = \sum_ {i = 1} ^ {T} \mathcal {L} _ {c _ {i}} (t) = - \sum_ {i = 1} ^ {T} \log \hat {P} \left(c _ {i} ^ {t + 1} | \mathcal {V}, c _ {i} ^ {[ 1: t ]}\right). \tag {5} +$$ + +After the caption head is trained under word-level supervision, we fine-tune it with SCST. During SCST, the model generates multiple captions $\hat{c}_{1,\dots,k}$ with a beam size of $k$ and another $\hat{g}$ through greedy search as a baseline. The loss function for SCST is defined as: + +$$ +\mathcal {L} _ {c _ {i}} = - \sum_ {i = 1} ^ {k} \left(R \left(\hat {c} _ {i}\right) - R (\hat {g})\right) \cdot \frac {1}{| \hat {c} _ {i} |} \log \hat {P} (\hat {c} _ {i} | \mathcal {V}). \tag {6} +$$ + +Here, the reward function $R(\cdot)$ is the CIDEr metric for caption evaluation, and the log probability of caption $\hat{c}_i$ is normalized by caption length $|\hat{c}_i|$ to encourage the model to treat captions in different length with equal importance. + +Set to Set Training for 3D Dense Captioning. We propose an easy-to-implement set-to-set training strategy for 3D dense captioning. Given a 3D scene, we randomly sample one sentence from the corpus for each annotated instance. Then, we assign language annotations to the corresponding number of proposals in the corresponding scene with the same Hungarian algorithm. During training, we average losses for captions $\mathcal{L}_{c_i}$ on all annotated instances in + +a batch to compute the caption loss $\mathcal{L}_{cap}$ . To balance loss for different tasks, our loss function is defined as: + +$$ +\mathcal {L} = \beta_ {1} \mathcal {L} _ {v q} + \beta_ {2} \sum_ {i = 1} ^ {n _ {\text {d e c - l a y e r}}} \mathcal {L} _ {\text {s e t}} + \beta_ {3} \mathcal {L} _ {\text {c a p}}, \tag {7} +$$ + +where $\beta_{1} = 10, \beta_{2} = 1, \beta_{3} = 5$ are set heuristically. + +# 4. Experiments + +We first present the datasets, metrics, and implementation details for 3D dense captioning (section 4.1). Then, we provide comparisons with all state-of-the-art methods (section 4.2). We also provide studies on the effectiveness of different parts in our model (section 4.3). Finally, we visualize several qualitative results to address the effectiveness of our method (section 4.4). + +# 4.1. Datasets, Metrics, and Implementation Details + +Datasets. We analyze performance on ScanRefer [6] and $\mathrm{Nr3D}$ [1], both of which are built on 3D scenes from ScanNet [15]. ScanRefer/Nr3D contains 36,665/32,919 freeform language annotations describing 7,875/4,664 objects from 562/511 out of 1201 3D scenes in ScanNet for training and evaluates on 9,508/8,584 sentences for 2,068/1,214 objects from 141/130 out of 312 3D scenes in ScanNet. + +Evaluation Metrics. Following [4, 13, 20, 39], we first apply NMS on object proposals to drop duplicate object predictions. Each object proposal is a box-caption pair $(\hat{b}_i, \hat{c}_i)$ , containing box corner prediction $\hat{b}_i$ and generated caption $\hat{c}_i$ . Then, each annotated instance is assigned an object proposal with the largest IoU among the remaining proposals. Here, we use $(b_i, C_i)$ to represent an instance's label, where $b_i$ is an instance's box corner label, and $C_i$ is the corpus containing all caption annotations for this instance. To jointly evaluate the model's localization and caption generation capability, we adopt the $m@kIoU$ metric [13]: + +$$ +m @ k I o U = \frac {1}{N} \sum_ {i = 1} ^ {N} m \left(\hat {c} _ {i}, C _ {i}\right) \cdot \mathbb {I} \left\{I o U \left(\hat {b} _ {i}, b _ {i}\right) \geq k \right\}. \tag {8} +$$ + +Here, $N$ is the number of total annotated instances in the evaluation dataset, and $m$ could be any metric for natural language generation, such as CIDEr [38], METEOR [3], BLEU-4 [31], and ROUGE-L [22]. + +Implementation Details. We offer implementation details of different baselines. "w/o additional 2D" means the input $\mathcal{PC} \in \mathbb{R}^{40,000 \times 10}$ contains absolute location as well as color, normal and height for 40,000 points representing a 3D scene. "additional 2D" means we replace color information with 128-dimensional multiview feature extracted by ENet [8] from 2D images following [13]. + +We first pre-train the whole network without the caption head on ScanNet [15] for 1,080 epochs (163k iterations, + +$\sim 34$ hours) using an AdamW optimizer [25] with a learning rate decaying from $5 \times 10^{-4}$ to $10^{-6}$ by a cosine annealing scheduler, a weight decay of 0.1, a gradient clipping of 0.1, and a batch size of 8 following [27]. Then, we jointly train the full model from pre-trained weights with the MLE caption loss for another 720 epochs (51k/46k iterations for ScanRefer/Nr3D, $\sim 11 / 10$ hours). To prevent overfitting, we fix the learning rate of the detector as $10^{-6}$ , and set that of the caption head decaying from $10^{-4}$ to $10^{-6}$ using another cosine annealing scheduler. During SCST, we tune the caption head with a batch size of 2 and freeze the detector for 180 epochs because of high memory cost (50k/46k iterations for ScanRefer/Nr3D, $\sim 14 / 11$ hours) with a fixed learning rate of $10^{-6}$ . We evaluate the model every 2,000 iterations during training for consistency with existing works [13, 39], and all experiments mentioned above are conducted on a single RTX3090 GPU. + +# 4.2. Comparison with Existing Methods + +In this section, we compare performance with existing works on metrics C, M, B-4, R as abbreviations for CIDEr [38], METEOR [3], BLEU-4 [31], Rouge-L [22] under IoU thresholds of 0.25, 0.5 for ScanRefer (Table 1) and 0.5 for Nr3D (Table 2). In both tables, “-” indicates that neither the original paper nor any follow-up works provide such results. We make separate comparisons for MLE training and SCST since different supervisions on the caption head have huge influence on the captioning performance. Among all the listed methods, experiments other than D3Net [7] and 3DJCG [4] utilize the standard VoteNet [32] detector. Meanwhile, D3Net adopts PointGroup [19], a 3D instance segmentation model, for better object detection. 3DJCG substitute the proposal head with an FCOS [36] head to improve VoteNet's localization performance. Additionally, 3DJCG and D3Net are trained on 3D dense captioning as well as 3D visual grounding to study the joint promotion of both tasks. Among methods listed under SCST, $\chi$ -Trans2Cap [43] combines MLE training with standard SCST in an additive manner, while Scan2Cap and D3Net [7] adopt the same reward that combines CIDEr score with a listener's [47] grounding loss by weighted summation. Meanwhile, our method adopts the standard SCST with CIDEr reward. + +Table 1 reports comparisons on ScanRefer [6] validation dataset. Our Vote2Cap-DETR surpasses current state-of-the-art methods. Under MLE training with additional 2D inputs, Vote2Cap-DETR achieves $59.32\%$ C@0.5 while 3DJCG [4] achieves $49.48\%$ (9.84% C@0.5↑) with additional training data. Under SCST, our Vote2Cap-DETR achieves $70.63\%$ C@0.5 comparing to $62.64\%$ (7.99% C@0.5↑) for current state-of-the-art D3Net [7]. + +In Table 2, we list results on the Nr3D [1] dataset with additional 2D input following [39]. Since Scan2Cap [13] + +has not reported results on $\mathrm{Nr3D}$ , we adopt the best-reported result from [4]. Our Vote2Cap-DETR also surpasses current state-of-the-art methods (5.78%/7.11% C@0.5↑ for MLE training/SCST). + +# 4.3. Ablation Study + +Since 3D dense captioning concerns both localization and caption generation, we perform ablation studies to understand the effectiveness of different components. + +Does the vote query improve 3DETR? We performed ablation experiments in Table 3 and Figure 5 to see if the vote query can improve 3DETR's localization and convergence. We notice that introducing position features $p_{vq}$ alone helps improve detection performance (0.97% mAP50↑). However, it (green line in Figure 5) converges slower in the earlier training procedure than the 3DETR baseline (blue line in Figure 5), inferring the vote query generation module is not well learned to predict accurate spatial offset estimations at early training epochs. Introducing additional content feature $f_{vq}$ in vote query features results in another boost in both detection performance (2.98% mAP50↑) and training speed (red line in Figure 5). The overall localization performance of Vote2Cap-DETR is about 7.2% mAP higher than the popular VoteNet. + +![](images/e3bc14e3aabed028ea7b167beee694bdf8b15030260d0563c9dd06fb4cf0aa48.jpg) +Figure 5. Vote query and convergence. We take out convergence study on a different combination of content feature $f_{vq}$ and position $p_{vq}$ in vote query. The baseline model $(p_{query}, f_{query}^{0}) = (p_{seed}, 0)$ downgrades to 3DETR. Introducing $p_{vq}$ boosts performance but decelerates training since $FFN_{vote}$ requires time to converge, and $f_{vq}$ accelerates training. + +Does 3D context feature help captioning? Since the performance of 3D dense captioning is affected by both localization and caption capability, we freeze all parameters other than the caption head and train with 3D only input and standard cross entropy loss (MLE training) for a fair evaluation. We use object-centric decoder [39] as our baseline, which is a decoder that generates captions with object feature as a caption's prefix. In Table 4, “-” refers to the object-centric decoder baseline, “global” means naively including all context tokens extracted from the scene encoder in the decoder, “local” is our proposed caption head that + +
MethodLdesw/o additional 2D inputw/ additional 2D input
IoU = 0.25IoU = 0.50IoU = 0.25IoU = 0.50
C↑B-4↑M↑R↑C↑B-4↑M↑R↑C↑B-4↑M↑R↑C↑B-4↑M↑R↑
Scan2Cap [13]53.7334.2526.1454.9535.2022.3621.4443.5756.8234.1826.2955.2739.0823.3221.9744.78
MORE [20]58.8935.4126.3655.4138.9823.0121.6544.3362.9136.2526.7556.3340.9422.9321.6644.42
SpaCap3d [39]58.0635.3026.1655.0342.7625.3822.8445.6663.3036.4626.7155.7144.0225.2622.3345.36
3DJCG [4]MLE60.8639.6727.4559.0247.6831.5324.2851.8064.7040.1727.6659.2349.4831.0324.2250.80
D3Net [7]------------46.0730.2924.3551.67
Ours71.4539.3428.2559.3361.8134.4626.2254.4072.7939.1728.0659.2359.3232.4225.2852.53
x-Trans2Cap [43]58.8134.1725.8154.1041.5223.8321.9044.9761.8335.6526.6154.7043.8725.0522.4645.28
Scan2Cap [13]------------48.3826.0922.1544.74
D3Net [7]SCST------------62.6435.6825.7253.90
Ours84.1542.5128.4759.2673.7738.2126.6454.7186.2842.6428.2759.0770.6335.6925.5152.28
+ +Table 1. Evaluating Vote2Cap-DETR on ScanRefer [6]. We compare Vote2Cap-DETR with all published state-of-the-art 3D dense caption methods on the ScanRefer dataset. Though our method does not depend on hand-crafted NMS [28] to drop overlapped boxes, we follow the standard evaluation protocol from [13] for fair comparison and provide evaluation without NMS in Table 7. Our proposed Vote2Cap-DETR achieves new state-of-the-art under both MLE training and SCST. + +
MethodLdesC@0.5↑B-4@0.5↑M@0.5↑R@0.5↑
Scan2Cap [13]27.4717.2421.8049.06
SpaCap3d [39]33.7119.9222.6150.50
D3Net [7]MLE33.8520.7023.1353.38
3DJCG [4]38.0622.8223.7752.99
Ours43.8426.6825.4154.43
x-Tran2Cap [43]33.6219.2922.2750.00
D3Net [7]SCST38.4222.2224.7454.37
Ours45.5326.8825.4354.76
+ +Table 2. Evaluating Vote2Cap-DETR on Nr3D [1]. Likewise, we perform the standard evaluation on the Nr3D dataset, and our proposed Vote2Cap-DETR surpasses prior arts. + +
\( {p}_{query} \)\( {f}_{query}^{0} \)IoU=0.25IoU=0.501st layer IoU=0.50
mAP↑AR↑mAP↑AR↑mAP↑AR↑
VoteNet Baseline63.4282.1844.9660.65--
\( {p}_{seed} \)067.2584.9148.1864.9834.8055.06
\( {p}_{vq} \)067.3385.6049.1566.3830.2358.44
\( {p}_{vq} \)\( {f}_{vq} \)69.6187.2052.1369.1246.5366.51
+ +includes a vote query's $k_{s}$ ( $k_{s} = 128$ empirically) nearest context tokens extracted from the scene encoder. + +Results show that the caption generation performance benefits from the introduction of additional contextual information. Additionally, compared with naively introducing contextual information from the whole scene, the introduction of local context could be more beneficial. This demonstrates our motivation that close surroundings matter when describing an object. + +Table 3. Vote query and performance. We provide quantitative results for Figure 5. Introducing $p_{vq}$ as query positions improves detection, and gathering $f_{vq}$ from content further boosts performance. + +
keyIoU=0.25IoU=0.5
C↑B-4↑M↑R↑C↑B-4↑M↑R↑
-68.6238.6127.6758.4760.1534.0225.8053.82
global70.0539.2327.8458.4461.2034.6625.9353.79
local70.4239.9827.9958.8961.3935.2426.0254.12
+ +Do set-to-set training benefit dense captioning? To analyze the effectiveness of set-to-set training, we use a smaller learning rate $(10^{-6})$ for all parameters other than the caption head and freeze these parameters during SCST. We name the traditional training strategy as "Sentence Training" adopted in previous works [13, 39], which traverses through all sentence annotations in the dataset. As is shown in Figure 7, our proposed "Set-to-Set" training achieves comparable results with the traditional strategy during MLE training and converges faster because of a bigger batch size on the caption head, which also benefits SCST. + +Table 4. Different keys for caption generation. We provide a comparison on different keys used in caption generation. Introducing contextual information relates to more informative captions generated. Since 3D dense captioning is more object-centric, introducing vote queries' local contextual feature is a better choice. + +
TrainingLdesC@0.5↑B-4@0.5↑M@0.5↑R@0.5↑
SentenceMLE61.2135.3526.1254.52
Set-to-Set61.8134.4626.2254.40
SentenceSCST71.3937.5726.0154.28
Set-to-Set73.7738.2126.6454.71
+ +End to end training from scratch. Our Vote2Cap-DETR also supports end-to-end training from scratch for 3D dense captioning. However, both ScanRefer and Nr3D are annotated on limited scenes (562/511 scenes) for training; thus, directly training Vote2Cap-DETR from scratch will underperform given to satisfy two objectives simultaneously. Experiments on Scanrefer in Table 6 show that the greedy strategy we choose by pre-training detection head as a good pre-requisite for captioning achieves better performance. + +Table 5. Set to Set training and performance. We compare our proposed set-to-set training with traditional "Sentence Training", which traverses through all sentence annotations. We achieve comparable performance with MLE training, and $2.38\%$ C@0.5 improvement with SCST. + +
pretrain/end2endC@0.5↑B-4@0.5↑M@0.5↑R@0.5↑AP@0.5↑AR@0.5↑
end2end52.1528.8724.6849.7646.6862.17
pretrain+end2end62.0334.9026.0654.3351.2667.57
+ +Table 6. Ablation study for training strategies. The greedy strategy we choose by pre-training detection head as a good prerequisite for captioning achieves better performance than directly end to end training from scratch. + +![](images/03cb43e70539653fe553a620890c611add75e2d5f940a8524f601c949c007efc.jpg) +scene0011_00 + +![](images/831e1c0ce41a1028e27e929c4f0222271f1a12c4f9964e11c203c5c0e810f8d4.jpg) +scene0015_00 +3DJCG: This is a rectangular whiteboard. It is on the wall. +3DJCG: This is a brown table. It is in the middle of the room. +SpaCap3D: This is a wooden table. It is in the center of the room. +Ours: This is a wooden table. It is in the corner of the room. + +![](images/c456dfcaa8143962bbae4175e7a69723a047d1d2944d8d6e9491371688506220.jpg) +scene0025_00 +3DJCG: The is a small brown cabinet. It is to the right of the desk. +SpaCap3D: The cabinet is below the desk. It is to the left of the chair. +Ours: The tv is on the wall. It is to the right of the table. +Ours: This is a white cabinet. It is to the right of the table. + +![](images/328921ee1bbcaf70805e923e55b2b870420b69908f8a8fe596a484864be2fae0.jpg) +scene0050_00 +3DJCG: This is a brown table. It is in front of the couch. +SpaCap3D: This is a wooden coffee table. It is in front of the couch. +Ours: This is a brown ottoman. It is to the right of the chair. +GT: This is a brown ottoman. It is in front of a couch. + +![](images/0c53d57d5bc9ca0e78c887611afbc6ea08a02364435a9e8a1fef9668d8ae224e.jpg) +SpaCap3D: The whiteboard is affixed to the wall. It is to the right of the window. +GT: This is a big black tv. It is above a thin table. +GT: This is a small table with a wood look. It is the table closest to the front of the room in the upper left corner. +GT: A white cabinet is sitting on the floor next to the wall. It is to the left of the couch. +Figure 6. Qualitative Comparisons. We compare qualitative results with two state-of-the-art "detect-then-describe" methods, 3DJCG [4] and SpaCap3D [39]. We underline phrases describing spatial locations, and mark correct attribute words in green and wrong description in red. Our Vote2Cap-DETR produces tight bounding boxes close to the ground truth and accurate descriptions. +Figure 7. Set-to-Set training and convergence. Convergence speed analysis of two different training strategies with MLE training as well as SCST. Set-to-Set training enables a larger batch size for the caption head and accelerates convergence. + +Is Vote2Cap-DETR robust to NMS? Similar to other DETR works, the set loss encourages the model to produce compact predictions. We compare performance on both 3D dense caption (C@0.5) and detection (mAP50, AR50) in Table 7. Since the $m@kIoU$ metric (Eq. 8) does not contain any penalties on redundant predictions, getting rid of NMS [28] results in performance growth in C@0.5. Results show that Vote2Cap-DETR is more stable compared to VoteNet based methods with the absence of NMS. + +
Modelsw/NMSw/o NMS
C@0.5↑mAP50↑AR50↑C@0.5↑mAP50↑AR50↑
SpaCap3D43.9337.7753.9651.3523.3064.14
3DJCG50.2247.5862.1254.9430.0368.69
Vote2Cap-DETR70.6352.7966.0971.5752.8267.80
+ +Table 7. Effect of NMS. We analyze whether the absence of NMS affects the 3D dense captioning performance (C@0.5) as well as detection performance (mAP50, AR50). + +# 4.4. Qualitative Results + +We compare qualitative results with two state-of-the-art models, SpaCap3D [39] and 3DJCG [4] in Figure 6. One can see that our method produces tight bounding boxes close to the ground truth as well as accurate descriptions of object attributes, classes, and spatial relationships. + +# 5. Conclusion + +In this work, we present Vote2Cap-DETR, a transformer based one-stage approach, for 3D dense captioning. The proposed Vote2Cap-DETR adopts a full transformer encoder-decoder architecture that decodes a set of vote queries to box predictions and captions in parallel. We show that by introducing spatial bias and content-aware features, vote query boosts both convergence and detection performance. Additionally, we develop a novel lightweight query-driven caption head for informative caption generation. Experiments on two widely used datasets for 3D dense captioning validate that our proposed one-stage Vote2Cap-DETR model surpasses prior works with heavy dependence on hand-crafted components by a large margin. + +# 6. Acknowledgements + +This work is supported by National Natural Science Foundation of China (No. U1909207, 62071127, and 62276176), Shanghai Natural Science Foundation (No. 23ZR1402900), Zhejiang Lab Project (No. 2021KH0AB05), and in part by A*STAR AME Programmatic Funding A18A2b0046, RobotHTPO Seed Fund under Project C211518008, and EDB Space Technology Development Grant under Project S22-19016-STDP. + +# References + +[1] Panos Achlioptas, Ahmed Abdelreehm, Fei Xia, Mohamed Elhoseiny, and Leonidas Guibas. Referit3d: Neural listeners for fine-grained 3d object identification in real-world scenes. In European Conference on Computer Vision, pages 422-440. 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Existing methods follow a sophisticated \"detect-then-describe\" pipeline equipped with numerous hand-crafted components. However, these hand-crafted components would yield suboptimal performance given cluttered object spatial and class distributions among different scenes. In this paper, we propose a simple-yet-effective transformer framework Vote2Cap-DETR based on recent popular DEetection Transformer (DETR). Compared with prior arts, our framework has several appealing advantages: 1) Without resorting to numerous hand-crafted components, our method is based on a full transformer encoder-decoder architecture with a learnable vote query driven object decoder, and a caption decoder that produces the dense captions in a set-prediction manner. 2) In contrast to the two-stage scheme, our method can perform detection and captioning in one-stage. 3) Without bells and whistles, extensive experiments on two commonly used datasets, ScanRefer and Nr3D, demonstrate that our Vote2Cap-DETR surpasses current state-of-the-arts by " + }, + { + "bbox": [ + 46, + 251, + 290, + 515 + ], + "type": "inline_equation", + "content": "11.13\\%" + }, + { + "bbox": [ + 46, + 251, + 290, + 515 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 251, + 290, + 515 + ], + "type": "inline_equation", + "content": "7.11\\%" + }, + { + "bbox": [ + 46, + 251, + 290, + 515 + ], + "type": "text", + "content": " in CIDEr@0.5IoU, respectively. Codes will be released soon." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 47, + 537, + 128, + 550 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 537, + 128, + 550 + ], + "spans": [ + { + "bbox": [ + 47, + 537, + 128, + 550 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 46, + 557, + 287, + 641 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 557, + 287, + 641 + ], + "spans": [ + { + "bbox": [ + 46, + 557, + 287, + 641 + ], + "type": "text", + "content": "In recent years, works on 3D learning has grown dramatically for various applications [10, 11, 21, 41, 42]. Among them, 3D dense captioning [7, 13] requires a system to localize all the objects in a 3D scene and generate descriptive sentences for each object. This problem is challenging, given 1) the sparsity of point clouds and 2) the cluttered distribution of objects." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 46, + 641, + 287, + 677 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 641, + 287, + 677 + ], + "spans": [ + { + "bbox": [ + 46, + 641, + 287, + 677 + ], + "type": "text", + "content": "3D dense captioning can be divided into two tasks, object detection, and object caption generation. Scan2Cap [13], MORE [20], and SpaCap3D [39] propose well-designed re" + } + ] + } + ], + "index": 14 + }, + { + "type": "image", + "bbox": [ + 308, + 228, + 547, + 387 + ], + "blocks": [ + { + "bbox": [ + 308, + 228, + 547, + 387 + ], + "lines": [ + { + "bbox": [ + 308, + 228, + 547, + 387 + ], + "spans": [ + { + "bbox": [ + 308, + 228, + 547, + 387 + ], + "type": "image", + "image_path": "07449a239b3ac7eb9654da11b4f22bdc9e076b4a2fe3aa3d3a9580a9bc634ca7.jpg" + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 394, + 547, + 460 + ], + "lines": [ + { + "bbox": [ + 305, + 394, + 547, + 460 + ], + "spans": [ + { + "bbox": [ + 305, + 394, + 547, + 460 + ], + "type": "text", + "content": "Figure 1. Illustration of existing two-stage 3D dense captioning method (upper) and our Vote2Cap-DETR (bottom). Existing methods adopt a two-stage pipeline that heavily depends on a detector's output. Therefore, we propose a transformer-based one-stage model, Vote2Cap-DETR, that frames 3D dense captioning as a set prediction problem." + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "image_caption" + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 472, + 547, + 568 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 472, + 547, + 568 + ], + "spans": [ + { + "bbox": [ + 304, + 472, + 547, + 568 + ], + "type": "text", + "content": "lation reasoning modules to model relations among object proposals efficiently. [48] introduces contextual information from two branches to improve the caption. 3DJCG [4] and D3Net [7] study the correlation between 3D visual grounding and 3D dense captioning and point out that these two tasks promote each other. Additionally, " + }, + { + "bbox": [ + 304, + 472, + 547, + 568 + ], + "type": "inline_equation", + "content": "\\chi" + }, + { + "bbox": [ + 304, + 472, + 547, + 568 + ], + "type": "text", + "content": "-Trans2Cap [43] discusses how to transfer knowledge from additional 2d information to boost 3d dense captioning." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 570, + 548, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 548, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 548, + 715 + ], + "type": "text", + "content": "Among existing methods, they all adopt a two-stage \"detect-then-describe\" pipeline [4, 7, 13, 20, 39, 48] (Figure 1). This pipeline first generates a set of object proposals, then decodes each object by a caption generator with an explicit reasoning procedure. Though these methods have achieved remarkable performance, the \"detect-then-describe\" pipeline suffers from the following issues: 1) Because of the serial and explicit reasoning, the captioning performance highly depends on the object detection performance, which limits the mutual promotion of detection and captioning. 2) The heavy reliance on hand-crafted components, e.g., radii, 3D operators, the definition of pro" + } + ] + } + ], + "index": 18 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 683, + 287, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 683, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 683, + 287, + 713 + ], + "type": "text", + "content": "*Part of this work was accomplished under supervision by Dr. Hongyuan Zhu from A*STAR, Singapore. \n†Corresponding author." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "11124" + } + ] + } + ], + "index": 20 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "type": "text", + "content": "posal neighbors, and post-processing (non-maximum suppression [28]) introduces additional hyper-parameters, leading to a sub-optimal performance given the sparse object surfaces and cluttered object distributions among different indoor scenes. This inspires us to design a one-stage 3D dense captioning system." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 144, + 288, + 300 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 144, + 288, + 300 + ], + "spans": [ + { + "bbox": [ + 46, + 144, + 288, + 300 + ], + "type": "text", + "content": "To address the above issues, we propose Vote2CapDETR, a full transformer encoder-decoder architecture for one-stage 3D dense captioning. Unlike traditional \"detect-then-describe\" pipelines, we directly feed the decoder's output into the localization head and caption head in parallel. By casting 3D dense captioning as a set-to-set problem, each target instance and its language annotation is matched with a query in a one-to-one correspondence manner, enabling a more discriminative feature representation for proposals to identify each distinctive object in a 3D scene. Additionally, we also propose a novel vote query driven decoder to introduce spatial bias for better localization of objects in a cluttered 3D scene." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 301, + 288, + 576 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 301, + 288, + 576 + ], + "spans": [ + { + "bbox": [ + 46, + 301, + 288, + 576 + ], + "type": "text", + "content": "With fully attentional design, we resolve 3D dense captioning with the following innovations: 1) Our method treats the 3D dense captioning task as a set prediction problem. The proposed Vote2Cap-DETR directly decodes the features into object sets with their locations and corresponding captions by applying two parallel prediction heads. 2) We propose a novel vote decoder by reformulating the object queries in 3DETR into the format of the vote query, which is a composition of the embeddings of the seeds point and the vote transformation with respect to the seeds. This indicates the connection between the vote query in Vote2Cap-DETR with the VoteNet, but with better localization and higher training efficiencies; 3) We develop a novel query driven caption head, which absorbs the relation and attribute modeling into self- and cross-attention, so that it can look into both local and global contexts for better scene description. Extensive experiments on two commonly used datasets, ScanRefer and Nr3D, demonstrate that our approach surpasses prior arts with many hand-crafted procedures by a large margin, which demonstrates the superiority that fully transformer architecture with sophisticated vote head and caption head can inspire many 3D vision and language tasks." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 577, + 287, + 601 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 577, + 287, + 601 + ], + "spans": [ + { + "bbox": [ + 47, + 577, + 287, + 601 + ], + "type": "text", + "content": "To summarize, the main contributions of this work include:" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 58, + 612, + 286, + 712 + ], + "type": "list", + "angle": 0, + "index": 6, + "blocks": [ + { + "bbox": [ + 58, + 612, + 286, + 659 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 612, + 286, + 659 + ], + "spans": [ + { + "bbox": [ + 58, + 612, + 286, + 659 + ], + "type": "text", + "content": "- We propose a novel one-stage and fully attention driven architecture for 3D dense captioning as a set-to-set prediction problem, which achieves object localization and caption generation in parallel." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 58, + 666, + 286, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 666, + 286, + 712 + ], + "spans": [ + { + "bbox": [ + 58, + 666, + 286, + 712 + ], + "type": "text", + "content": "- Extensive experiments show that our proposed Vote2Cap approach achieves a new state-of-the-art performance on both Nr3D [1] (45.53% C@0.5) and ScanRefer [13] (73.77% C@0.5)." + } + ] + } + ], + "index": 5 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 306, + 71, + 392, + 84 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 71, + 392, + 84 + ], + "spans": [ + { + "bbox": [ + 306, + 71, + 392, + 84 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 305, + 95, + 545, + 142 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 95, + 545, + 142 + ], + "spans": [ + { + "bbox": [ + 305, + 95, + 545, + 142 + ], + "type": "text", + "content": "We briefly summarize works on 3D and video dense captioning, and DETR-based methods for images and 3D point clouds. Additionally, we also introduce some methods for image captioning, which are closely related to our work." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 147, + 545, + 494 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 147, + 545, + 494 + ], + "spans": [ + { + "bbox": [ + 305, + 147, + 545, + 494 + ], + "type": "text", + "content": "3D and Video Dense Captioning. 3D dense captioning, a task that requires translating 3D scene information to a set of bounding boxes and natural language descriptions, is challenging and has raised great interest among scholars recent years. Scan2Cap [13] and MORE [20] build graph on a detector's [19, 32] box estimations with handcrafted rules for complex relation reasoning among objects in a 3D scene. SpaCap3D [39] build a spatiality-guided transformer to model spatial relations among the detector's output. 3DJCG [4] and D3Net [7] study the joint promotion of 3D dense captioning and 3D visual grounding. " + }, + { + "bbox": [ + 305, + 147, + 545, + 494 + ], + "type": "inline_equation", + "content": "\\chi" + }, + { + "bbox": [ + 305, + 147, + 545, + 494 + ], + "type": "text", + "content": "-Trans2Cap [43] introduces additional 2D prior to complement information for 3D dense captioning with knowledge transfer. Recently, [48] shifts attention to contextual information for the perception of non-object information. Though these approaches have made great attempts at 3D dense captioning, they all follow a \"detect-then-describe\" pipeline, which heavily depends on a detector's performance. Our proposed Vote2Cap-DETR differs from existing works in that our method is a one-stage model that detects and generates captions in parallel and treats 3D dense captioning as a set prediction problem. Video dense captioning requires a model to segment and describe video clips from an input video. [40, 49] propose transformer architecture for end-to-end video dense captioning. In this paper, we design elements specially for 3D dense captioning, such as vote queries for better localization in sparse 3D space and the utilization of local contextual information through cross attention for informative object description." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 498, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 498, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 498, + 545, + 713 + ], + "type": "text", + "content": "DETR: from 2D to 3D. DETection Transformer(DETR) [5] is a transformer [37] based architecture that treats object detection as a set prediction problem and does not require nonmaximum suppression [28] for post-processing. Though great results have been achieved, DETR suffers from slow convergence. Many follow-up works [9, 16, 18, 26, 44, 50] put efforts on speeding up DETR's training by introducing multi-scale features, cross attention designs, and label assignment techniques. Researchers also attempt to introduce transformer architectures to 3D object detection. GroupFree3D [24] learns proposal features from the whole point cloud through the transformer rather than grouping local points. 3DETR [27] analyzes the potential of the standard transformer model and generates proposals by uniformly sampling seed points from a 3D scene. In our work, we extend the DETR architecture for 3D dense captioning that makes caption generation and box localization fully interrelated with parallel decoding. Additionally, we propose" + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "11125" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 286, + 83 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 286, + 83 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 286, + 83 + ], + "type": "text", + "content": "vote query for better performance and faster convergence." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 85, + 287, + 289 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 85, + 287, + 289 + ], + "spans": [ + { + "bbox": [ + 46, + 85, + 287, + 289 + ], + "type": "text", + "content": "Image Captioning. Image captioning requires a model to generate sentences describing key elements in an image, which has become a hot topic in computer vision. Existing image captioning works adopt an encoder-decoder architecture, where the decoder generates sentences from visual features extracted by the encoder. [2, 14, 17, 30] adopt a detector to extract region features as visual clues for the decoder, while [23, 46] extract grid features directly from an image. Additionally, [29] generates captions from both region and grid visual features. Though these methods are effective in image captioning, they cannot be directly applied to 3D dense captioning since it requires describing each 3D object in a scene with respect to its surroundings. In contrast, our proposed caption head sufficiently leverages the rich context information in a 3D point cloud, receives visual clues from both the object query and its local context, and fuses them to achieve effective 3D dense captioning." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 297, + 102, + 309 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 297, + 102, + 309 + ], + "spans": [ + { + "bbox": [ + 47, + 297, + 102, + 309 + ], + "type": "text", + "content": "3. Method" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 317, + 287, + 449 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 317, + 287, + 449 + ], + "spans": [ + { + "bbox": [ + 46, + 317, + 287, + 449 + ], + "type": "text", + "content": "As shown in Fig. 2, given a 3D scene, our goal is to localize objects of interest and generate informative natural language descriptions for each object. The input of our model is a point cloud " + }, + { + "bbox": [ + 46, + 317, + 287, + 449 + ], + "type": "inline_equation", + "content": "PC = [p_{in};f_{in}]\\in \\mathbb{R}^{N\\times (3 + F)}" + }, + { + "bbox": [ + 46, + 317, + 287, + 449 + ], + "type": "text", + "content": " representing an indoor 3D scene. Here, " + }, + { + "bbox": [ + 46, + 317, + 287, + 449 + ], + "type": "inline_equation", + "content": "p_{in}\\in \\mathbb{R}^{N\\times 3}" + }, + { + "bbox": [ + 46, + 317, + 287, + 449 + ], + "type": "text", + "content": " is the absolute locations for each point, and " + }, + { + "bbox": [ + 46, + 317, + 287, + 449 + ], + "type": "inline_equation", + "content": "f_{in}\\in \\mathbb{R}^{N\\times F}" + }, + { + "bbox": [ + 46, + 317, + 287, + 449 + ], + "type": "text", + "content": " is additional input feature for each point, such as color, normal, height, or multiview feature introduced by [6,13]. The expected output is a set of box-caption pairs " + }, + { + "bbox": [ + 46, + 317, + 287, + 449 + ], + "type": "inline_equation", + "content": "(\\hat{B},\\hat{C}) = \\{(\\hat{b}_1,\\hat{c}_1),\\dots ,(\\hat{b}_K,\\hat{c}_K)\\}" + }, + { + "bbox": [ + 46, + 317, + 287, + 449 + ], + "type": "text", + "content": ", representing an estimation of " + }, + { + "bbox": [ + 46, + 317, + 287, + 449 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 46, + 317, + 287, + 449 + ], + "type": "text", + "content": " distinctive objects in this 3D scene." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 450, + 287, + 521 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 450, + 287, + 521 + ], + "spans": [ + { + "bbox": [ + 46, + 450, + 287, + 521 + ], + "type": "text", + "content": "Specifically, our system adopts 3DETR [27] encoder as our scene encoder and a transformer decoder to capture both object-object and object-scene interactions through the attention mechanism. Then, we feed the query feature to two parallel task-specific heads for object detection and caption generation." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 527, + 148, + 539 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 527, + 148, + 539 + ], + "spans": [ + { + "bbox": [ + 47, + 527, + 148, + 539 + ], + "type": "text", + "content": "3.1. 3DETR Encoder" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 545, + 287, + 605 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 545, + 287, + 605 + ], + "spans": [ + { + "bbox": [ + 46, + 545, + 287, + 605 + ], + "type": "text", + "content": "Inspired by DETR [5], 3DETR [27] has made a successful attempt at bringing full transformer architecture to the 3D object detection task, which removes many hand-coded design decisions as the popular VoteNet and PointNet++ modules in most two-stage methods." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 605, + 287, + 666 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 605, + 287, + 666 + ], + "spans": [ + { + "bbox": [ + 46, + 605, + 287, + 666 + ], + "type": "text", + "content": "In 3DETR encoder, the input " + }, + { + "bbox": [ + 46, + 605, + 287, + 666 + ], + "type": "inline_equation", + "content": "PC" + }, + { + "bbox": [ + 46, + 605, + 287, + 666 + ], + "type": "text", + "content": " is first tokenized with a set-abstraction layer [33]. Then, point tokens are fed into a masked transformer encoder with a set-abstraction layer followed by another two encoder layers. We denote the encoded scene tokens as " + }, + { + "bbox": [ + 46, + 605, + 287, + 666 + ], + "type": "inline_equation", + "content": "[p_{enc};f_{enc}]\\in \\mathbb{R}^{1,024\\times (3 + 256)}" + }, + { + "bbox": [ + 46, + 605, + 287, + 666 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 671, + 123, + 684 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 671, + 123, + 684 + ], + "spans": [ + { + "bbox": [ + 47, + 671, + 123, + 684 + ], + "type": "text", + "content": "3.2. Vote Query" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 689, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 689, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 689, + 287, + 713 + ], + "type": "text", + "content": "Though 3DETR has achieved initial success in 3D object detection, it suffers from certain limitations. 3DETR" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 72, + 545, + 131 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 131 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 131 + ], + "type": "text", + "content": "proposes box estimations around the query points (aka proposal centers) sampled from the scenes, which can make these predictions far away from real objects given the sparse object surfaces, resulting in slow convergence to capture discriminative object features with further miss detections." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 132, + 545, + 215 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 132, + 545, + 215 + ], + "spans": [ + { + "bbox": [ + 304, + 132, + 545, + 215 + ], + "type": "text", + "content": "Prior works on fast convergence DETR models [12, 26, 45] show that injecting more structured bias to initialize object queries, such as anchor points or content-aware queries, accelerates training. Therefore, we propose the vote query, which introduces both 3D spatial bias and content-related information, for faster convergence and performance improvement." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 216, + 545, + 287 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 216, + 545, + 287 + ], + "spans": [ + { + "bbox": [ + 304, + 216, + 545, + 287 + ], + "type": "text", + "content": "More specifically, we reformulate the object queries in 3DETR into the format of vote query as a composition of the embedding of the reference points and vote transformation around them. This helps build the connection between the object query in 3DETR and the vote set prediction widely studied in VoteNet [32]." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 287, + 545, + 335 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 287, + 545, + 335 + ], + "spans": [ + { + "bbox": [ + 304, + 287, + 545, + 335 + ], + "type": "text", + "content": "The detailed structure is shown in Figure 3. Here, vote " + }, + { + "bbox": [ + 304, + 287, + 545, + 335 + ], + "type": "inline_equation", + "content": "\\Delta p_{vote}" + }, + { + "bbox": [ + 304, + 287, + 545, + 335 + ], + "type": "text", + "content": " is predicted from encoded scene token feature " + }, + { + "bbox": [ + 304, + 287, + 545, + 335 + ], + "type": "inline_equation", + "content": "f_{enc}" + }, + { + "bbox": [ + 304, + 287, + 545, + 335 + ], + "type": "text", + "content": " with a Feed Forward Network (FFN) " + }, + { + "bbox": [ + 304, + 287, + 545, + 335 + ], + "type": "inline_equation", + "content": "FFN_{vote}" + }, + { + "bbox": [ + 304, + 287, + 545, + 335 + ], + "type": "text", + "content": " that learns to shift the encoded points to objects' centers spatially:" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 314, + 345, + 545, + 358 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 314, + 345, + 545, + 358 + ], + "spans": [ + { + "bbox": [ + 314, + 345, + 545, + 358 + ], + "type": "interline_equation", + "content": "p _ {v o t e} = p _ {e n c} + \\Delta p _ {v o t e} = p _ {e n c} + F F N _ {v o t e} \\left(f _ {e n c}\\right). \\tag {1}", + "image_path": "5e5ead2e84160d46195bf6aae505d8fbb0ef10b488590b4a14472e50cf7fe5ce.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 366, + 545, + 438 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 366, + 545, + 438 + ], + "spans": [ + { + "bbox": [ + 304, + 366, + 545, + 438 + ], + "type": "text", + "content": "Then, we sample 256 points " + }, + { + "bbox": [ + 304, + 366, + 545, + 438 + ], + "type": "inline_equation", + "content": "p_{seed}" + }, + { + "bbox": [ + 304, + 366, + 545, + 438 + ], + "type": "text", + "content": " from " + }, + { + "bbox": [ + 304, + 366, + 545, + 438 + ], + "type": "inline_equation", + "content": "p_{enc}" + }, + { + "bbox": [ + 304, + 366, + 545, + 438 + ], + "type": "text", + "content": " with farthest point sampling and locate each point's offset estimation for " + }, + { + "bbox": [ + 304, + 366, + 545, + 438 + ], + "type": "inline_equation", + "content": "p_{vq} = p_{seed} + \\Delta p_{vote}" + }, + { + "bbox": [ + 304, + 366, + 545, + 438 + ], + "type": "text", + "content": ". Finally, we gather features from " + }, + { + "bbox": [ + 304, + 366, + 545, + 438 + ], + "type": "inline_equation", + "content": "(p_{enc}, f_{enc})" + }, + { + "bbox": [ + 304, + 366, + 545, + 438 + ], + "type": "text", + "content": " for " + }, + { + "bbox": [ + 304, + 366, + 545, + 438 + ], + "type": "inline_equation", + "content": "p_{vq}" + }, + { + "bbox": [ + 304, + 366, + 545, + 438 + ], + "type": "text", + "content": " with a set-abstraction layer [33], to formulate the vote query feature " + }, + { + "bbox": [ + 304, + 366, + 545, + 438 + ], + "type": "inline_equation", + "content": "f_{vq} \\in \\mathbb{R}^{256 \\times 256}" + }, + { + "bbox": [ + 304, + 366, + 545, + 438 + ], + "type": "text", + "content": ". We represent vote query as " + }, + { + "bbox": [ + 304, + 366, + 545, + 438 + ], + "type": "inline_equation", + "content": "(p_{vq}, f_{vq})" + }, + { + "bbox": [ + 304, + 366, + 545, + 438 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 439, + 545, + 476 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 439, + 545, + 476 + ], + "spans": [ + { + "bbox": [ + 304, + 439, + 545, + 476 + ], + "type": "text", + "content": "Following 3DETR [27], our model adopts an eight-layer transformer decoder, and the " + }, + { + "bbox": [ + 304, + 439, + 545, + 476 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 304, + 439, + 545, + 476 + ], + "type": "text", + "content": "-th layer's input query feature " + }, + { + "bbox": [ + 304, + 439, + 545, + 476 + ], + "type": "inline_equation", + "content": "f_{query}^{i}" + }, + { + "bbox": [ + 304, + 439, + 545, + 476 + ], + "type": "text", + "content": " is calculated through" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 315, + 484, + 545, + 499 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 315, + 484, + 545, + 499 + ], + "spans": [ + { + "bbox": [ + 315, + 484, + 545, + 499 + ], + "type": "interline_equation", + "content": "f _ {q u e r y} ^ {i} = \\operatorname {L a y e r} _ {i - 1} \\left(f _ {q u e r y} ^ {i - 1} + F F N \\left(P E \\left(p _ {v q}\\right)\\right)\\right), \\tag {2}", + "image_path": "d9abec20eac50e33dfea8bc008d3a656c5bd669e21125056e1b0afde61d7b0bc.jpg" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 506, + 545, + 579 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 506, + 545, + 579 + ], + "spans": [ + { + "bbox": [ + 304, + 506, + 545, + 579 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 506, + 545, + 579 + ], + "type": "inline_equation", + "content": "f_{query}^{0} = f_{vq}" + }, + { + "bbox": [ + 304, + 506, + 545, + 579 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 304, + 506, + 545, + 579 + ], + "type": "inline_equation", + "content": "PE(\\cdot)" + }, + { + "bbox": [ + 304, + 506, + 545, + 579 + ], + "type": "text", + "content": " is the 3D Fourier positional encoding function [35]. Experiments in later sections demonstrate that: 1) Vote query injects additional spatial bias to object detection and boosts the detection performance. 2) Encoding features from the point cloud as initial queries accelerates convergence." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 306, + 586, + 411, + 599 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 586, + 411, + 599 + ], + "spans": [ + { + "bbox": [ + 306, + 586, + 411, + 599 + ], + "type": "text", + "content": "3.3. Parallel Decoding" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 605, + 545, + 640 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 545, + 640 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 545, + 640 + ], + "type": "text", + "content": "We adopt two task-specific heads for simultaneous object detection and caption generation. The two task heads are agnostic to each other's output." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "type": "text", + "content": "Detection Head. Detecting objects in a 3D scene requires box corner estimation " + }, + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\hat{B}" + }, + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "type": "text", + "content": " and class estimation " + }, + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\hat{S}" + }, + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "type": "text", + "content": " (containing \"no object\" class) from each object query feature. Following 3DETR [27], box corner estimation is generated by learning spatial offset from a query point to an object's center and box size regression. All subtasks are implemented" + } + ] + } + ], + "index": 21 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "type": "text", + "content": "11126" + } + ] + } + ], + "index": 22 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 49, + 61, + 231, + 275 + ], + "blocks": [ + { + "bbox": [ + 49, + 61, + 231, + 275 + ], + "lines": [ + { + "bbox": [ + 49, + 61, + 231, + 275 + ], + "spans": [ + { + "bbox": [ + 49, + 61, + 231, + 275 + ], + "type": "image", + "image_path": "37b209ed6ca2864135c523d8cf2fe09e1f818b93f825c68fe8ee16396787b438.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 277, + 547, + 333 + ], + "lines": [ + { + "bbox": [ + 46, + 277, + 547, + 333 + ], + "spans": [ + { + "bbox": [ + 46, + 277, + 547, + 333 + ], + "type": "text", + "content": "Figure 2. Approach. Vote2Cap-DETR is a one-stage transformer model that takes a 3D point cloud as its input, and generates a set of box predictions and sentences localizing and describing each object in the point cloud. The scene encoder first generates encoded scene tokens " + }, + { + "bbox": [ + 46, + 277, + 547, + 333 + ], + "type": "inline_equation", + "content": "(p_{enc}, f_{enc})" + }, + { + "bbox": [ + 46, + 277, + 547, + 333 + ], + "type": "text", + "content": " from the input point cloud. Then, we generate vote query " + }, + { + "bbox": [ + 46, + 277, + 547, + 333 + ], + "type": "inline_equation", + "content": "(p_{vq}, f_{vq})" + }, + { + "bbox": [ + 46, + 277, + 547, + 333 + ], + "type": "text", + "content": " from the encoded scene tokens, which introduce both spatial bias " + }, + { + "bbox": [ + 46, + 277, + 547, + 333 + ], + "type": "inline_equation", + "content": "p_{vq}" + }, + { + "bbox": [ + 46, + 277, + 547, + 333 + ], + "type": "text", + "content": " and content-aware feature " + }, + { + "bbox": [ + 46, + 277, + 547, + 333 + ], + "type": "inline_equation", + "content": "f_{vq}" + }, + { + "bbox": [ + 46, + 277, + 547, + 333 + ], + "type": "text", + "content": " to initial object queries. The transformer decoder decodes each vote query with two parallel task heads for captioning and detection. We optimize Vote2Cap-DETR with a set loss." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 235, + 62, + 395, + 275 + ], + "blocks": [ + { + "bbox": [ + 235, + 62, + 395, + 275 + ], + "lines": [ + { + "bbox": [ + 235, + 62, + 395, + 275 + ], + "spans": [ + { + "bbox": [ + 235, + 62, + 395, + 275 + ], + "type": "image", + "image_path": "bb0740e2ed932f39423205db07b664eb02d165c8b20ae85b9140146b0217bac1.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 395, + 61, + 547, + 274 + ], + "blocks": [ + { + "bbox": [ + 395, + 61, + 547, + 274 + ], + "lines": [ + { + "bbox": [ + 395, + 61, + 547, + 274 + ], + "spans": [ + { + "bbox": [ + 395, + 61, + 547, + 274 + ], + "type": "image", + "image_path": "3ea17e8bfdfd5eb2f57ce342a4f0195e6ddf39fd91bf15f18c0533ea1a50f37c.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 74, + 347, + 259, + 437 + ], + "blocks": [ + { + "bbox": [ + 74, + 347, + 259, + 437 + ], + "lines": [ + { + "bbox": [ + 74, + 347, + 259, + 437 + ], + "spans": [ + { + "bbox": [ + 74, + 347, + 259, + 437 + ], + "type": "image", + "image_path": "ba46b383ed21182412643127266501b8e266daecd41dd6cb69d258f7407e93e5.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 439, + 288, + 483 + ], + "lines": [ + { + "bbox": [ + 46, + 439, + 288, + 483 + ], + "spans": [ + { + "bbox": [ + 46, + 439, + 288, + 483 + ], + "type": "text", + "content": "Figure 3. Vote Query Generation. Vote query " + }, + { + "bbox": [ + 46, + 439, + 288, + 483 + ], + "type": "inline_equation", + "content": "p_{vq}" + }, + { + "bbox": [ + 46, + 439, + 288, + 483 + ], + "type": "text", + "content": " contains spatial bias " + }, + { + "bbox": [ + 46, + 439, + 288, + 483 + ], + "type": "inline_equation", + "content": "(\\Delta p_{vote})" + }, + { + "bbox": [ + 46, + 439, + 288, + 483 + ], + "type": "text", + "content": " to initial object queries " + }, + { + "bbox": [ + 46, + 439, + 288, + 483 + ], + "type": "inline_equation", + "content": "(p_{seed})" + }, + { + "bbox": [ + 46, + 439, + 288, + 483 + ], + "type": "text", + "content": ", which are sampled from the scene with farthest point sampling (FPS) and gathered feature " + }, + { + "bbox": [ + 46, + 439, + 288, + 483 + ], + "type": "inline_equation", + "content": "f_{vq}" + }, + { + "bbox": [ + 46, + 439, + 288, + 483 + ], + "type": "text", + "content": " from the point cloud for each query." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 494, + 287, + 529 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 494, + 287, + 529 + ], + "spans": [ + { + "bbox": [ + 46, + 494, + 287, + 529 + ], + "type": "text", + "content": "by FFNs. In practice, the object localization head is shared through different layers in the decoder, following all existing works on DETR [5, 12, 26, 27]." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 532, + 287, + 616 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 532, + 287, + 616 + ], + "spans": [ + { + "bbox": [ + 46, + 532, + 287, + 616 + ], + "type": "text", + "content": "Caption Head. 3D dense captioning requires attribute details on an object and its relation with its close surroundings. However, the vote query itself is agnostic to box predictions and fails to provide adequate attribute and spatial relations for informative caption generation. Therefore, the main difficulty is how to leverage sufficient surrounding contextual information without confusing the caption head." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 617, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 617, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 617, + 288, + 714 + ], + "type": "text", + "content": "To address the above issues, we propose Dual-Clued Captioner(DCC), a lightweight transformer decoder-based caption head, for 3D dense captioning. DCC consists of a stack of 2 identical transformer decoder blocks, sinusoid position embedding, and a linear classification head. To generate informative captions, DCC receives two streams of visual clue " + }, + { + "bbox": [ + 46, + 617, + 288, + 714 + ], + "type": "inline_equation", + "content": "\\mathcal{V} = (\\mathcal{V}^q,\\mathcal{V}^s)" + }, + { + "bbox": [ + 46, + 617, + 288, + 714 + ], + "type": "text", + "content": ". Here, " + }, + { + "bbox": [ + 46, + 617, + 288, + 714 + ], + "type": "inline_equation", + "content": "\\mathcal{V}^q" + }, + { + "bbox": [ + 46, + 617, + 288, + 714 + ], + "type": "text", + "content": " is the last decoder layer's output feature of a vote query, and " + }, + { + "bbox": [ + 46, + 617, + 288, + 714 + ], + "type": "inline_equation", + "content": "\\mathcal{V}^s" + }, + { + "bbox": [ + 46, + 617, + 288, + 714 + ], + "type": "text", + "content": " is contextual" + } + ] + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 317, + 344, + 533, + 437 + ], + "blocks": [ + { + "bbox": [ + 317, + 344, + 533, + 437 + ], + "lines": [ + { + "bbox": [ + 317, + 344, + 533, + 437 + ], + "spans": [ + { + "bbox": [ + 317, + 344, + 533, + 437 + ], + "type": "image", + "image_path": "6764c5eb6eaf5a0a7e742b12fa983de332de13ac43c63dcf9f7ee89550868083.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 439, + 546, + 495 + ], + "lines": [ + { + "bbox": [ + 304, + 439, + 546, + 495 + ], + "spans": [ + { + "bbox": [ + 304, + 439, + 546, + 495 + ], + "type": "text", + "content": "Figure 4. Dual-Clued Captioner(DCC). DCC is a lightweight transformer based caption head that uses vote query feature " + }, + { + "bbox": [ + 304, + 439, + 546, + 495 + ], + "type": "inline_equation", + "content": "\\mathcal{V}_q" + }, + { + "bbox": [ + 304, + 439, + 546, + 495 + ], + "type": "text", + "content": " as caption perfix to identify the region to be described, and contextual features " + }, + { + "bbox": [ + 304, + 439, + 546, + 495 + ], + "type": "inline_equation", + "content": "\\nu_{s}" + }, + { + "bbox": [ + 304, + 439, + 546, + 495 + ], + "type": "text", + "content": " surrounding the vote query to complement with more surrounding information for descriptive caption generation." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 502, + 546, + 622 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 502, + 546, + 622 + ], + "spans": [ + { + "bbox": [ + 304, + 502, + 546, + 622 + ], + "type": "text", + "content": "information surrounding the absolute location of each vote query. When generating a caption for a proposal, we substitute the standard Start Of Sequenec( 'SOS') prefix with " + }, + { + "bbox": [ + 304, + 502, + 546, + 622 + ], + "type": "inline_equation", + "content": "\\nu^q" + }, + { + "bbox": [ + 304, + 502, + 546, + 622 + ], + "type": "text", + "content": " to identify the object to be described following [39]. Since the vote query is agnostic of actual neighbor object proposals because of the parallel detection branch, we introduce the vote query's " + }, + { + "bbox": [ + 304, + 502, + 546, + 622 + ], + "type": "inline_equation", + "content": "k_{s}" + }, + { + "bbox": [ + 304, + 502, + 546, + 622 + ], + "type": "text", + "content": " nearest local context token features as its local surroundings " + }, + { + "bbox": [ + 304, + 502, + 546, + 622 + ], + "type": "inline_equation", + "content": "\\nu^{s}" + }, + { + "bbox": [ + 304, + 502, + 546, + 622 + ], + "type": "text", + "content": " as keys for cross attention. During inference, we generate captions through beam search with a beam size of 5." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 632, + 533, + 646 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 632, + 533, + 646 + ], + "spans": [ + { + "bbox": [ + 306, + 632, + 533, + 646 + ], + "type": "text", + "content": "3.4. Set prediction loss for 3D Dense Captioning" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 651, + 546, + 688 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 651, + 546, + 688 + ], + "spans": [ + { + "bbox": [ + 304, + 651, + 546, + 688 + ], + "type": "text", + "content": "Our proposed Vote2Cap-DETR requires supervision for vote query " + }, + { + "bbox": [ + 304, + 651, + 546, + 688 + ], + "type": "inline_equation", + "content": "(\\mathcal{L}_{vq})" + }, + { + "bbox": [ + 304, + 651, + 546, + 688 + ], + "type": "text", + "content": ", detection head " + }, + { + "bbox": [ + 304, + 651, + 546, + 688 + ], + "type": "inline_equation", + "content": "(\\mathcal{L}_{det})" + }, + { + "bbox": [ + 304, + 651, + 546, + 688 + ], + "type": "text", + "content": ", and caption head " + }, + { + "bbox": [ + 304, + 651, + 546, + 688 + ], + "type": "inline_equation", + "content": "(\\mathcal{L}_{cap})" + }, + { + "bbox": [ + 304, + 651, + 546, + 688 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 689, + 546, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 689, + 546, + 715 + ], + "spans": [ + { + "bbox": [ + 305, + 689, + 546, + 715 + ], + "type": "text", + "content": "Vote Query Loss. We borrow vote loss from VoteNet [32] as " + }, + { + "bbox": [ + 305, + 689, + 546, + 715 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{vq}" + }, + { + "bbox": [ + 305, + 689, + 546, + 715 + ], + "type": "text", + "content": ", to help the vote query generation module learn to" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "11127" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 201, + 84 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 201, + 84 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 201, + 84 + ], + "type": "text", + "content": "shift points " + }, + { + "bbox": [ + 47, + 72, + 201, + 84 + ], + "type": "inline_equation", + "content": "p_{enc}" + }, + { + "bbox": [ + 47, + 72, + 201, + 84 + ], + "type": "text", + "content": " to an object's center:" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 55, + 95, + 287, + 129 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 55, + 95, + 287, + 129 + ], + "spans": [ + { + "bbox": [ + 55, + 95, + 287, + 129 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {v q} = \\frac {1}{M} \\sum_ {i = 1} ^ {M} \\sum_ {j = 1} ^ {N _ {g t}} \\left\\| p _ {v o t e} ^ {i} - c n t _ {j} \\right\\| _ {1} \\cdot \\mathbb {I} \\left\\{p _ {e n c} ^ {i} \\in I _ {j} \\right\\}. \\tag {3}", + "image_path": "dee9cd32fcb43d763a6c17a029d323e6d0de5f213801952877f9cdcafbfa4f24.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 139, + 287, + 187 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 139, + 287, + 187 + ], + "spans": [ + { + "bbox": [ + 47, + 139, + 287, + 187 + ], + "type": "text", + "content": "Here, " + }, + { + "bbox": [ + 47, + 139, + 287, + 187 + ], + "type": "inline_equation", + "content": "\\mathbb{I}(\\cdot)" + }, + { + "bbox": [ + 47, + 139, + 287, + 187 + ], + "type": "text", + "content": " is an indicator function that equals 1 when the condition meets and 0 otherwise, " + }, + { + "bbox": [ + 47, + 139, + 287, + 187 + ], + "type": "inline_equation", + "content": "N_{gt}" + }, + { + "bbox": [ + 47, + 139, + 287, + 187 + ], + "type": "text", + "content": " is the number of instances in a 3D scene, " + }, + { + "bbox": [ + 47, + 139, + 287, + 187 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 47, + 139, + 287, + 187 + ], + "type": "text", + "content": " is the size of " + }, + { + "bbox": [ + 47, + 139, + 287, + 187 + ], + "type": "inline_equation", + "content": "p_{vote}" + }, + { + "bbox": [ + 47, + 139, + 287, + 187 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 47, + 139, + 287, + 187 + ], + "type": "inline_equation", + "content": "cnt_j" + }, + { + "bbox": [ + 47, + 139, + 287, + 187 + ], + "type": "text", + "content": " is the center of " + }, + { + "bbox": [ + 47, + 139, + 287, + 187 + ], + "type": "inline_equation", + "content": "j" + }, + { + "bbox": [ + 47, + 139, + 287, + 187 + ], + "type": "text", + "content": "th instance " + }, + { + "bbox": [ + 47, + 139, + 287, + 187 + ], + "type": "inline_equation", + "content": "I_j" + }, + { + "bbox": [ + 47, + 139, + 287, + 187 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 189, + 287, + 248 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 189, + 287, + 248 + ], + "spans": [ + { + "bbox": [ + 47, + 189, + 287, + 248 + ], + "type": "text", + "content": "Detection Loss. Following 3DETR [27], we use the same Hungarian algorithm to assign each proposal with a ground truth label. Since 3D dense captioning cares much for the object localization ability, we apply a larger weight on the gIoU loss in set loss [27]:" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 259, + 287, + 282 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 259, + 287, + 282 + ], + "spans": [ + { + "bbox": [ + 47, + 259, + 287, + 282 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {s e t} = \\alpha_ {1} \\mathcal {L} _ {g i o u} + \\alpha_ {2} \\mathcal {L} _ {c l s} + \\alpha_ {3} \\mathcal {L} _ {\\text {c e n t e r - r e g}} + \\alpha_ {4} \\mathcal {L} _ {\\text {s i z e - r e g}}, \\tag {4}", + "image_path": "d83bbeabf4a99940c059bb97aab96729f97cbe5f0002ccbf8b5d87f32351a97c.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 283, + 287, + 319 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 283, + 287, + 319 + ], + "spans": [ + { + "bbox": [ + 47, + 283, + 287, + 319 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 283, + 287, + 319 + ], + "type": "inline_equation", + "content": "\\alpha_{1} = 10" + }, + { + "bbox": [ + 47, + 283, + 287, + 319 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 283, + 287, + 319 + ], + "type": "inline_equation", + "content": "\\alpha_{2} = 1" + }, + { + "bbox": [ + 47, + 283, + 287, + 319 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 283, + 287, + 319 + ], + "type": "inline_equation", + "content": "\\alpha_{3} = 5" + }, + { + "bbox": [ + 47, + 283, + 287, + 319 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 283, + 287, + 319 + ], + "type": "inline_equation", + "content": "\\alpha_{4} = 1" + }, + { + "bbox": [ + 47, + 283, + 287, + 319 + ], + "type": "text", + "content": " are set heuristically. The set loss " + }, + { + "bbox": [ + 47, + 283, + 287, + 319 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{set}" + }, + { + "bbox": [ + 47, + 283, + 287, + 319 + ], + "type": "text", + "content": " is applied to all " + }, + { + "bbox": [ + 47, + 283, + 287, + 319 + ], + "type": "inline_equation", + "content": "n_{dec - layer}" + }, + { + "bbox": [ + 47, + 283, + 287, + 319 + ], + "type": "text", + "content": " layers in the decoder for better convergence." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 320, + 287, + 406 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 320, + 287, + 406 + ], + "spans": [ + { + "bbox": [ + 47, + 320, + 287, + 406 + ], + "type": "text", + "content": "Caption Loss. Following the standard practice of image captioning, we train our caption head first with standard cross-entropy loss (MLE training), and then fine-tune it with Self-Critical Sequence Training (SCST) [34]. During MLE training, the model is trained to predict the " + }, + { + "bbox": [ + 47, + 320, + 287, + 406 + ], + "type": "inline_equation", + "content": "(t + 1)" + }, + { + "bbox": [ + 47, + 320, + 287, + 406 + ], + "type": "text", + "content": "th word " + }, + { + "bbox": [ + 47, + 320, + 287, + 406 + ], + "type": "inline_equation", + "content": "c_i^{t + 1}" + }, + { + "bbox": [ + 47, + 320, + 287, + 406 + ], + "type": "text", + "content": ", given the first " + }, + { + "bbox": [ + 47, + 320, + 287, + 406 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 47, + 320, + 287, + 406 + ], + "type": "text", + "content": " words " + }, + { + "bbox": [ + 47, + 320, + 287, + 406 + ], + "type": "inline_equation", + "content": "c_i^{[1:t]}" + }, + { + "bbox": [ + 47, + 320, + 287, + 406 + ], + "type": "text", + "content": " and the visual clue " + }, + { + "bbox": [ + 47, + 320, + 287, + 406 + ], + "type": "inline_equation", + "content": "\\mathcal{V}" + }, + { + "bbox": [ + 47, + 320, + 287, + 406 + ], + "type": "text", + "content": ". The loss function for a " + }, + { + "bbox": [ + 47, + 320, + 287, + 406 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 47, + 320, + 287, + 406 + ], + "type": "text", + "content": "-length sentence is defined as:" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 60, + 416, + 287, + 449 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 60, + 416, + 287, + 449 + ], + "spans": [ + { + "bbox": [ + 60, + 416, + 287, + 449 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {c _ {i}} = \\sum_ {i = 1} ^ {T} \\mathcal {L} _ {c _ {i}} (t) = - \\sum_ {i = 1} ^ {T} \\log \\hat {P} \\left(c _ {i} ^ {t + 1} | \\mathcal {V}, c _ {i} ^ {[ 1: t ]}\\right). \\tag {5}", + "image_path": "ee2d8fa8dd17f4317a703e4183d3e7dd24a724041abdeb5aa5ff94a203562649.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 458, + 287, + 517 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 458, + 287, + 517 + ], + "spans": [ + { + "bbox": [ + 47, + 458, + 287, + 517 + ], + "type": "text", + "content": "After the caption head is trained under word-level supervision, we fine-tune it with SCST. During SCST, the model generates multiple captions " + }, + { + "bbox": [ + 47, + 458, + 287, + 517 + ], + "type": "inline_equation", + "content": "\\hat{c}_{1,\\dots,k}" + }, + { + "bbox": [ + 47, + 458, + 287, + 517 + ], + "type": "text", + "content": " with a beam size of " + }, + { + "bbox": [ + 47, + 458, + 287, + 517 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 47, + 458, + 287, + 517 + ], + "type": "text", + "content": " and another " + }, + { + "bbox": [ + 47, + 458, + 287, + 517 + ], + "type": "inline_equation", + "content": "\\hat{g}" + }, + { + "bbox": [ + 47, + 458, + 287, + 517 + ], + "type": "text", + "content": " through greedy search as a baseline. The loss function for SCST is defined as:" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 61, + 526, + 287, + 559 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 61, + 526, + 287, + 559 + ], + "spans": [ + { + "bbox": [ + 61, + 526, + 287, + 559 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {c _ {i}} = - \\sum_ {i = 1} ^ {k} \\left(R \\left(\\hat {c} _ {i}\\right) - R (\\hat {g})\\right) \\cdot \\frac {1}{| \\hat {c} _ {i} |} \\log \\hat {P} (\\hat {c} _ {i} | \\mathcal {V}). \\tag {6}", + "image_path": "61ae5b28678a9042d76e5633ab843edd81fa7969817e6a2c84fe36a8ca4543d1.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 568, + 287, + 616 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 568, + 287, + 616 + ], + "spans": [ + { + "bbox": [ + 47, + 568, + 287, + 616 + ], + "type": "text", + "content": "Here, the reward function " + }, + { + "bbox": [ + 47, + 568, + 287, + 616 + ], + "type": "inline_equation", + "content": "R(\\cdot)" + }, + { + "bbox": [ + 47, + 568, + 287, + 616 + ], + "type": "text", + "content": " is the CIDEr metric for caption evaluation, and the log probability of caption " + }, + { + "bbox": [ + 47, + 568, + 287, + 616 + ], + "type": "inline_equation", + "content": "\\hat{c}_i" + }, + { + "bbox": [ + 47, + 568, + 287, + 616 + ], + "type": "text", + "content": " is normalized by caption length " + }, + { + "bbox": [ + 47, + 568, + 287, + 616 + ], + "type": "inline_equation", + "content": "|\\hat{c}_i|" + }, + { + "bbox": [ + 47, + 568, + 287, + 616 + ], + "type": "text", + "content": " to encourage the model to treat captions in different length with equal importance." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 47, + 617, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 617, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 47, + 617, + 287, + 714 + ], + "type": "text", + "content": "Set to Set Training for 3D Dense Captioning. We propose an easy-to-implement set-to-set training strategy for 3D dense captioning. Given a 3D scene, we randomly sample one sentence from the corpus for each annotated instance. Then, we assign language annotations to the corresponding number of proposals in the corresponding scene with the same Hungarian algorithm. During training, we average losses for captions " + }, + { + "bbox": [ + 47, + 617, + 287, + 714 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{c_i}" + }, + { + "bbox": [ + 47, + 617, + 287, + 714 + ], + "type": "text", + "content": " on all annotated instances in" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 72, + 545, + 95 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 72, + 545, + 95 + ], + "spans": [ + { + "bbox": [ + 306, + 72, + 545, + 95 + ], + "type": "text", + "content": "a batch to compute the caption loss " + }, + { + "bbox": [ + 306, + 72, + 545, + 95 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{cap}" + }, + { + "bbox": [ + 306, + 72, + 545, + 95 + ], + "type": "text", + "content": ". To balance loss for different tasks, our loss function is defined as:" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 338, + 102, + 545, + 134 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 338, + 102, + 545, + 134 + ], + "spans": [ + { + "bbox": [ + 338, + 102, + 545, + 134 + ], + "type": "interline_equation", + "content": "\\mathcal {L} = \\beta_ {1} \\mathcal {L} _ {v q} + \\beta_ {2} \\sum_ {i = 1} ^ {n _ {\\text {d e c - l a y e r}}} \\mathcal {L} _ {\\text {s e t}} + \\beta_ {3} \\mathcal {L} _ {\\text {c a p}}, \\tag {7}", + "image_path": "24a85cead2b458b9a8b3454cf1e5a9bc96186038ba111d082e50e7e6fba7a5a5.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 139, + 517, + 152 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 139, + 517, + 152 + ], + "spans": [ + { + "bbox": [ + 306, + 139, + 517, + 152 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 306, + 139, + 517, + 152 + ], + "type": "inline_equation", + "content": "\\beta_{1} = 10, \\beta_{2} = 1, \\beta_{3} = 5" + }, + { + "bbox": [ + 306, + 139, + 517, + 152 + ], + "type": "text", + "content": " are set heuristically." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 161, + 386, + 174 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 161, + 386, + 174 + ], + "spans": [ + { + "bbox": [ + 306, + 161, + 386, + 174 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 181, + 545, + 264 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 181, + 545, + 264 + ], + "spans": [ + { + "bbox": [ + 305, + 181, + 545, + 264 + ], + "type": "text", + "content": "We first present the datasets, metrics, and implementation details for 3D dense captioning (section 4.1). Then, we provide comparisons with all state-of-the-art methods (section 4.2). We also provide studies on the effectiveness of different parts in our model (section 4.3). Finally, we visualize several qualitative results to address the effectiveness of our method (section 4.4)." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 271, + 545, + 283 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 271, + 545, + 283 + ], + "spans": [ + { + "bbox": [ + 306, + 271, + 545, + 283 + ], + "type": "text", + "content": "4.1. Datasets, Metrics, and Implementation Details" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 305, + 290, + 545, + 373 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 290, + 545, + 373 + ], + "spans": [ + { + "bbox": [ + 305, + 290, + 545, + 373 + ], + "type": "text", + "content": "Datasets. We analyze performance on ScanRefer [6] and " + }, + { + "bbox": [ + 305, + 290, + 545, + 373 + ], + "type": "inline_equation", + "content": "\\mathrm{Nr3D}" + }, + { + "bbox": [ + 305, + 290, + 545, + 373 + ], + "type": "text", + "content": " [1], both of which are built on 3D scenes from ScanNet [15]. ScanRefer/Nr3D contains 36,665/32,919 freeform language annotations describing 7,875/4,664 objects from 562/511 out of 1201 3D scenes in ScanNet for training and evaluates on 9,508/8,584 sentences for 2,068/1,214 objects from 141/130 out of 312 3D scenes in ScanNet." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 305, + 375, + 545, + 508 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 375, + 545, + 508 + ], + "spans": [ + { + "bbox": [ + 305, + 375, + 545, + 508 + ], + "type": "text", + "content": "Evaluation Metrics. Following [4, 13, 20, 39], we first apply NMS on object proposals to drop duplicate object predictions. Each object proposal is a box-caption pair " + }, + { + "bbox": [ + 305, + 375, + 545, + 508 + ], + "type": "inline_equation", + "content": "(\\hat{b}_i, \\hat{c}_i)" + }, + { + "bbox": [ + 305, + 375, + 545, + 508 + ], + "type": "text", + "content": ", containing box corner prediction " + }, + { + "bbox": [ + 305, + 375, + 545, + 508 + ], + "type": "inline_equation", + "content": "\\hat{b}_i" + }, + { + "bbox": [ + 305, + 375, + 545, + 508 + ], + "type": "text", + "content": " and generated caption " + }, + { + "bbox": [ + 305, + 375, + 545, + 508 + ], + "type": "inline_equation", + "content": "\\hat{c}_i" + }, + { + "bbox": [ + 305, + 375, + 545, + 508 + ], + "type": "text", + "content": ". Then, each annotated instance is assigned an object proposal with the largest IoU among the remaining proposals. Here, we use " + }, + { + "bbox": [ + 305, + 375, + 545, + 508 + ], + "type": "inline_equation", + "content": "(b_i, C_i)" + }, + { + "bbox": [ + 305, + 375, + 545, + 508 + ], + "type": "text", + "content": " to represent an instance's label, where " + }, + { + "bbox": [ + 305, + 375, + 545, + 508 + ], + "type": "inline_equation", + "content": "b_i" + }, + { + "bbox": [ + 305, + 375, + 545, + 508 + ], + "type": "text", + "content": " is an instance's box corner label, and " + }, + { + "bbox": [ + 305, + 375, + 545, + 508 + ], + "type": "inline_equation", + "content": "C_i" + }, + { + "bbox": [ + 305, + 375, + 545, + 508 + ], + "type": "text", + "content": " is the corpus containing all caption annotations for this instance. To jointly evaluate the model's localization and caption generation capability, we adopt the " + }, + { + "bbox": [ + 305, + 375, + 545, + 508 + ], + "type": "inline_equation", + "content": "m@kIoU" + }, + { + "bbox": [ + 305, + 375, + 545, + 508 + ], + "type": "text", + "content": " metric [13]:" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 312, + 514, + 545, + 557 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 514, + 545, + 557 + ], + "spans": [ + { + "bbox": [ + 312, + 514, + 545, + 557 + ], + "type": "interline_equation", + "content": "m @ k I o U = \\frac {1}{N} \\sum_ {i = 1} ^ {N} m \\left(\\hat {c} _ {i}, C _ {i}\\right) \\cdot \\mathbb {I} \\left\\{I o U \\left(\\hat {b} _ {i}, b _ {i}\\right) \\geq k \\right\\}. \\tag {8}", + "image_path": "7867626a2e6f8a74a2a7c923069b7f94a59a2fbd34416485bbff4edc545143a8.jpg" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 305, + 557, + 545, + 605 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 557, + 545, + 605 + ], + "spans": [ + { + "bbox": [ + 305, + 557, + 545, + 605 + ], + "type": "text", + "content": "Here, " + }, + { + "bbox": [ + 305, + 557, + 545, + 605 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 305, + 557, + 545, + 605 + ], + "type": "text", + "content": " is the number of total annotated instances in the evaluation dataset, and " + }, + { + "bbox": [ + 305, + 557, + 545, + 605 + ], + "type": "inline_equation", + "content": "m" + }, + { + "bbox": [ + 305, + 557, + 545, + 605 + ], + "type": "text", + "content": " could be any metric for natural language generation, such as CIDEr [38], METEOR [3], BLEU-4 [31], and ROUGE-L [22]." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 305, + 605, + 545, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 605, + 545, + 689 + ], + "spans": [ + { + "bbox": [ + 305, + 605, + 545, + 689 + ], + "type": "text", + "content": "Implementation Details. We offer implementation details of different baselines. \"w/o additional 2D\" means the input " + }, + { + "bbox": [ + 305, + 605, + 545, + 689 + ], + "type": "inline_equation", + "content": "\\mathcal{PC} \\in \\mathbb{R}^{40,000 \\times 10}" + }, + { + "bbox": [ + 305, + 605, + 545, + 689 + ], + "type": "text", + "content": " contains absolute location as well as color, normal and height for 40,000 points representing a 3D scene. \"additional 2D\" means we replace color information with 128-dimensional multiview feature extracted by ENet [8] from 2D images following [13]." + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "type": "text", + "content": "We first pre-train the whole network without the caption head on ScanNet [15] for 1,080 epochs (163k iterations," + } + ] + } + ], + "index": 23 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "11128" + } + ] + } + ], + "index": 24 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 277 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 277 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 277 + ], + "type": "inline_equation", + "content": "\\sim 34" + }, + { + "bbox": [ + 46, + 72, + 289, + 277 + ], + "type": "text", + "content": " hours) using an AdamW optimizer [25] with a learning rate decaying from " + }, + { + "bbox": [ + 46, + 72, + 289, + 277 + ], + "type": "inline_equation", + "content": "5 \\times 10^{-4}" + }, + { + "bbox": [ + 46, + 72, + 289, + 277 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 46, + 72, + 289, + 277 + ], + "type": "inline_equation", + "content": "10^{-6}" + }, + { + "bbox": [ + 46, + 72, + 289, + 277 + ], + "type": "text", + "content": " by a cosine annealing scheduler, a weight decay of 0.1, a gradient clipping of 0.1, and a batch size of 8 following [27]. Then, we jointly train the full model from pre-trained weights with the MLE caption loss for another 720 epochs (51k/46k iterations for ScanRefer/Nr3D, " + }, + { + "bbox": [ + 46, + 72, + 289, + 277 + ], + "type": "inline_equation", + "content": "\\sim 11 / 10" + }, + { + "bbox": [ + 46, + 72, + 289, + 277 + ], + "type": "text", + "content": " hours). To prevent overfitting, we fix the learning rate of the detector as " + }, + { + "bbox": [ + 46, + 72, + 289, + 277 + ], + "type": "inline_equation", + "content": "10^{-6}" + }, + { + "bbox": [ + 46, + 72, + 289, + 277 + ], + "type": "text", + "content": ", and set that of the caption head decaying from " + }, + { + "bbox": [ + 46, + 72, + 289, + 277 + ], + "type": "inline_equation", + "content": "10^{-4}" + }, + { + "bbox": [ + 46, + 72, + 289, + 277 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 46, + 72, + 289, + 277 + ], + "type": "inline_equation", + "content": "10^{-6}" + }, + { + "bbox": [ + 46, + 72, + 289, + 277 + ], + "type": "text", + "content": " using another cosine annealing scheduler. During SCST, we tune the caption head with a batch size of 2 and freeze the detector for 180 epochs because of high memory cost (50k/46k iterations for ScanRefer/Nr3D, " + }, + { + "bbox": [ + 46, + 72, + 289, + 277 + ], + "type": "inline_equation", + "content": "\\sim 14 / 11" + }, + { + "bbox": [ + 46, + 72, + 289, + 277 + ], + "type": "text", + "content": " hours) with a fixed learning rate of " + }, + { + "bbox": [ + 46, + 72, + 289, + 277 + ], + "type": "inline_equation", + "content": "10^{-6}" + }, + { + "bbox": [ + 46, + 72, + 289, + 277 + ], + "type": "text", + "content": ". We evaluate the model every 2,000 iterations during training for consistency with existing works [13, 39], and all experiments mentioned above are conducted on a single RTX3090 GPU." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 285, + 237, + 300 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 285, + 237, + 300 + ], + "spans": [ + { + "bbox": [ + 47, + 285, + 237, + 300 + ], + "type": "text", + "content": "4.2. Comparison with Existing Methods" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 305, + 289, + 591 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 305, + 289, + 591 + ], + "spans": [ + { + "bbox": [ + 46, + 305, + 289, + 591 + ], + "type": "text", + "content": "In this section, we compare performance with existing works on metrics C, M, B-4, R as abbreviations for CIDEr [38], METEOR [3], BLEU-4 [31], Rouge-L [22] under IoU thresholds of 0.25, 0.5 for ScanRefer (Table 1) and 0.5 for Nr3D (Table 2). In both tables, “-” indicates that neither the original paper nor any follow-up works provide such results. We make separate comparisons for MLE training and SCST since different supervisions on the caption head have huge influence on the captioning performance. Among all the listed methods, experiments other than D3Net [7] and 3DJCG [4] utilize the standard VoteNet [32] detector. Meanwhile, D3Net adopts PointGroup [19], a 3D instance segmentation model, for better object detection. 3DJCG substitute the proposal head with an FCOS [36] head to improve VoteNet's localization performance. Additionally, 3DJCG and D3Net are trained on 3D dense captioning as well as 3D visual grounding to study the joint promotion of both tasks. Among methods listed under SCST, " + }, + { + "bbox": [ + 46, + 305, + 289, + 591 + ], + "type": "inline_equation", + "content": "\\chi" + }, + { + "bbox": [ + 46, + 305, + 289, + 591 + ], + "type": "text", + "content": "-Trans2Cap [43] combines MLE training with standard SCST in an additive manner, while Scan2Cap and D3Net [7] adopt the same reward that combines CIDEr score with a listener's [47] grounding loss by weighted summation. Meanwhile, our method adopts the standard SCST with CIDEr reward." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 593, + 288, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 593, + 288, + 689 + ], + "spans": [ + { + "bbox": [ + 46, + 593, + 288, + 689 + ], + "type": "text", + "content": "Table 1 reports comparisons on ScanRefer [6] validation dataset. Our Vote2Cap-DETR surpasses current state-of-the-art methods. Under MLE training with additional 2D inputs, Vote2Cap-DETR achieves " + }, + { + "bbox": [ + 46, + 593, + 288, + 689 + ], + "type": "inline_equation", + "content": "59.32\\%" + }, + { + "bbox": [ + 46, + 593, + 288, + 689 + ], + "type": "text", + "content": " C@0.5 while 3DJCG [4] achieves " + }, + { + "bbox": [ + 46, + 593, + 288, + 689 + ], + "type": "inline_equation", + "content": "49.48\\%" + }, + { + "bbox": [ + 46, + 593, + 288, + 689 + ], + "type": "text", + "content": " (9.84% C@0.5↑) with additional training data. Under SCST, our Vote2Cap-DETR achieves " + }, + { + "bbox": [ + 46, + 593, + 288, + 689 + ], + "type": "inline_equation", + "content": "70.63\\%" + }, + { + "bbox": [ + 46, + 593, + 288, + 689 + ], + "type": "text", + "content": " C@0.5 comparing to " + }, + { + "bbox": [ + 46, + 593, + 288, + 689 + ], + "type": "inline_equation", + "content": "62.64\\%" + }, + { + "bbox": [ + 46, + 593, + 288, + 689 + ], + "type": "text", + "content": " (7.99% C@0.5↑) for current state-of-the-art D3Net [7]." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 689, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 288, + 715 + ], + "type": "text", + "content": "In Table 2, we list results on the Nr3D [1] dataset with additional 2D input following [39]. Since Scan2Cap [13]" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 72, + 547, + 120 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 120 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 120 + ], + "type": "text", + "content": "has not reported results on " + }, + { + "bbox": [ + 304, + 72, + 547, + 120 + ], + "type": "inline_equation", + "content": "\\mathrm{Nr3D}" + }, + { + "bbox": [ + 304, + 72, + 547, + 120 + ], + "type": "text", + "content": ", we adopt the best-reported result from [4]. Our Vote2Cap-DETR also surpasses current state-of-the-art methods (5.78%/7.11% C@0.5↑ for MLE training/SCST)." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 305, + 130, + 400, + 144 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 130, + 400, + 144 + ], + "spans": [ + { + "bbox": [ + 305, + 130, + 400, + 144 + ], + "type": "text", + "content": "4.3. Ablation Study" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 150, + 547, + 186 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 150, + 547, + 186 + ], + "spans": [ + { + "bbox": [ + 304, + 150, + 547, + 186 + ], + "type": "text", + "content": "Since 3D dense captioning concerns both localization and caption generation, we perform ablation studies to understand the effectiveness of different components." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 188, + 548, + 369 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 188, + 548, + 369 + ], + "spans": [ + { + "bbox": [ + 304, + 188, + 548, + 369 + ], + "type": "text", + "content": "Does the vote query improve 3DETR? We performed ablation experiments in Table 3 and Figure 5 to see if the vote query can improve 3DETR's localization and convergence. We notice that introducing position features " + }, + { + "bbox": [ + 304, + 188, + 548, + 369 + ], + "type": "inline_equation", + "content": "p_{vq}" + }, + { + "bbox": [ + 304, + 188, + 548, + 369 + ], + "type": "text", + "content": " alone helps improve detection performance (0.97% mAP50↑). However, it (green line in Figure 5) converges slower in the earlier training procedure than the 3DETR baseline (blue line in Figure 5), inferring the vote query generation module is not well learned to predict accurate spatial offset estimations at early training epochs. Introducing additional content feature " + }, + { + "bbox": [ + 304, + 188, + 548, + 369 + ], + "type": "inline_equation", + "content": "f_{vq}" + }, + { + "bbox": [ + 304, + 188, + 548, + 369 + ], + "type": "text", + "content": " in vote query features results in another boost in both detection performance (2.98% mAP50↑) and training speed (red line in Figure 5). The overall localization performance of Vote2Cap-DETR is about 7.2% mAP higher than the popular VoteNet." + } + ] + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 310, + 375, + 542, + 503 + ], + "blocks": [ + { + "bbox": [ + 310, + 375, + 542, + 503 + ], + "lines": [ + { + "bbox": [ + 310, + 375, + 542, + 503 + ], + "spans": [ + { + "bbox": [ + 310, + 375, + 542, + 503 + ], + "type": "image", + "image_path": "e3bc14e3aabed028ea7b167beee694bdf8b15030260d0563c9dd06fb4cf0aa48.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 507, + 547, + 575 + ], + "lines": [ + { + "bbox": [ + 304, + 507, + 547, + 575 + ], + "spans": [ + { + "bbox": [ + 304, + 507, + 547, + 575 + ], + "type": "text", + "content": "Figure 5. Vote query and convergence. We take out convergence study on a different combination of content feature " + }, + { + "bbox": [ + 304, + 507, + 547, + 575 + ], + "type": "inline_equation", + "content": "f_{vq}" + }, + { + "bbox": [ + 304, + 507, + 547, + 575 + ], + "type": "text", + "content": " and position " + }, + { + "bbox": [ + 304, + 507, + 547, + 575 + ], + "type": "inline_equation", + "content": "p_{vq}" + }, + { + "bbox": [ + 304, + 507, + 547, + 575 + ], + "type": "text", + "content": " in vote query. The baseline model " + }, + { + "bbox": [ + 304, + 507, + 547, + 575 + ], + "type": "inline_equation", + "content": "(p_{query}, f_{query}^{0}) = (p_{seed}, 0)" + }, + { + "bbox": [ + 304, + 507, + 547, + 575 + ], + "type": "text", + "content": " downgrades to 3DETR. Introducing " + }, + { + "bbox": [ + 304, + 507, + 547, + 575 + ], + "type": "inline_equation", + "content": "p_{vq}" + }, + { + "bbox": [ + 304, + 507, + 547, + 575 + ], + "type": "text", + "content": " boosts performance but decelerates training since " + }, + { + "bbox": [ + 304, + 507, + 547, + 575 + ], + "type": "inline_equation", + "content": "FFN_{vote}" + }, + { + "bbox": [ + 304, + 507, + 547, + 575 + ], + "type": "text", + "content": " requires time to converge, and " + }, + { + "bbox": [ + 304, + 507, + 547, + 575 + ], + "type": "inline_equation", + "content": "f_{vq}" + }, + { + "bbox": [ + 304, + 507, + 547, + 575 + ], + "type": "text", + "content": " accelerates training." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 582, + 548, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 548, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 548, + 715 + ], + "type": "text", + "content": "Does 3D context feature help captioning? Since the performance of 3D dense captioning is affected by both localization and caption capability, we freeze all parameters other than the caption head and train with 3D only input and standard cross entropy loss (MLE training) for a fair evaluation. We use object-centric decoder [39] as our baseline, which is a decoder that generates captions with object feature as a caption's prefix. In Table 4, “-” refers to the object-centric decoder baseline, “global” means naively including all context tokens extracted from the scene encoder in the decoder, “local” is our proposed caption head that" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "11129" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 50, + 57, + 545, + 169 + ], + "blocks": [ + { + "bbox": [ + 50, + 57, + 545, + 169 + ], + "lines": [ + { + "bbox": [ + 50, + 57, + 545, + 169 + ], + "spans": [ + { + "bbox": [ + 50, + 57, + 545, + 169 + ], + "type": "table", + "html": "
MethodLdesw/o additional 2D inputw/ additional 2D input
IoU = 0.25IoU = 0.50IoU = 0.25IoU = 0.50
C↑B-4↑M↑R↑C↑B-4↑M↑R↑C↑B-4↑M↑R↑C↑B-4↑M↑R↑
Scan2Cap [13]53.7334.2526.1454.9535.2022.3621.4443.5756.8234.1826.2955.2739.0823.3221.9744.78
MORE [20]58.8935.4126.3655.4138.9823.0121.6544.3362.9136.2526.7556.3340.9422.9321.6644.42
SpaCap3d [39]58.0635.3026.1655.0342.7625.3822.8445.6663.3036.4626.7155.7144.0225.2622.3345.36
3DJCG [4]MLE60.8639.6727.4559.0247.6831.5324.2851.8064.7040.1727.6659.2349.4831.0324.2250.80
D3Net [7]------------46.0730.2924.3551.67
Ours71.4539.3428.2559.3361.8134.4626.2254.4072.7939.1728.0659.2359.3232.4225.2852.53
x-Trans2Cap [43]58.8134.1725.8154.1041.5223.8321.9044.9761.8335.6526.6154.7043.8725.0522.4645.28
Scan2Cap [13]------------48.3826.0922.1544.74
D3Net [7]SCST------------62.6435.6825.7253.90
Ours84.1542.5128.4759.2673.7738.2126.6454.7186.2842.6428.2759.0770.6335.6925.5152.28
", + "image_path": "0f93ae867db503f9f9dc0b9dea29db3a458ec6cd2e64a2e5b069dfa5b73a8f4c.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 50, + 237, + 285, + 326 + ], + "blocks": [ + { + "bbox": [ + 46, + 174, + 546, + 219 + ], + "lines": [ + { + "bbox": [ + 46, + 174, + 546, + 219 + ], + "spans": [ + { + "bbox": [ + 46, + 174, + 546, + 219 + ], + "type": "text", + "content": "Table 1. Evaluating Vote2Cap-DETR on ScanRefer [6]. We compare Vote2Cap-DETR with all published state-of-the-art 3D dense caption methods on the ScanRefer dataset. Though our method does not depend on hand-crafted NMS [28] to drop overlapped boxes, we follow the standard evaluation protocol from [13] for fair comparison and provide evaluation without NMS in Table 7. Our proposed Vote2Cap-DETR achieves new state-of-the-art under both MLE training and SCST." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 50, + 237, + 285, + 326 + ], + "lines": [ + { + "bbox": [ + 50, + 237, + 285, + 326 + ], + "spans": [ + { + "bbox": [ + 50, + 237, + 285, + 326 + ], + "type": "table", + "html": "
MethodLdesC@0.5↑B-4@0.5↑M@0.5↑R@0.5↑
Scan2Cap [13]27.4717.2421.8049.06
SpaCap3d [39]33.7119.9222.6150.50
D3Net [7]MLE33.8520.7023.1353.38
3DJCG [4]38.0622.8223.7752.99
Ours43.8426.6825.4154.43
x-Tran2Cap [43]33.6219.2922.2750.00
D3Net [7]SCST38.4222.2224.7454.37
Ours45.5326.8825.4354.76
", + "image_path": "c56cb66ed0b76c505bc85ed59c055d50f14fca116d0188e3af4f33d8881fb312.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "type": "table", + "bbox": [ + 49, + 373, + 285, + 428 + ], + "blocks": [ + { + "bbox": [ + 46, + 331, + 287, + 365 + ], + "lines": [ + { + "bbox": [ + 46, + 331, + 287, + 365 + ], + "spans": [ + { + "bbox": [ + 46, + 331, + 287, + 365 + ], + "type": "text", + "content": "Table 2. Evaluating Vote2Cap-DETR on Nr3D [1]. Likewise, we perform the standard evaluation on the Nr3D dataset, and our proposed Vote2Cap-DETR surpasses prior arts." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 49, + 373, + 285, + 428 + ], + "lines": [ + { + "bbox": [ + 49, + 373, + 285, + 428 + ], + "spans": [ + { + "bbox": [ + 49, + 373, + 285, + 428 + ], + "type": "table", + "html": "
\\( {p}_{query} \\)\\( {f}_{query}^{0} \\)IoU=0.25IoU=0.501st layer IoU=0.50
mAP↑AR↑mAP↑AR↑mAP↑AR↑
VoteNet Baseline63.4282.1844.9660.65--
\\( {p}_{seed} \\)067.2584.9148.1864.9834.8055.06
\\( {p}_{vq} \\)067.3385.6049.1566.3830.2358.44
\\( {p}_{vq} \\)\\( {f}_{vq} \\)69.6187.2052.1369.1246.5366.51
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keyIoU=0.25IoU=0.5
C↑B-4↑M↑R↑C↑B-4↑M↑R↑
-68.6238.6127.6758.4760.1534.0225.8053.82
global70.0539.2327.8458.4461.2034.6625.9353.79
local70.4239.9827.9958.8961.3935.2426.0254.12
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TrainingLdesC@0.5↑B-4@0.5↑M@0.5↑R@0.5↑
SentenceMLE61.2135.3526.1254.52
Set-to-Set61.8134.4626.2254.40
SentenceSCST71.3937.5726.0154.28
Set-to-Set73.7738.2126.6454.71
", + "image_path": "336db4fd26647d45e218fa4ae16b4b3fe98279a80d7e0a1e8b404cb9b32f8859.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "table_body" + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 508, + 545, + 617 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 508, + 545, + 617 + ], + "spans": [ + { + "bbox": [ + 304, + 508, + 545, + 617 + ], + "type": "text", + "content": "End to end training from scratch. Our Vote2Cap-DETR also supports end-to-end training from scratch for 3D dense captioning. However, both ScanRefer and Nr3D are annotated on limited scenes (562/511 scenes) for training; thus, directly training Vote2Cap-DETR from scratch will underperform given to satisfy two objectives simultaneously. Experiments on Scanrefer in Table 6 show that the greedy strategy we choose by pre-training detection head as a good pre-requisite for captioning achieves better performance." + } + ] + } + ], + "index": 13 + }, + { + "type": "table", + "bbox": [ + 306, + 627, + 545, + 658 + ], + "blocks": [ + { + "bbox": [ + 304, + 444, + 545, + 499 + ], + "lines": [ + { + "bbox": [ + 304, + 444, + 545, + 499 + ], + "spans": [ + { + "bbox": [ + 304, + 444, + 545, + 499 + ], + "type": "text", + "content": "Table 5. Set to Set training and performance. We compare our proposed set-to-set training with traditional \"Sentence Training\", which traverses through all sentence annotations. We achieve comparable performance with MLE training, and " + }, + { + "bbox": [ + 304, + 444, + 545, + 499 + ], + "type": "inline_equation", + "content": "2.38\\%" + }, + { + "bbox": [ + 304, + 444, + 545, + 499 + ], + "type": "text", + "content": " C@0.5 improvement with SCST." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 306, + 627, + 545, + 658 + ], + "lines": [ + { + "bbox": [ + 306, + 627, + 545, + 658 + ], + "spans": [ + { + "bbox": [ + 306, + 627, + 545, + 658 + ], + "type": "table", + "html": "
pretrain/end2endC@0.5↑B-4@0.5↑M@0.5↑R@0.5↑AP@0.5↑AR@0.5↑
end2end52.1528.8724.6849.7646.6862.17
pretrain+end2end62.0334.9026.0654.3351.2667.57
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The greedy strategy we choose by pre-training detection head as a good prerequisite for captioning achieves better performance than directly end to end training from scratch." + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "11130" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 59, + 79, + 168, + 147 + ], + "blocks": [ + { + "bbox": [ + 59, + 79, + 168, + 147 + ], + "lines": [ + { + "bbox": [ + 59, + 79, + 168, + 147 + ], + "spans": [ + { + "bbox": [ + 59, + 79, + 168, + 147 + ], + "type": "image", + "image_path": "03cb43e70539653fe553a620890c611add75e2d5f940a8524f601c949c007efc.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 87, + 149, + 139, + 160 + ], + "lines": [ + { + "bbox": [ + 87, + 149, + 139, + 160 + ], + "spans": [ + { + "bbox": [ + 87, + 149, + 139, + 160 + ], + "type": "text", + "content": "scene0011_00" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 181, + 80, + 290, + 147 + ], + "blocks": [ + { + "bbox": [ + 181, + 80, + 290, + 147 + ], + "lines": [ + { + "bbox": [ + 181, + 80, + 290, + 147 + ], + "spans": [ + { + "bbox": [ + 181, + 80, + 290, + 147 + ], + "type": "image", + "image_path": "831e1c0ce41a1028e27e929c4f0222271f1a12c4f9964e11c203c5c0e810f8d4.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 209, + 149, + 261, + 159 + ], + "lines": [ + { + "bbox": [ + 209, + 149, + 261, + 159 + ], + "spans": [ + { + "bbox": [ + 209, + 149, + 261, + 159 + ], + "type": "text", + "content": "scene0015_00" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 60, + 170, + 150, + 187 + ], + "lines": [ + { + "bbox": [ + 60, + 170, + 150, + 187 + ], + "spans": [ + { + "bbox": [ + 60, + 170, + 150, + 187 + ], + "type": "text", + "content": "3DJCG: This is a rectangular whiteboard. It is on the wall." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 182, + 170, + 282, + 186 + ], + "lines": [ + { + "bbox": [ + 182, + 170, + 282, + 186 + ], + "spans": [ + { + "bbox": [ + 182, + 170, + 282, + 186 + ], + "type": "text", + "content": "3DJCG: This is a brown table. It is in the middle of the room." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 182, + 198, + 274, + 222 + ], + "lines": [ + { + "bbox": [ + 182, + 198, + 274, + 222 + ], + "spans": [ + { + "bbox": [ + 182, + 198, + 274, + 222 + ], + "type": "text", + "content": "SpaCap3D: This is a wooden table. It is in the center of the room." + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 182, + 233, + 287, + 250 + ], + "lines": [ + { + "bbox": [ + 182, + 233, + 287, + 250 + ], + "spans": [ + { + "bbox": [ + 182, + 233, + 287, + 250 + ], + "type": "text", + "content": "Ours: This is a wooden table. It is in the corner of the room." + } + ] + } + ], + "index": 17, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 304, + 80, + 412, + 147 + ], + "blocks": [ + { + "bbox": [ + 304, + 80, + 412, + 147 + ], + "lines": [ + { + "bbox": [ + 304, + 80, + 412, + 147 + ], + "spans": [ + { + "bbox": [ + 304, + 80, + 412, + 147 + ], + "type": "image", + "image_path": "c456dfcaa8143962bbae4175e7a69723a047d1d2944d8d6e9491371688506220.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 331, + 149, + 384, + 159 + ], + "lines": [ + { + "bbox": [ + 331, + 149, + 384, + 159 + ], + "spans": [ + { + "bbox": [ + 331, + 149, + 384, + 159 + ], + "type": "text", + "content": "scene0025_00" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 305, + 166, + 396, + 190 + ], + "lines": [ + { + "bbox": [ + 305, + 166, + 396, + 190 + ], + "spans": [ + { + "bbox": [ + 305, + 166, + 396, + 190 + ], + "type": "text", + "content": "3DJCG: The is a small brown cabinet. It is to the right of the desk." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 305, + 198, + 407, + 222 + ], + "lines": [ + { + "bbox": [ + 305, + 198, + 407, + 222 + ], + "spans": [ + { + "bbox": [ + 305, + 198, + 407, + 222 + ], + "type": "text", + "content": "SpaCap3D: The cabinet is below the desk. It is to the left of the chair." + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 60, + 233, + 164, + 251 + ], + "lines": [ + { + "bbox": [ + 60, + 233, + 164, + 251 + ], + "spans": [ + { + "bbox": [ + 60, + 233, + 164, + 251 + ], + "type": "text", + "content": "Ours: The tv is on the wall. It is to the right of the table." + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 305, + 233, + 408, + 250 + ], + "lines": [ + { + "bbox": [ + 305, + 233, + 408, + 250 + ], + "spans": [ + { + "bbox": [ + 305, + 233, + 408, + 250 + ], + "type": "text", + "content": "Ours: This is a white cabinet. It is to the right of the table." + } + ] + } + ], + "index": 18, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "type": "image", + "bbox": [ + 426, + 80, + 534, + 147 + ], + "blocks": [ + { + "bbox": [ + 426, + 80, + 534, + 147 + ], + "lines": [ + { + "bbox": [ + 426, + 80, + 534, + 147 + ], + "spans": [ + { + "bbox": [ + 426, + 80, + 534, + 147 + ], + "type": "image", + "image_path": "328921ee1bbcaf70805e923e55b2b870420b69908f8a8fe596a484864be2fae0.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 454, + 149, + 506, + 159 + ], + "lines": [ + { + "bbox": [ + 454, + 149, + 506, + 159 + ], + "spans": [ + { + "bbox": [ + 454, + 149, + 506, + 159 + ], + "type": "text", + "content": "scene0050_00" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 428, + 170, + 526, + 187 + ], + "lines": [ + { + "bbox": [ + 428, + 170, + 526, + 187 + ], + "spans": [ + { + "bbox": [ + 428, + 170, + 526, + 187 + ], + "type": "text", + "content": "3DJCG: This is a brown table. It is in front of the couch." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 428, + 198, + 521, + 222 + ], + "lines": [ + { + "bbox": [ + 428, + 198, + 521, + 222 + ], + "spans": [ + { + "bbox": [ + 428, + 198, + 521, + 222 + ], + "type": "text", + "content": "SpaCap3D: This is a wooden coffee table. It is in front of the couch." + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 428, + 233, + 529, + 250 + ], + "lines": [ + { + "bbox": [ + 428, + 233, + 529, + 250 + ], + "spans": [ + { + "bbox": [ + 428, + 233, + 529, + 250 + ], + "type": "text", + "content": "Ours: This is a brown ottoman. It is to the right of the chair." + } + ] + } + ], + "index": 19, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 428, + 269, + 530, + 285 + ], + "lines": [ + { + "bbox": [ + 428, + 269, + 530, + 285 + ], + "spans": [ + { + "bbox": [ + 428, + 269, + 530, + 285 + ], + "type": "text", + "content": "GT: This is a brown ottoman. It is in front of a couch." + } + ] + } + ], + "index": 23, + "angle": 0, + "type": "image_caption" + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 52, + 345, + 282, + 485 + ], + "blocks": [ + { + "bbox": [ + 60, + 198, + 164, + 223 + ], + "lines": [ + { + "bbox": [ + 60, + 198, + 164, + 223 + ], + "spans": [ + { + "bbox": [ + 60, + 198, + 164, + 223 + ], + "type": "text", + "content": "SpaCap3D: The whiteboard is affixed to the wall. It is to the right of the window." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 60, + 269, + 151, + 285 + ], + "lines": [ + { + "bbox": [ + 60, + 269, + 151, + 285 + ], + "spans": [ + { + "bbox": [ + 60, + 269, + 151, + 285 + ], + "type": "text", + "content": "GT: This is a big black tv. It is above a thin table." + } + ] + } + ], + "index": 20, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 182, + 261, + 282, + 294 + ], + "lines": [ + { + "bbox": [ + 182, + 261, + 282, + 294 + ], + "spans": [ + { + "bbox": [ + 182, + 261, + 282, + 294 + ], + "type": "text", + "content": "GT: This is a small table with a wood look. It is the table closest to the front of the room in the upper left corner." + } + ] + } + ], + "index": 21, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 305, + 265, + 402, + 290 + ], + "lines": [ + { + "bbox": [ + 305, + 265, + 402, + 290 + ], + "spans": [ + { + "bbox": [ + 305, + 265, + 402, + 290 + ], + "type": "text", + "content": "GT: A white cabinet is sitting on the floor next to the wall. It is to the left of the couch." + } + ] + } + ], + "index": 22, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 46, + 302, + 547, + 335 + ], + "lines": [ + { + "bbox": [ + 46, + 302, + 547, + 335 + ], + "spans": [ + { + "bbox": [ + 46, + 302, + 547, + 335 + ], + "type": "text", + "content": "Figure 6. Qualitative Comparisons. We compare qualitative results with two state-of-the-art \"detect-then-describe\" methods, 3DJCG [4] and SpaCap3D [39]. We underline phrases describing spatial locations, and mark correct attribute words in green and wrong description in red. Our Vote2Cap-DETR produces tight bounding boxes close to the ground truth and accurate descriptions." + } + ] + } + ], + "index": 24, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 52, + 345, + 282, + 485 + ], + "lines": [ + { + "bbox": [ + 52, + 345, + 282, + 485 + ], + "spans": [ + { + "bbox": [ + 52, + 345, + 282, + 485 + ], + "type": "image", + "image_path": "0c53d57d5bc9ca0e78c887611afbc6ea08a02364435a9e8a1fef9668d8ae224e.jpg" + } + ] + } + ], + "index": 25, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 487, + 287, + 531 + ], + "lines": [ + { + "bbox": [ + 46, + 487, + 287, + 531 + ], + "spans": [ + { + "bbox": [ + 46, + 487, + 287, + 531 + ], + "type": "text", + "content": "Figure 7. Set-to-Set training and convergence. Convergence speed analysis of two different training strategies with MLE training as well as SCST. Set-to-Set training enables a larger batch size for the caption head and accelerates convergence." + } + ] + } + ], + "index": 26, + "angle": 0, + "type": "image_caption" + } + ], + "index": 25 + }, + { + "bbox": [ + 46, + 533, + 287, + 639 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 533, + 287, + 639 + ], + "spans": [ + { + "bbox": [ + 46, + 533, + 287, + 639 + ], + "type": "text", + "content": "Is Vote2Cap-DETR robust to NMS? Similar to other DETR works, the set loss encourages the model to produce compact predictions. We compare performance on both 3D dense caption (C@0.5) and detection (mAP50, AR50) in Table 7. Since the " + }, + { + "bbox": [ + 46, + 533, + 287, + 639 + ], + "type": "inline_equation", + "content": "m@kIoU" + }, + { + "bbox": [ + 46, + 533, + 287, + 639 + ], + "type": "text", + "content": " metric (Eq. 8) does not contain any penalties on redundant predictions, getting rid of NMS [28] results in performance growth in C@0.5. Results show that Vote2Cap-DETR is more stable compared to VoteNet based methods with the absence of NMS." + } + ] + } + ], + "index": 27 + }, + { + "type": "table", + "bbox": [ + 50, + 639, + 285, + 684 + ], + "blocks": [ + { + "bbox": [ + 50, + 639, + 285, + 684 + ], + "lines": [ + { + "bbox": [ + 50, + 639, + 285, + 684 + ], + "spans": [ + { + "bbox": [ + 50, + 639, + 285, + 684 + ], + "type": "table", + "html": "
Modelsw/NMSw/o NMS
C@0.5↑mAP50↑AR50↑C@0.5↑mAP50↑AR50↑
SpaCap3D43.9337.7753.9651.3523.3064.14
3DJCG50.2247.5862.1254.9430.0368.69
Vote2Cap-DETR70.6352.7966.0971.5752.8267.80
", + "image_path": "e336f7f759b1582cf233d5fa3baed24f83ae0e7252f1bcd42900160d5a76d5d9.jpg" + } + ] + } + ], + "index": 28, + "angle": 0, + "type": "table_body" + } + ], + "index": 28 + }, + { + "bbox": [ + 46, + 689, + 287, + 723 + ], + "lines": [ + { + "bbox": [ + 46, + 689, + 287, + 723 + ], + "spans": [ + { + "bbox": [ + 46, + 689, + 287, + 723 + ], + "type": "text", + "content": "Table 7. Effect of NMS. We analyze whether the absence of NMS affects the 3D dense captioning performance (C@0.5) as well as detection performance (mAP50, AR50)." + } + ] + } + ], + "index": 29, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 306, + 342, + 417, + 354 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 342, + 417, + 354 + ], + "spans": [ + { + "bbox": [ + 306, + 342, + 417, + 354 + ], + "type": "text", + "content": "4.4. Qualitative Results" + } + ] + } + ], + "index": 30 + }, + { + "bbox": [ + 304, + 355, + 545, + 415 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 355, + 545, + 415 + ], + "spans": [ + { + "bbox": [ + 304, + 355, + 545, + 415 + ], + "type": "text", + "content": "We compare qualitative results with two state-of-the-art models, SpaCap3D [39] and 3DJCG [4] in Figure 6. One can see that our method produces tight bounding boxes close to the ground truth as well as accurate descriptions of object attributes, classes, and spatial relationships." + } + ] + } + ], + "index": 31 + }, + { + "bbox": [ + 306, + 421, + 378, + 432 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 421, + 378, + 432 + ], + "spans": [ + { + "bbox": [ + 306, + 421, + 378, + 432 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 32 + }, + { + "bbox": [ + 304, + 437, + 545, + 593 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 437, + 545, + 593 + ], + "spans": [ + { + "bbox": [ + 304, + 437, + 545, + 593 + ], + "type": "text", + "content": "In this work, we present Vote2Cap-DETR, a transformer based one-stage approach, for 3D dense captioning. The proposed Vote2Cap-DETR adopts a full transformer encoder-decoder architecture that decodes a set of vote queries to box predictions and captions in parallel. We show that by introducing spatial bias and content-aware features, vote query boosts both convergence and detection performance. Additionally, we develop a novel lightweight query-driven caption head for informative caption generation. Experiments on two widely used datasets for 3D dense captioning validate that our proposed one-stage Vote2Cap-DETR model surpasses prior works with heavy dependence on hand-crafted components by a large margin." + } + ] + } + ], + "index": 33 + }, + { + "bbox": [ + 306, + 597, + 421, + 611 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 597, + 421, + 611 + ], + "spans": [ + { + "bbox": [ + 306, + 597, + 421, + 611 + ], + "type": "text", + "content": "6. Acknowledgements" + } + ] + } + ], + "index": 34 + }, + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "type": "text", + "content": "This work is supported by National Natural Science Foundation of China (No. U1909207, 62071127, and 62276176), Shanghai Natural Science Foundation (No. 23ZR1402900), Zhejiang Lab Project (No. 2021KH0AB05), and in part by A*STAR AME Programmatic Funding A18A2b0046, RobotHTPO Seed Fund under Project C211518008, and EDB Space Technology Development Grant under Project S22-19016-STDP." + } + ] + } + ], + "index": 35 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "11131" + } + ] + } + ], + "index": 36 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 288, + 713 + ], + "type": "list", + "angle": 0, + "index": 13, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 147 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 147 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 147 + ], + "type": "text", + "content": "[1] Panos Achlioptas, Ahmed Abdelreehm, Fei Xia, Mohamed Elhoseiny, and Leonidas Guibas. 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Most existing approaches first obtain rasterized map with the segmentation-based pipeline and then conduct heavy post-processing for downstream-friendly vectorization. In this paper, by delving into parameterization-based methods, we pioneer a concise and elegant scheme that adopts unified piecewise Bézier curve. In order to vectorize changed map elements end-to-end, we elaborate a simple yet effective architecture, named Piecewise Bézier HD-map Network (BeMapNet), which is formulated as a direct set prediction paradigm and postprocessing-free. Concretely, we first introduce a novel IPM-PE Align module to inject 3D geometry prior into BEV features through common position encoding in Transformer. Then a well-designed Piecewise Bézier Head is proposed to output the details of each map element, including the coordinate of control points and the segment number of curves. In addition, based on the progressively restoration of Bézier curve, we also present an efficient Point-Curve-Region Loss for supervising more robust and precise HD-map modeling. Extensive comparisons show that our method is remarkably superior to other existing SOTAs by $18.0\\mathrm{mAP}$ at least1.", + "bbox": [ + 75, + 300, + 473, + 662 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 690, + 209, + 705 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "As one of the most fundamental components in the autodriving system, high-definition map contains centimeter details of traffic elements, vectorized topology and navigation information, which instruct ego-vehicle to accurately locate itself on the road and understand what is coming up ahead. At present, conventional SLAM-based solutions [45, 46, 60] have been widely adopted in practice. Yet, due to dilemmas of high annotation costs and untimely updates, the offline approach is gradually being replaced by the learning-based online HD-map construction with onboard sensors.", + "bbox": [ + 75, + 715, + 468, + 867 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/c7b4aaef9bc985a4dd21444fae016e55e25f3582ea14c22aff66694181ed7d01.jpg", + "image_caption": [ + "(a) HD-map example" + ], + "image_footnote": [], + "bbox": [ + 522, + 268, + 645, + 446 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/2a5091792463974acaddf9d9e3171c80206eef53e99bd6811b9431695db9254e.jpg", + "image_caption": [ + "(b) vanilla Bezier vs. piecewise Bezier" + ], + "image_footnote": [], + "bbox": [ + 663, + 268, + 870, + 348 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/ded693c4009d7db33e25cc797f483baf00dd1af496b2fde200b87b23d006b926.jpg", + "image_caption": [ + "(c) map curve restored by real control points", + "Figure 1. Illustration of our motivation for piecewise Bézier curve, termed as $\\langle k, n \\rangle$ , where $k$ is the piece number and $n$ is the degree. Fig.(a) is a real HD-map case from NuScenes. Fig.(b) compares the difference between vanilla and piecewise Bézier curve through the same map element, where the light purple is the restored curve with Bézier process. The last is more efficient than previous ones with reducing the number of control points by $64\\%$ in this case. Fig.(c) illustrates that piecewise Bézier curve can model arbitrary-shaped curves. Note the blue circles denote actual control points." + ], + "image_footnote": [], + "bbox": [ + 665, + 364, + 870, + 445 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "The deep-based paradigm of online $HD$ -map building is gradually developing, but it still faces two main challenges: 1) modeling instance-level vectorized $HD$ -map end-to-end. Most existing works construct $HD$ -map by rasterizing $BEV$ (bird-eye-view) maps into semantic pixels with segmentation [24, 42], which not only lacks the modeling of instance-level details, but also requires heavy post-processing to obtain vectorized information. As a sub-task, lane detection makes a relatively better advance for this issue, that is, in addition to segmentation-based methods [39, 41, 62], there are also point-based [25, 47] and curve-based [12, 28] schemes. However, compared to the simple lane scenario, $HD$ -map contains more shape-changeful elements, so such methods cannot be directly adopted into the $HD$ -map construction. 2) performing 2D-3D perspective transformation efficiently. Obtaining 3D- $BEV$ perception from multi-view 2D images is an essential step for building $HD$ -map, which is mainly divided into three ideas, i.e. geometric priors [44], learnable parameters [40, 42], and a combination of the two [17, 43]. Note the assumptions of geometry-based methods often do", + "bbox": [ + 496, + 598, + 892, + 900 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 810, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Corresponding author.", + "bbox": [ + 93, + 875, + 225, + 887 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "1https://github.com/er-muyue/BeMapNet", + "bbox": [ + 96, + 887, + 387, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "13218", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "not conform to the actual situation, leading to such schemes are less adaptable, while learning-based methods require a large amount of labeled data to generalize across various scenarios. Combining the above two branches not only has multi-scenario scalability, but also reduces the demand for annotated data, has attracted increasing research interest.", + "bbox": [ + 75, + 90, + 468, + 181 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To the best of our knowledge, the curve parameterization construction of $HD$ -map in the $BEV$ space is vacancy and no one has explored it. Based on the widely used Bézier curve, which is mathematically defined by a set of control points, we pioneer to devise a concise and elegant $HD$ -map scheme that adopts piecewise Bézier curve, where each map curve is divided into multiple $k$ segments and each segment is then represented by a vanilla Bézier curve with degree $n$ , hence denoted as $\\langle k, n \\rangle$ . Despite $\\langle 1, n \\rangle$ is enough to express any map element with infinite $n$ in theory, more complex curve tends to require higher degree, meaning that there are more control points need to be modeled, which is shown in Fig.1. The proposed piecewise strategy allows us to parameterize a curve more compactly with fewer control points and higher capacity, which is extremely scalable and robust in practice.", + "bbox": [ + 75, + 181, + 470, + 407 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Inspired by the above motivations, we propose an end-to-end vectorized HD-map construction architecture, named as Piecewise Bézier HD-map Network (BeMapNet). The overall framework is illustrated in detail in Fig.2, which streamlines the architecture into four primary modules for gradually-enriched information, i.e. feature extractor shared among multi-view images, semantic BEV decoder for $2D-3D$ perspective elevation, instance Bézier decoder for curve-level descriptors, and piecewise Bézier head for point-level parameterization. To be concrete, we first introduce a novel IPM-PE Align module into Transformer-based decoders, which injects IPM (inverse perspective mapping) geometric priors into BEV features via PE (position encoding) and hardly adds any parameters except a FC layer. Secondly, we further design a Piecewise Bézier Head for dynamic curve modeling with adopting two branches as classification and regression, where the former classifies the number of pieces to determine the curve length and the latter regresses the coordinate of control points to determine the curve shape. Lastly, we present an Point-Curve-Region Loss for robust curve modeling by supervising restoration information as a progressive manner. Since it is modeled as a sparse set prediction task and optimized with a bipartite matching loss, our method is postprocessing-free and high-performance.", + "bbox": [ + 75, + 407, + 470, + 770 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "The main contributions of our approach are three-folds:", + "bbox": [ + 76, + 771, + 444, + 785 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- We pioneer the BeMapNet for concise and elegant modeling of HD-map with unified piecewise Bézier curve.", + "- We elaborate the overall end-to-end architecture with innovatively introducing IPM-PE Align Module, Piecewise Bézier Output Head and well-designed PCR-Loss.", + "- BeMapNet is remarkably superior to SOTAs on existing benchmarks, revealing the effectiveness of our approach." + ], + "bbox": [ + 83, + 787, + 467, + 900 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 500, + 89, + 640, + 104 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.1. Vectorized HD-map Construction", + "text_level": 1, + "bbox": [ + 500, + 114, + 785, + 131 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "$HD$ -map is precise at centimeter-level and consists of vectorized details not normally present on standard map [27], which highly aggravates the difficulty of obtaining accurate annotations in practice. Most previous methods focus on SLAM [11, 18, 22, 36, 46, 58] with exploring LiDAR points of the environment, involving large-scale data acquisition and labor-intensive annotations. Recently, more and more researchers formulate the process of building $HD$ -map as a segmentation task [6, 13, 20, 32] from various sensors, such as cameras [15, 26, 34, 35, 40, 43, 59, 63] and LiDAR [1, 57]. HDMapNet [24] extracts features from the observations of multi-modalities and groups semantic rasterized maps with heuristic post-processing for vectorized results. Without any further vectorization, [42] only obtains semantic map representations from a Transformer-based camera-to-BEV module. Different from the above segmentation-based frameworks, our proposed BeMapNet adopts the parameterization-based paradigm and constructs instance-level vectorized $HD$ -map end-to-end with a multiview and camera-only manner, which is a more flexible and scalable solution for downstream tasks.", + "bbox": [ + 496, + 138, + 890, + 455 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.2. Structure Modeling of Geometric Data", + "text_level": 1, + "bbox": [ + 500, + 468, + 831, + 484 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "HD-map contains various kinds of map elements, including lane-divider, ped-crossing, road-boundary, etc., which are typically regarded as geometric data, e.g. points, polygons and curves. To the best of knowledge, there are two mainstream exploration directions for deep geometric modeling, one is point-based, including uniform-points and keypoints estimation, and the other is curve-based, including polynomial curve and Bézier curve. Taking the most related lane detection as an example, LineCNN [25] presents a novel line proposal unit to detect lanes as a set of points, and later LaneATT [47] represents a lane by equally-spaced $2D$ -points that achieves good performance. GANet [54] focuses on keypoint estimation and association with adaptively lane feature aggregator. HDMapGen [37] proposes a hierarchical point generative model for producing high-quality HD lane map. As for cruve-based, [51] and [48] directly predict the polynomial coefficients with a differentiable least-squares fitting module and simple $FC$ respectively. Recently, based on the DETR [4], LSTR [28] presents a query-based detector to decode poly-parameters of a lane end-to-end. Apart from this, some studies also adopt Bézier curve for geometry, such as text boundary [29], center-line segment [3] and lane curve [12]. Unlike these approaches of addressing simple-shape elements, our method innovatively employs piecewise Bézier curves without any complicated geometric assumptions to parameterize arbitrary-shape geometry in HD-map scenarios.", + "bbox": [ + 496, + 493, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "13219", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/9cdd2ebeb92158f77acbeb5c176dfee9dccc3a8d15ff9b0e602a66dffa03cf98.jpg", + "image_caption": [ + "Figure 2. The architecture of our proposed BeMapNet, containing four primary components for extracting progressively richer information, i.e. image-level multi-scale features, semantic-level BEV feature, instance-level curve descriptors, and point-level Bézier control sequence. Right-top: The blue and orange circles represent explicit control points and implicit control offsets respectively. Note that the term GAP is global average pooling and MatMul is the matrix multiplication. Right-bottom: $(H_c, W_c) / (H_b, W_b)$ is the shape of image/BEV feature." + ], + "image_footnote": [], + "bbox": [ + 80, + 88, + 893, + 377 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "2.3. Multi-view Camera-to-BEV Transformation", + "text_level": 1, + "bbox": [ + 76, + 445, + 452, + 460 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In most $3D$ research studies, obtaining high-quality BEV representations from multi-view camera features is the top priority of various domains, such as $3D$ object detection [17, 30, 43, 55, 56], motion prediction [10, 16, 19, 23, 53] and map construction [24, 26, 40, 42]. IPM [44] is the most basic and straightforward method with a homography transformation, which is precisely calculated by camera parameters. Without adopting the $3D$ geometry prior, some methods [3, 40, 42] directly leverage learnable parameters to complete the perspective transformation. VPN [40] and Neat [9] both utilize a $FC$ layer to transform the image features into the BEV space, and [42] further designs a multi-camera deformable attention unit based on transformer. However, in order to obtain more explicit BEV representations, more and more researches argue that the geometry priors has great advantages for model convergence and performance. Based on VPN, [24] fuse the multi-camera BEV spaces with the camera poses. LSS [43] and BEVDet [17] build the connection between camera-view and BEV based on the depth distribution estimation. DETR3D [56] manipulates predictions directly in $3D$ space with linking $3D$ positions to $2D$ spaces and [5] generates BEV features by regarding camera parameters as a reference. PETR [30] encodes the $3D$ information as position embedding and conducts query decoding on position-aware features. In addition to introducing the $3D$ geometry prior, we further performs position embedding alignment for transforming the camera features and BEV features into the world coordinate system.", + "bbox": [ + 75, + 477, + 472, + 901 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Method", + "text_level": 1, + "bbox": [ + 500, + 444, + 589, + 460 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Problem Formulation", + "text_level": 1, + "bbox": [ + 500, + 469, + 702, + 484 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Preliminary on Piecewise Bézier Curve. A Bézier curve is a parametric curve which is formulated by a set of ordered control points $c_{0}$ through $c_{n}$ as,", + "bbox": [ + 498, + 493, + 890, + 539 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\np (t) = \\sum_ {i = 0} ^ {n} b _ {i, n} (t) c _ {i}, t \\in [ 0, 1 ] \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 591, + 547, + 890, + 585 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $n$ is the degree of the curve and $b_{i,n}(t)$ is known as Bernstein basis polynomial of degree $n$ ,", + "bbox": [ + 498, + 593, + 890, + 625 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nb _ {i, n} (t) = \\binom {n} {i} t ^ {i} (1 - t) ^ {n - i}, i = 0, \\dots , n \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 555, + 631, + 890, + 665 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "According to Eq.1, we know the first and last control points are endpoints of the curve, i.e. $p(0) = c_0$ , $p(1) = c_n$ . Then we define a piecewise Bézier curve $\\langle k, n \\rangle$ consists of $k$ segments, each of which is an $n$ -order Bézier and two consecutive segments satisfy the positional continuity condition as $p^j(1) = p^{j+1}(0)$ , where $j$ is the segment $id$ varying from 0 to $k-2$ . Hereafter, given a piecewise Bézier curve as shown in Fig.3, we denote its ordered control points as,", + "bbox": [ + 496, + 670, + 890, + 792 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbb {C} = \\left\\{c _ {i} ^ {j} \\in \\mathbb {R} ^ {2} \\mid i \\in [ 0, n ], j \\in [ 0, k - 1 ], c _ {n} ^ {j} = c _ {0} ^ {j + 1} \\right\\} \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 513, + 797, + 890, + 816 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Moreover, due to the first and last control points of each segment are always on the curve, we naturally term these points that retain a distinct significance as explicit control points $\\mathbb{C}^E$ and the remaining as implicit control points $\\mathbb{C}^I$ , where $\\mathbb{C} = \\mathbb{C}^E \\cup \\mathbb{C}^I$ , $|\\mathbb{C}^E| = k + 1$ and $|\\mathbb{C}^I| = nk - k$ .", + "bbox": [ + 496, + 824, + 892, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "13220", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/490ded093f6ddf2eaa436ee0fe4fd89c30bb15185a9d1c10fb525f4ea232a821.jpg", + "image_caption": [ + "Piecewise Bézier Curve" + ], + "image_footnote": [], + "bbox": [ + 84, + 89, + 367, + 224 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/935691aecb555a9e02d21cdf7ce9a485718574b6f121612f195fce03f20c51c0.jpg", + "image_caption": [ + "Bézier Control Polygon" + ], + "image_footnote": [], + "bbox": [ + 93, + 226, + 116, + 236 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/5530dbe275f868354976371c6852c6d404ef6c694a959ad81da71372315bfb4e.jpg", + "image_caption": [ + "Explicit Control Points" + ], + "image_footnote": [], + "bbox": [ + 243, + 226, + 256, + 234 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/d44b5c89a8edcdb644558d3d5453810e276b7e019ba2503694178011167a54d4.jpg", + "image_caption": [ + "Explicit Center" + ], + "image_footnote": [], + "bbox": [ + 372, + 90, + 460, + 224 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/93bbc57febb8affdb62846f3807ac50e845b020707c79fb33983d2ed02021cb5.jpg", + "image_caption": [ + "Figure 3. Illustration of a 3-pieces 3-order piecewiseBezier curve, denoted as $\\langle 3,3\\rangle$ for the left part. For each segment, we model the implicit control point coordinates by an offset $(\\Delta x,\\Delta y)$ from the center of explicit control points as shown on the right part." + ], + "image_footnote": [], + "bbox": [ + 93, + 241, + 116, + 250 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/14d32f1da02e93201d6be504cd034e7ddd7e0b8d4ee18ab4e2dac07596d9acb2.jpg", + "image_caption": [ + "Implicit Control Points" + ], + "image_footnote": [], + "bbox": [ + 243, + 241, + 256, + 250 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/56a6cca86c77a7579475d17135d05ebefbdc22d5032cdfb47aecb1d1a7aaddc1.jpg", + "image_caption": [ + "mplicit Offset" + ], + "image_footnote": [], + "bbox": [ + 377, + 241, + 393, + 250 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Vectorized HD-map Modeling. By sequentially sampling points along the elements in HD-map, each object can be structured as an open-shape curve as a vectorized manner. To uniformly parameterize these various shape-changeful map elements, including points, polygons and curves, we employ the piecewise Bézier curve proposed in Eq.3 and formalize a vectorized HD-map as a piecewise Bézier curve set $\\mathcal{M} = \\{\\mathbb{C}_i|i = 1,\\dots ,|\\mathcal{M}|\\}$ , where $|\\mathcal{M}|$ is the number of map instances. Our objective is to learn a model that extracts compact information from the camera sensors and predicts, for each map element, its corresponding Bézier control sequence, which uniquely determine the shape and position of the map curve. In addition, for the purpose of reducing the modeling complexity of implicit control points $\\mathbb{C}^{\\mathcal{I}}$ for each segment, we subtly generate implicit coordinates through the center of explicit control points and their relative offsets as shown in the right of Fig.3.", + "bbox": [ + 75, + 320, + 468, + 577 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Piecewise Bézier Curve Modeling Principle. Considering the large-variety and changeful-shape of map elements, we present a consistent-degree but dynamic-piece principle for modeling piecewise curve more precisely and efficiently as, (1) consistent-degree on semantic-level. Due to a Bézier curve of degree $k$ can be easily converted into degree $k + 1$ with the same shape, i.e. degree elevation in mathematics, the same curve may correspond to multiple Bézier solutions with only different degree. This kind of obfuscation is devastating for the network modeling. And we argue that keeping the consistent-degree within the same semantic category is the most efficient way to solve this dilemma.", + "bbox": [ + 75, + 580, + 467, + 762 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "(2) dynamic-piece on instance-level. Considering that the complexity of different map curves is always inconsistent, the modeling method with a fixed and large number of segments will not only cause excessive redundancy in the expression of each curve, but also lead to confusion in the definition of sub-segment, which places a certain burden on the model optimization. The dynamic-piece rule demands the model to choose the number of segments dynamically and parameterize a Bézier curve as compactly as possible.", + "bbox": [ + 75, + 763, + 467, + 901 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. Piecewise Bezier HD-map Network", + "text_level": 1, + "bbox": [ + 500, + 90, + 803, + 107 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2.1 Overall Architecture", + "text_level": 1, + "bbox": [ + 500, + 114, + 697, + 128 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The overall model architecture is illustrated in detail in Fig. 2, which streamlines the framework into four parts, namely feature extractor, semantic BEV decoder, instance Bézier decoder and piecewise Bézier output head respectively.", + "bbox": [ + 498, + 140, + 890, + 202 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Feature Extractor. Given surrounding images from multicamera as inputs, a shared CNN backbone is first employed to obtain each image feature, and then these multi-scale features from different stages are fed into FPN [50] to integrate rich environmental information. Last we upsample pyramid features to the same size and stack them together as outputs.", + "bbox": [ + 498, + 205, + 890, + 297 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Semantic BEV Decoder. We leverage a standard encoder-decoder paradigm based on Transformer to elevate camera-view features into canonical BEV spaces. By treating the perspective transformation as a direct set prediction task, the BEV decoder takes camera features with shape $H_{c} \\times W_{c}$ and $H_{q} \\times W_{q}$ learnable BEV queries as inputs, and produces BEV features $F_{b} \\in \\mathbb{R}^{C \\times H_{b} \\times W_{b}}$ by modeling all pairwise interactions among elements with self- and cross-attention. Different from the region-agnostic query in DETR, we correspond each query with a $\\gamma^{h} \\times \\gamma^{w}$ region on BEV features one-to-one, i.e. $H_{b} \\times W_{b} = \\gamma^{h}H_{q} \\times \\gamma^{w}W_{q}$ . The $F_{b}$ is then fed into a $1 \\times 1$ conv and upsample block to obtain the final semantic mask $\\mathbb{M}_{s} \\in \\mathbb{R}^{U \\times H_{s} \\times W_{s}}$ , where $U$ is the number of classes and $H_{s} \\times W_{s}$ is the map shape. In addition, we also propose a novel IPM-PE Align Layer to refactor the features in different coordinate systems through the most common position encoding layer in Transformer.", + "bbox": [ + 498, + 301, + 892, + 559 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Instance Bézier Decoder. So as to perform more accurate parametric modeling of each curve, we further equip an instance Bézier decoder based on masked cross-attention [8]. To be concrete, given semantic features $F_{b}$ and learnable instance Bézier queries $Q \\in \\mathbb{R}^{V \\times C}$ , where $V$ is the max number of instance, this module aggregates information and decodes Bézier descriptors $\\vec{z} \\in \\mathbb{R}^{V \\times C}$ , which contain key info of geometric and positional relationships between different map elements. With extra performing matrix multiplication between $\\vec{z}$ and $F_{b}$ , we obtain instance map mask $\\mathbb{M}_{z} \\in \\mathbb{R}^{V \\times H_{s} \\times W_{s}}$ , which is used as the foreground mask for next decoder layer and also to perform segmentation supervision for more spatial context information.", + "bbox": [ + 498, + 563, + 890, + 758 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Piecewise Bézier Output Head. Following the principle elaborated in Sec.3.1, we closely design a piecewise Bézier output head with two core modules, i.e. Split Coordinate Regression and Dynamic End-index Classification, which are utilized to output the coordinates of Bézier control point sequence and the number of segments respectively. With easily recovering piecewise Bézier curves and further introducing the bipartite matching setting, the proposed output head constructs vectorized local HD-map very efficiently.", + "bbox": [ + 498, + 763, + 890, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "13221", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2.2 IPM-PE Align Layer", + "text_level": 1, + "bbox": [ + 76, + 90, + 276, + 106 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "As a basic module of traditional Transformer architecture, positional encoding utilizes the sequence order by injecting information about the position of tokens [52], where sin-cos and learned-based functions are the most common practices. Yet, for the purpose of perspective transformation between 2D camera-views and 3D BEV, we argue it is not enough to only encode the position correspondence within single view, but it is also necessary to maintain the position consistency relationships between two perspectives. Thence we put forward a novel IPM-PE Align Layer to encode the 2D-3D geometry priors into features from different coordinate systems. To be concrete, given a point $p_c^{f_i} = (u,v,1)^\\top$ on the $i$ -th camera-view feature and its corresponding world point $p_c^w = (x,y,z)^\\top$ , the following mathematical equation is satisfied on the assumption of pinhole camera model,", + "bbox": [ + 75, + 114, + 473, + 340 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nd \\cdot A ^ {- 1} \\cdot p _ {c} ^ {f _ {i}} = K ^ {i} \\cdot T ^ {i} \\cdot p _ {c} ^ {w} \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 176, + 349, + 468, + 369 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $d$ is the depth, $A$ is the transformation matrix between image-grid and feature-grid, $K^i$ and $T^i$ are $i$ -th intrinsic and extrinsic matrices. Based on the assumption of that the ground surface is flat and at a fixed height in $IPM$ , the world position $(x,y)$ and depth $d$ can be easily calculated through Eq.4. Note $d < 0$ denotes the position is not valid. As for the other branch of BEV perspective, given a point $p_b^f$ from the BEV feature $F_{b}$ and its world point $p_b^w$ , there is usually only a scale relationship $\\kappa = (\\kappa_x,\\kappa_y)$ between them,", + "bbox": [ + 75, + 378, + 468, + 515 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\np _ {b} ^ {f} = \\boldsymbol {\\kappa} \\cdot p _ {b} ^ {w} \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 228, + 523, + 468, + 544 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Then we leverage the standard sin-cos function to convert all these world coordinates $P_{c}^{w}$ and $P_{b}^{w}$ as position embedding $f_{c}^{pe}$ and $f_{b}^{pe}$ respectively. Since the assumption of flat-ground and known-height usually does not hold in practice, $f_{c}^{pe}$ and $f_{b}^{pe}$ are not exactly aligned in the world coordinate system, we further adopt a shared FC layer on $f_{c}^{pe}$ and $f_{b}^{pe}$ to perform embedding alignment and then obtain more unified position encoding, which is shown in Fig.2 in detail.", + "bbox": [ + 75, + 553, + 468, + 675 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.2.3 Piecewise Bézier Output Head", + "text_level": 1, + "bbox": [ + 76, + 691, + 341, + 707 + ], + "page_idx": 4 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "Split Coordinate Regression Head. Following the illustration in the upper right corner of the Fig.2, we elaborate the forward flow of proposed regression head as four steps, $\\mathbf{I}$ with $i$ -th incoming Bézier descriptor $\\vec{z}_i \\in \\mathbb{R}^C$ , we first convert its channel from $C$ to $u \\cdot v$ with adopting a standard $FC$ layer and then split it into $u$ parts to get a collection of coordinate descriptors $x_i^j \\in \\mathbb{R}^v$ , where $j \\in [1, u]$ , $u$ is the number of coordinate and $v$ is the channel of descriptor.", + "2) given the desired output shape $(H_s, W_s)$ , a hard-coded candidate coordinates grid $G \\in \\mathbb{R}^{2 \\times H_s \\times W_s}$ is generated with X-Y two channels and next a $1 \\times 1$ conv layer is utilized to convert $G$ to its coordinate feature $F_G \\in \\mathbb{R}^{v \\times H_s \\times W_s}$ ." + ], + "bbox": [ + 75, + 719, + 468, + 900 + ], + "page_idx": 4 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "3) through conducting the matrix multiplication between the coordinate descriptor $x_{i}^{j}$ and feature $F_{G}$ , the coordinate activation map $h_{i}^{j}\\in \\mathbb{R}^{H_{s}\\times W_{s}}$ is obtained dynamically.", + "4) after using a global average pooling on the spatial of $h_i^j$ , the activation map is regressed to the final coordinate value." + ], + "bbox": [ + 496, + 90, + 890, + 170 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Dynamic End-index Classification Head. Based on the prior of that the end point of a piecewise Bézier curve must be explicit, the proposed module model the dynamic length of segments prediction task as a $N$ -classification problem, where $N$ is the maximum pieces number for a certain map class. Specifically, with using a common $FC$ and softmax block, each Bézier descriptor is naturally transformed into a $N$ -dimensional probability vector, where each position denotes the score of the current index as a termination point. This novel indeterminate length modeling greatly increases the adaptability and scalability of our proposed framework.", + "bbox": [ + 496, + 174, + 890, + 340 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.3. End-to-End Training", + "text_level": 1, + "bbox": [ + 498, + 349, + 699, + 366 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "According to the matrix form of Eq.1, that is, $P = BC$ , where $B \\in \\mathbb{R}^{m \\times n}$ is the Bernstein matrix, $C \\in \\mathbb{R}^{n \\times 2}$ is control points, $P \\in \\mathbb{R}^{m \\times 2}$ is vectorized points on the curve, $m$ is the number of points and $n$ is the degree. Obviously, given $m, n$ , we can easily implement following procedures:", + "bbox": [ + 496, + 373, + 890, + 450 + ], + "page_idx": 4 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "1) vectorization. Given the $C$ , its corresponding vectorized curve can be restored efficiently with matrix multiplication.", + "2) construction. Given the orderly sampling points $P$ , we readily construct $C$ with solving the least-squares problem, i.e. $C = B^{+}P$ where $^{+}$ is the pseudo-inverse of a matrix." + ], + "bbox": [ + 498, + 450, + 890, + 525 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Piecewise Bézier Ground Truth. The common $HD$ -map annotation protocol always represents a curve with a set of vectorized points. We propose to first select some annotated keypoints and then divide the curve into $k$ segments, where each is compactly modeled by an $n$ -order Bézier curve. Following the procedure of construction, we present the ground truth generation algorithm in the Algorithm 1.", + "bbox": [ + 496, + 530, + 890, + 636 + ], + "page_idx": 4 + }, + { + "type": "code", + "sub_type": "algorithm", + "code_caption": [ + "Algorithm 1: Piecewise Bézier Curve GenGT." + ], + "code_body": "input:Annotated points $P$ Parameters $n,m,\\epsilon$ output: Piecewise Bezier curves C \n1 $B =$ GetBernsteinCoefficient $(n,m)$ \n2 $B^{+} =$ MatrixPseudoInverse $(B)$ \n3 $l\\gets |P|,s\\gets 0,e\\gets l - 1$ \n4 while $s < e$ do \n5 $P^{\\dagger} =$ CurveInterpolate $(P[s,e])$ . \n6 $\\mathbb{C}^{\\dagger} = B^{+}\\times P^{\\dagger}$ . \n7 $P^{\\ddagger} = B\\times \\mathbb{C}^{\\dagger}$ . \n8 $D^{\\prime} =$ ChamferDistance $(P^{\\dagger},P^{\\ddagger})$ . \n9 if $D^{\\prime} < \\epsilon$ then \n10 $\\begin{array}{r}\\lfloor \\mathbb{C}\\leftarrow [\\mathbb{C},\\mathbb{C}^{\\dagger}],s\\leftarrow e,e\\leftarrow l - 1; \\end{array}$ \n11 else $e\\gets e - 1$", + "bbox": [ + 509, + 672, + 890, + 893 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "13222", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/8634e56fc830c3499328706b3f6b5b9745398d3c52c32a3b80754a4db4453771.jpg", + "image_caption": [ + "Figure 4. The first three diagrams are illustrations of Point-Curve-Region Recovery Loss for Bezier curve modeling. On the far right is a simple schematic diagram of coordinate dilation with $\\omega = 1$ ." + ], + "image_footnote": [], + "bbox": [ + 86, + 88, + 460, + 239 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Point-Curve-Region Recovery Loss. Given the Bezier control points, a novel $PCR$ -Loss is proposed to supervise the learning procedure from three progressive levels, i.e. point, curve and region, which is shown in Fig.4 in detail.", + "bbox": [ + 75, + 292, + 468, + 353 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "1) point-level supervision. Assume the prediction of control sequence from the output head as $\\widehat{\\mathbb{C}}$ and its corresponding ground truth is $\\mathbb{C}$ , we firstly leverage the $L1$ -loss between these coordinates sequentially as,", + "bbox": [ + 75, + 354, + 468, + 414 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\text {p o i n t}} = \\frac {1}{| \\widehat {\\mathbb {C}} |} \\sum_ {i = 1} ^ {| \\widehat {\\mathbb {C}} |} \\| \\mathbb {C} _ {i} - \\widehat {\\mathbb {C}} _ {i} \\| _ {1}, \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 169, + 415, + 468, + 460 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "2) curve-level supervision. Due to the parametric property of Bézier curve that a slight deviation of control points $\\hat{\\mathbb{C}}$ might cause a great change of the curve, we further restore the control sequence $\\widehat{\\mathbb{C}}$ (or $\\mathbb{C}$ ) to curve sequence $\\widehat{\\mathcal{P}}$ (or $\\mathcal{P}$ ) with the vectorization process and adopt the $L1$ -loss as,", + "bbox": [ + 75, + 465, + 468, + 542 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\text {c u r v e}} = \\frac {1}{| \\widehat {\\mathcal {P}} |} \\sum_ {i = 1} ^ {| \\widehat {\\mathcal {P}} |} \\| \\mathcal {P} _ {i} - \\widehat {\\mathcal {P}} _ {i} \\| _ {1} \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 169, + 542, + 468, + 585 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "3) region-level supervision. For digging out more intuitive supervision information, we further recover curve $\\widehat{\\mathcal{P}}$ from the form of discrete coordinates into region mask. First of all, we introduce a coordinate dilation operator, which takes the current coordinate $p_{ij}$ as the center and then generates $(2\\omega +1)^{2}$ surrounding coordinates $p_{\\alpha \\beta}$ with the giving dilation width $\\omega$ , where $\\alpha \\in [i - \\omega ,i + \\omega ]$ and $\\beta \\in [j - \\omega ,j + \\omega ]$ . Secondly, we conduct the coordinate dilation on each point from curve $\\widehat{\\mathcal{P}}$ and then obtain dilated curve points sequence $\\widehat{\\mathcal{P}}^{\\sharp}$ , which can be regarded as the foreground coordinates of the predicted mask $\\widehat{M}$ , i.e. $\\mathcal{S}(\\widehat{M},\\widehat{\\mathcal{P}}^{\\sharp}) = 1$ , where $\\mathcal{S}$ is the grid sampling operation to compute the output values using $\\widehat{M}$ and point coordinates $\\widehat{\\mathcal{P}}^{\\sharp}$ from grid. Finally, after preforming the grid sampling $\\mathcal{S}$ on ground truth map mask $M$ with the same dilated prediction curve, we then bridge a segmentation-base region supervision between $M$ and $\\widehat{\\mathcal{P}}^{\\sharp}$ , which can be formulated mathematically as,", + "bbox": [ + 75, + 593, + 468, + 852 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\text {r e g i o n}} = \\mathcal {L} _ {\\text {d i c e}} \\left(\\mathcal {S} \\left(M, \\widehat {\\mathcal {P}} ^ {\\sharp}\\right), \\mathcal {S} \\left(\\widehat {M}, \\widehat {\\mathcal {P}} ^ {\\sharp}\\right)\\right) \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 137, + 857, + 468, + 876 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $\\mathcal{L}_{\\text{dice}}$ is the common dice loss function in [38].", + "bbox": [ + 81, + 885, + 434, + 901 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4) overall $PCR$ -Loss. In order to exert the above three-level supervision at the same time, we put forward that the overall $PCR$ -Loss is a weighted sum of all three losses as,", + "bbox": [ + 498, + 90, + 890, + 137 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {P C R} = \\lambda_ {p} \\mathcal {L} _ {\\text {p o i n t}} + \\lambda_ {c} \\mathcal {L} _ {\\text {c u r v e}} + \\lambda_ {r} \\mathcal {L} _ {\\text {r e g i o n}} \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 545, + 142, + 890, + 160 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Multi-task Auxiliary Loss. The paradigm of multi-task learning can reduce the risk of overfitting by leveraging the domain-specific information included in the training signals of related tasks [61]. Thence, in addition to supervising the curve-level Bézier modeling procedure of the final head, we also perform auxiliary segmentation-based supervision on the intermediate modules, i.e. semantic-level BEV decoder and instance-level Bézier decoder. Given the output masks $\\widehat{\\mathbb{M}}_s$ and $\\widehat{\\mathbb{M}}_z$ in the Sec.3.2, we formulate the auxiliary loss with the combination of two tasks supervision as,", + "bbox": [ + 496, + 166, + 890, + 316 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {A U X} = \\lambda_ {s} \\mathcal {L} \\left(\\mathbb {M} _ {s}, \\widehat {\\mathbb {M}} _ {s}\\right) + \\lambda_ {z} \\mathcal {L} \\left(\\mathbb {M} _ {z}, \\widehat {\\mathbb {M}} _ {z}\\right) \\tag {10}\n$$\n", + "text_format": "latex", + "bbox": [ + 557, + 321, + 890, + 340 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $\\mathbb{M}_{\\star}$ denotes the ground truth and $\\lambda_{\\star}$ is the weighted factor. Note that $\\mathcal{L}$ is a compound loss with common cross entropy loss and dice loss, namely $\\mathcal{L} = \\mathcal{L}_{ce} + \\mathcal{L}_{dice}$ .", + "bbox": [ + 496, + 349, + 890, + 395 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 500, + 407, + 632, + 424 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.1. Experimental Settings", + "text_level": 1, + "bbox": [ + 500, + 431, + 705, + 449 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Existing Benchmarks. To evaluate the proposed approach, we conduct experiments on the popular NuScenes dataset [2], which consists of 28, 130/6, 019 samples and 700/150 driving scenes for the training/validation set respectively. Each scene contains roughly 40 samples and each sample includes 6 surrounding images, covering $360^{\\circ}$ FOV of the ego-vehicle. For the sake of fair comparison, we follow the previous work [24] and focus on three static map categories, i.e. lane-divider, ped-crossing and road-boundary. Taking the ego-vehicle as the center, we set the perception range to $[30, 30, 15, 15]m$ , which corresponds to the distances of front, rear, left and right respectively, and fix the resolution of ego-to-pixel as $0.15m/pixel$ . In addition, for exploring the performance of our method under different lighting and weather conditions, we further divide NuScenes into five kinds of scene, namely day, night, sunny, cloudy and rainy. Refer to the supplementary material for more details.", + "bbox": [ + 496, + 458, + 890, + 715 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Evaluation Metrics. We utilize the exact same evaluation protocol as [24] of average precision (AP) to access the map construction quality over the instance-level. To be concrete, given a pair of instances from ground-truth and predictions respectively, this protocol computes the Chamfer Distance between them and considers the prediction as true-positive only if the distance is less than a specified threshold, which is set to $[0.2, 0.5, 1.0]m$ in our experiment. Note the overall AP metric is obtained by averaging across three thresholds. Moreover, as for a more informative comparison, the results under different lighting/weather conditions and a much simpler threshold setup of $[0.5, 1.0, 1.5]m$ are further provided.", + "bbox": [ + 496, + 719, + 890, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "13223", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/747f3b3ea5c3b19ac12eea02adf35fb6ebc84892f7dc273c204aa5d5e41c5fac.jpg", + "table_caption": [], + "table_footnote": [ + "Table 1. Comparisons with SOTAs on NuScenes under thresholds of [0.2, 0.5, 1.0] $m$ and [0.5, 1.0, 1.5] $m$ , where the results of latter easier evaluation protocol is marked by Green shade. The Blue shade contains the results that used in all ablation studies for a fair comparison. Note ${}^{\\flat}$ and - indicate the results are re-implemented by us with public code and not available respectively." + ], + "table_body": "
MethodBackboneEpochAP_dividerAP_crossAP_boundmAPmAP_daymAP_nightmAP_sunnymAP.cloudymAP_rainy
IPM(B) [24]Eff-B03010.74.711.79.0-----
IPM(CB) [24]Eff-B03024.07.327.819.7-----
LSS [43]Eff-B03022.95.124.217.411.5b13.3b12.0b12.8b9.5b
VPN [40]Eff-B03022.15.225.317.517.9b17.5b18.2b18.5b15.9b
HMapNet [24]Eff-B03028.37.132.622.721.4b17.4b21.5b23.4b18.9b
BeMapNetEff-B03046.737.438.040.741.328.641.444.936.2
BeMapNetRes-503046.939.037.841.341.930.442.643.637.4
BeMapNetSwin-T3049.142.239.943.744.334.444.847.937.8
BeMapNetRes-5011052.744.544.247.147.739.248.750.341.4
BeMapNetSwin-T11054.246.546.549.149.837.350.453.542.8
BeMapNetSwin-B11055.347.049.450.551.238.052.254.843.6
BeMapNetRes-503062.357.759.459.860.546.962.561.953.0
BeMapNetSwin-T3064.461.361.662.563.153.264.766.054.2
BeMapNetSwin-B11069.064.469.767.768.354.670.371.658.0
", + "bbox": [ + 81, + 88, + 888, + 311 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Implementation Details. We employ EfficientNet-B0 [49], ResNet-50 [14] and SwinTR [31] as backbones, which are all initialized by ImageNet [21] pretraining. The following semantic $BEV$ decoder stacks 2 transformer encoder layers and 4 decoder layers with $64 \\times 32$ $BEV$ queries, and the instance Bézier decoder stacks 6 mask-transformer decoder layers with 60 queries, where 20, 25, 15 for lane-divider, ped-crossing and road-boundary respectively. The shape of input image is resized to $896 \\times 512$ and the mini-batch size is set to 1 per GPU. We train our model with 8 GPUs for 30/110 epochs and adopt multi-step schedule with milestone [0.7, 0.9] and $\\gamma = \\frac{1}{3}$ . The AdamW [33] optimizer is employed with a weight decay of $1e^{-4}$ and a learning rate of $2e^{-4}$ , which is multiplied by 0.1 for backbone. As for hyper-parameters of loss weight, we set $\\lambda_s$ , $\\lambda_z$ , $\\lambda_p$ , $\\lambda_c$ , $\\lambda_r$ to 1, 5, 5, 10, 1 respectively and the dilated width $\\omega$ in $\\mathcal{L}_{region}$ to 5. The deployments of piecewise Bézier curve $\\langle k, n \\rangle$ for lane-divider, ped-crossing and road-boundary are set to $\\langle 3, 2 \\rangle$ , $\\langle 1, 1 \\rangle$ , $\\langle 7, 3 \\rangle$ . Note $m$ in Algorithm 1 is set to 100.", + "bbox": [ + 75, + 375, + 472, + 664 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.2. Comparisons with State-of-the-art Methods", + "text_level": 1, + "bbox": [ + 76, + 678, + 449, + 695 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We present the overall evaluation results on NuScenes in Table 1, which shows that our BeMapNet is significantly superior to the existing SOTA approaches by a large margin (up to 18.0) under the same setting of EfficientNet-B0 and 30 epochs, indicating the effectiveness of our approach. In addition, after replacing the backbone with more common ResNet-50 and more popular SwinTiny, our model achieves a further improvement of 0.6 and 3.0 AP respectively. Next, considering the slow convergence of the Transformer-based model, we increase the training schedule to 110 epochs and gain at least another 5.4 improvements. Even in somewhat unconventional scenarios, such as night and rainy, our proposed approach still shows a great advantage, i.e. 13.2 and", + "bbox": [ + 75, + 703, + 472, + 902 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/548d009a1115b7e0622895bf8f7fabdd7927875991cf77df1fa2ef6a3d93ecad.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
Position EncodingAP_dividerAP_crossAP_boundmAP
Sine PE42.834.134.737.2
Learned PE40.232.233.835.4
IPM-PE46.439.237.841.1
+ Exclusive FC38.633.333.935.3
+ Shared FC49.142.239.943.7
", + "bbox": [ + 513, + 372, + 880, + 467 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 2. Comparisons on different methods of position encoding.", + "bbox": [ + 501, + 473, + 888, + 488 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "16.9 AP are obtained respectively. Furthermore, another interesting observation is that regardless of which method is used, we find that the performance of sunny scene is always slightly lower than cloudy. We believe that strong illuminations and ground shades on sunny day might have a certain impact on the perception of map objects. As a supplement, the last three rows of Table 1 show the performance of our approach on a much simpler evaluation protocol.", + "bbox": [ + 496, + 500, + 890, + 621 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.3. Ablation Study", + "text_level": 1, + "bbox": [ + 500, + 631, + 653, + 648 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "The Different Way of Position Encoding. Table 2 shows the performance of different $PE$ in semantic BEV decoder for the map construction. Compared with the sine/learned-based method, our proposed IPM-PE module improves AP by 3.9/5.7 respectively, which proves the multi-perspective $PE$ guided by the intrinsic and extrinsic parameters is very effective. Moreover, through the results in the 3-rd and 5-th row, we find that IPM-PE with shared FC layer alignment gains an further improvement of 2.6 points. Yet, in order to rule out the possibility of that the attached FC layer brings an increment, we then feed the position embeddings from IPM-PE into two exclusive FCs and the 4-th row results exclude the influence of FC. These comparisons indicate the shared align layer is the exactly essential part to mitigate the performance decline brought by the unreasonable assumption of IPM, which validates our conjecture in Sec.3.2.2.", + "bbox": [ + 496, + 657, + 893, + 901 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "13224", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/cee40b8254afb773901ebf807217fd10dc8aa039219eb16607ea573cdc045532.jpg", + "image_caption": [ + "Figure 5. The qualitative comparison results of HDMapNet [24], BeMapNet and GroundTruth [2] under different scenarios." + ], + "image_footnote": [], + "bbox": [ + 125, + 88, + 846, + 329 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Effectiveness of $PCR$ -Loss. The $PCR$ -Loss mainly consists of three parts, i.e. point, curve and region. Table 3 shows detailed ablation results of the role of each part. Specifically, with adopting only one supervision in rows $1 \\sim 3$ , the performance trend is roughly: curve > point > region. Among them, it is worth noting that the only region-based supervision shows very poor performance, which is understandable because the generation of region mask relies on a collection of relatively accurate points. This conjecture is also verified in rows $4 \\sim 5$ of the Table 3. Furthermore, when integrating multiple loss supervision, the final performance is consistently improved compared to the single one, and three parts used together achieves the optimal AP results of 43.7.", + "bbox": [ + 75, + 357, + 472, + 555 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/b24f3dbac49b277c85c0d8032d7bf05bbcb59a007493c7a9674a6c0d001a9244.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
PointCurveRegionAP_dividerAPPEDAPboundarymAP
✓XX39.133.323.732.0
X✓X47.235.135.939.4
XX✓3.22.60.52.1
✓X✓40.739.416.732.9
X✓✓48.238.539.742.1
✓✓X46.538.536.240.4
✓✓✓49.142.239.943.7
", + "bbox": [ + 83, + 563, + 464, + 674 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Effectiveness of Multi-task Auxiliary Loss. Without any auxiliary loss, the average AP of our proposed BeMapNet is only 20.0. Yet, after adopting another semantic/instance supervision, the result is improved to 34.5/38.4 respectively and goes further to 43.7 with employing both, which shows the auxiliary tasks for producing high-quality semantic $BEV$ features and instance descriptors are very important.", + "bbox": [ + 75, + 699, + 468, + 806 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/cb6ee7fb2c753fa994bd5dcf1c003094e00a3f0cbd239172b14ef85348c763a8.jpg", + "table_caption": [ + "Table 3. The effectiveness of different modules in ${PCR} - {Loss}$ ." + ], + "table_footnote": [], + "table_body": "
SemanticInstanceAPdividerAPpedAPboundarymAP
XX21.517.820.720.0
✓X39.331.532.834.5
X✓44.334.636.538.4
✓✓49.142.239.943.7
", + "bbox": [ + 81, + 809, + 467, + 887 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Comparison with Polyline Vectorization. An amusing fact is that a Bézier curve with $n = 1$ is simply a straight line between two control points. By setting the degree of all elements to 1, our framework naturally degenerates into the polyline-based method. Note we further set $k$ to 9, 1, 29 for lane-divider, ped-crossing and road-boundary respectively. The comparisons in Table 5 show the Bézier-based vectorization approach achieves better 4.5 AP. Interestingly, as the complexity of map element shape increases (usually ped-crossing $<$ lane-divider $<$ road-boundary), we find that the corresponding AP improvement increases as well.", + "bbox": [ + 496, + 357, + 890, + 525 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/d1c7988cf9909d55ea76febac90d9928eba137e0c3c1fd5c1b30a1a75933db29.jpg", + "table_caption": [ + "Table 4. The effectiveness of different modules in AUX-Loss." + ], + "table_footnote": [], + "table_body": "
VectorizationAPdividerAPpedAPboundarymAP
Polyline45.039.133.439.2
Bézier49.1 (+4.1)42.2 (+3.1)39.9 (+6.5)43.7(+4.5)
", + "bbox": [ + 504, + 529, + 890, + 579 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 5. Comparison with the different type of vectorization.", + "bbox": [ + 513, + 583, + 877, + 597 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Qualitative Analysis. We show the qualitative comparisons with SOTAs in Fig. 5. Besides avoiding complex vectorized post-processing, the proposed BeMapNet constructs various and changeful $HD$ -elements more compactly and robust. Note that more extensive visualizations under different conditions are further provided in our supplementary material.", + "bbox": [ + 496, + 604, + 890, + 698 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 709, + 619, + 724 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Vectorized $HD$ -map online construction focuses on the perception of centimeter-level environmental information. Starting from the conventional parameterization-based methods, this paper presents an end-to-end postprocessing-free architecture, namely BeMapNet, with leveraging unified piecewise Bézier curve for various and changeful map elements. By introducing three well-designed modules, i.e. IPM-PE Align Module, Piecewise Bézier Head and Point-Curve-Region Loss, the overall framework is concise and elegant, which reaches state-of-the-art performance and provides a new perspective for future $HD$ -map research.", + "bbox": [ + 496, + 734, + 890, + 902 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "13225", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Paul J Besl and Neil D McKay. Method for registration of 3-d shapes. 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In Proceedings of the IEEE Conference on Computer Vision and Pattern Recognition, pages 13760-13769, 2022. 2" + ], + "bbox": [ + 78, + 92, + 468, + 840 + ], + "page_idx": 10 + }, + { + "type": "page_number", + "text": "13228", + "bbox": [ + 480, + 945, + 517, + 955 + ], + "page_idx": 10 + } +] \ No newline at end of file diff --git a/2023/End-to-End Vectorized HD-Map Construction With Piecewise Bezier Curve/798a815c-ad48-46e8-9f91-80fae212fa9c_model.json b/2023/End-to-End Vectorized HD-Map Construction With Piecewise Bezier Curve/798a815c-ad48-46e8-9f91-80fae212fa9c_model.json new file mode 100644 index 0000000000000000000000000000000000000000..abf0a4ce7fc9e443494cf1dc6cda2b2103a3c97e --- /dev/null +++ b/2023/End-to-End Vectorized HD-Map Construction With Piecewise Bezier Curve/798a815c-ad48-46e8-9f91-80fae212fa9c_model.json @@ -0,0 +1,2422 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.001, + 0.812, + 0.047 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.108, + 0.13, + 0.865, + 0.154 + ], + "angle": 0, + "content": "End-to-End Vectorized HD-map Construction with Piecewise Bézier Curve" + }, + { + "type": "text", + "bbox": [ + 0.275, + 0.181, + 0.694, + 0.218 + ], + "angle": 0, + "content": "Limeng Qiao Wenjie Ding Xi Qiu* Chi Zhang MEGVII Technology" + }, + { + "type": "text", + "bbox": [ + 0.253, + 0.22, + 0.714, + 0.235 + ], + "angle": 0, + "content": "{qiaolimeng, dingwenjie, qiumi, zhangchi}@megvii.com" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.269, + 0.314, + 0.285 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.301, + 0.474, + 0.664 + ], + "angle": 0, + "content": "Vectorized high-definition map (HD-map) construction, which focuses on the perception of centimeter-level environmental information, has attracted significant research interest in the autonomous driving community. Most existing approaches first obtain rasterized map with the segmentation-based pipeline and then conduct heavy post-processing for downstream-friendly vectorization. In this paper, by delving into parameterization-based methods, we pioneer a concise and elegant scheme that adopts unified piecewise Bézier curve. In order to vectorize changed map elements end-to-end, we elaborate a simple yet effective architecture, named Piecewise Bézier HD-map Network (BeMapNet), which is formulated as a direct set prediction paradigm and postprocessing-free. Concretely, we first introduce a novel IPM-PE Align module to inject 3D geometry prior into BEV features through common position encoding in Transformer. Then a well-designed Piecewise Bézier Head is proposed to output the details of each map element, including the coordinate of control points and the segment number of curves. In addition, based on the progressively restoration of Bézier curve, we also present an efficient Point-Curve-Region Loss for supervising more robust and precise HD-map modeling. Extensive comparisons show that our method is remarkably superior to other existing SOTAs by \\(18.0\\mathrm{mAP}\\) at least1." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.691, + 0.21, + 0.707 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.716, + 0.47, + 0.868 + ], + "angle": 0, + "content": "As one of the most fundamental components in the autodriving system, high-definition map contains centimeter details of traffic elements, vectorized topology and navigation information, which instruct ego-vehicle to accurately locate itself on the road and understand what is coming up ahead. At present, conventional SLAM-based solutions [45, 46, 60] have been widely adopted in practice. Yet, due to dilemmas of high annotation costs and untimely updates, the offline approach is gradually being replaced by the learning-based online HD-map construction with onboard sensors." + }, + { + "type": "image", + "bbox": [ + 0.523, + 0.269, + 0.646, + 0.448 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.536, + 0.45, + 0.63, + 0.46 + ], + "angle": 0, + "content": "(a) HD-map example" + }, + { + "type": "image", + "bbox": [ + 0.665, + 0.27, + 0.871, + 0.349 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.685, + 0.352, + 0.854, + 0.362 + ], + "angle": 0, + "content": "(b) vanilla Bezier vs. piecewise Bezier" + }, + { + "type": "image", + "bbox": [ + 0.666, + 0.366, + 0.871, + 0.446 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.666, + 0.45, + 0.869, + 0.461 + ], + "angle": 0, + "content": "(c) map curve restored by real control points" + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.466, + 0.892, + 0.592 + ], + "angle": 0, + "content": "Figure 1. Illustration of our motivation for piecewise Bézier curve, termed as \\(\\langle k, n \\rangle\\), where \\(k\\) is the piece number and \\(n\\) is the degree. Fig.(a) is a real HD-map case from NuScenes. Fig.(b) compares the difference between vanilla and piecewise Bézier curve through the same map element, where the light purple is the restored curve with Bézier process. The last is more efficient than previous ones with reducing the number of control points by \\(64\\%\\) in this case. Fig.(c) illustrates that piecewise Bézier curve can model arbitrary-shaped curves. Note the blue circles denote actual control points." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.599, + 0.893, + 0.901 + ], + "angle": 0, + "content": "The deep-based paradigm of online \\( HD \\)-map building is gradually developing, but it still faces two main challenges: 1) modeling instance-level vectorized \\( HD \\)-map end-to-end. Most existing works construct \\( HD \\)-map by rasterizing \\( BEV \\) (bird-eye-view) maps into semantic pixels with segmentation [24, 42], which not only lacks the modeling of instance-level details, but also requires heavy post-processing to obtain vectorized information. As a sub-task, lane detection makes a relatively better advance for this issue, that is, in addition to segmentation-based methods [39, 41, 62], there are also point-based [25, 47] and curve-based [12, 28] schemes. However, compared to the simple lane scenario, \\( HD \\)-map contains more shape-changeful elements, so such methods cannot be directly adopted into the \\( HD \\)-map construction. 2) performing 2D-3D perspective transformation efficiently. Obtaining 3D- \\( BEV \\) perception from multi-view 2D images is an essential step for building \\( HD \\)-map, which is mainly divided into three ideas, i.e. geometric priors [44], learnable parameters [40, 42], and a combination of the two [17, 43]. Note the assumptions of geometry-based methods often do" + }, + { + "type": "page_footnote", + "bbox": [ + 0.094, + 0.875, + 0.227, + 0.888 + ], + "angle": 0, + "content": "*Corresponding author." + }, + { + "type": "page_footnote", + "bbox": [ + 0.098, + 0.888, + 0.388, + 0.9 + ], + "angle": 0, + "content": "1https://github.com/er-muyue/BeMapNet" + }, + { + "type": "list", + "bbox": [ + 0.094, + 0.875, + 0.388, + 0.9 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "13218" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.182 + ], + "angle": 0, + "content": "not conform to the actual situation, leading to such schemes are less adaptable, while learning-based methods require a large amount of labeled data to generalize across various scenarios. Combining the above two branches not only has multi-scenario scalability, but also reduces the demand for annotated data, has attracted increasing research interest." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.183, + 0.471, + 0.409 + ], + "angle": 0, + "content": "To the best of our knowledge, the curve parameterization construction of \\( HD \\)-map in the \\( BEV \\) space is vacancy and no one has explored it. Based on the widely used Bézier curve, which is mathematically defined by a set of control points, we pioneer to devise a concise and elegant \\( HD \\)-map scheme that adopts piecewise Bézier curve, where each map curve is divided into multiple \\( k \\) segments and each segment is then represented by a vanilla Bézier curve with degree \\( n \\), hence denoted as \\( \\langle k, n \\rangle \\). Despite \\( \\langle 1, n \\rangle \\) is enough to express any map element with infinite \\( n \\) in theory, more complex curve tends to require higher degree, meaning that there are more control points need to be modeled, which is shown in Fig.1. The proposed piecewise strategy allows us to parameterize a curve more compactly with fewer control points and higher capacity, which is extremely scalable and robust in practice." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.409, + 0.471, + 0.771 + ], + "angle": 0, + "content": "Inspired by the above motivations, we propose an end-to-end vectorized HD-map construction architecture, named as Piecewise Bézier HD-map Network (BeMapNet). The overall framework is illustrated in detail in Fig.2, which streamlines the architecture into four primary modules for gradually-enriched information, i.e. feature extractor shared among multi-view images, semantic BEV decoder for \\(2D-3D\\) perspective elevation, instance Bézier decoder for curve-level descriptors, and piecewise Bézier head for point-level parameterization. To be concrete, we first introduce a novel IPM-PE Align module into Transformer-based decoders, which injects IPM (inverse perspective mapping) geometric priors into BEV features via PE (position encoding) and hardly adds any parameters except a FC layer. Secondly, we further design a Piecewise Bézier Head for dynamic curve modeling with adopting two branches as classification and regression, where the former classifies the number of pieces to determine the curve length and the latter regresses the coordinate of control points to determine the curve shape. Lastly, we present an Point-Curve-Region Loss for robust curve modeling by supervising restoration information as a progressive manner. Since it is modeled as a sparse set prediction task and optimized with a bipartite matching loss, our method is postprocessing-free and high-performance." + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.772, + 0.445, + 0.786 + ], + "angle": 0, + "content": "The main contributions of our approach are three-folds:" + }, + { + "type": "text", + "bbox": [ + 0.084, + 0.788, + 0.468, + 0.817 + ], + "angle": 0, + "content": "- We pioneer the BeMapNet for concise and elegant modeling of HD-map with unified piecewise Bézier curve." + }, + { + "type": "text", + "bbox": [ + 0.084, + 0.822, + 0.468, + 0.867 + ], + "angle": 0, + "content": "- We elaborate the overall end-to-end architecture with innovatively introducing IPM-PE Align Module, Piecewise Bézier Output Head and well-designed PCR-Loss." + }, + { + "type": "text", + "bbox": [ + 0.084, + 0.871, + 0.468, + 0.901 + ], + "angle": 0, + "content": "- BeMapNet is remarkably superior to SOTAs on existing benchmarks, revealing the effectiveness of our approach." + }, + { + "type": "list", + "bbox": [ + 0.084, + 0.788, + 0.468, + 0.901 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.09, + 0.642, + 0.105 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.115, + 0.787, + 0.132 + ], + "angle": 0, + "content": "2.1. Vectorized HD-map Construction" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.14, + 0.892, + 0.456 + ], + "angle": 0, + "content": "\\(HD\\)-map is precise at centimeter-level and consists of vectorized details not normally present on standard map [27], which highly aggravates the difficulty of obtaining accurate annotations in practice. Most previous methods focus on SLAM [11, 18, 22, 36, 46, 58] with exploring LiDAR points of the environment, involving large-scale data acquisition and labor-intensive annotations. Recently, more and more researchers formulate the process of building \\(HD\\)-map as a segmentation task [6, 13, 20, 32] from various sensors, such as cameras [15, 26, 34, 35, 40, 43, 59, 63] and LiDAR [1, 57]. HDMapNet [24] extracts features from the observations of multi-modalities and groups semantic rasterized maps with heuristic post-processing for vectorized results. Without any further vectorization, [42] only obtains semantic map representations from a Transformer-based camera-to-BEV module. Different from the above segmentation-based frameworks, our proposed BeMapNet adopts the parameterization-based paradigm and constructs instance-level vectorized \\(HD\\)-map end-to-end with a multiview and camera-only manner, which is a more flexible and scalable solution for downstream tasks." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.469, + 0.833, + 0.485 + ], + "angle": 0, + "content": "2.2. Structure Modeling of Geometric Data" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.494, + 0.892, + 0.901 + ], + "angle": 0, + "content": "HD-map contains various kinds of map elements, including lane-divider, ped-crossing, road-boundary, etc., which are typically regarded as geometric data, e.g. points, polygons and curves. To the best of knowledge, there are two mainstream exploration directions for deep geometric modeling, one is point-based, including uniform-points and keypoints estimation, and the other is curve-based, including polynomial curve and Bézier curve. Taking the most related lane detection as an example, LineCNN [25] presents a novel line proposal unit to detect lanes as a set of points, and later LaneATT [47] represents a lane by equally-spaced \\(2D\\)-points that achieves good performance. GANet [54] focuses on keypoint estimation and association with adaptively lane feature aggregator. HDMapGen [37] proposes a hierarchical point generative model for producing high-quality HD lane map. As for cruve-based, [51] and [48] directly predict the polynomial coefficients with a differentiable least-squares fitting module and simple \\(FC\\) respectively. Recently, based on the DETR [4], LSTR [28] presents a query-based detector to decode poly-parameters of a lane end-to-end. Apart from this, some studies also adopt Bézier curve for geometry, such as text boundary [29], center-line segment [3] and lane curve [12]. Unlike these approaches of addressing simple-shape elements, our method innovatively employs piecewise Bézier curves without any complicated geometric assumptions to parameterize arbitrary-shape geometry in HD-map scenarios." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "13219" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.081, + 0.089, + 0.895, + 0.378 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.381, + 0.893, + 0.437 + ], + "angle": 0, + "content": "Figure 2. The architecture of our proposed BeMapNet, containing four primary components for extracting progressively richer information, i.e. image-level multi-scale features, semantic-level BEV feature, instance-level curve descriptors, and point-level Bézier control sequence. Right-top: The blue and orange circles represent explicit control points and implicit control offsets respectively. Note that the term GAP is global average pooling and MatMul is the matrix multiplication. Right-bottom: \\((H_c, W_c) / (H_b, W_b)\\) is the shape of image/BEV feature." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.446, + 0.453, + 0.461 + ], + "angle": 0, + "content": "2.3. Multi-view Camera-to-BEV Transformation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.478, + 0.473, + 0.902 + ], + "angle": 0, + "content": "In most \\(3D\\) research studies, obtaining high-quality BEV representations from multi-view camera features is the top priority of various domains, such as \\(3D\\) object detection [17, 30, 43, 55, 56], motion prediction [10, 16, 19, 23, 53] and map construction [24, 26, 40, 42]. IPM [44] is the most basic and straightforward method with a homography transformation, which is precisely calculated by camera parameters. Without adopting the \\(3D\\) geometry prior, some methods [3, 40, 42] directly leverage learnable parameters to complete the perspective transformation. VPN [40] and Neat [9] both utilize a \\(FC\\) layer to transform the image features into the BEV space, and [42] further designs a multi-camera deformable attention unit based on transformer. However, in order to obtain more explicit BEV representations, more and more researches argue that the geometry priors has great advantages for model convergence and performance. Based on VPN, [24] fuse the multi-camera BEV spaces with the camera poses. LSS [43] and BEVDet [17] build the connection between camera-view and BEV based on the depth distribution estimation. DETR3D [56] manipulates predictions directly in \\(3D\\) space with linking \\(3D\\) positions to \\(2D\\) spaces and [5] generates BEV features by regarding camera parameters as a reference. PETR [30] encodes the \\(3D\\) information as position embedding and conducts query decoding on position-aware features. In addition to introducing the \\(3D\\) geometry prior, we further performs position embedding alignment for transforming the camera features and BEV features into the world coordinate system." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.445, + 0.591, + 0.461 + ], + "angle": 0, + "content": "3. Method" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.47, + 0.703, + 0.485 + ], + "angle": 0, + "content": "3.1. Problem Formulation" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.494, + 0.892, + 0.54 + ], + "angle": 0, + "content": "Preliminary on Piecewise Bézier Curve. A Bézier curve is a parametric curve which is formulated by a set of ordered control points \\( c_{0} \\) through \\( c_{n} \\) as," + }, + { + "type": "equation", + "bbox": [ + 0.592, + 0.548, + 0.892, + 0.586 + ], + "angle": 0, + "content": "\\[\np (t) = \\sum_ {i = 0} ^ {n} b _ {i, n} (t) c _ {i}, t \\in [ 0, 1 ] \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.594, + 0.891, + 0.625 + ], + "angle": 0, + "content": "where \\(n\\) is the degree of the curve and \\(b_{i,n}(t)\\) is known as Bernstein basis polynomial of degree \\(n\\)," + }, + { + "type": "equation", + "bbox": [ + 0.556, + 0.632, + 0.892, + 0.666 + ], + "angle": 0, + "content": "\\[\nb _ {i, n} (t) = \\binom {n} {i} t ^ {i} (1 - t) ^ {n - i}, i = 0, \\dots , n \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.671, + 0.892, + 0.793 + ], + "angle": 0, + "content": "According to Eq.1, we know the first and last control points are endpoints of the curve, i.e. \\( p(0) = c_0 \\), \\( p(1) = c_n \\). Then we define a piecewise Bézier curve \\( \\langle k, n \\rangle \\) consists of \\( k \\) segments, each of which is an \\( n \\)-order Bézier and two consecutive segments satisfy the positional continuity condition as \\( p^j(1) = p^{j+1}(0) \\), where \\( j \\) is the segment \\( id \\) varying from 0 to \\( k-2 \\). Hereafter, given a piecewise Bézier curve as shown in Fig.3, we denote its ordered control points as," + }, + { + "type": "equation", + "bbox": [ + 0.514, + 0.798, + 0.891, + 0.818 + ], + "angle": 0, + "content": "\\[\n\\mathbb {C} = \\left\\{c _ {i} ^ {j} \\in \\mathbb {R} ^ {2} \\mid i \\in [ 0, n ], j \\in [ 0, k - 1 ], c _ {n} ^ {j} = c _ {0} ^ {j + 1} \\right\\} \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.825, + 0.893, + 0.901 + ], + "angle": 0, + "content": "Moreover, due to the first and last control points of each segment are always on the curve, we naturally term these points that retain a distinct significance as explicit control points \\(\\mathbb{C}^E\\) and the remaining as implicit control points \\(\\mathbb{C}^I\\), where \\(\\mathbb{C} = \\mathbb{C}^E \\cup \\mathbb{C}^I\\), \\(|\\mathbb{C}^E| = k + 1\\) and \\(|\\mathbb{C}^I| = nk - k\\)." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "13220" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.086, + 0.09, + 0.368, + 0.226 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.094, + 0.227, + 0.117, + 0.237 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.12, + 0.227, + 0.222, + 0.237 + ], + "angle": 0, + "content": "Piecewise Bézier Curve" + }, + { + "type": "image", + "bbox": [ + 0.244, + 0.227, + 0.257, + 0.236 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.261, + 0.227, + 0.355, + 0.237 + ], + "angle": 0, + "content": "Explicit Control Points" + }, + { + "type": "image", + "bbox": [ + 0.374, + 0.091, + 0.462, + 0.226 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.379, + 0.227, + 0.456, + 0.237 + ], + "angle": 0, + "content": "Explicit Center" + }, + { + "type": "image", + "bbox": [ + 0.094, + 0.242, + 0.117, + 0.25 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.12, + 0.242, + 0.222, + 0.252 + ], + "angle": 0, + "content": "Bézier Control Polygon" + }, + { + "type": "image", + "bbox": [ + 0.244, + 0.242, + 0.257, + 0.25 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.261, + 0.242, + 0.355, + 0.252 + ], + "angle": 0, + "content": "Implicit Control Points" + }, + { + "type": "image", + "bbox": [ + 0.379, + 0.242, + 0.394, + 0.25 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.398, + 0.242, + 0.455, + 0.252 + ], + "angle": 0, + "content": "mplicit Offset" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.258, + 0.47, + 0.314 + ], + "angle": 0, + "content": "Figure 3. Illustration of a 3-pieces 3-order piecewiseBezier curve, denoted as \\(\\langle 3,3\\rangle\\) for the left part. For each segment, we model the implicit control point coordinates by an offset \\((\\Delta x,\\Delta y)\\) from the center of explicit control points as shown on the right part." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.321, + 0.47, + 0.578 + ], + "angle": 0, + "content": "Vectorized HD-map Modeling. By sequentially sampling points along the elements in HD-map, each object can be structured as an open-shape curve as a vectorized manner. To uniformly parameterize these various shape-changeful map elements, including points, polygons and curves, we employ the piecewise Bézier curve proposed in Eq.3 and formalize a vectorized HD-map as a piecewise Bézier curve set \\(\\mathcal{M} = \\{\\mathbb{C}_i|i = 1,\\dots ,|\\mathcal{M}|\\}\\), where \\(|\\mathcal{M}|\\) is the number of map instances. Our objective is to learn a model that extracts compact information from the camera sensors and predicts, for each map element, its corresponding Bézier control sequence, which uniquely determine the shape and position of the map curve. In addition, for the purpose of reducing the modeling complexity of implicit control points \\(\\mathbb{C}^{\\mathcal{I}}\\) for each segment, we subtly generate implicit coordinates through the center of explicit control points and their relative offsets as shown in the right of Fig.3." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.582, + 0.468, + 0.763 + ], + "angle": 0, + "content": "Piecewise Bézier Curve Modeling Principle. Considering the large-variety and changeful-shape of map elements, we present a consistent-degree but dynamic-piece principle for modeling piecewise curve more precisely and efficiently as, (1) consistent-degree on semantic-level. Due to a Bézier curve of degree \\( k \\) can be easily converted into degree \\( k + 1 \\) with the same shape, i.e. degree elevation in mathematics, the same curve may correspond to multiple Bézier solutions with only different degree. This kind of obfuscation is devastating for the network modeling. And we argue that keeping the consistent-degree within the same semantic category is the most efficient way to solve this dilemma." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.765, + 0.468, + 0.902 + ], + "angle": 0, + "content": "(2) dynamic-piece on instance-level. Considering that the complexity of different map curves is always inconsistent, the modeling method with a fixed and large number of segments will not only cause excessive redundancy in the expression of each curve, but also lead to confusion in the definition of sub-segment, which places a certain burden on the model optimization. The dynamic-piece rule demands the model to choose the number of segments dynamically and parameterize a Bézier curve as compactly as possible." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.091, + 0.805, + 0.108 + ], + "angle": 0, + "content": "3.2. Piecewise Bezier HD-map Network" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.115, + 0.699, + 0.13 + ], + "angle": 0, + "content": "3.2.1 Overall Architecture" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.141, + 0.892, + 0.203 + ], + "angle": 0, + "content": "The overall model architecture is illustrated in detail in Fig. 2, which streamlines the framework into four parts, namely feature extractor, semantic BEV decoder, instance Bézier decoder and piecewise Bézier output head respectively." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.207, + 0.892, + 0.298 + ], + "angle": 0, + "content": "Feature Extractor. Given surrounding images from multicamera as inputs, a shared CNN backbone is first employed to obtain each image feature, and then these multi-scale features from different stages are fed into FPN [50] to integrate rich environmental information. Last we upsample pyramid features to the same size and stack them together as outputs." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.302, + 0.893, + 0.56 + ], + "angle": 0, + "content": "Semantic BEV Decoder. We leverage a standard encoder-decoder paradigm based on Transformer to elevate camera-view features into canonical BEV spaces. By treating the perspective transformation as a direct set prediction task, the BEV decoder takes camera features with shape \\( H_{c} \\times W_{c} \\) and \\( H_{q} \\times W_{q} \\) learnable BEV queries as inputs, and produces BEV features \\( F_{b} \\in \\mathbb{R}^{C \\times H_{b} \\times W_{b}} \\) by modeling all pairwise interactions among elements with self- and cross-attention. Different from the region-agnostic query in DETR, we correspond each query with a \\( \\gamma^{h} \\times \\gamma^{w} \\) region on BEV features one-to-one, i.e. \\( H_{b} \\times W_{b} = \\gamma^{h}H_{q} \\times \\gamma^{w}W_{q} \\). The \\( F_{b} \\) is then fed into a \\( 1 \\times 1 \\) conv and upsample block to obtain the final semantic mask \\( \\mathbb{M}_{s} \\in \\mathbb{R}^{U \\times H_{s} \\times W_{s}} \\), where \\( U \\) is the number of classes and \\( H_{s} \\times W_{s} \\) is the map shape. In addition, we also propose a novel IPM-PE Align Layer to refactor the features in different coordinate systems through the most common position encoding layer in Transformer." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.564, + 0.892, + 0.76 + ], + "angle": 0, + "content": "Instance Bézier Decoder. So as to perform more accurate parametric modeling of each curve, we further equip an instance Bézier decoder based on masked cross-attention [8]. To be concrete, given semantic features \\( F_{b} \\) and learnable instance Bézier queries \\( Q \\in \\mathbb{R}^{V \\times C} \\), where \\( V \\) is the max number of instance, this module aggregates information and decodes Bézier descriptors \\( \\vec{z} \\in \\mathbb{R}^{V \\times C} \\), which contain key info of geometric and positional relationships between different map elements. With extra performing matrix multiplication between \\( \\vec{z} \\) and \\( F_{b} \\), we obtain instance map mask \\( \\mathbb{M}_{z} \\in \\mathbb{R}^{V \\times H_{s} \\times W_{s}} \\), which is used as the foreground mask for next decoder layer and also to perform segmentation supervision for more spatial context information." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.765, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Piecewise Bézier Output Head. Following the principle elaborated in Sec.3.1, we closely design a piecewise Bézier output head with two core modules, i.e. Split Coordinate Regression and Dynamic End-index Classification, which are utilized to output the coordinates of Bézier control point sequence and the number of segments respectively. With easily recovering piecewise Bézier curves and further introducing the bipartite matching setting, the proposed output head constructs vectorized local HD-map very efficiently." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "13221" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.077, + 0.092, + 0.277, + 0.107 + ], + "angle": 0, + "content": "3.2.2 IPM-PE Align Layer" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.115, + 0.474, + 0.342 + ], + "angle": 0, + "content": "As a basic module of traditional Transformer architecture, positional encoding utilizes the sequence order by injecting information about the position of tokens [52], where sin-cos and learned-based functions are the most common practices. Yet, for the purpose of perspective transformation between 2D camera-views and 3D BEV, we argue it is not enough to only encode the position correspondence within single view, but it is also necessary to maintain the position consistency relationships between two perspectives. Thence we put forward a novel IPM-PE Align Layer to encode the 2D-3D geometry priors into features from different coordinate systems. To be concrete, given a point \\( p_c^{f_i} = (u,v,1)^\\top \\) on the \\( i \\)-th camera-view feature and its corresponding world point \\( p_c^w = (x,y,z)^\\top \\), the following mathematical equation is satisfied on the assumption of pinhole camera model," + }, + { + "type": "equation", + "bbox": [ + 0.178, + 0.351, + 0.47, + 0.37 + ], + "angle": 0, + "content": "\\[\nd \\cdot A ^ {- 1} \\cdot p _ {c} ^ {f _ {i}} = K ^ {i} \\cdot T ^ {i} \\cdot p _ {c} ^ {w} \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.379, + 0.47, + 0.516 + ], + "angle": 0, + "content": "where \\(d\\) is the depth, \\(A\\) is the transformation matrix between image-grid and feature-grid, \\(K^i\\) and \\(T^i\\) are \\(i\\)-th intrinsic and extrinsic matrices. Based on the assumption of that the ground surface is flat and at a fixed height in \\(IPM\\), the world position \\((x,y)\\) and depth \\(d\\) can be easily calculated through Eq.4. Note \\(d < 0\\) denotes the position is not valid. As for the other branch of BEV perspective, given a point \\(p_b^f\\) from the BEV feature \\(F_{b}\\) and its world point \\(p_b^w\\), there is usually only a scale relationship \\(\\kappa = (\\kappa_x,\\kappa_y)\\) between them," + }, + { + "type": "equation", + "bbox": [ + 0.23, + 0.525, + 0.47, + 0.545 + ], + "angle": 0, + "content": "\\[\np _ {b} ^ {f} = \\boldsymbol {\\kappa} \\cdot p _ {b} ^ {w} \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.554, + 0.47, + 0.676 + ], + "angle": 0, + "content": "Then we leverage the standard sin-cos function to convert all these world coordinates \\( P_{c}^{w} \\) and \\( P_{b}^{w} \\) as position embedding \\( f_{c}^{pe} \\) and \\( f_{b}^{pe} \\) respectively. Since the assumption of flat-ground and known-height usually does not hold in practice, \\( f_{c}^{pe} \\) and \\( f_{b}^{pe} \\) are not exactly aligned in the world coordinate system, we further adopt a shared FC layer on \\( f_{c}^{pe} \\) and \\( f_{b}^{pe} \\) to perform embedding alignment and then obtain more unified position encoding, which is shown in Fig.2 in detail." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.693, + 0.342, + 0.708 + ], + "angle": 0, + "content": "3.2.3 Piecewise Bézier Output Head" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.72, + 0.47, + 0.84 + ], + "angle": 0, + "content": "Split Coordinate Regression Head. Following the illustration in the upper right corner of the Fig.2, we elaborate the forward flow of proposed regression head as four steps, \\( \\mathbf{I} \\) with \\( i \\)-th incoming Bézier descriptor \\( \\vec{z}_i \\in \\mathbb{R}^C \\), we first convert its channel from \\( C \\) to \\( u \\cdot v \\) with adopting a standard \\( FC \\) layer and then split it into \\( u \\) parts to get a collection of coordinate descriptors \\( x_i^j \\in \\mathbb{R}^v \\), where \\( j \\in [1, u] \\), \\( u \\) is the number of coordinate and \\( v \\) is the channel of descriptor." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.47, + 0.901 + ], + "angle": 0, + "content": "2) given the desired output shape \\((H_s, W_s)\\), a hard-coded candidate coordinates grid \\(G \\in \\mathbb{R}^{2 \\times H_s \\times W_s}\\) is generated with X-Y two channels and next a \\(1 \\times 1\\) conv layer is utilized to convert \\(G\\) to its coordinate feature \\(F_G \\in \\mathbb{R}^{v \\times H_s \\times W_s}\\)." + }, + { + "type": "list", + "bbox": [ + 0.076, + 0.72, + 0.47, + 0.901 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.139 + ], + "angle": 0, + "content": "3) through conducting the matrix multiplication between the coordinate descriptor \\( x_{i}^{j} \\) and feature \\( F_{G} \\), the coordinate activation map \\( h_{i}^{j}\\in \\mathbb{R}^{H_{s}\\times W_{s}} \\) is obtained dynamically." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.14, + 0.892, + 0.171 + ], + "angle": 0, + "content": "4) after using a global average pooling on the spatial of \\( h_i^j \\), the activation map is regressed to the final coordinate value." + }, + { + "type": "list", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.171 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.175, + 0.892, + 0.341 + ], + "angle": 0, + "content": "Dynamic End-index Classification Head. Based on the prior of that the end point of a piecewise Bézier curve must be explicit, the proposed module model the dynamic length of segments prediction task as a \\(N\\)-classification problem, where \\(N\\) is the maximum pieces number for a certain map class. Specifically, with using a common \\(FC\\) and softmax block, each Bézier descriptor is naturally transformed into a \\(N\\)-dimensional probability vector, where each position denotes the score of the current index as a termination point. This novel indeterminate length modeling greatly increases the adaptability and scalability of our proposed framework." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.351, + 0.7, + 0.367 + ], + "angle": 0, + "content": "3.3. End-to-End Training" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.374, + 0.892, + 0.451 + ], + "angle": 0, + "content": "According to the matrix form of Eq.1, that is, \\(P = BC\\), where \\(B \\in \\mathbb{R}^{m \\times n}\\) is the Bernstein matrix, \\(C \\in \\mathbb{R}^{n \\times 2}\\) is control points, \\(P \\in \\mathbb{R}^{m \\times 2}\\) is vectorized points on the curve, \\(m\\) is the number of points and \\(n\\) is the degree. Obviously, given \\(m, n\\), we can easily implement following procedures:" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.451, + 0.892, + 0.479 + ], + "angle": 0, + "content": "1) vectorization. Given the \\(C\\), its corresponding vectorized curve can be restored efficiently with matrix multiplication." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.481, + 0.892, + 0.526 + ], + "angle": 0, + "content": "2) construction. Given the orderly sampling points \\( P \\), we readily construct \\( C \\) with solving the least-squares problem, i.e. \\( C = B^{+}P \\) where \\( ^{+} \\) is the pseudo-inverse of a matrix." + }, + { + "type": "list", + "bbox": [ + 0.499, + 0.451, + 0.892, + 0.526 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.531, + 0.892, + 0.637 + ], + "angle": 0, + "content": "Piecewise Bézier Ground Truth. The common \\( HD \\)-map annotation protocol always represents a curve with a set of vectorized points. We propose to first select some annotated keypoints and then divide the curve into \\( k \\) segments, where each is compactly modeled by an \\( n \\)-order Bézier curve. Following the procedure of construction, we present the ground truth generation algorithm in the Algorithm 1." + }, + { + "type": "code_caption", + "bbox": [ + 0.511, + 0.656, + 0.822, + 0.671 + ], + "angle": 0, + "content": "Algorithm 1: Piecewise Bézier Curve GenGT." + }, + { + "type": "algorithm", + "bbox": [ + 0.511, + 0.673, + 0.892, + 0.894 + ], + "angle": 0, + "content": "input:Annotated points \\(P\\) Parameters \\(n,m,\\epsilon\\) output: Piecewise Bezier curves C \n1 \\(B =\\) GetBernsteinCoefficient \\((n,m)\\) \n2 \\(B^{+} =\\) MatrixPseudoInverse \\((B)\\) \n3 \\(l\\gets |P|,s\\gets 0,e\\gets l - 1\\) \n4 while \\(s < e\\) do \n5 \\(P^{\\dagger} =\\) CurveInterpolate \\((P[s,e])\\) . \n6 \\(\\mathbb{C}^{\\dagger} = B^{+}\\times P^{\\dagger}\\) . \n7 \\(P^{\\ddagger} = B\\times \\mathbb{C}^{\\dagger}\\) . \n8 \\(D^{\\prime} =\\) ChamferDistance \\((P^{\\dagger},P^{\\ddagger})\\) . \n9 if \\(D^{\\prime} < \\epsilon\\) then \n10 \\(\\begin{array}{r}\\lfloor \\mathbb{C}\\leftarrow [\\mathbb{C},\\mathbb{C}^{\\dagger}],s\\leftarrow e,e\\leftarrow l - 1; \\end{array}\\) \n11 else \\(e\\gets e - 1\\)" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "13222" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.088, + 0.089, + 0.462, + 0.24 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.244, + 0.47, + 0.287 + ], + "angle": 0, + "content": "Figure 4. The first three diagrams are illustrations of Point-Curve-Region Recovery Loss for Bezier curve modeling. On the far right is a simple schematic diagram of coordinate dilation with \\(\\omega = 1\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.294, + 0.469, + 0.354 + ], + "angle": 0, + "content": "Point-Curve-Region Recovery Loss. Given the Bezier control points, a novel \\(PCR\\)-Loss is proposed to supervise the learning procedure from three progressive levels, i.e. point, curve and region, which is shown in Fig.4 in detail." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.355, + 0.469, + 0.415 + ], + "angle": 0, + "content": "1) point-level supervision. Assume the prediction of control sequence from the output head as \\(\\widehat{\\mathbb{C}}\\) and its corresponding ground truth is \\(\\mathbb{C}\\), we firstly leverage the \\(L1\\)-loss between these coordinates sequentially as," + }, + { + "type": "equation", + "bbox": [ + 0.17, + 0.416, + 0.469, + 0.461 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\text {p o i n t}} = \\frac {1}{| \\widehat {\\mathbb {C}} |} \\sum_ {i = 1} ^ {| \\widehat {\\mathbb {C}} |} \\| \\mathbb {C} _ {i} - \\widehat {\\mathbb {C}} _ {i} \\| _ {1}, \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.466, + 0.47, + 0.543 + ], + "angle": 0, + "content": "2) curve-level supervision. Due to the parametric property of Bézier curve that a slight deviation of control points \\(\\hat{\\mathbb{C}}\\) might cause a great change of the curve, we further restore the control sequence \\(\\widehat{\\mathbb{C}}\\) (or \\(\\mathbb{C}\\)) to curve sequence \\(\\widehat{\\mathcal{P}}\\) (or \\(\\mathcal{P}\\)) with the vectorization process and adopt the \\(L1\\)-loss as," + }, + { + "type": "equation", + "bbox": [ + 0.171, + 0.544, + 0.469, + 0.587 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\text {c u r v e}} = \\frac {1}{| \\widehat {\\mathcal {P}} |} \\sum_ {i = 1} ^ {| \\widehat {\\mathcal {P}} |} \\| \\mathcal {P} _ {i} - \\widehat {\\mathcal {P}} _ {i} \\| _ {1} \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.594, + 0.47, + 0.853 + ], + "angle": 0, + "content": "3) region-level supervision. For digging out more intuitive supervision information, we further recover curve \\(\\widehat{\\mathcal{P}}\\) from the form of discrete coordinates into region mask. First of all, we introduce a coordinate dilation operator, which takes the current coordinate \\(p_{ij}\\) as the center and then generates \\((2\\omega +1)^{2}\\) surrounding coordinates \\(p_{\\alpha \\beta}\\) with the giving dilation width \\(\\omega\\), where \\(\\alpha \\in [i - \\omega ,i + \\omega ]\\) and \\(\\beta \\in [j - \\omega ,j + \\omega ]\\). Secondly, we conduct the coordinate dilation on each point from curve \\(\\widehat{\\mathcal{P}}\\) and then obtain dilated curve points sequence \\(\\widehat{\\mathcal{P}}^{\\sharp}\\), which can be regarded as the foreground coordinates of the predicted mask \\(\\widehat{M}\\), i.e. \\(\\mathcal{S}(\\widehat{M},\\widehat{\\mathcal{P}}^{\\sharp}) = 1\\), where \\(\\mathcal{S}\\) is the grid sampling operation to compute the output values using \\(\\widehat{M}\\) and point coordinates \\(\\widehat{\\mathcal{P}}^{\\sharp}\\) from grid. Finally, after preforming the grid sampling \\(\\mathcal{S}\\) on ground truth map mask \\(M\\) with the same dilated prediction curve, we then bridge a segmentation-base region supervision between \\(M\\) and \\(\\widehat{\\mathcal{P}}^{\\sharp}\\), which can be formulated mathematically as," + }, + { + "type": "equation", + "bbox": [ + 0.138, + 0.858, + 0.469, + 0.877 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\text {r e g i o n}} = \\mathcal {L} _ {\\text {d i c e}} \\left(\\mathcal {S} \\left(M, \\widehat {\\mathcal {P}} ^ {\\sharp}\\right), \\mathcal {S} \\left(\\widehat {M}, \\widehat {\\mathcal {P}} ^ {\\sharp}\\right)\\right) \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.082, + 0.886, + 0.436, + 0.902 + ], + "angle": 0, + "content": "where \\(\\mathcal{L}_{\\text{dice}}\\) is the common dice loss function in [38]." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.092, + 0.892, + 0.138 + ], + "angle": 0, + "content": "4) overall \\(PCR\\)-Loss. In order to exert the above three-level supervision at the same time, we put forward that the overall \\(PCR\\)-Loss is a weighted sum of all three losses as," + }, + { + "type": "equation", + "bbox": [ + 0.547, + 0.143, + 0.892, + 0.161 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {P C R} = \\lambda_ {p} \\mathcal {L} _ {\\text {p o i n t}} + \\lambda_ {c} \\mathcal {L} _ {\\text {c u r v e}} + \\lambda_ {r} \\mathcal {L} _ {\\text {r e g i o n}} \\tag {9}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.167, + 0.892, + 0.317 + ], + "angle": 0, + "content": "Multi-task Auxiliary Loss. The paradigm of multi-task learning can reduce the risk of overfitting by leveraging the domain-specific information included in the training signals of related tasks [61]. Thence, in addition to supervising the curve-level Bézier modeling procedure of the final head, we also perform auxiliary segmentation-based supervision on the intermediate modules, i.e. semantic-level BEV decoder and instance-level Bézier decoder. Given the output masks \\(\\widehat{\\mathbb{M}}_s\\) and \\(\\widehat{\\mathbb{M}}_z\\) in the Sec.3.2, we formulate the auxiliary loss with the combination of two tasks supervision as," + }, + { + "type": "equation", + "bbox": [ + 0.558, + 0.323, + 0.892, + 0.341 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {A U X} = \\lambda_ {s} \\mathcal {L} \\left(\\mathbb {M} _ {s}, \\widehat {\\mathbb {M}} _ {s}\\right) + \\lambda_ {z} \\mathcal {L} \\left(\\mathbb {M} _ {z}, \\widehat {\\mathbb {M}} _ {z}\\right) \\tag {10}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.35, + 0.892, + 0.396 + ], + "angle": 0, + "content": "where \\(\\mathbb{M}_{\\star}\\) denotes the ground truth and \\(\\lambda_{\\star}\\) is the weighted factor. Note that \\(\\mathcal{L}\\) is a compound loss with common cross entropy loss and dice loss, namely \\(\\mathcal{L} = \\mathcal{L}_{ce} + \\mathcal{L}_{dice}\\)." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.408, + 0.633, + 0.425 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.433, + 0.706, + 0.45 + ], + "angle": 0, + "content": "4.1. Experimental Settings" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.459, + 0.892, + 0.717 + ], + "angle": 0, + "content": "Existing Benchmarks. To evaluate the proposed approach, we conduct experiments on the popular NuScenes dataset [2], which consists of 28, 130/6, 019 samples and 700/150 driving scenes for the training/validation set respectively. Each scene contains roughly 40 samples and each sample includes 6 surrounding images, covering \\(360^{\\circ}\\) FOV of the ego-vehicle. For the sake of fair comparison, we follow the previous work [24] and focus on three static map categories, i.e. lane-divider, ped-crossing and road-boundary. Taking the ego-vehicle as the center, we set the perception range to \\([30, 30, 15, 15]m\\), which corresponds to the distances of front, rear, left and right respectively, and fix the resolution of ego-to-pixel as \\(0.15m/pixel\\). In addition, for exploring the performance of our method under different lighting and weather conditions, we further divide NuScenes into five kinds of scene, namely day, night, sunny, cloudy and rainy. Refer to the supplementary material for more details." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Evaluation Metrics. We utilize the exact same evaluation protocol as [24] of average precision (AP) to access the map construction quality over the instance-level. To be concrete, given a pair of instances from ground-truth and predictions respectively, this protocol computes the Chamfer Distance between them and considers the prediction as true-positive only if the distance is less than a specified threshold, which is set to \\([0.2, 0.5, 1.0]m\\) in our experiment. Note the overall AP metric is obtained by averaging across three thresholds. Moreover, as for a more informative comparison, the results under different lighting/weather conditions and a much simpler threshold setup of \\([0.5, 1.0, 1.5]m\\) are further provided." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "13223" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.082, + 0.089, + 0.89, + 0.313 + ], + "angle": 0, + "content": "
MethodBackboneEpochAP_dividerAP_crossAP_boundmAPmAP_daymAP_nightmAP_sunnymAP.cloudymAP_rainy
IPM(B) [24]Eff-B03010.74.711.79.0-----
IPM(CB) [24]Eff-B03024.07.327.819.7-----
LSS [43]Eff-B03022.95.124.217.411.5b13.3b12.0b12.8b9.5b
VPN [40]Eff-B03022.15.225.317.517.9b17.5b18.2b18.5b15.9b
HMapNet [24]Eff-B03028.37.132.622.721.4b17.4b21.5b23.4b18.9b
BeMapNetEff-B03046.737.438.040.741.328.641.444.936.2
BeMapNetRes-503046.939.037.841.341.930.442.643.637.4
BeMapNetSwin-T3049.142.239.943.744.334.444.847.937.8
BeMapNetRes-5011052.744.544.247.147.739.248.750.341.4
BeMapNetSwin-T11054.246.546.549.149.837.350.453.542.8
BeMapNetSwin-B11055.347.049.450.551.238.052.254.843.6
BeMapNetRes-503062.357.759.459.860.546.962.561.953.0
BeMapNetSwin-T3064.461.361.662.563.153.264.766.054.2
BeMapNetSwin-B11069.064.469.767.768.354.670.371.658.0
" + }, + { + "type": "table_footnote", + "bbox": [ + 0.076, + 0.318, + 0.893, + 0.365 + ], + "angle": 0, + "content": "Table 1. Comparisons with SOTAs on NuScenes under thresholds of [0.2, 0.5, 1.0] \\(m\\) and [0.5, 1.0, 1.5] \\(m\\), where the results of latter easier evaluation protocol is marked by Green shade. The Blue shade contains the results that used in all ablation studies for a fair comparison. Note \\({}^{\\flat}\\) and - indicate the results are re-implemented by us with public code and not available respectively." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.376, + 0.473, + 0.665 + ], + "angle": 0, + "content": "Implementation Details. We employ EfficientNet-B0 [49], ResNet-50 [14] and SwinTR [31] as backbones, which are all initialized by ImageNet [21] pretraining. The following semantic \\(BEV\\) decoder stacks 2 transformer encoder layers and 4 decoder layers with \\(64 \\times 32\\) \\(BEV\\) queries, and the instance Bézier decoder stacks 6 mask-transformer decoder layers with 60 queries, where 20, 25, 15 for lane-divider, ped-crossing and road-boundary respectively. The shape of input image is resized to \\(896 \\times 512\\) and the mini-batch size is set to 1 per GPU. We train our model with 8 GPUs for 30/110 epochs and adopt multi-step schedule with milestone [0.7, 0.9] and \\(\\gamma = \\frac{1}{3}\\). The AdamW [33] optimizer is employed with a weight decay of \\(1e^{-4}\\) and a learning rate of \\(2e^{-4}\\), which is multiplied by 0.1 for backbone. As for hyper-parameters of loss weight, we set \\(\\lambda_s\\), \\(\\lambda_z\\), \\(\\lambda_p\\), \\(\\lambda_c\\), \\(\\lambda_r\\) to 1, 5, 5, 10, 1 respectively and the dilated width \\(\\omega\\) in \\(\\mathcal{L}_{region}\\) to 5. The deployments of piecewise Bézier curve \\(\\langle k, n \\rangle\\) for lane-divider, ped-crossing and road-boundary are set to \\(\\langle 3, 2 \\rangle\\), \\(\\langle 1, 1 \\rangle\\), \\(\\langle 7, 3 \\rangle\\). Note \\(m\\) in Algorithm 1 is set to 100." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.679, + 0.45, + 0.696 + ], + "angle": 0, + "content": "4.2. Comparisons with State-of-the-art Methods" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.704, + 0.473, + 0.903 + ], + "angle": 0, + "content": "We present the overall evaluation results on NuScenes in Table 1, which shows that our BeMapNet is significantly superior to the existing SOTA approaches by a large margin (up to 18.0) under the same setting of EfficientNet-B0 and 30 epochs, indicating the effectiveness of our approach. In addition, after replacing the backbone with more common ResNet-50 and more popular SwinTiny, our model achieves a further improvement of 0.6 and 3.0 AP respectively. Next, considering the slow convergence of the Transformer-based model, we increase the training schedule to 110 epochs and gain at least another 5.4 improvements. Even in somewhat unconventional scenarios, such as night and rainy, our proposed approach still shows a great advantage, i.e. 13.2 and" + }, + { + "type": "table", + "bbox": [ + 0.514, + 0.373, + 0.882, + 0.468 + ], + "angle": 0, + "content": "
Position EncodingAP_dividerAP_crossAP_boundmAP
Sine PE42.834.134.737.2
Learned PE40.232.233.835.4
IPM-PE46.439.237.841.1
+ Exclusive FC38.633.333.935.3
+ Shared FC49.142.239.943.7
" + }, + { + "type": "table_caption", + "bbox": [ + 0.502, + 0.474, + 0.89, + 0.489 + ], + "angle": 0, + "content": "Table 2. Comparisons on different methods of position encoding." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.5, + 0.892, + 0.622 + ], + "angle": 0, + "content": "16.9 AP are obtained respectively. Furthermore, another interesting observation is that regardless of which method is used, we find that the performance of sunny scene is always slightly lower than cloudy. We believe that strong illuminations and ground shades on sunny day might have a certain impact on the perception of map objects. As a supplement, the last three rows of Table 1 show the performance of our approach on a much simpler evaluation protocol." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.632, + 0.655, + 0.649 + ], + "angle": 0, + "content": "4.3. Ablation Study" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.659, + 0.895, + 0.902 + ], + "angle": 0, + "content": "The Different Way of Position Encoding. Table 2 shows the performance of different \\(PE\\) in semantic BEV decoder for the map construction. Compared with the sine/learned-based method, our proposed IPM-PE module improves AP by 3.9/5.7 respectively, which proves the multi-perspective \\(PE\\) guided by the intrinsic and extrinsic parameters is very effective. Moreover, through the results in the 3-rd and 5-th row, we find that IPM-PE with shared FC layer alignment gains an further improvement of 2.6 points. Yet, in order to rule out the possibility of that the attached FC layer brings an increment, we then feed the position embeddings from IPM-PE into two exclusive FCs and the 4-th row results exclude the influence of FC. These comparisons indicate the shared align layer is the exactly essential part to mitigate the performance decline brought by the unreasonable assumption of IPM, which validates our conjecture in Sec.3.2.2." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "13224" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.127, + 0.089, + 0.848, + 0.33 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.118, + 0.333, + 0.851, + 0.348 + ], + "angle": 0, + "content": "Figure 5. The qualitative comparison results of HDMapNet [24], BeMapNet and GroundTruth [2] under different scenarios." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.358, + 0.473, + 0.556 + ], + "angle": 0, + "content": "Effectiveness of \\(PCR\\)-Loss. The \\(PCR\\)-Loss mainly consists of three parts, i.e. point, curve and region. Table 3 shows detailed ablation results of the role of each part. Specifically, with adopting only one supervision in rows \\(1 \\sim 3\\), the performance trend is roughly: curve > point > region. Among them, it is worth noting that the only region-based supervision shows very poor performance, which is understandable because the generation of region mask relies on a collection of relatively accurate points. This conjecture is also verified in rows \\(4 \\sim 5\\) of the Table 3. Furthermore, when integrating multiple loss supervision, the final performance is consistently improved compared to the single one, and three parts used together achieves the optimal AP results of 43.7." + }, + { + "type": "table", + "bbox": [ + 0.084, + 0.564, + 0.465, + 0.675 + ], + "angle": 0, + "content": "
PointCurveRegionAP_dividerAPPEDAPboundarymAP
✓XX39.133.323.732.0
X✓X47.235.135.939.4
XX✓3.22.60.52.1
✓X✓40.739.416.732.9
X✓✓48.238.539.742.1
✓✓X46.538.536.240.4
✓✓✓49.142.239.943.7
" + }, + { + "type": "table_caption", + "bbox": [ + 0.091, + 0.678, + 0.455, + 0.692 + ], + "angle": 0, + "content": "Table 3. The effectiveness of different modules in \\( {PCR} - {Loss} \\) ." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.7, + 0.47, + 0.807 + ], + "angle": 0, + "content": "Effectiveness of Multi-task Auxiliary Loss. Without any auxiliary loss, the average AP of our proposed BeMapNet is only 20.0. Yet, after adopting another semantic/instance supervision, the result is improved to 34.5/38.4 respectively and goes further to 43.7 with employing both, which shows the auxiliary tasks for producing high-quality semantic \\(BEV\\) features and instance descriptors are very important." + }, + { + "type": "table", + "bbox": [ + 0.083, + 0.81, + 0.468, + 0.888 + ], + "angle": 0, + "content": "
SemanticInstanceAPdividerAPpedAPboundarymAP
XX21.517.820.720.0
✓X39.331.532.834.5
X✓44.334.636.538.4
✓✓49.142.239.943.7
" + }, + { + "type": "table_caption", + "bbox": [ + 0.091, + 0.892, + 0.455, + 0.905 + ], + "angle": 0, + "content": "Table 4. The effectiveness of different modules in AUX-Loss." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.358, + 0.892, + 0.526 + ], + "angle": 0, + "content": "Comparison with Polyline Vectorization. An amusing fact is that a Bézier curve with \\( n = 1 \\) is simply a straight line between two control points. By setting the degree of all elements to 1, our framework naturally degenerates into the polyline-based method. Note we further set \\( k \\) to 9, 1, 29 for lane-divider, ped-crossing and road-boundary respectively. The comparisons in Table 5 show the Bézier-based vectorization approach achieves better 4.5 AP. Interestingly, as the complexity of map element shape increases (usually ped-crossing \\( < \\) lane-divider \\( < \\) road-boundary), we find that the corresponding AP improvement increases as well." + }, + { + "type": "table", + "bbox": [ + 0.505, + 0.53, + 0.892, + 0.58 + ], + "angle": 0, + "content": "
VectorizationAPdividerAPpedAPboundarymAP
Polyline45.039.133.439.2
Bézier49.1 (+4.1)42.2 (+3.1)39.9 (+6.5)43.7(+4.5)
" + }, + { + "type": "table_caption", + "bbox": [ + 0.514, + 0.584, + 0.878, + 0.598 + ], + "angle": 0, + "content": "Table 5. Comparison with the different type of vectorization." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.606, + 0.892, + 0.699 + ], + "angle": 0, + "content": "Qualitative Analysis. We show the qualitative comparisons with SOTAs in Fig. 5. Besides avoiding complex vectorized post-processing, the proposed BeMapNet constructs various and changeful \\( HD \\)-elements more compactly and robust. Note that more extensive visualizations under different conditions are further provided in our supplementary material." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.71, + 0.62, + 0.725 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.735, + 0.892, + 0.903 + ], + "angle": 0, + "content": "Vectorized \\( HD \\)-map online construction focuses on the perception of centimeter-level environmental information. Starting from the conventional parameterization-based methods, this paper presents an end-to-end postprocessing-free architecture, namely BeMapNet, with leveraging unified piecewise Bézier curve for various and changeful map elements. By introducing three well-designed modules, i.e. IPM-PE Align Module, Piecewise Bézier Head and Point-Curve-Region Loss, the overall framework is concise and elegant, which reaches state-of-the-art performance and provides a new perspective for future \\( HD \\)-map research." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "13225" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.115, + 0.47, + 0.157 + ], + "angle": 0, + "content": "[1] Paul J Besl and Neil D McKay. Method for registration of 3-d shapes. 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Most existing approaches first obtain rasterized map with the segmentation-based pipeline and then conduct heavy post-processing for downstream-friendly vectorization. In this paper, by delving into parameterization-based methods, we pioneer a concise and elegant scheme that adopts unified piecewise Bézier curve. In order to vectorize changed map elements end-to-end, we elaborate a simple yet effective architecture, named Piecewise Bézier HD-map Network (BeMapNet), which is formulated as a direct set prediction paradigm and postprocessing-free. Concretely, we first introduce a novel IPM-PE Align module to inject 3D geometry prior into BEV features through common position encoding in Transformer. Then a well-designed Piecewise Bézier Head is proposed to output the details of each map element, including the coordinate of control points and the segment number of curves. In addition, based on the progressively restoration of Bézier curve, we also present an efficient Point-Curve-Region Loss for supervising more robust and precise HD-map modeling. Extensive comparisons show that our method is remarkably superior to other existing SOTAs by $18.0\mathrm{mAP}$ at least1. + +# 1. Introduction + +As one of the most fundamental components in the autodriving system, high-definition map contains centimeter details of traffic elements, vectorized topology and navigation information, which instruct ego-vehicle to accurately locate itself on the road and understand what is coming up ahead. At present, conventional SLAM-based solutions [45, 46, 60] have been widely adopted in practice. Yet, due to dilemmas of high annotation costs and untimely updates, the offline approach is gradually being replaced by the learning-based online HD-map construction with onboard sensors. + +![](images/c7b4aaef9bc985a4dd21444fae016e55e25f3582ea14c22aff66694181ed7d01.jpg) +(a) HD-map example + +![](images/2a5091792463974acaddf9d9e3171c80206eef53e99bd6811b9431695db9254e.jpg) +(b) vanilla Bezier vs. piecewise Bezier + +![](images/ded693c4009d7db33e25cc797f483baf00dd1af496b2fde200b87b23d006b926.jpg) +(c) map curve restored by real control points +Figure 1. Illustration of our motivation for piecewise Bézier curve, termed as $\langle k, n \rangle$ , where $k$ is the piece number and $n$ is the degree. Fig.(a) is a real HD-map case from NuScenes. Fig.(b) compares the difference between vanilla and piecewise Bézier curve through the same map element, where the light purple is the restored curve with Bézier process. The last is more efficient than previous ones with reducing the number of control points by $64\%$ in this case. Fig.(c) illustrates that piecewise Bézier curve can model arbitrary-shaped curves. Note the blue circles denote actual control points. + +The deep-based paradigm of online $HD$ -map building is gradually developing, but it still faces two main challenges: 1) modeling instance-level vectorized $HD$ -map end-to-end. Most existing works construct $HD$ -map by rasterizing $BEV$ (bird-eye-view) maps into semantic pixels with segmentation [24, 42], which not only lacks the modeling of instance-level details, but also requires heavy post-processing to obtain vectorized information. As a sub-task, lane detection makes a relatively better advance for this issue, that is, in addition to segmentation-based methods [39, 41, 62], there are also point-based [25, 47] and curve-based [12, 28] schemes. However, compared to the simple lane scenario, $HD$ -map contains more shape-changeful elements, so such methods cannot be directly adopted into the $HD$ -map construction. 2) performing 2D-3D perspective transformation efficiently. Obtaining 3D- $BEV$ perception from multi-view 2D images is an essential step for building $HD$ -map, which is mainly divided into three ideas, i.e. geometric priors [44], learnable parameters [40, 42], and a combination of the two [17, 43]. Note the assumptions of geometry-based methods often do + +not conform to the actual situation, leading to such schemes are less adaptable, while learning-based methods require a large amount of labeled data to generalize across various scenarios. Combining the above two branches not only has multi-scenario scalability, but also reduces the demand for annotated data, has attracted increasing research interest. + +To the best of our knowledge, the curve parameterization construction of $HD$ -map in the $BEV$ space is vacancy and no one has explored it. Based on the widely used Bézier curve, which is mathematically defined by a set of control points, we pioneer to devise a concise and elegant $HD$ -map scheme that adopts piecewise Bézier curve, where each map curve is divided into multiple $k$ segments and each segment is then represented by a vanilla Bézier curve with degree $n$ , hence denoted as $\langle k, n \rangle$ . Despite $\langle 1, n \rangle$ is enough to express any map element with infinite $n$ in theory, more complex curve tends to require higher degree, meaning that there are more control points need to be modeled, which is shown in Fig.1. The proposed piecewise strategy allows us to parameterize a curve more compactly with fewer control points and higher capacity, which is extremely scalable and robust in practice. + +Inspired by the above motivations, we propose an end-to-end vectorized HD-map construction architecture, named as Piecewise Bézier HD-map Network (BeMapNet). The overall framework is illustrated in detail in Fig.2, which streamlines the architecture into four primary modules for gradually-enriched information, i.e. feature extractor shared among multi-view images, semantic BEV decoder for $2D-3D$ perspective elevation, instance Bézier decoder for curve-level descriptors, and piecewise Bézier head for point-level parameterization. To be concrete, we first introduce a novel IPM-PE Align module into Transformer-based decoders, which injects IPM (inverse perspective mapping) geometric priors into BEV features via PE (position encoding) and hardly adds any parameters except a FC layer. Secondly, we further design a Piecewise Bézier Head for dynamic curve modeling with adopting two branches as classification and regression, where the former classifies the number of pieces to determine the curve length and the latter regresses the coordinate of control points to determine the curve shape. Lastly, we present an Point-Curve-Region Loss for robust curve modeling by supervising restoration information as a progressive manner. Since it is modeled as a sparse set prediction task and optimized with a bipartite matching loss, our method is postprocessing-free and high-performance. + +The main contributions of our approach are three-folds: + +- We pioneer the BeMapNet for concise and elegant modeling of HD-map with unified piecewise Bézier curve. +- We elaborate the overall end-to-end architecture with innovatively introducing IPM-PE Align Module, Piecewise Bézier Output Head and well-designed PCR-Loss. +- BeMapNet is remarkably superior to SOTAs on existing benchmarks, revealing the effectiveness of our approach. + +# 2. Related Work + +# 2.1. Vectorized HD-map Construction + +$HD$ -map is precise at centimeter-level and consists of vectorized details not normally present on standard map [27], which highly aggravates the difficulty of obtaining accurate annotations in practice. Most previous methods focus on SLAM [11, 18, 22, 36, 46, 58] with exploring LiDAR points of the environment, involving large-scale data acquisition and labor-intensive annotations. Recently, more and more researchers formulate the process of building $HD$ -map as a segmentation task [6, 13, 20, 32] from various sensors, such as cameras [15, 26, 34, 35, 40, 43, 59, 63] and LiDAR [1, 57]. HDMapNet [24] extracts features from the observations of multi-modalities and groups semantic rasterized maps with heuristic post-processing for vectorized results. Without any further vectorization, [42] only obtains semantic map representations from a Transformer-based camera-to-BEV module. Different from the above segmentation-based frameworks, our proposed BeMapNet adopts the parameterization-based paradigm and constructs instance-level vectorized $HD$ -map end-to-end with a multiview and camera-only manner, which is a more flexible and scalable solution for downstream tasks. + +# 2.2. Structure Modeling of Geometric Data + +HD-map contains various kinds of map elements, including lane-divider, ped-crossing, road-boundary, etc., which are typically regarded as geometric data, e.g. points, polygons and curves. To the best of knowledge, there are two mainstream exploration directions for deep geometric modeling, one is point-based, including uniform-points and keypoints estimation, and the other is curve-based, including polynomial curve and Bézier curve. Taking the most related lane detection as an example, LineCNN [25] presents a novel line proposal unit to detect lanes as a set of points, and later LaneATT [47] represents a lane by equally-spaced $2D$ -points that achieves good performance. GANet [54] focuses on keypoint estimation and association with adaptively lane feature aggregator. HDMapGen [37] proposes a hierarchical point generative model for producing high-quality HD lane map. As for cruve-based, [51] and [48] directly predict the polynomial coefficients with a differentiable least-squares fitting module and simple $FC$ respectively. Recently, based on the DETR [4], LSTR [28] presents a query-based detector to decode poly-parameters of a lane end-to-end. Apart from this, some studies also adopt Bézier curve for geometry, such as text boundary [29], center-line segment [3] and lane curve [12]. Unlike these approaches of addressing simple-shape elements, our method innovatively employs piecewise Bézier curves without any complicated geometric assumptions to parameterize arbitrary-shape geometry in HD-map scenarios. + +![](images/9cdd2ebeb92158f77acbeb5c176dfee9dccc3a8d15ff9b0e602a66dffa03cf98.jpg) +Figure 2. The architecture of our proposed BeMapNet, containing four primary components for extracting progressively richer information, i.e. image-level multi-scale features, semantic-level BEV feature, instance-level curve descriptors, and point-level Bézier control sequence. Right-top: The blue and orange circles represent explicit control points and implicit control offsets respectively. Note that the term GAP is global average pooling and MatMul is the matrix multiplication. Right-bottom: $(H_c, W_c) / (H_b, W_b)$ is the shape of image/BEV feature. + +# 2.3. Multi-view Camera-to-BEV Transformation + +In most $3D$ research studies, obtaining high-quality BEV representations from multi-view camera features is the top priority of various domains, such as $3D$ object detection [17, 30, 43, 55, 56], motion prediction [10, 16, 19, 23, 53] and map construction [24, 26, 40, 42]. IPM [44] is the most basic and straightforward method with a homography transformation, which is precisely calculated by camera parameters. Without adopting the $3D$ geometry prior, some methods [3, 40, 42] directly leverage learnable parameters to complete the perspective transformation. VPN [40] and Neat [9] both utilize a $FC$ layer to transform the image features into the BEV space, and [42] further designs a multi-camera deformable attention unit based on transformer. However, in order to obtain more explicit BEV representations, more and more researches argue that the geometry priors has great advantages for model convergence and performance. Based on VPN, [24] fuse the multi-camera BEV spaces with the camera poses. LSS [43] and BEVDet [17] build the connection between camera-view and BEV based on the depth distribution estimation. DETR3D [56] manipulates predictions directly in $3D$ space with linking $3D$ positions to $2D$ spaces and [5] generates BEV features by regarding camera parameters as a reference. PETR [30] encodes the $3D$ information as position embedding and conducts query decoding on position-aware features. In addition to introducing the $3D$ geometry prior, we further performs position embedding alignment for transforming the camera features and BEV features into the world coordinate system. + +# 3. Method + +# 3.1. Problem Formulation + +Preliminary on Piecewise Bézier Curve. A Bézier curve is a parametric curve which is formulated by a set of ordered control points $c_{0}$ through $c_{n}$ as, + +$$ +p (t) = \sum_ {i = 0} ^ {n} b _ {i, n} (t) c _ {i}, t \in [ 0, 1 ] \tag {1} +$$ + +where $n$ is the degree of the curve and $b_{i,n}(t)$ is known as Bernstein basis polynomial of degree $n$ , + +$$ +b _ {i, n} (t) = \binom {n} {i} t ^ {i} (1 - t) ^ {n - i}, i = 0, \dots , n \tag {2} +$$ + +According to Eq.1, we know the first and last control points are endpoints of the curve, i.e. $p(0) = c_0$ , $p(1) = c_n$ . Then we define a piecewise Bézier curve $\langle k, n \rangle$ consists of $k$ segments, each of which is an $n$ -order Bézier and two consecutive segments satisfy the positional continuity condition as $p^j(1) = p^{j+1}(0)$ , where $j$ is the segment $id$ varying from 0 to $k-2$ . Hereafter, given a piecewise Bézier curve as shown in Fig.3, we denote its ordered control points as, + +$$ +\mathbb {C} = \left\{c _ {i} ^ {j} \in \mathbb {R} ^ {2} \mid i \in [ 0, n ], j \in [ 0, k - 1 ], c _ {n} ^ {j} = c _ {0} ^ {j + 1} \right\} \tag {3} +$$ + +Moreover, due to the first and last control points of each segment are always on the curve, we naturally term these points that retain a distinct significance as explicit control points $\mathbb{C}^E$ and the remaining as implicit control points $\mathbb{C}^I$ , where $\mathbb{C} = \mathbb{C}^E \cup \mathbb{C}^I$ , $|\mathbb{C}^E| = k + 1$ and $|\mathbb{C}^I| = nk - k$ . + +![](images/490ded093f6ddf2eaa436ee0fe4fd89c30bb15185a9d1c10fb525f4ea232a821.jpg) +Piecewise Bézier Curve + +![](images/935691aecb555a9e02d21cdf7ce9a485718574b6f121612f195fce03f20c51c0.jpg) +Bézier Control Polygon + +![](images/5530dbe275f868354976371c6852c6d404ef6c694a959ad81da71372315bfb4e.jpg) +Explicit Control Points + +![](images/d44b5c89a8edcdb644558d3d5453810e276b7e019ba2503694178011167a54d4.jpg) +Explicit Center + +![](images/93bbc57febb8affdb62846f3807ac50e845b020707c79fb33983d2ed02021cb5.jpg) +Figure 3. Illustration of a 3-pieces 3-order piecewiseBezier curve, denoted as $\langle 3,3\rangle$ for the left part. For each segment, we model the implicit control point coordinates by an offset $(\Delta x,\Delta y)$ from the center of explicit control points as shown on the right part. + +![](images/14d32f1da02e93201d6be504cd034e7ddd7e0b8d4ee18ab4e2dac07596d9acb2.jpg) +Implicit Control Points + +![](images/56a6cca86c77a7579475d17135d05ebefbdc22d5032cdfb47aecb1d1a7aaddc1.jpg) +mplicit Offset + +Vectorized HD-map Modeling. By sequentially sampling points along the elements in HD-map, each object can be structured as an open-shape curve as a vectorized manner. To uniformly parameterize these various shape-changeful map elements, including points, polygons and curves, we employ the piecewise Bézier curve proposed in Eq.3 and formalize a vectorized HD-map as a piecewise Bézier curve set $\mathcal{M} = \{\mathbb{C}_i|i = 1,\dots ,|\mathcal{M}|\}$ , where $|\mathcal{M}|$ is the number of map instances. Our objective is to learn a model that extracts compact information from the camera sensors and predicts, for each map element, its corresponding Bézier control sequence, which uniquely determine the shape and position of the map curve. In addition, for the purpose of reducing the modeling complexity of implicit control points $\mathbb{C}^{\mathcal{I}}$ for each segment, we subtly generate implicit coordinates through the center of explicit control points and their relative offsets as shown in the right of Fig.3. + +Piecewise Bézier Curve Modeling Principle. Considering the large-variety and changeful-shape of map elements, we present a consistent-degree but dynamic-piece principle for modeling piecewise curve more precisely and efficiently as, (1) consistent-degree on semantic-level. Due to a Bézier curve of degree $k$ can be easily converted into degree $k + 1$ with the same shape, i.e. degree elevation in mathematics, the same curve may correspond to multiple Bézier solutions with only different degree. This kind of obfuscation is devastating for the network modeling. And we argue that keeping the consistent-degree within the same semantic category is the most efficient way to solve this dilemma. + +(2) dynamic-piece on instance-level. Considering that the complexity of different map curves is always inconsistent, the modeling method with a fixed and large number of segments will not only cause excessive redundancy in the expression of each curve, but also lead to confusion in the definition of sub-segment, which places a certain burden on the model optimization. The dynamic-piece rule demands the model to choose the number of segments dynamically and parameterize a Bézier curve as compactly as possible. + +# 3.2. Piecewise Bezier HD-map Network + +# 3.2.1 Overall Architecture + +The overall model architecture is illustrated in detail in Fig. 2, which streamlines the framework into four parts, namely feature extractor, semantic BEV decoder, instance Bézier decoder and piecewise Bézier output head respectively. + +Feature Extractor. Given surrounding images from multicamera as inputs, a shared CNN backbone is first employed to obtain each image feature, and then these multi-scale features from different stages are fed into FPN [50] to integrate rich environmental information. Last we upsample pyramid features to the same size and stack them together as outputs. + +Semantic BEV Decoder. We leverage a standard encoder-decoder paradigm based on Transformer to elevate camera-view features into canonical BEV spaces. By treating the perspective transformation as a direct set prediction task, the BEV decoder takes camera features with shape $H_{c} \times W_{c}$ and $H_{q} \times W_{q}$ learnable BEV queries as inputs, and produces BEV features $F_{b} \in \mathbb{R}^{C \times H_{b} \times W_{b}}$ by modeling all pairwise interactions among elements with self- and cross-attention. Different from the region-agnostic query in DETR, we correspond each query with a $\gamma^{h} \times \gamma^{w}$ region on BEV features one-to-one, i.e. $H_{b} \times W_{b} = \gamma^{h}H_{q} \times \gamma^{w}W_{q}$ . The $F_{b}$ is then fed into a $1 \times 1$ conv and upsample block to obtain the final semantic mask $\mathbb{M}_{s} \in \mathbb{R}^{U \times H_{s} \times W_{s}}$ , where $U$ is the number of classes and $H_{s} \times W_{s}$ is the map shape. In addition, we also propose a novel IPM-PE Align Layer to refactor the features in different coordinate systems through the most common position encoding layer in Transformer. + +Instance Bézier Decoder. So as to perform more accurate parametric modeling of each curve, we further equip an instance Bézier decoder based on masked cross-attention [8]. To be concrete, given semantic features $F_{b}$ and learnable instance Bézier queries $Q \in \mathbb{R}^{V \times C}$ , where $V$ is the max number of instance, this module aggregates information and decodes Bézier descriptors $\vec{z} \in \mathbb{R}^{V \times C}$ , which contain key info of geometric and positional relationships between different map elements. With extra performing matrix multiplication between $\vec{z}$ and $F_{b}$ , we obtain instance map mask $\mathbb{M}_{z} \in \mathbb{R}^{V \times H_{s} \times W_{s}}$ , which is used as the foreground mask for next decoder layer and also to perform segmentation supervision for more spatial context information. + +Piecewise Bézier Output Head. Following the principle elaborated in Sec.3.1, we closely design a piecewise Bézier output head with two core modules, i.e. Split Coordinate Regression and Dynamic End-index Classification, which are utilized to output the coordinates of Bézier control point sequence and the number of segments respectively. With easily recovering piecewise Bézier curves and further introducing the bipartite matching setting, the proposed output head constructs vectorized local HD-map very efficiently. + +# 3.2.2 IPM-PE Align Layer + +As a basic module of traditional Transformer architecture, positional encoding utilizes the sequence order by injecting information about the position of tokens [52], where sin-cos and learned-based functions are the most common practices. Yet, for the purpose of perspective transformation between 2D camera-views and 3D BEV, we argue it is not enough to only encode the position correspondence within single view, but it is also necessary to maintain the position consistency relationships between two perspectives. Thence we put forward a novel IPM-PE Align Layer to encode the 2D-3D geometry priors into features from different coordinate systems. To be concrete, given a point $p_c^{f_i} = (u,v,1)^\top$ on the $i$ -th camera-view feature and its corresponding world point $p_c^w = (x,y,z)^\top$ , the following mathematical equation is satisfied on the assumption of pinhole camera model, + +$$ +d \cdot A ^ {- 1} \cdot p _ {c} ^ {f _ {i}} = K ^ {i} \cdot T ^ {i} \cdot p _ {c} ^ {w} \tag {4} +$$ + +where $d$ is the depth, $A$ is the transformation matrix between image-grid and feature-grid, $K^i$ and $T^i$ are $i$ -th intrinsic and extrinsic matrices. Based on the assumption of that the ground surface is flat and at a fixed height in $IPM$ , the world position $(x,y)$ and depth $d$ can be easily calculated through Eq.4. Note $d < 0$ denotes the position is not valid. As for the other branch of BEV perspective, given a point $p_b^f$ from the BEV feature $F_{b}$ and its world point $p_b^w$ , there is usually only a scale relationship $\kappa = (\kappa_x,\kappa_y)$ between them, + +$$ +p _ {b} ^ {f} = \boldsymbol {\kappa} \cdot p _ {b} ^ {w} \tag {5} +$$ + +Then we leverage the standard sin-cos function to convert all these world coordinates $P_{c}^{w}$ and $P_{b}^{w}$ as position embedding $f_{c}^{pe}$ and $f_{b}^{pe}$ respectively. Since the assumption of flat-ground and known-height usually does not hold in practice, $f_{c}^{pe}$ and $f_{b}^{pe}$ are not exactly aligned in the world coordinate system, we further adopt a shared FC layer on $f_{c}^{pe}$ and $f_{b}^{pe}$ to perform embedding alignment and then obtain more unified position encoding, which is shown in Fig.2 in detail. + +# 3.2.3 Piecewise Bézier Output Head + +Split Coordinate Regression Head. Following the illustration in the upper right corner of the Fig.2, we elaborate the forward flow of proposed regression head as four steps, $\mathbf{I}$ with $i$ -th incoming Bézier descriptor $\vec{z}_i \in \mathbb{R}^C$ , we first convert its channel from $C$ to $u \cdot v$ with adopting a standard $FC$ layer and then split it into $u$ parts to get a collection of coordinate descriptors $x_i^j \in \mathbb{R}^v$ , where $j \in [1, u]$ , $u$ is the number of coordinate and $v$ is the channel of descriptor. +2) given the desired output shape $(H_s, W_s)$ , a hard-coded candidate coordinates grid $G \in \mathbb{R}^{2 \times H_s \times W_s}$ is generated with X-Y two channels and next a $1 \times 1$ conv layer is utilized to convert $G$ to its coordinate feature $F_G \in \mathbb{R}^{v \times H_s \times W_s}$ . + +3) through conducting the matrix multiplication between the coordinate descriptor $x_{i}^{j}$ and feature $F_{G}$ , the coordinate activation map $h_{i}^{j}\in \mathbb{R}^{H_{s}\times W_{s}}$ is obtained dynamically. +4) after using a global average pooling on the spatial of $h_i^j$ , the activation map is regressed to the final coordinate value. + +Dynamic End-index Classification Head. Based on the prior of that the end point of a piecewise Bézier curve must be explicit, the proposed module model the dynamic length of segments prediction task as a $N$ -classification problem, where $N$ is the maximum pieces number for a certain map class. Specifically, with using a common $FC$ and softmax block, each Bézier descriptor is naturally transformed into a $N$ -dimensional probability vector, where each position denotes the score of the current index as a termination point. This novel indeterminate length modeling greatly increases the adaptability and scalability of our proposed framework. + +# 3.3. End-to-End Training + +According to the matrix form of Eq.1, that is, $P = BC$ , where $B \in \mathbb{R}^{m \times n}$ is the Bernstein matrix, $C \in \mathbb{R}^{n \times 2}$ is control points, $P \in \mathbb{R}^{m \times 2}$ is vectorized points on the curve, $m$ is the number of points and $n$ is the degree. Obviously, given $m, n$ , we can easily implement following procedures: + +1) vectorization. Given the $C$ , its corresponding vectorized curve can be restored efficiently with matrix multiplication. +2) construction. Given the orderly sampling points $P$ , we readily construct $C$ with solving the least-squares problem, i.e. $C = B^{+}P$ where $^{+}$ is the pseudo-inverse of a matrix. + +Piecewise Bézier Ground Truth. The common $HD$ -map annotation protocol always represents a curve with a set of vectorized points. We propose to first select some annotated keypoints and then divide the curve into $k$ segments, where each is compactly modeled by an $n$ -order Bézier curve. Following the procedure of construction, we present the ground truth generation algorithm in the Algorithm 1. + +Algorithm 1: Piecewise Bézier Curve GenGT. +input:Annotated points $P$ Parameters $n,m,\epsilon$ output: Piecewise Bezier curves C +1 $B =$ GetBernsteinCoefficient $(n,m)$ +2 $B^{+} =$ MatrixPseudoInverse $(B)$ +3 $l\gets |P|,s\gets 0,e\gets l - 1$ +4 while $s < e$ do +5 $P^{\dagger} =$ CurveInterpolate $(P[s,e])$ . +6 $\mathbb{C}^{\dagger} = B^{+}\times P^{\dagger}$ . +7 $P^{\ddagger} = B\times \mathbb{C}^{\dagger}$ . +8 $D^{\prime} =$ ChamferDistance $(P^{\dagger},P^{\ddagger})$ . +9 if $D^{\prime} < \epsilon$ then +10 $\begin{array}{r}\lfloor \mathbb{C}\leftarrow [\mathbb{C},\mathbb{C}^{\dagger}],s\leftarrow e,e\leftarrow l - 1; \end{array}$ +11 else $e\gets e - 1$ + +![](images/8634e56fc830c3499328706b3f6b5b9745398d3c52c32a3b80754a4db4453771.jpg) +Figure 4. The first three diagrams are illustrations of Point-Curve-Region Recovery Loss for Bezier curve modeling. On the far right is a simple schematic diagram of coordinate dilation with $\omega = 1$ . + +Point-Curve-Region Recovery Loss. Given the Bezier control points, a novel $PCR$ -Loss is proposed to supervise the learning procedure from three progressive levels, i.e. point, curve and region, which is shown in Fig.4 in detail. + +1) point-level supervision. Assume the prediction of control sequence from the output head as $\widehat{\mathbb{C}}$ and its corresponding ground truth is $\mathbb{C}$ , we firstly leverage the $L1$ -loss between these coordinates sequentially as, + +$$ +\mathcal {L} _ {\text {p o i n t}} = \frac {1}{| \widehat {\mathbb {C}} |} \sum_ {i = 1} ^ {| \widehat {\mathbb {C}} |} \| \mathbb {C} _ {i} - \widehat {\mathbb {C}} _ {i} \| _ {1}, \tag {6} +$$ + +2) curve-level supervision. Due to the parametric property of Bézier curve that a slight deviation of control points $\hat{\mathbb{C}}$ might cause a great change of the curve, we further restore the control sequence $\widehat{\mathbb{C}}$ (or $\mathbb{C}$ ) to curve sequence $\widehat{\mathcal{P}}$ (or $\mathcal{P}$ ) with the vectorization process and adopt the $L1$ -loss as, + +$$ +\mathcal {L} _ {\text {c u r v e}} = \frac {1}{| \widehat {\mathcal {P}} |} \sum_ {i = 1} ^ {| \widehat {\mathcal {P}} |} \| \mathcal {P} _ {i} - \widehat {\mathcal {P}} _ {i} \| _ {1} \tag {7} +$$ + +3) region-level supervision. For digging out more intuitive supervision information, we further recover curve $\widehat{\mathcal{P}}$ from the form of discrete coordinates into region mask. First of all, we introduce a coordinate dilation operator, which takes the current coordinate $p_{ij}$ as the center and then generates $(2\omega +1)^{2}$ surrounding coordinates $p_{\alpha \beta}$ with the giving dilation width $\omega$ , where $\alpha \in [i - \omega ,i + \omega ]$ and $\beta \in [j - \omega ,j + \omega ]$ . Secondly, we conduct the coordinate dilation on each point from curve $\widehat{\mathcal{P}}$ and then obtain dilated curve points sequence $\widehat{\mathcal{P}}^{\sharp}$ , which can be regarded as the foreground coordinates of the predicted mask $\widehat{M}$ , i.e. $\mathcal{S}(\widehat{M},\widehat{\mathcal{P}}^{\sharp}) = 1$ , where $\mathcal{S}$ is the grid sampling operation to compute the output values using $\widehat{M}$ and point coordinates $\widehat{\mathcal{P}}^{\sharp}$ from grid. Finally, after preforming the grid sampling $\mathcal{S}$ on ground truth map mask $M$ with the same dilated prediction curve, we then bridge a segmentation-base region supervision between $M$ and $\widehat{\mathcal{P}}^{\sharp}$ , which can be formulated mathematically as, + +$$ +\mathcal {L} _ {\text {r e g i o n}} = \mathcal {L} _ {\text {d i c e}} \left(\mathcal {S} \left(M, \widehat {\mathcal {P}} ^ {\sharp}\right), \mathcal {S} \left(\widehat {M}, \widehat {\mathcal {P}} ^ {\sharp}\right)\right) \tag {8} +$$ + +where $\mathcal{L}_{\text{dice}}$ is the common dice loss function in [38]. + +4) overall $PCR$ -Loss. In order to exert the above three-level supervision at the same time, we put forward that the overall $PCR$ -Loss is a weighted sum of all three losses as, + +$$ +\mathcal {L} _ {P C R} = \lambda_ {p} \mathcal {L} _ {\text {p o i n t}} + \lambda_ {c} \mathcal {L} _ {\text {c u r v e}} + \lambda_ {r} \mathcal {L} _ {\text {r e g i o n}} \tag {9} +$$ + +Multi-task Auxiliary Loss. The paradigm of multi-task learning can reduce the risk of overfitting by leveraging the domain-specific information included in the training signals of related tasks [61]. Thence, in addition to supervising the curve-level Bézier modeling procedure of the final head, we also perform auxiliary segmentation-based supervision on the intermediate modules, i.e. semantic-level BEV decoder and instance-level Bézier decoder. Given the output masks $\widehat{\mathbb{M}}_s$ and $\widehat{\mathbb{M}}_z$ in the Sec.3.2, we formulate the auxiliary loss with the combination of two tasks supervision as, + +$$ +\mathcal {L} _ {A U X} = \lambda_ {s} \mathcal {L} \left(\mathbb {M} _ {s}, \widehat {\mathbb {M}} _ {s}\right) + \lambda_ {z} \mathcal {L} \left(\mathbb {M} _ {z}, \widehat {\mathbb {M}} _ {z}\right) \tag {10} +$$ + +where $\mathbb{M}_{\star}$ denotes the ground truth and $\lambda_{\star}$ is the weighted factor. Note that $\mathcal{L}$ is a compound loss with common cross entropy loss and dice loss, namely $\mathcal{L} = \mathcal{L}_{ce} + \mathcal{L}_{dice}$ . + +# 4. Experiments + +# 4.1. Experimental Settings + +Existing Benchmarks. To evaluate the proposed approach, we conduct experiments on the popular NuScenes dataset [2], which consists of 28, 130/6, 019 samples and 700/150 driving scenes for the training/validation set respectively. Each scene contains roughly 40 samples and each sample includes 6 surrounding images, covering $360^{\circ}$ FOV of the ego-vehicle. For the sake of fair comparison, we follow the previous work [24] and focus on three static map categories, i.e. lane-divider, ped-crossing and road-boundary. Taking the ego-vehicle as the center, we set the perception range to $[30, 30, 15, 15]m$ , which corresponds to the distances of front, rear, left and right respectively, and fix the resolution of ego-to-pixel as $0.15m/pixel$ . In addition, for exploring the performance of our method under different lighting and weather conditions, we further divide NuScenes into five kinds of scene, namely day, night, sunny, cloudy and rainy. Refer to the supplementary material for more details. + +Evaluation Metrics. We utilize the exact same evaluation protocol as [24] of average precision (AP) to access the map construction quality over the instance-level. To be concrete, given a pair of instances from ground-truth and predictions respectively, this protocol computes the Chamfer Distance between them and considers the prediction as true-positive only if the distance is less than a specified threshold, which is set to $[0.2, 0.5, 1.0]m$ in our experiment. Note the overall AP metric is obtained by averaging across three thresholds. Moreover, as for a more informative comparison, the results under different lighting/weather conditions and a much simpler threshold setup of $[0.5, 1.0, 1.5]m$ are further provided. + +
MethodBackboneEpochAP_dividerAP_crossAP_boundmAPmAP_daymAP_nightmAP_sunnymAP.cloudymAP_rainy
IPM(B) [24]Eff-B03010.74.711.79.0-----
IPM(CB) [24]Eff-B03024.07.327.819.7-----
LSS [43]Eff-B03022.95.124.217.411.5b13.3b12.0b12.8b9.5b
VPN [40]Eff-B03022.15.225.317.517.9b17.5b18.2b18.5b15.9b
HMapNet [24]Eff-B03028.37.132.622.721.4b17.4b21.5b23.4b18.9b
BeMapNetEff-B03046.737.438.040.741.328.641.444.936.2
BeMapNetRes-503046.939.037.841.341.930.442.643.637.4
BeMapNetSwin-T3049.142.239.943.744.334.444.847.937.8
BeMapNetRes-5011052.744.544.247.147.739.248.750.341.4
BeMapNetSwin-T11054.246.546.549.149.837.350.453.542.8
BeMapNetSwin-B11055.347.049.450.551.238.052.254.843.6
BeMapNetRes-503062.357.759.459.860.546.962.561.953.0
BeMapNetSwin-T3064.461.361.662.563.153.264.766.054.2
BeMapNetSwin-B11069.064.469.767.768.354.670.371.658.0
+ +Table 1. Comparisons with SOTAs on NuScenes under thresholds of [0.2, 0.5, 1.0] $m$ and [0.5, 1.0, 1.5] $m$ , where the results of latter easier evaluation protocol is marked by Green shade. The Blue shade contains the results that used in all ablation studies for a fair comparison. Note ${}^{\flat}$ and - indicate the results are re-implemented by us with public code and not available respectively. + +Implementation Details. We employ EfficientNet-B0 [49], ResNet-50 [14] and SwinTR [31] as backbones, which are all initialized by ImageNet [21] pretraining. The following semantic $BEV$ decoder stacks 2 transformer encoder layers and 4 decoder layers with $64 \times 32$ $BEV$ queries, and the instance Bézier decoder stacks 6 mask-transformer decoder layers with 60 queries, where 20, 25, 15 for lane-divider, ped-crossing and road-boundary respectively. The shape of input image is resized to $896 \times 512$ and the mini-batch size is set to 1 per GPU. We train our model with 8 GPUs for 30/110 epochs and adopt multi-step schedule with milestone [0.7, 0.9] and $\gamma = \frac{1}{3}$ . The AdamW [33] optimizer is employed with a weight decay of $1e^{-4}$ and a learning rate of $2e^{-4}$ , which is multiplied by 0.1 for backbone. As for hyper-parameters of loss weight, we set $\lambda_s$ , $\lambda_z$ , $\lambda_p$ , $\lambda_c$ , $\lambda_r$ to 1, 5, 5, 10, 1 respectively and the dilated width $\omega$ in $\mathcal{L}_{region}$ to 5. The deployments of piecewise Bézier curve $\langle k, n \rangle$ for lane-divider, ped-crossing and road-boundary are set to $\langle 3, 2 \rangle$ , $\langle 1, 1 \rangle$ , $\langle 7, 3 \rangle$ . Note $m$ in Algorithm 1 is set to 100. + +# 4.2. Comparisons with State-of-the-art Methods + +We present the overall evaluation results on NuScenes in Table 1, which shows that our BeMapNet is significantly superior to the existing SOTA approaches by a large margin (up to 18.0) under the same setting of EfficientNet-B0 and 30 epochs, indicating the effectiveness of our approach. In addition, after replacing the backbone with more common ResNet-50 and more popular SwinTiny, our model achieves a further improvement of 0.6 and 3.0 AP respectively. Next, considering the slow convergence of the Transformer-based model, we increase the training schedule to 110 epochs and gain at least another 5.4 improvements. Even in somewhat unconventional scenarios, such as night and rainy, our proposed approach still shows a great advantage, i.e. 13.2 and + +
Position EncodingAP_dividerAP_crossAP_boundmAP
Sine PE42.834.134.737.2
Learned PE40.232.233.835.4
IPM-PE46.439.237.841.1
+ Exclusive FC38.633.333.935.3
+ Shared FC49.142.239.943.7
+ +Table 2. Comparisons on different methods of position encoding. + +16.9 AP are obtained respectively. Furthermore, another interesting observation is that regardless of which method is used, we find that the performance of sunny scene is always slightly lower than cloudy. We believe that strong illuminations and ground shades on sunny day might have a certain impact on the perception of map objects. As a supplement, the last three rows of Table 1 show the performance of our approach on a much simpler evaluation protocol. + +# 4.3. Ablation Study + +The Different Way of Position Encoding. Table 2 shows the performance of different $PE$ in semantic BEV decoder for the map construction. Compared with the sine/learned-based method, our proposed IPM-PE module improves AP by 3.9/5.7 respectively, which proves the multi-perspective $PE$ guided by the intrinsic and extrinsic parameters is very effective. Moreover, through the results in the 3-rd and 5-th row, we find that IPM-PE with shared FC layer alignment gains an further improvement of 2.6 points. Yet, in order to rule out the possibility of that the attached FC layer brings an increment, we then feed the position embeddings from IPM-PE into two exclusive FCs and the 4-th row results exclude the influence of FC. These comparisons indicate the shared align layer is the exactly essential part to mitigate the performance decline brought by the unreasonable assumption of IPM, which validates our conjecture in Sec.3.2.2. + +![](images/cee40b8254afb773901ebf807217fd10dc8aa039219eb16607ea573cdc045532.jpg) +Figure 5. The qualitative comparison results of HDMapNet [24], BeMapNet and GroundTruth [2] under different scenarios. + +Effectiveness of $PCR$ -Loss. The $PCR$ -Loss mainly consists of three parts, i.e. point, curve and region. Table 3 shows detailed ablation results of the role of each part. Specifically, with adopting only one supervision in rows $1 \sim 3$ , the performance trend is roughly: curve > point > region. Among them, it is worth noting that the only region-based supervision shows very poor performance, which is understandable because the generation of region mask relies on a collection of relatively accurate points. This conjecture is also verified in rows $4 \sim 5$ of the Table 3. Furthermore, when integrating multiple loss supervision, the final performance is consistently improved compared to the single one, and three parts used together achieves the optimal AP results of 43.7. + +
PointCurveRegionAP_dividerAPPEDAPboundarymAP
✓XX39.133.323.732.0
X✓X47.235.135.939.4
XX✓3.22.60.52.1
✓X✓40.739.416.732.9
X✓✓48.238.539.742.1
✓✓X46.538.536.240.4
✓✓✓49.142.239.943.7
+ +Effectiveness of Multi-task Auxiliary Loss. Without any auxiliary loss, the average AP of our proposed BeMapNet is only 20.0. Yet, after adopting another semantic/instance supervision, the result is improved to 34.5/38.4 respectively and goes further to 43.7 with employing both, which shows the auxiliary tasks for producing high-quality semantic $BEV$ features and instance descriptors are very important. + +Table 3. The effectiveness of different modules in ${PCR} - {Loss}$ . + +
SemanticInstanceAPdividerAPpedAPboundarymAP
XX21.517.820.720.0
✓X39.331.532.834.5
X✓44.334.636.538.4
✓✓49.142.239.943.7
+ +Comparison with Polyline Vectorization. An amusing fact is that a Bézier curve with $n = 1$ is simply a straight line between two control points. By setting the degree of all elements to 1, our framework naturally degenerates into the polyline-based method. Note we further set $k$ to 9, 1, 29 for lane-divider, ped-crossing and road-boundary respectively. The comparisons in Table 5 show the Bézier-based vectorization approach achieves better 4.5 AP. Interestingly, as the complexity of map element shape increases (usually ped-crossing $<$ lane-divider $<$ road-boundary), we find that the corresponding AP improvement increases as well. + +Table 4. The effectiveness of different modules in AUX-Loss. + +
VectorizationAPdividerAPpedAPboundarymAP
Polyline45.039.133.439.2
Bézier49.1 (+4.1)42.2 (+3.1)39.9 (+6.5)43.7(+4.5)
+ +Table 5. Comparison with the different type of vectorization. + +Qualitative Analysis. We show the qualitative comparisons with SOTAs in Fig. 5. Besides avoiding complex vectorized post-processing, the proposed BeMapNet constructs various and changeful $HD$ -elements more compactly and robust. Note that more extensive visualizations under different conditions are further provided in our supplementary material. + +# 5. Conclusion + +Vectorized $HD$ -map online construction focuses on the perception of centimeter-level environmental information. Starting from the conventional parameterization-based methods, this paper presents an end-to-end postprocessing-free architecture, namely BeMapNet, with leveraging unified piecewise Bézier curve for various and changeful map elements. 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Most existing approaches first obtain rasterized map with the segmentation-based pipeline and then conduct heavy post-processing for downstream-friendly vectorization. In this paper, by delving into parameterization-based methods, we pioneer a concise and elegant scheme that adopts unified piecewise Bézier curve. In order to vectorize changed map elements end-to-end, we elaborate a simple yet effective architecture, named Piecewise Bézier HD-map Network (BeMapNet), which is formulated as a direct set prediction paradigm and postprocessing-free. Concretely, we first introduce a novel IPM-PE Align module to inject 3D geometry prior into BEV features through common position encoding in Transformer. Then a well-designed Piecewise Bézier Head is proposed to output the details of each map element, including the coordinate of control points and the segment number of curves. In addition, based on the progressively restoration of Bézier curve, we also present an efficient Point-Curve-Region Loss for supervising more robust and precise HD-map modeling. Extensive comparisons show that our method is remarkably superior to other existing SOTAs by " + }, + { + "bbox": [ + 46, + 238, + 290, + 525 + ], + "type": "inline_equation", + "content": "18.0\\mathrm{mAP}" + }, + { + "bbox": [ + 46, + 238, + 290, + 525 + ], + "type": "text", + "content": " at least1." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 547, + 128, + 559 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 547, + 128, + 559 + ], + "spans": [ + { + "bbox": [ + 47, + 547, + 128, + 559 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 567, + 287, + 687 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 567, + 287, + 687 + ], + "spans": [ + { + "bbox": [ + 46, + 567, + 287, + 687 + ], + "type": "text", + "content": "As one of the most fundamental components in the autodriving system, high-definition map contains centimeter details of traffic elements, vectorized topology and navigation information, which instruct ego-vehicle to accurately locate itself on the road and understand what is coming up ahead. At present, conventional SLAM-based solutions [45, 46, 60] have been widely adopted in practice. 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Illustration of our motivation for piecewise Bézier curve, termed as " + }, + { + "bbox": [ + 304, + 369, + 545, + 468 + ], + "type": "inline_equation", + "content": "\\langle k, n \\rangle" + }, + { + "bbox": [ + 304, + 369, + 545, + 468 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 369, + 545, + 468 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 304, + 369, + 545, + 468 + ], + "type": "text", + "content": " is the piece number and " + }, + { + "bbox": [ + 304, + 369, + 545, + 468 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 304, + 369, + 545, + 468 + ], + "type": "text", + "content": " is the degree. Fig.(a) is a real HD-map case from NuScenes. Fig.(b) compares the difference between vanilla and piecewise Bézier curve through the same map element, where the light purple is the restored curve with Bézier process. The last is more efficient than previous ones with reducing the number of control points by " + }, + { + "bbox": [ + 304, + 369, + 545, + 468 + ], + "type": "inline_equation", + "content": "64\\%" + }, + { + "bbox": [ + 304, + 369, + 545, + 468 + ], + "type": "text", + "content": " in this case. Fig.(c) illustrates that piecewise Bézier curve can model arbitrary-shaped curves. Note the blue circles denote actual control points." + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_caption" + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 474, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 474, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 474, + 546, + 713 + ], + "type": "text", + "content": "The deep-based paradigm of online " + }, + { + "bbox": [ + 304, + 474, + 546, + 713 + ], + "type": "inline_equation", + "content": "HD" + }, + { + "bbox": [ + 304, + 474, + 546, + 713 + ], + "type": "text", + "content": "-map building is gradually developing, but it still faces two main challenges: 1) modeling instance-level vectorized " + }, + { + "bbox": [ + 304, + 474, + 546, + 713 + ], + "type": "inline_equation", + "content": "HD" + }, + { + "bbox": [ + 304, + 474, + 546, + 713 + ], + "type": "text", + "content": "-map end-to-end. Most existing works construct " + }, + { + "bbox": [ + 304, + 474, + 546, + 713 + ], + "type": "inline_equation", + "content": "HD" + }, + { + "bbox": [ + 304, + 474, + 546, + 713 + ], + "type": "text", + "content": "-map by rasterizing " + }, + { + "bbox": [ + 304, + 474, + 546, + 713 + ], + "type": "inline_equation", + "content": "BEV" + }, + { + "bbox": [ + 304, + 474, + 546, + 713 + ], + "type": "text", + "content": " (bird-eye-view) maps into semantic pixels with segmentation [24, 42], which not only lacks the modeling of instance-level details, but also requires heavy post-processing to obtain vectorized information. As a sub-task, lane detection makes a relatively better advance for this issue, that is, in addition to segmentation-based methods [39, 41, 62], there are also point-based [25, 47] and curve-based [12, 28] schemes. However, compared to the simple lane scenario, " + }, + { + "bbox": [ + 304, + 474, + 546, + 713 + ], + "type": "inline_equation", + "content": "HD" + }, + { + "bbox": [ + 304, + 474, + 546, + 713 + ], + "type": "text", + "content": "-map contains more shape-changeful elements, so such methods cannot be directly adopted into the " + }, + { + "bbox": [ + 304, + 474, + 546, + 713 + ], + "type": "inline_equation", + "content": "HD" + }, + { + "bbox": [ + 304, + 474, + 546, + 713 + ], + "type": "text", + "content": "-map construction. 2) performing 2D-3D perspective transformation efficiently. Obtaining 3D- " + }, + { + "bbox": [ + 304, + 474, + 546, + 713 + ], + "type": "inline_equation", + "content": "BEV" + }, + { + "bbox": [ + 304, + 474, + 546, + 713 + ], + "type": "text", + "content": " perception from multi-view 2D images is an essential step for building " + }, + { + "bbox": [ + 304, + 474, + 546, + 713 + ], + "type": "inline_equation", + "content": "HD" + }, + { + "bbox": [ + 304, + 474, + 546, + 713 + ], + "type": "text", + "content": "-map, which is mainly divided into three ideas, i.e. geometric priors [44], learnable parameters [40, 42], and a combination of the two [17, 43]. Note the assumptions of geometry-based methods often do" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 57, + 693, + 138, + 703 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 57, + 693, + 138, + 703 + ], + "spans": [ + { + "bbox": [ + 57, + 693, + 138, + 703 + ], + "type": "text", + "content": "*Corresponding author." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 59, + 703, + 237, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 703, + 237, + 712 + ], + "spans": [ + { + "bbox": [ + 59, + 703, + 237, + 712 + ], + "type": "text", + "content": "1https://github.com/er-muyue/BeMapNet" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "13218" + } + ] + } + ], + "index": 20 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "type": "text", + "content": "not conform to the actual situation, leading to such schemes are less adaptable, while learning-based methods require a large amount of labeled data to generalize across various scenarios. Combining the above two branches not only has multi-scenario scalability, but also reduces the demand for annotated data, has attracted increasing research interest." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 144, + 288, + 323 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 144, + 288, + 323 + ], + "spans": [ + { + "bbox": [ + 46, + 144, + 288, + 323 + ], + "type": "text", + "content": "To the best of our knowledge, the curve parameterization construction of " + }, + { + "bbox": [ + 46, + 144, + 288, + 323 + ], + "type": "inline_equation", + "content": "HD" + }, + { + "bbox": [ + 46, + 144, + 288, + 323 + ], + "type": "text", + "content": "-map in the " + }, + { + "bbox": [ + 46, + 144, + 288, + 323 + ], + "type": "inline_equation", + "content": "BEV" + }, + { + "bbox": [ + 46, + 144, + 288, + 323 + ], + "type": "text", + "content": " space is vacancy and no one has explored it. Based on the widely used Bézier curve, which is mathematically defined by a set of control points, we pioneer to devise a concise and elegant " + }, + { + "bbox": [ + 46, + 144, + 288, + 323 + ], + "type": "inline_equation", + "content": "HD" + }, + { + "bbox": [ + 46, + 144, + 288, + 323 + ], + "type": "text", + "content": "-map scheme that adopts piecewise Bézier curve, where each map curve is divided into multiple " + }, + { + "bbox": [ + 46, + 144, + 288, + 323 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 144, + 288, + 323 + ], + "type": "text", + "content": " segments and each segment is then represented by a vanilla Bézier curve with degree " + }, + { + "bbox": [ + 46, + 144, + 288, + 323 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 46, + 144, + 288, + 323 + ], + "type": "text", + "content": ", hence denoted as " + }, + { + "bbox": [ + 46, + 144, + 288, + 323 + ], + "type": "inline_equation", + "content": "\\langle k, n \\rangle" + }, + { + "bbox": [ + 46, + 144, + 288, + 323 + ], + "type": "text", + "content": ". Despite " + }, + { + "bbox": [ + 46, + 144, + 288, + 323 + ], + "type": "inline_equation", + "content": "\\langle 1, n \\rangle" + }, + { + "bbox": [ + 46, + 144, + 288, + 323 + ], + "type": "text", + "content": " is enough to express any map element with infinite " + }, + { + "bbox": [ + 46, + 144, + 288, + 323 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 46, + 144, + 288, + 323 + ], + "type": "text", + "content": " in theory, more complex curve tends to require higher degree, meaning that there are more control points need to be modeled, which is shown in Fig.1. The proposed piecewise strategy allows us to parameterize a curve more compactly with fewer control points and higher capacity, which is extremely scalable and robust in practice." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 323, + 288, + 610 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 323, + 288, + 610 + ], + "spans": [ + { + "bbox": [ + 46, + 323, + 288, + 610 + ], + "type": "text", + "content": "Inspired by the above motivations, we propose an end-to-end vectorized HD-map construction architecture, named as Piecewise Bézier HD-map Network (BeMapNet). The overall framework is illustrated in detail in Fig.2, which streamlines the architecture into four primary modules for gradually-enriched information, i.e. feature extractor shared among multi-view images, semantic BEV decoder for " + }, + { + "bbox": [ + 46, + 323, + 288, + 610 + ], + "type": "inline_equation", + "content": "2D-3D" + }, + { + "bbox": [ + 46, + 323, + 288, + 610 + ], + "type": "text", + "content": " perspective elevation, instance Bézier decoder for curve-level descriptors, and piecewise Bézier head for point-level parameterization. To be concrete, we first introduce a novel IPM-PE Align module into Transformer-based decoders, which injects IPM (inverse perspective mapping) geometric priors into BEV features via PE (position encoding) and hardly adds any parameters except a FC layer. Secondly, we further design a Piecewise Bézier Head for dynamic curve modeling with adopting two branches as classification and regression, where the former classifies the number of pieces to determine the curve length and the latter regresses the coordinate of control points to determine the curve shape. Lastly, we present an Point-Curve-Region Loss for robust curve modeling by supervising restoration information as a progressive manner. Since it is modeled as a sparse set prediction task and optimized with a bipartite matching loss, our method is postprocessing-free and high-performance." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 611, + 272, + 622 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 611, + 272, + 622 + ], + "spans": [ + { + "bbox": [ + 47, + 611, + 272, + 622 + ], + "type": "text", + "content": "The main contributions of our approach are three-folds:" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 51, + 624, + 286, + 713 + ], + "type": "list", + "angle": 0, + "index": 7, + "blocks": [ + { + "bbox": [ + 51, + 624, + 286, + 647 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 51, + 624, + 286, + 647 + ], + "spans": [ + { + "bbox": [ + 51, + 624, + 286, + 647 + ], + "type": "text", + "content": "- We pioneer the BeMapNet for concise and elegant modeling of HD-map with unified piecewise Bézier curve." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 51, + 651, + 286, + 686 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 51, + 651, + 286, + 686 + ], + "spans": [ + { + "bbox": [ + 51, + 651, + 286, + 686 + ], + "type": "text", + "content": "- We elaborate the overall end-to-end architecture with innovatively introducing IPM-PE Align Module, Piecewise Bézier Output Head and well-designed PCR-Loss." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 51, + 689, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 51, + 689, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 51, + 689, + 286, + 713 + ], + "type": "text", + "content": "- BeMapNet is remarkably superior to SOTAs on existing benchmarks, revealing the effectiveness of our approach." + } + ] + } + ], + "index": 6 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 306, + 71, + 392, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 71, + 392, + 83 + ], + "spans": [ + { + "bbox": [ + 306, + 71, + 392, + 83 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 91, + 481, + 104 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 91, + 481, + 104 + ], + "spans": [ + { + "bbox": [ + 306, + 91, + 481, + 104 + ], + "type": "text", + "content": "2.1. Vectorized HD-map Construction" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 110, + 545, + 361 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 110, + 545, + 361 + ], + "spans": [ + { + "bbox": [ + 304, + 110, + 545, + 361 + ], + "type": "inline_equation", + "content": "HD" + }, + { + "bbox": [ + 304, + 110, + 545, + 361 + ], + "type": "text", + "content": "-map is precise at centimeter-level and consists of vectorized details not normally present on standard map [27], which highly aggravates the difficulty of obtaining accurate annotations in practice. Most previous methods focus on SLAM [11, 18, 22, 36, 46, 58] with exploring LiDAR points of the environment, involving large-scale data acquisition and labor-intensive annotations. Recently, more and more researchers formulate the process of building " + }, + { + "bbox": [ + 304, + 110, + 545, + 361 + ], + "type": "inline_equation", + "content": "HD" + }, + { + "bbox": [ + 304, + 110, + 545, + 361 + ], + "type": "text", + "content": "-map as a segmentation task [6, 13, 20, 32] from various sensors, such as cameras [15, 26, 34, 35, 40, 43, 59, 63] and LiDAR [1, 57]. HDMapNet [24] extracts features from the observations of multi-modalities and groups semantic rasterized maps with heuristic post-processing for vectorized results. Without any further vectorization, [42] only obtains semantic map representations from a Transformer-based camera-to-BEV module. Different from the above segmentation-based frameworks, our proposed BeMapNet adopts the parameterization-based paradigm and constructs instance-level vectorized " + }, + { + "bbox": [ + 304, + 110, + 545, + 361 + ], + "type": "inline_equation", + "content": "HD" + }, + { + "bbox": [ + 304, + 110, + 545, + 361 + ], + "type": "text", + "content": "-map end-to-end with a multiview and camera-only manner, which is a more flexible and scalable solution for downstream tasks." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 371, + 509, + 384 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 371, + 509, + 384 + ], + "spans": [ + { + "bbox": [ + 306, + 371, + 509, + 384 + ], + "type": "text", + "content": "2.2. Structure Modeling of Geometric Data" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 391, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 391, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 391, + 545, + 713 + ], + "type": "text", + "content": "HD-map contains various kinds of map elements, including lane-divider, ped-crossing, road-boundary, etc., which are typically regarded as geometric data, e.g. points, polygons and curves. To the best of knowledge, there are two mainstream exploration directions for deep geometric modeling, one is point-based, including uniform-points and keypoints estimation, and the other is curve-based, including polynomial curve and Bézier curve. Taking the most related lane detection as an example, LineCNN [25] presents a novel line proposal unit to detect lanes as a set of points, and later LaneATT [47] represents a lane by equally-spaced " + }, + { + "bbox": [ + 304, + 391, + 545, + 713 + ], + "type": "inline_equation", + "content": "2D" + }, + { + "bbox": [ + 304, + 391, + 545, + 713 + ], + "type": "text", + "content": "-points that achieves good performance. GANet [54] focuses on keypoint estimation and association with adaptively lane feature aggregator. HDMapGen [37] proposes a hierarchical point generative model for producing high-quality HD lane map. As for cruve-based, [51] and [48] directly predict the polynomial coefficients with a differentiable least-squares fitting module and simple " + }, + { + "bbox": [ + 304, + 391, + 545, + 713 + ], + "type": "inline_equation", + "content": "FC" + }, + { + "bbox": [ + 304, + 391, + 545, + 713 + ], + "type": "text", + "content": " respectively. Recently, based on the DETR [4], LSTR [28] presents a query-based detector to decode poly-parameters of a lane end-to-end. Apart from this, some studies also adopt Bézier curve for geometry, such as text boundary [29], center-line segment [3] and lane curve [12]. Unlike these approaches of addressing simple-shape elements, our method innovatively employs piecewise Bézier curves without any complicated geometric assumptions to parameterize arbitrary-shape geometry in HD-map scenarios." + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "13219" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 49, + 70, + 547, + 299 + ], + "blocks": [ + { + "bbox": [ + 49, + 70, + 547, + 299 + ], + "lines": [ + { + "bbox": [ + 49, + 70, + 547, + 299 + ], + "spans": [ + { + "bbox": [ + 49, + 70, + 547, + 299 + ], + "type": "image", + "image_path": "9cdd2ebeb92158f77acbeb5c176dfee9dccc3a8d15ff9b0e602a66dffa03cf98.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 301, + 546, + 346 + ], + "lines": [ + { + "bbox": [ + 46, + 301, + 546, + 346 + ], + "spans": [ + { + "bbox": [ + 46, + 301, + 546, + 346 + ], + "type": "text", + "content": "Figure 2. The architecture of our proposed BeMapNet, containing four primary components for extracting progressively richer information, i.e. image-level multi-scale features, semantic-level BEV feature, instance-level curve descriptors, and point-level Bézier control sequence. Right-top: The blue and orange circles represent explicit control points and implicit control offsets respectively. Note that the term GAP is global average pooling and MatMul is the matrix multiplication. Right-bottom: " + }, + { + "bbox": [ + 46, + 301, + 546, + 346 + ], + "type": "inline_equation", + "content": "(H_c, W_c) / (H_b, W_b)" + }, + { + "bbox": [ + 46, + 301, + 546, + 346 + ], + "type": "text", + "content": " is the shape of image/BEV feature." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 353, + 277, + 365 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 353, + 277, + 365 + ], + "spans": [ + { + "bbox": [ + 47, + 353, + 277, + 365 + ], + "type": "text", + "content": "2.3. Multi-view Camera-to-BEV Transformation" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 378, + 289, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 378, + 289, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 378, + 289, + 714 + ], + "type": "text", + "content": "In most " + }, + { + "bbox": [ + 46, + 378, + 289, + 714 + ], + "type": "inline_equation", + "content": "3D" + }, + { + "bbox": [ + 46, + 378, + 289, + 714 + ], + "type": "text", + "content": " research studies, obtaining high-quality BEV representations from multi-view camera features is the top priority of various domains, such as " + }, + { + "bbox": [ + 46, + 378, + 289, + 714 + ], + "type": "inline_equation", + "content": "3D" + }, + { + "bbox": [ + 46, + 378, + 289, + 714 + ], + "type": "text", + "content": " object detection [17, 30, 43, 55, 56], motion prediction [10, 16, 19, 23, 53] and map construction [24, 26, 40, 42]. IPM [44] is the most basic and straightforward method with a homography transformation, which is precisely calculated by camera parameters. Without adopting the " + }, + { + "bbox": [ + 46, + 378, + 289, + 714 + ], + "type": "inline_equation", + "content": "3D" + }, + { + "bbox": [ + 46, + 378, + 289, + 714 + ], + "type": "text", + "content": " geometry prior, some methods [3, 40, 42] directly leverage learnable parameters to complete the perspective transformation. VPN [40] and Neat [9] both utilize a " + }, + { + "bbox": [ + 46, + 378, + 289, + 714 + ], + "type": "inline_equation", + "content": "FC" + }, + { + "bbox": [ + 46, + 378, + 289, + 714 + ], + "type": "text", + "content": " layer to transform the image features into the BEV space, and [42] further designs a multi-camera deformable attention unit based on transformer. However, in order to obtain more explicit BEV representations, more and more researches argue that the geometry priors has great advantages for model convergence and performance. Based on VPN, [24] fuse the multi-camera BEV spaces with the camera poses. LSS [43] and BEVDet [17] build the connection between camera-view and BEV based on the depth distribution estimation. DETR3D [56] manipulates predictions directly in " + }, + { + "bbox": [ + 46, + 378, + 289, + 714 + ], + "type": "inline_equation", + "content": "3D" + }, + { + "bbox": [ + 46, + 378, + 289, + 714 + ], + "type": "text", + "content": " space with linking " + }, + { + "bbox": [ + 46, + 378, + 289, + 714 + ], + "type": "inline_equation", + "content": "3D" + }, + { + "bbox": [ + 46, + 378, + 289, + 714 + ], + "type": "text", + "content": " positions to " + }, + { + "bbox": [ + 46, + 378, + 289, + 714 + ], + "type": "inline_equation", + "content": "2D" + }, + { + "bbox": [ + 46, + 378, + 289, + 714 + ], + "type": "text", + "content": " spaces and [5] generates BEV features by regarding camera parameters as a reference. PETR [30] encodes the " + }, + { + "bbox": [ + 46, + 378, + 289, + 714 + ], + "type": "inline_equation", + "content": "3D" + }, + { + "bbox": [ + 46, + 378, + 289, + 714 + ], + "type": "text", + "content": " information as position embedding and conducts query decoding on position-aware features. In addition to introducing the " + }, + { + "bbox": [ + 46, + 378, + 289, + 714 + ], + "type": "inline_equation", + "content": "3D" + }, + { + "bbox": [ + 46, + 378, + 289, + 714 + ], + "type": "text", + "content": " geometry prior, we further performs position embedding alignment for transforming the camera features and BEV features into the world coordinate system." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 306, + 352, + 361, + 365 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 352, + 361, + 365 + ], + "spans": [ + { + "bbox": [ + 306, + 352, + 361, + 365 + ], + "type": "text", + "content": "3. Method" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 306, + 372, + 430, + 384 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 372, + 430, + 384 + ], + "spans": [ + { + "bbox": [ + 306, + 372, + 430, + 384 + ], + "type": "text", + "content": "3.1. Problem Formulation" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 305, + 391, + 545, + 427 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 391, + 545, + 427 + ], + "spans": [ + { + "bbox": [ + 305, + 391, + 545, + 427 + ], + "type": "text", + "content": "Preliminary on Piecewise Bézier Curve. A Bézier curve is a parametric curve which is formulated by a set of ordered control points " + }, + { + "bbox": [ + 305, + 391, + 545, + 427 + ], + "type": "inline_equation", + "content": "c_{0}" + }, + { + "bbox": [ + 305, + 391, + 545, + 427 + ], + "type": "text", + "content": " through " + }, + { + "bbox": [ + 305, + 391, + 545, + 427 + ], + "type": "inline_equation", + "content": "c_{n}" + }, + { + "bbox": [ + 305, + 391, + 545, + 427 + ], + "type": "text", + "content": " as," + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 362, + 434, + 545, + 464 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 362, + 434, + 545, + 464 + ], + "spans": [ + { + "bbox": [ + 362, + 434, + 545, + 464 + ], + "type": "interline_equation", + "content": "p (t) = \\sum_ {i = 0} ^ {n} b _ {i, n} (t) c _ {i}, t \\in [ 0, 1 ] \\tag {1}", + "image_path": "5db8219d5b7f4958161b12ddb0b13f14b3e8e29a42533dabd29fb524972cba24.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 305, + 470, + 545, + 495 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 470, + 545, + 495 + ], + "spans": [ + { + "bbox": [ + 305, + 470, + 545, + 495 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 470, + 545, + 495 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 305, + 470, + 545, + 495 + ], + "type": "text", + "content": " is the degree of the curve and " + }, + { + "bbox": [ + 305, + 470, + 545, + 495 + ], + "type": "inline_equation", + "content": "b_{i,n}(t)" + }, + { + "bbox": [ + 305, + 470, + 545, + 495 + ], + "type": "text", + "content": " is known as Bernstein basis polynomial of degree " + }, + { + "bbox": [ + 305, + 470, + 545, + 495 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 305, + 470, + 545, + 495 + ], + "type": "text", + "content": "," + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 340, + 500, + 545, + 527 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 340, + 500, + 545, + 527 + ], + "spans": [ + { + "bbox": [ + 340, + 500, + 545, + 527 + ], + "type": "interline_equation", + "content": "b _ {i, n} (t) = \\binom {n} {i} t ^ {i} (1 - t) ^ {n - i}, i = 0, \\dots , n \\tag {2}", + "image_path": "bc458404435b9ce4ea13b6053ed7e29638f34d86f19ae29bc3e390edfc1da744.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 531, + 545, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 531, + 545, + 628 + ], + "spans": [ + { + "bbox": [ + 304, + 531, + 545, + 628 + ], + "type": "text", + "content": "According to Eq.1, we know the first and last control points are endpoints of the curve, i.e. " + }, + { + "bbox": [ + 304, + 531, + 545, + 628 + ], + "type": "inline_equation", + "content": "p(0) = c_0" + }, + { + "bbox": [ + 304, + 531, + 545, + 628 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 531, + 545, + 628 + ], + "type": "inline_equation", + "content": "p(1) = c_n" + }, + { + "bbox": [ + 304, + 531, + 545, + 628 + ], + "type": "text", + "content": ". Then we define a piecewise Bézier curve " + }, + { + "bbox": [ + 304, + 531, + 545, + 628 + ], + "type": "inline_equation", + "content": "\\langle k, n \\rangle" + }, + { + "bbox": [ + 304, + 531, + 545, + 628 + ], + "type": "text", + "content": " consists of " + }, + { + "bbox": [ + 304, + 531, + 545, + 628 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 304, + 531, + 545, + 628 + ], + "type": "text", + "content": " segments, each of which is an " + }, + { + "bbox": [ + 304, + 531, + 545, + 628 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 304, + 531, + 545, + 628 + ], + "type": "text", + "content": "-order Bézier and two consecutive segments satisfy the positional continuity condition as " + }, + { + "bbox": [ + 304, + 531, + 545, + 628 + ], + "type": "inline_equation", + "content": "p^j(1) = p^{j+1}(0)" + }, + { + "bbox": [ + 304, + 531, + 545, + 628 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 531, + 545, + 628 + ], + "type": "inline_equation", + "content": "j" + }, + { + "bbox": [ + 304, + 531, + 545, + 628 + ], + "type": "text", + "content": " is the segment " + }, + { + "bbox": [ + 304, + 531, + 545, + 628 + ], + "type": "inline_equation", + "content": "id" + }, + { + "bbox": [ + 304, + 531, + 545, + 628 + ], + "type": "text", + "content": " varying from 0 to " + }, + { + "bbox": [ + 304, + 531, + 545, + 628 + ], + "type": "inline_equation", + "content": "k-2" + }, + { + "bbox": [ + 304, + 531, + 545, + 628 + ], + "type": "text", + "content": ". Hereafter, given a piecewise Bézier curve as shown in Fig.3, we denote its ordered control points as," + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 314, + 632, + 545, + 647 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 314, + 632, + 545, + 647 + ], + "spans": [ + { + "bbox": [ + 314, + 632, + 545, + 647 + ], + "type": "interline_equation", + "content": "\\mathbb {C} = \\left\\{c _ {i} ^ {j} \\in \\mathbb {R} ^ {2} \\mid i \\in [ 0, n ], j \\in [ 0, k - 1 ], c _ {n} ^ {j} = c _ {0} ^ {j + 1} \\right\\} \\tag {3}", + "image_path": "24bfc928c3c20bb95a42ddf6efb4a13de3c72164621b141a1c19b406399e561d.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 653, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 653, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 653, + 546, + 713 + ], + "type": "text", + "content": "Moreover, due to the first and last control points of each segment are always on the curve, we naturally term these points that retain a distinct significance as explicit control points " + }, + { + "bbox": [ + 304, + 653, + 546, + 713 + ], + "type": "inline_equation", + "content": "\\mathbb{C}^E" + }, + { + "bbox": [ + 304, + 653, + 546, + 713 + ], + "type": "text", + "content": " and the remaining as implicit control points " + }, + { + "bbox": [ + 304, + 653, + 546, + 713 + ], + "type": "inline_equation", + "content": "\\mathbb{C}^I" + }, + { + "bbox": [ + 304, + 653, + 546, + 713 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 653, + 546, + 713 + ], + "type": "inline_equation", + "content": "\\mathbb{C} = \\mathbb{C}^E \\cup \\mathbb{C}^I" + }, + { + "bbox": [ + 304, + 653, + 546, + 713 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 653, + 546, + 713 + ], + "type": "inline_equation", + "content": "|\\mathbb{C}^E| = k + 1" + }, + { + "bbox": [ + 304, + 653, + 546, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 653, + 546, + 713 + ], + "type": "inline_equation", + "content": "|\\mathbb{C}^I| = nk - k" + }, + { + "bbox": [ + 304, + 653, + 546, + 713 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "13220" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 52, + 71, + 225, + 178 + ], + "blocks": [ + { + "bbox": [ + 52, + 71, + 225, + 178 + ], + "lines": [ + { + "bbox": [ + 52, + 71, + 225, + 178 + ], + "spans": [ + { + "bbox": [ + 52, + 71, + 225, + 178 + ], + "type": "image", + "image_path": "490ded093f6ddf2eaa436ee0fe4fd89c30bb15185a9d1c10fb525f4ea232a821.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 73, + 179, + 135, + 187 + ], + "lines": [ + { + "bbox": [ + 73, + 179, + 135, + 187 + ], + "spans": [ + { + "bbox": [ + 73, + 179, + 135, + 187 + ], + "type": "text", + "content": "Piecewise Bézier Curve" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 57, + 179, + 71, + 187 + ], + "blocks": [ + { + "bbox": [ + 57, + 179, + 71, + 187 + ], + "lines": [ + { + "bbox": [ + 57, + 179, + 71, + 187 + ], + "spans": [ + { + "bbox": [ + 57, + 179, + 71, + 187 + ], + "type": "image", + "image_path": "935691aecb555a9e02d21cdf7ce9a485718574b6f121612f195fce03f20c51c0.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 73, + 191, + 135, + 199 + ], + "lines": [ + { + "bbox": [ + 73, + 191, + 135, + 199 + ], + "spans": [ + { + "bbox": [ + 73, + 191, + 135, + 199 + ], + "type": "text", + "content": "Bézier Control Polygon" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_caption" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 149, + 179, + 157, + 186 + ], + "blocks": [ + { + "bbox": [ + 149, + 179, + 157, + 186 + ], + "lines": [ + { + "bbox": [ + 149, + 179, + 157, + 186 + ], + "spans": [ + { + "bbox": [ + 149, + 179, + 157, + 186 + ], + "type": "image", + "image_path": "5530dbe275f868354976371c6852c6d404ef6c694a959ad81da71372315bfb4e.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 159, + 179, + 217, + 187 + ], + "lines": [ + { + "bbox": [ + 159, + 179, + 217, + 187 + ], + "spans": [ + { + "bbox": [ + 159, + 179, + 217, + 187 + ], + "type": "text", + "content": "Explicit Control Points" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_caption" + } + ], + "index": 3 + }, + { + "type": "image", + "bbox": [ + 228, + 72, + 282, + 178 + ], + "blocks": [ + { + "bbox": [ + 228, + 72, + 282, + 178 + ], + "lines": [ + { + "bbox": [ + 228, + 72, + 282, + 178 + ], + "spans": [ + { + "bbox": [ + 228, + 72, + 282, + 178 + ], + "type": "image", + "image_path": "d44b5c89a8edcdb644558d3d5453810e276b7e019ba2503694178011167a54d4.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 231, + 179, + 279, + 187 + ], + "lines": [ + { + "bbox": [ + 231, + 179, + 279, + 187 + ], + "spans": [ + { + "bbox": [ + 231, + 179, + 279, + 187 + ], + "type": "text", + "content": "Explicit Center" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_caption" + } + ], + "index": 5 + }, + { + "type": "image", + "bbox": [ + 57, + 191, + 71, + 198 + ], + "blocks": [ + { + "bbox": [ + 57, + 191, + 71, + 198 + ], + "lines": [ + { + "bbox": [ + 57, + 191, + 71, + 198 + ], + "spans": [ + { + "bbox": [ + 57, + 191, + 71, + 198 + ], + "type": "image", + "image_path": "93bbc57febb8affdb62846f3807ac50e845b020707c79fb33983d2ed02021cb5.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 204, + 287, + 248 + ], + "lines": [ + { + "bbox": [ + 46, + 204, + 287, + 248 + ], + "spans": [ + { + "bbox": [ + 46, + 204, + 287, + 248 + ], + "type": "text", + "content": "Figure 3. Illustration of a 3-pieces 3-order piecewiseBezier curve, denoted as " + }, + { + "bbox": [ + 46, + 204, + 287, + 248 + ], + "type": "inline_equation", + "content": "\\langle 3,3\\rangle" + }, + { + "bbox": [ + 46, + 204, + 287, + 248 + ], + "type": "text", + "content": " for the left part. For each segment, we model the implicit control point coordinates by an offset " + }, + { + "bbox": [ + 46, + 204, + 287, + 248 + ], + "type": "inline_equation", + "content": "(\\Delta x,\\Delta y)" + }, + { + "bbox": [ + 46, + 204, + 287, + 248 + ], + "type": "text", + "content": " from the center of explicit control points as shown on the right part." + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_caption" + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 149, + 191, + 157, + 198 + ], + "blocks": [ + { + "bbox": [ + 149, + 191, + 157, + 198 + ], + "lines": [ + { + "bbox": [ + 149, + 191, + 157, + 198 + ], + "spans": [ + { + "bbox": [ + 149, + 191, + 157, + 198 + ], + "type": "image", + "image_path": "14d32f1da02e93201d6be504cd034e7ddd7e0b8d4ee18ab4e2dac07596d9acb2.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 159, + 191, + 217, + 199 + ], + "lines": [ + { + "bbox": [ + 159, + 191, + 217, + 199 + ], + "spans": [ + { + "bbox": [ + 159, + 191, + 217, + 199 + ], + "type": "text", + "content": "Implicit Control Points" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 231, + 191, + 241, + 198 + ], + "blocks": [ + { + "bbox": [ + 231, + 191, + 241, + 198 + ], + "lines": [ + { + "bbox": [ + 231, + 191, + 241, + 198 + ], + "spans": [ + { + "bbox": [ + 231, + 191, + 241, + 198 + ], + "type": "image", + "image_path": "56a6cca86c77a7579475d17135d05ebefbdc22d5032cdfb47aecb1d1a7aaddc1.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 243, + 191, + 278, + 199 + ], + "lines": [ + { + "bbox": [ + 243, + 191, + 278, + 199 + ], + "spans": [ + { + "bbox": [ + 243, + 191, + 278, + 199 + ], + "type": "text", + "content": "mplicit Offset" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 11 + }, + { + "bbox": [ + 46, + 254, + 287, + 457 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 254, + 287, + 457 + ], + "spans": [ + { + "bbox": [ + 46, + 254, + 287, + 457 + ], + "type": "text", + "content": "Vectorized HD-map Modeling. By sequentially sampling points along the elements in HD-map, each object can be structured as an open-shape curve as a vectorized manner. To uniformly parameterize these various shape-changeful map elements, including points, polygons and curves, we employ the piecewise Bézier curve proposed in Eq.3 and formalize a vectorized HD-map as a piecewise Bézier curve set " + }, + { + "bbox": [ + 46, + 254, + 287, + 457 + ], + "type": "inline_equation", + "content": "\\mathcal{M} = \\{\\mathbb{C}_i|i = 1,\\dots ,|\\mathcal{M}|\\}" + }, + { + "bbox": [ + 46, + 254, + 287, + 457 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 254, + 287, + 457 + ], + "type": "inline_equation", + "content": "|\\mathcal{M}|" + }, + { + "bbox": [ + 46, + 254, + 287, + 457 + ], + "type": "text", + "content": " is the number of map instances. Our objective is to learn a model that extracts compact information from the camera sensors and predicts, for each map element, its corresponding Bézier control sequence, which uniquely determine the shape and position of the map curve. In addition, for the purpose of reducing the modeling complexity of implicit control points " + }, + { + "bbox": [ + 46, + 254, + 287, + 457 + ], + "type": "inline_equation", + "content": "\\mathbb{C}^{\\mathcal{I}}" + }, + { + "bbox": [ + 46, + 254, + 287, + 457 + ], + "type": "text", + "content": " for each segment, we subtly generate implicit coordinates through the center of explicit control points and their relative offsets as shown in the right of Fig.3." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 46, + 460, + 286, + 604 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 460, + 286, + 604 + ], + "spans": [ + { + "bbox": [ + 46, + 460, + 286, + 604 + ], + "type": "text", + "content": "Piecewise Bézier Curve Modeling Principle. Considering the large-variety and changeful-shape of map elements, we present a consistent-degree but dynamic-piece principle for modeling piecewise curve more precisely and efficiently as, (1) consistent-degree on semantic-level. Due to a Bézier curve of degree " + }, + { + "bbox": [ + 46, + 460, + 286, + 604 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 460, + 286, + 604 + ], + "type": "text", + "content": " can be easily converted into degree " + }, + { + "bbox": [ + 46, + 460, + 286, + 604 + ], + "type": "inline_equation", + "content": "k + 1" + }, + { + "bbox": [ + 46, + 460, + 286, + 604 + ], + "type": "text", + "content": " with the same shape, i.e. degree elevation in mathematics, the same curve may correspond to multiple Bézier solutions with only different degree. This kind of obfuscation is devastating for the network modeling. And we argue that keeping the consistent-degree within the same semantic category is the most efficient way to solve this dilemma." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 46, + 605, + 286, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 605, + 286, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 605, + 286, + 714 + ], + "type": "text", + "content": "(2) dynamic-piece on instance-level. Considering that the complexity of different map curves is always inconsistent, the modeling method with a fixed and large number of segments will not only cause excessive redundancy in the expression of each curve, but also lead to confusion in the definition of sub-segment, which places a certain burden on the model optimization. The dynamic-piece rule demands the model to choose the number of segments dynamically and parameterize a Bézier curve as compactly as possible." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 72, + 492, + 85 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 72, + 492, + 85 + ], + "spans": [ + { + "bbox": [ + 306, + 72, + 492, + 85 + ], + "type": "text", + "content": "3.2. Piecewise Bezier HD-map Network" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 306, + 91, + 427, + 102 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 91, + 427, + 102 + ], + "spans": [ + { + "bbox": [ + 306, + 91, + 427, + 102 + ], + "type": "text", + "content": "3.2.1 Overall Architecture" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 305, + 111, + 545, + 160 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 111, + 545, + 160 + ], + "spans": [ + { + "bbox": [ + 305, + 111, + 545, + 160 + ], + "type": "text", + "content": "The overall model architecture is illustrated in detail in Fig. 2, which streamlines the framework into four parts, namely feature extractor, semantic BEV decoder, instance Bézier decoder and piecewise Bézier output head respectively." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 305, + 163, + 545, + 236 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 163, + 545, + 236 + ], + "spans": [ + { + "bbox": [ + 305, + 163, + 545, + 236 + ], + "type": "text", + "content": "Feature Extractor. Given surrounding images from multicamera as inputs, a shared CNN backbone is first employed to obtain each image feature, and then these multi-scale features from different stages are fed into FPN [50] to integrate rich environmental information. Last we upsample pyramid features to the same size and stack them together as outputs." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 305, + 239, + 546, + 443 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 239, + 546, + 443 + ], + "spans": [ + { + "bbox": [ + 305, + 239, + 546, + 443 + ], + "type": "text", + "content": "Semantic BEV Decoder. We leverage a standard encoder-decoder paradigm based on Transformer to elevate camera-view features into canonical BEV spaces. By treating the perspective transformation as a direct set prediction task, the BEV decoder takes camera features with shape " + }, + { + "bbox": [ + 305, + 239, + 546, + 443 + ], + "type": "inline_equation", + "content": "H_{c} \\times W_{c}" + }, + { + "bbox": [ + 305, + 239, + 546, + 443 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 239, + 546, + 443 + ], + "type": "inline_equation", + "content": "H_{q} \\times W_{q}" + }, + { + "bbox": [ + 305, + 239, + 546, + 443 + ], + "type": "text", + "content": " learnable BEV queries as inputs, and produces BEV features " + }, + { + "bbox": [ + 305, + 239, + 546, + 443 + ], + "type": "inline_equation", + "content": "F_{b} \\in \\mathbb{R}^{C \\times H_{b} \\times W_{b}}" + }, + { + "bbox": [ + 305, + 239, + 546, + 443 + ], + "type": "text", + "content": " by modeling all pairwise interactions among elements with self- and cross-attention. Different from the region-agnostic query in DETR, we correspond each query with a " + }, + { + "bbox": [ + 305, + 239, + 546, + 443 + ], + "type": "inline_equation", + "content": "\\gamma^{h} \\times \\gamma^{w}" + }, + { + "bbox": [ + 305, + 239, + 546, + 443 + ], + "type": "text", + "content": " region on BEV features one-to-one, i.e. " + }, + { + "bbox": [ + 305, + 239, + 546, + 443 + ], + "type": "inline_equation", + "content": "H_{b} \\times W_{b} = \\gamma^{h}H_{q} \\times \\gamma^{w}W_{q}" + }, + { + "bbox": [ + 305, + 239, + 546, + 443 + ], + "type": "text", + "content": ". The " + }, + { + "bbox": [ + 305, + 239, + 546, + 443 + ], + "type": "inline_equation", + "content": "F_{b}" + }, + { + "bbox": [ + 305, + 239, + 546, + 443 + ], + "type": "text", + "content": " is then fed into a " + }, + { + "bbox": [ + 305, + 239, + 546, + 443 + ], + "type": "inline_equation", + "content": "1 \\times 1" + }, + { + "bbox": [ + 305, + 239, + 546, + 443 + ], + "type": "text", + "content": " conv and upsample block to obtain the final semantic mask " + }, + { + "bbox": [ + 305, + 239, + 546, + 443 + ], + "type": "inline_equation", + "content": "\\mathbb{M}_{s} \\in \\mathbb{R}^{U \\times H_{s} \\times W_{s}}" + }, + { + "bbox": [ + 305, + 239, + 546, + 443 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 305, + 239, + 546, + 443 + ], + "type": "inline_equation", + "content": "U" + }, + { + "bbox": [ + 305, + 239, + 546, + 443 + ], + "type": "text", + "content": " is the number of classes and " + }, + { + "bbox": [ + 305, + 239, + 546, + 443 + ], + "type": "inline_equation", + "content": "H_{s} \\times W_{s}" + }, + { + "bbox": [ + 305, + 239, + 546, + 443 + ], + "type": "text", + "content": " is the map shape. In addition, we also propose a novel IPM-PE Align Layer to refactor the features in different coordinate systems through the most common position encoding layer in Transformer." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 305, + 446, + 545, + 601 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 446, + 545, + 601 + ], + "spans": [ + { + "bbox": [ + 305, + 446, + 545, + 601 + ], + "type": "text", + "content": "Instance Bézier Decoder. So as to perform more accurate parametric modeling of each curve, we further equip an instance Bézier decoder based on masked cross-attention [8]. To be concrete, given semantic features " + }, + { + "bbox": [ + 305, + 446, + 545, + 601 + ], + "type": "inline_equation", + "content": "F_{b}" + }, + { + "bbox": [ + 305, + 446, + 545, + 601 + ], + "type": "text", + "content": " and learnable instance Bézier queries " + }, + { + "bbox": [ + 305, + 446, + 545, + 601 + ], + "type": "inline_equation", + "content": "Q \\in \\mathbb{R}^{V \\times C}" + }, + { + "bbox": [ + 305, + 446, + 545, + 601 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 305, + 446, + 545, + 601 + ], + "type": "inline_equation", + "content": "V" + }, + { + "bbox": [ + 305, + 446, + 545, + 601 + ], + "type": "text", + "content": " is the max number of instance, this module aggregates information and decodes Bézier descriptors " + }, + { + "bbox": [ + 305, + 446, + 545, + 601 + ], + "type": "inline_equation", + "content": "\\vec{z} \\in \\mathbb{R}^{V \\times C}" + }, + { + "bbox": [ + 305, + 446, + 545, + 601 + ], + "type": "text", + "content": ", which contain key info of geometric and positional relationships between different map elements. With extra performing matrix multiplication between " + }, + { + "bbox": [ + 305, + 446, + 545, + 601 + ], + "type": "inline_equation", + "content": "\\vec{z}" + }, + { + "bbox": [ + 305, + 446, + 545, + 601 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 446, + 545, + 601 + ], + "type": "inline_equation", + "content": "F_{b}" + }, + { + "bbox": [ + 305, + 446, + 545, + 601 + ], + "type": "text", + "content": ", we obtain instance map mask " + }, + { + "bbox": [ + 305, + 446, + 545, + 601 + ], + "type": "inline_equation", + "content": "\\mathbb{M}_{z} \\in \\mathbb{R}^{V \\times H_{s} \\times W_{s}}" + }, + { + "bbox": [ + 305, + 446, + 545, + 601 + ], + "type": "text", + "content": ", which is used as the foreground mask for next decoder layer and also to perform segmentation supervision for more spatial context information." + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 305, + 605, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 605, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 605, + 545, + 713 + ], + "type": "text", + "content": "Piecewise Bézier Output Head. Following the principle elaborated in Sec.3.1, we closely design a piecewise Bézier output head with two core modules, i.e. Split Coordinate Regression and Dynamic End-index Classification, which are utilized to output the coordinates of Bézier control point sequence and the number of segments respectively. With easily recovering piecewise Bézier curves and further introducing the bipartite matching setting, the proposed output head constructs vectorized local HD-map very efficiently." + } + ] + } + ], + "index": 23 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "13221" + } + ] + } + ], + "index": 24 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 169, + 84 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 169, + 84 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 169, + 84 + ], + "type": "text", + "content": "3.2.2 IPM-PE Align Layer" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 91, + 290, + 270 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 91, + 290, + 270 + ], + "spans": [ + { + "bbox": [ + 46, + 91, + 290, + 270 + ], + "type": "text", + "content": "As a basic module of traditional Transformer architecture, positional encoding utilizes the sequence order by injecting information about the position of tokens [52], where sin-cos and learned-based functions are the most common practices. Yet, for the purpose of perspective transformation between 2D camera-views and 3D BEV, we argue it is not enough to only encode the position correspondence within single view, but it is also necessary to maintain the position consistency relationships between two perspectives. Thence we put forward a novel IPM-PE Align Layer to encode the 2D-3D geometry priors into features from different coordinate systems. To be concrete, given a point " + }, + { + "bbox": [ + 46, + 91, + 290, + 270 + ], + "type": "inline_equation", + "content": "p_c^{f_i} = (u,v,1)^\\top" + }, + { + "bbox": [ + 46, + 91, + 290, + 270 + ], + "type": "text", + "content": " on the " + }, + { + "bbox": [ + 46, + 91, + 290, + 270 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 91, + 290, + 270 + ], + "type": "text", + "content": "-th camera-view feature and its corresponding world point " + }, + { + "bbox": [ + 46, + 91, + 290, + 270 + ], + "type": "inline_equation", + "content": "p_c^w = (x,y,z)^\\top" + }, + { + "bbox": [ + 46, + 91, + 290, + 270 + ], + "type": "text", + "content": ", the following mathematical equation is satisfied on the assumption of pinhole camera model," + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 108, + 277, + 287, + 293 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 108, + 277, + 287, + 293 + ], + "spans": [ + { + "bbox": [ + 108, + 277, + 287, + 293 + ], + "type": "interline_equation", + "content": "d \\cdot A ^ {- 1} \\cdot p _ {c} ^ {f _ {i}} = K ^ {i} \\cdot T ^ {i} \\cdot p _ {c} ^ {w} \\tag {4}", + "image_path": "7daad8d97cb1bb9db51bd890dddc36821a895c62337da30ed2a5a3026e19ee34.jpg" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 300, + 287, + 408 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 300, + 287, + 408 + ], + "spans": [ + { + "bbox": [ + 46, + 300, + 287, + 408 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 300, + 287, + 408 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 46, + 300, + 287, + 408 + ], + "type": "text", + "content": " is the depth, " + }, + { + "bbox": [ + 46, + 300, + 287, + 408 + ], + "type": "inline_equation", + "content": "A" + }, + { + "bbox": [ + 46, + 300, + 287, + 408 + ], + "type": "text", + "content": " is the transformation matrix between image-grid and feature-grid, " + }, + { + "bbox": [ + 46, + 300, + 287, + 408 + ], + "type": "inline_equation", + "content": "K^i" + }, + { + "bbox": [ + 46, + 300, + 287, + 408 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 300, + 287, + 408 + ], + "type": "inline_equation", + "content": "T^i" + }, + { + "bbox": [ + 46, + 300, + 287, + 408 + ], + "type": "text", + "content": " are " + }, + { + "bbox": [ + 46, + 300, + 287, + 408 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 300, + 287, + 408 + ], + "type": "text", + "content": "-th intrinsic and extrinsic matrices. Based on the assumption of that the ground surface is flat and at a fixed height in " + }, + { + "bbox": [ + 46, + 300, + 287, + 408 + ], + "type": "inline_equation", + "content": "IPM" + }, + { + "bbox": [ + 46, + 300, + 287, + 408 + ], + "type": "text", + "content": ", the world position " + }, + { + "bbox": [ + 46, + 300, + 287, + 408 + ], + "type": "inline_equation", + "content": "(x,y)" + }, + { + "bbox": [ + 46, + 300, + 287, + 408 + ], + "type": "text", + "content": " and depth " + }, + { + "bbox": [ + 46, + 300, + 287, + 408 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 46, + 300, + 287, + 408 + ], + "type": "text", + "content": " can be easily calculated through Eq.4. Note " + }, + { + "bbox": [ + 46, + 300, + 287, + 408 + ], + "type": "inline_equation", + "content": "d < 0" + }, + { + "bbox": [ + 46, + 300, + 287, + 408 + ], + "type": "text", + "content": " denotes the position is not valid. As for the other branch of BEV perspective, given a point " + }, + { + "bbox": [ + 46, + 300, + 287, + 408 + ], + "type": "inline_equation", + "content": "p_b^f" + }, + { + "bbox": [ + 46, + 300, + 287, + 408 + ], + "type": "text", + "content": " from the BEV feature " + }, + { + "bbox": [ + 46, + 300, + 287, + 408 + ], + "type": "inline_equation", + "content": "F_{b}" + }, + { + "bbox": [ + 46, + 300, + 287, + 408 + ], + "type": "text", + "content": " and its world point " + }, + { + "bbox": [ + 46, + 300, + 287, + 408 + ], + "type": "inline_equation", + "content": "p_b^w" + }, + { + "bbox": [ + 46, + 300, + 287, + 408 + ], + "type": "text", + "content": ", there is usually only a scale relationship " + }, + { + "bbox": [ + 46, + 300, + 287, + 408 + ], + "type": "inline_equation", + "content": "\\kappa = (\\kappa_x,\\kappa_y)" + }, + { + "bbox": [ + 46, + 300, + 287, + 408 + ], + "type": "text", + "content": " between them," + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 140, + 415, + 287, + 431 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 140, + 415, + 287, + 431 + ], + "spans": [ + { + "bbox": [ + 140, + 415, + 287, + 431 + ], + "type": "interline_equation", + "content": "p _ {b} ^ {f} = \\boldsymbol {\\kappa} \\cdot p _ {b} ^ {w} \\tag {5}", + "image_path": "09b194e0df2d0d5a190003d863b3bcd3b5f00a16ecb5d979a568130c802ad7bb.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 438, + 287, + 535 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 438, + 287, + 535 + ], + "spans": [ + { + "bbox": [ + 46, + 438, + 287, + 535 + ], + "type": "text", + "content": "Then we leverage the standard sin-cos function to convert all these world coordinates " + }, + { + "bbox": [ + 46, + 438, + 287, + 535 + ], + "type": "inline_equation", + "content": "P_{c}^{w}" + }, + { + "bbox": [ + 46, + 438, + 287, + 535 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 438, + 287, + 535 + ], + "type": "inline_equation", + "content": "P_{b}^{w}" + }, + { + "bbox": [ + 46, + 438, + 287, + 535 + ], + "type": "text", + "content": " as position embedding " + }, + { + "bbox": [ + 46, + 438, + 287, + 535 + ], + "type": "inline_equation", + "content": "f_{c}^{pe}" + }, + { + "bbox": [ + 46, + 438, + 287, + 535 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 438, + 287, + 535 + ], + "type": "inline_equation", + "content": "f_{b}^{pe}" + }, + { + "bbox": [ + 46, + 438, + 287, + 535 + ], + "type": "text", + "content": " respectively. Since the assumption of flat-ground and known-height usually does not hold in practice, " + }, + { + "bbox": [ + 46, + 438, + 287, + 535 + ], + "type": "inline_equation", + "content": "f_{c}^{pe}" + }, + { + "bbox": [ + 46, + 438, + 287, + 535 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 438, + 287, + 535 + ], + "type": "inline_equation", + "content": "f_{b}^{pe}" + }, + { + "bbox": [ + 46, + 438, + 287, + 535 + ], + "type": "text", + "content": " are not exactly aligned in the world coordinate system, we further adopt a shared FC layer on " + }, + { + "bbox": [ + 46, + 438, + 287, + 535 + ], + "type": "inline_equation", + "content": "f_{c}^{pe}" + }, + { + "bbox": [ + 46, + 438, + 287, + 535 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 438, + 287, + 535 + ], + "type": "inline_equation", + "content": "f_{b}^{pe}" + }, + { + "bbox": [ + 46, + 438, + 287, + 535 + ], + "type": "text", + "content": " to perform embedding alignment and then obtain more unified position encoding, which is shown in Fig.2 in detail." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 548, + 209, + 560 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 548, + 209, + 560 + ], + "spans": [ + { + "bbox": [ + 47, + 548, + 209, + 560 + ], + "type": "text", + "content": "3.2.3 Piecewise Bézier Output Head" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "list", + "angle": 0, + "index": 9, + "blocks": [ + { + "bbox": [ + 46, + 570, + 287, + 665 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 570, + 287, + 665 + ], + "spans": [ + { + "bbox": [ + 46, + 570, + 287, + 665 + ], + "type": "text", + "content": "Split Coordinate Regression Head. Following the illustration in the upper right corner of the Fig.2, we elaborate the forward flow of proposed regression head as four steps, " + }, + { + "bbox": [ + 46, + 570, + 287, + 665 + ], + "type": "inline_equation", + "content": "\\mathbf{I}" + }, + { + "bbox": [ + 46, + 570, + 287, + 665 + ], + "type": "text", + "content": " with " + }, + { + "bbox": [ + 46, + 570, + 287, + 665 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 570, + 287, + 665 + ], + "type": "text", + "content": "-th incoming Bézier descriptor " + }, + { + "bbox": [ + 46, + 570, + 287, + 665 + ], + "type": "inline_equation", + "content": "\\vec{z}_i \\in \\mathbb{R}^C" + }, + { + "bbox": [ + 46, + 570, + 287, + 665 + ], + "type": "text", + "content": ", we first convert its channel from " + }, + { + "bbox": [ + 46, + 570, + 287, + 665 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 46, + 570, + 287, + 665 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 46, + 570, + 287, + 665 + ], + "type": "inline_equation", + "content": "u \\cdot v" + }, + { + "bbox": [ + 46, + 570, + 287, + 665 + ], + "type": "text", + "content": " with adopting a standard " + }, + { + "bbox": [ + 46, + 570, + 287, + 665 + ], + "type": "inline_equation", + "content": "FC" + }, + { + "bbox": [ + 46, + 570, + 287, + 665 + ], + "type": "text", + "content": " layer and then split it into " + }, + { + "bbox": [ + 46, + 570, + 287, + 665 + ], + "type": "inline_equation", + "content": "u" + }, + { + "bbox": [ + 46, + 570, + 287, + 665 + ], + "type": "text", + "content": " parts to get a collection of coordinate descriptors " + }, + { + "bbox": [ + 46, + 570, + 287, + 665 + ], + "type": "inline_equation", + "content": "x_i^j \\in \\mathbb{R}^v" + }, + { + "bbox": [ + 46, + 570, + 287, + 665 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 570, + 287, + 665 + ], + "type": "inline_equation", + "content": "j \\in [1, u]" + }, + { + "bbox": [ + 46, + 570, + 287, + 665 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 570, + 287, + 665 + ], + "type": "inline_equation", + "content": "u" + }, + { + "bbox": [ + 46, + 570, + 287, + 665 + ], + "type": "text", + "content": " is the number of coordinate and " + }, + { + "bbox": [ + 46, + 570, + 287, + 665 + ], + "type": "inline_equation", + "content": "v" + }, + { + "bbox": [ + 46, + 570, + 287, + 665 + ], + "type": "text", + "content": " is the channel of descriptor." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "text", + "content": "2) given the desired output shape " + }, + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "inline_equation", + "content": "(H_s, W_s)" + }, + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "text", + "content": ", a hard-coded candidate coordinates grid " + }, + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "inline_equation", + "content": "G \\in \\mathbb{R}^{2 \\times H_s \\times W_s}" + }, + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "text", + "content": " is generated with X-Y two channels and next a " + }, + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "inline_equation", + "content": "1 \\times 1" + }, + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "text", + "content": " conv layer is utilized to convert " + }, + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "inline_equation", + "content": "G" + }, + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "text", + "content": " to its coordinate feature " + }, + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "inline_equation", + "content": "F_G \\in \\mathbb{R}^{v \\times H_s \\times W_s}" + }, + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 8 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 304, + 72, + 545, + 135 + ], + "type": "list", + "angle": 0, + "index": 12, + "blocks": [ + { + "bbox": [ + 304, + 72, + 545, + 110 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 110 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 110 + ], + "type": "text", + "content": "3) through conducting the matrix multiplication between the coordinate descriptor " + }, + { + "bbox": [ + 304, + 72, + 545, + 110 + ], + "type": "inline_equation", + "content": "x_{i}^{j}" + }, + { + "bbox": [ + 304, + 72, + 545, + 110 + ], + "type": "text", + "content": " and feature " + }, + { + "bbox": [ + 304, + 72, + 545, + 110 + ], + "type": "inline_equation", + "content": "F_{G}" + }, + { + "bbox": [ + 304, + 72, + 545, + 110 + ], + "type": "text", + "content": ", the coordinate activation map " + }, + { + "bbox": [ + 304, + 72, + 545, + 110 + ], + "type": "inline_equation", + "content": "h_{i}^{j}\\in \\mathbb{R}^{H_{s}\\times W_{s}}" + }, + { + "bbox": [ + 304, + 72, + 545, + 110 + ], + "type": "text", + "content": " is obtained dynamically." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 110, + 545, + 135 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 110, + 545, + 135 + ], + "spans": [ + { + "bbox": [ + 304, + 110, + 545, + 135 + ], + "type": "text", + "content": "4) after using a global average pooling on the spatial of " + }, + { + "bbox": [ + 304, + 110, + 545, + 135 + ], + "type": "inline_equation", + "content": "h_i^j" + }, + { + "bbox": [ + 304, + 110, + 545, + 135 + ], + "type": "text", + "content": ", the activation map is regressed to the final coordinate value." + } + ] + } + ], + "index": 11 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 304, + 138, + 545, + 270 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 138, + 545, + 270 + ], + "spans": [ + { + "bbox": [ + 304, + 138, + 545, + 270 + ], + "type": "text", + "content": "Dynamic End-index Classification Head. Based on the prior of that the end point of a piecewise Bézier curve must be explicit, the proposed module model the dynamic length of segments prediction task as a " + }, + { + "bbox": [ + 304, + 138, + 545, + 270 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 304, + 138, + 545, + 270 + ], + "type": "text", + "content": "-classification problem, where " + }, + { + "bbox": [ + 304, + 138, + 545, + 270 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 304, + 138, + 545, + 270 + ], + "type": "text", + "content": " is the maximum pieces number for a certain map class. Specifically, with using a common " + }, + { + "bbox": [ + 304, + 138, + 545, + 270 + ], + "type": "inline_equation", + "content": "FC" + }, + { + "bbox": [ + 304, + 138, + 545, + 270 + ], + "type": "text", + "content": " and softmax block, each Bézier descriptor is naturally transformed into a " + }, + { + "bbox": [ + 304, + 138, + 545, + 270 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 304, + 138, + 545, + 270 + ], + "type": "text", + "content": "-dimensional probability vector, where each position denotes the score of the current index as a termination point. This novel indeterminate length modeling greatly increases the adaptability and scalability of our proposed framework." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 277, + 428, + 290 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 277, + 428, + 290 + ], + "spans": [ + { + "bbox": [ + 305, + 277, + 428, + 290 + ], + "type": "text", + "content": "3.3. End-to-End Training" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 296, + 545, + 357 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 296, + 545, + 357 + ], + "spans": [ + { + "bbox": [ + 304, + 296, + 545, + 357 + ], + "type": "text", + "content": "According to the matrix form of Eq.1, that is, " + }, + { + "bbox": [ + 304, + 296, + 545, + 357 + ], + "type": "inline_equation", + "content": "P = BC" + }, + { + "bbox": [ + 304, + 296, + 545, + 357 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 296, + 545, + 357 + ], + "type": "inline_equation", + "content": "B \\in \\mathbb{R}^{m \\times n}" + }, + { + "bbox": [ + 304, + 296, + 545, + 357 + ], + "type": "text", + "content": " is the Bernstein matrix, " + }, + { + "bbox": [ + 304, + 296, + 545, + 357 + ], + "type": "inline_equation", + "content": "C \\in \\mathbb{R}^{n \\times 2}" + }, + { + "bbox": [ + 304, + 296, + 545, + 357 + ], + "type": "text", + "content": " is control points, " + }, + { + "bbox": [ + 304, + 296, + 545, + 357 + ], + "type": "inline_equation", + "content": "P \\in \\mathbb{R}^{m \\times 2}" + }, + { + "bbox": [ + 304, + 296, + 545, + 357 + ], + "type": "text", + "content": " is vectorized points on the curve, " + }, + { + "bbox": [ + 304, + 296, + 545, + 357 + ], + "type": "inline_equation", + "content": "m" + }, + { + "bbox": [ + 304, + 296, + 545, + 357 + ], + "type": "text", + "content": " is the number of points and " + }, + { + "bbox": [ + 304, + 296, + 545, + 357 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 304, + 296, + 545, + 357 + ], + "type": "text", + "content": " is the degree. Obviously, given " + }, + { + "bbox": [ + 304, + 296, + 545, + 357 + ], + "type": "inline_equation", + "content": "m, n" + }, + { + "bbox": [ + 304, + 296, + 545, + 357 + ], + "type": "text", + "content": ", we can easily implement following procedures:" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 357, + 545, + 416 + ], + "type": "list", + "angle": 0, + "index": 18, + "blocks": [ + { + "bbox": [ + 305, + 357, + 545, + 379 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 357, + 545, + 379 + ], + "spans": [ + { + "bbox": [ + 305, + 357, + 545, + 379 + ], + "type": "text", + "content": "1) vectorization. Given the " + }, + { + "bbox": [ + 305, + 357, + 545, + 379 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 305, + 357, + 545, + 379 + ], + "type": "text", + "content": ", its corresponding vectorized curve can be restored efficiently with matrix multiplication." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 305, + 380, + 545, + 416 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 380, + 545, + 416 + ], + "spans": [ + { + "bbox": [ + 305, + 380, + 545, + 416 + ], + "type": "text", + "content": "2) construction. Given the orderly sampling points " + }, + { + "bbox": [ + 305, + 380, + 545, + 416 + ], + "type": "inline_equation", + "content": "P" + }, + { + "bbox": [ + 305, + 380, + 545, + 416 + ], + "type": "text", + "content": ", we readily construct " + }, + { + "bbox": [ + 305, + 380, + 545, + 416 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 305, + 380, + 545, + 416 + ], + "type": "text", + "content": " with solving the least-squares problem, i.e. " + }, + { + "bbox": [ + 305, + 380, + 545, + 416 + ], + "type": "inline_equation", + "content": "C = B^{+}P" + }, + { + "bbox": [ + 305, + 380, + 545, + 416 + ], + "type": "text", + "content": " where " + }, + { + "bbox": [ + 305, + 380, + 545, + 416 + ], + "type": "inline_equation", + "content": "^{+}" + }, + { + "bbox": [ + 305, + 380, + 545, + 416 + ], + "type": "text", + "content": " is the pseudo-inverse of a matrix." + } + ] + } + ], + "index": 17 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 304, + 420, + 545, + 504 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 420, + 545, + 504 + ], + "spans": [ + { + "bbox": [ + 304, + 420, + 545, + 504 + ], + "type": "text", + "content": "Piecewise Bézier Ground Truth. The common " + }, + { + "bbox": [ + 304, + 420, + 545, + 504 + ], + "type": "inline_equation", + "content": "HD" + }, + { + "bbox": [ + 304, + 420, + 545, + 504 + ], + "type": "text", + "content": "-map annotation protocol always represents a curve with a set of vectorized points. We propose to first select some annotated keypoints and then divide the curve into " + }, + { + "bbox": [ + 304, + 420, + 545, + 504 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 304, + 420, + 545, + 504 + ], + "type": "text", + "content": " segments, where each is compactly modeled by an " + }, + { + "bbox": [ + 304, + 420, + 545, + 504 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 304, + 420, + 545, + 504 + ], + "type": "text", + "content": "-order Bézier curve. Following the procedure of construction, we present the ground truth generation algorithm in the Algorithm 1." + } + ] + } + ], + "index": 19 + }, + { + "type": "code", + "bbox": [ + 312, + 533, + 545, + 708 + ], + "blocks": [ + { + "bbox": [ + 312, + 519, + 503, + 531 + ], + "lines": [ + { + "bbox": [ + 312, + 519, + 503, + 531 + ], + "spans": [ + { + "bbox": [ + 312, + 519, + 503, + 531 + ], + "type": "text", + "content": "Algorithm 1: Piecewise Bézier Curve GenGT." + } + ] + } + ], + "index": 20, + "angle": 0, + "type": "code_caption" + }, + { + "bbox": [ + 312, + 533, + 545, + 708 + ], + "lines": [ + { + "bbox": [ + 312, + 533, + 545, + 708 + ], + "spans": [ + { + "bbox": [ + 312, + 533, + 545, + 708 + ], + "type": "text", + "content": "input:Annotated points " + }, + { + "bbox": [ + 312, + 533, + 545, + 708 + ], + "type": "inline_equation", + "content": "P" + }, + { + "bbox": [ + 312, + 533, + 545, + 708 + ], + "type": "text", + "content": " Parameters " + }, + { + "bbox": [ + 312, + 533, + 545, + 708 + ], + "type": "inline_equation", + "content": "n,m,\\epsilon" + }, + { + "bbox": [ + 312, + 533, + 545, + 708 + ], + "type": "text", + "content": " output: Piecewise Bezier curves C \n1 " + }, + { + "bbox": [ + 312, + 533, + 545, + 708 + ], + "type": "inline_equation", + "content": "B =" + }, + { + "bbox": [ + 312, + 533, + 545, + 708 + ], + "type": "text", + "content": " GetBernsteinCoefficient " + }, + { + "bbox": [ + 312, + 533, + 545, + 708 + ], + "type": "inline_equation", + "content": "(n,m)" + }, + { + "bbox": [ + 312, + 533, + 545, + 708 + ], + "type": "text", + "content": " \n2 " + }, + { + "bbox": [ + 312, + 533, + 545, + 708 + ], + "type": "inline_equation", + "content": "B^{+} =" + }, + { + "bbox": [ + 312, + 533, + 545, + 708 + ], + "type": "text", + "content": " MatrixPseudoInverse " + }, + { + "bbox": [ + 312, + 533, + 545, + 708 + ], + "type": "inline_equation", + "content": "(B)" + }, + { + "bbox": [ + 312, + 533, + 545, + 708 + ], + "type": "text", + "content": " \n3 " + }, + { + "bbox": [ + 312, + 533, + 545, + 708 + ], + "type": "inline_equation", + "content": "l\\gets |P|,s\\gets 0,e\\gets l - 1" + }, + { + "bbox": [ + 312, + 533, + 545, + 708 + ], + "type": "text", + "content": " \n4 while " + }, + { + "bbox": [ + 312, + 533, + 545, + 708 + ], + "type": "inline_equation", + "content": "s < e" + }, + { + "bbox": [ + 312, + 533, + 545, + 708 + ], + "type": "text", + "content": " do \n5 " + }, + { + "bbox": [ + 312, + 533, + 545, + 708 + ], + "type": "inline_equation", + "content": "P^{\\dagger} =" + }, + { + "bbox": [ + 312, + 533, + 545, + 708 + ], + "type": "text", + "content": " CurveInterpolate " + }, + { + "bbox": [ + 312, + 533, + 545, + 708 + ], + "type": "inline_equation", + "content": "(P[s,e])" + }, + { + "bbox": [ + 312, + 533, + 545, + 708 + ], + "type": "text", + "content": " . \n6 " + }, + { + "bbox": [ + 312, + 533, + 545, + 708 + ], + "type": "inline_equation", + "content": "\\mathbb{C}^{\\dagger} = B^{+}\\times P^{\\dagger}" + }, + { + "bbox": [ + 312, + 533, + 545, + 708 + ], + "type": "text", + "content": " . \n7 " + }, + { + "bbox": [ + 312, + 533, + 545, + 708 + ], + "type": "inline_equation", + "content": "P^{\\ddagger} = B\\times \\mathbb{C}^{\\dagger}" + }, + { + "bbox": [ + 312, + 533, + 545, + 708 + ], + "type": "text", + "content": " . \n8 " + }, + { + "bbox": [ + 312, + 533, + 545, + 708 + ], + "type": "inline_equation", + "content": "D^{\\prime} =" + }, + { + "bbox": [ + 312, + 533, + 545, + 708 + ], + "type": "text", + "content": " ChamferDistance " + }, + { + "bbox": [ + 312, + 533, + 545, + 708 + ], + "type": "inline_equation", + "content": "(P^{\\dagger},P^{\\ddagger})" + }, + { + "bbox": [ + 312, + 533, + 545, + 708 + ], + "type": "text", + "content": " . \n9 if " + }, + { + "bbox": [ + 312, + 533, + 545, + 708 + ], + "type": "inline_equation", + "content": "D^{\\prime} < \\epsilon" + }, + { + "bbox": [ + 312, + 533, + 545, + 708 + ], + "type": "text", + "content": " then \n10 " + }, + { + "bbox": [ + 312, + 533, + 545, + 708 + ], + "type": "inline_equation", + "content": "\\begin{array}{r}\\lfloor \\mathbb{C}\\leftarrow [\\mathbb{C},\\mathbb{C}^{\\dagger}],s\\leftarrow e,e\\leftarrow l - 1; \\end{array}" + }, + { + "bbox": [ + 312, + 533, + 545, + 708 + ], + "type": "text", + "content": " \n11 else " + }, + { + "bbox": [ + 312, + 533, + 545, + 708 + ], + "type": "inline_equation", + "content": "e\\gets e - 1" + } + ] + } + ], + "index": 21, + "angle": 0, + "type": "code_body" + } + ], + "index": 21, + "sub_type": "algorithm" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "13222" + } + ] + } + ], + "index": 22 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 53, + 70, + 282, + 190 + ], + "blocks": [ + { + "bbox": [ + 53, + 70, + 282, + 190 + ], + "lines": [ + { + "bbox": [ + 53, + 70, + 282, + 190 + ], + "spans": [ + { + "bbox": [ + 53, + 70, + 282, + 190 + ], + "type": "image", + "image_path": "8634e56fc830c3499328706b3f6b5b9745398d3c52c32a3b80754a4db4453771.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 193, + 287, + 227 + ], + "lines": [ + { + "bbox": [ + 46, + 193, + 287, + 227 + ], + "spans": [ + { + "bbox": [ + 46, + 193, + 287, + 227 + ], + "type": "text", + "content": "Figure 4. The first three diagrams are illustrations of Point-Curve-Region Recovery Loss for Bezier curve modeling. On the far right is a simple schematic diagram of coordinate dilation with " + }, + { + "bbox": [ + 46, + 193, + 287, + 227 + ], + "type": "inline_equation", + "content": "\\omega = 1" + }, + { + "bbox": [ + 46, + 193, + 287, + 227 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 232, + 287, + 280 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 232, + 287, + 280 + ], + "spans": [ + { + "bbox": [ + 46, + 232, + 287, + 280 + ], + "type": "text", + "content": "Point-Curve-Region Recovery Loss. Given the Bezier control points, a novel " + }, + { + "bbox": [ + 46, + 232, + 287, + 280 + ], + "type": "inline_equation", + "content": "PCR" + }, + { + "bbox": [ + 46, + 232, + 287, + 280 + ], + "type": "text", + "content": "-Loss is proposed to supervise the learning procedure from three progressive levels, i.e. point, curve and region, which is shown in Fig.4 in detail." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 281, + 287, + 328 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 281, + 287, + 328 + ], + "spans": [ + { + "bbox": [ + 46, + 281, + 287, + 328 + ], + "type": "text", + "content": "1) point-level supervision. Assume the prediction of control sequence from the output head as " + }, + { + "bbox": [ + 46, + 281, + 287, + 328 + ], + "type": "inline_equation", + "content": "\\widehat{\\mathbb{C}}" + }, + { + "bbox": [ + 46, + 281, + 287, + 328 + ], + "type": "text", + "content": " and its corresponding ground truth is " + }, + { + "bbox": [ + 46, + 281, + 287, + 328 + ], + "type": "inline_equation", + "content": "\\mathbb{C}" + }, + { + "bbox": [ + 46, + 281, + 287, + 328 + ], + "type": "text", + "content": ", we firstly leverage the " + }, + { + "bbox": [ + 46, + 281, + 287, + 328 + ], + "type": "inline_equation", + "content": "L1" + }, + { + "bbox": [ + 46, + 281, + 287, + 328 + ], + "type": "text", + "content": "-loss between these coordinates sequentially as," + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 104, + 329, + 287, + 365 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 104, + 329, + 287, + 365 + ], + "spans": [ + { + "bbox": [ + 104, + 329, + 287, + 365 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\text {p o i n t}} = \\frac {1}{| \\widehat {\\mathbb {C}} |} \\sum_ {i = 1} ^ {| \\widehat {\\mathbb {C}} |} \\| \\mathbb {C} _ {i} - \\widehat {\\mathbb {C}} _ {i} \\| _ {1}, \\tag {6}", + "image_path": "b13c990f46fe453c6aef5bd143282121c42c70fd997a8d427ecd1e9b00e6517d.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 369, + 287, + 430 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 369, + 287, + 430 + ], + "spans": [ + { + "bbox": [ + 46, + 369, + 287, + 430 + ], + "type": "text", + "content": "2) curve-level supervision. Due to the parametric property of Bézier curve that a slight deviation of control points " + }, + { + "bbox": [ + 46, + 369, + 287, + 430 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbb{C}}" + }, + { + "bbox": [ + 46, + 369, + 287, + 430 + ], + "type": "text", + "content": " might cause a great change of the curve, we further restore the control sequence " + }, + { + "bbox": [ + 46, + 369, + 287, + 430 + ], + "type": "inline_equation", + "content": "\\widehat{\\mathbb{C}}" + }, + { + "bbox": [ + 46, + 369, + 287, + 430 + ], + "type": "text", + "content": " (or " + }, + { + "bbox": [ + 46, + 369, + 287, + 430 + ], + "type": "inline_equation", + "content": "\\mathbb{C}" + }, + { + "bbox": [ + 46, + 369, + 287, + 430 + ], + "type": "text", + "content": ") to curve sequence " + }, + { + "bbox": [ + 46, + 369, + 287, + 430 + ], + "type": "inline_equation", + "content": "\\widehat{\\mathcal{P}}" + }, + { + "bbox": [ + 46, + 369, + 287, + 430 + ], + "type": "text", + "content": " (or " + }, + { + "bbox": [ + 46, + 369, + 287, + 430 + ], + "type": "inline_equation", + "content": "\\mathcal{P}" + }, + { + "bbox": [ + 46, + 369, + 287, + 430 + ], + "type": "text", + "content": ") with the vectorization process and adopt the " + }, + { + "bbox": [ + 46, + 369, + 287, + 430 + ], + "type": "inline_equation", + "content": "L1" + }, + { + "bbox": [ + 46, + 369, + 287, + 430 + ], + "type": "text", + "content": "-loss as," + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 104, + 430, + 287, + 464 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 104, + 430, + 287, + 464 + ], + "spans": [ + { + "bbox": [ + 104, + 430, + 287, + 464 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\text {c u r v e}} = \\frac {1}{| \\widehat {\\mathcal {P}} |} \\sum_ {i = 1} ^ {| \\widehat {\\mathcal {P}} |} \\| \\mathcal {P} _ {i} - \\widehat {\\mathcal {P}} _ {i} \\| _ {1} \\tag {7}", + "image_path": "f5daf0312729626cf825f9be790d4f9338acd325bdc52ef31fbce8faed75bfc2.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 470, + 287, + 675 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 470, + 287, + 675 + ], + "spans": [ + { + "bbox": [ + 46, + 470, + 287, + 675 + ], + "type": "text", + "content": "3) region-level supervision. For digging out more intuitive supervision information, we further recover curve " + }, + { + "bbox": [ + 46, + 470, + 287, + 675 + ], + "type": "inline_equation", + "content": "\\widehat{\\mathcal{P}}" + }, + { + "bbox": [ + 46, + 470, + 287, + 675 + ], + "type": "text", + "content": " from the form of discrete coordinates into region mask. First of all, we introduce a coordinate dilation operator, which takes the current coordinate " + }, + { + "bbox": [ + 46, + 470, + 287, + 675 + ], + "type": "inline_equation", + "content": "p_{ij}" + }, + { + "bbox": [ + 46, + 470, + 287, + 675 + ], + "type": "text", + "content": " as the center and then generates " + }, + { + "bbox": [ + 46, + 470, + 287, + 675 + ], + "type": "inline_equation", + "content": "(2\\omega +1)^{2}" + }, + { + "bbox": [ + 46, + 470, + 287, + 675 + ], + "type": "text", + "content": " surrounding coordinates " + }, + { + "bbox": [ + 46, + 470, + 287, + 675 + ], + "type": "inline_equation", + "content": "p_{\\alpha \\beta}" + }, + { + "bbox": [ + 46, + 470, + 287, + 675 + ], + "type": "text", + "content": " with the giving dilation width " + }, + { + "bbox": [ + 46, + 470, + 287, + 675 + ], + "type": "inline_equation", + "content": "\\omega" + }, + { + "bbox": [ + 46, + 470, + 287, + 675 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 470, + 287, + 675 + ], + "type": "inline_equation", + "content": "\\alpha \\in [i - \\omega ,i + \\omega ]" + }, + { + "bbox": [ + 46, + 470, + 287, + 675 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 470, + 287, + 675 + ], + "type": "inline_equation", + "content": "\\beta \\in [j - \\omega ,j + \\omega ]" + }, + { + "bbox": [ + 46, + 470, + 287, + 675 + ], + "type": "text", + "content": ". Secondly, we conduct the coordinate dilation on each point from curve " + }, + { + "bbox": [ + 46, + 470, + 287, + 675 + ], + "type": "inline_equation", + "content": "\\widehat{\\mathcal{P}}" + }, + { + "bbox": [ + 46, + 470, + 287, + 675 + ], + "type": "text", + "content": " and then obtain dilated curve points sequence " + }, + { + "bbox": [ + 46, + 470, + 287, + 675 + ], + "type": "inline_equation", + "content": "\\widehat{\\mathcal{P}}^{\\sharp}" + }, + { + "bbox": [ + 46, + 470, + 287, + 675 + ], + "type": "text", + "content": ", which can be regarded as the foreground coordinates of the predicted mask " + }, + { + "bbox": [ + 46, + 470, + 287, + 675 + ], + "type": "inline_equation", + "content": "\\widehat{M}" + }, + { + "bbox": [ + 46, + 470, + 287, + 675 + ], + "type": "text", + "content": ", i.e. " + }, + { + "bbox": [ + 46, + 470, + 287, + 675 + ], + "type": "inline_equation", + "content": "\\mathcal{S}(\\widehat{M},\\widehat{\\mathcal{P}}^{\\sharp}) = 1" + }, + { + "bbox": [ + 46, + 470, + 287, + 675 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 470, + 287, + 675 + ], + "type": "inline_equation", + "content": "\\mathcal{S}" + }, + { + "bbox": [ + 46, + 470, + 287, + 675 + ], + "type": "text", + "content": " is the grid sampling operation to compute the output values using " + }, + { + "bbox": [ + 46, + 470, + 287, + 675 + ], + "type": "inline_equation", + "content": "\\widehat{M}" + }, + { + "bbox": [ + 46, + 470, + 287, + 675 + ], + "type": "text", + "content": " and point coordinates " + }, + { + "bbox": [ + 46, + 470, + 287, + 675 + ], + "type": "inline_equation", + "content": "\\widehat{\\mathcal{P}}^{\\sharp}" + }, + { + "bbox": [ + 46, + 470, + 287, + 675 + ], + "type": "text", + "content": " from grid. Finally, after preforming the grid sampling " + }, + { + "bbox": [ + 46, + 470, + 287, + 675 + ], + "type": "inline_equation", + "content": "\\mathcal{S}" + }, + { + "bbox": [ + 46, + 470, + 287, + 675 + ], + "type": "text", + "content": " on ground truth map mask " + }, + { + "bbox": [ + 46, + 470, + 287, + 675 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 46, + 470, + 287, + 675 + ], + "type": "text", + "content": " with the same dilated prediction curve, we then bridge a segmentation-base region supervision between " + }, + { + "bbox": [ + 46, + 470, + 287, + 675 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 46, + 470, + 287, + 675 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 470, + 287, + 675 + ], + "type": "inline_equation", + "content": "\\widehat{\\mathcal{P}}^{\\sharp}" + }, + { + "bbox": [ + 46, + 470, + 287, + 675 + ], + "type": "text", + "content": ", which can be formulated mathematically as," + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 84, + 679, + 287, + 694 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 84, + 679, + 287, + 694 + ], + "spans": [ + { + "bbox": [ + 84, + 679, + 287, + 694 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\text {r e g i o n}} = \\mathcal {L} _ {\\text {d i c e}} \\left(\\mathcal {S} \\left(M, \\widehat {\\mathcal {P}} ^ {\\sharp}\\right), \\mathcal {S} \\left(\\widehat {M}, \\widehat {\\mathcal {P}} ^ {\\sharp}\\right)\\right) \\tag {8}", + "image_path": "c868e732b5aed256e3e2028d11e9118a1009a5c6deba2893f9e1697dea01a3e9.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 50, + 701, + 266, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 50, + 701, + 266, + 714 + ], + "spans": [ + { + "bbox": [ + 50, + 701, + 266, + 714 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 50, + 701, + 266, + 714 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\text{dice}}" + }, + { + "bbox": [ + 50, + 701, + 266, + 714 + ], + "type": "text", + "content": " is the common dice loss function in [38]." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 72, + 545, + 109 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 545, + 109 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 545, + 109 + ], + "type": "text", + "content": "4) overall " + }, + { + "bbox": [ + 305, + 72, + 545, + 109 + ], + "type": "inline_equation", + "content": "PCR" + }, + { + "bbox": [ + 305, + 72, + 545, + 109 + ], + "type": "text", + "content": "-Loss. In order to exert the above three-level supervision at the same time, we put forward that the overall " + }, + { + "bbox": [ + 305, + 72, + 545, + 109 + ], + "type": "inline_equation", + "content": "PCR" + }, + { + "bbox": [ + 305, + 72, + 545, + 109 + ], + "type": "text", + "content": "-Loss is a weighted sum of all three losses as," + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 334, + 113, + 545, + 127 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 334, + 113, + 545, + 127 + ], + "spans": [ + { + "bbox": [ + 334, + 113, + 545, + 127 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {P C R} = \\lambda_ {p} \\mathcal {L} _ {\\text {p o i n t}} + \\lambda_ {c} \\mathcal {L} _ {\\text {c u r v e}} + \\lambda_ {r} \\mathcal {L} _ {\\text {r e g i o n}} \\tag {9}", + "image_path": "f4031c369577d02df1c35f174d23de0ddc8e4bbfae2dd0c4a9ed8fe988b0fab2.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 132, + 545, + 251 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 132, + 545, + 251 + ], + "spans": [ + { + "bbox": [ + 304, + 132, + 545, + 251 + ], + "type": "text", + "content": "Multi-task Auxiliary Loss. The paradigm of multi-task learning can reduce the risk of overfitting by leveraging the domain-specific information included in the training signals of related tasks [61]. Thence, in addition to supervising the curve-level Bézier modeling procedure of the final head, we also perform auxiliary segmentation-based supervision on the intermediate modules, i.e. semantic-level BEV decoder and instance-level Bézier decoder. Given the output masks " + }, + { + "bbox": [ + 304, + 132, + 545, + 251 + ], + "type": "inline_equation", + "content": "\\widehat{\\mathbb{M}}_s" + }, + { + "bbox": [ + 304, + 132, + 545, + 251 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 132, + 545, + 251 + ], + "type": "inline_equation", + "content": "\\widehat{\\mathbb{M}}_z" + }, + { + "bbox": [ + 304, + 132, + 545, + 251 + ], + "type": "text", + "content": " in the Sec.3.2, we formulate the auxiliary loss with the combination of two tasks supervision as," + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 341, + 255, + 545, + 270 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 341, + 255, + 545, + 270 + ], + "spans": [ + { + "bbox": [ + 341, + 255, + 545, + 270 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {A U X} = \\lambda_ {s} \\mathcal {L} \\left(\\mathbb {M} _ {s}, \\widehat {\\mathbb {M}} _ {s}\\right) + \\lambda_ {z} \\mathcal {L} \\left(\\mathbb {M} _ {z}, \\widehat {\\mathbb {M}} _ {z}\\right) \\tag {10}", + "image_path": "d711a27b6ed7e94b93cc406abae10c04edf83cffd4aa6710863299de74a1b176.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 277, + 545, + 313 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 277, + 545, + 313 + ], + "spans": [ + { + "bbox": [ + 304, + 277, + 545, + 313 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 277, + 545, + 313 + ], + "type": "inline_equation", + "content": "\\mathbb{M}_{\\star}" + }, + { + "bbox": [ + 304, + 277, + 545, + 313 + ], + "type": "text", + "content": " denotes the ground truth and " + }, + { + "bbox": [ + 304, + 277, + 545, + 313 + ], + "type": "inline_equation", + "content": "\\lambda_{\\star}" + }, + { + "bbox": [ + 304, + 277, + 545, + 313 + ], + "type": "text", + "content": " is the weighted factor. Note that " + }, + { + "bbox": [ + 304, + 277, + 545, + 313 + ], + "type": "inline_equation", + "content": "\\mathcal{L}" + }, + { + "bbox": [ + 304, + 277, + 545, + 313 + ], + "type": "text", + "content": " is a compound loss with common cross entropy loss and dice loss, namely " + }, + { + "bbox": [ + 304, + 277, + 545, + 313 + ], + "type": "inline_equation", + "content": "\\mathcal{L} = \\mathcal{L}_{ce} + \\mathcal{L}_{dice}" + }, + { + "bbox": [ + 304, + 277, + 545, + 313 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 323, + 387, + 336 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 323, + 387, + 336 + ], + "spans": [ + { + "bbox": [ + 306, + 323, + 387, + 336 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 306, + 342, + 432, + 356 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 342, + 432, + 356 + ], + "spans": [ + { + "bbox": [ + 306, + 342, + 432, + 356 + ], + "type": "text", + "content": "4.1. Experimental Settings" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 363, + 545, + 567 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 363, + 545, + 567 + ], + "spans": [ + { + "bbox": [ + 304, + 363, + 545, + 567 + ], + "type": "text", + "content": "Existing Benchmarks. To evaluate the proposed approach, we conduct experiments on the popular NuScenes dataset [2], which consists of 28, 130/6, 019 samples and 700/150 driving scenes for the training/validation set respectively. Each scene contains roughly 40 samples and each sample includes 6 surrounding images, covering " + }, + { + "bbox": [ + 304, + 363, + 545, + 567 + ], + "type": "inline_equation", + "content": "360^{\\circ}" + }, + { + "bbox": [ + 304, + 363, + 545, + 567 + ], + "type": "text", + "content": " FOV of the ego-vehicle. For the sake of fair comparison, we follow the previous work [24] and focus on three static map categories, i.e. lane-divider, ped-crossing and road-boundary. Taking the ego-vehicle as the center, we set the perception range to " + }, + { + "bbox": [ + 304, + 363, + 545, + 567 + ], + "type": "inline_equation", + "content": "[30, 30, 15, 15]m" + }, + { + "bbox": [ + 304, + 363, + 545, + 567 + ], + "type": "text", + "content": ", which corresponds to the distances of front, rear, left and right respectively, and fix the resolution of ego-to-pixel as " + }, + { + "bbox": [ + 304, + 363, + 545, + 567 + ], + "type": "inline_equation", + "content": "0.15m/pixel" + }, + { + "bbox": [ + 304, + 363, + 545, + 567 + ], + "type": "text", + "content": ". In addition, for exploring the performance of our method under different lighting and weather conditions, we further divide NuScenes into five kinds of scene, namely day, night, sunny, cloudy and rainy. Refer to the supplementary material for more details." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "content": "Evaluation Metrics. We utilize the exact same evaluation protocol as [24] of average precision (AP) to access the map construction quality over the instance-level. To be concrete, given a pair of instances from ground-truth and predictions respectively, this protocol computes the Chamfer Distance between them and considers the prediction as true-positive only if the distance is less than a specified threshold, which is set to " + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "inline_equation", + "content": "[0.2, 0.5, 1.0]m" + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "content": " in our experiment. Note the overall AP metric is obtained by averaging across three thresholds. Moreover, as for a more informative comparison, the results under different lighting/weather conditions and a much simpler threshold setup of " + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "inline_equation", + "content": "[0.5, 1.0, 1.5]m" + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "content": " are further provided." + } + ] + } + ], + "index": 18 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "13223" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 50, + 70, + 544, + 247 + ], + "blocks": [ + { + "bbox": [ + 50, + 70, + 544, + 247 + ], + "lines": [ + { + "bbox": [ + 50, + 70, + 544, + 247 + ], + "spans": [ + { + "bbox": [ + 50, + 70, + 544, + 247 + ], + "type": "table", + "html": "
MethodBackboneEpochAP_dividerAP_crossAP_boundmAPmAP_daymAP_nightmAP_sunnymAP.cloudymAP_rainy
IPM(B) [24]Eff-B03010.74.711.79.0-----
IPM(CB) [24]Eff-B03024.07.327.819.7-----
LSS [43]Eff-B03022.95.124.217.411.5b13.3b12.0b12.8b9.5b
VPN [40]Eff-B03022.15.225.317.517.9b17.5b18.2b18.5b15.9b
HMapNet [24]Eff-B03028.37.132.622.721.4b17.4b21.5b23.4b18.9b
BeMapNetEff-B03046.737.438.040.741.328.641.444.936.2
BeMapNetRes-503046.939.037.841.341.930.442.643.637.4
BeMapNetSwin-T3049.142.239.943.744.334.444.847.937.8
BeMapNetRes-5011052.744.544.247.147.739.248.750.341.4
BeMapNetSwin-T11054.246.546.549.149.837.350.453.542.8
BeMapNetSwin-B11055.347.049.450.551.238.052.254.843.6
BeMapNetRes-503062.357.759.459.860.546.962.561.953.0
BeMapNetSwin-T3064.461.361.662.563.153.264.766.054.2
BeMapNetSwin-B11069.064.469.767.768.354.670.371.658.0
", + "image_path": "747f3b3ea5c3b19ac12eea02adf35fb6ebc84892f7dc273c204aa5d5e41c5fac.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + }, + { + "bbox": [ + 46, + 251, + 546, + 289 + ], + "lines": [ + { + "bbox": [ + 46, + 251, + 546, + 289 + ], + "spans": [ + { + "bbox": [ + 46, + 251, + 546, + 289 + ], + "type": "text", + "content": "Table 1. Comparisons with SOTAs on NuScenes under thresholds of [0.2, 0.5, 1.0] " + }, + { + "bbox": [ + 46, + 251, + 546, + 289 + ], + "type": "inline_equation", + "content": "m" + }, + { + "bbox": [ + 46, + 251, + 546, + 289 + ], + "type": "text", + "content": " and [0.5, 1.0, 1.5] " + }, + { + "bbox": [ + 46, + 251, + 546, + 289 + ], + "type": "inline_equation", + "content": "m" + }, + { + "bbox": [ + 46, + 251, + 546, + 289 + ], + "type": "text", + "content": ", where the results of latter easier evaluation protocol is marked by Green shade. The Blue shade contains the results that used in all ablation studies for a fair comparison. Note " + }, + { + "bbox": [ + 46, + 251, + 546, + 289 + ], + "type": "inline_equation", + "content": "{}^{\\flat}" + }, + { + "bbox": [ + 46, + 251, + 546, + 289 + ], + "type": "text", + "content": " and - indicate the results are re-implemented by us with public code and not available respectively." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_footnote" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 297, + 289, + 526 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 297, + 289, + 526 + ], + "spans": [ + { + "bbox": [ + 46, + 297, + 289, + 526 + ], + "type": "text", + "content": "Implementation Details. We employ EfficientNet-B0 [49], ResNet-50 [14] and SwinTR [31] as backbones, which are all initialized by ImageNet [21] pretraining. The following semantic " + }, + { + "bbox": [ + 46, + 297, + 289, + 526 + ], + "type": "inline_equation", + "content": "BEV" + }, + { + "bbox": [ + 46, + 297, + 289, + 526 + ], + "type": "text", + "content": " decoder stacks 2 transformer encoder layers and 4 decoder layers with " + }, + { + "bbox": [ + 46, + 297, + 289, + 526 + ], + "type": "inline_equation", + "content": "64 \\times 32" + }, + { + "bbox": [ + 46, + 297, + 289, + 526 + ], + "type": "inline_equation", + "content": "BEV" + }, + { + "bbox": [ + 46, + 297, + 289, + 526 + ], + "type": "text", + "content": " queries, and the instance Bézier decoder stacks 6 mask-transformer decoder layers with 60 queries, where 20, 25, 15 for lane-divider, ped-crossing and road-boundary respectively. The shape of input image is resized to " + }, + { + "bbox": [ + 46, + 297, + 289, + 526 + ], + "type": "inline_equation", + "content": "896 \\times 512" + }, + { + "bbox": [ + 46, + 297, + 289, + 526 + ], + "type": "text", + "content": " and the mini-batch size is set to 1 per GPU. We train our model with 8 GPUs for 30/110 epochs and adopt multi-step schedule with milestone [0.7, 0.9] and " + }, + { + "bbox": [ + 46, + 297, + 289, + 526 + ], + "type": "inline_equation", + "content": "\\gamma = \\frac{1}{3}" + }, + { + "bbox": [ + 46, + 297, + 289, + 526 + ], + "type": "text", + "content": ". The AdamW [33] optimizer is employed with a weight decay of " + }, + { + "bbox": [ + 46, + 297, + 289, + 526 + ], + "type": "inline_equation", + "content": "1e^{-4}" + }, + { + "bbox": [ + 46, + 297, + 289, + 526 + ], + "type": "text", + "content": " and a learning rate of " + }, + { + "bbox": [ + 46, + 297, + 289, + 526 + ], + "type": "inline_equation", + "content": "2e^{-4}" + }, + { + "bbox": [ + 46, + 297, + 289, + 526 + ], + "type": "text", + "content": ", which is multiplied by 0.1 for backbone. As for hyper-parameters of loss weight, we set " + }, + { + "bbox": [ + 46, + 297, + 289, + 526 + ], + "type": "inline_equation", + "content": "\\lambda_s" + }, + { + "bbox": [ + 46, + 297, + 289, + 526 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 297, + 289, + 526 + ], + "type": "inline_equation", + "content": "\\lambda_z" + }, + { + "bbox": [ + 46, + 297, + 289, + 526 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 297, + 289, + 526 + ], + "type": "inline_equation", + "content": "\\lambda_p" + }, + { + "bbox": [ + 46, + 297, + 289, + 526 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 297, + 289, + 526 + ], + "type": "inline_equation", + "content": "\\lambda_c" + }, + { + "bbox": [ + 46, + 297, + 289, + 526 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 297, + 289, + 526 + ], + "type": "inline_equation", + "content": "\\lambda_r" + }, + { + "bbox": [ + 46, + 297, + 289, + 526 + ], + "type": "text", + "content": " to 1, 5, 5, 10, 1 respectively and the dilated width " + }, + { + "bbox": [ + 46, + 297, + 289, + 526 + ], + "type": "inline_equation", + "content": "\\omega" + }, + { + "bbox": [ + 46, + 297, + 289, + 526 + ], + "type": "text", + "content": " in " + }, + { + "bbox": [ + 46, + 297, + 289, + 526 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{region}" + }, + { + "bbox": [ + 46, + 297, + 289, + 526 + ], + "type": "text", + "content": " to 5. The deployments of piecewise Bézier curve " + }, + { + "bbox": [ + 46, + 297, + 289, + 526 + ], + "type": "inline_equation", + "content": "\\langle k, n \\rangle" + }, + { + "bbox": [ + 46, + 297, + 289, + 526 + ], + "type": "text", + "content": " for lane-divider, ped-crossing and road-boundary are set to " + }, + { + "bbox": [ + 46, + 297, + 289, + 526 + ], + "type": "inline_equation", + "content": "\\langle 3, 2 \\rangle" + }, + { + "bbox": [ + 46, + 297, + 289, + 526 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 297, + 289, + 526 + ], + "type": "inline_equation", + "content": "\\langle 1, 1 \\rangle" + }, + { + "bbox": [ + 46, + 297, + 289, + 526 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 297, + 289, + 526 + ], + "type": "inline_equation", + "content": "\\langle 7, 3 \\rangle" + }, + { + "bbox": [ + 46, + 297, + 289, + 526 + ], + "type": "text", + "content": ". Note " + }, + { + "bbox": [ + 46, + 297, + 289, + 526 + ], + "type": "inline_equation", + "content": "m" + }, + { + "bbox": [ + 46, + 297, + 289, + 526 + ], + "type": "text", + "content": " in Algorithm 1 is set to 100." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 537, + 275, + 551 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 537, + 275, + 551 + ], + "spans": [ + { + "bbox": [ + 47, + 537, + 275, + 551 + ], + "type": "text", + "content": "4.2. Comparisons with State-of-the-art Methods" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 557, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 557, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 557, + 289, + 715 + ], + "type": "text", + "content": "We present the overall evaluation results on NuScenes in Table 1, which shows that our BeMapNet is significantly superior to the existing SOTA approaches by a large margin (up to 18.0) under the same setting of EfficientNet-B0 and 30 epochs, indicating the effectiveness of our approach. In addition, after replacing the backbone with more common ResNet-50 and more popular SwinTiny, our model achieves a further improvement of 0.6 and 3.0 AP respectively. Next, considering the slow convergence of the Transformer-based model, we increase the training schedule to 110 epochs and gain at least another 5.4 improvements. Even in somewhat unconventional scenarios, such as night and rainy, our proposed approach still shows a great advantage, i.e. 13.2 and" + } + ] + } + ], + "index": 4 + }, + { + "type": "table", + "bbox": [ + 314, + 295, + 539, + 370 + ], + "blocks": [ + { + "bbox": [ + 314, + 295, + 539, + 370 + ], + "lines": [ + { + "bbox": [ + 314, + 295, + 539, + 370 + ], + "spans": [ + { + "bbox": [ + 314, + 295, + 539, + 370 + ], + "type": "table", + "html": "
Position EncodingAP_dividerAP_crossAP_boundmAP
Sine PE42.834.134.737.2
Learned PE40.232.233.835.4
IPM-PE46.439.237.841.1
+ Exclusive FC38.633.333.935.3
+ Shared FC49.142.239.943.7
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We believe that strong illuminations and ground shades on sunny day might have a certain impact on the perception of map objects. As a supplement, the last three rows of Table 1 show the performance of our approach on a much simpler evaluation protocol." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 500, + 400, + 514 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 500, + 400, + 514 + ], + "spans": [ + { + "bbox": [ + 306, + 500, + 400, + 514 + ], + "type": "text", + "content": "4.3. Ablation Study" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 521, + 547, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 521, + 547, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 521, + 547, + 714 + ], + "type": "text", + "content": "The Different Way of Position Encoding. Table 2 shows the performance of different " + }, + { + "bbox": [ + 304, + 521, + 547, + 714 + ], + "type": "inline_equation", + "content": "PE" + }, + { + "bbox": [ + 304, + 521, + 547, + 714 + ], + "type": "text", + "content": " in semantic BEV decoder for the map construction. Compared with the sine/learned-based method, our proposed IPM-PE module improves AP by 3.9/5.7 respectively, which proves the multi-perspective " + }, + { + "bbox": [ + 304, + 521, + 547, + 714 + ], + "type": "inline_equation", + "content": "PE" + }, + { + "bbox": [ + 304, + 521, + 547, + 714 + ], + "type": "text", + "content": " guided by the intrinsic and extrinsic parameters is very effective. Moreover, through the results in the 3-rd and 5-th row, we find that IPM-PE with shared FC layer alignment gains an further improvement of 2.6 points. Yet, in order to rule out the possibility of that the attached FC layer brings an increment, we then feed the position embeddings from IPM-PE into two exclusive FCs and the 4-th row results exclude the influence of FC. These comparisons indicate the shared align layer is the exactly essential part to mitigate the performance decline brought by the unreasonable assumption of IPM, which validates our conjecture in Sec.3.2.2." + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "13224" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 77, + 70, + 518, + 261 + ], + "blocks": [ + { + "bbox": [ + 77, + 70, + 518, + 261 + ], + "lines": [ + { + "bbox": [ + 77, + 70, + 518, + 261 + ], + "spans": [ + { + "bbox": [ + 77, + 70, + 518, + 261 + ], + "type": "image", + "image_path": "cee40b8254afb773901ebf807217fd10dc8aa039219eb16607ea573cdc045532.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 72, + 263, + 520, + 275 + ], + "lines": [ + { + "bbox": [ + 72, + 263, + 520, + 275 + ], + "spans": [ + { + "bbox": [ + 72, + 263, + 520, + 275 + ], + "type": "text", + "content": "Figure 5. The qualitative comparison results of HDMapNet [24], BeMapNet and GroundTruth [2] under different scenarios." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 283, + 289, + 440 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 283, + 289, + 440 + ], + "spans": [ + { + "bbox": [ + 46, + 283, + 289, + 440 + ], + "type": "text", + "content": "Effectiveness of " + }, + { + "bbox": [ + 46, + 283, + 289, + 440 + ], + "type": "inline_equation", + "content": "PCR" + }, + { + "bbox": [ + 46, + 283, + 289, + 440 + ], + "type": "text", + "content": "-Loss. The " + }, + { + "bbox": [ + 46, + 283, + 289, + 440 + ], + "type": "inline_equation", + "content": "PCR" + }, + { + "bbox": [ + 46, + 283, + 289, + 440 + ], + "type": "text", + "content": "-Loss mainly consists of three parts, i.e. point, curve and region. Table 3 shows detailed ablation results of the role of each part. Specifically, with adopting only one supervision in rows " + }, + { + "bbox": [ + 46, + 283, + 289, + 440 + ], + "type": "inline_equation", + "content": "1 \\sim 3" + }, + { + "bbox": [ + 46, + 283, + 289, + 440 + ], + "type": "text", + "content": ", the performance trend is roughly: curve > point > region. Among them, it is worth noting that the only region-based supervision shows very poor performance, which is understandable because the generation of region mask relies on a collection of relatively accurate points. This conjecture is also verified in rows " + }, + { + "bbox": [ + 46, + 283, + 289, + 440 + ], + "type": "inline_equation", + "content": "4 \\sim 5" + }, + { + "bbox": [ + 46, + 283, + 289, + 440 + ], + "type": "text", + "content": " of the Table 3. Furthermore, when integrating multiple loss supervision, the final performance is consistently improved compared to the single one, and three parts used together achieves the optimal AP results of 43.7." + } + ] + } + ], + "index": 2 + }, + { + "type": "table", + "bbox": [ + 51, + 446, + 284, + 534 + ], + "blocks": [ + { + "bbox": [ + 51, + 446, + 284, + 534 + ], + "lines": [ + { + "bbox": [ + 51, + 446, + 284, + 534 + ], + "spans": [ + { + "bbox": [ + 51, + 446, + 284, + 534 + ], + "type": "table", + "html": "
PointCurveRegionAP_dividerAPPEDAPboundarymAP
✓XX39.133.323.732.0
X✓X47.235.135.939.4
XX✓3.22.60.52.1
✓X✓40.739.416.732.9
X✓✓48.238.539.742.1
✓✓X46.538.536.240.4
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SemanticInstanceAPdividerAPpedAPboundarymAP
XX21.517.820.720.0
✓X39.331.532.834.5
X✓44.334.636.538.4
✓✓49.142.239.943.7
", + "image_path": "cb6ee7fb2c753fa994bd5dcf1c003094e00a3f0cbd239172b14ef85348c763a8.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "table_body" + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 283, + 545, + 416 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 283, + 545, + 416 + ], + "spans": [ + { + "bbox": [ + 304, + 283, + 545, + 416 + ], + "type": "text", + "content": "Comparison with Polyline Vectorization. An amusing fact is that a Bézier curve with " + }, + { + "bbox": [ + 304, + 283, + 545, + 416 + ], + "type": "inline_equation", + "content": "n = 1" + }, + { + "bbox": [ + 304, + 283, + 545, + 416 + ], + "type": "text", + "content": " is simply a straight line between two control points. By setting the degree of all elements to 1, our framework naturally degenerates into the polyline-based method. Note we further set " + }, + { + "bbox": [ + 304, + 283, + 545, + 416 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 304, + 283, + 545, + 416 + ], + "type": "text", + "content": " to 9, 1, 29 for lane-divider, ped-crossing and road-boundary respectively. The comparisons in Table 5 show the Bézier-based vectorization approach achieves better 4.5 AP. Interestingly, as the complexity of map element shape increases (usually ped-crossing " + }, + { + "bbox": [ + 304, + 283, + 545, + 416 + ], + "type": "inline_equation", + "content": "<" + }, + { + "bbox": [ + 304, + 283, + 545, + 416 + ], + "type": "text", + "content": " lane-divider " + }, + { + "bbox": [ + 304, + 283, + 545, + 416 + ], + "type": "inline_equation", + "content": "<" + }, + { + "bbox": [ + 304, + 283, + 545, + 416 + ], + "type": "text", + "content": " road-boundary), we find that the corresponding AP improvement increases as well." + } + ] + } + ], + "index": 8 + }, + { + "type": "table", + "bbox": [ + 309, + 419, + 545, + 459 + ], + "blocks": [ + { + "bbox": [ + 55, + 706, + 278, + 716 + ], + "lines": [ + { + "bbox": [ + 55, + 706, + 278, + 716 + ], + "spans": [ + { + "bbox": [ + 55, + 706, + 278, + 716 + ], + "type": "text", + "content": "Table 4. The effectiveness of different modules in AUX-Loss." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 309, + 419, + 545, + 459 + ], + "lines": [ + { + "bbox": [ + 309, + 419, + 545, + 459 + ], + "spans": [ + { + "bbox": [ + 309, + 419, + 545, + 459 + ], + "type": "table", + "html": "
VectorizationAPdividerAPpedAPboundarymAP
Polyline45.039.133.439.2
Bézier49.1 (+4.1)42.2 (+3.1)39.9 (+6.5)43.7(+4.5)
", + "image_path": "d1c7988cf9909d55ea76febac90d9928eba137e0c3c1fd5c1b30a1a75933db29.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "table_body" + } + ], + "index": 9 + }, + { + "bbox": [ + 314, + 462, + 537, + 473 + ], + "lines": [ + { + "bbox": [ + 314, + 462, + 537, + 473 + ], + "spans": [ + { + "bbox": [ + 314, + 462, + 537, + 473 + ], + "type": "text", + "content": "Table 5. Comparison with the different type of vectorization." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 304, + 479, + 545, + 553 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 479, + 545, + 553 + ], + "spans": [ + { + "bbox": [ + 304, + 479, + 545, + 553 + ], + "type": "text", + "content": "Qualitative Analysis. We show the qualitative comparisons with SOTAs in Fig. 5. Besides avoiding complex vectorized post-processing, the proposed BeMapNet constructs various and changeful " + }, + { + "bbox": [ + 304, + 479, + 545, + 553 + ], + "type": "inline_equation", + "content": "HD" + }, + { + "bbox": [ + 304, + 479, + 545, + 553 + ], + "type": "text", + "content": "-elements more compactly and robust. Note that more extensive visualizations under different conditions are further provided in our supplementary material." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 562, + 379, + 574 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 562, + 379, + 574 + ], + "spans": [ + { + "bbox": [ + 306, + 562, + 379, + 574 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 582, + 545, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 545, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 545, + 715 + ], + "type": "text", + "content": "Vectorized " + }, + { + "bbox": [ + 304, + 582, + 545, + 715 + ], + "type": "inline_equation", + "content": "HD" + }, + { + "bbox": [ + 304, + 582, + 545, + 715 + ], + "type": "text", + "content": "-map online construction focuses on the perception of centimeter-level environmental information. Starting from the conventional parameterization-based methods, this paper presents an end-to-end postprocessing-free architecture, namely BeMapNet, with leveraging unified piecewise Bézier curve for various and changeful map elements. By introducing three well-designed modules, i.e. IPM-PE Align Module, Piecewise Bézier Head and Point-Curve-Region Loss, the overall framework is concise and elegant, which reaches state-of-the-art performance and provides a new perspective for future " + }, + { + "bbox": [ + 304, + 582, + 545, + 715 + ], + "type": "inline_equation", + "content": "HD" + }, + { + "bbox": [ + 304, + 582, + 545, + 715 + ], + "type": "text", + "content": "-map research." + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "13225" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 288, + 714 + ], + "type": "list", + "angle": 0, + "index": 13, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 124 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 124 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 124 + ], + "type": "text", + "content": "[1] Paul J Besl and Neil D McKay. 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In Proceedings of the IEEE Conference on Computer Vision and Pattern Recognition, pages 13760-13769, 2022. 2" + } + ] + } + ], + "index": 12 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "type": "text", + "content": "13228" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 10 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/End-to-End Video Matting With Trimap Propagation/5671e405-73cb-4243-be20-91144c26868b_content_list.json b/2023/End-to-End Video Matting With Trimap Propagation/5671e405-73cb-4243-be20-91144c26868b_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..9dc7bbe909ce539c00f54e9e233e869fa62f4115 --- /dev/null +++ b/2023/End-to-End Video Matting With Trimap Propagation/5671e405-73cb-4243-be20-91144c26868b_content_list.json @@ -0,0 +1,2048 @@ +[ + { + "type": "text", + "text": "End-to-end Video Matting with Trimap Propagation", + "text_level": 1, + "bbox": [ + 220, + 130, + 750, + 152 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Wei-Lun Huang National Taiwan University r09944040@csie.ntu.edu.tw", + "bbox": [ + 233, + 181, + 454, + 232 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 255, + 312, + 271 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "The research of video matting mainly focuses on temporal coherence and has gained significant improvement via neural networks. However, matting usually relies on user-annotated trimaps to estimate alpha values, which is a labor-intensive issue. Although recent studies exploit video object segmentation methods to propagate the given trimaps, they suffer inconsistent results. Here we present a more robust and faster end-to-end video matting model equipped with trimap propagation called FTP-VM (Fast Trimap Propagation - Video Matting). The FTP-VM combines trimap propagation and video matting in one model, where the additional backbone in memory matching is replaced with the proposed lightweight trimap fusion module. The segmentation consistency loss is adopted from automotive segmentation to fit trimap segmentation with the collaboration of RNN (Recurrent Neural Network) to improve the temporal coherence. The experimental results demonstrate that the FTP-VM performs competitively both in composited and real videos only with few given trimaps. The efficiency is eight times higher than the state-of-the-art methods, which confirms its robustness and applicability in real-time scenarios. The code is available at https://github.com/csvt32745/FTP-VM.", + "bbox": [ + 76, + 295, + 473, + 643 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 671, + 209, + 686 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Image matting aims to estimate the alpha value of each pixel for a target in the input image. Unlike general segmentation, which generates binary values, matting outputs values between 0 and 1, meaning the degree of transparency. The output alpha matrices can describe semi-transparent objects with precise details. As shown in Eq. (1), each pixel color $C$ of an image is composited by the foreground color $F$ , background color $B$ , and an alpha value $\\alpha$ , where the background can be substituted to generate a matting dataset.", + "bbox": [ + 75, + 696, + 468, + 833 + ], + "page_idx": 0 + }, + { + "type": "equation", + "text": "\n$$\nC = \\alpha F + (1 - \\alpha) B \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 197, + 847, + 468, + 863 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Given a frame like Fig. 1a, a trimap Fig. 1b is the common requirement for image matting, which divides the pixels", + "bbox": [ + 75, + 869, + 468, + 901 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Ming-Sui Lee \nNational Taiwan University \nmslee@csie.ntu.edu.tw", + "bbox": [ + 514, + 181, + 736, + 232 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/90cbd2482832de7c9bca669fde462cb74c463c80909c1ac9742795c54a512bd3.jpg", + "image_caption": [ + "(a) Memory frame" + ], + "image_footnote": [], + "bbox": [ + 503, + 253, + 696, + 339 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/686c336f3ab53895b03a65aab8a5caded4b4267db239ccd45a560359ece5315e.jpg", + "image_caption": [ + "(b) Memory trimap" + ], + "image_footnote": [], + "bbox": [ + 697, + 255, + 890, + 339 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/ce389bec65b69a9027eb68ee91d9203626a08a9a3b586587c940b835e4449388.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 504, + 354, + 697, + 438 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/aaa44252ea4df9244931126f9d00de930850dfaecccf1f6c9c30efc49e006d93.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 697, + 354, + 887, + 438 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/16fadd8de87ac6a6226227d138b61b810259bbd2595ec9e74ae09a23b4d65256.jpg", + "image_caption": [ + "(c) Query frame", + "(e) The result of OTVM [42]", + "Figure 1. An example of an in-street interview video. (d) Automatic matting, (e) Trimap-propagation-based method (f) The proposed method." + ], + "image_footnote": [], + "bbox": [ + 506, + 453, + 696, + 536 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/a3026f79a90fa09de1cfb98ee4458e9c2c85a85f7d02e16e8b98a442cfd68b22.jpg", + "image_caption": [ + "(d) The result of RVM [32]", + "(f) The result of FTP-VM (ours)" + ], + "image_footnote": [], + "bbox": [ + 697, + 453, + 885, + 536 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "into three regions: foreground, background and unknown. Matting methods adopt such information to solve alpha values of unknown (gray) regions.", + "bbox": [ + 498, + 609, + 890, + 656 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Video matting extracts an alpha matte of each frame of the given video. The resulting alpha mattes can be used for background replacement, which is decisive for video applications such as video conferencing and visual effects. It is intuitive to perform image matting on each frame of a video. However, severe flickering artifacts would occur in the resultant image sequence. In order to improve the robustness, considering spatial and temporal coherence is the main challenge for video matting as the temporal information helps infer the matting target from the previous frames. Another challenge is to provide a trimap for each frame, which is expected to be a massive cost to most users.", + "bbox": [ + 496, + 664, + 892, + 845 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "To tackle the above two issues, automatic matting and trimap propagation are addressed in this paper. Automatic matting captures specific targets without trimaps, but", + "bbox": [ + 498, + 854, + 893, + 900 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 807, + 44 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "14337", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "the input videos with ambiguous scenarios highly affect the results. Fig. 1 shows an example of an in-street interview video where an interviewee and passengers occasionally appear simultaneously. While the human matting method [32] attempts to capture all the people, the ambiguity caused by inconspicuous passengers results in unsatisfactory output Fig. 1d. Thus we opt for trimap propagation to select targets more stably as shown in Fig. 1f.", + "bbox": [ + 75, + 90, + 470, + 212 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "While performing trimap propagation, the user is required to provide a pair of so-called memory frame Fig. 1a and memory trimap Fig. 1b, and this information is utilized to propagate throughout the video. Since we are predicting a sequence of three-class segmentation masks, the trimap propagation can be treated as video object segmentation. Recent studies [42, 47, 55] leverage STM (Space-Time Memory network), [35] an emerging video object segmentation model, to produce the trimaps successfully. However, the resultant trimaps usually contain flickers and lead to unsatisfactory results. As STM lacks temporal coherence, we append ConvGRUs [2] to the model to improve stability. Moreover, the previous approaches containing two full models make them unsuitable for interactive applications. We thus combine the two models into an end-to-end model to enhance the speed and performance. The main contributions of this work are summarized as follows.", + "bbox": [ + 75, + 220, + 470, + 492 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- A novel end-to-end video matting model equipped with trimap propagation, called FTP-VM (Fast Trimap Propagation - Video Matting), is proposed. FTP-VM is faster than the previous two-model methods by a large margin while preserving competitive performance in different scenarios. While the frame rate of the previous methods is 5 FPS, the proposed method reaches 40 FPS on an NVIDIA RTX 2080Ti GPU.", + "- A lightweight trimap fusion module is designed to replace an additional encoder in the STM-based model to make FTP-VM efficient and more powerful.", + "- Motivated by [38], the segmentation consistency loss from automotive segmentation is adapted to trimap segmentation. The final setting reaching the more satisfactory performance is determined by conducting comprehensive experiments." + ], + "bbox": [ + 94, + 501, + 468, + 761 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 76, + 776, + 220, + 792 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.1. Image Matting", + "text_level": 1, + "bbox": [ + 76, + 801, + 228, + 816 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Non-deep-learning image matting includes two types of methods: The sampling-based approaches [12,16,18,44,48] construct the foreground and background priors, and infer the alpha values by solving the composition equation. The affinity-based methods [4,5,17,24-26,46] propagate the", + "bbox": [ + 75, + 824, + 470, + 902 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "alpha values from known pixels to unknown ones according to similarities under the assumption of local smoothness. These classical methods rely on low-level representations and often require assistance to deal with complex scenes. For deep-learning methods, CNN (Convolution Neural Network) based methods [9, 15, 20, 23, 30, 34, 51] exploit high-level features and achieve state-of-the-art results. Vision-transformer-based methods [36] are emerging by combining global similarity and inductive bias of images. These methods build prior from the extracted features or the similarity to estimate the alpha values and preserve details by the UNet-like [40] architecture.", + "bbox": [ + 496, + 90, + 890, + 272 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In order to annihilate the need for trimaps, automatic image matting combines segmentation and matting into one task. It aims to matte specific targets such as humans [21, 45] or salient objects [3, 28, 29, 37] without any auxiliary inputs. Mask-guided matting [54] takes a rough segmentation mask as an additional input followed by refinement. However, it cannot process semi-transparent objects due to the binary masks. Background-based methods [31, 41] require a background image instead of a trimap as an auxiliary input so that it needs to handle misaligned backgrounds better.", + "bbox": [ + 496, + 287, + 890, + 439 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.2. Video Matting", + "text_level": 1, + "bbox": [ + 500, + 454, + 648, + 470 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Temporal coherence plays an essential role in video matting. Most existing methods [1, 10, 27, 43] extend classical image matting methods to the temporal dimension and encounter a similar weakness. RVM [32] places ConvGRU hierarchically to maintain temporal coherency. It performs in real-time due to the efficiency of ConvGRU. DVM [47] uses deformable convolution to warp the feature temporally by estimated offsets but is limited by the kernel size of convolutions. TCVOM [55] leverages guided attention block to compute affinity between frames, and [49] analyzes inter-frame relationships by graph neural network. [21] reduces the flickers by applying post-processing tricks to the results, but the image matting methods still limit the performance.", + "bbox": [ + 496, + 478, + 890, + 690 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "For trimap propagation, [11] interpolates trimaps by optical flows and contains restrictions caused by weak low-level features from semi-transparent objects. Recent deep-learning-based methods [47, 55] leverage approaches from video object segmentation to perform trimap segmentation before video matting. Decoupling trimap propagation and video matting simplifies the problem and forms a two-stage method. However, the model sometimes needs to be finetuned based on the given trimaps to generate acceptable results. OTVM [42] further improves performance through multi-stage training and joint trimap and alpha prediction modeling. The joint modeling utilizes alpha mattes and trimaps to perform trimap propagation.", + "bbox": [ + 496, + 704, + 890, + 902 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "14338", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.3. Video Object Segmentation", + "text_level": 1, + "bbox": [ + 76, + 90, + 323, + 107 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Trimap propagation is a kind of video object segmentation in a semi-supervised setting. The model receives masks of a few frames as auxiliary inputs to hint targets and predicts masks of the remaining frames. After the success of STM [35], different memory matching based methods emerge. Memory matching uses a variant of self-attention to extract the features from the given masks. With frames to predict, called query, and pairs of frames and masks, called memory, the features from the memories are linearly combined based on the similarity between memory and query. If a pixel has a similar context to another one, its similarity score will be high. Thus STM can effectively capture the correspondence and segment the target correctly. STCN (Space-Time Correspondence Network) [8] decouples the relation between frames and masks in the memory encoder to become more efficient and effective. We leverage the similar mechanic of STCN to propagate the trimaps but with a more efficient module. In addition, neither STM nor STCN has a strong temporal correlation between consecutive frames, so ConvGRU [2] is appended to our model to strengthen the temporal coherence as XMem [6].", + "bbox": [ + 75, + 113, + 472, + 431 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Method", + "text_level": 1, + "bbox": [ + 76, + 446, + 169, + 462 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The overall network architecture containing an encoder, trimap fusion module, bottleneck fusion module, and two corresponding decoders is illustrated in Fig. 2. The encoder extracts features from the memory frame $I_{m}$ and query frame $I_{q}$ . The trimap fusion module encodes the memory trimap $T_{m}$ and memory features into memory values. The bottleneck fusion module propagates the trimap information to the query frame and aggregates the features globally. The decoders contain segmentation and matting decoders to estimate the trimap and boundary matte, respectively. Finally, the resulting trimap and boundary matte are integrated into a complete matte.", + "bbox": [ + 75, + 472, + 472, + 654 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Encoder", + "text_level": 1, + "bbox": [ + 76, + 665, + 179, + 680 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The MobileNetV3-Large [22] is adopted as the encoder for its efficiency. The encoder takes a single image as input and extracts features at strides of 2, 4, 8 and 16, respectively. The receptive fields are larger in deeper stages, which makes features at different strides focus on different tasks. The low-level features are for preserving details, while high-level ones are for inferring the matting target. This kind of hierarchy can be employed as an UNet-like structure [40] where it receives skip-connections of the features to avoid information diminishing due to the deeper networks. $I_{m}$ and $I_{q}$ are passed through the same encoder to reduce the size of the model to enhance efficiency. The extracted memory and query features are denoted as $F_{m}^{s}$ and $F_{q}^{s}$ where $s$ represents the stride of the feature.", + "bbox": [ + 75, + 688, + 472, + 902 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. Trimap Fusion Module", + "text_level": 1, + "bbox": [ + 500, + 90, + 714, + 107 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Fig. 3 shows the architecture of trimap fusion module. It integrates the extracted memory features $F_{m}^{s}$ and the memory trimap $T_{m}$ into the memory value $F_{m}^{*}$ , which will be used to perform memory matching in the bottleneck fusion module. In general video object segmentation methods, the memory value is generated through an additional encoder (e.g. ResNet18 [19]) with a 4-channel input. Introducing another encoder leads to more parameters and a longer training time. Thus we construct a lightweight module to reduce the computation cost and parameters. Illuminated by DeepFillV2 [53], the gated convolutions are utilized instead of vanilla convolutions [23]. DeepFillV2 performs inpainting and requires a multiple-channel mask as an additional input. A gated convolution is composed of two vanilla convolutions, where one extracts features, and the other predicts scales followed by a sigmoid function. The results are then combined by an element-wise multiplication. The gated convolution makes different channels concentrate on different regions and enhances the performance of vanilla convolutions. The downsampled trimaps $T_{m}^{s}$ , memory features $F_{m}^{s}$ and output features $F_{m}^{*(s/2)}$ from the previous level are concatenated and passed through a gated convolution block $g^{s}$ :", + "bbox": [ + 496, + 113, + 893, + 465 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nF _ {m} ^ {* s} = \\left\\{ \\begin{array}{l l} g ^ {s} \\left(\\left[ T _ {m} ^ {s}, F _ {m} ^ {s} \\right]\\right) & \\text {i f} s = 2 \\\\ g ^ {s} \\left(\\left[ T _ {m} ^ {s}, F _ {m} ^ {s}, F _ {m} ^ {* (s / 2)} \\right]\\right) & \\text {i f} s = 4, 8, 1 6 \\end{array} \\right. \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 522, + 483, + 890, + 523 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $s$ represents the stride and $[\\cdot, \\cdot]$ denotes channel-wise concatenation. $F_{m}^{*16}$ is the final output memory value $F_{m}^{*}$ .", + "bbox": [ + 496, + 542, + 890, + 575 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.3. Bottleneck Fusion Module", + "text_level": 1, + "bbox": [ + 500, + 590, + 738, + 604 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The bottleneck fusion module consists of a memory matching module, a convolution block attention module (CBAM) [50] and a pyramid pooling module (PPM) [56]. Memory matching module applies the same mechanism of cross-attention as STCN [8]. The query feature $F_{q}^{16}$ and memory feature $F_{m}^{16}$ are first projected to the query key $K_{q} \\in \\mathbb{R}^{ch_{k} \\times hw}$ and memory key $K_{m} \\in \\mathbb{R}^{ch_{k} \\times hw}$ through a shared convolution. $h$ and $w$ are 1/16 of the original resolution, and the channel of keys $ch_{k}$ is 32. The memory values $F_{m}^{*16}$ from the trimap fusion module are linearly combined based on the similarity score between $K_{q}$ and $K_{m}$ to generate the matched memory values $F_{m}^{'16}$ . In addition, the CBAM [50] and PPM [56] are leveraged to integrate the features competently. CBAM scales the features spatially and channel-wisely to strengthen different features from $F_{q}^{16}$ and $F_{m}^{'16}$ . PPM aggregates the global context from sub-regions of different scales by GAPs (Global Average Pooling), where the scales are set to be 1, 2, 4, and 8, respectively.", + "bbox": [ + 496, + 613, + 893, + 901 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "14339", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/f919be1d16db05e9de3628b39c0ad8275ad7f8cfc3e69e276087bcbfaa2b7ed1.jpg", + "image_caption": [ + "Figure 2. The overall network architecture of FTP-VM." + ], + "image_footnote": [], + "bbox": [ + 150, + 99, + 823, + 289 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/036cab46cc905ce9e190234017bfb700e9510d66066504a2e3ff867661b211f7.jpg", + "image_caption": [ + "Figure 3. The trimap fusion module." + ], + "image_footnote": [], + "bbox": [ + 109, + 344, + 434, + 477 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.4. Decoders", + "text_level": 1, + "bbox": [ + 76, + 508, + 184, + 523 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "As GFM [28] claims that decoding semantic information and edge details simultaneously may harm the matting quality, the decoding part is split into two decoders, trimap segmentation and matting. For frame-to-frame propagation, ConvGRU [2] is efficient but lacks long-term context and probably loses track after occlusions. Thus we apply it with memory matching in the bottleneck fusion module to maintain both short-term and long-term temporal coherence. These decoders are designed differently to boost performance and efficiency as PSPM [13]. They are both composed of bilinear upsampling, convolution blocks and ConvGRUs. Each ConvGRU is placed after a convolution block and is only employed for half of the channels of the input feature maps.", + "bbox": [ + 75, + 532, + 470, + 744 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The trimap segmentation decoder estimates the probability maps with three classes and they are converted into a trimap by selecting the class with the highest probability for each pixel. Since the trimap usually retains fewer details, it is output at a stride of 4 and bilinearly upsampled to the original resolution for speed and stability. ConvGRUs are placed at the stride of 8 and 16. For the matting decoder, it estimates precise matts of the foreground in the boundary with high resolution. Moreover, it is expected to focus on", + "bbox": [ + 75, + 763, + 470, + 902 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "details, so it starts with features at the stride of 4. $F_T^{16}$ is upsampled to the stride of 4 and concatenated with $F_T^4$ , where $F_T^s$ denotes the feature obtained from the trimap decoder with a stride of $s$ . Then it is upsampled and receives skip-connection from $F_q^4$ and $F_q^2$ until the original resolution. Finally, the pixels in the unknown regions of the resulting trimaps are replaced with the corresponding alpha values in the boundary mattes to generate complete mattes.", + "bbox": [ + 496, + 342, + 893, + 465 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.5. Loss Function", + "text_level": 1, + "bbox": [ + 500, + 474, + 645, + 489 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Segmentation Loss. The focal loss [33] and consistency loss [38] are considered as the loss functions. The focal loss makes the training focus on the more challenging pixels. $p_c$ and $y_c$ are the predicted and ground truth probability that a pixel belongs to a class $c$ in the trimap, and $\\gamma$ is set to be 2.", + "bbox": [ + 496, + 497, + 892, + 574 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\text {f o c a l}} = - \\sum_ {c = 1} ^ {3} y _ {c} (1 - p _ {c}) ^ {\\gamma} \\log \\left(p _ {c}\\right) \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 578, + 579, + 890, + 619 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The consistency loss penalizes pixels with different predictions in consecutive frames. Those pixels are required to be correct in at least one frame of the consecutive pair to avoid interruption in the basic segmentation training. This design ensures that the trimap decoder utilizes the temporal information more appropriately. While the loss in [38] is only used for the correct class, we apply it to all the classes regardless of correctness because we discovered that different weights assigned to correct and wrong classes further improve the performance. The segmentation consistency loss is defined as:", + "bbox": [ + 496, + 630, + 893, + 797 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\text {c o n s i s}} = \\sum_ {c = 1} ^ {3} w _ {t, h, w, c} \\cdot \\left\\| p _ {t, h, w, c} - p _ {t + 1, h, w, c} \\right\\| _ {1} \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 537, + 801, + 890, + 842 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $w_{t,h,w,c} = \\left\\{ \\begin{array}{ll}0.5 & \\text{if } y_{t,h,w} = c \\\\ 0.25 & \\text{else} \\end{array} \\right.$ .", + "bbox": [ + 500, + 863, + 769, + 905 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "14340", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The final trimap segmentation loss is", + "bbox": [ + 76, + 90, + 323, + 106 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\text {t r i m a p}} = \\mathcal {L} _ {\\text {f o c a l}} + \\mathcal {L} _ {\\text {c o n s i s .}} \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 189, + 119, + 468, + 136 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Matting Loss. Following RVM [32], the same loss functions are exploited to train the matting network. However, we additionally input masks of the unknown regions to make the matting decoder focus on the boundary more. For the predicted and ground truth alpha matte $\\alpha_{t},\\alpha_{t}^{*}$ at time $t$ and the given mask $M$ , L1 loss $\\mathcal{L}_{l1}$ and pyramid Laplacian loss $\\mathcal{L}_{lap}$ [15, 20] is considered to learn the alpha values and edge details. A temporal coherence loss $\\mathcal{L}_{tc}$ [47] is adopted as well to reduce flickers.", + "bbox": [ + 75, + 145, + 472, + 282 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {l 1} (M) = \\| M \\cdot \\left(\\alpha_ {t} - \\alpha_ {t} ^ {*}\\right) \\| _ {1} \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 171, + 294, + 468, + 311 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {l a p} (M) = \\sum_ {s = 1} ^ {5} \\frac {2 ^ {s - 1}}{5} \\| M \\cdot \\left(L _ {p y r} ^ {s} \\left(\\alpha_ {t}\\right) - L _ {p y r} ^ {s} \\left(\\alpha_ {t} ^ {*}\\right)\\right) \\| _ {1} \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 84, + 337, + 468, + 377 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {t c} (M) = \\| M \\cdot \\left(\\frac {\\mathrm {d} \\alpha_ {t}}{\\mathrm {d} t} - \\frac {\\mathrm {d} \\alpha_ {t} ^ {*}}{\\mathrm {d} t}\\right) \\| _ {2} \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 161, + 392, + 468, + 422 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The overall alpha loss is defined as", + "bbox": [ + 76, + 436, + 312, + 453 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\alpha} (M) = \\mathcal {L} _ {l 1} (M) + \\mathcal {L} _ {l a p} (M) + 5 \\cdot \\mathcal {L} _ {t c} (M), \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 117, + 465, + 468, + 484 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "and it is applied to the unknown region of the predicted trimap $T_{U}$ and the ground truth trimap $T_{U}^{*}$ . The final matting loss is", + "bbox": [ + 75, + 503, + 468, + 549 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\text {m a t t i n g}} = \\mathcal {L} _ {\\alpha} \\left(T _ {U}\\right) + \\mathcal {L} _ {\\alpha} \\left(T _ {U} ^ {*}\\right). \\tag {10}\n$$\n", + "text_format": "latex", + "bbox": [ + 169, + 556, + 468, + 574 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Experiment", + "text_level": 1, + "bbox": [ + 76, + 595, + 202, + 613 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.1. Dataset, Metric and Implementation Detail", + "text_level": 1, + "bbox": [ + 76, + 619, + 444, + 637 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Training Dataset. The models are trained on the image matting dataset, D646 [37], the video matting dataset, VM108 [55], and the background image dataset, BG-20k [29]. D646 contains 546 training images, VM108 includes 80 clips, and BG-20k comprises 15000 background images without salient objects. The foregrounds from the matting datasets and the backgrounds from BG-20k and VM108 are composites to form the training data. Additionally, the video segmentation dataset, Youtube-VIS [52], is adopted to train the trimap segmentation to improve the generalizability of the model. Following RVM [32], the motion augmentation is applied, including affine transformation, color jittering, noise and blur, which differs gradually over time with an easing function. Frames of the matting datasets are randomly cropped to $480 \\times 480$ while frames of the segmentation dataset are cropped to $352 \\times 352$ for the larger batch size.", + "bbox": [ + 75, + 643, + 472, + 901 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Evaluation Dataset. The experiments are conducted on three matting datasets: VM108 [55], VM240k [31], and Real Human dataset [49]. VM108 contains 28 composited HD (1920 × 1080) clips with about 23000 frames in the validation set. Due to the variety of objects and the longer length of the sequences, it is chosen as the benchmark in ablation studies. VM240k is a composited human video matting dataset that includes 20 4K (3840 × 2160) videos, each containing 100 frames. Real Human has 19 real HD videos about humans having about 7000 frames in total, with only 1/10 frames annotated. By default, the trimap of the first frame is given to perform trimap propagation and the input resolution is set to be $1024 \\times 576$ . All trimaps are produced by discretizing the dilated ground truth alpha matrices where $25 \\times 25$ is chosen as the dilation kernel.", + "bbox": [ + 496, + 90, + 893, + 318 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Evaluation Metric. The same metrics as in RVM [32] are reported. MAD (mean absolute difference) represents the basic alpha error, MSE (mean square error) focuses on segmentation error, Grad [39] denotes the gradient error, Conn [39] (connectivity) depicts the completeness and dtSSD (mean square error of direct temporal gradient) [14] evaluates the temporal coherence such as flickering. For all metrics, the lower the better. In addition, the number of parameters and FPS (frames per second) of each model are also presented to evaluate efficiency. FPS is measured as FP32 tensor throughput and represents the speed.", + "bbox": [ + 496, + 335, + 893, + 503 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Implementation Detail. The codes for training are referenced to [7]. All models are trained by an Adam optimizer with a Cosine Annealing learning rate scheduler. The learning rate is set to 1e-4 initially. It takes 120000 iterations in total to train the model. 30000 iterations are required for the image matting dataset, and the remainings are for the video matting dataset. The video segmentation training is interleaved between every 30000 iterations for 10000 iterations. Training is performed on an NVIDIA RTX A6000 and inference is conducted on an NVIDIA RTX 2080Ti GPU.", + "bbox": [ + 496, + 520, + 893, + 686 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.2. Comparative Result", + "text_level": 1, + "bbox": [ + 500, + 696, + 691, + 712 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We compared FTP-VM against previous methods with trimap propagation, including STM+TCVOM [35, 55] and OTVM [42]. STM+TCVOM first produces trimaps via STM and performs video matting by TCVOM. The GCA decoder is applied in TCVOM. In addition, STM is finetuned on the memory trimap to generate better results for reference, denoted as STM(ft). OTVM adopts the memory trimap and predicted alpha mattes to perform trimap propagation. Moreover, RVM [32], a human video matting method, is compared on the human matting datasets, including VM240k and Real Human dataset. The model weights from the original implementation are", + "bbox": [ + 496, + 719, + 893, + 901 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "14341", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "applied, which are trained on the VM240k training set and a human segmentation dataset. For methods with trimap propagation, the numbers of parameters and speed are reported in Tab. 1. As previous approaches use two complete models to achieve different tasks, much more parameters are introduced. Instead, the FTP-VM combines two models along with a lightweight trimap fusion module so that the model size is significantly reduced, demonstrating that the FTP-VM outperforms other methods by a large margin in terms of efficiency.", + "bbox": [ + 75, + 90, + 472, + 243 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/9cfae20483e3dd62d883706129e28a82a72e03011cef7471e3d82950bb297fc7.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodParameters (M) ↓FPS ↑
Trimap PropagationMatting
STM + TCVOM [35,55]38.9225.715.11
OTVM [42]38.9834.904.32
FTP-VM (Ours)5.1340.16
", + "bbox": [ + 78, + 250, + 467, + 330 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Quantitative and Qualitative Results. Tab. 2 demonstrates the quantitative results on different datasets. For VM108, OTVM achieves the best and FTP-VM is the second best in the five metrics. Both STM+TCVOM and the finetuned one perform unsatisfactorily in this dataset. An example is illustrated in Fig. 4. Although FTP-VM produces false predictions in the boundary region, it is considered comparative due to the merit of speed.", + "bbox": [ + 75, + 373, + 472, + 494 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/a9b12fe0ab9f9d9282b360d63141bbd7014c6fb41ce8f70308428fdfe6996848.jpg", + "table_caption": [ + "Table 1. Comparison on the number of parameters and speed." + ], + "table_footnote": [], + "table_body": "
DatasetMethodMSE ↓MAD ↓Grad ↓dtSSD ↓Conn ↓
VM108 [55]TCVOM [55]68.4793.1218.294.5955.51
TCVOM* [55]31.5448.9810.373.7728.60
OTVM [42]2.9213.382.462.097.28
FTP-VM (Ours)5.1920.743.922.4612.13
VM240k [31]TCVOM [55]19.2521.5711.134.6912.54
TCVOM* [55]1.512.983.011.961.44
OTVM [42]0.564.551.631.320.74
RVM [32]3.027.714.271.832.64
FTP-VM (Ours)0.454.481.541.300.70
Real Human [49]TCVOM [55]34.5940.8114.2310.5624.09
TCVOM* [55]11.7216.4611.208.649.58
OTVM [42]18.1322.798.658.2413.49
RVM [32]2.385.874.865.153.29
FTP-VM (Ours)2.805.875.295.293.27
", + "bbox": [ + 81, + 503, + 467, + 681 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 2. The quantitative comparison. TCVOM denotes STM+TCVOM and * represents the finetuned model.", + "bbox": [ + 75, + 685, + 468, + 714 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "For VM240k, FTP-VM outperforms other methods in most metrics except MAD. Although RVM is trained on the VM240k dataset, it reveals limited advantage. Fig. 5 compares the qualitative results. STM+TCVOM fails to provide a reasonable result in this example but the finetuned version greatly improves. OTVM occasionally produces unsatisfactory results. Both RVM and FTP-VM generate complete mattes but FTP-VM contains more details.", + "bbox": [ + 75, + 724, + 468, + 847 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "The Real Human dataset which contains real-world videos is also evaluated. As seen from Tab. 2 and Fig. 6, the performance of OTVM drops drastically. Since OTVM", + "bbox": [ + 75, + 854, + 470, + 902 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/9c87f9ddd4a3f2e76d26ac848b33250728933127d7d3d4ebf44a09f742aead24.jpg", + "image_caption": [ + "Query Frame" + ], + "image_footnote": [], + "bbox": [ + 501, + 88, + 629, + 155 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/ac32077c05ae253ec478d3f0cca3c9375c143204b7c09d45ab77e0116c1e9690.jpg", + "image_caption": [ + "Ground Truth" + ], + "image_footnote": [], + "bbox": [ + 630, + 88, + 758, + 155 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/ff1d7743d0cf8795a2a004665184f7cd2a7094b7881e1e05dd2998338e4394e0.jpg", + "image_caption": [ + "FTP-VM (Ours)" + ], + "image_footnote": [], + "bbox": [ + 761, + 88, + 888, + 155 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/2f62924737ab0c79137887850140d7ab00f752bec655e636e62011201683234f.jpg", + "image_caption": [ + "STM+TCVOM" + ], + "image_footnote": [], + "bbox": [ + 501, + 169, + 629, + 237 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/1aaf2a40872456c7d895c16131813c02ea1a81d09788a71426421563eb6ac527.jpg", + "image_caption": [ + "STM(ft) + TCVOM" + ], + "image_footnote": [], + "bbox": [ + 630, + 169, + 758, + 237 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/200816f1e4ba603f977000464e933dba4fd5193b92319b3e187019f7ed6f70b2.jpg", + "image_caption": [ + "OTVM", + "Figure 4. The qualitative comparison on VM108." + ], + "image_footnote": [], + "bbox": [ + 759, + 169, + 887, + 237 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "includes larger models and requires more training data, it might lead to overfitting the composited dataset, resulting in a lack of generalizability. RVM and FTP-VM both provide pleasing results with a slight difference. In Fig. 6, STM(ft)+TCVOM can produce an acceptable result but the details are missing. OTVM fails to infer the complete shape of the target and the hair part needs to be correctly captured. If the hair parts are zoomed in, it is apparent that FTP-VM describes the details better than RVM. In summary, OTVM outperforms others on VM108 but its performance drops on the other two datasets. On the contrary, RVM provides the best performance on the Real Human dataset but not on others. Overall speaking, FTP-VM reaches competitive results in all the experiments, demonstrating that the proposed method retains generalizability at a low cost.", + "bbox": [ + 496, + 282, + 893, + 508 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/22f3ace51ada1148ff4ca4c4c0f1c5e9a9e1726f5206c1d961d6b06a82e90f83.jpg", + "image_caption": [ + "Figure 5. The qualitative comparison on VM240k." + ], + "image_footnote": [], + "bbox": [ + 503, + 515, + 888, + 811 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Trimap Updating Period. In this experiment, various trimap updating periods are tested to evaluate the efficiency of trimap propagation. Fig. 7 depicts the mechanism of", + "bbox": [ + 496, + 854, + 893, + 902 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "14342", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/7a6c363af483b07f3e9c2a6044db8a09a7d9e823dd60139dd77bf6bc48ba0f1e.jpg", + "image_caption": [ + "Query Frame" + ], + "image_footnote": [], + "bbox": [ + 176, + 88, + 370, + 148 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/8487e8ba9632c3811ac6acccf8c023e923f1e51c22ee6f7f1f051099747de3e2.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 81, + 162, + 133, + 222 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/cc38c6a77cf936b731d0d918c4d2d396efd1dba87754b83b7f5ee4cf847fc246.jpg", + "image_caption": [ + "Ground Truth" + ], + "image_footnote": [], + "bbox": [ + 151, + 162, + 205, + 222 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/a4980e20d96731a2b34a5a5a8558d24ee56f16a912fa7c339a79329c34d25710.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 218, + 162, + 272, + 222 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/ee7d3b2fdbe89283db34b0e688d08a2dae9a537ce48e7d1988abcd04a50a32df.jpg", + "image_caption": [ + "FTP-VM (Ours)" + ], + "image_footnote": [], + "bbox": [ + 274, + 162, + 326, + 222 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/badd58e8bc124734f2fd6b35c1c622f194cf63c230b29d7d5006d34f773d0b71.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 344, + 162, + 398, + 222 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/10d6f42bf978d2b4414d7fb83445afe064e2fb276216c74b2deb1690a4a38a8f.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 418, + 162, + 465, + 222 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/f1401e2a9d05bdbcf0afb7dd36963ee9bade33c9df9a6ec93f38bb246a7502a4.jpg", + "image_caption": [ + "STM+TCVOM" + ], + "image_footnote": [], + "bbox": [ + 81, + 236, + 178, + 296 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/fa9b73258a7a076968003519956af9875abe927a6e915193b1206d44acd00a20.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 207, + 236, + 272, + 296 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/1d0f1121f5fb503b27195f00cb16ea8aac07979844dee2db98f5cba68e3de049.jpg", + "image_caption": [ + "STM(ft) + TCVOM" + ], + "image_footnote": [], + "bbox": [ + 274, + 237, + 325, + 296 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/ba65928e6f51f37a7f1184ef600dafbfca45de09bebba1a88556996ae3ea5c7c.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 344, + 237, + 397, + 296 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/2792b9c6a442f5c08309242c2eb451b5e53ef0e5de47b5cf8926c6ff1b237291.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 416, + 237, + 465, + 296 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/e6df73193921af2412cf23d71ad7d827504c6ea39394d83e880b8378ef5d7373.jpg", + "image_caption": [ + "OTVM" + ], + "image_footnote": [], + "bbox": [ + 81, + 310, + 178, + 369 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/b9755f06f0f7ce21d152688e05e4b3f648a4ae7534874fdca490b9d3187e70a6.jpg", + "image_caption": [ + "Figure 6. The qualitative comparison on Real Human dataset." + ], + "image_footnote": [], + "bbox": [ + 179, + 310, + 204, + 369 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/f512232e51375c66b57f98bc0425bb1c96c048175af4635e1a915db8c8b8af55.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 207, + 310, + 271, + 369 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/438e467107b75188713b44ff8d82a9cc7e7350df3c13499a40c97ae881f0c51d.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 274, + 310, + 323, + 369 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/f2914dcb35484ee532f36321b278ca425eb5cfcf8167bd0170a96d359687bce9.jpg", + "image_caption": [ + "RVM" + ], + "image_footnote": [], + "bbox": [ + 344, + 310, + 397, + 369 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/9d93f94773fea6219003922dba85b627208b6008b3e9fc8c4e01798d469b5da7.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 419, + 310, + 465, + 369 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "trimap updates. For example, with period $= 30$ , the trimap is updated every thirty frames. With period $= 1$ , the trimap is given at each frame, meaning that the models only concern matting performance without any trimap propagation. This is the setting where the best performance is expected. On the contrary, if only the first trimap is provided, it will be propagated through the whole video. The bidirectional inference strategy is used in trimap propagation as [55].", + "bbox": [ + 75, + 415, + 468, + 537 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/971fd2127f07d6e165095ab7aa4cff76755b2ed12fdd6e110809c146eb61684e.jpg", + "image_caption": [ + "Figure 7. Trimap updating mechanism." + ], + "image_footnote": [], + "bbox": [ + 84, + 547, + 468, + 614 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "The comparison on VM108 with different trimap updating periods is illustrated in Fig. 8. It is clear that the shorter the period, the better the performance. While the performance of both FTP-VM and OTVM is not significantly affected by the period, OTVM performs the best overall. Regarding MAD, FTP-VM reveals more advantages when the period becomes longer. However, STM(ft) + TCVOM surpasses FTP-VM with a shorter period, which indicates that the matting ability limits the performance of the proposed method. As for dtSSD, FTP-VM also delivers its merit with fewer flickers when the period is more extended, confirming the stability of the proposed trimap propagation.", + "bbox": [ + 75, + 652, + 468, + 835 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.3. Ablation Study", + "text_level": 1, + "bbox": [ + 76, + 847, + 230, + 863 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Ablation on Network Design. In order to justify the network design of FTP-VM, the results of models with", + "bbox": [ + 75, + 869, + 468, + 900 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/99ba83aaaaa683e6f038ba514ef8c009a6db59ef3daa49edfe951e8af16fdb9d.jpg", + "image_caption": [ + "Figure 8. The comparison of MAD and dtSSD with various trimap updating periods." + ], + "image_footnote": [], + "bbox": [ + 501, + 90, + 697, + 183 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/71871bb6ba4f6aa8ee3df5c1d9c902d7e682aac1e76d35d47c0bce179c2887ef.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 700, + 90, + 897, + 183 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "different concepts are displayed in Tab. 3. Two-stage model is the baseline which has similar architecture to the previous works. After combining trimap propagation and matting into a single model, the performance slightly drops but the speed is boosted. Separating the decoder into trimap segmentation and matting decoders, as GFM [28] does, both MSE and MAD are enhanced but Grad and dtSSD degrade. For the same decoders utilizing the single features, it leads to fair stability. The best performance comes from the specially designed decoders, which is shown at the bottom of Tab. 3. The dtSSD does not outperform others, explaining that decoupling the decoder still harms the stability in some sense.", + "bbox": [ + 496, + 227, + 890, + 425 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/779c325cf51bafa7d7dad09fc67185795f701a105ad5c42069f9c412dc6481d2.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodParam ↓FPS ↑MSE ↓MAD ↓Grad ↓dtSSD ↓Conn ↓
2-stage network8.4631.718.8030.005.872.9018.18
Single network4.8250.0710.2130.163.982.3017.24
Same decoders5.4437.339.7228.425.532.8017.51
Different decoders5.1340.165.1920.743.922.4612.13
", + "bbox": [ + 503, + 431, + 888, + 497 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Ablation on the Trimap Fusion Module. The trimap fusion module is designed to avoid introducing an additional backbone, which encodes memory frames and trimaps from scratch. As can be seen from Tab. 4, the additional backbone introduces the most parameters. The vanilla convolution improves efficiency and performance by integrating features from different levels. The gated convolution enables different channels to focus on distinct regions, so it outperforms others in all metrics with slightly increased parameters.", + "bbox": [ + 496, + 551, + 890, + 705 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/1736a522fd3f82f45b918bf6300922835d97e8e58b4f6b3428425d419ee32bfd.jpg", + "table_caption": [ + "Table 3. Ablation on the network designs. Param denotes the number of parameters (M)." + ], + "table_footnote": [], + "table_body": "
MethodParam ↓MSE ↓MAD ↓Grad ↓dtSSD ↓Conn ↓
Additional backbone7.5911.3430.755.722.8217.81
Vanilla convolution4.948.1224.74.872.7613.75
Gated convolution5.135.1920.743.922.4612.13
", + "bbox": [ + 503, + 710, + 890, + 771 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 4. Ablation on trimap fusion module. Param denotes the number of parameters (M). FPS is not reported since the trimap fusion does not operate at every frame.", + "bbox": [ + 498, + 775, + 890, + 816 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Ablation on Segmentation Consistency Loss. The segmentation consistency loss attempts to encourage the trimap segmentation employing information from previous frames. The results shown in Tab. 5 clearly exhibit the", + "bbox": [ + 498, + 839, + 890, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "14343", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "improvement of temporal consistency. If consistency loss is applied to all the classes, the performance degrades slightly. However, with the strategy of weighting the loss according to the correctness, the results are further enhanced at little cost in sharpness (Grad) and stability (dtSSD).", + "bbox": [ + 75, + 90, + 472, + 167 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/2c1a2469890fe8150c220b53b62aebb35847c78a48d2a3cd8956109a817c0749.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodMSE ↓MAD ↓Grad ↓dtSSD ↓Conn ↓
w/o consistency11.6628.544.432.4017.35
correct class only6.1923.333.752.2813.45
all classes8.7524.644.082.4514.26
all classes w/ weight5.1920.743.922.4612.13
", + "bbox": [ + 84, + 172, + 467, + 253 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 5. Ablation on the trimap segmentation consistency loss.", + "bbox": [ + 84, + 258, + 460, + 272 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.4. Discussion", + "text_level": 1, + "bbox": [ + 76, + 285, + 194, + 300 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In Fig. 9, suppose the memory trimap aims at the left person. FTP-VM provides a correct result but OTVM attempts to matte all the people. This is due to overfitting on the composited dataset where salient objects are selected as the foreground. Moreover, STM-based methods such as OTVM store the resulting masks to maintain temporal coherence during memory matching. In other words, memory matching operates globally and cannot regularize the pixels spatially, which results in weaker coherence. FTP-VM adopts ConvGRU to preserve coherence and performs better.", + "bbox": [ + 75, + 309, + 472, + 474 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/28978fb7fba3c70f2bfbdae808433dbb3eef9a0e0d3617aafe75f3ec11a36e46.jpg", + "image_caption": [ + "Memory Frame" + ], + "image_footnote": [], + "bbox": [ + 78, + 483, + 271, + 561 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/f504d607def775a2727739e4a508e584d25ce665ad163e0a0b78197bdd783023.jpg", + "image_caption": [ + "Query Frame" + ], + "image_footnote": [], + "bbox": [ + 272, + 483, + 465, + 560 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/21c60381ed39a689e554a9a31b979e367da52be0a5e9298a137353ed69b12296.jpg", + "image_caption": [ + "Memory Trimap" + ], + "image_footnote": [], + "bbox": [ + 176, + 575, + 370, + 652 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/7a60943305a6fcbdadf153b750c940c3a5bd5df87f67efd203f39d797395fe91.jpg", + "image_caption": [ + "OTVM", + "Figure 9. The qualitative comparison between OTVM and FTP-VM on the target selection of the human video." + ], + "image_footnote": [], + "bbox": [ + 80, + 667, + 272, + 744 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/a41d8b3284784ed34eae0b2005ae89552661d3fcdfd04c13956caad4453eaf1b.jpg", + "image_caption": [ + "FTP-VM (Ours)" + ], + "image_footnote": [], + "bbox": [ + 274, + 667, + 465, + 744 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "However, there remain some challenging cases as shown in Fig. 10. In the memory frame, there are four people in total; the leftmost is out of the screen. With the memory trimap aiming at three people on the right side, the model mattes them successfully at $t = 55$ (Fig. 10b). However, the video is zoomed in as considered a scene change at", + "bbox": [ + 75, + 803, + 470, + 893 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "$t = 65$ (Fig. 10c), which breaks the temporal coherence in ConvGRUs so that the result is unsatisfactory. The error will be reduced over time when reconstructing the temporal coherence gradually. Furthermore, the leftmost person at $t = 200$ (Fig. 10d) cannot be well removed. Since the memory frame only contains his jacket, the memory cannot recognize his face and clothes. As a result, the ambiguity degrades the result. It is known that dealing with unseen objects and scene changes is challenging for memory matching, requiring further discussions and explorations.", + "bbox": [ + 496, + 90, + 892, + 243 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/e9d4174e360e282b2ce43e2a037bc000f5cc6a5280da38a178a3b443742b9973.jpg", + "image_caption": [ + "(a) $t = 0$ (Memory frame and trimap)" + ], + "image_footnote": [], + "bbox": [ + 501, + 250, + 694, + 334 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/ecfa230601e4402c8b1ad378062d66c9007aadf1ebe400fa68f1cbe362583aca.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 696, + 250, + 887, + 334 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "$= 0$ (Memory frame and trimap)", + "bbox": [ + 625, + 335, + 795, + 348 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/5aac8538237766a536178c4c720da7b12dd52fc8c93d4092f794eb2233bef4fe.jpg", + "image_caption": [ + "(b) $t = 55$ (Normal result)" + ], + "image_footnote": [], + "bbox": [ + 501, + 349, + 694, + 433 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/4725efc555813efb23ad48e30b151c82dc99697d456aadbd010d65bc00fcb613.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 694, + 349, + 887, + 433 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/1e68ed8567ff5be206c4a733261a39f718c0c35924bac71f99e1c4612b024e15.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 602, + 448, + 691, + 532 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/bf0e0d0b93764ec371bad0044b8e975a7badb74b0d1239061f3298b6471aabe6.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 696, + 448, + 887, + 532 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/195bb6e24fc10107f89eb12899808f44c0995dbf234545eb6a35a4638d14e01b.jpg", + "image_caption": [ + "(c) $t = 65$ (Temporal incoherence)", + "(d) $t = 200$ (Unseen object)", + "Figure 10. Challenging cases. Left: query frames. Right: results." + ], + "image_footnote": [], + "bbox": [ + 501, + 547, + 694, + 632 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/040e88e55e13c0bca107c5153205e15e7e7177ec7df96d20177e1cf3a68104f4.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 694, + 547, + 887, + 632 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 684, + 619, + 699 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "FTP-VM, a novel end-to-end video matting model with trimap propagation, is proposed in this paper. The designed lightweight trimap fusion module is introduced to propagate the given trimap in the memory matching. Moreover, the segmentation consistency loss is adopted to fit trimap segmentation better and improve the performance. The proposed FTP-VM reaches 40 FPS, eight times faster than the cutting-edge two-model methods, TCVOM and OTVM. Extensive experiments are conducted to confirm the competitive performance in various scenarios. Its robustness and generalizability provide the foundation for more advanced developments and broader applications.", + "bbox": [ + 496, + 709, + 892, + 891 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "14344", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Nicholas Apostoloff and Andrew Fitzgibbon. Bayesian video matting using learnt image priors. In Proceedings of the 2004 IEEE Computer Society Conference on Computer Vision and Pattern Recognition, 2004. CVPR 2004., volume 1, pages I-I. IEEE, 2004. 2", + "[2] Nicolas Ballas, Li Yao, Chris Pal, and Aaron Courville. 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In Proceedings of the IEEE conference on computer vision and pattern recognition, pages 2881-2890, 2017. 3", + "bbox": [ + 78, + 90, + 470, + 148 + ], + "page_idx": 10 + }, + { + "type": "page_number", + "text": "14347", + "bbox": [ + 480, + 945, + 519, + 955 + ], + "page_idx": 10 + } +] \ No newline at end of file diff --git a/2023/End-to-End Video Matting With Trimap Propagation/5671e405-73cb-4243-be20-91144c26868b_model.json b/2023/End-to-End Video Matting With Trimap Propagation/5671e405-73cb-4243-be20-91144c26868b_model.json new file mode 100644 index 0000000000000000000000000000000000000000..d90858e7501f358c7c4be89022b73ba0195afde2 --- /dev/null +++ b/2023/End-to-End Video Matting With Trimap Propagation/5671e405-73cb-4243-be20-91144c26868b_model.json @@ -0,0 +1,2884 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.001, + 0.808, + 0.045 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.221, + 0.131, + 0.75, + 0.154 + ], + "angle": 0, + "content": "End-to-end Video Matting with Trimap Propagation" + }, + { + "type": "text", + "bbox": [ + 0.235, + 0.182, + 0.455, + 0.233 + ], + "angle": 0, + "content": "Wei-Lun Huang National Taiwan University r09944040@csie.ntu.edu.tw" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.256, + 0.313, + 0.272 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.296, + 0.474, + 0.645 + ], + "angle": 0, + "content": "The research of video matting mainly focuses on temporal coherence and has gained significant improvement via neural networks. However, matting usually relies on user-annotated trimaps to estimate alpha values, which is a labor-intensive issue. Although recent studies exploit video object segmentation methods to propagate the given trimaps, they suffer inconsistent results. Here we present a more robust and faster end-to-end video matting model equipped with trimap propagation called FTP-VM (Fast Trimap Propagation - Video Matting). The FTP-VM combines trimap propagation and video matting in one model, where the additional backbone in memory matching is replaced with the proposed lightweight trimap fusion module. The segmentation consistency loss is adopted from automotive segmentation to fit trimap segmentation with the collaboration of RNN (Recurrent Neural Network) to improve the temporal coherence. The experimental results demonstrate that the FTP-VM performs competitively both in composited and real videos only with few given trimaps. The efficiency is eight times higher than the state-of-the-art methods, which confirms its robustness and applicability in real-time scenarios. The code is available at https://github.com/csvt32745/FTP-VM." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.672, + 0.21, + 0.687 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.697, + 0.47, + 0.834 + ], + "angle": 0, + "content": "Image matting aims to estimate the alpha value of each pixel for a target in the input image. Unlike general segmentation, which generates binary values, matting outputs values between 0 and 1, meaning the degree of transparency. The output alpha matrices can describe semi-transparent objects with precise details. As shown in Eq. (1), each pixel color \\(C\\) of an image is composited by the foreground color \\(F\\), background color \\(B\\), and an alpha value \\(\\alpha\\), where the background can be substituted to generate a matting dataset." + }, + { + "type": "equation", + "bbox": [ + 0.199, + 0.848, + 0.469, + 0.864 + ], + "angle": 0, + "content": "\\[\nC = \\alpha F + (1 - \\alpha) B \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.871, + 0.47, + 0.902 + ], + "angle": 0, + "content": "Given a frame like Fig. 1a, a trimap Fig. 1b is the common requirement for image matting, which divides the pixels" + }, + { + "type": "text", + "bbox": [ + 0.516, + 0.182, + 0.737, + 0.233 + ], + "angle": 0, + "content": "Ming-Sui Lee \nNational Taiwan University \nmslee@csie.ntu.edu.tw" + }, + { + "type": "image", + "bbox": [ + 0.504, + 0.255, + 0.697, + 0.34 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.551, + 0.343, + 0.65, + 0.354 + ], + "angle": 0, + "content": "(a) Memory frame" + }, + { + "type": "image", + "bbox": [ + 0.698, + 0.256, + 0.891, + 0.34 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.741, + 0.343, + 0.846, + 0.354 + ], + "angle": 0, + "content": "(b) Memory trimap" + }, + { + "type": "image", + "bbox": [ + 0.506, + 0.355, + 0.698, + 0.439 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.559, + 0.442, + 0.645, + 0.453 + ], + "angle": 0, + "content": "(c) Query frame" + }, + { + "type": "image", + "bbox": [ + 0.698, + 0.356, + 0.888, + 0.439 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.722, + 0.442, + 0.866, + 0.453 + ], + "angle": 0, + "content": "(d) The result of RVM [32]" + }, + { + "type": "image", + "bbox": [ + 0.508, + 0.454, + 0.697, + 0.537 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.525, + 0.539, + 0.678, + 0.551 + ], + "angle": 0, + "content": "(e) The result of OTVM [42]" + }, + { + "type": "image", + "bbox": [ + 0.698, + 0.454, + 0.887, + 0.537 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.706, + 0.539, + 0.877, + 0.55 + ], + "angle": 0, + "content": "(f) The result of FTP-VM (ours)" + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.557, + 0.892, + 0.599 + ], + "angle": 0, + "content": "Figure 1. An example of an in-street interview video. (d) Automatic matting, (e) Trimap-propagation-based method (f) The proposed method." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.61, + 0.892, + 0.657 + ], + "angle": 0, + "content": "into three regions: foreground, background and unknown. Matting methods adopt such information to solve alpha values of unknown (gray) regions." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.665, + 0.893, + 0.846 + ], + "angle": 0, + "content": "Video matting extracts an alpha matte of each frame of the given video. The resulting alpha mattes can be used for background replacement, which is decisive for video applications such as video conferencing and visual effects. It is intuitive to perform image matting on each frame of a video. However, severe flickering artifacts would occur in the resultant image sequence. In order to improve the robustness, considering spatial and temporal coherence is the main challenge for video matting as the temporal information helps infer the matting target from the previous frames. Another challenge is to provide a trimap for each frame, which is expected to be a massive cost to most users." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.856, + 0.894, + 0.901 + ], + "angle": 0, + "content": "To tackle the above two issues, automatic matting and trimap propagation are addressed in this paper. Automatic matting captures specific targets without trimaps, but" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "14337" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.471, + 0.213 + ], + "angle": 0, + "content": "the input videos with ambiguous scenarios highly affect the results. Fig. 1 shows an example of an in-street interview video where an interviewee and passengers occasionally appear simultaneously. While the human matting method [32] attempts to capture all the people, the ambiguity caused by inconspicuous passengers results in unsatisfactory output Fig. 1d. Thus we opt for trimap propagation to select targets more stably as shown in Fig. 1f." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.221, + 0.471, + 0.493 + ], + "angle": 0, + "content": "While performing trimap propagation, the user is required to provide a pair of so-called memory frame Fig. 1a and memory trimap Fig. 1b, and this information is utilized to propagate throughout the video. Since we are predicting a sequence of three-class segmentation masks, the trimap propagation can be treated as video object segmentation. Recent studies [42, 47, 55] leverage STM (Space-Time Memory network), [35] an emerging video object segmentation model, to produce the trimaps successfully. However, the resultant trimaps usually contain flickers and lead to unsatisfactory results. As STM lacks temporal coherence, we append ConvGRUs [2] to the model to improve stability. Moreover, the previous approaches containing two full models make them unsuitable for interactive applications. We thus combine the two models into an end-to-end model to enhance the speed and performance. The main contributions of this work are summarized as follows." + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.502, + 0.47, + 0.623 + ], + "angle": 0, + "content": "- A novel end-to-end video matting model equipped with trimap propagation, called FTP-VM (Fast Trimap Propagation - Video Matting), is proposed. FTP-VM is faster than the previous two-model methods by a large margin while preserving competitive performance in different scenarios. While the frame rate of the previous methods is 5 FPS, the proposed method reaches 40 FPS on an NVIDIA RTX 2080Ti GPU." + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.632, + 0.469, + 0.678 + ], + "angle": 0, + "content": "- A lightweight trimap fusion module is designed to replace an additional encoder in the STM-based model to make FTP-VM efficient and more powerful." + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.687, + 0.469, + 0.762 + ], + "angle": 0, + "content": "- Motivated by [38], the segmentation consistency loss from automotive segmentation is adapted to trimap segmentation. The final setting reaching the more satisfactory performance is determined by conducting comprehensive experiments." + }, + { + "type": "list", + "bbox": [ + 0.096, + 0.502, + 0.47, + 0.762 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.777, + 0.221, + 0.793 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.802, + 0.229, + 0.818 + ], + "angle": 0, + "content": "2.1. Image Matting" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.825, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Non-deep-learning image matting includes two types of methods: The sampling-based approaches [12,16,18,44,48] construct the foreground and background priors, and infer the alpha values by solving the composition equation. The affinity-based methods [4,5,17,24-26,46] propagate the" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.273 + ], + "angle": 0, + "content": "alpha values from known pixels to unknown ones according to similarities under the assumption of local smoothness. These classical methods rely on low-level representations and often require assistance to deal with complex scenes. For deep-learning methods, CNN (Convolution Neural Network) based methods [9, 15, 20, 23, 30, 34, 51] exploit high-level features and achieve state-of-the-art results. Vision-transformer-based methods [36] are emerging by combining global similarity and inductive bias of images. These methods build prior from the extracted features or the similarity to estimate the alpha values and preserve details by the UNet-like [40] architecture." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.288, + 0.892, + 0.44 + ], + "angle": 0, + "content": "In order to annihilate the need for trimaps, automatic image matting combines segmentation and matting into one task. It aims to matte specific targets such as humans [21, 45] or salient objects [3, 28, 29, 37] without any auxiliary inputs. Mask-guided matting [54] takes a rough segmentation mask as an additional input followed by refinement. However, it cannot process semi-transparent objects due to the binary masks. Background-based methods [31, 41] require a background image instead of a trimap as an auxiliary input so that it needs to handle misaligned backgrounds better." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.455, + 0.649, + 0.472 + ], + "angle": 0, + "content": "2.2. Video Matting" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.479, + 0.892, + 0.691 + ], + "angle": 0, + "content": "Temporal coherence plays an essential role in video matting. Most existing methods [1, 10, 27, 43] extend classical image matting methods to the temporal dimension and encounter a similar weakness. RVM [32] places ConvGRU hierarchically to maintain temporal coherency. It performs in real-time due to the efficiency of ConvGRU. DVM [47] uses deformable convolution to warp the feature temporally by estimated offsets but is limited by the kernel size of convolutions. TCVOM [55] leverages guided attention block to compute affinity between frames, and [49] analyzes inter-frame relationships by graph neural network. [21] reduces the flickers by applying post-processing tricks to the results, but the image matting methods still limit the performance." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.705, + 0.892, + 0.903 + ], + "angle": 0, + "content": "For trimap propagation, [11] interpolates trimaps by optical flows and contains restrictions caused by weak low-level features from semi-transparent objects. Recent deep-learning-based methods [47, 55] leverage approaches from video object segmentation to perform trimap segmentation before video matting. Decoupling trimap propagation and video matting simplifies the problem and forms a two-stage method. However, the model sometimes needs to be finetuned based on the given trimaps to generate acceptable results. OTVM [42] further improves performance through multi-stage training and joint trimap and alpha prediction modeling. The joint modeling utilizes alpha mattes and trimaps to perform trimap propagation." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "14338" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.078, + 0.091, + 0.325, + 0.108 + ], + "angle": 0, + "content": "2.3. Video Object Segmentation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.114, + 0.473, + 0.433 + ], + "angle": 0, + "content": "Trimap propagation is a kind of video object segmentation in a semi-supervised setting. The model receives masks of a few frames as auxiliary inputs to hint targets and predicts masks of the remaining frames. After the success of STM [35], different memory matching based methods emerge. Memory matching uses a variant of self-attention to extract the features from the given masks. With frames to predict, called query, and pairs of frames and masks, called memory, the features from the memories are linearly combined based on the similarity between memory and query. If a pixel has a similar context to another one, its similarity score will be high. Thus STM can effectively capture the correspondence and segment the target correctly. STCN (Space-Time Correspondence Network) [8] decouples the relation between frames and masks in the memory encoder to become more efficient and effective. We leverage the similar mechanic of STCN to propagate the trimaps but with a more efficient module. In addition, neither STM nor STCN has a strong temporal correlation between consecutive frames, so ConvGRU [2] is appended to our model to strengthen the temporal coherence as XMem [6]." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.448, + 0.17, + 0.463 + ], + "angle": 0, + "content": "3. Method" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.473, + 0.473, + 0.655 + ], + "angle": 0, + "content": "The overall network architecture containing an encoder, trimap fusion module, bottleneck fusion module, and two corresponding decoders is illustrated in Fig. 2. The encoder extracts features from the memory frame \\( I_{m} \\) and query frame \\( I_{q} \\). The trimap fusion module encodes the memory trimap \\( T_{m} \\) and memory features into memory values. The bottleneck fusion module propagates the trimap information to the query frame and aggregates the features globally. The decoders contain segmentation and matting decoders to estimate the trimap and boundary matte, respectively. Finally, the resulting trimap and boundary matte are integrated into a complete matte." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.666, + 0.18, + 0.681 + ], + "angle": 0, + "content": "3.1. Encoder" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.689, + 0.473, + 0.903 + ], + "angle": 0, + "content": "The MobileNetV3-Large [22] is adopted as the encoder for its efficiency. The encoder takes a single image as input and extracts features at strides of 2, 4, 8 and 16, respectively. The receptive fields are larger in deeper stages, which makes features at different strides focus on different tasks. The low-level features are for preserving details, while high-level ones are for inferring the matting target. This kind of hierarchy can be employed as an UNet-like structure [40] where it receives skip-connections of the features to avoid information diminishing due to the deeper networks. \\( I_{m} \\) and \\( I_{q} \\) are passed through the same encoder to reduce the size of the model to enhance efficiency. The extracted memory and query features are denoted as \\( F_{m}^{s} \\) and \\( F_{q}^{s} \\) where \\( s \\) represents the stride of the feature." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.091, + 0.715, + 0.108 + ], + "angle": 0, + "content": "3.2. Trimap Fusion Module" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.114, + 0.895, + 0.466 + ], + "angle": 0, + "content": "Fig. 3 shows the architecture of trimap fusion module. It integrates the extracted memory features \\( F_{m}^{s} \\) and the memory trimap \\( T_{m} \\) into the memory value \\( F_{m}^{*} \\), which will be used to perform memory matching in the bottleneck fusion module. In general video object segmentation methods, the memory value is generated through an additional encoder (e.g. ResNet18 [19]) with a 4-channel input. Introducing another encoder leads to more parameters and a longer training time. Thus we construct a lightweight module to reduce the computation cost and parameters. Illuminated by DeepFillV2 [53], the gated convolutions are utilized instead of vanilla convolutions [23]. DeepFillV2 performs inpainting and requires a multiple-channel mask as an additional input. A gated convolution is composed of two vanilla convolutions, where one extracts features, and the other predicts scales followed by a sigmoid function. The results are then combined by an element-wise multiplication. The gated convolution makes different channels concentrate on different regions and enhances the performance of vanilla convolutions. The downsampled trimaps \\( T_{m}^{s} \\), memory features \\( F_{m}^{s} \\) and output features \\( F_{m}^{*(s/2)} \\) from the previous level are concatenated and passed through a gated convolution block \\( g^{s} \\):" + }, + { + "type": "equation", + "bbox": [ + 0.524, + 0.484, + 0.892, + 0.524 + ], + "angle": 0, + "content": "\\[\nF _ {m} ^ {* s} = \\left\\{ \\begin{array}{l l} g ^ {s} \\left(\\left[ T _ {m} ^ {s}, F _ {m} ^ {s} \\right]\\right) & \\text {i f} s = 2 \\\\ g ^ {s} \\left(\\left[ T _ {m} ^ {s}, F _ {m} ^ {s}, F _ {m} ^ {* (s / 2)} \\right]\\right) & \\text {i f} s = 4, 8, 1 6 \\end{array} \\right. \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.543, + 0.892, + 0.577 + ], + "angle": 0, + "content": "where \\(s\\) represents the stride and \\([\\cdot, \\cdot]\\) denotes channel-wise concatenation. \\(F_{m}^{*16}\\) is the final output memory value \\(F_{m}^{*}\\)." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.591, + 0.74, + 0.606 + ], + "angle": 0, + "content": "3.3. Bottleneck Fusion Module" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.614, + 0.895, + 0.902 + ], + "angle": 0, + "content": "The bottleneck fusion module consists of a memory matching module, a convolution block attention module (CBAM) [50] and a pyramid pooling module (PPM) [56]. Memory matching module applies the same mechanism of cross-attention as STCN [8]. The query feature \\( F_{q}^{16} \\) and memory feature \\( F_{m}^{16} \\) are first projected to the query key \\( K_{q} \\in \\mathbb{R}^{ch_{k} \\times hw} \\) and memory key \\( K_{m} \\in \\mathbb{R}^{ch_{k} \\times hw} \\) through a shared convolution. \\( h \\) and \\( w \\) are 1/16 of the original resolution, and the channel of keys \\( ch_{k} \\) is 32. The memory values \\( F_{m}^{*16} \\) from the trimap fusion module are linearly combined based on the similarity score between \\( K_{q} \\) and \\( K_{m} \\) to generate the matched memory values \\( F_{m}^{'16} \\). In addition, the CBAM [50] and PPM [56] are leveraged to integrate the features competently. CBAM scales the features spatially and channel-wisely to strengthen different features from \\( F_{q}^{16} \\) and \\( F_{m}^{'16} \\). PPM aggregates the global context from sub-regions of different scales by GAPs (Global Average Pooling), where the scales are set to be 1, 2, 4, and 8, respectively." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "14339" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.151, + 0.1, + 0.825, + 0.29 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.319, + 0.303, + 0.651, + 0.318 + ], + "angle": 0, + "content": "Figure 2. The overall network architecture of FTP-VM." + }, + { + "type": "image", + "bbox": [ + 0.11, + 0.345, + 0.436, + 0.478 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.163, + 0.485, + 0.383, + 0.5 + ], + "angle": 0, + "content": "Figure 3. The trimap fusion module." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.51, + 0.186, + 0.525 + ], + "angle": 0, + "content": "3.4. Decoders" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.533, + 0.471, + 0.745 + ], + "angle": 0, + "content": "As GFM [28] claims that decoding semantic information and edge details simultaneously may harm the matting quality, the decoding part is split into two decoders, trimap segmentation and matting. For frame-to-frame propagation, ConvGRU [2] is efficient but lacks long-term context and probably loses track after occlusions. Thus we apply it with memory matching in the bottleneck fusion module to maintain both short-term and long-term temporal coherence. These decoders are designed differently to boost performance and efficiency as PSPM [13]. They are both composed of bilinear upsampling, convolution blocks and ConvGRUs. Each ConvGRU is placed after a convolution block and is only employed for half of the channels of the input feature maps." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.765, + 0.471, + 0.903 + ], + "angle": 0, + "content": "The trimap segmentation decoder estimates the probability maps with three classes and they are converted into a trimap by selecting the class with the highest probability for each pixel. Since the trimap usually retains fewer details, it is output at a stride of 4 and bilinearly upsampled to the original resolution for speed and stability. ConvGRUs are placed at the stride of 8 and 16. For the matting decoder, it estimates precise matts of the foreground in the boundary with high resolution. Moreover, it is expected to focus on" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.343, + 0.895, + 0.466 + ], + "angle": 0, + "content": "details, so it starts with features at the stride of 4. \\( F_T^{16} \\) is upsampled to the stride of 4 and concatenated with \\( F_T^4 \\), where \\( F_T^s \\) denotes the feature obtained from the trimap decoder with a stride of \\( s \\). Then it is upsampled and receives skip-connection from \\( F_q^4 \\) and \\( F_q^2 \\) until the original resolution. Finally, the pixels in the unknown regions of the resulting trimaps are replaced with the corresponding alpha values in the boundary mattes to generate complete mattes." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.475, + 0.646, + 0.49 + ], + "angle": 0, + "content": "3.5. Loss Function" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.498, + 0.893, + 0.575 + ], + "angle": 0, + "content": "Segmentation Loss. The focal loss [33] and consistency loss [38] are considered as the loss functions. The focal loss makes the training focus on the more challenging pixels. \\( p_c \\) and \\( y_c \\) are the predicted and ground truth probability that a pixel belongs to a class \\( c \\) in the trimap, and \\( \\gamma \\) is set to be 2." + }, + { + "type": "equation", + "bbox": [ + 0.579, + 0.58, + 0.892, + 0.62 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\text {f o c a l}} = - \\sum_ {c = 1} ^ {3} y _ {c} (1 - p _ {c}) ^ {\\gamma} \\log \\left(p _ {c}\\right) \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.631, + 0.895, + 0.798 + ], + "angle": 0, + "content": "The consistency loss penalizes pixels with different predictions in consecutive frames. Those pixels are required to be correct in at least one frame of the consecutive pair to avoid interruption in the basic segmentation training. This design ensures that the trimap decoder utilizes the temporal information more appropriately. While the loss in [38] is only used for the correct class, we apply it to all the classes regardless of correctness because we discovered that different weights assigned to correct and wrong classes further improve the performance. The segmentation consistency loss is defined as:" + }, + { + "type": "equation", + "bbox": [ + 0.538, + 0.803, + 0.892, + 0.843 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\text {c o n s i s}} = \\sum_ {c = 1} ^ {3} w _ {t, h, w, c} \\cdot \\left\\| p _ {t, h, w, c} - p _ {t + 1, h, w, c} \\right\\| _ {1} \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.864, + 0.771, + 0.906 + ], + "angle": 0, + "content": "where \\(w_{t,h,w,c} = \\left\\{ \\begin{array}{ll}0.5 & \\text{if } y_{t,h,w} = c \\\\ 0.25 & \\text{else} \\end{array} \\right.\\)." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "14340" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.078, + 0.092, + 0.325, + 0.107 + ], + "angle": 0, + "content": "The final trimap segmentation loss is" + }, + { + "type": "equation", + "bbox": [ + 0.19, + 0.121, + 0.47, + 0.137 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\text {t r i m a p}} = \\mathcal {L} _ {\\text {f o c a l}} + \\mathcal {L} _ {\\text {c o n s i s .}} \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.146, + 0.473, + 0.283 + ], + "angle": 0, + "content": "Matting Loss. Following RVM [32], the same loss functions are exploited to train the matting network. However, we additionally input masks of the unknown regions to make the matting decoder focus on the boundary more. For the predicted and ground truth alpha matte \\(\\alpha_{t},\\alpha_{t}^{*}\\) at time \\(t\\) and the given mask \\(M\\), L1 loss \\(\\mathcal{L}_{l1}\\) and pyramid Laplacian loss \\(\\mathcal{L}_{lap}\\) [15, 20] is considered to learn the alpha values and edge details. A temporal coherence loss \\(\\mathcal{L}_{tc}\\) [47] is adopted as well to reduce flickers." + }, + { + "type": "equation", + "bbox": [ + 0.173, + 0.295, + 0.47, + 0.313 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {l 1} (M) = \\| M \\cdot \\left(\\alpha_ {t} - \\alpha_ {t} ^ {*}\\right) \\| _ {1} \\tag {6}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.085, + 0.338, + 0.47, + 0.378 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {l a p} (M) = \\sum_ {s = 1} ^ {5} \\frac {2 ^ {s - 1}}{5} \\| M \\cdot \\left(L _ {p y r} ^ {s} \\left(\\alpha_ {t}\\right) - L _ {p y r} ^ {s} \\left(\\alpha_ {t} ^ {*}\\right)\\right) \\| _ {1} \\tag {7}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.162, + 0.393, + 0.47, + 0.423 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {t c} (M) = \\| M \\cdot \\left(\\frac {\\mathrm {d} \\alpha_ {t}}{\\mathrm {d} t} - \\frac {\\mathrm {d} \\alpha_ {t} ^ {*}}{\\mathrm {d} t}\\right) \\| _ {2} \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.438, + 0.313, + 0.454 + ], + "angle": 0, + "content": "The overall alpha loss is defined as" + }, + { + "type": "equation", + "bbox": [ + 0.119, + 0.466, + 0.47, + 0.485 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\alpha} (M) = \\mathcal {L} _ {l 1} (M) + \\mathcal {L} _ {l a p} (M) + 5 \\cdot \\mathcal {L} _ {t c} (M), \\tag {9}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.504, + 0.47, + 0.55 + ], + "angle": 0, + "content": "and it is applied to the unknown region of the predicted trimap \\( T_{U} \\) and the ground truth trimap \\( T_{U}^{*} \\). The final matting loss is" + }, + { + "type": "equation", + "bbox": [ + 0.17, + 0.558, + 0.47, + 0.575 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\text {m a t t i n g}} = \\mathcal {L} _ {\\alpha} \\left(T _ {U}\\right) + \\mathcal {L} _ {\\alpha} \\left(T _ {U} ^ {*}\\right). \\tag {10}\n\\]" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.596, + 0.204, + 0.614 + ], + "angle": 0, + "content": "4. Experiment" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.621, + 0.445, + 0.638 + ], + "angle": 0, + "content": "4.1. Dataset, Metric and Implementation Detail" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.645, + 0.473, + 0.902 + ], + "angle": 0, + "content": "Training Dataset. The models are trained on the image matting dataset, D646 [37], the video matting dataset, VM108 [55], and the background image dataset, BG-20k [29]. D646 contains 546 training images, VM108 includes 80 clips, and BG-20k comprises 15000 background images without salient objects. The foregrounds from the matting datasets and the backgrounds from BG-20k and VM108 are composites to form the training data. Additionally, the video segmentation dataset, Youtube-VIS [52], is adopted to train the trimap segmentation to improve the generalizability of the model. Following RVM [32], the motion augmentation is applied, including affine transformation, color jittering, noise and blur, which differs gradually over time with an easing function. Frames of the matting datasets are randomly cropped to \\(480 \\times 480\\) while frames of the segmentation dataset are cropped to \\(352 \\times 352\\) for the larger batch size." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.895, + 0.319 + ], + "angle": 0, + "content": "Evaluation Dataset. The experiments are conducted on three matting datasets: VM108 [55], VM240k [31], and Real Human dataset [49]. VM108 contains 28 composited HD (1920 × 1080) clips with about 23000 frames in the validation set. Due to the variety of objects and the longer length of the sequences, it is chosen as the benchmark in ablation studies. VM240k is a composited human video matting dataset that includes 20 4K (3840 × 2160) videos, each containing 100 frames. Real Human has 19 real HD videos about humans having about 7000 frames in total, with only 1/10 frames annotated. By default, the trimap of the first frame is given to perform trimap propagation and the input resolution is set to be \\(1024 \\times 576\\). All trimaps are produced by discretizing the dilated ground truth alpha matrices where \\(25 \\times 25\\) is chosen as the dilation kernel." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.336, + 0.895, + 0.504 + ], + "angle": 0, + "content": "Evaluation Metric. The same metrics as in RVM [32] are reported. MAD (mean absolute difference) represents the basic alpha error, MSE (mean square error) focuses on segmentation error, Grad [39] denotes the gradient error, Conn [39] (connectivity) depicts the completeness and dtSSD (mean square error of direct temporal gradient) [14] evaluates the temporal coherence such as flickering. For all metrics, the lower the better. In addition, the number of parameters and FPS (frames per second) of each model are also presented to evaluate efficiency. FPS is measured as FP32 tensor throughput and represents the speed." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.521, + 0.895, + 0.687 + ], + "angle": 0, + "content": "Implementation Detail. The codes for training are referenced to [7]. All models are trained by an Adam optimizer with a Cosine Annealing learning rate scheduler. The learning rate is set to 1e-4 initially. It takes 120000 iterations in total to train the model. 30000 iterations are required for the image matting dataset, and the remainings are for the video matting dataset. The video segmentation training is interleaved between every 30000 iterations for 10000 iterations. Training is performed on an NVIDIA RTX A6000 and inference is conducted on an NVIDIA RTX 2080Ti GPU." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.697, + 0.692, + 0.713 + ], + "angle": 0, + "content": "4.2. Comparative Result" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.895, + 0.902 + ], + "angle": 0, + "content": "We compared FTP-VM against previous methods with trimap propagation, including STM+TCVOM [35, 55] and OTVM [42]. STM+TCVOM first produces trimaps via STM and performs video matting by TCVOM. The GCA decoder is applied in TCVOM. In addition, STM is finetuned on the memory trimap to generate better results for reference, denoted as STM(ft). OTVM adopts the memory trimap and predicted alpha mattes to perform trimap propagation. Moreover, RVM [32], a human video matting method, is compared on the human matting datasets, including VM240k and Real Human dataset. The model weights from the original implementation are" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "14341" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.244 + ], + "angle": 0, + "content": "applied, which are trained on the VM240k training set and a human segmentation dataset. For methods with trimap propagation, the numbers of parameters and speed are reported in Tab. 1. As previous approaches use two complete models to achieve different tasks, much more parameters are introduced. Instead, the FTP-VM combines two models along with a lightweight trimap fusion module so that the model size is significantly reduced, demonstrating that the FTP-VM outperforms other methods by a large margin in terms of efficiency." + }, + { + "type": "table", + "bbox": [ + 0.08, + 0.25, + 0.468, + 0.332 + ], + "angle": 0, + "content": "
MethodParameters (M) ↓FPS ↑
Trimap PropagationMatting
STM + TCVOM [35,55]38.9225.715.11
OTVM [42]38.9834.904.32
FTP-VM (Ours)5.1340.16
" + }, + { + "type": "table_caption", + "bbox": [ + 0.09, + 0.336, + 0.458, + 0.351 + ], + "angle": 0, + "content": "Table 1. Comparison on the number of parameters and speed." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.374, + 0.473, + 0.496 + ], + "angle": 0, + "content": "Quantitative and Qualitative Results. Tab. 2 demonstrates the quantitative results on different datasets. For VM108, OTVM achieves the best and FTP-VM is the second best in the five metrics. Both STM+TCVOM and the finetuned one perform unsatisfactorily in this dataset. An example is illustrated in Fig. 4. Although FTP-VM produces false predictions in the boundary region, it is considered comparative due to the merit of speed." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.504, + 0.468, + 0.682 + ], + "angle": 0, + "content": "
DatasetMethodMSE ↓MAD ↓Grad ↓dtSSD ↓Conn ↓
VM108 [55]TCVOM [55]68.4793.1218.294.5955.51
TCVOM* [55]31.5448.9810.373.7728.60
OTVM [42]2.9213.382.462.097.28
FTP-VM (Ours)5.1920.743.922.4612.13
VM240k [31]TCVOM [55]19.2521.5711.134.6912.54
TCVOM* [55]1.512.983.011.961.44
OTVM [42]0.564.551.631.320.74
RVM [32]3.027.714.271.832.64
FTP-VM (Ours)0.454.481.541.300.70
Real Human [49]TCVOM [55]34.5940.8114.2310.5624.09
TCVOM* [55]11.7216.4611.208.649.58
OTVM [42]18.1322.798.658.2413.49
RVM [32]2.385.874.865.153.29
FTP-VM (Ours)2.805.875.295.293.27
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.686, + 0.47, + 0.715 + ], + "angle": 0, + "content": "Table 2. The quantitative comparison. TCVOM denotes STM+TCVOM and * represents the finetuned model." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.726, + 0.47, + 0.848 + ], + "angle": 0, + "content": "For VM240k, FTP-VM outperforms other methods in most metrics except MAD. Although RVM is trained on the VM240k dataset, it reveals limited advantage. Fig. 5 compares the qualitative results. STM+TCVOM fails to provide a reasonable result in this example but the finetuned version greatly improves. OTVM occasionally produces unsatisfactory results. Both RVM and FTP-VM generate complete mattes but FTP-VM contains more details." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.471, + 0.903 + ], + "angle": 0, + "content": "The Real Human dataset which contains real-world videos is also evaluated. As seen from Tab. 2 and Fig. 6, the performance of OTVM drops drastically. Since OTVM" + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.089, + 0.63, + 0.156 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.534, + 0.158, + 0.603, + 0.169 + ], + "angle": 0, + "content": "Query Frame" + }, + { + "type": "image", + "bbox": [ + 0.631, + 0.089, + 0.759, + 0.156 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.66, + 0.158, + 0.733, + 0.169 + ], + "angle": 0, + "content": "Ground Truth" + }, + { + "type": "image", + "bbox": [ + 0.762, + 0.089, + 0.89, + 0.156 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.782, + 0.158, + 0.868, + 0.169 + ], + "angle": 0, + "content": "FTP-VM (Ours)" + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.17, + 0.63, + 0.238 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.524, + 0.24, + 0.612, + 0.25 + ], + "angle": 0, + "content": "STM+TCVOM" + }, + { + "type": "image", + "bbox": [ + 0.631, + 0.17, + 0.759, + 0.238 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.643, + 0.239, + 0.75, + 0.25 + ], + "angle": 0, + "content": "STM(ft) + TCVOM" + }, + { + "type": "image", + "bbox": [ + 0.761, + 0.17, + 0.888, + 0.238 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.806, + 0.239, + 0.845, + 0.249 + ], + "angle": 0, + "content": "OTVM" + }, + { + "type": "image_caption", + "bbox": [ + 0.549, + 0.257, + 0.842, + 0.271 + ], + "angle": 0, + "content": "Figure 4. The qualitative comparison on VM108." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.283, + 0.895, + 0.51 + ], + "angle": 0, + "content": "includes larger models and requires more training data, it might lead to overfitting the composited dataset, resulting in a lack of generalizability. RVM and FTP-VM both provide pleasing results with a slight difference. In Fig. 6, STM(ft)+TCVOM can produce an acceptable result but the details are missing. OTVM fails to infer the complete shape of the target and the hair part needs to be correctly captured. If the hair parts are zoomed in, it is apparent that FTP-VM describes the details better than RVM. In summary, OTVM outperforms others on VM108 but its performance drops on the other two datasets. On the contrary, RVM provides the best performance on the Real Human dataset but not on others. Overall speaking, FTP-VM reaches competitive results in all the experiments, demonstrating that the proposed method retains generalizability at a low cost." + }, + { + "type": "image", + "bbox": [ + 0.504, + 0.516, + 0.89, + 0.813 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.545, + 0.818, + 0.846, + 0.833 + ], + "angle": 0, + "content": "Figure 5. The qualitative comparison on VM240k." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.856, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Trimap Updating Period. In this experiment, various trimap updating periods are tested to evaluate the efficiency of trimap propagation. Fig. 7 depicts the mechanism of" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "14342" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.177, + 0.089, + 0.372, + 0.149 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.235, + 0.151, + 0.306, + 0.162 + ], + "angle": 0, + "content": "Query Frame" + }, + { + "type": "image", + "bbox": [ + 0.082, + 0.163, + 0.135, + 0.223 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.153, + 0.163, + 0.207, + 0.223 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.219, + 0.163, + 0.273, + 0.223 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.275, + 0.163, + 0.327, + 0.223 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.345, + 0.163, + 0.399, + 0.223 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.419, + 0.163, + 0.466, + 0.223 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.141, + 0.225, + 0.214, + 0.235 + ], + "angle": 0, + "content": "Ground Truth" + }, + { + "type": "image_caption", + "bbox": [ + 0.328, + 0.225, + 0.414, + 0.236 + ], + "angle": 0, + "content": "FTP-VM (Ours)" + }, + { + "type": "image", + "bbox": [ + 0.082, + 0.237, + 0.179, + 0.297 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.133, + 0.299, + 0.222, + 0.309 + ], + "angle": 0, + "content": "STM+TCVOM" + }, + { + "type": "image", + "bbox": [ + 0.208, + 0.237, + 0.273, + 0.297 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.275, + 0.238, + 0.326, + 0.297 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.345, + 0.238, + 0.398, + 0.297 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.418, + 0.238, + 0.466, + 0.297 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.318, + 0.299, + 0.424, + 0.31 + ], + "angle": 0, + "content": "STM(ft) + TCVOM" + }, + { + "type": "image", + "bbox": [ + 0.082, + 0.311, + 0.179, + 0.371 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.156, + 0.373, + 0.197, + 0.383 + ], + "angle": 0, + "content": "OTVM" + }, + { + "type": "image", + "bbox": [ + 0.18, + 0.311, + 0.205, + 0.37 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.209, + 0.311, + 0.272, + 0.37 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.275, + 0.311, + 0.325, + 0.37 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.345, + 0.311, + 0.398, + 0.37 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.42, + 0.311, + 0.466, + 0.37 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.356, + 0.373, + 0.386, + 0.383 + ], + "angle": 0, + "content": "RVM" + }, + { + "type": "image_caption", + "bbox": [ + 0.09, + 0.39, + 0.456, + 0.405 + ], + "angle": 0, + "content": "Figure 6. The qualitative comparison on Real Human dataset." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.416, + 0.47, + 0.538 + ], + "angle": 0, + "content": "trimap updates. For example, with period \\( = 30 \\), the trimap is updated every thirty frames. With period \\( = 1 \\), the trimap is given at each frame, meaning that the models only concern matting performance without any trimap propagation. This is the setting where the best performance is expected. On the contrary, if only the first trimap is provided, it will be propagated through the whole video. The bidirectional inference strategy is used in trimap propagation as [55]." + }, + { + "type": "image", + "bbox": [ + 0.085, + 0.549, + 0.469, + 0.615 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.156, + 0.619, + 0.39, + 0.633 + ], + "angle": 0, + "content": "Figure 7. Trimap updating mechanism." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.654, + 0.47, + 0.837 + ], + "angle": 0, + "content": "The comparison on VM108 with different trimap updating periods is illustrated in Fig. 8. It is clear that the shorter the period, the better the performance. While the performance of both FTP-VM and OTVM is not significantly affected by the period, OTVM performs the best overall. Regarding MAD, FTP-VM reveals more advantages when the period becomes longer. However, STM(ft) + TCVOM surpasses FTP-VM with a shorter period, which indicates that the matting ability limits the performance of the proposed method. As for dtSSD, FTP-VM also delivers its merit with fewer flickers when the period is more extended, confirming the stability of the proposed trimap propagation." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.848, + 0.231, + 0.864 + ], + "angle": 0, + "content": "4.3. Ablation Study" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.871, + 0.469, + 0.901 + ], + "angle": 0, + "content": "Ablation on Network Design. In order to justify the network design of FTP-VM, the results of models with" + }, + { + "type": "image", + "bbox": [ + 0.502, + 0.091, + 0.698, + 0.184 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.701, + 0.091, + 0.898, + 0.184 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.189, + 0.892, + 0.217 + ], + "angle": 0, + "content": "Figure 8. The comparison of MAD and dtSSD with various trimap updating periods." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.228, + 0.892, + 0.426 + ], + "angle": 0, + "content": "different concepts are displayed in Tab. 3. Two-stage model is the baseline which has similar architecture to the previous works. After combining trimap propagation and matting into a single model, the performance slightly drops but the speed is boosted. Separating the decoder into trimap segmentation and matting decoders, as GFM [28] does, both MSE and MAD are enhanced but Grad and dtSSD degrade. For the same decoders utilizing the single features, it leads to fair stability. The best performance comes from the specially designed decoders, which is shown at the bottom of Tab. 3. The dtSSD does not outperform others, explaining that decoupling the decoder still harms the stability in some sense." + }, + { + "type": "table", + "bbox": [ + 0.504, + 0.432, + 0.89, + 0.498 + ], + "angle": 0, + "content": "
MethodParam ↓FPS ↑MSE ↓MAD ↓Grad ↓dtSSD ↓Conn ↓
2-stage network8.4631.718.8030.005.872.9018.18
Single network4.8250.0710.2130.163.982.3017.24
Same decoders5.4437.339.7228.425.532.8017.51
Different decoders5.1340.165.1920.743.922.4612.13
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.503, + 0.892, + 0.531 + ], + "angle": 0, + "content": "Table 3. Ablation on the network designs. Param denotes the number of parameters (M)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.553, + 0.892, + 0.706 + ], + "angle": 0, + "content": "Ablation on the Trimap Fusion Module. The trimap fusion module is designed to avoid introducing an additional backbone, which encodes memory frames and trimaps from scratch. As can be seen from Tab. 4, the additional backbone introduces the most parameters. The vanilla convolution improves efficiency and performance by integrating features from different levels. The gated convolution enables different channels to focus on distinct regions, so it outperforms others in all metrics with slightly increased parameters." + }, + { + "type": "table", + "bbox": [ + 0.504, + 0.712, + 0.892, + 0.772 + ], + "angle": 0, + "content": "
MethodParam ↓MSE ↓MAD ↓Grad ↓dtSSD ↓Conn ↓
Additional backbone7.5911.3430.755.722.8217.81
Vanilla convolution4.948.1224.74.872.7613.75
Gated convolution5.135.1920.743.922.4612.13
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.776, + 0.892, + 0.818 + ], + "angle": 0, + "content": "Table 4. Ablation on trimap fusion module. Param denotes the number of parameters (M). FPS is not reported since the trimap fusion does not operate at every frame." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.84, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Ablation on Segmentation Consistency Loss. The segmentation consistency loss attempts to encourage the trimap segmentation employing information from previous frames. The results shown in Tab. 5 clearly exhibit the" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "14343" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.168 + ], + "angle": 0, + "content": "improvement of temporal consistency. If consistency loss is applied to all the classes, the performance degrades slightly. However, with the strategy of weighting the loss according to the correctness, the results are further enhanced at little cost in sharpness (Grad) and stability (dtSSD)." + }, + { + "type": "table", + "bbox": [ + 0.086, + 0.174, + 0.468, + 0.255 + ], + "angle": 0, + "content": "
MethodMSE ↓MAD ↓Grad ↓dtSSD ↓Conn ↓
w/o consistency11.6628.544.432.4017.35
correct class only6.1923.333.752.2813.45
all classes8.7524.644.082.4514.26
all classes w/ weight5.1920.743.922.4612.13
" + }, + { + "type": "table_caption", + "bbox": [ + 0.086, + 0.259, + 0.462, + 0.273 + ], + "angle": 0, + "content": "Table 5. Ablation on the trimap segmentation consistency loss." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.286, + 0.196, + 0.301 + ], + "angle": 0, + "content": "4.4. Discussion" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.31, + 0.473, + 0.476 + ], + "angle": 0, + "content": "In Fig. 9, suppose the memory trimap aims at the left person. FTP-VM provides a correct result but OTVM attempts to matte all the people. This is due to overfitting on the composited dataset where salient objects are selected as the foreground. Moreover, STM-based methods such as OTVM store the resulting masks to maintain temporal coherence during memory matching. In other words, memory matching operates globally and cannot regularize the pixels spatially, which results in weaker coherence. FTP-VM adopts ConvGRU to preserve coherence and performs better." + }, + { + "type": "image", + "bbox": [ + 0.08, + 0.484, + 0.272, + 0.562 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.136, + 0.564, + 0.22, + 0.574 + ], + "angle": 0, + "content": "Memory Frame" + }, + { + "type": "image", + "bbox": [ + 0.274, + 0.484, + 0.466, + 0.561 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.335, + 0.564, + 0.407, + 0.574 + ], + "angle": 0, + "content": "Query Frame" + }, + { + "type": "image", + "bbox": [ + 0.178, + 0.576, + 0.371, + 0.654 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.239, + 0.655, + 0.328, + 0.667 + ], + "angle": 0, + "content": "Memory Trimap" + }, + { + "type": "image", + "bbox": [ + 0.081, + 0.668, + 0.273, + 0.745 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.157, + 0.747, + 0.198, + 0.757 + ], + "angle": 0, + "content": "OTVM" + }, + { + "type": "image", + "bbox": [ + 0.275, + 0.668, + 0.467, + 0.745 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.327, + 0.747, + 0.415, + 0.758 + ], + "angle": 0, + "content": "FTP-VM (Ours)" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.765, + 0.47, + 0.793 + ], + "angle": 0, + "content": "Figure 9. The qualitative comparison between OTVM and FTP-VM on the target selection of the human video." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.804, + 0.471, + 0.895 + ], + "angle": 0, + "content": "However, there remain some challenging cases as shown in Fig. 10. In the memory frame, there are four people in total; the leftmost is out of the screen. With the memory trimap aiming at three people on the right side, the model mattes them successfully at \\( t = 55 \\) (Fig. 10b). However, the video is zoomed in as considered a scene change at" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.893, + 0.244 + ], + "angle": 0, + "content": "\\(t = 65\\) (Fig. 10c), which breaks the temporal coherence in ConvGRUs so that the result is unsatisfactory. The error will be reduced over time when reconstructing the temporal coherence gradually. Furthermore, the leftmost person at \\(t = 200\\) (Fig. 10d) cannot be well removed. Since the memory frame only contains his jacket, the memory cannot recognize his face and clothes. As a result, the ambiguity degrades the result. It is known that dealing with unseen objects and scene changes is challenging for memory matching, requiring further discussions and explorations." + }, + { + "type": "image", + "bbox": [ + 0.502, + 0.25, + 0.695, + 0.335 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.596, + 0.337, + 0.797, + 0.349 + ], + "angle": 0, + "content": "(a) \\(t = 0\\) (Memory frame and trimap)" + }, + { + "type": "image", + "bbox": [ + 0.697, + 0.25, + 0.888, + 0.335 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.626, + 0.337, + 0.796, + 0.349 + ], + "angle": 0, + "content": "\\(= 0\\) (Memory frame and trimap)" + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.35, + 0.695, + 0.434 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.626, + 0.436, + 0.768, + 0.448 + ], + "angle": 0, + "content": "(b) \\(t = 55\\) (Normal result)" + }, + { + "type": "image", + "bbox": [ + 0.696, + 0.35, + 0.888, + 0.434 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.604, + 0.449, + 0.692, + 0.533 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.697, + 0.449, + 0.888, + 0.533 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.604, + 0.535, + 0.79, + 0.547 + ], + "angle": 0, + "content": "(c) \\(t = 65\\) (Temporal incoherence)" + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.549, + 0.695, + 0.633 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.621, + 0.635, + 0.773, + 0.647 + ], + "angle": 0, + "content": "(d) \\(t = 200\\) (Unseen object)" + }, + { + "type": "image", + "bbox": [ + 0.696, + 0.549, + 0.888, + 0.633 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.502, + 0.653, + 0.888, + 0.668 + ], + "angle": 0, + "content": "Figure 10. Challenging cases. Left: query frames. Right: results." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.685, + 0.62, + 0.7 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.71, + 0.893, + 0.892 + ], + "angle": 0, + "content": "FTP-VM, a novel end-to-end video matting model with trimap propagation, is proposed in this paper. The designed lightweight trimap fusion module is introduced to propagate the given trimap in the memory matching. Moreover, the segmentation consistency loss is adopted to fit trimap segmentation better and improve the performance. The proposed FTP-VM reaches 40 FPS, eight times faster than the cutting-edge two-model methods, TCVOM and OTVM. Extensive experiments are conducted to confirm the competitive performance in various scenarios. Its robustness and generalizability provide the foundation for more advanced developments and broader applications." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "14344" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.115, + 0.47, + 0.183 + ], + "angle": 0, + "content": "[1] Nicholas Apostoloff and Andrew Fitzgibbon. Bayesian video matting using learnt image priors. In Proceedings of the 2004 IEEE Computer Society Conference on Computer Vision and Pattern Recognition, 2004. CVPR 2004., volume 1, pages I-I. IEEE, 2004. 2" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.184, + 0.472, + 0.239 + ], + "angle": 0, + "content": "[2] Nicolas Ballas, Li Yao, Chris Pal, and Aaron Courville. 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However, matting usually relies on user-annotated trimaps to estimate alpha values, which is a labor-intensive issue. Although recent studies exploit video object segmentation methods to propagate the given trimaps, they suffer inconsistent results. Here we present a more robust and faster end-to-end video matting model equipped with trimap propagation called FTP-VM (Fast Trimap Propagation - Video Matting). The FTP-VM combines trimap propagation and video matting in one model, where the additional backbone in memory matching is replaced with the proposed lightweight trimap fusion module. The segmentation consistency loss is adopted from automotive segmentation to fit trimap segmentation with the collaboration of RNN (Recurrent Neural Network) to improve the temporal coherence. The experimental results demonstrate that the FTP-VM performs competitively both in composited and real videos only with few given trimaps. The efficiency is eight times higher than the state-of-the-art methods, which confirms its robustness and applicability in real-time scenarios. The code is available at https://github.com/csvt32745/FTP-VM. + +# 1. Introduction + +Image matting aims to estimate the alpha value of each pixel for a target in the input image. Unlike general segmentation, which generates binary values, matting outputs values between 0 and 1, meaning the degree of transparency. The output alpha matrices can describe semi-transparent objects with precise details. As shown in Eq. (1), each pixel color $C$ of an image is composited by the foreground color $F$ , background color $B$ , and an alpha value $\alpha$ , where the background can be substituted to generate a matting dataset. + +$$ +C = \alpha F + (1 - \alpha) B \tag {1} +$$ + +Given a frame like Fig. 1a, a trimap Fig. 1b is the common requirement for image matting, which divides the pixels + +Ming-Sui Lee +National Taiwan University +mslee@csie.ntu.edu.tw + +![](images/90cbd2482832de7c9bca669fde462cb74c463c80909c1ac9742795c54a512bd3.jpg) +(a) Memory frame + +![](images/686c336f3ab53895b03a65aab8a5caded4b4267db239ccd45a560359ece5315e.jpg) +(b) Memory trimap + +![](images/ce389bec65b69a9027eb68ee91d9203626a08a9a3b586587c940b835e4449388.jpg) + +![](images/aaa44252ea4df9244931126f9d00de930850dfaecccf1f6c9c30efc49e006d93.jpg) + +![](images/16fadd8de87ac6a6226227d138b61b810259bbd2595ec9e74ae09a23b4d65256.jpg) +(c) Query frame +(e) The result of OTVM [42] +Figure 1. An example of an in-street interview video. (d) Automatic matting, (e) Trimap-propagation-based method (f) The proposed method. + +![](images/a3026f79a90fa09de1cfb98ee4458e9c2c85a85f7d02e16e8b98a442cfd68b22.jpg) +(d) The result of RVM [32] +(f) The result of FTP-VM (ours) + +into three regions: foreground, background and unknown. Matting methods adopt such information to solve alpha values of unknown (gray) regions. + +Video matting extracts an alpha matte of each frame of the given video. The resulting alpha mattes can be used for background replacement, which is decisive for video applications such as video conferencing and visual effects. It is intuitive to perform image matting on each frame of a video. However, severe flickering artifacts would occur in the resultant image sequence. In order to improve the robustness, considering spatial and temporal coherence is the main challenge for video matting as the temporal information helps infer the matting target from the previous frames. Another challenge is to provide a trimap for each frame, which is expected to be a massive cost to most users. + +To tackle the above two issues, automatic matting and trimap propagation are addressed in this paper. Automatic matting captures specific targets without trimaps, but + +the input videos with ambiguous scenarios highly affect the results. Fig. 1 shows an example of an in-street interview video where an interviewee and passengers occasionally appear simultaneously. While the human matting method [32] attempts to capture all the people, the ambiguity caused by inconspicuous passengers results in unsatisfactory output Fig. 1d. Thus we opt for trimap propagation to select targets more stably as shown in Fig. 1f. + +While performing trimap propagation, the user is required to provide a pair of so-called memory frame Fig. 1a and memory trimap Fig. 1b, and this information is utilized to propagate throughout the video. Since we are predicting a sequence of three-class segmentation masks, the trimap propagation can be treated as video object segmentation. Recent studies [42, 47, 55] leverage STM (Space-Time Memory network), [35] an emerging video object segmentation model, to produce the trimaps successfully. However, the resultant trimaps usually contain flickers and lead to unsatisfactory results. As STM lacks temporal coherence, we append ConvGRUs [2] to the model to improve stability. Moreover, the previous approaches containing two full models make them unsuitable for interactive applications. We thus combine the two models into an end-to-end model to enhance the speed and performance. The main contributions of this work are summarized as follows. + +- A novel end-to-end video matting model equipped with trimap propagation, called FTP-VM (Fast Trimap Propagation - Video Matting), is proposed. FTP-VM is faster than the previous two-model methods by a large margin while preserving competitive performance in different scenarios. While the frame rate of the previous methods is 5 FPS, the proposed method reaches 40 FPS on an NVIDIA RTX 2080Ti GPU. +- A lightweight trimap fusion module is designed to replace an additional encoder in the STM-based model to make FTP-VM efficient and more powerful. +- Motivated by [38], the segmentation consistency loss from automotive segmentation is adapted to trimap segmentation. The final setting reaching the more satisfactory performance is determined by conducting comprehensive experiments. + +# 2. Related Work + +# 2.1. Image Matting + +Non-deep-learning image matting includes two types of methods: The sampling-based approaches [12,16,18,44,48] construct the foreground and background priors, and infer the alpha values by solving the composition equation. The affinity-based methods [4,5,17,24-26,46] propagate the + +alpha values from known pixels to unknown ones according to similarities under the assumption of local smoothness. These classical methods rely on low-level representations and often require assistance to deal with complex scenes. For deep-learning methods, CNN (Convolution Neural Network) based methods [9, 15, 20, 23, 30, 34, 51] exploit high-level features and achieve state-of-the-art results. Vision-transformer-based methods [36] are emerging by combining global similarity and inductive bias of images. These methods build prior from the extracted features or the similarity to estimate the alpha values and preserve details by the UNet-like [40] architecture. + +In order to annihilate the need for trimaps, automatic image matting combines segmentation and matting into one task. It aims to matte specific targets such as humans [21, 45] or salient objects [3, 28, 29, 37] without any auxiliary inputs. Mask-guided matting [54] takes a rough segmentation mask as an additional input followed by refinement. However, it cannot process semi-transparent objects due to the binary masks. Background-based methods [31, 41] require a background image instead of a trimap as an auxiliary input so that it needs to handle misaligned backgrounds better. + +# 2.2. Video Matting + +Temporal coherence plays an essential role in video matting. Most existing methods [1, 10, 27, 43] extend classical image matting methods to the temporal dimension and encounter a similar weakness. RVM [32] places ConvGRU hierarchically to maintain temporal coherency. It performs in real-time due to the efficiency of ConvGRU. DVM [47] uses deformable convolution to warp the feature temporally by estimated offsets but is limited by the kernel size of convolutions. TCVOM [55] leverages guided attention block to compute affinity between frames, and [49] analyzes inter-frame relationships by graph neural network. [21] reduces the flickers by applying post-processing tricks to the results, but the image matting methods still limit the performance. + +For trimap propagation, [11] interpolates trimaps by optical flows and contains restrictions caused by weak low-level features from semi-transparent objects. Recent deep-learning-based methods [47, 55] leverage approaches from video object segmentation to perform trimap segmentation before video matting. Decoupling trimap propagation and video matting simplifies the problem and forms a two-stage method. However, the model sometimes needs to be finetuned based on the given trimaps to generate acceptable results. OTVM [42] further improves performance through multi-stage training and joint trimap and alpha prediction modeling. The joint modeling utilizes alpha mattes and trimaps to perform trimap propagation. + +# 2.3. Video Object Segmentation + +Trimap propagation is a kind of video object segmentation in a semi-supervised setting. The model receives masks of a few frames as auxiliary inputs to hint targets and predicts masks of the remaining frames. After the success of STM [35], different memory matching based methods emerge. Memory matching uses a variant of self-attention to extract the features from the given masks. With frames to predict, called query, and pairs of frames and masks, called memory, the features from the memories are linearly combined based on the similarity between memory and query. If a pixel has a similar context to another one, its similarity score will be high. Thus STM can effectively capture the correspondence and segment the target correctly. STCN (Space-Time Correspondence Network) [8] decouples the relation between frames and masks in the memory encoder to become more efficient and effective. We leverage the similar mechanic of STCN to propagate the trimaps but with a more efficient module. In addition, neither STM nor STCN has a strong temporal correlation between consecutive frames, so ConvGRU [2] is appended to our model to strengthen the temporal coherence as XMem [6]. + +# 3. Method + +The overall network architecture containing an encoder, trimap fusion module, bottleneck fusion module, and two corresponding decoders is illustrated in Fig. 2. The encoder extracts features from the memory frame $I_{m}$ and query frame $I_{q}$ . The trimap fusion module encodes the memory trimap $T_{m}$ and memory features into memory values. The bottleneck fusion module propagates the trimap information to the query frame and aggregates the features globally. The decoders contain segmentation and matting decoders to estimate the trimap and boundary matte, respectively. Finally, the resulting trimap and boundary matte are integrated into a complete matte. + +# 3.1. Encoder + +The MobileNetV3-Large [22] is adopted as the encoder for its efficiency. The encoder takes a single image as input and extracts features at strides of 2, 4, 8 and 16, respectively. The receptive fields are larger in deeper stages, which makes features at different strides focus on different tasks. The low-level features are for preserving details, while high-level ones are for inferring the matting target. This kind of hierarchy can be employed as an UNet-like structure [40] where it receives skip-connections of the features to avoid information diminishing due to the deeper networks. $I_{m}$ and $I_{q}$ are passed through the same encoder to reduce the size of the model to enhance efficiency. The extracted memory and query features are denoted as $F_{m}^{s}$ and $F_{q}^{s}$ where $s$ represents the stride of the feature. + +# 3.2. Trimap Fusion Module + +Fig. 3 shows the architecture of trimap fusion module. It integrates the extracted memory features $F_{m}^{s}$ and the memory trimap $T_{m}$ into the memory value $F_{m}^{*}$ , which will be used to perform memory matching in the bottleneck fusion module. In general video object segmentation methods, the memory value is generated through an additional encoder (e.g. ResNet18 [19]) with a 4-channel input. Introducing another encoder leads to more parameters and a longer training time. Thus we construct a lightweight module to reduce the computation cost and parameters. Illuminated by DeepFillV2 [53], the gated convolutions are utilized instead of vanilla convolutions [23]. DeepFillV2 performs inpainting and requires a multiple-channel mask as an additional input. A gated convolution is composed of two vanilla convolutions, where one extracts features, and the other predicts scales followed by a sigmoid function. The results are then combined by an element-wise multiplication. The gated convolution makes different channels concentrate on different regions and enhances the performance of vanilla convolutions. The downsampled trimaps $T_{m}^{s}$ , memory features $F_{m}^{s}$ and output features $F_{m}^{*(s/2)}$ from the previous level are concatenated and passed through a gated convolution block $g^{s}$ : + +$$ +F _ {m} ^ {* s} = \left\{ \begin{array}{l l} g ^ {s} \left(\left[ T _ {m} ^ {s}, F _ {m} ^ {s} \right]\right) & \text {i f} s = 2 \\ g ^ {s} \left(\left[ T _ {m} ^ {s}, F _ {m} ^ {s}, F _ {m} ^ {* (s / 2)} \right]\right) & \text {i f} s = 4, 8, 1 6 \end{array} \right. \tag {2} +$$ + +where $s$ represents the stride and $[\cdot, \cdot]$ denotes channel-wise concatenation. $F_{m}^{*16}$ is the final output memory value $F_{m}^{*}$ . + +# 3.3. Bottleneck Fusion Module + +The bottleneck fusion module consists of a memory matching module, a convolution block attention module (CBAM) [50] and a pyramid pooling module (PPM) [56]. Memory matching module applies the same mechanism of cross-attention as STCN [8]. The query feature $F_{q}^{16}$ and memory feature $F_{m}^{16}$ are first projected to the query key $K_{q} \in \mathbb{R}^{ch_{k} \times hw}$ and memory key $K_{m} \in \mathbb{R}^{ch_{k} \times hw}$ through a shared convolution. $h$ and $w$ are 1/16 of the original resolution, and the channel of keys $ch_{k}$ is 32. The memory values $F_{m}^{*16}$ from the trimap fusion module are linearly combined based on the similarity score between $K_{q}$ and $K_{m}$ to generate the matched memory values $F_{m}^{'16}$ . In addition, the CBAM [50] and PPM [56] are leveraged to integrate the features competently. CBAM scales the features spatially and channel-wisely to strengthen different features from $F_{q}^{16}$ and $F_{m}^{'16}$ . PPM aggregates the global context from sub-regions of different scales by GAPs (Global Average Pooling), where the scales are set to be 1, 2, 4, and 8, respectively. + +![](images/f919be1d16db05e9de3628b39c0ad8275ad7f8cfc3e69e276087bcbfaa2b7ed1.jpg) +Figure 2. The overall network architecture of FTP-VM. + +![](images/036cab46cc905ce9e190234017bfb700e9510d66066504a2e3ff867661b211f7.jpg) +Figure 3. The trimap fusion module. + +# 3.4. Decoders + +As GFM [28] claims that decoding semantic information and edge details simultaneously may harm the matting quality, the decoding part is split into two decoders, trimap segmentation and matting. For frame-to-frame propagation, ConvGRU [2] is efficient but lacks long-term context and probably loses track after occlusions. Thus we apply it with memory matching in the bottleneck fusion module to maintain both short-term and long-term temporal coherence. These decoders are designed differently to boost performance and efficiency as PSPM [13]. They are both composed of bilinear upsampling, convolution blocks and ConvGRUs. Each ConvGRU is placed after a convolution block and is only employed for half of the channels of the input feature maps. + +The trimap segmentation decoder estimates the probability maps with three classes and they are converted into a trimap by selecting the class with the highest probability for each pixel. Since the trimap usually retains fewer details, it is output at a stride of 4 and bilinearly upsampled to the original resolution for speed and stability. ConvGRUs are placed at the stride of 8 and 16. For the matting decoder, it estimates precise matts of the foreground in the boundary with high resolution. Moreover, it is expected to focus on + +details, so it starts with features at the stride of 4. $F_T^{16}$ is upsampled to the stride of 4 and concatenated with $F_T^4$ , where $F_T^s$ denotes the feature obtained from the trimap decoder with a stride of $s$ . Then it is upsampled and receives skip-connection from $F_q^4$ and $F_q^2$ until the original resolution. Finally, the pixels in the unknown regions of the resulting trimaps are replaced with the corresponding alpha values in the boundary mattes to generate complete mattes. + +# 3.5. Loss Function + +Segmentation Loss. The focal loss [33] and consistency loss [38] are considered as the loss functions. The focal loss makes the training focus on the more challenging pixels. $p_c$ and $y_c$ are the predicted and ground truth probability that a pixel belongs to a class $c$ in the trimap, and $\gamma$ is set to be 2. + +$$ +\mathcal {L} _ {\text {f o c a l}} = - \sum_ {c = 1} ^ {3} y _ {c} (1 - p _ {c}) ^ {\gamma} \log \left(p _ {c}\right) \tag {3} +$$ + +The consistency loss penalizes pixels with different predictions in consecutive frames. Those pixels are required to be correct in at least one frame of the consecutive pair to avoid interruption in the basic segmentation training. This design ensures that the trimap decoder utilizes the temporal information more appropriately. While the loss in [38] is only used for the correct class, we apply it to all the classes regardless of correctness because we discovered that different weights assigned to correct and wrong classes further improve the performance. The segmentation consistency loss is defined as: + +$$ +\mathcal {L} _ {\text {c o n s i s}} = \sum_ {c = 1} ^ {3} w _ {t, h, w, c} \cdot \left\| p _ {t, h, w, c} - p _ {t + 1, h, w, c} \right\| _ {1} \tag {4} +$$ + +where $w_{t,h,w,c} = \left\{ \begin{array}{ll}0.5 & \text{if } y_{t,h,w} = c \\ 0.25 & \text{else} \end{array} \right.$ . + +The final trimap segmentation loss is + +$$ +\mathcal {L} _ {\text {t r i m a p}} = \mathcal {L} _ {\text {f o c a l}} + \mathcal {L} _ {\text {c o n s i s .}} \tag {5} +$$ + +Matting Loss. Following RVM [32], the same loss functions are exploited to train the matting network. However, we additionally input masks of the unknown regions to make the matting decoder focus on the boundary more. For the predicted and ground truth alpha matte $\alpha_{t},\alpha_{t}^{*}$ at time $t$ and the given mask $M$ , L1 loss $\mathcal{L}_{l1}$ and pyramid Laplacian loss $\mathcal{L}_{lap}$ [15, 20] is considered to learn the alpha values and edge details. A temporal coherence loss $\mathcal{L}_{tc}$ [47] is adopted as well to reduce flickers. + +$$ +\mathcal {L} _ {l 1} (M) = \| M \cdot \left(\alpha_ {t} - \alpha_ {t} ^ {*}\right) \| _ {1} \tag {6} +$$ + +$$ +\mathcal {L} _ {l a p} (M) = \sum_ {s = 1} ^ {5} \frac {2 ^ {s - 1}}{5} \| M \cdot \left(L _ {p y r} ^ {s} \left(\alpha_ {t}\right) - L _ {p y r} ^ {s} \left(\alpha_ {t} ^ {*}\right)\right) \| _ {1} \tag {7} +$$ + +$$ +\mathcal {L} _ {t c} (M) = \| M \cdot \left(\frac {\mathrm {d} \alpha_ {t}}{\mathrm {d} t} - \frac {\mathrm {d} \alpha_ {t} ^ {*}}{\mathrm {d} t}\right) \| _ {2} \tag {8} +$$ + +The overall alpha loss is defined as + +$$ +\mathcal {L} _ {\alpha} (M) = \mathcal {L} _ {l 1} (M) + \mathcal {L} _ {l a p} (M) + 5 \cdot \mathcal {L} _ {t c} (M), \tag {9} +$$ + +and it is applied to the unknown region of the predicted trimap $T_{U}$ and the ground truth trimap $T_{U}^{*}$ . The final matting loss is + +$$ +\mathcal {L} _ {\text {m a t t i n g}} = \mathcal {L} _ {\alpha} \left(T _ {U}\right) + \mathcal {L} _ {\alpha} \left(T _ {U} ^ {*}\right). \tag {10} +$$ + +# 4. Experiment + +# 4.1. Dataset, Metric and Implementation Detail + +Training Dataset. The models are trained on the image matting dataset, D646 [37], the video matting dataset, VM108 [55], and the background image dataset, BG-20k [29]. D646 contains 546 training images, VM108 includes 80 clips, and BG-20k comprises 15000 background images without salient objects. The foregrounds from the matting datasets and the backgrounds from BG-20k and VM108 are composites to form the training data. Additionally, the video segmentation dataset, Youtube-VIS [52], is adopted to train the trimap segmentation to improve the generalizability of the model. Following RVM [32], the motion augmentation is applied, including affine transformation, color jittering, noise and blur, which differs gradually over time with an easing function. Frames of the matting datasets are randomly cropped to $480 \times 480$ while frames of the segmentation dataset are cropped to $352 \times 352$ for the larger batch size. + +Evaluation Dataset. The experiments are conducted on three matting datasets: VM108 [55], VM240k [31], and Real Human dataset [49]. VM108 contains 28 composited HD (1920 × 1080) clips with about 23000 frames in the validation set. Due to the variety of objects and the longer length of the sequences, it is chosen as the benchmark in ablation studies. VM240k is a composited human video matting dataset that includes 20 4K (3840 × 2160) videos, each containing 100 frames. Real Human has 19 real HD videos about humans having about 7000 frames in total, with only 1/10 frames annotated. By default, the trimap of the first frame is given to perform trimap propagation and the input resolution is set to be $1024 \times 576$ . All trimaps are produced by discretizing the dilated ground truth alpha matrices where $25 \times 25$ is chosen as the dilation kernel. + +Evaluation Metric. The same metrics as in RVM [32] are reported. MAD (mean absolute difference) represents the basic alpha error, MSE (mean square error) focuses on segmentation error, Grad [39] denotes the gradient error, Conn [39] (connectivity) depicts the completeness and dtSSD (mean square error of direct temporal gradient) [14] evaluates the temporal coherence such as flickering. For all metrics, the lower the better. In addition, the number of parameters and FPS (frames per second) of each model are also presented to evaluate efficiency. FPS is measured as FP32 tensor throughput and represents the speed. + +Implementation Detail. The codes for training are referenced to [7]. All models are trained by an Adam optimizer with a Cosine Annealing learning rate scheduler. The learning rate is set to 1e-4 initially. It takes 120000 iterations in total to train the model. 30000 iterations are required for the image matting dataset, and the remainings are for the video matting dataset. The video segmentation training is interleaved between every 30000 iterations for 10000 iterations. Training is performed on an NVIDIA RTX A6000 and inference is conducted on an NVIDIA RTX 2080Ti GPU. + +# 4.2. Comparative Result + +We compared FTP-VM against previous methods with trimap propagation, including STM+TCVOM [35, 55] and OTVM [42]. STM+TCVOM first produces trimaps via STM and performs video matting by TCVOM. The GCA decoder is applied in TCVOM. In addition, STM is finetuned on the memory trimap to generate better results for reference, denoted as STM(ft). OTVM adopts the memory trimap and predicted alpha mattes to perform trimap propagation. Moreover, RVM [32], a human video matting method, is compared on the human matting datasets, including VM240k and Real Human dataset. The model weights from the original implementation are + +applied, which are trained on the VM240k training set and a human segmentation dataset. For methods with trimap propagation, the numbers of parameters and speed are reported in Tab. 1. As previous approaches use two complete models to achieve different tasks, much more parameters are introduced. Instead, the FTP-VM combines two models along with a lightweight trimap fusion module so that the model size is significantly reduced, demonstrating that the FTP-VM outperforms other methods by a large margin in terms of efficiency. + +
MethodParameters (M) ↓FPS ↑
Trimap PropagationMatting
STM + TCVOM [35,55]38.9225.715.11
OTVM [42]38.9834.904.32
FTP-VM (Ours)5.1340.16
+ +Quantitative and Qualitative Results. Tab. 2 demonstrates the quantitative results on different datasets. For VM108, OTVM achieves the best and FTP-VM is the second best in the five metrics. Both STM+TCVOM and the finetuned one perform unsatisfactorily in this dataset. An example is illustrated in Fig. 4. Although FTP-VM produces false predictions in the boundary region, it is considered comparative due to the merit of speed. + +Table 1. Comparison on the number of parameters and speed. + +
DatasetMethodMSE ↓MAD ↓Grad ↓dtSSD ↓Conn ↓
VM108 [55]TCVOM [55]68.4793.1218.294.5955.51
TCVOM* [55]31.5448.9810.373.7728.60
OTVM [42]2.9213.382.462.097.28
FTP-VM (Ours)5.1920.743.922.4612.13
VM240k [31]TCVOM [55]19.2521.5711.134.6912.54
TCVOM* [55]1.512.983.011.961.44
OTVM [42]0.564.551.631.320.74
RVM [32]3.027.714.271.832.64
FTP-VM (Ours)0.454.481.541.300.70
Real Human [49]TCVOM [55]34.5940.8114.2310.5624.09
TCVOM* [55]11.7216.4611.208.649.58
OTVM [42]18.1322.798.658.2413.49
RVM [32]2.385.874.865.153.29
FTP-VM (Ours)2.805.875.295.293.27
+ +Table 2. The quantitative comparison. TCVOM denotes STM+TCVOM and * represents the finetuned model. + +For VM240k, FTP-VM outperforms other methods in most metrics except MAD. Although RVM is trained on the VM240k dataset, it reveals limited advantage. Fig. 5 compares the qualitative results. STM+TCVOM fails to provide a reasonable result in this example but the finetuned version greatly improves. OTVM occasionally produces unsatisfactory results. Both RVM and FTP-VM generate complete mattes but FTP-VM contains more details. + +The Real Human dataset which contains real-world videos is also evaluated. As seen from Tab. 2 and Fig. 6, the performance of OTVM drops drastically. Since OTVM + +![](images/9c87f9ddd4a3f2e76d26ac848b33250728933127d7d3d4ebf44a09f742aead24.jpg) +Query Frame + +![](images/ac32077c05ae253ec478d3f0cca3c9375c143204b7c09d45ab77e0116c1e9690.jpg) +Ground Truth + +![](images/ff1d7743d0cf8795a2a004665184f7cd2a7094b7881e1e05dd2998338e4394e0.jpg) +FTP-VM (Ours) + +![](images/2f62924737ab0c79137887850140d7ab00f752bec655e636e62011201683234f.jpg) +STM+TCVOM + +![](images/1aaf2a40872456c7d895c16131813c02ea1a81d09788a71426421563eb6ac527.jpg) +STM(ft) + TCVOM + +![](images/200816f1e4ba603f977000464e933dba4fd5193b92319b3e187019f7ed6f70b2.jpg) +OTVM +Figure 4. The qualitative comparison on VM108. + +includes larger models and requires more training data, it might lead to overfitting the composited dataset, resulting in a lack of generalizability. RVM and FTP-VM both provide pleasing results with a slight difference. In Fig. 6, STM(ft)+TCVOM can produce an acceptable result but the details are missing. OTVM fails to infer the complete shape of the target and the hair part needs to be correctly captured. If the hair parts are zoomed in, it is apparent that FTP-VM describes the details better than RVM. In summary, OTVM outperforms others on VM108 but its performance drops on the other two datasets. On the contrary, RVM provides the best performance on the Real Human dataset but not on others. Overall speaking, FTP-VM reaches competitive results in all the experiments, demonstrating that the proposed method retains generalizability at a low cost. + +![](images/22f3ace51ada1148ff4ca4c4c0f1c5e9a9e1726f5206c1d961d6b06a82e90f83.jpg) +Figure 5. The qualitative comparison on VM240k. + +Trimap Updating Period. In this experiment, various trimap updating periods are tested to evaluate the efficiency of trimap propagation. Fig. 7 depicts the mechanism of + +![](images/7a6c363af483b07f3e9c2a6044db8a09a7d9e823dd60139dd77bf6bc48ba0f1e.jpg) +Query Frame + +![](images/8487e8ba9632c3811ac6acccf8c023e923f1e51c22ee6f7f1f051099747de3e2.jpg) + +![](images/cc38c6a77cf936b731d0d918c4d2d396efd1dba87754b83b7f5ee4cf847fc246.jpg) +Ground Truth + +![](images/a4980e20d96731a2b34a5a5a8558d24ee56f16a912fa7c339a79329c34d25710.jpg) + +![](images/ee7d3b2fdbe89283db34b0e688d08a2dae9a537ce48e7d1988abcd04a50a32df.jpg) +FTP-VM (Ours) + +![](images/badd58e8bc124734f2fd6b35c1c622f194cf63c230b29d7d5006d34f773d0b71.jpg) + +![](images/10d6f42bf978d2b4414d7fb83445afe064e2fb276216c74b2deb1690a4a38a8f.jpg) + +![](images/f1401e2a9d05bdbcf0afb7dd36963ee9bade33c9df9a6ec93f38bb246a7502a4.jpg) +STM+TCVOM + +![](images/fa9b73258a7a076968003519956af9875abe927a6e915193b1206d44acd00a20.jpg) + +![](images/1d0f1121f5fb503b27195f00cb16ea8aac07979844dee2db98f5cba68e3de049.jpg) +STM(ft) + TCVOM + +![](images/ba65928e6f51f37a7f1184ef600dafbfca45de09bebba1a88556996ae3ea5c7c.jpg) + +![](images/2792b9c6a442f5c08309242c2eb451b5e53ef0e5de47b5cf8926c6ff1b237291.jpg) + +![](images/e6df73193921af2412cf23d71ad7d827504c6ea39394d83e880b8378ef5d7373.jpg) +OTVM + +![](images/b9755f06f0f7ce21d152688e05e4b3f648a4ae7534874fdca490b9d3187e70a6.jpg) +Figure 6. The qualitative comparison on Real Human dataset. + +![](images/f512232e51375c66b57f98bc0425bb1c96c048175af4635e1a915db8c8b8af55.jpg) + +![](images/438e467107b75188713b44ff8d82a9cc7e7350df3c13499a40c97ae881f0c51d.jpg) + +![](images/f2914dcb35484ee532f36321b278ca425eb5cfcf8167bd0170a96d359687bce9.jpg) +RVM + +![](images/9d93f94773fea6219003922dba85b627208b6008b3e9fc8c4e01798d469b5da7.jpg) + +trimap updates. For example, with period $= 30$ , the trimap is updated every thirty frames. With period $= 1$ , the trimap is given at each frame, meaning that the models only concern matting performance without any trimap propagation. This is the setting where the best performance is expected. On the contrary, if only the first trimap is provided, it will be propagated through the whole video. The bidirectional inference strategy is used in trimap propagation as [55]. + +![](images/971fd2127f07d6e165095ab7aa4cff76755b2ed12fdd6e110809c146eb61684e.jpg) +Figure 7. Trimap updating mechanism. + +The comparison on VM108 with different trimap updating periods is illustrated in Fig. 8. It is clear that the shorter the period, the better the performance. While the performance of both FTP-VM and OTVM is not significantly affected by the period, OTVM performs the best overall. Regarding MAD, FTP-VM reveals more advantages when the period becomes longer. However, STM(ft) + TCVOM surpasses FTP-VM with a shorter period, which indicates that the matting ability limits the performance of the proposed method. As for dtSSD, FTP-VM also delivers its merit with fewer flickers when the period is more extended, confirming the stability of the proposed trimap propagation. + +# 4.3. Ablation Study + +Ablation on Network Design. In order to justify the network design of FTP-VM, the results of models with + +![](images/99ba83aaaaa683e6f038ba514ef8c009a6db59ef3daa49edfe951e8af16fdb9d.jpg) +Figure 8. The comparison of MAD and dtSSD with various trimap updating periods. + +![](images/71871bb6ba4f6aa8ee3df5c1d9c902d7e682aac1e76d35d47c0bce179c2887ef.jpg) + +different concepts are displayed in Tab. 3. Two-stage model is the baseline which has similar architecture to the previous works. After combining trimap propagation and matting into a single model, the performance slightly drops but the speed is boosted. Separating the decoder into trimap segmentation and matting decoders, as GFM [28] does, both MSE and MAD are enhanced but Grad and dtSSD degrade. For the same decoders utilizing the single features, it leads to fair stability. The best performance comes from the specially designed decoders, which is shown at the bottom of Tab. 3. The dtSSD does not outperform others, explaining that decoupling the decoder still harms the stability in some sense. + +
MethodParam ↓FPS ↑MSE ↓MAD ↓Grad ↓dtSSD ↓Conn ↓
2-stage network8.4631.718.8030.005.872.9018.18
Single network4.8250.0710.2130.163.982.3017.24
Same decoders5.4437.339.7228.425.532.8017.51
Different decoders5.1340.165.1920.743.922.4612.13
+ +Ablation on the Trimap Fusion Module. The trimap fusion module is designed to avoid introducing an additional backbone, which encodes memory frames and trimaps from scratch. As can be seen from Tab. 4, the additional backbone introduces the most parameters. The vanilla convolution improves efficiency and performance by integrating features from different levels. The gated convolution enables different channels to focus on distinct regions, so it outperforms others in all metrics with slightly increased parameters. + +Table 3. Ablation on the network designs. Param denotes the number of parameters (M). + +
MethodParam ↓MSE ↓MAD ↓Grad ↓dtSSD ↓Conn ↓
Additional backbone7.5911.3430.755.722.8217.81
Vanilla convolution4.948.1224.74.872.7613.75
Gated convolution5.135.1920.743.922.4612.13
+ +Table 4. Ablation on trimap fusion module. Param denotes the number of parameters (M). FPS is not reported since the trimap fusion does not operate at every frame. + +Ablation on Segmentation Consistency Loss. The segmentation consistency loss attempts to encourage the trimap segmentation employing information from previous frames. The results shown in Tab. 5 clearly exhibit the + +improvement of temporal consistency. If consistency loss is applied to all the classes, the performance degrades slightly. However, with the strategy of weighting the loss according to the correctness, the results are further enhanced at little cost in sharpness (Grad) and stability (dtSSD). + +
MethodMSE ↓MAD ↓Grad ↓dtSSD ↓Conn ↓
w/o consistency11.6628.544.432.4017.35
correct class only6.1923.333.752.2813.45
all classes8.7524.644.082.4514.26
all classes w/ weight5.1920.743.922.4612.13
+ +Table 5. Ablation on the trimap segmentation consistency loss. + +# 4.4. Discussion + +In Fig. 9, suppose the memory trimap aims at the left person. FTP-VM provides a correct result but OTVM attempts to matte all the people. This is due to overfitting on the composited dataset where salient objects are selected as the foreground. Moreover, STM-based methods such as OTVM store the resulting masks to maintain temporal coherence during memory matching. In other words, memory matching operates globally and cannot regularize the pixels spatially, which results in weaker coherence. FTP-VM adopts ConvGRU to preserve coherence and performs better. + +![](images/28978fb7fba3c70f2bfbdae808433dbb3eef9a0e0d3617aafe75f3ec11a36e46.jpg) +Memory Frame + +![](images/f504d607def775a2727739e4a508e584d25ce665ad163e0a0b78197bdd783023.jpg) +Query Frame + +![](images/21c60381ed39a689e554a9a31b979e367da52be0a5e9298a137353ed69b12296.jpg) +Memory Trimap + +![](images/7a60943305a6fcbdadf153b750c940c3a5bd5df87f67efd203f39d797395fe91.jpg) +OTVM +Figure 9. The qualitative comparison between OTVM and FTP-VM on the target selection of the human video. + +![](images/a41d8b3284784ed34eae0b2005ae89552661d3fcdfd04c13956caad4453eaf1b.jpg) +FTP-VM (Ours) + +However, there remain some challenging cases as shown in Fig. 10. In the memory frame, there are four people in total; the leftmost is out of the screen. With the memory trimap aiming at three people on the right side, the model mattes them successfully at $t = 55$ (Fig. 10b). However, the video is zoomed in as considered a scene change at + +$t = 65$ (Fig. 10c), which breaks the temporal coherence in ConvGRUs so that the result is unsatisfactory. The error will be reduced over time when reconstructing the temporal coherence gradually. Furthermore, the leftmost person at $t = 200$ (Fig. 10d) cannot be well removed. Since the memory frame only contains his jacket, the memory cannot recognize his face and clothes. As a result, the ambiguity degrades the result. It is known that dealing with unseen objects and scene changes is challenging for memory matching, requiring further discussions and explorations. + +![](images/e9d4174e360e282b2ce43e2a037bc000f5cc6a5280da38a178a3b443742b9973.jpg) +(a) $t = 0$ (Memory frame and trimap) + +![](images/ecfa230601e4402c8b1ad378062d66c9007aadf1ebe400fa68f1cbe362583aca.jpg) + +$= 0$ (Memory frame and trimap) + +![](images/5aac8538237766a536178c4c720da7b12dd52fc8c93d4092f794eb2233bef4fe.jpg) +(b) $t = 55$ (Normal result) + +![](images/4725efc555813efb23ad48e30b151c82dc99697d456aadbd010d65bc00fcb613.jpg) + +![](images/1e68ed8567ff5be206c4a733261a39f718c0c35924bac71f99e1c4612b024e15.jpg) + +![](images/bf0e0d0b93764ec371bad0044b8e975a7badb74b0d1239061f3298b6471aabe6.jpg) + +![](images/195bb6e24fc10107f89eb12899808f44c0995dbf234545eb6a35a4638d14e01b.jpg) +(c) $t = 65$ (Temporal incoherence) +(d) $t = 200$ (Unseen object) +Figure 10. Challenging cases. Left: query frames. Right: results. + +![](images/040e88e55e13c0bca107c5153205e15e7e7177ec7df96d20177e1cf3a68104f4.jpg) + +# 5. Conclusion + +FTP-VM, a novel end-to-end video matting model with trimap propagation, is proposed in this paper. The designed lightweight trimap fusion module is introduced to propagate the given trimap in the memory matching. Moreover, the segmentation consistency loss is adopted to fit trimap segmentation better and improve the performance. The proposed FTP-VM reaches 40 FPS, eight times faster than the cutting-edge two-model methods, TCVOM and OTVM. Extensive experiments are conducted to confirm the competitive performance in various scenarios. Its robustness and generalizability provide the foundation for more advanced developments and broader applications. + +# References + +[1] Nicholas Apostoloff and Andrew Fitzgibbon. Bayesian video matting using learnt image priors. 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In Proceedings of the IEEE conference on computer vision and pattern recognition, pages 2881-2890, 2017. 3 \ No newline at end of file diff --git a/2023/End-to-End Video Matting With Trimap Propagation/images.zip b/2023/End-to-End Video Matting With Trimap Propagation/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..5b0ed8d209045c9a35ccca4497faed5bdc461fd2 --- /dev/null +++ b/2023/End-to-End Video Matting With Trimap Propagation/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:01514a3e775c50c33d18d0b607f4f406209bdd1ae8a89980e604407925a4c357 +size 610575 diff --git a/2023/End-to-End Video Matting With Trimap Propagation/layout.json b/2023/End-to-End Video Matting With Trimap Propagation/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..6ca0b55cec060510b3716e73ad4bf8fd92987fa5 --- /dev/null +++ b/2023/End-to-End Video Matting With Trimap Propagation/layout.json @@ -0,0 +1,10655 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 135, + 103, + 459, + 121 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 135, + 103, + 459, + 121 + ], + "spans": [ + { + "bbox": [ + 135, + 103, + 459, + 121 + ], + "type": "text", + "content": "End-to-end Video Matting with Trimap Propagation" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 143, + 144, + 278, + 184 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 144, + 278, + 184 + ], + "spans": [ + { + "bbox": [ + 143, + 144, + 278, + 184 + ], + "type": "text", + "content": "Wei-Lun Huang National Taiwan University r09944040@csie.ntu.edu.tw" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 143, + 202, + 191, + 215 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 202, + 191, + 215 + ], + "spans": [ + { + "bbox": [ + 143, + 202, + 191, + 215 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 234, + 290, + 510 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 234, + 290, + 510 + ], + "spans": [ + { + "bbox": [ + 47, + 234, + 290, + 510 + ], + "type": "text", + "content": "The research of video matting mainly focuses on temporal coherence and has gained significant improvement via neural networks. However, matting usually relies on user-annotated trimaps to estimate alpha values, which is a labor-intensive issue. Although recent studies exploit video object segmentation methods to propagate the given trimaps, they suffer inconsistent results. Here we present a more robust and faster end-to-end video matting model equipped with trimap propagation called FTP-VM (Fast Trimap Propagation - Video Matting). The FTP-VM combines trimap propagation and video matting in one model, where the additional backbone in memory matching is replaced with the proposed lightweight trimap fusion module. The segmentation consistency loss is adopted from automotive segmentation to fit trimap segmentation with the collaboration of RNN (Recurrent Neural Network) to improve the temporal coherence. The experimental results demonstrate that the FTP-VM performs competitively both in composited and real videos only with few given trimaps. The efficiency is eight times higher than the state-of-the-art methods, which confirms its robustness and applicability in real-time scenarios. The code is available at https://github.com/csvt32745/FTP-VM." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 532, + 128, + 544 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 532, + 128, + 544 + ], + "spans": [ + { + "bbox": [ + 47, + 532, + 128, + 544 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 552, + 287, + 660 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 552, + 287, + 660 + ], + "spans": [ + { + "bbox": [ + 46, + 552, + 287, + 660 + ], + "type": "text", + "content": "Image matting aims to estimate the alpha value of each pixel for a target in the input image. Unlike general segmentation, which generates binary values, matting outputs values between 0 and 1, meaning the degree of transparency. The output alpha matrices can describe semi-transparent objects with precise details. As shown in Eq. (1), each pixel color " + }, + { + "bbox": [ + 46, + 552, + 287, + 660 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 46, + 552, + 287, + 660 + ], + "type": "text", + "content": " of an image is composited by the foreground color " + }, + { + "bbox": [ + 46, + 552, + 287, + 660 + ], + "type": "inline_equation", + "content": "F" + }, + { + "bbox": [ + 46, + 552, + 287, + 660 + ], + "type": "text", + "content": ", background color " + }, + { + "bbox": [ + 46, + 552, + 287, + 660 + ], + "type": "inline_equation", + "content": "B" + }, + { + "bbox": [ + 46, + 552, + 287, + 660 + ], + "type": "text", + "content": ", and an alpha value " + }, + { + "bbox": [ + 46, + 552, + 287, + 660 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 46, + 552, + 287, + 660 + ], + "type": "text", + "content": ", where the background can be substituted to generate a matting dataset." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 121, + 671, + 287, + 684 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 121, + 671, + 287, + 684 + ], + "spans": [ + { + "bbox": [ + 121, + 671, + 287, + 684 + ], + "type": "interline_equation", + "content": "C = \\alpha F + (1 - \\alpha) B \\tag {1}", + "image_path": "40c5f66629fdfd43f37ce36bea1c85d73bdb533080498882aee6283e9502e8ad.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 689, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 689, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 689, + 287, + 714 + ], + "type": "text", + "content": "Given a frame like Fig. 1a, a trimap Fig. 1b is the common requirement for image matting, which divides the pixels" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 315, + 144, + 451, + 184 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 315, + 144, + 451, + 184 + ], + "spans": [ + { + "bbox": [ + 315, + 144, + 451, + 184 + ], + "type": "text", + "content": "Ming-Sui Lee \nNational Taiwan University \nmslee@csie.ntu.edu.tw" + } + ] + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 308, + 201, + 426, + 269 + ], + "blocks": [ + { + "bbox": [ + 308, + 201, + 426, + 269 + ], + "lines": [ + { + "bbox": [ + 308, + 201, + 426, + 269 + ], + "spans": [ + { + "bbox": [ + 308, + 201, + 426, + 269 + ], + "type": "image", + "image_path": "90cbd2482832de7c9bca669fde462cb74c463c80909c1ac9742795c54a512bd3.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 337, + 271, + 397, + 280 + ], + "lines": [ + { + "bbox": [ + 337, + 271, + 397, + 280 + ], + "spans": [ + { + "bbox": [ + 337, + 271, + 397, + 280 + ], + "type": "text", + "content": "(a) Memory frame" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 11 + }, + { + "type": "image", + "bbox": [ + 427, + 202, + 545, + 269 + ], + "blocks": [ + { + "bbox": [ + 427, + 202, + 545, + 269 + ], + "lines": [ + { + "bbox": [ + 427, + 202, + 545, + 269 + ], + "spans": [ + { + "bbox": [ + 427, + 202, + 545, + 269 + ], + "type": "image", + "image_path": "686c336f3ab53895b03a65aab8a5caded4b4267db239ccd45a560359ece5315e.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 453, + 271, + 517, + 280 + ], + "lines": [ + { + "bbox": [ + 453, + 271, + 517, + 280 + ], + "spans": [ + { + "bbox": [ + 453, + 271, + 517, + 280 + ], + "type": "text", + "content": "(b) Memory trimap" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_caption" + } + ], + "index": 13 + }, + { + "type": "image", + "bbox": [ + 309, + 281, + 427, + 347 + ], + "blocks": [ + { + "bbox": [ + 309, + 281, + 427, + 347 + ], + "lines": [ + { + "bbox": [ + 309, + 281, + 427, + 347 + ], + "spans": [ + { + "bbox": [ + 309, + 281, + 427, + 347 + ], + "type": "image", + "image_path": "ce389bec65b69a9027eb68ee91d9203626a08a9a3b586587c940b835e4449388.jpg" + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_body" + } + ], + "index": 15 + }, + { + "type": "image", + "bbox": [ + 427, + 281, + 543, + 347 + ], + "blocks": [ + { + "bbox": [ + 427, + 281, + 543, + 347 + ], + "lines": [ + { + "bbox": [ + 427, + 281, + 543, + 347 + ], + "spans": [ + { + "bbox": [ + 427, + 281, + 543, + 347 + ], + "type": "image", + "image_path": "aaa44252ea4df9244931126f9d00de930850dfaecccf1f6c9c30efc49e006d93.jpg" + } + ] + } + ], + "index": 17, + "angle": 0, + "type": "image_body" + } + ], + "index": 17 + }, + { + "type": "image", + "bbox": [ + 310, + 359, + 426, + 425 + ], + "blocks": [ + { + "bbox": [ + 342, + 350, + 394, + 358 + ], + "lines": [ + { + "bbox": [ + 342, + 350, + 394, + 358 + ], + "spans": [ + { + "bbox": [ + 342, + 350, + 394, + 358 + ], + "type": "text", + "content": "(c) Query frame" + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 310, + 359, + 426, + 425 + ], + "lines": [ + { + "bbox": [ + 310, + 359, + 426, + 425 + ], + "spans": [ + { + "bbox": [ + 310, + 359, + 426, + 425 + ], + "type": "image", + "image_path": "16fadd8de87ac6a6226227d138b61b810259bbd2595ec9e74ae09a23b4d65256.jpg" + } + ] + } + ], + "index": 19, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 321, + 426, + 414, + 436 + ], + "lines": [ + { + "bbox": [ + 321, + 426, + 414, + 436 + ], + "spans": [ + { + "bbox": [ + 321, + 426, + 414, + 436 + ], + "type": "text", + "content": "(e) The result of OTVM [42]" + } + ] + } + ], + "index": 20, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 305, + 441, + 545, + 474 + ], + "lines": [ + { + "bbox": [ + 305, + 441, + 545, + 474 + ], + "spans": [ + { + "bbox": [ + 305, + 441, + 545, + 474 + ], + "type": "text", + "content": "Figure 1. An example of an in-street interview video. (d) Automatic matting, (e) Trimap-propagation-based method (f) The proposed method." + } + ] + } + ], + "index": 23, + "angle": 0, + "type": "image_caption" + } + ], + "index": 19 + }, + { + "type": "image", + "bbox": [ + 427, + 359, + 542, + 425 + ], + "blocks": [ + { + "bbox": [ + 441, + 350, + 529, + 358 + ], + "lines": [ + { + "bbox": [ + 441, + 350, + 529, + 358 + ], + "spans": [ + { + "bbox": [ + 441, + 350, + 529, + 358 + ], + "type": "text", + "content": "(d) The result of RVM [32]" + } + ] + } + ], + "index": 18, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 427, + 359, + 542, + 425 + ], + "lines": [ + { + "bbox": [ + 427, + 359, + 542, + 425 + ], + "spans": [ + { + "bbox": [ + 427, + 359, + 542, + 425 + ], + "type": "image", + "image_path": "a3026f79a90fa09de1cfb98ee4458e9c2c85a85f7d02e16e8b98a442cfd68b22.jpg" + } + ] + } + ], + "index": 21, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 432, + 426, + 536, + 435 + ], + "lines": [ + { + "bbox": [ + 432, + 426, + 536, + 435 + ], + "spans": [ + { + "bbox": [ + 432, + 426, + 536, + 435 + ], + "type": "text", + "content": "(f) The result of FTP-VM (ours)" + } + ] + } + ], + "index": 22, + "angle": 0, + "type": "image_caption" + } + ], + "index": 21 + }, + { + "bbox": [ + 305, + 483, + 545, + 520 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 483, + 545, + 520 + ], + "spans": [ + { + "bbox": [ + 305, + 483, + 545, + 520 + ], + "type": "text", + "content": "into three regions: foreground, background and unknown. Matting methods adopt such information to solve alpha values of unknown (gray) regions." + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 304, + 526, + 546, + 670 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 526, + 546, + 670 + ], + "spans": [ + { + "bbox": [ + 304, + 526, + 546, + 670 + ], + "type": "text", + "content": "Video matting extracts an alpha matte of each frame of the given video. The resulting alpha mattes can be used for background replacement, which is decisive for video applications such as video conferencing and visual effects. It is intuitive to perform image matting on each frame of a video. However, severe flickering artifacts would occur in the resultant image sequence. In order to improve the robustness, considering spatial and temporal coherence is the main challenge for video matting as the temporal information helps infer the matting target from the previous frames. Another challenge is to provide a trimap for each frame, which is expected to be a massive cost to most users." + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 305, + 677, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 677, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 677, + 547, + 713 + ], + "type": "text", + "content": "To tackle the above two issues, automatic matting and trimap propagation are addressed in this paper. Automatic matting captures specific targets without trimaps, but" + } + ] + } + ], + "index": 26 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 494, + 35 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 494, + 35 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 494, + 35 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "14337" + } + ] + } + ], + "index": 27 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 288, + 168 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 288, + 168 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 288, + 168 + ], + "type": "text", + "content": "the input videos with ambiguous scenarios highly affect the results. Fig. 1 shows an example of an in-street interview video where an interviewee and passengers occasionally appear simultaneously. While the human matting method [32] attempts to capture all the people, the ambiguity caused by inconspicuous passengers results in unsatisfactory output Fig. 1d. Thus we opt for trimap propagation to select targets more stably as shown in Fig. 1f." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 175, + 288, + 390 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 175, + 288, + 390 + ], + "spans": [ + { + "bbox": [ + 46, + 175, + 288, + 390 + ], + "type": "text", + "content": "While performing trimap propagation, the user is required to provide a pair of so-called memory frame Fig. 1a and memory trimap Fig. 1b, and this information is utilized to propagate throughout the video. Since we are predicting a sequence of three-class segmentation masks, the trimap propagation can be treated as video object segmentation. Recent studies [42, 47, 55] leverage STM (Space-Time Memory network), [35] an emerging video object segmentation model, to produce the trimaps successfully. However, the resultant trimaps usually contain flickers and lead to unsatisfactory results. As STM lacks temporal coherence, we append ConvGRUs [2] to the model to improve stability. Moreover, the previous approaches containing two full models make them unsuitable for interactive applications. We thus combine the two models into an end-to-end model to enhance the speed and performance. The main contributions of this work are summarized as follows." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 397, + 287, + 603 + ], + "type": "list", + "angle": 0, + "index": 5, + "blocks": [ + { + "bbox": [ + 58, + 397, + 287, + 493 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 397, + 287, + 493 + ], + "spans": [ + { + "bbox": [ + 58, + 397, + 287, + 493 + ], + "type": "text", + "content": "- A novel end-to-end video matting model equipped with trimap propagation, called FTP-VM (Fast Trimap Propagation - Video Matting), is proposed. FTP-VM is faster than the previous two-model methods by a large margin while preserving competitive performance in different scenarios. While the frame rate of the previous methods is 5 FPS, the proposed method reaches 40 FPS on an NVIDIA RTX 2080Ti GPU." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 58, + 500, + 287, + 536 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 500, + 287, + 536 + ], + "spans": [ + { + "bbox": [ + 58, + 500, + 287, + 536 + ], + "type": "text", + "content": "- A lightweight trimap fusion module is designed to replace an additional encoder in the STM-based model to make FTP-VM efficient and more powerful." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 58, + 544, + 287, + 603 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 544, + 287, + 603 + ], + "spans": [ + { + "bbox": [ + 58, + 544, + 287, + 603 + ], + "type": "text", + "content": "- Motivated by [38], the segmentation consistency loss from automotive segmentation is adapted to trimap segmentation. The final setting reaching the more satisfactory performance is determined by conducting comprehensive experiments." + } + ] + } + ], + "index": 4 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 47, + 615, + 135, + 628 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 615, + 135, + 628 + ], + "spans": [ + { + "bbox": [ + 47, + 615, + 135, + 628 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 635, + 140, + 647 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 635, + 140, + 647 + ], + "spans": [ + { + "bbox": [ + 47, + 635, + 140, + 647 + ], + "type": "text", + "content": "2.1. Image Matting" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 653, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 653, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 653, + 288, + 715 + ], + "type": "text", + "content": "Non-deep-learning image matting includes two types of methods: The sampling-based approaches [12,16,18,44,48] construct the foreground and background priors, and infer the alpha values by solving the composition equation. The affinity-based methods [4,5,17,24-26,46] propagate the" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 72, + 545, + 216 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 216 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 216 + ], + "type": "text", + "content": "alpha values from known pixels to unknown ones according to similarities under the assumption of local smoothness. These classical methods rely on low-level representations and often require assistance to deal with complex scenes. For deep-learning methods, CNN (Convolution Neural Network) based methods [9, 15, 20, 23, 30, 34, 51] exploit high-level features and achieve state-of-the-art results. Vision-transformer-based methods [36] are emerging by combining global similarity and inductive bias of images. These methods build prior from the extracted features or the similarity to estimate the alpha values and preserve details by the UNet-like [40] architecture." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 228, + 545, + 348 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 228, + 545, + 348 + ], + "spans": [ + { + "bbox": [ + 304, + 228, + 545, + 348 + ], + "type": "text", + "content": "In order to annihilate the need for trimaps, automatic image matting combines segmentation and matting into one task. It aims to matte specific targets such as humans [21, 45] or salient objects [3, 28, 29, 37] without any auxiliary inputs. Mask-guided matting [54] takes a rough segmentation mask as an additional input followed by refinement. However, it cannot process semi-transparent objects due to the binary masks. Background-based methods [31, 41] require a background image instead of a trimap as an auxiliary input so that it needs to handle misaligned backgrounds better." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 360, + 397, + 373 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 360, + 397, + 373 + ], + "spans": [ + { + "bbox": [ + 306, + 360, + 397, + 373 + ], + "type": "text", + "content": "2.2. Video Matting" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 379, + 545, + 547 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 379, + 545, + 547 + ], + "spans": [ + { + "bbox": [ + 304, + 379, + 545, + 547 + ], + "type": "text", + "content": "Temporal coherence plays an essential role in video matting. Most existing methods [1, 10, 27, 43] extend classical image matting methods to the temporal dimension and encounter a similar weakness. RVM [32] places ConvGRU hierarchically to maintain temporal coherency. It performs in real-time due to the efficiency of ConvGRU. DVM [47] uses deformable convolution to warp the feature temporally by estimated offsets but is limited by the kernel size of convolutions. TCVOM [55] leverages guided attention block to compute affinity between frames, and [49] analyzes inter-frame relationships by graph neural network. [21] reduces the flickers by applying post-processing tricks to the results, but the image matting methods still limit the performance." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 558, + 545, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 558, + 545, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 558, + 545, + 715 + ], + "type": "text", + "content": "For trimap propagation, [11] interpolates trimaps by optical flows and contains restrictions caused by weak low-level features from semi-transparent objects. Recent deep-learning-based methods [47, 55] leverage approaches from video object segmentation to perform trimap segmentation before video matting. Decoupling trimap propagation and video matting simplifies the problem and forms a two-stage method. However, the model sometimes needs to be finetuned based on the given trimaps to generate acceptable results. OTVM [42] further improves performance through multi-stage training and joint trimap and alpha prediction modeling. The joint modeling utilizes alpha mattes and trimaps to perform trimap propagation." + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "14338" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 198, + 85 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 198, + 85 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 198, + 85 + ], + "type": "text", + "content": "2.3. Video Object Segmentation" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 90, + 289, + 342 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 90, + 289, + 342 + ], + "spans": [ + { + "bbox": [ + 46, + 90, + 289, + 342 + ], + "type": "text", + "content": "Trimap propagation is a kind of video object segmentation in a semi-supervised setting. The model receives masks of a few frames as auxiliary inputs to hint targets and predicts masks of the remaining frames. After the success of STM [35], different memory matching based methods emerge. Memory matching uses a variant of self-attention to extract the features from the given masks. With frames to predict, called query, and pairs of frames and masks, called memory, the features from the memories are linearly combined based on the similarity between memory and query. If a pixel has a similar context to another one, its similarity score will be high. Thus STM can effectively capture the correspondence and segment the target correctly. STCN (Space-Time Correspondence Network) [8] decouples the relation between frames and masks in the memory encoder to become more efficient and effective. We leverage the similar mechanic of STCN to propagate the trimaps but with a more efficient module. In addition, neither STM nor STCN has a strong temporal correlation between consecutive frames, so ConvGRU [2] is appended to our model to strengthen the temporal coherence as XMem [6]." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 354, + 104, + 366 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 354, + 104, + 366 + ], + "spans": [ + { + "bbox": [ + 47, + 354, + 104, + 366 + ], + "type": "text", + "content": "3. Method" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 374, + 289, + 518 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 374, + 289, + 518 + ], + "spans": [ + { + "bbox": [ + 46, + 374, + 289, + 518 + ], + "type": "text", + "content": "The overall network architecture containing an encoder, trimap fusion module, bottleneck fusion module, and two corresponding decoders is illustrated in Fig. 2. The encoder extracts features from the memory frame " + }, + { + "bbox": [ + 46, + 374, + 289, + 518 + ], + "type": "inline_equation", + "content": "I_{m}" + }, + { + "bbox": [ + 46, + 374, + 289, + 518 + ], + "type": "text", + "content": " and query frame " + }, + { + "bbox": [ + 46, + 374, + 289, + 518 + ], + "type": "inline_equation", + "content": "I_{q}" + }, + { + "bbox": [ + 46, + 374, + 289, + 518 + ], + "type": "text", + "content": ". The trimap fusion module encodes the memory trimap " + }, + { + "bbox": [ + 46, + 374, + 289, + 518 + ], + "type": "inline_equation", + "content": "T_{m}" + }, + { + "bbox": [ + 46, + 374, + 289, + 518 + ], + "type": "text", + "content": " and memory features into memory values. The bottleneck fusion module propagates the trimap information to the query frame and aggregates the features globally. The decoders contain segmentation and matting decoders to estimate the trimap and boundary matte, respectively. Finally, the resulting trimap and boundary matte are integrated into a complete matte." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 527, + 110, + 539 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 527, + 110, + 539 + ], + "spans": [ + { + "bbox": [ + 47, + 527, + 110, + 539 + ], + "type": "text", + "content": "3.1. Encoder" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 545, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 545, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 545, + 289, + 715 + ], + "type": "text", + "content": "The MobileNetV3-Large [22] is adopted as the encoder for its efficiency. The encoder takes a single image as input and extracts features at strides of 2, 4, 8 and 16, respectively. The receptive fields are larger in deeper stages, which makes features at different strides focus on different tasks. The low-level features are for preserving details, while high-level ones are for inferring the matting target. This kind of hierarchy can be employed as an UNet-like structure [40] where it receives skip-connections of the features to avoid information diminishing due to the deeper networks. " + }, + { + "bbox": [ + 46, + 545, + 289, + 715 + ], + "type": "inline_equation", + "content": "I_{m}" + }, + { + "bbox": [ + 46, + 545, + 289, + 715 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 545, + 289, + 715 + ], + "type": "inline_equation", + "content": "I_{q}" + }, + { + "bbox": [ + 46, + 545, + 289, + 715 + ], + "type": "text", + "content": " are passed through the same encoder to reduce the size of the model to enhance efficiency. The extracted memory and query features are denoted as " + }, + { + "bbox": [ + 46, + 545, + 289, + 715 + ], + "type": "inline_equation", + "content": "F_{m}^{s}" + }, + { + "bbox": [ + 46, + 545, + 289, + 715 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 545, + 289, + 715 + ], + "type": "inline_equation", + "content": "F_{q}^{s}" + }, + { + "bbox": [ + 46, + 545, + 289, + 715 + ], + "type": "text", + "content": " where " + }, + { + "bbox": [ + 46, + 545, + 289, + 715 + ], + "type": "inline_equation", + "content": "s" + }, + { + "bbox": [ + 46, + 545, + 289, + 715 + ], + "type": "text", + "content": " represents the stride of the feature." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 306, + 72, + 437, + 85 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 72, + 437, + 85 + ], + "spans": [ + { + "bbox": [ + 306, + 72, + 437, + 85 + ], + "type": "text", + "content": "3.2. Trimap Fusion Module" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 90, + 547, + 369 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 90, + 547, + 369 + ], + "spans": [ + { + "bbox": [ + 304, + 90, + 547, + 369 + ], + "type": "text", + "content": "Fig. 3 shows the architecture of trimap fusion module. It integrates the extracted memory features " + }, + { + "bbox": [ + 304, + 90, + 547, + 369 + ], + "type": "inline_equation", + "content": "F_{m}^{s}" + }, + { + "bbox": [ + 304, + 90, + 547, + 369 + ], + "type": "text", + "content": " and the memory trimap " + }, + { + "bbox": [ + 304, + 90, + 547, + 369 + ], + "type": "inline_equation", + "content": "T_{m}" + }, + { + "bbox": [ + 304, + 90, + 547, + 369 + ], + "type": "text", + "content": " into the memory value " + }, + { + "bbox": [ + 304, + 90, + 547, + 369 + ], + "type": "inline_equation", + "content": "F_{m}^{*}" + }, + { + "bbox": [ + 304, + 90, + 547, + 369 + ], + "type": "text", + "content": ", which will be used to perform memory matching in the bottleneck fusion module. In general video object segmentation methods, the memory value is generated through an additional encoder (e.g. ResNet18 [19]) with a 4-channel input. Introducing another encoder leads to more parameters and a longer training time. Thus we construct a lightweight module to reduce the computation cost and parameters. Illuminated by DeepFillV2 [53], the gated convolutions are utilized instead of vanilla convolutions [23]. DeepFillV2 performs inpainting and requires a multiple-channel mask as an additional input. A gated convolution is composed of two vanilla convolutions, where one extracts features, and the other predicts scales followed by a sigmoid function. The results are then combined by an element-wise multiplication. The gated convolution makes different channels concentrate on different regions and enhances the performance of vanilla convolutions. The downsampled trimaps " + }, + { + "bbox": [ + 304, + 90, + 547, + 369 + ], + "type": "inline_equation", + "content": "T_{m}^{s}" + }, + { + "bbox": [ + 304, + 90, + 547, + 369 + ], + "type": "text", + "content": ", memory features " + }, + { + "bbox": [ + 304, + 90, + 547, + 369 + ], + "type": "inline_equation", + "content": "F_{m}^{s}" + }, + { + "bbox": [ + 304, + 90, + 547, + 369 + ], + "type": "text", + "content": " and output features " + }, + { + "bbox": [ + 304, + 90, + 547, + 369 + ], + "type": "inline_equation", + "content": "F_{m}^{*(s/2)}" + }, + { + "bbox": [ + 304, + 90, + 547, + 369 + ], + "type": "text", + "content": " from the previous level are concatenated and passed through a gated convolution block " + }, + { + "bbox": [ + 304, + 90, + 547, + 369 + ], + "type": "inline_equation", + "content": "g^{s}" + }, + { + "bbox": [ + 304, + 90, + 547, + 369 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 320, + 383, + 545, + 415 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 320, + 383, + 545, + 415 + ], + "spans": [ + { + "bbox": [ + 320, + 383, + 545, + 415 + ], + "type": "interline_equation", + "content": "F _ {m} ^ {* s} = \\left\\{ \\begin{array}{l l} g ^ {s} \\left(\\left[ T _ {m} ^ {s}, F _ {m} ^ {s} \\right]\\right) & \\text {i f} s = 2 \\\\ g ^ {s} \\left(\\left[ T _ {m} ^ {s}, F _ {m} ^ {s}, F _ {m} ^ {* (s / 2)} \\right]\\right) & \\text {i f} s = 4, 8, 1 6 \\end{array} \\right. \\tag {2}", + "image_path": "e1119a9427d5d6716451b4cb91642f6cdff5b8395304d73ef54f594fcc53093d.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 430, + 545, + 456 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 430, + 545, + 456 + ], + "spans": [ + { + "bbox": [ + 304, + 430, + 545, + 456 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 430, + 545, + 456 + ], + "type": "inline_equation", + "content": "s" + }, + { + "bbox": [ + 304, + 430, + 545, + 456 + ], + "type": "text", + "content": " represents the stride and " + }, + { + "bbox": [ + 304, + 430, + 545, + 456 + ], + "type": "inline_equation", + "content": "[\\cdot, \\cdot]" + }, + { + "bbox": [ + 304, + 430, + 545, + 456 + ], + "type": "text", + "content": " denotes channel-wise concatenation. " + }, + { + "bbox": [ + 304, + 430, + 545, + 456 + ], + "type": "inline_equation", + "content": "F_{m}^{*16}" + }, + { + "bbox": [ + 304, + 430, + 545, + 456 + ], + "type": "text", + "content": " is the final output memory value " + }, + { + "bbox": [ + 304, + 430, + 545, + 456 + ], + "type": "inline_equation", + "content": "F_{m}^{*}" + }, + { + "bbox": [ + 304, + 430, + 545, + 456 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 468, + 452, + 479 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 468, + 452, + 479 + ], + "spans": [ + { + "bbox": [ + 306, + 468, + 452, + 479 + ], + "type": "text", + "content": "3.3. Bottleneck Fusion Module" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 486, + 547, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 486, + 547, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 486, + 547, + 714 + ], + "type": "text", + "content": "The bottleneck fusion module consists of a memory matching module, a convolution block attention module (CBAM) [50] and a pyramid pooling module (PPM) [56]. Memory matching module applies the same mechanism of cross-attention as STCN [8]. The query feature " + }, + { + "bbox": [ + 304, + 486, + 547, + 714 + ], + "type": "inline_equation", + "content": "F_{q}^{16}" + }, + { + "bbox": [ + 304, + 486, + 547, + 714 + ], + "type": "text", + "content": " and memory feature " + }, + { + "bbox": [ + 304, + 486, + 547, + 714 + ], + "type": "inline_equation", + "content": "F_{m}^{16}" + }, + { + "bbox": [ + 304, + 486, + 547, + 714 + ], + "type": "text", + "content": " are first projected to the query key " + }, + { + "bbox": [ + 304, + 486, + 547, + 714 + ], + "type": "inline_equation", + "content": "K_{q} \\in \\mathbb{R}^{ch_{k} \\times hw}" + }, + { + "bbox": [ + 304, + 486, + 547, + 714 + ], + "type": "text", + "content": " and memory key " + }, + { + "bbox": [ + 304, + 486, + 547, + 714 + ], + "type": "inline_equation", + "content": "K_{m} \\in \\mathbb{R}^{ch_{k} \\times hw}" + }, + { + "bbox": [ + 304, + 486, + 547, + 714 + ], + "type": "text", + "content": " through a shared convolution. " + }, + { + "bbox": [ + 304, + 486, + 547, + 714 + ], + "type": "inline_equation", + "content": "h" + }, + { + "bbox": [ + 304, + 486, + 547, + 714 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 486, + 547, + 714 + ], + "type": "inline_equation", + "content": "w" + }, + { + "bbox": [ + 304, + 486, + 547, + 714 + ], + "type": "text", + "content": " are 1/16 of the original resolution, and the channel of keys " + }, + { + "bbox": [ + 304, + 486, + 547, + 714 + ], + "type": "inline_equation", + "content": "ch_{k}" + }, + { + "bbox": [ + 304, + 486, + 547, + 714 + ], + "type": "text", + "content": " is 32. The memory values " + }, + { + "bbox": [ + 304, + 486, + 547, + 714 + ], + "type": "inline_equation", + "content": "F_{m}^{*16}" + }, + { + "bbox": [ + 304, + 486, + 547, + 714 + ], + "type": "text", + "content": " from the trimap fusion module are linearly combined based on the similarity score between " + }, + { + "bbox": [ + 304, + 486, + 547, + 714 + ], + "type": "inline_equation", + "content": "K_{q}" + }, + { + "bbox": [ + 304, + 486, + 547, + 714 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 486, + 547, + 714 + ], + "type": "inline_equation", + "content": "K_{m}" + }, + { + "bbox": [ + 304, + 486, + 547, + 714 + ], + "type": "text", + "content": " to generate the matched memory values " + }, + { + "bbox": [ + 304, + 486, + 547, + 714 + ], + "type": "inline_equation", + "content": "F_{m}^{'16}" + }, + { + "bbox": [ + 304, + 486, + 547, + 714 + ], + "type": "text", + "content": ". In addition, the CBAM [50] and PPM [56] are leveraged to integrate the features competently. CBAM scales the features spatially and channel-wisely to strengthen different features from " + }, + { + "bbox": [ + 304, + 486, + 547, + 714 + ], + "type": "inline_equation", + "content": "F_{q}^{16}" + }, + { + "bbox": [ + 304, + 486, + 547, + 714 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 486, + 547, + 714 + ], + "type": "inline_equation", + "content": "F_{m}^{'16}" + }, + { + "bbox": [ + 304, + 486, + 547, + 714 + ], + "type": "text", + "content": ". PPM aggregates the global context from sub-regions of different scales by GAPs (Global Average Pooling), where the scales are set to be 1, 2, 4, and 8, respectively." + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "14339" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 92, + 79, + 504, + 229 + ], + "blocks": [ + { + "bbox": [ + 92, + 79, + 504, + 229 + ], + "lines": [ + { + "bbox": [ + 92, + 79, + 504, + 229 + ], + "spans": [ + { + "bbox": [ + 92, + 79, + 504, + 229 + ], + "type": "image", + "image_path": "f919be1d16db05e9de3628b39c0ad8275ad7f8cfc3e69e276087bcbfaa2b7ed1.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 195, + 239, + 398, + 251 + ], + "lines": [ + { + "bbox": [ + 195, + 239, + 398, + 251 + ], + "spans": [ + { + "bbox": [ + 195, + 239, + 398, + 251 + ], + "type": "text", + "content": "Figure 2. The overall network architecture of FTP-VM." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 67, + 273, + 266, + 378 + ], + "blocks": [ + { + "bbox": [ + 67, + 273, + 266, + 378 + ], + "lines": [ + { + "bbox": [ + 67, + 273, + 266, + 378 + ], + "spans": [ + { + "bbox": [ + 67, + 273, + 266, + 378 + ], + "type": "image", + "image_path": "036cab46cc905ce9e190234017bfb700e9510d66066504a2e3ff867661b211f7.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 99, + 384, + 234, + 396 + ], + "lines": [ + { + "bbox": [ + 99, + 384, + 234, + 396 + ], + "spans": [ + { + "bbox": [ + 99, + 384, + 234, + 396 + ], + "type": "text", + "content": "Figure 3. The trimap fusion module." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 403, + 113, + 415 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 403, + 113, + 415 + ], + "spans": [ + { + "bbox": [ + 47, + 403, + 113, + 415 + ], + "type": "text", + "content": "3.4. Decoders" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 422, + 288, + 590 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 422, + 288, + 590 + ], + "spans": [ + { + "bbox": [ + 46, + 422, + 288, + 590 + ], + "type": "text", + "content": "As GFM [28] claims that decoding semantic information and edge details simultaneously may harm the matting quality, the decoding part is split into two decoders, trimap segmentation and matting. For frame-to-frame propagation, ConvGRU [2] is efficient but lacks long-term context and probably loses track after occlusions. Thus we apply it with memory matching in the bottleneck fusion module to maintain both short-term and long-term temporal coherence. These decoders are designed differently to boost performance and efficiency as PSPM [13]. They are both composed of bilinear upsampling, convolution blocks and ConvGRUs. Each ConvGRU is placed after a convolution block and is only employed for half of the channels of the input feature maps." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "text", + "content": "The trimap segmentation decoder estimates the probability maps with three classes and they are converted into a trimap by selecting the class with the highest probability for each pixel. Since the trimap usually retains fewer details, it is output at a stride of 4 and bilinearly upsampled to the original resolution for speed and stability. ConvGRUs are placed at the stride of 8 and 16. For the matting decoder, it estimates precise matts of the foreground in the boundary with high resolution. Moreover, it is expected to focus on" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 271, + 547, + 369 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 271, + 547, + 369 + ], + "spans": [ + { + "bbox": [ + 304, + 271, + 547, + 369 + ], + "type": "text", + "content": "details, so it starts with features at the stride of 4. " + }, + { + "bbox": [ + 304, + 271, + 547, + 369 + ], + "type": "inline_equation", + "content": "F_T^{16}" + }, + { + "bbox": [ + 304, + 271, + 547, + 369 + ], + "type": "text", + "content": " is upsampled to the stride of 4 and concatenated with " + }, + { + "bbox": [ + 304, + 271, + 547, + 369 + ], + "type": "inline_equation", + "content": "F_T^4" + }, + { + "bbox": [ + 304, + 271, + 547, + 369 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 271, + 547, + 369 + ], + "type": "inline_equation", + "content": "F_T^s" + }, + { + "bbox": [ + 304, + 271, + 547, + 369 + ], + "type": "text", + "content": " denotes the feature obtained from the trimap decoder with a stride of " + }, + { + "bbox": [ + 304, + 271, + 547, + 369 + ], + "type": "inline_equation", + "content": "s" + }, + { + "bbox": [ + 304, + 271, + 547, + 369 + ], + "type": "text", + "content": ". Then it is upsampled and receives skip-connection from " + }, + { + "bbox": [ + 304, + 271, + 547, + 369 + ], + "type": "inline_equation", + "content": "F_q^4" + }, + { + "bbox": [ + 304, + 271, + 547, + 369 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 271, + 547, + 369 + ], + "type": "inline_equation", + "content": "F_q^2" + }, + { + "bbox": [ + 304, + 271, + 547, + 369 + ], + "type": "text", + "content": " until the original resolution. Finally, the pixels in the unknown regions of the resulting trimaps are replaced with the corresponding alpha values in the boundary mattes to generate complete mattes." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 376, + 395, + 388 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 376, + 395, + 388 + ], + "spans": [ + { + "bbox": [ + 306, + 376, + 395, + 388 + ], + "type": "text", + "content": "3.5. Loss Function" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 394, + 546, + 455 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 394, + 546, + 455 + ], + "spans": [ + { + "bbox": [ + 304, + 394, + 546, + 455 + ], + "type": "text", + "content": "Segmentation Loss. The focal loss [33] and consistency loss [38] are considered as the loss functions. The focal loss makes the training focus on the more challenging pixels. " + }, + { + "bbox": [ + 304, + 394, + 546, + 455 + ], + "type": "inline_equation", + "content": "p_c" + }, + { + "bbox": [ + 304, + 394, + 546, + 455 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 394, + 546, + 455 + ], + "type": "inline_equation", + "content": "y_c" + }, + { + "bbox": [ + 304, + 394, + 546, + 455 + ], + "type": "text", + "content": " are the predicted and ground truth probability that a pixel belongs to a class " + }, + { + "bbox": [ + 304, + 394, + 546, + 455 + ], + "type": "inline_equation", + "content": "c" + }, + { + "bbox": [ + 304, + 394, + 546, + 455 + ], + "type": "text", + "content": " in the trimap, and " + }, + { + "bbox": [ + 304, + 394, + 546, + 455 + ], + "type": "inline_equation", + "content": "\\gamma" + }, + { + "bbox": [ + 304, + 394, + 546, + 455 + ], + "type": "text", + "content": " is set to be 2." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 354, + 459, + 545, + 491 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 354, + 459, + 545, + 491 + ], + "spans": [ + { + "bbox": [ + 354, + 459, + 545, + 491 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\text {f o c a l}} = - \\sum_ {c = 1} ^ {3} y _ {c} (1 - p _ {c}) ^ {\\gamma} \\log \\left(p _ {c}\\right) \\tag {3}", + "image_path": "2d267736db75320d4463f70a9c943cb8b8ab1916a45db7f4db9d09d45b783ba2.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 499, + 547, + 632 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 499, + 547, + 632 + ], + "spans": [ + { + "bbox": [ + 304, + 499, + 547, + 632 + ], + "type": "text", + "content": "The consistency loss penalizes pixels with different predictions in consecutive frames. Those pixels are required to be correct in at least one frame of the consecutive pair to avoid interruption in the basic segmentation training. This design ensures that the trimap decoder utilizes the temporal information more appropriately. While the loss in [38] is only used for the correct class, we apply it to all the classes regardless of correctness because we discovered that different weights assigned to correct and wrong classes further improve the performance. The segmentation consistency loss is defined as:" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 329, + 635, + 545, + 667 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 329, + 635, + 545, + 667 + ], + "spans": [ + { + "bbox": [ + 329, + 635, + 545, + 667 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\text {c o n s i s}} = \\sum_ {c = 1} ^ {3} w _ {t, h, w, c} \\cdot \\left\\| p _ {t, h, w, c} - p _ {t + 1, h, w, c} \\right\\| _ {1} \\tag {4}", + "image_path": "ce807a9b626eca0f2811cbf7ba674a3f7a60ddc908f35362062fbdf3f04e040e.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 684, + 471, + 717 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 684, + 471, + 717 + ], + "spans": [ + { + "bbox": [ + 306, + 684, + 471, + 717 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 306, + 684, + 471, + 717 + ], + "type": "inline_equation", + "content": "w_{t,h,w,c} = \\left\\{ \\begin{array}{ll}0.5 & \\text{if } y_{t,h,w} = c \\\\ 0.25 & \\text{else} \\end{array} \\right." + }, + { + "bbox": [ + 306, + 684, + 471, + 717 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "14340" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 198, + 84 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 198, + 84 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 198, + 84 + ], + "type": "text", + "content": "The final trimap segmentation loss is" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 116, + 95, + 287, + 108 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 116, + 95, + 287, + 108 + ], + "spans": [ + { + "bbox": [ + 116, + 95, + 287, + 108 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\text {t r i m a p}} = \\mathcal {L} _ {\\text {f o c a l}} + \\mathcal {L} _ {\\text {c o n s i s .}} \\tag {5}", + "image_path": "c051e95c9c05f1ac2940539f8422cff976bc6e94970ad53b9a1c20c5ef3fa586.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 115, + 289, + 224 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 115, + 289, + 224 + ], + "spans": [ + { + "bbox": [ + 46, + 115, + 289, + 224 + ], + "type": "text", + "content": "Matting Loss. Following RVM [32], the same loss functions are exploited to train the matting network. However, we additionally input masks of the unknown regions to make the matting decoder focus on the boundary more. For the predicted and ground truth alpha matte " + }, + { + "bbox": [ + 46, + 115, + 289, + 224 + ], + "type": "inline_equation", + "content": "\\alpha_{t},\\alpha_{t}^{*}" + }, + { + "bbox": [ + 46, + 115, + 289, + 224 + ], + "type": "text", + "content": " at time " + }, + { + "bbox": [ + 46, + 115, + 289, + 224 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 115, + 289, + 224 + ], + "type": "text", + "content": " and the given mask " + }, + { + "bbox": [ + 46, + 115, + 289, + 224 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 46, + 115, + 289, + 224 + ], + "type": "text", + "content": ", L1 loss " + }, + { + "bbox": [ + 46, + 115, + 289, + 224 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{l1}" + }, + { + "bbox": [ + 46, + 115, + 289, + 224 + ], + "type": "text", + "content": " and pyramid Laplacian loss " + }, + { + "bbox": [ + 46, + 115, + 289, + 224 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{lap}" + }, + { + "bbox": [ + 46, + 115, + 289, + 224 + ], + "type": "text", + "content": " [15, 20] is considered to learn the alpha values and edge details. A temporal coherence loss " + }, + { + "bbox": [ + 46, + 115, + 289, + 224 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{tc}" + }, + { + "bbox": [ + 46, + 115, + 289, + 224 + ], + "type": "text", + "content": " [47] is adopted as well to reduce flickers." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 105, + 233, + 287, + 247 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 105, + 233, + 287, + 247 + ], + "spans": [ + { + "bbox": [ + 105, + 233, + 287, + 247 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {l 1} (M) = \\| M \\cdot \\left(\\alpha_ {t} - \\alpha_ {t} ^ {*}\\right) \\| _ {1} \\tag {6}", + "image_path": "faee1558f3cc756edf1a10a3e32dc0fda6c5bcfdf706ef4abb504f689dd320e5.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 52, + 267, + 287, + 299 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 52, + 267, + 287, + 299 + ], + "spans": [ + { + "bbox": [ + 52, + 267, + 287, + 299 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {l a p} (M) = \\sum_ {s = 1} ^ {5} \\frac {2 ^ {s - 1}}{5} \\| M \\cdot \\left(L _ {p y r} ^ {s} \\left(\\alpha_ {t}\\right) - L _ {p y r} ^ {s} \\left(\\alpha_ {t} ^ {*}\\right)\\right) \\| _ {1} \\tag {7}", + "image_path": "526a7583eacd540ac0dbd5703b115515df605fcfe111d99d22e793d8fd7c9560.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 99, + 311, + 287, + 335 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 99, + 311, + 287, + 335 + ], + "spans": [ + { + "bbox": [ + 99, + 311, + 287, + 335 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {t c} (M) = \\| M \\cdot \\left(\\frac {\\mathrm {d} \\alpha_ {t}}{\\mathrm {d} t} - \\frac {\\mathrm {d} \\alpha_ {t} ^ {*}}{\\mathrm {d} t}\\right) \\| _ {2} \\tag {8}", + "image_path": "8e96876ff00439d02ec3a213bf5fdec8fb0e1e09d861447dca0c39612deea3e2.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 346, + 191, + 359 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 346, + 191, + 359 + ], + "spans": [ + { + "bbox": [ + 47, + 346, + 191, + 359 + ], + "type": "text", + "content": "The overall alpha loss is defined as" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 72, + 369, + 287, + 384 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 72, + 369, + 287, + 384 + ], + "spans": [ + { + "bbox": [ + 72, + 369, + 287, + 384 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\alpha} (M) = \\mathcal {L} _ {l 1} (M) + \\mathcal {L} _ {l a p} (M) + 5 \\cdot \\mathcal {L} _ {t c} (M), \\tag {9}", + "image_path": "fbbacd89c00f8b7794ef34095a0b812d9e57f3e8483446b76edbd9e6d87b6d2c.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 399, + 287, + 435 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 399, + 287, + 435 + ], + "spans": [ + { + "bbox": [ + 46, + 399, + 287, + 435 + ], + "type": "text", + "content": "and it is applied to the unknown region of the predicted trimap " + }, + { + "bbox": [ + 46, + 399, + 287, + 435 + ], + "type": "inline_equation", + "content": "T_{U}" + }, + { + "bbox": [ + 46, + 399, + 287, + 435 + ], + "type": "text", + "content": " and the ground truth trimap " + }, + { + "bbox": [ + 46, + 399, + 287, + 435 + ], + "type": "inline_equation", + "content": "T_{U}^{*}" + }, + { + "bbox": [ + 46, + 399, + 287, + 435 + ], + "type": "text", + "content": ". The final matting loss is" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 104, + 441, + 287, + 455 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 104, + 441, + 287, + 455 + ], + "spans": [ + { + "bbox": [ + 104, + 441, + 287, + 455 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\text {m a t t i n g}} = \\mathcal {L} _ {\\alpha} \\left(T _ {U}\\right) + \\mathcal {L} _ {\\alpha} \\left(T _ {U} ^ {*}\\right). \\tag {10}", + "image_path": "aba9552d9fe1f4010971e27035f15db6b590f4f15b7b05f27b9058d2c32c51d8.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 472, + 124, + 486 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 472, + 124, + 486 + ], + "spans": [ + { + "bbox": [ + 47, + 472, + 124, + 486 + ], + "type": "text", + "content": "4. Experiment" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 47, + 491, + 272, + 505 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 491, + 272, + 505 + ], + "spans": [ + { + "bbox": [ + 47, + 491, + 272, + 505 + ], + "type": "text", + "content": "4.1. Dataset, Metric and Implementation Detail" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 46, + 510, + 289, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 510, + 289, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 510, + 289, + 714 + ], + "type": "text", + "content": "Training Dataset. The models are trained on the image matting dataset, D646 [37], the video matting dataset, VM108 [55], and the background image dataset, BG-20k [29]. D646 contains 546 training images, VM108 includes 80 clips, and BG-20k comprises 15000 background images without salient objects. The foregrounds from the matting datasets and the backgrounds from BG-20k and VM108 are composites to form the training data. Additionally, the video segmentation dataset, Youtube-VIS [52], is adopted to train the trimap segmentation to improve the generalizability of the model. Following RVM [32], the motion augmentation is applied, including affine transformation, color jittering, noise and blur, which differs gradually over time with an easing function. Frames of the matting datasets are randomly cropped to " + }, + { + "bbox": [ + 46, + 510, + 289, + 714 + ], + "type": "inline_equation", + "content": "480 \\times 480" + }, + { + "bbox": [ + 46, + 510, + 289, + 714 + ], + "type": "text", + "content": " while frames of the segmentation dataset are cropped to " + }, + { + "bbox": [ + 46, + 510, + 289, + 714 + ], + "type": "inline_equation", + "content": "352 \\times 352" + }, + { + "bbox": [ + 46, + 510, + 289, + 714 + ], + "type": "text", + "content": " for the larger batch size." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 72, + 547, + 252 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 252 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 252 + ], + "type": "text", + "content": "Evaluation Dataset. The experiments are conducted on three matting datasets: VM108 [55], VM240k [31], and Real Human dataset [49]. VM108 contains 28 composited HD (1920 × 1080) clips with about 23000 frames in the validation set. Due to the variety of objects and the longer length of the sequences, it is chosen as the benchmark in ablation studies. VM240k is a composited human video matting dataset that includes 20 4K (3840 × 2160) videos, each containing 100 frames. Real Human has 19 real HD videos about humans having about 7000 frames in total, with only 1/10 frames annotated. By default, the trimap of the first frame is given to perform trimap propagation and the input resolution is set to be " + }, + { + "bbox": [ + 304, + 72, + 547, + 252 + ], + "type": "inline_equation", + "content": "1024 \\times 576" + }, + { + "bbox": [ + 304, + 72, + 547, + 252 + ], + "type": "text", + "content": ". All trimaps are produced by discretizing the dilated ground truth alpha matrices where " + }, + { + "bbox": [ + 304, + 72, + 547, + 252 + ], + "type": "inline_equation", + "content": "25 \\times 25" + }, + { + "bbox": [ + 304, + 72, + 547, + 252 + ], + "type": "text", + "content": " is chosen as the dilation kernel." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 266, + 547, + 399 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 266, + 547, + 399 + ], + "spans": [ + { + "bbox": [ + 304, + 266, + 547, + 399 + ], + "type": "text", + "content": "Evaluation Metric. The same metrics as in RVM [32] are reported. MAD (mean absolute difference) represents the basic alpha error, MSE (mean square error) focuses on segmentation error, Grad [39] denotes the gradient error, Conn [39] (connectivity) depicts the completeness and dtSSD (mean square error of direct temporal gradient) [14] evaluates the temporal coherence such as flickering. For all metrics, the lower the better. In addition, the number of parameters and FPS (frames per second) of each model are also presented to evaluate efficiency. FPS is measured as FP32 tensor throughput and represents the speed." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 412, + 547, + 544 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 412, + 547, + 544 + ], + "spans": [ + { + "bbox": [ + 304, + 412, + 547, + 544 + ], + "type": "text", + "content": "Implementation Detail. The codes for training are referenced to [7]. All models are trained by an Adam optimizer with a Cosine Annealing learning rate scheduler. The learning rate is set to 1e-4 initially. It takes 120000 iterations in total to train the model. 30000 iterations are required for the image matting dataset, and the remainings are for the video matting dataset. The video segmentation training is interleaved between every 30000 iterations for 10000 iterations. Training is performed on an NVIDIA RTX A6000 and inference is conducted on an NVIDIA RTX 2080Ti GPU." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 306, + 552, + 423, + 564 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 552, + 423, + 564 + ], + "spans": [ + { + "bbox": [ + 306, + 552, + 423, + 564 + ], + "type": "text", + "content": "4.2. Comparative Result" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "type": "text", + "content": "We compared FTP-VM against previous methods with trimap propagation, including STM+TCVOM [35, 55] and OTVM [42]. STM+TCVOM first produces trimaps via STM and performs video matting by TCVOM. The GCA decoder is applied in TCVOM. In addition, STM is finetuned on the memory trimap to generate better results for reference, denoted as STM(ft). OTVM adopts the memory trimap and predicted alpha mattes to perform trimap propagation. Moreover, RVM [32], a human video matting method, is compared on the human matting datasets, including VM240k and Real Human dataset. The model weights from the original implementation are" + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "14341" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 193 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 193 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 193 + ], + "type": "text", + "content": "applied, which are trained on the VM240k training set and a human segmentation dataset. For methods with trimap propagation, the numbers of parameters and speed are reported in Tab. 1. As previous approaches use two complete models to achieve different tasks, much more parameters are introduced. Instead, the FTP-VM combines two models along with a lightweight trimap fusion module so that the model size is significantly reduced, demonstrating that the FTP-VM outperforms other methods by a large margin in terms of efficiency." + } + ] + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 48, + 198, + 286, + 262 + ], + "blocks": [ + { + "bbox": [ + 48, + 198, + 286, + 262 + ], + "lines": [ + { + "bbox": [ + 48, + 198, + 286, + 262 + ], + "spans": [ + { + "bbox": [ + 48, + 198, + 286, + 262 + ], + "type": "table", + "html": "
MethodParameters (M) ↓FPS ↑
Trimap PropagationMatting
STM + TCVOM [35,55]38.9225.715.11
OTVM [42]38.9834.904.32
FTP-VM (Ours)5.1340.16
", + "image_path": "9cfae20483e3dd62d883706129e28a82a72e03011cef7471e3d82950bb297fc7.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 296, + 289, + 392 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 296, + 289, + 392 + ], + "spans": [ + { + "bbox": [ + 46, + 296, + 289, + 392 + ], + "type": "text", + "content": "Quantitative and Qualitative Results. Tab. 2 demonstrates the quantitative results on different datasets. For VM108, OTVM achieves the best and FTP-VM is the second best in the five metrics. Both STM+TCVOM and the finetuned one perform unsatisfactorily in this dataset. An example is illustrated in Fig. 4. Although FTP-VM produces false predictions in the boundary region, it is considered comparative due to the merit of speed." + } + ] + } + ], + "index": 3 + }, + { + "type": "table", + "bbox": [ + 50, + 399, + 286, + 540 + ], + "blocks": [ + { + "bbox": [ + 55, + 266, + 280, + 277 + ], + "lines": [ + { + "bbox": [ + 55, + 266, + 280, + 277 + ], + "spans": [ + { + "bbox": [ + 55, + 266, + 280, + 277 + ], + "type": "text", + "content": "Table 1. Comparison on the number of parameters and speed." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 50, + 399, + 286, + 540 + ], + "lines": [ + { + "bbox": [ + 50, + 399, + 286, + 540 + ], + "spans": [ + { + "bbox": [ + 50, + 399, + 286, + 540 + ], + "type": "table", + "html": "
DatasetMethodMSE ↓MAD ↓Grad ↓dtSSD ↓Conn ↓
VM108 [55]TCVOM [55]68.4793.1218.294.5955.51
TCVOM* [55]31.5448.9810.373.7728.60
OTVM [42]2.9213.382.462.097.28
FTP-VM (Ours)5.1920.743.922.4612.13
VM240k [31]TCVOM [55]19.2521.5711.134.6912.54
TCVOM* [55]1.512.983.011.961.44
OTVM [42]0.564.551.631.320.74
RVM [32]3.027.714.271.832.64
FTP-VM (Ours)0.454.481.541.300.70
Real Human [49]TCVOM [55]34.5940.8114.2310.5624.09
TCVOM* [55]11.7216.4611.208.649.58
OTVM [42]18.1322.798.658.2413.49
RVM [32]2.385.874.865.153.29
FTP-VM (Ours)2.805.875.295.293.27
", + "image_path": "a9b12fe0ab9f9d9282b360d63141bbd7014c6fb41ce8f70308428fdfe6996848.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_body" + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 543, + 287, + 566 + ], + "lines": [ + { + "bbox": [ + 46, + 543, + 287, + 566 + ], + "spans": [ + { + "bbox": [ + 46, + 543, + 287, + 566 + ], + "type": "text", + "content": "Table 2. The quantitative comparison. TCVOM denotes STM+TCVOM and * represents the finetuned model." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 574, + 287, + 671 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 574, + 287, + 671 + ], + "spans": [ + { + "bbox": [ + 46, + 574, + 287, + 671 + ], + "type": "text", + "content": "For VM240k, FTP-VM outperforms other methods in most metrics except MAD. Although RVM is trained on the VM240k dataset, it reveals limited advantage. Fig. 5 compares the qualitative results. STM+TCVOM fails to provide a reasonable result in this example but the finetuned version greatly improves. OTVM occasionally produces unsatisfactory results. Both RVM and FTP-VM generate complete mattes but FTP-VM contains more details." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 677, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 288, + 715 + ], + "type": "text", + "content": "The Real Human dataset which contains real-world videos is also evaluated. As seen from Tab. 2 and Fig. 6, the performance of OTVM drops drastically. 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The qualitative comparison on VM108." + } + ] + } + ], + "index": 20, + "angle": 0, + "type": "image_caption" + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 224, + 547, + 403 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 224, + 547, + 403 + ], + "spans": [ + { + "bbox": [ + 304, + 224, + 547, + 403 + ], + "type": "text", + "content": "includes larger models and requires more training data, it might lead to overfitting the composited dataset, resulting in a lack of generalizability. RVM and FTP-VM both provide pleasing results with a slight difference. In Fig. 6, STM(ft)+TCVOM can produce an acceptable result but the details are missing. OTVM fails to infer the complete shape of the target and the hair part needs to be correctly captured. If the hair parts are zoomed in, it is apparent that FTP-VM describes the details better than RVM. In summary, OTVM outperforms others on VM108 but its performance drops on the other two datasets. 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The qualitative comparison on VM240k." + } + ] + } + ], + "index": 23, + "angle": 0, + "type": "image_caption" + } + ], + "index": 22 + }, + { + "bbox": [ + 304, + 677, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 547, + 715 + ], + "type": "text", + "content": "Trimap Updating Period. In this experiment, various trimap updating periods are tested to evaluate the efficiency of trimap propagation. 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The qualitative comparison on Real Human dataset." + } + ] + } + ], + "index": 25, + "angle": 0, + "type": "image_caption" + } + ], + "index": 19 + }, + { + "type": "image", + "bbox": [ + 127, + 246, + 166, + 293 + ], + "blocks": [ + { + "bbox": [ + 127, + 246, + 166, + 293 + ], + "lines": [ + { + "bbox": [ + 127, + 246, + 166, + 293 + ], + "spans": [ + { + "bbox": [ + 127, + 246, + 166, + 293 + ], + "type": "image", + "image_path": "f512232e51375c66b57f98bc0425bb1c96c048175af4635e1a915db8c8b8af55.jpg" + } + ] + } + ], + "index": 20, + "angle": 0, + "type": "image_body" + } + ], + "index": 20 + }, + { + "type": "image", + "bbox": [ + 168, + 246, + 198, + 293 + ], + "blocks": [ + { + "bbox": [ + 168, + 246, + 198, + 293 + ], + "lines": [ + { + "bbox": [ + 168, + 246, + 198, + 293 + ], + "spans": [ + { + "bbox": [ + 168, + 246, + 198, + 293 + ], + "type": "image", + "image_path": "438e467107b75188713b44ff8d82a9cc7e7350df3c13499a40c97ae881f0c51d.jpg" + } + ] + } + ], + "index": 21, + "angle": 0, + "type": "image_body" + } + ], + "index": 21 + }, + { + "type": "image", + "bbox": [ + 211, + 246, + 243, + 293 + ], + "blocks": [ + { + "bbox": [ + 211, + 246, + 243, + 293 + ], + "lines": [ + { + "bbox": [ + 211, + 246, + 243, + 293 + ], + "spans": [ + { + "bbox": [ + 211, + 246, + 243, + 293 + ], + "type": "image", + "image_path": "f2914dcb35484ee532f36321b278ca425eb5cfcf8167bd0170a96d359687bce9.jpg" + } + ] + } + ], + "index": 22, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 217, + 295, + 236, + 303 + ], + "lines": [ + { + "bbox": [ + 217, + 295, + 236, + 303 + ], + "spans": [ + { + "bbox": [ + 217, + 295, + 236, + 303 + ], + "type": "text", + "content": "RVM" + } + ] + } + ], + "index": 24, + "angle": 0, + "type": "image_caption" + } + ], + "index": 22 + }, + { + "type": "image", + "bbox": [ + 257, + 246, + 285, + 293 + ], + "blocks": [ + { + "bbox": [ + 257, + 246, + 285, + 293 + ], + "lines": [ + { + "bbox": [ + 257, + 246, + 285, + 293 + ], + "spans": [ + { + "bbox": [ + 257, + 246, + 285, + 293 + ], + "type": "image", + "image_path": "9d93f94773fea6219003922dba85b627208b6008b3e9fc8c4e01798d469b5da7.jpg" + } + ] + } + ], + "index": 23, + "angle": 0, + "type": "image_body" + } + ], + "index": 23 + }, + { + "bbox": [ + 46, + 329, + 287, + 426 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 329, + 287, + 426 + ], + "spans": [ + { + "bbox": [ + 46, + 329, + 287, + 426 + ], + "type": "text", + "content": "trimap updates. For example, with period " + }, + { + "bbox": [ + 46, + 329, + 287, + 426 + ], + "type": "inline_equation", + "content": "= 30" + }, + { + "bbox": [ + 46, + 329, + 287, + 426 + ], + "type": "text", + "content": ", the trimap is updated every thirty frames. With period " + }, + { + "bbox": [ + 46, + 329, + 287, + 426 + ], + "type": "inline_equation", + "content": "= 1" + }, + { + "bbox": [ + 46, + 329, + 287, + 426 + ], + "type": "text", + "content": ", the trimap is given at each frame, meaning that the models only concern matting performance without any trimap propagation. This is the setting where the best performance is expected. On the contrary, if only the first trimap is provided, it will be propagated through the whole video. The bidirectional inference strategy is used in trimap propagation as [55]." + } + ] + } + ], + "index": 26 + }, + { + "type": "image", + "bbox": [ + 52, + 434, + 287, + 487 + ], + "blocks": [ + { + "bbox": [ + 52, + 434, + 287, + 487 + ], + "lines": [ + { + "bbox": [ + 52, + 434, + 287, + 487 + ], + "spans": [ + { + "bbox": [ + 52, + 434, + 287, + 487 + ], + "type": "image", + "image_path": "971fd2127f07d6e165095ab7aa4cff76755b2ed12fdd6e110809c146eb61684e.jpg" + } + ] + } + ], + "index": 27, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 95, + 490, + 238, + 501 + ], + "lines": [ + { + "bbox": [ + 95, + 490, + 238, + 501 + ], + "spans": [ + { + "bbox": [ + 95, + 490, + 238, + 501 + ], + "type": "text", + "content": "Figure 7. Trimap updating mechanism." + } + ] + } + ], + "index": 28, + "angle": 0, + "type": "image_caption" + } + ], + "index": 27 + }, + { + "bbox": [ + 46, + 517, + 287, + 662 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 517, + 287, + 662 + ], + "spans": [ + { + "bbox": [ + 46, + 517, + 287, + 662 + ], + "type": "text", + "content": "The comparison on VM108 with different trimap updating periods is illustrated in Fig. 8. It is clear that the shorter the period, the better the performance. While the performance of both FTP-VM and OTVM is not significantly affected by the period, OTVM performs the best overall. Regarding MAD, FTP-VM reveals more advantages when the period becomes longer. However, STM(ft) + TCVOM surpasses FTP-VM with a shorter period, which indicates that the matting ability limits the performance of the proposed method. As for dtSSD, FTP-VM also delivers its merit with fewer flickers when the period is more extended, confirming the stability of the proposed trimap propagation." + } + ] + } + ], + "index": 29 + }, + { + "bbox": [ + 47, + 671, + 141, + 684 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 671, + 141, + 684 + ], + "spans": [ + { + "bbox": [ + 47, + 671, + 141, + 684 + ], + "type": "text", + "content": "4.3. Ablation Study" + } + ] + } + ], + "index": 30 + }, + { + "bbox": [ + 46, + 689, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 689, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 689, + 287, + 713 + ], + "type": "text", + "content": "Ablation on Network Design. In order to justify the network design of FTP-VM, the results of models with" + } + ] + } + ], + "index": 31 + }, + { + "type": "image", + "bbox": [ + 307, + 72, + 427, + 145 + ], + "blocks": [ + { + "bbox": [ + 307, + 72, + 427, + 145 + ], + "lines": [ + { + "bbox": [ + 307, + 72, + 427, + 145 + ], + "spans": [ + { + "bbox": [ + 307, + 72, + 427, + 145 + ], + "type": "image", + "image_path": "99ba83aaaaa683e6f038ba514ef8c009a6db59ef3daa49edfe951e8af16fdb9d.jpg" + } + ] + } + ], + "index": 32, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 149, + 545, + 171 + ], + "lines": [ + { + "bbox": [ + 305, + 149, + 545, + 171 + ], + "spans": [ + { + "bbox": [ + 305, + 149, + 545, + 171 + ], + "type": "text", + "content": "Figure 8. The comparison of MAD and dtSSD with various trimap updating periods." + } + ] + } + ], + "index": 34, + "angle": 0, + "type": "image_caption" + } + ], + "index": 32 + }, + { + "type": "image", + "bbox": [ + 429, + 72, + 549, + 145 + ], + "blocks": [ + { + "bbox": [ + 429, + 72, + 549, + 145 + ], + "lines": [ + { + "bbox": [ + 429, + 72, + 549, + 145 + ], + "spans": [ + { + "bbox": [ + 429, + 72, + 549, + 145 + ], + "type": "image", + "image_path": "71871bb6ba4f6aa8ee3df5c1d9c902d7e682aac1e76d35d47c0bce179c2887ef.jpg" + } + ] + } + ], + "index": 33, + "angle": 0, + "type": "image_body" + } + ], + "index": 33 + }, + { + "bbox": [ + 304, + 180, + 545, + 337 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 180, + 545, + 337 + ], + "spans": [ + { + "bbox": [ + 304, + 180, + 545, + 337 + ], + "type": "text", + "content": "different concepts are displayed in Tab. 3. Two-stage model is the baseline which has similar architecture to the previous works. After combining trimap propagation and matting into a single model, the performance slightly drops but the speed is boosted. Separating the decoder into trimap segmentation and matting decoders, as GFM [28] does, both MSE and MAD are enhanced but Grad and dtSSD degrade. For the same decoders utilizing the single features, it leads to fair stability. The best performance comes from the specially designed decoders, which is shown at the bottom of Tab. 3. The dtSSD does not outperform others, explaining that decoupling the decoder still harms the stability in some sense." + } + ] + } + ], + "index": 35 + }, + { + "type": "table", + "bbox": [ + 308, + 342, + 544, + 394 + ], + "blocks": [ + { + "bbox": [ + 308, + 342, + 544, + 394 + ], + "lines": [ + { + "bbox": [ + 308, + 342, + 544, + 394 + ], + "spans": [ + { + "bbox": [ + 308, + 342, + 544, + 394 + ], + "type": "table", + "html": "
MethodParam ↓FPS ↑MSE ↓MAD ↓Grad ↓dtSSD ↓Conn ↓
2-stage network8.4631.718.8030.005.872.9018.18
Single network4.8250.0710.2130.163.982.3017.24
Same decoders5.4437.339.7228.425.532.8017.51
Different decoders5.1340.165.1920.743.922.4612.13
", + "image_path": "779c325cf51bafa7d7dad09fc67185795f701a105ad5c42069f9c412dc6481d2.jpg" + } + ] + } + ], + "index": 36, + "angle": 0, + "type": "table_body" + } + ], + "index": 36 + }, + { + "bbox": [ + 304, + 437, + 545, + 559 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 437, + 545, + 559 + ], + "spans": [ + { + "bbox": [ + 304, + 437, + 545, + 559 + ], + "type": "text", + "content": "Ablation on the Trimap Fusion Module. The trimap fusion module is designed to avoid introducing an additional backbone, which encodes memory frames and trimaps from scratch. As can be seen from Tab. 4, the additional backbone introduces the most parameters. The vanilla convolution improves efficiency and performance by integrating features from different levels. The gated convolution enables different channels to focus on distinct regions, so it outperforms others in all metrics with slightly increased parameters." + } + ] + } + ], + "index": 38 + }, + { + "type": "table", + "bbox": [ + 308, + 563, + 545, + 611 + ], + "blocks": [ + { + "bbox": [ + 305, + 398, + 545, + 420 + ], + "lines": [ + { + "bbox": [ + 305, + 398, + 545, + 420 + ], + "spans": [ + { + "bbox": [ + 305, + 398, + 545, + 420 + ], + "type": "text", + "content": "Table 3. Ablation on the network designs. Param denotes the number of parameters (M)." + } + ] + } + ], + "index": 37, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 308, + 563, + 545, + 611 + ], + "lines": [ + { + "bbox": [ + 308, + 563, + 545, + 611 + ], + "spans": [ + { + "bbox": [ + 308, + 563, + 545, + 611 + ], + "type": "table", + "html": "
MethodParam ↓MSE ↓MAD ↓Grad ↓dtSSD ↓Conn ↓
Additional backbone7.5911.3430.755.722.8217.81
Vanilla convolution4.948.1224.74.872.7613.75
Gated convolution5.135.1920.743.922.4612.13
", + "image_path": "1736a522fd3f82f45b918bf6300922835d97e8e58b4f6b3428425d419ee32bfd.jpg" + } + ] + } + ], + "index": 39, + "angle": 0, + "type": "table_body" + } + ], + "index": 39 + }, + { + "bbox": [ + 305, + 614, + 545, + 647 + ], + "lines": [ + { + "bbox": [ + 305, + 614, + 545, + 647 + ], + "spans": [ + { + "bbox": [ + 305, + 614, + 545, + 647 + ], + "type": "text", + "content": "Table 4. Ablation on trimap fusion module. Param denotes the number of parameters (M). FPS is not reported since the trimap fusion does not operate at every frame." + } + ] + } + ], + "index": 40, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 305, + 665, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 665, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 665, + 545, + 713 + ], + "type": "text", + "content": "Ablation on Segmentation Consistency Loss. The segmentation consistency loss attempts to encourage the trimap segmentation employing information from previous frames. The results shown in Tab. 5 clearly exhibit the" + } + ] + } + ], + "index": 41 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "14343" + } + ] + } + ], + "index": 42 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 133 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 133 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 133 + ], + "type": "text", + "content": "improvement of temporal consistency. If consistency loss is applied to all the classes, the performance degrades slightly. However, with the strategy of weighting the loss according to the correctness, the results are further enhanced at little cost in sharpness (Grad) and stability (dtSSD)." + } + ] + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 52, + 137, + 286, + 201 + ], + "blocks": [ + { + "bbox": [ + 52, + 137, + 286, + 201 + ], + "lines": [ + { + "bbox": [ + 52, + 137, + 286, + 201 + ], + "spans": [ + { + "bbox": [ + 52, + 137, + 286, + 201 + ], + "type": "table", + "html": "
MethodMSE ↓MAD ↓Grad ↓dtSSD ↓Conn ↓
w/o consistency11.6628.544.432.4017.35
correct class only6.1923.333.752.2813.45
all classes8.7524.644.082.4514.26
all classes w/ weight5.1920.743.922.4612.13
", + "image_path": "2c1a2469890fe8150c220b53b62aebb35847c78a48d2a3cd8956109a817c0749.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 52, + 205, + 282, + 216 + ], + "lines": [ + { + "bbox": [ + 52, + 205, + 282, + 216 + ], + "spans": [ + { + "bbox": [ + 52, + 205, + 282, + 216 + ], + "type": "text", + "content": "Table 5. Ablation on the trimap segmentation consistency loss." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 47, + 226, + 119, + 238 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 226, + 119, + 238 + ], + "spans": [ + { + "bbox": [ + 47, + 226, + 119, + 238 + ], + "type": "text", + "content": "4.4. Discussion" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 245, + 289, + 376 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 245, + 289, + 376 + ], + "spans": [ + { + "bbox": [ + 46, + 245, + 289, + 376 + ], + "type": "text", + "content": "In Fig. 9, suppose the memory trimap aims at the left person. FTP-VM provides a correct result but OTVM attempts to matte all the people. This is due to overfitting on the composited dataset where salient objects are selected as the foreground. Moreover, STM-based methods such as OTVM store the resulting masks to maintain temporal coherence during memory matching. In other words, memory matching operates globally and cannot regularize the pixels spatially, which results in weaker coherence. 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The qualitative comparison between OTVM and FTP-VM on the target selection of the human video." + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_caption" + } + ], + "index": 11 + }, + { + "type": "image", + "bbox": [ + 168, + 529, + 285, + 590 + ], + "blocks": [ + { + "bbox": [ + 168, + 529, + 285, + 590 + ], + "lines": [ + { + "bbox": [ + 168, + 529, + 285, + 590 + ], + "spans": [ + { + "bbox": [ + 168, + 529, + 285, + 590 + ], + "type": "image", + "image_path": "a41d8b3284784ed34eae0b2005ae89552661d3fcdfd04c13956caad4453eaf1b.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 200, + 591, + 253, + 600 + ], + "lines": [ + { + "bbox": [ + 200, + 591, + 253, + 600 + ], + "spans": [ + { + "bbox": [ + 200, + 591, + 253, + 600 + ], + "type": "text", + "content": "FTP-VM (Ours)" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_caption" + } + ], + "index": 13 + }, + { + "bbox": [ + 46, + 636, + 288, + 708 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 636, + 288, + 708 + ], + "spans": [ + { + "bbox": [ + 46, + 636, + 288, + 708 + ], + "type": "text", + "content": "However, there remain some challenging cases as shown in Fig. 10. 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Challenging cases. Left: query frames. Right: results." + } + ] + } + ], + "index": 31, + "angle": 0, + "type": "image_caption" + } + ], + "index": 28 + }, + { + "type": "image", + "bbox": [ + 425, + 434, + 543, + 501 + ], + "blocks": [ + { + "bbox": [ + 425, + 434, + 543, + 501 + ], + "lines": [ + { + "bbox": [ + 425, + 434, + 543, + 501 + ], + "spans": [ + { + "bbox": [ + 425, + 434, + 543, + 501 + ], + "type": "image", + "image_path": "040e88e55e13c0bca107c5153205e15e7e7177ec7df96d20177e1cf3a68104f4.jpg" + } + ] + } + ], + "index": 30, + "angle": 0, + "type": "image_body" + } + ], + "index": 30 + }, + { + "bbox": [ + 306, + 542, + 379, + 554 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 542, + 379, + 554 + ], + "spans": [ + { + "bbox": [ + 306, + 542, + 379, + 554 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 32 + }, + { + "bbox": [ + 304, + 562, + 546, + 706 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 562, + 546, + 706 + ], + "spans": [ + { + "bbox": [ + 304, + 562, + 546, + 706 + ], + "type": "text", + "content": "FTP-VM, a novel end-to-end video matting model with trimap propagation, is proposed in this paper. The designed lightweight trimap fusion module is introduced to propagate the given trimap in the memory matching. Moreover, the segmentation consistency loss is adopted to fit trimap segmentation better and improve the performance. The proposed FTP-VM reaches 40 FPS, eight times faster than the cutting-edge two-model methods, TCVOM and OTVM. Extensive experiments are conducted to confirm the competitive performance in various scenarios. Its robustness and generalizability provide the foundation for more advanced developments and broader applications." + } + ] + } + ], + "index": 33 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "14344" + } + ] + } + ], + "index": 34 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 288, + 713 + ], + "type": "list", + "angle": 0, + "index": 15, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 144 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 144 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 144 + ], + "type": "text", + "content": "[1] Nicholas Apostoloff and Andrew Fitzgibbon. 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In Proceedings of the IEEE conference on computer vision and pattern recognition, pages 2881-2890, 2017. 3" + } + ] + } + ], + "index": 0 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 749, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 749, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 749, + 318, + 757 + ], + "type": "text", + "content": "14347" + } + ] + } + ], + "index": 1 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 10 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Endpoints Weight Fusion for Class Incremental Semantic Segmentation/ff7be89f-f21f-4256-a5c9-a98275c1a5e9_content_list.json b/2023/Endpoints Weight Fusion for Class Incremental Semantic Segmentation/ff7be89f-f21f-4256-a5c9-a98275c1a5e9_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..f399b35bbadd2fad39fc070eb7b6359c46a8215a --- /dev/null +++ b/2023/Endpoints Weight Fusion for Class Incremental Semantic Segmentation/ff7be89f-f21f-4256-a5c9-a98275c1a5e9_content_list.json @@ -0,0 +1,1329 @@ +[ + { + "type": "text", + "text": "Endpoints Weight Fusion for Class Incremental Semantic Segmentation", + "text_level": 1, + "bbox": [ + 124, + 130, + 846, + 152 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Jia-Wen Xiao $^{1*}$ Chang-Bin Zhang $^{1*}$ Jiekang Feng $^{2}$ Xialei Liu $^{1\\dagger}$ Joost van de Weijer $^{3}$ Ming-Ming Cheng $^{1}$ VCIP, CS, Nankai University $^{2}$ Tianjin University $^{3}$ Computer Vision Center, Universitat Autònoma de Barcelona", + "bbox": [ + 200, + 179, + 774, + 252 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 286, + 313, + 301 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Class incremental semantic segmentation (CISS) focuses on alleviating catastrophic forgetting to improve discrimination. Previous work mainly exploits regularization (e.g., knowledge distillation) to maintain previous knowledge in the current model. However, distillation alone often yields limited gain to the model since only the representations of old and new models are restricted to be consistent. In this paper, we propose a simple yet effective method to obtain a model with a strong memory of old knowledge, named Endpoints Weight Fusion (EWF). In our method, the model containing old knowledge is fused with the model retaining new knowledge in a dynamic fusion manner, strengthening the memory of old classes in ever-changing distributions. In addition, we analyze the relationship between our fusion strategy and a popular moving average technique EMA, which reveals why our method is more suitable for class-incremental learning. To facilitate parameter fusion with closer distance in the parameter space, we use distillation to enhance the optimization process. Furthermore, we conduct experiments on two widely used datasets, achieving state-of-the-art performance.", + "bbox": [ + 75, + 316, + 473, + 636 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 672, + 209, + 688 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "As a fundamental task, semantic segmentation plays a key role in visual applications [10, 25]. Previous fully-supervised works aim to segment fixed classes defined in the training set. However, the trained segmentation model is expected to recognize more classes in realistic applications. One straightforward solution is to re-train the model on the entire dataset by mixing old and new data. Nevertheless, this strategy will bring huge labeling and training costs. From the transfer learning perspective [22, 30], another plain solution is to adjust the previously learned model on the newly added data. But the model will overfit to new", + "bbox": [ + 75, + 699, + 468, + 864 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/da9cb0f42c6b0e5591a921adb95d161b04904ac4ebded0bcf9d462a924d5dac2.jpg", + "image_caption": [ + "Figure 1. Illustration of different fusion strategies for incremental learning. Ensemble methods utilize multiple models to accumulate more knowledge. Compression methods reduce the model size and distill the knowledge into a small network. While Reparameterization methods use equivalent operations for model fusion. Our Endpoints Weight Fusion (EWF) proposes model addition with a dynamic factor $(\\alpha_{t})$ with no further training." + ], + "image_footnote": [], + "bbox": [ + 511, + 292, + 877, + 569 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "classes quickly, while forgetting previous old classes. This phenomenon is also known as catastrophic forgetting [35].", + "bbox": [ + 496, + 729, + 892, + 760 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "To alleviate the problem of catastrophic forgetting without extra labeling or training cost, class incremental semantic segmentation (CISS) [3, 16, 50] aims at optimizing the trade-off between maintaining discrimination for old classes and learning knowledge of new classes. Most works [3, 16, 17, 37] designed regularization methods to maintain a balance between memorizing old knowledge and learning new one. We observe that existing works can still suffer from catastrophic forgetting, resulting in a significant", + "bbox": [ + 496, + 763, + 893, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 810, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*The first two authors contribute equally.", + "bbox": [ + 94, + 875, + 344, + 887 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "† Corresponding author (xialei@nankai.edu.cn)", + "bbox": [ + 96, + 887, + 344, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "7204", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "performance drop in old classes. In the scenario of CISS, not only the previous data is not accessible due to privacy issues or data storage limitations, but regions of old classes in the newly added dataset are labeled as background, which further exacerbates the model over-fitting.", + "bbox": [ + 75, + 90, + 468, + 165 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Besides, training a new model from the old one and fusing them to obtain the final model is a common strategy in continual learning. As shown in Fig. 1, we roughly divide them into four categories with two stages of model expansion and fusion. Some methods [27, 33, 42, 47] propose to expand the model in incremental steps and ensemble the old and new outputs, which have large memory and inference costs. While some works apply compression [46, 47] to compress the old and new model to a unified model with fewer parameters. Nevertheless, these require further training on only new data, which can lead to a bias toward new data. Subsequently, some works [50, 53] explore knowledge decoupling and perform linear parameter fusion with reparameterization. However, this is an intra-module fusion strategy, which is restricted to certain operations. As the last category, we propose Endpoints Weight Fusion (EWF) in the form of parameter addition between the old and new model with a dynamic factor, which requires no further training and re-parameterization, and maintains a constant model size as more tasks are encountered.", + "bbox": [ + 75, + 167, + 470, + 467 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In this work, we adapt weight fusion to CISS and propose the EWF strategy, which aims at utilizing weight fusion to find a new balance between old and new knowledge. During incremental training, we choose a starting point and an ending point model of the current task training trajectory. The starting point represents the old knowledge, while the ending point represents the new knowledge. After learning the current task, a dynamic weight fusion is proposed for efficient knowledge integration. We aggregate them by taking the weighted average of the corresponding parameters of the two models. Nevertheless, the training procedure without restraints on the model would increase the parameter distance between the start and end points, limiting the performance improvement brought by the EWF strategy. To overcome this shortcoming, we further enhance the EWF strategy with a knowledge distillation scheme [16, 17, 50], which can largely increase the similarity of the models at the two points and boost the efficiency of EWF.", + "bbox": [ + 75, + 469, + 468, + 739 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To summarize, the main contributions of this paper are:", + "bbox": [ + 96, + 741, + 460, + 757 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- We propose an Endpoints Weight Fusion strategy, which has no cost of further training and keeps the model size the same. It can effectively find a new balance between old and new categories and alleviate catastrophic forgetting.", + "- Our method can be easily integrated with several state-of-the-art methods. In several CISS scenarios of long sequences, it can boost the baseline performance by" + ], + "bbox": [ + 94, + 768, + 467, + 900 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "more than $20\\%$ .", + "bbox": [ + 532, + 90, + 640, + 104 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "- We conduct experiments on various CISS scenarios, which demonstrate that our method achieves the state-of-the-art performance on both PASCAL VOC and ADE20K.", + "bbox": [ + 517, + 118, + 890, + 178 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 500, + 194, + 640, + 210 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Class Incremental Learning. Class incremental learning mainly focuses on alleviating catastrophic forgetting while learning the discriminative information required for the newly coming classes. It is most commonly analyzed in image classification, and the techniques can be roughly divided into three categories [11]. Many works [43-45] focus on the structural properties of the model (i.e., Structural-Based Method). The idea is to freeze old models and expand the architecture space to learn new knowledge, which normally results in a growing capacity and memory size of the model. Another way is to regularize models during incremental learning (i.e., Regularization-Based Method) [7, 8, 12, 17], strengthening memory via constraints (e.g., knowledge distillation [39, 41] or gradient penalty [26, 29]). These methods bring the negligible cost to the learning process, but they allow for less freedom for parameter updates. Some other methods [1,2,28] propose to review knowledge through rehearsal (i.e., Rehearsal-Based Method). They store old data and mix it with new data to re-train the model [5, 21, 52].", + "bbox": [ + 496, + 219, + 890, + 521 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Class Incremental Semantic Segmentation. Semantic segmentation [19] aims at assigning different categories to each single pixel, and has recently attracted attention for learning in a class incremental learning scenario [3, 16]. Nevertheless, data for semantic segmentation takes more space [24, 48] to be stored compared to the classification problem. Therefore, recent work mainly concentrates on utilizing distillation to transfer old knowledge to the new model without saving exemplars from old tasks.", + "bbox": [ + 496, + 523, + 890, + 657 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "MiB [4] proposes to model the potential classes to tackle semantic drift. PLOP [16] applies feature distillation to restrict representation ability. SDR [37] uses prototype matching to strengthen consistency in latent space. And RC-IL [50] analyzes the disadvantages of strip pooling and proposes average-pooling-based distillation to back up training. On the contrary, SSUL [6] does not apply distillation and proposes to fix the feature extractor instead of updating its parameters. In addition, they introduce thousands of extra data to help generate pseudo labels. But, simply fixing the model definitely does damage to the balance between plasticity and stability, and it is not sustainable when facing huge amounts of newly coming data. On the other hand, only applying distillation can restrict performance, since it can just limit the representation of new data to be the same. Summarizing the above thoughts and", + "bbox": [ + 496, + 659, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "7205", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/72d967673e47332c1b2196771fce9283c8664ceff66cd805ef96b72dab107e01.jpg", + "image_caption": [ + "Figure 2. Illustration of our Endpoints Weight Fusion (EWF) framework. On the left side, we illustrate training and testing processes. Training is enhanced by knowledge distillation and fusion is applied after training to accumulate all seen knowledge. On the right side, given a $3 \\times 3$ convolution layer and a normalization layer, they are fused by using a dynamic trade-off parameter $\\alpha_{t}$ . Note that there is no computation cost for our fusion process." + ], + "image_footnote": [], + "bbox": [ + 80, + 84, + 890, + 340 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "inspired by RC-IL [50], we design a strategy different from the above, cooperating with distillation and maintaining the balance between the old and new knowledge with model weight fusion.", + "bbox": [ + 75, + 406, + 470, + 467 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Weight Fusion Method. Weight Fusion is widely used in neural network training to improve performance. It can be applied with both linear and nonlinear operations. In linear mode, RCM [27] explores the additivity of convolution and applies it on multi-task learning. ACNet [14] and RepVGG [15] first propose structural re-parameterization, which is used to merge multi-branch Convolution-Batch Normalization serial sequences to a plain Convolution layer. RC-IL ingeniously exploits this operation to establish a representation compensation mechanism in continual learning. In nonlinear mode, weight averaging is commonly used to bring closer connections between different models. Famous methods like BYOL [20] use EMA [38] to improve the knowledge transfer effect or model robustness. From this point, we design a strategy to reach a new balance, which has no effect on the current training process and fully releases the learning ability of the model.", + "bbox": [ + 75, + 468, + 468, + 726 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Method", + "text_level": 1, + "bbox": [ + 76, + 743, + 166, + 758 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Preliminaries", + "text_level": 1, + "bbox": [ + 76, + 768, + 217, + 784 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We consider a multi-step training process where $T$ tasks are sequentially learned by model $f_{\\theta}$ in a fully supervised scenario for semantic segmentation, where $f$ is parameterized by parameter $\\theta$ . Here $f_{\\theta_t}$ denotes the model at task $t$ . Each task contains a dataset $\\mathcal{D}_t = \\{x_i,y_i\\}$ , where $x_{i}$ denotes the data and $y_{i}$ denotes the corresponding label. The training label space of the task $T$ is denoted as $C_t\\bigcup \\{c_b\\}$ ,", + "bbox": [ + 75, + 794, + 470, + 902 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $C_t$ includes all classes that appear in this task, and $c_b$ represents the background. Since $C_i \\cap C_j = \\emptyset$ , the objective of different tasks are not the same, easily leading to catastrophic forgetting. To save annotation costs, only the categories that need to be learned at this stage will be labeled. Thus, $c_b$ contains not only the real background, but also the classes appearing in past and future tasks. This complicates the training of the model $f_\\theta$ since the background label $c_b$ can refer to different classes at different tasks. This exacerbates the severity of forgetting.", + "bbox": [ + 496, + 406, + 892, + 558 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. Endpoints Weight Fusion (EWF)", + "text_level": 1, + "bbox": [ + 498, + 566, + 789, + 583 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "As illustrated in Fig. 1, the existing model expansion-fusion methods have their own drawbacks for enhancing the model's memory of old knowledge. Thus, to better retain the old knowledge while boosting the learning ability of the model, we introduce our Endpoints Weight Fusion strategy. Considering the training process at step $t$ , we choose a starting point model and an ending point model. The final model of the previous step $(\\theta_{old})$ is regarded as the best container of old knowledge. While the model after training on the current task $(\\theta_{new})$ contains the discriminative information for new classes. Additionally, we introduce another parameter $\\alpha$ for the endpoints weight fusion, aiming at fusing two sets of parameters in a certain ratio. This ratio can be seen as a balance factor. Therefore, the operation of endpoints weight fusion can be written as:", + "bbox": [ + 496, + 590, + 890, + 816 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\theta_ {\\text {b a l a n c e d}} = \\alpha_ {t} \\theta_ {\\text {n e w}} + (1 - \\alpha_ {t}) \\theta_ {\\text {o l d}} \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 575, + 828, + 890, + 844 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where the $\\theta_{\\text{balanced}}$ denotes the final model of this task, and the $\\theta_{old}, \\theta_{new}$ are defined as above. Furthermore, the number of incremental categories (denoted as $N_{\\text{new}}$ ) and orig-", + "bbox": [ + 496, + 854, + 892, + 902 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "7206", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "inal categories (denoted as $N_{old}$ ) to a certain extent represent the degree of emphasis on the $\\theta_{new}$ and $\\theta_{old}$ . For the selection of $\\alpha_{t}$ , we need to consider $N_{new}$ and $N_{old}$ in the current learning step. We decide to replace the constant ratio with an equation related to $N_{new}$ and $N_{old}$ . In detail, this formula can be expressed as:", + "bbox": [ + 75, + 90, + 472, + 183 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\alpha_ {t} = \\sqrt {\\frac {N _ {n e w}}{N _ {n e w} + N _ {o l d}}} \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 194, + 190, + 468, + 224 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "It can be used across different tasks and scenarios. It can adapt to each task in CISS with a dynamic factor. We illustrate the main idea of our method in Fig. 2.", + "bbox": [ + 75, + 231, + 468, + 276 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Knowledge distillation enhanced for EWF. In practice, training without any constraint will significantly increase the distance between different models and break the similarity of model representations. That means it deteriorates the forgetting of the model, which further undermines the model's ability to discriminate new classes. Moreover, guaranteeing a low error linear path between two distant models is an overly strong assumption. Thus, choosing a model trained without constraints as an ending point is potentially harmful, and we, therefore, introduce knowledge distillation to enhance the compatibility of the models of our Endpoints Weight Fusion method.", + "bbox": [ + 75, + 276, + 470, + 455 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Knowledge distillation is a commonly used technique to prevent models from forgetting. As stated above, we utilize distillation to back up our strategy, limiting the distance between two endpoints and forcing them to be similar. In general, distillation used in continual learning is mainly divided into two categories, i.e., feature-based distillation and logit-based distillation. They can be represented as:", + "bbox": [ + 75, + 458, + 472, + 565 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} L _ {F D} = \\frac {1}{| D |} \\sum_ {(x _ {i}, y _ {i}) \\sim D} | | \\Psi_ {o l d} (x _ {i}) - \\Psi_ {n e w} (x _ {i}) | | ^ {2} \\\\ L _ {L D} = \\frac {1}{| D |} \\sum_ {\\left(x _ {i}, y _ {i}\\right) \\sim D} K L \\left(\\Phi_ {o l d} \\left(\\Psi_ {o l d} \\left(x _ {i}\\right)\\right), \\Phi_ {n e w} \\left(\\Psi_ {n e w} \\left(x _ {i}\\right)\\right)\\right) \\tag {3} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 76, + 571, + 486, + 662 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "$\\Psi_{old} / \\Phi_{old}$ and $\\Psi_{new} / \\Phi_{new}$ denote old and new feature extractor/classifier respectively, and $D$ is the corresponding dataset of the incremental learning step. In CISS, two popular distillation losses (i.e., UNKD, POD) are proposed by [3, 16], respectively. The former is a logit-based distillation and the latter is a feature-based distillation. They can be easily integrated into our method.", + "bbox": [ + 75, + 664, + 468, + 768 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Discussion on EMA v.s. EWF. An update strategy similar to our method is using EMA [38] to update the model. Here we will discuss the difference between our method EWF and EMA, and the advantages of EWF. The EMA strategy maintains a moving average model during training, and uses this model to replace the final model for inference. The moving average model can be represented as:", + "bbox": [ + 75, + 768, + 470, + 875 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nv ^ {i} = \\beta v ^ {i - 1} + (1 - \\beta) \\theta^ {i} \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 181, + 883, + 468, + 902 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/54381d139f166d324c550961ec8036ff16a9aefec15b0990e92169561ab052ed.jpg", + "image_caption": [ + "Figure 3. Representation similarity between old model $\\theta^1$ before training and being trained new model $\\theta^i$ . The similarity measure we use is cosine similarity. We extract the intermediate results of the feature extractors of the old and new networks and calculate the average of the cosine similarity between them." + ], + "image_footnote": [], + "bbox": [ + 519, + 90, + 875, + 271 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where the $v^{i}$ denotes the moving average of the first $i$ models, and $\\theta^i$ denotes the model after $i$ th iteration. $\\beta$ is the moving average parameter, which is usually set as 0.9/0.99. It is easy to see that the EMA is an inter-iteration operation, which is easier to realize due to the low distance between models. Since we use SGD as an optimizer, following Eq. 5, the results of EMA and EWF can be represented as $v^n$ and $\\theta_{\\text{balanced}}$ in Eq. 6. Note that the learning rate does not affect the result of the analysis, so we set the learning rate to 1. The more detailed derivations are in the Appendix.", + "bbox": [ + 496, + 392, + 893, + 545 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\theta^ {n} = \\theta^ {n - 1} - \\nabla_ {L} \\left(\\theta^ {n - 1}\\right) \\\\ = \\theta^ {1} - \\sum_ {k = 1} ^ {n} \\nabla_ {L} \\left(\\theta^ {k}\\right) \\tag {5} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 604, + 554, + 890, + 614 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nv ^ {n} = \\theta^ {1} - \\sum_ {k = 1} ^ {n - 1} (1 - \\beta^ {n - k}) \\nabla_ {L} \\left(\\theta^ {k}\\right) \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 570, + 627, + 890, + 676 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\theta_ {b a l a n c e d} = \\theta^ {1} - \\alpha \\sum_ {k = 1} ^ {n - 1} \\nabla_ {L} \\left(\\theta^ {k}\\right)\n$$\n", + "text_format": "latex", + "bbox": [ + 570, + 672, + 785, + 712 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Since the $\\beta$ is usually set to $0.9 / 0.99$ and the $\\alpha$ is set following Eq. 2, $\\alpha$ is always smaller than $\\beta$ . According to Eq. 6, EMA gives more weight to the gradient of early time, and then gradually attenuates the influence of gradients in subsequent iterations. On the contrary, EWF gives the gradient of different parts a relatively uniform weight. Besides, to better observe the stability of incremental learning step, we calculate the representations similarity between $\\theta^1$ and $\\theta^i$ . According to our observation in an incremental step, as shown in Fig. 3, the similarity of representations between $\\theta^1$ and $\\theta^i$ first decreases and then increases, and gradually stabilizes in the subsequent stages. This reveals that in order", + "bbox": [ + 496, + 719, + 893, + 901 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "7207", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 3 + }, + { + "type": "code", + "sub_type": "algorithm", + "code_caption": [ + "Algorithm 1 Pseudo Code for EWF in incremental steps" + ], + "code_body": "Require: $f,\\theta_0,T,D_T$ and learning rate $\\gamma$ $t\\gets 1$ \nwhile $t\\leq T$ do Initialize $N_{new},N_{old}$ $\\theta^1\\gets \\theta_{t - 1}$ $\\alpha_{t}\\leftarrow \\sqrt{\\frac{N_{new}}{N_{new} + N_{old}}}$ $i\\gets 1$ \nwhile not converged do Sample mini-batch $\\{x_i,y_i\\} \\sim D$ $\\theta^{i + 1}\\gets \\theta^i -\\gamma \\nabla_{LCE + LKD}(f_{\\theta^i})$ $i\\gets i + 1$ \nend while \n $\\theta_{old}\\gets \\theta^1,\\theta_{new}\\gets \\theta^i$ $\\theta_{balanced}\\gets \\alpha_t\\theta_{new} + (1 - \\alpha_t)\\theta_{old}$ $\\theta_t\\gets \\theta_{balanced}$ $t\\gets t + 1$ \nend while", + "bbox": [ + 76, + 109, + 356, + 375 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "to learn new knowledge, the representation will first collapse and then recover under the action of the distillation and cross-entropy losses. Then EMA concentrates more of the gradient on the early collapsed process, while our method pays more attention to the useful gradient information after the recovery. From this perspective, our method is theoretically better than EMA in CISS.", + "bbox": [ + 75, + 402, + 468, + 508 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.3. Overall Framework", + "text_level": 1, + "bbox": [ + 76, + 521, + 266, + 536 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "As stated above, to remember knowledge from old tasks, we borrow knowledge distillation to strengthen the model's memory. To learn the discrimination of new classes, we use the Cross-Entropy loss to optimize the model. In general, the objective is given by:", + "bbox": [ + 75, + 546, + 468, + 622 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\min _ {\\theta_ {t}} \\mathcal {L} _ {C E} \\left(\\theta_ {t}\\right) + \\mathcal {L} _ {K D} \\left(\\theta_ {t}; \\theta_ {t - 1}\\right) \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 166, + 635, + 468, + 656 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "And the overall algorithm of EWF is shown in Alg. 1.", + "bbox": [ + 76, + 670, + 433, + 686 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 76, + 702, + 209, + 719 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We demonstrate experimental protocols, scenarios and training details. Furthermore, we evaluate our algorithm through quantitative and qualitative experiments.", + "bbox": [ + 75, + 728, + 468, + 773 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.1. Experimental setups", + "text_level": 1, + "bbox": [ + 76, + 785, + 271, + 801 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Protocols. In general, the training for CISS is divided into $T$ steps, and each step denotes a task, where the labeled classes are disjoint in each of them. We adopt the overlapped setting as other works, in which the current training data may contain potential classes labeled as background in previous steps. The overlapped setting is more realistic, and", + "bbox": [ + 75, + 809, + 470, + 902 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "therefore we only evaluate on this setup as previous methods [6, 16]. Following existing works [3, 16, 50], we conduct experiments on two widely used segmentation datasets, PASCAL VOC 2012 [18] and ADE20K [51]. The PASCAL VOC 2012 dataset [18] contains 10,582 training images and 1449 validation images with 20 object classes and the background class. The ADE20K dataset [51] is composed of 150 classes and contains 20, 210 training images, and 2000 validation images. Following previous works [3, 16, 50], $X - Y$ denotes different settings for CISS. In the $X - Y$ setting, the model can recognize $X$ classes in the initial step, and then is supposed to learn $Y$ newly added classes in each following step. At each step, only current task data is available for training. We perform experiments on PASCAL VOC 2012 [18] with four settings, 15-1, 10-1, 5-3 and 19-1. On ADE20K [51], we verify the effectiveness of our method on three settings, 100-5, 100-10, and 100-50.", + "bbox": [ + 496, + 90, + 890, + 347 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Implementation Details. Following existing works [3, 16, 50], we apply Deeplab-v3 [9] as our segmentation model with ResNet-101 [23] as a backbone. We also use in-place activated batch normalization [40] in the backbone. In our experiments, we use some data augmentations, including horizontal flip and random crop. The ratio $\\alpha_{t}$ for EWF is defined as Eq.2. Using SGD optimizer, we train the model for 30 (PASCAL VOC 2012) and 60 (ADE20K) epochs in each step with a batch size of 24. We set the initial learning rate as 0.01 for the first training step and 0.001 for the next continual learning steps. All experiments are conducted on 4 RTX 2080Ti GPUs. The learning rate is decayed with poly schedule. During training, we use $20\\%$ of the training set as validation, and report the mean Intersect over Union (mIoU) on the original validation set.", + "bbox": [ + 496, + 349, + 892, + 575 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.2. Comparison to competing methods", + "text_level": 1, + "bbox": [ + 498, + 588, + 805, + 604 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In this section, we apply our method to MiB [3] and PLOP [16]. Additionally, we also compare our method with LwF [31], ILT [36], SDR [37], and RCIL [50].", + "bbox": [ + 496, + 612, + 890, + 657 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "PASCAL VOC 2012. In this dataset, we use the same experimental settings as [3, 16, 50], we performed the experiments with the class incremental learning settings 15-1, 10-1, 5-3, 19-1. As shown in Table 1, we report the result of our experiments on the final task. From the results, we can observe that our method improves the results of both MiB and PLOP by a large margin, on the more challenging settings (e.g., 15-1, 10-1, 5-3. For instance, on the 15-1 setting, our algorithm obtains performance gains of $12.4\\%$ and $33.3\\%$ mIoU for PLOP and MIB, respectively. Furthermore, on the longest learning sequence, the 10-1 setting, our method obtains a large gain consistently, improving the performance of PLOP and MIB by $21.4\\%$ and $24.7\\%$ , respectively. In Table 1 we also report the performance of the old and new classes for different settings. Our method achieves significant performance gains for old classes. This demon", + "bbox": [ + 496, + 659, + 892, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "7208", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/106c653be07d716e47e94c5b5d2e9bd0c48e6a71eda8c705547b37a58575ae31.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
Method15-1 (6 steps)10-1 (11 steps)5-3 (6 steps)19-1 (2 steps)
0-1516-20all0-1011-20all0-56-20all0-1920all
LwF [31] (TPAMI2017)6.03.95.58.02.04.820.936.724.753.08.550.9
ILT [36] (ICCVW2019)9.67.89.27.23.75.522.531.729.068.212.365.5
SDR [37] (CVPR2021)47.314.739.532.417.125.1---69.132.667.4
RCIL [50] (CVPR2022)70.623.759.455.415.134.363.134.642.877.031.574.7
MiB [3] (CVPR2020)38.013.532.212.213.112.657.142.546.771.222.168.9
MiB+EWF (Ours)78.025.565.556.016.737.369.045.051.877.812.274.7
PLOP [16] (CVPR2021)65.121.154.644.015.530.525.730.028.775.437.373.5
PLOP+EWF (Ours)77.732.767.071.530.351.961.742.247.777.96.774.5
Joint79.872.678.279.872.678.278.278.078.276.977.677.4
", + "bbox": [ + 84, + 88, + 888, + 229 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 1. The mIoU(%) of the last step on the Pascal VOC 2012 dataset for different class-incremental segmentation scenarios.", + "bbox": [ + 109, + 239, + 854, + 255 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/5ada5be248ee09c3758989ab061393427a3453278627f9d66d24b08b70756163.jpg", + "image_caption": [ + "(a) 10-1 scenario on PASCAL VOC", + "Figure 4. The mIoU $(\\%)$ at each step for the settings 10-1 (a) and 15-1 (b)." + ], + "image_footnote": [], + "bbox": [ + 124, + 273, + 480, + 476 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/f374888c7889b0140a11ec38943f3cc0897757307e97e1712d8eae4a8b207883.jpg", + "image_caption": [ + "(b) 15-1 scenario on PASCAL VOC" + ], + "image_footnote": [], + "bbox": [ + 491, + 273, + 848, + 474 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "strates that our EWF strategy can enhance significantly the model's memory of old knowledge (by successfully countering forgetting). In the more challenging settings, e.g., 15-1, 5-3, 10-1, our method also boosts the performance of new classes. This shows that EWF can achieve high plasticity on new steps, and that the proposed dynamically weighted combination of the network allows achieving a good tradeoff between plasticity and stability. We also show dynamic performance changes during the continual learning process in Fig. 4. It is clear that with more learning steps, the gap between our method and the best baseline is growing, and that the curve of our method for different settings (15-1 and 5-3) is on the top throughout most of the learning trajectory.", + "bbox": [ + 75, + 550, + 472, + 748 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Comparison with methods that introduce auxiliary data. It is worth noting that there are several methods [6, 34, 49] that introduce different forms of auxiliary data to assist continual semantic segmentation, helping the model build better pseudo-labels or enhance memory for old knowledge. RECALL [34] learns a generative model or retrieves from web-crawled data for replay, while SSUL [6] leverages salient object detectors (trained on MSRA-B dataset [32] with 5000 images) to generate saliency maps as auxiliary", + "bbox": [ + 75, + 763, + 468, + 902 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "data. And ST-CIL [49] exploits unlabelled datasets with pseudo labels as ground truth. Even if our algorithm is designed to deal with extra-data-free scenarios, to further demonstrate the effectiveness of our method, we integrate our method to SSUL and compare it with the above methods in Table 2. Note that SSUL freezes the backbone completely and it is hard to directly apply our method on it. Therefore, we learned part of the backbone network parameters when we apply our method to SSUL. In detail, we set the second stage of the backbone in SSUL as learnable parameters for model fusion. SSUL obtains the best performance among these methods using auxiliary data, and our method applied to SSUL can further improve it by about $1\\%$ for all classes.", + "bbox": [ + 496, + 550, + 890, + 760 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Visualization. As shown in Fig. 5, we compare our method based on MiB, and we show a sample from the base task (step 0) and a sample from step 2. From the top two rows, the person and bike classes are largely preserved with our method, but it forgets gradually for the baseline MiB. From the bottom two rows, it shows an example with both old classes and a new sheep class. Our method can keep the old knowledge better while incorporating new knowledge.", + "bbox": [ + 496, + 762, + 890, + 883 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "ADE20K. In order to further evaluate the effectiveness of", + "bbox": [ + 500, + 885, + 890, + 898 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "7209", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/458b5318f3da581b46aa4f9fffa878f9501db768ddac07ac60e7b566710e0d25.jpg", + "image_caption": [ + "Figure 5. The qualitative comparison between different methods. All prediction results are from the last step of 15-1 overlapped setting. In the initial step, 15 classes are learned and 5 tasks are learned incrementally with class potted plant, sheep, sofa, train and monitor." + ], + "image_footnote": [], + "bbox": [ + 81, + 85, + 890, + 441 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/cf21ae2b3306eea7cd47b9849486c67f1b198c38eeeae752b9db46cc830b4f4e.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodAuxiliary Data15-1 (PASCAL VOC 2012)10-1 (PASCAL VOC 2012)
0-1516-20all0-1011-20all
RECALL [34] (ICCV2021)GAN / Web-Data65.747.862.759.546.754.8
ST-CIL [49] (TNNLS2022)Unlabeled Data71.440.063.6---
SSUL [6] (NeurIPS2021)Saliency Map77.336.667.671.345.959.2
SSUL + EWF (Ours)Saliency Map77.938.968.672.447.460.5
", + "bbox": [ + 174, + 492, + 802, + 583 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 2. The mIoU(%) of the last step on the Pascal VOC 2012 15-1 and 10-1 overlapped setting.", + "bbox": [ + 194, + 590, + 772, + 606 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "our method, we conduct experiments on ADE20K dataset. In Table 3, we show the experimental results with settings 100-50, 100-10 and 100-5. As shown in Table 3, our method reaches superior performance on this dataset. Especially on the most challenging settings 100-5 and 100-10, our method achieves $6.2\\%$ and $3.0\\%$ improvement over MiB [3], respectively. It also surpasses the state-of-the-art method RC-IL by a large margin on 100-5 setting. This indicates that our EWF is effective on large-scale datasets as well.", + "bbox": [ + 75, + 625, + 470, + 775 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.3. Ablation Study", + "text_level": 1, + "bbox": [ + 76, + 785, + 230, + 801 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "In this part, we demonstrate and analyze the effectiveness of weight fusion and its dynamic factor selection. We use MiB [3] for the ablation experiments.", + "bbox": [ + 75, + 809, + 468, + 854 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Fusion Strategy. In Table 4, we demonstrate the performance of different fusion strategies. These experiments are conducted with the setting 15-1 on PASCAL VOC 2012.", + "bbox": [ + 75, + 854, + 470, + 900 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Most of these methods perform continual learning by fusing the information present in the previous step model. Among these, EMA [38] updates a stored set of parameters with moving average during training, and uses it for inference. Model ensemble fuses the previous model's prediction and new prediction in an average way during inference. And None denotes the model trained only with Distillation and Cross-Entropy (i.e., MiB [3]). Compared with no fusion method, EMA and model ensemble have $5.1\\%$ and $5.0\\%$ performance improvement, respectively. While Our EWF has a $33.3\\%$ improvement on the basis of a simple fusion strategy, which again verifies the discussions in Sec. 3.2.", + "bbox": [ + 496, + 625, + 890, + 805 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Fusion Factor Selection. In this part, we conduct experiments on the fusion factor selection. To prove the advantages of our parameter selection strategy, we use some fixed values as balance parameters in the fusion process, and we compare the difference between our method and theirs to evaluate its advantage. In detail, we choose three scenarios", + "bbox": [ + 496, + 809, + 892, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "7210", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/fce67476ef2afbf739cd1ee1ad7a2e6444c858db7ef502ff480fa0b57b376fa5.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
Method100-50 (2 steps)100-10 (6 steps)100-5 (3 steps)
1-100101-150all1-100101-110111-120121-130131-140141-150all1-100101-150all
ILT [36] (ICCVW2019)18.314.817.00.10.00.10.94.19.31.10.11.30.5
PLOP [16] (CVPR2021)41.914.932.940.615.216.918.711.97.931.639.17.828.7
RC-IL [50] (CVPR2022)42.318.834.539.314.626.323.212.111.832.138.511.529.6
MiB [3] (CVPR2020)40.717.732.838.312.610.68.79.515.129.236.05.625.9
MiB+EWF(Ours)41.221.334.641.512.822.523.214.48.833.241.413.432.1
Joint44.328.238.944.326.142.826.728.117.338.944.328.238.9
", + "bbox": [ + 78, + 89, + 895, + 210 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/ca2d6b5151acadf397db35338da71d0c9a602e3d657821615f1fac0bd3c53be7.jpg", + "table_caption": [ + "Table 3. The mIoU(%) of the last step on the ADE20K dataset for different overlapped continual learning scenarios." + ], + "table_footnote": [], + "table_body": "
Fusion strategystep1step2step3step4step5
None [3]71.456.151.936.532.2
EMA [38]74.059.659.840.937.3
model ensemble [13]74.160.160.341.537.2
EWF (Ours)76.173.870.568.365.6
", + "bbox": [ + 78, + 251, + 491, + 330 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/352138f9abce81aa9a5851d8653eb7ef13262443a9381f585956e9ee05c90052.jpg", + "table_caption": [ + "Table 4. Ablation study of fusion strategies. All performances are reported on PASCAL VOC 2012 15-1 setting." + ], + "table_footnote": [], + "table_body": "
Parameter SelectionOurs0.20.40.60.8
15-165.665.663.760.153.3
10-137.339.531.822.714.3
5-351.838.051.256.152.9
Average51.647.748.946.340.2
", + "bbox": [ + 88, + 387, + 457, + 468 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 5. Comparison between our dynamic parameter fusion strategy and fixed balance factors.", + "bbox": [ + 76, + 479, + 467, + 507 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "to conduct our experiments (i.e., 15-1, 10-1, 5-3), and we calculate the average mIoU of different strategies for three scenarios to measure the final performance. Since the balance factor $\\alpha \\in [0,1]$ , we take 0.2, 0.4, 0.6, and 0.8 as the fixed values to compare to our parameter selection strategy. As shown in Table 5, for the 15-1 setting, our method reaches the highest performance compared with other fixed parameters. In addition, although our method is slightly below the highest performance for fixed parameters on other settings, the parameters for the highest performance on different settings vary widely. It means that choosing a fixed parameter for all scenarios is unrealistic and harmful to the algorithm. Importantly, our method reaches the highest average performance among all other fixed values, which indicates that our strategy can be easily applied to different settings without tuning the hyper-parameters manually.", + "bbox": [ + 75, + 537, + 467, + 777 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Robustness of Class Order. In the scenario of class incremental semantic segmentation, the order of classes encountered by the model is significant in measuring the effectiveness of an algorithm. Thus, to verify the effectiveness of our algorithm and the robustness to different class orders, we conduct experiments on five different class orders to calculate the average performance and their standard deviation. As shown in Fig. 6, our method significantly improves the", + "bbox": [ + 75, + 779, + 467, + 900 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/df4a1e676e976a79c309a63759bdb815e1b17ec1982527d2f09a477078be9ceb.jpg", + "image_caption": [ + "Figure 6. Illustration on robustness with respect to different orders." + ], + "image_footnote": [], + "bbox": [ + 540, + 255, + 846, + 439 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "performance while also significantly enhancing the robustness to different class orders.", + "bbox": [ + 498, + 494, + 888, + 523 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusions", + "text_level": 1, + "bbox": [ + 500, + 539, + 625, + 554 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this work, we address the class incremental semantic segmentation (CISS) problem with a simple yet effective endpoints weight fusion method. It is enhanced by the existing distillation-based methods and easily integrated with them. A dynamic parameter fusion strategy is proven to be flexible for different settings and it avoids the further tuning of hyper-parameters. Interestingly, we discuss the relationship between our method and a popular weight fusion method EMA, which reveals why our method is more effective in incremental learning. The experimental results demonstrate that our method can obtain a significant gain compared to the baselines and achieve superior performance. In future work, we will investigate further the underlining reasons why our simple EWF strategy works so well in CISS. Moreover, we are planning to evaluate our incremental learning strategies for other application domains. Acknowledgment. This work is funded by NSFC (NO. 62225604 and 62206135), Fundamental Research Funds for the Central Universities (Nankai University, NO. 63223050), and Bytedance Limited. We acknowledge the Spanish Government funding for projects PID2019-104174GB-I00, TED2021-132513B-I00.", + "bbox": [ + 496, + 564, + 890, + 895 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "7211", + "bbox": [ + 482, + 945, + 513, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 174, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Jihwan Bang, Heesu Kim, YoungJoon Yoo, Jung-Woo Ha, and Jonghyun Choi. Rainbow memory: Continual learning with a memory of diverse samples. In CVPR, 2021. 2", + "[2] Eden Belouadah and Adrian Popescu. II2m: Class incremental learning with dual memory. In ICCV, pages 583-592, 2019. 2", + "[3] Fabio Cermelli, Massimiliano Mancini, Samuel Rota Bulo, Elisa Ricci, and Barbara Caputo. Modeling the background for incremental learning in semantic segmentation. 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In CVPR, pages 9296-9305, 2022. 2" + ], + "bbox": [ + 501, + 90, + 890, + 430 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "7213", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/Endpoints Weight Fusion for Class Incremental Semantic Segmentation/ff7be89f-f21f-4256-a5c9-a98275c1a5e9_model.json b/2023/Endpoints Weight Fusion for Class Incremental Semantic Segmentation/ff7be89f-f21f-4256-a5c9-a98275c1a5e9_model.json new file mode 100644 index 0000000000000000000000000000000000000000..88a05e94ee680b5df344df5fa66a2ce83b6c06fd --- /dev/null +++ b/2023/Endpoints Weight Fusion for Class Incremental Semantic Segmentation/ff7be89f-f21f-4256-a5c9-a98275c1a5e9_model.json @@ -0,0 +1,1947 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.001, + 0.812, + 0.047 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.125, + 0.131, + 0.848, + 0.154 + ], + "angle": 0, + "content": "Endpoints Weight Fusion for Class Incremental Semantic Segmentation" + }, + { + "type": "text", + "bbox": [ + 0.201, + 0.18, + 0.775, + 0.253 + ], + "angle": 0, + "content": "Jia-Wen Xiao \\(^{1*}\\) Chang-Bin Zhang \\(^{1*}\\) Jiekang Feng \\(^{2}\\) Xialei Liu \\(^{1\\dagger}\\) Joost van de Weijer \\(^{3}\\) Ming-Ming Cheng \\(^{1}\\) VCIP, CS, Nankai University \\(^{2}\\) Tianjin University \\(^{3}\\) Computer Vision Center, Universitat Autònoma de Barcelona" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.287, + 0.314, + 0.303 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.318, + 0.474, + 0.637 + ], + "angle": 0, + "content": "Class incremental semantic segmentation (CISS) focuses on alleviating catastrophic forgetting to improve discrimination. Previous work mainly exploits regularization (e.g., knowledge distillation) to maintain previous knowledge in the current model. However, distillation alone often yields limited gain to the model since only the representations of old and new models are restricted to be consistent. In this paper, we propose a simple yet effective method to obtain a model with a strong memory of old knowledge, named Endpoints Weight Fusion (EWF). In our method, the model containing old knowledge is fused with the model retaining new knowledge in a dynamic fusion manner, strengthening the memory of old classes in ever-changing distributions. In addition, we analyze the relationship between our fusion strategy and a popular moving average technique EMA, which reveals why our method is more suitable for class-incremental learning. To facilitate parameter fusion with closer distance in the parameter space, we use distillation to enhance the optimization process. Furthermore, we conduct experiments on two widely used datasets, achieving state-of-the-art performance." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.674, + 0.21, + 0.689 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.7, + 0.47, + 0.866 + ], + "angle": 0, + "content": "As a fundamental task, semantic segmentation plays a key role in visual applications [10, 25]. Previous fully-supervised works aim to segment fixed classes defined in the training set. However, the trained segmentation model is expected to recognize more classes in realistic applications. One straightforward solution is to re-train the model on the entire dataset by mixing old and new data. Nevertheless, this strategy will bring huge labeling and training costs. From the transfer learning perspective [22, 30], another plain solution is to adjust the previously learned model on the newly added data. But the model will overfit to new" + }, + { + "type": "image", + "bbox": [ + 0.513, + 0.293, + 0.878, + 0.57 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.597, + 0.895, + 0.697 + ], + "angle": 0, + "content": "Figure 1. Illustration of different fusion strategies for incremental learning. Ensemble methods utilize multiple models to accumulate more knowledge. Compression methods reduce the model size and distill the knowledge into a small network. While Reparameterization methods use equivalent operations for model fusion. Our Endpoints Weight Fusion (EWF) proposes model addition with a dynamic factor \\((\\alpha_{t})\\) with no further training." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.731, + 0.893, + 0.761 + ], + "angle": 0, + "content": "classes quickly, while forgetting previous old classes. This phenomenon is also known as catastrophic forgetting [35]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.895, + 0.903 + ], + "angle": 0, + "content": "To alleviate the problem of catastrophic forgetting without extra labeling or training cost, class incremental semantic segmentation (CISS) [3, 16, 50] aims at optimizing the trade-off between maintaining discrimination for old classes and learning knowledge of new classes. Most works [3, 16, 17, 37] designed regularization methods to maintain a balance between memorizing old knowledge and learning new one. We observe that existing works can still suffer from catastrophic forgetting, resulting in a significant" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.875, + 0.346, + 0.888 + ], + "angle": 0, + "content": "*The first two authors contribute equally." + }, + { + "type": "page_footnote", + "bbox": [ + 0.097, + 0.888, + 0.345, + 0.9 + ], + "angle": 0, + "content": "† Corresponding author (xialei@nankai.edu.cn)" + }, + { + "type": "list", + "bbox": [ + 0.096, + 0.875, + 0.346, + 0.9 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "7204" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.166 + ], + "angle": 0, + "content": "performance drop in old classes. In the scenario of CISS, not only the previous data is not accessible due to privacy issues or data storage limitations, but regions of old classes in the newly added dataset are labeled as background, which further exacerbates the model over-fitting." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.168, + 0.471, + 0.468 + ], + "angle": 0, + "content": "Besides, training a new model from the old one and fusing them to obtain the final model is a common strategy in continual learning. As shown in Fig. 1, we roughly divide them into four categories with two stages of model expansion and fusion. Some methods [27, 33, 42, 47] propose to expand the model in incremental steps and ensemble the old and new outputs, which have large memory and inference costs. While some works apply compression [46, 47] to compress the old and new model to a unified model with fewer parameters. Nevertheless, these require further training on only new data, which can lead to a bias toward new data. Subsequently, some works [50, 53] explore knowledge decoupling and perform linear parameter fusion with reparameterization. However, this is an intra-module fusion strategy, which is restricted to certain operations. As the last category, we propose Endpoints Weight Fusion (EWF) in the form of parameter addition between the old and new model with a dynamic factor, which requires no further training and re-parameterization, and maintains a constant model size as more tasks are encountered." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.47, + 0.47, + 0.741 + ], + "angle": 0, + "content": "In this work, we adapt weight fusion to CISS and propose the EWF strategy, which aims at utilizing weight fusion to find a new balance between old and new knowledge. During incremental training, we choose a starting point and an ending point model of the current task training trajectory. The starting point represents the old knowledge, while the ending point represents the new knowledge. After learning the current task, a dynamic weight fusion is proposed for efficient knowledge integration. We aggregate them by taking the weighted average of the corresponding parameters of the two models. Nevertheless, the training procedure without restraints on the model would increase the parameter distance between the start and end points, limiting the performance improvement brought by the EWF strategy. To overcome this shortcoming, we further enhance the EWF strategy with a knowledge distillation scheme [16, 17, 50], which can largely increase the similarity of the models at the two points and boost the efficiency of EWF." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.742, + 0.462, + 0.758 + ], + "angle": 0, + "content": "To summarize, the main contributions of this paper are:" + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.769, + 0.468, + 0.844 + ], + "angle": 0, + "content": "- We propose an Endpoints Weight Fusion strategy, which has no cost of further training and keeps the model size the same. It can effectively find a new balance between old and new categories and alleviate catastrophic forgetting." + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.856, + 0.468, + 0.901 + ], + "angle": 0, + "content": "- Our method can be easily integrated with several state-of-the-art methods. In several CISS scenarios of long sequences, it can boost the baseline performance by" + }, + { + "type": "list", + "bbox": [ + 0.096, + 0.769, + 0.468, + 0.901 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.533, + 0.092, + 0.641, + 0.106 + ], + "angle": 0, + "content": "more than \\(20\\%\\)." + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.119, + 0.892, + 0.179 + ], + "angle": 0, + "content": "- We conduct experiments on various CISS scenarios, which demonstrate that our method achieves the state-of-the-art performance on both PASCAL VOC and ADE20K." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.195, + 0.642, + 0.211 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.22, + 0.892, + 0.522 + ], + "angle": 0, + "content": "Class Incremental Learning. Class incremental learning mainly focuses on alleviating catastrophic forgetting while learning the discriminative information required for the newly coming classes. It is most commonly analyzed in image classification, and the techniques can be roughly divided into three categories [11]. Many works [43-45] focus on the structural properties of the model (i.e., Structural-Based Method). The idea is to freeze old models and expand the architecture space to learn new knowledge, which normally results in a growing capacity and memory size of the model. Another way is to regularize models during incremental learning (i.e., Regularization-Based Method) [7, 8, 12, 17], strengthening memory via constraints (e.g., knowledge distillation [39, 41] or gradient penalty [26, 29]). These methods bring the negligible cost to the learning process, but they allow for less freedom for parameter updates. Some other methods [1,2,28] propose to review knowledge through rehearsal (i.e., Rehearsal-Based Method). They store old data and mix it with new data to re-train the model [5, 21, 52]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.524, + 0.892, + 0.658 + ], + "angle": 0, + "content": "Class Incremental Semantic Segmentation. Semantic segmentation [19] aims at assigning different categories to each single pixel, and has recently attracted attention for learning in a class incremental learning scenario [3, 16]. Nevertheless, data for semantic segmentation takes more space [24, 48] to be stored compared to the classification problem. Therefore, recent work mainly concentrates on utilizing distillation to transfer old knowledge to the new model without saving exemplars from old tasks." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.66, + 0.892, + 0.901 + ], + "angle": 0, + "content": "MiB [4] proposes to model the potential classes to tackle semantic drift. PLOP [16] applies feature distillation to restrict representation ability. SDR [37] uses prototype matching to strengthen consistency in latent space. And RC-IL [50] analyzes the disadvantages of strip pooling and proposes average-pooling-based distillation to back up training. On the contrary, SSUL [6] does not apply distillation and proposes to fix the feature extractor instead of updating its parameters. In addition, they introduce thousands of extra data to help generate pseudo labels. But, simply fixing the model definitely does damage to the balance between plasticity and stability, and it is not sustainable when facing huge amounts of newly coming data. On the other hand, only applying distillation can restrict performance, since it can just limit the representation of new data to be the same. Summarizing the above thoughts and" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "7205" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.081, + 0.085, + 0.891, + 0.341 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.343, + 0.893, + 0.399 + ], + "angle": 0, + "content": "Figure 2. Illustration of our Endpoints Weight Fusion (EWF) framework. On the left side, we illustrate training and testing processes. Training is enhanced by knowledge distillation and fusion is applied after training to accumulate all seen knowledge. On the right side, given a \\(3 \\times 3\\) convolution layer and a normalization layer, they are fused by using a dynamic trade-off parameter \\(\\alpha_{t}\\). Note that there is no computation cost for our fusion process." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.407, + 0.471, + 0.468 + ], + "angle": 0, + "content": "inspired by RC-IL [50], we design a strategy different from the above, cooperating with distillation and maintaining the balance between the old and new knowledge with model weight fusion." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.469, + 0.47, + 0.727 + ], + "angle": 0, + "content": "Weight Fusion Method. Weight Fusion is widely used in neural network training to improve performance. It can be applied with both linear and nonlinear operations. In linear mode, RCM [27] explores the additivity of convolution and applies it on multi-task learning. ACNet [14] and RepVGG [15] first propose structural re-parameterization, which is used to merge multi-branch Convolution-Batch Normalization serial sequences to a plain Convolution layer. RC-IL ingeniously exploits this operation to establish a representation compensation mechanism in continual learning. In nonlinear mode, weight averaging is commonly used to bring closer connections between different models. Famous methods like BYOL [20] use EMA [38] to improve the knowledge transfer effect or model robustness. From this point, we design a strategy to reach a new balance, which has no effect on the current training process and fully releases the learning ability of the model." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.744, + 0.168, + 0.759 + ], + "angle": 0, + "content": "3. Method" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.77, + 0.218, + 0.785 + ], + "angle": 0, + "content": "3.1. Preliminaries" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.795, + 0.471, + 0.903 + ], + "angle": 0, + "content": "We consider a multi-step training process where \\(T\\) tasks are sequentially learned by model \\(f_{\\theta}\\) in a fully supervised scenario for semantic segmentation, where \\(f\\) is parameterized by parameter \\(\\theta\\). Here \\(f_{\\theta_t}\\) denotes the model at task \\(t\\). Each task contains a dataset \\(\\mathcal{D}_t = \\{x_i,y_i\\}\\), where \\(x_{i}\\) denotes the data and \\(y_{i}\\) denotes the corresponding label. The training label space of the task \\(T\\) is denoted as \\(C_t\\bigcup \\{c_b\\}\\)," + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.407, + 0.893, + 0.559 + ], + "angle": 0, + "content": "where \\( C_t \\) includes all classes that appear in this task, and \\( c_b \\) represents the background. Since \\( C_i \\cap C_j = \\emptyset \\), the objective of different tasks are not the same, easily leading to catastrophic forgetting. To save annotation costs, only the categories that need to be learned at this stage will be labeled. Thus, \\( c_b \\) contains not only the real background, but also the classes appearing in past and future tasks. This complicates the training of the model \\( f_\\theta \\) since the background label \\( c_b \\) can refer to different classes at different tasks. This exacerbates the severity of forgetting." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.567, + 0.79, + 0.584 + ], + "angle": 0, + "content": "3.2. Endpoints Weight Fusion (EWF)" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.591, + 0.892, + 0.818 + ], + "angle": 0, + "content": "As illustrated in Fig. 1, the existing model expansion-fusion methods have their own drawbacks for enhancing the model's memory of old knowledge. Thus, to better retain the old knowledge while boosting the learning ability of the model, we introduce our Endpoints Weight Fusion strategy. Considering the training process at step \\( t \\), we choose a starting point model and an ending point model. The final model of the previous step \\( (\\theta_{old}) \\) is regarded as the best container of old knowledge. While the model after training on the current task \\( (\\theta_{new}) \\) contains the discriminative information for new classes. Additionally, we introduce another parameter \\( \\alpha \\) for the endpoints weight fusion, aiming at fusing two sets of parameters in a certain ratio. This ratio can be seen as a balance factor. Therefore, the operation of endpoints weight fusion can be written as:" + }, + { + "type": "equation", + "bbox": [ + 0.576, + 0.829, + 0.891, + 0.845 + ], + "angle": 0, + "content": "\\[\n\\theta_ {\\text {b a l a n c e d}} = \\alpha_ {t} \\theta_ {\\text {n e w}} + (1 - \\alpha_ {t}) \\theta_ {\\text {o l d}} \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.856, + 0.893, + 0.903 + ], + "angle": 0, + "content": "where the \\(\\theta_{\\text{balanced}}\\) denotes the final model of this task, and the \\(\\theta_{old}, \\theta_{new}\\) are defined as above. Furthermore, the number of incremental categories (denoted as \\(N_{\\text{new}}\\)) and orig-" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "7206" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.184 + ], + "angle": 0, + "content": "inal categories (denoted as \\(N_{old}\\)) to a certain extent represent the degree of emphasis on the \\(\\theta_{new}\\) and \\(\\theta_{old}\\). For the selection of \\(\\alpha_{t}\\), we need to consider \\(N_{new}\\) and \\(N_{old}\\) in the current learning step. We decide to replace the constant ratio with an equation related to \\(N_{new}\\) and \\(N_{old}\\). In detail, this formula can be expressed as:" + }, + { + "type": "equation", + "bbox": [ + 0.196, + 0.191, + 0.47, + 0.226 + ], + "angle": 0, + "content": "\\[\n\\alpha_ {t} = \\sqrt {\\frac {N _ {n e w}}{N _ {n e w} + N _ {o l d}}} \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.232, + 0.47, + 0.277 + ], + "angle": 0, + "content": "It can be used across different tasks and scenarios. It can adapt to each task in CISS with a dynamic factor. We illustrate the main idea of our method in Fig. 2." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.277, + 0.471, + 0.457 + ], + "angle": 0, + "content": "Knowledge distillation enhanced for EWF. In practice, training without any constraint will significantly increase the distance between different models and break the similarity of model representations. That means it deteriorates the forgetting of the model, which further undermines the model's ability to discriminate new classes. Moreover, guaranteeing a low error linear path between two distant models is an overly strong assumption. Thus, choosing a model trained without constraints as an ending point is potentially harmful, and we, therefore, introduce knowledge distillation to enhance the compatibility of the models of our Endpoints Weight Fusion method." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.459, + 0.473, + 0.566 + ], + "angle": 0, + "content": "Knowledge distillation is a commonly used technique to prevent models from forgetting. As stated above, we utilize distillation to back up our strategy, limiting the distance between two endpoints and forcing them to be similar. In general, distillation used in continual learning is mainly divided into two categories, i.e., feature-based distillation and logit-based distillation. They can be represented as:" + }, + { + "type": "equation", + "bbox": [ + 0.077, + 0.572, + 0.488, + 0.664 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} L _ {F D} = \\frac {1}{| D |} \\sum_ {(x _ {i}, y _ {i}) \\sim D} | | \\Psi_ {o l d} (x _ {i}) - \\Psi_ {n e w} (x _ {i}) | | ^ {2} \\\\ L _ {L D} = \\frac {1}{| D |} \\sum_ {\\left(x _ {i}, y _ {i}\\right) \\sim D} K L \\left(\\Phi_ {o l d} \\left(\\Psi_ {o l d} \\left(x _ {i}\\right)\\right), \\Phi_ {n e w} \\left(\\Psi_ {n e w} \\left(x _ {i}\\right)\\right)\\right) \\tag {3} \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.665, + 0.47, + 0.77 + ], + "angle": 0, + "content": "\\(\\Psi_{old} / \\Phi_{old}\\) and \\(\\Psi_{new} / \\Phi_{new}\\) denote old and new feature extractor/classifier respectively, and \\(D\\) is the corresponding dataset of the incremental learning step. In CISS, two popular distillation losses (i.e., UNKD, POD) are proposed by [3, 16], respectively. The former is a logit-based distillation and the latter is a feature-based distillation. They can be easily integrated into our method." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.77, + 0.471, + 0.876 + ], + "angle": 0, + "content": "Discussion on EMA v.s. EWF. An update strategy similar to our method is using EMA [38] to update the model. Here we will discuss the difference between our method EWF and EMA, and the advantages of EWF. The EMA strategy maintains a moving average model during training, and uses this model to replace the final model for inference. The moving average model can be represented as:" + }, + { + "type": "equation", + "bbox": [ + 0.182, + 0.884, + 0.47, + 0.903 + ], + "angle": 0, + "content": "\\[\nv ^ {i} = \\beta v ^ {i - 1} + (1 - \\beta) \\theta^ {i} \\tag {4}\n\\]" + }, + { + "type": "image", + "bbox": [ + 0.521, + 0.092, + 0.877, + 0.272 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.287, + 0.895, + 0.358 + ], + "angle": 0, + "content": "Figure 3. Representation similarity between old model \\(\\theta^1\\) before training and being trained new model \\(\\theta^i\\). The similarity measure we use is cosine similarity. We extract the intermediate results of the feature extractors of the old and new networks and calculate the average of the cosine similarity between them." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.393, + 0.895, + 0.546 + ], + "angle": 0, + "content": "where the \\( v^{i} \\) denotes the moving average of the first \\( i \\) models, and \\( \\theta^i \\) denotes the model after \\( i \\)th iteration. \\( \\beta \\) is the moving average parameter, which is usually set as 0.9/0.99. It is easy to see that the EMA is an inter-iteration operation, which is easier to realize due to the low distance between models. Since we use SGD as an optimizer, following Eq. 5, the results of EMA and EWF can be represented as \\( v^n \\) and \\( \\theta_{\\text{balanced}} \\) in Eq. 6. Note that the learning rate does not affect the result of the analysis, so we set the learning rate to 1. The more detailed derivations are in the Appendix." + }, + { + "type": "equation", + "bbox": [ + 0.605, + 0.555, + 0.892, + 0.616 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\theta^ {n} = \\theta^ {n - 1} - \\nabla_ {L} \\left(\\theta^ {n - 1}\\right) \\\\ = \\theta^ {1} - \\sum_ {k = 1} ^ {n} \\nabla_ {L} \\left(\\theta^ {k}\\right) \\tag {5} \\\\ \\end{array}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.571, + 0.628, + 0.892, + 0.678 + ], + "angle": 0, + "content": "\\[\nv ^ {n} = \\theta^ {1} - \\sum_ {k = 1} ^ {n - 1} (1 - \\beta^ {n - k}) \\nabla_ {L} \\left(\\theta^ {k}\\right) \\tag {6}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.571, + 0.673, + 0.787, + 0.713 + ], + "angle": 0, + "content": "\\[\n\\theta_ {b a l a n c e d} = \\theta^ {1} - \\alpha \\sum_ {k = 1} ^ {n - 1} \\nabla_ {L} \\left(\\theta^ {k}\\right)\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.895, + 0.902 + ], + "angle": 0, + "content": "Since the \\(\\beta\\) is usually set to \\(0.9 / 0.99\\) and the \\(\\alpha\\) is set following Eq. 2, \\(\\alpha\\) is always smaller than \\(\\beta\\). According to Eq. 6, EMA gives more weight to the gradient of early time, and then gradually attenuates the influence of gradients in subsequent iterations. On the contrary, EWF gives the gradient of different parts a relatively uniform weight. Besides, to better observe the stability of incremental learning step, we calculate the representations similarity between \\(\\theta^1\\) and \\(\\theta^i\\). According to our observation in an incremental step, as shown in Fig. 3, the similarity of representations between \\(\\theta^1\\) and \\(\\theta^i\\) first decreases and then increases, and gradually stabilizes in the subsequent stages. This reveals that in order" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "7207" + } + ], + [ + { + "type": "code_caption", + "bbox": [ + 0.079, + 0.091, + 0.454, + 0.107 + ], + "angle": 0, + "content": "Algorithm 1 Pseudo Code for EWF in incremental steps" + }, + { + "type": "algorithm", + "bbox": [ + 0.078, + 0.11, + 0.357, + 0.375 + ], + "angle": 0, + "content": "Require: \\(f,\\theta_0,T,D_T\\) and learning rate \\(\\gamma\\) \\(t\\gets 1\\) \nwhile \\(t\\leq T\\) do Initialize \\(N_{new},N_{old}\\) \\(\\theta^1\\gets \\theta_{t - 1}\\) \\(\\alpha_{t}\\leftarrow \\sqrt{\\frac{N_{new}}{N_{new} + N_{old}}}\\) \\(i\\gets 1\\) \nwhile not converged do Sample mini-batch \\(\\{x_i,y_i\\} \\sim D\\) \\(\\theta^{i + 1}\\gets \\theta^i -\\gamma \\nabla_{LCE + LKD}(f_{\\theta^i})\\) \\(i\\gets i + 1\\) \nend while \n\\(\\theta_{old}\\gets \\theta^1,\\theta_{new}\\gets \\theta^i\\) \n\\(\\theta_{balanced}\\gets \\alpha_t\\theta_{new} + (1 - \\alpha_t)\\theta_{old}\\) \n\\(\\theta_t\\gets \\theta_{balanced}\\) \n\\(t\\gets t + 1\\) \nend while" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.404, + 0.47, + 0.51 + ], + "angle": 0, + "content": "to learn new knowledge, the representation will first collapse and then recover under the action of the distillation and cross-entropy losses. Then EMA concentrates more of the gradient on the early collapsed process, while our method pays more attention to the useful gradient information after the recovery. From this perspective, our method is theoretically better than EMA in CISS." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.522, + 0.267, + 0.537 + ], + "angle": 0, + "content": "3.3. Overall Framework" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.547, + 0.47, + 0.623 + ], + "angle": 0, + "content": "As stated above, to remember knowledge from old tasks, we borrow knowledge distillation to strengthen the model's memory. To learn the discrimination of new classes, we use the Cross-Entropy loss to optimize the model. In general, the objective is given by:" + }, + { + "type": "equation", + "bbox": [ + 0.167, + 0.636, + 0.47, + 0.657 + ], + "angle": 0, + "content": "\\[\n\\min _ {\\theta_ {t}} \\mathcal {L} _ {C E} \\left(\\theta_ {t}\\right) + \\mathcal {L} _ {K D} \\left(\\theta_ {t}; \\theta_ {t - 1}\\right) \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.671, + 0.434, + 0.687 + ], + "angle": 0, + "content": "And the overall algorithm of EWF is shown in Alg. 1." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.703, + 0.21, + 0.72 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.729, + 0.47, + 0.775 + ], + "angle": 0, + "content": "We demonstrate experimental protocols, scenarios and training details. Furthermore, we evaluate our algorithm through quantitative and qualitative experiments." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.786, + 0.272, + 0.803 + ], + "angle": 0, + "content": "4.1. Experimental setups" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.81, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Protocols. In general, the training for CISS is divided into \\( T \\) steps, and each step denotes a task, where the labeled classes are disjoint in each of them. We adopt the overlapped setting as other works, in which the current training data may contain potential classes labeled as background in previous steps. The overlapped setting is more realistic, and" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.348 + ], + "angle": 0, + "content": "therefore we only evaluate on this setup as previous methods [6, 16]. Following existing works [3, 16, 50], we conduct experiments on two widely used segmentation datasets, PASCAL VOC 2012 [18] and ADE20K [51]. The PASCAL VOC 2012 dataset [18] contains 10,582 training images and 1449 validation images with 20 object classes and the background class. The ADE20K dataset [51] is composed of 150 classes and contains 20, 210 training images, and 2000 validation images. Following previous works [3, 16, 50], \\( X - Y \\) denotes different settings for CISS. In the \\( X - Y \\) setting, the model can recognize \\( X \\) classes in the initial step, and then is supposed to learn \\( Y \\) newly added classes in each following step. At each step, only current task data is available for training. We perform experiments on PASCAL VOC 2012 [18] with four settings, 15-1, 10-1, 5-3 and 19-1. On ADE20K [51], we verify the effectiveness of our method on three settings, 100-5, 100-10, and 100-50." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.35, + 0.893, + 0.577 + ], + "angle": 0, + "content": "Implementation Details. Following existing works [3, 16, 50], we apply Deeplab-v3 [9] as our segmentation model with ResNet-101 [23] as a backbone. We also use in-place activated batch normalization [40] in the backbone. In our experiments, we use some data augmentations, including horizontal flip and random crop. The ratio \\(\\alpha_{t}\\) for EWF is defined as Eq.2. Using SGD optimizer, we train the model for 30 (PASCAL VOC 2012) and 60 (ADE20K) epochs in each step with a batch size of 24. We set the initial learning rate as 0.01 for the first training step and 0.001 for the next continual learning steps. All experiments are conducted on 4 RTX 2080Ti GPUs. The learning rate is decayed with poly schedule. During training, we use \\(20\\%\\) of the training set as validation, and report the mean Intersect over Union (mIoU) on the original validation set." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.589, + 0.807, + 0.606 + ], + "angle": 0, + "content": "4.2. Comparison to competing methods" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.613, + 0.892, + 0.658 + ], + "angle": 0, + "content": "In this section, we apply our method to MiB [3] and PLOP [16]. Additionally, we also compare our method with LwF [31], ILT [36], SDR [37], and RCIL [50]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.66, + 0.893, + 0.901 + ], + "angle": 0, + "content": "PASCAL VOC 2012. In this dataset, we use the same experimental settings as [3, 16, 50], we performed the experiments with the class incremental learning settings 15-1, 10-1, 5-3, 19-1. As shown in Table 1, we report the result of our experiments on the final task. From the results, we can observe that our method improves the results of both MiB and PLOP by a large margin, on the more challenging settings (e.g., 15-1, 10-1, 5-3. For instance, on the 15-1 setting, our algorithm obtains performance gains of \\(12.4\\%\\) and \\(33.3\\%\\) mIoU for PLOP and MIB, respectively. Furthermore, on the longest learning sequence, the 10-1 setting, our method obtains a large gain consistently, improving the performance of PLOP and MIB by \\(21.4\\%\\) and \\(24.7\\%\\), respectively. In Table 1 we also report the performance of the old and new classes for different settings. Our method achieves significant performance gains for old classes. This demon" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "7208" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.086, + 0.089, + 0.89, + 0.23 + ], + "angle": 0, + "content": "
Method15-1 (6 steps)10-1 (11 steps)5-3 (6 steps)19-1 (2 steps)
0-1516-20all0-1011-20all0-56-20all0-1920all
LwF [31] (TPAMI2017)6.03.95.58.02.04.820.936.724.753.08.550.9
ILT [36] (ICCVW2019)9.67.89.27.23.75.522.531.729.068.212.365.5
SDR [37] (CVPR2021)47.314.739.532.417.125.1---69.132.667.4
RCIL [50] (CVPR2022)70.623.759.455.415.134.363.134.642.877.031.574.7
MiB [3] (CVPR2020)38.013.532.212.213.112.657.142.546.771.222.168.9
MiB+EWF (Ours)78.025.565.556.016.737.369.045.051.877.812.274.7
PLOP [16] (CVPR2021)65.121.154.644.015.530.525.730.028.775.437.373.5
PLOP+EWF (Ours)77.732.767.071.530.351.961.742.247.777.96.774.5
Joint79.872.678.279.872.678.278.278.078.276.977.677.4
" + }, + { + "type": "table_caption", + "bbox": [ + 0.111, + 0.241, + 0.856, + 0.256 + ], + "angle": 0, + "content": "Table 1. The mIoU(%) of the last step on the Pascal VOC 2012 dataset for different class-incremental segmentation scenarios." + }, + { + "type": "image", + "bbox": [ + 0.125, + 0.274, + 0.481, + 0.477 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.207, + 0.485, + 0.397, + 0.497 + ], + "angle": 0, + "content": "(a) 10-1 scenario on PASCAL VOC" + }, + { + "type": "image", + "bbox": [ + 0.493, + 0.274, + 0.849, + 0.476 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.574, + 0.485, + 0.766, + 0.497 + ], + "angle": 0, + "content": "(b) 15-1 scenario on PASCAL VOC" + }, + { + "type": "image_caption", + "bbox": [ + 0.262, + 0.51, + 0.706, + 0.525 + ], + "angle": 0, + "content": "Figure 4. The mIoU \\((\\%)\\) at each step for the settings 10-1 (a) and 15-1 (b)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.551, + 0.473, + 0.749 + ], + "angle": 0, + "content": "strates that our EWF strategy can enhance significantly the model's memory of old knowledge (by successfully countering forgetting). In the more challenging settings, e.g., 15-1, 5-3, 10-1, our method also boosts the performance of new classes. This shows that EWF can achieve high plasticity on new steps, and that the proposed dynamically weighted combination of the network allows achieving a good tradeoff between plasticity and stability. We also show dynamic performance changes during the continual learning process in Fig. 4. It is clear that with more learning steps, the gap between our method and the best baseline is growing, and that the curve of our method for different settings (15-1 and 5-3) is on the top throughout most of the learning trajectory." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.765, + 0.47, + 0.903 + ], + "angle": 0, + "content": "Comparison with methods that introduce auxiliary data. It is worth noting that there are several methods [6, 34, 49] that introduce different forms of auxiliary data to assist continual semantic segmentation, helping the model build better pseudo-labels or enhance memory for old knowledge. RECALL [34] learns a generative model or retrieves from web-crawled data for replay, while SSUL [6] leverages salient object detectors (trained on MSRA-B dataset [32] with 5000 images) to generate saliency maps as auxiliary" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.551, + 0.892, + 0.761 + ], + "angle": 0, + "content": "data. And ST-CIL [49] exploits unlabelled datasets with pseudo labels as ground truth. Even if our algorithm is designed to deal with extra-data-free scenarios, to further demonstrate the effectiveness of our method, we integrate our method to SSUL and compare it with the above methods in Table 2. Note that SSUL freezes the backbone completely and it is hard to directly apply our method on it. Therefore, we learned part of the backbone network parameters when we apply our method to SSUL. In detail, we set the second stage of the backbone in SSUL as learnable parameters for model fusion. SSUL obtains the best performance among these methods using auxiliary data, and our method applied to SSUL can further improve it by about \\(1\\%\\) for all classes." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.763, + 0.892, + 0.884 + ], + "angle": 0, + "content": "Visualization. As shown in Fig. 5, we compare our method based on MiB, and we show a sample from the base task (step 0) and a sample from step 2. From the top two rows, the person and bike classes are largely preserved with our method, but it forgets gradually for the baseline MiB. From the bottom two rows, it shows an example with both old classes and a new sheep class. Our method can keep the old knowledge better while incorporating new knowledge." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.886, + 0.892, + 0.9 + ], + "angle": 0, + "content": "ADE20K. In order to further evaluate the effectiveness of" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "7209" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.086, + 0.891, + 0.442 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.451, + 0.893, + 0.481 + ], + "angle": 0, + "content": "Figure 5. The qualitative comparison between different methods. All prediction results are from the last step of 15-1 overlapped setting. In the initial step, 15 classes are learned and 5 tasks are learned incrementally with class potted plant, sheep, sofa, train and monitor." + }, + { + "type": "table", + "bbox": [ + 0.176, + 0.493, + 0.803, + 0.584 + ], + "angle": 0, + "content": "
MethodAuxiliary Data15-1 (PASCAL VOC 2012)10-1 (PASCAL VOC 2012)
0-1516-20all0-1011-20all
RECALL [34] (ICCV2021)GAN / Web-Data65.747.862.759.546.754.8
ST-CIL [49] (TNNLS2022)Unlabeled Data71.440.063.6---
SSUL [6] (NeurIPS2021)Saliency Map77.336.667.671.345.959.2
SSUL + EWF (Ours)Saliency Map77.938.968.672.447.460.5
" + }, + { + "type": "table_caption", + "bbox": [ + 0.195, + 0.592, + 0.773, + 0.607 + ], + "angle": 0, + "content": "Table 2. The mIoU(%) of the last step on the Pascal VOC 2012 15-1 and 10-1 overlapped setting." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.625, + 0.471, + 0.776 + ], + "angle": 0, + "content": "our method, we conduct experiments on ADE20K dataset. In Table 3, we show the experimental results with settings 100-50, 100-10 and 100-5. As shown in Table 3, our method reaches superior performance on this dataset. Especially on the most challenging settings 100-5 and 100-10, our method achieves \\(6.2\\%\\) and \\(3.0\\%\\) improvement over MiB [3], respectively. It also surpasses the state-of-the-art method RC-IL by a large margin on 100-5 setting. This indicates that our EWF is effective on large-scale datasets as well." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.786, + 0.231, + 0.803 + ], + "angle": 0, + "content": "4.3. Ablation Study" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.81, + 0.47, + 0.856 + ], + "angle": 0, + "content": "In this part, we demonstrate and analyze the effectiveness of weight fusion and its dynamic factor selection. We use MiB [3] for the ablation experiments." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.471, + 0.901 + ], + "angle": 0, + "content": "Fusion Strategy. In Table 4, we demonstrate the performance of different fusion strategies. These experiments are conducted with the setting 15-1 on PASCAL VOC 2012." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.625, + 0.892, + 0.806 + ], + "angle": 0, + "content": "Most of these methods perform continual learning by fusing the information present in the previous step model. Among these, EMA [38] updates a stored set of parameters with moving average during training, and uses it for inference. Model ensemble fuses the previous model's prediction and new prediction in an average way during inference. And None denotes the model trained only with Distillation and Cross-Entropy (i.e., MiB [3]). Compared with no fusion method, EMA and model ensemble have \\(5.1\\%\\) and \\(5.0\\%\\) performance improvement, respectively. While Our EWF has a \\(33.3\\%\\) improvement on the basis of a simple fusion strategy, which again verifies the discussions in Sec. 3.2." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.81, + 0.893, + 0.901 + ], + "angle": 0, + "content": "Fusion Factor Selection. In this part, we conduct experiments on the fusion factor selection. To prove the advantages of our parameter selection strategy, we use some fixed values as balance parameters in the fusion process, and we compare the difference between our method and theirs to evaluate its advantage. In detail, we choose three scenarios" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "7210" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.08, + 0.09, + 0.897, + 0.211 + ], + "angle": 0, + "content": "
Method100-50 (2 steps)100-10 (6 steps)100-5 (3 steps)
1-100101-150all1-100101-110111-120121-130131-140141-150all1-100101-150all
ILT [36] (ICCVW2019)18.314.817.00.10.00.10.94.19.31.10.11.30.5
PLOP [16] (CVPR2021)41.914.932.940.615.216.918.711.97.931.639.17.828.7
RC-IL [50] (CVPR2022)42.318.834.539.314.626.323.212.111.832.138.511.529.6
MiB [3] (CVPR2020)40.717.732.838.312.610.68.79.515.129.236.05.625.9
MiB+EWF(Ours)41.221.334.641.512.822.523.214.48.833.241.413.432.1
Joint44.328.238.944.326.142.826.728.117.338.944.328.238.9
" + }, + { + "type": "table_caption", + "bbox": [ + 0.141, + 0.222, + 0.826, + 0.236 + ], + "angle": 0, + "content": "Table 3. The mIoU(%) of the last step on the ADE20K dataset for different overlapped continual learning scenarios." + }, + { + "type": "table", + "bbox": [ + 0.08, + 0.252, + 0.492, + 0.332 + ], + "angle": 0, + "content": "
Fusion strategystep1step2step3step4step5
None [3]71.456.151.936.532.2
EMA [38]74.059.659.840.937.3
model ensemble [13]74.160.160.341.537.2
EWF (Ours)76.173.870.568.365.6
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.344, + 0.468, + 0.371 + ], + "angle": 0, + "content": "Table 4. Ablation study of fusion strategies. All performances are reported on PASCAL VOC 2012 15-1 setting." + }, + { + "type": "table", + "bbox": [ + 0.089, + 0.388, + 0.459, + 0.469 + ], + "angle": 0, + "content": "
Parameter SelectionOurs0.20.40.60.8
15-165.665.663.760.153.3
10-137.339.531.822.714.3
5-351.838.051.256.152.9
Average51.647.748.946.340.2
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.48, + 0.468, + 0.508 + ], + "angle": 0, + "content": "Table 5. Comparison between our dynamic parameter fusion strategy and fixed balance factors." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.538, + 0.468, + 0.779 + ], + "angle": 0, + "content": "to conduct our experiments (i.e., 15-1, 10-1, 5-3), and we calculate the average mIoU of different strategies for three scenarios to measure the final performance. Since the balance factor \\(\\alpha \\in [0,1]\\), we take 0.2, 0.4, 0.6, and 0.8 as the fixed values to compare to our parameter selection strategy. As shown in Table 5, for the 15-1 setting, our method reaches the highest performance compared with other fixed parameters. In addition, although our method is slightly below the highest performance for fixed parameters on other settings, the parameters for the highest performance on different settings vary widely. It means that choosing a fixed parameter for all scenarios is unrealistic and harmful to the algorithm. Importantly, our method reaches the highest average performance among all other fixed values, which indicates that our strategy can be easily applied to different settings without tuning the hyper-parameters manually." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.78, + 0.468, + 0.901 + ], + "angle": 0, + "content": "Robustness of Class Order. In the scenario of class incremental semantic segmentation, the order of classes encountered by the model is significant in measuring the effectiveness of an algorithm. Thus, to verify the effectiveness of our algorithm and the robustness to different class orders, we conduct experiments on five different class orders to calculate the average performance and their standard deviation. As shown in Fig. 6, our method significantly improves the" + }, + { + "type": "image", + "bbox": [ + 0.541, + 0.256, + 0.847, + 0.44 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.5, + 0.455, + 0.89, + 0.469 + ], + "angle": 0, + "content": "Figure 6. Illustration on robustness with respect to different orders." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.495, + 0.89, + 0.525 + ], + "angle": 0, + "content": "performance while also significantly enhancing the robustness to different class orders." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.54, + 0.627, + 0.555 + ], + "angle": 0, + "content": "5. Conclusions" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.565, + 0.892, + 0.896 + ], + "angle": 0, + "content": "In this work, we address the class incremental semantic segmentation (CISS) problem with a simple yet effective endpoints weight fusion method. It is enhanced by the existing distillation-based methods and easily integrated with them. A dynamic parameter fusion strategy is proven to be flexible for different settings and it avoids the further tuning of hyper-parameters. Interestingly, we discuss the relationship between our method and a popular weight fusion method EMA, which reveals why our method is more effective in incremental learning. The experimental results demonstrate that our method can obtain a significant gain compared to the baselines and achieve superior performance. In future work, we will investigate further the underlining reasons why our simple EWF strategy works so well in CISS. Moreover, we are planning to evaluate our incremental learning strategies for other application domains. Acknowledgment. This work is funded by NSFC (NO. 62225604 and 62206135), Fundamental Research Funds for the Central Universities (Nankai University, NO. 63223050), and Bytedance Limited. We acknowledge the Spanish Government funding for projects PID2019-104174GB-I00, TED2021-132513B-I00." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.946, + 0.514, + 0.957 + ], + "angle": 0, + "content": "7211" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.175, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.116, + 0.47, + 0.157 + ], + "angle": 0, + "content": "[1] Jihwan Bang, Heesu Kim, YoungJoon Yoo, Jung-Woo Ha, and Jonghyun Choi. Rainbow memory: Continual learning with a memory of diverse samples. In CVPR, 2021. 2" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.16, + 0.47, + 0.2 + ], + "angle": 0, + "content": "[2] Eden Belouadah and Adrian Popescu. II2m: Class incremental learning with dual memory. 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In CVPR, pages 9296-9305, 2022. 2" + }, + { + "type": "list", + "bbox": [ + 0.503, + 0.092, + 0.892, + 0.431 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "7213" + } + ] +] \ No newline at end of file diff --git a/2023/Endpoints Weight Fusion for Class Incremental Semantic Segmentation/ff7be89f-f21f-4256-a5c9-a98275c1a5e9_origin.pdf b/2023/Endpoints Weight Fusion for Class Incremental Semantic Segmentation/ff7be89f-f21f-4256-a5c9-a98275c1a5e9_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..4139cf23517cc692136cebab6c05a9bca4d78250 --- /dev/null +++ b/2023/Endpoints Weight Fusion for Class Incremental Semantic Segmentation/ff7be89f-f21f-4256-a5c9-a98275c1a5e9_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:ef68dedefe374e3d214ab370a928ca7838c12d54d6e8f6f8baebff8117a4cfe5 +size 2189520 diff --git a/2023/Endpoints Weight Fusion for Class Incremental Semantic Segmentation/full.md b/2023/Endpoints Weight Fusion for Class Incremental Semantic Segmentation/full.md new file mode 100644 index 0000000000000000000000000000000000000000..0790ae11bae37a0ad5a5301af8deace9392e7467 --- /dev/null +++ b/2023/Endpoints Weight Fusion for Class Incremental Semantic Segmentation/full.md @@ -0,0 +1,271 @@ +# Endpoints Weight Fusion for Class Incremental Semantic Segmentation + +Jia-Wen Xiao $^{1*}$ Chang-Bin Zhang $^{1*}$ Jiekang Feng $^{2}$ Xialei Liu $^{1\dagger}$ Joost van de Weijer $^{3}$ Ming-Ming Cheng $^{1}$ VCIP, CS, Nankai University $^{2}$ Tianjin University $^{3}$ Computer Vision Center, Universitat Autònoma de Barcelona + +# Abstract + +Class incremental semantic segmentation (CISS) focuses on alleviating catastrophic forgetting to improve discrimination. Previous work mainly exploits regularization (e.g., knowledge distillation) to maintain previous knowledge in the current model. However, distillation alone often yields limited gain to the model since only the representations of old and new models are restricted to be consistent. In this paper, we propose a simple yet effective method to obtain a model with a strong memory of old knowledge, named Endpoints Weight Fusion (EWF). In our method, the model containing old knowledge is fused with the model retaining new knowledge in a dynamic fusion manner, strengthening the memory of old classes in ever-changing distributions. In addition, we analyze the relationship between our fusion strategy and a popular moving average technique EMA, which reveals why our method is more suitable for class-incremental learning. To facilitate parameter fusion with closer distance in the parameter space, we use distillation to enhance the optimization process. Furthermore, we conduct experiments on two widely used datasets, achieving state-of-the-art performance. + +# 1. Introduction + +As a fundamental task, semantic segmentation plays a key role in visual applications [10, 25]. Previous fully-supervised works aim to segment fixed classes defined in the training set. However, the trained segmentation model is expected to recognize more classes in realistic applications. One straightforward solution is to re-train the model on the entire dataset by mixing old and new data. Nevertheless, this strategy will bring huge labeling and training costs. From the transfer learning perspective [22, 30], another plain solution is to adjust the previously learned model on the newly added data. But the model will overfit to new + +![](images/da9cb0f42c6b0e5591a921adb95d161b04904ac4ebded0bcf9d462a924d5dac2.jpg) +Figure 1. Illustration of different fusion strategies for incremental learning. Ensemble methods utilize multiple models to accumulate more knowledge. Compression methods reduce the model size and distill the knowledge into a small network. While Reparameterization methods use equivalent operations for model fusion. Our Endpoints Weight Fusion (EWF) proposes model addition with a dynamic factor $(\alpha_{t})$ with no further training. + +classes quickly, while forgetting previous old classes. This phenomenon is also known as catastrophic forgetting [35]. + +To alleviate the problem of catastrophic forgetting without extra labeling or training cost, class incremental semantic segmentation (CISS) [3, 16, 50] aims at optimizing the trade-off between maintaining discrimination for old classes and learning knowledge of new classes. Most works [3, 16, 17, 37] designed regularization methods to maintain a balance between memorizing old knowledge and learning new one. We observe that existing works can still suffer from catastrophic forgetting, resulting in a significant + +performance drop in old classes. In the scenario of CISS, not only the previous data is not accessible due to privacy issues or data storage limitations, but regions of old classes in the newly added dataset are labeled as background, which further exacerbates the model over-fitting. + +Besides, training a new model from the old one and fusing them to obtain the final model is a common strategy in continual learning. As shown in Fig. 1, we roughly divide them into four categories with two stages of model expansion and fusion. Some methods [27, 33, 42, 47] propose to expand the model in incremental steps and ensemble the old and new outputs, which have large memory and inference costs. While some works apply compression [46, 47] to compress the old and new model to a unified model with fewer parameters. Nevertheless, these require further training on only new data, which can lead to a bias toward new data. Subsequently, some works [50, 53] explore knowledge decoupling and perform linear parameter fusion with reparameterization. However, this is an intra-module fusion strategy, which is restricted to certain operations. As the last category, we propose Endpoints Weight Fusion (EWF) in the form of parameter addition between the old and new model with a dynamic factor, which requires no further training and re-parameterization, and maintains a constant model size as more tasks are encountered. + +In this work, we adapt weight fusion to CISS and propose the EWF strategy, which aims at utilizing weight fusion to find a new balance between old and new knowledge. During incremental training, we choose a starting point and an ending point model of the current task training trajectory. The starting point represents the old knowledge, while the ending point represents the new knowledge. After learning the current task, a dynamic weight fusion is proposed for efficient knowledge integration. We aggregate them by taking the weighted average of the corresponding parameters of the two models. Nevertheless, the training procedure without restraints on the model would increase the parameter distance between the start and end points, limiting the performance improvement brought by the EWF strategy. To overcome this shortcoming, we further enhance the EWF strategy with a knowledge distillation scheme [16, 17, 50], which can largely increase the similarity of the models at the two points and boost the efficiency of EWF. + +To summarize, the main contributions of this paper are: + +- We propose an Endpoints Weight Fusion strategy, which has no cost of further training and keeps the model size the same. It can effectively find a new balance between old and new categories and alleviate catastrophic forgetting. +- Our method can be easily integrated with several state-of-the-art methods. In several CISS scenarios of long sequences, it can boost the baseline performance by + +more than $20\%$ . + +- We conduct experiments on various CISS scenarios, which demonstrate that our method achieves the state-of-the-art performance on both PASCAL VOC and ADE20K. + +# 2. Related Work + +Class Incremental Learning. Class incremental learning mainly focuses on alleviating catastrophic forgetting while learning the discriminative information required for the newly coming classes. It is most commonly analyzed in image classification, and the techniques can be roughly divided into three categories [11]. Many works [43-45] focus on the structural properties of the model (i.e., Structural-Based Method). The idea is to freeze old models and expand the architecture space to learn new knowledge, which normally results in a growing capacity and memory size of the model. Another way is to regularize models during incremental learning (i.e., Regularization-Based Method) [7, 8, 12, 17], strengthening memory via constraints (e.g., knowledge distillation [39, 41] or gradient penalty [26, 29]). These methods bring the negligible cost to the learning process, but they allow for less freedom for parameter updates. Some other methods [1,2,28] propose to review knowledge through rehearsal (i.e., Rehearsal-Based Method). They store old data and mix it with new data to re-train the model [5, 21, 52]. + +Class Incremental Semantic Segmentation. Semantic segmentation [19] aims at assigning different categories to each single pixel, and has recently attracted attention for learning in a class incremental learning scenario [3, 16]. Nevertheless, data for semantic segmentation takes more space [24, 48] to be stored compared to the classification problem. Therefore, recent work mainly concentrates on utilizing distillation to transfer old knowledge to the new model without saving exemplars from old tasks. + +MiB [4] proposes to model the potential classes to tackle semantic drift. PLOP [16] applies feature distillation to restrict representation ability. SDR [37] uses prototype matching to strengthen consistency in latent space. And RC-IL [50] analyzes the disadvantages of strip pooling and proposes average-pooling-based distillation to back up training. On the contrary, SSUL [6] does not apply distillation and proposes to fix the feature extractor instead of updating its parameters. In addition, they introduce thousands of extra data to help generate pseudo labels. But, simply fixing the model definitely does damage to the balance between plasticity and stability, and it is not sustainable when facing huge amounts of newly coming data. On the other hand, only applying distillation can restrict performance, since it can just limit the representation of new data to be the same. Summarizing the above thoughts and + +![](images/72d967673e47332c1b2196771fce9283c8664ceff66cd805ef96b72dab107e01.jpg) +Figure 2. Illustration of our Endpoints Weight Fusion (EWF) framework. On the left side, we illustrate training and testing processes. Training is enhanced by knowledge distillation and fusion is applied after training to accumulate all seen knowledge. On the right side, given a $3 \times 3$ convolution layer and a normalization layer, they are fused by using a dynamic trade-off parameter $\alpha_{t}$ . Note that there is no computation cost for our fusion process. + +inspired by RC-IL [50], we design a strategy different from the above, cooperating with distillation and maintaining the balance between the old and new knowledge with model weight fusion. + +Weight Fusion Method. Weight Fusion is widely used in neural network training to improve performance. It can be applied with both linear and nonlinear operations. In linear mode, RCM [27] explores the additivity of convolution and applies it on multi-task learning. ACNet [14] and RepVGG [15] first propose structural re-parameterization, which is used to merge multi-branch Convolution-Batch Normalization serial sequences to a plain Convolution layer. RC-IL ingeniously exploits this operation to establish a representation compensation mechanism in continual learning. In nonlinear mode, weight averaging is commonly used to bring closer connections between different models. Famous methods like BYOL [20] use EMA [38] to improve the knowledge transfer effect or model robustness. From this point, we design a strategy to reach a new balance, which has no effect on the current training process and fully releases the learning ability of the model. + +# 3. Method + +# 3.1. Preliminaries + +We consider a multi-step training process where $T$ tasks are sequentially learned by model $f_{\theta}$ in a fully supervised scenario for semantic segmentation, where $f$ is parameterized by parameter $\theta$ . Here $f_{\theta_t}$ denotes the model at task $t$ . Each task contains a dataset $\mathcal{D}_t = \{x_i,y_i\}$ , where $x_{i}$ denotes the data and $y_{i}$ denotes the corresponding label. The training label space of the task $T$ is denoted as $C_t\bigcup \{c_b\}$ , + +where $C_t$ includes all classes that appear in this task, and $c_b$ represents the background. Since $C_i \cap C_j = \emptyset$ , the objective of different tasks are not the same, easily leading to catastrophic forgetting. To save annotation costs, only the categories that need to be learned at this stage will be labeled. Thus, $c_b$ contains not only the real background, but also the classes appearing in past and future tasks. This complicates the training of the model $f_\theta$ since the background label $c_b$ can refer to different classes at different tasks. This exacerbates the severity of forgetting. + +# 3.2. Endpoints Weight Fusion (EWF) + +As illustrated in Fig. 1, the existing model expansion-fusion methods have their own drawbacks for enhancing the model's memory of old knowledge. Thus, to better retain the old knowledge while boosting the learning ability of the model, we introduce our Endpoints Weight Fusion strategy. Considering the training process at step $t$ , we choose a starting point model and an ending point model. The final model of the previous step $(\theta_{old})$ is regarded as the best container of old knowledge. While the model after training on the current task $(\theta_{new})$ contains the discriminative information for new classes. Additionally, we introduce another parameter $\alpha$ for the endpoints weight fusion, aiming at fusing two sets of parameters in a certain ratio. This ratio can be seen as a balance factor. Therefore, the operation of endpoints weight fusion can be written as: + +$$ +\theta_ {\text {b a l a n c e d}} = \alpha_ {t} \theta_ {\text {n e w}} + (1 - \alpha_ {t}) \theta_ {\text {o l d}} \tag {1} +$$ + +where the $\theta_{\text{balanced}}$ denotes the final model of this task, and the $\theta_{old}, \theta_{new}$ are defined as above. Furthermore, the number of incremental categories (denoted as $N_{\text{new}}$ ) and orig- + +inal categories (denoted as $N_{old}$ ) to a certain extent represent the degree of emphasis on the $\theta_{new}$ and $\theta_{old}$ . For the selection of $\alpha_{t}$ , we need to consider $N_{new}$ and $N_{old}$ in the current learning step. We decide to replace the constant ratio with an equation related to $N_{new}$ and $N_{old}$ . In detail, this formula can be expressed as: + +$$ +\alpha_ {t} = \sqrt {\frac {N _ {n e w}}{N _ {n e w} + N _ {o l d}}} \tag {2} +$$ + +It can be used across different tasks and scenarios. It can adapt to each task in CISS with a dynamic factor. We illustrate the main idea of our method in Fig. 2. + +Knowledge distillation enhanced for EWF. In practice, training without any constraint will significantly increase the distance between different models and break the similarity of model representations. That means it deteriorates the forgetting of the model, which further undermines the model's ability to discriminate new classes. Moreover, guaranteeing a low error linear path between two distant models is an overly strong assumption. Thus, choosing a model trained without constraints as an ending point is potentially harmful, and we, therefore, introduce knowledge distillation to enhance the compatibility of the models of our Endpoints Weight Fusion method. + +Knowledge distillation is a commonly used technique to prevent models from forgetting. As stated above, we utilize distillation to back up our strategy, limiting the distance between two endpoints and forcing them to be similar. In general, distillation used in continual learning is mainly divided into two categories, i.e., feature-based distillation and logit-based distillation. They can be represented as: + +$$ +\begin{array}{l} L _ {F D} = \frac {1}{| D |} \sum_ {(x _ {i}, y _ {i}) \sim D} | | \Psi_ {o l d} (x _ {i}) - \Psi_ {n e w} (x _ {i}) | | ^ {2} \\ L _ {L D} = \frac {1}{| D |} \sum_ {\left(x _ {i}, y _ {i}\right) \sim D} K L \left(\Phi_ {o l d} \left(\Psi_ {o l d} \left(x _ {i}\right)\right), \Phi_ {n e w} \left(\Psi_ {n e w} \left(x _ {i}\right)\right)\right) \tag {3} \\ \end{array} +$$ + +$\Psi_{old} / \Phi_{old}$ and $\Psi_{new} / \Phi_{new}$ denote old and new feature extractor/classifier respectively, and $D$ is the corresponding dataset of the incremental learning step. In CISS, two popular distillation losses (i.e., UNKD, POD) are proposed by [3, 16], respectively. The former is a logit-based distillation and the latter is a feature-based distillation. They can be easily integrated into our method. + +Discussion on EMA v.s. EWF. An update strategy similar to our method is using EMA [38] to update the model. Here we will discuss the difference between our method EWF and EMA, and the advantages of EWF. The EMA strategy maintains a moving average model during training, and uses this model to replace the final model for inference. The moving average model can be represented as: + +$$ +v ^ {i} = \beta v ^ {i - 1} + (1 - \beta) \theta^ {i} \tag {4} +$$ + +![](images/54381d139f166d324c550961ec8036ff16a9aefec15b0990e92169561ab052ed.jpg) +Figure 3. Representation similarity between old model $\theta^1$ before training and being trained new model $\theta^i$ . The similarity measure we use is cosine similarity. We extract the intermediate results of the feature extractors of the old and new networks and calculate the average of the cosine similarity between them. + +where the $v^{i}$ denotes the moving average of the first $i$ models, and $\theta^i$ denotes the model after $i$ th iteration. $\beta$ is the moving average parameter, which is usually set as 0.9/0.99. It is easy to see that the EMA is an inter-iteration operation, which is easier to realize due to the low distance between models. Since we use SGD as an optimizer, following Eq. 5, the results of EMA and EWF can be represented as $v^n$ and $\theta_{\text{balanced}}$ in Eq. 6. Note that the learning rate does not affect the result of the analysis, so we set the learning rate to 1. The more detailed derivations are in the Appendix. + +$$ +\begin{array}{l} \theta^ {n} = \theta^ {n - 1} - \nabla_ {L} \left(\theta^ {n - 1}\right) \\ = \theta^ {1} - \sum_ {k = 1} ^ {n} \nabla_ {L} \left(\theta^ {k}\right) \tag {5} \\ \end{array} +$$ + +$$ +v ^ {n} = \theta^ {1} - \sum_ {k = 1} ^ {n - 1} (1 - \beta^ {n - k}) \nabla_ {L} \left(\theta^ {k}\right) \tag {6} +$$ + +$$ +\theta_ {b a l a n c e d} = \theta^ {1} - \alpha \sum_ {k = 1} ^ {n - 1} \nabla_ {L} \left(\theta^ {k}\right) +$$ + +Since the $\beta$ is usually set to $0.9 / 0.99$ and the $\alpha$ is set following Eq. 2, $\alpha$ is always smaller than $\beta$ . According to Eq. 6, EMA gives more weight to the gradient of early time, and then gradually attenuates the influence of gradients in subsequent iterations. On the contrary, EWF gives the gradient of different parts a relatively uniform weight. Besides, to better observe the stability of incremental learning step, we calculate the representations similarity between $\theta^1$ and $\theta^i$ . According to our observation in an incremental step, as shown in Fig. 3, the similarity of representations between $\theta^1$ and $\theta^i$ first decreases and then increases, and gradually stabilizes in the subsequent stages. This reveals that in order + +Algorithm 1 Pseudo Code for EWF in incremental steps +Require: $f,\theta_0,T,D_T$ and learning rate $\gamma$ $t\gets 1$ +while $t\leq T$ do Initialize $N_{new},N_{old}$ $\theta^1\gets \theta_{t - 1}$ $\alpha_{t}\leftarrow \sqrt{\frac{N_{new}}{N_{new} + N_{old}}}$ $i\gets 1$ +while not converged do Sample mini-batch $\{x_i,y_i\} \sim D$ $\theta^{i + 1}\gets \theta^i -\gamma \nabla_{LCE + LKD}(f_{\theta^i})$ $i\gets i + 1$ +end while + $\theta_{old}\gets \theta^1,\theta_{new}\gets \theta^i$ $\theta_{balanced}\gets \alpha_t\theta_{new} + (1 - \alpha_t)\theta_{old}$ $\theta_t\gets \theta_{balanced}$ $t\gets t + 1$ +end while + +to learn new knowledge, the representation will first collapse and then recover under the action of the distillation and cross-entropy losses. Then EMA concentrates more of the gradient on the early collapsed process, while our method pays more attention to the useful gradient information after the recovery. From this perspective, our method is theoretically better than EMA in CISS. + +# 3.3. Overall Framework + +As stated above, to remember knowledge from old tasks, we borrow knowledge distillation to strengthen the model's memory. To learn the discrimination of new classes, we use the Cross-Entropy loss to optimize the model. In general, the objective is given by: + +$$ +\min _ {\theta_ {t}} \mathcal {L} _ {C E} \left(\theta_ {t}\right) + \mathcal {L} _ {K D} \left(\theta_ {t}; \theta_ {t - 1}\right) \tag {7} +$$ + +And the overall algorithm of EWF is shown in Alg. 1. + +# 4. Experiments + +We demonstrate experimental protocols, scenarios and training details. Furthermore, we evaluate our algorithm through quantitative and qualitative experiments. + +# 4.1. Experimental setups + +Protocols. In general, the training for CISS is divided into $T$ steps, and each step denotes a task, where the labeled classes are disjoint in each of them. We adopt the overlapped setting as other works, in which the current training data may contain potential classes labeled as background in previous steps. The overlapped setting is more realistic, and + +therefore we only evaluate on this setup as previous methods [6, 16]. Following existing works [3, 16, 50], we conduct experiments on two widely used segmentation datasets, PASCAL VOC 2012 [18] and ADE20K [51]. The PASCAL VOC 2012 dataset [18] contains 10,582 training images and 1449 validation images with 20 object classes and the background class. The ADE20K dataset [51] is composed of 150 classes and contains 20, 210 training images, and 2000 validation images. Following previous works [3, 16, 50], $X - Y$ denotes different settings for CISS. In the $X - Y$ setting, the model can recognize $X$ classes in the initial step, and then is supposed to learn $Y$ newly added classes in each following step. At each step, only current task data is available for training. We perform experiments on PASCAL VOC 2012 [18] with four settings, 15-1, 10-1, 5-3 and 19-1. On ADE20K [51], we verify the effectiveness of our method on three settings, 100-5, 100-10, and 100-50. + +Implementation Details. Following existing works [3, 16, 50], we apply Deeplab-v3 [9] as our segmentation model with ResNet-101 [23] as a backbone. We also use in-place activated batch normalization [40] in the backbone. In our experiments, we use some data augmentations, including horizontal flip and random crop. The ratio $\alpha_{t}$ for EWF is defined as Eq.2. Using SGD optimizer, we train the model for 30 (PASCAL VOC 2012) and 60 (ADE20K) epochs in each step with a batch size of 24. We set the initial learning rate as 0.01 for the first training step and 0.001 for the next continual learning steps. All experiments are conducted on 4 RTX 2080Ti GPUs. The learning rate is decayed with poly schedule. During training, we use $20\%$ of the training set as validation, and report the mean Intersect over Union (mIoU) on the original validation set. + +# 4.2. Comparison to competing methods + +In this section, we apply our method to MiB [3] and PLOP [16]. Additionally, we also compare our method with LwF [31], ILT [36], SDR [37], and RCIL [50]. + +PASCAL VOC 2012. In this dataset, we use the same experimental settings as [3, 16, 50], we performed the experiments with the class incremental learning settings 15-1, 10-1, 5-3, 19-1. As shown in Table 1, we report the result of our experiments on the final task. From the results, we can observe that our method improves the results of both MiB and PLOP by a large margin, on the more challenging settings (e.g., 15-1, 10-1, 5-3. For instance, on the 15-1 setting, our algorithm obtains performance gains of $12.4\%$ and $33.3\%$ mIoU for PLOP and MIB, respectively. Furthermore, on the longest learning sequence, the 10-1 setting, our method obtains a large gain consistently, improving the performance of PLOP and MIB by $21.4\%$ and $24.7\%$ , respectively. In Table 1 we also report the performance of the old and new classes for different settings. Our method achieves significant performance gains for old classes. This demon + +
Method15-1 (6 steps)10-1 (11 steps)5-3 (6 steps)19-1 (2 steps)
0-1516-20all0-1011-20all0-56-20all0-1920all
LwF [31] (TPAMI2017)6.03.95.58.02.04.820.936.724.753.08.550.9
ILT [36] (ICCVW2019)9.67.89.27.23.75.522.531.729.068.212.365.5
SDR [37] (CVPR2021)47.314.739.532.417.125.1---69.132.667.4
RCIL [50] (CVPR2022)70.623.759.455.415.134.363.134.642.877.031.574.7
MiB [3] (CVPR2020)38.013.532.212.213.112.657.142.546.771.222.168.9
MiB+EWF (Ours)78.025.565.556.016.737.369.045.051.877.812.274.7
PLOP [16] (CVPR2021)65.121.154.644.015.530.525.730.028.775.437.373.5
PLOP+EWF (Ours)77.732.767.071.530.351.961.742.247.777.96.774.5
Joint79.872.678.279.872.678.278.278.078.276.977.677.4
+ +Table 1. The mIoU(%) of the last step on the Pascal VOC 2012 dataset for different class-incremental segmentation scenarios. + +![](images/5ada5be248ee09c3758989ab061393427a3453278627f9d66d24b08b70756163.jpg) +(a) 10-1 scenario on PASCAL VOC +Figure 4. The mIoU $(\%)$ at each step for the settings 10-1 (a) and 15-1 (b). + +![](images/f374888c7889b0140a11ec38943f3cc0897757307e97e1712d8eae4a8b207883.jpg) +(b) 15-1 scenario on PASCAL VOC + +strates that our EWF strategy can enhance significantly the model's memory of old knowledge (by successfully countering forgetting). In the more challenging settings, e.g., 15-1, 5-3, 10-1, our method also boosts the performance of new classes. This shows that EWF can achieve high plasticity on new steps, and that the proposed dynamically weighted combination of the network allows achieving a good tradeoff between plasticity and stability. We also show dynamic performance changes during the continual learning process in Fig. 4. It is clear that with more learning steps, the gap between our method and the best baseline is growing, and that the curve of our method for different settings (15-1 and 5-3) is on the top throughout most of the learning trajectory. + +Comparison with methods that introduce auxiliary data. It is worth noting that there are several methods [6, 34, 49] that introduce different forms of auxiliary data to assist continual semantic segmentation, helping the model build better pseudo-labels or enhance memory for old knowledge. RECALL [34] learns a generative model or retrieves from web-crawled data for replay, while SSUL [6] leverages salient object detectors (trained on MSRA-B dataset [32] with 5000 images) to generate saliency maps as auxiliary + +data. And ST-CIL [49] exploits unlabelled datasets with pseudo labels as ground truth. Even if our algorithm is designed to deal with extra-data-free scenarios, to further demonstrate the effectiveness of our method, we integrate our method to SSUL and compare it with the above methods in Table 2. Note that SSUL freezes the backbone completely and it is hard to directly apply our method on it. Therefore, we learned part of the backbone network parameters when we apply our method to SSUL. In detail, we set the second stage of the backbone in SSUL as learnable parameters for model fusion. SSUL obtains the best performance among these methods using auxiliary data, and our method applied to SSUL can further improve it by about $1\%$ for all classes. + +Visualization. As shown in Fig. 5, we compare our method based on MiB, and we show a sample from the base task (step 0) and a sample from step 2. From the top two rows, the person and bike classes are largely preserved with our method, but it forgets gradually for the baseline MiB. From the bottom two rows, it shows an example with both old classes and a new sheep class. Our method can keep the old knowledge better while incorporating new knowledge. + +ADE20K. In order to further evaluate the effectiveness of + +![](images/458b5318f3da581b46aa4f9fffa878f9501db768ddac07ac60e7b566710e0d25.jpg) +Figure 5. The qualitative comparison between different methods. All prediction results are from the last step of 15-1 overlapped setting. In the initial step, 15 classes are learned and 5 tasks are learned incrementally with class potted plant, sheep, sofa, train and monitor. + +
MethodAuxiliary Data15-1 (PASCAL VOC 2012)10-1 (PASCAL VOC 2012)
0-1516-20all0-1011-20all
RECALL [34] (ICCV2021)GAN / Web-Data65.747.862.759.546.754.8
ST-CIL [49] (TNNLS2022)Unlabeled Data71.440.063.6---
SSUL [6] (NeurIPS2021)Saliency Map77.336.667.671.345.959.2
SSUL + EWF (Ours)Saliency Map77.938.968.672.447.460.5
+ +Table 2. The mIoU(%) of the last step on the Pascal VOC 2012 15-1 and 10-1 overlapped setting. + +our method, we conduct experiments on ADE20K dataset. In Table 3, we show the experimental results with settings 100-50, 100-10 and 100-5. As shown in Table 3, our method reaches superior performance on this dataset. Especially on the most challenging settings 100-5 and 100-10, our method achieves $6.2\%$ and $3.0\%$ improvement over MiB [3], respectively. It also surpasses the state-of-the-art method RC-IL by a large margin on 100-5 setting. This indicates that our EWF is effective on large-scale datasets as well. + +# 4.3. Ablation Study + +In this part, we demonstrate and analyze the effectiveness of weight fusion and its dynamic factor selection. We use MiB [3] for the ablation experiments. + +Fusion Strategy. In Table 4, we demonstrate the performance of different fusion strategies. These experiments are conducted with the setting 15-1 on PASCAL VOC 2012. + +Most of these methods perform continual learning by fusing the information present in the previous step model. Among these, EMA [38] updates a stored set of parameters with moving average during training, and uses it for inference. Model ensemble fuses the previous model's prediction and new prediction in an average way during inference. And None denotes the model trained only with Distillation and Cross-Entropy (i.e., MiB [3]). Compared with no fusion method, EMA and model ensemble have $5.1\%$ and $5.0\%$ performance improvement, respectively. While Our EWF has a $33.3\%$ improvement on the basis of a simple fusion strategy, which again verifies the discussions in Sec. 3.2. + +Fusion Factor Selection. In this part, we conduct experiments on the fusion factor selection. To prove the advantages of our parameter selection strategy, we use some fixed values as balance parameters in the fusion process, and we compare the difference between our method and theirs to evaluate its advantage. In detail, we choose three scenarios + +
Method100-50 (2 steps)100-10 (6 steps)100-5 (3 steps)
1-100101-150all1-100101-110111-120121-130131-140141-150all1-100101-150all
ILT [36] (ICCVW2019)18.314.817.00.10.00.10.94.19.31.10.11.30.5
PLOP [16] (CVPR2021)41.914.932.940.615.216.918.711.97.931.639.17.828.7
RC-IL [50] (CVPR2022)42.318.834.539.314.626.323.212.111.832.138.511.529.6
MiB [3] (CVPR2020)40.717.732.838.312.610.68.79.515.129.236.05.625.9
MiB+EWF(Ours)41.221.334.641.512.822.523.214.48.833.241.413.432.1
Joint44.328.238.944.326.142.826.728.117.338.944.328.238.9
+ +Table 3. The mIoU(%) of the last step on the ADE20K dataset for different overlapped continual learning scenarios. + +
Fusion strategystep1step2step3step4step5
None [3]71.456.151.936.532.2
EMA [38]74.059.659.840.937.3
model ensemble [13]74.160.160.341.537.2
EWF (Ours)76.173.870.568.365.6
+ +Table 4. Ablation study of fusion strategies. All performances are reported on PASCAL VOC 2012 15-1 setting. + +
Parameter SelectionOurs0.20.40.60.8
15-165.665.663.760.153.3
10-137.339.531.822.714.3
5-351.838.051.256.152.9
Average51.647.748.946.340.2
+ +Table 5. Comparison between our dynamic parameter fusion strategy and fixed balance factors. + +to conduct our experiments (i.e., 15-1, 10-1, 5-3), and we calculate the average mIoU of different strategies for three scenarios to measure the final performance. Since the balance factor $\alpha \in [0,1]$ , we take 0.2, 0.4, 0.6, and 0.8 as the fixed values to compare to our parameter selection strategy. As shown in Table 5, for the 15-1 setting, our method reaches the highest performance compared with other fixed parameters. In addition, although our method is slightly below the highest performance for fixed parameters on other settings, the parameters for the highest performance on different settings vary widely. It means that choosing a fixed parameter for all scenarios is unrealistic and harmful to the algorithm. Importantly, our method reaches the highest average performance among all other fixed values, which indicates that our strategy can be easily applied to different settings without tuning the hyper-parameters manually. + +Robustness of Class Order. In the scenario of class incremental semantic segmentation, the order of classes encountered by the model is significant in measuring the effectiveness of an algorithm. Thus, to verify the effectiveness of our algorithm and the robustness to different class orders, we conduct experiments on five different class orders to calculate the average performance and their standard deviation. As shown in Fig. 6, our method significantly improves the + +![](images/df4a1e676e976a79c309a63759bdb815e1b17ec1982527d2f09a477078be9ceb.jpg) +Figure 6. Illustration on robustness with respect to different orders. + +performance while also significantly enhancing the robustness to different class orders. + +# 5. Conclusions + +In this work, we address the class incremental semantic segmentation (CISS) problem with a simple yet effective endpoints weight fusion method. It is enhanced by the existing distillation-based methods and easily integrated with them. A dynamic parameter fusion strategy is proven to be flexible for different settings and it avoids the further tuning of hyper-parameters. Interestingly, we discuss the relationship between our method and a popular weight fusion method EMA, which reveals why our method is more effective in incremental learning. The experimental results demonstrate that our method can obtain a significant gain compared to the baselines and achieve superior performance. In future work, we will investigate further the underlining reasons why our simple EWF strategy works so well in CISS. Moreover, we are planning to evaluate our incremental learning strategies for other application domains. Acknowledgment. This work is funded by NSFC (NO. 62225604 and 62206135), Fundamental Research Funds for the Central Universities (Nankai University, NO. 63223050), and Bytedance Limited. We acknowledge the Spanish Government funding for projects PID2019-104174GB-I00, TED2021-132513B-I00. + +# References + +[1] Jihwan Bang, Heesu Kim, YoungJoon Yoo, Jung-Woo Ha, and Jonghyun Choi. Rainbow memory: Continual learning with a memory of diverse samples. In CVPR, 2021. 2 +[2] Eden Belouadah and Adrian Popescu. II2m: Class incremental learning with dual memory. In ICCV, pages 583-592, 2019. 2 +[3] Fabio Cermelli, Massimiliano Mancini, Samuel Rota Bulo, Elisa Ricci, and Barbara Caputo. Modeling the background for incremental learning in semantic segmentation. In CVPR, pages 9233-9242, 2020. 1, 2, 4, 5, 6, 7, 8 +[4] Fabio Cermelli, Massimiliano Mancini, Samuel Rota Bulo, Elisa Ricci, and Barbara Caputo. Modeling the background for incremental learning in semantic segmentation. 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In CVPR, pages 9296-9305, 2022. 2 \ No newline at end of file diff --git a/2023/Endpoints Weight Fusion for Class Incremental Semantic Segmentation/images.zip b/2023/Endpoints Weight Fusion for Class Incremental Semantic Segmentation/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..897275e20053e5525093c7c3aee8f62e451da47f --- /dev/null +++ b/2023/Endpoints Weight Fusion for Class Incremental Semantic Segmentation/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:9de97740e76cfaf0a4a2681f1fa3ecd82fef30ae3176e830b8a683975eecea96 +size 617677 diff --git a/2023/Endpoints Weight Fusion for Class Incremental Semantic Segmentation/layout.json b/2023/Endpoints Weight Fusion for Class Incremental Semantic Segmentation/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..5e774b293a606ba8f1ff765c18e59534007d298a --- /dev/null +++ b/2023/Endpoints Weight Fusion for Class Incremental Semantic Segmentation/layout.json @@ -0,0 +1,7813 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 76, + 103, + 518, + 121 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 76, + 103, + 518, + 121 + ], + "spans": [ + { + "bbox": [ + 76, + 103, + 518, + 121 + ], + "type": "text", + "content": "Endpoints Weight Fusion for Class Incremental Semantic Segmentation" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 123, + 142, + 474, + 200 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 123, + 142, + 474, + 200 + ], + "spans": [ + { + "bbox": [ + 123, + 142, + 474, + 200 + ], + "type": "text", + "content": "Jia-Wen Xiao " + }, + { + "bbox": [ + 123, + 142, + 474, + 200 + ], + "type": "inline_equation", + "content": "^{1*}" + }, + { + "bbox": [ + 123, + 142, + 474, + 200 + ], + "type": "text", + "content": " Chang-Bin Zhang " + }, + { + "bbox": [ + 123, + 142, + 474, + 200 + ], + "type": "inline_equation", + "content": "^{1*}" + }, + { + "bbox": [ + 123, + 142, + 474, + 200 + ], + "type": "text", + "content": " Jiekang Feng " + }, + { + "bbox": [ + 123, + 142, + 474, + 200 + ], + "type": "inline_equation", + "content": "^{2}" + }, + { + "bbox": [ + 123, + 142, + 474, + 200 + ], + "type": "text", + "content": " Xialei Liu " + }, + { + "bbox": [ + 123, + 142, + 474, + 200 + ], + "type": "inline_equation", + "content": "^{1\\dagger}" + }, + { + "bbox": [ + 123, + 142, + 474, + 200 + ], + "type": "text", + "content": " Joost van de Weijer " + }, + { + "bbox": [ + 123, + 142, + 474, + 200 + ], + "type": "inline_equation", + "content": "^{3}" + }, + { + "bbox": [ + 123, + 142, + 474, + 200 + ], + "type": "text", + "content": " Ming-Ming Cheng " + }, + { + "bbox": [ + 123, + 142, + 474, + 200 + ], + "type": "inline_equation", + "content": "^{1}" + }, + { + "bbox": [ + 123, + 142, + 474, + 200 + ], + "type": "text", + "content": " VCIP, CS, Nankai University " + }, + { + "bbox": [ + 123, + 142, + 474, + 200 + ], + "type": "inline_equation", + "content": "^{2}" + }, + { + "bbox": [ + 123, + 142, + 474, + 200 + ], + "type": "text", + "content": " Tianjin University " + }, + { + "bbox": [ + 123, + 142, + 474, + 200 + ], + "type": "inline_equation", + "content": "^{3}" + }, + { + "bbox": [ + 123, + 142, + 474, + 200 + ], + "type": "text", + "content": " Computer Vision Center, Universitat Autònoma de Barcelona" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 143, + 227, + 192, + 239 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 227, + 192, + 239 + ], + "spans": [ + { + "bbox": [ + 143, + 227, + 192, + 239 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 251, + 290, + 504 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 251, + 290, + 504 + ], + "spans": [ + { + "bbox": [ + 46, + 251, + 290, + 504 + ], + "type": "text", + "content": "Class incremental semantic segmentation (CISS) focuses on alleviating catastrophic forgetting to improve discrimination. Previous work mainly exploits regularization (e.g., knowledge distillation) to maintain previous knowledge in the current model. However, distillation alone often yields limited gain to the model since only the representations of old and new models are restricted to be consistent. In this paper, we propose a simple yet effective method to obtain a model with a strong memory of old knowledge, named Endpoints Weight Fusion (EWF). In our method, the model containing old knowledge is fused with the model retaining new knowledge in a dynamic fusion manner, strengthening the memory of old classes in ever-changing distributions. In addition, we analyze the relationship between our fusion strategy and a popular moving average technique EMA, which reveals why our method is more suitable for class-incremental learning. To facilitate parameter fusion with closer distance in the parameter space, we use distillation to enhance the optimization process. Furthermore, we conduct experiments on two widely used datasets, achieving state-of-the-art performance." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 533, + 128, + 545 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 533, + 128, + 545 + ], + "spans": [ + { + "bbox": [ + 47, + 533, + 128, + 545 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 554, + 287, + 685 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 554, + 287, + 685 + ], + "spans": [ + { + "bbox": [ + 46, + 554, + 287, + 685 + ], + "type": "text", + "content": "As a fundamental task, semantic segmentation plays a key role in visual applications [10, 25]. Previous fully-supervised works aim to segment fixed classes defined in the training set. However, the trained segmentation model is expected to recognize more classes in realistic applications. One straightforward solution is to re-train the model on the entire dataset by mixing old and new data. Nevertheless, this strategy will bring huge labeling and training costs. From the transfer learning perspective [22, 30], another plain solution is to adjust the previously learned model on the newly added data. But the model will overfit to new" + } + ] + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 313, + 232, + 537, + 451 + ], + "blocks": [ + { + "bbox": [ + 313, + 232, + 537, + 451 + ], + "lines": [ + { + "bbox": [ + 313, + 232, + 537, + 451 + ], + "spans": [ + { + "bbox": [ + 313, + 232, + 537, + 451 + ], + "type": "image", + "image_path": "da9cb0f42c6b0e5591a921adb95d161b04904ac4ebded0bcf9d462a924d5dac2.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 472, + 547, + 552 + ], + "lines": [ + { + "bbox": [ + 304, + 472, + 547, + 552 + ], + "spans": [ + { + "bbox": [ + 304, + 472, + 547, + 552 + ], + "type": "text", + "content": "Figure 1. Illustration of different fusion strategies for incremental learning. Ensemble methods utilize multiple models to accumulate more knowledge. Compression methods reduce the model size and distill the knowledge into a small network. While Reparameterization methods use equivalent operations for model fusion. Our Endpoints Weight Fusion (EWF) proposes model addition with a dynamic factor " + }, + { + "bbox": [ + 304, + 472, + 547, + 552 + ], + "type": "inline_equation", + "content": "(\\alpha_{t})" + }, + { + "bbox": [ + 304, + 472, + 547, + 552 + ], + "type": "text", + "content": " with no further training." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 578, + 546, + 602 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 578, + 546, + 602 + ], + "spans": [ + { + "bbox": [ + 304, + 578, + 546, + 602 + ], + "type": "text", + "content": "classes quickly, while forgetting previous old classes. This phenomenon is also known as catastrophic forgetting [35]." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 605, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 547, + 715 + ], + "type": "text", + "content": "To alleviate the problem of catastrophic forgetting without extra labeling or training cost, class incremental semantic segmentation (CISS) [3, 16, 50] aims at optimizing the trade-off between maintaining discrimination for old classes and learning knowledge of new classes. Most works [3, 16, 17, 37] designed regularization methods to maintain a balance between memorizing old knowledge and learning new one. We observe that existing works can still suffer from catastrophic forgetting, resulting in a significant" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 693, + 211, + 703 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 693, + 211, + 703 + ], + "spans": [ + { + "bbox": [ + 58, + 693, + 211, + 703 + ], + "type": "text", + "content": "*The first two authors contribute equally." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 59, + 703, + 211, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 703, + 211, + 712 + ], + "spans": [ + { + "bbox": [ + 59, + 703, + 211, + 712 + ], + "type": "text", + "content": "† Corresponding author (xialei@nankai.edu.cn)" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "7204" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 131 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 131 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 131 + ], + "type": "text", + "content": "performance drop in old classes. In the scenario of CISS, not only the previous data is not accessible due to privacy issues or data storage limitations, but regions of old classes in the newly added dataset are labeled as background, which further exacerbates the model over-fitting." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 133, + 288, + 370 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 133, + 288, + 370 + ], + "spans": [ + { + "bbox": [ + 46, + 133, + 288, + 370 + ], + "type": "text", + "content": "Besides, training a new model from the old one and fusing them to obtain the final model is a common strategy in continual learning. As shown in Fig. 1, we roughly divide them into four categories with two stages of model expansion and fusion. Some methods [27, 33, 42, 47] propose to expand the model in incremental steps and ensemble the old and new outputs, which have large memory and inference costs. While some works apply compression [46, 47] to compress the old and new model to a unified model with fewer parameters. Nevertheless, these require further training on only new data, which can lead to a bias toward new data. Subsequently, some works [50, 53] explore knowledge decoupling and perform linear parameter fusion with reparameterization. However, this is an intra-module fusion strategy, which is restricted to certain operations. As the last category, we propose Endpoints Weight Fusion (EWF) in the form of parameter addition between the old and new model with a dynamic factor, which requires no further training and re-parameterization, and maintains a constant model size as more tasks are encountered." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 372, + 287, + 586 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 372, + 287, + 586 + ], + "spans": [ + { + "bbox": [ + 46, + 372, + 287, + 586 + ], + "type": "text", + "content": "In this work, we adapt weight fusion to CISS and propose the EWF strategy, which aims at utilizing weight fusion to find a new balance between old and new knowledge. During incremental training, we choose a starting point and an ending point model of the current task training trajectory. The starting point represents the old knowledge, while the ending point represents the new knowledge. After learning the current task, a dynamic weight fusion is proposed for efficient knowledge integration. We aggregate them by taking the weighted average of the corresponding parameters of the two models. Nevertheless, the training procedure without restraints on the model would increase the parameter distance between the start and end points, limiting the performance improvement brought by the EWF strategy. To overcome this shortcoming, we further enhance the EWF strategy with a knowledge distillation scheme [16, 17, 50], which can largely increase the similarity of the models at the two points and boost the efficiency of EWF." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 59, + 587, + 282, + 600 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 587, + 282, + 600 + ], + "spans": [ + { + "bbox": [ + 59, + 587, + 282, + 600 + ], + "type": "text", + "content": "To summarize, the main contributions of this paper are:" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 58, + 609, + 286, + 713 + ], + "type": "list", + "angle": 0, + "index": 6, + "blocks": [ + { + "bbox": [ + 59, + 609, + 286, + 668 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 609, + 286, + 668 + ], + "spans": [ + { + "bbox": [ + 59, + 609, + 286, + 668 + ], + "type": "text", + "content": "- We propose an Endpoints Weight Fusion strategy, which has no cost of further training and keeps the model size the same. It can effectively find a new balance between old and new categories and alleviate catastrophic forgetting." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 58, + 677, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 677, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 58, + 677, + 286, + 713 + ], + "type": "text", + "content": "- Our method can be easily integrated with several state-of-the-art methods. In several CISS scenarios of long sequences, it can boost the baseline performance by" + } + ] + } + ], + "index": 5 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 326, + 72, + 392, + 83 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 326, + 72, + 392, + 83 + ], + "spans": [ + { + "bbox": [ + 326, + 72, + 392, + 83 + ], + "type": "text", + "content": "more than " + }, + { + "bbox": [ + 326, + 72, + 392, + 83 + ], + "type": "inline_equation", + "content": "20\\%" + }, + { + "bbox": [ + 326, + 72, + 392, + 83 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 317, + 94, + 545, + 141 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 94, + 545, + 141 + ], + "spans": [ + { + "bbox": [ + 317, + 94, + 545, + 141 + ], + "type": "text", + "content": "- We conduct experiments on various CISS scenarios, which demonstrate that our method achieves the state-of-the-art performance on both PASCAL VOC and ADE20K." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 154, + 392, + 167 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 154, + 392, + 167 + ], + "spans": [ + { + "bbox": [ + 306, + 154, + 392, + 167 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 174, + 545, + 413 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 174, + 545, + 413 + ], + "spans": [ + { + "bbox": [ + 304, + 174, + 545, + 413 + ], + "type": "text", + "content": "Class Incremental Learning. Class incremental learning mainly focuses on alleviating catastrophic forgetting while learning the discriminative information required for the newly coming classes. It is most commonly analyzed in image classification, and the techniques can be roughly divided into three categories [11]. Many works [43-45] focus on the structural properties of the model (i.e., Structural-Based Method). The idea is to freeze old models and expand the architecture space to learn new knowledge, which normally results in a growing capacity and memory size of the model. Another way is to regularize models during incremental learning (i.e., Regularization-Based Method) [7, 8, 12, 17], strengthening memory via constraints (e.g., knowledge distillation [39, 41] or gradient penalty [26, 29]). These methods bring the negligible cost to the learning process, but they allow for less freedom for parameter updates. Some other methods [1,2,28] propose to review knowledge through rehearsal (i.e., Rehearsal-Based Method). They store old data and mix it with new data to re-train the model [5, 21, 52]." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 415, + 545, + 521 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 415, + 545, + 521 + ], + "spans": [ + { + "bbox": [ + 304, + 415, + 545, + 521 + ], + "type": "text", + "content": "Class Incremental Semantic Segmentation. Semantic segmentation [19] aims at assigning different categories to each single pixel, and has recently attracted attention for learning in a class incremental learning scenario [3, 16]. Nevertheless, data for semantic segmentation takes more space [24, 48] to be stored compared to the classification problem. Therefore, recent work mainly concentrates on utilizing distillation to transfer old knowledge to the new model without saving exemplars from old tasks." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 522, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 522, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 522, + 545, + 713 + ], + "type": "text", + "content": "MiB [4] proposes to model the potential classes to tackle semantic drift. PLOP [16] applies feature distillation to restrict representation ability. SDR [37] uses prototype matching to strengthen consistency in latent space. And RC-IL [50] analyzes the disadvantages of strip pooling and proposes average-pooling-based distillation to back up training. On the contrary, SSUL [6] does not apply distillation and proposes to fix the feature extractor instead of updating its parameters. In addition, they introduce thousands of extra data to help generate pseudo labels. But, simply fixing the model definitely does damage to the balance between plasticity and stability, and it is not sustainable when facing huge amounts of newly coming data. On the other hand, only applying distillation can restrict performance, since it can just limit the representation of new data to be the same. Summarizing the above thoughts and" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "7205" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 49, + 67, + 545, + 270 + ], + "blocks": [ + { + "bbox": [ + 49, + 67, + 545, + 270 + ], + "lines": [ + { + "bbox": [ + 49, + 67, + 545, + 270 + ], + "spans": [ + { + "bbox": [ + 49, + 67, + 545, + 270 + ], + "type": "image", + "image_path": "72d967673e47332c1b2196771fce9283c8664ceff66cd805ef96b72dab107e01.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 271, + 546, + 316 + ], + "lines": [ + { + "bbox": [ + 46, + 271, + 546, + 316 + ], + "spans": [ + { + "bbox": [ + 46, + 271, + 546, + 316 + ], + "type": "text", + "content": "Figure 2. Illustration of our Endpoints Weight Fusion (EWF) framework. On the left side, we illustrate training and testing processes. Training is enhanced by knowledge distillation and fusion is applied after training to accumulate all seen knowledge. On the right side, given a " + }, + { + "bbox": [ + 46, + 271, + 546, + 316 + ], + "type": "inline_equation", + "content": "3 \\times 3" + }, + { + "bbox": [ + 46, + 271, + 546, + 316 + ], + "type": "text", + "content": " convolution layer and a normalization layer, they are fused by using a dynamic trade-off parameter " + }, + { + "bbox": [ + 46, + 271, + 546, + 316 + ], + "type": "inline_equation", + "content": "\\alpha_{t}" + }, + { + "bbox": [ + 46, + 271, + 546, + 316 + ], + "type": "text", + "content": ". Note that there is no computation cost for our fusion process." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 322, + 288, + 370 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 322, + 288, + 370 + ], + "spans": [ + { + "bbox": [ + 46, + 322, + 288, + 370 + ], + "type": "text", + "content": "inspired by RC-IL [50], we design a strategy different from the above, cooperating with distillation and maintaining the balance between the old and new knowledge with model weight fusion." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 371, + 287, + 575 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 371, + 287, + 575 + ], + "spans": [ + { + "bbox": [ + 46, + 371, + 287, + 575 + ], + "type": "text", + "content": "Weight Fusion Method. Weight Fusion is widely used in neural network training to improve performance. It can be applied with both linear and nonlinear operations. In linear mode, RCM [27] explores the additivity of convolution and applies it on multi-task learning. ACNet [14] and RepVGG [15] first propose structural re-parameterization, which is used to merge multi-branch Convolution-Batch Normalization serial sequences to a plain Convolution layer. RC-IL ingeniously exploits this operation to establish a representation compensation mechanism in continual learning. In nonlinear mode, weight averaging is commonly used to bring closer connections between different models. Famous methods like BYOL [20] use EMA [38] to improve the knowledge transfer effect or model robustness. From this point, we design a strategy to reach a new balance, which has no effect on the current training process and fully releases the learning ability of the model." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 589, + 102, + 601 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 589, + 102, + 601 + ], + "spans": [ + { + "bbox": [ + 47, + 589, + 102, + 601 + ], + "type": "text", + "content": "3. Method" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 609, + 133, + 621 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 609, + 133, + 621 + ], + "spans": [ + { + "bbox": [ + 47, + 609, + 133, + 621 + ], + "type": "text", + "content": "3.1. Preliminaries" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 629, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 629, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 629, + 288, + 715 + ], + "type": "text", + "content": "We consider a multi-step training process where " + }, + { + "bbox": [ + 46, + 629, + 288, + 715 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 46, + 629, + 288, + 715 + ], + "type": "text", + "content": " tasks are sequentially learned by model " + }, + { + "bbox": [ + 46, + 629, + 288, + 715 + ], + "type": "inline_equation", + "content": "f_{\\theta}" + }, + { + "bbox": [ + 46, + 629, + 288, + 715 + ], + "type": "text", + "content": " in a fully supervised scenario for semantic segmentation, where " + }, + { + "bbox": [ + 46, + 629, + 288, + 715 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 46, + 629, + 288, + 715 + ], + "type": "text", + "content": " is parameterized by parameter " + }, + { + "bbox": [ + 46, + 629, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 46, + 629, + 288, + 715 + ], + "type": "text", + "content": ". Here " + }, + { + "bbox": [ + 46, + 629, + 288, + 715 + ], + "type": "inline_equation", + "content": "f_{\\theta_t}" + }, + { + "bbox": [ + 46, + 629, + 288, + 715 + ], + "type": "text", + "content": " denotes the model at task " + }, + { + "bbox": [ + 46, + 629, + 288, + 715 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 629, + 288, + 715 + ], + "type": "text", + "content": ". Each task contains a dataset " + }, + { + "bbox": [ + 46, + 629, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\mathcal{D}_t = \\{x_i,y_i\\}" + }, + { + "bbox": [ + 46, + 629, + 288, + 715 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 629, + 288, + 715 + ], + "type": "inline_equation", + "content": "x_{i}" + }, + { + "bbox": [ + 46, + 629, + 288, + 715 + ], + "type": "text", + "content": " denotes the data and " + }, + { + "bbox": [ + 46, + 629, + 288, + 715 + ], + "type": "inline_equation", + "content": "y_{i}" + }, + { + "bbox": [ + 46, + 629, + 288, + 715 + ], + "type": "text", + "content": " denotes the corresponding label. The training label space of the task " + }, + { + "bbox": [ + 46, + 629, + 288, + 715 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 46, + 629, + 288, + 715 + ], + "type": "text", + "content": " is denoted as " + }, + { + "bbox": [ + 46, + 629, + 288, + 715 + ], + "type": "inline_equation", + "content": "C_t\\bigcup \\{c_b\\}" + }, + { + "bbox": [ + 46, + 629, + 288, + 715 + ], + "type": "text", + "content": "," + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 322, + 546, + 442 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 322, + 546, + 442 + ], + "spans": [ + { + "bbox": [ + 304, + 322, + 546, + 442 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 322, + 546, + 442 + ], + "type": "inline_equation", + "content": "C_t" + }, + { + "bbox": [ + 304, + 322, + 546, + 442 + ], + "type": "text", + "content": " includes all classes that appear in this task, and " + }, + { + "bbox": [ + 304, + 322, + 546, + 442 + ], + "type": "inline_equation", + "content": "c_b" + }, + { + "bbox": [ + 304, + 322, + 546, + 442 + ], + "type": "text", + "content": " represents the background. Since " + }, + { + "bbox": [ + 304, + 322, + 546, + 442 + ], + "type": "inline_equation", + "content": "C_i \\cap C_j = \\emptyset" + }, + { + "bbox": [ + 304, + 322, + 546, + 442 + ], + "type": "text", + "content": ", the objective of different tasks are not the same, easily leading to catastrophic forgetting. To save annotation costs, only the categories that need to be learned at this stage will be labeled. Thus, " + }, + { + "bbox": [ + 304, + 322, + 546, + 442 + ], + "type": "inline_equation", + "content": "c_b" + }, + { + "bbox": [ + 304, + 322, + 546, + 442 + ], + "type": "text", + "content": " contains not only the real background, but also the classes appearing in past and future tasks. This complicates the training of the model " + }, + { + "bbox": [ + 304, + 322, + 546, + 442 + ], + "type": "inline_equation", + "content": "f_\\theta" + }, + { + "bbox": [ + 304, + 322, + 546, + 442 + ], + "type": "text", + "content": " since the background label " + }, + { + "bbox": [ + 304, + 322, + 546, + 442 + ], + "type": "inline_equation", + "content": "c_b" + }, + { + "bbox": [ + 304, + 322, + 546, + 442 + ], + "type": "text", + "content": " can refer to different classes at different tasks. This exacerbates the severity of forgetting." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 305, + 449, + 483, + 462 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 449, + 483, + 462 + ], + "spans": [ + { + "bbox": [ + 305, + 449, + 483, + 462 + ], + "type": "text", + "content": "3.2. Endpoints Weight Fusion (EWF)" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 468, + 545, + 647 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 468, + 545, + 647 + ], + "spans": [ + { + "bbox": [ + 304, + 468, + 545, + 647 + ], + "type": "text", + "content": "As illustrated in Fig. 1, the existing model expansion-fusion methods have their own drawbacks for enhancing the model's memory of old knowledge. Thus, to better retain the old knowledge while boosting the learning ability of the model, we introduce our Endpoints Weight Fusion strategy. Considering the training process at step " + }, + { + "bbox": [ + 304, + 468, + 545, + 647 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 468, + 545, + 647 + ], + "type": "text", + "content": ", we choose a starting point model and an ending point model. The final model of the previous step " + }, + { + "bbox": [ + 304, + 468, + 545, + 647 + ], + "type": "inline_equation", + "content": "(\\theta_{old})" + }, + { + "bbox": [ + 304, + 468, + 545, + 647 + ], + "type": "text", + "content": " is regarded as the best container of old knowledge. While the model after training on the current task " + }, + { + "bbox": [ + 304, + 468, + 545, + 647 + ], + "type": "inline_equation", + "content": "(\\theta_{new})" + }, + { + "bbox": [ + 304, + 468, + 545, + 647 + ], + "type": "text", + "content": " contains the discriminative information for new classes. Additionally, we introduce another parameter " + }, + { + "bbox": [ + 304, + 468, + 545, + 647 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 304, + 468, + 545, + 647 + ], + "type": "text", + "content": " for the endpoints weight fusion, aiming at fusing two sets of parameters in a certain ratio. This ratio can be seen as a balance factor. Therefore, the operation of endpoints weight fusion can be written as:" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 352, + 656, + 545, + 669 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 352, + 656, + 545, + 669 + ], + "spans": [ + { + "bbox": [ + 352, + 656, + 545, + 669 + ], + "type": "interline_equation", + "content": "\\theta_ {\\text {b a l a n c e d}} = \\alpha_ {t} \\theta_ {\\text {n e w}} + (1 - \\alpha_ {t}) \\theta_ {\\text {o l d}} \\tag {1}", + "image_path": "b8a206a2ce4a71d53c7f85048130da6917b100283b797a0cdeea6da4631c65f7.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 677, + 546, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 546, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 546, + 715 + ], + "type": "text", + "content": "where the " + }, + { + "bbox": [ + 304, + 677, + 546, + 715 + ], + "type": "inline_equation", + "content": "\\theta_{\\text{balanced}}" + }, + { + "bbox": [ + 304, + 677, + 546, + 715 + ], + "type": "text", + "content": " denotes the final model of this task, and the " + }, + { + "bbox": [ + 304, + 677, + 546, + 715 + ], + "type": "inline_equation", + "content": "\\theta_{old}, \\theta_{new}" + }, + { + "bbox": [ + 304, + 677, + 546, + 715 + ], + "type": "text", + "content": " are defined as above. Furthermore, the number of incremental categories (denoted as " + }, + { + "bbox": [ + 304, + 677, + 546, + 715 + ], + "type": "inline_equation", + "content": "N_{\\text{new}}" + }, + { + "bbox": [ + 304, + 677, + 546, + 715 + ], + "type": "text", + "content": ") and orig-" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "7206" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 145 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 145 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 145 + ], + "type": "text", + "content": "inal categories (denoted as " + }, + { + "bbox": [ + 46, + 72, + 289, + 145 + ], + "type": "inline_equation", + "content": "N_{old}" + }, + { + "bbox": [ + 46, + 72, + 289, + 145 + ], + "type": "text", + "content": ") to a certain extent represent the degree of emphasis on the " + }, + { + "bbox": [ + 46, + 72, + 289, + 145 + ], + "type": "inline_equation", + "content": "\\theta_{new}" + }, + { + "bbox": [ + 46, + 72, + 289, + 145 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 72, + 289, + 145 + ], + "type": "inline_equation", + "content": "\\theta_{old}" + }, + { + "bbox": [ + 46, + 72, + 289, + 145 + ], + "type": "text", + "content": ". For the selection of " + }, + { + "bbox": [ + 46, + 72, + 289, + 145 + ], + "type": "inline_equation", + "content": "\\alpha_{t}" + }, + { + "bbox": [ + 46, + 72, + 289, + 145 + ], + "type": "text", + "content": ", we need to consider " + }, + { + "bbox": [ + 46, + 72, + 289, + 145 + ], + "type": "inline_equation", + "content": "N_{new}" + }, + { + "bbox": [ + 46, + 72, + 289, + 145 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 72, + 289, + 145 + ], + "type": "inline_equation", + "content": "N_{old}" + }, + { + "bbox": [ + 46, + 72, + 289, + 145 + ], + "type": "text", + "content": " in the current learning step. We decide to replace the constant ratio with an equation related to " + }, + { + "bbox": [ + 46, + 72, + 289, + 145 + ], + "type": "inline_equation", + "content": "N_{new}" + }, + { + "bbox": [ + 46, + 72, + 289, + 145 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 72, + 289, + 145 + ], + "type": "inline_equation", + "content": "N_{old}" + }, + { + "bbox": [ + 46, + 72, + 289, + 145 + ], + "type": "text", + "content": ". In detail, this formula can be expressed as:" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 119, + 151, + 287, + 178 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 119, + 151, + 287, + 178 + ], + "spans": [ + { + "bbox": [ + 119, + 151, + 287, + 178 + ], + "type": "interline_equation", + "content": "\\alpha_ {t} = \\sqrt {\\frac {N _ {n e w}}{N _ {n e w} + N _ {o l d}}} \\tag {2}", + "image_path": "724a966f5acd0743a3f2b462ec9ef855ad0e6d0332affbde2db04e06ee8a4f94.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 183, + 287, + 219 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 183, + 287, + 219 + ], + "spans": [ + { + "bbox": [ + 46, + 183, + 287, + 219 + ], + "type": "text", + "content": "It can be used across different tasks and scenarios. It can adapt to each task in CISS with a dynamic factor. We illustrate the main idea of our method in Fig. 2." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 219, + 288, + 361 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 219, + 288, + 361 + ], + "spans": [ + { + "bbox": [ + 46, + 219, + 288, + 361 + ], + "type": "text", + "content": "Knowledge distillation enhanced for EWF. In practice, training without any constraint will significantly increase the distance between different models and break the similarity of model representations. That means it deteriorates the forgetting of the model, which further undermines the model's ability to discriminate new classes. Moreover, guaranteeing a low error linear path between two distant models is an overly strong assumption. Thus, choosing a model trained without constraints as an ending point is potentially harmful, and we, therefore, introduce knowledge distillation to enhance the compatibility of the models of our Endpoints Weight Fusion method." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 363, + 289, + 448 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 363, + 289, + 448 + ], + "spans": [ + { + "bbox": [ + 46, + 363, + 289, + 448 + ], + "type": "text", + "content": "Knowledge distillation is a commonly used technique to prevent models from forgetting. As stated above, we utilize distillation to back up our strategy, limiting the distance between two endpoints and forcing them to be similar. In general, distillation used in continual learning is mainly divided into two categories, i.e., feature-based distillation and logit-based distillation. They can be represented as:" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 453, + 298, + 525 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 453, + 298, + 525 + ], + "spans": [ + { + "bbox": [ + 47, + 453, + 298, + 525 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} L _ {F D} = \\frac {1}{| D |} \\sum_ {(x _ {i}, y _ {i}) \\sim D} | | \\Psi_ {o l d} (x _ {i}) - \\Psi_ {n e w} (x _ {i}) | | ^ {2} \\\\ L _ {L D} = \\frac {1}{| D |} \\sum_ {\\left(x _ {i}, y _ {i}\\right) \\sim D} K L \\left(\\Phi_ {o l d} \\left(\\Psi_ {o l d} \\left(x _ {i}\\right)\\right), \\Phi_ {n e w} \\left(\\Psi_ {n e w} \\left(x _ {i}\\right)\\right)\\right) \\tag {3} \\\\ \\end{array}", + "image_path": "0036e09293157b6b121a6a701d35c780ae471439005bef2cd013134d3c01ab31.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 526, + 287, + 609 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 526, + 287, + 609 + ], + "spans": [ + { + "bbox": [ + 46, + 526, + 287, + 609 + ], + "type": "inline_equation", + "content": "\\Psi_{old} / \\Phi_{old}" + }, + { + "bbox": [ + 46, + 526, + 287, + 609 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 526, + 287, + 609 + ], + "type": "inline_equation", + "content": "\\Psi_{new} / \\Phi_{new}" + }, + { + "bbox": [ + 46, + 526, + 287, + 609 + ], + "type": "text", + "content": " denote old and new feature extractor/classifier respectively, and " + }, + { + "bbox": [ + 46, + 526, + 287, + 609 + ], + "type": "inline_equation", + "content": "D" + }, + { + "bbox": [ + 46, + 526, + 287, + 609 + ], + "type": "text", + "content": " is the corresponding dataset of the incremental learning step. In CISS, two popular distillation losses (i.e., UNKD, POD) are proposed by [3, 16], respectively. The former is a logit-based distillation and the latter is a feature-based distillation. They can be easily integrated into our method." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 609, + 288, + 693 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 609, + 288, + 693 + ], + "spans": [ + { + "bbox": [ + 46, + 609, + 288, + 693 + ], + "type": "text", + "content": "Discussion on EMA v.s. EWF. An update strategy similar to our method is using EMA [38] to update the model. Here we will discuss the difference between our method EWF and EMA, and the advantages of EWF. The EMA strategy maintains a moving average model during training, and uses this model to replace the final model for inference. The moving average model can be represented as:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 111, + 700, + 287, + 715 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 111, + 700, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 111, + 700, + 287, + 715 + ], + "type": "interline_equation", + "content": "v ^ {i} = \\beta v ^ {i - 1} + (1 - \\beta) \\theta^ {i} \\tag {4}", + "image_path": "2d753b007c1852cfc074a38acf2ff22c214ea3fcabb588ff014b792d6427d41e.jpg" + } + ] + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 318, + 72, + 536, + 215 + ], + "blocks": [ + { + "bbox": [ + 318, + 72, + 536, + 215 + ], + "lines": [ + { + "bbox": [ + 318, + 72, + 536, + 215 + ], + "spans": [ + { + "bbox": [ + 318, + 72, + 536, + 215 + ], + "type": "image", + "image_path": "54381d139f166d324c550961ec8036ff16a9aefec15b0990e92169561ab052ed.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 227, + 547, + 283 + ], + "lines": [ + { + "bbox": [ + 304, + 227, + 547, + 283 + ], + "spans": [ + { + "bbox": [ + 304, + 227, + 547, + 283 + ], + "type": "text", + "content": "Figure 3. Representation similarity between old model " + }, + { + "bbox": [ + 304, + 227, + 547, + 283 + ], + "type": "inline_equation", + "content": "\\theta^1" + }, + { + "bbox": [ + 304, + 227, + 547, + 283 + ], + "type": "text", + "content": " before training and being trained new model " + }, + { + "bbox": [ + 304, + 227, + 547, + 283 + ], + "type": "inline_equation", + "content": "\\theta^i" + }, + { + "bbox": [ + 304, + 227, + 547, + 283 + ], + "type": "text", + "content": ". The similarity measure we use is cosine similarity. We extract the intermediate results of the feature extractors of the old and new networks and calculate the average of the cosine similarity between them." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 311, + 547, + 432 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 311, + 547, + 432 + ], + "spans": [ + { + "bbox": [ + 304, + 311, + 547, + 432 + ], + "type": "text", + "content": "where the " + }, + { + "bbox": [ + 304, + 311, + 547, + 432 + ], + "type": "inline_equation", + "content": "v^{i}" + }, + { + "bbox": [ + 304, + 311, + 547, + 432 + ], + "type": "text", + "content": " denotes the moving average of the first " + }, + { + "bbox": [ + 304, + 311, + 547, + 432 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 304, + 311, + 547, + 432 + ], + "type": "text", + "content": " models, and " + }, + { + "bbox": [ + 304, + 311, + 547, + 432 + ], + "type": "inline_equation", + "content": "\\theta^i" + }, + { + "bbox": [ + 304, + 311, + 547, + 432 + ], + "type": "text", + "content": " denotes the model after " + }, + { + "bbox": [ + 304, + 311, + 547, + 432 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 304, + 311, + 547, + 432 + ], + "type": "text", + "content": "th iteration. " + }, + { + "bbox": [ + 304, + 311, + 547, + 432 + ], + "type": "inline_equation", + "content": "\\beta" + }, + { + "bbox": [ + 304, + 311, + 547, + 432 + ], + "type": "text", + "content": " is the moving average parameter, which is usually set as 0.9/0.99. It is easy to see that the EMA is an inter-iteration operation, which is easier to realize due to the low distance between models. Since we use SGD as an optimizer, following Eq. 5, the results of EMA and EWF can be represented as " + }, + { + "bbox": [ + 304, + 311, + 547, + 432 + ], + "type": "inline_equation", + "content": "v^n" + }, + { + "bbox": [ + 304, + 311, + 547, + 432 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 311, + 547, + 432 + ], + "type": "inline_equation", + "content": "\\theta_{\\text{balanced}}" + }, + { + "bbox": [ + 304, + 311, + 547, + 432 + ], + "type": "text", + "content": " in Eq. 6. Note that the learning rate does not affect the result of the analysis, so we set the learning rate to 1. The more detailed derivations are in the Appendix." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 370, + 439, + 545, + 487 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 370, + 439, + 545, + 487 + ], + "spans": [ + { + "bbox": [ + 370, + 439, + 545, + 487 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\theta^ {n} = \\theta^ {n - 1} - \\nabla_ {L} \\left(\\theta^ {n - 1}\\right) \\\\ = \\theta^ {1} - \\sum_ {k = 1} ^ {n} \\nabla_ {L} \\left(\\theta^ {k}\\right) \\tag {5} \\\\ \\end{array}", + "image_path": "1bff39521e9332bed7c757db6b3577b5468f15c0179a7b1671d783eae492202c.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 349, + 497, + 545, + 536 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 349, + 497, + 545, + 536 + ], + "spans": [ + { + "bbox": [ + 349, + 497, + 545, + 536 + ], + "type": "interline_equation", + "content": "v ^ {n} = \\theta^ {1} - \\sum_ {k = 1} ^ {n - 1} (1 - \\beta^ {n - k}) \\nabla_ {L} \\left(\\theta^ {k}\\right) \\tag {6}", + "image_path": "3b77b64858e056cf36494384de1823fb586708ca6db926ba7f7e2b39c01d40e2.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 349, + 533, + 481, + 564 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 349, + 533, + 481, + 564 + ], + "spans": [ + { + "bbox": [ + 349, + 533, + 481, + 564 + ], + "type": "interline_equation", + "content": "\\theta_ {b a l a n c e d} = \\theta^ {1} - \\alpha \\sum_ {k = 1} ^ {n - 1} \\nabla_ {L} \\left(\\theta^ {k}\\right)", + "image_path": "3b408576e7fe1e70dadf0074864f2193f05c730786fd016c025f01d2bcfd7e08.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "type": "text", + "content": "Since the " + }, + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "type": "inline_equation", + "content": "\\beta" + }, + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "type": "text", + "content": " is usually set to " + }, + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "type": "inline_equation", + "content": "0.9 / 0.99" + }, + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "type": "text", + "content": " and the " + }, + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "type": "text", + "content": " is set following Eq. 2, " + }, + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "type": "text", + "content": " is always smaller than " + }, + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "type": "inline_equation", + "content": "\\beta" + }, + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "type": "text", + "content": ". According to Eq. 6, EMA gives more weight to the gradient of early time, and then gradually attenuates the influence of gradients in subsequent iterations. On the contrary, EWF gives the gradient of different parts a relatively uniform weight. Besides, to better observe the stability of incremental learning step, we calculate the representations similarity between " + }, + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "type": "inline_equation", + "content": "\\theta^1" + }, + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "type": "inline_equation", + "content": "\\theta^i" + }, + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "type": "text", + "content": ". According to our observation in an incremental step, as shown in Fig. 3, the similarity of representations between " + }, + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "type": "inline_equation", + "content": "\\theta^1" + }, + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "type": "inline_equation", + "content": "\\theta^i" + }, + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "type": "text", + "content": " first decreases and then increases, and gradually stabilizes in the subsequent stages. This reveals that in order" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "7207" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "code", + "bbox": [ + 47, + 87, + 218, + 297 + ], + "blocks": [ + { + "bbox": [ + 48, + 72, + 277, + 84 + ], + "lines": [ + { + "bbox": [ + 48, + 72, + 277, + 84 + ], + "spans": [ + { + "bbox": [ + 48, + 72, + 277, + 84 + ], + "type": "text", + "content": "Algorithm 1 Pseudo Code for EWF in incremental steps" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "code_caption" + }, + { + "bbox": [ + 47, + 87, + 218, + 297 + ], + "lines": [ + { + "bbox": [ + 47, + 87, + 218, + 297 + ], + "spans": [ + { + "bbox": [ + 47, + 87, + 218, + 297 + ], + "type": "text", + "content": "Require: " + }, + { + "bbox": [ + 47, + 87, + 218, + 297 + ], + "type": "inline_equation", + "content": "f,\\theta_0,T,D_T" + }, + { + "bbox": [ + 47, + 87, + 218, + 297 + ], + "type": "text", + "content": " and learning rate " + }, + { + "bbox": [ + 47, + 87, + 218, + 297 + ], + "type": "inline_equation", + "content": "\\gamma" + }, + { + "bbox": [ + 47, + 87, + 218, + 297 + ], + "type": "inline_equation", + "content": "t\\gets 1" + }, + { + "bbox": [ + 47, + 87, + 218, + 297 + ], + "type": "text", + "content": " \nwhile " + }, + { + "bbox": [ + 47, + 87, + 218, + 297 + ], + "type": "inline_equation", + "content": "t\\leq T" + }, + { + "bbox": [ + 47, + 87, + 218, + 297 + ], + "type": "text", + "content": " do Initialize " + }, + { + "bbox": [ + 47, + 87, + 218, + 297 + ], + "type": "inline_equation", + "content": "N_{new},N_{old}" + }, + { + "bbox": [ + 47, + 87, + 218, + 297 + ], + "type": "inline_equation", + "content": "\\theta^1\\gets \\theta_{t - 1}" + }, + { + "bbox": [ + 47, + 87, + 218, + 297 + ], + "type": "inline_equation", + "content": "\\alpha_{t}\\leftarrow \\sqrt{\\frac{N_{new}}{N_{new} + N_{old}}}" + }, + { + "bbox": [ + 47, + 87, + 218, + 297 + ], + "type": "inline_equation", + "content": "i\\gets 1" + }, + { + "bbox": [ + 47, + 87, + 218, + 297 + ], + "type": "text", + "content": " \nwhile not converged do Sample mini-batch " + }, + { + "bbox": [ + 47, + 87, + 218, + 297 + ], + "type": "inline_equation", + "content": "\\{x_i,y_i\\} \\sim D" + }, + { + "bbox": [ + 47, + 87, + 218, + 297 + ], + "type": "inline_equation", + "content": "\\theta^{i + 1}\\gets \\theta^i -\\gamma \\nabla_{LCE + LKD}(f_{\\theta^i})" + }, + { + "bbox": [ + 47, + 87, + 218, + 297 + ], + "type": "inline_equation", + "content": "i\\gets i + 1" + }, + { + "bbox": [ + 47, + 87, + 218, + 297 + ], + "type": "text", + "content": " \nend while \n" + }, + { + "bbox": [ + 47, + 87, + 218, + 297 + ], + "type": "inline_equation", + "content": "\\theta_{old}\\gets \\theta^1,\\theta_{new}\\gets \\theta^i" + }, + { + "bbox": [ + 47, + 87, + 218, + 297 + ], + "type": "inline_equation", + "content": "\\theta_{balanced}\\gets \\alpha_t\\theta_{new} + (1 - \\alpha_t)\\theta_{old}" + }, + { + "bbox": [ + 47, + 87, + 218, + 297 + ], + "type": "inline_equation", + "content": "\\theta_t\\gets \\theta_{balanced}" + }, + { + "bbox": [ + 47, + 87, + 218, + 297 + ], + "type": "inline_equation", + "content": "t\\gets t + 1" + }, + { + "bbox": [ + 47, + 87, + 218, + 297 + ], + "type": "text", + "content": " \nend while" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "code_body" + } + ], + "index": 1, + "sub_type": "algorithm" + }, + { + "bbox": [ + 46, + 319, + 287, + 403 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 319, + 287, + 403 + ], + "spans": [ + { + "bbox": [ + 46, + 319, + 287, + 403 + ], + "type": "text", + "content": "to learn new knowledge, the representation will first collapse and then recover under the action of the distillation and cross-entropy losses. Then EMA concentrates more of the gradient on the early collapsed process, while our method pays more attention to the useful gradient information after the recovery. From this perspective, our method is theoretically better than EMA in CISS." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 413, + 163, + 425 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 413, + 163, + 425 + ], + "spans": [ + { + "bbox": [ + 47, + 413, + 163, + 425 + ], + "type": "text", + "content": "3.3. Overall Framework" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 433, + 287, + 493 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 433, + 287, + 493 + ], + "spans": [ + { + "bbox": [ + 46, + 433, + 287, + 493 + ], + "type": "text", + "content": "As stated above, to remember knowledge from old tasks, we borrow knowledge distillation to strengthen the model's memory. To learn the discrimination of new classes, we use the Cross-Entropy loss to optimize the model. In general, the objective is given by:" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 102, + 503, + 287, + 520 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 102, + 503, + 287, + 520 + ], + "spans": [ + { + "bbox": [ + 102, + 503, + 287, + 520 + ], + "type": "interline_equation", + "content": "\\min _ {\\theta_ {t}} \\mathcal {L} _ {C E} \\left(\\theta_ {t}\\right) + \\mathcal {L} _ {K D} \\left(\\theta_ {t}; \\theta_ {t - 1}\\right) \\tag {7}", + "image_path": "a310c201cfe38ac39fe09d0524fa8afeffd64b062566b225c12d9121601cc9d9.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 531, + 265, + 544 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 531, + 265, + 544 + ], + "spans": [ + { + "bbox": [ + 47, + 531, + 265, + 544 + ], + "type": "text", + "content": "And the overall algorithm of EWF is shown in Alg. 1." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 556, + 128, + 570 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 556, + 128, + 570 + ], + "spans": [ + { + "bbox": [ + 47, + 556, + 128, + 570 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 577, + 287, + 613 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 577, + 287, + 613 + ], + "spans": [ + { + "bbox": [ + 46, + 577, + 287, + 613 + ], + "type": "text", + "content": "We demonstrate experimental protocols, scenarios and training details. Furthermore, we evaluate our algorithm through quantitative and qualitative experiments." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 622, + 166, + 635 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 622, + 166, + 635 + ], + "spans": [ + { + "bbox": [ + 47, + 622, + 166, + 635 + ], + "type": "text", + "content": "4.1. Experimental setups" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 641, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 641, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 641, + 288, + 715 + ], + "type": "text", + "content": "Protocols. In general, the training for CISS is divided into " + }, + { + "bbox": [ + 46, + 641, + 288, + 715 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 46, + 641, + 288, + 715 + ], + "type": "text", + "content": " steps, and each step denotes a task, where the labeled classes are disjoint in each of them. We adopt the overlapped setting as other works, in which the current training data may contain potential classes labeled as background in previous steps. The overlapped setting is more realistic, and" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 72, + 545, + 275 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 275 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 275 + ], + "type": "text", + "content": "therefore we only evaluate on this setup as previous methods [6, 16]. Following existing works [3, 16, 50], we conduct experiments on two widely used segmentation datasets, PASCAL VOC 2012 [18] and ADE20K [51]. The PASCAL VOC 2012 dataset [18] contains 10,582 training images and 1449 validation images with 20 object classes and the background class. The ADE20K dataset [51] is composed of 150 classes and contains 20, 210 training images, and 2000 validation images. Following previous works [3, 16, 50], " + }, + { + "bbox": [ + 304, + 72, + 545, + 275 + ], + "type": "inline_equation", + "content": "X - Y" + }, + { + "bbox": [ + 304, + 72, + 545, + 275 + ], + "type": "text", + "content": " denotes different settings for CISS. In the " + }, + { + "bbox": [ + 304, + 72, + 545, + 275 + ], + "type": "inline_equation", + "content": "X - Y" + }, + { + "bbox": [ + 304, + 72, + 545, + 275 + ], + "type": "text", + "content": " setting, the model can recognize " + }, + { + "bbox": [ + 304, + 72, + 545, + 275 + ], + "type": "inline_equation", + "content": "X" + }, + { + "bbox": [ + 304, + 72, + 545, + 275 + ], + "type": "text", + "content": " classes in the initial step, and then is supposed to learn " + }, + { + "bbox": [ + 304, + 72, + 545, + 275 + ], + "type": "inline_equation", + "content": "Y" + }, + { + "bbox": [ + 304, + 72, + 545, + 275 + ], + "type": "text", + "content": " newly added classes in each following step. At each step, only current task data is available for training. We perform experiments on PASCAL VOC 2012 [18] with four settings, 15-1, 10-1, 5-3 and 19-1. On ADE20K [51], we verify the effectiveness of our method on three settings, 100-5, 100-10, and 100-50." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 277, + 546, + 456 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 277, + 546, + 456 + ], + "spans": [ + { + "bbox": [ + 304, + 277, + 546, + 456 + ], + "type": "text", + "content": "Implementation Details. Following existing works [3, 16, 50], we apply Deeplab-v3 [9] as our segmentation model with ResNet-101 [23] as a backbone. We also use in-place activated batch normalization [40] in the backbone. In our experiments, we use some data augmentations, including horizontal flip and random crop. The ratio " + }, + { + "bbox": [ + 304, + 277, + 546, + 456 + ], + "type": "inline_equation", + "content": "\\alpha_{t}" + }, + { + "bbox": [ + 304, + 277, + 546, + 456 + ], + "type": "text", + "content": " for EWF is defined as Eq.2. Using SGD optimizer, we train the model for 30 (PASCAL VOC 2012) and 60 (ADE20K) epochs in each step with a batch size of 24. We set the initial learning rate as 0.01 for the first training step and 0.001 for the next continual learning steps. All experiments are conducted on 4 RTX 2080Ti GPUs. The learning rate is decayed with poly schedule. During training, we use " + }, + { + "bbox": [ + 304, + 277, + 546, + 456 + ], + "type": "inline_equation", + "content": "20\\%" + }, + { + "bbox": [ + 304, + 277, + 546, + 456 + ], + "type": "text", + "content": " of the training set as validation, and report the mean Intersect over Union (mIoU) on the original validation set." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 466, + 493, + 479 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 466, + 493, + 479 + ], + "spans": [ + { + "bbox": [ + 305, + 466, + 493, + 479 + ], + "type": "text", + "content": "4.2. Comparison to competing methods" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 485, + 545, + 521 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 485, + 545, + 521 + ], + "spans": [ + { + "bbox": [ + 304, + 485, + 545, + 521 + ], + "type": "text", + "content": "In this section, we apply our method to MiB [3] and PLOP [16]. Additionally, we also compare our method with LwF [31], ILT [36], SDR [37], and RCIL [50]." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "type": "text", + "content": "PASCAL VOC 2012. In this dataset, we use the same experimental settings as [3, 16, 50], we performed the experiments with the class incremental learning settings 15-1, 10-1, 5-3, 19-1. As shown in Table 1, we report the result of our experiments on the final task. From the results, we can observe that our method improves the results of both MiB and PLOP by a large margin, on the more challenging settings (e.g., 15-1, 10-1, 5-3. For instance, on the 15-1 setting, our algorithm obtains performance gains of " + }, + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "type": "inline_equation", + "content": "12.4\\%" + }, + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "type": "inline_equation", + "content": "33.3\\%" + }, + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "type": "text", + "content": " mIoU for PLOP and MIB, respectively. Furthermore, on the longest learning sequence, the 10-1 setting, our method obtains a large gain consistently, improving the performance of PLOP and MIB by " + }, + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "type": "inline_equation", + "content": "21.4\\%" + }, + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "type": "inline_equation", + "content": "24.7\\%" + }, + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "type": "text", + "content": ", respectively. In Table 1 we also report the performance of the old and new classes for different settings. Our method achieves significant performance gains for old classes. This demon" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "7208" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 52, + 70, + 544, + 182 + ], + "blocks": [ + { + "bbox": [ + 52, + 70, + 544, + 182 + ], + "lines": [ + { + "bbox": [ + 52, + 70, + 544, + 182 + ], + "spans": [ + { + "bbox": [ + 52, + 70, + 544, + 182 + ], + "type": "table", + "html": "
Method15-1 (6 steps)10-1 (11 steps)5-3 (6 steps)19-1 (2 steps)
0-1516-20all0-1011-20all0-56-20all0-1920all
LwF [31] (TPAMI2017)6.03.95.58.02.04.820.936.724.753.08.550.9
ILT [36] (ICCVW2019)9.67.89.27.23.75.522.531.729.068.212.365.5
SDR [37] (CVPR2021)47.314.739.532.417.125.1---69.132.667.4
RCIL [50] (CVPR2022)70.623.759.455.415.134.363.134.642.877.031.574.7
MiB [3] (CVPR2020)38.013.532.212.213.112.657.142.546.771.222.168.9
MiB+EWF (Ours)78.025.565.556.016.737.369.045.051.877.812.274.7
PLOP [16] (CVPR2021)65.121.154.644.015.530.525.730.028.775.437.373.5
PLOP+EWF (Ours)77.732.767.071.530.351.961.742.247.777.96.774.5
Joint79.872.678.279.872.678.278.278.078.276.977.677.4
", + "image_path": "106c653be07d716e47e94c5b5d2e9bd0c48e6a71eda8c705547b37a58575ae31.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 67, + 190, + 523, + 202 + ], + "lines": [ + { + "bbox": [ + 67, + 190, + 523, + 202 + ], + "spans": [ + { + "bbox": [ + 67, + 190, + 523, + 202 + ], + "type": "text", + "content": "Table 1. The mIoU(%) of the last step on the Pascal VOC 2012 dataset for different class-incremental segmentation scenarios." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "text" + }, + { + "type": "image", + "bbox": [ + 76, + 217, + 294, + 377 + ], + "blocks": [ + { + "bbox": [ + 76, + 217, + 294, + 377 + ], + "lines": [ + { + "bbox": [ + 76, + 217, + 294, + 377 + ], + "spans": [ + { + "bbox": [ + 76, + 217, + 294, + 377 + ], + "type": "image", + "image_path": "5ada5be248ee09c3758989ab061393427a3453278627f9d66d24b08b70756163.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 126, + 384, + 242, + 393 + ], + "lines": [ + { + "bbox": [ + 126, + 384, + 242, + 393 + ], + "spans": [ + { + "bbox": [ + 126, + 384, + 242, + 393 + ], + "type": "text", + "content": "(a) 10-1 scenario on PASCAL VOC" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 160, + 403, + 432, + 415 + ], + "lines": [ + { + "bbox": [ + 160, + 403, + 432, + 415 + ], + "spans": [ + { + "bbox": [ + 160, + 403, + 432, + 415 + ], + "type": "text", + "content": "Figure 4. The mIoU " + }, + { + "bbox": [ + 160, + 403, + 432, + 415 + ], + "type": "inline_equation", + "content": "(\\%)" + }, + { + "bbox": [ + 160, + 403, + 432, + 415 + ], + "type": "text", + "content": " at each step for the settings 10-1 (a) and 15-1 (b)." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 301, + 217, + 519, + 376 + ], + "blocks": [ + { + "bbox": [ + 301, + 217, + 519, + 376 + ], + "lines": [ + { + "bbox": [ + 301, + 217, + 519, + 376 + ], + "spans": [ + { + "bbox": [ + 301, + 217, + 519, + 376 + ], + "type": "image", + "image_path": "f374888c7889b0140a11ec38943f3cc0897757307e97e1712d8eae4a8b207883.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 351, + 384, + 468, + 393 + ], + "lines": [ + { + "bbox": [ + 351, + 384, + 468, + 393 + ], + "spans": [ + { + "bbox": [ + 351, + 384, + 468, + 393 + ], + "type": "text", + "content": "(b) 15-1 scenario on PASCAL VOC" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 436, + 289, + 593 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 436, + 289, + 593 + ], + "spans": [ + { + "bbox": [ + 46, + 436, + 289, + 593 + ], + "type": "text", + "content": "strates that our EWF strategy can enhance significantly the model's memory of old knowledge (by successfully countering forgetting). In the more challenging settings, e.g., 15-1, 5-3, 10-1, our method also boosts the performance of new classes. This shows that EWF can achieve high plasticity on new steps, and that the proposed dynamically weighted combination of the network allows achieving a good tradeoff between plasticity and stability. We also show dynamic performance changes during the continual learning process in Fig. 4. It is clear that with more learning steps, the gap between our method and the best baseline is growing, and that the curve of our method for different settings (15-1 and 5-3) is on the top throughout most of the learning trajectory." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 605, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 605, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 605, + 287, + 715 + ], + "type": "text", + "content": "Comparison with methods that introduce auxiliary data. It is worth noting that there are several methods [6, 34, 49] that introduce different forms of auxiliary data to assist continual semantic segmentation, helping the model build better pseudo-labels or enhance memory for old knowledge. RECALL [34] learns a generative model or retrieves from web-crawled data for replay, while SSUL [6] leverages salient object detectors (trained on MSRA-B dataset [32] with 5000 images) to generate saliency maps as auxiliary" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 436, + 545, + 602 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 436, + 545, + 602 + ], + "spans": [ + { + "bbox": [ + 304, + 436, + 545, + 602 + ], + "type": "text", + "content": "data. And ST-CIL [49] exploits unlabelled datasets with pseudo labels as ground truth. Even if our algorithm is designed to deal with extra-data-free scenarios, to further demonstrate the effectiveness of our method, we integrate our method to SSUL and compare it with the above methods in Table 2. Note that SSUL freezes the backbone completely and it is hard to directly apply our method on it. Therefore, we learned part of the backbone network parameters when we apply our method to SSUL. In detail, we set the second stage of the backbone in SSUL as learnable parameters for model fusion. SSUL obtains the best performance among these methods using auxiliary data, and our method applied to SSUL can further improve it by about " + }, + { + "bbox": [ + 304, + 436, + 545, + 602 + ], + "type": "inline_equation", + "content": "1\\%" + }, + { + "bbox": [ + 304, + 436, + 545, + 602 + ], + "type": "text", + "content": " for all classes." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 604, + 545, + 700 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 604, + 545, + 700 + ], + "spans": [ + { + "bbox": [ + 304, + 604, + 545, + 700 + ], + "type": "text", + "content": "Visualization. As shown in Fig. 5, we compare our method based on MiB, and we show a sample from the base task (step 0) and a sample from step 2. From the top two rows, the person and bike classes are largely preserved with our method, but it forgets gradually for the baseline MiB. From the bottom two rows, it shows an example with both old classes and a new sheep class. Our method can keep the old knowledge better while incorporating new knowledge." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 701, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 701, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 306, + 701, + 545, + 712 + ], + "type": "text", + "content": "ADE20K. In order to further evaluate the effectiveness of" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "7209" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 50, + 68, + 545, + 350 + ], + "blocks": [ + { + "bbox": [ + 50, + 68, + 545, + 350 + ], + "lines": [ + { + "bbox": [ + 50, + 68, + 545, + 350 + ], + "spans": [ + { + "bbox": [ + 50, + 68, + 545, + 350 + ], + "type": "image", + "image_path": "458b5318f3da581b46aa4f9fffa878f9501db768ddac07ac60e7b566710e0d25.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 357, + 546, + 380 + ], + "lines": [ + { + "bbox": [ + 46, + 357, + 546, + 380 + ], + "spans": [ + { + "bbox": [ + 46, + 357, + 546, + 380 + ], + "type": "text", + "content": "Figure 5. The qualitative comparison between different methods. All prediction results are from the last step of 15-1 overlapped setting. In the initial step, 15 classes are learned and 5 tasks are learned incrementally with class potted plant, sheep, sofa, train and monitor." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 107, + 390, + 491, + 462 + ], + "blocks": [ + { + "bbox": [ + 107, + 390, + 491, + 462 + ], + "lines": [ + { + "bbox": [ + 107, + 390, + 491, + 462 + ], + "spans": [ + { + "bbox": [ + 107, + 390, + 491, + 462 + ], + "type": "table", + "html": "
MethodAuxiliary Data15-1 (PASCAL VOC 2012)10-1 (PASCAL VOC 2012)
0-1516-20all0-1011-20all
RECALL [34] (ICCV2021)GAN / Web-Data65.747.862.759.546.754.8
ST-CIL [49] (TNNLS2022)Unlabeled Data71.440.063.6---
SSUL [6] (NeurIPS2021)Saliency Map77.336.667.671.345.959.2
SSUL + EWF (Ours)Saliency Map77.938.968.672.447.460.5
", + "image_path": "cf21ae2b3306eea7cd47b9849486c67f1b198c38eeeae752b9db46cc830b4f4e.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 119, + 468, + 473, + 480 + ], + "lines": [ + { + "bbox": [ + 119, + 468, + 473, + 480 + ], + "spans": [ + { + "bbox": [ + 119, + 468, + 473, + 480 + ], + "type": "text", + "content": "Table 2. The mIoU(%) of the last step on the Pascal VOC 2012 15-1 and 10-1 overlapped setting." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 495, + 288, + 614 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 495, + 288, + 614 + ], + "spans": [ + { + "bbox": [ + 46, + 495, + 288, + 614 + ], + "type": "text", + "content": "our method, we conduct experiments on ADE20K dataset. In Table 3, we show the experimental results with settings 100-50, 100-10 and 100-5. As shown in Table 3, our method reaches superior performance on this dataset. Especially on the most challenging settings 100-5 and 100-10, our method achieves " + }, + { + "bbox": [ + 46, + 495, + 288, + 614 + ], + "type": "inline_equation", + "content": "6.2\\%" + }, + { + "bbox": [ + 46, + 495, + 288, + 614 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 495, + 288, + 614 + ], + "type": "inline_equation", + "content": "3.0\\%" + }, + { + "bbox": [ + 46, + 495, + 288, + 614 + ], + "type": "text", + "content": " improvement over MiB [3], respectively. It also surpasses the state-of-the-art method RC-IL by a large margin on 100-5 setting. This indicates that our EWF is effective on large-scale datasets as well." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 622, + 141, + 635 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 622, + 141, + 635 + ], + "spans": [ + { + "bbox": [ + 47, + 622, + 141, + 635 + ], + "type": "text", + "content": "4.3. Ablation Study" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 641, + 287, + 677 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 641, + 287, + 677 + ], + "spans": [ + { + "bbox": [ + 46, + 641, + 287, + 677 + ], + "type": "text", + "content": "In this part, we demonstrate and analyze the effectiveness of weight fusion and its dynamic factor selection. We use MiB [3] for the ablation experiments." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 677, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 288, + 713 + ], + "type": "text", + "content": "Fusion Strategy. In Table 4, we demonstrate the performance of different fusion strategies. These experiments are conducted with the setting 15-1 on PASCAL VOC 2012." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 495, + 545, + 638 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 495, + 545, + 638 + ], + "spans": [ + { + "bbox": [ + 304, + 495, + 545, + 638 + ], + "type": "text", + "content": "Most of these methods perform continual learning by fusing the information present in the previous step model. Among these, EMA [38] updates a stored set of parameters with moving average during training, and uses it for inference. Model ensemble fuses the previous model's prediction and new prediction in an average way during inference. And None denotes the model trained only with Distillation and Cross-Entropy (i.e., MiB [3]). Compared with no fusion method, EMA and model ensemble have " + }, + { + "bbox": [ + 304, + 495, + 545, + 638 + ], + "type": "inline_equation", + "content": "5.1\\%" + }, + { + "bbox": [ + 304, + 495, + 545, + 638 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 495, + 545, + 638 + ], + "type": "inline_equation", + "content": "5.0\\%" + }, + { + "bbox": [ + 304, + 495, + 545, + 638 + ], + "type": "text", + "content": " performance improvement, respectively. While Our EWF has a " + }, + { + "bbox": [ + 304, + 495, + 545, + 638 + ], + "type": "inline_equation", + "content": "33.3\\%" + }, + { + "bbox": [ + 304, + 495, + 545, + 638 + ], + "type": "text", + "content": " improvement on the basis of a simple fusion strategy, which again verifies the discussions in Sec. 3.2." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 641, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 641, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 641, + 546, + 713 + ], + "type": "text", + "content": "Fusion Factor Selection. In this part, we conduct experiments on the fusion factor selection. To prove the advantages of our parameter selection strategy, we use some fixed values as balance parameters in the fusion process, and we compare the difference between our method and theirs to evaluate its advantage. In detail, we choose three scenarios" + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "7210" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 48, + 71, + 548, + 167 + ], + "blocks": [ + { + "bbox": [ + 48, + 71, + 548, + 167 + ], + "lines": [ + { + "bbox": [ + 48, + 71, + 548, + 167 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 548, + 167 + ], + "type": "table", + "html": "
Method100-50 (2 steps)100-10 (6 steps)100-5 (3 steps)
1-100101-150all1-100101-110111-120121-130131-140141-150all1-100101-150all
ILT [36] (ICCVW2019)18.314.817.00.10.00.10.94.19.31.10.11.30.5
PLOP [16] (CVPR2021)41.914.932.940.615.216.918.711.97.931.639.17.828.7
RC-IL [50] (CVPR2022)42.318.834.539.314.626.323.212.111.832.138.511.529.6
MiB [3] (CVPR2020)40.717.732.838.312.610.68.79.515.129.236.05.625.9
MiB+EWF(Ours)41.221.334.641.512.822.523.214.48.833.241.413.432.1
Joint44.328.238.944.326.142.826.728.117.338.944.328.238.9
", + "image_path": "fce67476ef2afbf739cd1ee1ad7a2e6444c858db7ef502ff480fa0b57b376fa5.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 48, + 199, + 301, + 262 + ], + "blocks": [ + { + "bbox": [ + 86, + 175, + 505, + 186 + ], + "lines": [ + { + "bbox": [ + 86, + 175, + 505, + 186 + ], + "spans": [ + { + "bbox": [ + 86, + 175, + 505, + 186 + ], + "type": "text", + "content": "Table 3. The mIoU(%) of the last step on the ADE20K dataset for different overlapped continual learning scenarios." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 48, + 199, + 301, + 262 + ], + "lines": [ + { + "bbox": [ + 48, + 199, + 301, + 262 + ], + "spans": [ + { + "bbox": [ + 48, + 199, + 301, + 262 + ], + "type": "table", + "html": "
Fusion strategystep1step2step3step4step5
None [3]71.456.151.936.532.2
EMA [38]74.059.659.840.937.3
model ensemble [13]74.160.160.341.537.2
EWF (Ours)76.173.870.568.365.6
", + "image_path": "ca2d6b5151acadf397db35338da71d0c9a602e3d657821615f1fac0bd3c53be7.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "type": "table", + "bbox": [ + 54, + 307, + 280, + 371 + ], + "blocks": [ + { + "bbox": [ + 47, + 272, + 286, + 293 + ], + "lines": [ + { + "bbox": [ + 47, + 272, + 286, + 293 + ], + "spans": [ + { + "bbox": [ + 47, + 272, + 286, + 293 + ], + "type": "text", + "content": "Table 4. Ablation study of fusion strategies. All performances are reported on PASCAL VOC 2012 15-1 setting." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 54, + 307, + 280, + 371 + ], + "lines": [ + { + "bbox": [ + 54, + 307, + 280, + 371 + ], + "spans": [ + { + "bbox": [ + 54, + 307, + 280, + 371 + ], + "type": "table", + "html": "
Parameter SelectionOurs0.20.40.60.8
15-165.665.663.760.153.3
10-137.339.531.822.714.3
5-351.838.051.256.152.9
Average51.647.748.946.340.2
", + "image_path": "352138f9abce81aa9a5851d8653eb7ef13262443a9381f585956e9ee05c90052.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_body" + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 380, + 286, + 402 + ], + "lines": [ + { + "bbox": [ + 47, + 380, + 286, + 402 + ], + "spans": [ + { + "bbox": [ + 47, + 380, + 286, + 402 + ], + "type": "text", + "content": "Table 5. Comparison between our dynamic parameter fusion strategy and fixed balance factors." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 426, + 286, + 616 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 426, + 286, + 616 + ], + "spans": [ + { + "bbox": [ + 46, + 426, + 286, + 616 + ], + "type": "text", + "content": "to conduct our experiments (i.e., 15-1, 10-1, 5-3), and we calculate the average mIoU of different strategies for three scenarios to measure the final performance. Since the balance factor " + }, + { + "bbox": [ + 46, + 426, + 286, + 616 + ], + "type": "inline_equation", + "content": "\\alpha \\in [0,1]" + }, + { + "bbox": [ + 46, + 426, + 286, + 616 + ], + "type": "text", + "content": ", we take 0.2, 0.4, 0.6, and 0.8 as the fixed values to compare to our parameter selection strategy. As shown in Table 5, for the 15-1 setting, our method reaches the highest performance compared with other fixed parameters. In addition, although our method is slightly below the highest performance for fixed parameters on other settings, the parameters for the highest performance on different settings vary widely. It means that choosing a fixed parameter for all scenarios is unrealistic and harmful to the algorithm. Importantly, our method reaches the highest average performance among all other fixed values, which indicates that our strategy can be easily applied to different settings without tuning the hyper-parameters manually." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 617, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 617, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 617, + 286, + 713 + ], + "type": "text", + "content": "Robustness of Class Order. In the scenario of class incremental semantic segmentation, the order of classes encountered by the model is significant in measuring the effectiveness of an algorithm. Thus, to verify the effectiveness of our algorithm and the robustness to different class orders, we conduct experiments on five different class orders to calculate the average performance and their standard deviation. As shown in Fig. 6, our method significantly improves the" + } + ] + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 331, + 202, + 518, + 348 + ], + "blocks": [ + { + "bbox": [ + 331, + 202, + 518, + 348 + ], + "lines": [ + { + "bbox": [ + 331, + 202, + 518, + 348 + ], + "spans": [ + { + "bbox": [ + 331, + 202, + 518, + 348 + ], + "type": "image", + "image_path": "df4a1e676e976a79c309a63759bdb815e1b17ec1982527d2f09a477078be9ceb.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 306, + 360, + 544, + 371 + ], + "lines": [ + { + "bbox": [ + 306, + 360, + 544, + 371 + ], + "spans": [ + { + "bbox": [ + 306, + 360, + 544, + 371 + ], + "type": "text", + "content": "Figure 6. Illustration on robustness with respect to different orders." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 392, + 544, + 415 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 392, + 544, + 415 + ], + "spans": [ + { + "bbox": [ + 305, + 392, + 544, + 415 + ], + "type": "text", + "content": "performance while also significantly enhancing the robustness to different class orders." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 427, + 383, + 439 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 427, + 383, + 439 + ], + "spans": [ + { + "bbox": [ + 306, + 427, + 383, + 439 + ], + "type": "text", + "content": "5. Conclusions" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 447, + 545, + 709 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 447, + 545, + 709 + ], + "spans": [ + { + "bbox": [ + 304, + 447, + 545, + 709 + ], + "type": "text", + "content": "In this work, we address the class incremental semantic segmentation (CISS) problem with a simple yet effective endpoints weight fusion method. It is enhanced by the existing distillation-based methods and easily integrated with them. A dynamic parameter fusion strategy is proven to be flexible for different settings and it avoids the further tuning of hyper-parameters. Interestingly, we discuss the relationship between our method and a popular weight fusion method EMA, which reveals why our method is more effective in incremental learning. The experimental results demonstrate that our method can obtain a significant gain compared to the baselines and achieve superior performance. In future work, we will investigate further the underlining reasons why our simple EWF strategy works so well in CISS. Moreover, we are planning to evaluate our incremental learning strategies for other application domains. Acknowledgment. This work is funded by NSFC (NO. 62225604 and 62206135), Fundamental Research Funds for the Central Universities (Nankai University, NO. 63223050), and Bytedance Limited. 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Koppal $^{1}$ Yicheng Wu $^{3}$ Georgios Evangelidis $^{3}$ Ramzi Zahreddine $^{3}$ Gurunandan Krishnan $^{3}$ Sizhuo Ma $^{3\\dagger}$ Jian Wang $^{3\\dagger}$ $^{1}$ University of Florida $^{2}$ Stanford University $^{3}$ Snap Inc.", + "bbox": [ + 94, + 179, + 869, + 236 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 268, + 313, + 284 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Active depth sensing achieves robust depth estimation but is usually limited by the sensing range. Naively increasing the optical power can improve sensing range but induces eye-safety concerns for many applications, including autonomous robots and augmented reality. In this paper, we propose an adaptive active depth sensor that jointly optimizes range, power consumption, and eye-safety. The main observation is that we need not project light patterns to the entire scene but only to small regions of interest where depth is necessary for the application and passive stereo depth estimation fails. We theoretically compare this adaptive sensing scheme with other sensing strategies, such as full-frame projection, line scanning, and point scanning. We show that, to achieve the same maximum sensing distance, the proposed method consumes the least power while having the shortest (best) eye-safety distance. We implement this adaptive sensing scheme with two hardware prototypes, one with a phase-only spatial light modulator (SLM) and the other with a micro-electro-mechanical (MEMS) mirror and diffractive optical elements (DOE). Experimental results validate the advantage of our method and demonstrate its capability of acquiring higher quality geometry adaptively. Please see our project website for video results and code: https://btilmon.github.io/e3d.html.", + "bbox": [ + 76, + 301, + 473, + 664 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 696, + 209, + 713 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Active 3D depth sensors have diverse applications in augmented reality, navigation, and robotics. Recently, these sensor modules are widely used in consumer products, such as time-of-flight (e.g., Lidar [15]), structured light (e.g., Kinect V1 [18]) and others. In addition, many computer vision algorithms have been proposed to process the acquired data for downstream tasks such as 3D semantic understanding [29], object tracking [17], guided upsampling in SLAM [24], etc.", + "bbox": [ + 75, + 724, + 468, + 861 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/3fa6cf467037b4cfd3a2694c4f3c0bcc716d624b769220478dfa87298f96b647.jpg", + "image_caption": [ + "(a) Depth sensing on wearables faces challenges" + ], + "image_footnote": [], + "bbox": [ + 506, + 268, + 647, + 367 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/137dc01153f8ae057a61a80f64024fd42cbd7db182aa1a52f3f68ab5dc31508a.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 669, + 268, + 880, + 368 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/1c347786db62a9044cc5e15a5a3bf2e02e9191d3b5148bc4ae7c1192473172bd.jpg", + "image_caption": [ + "(b) Our system with adaptive projection", + "Figure 1. Energy-efficient adaptive 3D sensing. (a) Depth sensing devices have three key optimization goals: minimizing the power consumption and eye-safety distance while maximizing sensing distance. However, these goals are coupled to each other. (b) We propose a novel adaptive sensing method with an active stereo setup and a projector that can redistribute the light energy and project the pattern only to the required regions (e.g., textureless regions). (c) The proposed approach outperforms previous methods including full-frame pattern systems (like Intel RealSense) and line-scanning systems (like Episcan3D [22]): When the maximum sensing distance is the same, the required power is much less and the eye-safety distance is also shorter." + ], + "image_footnote": [], + "bbox": [ + 503, + 400, + 735, + 549 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/1b0bbb14711549d34ef2e2584427c7ee7df71d1a4bda1e35f5d1ef2f5da7cdc8.jpg", + "image_caption": [ + "(c) Comparison" + ], + "image_footnote": [], + "bbox": [ + 748, + 398, + 885, + 549 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Unlike stereo cameras that only sense reflected ambient light passively, active depth sensors illuminate the scene with modulated light patterns, either spatially, temporally, or both. The illumination encodings allow robust estimation of scene depths. However, this also leads to three shortcomings: First, active depth sensors consume optical power, burdening wearable devices that are on a tight power budget. Second, the number of received photons reflected back from the scene drops with inverse-square relationship", + "bbox": [ + 496, + 763, + 893, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 810, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Work done during internship at Snap Research.", + "bbox": [ + 94, + 875, + 351, + 887 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "†Co-corresponding authors", + "bbox": [ + 96, + 887, + 241, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "5054", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/3d3f63ee29f35666096c5fd5c85d56a03df34fc430941553517bef2a5533148b.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 86, + 94, + 222, + 224 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/1d0c9b5ff8bf5b4171a427b394817ffd82d154b9d57c311514cd78487b3197d4.jpg", + "image_caption": [ + "e.g., region of interest & textureless region" + ], + "image_footnote": [], + "bbox": [ + 225, + 94, + 354, + 210 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/5614de34bbae799f106f0be14cc3c1de9124d48caab850ffdde3ab525a1f9f6b.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 356, + 94, + 493, + 188 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/fab487e22e6ced4ebcb7350fa62cd98af6980613890171e2f95c4bd70e230e1e.jpg", + "image_caption": [ + "Figure 2. Method overview. Our system consists of a stereo-camera pair and an adaptive projector. The system first captures an image of the scene (Step 1) and then computes an attention map to determine the ROI (Step 2). This attention map is used to compute the control signal for the specific projector implementation (Step 3) such that light is only projected to the ROI (Step 4). A depth map is then computed from the new stereo images, which can be used for applications such as augmented reality (Step 5)." + ], + "image_footnote": [], + "bbox": [ + 493, + 95, + 630, + 224 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/6df9b4459bebd97e46cb7342c971bd2acd5a17ce17390e6ee07c658c085e277d.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 630, + 94, + 756, + 190 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/bd7a0ab7b5111129f96ab97671c7f8199cb6ed1acc0780c20be0bb92464653d8.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 761, + 94, + 890, + 190 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "to scene depth. The maximum sensing distance is thereby limited by the received signal-to-noise ratio (SNR). Third, strong, active light sources on the device may unintentionally hurt the user or other people around. For consumer devices, this constraint can be as strict as ensuring safety when a baby accidentally stares at the light source directly. Interestingly, these three factors are often entangled with each other. For example, naively increasing range by raising optical power makes the device less eye-safe. An active 3d sensor would benefit from the joint optimization of these three goals, as illustrated in Fig. 1(a).", + "bbox": [ + 75, + 325, + 468, + 492 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In this paper, we present an adaptive depth-sensing strategy. Our key idea is that the coded scene illumination need not be sent to the entire scene (Fig. 1(b)). Intuitively, by limiting the illumination samples, the optical power per sample is increased, therefore extending the maximum sensing distance. This idea of adaptive sensing is supported by three observations: First, illumination samples only need to be sent to parts of a scene where passive depth estimation fails (e.g., due to lack of texture). Second, depth estimation is often application-driven, e.g., accurate depths are only needed around AR objects to be inserted into the scene. Finally, for video applications, sending light to regions where depths are already available from previous frames is redundant. Based on these observations, we demonstrate this adaptive idea with a stereo-projector setup (i.e., active stereo [4,9,34]), where an attention map is computed from the camera images for efficient light redistribution.", + "bbox": [ + 75, + 492, + 468, + 750 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To quantitatively understand the benefits of our approach, we propose a sensor model that analytically characterizes various sensing strategies, including full-frame (e.g., RealSense [19]), line-scanning (e.g., Episcan3D [22]), point-scanning (e.g., Lidar [25]) and proposed adaptive sensing. We establish, for the first time, a framework that jointly analyzes the power, range, and eye-safety of different strategies and demonstrates that, for the same maximum sensing distance, adaptive sensing consumes the least power while achieving the shortest (best) eye-safety distance.", + "bbox": [ + 75, + 750, + 468, + 901 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Note that the realization of scene-adaptive illumination is not trivial: Common off-the-shelf projectors simply block part of the incident light, which wastes optical power. We propose two hardware implementations for adaptive illumination: One is inspired by digital holography, which uses Liquid Crystal on Silicon (LCoS) Spatial Light Modulators (SLM) to achieve free-form light projection. The other implementation uses diffractive optical elements (DOE) to generate dot patterns in a local region of interest (ROI), which is directed to different portions of the scene by a micro-electro-mechanical (MEMS) mirror.", + "bbox": [ + 496, + 325, + 890, + 492 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Our contributions are summarized as follows:", + "bbox": [ + 517, + 493, + 821, + 507 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- Adaptive 3D sensing theory: We propose adaptive 3D sensing and demonstrate its advantage in a theoretical framework that jointly considers range, power and eye-safety.", + "- Hardware implementation: We implement the proposed adaptive active stereo approach with two hardware prototypes based on SLM and MEMS + DOE.", + "- Experimental validation: Real-world experimental results validate that our sensor can adapt to the scene and outperform existing sensing strategies." + ], + "bbox": [ + 517, + 510, + 890, + 660 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 500, + 676, + 640, + 693 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Active 3D sensing with ambient light noise. Various techniques have been proposed to address photon noise due to strong ambient light (e.g., sunlight), such as choosing a wavelength where sunlight is weak [23, 32], using a polarizing filter [23]. Gupta et al. [13] uses a theoretical model to show that instead of illuminating the full scene, concentrating light on different parts of a scene sequentially improves SNR for structured light, which is demonstrated with a rotating polygonal mirror. Based on similar principles, MC3D [21] uses a MEMS/galvo-driven laser and an event camera to achieve bandwidth-efficient scanning. Episcan3D [22] and EpiToF [1] use a line-scanning laser and a synchronized rolling-shutter camera to achieve fast", + "bbox": [ + 496, + 704, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "5055", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "and efficient depth sensing. This paper further extends this line of work by showing that, with the freedom to adaptively illuminate part of the scene, a lower power budget is needed to achieve the same sensing range while being safer to the eyes.", + "bbox": [ + 75, + 90, + 468, + 167 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Adaptive 3D sensing. Ideas from visual attention [6, 11] have influenced vision and robotics. Efficient estimation algorithms have been shown for adaptive sensing and pointzoom-tilt (PZT) cameras [7, 33]. In the 3D sensor space, 3D light-curtains [5,8,31] represent a flexible system where curtains can be adaptively placed in the scene for robotics, and other applications [2,3,26]. Full control of the MEMS mirror enables adaptive sampling for LIDAR [25, 27, 28] and adaptive passive camera resolution for monocular depth sensing [30]. While previous adaptive systems focus on different aspects such as flexibility, frame rate, etc., this work studies the interplay between range, power, and eye-safety.", + "bbox": [ + 75, + 169, + 470, + 351 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Energy-Efficient Adaptive 3D Sensing", + "text_level": 1, + "bbox": [ + 76, + 363, + 418, + 381 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The workflow of the proposed adaptive 3D sensing is shown in Fig. 2. We use an active stereo design with two cameras and a projector. The device first captures an image of the scene and computes an attention map to determine the region of interest (ROI). Hardware-specific control signals are computed from the attention map such that the projector redistributes the light to the ROI. Finally, a high-quality depth map can be calculated from captured stereo images.", + "bbox": [ + 75, + 388, + 468, + 508 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Before getting into details on how to implement this adaptive illumination in practice, let us assume an ideal flexible projector for a moment: If we can redistribute the optical power to an arbitrarily-shaped ROI, how well can it perform? We adopt a model to quantify its depth estimation performance and compare it to other existing or naively conceived active depth sensing strategies.", + "bbox": [ + 75, + 508, + 468, + 613 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Sensor Model and SNR Analysis", + "text_level": 1, + "bbox": [ + 76, + 622, + 361, + 638 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The accuracy of various active depth sensors, including structured light, active stereo, continuous-wave time-of-flight (CW-ToF), etc., can be quantified by a single metric: the SNR of the measured light signal (projected by the active illumination source and reflected by the scene). The noise consists of the photon noise from both the signal itself and the ambient light, and the sensor readout noise, mathematically defined as follows [13, 14]:", + "bbox": [ + 75, + 646, + 468, + 766 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} S N R = \\frac {\\text {S i g n a l} _ {\\text {p r o j e c t o r}}}{\\sqrt {N _ {\\text {p h o t o n} , \\text {a m b i e n t}} ^ {2} + N _ {\\text {p h o t o n} , \\text {p r o j e c t o r}} ^ {2} + N _ {\\text {r e a d}} ^ {2}}} \\tag {1} \\\\ = \\frac {\\frac {P}{d ^ {2} a} t _ {1}}{\\sqrt {P _ {\\mathrm {s u n}} t _ {2} + \\frac {P}{d ^ {2} a} t _ {1} + N _ {\\mathrm {r e a d}} ^ {2}}} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 98, + 773, + 468, + 864 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $P$ is the optical power of the projector (assuming an albedo of 1 in the scene), $a$ is the illuminated area at unit", + "bbox": [ + 76, + 869, + 468, + 898 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "distance, $d$ is the distance of the scene (thus the inverse-square fall-off), $P_{\\mathrm{sun}}$ is the optical power of the ambient light, $t_1$ and $t_2$ are the duration when the laser is on and the camera is active, respectively, and $N_{\\mathrm{read}}$ is the standard deviation of the read noise. Ambient light-induced photon noise dominates in outdoor scenarios and also indoors with power-limited devices, which is the major focus of the following analysis. In these situations, SNR can be simplified as:", + "bbox": [ + 496, + 90, + 890, + 223 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nS N R \\approx \\frac {\\frac {P}{d ^ {2} a} t _ {1}}{\\sqrt {P _ {\\mathrm {s u n}} t _ {2}}}. \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 632, + 223, + 890, + 258 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "When readout noise dominates, which happens in a dark room or at night, SNR can be simplified as this", + "bbox": [ + 498, + 262, + 890, + 292 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nS N R \\approx \\frac {\\frac {P}{d ^ {2} a} t _ {1}}{N _ {\\text {r e a d}}}. \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 640, + 301, + 890, + 337 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Analyzing different sensing strategies. We use this SNR model to compare the performance of different depth sensors. For a fair comparison, we assume all depth sensors have equal total optical power $P$ , sensing at same depth $d$ . Their performance is then uniquely determined by $t_1$ , $t_2$ and $a$ . For off-the-shelf full-frame projectors (Fig. 3(e)), we denote $a = A$ which corresponds to the entire FOV, and $t_1 = t_2 = T$ as both the sensor and the projector are active during the entire camera exposure $T$ .", + "bbox": [ + 496, + 349, + 890, + 484 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Previous work [1, 13, 21, 22] has shown that, instead of flood-illuminating the entire scene, focusing optical power on different parts of the scene sequentially can lead to higher SNR. To quantitatively analyze this effect, we represent the illuminated area, laser exposure and camera exposure as a division of the full-frame case:", + "bbox": [ + 496, + 484, + 890, + 575 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\na = A / R _ {a}, \\quad t _ {1} = T / R _ {t 1}, \\quad t _ {2} = T / R _ {t 2}, \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 526, + 587, + 890, + 604 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $R_{a}, R_{t1}, R_{t2}$ are defined as illuminated area divisor, laser exposure divisor, camera exposure divisor, respectively. SNR is then a function of these divisors:", + "bbox": [ + 496, + 614, + 890, + 659 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nS N R = \\frac {\\frac {P}{d ^ {2} A / R _ {a}} T / R _ {t 1}}{\\sqrt {P _ {\\mathrm {s u n}} T / R _ {t 2}}} = \\underbrace {\\frac {P \\sqrt {T}}{d ^ {2} A \\sqrt {P _ {\\mathrm {s u n}}}}} _ {c} \\underbrace {\\frac {R _ {a} \\sqrt {R _ {t 2}}}{R _ {t 1}}} _ {X}, \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 519, + 669, + 890, + 724 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $c$ is the SNR of full-frame projection. $X$ is a factor that describes how each method compares with the baseline full-frame projection. It is difficult to optimize $X$ directly since not every combination of $(R_{a}, R_{t1}, R_{t2})$ is feasible in hardware. Nevertheless, it provides a useful tool to characterize different sensing strategies.", + "bbox": [ + 496, + 734, + 890, + 824 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "State-of-the-art systems such as Episcan3D [22] implement this idea as a line scanning scheme, as shown in Fig. 3(c). If we assume the total illuminated region of line scanning is the same as full-pattern, then $R_{a} = R_{t1} = R_{t2} = N$ , where $N$ is the number of scanlines (typically", + "bbox": [ + 496, + 825, + 890, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "5056", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 2 + }, + { + "type": "table", + "img_path": "images/7066869f2e972d459fb8944f1c1e112336f4f6a6f6c1fe8b8d728c81a1107aab.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
Point scanningLine scanning(e) Full-frame pattern(f) Adaptive (Proposed)
(a) V1: Synced(b) V2: Unsynced(c) V1: Synced(d) V2: Unsynced
*Typically, N = 102~103Single pixel 2D MEMS2D MEMS1D laser + 1D MEMS or 2D rolling-shutter cam1D laser + 1D MEMS2D projector2D flexible projector
Illuminated Area Divisor (Ra)N2N2NN1N
Laser Exposure Divisor (Rt1)N2N2NN11
Camera Exposure Divisor (Rt2)N21N111
Same power, sensing at same distance:
SNR = c Ra√Rt2/Rt1cNcc√NcccN
Same maximum sensing distance dmax:
Power Pkp d2maxN-1kp d2maxkp d2maxN-0.5kp d2maxkp d2maxkp d2maxN-1
Eye-safety distance lminklddmaxN0.25klddmaxN0.75klddmaxN0.125klddmaxN0.375klddmaxklddmax
", + "bbox": [ + 83, + 89, + 890, + 392 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Figure 3. Schematic diagrams and analysis of various sensing strategies. When ambient light noise dominates, the proposed adaptive sensing achieves best SNR. To achieve the same maximum sensing distance, adaptive sensing consumes least power while having shortest eye-safety distance. (Best performing methods in each row are highlighted in blue)", + "bbox": [ + 75, + 402, + 892, + 445 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "$10^{2} - 10^{3})$ . By plugging these terms into Eq. 5, the SNR of line scanning is $X = \\sqrt{N}$ times higher than the full-pattern.", + "bbox": [ + 76, + 470, + 470, + 502 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "One interesting question is: Can we push this idea further and scan a dot at a time? This point scanning idea can be implemented with a co-located laser and single-pixel sensor deflected by a 2D MEMS mirror. Using the same assumption, $R_{a} = R_{t1} = R_{t2} = N_{p}$ , where $N_{p}$ is the number of dots (typically $N_{p} = N^{2} = 10^{4} - 10^{6}$ ). Fig. 3(a) shows that dot scanning does offer a higher SNR and is $X = N$ times higher than the full-pattern. Notice that this SNR benefit comes from the fact that the laser and the sensor are synchronized: The sensor only receives light from the area illuminated by the laser at any instant. For their unsynchronized counterparts where the sensor is a 2D camera that captures the entire 2D FOV during the whole imaging time (easier to implement in hardware), their SNR is exactly the same as the full-pattern approach (Fig. 3(b,d)).", + "bbox": [ + 75, + 517, + 468, + 744 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Adaptive sensing. Our adaptive sensor projects a static pattern that does not change during the entire exposure, i.e. $R_{t1} = R_{t2} = 1$ . However, the optical power is concentrated to a small ROI, which we assume can be as small as one line in the line-scanning approach $R_{a} = N$ . As shown in Fig. 3(f), our adaptive sensor has a $N_{l}$ times higher SNR than the full-pattern approach. In summary, we observed that $SNR_{\\mathrm{adaptive}} = SNR_{\\mathrm{point}} \\gg SNR_{\\mathrm{line}} \\gg SNR_{\\mathrm{full}}$ .", + "bbox": [ + 76, + 780, + 470, + 902 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. Comparison of Power, Range, and Eye-Safety", + "text_level": 1, + "bbox": [ + 498, + 470, + 883, + 486 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Sec. 3.1 analyzes the SNR for different sensors at the same depth. However, this analysis is insufficient, since increasing SNR and the maximum range implies a higher risk of eye injury. In this section, we discuss how this model can be extended to analyze the trade-off between power, range and eye-safety. We consider two key constraints: maximum sensing distance and minimum eye-safety distance.", + "bbox": [ + 496, + 493, + 890, + 599 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Maximum sensing distance. We assume that for reliable estimation of the depth, the SNR must be greater than a minimum detection threshold $\\mathrm{SNR}_{\\mathrm{thres}}$ . The equality holds when the maximum sensing distance $d = d_{max}$ is reached,", + "bbox": [ + 496, + 602, + 890, + 662 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nS N R _ {\\text {t h r e s}} = \\frac {P \\sqrt {T}}{d _ {\\max } ^ {2} A \\sqrt {P _ {s u n}}} X. \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 596, + 672, + 890, + 709 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Rearranging this equation gives", + "bbox": [ + 500, + 710, + 712, + 727 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\boxed {P = k _ {p} \\cdot d _ {\\max } ^ {2} X ^ {- 1} = k _ {p} \\cdot d _ {\\max } ^ {2} R _ {a} ^ {- 1} R _ {t 1} R _ {t 2} ^ {- 0. 5},} \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 527, + 732, + 890, + 757 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $k_{p}$ is a method-independent constant.", + "bbox": [ + 500, + 763, + 790, + 777 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Minimum eye-safety distance. A minimum eye-safety distance can be defined when the maximum permissible exposure (MPE, defined in ANSI Z136) is reached:", + "bbox": [ + 496, + 781, + 890, + 825 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\frac {P}{l _ {\\min } ^ {2} a} = \\frac {M P E \\left(t _ {1}\\right)}{t _ {1}}, \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 624, + 830, + 890, + 864 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "It is considered dangerous for eyes to be exposed at a distance shorter than $l_{\\min}$ . Intuitively, the shorter the minimal", + "bbox": [ + 496, + 869, + 890, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "5057", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "eye-safety distance is, the more eye-safe the device is. We expand MPE based on definitions from ANSI Z136:", + "bbox": [ + 75, + 90, + 468, + 121 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\frac {P}{l _ {\\operatorname* {m i n}} ^ {2} a} = \\frac {M P E (t _ {1})}{t _ {1}} = \\frac {C _ {\\lambda} t _ {1} ^ {0 . 7 5} 1 0 ^ {- 3} (\\mathrm {J} \\cdot \\mathrm {c m} ^ {- 2})}{t _ {1}} = k _ {e} t _ {1} ^ {- 0. 2 5}, \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 76, + 131, + 475, + 178 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $k_{e}$ is a method-independent constant. Please find a detailed discussion on this analytic expression in the supplementary report. Plug in Eq. 4 and rearrange,", + "bbox": [ + 75, + 179, + 468, + 224 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nl _ {\\min } = k _ {l} \\cdot P ^ {0. 5} R _ {a} ^ {0. 5} R _ {t 1} ^ {- 0. 1 2 5}, \\tag {10}\n$$\n", + "text_format": "latex", + "bbox": [ + 174, + 234, + 468, + 253 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $k_{l}$ is a method-independent constant.", + "bbox": [ + 76, + 265, + 366, + 279 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Comparing different sensors. From Eq. 7 and Eq. 10, it is clear that for a depth sensing method, specifying one quantity among $P$ , $d_{\\mathrm{max}}$ and $l_{\\mathrm{min}}$ will also determine the other two. We thus focus on the following question: To reach the same maximum sensing distance $d_{\\mathrm{max}}$ , what is the power consumption $P$ and eye-safety distance $l_{\\mathrm{min}}$ of each method? This is a key problem for consumer devices with limited power budget. Plug Eq. 7 into Eq. 10 and rearrange:", + "bbox": [ + 75, + 282, + 468, + 405 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\boxed {l _ {\\min } = k _ {l d} \\cdot d _ {\\max } R _ {t 1} ^ {0. 3 7 5} R _ {t 2} ^ {- 0. 2 5},} \\tag {11}\n$$\n", + "text_format": "latex", + "bbox": [ + 163, + 416, + 468, + 441 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $k_{ld}$ is a method-independent constant.", + "bbox": [ + 76, + 446, + 372, + 460 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Fig. 3 summarizes the results derived from Eq. 7 and Eq. 11 for different sensing methods. Full-frame pattern method is the most eye-safe but consumes the most power. Conversely, point scanning (synced) consumes the least power but is also the least eye-safe, which highly limits its application in consumer devices (e.g., laser projectors). Line scanning (synced) strikes the sweet middle ground, which extends the distance by a large margin while maintaining eye safety. Finally, by concentrating to a small ROI, the proposed adaptive method consumes the least power and achieves the best eye-safety.", + "bbox": [ + 75, + 462, + 468, + 628 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "To intuitively showcase this advantage, we assume $N \\sim 100$ to 500, which is consistent with the spatial resolution of most concurrent 3D sensors. For high-resolution depth sensors with $N > 1000$ , the gain is even greater. At the same maximum sensing distance, adaptive sensing:", + "bbox": [ + 75, + 628, + 468, + 703 + ], + "page_idx": 4 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- has the same eye-safety distance as full-frame sensors, while consuming $N^{-1}$ (0.01 to 0.002)× lower power.", + "- has $N^{-0.125}$ (0.56 to 0.46) × shorter (better) eye-safety distance as line-scanning, while consuming $N^{-0.5}$ (0.1 to 0.04) × lower power." + ], + "bbox": [ + 94, + 704, + 467, + 777 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "It is important to mention that these calculations are based on the assumption that the illuminated area for adaptive sensing is the same as line scanning: $R_{a} = N$ . In practice, this area may be larger depending on the scene and application. The adaptive projector (e.g., SLM) may also have a limited light efficiency, which gives an effectively smaller $R_{a}$ and thus lower SNR. Nonetheless, at the same maximum distance, adaptive sensing still has a power benefit as", + "bbox": [ + 75, + 780, + 468, + 900 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/de53f64ea62f34f430fc82430f37aa36f470bcd0bf245040dfb9f1eba1ba9cd7.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
SNRPlmin
V1cNkp d2maxN-1kldmax
V1-acNK-1kp d2maxN-1KkldmaxK0.375
V1-bcNK-0.5kp d2maxN-1K0.5kldmaxK0.125
", + "bbox": [ + 501, + 89, + 898, + 165 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Table 1. Variations of adaptive sensing.", + "bbox": [ + 571, + 176, + 818, + 189 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "long as $R_{a} > \\sqrt{N}$ , and it always has a eye-safety benefit since $l_{\\min}$ is independent of $R_{a}$ . The theoretical analysis forms the foundation for the proposed adaptive 3D sensing. We validate the analysis in a real-world prototype in Sec. 5.", + "bbox": [ + 496, + 218, + 890, + 280 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Disjoint ROIs. So far, we assume an ideal flexible projector which can project light to arbitrarily-shaped, even disjoint ROIs simultaneously. In practice, certain hardware implementations do not have this capability (an example is discussed in Sec. 4.2). To this end, we propose a more flexible scanning strategy: During the camera exposure, the system scans $K$ disjoint ROIs sequentially (typically $2 \\leq K \\leq 5$ ). This adaptive V1-a method consumes slightly more power and has a slightly longer eye-safety distance (Tab. 1). Another option is to divide the camera exposure into $K$ shorter exposures, and the system scans a single ROI during each exposure. This adaptive V1-b method performs comparably as V1, but requires a $K$ times higher camera frame rate. Please refer to the supplementary technical report for more design variations and detailed comparisons.", + "bbox": [ + 496, + 286, + 890, + 512 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Implementation of Adaptive Illumination", + "text_level": 1, + "bbox": [ + 498, + 530, + 867, + 547 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Now that we have theoretically analyzed the benefit of the proposed adaptive illumination, how can the proposed adaptive illumination be realized? Notice that this is not a trivial problem. The hardware implementation must satisfy two criteria: (1) The system can redistribute the optical power to a small ROI (guided by an attention map), and (2) This ROI can be projected to different parts of the scene flexibly and in real-time (e.g., 30Hz). A common LCD or DLP projector satisfies (2) but does not satisfy (1). In this section, we propose two hardware configurations that satisfy both conditions.", + "bbox": [ + 496, + 556, + 890, + 723 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.1. Implementation 1: Phase SLM", + "text_level": 1, + "bbox": [ + 500, + 736, + 772, + 752 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Fig. 4(a) shows our SLM-based implementation. Our holographic projection approach is inspired by recent work on holographic near-eye 3D displays [20]. Specifically, a hologram to be reproduced by the SLM is decomposed as a sum of sub-holograms, where each sub-hologram diffracts light to a single object point in the scene. In [20], each sub-hologram is created using a lens phase function:", + "bbox": [ + 496, + 760, + 890, + 867 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nf _ {n} ^ {\\text {l e n s}} (\\mathbf {X}) = e ^ {j 2 \\pi \\sqrt {(X - x _ {n}) ^ {2} + (Y - y _ {n}) ^ {2} + (Z - z _ {n}) ^ {2})} / \\lambda , \\tag {12}\n$$\n", + "text_format": "latex", + "bbox": [ + 519, + 881, + 890, + 901 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "5058", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/ee1ec079ae840fb7b84e24a2ecbe1854f14d18ef329d32826c883bb35cc61a46.jpg", + "image_caption": [ + "(a) Phase SLM-based implementation" + ], + "image_footnote": [], + "bbox": [ + 143, + 90, + 480, + 190 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/4771f1b29a3eb3f20a60be6db724322b9e0e061ae2fe8179956f33b17d700f8c.jpg", + "image_caption": [ + "(b) MEMS + DOE-based method", + "Figure 4. Hardware implementations. (a) Our first implementation is based on a phase-only SLM, which can redistribute light to arbitrarily-shaped, even disjointed ROIs. (b) Our second implementation is based on a DOE pattern generator with a 2D MEMS mirror. It has less flexibility and can only concentrate on one fixed-shape ROI at a time, but it benefits from low cost, simple optics and small form factor which makes it potentially easier to be miniaturized." + ], + "image_footnote": [], + "bbox": [ + 521, + 95, + 826, + 189 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $(X,Y,Z)$ is the 3D position of each pixel in the subhologram, $(x_{n},y_{n},z_{n})$ is the 3D position of the $n$ -th object point, and $\\lambda$ is the light wavelength. The full hologram is,", + "bbox": [ + 75, + 306, + 470, + 354 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\nH (\\mathbf {X}) = \\sum_ {n = 1} ^ {N} f _ {n} ^ {\\text {l e n s}}. \\tag {13}\n$$\n", + "text_format": "latex", + "bbox": [ + 207, + 357, + 468, + 397 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "This lens phase function mimics a lens that focuses light to the object point at the correct depth, which works well for near-eye displays. One limitation of this lens phase function approach is that light is only redistributed locally. This is because the SLM can only reproduce a smooth hologram due to the Nyquist frequency determined by the finite pixel pitch. However, $f^{\\mathrm{lens}}$ varies rapidly for off-center pixels (i.e. $X, Y$ far away from $x_{n}, y_{n}$ ), causing aliasing artifacts. Therefore, sub-holograms of much smaller sizes must be used, which greatly limits the light efficiency.", + "bbox": [ + 75, + 402, + 468, + 553 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "To alleviate this limitation, we propose the use of mirror phase function:", + "bbox": [ + 75, + 554, + 468, + 585 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\nf _ {n} ^ {\\text {m i r r o r}} (\\mathbf {X}) = e ^ {j \\left(X \\cdot x _ {n} + Y \\cdot y _ {n}\\right)}, H (\\mathbf {X}) = \\sum_ {n = 1} ^ {N} f _ {n} ^ {\\text {m i r r o r}}. \\tag {14}\n$$\n", + "text_format": "latex", + "bbox": [ + 91, + 589, + 468, + 631 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "The mirror phase function corresponds to a smooth phase map linear in terms of $X, Y$ , and can be implemented on the SLM without aliasing. It allows us to use each sub-hologram as a mirror that reflects light to the right direction. By taking the sum of sub-holograms that reflect to different directions, desired projection patterns can be achieved. Please see the supplementary for detailed optical diagrams and discussion.", + "bbox": [ + 75, + 633, + 468, + 755 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Conversion to phase-only holograms. Notice that Eq. 14 creates a hologram with both amplitudes and phases being spatially-variant, which cannot be implemented on a phase-only SLM. Several approaches [12, 16] have been proposed to convert such a full hologram to a phase-only hologram. Fortunately, our goal is not to project a high-quality image, and simple amplitude discarding is sufficient to project unique texture to the scene:", + "bbox": [ + 75, + 758, + 470, + 878 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\nH _ {\\text {p h a s e}} = \\operatorname {A r g} [ H ]. \\tag {15}\n$$\n", + "text_format": "latex", + "bbox": [ + 207, + 883, + 468, + 902 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/0dd3c5e05548c4ad1b35ed419f1f652bc28df134b4d6ec38a59831b96541ecaf.jpg", + "image_caption": [ + "Implementation 1: Phase SLM" + ], + "image_footnote": [], + "bbox": [ + 545, + 321, + 821, + 411 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/92475a32c762f22f669a9f85a9efc95696a0d1e4cd362c32f3987820d2a17460.jpg", + "image_caption": [ + "Implementation 2: MEMS + DOE", + "Figure 5. Hardware prototypes. (Upper) Spatial Light Modulator (SLM) implementation. (Lower) Micro-electromechanical (MEMS) mirror + diffractive optical element (DOE) implementation." + ], + "image_footnote": [], + "bbox": [ + 545, + 439, + 821, + 527 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/deac0b741cc8948470960e1db8f41eafb2f1fcffd3d09992d254465714d7df33.jpg", + "image_caption": [ + "Figure 6. Examples of emulating full frame, line scanning, and adaptive sensors on a phase only spatial light modulator. Note that the full frame and adaptive patterns are captured within the full exposure time, while each line in the line scanning pattern is captured within $1/N$ of the time. We scale the intensities for visualization. Note that the bright center dot is caused by the SLM DC term, and can be mitigated with additional optical filters and manufacturing processes." + ], + "image_footnote": [], + "bbox": [ + 500, + 621, + 890, + 734 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Efficient implementation. The mirror phase function consists of simple arithmetic operations on large matri", + "bbox": [ + 500, + 869, + 892, + 901 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "5059", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/7222947253c0b01a86582189710fb66fd088aba817648c19d482d62cb76d87e5.jpg", + "image_caption": [ + "Figure 7. Comparison between sensing strategies. Our approach is more robust to ambient light than line scanning and full frame sensors; notice how our adaptive approach degrades less than line scanning and full frame from low ambient lighting (700 lux) to high ambient lighting (4000 lux). We keep sensor settings constant for each low ambient-high ambient pair. The total number of dots in the adaptive method (ours), line scanning and full frame is around 150, $108 \\times 150$ and $150^2$ , respectively. Zoom in to see the red dots in the camera images." + ], + "image_footnote": [], + "bbox": [ + 83, + 89, + 893, + 393 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "ces, which can be implemented efficiently on a GPU. We implement our hologram generator in CUDA and render the resulting hologram phase from the frame-buffer to the SLM using OpenGL-CUDA interoperability. On a NVIDIA Jetson Nano, an embedded system-on-module with a Tegra X1 Maxwell 256-core GPU and limited computing resources, we are able to generate 1080p holograms with around 100 points or less at 30 fps. Our implementation and simulator can be found at https://github.com/btilmon/holoCu.", + "bbox": [ + 75, + 484, + 472, + 636 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.2. Implementation 2: MEMS + DOE", + "text_level": 1, + "bbox": [ + 76, + 646, + 377, + 662 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Our second implementation is to adjust the beam incident angle of a diffractive optical element (DOE) with a MEMS mirror, as shown in Fig. 4(b). DOE offers a cheap, energy-efficient solution for random dot projection in single-shot structured light (Kinect V1) or active stereo (RealSense). While those systems use a DOE that covers the entire scene, we use a small FOV ( $\\approx 5^{\\circ}$ ) that only corresponds to a small ROI. By rotating the MEMS mirror, the deflected laser beam hits the DOE at different angles, thus generating a dot pattern at different ROIs of the scene.", + "bbox": [ + 75, + 670, + 468, + 821 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Comparison with phase SLM. The MEMS + DOE implementation is less flexible than the SLM implementation since the hologram shape is fixed (determined by the DOE phase pattern). This is schematically shown in Fig. 4: While SLM can illuminate ROIs of various shapes (P1-", + "bbox": [ + 75, + 824, + 470, + 902 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "P3), MEMS + DOE can only create the same shape shifted across the scene. Moreover, while the SLM can redistribute the optical power over two disjoint ROIs during the same camera exposure (P4), different ROIs are scanned and imaged sequentially by the MEMS mirror, which slightly decreases the SNR (see Sec. 3.2 for detailed analysis). Nevertheless, the MEMS + DOE approach benefits from low cost, simple optics and small form factor, which are important factors for mobile and wearable devices.", + "bbox": [ + 496, + 484, + 892, + 621 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/e1fc8a796eabed2c4ba4b6ce285d961e52ddefdf7a811b4b5e11fac67aa740dd.jpg", + "image_caption": [ + "Figure 8. Outdoor active depth sensing under 50 kilolux direct sunlight with Phase SLM. Our sensor works outdoors under direct sunlight. We show results up to 2 meters but believe this range could be extended with further SLM optical engineering. Zoom in to see the red dots in the camera images." + ], + "image_footnote": [], + "bbox": [ + 506, + 637, + 893, + 818 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "5060", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/241af25f8f11a991852d4a79699c6abbcd1212e2d264a8fd9bcc90a85d7acc85.jpg", + "image_caption": [ + "Figure 9. MEMS + DOE implementation. The MEMS voltages are updated to direct the dot pattern onto the predominant textureless region in both frames. Zoom in the camera images to see the red dots." + ], + "image_footnote": [], + "bbox": [ + 84, + 92, + 467, + 229 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Experiments", + "text_level": 1, + "bbox": [ + 76, + 308, + 207, + 324 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Hardware prototypes. Fig. 5 shows both hardware prototypes of our proposed method. We use two FLIR BFS-U3-16S2C-CS cameras equipped with $20\\mathrm{mm}$ lenses as a stereo pair. Our SLM implementation uses a Holoyeye GAEA LCoS (phase-only) SLM, which can display 4K phase maps at 30 frames per second. Our MEMS + DOE implementation uses a $0.8\\mathrm{mm}$ diameter bonded Mirrorcle MEMS Mirror. A random dot DOE with a small FOV is preferred. Here, we used a Holoyeye DE-R 339 DOE that produces a periodic 6x6 dot pattern with $5^{\\circ}$ FOV instead and we tilt the DOE such that the pattern is still unique locally on the epipolar line. Please refer to the supplementary report for detailed setup and calibration procedures.", + "bbox": [ + 75, + 333, + 467, + 529 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Attention map and depth estimation. We adopt classical semi global block matching for depth estimation [10]. The attention map is determined by randomly choosing pixels that do not have a valid depth value from the depth map computed from passive images. In practice, the attention map can be conditioned by the application such that illumination is only needed within the regions where AR objects are inserted. Our goal is to present a general sensor that can fit into many different perception systems and improve active depth sensing.", + "bbox": [ + 75, + 534, + 467, + 685 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Comparison between sensing strategies. We emulate full-frame and line-scanning strategies on our SLM implementation and compare them with our adaptive sensing strategy. An example of each emulated sensor can be found in Fig. 6. For line scanning, we compute and project the hologram of the dot pattern line-by-line. We capture the image for each line individually and stitch the corresponding camera rows together into a single image.", + "bbox": [ + 75, + 689, + 467, + 809 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Fig. 7 shows the results for three different scenes. All scenes are illuminated with the same ambient lighting and laser power. Laser power, exposure time and illuminated area are chosen to ensure fair comparison. Due to the dominating photon noise from the ambient light, full-frame and line scanning methods have a low SNR. As a result, depth", + "bbox": [ + 75, + 810, + 467, + 898 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "estimation fails in the textureless regions. Since the proposed adaptive sensing technique concentrates light to the textureless regions, it achieves much higher SNR and obtains higher-quality depth maps, which validates our theoretical analysis.", + "bbox": [ + 496, + 90, + 890, + 166 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Outdoor depth sensing under direct sunlight. Fig. 8 demonstrates our Phase SLM prototype working outdoors under 50 kilolux direct sunlight. We can rely on passive stereo to compute depth for the majority of the scene and only project light where necessary, such as the white textureless pot. We also show a distance test of the Phase SLM prototype at 2 meters. We believe this distance could be increased with further SLM optical engineering in future work.", + "bbox": [ + 496, + 172, + 890, + 306 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "MEMS + DOE implementation. Fig. 9 demonstrates our MEMS + DOE prototype. The dot pattern is projected to a textureless object which improves the disparity compared to passive stereo. When the system moves to another location at $t_1$ , it analyzes the new captured images and directs the ROI to the new position of the textureless object.", + "bbox": [ + 496, + 314, + 890, + 404 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "6. Limitations and Discussion", + "text_level": 1, + "bbox": [ + 498, + 422, + 750, + 436 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Optical power vs computation power. Although we do not explicitly compare the optical power savings from adaptive sensing with the additional computation power needed for computing the attention map and projector control signal (e.g., phase map for SLM), we show that such computations consist of basic arithmetic operations and can be implemented on embedded systems like NVIDIA Jetson Nano, suggesting that our approach can be deployed on increasingly available mobile GPUs. Our system will have even higher benefits for outdoor applications where optical power dominates.", + "bbox": [ + 496, + 449, + 890, + 613 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Learning-based attention map and depth estimation. In this work, we use simple, low-complexity texture analysis and semi global matching for attention map and depth estimation. It is possible to design neural networks to achieve better depth estimation, at the cost of higher computation. Our focus in on validating the proposed adaptive sensing as a promising novel sensing strategy, and we expect more practical algorithms to be developed in future work.", + "bbox": [ + 496, + 621, + 890, + 742 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Other active depth sensing mechanisms. Although this paper only shows hardware implementations for active stereo, the adaptive sensing strategy can be applied to other depth sensing mechanisms such as single/multi-shot structured light, direct/indirect ToF, FMCW Lidar, etc., which can be a promising future direction.", + "bbox": [ + 496, + 748, + 890, + 838 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgements. The authors acknowledge partial funding from the Office of Naval Research through ONR N00014-18-1-2663 and the National Science Foundation through NSF 1942444.", + "bbox": [ + 496, + 839, + 890, + 898 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "5061", + "bbox": [ + 482, + 944, + 513, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Supreeth Achar, Joseph R. Bartels, William L. 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IEEE, 2003. 2" + ], + "bbox": [ + 78, + 92, + 468, + 527 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "5063", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/Energy-Efficient Adaptive 3D Sensing/84eaed71-d9fd-4068-b870-f6dc2370efb9_model.json b/2023/Energy-Efficient Adaptive 3D Sensing/84eaed71-d9fd-4068-b870-f6dc2370efb9_model.json new file mode 100644 index 0000000000000000000000000000000000000000..c71b400f5191cbef45212bc31906f588e60d877f --- /dev/null +++ b/2023/Energy-Efficient Adaptive 3D Sensing/84eaed71-d9fd-4068-b870-f6dc2370efb9_model.json @@ -0,0 +1,2123 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.044 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.001, + 0.812, + 0.047 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.293, + 0.131, + 0.68, + 0.154 + ], + "angle": 0, + "content": "Energy-Efficient Adaptive 3D Sensing" + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.18, + 0.87, + 0.237 + ], + "angle": 0, + "content": "Brevin Tilmon\\(^{1*}\\) Zhanghao Sun\\(^{2}\\) Sanjeev J. Koppal\\(^{1}\\) Yicheng Wu\\(^{3}\\) Georgios Evangelidis\\(^{3}\\) Ramzi Zahreddine\\(^{3}\\) Gurunandan Krishnan\\(^{3}\\) Sizhuo Ma\\(^{3\\dagger}\\) Jian Wang\\(^{3\\dagger}\\) \\(^{1}\\)University of Florida \\(^{2}\\)Stanford University \\(^{3}\\)Snap Inc." + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.269, + 0.314, + 0.285 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.302, + 0.474, + 0.665 + ], + "angle": 0, + "content": "Active depth sensing achieves robust depth estimation but is usually limited by the sensing range. Naively increasing the optical power can improve sensing range but induces eye-safety concerns for many applications, including autonomous robots and augmented reality. In this paper, we propose an adaptive active depth sensor that jointly optimizes range, power consumption, and eye-safety. The main observation is that we need not project light patterns to the entire scene but only to small regions of interest where depth is necessary for the application and passive stereo depth estimation fails. We theoretically compare this adaptive sensing scheme with other sensing strategies, such as full-frame projection, line scanning, and point scanning. We show that, to achieve the same maximum sensing distance, the proposed method consumes the least power while having the shortest (best) eye-safety distance. We implement this adaptive sensing scheme with two hardware prototypes, one with a phase-only spatial light modulator (SLM) and the other with a micro-electro-mechanical (MEMS) mirror and diffractive optical elements (DOE). Experimental results validate the advantage of our method and demonstrate its capability of acquiring higher quality geometry adaptively. Please see our project website for video results and code: https://btilmon.github.io/e3d.html." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.698, + 0.21, + 0.714 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.725, + 0.47, + 0.862 + ], + "angle": 0, + "content": "Active 3D depth sensors have diverse applications in augmented reality, navigation, and robotics. Recently, these sensor modules are widely used in consumer products, such as time-of-flight (e.g., Lidar [15]), structured light (e.g., Kinect V1 [18]) and others. In addition, many computer vision algorithms have been proposed to process the acquired data for downstream tasks such as 3D semantic understanding [29], object tracking [17], guided upsampling in SLAM [24], etc." + }, + { + "type": "image", + "bbox": [ + 0.507, + 0.27, + 0.648, + 0.368 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.671, + 0.27, + 0.882, + 0.369 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.559, + 0.38, + 0.822, + 0.393 + ], + "angle": 0, + "content": "(a) Depth sensing on wearables faces challenges" + }, + { + "type": "image", + "bbox": [ + 0.504, + 0.401, + 0.736, + 0.55 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.51, + 0.55, + 0.727, + 0.562 + ], + "angle": 0, + "content": "(b) Our system with adaptive projection" + }, + { + "type": "image", + "bbox": [ + 0.749, + 0.399, + 0.886, + 0.55 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.771, + 0.55, + 0.855, + 0.562 + ], + "angle": 0, + "content": "(c) Comparison" + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.579, + 0.895, + 0.747 + ], + "angle": 0, + "content": "Figure 1. Energy-efficient adaptive 3D sensing. (a) Depth sensing devices have three key optimization goals: minimizing the power consumption and eye-safety distance while maximizing sensing distance. However, these goals are coupled to each other. (b) We propose a novel adaptive sensing method with an active stereo setup and a projector that can redistribute the light energy and project the pattern only to the required regions (e.g., textureless regions). (c) The proposed approach outperforms previous methods including full-frame pattern systems (like Intel RealSense) and line-scanning systems (like Episcan3D [22]): When the maximum sensing distance is the same, the required power is much less and the eye-safety distance is also shorter." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Unlike stereo cameras that only sense reflected ambient light passively, active depth sensors illuminate the scene with modulated light patterns, either spatially, temporally, or both. The illumination encodings allow robust estimation of scene depths. However, this also leads to three shortcomings: First, active depth sensors consume optical power, burdening wearable devices that are on a tight power budget. Second, the number of received photons reflected back from the scene drops with inverse-square relationship" + }, + { + "type": "page_footnote", + "bbox": [ + 0.095, + 0.875, + 0.352, + 0.888 + ], + "angle": 0, + "content": "*Work done during internship at Snap Research." + }, + { + "type": "page_footnote", + "bbox": [ + 0.098, + 0.888, + 0.242, + 0.9 + ], + "angle": 0, + "content": "†Co-corresponding authors" + }, + { + "type": "list", + "bbox": [ + 0.095, + 0.875, + 0.352, + 0.9 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "5054" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.088, + 0.095, + 0.223, + 0.226 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.226, + 0.095, + 0.356, + 0.211 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.357, + 0.095, + 0.495, + 0.189 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.232, + 0.191, + 0.346, + 0.21 + ], + "angle": 0, + "content": "e.g., region of interest & textureless region" + }, + { + "type": "image", + "bbox": [ + 0.495, + 0.096, + 0.631, + 0.226 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.631, + 0.095, + 0.758, + 0.191 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.763, + 0.095, + 0.892, + 0.191 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.244, + 0.895, + 0.302 + ], + "angle": 0, + "content": "Figure 2. Method overview. Our system consists of a stereo-camera pair and an adaptive projector. The system first captures an image of the scene (Step 1) and then computes an attention map to determine the ROI (Step 2). This attention map is used to compute the control signal for the specific projector implementation (Step 3) such that light is only projected to the ROI (Step 4). A depth map is then computed from the new stereo images, which can be used for applications such as augmented reality (Step 5)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.327, + 0.469, + 0.493 + ], + "angle": 0, + "content": "to scene depth. The maximum sensing distance is thereby limited by the received signal-to-noise ratio (SNR). Third, strong, active light sources on the device may unintentionally hurt the user or other people around. For consumer devices, this constraint can be as strict as ensuring safety when a baby accidentally stares at the light source directly. Interestingly, these three factors are often entangled with each other. For example, naively increasing range by raising optical power makes the device less eye-safe. An active 3d sensor would benefit from the joint optimization of these three goals, as illustrated in Fig. 1(a)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.493, + 0.469, + 0.75 + ], + "angle": 0, + "content": "In this paper, we present an adaptive depth-sensing strategy. Our key idea is that the coded scene illumination need not be sent to the entire scene (Fig. 1(b)). Intuitively, by limiting the illumination samples, the optical power per sample is increased, therefore extending the maximum sensing distance. This idea of adaptive sensing is supported by three observations: First, illumination samples only need to be sent to parts of a scene where passive depth estimation fails (e.g., due to lack of texture). Second, depth estimation is often application-driven, e.g., accurate depths are only needed around AR objects to be inserted into the scene. Finally, for video applications, sending light to regions where depths are already available from previous frames is redundant. Based on these observations, we demonstrate this adaptive idea with a stereo-projector setup (i.e., active stereo [4,9,34]), where an attention map is computed from the camera images for efficient light redistribution." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.75, + 0.47, + 0.902 + ], + "angle": 0, + "content": "To quantitatively understand the benefits of our approach, we propose a sensor model that analytically characterizes various sensing strategies, including full-frame (e.g., RealSense [19]), line-scanning (e.g., Episcan3D [22]), point-scanning (e.g., Lidar [25]) and proposed adaptive sensing. We establish, for the first time, a framework that jointly analyzes the power, range, and eye-safety of different strategies and demonstrates that, for the same maximum sensing distance, adaptive sensing consumes the least power while achieving the shortest (best) eye-safety distance." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.327, + 0.892, + 0.493 + ], + "angle": 0, + "content": "Note that the realization of scene-adaptive illumination is not trivial: Common off-the-shelf projectors simply block part of the incident light, which wastes optical power. We propose two hardware implementations for adaptive illumination: One is inspired by digital holography, which uses Liquid Crystal on Silicon (LCoS) Spatial Light Modulators (SLM) to achieve free-form light projection. The other implementation uses diffractive optical elements (DOE) to generate dot patterns in a local region of interest (ROI), which is directed to different portions of the scene by a micro-electro-mechanical (MEMS) mirror." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.494, + 0.822, + 0.508 + ], + "angle": 0, + "content": "Our contributions are summarized as follows:" + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.511, + 0.892, + 0.57 + ], + "angle": 0, + "content": "- Adaptive 3D sensing theory: We propose adaptive 3D sensing and demonstrate its advantage in a theoretical framework that jointly considers range, power and eye-safety." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.571, + 0.891, + 0.616 + ], + "angle": 0, + "content": "- Hardware implementation: We implement the proposed adaptive active stereo approach with two hardware prototypes based on SLM and MEMS + DOE." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.616, + 0.892, + 0.661 + ], + "angle": 0, + "content": "- Experimental validation: Real-world experimental results validate that our sensor can adapt to the scene and outperform existing sensing strategies." + }, + { + "type": "list", + "bbox": [ + 0.518, + 0.511, + 0.892, + 0.661 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.678, + 0.641, + 0.694 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.705, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Active 3D sensing with ambient light noise. Various techniques have been proposed to address photon noise due to strong ambient light (e.g., sunlight), such as choosing a wavelength where sunlight is weak [23, 32], using a polarizing filter [23]. Gupta et al. [13] uses a theoretical model to show that instead of illuminating the full scene, concentrating light on different parts of a scene sequentially improves SNR for structured light, which is demonstrated with a rotating polygonal mirror. Based on similar principles, MC3D [21] uses a MEMS/galvo-driven laser and an event camera to achieve bandwidth-efficient scanning. Episcan3D [22] and EpiToF [1] use a line-scanning laser and a synchronized rolling-shutter camera to achieve fast" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "5055" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.168 + ], + "angle": 0, + "content": "and efficient depth sensing. This paper further extends this line of work by showing that, with the freedom to adaptively illuminate part of the scene, a lower power budget is needed to achieve the same sensing range while being safer to the eyes." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.17, + 0.471, + 0.352 + ], + "angle": 0, + "content": "Adaptive 3D sensing. Ideas from visual attention [6, 11] have influenced vision and robotics. Efficient estimation algorithms have been shown for adaptive sensing and pointzoom-tilt (PZT) cameras [7, 33]. In the 3D sensor space, 3D light-curtains [5,8,31] represent a flexible system where curtains can be adaptively placed in the scene for robotics, and other applications [2,3,26]. Full control of the MEMS mirror enables adaptive sampling for LIDAR [25, 27, 28] and adaptive passive camera resolution for monocular depth sensing [30]. While previous adaptive systems focus on different aspects such as flexibility, frame rate, etc., this work studies the interplay between range, power, and eye-safety." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.364, + 0.419, + 0.382 + ], + "angle": 0, + "content": "3. Energy-Efficient Adaptive 3D Sensing" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.389, + 0.469, + 0.509 + ], + "angle": 0, + "content": "The workflow of the proposed adaptive 3D sensing is shown in Fig. 2. We use an active stereo design with two cameras and a projector. The device first captures an image of the scene and computes an attention map to determine the region of interest (ROI). Hardware-specific control signals are computed from the attention map such that the projector redistributes the light to the ROI. Finally, a high-quality depth map can be calculated from captured stereo images." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.51, + 0.469, + 0.614 + ], + "angle": 0, + "content": "Before getting into details on how to implement this adaptive illumination in practice, let us assume an ideal flexible projector for a moment: If we can redistribute the optical power to an arbitrarily-shaped ROI, how well can it perform? We adopt a model to quantify its depth estimation performance and compare it to other existing or naively conceived active depth sensing strategies." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.623, + 0.362, + 0.639 + ], + "angle": 0, + "content": "3.1. Sensor Model and SNR Analysis" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.647, + 0.469, + 0.767 + ], + "angle": 0, + "content": "The accuracy of various active depth sensors, including structured light, active stereo, continuous-wave time-of-flight (CW-ToF), etc., can be quantified by a single metric: the SNR of the measured light signal (projected by the active illumination source and reflected by the scene). The noise consists of the photon noise from both the signal itself and the ambient light, and the sensor readout noise, mathematically defined as follows [13, 14]:" + }, + { + "type": "equation", + "bbox": [ + 0.099, + 0.775, + 0.47, + 0.865 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} S N R = \\frac {\\text {S i g n a l} _ {\\text {p r o j e c t o r}}}{\\sqrt {N _ {\\text {p h o t o n} , \\text {a m b i e n t}} ^ {2} + N _ {\\text {p h o t o n} , \\text {p r o j e c t o r}} ^ {2} + N _ {\\text {r e a d}} ^ {2}}} \\tag {1} \\\\ = \\frac {\\frac {P}{d ^ {2} a} t _ {1}}{\\sqrt {P _ {\\mathrm {s u n}} t _ {2} + \\frac {P}{d ^ {2} a} t _ {1} + N _ {\\mathrm {r e a d}} ^ {2}}} \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.469, + 0.9 + ], + "angle": 0, + "content": "where \\(P\\) is the optical power of the projector (assuming an albedo of 1 in the scene), \\(a\\) is the illuminated area at unit" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.224 + ], + "angle": 0, + "content": "distance, \\(d\\) is the distance of the scene (thus the inverse-square fall-off), \\(P_{\\mathrm{sun}}\\) is the optical power of the ambient light, \\(t_1\\) and \\(t_2\\) are the duration when the laser is on and the camera is active, respectively, and \\(N_{\\mathrm{read}}\\) is the standard deviation of the read noise. Ambient light-induced photon noise dominates in outdoor scenarios and also indoors with power-limited devices, which is the major focus of the following analysis. In these situations, SNR can be simplified as:" + }, + { + "type": "equation", + "bbox": [ + 0.633, + 0.224, + 0.891, + 0.259 + ], + "angle": 0, + "content": "\\[\nS N R \\approx \\frac {\\frac {P}{d ^ {2} a} t _ {1}}{\\sqrt {P _ {\\mathrm {s u n}} t _ {2}}}. \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.263, + 0.891, + 0.293 + ], + "angle": 0, + "content": "When readout noise dominates, which happens in a dark room or at night, SNR can be simplified as this" + }, + { + "type": "equation", + "bbox": [ + 0.641, + 0.303, + 0.891, + 0.338 + ], + "angle": 0, + "content": "\\[\nS N R \\approx \\frac {\\frac {P}{d ^ {2} a} t _ {1}}{N _ {\\text {r e a d}}}. \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.35, + 0.892, + 0.485 + ], + "angle": 0, + "content": "Analyzing different sensing strategies. We use this SNR model to compare the performance of different depth sensors. For a fair comparison, we assume all depth sensors have equal total optical power \\( P \\), sensing at same depth \\( d \\). Their performance is then uniquely determined by \\( t_1 \\), \\( t_2 \\) and \\( a \\). For off-the-shelf full-frame projectors (Fig. 3(e)), we denote \\( a = A \\) which corresponds to the entire FOV, and \\( t_1 = t_2 = T \\) as both the sensor and the projector are active during the entire camera exposure \\( T \\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.486, + 0.892, + 0.576 + ], + "angle": 0, + "content": "Previous work [1, 13, 21, 22] has shown that, instead of flood-illuminating the entire scene, focusing optical power on different parts of the scene sequentially can lead to higher SNR. To quantitatively analyze this effect, we represent the illuminated area, laser exposure and camera exposure as a division of the full-frame case:" + }, + { + "type": "equation", + "bbox": [ + 0.527, + 0.588, + 0.891, + 0.605 + ], + "angle": 0, + "content": "\\[\na = A / R _ {a}, \\quad t _ {1} = T / R _ {t 1}, \\quad t _ {2} = T / R _ {t 2}, \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.615, + 0.891, + 0.66 + ], + "angle": 0, + "content": "where \\(R_{a}, R_{t1}, R_{t2}\\) are defined as illuminated area divisor, laser exposure divisor, camera exposure divisor, respectively. SNR is then a function of these divisors:" + }, + { + "type": "equation", + "bbox": [ + 0.52, + 0.67, + 0.891, + 0.726 + ], + "angle": 0, + "content": "\\[\nS N R = \\frac {\\frac {P}{d ^ {2} A / R _ {a}} T / R _ {t 1}}{\\sqrt {P _ {\\mathrm {s u n}} T / R _ {t 2}}} = \\underbrace {\\frac {P \\sqrt {T}}{d ^ {2} A \\sqrt {P _ {\\mathrm {s u n}}}}} _ {c} \\underbrace {\\frac {R _ {a} \\sqrt {R _ {t 2}}}{R _ {t 1}}} _ {X}, \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.735, + 0.891, + 0.825 + ], + "angle": 0, + "content": "where \\( c \\) is the SNR of full-frame projection. \\( X \\) is a factor that describes how each method compares with the baseline full-frame projection. It is difficult to optimize \\( X \\) directly since not every combination of \\( (R_{a}, R_{t1}, R_{t2}) \\) is feasible in hardware. Nevertheless, it provides a useful tool to characterize different sensing strategies." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.826, + 0.892, + 0.901 + ], + "angle": 0, + "content": "State-of-the-art systems such as Episcan3D [22] implement this idea as a line scanning scheme, as shown in Fig. 3(c). If we assume the total illuminated region of line scanning is the same as full-pattern, then \\( R_{a} = R_{t1} = R_{t2} = N \\), where \\( N \\) is the number of scanlines (typically" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "5056" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.084, + 0.09, + 0.892, + 0.393 + ], + "angle": 0, + "content": "
Point scanningLine scanning(e) Full-frame pattern(f) Adaptive (Proposed)
(a) V1: Synced(b) V2: Unsynced(c) V1: Synced(d) V2: Unsynced
*Typically, N = 102~103Single pixel 2D MEMS2D MEMS1D laser + 1D MEMS or 2D rolling-shutter cam1D laser + 1D MEMS2D projector2D flexible projector
Illuminated Area Divisor (Ra)N2N2NN1N
Laser Exposure Divisor (Rt1)N2N2NN11
Camera Exposure Divisor (Rt2)N21N111
Same power, sensing at same distance:
SNR = c Ra√Rt2/Rt1cNcc√NcccN
Same maximum sensing distance dmax:
Power Pkp d2maxN-1kp d2maxkp d2maxN-0.5kp d2maxkp d2maxkp d2maxN-1
Eye-safety distance lminklddmaxN0.25klddmaxN0.75klddmaxN0.125klddmaxN0.375klddmaxklddmax
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.403, + 0.893, + 0.446 + ], + "angle": 0, + "content": "Figure 3. Schematic diagrams and analysis of various sensing strategies. When ambient light noise dominates, the proposed adaptive sensing achieves best SNR. To achieve the same maximum sensing distance, adaptive sensing consumes least power while having shortest eye-safety distance. (Best performing methods in each row are highlighted in blue)" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.471, + 0.471, + 0.503 + ], + "angle": 0, + "content": "\\(10^{2} - 10^{3})\\). By plugging these terms into Eq. 5, the SNR of line scanning is \\(X = \\sqrt{N}\\) times higher than the full-pattern." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.518, + 0.47, + 0.745 + ], + "angle": 0, + "content": "One interesting question is: Can we push this idea further and scan a dot at a time? This point scanning idea can be implemented with a co-located laser and single-pixel sensor deflected by a 2D MEMS mirror. Using the same assumption, \\( R_{a} = R_{t1} = R_{t2} = N_{p} \\), where \\( N_{p} \\) is the number of dots (typically \\( N_{p} = N^{2} = 10^{4} - 10^{6} \\)). Fig. 3(a) shows that dot scanning does offer a higher SNR and is \\( X = N \\) times higher than the full-pattern. Notice that this SNR benefit comes from the fact that the laser and the sensor are synchronized: The sensor only receives light from the area illuminated by the laser at any instant. For their unsynchronized counterparts where the sensor is a 2D camera that captures the entire 2D FOV during the whole imaging time (easier to implement in hardware), their SNR is exactly the same as the full-pattern approach (Fig. 3(b,d))." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.781, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Adaptive sensing. Our adaptive sensor projects a static pattern that does not change during the entire exposure, i.e. \\( R_{t1} = R_{t2} = 1 \\). However, the optical power is concentrated to a small ROI, which we assume can be as small as one line in the line-scanning approach \\( R_{a} = N \\). As shown in Fig. 3(f), our adaptive sensor has a \\( N_{l} \\) times higher SNR than the full-pattern approach. In summary, we observed that \\( SNR_{\\mathrm{adaptive}} = SNR_{\\mathrm{point}} \\gg SNR_{\\mathrm{line}} \\gg SNR_{\\mathrm{full}} \\)." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.471, + 0.885, + 0.487 + ], + "angle": 0, + "content": "3.2. Comparison of Power, Range, and Eye-Safety" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.494, + 0.892, + 0.601 + ], + "angle": 0, + "content": "Sec. 3.1 analyzes the SNR for different sensors at the same depth. However, this analysis is insufficient, since increasing SNR and the maximum range implies a higher risk of eye injury. In this section, we discuss how this model can be extended to analyze the trade-off between power, range and eye-safety. We consider two key constraints: maximum sensing distance and minimum eye-safety distance." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.603, + 0.892, + 0.664 + ], + "angle": 0, + "content": "Maximum sensing distance. We assume that for reliable estimation of the depth, the SNR must be greater than a minimum detection threshold \\(\\mathrm{SNR}_{\\mathrm{thres}}\\). The equality holds when the maximum sensing distance \\(d = d_{max}\\) is reached," + }, + { + "type": "equation", + "bbox": [ + 0.597, + 0.674, + 0.891, + 0.71 + ], + "angle": 0, + "content": "\\[\nS N R _ {\\text {t h r e s}} = \\frac {P \\sqrt {T}}{d _ {\\max } ^ {2} A \\sqrt {P _ {s u n}}} X. \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.712, + 0.714, + 0.728 + ], + "angle": 0, + "content": "Rearranging this equation gives" + }, + { + "type": "equation", + "bbox": [ + 0.528, + 0.733, + 0.892, + 0.758 + ], + "angle": 0, + "content": "\\[\n\\boxed {P = k _ {p} \\cdot d _ {\\max } ^ {2} X ^ {- 1} = k _ {p} \\cdot d _ {\\max } ^ {2} R _ {a} ^ {- 1} R _ {t 1} R _ {t 2} ^ {- 0. 5},} \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.765, + 0.792, + 0.779 + ], + "angle": 0, + "content": "where \\(k_{p}\\) is a method-independent constant." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.782, + 0.892, + 0.827 + ], + "angle": 0, + "content": "Minimum eye-safety distance. A minimum eye-safety distance can be defined when the maximum permissible exposure (MPE, defined in ANSI Z136) is reached:" + }, + { + "type": "equation", + "bbox": [ + 0.625, + 0.832, + 0.891, + 0.866 + ], + "angle": 0, + "content": "\\[\n\\frac {P}{l _ {\\min } ^ {2} a} = \\frac {M P E \\left(t _ {1}\\right)}{t _ {1}}, \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.871, + 0.892, + 0.901 + ], + "angle": 0, + "content": "It is considered dangerous for eyes to be exposed at a distance shorter than \\(l_{\\min}\\). Intuitively, the shorter the minimal" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "5057" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.122 + ], + "angle": 0, + "content": "eye-safety distance is, the more eye-safe the device is. We expand MPE based on definitions from ANSI Z136:" + }, + { + "type": "equation", + "bbox": [ + 0.078, + 0.132, + 0.476, + 0.179 + ], + "angle": 0, + "content": "\\[\n\\frac {P}{l _ {\\operatorname* {m i n}} ^ {2} a} = \\frac {M P E (t _ {1})}{t _ {1}} = \\frac {C _ {\\lambda} t _ {1} ^ {0 . 7 5} 1 0 ^ {- 3} (\\mathrm {J} \\cdot \\mathrm {c m} ^ {- 2})}{t _ {1}} = k _ {e} t _ {1} ^ {- 0. 2 5}, \\tag {9}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.18, + 0.47, + 0.226 + ], + "angle": 0, + "content": "where \\( k_{e} \\) is a method-independent constant. Please find a detailed discussion on this analytic expression in the supplementary report. Plug in Eq. 4 and rearrange," + }, + { + "type": "equation", + "bbox": [ + 0.175, + 0.235, + 0.469, + 0.254 + ], + "angle": 0, + "content": "\\[\nl _ {\\min } = k _ {l} \\cdot P ^ {0. 5} R _ {a} ^ {0. 5} R _ {t 1} ^ {- 0. 1 2 5}, \\tag {10}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.266, + 0.367, + 0.28 + ], + "angle": 0, + "content": "where \\( k_{l} \\) is a method-independent constant." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.284, + 0.469, + 0.406 + ], + "angle": 0, + "content": "Comparing different sensors. From Eq. 7 and Eq. 10, it is clear that for a depth sensing method, specifying one quantity among \\( P \\), \\( d_{\\mathrm{max}} \\) and \\( l_{\\mathrm{min}} \\) will also determine the other two. We thus focus on the following question: To reach the same maximum sensing distance \\( d_{\\mathrm{max}} \\), what is the power consumption \\( P \\) and eye-safety distance \\( l_{\\mathrm{min}} \\) of each method? This is a key problem for consumer devices with limited power budget. Plug Eq. 7 into Eq. 10 and rearrange:" + }, + { + "type": "equation", + "bbox": [ + 0.165, + 0.417, + 0.469, + 0.442 + ], + "angle": 0, + "content": "\\[\n\\boxed {l _ {\\min } = k _ {l d} \\cdot d _ {\\max } R _ {t 1} ^ {0. 3 7 5} R _ {t 2} ^ {- 0. 2 5},} \\tag {11}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.448, + 0.374, + 0.462 + ], + "angle": 0, + "content": "where \\( k_{ld} \\) is a method-independent constant." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.463, + 0.469, + 0.629 + ], + "angle": 0, + "content": "Fig. 3 summarizes the results derived from Eq. 7 and Eq. 11 for different sensing methods. Full-frame pattern method is the most eye-safe but consumes the most power. Conversely, point scanning (synced) consumes the least power but is also the least eye-safe, which highly limits its application in consumer devices (e.g., laser projectors). Line scanning (synced) strikes the sweet middle ground, which extends the distance by a large margin while maintaining eye safety. Finally, by concentrating to a small ROI, the proposed adaptive method consumes the least power and achieves the best eye-safety." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.63, + 0.469, + 0.704 + ], + "angle": 0, + "content": "To intuitively showcase this advantage, we assume \\( N \\sim 100 \\) to 500, which is consistent with the spatial resolution of most concurrent 3D sensors. For high-resolution depth sensors with \\( N > 1000 \\), the gain is even greater. At the same maximum sensing distance, adaptive sensing:" + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.705, + 0.468, + 0.734 + ], + "angle": 0, + "content": "- has the same eye-safety distance as full-frame sensors, while consuming \\( N^{-1} \\) (0.01 to 0.002)× lower power." + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.735, + 0.468, + 0.779 + ], + "angle": 0, + "content": "- has \\( N^{-0.125} \\) (0.56 to 0.46) × shorter (better) eye-safety distance as line-scanning, while consuming \\( N^{-0.5} \\) (0.1 to 0.04) × lower power." + }, + { + "type": "list", + "bbox": [ + 0.096, + 0.705, + 0.468, + 0.779 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.781, + 0.469, + 0.901 + ], + "angle": 0, + "content": "It is important to mention that these calculations are based on the assumption that the illuminated area for adaptive sensing is the same as line scanning: \\( R_{a} = N \\). In practice, this area may be larger depending on the scene and application. The adaptive projector (e.g., SLM) may also have a limited light efficiency, which gives an effectively smaller \\( R_{a} \\) and thus lower SNR. Nonetheless, at the same maximum distance, adaptive sensing still has a power benefit as" + }, + { + "type": "table", + "bbox": [ + 0.502, + 0.09, + 0.899, + 0.166 + ], + "angle": 0, + "content": "
SNRPlmin
V1cNkp d2maxN-1kldmax
V1-acNK-1kp d2maxN-1KkldmaxK0.375
V1-bcNK-0.5kp d2maxN-1K0.5kldmaxK0.125
" + }, + { + "type": "table_caption", + "bbox": [ + 0.572, + 0.177, + 0.819, + 0.19 + ], + "angle": 0, + "content": "Table 1. Variations of adaptive sensing." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.219, + 0.892, + 0.281 + ], + "angle": 0, + "content": "long as \\( R_{a} > \\sqrt{N} \\), and it always has a eye-safety benefit since \\( l_{\\min} \\) is independent of \\( R_{a} \\). The theoretical analysis forms the foundation for the proposed adaptive 3D sensing. We validate the analysis in a real-world prototype in Sec. 5." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.287, + 0.892, + 0.513 + ], + "angle": 0, + "content": "Disjoint ROIs. So far, we assume an ideal flexible projector which can project light to arbitrarily-shaped, even disjoint ROIs simultaneously. In practice, certain hardware implementations do not have this capability (an example is discussed in Sec. 4.2). To this end, we propose a more flexible scanning strategy: During the camera exposure, the system scans \\(K\\) disjoint ROIs sequentially (typically \\(2 \\leq K \\leq 5\\)). This adaptive V1-a method consumes slightly more power and has a slightly longer eye-safety distance (Tab. 1). Another option is to divide the camera exposure into \\(K\\) shorter exposures, and the system scans a single ROI during each exposure. This adaptive V1-b method performs comparably as V1, but requires a \\(K\\) times higher camera frame rate. Please refer to the supplementary technical report for more design variations and detailed comparisons." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.531, + 0.869, + 0.548 + ], + "angle": 0, + "content": "4. Implementation of Adaptive Illumination" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.558, + 0.892, + 0.724 + ], + "angle": 0, + "content": "Now that we have theoretically analyzed the benefit of the proposed adaptive illumination, how can the proposed adaptive illumination be realized? Notice that this is not a trivial problem. The hardware implementation must satisfy two criteria: (1) The system can redistribute the optical power to a small ROI (guided by an attention map), and (2) This ROI can be projected to different parts of the scene flexibly and in real-time (e.g., 30Hz). A common LCD or DLP projector satisfies (2) but does not satisfy (1). In this section, we propose two hardware configurations that satisfy both conditions." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.737, + 0.774, + 0.753 + ], + "angle": 0, + "content": "4.1. Implementation 1: Phase SLM" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.761, + 0.892, + 0.868 + ], + "angle": 0, + "content": "Fig. 4(a) shows our SLM-based implementation. Our holographic projection approach is inspired by recent work on holographic near-eye 3D displays [20]. Specifically, a hologram to be reproduced by the SLM is decomposed as a sum of sub-holograms, where each sub-hologram diffracts light to a single object point in the scene. In [20], each sub-hologram is created using a lens phase function:" + }, + { + "type": "equation", + "bbox": [ + 0.52, + 0.882, + 0.892, + 0.902 + ], + "angle": 0, + "content": "\\[\nf _ {n} ^ {\\text {l e n s}} (\\mathbf {X}) = e ^ {j 2 \\pi \\sqrt {(X - x _ {n}) ^ {2} + (Y - y _ {n}) ^ {2} + (Z - z _ {n}) ^ {2})} / \\lambda , \\tag {12}\n\\]" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "5058" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.144, + 0.091, + 0.482, + 0.191 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.213, + 0.199, + 0.396, + 0.211 + ], + "angle": 0, + "content": "(a) Phase SLM-based implementation" + }, + { + "type": "image", + "bbox": [ + 0.522, + 0.096, + 0.828, + 0.19 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.581, + 0.199, + 0.738, + 0.21 + ], + "angle": 0, + "content": "(b) MEMS + DOE-based method" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.224, + 0.895, + 0.281 + ], + "angle": 0, + "content": "Figure 4. Hardware implementations. (a) Our first implementation is based on a phase-only SLM, which can redistribute light to arbitrarily-shaped, even disjointed ROIs. (b) Our second implementation is based on a DOE pattern generator with a 2D MEMS mirror. It has less flexibility and can only concentrate on one fixed-shape ROI at a time, but it benefits from low cost, simple optics and small form factor which makes it potentially easier to be miniaturized." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.307, + 0.471, + 0.355 + ], + "angle": 0, + "content": "where \\((X,Y,Z)\\) is the 3D position of each pixel in the subhologram, \\((x_{n},y_{n},z_{n})\\) is the 3D position of the \\(n\\)-th object point, and \\(\\lambda\\) is the light wavelength. The full hologram is," + }, + { + "type": "equation", + "bbox": [ + 0.209, + 0.358, + 0.47, + 0.398 + ], + "angle": 0, + "content": "\\[\nH (\\mathbf {X}) = \\sum_ {n = 1} ^ {N} f _ {n} ^ {\\text {l e n s}}. \\tag {13}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.403, + 0.47, + 0.554 + ], + "angle": 0, + "content": "This lens phase function mimics a lens that focuses light to the object point at the correct depth, which works well for near-eye displays. One limitation of this lens phase function approach is that light is only redistributed locally. This is because the SLM can only reproduce a smooth hologram due to the Nyquist frequency determined by the finite pixel pitch. However, \\( f^{\\mathrm{lens}} \\) varies rapidly for off-center pixels (i.e. \\( X, Y \\) far away from \\( x_{n}, y_{n} \\)), causing aliasing artifacts. Therefore, sub-holograms of much smaller sizes must be used, which greatly limits the light efficiency." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.555, + 0.47, + 0.586 + ], + "angle": 0, + "content": "To alleviate this limitation, we propose the use of mirror phase function:" + }, + { + "type": "equation", + "bbox": [ + 0.092, + 0.59, + 0.47, + 0.632 + ], + "angle": 0, + "content": "\\[\nf _ {n} ^ {\\text {m i r r o r}} (\\mathbf {X}) = e ^ {j \\left(X \\cdot x _ {n} + Y \\cdot y _ {n}\\right)}, H (\\mathbf {X}) = \\sum_ {n = 1} ^ {N} f _ {n} ^ {\\text {m i r r o r}}. \\tag {14}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.635, + 0.47, + 0.756 + ], + "angle": 0, + "content": "The mirror phase function corresponds to a smooth phase map linear in terms of \\( X, Y \\), and can be implemented on the SLM without aliasing. It allows us to use each sub-hologram as a mirror that reflects light to the right direction. By taking the sum of sub-holograms that reflect to different directions, desired projection patterns can be achieved. Please see the supplementary for detailed optical diagrams and discussion." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.759, + 0.471, + 0.879 + ], + "angle": 0, + "content": "Conversion to phase-only holograms. Notice that Eq. 14 creates a hologram with both amplitudes and phases being spatially-variant, which cannot be implemented on a phase-only SLM. Several approaches [12, 16] have been proposed to convert such a full hologram to a phase-only hologram. Fortunately, our goal is not to project a high-quality image, and simple amplitude discarding is sufficient to project unique texture to the scene:" + }, + { + "type": "equation", + "bbox": [ + 0.209, + 0.885, + 0.47, + 0.904 + ], + "angle": 0, + "content": "\\[\nH _ {\\text {p h a s e}} = \\operatorname {A r g} [ H ]. \\tag {15}\n\\]" + }, + { + "type": "image_caption", + "bbox": [ + 0.607, + 0.309, + 0.762, + 0.32 + ], + "angle": 0, + "content": "Implementation 1: Phase SLM" + }, + { + "type": "image", + "bbox": [ + 0.547, + 0.322, + 0.822, + 0.412 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.613, + 0.427, + 0.78, + 0.438 + ], + "angle": 0, + "content": "Implementation 2: MEMS + DOE" + }, + { + "type": "image", + "bbox": [ + 0.547, + 0.44, + 0.822, + 0.529 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.543, + 0.894, + 0.598 + ], + "angle": 0, + "content": "Figure 5. Hardware prototypes. (Upper) Spatial Light Modulator (SLM) implementation. (Lower) Micro-electromechanical (MEMS) mirror + diffractive optical element (DOE) implementation." + }, + { + "type": "image", + "bbox": [ + 0.501, + 0.622, + 0.892, + 0.735 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.744, + 0.894, + 0.856 + ], + "angle": 0, + "content": "Figure 6. Examples of emulating full frame, line scanning, and adaptive sensors on a phase only spatial light modulator. Note that the full frame and adaptive patterns are captured within the full exposure time, while each line in the line scanning pattern is captured within \\(1/N\\) of the time. We scale the intensities for visualization. Note that the bright center dot is caused by the SLM DC term, and can be mitigated with additional optical filters and manufacturing processes." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.871, + 0.893, + 0.902 + ], + "angle": 0, + "content": "Efficient implementation. The mirror phase function consists of simple arithmetic operations on large matri" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "5059" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.084, + 0.09, + 0.895, + 0.395 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.404, + 0.893, + 0.475 + ], + "angle": 0, + "content": "Figure 7. Comparison between sensing strategies. Our approach is more robust to ambient light than line scanning and full frame sensors; notice how our adaptive approach degrades less than line scanning and full frame from low ambient lighting (700 lux) to high ambient lighting (4000 lux). We keep sensor settings constant for each low ambient-high ambient pair. The total number of dots in the adaptive method (ours), line scanning and full frame is around 150, \\(108 \\times 150\\) and \\(150^2\\), respectively. Zoom in to see the red dots in the camera images." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.486, + 0.473, + 0.637 + ], + "angle": 0, + "content": "ces, which can be implemented efficiently on a GPU. We implement our hologram generator in CUDA and render the resulting hologram phase from the frame-buffer to the SLM using OpenGL-CUDA interoperability. On a NVIDIA Jetson Nano, an embedded system-on-module with a Tegra X1 Maxwell 256-core GPU and limited computing resources, we are able to generate 1080p holograms with around 100 points or less at 30 fps. Our implementation and simulator can be found at https://github.com/btilmon/holoCu." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.647, + 0.378, + 0.663 + ], + "angle": 0, + "content": "4.2. Implementation 2: MEMS + DOE" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.671, + 0.47, + 0.822 + ], + "angle": 0, + "content": "Our second implementation is to adjust the beam incident angle of a diffractive optical element (DOE) with a MEMS mirror, as shown in Fig. 4(b). DOE offers a cheap, energy-efficient solution for random dot projection in single-shot structured light (Kinect V1) or active stereo (RealSense). While those systems use a DOE that covers the entire scene, we use a small FOV (\\(\\approx 5^{\\circ}\\)) that only corresponds to a small ROI. By rotating the MEMS mirror, the deflected laser beam hits the DOE at different angles, thus generating a dot pattern at different ROIs of the scene." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.825, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Comparison with phase SLM. The MEMS + DOE implementation is less flexible than the SLM implementation since the hologram shape is fixed (determined by the DOE phase pattern). This is schematically shown in Fig. 4: While SLM can illuminate ROIs of various shapes (P1-" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.486, + 0.893, + 0.622 + ], + "angle": 0, + "content": "P3), MEMS + DOE can only create the same shape shifted across the scene. Moreover, while the SLM can redistribute the optical power over two disjoint ROIs during the same camera exposure (P4), different ROIs are scanned and imaged sequentially by the MEMS mirror, which slightly decreases the SNR (see Sec. 3.2 for detailed analysis). Nevertheless, the MEMS + DOE approach benefits from low cost, simple optics and small form factor, which are important factors for mobile and wearable devices." + }, + { + "type": "image", + "bbox": [ + 0.507, + 0.638, + 0.895, + 0.819 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.827, + 0.895, + 0.898 + ], + "angle": 0, + "content": "Figure 8. Outdoor active depth sensing under 50 kilolux direct sunlight with Phase SLM. Our sensor works outdoors under direct sunlight. We show results up to 2 meters but believe this range could be extended with further SLM optical engineering. Zoom in to see the red dots in the camera images." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "5060" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.086, + 0.093, + 0.468, + 0.23 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.242, + 0.468, + 0.297 + ], + "angle": 0, + "content": "Figure 9. MEMS + DOE implementation. The MEMS voltages are updated to direct the dot pattern onto the predominant textureless region in both frames. Zoom in the camera images to see the red dots." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.309, + 0.208, + 0.325 + ], + "angle": 0, + "content": "5. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.334, + 0.468, + 0.53 + ], + "angle": 0, + "content": "Hardware prototypes. Fig. 5 shows both hardware prototypes of our proposed method. We use two FLIR BFS-U3-16S2C-CS cameras equipped with \\(20\\mathrm{mm}\\) lenses as a stereo pair. Our SLM implementation uses a Holoyeye GAEA LCoS (phase-only) SLM, which can display 4K phase maps at 30 frames per second. Our MEMS + DOE implementation uses a \\(0.8\\mathrm{mm}\\) diameter bonded Mirrorcle MEMS Mirror. A random dot DOE with a small FOV is preferred. Here, we used a Holoyeye DE-R 339 DOE that produces a periodic 6x6 dot pattern with \\(5^{\\circ}\\) FOV instead and we tilt the DOE such that the pattern is still unique locally on the epipolar line. Please refer to the supplementary report for detailed setup and calibration procedures." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.535, + 0.468, + 0.686 + ], + "angle": 0, + "content": "Attention map and depth estimation. We adopt classical semi global block matching for depth estimation [10]. The attention map is determined by randomly choosing pixels that do not have a valid depth value from the depth map computed from passive images. In practice, the attention map can be conditioned by the application such that illumination is only needed within the regions where AR objects are inserted. Our goal is to present a general sensor that can fit into many different perception systems and improve active depth sensing." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.69, + 0.468, + 0.81 + ], + "angle": 0, + "content": "Comparison between sensing strategies. We emulate full-frame and line-scanning strategies on our SLM implementation and compare them with our adaptive sensing strategy. An example of each emulated sensor can be found in Fig. 6. For line scanning, we compute and project the hologram of the dot pattern line-by-line. We capture the image for each line individually and stitch the corresponding camera rows together into a single image." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.811, + 0.468, + 0.9 + ], + "angle": 0, + "content": "Fig. 7 shows the results for three different scenes. All scenes are illuminated with the same ambient lighting and laser power. Laser power, exposure time and illuminated area are chosen to ensure fair comparison. Due to the dominating photon noise from the ambient light, full-frame and line scanning methods have a low SNR. As a result, depth" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.891, + 0.167 + ], + "angle": 0, + "content": "estimation fails in the textureless regions. Since the proposed adaptive sensing technique concentrates light to the textureless regions, it achieves much higher SNR and obtains higher-quality depth maps, which validates our theoretical analysis." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.173, + 0.892, + 0.308 + ], + "angle": 0, + "content": "Outdoor depth sensing under direct sunlight. Fig. 8 demonstrates our Phase SLM prototype working outdoors under 50 kilolux direct sunlight. We can rely on passive stereo to compute depth for the majority of the scene and only project light where necessary, such as the white textureless pot. We also show a distance test of the Phase SLM prototype at 2 meters. We believe this distance could be increased with further SLM optical engineering in future work." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.315, + 0.892, + 0.405 + ], + "angle": 0, + "content": "MEMS + DOE implementation. Fig. 9 demonstrates our MEMS + DOE prototype. The dot pattern is projected to a textureless object which improves the disparity compared to passive stereo. When the system moves to another location at \\( t_1 \\), it analyzes the new captured images and directs the ROI to the new position of the textureless object." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.423, + 0.75, + 0.438 + ], + "angle": 0, + "content": "6. Limitations and Discussion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.45, + 0.892, + 0.614 + ], + "angle": 0, + "content": "Optical power vs computation power. Although we do not explicitly compare the optical power savings from adaptive sensing with the additional computation power needed for computing the attention map and projector control signal (e.g., phase map for SLM), we show that such computations consist of basic arithmetic operations and can be implemented on embedded systems like NVIDIA Jetson Nano, suggesting that our approach can be deployed on increasingly available mobile GPUs. Our system will have even higher benefits for outdoor applications where optical power dominates." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.622, + 0.891, + 0.743 + ], + "angle": 0, + "content": "Learning-based attention map and depth estimation. In this work, we use simple, low-complexity texture analysis and semi global matching for attention map and depth estimation. It is possible to design neural networks to achieve better depth estimation, at the cost of higher computation. Our focus in on validating the proposed adaptive sensing as a promising novel sensing strategy, and we expect more practical algorithms to be developed in future work." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.749, + 0.891, + 0.839 + ], + "angle": 0, + "content": "Other active depth sensing mechanisms. Although this paper only shows hardware implementations for active stereo, the adaptive sensing strategy can be applied to other depth sensing mechanisms such as single/multi-shot structured light, direct/indirect ToF, FMCW Lidar, etc., which can be a promising future direction." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.891, + 0.9 + ], + "angle": 0, + "content": "Acknowledgements. The authors acknowledge partial funding from the Office of Naval Research through ONR N00014-18-1-2663 and the National Science Foundation through NSF 1942444." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.514, + 0.956 + ], + "angle": 0, + "content": "5061" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.116, + 0.47, + 0.171 + ], + "angle": 0, + "content": "[1] Supreeth Achar, Joseph R. Bartels, William L. 'Red' Whittaker, Kiriakos N. 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IEEE, 2003. 2" + }, + { + "type": "list", + "bbox": [ + 0.08, + 0.093, + 0.47, + 0.528 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.956 + ], + "angle": 0, + "content": "5063" + } + ] +] \ No newline at end of file diff --git a/2023/Energy-Efficient Adaptive 3D Sensing/84eaed71-d9fd-4068-b870-f6dc2370efb9_origin.pdf b/2023/Energy-Efficient Adaptive 3D Sensing/84eaed71-d9fd-4068-b870-f6dc2370efb9_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..daa7f4de54292fb371dee54d699bf973dfbed349 --- /dev/null +++ b/2023/Energy-Efficient Adaptive 3D Sensing/84eaed71-d9fd-4068-b870-f6dc2370efb9_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:b6ea4a53844735670ce8f70ffa04c4ac09ca679c7d878bda61770ac1005d20ea +size 8836675 diff --git a/2023/Energy-Efficient Adaptive 3D Sensing/full.md b/2023/Energy-Efficient Adaptive 3D Sensing/full.md new file mode 100644 index 0000000000000000000000000000000000000000..5d8dd6db14998124a401182afaefb3ded357ebcc --- /dev/null +++ b/2023/Energy-Efficient Adaptive 3D Sensing/full.md @@ -0,0 +1,320 @@ +# Energy-Efficient Adaptive 3D Sensing + +Brevin Tilmon $^{1*}$ Zhanghao Sun $^{2}$ Sanjeev J. Koppal $^{1}$ Yicheng Wu $^{3}$ Georgios Evangelidis $^{3}$ Ramzi Zahreddine $^{3}$ Gurunandan Krishnan $^{3}$ Sizhuo Ma $^{3\dagger}$ Jian Wang $^{3\dagger}$ $^{1}$ University of Florida $^{2}$ Stanford University $^{3}$ Snap Inc. + +# Abstract + +Active depth sensing achieves robust depth estimation but is usually limited by the sensing range. Naively increasing the optical power can improve sensing range but induces eye-safety concerns for many applications, including autonomous robots and augmented reality. In this paper, we propose an adaptive active depth sensor that jointly optimizes range, power consumption, and eye-safety. The main observation is that we need not project light patterns to the entire scene but only to small regions of interest where depth is necessary for the application and passive stereo depth estimation fails. We theoretically compare this adaptive sensing scheme with other sensing strategies, such as full-frame projection, line scanning, and point scanning. We show that, to achieve the same maximum sensing distance, the proposed method consumes the least power while having the shortest (best) eye-safety distance. We implement this adaptive sensing scheme with two hardware prototypes, one with a phase-only spatial light modulator (SLM) and the other with a micro-electro-mechanical (MEMS) mirror and diffractive optical elements (DOE). Experimental results validate the advantage of our method and demonstrate its capability of acquiring higher quality geometry adaptively. Please see our project website for video results and code: https://btilmon.github.io/e3d.html. + +# 1. Introduction + +Active 3D depth sensors have diverse applications in augmented reality, navigation, and robotics. Recently, these sensor modules are widely used in consumer products, such as time-of-flight (e.g., Lidar [15]), structured light (e.g., Kinect V1 [18]) and others. In addition, many computer vision algorithms have been proposed to process the acquired data for downstream tasks such as 3D semantic understanding [29], object tracking [17], guided upsampling in SLAM [24], etc. + +![](images/3fa6cf467037b4cfd3a2694c4f3c0bcc716d624b769220478dfa87298f96b647.jpg) +(a) Depth sensing on wearables faces challenges + +![](images/137dc01153f8ae057a61a80f64024fd42cbd7db182aa1a52f3f68ab5dc31508a.jpg) + +![](images/1c347786db62a9044cc5e15a5a3bf2e02e9191d3b5148bc4ae7c1192473172bd.jpg) +(b) Our system with adaptive projection +Figure 1. Energy-efficient adaptive 3D sensing. (a) Depth sensing devices have three key optimization goals: minimizing the power consumption and eye-safety distance while maximizing sensing distance. However, these goals are coupled to each other. (b) We propose a novel adaptive sensing method with an active stereo setup and a projector that can redistribute the light energy and project the pattern only to the required regions (e.g., textureless regions). (c) The proposed approach outperforms previous methods including full-frame pattern systems (like Intel RealSense) and line-scanning systems (like Episcan3D [22]): When the maximum sensing distance is the same, the required power is much less and the eye-safety distance is also shorter. + +![](images/1b0bbb14711549d34ef2e2584427c7ee7df71d1a4bda1e35f5d1ef2f5da7cdc8.jpg) +(c) Comparison + +Unlike stereo cameras that only sense reflected ambient light passively, active depth sensors illuminate the scene with modulated light patterns, either spatially, temporally, or both. The illumination encodings allow robust estimation of scene depths. However, this also leads to three shortcomings: First, active depth sensors consume optical power, burdening wearable devices that are on a tight power budget. Second, the number of received photons reflected back from the scene drops with inverse-square relationship + +![](images/3d3f63ee29f35666096c5fd5c85d56a03df34fc430941553517bef2a5533148b.jpg) + +![](images/1d0c9b5ff8bf5b4171a427b394817ffd82d154b9d57c311514cd78487b3197d4.jpg) +e.g., region of interest & textureless region + +![](images/5614de34bbae799f106f0be14cc3c1de9124d48caab850ffdde3ab525a1f9f6b.jpg) + +![](images/fab487e22e6ced4ebcb7350fa62cd98af6980613890171e2f95c4bd70e230e1e.jpg) +Figure 2. Method overview. Our system consists of a stereo-camera pair and an adaptive projector. The system first captures an image of the scene (Step 1) and then computes an attention map to determine the ROI (Step 2). This attention map is used to compute the control signal for the specific projector implementation (Step 3) such that light is only projected to the ROI (Step 4). A depth map is then computed from the new stereo images, which can be used for applications such as augmented reality (Step 5). + +![](images/6df9b4459bebd97e46cb7342c971bd2acd5a17ce17390e6ee07c658c085e277d.jpg) + +![](images/bd7a0ab7b5111129f96ab97671c7f8199cb6ed1acc0780c20be0bb92464653d8.jpg) + +to scene depth. The maximum sensing distance is thereby limited by the received signal-to-noise ratio (SNR). Third, strong, active light sources on the device may unintentionally hurt the user or other people around. For consumer devices, this constraint can be as strict as ensuring safety when a baby accidentally stares at the light source directly. Interestingly, these three factors are often entangled with each other. For example, naively increasing range by raising optical power makes the device less eye-safe. An active 3d sensor would benefit from the joint optimization of these three goals, as illustrated in Fig. 1(a). + +In this paper, we present an adaptive depth-sensing strategy. Our key idea is that the coded scene illumination need not be sent to the entire scene (Fig. 1(b)). Intuitively, by limiting the illumination samples, the optical power per sample is increased, therefore extending the maximum sensing distance. This idea of adaptive sensing is supported by three observations: First, illumination samples only need to be sent to parts of a scene where passive depth estimation fails (e.g., due to lack of texture). Second, depth estimation is often application-driven, e.g., accurate depths are only needed around AR objects to be inserted into the scene. Finally, for video applications, sending light to regions where depths are already available from previous frames is redundant. Based on these observations, we demonstrate this adaptive idea with a stereo-projector setup (i.e., active stereo [4,9,34]), where an attention map is computed from the camera images for efficient light redistribution. + +To quantitatively understand the benefits of our approach, we propose a sensor model that analytically characterizes various sensing strategies, including full-frame (e.g., RealSense [19]), line-scanning (e.g., Episcan3D [22]), point-scanning (e.g., Lidar [25]) and proposed adaptive sensing. We establish, for the first time, a framework that jointly analyzes the power, range, and eye-safety of different strategies and demonstrates that, for the same maximum sensing distance, adaptive sensing consumes the least power while achieving the shortest (best) eye-safety distance. + +Note that the realization of scene-adaptive illumination is not trivial: Common off-the-shelf projectors simply block part of the incident light, which wastes optical power. We propose two hardware implementations for adaptive illumination: One is inspired by digital holography, which uses Liquid Crystal on Silicon (LCoS) Spatial Light Modulators (SLM) to achieve free-form light projection. The other implementation uses diffractive optical elements (DOE) to generate dot patterns in a local region of interest (ROI), which is directed to different portions of the scene by a micro-electro-mechanical (MEMS) mirror. + +Our contributions are summarized as follows: + +- Adaptive 3D sensing theory: We propose adaptive 3D sensing and demonstrate its advantage in a theoretical framework that jointly considers range, power and eye-safety. +- Hardware implementation: We implement the proposed adaptive active stereo approach with two hardware prototypes based on SLM and MEMS + DOE. +- Experimental validation: Real-world experimental results validate that our sensor can adapt to the scene and outperform existing sensing strategies. + +# 2. Related Work + +Active 3D sensing with ambient light noise. Various techniques have been proposed to address photon noise due to strong ambient light (e.g., sunlight), such as choosing a wavelength where sunlight is weak [23, 32], using a polarizing filter [23]. Gupta et al. [13] uses a theoretical model to show that instead of illuminating the full scene, concentrating light on different parts of a scene sequentially improves SNR for structured light, which is demonstrated with a rotating polygonal mirror. Based on similar principles, MC3D [21] uses a MEMS/galvo-driven laser and an event camera to achieve bandwidth-efficient scanning. Episcan3D [22] and EpiToF [1] use a line-scanning laser and a synchronized rolling-shutter camera to achieve fast + +and efficient depth sensing. This paper further extends this line of work by showing that, with the freedom to adaptively illuminate part of the scene, a lower power budget is needed to achieve the same sensing range while being safer to the eyes. + +Adaptive 3D sensing. Ideas from visual attention [6, 11] have influenced vision and robotics. Efficient estimation algorithms have been shown for adaptive sensing and pointzoom-tilt (PZT) cameras [7, 33]. In the 3D sensor space, 3D light-curtains [5,8,31] represent a flexible system where curtains can be adaptively placed in the scene for robotics, and other applications [2,3,26]. Full control of the MEMS mirror enables adaptive sampling for LIDAR [25, 27, 28] and adaptive passive camera resolution for monocular depth sensing [30]. While previous adaptive systems focus on different aspects such as flexibility, frame rate, etc., this work studies the interplay between range, power, and eye-safety. + +# 3. Energy-Efficient Adaptive 3D Sensing + +The workflow of the proposed adaptive 3D sensing is shown in Fig. 2. We use an active stereo design with two cameras and a projector. The device first captures an image of the scene and computes an attention map to determine the region of interest (ROI). Hardware-specific control signals are computed from the attention map such that the projector redistributes the light to the ROI. Finally, a high-quality depth map can be calculated from captured stereo images. + +Before getting into details on how to implement this adaptive illumination in practice, let us assume an ideal flexible projector for a moment: If we can redistribute the optical power to an arbitrarily-shaped ROI, how well can it perform? We adopt a model to quantify its depth estimation performance and compare it to other existing or naively conceived active depth sensing strategies. + +# 3.1. Sensor Model and SNR Analysis + +The accuracy of various active depth sensors, including structured light, active stereo, continuous-wave time-of-flight (CW-ToF), etc., can be quantified by a single metric: the SNR of the measured light signal (projected by the active illumination source and reflected by the scene). The noise consists of the photon noise from both the signal itself and the ambient light, and the sensor readout noise, mathematically defined as follows [13, 14]: + +$$ +\begin{array}{l} S N R = \frac {\text {S i g n a l} _ {\text {p r o j e c t o r}}}{\sqrt {N _ {\text {p h o t o n} , \text {a m b i e n t}} ^ {2} + N _ {\text {p h o t o n} , \text {p r o j e c t o r}} ^ {2} + N _ {\text {r e a d}} ^ {2}}} \tag {1} \\ = \frac {\frac {P}{d ^ {2} a} t _ {1}}{\sqrt {P _ {\mathrm {s u n}} t _ {2} + \frac {P}{d ^ {2} a} t _ {1} + N _ {\mathrm {r e a d}} ^ {2}}} \\ \end{array} +$$ + +where $P$ is the optical power of the projector (assuming an albedo of 1 in the scene), $a$ is the illuminated area at unit + +distance, $d$ is the distance of the scene (thus the inverse-square fall-off), $P_{\mathrm{sun}}$ is the optical power of the ambient light, $t_1$ and $t_2$ are the duration when the laser is on and the camera is active, respectively, and $N_{\mathrm{read}}$ is the standard deviation of the read noise. Ambient light-induced photon noise dominates in outdoor scenarios and also indoors with power-limited devices, which is the major focus of the following analysis. In these situations, SNR can be simplified as: + +$$ +S N R \approx \frac {\frac {P}{d ^ {2} a} t _ {1}}{\sqrt {P _ {\mathrm {s u n}} t _ {2}}}. \tag {2} +$$ + +When readout noise dominates, which happens in a dark room or at night, SNR can be simplified as this + +$$ +S N R \approx \frac {\frac {P}{d ^ {2} a} t _ {1}}{N _ {\text {r e a d}}}. \tag {3} +$$ + +Analyzing different sensing strategies. We use this SNR model to compare the performance of different depth sensors. For a fair comparison, we assume all depth sensors have equal total optical power $P$ , sensing at same depth $d$ . Their performance is then uniquely determined by $t_1$ , $t_2$ and $a$ . For off-the-shelf full-frame projectors (Fig. 3(e)), we denote $a = A$ which corresponds to the entire FOV, and $t_1 = t_2 = T$ as both the sensor and the projector are active during the entire camera exposure $T$ . + +Previous work [1, 13, 21, 22] has shown that, instead of flood-illuminating the entire scene, focusing optical power on different parts of the scene sequentially can lead to higher SNR. To quantitatively analyze this effect, we represent the illuminated area, laser exposure and camera exposure as a division of the full-frame case: + +$$ +a = A / R _ {a}, \quad t _ {1} = T / R _ {t 1}, \quad t _ {2} = T / R _ {t 2}, \tag {4} +$$ + +where $R_{a}, R_{t1}, R_{t2}$ are defined as illuminated area divisor, laser exposure divisor, camera exposure divisor, respectively. SNR is then a function of these divisors: + +$$ +S N R = \frac {\frac {P}{d ^ {2} A / R _ {a}} T / R _ {t 1}}{\sqrt {P _ {\mathrm {s u n}} T / R _ {t 2}}} = \underbrace {\frac {P \sqrt {T}}{d ^ {2} A \sqrt {P _ {\mathrm {s u n}}}}} _ {c} \underbrace {\frac {R _ {a} \sqrt {R _ {t 2}}}{R _ {t 1}}} _ {X}, \tag {5} +$$ + +where $c$ is the SNR of full-frame projection. $X$ is a factor that describes how each method compares with the baseline full-frame projection. It is difficult to optimize $X$ directly since not every combination of $(R_{a}, R_{t1}, R_{t2})$ is feasible in hardware. Nevertheless, it provides a useful tool to characterize different sensing strategies. + +State-of-the-art systems such as Episcan3D [22] implement this idea as a line scanning scheme, as shown in Fig. 3(c). If we assume the total illuminated region of line scanning is the same as full-pattern, then $R_{a} = R_{t1} = R_{t2} = N$ , where $N$ is the number of scanlines (typically + +
Point scanningLine scanning(e) Full-frame pattern(f) Adaptive (Proposed)
(a) V1: Synced(b) V2: Unsynced(c) V1: Synced(d) V2: Unsynced
*Typically, N = 102~103Single pixel 2D MEMS2D MEMS1D laser + 1D MEMS or 2D rolling-shutter cam1D laser + 1D MEMS2D projector2D flexible projector
Illuminated Area Divisor (Ra)N2N2NN1N
Laser Exposure Divisor (Rt1)N2N2NN11
Camera Exposure Divisor (Rt2)N21N111
Same power, sensing at same distance:
SNR = c Ra√Rt2/Rt1cNcc√NcccN
Same maximum sensing distance dmax:
Power Pkp d2maxN-1kp d2maxkp d2maxN-0.5kp d2maxkp d2maxkp d2maxN-1
Eye-safety distance lminklddmaxN0.25klddmaxN0.75klddmaxN0.125klddmaxN0.375klddmaxklddmax
+ +Figure 3. Schematic diagrams and analysis of various sensing strategies. When ambient light noise dominates, the proposed adaptive sensing achieves best SNR. To achieve the same maximum sensing distance, adaptive sensing consumes least power while having shortest eye-safety distance. (Best performing methods in each row are highlighted in blue) + +$10^{2} - 10^{3})$ . By plugging these terms into Eq. 5, the SNR of line scanning is $X = \sqrt{N}$ times higher than the full-pattern. + +One interesting question is: Can we push this idea further and scan a dot at a time? This point scanning idea can be implemented with a co-located laser and single-pixel sensor deflected by a 2D MEMS mirror. Using the same assumption, $R_{a} = R_{t1} = R_{t2} = N_{p}$ , where $N_{p}$ is the number of dots (typically $N_{p} = N^{2} = 10^{4} - 10^{6}$ ). Fig. 3(a) shows that dot scanning does offer a higher SNR and is $X = N$ times higher than the full-pattern. Notice that this SNR benefit comes from the fact that the laser and the sensor are synchronized: The sensor only receives light from the area illuminated by the laser at any instant. For their unsynchronized counterparts where the sensor is a 2D camera that captures the entire 2D FOV during the whole imaging time (easier to implement in hardware), their SNR is exactly the same as the full-pattern approach (Fig. 3(b,d)). + +Adaptive sensing. Our adaptive sensor projects a static pattern that does not change during the entire exposure, i.e. $R_{t1} = R_{t2} = 1$ . However, the optical power is concentrated to a small ROI, which we assume can be as small as one line in the line-scanning approach $R_{a} = N$ . As shown in Fig. 3(f), our adaptive sensor has a $N_{l}$ times higher SNR than the full-pattern approach. In summary, we observed that $SNR_{\mathrm{adaptive}} = SNR_{\mathrm{point}} \gg SNR_{\mathrm{line}} \gg SNR_{\mathrm{full}}$ . + +# 3.2. Comparison of Power, Range, and Eye-Safety + +Sec. 3.1 analyzes the SNR for different sensors at the same depth. However, this analysis is insufficient, since increasing SNR and the maximum range implies a higher risk of eye injury. In this section, we discuss how this model can be extended to analyze the trade-off between power, range and eye-safety. We consider two key constraints: maximum sensing distance and minimum eye-safety distance. + +Maximum sensing distance. We assume that for reliable estimation of the depth, the SNR must be greater than a minimum detection threshold $\mathrm{SNR}_{\mathrm{thres}}$ . The equality holds when the maximum sensing distance $d = d_{max}$ is reached, + +$$ +S N R _ {\text {t h r e s}} = \frac {P \sqrt {T}}{d _ {\max } ^ {2} A \sqrt {P _ {s u n}}} X. \tag {6} +$$ + +Rearranging this equation gives + +$$ +\boxed {P = k _ {p} \cdot d _ {\max } ^ {2} X ^ {- 1} = k _ {p} \cdot d _ {\max } ^ {2} R _ {a} ^ {- 1} R _ {t 1} R _ {t 2} ^ {- 0. 5},} \tag {7} +$$ + +where $k_{p}$ is a method-independent constant. + +Minimum eye-safety distance. A minimum eye-safety distance can be defined when the maximum permissible exposure (MPE, defined in ANSI Z136) is reached: + +$$ +\frac {P}{l _ {\min } ^ {2} a} = \frac {M P E \left(t _ {1}\right)}{t _ {1}}, \tag {8} +$$ + +It is considered dangerous for eyes to be exposed at a distance shorter than $l_{\min}$ . Intuitively, the shorter the minimal + +eye-safety distance is, the more eye-safe the device is. We expand MPE based on definitions from ANSI Z136: + +$$ +\frac {P}{l _ {\operatorname* {m i n}} ^ {2} a} = \frac {M P E (t _ {1})}{t _ {1}} = \frac {C _ {\lambda} t _ {1} ^ {0 . 7 5} 1 0 ^ {- 3} (\mathrm {J} \cdot \mathrm {c m} ^ {- 2})}{t _ {1}} = k _ {e} t _ {1} ^ {- 0. 2 5}, \tag {9} +$$ + +where $k_{e}$ is a method-independent constant. Please find a detailed discussion on this analytic expression in the supplementary report. Plug in Eq. 4 and rearrange, + +$$ +l _ {\min } = k _ {l} \cdot P ^ {0. 5} R _ {a} ^ {0. 5} R _ {t 1} ^ {- 0. 1 2 5}, \tag {10} +$$ + +where $k_{l}$ is a method-independent constant. + +Comparing different sensors. From Eq. 7 and Eq. 10, it is clear that for a depth sensing method, specifying one quantity among $P$ , $d_{\mathrm{max}}$ and $l_{\mathrm{min}}$ will also determine the other two. We thus focus on the following question: To reach the same maximum sensing distance $d_{\mathrm{max}}$ , what is the power consumption $P$ and eye-safety distance $l_{\mathrm{min}}$ of each method? This is a key problem for consumer devices with limited power budget. Plug Eq. 7 into Eq. 10 and rearrange: + +$$ +\boxed {l _ {\min } = k _ {l d} \cdot d _ {\max } R _ {t 1} ^ {0. 3 7 5} R _ {t 2} ^ {- 0. 2 5},} \tag {11} +$$ + +where $k_{ld}$ is a method-independent constant. + +Fig. 3 summarizes the results derived from Eq. 7 and Eq. 11 for different sensing methods. Full-frame pattern method is the most eye-safe but consumes the most power. Conversely, point scanning (synced) consumes the least power but is also the least eye-safe, which highly limits its application in consumer devices (e.g., laser projectors). Line scanning (synced) strikes the sweet middle ground, which extends the distance by a large margin while maintaining eye safety. Finally, by concentrating to a small ROI, the proposed adaptive method consumes the least power and achieves the best eye-safety. + +To intuitively showcase this advantage, we assume $N \sim 100$ to 500, which is consistent with the spatial resolution of most concurrent 3D sensors. For high-resolution depth sensors with $N > 1000$ , the gain is even greater. At the same maximum sensing distance, adaptive sensing: + +- has the same eye-safety distance as full-frame sensors, while consuming $N^{-1}$ (0.01 to 0.002)× lower power. +- has $N^{-0.125}$ (0.56 to 0.46) × shorter (better) eye-safety distance as line-scanning, while consuming $N^{-0.5}$ (0.1 to 0.04) × lower power. + +It is important to mention that these calculations are based on the assumption that the illuminated area for adaptive sensing is the same as line scanning: $R_{a} = N$ . In practice, this area may be larger depending on the scene and application. The adaptive projector (e.g., SLM) may also have a limited light efficiency, which gives an effectively smaller $R_{a}$ and thus lower SNR. Nonetheless, at the same maximum distance, adaptive sensing still has a power benefit as + +
SNRPlmin
V1cNkp d2maxN-1kldmax
V1-acNK-1kp d2maxN-1KkldmaxK0.375
V1-bcNK-0.5kp d2maxN-1K0.5kldmaxK0.125
+ +Table 1. Variations of adaptive sensing. + +long as $R_{a} > \sqrt{N}$ , and it always has a eye-safety benefit since $l_{\min}$ is independent of $R_{a}$ . The theoretical analysis forms the foundation for the proposed adaptive 3D sensing. We validate the analysis in a real-world prototype in Sec. 5. + +Disjoint ROIs. So far, we assume an ideal flexible projector which can project light to arbitrarily-shaped, even disjoint ROIs simultaneously. In practice, certain hardware implementations do not have this capability (an example is discussed in Sec. 4.2). To this end, we propose a more flexible scanning strategy: During the camera exposure, the system scans $K$ disjoint ROIs sequentially (typically $2 \leq K \leq 5$ ). This adaptive V1-a method consumes slightly more power and has a slightly longer eye-safety distance (Tab. 1). Another option is to divide the camera exposure into $K$ shorter exposures, and the system scans a single ROI during each exposure. This adaptive V1-b method performs comparably as V1, but requires a $K$ times higher camera frame rate. Please refer to the supplementary technical report for more design variations and detailed comparisons. + +# 4. Implementation of Adaptive Illumination + +Now that we have theoretically analyzed the benefit of the proposed adaptive illumination, how can the proposed adaptive illumination be realized? Notice that this is not a trivial problem. The hardware implementation must satisfy two criteria: (1) The system can redistribute the optical power to a small ROI (guided by an attention map), and (2) This ROI can be projected to different parts of the scene flexibly and in real-time (e.g., 30Hz). A common LCD or DLP projector satisfies (2) but does not satisfy (1). In this section, we propose two hardware configurations that satisfy both conditions. + +# 4.1. Implementation 1: Phase SLM + +Fig. 4(a) shows our SLM-based implementation. Our holographic projection approach is inspired by recent work on holographic near-eye 3D displays [20]. Specifically, a hologram to be reproduced by the SLM is decomposed as a sum of sub-holograms, where each sub-hologram diffracts light to a single object point in the scene. In [20], each sub-hologram is created using a lens phase function: + +$$ +f _ {n} ^ {\text {l e n s}} (\mathbf {X}) = e ^ {j 2 \pi \sqrt {(X - x _ {n}) ^ {2} + (Y - y _ {n}) ^ {2} + (Z - z _ {n}) ^ {2})} / \lambda , \tag {12} +$$ + +![](images/ee1ec079ae840fb7b84e24a2ecbe1854f14d18ef329d32826c883bb35cc61a46.jpg) +(a) Phase SLM-based implementation + +![](images/4771f1b29a3eb3f20a60be6db724322b9e0e061ae2fe8179956f33b17d700f8c.jpg) +(b) MEMS + DOE-based method +Figure 4. Hardware implementations. (a) Our first implementation is based on a phase-only SLM, which can redistribute light to arbitrarily-shaped, even disjointed ROIs. (b) Our second implementation is based on a DOE pattern generator with a 2D MEMS mirror. It has less flexibility and can only concentrate on one fixed-shape ROI at a time, but it benefits from low cost, simple optics and small form factor which makes it potentially easier to be miniaturized. + +where $(X,Y,Z)$ is the 3D position of each pixel in the subhologram, $(x_{n},y_{n},z_{n})$ is the 3D position of the $n$ -th object point, and $\lambda$ is the light wavelength. The full hologram is, + +$$ +H (\mathbf {X}) = \sum_ {n = 1} ^ {N} f _ {n} ^ {\text {l e n s}}. \tag {13} +$$ + +This lens phase function mimics a lens that focuses light to the object point at the correct depth, which works well for near-eye displays. One limitation of this lens phase function approach is that light is only redistributed locally. This is because the SLM can only reproduce a smooth hologram due to the Nyquist frequency determined by the finite pixel pitch. However, $f^{\mathrm{lens}}$ varies rapidly for off-center pixels (i.e. $X, Y$ far away from $x_{n}, y_{n}$ ), causing aliasing artifacts. Therefore, sub-holograms of much smaller sizes must be used, which greatly limits the light efficiency. + +To alleviate this limitation, we propose the use of mirror phase function: + +$$ +f _ {n} ^ {\text {m i r r o r}} (\mathbf {X}) = e ^ {j \left(X \cdot x _ {n} + Y \cdot y _ {n}\right)}, H (\mathbf {X}) = \sum_ {n = 1} ^ {N} f _ {n} ^ {\text {m i r r o r}}. \tag {14} +$$ + +The mirror phase function corresponds to a smooth phase map linear in terms of $X, Y$ , and can be implemented on the SLM without aliasing. It allows us to use each sub-hologram as a mirror that reflects light to the right direction. By taking the sum of sub-holograms that reflect to different directions, desired projection patterns can be achieved. Please see the supplementary for detailed optical diagrams and discussion. + +Conversion to phase-only holograms. Notice that Eq. 14 creates a hologram with both amplitudes and phases being spatially-variant, which cannot be implemented on a phase-only SLM. Several approaches [12, 16] have been proposed to convert such a full hologram to a phase-only hologram. Fortunately, our goal is not to project a high-quality image, and simple amplitude discarding is sufficient to project unique texture to the scene: + +$$ +H _ {\text {p h a s e}} = \operatorname {A r g} [ H ]. \tag {15} +$$ + +![](images/0dd3c5e05548c4ad1b35ed419f1f652bc28df134b4d6ec38a59831b96541ecaf.jpg) +Implementation 1: Phase SLM + +![](images/92475a32c762f22f669a9f85a9efc95696a0d1e4cd362c32f3987820d2a17460.jpg) +Implementation 2: MEMS + DOE +Figure 5. Hardware prototypes. (Upper) Spatial Light Modulator (SLM) implementation. (Lower) Micro-electromechanical (MEMS) mirror + diffractive optical element (DOE) implementation. + +![](images/deac0b741cc8948470960e1db8f41eafb2f1fcffd3d09992d254465714d7df33.jpg) +Figure 6. Examples of emulating full frame, line scanning, and adaptive sensors on a phase only spatial light modulator. Note that the full frame and adaptive patterns are captured within the full exposure time, while each line in the line scanning pattern is captured within $1/N$ of the time. We scale the intensities for visualization. Note that the bright center dot is caused by the SLM DC term, and can be mitigated with additional optical filters and manufacturing processes. + +Efficient implementation. The mirror phase function consists of simple arithmetic operations on large matri + +![](images/7222947253c0b01a86582189710fb66fd088aba817648c19d482d62cb76d87e5.jpg) +Figure 7. Comparison between sensing strategies. Our approach is more robust to ambient light than line scanning and full frame sensors; notice how our adaptive approach degrades less than line scanning and full frame from low ambient lighting (700 lux) to high ambient lighting (4000 lux). We keep sensor settings constant for each low ambient-high ambient pair. The total number of dots in the adaptive method (ours), line scanning and full frame is around 150, $108 \times 150$ and $150^2$ , respectively. Zoom in to see the red dots in the camera images. + +ces, which can be implemented efficiently on a GPU. We implement our hologram generator in CUDA and render the resulting hologram phase from the frame-buffer to the SLM using OpenGL-CUDA interoperability. On a NVIDIA Jetson Nano, an embedded system-on-module with a Tegra X1 Maxwell 256-core GPU and limited computing resources, we are able to generate 1080p holograms with around 100 points or less at 30 fps. Our implementation and simulator can be found at https://github.com/btilmon/holoCu. + +# 4.2. Implementation 2: MEMS + DOE + +Our second implementation is to adjust the beam incident angle of a diffractive optical element (DOE) with a MEMS mirror, as shown in Fig. 4(b). DOE offers a cheap, energy-efficient solution for random dot projection in single-shot structured light (Kinect V1) or active stereo (RealSense). While those systems use a DOE that covers the entire scene, we use a small FOV ( $\approx 5^{\circ}$ ) that only corresponds to a small ROI. By rotating the MEMS mirror, the deflected laser beam hits the DOE at different angles, thus generating a dot pattern at different ROIs of the scene. + +Comparison with phase SLM. The MEMS + DOE implementation is less flexible than the SLM implementation since the hologram shape is fixed (determined by the DOE phase pattern). This is schematically shown in Fig. 4: While SLM can illuminate ROIs of various shapes (P1- + +P3), MEMS + DOE can only create the same shape shifted across the scene. Moreover, while the SLM can redistribute the optical power over two disjoint ROIs during the same camera exposure (P4), different ROIs are scanned and imaged sequentially by the MEMS mirror, which slightly decreases the SNR (see Sec. 3.2 for detailed analysis). Nevertheless, the MEMS + DOE approach benefits from low cost, simple optics and small form factor, which are important factors for mobile and wearable devices. + +![](images/e1fc8a796eabed2c4ba4b6ce285d961e52ddefdf7a811b4b5e11fac67aa740dd.jpg) +Figure 8. Outdoor active depth sensing under 50 kilolux direct sunlight with Phase SLM. Our sensor works outdoors under direct sunlight. We show results up to 2 meters but believe this range could be extended with further SLM optical engineering. Zoom in to see the red dots in the camera images. + +![](images/241af25f8f11a991852d4a79699c6abbcd1212e2d264a8fd9bcc90a85d7acc85.jpg) +Figure 9. MEMS + DOE implementation. The MEMS voltages are updated to direct the dot pattern onto the predominant textureless region in both frames. Zoom in the camera images to see the red dots. + +# 5. Experiments + +Hardware prototypes. Fig. 5 shows both hardware prototypes of our proposed method. We use two FLIR BFS-U3-16S2C-CS cameras equipped with $20\mathrm{mm}$ lenses as a stereo pair. Our SLM implementation uses a Holoyeye GAEA LCoS (phase-only) SLM, which can display 4K phase maps at 30 frames per second. Our MEMS + DOE implementation uses a $0.8\mathrm{mm}$ diameter bonded Mirrorcle MEMS Mirror. A random dot DOE with a small FOV is preferred. Here, we used a Holoyeye DE-R 339 DOE that produces a periodic 6x6 dot pattern with $5^{\circ}$ FOV instead and we tilt the DOE such that the pattern is still unique locally on the epipolar line. Please refer to the supplementary report for detailed setup and calibration procedures. + +Attention map and depth estimation. We adopt classical semi global block matching for depth estimation [10]. The attention map is determined by randomly choosing pixels that do not have a valid depth value from the depth map computed from passive images. In practice, the attention map can be conditioned by the application such that illumination is only needed within the regions where AR objects are inserted. Our goal is to present a general sensor that can fit into many different perception systems and improve active depth sensing. + +Comparison between sensing strategies. We emulate full-frame and line-scanning strategies on our SLM implementation and compare them with our adaptive sensing strategy. An example of each emulated sensor can be found in Fig. 6. For line scanning, we compute and project the hologram of the dot pattern line-by-line. We capture the image for each line individually and stitch the corresponding camera rows together into a single image. + +Fig. 7 shows the results for three different scenes. All scenes are illuminated with the same ambient lighting and laser power. Laser power, exposure time and illuminated area are chosen to ensure fair comparison. Due to the dominating photon noise from the ambient light, full-frame and line scanning methods have a low SNR. As a result, depth + +estimation fails in the textureless regions. Since the proposed adaptive sensing technique concentrates light to the textureless regions, it achieves much higher SNR and obtains higher-quality depth maps, which validates our theoretical analysis. + +Outdoor depth sensing under direct sunlight. Fig. 8 demonstrates our Phase SLM prototype working outdoors under 50 kilolux direct sunlight. We can rely on passive stereo to compute depth for the majority of the scene and only project light where necessary, such as the white textureless pot. We also show a distance test of the Phase SLM prototype at 2 meters. We believe this distance could be increased with further SLM optical engineering in future work. + +MEMS + DOE implementation. Fig. 9 demonstrates our MEMS + DOE prototype. The dot pattern is projected to a textureless object which improves the disparity compared to passive stereo. When the system moves to another location at $t_1$ , it analyzes the new captured images and directs the ROI to the new position of the textureless object. + +# 6. Limitations and Discussion + +Optical power vs computation power. Although we do not explicitly compare the optical power savings from adaptive sensing with the additional computation power needed for computing the attention map and projector control signal (e.g., phase map for SLM), we show that such computations consist of basic arithmetic operations and can be implemented on embedded systems like NVIDIA Jetson Nano, suggesting that our approach can be deployed on increasingly available mobile GPUs. Our system will have even higher benefits for outdoor applications where optical power dominates. + +Learning-based attention map and depth estimation. In this work, we use simple, low-complexity texture analysis and semi global matching for attention map and depth estimation. It is possible to design neural networks to achieve better depth estimation, at the cost of higher computation. Our focus in on validating the proposed adaptive sensing as a promising novel sensing strategy, and we expect more practical algorithms to be developed in future work. + +Other active depth sensing mechanisms. Although this paper only shows hardware implementations for active stereo, the adaptive sensing strategy can be applied to other depth sensing mechanisms such as single/multi-shot structured light, direct/indirect ToF, FMCW Lidar, etc., which can be a promising future direction. + +Acknowledgements. The authors acknowledge partial funding from the Office of Naval Research through ONR N00014-18-1-2663 and the National Science Foundation through NSF 1942444. + +# References + +[1] Supreeth Achar, Joseph R. Bartels, William L. 'Red' Whittaker, Kiriakos N. Kutulakos, and Srinivasa G. Narasimhan. Epipolar time-of-flight imaging. ACM Transactions on Graphics, 36(4):1-8, July 2017. 2, 3 +[2] Siddharth Ancha, Gaurav Pathak, Srinivasa G Narasimhan, and David Held. Active safety envelopes using light curtains with probabilistic guarantees. arXiv preprint arXiv:2107.04000, 2021.3 +[3] Siddharth Ancha, Yaadhav Raaj, Peiyun Hu, Srinivasa G Narasimhan, and David Held. Active perception using light curtains for autonomous driving. In European Conference on Computer Vision, pages 751-766. Springer, 2020. 3 +[4] Seung-Hwan Baek and Felix Heide. Polka lines: Learning structured illumination and reconstruction for active stereo. 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IEEE Transactions on Automatic Control, 64(1):159–173, 2018. 3 +[34] Li Zhang, Brian Curless, and Steven M Seitz. Spacetime stereo: Shape recovery for dynamic scenes. In 2003 IEEE Computer Society Conference on Computer Vision and Pattern Recognition, 2003. Proceedings., volume 2, pages II-367. 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Naively increasing the optical power can improve sensing range but induces eye-safety concerns for many applications, including autonomous robots and augmented reality. In this paper, we propose an adaptive active depth sensor that jointly optimizes range, power consumption, and eye-safety. The main observation is that we need not project light patterns to the entire scene but only to small regions of interest where depth is necessary for the application and passive stereo depth estimation fails. We theoretically compare this adaptive sensing scheme with other sensing strategies, such as full-frame projection, line scanning, and point scanning. We show that, to achieve the same maximum sensing distance, the proposed method consumes the least power while having the shortest (best) eye-safety distance. We implement this adaptive sensing scheme with two hardware prototypes, one with a phase-only spatial light modulator (SLM) and the other with a micro-electro-mechanical (MEMS) mirror and diffractive optical elements (DOE). Experimental results validate the advantage of our method and demonstrate its capability of acquiring higher quality geometry adaptively. Please see our project website for video results and code: https://btilmon.github.io/e3d.html." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 552, + 128, + 565 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 552, + 128, + 565 + ], + "spans": [ + { + "bbox": [ + 47, + 552, + 128, + 565 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 574, + 287, + 682 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 574, + 287, + 682 + ], + "spans": [ + { + "bbox": [ + 46, + 574, + 287, + 682 + ], + "type": "text", + "content": "Active 3D depth sensors have diverse applications in augmented reality, navigation, and robotics. Recently, these sensor modules are widely used in consumer products, such as time-of-flight (e.g., Lidar [15]), structured light (e.g., Kinect V1 [18]) and others. In addition, many computer vision algorithms have been proposed to process the acquired data for downstream tasks such as 3D semantic understanding [29], object tracking [17], guided upsampling in SLAM [24], etc." + } + ] + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 310, + 213, + 396, + 291 + ], + "blocks": [ + { + "bbox": [ + 310, + 213, + 396, + 291 + ], + "lines": [ + { + "bbox": [ + 310, + 213, + 396, + 291 + ], + "spans": [ + { + "bbox": [ + 310, + 213, + 396, + 291 + ], + "type": "image", + "image_path": "3fa6cf467037b4cfd3a2694c4f3c0bcc716d624b769220478dfa87298f96b647.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 342, + 300, + 503, + 311 + ], + "lines": [ + { + "bbox": [ + 342, + 300, + 503, + 311 + ], + "spans": [ + { + "bbox": [ + 342, + 300, + 503, + 311 + ], + "type": "text", + "content": "(a) Depth sensing on wearables faces challenges" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 410, + 213, + 539, + 292 + ], + "blocks": [ + { + "bbox": [ + 410, + 213, + 539, + 292 + ], + "lines": [ + { + "bbox": [ + 410, + 213, + 539, + 292 + ], + "spans": [ + { + "bbox": [ + 410, + 213, + 539, + 292 + ], + "type": "image", + "image_path": "137dc01153f8ae057a61a80f64024fd42cbd7db182aa1a52f3f68ab5dc31508a.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 308, + 317, + 450, + 435 + ], + "blocks": [ + { + "bbox": [ + 308, + 317, + 450, + 435 + ], + "lines": [ + { + "bbox": [ + 308, + 317, + 450, + 435 + ], + "spans": [ + { + "bbox": [ + 308, + 317, + 450, + 435 + ], + "type": "image", + "image_path": "1c347786db62a9044cc5e15a5a3bf2e02e9191d3b5148bc4ae7c1192473172bd.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 312, + 435, + 444, + 445 + ], + "lines": [ + { + "bbox": [ + 312, + 435, + 444, + 445 + ], + "spans": [ + { + "bbox": [ + 312, + 435, + 444, + 445 + ], + "type": "text", + "content": "(b) Our system with adaptive projection" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 304, + 458, + 547, + 591 + ], + "lines": [ + { + "bbox": [ + 304, + 458, + 547, + 591 + ], + "spans": [ + { + "bbox": [ + 304, + 458, + 547, + 591 + ], + "type": "text", + "content": "Figure 1. Energy-efficient adaptive 3D sensing. (a) Depth sensing devices have three key optimization goals: minimizing the power consumption and eye-safety distance while maximizing sensing distance. However, these goals are coupled to each other. (b) We propose a novel adaptive sensing method with an active stereo setup and a projector that can redistribute the light energy and project the pattern only to the required regions (e.g., textureless regions). (c) The proposed approach outperforms previous methods including full-frame pattern systems (like Intel RealSense) and line-scanning systems (like Episcan3D [22]): When the maximum sensing distance is the same, the required power is much less and the eye-safety distance is also shorter." + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_caption" + } + ], + "index": 11 + }, + { + "type": "image", + "bbox": [ + 458, + 316, + 542, + 435 + ], + "blocks": [ + { + "bbox": [ + 458, + 316, + 542, + 435 + ], + "lines": [ + { + "bbox": [ + 458, + 316, + 542, + 435 + ], + "spans": [ + { + "bbox": [ + 458, + 316, + 542, + 435 + ], + "type": "image", + "image_path": "1b0bbb14711549d34ef2e2584427c7ee7df71d1a4bda1e35f5d1ef2f5da7cdc8.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 471, + 435, + 523, + 445 + ], + "lines": [ + { + "bbox": [ + 471, + 435, + 523, + 445 + ], + "spans": [ + { + "bbox": [ + 471, + 435, + 523, + 445 + ], + "type": "text", + "content": "(c) Comparison" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_caption" + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 605, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 547, + 715 + ], + "type": "text", + "content": "Unlike stereo cameras that only sense reflected ambient light passively, active depth sensors illuminate the scene with modulated light patterns, either spatially, temporally, or both. The illumination encodings allow robust estimation of scene depths. However, this also leads to three shortcomings: First, active depth sensors consume optical power, burdening wearable devices that are on a tight power budget. Second, the number of received photons reflected back from the scene drops with inverse-square relationship" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 693, + 215, + 703 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 693, + 215, + 703 + ], + "spans": [ + { + "bbox": [ + 58, + 693, + 215, + 703 + ], + "type": "text", + "content": "*Work done during internship at Snap Research." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 59, + 703, + 148, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 703, + 148, + 712 + ], + "spans": [ + { + "bbox": [ + 59, + 703, + 148, + 712 + ], + "type": "text", + "content": "†Co-corresponding authors" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "5054" + } + ] + } + ], + "index": 20 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 53, + 75, + 136, + 178 + ], + "blocks": [ + { + "bbox": [ + 53, + 75, + 136, + 178 + ], + "lines": [ + { + "bbox": [ + 53, + 75, + 136, + 178 + ], + "spans": [ + { + "bbox": [ + 53, + 75, + 136, + 178 + ], + "type": "image", + "image_path": "3d3f63ee29f35666096c5fd5c85d56a03df34fc430941553517bef2a5533148b.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 138, + 75, + 217, + 167 + ], + "blocks": [ + { + "bbox": [ + 138, + 75, + 217, + 167 + ], + "lines": [ + { + "bbox": [ + 138, + 75, + 217, + 167 + ], + "spans": [ + { + "bbox": [ + 138, + 75, + 217, + 167 + ], + "type": "image", + "image_path": "1d0c9b5ff8bf5b4171a427b394817ffd82d154b9d57c311514cd78487b3197d4.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 141, + 151, + 211, + 166 + ], + "lines": [ + { + "bbox": [ + 141, + 151, + 211, + 166 + ], + "spans": [ + { + "bbox": [ + 141, + 151, + 211, + 166 + ], + "type": "text", + "content": "e.g., region of interest & textureless region" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 218, + 75, + 302, + 149 + ], + "blocks": [ + { + "bbox": [ + 218, + 75, + 302, + 149 + ], + "lines": [ + { + "bbox": [ + 218, + 75, + 302, + 149 + ], + "spans": [ + { + "bbox": [ + 218, + 75, + 302, + 149 + ], + "type": "image", + "image_path": "5614de34bbae799f106f0be14cc3c1de9124d48caab850ffdde3ab525a1f9f6b.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 302, + 76, + 386, + 178 + ], + "blocks": [ + { + "bbox": [ + 302, + 76, + 386, + 178 + ], + "lines": [ + { + "bbox": [ + 302, + 76, + 386, + 178 + ], + "spans": [ + { + "bbox": [ + 302, + 76, + 386, + 178 + ], + "type": "image", + "image_path": "fab487e22e6ced4ebcb7350fa62cd98af6980613890171e2f95c4bd70e230e1e.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 193, + 547, + 239 + ], + "lines": [ + { + "bbox": [ + 46, + 193, + 547, + 239 + ], + "spans": [ + { + "bbox": [ + 46, + 193, + 547, + 239 + ], + "type": "text", + "content": "Figure 2. Method overview. Our system consists of a stereo-camera pair and an adaptive projector. The system first captures an image of the scene (Step 1) and then computes an attention map to determine the ROI (Step 2). This attention map is used to compute the control signal for the specific projector implementation (Step 3) such that light is only projected to the ROI (Step 4). A depth map is then computed from the new stereo images, which can be used for applications such as augmented reality (Step 5)." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "type": "image", + "bbox": [ + 386, + 75, + 463, + 151 + ], + "blocks": [ + { + "bbox": [ + 386, + 75, + 463, + 151 + ], + "lines": [ + { + "bbox": [ + 386, + 75, + 463, + 151 + ], + "spans": [ + { + "bbox": [ + 386, + 75, + 463, + 151 + ], + "type": "image", + "image_path": "6df9b4459bebd97e46cb7342c971bd2acd5a17ce17390e6ee07c658c085e277d.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_body" + } + ], + "index": 5 + }, + { + "type": "image", + "bbox": [ + 466, + 75, + 545, + 151 + ], + "blocks": [ + { + "bbox": [ + 466, + 75, + 545, + 151 + ], + "lines": [ + { + "bbox": [ + 466, + 75, + 545, + 151 + ], + "spans": [ + { + "bbox": [ + 466, + 75, + 545, + 151 + ], + "type": "image", + "image_path": "bd7a0ab7b5111129f96ab97671c7f8199cb6ed1acc0780c20be0bb92464653d8.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_body" + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 258, + 287, + 390 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 258, + 287, + 390 + ], + "spans": [ + { + "bbox": [ + 46, + 258, + 287, + 390 + ], + "type": "text", + "content": "to scene depth. The maximum sensing distance is thereby limited by the received signal-to-noise ratio (SNR). Third, strong, active light sources on the device may unintentionally hurt the user or other people around. For consumer devices, this constraint can be as strict as ensuring safety when a baby accidentally stares at the light source directly. Interestingly, these three factors are often entangled with each other. For example, naively increasing range by raising optical power makes the device less eye-safe. An active 3d sensor would benefit from the joint optimization of these three goals, as illustrated in Fig. 1(a)." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 390, + 287, + 594 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 390, + 287, + 594 + ], + "spans": [ + { + "bbox": [ + 46, + 390, + 287, + 594 + ], + "type": "text", + "content": "In this paper, we present an adaptive depth-sensing strategy. Our key idea is that the coded scene illumination need not be sent to the entire scene (Fig. 1(b)). Intuitively, by limiting the illumination samples, the optical power per sample is increased, therefore extending the maximum sensing distance. This idea of adaptive sensing is supported by three observations: First, illumination samples only need to be sent to parts of a scene where passive depth estimation fails (e.g., due to lack of texture). Second, depth estimation is often application-driven, e.g., accurate depths are only needed around AR objects to be inserted into the scene. Finally, for video applications, sending light to regions where depths are already available from previous frames is redundant. Based on these observations, we demonstrate this adaptive idea with a stereo-projector setup (i.e., active stereo [4,9,34]), where an attention map is computed from the camera images for efficient light redistribution." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 594, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 594, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 287, + 714 + ], + "type": "text", + "content": "To quantitatively understand the benefits of our approach, we propose a sensor model that analytically characterizes various sensing strategies, including full-frame (e.g., RealSense [19]), line-scanning (e.g., Episcan3D [22]), point-scanning (e.g., Lidar [25]) and proposed adaptive sensing. We establish, for the first time, a framework that jointly analyzes the power, range, and eye-safety of different strategies and demonstrates that, for the same maximum sensing distance, adaptive sensing consumes the least power while achieving the shortest (best) eye-safety distance." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 258, + 545, + 390 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 258, + 545, + 390 + ], + "spans": [ + { + "bbox": [ + 304, + 258, + 545, + 390 + ], + "type": "text", + "content": "Note that the realization of scene-adaptive illumination is not trivial: Common off-the-shelf projectors simply block part of the incident light, which wastes optical power. We propose two hardware implementations for adaptive illumination: One is inspired by digital holography, which uses Liquid Crystal on Silicon (LCoS) Spatial Light Modulators (SLM) to achieve free-form light projection. The other implementation uses diffractive optical elements (DOE) to generate dot patterns in a local region of interest (ROI), which is directed to different portions of the scene by a micro-electro-mechanical (MEMS) mirror." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 317, + 391, + 503, + 402 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 391, + 503, + 402 + ], + "spans": [ + { + "bbox": [ + 317, + 391, + 503, + 402 + ], + "type": "text", + "content": "Our contributions are summarized as follows:" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 317, + 404, + 545, + 523 + ], + "type": "list", + "angle": 0, + "index": 16, + "blocks": [ + { + "bbox": [ + 317, + 404, + 545, + 451 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 404, + 545, + 451 + ], + "spans": [ + { + "bbox": [ + 317, + 404, + 545, + 451 + ], + "type": "text", + "content": "- Adaptive 3D sensing theory: We propose adaptive 3D sensing and demonstrate its advantage in a theoretical framework that jointly considers range, power and eye-safety." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 317, + 452, + 545, + 487 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 452, + 545, + 487 + ], + "spans": [ + { + "bbox": [ + 317, + 452, + 545, + 487 + ], + "type": "text", + "content": "- Hardware implementation: We implement the proposed adaptive active stereo approach with two hardware prototypes based on SLM and MEMS + DOE." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 317, + 487, + 545, + 523 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 487, + 545, + 523 + ], + "spans": [ + { + "bbox": [ + 317, + 487, + 545, + 523 + ], + "type": "text", + "content": "- Experimental validation: Real-world experimental results validate that our sensor can adapt to the scene and outperform existing sensing strategies." + } + ] + } + ], + "index": 15 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 306, + 536, + 392, + 549 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 536, + 392, + 549 + ], + "spans": [ + { + "bbox": [ + 306, + 536, + 392, + 549 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 558, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 558, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 558, + 545, + 713 + ], + "type": "text", + "content": "Active 3D sensing with ambient light noise. Various techniques have been proposed to address photon noise due to strong ambient light (e.g., sunlight), such as choosing a wavelength where sunlight is weak [23, 32], using a polarizing filter [23]. Gupta et al. [13] uses a theoretical model to show that instead of illuminating the full scene, concentrating light on different parts of a scene sequentially improves SNR for structured light, which is demonstrated with a rotating polygonal mirror. Based on similar principles, MC3D [21] uses a MEMS/galvo-driven laser and an event camera to achieve bandwidth-efficient scanning. Episcan3D [22] and EpiToF [1] use a line-scanning laser and a synchronized rolling-shutter camera to achieve fast" + } + ] + } + ], + "index": 18 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "5055" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 133 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 133 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 133 + ], + "type": "text", + "content": "and efficient depth sensing. This paper further extends this line of work by showing that, with the freedom to adaptively illuminate part of the scene, a lower power budget is needed to achieve the same sensing range while being safer to the eyes." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 134, + 288, + 278 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 134, + 288, + 278 + ], + "spans": [ + { + "bbox": [ + 46, + 134, + 288, + 278 + ], + "type": "text", + "content": "Adaptive 3D sensing. Ideas from visual attention [6, 11] have influenced vision and robotics. Efficient estimation algorithms have been shown for adaptive sensing and pointzoom-tilt (PZT) cameras [7, 33]. In the 3D sensor space, 3D light-curtains [5,8,31] represent a flexible system where curtains can be adaptively placed in the scene for robotics, and other applications [2,3,26]. Full control of the MEMS mirror enables adaptive sampling for LIDAR [25, 27, 28] and adaptive passive camera resolution for monocular depth sensing [30]. While previous adaptive systems focus on different aspects such as flexibility, frame rate, etc., this work studies the interplay between range, power, and eye-safety." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 288, + 256, + 302 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 288, + 256, + 302 + ], + "spans": [ + { + "bbox": [ + 47, + 288, + 256, + 302 + ], + "type": "text", + "content": "3. Energy-Efficient Adaptive 3D Sensing" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 308, + 287, + 403 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 308, + 287, + 403 + ], + "spans": [ + { + "bbox": [ + 46, + 308, + 287, + 403 + ], + "type": "text", + "content": "The workflow of the proposed adaptive 3D sensing is shown in Fig. 2. We use an active stereo design with two cameras and a projector. The device first captures an image of the scene and computes an attention map to determine the region of interest (ROI). Hardware-specific control signals are computed from the attention map such that the projector redistributes the light to the ROI. Finally, a high-quality depth map can be calculated from captured stereo images." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 403, + 287, + 486 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 403, + 287, + 486 + ], + "spans": [ + { + "bbox": [ + 46, + 403, + 287, + 486 + ], + "type": "text", + "content": "Before getting into details on how to implement this adaptive illumination in practice, let us assume an ideal flexible projector for a moment: If we can redistribute the optical power to an arbitrarily-shaped ROI, how well can it perform? We adopt a model to quantify its depth estimation performance and compare it to other existing or naively conceived active depth sensing strategies." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 493, + 221, + 506 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 493, + 221, + 506 + ], + "spans": [ + { + "bbox": [ + 47, + 493, + 221, + 506 + ], + "type": "text", + "content": "3.1. Sensor Model and SNR Analysis" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 512, + 287, + 607 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 512, + 287, + 607 + ], + "spans": [ + { + "bbox": [ + 46, + 512, + 287, + 607 + ], + "type": "text", + "content": "The accuracy of various active depth sensors, including structured light, active stereo, continuous-wave time-of-flight (CW-ToF), etc., can be quantified by a single metric: the SNR of the measured light signal (projected by the active illumination source and reflected by the scene). The noise consists of the photon noise from both the signal itself and the ambient light, and the sensor readout noise, mathematically defined as follows [13, 14]:" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 60, + 613, + 287, + 685 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 60, + 613, + 287, + 685 + ], + "spans": [ + { + "bbox": [ + 60, + 613, + 287, + 685 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} S N R = \\frac {\\text {S i g n a l} _ {\\text {p r o j e c t o r}}}{\\sqrt {N _ {\\text {p h o t o n} , \\text {a m b i e n t}} ^ {2} + N _ {\\text {p h o t o n} , \\text {p r o j e c t o r}} ^ {2} + N _ {\\text {r e a d}} ^ {2}}} \\tag {1} \\\\ = \\frac {\\frac {P}{d ^ {2} a} t _ {1}}{\\sqrt {P _ {\\mathrm {s u n}} t _ {2} + \\frac {P}{d ^ {2} a} t _ {1} + N _ {\\mathrm {r e a d}} ^ {2}}} \\\\ \\end{array}", + "image_path": "a615bed7a059295a3a49f26ccf56aef1b74cf2f6150b7af1165f594d02d9a41d.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 689, + 287, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 712 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 712 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 689, + 287, + 712 + ], + "type": "inline_equation", + "content": "P" + }, + { + "bbox": [ + 47, + 689, + 287, + 712 + ], + "type": "text", + "content": " is the optical power of the projector (assuming an albedo of 1 in the scene), " + }, + { + "bbox": [ + 47, + 689, + 287, + 712 + ], + "type": "inline_equation", + "content": "a" + }, + { + "bbox": [ + 47, + 689, + 287, + 712 + ], + "type": "text", + "content": " is the illuminated area at unit" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 72, + 545, + 177 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 177 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 177 + ], + "type": "text", + "content": "distance, " + }, + { + "bbox": [ + 304, + 72, + 545, + 177 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 304, + 72, + 545, + 177 + ], + "type": "text", + "content": " is the distance of the scene (thus the inverse-square fall-off), " + }, + { + "bbox": [ + 304, + 72, + 545, + 177 + ], + "type": "inline_equation", + "content": "P_{\\mathrm{sun}}" + }, + { + "bbox": [ + 304, + 72, + 545, + 177 + ], + "type": "text", + "content": " is the optical power of the ambient light, " + }, + { + "bbox": [ + 304, + 72, + 545, + 177 + ], + "type": "inline_equation", + "content": "t_1" + }, + { + "bbox": [ + 304, + 72, + 545, + 177 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 72, + 545, + 177 + ], + "type": "inline_equation", + "content": "t_2" + }, + { + "bbox": [ + 304, + 72, + 545, + 177 + ], + "type": "text", + "content": " are the duration when the laser is on and the camera is active, respectively, and " + }, + { + "bbox": [ + 304, + 72, + 545, + 177 + ], + "type": "inline_equation", + "content": "N_{\\mathrm{read}}" + }, + { + "bbox": [ + 304, + 72, + 545, + 177 + ], + "type": "text", + "content": " is the standard deviation of the read noise. Ambient light-induced photon noise dominates in outdoor scenarios and also indoors with power-limited devices, which is the major focus of the following analysis. In these situations, SNR can be simplified as:" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 387, + 177, + 545, + 205 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 387, + 177, + 545, + 205 + ], + "spans": [ + { + "bbox": [ + 387, + 177, + 545, + 205 + ], + "type": "interline_equation", + "content": "S N R \\approx \\frac {\\frac {P}{d ^ {2} a} t _ {1}}{\\sqrt {P _ {\\mathrm {s u n}} t _ {2}}}. \\tag {2}", + "image_path": "7c13c02e4d9afe01612b01051b234eec822240a28d843202657e8e26fc7a791d.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 208, + 545, + 232 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 208, + 545, + 232 + ], + "spans": [ + { + "bbox": [ + 305, + 208, + 545, + 232 + ], + "type": "text", + "content": "When readout noise dominates, which happens in a dark room or at night, SNR can be simplified as this" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 392, + 239, + 545, + 267 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 392, + 239, + 545, + 267 + ], + "spans": [ + { + "bbox": [ + 392, + 239, + 545, + 267 + ], + "type": "interline_equation", + "content": "S N R \\approx \\frac {\\frac {P}{d ^ {2} a} t _ {1}}{N _ {\\text {r e a d}}}. \\tag {3}", + "image_path": "8992203d3ae343221635923091e722f696a34af02373c5400d6ce396a9ded7a4.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 277, + 545, + 384 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 277, + 545, + 384 + ], + "spans": [ + { + "bbox": [ + 304, + 277, + 545, + 384 + ], + "type": "text", + "content": "Analyzing different sensing strategies. We use this SNR model to compare the performance of different depth sensors. For a fair comparison, we assume all depth sensors have equal total optical power " + }, + { + "bbox": [ + 304, + 277, + 545, + 384 + ], + "type": "inline_equation", + "content": "P" + }, + { + "bbox": [ + 304, + 277, + 545, + 384 + ], + "type": "text", + "content": ", sensing at same depth " + }, + { + "bbox": [ + 304, + 277, + 545, + 384 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 304, + 277, + 545, + 384 + ], + "type": "text", + "content": ". Their performance is then uniquely determined by " + }, + { + "bbox": [ + 304, + 277, + 545, + 384 + ], + "type": "inline_equation", + "content": "t_1" + }, + { + "bbox": [ + 304, + 277, + 545, + 384 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 277, + 545, + 384 + ], + "type": "inline_equation", + "content": "t_2" + }, + { + "bbox": [ + 304, + 277, + 545, + 384 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 277, + 545, + 384 + ], + "type": "inline_equation", + "content": "a" + }, + { + "bbox": [ + 304, + 277, + 545, + 384 + ], + "type": "text", + "content": ". For off-the-shelf full-frame projectors (Fig. 3(e)), we denote " + }, + { + "bbox": [ + 304, + 277, + 545, + 384 + ], + "type": "inline_equation", + "content": "a = A" + }, + { + "bbox": [ + 304, + 277, + 545, + 384 + ], + "type": "text", + "content": " which corresponds to the entire FOV, and " + }, + { + "bbox": [ + 304, + 277, + 545, + 384 + ], + "type": "inline_equation", + "content": "t_1 = t_2 = T" + }, + { + "bbox": [ + 304, + 277, + 545, + 384 + ], + "type": "text", + "content": " as both the sensor and the projector are active during the entire camera exposure " + }, + { + "bbox": [ + 304, + 277, + 545, + 384 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 304, + 277, + 545, + 384 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 384, + 545, + 456 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 384, + 545, + 456 + ], + "spans": [ + { + "bbox": [ + 304, + 384, + 545, + 456 + ], + "type": "text", + "content": "Previous work [1, 13, 21, 22] has shown that, instead of flood-illuminating the entire scene, focusing optical power on different parts of the scene sequentially can lead to higher SNR. To quantitatively analyze this effect, we represent the illuminated area, laser exposure and camera exposure as a division of the full-frame case:" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 322, + 465, + 545, + 479 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 322, + 465, + 545, + 479 + ], + "spans": [ + { + "bbox": [ + 322, + 465, + 545, + 479 + ], + "type": "interline_equation", + "content": "a = A / R _ {a}, \\quad t _ {1} = T / R _ {t 1}, \\quad t _ {2} = T / R _ {t 2}, \\tag {4}", + "image_path": "3311306adcb70c1a3ce410d90e05dd5e3e4d30d3656e06adb79ca9b5f60f0b7c.jpg" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 487, + 545, + 522 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 487, + 545, + 522 + ], + "spans": [ + { + "bbox": [ + 304, + 487, + 545, + 522 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 487, + 545, + 522 + ], + "type": "inline_equation", + "content": "R_{a}, R_{t1}, R_{t2}" + }, + { + "bbox": [ + 304, + 487, + 545, + 522 + ], + "type": "text", + "content": " are defined as illuminated area divisor, laser exposure divisor, camera exposure divisor, respectively. SNR is then a function of these divisors:" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 318, + 530, + 545, + 574 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 318, + 530, + 545, + 574 + ], + "spans": [ + { + "bbox": [ + 318, + 530, + 545, + 574 + ], + "type": "interline_equation", + "content": "S N R = \\frac {\\frac {P}{d ^ {2} A / R _ {a}} T / R _ {t 1}}{\\sqrt {P _ {\\mathrm {s u n}} T / R _ {t 2}}} = \\underbrace {\\frac {P \\sqrt {T}}{d ^ {2} A \\sqrt {P _ {\\mathrm {s u n}}}}} _ {c} \\underbrace {\\frac {R _ {a} \\sqrt {R _ {t 2}}}{R _ {t 1}}} _ {X}, \\tag {5}", + "image_path": "a14527df33cbdb9493bb19770f3a988a464ffceb9ddd11893c3c0de3f798afb6.jpg" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 582, + 545, + 653 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 545, + 653 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 545, + 653 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 582, + 545, + 653 + ], + "type": "inline_equation", + "content": "c" + }, + { + "bbox": [ + 304, + 582, + 545, + 653 + ], + "type": "text", + "content": " is the SNR of full-frame projection. " + }, + { + "bbox": [ + 304, + 582, + 545, + 653 + ], + "type": "inline_equation", + "content": "X" + }, + { + "bbox": [ + 304, + 582, + 545, + 653 + ], + "type": "text", + "content": " is a factor that describes how each method compares with the baseline full-frame projection. It is difficult to optimize " + }, + { + "bbox": [ + 304, + 582, + 545, + 653 + ], + "type": "inline_equation", + "content": "X" + }, + { + "bbox": [ + 304, + 582, + 545, + 653 + ], + "type": "text", + "content": " directly since not every combination of " + }, + { + "bbox": [ + 304, + 582, + 545, + 653 + ], + "type": "inline_equation", + "content": "(R_{a}, R_{t1}, R_{t2})" + }, + { + "bbox": [ + 304, + 582, + 545, + 653 + ], + "type": "text", + "content": " is feasible in hardware. Nevertheless, it provides a useful tool to characterize different sensing strategies." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 654, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 654, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 654, + 545, + 713 + ], + "type": "text", + "content": "State-of-the-art systems such as Episcan3D [22] implement this idea as a line scanning scheme, as shown in Fig. 3(c). If we assume the total illuminated region of line scanning is the same as full-pattern, then " + }, + { + "bbox": [ + 304, + 654, + 545, + 713 + ], + "type": "inline_equation", + "content": "R_{a} = R_{t1} = R_{t2} = N" + }, + { + "bbox": [ + 304, + 654, + 545, + 713 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 654, + 545, + 713 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 304, + 654, + 545, + 713 + ], + "type": "text", + "content": " is the number of scanlines (typically" + } + ] + } + ], + "index": 19 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "5056" + } + ] + } + ], + "index": 20 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 51, + 71, + 545, + 311 + ], + "blocks": [ + { + "bbox": [ + 51, + 71, + 545, + 311 + ], + "lines": [ + { + "bbox": [ + 51, + 71, + 545, + 311 + ], + "spans": [ + { + "bbox": [ + 51, + 71, + 545, + 311 + ], + "type": "table", + "html": "
Point scanningLine scanning(e) Full-frame pattern(f) Adaptive (Proposed)
(a) V1: Synced(b) V2: Unsynced(c) V1: Synced(d) V2: Unsynced
*Typically, N = 102~103Single pixel 2D MEMS2D MEMS1D laser + 1D MEMS or 2D rolling-shutter cam1D laser + 1D MEMS2D projector2D flexible projector
Illuminated Area Divisor (Ra)N2N2NN1N
Laser Exposure Divisor (Rt1)N2N2NN11
Camera Exposure Divisor (Rt2)N21N111
Same power, sensing at same distance:
SNR = c Ra√Rt2/Rt1cNcc√NcccN
Same maximum sensing distance dmax:
Power Pkp d2maxN-1kp d2maxkp d2maxN-0.5kp d2maxkp d2maxkp d2maxN-1
Eye-safety distance lminklddmaxN0.25klddmaxN0.75klddmaxN0.125klddmaxN0.375klddmaxklddmax
", + "image_path": "7066869f2e972d459fb8944f1c1e112336f4f6a6f6c1fe8b8d728c81a1107aab.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 319, + 546, + 353 + ], + "lines": [ + { + "bbox": [ + 46, + 319, + 546, + 353 + ], + "spans": [ + { + "bbox": [ + 46, + 319, + 546, + 353 + ], + "type": "text", + "content": "Figure 3. Schematic diagrams and analysis of various sensing strategies. When ambient light noise dominates, the proposed adaptive sensing achieves best SNR. To achieve the same maximum sensing distance, adaptive sensing consumes least power while having shortest eye-safety distance. (Best performing methods in each row are highlighted in blue)" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 47, + 373, + 288, + 398 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 373, + 288, + 398 + ], + "spans": [ + { + "bbox": [ + 47, + 373, + 288, + 398 + ], + "type": "inline_equation", + "content": "10^{2} - 10^{3})" + }, + { + "bbox": [ + 47, + 373, + 288, + 398 + ], + "type": "text", + "content": ". By plugging these terms into Eq. 5, the SNR of line scanning is " + }, + { + "bbox": [ + 47, + 373, + 288, + 398 + ], + "type": "inline_equation", + "content": "X = \\sqrt{N}" + }, + { + "bbox": [ + 47, + 373, + 288, + 398 + ], + "type": "text", + "content": " times higher than the full-pattern." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 410, + 287, + 590 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 410, + 287, + 590 + ], + "spans": [ + { + "bbox": [ + 46, + 410, + 287, + 590 + ], + "type": "text", + "content": "One interesting question is: Can we push this idea further and scan a dot at a time? This point scanning idea can be implemented with a co-located laser and single-pixel sensor deflected by a 2D MEMS mirror. Using the same assumption, " + }, + { + "bbox": [ + 46, + 410, + 287, + 590 + ], + "type": "inline_equation", + "content": "R_{a} = R_{t1} = R_{t2} = N_{p}" + }, + { + "bbox": [ + 46, + 410, + 287, + 590 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 410, + 287, + 590 + ], + "type": "inline_equation", + "content": "N_{p}" + }, + { + "bbox": [ + 46, + 410, + 287, + 590 + ], + "type": "text", + "content": " is the number of dots (typically " + }, + { + "bbox": [ + 46, + 410, + 287, + 590 + ], + "type": "inline_equation", + "content": "N_{p} = N^{2} = 10^{4} - 10^{6}" + }, + { + "bbox": [ + 46, + 410, + 287, + 590 + ], + "type": "text", + "content": "). Fig. 3(a) shows that dot scanning does offer a higher SNR and is " + }, + { + "bbox": [ + 46, + 410, + 287, + 590 + ], + "type": "inline_equation", + "content": "X = N" + }, + { + "bbox": [ + 46, + 410, + 287, + 590 + ], + "type": "text", + "content": " times higher than the full-pattern. Notice that this SNR benefit comes from the fact that the laser and the sensor are synchronized: The sensor only receives light from the area illuminated by the laser at any instant. For their unsynchronized counterparts where the sensor is a 2D camera that captures the entire 2D FOV during the whole imaging time (easier to implement in hardware), their SNR is exactly the same as the full-pattern approach (Fig. 3(b,d))." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 618, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 618, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 47, + 618, + 288, + 715 + ], + "type": "text", + "content": "Adaptive sensing. Our adaptive sensor projects a static pattern that does not change during the entire exposure, i.e. " + }, + { + "bbox": [ + 47, + 618, + 288, + 715 + ], + "type": "inline_equation", + "content": "R_{t1} = R_{t2} = 1" + }, + { + "bbox": [ + 47, + 618, + 288, + 715 + ], + "type": "text", + "content": ". However, the optical power is concentrated to a small ROI, which we assume can be as small as one line in the line-scanning approach " + }, + { + "bbox": [ + 47, + 618, + 288, + 715 + ], + "type": "inline_equation", + "content": "R_{a} = N" + }, + { + "bbox": [ + 47, + 618, + 288, + 715 + ], + "type": "text", + "content": ". As shown in Fig. 3(f), our adaptive sensor has a " + }, + { + "bbox": [ + 47, + 618, + 288, + 715 + ], + "type": "inline_equation", + "content": "N_{l}" + }, + { + "bbox": [ + 47, + 618, + 288, + 715 + ], + "type": "text", + "content": " times higher SNR than the full-pattern approach. In summary, we observed that " + }, + { + "bbox": [ + 47, + 618, + 288, + 715 + ], + "type": "inline_equation", + "content": "SNR_{\\mathrm{adaptive}} = SNR_{\\mathrm{point}} \\gg SNR_{\\mathrm{line}} \\gg SNR_{\\mathrm{full}}" + }, + { + "bbox": [ + 47, + 618, + 288, + 715 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 305, + 373, + 541, + 385 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 373, + 541, + 385 + ], + "spans": [ + { + "bbox": [ + 305, + 373, + 541, + 385 + ], + "type": "text", + "content": "3.2. Comparison of Power, Range, and Eye-Safety" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 391, + 545, + 475 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 391, + 545, + 475 + ], + "spans": [ + { + "bbox": [ + 304, + 391, + 545, + 475 + ], + "type": "text", + "content": "Sec. 3.1 analyzes the SNR for different sensors at the same depth. However, this analysis is insufficient, since increasing SNR and the maximum range implies a higher risk of eye injury. In this section, we discuss how this model can be extended to analyze the trade-off between power, range and eye-safety. We consider two key constraints: maximum sensing distance and minimum eye-safety distance." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 477, + 545, + 525 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 477, + 545, + 525 + ], + "spans": [ + { + "bbox": [ + 304, + 477, + 545, + 525 + ], + "type": "text", + "content": "Maximum sensing distance. We assume that for reliable estimation of the depth, the SNR must be greater than a minimum detection threshold " + }, + { + "bbox": [ + 304, + 477, + 545, + 525 + ], + "type": "inline_equation", + "content": "\\mathrm{SNR}_{\\mathrm{thres}}" + }, + { + "bbox": [ + 304, + 477, + 545, + 525 + ], + "type": "text", + "content": ". The equality holds when the maximum sensing distance " + }, + { + "bbox": [ + 304, + 477, + 545, + 525 + ], + "type": "inline_equation", + "content": "d = d_{max}" + }, + { + "bbox": [ + 304, + 477, + 545, + 525 + ], + "type": "text", + "content": " is reached," + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 365, + 533, + 545, + 562 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 365, + 533, + 545, + 562 + ], + "spans": [ + { + "bbox": [ + 365, + 533, + 545, + 562 + ], + "type": "interline_equation", + "content": "S N R _ {\\text {t h r e s}} = \\frac {P \\sqrt {T}}{d _ {\\max } ^ {2} A \\sqrt {P _ {s u n}}} X. \\tag {6}", + "image_path": "d6dff16463a0f3a95c6c35fbbac6b0841fc1d6da9aa0197cf363df548b7eaafc.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 563, + 436, + 576 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 563, + 436, + 576 + ], + "spans": [ + { + "bbox": [ + 306, + 563, + 436, + 576 + ], + "type": "text", + "content": "Rearranging this equation gives" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 323, + 580, + 545, + 600 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 323, + 580, + 545, + 600 + ], + "spans": [ + { + "bbox": [ + 323, + 580, + 545, + 600 + ], + "type": "interline_equation", + "content": "\\boxed {P = k _ {p} \\cdot d _ {\\max } ^ {2} X ^ {- 1} = k _ {p} \\cdot d _ {\\max } ^ {2} R _ {a} ^ {- 1} R _ {t 1} R _ {t 2} ^ {- 0. 5},} \\tag {7}", + "image_path": "43b475790646879bae06d02001a955c39eff5354caebddb98f847d2424b1fe08.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 605, + 484, + 616 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 605, + 484, + 616 + ], + "spans": [ + { + "bbox": [ + 306, + 605, + 484, + 616 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 306, + 605, + 484, + 616 + ], + "type": "inline_equation", + "content": "k_{p}" + }, + { + "bbox": [ + 306, + 605, + 484, + 616 + ], + "type": "text", + "content": " is a method-independent constant." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 619, + 545, + 654 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 619, + 545, + 654 + ], + "spans": [ + { + "bbox": [ + 304, + 619, + 545, + 654 + ], + "type": "text", + "content": "Minimum eye-safety distance. A minimum eye-safety distance can be defined when the maximum permissible exposure (MPE, defined in ANSI Z136) is reached:" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 382, + 658, + 545, + 685 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 382, + 658, + 545, + 685 + ], + "spans": [ + { + "bbox": [ + 382, + 658, + 545, + 685 + ], + "type": "interline_equation", + "content": "\\frac {P}{l _ {\\min } ^ {2} a} = \\frac {M P E \\left(t _ {1}\\right)}{t _ {1}}, \\tag {8}", + "image_path": "0428335fc156e2166d9d7f345fb890260e5ea557fb6d9a87bc0cb07e2dec3f52.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 689, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 689, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 689, + 545, + 713 + ], + "type": "text", + "content": "It is considered dangerous for eyes to be exposed at a distance shorter than " + }, + { + "bbox": [ + 304, + 689, + 545, + 713 + ], + "type": "inline_equation", + "content": "l_{\\min}" + }, + { + "bbox": [ + 304, + 689, + 545, + 713 + ], + "type": "text", + "content": ". Intuitively, the shorter the minimal" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "5057" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 96 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 96 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 96 + ], + "type": "text", + "content": "eye-safety distance is, the more eye-safe the device is. We expand MPE based on definitions from ANSI Z136:" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 104, + 291, + 141 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 104, + 291, + 141 + ], + "spans": [ + { + "bbox": [ + 47, + 104, + 291, + 141 + ], + "type": "interline_equation", + "content": "\\frac {P}{l _ {\\operatorname* {m i n}} ^ {2} a} = \\frac {M P E (t _ {1})}{t _ {1}} = \\frac {C _ {\\lambda} t _ {1} ^ {0 . 7 5} 1 0 ^ {- 3} (\\mathrm {J} \\cdot \\mathrm {c m} ^ {- 2})}{t _ {1}} = k _ {e} t _ {1} ^ {- 0. 2 5}, \\tag {9}", + "image_path": "816dfc98990cd0f2319d1d69b24dca4daddb8e3c07493fa6952b4cb04babb787.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 142, + 287, + 178 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 142, + 287, + 178 + ], + "spans": [ + { + "bbox": [ + 46, + 142, + 287, + 178 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 142, + 287, + 178 + ], + "type": "inline_equation", + "content": "k_{e}" + }, + { + "bbox": [ + 46, + 142, + 287, + 178 + ], + "type": "text", + "content": " is a method-independent constant. Please find a detailed discussion on this analytic expression in the supplementary report. Plug in Eq. 4 and rearrange," + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 107, + 186, + 287, + 201 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 107, + 186, + 287, + 201 + ], + "spans": [ + { + "bbox": [ + 107, + 186, + 287, + 201 + ], + "type": "interline_equation", + "content": "l _ {\\min } = k _ {l} \\cdot P ^ {0. 5} R _ {a} ^ {0. 5} R _ {t 1} ^ {- 0. 1 2 5}, \\tag {10}", + "image_path": "0c9a09df305f741a1fc09a174992ebd15b2925be1bc5e9476c2b50ba2ea8ec00.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 210, + 224, + 221 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 210, + 224, + 221 + ], + "spans": [ + { + "bbox": [ + 47, + 210, + 224, + 221 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 210, + 224, + 221 + ], + "type": "inline_equation", + "content": "k_{l}" + }, + { + "bbox": [ + 47, + 210, + 224, + 221 + ], + "type": "text", + "content": " is a method-independent constant." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 224, + 287, + 321 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 224, + 287, + 321 + ], + "spans": [ + { + "bbox": [ + 46, + 224, + 287, + 321 + ], + "type": "text", + "content": "Comparing different sensors. From Eq. 7 and Eq. 10, it is clear that for a depth sensing method, specifying one quantity among " + }, + { + "bbox": [ + 46, + 224, + 287, + 321 + ], + "type": "inline_equation", + "content": "P" + }, + { + "bbox": [ + 46, + 224, + 287, + 321 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 224, + 287, + 321 + ], + "type": "inline_equation", + "content": "d_{\\mathrm{max}}" + }, + { + "bbox": [ + 46, + 224, + 287, + 321 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 224, + 287, + 321 + ], + "type": "inline_equation", + "content": "l_{\\mathrm{min}}" + }, + { + "bbox": [ + 46, + 224, + 287, + 321 + ], + "type": "text", + "content": " will also determine the other two. We thus focus on the following question: To reach the same maximum sensing distance " + }, + { + "bbox": [ + 46, + 224, + 287, + 321 + ], + "type": "inline_equation", + "content": "d_{\\mathrm{max}}" + }, + { + "bbox": [ + 46, + 224, + 287, + 321 + ], + "type": "text", + "content": ", what is the power consumption " + }, + { + "bbox": [ + 46, + 224, + 287, + 321 + ], + "type": "inline_equation", + "content": "P" + }, + { + "bbox": [ + 46, + 224, + 287, + 321 + ], + "type": "text", + "content": " and eye-safety distance " + }, + { + "bbox": [ + 46, + 224, + 287, + 321 + ], + "type": "inline_equation", + "content": "l_{\\mathrm{min}}" + }, + { + "bbox": [ + 46, + 224, + 287, + 321 + ], + "type": "text", + "content": " of each method? This is a key problem for consumer devices with limited power budget. Plug Eq. 7 into Eq. 10 and rearrange:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 100, + 330, + 287, + 350 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 100, + 330, + 287, + 350 + ], + "spans": [ + { + "bbox": [ + 100, + 330, + 287, + 350 + ], + "type": "interline_equation", + "content": "\\boxed {l _ {\\min } = k _ {l d} \\cdot d _ {\\max } R _ {t 1} ^ {0. 3 7 5} R _ {t 2} ^ {- 0. 2 5},} \\tag {11}", + "image_path": "abe0459bdb0358396954d0f5b8875f64940a7c59233fa9d013b24ef2687e9e8c.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 354, + 228, + 365 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 354, + 228, + 365 + ], + "spans": [ + { + "bbox": [ + 47, + 354, + 228, + 365 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 354, + 228, + 365 + ], + "type": "inline_equation", + "content": "k_{ld}" + }, + { + "bbox": [ + 47, + 354, + 228, + 365 + ], + "type": "text", + "content": " is a method-independent constant." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 366, + 287, + 498 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 366, + 287, + 498 + ], + "spans": [ + { + "bbox": [ + 46, + 366, + 287, + 498 + ], + "type": "text", + "content": "Fig. 3 summarizes the results derived from Eq. 7 and Eq. 11 for different sensing methods. Full-frame pattern method is the most eye-safe but consumes the most power. Conversely, point scanning (synced) consumes the least power but is also the least eye-safe, which highly limits its application in consumer devices (e.g., laser projectors). Line scanning (synced) strikes the sweet middle ground, which extends the distance by a large margin while maintaining eye safety. Finally, by concentrating to a small ROI, the proposed adaptive method consumes the least power and achieves the best eye-safety." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 498, + 287, + 557 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 498, + 287, + 557 + ], + "spans": [ + { + "bbox": [ + 46, + 498, + 287, + 557 + ], + "type": "text", + "content": "To intuitively showcase this advantage, we assume " + }, + { + "bbox": [ + 46, + 498, + 287, + 557 + ], + "type": "inline_equation", + "content": "N \\sim 100" + }, + { + "bbox": [ + 46, + 498, + 287, + 557 + ], + "type": "text", + "content": " to 500, which is consistent with the spatial resolution of most concurrent 3D sensors. For high-resolution depth sensors with " + }, + { + "bbox": [ + 46, + 498, + 287, + 557 + ], + "type": "inline_equation", + "content": "N > 1000" + }, + { + "bbox": [ + 46, + 498, + 287, + 557 + ], + "type": "text", + "content": ", the gain is even greater. At the same maximum sensing distance, adaptive sensing:" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 58, + 558, + 286, + 616 + ], + "type": "list", + "angle": 0, + "index": 12, + "blocks": [ + { + "bbox": [ + 58, + 558, + 286, + 581 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 558, + 286, + 581 + ], + "spans": [ + { + "bbox": [ + 58, + 558, + 286, + 581 + ], + "type": "text", + "content": "- has the same eye-safety distance as full-frame sensors, while consuming " + }, + { + "bbox": [ + 58, + 558, + 286, + 581 + ], + "type": "inline_equation", + "content": "N^{-1}" + }, + { + "bbox": [ + 58, + 558, + 286, + 581 + ], + "type": "text", + "content": " (0.01 to 0.002)× lower power." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 58, + 582, + 286, + 616 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 582, + 286, + 616 + ], + "spans": [ + { + "bbox": [ + 58, + 582, + 286, + 616 + ], + "type": "text", + "content": "- has " + }, + { + "bbox": [ + 58, + 582, + 286, + 616 + ], + "type": "inline_equation", + "content": "N^{-0.125}" + }, + { + "bbox": [ + 58, + 582, + 286, + 616 + ], + "type": "text", + "content": " (0.56 to 0.46) × shorter (better) eye-safety distance as line-scanning, while consuming " + }, + { + "bbox": [ + 58, + 582, + 286, + 616 + ], + "type": "inline_equation", + "content": "N^{-0.5}" + }, + { + "bbox": [ + 58, + 582, + 286, + 616 + ], + "type": "text", + "content": " (0.1 to 0.04) × lower power." + } + ] + } + ], + "index": 11 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 46, + 618, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 618, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 618, + 287, + 713 + ], + "type": "text", + "content": "It is important to mention that these calculations are based on the assumption that the illuminated area for adaptive sensing is the same as line scanning: " + }, + { + "bbox": [ + 46, + 618, + 287, + 713 + ], + "type": "inline_equation", + "content": "R_{a} = N" + }, + { + "bbox": [ + 46, + 618, + 287, + 713 + ], + "type": "text", + "content": ". In practice, this area may be larger depending on the scene and application. The adaptive projector (e.g., SLM) may also have a limited light efficiency, which gives an effectively smaller " + }, + { + "bbox": [ + 46, + 618, + 287, + 713 + ], + "type": "inline_equation", + "content": "R_{a}" + }, + { + "bbox": [ + 46, + 618, + 287, + 713 + ], + "type": "text", + "content": " and thus lower SNR. Nonetheless, at the same maximum distance, adaptive sensing still has a power benefit as" + } + ] + } + ], + "index": 13 + }, + { + "type": "table", + "bbox": [ + 307, + 71, + 550, + 131 + ], + "blocks": [ + { + "bbox": [ + 307, + 71, + 550, + 131 + ], + "lines": [ + { + "bbox": [ + 307, + 71, + 550, + 131 + ], + "spans": [ + { + "bbox": [ + 307, + 71, + 550, + 131 + ], + "type": "table", + "html": "
SNRPlmin
V1cNkp d2maxN-1kldmax
V1-acNK-1kp d2maxN-1KkldmaxK0.375
V1-bcNK-0.5kp d2maxN-1K0.5kldmaxK0.125
", + "image_path": "de53f64ea62f34f430fc82430f37aa36f470bcd0bf245040dfb9f1eba1ba9cd7.jpg" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "table_body" + } + ], + "index": 14 + }, + { + "bbox": [ + 350, + 140, + 501, + 150 + ], + "lines": [ + { + "bbox": [ + 350, + 140, + 501, + 150 + ], + "spans": [ + { + "bbox": [ + 350, + 140, + 501, + 150 + ], + "type": "text", + "content": "Table 1. Variations of adaptive sensing." + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 304, + 173, + 545, + 222 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 173, + 545, + 222 + ], + "spans": [ + { + "bbox": [ + 304, + 173, + 545, + 222 + ], + "type": "text", + "content": "long as " + }, + { + "bbox": [ + 304, + 173, + 545, + 222 + ], + "type": "inline_equation", + "content": "R_{a} > \\sqrt{N}" + }, + { + "bbox": [ + 304, + 173, + 545, + 222 + ], + "type": "text", + "content": ", and it always has a eye-safety benefit since " + }, + { + "bbox": [ + 304, + 173, + 545, + 222 + ], + "type": "inline_equation", + "content": "l_{\\min}" + }, + { + "bbox": [ + 304, + 173, + 545, + 222 + ], + "type": "text", + "content": " is independent of " + }, + { + "bbox": [ + 304, + 173, + 545, + 222 + ], + "type": "inline_equation", + "content": "R_{a}" + }, + { + "bbox": [ + 304, + 173, + 545, + 222 + ], + "type": "text", + "content": ". The theoretical analysis forms the foundation for the proposed adaptive 3D sensing. We validate the analysis in a real-world prototype in Sec. 5." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 227, + 545, + 406 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 227, + 545, + 406 + ], + "spans": [ + { + "bbox": [ + 304, + 227, + 545, + 406 + ], + "type": "text", + "content": "Disjoint ROIs. So far, we assume an ideal flexible projector which can project light to arbitrarily-shaped, even disjoint ROIs simultaneously. In practice, certain hardware implementations do not have this capability (an example is discussed in Sec. 4.2). To this end, we propose a more flexible scanning strategy: During the camera exposure, the system scans " + }, + { + "bbox": [ + 304, + 227, + 545, + 406 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 304, + 227, + 545, + 406 + ], + "type": "text", + "content": " disjoint ROIs sequentially (typically " + }, + { + "bbox": [ + 304, + 227, + 545, + 406 + ], + "type": "inline_equation", + "content": "2 \\leq K \\leq 5" + }, + { + "bbox": [ + 304, + 227, + 545, + 406 + ], + "type": "text", + "content": "). This adaptive V1-a method consumes slightly more power and has a slightly longer eye-safety distance (Tab. 1). Another option is to divide the camera exposure into " + }, + { + "bbox": [ + 304, + 227, + 545, + 406 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 304, + 227, + 545, + 406 + ], + "type": "text", + "content": " shorter exposures, and the system scans a single ROI during each exposure. This adaptive V1-b method performs comparably as V1, but requires a " + }, + { + "bbox": [ + 304, + 227, + 545, + 406 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 304, + 227, + 545, + 406 + ], + "type": "text", + "content": " times higher camera frame rate. Please refer to the supplementary technical report for more design variations and detailed comparisons." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 305, + 420, + 531, + 434 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 420, + 531, + 434 + ], + "spans": [ + { + "bbox": [ + 305, + 420, + 531, + 434 + ], + "type": "text", + "content": "4. Implementation of Adaptive Illumination" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 441, + 545, + 573 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 441, + 545, + 573 + ], + "spans": [ + { + "bbox": [ + 304, + 441, + 545, + 573 + ], + "type": "text", + "content": "Now that we have theoretically analyzed the benefit of the proposed adaptive illumination, how can the proposed adaptive illumination be realized? Notice that this is not a trivial problem. The hardware implementation must satisfy two criteria: (1) The system can redistribute the optical power to a small ROI (guided by an attention map), and (2) This ROI can be projected to different parts of the scene flexibly and in real-time (e.g., 30Hz). A common LCD or DLP projector satisfies (2) but does not satisfy (1). In this section, we propose two hardware configurations that satisfy both conditions." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 306, + 583, + 473, + 596 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 583, + 473, + 596 + ], + "spans": [ + { + "bbox": [ + 306, + 583, + 473, + 596 + ], + "type": "text", + "content": "4.1. Implementation 1: Phase SLM" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 304, + 602, + 545, + 687 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 602, + 545, + 687 + ], + "spans": [ + { + "bbox": [ + 304, + 602, + 545, + 687 + ], + "type": "text", + "content": "Fig. 4(a) shows our SLM-based implementation. Our holographic projection approach is inspired by recent work on holographic near-eye 3D displays [20]. Specifically, a hologram to be reproduced by the SLM is decomposed as a sum of sub-holograms, where each sub-hologram diffracts light to a single object point in the scene. In [20], each sub-hologram is created using a lens phase function:" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 318, + 698, + 545, + 714 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 318, + 698, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 318, + 698, + 545, + 714 + ], + "type": "interline_equation", + "content": "f _ {n} ^ {\\text {l e n s}} (\\mathbf {X}) = e ^ {j 2 \\pi \\sqrt {(X - x _ {n}) ^ {2} + (Y - y _ {n}) ^ {2} + (Z - z _ {n}) ^ {2})} / \\lambda , \\tag {12}", + "image_path": "8c7f1f681ef6ded1ccb7c63e0744add261b300dbab7d29c3d0c57b9375f68ea5.jpg" + } + ] + } + ], + "index": 22 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "5058" + } + ] + } + ], + "index": 23 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 88, + 72, + 294, + 151 + ], + "blocks": [ + { + "bbox": [ + 88, + 72, + 294, + 151 + ], + "lines": [ + { + "bbox": [ + 88, + 72, + 294, + 151 + ], + "spans": [ + { + "bbox": [ + 88, + 72, + 294, + 151 + ], + "type": "image", + "image_path": "ee1ec079ae840fb7b84e24a2ecbe1854f14d18ef329d32826c883bb35cc61a46.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 130, + 157, + 242, + 167 + ], + "lines": [ + { + "bbox": [ + 130, + 157, + 242, + 167 + ], + "spans": [ + { + "bbox": [ + 130, + 157, + 242, + 167 + ], + "type": "text", + "content": "(a) Phase SLM-based implementation" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 319, + 76, + 506, + 150 + ], + "blocks": [ + { + "bbox": [ + 319, + 76, + 506, + 150 + ], + "lines": [ + { + "bbox": [ + 319, + 76, + 506, + 150 + ], + "spans": [ + { + "bbox": [ + 319, + 76, + 506, + 150 + ], + "type": "image", + "image_path": "4771f1b29a3eb3f20a60be6db724322b9e0e061ae2fe8179956f33b17d700f8c.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 355, + 157, + 451, + 166 + ], + "lines": [ + { + "bbox": [ + 355, + 157, + 451, + 166 + ], + "spans": [ + { + "bbox": [ + 355, + 157, + 451, + 166 + ], + "type": "text", + "content": "(b) MEMS + DOE-based method" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 46, + 177, + 547, + 222 + ], + "lines": [ + { + "bbox": [ + 46, + 177, + 547, + 222 + ], + "spans": [ + { + "bbox": [ + 46, + 177, + 547, + 222 + ], + "type": "text", + "content": "Figure 4. Hardware implementations. (a) Our first implementation is based on a phase-only SLM, which can redistribute light to arbitrarily-shaped, even disjointed ROIs. (b) Our second implementation is based on a DOE pattern generator with a 2D MEMS mirror. It has less flexibility and can only concentrate on one fixed-shape ROI at a time, but it benefits from low cost, simple optics and small form factor which makes it potentially easier to be miniaturized." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 243, + 288, + 281 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 243, + 288, + 281 + ], + "spans": [ + { + "bbox": [ + 46, + 243, + 288, + 281 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 243, + 288, + 281 + ], + "type": "inline_equation", + "content": "(X,Y,Z)" + }, + { + "bbox": [ + 46, + 243, + 288, + 281 + ], + "type": "text", + "content": " is the 3D position of each pixel in the subhologram, " + }, + { + "bbox": [ + 46, + 243, + 288, + 281 + ], + "type": "inline_equation", + "content": "(x_{n},y_{n},z_{n})" + }, + { + "bbox": [ + 46, + 243, + 288, + 281 + ], + "type": "text", + "content": " is the 3D position of the " + }, + { + "bbox": [ + 46, + 243, + 288, + 281 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 46, + 243, + 288, + 281 + ], + "type": "text", + "content": "-th object point, and " + }, + { + "bbox": [ + 46, + 243, + 288, + 281 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 46, + 243, + 288, + 281 + ], + "type": "text", + "content": " is the light wavelength. The full hologram is," + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 127, + 283, + 287, + 315 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 127, + 283, + 287, + 315 + ], + "spans": [ + { + "bbox": [ + 127, + 283, + 287, + 315 + ], + "type": "interline_equation", + "content": "H (\\mathbf {X}) = \\sum_ {n = 1} ^ {N} f _ {n} ^ {\\text {l e n s}}. \\tag {13}", + "image_path": "6420e829ea81eabe4ff99f5a9d73240933c881af6777ae96c986d48c8987fc54.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 319, + 287, + 438 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 319, + 287, + 438 + ], + "spans": [ + { + "bbox": [ + 46, + 319, + 287, + 438 + ], + "type": "text", + "content": "This lens phase function mimics a lens that focuses light to the object point at the correct depth, which works well for near-eye displays. One limitation of this lens phase function approach is that light is only redistributed locally. This is because the SLM can only reproduce a smooth hologram due to the Nyquist frequency determined by the finite pixel pitch. However, " + }, + { + "bbox": [ + 46, + 319, + 287, + 438 + ], + "type": "inline_equation", + "content": "f^{\\mathrm{lens}}" + }, + { + "bbox": [ + 46, + 319, + 287, + 438 + ], + "type": "text", + "content": " varies rapidly for off-center pixels (i.e. " + }, + { + "bbox": [ + 46, + 319, + 287, + 438 + ], + "type": "inline_equation", + "content": "X, Y" + }, + { + "bbox": [ + 46, + 319, + 287, + 438 + ], + "type": "text", + "content": " far away from " + }, + { + "bbox": [ + 46, + 319, + 287, + 438 + ], + "type": "inline_equation", + "content": "x_{n}, y_{n}" + }, + { + "bbox": [ + 46, + 319, + 287, + 438 + ], + "type": "text", + "content": "), causing aliasing artifacts. Therefore, sub-holograms of much smaller sizes must be used, which greatly limits the light efficiency." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 439, + 287, + 464 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 439, + 287, + 464 + ], + "spans": [ + { + "bbox": [ + 46, + 439, + 287, + 464 + ], + "type": "text", + "content": "To alleviate this limitation, we propose the use of mirror phase function:" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 56, + 467, + 287, + 500 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 56, + 467, + 287, + 500 + ], + "spans": [ + { + "bbox": [ + 56, + 467, + 287, + 500 + ], + "type": "interline_equation", + "content": "f _ {n} ^ {\\text {m i r r o r}} (\\mathbf {X}) = e ^ {j \\left(X \\cdot x _ {n} + Y \\cdot y _ {n}\\right)}, H (\\mathbf {X}) = \\sum_ {n = 1} ^ {N} f _ {n} ^ {\\text {m i r r o r}}. \\tag {14}", + "image_path": "18563b5dc1bda26d54cf7109f551ce4b62d1da3d16dd21dbee34220f8f99f43e.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 502, + 287, + 598 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 502, + 287, + 598 + ], + "spans": [ + { + "bbox": [ + 46, + 502, + 287, + 598 + ], + "type": "text", + "content": "The mirror phase function corresponds to a smooth phase map linear in terms of " + }, + { + "bbox": [ + 46, + 502, + 287, + 598 + ], + "type": "inline_equation", + "content": "X, Y" + }, + { + "bbox": [ + 46, + 502, + 287, + 598 + ], + "type": "text", + "content": ", and can be implemented on the SLM without aliasing. It allows us to use each sub-hologram as a mirror that reflects light to the right direction. By taking the sum of sub-holograms that reflect to different directions, desired projection patterns can be achieved. Please see the supplementary for detailed optical diagrams and discussion." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 601, + 288, + 696 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 601, + 288, + 696 + ], + "spans": [ + { + "bbox": [ + 46, + 601, + 288, + 696 + ], + "type": "text", + "content": "Conversion to phase-only holograms. Notice that Eq. 14 creates a hologram with both amplitudes and phases being spatially-variant, which cannot be implemented on a phase-only SLM. Several approaches [12, 16] have been proposed to convert such a full hologram to a phase-only hologram. Fortunately, our goal is not to project a high-quality image, and simple amplitude discarding is sufficient to project unique texture to the scene:" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 127, + 700, + 287, + 715 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 127, + 700, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 127, + 700, + 287, + 715 + ], + "type": "interline_equation", + "content": "H _ {\\text {p h a s e}} = \\operatorname {A r g} [ H ]. \\tag {15}", + "image_path": "d490244a7a3a8152a930699d44d0852cad48349720d7112e323be639f794d0b3.jpg" + } + ] + } + ], + "index": 12 + }, + { + "type": "image", + "bbox": [ + 334, + 255, + 503, + 326 + ], + "blocks": [ + { + "bbox": [ + 371, + 244, + 466, + 253 + ], + "lines": [ + { + "bbox": [ + 371, + 244, + 466, + 253 + ], + "spans": [ + { + "bbox": [ + 371, + 244, + 466, + 253 + ], + "type": "text", + "content": "Implementation 1: Phase SLM" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 334, + 255, + 503, + 326 + ], + "lines": [ + { + "bbox": [ + 334, + 255, + 503, + 326 + ], + "spans": [ + { + "bbox": [ + 334, + 255, + 503, + 326 + ], + "type": "image", + "image_path": "0dd3c5e05548c4ad1b35ed419f1f652bc28df134b4d6ec38a59831b96541ecaf.jpg" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_body" + } + ], + "index": 14 + }, + { + "type": "image", + "bbox": [ + 334, + 348, + 503, + 418 + ], + "blocks": [ + { + "bbox": [ + 375, + 338, + 477, + 346 + ], + "lines": [ + { + "bbox": [ + 375, + 338, + 477, + 346 + ], + "spans": [ + { + "bbox": [ + 375, + 338, + 477, + 346 + ], + "type": "text", + "content": "Implementation 2: MEMS + DOE" + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 334, + 348, + 503, + 418 + ], + "lines": [ + { + "bbox": [ + 334, + 348, + 503, + 418 + ], + "spans": [ + { + "bbox": [ + 334, + 348, + 503, + 418 + ], + "type": "image", + "image_path": "92475a32c762f22f669a9f85a9efc95696a0d1e4cd362c32f3987820d2a17460.jpg" + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 430, + 547, + 473 + ], + "lines": [ + { + "bbox": [ + 305, + 430, + 547, + 473 + ], + "spans": [ + { + "bbox": [ + 305, + 430, + 547, + 473 + ], + "type": "text", + "content": "Figure 5. Hardware prototypes. (Upper) Spatial Light Modulator (SLM) implementation. (Lower) Micro-electromechanical (MEMS) mirror + diffractive optical element (DOE) implementation." + } + ] + } + ], + "index": 17, + "angle": 0, + "type": "image_caption" + } + ], + "index": 16 + }, + { + "type": "image", + "bbox": [ + 306, + 492, + 545, + 582 + ], + "blocks": [ + { + "bbox": [ + 306, + 492, + 545, + 582 + ], + "lines": [ + { + "bbox": [ + 306, + 492, + 545, + 582 + ], + "spans": [ + { + "bbox": [ + 306, + 492, + 545, + 582 + ], + "type": "image", + "image_path": "deac0b741cc8948470960e1db8f41eafb2f1fcffd3d09992d254465714d7df33.jpg" + } + ] + } + ], + "index": 18, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 589, + 547, + 677 + ], + "lines": [ + { + "bbox": [ + 305, + 589, + 547, + 677 + ], + "spans": [ + { + "bbox": [ + 305, + 589, + 547, + 677 + ], + "type": "text", + "content": "Figure 6. Examples of emulating full frame, line scanning, and adaptive sensors on a phase only spatial light modulator. Note that the full frame and adaptive patterns are captured within the full exposure time, while each line in the line scanning pattern is captured within " + }, + { + "bbox": [ + 305, + 589, + 547, + 677 + ], + "type": "inline_equation", + "content": "1/N" + }, + { + "bbox": [ + 305, + 589, + 547, + 677 + ], + "type": "text", + "content": " of the time. We scale the intensities for visualization. Note that the bright center dot is caused by the SLM DC term, and can be mitigated with additional optical filters and manufacturing processes." + } + ] + } + ], + "index": 19, + "angle": 0, + "type": "image_caption" + } + ], + "index": 18 + }, + { + "bbox": [ + 306, + 689, + 546, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 689, + 546, + 714 + ], + "spans": [ + { + "bbox": [ + 306, + 689, + 546, + 714 + ], + "type": "text", + "content": "Efficient implementation. The mirror phase function consists of simple arithmetic operations on large matri" + } + ] + } + ], + "index": 20 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "5059" + } + ] + } + ], + "index": 21 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 51, + 71, + 547, + 312 + ], + "blocks": [ + { + "bbox": [ + 51, + 71, + 547, + 312 + ], + "lines": [ + { + "bbox": [ + 51, + 71, + 547, + 312 + ], + "spans": [ + { + "bbox": [ + 51, + 71, + 547, + 312 + ], + "type": "image", + "image_path": "7222947253c0b01a86582189710fb66fd088aba817648c19d482d62cb76d87e5.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 319, + 546, + 376 + ], + "lines": [ + { + "bbox": [ + 46, + 319, + 546, + 376 + ], + "spans": [ + { + "bbox": [ + 46, + 319, + 546, + 376 + ], + "type": "text", + "content": "Figure 7. Comparison between sensing strategies. Our approach is more robust to ambient light than line scanning and full frame sensors; notice how our adaptive approach degrades less than line scanning and full frame from low ambient lighting (700 lux) to high ambient lighting (4000 lux). We keep sensor settings constant for each low ambient-high ambient pair. The total number of dots in the adaptive method (ours), line scanning and full frame is around 150, " + }, + { + "bbox": [ + 46, + 319, + 546, + 376 + ], + "type": "inline_equation", + "content": "108 \\times 150" + }, + { + "bbox": [ + 46, + 319, + 546, + 376 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 319, + 546, + 376 + ], + "type": "inline_equation", + "content": "150^2" + }, + { + "bbox": [ + 46, + 319, + 546, + 376 + ], + "type": "text", + "content": ", respectively. Zoom in to see the red dots in the camera images." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 384, + 289, + 504 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 384, + 289, + 504 + ], + "spans": [ + { + "bbox": [ + 46, + 384, + 289, + 504 + ], + "type": "text", + "content": "ces, which can be implemented efficiently on a GPU. We implement our hologram generator in CUDA and render the resulting hologram phase from the frame-buffer to the SLM using OpenGL-CUDA interoperability. On a NVIDIA Jetson Nano, an embedded system-on-module with a Tegra X1 Maxwell 256-core GPU and limited computing resources, we are able to generate 1080p holograms with around 100 points or less at 30 fps. Our implementation and simulator can be found at https://github.com/btilmon/holoCu." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 512, + 231, + 525 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 512, + 231, + 525 + ], + "spans": [ + { + "bbox": [ + 47, + 512, + 231, + 525 + ], + "type": "text", + "content": "4.2. Implementation 2: MEMS + DOE" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 531, + 287, + 651 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 531, + 287, + 651 + ], + "spans": [ + { + "bbox": [ + 46, + 531, + 287, + 651 + ], + "type": "text", + "content": "Our second implementation is to adjust the beam incident angle of a diffractive optical element (DOE) with a MEMS mirror, as shown in Fig. 4(b). DOE offers a cheap, energy-efficient solution for random dot projection in single-shot structured light (Kinect V1) or active stereo (RealSense). While those systems use a DOE that covers the entire scene, we use a small FOV (" + }, + { + "bbox": [ + 46, + 531, + 287, + 651 + ], + "type": "inline_equation", + "content": "\\approx 5^{\\circ}" + }, + { + "bbox": [ + 46, + 531, + 287, + 651 + ], + "type": "text", + "content": ") that only corresponds to a small ROI. By rotating the MEMS mirror, the deflected laser beam hits the DOE at different angles, thus generating a dot pattern at different ROIs of the scene." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 653, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 653, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 653, + 288, + 715 + ], + "type": "text", + "content": "Comparison with phase SLM. The MEMS + DOE implementation is less flexible than the SLM implementation since the hologram shape is fixed (determined by the DOE phase pattern). This is schematically shown in Fig. 4: While SLM can illuminate ROIs of various shapes (P1-" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 384, + 546, + 492 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 384, + 546, + 492 + ], + "spans": [ + { + "bbox": [ + 304, + 384, + 546, + 492 + ], + "type": "text", + "content": "P3), MEMS + DOE can only create the same shape shifted across the scene. Moreover, while the SLM can redistribute the optical power over two disjoint ROIs during the same camera exposure (P4), different ROIs are scanned and imaged sequentially by the MEMS mirror, which slightly decreases the SNR (see Sec. 3.2 for detailed analysis). Nevertheless, the MEMS + DOE approach benefits from low cost, simple optics and small form factor, which are important factors for mobile and wearable devices." + } + ] + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 310, + 505, + 547, + 648 + ], + "blocks": [ + { + "bbox": [ + 310, + 505, + 547, + 648 + ], + "lines": [ + { + "bbox": [ + 310, + 505, + 547, + 648 + ], + "spans": [ + { + "bbox": [ + 310, + 505, + 547, + 648 + ], + "type": "image", + "image_path": "e1fc8a796eabed2c4ba4b6ce285d961e52ddefdf7a811b4b5e11fac67aa740dd.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 654, + 547, + 711 + ], + "lines": [ + { + "bbox": [ + 304, + 654, + 547, + 711 + ], + "spans": [ + { + "bbox": [ + 304, + 654, + 547, + 711 + ], + "type": "text", + "content": "Figure 8. Outdoor active depth sensing under 50 kilolux direct sunlight with Phase SLM. Our sensor works outdoors under direct sunlight. We show results up to 2 meters but believe this range could be extended with further SLM optical engineering. Zoom in to see the red dots in the camera images." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_caption" + } + ], + "index": 7 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "5060" + } + ] + } + ], + "index": 9 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 52, + 73, + 286, + 182 + ], + "blocks": [ + { + "bbox": [ + 52, + 73, + 286, + 182 + ], + "lines": [ + { + "bbox": [ + 52, + 73, + 286, + 182 + ], + "spans": [ + { + "bbox": [ + 52, + 73, + 286, + 182 + ], + "type": "image", + "image_path": "241af25f8f11a991852d4a79699c6abbcd1212e2d264a8fd9bcc90a85d7acc85.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 191, + 286, + 235 + ], + "lines": [ + { + "bbox": [ + 46, + 191, + 286, + 235 + ], + "spans": [ + { + "bbox": [ + 46, + 191, + 286, + 235 + ], + "type": "text", + "content": "Figure 9. MEMS + DOE implementation. The MEMS voltages are updated to direct the dot pattern onto the predominant textureless region in both frames. Zoom in the camera images to see the red dots." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 244, + 127, + 257 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 244, + 127, + 257 + ], + "spans": [ + { + "bbox": [ + 47, + 244, + 127, + 257 + ], + "type": "text", + "content": "5. Experiments" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 264, + 286, + 419 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 264, + 286, + 419 + ], + "spans": [ + { + "bbox": [ + 46, + 264, + 286, + 419 + ], + "type": "text", + "content": "Hardware prototypes. Fig. 5 shows both hardware prototypes of our proposed method. We use two FLIR BFS-U3-16S2C-CS cameras equipped with " + }, + { + "bbox": [ + 46, + 264, + 286, + 419 + ], + "type": "inline_equation", + "content": "20\\mathrm{mm}" + }, + { + "bbox": [ + 46, + 264, + 286, + 419 + ], + "type": "text", + "content": " lenses as a stereo pair. Our SLM implementation uses a Holoyeye GAEA LCoS (phase-only) SLM, which can display 4K phase maps at 30 frames per second. Our MEMS + DOE implementation uses a " + }, + { + "bbox": [ + 46, + 264, + 286, + 419 + ], + "type": "inline_equation", + "content": "0.8\\mathrm{mm}" + }, + { + "bbox": [ + 46, + 264, + 286, + 419 + ], + "type": "text", + "content": " diameter bonded Mirrorcle MEMS Mirror. A random dot DOE with a small FOV is preferred. Here, we used a Holoyeye DE-R 339 DOE that produces a periodic 6x6 dot pattern with " + }, + { + "bbox": [ + 46, + 264, + 286, + 419 + ], + "type": "inline_equation", + "content": "5^{\\circ}" + }, + { + "bbox": [ + 46, + 264, + 286, + 419 + ], + "type": "text", + "content": " FOV instead and we tilt the DOE such that the pattern is still unique locally on the epipolar line. Please refer to the supplementary report for detailed setup and calibration procedures." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 423, + 286, + 543 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 423, + 286, + 543 + ], + "spans": [ + { + "bbox": [ + 46, + 423, + 286, + 543 + ], + "type": "text", + "content": "Attention map and depth estimation. We adopt classical semi global block matching for depth estimation [10]. The attention map is determined by randomly choosing pixels that do not have a valid depth value from the depth map computed from passive images. In practice, the attention map can be conditioned by the application such that illumination is only needed within the regions where AR objects are inserted. Our goal is to present a general sensor that can fit into many different perception systems and improve active depth sensing." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 546, + 286, + 641 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 546, + 286, + 641 + ], + "spans": [ + { + "bbox": [ + 46, + 546, + 286, + 641 + ], + "type": "text", + "content": "Comparison between sensing strategies. We emulate full-frame and line-scanning strategies on our SLM implementation and compare them with our adaptive sensing strategy. An example of each emulated sensor can be found in Fig. 6. For line scanning, we compute and project the hologram of the dot pattern line-by-line. We capture the image for each line individually and stitch the corresponding camera rows together into a single image." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 642, + 286, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 642, + 286, + 712 + ], + "spans": [ + { + "bbox": [ + 46, + 642, + 286, + 712 + ], + "type": "text", + "content": "Fig. 7 shows the results for three different scenes. All scenes are illuminated with the same ambient lighting and laser power. Laser power, exposure time and illuminated area are chosen to ensure fair comparison. Due to the dominating photon noise from the ambient light, full-frame and line scanning methods have a low SNR. As a result, depth" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 72, + 545, + 132 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 132 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 132 + ], + "type": "text", + "content": "estimation fails in the textureless regions. Since the proposed adaptive sensing technique concentrates light to the textureless regions, it achieves much higher SNR and obtains higher-quality depth maps, which validates our theoretical analysis." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 137, + 545, + 243 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 137, + 545, + 243 + ], + "spans": [ + { + "bbox": [ + 304, + 137, + 545, + 243 + ], + "type": "text", + "content": "Outdoor depth sensing under direct sunlight. Fig. 8 demonstrates our Phase SLM prototype working outdoors under 50 kilolux direct sunlight. We can rely on passive stereo to compute depth for the majority of the scene and only project light where necessary, such as the white textureless pot. We also show a distance test of the Phase SLM prototype at 2 meters. We believe this distance could be increased with further SLM optical engineering in future work." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 249, + 545, + 320 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 249, + 545, + 320 + ], + "spans": [ + { + "bbox": [ + 304, + 249, + 545, + 320 + ], + "type": "text", + "content": "MEMS + DOE implementation. Fig. 9 demonstrates our MEMS + DOE prototype. The dot pattern is projected to a textureless object which improves the disparity compared to passive stereo. When the system moves to another location at " + }, + { + "bbox": [ + 304, + 249, + 545, + 320 + ], + "type": "inline_equation", + "content": "t_1" + }, + { + "bbox": [ + 304, + 249, + 545, + 320 + ], + "type": "text", + "content": ", it analyzes the new captured images and directs the ROI to the new position of the textureless object." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 335, + 459, + 346 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 335, + 459, + 346 + ], + "spans": [ + { + "bbox": [ + 305, + 335, + 459, + 346 + ], + "type": "text", + "content": "6. Limitations and Discussion" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 356, + 545, + 486 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 356, + 545, + 486 + ], + "spans": [ + { + "bbox": [ + 304, + 356, + 545, + 486 + ], + "type": "text", + "content": "Optical power vs computation power. Although we do not explicitly compare the optical power savings from adaptive sensing with the additional computation power needed for computing the attention map and projector control signal (e.g., phase map for SLM), we show that such computations consist of basic arithmetic operations and can be implemented on embedded systems like NVIDIA Jetson Nano, suggesting that our approach can be deployed on increasingly available mobile GPUs. Our system will have even higher benefits for outdoor applications where optical power dominates." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 492, + 545, + 588 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 492, + 545, + 588 + ], + "spans": [ + { + "bbox": [ + 304, + 492, + 545, + 588 + ], + "type": "text", + "content": "Learning-based attention map and depth estimation. In this work, we use simple, low-complexity texture analysis and semi global matching for attention map and depth estimation. It is possible to design neural networks to achieve better depth estimation, at the cost of higher computation. Our focus in on validating the proposed adaptive sensing as a promising novel sensing strategy, and we expect more practical algorithms to be developed in future work." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 593, + 545, + 664 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 593, + 545, + 664 + ], + "spans": [ + { + "bbox": [ + 304, + 593, + 545, + 664 + ], + "type": "text", + "content": "Other active depth sensing mechanisms. Although this paper only shows hardware implementations for active stereo, the adaptive sensing strategy can be applied to other depth sensing mechanisms such as single/multi-shot structured light, direct/indirect ToF, FMCW Lidar, etc., which can be a promising future direction." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 665, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 545, + 712 + ], + "type": "text", + "content": "Acknowledgements. The authors acknowledge partial funding from the Office of Naval Research through ONR N00014-18-1-2663 and the National Science Foundation through NSF 1942444." + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "type": "text", + "content": "5061" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 288, + 712 + ], + "type": "list", + "angle": 0, + "index": 15, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 135 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 135 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 135 + ], + "type": "text", + "content": "[1] Supreeth Achar, Joseph R. 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IEEE, 2003. 2" + } + ] + } + ], + "index": 6 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "5063" + } + ] + } + ], + "index": 8 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 9 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Enhanced Multimodal Representation Learning With Cross-Modal KD/550b12f3-e75d-4ee0-8736-cf2526b0aff9_content_list.json b/2023/Enhanced Multimodal Representation Learning With Cross-Modal KD/550b12f3-e75d-4ee0-8736-cf2526b0aff9_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..89c00e809c3bca18e953dfa6e26ccc01a7eccd54 --- /dev/null +++ b/2023/Enhanced Multimodal Representation Learning With Cross-Modal KD/550b12f3-e75d-4ee0-8736-cf2526b0aff9_content_list.json @@ -0,0 +1,1658 @@ +[ + { + "type": "text", + "text": "Enhanced Multimodal Representation Learning with Cross-modal KD", + "text_level": 1, + "bbox": [ + 129, + 130, + 839, + 151 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Mengxi Chen $^{1}$ , Linyu Xing $^{1}$ , Yu Wang $^{1,2\\boxtimes}$ , Ya Zhang $^{1,2\\boxtimes}$", + "bbox": [ + 256, + 186, + 712, + 208 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "$^{1}$ Shanghai Jiao Tong University, $^{2}$ Shanghai AI Laboratory", + "bbox": [ + 256, + 208, + 712, + 226 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "{mxchen_mc,xly8991,yuwanhsjtu,ya_zhang}@sjtu.edu.cn", + "bbox": [ + 261, + 227, + 702, + 243 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 277, + 312, + 292 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "This paper explores the tasks of leveraging auxiliary modalities which are only available at training to enhance multimodal representation learning through cross-modal Knowledge Distillation (KD). The widely adopted mutual information maximization-based objective leads to a shortcut solution of the weak teacher, i.e., achieving the maximum mutual information by simply making the teacher model as weak as the student model. To prevent such a weak solution, we introduce an additional objective term, i.e., the mutual information between the teacher and the auxiliary modality model. Besides, to narrow down the information gap between the student and teacher, we further propose to minimize the conditional entropy of the teacher given the student. Novel training schemes based on contrastive learning and adversarial learning are designed to optimize the mutual information and the conditional entropy, respectively. Experimental results on three popular multimodal benchmark datasets have shown that the proposed method outperforms a range of state-of-the-art approaches for video recognition, video retrieval and emotion classification.", + "bbox": [ + 75, + 311, + 473, + 628 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 662, + 207, + 678 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Multimodal learning has shown much promise in a wide spectrum of applications, such as video understanding [20, 39, 44], sentiment analysis [1, 19, 47] and medical image segmentation [7, 49]. It is generally recognized that including more modalities helps the prediction accuracy. For many real-world applications, while one has to make predictions based on limited modalities due to efficiency or cost concerns, it is usually possible to collect additional modalities at training. To enhance the representation learned, several studies have thus considered to leverage such modalities as a form of auxiliary information at training [11, 23, 29, 50]. Several attempts have explored to fill in the auxiliary modalities at test time, by employing approaches such as Generative Adversarial Network", + "bbox": [ + 75, + 688, + 468, + 900 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/4fa345fa4a238ee1ec657c402db9192b2ec53df16a324b9a667593c646b1c51c.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 514, + 280, + 879, + 388 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/236838d44f4acc4a149a4621469e1da40f1a611edf0a578df0d76cb9f127624e.jpg", + "image_caption": [ + "Figure 1. Illustration of the difference between the MI-based method and the proposed AMID method. (a) MI-based methods maximize $I(M;S)$ . (b) AMID maximizes $I(M;S)$ and $I(M;A)$ , while minimizing $H(M|S)$ ." + ], + "image_footnote": [], + "bbox": [ + 516, + 391, + 877, + 498 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "(GAN) [4, 22]. However, such data generation-based approaches introduce extra computation costs at inference.", + "bbox": [ + 498, + 595, + 890, + 626 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "As an alternative, cross-modal knowledge distillation is proposed, where a teacher model trained with both the target modalities and the auxiliary modalities (denoted as full modalities hereafter), is employed to guide the training of a student model with target modalities only [10, 11, 16, 23, 45, 46]. In such a way, the student model directly learns to embed information about auxiliary modalities and involves no additional computational cost at inference. A typical practice is to pre-train the teacher model from the full modality data, and fix it during the training. While such a setting enables the teacher to provide information-rich representation [23, 46], it may not be favorable for the alignment of the teacher and student, due to the large information gap between them, especially at the early stage of training [32].", + "bbox": [ + 496, + 627, + 892, + 839 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "To better facilitate the knowledge transfer, online KD is proposed to jointly train the teacher and the student. One common solution is to maximize the mutual information (MI) between the teacher and the student in a shared", + "bbox": [ + 496, + 839, + 893, + 898 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 808, + 44 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "11766", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "space [42]. However, such an objective only focuses on maximizing the shared knowledge, in terms of percentage, from the teacher to the student, which is necessary but not sufficient to guarantee a complete knowledge transfer. As illustrated in Fig. 1(a), a short-cut solution is to simply make the teacher model capture less information, i.e., shrinking the entropy of the teacher.", + "bbox": [ + 75, + 90, + 468, + 196 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Under the framework online KD, this paper explores to simultaneously achieve: 1) maintaining the representation capacity of the full modality teacher as much as possible, and 2) narrowing down the information gap between the teacher and the student. As Fig. 1(b) shows, in addition to maximizing the MI between the teacher and the student, maximizing the MI between the teacher and an additional auxiliary model may contribute to the former goal, while minimizing the conditional entropy of the teacher given the student may benefit the latter goal. We thus propose a new objective function consisting of all the above three terms. To achieve the optimization of the MI, we further derive a new form of its lower bound by taking into account the supervision of the label, and propose a contrastive learning-based approach to implement it. To minimize the conditional entropy, an adversarial learning-based approach is introduced, where additional discriminators are used to distinguish representations between the teacher and the student. We name the proposed method Adversarial Mutual Information Distillation (AMID) hereafter.", + "bbox": [ + 75, + 198, + 470, + 498 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To validate the effectiveness of AMID, extensive experiments on three popular multimodal tasks including video recognition, video retrieval and emotion classification tasks are conducted. The performance of these tasks are conducted on UCF51 [40], ActivityNet [20] and IEMOCAP [6] benchmark datasets, respectively. The results show that AMID outperforms a range of state-of-the-art approaches on all three tasks. To summarize, the main contribution of this paper is threefold:", + "bbox": [ + 75, + 500, + 468, + 635 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- We propose a novel cross-modal KD method, Adversarial Mutual Information Distillation (AMID), to prevent the teacher from losing information by maximizing the MI between it and an auxiliary modality model.", + "- AMID maximally transfers information from the teacher to the student by optimizing the MI between them and minimizing the conditional entropy of the teacher given the student.", + "- To implement the joint optimization of the three objective terms, a novel training approach that leverages the combined advantage of both contrastive learning and adversarial learning is proposed." + ], + "bbox": [ + 96, + 645, + 467, + 845 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 76, + 859, + 218, + 875 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Knowledge Distillation. Knowledge distillation (KD) is", + "bbox": [ + 96, + 885, + 467, + 900 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "first proposed in [21], where soft labels in predictive space produced by the teacher through temperature hyperparameter transfer the dark knowledge to the student. Later, many works studied and demonstrated the benefits of distilling knowledge in the latent space [25, 35, 38, 48]. There have been some works that explore KD-based methods for cross-modal representation learning. CMC [41] aligns different views of the same samples by contrastive learning to extract shared information. CRD [42] leverages instance-level contrastive objectives to perform KD. GMC [36] learns geometrically aligned representations by aligning modality-specific representations with that of the corresponding complete observation. However, these methods can not transfer the correlation among instances, which are also valuable in many tasks. To transfer the inter-sample relation, [9] propose CCL to close the cross-modal semantic gap between the multimodality teacher and the student by contrasting different modal embeddings in the same classes in a common latent space. CRCD [51] distills the information of the teacher space by maximizing two complementary MI criteria. In contrast to these recent KD works which only consider the alignment between the teacher and student but neglect the objectives' impact on the teacher, we proposed a new KD objective that helps the teacher capture as much auxiliary information as possible and constraints the alignment simultaneously.", + "bbox": [ + 496, + 90, + 890, + 484 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Mutual Information Maximization. MI is first introduced to deep learning in [2], and since then, many methods have proposed to combine variational bounds with parameterized neural networks to enable differentiable and tractable estimation of MI in high-dimensional spaces [15, 34]. The character that MI can be used to represent the relationship between two variables is well-suited for correlated multimodal data. [19] hierarchically optimizes MI in unimodal pairs and between multimodal and unimodal representations for maintaining useful information while filtering noise in unimodal input. [28] proposed TupleInfoNCE to optimize MI in multimodal input tuples which enables the model to capture both the modal-shared information and the specific information. However, these methods rarely consider the correlation among samples with the supervision of the label, which are still useful. In this paper, we derive a new lower bound on MI in teacher-student pairs which takes into account the inter-sample correlation and propose a contrastive-learning method for its maximization.", + "bbox": [ + 496, + 488, + 890, + 773 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Adversarial Learning. Since [18] developed adversarial learning in deep learning, many researchers attempt to improve its performance by stabilizing the training process. In addition to modifying the structure of discriminator or generator [8, 31, 37], several works still considered incorporating multiple discriminators to improve learning [13, 14, 33]. Similar to [13], in this paper, we design two additional discriminators and adjust their weights adaptively.", + "bbox": [ + 496, + 780, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "11767", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "3. Method", + "text_level": 1, + "bbox": [ + 76, + 89, + 168, + 104 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Suppose we have a multimodal dataset with $n$ modalities, consisting of $k$ target modalities $\\{x_1, \\dots, x_k\\}$ and $n - k$ auxiliary modalities $\\{x_{k + 1}, \\dots, x_n\\}$ . Denote the model trained with all $n$ modalities, $k$ target modalities only, and $n - k$ auxiliary modalities only as full modality model $M(x_1, \\dots, x_n)$ , target modality model $S(x_1, \\dots, x_k)$ , and auxiliary modality model $A(x_{k + 1}, \\dots, x_n)$ , respectively. This paper aims to transfer knowledge from the full modality model $M$ to the target modality model $S$ with the assistant of auxiliary modalities at training.", + "bbox": [ + 75, + 114, + 468, + 265 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "A widely adopted objective for cross-modal knowledge transfer is to maximize the MI between the representation of the full modality teacher $M$ and the representation of the target modality student $S$ , i.e. $I(M; S)$ . But there exists a shout-cut solution as shown in Fig. 1(a). In order to prevent this problem, we propose AMID, which maximizes the MI between $M$ and $A$ , i.e. $I(M; A)$ , so as to ensure the full modality model captures information from both target modalities and auxiliary modalities, and maximizes $I(M; S)$ while minimizing the conditional entropy of the teacher given the student $H(M|S)$ , so as to narrow down the information gap between the teacher and the student. For optimizing the MI, we derive a new form of its lower bound and maximize it through a contrastive learning-based approach. For minimizing $H(M|S)$ , we introduce an adversarial learning-based approach.", + "bbox": [ + 75, + 266, + 470, + 507 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "To sum up, the overall objective is to optimize:", + "bbox": [ + 96, + 507, + 406, + 522 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {O} = \\alpha_ {1} \\mathrm {l b} (I (M; S)) + \\alpha_ {2} \\mathrm {l b} (I (M; A)) - \\alpha_ {3} H (M | S), \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 75, + 527, + 468, + 545 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\mathrm{lb}(\\cdot)$ means the lower bound on MI, $\\alpha_{1},\\alpha_{2},\\alpha_{3}$ are the different weights for the corresponding terms.", + "bbox": [ + 75, + 551, + 468, + 582 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Mutual Information Optimization", + "text_level": 1, + "bbox": [ + 76, + 589, + 375, + 604 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In this section, we will focus on how to optimize $I(M;S)$ and $I(M;A)$ through maximizing their lower bounds for capturing as much information as possible. Unlike [42] which only considers the correlation between the teacher's representation and that of the student in the same sample, we derive a new form of lower bound on MI by taking into account the correlation of samples within a class. Notice that as the deduction procedures for $I(M;S)$ and $I(M;A)$ are the same, we will construct an approximate loss for optimizing $I(M;S)$ .", + "bbox": [ + 75, + 612, + 468, + 762 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Firstly, we define a distribution $q$ which models the joint distribution of $M$ and $S$ . A latent variable, $C$ , is used to indicate whether a tuple $(M, S)$ comes from the same class $(C = 1)$ or not $(C = 0)$ :", + "bbox": [ + 75, + 763, + 468, + 823 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} q (M, S | C = 1) = p (M, S); \\\\ q (M, S \\mid C = 0) = p (M) p (S). \\tag {2} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 171, + 829, + 467, + 864 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We sample $(M, S)$ by considering the relationship between full modality and target modality representations in the", + "bbox": [ + 75, + 869, + 468, + 900 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "same classes, which is more effective for transferring information. The pair $(M, S)$ is from the joint distribution when $M, S$ are in the same class or from the product of the marginal distributions when $M, S$ are in different classes.", + "bbox": [ + 496, + 90, + 890, + 151 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Suppose in a mini-batch, given a specific $M_{i}$ , there are $k - 1$ positive pairs $(M_{i}, S_{i}^{\\eta_{j}})$ drawn from the joint distribution, where $\\{\\eta_{j}\\}_{j = 1}^{k - 1}$ is an index set and every element indicates the position of other $S$ with the same class as $M_{i}$ , 1 positive pair $(M_{i}, S_{i}^{\\eta_{0}})$ from the same sample, and $N$ negative pairs $(M_{i}, S_{i}^{\\xi_{l}})$ from the product of marginals, where $\\{S_{i}^{\\xi_{l}}\\}_{l = 1}^{N}$ are $N$ target modality representations from different classes than $M_{i}$ . Then the priors of $C$ can be calculated as $q(C = 1) = \\frac{k}{N + k}$ and $q(C = 0) = \\frac{N}{N + k}$ . Using Bayes' rule, the logarithmic posterior for $C = 1$ is given by:", + "bbox": [ + 496, + 152, + 890, + 306 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\log q (C = 1 | M, S) = \\log \\frac {q (M , S | C = 1) q (C = 1)}{\\sum_ {c = 0 , 1} q (M , S | C = c) q (C = c)} \\\\ = - \\log (1 + \\frac {N}{k} \\frac {p (M) p (S)}{p (M , S)}) \\\\ \\leq - \\log (\\frac {N}{k}) + \\log \\frac {p (M , S)}{p (M) p (S)}. \\tag {3} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 500, + 314, + 890, + 419 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "With Eq. (3), we can get a lower bound on $I(M; S)$ as:", + "bbox": [ + 519, + 426, + 883, + 443 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} I (M; S) = \\mathbb {E} _ {(M, S) \\sim p (M, S)} \\log \\frac {p (M , S)}{p (M) p (S)} \\tag {4} \\\\ \\geq \\log (\\frac {N}{k}) + \\mathbb {E} _ {q (M, S | C = 1)} \\log q (C = 1 | M, S). \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 540, + 450, + 890, + 515 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Thus maximizing $\\mathbb{E}_{q(M,S|C = 1)}\\log q(C = 1|M,S)$ is to maximize the lower bound on $I(M;S)$ . However, the true distribution $q(C = 1|M,S)$ cannot be calculated directly. A classification model $h:\\{M,S\\} \\to [0,1]$ is fitted to approximate this distribution. The log-likelihood of the sampled tuples with model $h$ is defined as:", + "bbox": [ + 496, + 522, + 890, + 613 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\mathcal {I} (h) = k \\mathbb {E} _ {q (M, S \\mid C = 1)} [ \\log h (M, S) ] \\\\ + N \\mathbb {E} _ {q (M, S | C = 0)} [ \\log (1 - h (M, S)) ]. \\tag {5} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 526, + 622, + 890, + 659 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "This likelihood is maximized to make $h$ a good approximation to $q(C = 1|M,S)$ . Thus, we can get the optimal $h^{*}(M,S) = q(C = 1|M,S)$ . Because that both $\\log h(M,S)$ and $\\log (1 - h(M,S))$ are non-positive for any $h$ , we can rewrite Eq. (4) according to Eq. (5):", + "bbox": [ + 496, + 666, + 890, + 743 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} I (M; S) \\geq \\log (\\frac {N}{k}) + \\mathbb {E} _ {q (M, S | C = 1)} [ \\log h ^ {*} (M, S) ] \\\\ \\geq \\log \\left(\\frac {N}{k}\\right) + k \\mathbb {E} _ {q (M, S | C = 1)} \\left[ \\log h ^ {*} (M, S) \\right] \\\\ + N \\mathbb {E} _ {q (M, S | C = 0)} [ \\log (1 - h ^ {*} (M, S)) ] \\\\ = \\log \\left(\\frac {N}{k}\\right) + \\max _ {h} \\mathcal {I} (h) \\geq \\log \\left(\\frac {N}{k}\\right) + \\mathcal {I} (h) \\tag {6} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 513, + 751, + 890, + 861 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Thus we can optimize $I(M; S)$ indirectly by maximizing this lower bound $\\log \\left( \\frac{N}{k} \\right) + \\mathcal{I}(h)$ . Inspired by [9], we", + "bbox": [ + 496, + 869, + 890, + 902 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "11768", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/c59c3d9b95ea3ea896a8e908fc281333ab1a2b06c73cef18f537b7df8a11df0c.jpg", + "image_caption": [ + "Figure 2. An overview of the proposed AMID. There are three different models, $M$ , $S$ and $A$ , in AMID for the full modality, target modality and auxiliary modality, respectively. AMID distills multimodal information to the target modality by maximizing the lower bound on $I(M;S)$ and minimizing $H(M|S)$ , and prevents the shout-cut solution by maximizing the lower bound on $I(M;A)$ . MI optimization is a contrastive-based approach, and conditional entropy minimization is an adversarial learning-based approach that contains two discriminators with different inputs." + ], + "image_footnote": [], + "bbox": [ + 98, + 90, + 872, + 203 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "choose $h$ as:", + "bbox": [ + 76, + 311, + 163, + 325 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nh \\left(M _ {i}, S _ {u}\\right) = \\frac {\\exp \\left(\\Phi \\left(M _ {i} , S _ {u}\\right) / \\tau\\right)}{\\sum_ {j = 1} ^ {N + k} \\exp \\left(\\Phi \\left(M _ {i} , S _ {j}\\right) / \\tau\\right)}, \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 130, + 334, + 468, + 375 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\Phi$ is a cosine similarity function, $\\tau$ is a temperature adjusting the correlation of different pairs. Substitute Eq. (7) into Eq. (6), optimizing $I(M;S)$ is equivalent to minimizing the following loss:", + "bbox": [ + 75, + 383, + 470, + 444 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\mathcal {L} _ {M I _ {s}} = - \\frac {1}{N + k} \\sum_ {i = 1} ^ {N + k} \\left(\\sum_ {j = 0} ^ {k - 1} \\log h \\left(M _ {i}, S _ {i} ^ {\\eta_ {j}}\\right) \\right. \\tag {8} \\\\ \\left. + \\sum_ {l = 1} ^ {N} \\log \\left(1 - h (M _ {i}, S _ {i} ^ {\\xi_ {l}})\\right)\\right). \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 120, + 454, + 468, + 547 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Similarly, we can optimize the $I(M; A)$ by minimizing the following loss:", + "bbox": [ + 75, + 556, + 468, + 588 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\mathcal {L} _ {M I _ {a}} = - \\frac {1}{N + k} \\sum_ {i = 1} ^ {N + k} \\left(\\sum_ {j = 0} ^ {k - 1} \\log h \\left(M _ {i}, A _ {i} ^ {\\eta_ {j}}\\right) \\right. \\tag {9} \\\\ \\left. + \\sum_ {l = 1} ^ {N} \\log \\left(1 - h (M _ {i}, A _ {i} ^ {\\xi_ {l}})\\right)\\right). \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 120, + 598, + 468, + 691 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The form of Eq. (8) and Eq. (9) are similar to the CCL loss in [9]. However, our formulation is associated with MI and derives a tighter lower bound on it by taking account into the supervision of the label, which in our experiments is found to be more effective.", + "bbox": [ + 75, + 700, + 468, + 777 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. Conditional Entropy Minimization", + "text_level": 1, + "bbox": [ + 76, + 786, + 382, + 803 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Maximizing the lower bound on $I(M; S)$ is insufficient for narrowing the information gap between the teacher and the student as the optimal lower bound does not mean that MI is maximum. This subsection focuses on further transferring knowledge by minimizing the conditional entropy of the teacher given the student $H(M|S)$ .", + "bbox": [ + 75, + 809, + 470, + 902 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The posterior $p(M|S)$ is difficult to calculate, thus we define a new distribution $q(M|S)$ to approximate it. Then $H(M|S)$ can be calculated as in [8]:", + "bbox": [ + 498, + 311, + 892, + 358 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} H (M | S) = - \\mathbb {E} _ {S \\sim p (S)} \\left[ \\mathbb {E} _ {M ^ {\\prime} \\sim p (M | S)} \\left[ \\log p \\left(M ^ {\\prime} | S\\right) \\right] \\right] \\\\ = - \\mathbb {E} _ {S \\sim p (S)} [ \\mathbb {E} _ {M ^ {\\prime} \\sim p (M | S)} [ \\log q (M ^ {\\prime} | S) ] \\\\ \\left. - D _ {K L} \\left(p (M | S) | | q (M | S)\\right) \\right] \\\\ \\leq - \\mathbb {E} _ {S \\sim p (S)} \\left[ \\mathbb {E} _ {M ^ {\\prime} \\sim p (M | S)} [ \\log q (M ^ {\\prime} | S) ] \\right]. \\tag {10} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 501, + 364, + 890, + 441 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Thus we can minimize $H(M|S)$ by maximizing the negative of its upper bound. We achieve this by introducing an adversarial learning-based approach, and using it to maximize $\\mathbb{E}_{S\\sim p(S)}\\left[\\mathbb{E}_{M^{\\prime}\\sim p(M|S)}[\\log q(M^{\\prime}|S)]\\right]$ w.r.t. the parameters of the student network during the generation and minimize $\\mathbb{E}_{S\\sim p(S)}[\\mathbb{E}_{M^{\\prime}\\sim p(M|S)}[\\log q(M^{\\prime}|S)] - \\log p(M|S)]$ w.r.t. the parameters of the discriminators. In other words, we use the discriminator $D(\\cdot)$ to recognize whether features come from multimodal distribution or not and feedback informative gradient to the student model through minimizing:", + "bbox": [ + 496, + 449, + 892, + 616 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {a d v} = - \\mathbb {E} _ {S \\sim p (S)} \\left[ \\mathbb {E} _ {M ^ {\\prime} \\sim p (M | S)} [ \\log D (S) ] \\right]. \\tag {11}\n$$\n", + "text_format": "latex", + "bbox": [ + 529, + 621, + 890, + 640 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Minimizing Eq. (11) w.r.t. the parameters of the target modality student enables the student to imitate representations coming from the multimodal distribution. It is worth noting that optimizing $H(M|S)$ through Eq. (11) does not affect the learning of the teacher since no gradient back propagates to the teacher.", + "bbox": [ + 496, + 643, + 890, + 733 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Nevertheless, for the samples of the same class, it is more challenging to transfer the multimodal information by adversarial learning. This is because the generated target modality representation tends to mimic that of multimodality in the same instance with the constraint of MI, easier but can not capture the correlation among samples with the supervision of the label. As a result, we introduce two discriminators to learn more informative target modal representations. One discriminator called fundamental discriminator $(D_{1})$ is designed to distinguish the target modality and full modality representations from the entire training data. The other discriminator, which is called enhanced dis", + "bbox": [ + 496, + 733, + 892, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "11769", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "criminator $(D_{2})$ , is designed to further distinguish the two kinds of representations coming from the classes with more than one sample in a batch since we think paying attention to these representations can help the student further aggregate representations in the same class. Thus, minimizing Eq. (11) w.r.t. the parameters of the student becomes minimizing:", + "bbox": [ + 75, + 90, + 472, + 189 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {a d v} = - \\frac {\\lambda_ {1}}{N + k} \\sum_ {i = 1} ^ {N + k} \\log D _ {1} \\left(S _ {i} ^ {\\eta_ {0}}\\right) - \\frac {\\lambda_ {2}}{d} \\sum_ {v = 1} ^ {w} \\log D _ {2} \\left(S _ {v} ^ {\\eta_ {1}}\\right). \\tag {12}\n$$\n", + "text_format": "latex", + "bbox": [ + 86, + 195, + 468, + 232 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "And the parameters of discriminators are trained by minimizing:", + "bbox": [ + 76, + 234, + 468, + 265 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\mathcal {L} _ {D} = - \\frac {\\lambda_ {1}}{N + k} \\sum_ {i = 1} ^ {N + k} \\left(\\log D _ {1} \\left(M _ {i}\\right) + \\log \\left(1 - D _ {1} \\left(S _ {i} ^ {\\eta_ {0}}\\right)\\right)\\right) \\tag {13} \\\\ - \\frac {\\lambda_ {2}}{d} \\sum_ {v = 1} ^ {w} \\left(\\log D _ {2} \\left(M _ {v}\\right) + \\log \\left(1 - D _ {2} \\left(S _ {v} ^ {\\eta_ {1}}\\right)\\right)\\right), \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 91, + 270, + 468, + 345 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\{M_v\\}_{v=1}^w$ is a set where every element comes from the classes with more than one samples and $\\{S_v^{\\eta_1}\\}_{v=1}^w$ is its corresponding set of target modal representations. $d$ is used for more stabilized training and we set it by the frequency of the data with samples of the same classes. $\\lambda_1$ and $\\lambda_2$ are weighting parameters for $D_1$ and $D_2$ respectively, and $\\lambda_1 + \\lambda_2 = 1$ . To further improve the efficiency of the transfer, we adjust $\\lambda_1$ and $\\lambda_2$ adaptively according to the alignment between $S$ and $M$ for each epoch $t$ . More specifically, we use the averaged cosine similarity in the tuples $\\Phi(M_i, S_i^{\\eta_0})$ and $\\Phi(M_v, S_v^{\\eta_j}), j \\neq 0$ in Eq. (7) to provide meaningful feedback for the cooperation of discriminators. Large cosine similarity indicates that $M$ and $S$ are well aligned, thus the weight of the corresponding discriminator can be relatively small. Moving average [30] is also applied to improve the training stability. The formula of $\\lambda$ is given as:", + "bbox": [ + 75, + 349, + 472, + 607 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\tilde {\\lambda} (t + 1) = \\beta \\tilde {\\lambda} (t) + (1 - \\beta) (1 - \\operatorname {A v g} _ {t} (\\Phi (M, S)))) \\tag {14} \\\\ \\lambda (t + 1) = \\sigma (\\tilde {\\lambda} (t + 1)), \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 78, + 612, + 468, + 652 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\sigma (\\cdot)$ is the softmax function, $\\mathrm{Avg}_t(\\cdot)$ represents the average of cosine similarity on epoch $t$ , and $\\beta \\in (0,1)$ is the smoothing parameter, and we set $\\beta = 0.9$ empirically.", + "bbox": [ + 75, + 657, + 468, + 704 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Adversarial learning is known to often generate random images if not constrained [31]. This also occurs when target modality representations are generated without any constraints. Our method implicitly overcomes this problem by maximizing the lower bound on $I(M; S)$ and its advantages come twofold: First, the maximization of the lower bound on MI can not only transfer the multimodal information but also place a constraint on the adversarial distillation. Second, adversarial distillation further reduces the information gap that still exists after maximizing the lower bound on MI. Thus, the maximization of the lower bound on MI and adversarial distillation are complementary to each other in AMID to generate informative and robust representations.", + "bbox": [ + 75, + 704, + 472, + 901 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.3. Overall Loss", + "text_level": 1, + "bbox": [ + 500, + 90, + 635, + 106 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Assuming that after the optimization above, the target modality and full modality representations are already aligned, then we can use two classifiers with shared parameters to perform the classification task for these representations respectively. The overall classification loss is:", + "bbox": [ + 496, + 113, + 892, + 189 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {c l s} = \\mathcal {L} _ {c e} ^ {S} \\left(S _ {i}, y _ {i}\\right) + \\mathcal {L} _ {c e} ^ {M} \\left(M _ {i}, y _ {i}\\right), \\tag {15}\n$$\n", + "text_format": "latex", + "bbox": [ + 578, + 198, + 892, + 217 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\mathcal{L}_{ce}$ is the cross-entropy loss, $y_{i}$ is the ground-truth. Classifiers with the same parameters can also help facilitate the generation of representations from the target modality network to imitate those of multimodality. In addition, the target modality can be aligned with the full modality in the predictive space. We use the Jensen-Shannon divergence (JSD) [27] to optimize the MI between the predictive target modality distribution $(P_S)$ and the multimodality distribution $(P_M)$ :", + "bbox": [ + 496, + 227, + 893, + 364 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {J S D} = \\frac {1}{N + k} \\sum_ {i = 1} ^ {N + k} J S D \\left(P _ {S _ {i}} \\| P _ {M _ {i}}\\right). \\tag {16}\n$$\n", + "text_format": "latex", + "bbox": [ + 562, + 375, + 890, + 415 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The final loss function for distilling knowledge from auxiliary modalities is given as:", + "bbox": [ + 498, + 425, + 892, + 455 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} = \\mathcal {L} _ {c l s} + \\mathcal {L} _ {J S D} + \\alpha_ {1} \\mathcal {L} _ {M I _ {s}} + \\alpha_ {2} \\mathcal {L} _ {M I _ {a}} + \\alpha_ {3} \\mathcal {L} _ {a d v}, \\tag {17}\n$$\n", + "text_format": "latex", + "bbox": [ + 506, + 467, + 890, + 484 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The whole procedure is shown in the supplementary and the overall model structure is shown in Fig. 2.", + "bbox": [ + 498, + 493, + 890, + 525 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 500, + 537, + 633, + 554 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.1. Datasets", + "text_level": 1, + "bbox": [ + 500, + 561, + 602, + 575 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Video understanding. We experiment on two popular multimodal datasets for video recognition (Top-1 accuracy, %) and kNN video retrieval (R@K, %) [5]. Cross-modal knowledge distillation is performed from the acoustic to the visual modality.", + "bbox": [ + 496, + 585, + 892, + 661 + ], + "page_idx": 4 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- UCF51, as a subset of UCF101 [40], includes 6,845 videos with audio belonging to 51 categories. The public split1 is adopted.", + "- ActivityNet [20] is a large-scale video benchmark of 14,950 videos with audio, covering 200 complex human activities, where the training set has 10,024 videos while 4,926 videos in the validation set." + ], + "bbox": [ + 517, + 669, + 893, + 785 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Emotion classification. We conduct experiments on IEMOCAP [6], a popular multimodal dataset for 4-class emotion classification, which contains totaling 5531 videos in 5 dyadic conversation sessions. Each video consists of acoustic, textual and visual modalities, and the target model is based on visual modality only. A 5-fold cross-validation is adopted for the evaluation, taking one session as the test", + "bbox": [ + 496, + 794, + 893, + 901 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "11770", + "bbox": [ + 478, + 944, + 519, + 955 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/345a7ef73304fb4da28145b23887918a80cbe3c3819b2aa8b23bee24a6d06f7c.jpg", + "table_caption": [ + "Table 1. The Top-1 accuracy $(\\%)$ of video recognition on UCF51 and ActivityNet. Notice that we change all the activation functions to LeakyReLU to ensure a fair comparison." + ], + "table_footnote": [], + "table_body": "
UCF51ActivityNet
Baseline66.748.8
CRD [42]67.150.4
GMC [36]64.153.1
CRCD [51]69.652.4
CCL [9]68.951.9
AMID (Ours)73.853.6
", + "bbox": [ + 133, + 130, + 408, + 241 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "set for each fold. Following [50], two evaluation metrics, weighted accuracy (WA, %) and unweighted accuracy (UA, %), are adopted.", + "bbox": [ + 76, + 268, + 468, + 316 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.2. Experimental Setup", + "text_level": 1, + "bbox": [ + 76, + 335, + 267, + 353 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Because different modalities such as audio, video and text are heterogeneous, we use individual extractors for each modality, then the features are concatenated and passed through a 2-layer MLP as the full modality teacher. The teacher shares the same extractors as that of the student and the auxiliary model for reducing the number of parameters. Video recognition and retrieval. Following [9], we use a 1D-CNN14 [26] pre-trained on AudioSet [17] as the audio extractor and use R(2+1)D-18 [43] as the student video network. The two discriminators are 5-layer MLP and 3-layer MLP respectively. Besides, we change all activation functions to Leaky ReLU for adversarial learning because it gives better training stability compared to the ReLU. The dimension of the representations is set to 512. The batch size and temperature $\\tau$ are set to 16 and 0.5, respectively. $\\alpha_{1},\\alpha_{2},\\alpha_{3}$ are set to 4, 1.6, 1. More details are shown in the supplementary.", + "bbox": [ + 75, + 363, + 470, + 619 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Emotion classification. We extract raw acoustic, textual and visual embeddings by the pre-trained wav2vec 2.0 [3], BERT [12] and DenseNet [24] respectively. RNN is adopted as the student network with a final feature dimension of 768. The batch size and temperature $\\tau$ are set to 128 and 0.6, respectively.", + "bbox": [ + 76, + 625, + 468, + 715 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "A warm-up stage is employed for all experiments. At the first $T_{start}$ epochs, the student model and the teacher model are trained by minimizing $\\mathcal{L} = \\mathcal{L}_{cls} + \\mathcal{L}_{JSD}$ to alleviate the converge difficulties of adversarial learning. This helps a preliminary alignment between the teacher and student and can also prevent discriminators from recognizing readily at the beginning of the training. $T_{start}$ is set to 20 for the video understanding tasks and 5 for the emotion classification task. And notice that without special mention, the leveraged pre-trained auxiliary modality extractors are fixed since the generated representations already contain rich auxiliary information.", + "bbox": [ + 75, + 719, + 470, + 901 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/d97769e4b595e4e79312e851a7a26a6b0c1ef78183f27d54db084aaacfdb8147.jpg", + "table_caption": [ + "Table 2. $\\mathrm{R@K(K = 1,5)}$ of video retrieval on UCF51 and ActivityNet." + ], + "table_footnote": [], + "table_body": "
UCF51ActivityNet
MetricR1R5R1R5
Baseline64.071.941.563.9
CRD [42]66.072.343.665.5
GMC [36]61.871.046.167.7
CRCD [51]68.275.245.767.0
CCL [9]67.071.746.264.8
AMID (Ours)73.677.146.467.2
", + "bbox": [ + 542, + 116, + 846, + 243 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/7a7046e504d9b6090543ab57af3f5c169844a7dd761a9c19bfbbed8901d7f2eb.jpg", + "image_caption": [ + "Figure 3. The per-class Top-1 accuracy $(\\%)$ of video recognition on UCF51 comparing AMD with CCL." + ], + "image_footnote": [], + "bbox": [ + 509, + 263, + 880, + 411 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.3. Comparison with State-of-the-arts", + "text_level": 1, + "bbox": [ + 500, + 479, + 799, + 494 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Video recognition. We compare AMD with two types of SOTA cross-modal KD methods, i.e. intra-sample methods including CRD [42], GMC [36], and inter-sample methods including CCL [9], CRCD [51]. The results are summarized in Tab. 1. Here \"Baseline\" represents the model directly trained with the visual modality only, representing a lower bound for the tasks. It can be seen that AMD significantly outperforms all the compared methods, suggesting that it is more effective and consistent in learning information from auxiliary modalities. AMD outperforms the second-best method by $4.2\\%$ and $0.5\\%$ on the two datasets, respectively.", + "bbox": [ + 496, + 503, + 890, + 685 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "To further investigate the breakdown of performance, we compare AMD with CCL on UCF51 and give the results of class-wise Top-1 accuracy in Fig. 3. It can be seen that AMD achieves better performance than CCL for most of the classes, although for a few of them it is comparable to or slightly worse than CCL. The classes where AMD is of inferior performance are mainly those audio events that are not or weakly correlated with the videos, such as 'FrisbeeCatch' and 'SkyDiving'. In these classes, the auxiliary modal information is less helpful. Thus, AMD, which is proposed for better cross-modal knowledge distillation, is not very effective for these classes.", + "bbox": [ + 496, + 686, + 890, + 867 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Video retrieval. Tab. 2 presents the results of video retrieval on the UCF51 and ActivityNet datasets, which is a", + "bbox": [ + 500, + 869, + 890, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "11771", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/858f5d9a196f4a79e3ea99e3567114c5637d8e3bf52cbc7b24ef3fb6933f0427.jpg", + "table_caption": [ + "Table 3. Performance comparison under different setups on IEMOCAP, where A-V, L-V, AL-V mean distillation from acoustic to visual, textual to visual, and acoustic and textual to visual." + ], + "table_footnote": [], + "table_body": "
SetupMethodWAUA
VBaseline51.250.8
A-VGMC [36]51.750.9
CRCD [51]51.850.2
CCL [9]51.551.4
AMID (Ours)52.551.7
L-VGMC [36]50.950.5
CRCD [51]50.249.9
CCL [9]52.751.8
AMID (Ours)53.052.4
AL-VGMC [36]51.950.5
CRCD [51]52.049.4
CCL [9]53.251.4
AMID (Ours)53.852.7
", + "bbox": [ + 111, + 131, + 431, + 347 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "more fine-grained task to evaluate the discriminability of video representations. The results show that AMD consistently outperforms almost all competing approaches in terms of R@1 and R@5.", + "bbox": [ + 75, + 372, + 468, + 433 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Emotion classification. Tab. 3 compares AMID with three state-of-the-art methods, CCL, CRCD and GMC, for emotion classification. We conduct experiences on IEMOCAP, a three-modality dataset, to further evaluate the performance of AMID in different auxiliary modalities. It is worth noting that the \"Baseline\" model is trained directly with only the visual modality. The results demonstrate that AMID outperforms the Baseline model for all setups, where the UA metrics increase by $0.9\\%$ , $1.6\\%$ and $1.9\\%$ respectively, while the other three methods are not always effective. Besides, AMID outperforms CCL, CRCD and GMC on almost all the setups.", + "bbox": [ + 75, + 434, + 470, + 616 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.4. Ablation Study", + "text_level": 1, + "bbox": [ + 76, + 625, + 230, + 642 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.4.1 Effectiveness of MI and conditional entropy", + "text_level": 1, + "bbox": [ + 76, + 648, + 434, + 666 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "In order to verify the effectiveness of our proposed method for capturing as much multimodal information as possible, the impact of using different training configurations on UCF51 is studied in Tab. 4. Here \"student alone\" represents the result of a model trained with the visual modality only and \"teacher alone\" represents that of the teacher model with the full modalities. These two cases show the initial performance of the student and the teacher without distillation, respectively. When optimizing $\\mathcal{L}_{MI_s}$ alone for the distillation, although the student model can achieve performance gains, from $66.7\\%$ to $69.8\\%$ , it degrades the teacher's performance, from $74.3\\%$ to $71.2\\%$ and thereby reducing the upper bound of the student's performance. Alternatively, more informative multimodal representations can be obtained by maximizing the lower bound on $I(M;A)$ and", + "bbox": [ + 75, + 672, + 470, + 902 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/5968b6fda64fd69d497ba30ec5d378ead74e1f130d163cc8f11078efdcbb9d48.jpg", + "table_caption": [ + "Table 4. Ablation study for the proposed loss functions." + ], + "table_footnote": [], + "table_body": "
ConfigurationTop-1 accuracy
StudentTeacher
student alone (w/o distillation)66.7\\
teacher alone (w/o distillation)\\74.3
\\( \\mathcal{L}_{MI_s} \\)69.871.2
\\( \\mathcal{L}_{MI_s} + \\mathcal{L}_{MI_a} \\)72.776.0
\\( \\mathcal{L}_{MI_s} + \\mathcal{L}_{MI_a} + \\mathcal{L}_{adv} \\) (AMID)73.875.7
AMID with \\( \\mathcal{L}_{nce} \\)72.374.3
", + "bbox": [ + 503, + 102, + 885, + 229 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/6fd9862a33181428be842a112be361395d263169daf3df3a80a9eea94bd2745c.jpg", + "image_caption": [ + "Figure 4. The accuracy gap between the teacher and student in using $\\mathcal{L}_{MI_s} + \\mathcal{L}_{MI_a}$ and AMD loss." + ], + "image_footnote": [], + "bbox": [ + 578, + 244, + 815, + 402 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "$I(M;S)$ simultaneously $(\\mathcal{L}_{MI_s} + \\mathcal{L}_{MI_a})$ , since a better teacher can improve the distillation performance. Tab. 4 shows that this improves the accuracy of the student from $66.7\\%$ to $72.7\\%$ and also improves that of the teacher from $74.3\\%$ to $76.0\\%$ . Besides, adding $\\mathcal{L}_{adv}$ (i.e., AMD) to $\\mathcal{L}_{MI_s} + \\mathcal{L}_{MI_a}$ does improve the performance from $72.7\\%$ to $73.8\\%$ , and the performance gap of AMD is smaller than $\\mathcal{L}_{MI_s} + \\mathcal{L}_{MI_a}$ , which indicates that AMD achieves better alignment between the teacher and the student due to the further constraint on the gap by minimizing $H(M|S)$ without degrading the teacher's performance obviously (the teacher's performance decreases from $76.0\\%$ to $75.7\\%$ ).", + "bbox": [ + 496, + 458, + 890, + 638 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "To further understand the effectiveness of the conditional entropy minimization approach in reducing the information gap between the teacher and the student, we explore the gap of AMID and $\\mathcal{L}_{MI_s} + \\mathcal{L}_{MI_a}$ during training. This information gap is represented by the gap of accuracy between the teacher and student on the validation set over the training epochs. The results are shown in Fig. 4. It can be seen that the accuracy gap of using AMID loss is consistently smaller than that of $\\mathcal{L}_{MI_s} + \\mathcal{L}_{MI_a}$ , which validates the proposed adversarial learning-based approach indeed helps to narrow down the information gap.", + "bbox": [ + 496, + 641, + 890, + 808 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "AMID is also compared to an ablative setup using the contrastive loss $\\mathcal{L}_{nce}$ [9] to verify the effectiveness of the proposed loss function in maximizing the lower bound on MI. The result in Tab. 4 shows that AMD performs much better than the baseline \"AMID with $\\mathcal{L}_{nce}$ \", improving the accuracy by $1.5\\%$ . This validates that our proposed ap", + "bbox": [ + 496, + 809, + 890, + 901 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "11772", + "bbox": [ + 478, + 944, + 519, + 955 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/26b8c3ca0f7e19da60a6d605fff9b9d4ab24d02baf6850f526487bc4327561b9.jpg", + "table_caption": [ + "Table 5. Effectiveness of proposed training modifications." + ], + "table_footnote": [], + "table_body": "
ModificationTop-1 accuracy
AMID73.8
with fixed teacher66.0
w/o warm-up65.8
w/o D272.8
w/o dynamic weight72.7
", + "bbox": [ + 130, + 103, + 408, + 198 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/5026e5b7f1e7b8f4eae9aed027438887d55a114365c22471ab23d64206c59c3b.jpg", + "image_caption": [ + "Figure 5. (Left) The cosine similarity between the teacher's and student's representations only in the same class during training. (Right) The cosine similarity during testing." + ], + "image_footnote": [], + "bbox": [ + 91, + 208, + 271, + 325 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/1dafd05386d9476d0fef9309f58c49a39f69d1eff5f72bc445d629ef57c832de.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 274, + 210, + 452, + 324 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "proach, which takes into account the correlation of samples within a class, achieves better optimization for MI.", + "bbox": [ + 75, + 396, + 468, + 426 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.4.2 Effectiveness of training modifications", + "text_level": 1, + "bbox": [ + 76, + 440, + 397, + 455 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "To evaluate the effect of each modification applied in AMD, we conduct a set of experiments on UCF51 and give the results in Tab. 5. As mentioned before, using a fixed pre-trained teacher to guide the student's learning leads to an undesired gap between the teacher and the student at the beginning of training, which is unfavorable for distillation. The result affirms this, where the performance of AMD degrades from $73.8\\%$ to $66.0\\%$ without joint training. In addition, it also shows that without employing the warm-up setup described before, the recognition performance degrades by $8.0\\%$ . The reason may be that the target modality and multimodality representations are noisy and uncorrelated at the start of the training, which results in that the discriminators can recognize them readily and thus affecting the feedback of the informative gradient of adversarial learning.", + "bbox": [ + 75, + 460, + 468, + 702 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We also study the effectiveness of the two discriminators of our proposed AMD by comparing AMD with two ablative cases: w/o $D_{2}$ and w/o dynamic weight. One constraint is removed at a time. The results of these ablation studies are shown in Tab. 5. The accuracy decreases by $1.0\\%$ when only the fundamental discriminator $D_{1}$ is used, suggesting that the enhanced discriminator $D_{2}$ indeed helps to distill the multimodal information of samples of the same class. Moreover, it also demonstrates that using uniform weight leads to a performance drop, indicating the effectiveness of the proposed dynamic weighting scheme.", + "bbox": [ + 75, + 703, + 468, + 869 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "To further investigate the effectiveness of the proposed adversarial learning-based approach in transferring the", + "bbox": [ + 76, + 869, + 468, + 900 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/1c5f98568686a3ad0179ada8426a37132e46199724a60c844a4cd5a70549bdf2.jpg", + "table_caption": [ + "Table 6. Top-1 accuracy (%) on UCF51 with different hyperparameters." + ], + "table_footnote": [], + "table_body": "
α1value3.73.83.94.04.14.2
accuracy72.673.773.773.873.873.4
α2value1.31.41.51.61.71.8
accuracy71.273.773.873.873.672.4
α3value0.70.80.91.01.11.2
accuracy73.373.473.773.873.473.1
", + "bbox": [ + 504, + 116, + 880, + 210 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "inter-sample multimodal information, we compare AMID with two cases: w/o $D_{2}$ and w/o $\\mathcal{L}_{adv}$ . Fig. 5 displays the average of cosine similarity between the teacher and the student only in the same class, i.e. the average of all $\\Phi (M_v,S_v^{\\eta_j}), j\\neq 0$ in Eq. (7). We can see that the cosine similarity of AMID is consistently larger than that of the other two cases and the cosine similarity of w/o $D_{2}$ is larger than that of w/o $\\mathcal{L}_{adv}$ , meaning that the proposed approach indeed helps the student to learn more compact representations for each class.", + "bbox": [ + 496, + 227, + 890, + 377 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.5. Hyperparameters Analysis", + "text_level": 1, + "bbox": [ + 500, + 387, + 741, + 402 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Sensitivity analysis studies are conducted for the hyperparameters, $\\alpha_{1}$ , $\\alpha_{2}$ and $\\alpha_{3}$ , referenced in the loss function Eq. (17). Similar to the previous study, we experiment on UCF51 and show the results in Tab. 6. The other two hyperparameters are kept the same when one changes. We test different values for $\\alpha_{1}$ from 3.7 to 4.2, $\\alpha_{2}$ from 1.3 to 4.8 and $\\alpha_{3}$ from 0.7 to 1.2, all with an increment of 0.1. The results show that the hyperparameters $\\alpha_{1}$ , $\\alpha_{2}$ and $\\alpha_{3}$ are not sensitive within a certain range. In general, $\\alpha_{1}$ between 3.8 to 4.1 and $\\alpha_{2}$ between 1.4 to 1.7 works well, and we set $\\alpha_{3} = 1.0$ for all other experiments.", + "bbox": [ + 496, + 406, + 890, + 571 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 585, + 617, + 599 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this paper, we propose a generic cross-modal distillation method, AMID, to enhance the target modality representations. The proposed approach simultaneously maximizes the lower bounds on MI between the teacher and the student as well as between the teacher and an auxiliary model while minimizing the conditional entropy of the teacher given the student. For optimizing the lower bound on MI, we derive a new form and solve it by a contrastive learning-based approach. For minimizing the conditional entropy, an adversarial learning-based approach is used. Our extensive experimental evaluation demonstrates the effectiveness of AMID on three popular datasets.", + "bbox": [ + 496, + 609, + 890, + 791 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgement", + "text_level": 1, + "bbox": [ + 500, + 796, + 660, + 811 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "This work is supported by the National Key R&D Program of China (No. 2022ZD0160702), STCSM (No. 2251 1106101, No. 18DZ2270700, No. 21DZ1100100, No. 215 11101100), 111 plan (No. BP0719010), and State Key Laboratory of UHD Video and Audio Production and Presentation.", + "bbox": [ + 496, + 816, + 890, + 898 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "11773", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Sarah A. 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In IEEE Conference on Computer Vision and Pattern Recognition, CVPR, pages 9260-9269, 2021. 2, 6, 7" + ], + "bbox": [ + 503, + 92, + 890, + 896 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "11775", + "bbox": [ + 480, + 945, + 517, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/Enhanced Multimodal Representation Learning With Cross-Modal KD/550b12f3-e75d-4ee0-8736-cf2526b0aff9_model.json b/2023/Enhanced Multimodal Representation Learning With Cross-Modal KD/550b12f3-e75d-4ee0-8736-cf2526b0aff9_model.json new file mode 100644 index 0000000000000000000000000000000000000000..4fad03feffb40f9309ffa97ad40d0b996ec2da8c --- /dev/null +++ b/2023/Enhanced Multimodal Representation Learning With Cross-Modal KD/550b12f3-e75d-4ee0-8736-cf2526b0aff9_model.json @@ -0,0 +1,2277 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.0, + 0.809, + 0.045 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.13, + 0.131, + 0.84, + 0.152 + ], + "angle": 0, + "content": "Enhanced Multimodal Representation Learning with Cross-modal KD" + }, + { + "type": "text", + "bbox": [ + 0.257, + 0.188, + 0.713, + 0.209 + ], + "angle": 0, + "content": "Mengxi Chen\\(^{1}\\), Linyu Xing\\(^{1}\\), Yu Wang\\(^{1,2\\boxtimes}\\), Ya Zhang\\(^{1,2\\boxtimes}\\)" + }, + { + "type": "text", + "bbox": [ + 0.257, + 0.209, + 0.713, + 0.227 + ], + "angle": 0, + "content": "\\(^{1}\\)Shanghai Jiao Tong University, \\(^{2}\\)Shanghai AI Laboratory" + }, + { + "type": "text", + "bbox": [ + 0.262, + 0.228, + 0.704, + 0.244 + ], + "angle": 0, + "content": "{mxchen_mc,xly8991,yuwanhsjtu,ya_zhang}@sjtu.edu.cn" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.279, + 0.313, + 0.294 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.312, + 0.474, + 0.629 + ], + "angle": 0, + "content": "This paper explores the tasks of leveraging auxiliary modalities which are only available at training to enhance multimodal representation learning through cross-modal Knowledge Distillation (KD). The widely adopted mutual information maximization-based objective leads to a shortcut solution of the weak teacher, i.e., achieving the maximum mutual information by simply making the teacher model as weak as the student model. To prevent such a weak solution, we introduce an additional objective term, i.e., the mutual information between the teacher and the auxiliary modality model. Besides, to narrow down the information gap between the student and teacher, we further propose to minimize the conditional entropy of the teacher given the student. Novel training schemes based on contrastive learning and adversarial learning are designed to optimize the mutual information and the conditional entropy, respectively. Experimental results on three popular multimodal benchmark datasets have shown that the proposed method outperforms a range of state-of-the-art approaches for video recognition, video retrieval and emotion classification." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.663, + 0.208, + 0.679 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.689, + 0.47, + 0.901 + ], + "angle": 0, + "content": "Multimodal learning has shown much promise in a wide spectrum of applications, such as video understanding [20, 39, 44], sentiment analysis [1, 19, 47] and medical image segmentation [7, 49]. It is generally recognized that including more modalities helps the prediction accuracy. For many real-world applications, while one has to make predictions based on limited modalities due to efficiency or cost concerns, it is usually possible to collect additional modalities at training. To enhance the representation learned, several studies have thus considered to leverage such modalities as a form of auxiliary information at training [11, 23, 29, 50]. Several attempts have explored to fill in the auxiliary modalities at test time, by employing approaches such as Generative Adversarial Network" + }, + { + "type": "image", + "bbox": [ + 0.516, + 0.281, + 0.88, + 0.39 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.517, + 0.392, + 0.879, + 0.499 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.512, + 0.892, + 0.568 + ], + "angle": 0, + "content": "Figure 1. Illustration of the difference between the MI-based method and the proposed AMID method. (a) MI-based methods maximize \\( I(M;S) \\). (b) AMID maximizes \\( I(M;S) \\) and \\( I(M;A) \\), while minimizing \\( H(M|S) \\)." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.597, + 0.891, + 0.627 + ], + "angle": 0, + "content": "(GAN) [4, 22]. However, such data generation-based approaches introduce extra computation costs at inference." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.628, + 0.893, + 0.84 + ], + "angle": 0, + "content": "As an alternative, cross-modal knowledge distillation is proposed, where a teacher model trained with both the target modalities and the auxiliary modalities (denoted as full modalities hereafter), is employed to guide the training of a student model with target modalities only [10, 11, 16, 23, 45, 46]. In such a way, the student model directly learns to embed information about auxiliary modalities and involves no additional computational cost at inference. A typical practice is to pre-train the teacher model from the full modality data, and fix it during the training. While such a setting enables the teacher to provide information-rich representation [23, 46], it may not be favorable for the alignment of the teacher and student, due to the large information gap between them, especially at the early stage of training [32]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.894, + 0.9 + ], + "angle": 0, + "content": "To better facilitate the knowledge transfer, online KD is proposed to jointly train the teacher and the student. One common solution is to maximize the mutual information (MI) between the teacher and the student in a shared" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "11766" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.198 + ], + "angle": 0, + "content": "space [42]. However, such an objective only focuses on maximizing the shared knowledge, in terms of percentage, from the teacher to the student, which is necessary but not sufficient to guarantee a complete knowledge transfer. As illustrated in Fig. 1(a), a short-cut solution is to simply make the teacher model capture less information, i.e., shrinking the entropy of the teacher." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.199, + 0.471, + 0.499 + ], + "angle": 0, + "content": "Under the framework online KD, this paper explores to simultaneously achieve: 1) maintaining the representation capacity of the full modality teacher as much as possible, and 2) narrowing down the information gap between the teacher and the student. As Fig. 1(b) shows, in addition to maximizing the MI between the teacher and the student, maximizing the MI between the teacher and an additional auxiliary model may contribute to the former goal, while minimizing the conditional entropy of the teacher given the student may benefit the latter goal. We thus propose a new objective function consisting of all the above three terms. To achieve the optimization of the MI, we further derive a new form of its lower bound by taking into account the supervision of the label, and propose a contrastive learning-based approach to implement it. To minimize the conditional entropy, an adversarial learning-based approach is introduced, where additional discriminators are used to distinguish representations between the teacher and the student. We name the proposed method Adversarial Mutual Information Distillation (AMID) hereafter." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.5, + 0.47, + 0.636 + ], + "angle": 0, + "content": "To validate the effectiveness of AMID, extensive experiments on three popular multimodal tasks including video recognition, video retrieval and emotion classification tasks are conducted. The performance of these tasks are conducted on UCF51 [40], ActivityNet [20] and IEMOCAP [6] benchmark datasets, respectively. The results show that AMID outperforms a range of state-of-the-art approaches on all three tasks. To summarize, the main contribution of this paper is threefold:" + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.646, + 0.468, + 0.706 + ], + "angle": 0, + "content": "- We propose a novel cross-modal KD method, Adversarial Mutual Information Distillation (AMID), to prevent the teacher from losing information by maximizing the MI between it and an auxiliary modality model." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.716, + 0.468, + 0.775 + ], + "angle": 0, + "content": "- AMID maximally transfers information from the teacher to the student by optimizing the MI between them and minimizing the conditional entropy of the teacher given the student." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.786, + 0.468, + 0.847 + ], + "angle": 0, + "content": "- To implement the joint optimization of the three objective terms, a novel training approach that leverages the combined advantage of both contrastive learning and adversarial learning is proposed." + }, + { + "type": "list", + "bbox": [ + 0.097, + 0.646, + 0.468, + 0.847 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.86, + 0.22, + 0.876 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.886, + 0.468, + 0.901 + ], + "angle": 0, + "content": "Knowledge Distillation. Knowledge distillation (KD) is" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.485 + ], + "angle": 0, + "content": "first proposed in [21], where soft labels in predictive space produced by the teacher through temperature hyperparameter transfer the dark knowledge to the student. Later, many works studied and demonstrated the benefits of distilling knowledge in the latent space [25, 35, 38, 48]. There have been some works that explore KD-based methods for cross-modal representation learning. CMC [41] aligns different views of the same samples by contrastive learning to extract shared information. CRD [42] leverages instance-level contrastive objectives to perform KD. GMC [36] learns geometrically aligned representations by aligning modality-specific representations with that of the corresponding complete observation. However, these methods can not transfer the correlation among instances, which are also valuable in many tasks. To transfer the inter-sample relation, [9] propose CCL to close the cross-modal semantic gap between the multimodality teacher and the student by contrasting different modal embeddings in the same classes in a common latent space. CRCD [51] distills the information of the teacher space by maximizing two complementary MI criteria. In contrast to these recent KD works which only consider the alignment between the teacher and student but neglect the objectives' impact on the teacher, we proposed a new KD objective that helps the teacher capture as much auxiliary information as possible and constraints the alignment simultaneously." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.489, + 0.892, + 0.775 + ], + "angle": 0, + "content": "Mutual Information Maximization. MI is first introduced to deep learning in [2], and since then, many methods have proposed to combine variational bounds with parameterized neural networks to enable differentiable and tractable estimation of MI in high-dimensional spaces [15, 34]. The character that MI can be used to represent the relationship between two variables is well-suited for correlated multimodal data. [19] hierarchically optimizes MI in unimodal pairs and between multimodal and unimodal representations for maintaining useful information while filtering noise in unimodal input. [28] proposed TupleInfoNCE to optimize MI in multimodal input tuples which enables the model to capture both the modal-shared information and the specific information. However, these methods rarely consider the correlation among samples with the supervision of the label, which are still useful. In this paper, we derive a new lower bound on MI in teacher-student pairs which takes into account the inter-sample correlation and propose a contrastive-learning method for its maximization." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.781, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Adversarial Learning. Since [18] developed adversarial learning in deep learning, many researchers attempt to improve its performance by stabilizing the training process. In addition to modifying the structure of discriminator or generator [8, 31, 37], several works still considered incorporating multiple discriminators to improve learning [13, 14, 33]. Similar to [13], in this paper, we design two additional discriminators and adjust their weights adaptively." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "11767" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.078, + 0.09, + 0.169, + 0.105 + ], + "angle": 0, + "content": "3. Method" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.115, + 0.47, + 0.266 + ], + "angle": 0, + "content": "Suppose we have a multimodal dataset with \\( n \\) modalities, consisting of \\( k \\) target modalities \\( \\{x_1, \\dots, x_k\\} \\) and \\( n - k \\) auxiliary modalities \\( \\{x_{k + 1}, \\dots, x_n\\} \\). Denote the model trained with all \\( n \\) modalities, \\( k \\) target modalities only, and \\( n - k \\) auxiliary modalities only as full modality model \\( M(x_1, \\dots, x_n) \\), target modality model \\( S(x_1, \\dots, x_k) \\), and auxiliary modality model \\( A(x_{k + 1}, \\dots, x_n) \\), respectively. This paper aims to transfer knowledge from the full modality model \\( M \\) to the target modality model \\( S \\) with the assistant of auxiliary modalities at training." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.267, + 0.471, + 0.508 + ], + "angle": 0, + "content": "A widely adopted objective for cross-modal knowledge transfer is to maximize the MI between the representation of the full modality teacher \\(M\\) and the representation of the target modality student \\(S\\), i.e. \\(I(M; S)\\). But there exists a shout-cut solution as shown in Fig. 1(a). In order to prevent this problem, we propose AMID, which maximizes the MI between \\(M\\) and \\(A\\), i.e. \\(I(M; A)\\), so as to ensure the full modality model captures information from both target modalities and auxiliary modalities, and maximizes \\(I(M; S)\\) while minimizing the conditional entropy of the teacher given the student \\(H(M|S)\\), so as to narrow down the information gap between the teacher and the student. For optimizing the MI, we derive a new form of its lower bound and maximize it through a contrastive learning-based approach. For minimizing \\(H(M|S)\\), we introduce an adversarial learning-based approach." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.508, + 0.408, + 0.523 + ], + "angle": 0, + "content": "To sum up, the overall objective is to optimize:" + }, + { + "type": "equation", + "bbox": [ + 0.076, + 0.529, + 0.469, + 0.546 + ], + "angle": 0, + "content": "\\[\n\\mathcal {O} = \\alpha_ {1} \\mathrm {l b} (I (M; S)) + \\alpha_ {2} \\mathrm {l b} (I (M; A)) - \\alpha_ {3} H (M | S), \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.552, + 0.469, + 0.583 + ], + "angle": 0, + "content": "where \\(\\mathrm{lb}(\\cdot)\\) means the lower bound on MI, \\(\\alpha_{1},\\alpha_{2},\\alpha_{3}\\) are the different weights for the corresponding terms." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.59, + 0.376, + 0.605 + ], + "angle": 0, + "content": "3.1. Mutual Information Optimization" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.613, + 0.469, + 0.763 + ], + "angle": 0, + "content": "In this section, we will focus on how to optimize \\( I(M;S) \\) and \\( I(M;A) \\) through maximizing their lower bounds for capturing as much information as possible. Unlike [42] which only considers the correlation between the teacher's representation and that of the student in the same sample, we derive a new form of lower bound on MI by taking into account the correlation of samples within a class. Notice that as the deduction procedures for \\( I(M;S) \\) and \\( I(M;A) \\) are the same, we will construct an approximate loss for optimizing \\( I(M;S) \\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.764, + 0.469, + 0.824 + ], + "angle": 0, + "content": "Firstly, we define a distribution \\( q \\) which models the joint distribution of \\( M \\) and \\( S \\). A latent variable, \\( C \\), is used to indicate whether a tuple \\( (M, S) \\) comes from the same class \\( (C = 1) \\) or not \\( (C = 0) \\):" + }, + { + "type": "equation", + "bbox": [ + 0.173, + 0.83, + 0.468, + 0.865 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} q (M, S | C = 1) = p (M, S); \\\\ q (M, S \\mid C = 0) = p (M) p (S). \\tag {2} \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.871, + 0.469, + 0.901 + ], + "angle": 0, + "content": "We sample \\((M, S)\\) by considering the relationship between full modality and target modality representations in the" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.152 + ], + "angle": 0, + "content": "same classes, which is more effective for transferring information. The pair \\((M, S)\\) is from the joint distribution when \\(M, S\\) are in the same class or from the product of the marginal distributions when \\(M, S\\) are in different classes." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.153, + 0.892, + 0.307 + ], + "angle": 0, + "content": "Suppose in a mini-batch, given a specific \\( M_{i} \\), there are \\( k - 1 \\) positive pairs \\( (M_{i}, S_{i}^{\\eta_{j}}) \\) drawn from the joint distribution, where \\( \\{\\eta_{j}\\}_{j = 1}^{k - 1} \\) is an index set and every element indicates the position of other \\( S \\) with the same class as \\( M_{i} \\), 1 positive pair \\( (M_{i}, S_{i}^{\\eta_{0}}) \\) from the same sample, and \\( N \\) negative pairs \\( (M_{i}, S_{i}^{\\xi_{l}}) \\) from the product of marginals, where \\( \\{S_{i}^{\\xi_{l}}\\}_{l = 1}^{N} \\) are \\( N \\) target modality representations from different classes than \\( M_{i} \\). Then the priors of \\( C \\) can be calculated as \\( q(C = 1) = \\frac{k}{N + k} \\) and \\( q(C = 0) = \\frac{N}{N + k} \\). Using Bayes' rule, the logarithmic posterior for \\( C = 1 \\) is given by:" + }, + { + "type": "equation", + "bbox": [ + 0.5, + 0.315, + 0.891, + 0.42 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\log q (C = 1 | M, S) = \\log \\frac {q (M , S | C = 1) q (C = 1)}{\\sum_ {c = 0 , 1} q (M , S | C = c) q (C = c)} \\\\ = - \\log (1 + \\frac {N}{k} \\frac {p (M) p (S)}{p (M , S)}) \\\\ \\leq - \\log (\\frac {N}{k}) + \\log \\frac {p (M , S)}{p (M) p (S)}. \\tag {3} \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.52, + 0.428, + 0.884, + 0.444 + ], + "angle": 0, + "content": "With Eq. (3), we can get a lower bound on \\( I(M; S) \\) as:" + }, + { + "type": "equation", + "bbox": [ + 0.541, + 0.452, + 0.891, + 0.516 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} I (M; S) = \\mathbb {E} _ {(M, S) \\sim p (M, S)} \\log \\frac {p (M , S)}{p (M) p (S)} \\tag {4} \\\\ \\geq \\log (\\frac {N}{k}) + \\mathbb {E} _ {q (M, S | C = 1)} \\log q (C = 1 | M, S). \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.523, + 0.892, + 0.614 + ], + "angle": 0, + "content": "Thus maximizing \\(\\mathbb{E}_{q(M,S|C = 1)}\\log q(C = 1|M,S)\\) is to maximize the lower bound on \\(I(M;S)\\). However, the true distribution \\(q(C = 1|M,S)\\) cannot be calculated directly. A classification model \\(h:\\{M,S\\} \\to [0,1]\\) is fitted to approximate this distribution. The log-likelihood of the sampled tuples with model \\(h\\) is defined as:" + }, + { + "type": "equation", + "bbox": [ + 0.527, + 0.623, + 0.891, + 0.66 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\mathcal {I} (h) = k \\mathbb {E} _ {q (M, S \\mid C = 1)} [ \\log h (M, S) ] \\\\ + N \\mathbb {E} _ {q (M, S | C = 0)} [ \\log (1 - h (M, S)) ]. \\tag {5} \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.667, + 0.892, + 0.744 + ], + "angle": 0, + "content": "This likelihood is maximized to make \\( h \\) a good approximation to \\( q(C = 1|M,S) \\). Thus, we can get the optimal \\( h^{*}(M,S) = q(C = 1|M,S) \\). Because that both \\( \\log h(M,S) \\) and \\( \\log (1 - h(M,S)) \\) are non-positive for any \\( h \\), we can rewrite Eq. (4) according to Eq. (5):" + }, + { + "type": "equation", + "bbox": [ + 0.514, + 0.752, + 0.891, + 0.862 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} I (M; S) \\geq \\log (\\frac {N}{k}) + \\mathbb {E} _ {q (M, S | C = 1)} [ \\log h ^ {*} (M, S) ] \\\\ \\geq \\log \\left(\\frac {N}{k}\\right) + k \\mathbb {E} _ {q (M, S | C = 1)} \\left[ \\log h ^ {*} (M, S) \\right] \\\\ + N \\mathbb {E} _ {q (M, S | C = 0)} [ \\log (1 - h ^ {*} (M, S)) ] \\\\ = \\log \\left(\\frac {N}{k}\\right) + \\max _ {h} \\mathcal {I} (h) \\geq \\log \\left(\\frac {N}{k}\\right) + \\mathcal {I} (h) \\tag {6} \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.871, + 0.892, + 0.903 + ], + "angle": 0, + "content": "Thus we can optimize \\( I(M; S) \\) indirectly by maximizing this lower bound \\( \\log \\left( \\frac{N}{k} \\right) + \\mathcal{I}(h) \\). Inspired by [9], we" + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "11768" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.099, + 0.091, + 0.874, + 0.204 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.216, + 0.895, + 0.288 + ], + "angle": 0, + "content": "Figure 2. An overview of the proposed AMID. There are three different models, \\( M \\), \\( S \\) and \\( A \\), in AMID for the full modality, target modality and auxiliary modality, respectively. AMID distills multimodal information to the target modality by maximizing the lower bound on \\( I(M;S) \\) and minimizing \\( H(M|S) \\), and prevents the shout-cut solution by maximizing the lower bound on \\( I(M;A) \\). MI optimization is a contrastive-based approach, and conditional entropy minimization is an adversarial learning-based approach that contains two discriminators with different inputs." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.313, + 0.165, + 0.326 + ], + "angle": 0, + "content": "choose \\(h\\) as:" + }, + { + "type": "equation", + "bbox": [ + 0.132, + 0.335, + 0.47, + 0.375 + ], + "angle": 0, + "content": "\\[\nh \\left(M _ {i}, S _ {u}\\right) = \\frac {\\exp \\left(\\Phi \\left(M _ {i} , S _ {u}\\right) / \\tau\\right)}{\\sum_ {j = 1} ^ {N + k} \\exp \\left(\\Phi \\left(M _ {i} , S _ {j}\\right) / \\tau\\right)}, \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.384, + 0.471, + 0.445 + ], + "angle": 0, + "content": "where \\(\\Phi\\) is a cosine similarity function, \\(\\tau\\) is a temperature adjusting the correlation of different pairs. Substitute Eq. (7) into Eq. (6), optimizing \\(I(M;S)\\) is equivalent to minimizing the following loss:" + }, + { + "type": "equation", + "bbox": [ + 0.122, + 0.455, + 0.47, + 0.548 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\mathcal {L} _ {M I _ {s}} = - \\frac {1}{N + k} \\sum_ {i = 1} ^ {N + k} \\left(\\sum_ {j = 0} ^ {k - 1} \\log h \\left(M _ {i}, S _ {i} ^ {\\eta_ {j}}\\right) \\right. \\tag {8} \\\\ \\left. + \\sum_ {l = 1} ^ {N} \\log \\left(1 - h (M _ {i}, S _ {i} ^ {\\xi_ {l}})\\right)\\right). \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.558, + 0.47, + 0.589 + ], + "angle": 0, + "content": "Similarly, we can optimize the \\( I(M; A) \\) by minimizing the following loss:" + }, + { + "type": "equation", + "bbox": [ + 0.121, + 0.599, + 0.47, + 0.692 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\mathcal {L} _ {M I _ {a}} = - \\frac {1}{N + k} \\sum_ {i = 1} ^ {N + k} \\left(\\sum_ {j = 0} ^ {k - 1} \\log h \\left(M _ {i}, A _ {i} ^ {\\eta_ {j}}\\right) \\right. \\tag {9} \\\\ \\left. + \\sum_ {l = 1} ^ {N} \\log \\left(1 - h (M _ {i}, A _ {i} ^ {\\xi_ {l}})\\right)\\right). \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.702, + 0.47, + 0.779 + ], + "angle": 0, + "content": "The form of Eq. (8) and Eq. (9) are similar to the CCL loss in [9]. However, our formulation is associated with MI and derives a tighter lower bound on it by taking account into the supervision of the label, which in our experiments is found to be more effective." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.787, + 0.383, + 0.804 + ], + "angle": 0, + "content": "3.2. Conditional Entropy Minimization" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.81, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Maximizing the lower bound on \\( I(M; S) \\) is insufficient for narrowing the information gap between the teacher and the student as the optimal lower bound does not mean that MI is maximum. This subsection focuses on further transferring knowledge by minimizing the conditional entropy of the teacher given the student \\( H(M|S) \\)." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.312, + 0.893, + 0.359 + ], + "angle": 0, + "content": "The posterior \\( p(M|S) \\) is difficult to calculate, thus we define a new distribution \\( q(M|S) \\) to approximate it. Then \\( H(M|S) \\) can be calculated as in [8]:" + }, + { + "type": "equation", + "bbox": [ + 0.502, + 0.366, + 0.892, + 0.443 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} H (M | S) = - \\mathbb {E} _ {S \\sim p (S)} \\left[ \\mathbb {E} _ {M ^ {\\prime} \\sim p (M | S)} \\left[ \\log p \\left(M ^ {\\prime} | S\\right) \\right] \\right] \\\\ = - \\mathbb {E} _ {S \\sim p (S)} [ \\mathbb {E} _ {M ^ {\\prime} \\sim p (M | S)} [ \\log q (M ^ {\\prime} | S) ] \\\\ \\left. - D _ {K L} \\left(p (M | S) | | q (M | S)\\right) \\right] \\\\ \\leq - \\mathbb {E} _ {S \\sim p (S)} \\left[ \\mathbb {E} _ {M ^ {\\prime} \\sim p (M | S)} [ \\log q (M ^ {\\prime} | S) ] \\right]. \\tag {10} \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.45, + 0.893, + 0.617 + ], + "angle": 0, + "content": "Thus we can minimize \\( H(M|S) \\) by maximizing the negative of its upper bound. We achieve this by introducing an adversarial learning-based approach, and using it to maximize \\( \\mathbb{E}_{S\\sim p(S)}\\left[\\mathbb{E}_{M^{\\prime}\\sim p(M|S)}[\\log q(M^{\\prime}|S)]\\right] \\) w.r.t. the parameters of the student network during the generation and minimize \\( \\mathbb{E}_{S\\sim p(S)}[\\mathbb{E}_{M^{\\prime}\\sim p(M|S)}[\\log q(M^{\\prime}|S)] - \\log p(M|S)] \\) w.r.t. the parameters of the discriminators. In other words, we use the discriminator \\( D(\\cdot) \\) to recognize whether features come from multimodal distribution or not and feedback informative gradient to the student model through minimizing:" + }, + { + "type": "equation", + "bbox": [ + 0.53, + 0.622, + 0.892, + 0.641 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {a d v} = - \\mathbb {E} _ {S \\sim p (S)} \\left[ \\mathbb {E} _ {M ^ {\\prime} \\sim p (M | S)} [ \\log D (S) ] \\right]. \\tag {11}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.644, + 0.892, + 0.734 + ], + "angle": 0, + "content": "Minimizing Eq. (11) w.r.t. the parameters of the target modality student enables the student to imitate representations coming from the multimodal distribution. It is worth noting that optimizing \\( H(M|S) \\) through Eq. (11) does not affect the learning of the teacher since no gradient back propagates to the teacher." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.734, + 0.893, + 0.901 + ], + "angle": 0, + "content": "Nevertheless, for the samples of the same class, it is more challenging to transfer the multimodal information by adversarial learning. This is because the generated target modality representation tends to mimic that of multimodality in the same instance with the constraint of MI, easier but can not capture the correlation among samples with the supervision of the label. As a result, we introduce two discriminators to learn more informative target modal representations. One discriminator called fundamental discriminator \\((D_{1})\\) is designed to distinguish the target modality and full modality representations from the entire training data. The other discriminator, which is called enhanced dis" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "11769" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.19 + ], + "angle": 0, + "content": "criminator \\((D_{2})\\), is designed to further distinguish the two kinds of representations coming from the classes with more than one sample in a batch since we think paying attention to these representations can help the student further aggregate representations in the same class. Thus, minimizing Eq. (11) w.r.t. the parameters of the student becomes minimizing:" + }, + { + "type": "equation", + "bbox": [ + 0.088, + 0.196, + 0.47, + 0.233 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {a d v} = - \\frac {\\lambda_ {1}}{N + k} \\sum_ {i = 1} ^ {N + k} \\log D _ {1} \\left(S _ {i} ^ {\\eta_ {0}}\\right) - \\frac {\\lambda_ {2}}{d} \\sum_ {v = 1} ^ {w} \\log D _ {2} \\left(S _ {v} ^ {\\eta_ {1}}\\right). \\tag {12}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.236, + 0.47, + 0.266 + ], + "angle": 0, + "content": "And the parameters of discriminators are trained by minimizing:" + }, + { + "type": "equation", + "bbox": [ + 0.093, + 0.271, + 0.47, + 0.346 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\mathcal {L} _ {D} = - \\frac {\\lambda_ {1}}{N + k} \\sum_ {i = 1} ^ {N + k} \\left(\\log D _ {1} \\left(M _ {i}\\right) + \\log \\left(1 - D _ {1} \\left(S _ {i} ^ {\\eta_ {0}}\\right)\\right)\\right) \\tag {13} \\\\ - \\frac {\\lambda_ {2}}{d} \\sum_ {v = 1} ^ {w} \\left(\\log D _ {2} \\left(M _ {v}\\right) + \\log \\left(1 - D _ {2} \\left(S _ {v} ^ {\\eta_ {1}}\\right)\\right)\\right), \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.351, + 0.473, + 0.608 + ], + "angle": 0, + "content": "where \\(\\{M_v\\}_{v=1}^w\\) is a set where every element comes from the classes with more than one samples and \\(\\{S_v^{\\eta_1}\\}_{v=1}^w\\) is its corresponding set of target modal representations. \\(d\\) is used for more stabilized training and we set it by the frequency of the data with samples of the same classes. \\(\\lambda_1\\) and \\(\\lambda_2\\) are weighting parameters for \\(D_1\\) and \\(D_2\\) respectively, and \\(\\lambda_1 + \\lambda_2 = 1\\). To further improve the efficiency of the transfer, we adjust \\(\\lambda_1\\) and \\(\\lambda_2\\) adaptively according to the alignment between \\(S\\) and \\(M\\) for each epoch \\(t\\). More specifically, we use the averaged cosine similarity in the tuples \\(\\Phi(M_i, S_i^{\\eta_0})\\) and \\(\\Phi(M_v, S_v^{\\eta_j}), j \\neq 0\\) in Eq. (7) to provide meaningful feedback for the cooperation of discriminators. Large cosine similarity indicates that \\(M\\) and \\(S\\) are well aligned, thus the weight of the corresponding discriminator can be relatively small. Moving average [30] is also applied to improve the training stability. The formula of \\(\\lambda\\) is given as:" + }, + { + "type": "equation", + "bbox": [ + 0.08, + 0.613, + 0.47, + 0.653 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\tilde {\\lambda} (t + 1) = \\beta \\tilde {\\lambda} (t) + (1 - \\beta) (1 - \\operatorname {A v g} _ {t} (\\Phi (M, S)))) \\tag {14} \\\\ \\lambda (t + 1) = \\sigma (\\tilde {\\lambda} (t + 1)), \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.659, + 0.47, + 0.705 + ], + "angle": 0, + "content": "where \\(\\sigma (\\cdot)\\) is the softmax function, \\(\\mathrm{Avg}_t(\\cdot)\\) represents the average of cosine similarity on epoch \\(t\\), and \\(\\beta \\in (0,1)\\) is the smoothing parameter, and we set \\(\\beta = 0.9\\) empirically." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.705, + 0.473, + 0.902 + ], + "angle": 0, + "content": "Adversarial learning is known to often generate random images if not constrained [31]. This also occurs when target modality representations are generated without any constraints. Our method implicitly overcomes this problem by maximizing the lower bound on \\( I(M; S) \\) and its advantages come twofold: First, the maximization of the lower bound on MI can not only transfer the multimodal information but also place a constraint on the adversarial distillation. Second, adversarial distillation further reduces the information gap that still exists after maximizing the lower bound on MI. Thus, the maximization of the lower bound on MI and adversarial distillation are complementary to each other in AMID to generate informative and robust representations." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.091, + 0.636, + 0.107 + ], + "angle": 0, + "content": "3.3. Overall Loss" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.114, + 0.893, + 0.19 + ], + "angle": 0, + "content": "Assuming that after the optimization above, the target modality and full modality representations are already aligned, then we can use two classifiers with shared parameters to perform the classification task for these representations respectively. The overall classification loss is:" + }, + { + "type": "equation", + "bbox": [ + 0.579, + 0.199, + 0.893, + 0.218 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {c l s} = \\mathcal {L} _ {c e} ^ {S} \\left(S _ {i}, y _ {i}\\right) + \\mathcal {L} _ {c e} ^ {M} \\left(M _ {i}, y _ {i}\\right), \\tag {15}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.228, + 0.895, + 0.365 + ], + "angle": 0, + "content": "where \\(\\mathcal{L}_{ce}\\) is the cross-entropy loss, \\(y_{i}\\) is the ground-truth. Classifiers with the same parameters can also help facilitate the generation of representations from the target modality network to imitate those of multimodality. In addition, the target modality can be aligned with the full modality in the predictive space. We use the Jensen-Shannon divergence (JSD) [27] to optimize the MI between the predictive target modality distribution \\((P_S)\\) and the multimodality distribution \\((P_M)\\):" + }, + { + "type": "equation", + "bbox": [ + 0.563, + 0.375, + 0.892, + 0.416 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {J S D} = \\frac {1}{N + k} \\sum_ {i = 1} ^ {N + k} J S D \\left(P _ {S _ {i}} \\| P _ {M _ {i}}\\right). \\tag {16}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.426, + 0.893, + 0.457 + ], + "angle": 0, + "content": "The final loss function for distilling knowledge from auxiliary modalities is given as:" + }, + { + "type": "equation", + "bbox": [ + 0.508, + 0.468, + 0.892, + 0.485 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} = \\mathcal {L} _ {c l s} + \\mathcal {L} _ {J S D} + \\alpha_ {1} \\mathcal {L} _ {M I _ {s}} + \\alpha_ {2} \\mathcal {L} _ {M I _ {a}} + \\alpha_ {3} \\mathcal {L} _ {a d v}, \\tag {17}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.494, + 0.892, + 0.526 + ], + "angle": 0, + "content": "The whole procedure is shown in the supplementary and the overall model structure is shown in Fig. 2." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.538, + 0.634, + 0.555 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.563, + 0.603, + 0.577 + ], + "angle": 0, + "content": "4.1. Datasets" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.586, + 0.893, + 0.662 + ], + "angle": 0, + "content": "Video understanding. We experiment on two popular multimodal datasets for video recognition (Top-1 accuracy, %) and kNN video retrieval (R@K, %) [5]. Cross-modal knowledge distillation is performed from the acoustic to the visual modality." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.67, + 0.892, + 0.717 + ], + "angle": 0, + "content": "- UCF51, as a subset of UCF101 [40], includes 6,845 videos with audio belonging to 51 categories. The public split1 is adopted." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.725, + 0.894, + 0.786 + ], + "angle": 0, + "content": "- ActivityNet [20] is a large-scale video benchmark of 14,950 videos with audio, covering 200 complex human activities, where the training set has 10,024 videos while 4,926 videos in the validation set." + }, + { + "type": "list", + "bbox": [ + 0.518, + 0.67, + 0.894, + 0.786 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.795, + 0.895, + 0.902 + ], + "angle": 0, + "content": "Emotion classification. We conduct experiments on IEMOCAP [6], a popular multimodal dataset for 4-class emotion classification, which contains totaling 5531 videos in 5 dyadic conversation sessions. Each video consists of acoustic, textual and visual modalities, and the target model is based on visual modality only. A 5-fold cross-validation is adopted for the evaluation, taking one session as the test" + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "11770" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.089, + 0.47, + 0.131 + ], + "angle": 0, + "content": "Table 1. The Top-1 accuracy \\((\\%)\\) of video recognition on UCF51 and ActivityNet. Notice that we change all the activation functions to LeakyReLU to ensure a fair comparison." + }, + { + "type": "table", + "bbox": [ + 0.134, + 0.131, + 0.41, + 0.242 + ], + "angle": 0, + "content": "
UCF51ActivityNet
Baseline66.748.8
CRD [42]67.150.4
GMC [36]64.153.1
CRCD [51]69.652.4
CCL [9]68.951.9
AMID (Ours)73.853.6
" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.269, + 0.47, + 0.318 + ], + "angle": 0, + "content": "set for each fold. Following [50], two evaluation metrics, weighted accuracy (WA, %) and unweighted accuracy (UA, %), are adopted." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.337, + 0.268, + 0.354 + ], + "angle": 0, + "content": "4.2. Experimental Setup" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.364, + 0.471, + 0.621 + ], + "angle": 0, + "content": "Because different modalities such as audio, video and text are heterogeneous, we use individual extractors for each modality, then the features are concatenated and passed through a 2-layer MLP as the full modality teacher. The teacher shares the same extractors as that of the student and the auxiliary model for reducing the number of parameters. Video recognition and retrieval. Following [9], we use a 1D-CNN14 [26] pre-trained on AudioSet [17] as the audio extractor and use R(2+1)D-18 [43] as the student video network. The two discriminators are 5-layer MLP and 3-layer MLP respectively. Besides, we change all activation functions to Leaky ReLU for adversarial learning because it gives better training stability compared to the ReLU. The dimension of the representations is set to 512. The batch size and temperature \\(\\tau\\) are set to 16 and 0.5, respectively. \\(\\alpha_{1},\\alpha_{2},\\alpha_{3}\\) are set to 4, 1.6, 1. More details are shown in the supplementary." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.625, + 0.47, + 0.716 + ], + "angle": 0, + "content": "Emotion classification. We extract raw acoustic, textual and visual embeddings by the pre-trained wav2vec 2.0 [3], BERT [12] and DenseNet [24] respectively. RNN is adopted as the student network with a final feature dimension of 768. The batch size and temperature \\(\\tau\\) are set to 128 and 0.6, respectively." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.72, + 0.471, + 0.902 + ], + "angle": 0, + "content": "A warm-up stage is employed for all experiments. At the first \\( T_{start} \\) epochs, the student model and the teacher model are trained by minimizing \\( \\mathcal{L} = \\mathcal{L}_{cls} + \\mathcal{L}_{JSD} \\) to alleviate the converge difficulties of adversarial learning. This helps a preliminary alignment between the teacher and student and can also prevent discriminators from recognizing readily at the beginning of the training. \\( T_{start} \\) is set to 20 for the video understanding tasks and 5 for the emotion classification task. And notice that without special mention, the leveraged pre-trained auxiliary modality extractors are fixed since the generated representations already contain rich auxiliary information." + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.089, + 0.892, + 0.117 + ], + "angle": 0, + "content": "Table 2. \\(\\mathrm{R@K(K = 1,5)}\\) of video retrieval on UCF51 and ActivityNet." + }, + { + "type": "table", + "bbox": [ + 0.543, + 0.117, + 0.847, + 0.244 + ], + "angle": 0, + "content": "
UCF51ActivityNet
MetricR1R5R1R5
Baseline64.071.941.563.9
CRD [42]66.072.343.665.5
GMC [36]61.871.046.167.7
CRCD [51]68.275.245.767.0
CCL [9]67.071.746.264.8
AMID (Ours)73.677.146.467.2
" + }, + { + "type": "image", + "bbox": [ + 0.511, + 0.265, + 0.882, + 0.412 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.427, + 0.892, + 0.456 + ], + "angle": 0, + "content": "Figure 3. The per-class Top-1 accuracy \\((\\%)\\) of video recognition on UCF51 comparing AMD with CCL." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.48, + 0.8, + 0.495 + ], + "angle": 0, + "content": "4.3. Comparison with State-of-the-arts" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.505, + 0.892, + 0.686 + ], + "angle": 0, + "content": "Video recognition. We compare AMD with two types of SOTA cross-modal KD methods, i.e. intra-sample methods including CRD [42], GMC [36], and inter-sample methods including CCL [9], CRCD [51]. The results are summarized in Tab. 1. Here \"Baseline\" represents the model directly trained with the visual modality only, representing a lower bound for the tasks. It can be seen that AMD significantly outperforms all the compared methods, suggesting that it is more effective and consistent in learning information from auxiliary modalities. AMD outperforms the second-best method by \\(4.2\\%\\) and \\(0.5\\%\\) on the two datasets, respectively." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.688, + 0.892, + 0.868 + ], + "angle": 0, + "content": "To further investigate the breakdown of performance, we compare AMD with CCL on UCF51 and give the results of class-wise Top-1 accuracy in Fig. 3. It can be seen that AMD achieves better performance than CCL for most of the classes, although for a few of them it is comparable to or slightly worse than CCL. The classes where AMD is of inferior performance are mainly those audio events that are not or weakly correlated with the videos, such as 'FrisbeeCatch' and 'SkyDiving'. In these classes, the auxiliary modal information is less helpful. Thus, AMD, which is proposed for better cross-modal knowledge distillation, is not very effective for these classes." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.871, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Video retrieval. Tab. 2 presents the results of video retrieval on the UCF51 and ActivityNet datasets, which is a" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "11771" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.09, + 0.47, + 0.131 + ], + "angle": 0, + "content": "Table 3. Performance comparison under different setups on IEMOCAP, where A-V, L-V, AL-V mean distillation from acoustic to visual, textual to visual, and acoustic and textual to visual." + }, + { + "type": "table", + "bbox": [ + 0.112, + 0.132, + 0.432, + 0.348 + ], + "angle": 0, + "content": "
SetupMethodWAUA
VBaseline51.250.8
A-VGMC [36]51.750.9
CRCD [51]51.850.2
CCL [9]51.551.4
AMID (Ours)52.551.7
L-VGMC [36]50.950.5
CRCD [51]50.249.9
CCL [9]52.751.8
AMID (Ours)53.052.4
AL-VGMC [36]51.950.5
CRCD [51]52.049.4
CCL [9]53.251.4
AMID (Ours)53.852.7
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.373, + 0.47, + 0.434 + ], + "angle": 0, + "content": "more fine-grained task to evaluate the discriminability of video representations. The results show that AMD consistently outperforms almost all competing approaches in terms of R@1 and R@5." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.435, + 0.471, + 0.617 + ], + "angle": 0, + "content": "Emotion classification. Tab. 3 compares AMID with three state-of-the-art methods, CCL, CRCD and GMC, for emotion classification. We conduct experiences on IEMOCAP, a three-modality dataset, to further evaluate the performance of AMID in different auxiliary modalities. It is worth noting that the \"Baseline\" model is trained directly with only the visual modality. The results demonstrate that AMID outperforms the Baseline model for all setups, where the UA metrics increase by \\(0.9\\%\\), \\(1.6\\%\\) and \\(1.9\\%\\) respectively, while the other three methods are not always effective. Besides, AMID outperforms CCL, CRCD and GMC on almost all the setups." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.626, + 0.231, + 0.643 + ], + "angle": 0, + "content": "4.4. Ablation Study" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.65, + 0.436, + 0.667 + ], + "angle": 0, + "content": "4.4.1 Effectiveness of MI and conditional entropy" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.674, + 0.471, + 0.903 + ], + "angle": 0, + "content": "In order to verify the effectiveness of our proposed method for capturing as much multimodal information as possible, the impact of using different training configurations on UCF51 is studied in Tab. 4. Here \"student alone\" represents the result of a model trained with the visual modality only and \"teacher alone\" represents that of the teacher model with the full modalities. These two cases show the initial performance of the student and the teacher without distillation, respectively. When optimizing \\(\\mathcal{L}_{MI_s}\\) alone for the distillation, although the student model can achieve performance gains, from \\(66.7\\%\\) to \\(69.8\\%\\), it degrades the teacher's performance, from \\(74.3\\%\\) to \\(71.2\\%\\) and thereby reducing the upper bound of the student's performance. Alternatively, more informative multimodal representations can be obtained by maximizing the lower bound on \\(I(M;A)\\) and" + }, + { + "type": "table_caption", + "bbox": [ + 0.529, + 0.09, + 0.86, + 0.103 + ], + "angle": 0, + "content": "Table 4. Ablation study for the proposed loss functions." + }, + { + "type": "table", + "bbox": [ + 0.504, + 0.103, + 0.887, + 0.23 + ], + "angle": 0, + "content": "
ConfigurationTop-1 accuracy
StudentTeacher
student alone (w/o distillation)66.7\\
teacher alone (w/o distillation)\\74.3
\\( \\mathcal{L}_{MI_s} \\)69.871.2
\\( \\mathcal{L}_{MI_s} + \\mathcal{L}_{MI_a} \\)72.776.0
\\( \\mathcal{L}_{MI_s} + \\mathcal{L}_{MI_a} + \\mathcal{L}_{adv} \\) (AMID)73.875.7
AMID with \\( \\mathcal{L}_{nce} \\)72.374.3
" + }, + { + "type": "image", + "bbox": [ + 0.58, + 0.246, + 0.816, + 0.403 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.406, + 0.892, + 0.435 + ], + "angle": 0, + "content": "Figure 4. The accuracy gap between the teacher and student in using \\(\\mathcal{L}_{MI_s} + \\mathcal{L}_{MI_a}\\) and AMD loss." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.459, + 0.892, + 0.64 + ], + "angle": 0, + "content": "\\(I(M;S)\\) simultaneously \\((\\mathcal{L}_{MI_s} + \\mathcal{L}_{MI_a})\\), since a better teacher can improve the distillation performance. Tab. 4 shows that this improves the accuracy of the student from \\(66.7\\%\\) to \\(72.7\\%\\) and also improves that of the teacher from \\(74.3\\%\\) to \\(76.0\\%\\). Besides, adding \\(\\mathcal{L}_{adv}\\) (i.e., AMD) to \\(\\mathcal{L}_{MI_s} + \\mathcal{L}_{MI_a}\\) does improve the performance from \\(72.7\\%\\) to \\(73.8\\%\\), and the performance gap of AMD is smaller than \\(\\mathcal{L}_{MI_s} + \\mathcal{L}_{MI_a}\\), which indicates that AMD achieves better alignment between the teacher and the student due to the further constraint on the gap by minimizing \\(H(M|S)\\) without degrading the teacher's performance obviously (the teacher's performance decreases from \\(76.0\\%\\) to \\(75.7\\%\\))." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.642, + 0.892, + 0.809 + ], + "angle": 0, + "content": "To further understand the effectiveness of the conditional entropy minimization approach in reducing the information gap between the teacher and the student, we explore the gap of AMID and \\(\\mathcal{L}_{MI_s} + \\mathcal{L}_{MI_a}\\) during training. This information gap is represented by the gap of accuracy between the teacher and student on the validation set over the training epochs. The results are shown in Fig. 4. It can be seen that the accuracy gap of using AMID loss is consistently smaller than that of \\(\\mathcal{L}_{MI_s} + \\mathcal{L}_{MI_a}\\), which validates the proposed adversarial learning-based approach indeed helps to narrow down the information gap." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.81, + 0.892, + 0.902 + ], + "angle": 0, + "content": "AMID is also compared to an ablative setup using the contrastive loss \\(\\mathcal{L}_{nce}\\) [9] to verify the effectiveness of the proposed loss function in maximizing the lower bound on MI. The result in Tab. 4 shows that AMD performs much better than the baseline \"AMID with \\(\\mathcal{L}_{nce}\\)\", improving the accuracy by \\(1.5\\%\\). This validates that our proposed ap" + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "11772" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.102, + 0.09, + 0.444, + 0.103 + ], + "angle": 0, + "content": "Table 5. Effectiveness of proposed training modifications." + }, + { + "type": "table", + "bbox": [ + 0.132, + 0.104, + 0.409, + 0.199 + ], + "angle": 0, + "content": "
ModificationTop-1 accuracy
AMID73.8
with fixed teacher66.0
w/o warm-up65.8
w/o D272.8
w/o dynamic weight72.7
" + }, + { + "type": "image", + "bbox": [ + 0.093, + 0.209, + 0.272, + 0.326 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.276, + 0.211, + 0.454, + 0.325 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.337, + 0.47, + 0.38 + ], + "angle": 0, + "content": "Figure 5. (Left) The cosine similarity between the teacher's and student's representations only in the same class during training. (Right) The cosine similarity during testing." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.397, + 0.469, + 0.427 + ], + "angle": 0, + "content": "proach, which takes into account the correlation of samples within a class, achieves better optimization for MI." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.441, + 0.398, + 0.456 + ], + "angle": 0, + "content": "4.4.2 Effectiveness of training modifications" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.462, + 0.47, + 0.703 + ], + "angle": 0, + "content": "To evaluate the effect of each modification applied in AMD, we conduct a set of experiments on UCF51 and give the results in Tab. 5. As mentioned before, using a fixed pre-trained teacher to guide the student's learning leads to an undesired gap between the teacher and the student at the beginning of training, which is unfavorable for distillation. The result affirms this, where the performance of AMD degrades from \\(73.8\\%\\) to \\(66.0\\%\\) without joint training. In addition, it also shows that without employing the warm-up setup described before, the recognition performance degrades by \\(8.0\\%\\). The reason may be that the target modality and multimodality representations are noisy and uncorrelated at the start of the training, which results in that the discriminators can recognize them readily and thus affecting the feedback of the informative gradient of adversarial learning." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.704, + 0.47, + 0.87 + ], + "angle": 0, + "content": "We also study the effectiveness of the two discriminators of our proposed AMD by comparing AMD with two ablative cases: w/o \\( D_{2} \\) and w/o dynamic weight. One constraint is removed at a time. The results of these ablation studies are shown in Tab. 5. The accuracy decreases by \\( 1.0\\% \\) when only the fundamental discriminator \\( D_{1} \\) is used, suggesting that the enhanced discriminator \\( D_{2} \\) indeed helps to distill the multimodal information of samples of the same class. Moreover, it also demonstrates that using uniform weight leads to a performance drop, indicating the effectiveness of the proposed dynamic weighting scheme." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.469, + 0.901 + ], + "angle": 0, + "content": "To further investigate the effectiveness of the proposed adversarial learning-based approach in transferring the" + }, + { + "type": "table_caption", + "bbox": [ + 0.5, + 0.09, + 0.89, + 0.116 + ], + "angle": 0, + "content": "Table 6. Top-1 accuracy (%) on UCF51 with different hyperparameters." + }, + { + "type": "table", + "bbox": [ + 0.505, + 0.117, + 0.882, + 0.212 + ], + "angle": 0, + "content": "
α1value3.73.83.94.04.14.2
accuracy72.673.773.773.873.873.4
α2value1.31.41.51.61.71.8
accuracy71.273.773.873.873.672.4
α3value0.70.80.91.01.11.2
accuracy73.373.473.773.873.473.1
" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.228, + 0.892, + 0.378 + ], + "angle": 0, + "content": "inter-sample multimodal information, we compare AMID with two cases: w/o \\( D_{2} \\) and w/o \\( \\mathcal{L}_{adv} \\). Fig. 5 displays the average of cosine similarity between the teacher and the student only in the same class, i.e. the average of all \\( \\Phi (M_v,S_v^{\\eta_j}), j\\neq 0 \\) in Eq. (7). We can see that the cosine similarity of AMID is consistently larger than that of the other two cases and the cosine similarity of w/o \\( D_{2} \\) is larger than that of w/o \\( \\mathcal{L}_{adv} \\), meaning that the proposed approach indeed helps the student to learn more compact representations for each class." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.388, + 0.743, + 0.403 + ], + "angle": 0, + "content": "4.5. Hyperparameters Analysis" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.407, + 0.892, + 0.573 + ], + "angle": 0, + "content": "Sensitivity analysis studies are conducted for the hyperparameters, \\(\\alpha_{1}\\), \\(\\alpha_{2}\\) and \\(\\alpha_{3}\\), referenced in the loss function Eq. (17). Similar to the previous study, we experiment on UCF51 and show the results in Tab. 6. The other two hyperparameters are kept the same when one changes. We test different values for \\(\\alpha_{1}\\) from 3.7 to 4.2, \\(\\alpha_{2}\\) from 1.3 to 4.8 and \\(\\alpha_{3}\\) from 0.7 to 1.2, all with an increment of 0.1. The results show that the hyperparameters \\(\\alpha_{1}\\), \\(\\alpha_{2}\\) and \\(\\alpha_{3}\\) are not sensitive within a certain range. In general, \\(\\alpha_{1}\\) between 3.8 to 4.1 and \\(\\alpha_{2}\\) between 1.4 to 1.7 works well, and we set \\(\\alpha_{3} = 1.0\\) for all other experiments." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.586, + 0.619, + 0.601 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.611, + 0.892, + 0.792 + ], + "angle": 0, + "content": "In this paper, we propose a generic cross-modal distillation method, AMID, to enhance the target modality representations. The proposed approach simultaneously maximizes the lower bounds on MI between the teacher and the student as well as between the teacher and an auxiliary model while minimizing the conditional entropy of the teacher given the student. For optimizing the lower bound on MI, we derive a new form and solve it by a contrastive learning-based approach. For minimizing the conditional entropy, an adversarial learning-based approach is used. Our extensive experimental evaluation demonstrates the effectiveness of AMID on three popular datasets." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.797, + 0.661, + 0.813 + ], + "angle": 0, + "content": "Acknowledgement" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.817, + 0.892, + 0.9 + ], + "angle": 0, + "content": "This work is supported by the National Key R&D Program of China (No. 2022ZD0160702), STCSM (No. 2251 1106101, No. 18DZ2270700, No. 21DZ1100100, No. 215 11101100), 111 plan (No. BP0719010), and State Key Laboratory of UHD Video and Audio Production and Presentation." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "11773" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.105 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.116, + 0.47, + 0.171 + ], + "angle": 0, + "content": "[1] Sarah A. Abdu, Ahmed H. 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In IEEE Conference on Computer Vision and Pattern Recognition, CVPR, pages 9260-9269, 2021. 2, 6, 7" + }, + { + "type": "list", + "bbox": [ + 0.504, + 0.093, + 0.892, + 0.897 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.946, + 0.519, + 0.956 + ], + "angle": 0, + "content": "11775" + } + ] +] \ No newline at end of file diff --git a/2023/Enhanced Multimodal Representation Learning With Cross-Modal KD/550b12f3-e75d-4ee0-8736-cf2526b0aff9_origin.pdf b/2023/Enhanced Multimodal Representation Learning With Cross-Modal KD/550b12f3-e75d-4ee0-8736-cf2526b0aff9_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..488014ae9f3f7bde0137c902ef3069b1eb47fe0d --- /dev/null +++ b/2023/Enhanced Multimodal Representation Learning With Cross-Modal KD/550b12f3-e75d-4ee0-8736-cf2526b0aff9_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:85a66fa34b2018f9d2d7618a8443d7e99d58de73b72a36388c08cde72eabc460 +size 1365067 diff --git a/2023/Enhanced Multimodal Representation Learning With Cross-Modal KD/full.md b/2023/Enhanced Multimodal Representation Learning With Cross-Modal KD/full.md new file mode 100644 index 0000000000000000000000000000000000000000..789d5ffa0d6f3ebfa2992e2eaab68431fb8fd0cf --- /dev/null +++ b/2023/Enhanced Multimodal Representation Learning With Cross-Modal KD/full.md @@ -0,0 +1,350 @@ +# Enhanced Multimodal Representation Learning with Cross-modal KD + +Mengxi Chen $^{1}$ , Linyu Xing $^{1}$ , Yu Wang $^{1,2\boxtimes}$ , Ya Zhang $^{1,2\boxtimes}$ + +$^{1}$ Shanghai Jiao Tong University, $^{2}$ Shanghai AI Laboratory + +{mxchen_mc,xly8991,yuwanhsjtu,ya_zhang}@sjtu.edu.cn + +# Abstract + +This paper explores the tasks of leveraging auxiliary modalities which are only available at training to enhance multimodal representation learning through cross-modal Knowledge Distillation (KD). The widely adopted mutual information maximization-based objective leads to a shortcut solution of the weak teacher, i.e., achieving the maximum mutual information by simply making the teacher model as weak as the student model. To prevent such a weak solution, we introduce an additional objective term, i.e., the mutual information between the teacher and the auxiliary modality model. Besides, to narrow down the information gap between the student and teacher, we further propose to minimize the conditional entropy of the teacher given the student. Novel training schemes based on contrastive learning and adversarial learning are designed to optimize the mutual information and the conditional entropy, respectively. Experimental results on three popular multimodal benchmark datasets have shown that the proposed method outperforms a range of state-of-the-art approaches for video recognition, video retrieval and emotion classification. + +# 1. Introduction + +Multimodal learning has shown much promise in a wide spectrum of applications, such as video understanding [20, 39, 44], sentiment analysis [1, 19, 47] and medical image segmentation [7, 49]. It is generally recognized that including more modalities helps the prediction accuracy. For many real-world applications, while one has to make predictions based on limited modalities due to efficiency or cost concerns, it is usually possible to collect additional modalities at training. To enhance the representation learned, several studies have thus considered to leverage such modalities as a form of auxiliary information at training [11, 23, 29, 50]. Several attempts have explored to fill in the auxiliary modalities at test time, by employing approaches such as Generative Adversarial Network + +![](images/4fa345fa4a238ee1ec657c402db9192b2ec53df16a324b9a667593c646b1c51c.jpg) + +![](images/236838d44f4acc4a149a4621469e1da40f1a611edf0a578df0d76cb9f127624e.jpg) +Figure 1. Illustration of the difference between the MI-based method and the proposed AMID method. (a) MI-based methods maximize $I(M;S)$ . (b) AMID maximizes $I(M;S)$ and $I(M;A)$ , while minimizing $H(M|S)$ . + +(GAN) [4, 22]. However, such data generation-based approaches introduce extra computation costs at inference. + +As an alternative, cross-modal knowledge distillation is proposed, where a teacher model trained with both the target modalities and the auxiliary modalities (denoted as full modalities hereafter), is employed to guide the training of a student model with target modalities only [10, 11, 16, 23, 45, 46]. In such a way, the student model directly learns to embed information about auxiliary modalities and involves no additional computational cost at inference. A typical practice is to pre-train the teacher model from the full modality data, and fix it during the training. While such a setting enables the teacher to provide information-rich representation [23, 46], it may not be favorable for the alignment of the teacher and student, due to the large information gap between them, especially at the early stage of training [32]. + +To better facilitate the knowledge transfer, online KD is proposed to jointly train the teacher and the student. One common solution is to maximize the mutual information (MI) between the teacher and the student in a shared + +space [42]. However, such an objective only focuses on maximizing the shared knowledge, in terms of percentage, from the teacher to the student, which is necessary but not sufficient to guarantee a complete knowledge transfer. As illustrated in Fig. 1(a), a short-cut solution is to simply make the teacher model capture less information, i.e., shrinking the entropy of the teacher. + +Under the framework online KD, this paper explores to simultaneously achieve: 1) maintaining the representation capacity of the full modality teacher as much as possible, and 2) narrowing down the information gap between the teacher and the student. As Fig. 1(b) shows, in addition to maximizing the MI between the teacher and the student, maximizing the MI between the teacher and an additional auxiliary model may contribute to the former goal, while minimizing the conditional entropy of the teacher given the student may benefit the latter goal. We thus propose a new objective function consisting of all the above three terms. To achieve the optimization of the MI, we further derive a new form of its lower bound by taking into account the supervision of the label, and propose a contrastive learning-based approach to implement it. To minimize the conditional entropy, an adversarial learning-based approach is introduced, where additional discriminators are used to distinguish representations between the teacher and the student. We name the proposed method Adversarial Mutual Information Distillation (AMID) hereafter. + +To validate the effectiveness of AMID, extensive experiments on three popular multimodal tasks including video recognition, video retrieval and emotion classification tasks are conducted. The performance of these tasks are conducted on UCF51 [40], ActivityNet [20] and IEMOCAP [6] benchmark datasets, respectively. The results show that AMID outperforms a range of state-of-the-art approaches on all three tasks. To summarize, the main contribution of this paper is threefold: + +- We propose a novel cross-modal KD method, Adversarial Mutual Information Distillation (AMID), to prevent the teacher from losing information by maximizing the MI between it and an auxiliary modality model. +- AMID maximally transfers information from the teacher to the student by optimizing the MI between them and minimizing the conditional entropy of the teacher given the student. +- To implement the joint optimization of the three objective terms, a novel training approach that leverages the combined advantage of both contrastive learning and adversarial learning is proposed. + +# 2. Related Work + +Knowledge Distillation. Knowledge distillation (KD) is + +first proposed in [21], where soft labels in predictive space produced by the teacher through temperature hyperparameter transfer the dark knowledge to the student. Later, many works studied and demonstrated the benefits of distilling knowledge in the latent space [25, 35, 38, 48]. There have been some works that explore KD-based methods for cross-modal representation learning. CMC [41] aligns different views of the same samples by contrastive learning to extract shared information. CRD [42] leverages instance-level contrastive objectives to perform KD. GMC [36] learns geometrically aligned representations by aligning modality-specific representations with that of the corresponding complete observation. However, these methods can not transfer the correlation among instances, which are also valuable in many tasks. To transfer the inter-sample relation, [9] propose CCL to close the cross-modal semantic gap between the multimodality teacher and the student by contrasting different modal embeddings in the same classes in a common latent space. CRCD [51] distills the information of the teacher space by maximizing two complementary MI criteria. In contrast to these recent KD works which only consider the alignment between the teacher and student but neglect the objectives' impact on the teacher, we proposed a new KD objective that helps the teacher capture as much auxiliary information as possible and constraints the alignment simultaneously. + +Mutual Information Maximization. MI is first introduced to deep learning in [2], and since then, many methods have proposed to combine variational bounds with parameterized neural networks to enable differentiable and tractable estimation of MI in high-dimensional spaces [15, 34]. The character that MI can be used to represent the relationship between two variables is well-suited for correlated multimodal data. [19] hierarchically optimizes MI in unimodal pairs and between multimodal and unimodal representations for maintaining useful information while filtering noise in unimodal input. [28] proposed TupleInfoNCE to optimize MI in multimodal input tuples which enables the model to capture both the modal-shared information and the specific information. However, these methods rarely consider the correlation among samples with the supervision of the label, which are still useful. In this paper, we derive a new lower bound on MI in teacher-student pairs which takes into account the inter-sample correlation and propose a contrastive-learning method for its maximization. + +Adversarial Learning. Since [18] developed adversarial learning in deep learning, many researchers attempt to improve its performance by stabilizing the training process. In addition to modifying the structure of discriminator or generator [8, 31, 37], several works still considered incorporating multiple discriminators to improve learning [13, 14, 33]. Similar to [13], in this paper, we design two additional discriminators and adjust their weights adaptively. + +# 3. Method + +Suppose we have a multimodal dataset with $n$ modalities, consisting of $k$ target modalities $\{x_1, \dots, x_k\}$ and $n - k$ auxiliary modalities $\{x_{k + 1}, \dots, x_n\}$ . Denote the model trained with all $n$ modalities, $k$ target modalities only, and $n - k$ auxiliary modalities only as full modality model $M(x_1, \dots, x_n)$ , target modality model $S(x_1, \dots, x_k)$ , and auxiliary modality model $A(x_{k + 1}, \dots, x_n)$ , respectively. This paper aims to transfer knowledge from the full modality model $M$ to the target modality model $S$ with the assistant of auxiliary modalities at training. + +A widely adopted objective for cross-modal knowledge transfer is to maximize the MI between the representation of the full modality teacher $M$ and the representation of the target modality student $S$ , i.e. $I(M; S)$ . But there exists a shout-cut solution as shown in Fig. 1(a). In order to prevent this problem, we propose AMID, which maximizes the MI between $M$ and $A$ , i.e. $I(M; A)$ , so as to ensure the full modality model captures information from both target modalities and auxiliary modalities, and maximizes $I(M; S)$ while minimizing the conditional entropy of the teacher given the student $H(M|S)$ , so as to narrow down the information gap between the teacher and the student. For optimizing the MI, we derive a new form of its lower bound and maximize it through a contrastive learning-based approach. For minimizing $H(M|S)$ , we introduce an adversarial learning-based approach. + +To sum up, the overall objective is to optimize: + +$$ +\mathcal {O} = \alpha_ {1} \mathrm {l b} (I (M; S)) + \alpha_ {2} \mathrm {l b} (I (M; A)) - \alpha_ {3} H (M | S), \tag {1} +$$ + +where $\mathrm{lb}(\cdot)$ means the lower bound on MI, $\alpha_{1},\alpha_{2},\alpha_{3}$ are the different weights for the corresponding terms. + +# 3.1. Mutual Information Optimization + +In this section, we will focus on how to optimize $I(M;S)$ and $I(M;A)$ through maximizing their lower bounds for capturing as much information as possible. Unlike [42] which only considers the correlation between the teacher's representation and that of the student in the same sample, we derive a new form of lower bound on MI by taking into account the correlation of samples within a class. Notice that as the deduction procedures for $I(M;S)$ and $I(M;A)$ are the same, we will construct an approximate loss for optimizing $I(M;S)$ . + +Firstly, we define a distribution $q$ which models the joint distribution of $M$ and $S$ . A latent variable, $C$ , is used to indicate whether a tuple $(M, S)$ comes from the same class $(C = 1)$ or not $(C = 0)$ : + +$$ +\begin{array}{l} q (M, S | C = 1) = p (M, S); \\ q (M, S \mid C = 0) = p (M) p (S). \tag {2} \\ \end{array} +$$ + +We sample $(M, S)$ by considering the relationship between full modality and target modality representations in the + +same classes, which is more effective for transferring information. The pair $(M, S)$ is from the joint distribution when $M, S$ are in the same class or from the product of the marginal distributions when $M, S$ are in different classes. + +Suppose in a mini-batch, given a specific $M_{i}$ , there are $k - 1$ positive pairs $(M_{i}, S_{i}^{\eta_{j}})$ drawn from the joint distribution, where $\{\eta_{j}\}_{j = 1}^{k - 1}$ is an index set and every element indicates the position of other $S$ with the same class as $M_{i}$ , 1 positive pair $(M_{i}, S_{i}^{\eta_{0}})$ from the same sample, and $N$ negative pairs $(M_{i}, S_{i}^{\xi_{l}})$ from the product of marginals, where $\{S_{i}^{\xi_{l}}\}_{l = 1}^{N}$ are $N$ target modality representations from different classes than $M_{i}$ . Then the priors of $C$ can be calculated as $q(C = 1) = \frac{k}{N + k}$ and $q(C = 0) = \frac{N}{N + k}$ . Using Bayes' rule, the logarithmic posterior for $C = 1$ is given by: + +$$ +\begin{array}{l} \log q (C = 1 | M, S) = \log \frac {q (M , S | C = 1) q (C = 1)}{\sum_ {c = 0 , 1} q (M , S | C = c) q (C = c)} \\ = - \log (1 + \frac {N}{k} \frac {p (M) p (S)}{p (M , S)}) \\ \leq - \log (\frac {N}{k}) + \log \frac {p (M , S)}{p (M) p (S)}. \tag {3} \\ \end{array} +$$ + +With Eq. (3), we can get a lower bound on $I(M; S)$ as: + +$$ +\begin{array}{l} I (M; S) = \mathbb {E} _ {(M, S) \sim p (M, S)} \log \frac {p (M , S)}{p (M) p (S)} \tag {4} \\ \geq \log (\frac {N}{k}) + \mathbb {E} _ {q (M, S | C = 1)} \log q (C = 1 | M, S). \\ \end{array} +$$ + +Thus maximizing $\mathbb{E}_{q(M,S|C = 1)}\log q(C = 1|M,S)$ is to maximize the lower bound on $I(M;S)$ . However, the true distribution $q(C = 1|M,S)$ cannot be calculated directly. A classification model $h:\{M,S\} \to [0,1]$ is fitted to approximate this distribution. The log-likelihood of the sampled tuples with model $h$ is defined as: + +$$ +\begin{array}{l} \mathcal {I} (h) = k \mathbb {E} _ {q (M, S \mid C = 1)} [ \log h (M, S) ] \\ + N \mathbb {E} _ {q (M, S | C = 0)} [ \log (1 - h (M, S)) ]. \tag {5} \\ \end{array} +$$ + +This likelihood is maximized to make $h$ a good approximation to $q(C = 1|M,S)$ . Thus, we can get the optimal $h^{*}(M,S) = q(C = 1|M,S)$ . Because that both $\log h(M,S)$ and $\log (1 - h(M,S))$ are non-positive for any $h$ , we can rewrite Eq. (4) according to Eq. (5): + +$$ +\begin{array}{l} I (M; S) \geq \log (\frac {N}{k}) + \mathbb {E} _ {q (M, S | C = 1)} [ \log h ^ {*} (M, S) ] \\ \geq \log \left(\frac {N}{k}\right) + k \mathbb {E} _ {q (M, S | C = 1)} \left[ \log h ^ {*} (M, S) \right] \\ + N \mathbb {E} _ {q (M, S | C = 0)} [ \log (1 - h ^ {*} (M, S)) ] \\ = \log \left(\frac {N}{k}\right) + \max _ {h} \mathcal {I} (h) \geq \log \left(\frac {N}{k}\right) + \mathcal {I} (h) \tag {6} \\ \end{array} +$$ + +Thus we can optimize $I(M; S)$ indirectly by maximizing this lower bound $\log \left( \frac{N}{k} \right) + \mathcal{I}(h)$ . Inspired by [9], we + +![](images/c59c3d9b95ea3ea896a8e908fc281333ab1a2b06c73cef18f537b7df8a11df0c.jpg) +Figure 2. An overview of the proposed AMID. There are three different models, $M$ , $S$ and $A$ , in AMID for the full modality, target modality and auxiliary modality, respectively. AMID distills multimodal information to the target modality by maximizing the lower bound on $I(M;S)$ and minimizing $H(M|S)$ , and prevents the shout-cut solution by maximizing the lower bound on $I(M;A)$ . MI optimization is a contrastive-based approach, and conditional entropy minimization is an adversarial learning-based approach that contains two discriminators with different inputs. + +choose $h$ as: + +$$ +h \left(M _ {i}, S _ {u}\right) = \frac {\exp \left(\Phi \left(M _ {i} , S _ {u}\right) / \tau\right)}{\sum_ {j = 1} ^ {N + k} \exp \left(\Phi \left(M _ {i} , S _ {j}\right) / \tau\right)}, \tag {7} +$$ + +where $\Phi$ is a cosine similarity function, $\tau$ is a temperature adjusting the correlation of different pairs. Substitute Eq. (7) into Eq. (6), optimizing $I(M;S)$ is equivalent to minimizing the following loss: + +$$ +\begin{array}{l} \mathcal {L} _ {M I _ {s}} = - \frac {1}{N + k} \sum_ {i = 1} ^ {N + k} \left(\sum_ {j = 0} ^ {k - 1} \log h \left(M _ {i}, S _ {i} ^ {\eta_ {j}}\right) \right. \tag {8} \\ \left. + \sum_ {l = 1} ^ {N} \log \left(1 - h (M _ {i}, S _ {i} ^ {\xi_ {l}})\right)\right). \\ \end{array} +$$ + +Similarly, we can optimize the $I(M; A)$ by minimizing the following loss: + +$$ +\begin{array}{l} \mathcal {L} _ {M I _ {a}} = - \frac {1}{N + k} \sum_ {i = 1} ^ {N + k} \left(\sum_ {j = 0} ^ {k - 1} \log h \left(M _ {i}, A _ {i} ^ {\eta_ {j}}\right) \right. \tag {9} \\ \left. + \sum_ {l = 1} ^ {N} \log \left(1 - h (M _ {i}, A _ {i} ^ {\xi_ {l}})\right)\right). \\ \end{array} +$$ + +The form of Eq. (8) and Eq. (9) are similar to the CCL loss in [9]. However, our formulation is associated with MI and derives a tighter lower bound on it by taking account into the supervision of the label, which in our experiments is found to be more effective. + +# 3.2. Conditional Entropy Minimization + +Maximizing the lower bound on $I(M; S)$ is insufficient for narrowing the information gap between the teacher and the student as the optimal lower bound does not mean that MI is maximum. This subsection focuses on further transferring knowledge by minimizing the conditional entropy of the teacher given the student $H(M|S)$ . + +The posterior $p(M|S)$ is difficult to calculate, thus we define a new distribution $q(M|S)$ to approximate it. Then $H(M|S)$ can be calculated as in [8]: + +$$ +\begin{array}{l} H (M | S) = - \mathbb {E} _ {S \sim p (S)} \left[ \mathbb {E} _ {M ^ {\prime} \sim p (M | S)} \left[ \log p \left(M ^ {\prime} | S\right) \right] \right] \\ = - \mathbb {E} _ {S \sim p (S)} [ \mathbb {E} _ {M ^ {\prime} \sim p (M | S)} [ \log q (M ^ {\prime} | S) ] \\ \left. - D _ {K L} \left(p (M | S) | | q (M | S)\right) \right] \\ \leq - \mathbb {E} _ {S \sim p (S)} \left[ \mathbb {E} _ {M ^ {\prime} \sim p (M | S)} [ \log q (M ^ {\prime} | S) ] \right]. \tag {10} \\ \end{array} +$$ + +Thus we can minimize $H(M|S)$ by maximizing the negative of its upper bound. We achieve this by introducing an adversarial learning-based approach, and using it to maximize $\mathbb{E}_{S\sim p(S)}\left[\mathbb{E}_{M^{\prime}\sim p(M|S)}[\log q(M^{\prime}|S)]\right]$ w.r.t. the parameters of the student network during the generation and minimize $\mathbb{E}_{S\sim p(S)}[\mathbb{E}_{M^{\prime}\sim p(M|S)}[\log q(M^{\prime}|S)] - \log p(M|S)]$ w.r.t. the parameters of the discriminators. In other words, we use the discriminator $D(\cdot)$ to recognize whether features come from multimodal distribution or not and feedback informative gradient to the student model through minimizing: + +$$ +\mathcal {L} _ {a d v} = - \mathbb {E} _ {S \sim p (S)} \left[ \mathbb {E} _ {M ^ {\prime} \sim p (M | S)} [ \log D (S) ] \right]. \tag {11} +$$ + +Minimizing Eq. (11) w.r.t. the parameters of the target modality student enables the student to imitate representations coming from the multimodal distribution. It is worth noting that optimizing $H(M|S)$ through Eq. (11) does not affect the learning of the teacher since no gradient back propagates to the teacher. + +Nevertheless, for the samples of the same class, it is more challenging to transfer the multimodal information by adversarial learning. This is because the generated target modality representation tends to mimic that of multimodality in the same instance with the constraint of MI, easier but can not capture the correlation among samples with the supervision of the label. As a result, we introduce two discriminators to learn more informative target modal representations. One discriminator called fundamental discriminator $(D_{1})$ is designed to distinguish the target modality and full modality representations from the entire training data. The other discriminator, which is called enhanced dis + +criminator $(D_{2})$ , is designed to further distinguish the two kinds of representations coming from the classes with more than one sample in a batch since we think paying attention to these representations can help the student further aggregate representations in the same class. Thus, minimizing Eq. (11) w.r.t. the parameters of the student becomes minimizing: + +$$ +\mathcal {L} _ {a d v} = - \frac {\lambda_ {1}}{N + k} \sum_ {i = 1} ^ {N + k} \log D _ {1} \left(S _ {i} ^ {\eta_ {0}}\right) - \frac {\lambda_ {2}}{d} \sum_ {v = 1} ^ {w} \log D _ {2} \left(S _ {v} ^ {\eta_ {1}}\right). \tag {12} +$$ + +And the parameters of discriminators are trained by minimizing: + +$$ +\begin{array}{l} \mathcal {L} _ {D} = - \frac {\lambda_ {1}}{N + k} \sum_ {i = 1} ^ {N + k} \left(\log D _ {1} \left(M _ {i}\right) + \log \left(1 - D _ {1} \left(S _ {i} ^ {\eta_ {0}}\right)\right)\right) \tag {13} \\ - \frac {\lambda_ {2}}{d} \sum_ {v = 1} ^ {w} \left(\log D _ {2} \left(M _ {v}\right) + \log \left(1 - D _ {2} \left(S _ {v} ^ {\eta_ {1}}\right)\right)\right), \\ \end{array} +$$ + +where $\{M_v\}_{v=1}^w$ is a set where every element comes from the classes with more than one samples and $\{S_v^{\eta_1}\}_{v=1}^w$ is its corresponding set of target modal representations. $d$ is used for more stabilized training and we set it by the frequency of the data with samples of the same classes. $\lambda_1$ and $\lambda_2$ are weighting parameters for $D_1$ and $D_2$ respectively, and $\lambda_1 + \lambda_2 = 1$ . To further improve the efficiency of the transfer, we adjust $\lambda_1$ and $\lambda_2$ adaptively according to the alignment between $S$ and $M$ for each epoch $t$ . More specifically, we use the averaged cosine similarity in the tuples $\Phi(M_i, S_i^{\eta_0})$ and $\Phi(M_v, S_v^{\eta_j}), j \neq 0$ in Eq. (7) to provide meaningful feedback for the cooperation of discriminators. Large cosine similarity indicates that $M$ and $S$ are well aligned, thus the weight of the corresponding discriminator can be relatively small. Moving average [30] is also applied to improve the training stability. The formula of $\lambda$ is given as: + +$$ +\begin{array}{l} \tilde {\lambda} (t + 1) = \beta \tilde {\lambda} (t) + (1 - \beta) (1 - \operatorname {A v g} _ {t} (\Phi (M, S)))) \tag {14} \\ \lambda (t + 1) = \sigma (\tilde {\lambda} (t + 1)), \\ \end{array} +$$ + +where $\sigma (\cdot)$ is the softmax function, $\mathrm{Avg}_t(\cdot)$ represents the average of cosine similarity on epoch $t$ , and $\beta \in (0,1)$ is the smoothing parameter, and we set $\beta = 0.9$ empirically. + +Adversarial learning is known to often generate random images if not constrained [31]. This also occurs when target modality representations are generated without any constraints. Our method implicitly overcomes this problem by maximizing the lower bound on $I(M; S)$ and its advantages come twofold: First, the maximization of the lower bound on MI can not only transfer the multimodal information but also place a constraint on the adversarial distillation. Second, adversarial distillation further reduces the information gap that still exists after maximizing the lower bound on MI. Thus, the maximization of the lower bound on MI and adversarial distillation are complementary to each other in AMID to generate informative and robust representations. + +# 3.3. Overall Loss + +Assuming that after the optimization above, the target modality and full modality representations are already aligned, then we can use two classifiers with shared parameters to perform the classification task for these representations respectively. The overall classification loss is: + +$$ +\mathcal {L} _ {c l s} = \mathcal {L} _ {c e} ^ {S} \left(S _ {i}, y _ {i}\right) + \mathcal {L} _ {c e} ^ {M} \left(M _ {i}, y _ {i}\right), \tag {15} +$$ + +where $\mathcal{L}_{ce}$ is the cross-entropy loss, $y_{i}$ is the ground-truth. Classifiers with the same parameters can also help facilitate the generation of representations from the target modality network to imitate those of multimodality. In addition, the target modality can be aligned with the full modality in the predictive space. We use the Jensen-Shannon divergence (JSD) [27] to optimize the MI between the predictive target modality distribution $(P_S)$ and the multimodality distribution $(P_M)$ : + +$$ +\mathcal {L} _ {J S D} = \frac {1}{N + k} \sum_ {i = 1} ^ {N + k} J S D \left(P _ {S _ {i}} \| P _ {M _ {i}}\right). \tag {16} +$$ + +The final loss function for distilling knowledge from auxiliary modalities is given as: + +$$ +\mathcal {L} = \mathcal {L} _ {c l s} + \mathcal {L} _ {J S D} + \alpha_ {1} \mathcal {L} _ {M I _ {s}} + \alpha_ {2} \mathcal {L} _ {M I _ {a}} + \alpha_ {3} \mathcal {L} _ {a d v}, \tag {17} +$$ + +The whole procedure is shown in the supplementary and the overall model structure is shown in Fig. 2. + +# 4. Experiments + +# 4.1. Datasets + +Video understanding. We experiment on two popular multimodal datasets for video recognition (Top-1 accuracy, %) and kNN video retrieval (R@K, %) [5]. Cross-modal knowledge distillation is performed from the acoustic to the visual modality. + +- UCF51, as a subset of UCF101 [40], includes 6,845 videos with audio belonging to 51 categories. The public split1 is adopted. +- ActivityNet [20] is a large-scale video benchmark of 14,950 videos with audio, covering 200 complex human activities, where the training set has 10,024 videos while 4,926 videos in the validation set. + +Emotion classification. We conduct experiments on IEMOCAP [6], a popular multimodal dataset for 4-class emotion classification, which contains totaling 5531 videos in 5 dyadic conversation sessions. Each video consists of acoustic, textual and visual modalities, and the target model is based on visual modality only. A 5-fold cross-validation is adopted for the evaluation, taking one session as the test + +Table 1. The Top-1 accuracy $(\%)$ of video recognition on UCF51 and ActivityNet. Notice that we change all the activation functions to LeakyReLU to ensure a fair comparison. + +
UCF51ActivityNet
Baseline66.748.8
CRD [42]67.150.4
GMC [36]64.153.1
CRCD [51]69.652.4
CCL [9]68.951.9
AMID (Ours)73.853.6
+ +set for each fold. Following [50], two evaluation metrics, weighted accuracy (WA, %) and unweighted accuracy (UA, %), are adopted. + +# 4.2. Experimental Setup + +Because different modalities such as audio, video and text are heterogeneous, we use individual extractors for each modality, then the features are concatenated and passed through a 2-layer MLP as the full modality teacher. The teacher shares the same extractors as that of the student and the auxiliary model for reducing the number of parameters. Video recognition and retrieval. Following [9], we use a 1D-CNN14 [26] pre-trained on AudioSet [17] as the audio extractor and use R(2+1)D-18 [43] as the student video network. The two discriminators are 5-layer MLP and 3-layer MLP respectively. Besides, we change all activation functions to Leaky ReLU for adversarial learning because it gives better training stability compared to the ReLU. The dimension of the representations is set to 512. The batch size and temperature $\tau$ are set to 16 and 0.5, respectively. $\alpha_{1},\alpha_{2},\alpha_{3}$ are set to 4, 1.6, 1. More details are shown in the supplementary. + +Emotion classification. We extract raw acoustic, textual and visual embeddings by the pre-trained wav2vec 2.0 [3], BERT [12] and DenseNet [24] respectively. RNN is adopted as the student network with a final feature dimension of 768. The batch size and temperature $\tau$ are set to 128 and 0.6, respectively. + +A warm-up stage is employed for all experiments. At the first $T_{start}$ epochs, the student model and the teacher model are trained by minimizing $\mathcal{L} = \mathcal{L}_{cls} + \mathcal{L}_{JSD}$ to alleviate the converge difficulties of adversarial learning. This helps a preliminary alignment between the teacher and student and can also prevent discriminators from recognizing readily at the beginning of the training. $T_{start}$ is set to 20 for the video understanding tasks and 5 for the emotion classification task. And notice that without special mention, the leveraged pre-trained auxiliary modality extractors are fixed since the generated representations already contain rich auxiliary information. + +Table 2. $\mathrm{R@K(K = 1,5)}$ of video retrieval on UCF51 and ActivityNet. + +
UCF51ActivityNet
MetricR1R5R1R5
Baseline64.071.941.563.9
CRD [42]66.072.343.665.5
GMC [36]61.871.046.167.7
CRCD [51]68.275.245.767.0
CCL [9]67.071.746.264.8
AMID (Ours)73.677.146.467.2
+ +![](images/7a7046e504d9b6090543ab57af3f5c169844a7dd761a9c19bfbbed8901d7f2eb.jpg) +Figure 3. The per-class Top-1 accuracy $(\%)$ of video recognition on UCF51 comparing AMD with CCL. + +# 4.3. Comparison with State-of-the-arts + +Video recognition. We compare AMD with two types of SOTA cross-modal KD methods, i.e. intra-sample methods including CRD [42], GMC [36], and inter-sample methods including CCL [9], CRCD [51]. The results are summarized in Tab. 1. Here "Baseline" represents the model directly trained with the visual modality only, representing a lower bound for the tasks. It can be seen that AMD significantly outperforms all the compared methods, suggesting that it is more effective and consistent in learning information from auxiliary modalities. AMD outperforms the second-best method by $4.2\%$ and $0.5\%$ on the two datasets, respectively. + +To further investigate the breakdown of performance, we compare AMD with CCL on UCF51 and give the results of class-wise Top-1 accuracy in Fig. 3. It can be seen that AMD achieves better performance than CCL for most of the classes, although for a few of them it is comparable to or slightly worse than CCL. The classes where AMD is of inferior performance are mainly those audio events that are not or weakly correlated with the videos, such as 'FrisbeeCatch' and 'SkyDiving'. In these classes, the auxiliary modal information is less helpful. Thus, AMD, which is proposed for better cross-modal knowledge distillation, is not very effective for these classes. + +Video retrieval. Tab. 2 presents the results of video retrieval on the UCF51 and ActivityNet datasets, which is a + +Table 3. Performance comparison under different setups on IEMOCAP, where A-V, L-V, AL-V mean distillation from acoustic to visual, textual to visual, and acoustic and textual to visual. + +
SetupMethodWAUA
VBaseline51.250.8
A-VGMC [36]51.750.9
CRCD [51]51.850.2
CCL [9]51.551.4
AMID (Ours)52.551.7
L-VGMC [36]50.950.5
CRCD [51]50.249.9
CCL [9]52.751.8
AMID (Ours)53.052.4
AL-VGMC [36]51.950.5
CRCD [51]52.049.4
CCL [9]53.251.4
AMID (Ours)53.852.7
+ +more fine-grained task to evaluate the discriminability of video representations. The results show that AMD consistently outperforms almost all competing approaches in terms of R@1 and R@5. + +Emotion classification. Tab. 3 compares AMID with three state-of-the-art methods, CCL, CRCD and GMC, for emotion classification. We conduct experiences on IEMOCAP, a three-modality dataset, to further evaluate the performance of AMID in different auxiliary modalities. It is worth noting that the "Baseline" model is trained directly with only the visual modality. The results demonstrate that AMID outperforms the Baseline model for all setups, where the UA metrics increase by $0.9\%$ , $1.6\%$ and $1.9\%$ respectively, while the other three methods are not always effective. Besides, AMID outperforms CCL, CRCD and GMC on almost all the setups. + +# 4.4. Ablation Study + +# 4.4.1 Effectiveness of MI and conditional entropy + +In order to verify the effectiveness of our proposed method for capturing as much multimodal information as possible, the impact of using different training configurations on UCF51 is studied in Tab. 4. Here "student alone" represents the result of a model trained with the visual modality only and "teacher alone" represents that of the teacher model with the full modalities. These two cases show the initial performance of the student and the teacher without distillation, respectively. When optimizing $\mathcal{L}_{MI_s}$ alone for the distillation, although the student model can achieve performance gains, from $66.7\%$ to $69.8\%$ , it degrades the teacher's performance, from $74.3\%$ to $71.2\%$ and thereby reducing the upper bound of the student's performance. Alternatively, more informative multimodal representations can be obtained by maximizing the lower bound on $I(M;A)$ and + +Table 4. Ablation study for the proposed loss functions. + +
ConfigurationTop-1 accuracy
StudentTeacher
student alone (w/o distillation)66.7\
teacher alone (w/o distillation)\74.3
\( \mathcal{L}_{MI_s} \)69.871.2
\( \mathcal{L}_{MI_s} + \mathcal{L}_{MI_a} \)72.776.0
\( \mathcal{L}_{MI_s} + \mathcal{L}_{MI_a} + \mathcal{L}_{adv} \) (AMID)73.875.7
AMID with \( \mathcal{L}_{nce} \)72.374.3
+ +![](images/6fd9862a33181428be842a112be361395d263169daf3df3a80a9eea94bd2745c.jpg) +Figure 4. The accuracy gap between the teacher and student in using $\mathcal{L}_{MI_s} + \mathcal{L}_{MI_a}$ and AMD loss. + +$I(M;S)$ simultaneously $(\mathcal{L}_{MI_s} + \mathcal{L}_{MI_a})$ , since a better teacher can improve the distillation performance. Tab. 4 shows that this improves the accuracy of the student from $66.7\%$ to $72.7\%$ and also improves that of the teacher from $74.3\%$ to $76.0\%$ . Besides, adding $\mathcal{L}_{adv}$ (i.e., AMD) to $\mathcal{L}_{MI_s} + \mathcal{L}_{MI_a}$ does improve the performance from $72.7\%$ to $73.8\%$ , and the performance gap of AMD is smaller than $\mathcal{L}_{MI_s} + \mathcal{L}_{MI_a}$ , which indicates that AMD achieves better alignment between the teacher and the student due to the further constraint on the gap by minimizing $H(M|S)$ without degrading the teacher's performance obviously (the teacher's performance decreases from $76.0\%$ to $75.7\%$ ). + +To further understand the effectiveness of the conditional entropy minimization approach in reducing the information gap between the teacher and the student, we explore the gap of AMID and $\mathcal{L}_{MI_s} + \mathcal{L}_{MI_a}$ during training. This information gap is represented by the gap of accuracy between the teacher and student on the validation set over the training epochs. The results are shown in Fig. 4. It can be seen that the accuracy gap of using AMID loss is consistently smaller than that of $\mathcal{L}_{MI_s} + \mathcal{L}_{MI_a}$ , which validates the proposed adversarial learning-based approach indeed helps to narrow down the information gap. + +AMID is also compared to an ablative setup using the contrastive loss $\mathcal{L}_{nce}$ [9] to verify the effectiveness of the proposed loss function in maximizing the lower bound on MI. The result in Tab. 4 shows that AMD performs much better than the baseline "AMID with $\mathcal{L}_{nce}$ ", improving the accuracy by $1.5\%$ . This validates that our proposed ap + +Table 5. Effectiveness of proposed training modifications. + +
ModificationTop-1 accuracy
AMID73.8
with fixed teacher66.0
w/o warm-up65.8
w/o D272.8
w/o dynamic weight72.7
+ +![](images/5026e5b7f1e7b8f4eae9aed027438887d55a114365c22471ab23d64206c59c3b.jpg) +Figure 5. (Left) The cosine similarity between the teacher's and student's representations only in the same class during training. (Right) The cosine similarity during testing. + +![](images/1dafd05386d9476d0fef9309f58c49a39f69d1eff5f72bc445d629ef57c832de.jpg) + +proach, which takes into account the correlation of samples within a class, achieves better optimization for MI. + +# 4.4.2 Effectiveness of training modifications + +To evaluate the effect of each modification applied in AMD, we conduct a set of experiments on UCF51 and give the results in Tab. 5. As mentioned before, using a fixed pre-trained teacher to guide the student's learning leads to an undesired gap between the teacher and the student at the beginning of training, which is unfavorable for distillation. The result affirms this, where the performance of AMD degrades from $73.8\%$ to $66.0\%$ without joint training. In addition, it also shows that without employing the warm-up setup described before, the recognition performance degrades by $8.0\%$ . The reason may be that the target modality and multimodality representations are noisy and uncorrelated at the start of the training, which results in that the discriminators can recognize them readily and thus affecting the feedback of the informative gradient of adversarial learning. + +We also study the effectiveness of the two discriminators of our proposed AMD by comparing AMD with two ablative cases: w/o $D_{2}$ and w/o dynamic weight. One constraint is removed at a time. The results of these ablation studies are shown in Tab. 5. The accuracy decreases by $1.0\%$ when only the fundamental discriminator $D_{1}$ is used, suggesting that the enhanced discriminator $D_{2}$ indeed helps to distill the multimodal information of samples of the same class. Moreover, it also demonstrates that using uniform weight leads to a performance drop, indicating the effectiveness of the proposed dynamic weighting scheme. + +To further investigate the effectiveness of the proposed adversarial learning-based approach in transferring the + +Table 6. Top-1 accuracy (%) on UCF51 with different hyperparameters. + +
α1value3.73.83.94.04.14.2
accuracy72.673.773.773.873.873.4
α2value1.31.41.51.61.71.8
accuracy71.273.773.873.873.672.4
α3value0.70.80.91.01.11.2
accuracy73.373.473.773.873.473.1
+ +inter-sample multimodal information, we compare AMID with two cases: w/o $D_{2}$ and w/o $\mathcal{L}_{adv}$ . Fig. 5 displays the average of cosine similarity between the teacher and the student only in the same class, i.e. the average of all $\Phi (M_v,S_v^{\eta_j}), j\neq 0$ in Eq. (7). We can see that the cosine similarity of AMID is consistently larger than that of the other two cases and the cosine similarity of w/o $D_{2}$ is larger than that of w/o $\mathcal{L}_{adv}$ , meaning that the proposed approach indeed helps the student to learn more compact representations for each class. + +# 4.5. Hyperparameters Analysis + +Sensitivity analysis studies are conducted for the hyperparameters, $\alpha_{1}$ , $\alpha_{2}$ and $\alpha_{3}$ , referenced in the loss function Eq. (17). Similar to the previous study, we experiment on UCF51 and show the results in Tab. 6. The other two hyperparameters are kept the same when one changes. We test different values for $\alpha_{1}$ from 3.7 to 4.2, $\alpha_{2}$ from 1.3 to 4.8 and $\alpha_{3}$ from 0.7 to 1.2, all with an increment of 0.1. The results show that the hyperparameters $\alpha_{1}$ , $\alpha_{2}$ and $\alpha_{3}$ are not sensitive within a certain range. In general, $\alpha_{1}$ between 3.8 to 4.1 and $\alpha_{2}$ between 1.4 to 1.7 works well, and we set $\alpha_{3} = 1.0$ for all other experiments. + +# 5. Conclusion + +In this paper, we propose a generic cross-modal distillation method, AMID, to enhance the target modality representations. The proposed approach simultaneously maximizes the lower bounds on MI between the teacher and the student as well as between the teacher and an auxiliary model while minimizing the conditional entropy of the teacher given the student. For optimizing the lower bound on MI, we derive a new form and solve it by a contrastive learning-based approach. For minimizing the conditional entropy, an adversarial learning-based approach is used. Our extensive experimental evaluation demonstrates the effectiveness of AMID on three popular datasets. + +# Acknowledgement + +This work is supported by the National Key R&D Program of China (No. 2022ZD0160702), STCSM (No. 2251 1106101, No. 18DZ2270700, No. 21DZ1100100, No. 215 11101100), 111 plan (No. BP0719010), and State Key Laboratory of UHD Video and Audio Production and Presentation. + +# References + +[1] Sarah A. Abdu, Ahmed H. Yousef, and Ashraf Salem. Multimodal video sentiment analysis using deep learning approaches, a survey. Information Fusion, pages 204-226, 2021. 1 +[2] Alexander A. Alemi, Ian Fischer, Joshua V. Dillon, and Kevin Murphy. Deep variational information bottleneck. 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Temporal segment networks: Towards good practices for deep action recognition. In Proceedings of the European Conference on Computer Vision, ECCV, pages 20-36, 2016. 1 +[45] Chen Xu, Quan Li, Junfeng Ge, Jinyang Gao, Xiaoyong Yang, Changhua Pei, Fei Sun, Jian Wu, Hanxiao Sun, and Wenwu Ou. Privileged features distillation at taobao recommendations. In Conference on Knowledge Discovery and Data Mining, KDD, pages 2590-2598, 2020. 1 +[46] Chen Xu, Quan Li, Junfeng Ge, Jinyang Gao, Xiaoyong Yang, Changhua Pei, Fei Sun, Jian Wu, Hanxiao Sun, and Wenwu Ou. Privileged features distillation at taobao recommendations. In Proceedings of the 26th ACM SIGKDD International Conference on Knowledge Discovery & Data Mining, pages 2590-2598, 2020. 1 +[47] Amir Zadeh, Paul Pu Liang, Soujanya Poria, Erik Cambria, and Louis-Philippe Morency. Multimodal language analysis in the wild: CMU-MOSEI dataset and interpretable dynamic fusion graph. 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In IEEE Conference on Computer Vision and Pattern Recognition, CVPR, pages 9260-9269, 2021. 2, 6, 7 \ No newline at end of file diff --git a/2023/Enhanced Multimodal Representation Learning With Cross-Modal KD/images.zip b/2023/Enhanced Multimodal Representation Learning With Cross-Modal KD/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..afe1539df33a35c51441febf72836b666b509e01 --- /dev/null +++ b/2023/Enhanced Multimodal Representation Learning With Cross-Modal KD/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:920b9589ada26493c136f960080033e8bc74963a9fe338c8b9e5307d37495250 +size 530422 diff --git a/2023/Enhanced Multimodal Representation Learning With Cross-Modal KD/layout.json b/2023/Enhanced Multimodal Representation Learning With Cross-Modal KD/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..73460a92dcaa11dcf31197219c61b48bc1a76c47 --- /dev/null +++ b/2023/Enhanced Multimodal Representation Learning With Cross-Modal KD/layout.json @@ -0,0 +1,10816 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 79, + 103, + 514, + 120 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 79, + 103, + 514, + 120 + ], + "spans": [ + { + "bbox": [ + 79, + 103, + 514, + 120 + ], + "type": "text", + "content": "Enhanced Multimodal Representation Learning with Cross-modal KD" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 157, + 148, + 436, + 165 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 157, + 148, + 436, + 165 + ], + "spans": [ + { + "bbox": [ + 157, + 148, + 436, + 165 + ], + "type": "text", + "content": "Mengxi Chen" + }, + { + "bbox": [ + 157, + 148, + 436, + 165 + ], + "type": "inline_equation", + "content": "^{1}" + }, + { + "bbox": [ + 157, + 148, + 436, + 165 + ], + "type": "text", + "content": ", Linyu Xing" + }, + { + "bbox": [ + 157, + 148, + 436, + 165 + ], + "type": "inline_equation", + "content": "^{1}" + }, + { + "bbox": [ + 157, + 148, + 436, + 165 + ], + "type": "text", + "content": ", Yu Wang" + }, + { + "bbox": [ + 157, + 148, + 436, + 165 + ], + "type": "inline_equation", + "content": "^{1,2\\boxtimes}" + }, + { + "bbox": [ + 157, + 148, + 436, + 165 + ], + "type": "text", + "content": ", Ya Zhang" + }, + { + "bbox": [ + 157, + 148, + 436, + 165 + ], + "type": "inline_equation", + "content": "^{1,2\\boxtimes}" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 157, + 165, + 436, + 179 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 157, + 165, + 436, + 179 + ], + "spans": [ + { + "bbox": [ + 157, + 165, + 436, + 179 + ], + "type": "inline_equation", + "content": "^{1}" + }, + { + "bbox": [ + 157, + 165, + 436, + 179 + ], + "type": "text", + "content": "Shanghai Jiao Tong University, " + }, + { + "bbox": [ + 157, + 165, + 436, + 179 + ], + "type": "inline_equation", + "content": "^{2}" + }, + { + "bbox": [ + 157, + 165, + 436, + 179 + ], + "type": "text", + "content": "Shanghai AI Laboratory" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 160, + 180, + 430, + 193 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 160, + 180, + 430, + 193 + ], + "spans": [ + { + "bbox": [ + 160, + 180, + 430, + 193 + ], + "type": "text", + "content": "{mxchen_mc,xly8991,yuwanhsjtu,ya_zhang}@sjtu.edu.cn" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 143, + 220, + 191, + 232 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 220, + 191, + 232 + ], + "spans": [ + { + "bbox": [ + 143, + 220, + 191, + 232 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 247, + 290, + 498 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 247, + 290, + 498 + ], + "spans": [ + { + "bbox": [ + 46, + 247, + 290, + 498 + ], + "type": "text", + "content": "This paper explores the tasks of leveraging auxiliary modalities which are only available at training to enhance multimodal representation learning through cross-modal Knowledge Distillation (KD). The widely adopted mutual information maximization-based objective leads to a shortcut solution of the weak teacher, i.e., achieving the maximum mutual information by simply making the teacher model as weak as the student model. To prevent such a weak solution, we introduce an additional objective term, i.e., the mutual information between the teacher and the auxiliary modality model. Besides, to narrow down the information gap between the student and teacher, we further propose to minimize the conditional entropy of the teacher given the student. Novel training schemes based on contrastive learning and adversarial learning are designed to optimize the mutual information and the conditional entropy, respectively. Experimental results on three popular multimodal benchmark datasets have shown that the proposed method outperforms a range of state-of-the-art approaches for video recognition, video retrieval and emotion classification." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 525, + 127, + 537 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 525, + 127, + 537 + ], + "spans": [ + { + "bbox": [ + 47, + 525, + 127, + 537 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 545, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 545, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 545, + 287, + 713 + ], + "type": "text", + "content": "Multimodal learning has shown much promise in a wide spectrum of applications, such as video understanding [20, 39, 44], sentiment analysis [1, 19, 47] and medical image segmentation [7, 49]. It is generally recognized that including more modalities helps the prediction accuracy. For many real-world applications, while one has to make predictions based on limited modalities due to efficiency or cost concerns, it is usually possible to collect additional modalities at training. To enhance the representation learned, several studies have thus considered to leverage such modalities as a form of auxiliary information at training [11, 23, 29, 50]. Several attempts have explored to fill in the auxiliary modalities at test time, by employing approaches such as Generative Adversarial Network" + } + ] + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 315, + 222, + 538, + 308 + ], + "blocks": [ + { + "bbox": [ + 315, + 222, + 538, + 308 + ], + "lines": [ + { + "bbox": [ + 315, + 222, + 538, + 308 + ], + "spans": [ + { + "bbox": [ + 315, + 222, + 538, + 308 + ], + "type": "image", + "image_path": "4fa345fa4a238ee1ec657c402db9192b2ec53df16a324b9a667593c646b1c51c.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 316, + 310, + 537, + 395 + ], + "blocks": [ + { + "bbox": [ + 316, + 310, + 537, + 395 + ], + "lines": [ + { + "bbox": [ + 316, + 310, + 537, + 395 + ], + "spans": [ + { + "bbox": [ + 316, + 310, + 537, + 395 + ], + "type": "image", + "image_path": "236838d44f4acc4a149a4621469e1da40f1a611edf0a578df0d76cb9f127624e.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 405, + 545, + 449 + ], + "lines": [ + { + "bbox": [ + 305, + 405, + 545, + 449 + ], + "spans": [ + { + "bbox": [ + 305, + 405, + 545, + 449 + ], + "type": "text", + "content": "Figure 1. Illustration of the difference between the MI-based method and the proposed AMID method. (a) MI-based methods maximize " + }, + { + "bbox": [ + 305, + 405, + 545, + 449 + ], + "type": "inline_equation", + "content": "I(M;S)" + }, + { + "bbox": [ + 305, + 405, + 545, + 449 + ], + "type": "text", + "content": ". (b) AMID maximizes " + }, + { + "bbox": [ + 305, + 405, + 545, + 449 + ], + "type": "inline_equation", + "content": "I(M;S)" + }, + { + "bbox": [ + 305, + 405, + 545, + 449 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 405, + 545, + 449 + ], + "type": "inline_equation", + "content": "I(M;A)" + }, + { + "bbox": [ + 305, + 405, + 545, + 449 + ], + "type": "text", + "content": ", while minimizing " + }, + { + "bbox": [ + 305, + 405, + 545, + 449 + ], + "type": "inline_equation", + "content": "H(M|S)" + }, + { + "bbox": [ + 305, + 405, + 545, + 449 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 472, + 545, + 496 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 472, + 545, + 496 + ], + "spans": [ + { + "bbox": [ + 305, + 472, + 545, + 496 + ], + "type": "text", + "content": "(GAN) [4, 22]. However, such data generation-based approaches introduce extra computation costs at inference." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 497, + 546, + 665 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 497, + 546, + 665 + ], + "spans": [ + { + "bbox": [ + 304, + 497, + 546, + 665 + ], + "type": "text", + "content": "As an alternative, cross-modal knowledge distillation is proposed, where a teacher model trained with both the target modalities and the auxiliary modalities (denoted as full modalities hereafter), is employed to guide the training of a student model with target modalities only [10, 11, 16, 23, 45, 46]. In such a way, the student model directly learns to embed information about auxiliary modalities and involves no additional computational cost at inference. A typical practice is to pre-train the teacher model from the full modality data, and fix it during the training. While such a setting enables the teacher to provide information-rich representation [23, 46], it may not be favorable for the alignment of the teacher and student, due to the large information gap between them, especially at the early stage of training [32]." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 665, + 547, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 547, + 712 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 547, + 712 + ], + "type": "text", + "content": "To better facilitate the knowledge transfer, online KD is proposed to jointly train the teacher and the student. One common solution is to maximize the mutual information (MI) between the teacher and the student in a shared" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 495, + 35 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 495, + 35 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 495, + 35 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "11766" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 156 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 156 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 156 + ], + "type": "text", + "content": "space [42]. However, such an objective only focuses on maximizing the shared knowledge, in terms of percentage, from the teacher to the student, which is necessary but not sufficient to guarantee a complete knowledge transfer. As illustrated in Fig. 1(a), a short-cut solution is to simply make the teacher model capture less information, i.e., shrinking the entropy of the teacher." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 157, + 288, + 395 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 157, + 288, + 395 + ], + "spans": [ + { + "bbox": [ + 46, + 157, + 288, + 395 + ], + "type": "text", + "content": "Under the framework online KD, this paper explores to simultaneously achieve: 1) maintaining the representation capacity of the full modality teacher as much as possible, and 2) narrowing down the information gap between the teacher and the student. As Fig. 1(b) shows, in addition to maximizing the MI between the teacher and the student, maximizing the MI between the teacher and an additional auxiliary model may contribute to the former goal, while minimizing the conditional entropy of the teacher given the student may benefit the latter goal. We thus propose a new objective function consisting of all the above three terms. To achieve the optimization of the MI, we further derive a new form of its lower bound by taking into account the supervision of the label, and propose a contrastive learning-based approach to implement it. To minimize the conditional entropy, an adversarial learning-based approach is introduced, where additional discriminators are used to distinguish representations between the teacher and the student. We name the proposed method Adversarial Mutual Information Distillation (AMID) hereafter." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 396, + 287, + 503 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 396, + 287, + 503 + ], + "spans": [ + { + "bbox": [ + 46, + 396, + 287, + 503 + ], + "type": "text", + "content": "To validate the effectiveness of AMID, extensive experiments on three popular multimodal tasks including video recognition, video retrieval and emotion classification tasks are conducted. The performance of these tasks are conducted on UCF51 [40], ActivityNet [20] and IEMOCAP [6] benchmark datasets, respectively. The results show that AMID outperforms a range of state-of-the-art approaches on all three tasks. To summarize, the main contribution of this paper is threefold:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 59, + 511, + 286, + 670 + ], + "type": "list", + "angle": 0, + "index": 6, + "blocks": [ + { + "bbox": [ + 59, + 511, + 286, + 559 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 511, + 286, + 559 + ], + "spans": [ + { + "bbox": [ + 59, + 511, + 286, + 559 + ], + "type": "text", + "content": "- We propose a novel cross-modal KD method, Adversarial Mutual Information Distillation (AMID), to prevent the teacher from losing information by maximizing the MI between it and an auxiliary modality model." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 59, + 567, + 286, + 613 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 567, + 286, + 613 + ], + "spans": [ + { + "bbox": [ + 59, + 567, + 286, + 613 + ], + "type": "text", + "content": "- AMID maximally transfers information from the teacher to the student by optimizing the MI between them and minimizing the conditional entropy of the teacher given the student." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 59, + 622, + 286, + 670 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 622, + 286, + 670 + ], + "spans": [ + { + "bbox": [ + 59, + 622, + 286, + 670 + ], + "type": "text", + "content": "- To implement the joint optimization of the three objective terms, a novel training approach that leverages the combined advantage of both contrastive learning and adversarial learning is proposed." + } + ] + } + ], + "index": 5 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 47, + 681, + 134, + 693 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 681, + 134, + 693 + ], + "spans": [ + { + "bbox": [ + 47, + 681, + 134, + 693 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 59, + 701, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 701, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 59, + 701, + 286, + 713 + ], + "type": "text", + "content": "Knowledge Distillation. Knowledge distillation (KD) is" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 72, + 545, + 384 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 384 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 384 + ], + "type": "text", + "content": "first proposed in [21], where soft labels in predictive space produced by the teacher through temperature hyperparameter transfer the dark knowledge to the student. Later, many works studied and demonstrated the benefits of distilling knowledge in the latent space [25, 35, 38, 48]. There have been some works that explore KD-based methods for cross-modal representation learning. CMC [41] aligns different views of the same samples by contrastive learning to extract shared information. CRD [42] leverages instance-level contrastive objectives to perform KD. GMC [36] learns geometrically aligned representations by aligning modality-specific representations with that of the corresponding complete observation. However, these methods can not transfer the correlation among instances, which are also valuable in many tasks. To transfer the inter-sample relation, [9] propose CCL to close the cross-modal semantic gap between the multimodality teacher and the student by contrasting different modal embeddings in the same classes in a common latent space. CRCD [51] distills the information of the teacher space by maximizing two complementary MI criteria. In contrast to these recent KD works which only consider the alignment between the teacher and student but neglect the objectives' impact on the teacher, we proposed a new KD objective that helps the teacher capture as much auxiliary information as possible and constraints the alignment simultaneously." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 387, + 545, + 613 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 387, + 545, + 613 + ], + "spans": [ + { + "bbox": [ + 304, + 387, + 545, + 613 + ], + "type": "text", + "content": "Mutual Information Maximization. MI is first introduced to deep learning in [2], and since then, many methods have proposed to combine variational bounds with parameterized neural networks to enable differentiable and tractable estimation of MI in high-dimensional spaces [15, 34]. The character that MI can be used to represent the relationship between two variables is well-suited for correlated multimodal data. [19] hierarchically optimizes MI in unimodal pairs and between multimodal and unimodal representations for maintaining useful information while filtering noise in unimodal input. [28] proposed TupleInfoNCE to optimize MI in multimodal input tuples which enables the model to capture both the modal-shared information and the specific information. However, these methods rarely consider the correlation among samples with the supervision of the label, which are still useful. In this paper, we derive a new lower bound on MI in teacher-student pairs which takes into account the inter-sample correlation and propose a contrastive-learning method for its maximization." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 618, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 618, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 618, + 545, + 713 + ], + "type": "text", + "content": "Adversarial Learning. Since [18] developed adversarial learning in deep learning, many researchers attempt to improve its performance by stabilizing the training process. In addition to modifying the structure of discriminator or generator [8, 31, 37], several works still considered incorporating multiple discriminators to improve learning [13, 14, 33]. Similar to [13], in this paper, we design two additional discriminators and adjust their weights adaptively." + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "11767" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 71, + 103, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 71, + 103, + 83 + ], + "spans": [ + { + "bbox": [ + 47, + 71, + 103, + 83 + ], + "type": "text", + "content": "3. Method" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 91, + 287, + 210 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 91, + 287, + 210 + ], + "spans": [ + { + "bbox": [ + 46, + 91, + 287, + 210 + ], + "type": "text", + "content": "Suppose we have a multimodal dataset with " + }, + { + "bbox": [ + 46, + 91, + 287, + 210 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 46, + 91, + 287, + 210 + ], + "type": "text", + "content": " modalities, consisting of " + }, + { + "bbox": [ + 46, + 91, + 287, + 210 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 91, + 287, + 210 + ], + "type": "text", + "content": " target modalities " + }, + { + "bbox": [ + 46, + 91, + 287, + 210 + ], + "type": "inline_equation", + "content": "\\{x_1, \\dots, x_k\\}" + }, + { + "bbox": [ + 46, + 91, + 287, + 210 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 91, + 287, + 210 + ], + "type": "inline_equation", + "content": "n - k" + }, + { + "bbox": [ + 46, + 91, + 287, + 210 + ], + "type": "text", + "content": " auxiliary modalities " + }, + { + "bbox": [ + 46, + 91, + 287, + 210 + ], + "type": "inline_equation", + "content": "\\{x_{k + 1}, \\dots, x_n\\}" + }, + { + "bbox": [ + 46, + 91, + 287, + 210 + ], + "type": "text", + "content": ". Denote the model trained with all " + }, + { + "bbox": [ + 46, + 91, + 287, + 210 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 46, + 91, + 287, + 210 + ], + "type": "text", + "content": " modalities, " + }, + { + "bbox": [ + 46, + 91, + 287, + 210 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 91, + 287, + 210 + ], + "type": "text", + "content": " target modalities only, and " + }, + { + "bbox": [ + 46, + 91, + 287, + 210 + ], + "type": "inline_equation", + "content": "n - k" + }, + { + "bbox": [ + 46, + 91, + 287, + 210 + ], + "type": "text", + "content": " auxiliary modalities only as full modality model " + }, + { + "bbox": [ + 46, + 91, + 287, + 210 + ], + "type": "inline_equation", + "content": "M(x_1, \\dots, x_n)" + }, + { + "bbox": [ + 46, + 91, + 287, + 210 + ], + "type": "text", + "content": ", target modality model " + }, + { + "bbox": [ + 46, + 91, + 287, + 210 + ], + "type": "inline_equation", + "content": "S(x_1, \\dots, x_k)" + }, + { + "bbox": [ + 46, + 91, + 287, + 210 + ], + "type": "text", + "content": ", and auxiliary modality model " + }, + { + "bbox": [ + 46, + 91, + 287, + 210 + ], + "type": "inline_equation", + "content": "A(x_{k + 1}, \\dots, x_n)" + }, + { + "bbox": [ + 46, + 91, + 287, + 210 + ], + "type": "text", + "content": ", respectively. This paper aims to transfer knowledge from the full modality model " + }, + { + "bbox": [ + 46, + 91, + 287, + 210 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 46, + 91, + 287, + 210 + ], + "type": "text", + "content": " to the target modality model " + }, + { + "bbox": [ + 46, + 91, + 287, + 210 + ], + "type": "inline_equation", + "content": "S" + }, + { + "bbox": [ + 46, + 91, + 287, + 210 + ], + "type": "text", + "content": " with the assistant of auxiliary modalities at training." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 211, + 288, + 402 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 211, + 288, + 402 + ], + "spans": [ + { + "bbox": [ + 46, + 211, + 288, + 402 + ], + "type": "text", + "content": "A widely adopted objective for cross-modal knowledge transfer is to maximize the MI between the representation of the full modality teacher " + }, + { + "bbox": [ + 46, + 211, + 288, + 402 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 46, + 211, + 288, + 402 + ], + "type": "text", + "content": " and the representation of the target modality student " + }, + { + "bbox": [ + 46, + 211, + 288, + 402 + ], + "type": "inline_equation", + "content": "S" + }, + { + "bbox": [ + 46, + 211, + 288, + 402 + ], + "type": "text", + "content": ", i.e. " + }, + { + "bbox": [ + 46, + 211, + 288, + 402 + ], + "type": "inline_equation", + "content": "I(M; S)" + }, + { + "bbox": [ + 46, + 211, + 288, + 402 + ], + "type": "text", + "content": ". But there exists a shout-cut solution as shown in Fig. 1(a). In order to prevent this problem, we propose AMID, which maximizes the MI between " + }, + { + "bbox": [ + 46, + 211, + 288, + 402 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 46, + 211, + 288, + 402 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 211, + 288, + 402 + ], + "type": "inline_equation", + "content": "A" + }, + { + "bbox": [ + 46, + 211, + 288, + 402 + ], + "type": "text", + "content": ", i.e. " + }, + { + "bbox": [ + 46, + 211, + 288, + 402 + ], + "type": "inline_equation", + "content": "I(M; A)" + }, + { + "bbox": [ + 46, + 211, + 288, + 402 + ], + "type": "text", + "content": ", so as to ensure the full modality model captures information from both target modalities and auxiliary modalities, and maximizes " + }, + { + "bbox": [ + 46, + 211, + 288, + 402 + ], + "type": "inline_equation", + "content": "I(M; S)" + }, + { + "bbox": [ + 46, + 211, + 288, + 402 + ], + "type": "text", + "content": " while minimizing the conditional entropy of the teacher given the student " + }, + { + "bbox": [ + 46, + 211, + 288, + 402 + ], + "type": "inline_equation", + "content": "H(M|S)" + }, + { + "bbox": [ + 46, + 211, + 288, + 402 + ], + "type": "text", + "content": ", so as to narrow down the information gap between the teacher and the student. For optimizing the MI, we derive a new form of its lower bound and maximize it through a contrastive learning-based approach. For minimizing " + }, + { + "bbox": [ + 46, + 211, + 288, + 402 + ], + "type": "inline_equation", + "content": "H(M|S)" + }, + { + "bbox": [ + 46, + 211, + 288, + 402 + ], + "type": "text", + "content": ", we introduce an adversarial learning-based approach." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 59, + 402, + 249, + 414 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 402, + 249, + 414 + ], + "spans": [ + { + "bbox": [ + 59, + 402, + 249, + 414 + ], + "type": "text", + "content": "To sum up, the overall objective is to optimize:" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 418, + 287, + 432 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 418, + 287, + 432 + ], + "spans": [ + { + "bbox": [ + 46, + 418, + 287, + 432 + ], + "type": "interline_equation", + "content": "\\mathcal {O} = \\alpha_ {1} \\mathrm {l b} (I (M; S)) + \\alpha_ {2} \\mathrm {l b} (I (M; A)) - \\alpha_ {3} H (M | S), \\tag {1}", + "image_path": "5853e03b04f2bcbe1e600ad70e55f926b95fc75dcaf0dcd7c4132b7ab7b21e94.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 437, + 287, + 461 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 437, + 287, + 461 + ], + "spans": [ + { + "bbox": [ + 46, + 437, + 287, + 461 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 437, + 287, + 461 + ], + "type": "inline_equation", + "content": "\\mathrm{lb}(\\cdot)" + }, + { + "bbox": [ + 46, + 437, + 287, + 461 + ], + "type": "text", + "content": " means the lower bound on MI, " + }, + { + "bbox": [ + 46, + 437, + 287, + 461 + ], + "type": "inline_equation", + "content": "\\alpha_{1},\\alpha_{2},\\alpha_{3}" + }, + { + "bbox": [ + 46, + 437, + 287, + 461 + ], + "type": "text", + "content": " are the different weights for the corresponding terms." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 467, + 230, + 479 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 467, + 230, + 479 + ], + "spans": [ + { + "bbox": [ + 47, + 467, + 230, + 479 + ], + "type": "text", + "content": "3.1. Mutual Information Optimization" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 485, + 287, + 604 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 485, + 287, + 604 + ], + "spans": [ + { + "bbox": [ + 46, + 485, + 287, + 604 + ], + "type": "text", + "content": "In this section, we will focus on how to optimize " + }, + { + "bbox": [ + 46, + 485, + 287, + 604 + ], + "type": "inline_equation", + "content": "I(M;S)" + }, + { + "bbox": [ + 46, + 485, + 287, + 604 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 485, + 287, + 604 + ], + "type": "inline_equation", + "content": "I(M;A)" + }, + { + "bbox": [ + 46, + 485, + 287, + 604 + ], + "type": "text", + "content": " through maximizing their lower bounds for capturing as much information as possible. Unlike [42] which only considers the correlation between the teacher's representation and that of the student in the same sample, we derive a new form of lower bound on MI by taking into account the correlation of samples within a class. Notice that as the deduction procedures for " + }, + { + "bbox": [ + 46, + 485, + 287, + 604 + ], + "type": "inline_equation", + "content": "I(M;S)" + }, + { + "bbox": [ + 46, + 485, + 287, + 604 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 485, + 287, + 604 + ], + "type": "inline_equation", + "content": "I(M;A)" + }, + { + "bbox": [ + 46, + 485, + 287, + 604 + ], + "type": "text", + "content": " are the same, we will construct an approximate loss for optimizing " + }, + { + "bbox": [ + 46, + 485, + 287, + 604 + ], + "type": "inline_equation", + "content": "I(M;S)" + }, + { + "bbox": [ + 46, + 485, + 287, + 604 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 605, + 287, + 652 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 605, + 287, + 652 + ], + "spans": [ + { + "bbox": [ + 46, + 605, + 287, + 652 + ], + "type": "text", + "content": "Firstly, we define a distribution " + }, + { + "bbox": [ + 46, + 605, + 287, + 652 + ], + "type": "inline_equation", + "content": "q" + }, + { + "bbox": [ + 46, + 605, + 287, + 652 + ], + "type": "text", + "content": " which models the joint distribution of " + }, + { + "bbox": [ + 46, + 605, + 287, + 652 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 46, + 605, + 287, + 652 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 605, + 287, + 652 + ], + "type": "inline_equation", + "content": "S" + }, + { + "bbox": [ + 46, + 605, + 287, + 652 + ], + "type": "text", + "content": ". A latent variable, " + }, + { + "bbox": [ + 46, + 605, + 287, + 652 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 46, + 605, + 287, + 652 + ], + "type": "text", + "content": ", is used to indicate whether a tuple " + }, + { + "bbox": [ + 46, + 605, + 287, + 652 + ], + "type": "inline_equation", + "content": "(M, S)" + }, + { + "bbox": [ + 46, + 605, + 287, + 652 + ], + "type": "text", + "content": " comes from the same class " + }, + { + "bbox": [ + 46, + 605, + 287, + 652 + ], + "type": "inline_equation", + "content": "(C = 1)" + }, + { + "bbox": [ + 46, + 605, + 287, + 652 + ], + "type": "text", + "content": " or not " + }, + { + "bbox": [ + 46, + 605, + 287, + 652 + ], + "type": "inline_equation", + "content": "(C = 0)" + }, + { + "bbox": [ + 46, + 605, + 287, + 652 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 105, + 657, + 286, + 685 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 105, + 657, + 286, + 685 + ], + "spans": [ + { + "bbox": [ + 105, + 657, + 286, + 685 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} q (M, S | C = 1) = p (M, S); \\\\ q (M, S \\mid C = 0) = p (M) p (S). \\tag {2} \\\\ \\end{array}", + "image_path": "9e88f0564e3b26234cf232c9670021b64c0ed608ef5e2f7f170dec2b19dea5bf.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 689, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 689, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 689, + 287, + 713 + ], + "type": "text", + "content": "We sample " + }, + { + "bbox": [ + 46, + 689, + 287, + 713 + ], + "type": "inline_equation", + "content": "(M, S)" + }, + { + "bbox": [ + 46, + 689, + 287, + 713 + ], + "type": "text", + "content": " by considering the relationship between full modality and target modality representations in the" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "text", + "content": "same classes, which is more effective for transferring information. The pair " + }, + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "inline_equation", + "content": "(M, S)" + }, + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "text", + "content": " is from the joint distribution when " + }, + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "inline_equation", + "content": "M, S" + }, + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "text", + "content": " are in the same class or from the product of the marginal distributions when " + }, + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "inline_equation", + "content": "M, S" + }, + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "text", + "content": " are in different classes." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 121, + 545, + 243 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 121, + 545, + 243 + ], + "spans": [ + { + "bbox": [ + 304, + 121, + 545, + 243 + ], + "type": "text", + "content": "Suppose in a mini-batch, given a specific " + }, + { + "bbox": [ + 304, + 121, + 545, + 243 + ], + "type": "inline_equation", + "content": "M_{i}" + }, + { + "bbox": [ + 304, + 121, + 545, + 243 + ], + "type": "text", + "content": ", there are " + }, + { + "bbox": [ + 304, + 121, + 545, + 243 + ], + "type": "inline_equation", + "content": "k - 1" + }, + { + "bbox": [ + 304, + 121, + 545, + 243 + ], + "type": "text", + "content": " positive pairs " + }, + { + "bbox": [ + 304, + 121, + 545, + 243 + ], + "type": "inline_equation", + "content": "(M_{i}, S_{i}^{\\eta_{j}})" + }, + { + "bbox": [ + 304, + 121, + 545, + 243 + ], + "type": "text", + "content": " drawn from the joint distribution, where " + }, + { + "bbox": [ + 304, + 121, + 545, + 243 + ], + "type": "inline_equation", + "content": "\\{\\eta_{j}\\}_{j = 1}^{k - 1}" + }, + { + "bbox": [ + 304, + 121, + 545, + 243 + ], + "type": "text", + "content": " is an index set and every element indicates the position of other " + }, + { + "bbox": [ + 304, + 121, + 545, + 243 + ], + "type": "inline_equation", + "content": "S" + }, + { + "bbox": [ + 304, + 121, + 545, + 243 + ], + "type": "text", + "content": " with the same class as " + }, + { + "bbox": [ + 304, + 121, + 545, + 243 + ], + "type": "inline_equation", + "content": "M_{i}" + }, + { + "bbox": [ + 304, + 121, + 545, + 243 + ], + "type": "text", + "content": ", 1 positive pair " + }, + { + "bbox": [ + 304, + 121, + 545, + 243 + ], + "type": "inline_equation", + "content": "(M_{i}, S_{i}^{\\eta_{0}})" + }, + { + "bbox": [ + 304, + 121, + 545, + 243 + ], + "type": "text", + "content": " from the same sample, and " + }, + { + "bbox": [ + 304, + 121, + 545, + 243 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 304, + 121, + 545, + 243 + ], + "type": "text", + "content": " negative pairs " + }, + { + "bbox": [ + 304, + 121, + 545, + 243 + ], + "type": "inline_equation", + "content": "(M_{i}, S_{i}^{\\xi_{l}})" + }, + { + "bbox": [ + 304, + 121, + 545, + 243 + ], + "type": "text", + "content": " from the product of marginals, where " + }, + { + "bbox": [ + 304, + 121, + 545, + 243 + ], + "type": "inline_equation", + "content": "\\{S_{i}^{\\xi_{l}}\\}_{l = 1}^{N}" + }, + { + "bbox": [ + 304, + 121, + 545, + 243 + ], + "type": "text", + "content": " are " + }, + { + "bbox": [ + 304, + 121, + 545, + 243 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 304, + 121, + 545, + 243 + ], + "type": "text", + "content": " target modality representations from different classes than " + }, + { + "bbox": [ + 304, + 121, + 545, + 243 + ], + "type": "inline_equation", + "content": "M_{i}" + }, + { + "bbox": [ + 304, + 121, + 545, + 243 + ], + "type": "text", + "content": ". Then the priors of " + }, + { + "bbox": [ + 304, + 121, + 545, + 243 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 304, + 121, + 545, + 243 + ], + "type": "text", + "content": " can be calculated as " + }, + { + "bbox": [ + 304, + 121, + 545, + 243 + ], + "type": "inline_equation", + "content": "q(C = 1) = \\frac{k}{N + k}" + }, + { + "bbox": [ + 304, + 121, + 545, + 243 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 121, + 545, + 243 + ], + "type": "inline_equation", + "content": "q(C = 0) = \\frac{N}{N + k}" + }, + { + "bbox": [ + 304, + 121, + 545, + 243 + ], + "type": "text", + "content": ". Using Bayes' rule, the logarithmic posterior for " + }, + { + "bbox": [ + 304, + 121, + 545, + 243 + ], + "type": "inline_equation", + "content": "C = 1" + }, + { + "bbox": [ + 304, + 121, + 545, + 243 + ], + "type": "text", + "content": " is given by:" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 249, + 545, + 332 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 249, + 545, + 332 + ], + "spans": [ + { + "bbox": [ + 306, + 249, + 545, + 332 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\log q (C = 1 | M, S) = \\log \\frac {q (M , S | C = 1) q (C = 1)}{\\sum_ {c = 0 , 1} q (M , S | C = c) q (C = c)} \\\\ = - \\log (1 + \\frac {N}{k} \\frac {p (M) p (S)}{p (M , S)}) \\\\ \\leq - \\log (\\frac {N}{k}) + \\log \\frac {p (M , S)}{p (M) p (S)}. \\tag {3} \\\\ \\end{array}", + "image_path": "b372bc10a70d42c12e1056df06d04a4bc1dfdc1726e010c2791672c065b4718b.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 318, + 338, + 541, + 351 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 318, + 338, + 541, + 351 + ], + "spans": [ + { + "bbox": [ + 318, + 338, + 541, + 351 + ], + "type": "text", + "content": "With Eq. (3), we can get a lower bound on " + }, + { + "bbox": [ + 318, + 338, + 541, + 351 + ], + "type": "inline_equation", + "content": "I(M; S)" + }, + { + "bbox": [ + 318, + 338, + 541, + 351 + ], + "type": "text", + "content": " as:" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 331, + 357, + 545, + 408 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 331, + 357, + 545, + 408 + ], + "spans": [ + { + "bbox": [ + 331, + 357, + 545, + 408 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} I (M; S) = \\mathbb {E} _ {(M, S) \\sim p (M, S)} \\log \\frac {p (M , S)}{p (M) p (S)} \\tag {4} \\\\ \\geq \\log (\\frac {N}{k}) + \\mathbb {E} _ {q (M, S | C = 1)} \\log q (C = 1 | M, S). \\\\ \\end{array}", + "image_path": "fb0cb8afa9a44affaf3cec9043a1d3fead98260ea44db81ed9e4692704d9825d.jpg" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 414, + 545, + 486 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 414, + 545, + 486 + ], + "spans": [ + { + "bbox": [ + 304, + 414, + 545, + 486 + ], + "type": "text", + "content": "Thus maximizing " + }, + { + "bbox": [ + 304, + 414, + 545, + 486 + ], + "type": "inline_equation", + "content": "\\mathbb{E}_{q(M,S|C = 1)}\\log q(C = 1|M,S)" + }, + { + "bbox": [ + 304, + 414, + 545, + 486 + ], + "type": "text", + "content": " is to maximize the lower bound on " + }, + { + "bbox": [ + 304, + 414, + 545, + 486 + ], + "type": "inline_equation", + "content": "I(M;S)" + }, + { + "bbox": [ + 304, + 414, + 545, + 486 + ], + "type": "text", + "content": ". However, the true distribution " + }, + { + "bbox": [ + 304, + 414, + 545, + 486 + ], + "type": "inline_equation", + "content": "q(C = 1|M,S)" + }, + { + "bbox": [ + 304, + 414, + 545, + 486 + ], + "type": "text", + "content": " cannot be calculated directly. A classification model " + }, + { + "bbox": [ + 304, + 414, + 545, + 486 + ], + "type": "inline_equation", + "content": "h:\\{M,S\\} \\to [0,1]" + }, + { + "bbox": [ + 304, + 414, + 545, + 486 + ], + "type": "text", + "content": " is fitted to approximate this distribution. The log-likelihood of the sampled tuples with model " + }, + { + "bbox": [ + 304, + 414, + 545, + 486 + ], + "type": "inline_equation", + "content": "h" + }, + { + "bbox": [ + 304, + 414, + 545, + 486 + ], + "type": "text", + "content": " is defined as:" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 322, + 493, + 545, + 522 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 322, + 493, + 545, + 522 + ], + "spans": [ + { + "bbox": [ + 322, + 493, + 545, + 522 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\mathcal {I} (h) = k \\mathbb {E} _ {q (M, S \\mid C = 1)} [ \\log h (M, S) ] \\\\ + N \\mathbb {E} _ {q (M, S | C = 0)} [ \\log (1 - h (M, S)) ]. \\tag {5} \\\\ \\end{array}", + "image_path": "03270a78cb4afadec68914f453995d5fb70438dcb326b7658e19305de38bc627.jpg" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 528, + 545, + 589 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 528, + 545, + 589 + ], + "spans": [ + { + "bbox": [ + 304, + 528, + 545, + 589 + ], + "type": "text", + "content": "This likelihood is maximized to make " + }, + { + "bbox": [ + 304, + 528, + 545, + 589 + ], + "type": "inline_equation", + "content": "h" + }, + { + "bbox": [ + 304, + 528, + 545, + 589 + ], + "type": "text", + "content": " a good approximation to " + }, + { + "bbox": [ + 304, + 528, + 545, + 589 + ], + "type": "inline_equation", + "content": "q(C = 1|M,S)" + }, + { + "bbox": [ + 304, + 528, + 545, + 589 + ], + "type": "text", + "content": ". Thus, we can get the optimal " + }, + { + "bbox": [ + 304, + 528, + 545, + 589 + ], + "type": "inline_equation", + "content": "h^{*}(M,S) = q(C = 1|M,S)" + }, + { + "bbox": [ + 304, + 528, + 545, + 589 + ], + "type": "text", + "content": ". Because that both " + }, + { + "bbox": [ + 304, + 528, + 545, + 589 + ], + "type": "inline_equation", + "content": "\\log h(M,S)" + }, + { + "bbox": [ + 304, + 528, + 545, + 589 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 528, + 545, + 589 + ], + "type": "inline_equation", + "content": "\\log (1 - h(M,S))" + }, + { + "bbox": [ + 304, + 528, + 545, + 589 + ], + "type": "text", + "content": " are non-positive for any " + }, + { + "bbox": [ + 304, + 528, + 545, + 589 + ], + "type": "inline_equation", + "content": "h" + }, + { + "bbox": [ + 304, + 528, + 545, + 589 + ], + "type": "text", + "content": ", we can rewrite Eq. (4) according to Eq. (5):" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 314, + 595, + 545, + 682 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 314, + 595, + 545, + 682 + ], + "spans": [ + { + "bbox": [ + 314, + 595, + 545, + 682 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} I (M; S) \\geq \\log (\\frac {N}{k}) + \\mathbb {E} _ {q (M, S | C = 1)} [ \\log h ^ {*} (M, S) ] \\\\ \\geq \\log \\left(\\frac {N}{k}\\right) + k \\mathbb {E} _ {q (M, S | C = 1)} \\left[ \\log h ^ {*} (M, S) \\right] \\\\ + N \\mathbb {E} _ {q (M, S | C = 0)} [ \\log (1 - h ^ {*} (M, S)) ] \\\\ = \\log \\left(\\frac {N}{k}\\right) + \\max _ {h} \\mathcal {I} (h) \\geq \\log \\left(\\frac {N}{k}\\right) + \\mathcal {I} (h) \\tag {6} \\\\ \\end{array}", + "image_path": "22ab38c677df4e9bed345062af38657db60ad52fc2cb8c3a5e8238c9f66dd546.jpg" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 689, + 545, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 689, + 545, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 689, + 545, + 715 + ], + "type": "text", + "content": "Thus we can optimize " + }, + { + "bbox": [ + 304, + 689, + 545, + 715 + ], + "type": "inline_equation", + "content": "I(M; S)" + }, + { + "bbox": [ + 304, + 689, + 545, + 715 + ], + "type": "text", + "content": " indirectly by maximizing this lower bound " + }, + { + "bbox": [ + 304, + 689, + 545, + 715 + ], + "type": "inline_equation", + "content": "\\log \\left( \\frac{N}{k} \\right) + \\mathcal{I}(h)" + }, + { + "bbox": [ + 304, + 689, + 545, + 715 + ], + "type": "text", + "content": ". Inspired by [9], we" + } + ] + } + ], + "index": 20 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "11768" + } + ] + } + ], + "index": 21 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 60, + 72, + 534, + 161 + ], + "blocks": [ + { + "bbox": [ + 60, + 72, + 534, + 161 + ], + "lines": [ + { + "bbox": [ + 60, + 72, + 534, + 161 + ], + "spans": [ + { + "bbox": [ + 60, + 72, + 534, + 161 + ], + "type": "image", + "image_path": "c59c3d9b95ea3ea896a8e908fc281333ab1a2b06c73cef18f537b7df8a11df0c.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 171, + 547, + 228 + ], + "lines": [ + { + "bbox": [ + 46, + 171, + 547, + 228 + ], + "spans": [ + { + "bbox": [ + 46, + 171, + 547, + 228 + ], + "type": "text", + "content": "Figure 2. An overview of the proposed AMID. There are three different models, " + }, + { + "bbox": [ + 46, + 171, + 547, + 228 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 46, + 171, + 547, + 228 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 171, + 547, + 228 + ], + "type": "inline_equation", + "content": "S" + }, + { + "bbox": [ + 46, + 171, + 547, + 228 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 171, + 547, + 228 + ], + "type": "inline_equation", + "content": "A" + }, + { + "bbox": [ + 46, + 171, + 547, + 228 + ], + "type": "text", + "content": ", in AMID for the full modality, target modality and auxiliary modality, respectively. AMID distills multimodal information to the target modality by maximizing the lower bound on " + }, + { + "bbox": [ + 46, + 171, + 547, + 228 + ], + "type": "inline_equation", + "content": "I(M;S)" + }, + { + "bbox": [ + 46, + 171, + 547, + 228 + ], + "type": "text", + "content": " and minimizing " + }, + { + "bbox": [ + 46, + 171, + 547, + 228 + ], + "type": "inline_equation", + "content": "H(M|S)" + }, + { + "bbox": [ + 46, + 171, + 547, + 228 + ], + "type": "text", + "content": ", and prevents the shout-cut solution by maximizing the lower bound on " + }, + { + "bbox": [ + 46, + 171, + 547, + 228 + ], + "type": "inline_equation", + "content": "I(M;A)" + }, + { + "bbox": [ + 46, + 171, + 547, + 228 + ], + "type": "text", + "content": ". MI optimization is a contrastive-based approach, and conditional entropy minimization is an adversarial learning-based approach that contains two discriminators with different inputs." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 247, + 100, + 258 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 247, + 100, + 258 + ], + "spans": [ + { + "bbox": [ + 47, + 247, + 100, + 258 + ], + "type": "text", + "content": "choose " + }, + { + "bbox": [ + 47, + 247, + 100, + 258 + ], + "type": "inline_equation", + "content": "h" + }, + { + "bbox": [ + 47, + 247, + 100, + 258 + ], + "type": "text", + "content": " as:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 80, + 265, + 287, + 297 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 80, + 265, + 287, + 297 + ], + "spans": [ + { + "bbox": [ + 80, + 265, + 287, + 297 + ], + "type": "interline_equation", + "content": "h \\left(M _ {i}, S _ {u}\\right) = \\frac {\\exp \\left(\\Phi \\left(M _ {i} , S _ {u}\\right) / \\tau\\right)}{\\sum_ {j = 1} ^ {N + k} \\exp \\left(\\Phi \\left(M _ {i} , S _ {j}\\right) / \\tau\\right)}, \\tag {7}", + "image_path": "7baf6403b35b41c02852523c04c6e60e128174ae767b7b88f104076c022d215d.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 304, + 288, + 352 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 304, + 288, + 352 + ], + "spans": [ + { + "bbox": [ + 46, + 304, + 288, + 352 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 304, + 288, + 352 + ], + "type": "inline_equation", + "content": "\\Phi" + }, + { + "bbox": [ + 46, + 304, + 288, + 352 + ], + "type": "text", + "content": " is a cosine similarity function, " + }, + { + "bbox": [ + 46, + 304, + 288, + 352 + ], + "type": "inline_equation", + "content": "\\tau" + }, + { + "bbox": [ + 46, + 304, + 288, + 352 + ], + "type": "text", + "content": " is a temperature adjusting the correlation of different pairs. Substitute Eq. (7) into Eq. (6), optimizing " + }, + { + "bbox": [ + 46, + 304, + 288, + 352 + ], + "type": "inline_equation", + "content": "I(M;S)" + }, + { + "bbox": [ + 46, + 304, + 288, + 352 + ], + "type": "text", + "content": " is equivalent to minimizing the following loss:" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 74, + 360, + 287, + 434 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 74, + 360, + 287, + 434 + ], + "spans": [ + { + "bbox": [ + 74, + 360, + 287, + 434 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\mathcal {L} _ {M I _ {s}} = - \\frac {1}{N + k} \\sum_ {i = 1} ^ {N + k} \\left(\\sum_ {j = 0} ^ {k - 1} \\log h \\left(M _ {i}, S _ {i} ^ {\\eta_ {j}}\\right) \\right. \\tag {8} \\\\ \\left. + \\sum_ {l = 1} ^ {N} \\log \\left(1 - h (M _ {i}, S _ {i} ^ {\\xi_ {l}})\\right)\\right). \\\\ \\end{array}", + "image_path": "4ac9f54fa3864754e5f20b31a6eccb34848e4c9250c8127b690f0e2920d1055a.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 441, + 287, + 466 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 441, + 287, + 466 + ], + "spans": [ + { + "bbox": [ + 46, + 441, + 287, + 466 + ], + "type": "text", + "content": "Similarly, we can optimize the " + }, + { + "bbox": [ + 46, + 441, + 287, + 466 + ], + "type": "inline_equation", + "content": "I(M; A)" + }, + { + "bbox": [ + 46, + 441, + 287, + 466 + ], + "type": "text", + "content": " by minimizing the following loss:" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 74, + 474, + 287, + 548 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 74, + 474, + 287, + 548 + ], + "spans": [ + { + "bbox": [ + 74, + 474, + 287, + 548 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\mathcal {L} _ {M I _ {a}} = - \\frac {1}{N + k} \\sum_ {i = 1} ^ {N + k} \\left(\\sum_ {j = 0} ^ {k - 1} \\log h \\left(M _ {i}, A _ {i} ^ {\\eta_ {j}}\\right) \\right. \\tag {9} \\\\ \\left. + \\sum_ {l = 1} ^ {N} \\log \\left(1 - h (M _ {i}, A _ {i} ^ {\\xi_ {l}})\\right)\\right). \\\\ \\end{array}", + "image_path": "5836bc79784df309182908329559c26a9f4dcf2562a25705302dbb9b9c363909.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 555, + 287, + 616 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 555, + 287, + 616 + ], + "spans": [ + { + "bbox": [ + 46, + 555, + 287, + 616 + ], + "type": "text", + "content": "The form of Eq. (8) and Eq. (9) are similar to the CCL loss in [9]. However, our formulation is associated with MI and derives a tighter lower bound on it by taking account into the supervision of the label, which in our experiments is found to be more effective." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 623, + 234, + 636 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 623, + 234, + 636 + ], + "spans": [ + { + "bbox": [ + 47, + 623, + 234, + 636 + ], + "type": "text", + "content": "3.2. Conditional Entropy Minimization" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 641, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 641, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 641, + 288, + 715 + ], + "type": "text", + "content": "Maximizing the lower bound on " + }, + { + "bbox": [ + 46, + 641, + 288, + 715 + ], + "type": "inline_equation", + "content": "I(M; S)" + }, + { + "bbox": [ + 46, + 641, + 288, + 715 + ], + "type": "text", + "content": " is insufficient for narrowing the information gap between the teacher and the student as the optimal lower bound does not mean that MI is maximum. This subsection focuses on further transferring knowledge by minimizing the conditional entropy of the teacher given the student " + }, + { + "bbox": [ + 46, + 641, + 288, + 715 + ], + "type": "inline_equation", + "content": "H(M|S)" + }, + { + "bbox": [ + 46, + 641, + 288, + 715 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 247, + 546, + 284 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 247, + 546, + 284 + ], + "spans": [ + { + "bbox": [ + 305, + 247, + 546, + 284 + ], + "type": "text", + "content": "The posterior " + }, + { + "bbox": [ + 305, + 247, + 546, + 284 + ], + "type": "inline_equation", + "content": "p(M|S)" + }, + { + "bbox": [ + 305, + 247, + 546, + 284 + ], + "type": "text", + "content": " is difficult to calculate, thus we define a new distribution " + }, + { + "bbox": [ + 305, + 247, + 546, + 284 + ], + "type": "inline_equation", + "content": "q(M|S)" + }, + { + "bbox": [ + 305, + 247, + 546, + 284 + ], + "type": "text", + "content": " to approximate it. Then " + }, + { + "bbox": [ + 305, + 247, + 546, + 284 + ], + "type": "inline_equation", + "content": "H(M|S)" + }, + { + "bbox": [ + 305, + 247, + 546, + 284 + ], + "type": "text", + "content": " can be calculated as in [8]:" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 307, + 289, + 545, + 350 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 307, + 289, + 545, + 350 + ], + "spans": [ + { + "bbox": [ + 307, + 289, + 545, + 350 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} H (M | S) = - \\mathbb {E} _ {S \\sim p (S)} \\left[ \\mathbb {E} _ {M ^ {\\prime} \\sim p (M | S)} \\left[ \\log p \\left(M ^ {\\prime} | S\\right) \\right] \\right] \\\\ = - \\mathbb {E} _ {S \\sim p (S)} [ \\mathbb {E} _ {M ^ {\\prime} \\sim p (M | S)} [ \\log q (M ^ {\\prime} | S) ] \\\\ \\left. - D _ {K L} \\left(p (M | S) | | q (M | S)\\right) \\right] \\\\ \\leq - \\mathbb {E} _ {S \\sim p (S)} \\left[ \\mathbb {E} _ {M ^ {\\prime} \\sim p (M | S)} [ \\log q (M ^ {\\prime} | S) ] \\right]. \\tag {10} \\\\ \\end{array}", + "image_path": "f2b5ca3a18bcb873e780ea4e53ee85e9e357137f81a241601f981a69eb041ee8.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 356, + 546, + 488 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 356, + 546, + 488 + ], + "spans": [ + { + "bbox": [ + 304, + 356, + 546, + 488 + ], + "type": "text", + "content": "Thus we can minimize " + }, + { + "bbox": [ + 304, + 356, + 546, + 488 + ], + "type": "inline_equation", + "content": "H(M|S)" + }, + { + "bbox": [ + 304, + 356, + 546, + 488 + ], + "type": "text", + "content": " by maximizing the negative of its upper bound. We achieve this by introducing an adversarial learning-based approach, and using it to maximize " + }, + { + "bbox": [ + 304, + 356, + 546, + 488 + ], + "type": "inline_equation", + "content": "\\mathbb{E}_{S\\sim p(S)}\\left[\\mathbb{E}_{M^{\\prime}\\sim p(M|S)}[\\log q(M^{\\prime}|S)]\\right]" + }, + { + "bbox": [ + 304, + 356, + 546, + 488 + ], + "type": "text", + "content": " w.r.t. the parameters of the student network during the generation and minimize " + }, + { + "bbox": [ + 304, + 356, + 546, + 488 + ], + "type": "inline_equation", + "content": "\\mathbb{E}_{S\\sim p(S)}[\\mathbb{E}_{M^{\\prime}\\sim p(M|S)}[\\log q(M^{\\prime}|S)] - \\log p(M|S)]" + }, + { + "bbox": [ + 304, + 356, + 546, + 488 + ], + "type": "text", + "content": " w.r.t. the parameters of the discriminators. In other words, we use the discriminator " + }, + { + "bbox": [ + 304, + 356, + 546, + 488 + ], + "type": "inline_equation", + "content": "D(\\cdot)" + }, + { + "bbox": [ + 304, + 356, + 546, + 488 + ], + "type": "text", + "content": " to recognize whether features come from multimodal distribution or not and feedback informative gradient to the student model through minimizing:" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 324, + 492, + 545, + 507 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 324, + 492, + 545, + 507 + ], + "spans": [ + { + "bbox": [ + 324, + 492, + 545, + 507 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {a d v} = - \\mathbb {E} _ {S \\sim p (S)} \\left[ \\mathbb {E} _ {M ^ {\\prime} \\sim p (M | S)} [ \\log D (S) ] \\right]. \\tag {11}", + "image_path": "bf37988e316ab4fb3acae5784271444ed84fe80e3f88b1a1fc2b9ae37eb57f70.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 510, + 545, + 581 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 510, + 545, + 581 + ], + "spans": [ + { + "bbox": [ + 304, + 510, + 545, + 581 + ], + "type": "text", + "content": "Minimizing Eq. (11) w.r.t. the parameters of the target modality student enables the student to imitate representations coming from the multimodal distribution. It is worth noting that optimizing " + }, + { + "bbox": [ + 304, + 510, + 545, + 581 + ], + "type": "inline_equation", + "content": "H(M|S)" + }, + { + "bbox": [ + 304, + 510, + 545, + 581 + ], + "type": "text", + "content": " through Eq. (11) does not affect the learning of the teacher since no gradient back propagates to the teacher." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 581, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 581, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 581, + 546, + 713 + ], + "type": "text", + "content": "Nevertheless, for the samples of the same class, it is more challenging to transfer the multimodal information by adversarial learning. This is because the generated target modality representation tends to mimic that of multimodality in the same instance with the constraint of MI, easier but can not capture the correlation among samples with the supervision of the label. As a result, we introduce two discriminators to learn more informative target modal representations. One discriminator called fundamental discriminator " + }, + { + "bbox": [ + 304, + 581, + 546, + 713 + ], + "type": "inline_equation", + "content": "(D_{1})" + }, + { + "bbox": [ + 304, + 581, + 546, + 713 + ], + "type": "text", + "content": " is designed to distinguish the target modality and full modality representations from the entire training data. The other discriminator, which is called enhanced dis" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "11769" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 150 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 150 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 150 + ], + "type": "text", + "content": "criminator " + }, + { + "bbox": [ + 46, + 72, + 289, + 150 + ], + "type": "inline_equation", + "content": "(D_{2})" + }, + { + "bbox": [ + 46, + 72, + 289, + 150 + ], + "type": "text", + "content": ", is designed to further distinguish the two kinds of representations coming from the classes with more than one sample in a batch since we think paying attention to these representations can help the student further aggregate representations in the same class. Thus, minimizing Eq. (11) w.r.t. the parameters of the student becomes minimizing:" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 53, + 155, + 287, + 184 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 155, + 287, + 184 + ], + "spans": [ + { + "bbox": [ + 53, + 155, + 287, + 184 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {a d v} = - \\frac {\\lambda_ {1}}{N + k} \\sum_ {i = 1} ^ {N + k} \\log D _ {1} \\left(S _ {i} ^ {\\eta_ {0}}\\right) - \\frac {\\lambda_ {2}}{d} \\sum_ {v = 1} ^ {w} \\log D _ {2} \\left(S _ {v} ^ {\\eta_ {1}}\\right). \\tag {12}", + "image_path": "404f05fe9ced658c765d53bb5a7bbe739f714f180ea841cca9832eb9505b3eba.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 186, + 287, + 210 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 186, + 287, + 210 + ], + "spans": [ + { + "bbox": [ + 47, + 186, + 287, + 210 + ], + "type": "text", + "content": "And the parameters of discriminators are trained by minimizing:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 56, + 214, + 287, + 274 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 56, + 214, + 287, + 274 + ], + "spans": [ + { + "bbox": [ + 56, + 214, + 287, + 274 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\mathcal {L} _ {D} = - \\frac {\\lambda_ {1}}{N + k} \\sum_ {i = 1} ^ {N + k} \\left(\\log D _ {1} \\left(M _ {i}\\right) + \\log \\left(1 - D _ {1} \\left(S _ {i} ^ {\\eta_ {0}}\\right)\\right)\\right) \\tag {13} \\\\ - \\frac {\\lambda_ {2}}{d} \\sum_ {v = 1} ^ {w} \\left(\\log D _ {2} \\left(M _ {v}\\right) + \\log \\left(1 - D _ {2} \\left(S _ {v} ^ {\\eta_ {1}}\\right)\\right)\\right), \\\\ \\end{array}", + "image_path": "516dfbcdcfaec39a2ed2e441af3c2aba10a3c9f7389eb1053ace851a51ba0071.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 277, + 289, + 481 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 277, + 289, + 481 + ], + "spans": [ + { + "bbox": [ + 46, + 277, + 289, + 481 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 277, + 289, + 481 + ], + "type": "inline_equation", + "content": "\\{M_v\\}_{v=1}^w" + }, + { + "bbox": [ + 46, + 277, + 289, + 481 + ], + "type": "text", + "content": " is a set where every element comes from the classes with more than one samples and " + }, + { + "bbox": [ + 46, + 277, + 289, + 481 + ], + "type": "inline_equation", + "content": "\\{S_v^{\\eta_1}\\}_{v=1}^w" + }, + { + "bbox": [ + 46, + 277, + 289, + 481 + ], + "type": "text", + "content": " is its corresponding set of target modal representations. " + }, + { + "bbox": [ + 46, + 277, + 289, + 481 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 46, + 277, + 289, + 481 + ], + "type": "text", + "content": " is used for more stabilized training and we set it by the frequency of the data with samples of the same classes. " + }, + { + "bbox": [ + 46, + 277, + 289, + 481 + ], + "type": "inline_equation", + "content": "\\lambda_1" + }, + { + "bbox": [ + 46, + 277, + 289, + 481 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 277, + 289, + 481 + ], + "type": "inline_equation", + "content": "\\lambda_2" + }, + { + "bbox": [ + 46, + 277, + 289, + 481 + ], + "type": "text", + "content": " are weighting parameters for " + }, + { + "bbox": [ + 46, + 277, + 289, + 481 + ], + "type": "inline_equation", + "content": "D_1" + }, + { + "bbox": [ + 46, + 277, + 289, + 481 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 277, + 289, + 481 + ], + "type": "inline_equation", + "content": "D_2" + }, + { + "bbox": [ + 46, + 277, + 289, + 481 + ], + "type": "text", + "content": " respectively, and " + }, + { + "bbox": [ + 46, + 277, + 289, + 481 + ], + "type": "inline_equation", + "content": "\\lambda_1 + \\lambda_2 = 1" + }, + { + "bbox": [ + 46, + 277, + 289, + 481 + ], + "type": "text", + "content": ". To further improve the efficiency of the transfer, we adjust " + }, + { + "bbox": [ + 46, + 277, + 289, + 481 + ], + "type": "inline_equation", + "content": "\\lambda_1" + }, + { + "bbox": [ + 46, + 277, + 289, + 481 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 277, + 289, + 481 + ], + "type": "inline_equation", + "content": "\\lambda_2" + }, + { + "bbox": [ + 46, + 277, + 289, + 481 + ], + "type": "text", + "content": " adaptively according to the alignment between " + }, + { + "bbox": [ + 46, + 277, + 289, + 481 + ], + "type": "inline_equation", + "content": "S" + }, + { + "bbox": [ + 46, + 277, + 289, + 481 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 277, + 289, + 481 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 46, + 277, + 289, + 481 + ], + "type": "text", + "content": " for each epoch " + }, + { + "bbox": [ + 46, + 277, + 289, + 481 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 277, + 289, + 481 + ], + "type": "text", + "content": ". More specifically, we use the averaged cosine similarity in the tuples " + }, + { + "bbox": [ + 46, + 277, + 289, + 481 + ], + "type": "inline_equation", + "content": "\\Phi(M_i, S_i^{\\eta_0})" + }, + { + "bbox": [ + 46, + 277, + 289, + 481 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 277, + 289, + 481 + ], + "type": "inline_equation", + "content": "\\Phi(M_v, S_v^{\\eta_j}), j \\neq 0" + }, + { + "bbox": [ + 46, + 277, + 289, + 481 + ], + "type": "text", + "content": " in Eq. (7) to provide meaningful feedback for the cooperation of discriminators. Large cosine similarity indicates that " + }, + { + "bbox": [ + 46, + 277, + 289, + 481 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 46, + 277, + 289, + 481 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 277, + 289, + 481 + ], + "type": "inline_equation", + "content": "S" + }, + { + "bbox": [ + 46, + 277, + 289, + 481 + ], + "type": "text", + "content": " are well aligned, thus the weight of the corresponding discriminator can be relatively small. Moving average [30] is also applied to improve the training stability. The formula of " + }, + { + "bbox": [ + 46, + 277, + 289, + 481 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 46, + 277, + 289, + 481 + ], + "type": "text", + "content": " is given as:" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 48, + 485, + 287, + 517 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 485, + 287, + 517 + ], + "spans": [ + { + "bbox": [ + 48, + 485, + 287, + 517 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\tilde {\\lambda} (t + 1) = \\beta \\tilde {\\lambda} (t) + (1 - \\beta) (1 - \\operatorname {A v g} _ {t} (\\Phi (M, S)))) \\tag {14} \\\\ \\lambda (t + 1) = \\sigma (\\tilde {\\lambda} (t + 1)), \\\\ \\end{array}", + "image_path": "ff4f106a2918beecc96f120af4fd6b921e181f90d857157daab91b121cec0a55.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 521, + 287, + 558 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 521, + 287, + 558 + ], + "spans": [ + { + "bbox": [ + 46, + 521, + 287, + 558 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 521, + 287, + 558 + ], + "type": "inline_equation", + "content": "\\sigma (\\cdot)" + }, + { + "bbox": [ + 46, + 521, + 287, + 558 + ], + "type": "text", + "content": " is the softmax function, " + }, + { + "bbox": [ + 46, + 521, + 287, + 558 + ], + "type": "inline_equation", + "content": "\\mathrm{Avg}_t(\\cdot)" + }, + { + "bbox": [ + 46, + 521, + 287, + 558 + ], + "type": "text", + "content": " represents the average of cosine similarity on epoch " + }, + { + "bbox": [ + 46, + 521, + 287, + 558 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 521, + 287, + 558 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 46, + 521, + 287, + 558 + ], + "type": "inline_equation", + "content": "\\beta \\in (0,1)" + }, + { + "bbox": [ + 46, + 521, + 287, + 558 + ], + "type": "text", + "content": " is the smoothing parameter, and we set " + }, + { + "bbox": [ + 46, + 521, + 287, + 558 + ], + "type": "inline_equation", + "content": "\\beta = 0.9" + }, + { + "bbox": [ + 46, + 521, + 287, + 558 + ], + "type": "text", + "content": " empirically." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 558, + 289, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 558, + 289, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 558, + 289, + 714 + ], + "type": "text", + "content": "Adversarial learning is known to often generate random images if not constrained [31]. This also occurs when target modality representations are generated without any constraints. Our method implicitly overcomes this problem by maximizing the lower bound on " + }, + { + "bbox": [ + 46, + 558, + 289, + 714 + ], + "type": "inline_equation", + "content": "I(M; S)" + }, + { + "bbox": [ + 46, + 558, + 289, + 714 + ], + "type": "text", + "content": " and its advantages come twofold: First, the maximization of the lower bound on MI can not only transfer the multimodal information but also place a constraint on the adversarial distillation. Second, adversarial distillation further reduces the information gap that still exists after maximizing the lower bound on MI. Thus, the maximization of the lower bound on MI and adversarial distillation are complementary to each other in AMID to generate informative and robust representations." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 72, + 389, + 84 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 72, + 389, + 84 + ], + "spans": [ + { + "bbox": [ + 306, + 72, + 389, + 84 + ], + "type": "text", + "content": "3.3. Overall Loss" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 90, + 546, + 150 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 90, + 546, + 150 + ], + "spans": [ + { + "bbox": [ + 304, + 90, + 546, + 150 + ], + "type": "text", + "content": "Assuming that after the optimization above, the target modality and full modality representations are already aligned, then we can use two classifiers with shared parameters to perform the classification task for these representations respectively. The overall classification loss is:" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 354, + 157, + 546, + 172 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 354, + 157, + 546, + 172 + ], + "spans": [ + { + "bbox": [ + 354, + 157, + 546, + 172 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {c l s} = \\mathcal {L} _ {c e} ^ {S} \\left(S _ {i}, y _ {i}\\right) + \\mathcal {L} _ {c e} ^ {M} \\left(M _ {i}, y _ {i}\\right), \\tag {15}", + "image_path": "8def32892600f59bc83831b3e37a11f0f2efcc1b879865a3603ad15858c9adbb.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 180, + 547, + 289 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 180, + 547, + 289 + ], + "spans": [ + { + "bbox": [ + 304, + 180, + 547, + 289 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 180, + 547, + 289 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{ce}" + }, + { + "bbox": [ + 304, + 180, + 547, + 289 + ], + "type": "text", + "content": " is the cross-entropy loss, " + }, + { + "bbox": [ + 304, + 180, + 547, + 289 + ], + "type": "inline_equation", + "content": "y_{i}" + }, + { + "bbox": [ + 304, + 180, + 547, + 289 + ], + "type": "text", + "content": " is the ground-truth. Classifiers with the same parameters can also help facilitate the generation of representations from the target modality network to imitate those of multimodality. In addition, the target modality can be aligned with the full modality in the predictive space. We use the Jensen-Shannon divergence (JSD) [27] to optimize the MI between the predictive target modality distribution " + }, + { + "bbox": [ + 304, + 180, + 547, + 289 + ], + "type": "inline_equation", + "content": "(P_S)" + }, + { + "bbox": [ + 304, + 180, + 547, + 289 + ], + "type": "text", + "content": " and the multimodality distribution " + }, + { + "bbox": [ + 304, + 180, + 547, + 289 + ], + "type": "inline_equation", + "content": "(P_M)" + }, + { + "bbox": [ + 304, + 180, + 547, + 289 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 344, + 297, + 545, + 329 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 344, + 297, + 545, + 329 + ], + "spans": [ + { + "bbox": [ + 344, + 297, + 545, + 329 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {J S D} = \\frac {1}{N + k} \\sum_ {i = 1} ^ {N + k} J S D \\left(P _ {S _ {i}} \\| P _ {M _ {i}}\\right). \\tag {16}", + "image_path": "a52c0ec4f9cf4d0ee9efd678dc7a613dda65de2752d114f12ca44f7f85c10672.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 337, + 546, + 361 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 337, + 546, + 361 + ], + "spans": [ + { + "bbox": [ + 305, + 337, + 546, + 361 + ], + "type": "text", + "content": "The final loss function for distilling knowledge from auxiliary modalities is given as:" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 310, + 370, + 545, + 384 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 310, + 370, + 545, + 384 + ], + "spans": [ + { + "bbox": [ + 310, + 370, + 545, + 384 + ], + "type": "interline_equation", + "content": "\\mathcal {L} = \\mathcal {L} _ {c l s} + \\mathcal {L} _ {J S D} + \\alpha_ {1} \\mathcal {L} _ {M I _ {s}} + \\alpha_ {2} \\mathcal {L} _ {M I _ {a}} + \\alpha_ {3} \\mathcal {L} _ {a d v}, \\tag {17}", + "image_path": "796328b91b1e31771a285bbd73aec6bee812812d6723c2e4eaf1fadb749193c4.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 391, + 545, + 416 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 391, + 545, + 416 + ], + "spans": [ + { + "bbox": [ + 305, + 391, + 545, + 416 + ], + "type": "text", + "content": "The whole procedure is shown in the supplementary and the overall model structure is shown in Fig. 2." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 306, + 426, + 388, + 439 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 426, + 388, + 439 + ], + "spans": [ + { + "bbox": [ + 306, + 426, + 388, + 439 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 445, + 369, + 456 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 445, + 369, + 456 + ], + "spans": [ + { + "bbox": [ + 306, + 445, + 369, + 456 + ], + "type": "text", + "content": "4.1. Datasets" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 464, + 546, + 524 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 464, + 546, + 524 + ], + "spans": [ + { + "bbox": [ + 304, + 464, + 546, + 524 + ], + "type": "text", + "content": "Video understanding. We experiment on two popular multimodal datasets for video recognition (Top-1 accuracy, %) and kNN video retrieval (R@K, %) [5]. Cross-modal knowledge distillation is performed from the acoustic to the visual modality." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 317, + 530, + 547, + 622 + ], + "type": "list", + "angle": 0, + "index": 21, + "blocks": [ + { + "bbox": [ + 317, + 530, + 545, + 567 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 530, + 545, + 567 + ], + "spans": [ + { + "bbox": [ + 317, + 530, + 545, + 567 + ], + "type": "text", + "content": "- UCF51, as a subset of UCF101 [40], includes 6,845 videos with audio belonging to 51 categories. The public split1 is adopted." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 317, + 574, + 547, + 622 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 574, + 547, + 622 + ], + "spans": [ + { + "bbox": [ + 317, + 574, + 547, + 622 + ], + "type": "text", + "content": "- ActivityNet [20] is a large-scale video benchmark of 14,950 videos with audio, covering 200 complex human activities, where the training set has 10,024 videos while 4,926 videos in the validation set." + } + ] + } + ], + "index": 20 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 304, + 629, + 547, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 629, + 547, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 629, + 547, + 714 + ], + "type": "text", + "content": "Emotion classification. We conduct experiments on IEMOCAP [6], a popular multimodal dataset for 4-class emotion classification, which contains totaling 5531 videos in 5 dyadic conversation sessions. Each video consists of acoustic, textual and visual modalities, and the target model is based on visual modality only. A 5-fold cross-validation is adopted for the evaluation, taking one session as the test" + } + ] + } + ], + "index": 22 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "type": "text", + "content": "11770" + } + ] + } + ], + "index": 23 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 82, + 103, + 250, + 191 + ], + "blocks": [ + { + "bbox": [ + 47, + 70, + 287, + 103 + ], + "lines": [ + { + "bbox": [ + 47, + 70, + 287, + 103 + ], + "spans": [ + { + "bbox": [ + 47, + 70, + 287, + 103 + ], + "type": "text", + "content": "Table 1. The Top-1 accuracy " + }, + { + "bbox": [ + 47, + 70, + 287, + 103 + ], + "type": "inline_equation", + "content": "(\\%)" + }, + { + "bbox": [ + 47, + 70, + 287, + 103 + ], + "type": "text", + "content": " of video recognition on UCF51 and ActivityNet. Notice that we change all the activation functions to LeakyReLU to ensure a fair comparison." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 82, + 103, + 250, + 191 + ], + "lines": [ + { + "bbox": [ + 82, + 103, + 250, + 191 + ], + "spans": [ + { + "bbox": [ + 82, + 103, + 250, + 191 + ], + "type": "table", + "html": "
UCF51ActivityNet
Baseline66.748.8
CRD [42]67.150.4
GMC [36]64.153.1
CRCD [51]69.652.4
CCL [9]68.951.9
AMID (Ours)73.853.6
", + "image_path": "345a7ef73304fb4da28145b23887918a80cbe3c3819b2aa8b23bee24a6d06f7c.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 213, + 287, + 251 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 213, + 287, + 251 + ], + "spans": [ + { + "bbox": [ + 47, + 213, + 287, + 251 + ], + "type": "text", + "content": "set for each fold. Following [50], two evaluation metrics, weighted accuracy (WA, %) and unweighted accuracy (UA, %), are adopted." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 266, + 164, + 280 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 266, + 164, + 280 + ], + "spans": [ + { + "bbox": [ + 47, + 266, + 164, + 280 + ], + "type": "text", + "content": "4.2. Experimental Setup" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 288, + 288, + 491 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 288, + 288, + 491 + ], + "spans": [ + { + "bbox": [ + 46, + 288, + 288, + 491 + ], + "type": "text", + "content": "Because different modalities such as audio, video and text are heterogeneous, we use individual extractors for each modality, then the features are concatenated and passed through a 2-layer MLP as the full modality teacher. The teacher shares the same extractors as that of the student and the auxiliary model for reducing the number of parameters. Video recognition and retrieval. Following [9], we use a 1D-CNN14 [26] pre-trained on AudioSet [17] as the audio extractor and use R(2+1)D-18 [43] as the student video network. The two discriminators are 5-layer MLP and 3-layer MLP respectively. Besides, we change all activation functions to Leaky ReLU for adversarial learning because it gives better training stability compared to the ReLU. The dimension of the representations is set to 512. The batch size and temperature " + }, + { + "bbox": [ + 46, + 288, + 288, + 491 + ], + "type": "inline_equation", + "content": "\\tau" + }, + { + "bbox": [ + 46, + 288, + 288, + 491 + ], + "type": "text", + "content": " are set to 16 and 0.5, respectively. " + }, + { + "bbox": [ + 46, + 288, + 288, + 491 + ], + "type": "inline_equation", + "content": "\\alpha_{1},\\alpha_{2},\\alpha_{3}" + }, + { + "bbox": [ + 46, + 288, + 288, + 491 + ], + "type": "text", + "content": " are set to 4, 1.6, 1. More details are shown in the supplementary." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 495, + 287, + 567 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 495, + 287, + 567 + ], + "spans": [ + { + "bbox": [ + 47, + 495, + 287, + 567 + ], + "type": "text", + "content": "Emotion classification. We extract raw acoustic, textual and visual embeddings by the pre-trained wav2vec 2.0 [3], BERT [12] and DenseNet [24] respectively. RNN is adopted as the student network with a final feature dimension of 768. The batch size and temperature " + }, + { + "bbox": [ + 47, + 495, + 287, + 567 + ], + "type": "inline_equation", + "content": "\\tau" + }, + { + "bbox": [ + 47, + 495, + 287, + 567 + ], + "type": "text", + "content": " are set to 128 and 0.6, respectively." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 570, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 570, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 570, + 288, + 714 + ], + "type": "text", + "content": "A warm-up stage is employed for all experiments. At the first " + }, + { + "bbox": [ + 46, + 570, + 288, + 714 + ], + "type": "inline_equation", + "content": "T_{start}" + }, + { + "bbox": [ + 46, + 570, + 288, + 714 + ], + "type": "text", + "content": " epochs, the student model and the teacher model are trained by minimizing " + }, + { + "bbox": [ + 46, + 570, + 288, + 714 + ], + "type": "inline_equation", + "content": "\\mathcal{L} = \\mathcal{L}_{cls} + \\mathcal{L}_{JSD}" + }, + { + "bbox": [ + 46, + 570, + 288, + 714 + ], + "type": "text", + "content": " to alleviate the converge difficulties of adversarial learning. This helps a preliminary alignment between the teacher and student and can also prevent discriminators from recognizing readily at the beginning of the training. " + }, + { + "bbox": [ + 46, + 570, + 288, + 714 + ], + "type": "inline_equation", + "content": "T_{start}" + }, + { + "bbox": [ + 46, + 570, + 288, + 714 + ], + "type": "text", + "content": " is set to 20 for the video understanding tasks and 5 for the emotion classification task. And notice that without special mention, the leveraged pre-trained auxiliary modality extractors are fixed since the generated representations already contain rich auxiliary information." + } + ] + } + ], + "index": 6 + }, + { + "type": "table", + "bbox": [ + 332, + 92, + 518, + 193 + ], + "blocks": [ + { + "bbox": [ + 305, + 70, + 545, + 92 + ], + "lines": [ + { + "bbox": [ + 305, + 70, + 545, + 92 + ], + "spans": [ + { + "bbox": [ + 305, + 70, + 545, + 92 + ], + "type": "text", + "content": "Table 2. " + }, + { + "bbox": [ + 305, + 70, + 545, + 92 + ], + "type": "inline_equation", + "content": "\\mathrm{R@K(K = 1,5)}" + }, + { + "bbox": [ + 305, + 70, + 545, + 92 + ], + "type": "text", + "content": " of video retrieval on UCF51 and ActivityNet." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 332, + 92, + 518, + 193 + ], + "lines": [ + { + "bbox": [ + 332, + 92, + 518, + 193 + ], + "spans": [ + { + "bbox": [ + 332, + 92, + 518, + 193 + ], + "type": "table", + "html": "
UCF51ActivityNet
MetricR1R5R1R5
Baseline64.071.941.563.9
CRD [42]66.072.343.665.5
GMC [36]61.871.046.167.7
CRCD [51]68.275.245.767.0
CCL [9]67.071.746.264.8
AMID (Ours)73.677.146.467.2
", + "image_path": "d97769e4b595e4e79312e851a7a26a6b0c1ef78183f27d54db084aaacfdb8147.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "table_body" + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 312, + 209, + 539, + 326 + ], + "blocks": [ + { + "bbox": [ + 312, + 209, + 539, + 326 + ], + "lines": [ + { + "bbox": [ + 312, + 209, + 539, + 326 + ], + "spans": [ + { + "bbox": [ + 312, + 209, + 539, + 326 + ], + "type": "image", + "image_path": "7a7046e504d9b6090543ab57af3f5c169844a7dd761a9c19bfbbed8901d7f2eb.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 338, + 545, + 361 + ], + "lines": [ + { + "bbox": [ + 305, + 338, + 545, + 361 + ], + "spans": [ + { + "bbox": [ + 305, + 338, + 545, + 361 + ], + "type": "text", + "content": "Figure 3. The per-class Top-1 accuracy " + }, + { + "bbox": [ + 305, + 338, + 545, + 361 + ], + "type": "inline_equation", + "content": "(\\%)" + }, + { + "bbox": [ + 305, + 338, + 545, + 361 + ], + "type": "text", + "content": " of video recognition on UCF51 comparing AMD with CCL." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 380, + 489, + 392 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 380, + 489, + 392 + ], + "spans": [ + { + "bbox": [ + 306, + 380, + 489, + 392 + ], + "type": "text", + "content": "4.3. Comparison with State-of-the-arts" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 399, + 545, + 543 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 399, + 545, + 543 + ], + "spans": [ + { + "bbox": [ + 304, + 399, + 545, + 543 + ], + "type": "text", + "content": "Video recognition. We compare AMD with two types of SOTA cross-modal KD methods, i.e. intra-sample methods including CRD [42], GMC [36], and inter-sample methods including CCL [9], CRCD [51]. The results are summarized in Tab. 1. Here \"Baseline\" represents the model directly trained with the visual modality only, representing a lower bound for the tasks. It can be seen that AMD significantly outperforms all the compared methods, suggesting that it is more effective and consistent in learning information from auxiliary modalities. AMD outperforms the second-best method by " + }, + { + "bbox": [ + 304, + 399, + 545, + 543 + ], + "type": "inline_equation", + "content": "4.2\\%" + }, + { + "bbox": [ + 304, + 399, + 545, + 543 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 399, + 545, + 543 + ], + "type": "inline_equation", + "content": "0.5\\%" + }, + { + "bbox": [ + 304, + 399, + 545, + 543 + ], + "type": "text", + "content": " on the two datasets, respectively." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 544, + 545, + 687 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 544, + 545, + 687 + ], + "spans": [ + { + "bbox": [ + 304, + 544, + 545, + 687 + ], + "type": "text", + "content": "To further investigate the breakdown of performance, we compare AMD with CCL on UCF51 and give the results of class-wise Top-1 accuracy in Fig. 3. It can be seen that AMD achieves better performance than CCL for most of the classes, although for a few of them it is comparable to or slightly worse than CCL. The classes where AMD is of inferior performance are mainly those audio events that are not or weakly correlated with the videos, such as 'FrisbeeCatch' and 'SkyDiving'. In these classes, the auxiliary modal information is less helpful. Thus, AMD, which is proposed for better cross-modal knowledge distillation, is not very effective for these classes." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "text", + "content": "Video retrieval. Tab. 2 presents the results of video retrieval on the UCF51 and ActivityNet datasets, which is a" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "11771" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 68, + 104, + 264, + 275 + ], + "blocks": [ + { + "bbox": [ + 47, + 71, + 287, + 103 + ], + "lines": [ + { + "bbox": [ + 47, + 71, + 287, + 103 + ], + "spans": [ + { + "bbox": [ + 47, + 71, + 287, + 103 + ], + "type": "text", + "content": "Table 3. Performance comparison under different setups on IEMOCAP, where A-V, L-V, AL-V mean distillation from acoustic to visual, textual to visual, and acoustic and textual to visual." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 68, + 104, + 264, + 275 + ], + "lines": [ + { + "bbox": [ + 68, + 104, + 264, + 275 + ], + "spans": [ + { + "bbox": [ + 68, + 104, + 264, + 275 + ], + "type": "table", + "html": "
SetupMethodWAUA
VBaseline51.250.8
A-VGMC [36]51.750.9
CRCD [51]51.850.2
CCL [9]51.551.4
AMID (Ours)52.551.7
L-VGMC [36]50.950.5
CRCD [51]50.249.9
CCL [9]52.751.8
AMID (Ours)53.052.4
AL-VGMC [36]51.950.5
CRCD [51]52.049.4
CCL [9]53.251.4
AMID (Ours)53.852.7
", + "image_path": "858f5d9a196f4a79e3ea99e3567114c5637d8e3bf52cbc7b24ef3fb6933f0427.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 295, + 287, + 343 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 295, + 287, + 343 + ], + "spans": [ + { + "bbox": [ + 46, + 295, + 287, + 343 + ], + "type": "text", + "content": "more fine-grained task to evaluate the discriminability of video representations. The results show that AMD consistently outperforms almost all competing approaches in terms of R@1 and R@5." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 344, + 288, + 488 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 344, + 288, + 488 + ], + "spans": [ + { + "bbox": [ + 46, + 344, + 288, + 488 + ], + "type": "text", + "content": "Emotion classification. Tab. 3 compares AMID with three state-of-the-art methods, CCL, CRCD and GMC, for emotion classification. We conduct experiences on IEMOCAP, a three-modality dataset, to further evaluate the performance of AMID in different auxiliary modalities. It is worth noting that the \"Baseline\" model is trained directly with only the visual modality. The results demonstrate that AMID outperforms the Baseline model for all setups, where the UA metrics increase by " + }, + { + "bbox": [ + 46, + 344, + 288, + 488 + ], + "type": "inline_equation", + "content": "0.9\\%" + }, + { + "bbox": [ + 46, + 344, + 288, + 488 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 344, + 288, + 488 + ], + "type": "inline_equation", + "content": "1.6\\%" + }, + { + "bbox": [ + 46, + 344, + 288, + 488 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 344, + 288, + 488 + ], + "type": "inline_equation", + "content": "1.9\\%" + }, + { + "bbox": [ + 46, + 344, + 288, + 488 + ], + "type": "text", + "content": " respectively, while the other three methods are not always effective. Besides, AMID outperforms CCL, CRCD and GMC on almost all the setups." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 495, + 141, + 509 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 495, + 141, + 509 + ], + "spans": [ + { + "bbox": [ + 47, + 495, + 141, + 509 + ], + "type": "text", + "content": "4.4. Ablation Study" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 514, + 266, + 528 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 514, + 266, + 528 + ], + "spans": [ + { + "bbox": [ + 47, + 514, + 266, + 528 + ], + "type": "text", + "content": "4.4.1 Effectiveness of MI and conditional entropy" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 533, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 533, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 533, + 288, + 715 + ], + "type": "text", + "content": "In order to verify the effectiveness of our proposed method for capturing as much multimodal information as possible, the impact of using different training configurations on UCF51 is studied in Tab. 4. Here \"student alone\" represents the result of a model trained with the visual modality only and \"teacher alone\" represents that of the teacher model with the full modalities. These two cases show the initial performance of the student and the teacher without distillation, respectively. When optimizing " + }, + { + "bbox": [ + 46, + 533, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{MI_s}" + }, + { + "bbox": [ + 46, + 533, + 288, + 715 + ], + "type": "text", + "content": " alone for the distillation, although the student model can achieve performance gains, from " + }, + { + "bbox": [ + 46, + 533, + 288, + 715 + ], + "type": "inline_equation", + "content": "66.7\\%" + }, + { + "bbox": [ + 46, + 533, + 288, + 715 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 46, + 533, + 288, + 715 + ], + "type": "inline_equation", + "content": "69.8\\%" + }, + { + "bbox": [ + 46, + 533, + 288, + 715 + ], + "type": "text", + "content": ", it degrades the teacher's performance, from " + }, + { + "bbox": [ + 46, + 533, + 288, + 715 + ], + "type": "inline_equation", + "content": "74.3\\%" + }, + { + "bbox": [ + 46, + 533, + 288, + 715 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 46, + 533, + 288, + 715 + ], + "type": "inline_equation", + "content": "71.2\\%" + }, + { + "bbox": [ + 46, + 533, + 288, + 715 + ], + "type": "text", + "content": " and thereby reducing the upper bound of the student's performance. Alternatively, more informative multimodal representations can be obtained by maximizing the lower bound on " + }, + { + "bbox": [ + 46, + 533, + 288, + 715 + ], + "type": "inline_equation", + "content": "I(M;A)" + }, + { + "bbox": [ + 46, + 533, + 288, + 715 + ], + "type": "text", + "content": " and" + } + ] + } + ], + "index": 6 + }, + { + "type": "table", + "bbox": [ + 308, + 81, + 542, + 182 + ], + "blocks": [ + { + "bbox": [ + 323, + 71, + 526, + 81 + ], + "lines": [ + { + "bbox": [ + 323, + 71, + 526, + 81 + ], + "spans": [ + { + "bbox": [ + 323, + 71, + 526, + 81 + ], + "type": "text", + "content": "Table 4. Ablation study for the proposed loss functions." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 308, + 81, + 542, + 182 + ], + "lines": [ + { + "bbox": [ + 308, + 81, + 542, + 182 + ], + "spans": [ + { + "bbox": [ + 308, + 81, + 542, + 182 + ], + "type": "table", + "html": "
ConfigurationTop-1 accuracy
StudentTeacher
student alone (w/o distillation)66.7\\
teacher alone (w/o distillation)\\74.3
\\( \\mathcal{L}_{MI_s} \\)69.871.2
\\( \\mathcal{L}_{MI_s} + \\mathcal{L}_{MI_a} \\)72.776.0
\\( \\mathcal{L}_{MI_s} + \\mathcal{L}_{MI_a} + \\mathcal{L}_{adv} \\) (AMID)73.875.7
AMID with \\( \\mathcal{L}_{nce} \\)72.374.3
", + "image_path": "5968b6fda64fd69d497ba30ec5d378ead74e1f130d163cc8f11078efdcbb9d48.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "table_body" + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 354, + 194, + 499, + 319 + ], + "blocks": [ + { + "bbox": [ + 354, + 194, + 499, + 319 + ], + "lines": [ + { + "bbox": [ + 354, + 194, + 499, + 319 + ], + "spans": [ + { + "bbox": [ + 354, + 194, + 499, + 319 + ], + "type": "image", + "image_path": "6fd9862a33181428be842a112be361395d263169daf3df3a80a9eea94bd2745c.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 321, + 545, + 344 + ], + "lines": [ + { + "bbox": [ + 305, + 321, + 545, + 344 + ], + "spans": [ + { + "bbox": [ + 305, + 321, + 545, + 344 + ], + "type": "text", + "content": "Figure 4. The accuracy gap between the teacher and student in using " + }, + { + "bbox": [ + 305, + 321, + 545, + 344 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{MI_s} + \\mathcal{L}_{MI_a}" + }, + { + "bbox": [ + 305, + 321, + 545, + 344 + ], + "type": "text", + "content": " and AMD loss." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 363, + 545, + 506 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 363, + 545, + 506 + ], + "spans": [ + { + "bbox": [ + 304, + 363, + 545, + 506 + ], + "type": "inline_equation", + "content": "I(M;S)" + }, + { + "bbox": [ + 304, + 363, + 545, + 506 + ], + "type": "text", + "content": " simultaneously " + }, + { + "bbox": [ + 304, + 363, + 545, + 506 + ], + "type": "inline_equation", + "content": "(\\mathcal{L}_{MI_s} + \\mathcal{L}_{MI_a})" + }, + { + "bbox": [ + 304, + 363, + 545, + 506 + ], + "type": "text", + "content": ", since a better teacher can improve the distillation performance. Tab. 4 shows that this improves the accuracy of the student from " + }, + { + "bbox": [ + 304, + 363, + 545, + 506 + ], + "type": "inline_equation", + "content": "66.7\\%" + }, + { + "bbox": [ + 304, + 363, + 545, + 506 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 304, + 363, + 545, + 506 + ], + "type": "inline_equation", + "content": "72.7\\%" + }, + { + "bbox": [ + 304, + 363, + 545, + 506 + ], + "type": "text", + "content": " and also improves that of the teacher from " + }, + { + "bbox": [ + 304, + 363, + 545, + 506 + ], + "type": "inline_equation", + "content": "74.3\\%" + }, + { + "bbox": [ + 304, + 363, + 545, + 506 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 304, + 363, + 545, + 506 + ], + "type": "inline_equation", + "content": "76.0\\%" + }, + { + "bbox": [ + 304, + 363, + 545, + 506 + ], + "type": "text", + "content": ". Besides, adding " + }, + { + "bbox": [ + 304, + 363, + 545, + 506 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{adv}" + }, + { + "bbox": [ + 304, + 363, + 545, + 506 + ], + "type": "text", + "content": " (i.e., AMD) to " + }, + { + "bbox": [ + 304, + 363, + 545, + 506 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{MI_s} + \\mathcal{L}_{MI_a}" + }, + { + "bbox": [ + 304, + 363, + 545, + 506 + ], + "type": "text", + "content": " does improve the performance from " + }, + { + "bbox": [ + 304, + 363, + 545, + 506 + ], + "type": "inline_equation", + "content": "72.7\\%" + }, + { + "bbox": [ + 304, + 363, + 545, + 506 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 304, + 363, + 545, + 506 + ], + "type": "inline_equation", + "content": "73.8\\%" + }, + { + "bbox": [ + 304, + 363, + 545, + 506 + ], + "type": "text", + "content": ", and the performance gap of AMD is smaller than " + }, + { + "bbox": [ + 304, + 363, + 545, + 506 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{MI_s} + \\mathcal{L}_{MI_a}" + }, + { + "bbox": [ + 304, + 363, + 545, + 506 + ], + "type": "text", + "content": ", which indicates that AMD achieves better alignment between the teacher and the student due to the further constraint on the gap by minimizing " + }, + { + "bbox": [ + 304, + 363, + 545, + 506 + ], + "type": "inline_equation", + "content": "H(M|S)" + }, + { + "bbox": [ + 304, + 363, + 545, + 506 + ], + "type": "text", + "content": " without degrading the teacher's performance obviously (the teacher's performance decreases from " + }, + { + "bbox": [ + 304, + 363, + 545, + 506 + ], + "type": "inline_equation", + "content": "76.0\\%" + }, + { + "bbox": [ + 304, + 363, + 545, + 506 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 304, + 363, + 545, + 506 + ], + "type": "inline_equation", + "content": "75.7\\%" + }, + { + "bbox": [ + 304, + 363, + 545, + 506 + ], + "type": "text", + "content": ")." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 508, + 545, + 640 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 508, + 545, + 640 + ], + "spans": [ + { + "bbox": [ + 304, + 508, + 545, + 640 + ], + "type": "text", + "content": "To further understand the effectiveness of the conditional entropy minimization approach in reducing the information gap between the teacher and the student, we explore the gap of AMID and " + }, + { + "bbox": [ + 304, + 508, + 545, + 640 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{MI_s} + \\mathcal{L}_{MI_a}" + }, + { + "bbox": [ + 304, + 508, + 545, + 640 + ], + "type": "text", + "content": " during training. This information gap is represented by the gap of accuracy between the teacher and student on the validation set over the training epochs. The results are shown in Fig. 4. It can be seen that the accuracy gap of using AMID loss is consistently smaller than that of " + }, + { + "bbox": [ + 304, + 508, + 545, + 640 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{MI_s} + \\mathcal{L}_{MI_a}" + }, + { + "bbox": [ + 304, + 508, + 545, + 640 + ], + "type": "text", + "content": ", which validates the proposed adversarial learning-based approach indeed helps to narrow down the information gap." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 641, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 641, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 641, + 545, + 714 + ], + "type": "text", + "content": "AMID is also compared to an ablative setup using the contrastive loss " + }, + { + "bbox": [ + 304, + 641, + 545, + 714 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{nce}" + }, + { + "bbox": [ + 304, + 641, + 545, + 714 + ], + "type": "text", + "content": " [9] to verify the effectiveness of the proposed loss function in maximizing the lower bound on MI. The result in Tab. 4 shows that AMD performs much better than the baseline \"AMID with " + }, + { + "bbox": [ + 304, + 641, + 545, + 714 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{nce}" + }, + { + "bbox": [ + 304, + 641, + 545, + 714 + ], + "type": "text", + "content": "\", improving the accuracy by " + }, + { + "bbox": [ + 304, + 641, + 545, + 714 + ], + "type": "inline_equation", + "content": "1.5\\%" + }, + { + "bbox": [ + 304, + 641, + 545, + 714 + ], + "type": "text", + "content": ". This validates that our proposed ap" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "type": "text", + "content": "11772" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 80, + 82, + 250, + 157 + ], + "blocks": [ + { + "bbox": [ + 62, + 71, + 271, + 81 + ], + "lines": [ + { + "bbox": [ + 62, + 71, + 271, + 81 + ], + "spans": [ + { + "bbox": [ + 62, + 71, + 271, + 81 + ], + "type": "text", + "content": "Table 5. Effectiveness of proposed training modifications." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 80, + 82, + 250, + 157 + ], + "lines": [ + { + "bbox": [ + 80, + 82, + 250, + 157 + ], + "spans": [ + { + "bbox": [ + 80, + 82, + 250, + 157 + ], + "type": "table", + "html": "
ModificationTop-1 accuracy
AMID73.8
with fixed teacher66.0
w/o warm-up65.8
w/o D272.8
w/o dynamic weight72.7
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(Right) The cosine similarity during testing." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 168, + 167, + 277, + 257 + ], + "blocks": [ + { + "bbox": [ + 168, + 167, + 277, + 257 + ], + "lines": [ + { + "bbox": [ + 168, + 167, + 277, + 257 + ], + "spans": [ + { + "bbox": [ + 168, + 167, + 277, + 257 + ], + "type": "image", + "image_path": "1dafd05386d9476d0fef9309f58c49a39f69d1eff5f72bc445d629ef57c832de.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 314, + 287, + 338 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 314, + 287, + 338 + ], + "spans": [ + { + "bbox": [ + 46, + 314, + 287, + 338 + ], + "type": "text", + "content": "proach, which takes into account the correlation of samples within a class, achieves better optimization for MI." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 349, + 243, + 361 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 349, + 243, + 361 + ], + "spans": [ + { + "bbox": [ + 47, + 349, + 243, + 361 + ], + "type": "text", + "content": "4.4.2 Effectiveness of training modifications" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 365, + 287, + 556 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 365, + 287, + 556 + ], + "spans": [ + { + "bbox": [ + 46, + 365, + 287, + 556 + ], + "type": "text", + "content": "To evaluate the effect of each modification applied in AMD, we conduct a set of experiments on UCF51 and give the results in Tab. 5. As mentioned before, using a fixed pre-trained teacher to guide the student's learning leads to an undesired gap between the teacher and the student at the beginning of training, which is unfavorable for distillation. The result affirms this, where the performance of AMD degrades from " + }, + { + "bbox": [ + 46, + 365, + 287, + 556 + ], + "type": "inline_equation", + "content": "73.8\\%" + }, + { + "bbox": [ + 46, + 365, + 287, + 556 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 46, + 365, + 287, + 556 + ], + "type": "inline_equation", + "content": "66.0\\%" + }, + { + "bbox": [ + 46, + 365, + 287, + 556 + ], + "type": "text", + "content": " without joint training. In addition, it also shows that without employing the warm-up setup described before, the recognition performance degrades by " + }, + { + "bbox": [ + 46, + 365, + 287, + 556 + ], + "type": "inline_equation", + "content": "8.0\\%" + }, + { + "bbox": [ + 46, + 365, + 287, + 556 + ], + "type": "text", + "content": ". The reason may be that the target modality and multimodality representations are noisy and uncorrelated at the start of the training, which results in that the discriminators can recognize them readily and thus affecting the feedback of the informative gradient of adversarial learning." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 557, + 287, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 557, + 287, + 689 + ], + "spans": [ + { + "bbox": [ + 46, + 557, + 287, + 689 + ], + "type": "text", + "content": "We also study the effectiveness of the two discriminators of our proposed AMD by comparing AMD with two ablative cases: w/o " + }, + { + "bbox": [ + 46, + 557, + 287, + 689 + ], + "type": "inline_equation", + "content": "D_{2}" + }, + { + "bbox": [ + 46, + 557, + 287, + 689 + ], + "type": "text", + "content": " and w/o dynamic weight. One constraint is removed at a time. The results of these ablation studies are shown in Tab. 5. The accuracy decreases by " + }, + { + "bbox": [ + 46, + 557, + 287, + 689 + ], + "type": "inline_equation", + "content": "1.0\\%" + }, + { + "bbox": [ + 46, + 557, + 287, + 689 + ], + "type": "text", + "content": " when only the fundamental discriminator " + }, + { + "bbox": [ + 46, + 557, + 287, + 689 + ], + "type": "inline_equation", + "content": "D_{1}" + }, + { + "bbox": [ + 46, + 557, + 287, + 689 + ], + "type": "text", + "content": " is used, suggesting that the enhanced discriminator " + }, + { + "bbox": [ + 46, + 557, + 287, + 689 + ], + "type": "inline_equation", + "content": "D_{2}" + }, + { + "bbox": [ + 46, + 557, + 287, + 689 + ], + "type": "text", + "content": " indeed helps to distill the multimodal information of samples of the same class. Moreover, it also demonstrates that using uniform weight leads to a performance drop, indicating the effectiveness of the proposed dynamic weighting scheme." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "content": "To further investigate the effectiveness of the proposed adversarial learning-based approach in transferring the" + } + ] + } + ], + "index": 9 + }, + { + "type": "table", + "bbox": [ + 309, + 92, + 539, + 167 + ], + "blocks": [ + { + "bbox": [ + 306, + 71, + 544, + 91 + ], + "lines": [ + { + "bbox": [ + 306, + 71, + 544, + 91 + ], + "spans": [ + { + "bbox": [ + 306, + 71, + 544, + 91 + ], + "type": "text", + "content": "Table 6. Top-1 accuracy (%) on UCF51 with different hyperparameters." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 309, + 92, + 539, + 167 + ], + "lines": [ + { + "bbox": [ + 309, + 92, + 539, + 167 + ], + "spans": [ + { + "bbox": [ + 309, + 92, + 539, + 167 + ], + "type": "table", + "html": "
α1value3.73.83.94.04.14.2
accuracy72.673.773.773.873.873.4
α2value1.31.41.51.61.71.8
accuracy71.273.773.873.873.672.4
α3value0.70.80.91.01.11.2
accuracy73.373.473.773.873.473.1
", + "image_path": "1c5f98568686a3ad0179ada8426a37132e46199724a60c844a4cd5a70549bdf2.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "table_body" + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 180, + 545, + 299 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 180, + 545, + 299 + ], + "spans": [ + { + "bbox": [ + 304, + 180, + 545, + 299 + ], + "type": "text", + "content": "inter-sample multimodal information, we compare AMID with two cases: w/o " + }, + { + "bbox": [ + 304, + 180, + 545, + 299 + ], + "type": "inline_equation", + "content": "D_{2}" + }, + { + "bbox": [ + 304, + 180, + 545, + 299 + ], + "type": "text", + "content": " and w/o " + }, + { + "bbox": [ + 304, + 180, + 545, + 299 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{adv}" + }, + { + "bbox": [ + 304, + 180, + 545, + 299 + ], + "type": "text", + "content": ". Fig. 5 displays the average of cosine similarity between the teacher and the student only in the same class, i.e. the average of all " + }, + { + "bbox": [ + 304, + 180, + 545, + 299 + ], + "type": "inline_equation", + "content": "\\Phi (M_v,S_v^{\\eta_j}), j\\neq 0" + }, + { + "bbox": [ + 304, + 180, + 545, + 299 + ], + "type": "text", + "content": " in Eq. (7). We can see that the cosine similarity of AMID is consistently larger than that of the other two cases and the cosine similarity of w/o " + }, + { + "bbox": [ + 304, + 180, + 545, + 299 + ], + "type": "inline_equation", + "content": "D_{2}" + }, + { + "bbox": [ + 304, + 180, + 545, + 299 + ], + "type": "text", + "content": " is larger than that of w/o " + }, + { + "bbox": [ + 304, + 180, + 545, + 299 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{adv}" + }, + { + "bbox": [ + 304, + 180, + 545, + 299 + ], + "type": "text", + "content": ", meaning that the proposed approach indeed helps the student to learn more compact representations for each class." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 307, + 454, + 319 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 307, + 454, + 319 + ], + "spans": [ + { + "bbox": [ + 306, + 307, + 454, + 319 + ], + "type": "text", + "content": "4.5. Hyperparameters Analysis" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 322, + 545, + 453 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 322, + 545, + 453 + ], + "spans": [ + { + "bbox": [ + 304, + 322, + 545, + 453 + ], + "type": "text", + "content": "Sensitivity analysis studies are conducted for the hyperparameters, " + }, + { + "bbox": [ + 304, + 322, + 545, + 453 + ], + "type": "inline_equation", + "content": "\\alpha_{1}" + }, + { + "bbox": [ + 304, + 322, + 545, + 453 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 322, + 545, + 453 + ], + "type": "inline_equation", + "content": "\\alpha_{2}" + }, + { + "bbox": [ + 304, + 322, + 545, + 453 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 322, + 545, + 453 + ], + "type": "inline_equation", + "content": "\\alpha_{3}" + }, + { + "bbox": [ + 304, + 322, + 545, + 453 + ], + "type": "text", + "content": ", referenced in the loss function Eq. (17). Similar to the previous study, we experiment on UCF51 and show the results in Tab. 6. The other two hyperparameters are kept the same when one changes. We test different values for " + }, + { + "bbox": [ + 304, + 322, + 545, + 453 + ], + "type": "inline_equation", + "content": "\\alpha_{1}" + }, + { + "bbox": [ + 304, + 322, + 545, + 453 + ], + "type": "text", + "content": " from 3.7 to 4.2, " + }, + { + "bbox": [ + 304, + 322, + 545, + 453 + ], + "type": "inline_equation", + "content": "\\alpha_{2}" + }, + { + "bbox": [ + 304, + 322, + 545, + 453 + ], + "type": "text", + "content": " from 1.3 to 4.8 and " + }, + { + "bbox": [ + 304, + 322, + 545, + 453 + ], + "type": "inline_equation", + "content": "\\alpha_{3}" + }, + { + "bbox": [ + 304, + 322, + 545, + 453 + ], + "type": "text", + "content": " from 0.7 to 1.2, all with an increment of 0.1. The results show that the hyperparameters " + }, + { + "bbox": [ + 304, + 322, + 545, + 453 + ], + "type": "inline_equation", + "content": "\\alpha_{1}" + }, + { + "bbox": [ + 304, + 322, + 545, + 453 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 322, + 545, + 453 + ], + "type": "inline_equation", + "content": "\\alpha_{2}" + }, + { + "bbox": [ + 304, + 322, + 545, + 453 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 322, + 545, + 453 + ], + "type": "inline_equation", + "content": "\\alpha_{3}" + }, + { + "bbox": [ + 304, + 322, + 545, + 453 + ], + "type": "text", + "content": " are not sensitive within a certain range. In general, " + }, + { + "bbox": [ + 304, + 322, + 545, + 453 + ], + "type": "inline_equation", + "content": "\\alpha_{1}" + }, + { + "bbox": [ + 304, + 322, + 545, + 453 + ], + "type": "text", + "content": " between 3.8 to 4.1 and " + }, + { + "bbox": [ + 304, + 322, + 545, + 453 + ], + "type": "inline_equation", + "content": "\\alpha_{2}" + }, + { + "bbox": [ + 304, + 322, + 545, + 453 + ], + "type": "text", + "content": " between 1.4 to 1.7 works well, and we set " + }, + { + "bbox": [ + 304, + 322, + 545, + 453 + ], + "type": "inline_equation", + "content": "\\alpha_{3} = 1.0" + }, + { + "bbox": [ + 304, + 322, + 545, + 453 + ], + "type": "text", + "content": " for all other experiments." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 464, + 378, + 475 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 464, + 378, + 475 + ], + "spans": [ + { + "bbox": [ + 306, + 464, + 378, + 475 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 483, + 545, + 627 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 483, + 545, + 627 + ], + "spans": [ + { + "bbox": [ + 304, + 483, + 545, + 627 + ], + "type": "text", + "content": "In this paper, we propose a generic cross-modal distillation method, AMID, to enhance the target modality representations. The proposed approach simultaneously maximizes the lower bounds on MI between the teacher and the student as well as between the teacher and an auxiliary model while minimizing the conditional entropy of the teacher given the student. For optimizing the lower bound on MI, we derive a new form and solve it by a contrastive learning-based approach. For minimizing the conditional entropy, an adversarial learning-based approach is used. Our extensive experimental evaluation demonstrates the effectiveness of AMID on three popular datasets." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 631, + 404, + 643 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 631, + 404, + 643 + ], + "spans": [ + { + "bbox": [ + 306, + 631, + 404, + 643 + ], + "type": "text", + "content": "Acknowledgement" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 647, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 647, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 304, + 647, + 545, + 712 + ], + "type": "text", + "content": "This work is supported by the National Key R&D Program of China (No. 2022ZD0160702), STCSM (No. 2251 1106101, No. 18DZ2270700, No. 21DZ1100100, No. 215 11101100), 111 plan (No. BP0719010), and State Key Laboratory of UHD Video and Audio Production and Presentation." + } + ] + } + ], + "index": 18 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "11773" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 288, + 713 + ], + "type": "list", + "angle": 0, + "index": 13, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 135 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 135 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 135 + ], + "type": "text", + "content": "[1] Sarah A. 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The introduced approach focuses on outdoor scenes where recovering accurate geometric scaffold and camera pose is challenging, leading to inferior results using the state-of-the-art stable view synthesis (SVS) method. SVS and related methods fail for outdoor scenes primarily due to (i) overrelying on the multiview stereo (MVS) for geometric scaffold recovery and (ii) assuming COLMAP computed camera poses as the best possible estimates, despite it being well-studied that MVS 3D reconstruction accuracy is limited to scene disparity and camera-pose accuracy is sensitive to key-point correspondence selection. This work proposes a principled way to enhance novel view synthesis solutions drawing inspiration from the basics of multiple view geometry. By leveraging the complementary behavior of MVS and monocular depth, we arrive at a better scene depth per view for nearby and far points, respectively. Moreover, our approach jointly refines camera poses with image-based rendering via multiple rotation averaging graph optimization. The recovered scene depth and the camera-pose help better view-dependent on-surface feature aggregation of the entire scene. Extensive evaluation of our approach on the popular benchmark dataset, such as Tanks and Temples, shows substantial improvement in view synthesis results compared to the prior art. For instance, our method shows $1.5\\mathbf{dB}$ of PSNR improvement on the Tank and Temples. Similar statistics are observed when tested on other benchmark datasets such as FVS, Mip-NeRF 360, and DTU.", + "bbox": [ + 75, + 318, + 472, + 758 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 789, + 209, + 806 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Image-based rendering, popularly re-branded as view synthesis, is a long-standing problem in computer vision and graphics [42, 44]. This problem aims to develop a", + "bbox": [ + 75, + 815, + 470, + 861 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "method that allows the user to seamlessly explore the scene via rendering of the scene from a sparse set of captured images [2, 20, 42]. Furthermore, the rendered images must be as realistic as possible for a better user experience [34-36]. Currently, among the existing approaches, Riegler and Koltun stable view synthesis (SVS) approach [36] has shown excellent results and demonstrated photorealism in novel view synthesis, without using synthetic gaming engine 3D data, unlike [34]. SVS is indeed stable in rendering photorealistic images from novel viewpoints for large-scale scenes. Yet, it assumes MVS [39, 40] based dense 3D scene reconstruction and camera poses from COLMAP [39] are correct. The off-the-shelf algorithms used for 3D data acquisition and camera poses from images are, of course, popular, and to assume these algorithms could provide favorable 3D reconstruction and camera poses is not an outlandish assumption. Nonetheless, taking a step forward, in this paper, we argue that although choices made by SVS for obtaining geometric scaffold and camera poses in the pursuit of improving view synthesis is commendable, we can do better by making mindful use of fundamentals from multiple-view geometry [11,12] and recent developments in deep-learning techniques for 3D computer vision problems.", + "bbox": [ + 500, + 287, + 892, + 635 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "To start with, we would like to emphasize that it is clearly unreasonable, especially in an outdoor setting, to assume that multi-view stereo (MVS) can provide accurate depth for all image pixels. It is natural that pixels with low disparity will not be reconstructed well using state-of-the-art MVS approaches [8, 39, 40, 46]. Even a precise selection of multiple view images with reasonable distance between them (assume good baseline for stereo) may not be helpful due to loss of common scene points visibility, foreshortening issue, etc. [43]. Such issues compel the practitioner to resort to post-processing steps for refining the MVS-based 3D geometry so that it can be helpful for rendering pipeline or neural-rendering network at train time.", + "bbox": [ + 496, + 638, + 893, + 835 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Another critical component to view synthesis, which is often brushed aside in the literature is the accurate recovery of the camera poses. In neural view synthesis approaches such as [36], if the camera pose is wrong, the feature ag-", + "bbox": [ + 496, + 839, + 893, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 810, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Equal Contribution \n†Corresponding Author (k.sur46@gmail.com)", + "bbox": [ + 94, + 875, + 339, + 900 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "13208", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/afa88c39f10e95619f038cb454706670e69a3fb4b7bc6ba18491a3fb7bdc34f2.jpg", + "image_caption": [ + "Figure 1. Qualitative comparison. Our result compared to the popular SVS method [36] on the M60 scene of the tanks and temples dataset [18]. It is easy to observe that our approach can better render fine details in the scene. For this scene, the PSNR values for SVS [36] and our method are 19.1 and 20.8, respectively, demonstrating improved PSNR result." + ], + "image_footnote": [], + "bbox": [ + 81, + 90, + 903, + 200 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "ggregation corresponding surface points could be misleading, providing inferior results. Therefore, we should have camera poses as accurate as possible. Unfortunately, despite the camera pose importance to this problem, discussion on improving camera pose is often ignored under the assumption that COLMAP [39] provide the best possible camera pose estimates for any possible scenarios. Practically speaking, this is generally not the case for outdoor scenes [5, 11, 15]. What is more surprising is that some recent benchmark datasets put COLMAP recovered poses as the ground-truth poses [33]. Hence, we want to get this out way upfront that a robust and better camera-pose estimates are vital for better modeling view synthesis problem.", + "bbox": [ + 75, + 281, + 468, + 477 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "From the above predication, it is apparent that a more mindful approach is required to make view synthesis approaches practically useful, automatic, and valuable for real-world application. To this end, we propose a principled and systematic approach that provides a better geometric scaffold and camera poses for reliable feature aggregation of the scene's surface points, leading to improved novel-view synthesis results enabling superior photorealism.", + "bbox": [ + 75, + 478, + 468, + 599 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In practice, we can have suitable initial camera poses from images using COLMAP. Yet, it must be refined further for improved image-feature aggregation corresponding to 3D surface points for neural rendering. It is well-studied in multiple-view geometry literature that we can improve and refine camera poses just from image key-point correspondences [10, 11]. Accordingly, we introduce a learning-based multiple motion averaging via graph neural network for camera pose recovery, where the pose graph is initialized using COLMAP poses for refinement.", + "bbox": [ + 75, + 599, + 468, + 750 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Meanwhile, it is challenging to accurately recover the 3D geometry of scene points with low or nearly-zero disparity using MVS methods [12, 43]. Another bad news from the theoretical side is that a precise estimation of scene depth from a single image is unlikely1, which is a correct statement and hard to argue. The good news is that advancements in deep-learning-based monocular depth prediction have led to some outstanding results in several practical", + "bbox": [ + 75, + 752, + 468, + 875 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "applications [24, 31]. Thus, at least practically, it seems possible to infer reliable monocular depth estimates up to scale. Using single image depth prediction, we can reason about the depth of scene points with low disparities. So, our proposed strategy is to use confidence based multiple-view stereo 3D that favours pixels with near-to-mid disparity and allows monocular depth estimates for the rest of the pixels. Overall depth is recovered after scaling all the scene depth appropriately using MVS reconstructed metric.", + "bbox": [ + 496, + 281, + 890, + 416 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "By encoding the image features via convolutional neural networks, we map the deep features to our estimated 3D geometric scaffold of the scene. Since we have better camera poses and scene reconstruction, we obtain and aggregate accurate feature vectors corresponding to each imaging view-rays—both from the camera to the surface point and from the surface point to viewing image pixels, giving us a feature tensor. We render the new image from the features tensor via a convolutional network and simultaneously refine the camera pose. In summary, our contributions are", + "bbox": [ + 496, + 416, + 892, + 566 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- A systematic and principled approach for improved stable view synthesis enabling enhanced photorealism.", + "- The introduced approach exploits the complementary nature of MVS and monocular depth estimation to recover better 3D geometric scaffold of the scene. Meanwhile, the robust camera poses are recovered using graph neural network based multiple motion averaging.", + "- Our approach proposes an improved loss function to jointly optimize and refine for poses, neural image rendering, and scene representation showing superior results." + ], + "bbox": [ + 500, + 569, + 890, + 720 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Our approach when tested on benchmark datasets such as Tank and Temples [18], FVS [35], Mip-NeRF 360 [1], and DTU [16] gives better image based rendering results with generally more than 1 dB PSNR gain (see Fig.1).", + "bbox": [ + 496, + 726, + 890, + 787 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Background and Preliminaries", + "text_level": 1, + "bbox": [ + 500, + 799, + 782, + 816 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Our work integrates the best of novel view synthesis and multiple view geometry approaches in computer vision in a mindful way. Both novel view synthesis and MVS are classical problems in computer graphics and computer vision, with an exhaustive list of literature. Thus, we confine our re", + "bbox": [ + 496, + 825, + 890, + 898 + ], + "page_idx": 1 + }, + { + "type": "page_footnote", + "text": "1As several 3D scene points can have same image projection.", + "bbox": [ + 94, + 886, + 419, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "13209", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "lated work discussion to the methods that is directly related to the proposed approach. The interested reader may refer to [4, 8, 12, 28, 38, 42, 44] for earlier and recent progress in these areas. Here, we briefly discuss relevant methods and the current state-of-the-art in neural image-based rendering.", + "bbox": [ + 75, + 90, + 472, + 167 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "(i) Uncalibrated Multi-View Stereo. Given the intrinsic camera calibration matrix, we can recover camera poses and the 3D structure of the scene using two or more images [8,21,22,39,40]. One popular and easy-to-use MVS framework is COLMAP [39], which includes several carefully crafted modules to estimate camera poses and sparse 3D structures from images. For camera pose estimation, it uses classical image key-point-based algorithms [13,27,45]. As is known that such methods can provide sub-optimal solutions and may not robustly handle outliers inherent to the unstructured images. Consequently, camera poses recovered using COLMAP can be unreliable, primarily for outdoor scenes. Moreover, since the 3D reconstruction via triangulation uses sparse key points, at best accurate semidense 3D reconstruction of the scene could be recovered. Still, many recent state-of-the-art methods in novel view synthesis heavily rely on it [25,35,36,49].", + "bbox": [ + 75, + 169, + 472, + 426 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "(ii) Image-based rendering. Earlier image-based rendering approaches enabled novel view synthesis from images without any 3D scene data under some mild assumptions about the camera, and imaging [9,23,41]. Later with the development of multiple-view stereo approaches and RGBD sensing modalities, several works used some form of 3D data to improve image-based rendering. Popular works along this line include [2,6,14,20,29]. In recent years, neural network-based methods have dominated this field and enabled data-driven approach to this problem with an outstanding level of photorealism [26,34-36,49].", + "bbox": [ + 75, + 429, + 472, + 595 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Among all the current methods we tested, SVS [36] stands out in novel view synthesis from images taken from a freely moving camera. This paper proposes an approach closely related to the SVS pipeline. SVS involves learning a scene representation from images using its dense 3D structure and camera poses predicted via uncalibrated MVS approaches detailed previously. The recovered 3D structure of the scene is post-processed to have a refined geometric scaffold in mesh representation. Using refined scene 3D, it learns a feature representation for a set of images and then projects it along the direction of the target view to be rendered. Finally, SVS involves re-projection from feature to image space resulting in the synthesized image for the target view. Given $S$ , the 3D structure for a scene, feature representation network $f_{\\theta}$ with $\\theta$ representing the network parameters, and the rendering network $G_{\\mu}$ with parameters $\\mu$ , the resulting image $\\mathcal{I}_r$ along the pose $\\mathbf{p}$ is rendered as", + "bbox": [ + 75, + 595, + 472, + 853 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {I} _ {r} = \\mathcal {G} _ {\\mu} \\left(\\phi_ {a} \\left(\\mathcal {S}, \\mathcal {I} _ {s}, \\mathbf {p}, f _ {\\theta}\\right), \\right. \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 183, + 859, + 468, + 878 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where, $\\mathcal{I}_s$ denotes the image set for a given seen. $\\phi_{a}()$ ag-", + "bbox": [ + 76, + 885, + 470, + 901 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "gregates features for all the images along a given direction in $\\mathcal{I}_s$ predicted when passed through $f_{\\theta}$ .", + "bbox": [ + 496, + 90, + 890, + 121 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Contrary to the choices made by the SVS, in this work, we put forward an approach for better estimation of the overall scene 3D geometric scaffold—for both low and high-disparity pixels—and camera poses. Our approach enables a better aggregation of surface features allowing an improved level of realism in novel view synthesis.", + "bbox": [ + 496, + 121, + 893, + 212 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Method", + "text_level": 1, + "bbox": [ + 500, + 223, + 591, + 239 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We begin with a discussion about formulating and estimating a better scene representation by carefully exploiting the complementary behavior of monocular depth and multiview stereo approaches in 3D data acquisition. During our implementation, we use confidence measures for precise reasoning of estimated 3D coming from both the modalities and their accuracy. Next, we detail integrating a camera pose-refining optimization to estimate better camera poses for accurately projecting our 3D scene representation to the target view. Finally, the proposed joint optimization objective to refine structure representation and camera poses simultaneously is discussed.", + "bbox": [ + 496, + 248, + 893, + 431 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Overview", + "text_level": 1, + "bbox": [ + 500, + 438, + 609, + 452 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Given a set of source images $\\mathcal{I}_s$ taken from a freely moving camera, the current state-of-the-art SVS [36] first estimates camera-poses $\\mathcal{P}$ and scene 3D structure $S$ . Next, it encodes the images via a CNN. Then, using the estimated camera, it maps the encoded features onto the scene 3D scaffold. For each point $\\mathbf{x} \\in \\mathbb{R}^3$ on the scaffold, SVS query set of images in which $\\mathbf{x}$ is visible to obtain its corresponding feature vectors. This feature vector is then conditioned on the output view direction via a network to produce a new feature vector. Such a new feature vector is obtained for all the points on the scaffold to form a feature tensor, which is then decoded using CNN to synthesize the output image. Denoting the complete set of parameters for learning the feature representation and rendering as $\\Theta$ , we can write SVS idea as", + "bbox": [ + 496, + 460, + 893, + 686 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\Theta \\sim \\Psi (\\Theta | \\mathcal {S}, \\mathcal {P}, \\mathcal {I} _ {s}) \\circ \\Psi (\\mathcal {S}, \\mathcal {P} | \\mathcal {I} _ {s}). \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 576, + 695, + 890, + 712 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "$\\Psi(.)$ symbolizes an abstract functional. Here, $S$ and $\\mathcal{P}$ are estimated using structure from motion and MVS [39, 40]. As mentioned before, we first aim to recover a much better 3D scene recovery by utilizing the complementary nature of the monocular depth and stereo depth. Furthermore, estimate improved camera poses using neural graph-based multiple motion averaging. We denote $\\mathcal{D}_s$ as monocular depth for each image in $\\mathcal{I}_s$ and $\\mathcal{S}_R$ , $\\mathcal{P}_R$ as our scene 3D reconstruction and camera poses, respectively.", + "bbox": [ + 496, + 719, + 893, + 854 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Once we estimate $S_{R},\\mathcal{P}_{R}$ , we jointly optimize for better neural scene representation and camera poses with the neural network parameters $\\Theta$ using the proposed loss function", + "bbox": [ + 496, + 854, + 893, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "13210", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "(Sec. 3.3). Our better scene representation and improved camera help in improved view-synthesis at test time. Our overall idea can be understood via the following equation:", + "bbox": [ + 75, + 90, + 468, + 137 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\Theta , \\mathcal {S} _ {R}, \\mathcal {P} _ {R} \\sim \\Psi (\\Theta , \\mathcal {S} _ {R}, \\mathcal {P} _ {R} | \\mathcal {S}, \\mathcal {P}, \\mathcal {D} _ {s}, \\mathcal {I} _ {s}) \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 133, + 147, + 468, + 162 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.1.1 3D Scene Features", + "text_level": 1, + "bbox": [ + 76, + 180, + 261, + 194 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Here, we describe feature aggregation for the output view obtained using the SVS pipeline [36] combined with the back-projected RGB-D features due to images and their monocular depth via a convolutional neural network (CNN). Given the output direction $\\mathbf{u}$ , for each $\\mathbf{x} \\in \\mathbb{R}^3$ on the geometric scaffold along $\\mathbf{u}$ there is a subset of source images, in which $\\mathbf{x}$ is visible. Assuming the total number of images in this subset to be $K$ , we denote the set of view directions corresponding to these images as $\\{\\mathbf{v}_k\\}_{k=1}^K$ .", + "bbox": [ + 75, + 203, + 468, + 340 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "(i) SVS Features. The source images in $\\mathcal{I}_s$ are first passed through a feature extraction CNN to obtain a feature tensor $\\mathcal{F}_k$ corresponding to $k^{th}$ image. Denoting $f_{k}(\\mathbf{x})$ as the feature corresponding to a point $\\mathbf{x} \\in \\mathbb{R}^3$ in $\\mathcal{F}_k$ located at the projection (or bilinear interpolation) of $\\mathbf{x}$ on $k^{th}$ image. To this end, SVS [36] proposed the following aggregation function $(\\phi_a)$ to compute the feature for $\\mathbf{x}$ along $\\mathbf{u}$", + "bbox": [ + 75, + 342, + 468, + 449 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\phi_ {a} (\\mathbf {u}, \\left\\{\\left(\\mathbf {v} _ {k}, f _ {k} (\\mathbf {x})\\right) \\right\\}) = \\frac {1}{W} \\sum_ {k = 1} ^ {K} \\max (0, \\mathbf {u} ^ {\\mathrm {T}} \\mathbf {v}) f _ {k} (\\mathbf {x}), \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 94, + 458, + 468, + 500 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where, $W = \\sum_{k=1}^{K} \\max(0, \\mathbf{u}^{\\mathrm{T}}\\mathbf{v})$ is sum of all the weights.", + "bbox": [ + 75, + 508, + 467, + 527 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "(ii) Monocular Features. Given an image, we predict its depth with a per-pixel confidence score. For this, we use an existing monocular depth prediction network [32] pretrained on Omnidata [7]. To predict a normalized depth prediction confidence score per pixel $w_{ij}$ , we add another network on top of it (refer supplementary for details), which takes both images and depth as input.", + "bbox": [ + 75, + 529, + 468, + 636 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\sum_ {i} \\sum_ {j} w _ {i j} \\cdot \\mathcal {L} \\left(d _ {i j}, \\hat {d} _ {i j}\\right); \\text {w h e r e}, w _ {i j} = \\phi_ {w} \\left(\\mathcal {I} _ {s}, \\mathcal {D} _ {s}\\right) _ {i j}. \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 84, + 645, + 468, + 678 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "$\\mathcal{L}$ symbolizes the $l_{2}$ loss between the known pixel depth $d_{ij}$ and the predicted depth $\\hat{d}_{ij}$ for $(i,j)$ pixel in the 2D depth image. We call network $\\phi_w$ as the \"confidence-prediction head\". We take the depths predicted by this network and fuse them with the source image using the Channel Exchange Network [47]. The fused information is then projected into $N$ dimensional feature space using network $\\mathcal{F}_{\\theta}$ , which is a CNN-based architecture. To compute the feature corresponding to a pixel $\\mathbf{p}$ in the target view $\\mathbf{u}$ , we warp the features predicted for each source views $\\mathbf{v}_k$ to this target view but now using the monocular depth $d \\in \\mathcal{D}_s$ of the source view.", + "bbox": [ + 75, + 686, + 468, + 869 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\ng _ {k} (\\mathbf {u}, \\mathbf {p}) = f _ {k} ^ {m} \\left(\\mathcal {W} (\\mathbf {p}, \\mathbf {u}, \\mathbf {v} _ {k}, d)\\right) \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 166, + 883, + 468, + 902 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where, $g_{k}$ denotes the feature warping function, $f_{k}^{m}(p)$ corresponds to feature in the tensor $\\mathcal{F}_{\\theta}(\\mathcal{T}_s^k,d)$ (corresponding to $k^{th}$ source image and corresponding monocular depth) at pixel $\\mathbf{p}$ , and $\\mathcal{W}$ is the warping function. We now aggregate the warped features corresponding to each source image using a weighted sum based on confidence scores:", + "bbox": [ + 498, + 90, + 890, + 181 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\phi_ {a} (\\mathbf {u}, \\left\\{\\left(\\mathbf {v} _ {k}, f _ {k} ^ {m} (\\mathbf {p})\\right) \\right\\}) = \\sum_ {k = 1} ^ {K} c _ {k} (\\mathbf {p}) f _ {k} ^ {m} (\\mathbf {p}) \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 555, + 190, + 890, + 232 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "here, $c_k$ symbolizes the predicted depth confidence map in the $k^{th}$ view.", + "bbox": [ + 498, + 239, + 890, + 268 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "(iii) Structure Feature Aggregation Per Scene Point. Given we have features from two different modalities i.e., monocular depth and MVS, we now propose an aggregated feature representation for the target view per scene point $h_f = h_\\theta(h_m, h_s)$ , where $h_\\theta$ is a CNN-based neural network with parameters $\\theta$ and $h_m$ is the final representation for the monocular estimation and $h_s$ for the stereo-estimation. We aim to attain maximal correlation from both of the input representations i.e.,", + "bbox": [ + 498, + 273, + 890, + 409 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\lambda_ {1} \\mathcal {C} \\left(h _ {f}, h _ {m}\\right) \\cdot \\mathcal {C} \\left(h _ {f}, h _ {s}\\right) + \\lambda_ {2} \\mathcal {C} \\left(h _ {f}, h _ {s}\\right) + \\lambda_ {3} \\mathcal {C} \\left(h _ {f}, h _ {m}\\right) \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 506, + 417, + 890, + 436 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where, $\\sum_{i=1}^{3} \\lambda_i = 1$ ; $\\lambda_i > 0 \\forall i \\in \\{1,2,3\\}$ and $\\mathcal{C}(.)$ being the standard correlation function [3]. We set $\\lambda_1 = 1$ for nearby points where confidence of monocular depth could be greater than a defined threshold ( $\\tau$ ). $\\lambda_2 = 1$ for nearby points where confidence of monocular depth is lower than a defined threshold and finally $\\lambda_3 = 1$ for far points whose relative depth is greater than a pre-defined threshold ( $\\sigma$ ). Such a choice is made since stereo features might be less accurate in certain depth range due to low disparity or too close to the lens. The final aggregation $h_f$ comprises of CNN networks $\\phi_\\alpha$ and $\\phi_\\beta$ , parameterized by $\\alpha$ and $\\beta$ , respectively. The transformed features from each of these modalities are then fed to a CNN network $\\phi_\\nu$ with parameters $\\nu$ . Overall aggregated features per scene point is represented as", + "bbox": [ + 498, + 444, + 890, + 672 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nh _ {f} = h _ {\\theta} \\left(h _ {m}, h _ {s}\\right) = \\phi_ {\\nu} \\left(\\phi_ {\\alpha} \\left(h _ {m}\\right), \\phi_ {\\beta} \\left(h _ {s}\\right)\\right). \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 552, + 681, + 890, + 699 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.1.2 Camera Pose Estimation", + "text_level": 1, + "bbox": [ + 500, + 724, + 725, + 739 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Given we have initially estimated pose-set $\\mathcal{P}$ , we use multiple motion averaging (MRA) to recover better camera poses. MRA is fast, efficient, and robust in camera pose estimation from noisy key-point correspondences and works well even for sparse image sets. MRA takes a global view of the camera recovery problem. A view-graph corresponding to the initial set of camera poses is constructed as a global representation, with each graph node as a pose. For pose optimization, MRA first performs rotation averaging to recover rotation and then solves for translation. Assume a", + "bbox": [ + 496, + 750, + 890, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "13211", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/4c602515800266cadd3dbebe829d221fb3a33b386227eb1e465dc1f8ae215223.jpg", + "image_caption": [ + "Figure 2. Overview. For a given set of input images, we first estimate the scene 3D structure and the initial value of camera poses using structure from motion (SFM) followed by MVS. We also estimate per-image depth using an existing Monocular Depth estimation model [7]. Next, we generate two sets of Projected Features for each target view: The first set (upper stream) by encoding the input images and then unprojecting the features onto the scaffold, followed by re-projection to the target view and aggregation. For the second set (lower stream), the images are first concatenated with their monocular depths (MD), and the encoded features are then projected using these depths, followed by aggregation. These two feature sets are then merged into Cumulative Features, and finally, the target view is rendered." + ], + "image_footnote": [], + "bbox": [ + 99, + 88, + 874, + 398 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "directed view-graph $\\mathcal{G} = (\\mathcal{V},\\mathcal{E})$ . A vertex $\\mathcal{V}_j\\in \\mathcal{V}$ in this view graph corresponds to $j^{th}$ camera absolute rotation $R_{j}$ and $\\mathcal{E}_{ij}\\in \\mathcal{E}$ corresponds to the relative orientation $\\tilde{R}_{ij}$ between view $i$ and $j$ . For our problem, relative orientations are given (noisy), and we aim to solve for absolute pose $R_{j}$ robustly. Conventionally, in the presence of noise, the solution is obtained by solving the following optimization problem to satisfy compatibility criteria.", + "bbox": [ + 75, + 522, + 472, + 647 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\underset {\\{R _ {j} \\}} {\\operatorname {a r g m i n}} \\sum_ {\\mathcal {E} _ {i j} \\in \\mathcal {E}} \\rho (\\gamma (\\tilde {R} _ {i j}, R _ {j} R _ {i} ^ {- 1})) \\tag {10}\n$$\n", + "text_format": "latex", + "bbox": [ + 161, + 655, + 468, + 691 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where, $\\gamma(.)$ denotes a metric on $SO(3)$ to measure distance between two rotation and $\\rho(.)$ is a robust $l_1$ norm. We use a graph-neural network to predict the robustified pose view-graph of the scene following the camera pose refining approach of NeuRoRA [30]. First, the camera poses are checked for outliers via a cyclic consistency in the posegraph [11]. Then, a view graph is initialized based on these filtered poses. This view graph is then optimized using the camera pose-refining network of NeuRoRA [30].", + "bbox": [ + 75, + 700, + 472, + 839 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.2. Rendering novel views", + "text_level": 1, + "bbox": [ + 76, + 847, + 287, + 864 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The aggregated feature tensor $\\mathcal{F}^a$ along a direction $\\mathbf{u}$ comprises of the features $h_f$ (Eq. 9) for each pixel along $\\mathbf{u}$ ,", + "bbox": [ + 75, + 869, + 470, + 902 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "obtained using 3D scene features (discussed in Sec. 3.1.1). This tensor is now projected to the image space function using $\\mathcal{G}_{\\theta}$ , a CNN-based network with parameters $\\theta$ . It is quite possible that the regions in the target image may not be encountered in any of the source images. For those points, the values in feature tensor $\\mathcal{F}$ are set to $\\mathbf{0}$ , and thus, they require some inpainting. Denoting the set of test images by $\\mathcal{I}_t$ , the rendered image corresponding to the $k^{th}$ image in the test set, $\\hat{\\mathcal{I}}_t^k$ , is predicted based on the following equation:", + "bbox": [ + 496, + 522, + 890, + 660 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {\\mathcal {I}} _ {t} ^ {k} = \\mathcal {G} _ {\\theta} \\left(\\mathcal {F} _ {k} ^ {a}\\right) \\tag {11}\n$$\n", + "text_format": "latex", + "bbox": [ + 645, + 672, + 890, + 691 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Similar to stable view synthesis, we parameterize the $\\mathcal{G}_{\\theta}$ function using a U-Net [37] style model which also deals with inpainting/hallucinating the newly discovered regions in the test image. Fig.(2) shows the complete overview of the proposed method.", + "bbox": [ + 496, + 695, + 893, + 771 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.3. Joint Optimization", + "text_level": 1, + "bbox": [ + 500, + 777, + 681, + 795 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Given $\\mathcal{I}_s$ , we train the model using our overall loss function $\\mathcal{L}$ comprising of two terms.", + "bbox": [ + 500, + 801, + 892, + 832 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} = \\mathcal {L} _ {s} + \\mathcal {L} _ {p} \\tag {12}\n$$\n", + "text_format": "latex", + "bbox": [ + 648, + 845, + 890, + 864 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "(i) The first loss term $\\mathcal{L}_s$ encourages the network to learn better features corresponding to the scene point. The $\\mathcal{L}_s$", + "bbox": [ + 496, + 869, + 893, + 902 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "13212", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/fc7b35637c65fecfed663e20c5bfd434a3860dfc9821926d8a32d65e17e4cd03.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
TruckM60PlaygroundTrain
PSNR↑LPIPS↓SSIM↑PSNR↑LPIPS↓SSIM↑PSNR↑LPIPS↓SSIM↑PSNR↑LPIPS↓SSIM↑
NeRF++ [49]21.80.310.8117.60.430.7321.90.390.7917.60.480.68
FVS [35]21.90.140.8415.80.320.7721.70.210.8317.30.280.75
SC-NeRF [17]22.30.290.8218.40.400.7622.40.350.8318.20.420.73
Point-NeRF [48]22.70.140.8719.60.210.8522.20.190.8318.60.160.83
SVS [36]22.90.120.8819.10.220.8322.90.170.8617.90.190.81
Ours24.10.120.9020.80.200.8923.90.140.9020.10.130.88
", + "bbox": [ + 81, + 87, + 890, + 186 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/15b1858a79e17f0ad30c84920319f68b8ebe223c539af6a5a77d5e74cd367710.jpg", + "table_caption": [ + "Table 1. Rendered image quality comparison with current state-of-the-art methods in novel view synthesis on the popular Tanks and Temples dataset [18]. We use the popular metrics i.e., PSNR, LPIPS and SSIM for the comparison." + ], + "table_footnote": [], + "table_body": "
BikeFlowersPirateDiggerSandboxSoccertable
SSIM↑LPIPS↓SSIM↑LPIPS↓SSIM↑LPIPS↓SSIM↑LPIPS↓SSIM↑LPIPS↓SSIM↑LPIPS↓
NeRF++ [49]0.710.270.800.310.710.430.650.350.840.240.870.21
FVS [35]0.610.280.790.270.690.370.680.240.780.320.820.21
SVS [36]0.740.220.840.210.750.320.770.180.850.200.910.15
Ours0.790.190.880.180.800.290.810.160.910.170.940.13
", + "bbox": [ + 81, + 234, + 890, + 311 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 2. Quantitative comparison on FVS dataset [35]. We use the popular metrics, i.e., PSNR, LPIPS and SSIM for the comparison.", + "bbox": [ + 89, + 320, + 875, + 335 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "comprises to two objective function $\\mathcal{L}_{rgb}$ and $\\mathcal{L}_{corr}$ . The function $\\mathcal{L}_{rgb}$ measures the discrepancies between the rendering of an image in the source set and the actual image available in the set. This objective is used to train the structure estimation and rendering network parameters jointly. Whereas $\\mathcal{L}_{corr}$ is used for maximizing the correlation objective discussed in Eq.(8) to arrive at the optimal aggregated scene representation.", + "bbox": [ + 75, + 361, + 468, + 482 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {s} = \\mathcal {L} _ {r g b} + \\mathcal {L} _ {c o r r} \\tag {13}\n$$\n", + "text_format": "latex", + "bbox": [ + 197, + 497, + 468, + 513 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "$\\mathcal{L}_{corr}$ takes the negative of the objective defined in Eq.(8). The structure network parameters corresponding to functions $f_{k}$ and $f_{k}^{m}$ (cf. Sec. 3.1.1) and is updated using $\\mathcal{L}_{corr}$ and $\\mathcal{L}_{rgb}$ . The rendering network parameters corresponding to $\\mathcal{G}_{\\theta}$ updated using only $\\mathcal{L}_{rgb}$ .", + "bbox": [ + 75, + 518, + 468, + 595 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "(ii) The second loss term $\\mathcal{L}_p$ corresponds to the camera pose refinement. We used the following loss $\\mathcal{L}_p$ to improve the camera pose estimation.", + "bbox": [ + 75, + 597, + 468, + 642 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {p} = \\mathcal {L} _ {m r a} \\tag {14}\n$$\n", + "text_format": "latex", + "bbox": [ + 230, + 652, + 468, + 670 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "As is known, the multiple motion averaging and the color rendering cost functions are directly impacted by the camera pose parameters. And therefore, the $\\mathcal{L}_{rgb}$ is inherently used as an intermediate objective in which the camera pose term is constant between the two different representations.", + "bbox": [ + 75, + 678, + 468, + 753 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4. Experiments, Results and Ablations", + "text_level": 1, + "bbox": [ + 76, + 766, + 401, + 782 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Here, we discuss our experimental results and their comparison to relevant baselines. Later, we provide critical ablation analysis, a study of our camera pose estimation idea, and 3D structure recovery. Finally, the section concludes with a discussion of a few extensions of our approach2.", + "bbox": [ + 75, + 791, + 468, + 867 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Baselines. We compare our approach with the recently proposed novel view synthesis methods that work well in practice for real-world scenes. Our baseline list includes NeRF++ [49], SC-NeRF [17], PointNeRF [48], FVS [35] and SVS [36]. All baseline methods are trained on the source image set of the testing sequence. Our method's train and test set are the same as SVS [36].", + "bbox": [ + 496, + 361, + 890, + 468 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.1. Dataset and Results", + "text_level": 1, + "bbox": [ + 500, + 477, + 687, + 491 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "For evaluation, we used popular benchmark datasets comprising real-world and synthetic datasets. Namely, we used the Tanks and Temples [18], FVS [35], Mip-NeRF 360 [1], and the DTU [16] dataset. The first two datasets contain real-world scenes, whereas the last is an object-centric synthetic benchmark dataset. Although our approach mainly targets realistic scenes, for completeness, we performed and tabulated results on a synthetic object-based DTU dataset (see supplementary). Next, we discuss datasets and results.", + "bbox": [ + 496, + 500, + 890, + 636 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "(i) Tanks and Temples Dataset. It consists of images of large-scale real-world scenes taken from a freely moving camera, consisting of indoor and outdoor scenes. Unfortunately, we have no ground-truth poses; thus, estimated poses using COLMAP [39] are treated as pseudo-ground-truth poses. The dataset consists of a total of 21 scenes. Similar to the SVS setup, we use 15 of 21 scenes for training, 2 for validation, and the rest as test scenes. We also use a disjoint set of target views from the test scenes to evaluate all the methods. The source views in test scenes are used for scene-specific fine-tuning if required. Table 1 shows the statistical comparison of our approach with competing baselines. Our approach consistently outperforms the relevant baselines on this challenging dataset. Furthermore, if we zoom into the scene's finer details, our approach clearly preserves details better than other approaches (see Fig. 3).", + "bbox": [ + 496, + 638, + 892, + 881 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "(ii) FVS Dataset. It comprises six real-world scenes. Each", + "bbox": [ + 500, + 885, + 890, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_footnote", + "text": "2Please refer supplementary for the train-test setup, implementation details regarding hyperparameters, and architectures to reproduce our results.", + "bbox": [ + 75, + 875, + 468, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "13213", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/602808eefcc6937a74c31185ff4b5daca1ddd8943892286066c5e2bc095b0bd6.jpg", + "image_caption": [ + "Figure 3. Qualitative comparison on tanks and temples dataset. If we zoom into the scene details, our approach results show considerably less artifacts than the state-of-the-art methods enabling unparalleled level of realism in image-based rendering. Our PSNR values for the above two scenes are (20.1, 23.9). In comparison, SC-NeRF [17] and SVS [36] provide (17.3, 22.4) and (17.9, 22.9), respectively." + ], + "image_footnote": [], + "bbox": [ + 117, + 89, + 491, + 487 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/0278469c477addaaccb4b9e4c44912ec58fb9fd0517eaf99638b2875afe89d5c.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 498, + 90, + 848, + 484 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "scene was recorded two or more times to completely differentiate the source image set to form the target image set. Table 2 summarises this dataset's view synthesis quantitative results. We compare our method with the state-of-the-art $\\mathrm{NeRF}++$ [49], Free-View synthesis [35], and SVS [36] methods. We observe that FVS improves over $\\mathrm{NeRF}++$ , whereas SVS results on this dataset do not consistently outperform other previous methods. On the contrary, our method consistently provides better results than prior art in all categories. The dataset's sample images and its qualitative results are provided in the supplementary.", + "bbox": [ + 75, + 566, + 472, + 733 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "(iii) Mip-NeRF 360 Dataset. We further test our approach on this recently proposed dataset comprising unbounded scenes [1]. We use the train-test setup per scene proposed by the authors to fine-tune our network and compare it with Mip-NeRF 360 [1], $\\mathrm{NeRF}++$ [49], and SVS [36] baseline. Table 3 shows the results for this comparison. Clearly, our methodical take on this problem generalizes well, outperforming other baseline methods for most examples.", + "bbox": [ + 75, + 779, + 468, + 902 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/36316fe1f899540b23c606373172202c0a9535ea96b7eeffce8449f07bf23519.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
PSNR↑LPIPS↓SSIM↑
NeRF++ [49]25.030.3550.682
SVS [36]25.280.2180.783
PBNR [19]23.550.2620.722
Mip-NeRF 360 [1]27.070.2510.781
Ours27.950.2320.797
", + "bbox": [ + 545, + 563, + 846, + 640 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 3. Quantitative comparison of our approach with existing baselines on the Mip-NeRF 360 dataset.", + "bbox": [ + 498, + 650, + 890, + 679 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.2. Ablation Analysis", + "text_level": 1, + "bbox": [ + 500, + 705, + 671, + 722 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "(i) Effect of our camera-pose estimation approach. We performed this experiment to show the benefit of using multiple motion averaging (MRA) instead of relying only on COLMAP poses and taking them for granted. For this experiment, we used the popular Lego dataset [25]. We first compute the COLMAP camera poses shown in Fig.4 (Left). Next, we use this initial camera pose set to perform MRA utilizing the view-graph optimization. Our recovered camera poses are shown in Fig.4 (Right). For clarity, we also show the ground-truth camera pose frustum and the error between the ground-truth pose and recovered pose for the", + "bbox": [ + 496, + 734, + 890, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "13214", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/9fc3d8b79d8e56f6098b4b74a005613de9dfbb125cfc0c21c9f36df3f41ccfbc.jpg", + "image_caption": [ + "Figure 4. COLMAP [39] and our method's camera poses on Lego dataset [25]. Here, we add some noise to the pairwise matched correspondences to simulate realistic scenarios. Left: Estimated camera pose from COLMAP and the ground truth pose. Here, black line shows the pose error. Right: Our recovered camera pose. It is easy to infer our approach robustness." + ], + "image_footnote": [], + "bbox": [ + 81, + 99, + 261, + 196 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/dcac75ebdec6d652b6f6ed42dfb97771b2780a23258a37c9eee3a2dc9f5d2ce6.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 272, + 99, + 452, + 196 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "two respective cases. It is clear from Fig.(4) that a principled approach is required for better camera-pose recovery in view-synthesis problem. Furthermore, to show the benefit of our estimated camera pose in novel-view synthesis, we show our network training loss curve with and without our camera pose estimation approach in Fig.(5). For clarity, we also plot the SVS training curve. Firstly, our method shows better loss response due to the improved 3D geometric scaffold of the scene. Moreover, we improve on training loss further by introducing neural graph-based MRA, showing the benefit of our proposed loss function.", + "bbox": [ + 75, + 301, + 470, + 468 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/78dbd409fe2322b377f581b8c1922724dd7a343ae26a7ec0e8dc3685f9e50fd2.jpg", + "image_caption": [ + "Figure 5. Training loss curve of our method with and without pose optimization compared to state-of-the-art SVS [36]" + ], + "image_footnote": [], + "bbox": [ + 106, + 486, + 439, + 656 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "(ii) Effect of using MVS with monocular depth. We performed this ablation to demonstrate the effectiveness of our approach in recovering geometric reconstruction of the scene. Fig.(6) clearly shows the complementary nature of the monocular depth and stereo depth in 3D reconstruction from images. While MVS provides reliable depth results for near and mid-range points, monocular depth can deliver a good depth inference (up to scale) on the far points in the scene. By carefully integrating both modalities' depth, we have better 3D information about the scene. Fig.(6) shows our results on a couple of scenes from Tanks and Temples dataset, demonstrating the suitability of our approach.", + "bbox": [ + 75, + 719, + 470, + 901 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/63b9b29820f788b482eed3514cff36548af2826f4a592a40cc01bcbb3e663144.jpg", + "image_caption": [ + "Figure 6. Comparison of depth predicted by monocular and stereo based method on the scenes from Tanks and Temples dataset." + ], + "image_footnote": [], + "bbox": [ + 521, + 97, + 864, + 492 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 568, + 617, + 583 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "The approach presented in this paper directly addresses the shortcomings of the currently popular methods in novel view synthesis. Our approach integrates concepts from the learning-based approaches and classical techniques in multiple-view geometry for solving novel-view synthesis. We demonstrate that by exploiting the $(i)$ complementary nature of monocular depth estimation and multiple view stereo (MVS) in the 3D reconstruction of the scene, and $(ii)$ usefulness of multiple rotation averaging in structure from motion, we can achieve better-rendering quality than other dominant approaches in novel view synthesis. We confirm the effectiveness of our approach via a comprehensive evaluation and quantitative comparison with baselines on several benchmark datasets. Although our work enabled improved photorealistic rendering, several exciting avenues exist for further improvement. One interesting future extension is fully automating our introduced view synthesis pipeline, i.e., adding a learnable MVS framework to estimate intrinsic, extrinsic camera parameters with scene reconstruction for better novel view synthesis.", + "bbox": [ + 496, + 598, + 890, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "13215", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Jonathan T Barron, Ben Mildenhall, Dor Verbin, Pratul P Srinivasan, and Peter Hedman. Mip-nerf 360: Unbounded anti-aliased neural radiance fields. 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Computer vision: algorithms and applications. Springer Nature, 2022.", + "[44] Ayush Tewari et al. State of the art on neural rendering. In Computer Graphics Forum, volume 39, pages 701-727. Wiley Online Library, 2020.", + "[45] Bill Triggs, Philip F. McLauchlan, Richard I. Hartley, and Andrew W. Fitzgibbon. Bundle adjustment - a modern synthesis. In Proceedings of the International Workshop on Vision Algorithms: Theory and Practice, ICCV '99, pages 298-372, London, UK, UK, 2000. Springer-Verlag.", + "[46] Fangjinhua Wang, Silvano Galliani, Christoph Vogel, Pablo Speciale, and Marc Pollefeys. Patchmatchnet: Learned multi-view patchmatch stereo. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 14194-14203, 2021." + ], + "bbox": [ + 78, + 90, + 470, + 900 + ], + "page_idx": 9 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[47] Yikai Wang, Wenbing Huang, Fuchun Sun, Tingyang Xu, Yu Rong, and Junzhou Huang. Deep multimodal fusion by channel exchanging. Advances in Neural Information Processing Systems, 33:4835-4845, 2020.", + "[48] Qiangeng Xu, Zexiang Xu, Julien Philip, Sai Bi, Zhixin Shu, Kalyan Sunkavalli, and Ulrich Neumann. Point-nerf: Point-based neural radiance fields. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 5438-5448, 2022.", + "[49] Kai Zhang, Gernot Riegler, Noah Snavely, and Vladlen Koltun. Nerf++: Analyzing and improving neural radiance fields. arXiv preprint arXiv:2010.07492, 2020." + ], + "bbox": [ + 501, + 92, + 890, + 260 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "13217", + "bbox": [ + 480, + 945, + 517, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/Enhanced Stable View Synthesis/0a0f1a7f-c68c-47e4-9fa7-95cd72aa0e19_model.json b/2023/Enhanced Stable View Synthesis/0a0f1a7f-c68c-47e4-9fa7-95cd72aa0e19_model.json new file mode 100644 index 0000000000000000000000000000000000000000..1136ed674c826f8542e2b57ad2102a959810dc27 --- /dev/null +++ b/2023/Enhanced Stable View Synthesis/0a0f1a7f-c68c-47e4-9fa7-95cd72aa0e19_model.json @@ -0,0 +1,2013 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.001, + 0.812, + 0.047 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.321, + 0.131, + 0.651, + 0.153 + ], + "angle": 0, + "content": "Enhanced Stable View Synthesis" + }, + { + "type": "text", + "bbox": [ + 0.173, + 0.181, + 0.414, + 0.251 + ], + "angle": 0, + "content": "Nishant Jain* \nIndian Institute of Technology \nRoorkee, India \nnjain@cs.iitr.ac.in" + }, + { + "type": "text", + "bbox": [ + 0.464, + 0.181, + 0.613, + 0.251 + ], + "angle": 0, + "content": "Suryansh Kumar\\*ETH ZürichSwitzerland sukumar@ethz.ch" + }, + { + "type": "text", + "bbox": [ + 0.656, + 0.182, + 0.792, + 0.251 + ], + "angle": 0, + "content": "Luc Van Gool \nETH Zürich \nSwitzerland \nvangool@ethz.ch" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.286, + 0.314, + 0.303 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.319, + 0.473, + 0.759 + ], + "angle": 0, + "content": "We introduce an approach to enhance the novel view synthesis from images taken from a freely moving camera. The introduced approach focuses on outdoor scenes where recovering accurate geometric scaffold and camera pose is challenging, leading to inferior results using the state-of-the-art stable view synthesis (SVS) method. SVS and related methods fail for outdoor scenes primarily due to (i) overrelying on the multiview stereo (MVS) for geometric scaffold recovery and (ii) assuming COLMAP computed camera poses as the best possible estimates, despite it being well-studied that MVS 3D reconstruction accuracy is limited to scene disparity and camera-pose accuracy is sensitive to key-point correspondence selection. This work proposes a principled way to enhance novel view synthesis solutions drawing inspiration from the basics of multiple view geometry. By leveraging the complementary behavior of MVS and monocular depth, we arrive at a better scene depth per view for nearby and far points, respectively. Moreover, our approach jointly refines camera poses with image-based rendering via multiple rotation averaging graph optimization. The recovered scene depth and the camera-pose help better view-dependent on-surface feature aggregation of the entire scene. Extensive evaluation of our approach on the popular benchmark dataset, such as Tanks and Temples, shows substantial improvement in view synthesis results compared to the prior art. For instance, our method shows \\(1.5\\mathbf{dB}\\) of PSNR improvement on the Tank and Temples. Similar statistics are observed when tested on other benchmark datasets such as FVS, Mip-NeRF 360, and DTU." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.79, + 0.21, + 0.807 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.816, + 0.471, + 0.862 + ], + "angle": 0, + "content": "Image-based rendering, popularly re-branded as view synthesis, is a long-standing problem in computer vision and graphics [42, 44]. This problem aims to develop a" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.288, + 0.893, + 0.636 + ], + "angle": 0, + "content": "method that allows the user to seamlessly explore the scene via rendering of the scene from a sparse set of captured images [2, 20, 42]. Furthermore, the rendered images must be as realistic as possible for a better user experience [34-36]. Currently, among the existing approaches, Riegler and Koltun stable view synthesis (SVS) approach [36] has shown excellent results and demonstrated photorealism in novel view synthesis, without using synthetic gaming engine 3D data, unlike [34]. SVS is indeed stable in rendering photorealistic images from novel viewpoints for large-scale scenes. Yet, it assumes MVS [39, 40] based dense 3D scene reconstruction and camera poses from COLMAP [39] are correct. The off-the-shelf algorithms used for 3D data acquisition and camera poses from images are, of course, popular, and to assume these algorithms could provide favorable 3D reconstruction and camera poses is not an outlandish assumption. Nonetheless, taking a step forward, in this paper, we argue that although choices made by SVS for obtaining geometric scaffold and camera poses in the pursuit of improving view synthesis is commendable, we can do better by making mindful use of fundamentals from multiple-view geometry [11,12] and recent developments in deep-learning techniques for 3D computer vision problems." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.639, + 0.895, + 0.837 + ], + "angle": 0, + "content": "To start with, we would like to emphasize that it is clearly unreasonable, especially in an outdoor setting, to assume that multi-view stereo (MVS) can provide accurate depth for all image pixels. It is natural that pixels with low disparity will not be reconstructed well using state-of-the-art MVS approaches [8, 39, 40, 46]. Even a precise selection of multiple view images with reasonable distance between them (assume good baseline for stereo) may not be helpful due to loss of common scene points visibility, foreshortening issue, etc. [43]. Such issues compel the practitioner to resort to post-processing steps for refining the MVS-based 3D geometry so that it can be helpful for rendering pipeline or neural-rendering network at train time." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Another critical component to view synthesis, which is often brushed aside in the literature is the accurate recovery of the camera poses. In neural view synthesis approaches such as [36], if the camera pose is wrong, the feature ag-" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.875, + 0.341, + 0.901 + ], + "angle": 0, + "content": "*Equal Contribution \n†Corresponding Author (k.sur46@gmail.com)" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "13208" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.092, + 0.905, + 0.201 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.212, + 0.895, + 0.255 + ], + "angle": 0, + "content": "Figure 1. Qualitative comparison. Our result compared to the popular SVS method [36] on the M60 scene of the tanks and temples dataset [18]. It is easy to observe that our approach can better render fine details in the scene. For this scene, the PSNR values for SVS [36] and our method are 19.1 and 20.8, respectively, demonstrating improved PSNR result." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.282, + 0.47, + 0.478 + ], + "angle": 0, + "content": "ggregation corresponding surface points could be misleading, providing inferior results. Therefore, we should have camera poses as accurate as possible. Unfortunately, despite the camera pose importance to this problem, discussion on improving camera pose is often ignored under the assumption that COLMAP [39] provide the best possible camera pose estimates for any possible scenarios. Practically speaking, this is generally not the case for outdoor scenes [5, 11, 15]. What is more surprising is that some recent benchmark datasets put COLMAP recovered poses as the ground-truth poses [33]. Hence, we want to get this out way upfront that a robust and better camera-pose estimates are vital for better modeling view synthesis problem." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.479, + 0.47, + 0.6 + ], + "angle": 0, + "content": "From the above predication, it is apparent that a more mindful approach is required to make view synthesis approaches practically useful, automatic, and valuable for real-world application. To this end, we propose a principled and systematic approach that provides a better geometric scaffold and camera poses for reliable feature aggregation of the scene's surface points, leading to improved novel-view synthesis results enabling superior photorealism." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.601, + 0.469, + 0.751 + ], + "angle": 0, + "content": "In practice, we can have suitable initial camera poses from images using COLMAP. Yet, it must be refined further for improved image-feature aggregation corresponding to 3D surface points for neural rendering. It is well-studied in multiple-view geometry literature that we can improve and refine camera poses just from image key-point correspondences [10, 11]. Accordingly, we introduce a learning-based multiple motion averaging via graph neural network for camera pose recovery, where the pose graph is initialized using COLMAP poses for refinement." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.753, + 0.47, + 0.875 + ], + "angle": 0, + "content": "Meanwhile, it is challenging to accurately recover the 3D geometry of scene points with low or nearly-zero disparity using MVS methods [12, 43]. Another bad news from the theoretical side is that a precise estimation of scene depth from a single image is unlikely1, which is a correct statement and hard to argue. The good news is that advancements in deep-learning-based monocular depth prediction have led to some outstanding results in several practical" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.282, + 0.892, + 0.417 + ], + "angle": 0, + "content": "applications [24, 31]. Thus, at least practically, it seems possible to infer reliable monocular depth estimates up to scale. Using single image depth prediction, we can reason about the depth of scene points with low disparities. So, our proposed strategy is to use confidence based multiple-view stereo 3D that favours pixels with near-to-mid disparity and allows monocular depth estimates for the rest of the pixels. Overall depth is recovered after scaling all the scene depth appropriately using MVS reconstructed metric." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.417, + 0.893, + 0.568 + ], + "angle": 0, + "content": "By encoding the image features via convolutional neural networks, we map the deep features to our estimated 3D geometric scaffold of the scene. Since we have better camera poses and scene reconstruction, we obtain and aggregate accurate feature vectors corresponding to each imaging view-rays—both from the camera to the surface point and from the surface point to viewing image pixels, giving us a feature tensor. We render the new image from the features tensor via a convolutional network and simultaneously refine the camera pose. In summary, our contributions are" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.57, + 0.892, + 0.601 + ], + "angle": 0, + "content": "- A systematic and principled approach for improved stable view synthesis enabling enhanced photorealism." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.601, + 0.892, + 0.676 + ], + "angle": 0, + "content": "- The introduced approach exploits the complementary nature of MVS and monocular depth estimation to recover better 3D geometric scaffold of the scene. Meanwhile, the robust camera poses are recovered using graph neural network based multiple motion averaging." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.676, + 0.892, + 0.722 + ], + "angle": 0, + "content": "- Our approach proposes an improved loss function to jointly optimize and refine for poses, neural image rendering, and scene representation showing superior results." + }, + { + "type": "list", + "bbox": [ + 0.5, + 0.57, + 0.892, + 0.722 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.727, + 0.892, + 0.789 + ], + "angle": 0, + "content": "Our approach when tested on benchmark datasets such as Tank and Temples [18], FVS [35], Mip-NeRF 360 [1], and DTU [16] gives better image based rendering results with generally more than 1 dB PSNR gain (see Fig.1)." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.8, + 0.783, + 0.818 + ], + "angle": 0, + "content": "2. Background and Preliminaries" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.826, + 0.892, + 0.9 + ], + "angle": 0, + "content": "Our work integrates the best of novel view synthesis and multiple view geometry approaches in computer vision in a mindful way. Both novel view synthesis and MVS are classical problems in computer graphics and computer vision, with an exhaustive list of literature. Thus, we confine our re" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.887, + 0.42, + 0.901 + ], + "angle": 0, + "content": "1As several 3D scene points can have same image projection." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "13209" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.168 + ], + "angle": 0, + "content": "lated work discussion to the methods that is directly related to the proposed approach. The interested reader may refer to [4, 8, 12, 28, 38, 42, 44] for earlier and recent progress in these areas. Here, we briefly discuss relevant methods and the current state-of-the-art in neural image-based rendering." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.17, + 0.473, + 0.428 + ], + "angle": 0, + "content": "(i) Uncalibrated Multi-View Stereo. Given the intrinsic camera calibration matrix, we can recover camera poses and the 3D structure of the scene using two or more images [8,21,22,39,40]. One popular and easy-to-use MVS framework is COLMAP [39], which includes several carefully crafted modules to estimate camera poses and sparse 3D structures from images. For camera pose estimation, it uses classical image key-point-based algorithms [13,27,45]. As is known that such methods can provide sub-optimal solutions and may not robustly handle outliers inherent to the unstructured images. Consequently, camera poses recovered using COLMAP can be unreliable, primarily for outdoor scenes. Moreover, since the 3D reconstruction via triangulation uses sparse key points, at best accurate semidense 3D reconstruction of the scene could be recovered. Still, many recent state-of-the-art methods in novel view synthesis heavily rely on it [25,35,36,49]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.43, + 0.473, + 0.596 + ], + "angle": 0, + "content": "(ii) Image-based rendering. Earlier image-based rendering approaches enabled novel view synthesis from images without any 3D scene data under some mild assumptions about the camera, and imaging [9,23,41]. Later with the development of multiple-view stereo approaches and RGBD sensing modalities, several works used some form of 3D data to improve image-based rendering. Popular works along this line include [2,6,14,20,29]. In recent years, neural network-based methods have dominated this field and enabled data-driven approach to this problem with an outstanding level of photorealism [26,34-36,49]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.596, + 0.473, + 0.854 + ], + "angle": 0, + "content": "Among all the current methods we tested, SVS [36] stands out in novel view synthesis from images taken from a freely moving camera. This paper proposes an approach closely related to the SVS pipeline. SVS involves learning a scene representation from images using its dense 3D structure and camera poses predicted via uncalibrated MVS approaches detailed previously. The recovered 3D structure of the scene is post-processed to have a refined geometric scaffold in mesh representation. Using refined scene 3D, it learns a feature representation for a set of images and then projects it along the direction of the target view to be rendered. Finally, SVS involves re-projection from feature to image space resulting in the synthesized image for the target view. Given \\( S \\), the 3D structure for a scene, feature representation network \\( f_{\\theta} \\) with \\( \\theta \\) representing the network parameters, and the rendering network \\( G_{\\mu} \\) with parameters \\( \\mu \\), the resulting image \\( \\mathcal{I}_r \\) along the pose \\( \\mathbf{p} \\) is rendered as" + }, + { + "type": "equation", + "bbox": [ + 0.184, + 0.861, + 0.47, + 0.879 + ], + "angle": 0, + "content": "\\[\n\\mathcal {I} _ {r} = \\mathcal {G} _ {\\mu} \\left(\\phi_ {a} \\left(\\mathcal {S}, \\mathcal {I} _ {s}, \\mathbf {p}, f _ {\\theta}\\right), \\right. \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.886, + 0.472, + 0.902 + ], + "angle": 0, + "content": "where, \\(\\mathcal{I}_s\\) denotes the image set for a given seen. \\(\\phi_{a}()\\) ag-" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.122 + ], + "angle": 0, + "content": "gregates features for all the images along a given direction in \\(\\mathcal{I}_s\\) predicted when passed through \\(f_{\\theta}\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.122, + 0.894, + 0.213 + ], + "angle": 0, + "content": "Contrary to the choices made by the SVS, in this work, we put forward an approach for better estimation of the overall scene 3D geometric scaffold—for both low and high-disparity pixels—and camera poses. Our approach enables a better aggregation of surface features allowing an improved level of realism in novel view synthesis." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.224, + 0.593, + 0.24 + ], + "angle": 0, + "content": "3. Method" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.249, + 0.895, + 0.432 + ], + "angle": 0, + "content": "We begin with a discussion about formulating and estimating a better scene representation by carefully exploiting the complementary behavior of monocular depth and multiview stereo approaches in 3D data acquisition. During our implementation, we use confidence measures for precise reasoning of estimated 3D coming from both the modalities and their accuracy. Next, we detail integrating a camera pose-refining optimization to estimate better camera poses for accurately projecting our 3D scene representation to the target view. Finally, the proposed joint optimization objective to refine structure representation and camera poses simultaneously is discussed." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.439, + 0.611, + 0.453 + ], + "angle": 0, + "content": "3.1. Overview" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.462, + 0.895, + 0.688 + ], + "angle": 0, + "content": "Given a set of source images \\(\\mathcal{I}_s\\) taken from a freely moving camera, the current state-of-the-art SVS [36] first estimates camera-poses \\(\\mathcal{P}\\) and scene 3D structure \\(S\\). Next, it encodes the images via a CNN. Then, using the estimated camera, it maps the encoded features onto the scene 3D scaffold. For each point \\(\\mathbf{x} \\in \\mathbb{R}^3\\) on the scaffold, SVS query set of images in which \\(\\mathbf{x}\\) is visible to obtain its corresponding feature vectors. This feature vector is then conditioned on the output view direction via a network to produce a new feature vector. Such a new feature vector is obtained for all the points on the scaffold to form a feature tensor, which is then decoded using CNN to synthesize the output image. Denoting the complete set of parameters for learning the feature representation and rendering as \\(\\Theta\\), we can write SVS idea as" + }, + { + "type": "equation", + "bbox": [ + 0.577, + 0.696, + 0.892, + 0.713 + ], + "angle": 0, + "content": "\\[\n\\Theta \\sim \\Psi (\\Theta | \\mathcal {S}, \\mathcal {P}, \\mathcal {I} _ {s}) \\circ \\Psi (\\mathcal {S}, \\mathcal {P} | \\mathcal {I} _ {s}). \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.894, + 0.856 + ], + "angle": 0, + "content": "\\(\\Psi(.)\\) symbolizes an abstract functional. Here, \\(S\\) and \\(\\mathcal{P}\\) are estimated using structure from motion and MVS [39, 40]. As mentioned before, we first aim to recover a much better 3D scene recovery by utilizing the complementary nature of the monocular depth and stereo depth. Furthermore, estimate improved camera poses using neural graph-based multiple motion averaging. We denote \\(\\mathcal{D}_s\\) as monocular depth for each image in \\(\\mathcal{I}_s\\) and \\(\\mathcal{S}_R\\), \\(\\mathcal{P}_R\\) as our scene 3D reconstruction and camera poses, respectively." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.856, + 0.894, + 0.901 + ], + "angle": 0, + "content": "Once we estimate \\(S_{R},\\mathcal{P}_{R}\\), we jointly optimize for better neural scene representation and camera poses with the neural network parameters \\(\\Theta\\) using the proposed loss function" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "13210" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.138 + ], + "angle": 0, + "content": "(Sec. 3.3). Our better scene representation and improved camera help in improved view-synthesis at test time. Our overall idea can be understood via the following equation:" + }, + { + "type": "equation", + "bbox": [ + 0.135, + 0.148, + 0.469, + 0.164 + ], + "angle": 0, + "content": "\\[\n\\Theta , \\mathcal {S} _ {R}, \\mathcal {P} _ {R} \\sim \\Psi (\\Theta , \\mathcal {S} _ {R}, \\mathcal {P} _ {R} | \\mathcal {S}, \\mathcal {P}, \\mathcal {D} _ {s}, \\mathcal {I} _ {s}) \\tag {3}\n\\]" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.181, + 0.262, + 0.195 + ], + "angle": 0, + "content": "3.1.1 3D Scene Features" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.204, + 0.469, + 0.341 + ], + "angle": 0, + "content": "Here, we describe feature aggregation for the output view obtained using the SVS pipeline [36] combined with the back-projected RGB-D features due to images and their monocular depth via a convolutional neural network (CNN). Given the output direction \\(\\mathbf{u}\\), for each \\(\\mathbf{x} \\in \\mathbb{R}^3\\) on the geometric scaffold along \\(\\mathbf{u}\\) there is a subset of source images, in which \\(\\mathbf{x}\\) is visible. Assuming the total number of images in this subset to be \\(K\\), we denote the set of view directions corresponding to these images as \\(\\{\\mathbf{v}_k\\}_{k=1}^K\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.343, + 0.469, + 0.45 + ], + "angle": 0, + "content": "(i) SVS Features. The source images in \\(\\mathcal{I}_s\\) are first passed through a feature extraction CNN to obtain a feature tensor \\(\\mathcal{F}_k\\) corresponding to \\(k^{th}\\) image. Denoting \\(f_{k}(\\mathbf{x})\\) as the feature corresponding to a point \\(\\mathbf{x} \\in \\mathbb{R}^3\\) in \\(\\mathcal{F}_k\\) located at the projection (or bilinear interpolation) of \\(\\mathbf{x}\\) on \\(k^{th}\\) image. To this end, SVS [36] proposed the following aggregation function \\((\\phi_a)\\) to compute the feature for \\(\\mathbf{x}\\) along \\(\\mathbf{u}\\)" + }, + { + "type": "equation", + "bbox": [ + 0.095, + 0.459, + 0.469, + 0.5 + ], + "angle": 0, + "content": "\\[\n\\phi_ {a} (\\mathbf {u}, \\left\\{\\left(\\mathbf {v} _ {k}, f _ {k} (\\mathbf {x})\\right) \\right\\}) = \\frac {1}{W} \\sum_ {k = 1} ^ {K} \\max (0, \\mathbf {u} ^ {\\mathrm {T}} \\mathbf {v}) f _ {k} (\\mathbf {x}), \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.51, + 0.468, + 0.529 + ], + "angle": 0, + "content": "where, \\(W = \\sum_{k=1}^{K} \\max(0, \\mathbf{u}^{\\mathrm{T}}\\mathbf{v})\\) is sum of all the weights." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.53, + 0.469, + 0.637 + ], + "angle": 0, + "content": "(ii) Monocular Features. Given an image, we predict its depth with a per-pixel confidence score. For this, we use an existing monocular depth prediction network [32] pretrained on Omnidata [7]. To predict a normalized depth prediction confidence score per pixel \\( w_{ij} \\), we add another network on top of it (refer supplementary for details), which takes both images and depth as input." + }, + { + "type": "equation", + "bbox": [ + 0.085, + 0.646, + 0.469, + 0.679 + ], + "angle": 0, + "content": "\\[\n\\sum_ {i} \\sum_ {j} w _ {i j} \\cdot \\mathcal {L} \\left(d _ {i j}, \\hat {d} _ {i j}\\right); \\text {w h e r e}, w _ {i j} = \\phi_ {w} \\left(\\mathcal {I} _ {s}, \\mathcal {D} _ {s}\\right) _ {i j}. \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.687, + 0.469, + 0.87 + ], + "angle": 0, + "content": "\\(\\mathcal{L}\\) symbolizes the \\(l_{2}\\) loss between the known pixel depth \\(d_{ij}\\) and the predicted depth \\(\\hat{d}_{ij}\\) for \\((i,j)\\) pixel in the 2D depth image. We call network \\(\\phi_w\\) as the \"confidence-prediction head\". We take the depths predicted by this network and fuse them with the source image using the Channel Exchange Network [47]. The fused information is then projected into \\(N\\) dimensional feature space using network \\(\\mathcal{F}_{\\theta}\\), which is a CNN-based architecture. To compute the feature corresponding to a pixel \\(\\mathbf{p}\\) in the target view \\(\\mathbf{u}\\), we warp the features predicted for each source views \\(\\mathbf{v}_k\\) to this target view but now using the monocular depth \\(d \\in \\mathcal{D}_s\\) of the source view." + }, + { + "type": "equation", + "bbox": [ + 0.168, + 0.885, + 0.469, + 0.903 + ], + "angle": 0, + "content": "\\[\ng _ {k} (\\mathbf {u}, \\mathbf {p}) = f _ {k} ^ {m} \\left(\\mathcal {W} (\\mathbf {p}, \\mathbf {u}, \\mathbf {v} _ {k}, d)\\right) \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.092, + 0.892, + 0.183 + ], + "angle": 0, + "content": "where, \\( g_{k} \\) denotes the feature warping function, \\( f_{k}^{m}(p) \\) corresponds to feature in the tensor \\( \\mathcal{F}_{\\theta}(\\mathcal{T}_s^k,d) \\) (corresponding to \\( k^{th} \\) source image and corresponding monocular depth) at pixel \\( \\mathbf{p} \\), and \\( \\mathcal{W} \\) is the warping function. We now aggregate the warped features corresponding to each source image using a weighted sum based on confidence scores:" + }, + { + "type": "equation", + "bbox": [ + 0.557, + 0.191, + 0.892, + 0.233 + ], + "angle": 0, + "content": "\\[\n\\phi_ {a} (\\mathbf {u}, \\left\\{\\left(\\mathbf {v} _ {k}, f _ {k} ^ {m} (\\mathbf {p})\\right) \\right\\}) = \\sum_ {k = 1} ^ {K} c _ {k} (\\mathbf {p}) f _ {k} ^ {m} (\\mathbf {p}) \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.24, + 0.892, + 0.269 + ], + "angle": 0, + "content": "here, \\( c_k \\) symbolizes the predicted depth confidence map in the \\( k^{th} \\) view." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.274, + 0.892, + 0.41 + ], + "angle": 0, + "content": "(iii) Structure Feature Aggregation Per Scene Point. Given we have features from two different modalities i.e., monocular depth and MVS, we now propose an aggregated feature representation for the target view per scene point \\( h_f = h_\\theta(h_m, h_s) \\), where \\( h_\\theta \\) is a CNN-based neural network with parameters \\( \\theta \\) and \\( h_m \\) is the final representation for the monocular estimation and \\( h_s \\) for the stereo-estimation. We aim to attain maximal correlation from both of the input representations i.e.," + }, + { + "type": "equation", + "bbox": [ + 0.508, + 0.419, + 0.892, + 0.437 + ], + "angle": 0, + "content": "\\[\n\\lambda_ {1} \\mathcal {C} \\left(h _ {f}, h _ {m}\\right) \\cdot \\mathcal {C} \\left(h _ {f}, h _ {s}\\right) + \\lambda_ {2} \\mathcal {C} \\left(h _ {f}, h _ {s}\\right) + \\lambda_ {3} \\mathcal {C} \\left(h _ {f}, h _ {m}\\right) \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.445, + 0.892, + 0.673 + ], + "angle": 0, + "content": "where, \\(\\sum_{i=1}^{3} \\lambda_i = 1\\); \\(\\lambda_i > 0 \\forall i \\in \\{1,2,3\\}\\) and \\(\\mathcal{C}(.)\\) being the standard correlation function [3]. We set \\(\\lambda_1 = 1\\) for nearby points where confidence of monocular depth could be greater than a defined threshold (\\(\\tau\\)). \\(\\lambda_2 = 1\\) for nearby points where confidence of monocular depth is lower than a defined threshold and finally \\(\\lambda_3 = 1\\) for far points whose relative depth is greater than a pre-defined threshold (\\(\\sigma\\)). Such a choice is made since stereo features might be less accurate in certain depth range due to low disparity or too close to the lens. The final aggregation \\(h_f\\) comprises of CNN networks \\(\\phi_\\alpha\\) and \\(\\phi_\\beta\\), parameterized by \\(\\alpha\\) and \\(\\beta\\), respectively. The transformed features from each of these modalities are then fed to a CNN network \\(\\phi_\\nu\\) with parameters \\(\\nu\\). Overall aggregated features per scene point is represented as" + }, + { + "type": "equation", + "bbox": [ + 0.553, + 0.683, + 0.892, + 0.7 + ], + "angle": 0, + "content": "\\[\nh _ {f} = h _ {\\theta} \\left(h _ {m}, h _ {s}\\right) = \\phi_ {\\nu} \\left(\\phi_ {\\alpha} \\left(h _ {m}\\right), \\phi_ {\\beta} \\left(h _ {s}\\right)\\right). \\tag {9}\n\\]" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.726, + 0.726, + 0.74 + ], + "angle": 0, + "content": "3.1.2 Camera Pose Estimation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.75, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Given we have initially estimated pose-set \\(\\mathcal{P}\\), we use multiple motion averaging (MRA) to recover better camera poses. MRA is fast, efficient, and robust in camera pose estimation from noisy key-point correspondences and works well even for sparse image sets. MRA takes a global view of the camera recovery problem. A view-graph corresponding to the initial set of camera poses is constructed as a global representation, with each graph node as a pose. For pose optimization, MRA first performs rotation averaging to recover rotation and then solves for translation. Assume a" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "13211" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.1, + 0.089, + 0.875, + 0.399 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.413, + 0.895, + 0.5 + ], + "angle": 0, + "content": "Figure 2. Overview. For a given set of input images, we first estimate the scene 3D structure and the initial value of camera poses using structure from motion (SFM) followed by MVS. We also estimate per-image depth using an existing Monocular Depth estimation model [7]. Next, we generate two sets of Projected Features for each target view: The first set (upper stream) by encoding the input images and then unprojecting the features onto the scaffold, followed by re-projection to the target view and aggregation. For the second set (lower stream), the images are first concatenated with their monocular depths (MD), and the encoded features are then projected using these depths, followed by aggregation. These two feature sets are then merged into Cumulative Features, and finally, the target view is rendered." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.523, + 0.473, + 0.648 + ], + "angle": 0, + "content": "directed view-graph \\(\\mathcal{G} = (\\mathcal{V},\\mathcal{E})\\). A vertex \\(\\mathcal{V}_j\\in \\mathcal{V}\\) in this view graph corresponds to \\(j^{th}\\) camera absolute rotation \\(R_{j}\\) and \\(\\mathcal{E}_{ij}\\in \\mathcal{E}\\) corresponds to the relative orientation \\(\\tilde{R}_{ij}\\) between view \\(i\\) and \\(j\\). For our problem, relative orientations are given (noisy), and we aim to solve for absolute pose \\(R_{j}\\) robustly. Conventionally, in the presence of noise, the solution is obtained by solving the following optimization problem to satisfy compatibility criteria." + }, + { + "type": "equation", + "bbox": [ + 0.162, + 0.656, + 0.47, + 0.693 + ], + "angle": 0, + "content": "\\[\n\\underset {\\{R _ {j} \\}} {\\operatorname {a r g m i n}} \\sum_ {\\mathcal {E} _ {i j} \\in \\mathcal {E}} \\rho (\\gamma (\\tilde {R} _ {i j}, R _ {j} R _ {i} ^ {- 1})) \\tag {10}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.702, + 0.473, + 0.84 + ], + "angle": 0, + "content": "where, \\(\\gamma(.)\\) denotes a metric on \\(SO(3)\\) to measure distance between two rotation and \\(\\rho(.)\\) is a robust \\(l_1\\) norm. We use a graph-neural network to predict the robustified pose view-graph of the scene following the camera pose refining approach of NeuRoRA [30]. First, the camera poses are checked for outliers via a cyclic consistency in the posegraph [11]. Then, a view graph is initialized based on these filtered poses. This view graph is then optimized using the camera pose-refining network of NeuRoRA [30]." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.848, + 0.288, + 0.865 + ], + "angle": 0, + "content": "3.2. Rendering novel views" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.871, + 0.472, + 0.903 + ], + "angle": 0, + "content": "The aggregated feature tensor \\(\\mathcal{F}^a\\) along a direction \\(\\mathbf{u}\\) comprises of the features \\(h_f\\) (Eq. 9) for each pixel along \\(\\mathbf{u}\\)," + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.523, + 0.892, + 0.661 + ], + "angle": 0, + "content": "obtained using 3D scene features (discussed in Sec. 3.1.1). This tensor is now projected to the image space function using \\(\\mathcal{G}_{\\theta}\\), a CNN-based network with parameters \\(\\theta\\). It is quite possible that the regions in the target image may not be encountered in any of the source images. For those points, the values in feature tensor \\(\\mathcal{F}\\) are set to \\(\\mathbf{0}\\), and thus, they require some inpainting. Denoting the set of test images by \\(\\mathcal{I}_t\\), the rendered image corresponding to the \\(k^{th}\\) image in the test set, \\(\\hat{\\mathcal{I}}_t^k\\), is predicted based on the following equation:" + }, + { + "type": "equation", + "bbox": [ + 0.647, + 0.673, + 0.891, + 0.693 + ], + "angle": 0, + "content": "\\[\n\\hat {\\mathcal {I}} _ {t} ^ {k} = \\mathcal {G} _ {\\theta} \\left(\\mathcal {F} _ {k} ^ {a}\\right) \\tag {11}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.696, + 0.894, + 0.772 + ], + "angle": 0, + "content": "Similar to stable view synthesis, we parameterize the \\(\\mathcal{G}_{\\theta}\\) function using a U-Net [37] style model which also deals with inpainting/hallucinating the newly discovered regions in the test image. Fig.(2) shows the complete overview of the proposed method." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.779, + 0.682, + 0.796 + ], + "angle": 0, + "content": "3.3. Joint Optimization" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.802, + 0.893, + 0.833 + ], + "angle": 0, + "content": "Given \\(\\mathcal{I}_s\\), we train the model using our overall loss function \\(\\mathcal{L}\\) comprising of two terms." + }, + { + "type": "equation", + "bbox": [ + 0.649, + 0.847, + 0.892, + 0.865 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} = \\mathcal {L} _ {s} + \\mathcal {L} _ {p} \\tag {12}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.871, + 0.894, + 0.903 + ], + "angle": 0, + "content": "(i) The first loss term \\(\\mathcal{L}_s\\) encourages the network to learn better features corresponding to the scene point. The \\(\\mathcal{L}_s\\)" + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "13212" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.082, + 0.088, + 0.891, + 0.187 + ], + "angle": 0, + "content": "
TruckM60PlaygroundTrain
PSNR↑LPIPS↓SSIM↑PSNR↑LPIPS↓SSIM↑PSNR↑LPIPS↓SSIM↑PSNR↑LPIPS↓SSIM↑
NeRF++ [49]21.80.310.8117.60.430.7321.90.390.7917.60.480.68
FVS [35]21.90.140.8415.80.320.7721.70.210.8317.30.280.75
SC-NeRF [17]22.30.290.8218.40.400.7622.40.350.8318.20.420.73
Point-NeRF [48]22.70.140.8719.60.210.8522.20.190.8318.60.160.83
SVS [36]22.90.120.8819.10.220.8322.90.170.8617.90.190.81
Ours24.10.120.9020.80.200.8923.90.140.9020.10.130.88
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.195, + 0.893, + 0.224 + ], + "angle": 0, + "content": "Table 1. Rendered image quality comparison with current state-of-the-art methods in novel view synthesis on the popular Tanks and Temples dataset [18]. We use the popular metrics i.e., PSNR, LPIPS and SSIM for the comparison." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.236, + 0.891, + 0.312 + ], + "angle": 0, + "content": "
BikeFlowersPirateDiggerSandboxSoccertable
SSIM↑LPIPS↓SSIM↑LPIPS↓SSIM↑LPIPS↓SSIM↑LPIPS↓SSIM↑LPIPS↓SSIM↑LPIPS↓
NeRF++ [49]0.710.270.800.310.710.430.650.350.840.240.870.21
FVS [35]0.610.280.790.270.690.370.680.240.780.320.820.21
SVS [36]0.740.220.840.210.750.320.770.180.850.200.910.15
Ours0.790.190.880.180.800.290.810.160.910.170.940.13
" + }, + { + "type": "table_caption", + "bbox": [ + 0.091, + 0.321, + 0.877, + 0.337 + ], + "angle": 0, + "content": "Table 2. Quantitative comparison on FVS dataset [35]. We use the popular metrics, i.e., PSNR, LPIPS and SSIM for the comparison." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.362, + 0.47, + 0.483 + ], + "angle": 0, + "content": "comprises to two objective function \\(\\mathcal{L}_{rgb}\\) and \\(\\mathcal{L}_{corr}\\). The function \\(\\mathcal{L}_{rgb}\\) measures the discrepancies between the rendering of an image in the source set and the actual image available in the set. This objective is used to train the structure estimation and rendering network parameters jointly. Whereas \\(\\mathcal{L}_{corr}\\) is used for maximizing the correlation objective discussed in Eq.(8) to arrive at the optimal aggregated scene representation." + }, + { + "type": "equation", + "bbox": [ + 0.198, + 0.498, + 0.469, + 0.515 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {s} = \\mathcal {L} _ {r g b} + \\mathcal {L} _ {c o r r} \\tag {13}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.52, + 0.469, + 0.596 + ], + "angle": 0, + "content": "\\(\\mathcal{L}_{corr}\\) takes the negative of the objective defined in Eq.(8). The structure network parameters corresponding to functions \\(f_{k}\\) and \\(f_{k}^{m}\\) (cf. Sec. 3.1.1) and is updated using \\(\\mathcal{L}_{corr}\\) and \\(\\mathcal{L}_{rgb}\\). The rendering network parameters corresponding to \\(\\mathcal{G}_{\\theta}\\) updated using only \\(\\mathcal{L}_{rgb}\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.598, + 0.469, + 0.643 + ], + "angle": 0, + "content": "(ii) The second loss term \\(\\mathcal{L}_p\\) corresponds to the camera pose refinement. We used the following loss \\(\\mathcal{L}_p\\) to improve the camera pose estimation." + }, + { + "type": "equation", + "bbox": [ + 0.232, + 0.653, + 0.469, + 0.671 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {p} = \\mathcal {L} _ {m r a} \\tag {14}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.679, + 0.469, + 0.754 + ], + "angle": 0, + "content": "As is known, the multiple motion averaging and the color rendering cost functions are directly impacted by the camera pose parameters. And therefore, the \\(\\mathcal{L}_{rgb}\\) is inherently used as an intermediate objective in which the camera pose term is constant between the two different representations." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.767, + 0.402, + 0.784 + ], + "angle": 0, + "content": "4. Experiments, Results and Ablations" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.792, + 0.469, + 0.868 + ], + "angle": 0, + "content": "Here, we discuss our experimental results and their comparison to relevant baselines. Later, we provide critical ablation analysis, a study of our camera pose estimation idea, and 3D structure recovery. Finally, the section concludes with a discussion of a few extensions of our approach2." + }, + { + "type": "page_footnote", + "bbox": [ + 0.076, + 0.875, + 0.469, + 0.901 + ], + "angle": 0, + "content": "2Please refer supplementary for the train-test setup, implementation details regarding hyperparameters, and architectures to reproduce our results." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.362, + 0.892, + 0.469 + ], + "angle": 0, + "content": "Baselines. We compare our approach with the recently proposed novel view synthesis methods that work well in practice for real-world scenes. Our baseline list includes NeRF++ [49], SC-NeRF [17], PointNeRF [48], FVS [35] and SVS [36]. All baseline methods are trained on the source image set of the testing sequence. Our method's train and test set are the same as SVS [36]." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.478, + 0.688, + 0.492 + ], + "angle": 0, + "content": "4.1. Dataset and Results" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.501, + 0.892, + 0.637 + ], + "angle": 0, + "content": "For evaluation, we used popular benchmark datasets comprising real-world and synthetic datasets. Namely, we used the Tanks and Temples [18], FVS [35], Mip-NeRF 360 [1], and the DTU [16] dataset. The first two datasets contain real-world scenes, whereas the last is an object-centric synthetic benchmark dataset. Although our approach mainly targets realistic scenes, for completeness, we performed and tabulated results on a synthetic object-based DTU dataset (see supplementary). Next, we discuss datasets and results." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.64, + 0.893, + 0.882 + ], + "angle": 0, + "content": "(i) Tanks and Temples Dataset. It consists of images of large-scale real-world scenes taken from a freely moving camera, consisting of indoor and outdoor scenes. Unfortunately, we have no ground-truth poses; thus, estimated poses using COLMAP [39] are treated as pseudo-ground-truth poses. The dataset consists of a total of 21 scenes. Similar to the SVS setup, we use 15 of 21 scenes for training, 2 for validation, and the rest as test scenes. We also use a disjoint set of target views from the test scenes to evaluate all the methods. The source views in test scenes are used for scene-specific fine-tuning if required. Table 1 shows the statistical comparison of our approach with competing baselines. Our approach consistently outperforms the relevant baselines on this challenging dataset. Furthermore, if we zoom into the scene's finer details, our approach clearly preserves details better than other approaches (see Fig. 3)." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.886, + 0.892, + 0.901 + ], + "angle": 0, + "content": "(ii) FVS Dataset. It comprises six real-world scenes. Each" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "13213" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.118, + 0.09, + 0.493, + 0.488 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.499, + 0.091, + 0.849, + 0.485 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.498, + 0.893, + 0.542 + ], + "angle": 0, + "content": "Figure 3. Qualitative comparison on tanks and temples dataset. If we zoom into the scene details, our approach results show considerably less artifacts than the state-of-the-art methods enabling unparalleled level of realism in image-based rendering. Our PSNR values for the above two scenes are (20.1, 23.9). In comparison, SC-NeRF [17] and SVS [36] provide (17.3, 22.4) and (17.9, 22.9), respectively." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.567, + 0.473, + 0.734 + ], + "angle": 0, + "content": "scene was recorded two or more times to completely differentiate the source image set to form the target image set. Table 2 summarises this dataset's view synthesis quantitative results. We compare our method with the state-of-the-art \\(\\mathrm{NeRF}++\\) [49], Free-View synthesis [35], and SVS [36] methods. We observe that FVS improves over \\(\\mathrm{NeRF}++\\), whereas SVS results on this dataset do not consistently outperform other previous methods. On the contrary, our method consistently provides better results than prior art in all categories. The dataset's sample images and its qualitative results are provided in the supplementary." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.78, + 0.47, + 0.903 + ], + "angle": 0, + "content": "(iii) Mip-NeRF 360 Dataset. We further test our approach on this recently proposed dataset comprising unbounded scenes [1]. We use the train-test setup per scene proposed by the authors to fine-tune our network and compare it with Mip-NeRF 360 [1], \\(\\mathrm{NeRF}++\\) [49], and SVS [36] baseline. Table 3 shows the results for this comparison. Clearly, our methodical take on this problem generalizes well, outperforming other baseline methods for most examples." + }, + { + "type": "table", + "bbox": [ + 0.547, + 0.564, + 0.848, + 0.641 + ], + "angle": 0, + "content": "
PSNR↑LPIPS↓SSIM↑
NeRF++ [49]25.030.3550.682
SVS [36]25.280.2180.783
PBNR [19]23.550.2620.722
Mip-NeRF 360 [1]27.070.2510.781
Ours27.950.2320.797
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.651, + 0.892, + 0.68 + ], + "angle": 0, + "content": "Table 3. Quantitative comparison of our approach with existing baselines on the Mip-NeRF 360 dataset." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.707, + 0.673, + 0.723 + ], + "angle": 0, + "content": "4.2. Ablation Analysis" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.735, + 0.892, + 0.901 + ], + "angle": 0, + "content": "(i) Effect of our camera-pose estimation approach. We performed this experiment to show the benefit of using multiple motion averaging (MRA) instead of relying only on COLMAP poses and taking them for granted. For this experiment, we used the popular Lego dataset [25]. We first compute the COLMAP camera poses shown in Fig.4 (Left). Next, we use this initial camera pose set to perform MRA utilizing the view-graph optimization. Our recovered camera poses are shown in Fig.4 (Right). For clarity, we also show the ground-truth camera pose frustum and the error between the ground-truth pose and recovered pose for the" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "13214" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.101, + 0.262, + 0.198 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.274, + 0.101, + 0.454, + 0.197 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.212, + 0.47, + 0.275 + ], + "angle": 0, + "content": "Figure 4. COLMAP [39] and our method's camera poses on Lego dataset [25]. Here, we add some noise to the pairwise matched correspondences to simulate realistic scenarios. Left: Estimated camera pose from COLMAP and the ground truth pose. Here, black line shows the pose error. Right: Our recovered camera pose. It is easy to infer our approach robustness." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.303, + 0.471, + 0.469 + ], + "angle": 0, + "content": "two respective cases. It is clear from Fig.(4) that a principled approach is required for better camera-pose recovery in view-synthesis problem. Furthermore, to show the benefit of our estimated camera pose in novel-view synthesis, we show our network training loss curve with and without our camera pose estimation approach in Fig.(5). For clarity, we also plot the SVS training curve. Firstly, our method shows better loss response due to the improved 3D geometric scaffold of the scene. Moreover, we improve on training loss further by introducing neural graph-based MRA, showing the benefit of our proposed loss function." + }, + { + "type": "image", + "bbox": [ + 0.107, + 0.487, + 0.44, + 0.657 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.67, + 0.47, + 0.698 + ], + "angle": 0, + "content": "Figure 5. Training loss curve of our method with and without pose optimization compared to state-of-the-art SVS [36]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.72, + 0.471, + 0.902 + ], + "angle": 0, + "content": "(ii) Effect of using MVS with monocular depth. We performed this ablation to demonstrate the effectiveness of our approach in recovering geometric reconstruction of the scene. Fig.(6) clearly shows the complementary nature of the monocular depth and stereo depth in 3D reconstruction from images. While MVS provides reliable depth results for near and mid-range points, monocular depth can deliver a good depth inference (up to scale) on the far points in the scene. By carefully integrating both modalities' depth, we have better 3D information about the scene. Fig.(6) shows our results on a couple of scenes from Tanks and Temples dataset, demonstrating the suitability of our approach." + }, + { + "type": "image", + "bbox": [ + 0.522, + 0.098, + 0.866, + 0.493 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.5, + 0.505, + 0.892, + 0.534 + ], + "angle": 0, + "content": "Figure 6. Comparison of depth predicted by monocular and stereo based method on the scenes from Tanks and Temples dataset." + }, + { + "type": "title", + "bbox": [ + 0.501, + 0.569, + 0.619, + 0.584 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.599, + 0.892, + 0.901 + ], + "angle": 0, + "content": "The approach presented in this paper directly addresses the shortcomings of the currently popular methods in novel view synthesis. Our approach integrates concepts from the learning-based approaches and classical techniques in multiple-view geometry for solving novel-view synthesis. We demonstrate that by exploiting the \\((i)\\) complementary nature of monocular depth estimation and multiple view stereo (MVS) in the 3D reconstruction of the scene, and \\((ii)\\) usefulness of multiple rotation averaging in structure from motion, we can achieve better-rendering quality than other dominant approaches in novel view synthesis. We confirm the effectiveness of our approach via a comprehensive evaluation and quantitative comparison with baselines on several benchmark datasets. Although our work enabled improved photorealistic rendering, several exciting avenues exist for further improvement. One interesting future extension is fully automating our introduced view synthesis pipeline, i.e., adding a learnable MVS framework to estimate intrinsic, extrinsic camera parameters with scene reconstruction for better novel view synthesis." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "13215" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.117, + 0.47, + 0.186 + ], + "angle": 0, + "content": "[1] Jonathan T Barron, Ben Mildenhall, Dor Verbin, Pratul P Srinivasan, and Peter Hedman. Mip-nerf 360: Unbounded anti-aliased neural radiance fields. 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The introduced approach focuses on outdoor scenes where recovering accurate geometric scaffold and camera pose is challenging, leading to inferior results using the state-of-the-art stable view synthesis (SVS) method. SVS and related methods fail for outdoor scenes primarily due to (i) overrelying on the multiview stereo (MVS) for geometric scaffold recovery and (ii) assuming COLMAP computed camera poses as the best possible estimates, despite it being well-studied that MVS 3D reconstruction accuracy is limited to scene disparity and camera-pose accuracy is sensitive to key-point correspondence selection. This work proposes a principled way to enhance novel view synthesis solutions drawing inspiration from the basics of multiple view geometry. By leveraging the complementary behavior of MVS and monocular depth, we arrive at a better scene depth per view for nearby and far points, respectively. Moreover, our approach jointly refines camera poses with image-based rendering via multiple rotation averaging graph optimization. The recovered scene depth and the camera-pose help better view-dependent on-surface feature aggregation of the entire scene. Extensive evaluation of our approach on the popular benchmark dataset, such as Tanks and Temples, shows substantial improvement in view synthesis results compared to the prior art. For instance, our method shows $1.5\mathbf{dB}$ of PSNR improvement on the Tank and Temples. Similar statistics are observed when tested on other benchmark datasets such as FVS, Mip-NeRF 360, and DTU. + +# 1. Introduction + +Image-based rendering, popularly re-branded as view synthesis, is a long-standing problem in computer vision and graphics [42, 44]. This problem aims to develop a + +method that allows the user to seamlessly explore the scene via rendering of the scene from a sparse set of captured images [2, 20, 42]. Furthermore, the rendered images must be as realistic as possible for a better user experience [34-36]. Currently, among the existing approaches, Riegler and Koltun stable view synthesis (SVS) approach [36] has shown excellent results and demonstrated photorealism in novel view synthesis, without using synthetic gaming engine 3D data, unlike [34]. SVS is indeed stable in rendering photorealistic images from novel viewpoints for large-scale scenes. Yet, it assumes MVS [39, 40] based dense 3D scene reconstruction and camera poses from COLMAP [39] are correct. The off-the-shelf algorithms used for 3D data acquisition and camera poses from images are, of course, popular, and to assume these algorithms could provide favorable 3D reconstruction and camera poses is not an outlandish assumption. Nonetheless, taking a step forward, in this paper, we argue that although choices made by SVS for obtaining geometric scaffold and camera poses in the pursuit of improving view synthesis is commendable, we can do better by making mindful use of fundamentals from multiple-view geometry [11,12] and recent developments in deep-learning techniques for 3D computer vision problems. + +To start with, we would like to emphasize that it is clearly unreasonable, especially in an outdoor setting, to assume that multi-view stereo (MVS) can provide accurate depth for all image pixels. It is natural that pixels with low disparity will not be reconstructed well using state-of-the-art MVS approaches [8, 39, 40, 46]. Even a precise selection of multiple view images with reasonable distance between them (assume good baseline for stereo) may not be helpful due to loss of common scene points visibility, foreshortening issue, etc. [43]. Such issues compel the practitioner to resort to post-processing steps for refining the MVS-based 3D geometry so that it can be helpful for rendering pipeline or neural-rendering network at train time. + +Another critical component to view synthesis, which is often brushed aside in the literature is the accurate recovery of the camera poses. In neural view synthesis approaches such as [36], if the camera pose is wrong, the feature ag- + +![](images/afa88c39f10e95619f038cb454706670e69a3fb4b7bc6ba18491a3fb7bdc34f2.jpg) +Figure 1. Qualitative comparison. Our result compared to the popular SVS method [36] on the M60 scene of the tanks and temples dataset [18]. It is easy to observe that our approach can better render fine details in the scene. For this scene, the PSNR values for SVS [36] and our method are 19.1 and 20.8, respectively, demonstrating improved PSNR result. + +ggregation corresponding surface points could be misleading, providing inferior results. Therefore, we should have camera poses as accurate as possible. Unfortunately, despite the camera pose importance to this problem, discussion on improving camera pose is often ignored under the assumption that COLMAP [39] provide the best possible camera pose estimates for any possible scenarios. Practically speaking, this is generally not the case for outdoor scenes [5, 11, 15]. What is more surprising is that some recent benchmark datasets put COLMAP recovered poses as the ground-truth poses [33]. Hence, we want to get this out way upfront that a robust and better camera-pose estimates are vital for better modeling view synthesis problem. + +From the above predication, it is apparent that a more mindful approach is required to make view synthesis approaches practically useful, automatic, and valuable for real-world application. To this end, we propose a principled and systematic approach that provides a better geometric scaffold and camera poses for reliable feature aggregation of the scene's surface points, leading to improved novel-view synthesis results enabling superior photorealism. + +In practice, we can have suitable initial camera poses from images using COLMAP. Yet, it must be refined further for improved image-feature aggregation corresponding to 3D surface points for neural rendering. It is well-studied in multiple-view geometry literature that we can improve and refine camera poses just from image key-point correspondences [10, 11]. Accordingly, we introduce a learning-based multiple motion averaging via graph neural network for camera pose recovery, where the pose graph is initialized using COLMAP poses for refinement. + +Meanwhile, it is challenging to accurately recover the 3D geometry of scene points with low or nearly-zero disparity using MVS methods [12, 43]. Another bad news from the theoretical side is that a precise estimation of scene depth from a single image is unlikely1, which is a correct statement and hard to argue. The good news is that advancements in deep-learning-based monocular depth prediction have led to some outstanding results in several practical + +applications [24, 31]. Thus, at least practically, it seems possible to infer reliable monocular depth estimates up to scale. Using single image depth prediction, we can reason about the depth of scene points with low disparities. So, our proposed strategy is to use confidence based multiple-view stereo 3D that favours pixels with near-to-mid disparity and allows monocular depth estimates for the rest of the pixels. Overall depth is recovered after scaling all the scene depth appropriately using MVS reconstructed metric. + +By encoding the image features via convolutional neural networks, we map the deep features to our estimated 3D geometric scaffold of the scene. Since we have better camera poses and scene reconstruction, we obtain and aggregate accurate feature vectors corresponding to each imaging view-rays—both from the camera to the surface point and from the surface point to viewing image pixels, giving us a feature tensor. We render the new image from the features tensor via a convolutional network and simultaneously refine the camera pose. In summary, our contributions are + +- A systematic and principled approach for improved stable view synthesis enabling enhanced photorealism. +- The introduced approach exploits the complementary nature of MVS and monocular depth estimation to recover better 3D geometric scaffold of the scene. Meanwhile, the robust camera poses are recovered using graph neural network based multiple motion averaging. +- Our approach proposes an improved loss function to jointly optimize and refine for poses, neural image rendering, and scene representation showing superior results. + +Our approach when tested on benchmark datasets such as Tank and Temples [18], FVS [35], Mip-NeRF 360 [1], and DTU [16] gives better image based rendering results with generally more than 1 dB PSNR gain (see Fig.1). + +# 2. Background and Preliminaries + +Our work integrates the best of novel view synthesis and multiple view geometry approaches in computer vision in a mindful way. Both novel view synthesis and MVS are classical problems in computer graphics and computer vision, with an exhaustive list of literature. Thus, we confine our re + +lated work discussion to the methods that is directly related to the proposed approach. The interested reader may refer to [4, 8, 12, 28, 38, 42, 44] for earlier and recent progress in these areas. Here, we briefly discuss relevant methods and the current state-of-the-art in neural image-based rendering. + +(i) Uncalibrated Multi-View Stereo. Given the intrinsic camera calibration matrix, we can recover camera poses and the 3D structure of the scene using two or more images [8,21,22,39,40]. One popular and easy-to-use MVS framework is COLMAP [39], which includes several carefully crafted modules to estimate camera poses and sparse 3D structures from images. For camera pose estimation, it uses classical image key-point-based algorithms [13,27,45]. As is known that such methods can provide sub-optimal solutions and may not robustly handle outliers inherent to the unstructured images. Consequently, camera poses recovered using COLMAP can be unreliable, primarily for outdoor scenes. Moreover, since the 3D reconstruction via triangulation uses sparse key points, at best accurate semidense 3D reconstruction of the scene could be recovered. Still, many recent state-of-the-art methods in novel view synthesis heavily rely on it [25,35,36,49]. + +(ii) Image-based rendering. Earlier image-based rendering approaches enabled novel view synthesis from images without any 3D scene data under some mild assumptions about the camera, and imaging [9,23,41]. Later with the development of multiple-view stereo approaches and RGBD sensing modalities, several works used some form of 3D data to improve image-based rendering. Popular works along this line include [2,6,14,20,29]. In recent years, neural network-based methods have dominated this field and enabled data-driven approach to this problem with an outstanding level of photorealism [26,34-36,49]. + +Among all the current methods we tested, SVS [36] stands out in novel view synthesis from images taken from a freely moving camera. This paper proposes an approach closely related to the SVS pipeline. SVS involves learning a scene representation from images using its dense 3D structure and camera poses predicted via uncalibrated MVS approaches detailed previously. The recovered 3D structure of the scene is post-processed to have a refined geometric scaffold in mesh representation. Using refined scene 3D, it learns a feature representation for a set of images and then projects it along the direction of the target view to be rendered. Finally, SVS involves re-projection from feature to image space resulting in the synthesized image for the target view. Given $S$ , the 3D structure for a scene, feature representation network $f_{\theta}$ with $\theta$ representing the network parameters, and the rendering network $G_{\mu}$ with parameters $\mu$ , the resulting image $\mathcal{I}_r$ along the pose $\mathbf{p}$ is rendered as + +$$ +\mathcal {I} _ {r} = \mathcal {G} _ {\mu} \left(\phi_ {a} \left(\mathcal {S}, \mathcal {I} _ {s}, \mathbf {p}, f _ {\theta}\right), \right. \tag {1} +$$ + +where, $\mathcal{I}_s$ denotes the image set for a given seen. $\phi_{a}()$ ag- + +gregates features for all the images along a given direction in $\mathcal{I}_s$ predicted when passed through $f_{\theta}$ . + +Contrary to the choices made by the SVS, in this work, we put forward an approach for better estimation of the overall scene 3D geometric scaffold—for both low and high-disparity pixels—and camera poses. Our approach enables a better aggregation of surface features allowing an improved level of realism in novel view synthesis. + +# 3. Method + +We begin with a discussion about formulating and estimating a better scene representation by carefully exploiting the complementary behavior of monocular depth and multiview stereo approaches in 3D data acquisition. During our implementation, we use confidence measures for precise reasoning of estimated 3D coming from both the modalities and their accuracy. Next, we detail integrating a camera pose-refining optimization to estimate better camera poses for accurately projecting our 3D scene representation to the target view. Finally, the proposed joint optimization objective to refine structure representation and camera poses simultaneously is discussed. + +# 3.1. Overview + +Given a set of source images $\mathcal{I}_s$ taken from a freely moving camera, the current state-of-the-art SVS [36] first estimates camera-poses $\mathcal{P}$ and scene 3D structure $S$ . Next, it encodes the images via a CNN. Then, using the estimated camera, it maps the encoded features onto the scene 3D scaffold. For each point $\mathbf{x} \in \mathbb{R}^3$ on the scaffold, SVS query set of images in which $\mathbf{x}$ is visible to obtain its corresponding feature vectors. This feature vector is then conditioned on the output view direction via a network to produce a new feature vector. Such a new feature vector is obtained for all the points on the scaffold to form a feature tensor, which is then decoded using CNN to synthesize the output image. Denoting the complete set of parameters for learning the feature representation and rendering as $\Theta$ , we can write SVS idea as + +$$ +\Theta \sim \Psi (\Theta | \mathcal {S}, \mathcal {P}, \mathcal {I} _ {s}) \circ \Psi (\mathcal {S}, \mathcal {P} | \mathcal {I} _ {s}). \tag {2} +$$ + +$\Psi(.)$ symbolizes an abstract functional. Here, $S$ and $\mathcal{P}$ are estimated using structure from motion and MVS [39, 40]. As mentioned before, we first aim to recover a much better 3D scene recovery by utilizing the complementary nature of the monocular depth and stereo depth. Furthermore, estimate improved camera poses using neural graph-based multiple motion averaging. We denote $\mathcal{D}_s$ as monocular depth for each image in $\mathcal{I}_s$ and $\mathcal{S}_R$ , $\mathcal{P}_R$ as our scene 3D reconstruction and camera poses, respectively. + +Once we estimate $S_{R},\mathcal{P}_{R}$ , we jointly optimize for better neural scene representation and camera poses with the neural network parameters $\Theta$ using the proposed loss function + +(Sec. 3.3). Our better scene representation and improved camera help in improved view-synthesis at test time. Our overall idea can be understood via the following equation: + +$$ +\Theta , \mathcal {S} _ {R}, \mathcal {P} _ {R} \sim \Psi (\Theta , \mathcal {S} _ {R}, \mathcal {P} _ {R} | \mathcal {S}, \mathcal {P}, \mathcal {D} _ {s}, \mathcal {I} _ {s}) \tag {3} +$$ + +# 3.1.1 3D Scene Features + +Here, we describe feature aggregation for the output view obtained using the SVS pipeline [36] combined with the back-projected RGB-D features due to images and their monocular depth via a convolutional neural network (CNN). Given the output direction $\mathbf{u}$ , for each $\mathbf{x} \in \mathbb{R}^3$ on the geometric scaffold along $\mathbf{u}$ there is a subset of source images, in which $\mathbf{x}$ is visible. Assuming the total number of images in this subset to be $K$ , we denote the set of view directions corresponding to these images as $\{\mathbf{v}_k\}_{k=1}^K$ . + +(i) SVS Features. The source images in $\mathcal{I}_s$ are first passed through a feature extraction CNN to obtain a feature tensor $\mathcal{F}_k$ corresponding to $k^{th}$ image. Denoting $f_{k}(\mathbf{x})$ as the feature corresponding to a point $\mathbf{x} \in \mathbb{R}^3$ in $\mathcal{F}_k$ located at the projection (or bilinear interpolation) of $\mathbf{x}$ on $k^{th}$ image. To this end, SVS [36] proposed the following aggregation function $(\phi_a)$ to compute the feature for $\mathbf{x}$ along $\mathbf{u}$ + +$$ +\phi_ {a} (\mathbf {u}, \left\{\left(\mathbf {v} _ {k}, f _ {k} (\mathbf {x})\right) \right\}) = \frac {1}{W} \sum_ {k = 1} ^ {K} \max (0, \mathbf {u} ^ {\mathrm {T}} \mathbf {v}) f _ {k} (\mathbf {x}), \tag {4} +$$ + +where, $W = \sum_{k=1}^{K} \max(0, \mathbf{u}^{\mathrm{T}}\mathbf{v})$ is sum of all the weights. + +(ii) Monocular Features. Given an image, we predict its depth with a per-pixel confidence score. For this, we use an existing monocular depth prediction network [32] pretrained on Omnidata [7]. To predict a normalized depth prediction confidence score per pixel $w_{ij}$ , we add another network on top of it (refer supplementary for details), which takes both images and depth as input. + +$$ +\sum_ {i} \sum_ {j} w _ {i j} \cdot \mathcal {L} \left(d _ {i j}, \hat {d} _ {i j}\right); \text {w h e r e}, w _ {i j} = \phi_ {w} \left(\mathcal {I} _ {s}, \mathcal {D} _ {s}\right) _ {i j}. \tag {5} +$$ + +$\mathcal{L}$ symbolizes the $l_{2}$ loss between the known pixel depth $d_{ij}$ and the predicted depth $\hat{d}_{ij}$ for $(i,j)$ pixel in the 2D depth image. We call network $\phi_w$ as the "confidence-prediction head". We take the depths predicted by this network and fuse them with the source image using the Channel Exchange Network [47]. The fused information is then projected into $N$ dimensional feature space using network $\mathcal{F}_{\theta}$ , which is a CNN-based architecture. To compute the feature corresponding to a pixel $\mathbf{p}$ in the target view $\mathbf{u}$ , we warp the features predicted for each source views $\mathbf{v}_k$ to this target view but now using the monocular depth $d \in \mathcal{D}_s$ of the source view. + +$$ +g _ {k} (\mathbf {u}, \mathbf {p}) = f _ {k} ^ {m} \left(\mathcal {W} (\mathbf {p}, \mathbf {u}, \mathbf {v} _ {k}, d)\right) \tag {6} +$$ + +where, $g_{k}$ denotes the feature warping function, $f_{k}^{m}(p)$ corresponds to feature in the tensor $\mathcal{F}_{\theta}(\mathcal{T}_s^k,d)$ (corresponding to $k^{th}$ source image and corresponding monocular depth) at pixel $\mathbf{p}$ , and $\mathcal{W}$ is the warping function. We now aggregate the warped features corresponding to each source image using a weighted sum based on confidence scores: + +$$ +\phi_ {a} (\mathbf {u}, \left\{\left(\mathbf {v} _ {k}, f _ {k} ^ {m} (\mathbf {p})\right) \right\}) = \sum_ {k = 1} ^ {K} c _ {k} (\mathbf {p}) f _ {k} ^ {m} (\mathbf {p}) \tag {7} +$$ + +here, $c_k$ symbolizes the predicted depth confidence map in the $k^{th}$ view. + +(iii) Structure Feature Aggregation Per Scene Point. Given we have features from two different modalities i.e., monocular depth and MVS, we now propose an aggregated feature representation for the target view per scene point $h_f = h_\theta(h_m, h_s)$ , where $h_\theta$ is a CNN-based neural network with parameters $\theta$ and $h_m$ is the final representation for the monocular estimation and $h_s$ for the stereo-estimation. We aim to attain maximal correlation from both of the input representations i.e., + +$$ +\lambda_ {1} \mathcal {C} \left(h _ {f}, h _ {m}\right) \cdot \mathcal {C} \left(h _ {f}, h _ {s}\right) + \lambda_ {2} \mathcal {C} \left(h _ {f}, h _ {s}\right) + \lambda_ {3} \mathcal {C} \left(h _ {f}, h _ {m}\right) \tag {8} +$$ + +where, $\sum_{i=1}^{3} \lambda_i = 1$ ; $\lambda_i > 0 \forall i \in \{1,2,3\}$ and $\mathcal{C}(.)$ being the standard correlation function [3]. We set $\lambda_1 = 1$ for nearby points where confidence of monocular depth could be greater than a defined threshold ( $\tau$ ). $\lambda_2 = 1$ for nearby points where confidence of monocular depth is lower than a defined threshold and finally $\lambda_3 = 1$ for far points whose relative depth is greater than a pre-defined threshold ( $\sigma$ ). Such a choice is made since stereo features might be less accurate in certain depth range due to low disparity or too close to the lens. The final aggregation $h_f$ comprises of CNN networks $\phi_\alpha$ and $\phi_\beta$ , parameterized by $\alpha$ and $\beta$ , respectively. The transformed features from each of these modalities are then fed to a CNN network $\phi_\nu$ with parameters $\nu$ . Overall aggregated features per scene point is represented as + +$$ +h _ {f} = h _ {\theta} \left(h _ {m}, h _ {s}\right) = \phi_ {\nu} \left(\phi_ {\alpha} \left(h _ {m}\right), \phi_ {\beta} \left(h _ {s}\right)\right). \tag {9} +$$ + +# 3.1.2 Camera Pose Estimation + +Given we have initially estimated pose-set $\mathcal{P}$ , we use multiple motion averaging (MRA) to recover better camera poses. MRA is fast, efficient, and robust in camera pose estimation from noisy key-point correspondences and works well even for sparse image sets. MRA takes a global view of the camera recovery problem. A view-graph corresponding to the initial set of camera poses is constructed as a global representation, with each graph node as a pose. For pose optimization, MRA first performs rotation averaging to recover rotation and then solves for translation. Assume a + +![](images/4c602515800266cadd3dbebe829d221fb3a33b386227eb1e465dc1f8ae215223.jpg) +Figure 2. Overview. For a given set of input images, we first estimate the scene 3D structure and the initial value of camera poses using structure from motion (SFM) followed by MVS. We also estimate per-image depth using an existing Monocular Depth estimation model [7]. Next, we generate two sets of Projected Features for each target view: The first set (upper stream) by encoding the input images and then unprojecting the features onto the scaffold, followed by re-projection to the target view and aggregation. For the second set (lower stream), the images are first concatenated with their monocular depths (MD), and the encoded features are then projected using these depths, followed by aggregation. These two feature sets are then merged into Cumulative Features, and finally, the target view is rendered. + +directed view-graph $\mathcal{G} = (\mathcal{V},\mathcal{E})$ . A vertex $\mathcal{V}_j\in \mathcal{V}$ in this view graph corresponds to $j^{th}$ camera absolute rotation $R_{j}$ and $\mathcal{E}_{ij}\in \mathcal{E}$ corresponds to the relative orientation $\tilde{R}_{ij}$ between view $i$ and $j$ . For our problem, relative orientations are given (noisy), and we aim to solve for absolute pose $R_{j}$ robustly. Conventionally, in the presence of noise, the solution is obtained by solving the following optimization problem to satisfy compatibility criteria. + +$$ +\underset {\{R _ {j} \}} {\operatorname {a r g m i n}} \sum_ {\mathcal {E} _ {i j} \in \mathcal {E}} \rho (\gamma (\tilde {R} _ {i j}, R _ {j} R _ {i} ^ {- 1})) \tag {10} +$$ + +where, $\gamma(.)$ denotes a metric on $SO(3)$ to measure distance between two rotation and $\rho(.)$ is a robust $l_1$ norm. We use a graph-neural network to predict the robustified pose view-graph of the scene following the camera pose refining approach of NeuRoRA [30]. First, the camera poses are checked for outliers via a cyclic consistency in the posegraph [11]. Then, a view graph is initialized based on these filtered poses. This view graph is then optimized using the camera pose-refining network of NeuRoRA [30]. + +# 3.2. Rendering novel views + +The aggregated feature tensor $\mathcal{F}^a$ along a direction $\mathbf{u}$ comprises of the features $h_f$ (Eq. 9) for each pixel along $\mathbf{u}$ , + +obtained using 3D scene features (discussed in Sec. 3.1.1). This tensor is now projected to the image space function using $\mathcal{G}_{\theta}$ , a CNN-based network with parameters $\theta$ . It is quite possible that the regions in the target image may not be encountered in any of the source images. For those points, the values in feature tensor $\mathcal{F}$ are set to $\mathbf{0}$ , and thus, they require some inpainting. Denoting the set of test images by $\mathcal{I}_t$ , the rendered image corresponding to the $k^{th}$ image in the test set, $\hat{\mathcal{I}}_t^k$ , is predicted based on the following equation: + +$$ +\hat {\mathcal {I}} _ {t} ^ {k} = \mathcal {G} _ {\theta} \left(\mathcal {F} _ {k} ^ {a}\right) \tag {11} +$$ + +Similar to stable view synthesis, we parameterize the $\mathcal{G}_{\theta}$ function using a U-Net [37] style model which also deals with inpainting/hallucinating the newly discovered regions in the test image. Fig.(2) shows the complete overview of the proposed method. + +# 3.3. Joint Optimization + +Given $\mathcal{I}_s$ , we train the model using our overall loss function $\mathcal{L}$ comprising of two terms. + +$$ +\mathcal {L} = \mathcal {L} _ {s} + \mathcal {L} _ {p} \tag {12} +$$ + +(i) The first loss term $\mathcal{L}_s$ encourages the network to learn better features corresponding to the scene point. The $\mathcal{L}_s$ + +
TruckM60PlaygroundTrain
PSNR↑LPIPS↓SSIM↑PSNR↑LPIPS↓SSIM↑PSNR↑LPIPS↓SSIM↑PSNR↑LPIPS↓SSIM↑
NeRF++ [49]21.80.310.8117.60.430.7321.90.390.7917.60.480.68
FVS [35]21.90.140.8415.80.320.7721.70.210.8317.30.280.75
SC-NeRF [17]22.30.290.8218.40.400.7622.40.350.8318.20.420.73
Point-NeRF [48]22.70.140.8719.60.210.8522.20.190.8318.60.160.83
SVS [36]22.90.120.8819.10.220.8322.90.170.8617.90.190.81
Ours24.10.120.9020.80.200.8923.90.140.9020.10.130.88
+ +Table 1. Rendered image quality comparison with current state-of-the-art methods in novel view synthesis on the popular Tanks and Temples dataset [18]. We use the popular metrics i.e., PSNR, LPIPS and SSIM for the comparison. + +
BikeFlowersPirateDiggerSandboxSoccertable
SSIM↑LPIPS↓SSIM↑LPIPS↓SSIM↑LPIPS↓SSIM↑LPIPS↓SSIM↑LPIPS↓SSIM↑LPIPS↓
NeRF++ [49]0.710.270.800.310.710.430.650.350.840.240.870.21
FVS [35]0.610.280.790.270.690.370.680.240.780.320.820.21
SVS [36]0.740.220.840.210.750.320.770.180.850.200.910.15
Ours0.790.190.880.180.800.290.810.160.910.170.940.13
+ +Table 2. Quantitative comparison on FVS dataset [35]. We use the popular metrics, i.e., PSNR, LPIPS and SSIM for the comparison. + +comprises to two objective function $\mathcal{L}_{rgb}$ and $\mathcal{L}_{corr}$ . The function $\mathcal{L}_{rgb}$ measures the discrepancies between the rendering of an image in the source set and the actual image available in the set. This objective is used to train the structure estimation and rendering network parameters jointly. Whereas $\mathcal{L}_{corr}$ is used for maximizing the correlation objective discussed in Eq.(8) to arrive at the optimal aggregated scene representation. + +$$ +\mathcal {L} _ {s} = \mathcal {L} _ {r g b} + \mathcal {L} _ {c o r r} \tag {13} +$$ + +$\mathcal{L}_{corr}$ takes the negative of the objective defined in Eq.(8). The structure network parameters corresponding to functions $f_{k}$ and $f_{k}^{m}$ (cf. Sec. 3.1.1) and is updated using $\mathcal{L}_{corr}$ and $\mathcal{L}_{rgb}$ . The rendering network parameters corresponding to $\mathcal{G}_{\theta}$ updated using only $\mathcal{L}_{rgb}$ . + +(ii) The second loss term $\mathcal{L}_p$ corresponds to the camera pose refinement. We used the following loss $\mathcal{L}_p$ to improve the camera pose estimation. + +$$ +\mathcal {L} _ {p} = \mathcal {L} _ {m r a} \tag {14} +$$ + +As is known, the multiple motion averaging and the color rendering cost functions are directly impacted by the camera pose parameters. And therefore, the $\mathcal{L}_{rgb}$ is inherently used as an intermediate objective in which the camera pose term is constant between the two different representations. + +# 4. Experiments, Results and Ablations + +Here, we discuss our experimental results and their comparison to relevant baselines. Later, we provide critical ablation analysis, a study of our camera pose estimation idea, and 3D structure recovery. Finally, the section concludes with a discussion of a few extensions of our approach2. + +Baselines. We compare our approach with the recently proposed novel view synthesis methods that work well in practice for real-world scenes. Our baseline list includes NeRF++ [49], SC-NeRF [17], PointNeRF [48], FVS [35] and SVS [36]. All baseline methods are trained on the source image set of the testing sequence. Our method's train and test set are the same as SVS [36]. + +# 4.1. Dataset and Results + +For evaluation, we used popular benchmark datasets comprising real-world and synthetic datasets. Namely, we used the Tanks and Temples [18], FVS [35], Mip-NeRF 360 [1], and the DTU [16] dataset. The first two datasets contain real-world scenes, whereas the last is an object-centric synthetic benchmark dataset. Although our approach mainly targets realistic scenes, for completeness, we performed and tabulated results on a synthetic object-based DTU dataset (see supplementary). Next, we discuss datasets and results. + +(i) Tanks and Temples Dataset. It consists of images of large-scale real-world scenes taken from a freely moving camera, consisting of indoor and outdoor scenes. Unfortunately, we have no ground-truth poses; thus, estimated poses using COLMAP [39] are treated as pseudo-ground-truth poses. The dataset consists of a total of 21 scenes. Similar to the SVS setup, we use 15 of 21 scenes for training, 2 for validation, and the rest as test scenes. We also use a disjoint set of target views from the test scenes to evaluate all the methods. The source views in test scenes are used for scene-specific fine-tuning if required. Table 1 shows the statistical comparison of our approach with competing baselines. Our approach consistently outperforms the relevant baselines on this challenging dataset. Furthermore, if we zoom into the scene's finer details, our approach clearly preserves details better than other approaches (see Fig. 3). + +(ii) FVS Dataset. It comprises six real-world scenes. Each + +![](images/602808eefcc6937a74c31185ff4b5daca1ddd8943892286066c5e2bc095b0bd6.jpg) +Figure 3. Qualitative comparison on tanks and temples dataset. If we zoom into the scene details, our approach results show considerably less artifacts than the state-of-the-art methods enabling unparalleled level of realism in image-based rendering. Our PSNR values for the above two scenes are (20.1, 23.9). In comparison, SC-NeRF [17] and SVS [36] provide (17.3, 22.4) and (17.9, 22.9), respectively. + +![](images/0278469c477addaaccb4b9e4c44912ec58fb9fd0517eaf99638b2875afe89d5c.jpg) + +scene was recorded two or more times to completely differentiate the source image set to form the target image set. Table 2 summarises this dataset's view synthesis quantitative results. We compare our method with the state-of-the-art $\mathrm{NeRF}++$ [49], Free-View synthesis [35], and SVS [36] methods. We observe that FVS improves over $\mathrm{NeRF}++$ , whereas SVS results on this dataset do not consistently outperform other previous methods. On the contrary, our method consistently provides better results than prior art in all categories. The dataset's sample images and its qualitative results are provided in the supplementary. + +(iii) Mip-NeRF 360 Dataset. We further test our approach on this recently proposed dataset comprising unbounded scenes [1]. We use the train-test setup per scene proposed by the authors to fine-tune our network and compare it with Mip-NeRF 360 [1], $\mathrm{NeRF}++$ [49], and SVS [36] baseline. Table 3 shows the results for this comparison. Clearly, our methodical take on this problem generalizes well, outperforming other baseline methods for most examples. + +
PSNR↑LPIPS↓SSIM↑
NeRF++ [49]25.030.3550.682
SVS [36]25.280.2180.783
PBNR [19]23.550.2620.722
Mip-NeRF 360 [1]27.070.2510.781
Ours27.950.2320.797
+ +Table 3. Quantitative comparison of our approach with existing baselines on the Mip-NeRF 360 dataset. + +# 4.2. Ablation Analysis + +(i) Effect of our camera-pose estimation approach. We performed this experiment to show the benefit of using multiple motion averaging (MRA) instead of relying only on COLMAP poses and taking them for granted. For this experiment, we used the popular Lego dataset [25]. We first compute the COLMAP camera poses shown in Fig.4 (Left). Next, we use this initial camera pose set to perform MRA utilizing the view-graph optimization. Our recovered camera poses are shown in Fig.4 (Right). For clarity, we also show the ground-truth camera pose frustum and the error between the ground-truth pose and recovered pose for the + +![](images/9fc3d8b79d8e56f6098b4b74a005613de9dfbb125cfc0c21c9f36df3f41ccfbc.jpg) +Figure 4. COLMAP [39] and our method's camera poses on Lego dataset [25]. Here, we add some noise to the pairwise matched correspondences to simulate realistic scenarios. Left: Estimated camera pose from COLMAP and the ground truth pose. Here, black line shows the pose error. Right: Our recovered camera pose. It is easy to infer our approach robustness. + +![](images/dcac75ebdec6d652b6f6ed42dfb97771b2780a23258a37c9eee3a2dc9f5d2ce6.jpg) + +two respective cases. It is clear from Fig.(4) that a principled approach is required for better camera-pose recovery in view-synthesis problem. Furthermore, to show the benefit of our estimated camera pose in novel-view synthesis, we show our network training loss curve with and without our camera pose estimation approach in Fig.(5). For clarity, we also plot the SVS training curve. Firstly, our method shows better loss response due to the improved 3D geometric scaffold of the scene. Moreover, we improve on training loss further by introducing neural graph-based MRA, showing the benefit of our proposed loss function. + +![](images/78dbd409fe2322b377f581b8c1922724dd7a343ae26a7ec0e8dc3685f9e50fd2.jpg) +Figure 5. Training loss curve of our method with and without pose optimization compared to state-of-the-art SVS [36] + +(ii) Effect of using MVS with monocular depth. We performed this ablation to demonstrate the effectiveness of our approach in recovering geometric reconstruction of the scene. Fig.(6) clearly shows the complementary nature of the monocular depth and stereo depth in 3D reconstruction from images. While MVS provides reliable depth results for near and mid-range points, monocular depth can deliver a good depth inference (up to scale) on the far points in the scene. By carefully integrating both modalities' depth, we have better 3D information about the scene. Fig.(6) shows our results on a couple of scenes from Tanks and Temples dataset, demonstrating the suitability of our approach. + +![](images/63b9b29820f788b482eed3514cff36548af2826f4a592a40cc01bcbb3e663144.jpg) +Figure 6. Comparison of depth predicted by monocular and stereo based method on the scenes from Tanks and Temples dataset. + +# 5. Conclusion + +The approach presented in this paper directly addresses the shortcomings of the currently popular methods in novel view synthesis. Our approach integrates concepts from the learning-based approaches and classical techniques in multiple-view geometry for solving novel-view synthesis. We demonstrate that by exploiting the $(i)$ complementary nature of monocular depth estimation and multiple view stereo (MVS) in the 3D reconstruction of the scene, and $(ii)$ usefulness of multiple rotation averaging in structure from motion, we can achieve better-rendering quality than other dominant approaches in novel view synthesis. We confirm the effectiveness of our approach via a comprehensive evaluation and quantitative comparison with baselines on several benchmark datasets. Although our work enabled improved photorealistic rendering, several exciting avenues exist for further improvement. One interesting future extension is fully automating our introduced view synthesis pipeline, i.e., adding a learnable MVS framework to estimate intrinsic, extrinsic camera parameters with scene reconstruction for better novel view synthesis. + +# References + +[1] Jonathan T Barron, Ben Mildenhall, Dor Verbin, Pratul P Srinivasan, and Peter Hedman. Mip-nerf 360: Unbounded anti-aliased neural radiance fields. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 5470-5479, 2022. +[2] Chris Buehler, Michael Bosse, Leonard McMillan, Steven Gortler, and Michael Cohen. Unstructured lumigraph rendering. 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In Visual Communications and Image Processing 2000, volume 4067, pages 2-13. SPIE, 2000. +[43] Richard Szeliski. Computer vision: algorithms and applications. Springer Nature, 2022. +[44] Ayush Tewari et al. State of the art on neural rendering. In Computer Graphics Forum, volume 39, pages 701-727. Wiley Online Library, 2020. +[45] Bill Triggs, Philip F. McLauchlan, Richard I. Hartley, and Andrew W. Fitzgibbon. Bundle adjustment - a modern synthesis. In Proceedings of the International Workshop on Vision Algorithms: Theory and Practice, ICCV '99, pages 298-372, London, UK, UK, 2000. Springer-Verlag. +[46] Fangjinhua Wang, Silvano Galliani, Christoph Vogel, Pablo Speciale, and Marc Pollefeys. Patchmatchnet: Learned multi-view patchmatch stereo. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 14194-14203, 2021. + +[47] Yikai Wang, Wenbing Huang, Fuchun Sun, Tingyang Xu, Yu Rong, and Junzhou Huang. Deep multimodal fusion by channel exchanging. 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Nerf++: Analyzing and improving neural radiance fields. arXiv preprint arXiv:2010.07492, 2020. \ No newline at end of file diff --git a/2023/Enhanced Stable View Synthesis/images.zip b/2023/Enhanced Stable View Synthesis/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..8f383d0aa5c9c6552fba21cd4b02c63095deeab7 --- /dev/null +++ b/2023/Enhanced Stable View Synthesis/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:7e9899f7d7a1ddc47f848b765f55dc921c87b3b5d60c753e58acb55c3b6ee814 +size 634356 diff --git a/2023/Enhanced Stable View Synthesis/layout.json b/2023/Enhanced Stable View Synthesis/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..db2db811cd94c2de8247e387b8fd26a59171dea9 --- /dev/null +++ b/2023/Enhanced Stable View Synthesis/layout.json @@ -0,0 +1,8793 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 196, + 103, + 398, + 121 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 196, + 103, + 398, + 121 + ], + "spans": [ + { + "bbox": [ + 196, + 103, + 398, + 121 + ], + "type": "text", + "content": "Enhanced Stable View Synthesis" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 105, + 143, + 253, + 198 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 105, + 143, + 253, + 198 + ], + "spans": [ + { + "bbox": [ + 105, + 143, + 253, + 198 + ], + "type": "text", + "content": "Nishant Jain* \nIndian Institute of Technology \nRoorkee, India \nnjain@cs.iitr.ac.in" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 283, + 143, + 375, + 198 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 283, + 143, + 375, + 198 + ], + "spans": [ + { + "bbox": [ + 283, + 143, + 375, + 198 + ], + "type": "text", + "content": "Suryansh Kumar\\*ETH ZürichSwitzerland sukumar@ethz.ch" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 401, + 144, + 484, + 198 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 401, + 144, + 484, + 198 + ], + "spans": [ + { + "bbox": [ + 401, + 144, + 484, + 198 + ], + "type": "text", + "content": "Luc Van Gool \nETH Zürich \nSwitzerland \nvangool@ethz.ch" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 143, + 226, + 192, + 239 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 226, + 192, + 239 + ], + "spans": [ + { + "bbox": [ + 143, + 226, + 192, + 239 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 252, + 289, + 601 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 252, + 289, + 601 + ], + "spans": [ + { + "bbox": [ + 46, + 252, + 289, + 601 + ], + "type": "text", + "content": "We introduce an approach to enhance the novel view synthesis from images taken from a freely moving camera. The introduced approach focuses on outdoor scenes where recovering accurate geometric scaffold and camera pose is challenging, leading to inferior results using the state-of-the-art stable view synthesis (SVS) method. SVS and related methods fail for outdoor scenes primarily due to (i) overrelying on the multiview stereo (MVS) for geometric scaffold recovery and (ii) assuming COLMAP computed camera poses as the best possible estimates, despite it being well-studied that MVS 3D reconstruction accuracy is limited to scene disparity and camera-pose accuracy is sensitive to key-point correspondence selection. This work proposes a principled way to enhance novel view synthesis solutions drawing inspiration from the basics of multiple view geometry. By leveraging the complementary behavior of MVS and monocular depth, we arrive at a better scene depth per view for nearby and far points, respectively. Moreover, our approach jointly refines camera poses with image-based rendering via multiple rotation averaging graph optimization. The recovered scene depth and the camera-pose help better view-dependent on-surface feature aggregation of the entire scene. Extensive evaluation of our approach on the popular benchmark dataset, such as Tanks and Temples, shows substantial improvement in view synthesis results compared to the prior art. For instance, our method shows " + }, + { + "bbox": [ + 46, + 252, + 289, + 601 + ], + "type": "inline_equation", + "content": "1.5\\mathbf{dB}" + }, + { + "bbox": [ + 46, + 252, + 289, + 601 + ], + "type": "text", + "content": " of PSNR improvement on the Tank and Temples. Similar statistics are observed when tested on other benchmark datasets such as FVS, Mip-NeRF 360, and DTU." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 625, + 128, + 639 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 625, + 128, + 639 + ], + "spans": [ + { + "bbox": [ + 47, + 625, + 128, + 639 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 646, + 288, + 682 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 646, + 288, + 682 + ], + "spans": [ + { + "bbox": [ + 46, + 646, + 288, + 682 + ], + "type": "text", + "content": "Image-based rendering, popularly re-branded as view synthesis, is a long-standing problem in computer vision and graphics [42, 44]. This problem aims to develop a" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 228, + 546, + 503 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 228, + 546, + 503 + ], + "spans": [ + { + "bbox": [ + 306, + 228, + 546, + 503 + ], + "type": "text", + "content": "method that allows the user to seamlessly explore the scene via rendering of the scene from a sparse set of captured images [2, 20, 42]. Furthermore, the rendered images must be as realistic as possible for a better user experience [34-36]. Currently, among the existing approaches, Riegler and Koltun stable view synthesis (SVS) approach [36] has shown excellent results and demonstrated photorealism in novel view synthesis, without using synthetic gaming engine 3D data, unlike [34]. SVS is indeed stable in rendering photorealistic images from novel viewpoints for large-scale scenes. Yet, it assumes MVS [39, 40] based dense 3D scene reconstruction and camera poses from COLMAP [39] are correct. The off-the-shelf algorithms used for 3D data acquisition and camera poses from images are, of course, popular, and to assume these algorithms could provide favorable 3D reconstruction and camera poses is not an outlandish assumption. Nonetheless, taking a step forward, in this paper, we argue that although choices made by SVS for obtaining geometric scaffold and camera poses in the pursuit of improving view synthesis is commendable, we can do better by making mindful use of fundamentals from multiple-view geometry [11,12] and recent developments in deep-learning techniques for 3D computer vision problems." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 506, + 547, + 662 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 506, + 547, + 662 + ], + "spans": [ + { + "bbox": [ + 304, + 506, + 547, + 662 + ], + "type": "text", + "content": "To start with, we would like to emphasize that it is clearly unreasonable, especially in an outdoor setting, to assume that multi-view stereo (MVS) can provide accurate depth for all image pixels. It is natural that pixels with low disparity will not be reconstructed well using state-of-the-art MVS approaches [8, 39, 40, 46]. Even a precise selection of multiple view images with reasonable distance between them (assume good baseline for stereo) may not be helpful due to loss of common scene points visibility, foreshortening issue, etc. [43]. Such issues compel the practitioner to resort to post-processing steps for refining the MVS-based 3D geometry so that it can be helpful for rendering pipeline or neural-rendering network at train time." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 665, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 547, + 715 + ], + "type": "text", + "content": "Another critical component to view synthesis, which is often brushed aside in the literature is the accurate recovery of the camera poses. In neural view synthesis approaches such as [36], if the camera pose is wrong, the feature ag-" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 693, + 208, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 693, + 208, + 713 + ], + "spans": [ + { + "bbox": [ + 58, + 693, + 208, + 713 + ], + "type": "text", + "content": "*Equal Contribution \n†Corresponding Author (k.sur46@gmail.com)" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "13208" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 50, + 72, + 553, + 159 + ], + "blocks": [ + { + "bbox": [ + 50, + 72, + 553, + 159 + ], + "lines": [ + { + "bbox": [ + 50, + 72, + 553, + 159 + ], + "spans": [ + { + "bbox": [ + 50, + 72, + 553, + 159 + ], + "type": "image", + "image_path": "afa88c39f10e95619f038cb454706670e69a3fb4b7bc6ba18491a3fb7bdc34f2.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 167, + 547, + 201 + ], + "lines": [ + { + "bbox": [ + 46, + 167, + 547, + 201 + ], + "spans": [ + { + "bbox": [ + 46, + 167, + 547, + 201 + ], + "type": "text", + "content": "Figure 1. Qualitative comparison. Our result compared to the popular SVS method [36] on the M60 scene of the tanks and temples dataset [18]. It is easy to observe that our approach can better render fine details in the scene. For this scene, the PSNR values for SVS [36] and our method are 19.1 and 20.8, respectively, demonstrating improved PSNR result." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 223, + 287, + 378 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 223, + 287, + 378 + ], + "spans": [ + { + "bbox": [ + 46, + 223, + 287, + 378 + ], + "type": "text", + "content": "ggregation corresponding surface points could be misleading, providing inferior results. Therefore, we should have camera poses as accurate as possible. Unfortunately, despite the camera pose importance to this problem, discussion on improving camera pose is often ignored under the assumption that COLMAP [39] provide the best possible camera pose estimates for any possible scenarios. Practically speaking, this is generally not the case for outdoor scenes [5, 11, 15]. What is more surprising is that some recent benchmark datasets put COLMAP recovered poses as the ground-truth poses [33]. Hence, we want to get this out way upfront that a robust and better camera-pose estimates are vital for better modeling view synthesis problem." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 379, + 287, + 475 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 379, + 287, + 475 + ], + "spans": [ + { + "bbox": [ + 46, + 379, + 287, + 475 + ], + "type": "text", + "content": "From the above predication, it is apparent that a more mindful approach is required to make view synthesis approaches practically useful, automatic, and valuable for real-world application. To this end, we propose a principled and systematic approach that provides a better geometric scaffold and camera poses for reliable feature aggregation of the scene's surface points, leading to improved novel-view synthesis results enabling superior photorealism." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 475, + 287, + 594 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 475, + 287, + 594 + ], + "spans": [ + { + "bbox": [ + 46, + 475, + 287, + 594 + ], + "type": "text", + "content": "In practice, we can have suitable initial camera poses from images using COLMAP. Yet, it must be refined further for improved image-feature aggregation corresponding to 3D surface points for neural rendering. It is well-studied in multiple-view geometry literature that we can improve and refine camera poses just from image key-point correspondences [10, 11]. Accordingly, we introduce a learning-based multiple motion averaging via graph neural network for camera pose recovery, where the pose graph is initialized using COLMAP poses for refinement." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 596, + 287, + 693 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 596, + 287, + 693 + ], + "spans": [ + { + "bbox": [ + 46, + 596, + 287, + 693 + ], + "type": "text", + "content": "Meanwhile, it is challenging to accurately recover the 3D geometry of scene points with low or nearly-zero disparity using MVS methods [12, 43]. Another bad news from the theoretical side is that a precise estimation of scene depth from a single image is unlikely1, which is a correct statement and hard to argue. The good news is that advancements in deep-learning-based monocular depth prediction have led to some outstanding results in several practical" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 223, + 545, + 330 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 223, + 545, + 330 + ], + "spans": [ + { + "bbox": [ + 304, + 223, + 545, + 330 + ], + "type": "text", + "content": "applications [24, 31]. Thus, at least practically, it seems possible to infer reliable monocular depth estimates up to scale. Using single image depth prediction, we can reason about the depth of scene points with low disparities. So, our proposed strategy is to use confidence based multiple-view stereo 3D that favours pixels with near-to-mid disparity and allows monocular depth estimates for the rest of the pixels. Overall depth is recovered after scaling all the scene depth appropriately using MVS reconstructed metric." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 330, + 546, + 449 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 330, + 546, + 449 + ], + "spans": [ + { + "bbox": [ + 304, + 330, + 546, + 449 + ], + "type": "text", + "content": "By encoding the image features via convolutional neural networks, we map the deep features to our estimated 3D geometric scaffold of the scene. Since we have better camera poses and scene reconstruction, we obtain and aggregate accurate feature vectors corresponding to each imaging view-rays—both from the camera to the surface point and from the surface point to viewing image pixels, giving us a feature tensor. We render the new image from the features tensor via a convolutional network and simultaneously refine the camera pose. In summary, our contributions are" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 451, + 545, + 571 + ], + "type": "list", + "angle": 0, + "index": 11, + "blocks": [ + { + "bbox": [ + 306, + 451, + 545, + 475 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 451, + 545, + 475 + ], + "spans": [ + { + "bbox": [ + 306, + 451, + 545, + 475 + ], + "type": "text", + "content": "- A systematic and principled approach for improved stable view synthesis enabling enhanced photorealism." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 475, + 545, + 535 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 475, + 545, + 535 + ], + "spans": [ + { + "bbox": [ + 306, + 475, + 545, + 535 + ], + "type": "text", + "content": "- The introduced approach exploits the complementary nature of MVS and monocular depth estimation to recover better 3D geometric scaffold of the scene. Meanwhile, the robust camera poses are recovered using graph neural network based multiple motion averaging." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 535, + 545, + 571 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 535, + 545, + 571 + ], + "spans": [ + { + "bbox": [ + 306, + 535, + 545, + 571 + ], + "type": "text", + "content": "- Our approach proposes an improved loss function to jointly optimize and refine for poses, neural image rendering, and scene representation showing superior results." + } + ] + } + ], + "index": 10 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 304, + 575, + 545, + 624 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 575, + 545, + 624 + ], + "spans": [ + { + "bbox": [ + 304, + 575, + 545, + 624 + ], + "type": "text", + "content": "Our approach when tested on benchmark datasets such as Tank and Temples [18], FVS [35], Mip-NeRF 360 [1], and DTU [16] gives better image based rendering results with generally more than 1 dB PSNR gain (see Fig.1)." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 633, + 479, + 647 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 633, + 479, + 647 + ], + "spans": [ + { + "bbox": [ + 306, + 633, + 479, + 647 + ], + "type": "text", + "content": "2. Background and Preliminaries" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 654, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 654, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 304, + 654, + 545, + 712 + ], + "type": "text", + "content": "Our work integrates the best of novel view synthesis and multiple view geometry approaches in computer vision in a mindful way. Both novel view synthesis and MVS are classical problems in computer graphics and computer vision, with an exhaustive list of literature. Thus, we confine our re" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 58, + 702, + 257, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 702, + 257, + 713 + ], + "spans": [ + { + "bbox": [ + 58, + 702, + 257, + 713 + ], + "type": "text", + "content": "1As several 3D scene points can have same image projection." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "13209" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 133 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 133 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 133 + ], + "type": "text", + "content": "lated work discussion to the methods that is directly related to the proposed approach. The interested reader may refer to [4, 8, 12, 28, 38, 42, 44] for earlier and recent progress in these areas. Here, we briefly discuss relevant methods and the current state-of-the-art in neural image-based rendering." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 134, + 289, + 338 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 134, + 289, + 338 + ], + "spans": [ + { + "bbox": [ + 46, + 134, + 289, + 338 + ], + "type": "text", + "content": "(i) Uncalibrated Multi-View Stereo. Given the intrinsic camera calibration matrix, we can recover camera poses and the 3D structure of the scene using two or more images [8,21,22,39,40]. One popular and easy-to-use MVS framework is COLMAP [39], which includes several carefully crafted modules to estimate camera poses and sparse 3D structures from images. For camera pose estimation, it uses classical image key-point-based algorithms [13,27,45]. As is known that such methods can provide sub-optimal solutions and may not robustly handle outliers inherent to the unstructured images. Consequently, camera poses recovered using COLMAP can be unreliable, primarily for outdoor scenes. Moreover, since the 3D reconstruction via triangulation uses sparse key points, at best accurate semidense 3D reconstruction of the scene could be recovered. Still, many recent state-of-the-art methods in novel view synthesis heavily rely on it [25,35,36,49]." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 340, + 289, + 472 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 340, + 289, + 472 + ], + "spans": [ + { + "bbox": [ + 46, + 340, + 289, + 472 + ], + "type": "text", + "content": "(ii) Image-based rendering. Earlier image-based rendering approaches enabled novel view synthesis from images without any 3D scene data under some mild assumptions about the camera, and imaging [9,23,41]. Later with the development of multiple-view stereo approaches and RGBD sensing modalities, several works used some form of 3D data to improve image-based rendering. Popular works along this line include [2,6,14,20,29]. In recent years, neural network-based methods have dominated this field and enabled data-driven approach to this problem with an outstanding level of photorealism [26,34-36,49]." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 472, + 289, + 676 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 472, + 289, + 676 + ], + "spans": [ + { + "bbox": [ + 46, + 472, + 289, + 676 + ], + "type": "text", + "content": "Among all the current methods we tested, SVS [36] stands out in novel view synthesis from images taken from a freely moving camera. This paper proposes an approach closely related to the SVS pipeline. SVS involves learning a scene representation from images using its dense 3D structure and camera poses predicted via uncalibrated MVS approaches detailed previously. The recovered 3D structure of the scene is post-processed to have a refined geometric scaffold in mesh representation. Using refined scene 3D, it learns a feature representation for a set of images and then projects it along the direction of the target view to be rendered. Finally, SVS involves re-projection from feature to image space resulting in the synthesized image for the target view. Given " + }, + { + "bbox": [ + 46, + 472, + 289, + 676 + ], + "type": "inline_equation", + "content": "S" + }, + { + "bbox": [ + 46, + 472, + 289, + 676 + ], + "type": "text", + "content": ", the 3D structure for a scene, feature representation network " + }, + { + "bbox": [ + 46, + 472, + 289, + 676 + ], + "type": "inline_equation", + "content": "f_{\\theta}" + }, + { + "bbox": [ + 46, + 472, + 289, + 676 + ], + "type": "text", + "content": " with " + }, + { + "bbox": [ + 46, + 472, + 289, + 676 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 46, + 472, + 289, + 676 + ], + "type": "text", + "content": " representing the network parameters, and the rendering network " + }, + { + "bbox": [ + 46, + 472, + 289, + 676 + ], + "type": "inline_equation", + "content": "G_{\\mu}" + }, + { + "bbox": [ + 46, + 472, + 289, + 676 + ], + "type": "text", + "content": " with parameters " + }, + { + "bbox": [ + 46, + 472, + 289, + 676 + ], + "type": "inline_equation", + "content": "\\mu" + }, + { + "bbox": [ + 46, + 472, + 289, + 676 + ], + "type": "text", + "content": ", the resulting image " + }, + { + "bbox": [ + 46, + 472, + 289, + 676 + ], + "type": "inline_equation", + "content": "\\mathcal{I}_r" + }, + { + "bbox": [ + 46, + 472, + 289, + 676 + ], + "type": "text", + "content": " along the pose " + }, + { + "bbox": [ + 46, + 472, + 289, + 676 + ], + "type": "inline_equation", + "content": "\\mathbf{p}" + }, + { + "bbox": [ + 46, + 472, + 289, + 676 + ], + "type": "text", + "content": " is rendered as" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 112, + 681, + 287, + 696 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 112, + 681, + 287, + 696 + ], + "spans": [ + { + "bbox": [ + 112, + 681, + 287, + 696 + ], + "type": "interline_equation", + "content": "\\mathcal {I} _ {r} = \\mathcal {G} _ {\\mu} \\left(\\phi_ {a} \\left(\\mathcal {S}, \\mathcal {I} _ {s}, \\mathbf {p}, f _ {\\theta}\\right), \\right. \\tag {1}", + "image_path": "fbff91d92c25ac4c18ee2fad2aadd77bf948360a4d36b27c1eecf3dfb454747c.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 701, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 701, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 47, + 701, + 288, + 714 + ], + "type": "text", + "content": "where, " + }, + { + "bbox": [ + 47, + 701, + 288, + 714 + ], + "type": "inline_equation", + "content": "\\mathcal{I}_s" + }, + { + "bbox": [ + 47, + 701, + 288, + 714 + ], + "type": "text", + "content": " denotes the image set for a given seen. " + }, + { + "bbox": [ + 47, + 701, + 288, + 714 + ], + "type": "inline_equation", + "content": "\\phi_{a}()" + }, + { + "bbox": [ + 47, + 701, + 288, + 714 + ], + "type": "text", + "content": " ag-" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 72, + 545, + 96 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 96 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 96 + ], + "type": "text", + "content": "gregates features for all the images along a given direction in " + }, + { + "bbox": [ + 304, + 72, + 545, + 96 + ], + "type": "inline_equation", + "content": "\\mathcal{I}_s" + }, + { + "bbox": [ + 304, + 72, + 545, + 96 + ], + "type": "text", + "content": " predicted when passed through " + }, + { + "bbox": [ + 304, + 72, + 545, + 96 + ], + "type": "inline_equation", + "content": "f_{\\theta}" + }, + { + "bbox": [ + 304, + 72, + 545, + 96 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 96, + 547, + 168 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 96, + 547, + 168 + ], + "spans": [ + { + "bbox": [ + 304, + 96, + 547, + 168 + ], + "type": "text", + "content": "Contrary to the choices made by the SVS, in this work, we put forward an approach for better estimation of the overall scene 3D geometric scaffold—for both low and high-disparity pixels—and camera poses. Our approach enables a better aggregation of surface features allowing an improved level of realism in novel view synthesis." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 177, + 362, + 190 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 177, + 362, + 190 + ], + "spans": [ + { + "bbox": [ + 306, + 177, + 362, + 190 + ], + "type": "text", + "content": "3. Method" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 197, + 547, + 342 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 197, + 547, + 342 + ], + "spans": [ + { + "bbox": [ + 304, + 197, + 547, + 342 + ], + "type": "text", + "content": "We begin with a discussion about formulating and estimating a better scene representation by carefully exploiting the complementary behavior of monocular depth and multiview stereo approaches in 3D data acquisition. During our implementation, we use confidence measures for precise reasoning of estimated 3D coming from both the modalities and their accuracy. Next, we detail integrating a camera pose-refining optimization to estimate better camera poses for accurately projecting our 3D scene representation to the target view. Finally, the proposed joint optimization objective to refine structure representation and camera poses simultaneously is discussed." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 347, + 373, + 358 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 347, + 373, + 358 + ], + "spans": [ + { + "bbox": [ + 306, + 347, + 373, + 358 + ], + "type": "text", + "content": "3.1. Overview" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 365, + 547, + 544 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 365, + 547, + 544 + ], + "spans": [ + { + "bbox": [ + 304, + 365, + 547, + 544 + ], + "type": "text", + "content": "Given a set of source images " + }, + { + "bbox": [ + 304, + 365, + 547, + 544 + ], + "type": "inline_equation", + "content": "\\mathcal{I}_s" + }, + { + "bbox": [ + 304, + 365, + 547, + 544 + ], + "type": "text", + "content": " taken from a freely moving camera, the current state-of-the-art SVS [36] first estimates camera-poses " + }, + { + "bbox": [ + 304, + 365, + 547, + 544 + ], + "type": "inline_equation", + "content": "\\mathcal{P}" + }, + { + "bbox": [ + 304, + 365, + 547, + 544 + ], + "type": "text", + "content": " and scene 3D structure " + }, + { + "bbox": [ + 304, + 365, + 547, + 544 + ], + "type": "inline_equation", + "content": "S" + }, + { + "bbox": [ + 304, + 365, + 547, + 544 + ], + "type": "text", + "content": ". Next, it encodes the images via a CNN. Then, using the estimated camera, it maps the encoded features onto the scene 3D scaffold. For each point " + }, + { + "bbox": [ + 304, + 365, + 547, + 544 + ], + "type": "inline_equation", + "content": "\\mathbf{x} \\in \\mathbb{R}^3" + }, + { + "bbox": [ + 304, + 365, + 547, + 544 + ], + "type": "text", + "content": " on the scaffold, SVS query set of images in which " + }, + { + "bbox": [ + 304, + 365, + 547, + 544 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 304, + 365, + 547, + 544 + ], + "type": "text", + "content": " is visible to obtain its corresponding feature vectors. This feature vector is then conditioned on the output view direction via a network to produce a new feature vector. Such a new feature vector is obtained for all the points on the scaffold to form a feature tensor, which is then decoded using CNN to synthesize the output image. Denoting the complete set of parameters for learning the feature representation and rendering as " + }, + { + "bbox": [ + 304, + 365, + 547, + 544 + ], + "type": "inline_equation", + "content": "\\Theta" + }, + { + "bbox": [ + 304, + 365, + 547, + 544 + ], + "type": "text", + "content": ", we can write SVS idea as" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 353, + 551, + 545, + 564 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 353, + 551, + 545, + 564 + ], + "spans": [ + { + "bbox": [ + 353, + 551, + 545, + 564 + ], + "type": "interline_equation", + "content": "\\Theta \\sim \\Psi (\\Theta | \\mathcal {S}, \\mathcal {P}, \\mathcal {I} _ {s}) \\circ \\Psi (\\mathcal {S}, \\mathcal {P} | \\mathcal {I} _ {s}). \\tag {2}", + "image_path": "96747e3aa9b2ff83d6714a0b32fc905ad942992af16775e6f2b935e0945feb32.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 570, + 547, + 677 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 547, + 677 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 547, + 677 + ], + "type": "inline_equation", + "content": "\\Psi(.)" + }, + { + "bbox": [ + 304, + 570, + 547, + 677 + ], + "type": "text", + "content": " symbolizes an abstract functional. Here, " + }, + { + "bbox": [ + 304, + 570, + 547, + 677 + ], + "type": "inline_equation", + "content": "S" + }, + { + "bbox": [ + 304, + 570, + 547, + 677 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 570, + 547, + 677 + ], + "type": "inline_equation", + "content": "\\mathcal{P}" + }, + { + "bbox": [ + 304, + 570, + 547, + 677 + ], + "type": "text", + "content": " are estimated using structure from motion and MVS [39, 40]. As mentioned before, we first aim to recover a much better 3D scene recovery by utilizing the complementary nature of the monocular depth and stereo depth. Furthermore, estimate improved camera poses using neural graph-based multiple motion averaging. We denote " + }, + { + "bbox": [ + 304, + 570, + 547, + 677 + ], + "type": "inline_equation", + "content": "\\mathcal{D}_s" + }, + { + "bbox": [ + 304, + 570, + 547, + 677 + ], + "type": "text", + "content": " as monocular depth for each image in " + }, + { + "bbox": [ + 304, + 570, + 547, + 677 + ], + "type": "inline_equation", + "content": "\\mathcal{I}_s" + }, + { + "bbox": [ + 304, + 570, + 547, + 677 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 570, + 547, + 677 + ], + "type": "inline_equation", + "content": "\\mathcal{S}_R" + }, + { + "bbox": [ + 304, + 570, + 547, + 677 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 570, + 547, + 677 + ], + "type": "inline_equation", + "content": "\\mathcal{P}_R" + }, + { + "bbox": [ + 304, + 570, + 547, + 677 + ], + "type": "text", + "content": " as our scene 3D reconstruction and camera poses, respectively." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 677, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 547, + 713 + ], + "type": "text", + "content": "Once we estimate " + }, + { + "bbox": [ + 304, + 677, + 547, + 713 + ], + "type": "inline_equation", + "content": "S_{R},\\mathcal{P}_{R}" + }, + { + "bbox": [ + 304, + 677, + 547, + 713 + ], + "type": "text", + "content": ", we jointly optimize for better neural scene representation and camera poses with the neural network parameters " + }, + { + "bbox": [ + 304, + 677, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\Theta" + }, + { + "bbox": [ + 304, + 677, + 547, + 713 + ], + "type": "text", + "content": " using the proposed loss function" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "13210" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 109 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 109 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 109 + ], + "type": "text", + "content": "(Sec. 3.3). Our better scene representation and improved camera help in improved view-synthesis at test time. Our overall idea can be understood via the following equation:" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 82, + 117, + 287, + 129 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 82, + 117, + 287, + 129 + ], + "spans": [ + { + "bbox": [ + 82, + 117, + 287, + 129 + ], + "type": "interline_equation", + "content": "\\Theta , \\mathcal {S} _ {R}, \\mathcal {P} _ {R} \\sim \\Psi (\\Theta , \\mathcal {S} _ {R}, \\mathcal {P} _ {R} | \\mathcal {S}, \\mathcal {P}, \\mathcal {D} _ {s}, \\mathcal {I} _ {s}) \\tag {3}", + "image_path": "27e3081818aaed704ad2b3eb78ed525b7855130f4f0d760fc447cf0e87ac56b8.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 143, + 160, + 154 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 143, + 160, + 154 + ], + "spans": [ + { + "bbox": [ + 47, + 143, + 160, + 154 + ], + "type": "text", + "content": "3.1.1 3D Scene Features" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 161, + 287, + 270 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 161, + 287, + 270 + ], + "spans": [ + { + "bbox": [ + 46, + 161, + 287, + 270 + ], + "type": "text", + "content": "Here, we describe feature aggregation for the output view obtained using the SVS pipeline [36] combined with the back-projected RGB-D features due to images and their monocular depth via a convolutional neural network (CNN). Given the output direction " + }, + { + "bbox": [ + 46, + 161, + 287, + 270 + ], + "type": "inline_equation", + "content": "\\mathbf{u}" + }, + { + "bbox": [ + 46, + 161, + 287, + 270 + ], + "type": "text", + "content": ", for each " + }, + { + "bbox": [ + 46, + 161, + 287, + 270 + ], + "type": "inline_equation", + "content": "\\mathbf{x} \\in \\mathbb{R}^3" + }, + { + "bbox": [ + 46, + 161, + 287, + 270 + ], + "type": "text", + "content": " on the geometric scaffold along " + }, + { + "bbox": [ + 46, + 161, + 287, + 270 + ], + "type": "inline_equation", + "content": "\\mathbf{u}" + }, + { + "bbox": [ + 46, + 161, + 287, + 270 + ], + "type": "text", + "content": " there is a subset of source images, in which " + }, + { + "bbox": [ + 46, + 161, + 287, + 270 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 46, + 161, + 287, + 270 + ], + "type": "text", + "content": " is visible. Assuming the total number of images in this subset to be " + }, + { + "bbox": [ + 46, + 161, + 287, + 270 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 46, + 161, + 287, + 270 + ], + "type": "text", + "content": ", we denote the set of view directions corresponding to these images as " + }, + { + "bbox": [ + 46, + 161, + 287, + 270 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{v}_k\\}_{k=1}^K" + }, + { + "bbox": [ + 46, + 161, + 287, + 270 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 271, + 287, + 356 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 271, + 287, + 356 + ], + "spans": [ + { + "bbox": [ + 46, + 271, + 287, + 356 + ], + "type": "text", + "content": "(i) SVS Features. The source images in " + }, + { + "bbox": [ + 46, + 271, + 287, + 356 + ], + "type": "inline_equation", + "content": "\\mathcal{I}_s" + }, + { + "bbox": [ + 46, + 271, + 287, + 356 + ], + "type": "text", + "content": " are first passed through a feature extraction CNN to obtain a feature tensor " + }, + { + "bbox": [ + 46, + 271, + 287, + 356 + ], + "type": "inline_equation", + "content": "\\mathcal{F}_k" + }, + { + "bbox": [ + 46, + 271, + 287, + 356 + ], + "type": "text", + "content": " corresponding to " + }, + { + "bbox": [ + 46, + 271, + 287, + 356 + ], + "type": "inline_equation", + "content": "k^{th}" + }, + { + "bbox": [ + 46, + 271, + 287, + 356 + ], + "type": "text", + "content": " image. Denoting " + }, + { + "bbox": [ + 46, + 271, + 287, + 356 + ], + "type": "inline_equation", + "content": "f_{k}(\\mathbf{x})" + }, + { + "bbox": [ + 46, + 271, + 287, + 356 + ], + "type": "text", + "content": " as the feature corresponding to a point " + }, + { + "bbox": [ + 46, + 271, + 287, + 356 + ], + "type": "inline_equation", + "content": "\\mathbf{x} \\in \\mathbb{R}^3" + }, + { + "bbox": [ + 46, + 271, + 287, + 356 + ], + "type": "text", + "content": " in " + }, + { + "bbox": [ + 46, + 271, + 287, + 356 + ], + "type": "inline_equation", + "content": "\\mathcal{F}_k" + }, + { + "bbox": [ + 46, + 271, + 287, + 356 + ], + "type": "text", + "content": " located at the projection (or bilinear interpolation) of " + }, + { + "bbox": [ + 46, + 271, + 287, + 356 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 46, + 271, + 287, + 356 + ], + "type": "text", + "content": " on " + }, + { + "bbox": [ + 46, + 271, + 287, + 356 + ], + "type": "inline_equation", + "content": "k^{th}" + }, + { + "bbox": [ + 46, + 271, + 287, + 356 + ], + "type": "text", + "content": " image. To this end, SVS [36] proposed the following aggregation function " + }, + { + "bbox": [ + 46, + 271, + 287, + 356 + ], + "type": "inline_equation", + "content": "(\\phi_a)" + }, + { + "bbox": [ + 46, + 271, + 287, + 356 + ], + "type": "text", + "content": " to compute the feature for " + }, + { + "bbox": [ + 46, + 271, + 287, + 356 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 46, + 271, + 287, + 356 + ], + "type": "text", + "content": " along " + }, + { + "bbox": [ + 46, + 271, + 287, + 356 + ], + "type": "inline_equation", + "content": "\\mathbf{u}" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 58, + 363, + 287, + 396 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 363, + 287, + 396 + ], + "spans": [ + { + "bbox": [ + 58, + 363, + 287, + 396 + ], + "type": "interline_equation", + "content": "\\phi_ {a} (\\mathbf {u}, \\left\\{\\left(\\mathbf {v} _ {k}, f _ {k} (\\mathbf {x})\\right) \\right\\}) = \\frac {1}{W} \\sum_ {k = 1} ^ {K} \\max (0, \\mathbf {u} ^ {\\mathrm {T}} \\mathbf {v}) f _ {k} (\\mathbf {x}), \\tag {4}", + "image_path": "271266e9eeca376c2bd8bdd87c6421f127546d3e8cd7b3ebfeea8e2593c00f30.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 403, + 286, + 418 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 403, + 286, + 418 + ], + "spans": [ + { + "bbox": [ + 46, + 403, + 286, + 418 + ], + "type": "text", + "content": "where, " + }, + { + "bbox": [ + 46, + 403, + 286, + 418 + ], + "type": "inline_equation", + "content": "W = \\sum_{k=1}^{K} \\max(0, \\mathbf{u}^{\\mathrm{T}}\\mathbf{v})" + }, + { + "bbox": [ + 46, + 403, + 286, + 418 + ], + "type": "text", + "content": " is sum of all the weights." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 419, + 287, + 504 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 419, + 287, + 504 + ], + "spans": [ + { + "bbox": [ + 46, + 419, + 287, + 504 + ], + "type": "text", + "content": "(ii) Monocular Features. Given an image, we predict its depth with a per-pixel confidence score. For this, we use an existing monocular depth prediction network [32] pretrained on Omnidata [7]. To predict a normalized depth prediction confidence score per pixel " + }, + { + "bbox": [ + 46, + 419, + 287, + 504 + ], + "type": "inline_equation", + "content": "w_{ij}" + }, + { + "bbox": [ + 46, + 419, + 287, + 504 + ], + "type": "text", + "content": ", we add another network on top of it (refer supplementary for details), which takes both images and depth as input." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 52, + 511, + 287, + 537 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 52, + 511, + 287, + 537 + ], + "spans": [ + { + "bbox": [ + 52, + 511, + 287, + 537 + ], + "type": "interline_equation", + "content": "\\sum_ {i} \\sum_ {j} w _ {i j} \\cdot \\mathcal {L} \\left(d _ {i j}, \\hat {d} _ {i j}\\right); \\text {w h e r e}, w _ {i j} = \\phi_ {w} \\left(\\mathcal {I} _ {s}, \\mathcal {D} _ {s}\\right) _ {i j}. \\tag {5}", + "image_path": "a549afd6b1cde8283503587f709d38928df6b6394b38e6fb12b73decdda570aa.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 544, + 287, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 544, + 287, + 689 + ], + "spans": [ + { + "bbox": [ + 46, + 544, + 287, + 689 + ], + "type": "inline_equation", + "content": "\\mathcal{L}" + }, + { + "bbox": [ + 46, + 544, + 287, + 689 + ], + "type": "text", + "content": " symbolizes the " + }, + { + "bbox": [ + 46, + 544, + 287, + 689 + ], + "type": "inline_equation", + "content": "l_{2}" + }, + { + "bbox": [ + 46, + 544, + 287, + 689 + ], + "type": "text", + "content": " loss between the known pixel depth " + }, + { + "bbox": [ + 46, + 544, + 287, + 689 + ], + "type": "inline_equation", + "content": "d_{ij}" + }, + { + "bbox": [ + 46, + 544, + 287, + 689 + ], + "type": "text", + "content": " and the predicted depth " + }, + { + "bbox": [ + 46, + 544, + 287, + 689 + ], + "type": "inline_equation", + "content": "\\hat{d}_{ij}" + }, + { + "bbox": [ + 46, + 544, + 287, + 689 + ], + "type": "text", + "content": " for " + }, + { + "bbox": [ + 46, + 544, + 287, + 689 + ], + "type": "inline_equation", + "content": "(i,j)" + }, + { + "bbox": [ + 46, + 544, + 287, + 689 + ], + "type": "text", + "content": " pixel in the 2D depth image. We call network " + }, + { + "bbox": [ + 46, + 544, + 287, + 689 + ], + "type": "inline_equation", + "content": "\\phi_w" + }, + { + "bbox": [ + 46, + 544, + 287, + 689 + ], + "type": "text", + "content": " as the \"confidence-prediction head\". We take the depths predicted by this network and fuse them with the source image using the Channel Exchange Network [47]. The fused information is then projected into " + }, + { + "bbox": [ + 46, + 544, + 287, + 689 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 544, + 287, + 689 + ], + "type": "text", + "content": " dimensional feature space using network " + }, + { + "bbox": [ + 46, + 544, + 287, + 689 + ], + "type": "inline_equation", + "content": "\\mathcal{F}_{\\theta}" + }, + { + "bbox": [ + 46, + 544, + 287, + 689 + ], + "type": "text", + "content": ", which is a CNN-based architecture. To compute the feature corresponding to a pixel " + }, + { + "bbox": [ + 46, + 544, + 287, + 689 + ], + "type": "inline_equation", + "content": "\\mathbf{p}" + }, + { + "bbox": [ + 46, + 544, + 287, + 689 + ], + "type": "text", + "content": " in the target view " + }, + { + "bbox": [ + 46, + 544, + 287, + 689 + ], + "type": "inline_equation", + "content": "\\mathbf{u}" + }, + { + "bbox": [ + 46, + 544, + 287, + 689 + ], + "type": "text", + "content": ", we warp the features predicted for each source views " + }, + { + "bbox": [ + 46, + 544, + 287, + 689 + ], + "type": "inline_equation", + "content": "\\mathbf{v}_k" + }, + { + "bbox": [ + 46, + 544, + 287, + 689 + ], + "type": "text", + "content": " to this target view but now using the monocular depth " + }, + { + "bbox": [ + 46, + 544, + 287, + 689 + ], + "type": "inline_equation", + "content": "d \\in \\mathcal{D}_s" + }, + { + "bbox": [ + 46, + 544, + 287, + 689 + ], + "type": "text", + "content": " of the source view." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 102, + 700, + 287, + 715 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 102, + 700, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 102, + 700, + 287, + 715 + ], + "type": "interline_equation", + "content": "g _ {k} (\\mathbf {u}, \\mathbf {p}) = f _ {k} ^ {m} \\left(\\mathcal {W} (\\mathbf {p}, \\mathbf {u}, \\mathbf {v} _ {k}, d)\\right) \\tag {6}", + "image_path": "08fa3f921d63ede39e5f157c51f26f5427d41469e1d5d8cedb6ab737abee3ed6.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 72, + 545, + 144 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 545, + 144 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 545, + 144 + ], + "type": "text", + "content": "where, " + }, + { + "bbox": [ + 305, + 72, + 545, + 144 + ], + "type": "inline_equation", + "content": "g_{k}" + }, + { + "bbox": [ + 305, + 72, + 545, + 144 + ], + "type": "text", + "content": " denotes the feature warping function, " + }, + { + "bbox": [ + 305, + 72, + 545, + 144 + ], + "type": "inline_equation", + "content": "f_{k}^{m}(p)" + }, + { + "bbox": [ + 305, + 72, + 545, + 144 + ], + "type": "text", + "content": " corresponds to feature in the tensor " + }, + { + "bbox": [ + 305, + 72, + 545, + 144 + ], + "type": "inline_equation", + "content": "\\mathcal{F}_{\\theta}(\\mathcal{T}_s^k,d)" + }, + { + "bbox": [ + 305, + 72, + 545, + 144 + ], + "type": "text", + "content": " (corresponding to " + }, + { + "bbox": [ + 305, + 72, + 545, + 144 + ], + "type": "inline_equation", + "content": "k^{th}" + }, + { + "bbox": [ + 305, + 72, + 545, + 144 + ], + "type": "text", + "content": " source image and corresponding monocular depth) at pixel " + }, + { + "bbox": [ + 305, + 72, + 545, + 144 + ], + "type": "inline_equation", + "content": "\\mathbf{p}" + }, + { + "bbox": [ + 305, + 72, + 545, + 144 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 305, + 72, + 545, + 144 + ], + "type": "inline_equation", + "content": "\\mathcal{W}" + }, + { + "bbox": [ + 305, + 72, + 545, + 144 + ], + "type": "text", + "content": " is the warping function. We now aggregate the warped features corresponding to each source image using a weighted sum based on confidence scores:" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 340, + 151, + 545, + 184 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 340, + 151, + 545, + 184 + ], + "spans": [ + { + "bbox": [ + 340, + 151, + 545, + 184 + ], + "type": "interline_equation", + "content": "\\phi_ {a} (\\mathbf {u}, \\left\\{\\left(\\mathbf {v} _ {k}, f _ {k} ^ {m} (\\mathbf {p})\\right) \\right\\}) = \\sum_ {k = 1} ^ {K} c _ {k} (\\mathbf {p}) f _ {k} ^ {m} (\\mathbf {p}) \\tag {7}", + "image_path": "f6cbd99ae6ec07310ccc5e83eddaae48488a3f1fbd5b1b9b543413ed8bd27699.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 190, + 545, + 213 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 190, + 545, + 213 + ], + "spans": [ + { + "bbox": [ + 305, + 190, + 545, + 213 + ], + "type": "text", + "content": "here, " + }, + { + "bbox": [ + 305, + 190, + 545, + 213 + ], + "type": "inline_equation", + "content": "c_k" + }, + { + "bbox": [ + 305, + 190, + 545, + 213 + ], + "type": "text", + "content": " symbolizes the predicted depth confidence map in the " + }, + { + "bbox": [ + 305, + 190, + 545, + 213 + ], + "type": "inline_equation", + "content": "k^{th}" + }, + { + "bbox": [ + 305, + 190, + 545, + 213 + ], + "type": "text", + "content": " view." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 217, + 545, + 324 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 217, + 545, + 324 + ], + "spans": [ + { + "bbox": [ + 305, + 217, + 545, + 324 + ], + "type": "text", + "content": "(iii) Structure Feature Aggregation Per Scene Point. Given we have features from two different modalities i.e., monocular depth and MVS, we now propose an aggregated feature representation for the target view per scene point " + }, + { + "bbox": [ + 305, + 217, + 545, + 324 + ], + "type": "inline_equation", + "content": "h_f = h_\\theta(h_m, h_s)" + }, + { + "bbox": [ + 305, + 217, + 545, + 324 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 305, + 217, + 545, + 324 + ], + "type": "inline_equation", + "content": "h_\\theta" + }, + { + "bbox": [ + 305, + 217, + 545, + 324 + ], + "type": "text", + "content": " is a CNN-based neural network with parameters " + }, + { + "bbox": [ + 305, + 217, + 545, + 324 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 305, + 217, + 545, + 324 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 217, + 545, + 324 + ], + "type": "inline_equation", + "content": "h_m" + }, + { + "bbox": [ + 305, + 217, + 545, + 324 + ], + "type": "text", + "content": " is the final representation for the monocular estimation and " + }, + { + "bbox": [ + 305, + 217, + 545, + 324 + ], + "type": "inline_equation", + "content": "h_s" + }, + { + "bbox": [ + 305, + 217, + 545, + 324 + ], + "type": "text", + "content": " for the stereo-estimation. We aim to attain maximal correlation from both of the input representations i.e.," + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 310, + 331, + 545, + 346 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 310, + 331, + 545, + 346 + ], + "spans": [ + { + "bbox": [ + 310, + 331, + 545, + 346 + ], + "type": "interline_equation", + "content": "\\lambda_ {1} \\mathcal {C} \\left(h _ {f}, h _ {m}\\right) \\cdot \\mathcal {C} \\left(h _ {f}, h _ {s}\\right) + \\lambda_ {2} \\mathcal {C} \\left(h _ {f}, h _ {s}\\right) + \\lambda_ {3} \\mathcal {C} \\left(h _ {f}, h _ {m}\\right) \\tag {8}", + "image_path": "ba42d376ce0b030be22f7ab4d9c7fecc3fac957b97a7c88deaecfe40e553321a.jpg" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 352, + 545, + 533 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 352, + 545, + 533 + ], + "spans": [ + { + "bbox": [ + 305, + 352, + 545, + 533 + ], + "type": "text", + "content": "where, " + }, + { + "bbox": [ + 305, + 352, + 545, + 533 + ], + "type": "inline_equation", + "content": "\\sum_{i=1}^{3} \\lambda_i = 1" + }, + { + "bbox": [ + 305, + 352, + 545, + 533 + ], + "type": "text", + "content": "; " + }, + { + "bbox": [ + 305, + 352, + 545, + 533 + ], + "type": "inline_equation", + "content": "\\lambda_i > 0 \\forall i \\in \\{1,2,3\\}" + }, + { + "bbox": [ + 305, + 352, + 545, + 533 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 352, + 545, + 533 + ], + "type": "inline_equation", + "content": "\\mathcal{C}(.)" + }, + { + "bbox": [ + 305, + 352, + 545, + 533 + ], + "type": "text", + "content": " being the standard correlation function [3]. We set " + }, + { + "bbox": [ + 305, + 352, + 545, + 533 + ], + "type": "inline_equation", + "content": "\\lambda_1 = 1" + }, + { + "bbox": [ + 305, + 352, + 545, + 533 + ], + "type": "text", + "content": " for nearby points where confidence of monocular depth could be greater than a defined threshold (" + }, + { + "bbox": [ + 305, + 352, + 545, + 533 + ], + "type": "inline_equation", + "content": "\\tau" + }, + { + "bbox": [ + 305, + 352, + 545, + 533 + ], + "type": "text", + "content": "). " + }, + { + "bbox": [ + 305, + 352, + 545, + 533 + ], + "type": "inline_equation", + "content": "\\lambda_2 = 1" + }, + { + "bbox": [ + 305, + 352, + 545, + 533 + ], + "type": "text", + "content": " for nearby points where confidence of monocular depth is lower than a defined threshold and finally " + }, + { + "bbox": [ + 305, + 352, + 545, + 533 + ], + "type": "inline_equation", + "content": "\\lambda_3 = 1" + }, + { + "bbox": [ + 305, + 352, + 545, + 533 + ], + "type": "text", + "content": " for far points whose relative depth is greater than a pre-defined threshold (" + }, + { + "bbox": [ + 305, + 352, + 545, + 533 + ], + "type": "inline_equation", + "content": "\\sigma" + }, + { + "bbox": [ + 305, + 352, + 545, + 533 + ], + "type": "text", + "content": "). Such a choice is made since stereo features might be less accurate in certain depth range due to low disparity or too close to the lens. The final aggregation " + }, + { + "bbox": [ + 305, + 352, + 545, + 533 + ], + "type": "inline_equation", + "content": "h_f" + }, + { + "bbox": [ + 305, + 352, + 545, + 533 + ], + "type": "text", + "content": " comprises of CNN networks " + }, + { + "bbox": [ + 305, + 352, + 545, + 533 + ], + "type": "inline_equation", + "content": "\\phi_\\alpha" + }, + { + "bbox": [ + 305, + 352, + 545, + 533 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 352, + 545, + 533 + ], + "type": "inline_equation", + "content": "\\phi_\\beta" + }, + { + "bbox": [ + 305, + 352, + 545, + 533 + ], + "type": "text", + "content": ", parameterized by " + }, + { + "bbox": [ + 305, + 352, + 545, + 533 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 305, + 352, + 545, + 533 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 352, + 545, + 533 + ], + "type": "inline_equation", + "content": "\\beta" + }, + { + "bbox": [ + 305, + 352, + 545, + 533 + ], + "type": "text", + "content": ", respectively. The transformed features from each of these modalities are then fed to a CNN network " + }, + { + "bbox": [ + 305, + 352, + 545, + 533 + ], + "type": "inline_equation", + "content": "\\phi_\\nu" + }, + { + "bbox": [ + 305, + 352, + 545, + 533 + ], + "type": "text", + "content": " with parameters " + }, + { + "bbox": [ + 305, + 352, + 545, + 533 + ], + "type": "inline_equation", + "content": "\\nu" + }, + { + "bbox": [ + 305, + 352, + 545, + 533 + ], + "type": "text", + "content": ". Overall aggregated features per scene point is represented as" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 338, + 540, + 545, + 554 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 338, + 540, + 545, + 554 + ], + "spans": [ + { + "bbox": [ + 338, + 540, + 545, + 554 + ], + "type": "interline_equation", + "content": "h _ {f} = h _ {\\theta} \\left(h _ {m}, h _ {s}\\right) = \\phi_ {\\nu} \\left(\\phi_ {\\alpha} \\left(h _ {m}\\right), \\phi_ {\\beta} \\left(h _ {s}\\right)\\right). \\tag {9}", + "image_path": "629be73b91caa8685ebd38112c75e84238ee408d402a0d27247470ea4e81726b.jpg" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 306, + 574, + 444, + 586 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 574, + 444, + 586 + ], + "spans": [ + { + "bbox": [ + 306, + 574, + 444, + 586 + ], + "type": "text", + "content": "3.1.2 Camera Pose Estimation" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 594, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 594, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 594, + 545, + 713 + ], + "type": "text", + "content": "Given we have initially estimated pose-set " + }, + { + "bbox": [ + 304, + 594, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{P}" + }, + { + "bbox": [ + 304, + 594, + 545, + 713 + ], + "type": "text", + "content": ", we use multiple motion averaging (MRA) to recover better camera poses. MRA is fast, efficient, and robust in camera pose estimation from noisy key-point correspondences and works well even for sparse image sets. MRA takes a global view of the camera recovery problem. A view-graph corresponding to the initial set of camera poses is constructed as a global representation, with each graph node as a pose. For pose optimization, MRA first performs rotation averaging to recover rotation and then solves for translation. Assume a" + } + ] + } + ], + "index": 19 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "13211" + } + ] + } + ], + "index": 20 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 61, + 70, + 535, + 316 + ], + "blocks": [ + { + "bbox": [ + 61, + 70, + 535, + 316 + ], + "lines": [ + { + "bbox": [ + 61, + 70, + 535, + 316 + ], + "spans": [ + { + "bbox": [ + 61, + 70, + 535, + 316 + ], + "type": "image", + "image_path": "4c602515800266cadd3dbebe829d221fb3a33b386227eb1e465dc1f8ae215223.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 327, + 547, + 396 + ], + "lines": [ + { + "bbox": [ + 46, + 327, + 547, + 396 + ], + "spans": [ + { + "bbox": [ + 46, + 327, + 547, + 396 + ], + "type": "text", + "content": "Figure 2. Overview. For a given set of input images, we first estimate the scene 3D structure and the initial value of camera poses using structure from motion (SFM) followed by MVS. We also estimate per-image depth using an existing Monocular Depth estimation model [7]. Next, we generate two sets of Projected Features for each target view: The first set (upper stream) by encoding the input images and then unprojecting the features onto the scaffold, followed by re-projection to the target view and aggregation. For the second set (lower stream), the images are first concatenated with their monocular depths (MD), and the encoded features are then projected using these depths, followed by aggregation. These two feature sets are then merged into Cumulative Features, and finally, the target view is rendered." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 414, + 289, + 513 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 414, + 289, + 513 + ], + "spans": [ + { + "bbox": [ + 46, + 414, + 289, + 513 + ], + "type": "text", + "content": "directed view-graph " + }, + { + "bbox": [ + 46, + 414, + 289, + 513 + ], + "type": "inline_equation", + "content": "\\mathcal{G} = (\\mathcal{V},\\mathcal{E})" + }, + { + "bbox": [ + 46, + 414, + 289, + 513 + ], + "type": "text", + "content": ". A vertex " + }, + { + "bbox": [ + 46, + 414, + 289, + 513 + ], + "type": "inline_equation", + "content": "\\mathcal{V}_j\\in \\mathcal{V}" + }, + { + "bbox": [ + 46, + 414, + 289, + 513 + ], + "type": "text", + "content": " in this view graph corresponds to " + }, + { + "bbox": [ + 46, + 414, + 289, + 513 + ], + "type": "inline_equation", + "content": "j^{th}" + }, + { + "bbox": [ + 46, + 414, + 289, + 513 + ], + "type": "text", + "content": " camera absolute rotation " + }, + { + "bbox": [ + 46, + 414, + 289, + 513 + ], + "type": "inline_equation", + "content": "R_{j}" + }, + { + "bbox": [ + 46, + 414, + 289, + 513 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 414, + 289, + 513 + ], + "type": "inline_equation", + "content": "\\mathcal{E}_{ij}\\in \\mathcal{E}" + }, + { + "bbox": [ + 46, + 414, + 289, + 513 + ], + "type": "text", + "content": " corresponds to the relative orientation " + }, + { + "bbox": [ + 46, + 414, + 289, + 513 + ], + "type": "inline_equation", + "content": "\\tilde{R}_{ij}" + }, + { + "bbox": [ + 46, + 414, + 289, + 513 + ], + "type": "text", + "content": " between view " + }, + { + "bbox": [ + 46, + 414, + 289, + 513 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 414, + 289, + 513 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 414, + 289, + 513 + ], + "type": "inline_equation", + "content": "j" + }, + { + "bbox": [ + 46, + 414, + 289, + 513 + ], + "type": "text", + "content": ". For our problem, relative orientations are given (noisy), and we aim to solve for absolute pose " + }, + { + "bbox": [ + 46, + 414, + 289, + 513 + ], + "type": "inline_equation", + "content": "R_{j}" + }, + { + "bbox": [ + 46, + 414, + 289, + 513 + ], + "type": "text", + "content": " robustly. Conventionally, in the presence of noise, the solution is obtained by solving the following optimization problem to satisfy compatibility criteria." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 99, + 519, + 287, + 548 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 99, + 519, + 287, + 548 + ], + "spans": [ + { + "bbox": [ + 99, + 519, + 287, + 548 + ], + "type": "interline_equation", + "content": "\\underset {\\{R _ {j} \\}} {\\operatorname {a r g m i n}} \\sum_ {\\mathcal {E} _ {i j} \\in \\mathcal {E}} \\rho (\\gamma (\\tilde {R} _ {i j}, R _ {j} R _ {i} ^ {- 1})) \\tag {10}", + "image_path": "84524b221761dfeed118b0959e18aaec7751cee6a7d4e535fbae1fc70cd6cf4d.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 555, + 289, + 665 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 555, + 289, + 665 + ], + "spans": [ + { + "bbox": [ + 46, + 555, + 289, + 665 + ], + "type": "text", + "content": "where, " + }, + { + "bbox": [ + 46, + 555, + 289, + 665 + ], + "type": "inline_equation", + "content": "\\gamma(.)" + }, + { + "bbox": [ + 46, + 555, + 289, + 665 + ], + "type": "text", + "content": " denotes a metric on " + }, + { + "bbox": [ + 46, + 555, + 289, + 665 + ], + "type": "inline_equation", + "content": "SO(3)" + }, + { + "bbox": [ + 46, + 555, + 289, + 665 + ], + "type": "text", + "content": " to measure distance between two rotation and " + }, + { + "bbox": [ + 46, + 555, + 289, + 665 + ], + "type": "inline_equation", + "content": "\\rho(.)" + }, + { + "bbox": [ + 46, + 555, + 289, + 665 + ], + "type": "text", + "content": " is a robust " + }, + { + "bbox": [ + 46, + 555, + 289, + 665 + ], + "type": "inline_equation", + "content": "l_1" + }, + { + "bbox": [ + 46, + 555, + 289, + 665 + ], + "type": "text", + "content": " norm. We use a graph-neural network to predict the robustified pose view-graph of the scene following the camera pose refining approach of NeuRoRA [30]. First, the camera poses are checked for outliers via a cyclic consistency in the posegraph [11]. Then, a view graph is initialized based on these filtered poses. This view graph is then optimized using the camera pose-refining network of NeuRoRA [30]." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 671, + 176, + 685 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 671, + 176, + 685 + ], + "spans": [ + { + "bbox": [ + 47, + 671, + 176, + 685 + ], + "type": "text", + "content": "3.2. Rendering novel views" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 689, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 689, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 689, + 288, + 715 + ], + "type": "text", + "content": "The aggregated feature tensor " + }, + { + "bbox": [ + 46, + 689, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\mathcal{F}^a" + }, + { + "bbox": [ + 46, + 689, + 288, + 715 + ], + "type": "text", + "content": " along a direction " + }, + { + "bbox": [ + 46, + 689, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\mathbf{u}" + }, + { + "bbox": [ + 46, + 689, + 288, + 715 + ], + "type": "text", + "content": " comprises of the features " + }, + { + "bbox": [ + 46, + 689, + 288, + 715 + ], + "type": "inline_equation", + "content": "h_f" + }, + { + "bbox": [ + 46, + 689, + 288, + 715 + ], + "type": "text", + "content": " (Eq. 9) for each pixel along " + }, + { + "bbox": [ + 46, + 689, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\mathbf{u}" + }, + { + "bbox": [ + 46, + 689, + 288, + 715 + ], + "type": "text", + "content": "," + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 414, + 545, + 523 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 414, + 545, + 523 + ], + "spans": [ + { + "bbox": [ + 304, + 414, + 545, + 523 + ], + "type": "text", + "content": "obtained using 3D scene features (discussed in Sec. 3.1.1). This tensor is now projected to the image space function using " + }, + { + "bbox": [ + 304, + 414, + 545, + 523 + ], + "type": "inline_equation", + "content": "\\mathcal{G}_{\\theta}" + }, + { + "bbox": [ + 304, + 414, + 545, + 523 + ], + "type": "text", + "content": ", a CNN-based network with parameters " + }, + { + "bbox": [ + 304, + 414, + 545, + 523 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 304, + 414, + 545, + 523 + ], + "type": "text", + "content": ". It is quite possible that the regions in the target image may not be encountered in any of the source images. For those points, the values in feature tensor " + }, + { + "bbox": [ + 304, + 414, + 545, + 523 + ], + "type": "inline_equation", + "content": "\\mathcal{F}" + }, + { + "bbox": [ + 304, + 414, + 545, + 523 + ], + "type": "text", + "content": " are set to " + }, + { + "bbox": [ + 304, + 414, + 545, + 523 + ], + "type": "inline_equation", + "content": "\\mathbf{0}" + }, + { + "bbox": [ + 304, + 414, + 545, + 523 + ], + "type": "text", + "content": ", and thus, they require some inpainting. Denoting the set of test images by " + }, + { + "bbox": [ + 304, + 414, + 545, + 523 + ], + "type": "inline_equation", + "content": "\\mathcal{I}_t" + }, + { + "bbox": [ + 304, + 414, + 545, + 523 + ], + "type": "text", + "content": ", the rendered image corresponding to the " + }, + { + "bbox": [ + 304, + 414, + 545, + 523 + ], + "type": "inline_equation", + "content": "k^{th}" + }, + { + "bbox": [ + 304, + 414, + 545, + 523 + ], + "type": "text", + "content": " image in the test set, " + }, + { + "bbox": [ + 304, + 414, + 545, + 523 + ], + "type": "inline_equation", + "content": "\\hat{\\mathcal{I}}_t^k" + }, + { + "bbox": [ + 304, + 414, + 545, + 523 + ], + "type": "text", + "content": ", is predicted based on the following equation:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 395, + 533, + 545, + 548 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 395, + 533, + 545, + 548 + ], + "spans": [ + { + "bbox": [ + 395, + 533, + 545, + 548 + ], + "type": "interline_equation", + "content": "\\hat {\\mathcal {I}} _ {t} ^ {k} = \\mathcal {G} _ {\\theta} \\left(\\mathcal {F} _ {k} ^ {a}\\right) \\tag {11}", + "image_path": "b788e01e034059b888cf9918222d67b56e2b38eb020cb0c008477011edf25065.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 551, + 547, + 611 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 551, + 547, + 611 + ], + "spans": [ + { + "bbox": [ + 304, + 551, + 547, + 611 + ], + "type": "text", + "content": "Similar to stable view synthesis, we parameterize the " + }, + { + "bbox": [ + 304, + 551, + 547, + 611 + ], + "type": "inline_equation", + "content": "\\mathcal{G}_{\\theta}" + }, + { + "bbox": [ + 304, + 551, + 547, + 611 + ], + "type": "text", + "content": " function using a U-Net [37] style model which also deals with inpainting/hallucinating the newly discovered regions in the test image. Fig.(2) shows the complete overview of the proposed method." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 616, + 417, + 630 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 616, + 417, + 630 + ], + "spans": [ + { + "bbox": [ + 306, + 616, + 417, + 630 + ], + "type": "text", + "content": "3.3. Joint Optimization" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 635, + 546, + 659 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 635, + 546, + 659 + ], + "spans": [ + { + "bbox": [ + 306, + 635, + 546, + 659 + ], + "type": "text", + "content": "Given " + }, + { + "bbox": [ + 306, + 635, + 546, + 659 + ], + "type": "inline_equation", + "content": "\\mathcal{I}_s" + }, + { + "bbox": [ + 306, + 635, + 546, + 659 + ], + "type": "text", + "content": ", we train the model using our overall loss function " + }, + { + "bbox": [ + 306, + 635, + 546, + 659 + ], + "type": "inline_equation", + "content": "\\mathcal{L}" + }, + { + "bbox": [ + 306, + 635, + 546, + 659 + ], + "type": "text", + "content": " comprising of two terms." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 397, + 670, + 545, + 685 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 397, + 670, + 545, + 685 + ], + "spans": [ + { + "bbox": [ + 397, + 670, + 545, + 685 + ], + "type": "interline_equation", + "content": "\\mathcal {L} = \\mathcal {L} _ {s} + \\mathcal {L} _ {p} \\tag {12}", + "image_path": "d945fee8d7dd87deccfab56cc6b175edf902b697bd326cb1955d10bdb2b203c0.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 689, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 689, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 689, + 547, + 715 + ], + "type": "text", + "content": "(i) The first loss term " + }, + { + "bbox": [ + 304, + 689, + 547, + 715 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_s" + }, + { + "bbox": [ + 304, + 689, + 547, + 715 + ], + "type": "text", + "content": " encourages the network to learn better features corresponding to the scene point. The " + }, + { + "bbox": [ + 304, + 689, + 547, + 715 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_s" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "13212" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 50, + 69, + 545, + 148 + ], + "blocks": [ + { + "bbox": [ + 50, + 69, + 545, + 148 + ], + "lines": [ + { + "bbox": [ + 50, + 69, + 545, + 148 + ], + "spans": [ + { + "bbox": [ + 50, + 69, + 545, + 148 + ], + "type": "table", + "html": "
TruckM60PlaygroundTrain
PSNR↑LPIPS↓SSIM↑PSNR↑LPIPS↓SSIM↑PSNR↑LPIPS↓SSIM↑PSNR↑LPIPS↓SSIM↑
NeRF++ [49]21.80.310.8117.60.430.7321.90.390.7917.60.480.68
FVS [35]21.90.140.8415.80.320.7721.70.210.8317.30.280.75
SC-NeRF [17]22.30.290.8218.40.400.7622.40.350.8318.20.420.73
Point-NeRF [48]22.70.140.8719.60.210.8522.20.190.8318.60.160.83
SVS [36]22.90.120.8819.10.220.8322.90.170.8617.90.190.81
Ours24.10.120.9020.80.200.8923.90.140.9020.10.130.88
", + "image_path": "fc7b35637c65fecfed663e20c5bfd434a3860dfc9821926d8a32d65e17e4cd03.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 50, + 186, + 545, + 247 + ], + "blocks": [ + { + "bbox": [ + 46, + 154, + 546, + 177 + ], + "lines": [ + { + "bbox": [ + 46, + 154, + 546, + 177 + ], + "spans": [ + { + "bbox": [ + 46, + 154, + 546, + 177 + ], + "type": "text", + "content": "Table 1. Rendered image quality comparison with current state-of-the-art methods in novel view synthesis on the popular Tanks and Temples dataset [18]. We use the popular metrics i.e., PSNR, LPIPS and SSIM for the comparison." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 50, + 186, + 545, + 247 + ], + "lines": [ + { + "bbox": [ + 50, + 186, + 545, + 247 + ], + "spans": [ + { + "bbox": [ + 50, + 186, + 545, + 247 + ], + "type": "table", + "html": "
BikeFlowersPirateDiggerSandboxSoccertable
SSIM↑LPIPS↓SSIM↑LPIPS↓SSIM↑LPIPS↓SSIM↑LPIPS↓SSIM↑LPIPS↓SSIM↑LPIPS↓
NeRF++ [49]0.710.270.800.310.710.430.650.350.840.240.870.21
FVS [35]0.610.280.790.270.690.370.680.240.780.320.820.21
SVS [36]0.740.220.840.210.750.320.770.180.850.200.910.15
Ours0.790.190.880.180.800.290.810.160.910.170.940.13
", + "image_path": "15b1858a79e17f0ad30c84920319f68b8ebe223c539af6a5a77d5e74cd367710.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 55, + 254, + 536, + 266 + ], + "lines": [ + { + "bbox": [ + 55, + 254, + 536, + 266 + ], + "spans": [ + { + "bbox": [ + 55, + 254, + 536, + 266 + ], + "type": "text", + "content": "Table 2. Quantitative comparison on FVS dataset [35]. We use the popular metrics, i.e., PSNR, LPIPS and SSIM for the comparison." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 286, + 287, + 382 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 286, + 287, + 382 + ], + "spans": [ + { + "bbox": [ + 46, + 286, + 287, + 382 + ], + "type": "text", + "content": "comprises to two objective function " + }, + { + "bbox": [ + 46, + 286, + 287, + 382 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{rgb}" + }, + { + "bbox": [ + 46, + 286, + 287, + 382 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 286, + 287, + 382 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{corr}" + }, + { + "bbox": [ + 46, + 286, + 287, + 382 + ], + "type": "text", + "content": ". The function " + }, + { + "bbox": [ + 46, + 286, + 287, + 382 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{rgb}" + }, + { + "bbox": [ + 46, + 286, + 287, + 382 + ], + "type": "text", + "content": " measures the discrepancies between the rendering of an image in the source set and the actual image available in the set. This objective is used to train the structure estimation and rendering network parameters jointly. Whereas " + }, + { + "bbox": [ + 46, + 286, + 287, + 382 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{corr}" + }, + { + "bbox": [ + 46, + 286, + 287, + 382 + ], + "type": "text", + "content": " is used for maximizing the correlation objective discussed in Eq.(8) to arrive at the optimal aggregated scene representation." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 121, + 394, + 287, + 407 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 121, + 394, + 287, + 407 + ], + "spans": [ + { + "bbox": [ + 121, + 394, + 287, + 407 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {s} = \\mathcal {L} _ {r g b} + \\mathcal {L} _ {c o r r} \\tag {13}", + "image_path": "f2e16ba7ab56a0fc341b17ee1ab1e7a9ee2ef94c4484bc590414872a89f8b562.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 411, + 287, + 472 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 411, + 287, + 472 + ], + "spans": [ + { + "bbox": [ + 46, + 411, + 287, + 472 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{corr}" + }, + { + "bbox": [ + 46, + 411, + 287, + 472 + ], + "type": "text", + "content": " takes the negative of the objective defined in Eq.(8). The structure network parameters corresponding to functions " + }, + { + "bbox": [ + 46, + 411, + 287, + 472 + ], + "type": "inline_equation", + "content": "f_{k}" + }, + { + "bbox": [ + 46, + 411, + 287, + 472 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 411, + 287, + 472 + ], + "type": "inline_equation", + "content": "f_{k}^{m}" + }, + { + "bbox": [ + 46, + 411, + 287, + 472 + ], + "type": "text", + "content": " (cf. Sec. 3.1.1) and is updated using " + }, + { + "bbox": [ + 46, + 411, + 287, + 472 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{corr}" + }, + { + "bbox": [ + 46, + 411, + 287, + 472 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 411, + 287, + 472 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{rgb}" + }, + { + "bbox": [ + 46, + 411, + 287, + 472 + ], + "type": "text", + "content": ". The rendering network parameters corresponding to " + }, + { + "bbox": [ + 46, + 411, + 287, + 472 + ], + "type": "inline_equation", + "content": "\\mathcal{G}_{\\theta}" + }, + { + "bbox": [ + 46, + 411, + 287, + 472 + ], + "type": "text", + "content": " updated using only " + }, + { + "bbox": [ + 46, + 411, + 287, + 472 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{rgb}" + }, + { + "bbox": [ + 46, + 411, + 287, + 472 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 473, + 287, + 509 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 473, + 287, + 509 + ], + "spans": [ + { + "bbox": [ + 46, + 473, + 287, + 509 + ], + "type": "text", + "content": "(ii) The second loss term " + }, + { + "bbox": [ + 46, + 473, + 287, + 509 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_p" + }, + { + "bbox": [ + 46, + 473, + 287, + 509 + ], + "type": "text", + "content": " corresponds to the camera pose refinement. We used the following loss " + }, + { + "bbox": [ + 46, + 473, + 287, + 509 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_p" + }, + { + "bbox": [ + 46, + 473, + 287, + 509 + ], + "type": "text", + "content": " to improve the camera pose estimation." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 141, + 517, + 287, + 531 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 141, + 517, + 287, + 531 + ], + "spans": [ + { + "bbox": [ + 141, + 517, + 287, + 531 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {p} = \\mathcal {L} _ {m r a} \\tag {14}", + "image_path": "9289ede5cb4878edabe79b55d04ed7e80abc14cc749077a9c4ffa401962409cd.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 537, + 287, + 597 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 537, + 287, + 597 + ], + "spans": [ + { + "bbox": [ + 46, + 537, + 287, + 597 + ], + "type": "text", + "content": "As is known, the multiple motion averaging and the color rendering cost functions are directly impacted by the camera pose parameters. And therefore, the " + }, + { + "bbox": [ + 46, + 537, + 287, + 597 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{rgb}" + }, + { + "bbox": [ + 46, + 537, + 287, + 597 + ], + "type": "text", + "content": " is inherently used as an intermediate objective in which the camera pose term is constant between the two different representations." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 607, + 246, + 620 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 607, + 246, + 620 + ], + "spans": [ + { + "bbox": [ + 47, + 607, + 246, + 620 + ], + "type": "text", + "content": "4. Experiments, Results and Ablations" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 627, + 287, + 687 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 627, + 287, + 687 + ], + "spans": [ + { + "bbox": [ + 46, + 627, + 287, + 687 + ], + "type": "text", + "content": "Here, we discuss our experimental results and their comparison to relevant baselines. Later, we provide critical ablation analysis, a study of our camera pose estimation idea, and 3D structure recovery. Finally, the section concludes with a discussion of a few extensions of our approach2." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 286, + 545, + 371 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 286, + 545, + 371 + ], + "spans": [ + { + "bbox": [ + 304, + 286, + 545, + 371 + ], + "type": "text", + "content": "Baselines. We compare our approach with the recently proposed novel view synthesis methods that work well in practice for real-world scenes. Our baseline list includes NeRF++ [49], SC-NeRF [17], PointNeRF [48], FVS [35] and SVS [36]. All baseline methods are trained on the source image set of the testing sequence. Our method's train and test set are the same as SVS [36]." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 378, + 421, + 389 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 378, + 421, + 389 + ], + "spans": [ + { + "bbox": [ + 306, + 378, + 421, + 389 + ], + "type": "text", + "content": "4.1. Dataset and Results" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 396, + 545, + 504 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 396, + 545, + 504 + ], + "spans": [ + { + "bbox": [ + 304, + 396, + 545, + 504 + ], + "type": "text", + "content": "For evaluation, we used popular benchmark datasets comprising real-world and synthetic datasets. Namely, we used the Tanks and Temples [18], FVS [35], Mip-NeRF 360 [1], and the DTU [16] dataset. The first two datasets contain real-world scenes, whereas the last is an object-centric synthetic benchmark dataset. Although our approach mainly targets realistic scenes, for completeness, we performed and tabulated results on a synthetic object-based DTU dataset (see supplementary). Next, we discuss datasets and results." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 506, + 546, + 698 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 506, + 546, + 698 + ], + "spans": [ + { + "bbox": [ + 304, + 506, + 546, + 698 + ], + "type": "text", + "content": "(i) Tanks and Temples Dataset. It consists of images of large-scale real-world scenes taken from a freely moving camera, consisting of indoor and outdoor scenes. Unfortunately, we have no ground-truth poses; thus, estimated poses using COLMAP [39] are treated as pseudo-ground-truth poses. The dataset consists of a total of 21 scenes. Similar to the SVS setup, we use 15 of 21 scenes for training, 2 for validation, and the rest as test scenes. We also use a disjoint set of target views from the test scenes to evaluate all the methods. The source views in test scenes are used for scene-specific fine-tuning if required. Table 1 shows the statistical comparison of our approach with competing baselines. Our approach consistently outperforms the relevant baselines on this challenging dataset. Furthermore, if we zoom into the scene's finer details, our approach clearly preserves details better than other approaches (see Fig. 3)." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 701, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 701, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 306, + 701, + 545, + 713 + ], + "type": "text", + "content": "(ii) FVS Dataset. It comprises six real-world scenes. Each" + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 46, + 693, + 287, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 693, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 693, + 287, + 713 + ], + "type": "text", + "content": "2Please refer supplementary for the train-test setup, implementation details regarding hyperparameters, and architectures to reproduce our results." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "13213" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 72, + 71, + 301, + 386 + ], + "blocks": [ + { + "bbox": [ + 72, + 71, + 301, + 386 + ], + "lines": [ + { + "bbox": [ + 72, + 71, + 301, + 386 + ], + "spans": [ + { + "bbox": [ + 72, + 71, + 301, + 386 + ], + "type": "image", + "image_path": "602808eefcc6937a74c31185ff4b5daca1ddd8943892286066c5e2bc095b0bd6.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 394, + 546, + 429 + ], + "lines": [ + { + "bbox": [ + 46, + 394, + 546, + 429 + ], + "spans": [ + { + "bbox": [ + 46, + 394, + 546, + 429 + ], + "type": "text", + "content": "Figure 3. Qualitative comparison on tanks and temples dataset. If we zoom into the scene details, our approach results show considerably less artifacts than the state-of-the-art methods enabling unparalleled level of realism in image-based rendering. Our PSNR values for the above two scenes are (20.1, 23.9). In comparison, SC-NeRF [17] and SVS [36] provide (17.3, 22.4) and (17.9, 22.9), respectively." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 305, + 72, + 519, + 384 + ], + "blocks": [ + { + "bbox": [ + 305, + 72, + 519, + 384 + ], + "lines": [ + { + "bbox": [ + 305, + 72, + 519, + 384 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 519, + 384 + ], + "type": "image", + "image_path": "0278469c477addaaccb4b9e4c44912ec58fb9fd0517eaf99638b2875afe89d5c.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 449, + 289, + 581 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 449, + 289, + 581 + ], + "spans": [ + { + "bbox": [ + 46, + 449, + 289, + 581 + ], + "type": "text", + "content": "scene was recorded two or more times to completely differentiate the source image set to form the target image set. Table 2 summarises this dataset's view synthesis quantitative results. We compare our method with the state-of-the-art " + }, + { + "bbox": [ + 46, + 449, + 289, + 581 + ], + "type": "inline_equation", + "content": "\\mathrm{NeRF}++" + }, + { + "bbox": [ + 46, + 449, + 289, + 581 + ], + "type": "text", + "content": " [49], Free-View synthesis [35], and SVS [36] methods. We observe that FVS improves over " + }, + { + "bbox": [ + 46, + 449, + 289, + 581 + ], + "type": "inline_equation", + "content": "\\mathrm{NeRF}++" + }, + { + "bbox": [ + 46, + 449, + 289, + 581 + ], + "type": "text", + "content": ", whereas SVS results on this dataset do not consistently outperform other previous methods. On the contrary, our method consistently provides better results than prior art in all categories. The dataset's sample images and its qualitative results are provided in the supplementary." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 617, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 617, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 617, + 287, + 715 + ], + "type": "text", + "content": "(iii) Mip-NeRF 360 Dataset. We further test our approach on this recently proposed dataset comprising unbounded scenes [1]. We use the train-test setup per scene proposed by the authors to fine-tune our network and compare it with Mip-NeRF 360 [1], " + }, + { + "bbox": [ + 46, + 617, + 287, + 715 + ], + "type": "inline_equation", + "content": "\\mathrm{NeRF}++" + }, + { + "bbox": [ + 46, + 617, + 287, + 715 + ], + "type": "text", + "content": " [49], and SVS [36] baseline. Table 3 shows the results for this comparison. Clearly, our methodical take on this problem generalizes well, outperforming other baseline methods for most examples." + } + ] + } + ], + "index": 4 + }, + { + "type": "table", + "bbox": [ + 334, + 446, + 518, + 507 + ], + "blocks": [ + { + "bbox": [ + 334, + 446, + 518, + 507 + ], + "lines": [ + { + "bbox": [ + 334, + 446, + 518, + 507 + ], + "spans": [ + { + "bbox": [ + 334, + 446, + 518, + 507 + ], + "type": "table", + "html": "
PSNR↑LPIPS↓SSIM↑
NeRF++ [49]25.030.3550.682
SVS [36]25.280.2180.783
PBNR [19]23.550.2620.722
Mip-NeRF 360 [1]27.070.2510.781
Ours27.950.2320.797
", + "image_path": "36316fe1f899540b23c606373172202c0a9535ea96b7eeffce8449f07bf23519.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "table_body" + } + ], + "index": 5 + }, + { + "bbox": [ + 305, + 515, + 545, + 538 + ], + "lines": [ + { + "bbox": [ + 305, + 515, + 545, + 538 + ], + "spans": [ + { + "bbox": [ + 305, + 515, + 545, + 538 + ], + "type": "text", + "content": "Table 3. Quantitative comparison of our approach with existing baselines on the Mip-NeRF 360 dataset." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 306, + 559, + 411, + 572 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 559, + 411, + 572 + ], + "spans": [ + { + "bbox": [ + 306, + 559, + 411, + 572 + ], + "type": "text", + "content": "4.2. Ablation Analysis" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "content": "(i) Effect of our camera-pose estimation approach. We performed this experiment to show the benefit of using multiple motion averaging (MRA) instead of relying only on COLMAP poses and taking them for granted. For this experiment, we used the popular Lego dataset [25]. We first compute the COLMAP camera poses shown in Fig.4 (Left). Next, we use this initial camera pose set to perform MRA utilizing the view-graph optimization. Our recovered camera poses are shown in Fig.4 (Right). For clarity, we also show the ground-truth camera pose frustum and the error between the ground-truth pose and recovered pose for the" + } + ] + } + ], + "index": 8 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "13214" + } + ] + } + ], + "index": 9 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 50, + 79, + 160, + 156 + ], + "blocks": [ + { + "bbox": [ + 50, + 79, + 160, + 156 + ], + "lines": [ + { + "bbox": [ + 50, + 79, + 160, + 156 + ], + "spans": [ + { + "bbox": [ + 50, + 79, + 160, + 156 + ], + "type": "image", + "image_path": "9fc3d8b79d8e56f6098b4b74a005613de9dfbb125cfc0c21c9f36df3f41ccfbc.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 47, + 167, + 287, + 217 + ], + "lines": [ + { + "bbox": [ + 47, + 167, + 287, + 217 + ], + "spans": [ + { + "bbox": [ + 47, + 167, + 287, + 217 + ], + "type": "text", + "content": "Figure 4. COLMAP [39] and our method's camera poses on Lego dataset [25]. Here, we add some noise to the pairwise matched correspondences to simulate realistic scenarios. Left: Estimated camera pose from COLMAP and the ground truth pose. Here, black line shows the pose error. Right: Our recovered camera pose. It is easy to infer our approach robustness." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 167, + 79, + 277, + 156 + ], + "blocks": [ + { + "bbox": [ + 167, + 79, + 277, + 156 + ], + "lines": [ + { + "bbox": [ + 167, + 79, + 277, + 156 + ], + "spans": [ + { + "bbox": [ + 167, + 79, + 277, + 156 + ], + "type": "image", + "image_path": "dcac75ebdec6d652b6f6ed42dfb97771b2780a23258a37c9eee3a2dc9f5d2ce6.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 239, + 288, + 371 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 239, + 288, + 371 + ], + "spans": [ + { + "bbox": [ + 46, + 239, + 288, + 371 + ], + "type": "text", + "content": "two respective cases. It is clear from Fig.(4) that a principled approach is required for better camera-pose recovery in view-synthesis problem. Furthermore, to show the benefit of our estimated camera pose in novel-view synthesis, we show our network training loss curve with and without our camera pose estimation approach in Fig.(5). For clarity, we also plot the SVS training curve. Firstly, our method shows better loss response due to the improved 3D geometric scaffold of the scene. Moreover, we improve on training loss further by introducing neural graph-based MRA, showing the benefit of our proposed loss function." + } + ] + } + ], + "index": 3 + }, + { + "type": "image", + "bbox": [ + 65, + 385, + 269, + 520 + ], + "blocks": [ + { + "bbox": [ + 65, + 385, + 269, + 520 + ], + "lines": [ + { + "bbox": [ + 65, + 385, + 269, + 520 + ], + "spans": [ + { + "bbox": [ + 65, + 385, + 269, + 520 + ], + "type": "image", + "image_path": "78dbd409fe2322b377f581b8c1922724dd7a343ae26a7ec0e8dc3685f9e50fd2.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 47, + 530, + 287, + 552 + ], + "lines": [ + { + "bbox": [ + 47, + 530, + 287, + 552 + ], + "spans": [ + { + "bbox": [ + 47, + 530, + 287, + 552 + ], + "type": "text", + "content": "Figure 5. Training loss curve of our method with and without pose optimization compared to state-of-the-art SVS [36]" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 570, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 570, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 570, + 288, + 714 + ], + "type": "text", + "content": "(ii) Effect of using MVS with monocular depth. We performed this ablation to demonstrate the effectiveness of our approach in recovering geometric reconstruction of the scene. Fig.(6) clearly shows the complementary nature of the monocular depth and stereo depth in 3D reconstruction from images. While MVS provides reliable depth results for near and mid-range points, monocular depth can deliver a good depth inference (up to scale) on the far points in the scene. By carefully integrating both modalities' depth, we have better 3D information about the scene. Fig.(6) shows our results on a couple of scenes from Tanks and Temples dataset, demonstrating the suitability of our approach." + } + ] + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 319, + 77, + 529, + 390 + ], + "blocks": [ + { + "bbox": [ + 319, + 77, + 529, + 390 + ], + "lines": [ + { + "bbox": [ + 319, + 77, + 529, + 390 + ], + "spans": [ + { + "bbox": [ + 319, + 77, + 529, + 390 + ], + "type": "image", + "image_path": "63b9b29820f788b482eed3514cff36548af2826f4a592a40cc01bcbb3e663144.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 306, + 399, + 545, + 422 + ], + "lines": [ + { + "bbox": [ + 306, + 399, + 545, + 422 + ], + "spans": [ + { + "bbox": [ + 306, + 399, + 545, + 422 + ], + "type": "text", + "content": "Figure 6. Comparison of depth predicted by monocular and stereo based method on the scenes from Tanks and Temples dataset." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_caption" + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 450, + 378, + 462 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 450, + 378, + 462 + ], + "spans": [ + { + "bbox": [ + 306, + 450, + 378, + 462 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 474, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 474, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 474, + 545, + 713 + ], + "type": "text", + "content": "The approach presented in this paper directly addresses the shortcomings of the currently popular methods in novel view synthesis. Our approach integrates concepts from the learning-based approaches and classical techniques in multiple-view geometry for solving novel-view synthesis. We demonstrate that by exploiting the " + }, + { + "bbox": [ + 304, + 474, + 545, + 713 + ], + "type": "inline_equation", + "content": "(i)" + }, + { + "bbox": [ + 304, + 474, + 545, + 713 + ], + "type": "text", + "content": " complementary nature of monocular depth estimation and multiple view stereo (MVS) in the 3D reconstruction of the scene, and " + }, + { + "bbox": [ + 304, + 474, + 545, + 713 + ], + "type": "inline_equation", + "content": "(ii)" + }, + { + "bbox": [ + 304, + 474, + 545, + 713 + ], + "type": "text", + "content": " usefulness of multiple rotation averaging in structure from motion, we can achieve better-rendering quality than other dominant approaches in novel view synthesis. We confirm the effectiveness of our approach via a comprehensive evaluation and quantitative comparison with baselines on several benchmark datasets. Although our work enabled improved photorealistic rendering, several exciting avenues exist for further improvement. One interesting future extension is fully automating our introduced view synthesis pipeline, i.e., adding a learnable MVS framework to estimate intrinsic, extrinsic camera parameters with scene reconstruction for better novel view synthesis." + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "13215" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 92, + 288, + 712 + ], + "type": "list", + "angle": 0, + "index": 16, + "blocks": [ + { + "bbox": [ + 53, + 92, + 287, + 147 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 92, + 287, + 147 + ], + "spans": [ + { + "bbox": [ + 53, + 92, + 287, + 147 + ], + "type": "text", + "content": "[1] Jonathan T Barron, Ben Mildenhall, Dor Verbin, Pratul P Srinivasan, and Peter Hedman. 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Nerf++: Analyzing and improving neural radiance fields. arXiv preprint arXiv:2010.07492, 2020." + } + ] + } + ], + "index": 18 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "type": "text", + "content": "13217" + } + ] + } + ], + "index": 20 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 9 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Enhanced Training of Query-Based Object Detection via Selective Query Recollection/514d250b-ea10-4630-9256-9e649ac9271f_content_list.json b/2023/Enhanced Training of Query-Based Object Detection via Selective Query Recollection/514d250b-ea10-4630-9256-9e649ac9271f_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..2badab3da67ca150cc17b0f34234e95dfed80c58 --- /dev/null +++ b/2023/Enhanced Training of Query-Based Object Detection via Selective Query Recollection/514d250b-ea10-4630-9256-9e649ac9271f_content_list.json @@ -0,0 +1,1690 @@ +[ + { + "type": "text", + "text": "Enhanced Training of Query-Based Object Detection via Selective Query Recollection", + "text_level": 1, + "bbox": [ + 199, + 130, + 772, + 176 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Fangyi Chen $^{1}$ Han Zhang $^{1}$ Kai Hu $^{1}$ Yu-Kai Huang $^{1}$ Chenchen Zhu $^{2}$ Marios Savvides $^{1}$ Carnegie Mellon University $^{1}$ Meta AI $^{2}$", + "bbox": [ + 96, + 200, + 872, + 239 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "{fangyic,hanz3,kaihu,yukaih2,marioss}@andrew.cmu.edu chenchenz@fb.com", + "bbox": [ + 165, + 241, + 790, + 255 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 291, + 313, + 306 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "This paper investigates a phenomenon where query-based object detectors mispredict at the last decoding stage while predicting correctly at an intermediate stage. We review the training process and attribute the overlooked phenomenon to two limitations: lack of training emphasis and cascading errors from decoding sequence. We design and present Selective Query Recollection (SQR), a simple and effective training strategy for query-based object detectors. It cumulatively collects intermediate queries as decoding stages go deeper and selectively forwards the queries to the downstream stages aside from the sequential structure. Such-wise, SQR places training emphasis on later stages and allows later stages to work with intermediate queries from earlier stages directly. SQR can be easily plugged into various query-based object detectors and significantly enhances their performance while leaving the inference pipeline unchanged. As a result, we apply SQR on Adamixer, DAB-DETR, and Deformable-DETR across various settings (backbone, number of queries, schedule) and consistently brings $1.4 \\sim 2.8$ AP improvement. Code is available at https://github.com/Fangyi-Chen/SQR", + "bbox": [ + 75, + 324, + 473, + 657 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 690, + 209, + 705 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Object detection is a long-established topic in computer vision aiming to localize and categorize objects of interest. Previous methods [4, 7, 10, 11, 16, 18, 21, 25, 26, 29, 32, 33, 35-37] rely on dense priors tiled at feature grids so as to detect in a sliding-window paradigm, and have dominated object detection for the recent decade, but these methods fail to shake off many hand-crafted processing steps such as anchor generation or non-maximum suppression, which block end-to-end optimization.", + "bbox": [ + 75, + 717, + 468, + 853 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Recent research attention has been geared towards query-based object detection [3, 17, 20, 23, 28, 31, 38] since the thriving of transformer [30] and DETR [3]. By view-", + "bbox": [ + 75, + 854, + 470, + 901 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/5eba7844be233a7b70a005d08936daca5e68e5fa6f30d0ae9d5883b545493ff3.jpg", + "image_caption": [ + "Figure 1. The inference speed and AP for various networks on the MS-COCO val set. The red stars are the results trained with SQR. The blue circles are the results of baselines without SQR. SQR enhances the training of query-based object detectors while leaving the inference pipeline unchanged." + ], + "image_footnote": [], + "bbox": [ + 504, + 292, + 890, + 474 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "ing detection as a direct set prediction problem, the new archetype represents the set of objects using a set of learnable embeddings, termed as queries, which are fed to a decoder consisting of a stack (typically six) of decoding stages. Each stage performs similar operations: (1) interacting queries with image features via an attention-like mechanism, so the queries are aggregated with valuable information that represents objects; (2) reasoning the relation among all queries so that global dependency on objects cooccurrence and duplicates could be captured; (3) interpreting bounding box and category from each query by a feed forward network. Queries are sequentially processed stage-by-stage, and each stage is formulated to learn a residual function with reference to the former stage's output, aiming to refine queries in a cascaded style.", + "bbox": [ + 496, + 582, + 893, + 809 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "As such wise, the decoding procedure implies that detection should be stage-by-stage enhanced in terms of IoU and confidence score. Indeed, monotonically improved AP is empirically achieved by this procedure. However, when visualizing the stage-wise predictions, we surprisingly observe that decoder makes mistakes in a decent proportion of", + "bbox": [ + 496, + 810, + 893, + 900 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 810, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "23756", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/f7ee72d612269f1bfb5db20a6a2fbab9907706b36ad2b5ddf9f9adb5f83c455d.jpg", + "image_caption": [ + "stage 1", + "Traffic light | 0.41" + ], + "image_footnote": [], + "bbox": [ + 88, + 114, + 215, + 233 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/5764dc08516e452d5a37a9b0820dafb6c2d714218dac6b8035e14a29a2ac92c4.jpg", + "image_caption": [ + "stage 2", + "Traffic light | 0.38" + ], + "image_footnote": [], + "bbox": [ + 220, + 114, + 346, + 233 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/09556f905835bc2504dc73a6d8deaf9af11fab38b4cf189619bd9711f5302027.jpg", + "image_caption": [ + "stage 3", + "Traffic light | 0.38" + ], + "image_footnote": [], + "bbox": [ + 354, + 114, + 480, + 232 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/475cf55ff4fbb48a756331b06de7281db46c77fd8d0a25cd97ab7b1f033c1437.jpg", + "image_caption": [ + "stage 4", + "Traffic light | 0.37" + ], + "image_footnote": [], + "bbox": [ + 490, + 114, + 614, + 233 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/d9547234da132826439d66c7fd9720b7baf3dc228439845e4d703703749b978e.jpg", + "image_caption": [ + "stage 5", + "Traffic light | 0.21" + ], + "image_footnote": [], + "bbox": [ + 622, + 114, + 751, + 233 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/4141addd285ff582faae1398e163bc7c42671e2b85afa2db345e137cbc866a7e.jpg", + "image_caption": [ + "stage 6", + "Traffic light | 0.27" + ], + "image_footnote": [], + "bbox": [ + 759, + 114, + 885, + 233 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/880bd3111cac443f6e17f9bac75698e4e917ad7b04b789df1e358f509870e069.jpg", + "image_caption": [ + "Cell phone | 0.23 \nCell phone | 0.22", + "Figure 2. Are query-based object detectors always enhancing predictions stage-by-stage? The traffic light at stage 1 gets a confident score of 0.41, while from stage 2 to 5 the confidence gradually decreases to 0.21 (Upper); the remote at stage 3 was wrongly classified as a cell phone, and from stage 3 to 6 the mistake was amplified from 0.26 to 0.42 (Lower). The visualization is acquired from Adamixer-R50 (42.5 AP) tested on COCO val set." + ], + "image_footnote": [], + "bbox": [ + 88, + 258, + 214, + 385 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/250da6a0b9af727c8a41cdf17e1c31be41386fc0542cd5d872a4d1db9dbc9678.jpg", + "image_caption": [ + "Remote | 0.25 \nRemote | 0.22" + ], + "image_footnote": [], + "bbox": [ + 222, + 258, + 346, + 383 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/a0f9664877f9cf9f2e3679533cca31f8c84f2514aa6677f380b3683190f7443b.jpg", + "image_caption": [ + "Cell phone | 0.26 \nRemote | 0.12" + ], + "image_footnote": [], + "bbox": [ + 356, + 258, + 480, + 383 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/0b066fb1215bde4301e71399bdfb963ef57350b65b4d5e90328322d3990a0ac6.jpg", + "image_caption": [ + "Cell phone | 0.35 \nRemote | 0.12" + ], + "image_footnote": [], + "bbox": [ + 488, + 258, + 616, + 385 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/42ca2e58466234f7bf556857b7a555f1fafe7e187cd54fe8735316ffaf173e23.jpg", + "image_caption": [ + "Cell phone | 0.39 \nRemote | 0.12" + ], + "image_footnote": [], + "bbox": [ + 624, + 258, + 751, + 385 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/411bf865a50ed1e600dfca37a871e40a203c7611b0a24addac50579e76da59e2.jpg", + "image_caption": [ + "Cell phone | 0.42 \nRemote | 0.10" + ], + "image_footnote": [], + "bbox": [ + 759, + 258, + 883, + 385 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "cases where the later stages degrade true-positives and upgrade false-positives from the former stages. As shown in Fig.2, the traffic light at stage 1 gets categorical confidence of 0.41, while from stage 2 to 5 the confidence gradually decreases to 0.21; the remote at stage 3 was wrongly classified as a cell phone, while from stage 3 to 6 the error was exacerbated from 0.26 to 0.42. We present a more detailed statistic in Section 3.", + "bbox": [ + 75, + 518, + 468, + 638 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "This phenomenon inspires us to review the current training strategy and bring two conjectures. Firstly, the responsibility that each stage takes is unbalanced, while supervision applied to them is analogous. An early stage could make mistakes without causing too much impact because it gets chances to be corrected later, and the later stages are more responsible for the final prediction. But during training, all of these stages are supervised in an equivalent manner and there lacks such a mechanism that places particular training emphasis on later stages. Secondly, due to the sequential structure of the decoder, an intermediate query refined by a stage - no matter whether this refinement brings positive or negative effects - will be cascaded to the following stages, while the query prior to the refinement never gets an opportunity to be propagated forward even though it emerges unscathed and might be more representative than the refined one. The cascading errors increase the diffi", + "bbox": [ + 75, + 643, + 468, + 900 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "culty of convergence and the sequential structure impedes the later stages from seeing prior queries during training.", + "bbox": [ + 498, + 518, + 890, + 550 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Based on these intuitions, we present Query Recollection (QR) as a training strategy for query-based object detectors. It cumulatively collects intermediate queries as stages go deeper, and feeds the collected queries to the downstream stages aside from the sequential structure. By each stage, the new add-ins alongside the original inputs are independently treated among each other, so the attentions and losses are calculated individually. In such a manner, QR enjoys two key features: (1) The number of supervision signals per stage grows in geometric progression, so that later stages get more supervision than the former ones, for example, the sixth stage got 32 times more supervision than the first; (2) Later stages get chance to view the outputs beyond its neighboring stage for training, which mitigates the potential impact due to cascading errors. We further discover that selectively forward queries to each stage, not with the entire query collection but only those from the prior two stages, can raise the number of supervision in a Fibonacci sequence which halves the extra computing cost and brings even better results. We name it Selective Query Recollection (SQR).", + "bbox": [ + 496, + 551, + 892, + 852 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Our contributions are summarized in three folds: (1) We quantitatively investigate the phenomenon where query-based object detectors mispredict at the last decoding stage", + "bbox": [ + 498, + 854, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "23757", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "while predicting correctly at an intermediate one. (2) We attribute the overlooked phenomenon to two training limitations, and propose a simple and effective training strategy SQR that elegantly fits query-based object detectors. (3) We conduct experiments on Adamixer, DAB DETR, and Deformable DETR across various training settings that verify its effectiveness (Fig.1).", + "bbox": [ + 75, + 90, + 472, + 196 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 76, + 210, + 218, + 227 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "2.1. Training Strategy for Object Detection", + "text_level": 1, + "bbox": [ + 76, + 237, + 410, + 253 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Detectors based on dense priors have been dominating the community for decades. The abstract concept anchor box or anchor point [26, 29] aims to match with ground truth (GT) objects depending on their Intersection-over-Union (IoU) values or other advanced soft scoring factors [7, 15, 18, 29, 37]. Among anchor-based detectors, multistage models iteratively refine bounding box and category stage-by-stage. A typical example is Cascade RCNN [2] which is based on the design that the output of an intermediate stage is sampled and re-labeled to train the next stage with increasing IoU thresholds, so these stages are guaranteed to be progressively refined. Recently, DETR [3] starts a family of end-to-end query-based models where object detection is regarded as a set prediction problem. To train DETR, a predefined number of object queries are matched to either a ground-truth or background by solving the Hungarian Matching problem. The queries are refined by several decoder stages similar to Cascade RCNN, and each intermediate stage is supervised by the matching results.", + "bbox": [ + 75, + 261, + 472, + 549 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "2.2. Query-Based Object Detection", + "text_level": 1, + "bbox": [ + 76, + 559, + 348, + 575 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Recently, many algorithms have been following the idea of DETR. Deformable DETR [38] proposes a deformable attention module that alleviates the aforementioned issues and massively improves the convergence speed by a factor of 10. Conditional DETR [23] decouples the object query into content query and spatial query in the decoder cross-attention module and learns a conditional spatial query from the decoder embedding to enable fast learning of the distinctive extremity of the ground-truth objects. Anchor-DETR [31] formulates the object queries as anchor points such that each object query may only focus on a certain region near its anchor point. Many future works are inspired by this design. DAB-DETR [20] dives deep into the role of object queries. It directly uses anchor box coordinates as spatial query to speed up training. The model benefits from the spatial prior by modulating the positional attention map using the width and height of the box. DN-DETR [17] further improves the convergence speed and query matching stability of DAB-DETR with the help of the Ground Truth denoising task. Adamixer [9] re-designs the query-key pooling mechanism by letting the query adaptively attend to the mean", + "bbox": [ + 75, + 583, + 472, + 902 + ], + "page_idx": 2 + }, + { + "type": "table", + "img_path": "images/7eee5a25ddc44b5e2aa8120e689d3647c71d25a8e5749d60c40077ef9abf5171.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
ModelS1S2S3S4S5S6
Deformable38.442.243.744.244.444.5
Adamixer15.130.337.740.642.142.5
", + "bbox": [ + 501, + 89, + 895, + 150 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Table 1. Stage-wise AP results. Deformable DETR(300 queries) and Adamixer(100 queries) are trained using official implementation, both of their decoders consist of 6 stages, and per stage AP is reported on COCO val set.", + "bbox": [ + 498, + 160, + 893, + 217 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/67b7b5e3dbb4e4ee8e0d195a19bf8db7af2b151ad2b06645290decb703d92e7a.jpg", + "image_caption": [ + "Figure 3. Typical structure of a single decoding stage." + ], + "image_footnote": [], + "bbox": [ + 506, + 232, + 890, + 327 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "ingful regions of the encoded features directly through bilinear sampling. An MLP-Mixer then dynamically decodes the pooled features into final predictions. DETA (Detection Transformers with Assignment) [24] proposes a novel overlap-based assignment that enables one-to-many assignments to DETR.", + "bbox": [ + 496, + 378, + 890, + 468 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Despite their significant improvement on DETR, they focus little on the training emphasis and cascading errors. We propose SQR to pay attention to the two problems.", + "bbox": [ + 496, + 469, + 890, + 515 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Motivation", + "text_level": 1, + "bbox": [ + 500, + 529, + 617, + 544 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Are query-based object detectors always predicting the optimal detections at the last stage? Table.1 shows that AP gradually increases with stages going deeper, indicating improved predictions on a general scale. While the observation in Fig.2 implies that simple AP results are insufficient for an in-depth analysis of that question.", + "bbox": [ + 496, + 555, + 890, + 645 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Preliminary. Queries are updated successively. A typical structure of a decoding stage is illustrated in Fig.3. An initial query $q_{i}^{0}$ ( $i \\in N = \\{1,2,\\dots,n\\}$ ) is an embedding trained through back-propagation, and $n$ is the total number of initial queries. During inference, the first stage updates the initial query by adding a residual term to it, producing intermediate query $q_{i}^{1}$ , followed by later stages sequentially updating the intermediate query in the same way. The procedure can be formulated as", + "bbox": [ + 496, + 646, + 890, + 781 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nq _ {i} ^ {s} = D ^ {s} \\left(q _ {i} ^ {s - 1}, q ^ {s - 1}, x\\right) = q _ {i} ^ {s - 1} + (\\mathcal {A} \\circ \\mathcal {F}) \\left(q _ {i} ^ {s - 1}, q ^ {s - 1}, x\\right) \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 500, + 792, + 890, + 824 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "$D^{s}$ is a decoding stage where $s$ is stage index; $q_{i}^{s}$ is the $i_{th}$ query at stage $s$ ; $q^{s}$ is a set of queries $q^{s} = \\{q_{i}^{s} | i \\in N\\}$ ; $(\\mathcal{A} \\circ \\mathcal{F})$ stands for a bundle of modules including self and cross attention and feed forward network; $x$ means features; and LayerNorm [1] that applied on each module is omitted", + "bbox": [ + 496, + 825, + 893, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "23758", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 2 + }, + { + "type": "table", + "img_path": "images/bb832205eef62226c8e13373781c3e5f5aa55e2a5662d0f4b4b8af14346c190f.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
ModelTP ThresholdTP F RateFP E Rate
DeformableIoU>0.5051.4%55.7%
DETRIoU>0.7549.5%55.9%
AdamixerIoU>0.5028.6%50.8%
IoU>0.7526.7%51.2%
", + "bbox": [ + 81, + 88, + 467, + 186 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Table 2. True-positive Fading Rate and False-positive Exacerbation Rate.", + "bbox": [ + 76, + 196, + 468, + 224 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "for simplicity. Afterward, $q_{i}^{s}$ predicts an object $P_{i}^{s}$ via two multi-layer perceptrons for classification and regression:", + "bbox": [ + 76, + 253, + 468, + 285 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nP _ {i} ^ {s} = \\left(M L P _ {c l s} \\left(q _ {i} ^ {s}\\right), M L P _ {r e g} \\left(q _ {i} ^ {s}\\right)\\right) \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 145, + 300, + 468, + 316 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "$P_{i}^{1\\sim 6}$ are predicted by the $q_{i}^{1\\sim 6}$ rooted in $q_{i}^{0}$ , where $P_{i}^{6}$ is the expected outcome and $P_{i}^{1\\sim 5}$ are intermediate results. $P_{i}^{s}$ is regarded as a true-positive towards a ground-truth $G$ only if the IoU $(P_{i}^{s}, G)$ exceeds a threshold, its category matches with $G$ , and the categorical score is ranked as the highest among all other counterparts.", + "bbox": [ + 76, + 323, + 467, + 416 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Investigation. We study the stage-wise testing results by first defining two rates: (1) If $P_{i}^{6}$ is a true-positive (TP) towards a ground-truth $G$ , we check whether $P_{i}^{1\\sim 5}$ generate a better TP towards the same $G$ that has higher IoU & higher category score than $P_{i}^{6}$ . The occurrence rate is denoted as TP fading rate. (2) If $P_{i}^{6}$ is a false-positive (FP), we check whether $P_{i}^{1\\sim 5}$ produce a FP but with lower category score than $P_{i}^{6}$ . The occurrence rate is denoted as FP exacerbation rate.", + "bbox": [ + 75, + 416, + 467, + 550 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The statistics are shown in Table.2. We can see that TP fading rate achieves $50\\%$ and $27\\%$ on the two models. Considering the strict constraints it holds, the TP fading rate reaches an impressively high level. Deformable DETR is much higher than Adamixer due to the smaller AP gap among stages, thus, in many cases, earlier stages are more likely to outperform the last stage. FP exacerbation holds looser constraints and is easier to be satisfied, its rate is above $50\\%$ on the two models. Higher TP threshold implies higher quality of $P_{i}^{6}$ and it is harder to find qualifiers in $P_{i}^{1\\sim 5}$ , but the two rates are similar with 0.75 as with 0.5, pointing out the consistency of this phenomenon. We also observe that more than half of the occurred cases are marginally triggered, i.e. the predictions from the triggered $P_{i}^{1\\sim 5}$ are only marginally better than the sixth. This is a further reason why the deformable DETR has those high rates - the results from the 5th and 6th stages are extremely visually close. In dominated number of cases, the final stage is (one of) the best, after all, its mAP is the highest.", + "bbox": [ + 75, + 551, + 467, + 838 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "When the conditions of the two rates establish, we further replace $P_{i}^{6}$ with the optimal prediction found in $P_{i}^{1\\sim 6}$ and measure the AP. On Deformable DETR, AP grows from 44.5 AP to 51.7 (+7.2 AP); on Adamixer, AP grows from", + "bbox": [ + 75, + 839, + 467, + 900 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "42.5 AP to 53.3 (+10.7 AP), demonstrating huge potential in query-based detectors yet to be mined.", + "bbox": [ + 498, + 90, + 890, + 121 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Conclusion. This reveals that models frequently predict the optimum at intermediate stages instead of the last one. We view the problem from the training's perspective and identify the lack of training emphasis and the cascading errors from query sequence as two obstacles impeding the occurrence of the most reliable predictions in the last stage, elaborated in Section 1.", + "bbox": [ + 496, + 122, + 890, + 227 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4. Query Recollection", + "text_level": 1, + "bbox": [ + 498, + 244, + 684, + 262 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4.1. Expectancy", + "text_level": 1, + "bbox": [ + 500, + 270, + 625, + 286 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We desire such a training strategy that embraces:", + "bbox": [ + 517, + 294, + 841, + 310 + ], + "page_idx": 3 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- Uneven supervision applied to decoding stages that places emphasis on later ones, enhancing later stages for better final outcomes.", + "- A variety of early-stage queries directly introduced to later stages, mitigating the impact of cascading errors." + ], + "bbox": [ + 517, + 311, + 890, + 386 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "To this end, we design a concise training strategy coined as Query Recollection (QR). Compared with prior arts, it collects intermediate queries at every stage and forwards them along the original pathway. Dense Query Recollection (DQR) is the fundamental form and Selective Query Recollection (SQR) is an advanced variant.", + "bbox": [ + 496, + 388, + 890, + 479 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4.2. Dense Query Recollection", + "text_level": 1, + "bbox": [ + 498, + 491, + 733, + 507 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Notation. The process of single decoding stage (self-attention, cross-attention, FFN), the ground-truth assignment, and loss calculations are applied within a set of queries $\\{q_i | i \\in \\{1, 2, \\dots, n\\}\\}$ , where $n$ is typically 100/300/500. We regard the set of queries as a basic unit in our method and generally denote as $q$ .", + "bbox": [ + 496, + 515, + 890, + 606 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Basic Pathway. Query along the basic pathway is refined by all stages. We illustrate it in Fig.4(a). Taking a 4-stages decoder as an example, we denote $q^{0-1-2-3-4}$ as the final query that is refined by all stages. So the basic $\\mathcal{PT}$ finally produces", + "bbox": [ + 496, + 607, + 890, + 683 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} q ^ {0 - 1 - 2 - 3 - 4} = D ^ {4} \\left(D ^ {3} \\left(D ^ {2} \\left(D ^ {1} \\left(q ^ {0}\\right)\\right)\\right)\\right) (3) \\\\ = \\mathcal {P T} ^ {1 - 2 - 3 - 4} \\left(q ^ {0}\\right) (4) \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 566, + 710, + 890, + 750 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "During training, the queries from each stage, i.e. $q^{0-1}$ , $q^{0-1-2}$ , $q^{0-1-2-3}$ , and $q^{0-1-2-3-4}$ are independently followed by Hungarian Assignment that matches ground-truth with $q$ in a one-to-one manner, and then followed by loss calculation for supervision. In Fig.4, we mark those $q$ that require supervision as $\\hat{q}$ . Along the basic pathway, the number of $\\hat{q}$ at each stage is 1.", + "bbox": [ + 496, + 762, + 890, + 868 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "DQR Formulation. We densely collect every intermediate $q$ and independently forward them to every downstream", + "bbox": [ + 498, + 869, + 890, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "23759", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/fc8ee8a9aa62956f3435d6cee25a31f9b1c6dc80506d2932d9781aff8fc6d50d.jpg", + "image_caption": [ + "(a)Basic (b)Dense QR" + ], + "image_footnote": [], + "bbox": [ + 76, + 112, + 486, + 489 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/152d414d27b5e29816771156de4a8b5a368e60734d02a08d043ba6f07b518149.jpg", + "image_caption": [ + "Figure 4. (a). Basic process for decoding queries stage by stage, applied in both training and testing. (b). Dense query recollection. (c). Selective query recollection." + ], + "image_footnote": [ + "Collection C $q^{0I2}$ Query, from initial to stage 1 then to 2", + "Output of stage/QR $\\hat{\\pmb{q}}$ Query with supervision applied" + ], + "bbox": [ + 80, + 513, + 119, + 551 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "stage, as illustrated in Fig.4(b). After each stage, a collection $C$ is formed where the number of $q$ grows geometrically, namely $2^{s}$ at $s_{th}$ stage. Formally,", + "bbox": [ + 75, + 630, + 468, + 676 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nC ^ {0} = \\{q ^ {0} \\} \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 233, + 689, + 468, + 705 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nC ^ {s} = \\left\\{D ^ {s} (q) | q \\in C ^ {s - 1} \\right\\} \\cup C ^ {s - 1} \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 158, + 710, + 468, + 729 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In a collection $C$ , half of queries inside are newly generated by the current stage, i.e. from $\\{D^s(q)|q \\in C^{s-1}\\}$ , while another half are from previous stages, $C^{s-1}$ . Separately, for each $q$ in the former half, we apply Hungarian assignment and loss calculation, so the number of supervision signals grows in geometric progression as well, namely $2^{s-1}$ at $s_{th}$ stage.", + "bbox": [ + 75, + 734, + 468, + 839 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Such-wise, Dense Query Recollection satisfies our expectancy where the number of supervision signal for each stage grows as (1,2,4,8,16,32), meanwhile, all prior queries would be visible in all later stages.", + "bbox": [ + 75, + 839, + 468, + 901 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/f58ad0773cd493228b23e0e7d72922e8530e2bde08c411ede0b8fc75599dc46e.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
stage12345
TP F Rate(%)1.24.48.512.416.9
FP E Rate(%)14.318.620.824.530.2
stage1~34&53~52~51~5
TP F Rate(%)11.223.926.928.328.6
FP E Rate(%)32.440.845.348.550.8
", + "bbox": [ + 516, + 89, + 877, + 209 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Table 3. Stage-wise TP Fading Rate and FP Exacerbation Rate with Adamixer.", + "bbox": [ + 498, + 219, + 890, + 246 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "During inference, we only use the basic pathway, so the inference process is untouched. For a standard 6-stage decoder, the pathway is $\\mathcal{PT}^{1-2-3-4-5-6}$", + "bbox": [ + 498, + 275, + 890, + 321 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.3. Selective Query Recollection", + "text_level": 1, + "bbox": [ + 500, + 330, + 754, + 347 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The last proposal empirically enhances training, but the query collection process is indiscriminate, which brings two defects: First, the geometrical growth of the number of $\\hat{q}$ and their attention/loss calculations cost a lot. Second, if we input an early $q$ that skips too many stages to a far-away late stage, the potential benefit could be overshadowed by the huge learning gap between the stages and query. For instance, if the initial $q^0$ is directly introduced to stage 6 and produces $\\hat{q}^{0 - 6}$ , this query would have the highest difficulty among all queries at stage 6 and the calculated loss would dominate the overall losses. So we are inclined to selectively collect intermediate $q$ rather than densely collect all of them.", + "bbox": [ + 496, + 354, + 890, + 550 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Selection. To find a better query recollection scheme, we further conduct a detailed analysis on the TP Fading Rate and FP Exacerbation Rate introduced in Section 3.", + "bbox": [ + 496, + 551, + 890, + 595 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Recall the spirits of the two rates where we seek from $P_{i}^{1\\sim 5}$ for an alternative that is better than $P_{i}^{6}$ , we want to investigate which specific intermediate stage/stages contribute the most. Concretely, if $P_{i}^{6}$ is a true-positive towards a ground-truth $G$ , we separately check each stage whether generating a better TP; similarly, if $P_{i}^{6}$ is a false-positive, we separately check each stage whether generating a better FP. The results are summarized in Table 3. We find that the majority of alternatives of $P_{i}^{6}$ are from stage 4&5, where the corresponding TP fading rate and FP exacerbation rate reach $23.9\\%$ and $40.8\\%$ , respectively, which are close to the results of stages $1 \\sim 5$ . While stage $1 \\sim 3$ together only produces $11.2\\%$ and $32.4\\%$ .", + "bbox": [ + 496, + 597, + 892, + 792 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The above analysis implies that the queries from the adjacent stage and the stage prior to the adjacent stage are more likely to bring positive effects. We intuitively follow the observations and selectively operate collection along the basic pathway: before starting stage $D^{s}$ , we collect $q$ from the 2 nearest stages, i.e. $D^{s - 1}$ and $D^{s - 2}$ as the input of $D^{s}$ .", + "bbox": [ + 496, + 794, + 890, + 883 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "SQR Formulation. The Selective Query Recollection", + "bbox": [ + 517, + 885, + 890, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "23760", + "bbox": [ + 478, + 944, + 519, + 955 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "can be formulated as", + "bbox": [ + 76, + 90, + 218, + 104 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\nC ^ {0} = \\left\\{q ^ {0} \\right\\} \\quad C ^ {1} = \\left\\{q ^ {0}, q ^ {0 - 1} \\right\\} \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 163, + 114, + 468, + 133 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} C ^ {s} = \\{D ^ {s} (q) | q \\in C ^ {s - 1} \\} \\cup \\operatorname {s e l e c t} \\left(C ^ {s - 1}\\right) \\tag {8} \\\\ = \\{D ^ {s} (q) | q \\in C ^ {s - 1} \\} \\cup \\{D ^ {s - 1} (q) | q \\in C ^ {s - 2} \\} (9) \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 93, + 150, + 468, + 188 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Such wise, Selective Query Recollection (Fig.4(c)) still satisfies our expectancy, and the number of supervision signals grows in a Fibonacci sequence (1,2,3,5,8,13). Compared to the Dense Recollection, to a great extent, SQR reduces the computing burden and we observe that SQR even outperforms the dense counterpart in terms of precision. This verifies our assumption that a $q$ skipping too many stages might be noise for remote stages overshadowing its positive effects.", + "bbox": [ + 75, + 196, + 468, + 330 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Recollection Starting Stage. Above we collect queries starting from stage 1. Instead, we can practically vary this starting stage, and this will further reduce the total queries in each collection and further reduce the computing burden. E.g., if starts SQR from stage 2, the Fibonacci sequence will start from stage 2 and result in $(1,1,2,3,5,8)$ ; if starts from stage 3, result in $(1,1,1,2,3,5)$ . The starting stage is regarded as a hyper-parameter for SQR.", + "bbox": [ + 75, + 332, + 468, + 454 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5. Experiments", + "text_level": 1, + "bbox": [ + 76, + 465, + 209, + 483 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We conduct our experiments on the MS-COCO [19] detection track using the MMDetection [5] and Detrex [27] code-bases. All models are trained on train2017 split. Unless otherwise specified, models are trained and tested with image scale of 800 pixels, where AdamW optimizer with a standard 1x schedule (12 epochs) is utilized for training. For ablation study and analysis, Adamixer [9] with R50 [12] is chosen because of its good performance and fast convergence speed (42.5 AP with 1x schedule). We further apply SQR on other detectors to verify its effectiveness.", + "bbox": [ + 75, + 491, + 468, + 642 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5.1. Ablation Study", + "text_level": 1, + "bbox": [ + 76, + 650, + 230, + 667 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Baseline vs DQR vs SQR. Table.4 shows that both DQR and SQR improve the baseline by a large margin. DQR reaches 44.2 (+1.7 AP) while SQR reaches a slightly high result 44.4 (+1.9 AP). Note that SQR is much more efficient than DQR. As shown in Table.5, under the same training setting, SQR cuts down a great amount of training time of DQR and still achieves equal or higher AP.", + "bbox": [ + 75, + 672, + 468, + 779 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Varying Starting Stage of SQR. We present how SQR performs when varying the starting stage in Table.5. The best performance is acquired when query recollection starts at stage 1 but with the most computational cost. We can see that starting at stage 2 performs similarly to starting at stage 1 while the computing burden is decently reduced. With recollection starting later, the benefits from SQR decrease as expected since the recollected queries from early", + "bbox": [ + 75, + 779, + 468, + 901 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/dca4b4715ae58889cb0943496665e5675d6d8daa202b2369a8821ad02f4af3a5.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodsAP\\( AP_{50} \\)\\( AP_{75} \\)\\( AP_S \\)\\( AP_M \\)\\( AP_L \\)
Baseline42.561.545.624.645.159.2
DQR44.262.847.926.746.960.5
SQR44.463.247.825.747.460.2
", + "bbox": [ + 504, + 89, + 888, + 165 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/e8bae55a41f8c0dc60f6ba6c931ed1eaac40f04633272446fbdcb49d1677b3b3.jpg", + "table_caption": [ + "Table 4. AP comparison among Baseline, DQR, and SQR" + ], + "table_footnote": [], + "table_body": "
MethodStart StageTrain TimeAP\\( AP_{50} \\)
Baseline-1x(5hours)42.561.5
Baseline-2x42.561.3
Baseline-3x42.561.4
DQR-2.24x44.262.8
SQR11.57x44.463.2
SQR21.34x44.263.0
SQR31.18x43.862.3
SQR41.07x42.961.4
", + "bbox": [ + 514, + 205, + 879, + 357 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/754cd665cee1b3940ce38e5eb791f7b60f07a8fa316a2fb61e020eb1fdc62f92.jpg", + "table_caption": [ + "Table 5. Further comparison among Baseline, DQR, and SQR with different starting stage in terms of training time and AP." + ], + "table_footnote": [], + "table_body": "
MethodTP ThresholdTP F RateFP E Rate
BaselineIoU>0.5028.6%50.8%
SQRIoU>0.5023.3 %47.3 %
BaselineIoU>0.7526.7%51.2%
SQRIoU>0.7521.1%47.0%
", + "bbox": [ + 514, + 412, + 877, + 511 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 6. Baseline vs. SQR on true-positive fading rate and false-positive exacerbation rate.", + "bbox": [ + 500, + 521, + 890, + 550 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "stages become fewer and training emphasis gets gradually balanced.", + "bbox": [ + 498, + 578, + 890, + 606 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "TP Fading Rate And FP Exacerbation Rate. We present Table.6 to verify that TP fading rate and FP exacerbation rate decrease due to the training effect when applied SQR. Specifically, TP fading rate decreases from $28.6\\%$ to $23.3\\%$ and from $26.7\\%$ to $21.1\\%$ across two IoU thresholds. FP exacerbation rate downgrades from $50.8\\%$ to 47.3 and $51.2\\%$ to $47.0\\%$ .", + "bbox": [ + 498, + 608, + 890, + 714 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5.2. Relation with Increased Number of Supervision", + "text_level": 1, + "bbox": [ + 500, + 724, + 890, + 742 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Some concurrent studies reveal that query-based detectors suffer from training inefficiency due to the one-to-one matching, and propose to add extra parallel query groups and match them with ground-truths in a one-to-many manner, such as Group DETR [6] and H-DETR [14]. We recognize them as increased number of supervision, i.e., each ground-truth is matched to multiple queries, and thus the number of supervision $(\\hat{q})$ is greatly increased. However, simply adding more query groups is a sub-optimal solution according to our motivation, since these extra supervisions", + "bbox": [ + 496, + 750, + 890, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "23761", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/1b0b5f45bd2ec37efe2ec863301c382143f735f0275d6ccf28b7d08a072ffa79.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
Design#Supv / stage#SupvAP
I (Group DETR)3,3,3,3,3,31843.4
II4,4,4,3,2,11843.0
III1,2,3,4,4,41843.7
IV (SQR)1,1,2,3,5,82044.2
V (Group DETR)6,6,6,6,6,63643.6
VI (SQR)1,2,3,5,8,133244.4
", + "bbox": [ + 88, + 88, + 459, + 218 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 7. Results of the 6 designed training strategies on Adamixer to investigate the relation with number of supervision. The inference is untouched. #Supv denotes the number of supervision.", + "bbox": [ + 75, + 227, + 468, + 270 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "are given uniformly among stages. So we present 6 designs as training strategies for investigation.", + "bbox": [ + 75, + 294, + 467, + 324 + ], + "page_idx": 6 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- Design I: Following Group DETR, 3 groups of queries are initialized and independently undergo the whole process of the decoder. The pathway is $3 \\times \\mathcal{PT}^{1-2-3-4-5-6}$ , and number of supervision is 3 groups $\\times 6$ stages $= 18$ .", + "- Design II: 4 groups of queries are initialized but the pathways are $\\mathcal{PT}^{1-2-3-4-5-6}$ , $\\mathcal{PT}^{1-2-3-4-5}$ , $\\mathcal{PT}^{1-2-3-4}$ , $\\mathcal{PT}^{1-2-3}$ , so, with training emphasis on early stages, the number of supervision is $4 + 4 + 4 + 3 + 2 + 1 = 18$ .", + "- Design III: Similar to Design II but not every initialized queries starts from stage 1. The pathways for the 4 groups are $\\mathcal{PT}^{1-2-3-4-5-6}$ , $\\mathcal{PT}^{2-3-4-5-6}$ , $\\mathcal{PT}^{3-4-5-6}$ , $\\mathcal{PT}^{4-5-6}$ , so, with training emphasis on later stages, the number of supervision is $1 + 2 + 3 + 4 + 4 + 4 = 18$ .", + "- Design IV: $SQR^{starting stage=2}$ , the number of supervision is $1 + 1 + 2 + 3 + 5 + 8 = 20$ .", + "- Design V: Same as Design I but with 6 groups. The number of supervision is 6 groups $\\times 6$ stages $= 36$ .", + "- Design VI: $SQR^{starting stage=1}$ , the number of supervision is $1 + 2 + 3 + 5 + 8 + 13 = 32$ ." + ], + "bbox": [ + 94, + 325, + 467, + 626 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table.7 summarizes the results. From the controlled experiments with Design I, II, III, we conclude training with emphasis on late stages is the best option. Design IV and VI are SQR with different starting stages. We show that with similar or even fewer supervisions, SQR outperforms other designs by a large margin. These comparisons verify our motivation and prove that the enhancement from SQR is not simply from the increased number of supervisions.", + "bbox": [ + 75, + 627, + 467, + 748 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.3. Training Emphasis via Re-weighted Loss", + "text_level": 1, + "bbox": [ + 76, + 756, + 426, + 772 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Although the training emphasis contributes to the success of SQR, the access to the early intermediate queries is irreplaceable. We attempt another way to place training emphasis without query recollection, i.e. re-weighting the losses of six decoding stages following the Fibonacci sequence (1,2,3,5,8,13). The AP slightly degrades by (-0.6) compared to the baseline, indicating access to the intermediate queries is necessary for emphasized supervision.", + "bbox": [ + 75, + 780, + 467, + 900 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/6c824e7a7b40eb41a84f17e546653987396226f26c205f741bc61fda4ab4801e.jpg", + "image_caption": [ + "Figure 5. Equal training-time comparison: Baseline vs. SQR" + ], + "image_footnote": [], + "bbox": [ + 501, + 89, + 888, + 196 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.4. Relation with Stochastic Depth", + "text_level": 1, + "bbox": [ + 500, + 251, + 772, + 267 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Stochastic Depth (SD) [13] is a training strategy for very deep network where it randomly removes a fraction of layers independently for each mini-batch, so the depth of pathway varies during training just like SQR. However, SD is of vital inefficiency, because an image has to first pass through a backbone and then be processed by a varying-depth pathway, but for SQR, an image that passes through the backbone can be processed by multiple varying-depth pathways at the same time. To verify this point, we apply SD on the vanilla decoder: During training, for each mini-batch we randomly remove decoding stages following a series of predefined probabilities. From stage $1 \\sim 6$ , the removal probability $\\mathbb{R}$ could be either a constant (0.1), increasing (0.0, 0.1,..., 0.5), or decreasing (0.5, 0.4,..., 0.0). During testing, SD requires the outputs of each decoding stage to be calibrated by the expected times the stage participates in training, so we multiply (1- $\\mathbb{R}$ ) with the residual term in Equ.1. As a result, SD (40.7 mAP) is not comparable to SQR.", + "bbox": [ + 496, + 273, + 890, + 547 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.5. Training efficiency", + "text_level": 1, + "bbox": [ + 500, + 556, + 679, + 571 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "SQR leads to an extra computing burden compared to the baseline since the number of $\\hat{q}$ grows. In Table.5, SQR increases training time of Adamixer-R50 by $0.35\\sim 2.85$ hours $(+0.07\\% \\sim 57\\%)$ . In practice, the effects on different models/implementations/platforms vary. For instance, ResNet-50 is a light-weighted backbone, so the effects of applying SQR are relatively high, while with heavier backbones like ResNet-101 and Swin Transformer [22], the training time is less impacted $(+10\\%)$ .", + "bbox": [ + 496, + 579, + 890, + 715 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "For comparison under equal training time, we train the baseline Adamixer with extra epochs $(+200\\%$ epochs) and baseline Deformable DETR with $(+50\\%$ epochs). Both models' performances (see Fig.5) saturate early and there is no significant improvement over the extended training time, indicating that the benefit of SQR cannot be compensated by including more training iterations.", + "bbox": [ + 496, + 715, + 890, + 821 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.6. Comparison with State-of-the-art", + "text_level": 1, + "bbox": [ + 500, + 830, + 792, + 847 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We conduct experiments on recent query-based detectors with different training settings and various backbones, with and without SQR. We primarily follow the original training", + "bbox": [ + 496, + 854, + 890, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "23762", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/7603bba8ef33dcab95d8eb94af30f40425a58be2b09bc52cae6a9f75851a9c78.jpg", + "table_caption": [], + "table_footnote": [ + "Table 8. Comparison results with various query-based detectors on COCO 2017 val. #query: the number of queries used during inference. * indicates models trained with multi-scale augmentation, † marks models with 7 decoder stages." + ], + "table_body": "
Modelw/ SQR#query#epochsCOCO 2017 validation split
AP\\(AP_{50}\\)\\(AP_{75}\\)\\(AP_S\\)\\(AP_M\\)\\(AP_L\\)
DETR-R50 [3]10050042.062.444.220.545.861.1
Conditional DETR-R50 [23]3005040.961.843.320.844.660.2
Conditional DETR-R101 [23]3005042.863.746.021.746.660.9
Anchor-DETR-R50 [31]3005042.163.144.922.346.260.0
Anchor-DETR-R101 [31]3005043.564.346.623.247.761.4
SAM-DETR-R50 [34]3005039.861.841.620.543.459.6
*SMCA-DETR-R50 [8]3005043.763.647.224.247.060.4
*SMCA-DETR-R50 [8]30010845.665.549.125.949.362.6
*DN-DAB-DETR-R50 [17]3005044.164.446.722.948.063.4
*DN-DAB-DETR-R101 [17]3005045.265.548.324.149.165.1
*DAB-DETR-R50 [20]3005042.263.144.721.545.760.3
*SQR-DAB-DETR-R50✓3005044.5 (+2.3)64.447.524.848.661.7
*DAB-DETR-SwinB [20]3005049.071.053.029.653.868.3
*SQR-DAB-DETR-SwinB✓3005051.6 (+2.6)72.555.932.056.871.0
*Deformable DETR-R50 [38]3001237.255.240.420.640.250.2
*SQR-Deformable DETR-R50✓3001239.9 (+2.7)58.443.723.843.253.3
*Deformable DETR-R50 [38]3005044.563.248.928.047.858.8
*SQR-Deformable DETR-R50✓3005045.9 (+1.4)64.750.227.749.260.5
Adamixer-R50 [9]1001242.561.545.624.645.159.2
SQR-Adamixer-R50✓1001244.4 (+1.9)63.247.825.747.460.2
†Adamixer-R50 [9]1001242.561.545.824.445.258.7
†SQR-Adamixer-R50✓1001245.3 (+2.8)63.849.026.848.162.2
*†Adamixer-R501003645.163.948.928.347.860.6
*†SQR-Adamixer-R50✓1003646.7 (+1.6)65.250.329.449.662.1
*†Adamixer-R503003646.665.550.629.349.362.3
*†SQR-Adamixer-R50✓3003648.9 (+2.3)67.553.232.051.863.7
*†Adamixer-R101 [9]1003645.764.749.627.849.161.2
*†SQR-Adamixer-R101✓1003647.3 (+1.6)66.051.330.150.762.2
*†Adamixer-R101 [9]3003647.666.751.829.550.563.3
*†SQR-Adamixer-R101✓3003649.8 (+2.2)68.854.032.053.465.1
", + "bbox": [ + 102, + 87, + 867, + 614 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "setting of our baselines, where training schedules consists of standard 12, 36, and 50 epochs; the number of queries is chosen between 100 and 300; multi-scale training is applied to 36e and 50e schedules as the shorter side of images range $480 \\sim 800$ . The training is conducted on 8x Nvidia A100.", + "bbox": [ + 80, + 680, + 467, + 755 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "The result is summarized in Fig.1 and Table 8. SQR consistently brings AP improvements to Adamixer, DAB-DETR and Deformable-DETR at the same inference speed. Concretely, on DAB-DETR, SQR brings $+2.3$ and $+2.6$ AP with R50 and SwinB, respectively; on Deformable DETR, SQR boosts it by 2.7 AP under 12e and by 1.4 AP under 50e; on Adamixer with R50, SQR achieves $+1.9$ AP under the basic setting (100 queries, 12e). With an additional stage, the gap between w/ and w/o SQR is enlarged $+2.8$ AP.", + "bbox": [ + 80, + 763, + 467, + 898 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "SQR consistently improves these models by $1.4\\sim 2.8$ AP.", + "bbox": [ + 503, + 680, + 875, + 695 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "6. Conclusion", + "text_level": 1, + "bbox": [ + 503, + 720, + 616, + 734 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this work, we investigate the phenomenon where the optimal detections of query-based object detectors are not always from the last decoding stage, but can sometimes come from an intermediate decoding stage. We first recognize two limitations causing the issue, i.e. lack of training emphasis and cascading errors from query sequence. The problem is addressed by Selective Query Recollection (SQR) as a simple and effective training strategy. 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Bridging the gap between anchor-based and anchor-free detection via adaptive training sample selection. 2020 IEEE/CVF Conference on Computer Vision and Pattern Recognition (CVPR), pages 9756-9765, 2020. 1", + "[37] Chenchen Zhu, Fangyi Chen, Zhiqiang Shen, and Marios Savvides. Soft anchor-point object detection. In ECCV, 2020. 1, 3", + "[38] Xizhou Zhu, Weijie Su, Lewei Lu, Bin Li, Xiaogang Wang, and Jifeng Dai. Deformable detr: Deformable transformers for end-to-end object detection. ArXiv, abs/2010.04159, 2021. 1, 3, 8" + ], + "bbox": [ + 78, + 90, + 468, + 753 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "23765", + "bbox": [ + 478, + 945, + 517, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/Enhanced Training of Query-Based Object Detection via Selective Query Recollection/514d250b-ea10-4630-9256-9e649ac9271f_model.json b/2023/Enhanced Training of Query-Based Object Detection via Selective Query Recollection/514d250b-ea10-4630-9256-9e649ac9271f_model.json new file mode 100644 index 0000000000000000000000000000000000000000..147f268ee5e18c9919899608b9cefd78b77afd38 --- /dev/null +++ b/2023/Enhanced Training of Query-Based Object Detection via Selective Query Recollection/514d250b-ea10-4630-9256-9e649ac9271f_model.json @@ -0,0 +1,2365 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.0, + 0.812, + 0.047 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.2, + 0.131, + 0.773, + 0.177 + ], + "angle": 0, + "content": "Enhanced Training of Query-Based Object Detection via Selective Query Recollection" + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.202, + 0.873, + 0.24 + ], + "angle": 0, + "content": "Fangyi Chen\\(^{1}\\) Han Zhang\\(^{1}\\) Kai Hu\\(^{1}\\) Yu-Kai Huang\\(^{1}\\) Chenchen Zhu\\(^{2}\\) Marios Savvides\\(^{1}\\) Carnegie Mellon University\\(^{1}\\) Meta AI\\(^{2}\\)" + }, + { + "type": "text", + "bbox": [ + 0.166, + 0.242, + 0.792, + 0.256 + ], + "angle": 0, + "content": "{fangyic,hanz3,kaihu,yukaih2,marioss}@andrew.cmu.edu chenchenz@fb.com" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.292, + 0.314, + 0.308 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.325, + 0.474, + 0.658 + ], + "angle": 0, + "content": "This paper investigates a phenomenon where query-based object detectors mispredict at the last decoding stage while predicting correctly at an intermediate stage. We review the training process and attribute the overlooked phenomenon to two limitations: lack of training emphasis and cascading errors from decoding sequence. We design and present Selective Query Recollection (SQR), a simple and effective training strategy for query-based object detectors. It cumulatively collects intermediate queries as decoding stages go deeper and selectively forwards the queries to the downstream stages aside from the sequential structure. Such-wise, SQR places training emphasis on later stages and allows later stages to work with intermediate queries from earlier stages directly. SQR can be easily plugged into various query-based object detectors and significantly enhances their performance while leaving the inference pipeline unchanged. As a result, we apply SQR on Adamixer, DAB-DETR, and Deformable-DETR across various settings (backbone, number of queries, schedule) and consistently brings \\(1.4 \\sim 2.8\\) AP improvement. Code is available at https://github.com/Fangyi-Chen/SQR" + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.691, + 0.21, + 0.707 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.718, + 0.47, + 0.854 + ], + "angle": 0, + "content": "Object detection is a long-established topic in computer vision aiming to localize and categorize objects of interest. Previous methods [4, 7, 10, 11, 16, 18, 21, 25, 26, 29, 32, 33, 35-37] rely on dense priors tiled at feature grids so as to detect in a sliding-window paradigm, and have dominated object detection for the recent decade, but these methods fail to shake off many hand-crafted processing steps such as anchor generation or non-maximum suppression, which block end-to-end optimization." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.471, + 0.902 + ], + "angle": 0, + "content": "Recent research attention has been geared towards query-based object detection [3, 17, 20, 23, 28, 31, 38] since the thriving of transformer [30] and DETR [3]. By view-" + }, + { + "type": "image", + "bbox": [ + 0.505, + 0.293, + 0.891, + 0.475 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.486, + 0.895, + 0.557 + ], + "angle": 0, + "content": "Figure 1. The inference speed and AP for various networks on the MS-COCO val set. The red stars are the results trained with SQR. The blue circles are the results of baselines without SQR. SQR enhances the training of query-based object detectors while leaving the inference pipeline unchanged." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.583, + 0.895, + 0.81 + ], + "angle": 0, + "content": "ing detection as a direct set prediction problem, the new archetype represents the set of objects using a set of learnable embeddings, termed as queries, which are fed to a decoder consisting of a stack (typically six) of decoding stages. Each stage performs similar operations: (1) interacting queries with image features via an attention-like mechanism, so the queries are aggregated with valuable information that represents objects; (2) reasoning the relation among all queries so that global dependency on objects cooccurrence and duplicates could be captured; (3) interpreting bounding box and category from each query by a feed forward network. Queries are sequentially processed stage-by-stage, and each stage is formulated to learn a residual function with reference to the former stage's output, aiming to refine queries in a cascaded style." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.811, + 0.895, + 0.901 + ], + "angle": 0, + "content": "As such wise, the decoding procedure implies that detection should be stage-by-stage enhanced in terms of IoU and confidence score. Indeed, monotonically improved AP is empirically achieved by this procedure. However, when visualizing the stage-wise predictions, we surprisingly observe that decoder makes mistakes in a decent proportion of" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "23756" + } + ], + [ + { + "type": "image_caption", + "bbox": [ + 0.122, + 0.098, + 0.18, + 0.114 + ], + "angle": 0, + "content": "stage 1" + }, + { + "type": "image", + "bbox": [ + 0.089, + 0.116, + 0.216, + 0.234 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.09, + 0.236, + 0.197, + 0.248 + ], + "angle": 0, + "content": "Traffic light | 0.41" + }, + { + "type": "image_caption", + "bbox": [ + 0.252, + 0.098, + 0.313, + 0.114 + ], + "angle": 0, + "content": "stage 2" + }, + { + "type": "image", + "bbox": [ + 0.222, + 0.115, + 0.348, + 0.234 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.225, + 0.236, + 0.332, + 0.248 + ], + "angle": 0, + "content": "Traffic light | 0.38" + }, + { + "type": "image_caption", + "bbox": [ + 0.388, + 0.098, + 0.447, + 0.114 + ], + "angle": 0, + "content": "stage 3" + }, + { + "type": "image", + "bbox": [ + 0.356, + 0.115, + 0.482, + 0.233 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.358, + 0.236, + 0.465, + 0.248 + ], + "angle": 0, + "content": "Traffic light | 0.38" + }, + { + "type": "image_caption", + "bbox": [ + 0.523, + 0.098, + 0.583, + 0.114 + ], + "angle": 0, + "content": "stage 4" + }, + { + "type": "image", + "bbox": [ + 0.491, + 0.115, + 0.616, + 0.234 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.492, + 0.236, + 0.599, + 0.248 + ], + "angle": 0, + "content": "Traffic light | 0.37" + }, + { + "type": "image_caption", + "bbox": [ + 0.654, + 0.098, + 0.712, + 0.114 + ], + "angle": 0, + "content": "stage 5" + }, + { + "type": "image", + "bbox": [ + 0.624, + 0.115, + 0.752, + 0.234 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.626, + 0.236, + 0.733, + 0.248 + ], + "angle": 0, + "content": "Traffic light | 0.21" + }, + { + "type": "image_caption", + "bbox": [ + 0.789, + 0.098, + 0.848, + 0.114 + ], + "angle": 0, + "content": "stage 6" + }, + { + "type": "image", + "bbox": [ + 0.76, + 0.115, + 0.886, + 0.234 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.763, + 0.236, + 0.871, + 0.248 + ], + "angle": 0, + "content": "Traffic light | 0.27" + }, + { + "type": "image", + "bbox": [ + 0.089, + 0.259, + 0.215, + 0.386 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.089, + 0.388, + 0.191, + 0.414 + ], + "angle": 0, + "content": "Cell phone | 0.23 \nCell phone | 0.22" + }, + { + "type": "image", + "bbox": [ + 0.223, + 0.259, + 0.348, + 0.385 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.223, + 0.388, + 0.307, + 0.413 + ], + "angle": 0, + "content": "Remote | 0.25 \nRemote | 0.22" + }, + { + "type": "image", + "bbox": [ + 0.357, + 0.259, + 0.482, + 0.385 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.356, + 0.388, + 0.459, + 0.413 + ], + "angle": 0, + "content": "Cell phone | 0.26 \nRemote | 0.12" + }, + { + "type": "image", + "bbox": [ + 0.49, + 0.259, + 0.617, + 0.386 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.49, + 0.388, + 0.593, + 0.413 + ], + "angle": 0, + "content": "Cell phone | 0.35 \nRemote | 0.12" + }, + { + "type": "image", + "bbox": [ + 0.625, + 0.259, + 0.752, + 0.386 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.626, + 0.388, + 0.727, + 0.413 + ], + "angle": 0, + "content": "Cell phone | 0.39 \nRemote | 0.12" + }, + { + "type": "image", + "bbox": [ + 0.761, + 0.259, + 0.885, + 0.386 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.761, + 0.388, + 0.863, + 0.413 + ], + "angle": 0, + "content": "Cell phone | 0.42 \nRemote | 0.10" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.438, + 0.894, + 0.493 + ], + "angle": 0, + "content": "Figure 2. Are query-based object detectors always enhancing predictions stage-by-stage? The traffic light at stage 1 gets a confident score of 0.41, while from stage 2 to 5 the confidence gradually decreases to 0.21 (Upper); the remote at stage 3 was wrongly classified as a cell phone, and from stage 3 to 6 the mistake was amplified from 0.26 to 0.42 (Lower). The visualization is acquired from Adamixer-R50 (42.5 AP) tested on COCO val set." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.52, + 0.469, + 0.64 + ], + "angle": 0, + "content": "cases where the later stages degrade true-positives and upgrade false-positives from the former stages. As shown in Fig.2, the traffic light at stage 1 gets categorical confidence of 0.41, while from stage 2 to 5 the confidence gradually decreases to 0.21; the remote at stage 3 was wrongly classified as a cell phone, while from stage 3 to 6 the error was exacerbated from 0.26 to 0.42. We present a more detailed statistic in Section 3." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.645, + 0.47, + 0.901 + ], + "angle": 0, + "content": "This phenomenon inspires us to review the current training strategy and bring two conjectures. Firstly, the responsibility that each stage takes is unbalanced, while supervision applied to them is analogous. An early stage could make mistakes without causing too much impact because it gets chances to be corrected later, and the later stages are more responsible for the final prediction. But during training, all of these stages are supervised in an equivalent manner and there lacks such a mechanism that places particular training emphasis on later stages. Secondly, due to the sequential structure of the decoder, an intermediate query refined by a stage - no matter whether this refinement brings positive or negative effects - will be cascaded to the following stages, while the query prior to the refinement never gets an opportunity to be propagated forward even though it emerges unscathed and might be more representative than the refined one. The cascading errors increase the diffi" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.52, + 0.892, + 0.551 + ], + "angle": 0, + "content": "culty of convergence and the sequential structure impedes the later stages from seeing prior queries during training." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.552, + 0.893, + 0.853 + ], + "angle": 0, + "content": "Based on these intuitions, we present Query Recollection (QR) as a training strategy for query-based object detectors. It cumulatively collects intermediate queries as stages go deeper, and feeds the collected queries to the downstream stages aside from the sequential structure. By each stage, the new add-ins alongside the original inputs are independently treated among each other, so the attentions and losses are calculated individually. In such a manner, QR enjoys two key features: (1) The number of supervision signals per stage grows in geometric progression, so that later stages get more supervision than the former ones, for example, the sixth stage got 32 times more supervision than the first; (2) Later stages get chance to view the outputs beyond its neighboring stage for training, which mitigates the potential impact due to cascading errors. We further discover that selectively forward queries to each stage, not with the entire query collection but only those from the prior two stages, can raise the number of supervision in a Fibonacci sequence which halves the extra computing cost and brings even better results. We name it Selective Query Recollection (SQR)." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.856, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Our contributions are summarized in three folds: (1) We quantitatively investigate the phenomenon where query-based object detectors mispredict at the last decoding stage" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "23757" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.198 + ], + "angle": 0, + "content": "while predicting correctly at an intermediate one. (2) We attribute the overlooked phenomenon to two training limitations, and propose a simple and effective training strategy SQR that elegantly fits query-based object detectors. (3) We conduct experiments on Adamixer, DAB DETR, and Deformable DETR across various training settings that verify its effectiveness (Fig.1)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.212, + 0.22, + 0.228 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.238, + 0.411, + 0.254 + ], + "angle": 0, + "content": "2.1. Training Strategy for Object Detection" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.262, + 0.473, + 0.55 + ], + "angle": 0, + "content": "Detectors based on dense priors have been dominating the community for decades. The abstract concept anchor box or anchor point [26, 29] aims to match with ground truth (GT) objects depending on their Intersection-over-Union (IoU) values or other advanced soft scoring factors [7, 15, 18, 29, 37]. Among anchor-based detectors, multistage models iteratively refine bounding box and category stage-by-stage. A typical example is Cascade RCNN [2] which is based on the design that the output of an intermediate stage is sampled and re-labeled to train the next stage with increasing IoU thresholds, so these stages are guaranteed to be progressively refined. Recently, DETR [3] starts a family of end-to-end query-based models where object detection is regarded as a set prediction problem. To train DETR, a predefined number of object queries are matched to either a ground-truth or background by solving the Hungarian Matching problem. The queries are refined by several decoder stages similar to Cascade RCNN, and each intermediate stage is supervised by the matching results." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.56, + 0.349, + 0.577 + ], + "angle": 0, + "content": "2.2. Query-Based Object Detection" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.584, + 0.473, + 0.903 + ], + "angle": 0, + "content": "Recently, many algorithms have been following the idea of DETR. Deformable DETR [38] proposes a deformable attention module that alleviates the aforementioned issues and massively improves the convergence speed by a factor of 10. Conditional DETR [23] decouples the object query into content query and spatial query in the decoder cross-attention module and learns a conditional spatial query from the decoder embedding to enable fast learning of the distinctive extremity of the ground-truth objects. Anchor-DETR [31] formulates the object queries as anchor points such that each object query may only focus on a certain region near its anchor point. Many future works are inspired by this design. DAB-DETR [20] dives deep into the role of object queries. It directly uses anchor box coordinates as spatial query to speed up training. The model benefits from the spatial prior by modulating the positional attention map using the width and height of the box. DN-DETR [17] further improves the convergence speed and query matching stability of DAB-DETR with the help of the Ground Truth denoising task. Adamixer [9] re-designs the query-key pooling mechanism by letting the query adaptively attend to the mean" + }, + { + "type": "table", + "bbox": [ + 0.502, + 0.09, + 0.897, + 0.151 + ], + "angle": 0, + "content": "
ModelS1S2S3S4S5S6
Deformable38.442.243.744.244.444.5
Adamixer15.130.337.740.642.142.5
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.161, + 0.895, + 0.218 + ], + "angle": 0, + "content": "Table 1. Stage-wise AP results. Deformable DETR(300 queries) and Adamixer(100 queries) are trained using official implementation, both of their decoders consist of 6 stages, and per stage AP is reported on COCO val set." + }, + { + "type": "image", + "bbox": [ + 0.507, + 0.233, + 0.892, + 0.328 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.535, + 0.338, + 0.856, + 0.352 + ], + "angle": 0, + "content": "Figure 3. Typical structure of a single decoding stage." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.379, + 0.892, + 0.469 + ], + "angle": 0, + "content": "ingful regions of the encoded features directly through bilinear sampling. An MLP-Mixer then dynamically decodes the pooled features into final predictions. DETA (Detection Transformers with Assignment) [24] proposes a novel overlap-based assignment that enables one-to-many assignments to DETR." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.47, + 0.892, + 0.516 + ], + "angle": 0, + "content": "Despite their significant improvement on DETR, they focus little on the training emphasis and cascading errors. We propose SQR to pay attention to the two problems." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.53, + 0.618, + 0.545 + ], + "angle": 0, + "content": "3. Motivation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.556, + 0.892, + 0.646 + ], + "angle": 0, + "content": "Are query-based object detectors always predicting the optimal detections at the last stage? Table.1 shows that AP gradually increases with stages going deeper, indicating improved predictions on a general scale. While the observation in Fig.2 implies that simple AP results are insufficient for an in-depth analysis of that question." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.647, + 0.892, + 0.782 + ], + "angle": 0, + "content": "Preliminary. Queries are updated successively. A typical structure of a decoding stage is illustrated in Fig.3. An initial query \\( q_{i}^{0} \\) (\\( i \\in N = \\{1,2,\\dots,n\\} \\)) is an embedding trained through back-propagation, and \\( n \\) is the total number of initial queries. During inference, the first stage updates the initial query by adding a residual term to it, producing intermediate query \\( q_{i}^{1} \\), followed by later stages sequentially updating the intermediate query in the same way. The procedure can be formulated as" + }, + { + "type": "equation", + "bbox": [ + 0.5, + 0.793, + 0.891, + 0.825 + ], + "angle": 0, + "content": "\\[\nq _ {i} ^ {s} = D ^ {s} \\left(q _ {i} ^ {s - 1}, q ^ {s - 1}, x\\right) = q _ {i} ^ {s - 1} + (\\mathcal {A} \\circ \\mathcal {F}) \\left(q _ {i} ^ {s - 1}, q ^ {s - 1}, x\\right) \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.826, + 0.894, + 0.901 + ], + "angle": 0, + "content": "\\(D^{s}\\) is a decoding stage where \\(s\\) is stage index; \\(q_{i}^{s}\\) is the \\(i_{th}\\) query at stage \\(s\\); \\(q^{s}\\) is a set of queries \\(q^{s} = \\{q_{i}^{s} | i \\in N\\}\\); \\((\\mathcal{A} \\circ \\mathcal{F})\\) stands for a bundle of modules including self and cross attention and feed forward network; \\(x\\) means features; and LayerNorm [1] that applied on each module is omitted" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "23758" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.082, + 0.089, + 0.468, + 0.188 + ], + "angle": 0, + "content": "
ModelTP ThresholdTP F RateFP E Rate
DeformableIoU>0.5051.4%55.7%
DETRIoU>0.7549.5%55.9%
AdamixerIoU>0.5028.6%50.8%
IoU>0.7526.7%51.2%
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.198, + 0.47, + 0.226 + ], + "angle": 0, + "content": "Table 2. True-positive Fading Rate and False-positive Exacerbation Rate." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.254, + 0.47, + 0.286 + ], + "angle": 0, + "content": "for simplicity. Afterward, \\( q_{i}^{s} \\) predicts an object \\( P_{i}^{s} \\) via two multi-layer perceptrons for classification and regression:" + }, + { + "type": "equation", + "bbox": [ + 0.146, + 0.301, + 0.47, + 0.318 + ], + "angle": 0, + "content": "\\[\nP _ {i} ^ {s} = \\left(M L P _ {c l s} \\left(q _ {i} ^ {s}\\right), M L P _ {r e g} \\left(q _ {i} ^ {s}\\right)\\right) \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.324, + 0.468, + 0.417 + ], + "angle": 0, + "content": "\\(P_{i}^{1\\sim 6}\\) are predicted by the \\(q_{i}^{1\\sim 6}\\) rooted in \\(q_{i}^{0}\\), where \\(P_{i}^{6}\\) is the expected outcome and \\(P_{i}^{1\\sim 5}\\) are intermediate results. \\(P_{i}^{s}\\) is regarded as a true-positive towards a ground-truth \\(G\\) only if the IoU \\((P_{i}^{s}, G)\\) exceeds a threshold, its category matches with \\(G\\), and the categorical score is ranked as the highest among all other counterparts." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.417, + 0.468, + 0.551 + ], + "angle": 0, + "content": "Investigation. We study the stage-wise testing results by first defining two rates: (1) If \\( P_{i}^{6} \\) is a true-positive (TP) towards a ground-truth \\( G \\), we check whether \\( P_{i}^{1\\sim 5} \\) generate a better TP towards the same \\( G \\) that has higher IoU & higher category score than \\( P_{i}^{6} \\). The occurrence rate is denoted as TP fading rate. (2) If \\( P_{i}^{6} \\) is a false-positive (FP), we check whether \\( P_{i}^{1\\sim 5} \\) produce a FP but with lower category score than \\( P_{i}^{6} \\). The occurrence rate is denoted as FP exacerbation rate." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.553, + 0.468, + 0.839 + ], + "angle": 0, + "content": "The statistics are shown in Table.2. We can see that TP fading rate achieves \\(50\\%\\) and \\(27\\%\\) on the two models. Considering the strict constraints it holds, the TP fading rate reaches an impressively high level. Deformable DETR is much higher than Adamixer due to the smaller AP gap among stages, thus, in many cases, earlier stages are more likely to outperform the last stage. FP exacerbation holds looser constraints and is easier to be satisfied, its rate is above \\(50\\%\\) on the two models. Higher TP threshold implies higher quality of \\(P_{i}^{6}\\) and it is harder to find qualifiers in \\(P_{i}^{1\\sim 5}\\), but the two rates are similar with 0.75 as with 0.5, pointing out the consistency of this phenomenon. We also observe that more than half of the occurred cases are marginally triggered, i.e. the predictions from the triggered \\(P_{i}^{1\\sim 5}\\) are only marginally better than the sixth. This is a further reason why the deformable DETR has those high rates - the results from the 5th and 6th stages are extremely visually close. In dominated number of cases, the final stage is (one of) the best, after all, its mAP is the highest." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.468, + 0.901 + ], + "angle": 0, + "content": "When the conditions of the two rates establish, we further replace \\( P_{i}^{6} \\) with the optimal prediction found in \\( P_{i}^{1\\sim 6} \\) and measure the AP. On Deformable DETR, AP grows from 44.5 AP to 51.7 (+7.2 AP); on Adamixer, AP grows from" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.092, + 0.892, + 0.122 + ], + "angle": 0, + "content": "42.5 AP to 53.3 (+10.7 AP), demonstrating huge potential in query-based detectors yet to be mined." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.123, + 0.892, + 0.228 + ], + "angle": 0, + "content": "Conclusion. This reveals that models frequently predict the optimum at intermediate stages instead of the last one. We view the problem from the training's perspective and identify the lack of training emphasis and the cascading errors from query sequence as two obstacles impeding the occurrence of the most reliable predictions in the last stage, elaborated in Section 1." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.245, + 0.686, + 0.263 + ], + "angle": 0, + "content": "4. Query Recollection" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.271, + 0.627, + 0.287 + ], + "angle": 0, + "content": "4.1. Expectancy" + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.295, + 0.842, + 0.311 + ], + "angle": 0, + "content": "We desire such a training strategy that embraces:" + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.312, + 0.892, + 0.356 + ], + "angle": 0, + "content": "- Uneven supervision applied to decoding stages that places emphasis on later ones, enhancing later stages for better final outcomes." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.358, + 0.892, + 0.387 + ], + "angle": 0, + "content": "- A variety of early-stage queries directly introduced to later stages, mitigating the impact of cascading errors." + }, + { + "type": "list", + "bbox": [ + 0.518, + 0.312, + 0.892, + 0.387 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.389, + 0.892, + 0.48 + ], + "angle": 0, + "content": "To this end, we design a concise training strategy coined as Query Recollection (QR). Compared with prior arts, it collects intermediate queries at every stage and forwards them along the original pathway. Dense Query Recollection (DQR) is the fundamental form and Selective Query Recollection (SQR) is an advanced variant." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.492, + 0.734, + 0.508 + ], + "angle": 0, + "content": "4.2. Dense Query Recollection" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.516, + 0.892, + 0.607 + ], + "angle": 0, + "content": "Notation. The process of single decoding stage (self-attention, cross-attention, FFN), the ground-truth assignment, and loss calculations are applied within a set of queries \\(\\{q_i | i \\in \\{1, 2, \\dots, n\\}\\}\\), where \\(n\\) is typically 100/300/500. We regard the set of queries as a basic unit in our method and generally denote as \\(q\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.608, + 0.892, + 0.684 + ], + "angle": 0, + "content": "Basic Pathway. Query along the basic pathway is refined by all stages. We illustrate it in Fig.4(a). Taking a 4-stages decoder as an example, we denote \\( q^{0-1-2-3-4} \\) as the final query that is refined by all stages. So the basic \\( \\mathcal{PT} \\) finally produces" + }, + { + "type": "equation", + "bbox": [ + 0.567, + 0.712, + 0.891, + 0.75 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} q ^ {0 - 1 - 2 - 3 - 4} = D ^ {4} \\left(D ^ {3} \\left(D ^ {2} \\left(D ^ {1} \\left(q ^ {0}\\right)\\right)\\right)\\right) (3) \\\\ = \\mathcal {P T} ^ {1 - 2 - 3 - 4} \\left(q ^ {0}\\right) (4) \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.763, + 0.892, + 0.869 + ], + "angle": 0, + "content": "During training, the queries from each stage, i.e. \\( q^{0-1} \\), \\( q^{0-1-2} \\), \\( q^{0-1-2-3} \\), and \\( q^{0-1-2-3-4} \\) are independently followed by Hungarian Assignment that matches ground-truth with \\( q \\) in a one-to-one manner, and then followed by loss calculation for supervision. In Fig.4, we mark those \\( q \\) that require supervision as \\( \\hat{q} \\). Along the basic pathway, the number of \\( \\hat{q} \\) at each stage is 1." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.871, + 0.892, + 0.901 + ], + "angle": 0, + "content": "DQR Formulation. We densely collect every intermediate \\( q \\) and independently forward them to every downstream" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "23759" + } + ], + [ + { + "type": "image_caption", + "bbox": [ + 0.078, + 0.09, + 0.249, + 0.107 + ], + "angle": 0, + "content": "(a)Basic (b)Dense QR" + }, + { + "type": "image", + "bbox": [ + 0.078, + 0.113, + 0.487, + 0.49 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.081, + 0.514, + 0.12, + 0.553 + ], + "angle": 0, + "content": null + }, + { + "type": "image_footnote", + "bbox": [ + 0.121, + 0.519, + 0.483, + 0.532 + ], + "angle": 0, + "content": "Collection C \\(q^{0I2}\\) Query, from initial to stage 1 then to 2" + }, + { + "type": "image_footnote", + "bbox": [ + 0.121, + 0.538, + 0.447, + 0.552 + ], + "angle": 0, + "content": "Output of stage/QR \\(\\hat{\\pmb{q}}\\) Query with supervision applied" + }, + { + "type": "list", + "bbox": [ + 0.121, + 0.519, + 0.483, + 0.552 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.564, + 0.47, + 0.606 + ], + "angle": 0, + "content": "Figure 4. (a). Basic process for decoding queries stage by stage, applied in both training and testing. (b). Dense query recollection. (c). Selective query recollection." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.631, + 0.47, + 0.678 + ], + "angle": 0, + "content": "stage, as illustrated in Fig.4(b). After each stage, a collection \\(C\\) is formed where the number of \\(q\\) grows geometrically, namely \\(2^{s}\\) at \\(s_{th}\\) stage. Formally," + }, + { + "type": "equation", + "bbox": [ + 0.234, + 0.69, + 0.469, + 0.707 + ], + "angle": 0, + "content": "\\[\nC ^ {0} = \\{q ^ {0} \\} \\tag {5}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.16, + 0.712, + 0.469, + 0.73 + ], + "angle": 0, + "content": "\\[\nC ^ {s} = \\left\\{D ^ {s} (q) | q \\in C ^ {s - 1} \\right\\} \\cup C ^ {s - 1} \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.735, + 0.469, + 0.84 + ], + "angle": 0, + "content": "In a collection \\( C \\), half of queries inside are newly generated by the current stage, i.e. from \\( \\{D^s(q)|q \\in C^{s-1}\\} \\), while another half are from previous stages, \\( C^{s-1} \\). Separately, for each \\( q \\) in the former half, we apply Hungarian assignment and loss calculation, so the number of supervision signals grows in geometric progression as well, namely \\( 2^{s-1} \\) at \\( s_{th} \\) stage." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.469, + 0.902 + ], + "angle": 0, + "content": "Such-wise, Dense Query Recollection satisfies our expectancy where the number of supervision signal for each stage grows as (1,2,4,8,16,32), meanwhile, all prior queries would be visible in all later stages." + }, + { + "type": "table", + "bbox": [ + 0.517, + 0.09, + 0.878, + 0.21 + ], + "angle": 0, + "content": "
stage12345
TP F Rate(%)1.24.48.512.416.9
FP E Rate(%)14.318.620.824.530.2
stage1~34&53~52~51~5
TP F Rate(%)11.223.926.928.328.6
FP E Rate(%)32.440.845.348.550.8
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.22, + 0.892, + 0.247 + ], + "angle": 0, + "content": "Table 3. Stage-wise TP Fading Rate and FP Exacerbation Rate with Adamixer." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.276, + 0.892, + 0.322 + ], + "angle": 0, + "content": "During inference, we only use the basic pathway, so the inference process is untouched. For a standard 6-stage decoder, the pathway is \\(\\mathcal{PT}^{1-2-3-4-5-6}\\)" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.332, + 0.756, + 0.348 + ], + "angle": 0, + "content": "4.3. Selective Query Recollection" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.356, + 0.892, + 0.551 + ], + "angle": 0, + "content": "The last proposal empirically enhances training, but the query collection process is indiscriminate, which brings two defects: First, the geometrical growth of the number of \\(\\hat{q}\\) and their attention/loss calculations cost a lot. Second, if we input an early \\(q\\) that skips too many stages to a far-away late stage, the potential benefit could be overshadowed by the huge learning gap between the stages and query. For instance, if the initial \\(q^0\\) is directly introduced to stage 6 and produces \\(\\hat{q}^{0 - 6}\\), this query would have the highest difficulty among all queries at stage 6 and the calculated loss would dominate the overall losses. So we are inclined to selectively collect intermediate \\(q\\) rather than densely collect all of them." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.552, + 0.892, + 0.597 + ], + "angle": 0, + "content": "Selection. To find a better query recollection scheme, we further conduct a detailed analysis on the TP Fading Rate and FP Exacerbation Rate introduced in Section 3." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.598, + 0.893, + 0.794 + ], + "angle": 0, + "content": "Recall the spirits of the two rates where we seek from \\( P_{i}^{1\\sim 5} \\) for an alternative that is better than \\( P_{i}^{6} \\), we want to investigate which specific intermediate stage/stages contribute the most. Concretely, if \\( P_{i}^{6} \\) is a true-positive towards a ground-truth \\( G \\), we separately check each stage whether generating a better TP; similarly, if \\( P_{i}^{6} \\) is a false-positive, we separately check each stage whether generating a better FP. The results are summarized in Table 3. We find that the majority of alternatives of \\( P_{i}^{6} \\) are from stage 4&5, where the corresponding TP fading rate and FP exacerbation rate reach \\( 23.9\\% \\) and \\( 40.8\\% \\), respectively, which are close to the results of stages \\( 1 \\sim 5 \\). While stage \\( 1 \\sim 3 \\) together only produces \\( 11.2\\% \\) and \\( 32.4\\% \\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.795, + 0.892, + 0.885 + ], + "angle": 0, + "content": "The above analysis implies that the queries from the adjacent stage and the stage prior to the adjacent stage are more likely to bring positive effects. We intuitively follow the observations and selectively operate collection along the basic pathway: before starting stage \\( D^{s} \\), we collect \\( q \\) from the 2 nearest stages, i.e. \\( D^{s - 1} \\) and \\( D^{s - 2} \\) as the input of \\( D^{s} \\)." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.886, + 0.892, + 0.901 + ], + "angle": 0, + "content": "SQR Formulation. The Selective Query Recollection" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "23760" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.22, + 0.106 + ], + "angle": 0, + "content": "can be formulated as" + }, + { + "type": "equation", + "bbox": [ + 0.165, + 0.115, + 0.47, + 0.134 + ], + "angle": 0, + "content": "\\[\nC ^ {0} = \\left\\{q ^ {0} \\right\\} \\quad C ^ {1} = \\left\\{q ^ {0}, q ^ {0 - 1} \\right\\} \\tag {7}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.094, + 0.151, + 0.47, + 0.189 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} C ^ {s} = \\{D ^ {s} (q) | q \\in C ^ {s - 1} \\} \\cup \\operatorname {s e l e c t} \\left(C ^ {s - 1}\\right) \\tag {8} \\\\ = \\{D ^ {s} (q) | q \\in C ^ {s - 1} \\} \\cup \\{D ^ {s - 1} (q) | q \\in C ^ {s - 2} \\} (9) \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.197, + 0.469, + 0.332 + ], + "angle": 0, + "content": "Such wise, Selective Query Recollection (Fig.4(c)) still satisfies our expectancy, and the number of supervision signals grows in a Fibonacci sequence (1,2,3,5,8,13). Compared to the Dense Recollection, to a great extent, SQR reduces the computing burden and we observe that SQR even outperforms the dense counterpart in terms of precision. This verifies our assumption that a \\( q \\) skipping too many stages might be noise for remote stages overshadowing its positive effects." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.333, + 0.469, + 0.455 + ], + "angle": 0, + "content": "Recollection Starting Stage. Above we collect queries starting from stage 1. Instead, we can practically vary this starting stage, and this will further reduce the total queries in each collection and further reduce the computing burden. E.g., if starts SQR from stage 2, the Fibonacci sequence will start from stage 2 and result in \\((1,1,2,3,5,8)\\); if starts from stage 3, result in \\((1,1,1,2,3,5)\\). The starting stage is regarded as a hyper-parameter for SQR." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.466, + 0.21, + 0.484 + ], + "angle": 0, + "content": "5. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.492, + 0.469, + 0.643 + ], + "angle": 0, + "content": "We conduct our experiments on the MS-COCO [19] detection track using the MMDetection [5] and Detrex [27] code-bases. All models are trained on train2017 split. Unless otherwise specified, models are trained and tested with image scale of 800 pixels, where AdamW optimizer with a standard 1x schedule (12 epochs) is utilized for training. For ablation study and analysis, Adamixer [9] with R50 [12] is chosen because of its good performance and fast convergence speed (42.5 AP with 1x schedule). We further apply SQR on other detectors to verify its effectiveness." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.651, + 0.231, + 0.668 + ], + "angle": 0, + "content": "5.1. Ablation Study" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.674, + 0.469, + 0.78 + ], + "angle": 0, + "content": "Baseline vs DQR vs SQR. Table.4 shows that both DQR and SQR improve the baseline by a large margin. DQR reaches 44.2 (+1.7 AP) while SQR reaches a slightly high result 44.4 (+1.9 AP). Note that SQR is much more efficient than DQR. As shown in Table.5, under the same training setting, SQR cuts down a great amount of training time of DQR and still achieves equal or higher AP." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.78, + 0.469, + 0.902 + ], + "angle": 0, + "content": "Varying Starting Stage of SQR. We present how SQR performs when varying the starting stage in Table.5. The best performance is acquired when query recollection starts at stage 1 but with the most computational cost. We can see that starting at stage 2 performs similarly to starting at stage 1 while the computing burden is decently reduced. With recollection starting later, the benefits from SQR decrease as expected since the recollected queries from early" + }, + { + "type": "table", + "bbox": [ + 0.505, + 0.09, + 0.89, + 0.166 + ], + "angle": 0, + "content": "
MethodsAP\\( AP_{50} \\)\\( AP_{75} \\)\\( AP_S \\)\\( AP_M \\)\\( AP_L \\)
Baseline42.561.545.624.645.159.2
DQR44.262.847.926.746.960.5
SQR44.463.247.825.747.460.2
" + }, + { + "type": "table_caption", + "bbox": [ + 0.523, + 0.177, + 0.868, + 0.192 + ], + "angle": 0, + "content": "Table 4. AP comparison among Baseline, DQR, and SQR" + }, + { + "type": "table", + "bbox": [ + 0.515, + 0.207, + 0.88, + 0.358 + ], + "angle": 0, + "content": "
MethodStart StageTrain TimeAP\\( AP_{50} \\)
Baseline-1x(5hours)42.561.5
Baseline-2x42.561.3
Baseline-3x42.561.4
DQR-2.24x44.262.8
SQR11.57x44.463.2
SQR21.34x44.263.0
SQR31.18x43.862.3
SQR41.07x42.961.4
" + }, + { + "type": "table_caption", + "bbox": [ + 0.5, + 0.369, + 0.892, + 0.398 + ], + "angle": 0, + "content": "Table 5. Further comparison among Baseline, DQR, and SQR with different starting stage in terms of training time and AP." + }, + { + "type": "table", + "bbox": [ + 0.516, + 0.413, + 0.879, + 0.512 + ], + "angle": 0, + "content": "
MethodTP ThresholdTP F RateFP E Rate
BaselineIoU>0.5028.6%50.8%
SQRIoU>0.5023.3 %47.3 %
BaselineIoU>0.7526.7%51.2%
SQRIoU>0.7521.1%47.0%
" + }, + { + "type": "table_caption", + "bbox": [ + 0.5, + 0.522, + 0.892, + 0.551 + ], + "angle": 0, + "content": "Table 6. Baseline vs. SQR on true-positive fading rate and false-positive exacerbation rate." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.579, + 0.891, + 0.607 + ], + "angle": 0, + "content": "stages become fewer and training emphasis gets gradually balanced." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.609, + 0.892, + 0.715 + ], + "angle": 0, + "content": "TP Fading Rate And FP Exacerbation Rate. We present Table.6 to verify that TP fading rate and FP exacerbation rate decrease due to the training effect when applied SQR. Specifically, TP fading rate decreases from \\(28.6\\%\\) to \\(23.3\\%\\) and from \\(26.7\\%\\) to \\(21.1\\%\\) across two IoU thresholds. FP exacerbation rate downgrades from \\(50.8\\%\\) to 47.3 and \\(51.2\\%\\) to \\(47.0\\%\\)." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.726, + 0.891, + 0.743 + ], + "angle": 0, + "content": "5.2. Relation with Increased Number of Supervision" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.75, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Some concurrent studies reveal that query-based detectors suffer from training inefficiency due to the one-to-one matching, and propose to add extra parallel query groups and match them with ground-truths in a one-to-many manner, such as Group DETR [6] and H-DETR [14]. We recognize them as increased number of supervision, i.e., each ground-truth is matched to multiple queries, and thus the number of supervision \\((\\hat{q})\\) is greatly increased. However, simply adding more query groups is a sub-optimal solution according to our motivation, since these extra supervisions" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "23761" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.089, + 0.089, + 0.46, + 0.219 + ], + "angle": 0, + "content": "
Design#Supv / stage#SupvAP
I (Group DETR)3,3,3,3,3,31843.4
II4,4,4,3,2,11843.0
III1,2,3,4,4,41843.7
IV (SQR)1,1,2,3,5,82044.2
V (Group DETR)6,6,6,6,6,63643.6
VI (SQR)1,2,3,5,8,133244.4
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.228, + 0.47, + 0.271 + ], + "angle": 0, + "content": "Table 7. Results of the 6 designed training strategies on Adamixer to investigate the relation with number of supervision. The inference is untouched. #Supv denotes the number of supervision." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.295, + 0.468, + 0.325 + ], + "angle": 0, + "content": "are given uniformly among stages. So we present 6 designs as training strategies for investigation." + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.326, + 0.468, + 0.4 + ], + "angle": 0, + "content": "- Design I: Following Group DETR, 3 groups of queries are initialized and independently undergo the whole process of the decoder. The pathway is \\(3 \\times \\mathcal{PT}^{1-2-3-4-5-6}\\), and number of supervision is 3 groups \\(\\times 6\\) stages \\(= 18\\)." + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.402, + 0.468, + 0.461 + ], + "angle": 0, + "content": "- Design II: 4 groups of queries are initialized but the pathways are \\(\\mathcal{PT}^{1-2-3-4-5-6}\\), \\(\\mathcal{PT}^{1-2-3-4-5}\\), \\(\\mathcal{PT}^{1-2-3-4}\\), \\(\\mathcal{PT}^{1-2-3}\\), so, with training emphasis on early stages, the number of supervision is \\(4 + 4 + 4 + 3 + 2 + 1 = 18\\)." + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.462, + 0.468, + 0.536 + ], + "angle": 0, + "content": "- Design III: Similar to Design II but not every initialized queries starts from stage 1. The pathways for the 4 groups are \\(\\mathcal{PT}^{1-2-3-4-5-6}\\), \\(\\mathcal{PT}^{2-3-4-5-6}\\), \\(\\mathcal{PT}^{3-4-5-6}\\), \\(\\mathcal{PT}^{4-5-6}\\), so, with training emphasis on later stages, the number of supervision is \\(1 + 2 + 3 + 4 + 4 + 4 = 18\\)." + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.537, + 0.468, + 0.566 + ], + "angle": 0, + "content": "- Design IV: \\( SQR^{starting stage=2} \\), the number of supervision is \\( 1 + 1 + 2 + 3 + 5 + 8 = 20 \\)." + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.568, + 0.468, + 0.597 + ], + "angle": 0, + "content": "- Design V: Same as Design I but with 6 groups. The number of supervision is 6 groups \\(\\times 6\\) stages \\(= 36\\)." + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.598, + 0.468, + 0.627 + ], + "angle": 0, + "content": "- Design VI: \\( SQR^{starting stage=1} \\), the number of supervision is \\( 1 + 2 + 3 + 5 + 8 + 13 = 32 \\)." + }, + { + "type": "list", + "bbox": [ + 0.096, + 0.326, + 0.468, + 0.627 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.628, + 0.468, + 0.749 + ], + "angle": 0, + "content": "Table.7 summarizes the results. From the controlled experiments with Design I, II, III, we conclude training with emphasis on late stages is the best option. Design IV and VI are SQR with different starting stages. We show that with similar or even fewer supervisions, SQR outperforms other designs by a large margin. These comparisons verify our motivation and prove that the enhancement from SQR is not simply from the increased number of supervisions." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.757, + 0.427, + 0.773 + ], + "angle": 0, + "content": "5.3. Training Emphasis via Re-weighted Loss" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.781, + 0.468, + 0.901 + ], + "angle": 0, + "content": "Although the training emphasis contributes to the success of SQR, the access to the early intermediate queries is irreplaceable. We attempt another way to place training emphasis without query recollection, i.e. re-weighting the losses of six decoding stages following the Fibonacci sequence (1,2,3,5,8,13). The AP slightly degrades by (-0.6) compared to the baseline, indicating access to the intermediate queries is necessary for emphasized supervision." + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.09, + 0.89, + 0.198 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.515, + 0.211, + 0.878, + 0.225 + ], + "angle": 0, + "content": "Figure 5. Equal training-time comparison: Baseline vs. SQR" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.252, + 0.773, + 0.268 + ], + "angle": 0, + "content": "5.4. Relation with Stochastic Depth" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.275, + 0.892, + 0.548 + ], + "angle": 0, + "content": "Stochastic Depth (SD) [13] is a training strategy for very deep network where it randomly removes a fraction of layers independently for each mini-batch, so the depth of pathway varies during training just like SQR. However, SD is of vital inefficiency, because an image has to first pass through a backbone and then be processed by a varying-depth pathway, but for SQR, an image that passes through the backbone can be processed by multiple varying-depth pathways at the same time. To verify this point, we apply SD on the vanilla decoder: During training, for each mini-batch we randomly remove decoding stages following a series of predefined probabilities. From stage \\(1 \\sim 6\\), the removal probability \\(\\mathbb{R}\\) could be either a constant (0.1), increasing (0.0, 0.1,..., 0.5), or decreasing (0.5, 0.4,..., 0.0). During testing, SD requires the outputs of each decoding stage to be calibrated by the expected times the stage participates in training, so we multiply (1-\\(\\mathbb{R}\\)) with the residual term in Equ.1. As a result, SD (40.7 mAP) is not comparable to SQR." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.557, + 0.68, + 0.573 + ], + "angle": 0, + "content": "5.5. Training efficiency" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.58, + 0.892, + 0.716 + ], + "angle": 0, + "content": "SQR leads to an extra computing burden compared to the baseline since the number of \\(\\hat{q}\\) grows. In Table.5, SQR increases training time of Adamixer-R50 by \\(0.35\\sim 2.85\\) hours \\((+0.07\\% \\sim 57\\%)\\). In practice, the effects on different models/implementations/platforms vary. For instance, ResNet-50 is a light-weighted backbone, so the effects of applying SQR are relatively high, while with heavier backbones like ResNet-101 and Swin Transformer [22], the training time is less impacted \\((+10\\%)\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.717, + 0.892, + 0.822 + ], + "angle": 0, + "content": "For comparison under equal training time, we train the baseline Adamixer with extra epochs \\((+200\\%\\) epochs) and baseline Deformable DETR with \\((+50\\%\\) epochs). Both models' performances (see Fig.5) saturate early and there is no significant improvement over the extended training time, indicating that the benefit of SQR cannot be compensated by including more training iterations." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.832, + 0.794, + 0.848 + ], + "angle": 0, + "content": "5.6. Comparison with State-of-the-art" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.856, + 0.892, + 0.901 + ], + "angle": 0, + "content": "We conduct experiments on recent query-based detectors with different training settings and various backbones, with and without SQR. We primarily follow the original training" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "23762" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.104, + 0.088, + 0.868, + 0.616 + ], + "angle": 0, + "content": "
Modelw/ SQR#query#epochsCOCO 2017 validation split
AP\\(AP_{50}\\)\\(AP_{75}\\)\\(AP_S\\)\\(AP_M\\)\\(AP_L\\)
DETR-R50 [3]10050042.062.444.220.545.861.1
Conditional DETR-R50 [23]3005040.961.843.320.844.660.2
Conditional DETR-R101 [23]3005042.863.746.021.746.660.9
Anchor-DETR-R50 [31]3005042.163.144.922.346.260.0
Anchor-DETR-R101 [31]3005043.564.346.623.247.761.4
SAM-DETR-R50 [34]3005039.861.841.620.543.459.6
*SMCA-DETR-R50 [8]3005043.763.647.224.247.060.4
*SMCA-DETR-R50 [8]30010845.665.549.125.949.362.6
*DN-DAB-DETR-R50 [17]3005044.164.446.722.948.063.4
*DN-DAB-DETR-R101 [17]3005045.265.548.324.149.165.1
*DAB-DETR-R50 [20]3005042.263.144.721.545.760.3
*SQR-DAB-DETR-R50✓3005044.5 (+2.3)64.447.524.848.661.7
*DAB-DETR-SwinB [20]3005049.071.053.029.653.868.3
*SQR-DAB-DETR-SwinB✓3005051.6 (+2.6)72.555.932.056.871.0
*Deformable DETR-R50 [38]3001237.255.240.420.640.250.2
*SQR-Deformable DETR-R50✓3001239.9 (+2.7)58.443.723.843.253.3
*Deformable DETR-R50 [38]3005044.563.248.928.047.858.8
*SQR-Deformable DETR-R50✓3005045.9 (+1.4)64.750.227.749.260.5
Adamixer-R50 [9]1001242.561.545.624.645.159.2
SQR-Adamixer-R50✓1001244.4 (+1.9)63.247.825.747.460.2
†Adamixer-R50 [9]1001242.561.545.824.445.258.7
†SQR-Adamixer-R50✓1001245.3 (+2.8)63.849.026.848.162.2
*†Adamixer-R501003645.163.948.928.347.860.6
*†SQR-Adamixer-R50✓1003646.7 (+1.6)65.250.329.449.662.1
*†Adamixer-R503003646.665.550.629.349.362.3
*†SQR-Adamixer-R50✓3003648.9 (+2.3)67.553.232.051.863.7
*†Adamixer-R101 [9]1003645.764.749.627.849.161.2
*†SQR-Adamixer-R101✓1003647.3 (+1.6)66.051.330.150.762.2
*†Adamixer-R101 [9]3003647.666.751.829.550.563.3
*†SQR-Adamixer-R101✓3003649.8 (+2.2)68.854.032.053.465.1
" + }, + { + "type": "table_footnote", + "bbox": [ + 0.081, + 0.626, + 0.89, + 0.654 + ], + "angle": 0, + "content": "Table 8. Comparison results with various query-based detectors on COCO 2017 val. #query: the number of queries used during inference. * indicates models trained with multi-scale augmentation, † marks models with 7 decoder stages." + }, + { + "type": "text", + "bbox": [ + 0.081, + 0.681, + 0.468, + 0.756 + ], + "angle": 0, + "content": "setting of our baselines, where training schedules consists of standard 12, 36, and 50 epochs; the number of queries is chosen between 100 and 300; multi-scale training is applied to 36e and 50e schedules as the shorter side of images range \\(480 \\sim 800\\). The training is conducted on 8x Nvidia A100." + }, + { + "type": "text", + "bbox": [ + 0.081, + 0.765, + 0.468, + 0.9 + ], + "angle": 0, + "content": "The result is summarized in Fig.1 and Table 8. SQR consistently brings AP improvements to Adamixer, DAB-DETR and Deformable-DETR at the same inference speed. Concretely, on DAB-DETR, SQR brings \\(+2.3\\) and \\(+2.6\\) AP with R50 and SwinB, respectively; on Deformable DETR, SQR boosts it by 2.7 AP under 12e and by 1.4 AP under 50e; on Adamixer with R50, SQR achieves \\(+1.9\\) AP under the basic setting (100 queries, 12e). With an additional stage, the gap between w/ and w/o SQR is enlarged \\(+2.8\\) AP." + }, + { + "type": "text", + "bbox": [ + 0.504, + 0.681, + 0.876, + 0.696 + ], + "angle": 0, + "content": "SQR consistently improves these models by \\(1.4\\sim 2.8\\) AP." + }, + { + "type": "title", + "bbox": [ + 0.504, + 0.721, + 0.617, + 0.736 + ], + "angle": 0, + "content": "6. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.504, + 0.75, + 0.891, + 0.9 + ], + "angle": 0, + "content": "In this work, we investigate the phenomenon where the optimal detections of query-based object detectors are not always from the last decoding stage, but can sometimes come from an intermediate decoding stage. We first recognize two limitations causing the issue, i.e. lack of training emphasis and cascading errors from query sequence. The problem is addressed by Selective Query Recollection (SQR) as a simple and effective training strategy. 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ArXiv, abs/2010.04159, 2021. 1, 3, 8" + }, + { + "type": "list", + "bbox": [ + 0.08, + 0.092, + 0.469, + 0.755 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.946, + 0.518, + 0.956 + ], + "angle": 0, + "content": "23765" + } + ] +] \ No newline at end of file diff --git a/2023/Enhanced Training of Query-Based Object Detection via Selective Query Recollection/514d250b-ea10-4630-9256-9e649ac9271f_origin.pdf b/2023/Enhanced Training of Query-Based Object Detection via Selective Query Recollection/514d250b-ea10-4630-9256-9e649ac9271f_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..695c6f35aa022b3398faf59604b6693329349d9f --- /dev/null +++ b/2023/Enhanced Training of Query-Based Object Detection via Selective Query Recollection/514d250b-ea10-4630-9256-9e649ac9271f_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:ce0dcf4d72faa423c0969eec2f52dc9aa22a8c8728be2ec368ad16b0ebb30d8d +size 717088 diff --git a/2023/Enhanced Training of Query-Based Object Detection via Selective Query Recollection/full.md b/2023/Enhanced Training of Query-Based Object Detection via Selective Query Recollection/full.md new file mode 100644 index 0000000000000000000000000000000000000000..3547938c2f3b1b62bb9c19475baba4c4aa89ae4e --- /dev/null +++ b/2023/Enhanced Training of Query-Based Object Detection via Selective Query Recollection/full.md @@ -0,0 +1,341 @@ +# Enhanced Training of Query-Based Object Detection via Selective Query Recollection + +Fangyi Chen $^{1}$ Han Zhang $^{1}$ Kai Hu $^{1}$ Yu-Kai Huang $^{1}$ Chenchen Zhu $^{2}$ Marios Savvides $^{1}$ Carnegie Mellon University $^{1}$ Meta AI $^{2}$ + +{fangyic,hanz3,kaihu,yukaih2,marioss}@andrew.cmu.edu chenchenz@fb.com + +# Abstract + +This paper investigates a phenomenon where query-based object detectors mispredict at the last decoding stage while predicting correctly at an intermediate stage. We review the training process and attribute the overlooked phenomenon to two limitations: lack of training emphasis and cascading errors from decoding sequence. We design and present Selective Query Recollection (SQR), a simple and effective training strategy for query-based object detectors. It cumulatively collects intermediate queries as decoding stages go deeper and selectively forwards the queries to the downstream stages aside from the sequential structure. Such-wise, SQR places training emphasis on later stages and allows later stages to work with intermediate queries from earlier stages directly. SQR can be easily plugged into various query-based object detectors and significantly enhances their performance while leaving the inference pipeline unchanged. As a result, we apply SQR on Adamixer, DAB-DETR, and Deformable-DETR across various settings (backbone, number of queries, schedule) and consistently brings $1.4 \sim 2.8$ AP improvement. Code is available at https://github.com/Fangyi-Chen/SQR + +# 1. Introduction + +Object detection is a long-established topic in computer vision aiming to localize and categorize objects of interest. Previous methods [4, 7, 10, 11, 16, 18, 21, 25, 26, 29, 32, 33, 35-37] rely on dense priors tiled at feature grids so as to detect in a sliding-window paradigm, and have dominated object detection for the recent decade, but these methods fail to shake off many hand-crafted processing steps such as anchor generation or non-maximum suppression, which block end-to-end optimization. + +Recent research attention has been geared towards query-based object detection [3, 17, 20, 23, 28, 31, 38] since the thriving of transformer [30] and DETR [3]. By view- + +![](images/5eba7844be233a7b70a005d08936daca5e68e5fa6f30d0ae9d5883b545493ff3.jpg) +Figure 1. The inference speed and AP for various networks on the MS-COCO val set. The red stars are the results trained with SQR. The blue circles are the results of baselines without SQR. SQR enhances the training of query-based object detectors while leaving the inference pipeline unchanged. + +ing detection as a direct set prediction problem, the new archetype represents the set of objects using a set of learnable embeddings, termed as queries, which are fed to a decoder consisting of a stack (typically six) of decoding stages. Each stage performs similar operations: (1) interacting queries with image features via an attention-like mechanism, so the queries are aggregated with valuable information that represents objects; (2) reasoning the relation among all queries so that global dependency on objects cooccurrence and duplicates could be captured; (3) interpreting bounding box and category from each query by a feed forward network. Queries are sequentially processed stage-by-stage, and each stage is formulated to learn a residual function with reference to the former stage's output, aiming to refine queries in a cascaded style. + +As such wise, the decoding procedure implies that detection should be stage-by-stage enhanced in terms of IoU and confidence score. Indeed, monotonically improved AP is empirically achieved by this procedure. However, when visualizing the stage-wise predictions, we surprisingly observe that decoder makes mistakes in a decent proportion of + +![](images/f7ee72d612269f1bfb5db20a6a2fbab9907706b36ad2b5ddf9f9adb5f83c455d.jpg) +stage 1 +Traffic light | 0.41 + +![](images/5764dc08516e452d5a37a9b0820dafb6c2d714218dac6b8035e14a29a2ac92c4.jpg) +stage 2 +Traffic light | 0.38 + +![](images/09556f905835bc2504dc73a6d8deaf9af11fab38b4cf189619bd9711f5302027.jpg) +stage 3 +Traffic light | 0.38 + +![](images/475cf55ff4fbb48a756331b06de7281db46c77fd8d0a25cd97ab7b1f033c1437.jpg) +stage 4 +Traffic light | 0.37 + +![](images/d9547234da132826439d66c7fd9720b7baf3dc228439845e4d703703749b978e.jpg) +stage 5 +Traffic light | 0.21 + +![](images/4141addd285ff582faae1398e163bc7c42671e2b85afa2db345e137cbc866a7e.jpg) +stage 6 +Traffic light | 0.27 + +![](images/880bd3111cac443f6e17f9bac75698e4e917ad7b04b789df1e358f509870e069.jpg) +Cell phone | 0.23 +Cell phone | 0.22 +Figure 2. Are query-based object detectors always enhancing predictions stage-by-stage? The traffic light at stage 1 gets a confident score of 0.41, while from stage 2 to 5 the confidence gradually decreases to 0.21 (Upper); the remote at stage 3 was wrongly classified as a cell phone, and from stage 3 to 6 the mistake was amplified from 0.26 to 0.42 (Lower). The visualization is acquired from Adamixer-R50 (42.5 AP) tested on COCO val set. + +![](images/250da6a0b9af727c8a41cdf17e1c31be41386fc0542cd5d872a4d1db9dbc9678.jpg) +Remote | 0.25 +Remote | 0.22 + +![](images/a0f9664877f9cf9f2e3679533cca31f8c84f2514aa6677f380b3683190f7443b.jpg) +Cell phone | 0.26 +Remote | 0.12 + +![](images/0b066fb1215bde4301e71399bdfb963ef57350b65b4d5e90328322d3990a0ac6.jpg) +Cell phone | 0.35 +Remote | 0.12 + +![](images/42ca2e58466234f7bf556857b7a555f1fafe7e187cd54fe8735316ffaf173e23.jpg) +Cell phone | 0.39 +Remote | 0.12 + +![](images/411bf865a50ed1e600dfca37a871e40a203c7611b0a24addac50579e76da59e2.jpg) +Cell phone | 0.42 +Remote | 0.10 + +cases where the later stages degrade true-positives and upgrade false-positives from the former stages. As shown in Fig.2, the traffic light at stage 1 gets categorical confidence of 0.41, while from stage 2 to 5 the confidence gradually decreases to 0.21; the remote at stage 3 was wrongly classified as a cell phone, while from stage 3 to 6 the error was exacerbated from 0.26 to 0.42. We present a more detailed statistic in Section 3. + +This phenomenon inspires us to review the current training strategy and bring two conjectures. Firstly, the responsibility that each stage takes is unbalanced, while supervision applied to them is analogous. An early stage could make mistakes without causing too much impact because it gets chances to be corrected later, and the later stages are more responsible for the final prediction. But during training, all of these stages are supervised in an equivalent manner and there lacks such a mechanism that places particular training emphasis on later stages. Secondly, due to the sequential structure of the decoder, an intermediate query refined by a stage - no matter whether this refinement brings positive or negative effects - will be cascaded to the following stages, while the query prior to the refinement never gets an opportunity to be propagated forward even though it emerges unscathed and might be more representative than the refined one. The cascading errors increase the diffi + +culty of convergence and the sequential structure impedes the later stages from seeing prior queries during training. + +Based on these intuitions, we present Query Recollection (QR) as a training strategy for query-based object detectors. It cumulatively collects intermediate queries as stages go deeper, and feeds the collected queries to the downstream stages aside from the sequential structure. By each stage, the new add-ins alongside the original inputs are independently treated among each other, so the attentions and losses are calculated individually. In such a manner, QR enjoys two key features: (1) The number of supervision signals per stage grows in geometric progression, so that later stages get more supervision than the former ones, for example, the sixth stage got 32 times more supervision than the first; (2) Later stages get chance to view the outputs beyond its neighboring stage for training, which mitigates the potential impact due to cascading errors. We further discover that selectively forward queries to each stage, not with the entire query collection but only those from the prior two stages, can raise the number of supervision in a Fibonacci sequence which halves the extra computing cost and brings even better results. We name it Selective Query Recollection (SQR). + +Our contributions are summarized in three folds: (1) We quantitatively investigate the phenomenon where query-based object detectors mispredict at the last decoding stage + +while predicting correctly at an intermediate one. (2) We attribute the overlooked phenomenon to two training limitations, and propose a simple and effective training strategy SQR that elegantly fits query-based object detectors. (3) We conduct experiments on Adamixer, DAB DETR, and Deformable DETR across various training settings that verify its effectiveness (Fig.1). + +# 2. Related Work + +# 2.1. Training Strategy for Object Detection + +Detectors based on dense priors have been dominating the community for decades. The abstract concept anchor box or anchor point [26, 29] aims to match with ground truth (GT) objects depending on their Intersection-over-Union (IoU) values or other advanced soft scoring factors [7, 15, 18, 29, 37]. Among anchor-based detectors, multistage models iteratively refine bounding box and category stage-by-stage. A typical example is Cascade RCNN [2] which is based on the design that the output of an intermediate stage is sampled and re-labeled to train the next stage with increasing IoU thresholds, so these stages are guaranteed to be progressively refined. Recently, DETR [3] starts a family of end-to-end query-based models where object detection is regarded as a set prediction problem. To train DETR, a predefined number of object queries are matched to either a ground-truth or background by solving the Hungarian Matching problem. The queries are refined by several decoder stages similar to Cascade RCNN, and each intermediate stage is supervised by the matching results. + +# 2.2. Query-Based Object Detection + +Recently, many algorithms have been following the idea of DETR. Deformable DETR [38] proposes a deformable attention module that alleviates the aforementioned issues and massively improves the convergence speed by a factor of 10. Conditional DETR [23] decouples the object query into content query and spatial query in the decoder cross-attention module and learns a conditional spatial query from the decoder embedding to enable fast learning of the distinctive extremity of the ground-truth objects. Anchor-DETR [31] formulates the object queries as anchor points such that each object query may only focus on a certain region near its anchor point. Many future works are inspired by this design. DAB-DETR [20] dives deep into the role of object queries. It directly uses anchor box coordinates as spatial query to speed up training. The model benefits from the spatial prior by modulating the positional attention map using the width and height of the box. DN-DETR [17] further improves the convergence speed and query matching stability of DAB-DETR with the help of the Ground Truth denoising task. Adamixer [9] re-designs the query-key pooling mechanism by letting the query adaptively attend to the mean + +
ModelS1S2S3S4S5S6
Deformable38.442.243.744.244.444.5
Adamixer15.130.337.740.642.142.5
+ +Table 1. Stage-wise AP results. Deformable DETR(300 queries) and Adamixer(100 queries) are trained using official implementation, both of their decoders consist of 6 stages, and per stage AP is reported on COCO val set. + +![](images/67b7b5e3dbb4e4ee8e0d195a19bf8db7af2b151ad2b06645290decb703d92e7a.jpg) +Figure 3. Typical structure of a single decoding stage. + +ingful regions of the encoded features directly through bilinear sampling. An MLP-Mixer then dynamically decodes the pooled features into final predictions. DETA (Detection Transformers with Assignment) [24] proposes a novel overlap-based assignment that enables one-to-many assignments to DETR. + +Despite their significant improvement on DETR, they focus little on the training emphasis and cascading errors. We propose SQR to pay attention to the two problems. + +# 3. Motivation + +Are query-based object detectors always predicting the optimal detections at the last stage? Table.1 shows that AP gradually increases with stages going deeper, indicating improved predictions on a general scale. While the observation in Fig.2 implies that simple AP results are insufficient for an in-depth analysis of that question. + +Preliminary. Queries are updated successively. A typical structure of a decoding stage is illustrated in Fig.3. An initial query $q_{i}^{0}$ ( $i \in N = \{1,2,\dots,n\}$ ) is an embedding trained through back-propagation, and $n$ is the total number of initial queries. During inference, the first stage updates the initial query by adding a residual term to it, producing intermediate query $q_{i}^{1}$ , followed by later stages sequentially updating the intermediate query in the same way. The procedure can be formulated as + +$$ +q _ {i} ^ {s} = D ^ {s} \left(q _ {i} ^ {s - 1}, q ^ {s - 1}, x\right) = q _ {i} ^ {s - 1} + (\mathcal {A} \circ \mathcal {F}) \left(q _ {i} ^ {s - 1}, q ^ {s - 1}, x\right) \tag {1} +$$ + +$D^{s}$ is a decoding stage where $s$ is stage index; $q_{i}^{s}$ is the $i_{th}$ query at stage $s$ ; $q^{s}$ is a set of queries $q^{s} = \{q_{i}^{s} | i \in N\}$ ; $(\mathcal{A} \circ \mathcal{F})$ stands for a bundle of modules including self and cross attention and feed forward network; $x$ means features; and LayerNorm [1] that applied on each module is omitted + +
ModelTP ThresholdTP F RateFP E Rate
DeformableIoU>0.5051.4%55.7%
DETRIoU>0.7549.5%55.9%
AdamixerIoU>0.5028.6%50.8%
IoU>0.7526.7%51.2%
+ +Table 2. True-positive Fading Rate and False-positive Exacerbation Rate. + +for simplicity. Afterward, $q_{i}^{s}$ predicts an object $P_{i}^{s}$ via two multi-layer perceptrons for classification and regression: + +$$ +P _ {i} ^ {s} = \left(M L P _ {c l s} \left(q _ {i} ^ {s}\right), M L P _ {r e g} \left(q _ {i} ^ {s}\right)\right) \tag {2} +$$ + +$P_{i}^{1\sim 6}$ are predicted by the $q_{i}^{1\sim 6}$ rooted in $q_{i}^{0}$ , where $P_{i}^{6}$ is the expected outcome and $P_{i}^{1\sim 5}$ are intermediate results. $P_{i}^{s}$ is regarded as a true-positive towards a ground-truth $G$ only if the IoU $(P_{i}^{s}, G)$ exceeds a threshold, its category matches with $G$ , and the categorical score is ranked as the highest among all other counterparts. + +Investigation. We study the stage-wise testing results by first defining two rates: (1) If $P_{i}^{6}$ is a true-positive (TP) towards a ground-truth $G$ , we check whether $P_{i}^{1\sim 5}$ generate a better TP towards the same $G$ that has higher IoU & higher category score than $P_{i}^{6}$ . The occurrence rate is denoted as TP fading rate. (2) If $P_{i}^{6}$ is a false-positive (FP), we check whether $P_{i}^{1\sim 5}$ produce a FP but with lower category score than $P_{i}^{6}$ . The occurrence rate is denoted as FP exacerbation rate. + +The statistics are shown in Table.2. We can see that TP fading rate achieves $50\%$ and $27\%$ on the two models. Considering the strict constraints it holds, the TP fading rate reaches an impressively high level. Deformable DETR is much higher than Adamixer due to the smaller AP gap among stages, thus, in many cases, earlier stages are more likely to outperform the last stage. FP exacerbation holds looser constraints and is easier to be satisfied, its rate is above $50\%$ on the two models. Higher TP threshold implies higher quality of $P_{i}^{6}$ and it is harder to find qualifiers in $P_{i}^{1\sim 5}$ , but the two rates are similar with 0.75 as with 0.5, pointing out the consistency of this phenomenon. We also observe that more than half of the occurred cases are marginally triggered, i.e. the predictions from the triggered $P_{i}^{1\sim 5}$ are only marginally better than the sixth. This is a further reason why the deformable DETR has those high rates - the results from the 5th and 6th stages are extremely visually close. In dominated number of cases, the final stage is (one of) the best, after all, its mAP is the highest. + +When the conditions of the two rates establish, we further replace $P_{i}^{6}$ with the optimal prediction found in $P_{i}^{1\sim 6}$ and measure the AP. On Deformable DETR, AP grows from 44.5 AP to 51.7 (+7.2 AP); on Adamixer, AP grows from + +42.5 AP to 53.3 (+10.7 AP), demonstrating huge potential in query-based detectors yet to be mined. + +Conclusion. This reveals that models frequently predict the optimum at intermediate stages instead of the last one. We view the problem from the training's perspective and identify the lack of training emphasis and the cascading errors from query sequence as two obstacles impeding the occurrence of the most reliable predictions in the last stage, elaborated in Section 1. + +# 4. Query Recollection + +# 4.1. Expectancy + +We desire such a training strategy that embraces: + +- Uneven supervision applied to decoding stages that places emphasis on later ones, enhancing later stages for better final outcomes. +- A variety of early-stage queries directly introduced to later stages, mitigating the impact of cascading errors. + +To this end, we design a concise training strategy coined as Query Recollection (QR). Compared with prior arts, it collects intermediate queries at every stage and forwards them along the original pathway. Dense Query Recollection (DQR) is the fundamental form and Selective Query Recollection (SQR) is an advanced variant. + +# 4.2. Dense Query Recollection + +Notation. The process of single decoding stage (self-attention, cross-attention, FFN), the ground-truth assignment, and loss calculations are applied within a set of queries $\{q_i | i \in \{1, 2, \dots, n\}\}$ , where $n$ is typically 100/300/500. We regard the set of queries as a basic unit in our method and generally denote as $q$ . + +Basic Pathway. Query along the basic pathway is refined by all stages. We illustrate it in Fig.4(a). Taking a 4-stages decoder as an example, we denote $q^{0-1-2-3-4}$ as the final query that is refined by all stages. So the basic $\mathcal{PT}$ finally produces + +$$ +\begin{array}{l} q ^ {0 - 1 - 2 - 3 - 4} = D ^ {4} \left(D ^ {3} \left(D ^ {2} \left(D ^ {1} \left(q ^ {0}\right)\right)\right)\right) (3) \\ = \mathcal {P T} ^ {1 - 2 - 3 - 4} \left(q ^ {0}\right) (4) \\ \end{array} +$$ + +During training, the queries from each stage, i.e. $q^{0-1}$ , $q^{0-1-2}$ , $q^{0-1-2-3}$ , and $q^{0-1-2-3-4}$ are independently followed by Hungarian Assignment that matches ground-truth with $q$ in a one-to-one manner, and then followed by loss calculation for supervision. In Fig.4, we mark those $q$ that require supervision as $\hat{q}$ . Along the basic pathway, the number of $\hat{q}$ at each stage is 1. + +DQR Formulation. We densely collect every intermediate $q$ and independently forward them to every downstream + +![](images/fc8ee8a9aa62956f3435d6cee25a31f9b1c6dc80506d2932d9781aff8fc6d50d.jpg) +(a)Basic (b)Dense QR + +Figure 4. (a). Basic process for decoding queries stage by stage, applied in both training and testing. (b). Dense query recollection. (c). Selective query recollection. +![](images/152d414d27b5e29816771156de4a8b5a368e60734d02a08d043ba6f07b518149.jpg) +Collection C $q^{0I2}$ Query, from initial to stage 1 then to 2 +Output of stage/QR $\hat{\pmb{q}}$ Query with supervision applied + +stage, as illustrated in Fig.4(b). After each stage, a collection $C$ is formed where the number of $q$ grows geometrically, namely $2^{s}$ at $s_{th}$ stage. Formally, + +$$ +C ^ {0} = \{q ^ {0} \} \tag {5} +$$ + +$$ +C ^ {s} = \left\{D ^ {s} (q) | q \in C ^ {s - 1} \right\} \cup C ^ {s - 1} \tag {6} +$$ + +In a collection $C$ , half of queries inside are newly generated by the current stage, i.e. from $\{D^s(q)|q \in C^{s-1}\}$ , while another half are from previous stages, $C^{s-1}$ . Separately, for each $q$ in the former half, we apply Hungarian assignment and loss calculation, so the number of supervision signals grows in geometric progression as well, namely $2^{s-1}$ at $s_{th}$ stage. + +Such-wise, Dense Query Recollection satisfies our expectancy where the number of supervision signal for each stage grows as (1,2,4,8,16,32), meanwhile, all prior queries would be visible in all later stages. + +
stage12345
TP F Rate(%)1.24.48.512.416.9
FP E Rate(%)14.318.620.824.530.2
stage1~34&53~52~51~5
TP F Rate(%)11.223.926.928.328.6
FP E Rate(%)32.440.845.348.550.8
+ +Table 3. Stage-wise TP Fading Rate and FP Exacerbation Rate with Adamixer. + +During inference, we only use the basic pathway, so the inference process is untouched. For a standard 6-stage decoder, the pathway is $\mathcal{PT}^{1-2-3-4-5-6}$ + +# 4.3. Selective Query Recollection + +The last proposal empirically enhances training, but the query collection process is indiscriminate, which brings two defects: First, the geometrical growth of the number of $\hat{q}$ and their attention/loss calculations cost a lot. Second, if we input an early $q$ that skips too many stages to a far-away late stage, the potential benefit could be overshadowed by the huge learning gap between the stages and query. For instance, if the initial $q^0$ is directly introduced to stage 6 and produces $\hat{q}^{0 - 6}$ , this query would have the highest difficulty among all queries at stage 6 and the calculated loss would dominate the overall losses. So we are inclined to selectively collect intermediate $q$ rather than densely collect all of them. + +Selection. To find a better query recollection scheme, we further conduct a detailed analysis on the TP Fading Rate and FP Exacerbation Rate introduced in Section 3. + +Recall the spirits of the two rates where we seek from $P_{i}^{1\sim 5}$ for an alternative that is better than $P_{i}^{6}$ , we want to investigate which specific intermediate stage/stages contribute the most. Concretely, if $P_{i}^{6}$ is a true-positive towards a ground-truth $G$ , we separately check each stage whether generating a better TP; similarly, if $P_{i}^{6}$ is a false-positive, we separately check each stage whether generating a better FP. The results are summarized in Table 3. We find that the majority of alternatives of $P_{i}^{6}$ are from stage 4&5, where the corresponding TP fading rate and FP exacerbation rate reach $23.9\%$ and $40.8\%$ , respectively, which are close to the results of stages $1 \sim 5$ . While stage $1 \sim 3$ together only produces $11.2\%$ and $32.4\%$ . + +The above analysis implies that the queries from the adjacent stage and the stage prior to the adjacent stage are more likely to bring positive effects. We intuitively follow the observations and selectively operate collection along the basic pathway: before starting stage $D^{s}$ , we collect $q$ from the 2 nearest stages, i.e. $D^{s - 1}$ and $D^{s - 2}$ as the input of $D^{s}$ . + +SQR Formulation. The Selective Query Recollection + +can be formulated as + +$$ +C ^ {0} = \left\{q ^ {0} \right\} \quad C ^ {1} = \left\{q ^ {0}, q ^ {0 - 1} \right\} \tag {7} +$$ + +$$ +\begin{array}{l} C ^ {s} = \{D ^ {s} (q) | q \in C ^ {s - 1} \} \cup \operatorname {s e l e c t} \left(C ^ {s - 1}\right) \tag {8} \\ = \{D ^ {s} (q) | q \in C ^ {s - 1} \} \cup \{D ^ {s - 1} (q) | q \in C ^ {s - 2} \} (9) \\ \end{array} +$$ + +Such wise, Selective Query Recollection (Fig.4(c)) still satisfies our expectancy, and the number of supervision signals grows in a Fibonacci sequence (1,2,3,5,8,13). Compared to the Dense Recollection, to a great extent, SQR reduces the computing burden and we observe that SQR even outperforms the dense counterpart in terms of precision. This verifies our assumption that a $q$ skipping too many stages might be noise for remote stages overshadowing its positive effects. + +Recollection Starting Stage. Above we collect queries starting from stage 1. Instead, we can practically vary this starting stage, and this will further reduce the total queries in each collection and further reduce the computing burden. E.g., if starts SQR from stage 2, the Fibonacci sequence will start from stage 2 and result in $(1,1,2,3,5,8)$ ; if starts from stage 3, result in $(1,1,1,2,3,5)$ . The starting stage is regarded as a hyper-parameter for SQR. + +# 5. Experiments + +We conduct our experiments on the MS-COCO [19] detection track using the MMDetection [5] and Detrex [27] code-bases. All models are trained on train2017 split. Unless otherwise specified, models are trained and tested with image scale of 800 pixels, where AdamW optimizer with a standard 1x schedule (12 epochs) is utilized for training. For ablation study and analysis, Adamixer [9] with R50 [12] is chosen because of its good performance and fast convergence speed (42.5 AP with 1x schedule). We further apply SQR on other detectors to verify its effectiveness. + +# 5.1. Ablation Study + +Baseline vs DQR vs SQR. Table.4 shows that both DQR and SQR improve the baseline by a large margin. DQR reaches 44.2 (+1.7 AP) while SQR reaches a slightly high result 44.4 (+1.9 AP). Note that SQR is much more efficient than DQR. As shown in Table.5, under the same training setting, SQR cuts down a great amount of training time of DQR and still achieves equal or higher AP. + +Varying Starting Stage of SQR. We present how SQR performs when varying the starting stage in Table.5. The best performance is acquired when query recollection starts at stage 1 but with the most computational cost. We can see that starting at stage 2 performs similarly to starting at stage 1 while the computing burden is decently reduced. With recollection starting later, the benefits from SQR decrease as expected since the recollected queries from early + +
MethodsAP\( AP_{50} \)\( AP_{75} \)\( AP_S \)\( AP_M \)\( AP_L \)
Baseline42.561.545.624.645.159.2
DQR44.262.847.926.746.960.5
SQR44.463.247.825.747.460.2
+ +Table 4. AP comparison among Baseline, DQR, and SQR + +
MethodStart StageTrain TimeAP\( AP_{50} \)
Baseline-1x(5hours)42.561.5
Baseline-2x42.561.3
Baseline-3x42.561.4
DQR-2.24x44.262.8
SQR11.57x44.463.2
SQR21.34x44.263.0
SQR31.18x43.862.3
SQR41.07x42.961.4
+ +Table 5. Further comparison among Baseline, DQR, and SQR with different starting stage in terms of training time and AP. + +
MethodTP ThresholdTP F RateFP E Rate
BaselineIoU>0.5028.6%50.8%
SQRIoU>0.5023.3 %47.3 %
BaselineIoU>0.7526.7%51.2%
SQRIoU>0.7521.1%47.0%
+ +Table 6. Baseline vs. SQR on true-positive fading rate and false-positive exacerbation rate. + +stages become fewer and training emphasis gets gradually balanced. + +TP Fading Rate And FP Exacerbation Rate. We present Table.6 to verify that TP fading rate and FP exacerbation rate decrease due to the training effect when applied SQR. Specifically, TP fading rate decreases from $28.6\%$ to $23.3\%$ and from $26.7\%$ to $21.1\%$ across two IoU thresholds. FP exacerbation rate downgrades from $50.8\%$ to 47.3 and $51.2\%$ to $47.0\%$ . + +# 5.2. Relation with Increased Number of Supervision + +Some concurrent studies reveal that query-based detectors suffer from training inefficiency due to the one-to-one matching, and propose to add extra parallel query groups and match them with ground-truths in a one-to-many manner, such as Group DETR [6] and H-DETR [14]. We recognize them as increased number of supervision, i.e., each ground-truth is matched to multiple queries, and thus the number of supervision $(\hat{q})$ is greatly increased. However, simply adding more query groups is a sub-optimal solution according to our motivation, since these extra supervisions + +
Design#Supv / stage#SupvAP
I (Group DETR)3,3,3,3,3,31843.4
II4,4,4,3,2,11843.0
III1,2,3,4,4,41843.7
IV (SQR)1,1,2,3,5,82044.2
V (Group DETR)6,6,6,6,6,63643.6
VI (SQR)1,2,3,5,8,133244.4
+ +Table 7. Results of the 6 designed training strategies on Adamixer to investigate the relation with number of supervision. The inference is untouched. #Supv denotes the number of supervision. + +are given uniformly among stages. So we present 6 designs as training strategies for investigation. + +- Design I: Following Group DETR, 3 groups of queries are initialized and independently undergo the whole process of the decoder. The pathway is $3 \times \mathcal{PT}^{1-2-3-4-5-6}$ , and number of supervision is 3 groups $\times 6$ stages $= 18$ . +- Design II: 4 groups of queries are initialized but the pathways are $\mathcal{PT}^{1-2-3-4-5-6}$ , $\mathcal{PT}^{1-2-3-4-5}$ , $\mathcal{PT}^{1-2-3-4}$ , $\mathcal{PT}^{1-2-3}$ , so, with training emphasis on early stages, the number of supervision is $4 + 4 + 4 + 3 + 2 + 1 = 18$ . +- Design III: Similar to Design II but not every initialized queries starts from stage 1. The pathways for the 4 groups are $\mathcal{PT}^{1-2-3-4-5-6}$ , $\mathcal{PT}^{2-3-4-5-6}$ , $\mathcal{PT}^{3-4-5-6}$ , $\mathcal{PT}^{4-5-6}$ , so, with training emphasis on later stages, the number of supervision is $1 + 2 + 3 + 4 + 4 + 4 = 18$ . +- Design IV: $SQR^{starting stage=2}$ , the number of supervision is $1 + 1 + 2 + 3 + 5 + 8 = 20$ . +- Design V: Same as Design I but with 6 groups. The number of supervision is 6 groups $\times 6$ stages $= 36$ . +- Design VI: $SQR^{starting stage=1}$ , the number of supervision is $1 + 2 + 3 + 5 + 8 + 13 = 32$ . + +Table.7 summarizes the results. From the controlled experiments with Design I, II, III, we conclude training with emphasis on late stages is the best option. Design IV and VI are SQR with different starting stages. We show that with similar or even fewer supervisions, SQR outperforms other designs by a large margin. These comparisons verify our motivation and prove that the enhancement from SQR is not simply from the increased number of supervisions. + +# 5.3. Training Emphasis via Re-weighted Loss + +Although the training emphasis contributes to the success of SQR, the access to the early intermediate queries is irreplaceable. We attempt another way to place training emphasis without query recollection, i.e. re-weighting the losses of six decoding stages following the Fibonacci sequence (1,2,3,5,8,13). The AP slightly degrades by (-0.6) compared to the baseline, indicating access to the intermediate queries is necessary for emphasized supervision. + +![](images/6c824e7a7b40eb41a84f17e546653987396226f26c205f741bc61fda4ab4801e.jpg) +Figure 5. Equal training-time comparison: Baseline vs. SQR + +# 5.4. Relation with Stochastic Depth + +Stochastic Depth (SD) [13] is a training strategy for very deep network where it randomly removes a fraction of layers independently for each mini-batch, so the depth of pathway varies during training just like SQR. However, SD is of vital inefficiency, because an image has to first pass through a backbone and then be processed by a varying-depth pathway, but for SQR, an image that passes through the backbone can be processed by multiple varying-depth pathways at the same time. To verify this point, we apply SD on the vanilla decoder: During training, for each mini-batch we randomly remove decoding stages following a series of predefined probabilities. From stage $1 \sim 6$ , the removal probability $\mathbb{R}$ could be either a constant (0.1), increasing (0.0, 0.1,..., 0.5), or decreasing (0.5, 0.4,..., 0.0). During testing, SD requires the outputs of each decoding stage to be calibrated by the expected times the stage participates in training, so we multiply (1- $\mathbb{R}$ ) with the residual term in Equ.1. As a result, SD (40.7 mAP) is not comparable to SQR. + +# 5.5. Training efficiency + +SQR leads to an extra computing burden compared to the baseline since the number of $\hat{q}$ grows. In Table.5, SQR increases training time of Adamixer-R50 by $0.35\sim 2.85$ hours $(+0.07\% \sim 57\%)$ . In practice, the effects on different models/implementations/platforms vary. For instance, ResNet-50 is a light-weighted backbone, so the effects of applying SQR are relatively high, while with heavier backbones like ResNet-101 and Swin Transformer [22], the training time is less impacted $(+10\%)$ . + +For comparison under equal training time, we train the baseline Adamixer with extra epochs $(+200\%$ epochs) and baseline Deformable DETR with $(+50\%$ epochs). Both models' performances (see Fig.5) saturate early and there is no significant improvement over the extended training time, indicating that the benefit of SQR cannot be compensated by including more training iterations. + +# 5.6. Comparison with State-of-the-art + +We conduct experiments on recent query-based detectors with different training settings and various backbones, with and without SQR. We primarily follow the original training + +
Modelw/ SQR#query#epochsCOCO 2017 validation split
AP\(AP_{50}\)\(AP_{75}\)\(AP_S\)\(AP_M\)\(AP_L\)
DETR-R50 [3]10050042.062.444.220.545.861.1
Conditional DETR-R50 [23]3005040.961.843.320.844.660.2
Conditional DETR-R101 [23]3005042.863.746.021.746.660.9
Anchor-DETR-R50 [31]3005042.163.144.922.346.260.0
Anchor-DETR-R101 [31]3005043.564.346.623.247.761.4
SAM-DETR-R50 [34]3005039.861.841.620.543.459.6
*SMCA-DETR-R50 [8]3005043.763.647.224.247.060.4
*SMCA-DETR-R50 [8]30010845.665.549.125.949.362.6
*DN-DAB-DETR-R50 [17]3005044.164.446.722.948.063.4
*DN-DAB-DETR-R101 [17]3005045.265.548.324.149.165.1
*DAB-DETR-R50 [20]3005042.263.144.721.545.760.3
*SQR-DAB-DETR-R50✓3005044.5 (+2.3)64.447.524.848.661.7
*DAB-DETR-SwinB [20]3005049.071.053.029.653.868.3
*SQR-DAB-DETR-SwinB✓3005051.6 (+2.6)72.555.932.056.871.0
*Deformable DETR-R50 [38]3001237.255.240.420.640.250.2
*SQR-Deformable DETR-R50✓3001239.9 (+2.7)58.443.723.843.253.3
*Deformable DETR-R50 [38]3005044.563.248.928.047.858.8
*SQR-Deformable DETR-R50✓3005045.9 (+1.4)64.750.227.749.260.5
Adamixer-R50 [9]1001242.561.545.624.645.159.2
SQR-Adamixer-R50✓1001244.4 (+1.9)63.247.825.747.460.2
†Adamixer-R50 [9]1001242.561.545.824.445.258.7
†SQR-Adamixer-R50✓1001245.3 (+2.8)63.849.026.848.162.2
*†Adamixer-R501003645.163.948.928.347.860.6
*†SQR-Adamixer-R50✓1003646.7 (+1.6)65.250.329.449.662.1
*†Adamixer-R503003646.665.550.629.349.362.3
*†SQR-Adamixer-R50✓3003648.9 (+2.3)67.553.232.051.863.7
*†Adamixer-R101 [9]1003645.764.749.627.849.161.2
*†SQR-Adamixer-R101✓1003647.3 (+1.6)66.051.330.150.762.2
*†Adamixer-R101 [9]3003647.666.751.829.550.563.3
*†SQR-Adamixer-R101✓3003649.8 (+2.2)68.854.032.053.465.1
+ +Table 8. Comparison results with various query-based detectors on COCO 2017 val. #query: the number of queries used during inference. * indicates models trained with multi-scale augmentation, † marks models with 7 decoder stages. + +setting of our baselines, where training schedules consists of standard 12, 36, and 50 epochs; the number of queries is chosen between 100 and 300; multi-scale training is applied to 36e and 50e schedules as the shorter side of images range $480 \sim 800$ . The training is conducted on 8x Nvidia A100. + +The result is summarized in Fig.1 and Table 8. SQR consistently brings AP improvements to Adamixer, DAB-DETR and Deformable-DETR at the same inference speed. Concretely, on DAB-DETR, SQR brings $+2.3$ and $+2.6$ AP with R50 and SwinB, respectively; on Deformable DETR, SQR boosts it by 2.7 AP under 12e and by 1.4 AP under 50e; on Adamixer with R50, SQR achieves $+1.9$ AP under the basic setting (100 queries, 12e). 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ArXiv, abs/2010.04159, 2021. 1, 3, 8 \ No newline at end of file diff --git a/2023/Enhanced Training of Query-Based Object Detection via Selective Query Recollection/images.zip b/2023/Enhanced Training of Query-Based Object Detection via Selective Query Recollection/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..72ca528cd8281a89f8c88efdd6ece3f092234709 --- /dev/null +++ b/2023/Enhanced Training of Query-Based Object Detection via Selective Query Recollection/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:6b572f79d3ce4210c17c5558c3a350d8818a4327aae5266701395ff23d20dd3b +size 693558 diff --git a/2023/Enhanced Training of Query-Based Object Detection via Selective Query Recollection/layout.json b/2023/Enhanced Training of Query-Based Object Detection via Selective Query Recollection/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..8a4f32c4fc58ebf9830f022d9dc21828db584e6f --- /dev/null +++ b/2023/Enhanced Training of Query-Based Object Detection via Selective Query Recollection/layout.json @@ -0,0 +1,10152 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 122, + 103, + 473, + 140 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 122, + 103, + 473, + 140 + ], + "spans": [ + { + "bbox": [ + 122, + 103, + 473, + 140 + ], + "type": "text", + "content": "Enhanced Training of Query-Based Object Detection via Selective Query Recollection" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 59, + 159, + 534, + 190 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 159, + 534, + 190 + ], + "spans": [ + { + "bbox": [ + 59, + 159, + 534, + 190 + ], + "type": "text", + "content": "Fangyi Chen" + }, + { + "bbox": [ + 59, + 159, + 534, + 190 + ], + "type": "inline_equation", + "content": "^{1}" + }, + { + "bbox": [ + 59, + 159, + 534, + 190 + ], + "type": "text", + "content": " Han Zhang" + }, + { + "bbox": [ + 59, + 159, + 534, + 190 + ], + "type": "inline_equation", + "content": "^{1}" + }, + { + "bbox": [ + 59, + 159, + 534, + 190 + ], + "type": "text", + "content": " Kai Hu" + }, + { + "bbox": [ + 59, + 159, + 534, + 190 + ], + "type": "inline_equation", + "content": "^{1}" + }, + { + "bbox": [ + 59, + 159, + 534, + 190 + ], + "type": "text", + "content": " Yu-Kai Huang" + }, + { + "bbox": [ + 59, + 159, + 534, + 190 + ], + "type": "inline_equation", + "content": "^{1}" + }, + { + "bbox": [ + 59, + 159, + 534, + 190 + ], + "type": "text", + "content": " Chenchen Zhu" + }, + { + "bbox": [ + 59, + 159, + 534, + 190 + ], + "type": "inline_equation", + "content": "^{2}" + }, + { + "bbox": [ + 59, + 159, + 534, + 190 + ], + "type": "text", + "content": " Marios Savvides" + }, + { + "bbox": [ + 59, + 159, + 534, + 190 + ], + "type": "inline_equation", + "content": "^{1}" + }, + { + "bbox": [ + 59, + 159, + 534, + 190 + ], + "type": "text", + "content": " Carnegie Mellon University" + }, + { + "bbox": [ + 59, + 159, + 534, + 190 + ], + "type": "inline_equation", + "content": "^{1}" + }, + { + "bbox": [ + 59, + 159, + 534, + 190 + ], + "type": "text", + "content": " Meta AI" + }, + { + "bbox": [ + 59, + 159, + 534, + 190 + ], + "type": "inline_equation", + "content": "^{2}" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 101, + 191, + 484, + 202 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 101, + 191, + 484, + 202 + ], + "spans": [ + { + "bbox": [ + 101, + 191, + 484, + 202 + ], + "type": "text", + "content": "{fangyic,hanz3,kaihu,yukaih2,marioss}@andrew.cmu.edu chenchenz@fb.com" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 143, + 231, + 192, + 243 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 231, + 192, + 243 + ], + "spans": [ + { + "bbox": [ + 143, + 231, + 192, + 243 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 257, + 290, + 521 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 257, + 290, + 521 + ], + "spans": [ + { + "bbox": [ + 46, + 257, + 290, + 521 + ], + "type": "text", + "content": "This paper investigates a phenomenon where query-based object detectors mispredict at the last decoding stage while predicting correctly at an intermediate stage. We review the training process and attribute the overlooked phenomenon to two limitations: lack of training emphasis and cascading errors from decoding sequence. We design and present Selective Query Recollection (SQR), a simple and effective training strategy for query-based object detectors. It cumulatively collects intermediate queries as decoding stages go deeper and selectively forwards the queries to the downstream stages aside from the sequential structure. Such-wise, SQR places training emphasis on later stages and allows later stages to work with intermediate queries from earlier stages directly. SQR can be easily plugged into various query-based object detectors and significantly enhances their performance while leaving the inference pipeline unchanged. As a result, we apply SQR on Adamixer, DAB-DETR, and Deformable-DETR across various settings (backbone, number of queries, schedule) and consistently brings " + }, + { + "bbox": [ + 46, + 257, + 290, + 521 + ], + "type": "inline_equation", + "content": "1.4 \\sim 2.8" + }, + { + "bbox": [ + 46, + 257, + 290, + 521 + ], + "type": "text", + "content": " AP improvement. Code is available at https://github.com/Fangyi-Chen/SQR" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 547, + 128, + 559 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 547, + 128, + 559 + ], + "spans": [ + { + "bbox": [ + 47, + 547, + 128, + 559 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 568, + 287, + 676 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 568, + 287, + 676 + ], + "spans": [ + { + "bbox": [ + 46, + 568, + 287, + 676 + ], + "type": "text", + "content": "Object detection is a long-established topic in computer vision aiming to localize and categorize objects of interest. Previous methods [4, 7, 10, 11, 16, 18, 21, 25, 26, 29, 32, 33, 35-37] rely on dense priors tiled at feature grids so as to detect in a sliding-window paradigm, and have dominated object detection for the recent decade, but these methods fail to shake off many hand-crafted processing steps such as anchor generation or non-maximum suppression, which block end-to-end optimization." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 677, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 288, + 714 + ], + "type": "text", + "content": "Recent research attention has been geared towards query-based object detection [3, 17, 20, 23, 28, 31, 38] since the thriving of transformer [30] and DETR [3]. By view-" + } + ] + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 309, + 232, + 545, + 376 + ], + "blocks": [ + { + "bbox": [ + 309, + 232, + 545, + 376 + ], + "lines": [ + { + "bbox": [ + 309, + 232, + 545, + 376 + ], + "spans": [ + { + "bbox": [ + 309, + 232, + 545, + 376 + ], + "type": "image", + "image_path": "5eba7844be233a7b70a005d08936daca5e68e5fa6f30d0ae9d5883b545493ff3.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 384, + 547, + 441 + ], + "lines": [ + { + "bbox": [ + 304, + 384, + 547, + 441 + ], + "spans": [ + { + "bbox": [ + 304, + 384, + 547, + 441 + ], + "type": "text", + "content": "Figure 1. The inference speed and AP for various networks on the MS-COCO val set. The red stars are the results trained with SQR. The blue circles are the results of baselines without SQR. SQR enhances the training of query-based object detectors while leaving the inference pipeline unchanged." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 461, + 547, + 641 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 461, + 547, + 641 + ], + "spans": [ + { + "bbox": [ + 304, + 461, + 547, + 641 + ], + "type": "text", + "content": "ing detection as a direct set prediction problem, the new archetype represents the set of objects using a set of learnable embeddings, termed as queries, which are fed to a decoder consisting of a stack (typically six) of decoding stages. Each stage performs similar operations: (1) interacting queries with image features via an attention-like mechanism, so the queries are aggregated with valuable information that represents objects; (2) reasoning the relation among all queries so that global dependency on objects cooccurrence and duplicates could be captured; (3) interpreting bounding box and category from each query by a feed forward network. Queries are sequentially processed stage-by-stage, and each stage is formulated to learn a residual function with reference to the former stage's output, aiming to refine queries in a cascaded style." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 642, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 642, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 642, + 547, + 713 + ], + "type": "text", + "content": "As such wise, the decoding procedure implies that detection should be stage-by-stage enhanced in terms of IoU and confidence score. Indeed, monotonically improved AP is empirically achieved by this procedure. However, when visualizing the stage-wise predictions, we surprisingly observe that decoder makes mistakes in a decent proportion of" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. 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Are query-based object detectors always enhancing predictions stage-by-stage? The traffic light at stage 1 gets a confident score of 0.41, while from stage 2 to 5 the confidence gradually decreases to 0.21 (Upper); the remote at stage 3 was wrongly classified as a cell phone, and from stage 3 to 6 the mistake was amplified from 0.26 to 0.42 (Lower). The visualization is acquired from Adamixer-R50 (42.5 AP) tested on COCO val set." + } + ] + } + ], + "index": 30, + "angle": 0, + "type": "image_caption" + } + ], + "index": 18 + }, + { + "type": "image", + "bbox": [ + 136, + 205, + 212, + 304 + ], + "blocks": [ + { + "bbox": [ + 136, + 205, + 212, + 304 + ], + "lines": [ + { + "bbox": [ + 136, + 205, + 212, + 304 + ], + "spans": [ + { + "bbox": [ + 136, + 205, + 212, + 304 + ], + "type": "image", + "image_path": "250da6a0b9af727c8a41cdf17e1c31be41386fc0542cd5d872a4d1db9dbc9678.jpg" + } + ] + } + ], + "index": 20, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 136, + 307, + 187, + 327 + ], + "lines": [ + { + "bbox": [ + 136, + 307, + 187, + 327 + ], + "spans": [ + { + "bbox": [ + 136, + 307, + 187, + 327 + ], + "type": "text", + "content": "Remote | 0.25 \nRemote | 0.22" + } + ] + } + ], + "index": 21, + "angle": 0, + "type": "image_caption" + } + ], + "index": 20 + }, + { + "type": "image", + "bbox": [ + 218, + 205, + 294, + 304 + ], + "blocks": [ + { + "bbox": [ + 218, + 205, + 294, + 304 + ], + "lines": [ + { + "bbox": [ + 218, + 205, + 294, + 304 + ], + "spans": [ + { + "bbox": [ + 218, + 205, + 294, + 304 + ], + "type": "image", + "image_path": "a0f9664877f9cf9f2e3679533cca31f8c84f2514aa6677f380b3683190f7443b.jpg" + } + ] + } + ], + "index": 22, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 217, + 307, + 280, + 327 + ], + "lines": [ + { + "bbox": [ + 217, + 307, + 280, + 327 + ], + "spans": [ + { + "bbox": [ + 217, + 307, + 280, + 327 + ], + "type": "text", + "content": "Cell phone | 0.26 \nRemote | 0.12" + } + ] + } + ], + "index": 23, + "angle": 0, + "type": "image_caption" + } + ], + "index": 22 + }, + { + "type": "image", + "bbox": [ + 299, + 205, + 377, + 305 + ], + "blocks": [ + { + "bbox": [ + 299, + 205, + 377, + 305 + ], + "lines": [ + { + "bbox": [ + 299, + 205, + 377, + 305 + ], + "spans": [ + { + "bbox": [ + 299, + 205, + 377, + 305 + ], + "type": "image", + "image_path": "0b066fb1215bde4301e71399bdfb963ef57350b65b4d5e90328322d3990a0ac6.jpg" + } + ] + } + ], + "index": 24, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 299, + 307, + 362, + 327 + ], + "lines": [ + { + "bbox": [ + 299, + 307, + 362, + 327 + ], + "spans": [ + { + "bbox": [ + 299, + 307, + 362, + 327 + ], + "type": "text", + "content": "Cell phone | 0.35 \nRemote | 0.12" + } + ] + } + ], + "index": 25, + "angle": 0, + "type": "image_caption" + } + ], + "index": 24 + }, + { + "type": "image", + "bbox": [ + 382, + 205, + 460, + 305 + ], + "blocks": [ + { + "bbox": [ + 382, + 205, + 460, + 305 + ], + "lines": [ + { + "bbox": [ + 382, + 205, + 460, + 305 + ], + "spans": [ + { + "bbox": [ + 382, + 205, + 460, + 305 + ], + "type": "image", + "image_path": "42ca2e58466234f7bf556857b7a555f1fafe7e187cd54fe8735316ffaf173e23.jpg" + } + ] + } + ], + "index": 26, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 383, + 307, + 444, + 327 + ], + "lines": [ + { + "bbox": [ + 383, + 307, + 444, + 327 + ], + "spans": [ + { + "bbox": [ + 383, + 307, + 444, + 327 + ], + "type": "text", + "content": "Cell phone | 0.39 \nRemote | 0.12" + } + ] + } + ], + "index": 27, + "angle": 0, + "type": "image_caption" + } + ], + "index": 26 + }, + { + "type": "image", + "bbox": [ + 465, + 205, + 541, + 305 + ], + "blocks": [ + { + "bbox": [ + 465, + 205, + 541, + 305 + ], + "lines": [ + { + "bbox": [ + 465, + 205, + 541, + 305 + ], + "spans": [ + { + "bbox": [ + 465, + 205, + 541, + 305 + ], + "type": "image", + "image_path": "411bf865a50ed1e600dfca37a871e40a203c7611b0a24addac50579e76da59e2.jpg" + } + ] + } + ], + "index": 28, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 465, + 307, + 528, + 327 + ], + "lines": [ + { + "bbox": [ + 465, + 307, + 528, + 327 + ], + "spans": [ + { + "bbox": [ + 465, + 307, + 528, + 327 + ], + "type": "text", + "content": "Cell phone | 0.42 \nRemote | 0.10" + } + ] + } + ], + "index": 29, + "angle": 0, + "type": "image_caption" + } + ], + "index": 28 + }, + { + "bbox": [ + 46, + 411, + 287, + 506 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 411, + 287, + 506 + ], + "spans": [ + { + "bbox": [ + 46, + 411, + 287, + 506 + ], + "type": "text", + "content": "cases where the later stages degrade true-positives and upgrade false-positives from the former stages. As shown in Fig.2, the traffic light at stage 1 gets categorical confidence of 0.41, while from stage 2 to 5 the confidence gradually decreases to 0.21; the remote at stage 3 was wrongly classified as a cell phone, while from stage 3 to 6 the error was exacerbated from 0.26 to 0.42. We present a more detailed statistic in Section 3." + } + ] + } + ], + "index": 31 + }, + { + "bbox": [ + 46, + 510, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 510, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 510, + 287, + 713 + ], + "type": "text", + "content": "This phenomenon inspires us to review the current training strategy and bring two conjectures. Firstly, the responsibility that each stage takes is unbalanced, while supervision applied to them is analogous. An early stage could make mistakes without causing too much impact because it gets chances to be corrected later, and the later stages are more responsible for the final prediction. But during training, all of these stages are supervised in an equivalent manner and there lacks such a mechanism that places particular training emphasis on later stages. Secondly, due to the sequential structure of the decoder, an intermediate query refined by a stage - no matter whether this refinement brings positive or negative effects - will be cascaded to the following stages, while the query prior to the refinement never gets an opportunity to be propagated forward even though it emerges unscathed and might be more representative than the refined one. The cascading errors increase the diffi" + } + ] + } + ], + "index": 32 + }, + { + "bbox": [ + 305, + 411, + 545, + 436 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 411, + 545, + 436 + ], + "spans": [ + { + "bbox": [ + 305, + 411, + 545, + 436 + ], + "type": "text", + "content": "culty of convergence and the sequential structure impedes the later stages from seeing prior queries during training." + } + ] + } + ], + "index": 33 + }, + { + "bbox": [ + 304, + 437, + 546, + 675 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 437, + 546, + 675 + ], + "spans": [ + { + "bbox": [ + 304, + 437, + 546, + 675 + ], + "type": "text", + "content": "Based on these intuitions, we present Query Recollection (QR) as a training strategy for query-based object detectors. It cumulatively collects intermediate queries as stages go deeper, and feeds the collected queries to the downstream stages aside from the sequential structure. By each stage, the new add-ins alongside the original inputs are independently treated among each other, so the attentions and losses are calculated individually. In such a manner, QR enjoys two key features: (1) The number of supervision signals per stage grows in geometric progression, so that later stages get more supervision than the former ones, for example, the sixth stage got 32 times more supervision than the first; (2) Later stages get chance to view the outputs beyond its neighboring stage for training, which mitigates the potential impact due to cascading errors. We further discover that selectively forward queries to each stage, not with the entire query collection but only those from the prior two stages, can raise the number of supervision in a Fibonacci sequence which halves the extra computing cost and brings even better results. We name it Selective Query Recollection (SQR)." + } + ] + } + ], + "index": 34 + }, + { + "bbox": [ + 305, + 677, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 677, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 677, + 545, + 713 + ], + "type": "text", + "content": "Our contributions are summarized in three folds: (1) We quantitatively investigate the phenomenon where query-based object detectors mispredict at the last decoding stage" + } + ] + } + ], + "index": 35 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "23757" + } + ] + } + ], + "index": 36 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 156 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 156 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 156 + ], + "type": "text", + "content": "while predicting correctly at an intermediate one. (2) We attribute the overlooked phenomenon to two training limitations, and propose a simple and effective training strategy SQR that elegantly fits query-based object detectors. (3) We conduct experiments on Adamixer, DAB DETR, and Deformable DETR across various training settings that verify its effectiveness (Fig.1)." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 167, + 134, + 180 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 167, + 134, + 180 + ], + "spans": [ + { + "bbox": [ + 47, + 167, + 134, + 180 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 188, + 251, + 201 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 188, + 251, + 201 + ], + "spans": [ + { + "bbox": [ + 47, + 188, + 251, + 201 + ], + "type": "text", + "content": "2.1. Training Strategy for Object Detection" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 207, + 289, + 435 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 207, + 289, + 435 + ], + "spans": [ + { + "bbox": [ + 46, + 207, + 289, + 435 + ], + "type": "text", + "content": "Detectors based on dense priors have been dominating the community for decades. The abstract concept anchor box or anchor point [26, 29] aims to match with ground truth (GT) objects depending on their Intersection-over-Union (IoU) values or other advanced soft scoring factors [7, 15, 18, 29, 37]. Among anchor-based detectors, multistage models iteratively refine bounding box and category stage-by-stage. A typical example is Cascade RCNN [2] which is based on the design that the output of an intermediate stage is sampled and re-labeled to train the next stage with increasing IoU thresholds, so these stages are guaranteed to be progressively refined. Recently, DETR [3] starts a family of end-to-end query-based models where object detection is regarded as a set prediction problem. To train DETR, a predefined number of object queries are matched to either a ground-truth or background by solving the Hungarian Matching problem. The queries are refined by several decoder stages similar to Cascade RCNN, and each intermediate stage is supervised by the matching results." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 443, + 213, + 456 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 443, + 213, + 456 + ], + "spans": [ + { + "bbox": [ + 47, + 443, + 213, + 456 + ], + "type": "text", + "content": "2.2. Query-Based Object Detection" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 462, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 462, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 462, + 289, + 715 + ], + "type": "text", + "content": "Recently, many algorithms have been following the idea of DETR. Deformable DETR [38] proposes a deformable attention module that alleviates the aforementioned issues and massively improves the convergence speed by a factor of 10. Conditional DETR [23] decouples the object query into content query and spatial query in the decoder cross-attention module and learns a conditional spatial query from the decoder embedding to enable fast learning of the distinctive extremity of the ground-truth objects. Anchor-DETR [31] formulates the object queries as anchor points such that each object query may only focus on a certain region near its anchor point. Many future works are inspired by this design. DAB-DETR [20] dives deep into the role of object queries. It directly uses anchor box coordinates as spatial query to speed up training. The model benefits from the spatial prior by modulating the positional attention map using the width and height of the box. DN-DETR [17] further improves the convergence speed and query matching stability of DAB-DETR with the help of the Ground Truth denoising task. Adamixer [9] re-designs the query-key pooling mechanism by letting the query adaptively attend to the mean" + } + ] + } + ], + "index": 5 + }, + { + "type": "table", + "bbox": [ + 307, + 71, + 548, + 119 + ], + "blocks": [ + { + "bbox": [ + 307, + 71, + 548, + 119 + ], + "lines": [ + { + "bbox": [ + 307, + 71, + 548, + 119 + ], + "spans": [ + { + "bbox": [ + 307, + 71, + 548, + 119 + ], + "type": "table", + "html": "
ModelS1S2S3S4S5S6
Deformable38.442.243.744.244.444.5
Adamixer15.130.337.740.642.142.5
", + "image_path": "7eee5a25ddc44b5e2aa8120e689d3647c71d25a8e5749d60c40077ef9abf5171.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "table_body" + } + ], + "index": 6 + }, + { + "bbox": [ + 305, + 127, + 547, + 172 + ], + "lines": [ + { + "bbox": [ + 305, + 127, + 547, + 172 + ], + "spans": [ + { + "bbox": [ + 305, + 127, + 547, + 172 + ], + "type": "text", + "content": "Table 1. Stage-wise AP results. Deformable DETR(300 queries) and Adamixer(100 queries) are trained using official implementation, both of their decoders consist of 6 stages, and per stage AP is reported on COCO val set." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "text" + }, + { + "type": "image", + "bbox": [ + 310, + 184, + 545, + 259 + ], + "blocks": [ + { + "bbox": [ + 310, + 184, + 545, + 259 + ], + "lines": [ + { + "bbox": [ + 310, + 184, + 545, + 259 + ], + "spans": [ + { + "bbox": [ + 310, + 184, + 545, + 259 + ], + "type": "image", + "image_path": "67b7b5e3dbb4e4ee8e0d195a19bf8db7af2b151ad2b06645290decb703d92e7a.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 327, + 267, + 523, + 278 + ], + "lines": [ + { + "bbox": [ + 327, + 267, + 523, + 278 + ], + "spans": [ + { + "bbox": [ + 327, + 267, + 523, + 278 + ], + "type": "text", + "content": "Figure 3. Typical structure of a single decoding stage." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 300, + 545, + 371 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 300, + 545, + 371 + ], + "spans": [ + { + "bbox": [ + 304, + 300, + 545, + 371 + ], + "type": "text", + "content": "ingful regions of the encoded features directly through bilinear sampling. An MLP-Mixer then dynamically decodes the pooled features into final predictions. DETA (Detection Transformers with Assignment) [24] proposes a novel overlap-based assignment that enables one-to-many assignments to DETR." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 372, + 545, + 408 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 372, + 545, + 408 + ], + "spans": [ + { + "bbox": [ + 304, + 372, + 545, + 408 + ], + "type": "text", + "content": "Despite their significant improvement on DETR, they focus little on the training emphasis and cascading errors. We propose SQR to pay attention to the two problems." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 419, + 378, + 431 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 419, + 378, + 431 + ], + "spans": [ + { + "bbox": [ + 306, + 419, + 378, + 431 + ], + "type": "text", + "content": "3. Motivation" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 440, + 545, + 511 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 440, + 545, + 511 + ], + "spans": [ + { + "bbox": [ + 304, + 440, + 545, + 511 + ], + "type": "text", + "content": "Are query-based object detectors always predicting the optimal detections at the last stage? Table.1 shows that AP gradually increases with stages going deeper, indicating improved predictions on a general scale. While the observation in Fig.2 implies that simple AP results are insufficient for an in-depth analysis of that question." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 512, + 545, + 619 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 512, + 545, + 619 + ], + "spans": [ + { + "bbox": [ + 304, + 512, + 545, + 619 + ], + "type": "text", + "content": "Preliminary. Queries are updated successively. A typical structure of a decoding stage is illustrated in Fig.3. An initial query " + }, + { + "bbox": [ + 304, + 512, + 545, + 619 + ], + "type": "inline_equation", + "content": "q_{i}^{0}" + }, + { + "bbox": [ + 304, + 512, + 545, + 619 + ], + "type": "text", + "content": " (" + }, + { + "bbox": [ + 304, + 512, + 545, + 619 + ], + "type": "inline_equation", + "content": "i \\in N = \\{1,2,\\dots,n\\}" + }, + { + "bbox": [ + 304, + 512, + 545, + 619 + ], + "type": "text", + "content": ") is an embedding trained through back-propagation, and " + }, + { + "bbox": [ + 304, + 512, + 545, + 619 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 304, + 512, + 545, + 619 + ], + "type": "text", + "content": " is the total number of initial queries. 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The procedure can be formulated as" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 628, + 545, + 653 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 628, + 545, + 653 + ], + "spans": [ + { + "bbox": [ + 306, + 628, + 545, + 653 + ], + "type": "interline_equation", + "content": "q _ {i} ^ {s} = D ^ {s} \\left(q _ {i} ^ {s - 1}, q ^ {s - 1}, x\\right) = q _ {i} ^ {s - 1} + (\\mathcal {A} \\circ \\mathcal {F}) \\left(q _ {i} ^ {s - 1}, q ^ {s - 1}, x\\right) \\tag {1}", + "image_path": "263a66ab6f8efc4c6ca252ecde2e34b82e7f15486868e17f9a947190b5cd1b86.jpg" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 654, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 654, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 654, + 547, + 713 + ], + "type": "inline_equation", + "content": "D^{s}" + }, + { + "bbox": [ + 304, + 654, + 547, + 713 + ], + "type": "text", + "content": " is a decoding stage where " + }, + { + "bbox": [ + 304, + 654, + 547, + 713 + ], + "type": "inline_equation", + "content": "s" + }, + { + "bbox": [ + 304, + 654, + 547, + 713 + ], + "type": "text", + "content": " is stage index; " + }, + { + "bbox": [ + 304, + 654, + 547, + 713 + ], + "type": "inline_equation", + "content": "q_{i}^{s}" + }, + { + "bbox": [ + 304, + 654, + 547, + 713 + ], + "type": "text", + "content": " is the " + }, + { + "bbox": [ + 304, + 654, + 547, + 713 + ], + "type": "inline_equation", + "content": "i_{th}" + }, + { + "bbox": [ + 304, + 654, + 547, + 713 + ], + "type": "text", + "content": " query at stage " + }, + { + "bbox": [ + 304, + 654, + 547, + 713 + ], + "type": "inline_equation", + "content": "s" + }, + { + "bbox": [ + 304, + 654, + 547, + 713 + ], + "type": "text", + "content": "; " + }, + { + "bbox": [ + 304, + 654, + 547, + 713 + ], + "type": "inline_equation", + "content": "q^{s}" + }, + { + "bbox": [ + 304, + 654, + 547, + 713 + ], + "type": "text", + "content": " is a set of queries " + }, + { + "bbox": [ + 304, + 654, + 547, + 713 + ], + "type": "inline_equation", + "content": "q^{s} = \\{q_{i}^{s} | i \\in N\\}" + }, + { + "bbox": [ + 304, + 654, + 547, + 713 + ], + "type": "text", + "content": "; " + }, + { + "bbox": [ + 304, + 654, + 547, + 713 + ], + "type": "inline_equation", + "content": "(\\mathcal{A} \\circ \\mathcal{F})" + }, + { + "bbox": [ + 304, + 654, + 547, + 713 + ], + "type": "text", + "content": " stands for a bundle of modules including self and cross attention and feed forward network; " + }, + { + "bbox": [ + 304, + 654, + 547, + 713 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 304, + 654, + 547, + 713 + ], + "type": "text", + "content": " means features; and LayerNorm [1] that applied on each module is omitted" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "23758" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 50, + 70, + 286, + 148 + ], + "blocks": [ + { + "bbox": [ + 50, + 70, + 286, + 148 + ], + "lines": [ + { + "bbox": [ + 50, + 70, + 286, + 148 + ], + "spans": [ + { + "bbox": [ + 50, + 70, + 286, + 148 + ], + "type": "table", + "html": "
ModelTP ThresholdTP F RateFP E Rate
DeformableIoU>0.5051.4%55.7%
DETRIoU>0.7549.5%55.9%
AdamixerIoU>0.5028.6%50.8%
IoU>0.7526.7%51.2%
", + "image_path": "bb832205eef62226c8e13373781c3e5f5aa55e2a5662d0f4b4b8af14346c190f.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 156, + 287, + 178 + ], + "lines": [ + { + "bbox": [ + 47, + 156, + 287, + 178 + ], + "spans": [ + { + "bbox": [ + 47, + 156, + 287, + 178 + ], + "type": "text", + "content": "Table 2. True-positive Fading Rate and False-positive Exacerbation Rate." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 47, + 201, + 287, + 226 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 201, + 287, + 226 + ], + "spans": [ + { + "bbox": [ + 47, + 201, + 287, + 226 + ], + "type": "text", + "content": "for simplicity. Afterward, " + }, + { + "bbox": [ + 47, + 201, + 287, + 226 + ], + "type": "inline_equation", + "content": "q_{i}^{s}" + }, + { + "bbox": [ + 47, + 201, + 287, + 226 + ], + "type": "text", + "content": " predicts an object " + }, + { + "bbox": [ + 47, + 201, + 287, + 226 + ], + "type": "inline_equation", + "content": "P_{i}^{s}" + }, + { + "bbox": [ + 47, + 201, + 287, + 226 + ], + "type": "text", + "content": " via two multi-layer perceptrons for classification and regression:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 89, + 238, + 287, + 251 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 89, + 238, + 287, + 251 + ], + "spans": [ + { + "bbox": [ + 89, + 238, + 287, + 251 + ], + "type": "interline_equation", + "content": "P _ {i} ^ {s} = \\left(M L P _ {c l s} \\left(q _ {i} ^ {s}\\right), M L P _ {r e g} \\left(q _ {i} ^ {s}\\right)\\right) \\tag {2}", + "image_path": "fd246f7cc0ecdcac8ddb2623bfb1ca96044c26b294acdb2f44fcf2094abc43b4.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 256, + 286, + 330 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 256, + 286, + 330 + ], + "spans": [ + { + "bbox": [ + 47, + 256, + 286, + 330 + ], + "type": "inline_equation", + "content": "P_{i}^{1\\sim 6}" + }, + { + "bbox": [ + 47, + 256, + 286, + 330 + ], + "type": "text", + "content": " are predicted by the " + }, + { + "bbox": [ + 47, + 256, + 286, + 330 + ], + "type": "inline_equation", + "content": "q_{i}^{1\\sim 6}" + }, + { + "bbox": [ + 47, + 256, + 286, + 330 + ], + "type": "text", + "content": " rooted in " + }, + { + "bbox": [ + 47, + 256, + 286, + 330 + ], + "type": "inline_equation", + "content": "q_{i}^{0}" + }, + { + "bbox": [ + 47, + 256, + 286, + 330 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 47, + 256, + 286, + 330 + ], + "type": "inline_equation", + "content": "P_{i}^{6}" + }, + { + "bbox": [ + 47, + 256, + 286, + 330 + ], + "type": "text", + "content": " is the expected outcome and " + }, + { + "bbox": [ + 47, + 256, + 286, + 330 + ], + "type": "inline_equation", + "content": "P_{i}^{1\\sim 5}" + }, + { + "bbox": [ + 47, + 256, + 286, + 330 + ], + "type": "text", + "content": " are intermediate results. " + }, + { + "bbox": [ + 47, + 256, + 286, + 330 + ], + "type": "inline_equation", + "content": "P_{i}^{s}" + }, + { + "bbox": [ + 47, + 256, + 286, + 330 + ], + "type": "text", + "content": " is regarded as a true-positive towards a ground-truth " + }, + { + "bbox": [ + 47, + 256, + 286, + 330 + ], + "type": "inline_equation", + "content": "G" + }, + { + "bbox": [ + 47, + 256, + 286, + 330 + ], + "type": "text", + "content": " only if the IoU " + }, + { + "bbox": [ + 47, + 256, + 286, + 330 + ], + "type": "inline_equation", + "content": "(P_{i}^{s}, G)" + }, + { + "bbox": [ + 47, + 256, + 286, + 330 + ], + "type": "text", + "content": " exceeds a threshold, its category matches with " + }, + { + "bbox": [ + 47, + 256, + 286, + 330 + ], + "type": "inline_equation", + "content": "G" + }, + { + "bbox": [ + 47, + 256, + 286, + 330 + ], + "type": "text", + "content": ", and the categorical score is ranked as the highest among all other counterparts." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 330, + 286, + 436 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 330, + 286, + 436 + ], + "spans": [ + { + "bbox": [ + 46, + 330, + 286, + 436 + ], + "type": "text", + "content": "Investigation. We study the stage-wise testing results by first defining two rates: (1) If " + }, + { + "bbox": [ + 46, + 330, + 286, + 436 + ], + "type": "inline_equation", + "content": "P_{i}^{6}" + }, + { + "bbox": [ + 46, + 330, + 286, + 436 + ], + "type": "text", + "content": " is a true-positive (TP) towards a ground-truth " + }, + { + "bbox": [ + 46, + 330, + 286, + 436 + ], + "type": "inline_equation", + "content": "G" + }, + { + "bbox": [ + 46, + 330, + 286, + 436 + ], + "type": "text", + "content": ", we check whether " + }, + { + "bbox": [ + 46, + 330, + 286, + 436 + ], + "type": "inline_equation", + "content": "P_{i}^{1\\sim 5}" + }, + { + "bbox": [ + 46, + 330, + 286, + 436 + ], + "type": "text", + "content": " generate a better TP towards the same " + }, + { + "bbox": [ + 46, + 330, + 286, + 436 + ], + "type": "inline_equation", + "content": "G" + }, + { + "bbox": [ + 46, + 330, + 286, + 436 + ], + "type": "text", + "content": " that has higher IoU & higher category score than " + }, + { + "bbox": [ + 46, + 330, + 286, + 436 + ], + "type": "inline_equation", + "content": "P_{i}^{6}" + }, + { + "bbox": [ + 46, + 330, + 286, + 436 + ], + "type": "text", + "content": ". The occurrence rate is denoted as TP fading rate. (2) If " + }, + { + "bbox": [ + 46, + 330, + 286, + 436 + ], + "type": "inline_equation", + "content": "P_{i}^{6}" + }, + { + "bbox": [ + 46, + 330, + 286, + 436 + ], + "type": "text", + "content": " is a false-positive (FP), we check whether " + }, + { + "bbox": [ + 46, + 330, + 286, + 436 + ], + "type": "inline_equation", + "content": "P_{i}^{1\\sim 5}" + }, + { + "bbox": [ + 46, + 330, + 286, + 436 + ], + "type": "text", + "content": " produce a FP but with lower category score than " + }, + { + "bbox": [ + 46, + 330, + 286, + 436 + ], + "type": "inline_equation", + "content": "P_{i}^{6}" + }, + { + "bbox": [ + 46, + 330, + 286, + 436 + ], + "type": "text", + "content": ". The occurrence rate is denoted as FP exacerbation rate." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 437, + 286, + 664 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 437, + 286, + 664 + ], + "spans": [ + { + "bbox": [ + 46, + 437, + 286, + 664 + ], + "type": "text", + "content": "The statistics are shown in Table.2. We can see that TP fading rate achieves " + }, + { + "bbox": [ + 46, + 437, + 286, + 664 + ], + "type": "inline_equation", + "content": "50\\%" + }, + { + "bbox": [ + 46, + 437, + 286, + 664 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 437, + 286, + 664 + ], + "type": "inline_equation", + "content": "27\\%" + }, + { + "bbox": [ + 46, + 437, + 286, + 664 + ], + "type": "text", + "content": " on the two models. Considering the strict constraints it holds, the TP fading rate reaches an impressively high level. Deformable DETR is much higher than Adamixer due to the smaller AP gap among stages, thus, in many cases, earlier stages are more likely to outperform the last stage. FP exacerbation holds looser constraints and is easier to be satisfied, its rate is above " + }, + { + "bbox": [ + 46, + 437, + 286, + 664 + ], + "type": "inline_equation", + "content": "50\\%" + }, + { + "bbox": [ + 46, + 437, + 286, + 664 + ], + "type": "text", + "content": " on the two models. Higher TP threshold implies higher quality of " + }, + { + "bbox": [ + 46, + 437, + 286, + 664 + ], + "type": "inline_equation", + "content": "P_{i}^{6}" + }, + { + "bbox": [ + 46, + 437, + 286, + 664 + ], + "type": "text", + "content": " and it is harder to find qualifiers in " + }, + { + "bbox": [ + 46, + 437, + 286, + 664 + ], + "type": "inline_equation", + "content": "P_{i}^{1\\sim 5}" + }, + { + "bbox": [ + 46, + 437, + 286, + 664 + ], + "type": "text", + "content": ", but the two rates are similar with 0.75 as with 0.5, pointing out the consistency of this phenomenon. We also observe that more than half of the occurred cases are marginally triggered, i.e. the predictions from the triggered " + }, + { + "bbox": [ + 46, + 437, + 286, + 664 + ], + "type": "inline_equation", + "content": "P_{i}^{1\\sim 5}" + }, + { + "bbox": [ + 46, + 437, + 286, + 664 + ], + "type": "text", + "content": " are only marginally better than the sixth. This is a further reason why the deformable DETR has those high rates - the results from the 5th and 6th stages are extremely visually close. In dominated number of cases, the final stage is (one of) the best, after all, its mAP is the highest." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 665, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 286, + 713 + ], + "type": "text", + "content": "When the conditions of the two rates establish, we further replace " + }, + { + "bbox": [ + 46, + 665, + 286, + 713 + ], + "type": "inline_equation", + "content": "P_{i}^{6}" + }, + { + "bbox": [ + 46, + 665, + 286, + 713 + ], + "type": "text", + "content": " with the optimal prediction found in " + }, + { + "bbox": [ + 46, + 665, + 286, + 713 + ], + "type": "inline_equation", + "content": "P_{i}^{1\\sim 6}" + }, + { + "bbox": [ + 46, + 665, + 286, + 713 + ], + "type": "text", + "content": " and measure the AP. On Deformable DETR, AP grows from 44.5 AP to 51.7 (+7.2 AP); on Adamixer, AP grows from" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "type": "text", + "content": "42.5 AP to 53.3 (+10.7 AP), demonstrating huge potential in query-based detectors yet to be mined." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 97, + 545, + 180 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 97, + 545, + 180 + ], + "spans": [ + { + "bbox": [ + 304, + 97, + 545, + 180 + ], + "type": "text", + "content": "Conclusion. This reveals that models frequently predict the optimum at intermediate stages instead of the last one. We view the problem from the training's perspective and identify the lack of training emphasis and the cascading errors from query sequence as two obstacles impeding the occurrence of the most reliable predictions in the last stage, elaborated in Section 1." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 194, + 419, + 208 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 194, + 419, + 208 + ], + "spans": [ + { + "bbox": [ + 305, + 194, + 419, + 208 + ], + "type": "text", + "content": "4. Query Recollection" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 214, + 383, + 227 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 214, + 383, + 227 + ], + "spans": [ + { + "bbox": [ + 306, + 214, + 383, + 227 + ], + "type": "text", + "content": "4.1. Expectancy" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 317, + 233, + 515, + 246 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 233, + 515, + 246 + ], + "spans": [ + { + "bbox": [ + 317, + 233, + 515, + 246 + ], + "type": "text", + "content": "We desire such a training strategy that embraces:" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 317, + 247, + 545, + 306 + ], + "type": "list", + "angle": 0, + "index": 15, + "blocks": [ + { + "bbox": [ + 317, + 247, + 545, + 281 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 247, + 545, + 281 + ], + "spans": [ + { + "bbox": [ + 317, + 247, + 545, + 281 + ], + "type": "text", + "content": "- Uneven supervision applied to decoding stages that places emphasis on later ones, enhancing later stages for better final outcomes." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 317, + 283, + 545, + 306 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 283, + 545, + 306 + ], + "spans": [ + { + "bbox": [ + 317, + 283, + 545, + 306 + ], + "type": "text", + "content": "- A variety of early-stage queries directly introduced to later stages, mitigating the impact of cascading errors." + } + ] + } + ], + "index": 14 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 304, + 308, + 545, + 380 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 308, + 545, + 380 + ], + "spans": [ + { + "bbox": [ + 304, + 308, + 545, + 380 + ], + "type": "text", + "content": "To this end, we design a concise training strategy coined as Query Recollection (QR). Compared with prior arts, it collects intermediate queries at every stage and forwards them along the original pathway. Dense Query Recollection (DQR) is the fundamental form and Selective Query Recollection (SQR) is an advanced variant." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 305, + 389, + 449, + 402 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 389, + 449, + 402 + ], + "spans": [ + { + "bbox": [ + 305, + 389, + 449, + 402 + ], + "type": "text", + "content": "4.2. Dense Query Recollection" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 408, + 545, + 480 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 408, + 545, + 480 + ], + "spans": [ + { + "bbox": [ + 304, + 408, + 545, + 480 + ], + "type": "text", + "content": "Notation. The process of single decoding stage (self-attention, cross-attention, FFN), the ground-truth assignment, and loss calculations are applied within a set of queries " + }, + { + "bbox": [ + 304, + 408, + 545, + 480 + ], + "type": "inline_equation", + "content": "\\{q_i | i \\in \\{1, 2, \\dots, n\\}\\}" + }, + { + "bbox": [ + 304, + 408, + 545, + 480 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 408, + 545, + 480 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 304, + 408, + 545, + 480 + ], + "type": "text", + "content": " is typically 100/300/500. We regard the set of queries as a basic unit in our method and generally denote as " + }, + { + "bbox": [ + 304, + 408, + 545, + 480 + ], + "type": "inline_equation", + "content": "q" + }, + { + "bbox": [ + 304, + 408, + 545, + 480 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 481, + 545, + 541 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 481, + 545, + 541 + ], + "spans": [ + { + "bbox": [ + 304, + 481, + 545, + 541 + ], + "type": "text", + "content": "Basic Pathway. Query along the basic pathway is refined by all stages. We illustrate it in Fig.4(a). Taking a 4-stages decoder as an example, we denote " + }, + { + "bbox": [ + 304, + 481, + 545, + 541 + ], + "type": "inline_equation", + "content": "q^{0-1-2-3-4}" + }, + { + "bbox": [ + 304, + 481, + 545, + 541 + ], + "type": "text", + "content": " as the final query that is refined by all stages. So the basic " + }, + { + "bbox": [ + 304, + 481, + 545, + 541 + ], + "type": "inline_equation", + "content": "\\mathcal{PT}" + }, + { + "bbox": [ + 304, + 481, + 545, + 541 + ], + "type": "text", + "content": " finally produces" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 347, + 563, + 545, + 594 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 347, + 563, + 545, + 594 + ], + "spans": [ + { + "bbox": [ + 347, + 563, + 545, + 594 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} q ^ {0 - 1 - 2 - 3 - 4} = D ^ {4} \\left(D ^ {3} \\left(D ^ {2} \\left(D ^ {1} \\left(q ^ {0}\\right)\\right)\\right)\\right) (3) \\\\ = \\mathcal {P T} ^ {1 - 2 - 3 - 4} \\left(q ^ {0}\\right) (4) \\\\ \\end{array}", + "image_path": "ea44fae620423b5ad961bb530db60c76a3c60713ded630fecc76bc62c5beeb13.jpg" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 304, + 604, + 545, + 688 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 604, + 545, + 688 + ], + "spans": [ + { + "bbox": [ + 304, + 604, + 545, + 688 + ], + "type": "text", + "content": "During training, the queries from each stage, i.e. " + }, + { + "bbox": [ + 304, + 604, + 545, + 688 + ], + "type": "inline_equation", + "content": "q^{0-1}" + }, + { + "bbox": [ + 304, + 604, + 545, + 688 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 604, + 545, + 688 + ], + "type": "inline_equation", + "content": "q^{0-1-2}" + }, + { + "bbox": [ + 304, + 604, + 545, + 688 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 604, + 545, + 688 + ], + "type": "inline_equation", + "content": "q^{0-1-2-3}" + }, + { + "bbox": [ + 304, + 604, + 545, + 688 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 304, + 604, + 545, + 688 + ], + "type": "inline_equation", + "content": "q^{0-1-2-3-4}" + }, + { + "bbox": [ + 304, + 604, + 545, + 688 + ], + "type": "text", + "content": " are independently followed by Hungarian Assignment that matches ground-truth with " + }, + { + "bbox": [ + 304, + 604, + 545, + 688 + ], + "type": "inline_equation", + "content": "q" + }, + { + "bbox": [ + 304, + 604, + 545, + 688 + ], + "type": "text", + "content": " in a one-to-one manner, and then followed by loss calculation for supervision. In Fig.4, we mark those " + }, + { + "bbox": [ + 304, + 604, + 545, + 688 + ], + "type": "inline_equation", + "content": "q" + }, + { + "bbox": [ + 304, + 604, + 545, + 688 + ], + "type": "text", + "content": " that require supervision as " + }, + { + "bbox": [ + 304, + 604, + 545, + 688 + ], + "type": "inline_equation", + "content": "\\hat{q}" + }, + { + "bbox": [ + 304, + 604, + 545, + 688 + ], + "type": "text", + "content": ". Along the basic pathway, the number of " + }, + { + "bbox": [ + 304, + 604, + 545, + 688 + ], + "type": "inline_equation", + "content": "\\hat{q}" + }, + { + "bbox": [ + 304, + 604, + 545, + 688 + ], + "type": "text", + "content": " at each stage is 1." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "type": "text", + "content": "DQR Formulation. We densely collect every intermediate " + }, + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "type": "inline_equation", + "content": "q" + }, + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "type": "text", + "content": " and independently forward them to every downstream" + } + ] + } + ], + "index": 22 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "23759" + } + ] + } + ], + "index": 23 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 47, + 89, + 298, + 388 + ], + "blocks": [ + { + "bbox": [ + 47, + 71, + 152, + 84 + ], + "lines": [ + { + "bbox": [ + 47, + 71, + 152, + 84 + ], + "spans": [ + { + "bbox": [ + 47, + 71, + 152, + 84 + ], + "type": "text", + "content": "(a)Basic (b)Dense QR" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 47, + 89, + 298, + 388 + ], + "lines": [ + { + "bbox": [ + 47, + 89, + 298, + 388 + ], + "spans": [ + { + "bbox": [ + 47, + 89, + 298, + 388 + ], + "type": "image", + "image_path": "fc8ee8a9aa62956f3435d6cee25a31f9b1c6dc80506d2932d9781aff8fc6d50d.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 49, + 407, + 73, + 437 + ], + "blocks": [ + { + "bbox": [ + 49, + 407, + 73, + 437 + ], + "lines": [ + { + "bbox": [ + 49, + 407, + 73, + 437 + ], + "spans": [ + { + "bbox": [ + 49, + 407, + 73, + 437 + ], + "type": "image", + "image_path": "152d414d27b5e29816771156de4a8b5a368e60734d02a08d043ba6f07b518149.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 74, + 411, + 295, + 421 + ], + "lines": [ + { + "bbox": [ + 74, + 411, + 295, + 421 + ], + "spans": [ + { + "bbox": [ + 74, + 411, + 295, + 421 + ], + "type": "text", + "content": "Collection C " + }, + { + "bbox": [ + 74, + 411, + 295, + 421 + ], + "type": "inline_equation", + "content": "q^{0I2}" + }, + { + "bbox": [ + 74, + 411, + 295, + 421 + ], + "type": "text", + "content": " Query, from initial to stage 1 then to 2" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_footnote" + }, + { + "bbox": [ + 74, + 426, + 273, + 437 + ], + "lines": [ + { + "bbox": [ + 74, + 426, + 273, + 437 + ], + "spans": [ + { + "bbox": [ + 74, + 426, + 273, + 437 + ], + "type": "text", + "content": "Output of stage/QR " + }, + { + "bbox": [ + 74, + 426, + 273, + 437 + ], + "type": "inline_equation", + "content": "\\hat{\\pmb{q}}" + }, + { + "bbox": [ + 74, + 426, + 273, + 437 + ], + "type": "text", + "content": " Query with supervision applied" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_footnote" + }, + { + "bbox": [ + 46, + 446, + 287, + 479 + ], + "lines": [ + { + "bbox": [ + 46, + 446, + 287, + 479 + ], + "spans": [ + { + "bbox": [ + 46, + 446, + 287, + 479 + ], + "type": "text", + "content": "Figure 4. (a). Basic process for decoding queries stage by stage, applied in both training and testing. (b). Dense query recollection. (c). Selective query recollection." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 499, + 287, + 536 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 499, + 287, + 536 + ], + "spans": [ + { + "bbox": [ + 46, + 499, + 287, + 536 + ], + "type": "text", + "content": "stage, as illustrated in Fig.4(b). After each stage, a collection " + }, + { + "bbox": [ + 46, + 499, + 287, + 536 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 46, + 499, + 287, + 536 + ], + "type": "text", + "content": " is formed where the number of " + }, + { + "bbox": [ + 46, + 499, + 287, + 536 + ], + "type": "inline_equation", + "content": "q" + }, + { + "bbox": [ + 46, + 499, + 287, + 536 + ], + "type": "text", + "content": " grows geometrically, namely " + }, + { + "bbox": [ + 46, + 499, + 287, + 536 + ], + "type": "inline_equation", + "content": "2^{s}" + }, + { + "bbox": [ + 46, + 499, + 287, + 536 + ], + "type": "text", + "content": " at " + }, + { + "bbox": [ + 46, + 499, + 287, + 536 + ], + "type": "inline_equation", + "content": "s_{th}" + }, + { + "bbox": [ + 46, + 499, + 287, + 536 + ], + "type": "text", + "content": " stage. Formally," + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 143, + 546, + 287, + 559 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 546, + 287, + 559 + ], + "spans": [ + { + "bbox": [ + 143, + 546, + 287, + 559 + ], + "type": "interline_equation", + "content": "C ^ {0} = \\{q ^ {0} \\} \\tag {5}", + "image_path": "68c3a6bec1a38cddfe528750b03d0741b5234a0dedd5f3dde0b225334d42b7fe.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 97, + 563, + 287, + 578 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 97, + 563, + 287, + 578 + ], + "spans": [ + { + "bbox": [ + 97, + 563, + 287, + 578 + ], + "type": "interline_equation", + "content": "C ^ {s} = \\left\\{D ^ {s} (q) | q \\in C ^ {s - 1} \\right\\} \\cup C ^ {s - 1} \\tag {6}", + "image_path": "c2c3f2649f0e90bf43716dab40718db84a7398725cc2b050f5372d411a8fe993.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 582, + 287, + 665 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 582, + 287, + 665 + ], + "spans": [ + { + "bbox": [ + 46, + 582, + 287, + 665 + ], + "type": "text", + "content": "In a collection " + }, + { + "bbox": [ + 46, + 582, + 287, + 665 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 46, + 582, + 287, + 665 + ], + "type": "text", + "content": ", half of queries inside are newly generated by the current stage, i.e. from " + }, + { + "bbox": [ + 46, + 582, + 287, + 665 + ], + "type": "inline_equation", + "content": "\\{D^s(q)|q \\in C^{s-1}\\}" + }, + { + "bbox": [ + 46, + 582, + 287, + 665 + ], + "type": "text", + "content": ", while another half are from previous stages, " + }, + { + "bbox": [ + 46, + 582, + 287, + 665 + ], + "type": "inline_equation", + "content": "C^{s-1}" + }, + { + "bbox": [ + 46, + 582, + 287, + 665 + ], + "type": "text", + "content": ". Separately, for each " + }, + { + "bbox": [ + 46, + 582, + 287, + 665 + ], + "type": "inline_equation", + "content": "q" + }, + { + "bbox": [ + 46, + 582, + 287, + 665 + ], + "type": "text", + "content": " in the former half, we apply Hungarian assignment and loss calculation, so the number of supervision signals grows in geometric progression as well, namely " + }, + { + "bbox": [ + 46, + 582, + 287, + 665 + ], + "type": "inline_equation", + "content": "2^{s-1}" + }, + { + "bbox": [ + 46, + 582, + 287, + 665 + ], + "type": "text", + "content": " at " + }, + { + "bbox": [ + 46, + 582, + 287, + 665 + ], + "type": "inline_equation", + "content": "s_{th}" + }, + { + "bbox": [ + 46, + 582, + 287, + 665 + ], + "type": "text", + "content": " stage." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "text", + "content": "Such-wise, Dense Query Recollection satisfies our expectancy where the number of supervision signal for each stage grows as (1,2,4,8,16,32), meanwhile, all prior queries would be visible in all later stages." + } + ] + } + ], + "index": 11 + }, + { + "type": "table", + "bbox": [ + 316, + 71, + 537, + 166 + ], + "blocks": [ + { + "bbox": [ + 316, + 71, + 537, + 166 + ], + "lines": [ + { + "bbox": [ + 316, + 71, + 537, + 166 + ], + "spans": [ + { + "bbox": [ + 316, + 71, + 537, + 166 + ], + "type": "table", + "html": "
stage12345
TP F Rate(%)1.24.48.512.416.9
FP E Rate(%)14.318.620.824.530.2
stage1~34&53~52~51~5
TP F Rate(%)11.223.926.928.328.6
FP E Rate(%)32.440.845.348.550.8
", + "image_path": "f58ad0773cd493228b23e0e7d72922e8530e2bde08c411ede0b8fc75599dc46e.jpg" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "table_body" + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 174, + 545, + 195 + ], + "lines": [ + { + "bbox": [ + 305, + 174, + 545, + 195 + ], + "spans": [ + { + "bbox": [ + 305, + 174, + 545, + 195 + ], + "type": "text", + "content": "Table 3. Stage-wise TP Fading Rate and FP Exacerbation Rate with Adamixer." + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 305, + 218, + 545, + 255 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 218, + 545, + 255 + ], + "spans": [ + { + "bbox": [ + 305, + 218, + 545, + 255 + ], + "type": "text", + "content": "During inference, we only use the basic pathway, so the inference process is untouched. For a standard 6-stage decoder, the pathway is " + }, + { + "bbox": [ + 305, + 218, + 545, + 255 + ], + "type": "inline_equation", + "content": "\\mathcal{PT}^{1-2-3-4-5-6}" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 262, + 462, + 275 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 262, + 462, + 275 + ], + "spans": [ + { + "bbox": [ + 306, + 262, + 462, + 275 + ], + "type": "text", + "content": "4.3. Selective Query Recollection" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 281, + 545, + 436 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 281, + 545, + 436 + ], + "spans": [ + { + "bbox": [ + 304, + 281, + 545, + 436 + ], + "type": "text", + "content": "The last proposal empirically enhances training, but the query collection process is indiscriminate, which brings two defects: First, the geometrical growth of the number of " + }, + { + "bbox": [ + 304, + 281, + 545, + 436 + ], + "type": "inline_equation", + "content": "\\hat{q}" + }, + { + "bbox": [ + 304, + 281, + 545, + 436 + ], + "type": "text", + "content": " and their attention/loss calculations cost a lot. Second, if we input an early " + }, + { + "bbox": [ + 304, + 281, + 545, + 436 + ], + "type": "inline_equation", + "content": "q" + }, + { + "bbox": [ + 304, + 281, + 545, + 436 + ], + "type": "text", + "content": " that skips too many stages to a far-away late stage, the potential benefit could be overshadowed by the huge learning gap between the stages and query. For instance, if the initial " + }, + { + "bbox": [ + 304, + 281, + 545, + 436 + ], + "type": "inline_equation", + "content": "q^0" + }, + { + "bbox": [ + 304, + 281, + 545, + 436 + ], + "type": "text", + "content": " is directly introduced to stage 6 and produces " + }, + { + "bbox": [ + 304, + 281, + 545, + 436 + ], + "type": "inline_equation", + "content": "\\hat{q}^{0 - 6}" + }, + { + "bbox": [ + 304, + 281, + 545, + 436 + ], + "type": "text", + "content": ", this query would have the highest difficulty among all queries at stage 6 and the calculated loss would dominate the overall losses. So we are inclined to selectively collect intermediate " + }, + { + "bbox": [ + 304, + 281, + 545, + 436 + ], + "type": "inline_equation", + "content": "q" + }, + { + "bbox": [ + 304, + 281, + 545, + 436 + ], + "type": "text", + "content": " rather than densely collect all of them." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 437, + 545, + 472 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 437, + 545, + 472 + ], + "spans": [ + { + "bbox": [ + 304, + 437, + 545, + 472 + ], + "type": "text", + "content": "Selection. To find a better query recollection scheme, we further conduct a detailed analysis on the TP Fading Rate and FP Exacerbation Rate introduced in Section 3." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 473, + 546, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 473, + 546, + 628 + ], + "spans": [ + { + "bbox": [ + 304, + 473, + 546, + 628 + ], + "type": "text", + "content": "Recall the spirits of the two rates where we seek from " + }, + { + "bbox": [ + 304, + 473, + 546, + 628 + ], + "type": "inline_equation", + "content": "P_{i}^{1\\sim 5}" + }, + { + "bbox": [ + 304, + 473, + 546, + 628 + ], + "type": "text", + "content": " for an alternative that is better than " + }, + { + "bbox": [ + 304, + 473, + 546, + 628 + ], + "type": "inline_equation", + "content": "P_{i}^{6}" + }, + { + "bbox": [ + 304, + 473, + 546, + 628 + ], + "type": "text", + "content": ", we want to investigate which specific intermediate stage/stages contribute the most. Concretely, if " + }, + { + "bbox": [ + 304, + 473, + 546, + 628 + ], + "type": "inline_equation", + "content": "P_{i}^{6}" + }, + { + "bbox": [ + 304, + 473, + 546, + 628 + ], + "type": "text", + "content": " is a true-positive towards a ground-truth " + }, + { + "bbox": [ + 304, + 473, + 546, + 628 + ], + "type": "inline_equation", + "content": "G" + }, + { + "bbox": [ + 304, + 473, + 546, + 628 + ], + "type": "text", + "content": ", we separately check each stage whether generating a better TP; similarly, if " + }, + { + "bbox": [ + 304, + 473, + 546, + 628 + ], + "type": "inline_equation", + "content": "P_{i}^{6}" + }, + { + "bbox": [ + 304, + 473, + 546, + 628 + ], + "type": "text", + "content": " is a false-positive, we separately check each stage whether generating a better FP. The results are summarized in Table 3. We find that the majority of alternatives of " + }, + { + "bbox": [ + 304, + 473, + 546, + 628 + ], + "type": "inline_equation", + "content": "P_{i}^{6}" + }, + { + "bbox": [ + 304, + 473, + 546, + 628 + ], + "type": "text", + "content": " are from stage 4&5, where the corresponding TP fading rate and FP exacerbation rate reach " + }, + { + "bbox": [ + 304, + 473, + 546, + 628 + ], + "type": "inline_equation", + "content": "23.9\\%" + }, + { + "bbox": [ + 304, + 473, + 546, + 628 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 473, + 546, + 628 + ], + "type": "inline_equation", + "content": "40.8\\%" + }, + { + "bbox": [ + 304, + 473, + 546, + 628 + ], + "type": "text", + "content": ", respectively, which are close to the results of stages " + }, + { + "bbox": [ + 304, + 473, + 546, + 628 + ], + "type": "inline_equation", + "content": "1 \\sim 5" + }, + { + "bbox": [ + 304, + 473, + 546, + 628 + ], + "type": "text", + "content": ". While stage " + }, + { + "bbox": [ + 304, + 473, + 546, + 628 + ], + "type": "inline_equation", + "content": "1 \\sim 3" + }, + { + "bbox": [ + 304, + 473, + 546, + 628 + ], + "type": "text", + "content": " together only produces " + }, + { + "bbox": [ + 304, + 473, + 546, + 628 + ], + "type": "inline_equation", + "content": "11.2\\%" + }, + { + "bbox": [ + 304, + 473, + 546, + 628 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 473, + 546, + 628 + ], + "type": "inline_equation", + "content": "32.4\\%" + }, + { + "bbox": [ + 304, + 473, + 546, + 628 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 629, + 545, + 700 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 629, + 545, + 700 + ], + "spans": [ + { + "bbox": [ + 304, + 629, + 545, + 700 + ], + "type": "text", + "content": "The above analysis implies that the queries from the adjacent stage and the stage prior to the adjacent stage are more likely to bring positive effects. We intuitively follow the observations and selectively operate collection along the basic pathway: before starting stage " + }, + { + "bbox": [ + 304, + 629, + 545, + 700 + ], + "type": "inline_equation", + "content": "D^{s}" + }, + { + "bbox": [ + 304, + 629, + 545, + 700 + ], + "type": "text", + "content": ", we collect " + }, + { + "bbox": [ + 304, + 629, + 545, + 700 + ], + "type": "inline_equation", + "content": "q" + }, + { + "bbox": [ + 304, + 629, + 545, + 700 + ], + "type": "text", + "content": " from the 2 nearest stages, i.e. " + }, + { + "bbox": [ + 304, + 629, + 545, + 700 + ], + "type": "inline_equation", + "content": "D^{s - 1}" + }, + { + "bbox": [ + 304, + 629, + 545, + 700 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 629, + 545, + 700 + ], + "type": "inline_equation", + "content": "D^{s - 2}" + }, + { + "bbox": [ + 304, + 629, + 545, + 700 + ], + "type": "text", + "content": " as the input of " + }, + { + "bbox": [ + 304, + 629, + 545, + 700 + ], + "type": "inline_equation", + "content": "D^{s}" + }, + { + "bbox": [ + 304, + 629, + 545, + 700 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 317, + 701, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 701, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 317, + 701, + 545, + 713 + ], + "type": "text", + "content": "SQR Formulation. The Selective Query Recollection" + } + ] + } + ], + "index": 20 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "type": "text", + "content": "23760" + } + ] + } + ], + "index": 21 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 134, + 83 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 134, + 83 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 134, + 83 + ], + "type": "text", + "content": "can be formulated as" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 100, + 91, + 287, + 106 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 100, + 91, + 287, + 106 + ], + "spans": [ + { + "bbox": [ + 100, + 91, + 287, + 106 + ], + "type": "interline_equation", + "content": "C ^ {0} = \\left\\{q ^ {0} \\right\\} \\quad C ^ {1} = \\left\\{q ^ {0}, q ^ {0 - 1} \\right\\} \\tag {7}", + "image_path": "bbc76d36ca32fc3f88c6134c8b63d65aef77bd8584d00f3c9ec2441024d850da.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 57, + 119, + 287, + 149 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 57, + 119, + 287, + 149 + ], + "spans": [ + { + "bbox": [ + 57, + 119, + 287, + 149 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} C ^ {s} = \\{D ^ {s} (q) | q \\in C ^ {s - 1} \\} \\cup \\operatorname {s e l e c t} \\left(C ^ {s - 1}\\right) \\tag {8} \\\\ = \\{D ^ {s} (q) | q \\in C ^ {s - 1} \\} \\cup \\{D ^ {s - 1} (q) | q \\in C ^ {s - 2} \\} (9) \\\\ \\end{array}", + "image_path": "835b31108f708a9bafcf6f2ae47e6126072c35ac0f850d9cbb72123a7728aee6.jpg" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 156, + 287, + 262 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 156, + 287, + 262 + ], + "spans": [ + { + "bbox": [ + 46, + 156, + 287, + 262 + ], + "type": "text", + "content": "Such wise, Selective Query Recollection (Fig.4(c)) still satisfies our expectancy, and the number of supervision signals grows in a Fibonacci sequence (1,2,3,5,8,13). Compared to the Dense Recollection, to a great extent, SQR reduces the computing burden and we observe that SQR even outperforms the dense counterpart in terms of precision. This verifies our assumption that a " + }, + { + "bbox": [ + 46, + 156, + 287, + 262 + ], + "type": "inline_equation", + "content": "q" + }, + { + "bbox": [ + 46, + 156, + 287, + 262 + ], + "type": "text", + "content": " skipping too many stages might be noise for remote stages overshadowing its positive effects." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 263, + 287, + 360 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 263, + 287, + 360 + ], + "spans": [ + { + "bbox": [ + 46, + 263, + 287, + 360 + ], + "type": "text", + "content": "Recollection Starting Stage. Above we collect queries starting from stage 1. Instead, we can practically vary this starting stage, and this will further reduce the total queries in each collection and further reduce the computing burden. E.g., if starts SQR from stage 2, the Fibonacci sequence will start from stage 2 and result in " + }, + { + "bbox": [ + 46, + 263, + 287, + 360 + ], + "type": "inline_equation", + "content": "(1,1,2,3,5,8)" + }, + { + "bbox": [ + 46, + 263, + 287, + 360 + ], + "type": "text", + "content": "; if starts from stage 3, result in " + }, + { + "bbox": [ + 46, + 263, + 287, + 360 + ], + "type": "inline_equation", + "content": "(1,1,1,2,3,5)" + }, + { + "bbox": [ + 46, + 263, + 287, + 360 + ], + "type": "text", + "content": ". The starting stage is regarded as a hyper-parameter for SQR." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 369, + 128, + 383 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 369, + 128, + 383 + ], + "spans": [ + { + "bbox": [ + 47, + 369, + 128, + 383 + ], + "type": "text", + "content": "5. Experiments" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 389, + 287, + 509 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 389, + 287, + 509 + ], + "spans": [ + { + "bbox": [ + 46, + 389, + 287, + 509 + ], + "type": "text", + "content": "We conduct our experiments on the MS-COCO [19] detection track using the MMDetection [5] and Detrex [27] code-bases. All models are trained on train2017 split. Unless otherwise specified, models are trained and tested with image scale of 800 pixels, where AdamW optimizer with a standard 1x schedule (12 epochs) is utilized for training. For ablation study and analysis, Adamixer [9] with R50 [12] is chosen because of its good performance and fast convergence speed (42.5 AP with 1x schedule). We further apply SQR on other detectors to verify its effectiveness." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 515, + 141, + 529 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 515, + 141, + 529 + ], + "spans": [ + { + "bbox": [ + 47, + 515, + 141, + 529 + ], + "type": "text", + "content": "5.1. Ablation Study" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 533, + 287, + 617 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 533, + 287, + 617 + ], + "spans": [ + { + "bbox": [ + 46, + 533, + 287, + 617 + ], + "type": "text", + "content": "Baseline vs DQR vs SQR. Table.4 shows that both DQR and SQR improve the baseline by a large margin. DQR reaches 44.2 (+1.7 AP) while SQR reaches a slightly high result 44.4 (+1.9 AP). Note that SQR is much more efficient than DQR. As shown in Table.5, under the same training setting, SQR cuts down a great amount of training time of DQR and still achieves equal or higher AP." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 617, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 617, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 617, + 287, + 714 + ], + "type": "text", + "content": "Varying Starting Stage of SQR. We present how SQR performs when varying the starting stage in Table.5. The best performance is acquired when query recollection starts at stage 1 but with the most computational cost. We can see that starting at stage 2 performs similarly to starting at stage 1 while the computing burden is decently reduced. With recollection starting later, the benefits from SQR decrease as expected since the recollected queries from early" + } + ] + } + ], + "index": 9 + }, + { + "type": "table", + "bbox": [ + 309, + 71, + 544, + 131 + ], + "blocks": [ + { + "bbox": [ + 309, + 71, + 544, + 131 + ], + "lines": [ + { + "bbox": [ + 309, + 71, + 544, + 131 + ], + "spans": [ + { + "bbox": [ + 309, + 71, + 544, + 131 + ], + "type": "table", + "html": "
MethodsAP\\( AP_{50} \\)\\( AP_{75} \\)\\( AP_S \\)\\( AP_M \\)\\( AP_L \\)
Baseline42.561.545.624.645.159.2
DQR44.262.847.926.746.960.5
SQR44.463.247.825.747.460.2
", + "image_path": "dca4b4715ae58889cb0943496665e5675d6d8daa202b2369a8821ad02f4af3a5.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "table_body" + } + ], + "index": 10 + }, + { + "type": "table", + "bbox": [ + 315, + 163, + 538, + 283 + ], + "blocks": [ + { + "bbox": [ + 320, + 140, + 531, + 152 + ], + "lines": [ + { + "bbox": [ + 320, + 140, + 531, + 152 + ], + "spans": [ + { + "bbox": [ + 320, + 140, + 531, + 152 + ], + "type": "text", + "content": "Table 4. AP comparison among Baseline, DQR, and SQR" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 315, + 163, + 538, + 283 + ], + "lines": [ + { + "bbox": [ + 315, + 163, + 538, + 283 + ], + "spans": [ + { + "bbox": [ + 315, + 163, + 538, + 283 + ], + "type": "table", + "html": "
MethodStart StageTrain TimeAP\\( AP_{50} \\)
Baseline-1x(5hours)42.561.5
Baseline-2x42.561.3
Baseline-3x42.561.4
DQR-2.24x44.262.8
SQR11.57x44.463.2
SQR21.34x44.263.0
SQR31.18x43.862.3
SQR41.07x42.961.4
", + "image_path": "e8bae55a41f8c0dc60f6ba6c931ed1eaac40f04633272446fbdcb49d1677b3b3.jpg" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "table_body" + } + ], + "index": 12 + }, + { + "type": "table", + "bbox": [ + 315, + 327, + 537, + 405 + ], + "blocks": [ + { + "bbox": [ + 306, + 292, + 545, + 315 + ], + "lines": [ + { + "bbox": [ + 306, + 292, + 545, + 315 + ], + "spans": [ + { + "bbox": [ + 306, + 292, + 545, + 315 + ], + "type": "text", + "content": "Table 5. Further comparison among Baseline, DQR, and SQR with different starting stage in terms of training time and AP." + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 315, + 327, + 537, + 405 + ], + "lines": [ + { + "bbox": [ + 315, + 327, + 537, + 405 + ], + "spans": [ + { + "bbox": [ + 315, + 327, + 537, + 405 + ], + "type": "table", + "html": "
MethodTP ThresholdTP F RateFP E Rate
BaselineIoU>0.5028.6%50.8%
SQRIoU>0.5023.3 %47.3 %
BaselineIoU>0.7526.7%51.2%
SQRIoU>0.7521.1%47.0%
", + "image_path": "754cd665cee1b3940ce38e5eb791f7b60f07a8fa316a2fb61e020eb1fdc62f92.jpg" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "table_body" + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 413, + 545, + 436 + ], + "lines": [ + { + "bbox": [ + 306, + 413, + 545, + 436 + ], + "spans": [ + { + "bbox": [ + 306, + 413, + 545, + 436 + ], + "type": "text", + "content": "Table 6. Baseline vs. SQR on true-positive fading rate and false-positive exacerbation rate." + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 305, + 458, + 545, + 480 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 458, + 545, + 480 + ], + "spans": [ + { + "bbox": [ + 305, + 458, + 545, + 480 + ], + "type": "text", + "content": "stages become fewer and training emphasis gets gradually balanced." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 305, + 482, + 545, + 566 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 482, + 545, + 566 + ], + "spans": [ + { + "bbox": [ + 305, + 482, + 545, + 566 + ], + "type": "text", + "content": "TP Fading Rate And FP Exacerbation Rate. We present Table.6 to verify that TP fading rate and FP exacerbation rate decrease due to the training effect when applied SQR. Specifically, TP fading rate decreases from " + }, + { + "bbox": [ + 305, + 482, + 545, + 566 + ], + "type": "inline_equation", + "content": "28.6\\%" + }, + { + "bbox": [ + 305, + 482, + 545, + 566 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 305, + 482, + 545, + 566 + ], + "type": "inline_equation", + "content": "23.3\\%" + }, + { + "bbox": [ + 305, + 482, + 545, + 566 + ], + "type": "text", + "content": " and from " + }, + { + "bbox": [ + 305, + 482, + 545, + 566 + ], + "type": "inline_equation", + "content": "26.7\\%" + }, + { + "bbox": [ + 305, + 482, + 545, + 566 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 305, + 482, + 545, + 566 + ], + "type": "inline_equation", + "content": "21.1\\%" + }, + { + "bbox": [ + 305, + 482, + 545, + 566 + ], + "type": "text", + "content": " across two IoU thresholds. FP exacerbation rate downgrades from " + }, + { + "bbox": [ + 305, + 482, + 545, + 566 + ], + "type": "inline_equation", + "content": "50.8\\%" + }, + { + "bbox": [ + 305, + 482, + 545, + 566 + ], + "type": "text", + "content": " to 47.3 and " + }, + { + "bbox": [ + 305, + 482, + 545, + 566 + ], + "type": "inline_equation", + "content": "51.2\\%" + }, + { + "bbox": [ + 305, + 482, + 545, + 566 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 305, + 482, + 545, + 566 + ], + "type": "inline_equation", + "content": "47.0\\%" + }, + { + "bbox": [ + 305, + 482, + 545, + 566 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 306, + 574, + 545, + 588 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 574, + 545, + 588 + ], + "spans": [ + { + "bbox": [ + 306, + 574, + 545, + 588 + ], + "type": "text", + "content": "5.2. Relation with Increased Number of Supervision" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 594, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 594, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 594, + 545, + 713 + ], + "type": "text", + "content": "Some concurrent studies reveal that query-based detectors suffer from training inefficiency due to the one-to-one matching, and propose to add extra parallel query groups and match them with ground-truths in a one-to-many manner, such as Group DETR [6] and H-DETR [14]. We recognize them as increased number of supervision, i.e., each ground-truth is matched to multiple queries, and thus the number of supervision " + }, + { + "bbox": [ + 304, + 594, + 545, + 713 + ], + "type": "inline_equation", + "content": "(\\hat{q})" + }, + { + "bbox": [ + 304, + 594, + 545, + 713 + ], + "type": "text", + "content": " is greatly increased. However, simply adding more query groups is a sub-optimal solution according to our motivation, since these extra supervisions" + } + ] + } + ], + "index": 19 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "23761" + } + ] + } + ], + "index": 20 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 54, + 70, + 281, + 173 + ], + "blocks": [ + { + "bbox": [ + 54, + 70, + 281, + 173 + ], + "lines": [ + { + "bbox": [ + 54, + 70, + 281, + 173 + ], + "spans": [ + { + "bbox": [ + 54, + 70, + 281, + 173 + ], + "type": "table", + "html": "
Design#Supv / stage#SupvAP
I (Group DETR)3,3,3,3,3,31843.4
II4,4,4,3,2,11843.0
III1,2,3,4,4,41843.7
IV (SQR)1,1,2,3,5,82044.2
V (Group DETR)6,6,6,6,6,63643.6
VI (SQR)1,2,3,5,8,133244.4
", + "image_path": "1b0b5f45bd2ec37efe2ec863301c382143f735f0275d6ccf28b7d08a072ffa79.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 180, + 287, + 214 + ], + "lines": [ + { + "bbox": [ + 46, + 180, + 287, + 214 + ], + "spans": [ + { + "bbox": [ + 46, + 180, + 287, + 214 + ], + "type": "text", + "content": "Table 7. Results of the 6 designed training strategies on Adamixer to investigate the relation with number of supervision. The inference is untouched. #Supv denotes the number of supervision." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 233, + 286, + 257 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 233, + 286, + 257 + ], + "spans": [ + { + "bbox": [ + 46, + 233, + 286, + 257 + ], + "type": "text", + "content": "are given uniformly among stages. So we present 6 designs as training strategies for investigation." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 58, + 258, + 286, + 496 + ], + "type": "list", + "angle": 0, + "index": 9, + "blocks": [ + { + "bbox": [ + 58, + 258, + 286, + 316 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 258, + 286, + 316 + ], + "spans": [ + { + "bbox": [ + 58, + 258, + 286, + 316 + ], + "type": "text", + "content": "- Design I: Following Group DETR, 3 groups of queries are initialized and independently undergo the whole process of the decoder. The pathway is " + }, + { + "bbox": [ + 58, + 258, + 286, + 316 + ], + "type": "inline_equation", + "content": "3 \\times \\mathcal{PT}^{1-2-3-4-5-6}" + }, + { + "bbox": [ + 58, + 258, + 286, + 316 + ], + "type": "text", + "content": ", and number of supervision is 3 groups " + }, + { + "bbox": [ + 58, + 258, + 286, + 316 + ], + "type": "inline_equation", + "content": "\\times 6" + }, + { + "bbox": [ + 58, + 258, + 286, + 316 + ], + "type": "text", + "content": " stages " + }, + { + "bbox": [ + 58, + 258, + 286, + 316 + ], + "type": "inline_equation", + "content": "= 18" + }, + { + "bbox": [ + 58, + 258, + 286, + 316 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 58, + 318, + 286, + 365 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 318, + 286, + 365 + ], + "spans": [ + { + "bbox": [ + 58, + 318, + 286, + 365 + ], + "type": "text", + "content": "- Design II: 4 groups of queries are initialized but the pathways are " + }, + { + "bbox": [ + 58, + 318, + 286, + 365 + ], + "type": "inline_equation", + "content": "\\mathcal{PT}^{1-2-3-4-5-6}" + }, + { + "bbox": [ + 58, + 318, + 286, + 365 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 58, + 318, + 286, + 365 + ], + "type": "inline_equation", + "content": "\\mathcal{PT}^{1-2-3-4-5}" + }, + { + "bbox": [ + 58, + 318, + 286, + 365 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 58, + 318, + 286, + 365 + ], + "type": "inline_equation", + "content": "\\mathcal{PT}^{1-2-3-4}" + }, + { + "bbox": [ + 58, + 318, + 286, + 365 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 58, + 318, + 286, + 365 + ], + "type": "inline_equation", + "content": "\\mathcal{PT}^{1-2-3}" + }, + { + "bbox": [ + 58, + 318, + 286, + 365 + ], + "type": "text", + "content": ", so, with training emphasis on early stages, the number of supervision is " + }, + { + "bbox": [ + 58, + 318, + 286, + 365 + ], + "type": "inline_equation", + "content": "4 + 4 + 4 + 3 + 2 + 1 = 18" + }, + { + "bbox": [ + 58, + 318, + 286, + 365 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 58, + 365, + 286, + 424 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 365, + 286, + 424 + ], + "spans": [ + { + "bbox": [ + 58, + 365, + 286, + 424 + ], + "type": "text", + "content": "- Design III: Similar to Design II but not every initialized queries starts from stage 1. The pathways for the 4 groups are " + }, + { + "bbox": [ + 58, + 365, + 286, + 424 + ], + "type": "inline_equation", + "content": "\\mathcal{PT}^{1-2-3-4-5-6}" + }, + { + "bbox": [ + 58, + 365, + 286, + 424 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 58, + 365, + 286, + 424 + ], + "type": "inline_equation", + "content": "\\mathcal{PT}^{2-3-4-5-6}" + }, + { + "bbox": [ + 58, + 365, + 286, + 424 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 58, + 365, + 286, + 424 + ], + "type": "inline_equation", + "content": "\\mathcal{PT}^{3-4-5-6}" + }, + { + "bbox": [ + 58, + 365, + 286, + 424 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 58, + 365, + 286, + 424 + ], + "type": "inline_equation", + "content": "\\mathcal{PT}^{4-5-6}" + }, + { + "bbox": [ + 58, + 365, + 286, + 424 + ], + "type": "text", + "content": ", so, with training emphasis on later stages, the number of supervision is " + }, + { + "bbox": [ + 58, + 365, + 286, + 424 + ], + "type": "inline_equation", + "content": "1 + 2 + 3 + 4 + 4 + 4 = 18" + }, + { + "bbox": [ + 58, + 365, + 286, + 424 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 58, + 425, + 286, + 448 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 425, + 286, + 448 + ], + "spans": [ + { + "bbox": [ + 58, + 425, + 286, + 448 + ], + "type": "text", + "content": "- Design IV: " + }, + { + "bbox": [ + 58, + 425, + 286, + 448 + ], + "type": "inline_equation", + "content": "SQR^{starting stage=2}" + }, + { + "bbox": [ + 58, + 425, + 286, + 448 + ], + "type": "text", + "content": ", the number of supervision is " + }, + { + "bbox": [ + 58, + 425, + 286, + 448 + ], + "type": "inline_equation", + "content": "1 + 1 + 2 + 3 + 5 + 8 = 20" + }, + { + "bbox": [ + 58, + 425, + 286, + 448 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 58, + 449, + 286, + 472 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 449, + 286, + 472 + ], + "spans": [ + { + "bbox": [ + 58, + 449, + 286, + 472 + ], + "type": "text", + "content": "- Design V: Same as Design I but with 6 groups. The number of supervision is 6 groups " + }, + { + "bbox": [ + 58, + 449, + 286, + 472 + ], + "type": "inline_equation", + "content": "\\times 6" + }, + { + "bbox": [ + 58, + 449, + 286, + 472 + ], + "type": "text", + "content": " stages " + }, + { + "bbox": [ + 58, + 449, + 286, + 472 + ], + "type": "inline_equation", + "content": "= 36" + }, + { + "bbox": [ + 58, + 449, + 286, + 472 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 58, + 473, + 286, + 496 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 473, + 286, + 496 + ], + "spans": [ + { + "bbox": [ + 58, + 473, + 286, + 496 + ], + "type": "text", + "content": "- Design VI: " + }, + { + "bbox": [ + 58, + 473, + 286, + 496 + ], + "type": "inline_equation", + "content": "SQR^{starting stage=1}" + }, + { + "bbox": [ + 58, + 473, + 286, + 496 + ], + "type": "text", + "content": ", the number of supervision is " + }, + { + "bbox": [ + 58, + 473, + 286, + 496 + ], + "type": "inline_equation", + "content": "1 + 2 + 3 + 5 + 8 + 13 = 32" + }, + { + "bbox": [ + 58, + 473, + 286, + 496 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 8 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 46, + 497, + 286, + 593 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 497, + 286, + 593 + ], + "spans": [ + { + "bbox": [ + 46, + 497, + 286, + 593 + ], + "type": "text", + "content": "Table.7 summarizes the results. From the controlled experiments with Design I, II, III, we conclude training with emphasis on late stages is the best option. Design IV and VI are SQR with different starting stages. We show that with similar or even fewer supervisions, SQR outperforms other designs by a large margin. These comparisons verify our motivation and prove that the enhancement from SQR is not simply from the increased number of supervisions." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 47, + 599, + 261, + 612 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 599, + 261, + 612 + ], + "spans": [ + { + "bbox": [ + 47, + 599, + 261, + 612 + ], + "type": "text", + "content": "5.3. Training Emphasis via Re-weighted Loss" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 46, + 618, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 618, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 618, + 286, + 713 + ], + "type": "text", + "content": "Although the training emphasis contributes to the success of SQR, the access to the early intermediate queries is irreplaceable. We attempt another way to place training emphasis without query recollection, i.e. re-weighting the losses of six decoding stages following the Fibonacci sequence (1,2,3,5,8,13). The AP slightly degrades by (-0.6) compared to the baseline, indicating access to the intermediate queries is necessary for emphasized supervision." + } + ] + } + ], + "index": 12 + }, + { + "type": "image", + "bbox": [ + 307, + 71, + 544, + 156 + ], + "blocks": [ + { + "bbox": [ + 307, + 71, + 544, + 156 + ], + "lines": [ + { + "bbox": [ + 307, + 71, + 544, + 156 + ], + "spans": [ + { + "bbox": [ + 307, + 71, + 544, + 156 + ], + "type": "image", + "image_path": "6c824e7a7b40eb41a84f17e546653987396226f26c205f741bc61fda4ab4801e.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 315, + 167, + 537, + 178 + ], + "lines": [ + { + "bbox": [ + 315, + 167, + 537, + 178 + ], + "spans": [ + { + "bbox": [ + 315, + 167, + 537, + 178 + ], + "type": "text", + "content": "Figure 5. Equal training-time comparison: Baseline vs. SQR" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_caption" + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 199, + 473, + 212 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 199, + 473, + 212 + ], + "spans": [ + { + "bbox": [ + 306, + 199, + 473, + 212 + ], + "type": "text", + "content": "5.4. Relation with Stochastic Depth" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 217, + 545, + 434 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 217, + 545, + 434 + ], + "spans": [ + { + "bbox": [ + 304, + 217, + 545, + 434 + ], + "type": "text", + "content": "Stochastic Depth (SD) [13] is a training strategy for very deep network where it randomly removes a fraction of layers independently for each mini-batch, so the depth of pathway varies during training just like SQR. However, SD is of vital inefficiency, because an image has to first pass through a backbone and then be processed by a varying-depth pathway, but for SQR, an image that passes through the backbone can be processed by multiple varying-depth pathways at the same time. To verify this point, we apply SD on the vanilla decoder: During training, for each mini-batch we randomly remove decoding stages following a series of predefined probabilities. From stage " + }, + { + "bbox": [ + 304, + 217, + 545, + 434 + ], + "type": "inline_equation", + "content": "1 \\sim 6" + }, + { + "bbox": [ + 304, + 217, + 545, + 434 + ], + "type": "text", + "content": ", the removal probability " + }, + { + "bbox": [ + 304, + 217, + 545, + 434 + ], + "type": "inline_equation", + "content": "\\mathbb{R}" + }, + { + "bbox": [ + 304, + 217, + 545, + 434 + ], + "type": "text", + "content": " could be either a constant (0.1), increasing (0.0, 0.1,..., 0.5), or decreasing (0.5, 0.4,..., 0.0). During testing, SD requires the outputs of each decoding stage to be calibrated by the expected times the stage participates in training, so we multiply (1-" + }, + { + "bbox": [ + 304, + 217, + 545, + 434 + ], + "type": "inline_equation", + "content": "\\mathbb{R}" + }, + { + "bbox": [ + 304, + 217, + 545, + 434 + ], + "type": "text", + "content": ") with the residual term in Equ.1. As a result, SD (40.7 mAP) is not comparable to SQR." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 441, + 416, + 453 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 441, + 416, + 453 + ], + "spans": [ + { + "bbox": [ + 306, + 441, + 416, + 453 + ], + "type": "text", + "content": "5.5. Training efficiency" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 459, + 545, + 567 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 459, + 545, + 567 + ], + "spans": [ + { + "bbox": [ + 304, + 459, + 545, + 567 + ], + "type": "text", + "content": "SQR leads to an extra computing burden compared to the baseline since the number of " + }, + { + "bbox": [ + 304, + 459, + 545, + 567 + ], + "type": "inline_equation", + "content": "\\hat{q}" + }, + { + "bbox": [ + 304, + 459, + 545, + 567 + ], + "type": "text", + "content": " grows. In Table.5, SQR increases training time of Adamixer-R50 by " + }, + { + "bbox": [ + 304, + 459, + 545, + 567 + ], + "type": "inline_equation", + "content": "0.35\\sim 2.85" + }, + { + "bbox": [ + 304, + 459, + 545, + 567 + ], + "type": "text", + "content": " hours " + }, + { + "bbox": [ + 304, + 459, + 545, + 567 + ], + "type": "inline_equation", + "content": "(+0.07\\% \\sim 57\\%)" + }, + { + "bbox": [ + 304, + 459, + 545, + 567 + ], + "type": "text", + "content": ". In practice, the effects on different models/implementations/platforms vary. For instance, ResNet-50 is a light-weighted backbone, so the effects of applying SQR are relatively high, while with heavier backbones like ResNet-101 and Swin Transformer [22], the training time is less impacted " + }, + { + "bbox": [ + 304, + 459, + 545, + 567 + ], + "type": "inline_equation", + "content": "(+10\\%)" + }, + { + "bbox": [ + 304, + 459, + 545, + 567 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 567, + 545, + 651 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 567, + 545, + 651 + ], + "spans": [ + { + "bbox": [ + 304, + 567, + 545, + 651 + ], + "type": "text", + "content": "For comparison under equal training time, we train the baseline Adamixer with extra epochs " + }, + { + "bbox": [ + 304, + 567, + 545, + 651 + ], + "type": "inline_equation", + "content": "(+200\\%" + }, + { + "bbox": [ + 304, + 567, + 545, + 651 + ], + "type": "text", + "content": " epochs) and baseline Deformable DETR with " + }, + { + "bbox": [ + 304, + 567, + 545, + 651 + ], + "type": "inline_equation", + "content": "(+50\\%" + }, + { + "bbox": [ + 304, + 567, + 545, + 651 + ], + "type": "text", + "content": " epochs). Both models' performances (see Fig.5) saturate early and there is no significant improvement over the extended training time, indicating that the benefit of SQR cannot be compensated by including more training iterations." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 306, + 658, + 485, + 671 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 658, + 485, + 671 + ], + "spans": [ + { + "bbox": [ + 306, + 658, + 485, + 671 + ], + "type": "text", + "content": "5.6. Comparison with State-of-the-art" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "text", + "content": "We conduct experiments on recent query-based detectors with different training settings and various backbones, with and without SQR. We primarily follow the original training" + } + ] + } + ], + "index": 21 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "23762" + } + ] + } + ], + "index": 22 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 63, + 69, + 531, + 487 + ], + "blocks": [ + { + "bbox": [ + 63, + 69, + 531, + 487 + ], + "lines": [ + { + "bbox": [ + 63, + 69, + 531, + 487 + ], + "spans": [ + { + "bbox": [ + 63, + 69, + 531, + 487 + ], + "type": "table", + "html": "
Modelw/ SQR#query#epochsCOCO 2017 validation split
AP\\(AP_{50}\\)\\(AP_{75}\\)\\(AP_S\\)\\(AP_M\\)\\(AP_L\\)
DETR-R50 [3]10050042.062.444.220.545.861.1
Conditional DETR-R50 [23]3005040.961.843.320.844.660.2
Conditional DETR-R101 [23]3005042.863.746.021.746.660.9
Anchor-DETR-R50 [31]3005042.163.144.922.346.260.0
Anchor-DETR-R101 [31]3005043.564.346.623.247.761.4
SAM-DETR-R50 [34]3005039.861.841.620.543.459.6
*SMCA-DETR-R50 [8]3005043.763.647.224.247.060.4
*SMCA-DETR-R50 [8]30010845.665.549.125.949.362.6
*DN-DAB-DETR-R50 [17]3005044.164.446.722.948.063.4
*DN-DAB-DETR-R101 [17]3005045.265.548.324.149.165.1
*DAB-DETR-R50 [20]3005042.263.144.721.545.760.3
*SQR-DAB-DETR-R50✓3005044.5 (+2.3)64.447.524.848.661.7
*DAB-DETR-SwinB [20]3005049.071.053.029.653.868.3
*SQR-DAB-DETR-SwinB✓3005051.6 (+2.6)72.555.932.056.871.0
*Deformable DETR-R50 [38]3001237.255.240.420.640.250.2
*SQR-Deformable DETR-R50✓3001239.9 (+2.7)58.443.723.843.253.3
*Deformable DETR-R50 [38]3005044.563.248.928.047.858.8
*SQR-Deformable DETR-R50✓3005045.9 (+1.4)64.750.227.749.260.5
Adamixer-R50 [9]1001242.561.545.624.645.159.2
SQR-Adamixer-R50✓1001244.4 (+1.9)63.247.825.747.460.2
†Adamixer-R50 [9]1001242.561.545.824.445.258.7
†SQR-Adamixer-R50✓1001245.3 (+2.8)63.849.026.848.162.2
*†Adamixer-R501003645.163.948.928.347.860.6
*†SQR-Adamixer-R50✓1003646.7 (+1.6)65.250.329.449.662.1
*†Adamixer-R503003646.665.550.629.349.362.3
*†SQR-Adamixer-R50✓3003648.9 (+2.3)67.553.232.051.863.7
*†Adamixer-R101 [9]1003645.764.749.627.849.161.2
*†SQR-Adamixer-R101✓1003647.3 (+1.6)66.051.330.150.762.2
*†Adamixer-R101 [9]3003647.666.751.829.550.563.3
*†SQR-Adamixer-R101✓3003649.8 (+2.2)68.854.032.053.465.1
", + "image_path": "7603bba8ef33dcab95d8eb94af30f40425a58be2b09bc52cae6a9f75851a9c78.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + }, + { + "bbox": [ + 49, + 495, + 544, + 517 + ], + "lines": [ + { + "bbox": [ + 49, + 495, + 544, + 517 + ], + "spans": [ + { + "bbox": [ + 49, + 495, + 544, + 517 + ], + "type": "text", + "content": "Table 8. Comparison results with various query-based detectors on COCO 2017 val. #query: the number of queries used during inference. * indicates models trained with multi-scale augmentation, † marks models with 7 decoder stages." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_footnote" + } + ], + "index": 0 + }, + { + "bbox": [ + 49, + 539, + 286, + 598 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 539, + 286, + 598 + ], + "spans": [ + { + "bbox": [ + 49, + 539, + 286, + 598 + ], + "type": "text", + "content": "setting of our baselines, where training schedules consists of standard 12, 36, and 50 epochs; the number of queries is chosen between 100 and 300; multi-scale training is applied to 36e and 50e schedules as the shorter side of images range " + }, + { + "bbox": [ + 49, + 539, + 286, + 598 + ], + "type": "inline_equation", + "content": "480 \\sim 800" + }, + { + "bbox": [ + 49, + 539, + 286, + 598 + ], + "type": "text", + "content": ". The training is conducted on 8x Nvidia A100." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 49, + 605, + 286, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 605, + 286, + 712 + ], + "spans": [ + { + "bbox": [ + 49, + 605, + 286, + 712 + ], + "type": "text", + "content": "The result is summarized in Fig.1 and Table 8. SQR consistently brings AP improvements to Adamixer, DAB-DETR and Deformable-DETR at the same inference speed. Concretely, on DAB-DETR, SQR brings " + }, + { + "bbox": [ + 49, + 605, + 286, + 712 + ], + "type": "inline_equation", + "content": "+2.3" + }, + { + "bbox": [ + 49, + 605, + 286, + 712 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 49, + 605, + 286, + 712 + ], + "type": "inline_equation", + "content": "+2.6" + }, + { + "bbox": [ + 49, + 605, + 286, + 712 + ], + "type": "text", + "content": " AP with R50 and SwinB, respectively; on Deformable DETR, SQR boosts it by 2.7 AP under 12e and by 1.4 AP under 50e; on Adamixer with R50, SQR achieves " + }, + { + "bbox": [ + 49, + 605, + 286, + 712 + ], + "type": "inline_equation", + "content": "+1.9" + }, + { + "bbox": [ + 49, + 605, + 286, + 712 + ], + "type": "text", + "content": " AP under the basic setting (100 queries, 12e). With an additional stage, the gap between w/ and w/o SQR is enlarged " + }, + { + "bbox": [ + 49, + 605, + 286, + 712 + ], + "type": "inline_equation", + "content": "+2.8" + }, + { + "bbox": [ + 49, + 605, + 286, + 712 + ], + "type": "text", + "content": " AP." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 308, + 539, + 536, + 551 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 539, + 536, + 551 + ], + "spans": [ + { + "bbox": [ + 308, + 539, + 536, + 551 + ], + "type": "text", + "content": "SQR consistently improves these models by " + }, + { + "bbox": [ + 308, + 539, + 536, + 551 + ], + "type": "inline_equation", + "content": "1.4\\sim 2.8" + }, + { + "bbox": [ + 308, + 539, + 536, + 551 + ], + "type": "text", + "content": " AP." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 308, + 571, + 377, + 582 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 571, + 377, + 582 + ], + "spans": [ + { + "bbox": [ + 308, + 571, + 377, + 582 + ], + "type": "text", + "content": "6. Conclusion" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 308, + 594, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 594, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 308, + 594, + 545, + 712 + ], + "type": "text", + "content": "In this work, we investigate the phenomenon where the optimal detections of query-based object detectors are not always from the last decoding stage, but can sometimes come from an intermediate decoding stage. We first recognize two limitations causing the issue, i.e. lack of training emphasis and cascading errors from query sequence. The problem is addressed by Selective Query Recollection (SQR) as a simple and effective training strategy. Across various training settings, SQR boosts Adamixer, DABDETR, and Deformable-DETR by a large margin." + } + ] + } + ], + "index": 6 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 750, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 750, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 750, + 317, + 757 + ], + "type": "text", + "content": "23763" + } + ] + } + ], + "index": 7 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 287, + 712 + ], + "type": "list", + "angle": 0, + "index": 14, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 112 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 112 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 112 + ], + "type": "text", + "content": "[1] Jimmy Ba, Jamie Ryan Kiros, and Geoffrey E. 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Bridging the gap between anchor-based and anchor-free detection via adaptive training sample selection. 2020 IEEE/CVF Conference on Computer Vision and Pattern Recognition (CVPR), pages 9756-9765, 2020. 1" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 48, + 521, + 287, + 552 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 521, + 287, + 552 + ], + "spans": [ + { + "bbox": [ + 48, + 521, + 287, + 552 + ], + "type": "text", + "content": "[37] Chenchen Zhu, Fangyi Chen, Zhiqiang Shen, and Marios Savvides. Soft anchor-point object detection. In ECCV, 2020. 1, 3" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 48, + 554, + 287, + 597 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 554, + 287, + 597 + ], + "spans": [ + { + "bbox": [ + 48, + 554, + 287, + 597 + ], + "type": "text", + "content": "[38] Xizhou Zhu, Weijie Su, Lewei Lu, Bin Li, Xiaogang Wang, and Jifeng Dai. Deformable detr: Deformable transformers for end-to-end object detection. ArXiv, abs/2010.04159, 2021. 1, 3, 8" + } + ] + } + ], + "index": 10 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 749, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 749, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 749, + 317, + 757 + ], + "type": "text", + "content": "23765" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 9 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Enhancing Deformable Local Features by Jointly Learning To Detect and Describe Keypoints/16ef7ac5-e127-4979-a2b4-14363013dd09_content_list.json b/2023/Enhancing Deformable Local Features by Jointly Learning To Detect and Describe Keypoints/16ef7ac5-e127-4979-a2b4-14363013dd09_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..b941ca140b7df27c10835fdd43fdf151ab6556cb --- /dev/null +++ b/2023/Enhancing Deformable Local Features by Jointly Learning To Detect and Describe Keypoints/16ef7ac5-e127-4979-a2b4-14363013dd09_content_list.json @@ -0,0 +1,1286 @@ +[ + { + "type": "text", + "text": "Enhancing Deformable Local Features by Jointly Learning to Detect and Describe Keypoints", + "text_level": 1, + "bbox": [ + 187, + 130, + 782, + 176 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Guilherme Potje1 \nRenato Martins3,4", + "bbox": [ + 264, + 202, + 439, + 239 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Felipe Cadar1 André Araujo2 Erickson R. Nascimento1,5", + "bbox": [ + 446, + 203, + 720, + 239 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1Universidade Federal de Minas Gerais 2Google Research", + "bbox": [ + 261, + 250, + 730, + 267 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "3Université de Bourgogne 4Université de Lorraine, LORIA, Inria 5Microsoft", + "bbox": [ + 184, + 267, + 805, + 284 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "{guipotje, cadar, erickson}@dcc.ufgm.br, renato.martins@u-bourgogne.fr, andrearaujo@google.com", + "bbox": [ + 86, + 287, + 898, + 303 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 337, + 313, + 353 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Local feature extraction is a standard approach in computer vision for tackling important tasks such as image matching and retrieval. The core assumption of most methods is that images undergo affine transformations, disregarding more complicated effects such as non-rigid deformations. Furthermore, incipient works tailored for non-rigid correspondence still rely on keypoint detectors designed for rigid transformations, hindering performance due to the limitations of the detector. We propose DALF (Deformation-Aware Local Features), a novel deformation-aware network for jointly detecting and describing keypoints, to handle the challenging problem of matching deformable surfaces. All network components work cooperatively through a feature fusion approach that enforces the descriptors' distinctiveness and invariance. Experiments using real deforming objects showcase the superiority of our method, where it delivers $8\\%$ improvement in matching scores compared to the previous best results. Our approach also enhances the performance of two real-world applications: deformable object retrieval and non-rigid 3D surface registration. Code for training, inference, and applications are publicly available at verlab.dcc.ufmg.br/descriptors/dalf Cvpr23.", + "bbox": [ + 75, + 371, + 473, + 704 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 737, + 209, + 752 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Finding pixel-wise correspondences between images depicting the same surface is a long-standing problem in computer vision. Besides varying illumination, viewpoint, and distance to the object of interest, real-world scenes impose additional challenges. The vast majority of the correspondence algorithms in the literature assume that our world is rigid, but this assumption is far from the truth. It is noticeable that the community invests significant efforts into novel architectures and training strategies to improve image match-", + "bbox": [ + 75, + 763, + 470, + 901 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/b6841146961a8b91c8f9160bb4b64e4f1303c9e444d30c6903920336c0264323.jpg", + "image_caption": [ + "Figure 1. Image matching under deformations. We propose DALF, a deformation-aware keypoint detector and descriptor for matching deformable surfaces. DALF (top) enables local feature matching across deformable scenes with improved matching scores (MS) compared to state-of-the-art, as illustrated with DISK [37]. Green lines show correct matches, and red markers, the mismatches." + ], + "image_footnote": [], + "bbox": [ + 509, + 335, + 883, + 477 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "ing for rigid scenes [6, 19, 26, 34, 37, 42], but disregards the fact that many objects in the real world can deform in more complex ways than an affine transformation.", + "bbox": [ + 496, + 598, + 892, + 642 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Many applications in industry, medicine, and agriculture require tracking, retrieval, and monitoring of arbitrary deformable objects and surfaces, where a general-purpose matching algorithm is needed to achieve accurate results. Since the performance of standard affine local features significantly decreases for scenarios such as strong illumination changes and deformations, a few works considering a wider class of transformations have been proposed [24, 25, 30]. However, all the deformation-aware methods neglect the keypoint detection phase, limiting their applicability in challenging deformations. Although the problems of keypoint detection and description can be treated separately, recent works that jointly perform detection and description of features [4, 26] indicate an entanglement of the two tasks since the keypoint detection can impact the performance of the descriptor. The descriptor for its turn can be used to determine reliable points optimized for specific goals. In this work,", + "bbox": [ + 496, + 643, + 895, + 901 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 810, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "1306", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "we propose a new method for jointly learning keypoints and descriptors robust to deformations, viewpoint, and illumination changes. We show that the detection phase is critical to obtain robust matching under deformations. Fig. 1 depicts an image pair with challenging deformations, where our method can extract reliable keypoints and match them correctly, significantly increasing matching scores compared to the recent state-of-the-art approach DISK [37].", + "bbox": [ + 75, + 90, + 470, + 212 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Contributions. (1) Our first contribution is a new end-to-end method called DALF (Deformation-Aware Local Features), which jointly learns to detect keypoints and extract descriptors with a mutual assistance strategy to handle significant non-rigid deformations. Our method boosts the state-of-the-art in this type of feature matching by $8\\%$ using only synthetic warps as supervision, showing strong generalization capabilities. We leverage a reinforcement learning algorithm for unified training, combined with spatial transformers that capture deformations by learning context priors affecting the image; (2) Second, we introduce a feature fusion approach, a major difference from previous methods that allows the model to tackle challenging deformations with complementary features (with distinctiveness and invariance properties) obtained from both the backbone and the spatial transformer module. This approach is shown beneficial with substantial performance improvements compared to the non-fused features; (3) Finally, we demonstrate state-of-the-art results in non-rigid local feature applications for deformable object retrieval and non-rigid 3D surface registration. We also will make the code and both applications publicly available to the community.", + "bbox": [ + 75, + 231, + 473, + 564 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related work", + "text_level": 1, + "bbox": [ + 76, + 577, + 215, + 592 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Keypoint detection. Traditional image keypoint detection methods seek to extract repeatable regions in images, i.e., localized points that are stable under different viewing conditions. The classic Harris detector [10] employs image derivatives that are used to compute cornerness scores, while one the most used handcrafted detectors SIFT [14], for instance, detects blobs using the Difference of Gaussians. Key.Net [13] showed that it is possible to improve keypoint detection by combining handcrafted filters and learned filters. A recent trend for learning keypoint detection is to couple description and detection in the same pipeline [7,26,34,42], since it is advantageous performance-wise to solve both tasks simultaneously in terms of computation and matching accuracy. In the same direction, our proposed method has a backbone that computes both keypoints and descriptors but at the same time employs a deformation-aware module.", + "bbox": [ + 75, + 602, + 470, + 844 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Description of local patches. Until recently, detection and description were treated separately. While some works focused on both problems, such as the seminal works of", + "bbox": [ + 75, + 854, + 470, + 900 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "SIFT [14] and ORB [28], the detection and description were decoupled. SIFT and ORB descriptors employ a handcrafted gradient analysis to extract descriptors with scale and rotation invariance. Recent description approaches based on CNNs [8, 15, 19, 34, 39] consume a local patch assuming a pre-defined keypoint detector. These methods achieved state-of-the-art performance using SIFT keypoints in the image matching benchmark [12]. The networks are trained using metric learning [9, 39]. As patch-based methods rely on a pre-defined keypoint detector that may produce keypoints in unreliable or ambiguous regions, noise can be easily introduced because detection and description steps are decoupled. Unlike patch-based methods, our network is trained to produce reliable descriptions and keypoints optimized for non-rigid correspondence. Our description is also enhanced with a fusion strategy that combines complementary features into a single learned feature representation.", + "bbox": [ + 496, + 90, + 893, + 349 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Joint detection and description. DELF [22] and DELG [4] works demonstrated that coupling the detection and description phases using an attentive mechanism for keypoint selection based on higher-level image semantics can substantially improve retrieval performance. Local feature extraction has been shifting towards learning both detection and description of local features jointly [7, 16, 26, 37, 42]. Most methods follow a similar architecture, adopting a fully convolutional network (FCN) layout to produce a dense feature map, where most of the differences between the methods reside in the training scheme and loss design. The most recent describe-and-detect approaches are currently state-of-the-art on standard benchmarks [2, 12]. Differently from existing methods, we design the architecture and training to explicitly handle deformations in a coupled detection and description phase, devising a carefully tailored warper network.", + "bbox": [ + 496, + 359, + 895, + 602 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Deformation-aware methods. One of the first proposed image descriptors designed for deformable surfaces is DaLI [30]. DaLI interprets image patches as a local 3D surface, and computes the Scale-Invariant Heat Kernel Signatures [3] of the 3D surface to encode features robust to non-rigid deformations and illumination changes. Despite achieving improved matching performance compared to contemporary works, DaLI suffers from high computational and storage requirements. Similar to DaLI, GeoBit [21] and GeoPatch [24] descriptors brought ideas from computational geometry to computer vision, leveraging RGB-D images to extract visual features that are geodesic-aware. However, these geodesic-aware methods require RGB-D images and are sensitive to noise, significantly restricting their applicability. To remove the need for depth images for estimating geodesic patches, the DEAL descriptor [25] implicitly handles deformations from monocular images through a non-rigid warper module. The main shortcoming of DEAL is its dependency on existing keypoint detectors, which compro", + "bbox": [ + 496, + 613, + 895, + 902 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "1307", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/abc7b277c648f4ab46ba5b0438fefe264fd59e96022a6a0cd38cdad62e9d3d98.jpg", + "image_caption": [ + "Figure 2. DALF architecture. Our architecture jointly optimizes non-rigid keypoint detection and description, and explicitly models local deformations for descriptor extraction during training. An hourglass CNN computes a dense heat map providing specialized keypoints that are used by the Warner Net to extract deformation-aware matches. A feature fusion layer balances the trade-off between invariance and distinctiveness in the final descriptors." + ], + "image_footnote": [], + "bbox": [ + 89, + 90, + 457, + 343 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "mises the descriptor performance due to the lack of equivariance on keypoints locations from most existing detectors in the presence of deformation changes. In contrast, our method learns detection and description in the same framework, achieving significant performance gains.", + "bbox": [ + 75, + 453, + 470, + 530 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Methodology", + "text_level": 1, + "bbox": [ + 76, + 541, + 212, + 559 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "DALF jointly learns to detect and describe points robust to non-rigid deformations, in addition to perspective and illumination changes. Both detector and descriptor are trained with a cooperative scheme aiming at the invariance of feature representations. Specifically, the keypoint detector is trained using policy gradient, seeking to increase the probability of detections that are both repeatable and reliable; Concurrently, the descriptor extractor learns to undeform and extract discriminative and invariant features from local regions. The model is only trained on synthetic warps, i.e., it does not require expensive human annotation nor pseudo-ground-truth that may contain errors and bias, such as the output of an SfM pipeline that is used in several works [7, 16, 26, 29, 37]. Fig. 2 outlines the proposed method.", + "bbox": [ + 75, + 566, + 470, + 779 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1.Keypoint detector", + "text_level": 1, + "bbox": [ + 76, + 786, + 250, + 803 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The keypoint detection architecture uses a backbone hourglass CNN network $\\mathbf{f}(\\cdot)$ , similar to a U-net [27]. This network enables computing a keypoint heat map in the original image resolution efficiently, while also producing mid-level feature representations that are useful to describe the keypoints. We employ three downsampling blocks for the en", + "bbox": [ + 75, + 809, + 472, + 902 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "coder, and three upsampling blocks for the decoder, with skip connections, each having two convolutional layers composed of a 2D convolution followed by ReLU and batch normalization. Let $I \\in \\mathbb{R}^{h \\times w \\times c}$ be the input image of size $h \\times w$ and $c$ channels, $\\mathbf{f}(I)$ outputs two feature maps: mid-level representations $\\mathbf{X} \\in \\mathbb{R}^{h/8 \\times w/8 \\times d}$ and detection heatmap $\\mathbf{H} \\in \\mathbb{R}^{h \\times w}$ , where $d$ is the number of features.", + "bbox": [ + 496, + 90, + 893, + 196 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Keypoint detection in deforming images. An effective detector must output heatmaps $\\mathbf{H} \\in \\mathbb{R}^{h \\times w}$ with high responses in regions that can be matched well in non-rigid scenes containing view and illumination changes. Thus, during the training of the detection branch, we optimize $\\mathbf{H}$ using a strategy similar to DISK [37], but applying only the probabilistic framework to learn the detection heatmap. A key difference compared to DISK is that we enforce the reliability of the detected keypoints by penalizing wrong matches even if the keypoints are repeatable. A probabilistic approach has several advantages as dealing with the inhering discreteness of sparse keypoint detection, and a simpler and more intuitive loss can be used for better convergence and regularization of the detection heatmap, in contrast to works that require elaborated handcrafted losses [7, 16, 26].", + "bbox": [ + 496, + 219, + 893, + 445 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We seek to obtain high responses in confident regions not only for detection but also matching. To solve this problem with policy gradient, we divide the heatmap into a 2D grid of cells (Detection Heatmap in Fig. 3) and consider a set of actions that the network agent can make to select keypoints. Each cell $\\mathbf{c}_i$ has $m \\times n$ pixels, where the network can learn the probability of detecting a keypoint within each cell. Given an image pair $(A, B)$ of the same scene under different photometric and geometric transformations, and the ground-truth flow-field relating the two images, for each cell $\\mathbf{c}_i \\in \\mathbf{H}$ , we consider a probability distribution over the cell $\\mathbf{c} \\in \\mathbb{R}^{m \\times n}$ . Each logit value within the cell has a probability of being a keypoint. The probability mass function $\\mathbf{p}_{\\mathbf{c}_i}$ over the cell $\\mathbf{c}_i$ is computed by applying the Softmax function.", + "bbox": [ + 496, + 446, + 893, + 657 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Therefore, to train the detection branch, we employ the Reinforce algorithm [32]. During the forward pass of the network, we randomly sample an individual keypoint within each cell $\\mathbf{c}_i$ according to the probability mass function $\\mathbf{p}_{\\mathbf{c}_i}$ alongside the keypoint's spatial coordinates, its probability $p_s^i$ and its logit $l_s^i$ . Note that each cell can have exactly one keypoint; however, in practice, it is common that low texture and ambiguous regions result in low-quality keypoints that cannot be reliably matched or detected in other images. For that reason, we accept a keypoint proposal from a cell with probability $\\sigma (l_s^i)$ , where $\\sigma$ is the sigmoid activation. This way, the network can learn to filter out unreliable keypoint proposals during training. The final probabilities of detection for the image $I$ is given by the set $P_{I} = \\{\\sigma (l_{s}^{i})\\cdot p_{s}^{i}\\},\\forall \\mathbf{c}_{i}\\in$ $\\mathbf{H}$ , such that $\\sigma (l_s^i) > 0.5$ (we only sampled keypoints that has positive values in the heatmap). Since we want the", + "bbox": [ + 496, + 659, + 895, + 901 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "1308", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/e6015f497e529bea26a8ce4f3baf142570cdc6f439ebddab519c34de26c13a06.jpg", + "image_caption": [ + "Figure 3. Training strategy to learn to detect and describe keypoints aware of deformations. DALF network is used to produce a detection heatmap and a set of local features for each image. In the detector path, the heatmaps are optimized via the REINFORCE algorithm considering keypoint repeatability under deformations. In the descriptor path, feature space is learned via the hard triplet loss. A siamese setup using image pairs is employed to optimize the network. Notice that we penalize keypoints that cannot be described accurately during the second training stage; thus, the keypoints and combined descriptors are optimized jointly to be robust to deformations." + ], + "image_footnote": [], + "bbox": [ + 117, + 87, + 854, + 253 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "keypoints to be repeatable, we reward points that can be detected in both images $A$ and $B$ . Thus, given the pixel coordinate $\\mathbf{p}_A^j \\in \\mathbb{R}^2$ of detected point $j$ on image $A$ , we define the reward function $R(.)$ as follows:", + "bbox": [ + 75, + 345, + 470, + 407 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nR \\left(\\mathbf {p} _ {A} ^ {j}\\right) = \\left\\{ \\begin{array}{l l} 1 & \\text {i f} \\exists \\mathbf {p} _ {B} ^ {(.)} \\text {s . t .} \\| T \\left(\\mathbf {p} _ {A} ^ {j}\\right) - \\mathbf {p} _ {B} ^ {(.)} \\| < \\tau , \\\\ 0 & \\text {o t h e r w i s e}, \\end{array} \\right. \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 98, + 416, + 470, + 455 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $T(.)$ transforms pixels coordinates of image $A$ to image $B$ according to the ground-truth flow-field, and $\\tau$ is a pixel threshold to determine if the detected keypoint in $A$ has a correspondence in image $B$ .", + "bbox": [ + 75, + 465, + 468, + 526 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Once we have the set of probabilities $P_A$ and $P_B$ , we obtain the gradient of the parameter vector $\\theta$ with respect to the expected rewards over all pairwise keypoints $\\mathcal{K} = P_A \\times P_B$ where $\\times$ denotes the cartesian product (see Fig. 3). The gradient ascent is used to maximize the expected sum of rewards:", + "bbox": [ + 75, + 526, + 470, + 602 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\nabla_ {\\theta} \\mathbb {E} _ {\\mathcal {K}} [ R (.) ] = \\sum_ {(x, y) \\in \\mathcal {K}} \\nabla_ {\\theta} (\\log p (x; \\theta) + \\log p (y; \\theta)) R (.), \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 78, + 625, + 468, + 670 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $p(:,\\theta)$ denotes the probability of taking that action according to the network parametrized by $\\theta$ . The variables $x$ and $y$ are the probabilities of detection from a pairwise combination of keypoints.", + "bbox": [ + 75, + 671, + 468, + 733 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "During the invariant feature learning stage, after $70\\%$ of the training progress, we zero out the reward of the keypoints if their descriptors are unreliable. Details about the penalization term for the keypoints are described in Sec. 3.5.", + "bbox": [ + 75, + 732, + 470, + 792 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2.Keypoint descriptor", + "text_level": 1, + "bbox": [ + 76, + 801, + 266, + 818 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We observed that mid-level features extracted from the hourglass encoder do not explicitly model invariance to any kind of deformations, but tend to be highly distinctive on small to moderate photometric and geometric changes, such as varying illumination, and planar warps. Therefore, it is", + "bbox": [ + 75, + 824, + 468, + 902 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "advantageous to supervise the mid-level features since we obtain informative descriptors with no additional cost at inference. For that, during the first training stage, we bilinearly interpolate the feature maps $\\mathbf{X}$ at the detected keypoint positions to obtain a feature vector $\\mathbf{f}_d \\in \\mathbb{R}^D$ for each keypoint coordinate. Let $\\mathbf{F}_A \\in \\mathbb{R}^{N \\times D}$ and $\\mathbf{F}_B \\in \\mathbb{R}^{N \\times D}$ be matrices of $N$ L2-normalized feature vectors of corresponding descriptors $\\mathbf{f}_d$ extracted by the hourglass decoder at keypoint positions, from images $A$ and $B$ , and $\\mathbf{D}_{N \\times N} = \\sqrt{2 - 2\\mathbf{F}_A\\mathbf{F}_B^T}$ the distance matrix. To optimize the descriptors' embedding space, we employ the hard mining strategy [19] in the matrix $\\mathbf{D}$ and minimize the margin ranking loss:", + "bbox": [ + 496, + 345, + 893, + 535 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {d} \\left(\\delta_ {+} ^ {(.)}, \\delta_ {h} ^ {(.)}\\right) = \\frac {1}{N} \\sum_ {i = 1} ^ {N} \\max (0, \\mu + \\delta_ {+} ^ {(i)} - \\delta_ {h} ^ {(i)}), \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 521, + 547, + 892, + 589 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\mu$ is the margin, $\\delta_{+} = \\| \\mathbf{F}(p) - \\mathbf{F}(p^{\\prime})\\|_{2}$ is the distance between the corresponding features, and $\\delta_h = \\| \\mathbf{F}(p) - \\mathbf{F}(h)\\| _2$ is the distance to the hardest negative' sample in the batch.", + "bbox": [ + 496, + 603, + 893, + 664 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.3. Non-rigid warper module", + "text_level": 1, + "bbox": [ + 500, + 676, + 733, + 694 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "CNNs' translation equivariance property makes local descriptors invariant to image translation, and multi-scale strategies increase the robustness of description extraction to in-plane scale changes [7, 26, 37]. However, when non-rigid deformations arise, the local texture can significantly change in appearance, introducing matching ambiguities. DEAL [25] demonstrates that thin-plate-splines (TPS), coupled with spatial transformers, can be used to model deformations for the task of local feature description. Inspired by DEAL, we adopt a TPS deformation to learn local invariance to non-rigid transformations affecting the patches.", + "bbox": [ + 496, + 700, + 893, + 869 + ], + "page_idx": 3 + }, + { + "type": "page_footnote", + "text": "1The hardest negative example $h_i^j$ for each row $j$ of $\\mathbf{D}_{N \\times N}$ is computed as $\\min D_j$ , $i = j = \\{1, \\dots, N\\}$ s.t. $i \\neq j$ .", + "bbox": [ + 500, + 875, + 893, + 901 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "1309", + "bbox": [ + 483, + 944, + 514, + 955 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Spatial transformer network. We use the mid-level features from the backbone network to learn the parameters of the TPS with little additional overhead. The TPS parameter tensor $\\mathbf{M}_{\\theta} \\in \\mathbb{R}^{h/16 \\times w/16 \\times 2d}$ contains an intermediate representation useful to estimate a local non-rigid transformation for a keypoint. To obtain the parameter vector used in the TPS equation, first, we bilinearly interpolate a feature vector from $\\mathbf{M}_{\\theta}$ at the spatial position of the keypoint, obtaining an intermediate parameter vector $\\in \\mathbb{R}^{2d}$ . Then, an MLP is used to estimate the parameter vector $\\mu_{\\theta}$ that is used in the TPS transformation. The parameter vector $\\mu_{\\theta}$ encodes the affine matrix $\\mathbf{A} \\in \\mathbb{R}^{2 \\times 3}$ , and the non-rigid components $\\mathbf{w}_k \\in \\mathbb{R}^2$ separately representing offsets from the affine component. Given a homogeneous 2D point $\\mathbf{q} \\in \\mathbb{R}^3$ , weight coefficients and control points $\\mathbf{c}_k, \\in \\mathbb{R}^2$ , we use the parameters contained in $\\mu_{\\theta}$ to apply the TPS transformation to a fixed polar grid centered at the keypoint:", + "bbox": [ + 75, + 90, + 472, + 349 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {p} = \\mathbf {A q} + \\sum_ {k = 1} ^ {n _ {c}} \\rho \\left(\\left\\| \\mathbf {q} - \\mathbf {c} _ {k} \\right\\| ^ {2}\\right) \\mathbf {w} _ {k}, \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 158, + 359, + 470, + 400 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $n_c$ is the number of control points, $\\mathbf{q}$ is a normalized spatial image coordinate from the fixed polar grid around the keypoint, and $\\mathbf{p}$ is its transformed coordinate. Fig. 2 (Warper Net) shows the patch warping and sampling step. Since we are using the TPS Radial Basis Function, $\\rho = r^2\\log r$ is used. After the polar grid is transformed, a differentiable bilinear sampler [11] is used to obtain the transformed image patch that is used by a CNN similar to L2-Net architecture [34] to compute the invariant feature vector, supervised by the margin ranking loss (Eq. (3)). In our implementation, a major difference from the original L2-Net is that in the last convolutional block, we add an average pooling in the axis respective to the angular axis in the polar patch, attaining full rotation invariance.", + "bbox": [ + 75, + 411, + 472, + 623 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.4. Feature fusion layer", + "text_level": 1, + "bbox": [ + 76, + 633, + 267, + 648 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Distinctiveness and invariance are two desired attributes of a local feature descriptor. While invariance is vital for tasks that handle large appearance changes, such as rotation and scale, it usually implies distinctiveness loss [38]. By considering two complementary features, the distinctive ones coming from the backbone network with a larger receptive field but more sensitive to strong geometric transformations, and invariant features coming from the warper module that are robust to deformation and rotation by design, we propose to incorporate both information by a feature fusion step.", + "bbox": [ + 75, + 657, + 468, + 808 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The fusion is performed by an attention-based MLP that predicts weight coefficients. The two descriptor vectors are first concatenated and forwarded to the Fusion Layer as depicted in Fig. 2. Then, the concatenated descriptors are weighted by the predicted attention weights and L2-normalized to produce the final descriptor. During training,", + "bbox": [ + 75, + 810, + 472, + 901 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "we optimize each descriptor loss individually and the loss of the fused descriptors simultaneously to enforce the network to learn how to fuse the feature vectors to achieve a better feature representation. In the experiments, we demonstrate that combining the features allows the final descriptor to handle strong image transformations while maintaining its distinctiveness.", + "bbox": [ + 496, + 90, + 893, + 196 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.5. Training strategy and model optimization", + "text_level": 1, + "bbox": [ + 498, + 208, + 856, + 224 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Stage-wise training. During experiments, we observed that training the network end-to-end in a single phase causes the model to focus on the invariant features and ignores the distinctive features coming from the backbone, even when re-weighting the loss terms. To solve the issue, we perform a two-stage training. During the first training stage, we only train the backbone network. The backbone features have a larger receptive field and higher-level semantics compared to the Warner Net features but with less invariance to rotation and low-level deformations. In the second training phase, the Decoder, Warner Net and Fusion Layer are optimized, where the final feature representation is optimized considering both representations through the fusion step. Moreover, the decoder of the network is further refined and encouraged to detect keypoints that are optimal for the fused descriptors.", + "bbox": [ + 496, + 232, + 893, + 460 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Final loss. For the detection branch, we define the keypoint loss as $\\mathcal{L}_k = -\\mathbb{E}_{\\mathcal{K}}[R(.)]$ and add a regularization term for all the detected keypoints during training $\\mathcal{L}_p = -\\sum_x\\log p(x)\\cdot c$ , where $c$ is a small negative constant to discourage the network from detecting low-quality points. We employ the margin ranking loss described in Sec. 3.2 for all the descriptor vectors computed by our network. The final loss is then computed as $\\mathcal{L} = \\mathcal{L}_k + \\mathcal{L}_p + \\lambda \\mathcal{L}_d$ , where $\\lambda$ is a weight term to balance the magnitude between the triplet loss and the policy-gradient losses.", + "bbox": [ + 496, + 465, + 895, + 618 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 498, + 633, + 633, + 648 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Training and implementation details. We developed a carefully designed synthetic data generation pipeline to create plausible non-rigid deformations of surfaces to supervise the training. We perform photometric and geometric changes to real images obtained from large-scale Structure-from-Motion datasets [41]. We use only the raw images and do not use any information about correspondences or annotated labels. During the training, we add random photometric changes, random homographic projection, and random TPS warps to obtain ground-truth dense flows between image pairs depicting the same surface. The training starts with easier samples and progressively becomes more difficult, achieving the hardest difficulty at $60\\%$ of training iterations. In the experiments, we use the following hyperparameter values: $\\mu = 0.5$ in the triplet loss; pixel threshold $\\tau = 1.5$ ; $\\lambda = 0.005$ to balance the loss terms; keypoint penalization", + "bbox": [ + 496, + 657, + 895, + 902 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "1310", + "bbox": [ + 483, + 944, + 514, + 955 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "$c = -7e^{-5}$ ; cell size $m = n = 8$ pixels; and the number of control points $n_c = 64$ . As detailed in Sec. 3.5, we perform a two-stage training. Gradient accumulation was used for four forward passes before updating the weights. We trained the network for 80,000 iterations in the first stage and 100,000 iterations in the second stage. During inference, we use a non-maximal suppression of size $3 \\times 3$ pixels in order to extract the keypoint coordinates from $\\mathbf{H}$ . Our network is implemented on PyTorch, has about $1M$ trainable parameters, and takes 48 hours to train on a GeForce GTX Titan X GPU.", + "bbox": [ + 75, + 90, + 472, + 242 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Baselines and evaluation metrics. We compare our method with several patch-based descriptors [1, 8, 20, 28, 35, 36, 39], using the same set of SIFT [14] keypoints following the protocol of the image matching benchmark [12]. We also perform tests with a detector suitable for non-rigid correspondence [17] coupled with the deformation-aware descriptor DEAL [25]. Finally, we also include in the comparison the state-of-the-art detect-and-describe methods [6, 7, 16, 23, 26, 37, 42]. For each evaluated method, we detect the top 2,048 keypoints and match the descriptors using nearest neighbor search. In addition to the standard comparison, we include as the gold standard for image matching SuperPoint [6] with the SuperGlue [29] matcher, which holds the state-of-the-art for stereo and multi-view camera registration [12] assuming rigid scenes. As shown in Tab. 1, the methods are divided into three categories: (i) methods that only require RGB input (RGB) in contrast to methods that require additional information such as depth; (ii) Detect & Describe $(D\\& D)$ methods that provide both detection and description jointly within a single pipeline; and (iii) Deformation-Aware $(D - A)$ methods, which take into account deformation when computing the descriptors. Notice that a method may fulfill multiple categories simultaneously.", + "bbox": [ + 75, + 248, + 472, + 595 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We used the Matching Scores (MS) [18] to evaluate the matching performance of both the detected keypoints and descriptors. Given a ground-truth transformation and a threshold in pixels, we compute the set of correct correspondences $\\mathbf{S}_{gt}$ and obtain the score for an image pair $(i,j)$ as $MS = |\\mathbf{S}_{gt}| / \\min(|\\text{keypoints}_i|, |\\text{keypoints}_j|)$ . In addition, the mean matching accuracy (MMA) is also reported, which focuses on the accuracy of the descriptors to match the keypoints that were successfully detected on both images under the threshold denoted as the set $\\mathbf{K}_{gt}$ , and is computed as $MMA = |\\mathbf{S}_{gt}| / |\\mathbf{K}_{gt}|$ . Additional results regarding repeatability of keypoints can be found in the supplementary material. To conduct the evaluation, we adopt two existing datasets of deformable objects [24, 40].", + "bbox": [ + 75, + 595, + 472, + 808 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.1. Real-world benchmarking", + "text_level": 1, + "bbox": [ + 76, + 816, + 316, + 834 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Comparison with the state-of-the-art. Tab. 1 shows the MS and MMA scores achieved by all compared methods. DALF outperformed all descriptors on average in both MS and MMA metrics, including the methods that use additional", + "bbox": [ + 75, + 839, + 470, + 900 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "depth information to extract deformation-invariant features, improving the state-of-the-art in $8\\%$ p.p. in matching scores. Moreover, our method shows promising generalization properties to real deformations. DISK achieved the second-best results in MS, but the MMA indicates that its descriptors are more sensitive to non-rigid deformations. DEAL displays the second-best results in MMA thanks to its deformation-aware module but has poor performance on the MS score. It is noteworthy that DEAL relies on SIFT keypoints, which are not designed for non-rigid transformations.", + "bbox": [ + 496, + 90, + 893, + 241 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "SuperGlue, which is comprised of SuperPoint descriptors matched with a graph neural network, showed good performance, but the drop in the scores compared to the top methods is noticeable as SuperPoint and SuperGlue do not explicitly model scene deformations. We emphasize that our method can be easily coupled and trained with a learned matcher such as SuperGlue. We report the SuperGlue results using the outdoor pretrained weights since we observed that the outdoor weights performed better in all datasets. All the other methods achieve significantly worse scores due to their inability to cope with stronger deformations alongside illumination and affine transformations.", + "bbox": [ + 496, + 242, + 895, + 422 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Rotation and scale robustness. Aside from deformations, in-plane rotations and scale changes are two important geometric transformations. Thus, we conduct a study using the Simulation sequences from [24] containing challenging rotation and scale changes. Fig. 4 clearly indicates that our method holds the best invariance to image in-plane rotations in addition to deformation changes compared to the five stronger competitors. Our technique also displays considerable robustness to scale changes, outperforming SuperPoint and providing a similar level of robustness of SuperGlue.", + "bbox": [ + 496, + 428, + 893, + 580 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Time efficiency. DALF is one of the most time efficient methods among the joint detection and description architectures. While our method runs at 9 FPS, DISK runs at 5 FPS and R2D2 at 2 FPS in an NVIDIA GeForce RTX 3060 GPU to extract 2,048 keypoints from $1024 \\times 768$ images.", + "bbox": [ + 496, + 587, + 893, + 662 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/404f0fdfb3da3c368727c6426d1ac43d4e33a009bdf48991a708e1c3d9efcde8.jpg", + "image_caption": [ + "Figure 4. Invariance to rotation & scale. We evaluate the matching performance of the methods under rotation and scale changes between image pairs from the Simulation dataset. The objects are simultaneously deforming, rotating and scaling in image space." + ], + "image_footnote": [], + "bbox": [ + 513, + 688, + 694, + 837 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/ef55d095bd34cfaa71aebfb0ac0ec4acf75423694f6efbfe8836d88d3e9bd177.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 707, + 688, + 890, + 837 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "1311", + "bbox": [ + 483, + 944, + 513, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/186dcd924c84295c22e73376a2d8e26c880d0f281d2fabb08895e8775e779ac6.jpg", + "table_caption": [ + "Table 1. Performances using top 2,048 keypoints. The RGB methods only require color images. $D\\& D$ methods perform joint detection and description. The deformation-aware methods are shown as $D-A$ . The mark * indicates the use of a learned matcher. Best in bold and second-best underlined. The mean was calculated with full-precision values by averaging the scores of all 833 image pairs before rounding." + ], + "table_footnote": [], + "table_body": "
RGBD&DD-AMethodDatasets: 833 pairs total - MS / MMA @ 3 pixels ↑Mean
Kinect 1 [24]Kinect 2 [24]DeSurT [40]Simulation [24]
BRAND [20]0.17 / 0.340.22 / 0.490.14 / 0.330.04 / 0.090.16 / 0.34
✓ORB [28]0.19 / 0.380.25 / 0.550.18 / 0.400.14 / 0.300.20 / 0.43
✓DAISY [36]0.23 / 0.470.29 / 0.620.16 / 0.370.19 / 0.390.22 / 0.48
✓FREAK [1]0.24 / 0.490.33 / 0.720.16 / 0.380.15 / 0.310.23 / 0.51
✓TFeat [39]0.25 / 0.500.28 / 0.610.21 / 0.480.29 / 0.630.26 / 0.56
✓Log-Polar [8]0.28 / 0.580.30 / 0.650.23 / 0.540.22 / 0.490.26 / 0.57
✓SOSNet [35]0.17 / 0.340.25 / 0.550.17 / 0.380.26 / 0.570.22 / 0.47
✓✓LF-Net [23]0.44 / 0.400.51 / 0.430.28 / 0.770.21 / 0.740.36 / 0.59
✓✓LIFT [42]0.09 / 0.570.16 / 0.650.08 / 0.520.13 / 0.730.12 / 0.62
✓✓D2-Net [7]0.20 / 0.500.23 / 0.820.14 / 0.470.11 / 0.300.17 / 0.57
✓✓SuperPoint [6]0.45 / 0.740.54 / 0.850.39 / 0.680.18 / 0.340.41 / 0.69
✓✓R2D2 [26]0.17 / 0.360.25 / 0.590.14 / 0.320.06 / 0.160.17 / 0.39
✓✓ASLFeat [16]0.31 / 0.580.39 / 0.690.28 / 0.530.19 / 0.350.31 / 0.56
✓✓DISK [37]0.53 / 0.760.52 / 0.810.44 / 0.610.26 / 0.340.45 / 0.66
✓✓SuperGlue* [29]0.40 / 0.660.62 / 0.990.39 / 0.680.23 / 0.430.44 / 0.74
✓GeoBit [21]0.31 / 0.650.35 / 0.770.20 / 0.470.32 / 0.710.30 / 0.66
✓GeoPatch [24]0.32 / 0.660.35 / 0.800.26 / 0.600.39 / 0.860.33 / 0.73
✓✓DaLI [30]0.25 / 0.510.35 / 0.760.21 / 0.480.10 / 0.220.25 / 0.54
✓✓SIFT + DEAL [25]0.33 / 0.680.38 / 0.850.27 / 0.630.36 / 0.800.34 / 0.75
✓✓Det. [17] + DEAL0.44 / 0.740.49 / 0.820.33 / 0.640.31 / 0.740.40 / 0.74
✓✓✓DALF (ours)0.54 / 0.820.62 / 0.900.49 / 0.730.42 / 0.690.53 / 0.80
", + "bbox": [ + 107, + 142, + 859, + 494 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/0f00634bacce8bc15007b11d2f1c3c7dfc2ec0025407fb35f58604e485d60220.jpg", + "table_caption": [ + "Table 2. Ablation. Performance of our method when considering different network components and training strategies." + ], + "table_footnote": [], + "table_body": "
DistinctInvariant2-StageAttn.↑MS / MMA
✓--0.48 / 0.72
✓--0.51 / 0.78
✓✓0.53 / 0.79
✓✓✓0.53 / 0.78
✓✓✓✓0.53 / 0.80
", + "bbox": [ + 89, + 556, + 450, + 654 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.2. Ablation study", + "text_level": 1, + "bbox": [ + 76, + 679, + 227, + 695 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Our ablation study comprises five different configurations of our method: (i) using the U-net backbone only without the non-rigid warper module, which is similar to DISK excepting the descriptor loss term; (ii) computing the descriptors using the non-rigid warper module only; (iii) fusing the invariant and distinct features from the non-rigid warper and backbone respectively; (iv) perform a stage-wise training where the backbone is optimized first and the non-rigid warper second, and finally (v) we perform stage-wise training with an additional attention layer to fuse the invariant and distinctive descriptors instead of simple concatenation.", + "bbox": [ + 75, + 703, + 470, + 868 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "From Tab. 2, we can observe that the non-rigid warper contributes significantly to achieving more accurate matches", + "bbox": [ + 76, + 869, + 470, + 901 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "when compared to using a convolutional backbone alone. Furthermore, by fusing the features, it is possible to obtain an improved descriptor that is both invariant and distinct with complementary properties. The two-stage training provides similar matching scores and slightly reduced mean accuracy compared to end-to-end training. Still, according to a more detailed analysis available in the supplementary material, we observed that it is beneficial to perform stage-wise training. The invariant part tends to dominate the distinctive part during training, rendering the distinct part less useful in practice, which is not desired for applications needing more distinct features, such as image retrieval, and datasets without significant deformations. Finally, we test if an attention-based fusion layer can deliver better results than concatenating the descriptors in the fusion step. According to the results, it is possible to slightly increase the accuracy even further with a negligible cost in computation. Thus, we choose the model with the stage-wise training as the final architecture.", + "bbox": [ + 496, + 520, + 893, + 792 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Limitations. Although our network can improve overall scores by learning keypoints and deformation-aware features, estimating the deformation parameters from a single image is an ambiguous problem. Therefore, physical deformations may make textures similar for different objects, harming our method's performance. Nevertheless, the learned de", + "bbox": [ + 496, + 809, + 895, + 902 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "1312", + "bbox": [ + 482, + 944, + 516, + 957 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/858f54df73c46f9b197da86496289f926779cb68bf557b3011f11990f13a71ee.jpg", + "image_caption": [ + "Figure 5. Deformable object retrieval. Our method has the best result in retrieving images of deformed objects. The first column shows the image queries, and the rows show the results from different queries. Green images correspond to the same object as the query, and red images do not correspond. Black squares imply no more objects are available for that query." + ], + "image_footnote": [], + "bbox": [ + 86, + 88, + 467, + 252 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "formations demonstrate good generalization properties to real deformations due to the powerful combination of the keypoint extractor, warper module, and feature fusion steps.", + "bbox": [ + 75, + 363, + 470, + 409 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.3. Applications", + "text_level": 1, + "bbox": [ + 76, + 419, + 210, + 435 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "To further show the potential usage of our detection and description approach, we performed an evaluation in the two complementary tasks of object retrieval and 3D registration.", + "bbox": [ + 75, + 441, + 470, + 489 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Deformable object retrieval. We consider a database that contains images from various deformed objects. Each object appears multiple times with different deformations. The top K images from the database corresponding to an image query are retrieved. To evaluate the methods, we use the retrieval accuracy for different K values. K-Nearest Neighbors is used in conjunction with Bag-of-Visual-Worlds approach over the descriptors as the retrieval engine. We compare our method against the state-of-the-art description methods that demonstrated the top performances in Tab. 1, in addition to DELF [33], a state-of-the-art descriptor designed and trained specifically for image retrieval. We calculated the normalized area under the curve of each method for $K = \\{1, \\dots, 20\\}$ . DALF achieved the most accurate retrieval capabilities at $99.49\\%$ , while DELF, DEAL, SuperPoint, and DISK achieved $98.57\\%$ , $98.34\\%$ , $97.92\\%$ , and $96.12\\%$ , respectively. Fig. 5 shows some qualitative results2.", + "bbox": [ + 75, + 494, + 470, + 752 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Non-rigid 3D surface registration. In addition to the retrieval application, we also validate the performance of the methods in the challenging real-world task of surface registration. To that end, we employ the as-rigid-as-possible (ARAP) [31] registration to perform the surface alignment with the correspondences obtained from each method. In", + "bbox": [ + 75, + 773, + 470, + 864 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/252c02f837803986c297aabf0d6215ca1a6e599392060585f95d8f2ca6994bd1.jpg", + "table_caption": [ + "Table 3. 3D surface registration. The 2D and 3D accuracy is computed under varying thresholds in centimeters for the 3D residuals and in pixels for the 2D residuals. Best in bold." + ], + "table_footnote": [], + "table_body": "
Method2D Accuracy ↑3D Accuracy ↑
@2px@3px@5px@0.5cm@1.0cm@1.5cm
DISK21.330.541.236.351.758.8
SuperPoint23.234.447.442.660.568.4
SuperGlue34.951.068.142.864.473.6
GeoPatch28.941.555.941.062.371.1
DEAL29.442.056.242.964.372.8
DALF (ours)36.651.667.346.266.974.8
", + "bbox": [ + 503, + 142, + 887, + 247 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "these experiments, the correspondences are first filtered with an outlier removal approach [5] since the ARAP cannot handle outliers in the registration process. One of the challenges of non-rigid registration is that one cannot fit a global geometric transformation with a minimal sample using RANSAC.", + "bbox": [ + 496, + 262, + 893, + 338 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "After the filtering stage, the ARAP is used to align the meshes of the respective image pairs. The 2D error is then computed using the ground-truth TPS transformation provided with the datasets given in pixels. We also estimate the residual 3D error, assuming that the two corresponding surfaces must be perfectly adjusted in the 3D space, as their meshes are known beforehand. Tab. 3 shows the performance of the top methods under different thresholds for the 2D and the 3D errors considering all the datasets used in Tab. 1, where our approach stands out, improving over 3 p.p. in 3D registration accuracy compared to the best current method (SuperGlue) in the tightest threshold of $0.5\\mathrm{cm}$ . Visual results of the 3D registration are available in the supplementary material.", + "bbox": [ + 496, + 339, + 893, + 550 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusions", + "text_level": 1, + "bbox": [ + 500, + 564, + 627, + 579 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "This paper presents DALF, a method that considers both the detection and description of keypoints under the challenging case of non-rigid geometric transformations. From extensive experiments and two applications using real deformable objects, we draw the following conclusions: (i) standard approaches for image matching deliver subpar results compared to deformation-aware features; (ii) optimizing the keypoint detection stage together with deformation-aware descriptors brings significant performance gains compared to existing deformation-aware methods that rely on affine keypoint detectors; and (iii) the feature fusion component is a simple but effective approach to increase the network expressiveness to deformations while keeping distinctiveness.", + "bbox": [ + 496, + 590, + 893, + 787 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgements. The authors would like to thank CAPES (#88881.120236/2016-01), CNPq, FAPEMIG, and Google for funding different parts of this work. This work was also granted access to the HPC resources of CNRS IDRIS under the project 2021-AD011013154 and supported by the French Conseil Régional de Bourgogne-Franche-Comté.", + "bbox": [ + 496, + 794, + 895, + 898 + ], + "page_idx": 7 + }, + { + "type": "page_footnote", + "text": "2For the sake of clarity, we filtered out objects that all methods retrieved all correct images. Full results are available in the supplementary material.", + "bbox": [ + 76, + 875, + 470, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "1313", + "bbox": [ + 483, + 944, + 514, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Alexandre Alahi, Raphael Ortiz, and Pierre Vandergheynst. Freak: Fast retina keypoint. In 2012 IEEE Conference on Computer Vision and Pattern Recognition, pages 510-517. 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In ECCV, 2016. 1, 2, 6, 7" + ], + "bbox": [ + 501, + 90, + 893, + 527 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "1315", + "bbox": [ + 483, + 944, + 514, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/Enhancing Deformable Local Features by Jointly Learning To Detect and Describe Keypoints/16ef7ac5-e127-4979-a2b4-14363013dd09_model.json b/2023/Enhancing Deformable Local Features by Jointly Learning To Detect and Describe Keypoints/16ef7ac5-e127-4979-a2b4-14363013dd09_model.json new file mode 100644 index 0000000000000000000000000000000000000000..b63e6f6265e14929070747c3ab4944d2fbbc8efb --- /dev/null +++ b/2023/Enhancing Deformable Local Features by Jointly Learning To Detect and Describe Keypoints/16ef7ac5-e127-4979-a2b4-14363013dd09_model.json @@ -0,0 +1,1749 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.001, + 0.812, + 0.047 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.189, + 0.131, + 0.784, + 0.177 + ], + "angle": 0, + "content": "Enhancing Deformable Local Features by Jointly Learning to Detect and Describe Keypoints" + }, + { + "type": "text", + "bbox": [ + 0.265, + 0.203, + 0.44, + 0.24 + ], + "angle": 0, + "content": "Guilherme Potje1 \nRenato Martins3,4" + }, + { + "type": "text", + "bbox": [ + 0.447, + 0.204, + 0.721, + 0.24 + ], + "angle": 0, + "content": "Felipe Cadar1 André Araujo2 Erickson R. Nascimento1,5" + }, + { + "type": "text", + "bbox": [ + 0.262, + 0.25, + 0.731, + 0.268 + ], + "angle": 0, + "content": "1Universidade Federal de Minas Gerais 2Google Research" + }, + { + "type": "text", + "bbox": [ + 0.185, + 0.268, + 0.807, + 0.285 + ], + "angle": 0, + "content": "3Université de Bourgogne 4Université de Lorraine, LORIA, Inria 5Microsoft" + }, + { + "type": "text", + "bbox": [ + 0.088, + 0.289, + 0.9, + 0.304 + ], + "angle": 0, + "content": "{guipotje, cadar, erickson}@dcc.ufgm.br, renato.martins@u-bourgogne.fr, andrearaujo@google.com" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.338, + 0.314, + 0.354 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.372, + 0.474, + 0.705 + ], + "angle": 0, + "content": "Local feature extraction is a standard approach in computer vision for tackling important tasks such as image matching and retrieval. The core assumption of most methods is that images undergo affine transformations, disregarding more complicated effects such as non-rigid deformations. Furthermore, incipient works tailored for non-rigid correspondence still rely on keypoint detectors designed for rigid transformations, hindering performance due to the limitations of the detector. We propose DALF (Deformation-Aware Local Features), a novel deformation-aware network for jointly detecting and describing keypoints, to handle the challenging problem of matching deformable surfaces. All network components work cooperatively through a feature fusion approach that enforces the descriptors' distinctiveness and invariance. Experiments using real deforming objects showcase the superiority of our method, where it delivers \\(8\\%\\) improvement in matching scores compared to the previous best results. Our approach also enhances the performance of two real-world applications: deformable object retrieval and non-rigid 3D surface registration. Code for training, inference, and applications are publicly available at verlab.dcc.ufmg.br/descriptors/dalf Cvpr23." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.738, + 0.21, + 0.753 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.765, + 0.472, + 0.902 + ], + "angle": 0, + "content": "Finding pixel-wise correspondences between images depicting the same surface is a long-standing problem in computer vision. Besides varying illumination, viewpoint, and distance to the object of interest, real-world scenes impose additional challenges. The vast majority of the correspondence algorithms in the literature assume that our world is rigid, but this assumption is far from the truth. It is noticeable that the community invests significant efforts into novel architectures and training strategies to improve image match-" + }, + { + "type": "image", + "bbox": [ + 0.51, + 0.336, + 0.885, + 0.478 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.487, + 0.896, + 0.571 + ], + "angle": 0, + "content": "Figure 1. Image matching under deformations. We propose DALF, a deformation-aware keypoint detector and descriptor for matching deformable surfaces. DALF (top) enables local feature matching across deformable scenes with improved matching scores (MS) compared to state-of-the-art, as illustrated with DISK [37]. Green lines show correct matches, and red markers, the mismatches." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.599, + 0.893, + 0.643 + ], + "angle": 0, + "content": "ing for rigid scenes [6, 19, 26, 34, 37, 42], but disregards the fact that many objects in the real world can deform in more complex ways than an affine transformation." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.645, + 0.896, + 0.902 + ], + "angle": 0, + "content": "Many applications in industry, medicine, and agriculture require tracking, retrieval, and monitoring of arbitrary deformable objects and surfaces, where a general-purpose matching algorithm is needed to achieve accurate results. Since the performance of standard affine local features significantly decreases for scenarios such as strong illumination changes and deformations, a few works considering a wider class of transformations have been proposed [24, 25, 30]. However, all the deformation-aware methods neglect the keypoint detection phase, limiting their applicability in challenging deformations. Although the problems of keypoint detection and description can be treated separately, recent works that jointly perform detection and description of features [4, 26] indicate an entanglement of the two tasks since the keypoint detection can impact the performance of the descriptor. The descriptor for its turn can be used to determine reliable points optimized for specific goals. In this work," + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "1306" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.471, + 0.213 + ], + "angle": 0, + "content": "we propose a new method for jointly learning keypoints and descriptors robust to deformations, viewpoint, and illumination changes. We show that the detection phase is critical to obtain robust matching under deformations. Fig. 1 depicts an image pair with challenging deformations, where our method can extract reliable keypoints and match them correctly, significantly increasing matching scores compared to the recent state-of-the-art approach DISK [37]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.232, + 0.474, + 0.565 + ], + "angle": 0, + "content": "Contributions. (1) Our first contribution is a new end-to-end method called DALF (Deformation-Aware Local Features), which jointly learns to detect keypoints and extract descriptors with a mutual assistance strategy to handle significant non-rigid deformations. Our method boosts the state-of-the-art in this type of feature matching by \\(8\\%\\) using only synthetic warps as supervision, showing strong generalization capabilities. We leverage a reinforcement learning algorithm for unified training, combined with spatial transformers that capture deformations by learning context priors affecting the image; (2) Second, we introduce a feature fusion approach, a major difference from previous methods that allows the model to tackle challenging deformations with complementary features (with distinctiveness and invariance properties) obtained from both the backbone and the spatial transformer module. This approach is shown beneficial with substantial performance improvements compared to the non-fused features; (3) Finally, we demonstrate state-of-the-art results in non-rigid local feature applications for deformable object retrieval and non-rigid 3D surface registration. We also will make the code and both applications publicly available to the community." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.578, + 0.216, + 0.593 + ], + "angle": 0, + "content": "2. Related work" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.603, + 0.472, + 0.845 + ], + "angle": 0, + "content": "Keypoint detection. Traditional image keypoint detection methods seek to extract repeatable regions in images, i.e., localized points that are stable under different viewing conditions. The classic Harris detector [10] employs image derivatives that are used to compute cornerness scores, while one the most used handcrafted detectors SIFT [14], for instance, detects blobs using the Difference of Gaussians. Key.Net [13] showed that it is possible to improve keypoint detection by combining handcrafted filters and learned filters. A recent trend for learning keypoint detection is to couple description and detection in the same pipeline [7,26,34,42], since it is advantageous performance-wise to solve both tasks simultaneously in terms of computation and matching accuracy. In the same direction, our proposed method has a backbone that computes both keypoints and descriptors but at the same time employs a deformation-aware module." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.471, + 0.901 + ], + "angle": 0, + "content": "Description of local patches. Until recently, detection and description were treated separately. While some works focused on both problems, such as the seminal works of" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.895, + 0.35 + ], + "angle": 0, + "content": "SIFT [14] and ORB [28], the detection and description were decoupled. SIFT and ORB descriptors employ a handcrafted gradient analysis to extract descriptors with scale and rotation invariance. Recent description approaches based on CNNs [8, 15, 19, 34, 39] consume a local patch assuming a pre-defined keypoint detector. These methods achieved state-of-the-art performance using SIFT keypoints in the image matching benchmark [12]. The networks are trained using metric learning [9, 39]. As patch-based methods rely on a pre-defined keypoint detector that may produce keypoints in unreliable or ambiguous regions, noise can be easily introduced because detection and description steps are decoupled. Unlike patch-based methods, our network is trained to produce reliable descriptions and keypoints optimized for non-rigid correspondence. Our description is also enhanced with a fusion strategy that combines complementary features into a single learned feature representation." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.36, + 0.897, + 0.603 + ], + "angle": 0, + "content": "Joint detection and description. DELF [22] and DELG [4] works demonstrated that coupling the detection and description phases using an attentive mechanism for keypoint selection based on higher-level image semantics can substantially improve retrieval performance. Local feature extraction has been shifting towards learning both detection and description of local features jointly [7, 16, 26, 37, 42]. Most methods follow a similar architecture, adopting a fully convolutional network (FCN) layout to produce a dense feature map, where most of the differences between the methods reside in the training scheme and loss design. The most recent describe-and-detect approaches are currently state-of-the-art on standard benchmarks [2, 12]. Differently from existing methods, we design the architecture and training to explicitly handle deformations in a coupled detection and description phase, devising a carefully tailored warper network." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.614, + 0.897, + 0.903 + ], + "angle": 0, + "content": "Deformation-aware methods. One of the first proposed image descriptors designed for deformable surfaces is DaLI [30]. DaLI interprets image patches as a local 3D surface, and computes the Scale-Invariant Heat Kernel Signatures [3] of the 3D surface to encode features robust to non-rigid deformations and illumination changes. Despite achieving improved matching performance compared to contemporary works, DaLI suffers from high computational and storage requirements. Similar to DaLI, GeoBit [21] and GeoPatch [24] descriptors brought ideas from computational geometry to computer vision, leveraging RGB-D images to extract visual features that are geodesic-aware. However, these geodesic-aware methods require RGB-D images and are sensitive to noise, significantly restricting their applicability. To remove the need for depth images for estimating geodesic patches, the DEAL descriptor [25] implicitly handles deformations from monocular images through a non-rigid warper module. The main shortcoming of DEAL is its dependency on existing keypoint detectors, which compro" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "1307" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.091, + 0.092, + 0.459, + 0.344 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.349, + 0.473, + 0.448 + ], + "angle": 0, + "content": "Figure 2. DALF architecture. Our architecture jointly optimizes non-rigid keypoint detection and description, and explicitly models local deformations for descriptor extraction during training. An hourglass CNN computes a dense heat map providing specialized keypoints that are used by the Warner Net to extract deformation-aware matches. A feature fusion layer balances the trade-off between invariance and distinctiveness in the final descriptors." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.454, + 0.472, + 0.531 + ], + "angle": 0, + "content": "mises the descriptor performance due to the lack of equivariance on keypoints locations from most existing detectors in the presence of deformation changes. In contrast, our method learns detection and description in the same framework, achieving significant performance gains." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.542, + 0.214, + 0.56 + ], + "angle": 0, + "content": "3. Methodology" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.567, + 0.472, + 0.78 + ], + "angle": 0, + "content": "DALF jointly learns to detect and describe points robust to non-rigid deformations, in addition to perspective and illumination changes. Both detector and descriptor are trained with a cooperative scheme aiming at the invariance of feature representations. Specifically, the keypoint detector is trained using policy gradient, seeking to increase the probability of detections that are both repeatable and reliable; Concurrently, the descriptor extractor learns to undeform and extract discriminative and invariant features from local regions. The model is only trained on synthetic warps, i.e., it does not require expensive human annotation nor pseudo-ground-truth that may contain errors and bias, such as the output of an SfM pipeline that is used in several works [7, 16, 26, 29, 37]. Fig. 2 outlines the proposed method." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.787, + 0.251, + 0.804 + ], + "angle": 0, + "content": "3.1.Keypoint detector" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.81, + 0.473, + 0.903 + ], + "angle": 0, + "content": "The keypoint detection architecture uses a backbone hourglass CNN network \\(\\mathbf{f}(\\cdot)\\), similar to a U-net [27]. This network enables computing a keypoint heat map in the original image resolution efficiently, while also producing mid-level feature representations that are useful to describe the keypoints. We employ three downsampling blocks for the en" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.895, + 0.198 + ], + "angle": 0, + "content": "coder, and three upsampling blocks for the decoder, with skip connections, each having two convolutional layers composed of a 2D convolution followed by ReLU and batch normalization. Let \\( I \\in \\mathbb{R}^{h \\times w \\times c} \\) be the input image of size \\( h \\times w \\) and \\( c \\) channels, \\( \\mathbf{f}(I) \\) outputs two feature maps: mid-level representations \\( \\mathbf{X} \\in \\mathbb{R}^{h/8 \\times w/8 \\times d} \\) and detection heatmap \\( \\mathbf{H} \\in \\mathbb{R}^{h \\times w} \\), where \\( d \\) is the number of features." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.22, + 0.895, + 0.446 + ], + "angle": 0, + "content": "Keypoint detection in deforming images. An effective detector must output heatmaps \\(\\mathbf{H} \\in \\mathbb{R}^{h \\times w}\\) with high responses in regions that can be matched well in non-rigid scenes containing view and illumination changes. Thus, during the training of the detection branch, we optimize \\(\\mathbf{H}\\) using a strategy similar to DISK [37], but applying only the probabilistic framework to learn the detection heatmap. A key difference compared to DISK is that we enforce the reliability of the detected keypoints by penalizing wrong matches even if the keypoints are repeatable. A probabilistic approach has several advantages as dealing with the inhering discreteness of sparse keypoint detection, and a simpler and more intuitive loss can be used for better convergence and regularization of the detection heatmap, in contrast to works that require elaborated handcrafted losses [7, 16, 26]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.448, + 0.895, + 0.659 + ], + "angle": 0, + "content": "We seek to obtain high responses in confident regions not only for detection but also matching. To solve this problem with policy gradient, we divide the heatmap into a 2D grid of cells (Detection Heatmap in Fig. 3) and consider a set of actions that the network agent can make to select keypoints. Each cell \\(\\mathbf{c}_i\\) has \\(m \\times n\\) pixels, where the network can learn the probability of detecting a keypoint within each cell. Given an image pair \\((A, B)\\) of the same scene under different photometric and geometric transformations, and the ground-truth flow-field relating the two images, for each cell \\(\\mathbf{c}_i \\in \\mathbf{H}\\), we consider a probability distribution over the cell \\(\\mathbf{c} \\in \\mathbb{R}^{m \\times n}\\). Each logit value within the cell has a probability of being a keypoint. The probability mass function \\(\\mathbf{p}_{\\mathbf{c}_i}\\) over the cell \\(\\mathbf{c}_i\\) is computed by applying the Softmax function." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.66, + 0.896, + 0.902 + ], + "angle": 0, + "content": "Therefore, to train the detection branch, we employ the Reinforce algorithm [32]. During the forward pass of the network, we randomly sample an individual keypoint within each cell \\(\\mathbf{c}_i\\) according to the probability mass function \\(\\mathbf{p}_{\\mathbf{c}_i}\\) alongside the keypoint's spatial coordinates, its probability \\(p_s^i\\) and its logit \\(l_s^i\\). Note that each cell can have exactly one keypoint; however, in practice, it is common that low texture and ambiguous regions result in low-quality keypoints that cannot be reliably matched or detected in other images. For that reason, we accept a keypoint proposal from a cell with probability \\(\\sigma (l_s^i)\\), where \\(\\sigma\\) is the sigmoid activation. This way, the network can learn to filter out unreliable keypoint proposals during training. The final probabilities of detection for the image \\(I\\) is given by the set \\(P_{I} = \\{\\sigma (l_{s}^{i})\\cdot p_{s}^{i}\\},\\forall \\mathbf{c}_{i}\\in\\) \\(\\mathbf{H}\\), such that \\(\\sigma (l_s^i) > 0.5\\) (we only sampled keypoints that has positive values in the heatmap). Since we want the" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "1308" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.118, + 0.088, + 0.855, + 0.255 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.264, + 0.895, + 0.337 + ], + "angle": 0, + "content": "Figure 3. Training strategy to learn to detect and describe keypoints aware of deformations. DALF network is used to produce a detection heatmap and a set of local features for each image. In the detector path, the heatmaps are optimized via the REINFORCE algorithm considering keypoint repeatability under deformations. In the descriptor path, feature space is learned via the hard triplet loss. A siamese setup using image pairs is employed to optimize the network. Notice that we penalize keypoints that cannot be described accurately during the second training stage; thus, the keypoints and combined descriptors are optimized jointly to be robust to deformations." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.346, + 0.471, + 0.408 + ], + "angle": 0, + "content": "keypoints to be repeatable, we reward points that can be detected in both images \\(A\\) and \\(B\\). Thus, given the pixel coordinate \\(\\mathbf{p}_A^j \\in \\mathbb{R}^2\\) of detected point \\(j\\) on image \\(A\\), we define the reward function \\(R(.)\\) as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.099, + 0.417, + 0.472, + 0.456 + ], + "angle": 0, + "content": "\\[\nR \\left(\\mathbf {p} _ {A} ^ {j}\\right) = \\left\\{ \\begin{array}{l l} 1 & \\text {i f} \\exists \\mathbf {p} _ {B} ^ {(.)} \\text {s . t .} \\| T \\left(\\mathbf {p} _ {A} ^ {j}\\right) - \\mathbf {p} _ {B} ^ {(.)} \\| < \\tau , \\\\ 0 & \\text {o t h e r w i s e}, \\end{array} \\right. \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.466, + 0.47, + 0.527 + ], + "angle": 0, + "content": "where \\( T(.) \\) transforms pixels coordinates of image \\( A \\) to image \\( B \\) according to the ground-truth flow-field, and \\( \\tau \\) is a pixel threshold to determine if the detected keypoint in \\( A \\) has a correspondence in image \\( B \\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.527, + 0.472, + 0.603 + ], + "angle": 0, + "content": "Once we have the set of probabilities \\( P_A \\) and \\( P_B \\), we obtain the gradient of the parameter vector \\( \\theta \\) with respect to the expected rewards over all pairwise keypoints \\( \\mathcal{K} = P_A \\times P_B \\) where \\( \\times \\) denotes the cartesian product (see Fig. 3). The gradient ascent is used to maximize the expected sum of rewards:" + }, + { + "type": "equation", + "bbox": [ + 0.08, + 0.625, + 0.47, + 0.671 + ], + "angle": 0, + "content": "\\[\n\\nabla_ {\\theta} \\mathbb {E} _ {\\mathcal {K}} [ R (.) ] = \\sum_ {(x, y) \\in \\mathcal {K}} \\nabla_ {\\theta} (\\log p (x; \\theta) + \\log p (y; \\theta)) R (.), \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.672, + 0.47, + 0.734 + ], + "angle": 0, + "content": "where \\( p(:,\\theta) \\) denotes the probability of taking that action according to the network parametrized by \\( \\theta \\). The variables \\( x \\) and \\( y \\) are the probabilities of detection from a pairwise combination of keypoints." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.733, + 0.472, + 0.794 + ], + "angle": 0, + "content": "During the invariant feature learning stage, after \\(70\\%\\) of the training progress, we zero out the reward of the keypoints if their descriptors are unreliable. Details about the penalization term for the keypoints are described in Sec. 3.5." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.802, + 0.267, + 0.819 + ], + "angle": 0, + "content": "3.2.Keypoint descriptor" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.825, + 0.47, + 0.903 + ], + "angle": 0, + "content": "We observed that mid-level features extracted from the hourglass encoder do not explicitly model invariance to any kind of deformations, but tend to be highly distinctive on small to moderate photometric and geometric changes, such as varying illumination, and planar warps. Therefore, it is" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.346, + 0.895, + 0.536 + ], + "angle": 0, + "content": "advantageous to supervise the mid-level features since we obtain informative descriptors with no additional cost at inference. For that, during the first training stage, we bilinearly interpolate the feature maps \\(\\mathbf{X}\\) at the detected keypoint positions to obtain a feature vector \\(\\mathbf{f}_d \\in \\mathbb{R}^D\\) for each keypoint coordinate. Let \\(\\mathbf{F}_A \\in \\mathbb{R}^{N \\times D}\\) and \\(\\mathbf{F}_B \\in \\mathbb{R}^{N \\times D}\\) be matrices of \\(N\\) L2-normalized feature vectors of corresponding descriptors \\(\\mathbf{f}_d\\) extracted by the hourglass decoder at keypoint positions, from images \\(A\\) and \\(B\\), and \\(\\mathbf{D}_{N \\times N} = \\sqrt{2 - 2\\mathbf{F}_A\\mathbf{F}_B^T}\\) the distance matrix. To optimize the descriptors' embedding space, we employ the hard mining strategy [19] in the matrix \\(\\mathbf{D}\\) and minimize the margin ranking loss:" + }, + { + "type": "equation", + "bbox": [ + 0.522, + 0.549, + 0.893, + 0.59 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {d} \\left(\\delta_ {+} ^ {(.)}, \\delta_ {h} ^ {(.)}\\right) = \\frac {1}{N} \\sum_ {i = 1} ^ {N} \\max (0, \\mu + \\delta_ {+} ^ {(i)} - \\delta_ {h} ^ {(i)}), \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.604, + 0.895, + 0.665 + ], + "angle": 0, + "content": "where \\(\\mu\\) is the margin, \\(\\delta_{+} = \\| \\mathbf{F}(p) - \\mathbf{F}(p^{\\prime})\\|_{2}\\) is the distance between the corresponding features, and \\(\\delta_h = \\| \\mathbf{F}(p) - \\mathbf{F}(h)\\| _2\\) is the distance to the hardest negative' sample in the batch." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.678, + 0.734, + 0.695 + ], + "angle": 0, + "content": "3.3. Non-rigid warper module" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.702, + 0.895, + 0.87 + ], + "angle": 0, + "content": "CNNs' translation equivariance property makes local descriptors invariant to image translation, and multi-scale strategies increase the robustness of description extraction to in-plane scale changes [7, 26, 37]. However, when non-rigid deformations arise, the local texture can significantly change in appearance, introducing matching ambiguities. DEAL [25] demonstrates that thin-plate-splines (TPS), coupled with spatial transformers, can be used to model deformations for the task of local feature description. Inspired by DEAL, we adopt a TPS deformation to learn local invariance to non-rigid transformations affecting the patches." + }, + { + "type": "page_footnote", + "bbox": [ + 0.5, + 0.875, + 0.895, + 0.902 + ], + "angle": 0, + "content": "1The hardest negative example \\( h_i^j \\) for each row \\( j \\) of \\( \\mathbf{D}_{N \\times N} \\) is computed as \\( \\min D_j \\), \\( i = j = \\{1, \\dots, N\\} \\) s.t. \\( i \\neq j \\)." + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "1309" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.35 + ], + "angle": 0, + "content": "Spatial transformer network. We use the mid-level features from the backbone network to learn the parameters of the TPS with little additional overhead. The TPS parameter tensor \\(\\mathbf{M}_{\\theta} \\in \\mathbb{R}^{h/16 \\times w/16 \\times 2d}\\) contains an intermediate representation useful to estimate a local non-rigid transformation for a keypoint. To obtain the parameter vector used in the TPS equation, first, we bilinearly interpolate a feature vector from \\(\\mathbf{M}_{\\theta}\\) at the spatial position of the keypoint, obtaining an intermediate parameter vector \\(\\in \\mathbb{R}^{2d}\\). Then, an MLP is used to estimate the parameter vector \\(\\mu_{\\theta}\\) that is used in the TPS transformation. The parameter vector \\(\\mu_{\\theta}\\) encodes the affine matrix \\(\\mathbf{A} \\in \\mathbb{R}^{2 \\times 3}\\), and the non-rigid components \\(\\mathbf{w}_k \\in \\mathbb{R}^2\\) separately representing offsets from the affine component. Given a homogeneous 2D point \\(\\mathbf{q} \\in \\mathbb{R}^3\\), weight coefficients and control points \\(\\mathbf{c}_k, \\in \\mathbb{R}^2\\), we use the parameters contained in \\(\\mu_{\\theta}\\) to apply the TPS transformation to a fixed polar grid centered at the keypoint:" + }, + { + "type": "equation", + "bbox": [ + 0.16, + 0.361, + 0.472, + 0.401 + ], + "angle": 0, + "content": "\\[\n\\mathbf {p} = \\mathbf {A q} + \\sum_ {k = 1} ^ {n _ {c}} \\rho \\left(\\left\\| \\mathbf {q} - \\mathbf {c} _ {k} \\right\\| ^ {2}\\right) \\mathbf {w} _ {k}, \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.412, + 0.473, + 0.624 + ], + "angle": 0, + "content": "where \\( n_c \\) is the number of control points, \\( \\mathbf{q} \\) is a normalized spatial image coordinate from the fixed polar grid around the keypoint, and \\( \\mathbf{p} \\) is its transformed coordinate. Fig. 2 (Warper Net) shows the patch warping and sampling step. Since we are using the TPS Radial Basis Function, \\( \\rho = r^2\\log r \\) is used. After the polar grid is transformed, a differentiable bilinear sampler [11] is used to obtain the transformed image patch that is used by a CNN similar to L2-Net architecture [34] to compute the invariant feature vector, supervised by the margin ranking loss (Eq. (3)). In our implementation, a major difference from the original L2-Net is that in the last convolutional block, we add an average pooling in the axis respective to the angular axis in the polar patch, attaining full rotation invariance." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.635, + 0.268, + 0.65 + ], + "angle": 0, + "content": "3.4. Feature fusion layer" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.659, + 0.47, + 0.809 + ], + "angle": 0, + "content": "Distinctiveness and invariance are two desired attributes of a local feature descriptor. While invariance is vital for tasks that handle large appearance changes, such as rotation and scale, it usually implies distinctiveness loss [38]. By considering two complementary features, the distinctive ones coming from the backbone network with a larger receptive field but more sensitive to strong geometric transformations, and invariant features coming from the warper module that are robust to deformation and rotation by design, we propose to incorporate both information by a feature fusion step." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.811, + 0.473, + 0.902 + ], + "angle": 0, + "content": "The fusion is performed by an attention-based MLP that predicts weight coefficients. The two descriptor vectors are first concatenated and forwarded to the Fusion Layer as depicted in Fig. 2. Then, the concatenated descriptors are weighted by the predicted attention weights and L2-normalized to produce the final descriptor. During training," + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.895, + 0.198 + ], + "angle": 0, + "content": "we optimize each descriptor loss individually and the loss of the fused descriptors simultaneously to enforce the network to learn how to fuse the feature vectors to achieve a better feature representation. In the experiments, we demonstrate that combining the features allows the final descriptor to handle strong image transformations while maintaining its distinctiveness." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.209, + 0.857, + 0.226 + ], + "angle": 0, + "content": "3.5. Training strategy and model optimization" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.233, + 0.895, + 0.461 + ], + "angle": 0, + "content": "Stage-wise training. During experiments, we observed that training the network end-to-end in a single phase causes the model to focus on the invariant features and ignores the distinctive features coming from the backbone, even when re-weighting the loss terms. To solve the issue, we perform a two-stage training. During the first training stage, we only train the backbone network. The backbone features have a larger receptive field and higher-level semantics compared to the Warner Net features but with less invariance to rotation and low-level deformations. In the second training phase, the Decoder, Warner Net and Fusion Layer are optimized, where the final feature representation is optimized considering both representations through the fusion step. Moreover, the decoder of the network is further refined and encouraged to detect keypoints that are optimal for the fused descriptors." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.467, + 0.897, + 0.619 + ], + "angle": 0, + "content": "Final loss. For the detection branch, we define the keypoint loss as \\(\\mathcal{L}_k = -\\mathbb{E}_{\\mathcal{K}}[R(.)]\\) and add a regularization term for all the detected keypoints during training \\(\\mathcal{L}_p = -\\sum_x\\log p(x)\\cdot c\\), where \\(c\\) is a small negative constant to discourage the network from detecting low-quality points. We employ the margin ranking loss described in Sec. 3.2 for all the descriptor vectors computed by our network. The final loss is then computed as \\(\\mathcal{L} = \\mathcal{L}_k + \\mathcal{L}_p + \\lambda \\mathcal{L}_d\\), where \\(\\lambda\\) is a weight term to balance the magnitude between the triplet loss and the policy-gradient losses." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.634, + 0.634, + 0.65 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.659, + 0.897, + 0.903 + ], + "angle": 0, + "content": "Training and implementation details. We developed a carefully designed synthetic data generation pipeline to create plausible non-rigid deformations of surfaces to supervise the training. We perform photometric and geometric changes to real images obtained from large-scale Structure-from-Motion datasets [41]. We use only the raw images and do not use any information about correspondences or annotated labels. During the training, we add random photometric changes, random homographic projection, and random TPS warps to obtain ground-truth dense flows between image pairs depicting the same surface. The training starts with easier samples and progressively becomes more difficult, achieving the hardest difficulty at \\(60\\%\\) of training iterations. In the experiments, we use the following hyperparameter values: \\(\\mu = 0.5\\) in the triplet loss; pixel threshold \\(\\tau = 1.5\\); \\(\\lambda = 0.005\\) to balance the loss terms; keypoint penalization" + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "1310" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.091, + 0.473, + 0.243 + ], + "angle": 0, + "content": "\\(c = -7e^{-5}\\); cell size \\(m = n = 8\\) pixels; and the number of control points \\(n_c = 64\\). As detailed in Sec. 3.5, we perform a two-stage training. Gradient accumulation was used for four forward passes before updating the weights. We trained the network for 80,000 iterations in the first stage and 100,000 iterations in the second stage. During inference, we use a non-maximal suppression of size \\(3 \\times 3\\) pixels in order to extract the keypoint coordinates from \\(\\mathbf{H}\\). Our network is implemented on PyTorch, has about \\(1M\\) trainable parameters, and takes 48 hours to train on a GeForce GTX Titan X GPU." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.249, + 0.473, + 0.597 + ], + "angle": 0, + "content": "Baselines and evaluation metrics. We compare our method with several patch-based descriptors [1, 8, 20, 28, 35, 36, 39], using the same set of SIFT [14] keypoints following the protocol of the image matching benchmark [12]. We also perform tests with a detector suitable for non-rigid correspondence [17] coupled with the deformation-aware descriptor DEAL [25]. Finally, we also include in the comparison the state-of-the-art detect-and-describe methods [6, 7, 16, 23, 26, 37, 42]. For each evaluated method, we detect the top 2,048 keypoints and match the descriptors using nearest neighbor search. In addition to the standard comparison, we include as the gold standard for image matching SuperPoint [6] with the SuperGlue [29] matcher, which holds the state-of-the-art for stereo and multi-view camera registration [12] assuming rigid scenes. As shown in Tab. 1, the methods are divided into three categories: (i) methods that only require RGB input (RGB) in contrast to methods that require additional information such as depth; (ii) Detect & Describe \\((D\\& D)\\) methods that provide both detection and description jointly within a single pipeline; and (iii) Deformation-Aware \\((D - A)\\) methods, which take into account deformation when computing the descriptors. Notice that a method may fulfill multiple categories simultaneously." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.597, + 0.473, + 0.809 + ], + "angle": 0, + "content": "We used the Matching Scores (MS) [18] to evaluate the matching performance of both the detected keypoints and descriptors. Given a ground-truth transformation and a threshold in pixels, we compute the set of correct correspondences \\(\\mathbf{S}_{gt}\\) and obtain the score for an image pair \\((i,j)\\) as \\(MS = |\\mathbf{S}_{gt}| / \\min(|\\text{keypoints}_i|, |\\text{keypoints}_j|)\\). In addition, the mean matching accuracy (MMA) is also reported, which focuses on the accuracy of the descriptors to match the keypoints that were successfully detected on both images under the threshold denoted as the set \\(\\mathbf{K}_{gt}\\), and is computed as \\(MMA = |\\mathbf{S}_{gt}| / |\\mathbf{K}_{gt}|\\). Additional results regarding repeatability of keypoints can be found in the supplementary material. To conduct the evaluation, we adopt two existing datasets of deformable objects [24, 40]." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.818, + 0.317, + 0.835 + ], + "angle": 0, + "content": "4.1. Real-world benchmarking" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.472, + 0.901 + ], + "angle": 0, + "content": "Comparison with the state-of-the-art. Tab. 1 shows the MS and MMA scores achieved by all compared methods. DALF outperformed all descriptors on average in both MS and MMA metrics, including the methods that use additional" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.895, + 0.242 + ], + "angle": 0, + "content": "depth information to extract deformation-invariant features, improving the state-of-the-art in \\(8\\%\\) p.p. in matching scores. Moreover, our method shows promising generalization properties to real deformations. DISK achieved the second-best results in MS, but the MMA indicates that its descriptors are more sensitive to non-rigid deformations. DEAL displays the second-best results in MMA thanks to its deformation-aware module but has poor performance on the MS score. It is noteworthy that DEAL relies on SIFT keypoints, which are not designed for non-rigid transformations." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.243, + 0.897, + 0.424 + ], + "angle": 0, + "content": "SuperGlue, which is comprised of SuperPoint descriptors matched with a graph neural network, showed good performance, but the drop in the scores compared to the top methods is noticeable as SuperPoint and SuperGlue do not explicitly model scene deformations. We emphasize that our method can be easily coupled and trained with a learned matcher such as SuperGlue. We report the SuperGlue results using the outdoor pretrained weights since we observed that the outdoor weights performed better in all datasets. All the other methods achieve significantly worse scores due to their inability to cope with stronger deformations alongside illumination and affine transformations." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.429, + 0.895, + 0.581 + ], + "angle": 0, + "content": "Rotation and scale robustness. Aside from deformations, in-plane rotations and scale changes are two important geometric transformations. Thus, we conduct a study using the Simulation sequences from [24] containing challenging rotation and scale changes. Fig. 4 clearly indicates that our method holds the best invariance to image in-plane rotations in addition to deformation changes compared to the five stronger competitors. Our technique also displays considerable robustness to scale changes, outperforming SuperPoint and providing a similar level of robustness of SuperGlue." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.588, + 0.895, + 0.664 + ], + "angle": 0, + "content": "Time efficiency. DALF is one of the most time efficient methods among the joint detection and description architectures. While our method runs at 9 FPS, DISK runs at 5 FPS and R2D2 at 2 FPS in an NVIDIA GeForce RTX 3060 GPU to extract 2,048 keypoints from \\(1024 \\times 768\\) images." + }, + { + "type": "image", + "bbox": [ + 0.514, + 0.689, + 0.695, + 0.838 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.709, + 0.689, + 0.892, + 0.838 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.842, + 0.895, + 0.898 + ], + "angle": 0, + "content": "Figure 4. Invariance to rotation & scale. We evaluate the matching performance of the methods under rotation and scale changes between image pairs from the Simulation dataset. The objects are simultaneously deforming, rotating and scaling in image space." + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.945, + 0.514, + 0.957 + ], + "angle": 0, + "content": "1311" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.089, + 0.895, + 0.134 + ], + "angle": 0, + "content": "Table 1. Performances using top 2,048 keypoints. The RGB methods only require color images. \\(D\\& D\\) methods perform joint detection and description. The deformation-aware methods are shown as \\(D-A\\). The mark * indicates the use of a learned matcher. Best in bold and second-best underlined. The mean was calculated with full-precision values by averaging the scores of all 833 image pairs before rounding." + }, + { + "type": "table", + "bbox": [ + 0.109, + 0.143, + 0.86, + 0.496 + ], + "angle": 0, + "content": "
RGBD&DD-AMethodDatasets: 833 pairs total - MS / MMA @ 3 pixels ↑Mean
Kinect 1 [24]Kinect 2 [24]DeSurT [40]Simulation [24]
BRAND [20]0.17 / 0.340.22 / 0.490.14 / 0.330.04 / 0.090.16 / 0.34
✓ORB [28]0.19 / 0.380.25 / 0.550.18 / 0.400.14 / 0.300.20 / 0.43
✓DAISY [36]0.23 / 0.470.29 / 0.620.16 / 0.370.19 / 0.390.22 / 0.48
✓FREAK [1]0.24 / 0.490.33 / 0.720.16 / 0.380.15 / 0.310.23 / 0.51
✓TFeat [39]0.25 / 0.500.28 / 0.610.21 / 0.480.29 / 0.630.26 / 0.56
✓Log-Polar [8]0.28 / 0.580.30 / 0.650.23 / 0.540.22 / 0.490.26 / 0.57
✓SOSNet [35]0.17 / 0.340.25 / 0.550.17 / 0.380.26 / 0.570.22 / 0.47
✓✓LF-Net [23]0.44 / 0.400.51 / 0.430.28 / 0.770.21 / 0.740.36 / 0.59
✓✓LIFT [42]0.09 / 0.570.16 / 0.650.08 / 0.520.13 / 0.730.12 / 0.62
✓✓D2-Net [7]0.20 / 0.500.23 / 0.820.14 / 0.470.11 / 0.300.17 / 0.57
✓✓SuperPoint [6]0.45 / 0.740.54 / 0.850.39 / 0.680.18 / 0.340.41 / 0.69
✓✓R2D2 [26]0.17 / 0.360.25 / 0.590.14 / 0.320.06 / 0.160.17 / 0.39
✓✓ASLFeat [16]0.31 / 0.580.39 / 0.690.28 / 0.530.19 / 0.350.31 / 0.56
✓✓DISK [37]0.53 / 0.760.52 / 0.810.44 / 0.610.26 / 0.340.45 / 0.66
✓✓SuperGlue* [29]0.40 / 0.660.62 / 0.990.39 / 0.680.23 / 0.430.44 / 0.74
✓GeoBit [21]0.31 / 0.650.35 / 0.770.20 / 0.470.32 / 0.710.30 / 0.66
✓GeoPatch [24]0.32 / 0.660.35 / 0.800.26 / 0.600.39 / 0.860.33 / 0.73
✓✓DaLI [30]0.25 / 0.510.35 / 0.760.21 / 0.480.10 / 0.220.25 / 0.54
✓✓SIFT + DEAL [25]0.33 / 0.680.38 / 0.850.27 / 0.630.36 / 0.800.34 / 0.75
✓✓Det. [17] + DEAL0.44 / 0.740.49 / 0.820.33 / 0.640.31 / 0.740.40 / 0.74
✓✓✓DALF (ours)0.54 / 0.820.62 / 0.900.49 / 0.730.42 / 0.690.53 / 0.80
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.519, + 0.472, + 0.548 + ], + "angle": 0, + "content": "Table 2. Ablation. Performance of our method when considering different network components and training strategies." + }, + { + "type": "table", + "bbox": [ + 0.09, + 0.558, + 0.451, + 0.655 + ], + "angle": 0, + "content": "
DistinctInvariant2-StageAttn.↑MS / MMA
✓--0.48 / 0.72
✓--0.51 / 0.78
✓✓0.53 / 0.79
✓✓✓0.53 / 0.78
✓✓✓✓0.53 / 0.80
" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.68, + 0.228, + 0.696 + ], + "angle": 0, + "content": "4.2. Ablation study" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.704, + 0.471, + 0.869 + ], + "angle": 0, + "content": "Our ablation study comprises five different configurations of our method: (i) using the U-net backbone only without the non-rigid warper module, which is similar to DISK excepting the descriptor loss term; (ii) computing the descriptors using the non-rigid warper module only; (iii) fusing the invariant and distinct features from the non-rigid warper and backbone respectively; (iv) perform a stage-wise training where the backbone is optimized first and the non-rigid warper second, and finally (v) we perform stage-wise training with an additional attention layer to fuse the invariant and distinctive descriptors instead of simple concatenation." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.471, + 0.902 + ], + "angle": 0, + "content": "From Tab. 2, we can observe that the non-rigid warper contributes significantly to achieving more accurate matches" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.521, + 0.895, + 0.793 + ], + "angle": 0, + "content": "when compared to using a convolutional backbone alone. Furthermore, by fusing the features, it is possible to obtain an improved descriptor that is both invariant and distinct with complementary properties. The two-stage training provides similar matching scores and slightly reduced mean accuracy compared to end-to-end training. Still, according to a more detailed analysis available in the supplementary material, we observed that it is beneficial to perform stage-wise training. The invariant part tends to dominate the distinctive part during training, rendering the distinct part less useful in practice, which is not desired for applications needing more distinct features, such as image retrieval, and datasets without significant deformations. Finally, we test if an attention-based fusion layer can deliver better results than concatenating the descriptors in the fusion step. According to the results, it is possible to slightly increase the accuracy even further with a negligible cost in computation. Thus, we choose the model with the stage-wise training as the final architecture." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.81, + 0.897, + 0.903 + ], + "angle": 0, + "content": "Limitations. Although our network can improve overall scores by learning keypoints and deformation-aware features, estimating the deformation parameters from a single image is an ambiguous problem. Therefore, physical deformations may make textures similar for different objects, harming our method's performance. Nevertheless, the learned de" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.517, + 0.958 + ], + "angle": 0, + "content": "1312" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.088, + 0.089, + 0.468, + 0.253 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.263, + 0.472, + 0.348 + ], + "angle": 0, + "content": "Figure 5. Deformable object retrieval. Our method has the best result in retrieving images of deformed objects. The first column shows the image queries, and the rows show the results from different queries. Green images correspond to the same object as the query, and red images do not correspond. Black squares imply no more objects are available for that query." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.364, + 0.471, + 0.41 + ], + "angle": 0, + "content": "formations demonstrate good generalization properties to real deformations due to the powerful combination of the keypoint extractor, warper module, and feature fusion steps." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.42, + 0.212, + 0.436 + ], + "angle": 0, + "content": "4.3. Applications" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.443, + 0.471, + 0.49 + ], + "angle": 0, + "content": "To further show the potential usage of our detection and description approach, we performed an evaluation in the two complementary tasks of object retrieval and 3D registration." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.496, + 0.472, + 0.753 + ], + "angle": 0, + "content": "Deformable object retrieval. We consider a database that contains images from various deformed objects. Each object appears multiple times with different deformations. The top K images from the database corresponding to an image query are retrieved. To evaluate the methods, we use the retrieval accuracy for different K values. K-Nearest Neighbors is used in conjunction with Bag-of-Visual-Worlds approach over the descriptors as the retrieval engine. We compare our method against the state-of-the-art description methods that demonstrated the top performances in Tab. 1, in addition to DELF [33], a state-of-the-art descriptor designed and trained specifically for image retrieval. We calculated the normalized area under the curve of each method for \\(K = \\{1, \\dots, 20\\}\\). DALF achieved the most accurate retrieval capabilities at \\(99.49\\%\\), while DELF, DEAL, SuperPoint, and DISK achieved \\(98.57\\%\\), \\(98.34\\%\\), \\(97.92\\%\\), and \\(96.12\\%\\), respectively. Fig. 5 shows some qualitative results2." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.774, + 0.471, + 0.866 + ], + "angle": 0, + "content": "Non-rigid 3D surface registration. In addition to the retrieval application, we also validate the performance of the methods in the challenging real-world task of surface registration. To that end, we employ the as-rigid-as-possible (ARAP) [31] registration to perform the surface alignment with the correspondences obtained from each method. In" + }, + { + "type": "table_caption", + "bbox": [ + 0.5, + 0.089, + 0.895, + 0.132 + ], + "angle": 0, + "content": "Table 3. 3D surface registration. The 2D and 3D accuracy is computed under varying thresholds in centimeters for the 3D residuals and in pixels for the 2D residuals. Best in bold." + }, + { + "type": "table", + "bbox": [ + 0.504, + 0.143, + 0.888, + 0.248 + ], + "angle": 0, + "content": "
Method2D Accuracy ↑3D Accuracy ↑
@2px@3px@5px@0.5cm@1.0cm@1.5cm
DISK21.330.541.236.351.758.8
SuperPoint23.234.447.442.660.568.4
SuperGlue34.951.068.142.864.473.6
GeoPatch28.941.555.941.062.371.1
DEAL29.442.056.242.964.372.8
DALF (ours)36.651.667.346.266.974.8
" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.263, + 0.895, + 0.339 + ], + "angle": 0, + "content": "these experiments, the correspondences are first filtered with an outlier removal approach [5] since the ARAP cannot handle outliers in the registration process. One of the challenges of non-rigid registration is that one cannot fit a global geometric transformation with a minimal sample using RANSAC." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.34, + 0.895, + 0.551 + ], + "angle": 0, + "content": "After the filtering stage, the ARAP is used to align the meshes of the respective image pairs. The 2D error is then computed using the ground-truth TPS transformation provided with the datasets given in pixels. We also estimate the residual 3D error, assuming that the two corresponding surfaces must be perfectly adjusted in the 3D space, as their meshes are known beforehand. Tab. 3 shows the performance of the top methods under different thresholds for the 2D and the 3D errors considering all the datasets used in Tab. 1, where our approach stands out, improving over 3 p.p. in 3D registration accuracy compared to the best current method (SuperGlue) in the tightest threshold of \\(0.5\\mathrm{cm}\\). Visual results of the 3D registration are available in the supplementary material." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.565, + 0.628, + 0.58 + ], + "angle": 0, + "content": "5. Conclusions" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.591, + 0.895, + 0.789 + ], + "angle": 0, + "content": "This paper presents DALF, a method that considers both the detection and description of keypoints under the challenging case of non-rigid geometric transformations. From extensive experiments and two applications using real deformable objects, we draw the following conclusions: (i) standard approaches for image matching deliver subpar results compared to deformation-aware features; (ii) optimizing the keypoint detection stage together with deformation-aware descriptors brings significant performance gains compared to existing deformation-aware methods that rely on affine keypoint detectors; and (iii) the feature fusion component is a simple but effective approach to increase the network expressiveness to deformations while keeping distinctiveness." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.795, + 0.897, + 0.9 + ], + "angle": 0, + "content": "Acknowledgements. The authors would like to thank CAPES (#88881.120236/2016-01), CNPq, FAPEMIG, and Google for funding different parts of this work. This work was also granted access to the HPC resources of CNRS IDRIS under the project 2021-AD011013154 and supported by the French Conseil Régional de Bourgogne-Franche-Comté." + }, + { + "type": "page_footnote", + "bbox": [ + 0.077, + 0.875, + 0.471, + 0.901 + ], + "angle": 0, + "content": "2For the sake of clarity, we filtered out objects that all methods retrieved all correct images. Full results are available in the supplementary material." + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "1313" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.115, + 0.472, + 0.17 + ], + "angle": 0, + "content": "[1] Alexandre Alahi, Raphael Ortiz, and Pierre Vandergheynst. Freak: Fast retina keypoint. In 2012 IEEE Conference on Computer Vision and Pattern Recognition, pages 510-517. 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In ECCV, 2016. 1, 2, 6, 7" + }, + { + "type": "list", + "bbox": [ + 0.503, + 0.092, + 0.894, + 0.528 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "1315" + } + ] +] \ No newline at end of file diff --git a/2023/Enhancing Deformable Local Features by Jointly Learning To Detect and Describe Keypoints/16ef7ac5-e127-4979-a2b4-14363013dd09_origin.pdf b/2023/Enhancing Deformable Local Features by Jointly Learning To Detect and Describe Keypoints/16ef7ac5-e127-4979-a2b4-14363013dd09_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..23cb452f8957bc5ed7c9816a091f086e62ae763c --- /dev/null +++ b/2023/Enhancing Deformable Local Features by Jointly Learning To Detect and Describe Keypoints/16ef7ac5-e127-4979-a2b4-14363013dd09_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:2f500c4f704f06bdf0d131ca6b33ee5757f86461be8fc8329fda03a7f452b18b +size 6174017 diff --git a/2023/Enhancing Deformable Local Features by Jointly Learning To Detect and Describe Keypoints/full.md b/2023/Enhancing Deformable Local Features by Jointly Learning To Detect and Describe Keypoints/full.md new file mode 100644 index 0000000000000000000000000000000000000000..2bf4e54a552e5123b23e8ead4b600f00c42bb860 --- /dev/null +++ b/2023/Enhancing Deformable Local Features by Jointly Learning To Detect and Describe Keypoints/full.md @@ -0,0 +1,243 @@ +# Enhancing Deformable Local Features by Jointly Learning to Detect and Describe Keypoints + +Guilherme Potje1 +Renato Martins3,4 + +Felipe Cadar1 André Araujo2 Erickson R. Nascimento1,5 + +1Universidade Federal de Minas Gerais 2Google Research + +3Université de Bourgogne 4Université de Lorraine, LORIA, Inria 5Microsoft + +{guipotje, cadar, erickson}@dcc.ufgm.br, renato.martins@u-bourgogne.fr, andrearaujo@google.com + +# Abstract + +Local feature extraction is a standard approach in computer vision for tackling important tasks such as image matching and retrieval. The core assumption of most methods is that images undergo affine transformations, disregarding more complicated effects such as non-rigid deformations. Furthermore, incipient works tailored for non-rigid correspondence still rely on keypoint detectors designed for rigid transformations, hindering performance due to the limitations of the detector. We propose DALF (Deformation-Aware Local Features), a novel deformation-aware network for jointly detecting and describing keypoints, to handle the challenging problem of matching deformable surfaces. All network components work cooperatively through a feature fusion approach that enforces the descriptors' distinctiveness and invariance. Experiments using real deforming objects showcase the superiority of our method, where it delivers $8\%$ improvement in matching scores compared to the previous best results. Our approach also enhances the performance of two real-world applications: deformable object retrieval and non-rigid 3D surface registration. Code for training, inference, and applications are publicly available at verlab.dcc.ufmg.br/descriptors/dalf Cvpr23. + +# 1. Introduction + +Finding pixel-wise correspondences between images depicting the same surface is a long-standing problem in computer vision. Besides varying illumination, viewpoint, and distance to the object of interest, real-world scenes impose additional challenges. The vast majority of the correspondence algorithms in the literature assume that our world is rigid, but this assumption is far from the truth. It is noticeable that the community invests significant efforts into novel architectures and training strategies to improve image match- + +![](images/b6841146961a8b91c8f9160bb4b64e4f1303c9e444d30c6903920336c0264323.jpg) +Figure 1. Image matching under deformations. We propose DALF, a deformation-aware keypoint detector and descriptor for matching deformable surfaces. DALF (top) enables local feature matching across deformable scenes with improved matching scores (MS) compared to state-of-the-art, as illustrated with DISK [37]. Green lines show correct matches, and red markers, the mismatches. + +ing for rigid scenes [6, 19, 26, 34, 37, 42], but disregards the fact that many objects in the real world can deform in more complex ways than an affine transformation. + +Many applications in industry, medicine, and agriculture require tracking, retrieval, and monitoring of arbitrary deformable objects and surfaces, where a general-purpose matching algorithm is needed to achieve accurate results. Since the performance of standard affine local features significantly decreases for scenarios such as strong illumination changes and deformations, a few works considering a wider class of transformations have been proposed [24, 25, 30]. However, all the deformation-aware methods neglect the keypoint detection phase, limiting their applicability in challenging deformations. Although the problems of keypoint detection and description can be treated separately, recent works that jointly perform detection and description of features [4, 26] indicate an entanglement of the two tasks since the keypoint detection can impact the performance of the descriptor. The descriptor for its turn can be used to determine reliable points optimized for specific goals. In this work, + +we propose a new method for jointly learning keypoints and descriptors robust to deformations, viewpoint, and illumination changes. We show that the detection phase is critical to obtain robust matching under deformations. Fig. 1 depicts an image pair with challenging deformations, where our method can extract reliable keypoints and match them correctly, significantly increasing matching scores compared to the recent state-of-the-art approach DISK [37]. + +Contributions. (1) Our first contribution is a new end-to-end method called DALF (Deformation-Aware Local Features), which jointly learns to detect keypoints and extract descriptors with a mutual assistance strategy to handle significant non-rigid deformations. Our method boosts the state-of-the-art in this type of feature matching by $8\%$ using only synthetic warps as supervision, showing strong generalization capabilities. We leverage a reinforcement learning algorithm for unified training, combined with spatial transformers that capture deformations by learning context priors affecting the image; (2) Second, we introduce a feature fusion approach, a major difference from previous methods that allows the model to tackle challenging deformations with complementary features (with distinctiveness and invariance properties) obtained from both the backbone and the spatial transformer module. This approach is shown beneficial with substantial performance improvements compared to the non-fused features; (3) Finally, we demonstrate state-of-the-art results in non-rigid local feature applications for deformable object retrieval and non-rigid 3D surface registration. We also will make the code and both applications publicly available to the community. + +# 2. Related work + +Keypoint detection. Traditional image keypoint detection methods seek to extract repeatable regions in images, i.e., localized points that are stable under different viewing conditions. The classic Harris detector [10] employs image derivatives that are used to compute cornerness scores, while one the most used handcrafted detectors SIFT [14], for instance, detects blobs using the Difference of Gaussians. Key.Net [13] showed that it is possible to improve keypoint detection by combining handcrafted filters and learned filters. A recent trend for learning keypoint detection is to couple description and detection in the same pipeline [7,26,34,42], since it is advantageous performance-wise to solve both tasks simultaneously in terms of computation and matching accuracy. In the same direction, our proposed method has a backbone that computes both keypoints and descriptors but at the same time employs a deformation-aware module. + +Description of local patches. Until recently, detection and description were treated separately. While some works focused on both problems, such as the seminal works of + +SIFT [14] and ORB [28], the detection and description were decoupled. SIFT and ORB descriptors employ a handcrafted gradient analysis to extract descriptors with scale and rotation invariance. Recent description approaches based on CNNs [8, 15, 19, 34, 39] consume a local patch assuming a pre-defined keypoint detector. These methods achieved state-of-the-art performance using SIFT keypoints in the image matching benchmark [12]. The networks are trained using metric learning [9, 39]. As patch-based methods rely on a pre-defined keypoint detector that may produce keypoints in unreliable or ambiguous regions, noise can be easily introduced because detection and description steps are decoupled. Unlike patch-based methods, our network is trained to produce reliable descriptions and keypoints optimized for non-rigid correspondence. Our description is also enhanced with a fusion strategy that combines complementary features into a single learned feature representation. + +Joint detection and description. DELF [22] and DELG [4] works demonstrated that coupling the detection and description phases using an attentive mechanism for keypoint selection based on higher-level image semantics can substantially improve retrieval performance. Local feature extraction has been shifting towards learning both detection and description of local features jointly [7, 16, 26, 37, 42]. Most methods follow a similar architecture, adopting a fully convolutional network (FCN) layout to produce a dense feature map, where most of the differences between the methods reside in the training scheme and loss design. The most recent describe-and-detect approaches are currently state-of-the-art on standard benchmarks [2, 12]. Differently from existing methods, we design the architecture and training to explicitly handle deformations in a coupled detection and description phase, devising a carefully tailored warper network. + +Deformation-aware methods. One of the first proposed image descriptors designed for deformable surfaces is DaLI [30]. DaLI interprets image patches as a local 3D surface, and computes the Scale-Invariant Heat Kernel Signatures [3] of the 3D surface to encode features robust to non-rigid deformations and illumination changes. Despite achieving improved matching performance compared to contemporary works, DaLI suffers from high computational and storage requirements. Similar to DaLI, GeoBit [21] and GeoPatch [24] descriptors brought ideas from computational geometry to computer vision, leveraging RGB-D images to extract visual features that are geodesic-aware. However, these geodesic-aware methods require RGB-D images and are sensitive to noise, significantly restricting their applicability. To remove the need for depth images for estimating geodesic patches, the DEAL descriptor [25] implicitly handles deformations from monocular images through a non-rigid warper module. The main shortcoming of DEAL is its dependency on existing keypoint detectors, which compro + +![](images/abc7b277c648f4ab46ba5b0438fefe264fd59e96022a6a0cd38cdad62e9d3d98.jpg) +Figure 2. DALF architecture. Our architecture jointly optimizes non-rigid keypoint detection and description, and explicitly models local deformations for descriptor extraction during training. An hourglass CNN computes a dense heat map providing specialized keypoints that are used by the Warner Net to extract deformation-aware matches. A feature fusion layer balances the trade-off between invariance and distinctiveness in the final descriptors. + +mises the descriptor performance due to the lack of equivariance on keypoints locations from most existing detectors in the presence of deformation changes. In contrast, our method learns detection and description in the same framework, achieving significant performance gains. + +# 3. Methodology + +DALF jointly learns to detect and describe points robust to non-rigid deformations, in addition to perspective and illumination changes. Both detector and descriptor are trained with a cooperative scheme aiming at the invariance of feature representations. Specifically, the keypoint detector is trained using policy gradient, seeking to increase the probability of detections that are both repeatable and reliable; Concurrently, the descriptor extractor learns to undeform and extract discriminative and invariant features from local regions. The model is only trained on synthetic warps, i.e., it does not require expensive human annotation nor pseudo-ground-truth that may contain errors and bias, such as the output of an SfM pipeline that is used in several works [7, 16, 26, 29, 37]. Fig. 2 outlines the proposed method. + +# 3.1.Keypoint detector + +The keypoint detection architecture uses a backbone hourglass CNN network $\mathbf{f}(\cdot)$ , similar to a U-net [27]. This network enables computing a keypoint heat map in the original image resolution efficiently, while also producing mid-level feature representations that are useful to describe the keypoints. We employ three downsampling blocks for the en + +coder, and three upsampling blocks for the decoder, with skip connections, each having two convolutional layers composed of a 2D convolution followed by ReLU and batch normalization. Let $I \in \mathbb{R}^{h \times w \times c}$ be the input image of size $h \times w$ and $c$ channels, $\mathbf{f}(I)$ outputs two feature maps: mid-level representations $\mathbf{X} \in \mathbb{R}^{h/8 \times w/8 \times d}$ and detection heatmap $\mathbf{H} \in \mathbb{R}^{h \times w}$ , where $d$ is the number of features. + +Keypoint detection in deforming images. An effective detector must output heatmaps $\mathbf{H} \in \mathbb{R}^{h \times w}$ with high responses in regions that can be matched well in non-rigid scenes containing view and illumination changes. Thus, during the training of the detection branch, we optimize $\mathbf{H}$ using a strategy similar to DISK [37], but applying only the probabilistic framework to learn the detection heatmap. A key difference compared to DISK is that we enforce the reliability of the detected keypoints by penalizing wrong matches even if the keypoints are repeatable. A probabilistic approach has several advantages as dealing with the inhering discreteness of sparse keypoint detection, and a simpler and more intuitive loss can be used for better convergence and regularization of the detection heatmap, in contrast to works that require elaborated handcrafted losses [7, 16, 26]. + +We seek to obtain high responses in confident regions not only for detection but also matching. To solve this problem with policy gradient, we divide the heatmap into a 2D grid of cells (Detection Heatmap in Fig. 3) and consider a set of actions that the network agent can make to select keypoints. Each cell $\mathbf{c}_i$ has $m \times n$ pixels, where the network can learn the probability of detecting a keypoint within each cell. Given an image pair $(A, B)$ of the same scene under different photometric and geometric transformations, and the ground-truth flow-field relating the two images, for each cell $\mathbf{c}_i \in \mathbf{H}$ , we consider a probability distribution over the cell $\mathbf{c} \in \mathbb{R}^{m \times n}$ . Each logit value within the cell has a probability of being a keypoint. The probability mass function $\mathbf{p}_{\mathbf{c}_i}$ over the cell $\mathbf{c}_i$ is computed by applying the Softmax function. + +Therefore, to train the detection branch, we employ the Reinforce algorithm [32]. During the forward pass of the network, we randomly sample an individual keypoint within each cell $\mathbf{c}_i$ according to the probability mass function $\mathbf{p}_{\mathbf{c}_i}$ alongside the keypoint's spatial coordinates, its probability $p_s^i$ and its logit $l_s^i$ . Note that each cell can have exactly one keypoint; however, in practice, it is common that low texture and ambiguous regions result in low-quality keypoints that cannot be reliably matched or detected in other images. For that reason, we accept a keypoint proposal from a cell with probability $\sigma (l_s^i)$ , where $\sigma$ is the sigmoid activation. This way, the network can learn to filter out unreliable keypoint proposals during training. The final probabilities of detection for the image $I$ is given by the set $P_{I} = \{\sigma (l_{s}^{i})\cdot p_{s}^{i}\},\forall \mathbf{c}_{i}\in$ $\mathbf{H}$ , such that $\sigma (l_s^i) > 0.5$ (we only sampled keypoints that has positive values in the heatmap). Since we want the + +![](images/e6015f497e529bea26a8ce4f3baf142570cdc6f439ebddab519c34de26c13a06.jpg) +Figure 3. Training strategy to learn to detect and describe keypoints aware of deformations. DALF network is used to produce a detection heatmap and a set of local features for each image. In the detector path, the heatmaps are optimized via the REINFORCE algorithm considering keypoint repeatability under deformations. In the descriptor path, feature space is learned via the hard triplet loss. A siamese setup using image pairs is employed to optimize the network. Notice that we penalize keypoints that cannot be described accurately during the second training stage; thus, the keypoints and combined descriptors are optimized jointly to be robust to deformations. + +keypoints to be repeatable, we reward points that can be detected in both images $A$ and $B$ . Thus, given the pixel coordinate $\mathbf{p}_A^j \in \mathbb{R}^2$ of detected point $j$ on image $A$ , we define the reward function $R(.)$ as follows: + +$$ +R \left(\mathbf {p} _ {A} ^ {j}\right) = \left\{ \begin{array}{l l} 1 & \text {i f} \exists \mathbf {p} _ {B} ^ {(.)} \text {s . t .} \| T \left(\mathbf {p} _ {A} ^ {j}\right) - \mathbf {p} _ {B} ^ {(.)} \| < \tau , \\ 0 & \text {o t h e r w i s e}, \end{array} \right. \tag {1} +$$ + +where $T(.)$ transforms pixels coordinates of image $A$ to image $B$ according to the ground-truth flow-field, and $\tau$ is a pixel threshold to determine if the detected keypoint in $A$ has a correspondence in image $B$ . + +Once we have the set of probabilities $P_A$ and $P_B$ , we obtain the gradient of the parameter vector $\theta$ with respect to the expected rewards over all pairwise keypoints $\mathcal{K} = P_A \times P_B$ where $\times$ denotes the cartesian product (see Fig. 3). The gradient ascent is used to maximize the expected sum of rewards: + +$$ +\nabla_ {\theta} \mathbb {E} _ {\mathcal {K}} [ R (.) ] = \sum_ {(x, y) \in \mathcal {K}} \nabla_ {\theta} (\log p (x; \theta) + \log p (y; \theta)) R (.), \tag {2} +$$ + +where $p(:,\theta)$ denotes the probability of taking that action according to the network parametrized by $\theta$ . The variables $x$ and $y$ are the probabilities of detection from a pairwise combination of keypoints. + +During the invariant feature learning stage, after $70\%$ of the training progress, we zero out the reward of the keypoints if their descriptors are unreliable. Details about the penalization term for the keypoints are described in Sec. 3.5. + +# 3.2.Keypoint descriptor + +We observed that mid-level features extracted from the hourglass encoder do not explicitly model invariance to any kind of deformations, but tend to be highly distinctive on small to moderate photometric and geometric changes, such as varying illumination, and planar warps. Therefore, it is + +advantageous to supervise the mid-level features since we obtain informative descriptors with no additional cost at inference. For that, during the first training stage, we bilinearly interpolate the feature maps $\mathbf{X}$ at the detected keypoint positions to obtain a feature vector $\mathbf{f}_d \in \mathbb{R}^D$ for each keypoint coordinate. Let $\mathbf{F}_A \in \mathbb{R}^{N \times D}$ and $\mathbf{F}_B \in \mathbb{R}^{N \times D}$ be matrices of $N$ L2-normalized feature vectors of corresponding descriptors $\mathbf{f}_d$ extracted by the hourglass decoder at keypoint positions, from images $A$ and $B$ , and $\mathbf{D}_{N \times N} = \sqrt{2 - 2\mathbf{F}_A\mathbf{F}_B^T}$ the distance matrix. To optimize the descriptors' embedding space, we employ the hard mining strategy [19] in the matrix $\mathbf{D}$ and minimize the margin ranking loss: + +$$ +\mathcal {L} _ {d} \left(\delta_ {+} ^ {(.)}, \delta_ {h} ^ {(.)}\right) = \frac {1}{N} \sum_ {i = 1} ^ {N} \max (0, \mu + \delta_ {+} ^ {(i)} - \delta_ {h} ^ {(i)}), \tag {3} +$$ + +where $\mu$ is the margin, $\delta_{+} = \| \mathbf{F}(p) - \mathbf{F}(p^{\prime})\|_{2}$ is the distance between the corresponding features, and $\delta_h = \| \mathbf{F}(p) - \mathbf{F}(h)\| _2$ is the distance to the hardest negative' sample in the batch. + +# 3.3. Non-rigid warper module + +CNNs' translation equivariance property makes local descriptors invariant to image translation, and multi-scale strategies increase the robustness of description extraction to in-plane scale changes [7, 26, 37]. However, when non-rigid deformations arise, the local texture can significantly change in appearance, introducing matching ambiguities. DEAL [25] demonstrates that thin-plate-splines (TPS), coupled with spatial transformers, can be used to model deformations for the task of local feature description. Inspired by DEAL, we adopt a TPS deformation to learn local invariance to non-rigid transformations affecting the patches. + +Spatial transformer network. We use the mid-level features from the backbone network to learn the parameters of the TPS with little additional overhead. The TPS parameter tensor $\mathbf{M}_{\theta} \in \mathbb{R}^{h/16 \times w/16 \times 2d}$ contains an intermediate representation useful to estimate a local non-rigid transformation for a keypoint. To obtain the parameter vector used in the TPS equation, first, we bilinearly interpolate a feature vector from $\mathbf{M}_{\theta}$ at the spatial position of the keypoint, obtaining an intermediate parameter vector $\in \mathbb{R}^{2d}$ . Then, an MLP is used to estimate the parameter vector $\mu_{\theta}$ that is used in the TPS transformation. The parameter vector $\mu_{\theta}$ encodes the affine matrix $\mathbf{A} \in \mathbb{R}^{2 \times 3}$ , and the non-rigid components $\mathbf{w}_k \in \mathbb{R}^2$ separately representing offsets from the affine component. Given a homogeneous 2D point $\mathbf{q} \in \mathbb{R}^3$ , weight coefficients and control points $\mathbf{c}_k, \in \mathbb{R}^2$ , we use the parameters contained in $\mu_{\theta}$ to apply the TPS transformation to a fixed polar grid centered at the keypoint: + +$$ +\mathbf {p} = \mathbf {A q} + \sum_ {k = 1} ^ {n _ {c}} \rho \left(\left\| \mathbf {q} - \mathbf {c} _ {k} \right\| ^ {2}\right) \mathbf {w} _ {k}, \tag {4} +$$ + +where $n_c$ is the number of control points, $\mathbf{q}$ is a normalized spatial image coordinate from the fixed polar grid around the keypoint, and $\mathbf{p}$ is its transformed coordinate. Fig. 2 (Warper Net) shows the patch warping and sampling step. Since we are using the TPS Radial Basis Function, $\rho = r^2\log r$ is used. After the polar grid is transformed, a differentiable bilinear sampler [11] is used to obtain the transformed image patch that is used by a CNN similar to L2-Net architecture [34] to compute the invariant feature vector, supervised by the margin ranking loss (Eq. (3)). In our implementation, a major difference from the original L2-Net is that in the last convolutional block, we add an average pooling in the axis respective to the angular axis in the polar patch, attaining full rotation invariance. + +# 3.4. Feature fusion layer + +Distinctiveness and invariance are two desired attributes of a local feature descriptor. While invariance is vital for tasks that handle large appearance changes, such as rotation and scale, it usually implies distinctiveness loss [38]. By considering two complementary features, the distinctive ones coming from the backbone network with a larger receptive field but more sensitive to strong geometric transformations, and invariant features coming from the warper module that are robust to deformation and rotation by design, we propose to incorporate both information by a feature fusion step. + +The fusion is performed by an attention-based MLP that predicts weight coefficients. The two descriptor vectors are first concatenated and forwarded to the Fusion Layer as depicted in Fig. 2. Then, the concatenated descriptors are weighted by the predicted attention weights and L2-normalized to produce the final descriptor. During training, + +we optimize each descriptor loss individually and the loss of the fused descriptors simultaneously to enforce the network to learn how to fuse the feature vectors to achieve a better feature representation. In the experiments, we demonstrate that combining the features allows the final descriptor to handle strong image transformations while maintaining its distinctiveness. + +# 3.5. Training strategy and model optimization + +Stage-wise training. During experiments, we observed that training the network end-to-end in a single phase causes the model to focus on the invariant features and ignores the distinctive features coming from the backbone, even when re-weighting the loss terms. To solve the issue, we perform a two-stage training. During the first training stage, we only train the backbone network. The backbone features have a larger receptive field and higher-level semantics compared to the Warner Net features but with less invariance to rotation and low-level deformations. In the second training phase, the Decoder, Warner Net and Fusion Layer are optimized, where the final feature representation is optimized considering both representations through the fusion step. Moreover, the decoder of the network is further refined and encouraged to detect keypoints that are optimal for the fused descriptors. + +Final loss. For the detection branch, we define the keypoint loss as $\mathcal{L}_k = -\mathbb{E}_{\mathcal{K}}[R(.)]$ and add a regularization term for all the detected keypoints during training $\mathcal{L}_p = -\sum_x\log p(x)\cdot c$ , where $c$ is a small negative constant to discourage the network from detecting low-quality points. We employ the margin ranking loss described in Sec. 3.2 for all the descriptor vectors computed by our network. The final loss is then computed as $\mathcal{L} = \mathcal{L}_k + \mathcal{L}_p + \lambda \mathcal{L}_d$ , where $\lambda$ is a weight term to balance the magnitude between the triplet loss and the policy-gradient losses. + +# 4. Experiments + +Training and implementation details. We developed a carefully designed synthetic data generation pipeline to create plausible non-rigid deformations of surfaces to supervise the training. We perform photometric and geometric changes to real images obtained from large-scale Structure-from-Motion datasets [41]. We use only the raw images and do not use any information about correspondences or annotated labels. During the training, we add random photometric changes, random homographic projection, and random TPS warps to obtain ground-truth dense flows between image pairs depicting the same surface. The training starts with easier samples and progressively becomes more difficult, achieving the hardest difficulty at $60\%$ of training iterations. In the experiments, we use the following hyperparameter values: $\mu = 0.5$ in the triplet loss; pixel threshold $\tau = 1.5$ ; $\lambda = 0.005$ to balance the loss terms; keypoint penalization + +$c = -7e^{-5}$ ; cell size $m = n = 8$ pixels; and the number of control points $n_c = 64$ . As detailed in Sec. 3.5, we perform a two-stage training. Gradient accumulation was used for four forward passes before updating the weights. We trained the network for 80,000 iterations in the first stage and 100,000 iterations in the second stage. During inference, we use a non-maximal suppression of size $3 \times 3$ pixels in order to extract the keypoint coordinates from $\mathbf{H}$ . Our network is implemented on PyTorch, has about $1M$ trainable parameters, and takes 48 hours to train on a GeForce GTX Titan X GPU. + +Baselines and evaluation metrics. We compare our method with several patch-based descriptors [1, 8, 20, 28, 35, 36, 39], using the same set of SIFT [14] keypoints following the protocol of the image matching benchmark [12]. We also perform tests with a detector suitable for non-rigid correspondence [17] coupled with the deformation-aware descriptor DEAL [25]. Finally, we also include in the comparison the state-of-the-art detect-and-describe methods [6, 7, 16, 23, 26, 37, 42]. For each evaluated method, we detect the top 2,048 keypoints and match the descriptors using nearest neighbor search. In addition to the standard comparison, we include as the gold standard for image matching SuperPoint [6] with the SuperGlue [29] matcher, which holds the state-of-the-art for stereo and multi-view camera registration [12] assuming rigid scenes. As shown in Tab. 1, the methods are divided into three categories: (i) methods that only require RGB input (RGB) in contrast to methods that require additional information such as depth; (ii) Detect & Describe $(D\& D)$ methods that provide both detection and description jointly within a single pipeline; and (iii) Deformation-Aware $(D - A)$ methods, which take into account deformation when computing the descriptors. Notice that a method may fulfill multiple categories simultaneously. + +We used the Matching Scores (MS) [18] to evaluate the matching performance of both the detected keypoints and descriptors. Given a ground-truth transformation and a threshold in pixels, we compute the set of correct correspondences $\mathbf{S}_{gt}$ and obtain the score for an image pair $(i,j)$ as $MS = |\mathbf{S}_{gt}| / \min(|\text{keypoints}_i|, |\text{keypoints}_j|)$ . In addition, the mean matching accuracy (MMA) is also reported, which focuses on the accuracy of the descriptors to match the keypoints that were successfully detected on both images under the threshold denoted as the set $\mathbf{K}_{gt}$ , and is computed as $MMA = |\mathbf{S}_{gt}| / |\mathbf{K}_{gt}|$ . Additional results regarding repeatability of keypoints can be found in the supplementary material. To conduct the evaluation, we adopt two existing datasets of deformable objects [24, 40]. + +# 4.1. Real-world benchmarking + +Comparison with the state-of-the-art. Tab. 1 shows the MS and MMA scores achieved by all compared methods. DALF outperformed all descriptors on average in both MS and MMA metrics, including the methods that use additional + +depth information to extract deformation-invariant features, improving the state-of-the-art in $8\%$ p.p. in matching scores. Moreover, our method shows promising generalization properties to real deformations. DISK achieved the second-best results in MS, but the MMA indicates that its descriptors are more sensitive to non-rigid deformations. DEAL displays the second-best results in MMA thanks to its deformation-aware module but has poor performance on the MS score. It is noteworthy that DEAL relies on SIFT keypoints, which are not designed for non-rigid transformations. + +SuperGlue, which is comprised of SuperPoint descriptors matched with a graph neural network, showed good performance, but the drop in the scores compared to the top methods is noticeable as SuperPoint and SuperGlue do not explicitly model scene deformations. We emphasize that our method can be easily coupled and trained with a learned matcher such as SuperGlue. We report the SuperGlue results using the outdoor pretrained weights since we observed that the outdoor weights performed better in all datasets. All the other methods achieve significantly worse scores due to their inability to cope with stronger deformations alongside illumination and affine transformations. + +Rotation and scale robustness. Aside from deformations, in-plane rotations and scale changes are two important geometric transformations. Thus, we conduct a study using the Simulation sequences from [24] containing challenging rotation and scale changes. Fig. 4 clearly indicates that our method holds the best invariance to image in-plane rotations in addition to deformation changes compared to the five stronger competitors. Our technique also displays considerable robustness to scale changes, outperforming SuperPoint and providing a similar level of robustness of SuperGlue. + +Time efficiency. DALF is one of the most time efficient methods among the joint detection and description architectures. While our method runs at 9 FPS, DISK runs at 5 FPS and R2D2 at 2 FPS in an NVIDIA GeForce RTX 3060 GPU to extract 2,048 keypoints from $1024 \times 768$ images. + +![](images/404f0fdfb3da3c368727c6426d1ac43d4e33a009bdf48991a708e1c3d9efcde8.jpg) +Figure 4. Invariance to rotation & scale. We evaluate the matching performance of the methods under rotation and scale changes between image pairs from the Simulation dataset. The objects are simultaneously deforming, rotating and scaling in image space. + +![](images/ef55d095bd34cfaa71aebfb0ac0ec4acf75423694f6efbfe8836d88d3e9bd177.jpg) + +Table 1. Performances using top 2,048 keypoints. The RGB methods only require color images. $D\& D$ methods perform joint detection and description. The deformation-aware methods are shown as $D-A$ . The mark * indicates the use of a learned matcher. Best in bold and second-best underlined. The mean was calculated with full-precision values by averaging the scores of all 833 image pairs before rounding. + +
RGBD&DD-AMethodDatasets: 833 pairs total - MS / MMA @ 3 pixels ↑Mean
Kinect 1 [24]Kinect 2 [24]DeSurT [40]Simulation [24]
BRAND [20]0.17 / 0.340.22 / 0.490.14 / 0.330.04 / 0.090.16 / 0.34
✓ORB [28]0.19 / 0.380.25 / 0.550.18 / 0.400.14 / 0.300.20 / 0.43
✓DAISY [36]0.23 / 0.470.29 / 0.620.16 / 0.370.19 / 0.390.22 / 0.48
✓FREAK [1]0.24 / 0.490.33 / 0.720.16 / 0.380.15 / 0.310.23 / 0.51
✓TFeat [39]0.25 / 0.500.28 / 0.610.21 / 0.480.29 / 0.630.26 / 0.56
✓Log-Polar [8]0.28 / 0.580.30 / 0.650.23 / 0.540.22 / 0.490.26 / 0.57
✓SOSNet [35]0.17 / 0.340.25 / 0.550.17 / 0.380.26 / 0.570.22 / 0.47
✓✓LF-Net [23]0.44 / 0.400.51 / 0.430.28 / 0.770.21 / 0.740.36 / 0.59
✓✓LIFT [42]0.09 / 0.570.16 / 0.650.08 / 0.520.13 / 0.730.12 / 0.62
✓✓D2-Net [7]0.20 / 0.500.23 / 0.820.14 / 0.470.11 / 0.300.17 / 0.57
✓✓SuperPoint [6]0.45 / 0.740.54 / 0.850.39 / 0.680.18 / 0.340.41 / 0.69
✓✓R2D2 [26]0.17 / 0.360.25 / 0.590.14 / 0.320.06 / 0.160.17 / 0.39
✓✓ASLFeat [16]0.31 / 0.580.39 / 0.690.28 / 0.530.19 / 0.350.31 / 0.56
✓✓DISK [37]0.53 / 0.760.52 / 0.810.44 / 0.610.26 / 0.340.45 / 0.66
✓✓SuperGlue* [29]0.40 / 0.660.62 / 0.990.39 / 0.680.23 / 0.430.44 / 0.74
✓GeoBit [21]0.31 / 0.650.35 / 0.770.20 / 0.470.32 / 0.710.30 / 0.66
✓GeoPatch [24]0.32 / 0.660.35 / 0.800.26 / 0.600.39 / 0.860.33 / 0.73
✓✓DaLI [30]0.25 / 0.510.35 / 0.760.21 / 0.480.10 / 0.220.25 / 0.54
✓✓SIFT + DEAL [25]0.33 / 0.680.38 / 0.850.27 / 0.630.36 / 0.800.34 / 0.75
✓✓Det. [17] + DEAL0.44 / 0.740.49 / 0.820.33 / 0.640.31 / 0.740.40 / 0.74
✓✓✓DALF (ours)0.54 / 0.820.62 / 0.900.49 / 0.730.42 / 0.690.53 / 0.80
+ +Table 2. Ablation. Performance of our method when considering different network components and training strategies. + +
DistinctInvariant2-StageAttn.↑MS / MMA
✓--0.48 / 0.72
✓--0.51 / 0.78
✓✓0.53 / 0.79
✓✓✓0.53 / 0.78
✓✓✓✓0.53 / 0.80
+ +# 4.2. Ablation study + +Our ablation study comprises five different configurations of our method: (i) using the U-net backbone only without the non-rigid warper module, which is similar to DISK excepting the descriptor loss term; (ii) computing the descriptors using the non-rigid warper module only; (iii) fusing the invariant and distinct features from the non-rigid warper and backbone respectively; (iv) perform a stage-wise training where the backbone is optimized first and the non-rigid warper second, and finally (v) we perform stage-wise training with an additional attention layer to fuse the invariant and distinctive descriptors instead of simple concatenation. + +From Tab. 2, we can observe that the non-rigid warper contributes significantly to achieving more accurate matches + +when compared to using a convolutional backbone alone. Furthermore, by fusing the features, it is possible to obtain an improved descriptor that is both invariant and distinct with complementary properties. The two-stage training provides similar matching scores and slightly reduced mean accuracy compared to end-to-end training. Still, according to a more detailed analysis available in the supplementary material, we observed that it is beneficial to perform stage-wise training. The invariant part tends to dominate the distinctive part during training, rendering the distinct part less useful in practice, which is not desired for applications needing more distinct features, such as image retrieval, and datasets without significant deformations. Finally, we test if an attention-based fusion layer can deliver better results than concatenating the descriptors in the fusion step. According to the results, it is possible to slightly increase the accuracy even further with a negligible cost in computation. Thus, we choose the model with the stage-wise training as the final architecture. + +Limitations. Although our network can improve overall scores by learning keypoints and deformation-aware features, estimating the deformation parameters from a single image is an ambiguous problem. Therefore, physical deformations may make textures similar for different objects, harming our method's performance. Nevertheless, the learned de + +![](images/858f54df73c46f9b197da86496289f926779cb68bf557b3011f11990f13a71ee.jpg) +Figure 5. Deformable object retrieval. Our method has the best result in retrieving images of deformed objects. The first column shows the image queries, and the rows show the results from different queries. Green images correspond to the same object as the query, and red images do not correspond. Black squares imply no more objects are available for that query. + +formations demonstrate good generalization properties to real deformations due to the powerful combination of the keypoint extractor, warper module, and feature fusion steps. + +# 4.3. Applications + +To further show the potential usage of our detection and description approach, we performed an evaluation in the two complementary tasks of object retrieval and 3D registration. + +Deformable object retrieval. We consider a database that contains images from various deformed objects. Each object appears multiple times with different deformations. The top K images from the database corresponding to an image query are retrieved. To evaluate the methods, we use the retrieval accuracy for different K values. K-Nearest Neighbors is used in conjunction with Bag-of-Visual-Worlds approach over the descriptors as the retrieval engine. We compare our method against the state-of-the-art description methods that demonstrated the top performances in Tab. 1, in addition to DELF [33], a state-of-the-art descriptor designed and trained specifically for image retrieval. We calculated the normalized area under the curve of each method for $K = \{1, \dots, 20\}$ . DALF achieved the most accurate retrieval capabilities at $99.49\%$ , while DELF, DEAL, SuperPoint, and DISK achieved $98.57\%$ , $98.34\%$ , $97.92\%$ , and $96.12\%$ , respectively. Fig. 5 shows some qualitative results2. + +Non-rigid 3D surface registration. In addition to the retrieval application, we also validate the performance of the methods in the challenging real-world task of surface registration. To that end, we employ the as-rigid-as-possible (ARAP) [31] registration to perform the surface alignment with the correspondences obtained from each method. In + +Table 3. 3D surface registration. The 2D and 3D accuracy is computed under varying thresholds in centimeters for the 3D residuals and in pixels for the 2D residuals. Best in bold. + +
Method2D Accuracy ↑3D Accuracy ↑
@2px@3px@5px@0.5cm@1.0cm@1.5cm
DISK21.330.541.236.351.758.8
SuperPoint23.234.447.442.660.568.4
SuperGlue34.951.068.142.864.473.6
GeoPatch28.941.555.941.062.371.1
DEAL29.442.056.242.964.372.8
DALF (ours)36.651.667.346.266.974.8
+ +these experiments, the correspondences are first filtered with an outlier removal approach [5] since the ARAP cannot handle outliers in the registration process. One of the challenges of non-rigid registration is that one cannot fit a global geometric transformation with a minimal sample using RANSAC. + +After the filtering stage, the ARAP is used to align the meshes of the respective image pairs. The 2D error is then computed using the ground-truth TPS transformation provided with the datasets given in pixels. We also estimate the residual 3D error, assuming that the two corresponding surfaces must be perfectly adjusted in the 3D space, as their meshes are known beforehand. Tab. 3 shows the performance of the top methods under different thresholds for the 2D and the 3D errors considering all the datasets used in Tab. 1, where our approach stands out, improving over 3 p.p. in 3D registration accuracy compared to the best current method (SuperGlue) in the tightest threshold of $0.5\mathrm{cm}$ . Visual results of the 3D registration are available in the supplementary material. + +# 5. Conclusions + +This paper presents DALF, a method that considers both the detection and description of keypoints under the challenging case of non-rigid geometric transformations. From extensive experiments and two applications using real deformable objects, we draw the following conclusions: (i) standard approaches for image matching deliver subpar results compared to deformation-aware features; (ii) optimizing the keypoint detection stage together with deformation-aware descriptors brings significant performance gains compared to existing deformation-aware methods that rely on affine keypoint detectors; and (iii) the feature fusion component is a simple but effective approach to increase the network expressiveness to deformations while keeping distinctiveness. + +Acknowledgements. The authors would like to thank CAPES (#88881.120236/2016-01), CNPq, FAPEMIG, and Google for funding different parts of this work. 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In ECCV, 2016. 1, 2, 6, 7 \ No newline at end of file diff --git a/2023/Enhancing Deformable Local Features by Jointly Learning To Detect and Describe Keypoints/images.zip b/2023/Enhancing Deformable Local Features by Jointly Learning To Detect and Describe Keypoints/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..b2e59df2a9a0bc2c5c822160af18012446bb556c --- /dev/null +++ b/2023/Enhancing Deformable Local Features by Jointly Learning To Detect and Describe Keypoints/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:54c8e19c55e50f77dd434ea5676b426fafd068799e333c4b25651701cf3ff6d7 +size 518983 diff --git a/2023/Enhancing Deformable Local Features by Jointly Learning To Detect and Describe Keypoints/layout.json b/2023/Enhancing Deformable Local Features by Jointly Learning To Detect and Describe Keypoints/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..93a5b6d66419a809b88de6ef09140a0097d0aef9 --- /dev/null +++ b/2023/Enhancing Deformable Local Features by Jointly Learning To Detect and Describe Keypoints/layout.json @@ -0,0 +1,7656 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 115, + 103, + 479, + 140 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 115, + 103, + 479, + 140 + ], + "spans": [ + { + "bbox": [ + 115, + 103, + 479, + 140 + ], + "type": "text", + "content": "Enhancing Deformable Local Features by Jointly Learning to Detect and Describe Keypoints" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 162, + 160, + 269, + 190 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 162, + 160, + 269, + 190 + ], + "spans": [ + { + "bbox": [ + 162, + 160, + 269, + 190 + ], + "type": "text", + "content": "Guilherme Potje1 \nRenato Martins3,4" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 273, + 161, + 441, + 190 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 273, + 161, + 441, + 190 + ], + "spans": [ + { + "bbox": [ + 273, + 161, + 441, + 190 + ], + "type": "text", + "content": "Felipe Cadar1 André Araujo2 Erickson R. 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The core assumption of most methods is that images undergo affine transformations, disregarding more complicated effects such as non-rigid deformations. Furthermore, incipient works tailored for non-rigid correspondence still rely on keypoint detectors designed for rigid transformations, hindering performance due to the limitations of the detector. We propose DALF (Deformation-Aware Local Features), a novel deformation-aware network for jointly detecting and describing keypoints, to handle the challenging problem of matching deformable surfaces. All network components work cooperatively through a feature fusion approach that enforces the descriptors' distinctiveness and invariance. Experiments using real deforming objects showcase the superiority of our method, where it delivers " + }, + { + "bbox": [ + 46, + 294, + 290, + 558 + ], + "type": "inline_equation", + "content": "8\\%" + }, + { + "bbox": [ + 46, + 294, + 290, + 558 + ], + "type": "text", + "content": " improvement in matching scores compared to the previous best results. Our approach also enhances the performance of two real-world applications: deformable object retrieval and non-rigid 3D surface registration. Code for training, inference, and applications are publicly available at verlab.dcc.ufmg.br/descriptors/dalf Cvpr23." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 584, + 128, + 596 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 584, + 128, + 596 + ], + "spans": [ + { + "bbox": [ + 47, + 584, + 128, + 596 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 605, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 605, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 605, + 288, + 714 + ], + "type": "text", + "content": "Finding pixel-wise correspondences between images depicting the same surface is a long-standing problem in computer vision. Besides varying illumination, viewpoint, and distance to the object of interest, real-world scenes impose additional challenges. The vast majority of the correspondence algorithms in the literature assume that our world is rigid, but this assumption is far from the truth. It is noticeable that the community invests significant efforts into novel architectures and training strategies to improve image match-" + } + ] + } + ], + "index": 11 + }, + { + "type": "image", + "bbox": [ + 312, + 266, + 541, + 378 + ], + "blocks": [ + { + "bbox": [ + 312, + 266, + 541, + 378 + ], + "lines": [ + { + "bbox": [ + 312, + 266, + 541, + 378 + ], + "spans": [ + { + "bbox": [ + 312, + 266, + 541, + 378 + ], + "type": "image", + "image_path": "b6841146961a8b91c8f9160bb4b64e4f1303c9e444d30c6903920336c0264323.jpg" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 385, + 548, + 452 + ], + "lines": [ + { + "bbox": [ + 305, + 385, + 548, + 452 + ], + "spans": [ + { + "bbox": [ + 305, + 385, + 548, + 452 + ], + "type": "text", + "content": "Figure 1. Image matching under deformations. We propose DALF, a deformation-aware keypoint detector and descriptor for matching deformable surfaces. DALF (top) enables local feature matching across deformable scenes with improved matching scores (MS) compared to state-of-the-art, as illustrated with DISK [37]. Green lines show correct matches, and red markers, the mismatches." + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_caption" + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 474, + 546, + 509 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 474, + 546, + 509 + ], + "spans": [ + { + "bbox": [ + 304, + 474, + 546, + 509 + ], + "type": "text", + "content": "ing for rigid scenes [6, 19, 26, 34, 37, 42], but disregards the fact that many objects in the real world can deform in more complex ways than an affine transformation." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 510, + 548, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 510, + 548, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 510, + 548, + 714 + ], + "type": "text", + "content": "Many applications in industry, medicine, and agriculture require tracking, retrieval, and monitoring of arbitrary deformable objects and surfaces, where a general-purpose matching algorithm is needed to achieve accurate results. Since the performance of standard affine local features significantly decreases for scenarios such as strong illumination changes and deformations, a few works considering a wider class of transformations have been proposed [24, 25, 30]. However, all the deformation-aware methods neglect the keypoint detection phase, limiting their applicability in challenging deformations. Although the problems of keypoint detection and description can be treated separately, recent works that jointly perform detection and description of features [4, 26] indicate an entanglement of the two tasks since the keypoint detection can impact the performance of the descriptor. The descriptor for its turn can be used to determine reliable points optimized for specific goals. In this work," + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "1306" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 288, + 168 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 288, + 168 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 288, + 168 + ], + "type": "text", + "content": "we propose a new method for jointly learning keypoints and descriptors robust to deformations, viewpoint, and illumination changes. We show that the detection phase is critical to obtain robust matching under deformations. Fig. 1 depicts an image pair with challenging deformations, where our method can extract reliable keypoints and match them correctly, significantly increasing matching scores compared to the recent state-of-the-art approach DISK [37]." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 183, + 290, + 447 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 183, + 290, + 447 + ], + "spans": [ + { + "bbox": [ + 46, + 183, + 290, + 447 + ], + "type": "text", + "content": "Contributions. (1) Our first contribution is a new end-to-end method called DALF (Deformation-Aware Local Features), which jointly learns to detect keypoints and extract descriptors with a mutual assistance strategy to handle significant non-rigid deformations. Our method boosts the state-of-the-art in this type of feature matching by " + }, + { + "bbox": [ + 46, + 183, + 290, + 447 + ], + "type": "inline_equation", + "content": "8\\%" + }, + { + "bbox": [ + 46, + 183, + 290, + 447 + ], + "type": "text", + "content": " using only synthetic warps as supervision, showing strong generalization capabilities. We leverage a reinforcement learning algorithm for unified training, combined with spatial transformers that capture deformations by learning context priors affecting the image; (2) Second, we introduce a feature fusion approach, a major difference from previous methods that allows the model to tackle challenging deformations with complementary features (with distinctiveness and invariance properties) obtained from both the backbone and the spatial transformer module. This approach is shown beneficial with substantial performance improvements compared to the non-fused features; (3) Finally, we demonstrate state-of-the-art results in non-rigid local feature applications for deformable object retrieval and non-rigid 3D surface registration. We also will make the code and both applications publicly available to the community." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 457, + 132, + 469 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 457, + 132, + 469 + ], + "spans": [ + { + "bbox": [ + 47, + 457, + 132, + 469 + ], + "type": "text", + "content": "2. Related work" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 477, + 288, + 669 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 477, + 288, + 669 + ], + "spans": [ + { + "bbox": [ + 46, + 477, + 288, + 669 + ], + "type": "text", + "content": "Keypoint detection. Traditional image keypoint detection methods seek to extract repeatable regions in images, i.e., localized points that are stable under different viewing conditions. The classic Harris detector [10] employs image derivatives that are used to compute cornerness scores, while one the most used handcrafted detectors SIFT [14], for instance, detects blobs using the Difference of Gaussians. Key.Net [13] showed that it is possible to improve keypoint detection by combining handcrafted filters and learned filters. A recent trend for learning keypoint detection is to couple description and detection in the same pipeline [7,26,34,42], since it is advantageous performance-wise to solve both tasks simultaneously in terms of computation and matching accuracy. In the same direction, our proposed method has a backbone that computes both keypoints and descriptors but at the same time employs a deformation-aware module." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 677, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 288, + 713 + ], + "type": "text", + "content": "Description of local patches. Until recently, detection and description were treated separately. While some works focused on both problems, such as the seminal works of" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 72, + 547, + 277 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 277 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 277 + ], + "type": "text", + "content": "SIFT [14] and ORB [28], the detection and description were decoupled. SIFT and ORB descriptors employ a handcrafted gradient analysis to extract descriptors with scale and rotation invariance. Recent description approaches based on CNNs [8, 15, 19, 34, 39] consume a local patch assuming a pre-defined keypoint detector. These methods achieved state-of-the-art performance using SIFT keypoints in the image matching benchmark [12]. The networks are trained using metric learning [9, 39]. As patch-based methods rely on a pre-defined keypoint detector that may produce keypoints in unreliable or ambiguous regions, noise can be easily introduced because detection and description steps are decoupled. Unlike patch-based methods, our network is trained to produce reliable descriptions and keypoints optimized for non-rigid correspondence. Our description is also enhanced with a fusion strategy that combines complementary features into a single learned feature representation." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 285, + 548, + 477 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 285, + 548, + 477 + ], + "spans": [ + { + "bbox": [ + 304, + 285, + 548, + 477 + ], + "type": "text", + "content": "Joint detection and description. DELF [22] and DELG [4] works demonstrated that coupling the detection and description phases using an attentive mechanism for keypoint selection based on higher-level image semantics can substantially improve retrieval performance. Local feature extraction has been shifting towards learning both detection and description of local features jointly [7, 16, 26, 37, 42]. Most methods follow a similar architecture, adopting a fully convolutional network (FCN) layout to produce a dense feature map, where most of the differences between the methods reside in the training scheme and loss design. The most recent describe-and-detect approaches are currently state-of-the-art on standard benchmarks [2, 12]. Differently from existing methods, we design the architecture and training to explicitly handle deformations in a coupled detection and description phase, devising a carefully tailored warper network." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 486, + 548, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 486, + 548, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 486, + 548, + 715 + ], + "type": "text", + "content": "Deformation-aware methods. One of the first proposed image descriptors designed for deformable surfaces is DaLI [30]. DaLI interprets image patches as a local 3D surface, and computes the Scale-Invariant Heat Kernel Signatures [3] of the 3D surface to encode features robust to non-rigid deformations and illumination changes. Despite achieving improved matching performance compared to contemporary works, DaLI suffers from high computational and storage requirements. Similar to DaLI, GeoBit [21] and GeoPatch [24] descriptors brought ideas from computational geometry to computer vision, leveraging RGB-D images to extract visual features that are geodesic-aware. However, these geodesic-aware methods require RGB-D images and are sensitive to noise, significantly restricting their applicability. To remove the need for depth images for estimating geodesic patches, the DEAL descriptor [25] implicitly handles deformations from monocular images through a non-rigid warper module. The main shortcoming of DEAL is its dependency on existing keypoint detectors, which compro" + } + ] + } + ], + "index": 7 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "1307" + } + ] + } + ], + "index": 8 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 55, + 72, + 280, + 272 + ], + "blocks": [ + { + "bbox": [ + 55, + 72, + 280, + 272 + ], + "lines": [ + { + "bbox": [ + 55, + 72, + 280, + 272 + ], + "spans": [ + { + "bbox": [ + 55, + 72, + 280, + 272 + ], + "type": "image", + "image_path": "abc7b277c648f4ab46ba5b0438fefe264fd59e96022a6a0cd38cdad62e9d3d98.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 276, + 289, + 354 + ], + "lines": [ + { + "bbox": [ + 46, + 276, + 289, + 354 + ], + "spans": [ + { + "bbox": [ + 46, + 276, + 289, + 354 + ], + "type": "text", + "content": "Figure 2. DALF architecture. Our architecture jointly optimizes non-rigid keypoint detection and description, and explicitly models local deformations for descriptor extraction during training. An hourglass CNN computes a dense heat map providing specialized keypoints that are used by the Warner Net to extract deformation-aware matches. A feature fusion layer balances the trade-off between invariance and distinctiveness in the final descriptors." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 359, + 288, + 420 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 359, + 288, + 420 + ], + "spans": [ + { + "bbox": [ + 46, + 359, + 288, + 420 + ], + "type": "text", + "content": "mises the descriptor performance due to the lack of equivariance on keypoints locations from most existing detectors in the presence of deformation changes. In contrast, our method learns detection and description in the same framework, achieving significant performance gains." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 429, + 130, + 443 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 429, + 130, + 443 + ], + "spans": [ + { + "bbox": [ + 47, + 429, + 130, + 443 + ], + "type": "text", + "content": "3. Methodology" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 449, + 288, + 617 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 449, + 288, + 617 + ], + "spans": [ + { + "bbox": [ + 46, + 449, + 288, + 617 + ], + "type": "text", + "content": "DALF jointly learns to detect and describe points robust to non-rigid deformations, in addition to perspective and illumination changes. Both detector and descriptor are trained with a cooperative scheme aiming at the invariance of feature representations. Specifically, the keypoint detector is trained using policy gradient, seeking to increase the probability of detections that are both repeatable and reliable; Concurrently, the descriptor extractor learns to undeform and extract discriminative and invariant features from local regions. The model is only trained on synthetic warps, i.e., it does not require expensive human annotation nor pseudo-ground-truth that may contain errors and bias, such as the output of an SfM pipeline that is used in several works [7, 16, 26, 29, 37]. Fig. 2 outlines the proposed method." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 623, + 153, + 636 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 623, + 153, + 636 + ], + "spans": [ + { + "bbox": [ + 47, + 623, + 153, + 636 + ], + "type": "text", + "content": "3.1.Keypoint detector" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 641, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 641, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 641, + 289, + 715 + ], + "type": "text", + "content": "The keypoint detection architecture uses a backbone hourglass CNN network " + }, + { + "bbox": [ + 46, + 641, + 289, + 715 + ], + "type": "inline_equation", + "content": "\\mathbf{f}(\\cdot)" + }, + { + "bbox": [ + 46, + 641, + 289, + 715 + ], + "type": "text", + "content": ", similar to a U-net [27]. This network enables computing a keypoint heat map in the original image resolution efficiently, while also producing mid-level feature representations that are useful to describe the keypoints. We employ three downsampling blocks for the en" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 72, + 547, + 156 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 156 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 156 + ], + "type": "text", + "content": "coder, and three upsampling blocks for the decoder, with skip connections, each having two convolutional layers composed of a 2D convolution followed by ReLU and batch normalization. Let " + }, + { + "bbox": [ + 304, + 72, + 547, + 156 + ], + "type": "inline_equation", + "content": "I \\in \\mathbb{R}^{h \\times w \\times c}" + }, + { + "bbox": [ + 304, + 72, + 547, + 156 + ], + "type": "text", + "content": " be the input image of size " + }, + { + "bbox": [ + 304, + 72, + 547, + 156 + ], + "type": "inline_equation", + "content": "h \\times w" + }, + { + "bbox": [ + 304, + 72, + 547, + 156 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 72, + 547, + 156 + ], + "type": "inline_equation", + "content": "c" + }, + { + "bbox": [ + 304, + 72, + 547, + 156 + ], + "type": "text", + "content": " channels, " + }, + { + "bbox": [ + 304, + 72, + 547, + 156 + ], + "type": "inline_equation", + "content": "\\mathbf{f}(I)" + }, + { + "bbox": [ + 304, + 72, + 547, + 156 + ], + "type": "text", + "content": " outputs two feature maps: mid-level representations " + }, + { + "bbox": [ + 304, + 72, + 547, + 156 + ], + "type": "inline_equation", + "content": "\\mathbf{X} \\in \\mathbb{R}^{h/8 \\times w/8 \\times d}" + }, + { + "bbox": [ + 304, + 72, + 547, + 156 + ], + "type": "text", + "content": " and detection heatmap " + }, + { + "bbox": [ + 304, + 72, + 547, + 156 + ], + "type": "inline_equation", + "content": "\\mathbf{H} \\in \\mathbb{R}^{h \\times w}" + }, + { + "bbox": [ + 304, + 72, + 547, + 156 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 72, + 547, + 156 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 304, + 72, + 547, + 156 + ], + "type": "text", + "content": " is the number of features." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 174, + 547, + 353 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 174, + 547, + 353 + ], + "spans": [ + { + "bbox": [ + 304, + 174, + 547, + 353 + ], + "type": "text", + "content": "Keypoint detection in deforming images. An effective detector must output heatmaps " + }, + { + "bbox": [ + 304, + 174, + 547, + 353 + ], + "type": "inline_equation", + "content": "\\mathbf{H} \\in \\mathbb{R}^{h \\times w}" + }, + { + "bbox": [ + 304, + 174, + 547, + 353 + ], + "type": "text", + "content": " with high responses in regions that can be matched well in non-rigid scenes containing view and illumination changes. Thus, during the training of the detection branch, we optimize " + }, + { + "bbox": [ + 304, + 174, + 547, + 353 + ], + "type": "inline_equation", + "content": "\\mathbf{H}" + }, + { + "bbox": [ + 304, + 174, + 547, + 353 + ], + "type": "text", + "content": " using a strategy similar to DISK [37], but applying only the probabilistic framework to learn the detection heatmap. A key difference compared to DISK is that we enforce the reliability of the detected keypoints by penalizing wrong matches even if the keypoints are repeatable. A probabilistic approach has several advantages as dealing with the inhering discreteness of sparse keypoint detection, and a simpler and more intuitive loss can be used for better convergence and regularization of the detection heatmap, in contrast to works that require elaborated handcrafted losses [7, 16, 26]." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 354, + 547, + 521 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 354, + 547, + 521 + ], + "spans": [ + { + "bbox": [ + 304, + 354, + 547, + 521 + ], + "type": "text", + "content": "We seek to obtain high responses in confident regions not only for detection but also matching. To solve this problem with policy gradient, we divide the heatmap into a 2D grid of cells (Detection Heatmap in Fig. 3) and consider a set of actions that the network agent can make to select keypoints. Each cell " + }, + { + "bbox": [ + 304, + 354, + 547, + 521 + ], + "type": "inline_equation", + "content": "\\mathbf{c}_i" + }, + { + "bbox": [ + 304, + 354, + 547, + 521 + ], + "type": "text", + "content": " has " + }, + { + "bbox": [ + 304, + 354, + 547, + 521 + ], + "type": "inline_equation", + "content": "m \\times n" + }, + { + "bbox": [ + 304, + 354, + 547, + 521 + ], + "type": "text", + "content": " pixels, where the network can learn the probability of detecting a keypoint within each cell. Given an image pair " + }, + { + "bbox": [ + 304, + 354, + 547, + 521 + ], + "type": "inline_equation", + "content": "(A, B)" + }, + { + "bbox": [ + 304, + 354, + 547, + 521 + ], + "type": "text", + "content": " of the same scene under different photometric and geometric transformations, and the ground-truth flow-field relating the two images, for each cell " + }, + { + "bbox": [ + 304, + 354, + 547, + 521 + ], + "type": "inline_equation", + "content": "\\mathbf{c}_i \\in \\mathbf{H}" + }, + { + "bbox": [ + 304, + 354, + 547, + 521 + ], + "type": "text", + "content": ", we consider a probability distribution over the cell " + }, + { + "bbox": [ + 304, + 354, + 547, + 521 + ], + "type": "inline_equation", + "content": "\\mathbf{c} \\in \\mathbb{R}^{m \\times n}" + }, + { + "bbox": [ + 304, + 354, + 547, + 521 + ], + "type": "text", + "content": ". Each logit value within the cell has a probability of being a keypoint. The probability mass function " + }, + { + "bbox": [ + 304, + 354, + 547, + 521 + ], + "type": "inline_equation", + "content": "\\mathbf{p}_{\\mathbf{c}_i}" + }, + { + "bbox": [ + 304, + 354, + 547, + 521 + ], + "type": "text", + "content": " over the cell " + }, + { + "bbox": [ + 304, + 354, + 547, + 521 + ], + "type": "inline_equation", + "content": "\\mathbf{c}_i" + }, + { + "bbox": [ + 304, + 354, + 547, + 521 + ], + "type": "text", + "content": " is computed by applying the Softmax function." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 522, + 548, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 522, + 548, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 522, + 548, + 714 + ], + "type": "text", + "content": "Therefore, to train the detection branch, we employ the Reinforce algorithm [32]. During the forward pass of the network, we randomly sample an individual keypoint within each cell " + }, + { + "bbox": [ + 304, + 522, + 548, + 714 + ], + "type": "inline_equation", + "content": "\\mathbf{c}_i" + }, + { + "bbox": [ + 304, + 522, + 548, + 714 + ], + "type": "text", + "content": " according to the probability mass function " + }, + { + "bbox": [ + 304, + 522, + 548, + 714 + ], + "type": "inline_equation", + "content": "\\mathbf{p}_{\\mathbf{c}_i}" + }, + { + "bbox": [ + 304, + 522, + 548, + 714 + ], + "type": "text", + "content": " alongside the keypoint's spatial coordinates, its probability " + }, + { + "bbox": [ + 304, + 522, + 548, + 714 + ], + "type": "inline_equation", + "content": "p_s^i" + }, + { + "bbox": [ + 304, + 522, + 548, + 714 + ], + "type": "text", + "content": " and its logit " + }, + { + "bbox": [ + 304, + 522, + 548, + 714 + ], + "type": "inline_equation", + "content": "l_s^i" + }, + { + "bbox": [ + 304, + 522, + 548, + 714 + ], + "type": "text", + "content": ". Note that each cell can have exactly one keypoint; however, in practice, it is common that low texture and ambiguous regions result in low-quality keypoints that cannot be reliably matched or detected in other images. For that reason, we accept a keypoint proposal from a cell with probability " + }, + { + "bbox": [ + 304, + 522, + 548, + 714 + ], + "type": "inline_equation", + "content": "\\sigma (l_s^i)" + }, + { + "bbox": [ + 304, + 522, + 548, + 714 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 522, + 548, + 714 + ], + "type": "inline_equation", + "content": "\\sigma" + }, + { + "bbox": [ + 304, + 522, + 548, + 714 + ], + "type": "text", + "content": " is the sigmoid activation. This way, the network can learn to filter out unreliable keypoint proposals during training. The final probabilities of detection for the image " + }, + { + "bbox": [ + 304, + 522, + 548, + 714 + ], + "type": "inline_equation", + "content": "I" + }, + { + "bbox": [ + 304, + 522, + 548, + 714 + ], + "type": "text", + "content": " is given by the set " + }, + { + "bbox": [ + 304, + 522, + 548, + 714 + ], + "type": "inline_equation", + "content": "P_{I} = \\{\\sigma (l_{s}^{i})\\cdot p_{s}^{i}\\},\\forall \\mathbf{c}_{i}\\in" + }, + { + "bbox": [ + 304, + 522, + 548, + 714 + ], + "type": "inline_equation", + "content": "\\mathbf{H}" + }, + { + "bbox": [ + 304, + 522, + 548, + 714 + ], + "type": "text", + "content": ", such that " + }, + { + "bbox": [ + 304, + 522, + 548, + 714 + ], + "type": "inline_equation", + "content": "\\sigma (l_s^i) > 0.5" + }, + { + "bbox": [ + 304, + 522, + 548, + 714 + ], + "type": "text", + "content": " (we only sampled keypoints that has positive values in the heatmap). Since we want the" + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "1308" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 72, + 69, + 523, + 201 + ], + "blocks": [ + { + "bbox": [ + 72, + 69, + 523, + 201 + ], + "lines": [ + { + "bbox": [ + 72, + 69, + 523, + 201 + ], + "spans": [ + { + "bbox": [ + 72, + 69, + 523, + 201 + ], + "type": "image", + "image_path": "e6015f497e529bea26a8ce4f3baf142570cdc6f439ebddab519c34de26c13a06.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 209, + 547, + 266 + ], + "lines": [ + { + "bbox": [ + 46, + 209, + 547, + 266 + ], + "spans": [ + { + "bbox": [ + 46, + 209, + 547, + 266 + ], + "type": "text", + "content": "Figure 3. Training strategy to learn to detect and describe keypoints aware of deformations. DALF network is used to produce a detection heatmap and a set of local features for each image. In the detector path, the heatmaps are optimized via the REINFORCE algorithm considering keypoint repeatability under deformations. In the descriptor path, feature space is learned via the hard triplet loss. A siamese setup using image pairs is employed to optimize the network. Notice that we penalize keypoints that cannot be described accurately during the second training stage; thus, the keypoints and combined descriptors are optimized jointly to be robust to deformations." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 274, + 288, + 323 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 274, + 288, + 323 + ], + "spans": [ + { + "bbox": [ + 46, + 274, + 288, + 323 + ], + "type": "text", + "content": "keypoints to be repeatable, we reward points that can be detected in both images " + }, + { + "bbox": [ + 46, + 274, + 288, + 323 + ], + "type": "inline_equation", + "content": "A" + }, + { + "bbox": [ + 46, + 274, + 288, + 323 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 274, + 288, + 323 + ], + "type": "inline_equation", + "content": "B" + }, + { + "bbox": [ + 46, + 274, + 288, + 323 + ], + "type": "text", + "content": ". Thus, given the pixel coordinate " + }, + { + "bbox": [ + 46, + 274, + 288, + 323 + ], + "type": "inline_equation", + "content": "\\mathbf{p}_A^j \\in \\mathbb{R}^2" + }, + { + "bbox": [ + 46, + 274, + 288, + 323 + ], + "type": "text", + "content": " of detected point " + }, + { + "bbox": [ + 46, + 274, + 288, + 323 + ], + "type": "inline_equation", + "content": "j" + }, + { + "bbox": [ + 46, + 274, + 288, + 323 + ], + "type": "text", + "content": " on image " + }, + { + "bbox": [ + 46, + 274, + 288, + 323 + ], + "type": "inline_equation", + "content": "A" + }, + { + "bbox": [ + 46, + 274, + 288, + 323 + ], + "type": "text", + "content": ", we define the reward function " + }, + { + "bbox": [ + 46, + 274, + 288, + 323 + ], + "type": "inline_equation", + "content": "R(.)" + }, + { + "bbox": [ + 46, + 274, + 288, + 323 + ], + "type": "text", + "content": " as follows:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 60, + 330, + 288, + 361 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 60, + 330, + 288, + 361 + ], + "spans": [ + { + "bbox": [ + 60, + 330, + 288, + 361 + ], + "type": "interline_equation", + "content": "R \\left(\\mathbf {p} _ {A} ^ {j}\\right) = \\left\\{ \\begin{array}{l l} 1 & \\text {i f} \\exists \\mathbf {p} _ {B} ^ {(.)} \\text {s . t .} \\| T \\left(\\mathbf {p} _ {A} ^ {j}\\right) - \\mathbf {p} _ {B} ^ {(.)} \\| < \\tau , \\\\ 0 & \\text {o t h e r w i s e}, \\end{array} \\right. \\tag {1}", + "image_path": "f41e0c851937e15937b30aabbf9d5e858a3f3fcb55a795e781664dfeb7b4b1af.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 369, + 287, + 417 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 369, + 287, + 417 + ], + "spans": [ + { + "bbox": [ + 46, + 369, + 287, + 417 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 369, + 287, + 417 + ], + "type": "inline_equation", + "content": "T(.)" + }, + { + "bbox": [ + 46, + 369, + 287, + 417 + ], + "type": "text", + "content": " transforms pixels coordinates of image " + }, + { + "bbox": [ + 46, + 369, + 287, + 417 + ], + "type": "inline_equation", + "content": "A" + }, + { + "bbox": [ + 46, + 369, + 287, + 417 + ], + "type": "text", + "content": " to image " + }, + { + "bbox": [ + 46, + 369, + 287, + 417 + ], + "type": "inline_equation", + "content": "B" + }, + { + "bbox": [ + 46, + 369, + 287, + 417 + ], + "type": "text", + "content": " according to the ground-truth flow-field, and " + }, + { + "bbox": [ + 46, + 369, + 287, + 417 + ], + "type": "inline_equation", + "content": "\\tau" + }, + { + "bbox": [ + 46, + 369, + 287, + 417 + ], + "type": "text", + "content": " is a pixel threshold to determine if the detected keypoint in " + }, + { + "bbox": [ + 46, + 369, + 287, + 417 + ], + "type": "inline_equation", + "content": "A" + }, + { + "bbox": [ + 46, + 369, + 287, + 417 + ], + "type": "text", + "content": " has a correspondence in image " + }, + { + "bbox": [ + 46, + 369, + 287, + 417 + ], + "type": "inline_equation", + "content": "B" + }, + { + "bbox": [ + 46, + 369, + 287, + 417 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 417, + 288, + 477 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 417, + 288, + 477 + ], + "spans": [ + { + "bbox": [ + 46, + 417, + 288, + 477 + ], + "type": "text", + "content": "Once we have the set of probabilities " + }, + { + "bbox": [ + 46, + 417, + 288, + 477 + ], + "type": "inline_equation", + "content": "P_A" + }, + { + "bbox": [ + 46, + 417, + 288, + 477 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 417, + 288, + 477 + ], + "type": "inline_equation", + "content": "P_B" + }, + { + "bbox": [ + 46, + 417, + 288, + 477 + ], + "type": "text", + "content": ", we obtain the gradient of the parameter vector " + }, + { + "bbox": [ + 46, + 417, + 288, + 477 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 46, + 417, + 288, + 477 + ], + "type": "text", + "content": " with respect to the expected rewards over all pairwise keypoints " + }, + { + "bbox": [ + 46, + 417, + 288, + 477 + ], + "type": "inline_equation", + "content": "\\mathcal{K} = P_A \\times P_B" + }, + { + "bbox": [ + 46, + 417, + 288, + 477 + ], + "type": "text", + "content": " where " + }, + { + "bbox": [ + 46, + 417, + 288, + 477 + ], + "type": "inline_equation", + "content": "\\times" + }, + { + "bbox": [ + 46, + 417, + 288, + 477 + ], + "type": "text", + "content": " denotes the cartesian product (see Fig. 3). The gradient ascent is used to maximize the expected sum of rewards:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 48, + 495, + 287, + 531 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 495, + 287, + 531 + ], + "spans": [ + { + "bbox": [ + 48, + 495, + 287, + 531 + ], + "type": "interline_equation", + "content": "\\nabla_ {\\theta} \\mathbb {E} _ {\\mathcal {K}} [ R (.) ] = \\sum_ {(x, y) \\in \\mathcal {K}} \\nabla_ {\\theta} (\\log p (x; \\theta) + \\log p (y; \\theta)) R (.), \\tag {2}", + "image_path": "489fd4cd6bf0f03194659947839bac1c484e2d100448995b6bee6e1e52faf186.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 532, + 287, + 581 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 532, + 287, + 581 + ], + "spans": [ + { + "bbox": [ + 46, + 532, + 287, + 581 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 532, + 287, + 581 + ], + "type": "inline_equation", + "content": "p(:,\\theta)" + }, + { + "bbox": [ + 46, + 532, + 287, + 581 + ], + "type": "text", + "content": " denotes the probability of taking that action according to the network parametrized by " + }, + { + "bbox": [ + 46, + 532, + 287, + 581 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 46, + 532, + 287, + 581 + ], + "type": "text", + "content": ". The variables " + }, + { + "bbox": [ + 46, + 532, + 287, + 581 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 46, + 532, + 287, + 581 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 532, + 287, + 581 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 46, + 532, + 287, + 581 + ], + "type": "text", + "content": " are the probabilities of detection from a pairwise combination of keypoints." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 580, + 288, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 580, + 288, + 628 + ], + "spans": [ + { + "bbox": [ + 46, + 580, + 288, + 628 + ], + "type": "text", + "content": "During the invariant feature learning stage, after " + }, + { + "bbox": [ + 46, + 580, + 288, + 628 + ], + "type": "inline_equation", + "content": "70\\%" + }, + { + "bbox": [ + 46, + 580, + 288, + 628 + ], + "type": "text", + "content": " of the training progress, we zero out the reward of the keypoints if their descriptors are unreliable. Details about the penalization term for the keypoints are described in Sec. 3.5." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 635, + 163, + 648 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 635, + 163, + 648 + ], + "spans": [ + { + "bbox": [ + 47, + 635, + 163, + 648 + ], + "type": "text", + "content": "3.2.Keypoint descriptor" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "type": "text", + "content": "We observed that mid-level features extracted from the hourglass encoder do not explicitly model invariance to any kind of deformations, but tend to be highly distinctive on small to moderate photometric and geometric changes, such as varying illumination, and planar warps. Therefore, it is" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 274, + 547, + 424 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 274, + 547, + 424 + ], + "spans": [ + { + "bbox": [ + 304, + 274, + 547, + 424 + ], + "type": "text", + "content": "advantageous to supervise the mid-level features since we obtain informative descriptors with no additional cost at inference. For that, during the first training stage, we bilinearly interpolate the feature maps " + }, + { + "bbox": [ + 304, + 274, + 547, + 424 + ], + "type": "inline_equation", + "content": "\\mathbf{X}" + }, + { + "bbox": [ + 304, + 274, + 547, + 424 + ], + "type": "text", + "content": " at the detected keypoint positions to obtain a feature vector " + }, + { + "bbox": [ + 304, + 274, + 547, + 424 + ], + "type": "inline_equation", + "content": "\\mathbf{f}_d \\in \\mathbb{R}^D" + }, + { + "bbox": [ + 304, + 274, + 547, + 424 + ], + "type": "text", + "content": " for each keypoint coordinate. Let " + }, + { + "bbox": [ + 304, + 274, + 547, + 424 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_A \\in \\mathbb{R}^{N \\times D}" + }, + { + "bbox": [ + 304, + 274, + 547, + 424 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 274, + 547, + 424 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_B \\in \\mathbb{R}^{N \\times D}" + }, + { + "bbox": [ + 304, + 274, + 547, + 424 + ], + "type": "text", + "content": " be matrices of " + }, + { + "bbox": [ + 304, + 274, + 547, + 424 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 304, + 274, + 547, + 424 + ], + "type": "text", + "content": " L2-normalized feature vectors of corresponding descriptors " + }, + { + "bbox": [ + 304, + 274, + 547, + 424 + ], + "type": "inline_equation", + "content": "\\mathbf{f}_d" + }, + { + "bbox": [ + 304, + 274, + 547, + 424 + ], + "type": "text", + "content": " extracted by the hourglass decoder at keypoint positions, from images " + }, + { + "bbox": [ + 304, + 274, + 547, + 424 + ], + "type": "inline_equation", + "content": "A" + }, + { + "bbox": [ + 304, + 274, + 547, + 424 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 274, + 547, + 424 + ], + "type": "inline_equation", + "content": "B" + }, + { + "bbox": [ + 304, + 274, + 547, + 424 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 304, + 274, + 547, + 424 + ], + "type": "inline_equation", + "content": "\\mathbf{D}_{N \\times N} = \\sqrt{2 - 2\\mathbf{F}_A\\mathbf{F}_B^T}" + }, + { + "bbox": [ + 304, + 274, + 547, + 424 + ], + "type": "text", + "content": " the distance matrix. To optimize the descriptors' embedding space, we employ the hard mining strategy [19] in the matrix " + }, + { + "bbox": [ + 304, + 274, + 547, + 424 + ], + "type": "inline_equation", + "content": "\\mathbf{D}" + }, + { + "bbox": [ + 304, + 274, + 547, + 424 + ], + "type": "text", + "content": " and minimize the margin ranking loss:" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 319, + 434, + 546, + 467 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 319, + 434, + 546, + 467 + ], + "spans": [ + { + "bbox": [ + 319, + 434, + 546, + 467 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {d} \\left(\\delta_ {+} ^ {(.)}, \\delta_ {h} ^ {(.)}\\right) = \\frac {1}{N} \\sum_ {i = 1} ^ {N} \\max (0, \\mu + \\delta_ {+} ^ {(i)} - \\delta_ {h} ^ {(i)}), \\tag {3}", + "image_path": "61754d28e571fbeebb751690f3d6c24170819f725fcdf85e4d625945d9b38dd5.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 478, + 547, + 526 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 478, + 547, + 526 + ], + "spans": [ + { + "bbox": [ + 304, + 478, + 547, + 526 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 478, + 547, + 526 + ], + "type": "inline_equation", + "content": "\\mu" + }, + { + "bbox": [ + 304, + 478, + 547, + 526 + ], + "type": "text", + "content": " is the margin, " + }, + { + "bbox": [ + 304, + 478, + 547, + 526 + ], + "type": "inline_equation", + "content": "\\delta_{+} = \\| \\mathbf{F}(p) - \\mathbf{F}(p^{\\prime})\\|_{2}" + }, + { + "bbox": [ + 304, + 478, + 547, + 526 + ], + "type": "text", + "content": " is the distance between the corresponding features, and " + }, + { + "bbox": [ + 304, + 478, + 547, + 526 + ], + "type": "inline_equation", + "content": "\\delta_h = \\| \\mathbf{F}(p) - \\mathbf{F}(h)\\| _2" + }, + { + "bbox": [ + 304, + 478, + 547, + 526 + ], + "type": "text", + "content": " is the distance to the hardest negative' sample in the batch." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 536, + 449, + 550 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 536, + 449, + 550 + ], + "spans": [ + { + "bbox": [ + 306, + 536, + 449, + 550 + ], + "type": "text", + "content": "3.3. Non-rigid warper module" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 555, + 547, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 555, + 547, + 689 + ], + "spans": [ + { + "bbox": [ + 304, + 555, + 547, + 689 + ], + "type": "text", + "content": "CNNs' translation equivariance property makes local descriptors invariant to image translation, and multi-scale strategies increase the robustness of description extraction to in-plane scale changes [7, 26, 37]. However, when non-rigid deformations arise, the local texture can significantly change in appearance, introducing matching ambiguities. DEAL [25] demonstrates that thin-plate-splines (TPS), coupled with spatial transformers, can be used to model deformations for the task of local feature description. Inspired by DEAL, we adopt a TPS deformation to learn local invariance to non-rigid transformations affecting the patches." + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 306, + 693, + 547, + 714 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 693, + 547, + 714 + ], + "spans": [ + { + "bbox": [ + 306, + 693, + 547, + 714 + ], + "type": "text", + "content": "1The hardest negative example " + }, + { + "bbox": [ + 306, + 693, + 547, + 714 + ], + "type": "inline_equation", + "content": "h_i^j" + }, + { + "bbox": [ + 306, + 693, + 547, + 714 + ], + "type": "text", + "content": " for each row " + }, + { + "bbox": [ + 306, + 693, + 547, + 714 + ], + "type": "inline_equation", + "content": "j" + }, + { + "bbox": [ + 306, + 693, + 547, + 714 + ], + "type": "text", + "content": " of " + }, + { + "bbox": [ + 306, + 693, + 547, + 714 + ], + "type": "inline_equation", + "content": "\\mathbf{D}_{N \\times N}" + }, + { + "bbox": [ + 306, + 693, + 547, + 714 + ], + "type": "text", + "content": " is computed as " + }, + { + "bbox": [ + 306, + 693, + 547, + 714 + ], + "type": "inline_equation", + "content": "\\min D_j" + }, + { + "bbox": [ + 306, + 693, + 547, + 714 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 306, + 693, + 547, + 714 + ], + "type": "inline_equation", + "content": "i = j = \\{1, \\dots, N\\}" + }, + { + "bbox": [ + 306, + 693, + 547, + 714 + ], + "type": "text", + "content": " s.t. " + }, + { + "bbox": [ + 306, + 693, + 547, + 714 + ], + "type": "inline_equation", + "content": "i \\neq j" + }, + { + "bbox": [ + 306, + 693, + 547, + 714 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "text", + "content": "1309" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 277 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 277 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 277 + ], + "type": "text", + "content": "Spatial transformer network. We use the mid-level features from the backbone network to learn the parameters of the TPS with little additional overhead. The TPS parameter tensor " + }, + { + "bbox": [ + 46, + 72, + 289, + 277 + ], + "type": "inline_equation", + "content": "\\mathbf{M}_{\\theta} \\in \\mathbb{R}^{h/16 \\times w/16 \\times 2d}" + }, + { + "bbox": [ + 46, + 72, + 289, + 277 + ], + "type": "text", + "content": " contains an intermediate representation useful to estimate a local non-rigid transformation for a keypoint. To obtain the parameter vector used in the TPS equation, first, we bilinearly interpolate a feature vector from " + }, + { + "bbox": [ + 46, + 72, + 289, + 277 + ], + "type": "inline_equation", + "content": "\\mathbf{M}_{\\theta}" + }, + { + "bbox": [ + 46, + 72, + 289, + 277 + ], + "type": "text", + "content": " at the spatial position of the keypoint, obtaining an intermediate parameter vector " + }, + { + "bbox": [ + 46, + 72, + 289, + 277 + ], + "type": "inline_equation", + "content": "\\in \\mathbb{R}^{2d}" + }, + { + "bbox": [ + 46, + 72, + 289, + 277 + ], + "type": "text", + "content": ". Then, an MLP is used to estimate the parameter vector " + }, + { + "bbox": [ + 46, + 72, + 289, + 277 + ], + "type": "inline_equation", + "content": "\\mu_{\\theta}" + }, + { + "bbox": [ + 46, + 72, + 289, + 277 + ], + "type": "text", + "content": " that is used in the TPS transformation. The parameter vector " + }, + { + "bbox": [ + 46, + 72, + 289, + 277 + ], + "type": "inline_equation", + "content": "\\mu_{\\theta}" + }, + { + "bbox": [ + 46, + 72, + 289, + 277 + ], + "type": "text", + "content": " encodes the affine matrix " + }, + { + "bbox": [ + 46, + 72, + 289, + 277 + ], + "type": "inline_equation", + "content": "\\mathbf{A} \\in \\mathbb{R}^{2 \\times 3}" + }, + { + "bbox": [ + 46, + 72, + 289, + 277 + ], + "type": "text", + "content": ", and the non-rigid components " + }, + { + "bbox": [ + 46, + 72, + 289, + 277 + ], + "type": "inline_equation", + "content": "\\mathbf{w}_k \\in \\mathbb{R}^2" + }, + { + "bbox": [ + 46, + 72, + 289, + 277 + ], + "type": "text", + "content": " separately representing offsets from the affine component. Given a homogeneous 2D point " + }, + { + "bbox": [ + 46, + 72, + 289, + 277 + ], + "type": "inline_equation", + "content": "\\mathbf{q} \\in \\mathbb{R}^3" + }, + { + "bbox": [ + 46, + 72, + 289, + 277 + ], + "type": "text", + "content": ", weight coefficients and control points " + }, + { + "bbox": [ + 46, + 72, + 289, + 277 + ], + "type": "inline_equation", + "content": "\\mathbf{c}_k, \\in \\mathbb{R}^2" + }, + { + "bbox": [ + 46, + 72, + 289, + 277 + ], + "type": "text", + "content": ", we use the parameters contained in " + }, + { + "bbox": [ + 46, + 72, + 289, + 277 + ], + "type": "inline_equation", + "content": "\\mu_{\\theta}" + }, + { + "bbox": [ + 46, + 72, + 289, + 277 + ], + "type": "text", + "content": " to apply the TPS transformation to a fixed polar grid centered at the keypoint:" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 97, + 285, + 288, + 317 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 97, + 285, + 288, + 317 + ], + "spans": [ + { + "bbox": [ + 97, + 285, + 288, + 317 + ], + "type": "interline_equation", + "content": "\\mathbf {p} = \\mathbf {A q} + \\sum_ {k = 1} ^ {n _ {c}} \\rho \\left(\\left\\| \\mathbf {q} - \\mathbf {c} _ {k} \\right\\| ^ {2}\\right) \\mathbf {w} _ {k}, \\tag {4}", + "image_path": "8e5523ccbfd9e67da5a464f96be6976187c408b7edc56fa333c78d05f6feb8a6.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 326, + 289, + 494 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 326, + 289, + 494 + ], + "spans": [ + { + "bbox": [ + 46, + 326, + 289, + 494 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 326, + 289, + 494 + ], + "type": "inline_equation", + "content": "n_c" + }, + { + "bbox": [ + 46, + 326, + 289, + 494 + ], + "type": "text", + "content": " is the number of control points, " + }, + { + "bbox": [ + 46, + 326, + 289, + 494 + ], + "type": "inline_equation", + "content": "\\mathbf{q}" + }, + { + "bbox": [ + 46, + 326, + 289, + 494 + ], + "type": "text", + "content": " is a normalized spatial image coordinate from the fixed polar grid around the keypoint, and " + }, + { + "bbox": [ + 46, + 326, + 289, + 494 + ], + "type": "inline_equation", + "content": "\\mathbf{p}" + }, + { + "bbox": [ + 46, + 326, + 289, + 494 + ], + "type": "text", + "content": " is its transformed coordinate. Fig. 2 (Warper Net) shows the patch warping and sampling step. Since we are using the TPS Radial Basis Function, " + }, + { + "bbox": [ + 46, + 326, + 289, + 494 + ], + "type": "inline_equation", + "content": "\\rho = r^2\\log r" + }, + { + "bbox": [ + 46, + 326, + 289, + 494 + ], + "type": "text", + "content": " is used. After the polar grid is transformed, a differentiable bilinear sampler [11] is used to obtain the transformed image patch that is used by a CNN similar to L2-Net architecture [34] to compute the invariant feature vector, supervised by the margin ranking loss (Eq. (3)). In our implementation, a major difference from the original L2-Net is that in the last convolutional block, we add an average pooling in the axis respective to the angular axis in the polar patch, attaining full rotation invariance." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 502, + 164, + 514 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 502, + 164, + 514 + ], + "spans": [ + { + "bbox": [ + 47, + 502, + 164, + 514 + ], + "type": "text", + "content": "3.4. Feature fusion layer" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 521, + 287, + 640 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 521, + 287, + 640 + ], + "spans": [ + { + "bbox": [ + 46, + 521, + 287, + 640 + ], + "type": "text", + "content": "Distinctiveness and invariance are two desired attributes of a local feature descriptor. While invariance is vital for tasks that handle large appearance changes, such as rotation and scale, it usually implies distinctiveness loss [38]. By considering two complementary features, the distinctive ones coming from the backbone network with a larger receptive field but more sensitive to strong geometric transformations, and invariant features coming from the warper module that are robust to deformation and rotation by design, we propose to incorporate both information by a feature fusion step." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 642, + 289, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 642, + 289, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 642, + 289, + 714 + ], + "type": "text", + "content": "The fusion is performed by an attention-based MLP that predicts weight coefficients. The two descriptor vectors are first concatenated and forwarded to the Fusion Layer as depicted in Fig. 2. Then, the concatenated descriptors are weighted by the predicted attention weights and L2-normalized to produce the final descriptor. During training," + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 72, + 547, + 156 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 156 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 156 + ], + "type": "text", + "content": "we optimize each descriptor loss individually and the loss of the fused descriptors simultaneously to enforce the network to learn how to fuse the feature vectors to achieve a better feature representation. In the experiments, we demonstrate that combining the features allows the final descriptor to handle strong image transformations while maintaining its distinctiveness." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 305, + 165, + 524, + 178 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 165, + 524, + 178 + ], + "spans": [ + { + "bbox": [ + 305, + 165, + 524, + 178 + ], + "type": "text", + "content": "3.5. Training strategy and model optimization" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 184, + 547, + 365 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 184, + 547, + 365 + ], + "spans": [ + { + "bbox": [ + 304, + 184, + 547, + 365 + ], + "type": "text", + "content": "Stage-wise training. During experiments, we observed that training the network end-to-end in a single phase causes the model to focus on the invariant features and ignores the distinctive features coming from the backbone, even when re-weighting the loss terms. To solve the issue, we perform a two-stage training. During the first training stage, we only train the backbone network. The backbone features have a larger receptive field and higher-level semantics compared to the Warner Net features but with less invariance to rotation and low-level deformations. In the second training phase, the Decoder, Warner Net and Fusion Layer are optimized, where the final feature representation is optimized considering both representations through the fusion step. Moreover, the decoder of the network is further refined and encouraged to detect keypoints that are optimal for the fused descriptors." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 369, + 548, + 490 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 369, + 548, + 490 + ], + "spans": [ + { + "bbox": [ + 304, + 369, + 548, + 490 + ], + "type": "text", + "content": "Final loss. For the detection branch, we define the keypoint loss as " + }, + { + "bbox": [ + 304, + 369, + 548, + 490 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_k = -\\mathbb{E}_{\\mathcal{K}}[R(.)]" + }, + { + "bbox": [ + 304, + 369, + 548, + 490 + ], + "type": "text", + "content": " and add a regularization term for all the detected keypoints during training " + }, + { + "bbox": [ + 304, + 369, + 548, + 490 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_p = -\\sum_x\\log p(x)\\cdot c" + }, + { + "bbox": [ + 304, + 369, + 548, + 490 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 369, + 548, + 490 + ], + "type": "inline_equation", + "content": "c" + }, + { + "bbox": [ + 304, + 369, + 548, + 490 + ], + "type": "text", + "content": " is a small negative constant to discourage the network from detecting low-quality points. We employ the margin ranking loss described in Sec. 3.2 for all the descriptor vectors computed by our network. The final loss is then computed as " + }, + { + "bbox": [ + 304, + 369, + 548, + 490 + ], + "type": "inline_equation", + "content": "\\mathcal{L} = \\mathcal{L}_k + \\mathcal{L}_p + \\lambda \\mathcal{L}_d" + }, + { + "bbox": [ + 304, + 369, + 548, + 490 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 369, + 548, + 490 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 304, + 369, + 548, + 490 + ], + "type": "text", + "content": " is a weight term to balance the magnitude between the triplet loss and the policy-gradient losses." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 502, + 388, + 514 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 502, + 388, + 514 + ], + "spans": [ + { + "bbox": [ + 305, + 502, + 388, + 514 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 521, + 548, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 521, + 548, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 521, + 548, + 715 + ], + "type": "text", + "content": "Training and implementation details. We developed a carefully designed synthetic data generation pipeline to create plausible non-rigid deformations of surfaces to supervise the training. We perform photometric and geometric changes to real images obtained from large-scale Structure-from-Motion datasets [41]. We use only the raw images and do not use any information about correspondences or annotated labels. During the training, we add random photometric changes, random homographic projection, and random TPS warps to obtain ground-truth dense flows between image pairs depicting the same surface. The training starts with easier samples and progressively becomes more difficult, achieving the hardest difficulty at " + }, + { + "bbox": [ + 304, + 521, + 548, + 715 + ], + "type": "inline_equation", + "content": "60\\%" + }, + { + "bbox": [ + 304, + 521, + 548, + 715 + ], + "type": "text", + "content": " of training iterations. In the experiments, we use the following hyperparameter values: " + }, + { + "bbox": [ + 304, + 521, + 548, + 715 + ], + "type": "inline_equation", + "content": "\\mu = 0.5" + }, + { + "bbox": [ + 304, + 521, + 548, + 715 + ], + "type": "text", + "content": " in the triplet loss; pixel threshold " + }, + { + "bbox": [ + 304, + 521, + 548, + 715 + ], + "type": "inline_equation", + "content": "\\tau = 1.5" + }, + { + "bbox": [ + 304, + 521, + 548, + 715 + ], + "type": "text", + "content": "; " + }, + { + "bbox": [ + 304, + 521, + 548, + 715 + ], + "type": "inline_equation", + "content": "\\lambda = 0.005" + }, + { + "bbox": [ + 304, + 521, + 548, + 715 + ], + "type": "text", + "content": " to balance the loss terms; keypoint penalization" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "text", + "content": "1310" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 192 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 192 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 192 + ], + "type": "inline_equation", + "content": "c = -7e^{-5}" + }, + { + "bbox": [ + 46, + 72, + 289, + 192 + ], + "type": "text", + "content": "; cell size " + }, + { + "bbox": [ + 46, + 72, + 289, + 192 + ], + "type": "inline_equation", + "content": "m = n = 8" + }, + { + "bbox": [ + 46, + 72, + 289, + 192 + ], + "type": "text", + "content": " pixels; and the number of control points " + }, + { + "bbox": [ + 46, + 72, + 289, + 192 + ], + "type": "inline_equation", + "content": "n_c = 64" + }, + { + "bbox": [ + 46, + 72, + 289, + 192 + ], + "type": "text", + "content": ". As detailed in Sec. 3.5, we perform a two-stage training. Gradient accumulation was used for four forward passes before updating the weights. We trained the network for 80,000 iterations in the first stage and 100,000 iterations in the second stage. During inference, we use a non-maximal suppression of size " + }, + { + "bbox": [ + 46, + 72, + 289, + 192 + ], + "type": "inline_equation", + "content": "3 \\times 3" + }, + { + "bbox": [ + 46, + 72, + 289, + 192 + ], + "type": "text", + "content": " pixels in order to extract the keypoint coordinates from " + }, + { + "bbox": [ + 46, + 72, + 289, + 192 + ], + "type": "inline_equation", + "content": "\\mathbf{H}" + }, + { + "bbox": [ + 46, + 72, + 289, + 192 + ], + "type": "text", + "content": ". Our network is implemented on PyTorch, has about " + }, + { + "bbox": [ + 46, + 72, + 289, + 192 + ], + "type": "inline_equation", + "content": "1M" + }, + { + "bbox": [ + 46, + 72, + 289, + 192 + ], + "type": "text", + "content": " trainable parameters, and takes 48 hours to train on a GeForce GTX Titan X GPU." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 197, + 289, + 472 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 197, + 289, + 472 + ], + "spans": [ + { + "bbox": [ + 46, + 197, + 289, + 472 + ], + "type": "text", + "content": "Baselines and evaluation metrics. We compare our method with several patch-based descriptors [1, 8, 20, 28, 35, 36, 39], using the same set of SIFT [14] keypoints following the protocol of the image matching benchmark [12]. We also perform tests with a detector suitable for non-rigid correspondence [17] coupled with the deformation-aware descriptor DEAL [25]. Finally, we also include in the comparison the state-of-the-art detect-and-describe methods [6, 7, 16, 23, 26, 37, 42]. For each evaluated method, we detect the top 2,048 keypoints and match the descriptors using nearest neighbor search. In addition to the standard comparison, we include as the gold standard for image matching SuperPoint [6] with the SuperGlue [29] matcher, which holds the state-of-the-art for stereo and multi-view camera registration [12] assuming rigid scenes. As shown in Tab. 1, the methods are divided into three categories: (i) methods that only require RGB input (RGB) in contrast to methods that require additional information such as depth; (ii) Detect & Describe " + }, + { + "bbox": [ + 46, + 197, + 289, + 472 + ], + "type": "inline_equation", + "content": "(D\\& D)" + }, + { + "bbox": [ + 46, + 197, + 289, + 472 + ], + "type": "text", + "content": " methods that provide both detection and description jointly within a single pipeline; and (iii) Deformation-Aware " + }, + { + "bbox": [ + 46, + 197, + 289, + 472 + ], + "type": "inline_equation", + "content": "(D - A)" + }, + { + "bbox": [ + 46, + 197, + 289, + 472 + ], + "type": "text", + "content": " methods, which take into account deformation when computing the descriptors. Notice that a method may fulfill multiple categories simultaneously." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 472, + 289, + 640 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 472, + 289, + 640 + ], + "spans": [ + { + "bbox": [ + 46, + 472, + 289, + 640 + ], + "type": "text", + "content": "We used the Matching Scores (MS) [18] to evaluate the matching performance of both the detected keypoints and descriptors. Given a ground-truth transformation and a threshold in pixels, we compute the set of correct correspondences " + }, + { + "bbox": [ + 46, + 472, + 289, + 640 + ], + "type": "inline_equation", + "content": "\\mathbf{S}_{gt}" + }, + { + "bbox": [ + 46, + 472, + 289, + 640 + ], + "type": "text", + "content": " and obtain the score for an image pair " + }, + { + "bbox": [ + 46, + 472, + 289, + 640 + ], + "type": "inline_equation", + "content": "(i,j)" + }, + { + "bbox": [ + 46, + 472, + 289, + 640 + ], + "type": "text", + "content": " as " + }, + { + "bbox": [ + 46, + 472, + 289, + 640 + ], + "type": "inline_equation", + "content": "MS = |\\mathbf{S}_{gt}| / \\min(|\\text{keypoints}_i|, |\\text{keypoints}_j|)" + }, + { + "bbox": [ + 46, + 472, + 289, + 640 + ], + "type": "text", + "content": ". In addition, the mean matching accuracy (MMA) is also reported, which focuses on the accuracy of the descriptors to match the keypoints that were successfully detected on both images under the threshold denoted as the set " + }, + { + "bbox": [ + 46, + 472, + 289, + 640 + ], + "type": "inline_equation", + "content": "\\mathbf{K}_{gt}" + }, + { + "bbox": [ + 46, + 472, + 289, + 640 + ], + "type": "text", + "content": ", and is computed as " + }, + { + "bbox": [ + 46, + 472, + 289, + 640 + ], + "type": "inline_equation", + "content": "MMA = |\\mathbf{S}_{gt}| / |\\mathbf{K}_{gt}|" + }, + { + "bbox": [ + 46, + 472, + 289, + 640 + ], + "type": "text", + "content": ". Additional results regarding repeatability of keypoints can be found in the supplementary material. To conduct the evaluation, we adopt two existing datasets of deformable objects [24, 40]." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 647, + 194, + 661 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 647, + 194, + 661 + ], + "spans": [ + { + "bbox": [ + 47, + 647, + 194, + 661 + ], + "type": "text", + "content": "4.1. Real-world benchmarking" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 665, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 288, + 713 + ], + "type": "text", + "content": "Comparison with the state-of-the-art. Tab. 1 shows the MS and MMA scores achieved by all compared methods. DALF outperformed all descriptors on average in both MS and MMA metrics, including the methods that use additional" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 72, + 547, + 191 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 191 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 191 + ], + "type": "text", + "content": "depth information to extract deformation-invariant features, improving the state-of-the-art in " + }, + { + "bbox": [ + 304, + 72, + 547, + 191 + ], + "type": "inline_equation", + "content": "8\\%" + }, + { + "bbox": [ + 304, + 72, + 547, + 191 + ], + "type": "text", + "content": " p.p. in matching scores. Moreover, our method shows promising generalization properties to real deformations. DISK achieved the second-best results in MS, but the MMA indicates that its descriptors are more sensitive to non-rigid deformations. DEAL displays the second-best results in MMA thanks to its deformation-aware module but has poor performance on the MS score. It is noteworthy that DEAL relies on SIFT keypoints, which are not designed for non-rigid transformations." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 192, + 548, + 335 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 192, + 548, + 335 + ], + "spans": [ + { + "bbox": [ + 304, + 192, + 548, + 335 + ], + "type": "text", + "content": "SuperGlue, which is comprised of SuperPoint descriptors matched with a graph neural network, showed good performance, but the drop in the scores compared to the top methods is noticeable as SuperPoint and SuperGlue do not explicitly model scene deformations. We emphasize that our method can be easily coupled and trained with a learned matcher such as SuperGlue. We report the SuperGlue results using the outdoor pretrained weights since we observed that the outdoor weights performed better in all datasets. All the other methods achieve significantly worse scores due to their inability to cope with stronger deformations alongside illumination and affine transformations." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 339, + 547, + 460 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 339, + 547, + 460 + ], + "spans": [ + { + "bbox": [ + 304, + 339, + 547, + 460 + ], + "type": "text", + "content": "Rotation and scale robustness. Aside from deformations, in-plane rotations and scale changes are two important geometric transformations. Thus, we conduct a study using the Simulation sequences from [24] containing challenging rotation and scale changes. Fig. 4 clearly indicates that our method holds the best invariance to image in-plane rotations in addition to deformation changes compared to the five stronger competitors. Our technique also displays considerable robustness to scale changes, outperforming SuperPoint and providing a similar level of robustness of SuperGlue." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 465, + 547, + 525 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 465, + 547, + 525 + ], + "spans": [ + { + "bbox": [ + 304, + 465, + 547, + 525 + ], + "type": "text", + "content": "Time efficiency. DALF is one of the most time efficient methods among the joint detection and description architectures. While our method runs at 9 FPS, DISK runs at 5 FPS and R2D2 at 2 FPS in an NVIDIA GeForce RTX 3060 GPU to extract 2,048 keypoints from " + }, + { + "bbox": [ + 304, + 465, + 547, + 525 + ], + "type": "inline_equation", + "content": "1024 \\times 768" + }, + { + "bbox": [ + 304, + 465, + 547, + 525 + ], + "type": "text", + "content": " images." + } + ] + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 314, + 545, + 425, + 663 + ], + "blocks": [ + { + "bbox": [ + 314, + 545, + 425, + 663 + ], + "lines": [ + { + "bbox": [ + 314, + 545, + 425, + 663 + ], + "spans": [ + { + "bbox": [ + 314, + 545, + 425, + 663 + ], + "type": "image", + "image_path": "404f0fdfb3da3c368727c6426d1ac43d4e33a009bdf48991a708e1c3d9efcde8.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 666, + 547, + 711 + ], + "lines": [ + { + "bbox": [ + 304, + 666, + 547, + 711 + ], + "spans": [ + { + "bbox": [ + 304, + 666, + 547, + 711 + ], + "type": "text", + "content": "Figure 4. Invariance to rotation & scale. We evaluate the matching performance of the methods under rotation and scale changes between image pairs from the Simulation dataset. The objects are simultaneously deforming, rotating and scaling in image space." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 433, + 545, + 545, + 663 + ], + "blocks": [ + { + "bbox": [ + 433, + 545, + 545, + 663 + ], + "lines": [ + { + "bbox": [ + 433, + 545, + 545, + 663 + ], + "spans": [ + { + "bbox": [ + 433, + 545, + 545, + 663 + ], + "type": "image", + "image_path": "ef55d095bd34cfaa71aebfb0ac0ec4acf75423694f6efbfe8836d88d3e9bd177.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 296, + 748, + 314, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 748, + 314, + 757 + ], + "spans": [ + { + "bbox": [ + 296, + 748, + 314, + 757 + ], + "type": "text", + "content": "1311" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 66, + 113, + 526, + 392 + ], + "blocks": [ + { + "bbox": [ + 46, + 70, + 547, + 106 + ], + "lines": [ + { + "bbox": [ + 46, + 70, + 547, + 106 + ], + "spans": [ + { + "bbox": [ + 46, + 70, + 547, + 106 + ], + "type": "text", + "content": "Table 1. Performances using top 2,048 keypoints. The RGB methods only require color images. " + }, + { + "bbox": [ + 46, + 70, + 547, + 106 + ], + "type": "inline_equation", + "content": "D\\& D" + }, + { + "bbox": [ + 46, + 70, + 547, + 106 + ], + "type": "text", + "content": " methods perform joint detection and description. The deformation-aware methods are shown as " + }, + { + "bbox": [ + 46, + 70, + 547, + 106 + ], + "type": "inline_equation", + "content": "D-A" + }, + { + "bbox": [ + 46, + 70, + 547, + 106 + ], + "type": "text", + "content": ". The mark * indicates the use of a learned matcher. Best in bold and second-best underlined. The mean was calculated with full-precision values by averaging the scores of all 833 image pairs before rounding." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 66, + 113, + 526, + 392 + ], + "lines": [ + { + "bbox": [ + 66, + 113, + 526, + 392 + ], + "spans": [ + { + "bbox": [ + 66, + 113, + 526, + 392 + ], + "type": "table", + "html": "
RGBD&DD-AMethodDatasets: 833 pairs total - MS / MMA @ 3 pixels ↑Mean
Kinect 1 [24]Kinect 2 [24]DeSurT [40]Simulation [24]
BRAND [20]0.17 / 0.340.22 / 0.490.14 / 0.330.04 / 0.090.16 / 0.34
✓ORB [28]0.19 / 0.380.25 / 0.550.18 / 0.400.14 / 0.300.20 / 0.43
✓DAISY [36]0.23 / 0.470.29 / 0.620.16 / 0.370.19 / 0.390.22 / 0.48
✓FREAK [1]0.24 / 0.490.33 / 0.720.16 / 0.380.15 / 0.310.23 / 0.51
✓TFeat [39]0.25 / 0.500.28 / 0.610.21 / 0.480.29 / 0.630.26 / 0.56
✓Log-Polar [8]0.28 / 0.580.30 / 0.650.23 / 0.540.22 / 0.490.26 / 0.57
✓SOSNet [35]0.17 / 0.340.25 / 0.550.17 / 0.380.26 / 0.570.22 / 0.47
✓✓LF-Net [23]0.44 / 0.400.51 / 0.430.28 / 0.770.21 / 0.740.36 / 0.59
✓✓LIFT [42]0.09 / 0.570.16 / 0.650.08 / 0.520.13 / 0.730.12 / 0.62
✓✓D2-Net [7]0.20 / 0.500.23 / 0.820.14 / 0.470.11 / 0.300.17 / 0.57
✓✓SuperPoint [6]0.45 / 0.740.54 / 0.850.39 / 0.680.18 / 0.340.41 / 0.69
✓✓R2D2 [26]0.17 / 0.360.25 / 0.590.14 / 0.320.06 / 0.160.17 / 0.39
✓✓ASLFeat [16]0.31 / 0.580.39 / 0.690.28 / 0.530.19 / 0.350.31 / 0.56
✓✓DISK [37]0.53 / 0.760.52 / 0.810.44 / 0.610.26 / 0.340.45 / 0.66
✓✓SuperGlue* [29]0.40 / 0.660.62 / 0.990.39 / 0.680.23 / 0.430.44 / 0.74
✓GeoBit [21]0.31 / 0.650.35 / 0.770.20 / 0.470.32 / 0.710.30 / 0.66
✓GeoPatch [24]0.32 / 0.660.35 / 0.800.26 / 0.600.39 / 0.860.33 / 0.73
✓✓DaLI [30]0.25 / 0.510.35 / 0.760.21 / 0.480.10 / 0.220.25 / 0.54
✓✓SIFT + DEAL [25]0.33 / 0.680.38 / 0.850.27 / 0.630.36 / 0.800.34 / 0.75
✓✓Det. [17] + DEAL0.44 / 0.740.49 / 0.820.33 / 0.640.31 / 0.740.40 / 0.74
✓✓✓DALF (ours)0.54 / 0.820.62 / 0.900.49 / 0.730.42 / 0.690.53 / 0.80
", + "image_path": "186dcd924c84295c22e73376a2d8e26c880d0f281d2fabb08895e8775e779ac6.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "type": "table", + "bbox": [ + 55, + 441, + 276, + 518 + ], + "blocks": [ + { + "bbox": [ + 46, + 411, + 288, + 434 + ], + "lines": [ + { + "bbox": [ + 46, + 411, + 288, + 434 + ], + "spans": [ + { + "bbox": [ + 46, + 411, + 288, + 434 + ], + "type": "text", + "content": "Table 2. Ablation. Performance of our method when considering different network components and training strategies." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 55, + 441, + 276, + 518 + ], + "lines": [ + { + "bbox": [ + 55, + 441, + 276, + 518 + ], + "spans": [ + { + "bbox": [ + 55, + 441, + 276, + 518 + ], + "type": "table", + "html": "
DistinctInvariant2-StageAttn.↑MS / MMA
✓--0.48 / 0.72
✓--0.51 / 0.78
✓✓0.53 / 0.79
✓✓✓0.53 / 0.78
✓✓✓✓0.53 / 0.80
", + "image_path": "0f00634bacce8bc15007b11d2f1c3c7dfc2ec0025407fb35f58604e485d60220.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 538, + 139, + 551 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 538, + 139, + 551 + ], + "spans": [ + { + "bbox": [ + 47, + 538, + 139, + 551 + ], + "type": "text", + "content": "4.2. Ablation study" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 557, + 288, + 688 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 557, + 288, + 688 + ], + "spans": [ + { + "bbox": [ + 46, + 557, + 288, + 688 + ], + "type": "text", + "content": "Our ablation study comprises five different configurations of our method: (i) using the U-net backbone only without the non-rigid warper module, which is similar to DISK excepting the descriptor loss term; (ii) computing the descriptors using the non-rigid warper module only; (iii) fusing the invariant and distinct features from the non-rigid warper and backbone respectively; (iv) perform a stage-wise training where the backbone is optimized first and the non-rigid warper second, and finally (v) we perform stage-wise training with an additional attention layer to fuse the invariant and distinctive descriptors instead of simple concatenation." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 689, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 288, + 714 + ], + "type": "text", + "content": "From Tab. 2, we can observe that the non-rigid warper contributes significantly to achieving more accurate matches" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 412, + 547, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 412, + 547, + 628 + ], + "spans": [ + { + "bbox": [ + 304, + 412, + 547, + 628 + ], + "type": "text", + "content": "when compared to using a convolutional backbone alone. Furthermore, by fusing the features, it is possible to obtain an improved descriptor that is both invariant and distinct with complementary properties. The two-stage training provides similar matching scores and slightly reduced mean accuracy compared to end-to-end training. Still, according to a more detailed analysis available in the supplementary material, we observed that it is beneficial to perform stage-wise training. The invariant part tends to dominate the distinctive part during training, rendering the distinct part less useful in practice, which is not desired for applications needing more distinct features, such as image retrieval, and datasets without significant deformations. Finally, we test if an attention-based fusion layer can deliver better results than concatenating the descriptors in the fusion step. According to the results, it is possible to slightly increase the accuracy even further with a negligible cost in computation. Thus, we choose the model with the stage-wise training as the final architecture." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 641, + 548, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 641, + 548, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 641, + 548, + 715 + ], + "type": "text", + "content": "Limitations. Although our network can improve overall scores by learning keypoints and deformation-aware features, estimating the deformation parameters from a single image is an ambiguous problem. Therefore, physical deformations may make textures similar for different objects, harming our method's performance. Nevertheless, the learned de" + } + ] + } + ], + "index": 8 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 316, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 316, + 758 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 316, + 758 + ], + "type": "text", + "content": "1312" + } + ] + } + ], + "index": 9 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 53, + 70, + 286, + 200 + ], + "blocks": [ + { + "bbox": [ + 53, + 70, + 286, + 200 + ], + "lines": [ + { + "bbox": [ + 53, + 70, + 286, + 200 + ], + "spans": [ + { + "bbox": [ + 53, + 70, + 286, + 200 + ], + "type": "image", + "image_path": "858f54df73c46f9b197da86496289f926779cb68bf557b3011f11990f13a71ee.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 208, + 288, + 275 + ], + "lines": [ + { + "bbox": [ + 46, + 208, + 288, + 275 + ], + "spans": [ + { + "bbox": [ + 46, + 208, + 288, + 275 + ], + "type": "text", + "content": "Figure 5. Deformable object retrieval. Our method has the best result in retrieving images of deformed objects. The first column shows the image queries, and the rows show the results from different queries. Green images correspond to the same object as the query, and red images do not correspond. Black squares imply no more objects are available for that query." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 288, + 288, + 324 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 288, + 288, + 324 + ], + "spans": [ + { + "bbox": [ + 46, + 288, + 288, + 324 + ], + "type": "text", + "content": "formations demonstrate good generalization properties to real deformations due to the powerful combination of the keypoint extractor, warper module, and feature fusion steps." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 332, + 129, + 345 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 332, + 129, + 345 + ], + "spans": [ + { + "bbox": [ + 47, + 332, + 129, + 345 + ], + "type": "text", + "content": "4.3. Applications" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 350, + 288, + 388 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 350, + 288, + 388 + ], + "spans": [ + { + "bbox": [ + 46, + 350, + 288, + 388 + ], + "type": "text", + "content": "To further show the potential usage of our detection and description approach, we performed an evaluation in the two complementary tasks of object retrieval and 3D registration." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 392, + 288, + 596 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 392, + 288, + 596 + ], + "spans": [ + { + "bbox": [ + 46, + 392, + 288, + 596 + ], + "type": "text", + "content": "Deformable object retrieval. We consider a database that contains images from various deformed objects. Each object appears multiple times with different deformations. The top K images from the database corresponding to an image query are retrieved. To evaluate the methods, we use the retrieval accuracy for different K values. K-Nearest Neighbors is used in conjunction with Bag-of-Visual-Worlds approach over the descriptors as the retrieval engine. We compare our method against the state-of-the-art description methods that demonstrated the top performances in Tab. 1, in addition to DELF [33], a state-of-the-art descriptor designed and trained specifically for image retrieval. We calculated the normalized area under the curve of each method for " + }, + { + "bbox": [ + 46, + 392, + 288, + 596 + ], + "type": "inline_equation", + "content": "K = \\{1, \\dots, 20\\}" + }, + { + "bbox": [ + 46, + 392, + 288, + 596 + ], + "type": "text", + "content": ". DALF achieved the most accurate retrieval capabilities at " + }, + { + "bbox": [ + 46, + 392, + 288, + 596 + ], + "type": "inline_equation", + "content": "99.49\\%" + }, + { + "bbox": [ + 46, + 392, + 288, + 596 + ], + "type": "text", + "content": ", while DELF, DEAL, SuperPoint, and DISK achieved " + }, + { + "bbox": [ + 46, + 392, + 288, + 596 + ], + "type": "inline_equation", + "content": "98.57\\%" + }, + { + "bbox": [ + 46, + 392, + 288, + 596 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 392, + 288, + 596 + ], + "type": "inline_equation", + "content": "98.34\\%" + }, + { + "bbox": [ + 46, + 392, + 288, + 596 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 392, + 288, + 596 + ], + "type": "inline_equation", + "content": "97.92\\%" + }, + { + "bbox": [ + 46, + 392, + 288, + 596 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 46, + 392, + 288, + 596 + ], + "type": "inline_equation", + "content": "96.12\\%" + }, + { + "bbox": [ + 46, + 392, + 288, + 596 + ], + "type": "text", + "content": ", respectively. Fig. 5 shows some qualitative results2." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 613, + 288, + 685 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 613, + 288, + 685 + ], + "spans": [ + { + "bbox": [ + 46, + 613, + 288, + 685 + ], + "type": "text", + "content": "Non-rigid 3D surface registration. In addition to the retrieval application, we also validate the performance of the methods in the challenging real-world task of surface registration. To that end, we employ the as-rigid-as-possible (ARAP) [31] registration to perform the surface alignment with the correspondences obtained from each method. In" + } + ] + } + ], + "index": 6 + }, + { + "type": "table", + "bbox": [ + 308, + 113, + 543, + 196 + ], + "blocks": [ + { + "bbox": [ + 306, + 70, + 547, + 104 + ], + "lines": [ + { + "bbox": [ + 306, + 70, + 547, + 104 + ], + "spans": [ + { + "bbox": [ + 306, + 70, + 547, + 104 + ], + "type": "text", + "content": "Table 3. 3D surface registration. The 2D and 3D accuracy is computed under varying thresholds in centimeters for the 3D residuals and in pixels for the 2D residuals. Best in bold." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 308, + 113, + 543, + 196 + ], + "lines": [ + { + "bbox": [ + 308, + 113, + 543, + 196 + ], + "spans": [ + { + "bbox": [ + 308, + 113, + 543, + 196 + ], + "type": "table", + "html": "
Method2D Accuracy ↑3D Accuracy ↑
@2px@3px@5px@0.5cm@1.0cm@1.5cm
DISK21.330.541.236.351.758.8
SuperPoint23.234.447.442.660.568.4
SuperGlue34.951.068.142.864.473.6
GeoPatch28.941.555.941.062.371.1
DEAL29.442.056.242.964.372.8
DALF (ours)36.651.667.346.266.974.8
", + "image_path": "252c02f837803986c297aabf0d6215ca1a6e599392060585f95d8f2ca6994bd1.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "table_body" + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 208, + 547, + 268 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 208, + 547, + 268 + ], + "spans": [ + { + "bbox": [ + 304, + 208, + 547, + 268 + ], + "type": "text", + "content": "these experiments, the correspondences are first filtered with an outlier removal approach [5] since the ARAP cannot handle outliers in the registration process. One of the challenges of non-rigid registration is that one cannot fit a global geometric transformation with a minimal sample using RANSAC." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 269, + 547, + 436 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 269, + 547, + 436 + ], + "spans": [ + { + "bbox": [ + 304, + 269, + 547, + 436 + ], + "type": "text", + "content": "After the filtering stage, the ARAP is used to align the meshes of the respective image pairs. The 2D error is then computed using the ground-truth TPS transformation provided with the datasets given in pixels. We also estimate the residual 3D error, assuming that the two corresponding surfaces must be perfectly adjusted in the 3D space, as their meshes are known beforehand. Tab. 3 shows the performance of the top methods under different thresholds for the 2D and the 3D errors considering all the datasets used in Tab. 1, where our approach stands out, improving over 3 p.p. in 3D registration accuracy compared to the best current method (SuperGlue) in the tightest threshold of " + }, + { + "bbox": [ + 304, + 269, + 547, + 436 + ], + "type": "inline_equation", + "content": "0.5\\mathrm{cm}" + }, + { + "bbox": [ + 304, + 269, + 547, + 436 + ], + "type": "text", + "content": ". Visual results of the 3D registration are available in the supplementary material." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 447, + 384, + 459 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 447, + 384, + 459 + ], + "spans": [ + { + "bbox": [ + 306, + 447, + 384, + 459 + ], + "type": "text", + "content": "5. Conclusions" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 468, + 547, + 624 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 468, + 547, + 624 + ], + "spans": [ + { + "bbox": [ + 304, + 468, + 547, + 624 + ], + "type": "text", + "content": "This paper presents DALF, a method that considers both the detection and description of keypoints under the challenging case of non-rigid geometric transformations. From extensive experiments and two applications using real deformable objects, we draw the following conclusions: (i) standard approaches for image matching deliver subpar results compared to deformation-aware features; (ii) optimizing the keypoint detection stage together with deformation-aware descriptors brings significant performance gains compared to existing deformation-aware methods that rely on affine keypoint detectors; and (iii) the feature fusion component is a simple but effective approach to increase the network expressiveness to deformations while keeping distinctiveness." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 629, + 548, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 629, + 548, + 712 + ], + "spans": [ + { + "bbox": [ + 304, + 629, + 548, + 712 + ], + "type": "text", + "content": "Acknowledgements. The authors would like to thank CAPES (#88881.120236/2016-01), CNPq, FAPEMIG, and Google for funding different parts of this work. This work was also granted access to the HPC resources of CNRS IDRIS under the project 2021-AD011013154 and supported by the French Conseil Régional de Bourgogne-Franche-Comté." + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 47, + 693, + 288, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 693, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 693, + 288, + 713 + ], + "type": "text", + "content": "2For the sake of clarity, we filtered out objects that all methods retrieved all correct images. 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To bypass such failure modes, we consider an adversarial threat model under a mutual information constraint to cover a wider class of perturbations in training. This motivates us to extend the standard information bottleneck to additionally model the nuisance information. We propose an autoencoder-based training to implement the objective, as well as practical encoder designs to facilitate the proposed hybrid discriminative-generative training concerning both convolutional- and Transformer-based architectures. Our experimental results show that the proposed scheme improves robustness of learned representations (remarkably without using any domain-specific knowledge), with respect to multiple challenging reliability measures. For example, our model could advance the state-of-the-art on a recent challenging OBJECTS benchmark in novelty detection by $78.4\\% \\rightarrow 87.2\\%$ in AUROC, while simultaneously enjoying improved corruption, background and (certified) adversarial robustness. Code is available at https://github.com/jh-jeong/nuisance_ib.", + "bbox": [ + 76, + 323, + 473, + 686 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 78, + 729, + 207, + 744 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Despite the recent breakthroughs in computer vision in aid of deep learning, e.g., in image/video recognition [9, 20, 109], synthesis [42, 55, 96, 125], and 3D scene rendering [85, 86, 104], deploying deep learning models to the real-world still places a burden on contents providers as it affects the reliability of their services. In many cases, deep neural networks make substantially fragile predictions for out-of-distribution inputs, i.e., samples that are not likely", + "bbox": [ + 75, + 756, + 468, + 878 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/20fb6369cf65ff4f085c0b8fcd157c8cfa20bd7e9e23ddcecd509fb7591796df.jpg", + "image_caption": [ + "Figure 1. A high-level illustration of our method, nuisance-extended information bottleneck (NIB). In this paper, we focus on scenarios when the input $\\mathbf{x}$ can be corrupted $\\mathbf{x} \\rightarrow \\hat{\\mathbf{x}}$ in test-time while preserving its semantics. Unlike the standard cross-entropy training (CE), NIB aims to encode every target-correlated signal in $\\mathbf{x}$ , some of which can be more reliable under distribution shifts." + ], + "image_footnote": [], + "bbox": [ + 509, + 290, + 893, + 434 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "from the training distribution, even when the inputs are semantically close enough to in-distribution samples for humans [35, 102]. Such a vulnerability can be a significant threat in risk-sensitive systems, such as autonomous driving, medical imaging, and health-care applications, to name a few [2]. Overall, the phenomena highlight that deep neural networks tend to extract \"shortcut\" signals [26] from given limited (or potentially biased) training data in practice.", + "bbox": [ + 496, + 551, + 893, + 672 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "To address such concerns, multiple literatures have been independently developed based on different aspects of model reliability. Namely, their methods use different threat models and benchmarks, depending on how a shift in input distribution happens in test-time, and how to evaluate model performance against the shift. For example, in the context of adversarial robustness [11, 17, 82, 128], a typical threat model is to consider the worst-case noise inside a fixed $\\ell_p$ -ball around given test samples. Another example of corruption robustness [34, 35, 39, 116] instead assumes predefined types of common corruptions (e.g., Gaussian noise, fog, etc.) that applies to the test samples. Lastly, novelty detection [36, 72, 74, 76] usually tests whether a model can detect a specific benchmark dataset as out-of-distribution from the (in-distribution) test samples.", + "bbox": [ + 496, + 674, + 895, + 900 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Work done at KAIST.", + "bbox": [ + 94, + 886, + 218, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "16206", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Due to discrepancy between each of \"ideal\" objectives and its practical threat models, however, the literatures have commonly found that optimizing under a certain threat model often hardly generalizes to other threat ones: e.g., (a) several works [16, 62, 121] have observed that standard adversarial training [82] often harms other reliability measures such as corruption robustness or uncertainty estimation, as well as its classification performance; (b) Hendrycks et al. [34] criticize that none of the previous claims on corruption robustness could consistently generalize on a more comprehensive benchmark. This also happens even for threat models targeting the same objective: e.g., (c) Yang et al. [122] show that state-of-the-arts in novelty detection are often too sensitive, so that they tend to also detect \"near-in-distribution\" samples as out-of-distribution and perform poorly on a benchmark regarding this. Overall, these observations suggest that one should avoid optimizing reliability measures assuming a specific threat model or benchmark, and motivate to find a new threat model that is generally applicable for diverse scenarios of reliability concerns.", + "bbox": [ + 75, + 90, + 472, + 393 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Contribution. In this paper, we propose nuisance-extended information bottleneck (NIB), a new training objective targeting model reliability without assuming a prior on domain-specific tasks. Our method is motivated by rethinking the information bottleneck (IB) principle [107, 108] under presence of distribution shifts. Specifically, we argue that a \"robust\" representation $\\mathbf{z} \\coloneqq f(\\mathbf{x})$ should always encode every signal in the input $\\mathbf{x}$ that is correlated with the target $\\mathbf{y}$ , rather than extracting only a few shortcuts (e.g., Figure 1). This motivates us to consider an adversarial form of threat model on distribution shifts in $\\mathbf{x}$ , under a constraint on the mutual information $I(\\mathbf{x},\\mathbf{y})$ . To implement this idea, we propose a practical design by incorporating a nuisance representation $\\mathbf{z}_n$ alongside $\\mathbf{z}$ of the standard IB so that $(\\mathbf{z},\\mathbf{z}_n)$ can reconstruct $\\mathbf{x}$ . This results in a novel synthesis of adversarial autoencoder [83] and variational IB [1] into a single framework. For the architectural side, we propose (a) to utilize the internal feature statistics for convolutional network based encoders, and (b) to incorporate vector-quantized patch representations for Transformer-based [24] encoders to model $\\mathbf{z}_n$ , mainly to efficiently encode the nuisance $\\mathbf{z}_n$ (as well as $\\mathbf{z}$ ) in a scalable manner.", + "bbox": [ + 75, + 398, + 472, + 731 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "We perform an extensive evaluation on the representations learned by our scheme, showing comprehensive improvements in modern reliability metrics: including (a) novelty detection, (b) corruption (or natural) robustness, (c) background robustness and (d) certified adversarial robustness. The results are particularly remarkable as the gains are not from assuming a prior on each of specific threat models. For example, we obtain a significant reduction in CIFAR-10-C error rates of the highest severity, i.e., by $26.5\\% \\rightarrow 19.5\\%$ , without extra domain-specific prior as assumed in recent methods [39, 40]. Here, we also show that the effective", + "bbox": [ + 75, + 734, + 472, + 900 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "ness of our method is scalable to larger-scale (ImageNet) datasets. For novelty detection, we could advance AUROCs in recent OBJECTS [122] benchmarks by a large margin of $78.4\\% \\rightarrow 87.2\\%$ in average upon the state-of-the-art, showing that our representations can provide a more semantic information to better discriminate out-of-distribution samples. Finally, we also demonstrate how the representations can further offer enhanced robustness against adversarial examples, by applying randomized smoothing [17] on them.", + "bbox": [ + 496, + 90, + 893, + 227 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Background", + "text_level": 1, + "bbox": [ + 500, + 239, + 627, + 257 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Notation. Given two random variables $\\mathbf{x} \\in \\mathcal{X}$ , the input, and $\\mathbf{y} \\in \\mathcal{Y}$ , the target, our goal is to find a mapping (or an encoder) $f: \\mathcal{X} \\to \\mathcal{Z}$ from data $\\mathcal{D} = \\{(x_i, y_i)\\}_{i=1}^n$ so that $\\mathbf{z} := f(\\mathbf{x})$ , the representation, can predict $\\mathbf{y}$ with a simper (e.g., linear) mapping [7, 64]. We assume that $f$ is parametrized by a neural network, and is stochastic to adopt an information theoretic view [108], i.e., the encoder output is a random variable defined as $p_f(\\mathbf{z}|\\mathbf{x})$ rather than a constant. Such a modeling can be done through the reparametrization trick [61] with an independent random variable $\\epsilon$ and (deterministic) $f$ by assuming $\\mathbf{z} := f(\\mathbf{x}, \\epsilon)$ . For example, one of standard designs parametrizes $f$ by:", + "bbox": [ + 496, + 268, + 893, + 450 + ], + "page_idx": 1 + }, + { + "type": "equation", + "text": "\n$$\nf (\\mathbf {x}, \\epsilon) := f ^ {\\mu} (\\mathbf {x}) + \\epsilon \\cdot f ^ {\\sigma} (\\mathbf {x}), \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 591, + 460, + 890, + 476 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "where $f^{\\mu} \\in \\mathbb{R}^{|\\mathcal{Z}|}$ and $f^{\\sigma} \\in \\mathbb{R}_{+}^{|\\mathcal{Z}|}$ are deterministic mappings modeling $\\mu$ and $\\sigma$ in $\\mathcal{N}(\\mathbf{x};\\mu,\\sigma^2I)$ , respectively, so that they can still be learned through a gradient-based optimization.", + "bbox": [ + 496, + 484, + 890, + 532 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "The data $\\mathcal{D}$ is usually assumed to consist of i.i.d. samples from a certain data generating distribution $(x_{i},y_{i})\\sim p_{d}(\\mathbf{x},\\mathbf{y})$ . One expects that $f$ learned from $\\mathcal{D}$ could generalize to predict $p_d(\\mathbf{y}|\\mathbf{x})$ for unseen samples from $p_d(\\mathbf{x},\\mathbf{y})$ . The formulation, however, does not specify how $f$ should behave for inputs that are not likely from $p_d$ , say $\\hat{x}$ . This becomes problematic for those who expect that the decision making of $f$ should be close to that of human being, at least when $\\hat{x}$ differs from $p_d$ only up to what humans regard as nuisance. This is where the current neural networks commonly fail under the standard training practices.", + "bbox": [ + 496, + 532, + 893, + 699 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Information bottleneck. Intuitively, a \"good\" representation $\\mathbf{z}$ should keep information of $\\mathbf{x}$ that is correlated with $\\mathbf{y}$ , while preventing $\\mathbf{z}$ from being too complex. The information bottleneck [107, 108] (IB) is a principled approach to obtain such a succinct representation $\\mathbf{x} \\rightarrow \\mathbf{z}$ for a given downstream task $\\mathbf{x} \\rightarrow \\mathbf{y}$ : namely, it finds $\\mathbf{z}$ that (a) maximizes the (task-relevant) mutual information $I(\\mathbf{z}; \\mathbf{y})$ , while (b) minimizing $I(\\mathbf{x}; \\mathbf{z})$ to constrain the capacity of $\\mathbf{z}$ for better generalization. In other words, it sets the mutual information $I(\\mathbf{x}; \\mathbf{z})$ as the complexity measure of $\\mathbf{z}$ . Specifically,", + "bbox": [ + 496, + 703, + 893, + 854 + ], + "page_idx": 1 + }, + { + "type": "page_footnote", + "text": "1Although we focus on supervised learning, the framework itself in general does not rule out more general scenarios, e.g., when the target $\\mathbf{y}$ can be self-supervised from $\\mathbf{x}$ [14, 91].", + "bbox": [ + 496, + 862, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "16207", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/417bd75930c6b8cdd00836bb93021d4a3d0c293752e0f1dba38d06d336c744d3.jpg", + "image_caption": [ + "Figure 2. An overview of the proposed framework, the autoencoder-based nuisance-extended information bottleneck (AENIB). It illustrates the general pipeline, and Appendix C provides specific instantiations for convolutional and Transformer-based architectures. Overall, we incorporate adversarial autoencoder into variational information bottleneck by introducing a nuisance $\\mathbf{z}_n$ (to $\\mathbf{y}$ ) in representation learning." + ], + "image_footnote": [], + "bbox": [ + 117, + 85, + 854, + 263 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "it aims to maximize the following objective:", + "bbox": [ + 76, + 332, + 372, + 349 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\max _ {f} R _ {\\mathrm {I B}} (f), \\quad \\text {f o r} \\quad R _ {\\mathrm {I B}} (f) := I (\\mathbf {z}; \\mathbf {y}) - \\beta I (\\mathbf {x}; \\mathbf {z}), \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 89, + 359, + 468, + 383 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\beta \\geq 0$ controls the capacity constraint which ensures $I(\\mathbf{x};\\mathbf{z})\\leq I_{\\beta}$ for some $I_{\\beta}$ .", + "bbox": [ + 76, + 393, + 468, + 425 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Nuisance-extended information bottleneck", + "text_level": 1, + "bbox": [ + 76, + 438, + 455, + 454 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The standard information bottleneck (IB) objective (2) obtains a representation $\\mathbf{z} := f(\\mathbf{x})$ on premise that the future inputs will be also from $p_d(\\mathbf{x},\\mathbf{y})$ . In this paper, we aim to extend IB under assumption that the input $\\mathbf{x}$ can be corrupted through an unknown noisy channel in the future, say $\\mathbf{x} \\to \\hat{\\mathbf{x}}$ , while $\\hat{\\mathbf{x}}$ still preserves the semantics of $\\mathbf{x}$ with respect to $\\mathbf{y}$ : in other words, we assume $I(\\mathbf{x};\\mathbf{y}) = I(\\hat{\\mathbf{x}};\\mathbf{y}) > 0$ . Intuitively, one can imagine a scenario that $\\mathbf{x}$ contains multiple signals that each is already highly correlated with $\\mathbf{y}$ , i.e., filtering out the remainder from $\\mathbf{x}$ does not affect its mutual information with $\\mathbf{y}$ . It may or may not be surprising that such signals are quite prevalent in deep neural networks, e.g., [44] empirically observe that adversarial perturbations [29, 102] are sufficient for a model to perform accurate classification.", + "bbox": [ + 75, + 463, + 468, + 674 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In the context of IB framework, where the goal is to obtain a succinct encoder $f$ , it is now reasonable to presume that the noisy channel $\\hat{\\mathbf{x}}$ acts like an adversary, i.e., it minimizes:", + "bbox": [ + 75, + 675, + 470, + 720 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\min _ {\\hat {\\mathbf {x}}} I (\\hat {\\mathbf {z}} := f (\\hat {\\mathbf {x}}); \\mathbf {y}) \\text {s u b j e c t} I (\\mathbf {x}; \\mathbf {y}) = I (\\hat {\\mathbf {x}}; \\mathbf {y}), \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 91, + 731, + 468, + 753 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "given that one has no information on how the channel would behave a priori. This optimization thus would require $f$ to extract every signal in $\\mathbf{x}$ whenever it is highly correlated with $\\mathbf{y}$ , to avoid the case when $\\hat{\\mathbf{x}}$ filters out all the signal except one that $f$ has missed. We notice that, nevertheless, directly optimizing (3) with respect to $\\hat{\\mathbf{x}}$ is computationally infeasible in practice, considering that (a) it is in many cases an unconstrained optimization in a high-dimensional $\\mathcal{X}$ , (b) with a constraint on (hard-to-compute) mutual information.", + "bbox": [ + 75, + 763, + 468, + 900 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In this paper, to make sure that $f$ still exhibits the adversarial behavior without (3), we propose to let $f$ to model the nuisance representation $\\mathbf{z}_n$ as well as $\\mathbf{z}$ . Specifically, $\\mathbf{z}_n$ aims to model the \"remainder\" information from $\\mathbf{z}$ needed to reconstruct $\\mathbf{x}$ , i.e., it maximizes $I(\\mathbf{x};\\mathbf{z},\\mathbf{z}_n)$ . At the same time, $\\mathbf{z}_n$ compresses out any information that is correlated with $\\mathbf{y}$ , i.e., it also minimizes $I(\\mathbf{z}_n;\\mathbf{y})$ . Therefore, every information that is correlated with $\\mathbf{y}$ should be encoded into $\\mathbf{z}$ in a complementary manner. Here, we remark that now the role of the capacity constraint in (2) becomes more important: not only for regularizing $\\mathbf{z}$ to be simpler, it also penalizes $\\mathbf{z}_n$ from pushing out unnecessary information to predict $\\mathbf{y}$ into $\\mathbf{z}$ , making the objective competitive again between $\\mathbf{z}$ and $\\mathbf{z}_n$ as like in (3). Combined with the original IB (2), we define nuisance-extended IB (NIB) as the following:", + "bbox": [ + 496, + 332, + 893, + 559 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\max _ {f} R _ {\\mathrm {N I B}} (f) := R _ {\\mathrm {I B}} (f) - I \\left(\\mathbf {z} _ {n}; \\mathbf {y}\\right) + \\alpha I \\left(\\mathbf {x}; \\mathbf {z}, \\mathbf {z} _ {n}\\right), \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 511, + 574, + 890, + 598 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\alpha \\geq 0$ . The proposed NIB objective can be viewed as a regularized form of IB by introducing a nuisance $\\mathbf{z}_n$ . Specifically, this optimization additionally forces $I(\\mathbf{x};\\mathbf{z},\\mathbf{z}_n)$ and $I(\\mathbf{z}_n;\\mathbf{y})$ in (4) to be maximized and minimized, i.e., $H(\\mathbf{x}|\\mathbf{z},\\mathbf{z}_n) = 0$ and $I(\\mathbf{z}_n;\\mathbf{y}) = 0$ , respectively. The following highlights that having these conditions, also with the independence $\\mathbf{z}\\perp \\mathbf{z}_n$ , leads $f$ that can recover the original $I(\\mathbf{x};\\mathbf{y})$ from $I(\\hat{\\mathbf{z}};\\mathbf{y})$ (see Appendix E for the derivation):", + "bbox": [ + 496, + 612, + 893, + 734 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Lemma 1. Let $\\mathbf{x} \\in \\mathcal{X}$ , and $\\mathbf{y} \\in \\mathcal{Y}$ be random variables, $\\hat{\\mathbf{x}}$ be a noisy observation of $\\mathbf{x}$ with $I(\\mathbf{x};\\mathbf{y}) = I(\\hat{\\mathbf{x}};\\mathbf{y})$ . Given that $[\\hat{\\mathbf{z}},\\hat{\\mathbf{z}}_n] := f(\\hat{\\mathbf{x}})$ of $\\hat{\\mathbf{x}}$ satisfies (a) $H(\\hat{\\mathbf{x}}|\\hat{\\mathbf{z}},\\hat{\\mathbf{z}}_n) = 0$ , (b) $I(\\hat{\\mathbf{z}}_n;\\mathbf{y}) = 0$ , and (c) $\\hat{\\mathbf{z}} \\perp \\hat{\\mathbf{z}}_n$ , it holds $I(\\hat{\\mathbf{z}};\\mathbf{y}) = I(\\mathbf{x};\\mathbf{y})$ .", + "bbox": [ + 496, + 750, + 893, + 810 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In the following sections, we provide a practical design of the proposed NIB based on an autoencoder-based architecture. Section 3.1 and 3.2 detail out its losses and architectures, respectively, and Section 3.3 summarizes the overall training. Figure 2 illustrates an overview of our framework.", + "bbox": [ + 496, + 824, + 893, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "16208", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. AENIB: A practical autoencoder-based design", + "text_level": 1, + "bbox": [ + 76, + 90, + 467, + 107 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Based on the NIB objective defined in (4) and Lemma 1, we design a practical training objective to implement the proposed framework. Here, we present a simple instantiation of NIB with an autoencoder-based architecture upon variational information bottleneck (VIB) [1], calling it autoencoder-based NIB (AENIB).", + "bbox": [ + 75, + 113, + 468, + 203 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Overall, Lemma 1 states that a robust encoder $f$ demands for a \"good\" nuisance model that achieves generalization on $\\hat{\\mathbf{z}}$ in three aspects: (a) a good reconstruction, (b) nuisance, and (c) the independence between $\\mathbf{z}$ and $\\mathbf{z}_n$ . To model these behaviors, we consider a decoder $g: \\mathcal{Z} \\to \\mathcal{X}$ as well as the encoder $f: \\mathcal{X} \\to \\mathcal{Z}$ , and adopt the following practical training objectives which incorporates an autoencoder-based loss and two adversarial losses [28]:", + "bbox": [ + 75, + 204, + 470, + 325 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "(a) We first pose a reconstruction loss to maximize $\\log p(\\mathbf{x}|\\mathbf{z},\\mathbf{z}_n)$ ; standard designs assume the decoder output to follow $\\mathcal{N}(\\mathbf{x},\\sigma^2\\mathbf{I})$ , which is equivalent to the mean-squared error (MSE). Here, we use the normalized MSE to efficiently balance with other losses:", + "bbox": [ + 86, + 333, + 470, + 409 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nL _ {\\text {r e c o n}} := \\frac {1}{\\| \\mathbf {x} \\| _ {2} ^ {2}} \\| \\mathbf {x} - g (\\mathbf {z}, \\mathbf {z} _ {n}) \\| _ {2} ^ {2} \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 184, + 416, + 468, + 439 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "(b) To force the nuisance-ness of $\\mathbf{z}_n$ with respect to $\\mathbf{y}$ , we approximate $p(\\mathbf{y}|\\mathbf{z}_n)$ with a multi-layer perceptron (MLP), say $q_{n}$ , and perform an adversarial training:", + "bbox": [ + 86, + 450, + 470, + 496 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} L _ {\\mathrm {n u i s}} := \\mathbb {E} _ {\\mathbf {x}} [ \\mathbb {C E} (q _ {n} ^ {*} (\\mathbf {z} _ {n}), \\frac {1}{| \\mathcal {Y} |}) ], \\\\ \\text {w h e r e} q _ {n} ^ {*} := \\min _ {q _ {n}} \\mathbb {E} _ {\\mathbf {x}, \\mathbf {y}} [ \\mathbb {C E} (q _ {n} (\\mathbf {z} _ {n}), \\mathbf {y}) ], \\tag {6} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 129, + 507, + 468, + 554 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "and $\\mathbb{C}\\mathbb{E}$ denotes the cross entropy loss. Here, it optimizes $\\mathbb{C}\\mathbb{E}$ towards the uniform distribution in $\\mathcal{V}$ .3", + "bbox": [ + 112, + 561, + 470, + 592 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "(c) To induce the independence between $\\mathbf{z}$ and $\\mathbf{z}_n$ , we assume that the joint prior of $\\mathbf{z}$ and $\\mathbf{z}_n$ is the isotropic Gaussian, i.e., $p(\\mathbf{z},\\mathbf{z}_n)\\sim \\mathcal{N}(0,\\mathbf{I})$ , and performs a GAN training with a 2-layer MLP discriminator $q_{\\mathbf{z}}$ :", + "bbox": [ + 86, + 599, + 468, + 662 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} L _ {\\text {i n d}} := \\max _ {q _ {\\mathbf {z}}} \\mathbb {E} _ {\\mathbf {x}} \\left[ \\log \\left(q _ {\\mathbf {z}} (f (\\mathbf {x}))\\right) \\right] \\\\ + \\mathbb {E} _ {\\mathbf {z}, \\mathbf {z} _ {n}} \\sim \\mathcal {N} (0, \\mathbf {I}) [ \\log (1 - q _ {\\mathbf {z}} (\\mathbf {z}, \\mathbf {z} _ {n})) ]. \\tag {7} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 130, + 674, + 468, + 718 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Lastly, to approximate the original IB objective $R_{\\mathrm{IB}}(f)$ in NIB (4), we instead maximize the variational information bottleneck (VIB) [1] objective $L_{\\mathrm{VIB}}^{\\beta}$ , that can provide a lower bound on $R_{\\mathrm{IB}}$ . Specifically, it makes variational approximations of: (a) $p(\\mathbf{y}|\\mathbf{z})$ by a (parametrized) decoder neural", + "bbox": [ + 75, + 729, + 468, + 806 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "network $q(\\mathbf{y}|\\mathbf{z})$ , and (b) $p(\\mathbf{z})$ by an \"easier\" distribution $r(\\mathbf{z})$ , e.g., isotropic Gaussian $\\mathcal{N}(\\mathbf{z}|0,\\mathbf{I})$ . Assuming a Gaussian decoder (1) for $f(\\mathbf{x},\\epsilon)$ , we have:", + "bbox": [ + 498, + 90, + 893, + 137 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} L _ {\\mathrm {V I B}} ^ {\\beta} := \\frac {1}{n} \\sum_ {i = 1} ^ {n} \\mathbb {E} _ {\\epsilon} [ - \\log q (y _ {i} | f (x _ {i}, \\epsilon)) ] \\\\ + \\beta \\operatorname {K L} \\left(p (\\mathbf {z} | x _ {i}) \\| r (\\mathbf {z})\\right). \\tag {8} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 514, + 150, + 890, + 210 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. Architectures for nuisance modeling", + "text_level": 1, + "bbox": [ + 500, + 229, + 813, + 244 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In principle, our framework is generally compatible with any encoder architectures: e.g., say an encoder $f: \\mathcal{X} \\to \\mathcal{Z}$ and decoder $g: \\mathcal{Z} \\to \\mathcal{X}$ , respectively. In order to apply VIB, we assume that the encoder has two output heads of dimension $2K$ , where $K$ denotes the dimension of $\\mathbf{z}$ . Here, each output head models a Gaussian random variable by reparametrization, i.e., by modeling $(\\mu, \\sigma)$ as the encoder output for both $\\mathbf{z} \\in \\mathbb{R}^K$ and $\\mathbf{z}_n \\in \\mathbb{R}^{K_n}$ .", + "bbox": [ + 496, + 253, + 893, + 373 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Although it is possible that $f$ models $\\mathbf{z}$ and $\\mathbf{z}_n$ by simply taking deep feed-forward representations following conventions, we observe that modeling nuisances $\\mathbf{z}_n$ (which is essentially \"generative\") in standard (discriminative) architectures incur a training instability thus in performance: the nuisance information often requires to model finer details in a given inputs, which may be available rather in early layers of $f$ , but not in the later layers for classification.", + "bbox": [ + 496, + 375, + 893, + 494 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In this paper, we propose simple architectural treatments to improve the stability of nuisance modeling concerning both convolutional networks and Vision Transformers [24] (ViTs). This section focuses on introducing the design for convolutional networks, and we refer the readers for the ViT-based design to Appendix C: which is even simpler thanks to their patch-level representations available.", + "bbox": [ + 496, + 494, + 893, + 599 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Given a convolutional encoder $f$ , we encode $\\mathbf{z}_n$ (as well as $\\mathbf{z}$ ) from the collection of internal features statistics, rather than directly using the output of $f$ . Specifically, we extract $L$ intermediate feature maps of a given input $\\mathbf{x}$ , namely $\\mathbf{x}^{(1)}, \\dots, \\mathbf{x}^{(L)}$ from $f(\\mathbf{x})$ , and define the projection of $\\mathbf{x}$ by:", + "bbox": [ + 498, + 599, + 893, + 676 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\Pi_ {f} (\\mathbf {x}) := \\left[ \\begin{array}{c c c c} \\mathbf {m} ^ {(1)} & \\mathbf {m} ^ {(2)} & \\dots & \\mathbf {m} ^ {(L)} \\\\ \\mathbf {s} ^ {(1)} & \\mathbf {s} ^ {(2)} & \\dots & \\mathbf {s} ^ {(L)} \\end{array} \\right], \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 560, + 685, + 890, + 720 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\mathbf{m}^{(l)}$ and $\\mathbf{s}^{(l)}$ are the first and second moment of feature maps in $\\mathbf{x}^{(l)}$ , assuming that $\\mathbf{x}^{(l)} \\in \\mathbb{R}^{HWC}$ : $\\mathbf{m}_c^{(l)} := \\frac{1}{HW} \\sum_{hw} \\mathbf{x}_{hw_c}^{(l)}$ , and $\\mathbf{s}_c^{(l)} := \\frac{1}{HW} \\sum_{hw} (\\mathbf{x}_{hw_c}^{(l)} - \\mathbf{m}_c^{(l)})^2$ .", + "bbox": [ + 498, + 731, + 893, + 781 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In Appendix I, we demonstrate that this simple projection can sufficiently encode a generative representation of $\\mathbf{x}$ : viz., we show that one can successfully and efficiently train GANs with a discriminator defined upon $\\Pi_f$ . Motivated by this observation, we adopt $\\Pi_f$ in modeling the encoder representations $\\mathbf{z}$ and $\\mathbf{z}_n$ . We encode $\\mathbf{z}$ and $\\mathbf{z}_n$ by simply applying MLPs to $\\Pi_f(\\mathbf{x})$ (9). Despite its simplicity, we observe this treatment enables a stable training of AENIB.", + "bbox": [ + 496, + 781, + 893, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_footnote", + "text": "2We also explore a SSIM-based [118] reconstruction loss as given in Appendix C, which we found beneficial for robustness particularly with Transformer-based models.", + "bbox": [ + 75, + 813, + 468, + 849 + ], + "page_idx": 3 + }, + { + "type": "page_footnote", + "text": "3 Alternatively, one can directly maximize $\\mathbb{C}\\mathbb{E}(q_n^* (\\mathbf{z}_n),\\mathbf{y})$ ; we use the current design to avoid potential instability of the maximization-based loss.", + "bbox": [ + 76, + 849, + 468, + 875 + ], + "page_idx": 3 + }, + { + "type": "page_footnote", + "text": "4 A more detailed description on the VIB framework (as well as on GAN) can be found in Appendix F.2.", + "bbox": [ + 76, + 875, + 468, + 898 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "16209", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 3 + }, + { + "type": "table", + "img_path": "images/81e5643b59a6c909015320ca7325620dd34664866ad379534a0a953a156ab606.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
SeverityCIFAR-10-CCIFAR-100-C
Clean12345Avg.Clean12345Avg.
Cross-entropy6.088.8911.114.019.726.516.025.131.435.139.346.854.041.3
VIB [1]5.988.6810.713.418.624.915.226.031.935.940.447.855.242.2
AugMix [39]6.528.9710.813.418.423.915.124.929.933.337.143.651.139.0
PixMix† [40]5.437.108.149.4012.114.910.323.226.728.730.835.039.032.0
AENIB (ours)4.977.498.9611.014.819.512.322.627.630.534.139.847.135.8
+ AugMix [39]5.357.658.9911.014.218.412.021.926.429.132.437.844.334.0
+ PixMix† [40]4.675.906.557.459.1211.48.0821.224.426.027.831.134.828.8
", + "bbox": [ + 116, + 88, + 846, + 234 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/0d6fd9b030ce124a80fa672013994db1a7d75035fdbaffeb1a691cb99439e2df.jpg", + "table_caption": [ + "Table 1. Comparison of average corruption error rates $(\\% ;\\downarrow)$ per severity level on CIFAR-10/100-C [35]. Bold and underline denote the best and runner-up, respectively. $^{\\dagger}\\mathrm{PixMix}$ [40] utilizes an external dataset consisting of pattern- and fractal-like images." + ], + "table_footnote": [], + "table_body": "
MethodC10C10-CC10.1C10.2CINIC
Cross-entropy6.0816.013.418.323.7
VIB [1]5.9815.213.616.823.6
NLIB [65]6.8117.014.617.524.3
sq-NLIB [106]6.0215.513.017.123.7
DisenIB [92]5.7615.213.217.223.7
AugMix [39]6.5215.114.217.224.2
PixMix [40]5.4310.313.116.623.2
AENIB (ours)4.9712.311.615.522.2
+ AugMix [39]5.3512.012.515.822.6
+ PixMix [40]4.678.0810.414.822.1
", + "bbox": [ + 104, + 282, + 434, + 438 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Table 2. Comparison of test error rates $(\\% ;\\downarrow)$ on CIFAR-10 and its variants: CIFAR-10-C/10.1/10.2, and CINIC. Bold and underline indicate the best and runner-up results, respectively.", + "bbox": [ + 75, + 444, + 468, + 484 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.3. Overall training objective", + "text_level": 1, + "bbox": [ + 76, + 507, + 310, + 523 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Combining the proposed objectives as well as the VIB loss, $L_{\\mathrm{VIB}}^{\\beta}$ (8) leads us to the final objective. Although combining multiple losses in practice may introduce additional hyperparameters, we found most of the proposed losses can be added without scaling except for the reconstruction loss $L_{\\mathrm{recon}}$ and the $\\beta$ in the original VIB loss. Hence, we get:", + "bbox": [ + 75, + 532, + 470, + 625 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nL _ {\\mathrm {A E N I B}} := L _ {\\mathrm {V I B}} ^ {\\beta} + \\alpha \\cdot L _ {\\text {r e c o n}} + L _ {\\text {n u i s}} + L _ {\\text {i n d}}. \\tag {10}\n$$\n", + "text_format": "latex", + "bbox": [ + 109, + 637, + 468, + 656 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Algorithm 1 in Appendix A summarizes the procedure.", + "bbox": [ + 76, + 671, + 441, + 686 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 76, + 707, + 209, + 724 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We verify the effectiveness of our proposed AENIB training for various aspects of model reliability: specifically, we cover (a) corruption and natural robustness (Section 4.1), (b) novelty detection (Section 4.2), and (c) certified adversarial robustness (Section 4.3) tasks which all have been challenging without task-specific priors [37, 39, 82]. We provide an ablation study in Appendix D for a component-wise analysis. We also present an evaluation on our proposed components in the context of generative modeling in Appendix I. The full details on the experiments, e.g., datasets, training details, and hyperparameters, can be found in Appendix B.", + "bbox": [ + 75, + 734, + 472, + 902 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.1. Robustness against natural corruptions", + "text_level": 1, + "bbox": [ + 498, + 285, + 838, + 301 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We first evaluate corruption robustness of our method, i.e., its generalization ability under natural corruptions (e.g., fog, brightness, etc.) and distribution shifts those are still semantic to humans. To this end, we consider a wide range of benchmarks those are derived from CIFAR-10 and ImageNet for the purpose of measuring generalization. Namely, for CIFAR-10 models we test on (a) CIFAR-10/100-C [35], a corrupted version of CIFAR-10/100 simulating 15 common corruptions in 5 severity levels, as well as (b) CIFAR-10.1 [94], CIFAR-10.2 [81], and CINIC-10 [21], i.e., three regenerations of the CIFAR-10 test set. For ImageNet models, on the other hand, we test (a) ImageNet-C [35], a corrupted version of ImageNet validation set, (b) ImageNet-R [34], a collection of rendition images for 200 ImageNet classes, and ImageNet-Sketch [117], as well as (c) the Background Challenge [119] benchmark to evaluate model bias against background changes. This section mainly reports the results from ViT [24, 111] based architectures, but we also report the results with ResNet-18 [33] in Appendix H.", + "bbox": [ + 496, + 309, + 893, + 597 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Table 1 and 2 summarize the results on CIFAR-based models. In Table 1, we observe that AENIB significantly and consistently improves corruption errors upon VIB, and these gains are strong even compared with state-of-the-art methods: e.g., AENIB can solely outperform a strong baseline of AugMix [39]. Although a more recent method of PixMix [40] could achieve a lower corruption error by utilizing extra (pattern-like) data, we remark that (a) AENIB also benefit from PixMix (i.e., the extra data) as given in \"AENIB + PixMix\", and (b) the results on Table 2 show that the generalization capability of AENIB is better than PixMix on CIFAR-10.1, 10.2 and CINIC-10, i.e., in beyond common corruptions, by less relying on domain-specific data.", + "bbox": [ + 496, + 597, + 893, + 792 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Next, Table 3 highlights that the effectiveness of AENIB can generalize to a more larger-scale, higher-resolution dataset of ImageNet: we still observe that AENIB can consistently improve robust accuracy for diverse corruption types, again without leveraging any further data augmentation during training. Figure 3 compares the linear trends made by Cross-entropy and AENIB across different data augmenta", + "bbox": [ + 496, + 795, + 893, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "16210", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/c525eb7d087c912c01920e237e027579a8c34ea3232b31898c35230e44b1da66.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
DatasetViT-S/16ViT-B/16
BaselineAENIB (ours)BaselineAENIB (ours)
IN-1K25.125.121.821.9
IN-C (mCE)65.965.2 (−0.7)58.657.5 (−1.1)
IN-R70.367.1 (−3.2)66.364.4 (−1.9)
IN-Sketch80.377.7 (−2.6)76.574.4 (−2.1)
", + "bbox": [ + 78, + 88, + 470, + 186 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/c174fa1af0716a0a94f5c7a88295c752b1a9eaa4435af42d25db347cb236f609.jpg", + "table_caption": [ + "Table 3. Comparison of error rates $(\\% ;\\downarrow)$ or mean corruption error (mCE, $\\%$ . $\\downarrow$ ) on ImageNet (IN) and its variants, namely IN-C [35], IN-R [34], and IN-Sketch [117]. Bold indicates the best results." + ], + "table_footnote": [], + "table_body": "
BG-Challenge DatasetViT-S/16ViT-B/16
BaselineAENIB (ours)BaselineAENIB (ours)
ORIGINAL (IN-9; ↑)95.395.596.096.1
ONLY-BG-T (↓)20.317.8 (−2.5)24.221.1 (−3.1)
MIXED-SAME (↑)86.388.3 (+2.0)87.488.9 (+1.5)
MIXED-RAND (↑)77.880.5 (+2.7)80.181.8 (+0.7)
BG-gap (↓)8.57.8 (−0.7)7.37.1 (−0.2)
", + "bbox": [ + 78, + 238, + 470, + 338 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/69b6c9b33da467e8a5ec9f769d40334c17358d5d9334d18c16c78955f6d72dd3.jpg", + "table_caption": [ + "Table 4. Evaluation of AENIB on Backgrounds Challenge [119] compared to the cross-entropy baseline. All the models are trained on ImageNet, and warped to perform classification on ImageNet-9." + ], + "table_footnote": [], + "table_body": "
MethodScoreSVHNLSUNImageNetC100CelebA
JEM [31]log p(x)0.67--0.670.75
JEM [31]maxy p(y|x) [36]0.89--0.870.79
SupCon [56]maxy p(y|x) [36]0.970.930.910.89-
Cross-entropymaxy p(y|x) [36]0.940.940.920.860.64
Cross-entropylog Dir0.05(y)0.960.950.940.860.61
VIB [1]maxy p(y|x) [36]0.950.940.920.880.76
VIB [1]log Dir0.05(y)0.970.960.940.880.78
AENIB (ours)maxy p(y|x) [36]0.880.880.860.840.81
AENIB (ours)log Dir0.05(y)0.900.950.920.860.80
AENIB (ours)+ logN(zn;0,I)0.980.990.990.860.79
", + "bbox": [ + 78, + 391, + 467, + 529 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 5. Comparison of AUROC (\\%; ↑) for OOD detection from CIFAR-10 with five OOD datasets: SVHN, LSUN, ImageNet, CIFAR-100, and CelebA. Bolds indicate the best results.", + "bbox": [ + 76, + 537, + 468, + 579 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "tions and hyperparameters, confirming that AENIB exhibits a better operating points even in terms of effective robustness [105], given the recent observations on the correlation between in- vs. out-of-distribution performances across different models [34, 87, 105].", + "bbox": [ + 75, + 595, + 468, + 670 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Lastly, Table 4 further evaluates the ImageNet classifiers on Background Challenge [119], a benchmark established to test the model robustness against background shifts: specifically, it constructs variants of ImageNet-9 (that combines 370 subclasses of ImageNet; ORIGINAL) with different combinations of backgrounds. Our AENIB-based models still consistently improve upon the cross-entropy baseline on the benchmark, showing that AENIB indeed tends to learn less-biased features against background changes.", + "bbox": [ + 75, + 671, + 470, + 808 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.2. Novelty detection", + "text_level": 1, + "bbox": [ + 76, + 816, + 246, + 832 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Next, we show that our AENIB model can be also a good detector for out-of-distribution samples (OODs), i.e., to solve the novelty detection task. In general, the task is defined by a binary classification problem that aims to discriminate novel", + "bbox": [ + 75, + 839, + 470, + 900 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/1ada7f4ddc49c8c421d861503e06fd6f5ca51cc0704c763b9422bd390a9b32a2.jpg", + "image_caption": [ + "Figure 3. Comparison of trends in clean vs. corruption errors against Gaussian on ViT-S/4." + ], + "image_footnote": [], + "bbox": [ + 506, + 94, + 671, + 231 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/9b8d6236d57497bda1aafb35fba2f4483782aa6f503e064f5be7be996c737c9e.jpg", + "image_caption": [ + "Figure 4. Comparison of certified adversarial robust accuracy at various radii on CIFAR-10." + ], + "image_footnote": [], + "bbox": [ + 707, + 94, + 866, + 232 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "samples from in-distribution samples. A typical practice here is to define a score function for each input, e.g., the maximum confidence score [36], to threshold out samples as out-of-distribution when the score is low. To define a score function for AENIB models, we first observe that the log-likelihood of $\\mathbf{z}_n$ , which is only available for AENIB (and not for standard models), can be a strong score to detect novelties those are semantically far from in-distribution. Specifically, we use $\\log \\mathcal{N}(\\mathbf{z}_n;0,I) = -\\frac{1}{2}\\| \\mathbf{z}_n\\|^2$ , as we assume that $\\mathbf{z}$ follows isotropic Gaussian $\\mathcal{N}(0,I)$ . For detecting so-called \"harder\" novelties, we propose to use the log-likelihood score of $\\mathbf{y}$ under a symmetric Dirichlet distribution of parameter $\\alpha > 0$ , namely $\\mathrm{Dir}_{\\alpha}(\\mathbf{y}) \\in \\Delta^{|\\mathcal{Y}| - 1}$ , rather than simply using $\\max_y p(y|x)$ : i.e., $\\log \\mathrm{Dir}_{\\alpha}(\\mathbf{y}) = (\\alpha - 1)\\sum_i\\log y_i$ . Note that the distribution gets closer to the symmetric (discrete) one-hot distribution as $\\alpha \\to 0$ , which makes sense for most classification tasks, and here we simply use $\\alpha = 0.05$ throughout experiments.", + "bbox": [ + 496, + 292, + 893, + 564 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We consider two evaluation benchmarks: (a) the \"standard\" benchmark, that has been actively adopted in the literature [36, 72, 74], assumes the CIFAR-10 test set as in-distribution and measures the detection performance of other independent datasets; (b) a recent OBJECTS benchmark [122], on the other hand, extends the CIFAR-10 benchmark to also consider \"near\" in-distribution in OOD evaluation. Specifically, OBJECTS assumes CIFAR-10-C [35] and ImageNet-10 as in-distribution in test-time as well as CIFAR-10, making the detection much more challenging. In this experiment, we compare ResNet-18 [33] models trained on CIFAR-10 following the setup of [122].", + "bbox": [ + 496, + 564, + 893, + 744 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "The results are reported in Table 5 and 6 for the standard and OBJECTS benchmarks, respectively. Overall, we confirm that the score function combining the information of $\\mathbf{z}_n$ and $\\mathbf{y}$ of AENIB significantly improves novelty detection in a complementary manner over strong baselines, showing the effectiveness of modeling nuisance. For example, in Table 5, the combined score achieves near-perfect AUROCs for detecting SVHN, LSUN and ImageNet datasets.", + "bbox": [ + 496, + 744, + 893, + 866 + ], + "page_idx": 5 + }, + { + "type": "page_footnote", + "text": "In practice, we observe that other choices in a moderate range of $\\alpha$ near 0 do not much affect performance.", + "bbox": [ + 500, + 875, + 890, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "16211", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/0c17eafa51b587cc2fc595278398355ee123a072147b839c36b4d26e4b63dfe4.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
FS-OOD: OBJECTSAUROC (%; ↑) / AUPR (%; ↑) / FPR@TPR95 (%; ↓)
MethodScoreMNISTFashionMNISTTextureCIFAR-100-C
Cross-entropymaxy p(y|x) [36]66.98 / 52.66 / 93.5473.78 / 90.15 / 88.0874.18 / 93.34 / 85.6474.12 / 89.74 / 87.26
ODIN [74]70.31 / 49.58 / 82.0480.98 / 91.53 / 68.7370.14 / 89.97 / 72.9167.51 / 83.97 / 84.26
Energy-based [76]54.55 / 34.14 / 92.2376.50 / 89.80 / 72.4068.63 / 89.51 / 75.5768.37 / 85.54 / 83.64
Mahalanobis [72]77.04 / 65.31 / 84.5980.33 / 92.28 / 77.1772.02 / 88.46 / 72.9868.13 / 82.97 / 85.53
SEM [122]75.69 / 76.61 / 99.7079.40 / 93.14 / 93.7279.69 / 95.48 / 82.1578.89 / 92.07 / 83.92
log Dir0.05(y)76.75 / 66.26 / 83.5182.88 / 93.97 / 77.1970.69 / 92.68 / 91.3578.80 / 92.21 / 82.50
VIB [1]maxy p(y|x) [36]80.23 / 73.50 / 80.6976.35 / 91.22 / 84.7574.67 / 94.09 / 87.2276.12 / 91.03 / 84.99
log Dir0.05(y)86.13 / 79.45 / 64.9281.11 / 93.12 / 77.8273.84 / 93.50 / 88.0078.54 / 91.85 / 81.47
AENIB (ours)maxy p(y|x) [36]79.67 / 71.50 / 80.2277.33 / 91.63 / 84.3174.95 / 93.97 / 86.0174.31 / 89.89 / 86.26
log Dir0.05(y)90.53 / 85.68 / 52.0884.56 / 94.61 / 74.2475.04 / 93.83 / 86.0179.39 / 92.33 / 81.51
+ log N(zn; 0, I)92.43 / 89.38 / 48.1084.85 / 94.84 / 74.6788.91 / 97.49 / 48.4482.66 / 93.62 / 74.14
", + "bbox": [ + 104, + 88, + 859, + 303 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 6. Comparison of OOD detection performances on the OBJECTS benchmark [122], which considers CIFAR-10-C and ImageNet-10 as in-distribution as well as the training in-distribution of CIFAR-10. Bold and underline denote the best and runner-up results, respectively.", + "bbox": [ + 75, + 309, + 893, + 339 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Regarding Table 6, on the other hand, AENIB improves the previous best AUROC (of Mahalanobis [72]) on OBJECTS vs. MNIST from $77.04 \\rightarrow 92.43$ . The improved results on OBJECTS imply that both of the representation and score obtained from AENIB help to better discriminate in- vs. out-of-distribution in more semantic senses.", + "bbox": [ + 75, + 354, + 470, + 445 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.3. Certified adversarial robustness", + "text_level": 1, + "bbox": [ + 76, + 454, + 359, + 469 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We also evaluate adversarial robustness [29, 82, 102] adopting the randomized smoothing framework [17, 70] that can measure a certified robustness for a given representation. Specifically, any classifier can be robustified by averaging its predictions under Gaussian noise, where the robustness at input $x$ depends on how consistent the classifier is on classifying $\\mathcal{N}(x, \\sigma^2\\mathbf{I})$ [50]. Under this evaluation protocol, we suggest that adversarially-robust representations can be a natural byproduct from AENIB when combined with the randomized smoothing technique, without using any thorough adversarial training methods [82] that often require significant training cost with no certification on the robustness.", + "bbox": [ + 75, + 477, + 470, + 657 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We follow the standard certification protocol [17] to compare the certified test accuracy at radius $r$ , which is defined by the fraction of the test samples that a smoothed classifier classifies correctly with its certified radius larger than $r$ . We consider ViT-S models on CIFAR-10, and assume $\\sigma = 0.1$ for this experiment. The results summarized in Figure 4 show that our proposed AENIB achieves significantly better certified robustness compared to the baselines at all radii tested: e.g., it improves certified robust accuracy of VIB by $39.6\\% \\rightarrow 56.8\\%$ at $\\varepsilon = 0.1$ . Again, the robustness obtained from AENIB is not from specific knowledge on the threat model, which implies that AENIB could offer free adversarial robustness when combined with randomized smoothing. This confirms that the robustness of AENIB is not only significant but also consistent per input, especially considering its high certified robustness at higher $r$ 's.", + "bbox": [ + 75, + 659, + 470, + 900 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/b16c2cfa127bb6e37c30ef90014f2a2975e21f2bc20134fad100e6736a26ac95.jpg", + "image_caption": [ + "(a) DisenIB [92]" + ], + "image_footnote": [], + "bbox": [ + 531, + 352, + 862, + 390 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/7cd7d8b79060ff142f052b450592cafea7e4aa75e8afe5ca82499a6006a09535.jpg", + "image_caption": [ + "(b) AENIB (Ours)", + "Figure 5. Comparison of CIFAR-10 reconstructions when the nuisance $\\mathbf{z}_n$ is swapped with those of another (random) sample." + ], + "image_footnote": [], + "bbox": [ + 531, + 406, + 862, + 443 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.4. Comparison with DisenIB [92]", + "text_level": 1, + "bbox": [ + 500, + 511, + 769, + 527 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "In this section, we provide a comparison of AENIB with a related work of DisenIB [92], as well as other variants of VIB, namely Nonlinear-VIB [65] and Squared-VIB [106]. Here, DisenIB is a variant of IB which also considers a nuisance modeling (based on FactorVAE [57]), in a purpose of supervised disentangling. Specifically, DisenIB considers two independent encoders $\\mathbf{z} \\coloneqq f(\\mathbf{x})$ and $\\mathbf{z}_n \\coloneqq g(\\mathbf{x})$ , and aims to optimize the following objective:", + "bbox": [ + 496, + 534, + 893, + 655 + ], + "page_idx": 6 + }, + { + "type": "equation", + "text": "\n$$\n\\max _ {f, g} I (\\mathbf {z}; \\mathbf {y}) + I (\\mathbf {x}; \\mathbf {z} _ {n}, \\mathbf {y}) - I (\\mathbf {z} _ {n}; \\mathbf {z}). \\tag {11}\n$$\n", + "text_format": "latex", + "bbox": [ + 566, + 666, + 890, + 690 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Compared to our proposed NIB (4), the most important difference between the two objectives is in their \"reconstruction\" terms: i.e., $I(\\mathbf{x}; \\mathbf{z}_n, \\mathbf{y})$ of (11) vs. $I(\\mathbf{x}; \\mathbf{z}, \\mathbf{z}_n)$ of ours (4). Due to this difference, the DisenIB objective (11) cannot rule out the cases when $\\mathbf{z}$ only encode few of \"shortcut\" signals in $\\mathbf{x}$ (correlated to $\\mathbf{y}$ ) even at optimum, in contrast to our key motivation of NIB (4) that aims to let $\\mathbf{z}$ to encode every $\\mathbf{y}$ -correlated signal in $\\mathbf{x}$ as much as possible.", + "bbox": [ + 496, + 699, + 893, + 820 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We conduct experimental comparisons based on (a) our CIFAR-10 setups (Table 2), and (b) directly upon the official implementation6 of DisenIB on MNIST [69] (Table 9 of Ap", + "bbox": [ + 496, + 821, + 893, + 866 + ], + "page_idx": 6 + }, + { + "type": "page_footnote", + "text": "https://github.com/PanZiqiAI/disentangled-information-bottleneck", + "bbox": [ + 500, + 875, + 893, + 898 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "16212", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "pendix G). Here, we adopt and extend the benchmark to also cover MNIST-C [88], a corrupted version of the MNIST. For the latter comparison, we use a simple 4-layer convolutional network as the encoder architecture. We train every MNIST model here for 100K updates and follow the other training details from the CIFAR experiments (see Appendix B.1).", + "bbox": [ + 75, + 90, + 470, + 181 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Overall, we observe that the effectiveness of AENIB still applies to these benchmarks. This is in contrast to DisenIB, given that the effectiveness from DisenIB, e.g., its gain in AUROC on detecting Gaussian noise as an OOD (as conducted by [92]), could not be further generalized on CIFAR-10-C or MNIST-C, where AENIB still improves on as well as achieving the perfect score at the same OOD task. In Figure 5a, we further observe qualitatively that DisenIB often leaves highly semantic information in the nuisance $\\mathbf{z}_n$ : its reconstruction can be completely changed by swapping $\\mathbf{z}_n$ with those of another sample. This is essentially what AENIB addresses, as compared in Figure 5b.", + "bbox": [ + 75, + 183, + 473, + 364 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Related work", + "text_level": 1, + "bbox": [ + 76, + 380, + 215, + 396 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Out-of-distribution robustness. Since the seminal works [2, 90, 102] revealing the fragility of neural networks on out-of-distribution inputs, there have been significant attempts on identifying and improving various notions of robustness: e.g., detecting novel inputs [36,71,72,103], robustness against corruptions [27,35,39,119], and adversarial noise [5, 11, 17, 82], to name a few. Due to its fundamental challenges in making neural network to extrapolate, however, most of the advances in the robustness literature has been made under assuming priors closely related to the individual problems: e.g., an external data or data augmentations [37, 39], extra information from test-time samples [116], or specific knowledge in threat models [52, 112]. In this work, we aim to improve multiple notions of robustness without assuming such priors, through a new training scheme that extends the standard information bottleneck principle under noisy observations in test-time.", + "bbox": [ + 75, + 411, + 470, + 652 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Hybrid generative-discriminative modeling. Our proposed method can be also viewed as a new approach of improving the robustness of discriminative models by incorporating a generative model, in the context that has been explored in recent works [31,72,99,123]. For example, [72,73] have incorporated a simple (but of low expressivity for generation) Gaussian mixture model into discriminative classifiers; a line of research on Joint Energy-based Models (JEM) [31, 123] assumes an energy-based model but with a notable training instability for the purpose. In this work, we propose an autoencoder-based model to avoid such training instability, and consider a design that the nuisance can succinctly supplement the given discriminative representation to be generative. We demonstrate that our approach can take the best of two worlds; it enables (a) stable training, while (b) attaining the high expressive generative performances.", + "bbox": [ + 75, + 657, + 470, + 901 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Nuisance modeling. The idea of incorporating nuisances can be also considered in the context of invertible modeling, or as known as flow-based models [6, 23, 30, 59], where the nuisance can be defined by splitting the (full-information) encoding $\\mathbf{z}$ for a given subspace of interest as explored by [4, 46]. Unlike such approaches, our autoencoder-based nuisance modeling does not focus on the \"full\" invertibility for arbitrary inputs, but rather on inverting the data manifold given, which enabled (a) a much flexible encoder design in practice, and (b) a more scalable generative modeling of nuisance $\\mathbf{z}_n$ , e.g., beyond an MNIST-scale as done by [46]. Other related works [48, 49, 92] do introduce an encoder for nuisance factors, but the notion of nuisance-ness has been focused in terms of the independence to $\\mathbf{z}$ (for the purpose of feature disentangling), rather than to $\\mathbf{y}$ as we focus in this work (for the purpose of robustness): e.g., DisenIB [92] applies FactorVAE [57] between semantic and nuisance embeddings to force their independence. Yet, the literature has been also questioned on whether the idea can be scaled-up beyond, e.g., MNIST, and our work does explore and establish a practical design with recent architectures and datasets addressing diverse modern security metrics.", + "bbox": [ + 496, + 90, + 893, + 422 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We provide more extensive and detailed discussions on related works in Appendix F.", + "bbox": [ + 498, + 424, + 893, + 455 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "6. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 470, + 619, + 486 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We suggest that having a good nuisance model can be a tangible approach to induce a reliable representation. We develop a practical method of learning deep nuisance representation from data, and show its effectiveness to improve diverse reliability measures under a challenging setup of assuming no prior [105]. We believe our work can be a useful step towards better understanding of out-of-distribution generalization in deep learning. Although the current scope is on a particular design of autoencoder based models, our framework of nuisance-extended IB is not limited to it and future works could consider more diverse implementations. Ultimately, we aim to approximate a challenging form of adversarial training with a mutual information constraint, which we believe will be a promising direction to explore.", + "bbox": [ + 496, + 496, + 895, + 708 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgments", + "text_level": 1, + "bbox": [ + 500, + 723, + 660, + 739 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "This work was partly supported by Center for Applied Research in Artificial Intelligence (CARAI) grant funded by Defense Acquisition Program Administration (DAPA) and Agency for Defense Development (ADD) (UD190031RD), and by Institute of Information & communications Technology Planning & Evaluation (IITP) grant funded by the Korea government (MSIT) (No.2021-0-02068, Artificial Intelligence Innovation Hub; No.2019-0-00075, Artificial Intelligence Graduate School Program (KAIST)). We thank Subin Kim for the proofreading of our manuscript.", + "bbox": [ + 496, + 750, + 895, + 902 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "16213", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Alexander A Alemi, Ian Fischer, Joshua V Dillon, and Kevin Murphy. Deep variational information bottleneck. In International Conference on Learning Representations, 2017. 2, 4, 5, 6, 7, 20, 21, 22", + "[2] Dario Amodei, Chris Olah, Jacob Steinhardt, Paul Christiano, John Schulman, and Dan Mané. Concrete problems in AI safety. arXiv preprint arXiv:1606.06565, 2016. 1, 8, 19", + "[3] Jyoti Aneja, Alex Schwing, Jan Kautz, and Arash Vahdat. A contrastive learning approach for training variational autoencoder priors. 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Advances in Neural Information Processing Systems, 33:7559-7570, 2020. 22, 23" + ], + "bbox": [ + 503, + 92, + 893, + 768 + ], + "page_idx": 12 + }, + { + "type": "page_number", + "text": "16218", + "bbox": [ + 480, + 945, + 519, + 955 + ], + "page_idx": 12 + } +] \ No newline at end of file diff --git a/2023/Enhancing Multiple Reliability Measures via Nuisance-Extended Information Bottleneck/13a10611-b5a4-413b-b3b8-4101508c9783_model.json b/2023/Enhancing Multiple Reliability Measures via Nuisance-Extended Information Bottleneck/13a10611-b5a4-413b-b3b8-4101508c9783_model.json new file mode 100644 index 0000000000000000000000000000000000000000..f902d83715ef687545ed7b3b5dae715bf9a1f93e --- /dev/null +++ b/2023/Enhancing Multiple Reliability Measures via Nuisance-Extended Information Bottleneck/13a10611-b5a4-413b-b3b8-4101508c9783_model.json @@ -0,0 +1,3130 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.26, + 0.131, + 0.711, + 0.174 + ], + "angle": 0, + "content": "Enhancing Multiple Reliability Measures via Nuisance-extended Information Bottleneck" + }, + { + "type": "text", + "bbox": [ + 0.154, + 0.203, + 0.816, + 0.258 + ], + "angle": 0, + "content": "Jongheon Jeong† Sihyun Yu† Hankook Lee‡* Jinwoo Shin† \n†Korea Advanced Institute of Science and Technology (KAIST) ‡LG AI Research \n{jongheonj,sihyun.yu,jinwoos}@kaist.ac.kr hankook.lee@lgresearch.ai" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.292, + 0.312, + 0.308 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.324, + 0.474, + 0.687 + ], + "angle": 0, + "content": "In practical scenarios where training data is limited, many predictive signals in the data can be rather from some biases in data acquisition (i.e., less generalizable), so that one cannot prevent a model from co-adapting on such (so-called) \"shortcut\" signals: this makes the model fragile in various distribution shifts. To bypass such failure modes, we consider an adversarial threat model under a mutual information constraint to cover a wider class of perturbations in training. This motivates us to extend the standard information bottleneck to additionally model the nuisance information. We propose an autoencoder-based training to implement the objective, as well as practical encoder designs to facilitate the proposed hybrid discriminative-generative training concerning both convolutional- and Transformer-based architectures. Our experimental results show that the proposed scheme improves robustness of learned representations (remarkably without using any domain-specific knowledge), with respect to multiple challenging reliability measures. For example, our model could advance the state-of-the-art on a recent challenging OBJECTS benchmark in novelty detection by \\(78.4\\% \\rightarrow 87.2\\%\\) in AUROC, while simultaneously enjoying improved corruption, background and (certified) adversarial robustness. Code is available at https://github.com/jh-jeong/nuisance_ib." + }, + { + "type": "title", + "bbox": [ + 0.079, + 0.731, + 0.208, + 0.746 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.757, + 0.47, + 0.879 + ], + "angle": 0, + "content": "Despite the recent breakthroughs in computer vision in aid of deep learning, e.g., in image/video recognition [9, 20, 109], synthesis [42, 55, 96, 125], and 3D scene rendering [85, 86, 104], deploying deep learning models to the real-world still places a burden on contents providers as it affects the reliability of their services. In many cases, deep neural networks make substantially fragile predictions for out-of-distribution inputs, i.e., samples that are not likely" + }, + { + "type": "image", + "bbox": [ + 0.51, + 0.291, + 0.895, + 0.435 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.448, + 0.895, + 0.532 + ], + "angle": 0, + "content": "Figure 1. A high-level illustration of our method, nuisance-extended information bottleneck (NIB). In this paper, we focus on scenarios when the input \\(\\mathbf{x}\\) can be corrupted \\(\\mathbf{x} \\rightarrow \\hat{\\mathbf{x}}\\) in test-time while preserving its semantics. Unlike the standard cross-entropy training (CE), NIB aims to encode every target-correlated signal in \\(\\mathbf{x}\\), some of which can be more reliable under distribution shifts." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.552, + 0.895, + 0.674 + ], + "angle": 0, + "content": "from the training distribution, even when the inputs are semantically close enough to in-distribution samples for humans [35, 102]. Such a vulnerability can be a significant threat in risk-sensitive systems, such as autonomous driving, medical imaging, and health-care applications, to name a few [2]. Overall, the phenomena highlight that deep neural networks tend to extract \"shortcut\" signals [26] from given limited (or potentially biased) training data in practice." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.675, + 0.896, + 0.901 + ], + "angle": 0, + "content": "To address such concerns, multiple literatures have been independently developed based on different aspects of model reliability. Namely, their methods use different threat models and benchmarks, depending on how a shift in input distribution happens in test-time, and how to evaluate model performance against the shift. For example, in the context of adversarial robustness [11, 17, 82, 128], a typical threat model is to consider the worst-case noise inside a fixed \\(\\ell_p\\)-ball around given test samples. Another example of corruption robustness [34, 35, 39, 116] instead assumes predefined types of common corruptions (e.g., Gaussian noise, fog, etc.) that applies to the test samples. Lastly, novelty detection [36, 72, 74, 76] usually tests whether a model can detect a specific benchmark dataset as out-of-distribution from the (in-distribution) test samples." + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.887, + 0.22, + 0.899 + ], + "angle": 0, + "content": "*Work done at KAIST." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "16206" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.395 + ], + "angle": 0, + "content": "Due to discrepancy between each of \"ideal\" objectives and its practical threat models, however, the literatures have commonly found that optimizing under a certain threat model often hardly generalizes to other threat ones: e.g., (a) several works [16, 62, 121] have observed that standard adversarial training [82] often harms other reliability measures such as corruption robustness or uncertainty estimation, as well as its classification performance; (b) Hendrycks et al. [34] criticize that none of the previous claims on corruption robustness could consistently generalize on a more comprehensive benchmark. This also happens even for threat models targeting the same objective: e.g., (c) Yang et al. [122] show that state-of-the-arts in novelty detection are often too sensitive, so that they tend to also detect \"near-in-distribution\" samples as out-of-distribution and perform poorly on a benchmark regarding this. Overall, these observations suggest that one should avoid optimizing reliability measures assuming a specific threat model or benchmark, and motivate to find a new threat model that is generally applicable for diverse scenarios of reliability concerns." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.4, + 0.473, + 0.732 + ], + "angle": 0, + "content": "Contribution. In this paper, we propose nuisance-extended information bottleneck (NIB), a new training objective targeting model reliability without assuming a prior on domain-specific tasks. Our method is motivated by rethinking the information bottleneck (IB) principle [107, 108] under presence of distribution shifts. Specifically, we argue that a \"robust\" representation \\(\\mathbf{z} \\coloneqq f(\\mathbf{x})\\) should always encode every signal in the input \\(\\mathbf{x}\\) that is correlated with the target \\(\\mathbf{y}\\), rather than extracting only a few shortcuts (e.g., Figure 1). This motivates us to consider an adversarial form of threat model on distribution shifts in \\(\\mathbf{x}\\), under a constraint on the mutual information \\(I(\\mathbf{x},\\mathbf{y})\\). To implement this idea, we propose a practical design by incorporating a nuisance representation \\(\\mathbf{z}_n\\) alongside \\(\\mathbf{z}\\) of the standard IB so that \\((\\mathbf{z},\\mathbf{z}_n)\\) can reconstruct \\(\\mathbf{x}\\). This results in a novel synthesis of adversarial autoencoder [83] and variational IB [1] into a single framework. For the architectural side, we propose (a) to utilize the internal feature statistics for convolutional network based encoders, and (b) to incorporate vector-quantized patch representations for Transformer-based [24] encoders to model \\(\\mathbf{z}_n\\), mainly to efficiently encode the nuisance \\(\\mathbf{z}_n\\) (as well as \\(\\mathbf{z}\\)) in a scalable manner." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.735, + 0.473, + 0.901 + ], + "angle": 0, + "content": "We perform an extensive evaluation on the representations learned by our scheme, showing comprehensive improvements in modern reliability metrics: including (a) novelty detection, (b) corruption (or natural) robustness, (c) background robustness and (d) certified adversarial robustness. The results are particularly remarkable as the gains are not from assuming a prior on each of specific threat models. For example, we obtain a significant reduction in CIFAR-10-C error rates of the highest severity, i.e., by \\(26.5\\% \\rightarrow 19.5\\%\\), without extra domain-specific prior as assumed in recent methods [39, 40]. Here, we also show that the effective" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.895, + 0.228 + ], + "angle": 0, + "content": "ness of our method is scalable to larger-scale (ImageNet) datasets. For novelty detection, we could advance AUROCs in recent OBJECTS [122] benchmarks by a large margin of \\(78.4\\% \\rightarrow 87.2\\%\\) in average upon the state-of-the-art, showing that our representations can provide a more semantic information to better discriminate out-of-distribution samples. Finally, we also demonstrate how the representations can further offer enhanced robustness against adversarial examples, by applying randomized smoothing [17] on them." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.24, + 0.628, + 0.258 + ], + "angle": 0, + "content": "2. Background" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.27, + 0.895, + 0.452 + ], + "angle": 0, + "content": "Notation. Given two random variables \\(\\mathbf{x} \\in \\mathcal{X}\\), the input, and \\(\\mathbf{y} \\in \\mathcal{Y}\\), the target, our goal is to find a mapping (or an encoder) \\(f: \\mathcal{X} \\to \\mathcal{Z}\\) from data \\(\\mathcal{D} = \\{(x_i, y_i)\\}_{i=1}^n\\) so that \\(\\mathbf{z} := f(\\mathbf{x})\\), the representation, can predict \\(\\mathbf{y}\\) with a simper (e.g., linear) mapping [7, 64]. We assume that \\(f\\) is parametrized by a neural network, and is stochastic to adopt an information theoretic view [108], i.e., the encoder output is a random variable defined as \\(p_f(\\mathbf{z}|\\mathbf{x})\\) rather than a constant. Such a modeling can be done through the reparametrization trick [61] with an independent random variable \\(\\epsilon\\) and (deterministic) \\(f\\) by assuming \\(\\mathbf{z} := f(\\mathbf{x}, \\epsilon)\\). For example, one of standard designs parametrizes \\(f\\) by:" + }, + { + "type": "equation", + "bbox": [ + 0.593, + 0.461, + 0.892, + 0.477 + ], + "angle": 0, + "content": "\\[\nf (\\mathbf {x}, \\epsilon) := f ^ {\\mu} (\\mathbf {x}) + \\epsilon \\cdot f ^ {\\sigma} (\\mathbf {x}), \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.486, + 0.892, + 0.534 + ], + "angle": 0, + "content": "where \\(f^{\\mu} \\in \\mathbb{R}^{|\\mathcal{Z}|}\\) and \\(f^{\\sigma} \\in \\mathbb{R}_{+}^{|\\mathcal{Z}|}\\) are deterministic mappings modeling \\(\\mu\\) and \\(\\sigma\\) in \\(\\mathcal{N}(\\mathbf{x};\\mu,\\sigma^2I)\\), respectively, so that they can still be learned through a gradient-based optimization." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.534, + 0.895, + 0.7 + ], + "angle": 0, + "content": "The data \\(\\mathcal{D}\\) is usually assumed to consist of i.i.d. samples from a certain data generating distribution \\((x_{i},y_{i})\\sim p_{d}(\\mathbf{x},\\mathbf{y})\\). One expects that \\(f\\) learned from \\(\\mathcal{D}\\) could generalize to predict \\(p_d(\\mathbf{y}|\\mathbf{x})\\) for unseen samples from \\(p_d(\\mathbf{x},\\mathbf{y})\\). The formulation, however, does not specify how \\(f\\) should behave for inputs that are not likely from \\(p_d\\), say \\(\\hat{x}\\). This becomes problematic for those who expect that the decision making of \\(f\\) should be close to that of human being, at least when \\(\\hat{x}\\) differs from \\(p_d\\) only up to what humans regard as nuisance. This is where the current neural networks commonly fail under the standard training practices." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.704, + 0.895, + 0.856 + ], + "angle": 0, + "content": "Information bottleneck. Intuitively, a \"good\" representation \\(\\mathbf{z}\\) should keep information of \\(\\mathbf{x}\\) that is correlated with \\(\\mathbf{y}\\), while preventing \\(\\mathbf{z}\\) from being too complex. The information bottleneck [107, 108] (IB) is a principled approach to obtain such a succinct representation \\(\\mathbf{x} \\rightarrow \\mathbf{z}\\) for a given downstream task \\(\\mathbf{x} \\rightarrow \\mathbf{y}\\): namely, it finds \\(\\mathbf{z}\\) that (a) maximizes the (task-relevant) mutual information \\(I(\\mathbf{z}; \\mathbf{y})\\), while (b) minimizing \\(I(\\mathbf{x}; \\mathbf{z})\\) to constrain the capacity of \\(\\mathbf{z}\\) for better generalization. In other words, it sets the mutual information \\(I(\\mathbf{x}; \\mathbf{z})\\) as the complexity measure of \\(\\mathbf{z}\\). Specifically," + }, + { + "type": "page_footnote", + "bbox": [ + 0.498, + 0.863, + 0.892, + 0.901 + ], + "angle": 0, + "content": "1Although we focus on supervised learning, the framework itself in general does not rule out more general scenarios, e.g., when the target \\(\\mathbf{y}\\) can be self-supervised from \\(\\mathbf{x}\\) [14, 91]." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "16207" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.118, + 0.086, + 0.855, + 0.265 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.274, + 0.895, + 0.318 + ], + "angle": 0, + "content": "Figure 2. An overview of the proposed framework, the autoencoder-based nuisance-extended information bottleneck (AENIB). It illustrates the general pipeline, and Appendix C provides specific instantiations for convolutional and Transformer-based architectures. Overall, we incorporate adversarial autoencoder into variational information bottleneck by introducing a nuisance \\(\\mathbf{z}_n\\) (to \\(\\mathbf{y}\\)) in representation learning." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.333, + 0.373, + 0.35 + ], + "angle": 0, + "content": "it aims to maximize the following objective:" + }, + { + "type": "equation", + "bbox": [ + 0.09, + 0.36, + 0.47, + 0.385 + ], + "angle": 0, + "content": "\\[\n\\max _ {f} R _ {\\mathrm {I B}} (f), \\quad \\text {f o r} \\quad R _ {\\mathrm {I B}} (f) := I (\\mathbf {z}; \\mathbf {y}) - \\beta I (\\mathbf {x}; \\mathbf {z}), \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.394, + 0.47, + 0.426 + ], + "angle": 0, + "content": "where \\(\\beta \\geq 0\\) controls the capacity constraint which ensures \\(I(\\mathbf{x};\\mathbf{z})\\leq I_{\\beta}\\) for some \\(I_{\\beta}\\)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.439, + 0.456, + 0.455 + ], + "angle": 0, + "content": "3. Nuisance-extended information bottleneck" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.464, + 0.47, + 0.675 + ], + "angle": 0, + "content": "The standard information bottleneck (IB) objective (2) obtains a representation \\(\\mathbf{z} := f(\\mathbf{x})\\) on premise that the future inputs will be also from \\(p_d(\\mathbf{x},\\mathbf{y})\\). In this paper, we aim to extend IB under assumption that the input \\(\\mathbf{x}\\) can be corrupted through an unknown noisy channel in the future, say \\(\\mathbf{x} \\to \\hat{\\mathbf{x}}\\), while \\(\\hat{\\mathbf{x}}\\) still preserves the semantics of \\(\\mathbf{x}\\) with respect to \\(\\mathbf{y}\\): in other words, we assume \\(I(\\mathbf{x};\\mathbf{y}) = I(\\hat{\\mathbf{x}};\\mathbf{y}) > 0\\). Intuitively, one can imagine a scenario that \\(\\mathbf{x}\\) contains multiple signals that each is already highly correlated with \\(\\mathbf{y}\\), i.e., filtering out the remainder from \\(\\mathbf{x}\\) does not affect its mutual information with \\(\\mathbf{y}\\). It may or may not be surprising that such signals are quite prevalent in deep neural networks, e.g., [44] empirically observe that adversarial perturbations [29, 102] are sufficient for a model to perform accurate classification." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.676, + 0.472, + 0.721 + ], + "angle": 0, + "content": "In the context of IB framework, where the goal is to obtain a succinct encoder \\( f \\), it is now reasonable to presume that the noisy channel \\( \\hat{\\mathbf{x}} \\) acts like an adversary, i.e., it minimizes:" + }, + { + "type": "equation", + "bbox": [ + 0.093, + 0.732, + 0.47, + 0.755 + ], + "angle": 0, + "content": "\\[\n\\min _ {\\hat {\\mathbf {x}}} I (\\hat {\\mathbf {z}} := f (\\hat {\\mathbf {x}}); \\mathbf {y}) \\text {s u b j e c t} I (\\mathbf {x}; \\mathbf {y}) = I (\\hat {\\mathbf {x}}; \\mathbf {y}), \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.765, + 0.47, + 0.901 + ], + "angle": 0, + "content": "given that one has no information on how the channel would behave a priori. This optimization thus would require \\( f \\) to extract every signal in \\( \\mathbf{x} \\) whenever it is highly correlated with \\( \\mathbf{y} \\), to avoid the case when \\( \\hat{\\mathbf{x}} \\) filters out all the signal except one that \\( f \\) has missed. We notice that, nevertheless, directly optimizing (3) with respect to \\( \\hat{\\mathbf{x}} \\) is computationally infeasible in practice, considering that (a) it is in many cases an unconstrained optimization in a high-dimensional \\( \\mathcal{X} \\), (b) with a constraint on (hard-to-compute) mutual information." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.333, + 0.895, + 0.56 + ], + "angle": 0, + "content": "In this paper, to make sure that \\( f \\) still exhibits the adversarial behavior without (3), we propose to let \\( f \\) to model the nuisance representation \\( \\mathbf{z}_n \\) as well as \\( \\mathbf{z} \\). Specifically, \\( \\mathbf{z}_n \\) aims to model the \"remainder\" information from \\( \\mathbf{z} \\) needed to reconstruct \\( \\mathbf{x} \\), i.e., it maximizes \\( I(\\mathbf{x};\\mathbf{z},\\mathbf{z}_n) \\). At the same time, \\( \\mathbf{z}_n \\) compresses out any information that is correlated with \\( \\mathbf{y} \\), i.e., it also minimizes \\( I(\\mathbf{z}_n;\\mathbf{y}) \\). Therefore, every information that is correlated with \\( \\mathbf{y} \\) should be encoded into \\( \\mathbf{z} \\) in a complementary manner. Here, we remark that now the role of the capacity constraint in (2) becomes more important: not only for regularizing \\( \\mathbf{z} \\) to be simpler, it also penalizes \\( \\mathbf{z}_n \\) from pushing out unnecessary information to predict \\( \\mathbf{y} \\) into \\( \\mathbf{z} \\), making the objective competitive again between \\( \\mathbf{z} \\) and \\( \\mathbf{z}_n \\) as like in (3). Combined with the original IB (2), we define nuisance-extended IB (NIB) as the following:" + }, + { + "type": "equation", + "bbox": [ + 0.513, + 0.575, + 0.892, + 0.599 + ], + "angle": 0, + "content": "\\[\n\\max _ {f} R _ {\\mathrm {N I B}} (f) := R _ {\\mathrm {I B}} (f) - I \\left(\\mathbf {z} _ {n}; \\mathbf {y}\\right) + \\alpha I \\left(\\mathbf {x}; \\mathbf {z}, \\mathbf {z} _ {n}\\right), \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.613, + 0.895, + 0.735 + ], + "angle": 0, + "content": "where \\(\\alpha \\geq 0\\). The proposed NIB objective can be viewed as a regularized form of IB by introducing a nuisance \\(\\mathbf{z}_n\\). Specifically, this optimization additionally forces \\(I(\\mathbf{x};\\mathbf{z},\\mathbf{z}_n)\\) and \\(I(\\mathbf{z}_n;\\mathbf{y})\\) in (4) to be maximized and minimized, i.e., \\(H(\\mathbf{x}|\\mathbf{z},\\mathbf{z}_n) = 0\\) and \\(I(\\mathbf{z}_n;\\mathbf{y}) = 0\\), respectively. The following highlights that having these conditions, also with the independence \\(\\mathbf{z}\\perp \\mathbf{z}_n\\), leads \\(f\\) that can recover the original \\(I(\\mathbf{x};\\mathbf{y})\\) from \\(I(\\hat{\\mathbf{z}};\\mathbf{y})\\) (see Appendix E for the derivation):" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.75, + 0.895, + 0.811 + ], + "angle": 0, + "content": "Lemma 1. Let \\(\\mathbf{x} \\in \\mathcal{X}\\), and \\(\\mathbf{y} \\in \\mathcal{Y}\\) be random variables, \\(\\hat{\\mathbf{x}}\\) be a noisy observation of \\(\\mathbf{x}\\) with \\(I(\\mathbf{x};\\mathbf{y}) = I(\\hat{\\mathbf{x}};\\mathbf{y})\\). Given that \\([\\hat{\\mathbf{z}},\\hat{\\mathbf{z}}_n] := f(\\hat{\\mathbf{x}})\\) of \\(\\hat{\\mathbf{x}}\\) satisfies (a) \\(H(\\hat{\\mathbf{x}}|\\hat{\\mathbf{z}},\\hat{\\mathbf{z}}_n) = 0\\), (b) \\(I(\\hat{\\mathbf{z}}_n;\\mathbf{y}) = 0\\), and (c) \\(\\hat{\\mathbf{z}} \\perp \\hat{\\mathbf{z}}_n\\), it holds \\(I(\\hat{\\mathbf{z}};\\mathbf{y}) = I(\\mathbf{x};\\mathbf{y})\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.825, + 0.895, + 0.901 + ], + "angle": 0, + "content": "In the following sections, we provide a practical design of the proposed NIB based on an autoencoder-based architecture. Section 3.1 and 3.2 detail out its losses and architectures, respectively, and Section 3.3 summarizes the overall training. Figure 2 illustrates an overview of our framework." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "16208" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.077, + 0.091, + 0.468, + 0.108 + ], + "angle": 0, + "content": "3.1. AENIB: A practical autoencoder-based design" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.114, + 0.47, + 0.204 + ], + "angle": 0, + "content": "Based on the NIB objective defined in (4) and Lemma 1, we design a practical training objective to implement the proposed framework. Here, we present a simple instantiation of NIB with an autoencoder-based architecture upon variational information bottleneck (VIB) [1], calling it autoencoder-based NIB (AENIB)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.205, + 0.471, + 0.326 + ], + "angle": 0, + "content": "Overall, Lemma 1 states that a robust encoder \\( f \\) demands for a \"good\" nuisance model that achieves generalization on \\( \\hat{\\mathbf{z}} \\) in three aspects: (a) a good reconstruction, (b) nuisance, and (c) the independence between \\( \\mathbf{z} \\) and \\( \\mathbf{z}_n \\). To model these behaviors, we consider a decoder \\( g: \\mathcal{Z} \\to \\mathcal{X} \\) as well as the encoder \\( f: \\mathcal{X} \\to \\mathcal{Z} \\), and adopt the following practical training objectives which incorporates an autoencoder-based loss and two adversarial losses [28]:" + }, + { + "type": "text", + "bbox": [ + 0.088, + 0.334, + 0.472, + 0.41 + ], + "angle": 0, + "content": "(a) We first pose a reconstruction loss to maximize \\(\\log p(\\mathbf{x}|\\mathbf{z},\\mathbf{z}_n)\\); standard designs assume the decoder output to follow \\(\\mathcal{N}(\\mathbf{x},\\sigma^2\\mathbf{I})\\), which is equivalent to the mean-squared error (MSE). Here, we use the normalized MSE to efficiently balance with other losses:" + }, + { + "type": "equation", + "bbox": [ + 0.185, + 0.417, + 0.47, + 0.44 + ], + "angle": 0, + "content": "\\[\nL _ {\\text {r e c o n}} := \\frac {1}{\\| \\mathbf {x} \\| _ {2} ^ {2}} \\| \\mathbf {x} - g (\\mathbf {z}, \\mathbf {z} _ {n}) \\| _ {2} ^ {2} \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.088, + 0.451, + 0.471, + 0.497 + ], + "angle": 0, + "content": "(b) To force the nuisance-ness of \\(\\mathbf{z}_n\\) with respect to \\(\\mathbf{y}\\), we approximate \\(p(\\mathbf{y}|\\mathbf{z}_n)\\) with a multi-layer perceptron (MLP), say \\(q_{n}\\), and perform an adversarial training:" + }, + { + "type": "equation", + "bbox": [ + 0.13, + 0.508, + 0.47, + 0.555 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} L _ {\\mathrm {n u i s}} := \\mathbb {E} _ {\\mathbf {x}} [ \\mathbb {C E} (q _ {n} ^ {*} (\\mathbf {z} _ {n}), \\frac {1}{| \\mathcal {Y} |}) ], \\\\ \\text {w h e r e} q _ {n} ^ {*} := \\min _ {q _ {n}} \\mathbb {E} _ {\\mathbf {x}, \\mathbf {y}} [ \\mathbb {C E} (q _ {n} (\\mathbf {z} _ {n}), \\mathbf {y}) ], \\tag {6} \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.113, + 0.562, + 0.471, + 0.593 + ], + "angle": 0, + "content": "and \\(\\mathbb{C}\\mathbb{E}\\) denotes the cross entropy loss. Here, it optimizes \\(\\mathbb{C}\\mathbb{E}\\) towards the uniform distribution in \\(\\mathcal{V}\\).3" + }, + { + "type": "text", + "bbox": [ + 0.088, + 0.601, + 0.47, + 0.663 + ], + "angle": 0, + "content": "(c) To induce the independence between \\(\\mathbf{z}\\) and \\(\\mathbf{z}_n\\), we assume that the joint prior of \\(\\mathbf{z}\\) and \\(\\mathbf{z}_n\\) is the isotropic Gaussian, i.e., \\(p(\\mathbf{z},\\mathbf{z}_n)\\sim \\mathcal{N}(0,\\mathbf{I})\\), and performs a GAN training with a 2-layer MLP discriminator \\(q_{\\mathbf{z}}\\):" + }, + { + "type": "equation", + "bbox": [ + 0.131, + 0.675, + 0.469, + 0.719 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} L _ {\\text {i n d}} := \\max _ {q _ {\\mathbf {z}}} \\mathbb {E} _ {\\mathbf {x}} \\left[ \\log \\left(q _ {\\mathbf {z}} (f (\\mathbf {x}))\\right) \\right] \\\\ + \\mathbb {E} _ {\\mathbf {z}, \\mathbf {z} _ {n}} \\sim \\mathcal {N} (0, \\mathbf {I}) [ \\log (1 - q _ {\\mathbf {z}} (\\mathbf {z}, \\mathbf {z} _ {n})) ]. \\tag {7} \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.731, + 0.47, + 0.807 + ], + "angle": 0, + "content": "Lastly, to approximate the original IB objective \\( R_{\\mathrm{IB}}(f) \\) in NIB (4), we instead maximize the variational information bottleneck (VIB) [1] objective \\( L_{\\mathrm{VIB}}^{\\beta} \\), that can provide a lower bound on \\( R_{\\mathrm{IB}} \\). Specifically, it makes variational approximations of: (a) \\( p(\\mathbf{y}|\\mathbf{z}) \\) by a (parametrized) decoder neural" + }, + { + "type": "page_footnote", + "bbox": [ + 0.076, + 0.814, + 0.47, + 0.851 + ], + "angle": 0, + "content": "2We also explore a SSIM-based [118] reconstruction loss as given in Appendix C, which we found beneficial for robustness particularly with Transformer-based models." + }, + { + "type": "page_footnote", + "bbox": [ + 0.078, + 0.851, + 0.469, + 0.876 + ], + "angle": 0, + "content": "3 Alternatively, one can directly maximize \\(\\mathbb{C}\\mathbb{E}(q_n^* (\\mathbf{z}_n),\\mathbf{y})\\); we use the current design to avoid potential instability of the maximization-based loss." + }, + { + "type": "page_footnote", + "bbox": [ + 0.078, + 0.876, + 0.469, + 0.9 + ], + "angle": 0, + "content": "4 A more detailed description on the VIB framework (as well as on GAN) can be found in Appendix F.2." + }, + { + "type": "list", + "bbox": [ + 0.076, + 0.814, + 0.47, + 0.9 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.092, + 0.894, + 0.138 + ], + "angle": 0, + "content": "network \\(q(\\mathbf{y}|\\mathbf{z})\\), and (b) \\(p(\\mathbf{z})\\) by an \"easier\" distribution \\(r(\\mathbf{z})\\), e.g., isotropic Gaussian \\(\\mathcal{N}(\\mathbf{z}|0,\\mathbf{I})\\). Assuming a Gaussian decoder (1) for \\(f(\\mathbf{x},\\epsilon)\\), we have:" + }, + { + "type": "equation", + "bbox": [ + 0.516, + 0.151, + 0.892, + 0.211 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} L _ {\\mathrm {V I B}} ^ {\\beta} := \\frac {1}{n} \\sum_ {i = 1} ^ {n} \\mathbb {E} _ {\\epsilon} [ - \\log q (y _ {i} | f (x _ {i}, \\epsilon)) ] \\\\ + \\beta \\operatorname {K L} \\left(p (\\mathbf {z} | x _ {i}) \\| r (\\mathbf {z})\\right). \\tag {8} \\\\ \\end{array}\n\\]" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.23, + 0.815, + 0.246 + ], + "angle": 0, + "content": "3.2. Architectures for nuisance modeling" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.254, + 0.894, + 0.374 + ], + "angle": 0, + "content": "In principle, our framework is generally compatible with any encoder architectures: e.g., say an encoder \\( f: \\mathcal{X} \\to \\mathcal{Z} \\) and decoder \\( g: \\mathcal{Z} \\to \\mathcal{X} \\), respectively. In order to apply VIB, we assume that the encoder has two output heads of dimension \\( 2K \\), where \\( K \\) denotes the dimension of \\( \\mathbf{z} \\). Here, each output head models a Gaussian random variable by reparametrization, i.e., by modeling \\( (\\mu, \\sigma) \\) as the encoder output for both \\( \\mathbf{z} \\in \\mathbb{R}^K \\) and \\( \\mathbf{z}_n \\in \\mathbb{R}^{K_n} \\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.375, + 0.894, + 0.495 + ], + "angle": 0, + "content": "Although it is possible that \\( f \\) models \\( \\mathbf{z} \\) and \\( \\mathbf{z}_n \\) by simply taking deep feed-forward representations following conventions, we observe that modeling nuisances \\( \\mathbf{z}_n \\) (which is essentially \"generative\") in standard (discriminative) architectures incur a training instability thus in performance: the nuisance information often requires to model finer details in a given inputs, which may be available rather in early layers of \\( f \\), but not in the later layers for classification." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.496, + 0.894, + 0.6 + ], + "angle": 0, + "content": "In this paper, we propose simple architectural treatments to improve the stability of nuisance modeling concerning both convolutional networks and Vision Transformers [24] (ViTs). This section focuses on introducing the design for convolutional networks, and we refer the readers for the ViT-based design to Appendix C: which is even simpler thanks to their patch-level representations available." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.601, + 0.894, + 0.677 + ], + "angle": 0, + "content": "Given a convolutional encoder \\(f\\), we encode \\(\\mathbf{z}_n\\) (as well as \\(\\mathbf{z}\\)) from the collection of internal features statistics, rather than directly using the output of \\(f\\). Specifically, we extract \\(L\\) intermediate feature maps of a given input \\(\\mathbf{x}\\), namely \\(\\mathbf{x}^{(1)}, \\dots, \\mathbf{x}^{(L)}\\) from \\(f(\\mathbf{x})\\), and define the projection of \\(\\mathbf{x}\\) by:" + }, + { + "type": "equation", + "bbox": [ + 0.561, + 0.686, + 0.892, + 0.722 + ], + "angle": 0, + "content": "\\[\n\\Pi_ {f} (\\mathbf {x}) := \\left[ \\begin{array}{c c c c} \\mathbf {m} ^ {(1)} & \\mathbf {m} ^ {(2)} & \\dots & \\mathbf {m} ^ {(L)} \\\\ \\mathbf {s} ^ {(1)} & \\mathbf {s} ^ {(2)} & \\dots & \\mathbf {s} ^ {(L)} \\end{array} \\right], \\tag {9}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.732, + 0.894, + 0.782 + ], + "angle": 0, + "content": "where \\(\\mathbf{m}^{(l)}\\) and \\(\\mathbf{s}^{(l)}\\) are the first and second moment of feature maps in \\(\\mathbf{x}^{(l)}\\), assuming that \\(\\mathbf{x}^{(l)} \\in \\mathbb{R}^{HWC}\\): \\(\\mathbf{m}_c^{(l)} := \\frac{1}{HW} \\sum_{hw} \\mathbf{x}_{hw_c}^{(l)}\\), and \\(\\mathbf{s}_c^{(l)} := \\frac{1}{HW} \\sum_{hw} (\\mathbf{x}_{hw_c}^{(l)} - \\mathbf{m}_c^{(l)})^2\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.782, + 0.894, + 0.901 + ], + "angle": 0, + "content": "In Appendix I, we demonstrate that this simple projection can sufficiently encode a generative representation of \\(\\mathbf{x}\\): viz., we show that one can successfully and efficiently train GANs with a discriminator defined upon \\(\\Pi_f\\). Motivated by this observation, we adopt \\(\\Pi_f\\) in modeling the encoder representations \\(\\mathbf{z}\\) and \\(\\mathbf{z}_n\\). We encode \\(\\mathbf{z}\\) and \\(\\mathbf{z}_n\\) by simply applying MLPs to \\(\\Pi_f(\\mathbf{x})\\) (9). Despite its simplicity, we observe this treatment enables a stable training of AENIB." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "16209" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.117, + 0.089, + 0.847, + 0.235 + ], + "angle": 0, + "content": "
SeverityCIFAR-10-CCIFAR-100-C
Clean12345Avg.Clean12345Avg.
Cross-entropy6.088.8911.114.019.726.516.025.131.435.139.346.854.041.3
VIB [1]5.988.6810.713.418.624.915.226.031.935.940.447.855.242.2
AugMix [39]6.528.9710.813.418.423.915.124.929.933.337.143.651.139.0
PixMix† [40]5.437.108.149.4012.114.910.323.226.728.730.835.039.032.0
AENIB (ours)4.977.498.9611.014.819.512.322.627.630.534.139.847.135.8
+ AugMix [39]5.357.658.9911.014.218.412.021.926.429.132.437.844.334.0
+ PixMix† [40]4.675.906.557.459.1211.48.0821.224.426.027.831.134.828.8
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.241, + 0.892, + 0.27 + ], + "angle": 0, + "content": "Table 1. Comparison of average corruption error rates \\((\\% ;\\downarrow)\\) per severity level on CIFAR-10/100-C [35]. Bold and underline denote the best and runner-up, respectively. \\(^{\\dagger}\\mathrm{PixMix}\\) [40] utilizes an external dataset consisting of pattern- and fractal-like images." + }, + { + "type": "table", + "bbox": [ + 0.106, + 0.284, + 0.435, + 0.439 + ], + "angle": 0, + "content": "
MethodC10C10-CC10.1C10.2CINIC
Cross-entropy6.0816.013.418.323.7
VIB [1]5.9815.213.616.823.6
NLIB [65]6.8117.014.617.524.3
sq-NLIB [106]6.0215.513.017.123.7
DisenIB [92]5.7615.213.217.223.7
AugMix [39]6.5215.114.217.224.2
PixMix [40]5.4310.313.116.623.2
AENIB (ours)4.9712.311.615.522.2
+ AugMix [39]5.3512.012.515.822.6
+ PixMix [40]4.678.0810.414.822.1
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.445, + 0.47, + 0.486 + ], + "angle": 0, + "content": "Table 2. Comparison of test error rates \\((\\% ;\\downarrow)\\) on CIFAR-10 and its variants: CIFAR-10-C/10.1/10.2, and CINIC. Bold and underline indicate the best and runner-up results, respectively." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.508, + 0.312, + 0.525 + ], + "angle": 0, + "content": "3.3. Overall training objective" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.533, + 0.471, + 0.625 + ], + "angle": 0, + "content": "Combining the proposed objectives as well as the VIB loss, \\( L_{\\mathrm{VIB}}^{\\beta} \\) (8) leads us to the final objective. Although combining multiple losses in practice may introduce additional hyperparameters, we found most of the proposed losses can be added without scaling except for the reconstruction loss \\( L_{\\mathrm{recon}} \\) and the \\( \\beta \\) in the original VIB loss. Hence, we get:" + }, + { + "type": "equation", + "bbox": [ + 0.11, + 0.638, + 0.47, + 0.657 + ], + "angle": 0, + "content": "\\[\nL _ {\\mathrm {A E N I B}} := L _ {\\mathrm {V I B}} ^ {\\beta} + \\alpha \\cdot L _ {\\text {r e c o n}} + L _ {\\text {n u i s}} + L _ {\\text {i n d}}. \\tag {10}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.672, + 0.442, + 0.688 + ], + "angle": 0, + "content": "Algorithm 1 in Appendix A summarizes the procedure." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.708, + 0.21, + 0.725 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.735, + 0.473, + 0.903 + ], + "angle": 0, + "content": "We verify the effectiveness of our proposed AENIB training for various aspects of model reliability: specifically, we cover (a) corruption and natural robustness (Section 4.1), (b) novelty detection (Section 4.2), and (c) certified adversarial robustness (Section 4.3) tasks which all have been challenging without task-specific priors [37, 39, 82]. We provide an ablation study in Appendix D for a component-wise analysis. We also present an evaluation on our proposed components in the context of generative modeling in Appendix I. The full details on the experiments, e.g., datasets, training details, and hyperparameters, can be found in Appendix B." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.286, + 0.839, + 0.303 + ], + "angle": 0, + "content": "4.1. Robustness against natural corruptions" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.31, + 0.895, + 0.598 + ], + "angle": 0, + "content": "We first evaluate corruption robustness of our method, i.e., its generalization ability under natural corruptions (e.g., fog, brightness, etc.) and distribution shifts those are still semantic to humans. To this end, we consider a wide range of benchmarks those are derived from CIFAR-10 and ImageNet for the purpose of measuring generalization. Namely, for CIFAR-10 models we test on (a) CIFAR-10/100-C [35], a corrupted version of CIFAR-10/100 simulating 15 common corruptions in 5 severity levels, as well as (b) CIFAR-10.1 [94], CIFAR-10.2 [81], and CINIC-10 [21], i.e., three regenerations of the CIFAR-10 test set. For ImageNet models, on the other hand, we test (a) ImageNet-C [35], a corrupted version of ImageNet validation set, (b) ImageNet-R [34], a collection of rendition images for 200 ImageNet classes, and ImageNet-Sketch [117], as well as (c) the Background Challenge [119] benchmark to evaluate model bias against background changes. This section mainly reports the results from ViT [24, 111] based architectures, but we also report the results with ResNet-18 [33] in Appendix H." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.598, + 0.895, + 0.794 + ], + "angle": 0, + "content": "Table 1 and 2 summarize the results on CIFAR-based models. In Table 1, we observe that AENIB significantly and consistently improves corruption errors upon VIB, and these gains are strong even compared with state-of-the-art methods: e.g., AENIB can solely outperform a strong baseline of AugMix [39]. Although a more recent method of PixMix [40] could achieve a lower corruption error by utilizing extra (pattern-like) data, we remark that (a) AENIB also benefit from PixMix (i.e., the extra data) as given in \"AENIB + PixMix\", and (b) the results on Table 2 show that the generalization capability of AENIB is better than PixMix on CIFAR-10.1, 10.2 and CINIC-10, i.e., in beyond common corruptions, by less relying on domain-specific data." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.796, + 0.895, + 0.901 + ], + "angle": 0, + "content": "Next, Table 3 highlights that the effectiveness of AENIB can generalize to a more larger-scale, higher-resolution dataset of ImageNet: we still observe that AENIB can consistently improve robust accuracy for diverse corruption types, again without leveraging any further data augmentation during training. Figure 3 compares the linear trends made by Cross-entropy and AENIB across different data augmenta" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "16210" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.08, + 0.089, + 0.472, + 0.187 + ], + "angle": 0, + "content": "
DatasetViT-S/16ViT-B/16
BaselineAENIB (ours)BaselineAENIB (ours)
IN-1K25.125.121.821.9
IN-C (mCE)65.965.2 (−0.7)58.657.5 (−1.1)
IN-R70.367.1 (−3.2)66.364.4 (−1.9)
IN-Sketch80.377.7 (−2.6)76.574.4 (−2.1)
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.194, + 0.471, + 0.234 + ], + "angle": 0, + "content": "Table 3. Comparison of error rates \\((\\% ;\\downarrow)\\) or mean corruption error (mCE, \\(\\%\\) . \\(\\downarrow\\) ) on ImageNet (IN) and its variants, namely IN-C [35], IN-R [34], and IN-Sketch [117]. Bold indicates the best results." + }, + { + "type": "table", + "bbox": [ + 0.079, + 0.239, + 0.472, + 0.339 + ], + "angle": 0, + "content": "
BG-Challenge DatasetViT-S/16ViT-B/16
BaselineAENIB (ours)BaselineAENIB (ours)
ORIGINAL (IN-9; ↑)95.395.596.096.1
ONLY-BG-T (↓)20.317.8 (−2.5)24.221.1 (−3.1)
MIXED-SAME (↑)86.388.3 (+2.0)87.488.9 (+1.5)
MIXED-RAND (↑)77.880.5 (+2.7)80.181.8 (+0.7)
BG-gap (↓)8.57.8 (−0.7)7.37.1 (−0.2)
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.345, + 0.47, + 0.388 + ], + "angle": 0, + "content": "Table 4. Evaluation of AENIB on Backgrounds Challenge [119] compared to the cross-entropy baseline. All the models are trained on ImageNet, and warped to perform classification on ImageNet-9." + }, + { + "type": "table", + "bbox": [ + 0.08, + 0.392, + 0.468, + 0.53 + ], + "angle": 0, + "content": "
MethodScoreSVHNLSUNImageNetC100CelebA
JEM [31]log p(x)0.67--0.670.75
JEM [31]maxy p(y|x) [36]0.89--0.870.79
SupCon [56]maxy p(y|x) [36]0.970.930.910.89-
Cross-entropymaxy p(y|x) [36]0.940.940.920.860.64
Cross-entropylog Dir0.05(y)0.960.950.940.860.61
VIB [1]maxy p(y|x) [36]0.950.940.920.880.76
VIB [1]log Dir0.05(y)0.970.960.940.880.78
AENIB (ours)maxy p(y|x) [36]0.880.880.860.840.81
AENIB (ours)log Dir0.05(y)0.900.950.920.860.80
AENIB (ours)+ logN(zn;0,I)0.980.990.990.860.79
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.538, + 0.47, + 0.58 + ], + "angle": 0, + "content": "Table 5. Comparison of AUROC (\\%; ↑) for OOD detection from CIFAR-10 with five OOD datasets: SVHN, LSUN, ImageNet, CIFAR-100, and CelebA. Bolds indicate the best results." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.597, + 0.47, + 0.671 + ], + "angle": 0, + "content": "tions and hyperparameters, confirming that AENIB exhibits a better operating points even in terms of effective robustness [105], given the recent observations on the correlation between in- vs. out-of-distribution performances across different models [34, 87, 105]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.672, + 0.471, + 0.809 + ], + "angle": 0, + "content": "Lastly, Table 4 further evaluates the ImageNet classifiers on Background Challenge [119], a benchmark established to test the model robustness against background shifts: specifically, it constructs variants of ImageNet-9 (that combines 370 subclasses of ImageNet; ORIGINAL) with different combinations of backgrounds. Our AENIB-based models still consistently improve upon the cross-entropy baseline on the benchmark, showing that AENIB indeed tends to learn less-biased features against background changes." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.818, + 0.248, + 0.833 + ], + "angle": 0, + "content": "4.2. Novelty detection" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.471, + 0.901 + ], + "angle": 0, + "content": "Next, we show that our AENIB model can be also a good detector for out-of-distribution samples (OODs), i.e., to solve the novelty detection task. In general, the task is defined by a binary classification problem that aims to discriminate novel" + }, + { + "type": "image", + "bbox": [ + 0.508, + 0.095, + 0.672, + 0.232 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.5, + 0.237, + 0.688, + 0.278 + ], + "angle": 0, + "content": "Figure 3. Comparison of trends in clean vs. corruption errors against Gaussian on ViT-S/4." + }, + { + "type": "image", + "bbox": [ + 0.709, + 0.095, + 0.867, + 0.233 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.7, + 0.238, + 0.889, + 0.279 + ], + "angle": 0, + "content": "Figure 4. Comparison of certified adversarial robust accuracy at various radii on CIFAR-10." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.293, + 0.895, + 0.565 + ], + "angle": 0, + "content": "samples from in-distribution samples. A typical practice here is to define a score function for each input, e.g., the maximum confidence score [36], to threshold out samples as out-of-distribution when the score is low. To define a score function for AENIB models, we first observe that the log-likelihood of \\(\\mathbf{z}_n\\), which is only available for AENIB (and not for standard models), can be a strong score to detect novelties those are semantically far from in-distribution. Specifically, we use \\(\\log \\mathcal{N}(\\mathbf{z}_n;0,I) = -\\frac{1}{2}\\| \\mathbf{z}_n\\|^2\\), as we assume that \\(\\mathbf{z}\\) follows isotropic Gaussian \\(\\mathcal{N}(0,I)\\). For detecting so-called \"harder\" novelties, we propose to use the log-likelihood score of \\(\\mathbf{y}\\) under a symmetric Dirichlet distribution of parameter \\(\\alpha > 0\\), namely \\(\\mathrm{Dir}_{\\alpha}(\\mathbf{y}) \\in \\Delta^{|\\mathcal{Y}| - 1}\\), rather than simply using \\(\\max_y p(y|x)\\): i.e., \\(\\log \\mathrm{Dir}_{\\alpha}(\\mathbf{y}) = (\\alpha - 1)\\sum_i\\log y_i\\). Note that the distribution gets closer to the symmetric (discrete) one-hot distribution as \\(\\alpha \\to 0\\), which makes sense for most classification tasks, and here we simply use \\(\\alpha = 0.05\\) throughout experiments." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.565, + 0.895, + 0.746 + ], + "angle": 0, + "content": "We consider two evaluation benchmarks: (a) the \"standard\" benchmark, that has been actively adopted in the literature [36, 72, 74], assumes the CIFAR-10 test set as in-distribution and measures the detection performance of other independent datasets; (b) a recent OBJECTS benchmark [122], on the other hand, extends the CIFAR-10 benchmark to also consider \"near\" in-distribution in OOD evaluation. Specifically, OBJECTS assumes CIFAR-10-C [35] and ImageNet-10 as in-distribution in test-time as well as CIFAR-10, making the detection much more challenging. In this experiment, we compare ResNet-18 [33] models trained on CIFAR-10 following the setup of [122]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.746, + 0.895, + 0.867 + ], + "angle": 0, + "content": "The results are reported in Table 5 and 6 for the standard and OBJECTS benchmarks, respectively. Overall, we confirm that the score function combining the information of \\(\\mathbf{z}_n\\) and \\(\\mathbf{y}\\) of AENIB significantly improves novelty detection in a complementary manner over strong baselines, showing the effectiveness of modeling nuisance. For example, in Table 5, the combined score achieves near-perfect AUROCs for detecting SVHN, LSUN and ImageNet datasets." + }, + { + "type": "page_footnote", + "bbox": [ + 0.5, + 0.875, + 0.892, + 0.901 + ], + "angle": 0, + "content": "In practice, we observe that other choices in a moderate range of \\(\\alpha\\) near 0 do not much affect performance." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "16211" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.106, + 0.089, + 0.86, + 0.304 + ], + "angle": 0, + "content": "
FS-OOD: OBJECTSAUROC (%; ↑) / AUPR (%; ↑) / FPR@TPR95 (%; ↓)
MethodScoreMNISTFashionMNISTTextureCIFAR-100-C
Cross-entropymaxy p(y|x) [36]66.98 / 52.66 / 93.5473.78 / 90.15 / 88.0874.18 / 93.34 / 85.6474.12 / 89.74 / 87.26
ODIN [74]70.31 / 49.58 / 82.0480.98 / 91.53 / 68.7370.14 / 89.97 / 72.9167.51 / 83.97 / 84.26
Energy-based [76]54.55 / 34.14 / 92.2376.50 / 89.80 / 72.4068.63 / 89.51 / 75.5768.37 / 85.54 / 83.64
Mahalanobis [72]77.04 / 65.31 / 84.5980.33 / 92.28 / 77.1772.02 / 88.46 / 72.9868.13 / 82.97 / 85.53
SEM [122]75.69 / 76.61 / 99.7079.40 / 93.14 / 93.7279.69 / 95.48 / 82.1578.89 / 92.07 / 83.92
log Dir0.05(y)76.75 / 66.26 / 83.5182.88 / 93.97 / 77.1970.69 / 92.68 / 91.3578.80 / 92.21 / 82.50
VIB [1]maxy p(y|x) [36]80.23 / 73.50 / 80.6976.35 / 91.22 / 84.7574.67 / 94.09 / 87.2276.12 / 91.03 / 84.99
log Dir0.05(y)86.13 / 79.45 / 64.9281.11 / 93.12 / 77.8273.84 / 93.50 / 88.0078.54 / 91.85 / 81.47
AENIB (ours)maxy p(y|x) [36]79.67 / 71.50 / 80.2277.33 / 91.63 / 84.3174.95 / 93.97 / 86.0174.31 / 89.89 / 86.26
log Dir0.05(y)90.53 / 85.68 / 52.0884.56 / 94.61 / 74.2475.04 / 93.83 / 86.0179.39 / 92.33 / 81.51
+ log N(zn; 0, I)92.43 / 89.38 / 48.1084.85 / 94.84 / 74.6788.91 / 97.49 / 48.4482.66 / 93.62 / 74.14
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.31, + 0.894, + 0.34 + ], + "angle": 0, + "content": "Table 6. Comparison of OOD detection performances on the OBJECTS benchmark [122], which considers CIFAR-10-C and ImageNet-10 as in-distribution as well as the training in-distribution of CIFAR-10. Bold and underline denote the best and runner-up results, respectively." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.356, + 0.471, + 0.446 + ], + "angle": 0, + "content": "Regarding Table 6, on the other hand, AENIB improves the previous best AUROC (of Mahalanobis [72]) on OBJECTS vs. MNIST from \\(77.04 \\rightarrow 92.43\\). The improved results on OBJECTS imply that both of the representation and score obtained from AENIB help to better discriminate in- vs. out-of-distribution in more semantic senses." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.455, + 0.36, + 0.47 + ], + "angle": 0, + "content": "4.3. Certified adversarial robustness" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.478, + 0.471, + 0.659 + ], + "angle": 0, + "content": "We also evaluate adversarial robustness [29, 82, 102] adopting the randomized smoothing framework [17, 70] that can measure a certified robustness for a given representation. Specifically, any classifier can be robustified by averaging its predictions under Gaussian noise, where the robustness at input \\( x \\) depends on how consistent the classifier is on classifying \\( \\mathcal{N}(x, \\sigma^2\\mathbf{I}) \\) [50]. Under this evaluation protocol, we suggest that adversarially-robust representations can be a natural byproduct from AENIB when combined with the randomized smoothing technique, without using any thorough adversarial training methods [82] that often require significant training cost with no certification on the robustness." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.66, + 0.471, + 0.901 + ], + "angle": 0, + "content": "We follow the standard certification protocol [17] to compare the certified test accuracy at radius \\( r \\), which is defined by the fraction of the test samples that a smoothed classifier classifies correctly with its certified radius larger than \\( r \\). We consider ViT-S models on CIFAR-10, and assume \\( \\sigma = 0.1 \\) for this experiment. The results summarized in Figure 4 show that our proposed AENIB achieves significantly better certified robustness compared to the baselines at all radii tested: e.g., it improves certified robust accuracy of VIB by \\( 39.6\\% \\rightarrow 56.8\\% \\) at \\( \\varepsilon = 0.1 \\). Again, the robustness obtained from AENIB is not from specific knowledge on the threat model, which implies that AENIB could offer free adversarial robustness when combined with randomized smoothing. This confirms that the robustness of AENIB is not only significant but also consistent per input, especially considering its high certified robustness at higher \\( r \\)'s." + }, + { + "type": "image", + "bbox": [ + 0.532, + 0.353, + 0.863, + 0.391 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.653, + 0.393, + 0.741, + 0.406 + ], + "angle": 0, + "content": "(a) DisenIB [92]" + }, + { + "type": "image", + "bbox": [ + 0.532, + 0.407, + 0.863, + 0.444 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.648, + 0.446, + 0.746, + 0.457 + ], + "angle": 0, + "content": "(b) AENIB (Ours)" + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.467, + 0.892, + 0.495 + ], + "angle": 0, + "content": "Figure 5. Comparison of CIFAR-10 reconstructions when the nuisance \\(\\mathbf{z}_n\\) is swapped with those of another (random) sample." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.512, + 0.771, + 0.528 + ], + "angle": 0, + "content": "4.4. Comparison with DisenIB [92]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.535, + 0.894, + 0.656 + ], + "angle": 0, + "content": "In this section, we provide a comparison of AENIB with a related work of DisenIB [92], as well as other variants of VIB, namely Nonlinear-VIB [65] and Squared-VIB [106]. Here, DisenIB is a variant of IB which also considers a nuisance modeling (based on FactorVAE [57]), in a purpose of supervised disentangling. Specifically, DisenIB considers two independent encoders \\(\\mathbf{z} \\coloneqq f(\\mathbf{x})\\) and \\(\\mathbf{z}_n \\coloneqq g(\\mathbf{x})\\), and aims to optimize the following objective:" + }, + { + "type": "equation", + "bbox": [ + 0.568, + 0.667, + 0.892, + 0.691 + ], + "angle": 0, + "content": "\\[\n\\max _ {f, g} I (\\mathbf {z}; \\mathbf {y}) + I (\\mathbf {x}; \\mathbf {z} _ {n}, \\mathbf {y}) - I (\\mathbf {z} _ {n}; \\mathbf {z}). \\tag {11}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.7, + 0.895, + 0.821 + ], + "angle": 0, + "content": "Compared to our proposed NIB (4), the most important difference between the two objectives is in their \"reconstruction\" terms: i.e., \\( I(\\mathbf{x}; \\mathbf{z}_n, \\mathbf{y}) \\) of (11) vs. \\( I(\\mathbf{x}; \\mathbf{z}, \\mathbf{z}_n) \\) of ours (4). Due to this difference, the DisenIB objective (11) cannot rule out the cases when \\( \\mathbf{z} \\) only encode few of \"shortcut\" signals in \\( \\mathbf{x} \\) (correlated to \\( \\mathbf{y} \\)) even at optimum, in contrast to our key motivation of NIB (4) that aims to let \\( \\mathbf{z} \\) to encode every \\( \\mathbf{y} \\)-correlated signal in \\( \\mathbf{x} \\) as much as possible." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.822, + 0.894, + 0.867 + ], + "angle": 0, + "content": "We conduct experimental comparisons based on (a) our CIFAR-10 setups (Table 2), and (b) directly upon the official implementation6 of DisenIB on MNIST [69] (Table 9 of Ap" + }, + { + "type": "page_footnote", + "bbox": [ + 0.501, + 0.875, + 0.894, + 0.9 + ], + "angle": 0, + "content": "https://github.com/PanZiqiAI/disentangled-information-bottleneck" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "16212" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.471, + 0.183 + ], + "angle": 0, + "content": "pendix G). Here, we adopt and extend the benchmark to also cover MNIST-C [88], a corrupted version of the MNIST. For the latter comparison, we use a simple 4-layer convolutional network as the encoder architecture. We train every MNIST model here for 100K updates and follow the other training details from the CIFAR experiments (see Appendix B.1)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.184, + 0.474, + 0.365 + ], + "angle": 0, + "content": "Overall, we observe that the effectiveness of AENIB still applies to these benchmarks. This is in contrast to DisenIB, given that the effectiveness from DisenIB, e.g., its gain in AUROC on detecting Gaussian noise as an OOD (as conducted by [92]), could not be further generalized on CIFAR-10-C or MNIST-C, where AENIB still improves on as well as achieving the perfect score at the same OOD task. In Figure 5a, we further observe qualitatively that DisenIB often leaves highly semantic information in the nuisance \\(\\mathbf{z}_n\\): its reconstruction can be completely changed by swapping \\(\\mathbf{z}_n\\) with those of another sample. This is essentially what AENIB addresses, as compared in Figure 5b." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.381, + 0.216, + 0.397 + ], + "angle": 0, + "content": "5. Related work" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.412, + 0.472, + 0.653 + ], + "angle": 0, + "content": "Out-of-distribution robustness. Since the seminal works [2, 90, 102] revealing the fragility of neural networks on out-of-distribution inputs, there have been significant attempts on identifying and improving various notions of robustness: e.g., detecting novel inputs [36,71,72,103], robustness against corruptions [27,35,39,119], and adversarial noise [5, 11, 17, 82], to name a few. Due to its fundamental challenges in making neural network to extrapolate, however, most of the advances in the robustness literature has been made under assuming priors closely related to the individual problems: e.g., an external data or data augmentations [37, 39], extra information from test-time samples [116], or specific knowledge in threat models [52, 112]. In this work, we aim to improve multiple notions of robustness without assuming such priors, through a new training scheme that extends the standard information bottleneck principle under noisy observations in test-time." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.659, + 0.472, + 0.902 + ], + "angle": 0, + "content": "Hybrid generative-discriminative modeling. Our proposed method can be also viewed as a new approach of improving the robustness of discriminative models by incorporating a generative model, in the context that has been explored in recent works [31,72,99,123]. For example, [72,73] have incorporated a simple (but of low expressivity for generation) Gaussian mixture model into discriminative classifiers; a line of research on Joint Energy-based Models (JEM) [31, 123] assumes an energy-based model but with a notable training instability for the purpose. In this work, we propose an autoencoder-based model to avoid such training instability, and consider a design that the nuisance can succinctly supplement the given discriminative representation to be generative. We demonstrate that our approach can take the best of two worlds; it enables (a) stable training, while (b) attaining the high expressive generative performances." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.895, + 0.424 + ], + "angle": 0, + "content": "Nuisance modeling. The idea of incorporating nuisances can be also considered in the context of invertible modeling, or as known as flow-based models [6, 23, 30, 59], where the nuisance can be defined by splitting the (full-information) encoding \\(\\mathbf{z}\\) for a given subspace of interest as explored by [4, 46]. Unlike such approaches, our autoencoder-based nuisance modeling does not focus on the \"full\" invertibility for arbitrary inputs, but rather on inverting the data manifold given, which enabled (a) a much flexible encoder design in practice, and (b) a more scalable generative modeling of nuisance \\(\\mathbf{z}_n\\), e.g., beyond an MNIST-scale as done by [46]. Other related works [48, 49, 92] do introduce an encoder for nuisance factors, but the notion of nuisance-ness has been focused in terms of the independence to \\(\\mathbf{z}\\) (for the purpose of feature disentangling), rather than to \\(\\mathbf{y}\\) as we focus in this work (for the purpose of robustness): e.g., DisenIB [92] applies FactorVAE [57] between semantic and nuisance embeddings to force their independence. Yet, the literature has been also questioned on whether the idea can be scaled-up beyond, e.g., MNIST, and our work does explore and establish a practical design with recent architectures and datasets addressing diverse modern security metrics." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.425, + 0.895, + 0.456 + ], + "angle": 0, + "content": "We provide more extensive and detailed discussions on related works in Appendix F." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.471, + 0.62, + 0.487 + ], + "angle": 0, + "content": "6. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.497, + 0.897, + 0.709 + ], + "angle": 0, + "content": "We suggest that having a good nuisance model can be a tangible approach to induce a reliable representation. We develop a practical method of learning deep nuisance representation from data, and show its effectiveness to improve diverse reliability measures under a challenging setup of assuming no prior [105]. We believe our work can be a useful step towards better understanding of out-of-distribution generalization in deep learning. Although the current scope is on a particular design of autoencoder based models, our framework of nuisance-extended IB is not limited to it and future works could consider more diverse implementations. Ultimately, we aim to approximate a challenging form of adversarial training with a mutual information constraint, which we believe will be a promising direction to explore." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.724, + 0.661, + 0.741 + ], + "angle": 0, + "content": "Acknowledgments" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.75, + 0.897, + 0.903 + ], + "angle": 0, + "content": "This work was partly supported by Center for Applied Research in Artificial Intelligence (CARAI) grant funded by Defense Acquisition Program Administration (DAPA) and Agency for Defense Development (ADD) (UD190031RD), and by Institute of Information & communications Technology Planning & Evaluation (IITP) grant funded by the Korea government (MSIT) (No.2021-0-02068, Artificial Intelligence Innovation Hub; No.2019-0-00075, Artificial Intelligence Graduate School Program (KAIST)). We thank Subin Kim for the proofreading of our manuscript." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "16213" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.105 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.096, + 0.117, + 0.471, + 0.17 + ], + "angle": 0, + "content": "[1] Alexander A Alemi, Ian Fischer, Joshua V Dillon, and Kevin Murphy. Deep variational information bottleneck. In International Conference on Learning Representations, 2017. 2, 4, 5, 6, 7, 20, 21, 22" + }, + { + "type": "ref_text", + "bbox": [ + 0.096, + 0.174, + 0.471, + 0.215 + ], + "angle": 0, + "content": "[2] Dario Amodei, Chris Olah, Jacob Steinhardt, Paul Christiano, John Schulman, and Dan Mané. 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Advances in Neural Information Processing Systems, 33:7559-7570, 2020. 22, 23" + }, + { + "type": "list", + "bbox": [ + 0.504, + 0.093, + 0.894, + 0.769 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.946, + 0.52, + 0.957 + ], + "angle": 0, + "content": "16218" + } + ] +] \ No newline at end of file diff --git a/2023/Enhancing Multiple Reliability Measures via Nuisance-Extended Information Bottleneck/13a10611-b5a4-413b-b3b8-4101508c9783_origin.pdf b/2023/Enhancing Multiple Reliability Measures via Nuisance-Extended Information Bottleneck/13a10611-b5a4-413b-b3b8-4101508c9783_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..c97c9270a077ef0087b9d27bf6e0d642e890ef5c --- /dev/null +++ b/2023/Enhancing Multiple Reliability Measures via Nuisance-Extended Information Bottleneck/13a10611-b5a4-413b-b3b8-4101508c9783_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:3fd978b1709095170a715af4141fe6595adec94eab0f6505b5906bfa602a2029 +size 988358 diff --git a/2023/Enhancing Multiple Reliability Measures via Nuisance-Extended Information Bottleneck/full.md b/2023/Enhancing Multiple Reliability Measures via Nuisance-Extended Information Bottleneck/full.md new file mode 100644 index 0000000000000000000000000000000000000000..fad2cc0499c33de4bcb6ea644ef578a4593ccd25 --- /dev/null +++ b/2023/Enhancing Multiple Reliability Measures via Nuisance-Extended Information Bottleneck/full.md @@ -0,0 +1,390 @@ +# Enhancing Multiple Reliability Measures via Nuisance-extended Information Bottleneck + +Jongheon Jeong† Sihyun Yu† Hankook Lee‡* Jinwoo Shin† +†Korea Advanced Institute of Science and Technology (KAIST) ‡LG AI Research +{jongheonj,sihyun.yu,jinwoos}@kaist.ac.kr hankook.lee@lgresearch.ai + +# Abstract + +In practical scenarios where training data is limited, many predictive signals in the data can be rather from some biases in data acquisition (i.e., less generalizable), so that one cannot prevent a model from co-adapting on such (so-called) "shortcut" signals: this makes the model fragile in various distribution shifts. To bypass such failure modes, we consider an adversarial threat model under a mutual information constraint to cover a wider class of perturbations in training. This motivates us to extend the standard information bottleneck to additionally model the nuisance information. We propose an autoencoder-based training to implement the objective, as well as practical encoder designs to facilitate the proposed hybrid discriminative-generative training concerning both convolutional- and Transformer-based architectures. Our experimental results show that the proposed scheme improves robustness of learned representations (remarkably without using any domain-specific knowledge), with respect to multiple challenging reliability measures. For example, our model could advance the state-of-the-art on a recent challenging OBJECTS benchmark in novelty detection by $78.4\% \rightarrow 87.2\%$ in AUROC, while simultaneously enjoying improved corruption, background and (certified) adversarial robustness. Code is available at https://github.com/jh-jeong/nuisance_ib. + +# 1. Introduction + +Despite the recent breakthroughs in computer vision in aid of deep learning, e.g., in image/video recognition [9, 20, 109], synthesis [42, 55, 96, 125], and 3D scene rendering [85, 86, 104], deploying deep learning models to the real-world still places a burden on contents providers as it affects the reliability of their services. In many cases, deep neural networks make substantially fragile predictions for out-of-distribution inputs, i.e., samples that are not likely + +![](images/20fb6369cf65ff4f085c0b8fcd157c8cfa20bd7e9e23ddcecd509fb7591796df.jpg) +Figure 1. A high-level illustration of our method, nuisance-extended information bottleneck (NIB). In this paper, we focus on scenarios when the input $\mathbf{x}$ can be corrupted $\mathbf{x} \rightarrow \hat{\mathbf{x}}$ in test-time while preserving its semantics. Unlike the standard cross-entropy training (CE), NIB aims to encode every target-correlated signal in $\mathbf{x}$ , some of which can be more reliable under distribution shifts. + +from the training distribution, even when the inputs are semantically close enough to in-distribution samples for humans [35, 102]. Such a vulnerability can be a significant threat in risk-sensitive systems, such as autonomous driving, medical imaging, and health-care applications, to name a few [2]. Overall, the phenomena highlight that deep neural networks tend to extract "shortcut" signals [26] from given limited (or potentially biased) training data in practice. + +To address such concerns, multiple literatures have been independently developed based on different aspects of model reliability. Namely, their methods use different threat models and benchmarks, depending on how a shift in input distribution happens in test-time, and how to evaluate model performance against the shift. For example, in the context of adversarial robustness [11, 17, 82, 128], a typical threat model is to consider the worst-case noise inside a fixed $\ell_p$ -ball around given test samples. Another example of corruption robustness [34, 35, 39, 116] instead assumes predefined types of common corruptions (e.g., Gaussian noise, fog, etc.) that applies to the test samples. Lastly, novelty detection [36, 72, 74, 76] usually tests whether a model can detect a specific benchmark dataset as out-of-distribution from the (in-distribution) test samples. + +Due to discrepancy between each of "ideal" objectives and its practical threat models, however, the literatures have commonly found that optimizing under a certain threat model often hardly generalizes to other threat ones: e.g., (a) several works [16, 62, 121] have observed that standard adversarial training [82] often harms other reliability measures such as corruption robustness or uncertainty estimation, as well as its classification performance; (b) Hendrycks et al. [34] criticize that none of the previous claims on corruption robustness could consistently generalize on a more comprehensive benchmark. This also happens even for threat models targeting the same objective: e.g., (c) Yang et al. [122] show that state-of-the-arts in novelty detection are often too sensitive, so that they tend to also detect "near-in-distribution" samples as out-of-distribution and perform poorly on a benchmark regarding this. Overall, these observations suggest that one should avoid optimizing reliability measures assuming a specific threat model or benchmark, and motivate to find a new threat model that is generally applicable for diverse scenarios of reliability concerns. + +Contribution. In this paper, we propose nuisance-extended information bottleneck (NIB), a new training objective targeting model reliability without assuming a prior on domain-specific tasks. Our method is motivated by rethinking the information bottleneck (IB) principle [107, 108] under presence of distribution shifts. Specifically, we argue that a "robust" representation $\mathbf{z} \coloneqq f(\mathbf{x})$ should always encode every signal in the input $\mathbf{x}$ that is correlated with the target $\mathbf{y}$ , rather than extracting only a few shortcuts (e.g., Figure 1). This motivates us to consider an adversarial form of threat model on distribution shifts in $\mathbf{x}$ , under a constraint on the mutual information $I(\mathbf{x},\mathbf{y})$ . To implement this idea, we propose a practical design by incorporating a nuisance representation $\mathbf{z}_n$ alongside $\mathbf{z}$ of the standard IB so that $(\mathbf{z},\mathbf{z}_n)$ can reconstruct $\mathbf{x}$ . This results in a novel synthesis of adversarial autoencoder [83] and variational IB [1] into a single framework. For the architectural side, we propose (a) to utilize the internal feature statistics for convolutional network based encoders, and (b) to incorporate vector-quantized patch representations for Transformer-based [24] encoders to model $\mathbf{z}_n$ , mainly to efficiently encode the nuisance $\mathbf{z}_n$ (as well as $\mathbf{z}$ ) in a scalable manner. + +We perform an extensive evaluation on the representations learned by our scheme, showing comprehensive improvements in modern reliability metrics: including (a) novelty detection, (b) corruption (or natural) robustness, (c) background robustness and (d) certified adversarial robustness. The results are particularly remarkable as the gains are not from assuming a prior on each of specific threat models. For example, we obtain a significant reduction in CIFAR-10-C error rates of the highest severity, i.e., by $26.5\% \rightarrow 19.5\%$ , without extra domain-specific prior as assumed in recent methods [39, 40]. Here, we also show that the effective + +ness of our method is scalable to larger-scale (ImageNet) datasets. For novelty detection, we could advance AUROCs in recent OBJECTS [122] benchmarks by a large margin of $78.4\% \rightarrow 87.2\%$ in average upon the state-of-the-art, showing that our representations can provide a more semantic information to better discriminate out-of-distribution samples. Finally, we also demonstrate how the representations can further offer enhanced robustness against adversarial examples, by applying randomized smoothing [17] on them. + +# 2. Background + +Notation. Given two random variables $\mathbf{x} \in \mathcal{X}$ , the input, and $\mathbf{y} \in \mathcal{Y}$ , the target, our goal is to find a mapping (or an encoder) $f: \mathcal{X} \to \mathcal{Z}$ from data $\mathcal{D} = \{(x_i, y_i)\}_{i=1}^n$ so that $\mathbf{z} := f(\mathbf{x})$ , the representation, can predict $\mathbf{y}$ with a simper (e.g., linear) mapping [7, 64]. We assume that $f$ is parametrized by a neural network, and is stochastic to adopt an information theoretic view [108], i.e., the encoder output is a random variable defined as $p_f(\mathbf{z}|\mathbf{x})$ rather than a constant. Such a modeling can be done through the reparametrization trick [61] with an independent random variable $\epsilon$ and (deterministic) $f$ by assuming $\mathbf{z} := f(\mathbf{x}, \epsilon)$ . For example, one of standard designs parametrizes $f$ by: + +$$ +f (\mathbf {x}, \epsilon) := f ^ {\mu} (\mathbf {x}) + \epsilon \cdot f ^ {\sigma} (\mathbf {x}), \tag {1} +$$ + +where $f^{\mu} \in \mathbb{R}^{|\mathcal{Z}|}$ and $f^{\sigma} \in \mathbb{R}_{+}^{|\mathcal{Z}|}$ are deterministic mappings modeling $\mu$ and $\sigma$ in $\mathcal{N}(\mathbf{x};\mu,\sigma^2I)$ , respectively, so that they can still be learned through a gradient-based optimization. + +The data $\mathcal{D}$ is usually assumed to consist of i.i.d. samples from a certain data generating distribution $(x_{i},y_{i})\sim p_{d}(\mathbf{x},\mathbf{y})$ . One expects that $f$ learned from $\mathcal{D}$ could generalize to predict $p_d(\mathbf{y}|\mathbf{x})$ for unseen samples from $p_d(\mathbf{x},\mathbf{y})$ . The formulation, however, does not specify how $f$ should behave for inputs that are not likely from $p_d$ , say $\hat{x}$ . This becomes problematic for those who expect that the decision making of $f$ should be close to that of human being, at least when $\hat{x}$ differs from $p_d$ only up to what humans regard as nuisance. This is where the current neural networks commonly fail under the standard training practices. + +Information bottleneck. Intuitively, a "good" representation $\mathbf{z}$ should keep information of $\mathbf{x}$ that is correlated with $\mathbf{y}$ , while preventing $\mathbf{z}$ from being too complex. The information bottleneck [107, 108] (IB) is a principled approach to obtain such a succinct representation $\mathbf{x} \rightarrow \mathbf{z}$ for a given downstream task $\mathbf{x} \rightarrow \mathbf{y}$ : namely, it finds $\mathbf{z}$ that (a) maximizes the (task-relevant) mutual information $I(\mathbf{z}; \mathbf{y})$ , while (b) minimizing $I(\mathbf{x}; \mathbf{z})$ to constrain the capacity of $\mathbf{z}$ for better generalization. In other words, it sets the mutual information $I(\mathbf{x}; \mathbf{z})$ as the complexity measure of $\mathbf{z}$ . Specifically, + +![](images/417bd75930c6b8cdd00836bb93021d4a3d0c293752e0f1dba38d06d336c744d3.jpg) +Figure 2. An overview of the proposed framework, the autoencoder-based nuisance-extended information bottleneck (AENIB). It illustrates the general pipeline, and Appendix C provides specific instantiations for convolutional and Transformer-based architectures. Overall, we incorporate adversarial autoencoder into variational information bottleneck by introducing a nuisance $\mathbf{z}_n$ (to $\mathbf{y}$ ) in representation learning. + +it aims to maximize the following objective: + +$$ +\max _ {f} R _ {\mathrm {I B}} (f), \quad \text {f o r} \quad R _ {\mathrm {I B}} (f) := I (\mathbf {z}; \mathbf {y}) - \beta I (\mathbf {x}; \mathbf {z}), \tag {2} +$$ + +where $\beta \geq 0$ controls the capacity constraint which ensures $I(\mathbf{x};\mathbf{z})\leq I_{\beta}$ for some $I_{\beta}$ . + +# 3. Nuisance-extended information bottleneck + +The standard information bottleneck (IB) objective (2) obtains a representation $\mathbf{z} := f(\mathbf{x})$ on premise that the future inputs will be also from $p_d(\mathbf{x},\mathbf{y})$ . In this paper, we aim to extend IB under assumption that the input $\mathbf{x}$ can be corrupted through an unknown noisy channel in the future, say $\mathbf{x} \to \hat{\mathbf{x}}$ , while $\hat{\mathbf{x}}$ still preserves the semantics of $\mathbf{x}$ with respect to $\mathbf{y}$ : in other words, we assume $I(\mathbf{x};\mathbf{y}) = I(\hat{\mathbf{x}};\mathbf{y}) > 0$ . Intuitively, one can imagine a scenario that $\mathbf{x}$ contains multiple signals that each is already highly correlated with $\mathbf{y}$ , i.e., filtering out the remainder from $\mathbf{x}$ does not affect its mutual information with $\mathbf{y}$ . It may or may not be surprising that such signals are quite prevalent in deep neural networks, e.g., [44] empirically observe that adversarial perturbations [29, 102] are sufficient for a model to perform accurate classification. + +In the context of IB framework, where the goal is to obtain a succinct encoder $f$ , it is now reasonable to presume that the noisy channel $\hat{\mathbf{x}}$ acts like an adversary, i.e., it minimizes: + +$$ +\min _ {\hat {\mathbf {x}}} I (\hat {\mathbf {z}} := f (\hat {\mathbf {x}}); \mathbf {y}) \text {s u b j e c t} I (\mathbf {x}; \mathbf {y}) = I (\hat {\mathbf {x}}; \mathbf {y}), \tag {3} +$$ + +given that one has no information on how the channel would behave a priori. This optimization thus would require $f$ to extract every signal in $\mathbf{x}$ whenever it is highly correlated with $\mathbf{y}$ , to avoid the case when $\hat{\mathbf{x}}$ filters out all the signal except one that $f$ has missed. We notice that, nevertheless, directly optimizing (3) with respect to $\hat{\mathbf{x}}$ is computationally infeasible in practice, considering that (a) it is in many cases an unconstrained optimization in a high-dimensional $\mathcal{X}$ , (b) with a constraint on (hard-to-compute) mutual information. + +In this paper, to make sure that $f$ still exhibits the adversarial behavior without (3), we propose to let $f$ to model the nuisance representation $\mathbf{z}_n$ as well as $\mathbf{z}$ . Specifically, $\mathbf{z}_n$ aims to model the "remainder" information from $\mathbf{z}$ needed to reconstruct $\mathbf{x}$ , i.e., it maximizes $I(\mathbf{x};\mathbf{z},\mathbf{z}_n)$ . At the same time, $\mathbf{z}_n$ compresses out any information that is correlated with $\mathbf{y}$ , i.e., it also minimizes $I(\mathbf{z}_n;\mathbf{y})$ . Therefore, every information that is correlated with $\mathbf{y}$ should be encoded into $\mathbf{z}$ in a complementary manner. Here, we remark that now the role of the capacity constraint in (2) becomes more important: not only for regularizing $\mathbf{z}$ to be simpler, it also penalizes $\mathbf{z}_n$ from pushing out unnecessary information to predict $\mathbf{y}$ into $\mathbf{z}$ , making the objective competitive again between $\mathbf{z}$ and $\mathbf{z}_n$ as like in (3). Combined with the original IB (2), we define nuisance-extended IB (NIB) as the following: + +$$ +\max _ {f} R _ {\mathrm {N I B}} (f) := R _ {\mathrm {I B}} (f) - I \left(\mathbf {z} _ {n}; \mathbf {y}\right) + \alpha I \left(\mathbf {x}; \mathbf {z}, \mathbf {z} _ {n}\right), \tag {4} +$$ + +where $\alpha \geq 0$ . The proposed NIB objective can be viewed as a regularized form of IB by introducing a nuisance $\mathbf{z}_n$ . Specifically, this optimization additionally forces $I(\mathbf{x};\mathbf{z},\mathbf{z}_n)$ and $I(\mathbf{z}_n;\mathbf{y})$ in (4) to be maximized and minimized, i.e., $H(\mathbf{x}|\mathbf{z},\mathbf{z}_n) = 0$ and $I(\mathbf{z}_n;\mathbf{y}) = 0$ , respectively. The following highlights that having these conditions, also with the independence $\mathbf{z}\perp \mathbf{z}_n$ , leads $f$ that can recover the original $I(\mathbf{x};\mathbf{y})$ from $I(\hat{\mathbf{z}};\mathbf{y})$ (see Appendix E for the derivation): + +Lemma 1. Let $\mathbf{x} \in \mathcal{X}$ , and $\mathbf{y} \in \mathcal{Y}$ be random variables, $\hat{\mathbf{x}}$ be a noisy observation of $\mathbf{x}$ with $I(\mathbf{x};\mathbf{y}) = I(\hat{\mathbf{x}};\mathbf{y})$ . Given that $[\hat{\mathbf{z}},\hat{\mathbf{z}}_n] := f(\hat{\mathbf{x}})$ of $\hat{\mathbf{x}}$ satisfies (a) $H(\hat{\mathbf{x}}|\hat{\mathbf{z}},\hat{\mathbf{z}}_n) = 0$ , (b) $I(\hat{\mathbf{z}}_n;\mathbf{y}) = 0$ , and (c) $\hat{\mathbf{z}} \perp \hat{\mathbf{z}}_n$ , it holds $I(\hat{\mathbf{z}};\mathbf{y}) = I(\mathbf{x};\mathbf{y})$ . + +In the following sections, we provide a practical design of the proposed NIB based on an autoencoder-based architecture. Section 3.1 and 3.2 detail out its losses and architectures, respectively, and Section 3.3 summarizes the overall training. Figure 2 illustrates an overview of our framework. + +# 3.1. AENIB: A practical autoencoder-based design + +Based on the NIB objective defined in (4) and Lemma 1, we design a practical training objective to implement the proposed framework. Here, we present a simple instantiation of NIB with an autoencoder-based architecture upon variational information bottleneck (VIB) [1], calling it autoencoder-based NIB (AENIB). + +Overall, Lemma 1 states that a robust encoder $f$ demands for a "good" nuisance model that achieves generalization on $\hat{\mathbf{z}}$ in three aspects: (a) a good reconstruction, (b) nuisance, and (c) the independence between $\mathbf{z}$ and $\mathbf{z}_n$ . To model these behaviors, we consider a decoder $g: \mathcal{Z} \to \mathcal{X}$ as well as the encoder $f: \mathcal{X} \to \mathcal{Z}$ , and adopt the following practical training objectives which incorporates an autoencoder-based loss and two adversarial losses [28]: + +(a) We first pose a reconstruction loss to maximize $\log p(\mathbf{x}|\mathbf{z},\mathbf{z}_n)$ ; standard designs assume the decoder output to follow $\mathcal{N}(\mathbf{x},\sigma^2\mathbf{I})$ , which is equivalent to the mean-squared error (MSE). Here, we use the normalized MSE to efficiently balance with other losses: + +$$ +L _ {\text {r e c o n}} := \frac {1}{\| \mathbf {x} \| _ {2} ^ {2}} \| \mathbf {x} - g (\mathbf {z}, \mathbf {z} _ {n}) \| _ {2} ^ {2} \tag {5} +$$ + +(b) To force the nuisance-ness of $\mathbf{z}_n$ with respect to $\mathbf{y}$ , we approximate $p(\mathbf{y}|\mathbf{z}_n)$ with a multi-layer perceptron (MLP), say $q_{n}$ , and perform an adversarial training: + +$$ +\begin{array}{l} L _ {\mathrm {n u i s}} := \mathbb {E} _ {\mathbf {x}} [ \mathbb {C E} (q _ {n} ^ {*} (\mathbf {z} _ {n}), \frac {1}{| \mathcal {Y} |}) ], \\ \text {w h e r e} q _ {n} ^ {*} := \min _ {q _ {n}} \mathbb {E} _ {\mathbf {x}, \mathbf {y}} [ \mathbb {C E} (q _ {n} (\mathbf {z} _ {n}), \mathbf {y}) ], \tag {6} \\ \end{array} +$$ + +and $\mathbb{C}\mathbb{E}$ denotes the cross entropy loss. Here, it optimizes $\mathbb{C}\mathbb{E}$ towards the uniform distribution in $\mathcal{V}$ .3 + +(c) To induce the independence between $\mathbf{z}$ and $\mathbf{z}_n$ , we assume that the joint prior of $\mathbf{z}$ and $\mathbf{z}_n$ is the isotropic Gaussian, i.e., $p(\mathbf{z},\mathbf{z}_n)\sim \mathcal{N}(0,\mathbf{I})$ , and performs a GAN training with a 2-layer MLP discriminator $q_{\mathbf{z}}$ : + +$$ +\begin{array}{l} L _ {\text {i n d}} := \max _ {q _ {\mathbf {z}}} \mathbb {E} _ {\mathbf {x}} \left[ \log \left(q _ {\mathbf {z}} (f (\mathbf {x}))\right) \right] \\ + \mathbb {E} _ {\mathbf {z}, \mathbf {z} _ {n}} \sim \mathcal {N} (0, \mathbf {I}) [ \log (1 - q _ {\mathbf {z}} (\mathbf {z}, \mathbf {z} _ {n})) ]. \tag {7} \\ \end{array} +$$ + +Lastly, to approximate the original IB objective $R_{\mathrm{IB}}(f)$ in NIB (4), we instead maximize the variational information bottleneck (VIB) [1] objective $L_{\mathrm{VIB}}^{\beta}$ , that can provide a lower bound on $R_{\mathrm{IB}}$ . Specifically, it makes variational approximations of: (a) $p(\mathbf{y}|\mathbf{z})$ by a (parametrized) decoder neural + +network $q(\mathbf{y}|\mathbf{z})$ , and (b) $p(\mathbf{z})$ by an "easier" distribution $r(\mathbf{z})$ , e.g., isotropic Gaussian $\mathcal{N}(\mathbf{z}|0,\mathbf{I})$ . Assuming a Gaussian decoder (1) for $f(\mathbf{x},\epsilon)$ , we have: + +$$ +\begin{array}{l} L _ {\mathrm {V I B}} ^ {\beta} := \frac {1}{n} \sum_ {i = 1} ^ {n} \mathbb {E} _ {\epsilon} [ - \log q (y _ {i} | f (x _ {i}, \epsilon)) ] \\ + \beta \operatorname {K L} \left(p (\mathbf {z} | x _ {i}) \| r (\mathbf {z})\right). \tag {8} \\ \end{array} +$$ + +# 3.2. Architectures for nuisance modeling + +In principle, our framework is generally compatible with any encoder architectures: e.g., say an encoder $f: \mathcal{X} \to \mathcal{Z}$ and decoder $g: \mathcal{Z} \to \mathcal{X}$ , respectively. In order to apply VIB, we assume that the encoder has two output heads of dimension $2K$ , where $K$ denotes the dimension of $\mathbf{z}$ . Here, each output head models a Gaussian random variable by reparametrization, i.e., by modeling $(\mu, \sigma)$ as the encoder output for both $\mathbf{z} \in \mathbb{R}^K$ and $\mathbf{z}_n \in \mathbb{R}^{K_n}$ . + +Although it is possible that $f$ models $\mathbf{z}$ and $\mathbf{z}_n$ by simply taking deep feed-forward representations following conventions, we observe that modeling nuisances $\mathbf{z}_n$ (which is essentially "generative") in standard (discriminative) architectures incur a training instability thus in performance: the nuisance information often requires to model finer details in a given inputs, which may be available rather in early layers of $f$ , but not in the later layers for classification. + +In this paper, we propose simple architectural treatments to improve the stability of nuisance modeling concerning both convolutional networks and Vision Transformers [24] (ViTs). This section focuses on introducing the design for convolutional networks, and we refer the readers for the ViT-based design to Appendix C: which is even simpler thanks to their patch-level representations available. + +Given a convolutional encoder $f$ , we encode $\mathbf{z}_n$ (as well as $\mathbf{z}$ ) from the collection of internal features statistics, rather than directly using the output of $f$ . Specifically, we extract $L$ intermediate feature maps of a given input $\mathbf{x}$ , namely $\mathbf{x}^{(1)}, \dots, \mathbf{x}^{(L)}$ from $f(\mathbf{x})$ , and define the projection of $\mathbf{x}$ by: + +$$ +\Pi_ {f} (\mathbf {x}) := \left[ \begin{array}{c c c c} \mathbf {m} ^ {(1)} & \mathbf {m} ^ {(2)} & \dots & \mathbf {m} ^ {(L)} \\ \mathbf {s} ^ {(1)} & \mathbf {s} ^ {(2)} & \dots & \mathbf {s} ^ {(L)} \end{array} \right], \tag {9} +$$ + +where $\mathbf{m}^{(l)}$ and $\mathbf{s}^{(l)}$ are the first and second moment of feature maps in $\mathbf{x}^{(l)}$ , assuming that $\mathbf{x}^{(l)} \in \mathbb{R}^{HWC}$ : $\mathbf{m}_c^{(l)} := \frac{1}{HW} \sum_{hw} \mathbf{x}_{hw_c}^{(l)}$ , and $\mathbf{s}_c^{(l)} := \frac{1}{HW} \sum_{hw} (\mathbf{x}_{hw_c}^{(l)} - \mathbf{m}_c^{(l)})^2$ . + +In Appendix I, we demonstrate that this simple projection can sufficiently encode a generative representation of $\mathbf{x}$ : viz., we show that one can successfully and efficiently train GANs with a discriminator defined upon $\Pi_f$ . Motivated by this observation, we adopt $\Pi_f$ in modeling the encoder representations $\mathbf{z}$ and $\mathbf{z}_n$ . We encode $\mathbf{z}$ and $\mathbf{z}_n$ by simply applying MLPs to $\Pi_f(\mathbf{x})$ (9). Despite its simplicity, we observe this treatment enables a stable training of AENIB. + +
SeverityCIFAR-10-CCIFAR-100-C
Clean12345Avg.Clean12345Avg.
Cross-entropy6.088.8911.114.019.726.516.025.131.435.139.346.854.041.3
VIB [1]5.988.6810.713.418.624.915.226.031.935.940.447.855.242.2
AugMix [39]6.528.9710.813.418.423.915.124.929.933.337.143.651.139.0
PixMix† [40]5.437.108.149.4012.114.910.323.226.728.730.835.039.032.0
AENIB (ours)4.977.498.9611.014.819.512.322.627.630.534.139.847.135.8
+ AugMix [39]5.357.658.9911.014.218.412.021.926.429.132.437.844.334.0
+ PixMix† [40]4.675.906.557.459.1211.48.0821.224.426.027.831.134.828.8
+ +Table 1. Comparison of average corruption error rates $(\% ;\downarrow)$ per severity level on CIFAR-10/100-C [35]. Bold and underline denote the best and runner-up, respectively. $^{\dagger}\mathrm{PixMix}$ [40] utilizes an external dataset consisting of pattern- and fractal-like images. + +
MethodC10C10-CC10.1C10.2CINIC
Cross-entropy6.0816.013.418.323.7
VIB [1]5.9815.213.616.823.6
NLIB [65]6.8117.014.617.524.3
sq-NLIB [106]6.0215.513.017.123.7
DisenIB [92]5.7615.213.217.223.7
AugMix [39]6.5215.114.217.224.2
PixMix [40]5.4310.313.116.623.2
AENIB (ours)4.9712.311.615.522.2
+ AugMix [39]5.3512.012.515.822.6
+ PixMix [40]4.678.0810.414.822.1
+ +Table 2. Comparison of test error rates $(\% ;\downarrow)$ on CIFAR-10 and its variants: CIFAR-10-C/10.1/10.2, and CINIC. Bold and underline indicate the best and runner-up results, respectively. + +# 3.3. Overall training objective + +Combining the proposed objectives as well as the VIB loss, $L_{\mathrm{VIB}}^{\beta}$ (8) leads us to the final objective. Although combining multiple losses in practice may introduce additional hyperparameters, we found most of the proposed losses can be added without scaling except for the reconstruction loss $L_{\mathrm{recon}}$ and the $\beta$ in the original VIB loss. Hence, we get: + +$$ +L _ {\mathrm {A E N I B}} := L _ {\mathrm {V I B}} ^ {\beta} + \alpha \cdot L _ {\text {r e c o n}} + L _ {\text {n u i s}} + L _ {\text {i n d}}. \tag {10} +$$ + +Algorithm 1 in Appendix A summarizes the procedure. + +# 4. Experiments + +We verify the effectiveness of our proposed AENIB training for various aspects of model reliability: specifically, we cover (a) corruption and natural robustness (Section 4.1), (b) novelty detection (Section 4.2), and (c) certified adversarial robustness (Section 4.3) tasks which all have been challenging without task-specific priors [37, 39, 82]. We provide an ablation study in Appendix D for a component-wise analysis. We also present an evaluation on our proposed components in the context of generative modeling in Appendix I. The full details on the experiments, e.g., datasets, training details, and hyperparameters, can be found in Appendix B. + +# 4.1. Robustness against natural corruptions + +We first evaluate corruption robustness of our method, i.e., its generalization ability under natural corruptions (e.g., fog, brightness, etc.) and distribution shifts those are still semantic to humans. To this end, we consider a wide range of benchmarks those are derived from CIFAR-10 and ImageNet for the purpose of measuring generalization. Namely, for CIFAR-10 models we test on (a) CIFAR-10/100-C [35], a corrupted version of CIFAR-10/100 simulating 15 common corruptions in 5 severity levels, as well as (b) CIFAR-10.1 [94], CIFAR-10.2 [81], and CINIC-10 [21], i.e., three regenerations of the CIFAR-10 test set. For ImageNet models, on the other hand, we test (a) ImageNet-C [35], a corrupted version of ImageNet validation set, (b) ImageNet-R [34], a collection of rendition images for 200 ImageNet classes, and ImageNet-Sketch [117], as well as (c) the Background Challenge [119] benchmark to evaluate model bias against background changes. This section mainly reports the results from ViT [24, 111] based architectures, but we also report the results with ResNet-18 [33] in Appendix H. + +Table 1 and 2 summarize the results on CIFAR-based models. In Table 1, we observe that AENIB significantly and consistently improves corruption errors upon VIB, and these gains are strong even compared with state-of-the-art methods: e.g., AENIB can solely outperform a strong baseline of AugMix [39]. Although a more recent method of PixMix [40] could achieve a lower corruption error by utilizing extra (pattern-like) data, we remark that (a) AENIB also benefit from PixMix (i.e., the extra data) as given in "AENIB + PixMix", and (b) the results on Table 2 show that the generalization capability of AENIB is better than PixMix on CIFAR-10.1, 10.2 and CINIC-10, i.e., in beyond common corruptions, by less relying on domain-specific data. + +Next, Table 3 highlights that the effectiveness of AENIB can generalize to a more larger-scale, higher-resolution dataset of ImageNet: we still observe that AENIB can consistently improve robust accuracy for diverse corruption types, again without leveraging any further data augmentation during training. Figure 3 compares the linear trends made by Cross-entropy and AENIB across different data augmenta + +
DatasetViT-S/16ViT-B/16
BaselineAENIB (ours)BaselineAENIB (ours)
IN-1K25.125.121.821.9
IN-C (mCE)65.965.2 (−0.7)58.657.5 (−1.1)
IN-R70.367.1 (−3.2)66.364.4 (−1.9)
IN-Sketch80.377.7 (−2.6)76.574.4 (−2.1)
+ +Table 3. Comparison of error rates $(\% ;\downarrow)$ or mean corruption error (mCE, $\%$ . $\downarrow$ ) on ImageNet (IN) and its variants, namely IN-C [35], IN-R [34], and IN-Sketch [117]. Bold indicates the best results. + +
BG-Challenge DatasetViT-S/16ViT-B/16
BaselineAENIB (ours)BaselineAENIB (ours)
ORIGINAL (IN-9; ↑)95.395.596.096.1
ONLY-BG-T (↓)20.317.8 (−2.5)24.221.1 (−3.1)
MIXED-SAME (↑)86.388.3 (+2.0)87.488.9 (+1.5)
MIXED-RAND (↑)77.880.5 (+2.7)80.181.8 (+0.7)
BG-gap (↓)8.57.8 (−0.7)7.37.1 (−0.2)
+ +Table 4. Evaluation of AENIB on Backgrounds Challenge [119] compared to the cross-entropy baseline. All the models are trained on ImageNet, and warped to perform classification on ImageNet-9. + +
MethodScoreSVHNLSUNImageNetC100CelebA
JEM [31]log p(x)0.67--0.670.75
JEM [31]maxy p(y|x) [36]0.89--0.870.79
SupCon [56]maxy p(y|x) [36]0.970.930.910.89-
Cross-entropymaxy p(y|x) [36]0.940.940.920.860.64
Cross-entropylog Dir0.05(y)0.960.950.940.860.61
VIB [1]maxy p(y|x) [36]0.950.940.920.880.76
VIB [1]log Dir0.05(y)0.970.960.940.880.78
AENIB (ours)maxy p(y|x) [36]0.880.880.860.840.81
AENIB (ours)log Dir0.05(y)0.900.950.920.860.80
AENIB (ours)+ logN(zn;0,I)0.980.990.990.860.79
+ +Table 5. Comparison of AUROC (\%; ↑) for OOD detection from CIFAR-10 with five OOD datasets: SVHN, LSUN, ImageNet, CIFAR-100, and CelebA. Bolds indicate the best results. + +tions and hyperparameters, confirming that AENIB exhibits a better operating points even in terms of effective robustness [105], given the recent observations on the correlation between in- vs. out-of-distribution performances across different models [34, 87, 105]. + +Lastly, Table 4 further evaluates the ImageNet classifiers on Background Challenge [119], a benchmark established to test the model robustness against background shifts: specifically, it constructs variants of ImageNet-9 (that combines 370 subclasses of ImageNet; ORIGINAL) with different combinations of backgrounds. Our AENIB-based models still consistently improve upon the cross-entropy baseline on the benchmark, showing that AENIB indeed tends to learn less-biased features against background changes. + +# 4.2. Novelty detection + +Next, we show that our AENIB model can be also a good detector for out-of-distribution samples (OODs), i.e., to solve the novelty detection task. In general, the task is defined by a binary classification problem that aims to discriminate novel + +![](images/1ada7f4ddc49c8c421d861503e06fd6f5ca51cc0704c763b9422bd390a9b32a2.jpg) +Figure 3. Comparison of trends in clean vs. corruption errors against Gaussian on ViT-S/4. + +![](images/9b8d6236d57497bda1aafb35fba2f4483782aa6f503e064f5be7be996c737c9e.jpg) +Figure 4. Comparison of certified adversarial robust accuracy at various radii on CIFAR-10. + +samples from in-distribution samples. A typical practice here is to define a score function for each input, e.g., the maximum confidence score [36], to threshold out samples as out-of-distribution when the score is low. To define a score function for AENIB models, we first observe that the log-likelihood of $\mathbf{z}_n$ , which is only available for AENIB (and not for standard models), can be a strong score to detect novelties those are semantically far from in-distribution. Specifically, we use $\log \mathcal{N}(\mathbf{z}_n;0,I) = -\frac{1}{2}\| \mathbf{z}_n\|^2$ , as we assume that $\mathbf{z}$ follows isotropic Gaussian $\mathcal{N}(0,I)$ . For detecting so-called "harder" novelties, we propose to use the log-likelihood score of $\mathbf{y}$ under a symmetric Dirichlet distribution of parameter $\alpha > 0$ , namely $\mathrm{Dir}_{\alpha}(\mathbf{y}) \in \Delta^{|\mathcal{Y}| - 1}$ , rather than simply using $\max_y p(y|x)$ : i.e., $\log \mathrm{Dir}_{\alpha}(\mathbf{y}) = (\alpha - 1)\sum_i\log y_i$ . Note that the distribution gets closer to the symmetric (discrete) one-hot distribution as $\alpha \to 0$ , which makes sense for most classification tasks, and here we simply use $\alpha = 0.05$ throughout experiments. + +We consider two evaluation benchmarks: (a) the "standard" benchmark, that has been actively adopted in the literature [36, 72, 74], assumes the CIFAR-10 test set as in-distribution and measures the detection performance of other independent datasets; (b) a recent OBJECTS benchmark [122], on the other hand, extends the CIFAR-10 benchmark to also consider "near" in-distribution in OOD evaluation. Specifically, OBJECTS assumes CIFAR-10-C [35] and ImageNet-10 as in-distribution in test-time as well as CIFAR-10, making the detection much more challenging. In this experiment, we compare ResNet-18 [33] models trained on CIFAR-10 following the setup of [122]. + +The results are reported in Table 5 and 6 for the standard and OBJECTS benchmarks, respectively. Overall, we confirm that the score function combining the information of $\mathbf{z}_n$ and $\mathbf{y}$ of AENIB significantly improves novelty detection in a complementary manner over strong baselines, showing the effectiveness of modeling nuisance. For example, in Table 5, the combined score achieves near-perfect AUROCs for detecting SVHN, LSUN and ImageNet datasets. + +
FS-OOD: OBJECTSAUROC (%; ↑) / AUPR (%; ↑) / FPR@TPR95 (%; ↓)
MethodScoreMNISTFashionMNISTTextureCIFAR-100-C
Cross-entropymaxy p(y|x) [36]66.98 / 52.66 / 93.5473.78 / 90.15 / 88.0874.18 / 93.34 / 85.6474.12 / 89.74 / 87.26
ODIN [74]70.31 / 49.58 / 82.0480.98 / 91.53 / 68.7370.14 / 89.97 / 72.9167.51 / 83.97 / 84.26
Energy-based [76]54.55 / 34.14 / 92.2376.50 / 89.80 / 72.4068.63 / 89.51 / 75.5768.37 / 85.54 / 83.64
Mahalanobis [72]77.04 / 65.31 / 84.5980.33 / 92.28 / 77.1772.02 / 88.46 / 72.9868.13 / 82.97 / 85.53
SEM [122]75.69 / 76.61 / 99.7079.40 / 93.14 / 93.7279.69 / 95.48 / 82.1578.89 / 92.07 / 83.92
log Dir0.05(y)76.75 / 66.26 / 83.5182.88 / 93.97 / 77.1970.69 / 92.68 / 91.3578.80 / 92.21 / 82.50
VIB [1]maxy p(y|x) [36]80.23 / 73.50 / 80.6976.35 / 91.22 / 84.7574.67 / 94.09 / 87.2276.12 / 91.03 / 84.99
log Dir0.05(y)86.13 / 79.45 / 64.9281.11 / 93.12 / 77.8273.84 / 93.50 / 88.0078.54 / 91.85 / 81.47
AENIB (ours)maxy p(y|x) [36]79.67 / 71.50 / 80.2277.33 / 91.63 / 84.3174.95 / 93.97 / 86.0174.31 / 89.89 / 86.26
log Dir0.05(y)90.53 / 85.68 / 52.0884.56 / 94.61 / 74.2475.04 / 93.83 / 86.0179.39 / 92.33 / 81.51
+ log N(zn; 0, I)92.43 / 89.38 / 48.1084.85 / 94.84 / 74.6788.91 / 97.49 / 48.4482.66 / 93.62 / 74.14
+ +Table 6. Comparison of OOD detection performances on the OBJECTS benchmark [122], which considers CIFAR-10-C and ImageNet-10 as in-distribution as well as the training in-distribution of CIFAR-10. Bold and underline denote the best and runner-up results, respectively. + +Regarding Table 6, on the other hand, AENIB improves the previous best AUROC (of Mahalanobis [72]) on OBJECTS vs. MNIST from $77.04 \rightarrow 92.43$ . The improved results on OBJECTS imply that both of the representation and score obtained from AENIB help to better discriminate in- vs. out-of-distribution in more semantic senses. + +# 4.3. Certified adversarial robustness + +We also evaluate adversarial robustness [29, 82, 102] adopting the randomized smoothing framework [17, 70] that can measure a certified robustness for a given representation. Specifically, any classifier can be robustified by averaging its predictions under Gaussian noise, where the robustness at input $x$ depends on how consistent the classifier is on classifying $\mathcal{N}(x, \sigma^2\mathbf{I})$ [50]. Under this evaluation protocol, we suggest that adversarially-robust representations can be a natural byproduct from AENIB when combined with the randomized smoothing technique, without using any thorough adversarial training methods [82] that often require significant training cost with no certification on the robustness. + +We follow the standard certification protocol [17] to compare the certified test accuracy at radius $r$ , which is defined by the fraction of the test samples that a smoothed classifier classifies correctly with its certified radius larger than $r$ . We consider ViT-S models on CIFAR-10, and assume $\sigma = 0.1$ for this experiment. The results summarized in Figure 4 show that our proposed AENIB achieves significantly better certified robustness compared to the baselines at all radii tested: e.g., it improves certified robust accuracy of VIB by $39.6\% \rightarrow 56.8\%$ at $\varepsilon = 0.1$ . Again, the robustness obtained from AENIB is not from specific knowledge on the threat model, which implies that AENIB could offer free adversarial robustness when combined with randomized smoothing. This confirms that the robustness of AENIB is not only significant but also consistent per input, especially considering its high certified robustness at higher $r$ 's. + +![](images/b16c2cfa127bb6e37c30ef90014f2a2975e21f2bc20134fad100e6736a26ac95.jpg) +(a) DisenIB [92] + +![](images/7cd7d8b79060ff142f052b450592cafea7e4aa75e8afe5ca82499a6006a09535.jpg) +(b) AENIB (Ours) +Figure 5. Comparison of CIFAR-10 reconstructions when the nuisance $\mathbf{z}_n$ is swapped with those of another (random) sample. + +# 4.4. Comparison with DisenIB [92] + +In this section, we provide a comparison of AENIB with a related work of DisenIB [92], as well as other variants of VIB, namely Nonlinear-VIB [65] and Squared-VIB [106]. Here, DisenIB is a variant of IB which also considers a nuisance modeling (based on FactorVAE [57]), in a purpose of supervised disentangling. Specifically, DisenIB considers two independent encoders $\mathbf{z} \coloneqq f(\mathbf{x})$ and $\mathbf{z}_n \coloneqq g(\mathbf{x})$ , and aims to optimize the following objective: + +$$ +\max _ {f, g} I (\mathbf {z}; \mathbf {y}) + I (\mathbf {x}; \mathbf {z} _ {n}, \mathbf {y}) - I (\mathbf {z} _ {n}; \mathbf {z}). \tag {11} +$$ + +Compared to our proposed NIB (4), the most important difference between the two objectives is in their "reconstruction" terms: i.e., $I(\mathbf{x}; \mathbf{z}_n, \mathbf{y})$ of (11) vs. $I(\mathbf{x}; \mathbf{z}, \mathbf{z}_n)$ of ours (4). Due to this difference, the DisenIB objective (11) cannot rule out the cases when $\mathbf{z}$ only encode few of "shortcut" signals in $\mathbf{x}$ (correlated to $\mathbf{y}$ ) even at optimum, in contrast to our key motivation of NIB (4) that aims to let $\mathbf{z}$ to encode every $\mathbf{y}$ -correlated signal in $\mathbf{x}$ as much as possible. + +We conduct experimental comparisons based on (a) our CIFAR-10 setups (Table 2), and (b) directly upon the official implementation6 of DisenIB on MNIST [69] (Table 9 of Ap + +pendix G). Here, we adopt and extend the benchmark to also cover MNIST-C [88], a corrupted version of the MNIST. For the latter comparison, we use a simple 4-layer convolutional network as the encoder architecture. We train every MNIST model here for 100K updates and follow the other training details from the CIFAR experiments (see Appendix B.1). + +Overall, we observe that the effectiveness of AENIB still applies to these benchmarks. This is in contrast to DisenIB, given that the effectiveness from DisenIB, e.g., its gain in AUROC on detecting Gaussian noise as an OOD (as conducted by [92]), could not be further generalized on CIFAR-10-C or MNIST-C, where AENIB still improves on as well as achieving the perfect score at the same OOD task. In Figure 5a, we further observe qualitatively that DisenIB often leaves highly semantic information in the nuisance $\mathbf{z}_n$ : its reconstruction can be completely changed by swapping $\mathbf{z}_n$ with those of another sample. This is essentially what AENIB addresses, as compared in Figure 5b. + +# 5. Related work + +Out-of-distribution robustness. Since the seminal works [2, 90, 102] revealing the fragility of neural networks on out-of-distribution inputs, there have been significant attempts on identifying and improving various notions of robustness: e.g., detecting novel inputs [36,71,72,103], robustness against corruptions [27,35,39,119], and adversarial noise [5, 11, 17, 82], to name a few. Due to its fundamental challenges in making neural network to extrapolate, however, most of the advances in the robustness literature has been made under assuming priors closely related to the individual problems: e.g., an external data or data augmentations [37, 39], extra information from test-time samples [116], or specific knowledge in threat models [52, 112]. In this work, we aim to improve multiple notions of robustness without assuming such priors, through a new training scheme that extends the standard information bottleneck principle under noisy observations in test-time. + +Hybrid generative-discriminative modeling. Our proposed method can be also viewed as a new approach of improving the robustness of discriminative models by incorporating a generative model, in the context that has been explored in recent works [31,72,99,123]. For example, [72,73] have incorporated a simple (but of low expressivity for generation) Gaussian mixture model into discriminative classifiers; a line of research on Joint Energy-based Models (JEM) [31, 123] assumes an energy-based model but with a notable training instability for the purpose. In this work, we propose an autoencoder-based model to avoid such training instability, and consider a design that the nuisance can succinctly supplement the given discriminative representation to be generative. We demonstrate that our approach can take the best of two worlds; it enables (a) stable training, while (b) attaining the high expressive generative performances. + +Nuisance modeling. The idea of incorporating nuisances can be also considered in the context of invertible modeling, or as known as flow-based models [6, 23, 30, 59], where the nuisance can be defined by splitting the (full-information) encoding $\mathbf{z}$ for a given subspace of interest as explored by [4, 46]. Unlike such approaches, our autoencoder-based nuisance modeling does not focus on the "full" invertibility for arbitrary inputs, but rather on inverting the data manifold given, which enabled (a) a much flexible encoder design in practice, and (b) a more scalable generative modeling of nuisance $\mathbf{z}_n$ , e.g., beyond an MNIST-scale as done by [46]. Other related works [48, 49, 92] do introduce an encoder for nuisance factors, but the notion of nuisance-ness has been focused in terms of the independence to $\mathbf{z}$ (for the purpose of feature disentangling), rather than to $\mathbf{y}$ as we focus in this work (for the purpose of robustness): e.g., DisenIB [92] applies FactorVAE [57] between semantic and nuisance embeddings to force their independence. Yet, the literature has been also questioned on whether the idea can be scaled-up beyond, e.g., MNIST, and our work does explore and establish a practical design with recent architectures and datasets addressing diverse modern security metrics. + +We provide more extensive and detailed discussions on related works in Appendix F. + +# 6. Conclusion + +We suggest that having a good nuisance model can be a tangible approach to induce a reliable representation. We develop a practical method of learning deep nuisance representation from data, and show its effectiveness to improve diverse reliability measures under a challenging setup of assuming no prior [105]. We believe our work can be a useful step towards better understanding of out-of-distribution generalization in deep learning. Although the current scope is on a particular design of autoencoder based models, our framework of nuisance-extended IB is not limited to it and future works could consider more diverse implementations. Ultimately, we aim to approximate a challenging form of adversarial training with a mutual information constraint, which we believe will be a promising direction to explore. + +# Acknowledgments + +This work was partly supported by Center for Applied Research in Artificial Intelligence (CARAI) grant funded by Defense Acquisition Program Administration (DAPA) and Agency for Defense Development (ADD) (UD190031RD), and by Institute of Information & communications Technology Planning & Evaluation (IITP) grant funded by the Korea government (MSIT) (No.2021-0-02068, Artificial Intelligence Innovation Hub; No.2019-0-00075, Artificial Intelligence Graduate School Program (KAIST)). We thank Subin Kim for the proofreading of our manuscript. + +# References + +[1] Alexander A Alemi, Ian Fischer, Joshua V Dillon, and Kevin Murphy. Deep variational information bottleneck. 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Advances in Neural Information Processing Systems, 33:7559-7570, 2020. 22, 23 \ No newline at end of file diff --git a/2023/Enhancing Multiple Reliability Measures via Nuisance-Extended Information Bottleneck/images.zip b/2023/Enhancing Multiple Reliability Measures via Nuisance-Extended Information Bottleneck/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..0e1530aa71402796c1ffd3cff0fb7c1b82c34330 --- /dev/null +++ b/2023/Enhancing Multiple Reliability Measures via Nuisance-Extended Information Bottleneck/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:f7556dc8eaa405dadc22615a226870649f5633051c4e3abefb6718f8d56012a8 +size 525631 diff --git a/2023/Enhancing Multiple Reliability Measures via Nuisance-Extended Information Bottleneck/layout.json b/2023/Enhancing Multiple Reliability Measures via Nuisance-Extended Information Bottleneck/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..230f1b3b8fd9764102f7b827d253344dac5278c1 --- /dev/null +++ b/2023/Enhancing Multiple Reliability Measures via Nuisance-Extended Information Bottleneck/layout.json @@ -0,0 +1,14273 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 159, + 103, + 435, + 137 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 159, + 103, + 435, + 137 + ], + "spans": [ + { + "bbox": [ + 159, + 103, + 435, + 137 + ], + "type": "text", + "content": "Enhancing Multiple Reliability Measures via Nuisance-extended Information Bottleneck" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 94, + 160, + 499, + 204 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 94, + 160, + 499, + 204 + ], + "spans": [ + { + "bbox": [ + 94, + 160, + 499, + 204 + ], + "type": "text", + "content": "Jongheon Jeong† Sihyun Yu† Hankook Lee‡* Jinwoo Shin† \n†Korea Advanced Institute of Science and Technology (KAIST) ‡LG AI Research \n{jongheonj,sihyun.yu,jinwoos}@kaist.ac.kr hankook.lee@lgresearch.ai" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 143, + 231, + 190, + 243 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 231, + 190, + 243 + ], + "spans": [ + { + "bbox": [ + 143, + 231, + 190, + 243 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 256, + 290, + 544 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 256, + 290, + 544 + ], + "spans": [ + { + "bbox": [ + 47, + 256, + 290, + 544 + ], + "type": "text", + "content": "In practical scenarios where training data is limited, many predictive signals in the data can be rather from some biases in data acquisition (i.e., less generalizable), so that one cannot prevent a model from co-adapting on such (so-called) \"shortcut\" signals: this makes the model fragile in various distribution shifts. To bypass such failure modes, we consider an adversarial threat model under a mutual information constraint to cover a wider class of perturbations in training. This motivates us to extend the standard information bottleneck to additionally model the nuisance information. We propose an autoencoder-based training to implement the objective, as well as practical encoder designs to facilitate the proposed hybrid discriminative-generative training concerning both convolutional- and Transformer-based architectures. Our experimental results show that the proposed scheme improves robustness of learned representations (remarkably without using any domain-specific knowledge), with respect to multiple challenging reliability measures. For example, our model could advance the state-of-the-art on a recent challenging OBJECTS benchmark in novelty detection by " + }, + { + "bbox": [ + 47, + 256, + 290, + 544 + ], + "type": "inline_equation", + "content": "78.4\\% \\rightarrow 87.2\\%" + }, + { + "bbox": [ + 47, + 256, + 290, + 544 + ], + "type": "text", + "content": " in AUROC, while simultaneously enjoying improved corruption, background and (certified) adversarial robustness. Code is available at https://github.com/jh-jeong/nuisance_ib." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 48, + 578, + 127, + 590 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 578, + 127, + 590 + ], + "spans": [ + { + "bbox": [ + 48, + 578, + 127, + 590 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 599, + 287, + 696 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 599, + 287, + 696 + ], + "spans": [ + { + "bbox": [ + 46, + 599, + 287, + 696 + ], + "type": "text", + "content": "Despite the recent breakthroughs in computer vision in aid of deep learning, e.g., in image/video recognition [9, 20, 109], synthesis [42, 55, 96, 125], and 3D scene rendering [85, 86, 104], deploying deep learning models to the real-world still places a burden on contents providers as it affects the reliability of their services. In many cases, deep neural networks make substantially fragile predictions for out-of-distribution inputs, i.e., samples that are not likely" + } + ] + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 312, + 230, + 547, + 344 + ], + "blocks": [ + { + "bbox": [ + 312, + 230, + 547, + 344 + ], + "lines": [ + { + "bbox": [ + 312, + 230, + 547, + 344 + ], + "spans": [ + { + "bbox": [ + 312, + 230, + 547, + 344 + ], + "type": "image", + "image_path": "20fb6369cf65ff4f085c0b8fcd157c8cfa20bd7e9e23ddcecd509fb7591796df.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 354, + 547, + 421 + ], + "lines": [ + { + "bbox": [ + 305, + 354, + 547, + 421 + ], + "spans": [ + { + "bbox": [ + 305, + 354, + 547, + 421 + ], + "type": "text", + "content": "Figure 1. A high-level illustration of our method, nuisance-extended information bottleneck (NIB). In this paper, we focus on scenarios when the input " + }, + { + "bbox": [ + 305, + 354, + 547, + 421 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 305, + 354, + 547, + 421 + ], + "type": "text", + "content": " can be corrupted " + }, + { + "bbox": [ + 305, + 354, + 547, + 421 + ], + "type": "inline_equation", + "content": "\\mathbf{x} \\rightarrow \\hat{\\mathbf{x}}" + }, + { + "bbox": [ + 305, + 354, + 547, + 421 + ], + "type": "text", + "content": " in test-time while preserving its semantics. Unlike the standard cross-entropy training (CE), NIB aims to encode every target-correlated signal in " + }, + { + "bbox": [ + 305, + 354, + 547, + 421 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 305, + 354, + 547, + 421 + ], + "type": "text", + "content": ", some of which can be more reliable under distribution shifts." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 437, + 547, + 533 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 437, + 547, + 533 + ], + "spans": [ + { + "bbox": [ + 304, + 437, + 547, + 533 + ], + "type": "text", + "content": "from the training distribution, even when the inputs are semantically close enough to in-distribution samples for humans [35, 102]. Such a vulnerability can be a significant threat in risk-sensitive systems, such as autonomous driving, medical imaging, and health-care applications, to name a few [2]. Overall, the phenomena highlight that deep neural networks tend to extract \"shortcut\" signals [26] from given limited (or potentially biased) training data in practice." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 534, + 548, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 534, + 548, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 534, + 548, + 713 + ], + "type": "text", + "content": "To address such concerns, multiple literatures have been independently developed based on different aspects of model reliability. Namely, their methods use different threat models and benchmarks, depending on how a shift in input distribution happens in test-time, and how to evaluate model performance against the shift. For example, in the context of adversarial robustness [11, 17, 82, 128], a typical threat model is to consider the worst-case noise inside a fixed " + }, + { + "bbox": [ + 304, + 534, + 548, + 713 + ], + "type": "inline_equation", + "content": "\\ell_p" + }, + { + "bbox": [ + 304, + 534, + 548, + 713 + ], + "type": "text", + "content": "-ball around given test samples. Another example of corruption robustness [34, 35, 39, 116] instead assumes predefined types of common corruptions (e.g., Gaussian noise, fog, etc.) that applies to the test samples. Lastly, novelty detection [36, 72, 74, 76] usually tests whether a model can detect a specific benchmark dataset as out-of-distribution from the (in-distribution) test samples." + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 702, + 134, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 702, + 134, + 712 + ], + "spans": [ + { + "bbox": [ + 58, + 702, + 134, + 712 + ], + "type": "text", + "content": "*Work done at KAIST." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "16206" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 312 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 312 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 312 + ], + "type": "text", + "content": "Due to discrepancy between each of \"ideal\" objectives and its practical threat models, however, the literatures have commonly found that optimizing under a certain threat model often hardly generalizes to other threat ones: e.g., (a) several works [16, 62, 121] have observed that standard adversarial training [82] often harms other reliability measures such as corruption robustness or uncertainty estimation, as well as its classification performance; (b) Hendrycks et al. [34] criticize that none of the previous claims on corruption robustness could consistently generalize on a more comprehensive benchmark. This also happens even for threat models targeting the same objective: e.g., (c) Yang et al. [122] show that state-of-the-arts in novelty detection are often too sensitive, so that they tend to also detect \"near-in-distribution\" samples as out-of-distribution and perform poorly on a benchmark regarding this. Overall, these observations suggest that one should avoid optimizing reliability measures assuming a specific threat model or benchmark, and motivate to find a new threat model that is generally applicable for diverse scenarios of reliability concerns." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 316, + 289, + 579 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 316, + 289, + 579 + ], + "spans": [ + { + "bbox": [ + 46, + 316, + 289, + 579 + ], + "type": "text", + "content": "Contribution. In this paper, we propose nuisance-extended information bottleneck (NIB), a new training objective targeting model reliability without assuming a prior on domain-specific tasks. Our method is motivated by rethinking the information bottleneck (IB) principle [107, 108] under presence of distribution shifts. Specifically, we argue that a \"robust\" representation " + }, + { + "bbox": [ + 46, + 316, + 289, + 579 + ], + "type": "inline_equation", + "content": "\\mathbf{z} \\coloneqq f(\\mathbf{x})" + }, + { + "bbox": [ + 46, + 316, + 289, + 579 + ], + "type": "text", + "content": " should always encode every signal in the input " + }, + { + "bbox": [ + 46, + 316, + 289, + 579 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 46, + 316, + 289, + 579 + ], + "type": "text", + "content": " that is correlated with the target " + }, + { + "bbox": [ + 46, + 316, + 289, + 579 + ], + "type": "inline_equation", + "content": "\\mathbf{y}" + }, + { + "bbox": [ + 46, + 316, + 289, + 579 + ], + "type": "text", + "content": ", rather than extracting only a few shortcuts (e.g., Figure 1). This motivates us to consider an adversarial form of threat model on distribution shifts in " + }, + { + "bbox": [ + 46, + 316, + 289, + 579 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 46, + 316, + 289, + 579 + ], + "type": "text", + "content": ", under a constraint on the mutual information " + }, + { + "bbox": [ + 46, + 316, + 289, + 579 + ], + "type": "inline_equation", + "content": "I(\\mathbf{x},\\mathbf{y})" + }, + { + "bbox": [ + 46, + 316, + 289, + 579 + ], + "type": "text", + "content": ". To implement this idea, we propose a practical design by incorporating a nuisance representation " + }, + { + "bbox": [ + 46, + 316, + 289, + 579 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_n" + }, + { + "bbox": [ + 46, + 316, + 289, + 579 + ], + "type": "text", + "content": " alongside " + }, + { + "bbox": [ + 46, + 316, + 289, + 579 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 46, + 316, + 289, + 579 + ], + "type": "text", + "content": " of the standard IB so that " + }, + { + "bbox": [ + 46, + 316, + 289, + 579 + ], + "type": "inline_equation", + "content": "(\\mathbf{z},\\mathbf{z}_n)" + }, + { + "bbox": [ + 46, + 316, + 289, + 579 + ], + "type": "text", + "content": " can reconstruct " + }, + { + "bbox": [ + 46, + 316, + 289, + 579 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 46, + 316, + 289, + 579 + ], + "type": "text", + "content": ". This results in a novel synthesis of adversarial autoencoder [83] and variational IB [1] into a single framework. For the architectural side, we propose (a) to utilize the internal feature statistics for convolutional network based encoders, and (b) to incorporate vector-quantized patch representations for Transformer-based [24] encoders to model " + }, + { + "bbox": [ + 46, + 316, + 289, + 579 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_n" + }, + { + "bbox": [ + 46, + 316, + 289, + 579 + ], + "type": "text", + "content": ", mainly to efficiently encode the nuisance " + }, + { + "bbox": [ + 46, + 316, + 289, + 579 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_n" + }, + { + "bbox": [ + 46, + 316, + 289, + 579 + ], + "type": "text", + "content": " (as well as " + }, + { + "bbox": [ + 46, + 316, + 289, + 579 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 46, + 316, + 289, + 579 + ], + "type": "text", + "content": ") in a scalable manner." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 582, + 289, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 582, + 289, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 582, + 289, + 713 + ], + "type": "text", + "content": "We perform an extensive evaluation on the representations learned by our scheme, showing comprehensive improvements in modern reliability metrics: including (a) novelty detection, (b) corruption (or natural) robustness, (c) background robustness and (d) certified adversarial robustness. The results are particularly remarkable as the gains are not from assuming a prior on each of specific threat models. For example, we obtain a significant reduction in CIFAR-10-C error rates of the highest severity, i.e., by " + }, + { + "bbox": [ + 46, + 582, + 289, + 713 + ], + "type": "inline_equation", + "content": "26.5\\% \\rightarrow 19.5\\%" + }, + { + "bbox": [ + 46, + 582, + 289, + 713 + ], + "type": "text", + "content": ", without extra domain-specific prior as assumed in recent methods [39, 40]. Here, we also show that the effective" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 304, + 72, + 547, + 180 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 180 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 180 + ], + "type": "text", + "content": "ness of our method is scalable to larger-scale (ImageNet) datasets. For novelty detection, we could advance AUROCs in recent OBJECTS [122] benchmarks by a large margin of " + }, + { + "bbox": [ + 304, + 72, + 547, + 180 + ], + "type": "inline_equation", + "content": "78.4\\% \\rightarrow 87.2\\%" + }, + { + "bbox": [ + 304, + 72, + 547, + 180 + ], + "type": "text", + "content": " in average upon the state-of-the-art, showing that our representations can provide a more semantic information to better discriminate out-of-distribution samples. Finally, we also demonstrate how the representations can further offer enhanced robustness against adversarial examples, by applying randomized smoothing [17] on them." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 306, + 190, + 384, + 204 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 190, + 384, + 204 + ], + "spans": [ + { + "bbox": [ + 306, + 190, + 384, + 204 + ], + "type": "text", + "content": "2. Background" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 213, + 547, + 357 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 213, + 547, + 357 + ], + "spans": [ + { + "bbox": [ + 304, + 213, + 547, + 357 + ], + "type": "text", + "content": "Notation. Given two random variables " + }, + { + "bbox": [ + 304, + 213, + 547, + 357 + ], + "type": "inline_equation", + "content": "\\mathbf{x} \\in \\mathcal{X}" + }, + { + "bbox": [ + 304, + 213, + 547, + 357 + ], + "type": "text", + "content": ", the input, and " + }, + { + "bbox": [ + 304, + 213, + 547, + 357 + ], + "type": "inline_equation", + "content": "\\mathbf{y} \\in \\mathcal{Y}" + }, + { + "bbox": [ + 304, + 213, + 547, + 357 + ], + "type": "text", + "content": ", the target, our goal is to find a mapping (or an encoder) " + }, + { + "bbox": [ + 304, + 213, + 547, + 357 + ], + "type": "inline_equation", + "content": "f: \\mathcal{X} \\to \\mathcal{Z}" + }, + { + "bbox": [ + 304, + 213, + 547, + 357 + ], + "type": "text", + "content": " from data " + }, + { + "bbox": [ + 304, + 213, + 547, + 357 + ], + "type": "inline_equation", + "content": "\\mathcal{D} = \\{(x_i, y_i)\\}_{i=1}^n" + }, + { + "bbox": [ + 304, + 213, + 547, + 357 + ], + "type": "text", + "content": " so that " + }, + { + "bbox": [ + 304, + 213, + 547, + 357 + ], + "type": "inline_equation", + "content": "\\mathbf{z} := f(\\mathbf{x})" + }, + { + "bbox": [ + 304, + 213, + 547, + 357 + ], + "type": "text", + "content": ", the representation, can predict " + }, + { + "bbox": [ + 304, + 213, + 547, + 357 + ], + "type": "inline_equation", + "content": "\\mathbf{y}" + }, + { + "bbox": [ + 304, + 213, + 547, + 357 + ], + "type": "text", + "content": " with a simper (e.g., linear) mapping [7, 64]. We assume that " + }, + { + "bbox": [ + 304, + 213, + 547, + 357 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 304, + 213, + 547, + 357 + ], + "type": "text", + "content": " is parametrized by a neural network, and is stochastic to adopt an information theoretic view [108], i.e., the encoder output is a random variable defined as " + }, + { + "bbox": [ + 304, + 213, + 547, + 357 + ], + "type": "inline_equation", + "content": "p_f(\\mathbf{z}|\\mathbf{x})" + }, + { + "bbox": [ + 304, + 213, + 547, + 357 + ], + "type": "text", + "content": " rather than a constant. Such a modeling can be done through the reparametrization trick [61] with an independent random variable " + }, + { + "bbox": [ + 304, + 213, + 547, + 357 + ], + "type": "inline_equation", + "content": "\\epsilon" + }, + { + "bbox": [ + 304, + 213, + 547, + 357 + ], + "type": "text", + "content": " and (deterministic) " + }, + { + "bbox": [ + 304, + 213, + 547, + 357 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 304, + 213, + 547, + 357 + ], + "type": "text", + "content": " by assuming " + }, + { + "bbox": [ + 304, + 213, + 547, + 357 + ], + "type": "inline_equation", + "content": "\\mathbf{z} := f(\\mathbf{x}, \\epsilon)" + }, + { + "bbox": [ + 304, + 213, + 547, + 357 + ], + "type": "text", + "content": ". For example, one of standard designs parametrizes " + }, + { + "bbox": [ + 304, + 213, + 547, + 357 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 304, + 213, + 547, + 357 + ], + "type": "text", + "content": " by:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 362, + 365, + 545, + 377 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 362, + 365, + 545, + 377 + ], + "spans": [ + { + "bbox": [ + 362, + 365, + 545, + 377 + ], + "type": "interline_equation", + "content": "f (\\mathbf {x}, \\epsilon) := f ^ {\\mu} (\\mathbf {x}) + \\epsilon \\cdot f ^ {\\sigma} (\\mathbf {x}), \\tag {1}", + "image_path": "aff26b8d64df9c584ee50d6d018f02180f5cec54f5206e070581e49f66236c4b.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 384, + 545, + 422 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 384, + 545, + 422 + ], + "spans": [ + { + "bbox": [ + 304, + 384, + 545, + 422 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 384, + 545, + 422 + ], + "type": "inline_equation", + "content": "f^{\\mu} \\in \\mathbb{R}^{|\\mathcal{Z}|}" + }, + { + "bbox": [ + 304, + 384, + 545, + 422 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 384, + 545, + 422 + ], + "type": "inline_equation", + "content": "f^{\\sigma} \\in \\mathbb{R}_{+}^{|\\mathcal{Z}|}" + }, + { + "bbox": [ + 304, + 384, + 545, + 422 + ], + "type": "text", + "content": " are deterministic mappings modeling " + }, + { + "bbox": [ + 304, + 384, + 545, + 422 + ], + "type": "inline_equation", + "content": "\\mu" + }, + { + "bbox": [ + 304, + 384, + 545, + 422 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 384, + 545, + 422 + ], + "type": "inline_equation", + "content": "\\sigma" + }, + { + "bbox": [ + 304, + 384, + 545, + 422 + ], + "type": "text", + "content": " in " + }, + { + "bbox": [ + 304, + 384, + 545, + 422 + ], + "type": "inline_equation", + "content": "\\mathcal{N}(\\mathbf{x};\\mu,\\sigma^2I)" + }, + { + "bbox": [ + 304, + 384, + 545, + 422 + ], + "type": "text", + "content": ", respectively, so that they can still be learned through a gradient-based optimization." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 422, + 547, + 554 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 422, + 547, + 554 + ], + "spans": [ + { + "bbox": [ + 304, + 422, + 547, + 554 + ], + "type": "text", + "content": "The data " + }, + { + "bbox": [ + 304, + 422, + 547, + 554 + ], + "type": "inline_equation", + "content": "\\mathcal{D}" + }, + { + "bbox": [ + 304, + 422, + 547, + 554 + ], + "type": "text", + "content": " is usually assumed to consist of i.i.d. samples from a certain data generating distribution " + }, + { + "bbox": [ + 304, + 422, + 547, + 554 + ], + "type": "inline_equation", + "content": "(x_{i},y_{i})\\sim p_{d}(\\mathbf{x},\\mathbf{y})" + }, + { + "bbox": [ + 304, + 422, + 547, + 554 + ], + "type": "text", + "content": ". One expects that " + }, + { + "bbox": [ + 304, + 422, + 547, + 554 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 304, + 422, + 547, + 554 + ], + "type": "text", + "content": " learned from " + }, + { + "bbox": [ + 304, + 422, + 547, + 554 + ], + "type": "inline_equation", + "content": "\\mathcal{D}" + }, + { + "bbox": [ + 304, + 422, + 547, + 554 + ], + "type": "text", + "content": " could generalize to predict " + }, + { + "bbox": [ + 304, + 422, + 547, + 554 + ], + "type": "inline_equation", + "content": "p_d(\\mathbf{y}|\\mathbf{x})" + }, + { + "bbox": [ + 304, + 422, + 547, + 554 + ], + "type": "text", + "content": " for unseen samples from " + }, + { + "bbox": [ + 304, + 422, + 547, + 554 + ], + "type": "inline_equation", + "content": "p_d(\\mathbf{x},\\mathbf{y})" + }, + { + "bbox": [ + 304, + 422, + 547, + 554 + ], + "type": "text", + "content": ". The formulation, however, does not specify how " + }, + { + "bbox": [ + 304, + 422, + 547, + 554 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 304, + 422, + 547, + 554 + ], + "type": "text", + "content": " should behave for inputs that are not likely from " + }, + { + "bbox": [ + 304, + 422, + 547, + 554 + ], + "type": "inline_equation", + "content": "p_d" + }, + { + "bbox": [ + 304, + 422, + 547, + 554 + ], + "type": "text", + "content": ", say " + }, + { + "bbox": [ + 304, + 422, + 547, + 554 + ], + "type": "inline_equation", + "content": "\\hat{x}" + }, + { + "bbox": [ + 304, + 422, + 547, + 554 + ], + "type": "text", + "content": ". This becomes problematic for those who expect that the decision making of " + }, + { + "bbox": [ + 304, + 422, + 547, + 554 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 304, + 422, + 547, + 554 + ], + "type": "text", + "content": " should be close to that of human being, at least when " + }, + { + "bbox": [ + 304, + 422, + 547, + 554 + ], + "type": "inline_equation", + "content": "\\hat{x}" + }, + { + "bbox": [ + 304, + 422, + 547, + 554 + ], + "type": "text", + "content": " differs from " + }, + { + "bbox": [ + 304, + 422, + 547, + 554 + ], + "type": "inline_equation", + "content": "p_d" + }, + { + "bbox": [ + 304, + 422, + 547, + 554 + ], + "type": "text", + "content": " only up to what humans regard as nuisance. This is where the current neural networks commonly fail under the standard training practices." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 557, + 547, + 677 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 557, + 547, + 677 + ], + "spans": [ + { + "bbox": [ + 304, + 557, + 547, + 677 + ], + "type": "text", + "content": "Information bottleneck. Intuitively, a \"good\" representation " + }, + { + "bbox": [ + 304, + 557, + 547, + 677 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 304, + 557, + 547, + 677 + ], + "type": "text", + "content": " should keep information of " + }, + { + "bbox": [ + 304, + 557, + 547, + 677 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 304, + 557, + 547, + 677 + ], + "type": "text", + "content": " that is correlated with " + }, + { + "bbox": [ + 304, + 557, + 547, + 677 + ], + "type": "inline_equation", + "content": "\\mathbf{y}" + }, + { + "bbox": [ + 304, + 557, + 547, + 677 + ], + "type": "text", + "content": ", while preventing " + }, + { + "bbox": [ + 304, + 557, + 547, + 677 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 304, + 557, + 547, + 677 + ], + "type": "text", + "content": " from being too complex. The information bottleneck [107, 108] (IB) is a principled approach to obtain such a succinct representation " + }, + { + "bbox": [ + 304, + 557, + 547, + 677 + ], + "type": "inline_equation", + "content": "\\mathbf{x} \\rightarrow \\mathbf{z}" + }, + { + "bbox": [ + 304, + 557, + 547, + 677 + ], + "type": "text", + "content": " for a given downstream task " + }, + { + "bbox": [ + 304, + 557, + 547, + 677 + ], + "type": "inline_equation", + "content": "\\mathbf{x} \\rightarrow \\mathbf{y}" + }, + { + "bbox": [ + 304, + 557, + 547, + 677 + ], + "type": "text", + "content": ": namely, it finds " + }, + { + "bbox": [ + 304, + 557, + 547, + 677 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 304, + 557, + 547, + 677 + ], + "type": "text", + "content": " that (a) maximizes the (task-relevant) mutual information " + }, + { + "bbox": [ + 304, + 557, + 547, + 677 + ], + "type": "inline_equation", + "content": "I(\\mathbf{z}; \\mathbf{y})" + }, + { + "bbox": [ + 304, + 557, + 547, + 677 + ], + "type": "text", + "content": ", while (b) minimizing " + }, + { + "bbox": [ + 304, + 557, + 547, + 677 + ], + "type": "inline_equation", + "content": "I(\\mathbf{x}; \\mathbf{z})" + }, + { + "bbox": [ + 304, + 557, + 547, + 677 + ], + "type": "text", + "content": " to constrain the capacity of " + }, + { + "bbox": [ + 304, + 557, + 547, + 677 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 304, + 557, + 547, + 677 + ], + "type": "text", + "content": " for better generalization. In other words, it sets the mutual information " + }, + { + "bbox": [ + 304, + 557, + 547, + 677 + ], + "type": "inline_equation", + "content": "I(\\mathbf{x}; \\mathbf{z})" + }, + { + "bbox": [ + 304, + 557, + 547, + 677 + ], + "type": "text", + "content": " as the complexity measure of " + }, + { + "bbox": [ + 304, + 557, + 547, + 677 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 304, + 557, + 547, + 677 + ], + "type": "text", + "content": ". Specifically," + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 304, + 683, + 545, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 683, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 683, + 545, + 713 + ], + "type": "text", + "content": "1Although we focus on supervised learning, the framework itself in general does not rule out more general scenarios, e.g., when the target " + }, + { + "bbox": [ + 304, + 683, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{y}" + }, + { + "bbox": [ + 304, + 683, + 545, + 713 + ], + "type": "text", + "content": " can be self-supervised from " + }, + { + "bbox": [ + 304, + 683, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 304, + 683, + 545, + 713 + ], + "type": "text", + "content": " [14, 91]." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "16207" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 72, + 68, + 523, + 209 + ], + "blocks": [ + { + "bbox": [ + 72, + 68, + 523, + 209 + ], + "lines": [ + { + "bbox": [ + 72, + 68, + 523, + 209 + ], + "spans": [ + { + "bbox": [ + 72, + 68, + 523, + 209 + ], + "type": "image", + "image_path": "417bd75930c6b8cdd00836bb93021d4a3d0c293752e0f1dba38d06d336c744d3.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 217, + 547, + 251 + ], + "lines": [ + { + "bbox": [ + 46, + 217, + 547, + 251 + ], + "spans": [ + { + "bbox": [ + 46, + 217, + 547, + 251 + ], + "type": "text", + "content": "Figure 2. An overview of the proposed framework, the autoencoder-based nuisance-extended information bottleneck (AENIB). It illustrates the general pipeline, and Appendix C provides specific instantiations for convolutional and Transformer-based architectures. Overall, we incorporate adversarial autoencoder into variational information bottleneck by introducing a nuisance " + }, + { + "bbox": [ + 46, + 217, + 547, + 251 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_n" + }, + { + "bbox": [ + 46, + 217, + 547, + 251 + ], + "type": "text", + "content": " (to " + }, + { + "bbox": [ + 46, + 217, + 547, + 251 + ], + "type": "inline_equation", + "content": "\\mathbf{y}" + }, + { + "bbox": [ + 46, + 217, + 547, + 251 + ], + "type": "text", + "content": ") in representation learning." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 263, + 228, + 277 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 263, + 228, + 277 + ], + "spans": [ + { + "bbox": [ + 47, + 263, + 228, + 277 + ], + "type": "text", + "content": "it aims to maximize the following objective:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 55, + 285, + 287, + 304 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 55, + 285, + 287, + 304 + ], + "spans": [ + { + "bbox": [ + 55, + 285, + 287, + 304 + ], + "type": "interline_equation", + "content": "\\max _ {f} R _ {\\mathrm {I B}} (f), \\quad \\text {f o r} \\quad R _ {\\mathrm {I B}} (f) := I (\\mathbf {z}; \\mathbf {y}) - \\beta I (\\mathbf {x}; \\mathbf {z}), \\tag {2}", + "image_path": "dd4c3478b0de6f4659ef44c5bc19a10e5e5a7b3fbeb26afa7ebf28f10fab022c.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 312, + 287, + 337 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 312, + 287, + 337 + ], + "spans": [ + { + "bbox": [ + 47, + 312, + 287, + 337 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 312, + 287, + 337 + ], + "type": "inline_equation", + "content": "\\beta \\geq 0" + }, + { + "bbox": [ + 47, + 312, + 287, + 337 + ], + "type": "text", + "content": " controls the capacity constraint which ensures " + }, + { + "bbox": [ + 47, + 312, + 287, + 337 + ], + "type": "inline_equation", + "content": "I(\\mathbf{x};\\mathbf{z})\\leq I_{\\beta}" + }, + { + "bbox": [ + 47, + 312, + 287, + 337 + ], + "type": "text", + "content": " for some " + }, + { + "bbox": [ + 47, + 312, + 287, + 337 + ], + "type": "inline_equation", + "content": "I_{\\beta}" + }, + { + "bbox": [ + 47, + 312, + 287, + 337 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 347, + 279, + 360 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 347, + 279, + 360 + ], + "spans": [ + { + "bbox": [ + 47, + 347, + 279, + 360 + ], + "type": "text", + "content": "3. Nuisance-extended information bottleneck" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 367, + 287, + 534 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 367, + 287, + 534 + ], + "spans": [ + { + "bbox": [ + 46, + 367, + 287, + 534 + ], + "type": "text", + "content": "The standard information bottleneck (IB) objective (2) obtains a representation " + }, + { + "bbox": [ + 46, + 367, + 287, + 534 + ], + "type": "inline_equation", + "content": "\\mathbf{z} := f(\\mathbf{x})" + }, + { + "bbox": [ + 46, + 367, + 287, + 534 + ], + "type": "text", + "content": " on premise that the future inputs will be also from " + }, + { + "bbox": [ + 46, + 367, + 287, + 534 + ], + "type": "inline_equation", + "content": "p_d(\\mathbf{x},\\mathbf{y})" + }, + { + "bbox": [ + 46, + 367, + 287, + 534 + ], + "type": "text", + "content": ". In this paper, we aim to extend IB under assumption that the input " + }, + { + "bbox": [ + 46, + 367, + 287, + 534 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 46, + 367, + 287, + 534 + ], + "type": "text", + "content": " can be corrupted through an unknown noisy channel in the future, say " + }, + { + "bbox": [ + 46, + 367, + 287, + 534 + ], + "type": "inline_equation", + "content": "\\mathbf{x} \\to \\hat{\\mathbf{x}}" + }, + { + "bbox": [ + 46, + 367, + 287, + 534 + ], + "type": "text", + "content": ", while " + }, + { + "bbox": [ + 46, + 367, + 287, + 534 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{x}}" + }, + { + "bbox": [ + 46, + 367, + 287, + 534 + ], + "type": "text", + "content": " still preserves the semantics of " + }, + { + "bbox": [ + 46, + 367, + 287, + 534 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 46, + 367, + 287, + 534 + ], + "type": "text", + "content": " with respect to " + }, + { + "bbox": [ + 46, + 367, + 287, + 534 + ], + "type": "inline_equation", + "content": "\\mathbf{y}" + }, + { + "bbox": [ + 46, + 367, + 287, + 534 + ], + "type": "text", + "content": ": in other words, we assume " + }, + { + "bbox": [ + 46, + 367, + 287, + 534 + ], + "type": "inline_equation", + "content": "I(\\mathbf{x};\\mathbf{y}) = I(\\hat{\\mathbf{x}};\\mathbf{y}) > 0" + }, + { + "bbox": [ + 46, + 367, + 287, + 534 + ], + "type": "text", + "content": ". Intuitively, one can imagine a scenario that " + }, + { + "bbox": [ + 46, + 367, + 287, + 534 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 46, + 367, + 287, + 534 + ], + "type": "text", + "content": " contains multiple signals that each is already highly correlated with " + }, + { + "bbox": [ + 46, + 367, + 287, + 534 + ], + "type": "inline_equation", + "content": "\\mathbf{y}" + }, + { + "bbox": [ + 46, + 367, + 287, + 534 + ], + "type": "text", + "content": ", i.e., filtering out the remainder from " + }, + { + "bbox": [ + 46, + 367, + 287, + 534 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 46, + 367, + 287, + 534 + ], + "type": "text", + "content": " does not affect its mutual information with " + }, + { + "bbox": [ + 46, + 367, + 287, + 534 + ], + "type": "inline_equation", + "content": "\\mathbf{y}" + }, + { + "bbox": [ + 46, + 367, + 287, + 534 + ], + "type": "text", + "content": ". It may or may not be surprising that such signals are quite prevalent in deep neural networks, e.g., [44] empirically observe that adversarial perturbations [29, 102] are sufficient for a model to perform accurate classification." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 535, + 288, + 571 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 535, + 288, + 571 + ], + "spans": [ + { + "bbox": [ + 46, + 535, + 288, + 571 + ], + "type": "text", + "content": "In the context of IB framework, where the goal is to obtain a succinct encoder " + }, + { + "bbox": [ + 46, + 535, + 288, + 571 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 46, + 535, + 288, + 571 + ], + "type": "text", + "content": ", it is now reasonable to presume that the noisy channel " + }, + { + "bbox": [ + 46, + 535, + 288, + 571 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{x}}" + }, + { + "bbox": [ + 46, + 535, + 288, + 571 + ], + "type": "text", + "content": " acts like an adversary, i.e., it minimizes:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 56, + 579, + 287, + 597 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 56, + 579, + 287, + 597 + ], + "spans": [ + { + "bbox": [ + 56, + 579, + 287, + 597 + ], + "type": "interline_equation", + "content": "\\min _ {\\hat {\\mathbf {x}}} I (\\hat {\\mathbf {z}} := f (\\hat {\\mathbf {x}}); \\mathbf {y}) \\text {s u b j e c t} I (\\mathbf {x}; \\mathbf {y}) = I (\\hat {\\mathbf {x}}; \\mathbf {y}), \\tag {3}", + "image_path": "7f8470e6e58e6a89e2dc9afa5859285f54990ab38f04e1f1aede1906a311e6da.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 605, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 605, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 605, + 287, + 713 + ], + "type": "text", + "content": "given that one has no information on how the channel would behave a priori. This optimization thus would require " + }, + { + "bbox": [ + 46, + 605, + 287, + 713 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 46, + 605, + 287, + 713 + ], + "type": "text", + "content": " to extract every signal in " + }, + { + "bbox": [ + 46, + 605, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 46, + 605, + 287, + 713 + ], + "type": "text", + "content": " whenever it is highly correlated with " + }, + { + "bbox": [ + 46, + 605, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{y}" + }, + { + "bbox": [ + 46, + 605, + 287, + 713 + ], + "type": "text", + "content": ", to avoid the case when " + }, + { + "bbox": [ + 46, + 605, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{x}}" + }, + { + "bbox": [ + 46, + 605, + 287, + 713 + ], + "type": "text", + "content": " filters out all the signal except one that " + }, + { + "bbox": [ + 46, + 605, + 287, + 713 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 46, + 605, + 287, + 713 + ], + "type": "text", + "content": " has missed. We notice that, nevertheless, directly optimizing (3) with respect to " + }, + { + "bbox": [ + 46, + 605, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{x}}" + }, + { + "bbox": [ + 46, + 605, + 287, + 713 + ], + "type": "text", + "content": " is computationally infeasible in practice, considering that (a) it is in many cases an unconstrained optimization in a high-dimensional " + }, + { + "bbox": [ + 46, + 605, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{X}" + }, + { + "bbox": [ + 46, + 605, + 287, + 713 + ], + "type": "text", + "content": ", (b) with a constraint on (hard-to-compute) mutual information." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 263, + 547, + 443 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 263, + 547, + 443 + ], + "spans": [ + { + "bbox": [ + 304, + 263, + 547, + 443 + ], + "type": "text", + "content": "In this paper, to make sure that " + }, + { + "bbox": [ + 304, + 263, + 547, + 443 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 304, + 263, + 547, + 443 + ], + "type": "text", + "content": " still exhibits the adversarial behavior without (3), we propose to let " + }, + { + "bbox": [ + 304, + 263, + 547, + 443 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 304, + 263, + 547, + 443 + ], + "type": "text", + "content": " to model the nuisance representation " + }, + { + "bbox": [ + 304, + 263, + 547, + 443 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_n" + }, + { + "bbox": [ + 304, + 263, + 547, + 443 + ], + "type": "text", + "content": " as well as " + }, + { + "bbox": [ + 304, + 263, + 547, + 443 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 304, + 263, + 547, + 443 + ], + "type": "text", + "content": ". Specifically, " + }, + { + "bbox": [ + 304, + 263, + 547, + 443 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_n" + }, + { + "bbox": [ + 304, + 263, + 547, + 443 + ], + "type": "text", + "content": " aims to model the \"remainder\" information from " + }, + { + "bbox": [ + 304, + 263, + 547, + 443 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 304, + 263, + 547, + 443 + ], + "type": "text", + "content": " needed to reconstruct " + }, + { + "bbox": [ + 304, + 263, + 547, + 443 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 304, + 263, + 547, + 443 + ], + "type": "text", + "content": ", i.e., it maximizes " + }, + { + "bbox": [ + 304, + 263, + 547, + 443 + ], + "type": "inline_equation", + "content": "I(\\mathbf{x};\\mathbf{z},\\mathbf{z}_n)" + }, + { + "bbox": [ + 304, + 263, + 547, + 443 + ], + "type": "text", + "content": ". At the same time, " + }, + { + "bbox": [ + 304, + 263, + 547, + 443 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_n" + }, + { + "bbox": [ + 304, + 263, + 547, + 443 + ], + "type": "text", + "content": " compresses out any information that is correlated with " + }, + { + "bbox": [ + 304, + 263, + 547, + 443 + ], + "type": "inline_equation", + "content": "\\mathbf{y}" + }, + { + "bbox": [ + 304, + 263, + 547, + 443 + ], + "type": "text", + "content": ", i.e., it also minimizes " + }, + { + "bbox": [ + 304, + 263, + 547, + 443 + ], + "type": "inline_equation", + "content": "I(\\mathbf{z}_n;\\mathbf{y})" + }, + { + "bbox": [ + 304, + 263, + 547, + 443 + ], + "type": "text", + "content": ". Therefore, every information that is correlated with " + }, + { + "bbox": [ + 304, + 263, + 547, + 443 + ], + "type": "inline_equation", + "content": "\\mathbf{y}" + }, + { + "bbox": [ + 304, + 263, + 547, + 443 + ], + "type": "text", + "content": " should be encoded into " + }, + { + "bbox": [ + 304, + 263, + 547, + 443 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 304, + 263, + 547, + 443 + ], + "type": "text", + "content": " in a complementary manner. Here, we remark that now the role of the capacity constraint in (2) becomes more important: not only for regularizing " + }, + { + "bbox": [ + 304, + 263, + 547, + 443 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 304, + 263, + 547, + 443 + ], + "type": "text", + "content": " to be simpler, it also penalizes " + }, + { + "bbox": [ + 304, + 263, + 547, + 443 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_n" + }, + { + "bbox": [ + 304, + 263, + 547, + 443 + ], + "type": "text", + "content": " from pushing out unnecessary information to predict " + }, + { + "bbox": [ + 304, + 263, + 547, + 443 + ], + "type": "inline_equation", + "content": "\\mathbf{y}" + }, + { + "bbox": [ + 304, + 263, + 547, + 443 + ], + "type": "text", + "content": " into " + }, + { + "bbox": [ + 304, + 263, + 547, + 443 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 304, + 263, + 547, + 443 + ], + "type": "text", + "content": ", making the objective competitive again between " + }, + { + "bbox": [ + 304, + 263, + 547, + 443 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 304, + 263, + 547, + 443 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 263, + 547, + 443 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_n" + }, + { + "bbox": [ + 304, + 263, + 547, + 443 + ], + "type": "text", + "content": " as like in (3). Combined with the original IB (2), we define nuisance-extended IB (NIB) as the following:" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 313, + 455, + 545, + 474 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 313, + 455, + 545, + 474 + ], + "spans": [ + { + "bbox": [ + 313, + 455, + 545, + 474 + ], + "type": "interline_equation", + "content": "\\max _ {f} R _ {\\mathrm {N I B}} (f) := R _ {\\mathrm {I B}} (f) - I \\left(\\mathbf {z} _ {n}; \\mathbf {y}\\right) + \\alpha I \\left(\\mathbf {x}; \\mathbf {z}, \\mathbf {z} _ {n}\\right), \\tag {4}", + "image_path": "8a6bec0dfa1dc0bc2cf2b2883a6d66f0f8cfe462dc453e46d7dcbd47a4b83bf1.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 485, + 547, + 582 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 485, + 547, + 582 + ], + "spans": [ + { + "bbox": [ + 304, + 485, + 547, + 582 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 485, + 547, + 582 + ], + "type": "inline_equation", + "content": "\\alpha \\geq 0" + }, + { + "bbox": [ + 304, + 485, + 547, + 582 + ], + "type": "text", + "content": ". The proposed NIB objective can be viewed as a regularized form of IB by introducing a nuisance " + }, + { + "bbox": [ + 304, + 485, + 547, + 582 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_n" + }, + { + "bbox": [ + 304, + 485, + 547, + 582 + ], + "type": "text", + "content": ". Specifically, this optimization additionally forces " + }, + { + "bbox": [ + 304, + 485, + 547, + 582 + ], + "type": "inline_equation", + "content": "I(\\mathbf{x};\\mathbf{z},\\mathbf{z}_n)" + }, + { + "bbox": [ + 304, + 485, + 547, + 582 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 485, + 547, + 582 + ], + "type": "inline_equation", + "content": "I(\\mathbf{z}_n;\\mathbf{y})" + }, + { + "bbox": [ + 304, + 485, + 547, + 582 + ], + "type": "text", + "content": " in (4) to be maximized and minimized, i.e., " + }, + { + "bbox": [ + 304, + 485, + 547, + 582 + ], + "type": "inline_equation", + "content": "H(\\mathbf{x}|\\mathbf{z},\\mathbf{z}_n) = 0" + }, + { + "bbox": [ + 304, + 485, + 547, + 582 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 485, + 547, + 582 + ], + "type": "inline_equation", + "content": "I(\\mathbf{z}_n;\\mathbf{y}) = 0" + }, + { + "bbox": [ + 304, + 485, + 547, + 582 + ], + "type": "text", + "content": ", respectively. The following highlights that having these conditions, also with the independence " + }, + { + "bbox": [ + 304, + 485, + 547, + 582 + ], + "type": "inline_equation", + "content": "\\mathbf{z}\\perp \\mathbf{z}_n" + }, + { + "bbox": [ + 304, + 485, + 547, + 582 + ], + "type": "text", + "content": ", leads " + }, + { + "bbox": [ + 304, + 485, + 547, + 582 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 304, + 485, + 547, + 582 + ], + "type": "text", + "content": " that can recover the original " + }, + { + "bbox": [ + 304, + 485, + 547, + 582 + ], + "type": "inline_equation", + "content": "I(\\mathbf{x};\\mathbf{y})" + }, + { + "bbox": [ + 304, + 485, + 547, + 582 + ], + "type": "text", + "content": " from " + }, + { + "bbox": [ + 304, + 485, + 547, + 582 + ], + "type": "inline_equation", + "content": "I(\\hat{\\mathbf{z}};\\mathbf{y})" + }, + { + "bbox": [ + 304, + 485, + 547, + 582 + ], + "type": "text", + "content": " (see Appendix E for the derivation):" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 594, + 547, + 642 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 594, + 547, + 642 + ], + "spans": [ + { + "bbox": [ + 304, + 594, + 547, + 642 + ], + "type": "text", + "content": "Lemma 1. Let " + }, + { + "bbox": [ + 304, + 594, + 547, + 642 + ], + "type": "inline_equation", + "content": "\\mathbf{x} \\in \\mathcal{X}" + }, + { + "bbox": [ + 304, + 594, + 547, + 642 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 304, + 594, + 547, + 642 + ], + "type": "inline_equation", + "content": "\\mathbf{y} \\in \\mathcal{Y}" + }, + { + "bbox": [ + 304, + 594, + 547, + 642 + ], + "type": "text", + "content": " be random variables, " + }, + { + "bbox": [ + 304, + 594, + 547, + 642 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{x}}" + }, + { + "bbox": [ + 304, + 594, + 547, + 642 + ], + "type": "text", + "content": " be a noisy observation of " + }, + { + "bbox": [ + 304, + 594, + 547, + 642 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 304, + 594, + 547, + 642 + ], + "type": "text", + "content": " with " + }, + { + "bbox": [ + 304, + 594, + 547, + 642 + ], + "type": "inline_equation", + "content": "I(\\mathbf{x};\\mathbf{y}) = I(\\hat{\\mathbf{x}};\\mathbf{y})" + }, + { + "bbox": [ + 304, + 594, + 547, + 642 + ], + "type": "text", + "content": ". Given that " + }, + { + "bbox": [ + 304, + 594, + 547, + 642 + ], + "type": "inline_equation", + "content": "[\\hat{\\mathbf{z}},\\hat{\\mathbf{z}}_n] := f(\\hat{\\mathbf{x}})" + }, + { + "bbox": [ + 304, + 594, + 547, + 642 + ], + "type": "text", + "content": " of " + }, + { + "bbox": [ + 304, + 594, + 547, + 642 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{x}}" + }, + { + "bbox": [ + 304, + 594, + 547, + 642 + ], + "type": "text", + "content": " satisfies (a) " + }, + { + "bbox": [ + 304, + 594, + 547, + 642 + ], + "type": "inline_equation", + "content": "H(\\hat{\\mathbf{x}}|\\hat{\\mathbf{z}},\\hat{\\mathbf{z}}_n) = 0" + }, + { + "bbox": [ + 304, + 594, + 547, + 642 + ], + "type": "text", + "content": ", (b) " + }, + { + "bbox": [ + 304, + 594, + 547, + 642 + ], + "type": "inline_equation", + "content": "I(\\hat{\\mathbf{z}}_n;\\mathbf{y}) = 0" + }, + { + "bbox": [ + 304, + 594, + 547, + 642 + ], + "type": "text", + "content": ", and (c) " + }, + { + "bbox": [ + 304, + 594, + 547, + 642 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{z}} \\perp \\hat{\\mathbf{z}}_n" + }, + { + "bbox": [ + 304, + 594, + 547, + 642 + ], + "type": "text", + "content": ", it holds " + }, + { + "bbox": [ + 304, + 594, + 547, + 642 + ], + "type": "inline_equation", + "content": "I(\\hat{\\mathbf{z}};\\mathbf{y}) = I(\\mathbf{x};\\mathbf{y})" + }, + { + "bbox": [ + 304, + 594, + 547, + 642 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 653, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 653, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 653, + 547, + 713 + ], + "type": "text", + "content": "In the following sections, we provide a practical design of the proposed NIB based on an autoencoder-based architecture. Section 3.1 and 3.2 detail out its losses and architectures, respectively, and Section 3.3 summarizes the overall training. Figure 2 illustrates an overview of our framework." + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "16208" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 286, + 85 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 286, + 85 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 286, + 85 + ], + "type": "text", + "content": "3.1. AENIB: A practical autoencoder-based design" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 90, + 287, + 161 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 90, + 287, + 161 + ], + "spans": [ + { + "bbox": [ + 46, + 90, + 287, + 161 + ], + "type": "text", + "content": "Based on the NIB objective defined in (4) and Lemma 1, we design a practical training objective to implement the proposed framework. Here, we present a simple instantiation of NIB with an autoencoder-based architecture upon variational information bottleneck (VIB) [1], calling it autoencoder-based NIB (AENIB)." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 162, + 288, + 258 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 162, + 288, + 258 + ], + "spans": [ + { + "bbox": [ + 46, + 162, + 288, + 258 + ], + "type": "text", + "content": "Overall, Lemma 1 states that a robust encoder " + }, + { + "bbox": [ + 46, + 162, + 288, + 258 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 46, + 162, + 288, + 258 + ], + "type": "text", + "content": " demands for a \"good\" nuisance model that achieves generalization on " + }, + { + "bbox": [ + 46, + 162, + 288, + 258 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{z}}" + }, + { + "bbox": [ + 46, + 162, + 288, + 258 + ], + "type": "text", + "content": " in three aspects: (a) a good reconstruction, (b) nuisance, and (c) the independence between " + }, + { + "bbox": [ + 46, + 162, + 288, + 258 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 46, + 162, + 288, + 258 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 162, + 288, + 258 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_n" + }, + { + "bbox": [ + 46, + 162, + 288, + 258 + ], + "type": "text", + "content": ". To model these behaviors, we consider a decoder " + }, + { + "bbox": [ + 46, + 162, + 288, + 258 + ], + "type": "inline_equation", + "content": "g: \\mathcal{Z} \\to \\mathcal{X}" + }, + { + "bbox": [ + 46, + 162, + 288, + 258 + ], + "type": "text", + "content": " as well as the encoder " + }, + { + "bbox": [ + 46, + 162, + 288, + 258 + ], + "type": "inline_equation", + "content": "f: \\mathcal{X} \\to \\mathcal{Z}" + }, + { + "bbox": [ + 46, + 162, + 288, + 258 + ], + "type": "text", + "content": ", and adopt the following practical training objectives which incorporates an autoencoder-based loss and two adversarial losses [28]:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 53, + 264, + 288, + 324 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 264, + 288, + 324 + ], + "spans": [ + { + "bbox": [ + 53, + 264, + 288, + 324 + ], + "type": "text", + "content": "(a) We first pose a reconstruction loss to maximize " + }, + { + "bbox": [ + 53, + 264, + 288, + 324 + ], + "type": "inline_equation", + "content": "\\log p(\\mathbf{x}|\\mathbf{z},\\mathbf{z}_n)" + }, + { + "bbox": [ + 53, + 264, + 288, + 324 + ], + "type": "text", + "content": "; standard designs assume the decoder output to follow " + }, + { + "bbox": [ + 53, + 264, + 288, + 324 + ], + "type": "inline_equation", + "content": "\\mathcal{N}(\\mathbf{x},\\sigma^2\\mathbf{I})" + }, + { + "bbox": [ + 53, + 264, + 288, + 324 + ], + "type": "text", + "content": ", which is equivalent to the mean-squared error (MSE). Here, we use the normalized MSE to efficiently balance with other losses:" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 113, + 330, + 287, + 348 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 113, + 330, + 287, + 348 + ], + "spans": [ + { + "bbox": [ + 113, + 330, + 287, + 348 + ], + "type": "interline_equation", + "content": "L _ {\\text {r e c o n}} := \\frac {1}{\\| \\mathbf {x} \\| _ {2} ^ {2}} \\| \\mathbf {x} - g (\\mathbf {z}, \\mathbf {z} _ {n}) \\| _ {2} ^ {2} \\tag {5}", + "image_path": "789fd4c91cf4dec9805af15de6949a10d801df1eaa3329cf54aaa143d8908b6b.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 53, + 357, + 288, + 393 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 357, + 288, + 393 + ], + "spans": [ + { + "bbox": [ + 53, + 357, + 288, + 393 + ], + "type": "text", + "content": "(b) To force the nuisance-ness of " + }, + { + "bbox": [ + 53, + 357, + 288, + 393 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_n" + }, + { + "bbox": [ + 53, + 357, + 288, + 393 + ], + "type": "text", + "content": " with respect to " + }, + { + "bbox": [ + 53, + 357, + 288, + 393 + ], + "type": "inline_equation", + "content": "\\mathbf{y}" + }, + { + "bbox": [ + 53, + 357, + 288, + 393 + ], + "type": "text", + "content": ", we approximate " + }, + { + "bbox": [ + 53, + 357, + 288, + 393 + ], + "type": "inline_equation", + "content": "p(\\mathbf{y}|\\mathbf{z}_n)" + }, + { + "bbox": [ + 53, + 357, + 288, + 393 + ], + "type": "text", + "content": " with a multi-layer perceptron (MLP), say " + }, + { + "bbox": [ + 53, + 357, + 288, + 393 + ], + "type": "inline_equation", + "content": "q_{n}" + }, + { + "bbox": [ + 53, + 357, + 288, + 393 + ], + "type": "text", + "content": ", and perform an adversarial training:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 79, + 402, + 287, + 439 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 79, + 402, + 287, + 439 + ], + "spans": [ + { + "bbox": [ + 79, + 402, + 287, + 439 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} L _ {\\mathrm {n u i s}} := \\mathbb {E} _ {\\mathbf {x}} [ \\mathbb {C E} (q _ {n} ^ {*} (\\mathbf {z} _ {n}), \\frac {1}{| \\mathcal {Y} |}) ], \\\\ \\text {w h e r e} q _ {n} ^ {*} := \\min _ {q _ {n}} \\mathbb {E} _ {\\mathbf {x}, \\mathbf {y}} [ \\mathbb {C E} (q _ {n} (\\mathbf {z} _ {n}), \\mathbf {y}) ], \\tag {6} \\\\ \\end{array}", + "image_path": "d23338e3958306530f3634dc1fb67b72f4f355b6aa6382c5badba58fc7b986a0.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 69, + 445, + 288, + 469 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 69, + 445, + 288, + 469 + ], + "spans": [ + { + "bbox": [ + 69, + 445, + 288, + 469 + ], + "type": "text", + "content": "and " + }, + { + "bbox": [ + 69, + 445, + 288, + 469 + ], + "type": "inline_equation", + "content": "\\mathbb{C}\\mathbb{E}" + }, + { + "bbox": [ + 69, + 445, + 288, + 469 + ], + "type": "text", + "content": " denotes the cross entropy loss. Here, it optimizes " + }, + { + "bbox": [ + 69, + 445, + 288, + 469 + ], + "type": "inline_equation", + "content": "\\mathbb{C}\\mathbb{E}" + }, + { + "bbox": [ + 69, + 445, + 288, + 469 + ], + "type": "text", + "content": " towards the uniform distribution in " + }, + { + "bbox": [ + 69, + 445, + 288, + 469 + ], + "type": "inline_equation", + "content": "\\mathcal{V}" + }, + { + "bbox": [ + 69, + 445, + 288, + 469 + ], + "type": "text", + "content": ".3" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 53, + 475, + 287, + 525 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 475, + 287, + 525 + ], + "spans": [ + { + "bbox": [ + 53, + 475, + 287, + 525 + ], + "type": "text", + "content": "(c) To induce the independence between " + }, + { + "bbox": [ + 53, + 475, + 287, + 525 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 53, + 475, + 287, + 525 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 53, + 475, + 287, + 525 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_n" + }, + { + "bbox": [ + 53, + 475, + 287, + 525 + ], + "type": "text", + "content": ", we assume that the joint prior of " + }, + { + "bbox": [ + 53, + 475, + 287, + 525 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 53, + 475, + 287, + 525 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 53, + 475, + 287, + 525 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_n" + }, + { + "bbox": [ + 53, + 475, + 287, + 525 + ], + "type": "text", + "content": " is the isotropic Gaussian, i.e., " + }, + { + "bbox": [ + 53, + 475, + 287, + 525 + ], + "type": "inline_equation", + "content": "p(\\mathbf{z},\\mathbf{z}_n)\\sim \\mathcal{N}(0,\\mathbf{I})" + }, + { + "bbox": [ + 53, + 475, + 287, + 525 + ], + "type": "text", + "content": ", and performs a GAN training with a 2-layer MLP discriminator " + }, + { + "bbox": [ + 53, + 475, + 287, + 525 + ], + "type": "inline_equation", + "content": "q_{\\mathbf{z}}" + }, + { + "bbox": [ + 53, + 475, + 287, + 525 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 80, + 534, + 287, + 569 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 80, + 534, + 287, + 569 + ], + "spans": [ + { + "bbox": [ + 80, + 534, + 287, + 569 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} L _ {\\text {i n d}} := \\max _ {q _ {\\mathbf {z}}} \\mathbb {E} _ {\\mathbf {x}} \\left[ \\log \\left(q _ {\\mathbf {z}} (f (\\mathbf {x}))\\right) \\right] \\\\ + \\mathbb {E} _ {\\mathbf {z}, \\mathbf {z} _ {n}} \\sim \\mathcal {N} (0, \\mathbf {I}) [ \\log (1 - q _ {\\mathbf {z}} (\\mathbf {z}, \\mathbf {z} _ {n})) ]. \\tag {7} \\\\ \\end{array}", + "image_path": "50e26632d9018b5b433e60544e437d723c2348ae6190b2f0befa3fa0f3e0c34d.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 578, + 287, + 639 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 578, + 287, + 639 + ], + "spans": [ + { + "bbox": [ + 46, + 578, + 287, + 639 + ], + "type": "text", + "content": "Lastly, to approximate the original IB objective " + }, + { + "bbox": [ + 46, + 578, + 287, + 639 + ], + "type": "inline_equation", + "content": "R_{\\mathrm{IB}}(f)" + }, + { + "bbox": [ + 46, + 578, + 287, + 639 + ], + "type": "text", + "content": " in NIB (4), we instead maximize the variational information bottleneck (VIB) [1] objective " + }, + { + "bbox": [ + 46, + 578, + 287, + 639 + ], + "type": "inline_equation", + "content": "L_{\\mathrm{VIB}}^{\\beta}" + }, + { + "bbox": [ + 46, + 578, + 287, + 639 + ], + "type": "text", + "content": ", that can provide a lower bound on " + }, + { + "bbox": [ + 46, + 578, + 287, + 639 + ], + "type": "inline_equation", + "content": "R_{\\mathrm{IB}}" + }, + { + "bbox": [ + 46, + 578, + 287, + 639 + ], + "type": "text", + "content": ". Specifically, it makes variational approximations of: (a) " + }, + { + "bbox": [ + 46, + 578, + 287, + 639 + ], + "type": "inline_equation", + "content": "p(\\mathbf{y}|\\mathbf{z})" + }, + { + "bbox": [ + 46, + 578, + 287, + 639 + ], + "type": "text", + "content": " by a (parametrized) decoder neural" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 72, + 547, + 109 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 547, + 109 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 547, + 109 + ], + "type": "text", + "content": "network " + }, + { + "bbox": [ + 305, + 72, + 547, + 109 + ], + "type": "inline_equation", + "content": "q(\\mathbf{y}|\\mathbf{z})" + }, + { + "bbox": [ + 305, + 72, + 547, + 109 + ], + "type": "text", + "content": ", and (b) " + }, + { + "bbox": [ + 305, + 72, + 547, + 109 + ], + "type": "inline_equation", + "content": "p(\\mathbf{z})" + }, + { + "bbox": [ + 305, + 72, + 547, + 109 + ], + "type": "text", + "content": " by an \"easier\" distribution " + }, + { + "bbox": [ + 305, + 72, + 547, + 109 + ], + "type": "inline_equation", + "content": "r(\\mathbf{z})" + }, + { + "bbox": [ + 305, + 72, + 547, + 109 + ], + "type": "text", + "content": ", e.g., isotropic Gaussian " + }, + { + "bbox": [ + 305, + 72, + 547, + 109 + ], + "type": "inline_equation", + "content": "\\mathcal{N}(\\mathbf{z}|0,\\mathbf{I})" + }, + { + "bbox": [ + 305, + 72, + 547, + 109 + ], + "type": "text", + "content": ". Assuming a Gaussian decoder (1) for " + }, + { + "bbox": [ + 305, + 72, + 547, + 109 + ], + "type": "inline_equation", + "content": "f(\\mathbf{x},\\epsilon)" + }, + { + "bbox": [ + 305, + 72, + 547, + 109 + ], + "type": "text", + "content": ", we have:" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 315, + 119, + 545, + 167 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 315, + 119, + 545, + 167 + ], + "spans": [ + { + "bbox": [ + 315, + 119, + 545, + 167 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} L _ {\\mathrm {V I B}} ^ {\\beta} := \\frac {1}{n} \\sum_ {i = 1} ^ {n} \\mathbb {E} _ {\\epsilon} [ - \\log q (y _ {i} | f (x _ {i}, \\epsilon)) ] \\\\ + \\beta \\operatorname {K L} \\left(p (\\mathbf {z} | x _ {i}) \\| r (\\mathbf {z})\\right). \\tag {8} \\\\ \\end{array}", + "image_path": "fb3f0fd7136d1d6502f86e57aa9bdcf60179ea6840fd4dc408cf1dd887ab7e95.jpg" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 182, + 498, + 194 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 182, + 498, + 194 + ], + "spans": [ + { + "bbox": [ + 306, + 182, + 498, + 194 + ], + "type": "text", + "content": "3.2. Architectures for nuisance modeling" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 201, + 547, + 296 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 201, + 547, + 296 + ], + "spans": [ + { + "bbox": [ + 304, + 201, + 547, + 296 + ], + "type": "text", + "content": "In principle, our framework is generally compatible with any encoder architectures: e.g., say an encoder " + }, + { + "bbox": [ + 304, + 201, + 547, + 296 + ], + "type": "inline_equation", + "content": "f: \\mathcal{X} \\to \\mathcal{Z}" + }, + { + "bbox": [ + 304, + 201, + 547, + 296 + ], + "type": "text", + "content": " and decoder " + }, + { + "bbox": [ + 304, + 201, + 547, + 296 + ], + "type": "inline_equation", + "content": "g: \\mathcal{Z} \\to \\mathcal{X}" + }, + { + "bbox": [ + 304, + 201, + 547, + 296 + ], + "type": "text", + "content": ", respectively. In order to apply VIB, we assume that the encoder has two output heads of dimension " + }, + { + "bbox": [ + 304, + 201, + 547, + 296 + ], + "type": "inline_equation", + "content": "2K" + }, + { + "bbox": [ + 304, + 201, + 547, + 296 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 201, + 547, + 296 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 304, + 201, + 547, + 296 + ], + "type": "text", + "content": " denotes the dimension of " + }, + { + "bbox": [ + 304, + 201, + 547, + 296 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 304, + 201, + 547, + 296 + ], + "type": "text", + "content": ". Here, each output head models a Gaussian random variable by reparametrization, i.e., by modeling " + }, + { + "bbox": [ + 304, + 201, + 547, + 296 + ], + "type": "inline_equation", + "content": "(\\mu, \\sigma)" + }, + { + "bbox": [ + 304, + 201, + 547, + 296 + ], + "type": "text", + "content": " as the encoder output for both " + }, + { + "bbox": [ + 304, + 201, + 547, + 296 + ], + "type": "inline_equation", + "content": "\\mathbf{z} \\in \\mathbb{R}^K" + }, + { + "bbox": [ + 304, + 201, + 547, + 296 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 201, + 547, + 296 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_n \\in \\mathbb{R}^{K_n}" + }, + { + "bbox": [ + 304, + 201, + 547, + 296 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 297, + 547, + 392 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 297, + 547, + 392 + ], + "spans": [ + { + "bbox": [ + 304, + 297, + 547, + 392 + ], + "type": "text", + "content": "Although it is possible that " + }, + { + "bbox": [ + 304, + 297, + 547, + 392 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 304, + 297, + 547, + 392 + ], + "type": "text", + "content": " models " + }, + { + "bbox": [ + 304, + 297, + 547, + 392 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 304, + 297, + 547, + 392 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 297, + 547, + 392 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_n" + }, + { + "bbox": [ + 304, + 297, + 547, + 392 + ], + "type": "text", + "content": " by simply taking deep feed-forward representations following conventions, we observe that modeling nuisances " + }, + { + "bbox": [ + 304, + 297, + 547, + 392 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_n" + }, + { + "bbox": [ + 304, + 297, + 547, + 392 + ], + "type": "text", + "content": " (which is essentially \"generative\") in standard (discriminative) architectures incur a training instability thus in performance: the nuisance information often requires to model finer details in a given inputs, which may be available rather in early layers of " + }, + { + "bbox": [ + 304, + 297, + 547, + 392 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 304, + 297, + 547, + 392 + ], + "type": "text", + "content": ", but not in the later layers for classification." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 392, + 547, + 475 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 392, + 547, + 475 + ], + "spans": [ + { + "bbox": [ + 304, + 392, + 547, + 475 + ], + "type": "text", + "content": "In this paper, we propose simple architectural treatments to improve the stability of nuisance modeling concerning both convolutional networks and Vision Transformers [24] (ViTs). This section focuses on introducing the design for convolutional networks, and we refer the readers for the ViT-based design to Appendix C: which is even simpler thanks to their patch-level representations available." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 305, + 475, + 547, + 536 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 475, + 547, + 536 + ], + "spans": [ + { + "bbox": [ + 305, + 475, + 547, + 536 + ], + "type": "text", + "content": "Given a convolutional encoder " + }, + { + "bbox": [ + 305, + 475, + 547, + 536 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 305, + 475, + 547, + 536 + ], + "type": "text", + "content": ", we encode " + }, + { + "bbox": [ + 305, + 475, + 547, + 536 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_n" + }, + { + "bbox": [ + 305, + 475, + 547, + 536 + ], + "type": "text", + "content": " (as well as " + }, + { + "bbox": [ + 305, + 475, + 547, + 536 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 305, + 475, + 547, + 536 + ], + "type": "text", + "content": ") from the collection of internal features statistics, rather than directly using the output of " + }, + { + "bbox": [ + 305, + 475, + 547, + 536 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 305, + 475, + 547, + 536 + ], + "type": "text", + "content": ". Specifically, we extract " + }, + { + "bbox": [ + 305, + 475, + 547, + 536 + ], + "type": "inline_equation", + "content": "L" + }, + { + "bbox": [ + 305, + 475, + 547, + 536 + ], + "type": "text", + "content": " intermediate feature maps of a given input " + }, + { + "bbox": [ + 305, + 475, + 547, + 536 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 305, + 475, + 547, + 536 + ], + "type": "text", + "content": ", namely " + }, + { + "bbox": [ + 305, + 475, + 547, + 536 + ], + "type": "inline_equation", + "content": "\\mathbf{x}^{(1)}, \\dots, \\mathbf{x}^{(L)}" + }, + { + "bbox": [ + 305, + 475, + 547, + 536 + ], + "type": "text", + "content": " from " + }, + { + "bbox": [ + 305, + 475, + 547, + 536 + ], + "type": "inline_equation", + "content": "f(\\mathbf{x})" + }, + { + "bbox": [ + 305, + 475, + 547, + 536 + ], + "type": "text", + "content": ", and define the projection of " + }, + { + "bbox": [ + 305, + 475, + 547, + 536 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 305, + 475, + 547, + 536 + ], + "type": "text", + "content": " by:" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 343, + 543, + 545, + 571 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 343, + 543, + 545, + 571 + ], + "spans": [ + { + "bbox": [ + 343, + 543, + 545, + 571 + ], + "type": "interline_equation", + "content": "\\Pi_ {f} (\\mathbf {x}) := \\left[ \\begin{array}{c c c c} \\mathbf {m} ^ {(1)} & \\mathbf {m} ^ {(2)} & \\dots & \\mathbf {m} ^ {(L)} \\\\ \\mathbf {s} ^ {(1)} & \\mathbf {s} ^ {(2)} & \\dots & \\mathbf {s} ^ {(L)} \\end{array} \\right], \\tag {9}", + "image_path": "3a37b835777601c682ac7486f74e0a6049e3ce1500c4f6183bffef3e0f98bb9e.jpg" + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 305, + 579, + 547, + 619 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 579, + 547, + 619 + ], + "spans": [ + { + "bbox": [ + 305, + 579, + 547, + 619 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 579, + 547, + 619 + ], + "type": "inline_equation", + "content": "\\mathbf{m}^{(l)}" + }, + { + "bbox": [ + 305, + 579, + 547, + 619 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 579, + 547, + 619 + ], + "type": "inline_equation", + "content": "\\mathbf{s}^{(l)}" + }, + { + "bbox": [ + 305, + 579, + 547, + 619 + ], + "type": "text", + "content": " are the first and second moment of feature maps in " + }, + { + "bbox": [ + 305, + 579, + 547, + 619 + ], + "type": "inline_equation", + "content": "\\mathbf{x}^{(l)}" + }, + { + "bbox": [ + 305, + 579, + 547, + 619 + ], + "type": "text", + "content": ", assuming that " + }, + { + "bbox": [ + 305, + 579, + 547, + 619 + ], + "type": "inline_equation", + "content": "\\mathbf{x}^{(l)} \\in \\mathbb{R}^{HWC}" + }, + { + "bbox": [ + 305, + 579, + 547, + 619 + ], + "type": "text", + "content": ": " + }, + { + "bbox": [ + 305, + 579, + 547, + 619 + ], + "type": "inline_equation", + "content": "\\mathbf{m}_c^{(l)} := \\frac{1}{HW} \\sum_{hw} \\mathbf{x}_{hw_c}^{(l)}" + }, + { + "bbox": [ + 305, + 579, + 547, + 619 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 305, + 579, + 547, + 619 + ], + "type": "inline_equation", + "content": "\\mathbf{s}_c^{(l)} := \\frac{1}{HW} \\sum_{hw} (\\mathbf{x}_{hw_c}^{(l)} - \\mathbf{m}_c^{(l)})^2" + }, + { + "bbox": [ + 305, + 579, + 547, + 619 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 304, + 619, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 619, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 619, + 547, + 713 + ], + "type": "text", + "content": "In Appendix I, we demonstrate that this simple projection can sufficiently encode a generative representation of " + }, + { + "bbox": [ + 304, + 619, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 304, + 619, + 547, + 713 + ], + "type": "text", + "content": ": viz., we show that one can successfully and efficiently train GANs with a discriminator defined upon " + }, + { + "bbox": [ + 304, + 619, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\Pi_f" + }, + { + "bbox": [ + 304, + 619, + 547, + 713 + ], + "type": "text", + "content": ". Motivated by this observation, we adopt " + }, + { + "bbox": [ + 304, + 619, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\Pi_f" + }, + { + "bbox": [ + 304, + 619, + 547, + 713 + ], + "type": "text", + "content": " in modeling the encoder representations " + }, + { + "bbox": [ + 304, + 619, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 304, + 619, + 547, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 619, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_n" + }, + { + "bbox": [ + 304, + 619, + 547, + 713 + ], + "type": "text", + "content": ". We encode " + }, + { + "bbox": [ + 304, + 619, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 304, + 619, + 547, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 619, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_n" + }, + { + "bbox": [ + 304, + 619, + 547, + 713 + ], + "type": "text", + "content": " by simply applying MLPs to " + }, + { + "bbox": [ + 304, + 619, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\Pi_f(\\mathbf{x})" + }, + { + "bbox": [ + 304, + 619, + 547, + 713 + ], + "type": "text", + "content": " (9). Despite its simplicity, we observe this treatment enables a stable training of AENIB." + } + ] + } + ], + "index": 24 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 46, + 644, + 287, + 673 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 644, + 287, + 673 + ], + "spans": [ + { + "bbox": [ + 46, + 644, + 287, + 673 + ], + "type": "text", + "content": "2We also explore a SSIM-based [118] reconstruction loss as given in Appendix C, which we found beneficial for robustness particularly with Transformer-based models." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 47, + 673, + 287, + 693 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 673, + 287, + 693 + ], + "spans": [ + { + "bbox": [ + 47, + 673, + 287, + 693 + ], + "type": "text", + "content": "3 Alternatively, one can directly maximize " + }, + { + "bbox": [ + 47, + 673, + 287, + 693 + ], + "type": "inline_equation", + "content": "\\mathbb{C}\\mathbb{E}(q_n^* (\\mathbf{z}_n),\\mathbf{y})" + }, + { + "bbox": [ + 47, + 673, + 287, + 693 + ], + "type": "text", + "content": "; we use the current design to avoid potential instability of the maximization-based loss." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 47, + 693, + 287, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 693, + 287, + 712 + ], + "spans": [ + { + "bbox": [ + 47, + 693, + 287, + 712 + ], + "type": "text", + "content": "4 A more detailed description on the VIB framework (as well as on GAN) can be found in Appendix F.2." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "16209" + } + ] + } + ], + "index": 25 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 71, + 70, + 518, + 186 + ], + "blocks": [ + { + "bbox": [ + 71, + 70, + 518, + 186 + ], + "lines": [ + { + "bbox": [ + 71, + 70, + 518, + 186 + ], + "spans": [ + { + "bbox": [ + 71, + 70, + 518, + 186 + ], + "type": "table", + "html": "
SeverityCIFAR-10-CCIFAR-100-C
Clean12345Avg.Clean12345Avg.
Cross-entropy6.088.8911.114.019.726.516.025.131.435.139.346.854.041.3
VIB [1]5.988.6810.713.418.624.915.226.031.935.940.447.855.242.2
AugMix [39]6.528.9710.813.418.423.915.124.929.933.337.143.651.139.0
PixMix† [40]5.437.108.149.4012.114.910.323.226.728.730.835.039.032.0
AENIB (ours)4.977.498.9611.014.819.512.322.627.630.534.139.847.135.8
+ AugMix [39]5.357.658.9911.014.218.412.021.926.429.132.437.844.334.0
+ PixMix† [40]4.675.906.557.459.1211.48.0821.224.426.027.831.134.828.8
", + "image_path": "81e5643b59a6c909015320ca7325620dd34664866ad379534a0a953a156ab606.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 64, + 224, + 266, + 347 + ], + "blocks": [ + { + "bbox": [ + 46, + 190, + 545, + 213 + ], + "lines": [ + { + "bbox": [ + 46, + 190, + 545, + 213 + ], + "spans": [ + { + "bbox": [ + 46, + 190, + 545, + 213 + ], + "type": "text", + "content": "Table 1. Comparison of average corruption error rates " + }, + { + "bbox": [ + 46, + 190, + 545, + 213 + ], + "type": "inline_equation", + "content": "(\\% ;\\downarrow)" + }, + { + "bbox": [ + 46, + 190, + 545, + 213 + ], + "type": "text", + "content": " per severity level on CIFAR-10/100-C [35]. Bold and underline denote the best and runner-up, respectively. " + }, + { + "bbox": [ + 46, + 190, + 545, + 213 + ], + "type": "inline_equation", + "content": "^{\\dagger}\\mathrm{PixMix}" + }, + { + "bbox": [ + 46, + 190, + 545, + 213 + ], + "type": "text", + "content": " [40] utilizes an external dataset consisting of pattern- and fractal-like images." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 64, + 224, + 266, + 347 + ], + "lines": [ + { + "bbox": [ + 64, + 224, + 266, + 347 + ], + "spans": [ + { + "bbox": [ + 64, + 224, + 266, + 347 + ], + "type": "table", + "html": "
MethodC10C10-CC10.1C10.2CINIC
Cross-entropy6.0816.013.418.323.7
VIB [1]5.9815.213.616.823.6
NLIB [65]6.8117.014.617.524.3
sq-NLIB [106]6.0215.513.017.123.7
DisenIB [92]5.7615.213.217.223.7
AugMix [39]6.5215.114.217.224.2
PixMix [40]5.4310.313.116.623.2
AENIB (ours)4.9712.311.615.522.2
+ AugMix [39]5.3512.012.515.822.6
+ PixMix [40]4.678.0810.414.822.1
", + "image_path": "0d6fd9b030ce124a80fa672013994db1a7d75035fdbaffeb1a691cb99439e2df.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 352, + 287, + 384 + ], + "lines": [ + { + "bbox": [ + 46, + 352, + 287, + 384 + ], + "spans": [ + { + "bbox": [ + 46, + 352, + 287, + 384 + ], + "type": "text", + "content": "Table 2. Comparison of test error rates " + }, + { + "bbox": [ + 46, + 352, + 287, + 384 + ], + "type": "inline_equation", + "content": "(\\% ;\\downarrow)" + }, + { + "bbox": [ + 46, + 352, + 287, + 384 + ], + "type": "text", + "content": " on CIFAR-10 and its variants: CIFAR-10-C/10.1/10.2, and CINIC. Bold and underline indicate the best and runner-up results, respectively." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 47, + 402, + 190, + 415 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 402, + 190, + 415 + ], + "spans": [ + { + "bbox": [ + 47, + 402, + 190, + 415 + ], + "type": "text", + "content": "3.3. Overall training objective" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 422, + 288, + 495 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 422, + 288, + 495 + ], + "spans": [ + { + "bbox": [ + 46, + 422, + 288, + 495 + ], + "type": "text", + "content": "Combining the proposed objectives as well as the VIB loss, " + }, + { + "bbox": [ + 46, + 422, + 288, + 495 + ], + "type": "inline_equation", + "content": "L_{\\mathrm{VIB}}^{\\beta}" + }, + { + "bbox": [ + 46, + 422, + 288, + 495 + ], + "type": "text", + "content": " (8) leads us to the final objective. Although combining multiple losses in practice may introduce additional hyperparameters, we found most of the proposed losses can be added without scaling except for the reconstruction loss " + }, + { + "bbox": [ + 46, + 422, + 288, + 495 + ], + "type": "inline_equation", + "content": "L_{\\mathrm{recon}}" + }, + { + "bbox": [ + 46, + 422, + 288, + 495 + ], + "type": "text", + "content": " and the " + }, + { + "bbox": [ + 46, + 422, + 288, + 495 + ], + "type": "inline_equation", + "content": "\\beta" + }, + { + "bbox": [ + 46, + 422, + 288, + 495 + ], + "type": "text", + "content": " in the original VIB loss. Hence, we get:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 67, + 505, + 287, + 520 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 67, + 505, + 287, + 520 + ], + "spans": [ + { + "bbox": [ + 67, + 505, + 287, + 520 + ], + "type": "interline_equation", + "content": "L _ {\\mathrm {A E N I B}} := L _ {\\mathrm {V I B}} ^ {\\beta} + \\alpha \\cdot L _ {\\text {r e c o n}} + L _ {\\text {n u i s}} + L _ {\\text {i n d}}. \\tag {10}", + "image_path": "4ee79b054439e06d62fdba1e8281ce83bb5302e4ea6cf8fffb32ee297cf3c6a4.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 532, + 270, + 544 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 532, + 270, + 544 + ], + "spans": [ + { + "bbox": [ + 47, + 532, + 270, + 544 + ], + "type": "text", + "content": "Algorithm 1 in Appendix A summarizes the procedure." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 560, + 128, + 574 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 560, + 128, + 574 + ], + "spans": [ + { + "bbox": [ + 47, + 560, + 128, + 574 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "text", + "content": "We verify the effectiveness of our proposed AENIB training for various aspects of model reliability: specifically, we cover (a) corruption and natural robustness (Section 4.1), (b) novelty detection (Section 4.2), and (c) certified adversarial robustness (Section 4.3) tasks which all have been challenging without task-specific priors [37, 39, 82]. We provide an ablation study in Appendix D for a component-wise analysis. We also present an evaluation on our proposed components in the context of generative modeling in Appendix I. The full details on the experiments, e.g., datasets, training details, and hyperparameters, can be found in Appendix B." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 226, + 513, + 239 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 226, + 513, + 239 + ], + "spans": [ + { + "bbox": [ + 305, + 226, + 513, + 239 + ], + "type": "text", + "content": "4.1. Robustness against natural corruptions" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 245, + 547, + 473 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 245, + 547, + 473 + ], + "spans": [ + { + "bbox": [ + 304, + 245, + 547, + 473 + ], + "type": "text", + "content": "We first evaluate corruption robustness of our method, i.e., its generalization ability under natural corruptions (e.g., fog, brightness, etc.) and distribution shifts those are still semantic to humans. To this end, we consider a wide range of benchmarks those are derived from CIFAR-10 and ImageNet for the purpose of measuring generalization. Namely, for CIFAR-10 models we test on (a) CIFAR-10/100-C [35], a corrupted version of CIFAR-10/100 simulating 15 common corruptions in 5 severity levels, as well as (b) CIFAR-10.1 [94], CIFAR-10.2 [81], and CINIC-10 [21], i.e., three regenerations of the CIFAR-10 test set. For ImageNet models, on the other hand, we test (a) ImageNet-C [35], a corrupted version of ImageNet validation set, (b) ImageNet-R [34], a collection of rendition images for 200 ImageNet classes, and ImageNet-Sketch [117], as well as (c) the Background Challenge [119] benchmark to evaluate model bias against background changes. This section mainly reports the results from ViT [24, 111] based architectures, but we also report the results with ResNet-18 [33] in Appendix H." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 473, + 547, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 473, + 547, + 628 + ], + "spans": [ + { + "bbox": [ + 304, + 473, + 547, + 628 + ], + "type": "text", + "content": "Table 1 and 2 summarize the results on CIFAR-based models. In Table 1, we observe that AENIB significantly and consistently improves corruption errors upon VIB, and these gains are strong even compared with state-of-the-art methods: e.g., AENIB can solely outperform a strong baseline of AugMix [39]. Although a more recent method of PixMix [40] could achieve a lower corruption error by utilizing extra (pattern-like) data, we remark that (a) AENIB also benefit from PixMix (i.e., the extra data) as given in \"AENIB + PixMix\", and (b) the results on Table 2 show that the generalization capability of AENIB is better than PixMix on CIFAR-10.1, 10.2 and CINIC-10, i.e., in beyond common corruptions, by less relying on domain-specific data." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 630, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 630, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 630, + 547, + 713 + ], + "type": "text", + "content": "Next, Table 3 highlights that the effectiveness of AENIB can generalize to a more larger-scale, higher-resolution dataset of ImageNet: we still observe that AENIB can consistently improve robust accuracy for diverse corruption types, again without leveraging any further data augmentation during training. Figure 3 compares the linear trends made by Cross-entropy and AENIB across different data augmenta" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "16210" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 48, + 70, + 288, + 148 + ], + "blocks": [ + { + "bbox": [ + 48, + 70, + 288, + 148 + ], + "lines": [ + { + "bbox": [ + 48, + 70, + 288, + 148 + ], + "spans": [ + { + "bbox": [ + 48, + 70, + 288, + 148 + ], + "type": "table", + "html": "
DatasetViT-S/16ViT-B/16
BaselineAENIB (ours)BaselineAENIB (ours)
IN-1K25.125.121.821.9
IN-C (mCE)65.965.2 (−0.7)58.657.5 (−1.1)
IN-R70.367.1 (−3.2)66.364.4 (−1.9)
IN-Sketch80.377.7 (−2.6)76.574.4 (−2.1)
", + "image_path": "c525eb7d087c912c01920e237e027579a8c34ea3232b31898c35230e44b1da66.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 48, + 189, + 288, + 268 + ], + "blocks": [ + { + "bbox": [ + 47, + 153, + 288, + 185 + ], + "lines": [ + { + "bbox": [ + 47, + 153, + 288, + 185 + ], + "spans": [ + { + "bbox": [ + 47, + 153, + 288, + 185 + ], + "type": "text", + "content": "Table 3. Comparison of error rates " + }, + { + "bbox": [ + 47, + 153, + 288, + 185 + ], + "type": "inline_equation", + "content": "(\\% ;\\downarrow)" + }, + { + "bbox": [ + 47, + 153, + 288, + 185 + ], + "type": "text", + "content": " or mean corruption error (mCE, " + }, + { + "bbox": [ + 47, + 153, + 288, + 185 + ], + "type": "inline_equation", + "content": "\\%" + }, + { + "bbox": [ + 47, + 153, + 288, + 185 + ], + "type": "text", + "content": " . " + }, + { + "bbox": [ + 47, + 153, + 288, + 185 + ], + "type": "inline_equation", + "content": "\\downarrow" + }, + { + "bbox": [ + 47, + 153, + 288, + 185 + ], + "type": "text", + "content": " ) on ImageNet (IN) and its variants, namely IN-C [35], IN-R [34], and IN-Sketch [117]. Bold indicates the best results." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 48, + 189, + 288, + 268 + ], + "lines": [ + { + "bbox": [ + 48, + 189, + 288, + 268 + ], + "spans": [ + { + "bbox": [ + 48, + 189, + 288, + 268 + ], + "type": "table", + "html": "
BG-Challenge DatasetViT-S/16ViT-B/16
BaselineAENIB (ours)BaselineAENIB (ours)
ORIGINAL (IN-9; ↑)95.395.596.096.1
ONLY-BG-T (↓)20.317.8 (−2.5)24.221.1 (−3.1)
MIXED-SAME (↑)86.388.3 (+2.0)87.488.9 (+1.5)
MIXED-RAND (↑)77.880.5 (+2.7)80.181.8 (+0.7)
BG-gap (↓)8.57.8 (−0.7)7.37.1 (−0.2)
", + "image_path": "c174fa1af0716a0a94f5c7a88295c752b1a9eaa4435af42d25db347cb236f609.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "type": "table", + "bbox": [ + 48, + 310, + 286, + 419 + ], + "blocks": [ + { + "bbox": [ + 47, + 273, + 287, + 307 + ], + "lines": [ + { + "bbox": [ + 47, + 273, + 287, + 307 + ], + "spans": [ + { + "bbox": [ + 47, + 273, + 287, + 307 + ], + "type": "text", + "content": "Table 4. Evaluation of AENIB on Backgrounds Challenge [119] compared to the cross-entropy baseline. All the models are trained on ImageNet, and warped to perform classification on ImageNet-9." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 48, + 310, + 286, + 419 + ], + "lines": [ + { + "bbox": [ + 48, + 310, + 286, + 419 + ], + "spans": [ + { + "bbox": [ + 48, + 310, + 286, + 419 + ], + "type": "table", + "html": "
MethodScoreSVHNLSUNImageNetC100CelebA
JEM [31]log p(x)0.67--0.670.75
JEM [31]maxy p(y|x) [36]0.89--0.870.79
SupCon [56]maxy p(y|x) [36]0.970.930.910.89-
Cross-entropymaxy p(y|x) [36]0.940.940.920.860.64
Cross-entropylog Dir0.05(y)0.960.950.940.860.61
VIB [1]maxy p(y|x) [36]0.950.940.920.880.76
VIB [1]log Dir0.05(y)0.970.960.940.880.78
AENIB (ours)maxy p(y|x) [36]0.880.880.860.840.81
AENIB (ours)log Dir0.05(y)0.900.950.920.860.80
AENIB (ours)+ logN(zn;0,I)0.980.990.990.860.79
", + "image_path": "69b6c9b33da467e8a5ec9f769d40334c17358d5d9334d18c16c78955f6d72dd3.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_body" + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 426, + 287, + 459 + ], + "lines": [ + { + "bbox": [ + 47, + 426, + 287, + 459 + ], + "spans": [ + { + "bbox": [ + 47, + 426, + 287, + 459 + ], + "type": "text", + "content": "Table 5. Comparison of AUROC (\\%; ↑) for OOD detection from CIFAR-10 with five OOD datasets: SVHN, LSUN, ImageNet, CIFAR-100, and CelebA. Bolds indicate the best results." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 472, + 287, + 531 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 472, + 287, + 531 + ], + "spans": [ + { + "bbox": [ + 46, + 472, + 287, + 531 + ], + "type": "text", + "content": "tions and hyperparameters, confirming that AENIB exhibits a better operating points even in terms of effective robustness [105], given the recent observations on the correlation between in- vs. out-of-distribution performances across different models [34, 87, 105]." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 532, + 288, + 640 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 532, + 288, + 640 + ], + "spans": [ + { + "bbox": [ + 46, + 532, + 288, + 640 + ], + "type": "text", + "content": "Lastly, Table 4 further evaluates the ImageNet classifiers on Background Challenge [119], a benchmark established to test the model robustness against background shifts: specifically, it constructs variants of ImageNet-9 (that combines 370 subclasses of ImageNet; ORIGINAL) with different combinations of backgrounds. Our AENIB-based models still consistently improve upon the cross-entropy baseline on the benchmark, showing that AENIB indeed tends to learn less-biased features against background changes." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 647, + 151, + 659 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 647, + 151, + 659 + ], + "spans": [ + { + "bbox": [ + 47, + 647, + 151, + 659 + ], + "type": "text", + "content": "4.2. Novelty detection" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 665, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 288, + 713 + ], + "type": "text", + "content": "Next, we show that our AENIB model can be also a good detector for out-of-distribution samples (OODs), i.e., to solve the novelty detection task. In general, the task is defined by a binary classification problem that aims to discriminate novel" + } + ] + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 310, + 75, + 411, + 183 + ], + "blocks": [ + { + "bbox": [ + 310, + 75, + 411, + 183 + ], + "lines": [ + { + "bbox": [ + 310, + 75, + 411, + 183 + ], + "spans": [ + { + "bbox": [ + 310, + 75, + 411, + 183 + ], + "type": "image", + "image_path": "1ada7f4ddc49c8c421d861503e06fd6f5ca51cc0704c763b9422bd390a9b32a2.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 306, + 187, + 421, + 220 + ], + "lines": [ + { + "bbox": [ + 306, + 187, + 421, + 220 + ], + "spans": [ + { + "bbox": [ + 306, + 187, + 421, + 220 + ], + "type": "text", + "content": "Figure 3. Comparison of trends in clean vs. corruption errors against Gaussian on ViT-S/4." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 433, + 75, + 530, + 184 + ], + "blocks": [ + { + "bbox": [ + 433, + 75, + 530, + 184 + ], + "lines": [ + { + "bbox": [ + 433, + 75, + 530, + 184 + ], + "spans": [ + { + "bbox": [ + 433, + 75, + 530, + 184 + ], + "type": "image", + "image_path": "9b8d6236d57497bda1aafb35fba2f4483782aa6f503e064f5be7be996c737c9e.jpg" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 428, + 188, + 544, + 220 + ], + "lines": [ + { + "bbox": [ + 428, + 188, + 544, + 220 + ], + "spans": [ + { + "bbox": [ + 428, + 188, + 544, + 220 + ], + "type": "text", + "content": "Figure 4. Comparison of certified adversarial robust accuracy at various radii on CIFAR-10." + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_caption" + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 232, + 547, + 447 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 232, + 547, + 447 + ], + "spans": [ + { + "bbox": [ + 304, + 232, + 547, + 447 + ], + "type": "text", + "content": "samples from in-distribution samples. A typical practice here is to define a score function for each input, e.g., the maximum confidence score [36], to threshold out samples as out-of-distribution when the score is low. To define a score function for AENIB models, we first observe that the log-likelihood of " + }, + { + "bbox": [ + 304, + 232, + 547, + 447 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_n" + }, + { + "bbox": [ + 304, + 232, + 547, + 447 + ], + "type": "text", + "content": ", which is only available for AENIB (and not for standard models), can be a strong score to detect novelties those are semantically far from in-distribution. Specifically, we use " + }, + { + "bbox": [ + 304, + 232, + 547, + 447 + ], + "type": "inline_equation", + "content": "\\log \\mathcal{N}(\\mathbf{z}_n;0,I) = -\\frac{1}{2}\\| \\mathbf{z}_n\\|^2" + }, + { + "bbox": [ + 304, + 232, + 547, + 447 + ], + "type": "text", + "content": ", as we assume that " + }, + { + "bbox": [ + 304, + 232, + 547, + 447 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 304, + 232, + 547, + 447 + ], + "type": "text", + "content": " follows isotropic Gaussian " + }, + { + "bbox": [ + 304, + 232, + 547, + 447 + ], + "type": "inline_equation", + "content": "\\mathcal{N}(0,I)" + }, + { + "bbox": [ + 304, + 232, + 547, + 447 + ], + "type": "text", + "content": ". For detecting so-called \"harder\" novelties, we propose to use the log-likelihood score of " + }, + { + "bbox": [ + 304, + 232, + 547, + 447 + ], + "type": "inline_equation", + "content": "\\mathbf{y}" + }, + { + "bbox": [ + 304, + 232, + 547, + 447 + ], + "type": "text", + "content": " under a symmetric Dirichlet distribution of parameter " + }, + { + "bbox": [ + 304, + 232, + 547, + 447 + ], + "type": "inline_equation", + "content": "\\alpha > 0" + }, + { + "bbox": [ + 304, + 232, + 547, + 447 + ], + "type": "text", + "content": ", namely " + }, + { + "bbox": [ + 304, + 232, + 547, + 447 + ], + "type": "inline_equation", + "content": "\\mathrm{Dir}_{\\alpha}(\\mathbf{y}) \\in \\Delta^{|\\mathcal{Y}| - 1}" + }, + { + "bbox": [ + 304, + 232, + 547, + 447 + ], + "type": "text", + "content": ", rather than simply using " + }, + { + "bbox": [ + 304, + 232, + 547, + 447 + ], + "type": "inline_equation", + "content": "\\max_y p(y|x)" + }, + { + "bbox": [ + 304, + 232, + 547, + 447 + ], + "type": "text", + "content": ": i.e., " + }, + { + "bbox": [ + 304, + 232, + 547, + 447 + ], + "type": "inline_equation", + "content": "\\log \\mathrm{Dir}_{\\alpha}(\\mathbf{y}) = (\\alpha - 1)\\sum_i\\log y_i" + }, + { + "bbox": [ + 304, + 232, + 547, + 447 + ], + "type": "text", + "content": ". Note that the distribution gets closer to the symmetric (discrete) one-hot distribution as " + }, + { + "bbox": [ + 304, + 232, + 547, + 447 + ], + "type": "inline_equation", + "content": "\\alpha \\to 0" + }, + { + "bbox": [ + 304, + 232, + 547, + 447 + ], + "type": "text", + "content": ", which makes sense for most classification tasks, and here we simply use " + }, + { + "bbox": [ + 304, + 232, + 547, + 447 + ], + "type": "inline_equation", + "content": "\\alpha = 0.05" + }, + { + "bbox": [ + 304, + 232, + 547, + 447 + ], + "type": "text", + "content": " throughout experiments." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 447, + 547, + 590 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 447, + 547, + 590 + ], + "spans": [ + { + "bbox": [ + 304, + 447, + 547, + 590 + ], + "type": "text", + "content": "We consider two evaluation benchmarks: (a) the \"standard\" benchmark, that has been actively adopted in the literature [36, 72, 74], assumes the CIFAR-10 test set as in-distribution and measures the detection performance of other independent datasets; (b) a recent OBJECTS benchmark [122], on the other hand, extends the CIFAR-10 benchmark to also consider \"near\" in-distribution in OOD evaluation. Specifically, OBJECTS assumes CIFAR-10-C [35] and ImageNet-10 as in-distribution in test-time as well as CIFAR-10, making the detection much more challenging. In this experiment, we compare ResNet-18 [33] models trained on CIFAR-10 following the setup of [122]." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 590, + 547, + 686 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 590, + 547, + 686 + ], + "spans": [ + { + "bbox": [ + 304, + 590, + 547, + 686 + ], + "type": "text", + "content": "The results are reported in Table 5 and 6 for the standard and OBJECTS benchmarks, respectively. Overall, we confirm that the score function combining the information of " + }, + { + "bbox": [ + 304, + 590, + 547, + 686 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_n" + }, + { + "bbox": [ + 304, + 590, + 547, + 686 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 590, + 547, + 686 + ], + "type": "inline_equation", + "content": "\\mathbf{y}" + }, + { + "bbox": [ + 304, + 590, + 547, + 686 + ], + "type": "text", + "content": " of AENIB significantly improves novelty detection in a complementary manner over strong baselines, showing the effectiveness of modeling nuisance. For example, in Table 5, the combined score achieves near-perfect AUROCs for detecting SVHN, LSUN and ImageNet datasets." + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 306, + 693, + 545, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 693, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 306, + 693, + 545, + 713 + ], + "type": "text", + "content": "In practice, we observe that other choices in a moderate range of " + }, + { + "bbox": [ + 306, + 693, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 306, + 693, + 545, + 713 + ], + "type": "text", + "content": " near 0 do not much affect performance." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "16211" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 64, + 70, + 526, + 240 + ], + "blocks": [ + { + "bbox": [ + 64, + 70, + 526, + 240 + ], + "lines": [ + { + "bbox": [ + 64, + 70, + 526, + 240 + ], + "spans": [ + { + "bbox": [ + 64, + 70, + 526, + 240 + ], + "type": "table", + "html": "
FS-OOD: OBJECTSAUROC (%; ↑) / AUPR (%; ↑) / FPR@TPR95 (%; ↓)
MethodScoreMNISTFashionMNISTTextureCIFAR-100-C
Cross-entropymaxy p(y|x) [36]66.98 / 52.66 / 93.5473.78 / 90.15 / 88.0874.18 / 93.34 / 85.6474.12 / 89.74 / 87.26
ODIN [74]70.31 / 49.58 / 82.0480.98 / 91.53 / 68.7370.14 / 89.97 / 72.9167.51 / 83.97 / 84.26
Energy-based [76]54.55 / 34.14 / 92.2376.50 / 89.80 / 72.4068.63 / 89.51 / 75.5768.37 / 85.54 / 83.64
Mahalanobis [72]77.04 / 65.31 / 84.5980.33 / 92.28 / 77.1772.02 / 88.46 / 72.9868.13 / 82.97 / 85.53
SEM [122]75.69 / 76.61 / 99.7079.40 / 93.14 / 93.7279.69 / 95.48 / 82.1578.89 / 92.07 / 83.92
log Dir0.05(y)76.75 / 66.26 / 83.5182.88 / 93.97 / 77.1970.69 / 92.68 / 91.3578.80 / 92.21 / 82.50
VIB [1]maxy p(y|x) [36]80.23 / 73.50 / 80.6976.35 / 91.22 / 84.7574.67 / 94.09 / 87.2276.12 / 91.03 / 84.99
log Dir0.05(y)86.13 / 79.45 / 64.9281.11 / 93.12 / 77.8273.84 / 93.50 / 88.0078.54 / 91.85 / 81.47
AENIB (ours)maxy p(y|x) [36]79.67 / 71.50 / 80.2277.33 / 91.63 / 84.3174.95 / 93.97 / 86.0174.31 / 89.89 / 86.26
log Dir0.05(y)90.53 / 85.68 / 52.0884.56 / 94.61 / 74.2475.04 / 93.83 / 86.0179.39 / 92.33 / 81.51
+ log N(zn; 0, I)92.43 / 89.38 / 48.1084.85 / 94.84 / 74.6788.91 / 97.49 / 48.4482.66 / 93.62 / 74.14
", + "image_path": "0c17eafa51b587cc2fc595278398355ee123a072147b839c36b4d26e4b63dfe4.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 245, + 547, + 269 + ], + "lines": [ + { + "bbox": [ + 46, + 245, + 547, + 269 + ], + "spans": [ + { + "bbox": [ + 46, + 245, + 547, + 269 + ], + "type": "text", + "content": "Table 6. Comparison of OOD detection performances on the OBJECTS benchmark [122], which considers CIFAR-10-C and ImageNet-10 as in-distribution as well as the training in-distribution of CIFAR-10. Bold and underline denote the best and runner-up results, respectively." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 281, + 288, + 353 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 281, + 288, + 353 + ], + "spans": [ + { + "bbox": [ + 46, + 281, + 288, + 353 + ], + "type": "text", + "content": "Regarding Table 6, on the other hand, AENIB improves the previous best AUROC (of Mahalanobis [72]) on OBJECTS vs. MNIST from " + }, + { + "bbox": [ + 46, + 281, + 288, + 353 + ], + "type": "inline_equation", + "content": "77.04 \\rightarrow 92.43" + }, + { + "bbox": [ + 46, + 281, + 288, + 353 + ], + "type": "text", + "content": ". The improved results on OBJECTS imply that both of the representation and score obtained from AENIB help to better discriminate in- vs. out-of-distribution in more semantic senses." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 360, + 220, + 372 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 360, + 220, + 372 + ], + "spans": [ + { + "bbox": [ + 47, + 360, + 220, + 372 + ], + "type": "text", + "content": "4.3. Certified adversarial robustness" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 378, + 288, + 521 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 378, + 288, + 521 + ], + "spans": [ + { + "bbox": [ + 46, + 378, + 288, + 521 + ], + "type": "text", + "content": "We also evaluate adversarial robustness [29, 82, 102] adopting the randomized smoothing framework [17, 70] that can measure a certified robustness for a given representation. Specifically, any classifier can be robustified by averaging its predictions under Gaussian noise, where the robustness at input " + }, + { + "bbox": [ + 46, + 378, + 288, + 521 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 46, + 378, + 288, + 521 + ], + "type": "text", + "content": " depends on how consistent the classifier is on classifying " + }, + { + "bbox": [ + 46, + 378, + 288, + 521 + ], + "type": "inline_equation", + "content": "\\mathcal{N}(x, \\sigma^2\\mathbf{I})" + }, + { + "bbox": [ + 46, + 378, + 288, + 521 + ], + "type": "text", + "content": " [50]. Under this evaluation protocol, we suggest that adversarially-robust representations can be a natural byproduct from AENIB when combined with the randomized smoothing technique, without using any thorough adversarial training methods [82] that often require significant training cost with no certification on the robustness." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 522, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 522, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 522, + 288, + 713 + ], + "type": "text", + "content": "We follow the standard certification protocol [17] to compare the certified test accuracy at radius " + }, + { + "bbox": [ + 46, + 522, + 288, + 713 + ], + "type": "inline_equation", + "content": "r" + }, + { + "bbox": [ + 46, + 522, + 288, + 713 + ], + "type": "text", + "content": ", which is defined by the fraction of the test samples that a smoothed classifier classifies correctly with its certified radius larger than " + }, + { + "bbox": [ + 46, + 522, + 288, + 713 + ], + "type": "inline_equation", + "content": "r" + }, + { + "bbox": [ + 46, + 522, + 288, + 713 + ], + "type": "text", + "content": ". We consider ViT-S models on CIFAR-10, and assume " + }, + { + "bbox": [ + 46, + 522, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\sigma = 0.1" + }, + { + "bbox": [ + 46, + 522, + 288, + 713 + ], + "type": "text", + "content": " for this experiment. The results summarized in Figure 4 show that our proposed AENIB achieves significantly better certified robustness compared to the baselines at all radii tested: e.g., it improves certified robust accuracy of VIB by " + }, + { + "bbox": [ + 46, + 522, + 288, + 713 + ], + "type": "inline_equation", + "content": "39.6\\% \\rightarrow 56.8\\%" + }, + { + "bbox": [ + 46, + 522, + 288, + 713 + ], + "type": "text", + "content": " at " + }, + { + "bbox": [ + 46, + 522, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\varepsilon = 0.1" + }, + { + "bbox": [ + 46, + 522, + 288, + 713 + ], + "type": "text", + "content": ". Again, the robustness obtained from AENIB is not from specific knowledge on the threat model, which implies that AENIB could offer free adversarial robustness when combined with randomized smoothing. This confirms that the robustness of AENIB is not only significant but also consistent per input, especially considering its high certified robustness at higher " + }, + { + "bbox": [ + 46, + 522, + 288, + 713 + ], + "type": "inline_equation", + "content": "r" + }, + { + "bbox": [ + 46, + 522, + 288, + 713 + ], + "type": "text", + "content": "'s." + } + ] + } + ], + "index": 5 + }, + { + "type": "image", + "bbox": [ + 325, + 279, + 528, + 309 + ], + "blocks": [ + { + "bbox": [ + 325, + 279, + 528, + 309 + ], + "lines": [ + { + "bbox": [ + 325, + 279, + 528, + 309 + ], + "spans": [ + { + "bbox": [ + 325, + 279, + 528, + 309 + ], + "type": "image", + "image_path": "b16c2cfa127bb6e37c30ef90014f2a2975e21f2bc20134fad100e6736a26ac95.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 399, + 311, + 453, + 321 + ], + "lines": [ + { + "bbox": [ + 399, + 311, + 453, + 321 + ], + "spans": [ + { + "bbox": [ + 399, + 311, + 453, + 321 + ], + "type": "text", + "content": "(a) DisenIB [92]" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_caption" + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 325, + 322, + 528, + 351 + ], + "blocks": [ + { + "bbox": [ + 325, + 322, + 528, + 351 + ], + "lines": [ + { + "bbox": [ + 325, + 322, + 528, + 351 + ], + "spans": [ + { + "bbox": [ + 325, + 322, + 528, + 351 + ], + "type": "image", + "image_path": "7cd7d8b79060ff142f052b450592cafea7e4aa75e8afe5ca82499a6006a09535.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 396, + 353, + 456, + 361 + ], + "lines": [ + { + "bbox": [ + 396, + 353, + 456, + 361 + ], + "spans": [ + { + "bbox": [ + 396, + 353, + 456, + 361 + ], + "type": "text", + "content": "(b) AENIB (Ours)" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 305, + 369, + 545, + 392 + ], + "lines": [ + { + "bbox": [ + 305, + 369, + 545, + 392 + ], + "spans": [ + { + "bbox": [ + 305, + 369, + 545, + 392 + ], + "type": "text", + "content": "Figure 5. Comparison of CIFAR-10 reconstructions when the nuisance " + }, + { + "bbox": [ + 305, + 369, + 545, + 392 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_n" + }, + { + "bbox": [ + 305, + 369, + 545, + 392 + ], + "type": "text", + "content": " is swapped with those of another (random) sample." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 405, + 471, + 418 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 405, + 471, + 418 + ], + "spans": [ + { + "bbox": [ + 306, + 405, + 471, + 418 + ], + "type": "text", + "content": "4.4. Comparison with DisenIB [92]" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 423, + 547, + 519 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 423, + 547, + 519 + ], + "spans": [ + { + "bbox": [ + 304, + 423, + 547, + 519 + ], + "type": "text", + "content": "In this section, we provide a comparison of AENIB with a related work of DisenIB [92], as well as other variants of VIB, namely Nonlinear-VIB [65] and Squared-VIB [106]. Here, DisenIB is a variant of IB which also considers a nuisance modeling (based on FactorVAE [57]), in a purpose of supervised disentangling. Specifically, DisenIB considers two independent encoders " + }, + { + "bbox": [ + 304, + 423, + 547, + 519 + ], + "type": "inline_equation", + "content": "\\mathbf{z} \\coloneqq f(\\mathbf{x})" + }, + { + "bbox": [ + 304, + 423, + 547, + 519 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 423, + 547, + 519 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_n \\coloneqq g(\\mathbf{x})" + }, + { + "bbox": [ + 304, + 423, + 547, + 519 + ], + "type": "text", + "content": ", and aims to optimize the following objective:" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 347, + 528, + 545, + 547 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 347, + 528, + 545, + 547 + ], + "spans": [ + { + "bbox": [ + 347, + 528, + 545, + 547 + ], + "type": "interline_equation", + "content": "\\max _ {f, g} I (\\mathbf {z}; \\mathbf {y}) + I (\\mathbf {x}; \\mathbf {z} _ {n}, \\mathbf {y}) - I (\\mathbf {z} _ {n}; \\mathbf {z}). \\tag {11}", + "image_path": "47ab9b40b6580a606bf02dfb475ca967c88a56fc02294a443721ddd4b9427f2b.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 554, + 547, + 650 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 554, + 547, + 650 + ], + "spans": [ + { + "bbox": [ + 304, + 554, + 547, + 650 + ], + "type": "text", + "content": "Compared to our proposed NIB (4), the most important difference between the two objectives is in their \"reconstruction\" terms: i.e., " + }, + { + "bbox": [ + 304, + 554, + 547, + 650 + ], + "type": "inline_equation", + "content": "I(\\mathbf{x}; \\mathbf{z}_n, \\mathbf{y})" + }, + { + "bbox": [ + 304, + 554, + 547, + 650 + ], + "type": "text", + "content": " of (11) vs. " + }, + { + "bbox": [ + 304, + 554, + 547, + 650 + ], + "type": "inline_equation", + "content": "I(\\mathbf{x}; \\mathbf{z}, \\mathbf{z}_n)" + }, + { + "bbox": [ + 304, + 554, + 547, + 650 + ], + "type": "text", + "content": " of ours (4). Due to this difference, the DisenIB objective (11) cannot rule out the cases when " + }, + { + "bbox": [ + 304, + 554, + 547, + 650 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 304, + 554, + 547, + 650 + ], + "type": "text", + "content": " only encode few of \"shortcut\" signals in " + }, + { + "bbox": [ + 304, + 554, + 547, + 650 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 304, + 554, + 547, + 650 + ], + "type": "text", + "content": " (correlated to " + }, + { + "bbox": [ + 304, + 554, + 547, + 650 + ], + "type": "inline_equation", + "content": "\\mathbf{y}" + }, + { + "bbox": [ + 304, + 554, + 547, + 650 + ], + "type": "text", + "content": ") even at optimum, in contrast to our key motivation of NIB (4) that aims to let " + }, + { + "bbox": [ + 304, + 554, + 547, + 650 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 304, + 554, + 547, + 650 + ], + "type": "text", + "content": " to encode every " + }, + { + "bbox": [ + 304, + 554, + 547, + 650 + ], + "type": "inline_equation", + "content": "\\mathbf{y}" + }, + { + "bbox": [ + 304, + 554, + 547, + 650 + ], + "type": "text", + "content": "-correlated signal in " + }, + { + "bbox": [ + 304, + 554, + 547, + 650 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 304, + 554, + 547, + 650 + ], + "type": "text", + "content": " as much as possible." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 651, + 547, + 686 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 651, + 547, + 686 + ], + "spans": [ + { + "bbox": [ + 304, + 651, + 547, + 686 + ], + "type": "text", + "content": "We conduct experimental comparisons based on (a) our CIFAR-10 setups (Table 2), and (b) directly upon the official implementation6 of DisenIB on MNIST [69] (Table 9 of Ap" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 306, + 693, + 547, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 693, + 547, + 712 + ], + "spans": [ + { + "bbox": [ + 306, + 693, + 547, + 712 + ], + "type": "text", + "content": "https://github.com/PanZiqiAI/disentangled-information-bottleneck" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "16212" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 288, + 144 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 288, + 144 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 288, + 144 + ], + "type": "text", + "content": "pendix G). Here, we adopt and extend the benchmark to also cover MNIST-C [88], a corrupted version of the MNIST. For the latter comparison, we use a simple 4-layer convolutional network as the encoder architecture. We train every MNIST model here for 100K updates and follow the other training details from the CIFAR experiments (see Appendix B.1)." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 145, + 290, + 289 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 145, + 290, + 289 + ], + "spans": [ + { + "bbox": [ + 46, + 145, + 290, + 289 + ], + "type": "text", + "content": "Overall, we observe that the effectiveness of AENIB still applies to these benchmarks. This is in contrast to DisenIB, given that the effectiveness from DisenIB, e.g., its gain in AUROC on detecting Gaussian noise as an OOD (as conducted by [92]), could not be further generalized on CIFAR-10-C or MNIST-C, where AENIB still improves on as well as achieving the perfect score at the same OOD task. In Figure 5a, we further observe qualitatively that DisenIB often leaves highly semantic information in the nuisance " + }, + { + "bbox": [ + 46, + 145, + 290, + 289 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_n" + }, + { + "bbox": [ + 46, + 145, + 290, + 289 + ], + "type": "text", + "content": ": its reconstruction can be completely changed by swapping " + }, + { + "bbox": [ + 46, + 145, + 290, + 289 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_n" + }, + { + "bbox": [ + 46, + 145, + 290, + 289 + ], + "type": "text", + "content": " with those of another sample. This is essentially what AENIB addresses, as compared in Figure 5b." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 301, + 132, + 314 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 301, + 132, + 314 + ], + "spans": [ + { + "bbox": [ + 47, + 301, + 132, + 314 + ], + "type": "text", + "content": "5. Related work" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 326, + 288, + 517 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 326, + 288, + 517 + ], + "spans": [ + { + "bbox": [ + 46, + 326, + 288, + 517 + ], + "type": "text", + "content": "Out-of-distribution robustness. Since the seminal works [2, 90, 102] revealing the fragility of neural networks on out-of-distribution inputs, there have been significant attempts on identifying and improving various notions of robustness: e.g., detecting novel inputs [36,71,72,103], robustness against corruptions [27,35,39,119], and adversarial noise [5, 11, 17, 82], to name a few. Due to its fundamental challenges in making neural network to extrapolate, however, most of the advances in the robustness literature has been made under assuming priors closely related to the individual problems: e.g., an external data or data augmentations [37, 39], extra information from test-time samples [116], or specific knowledge in threat models [52, 112]. In this work, we aim to improve multiple notions of robustness without assuming such priors, through a new training scheme that extends the standard information bottleneck principle under noisy observations in test-time." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 521, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 521, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 521, + 288, + 714 + ], + "type": "text", + "content": "Hybrid generative-discriminative modeling. Our proposed method can be also viewed as a new approach of improving the robustness of discriminative models by incorporating a generative model, in the context that has been explored in recent works [31,72,99,123]. For example, [72,73] have incorporated a simple (but of low expressivity for generation) Gaussian mixture model into discriminative classifiers; a line of research on Joint Energy-based Models (JEM) [31, 123] assumes an energy-based model but with a notable training instability for the purpose. In this work, we propose an autoencoder-based model to avoid such training instability, and consider a design that the nuisance can succinctly supplement the given discriminative representation to be generative. We demonstrate that our approach can take the best of two worlds; it enables (a) stable training, while (b) attaining the high expressive generative performances." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 72, + 547, + 335 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 335 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 335 + ], + "type": "text", + "content": "Nuisance modeling. The idea of incorporating nuisances can be also considered in the context of invertible modeling, or as known as flow-based models [6, 23, 30, 59], where the nuisance can be defined by splitting the (full-information) encoding " + }, + { + "bbox": [ + 304, + 72, + 547, + 335 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 304, + 72, + 547, + 335 + ], + "type": "text", + "content": " for a given subspace of interest as explored by [4, 46]. Unlike such approaches, our autoencoder-based nuisance modeling does not focus on the \"full\" invertibility for arbitrary inputs, but rather on inverting the data manifold given, which enabled (a) a much flexible encoder design in practice, and (b) a more scalable generative modeling of nuisance " + }, + { + "bbox": [ + 304, + 72, + 547, + 335 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_n" + }, + { + "bbox": [ + 304, + 72, + 547, + 335 + ], + "type": "text", + "content": ", e.g., beyond an MNIST-scale as done by [46]. Other related works [48, 49, 92] do introduce an encoder for nuisance factors, but the notion of nuisance-ness has been focused in terms of the independence to " + }, + { + "bbox": [ + 304, + 72, + 547, + 335 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 304, + 72, + 547, + 335 + ], + "type": "text", + "content": " (for the purpose of feature disentangling), rather than to " + }, + { + "bbox": [ + 304, + 72, + 547, + 335 + ], + "type": "inline_equation", + "content": "\\mathbf{y}" + }, + { + "bbox": [ + 304, + 72, + 547, + 335 + ], + "type": "text", + "content": " as we focus in this work (for the purpose of robustness): e.g., DisenIB [92] applies FactorVAE [57] between semantic and nuisance embeddings to force their independence. Yet, the literature has been also questioned on whether the idea can be scaled-up beyond, e.g., MNIST, and our work does explore and establish a practical design with recent architectures and datasets addressing diverse modern security metrics." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 305, + 336, + 547, + 361 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 336, + 547, + 361 + ], + "spans": [ + { + "bbox": [ + 305, + 336, + 547, + 361 + ], + "type": "text", + "content": "We provide more extensive and detailed discussions on related works in Appendix F." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 373, + 379, + 385 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 373, + 379, + 385 + ], + "spans": [ + { + "bbox": [ + 306, + 373, + 379, + 385 + ], + "type": "text", + "content": "6. Conclusion" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 393, + 548, + 561 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 393, + 548, + 561 + ], + "spans": [ + { + "bbox": [ + 304, + 393, + 548, + 561 + ], + "type": "text", + "content": "We suggest that having a good nuisance model can be a tangible approach to induce a reliable representation. We develop a practical method of learning deep nuisance representation from data, and show its effectiveness to improve diverse reliability measures under a challenging setup of assuming no prior [105]. We believe our work can be a useful step towards better understanding of out-of-distribution generalization in deep learning. Although the current scope is on a particular design of autoencoder based models, our framework of nuisance-extended IB is not limited to it and future works could consider more diverse implementations. Ultimately, we aim to approximate a challenging form of adversarial training with a mutual information constraint, which we believe will be a promising direction to explore." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 573, + 404, + 586 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 573, + 404, + 586 + ], + "spans": [ + { + "bbox": [ + 306, + 573, + 404, + 586 + ], + "type": "text", + "content": "Acknowledgments" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 594, + 548, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 594, + 548, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 594, + 548, + 715 + ], + "type": "text", + "content": "This work was partly supported by Center for Applied Research in Artificial Intelligence (CARAI) grant funded by Defense Acquisition Program Administration (DAPA) and Agency for Defense Development (ADD) (UD190031RD), and by Institute of Information & communications Technology Planning & Evaluation (IITP) grant funded by the Korea government (MSIT) (No.2021-0-02068, Artificial Intelligence Innovation Hub; No.2019-0-00075, Artificial Intelligence Graduate School Program (KAIST)). We thank Subin Kim for the proofreading of our manuscript." + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "16213" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 53, + 92, + 288, + 713 + ], + "type": "list", + "angle": 0, + "index": 14, + "blocks": [ + { + "bbox": [ + 58, + 92, + 288, + 134 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 92, + 288, + 134 + ], + "spans": [ + { + "bbox": [ + 58, + 92, + 288, + 134 + ], + "type": "text", + "content": "[1] Alexander A Alemi, Ian Fischer, Joshua V Dillon, and Kevin Murphy. 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Info. Processing, School of CS, Fudan University \n $^{2}$ Shanghai Collaborative Innovation Center of Intelligent Visual Computing", + "bbox": [ + 173, + 179, + 795, + 234 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "zpwei21@m.fudan.edu.cn,{chenjingjing, zxwu, ygj}@fudan.edu.cn", + "bbox": [ + 210, + 236, + 751, + 252 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 286, + 313, + 301 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "In this paper, we propose a novel transfer-based targeted attack method that optimizes the adversarial perturbations without any extra training efforts for auxiliary networks on training data. Our new attack method is proposed based on the observation that highly universal adversarial perturbations tend to be more transferable for targeted attacks. Therefore, we propose to make the perturbation to be agnostic to different local regions within one image, which we called as self-universality. Instead of optimizing the perturbations on different images, optimizing on different regions to achieve self-universality can get rid of using extra data. Specifically, we introduce a feature similarity loss that encourages the learned perturbations to be universal by maximizing the feature similarity between adversarial perturbed global images and randomly cropped local regions. With the feature similarity loss, our method makes the features from adversarial perturbations to be more dominant than that of benign images, hence improving targeted transferability. We name the proposed attack method as Self-Universality (SU) attack. Extensive experiments demonstrate that SU can achieve high success rates for transfer-based targeted attacks. On ImageNet-compatible dataset, SU yields an improvement of $12\\%$ compared with existing state-of-the-art methods. Code is available at https://github.com/zhipeng-wei/Self-Universality.", + "bbox": [ + 76, + 318, + 472, + 710 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 742, + 209, + 758 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "It has been demonstrated in recent works that adversarial examples have the properties of transferability, which means an adversarial example generated on one white-box model can be used to fool other black-box models [3, 15, 27, 30, 33]. The existence of transferability brings convenience to performing black-box attacks, hence raising security concerns for deploying deep models in real-world", + "bbox": [ + 75, + 768, + 468, + 875 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "applications [14,22,28,35]. Consequently, considerable research attention has been spent on improving the transferability of adversarial examples for both non-targeted and targeted attacks [4, 29, 36].", + "bbox": [ + 500, + 287, + 890, + 348 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Compared to non-targeted attacks, transfer-based targeted attacks are inherently much more challenging since the goal is to fool deep models into predicting the specific target class. The major difficulty of transfer-based targeted attacks is caused by the fact that the gradient directions from a source image to a target class are usually different among different DNNs [16]. Hence, transfer-based attack methods designed for non-targeted attacks typically work poorly for targeted attacks. To increase the transferability, previous studies make efforts in aligning the feature of the generated adversarial example with the feature distributions of the targeted class, which are learned from class-specific auxiliary networks [7, 8] or generative adversarial networks [18]. However, these works assume that the training dataset is available and require extra training efforts for auxiliary networks, making it hard to apply in real-world scenarios.", + "bbox": [ + 496, + 352, + 893, + 608 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "This paper investigates the problem of transfer-based targeted attacks. Specifically, we propose a new method that improves the transferability of adversarial examples in a more efficient way, i.e., without any training efforts for auxiliary networks to learn the feature distributions of the targeted class. Our method is proposed based on the observation that more universal perturbations yield better attack success rates in targeted attacks. To this end, our goal is to enhance the universality of the generated adversarial perturbations, in order to improve its targeted transferability. Note that existing universal adversarial perturbation (UAP) attacks [17] require optimizing the perturbations on an abundant set of images to achieve universality, which is not applicable in our setting. To get rid of using extra data and make transfer-based targeted attacks as convenient as non-targeted attacks, we propose to make the perturbation to be agnostic to different local regions within one image, which we called as self-universality. Then our method optimizes the self-universality of adversarial pertur", + "bbox": [ + 496, + 613, + 893, + 901 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 810, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "† Corresponding author.", + "bbox": [ + 94, + 886, + 220, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "12281", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/9cf0e970e901a9cf9489e12017896756a0828c0afd4585fdef40b07e5c10abad.jpg", + "image_caption": [ + "Figure 1. Overview of the proposed SU attack. The random cropping is applied to the given benign image to generate the local image patch. After cropping, the local patch is resized to the shape of the benign image. Then both benign and local adversarial images with the shared perturbations are input to a surrogate white-box CNN model. Finally, the gradients obtained from the classification loss and the feature similarity loss are used to optimize perturbations." + ], + "image_footnote": [], + "bbox": [ + 158, + 88, + 803, + 275 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "bations instead. To be specific, in addition to classification loss, our Self-Universality (SU) attack method introduces a feature similarity loss that maximizes the feature similarity between adversarial perturbed global images and randomly cropped local regions to achieve self-universality. In this way, our method makes the features from adversarial perturbations to be more dominant than that of benign images, hence improving targeted transferability.", + "bbox": [ + 75, + 363, + 468, + 484 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Figure 1 gives an overview of the proposed Self-Universality (SU) attack. SU firstly applies random cropping on benign images to obtain local cropped patches. Then it resizes local patches to the same size with benign images. Consequently, global and local inputs with shared perturbations are input to the white-box model. Finally, adversarial perturbations are updated by minimizing the classification loss (e.g., Cross Entropy) between inputs and the target class and maximizing the feature similarity loss (e.g., Cosine Similarity) of adversarial intermediate features between local and global inputs. Benefiting from satisfying the prediction of the target class between global and local inputs and approximating adversarial intermediate features between the two, the proposed SU attack can generate perturbations with self-universality, thereby improving the cross-model targeted transferability. We briefly summarize our primary contributions as follows:", + "bbox": [ + 75, + 484, + 470, + 741 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- Through experiments, we find that highly universal adversarial perturbations tend to be more transferable for targeted attacks, which brings new insight into the design of transfer-based targeted attack methods.", + "- Based on the finding, we propose a novel Self-Universality (SU) attack method that enhances the universality of adversarial perturbations for better targeted transferability without the requirement for extra data.", + "- We conduct comprehensive experiments to demon" + ], + "bbox": [ + 94, + 747, + 468, + 900 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "strate that the proposed SU attack can significantly improve the cross-model targeted transferability of adversarial images. Notably, SU can be easily combined with other existing methods.", + "bbox": [ + 531, + 363, + 890, + 424 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 500, + 436, + 640, + 452 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In this section, we review existing works on non-targeted transferable attacks as well as targeted transferable attacks.", + "bbox": [ + 498, + 460, + 890, + 492 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.1. Non-targeted Transferable Attacks", + "text_level": 1, + "bbox": [ + 500, + 500, + 803, + 515 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Non-targeted transferable attacks are based on the Iterative-Fast Gradient Sign Method (I-FGSM) [11], which iteratively calculates the gradient of the classification loss with respect to the input and updates perturbations along the direction of maximizing the loss. The multiple-step update of I-FGSM leads to more wrong predictions of white-box models. However, the generated adversarial examples are hard to attack other black-box models. This phenomenon is called over-fitting to the white-box model [10]. Subsequently, several works perform data augmentation or advanced gradient calculation to overcome the over-fitting problem. Data augmentation creates various input patterns, which generate adversarial perturbations with a generic pattern. For the input images, Diverse Input (DI) [33] performs random resizing and padding, Scale-invariant method (SIM) [13] applies scale transformation, Admix [24] extends SIM by integrating images from other labels. However, these data augmentation approaches neglect to consider more diverse input patterns (e.g., random cropping in this paper), and focus on the loss-preserving transformation [13]. This is because the gradient direction fluctuates violently under more diverse input patterns without specified target classes in non-target attacks. Advanced gradient calculation pays attention to changing gradient calculation methods or designing a new loss function. For changing", + "bbox": [ + 496, + 523, + 890, + 902 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "12282", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "gradient calculation, the momentum term [3] and the Nesterov accelerated gradient [13] can be incorporated with I-FGSM to stabilize gradients. Translation-Invariant (TI) [4] smooths gradients through a predefined convolution kernel in order to mitigate the over-fitting problem. Skip Gradient Method (SGM) [31] modifies the path of gradient backpropagation by skipping residual modules. Variance Tuning [23] utilizes gradients from data points around previous data to avoid over-fitting. For designing a new loss function, Attention-guided Transfer Attack (ATA) [32] and Feature Importance-aware Attack (FIA) [26] disrupt important features that are likely to be utilized in other black-box models. ATA applies Grad-CAM [19] to represent attention weights of features. Different to ATA, FIA computes averaged gradients of features among various augmented inputs as attention weights. However, these new loss functions are restricted to global structures. In contrast, this paper calculates the feature similarity loss between global and local structures of images.", + "bbox": [ + 75, + 90, + 472, + 380 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "2.2. Targeted Transferable Attacks", + "text_level": 1, + "bbox": [ + 76, + 391, + 349, + 407 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The transfer-based targeted attacks are more challenging than the non-targeted attacks due to the requirement of fooling the model into predicting the specified target class. Previous efforts have been devoted into training class-specific auxiliary networks [7, 8] or generative adversarial networks (GANs) [18], in order to learn feature distributions of the targeted class. Feature Distribution Attack (FDA) [8] utilizes the intermediate features of the training dataset from the white-box model to train a binary classifier, which predicts the probability that the current feature belongs to the targeted class. Then, through learning class-wise and layer-wise feature distributions, FDA generates targeted transferable adversarial perturbations by maximizing the probability outputted from the trained binary classifier. Subsequently, $FDA^{N} + xent$ [7] incorporates the CE loss and multi-layer information with FDA, achieving better performance. Transferable targeted perturbations (TTP) [18] trains a generator to synthesize perturbations that seek to have similar features with targeted samples in the latent space of a pretrained discriminator. This series of FDA works and TTP improve the performance of targeted transferable attacks, but require additional training efforts for auxiliary networks on the training dataset.", + "bbox": [ + 75, + 415, + 472, + 763 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "To improve the efficiency of targeted transferable attacks, recent works pay more attention to iterative attacks based on I-FGSM. Activation Attack (AA) [9] replace the classification loss with a euclidean distance loss between features of adversarial and targeted images. However, AA depends on the selected examples of the targeted class and achieves low performance on the large resolution image dataset (e.g. ImageNet [2]). Different to AA, Po+Trip [12] utilizes Poincaré distance metric to solve the noise curing.", + "bbox": [ + 75, + 763, + 472, + 902 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "They also design a triplet loss for driving adversarial examples away from the original class. However, $\\mathrm{Po + Tri}$ evaluates the attack performance only on easy transfer scenarios, and also achieves poor performance on the targeted scenario used in the Logit attack [36]. Logit [36] attributes the poor performance of I-FGSM based methods to the restricted number of iterations. Thus, Logit enlarges the number of iterations for ensuring the convergence of attacks. In addition, to overcome the vanishing gradient caused by the large iterations, Logit utilizes gradients of the targeted logit output with respect to inputs to update perturbations. Different to them, our method leverages the global and local structures to generate adversarial examples with self-universality, hence improving targeted transferability. Note that the proposed SU attack can be easily combined with existing methods.", + "bbox": [ + 496, + 90, + 893, + 333 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Methodology", + "text_level": 1, + "bbox": [ + 500, + 343, + 635, + 362 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Preliminary", + "text_level": 1, + "bbox": [ + 500, + 368, + 630, + 386 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Let $f$ represent the white-box surrogate model, $v$ be the black-box victim model, $x \\in \\mathcal{X} \\subset \\mathbf{R}^{H \\times W \\times C}$ be the benign image with the ground-truth label $y \\in \\mathcal{Y} = \\{1, 2, \\dots, K\\}$ , where $f$ and $v$ are trained with the same training dataset, $H$ , $W$ , $C$ denote the number of height, width and channels respectively, and $K$ is the number of classes. We use $f(x), v(x)$ to be the prediction over the set of classes $\\mathcal{V}$ . Given a specified targeted class $y_{t}$ , the targeted transferable attacks aim to generate adversarial examples $x_{adv}$ from the white-box model $f$ that satisfy $v(x_{adv}) = y_{t}$ . Following previous works, we enforce a $L_{\\infty}$ -norm constraint on perturbations, which can be formulated as $||x_{adv} - x||_{\\infty} = ||\\delta||_{\\infty} \\leq \\epsilon$ , where $\\delta$ is the perturbation, $\\epsilon$ denotes a constant of the norm constraint. Given a classification loss $J$ (e.g. CE loss) of $f$ , the targeted attack of I-FGSM can be formulated as:", + "bbox": [ + 496, + 391, + 893, + 632 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\delta_ {0} = 0, g _ {0} = 0, \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 616, + 641, + 890, + 656 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\ng _ {i + 1} = \\nabla_ {\\delta} J (f (x + \\delta_ {i}), y _ {t}), \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 599, + 659, + 890, + 675 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\delta_ {i + 1} = \\delta_ {i} - \\alpha * \\operatorname {s i g n} \\left(g _ {i + 1}\\right), \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 599, + 678, + 890, + 694 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\delta_ {i + 1} = \\operatorname {C l i p} _ {x, \\epsilon} (\\delta_ {i + 1}), \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 599, + 696, + 890, + 713 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\delta_{i}, g_{i}$ denote the adversarial perturbation and the gradient of the $i$ -th iteration, $i = [0, \\dots, I - 1]$ and $I$ is the maximum number of iterations; $\\alpha$ is the step size; the function $Clip_{x,\\epsilon}(\\cdot)$ projects $\\delta$ to the vicinity of $x$ for satisfying the $L_{\\infty}$ -norm constraint. Specifically, I-FGSM first initializes $\\delta_0$ and $g_{0}$ as 0 (Eq.1). Then it calculates the gradients of the loss function with respect to the perturbation (Eq.2), and drives the prediction of $f$ on the adversarial example towards the targeted class by minimizing $J(f(x + \\delta_i), y_t)$ (Eq.3). Finally, it restricts the adversarial perturbation with the $L_{\\infty}$ -norm constraint (Eq.4). Eq.2, 3, 4 are performed alternately until the maximum iteration is reached. Through", + "bbox": [ + 496, + 719, + 893, + 902 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "12283", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/8ef664ac2e65f34a3891df8c8abc896cceb0a674acbb8dd55fe7a7db638f8dc7.jpg", + "image_caption": [ + "(a) Universal evaluation" + ], + "image_footnote": [], + "bbox": [ + 130, + 95, + 475, + 297 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/42c4654e040875b8b4ae0d74da068fdac2f3323f994f1f8fcce1f21cf1df7a67.jpg", + "image_caption": [ + "(b) Feature similarity analysis", + "Figure 2. (a) For each targeted perturbation generated by I-FGSM or DTMI, we calculate the number of successful targeted attacks caused by adding this perturbation to benign images other than the original optimized image. (b) We average the cosine similarity of intermediate features among different benign images or universal adversarial images that are generated by adding the same perturbation to these benign images." + ], + "image_footnote": [], + "bbox": [ + 488, + 117, + 838, + 296 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "this greedy update, I-FGSM is easily caught in local maxima and over-fitting to $f$ , which results in performing poorly for targeted attacks. Therefore, previous work [36] utilizes the combination of DI [33], TI [4] and MI [3] as the baseline, since it could achieve more stable performances with a large number of iteration compared to I-FGSM. For convenience, we abbreviate the name of this combination as DTMI. DTMI replaces Eq.2 with", + "bbox": [ + 75, + 402, + 468, + 523 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\ng _ {i + 1} = \\mu \\cdot g _ {i} + \\frac {W \\cdot \\nabla_ {\\delta} J (f (T (x + \\delta_ {i} , p)) , y _ {t})}{\\left| \\left| W \\cdot \\nabla_ {\\delta} J (f (T (x + \\delta_ {i} , p)), y _ {t}) \\right| \\right| _ {1}}, \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 89, + 527, + 468, + 564 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $T(x + \\delta_i, p)$ performs random resizing and padding with a probability $p$ in DI, $W$ is the pre-defined convolution kernel in TI, $\\mu$ is a decay factor in MI.", + "bbox": [ + 76, + 566, + 468, + 613 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. Universality of Targeted Perturbations", + "text_level": 1, + "bbox": [ + 76, + 619, + 410, + 636 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Transferable targeted attacks aim to generate cross-model perturbations that drive the prediction of different models towards predicting the same specified class. It requires perturbations generated from one white-box model are model-agnostic, i.e., universal to different models. A simple way to meet this requirement is to optimize perturbations on massive models. However, it may be impractical in the real world, because the number of white-box models is usually limited. In contrast, targeted universal adversarial perturbations (UAP) [17] lead to a specific prediction $y_{t}$ of DNNs for almost all images. [34] attributes this phenomenon to the dominant features produced by Targeted UAP. Specifically, let $\\delta_{u}$ denote targeted UAP, they conclude that the predictive logit vectors of $\\delta_{u}$ have a higher linear correlation with that of $x + \\delta_{u}$ , while the linear correlation between $x$ and $x + \\delta_{u}$ is low. It suggests that the features of $\\delta_{u}$ represent the feature distribution of the specific", + "bbox": [ + 75, + 643, + 470, + 902 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "targeted class and dominate the prediction of DNNs. Therefore, targeted UAP could transfer to attack other models trained on the same dataset, because these models share the similar feature distribution of the target class. In summary, universality may correlate to transferability in targeted attacks. Motivated by the above analysis, we delve into the divergence between perturbations crafted by I-FGSM and DTMI from the perspective of universality.", + "bbox": [ + 496, + 402, + 890, + 523 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "To further verify the findings in the above analysis, we conduct experiments to show the correlation between universality and targeted transferability. We optimize targeted perturbations on the ImageNet-compatible dataset (dataset details are in Section 4.1) by I-FGSM and DTMI using DenseNet121 as the white-box model. Here CE loss is utilized as classification loss. Given a set of benign images $\\Phi = \\{x^{1},\\dots,x^{m},\\dots,x^{M}\\}$ , we generate the perturbation for each image in the set. Denote $\\delta^m$ as the generated perturbation for $x^{m}$ . To evaluate the universality of $\\delta^m$ , we add $\\delta^m$ to all benign images other than $x^{m}$ , and calculate the number of successful targeted attacks on DenseNet121 by:", + "bbox": [ + 496, + 523, + 892, + 705 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\sum_ {j = 1, j \\neq m} ^ {M} \\left\\{ \\begin{array}{l l} 1, & \\text {i f} f \\left(x ^ {j} + \\delta^ {m}\\right) = y _ {t}, \\\\ 0, & \\text {o t h e r w i s e .} \\end{array} \\right. \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 575, + 713, + 890, + 757 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The number of successful targeted attacks is used as the metric to evaluate the universality of $\\delta^m$ . A higher number denotes better universality.", + "bbox": [ + 496, + 763, + 890, + 809 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Figure 2a shows the comparison of universality between each perturbation crafted by I-FGSM and DTMI. For better visualization, we sort perturbations in descending order based on their universality reported in I-FGSM. Notably, DTMI attains higher universality than I-FGSM for each perturbation. This is because, aided by the diverse input pat", + "bbox": [ + 496, + 810, + 890, + 901 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "12284", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "terns provided by DI, DTMI makes the perturbations to be universal to these input patterns. Since DTMI achieves better targeted transferability than I-FGSM [36], we can basically draw a conclusion that there is a relatively positive correlation between universality and targeted transferability.", + "bbox": [ + 75, + 90, + 468, + 181 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "To provide insights on how the targeted perturbation affects the image features, we compare the average cosine similarity of intermediate features between benign images and adversarial images that generated by adding one specific targeted perturbation to these benign images. Specifically, these benign images can be denoted by $\\Phi^m$ , which is the set of $x^j$ satisfying $f(x^{j} + \\delta^{m}) = y_{t}$ . Adversarial images can be denoted by $\\{x^{j} + \\delta^{m}\\}$ for $x_{j}\\in \\Phi^{m}$ . Figure 2b shows the changes in the feature similarity after adding the same perturbation $\\delta^m$ . It can be observed that after adding this perturbation, the image features become more similar. This is because the targeted perturbations drive features from different benign images towards the feature distribution of the target class. In other words, compared to benign images, targeted perturbations produce more dominant features. In addition, from Figure 2b, we can also find that compared to I-FGSM, targeted perturbations generated by DTMI make the image features more similar. Since DTMI achieves better targeted transferability than I-FGSM, the result basically indicates that perturbations with highly targeted transferability will produce more dominant features and enjoy higher universality. The above analysis suggests that adversarial examples with high universality tend to be more transferable in targeted attacks.", + "bbox": [ + 75, + 181, + 472, + 544 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.3. Self-Universality (SU) Attack", + "text_level": 1, + "bbox": [ + 76, + 554, + 338, + 570 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "To enhance the universality of adversarial perturbations for transferable targeted attacks, we propose the Self-Universality (SU) attack method. Instead of optimizing the perturbations on different images to achieve universality, our SU method optimizes the perturbation to be agnostic to different local regions within one image, which is called self-universality. In this way, our method is able to generate the universal perturbations without extra data. To achieve self-universality, our method generates perturbations by incorporating randomly cropped local regions within one image into the iterative attacks. To create local input patterns, we consider the random cropping, which crops images into a local image patch by the scale parameter $s = \\{s_l, s_{int}\\}$ . Where $s_l$ denotes the lower bound for the area of the random cropped images, and $s_{int}$ is the interval value between the lower and upper bounds, thus $s_l + s_{int}$ is the upper bound. After cropping images, we resize them to the same shape as benign images. Let $Loc(x, s)$ be the random cropping and the resizing operations*. In addition, we apply the same thresholding operation on all images in the image patches.", + "bbox": [ + 75, + 578, + 468, + 864 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Algorithm 1 DTMI-SU attack", + "text_level": 1, + "bbox": [ + 500, + 90, + 705, + 104 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Input: the classification loss function $J$ , white-box model $f$ , benign image $x$ , targeted class $y_{t}$ .", + "bbox": [ + 500, + 107, + 890, + 137 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Parameter: The perturbation budget $\\epsilon$ , iteration number I, step size $\\alpha$ , scale parameter $s = \\{s_l, s_{int}\\}$ , weighted parameter $\\lambda$ , and DTMI parameters $T(\\cdot, p)$ , $W$ , $\\mu$ .", + "bbox": [ + 498, + 138, + 890, + 183 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Output: The adversarial example $x_{adv}$ .", + "bbox": [ + 500, + 183, + 764, + 198 + ], + "page_idx": 4 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "1: Initialize $\\delta_0$ and $g_{0}$ by Eq.1", + "2: for $i = 0$ to $I - 1$ do", + "3: Random cropping and resizing: $\\hat{x} = Loc(x,s)$", + "4: $\\mathbf{DI}\\colon x^{\\prime} = T(x + \\delta_{i},p);\\hat{x}^{\\prime} = T(\\hat{x} +\\delta_{i},p)$", + "5: Calculate gradients: $g_{i+1} = \\nabla_{\\delta}(J(f(x'), y_t) + J(f(\\hat{x}', y_t) - \\lambda \\cdot CS(f_l(x'), f_l(\\hat{x})))$", + "6: $g_{i + 1} = \\mu \\cdot g_i + \\frac{W\\cdot g_{i + 1}}{||W\\cdot g_{i + 1}||_1}$", + "7: Update and Clip $\\delta_{i + 1}$ by Eq.3, 4", + "8: end for", + "9: return $x + \\delta_I$" + ], + "bbox": [ + 509, + 215, + 890, + 369 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "tion, motivated by Figure 2b, we propose a feature similarity loss to maximize the cosine similarity of intermediate features between the adversarial global and local inputs. Under this design, SU could generate perturbations with more dominant features. This loss can be formulated by $CS(f_{l}(x + \\delta_{i}),f_{l}(Loc(x,s) + \\delta_{i}))$ , where $f_{l}(\\cdot)$ means to extract features from the $l$ -th layer of the white-box model $f$ , the function $CS(\\cdot ,\\cdot)$ calculates cosine similarity score of features between adversarial global and local inputs. In summary, the proposed SU replaces Eq.2 with:", + "bbox": [ + 496, + 417, + 890, + 569 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} g _ {i + 1} = \\nabla_ {\\delta} \\left(J \\left(f \\left(x + \\delta_ {i}\\right), y _ {t}\\right) + J \\left(f \\left(L o c (x, s) + \\delta_ {i}\\right), y _ {t}\\right) \\right. \\\\ - \\lambda \\cdot C S \\left(f _ {l} \\left(x + \\delta_ {i}\\right), f _ {l} \\left(L o c (x, s) + \\delta_ {i}\\right)\\right)), \\tag {7} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 509, + 598, + 890, + 648 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\lambda$ weights the contribution of the classification loss and the proposed similarity loss.", + "bbox": [ + 498, + 679, + 890, + 710 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In this way, the perturbation optimization of SU can improve the self-universality of perturbations, and the maximization of the cosine similarity can align intermediate features between adversarial global and local inputs for improving the dominance of feature representation of perturbations. Following [36], we integrate SU with the baseline DTMI to further boost targeted transferability, which we named DTMI-SU. We show DTMI-SU in Algorithm 1. In the end, SU can generate adversarial perturbations with high dominant features by incorporating local images, as shown in Figure 2b, hence improving targeted transferability.", + "bbox": [ + 496, + 719, + 890, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_footnote", + "text": "*We perform it by RandomResizedCrop in torchvision and ignore the parameter of the random aspect ratio.", + "bbox": [ + 75, + 875, + 468, + 902 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "12285", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/fa3fb85ed7b92bbadbf5a679e4be0dbbd4d9d79b5bee4ef0b2d8c1afc3e76ea5.jpg", + "table_caption": [], + "table_footnote": [ + "Table 1. Intermediate layers for feature extraction. \"Block\" means the basic block in ResNet50 and DenseNet121. \"ReLU-k\" denotes the $k$ -th ReLU layer." + ], + "table_body": "
ModelLayer 1Layer 2Layer 3Layer 4
Res50Block-1Block-2Block-3Block-4
Den121Block-1Block-2Block-3Block-4
VGG16ReLU-4ReLU-7ReLU-10ReLU-13
Inc-v3Conv-4aMix-5dMix-6eMix-7c
", + "bbox": [ + 78, + 88, + 467, + 180 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4. Experiment", + "text_level": 1, + "bbox": [ + 76, + 251, + 200, + 268 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.1. Experimental Settings", + "text_level": 1, + "bbox": [ + 76, + 277, + 282, + 292 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.1.1 Dataset and models", + "text_level": 1, + "bbox": [ + 76, + 301, + 267, + 316 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Following [36], we attack four diverse classifier architectures: ResNet50 [5], DenseNet121 [6], VGGNet16 [20], and Inception-v3 [21] with the ImageNet-compatible dataset†. The architectures of these four models are more diverse and challenging than the ones used in [12]. The used dataset is first introduced by the NIPS 2017 Competition on Adversarial Attacks and Defenses. It consists of 1,000 images and corresponding labels for targeted attacks.", + "bbox": [ + 75, + 327, + 470, + 450 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.1.2 Attack setting", + "text_level": 1, + "bbox": [ + 76, + 472, + 230, + 487 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We use the Targeted Attack Success Rate (TASR) to evaluate the targeted attack on one black-box model, which is the rate of adversarial examples that are successfully classified as the targeted class by the black-box model. Hence, the methods with higher TASR can generate adversarial examples with high targeted transferability. Following [36], we set the maximum perturbation as $\\epsilon = 16$ , the step size as $\\alpha = 2$ , the maximum number of iterations as $I = 300$ . For each model, we select one layer $1/2/3/4$ from shallow to deep layers (as shown in Table 1) to extract features.", + "bbox": [ + 75, + 497, + 468, + 650 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.2. Performance Comparison", + "text_level": 1, + "bbox": [ + 76, + 660, + 312, + 678 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Following [36], we adopt the combination of DI, TI and MI (DTMI) as the baseline. The parameters of DTMI are the same as [36]. We then integrate the proposed SU method with several baselines: CE loss with DTMI (DTMI-CE) and Logit loss [36] with DTMI (DTMI-Logit). We exclude $\\mathrm{Po + }$ Trip [12] in the comparison because it has a worse performance than the Logit loss.", + "bbox": [ + 75, + 684, + 468, + 790 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "For SU, the weighted parameter $\\lambda$ is set as $10^{-3}$ , the scale parameters $s$ is set as $(0.1, 0)$ , and the layer 3 is used to extract features. These parameters will be discussed in Section 4.3.", + "bbox": [ + 75, + 791, + 468, + 852 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/7a90ea67337207534311eea373b1e752fe97a8015bb7fb9a9ea8487de9c163c9.jpg", + "image_caption": [ + "(a) TASR $(\\%)$" + ], + "image_footnote": [], + "bbox": [ + 504, + 92, + 689, + 180 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/47ae710ec8cb6f7afb578477f572d5681f057e3c2e137f257abb3e42278d4403.jpg", + "image_caption": [ + "(b) Gradient norm", + "Figure 3. (a) TASR $(\\%)$ of attacking ResNet50 from DenseNet121. (b) Gradient norm of performing DTMI-CE and DTMI-CE-SU when using DenseNet121 as the surrogate model." + ], + "image_footnote": [], + "bbox": [ + 696, + 90, + 883, + 180 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Single-model transferable attacks. We conduct single-model transferable experiments by selecting one model as the white-box model to attack the other three black-box models. Table 2 shows the results. We have the following observations. First, the proposed SU method achieves higher TASR than DTMI-CE and DTMI-Logit by a large margin in almost all cases. It suggests that the proposed SU is suitable for different classification loss functions. Second, the attacks using ResNet50 and DenseNet121 as white-box models outperform that using VGGNet16 and Inception-v3, which is also observed in [8, 9, 36]. It may be caused by the skip connection structure, which mitigates the gradient vanishing/exploding problem in a large number of iterations and emphasizes features of lower layers by backpropagating gradients on both residual modules and skip connections. These features tend to transfer among different models [30, 31]. Third, SU performs worse than other methods when using a small number of iterations (e.g. $I = 20$ ). This is because SU requires a large iteration for convergence, illustrated in Figure 3a. Especially for the CE loss, DTMI achieves the convergence at $I = 20$ , while DTMI-SU steadily improves performance as the iteration increases, since SU can eliminate the vanishing gradient caused by CE, as shown in 3b. We also perform experiments with a smaller perturbation budget $\\epsilon = 8$ , which are shown in Appendix. It follows a similar trend as Table 2. These results jointly demonstrate the effectiveness of SU. In addition, we visualize adversarial examples in Appendix. These adversarial examples, which humans can correctly understand, lead to the specific target prediction of DNNs.", + "bbox": [ + 496, + 277, + 892, + 731 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Ensemble model transferable attacks. As mentioned above, the targeted perturbations generated from a set of models are more model-agnostic, and thus can obtain high cross-model transferability. Hence, we select one black-box model to attack, and use the other three models as white-box models. Following [36], we simply assign equal weights to all white-box models. Results are shown in Table 3. As can be seen, compared to single-model transferable attacks, ensemble attacks achieve much better performance. It demonstrates that the model-agnostic perturbations can easily transfer to attack other models. In addition, we also show that the model-agnostic perturbations can easily transfer to attack other models.", + "bbox": [ + 496, + 734, + 893, + 902 + ], + "page_idx": 5 + }, + { + "type": "page_footnote", + "text": "$\\dagger$ https://github.com/cleverhans-lab/cleverhans/tree/master/cleverhans_v3.1.0/examples/nips17_adversarial_competition/dataset", + "bbox": [ + 76, + 862, + 468, + 902 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "12286", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/13dc6379d6546aed6a646b971d2dd217b77b7594dc337d16065eebeff196e581.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
AttackWhite-box Model: Res50White-box Model: Dense121
→ Dense121→ VGG16→ Inc-v3→ Res50→ VGG16→ Inc-v3
DTMI-CE27.1/39.7/44.318.9/27.6/29.42.2/3.4/4.112.9/16.7/18.48.1/10.6/10.61.7/2.2/3.2
DTMI-CE-SU6.2/27.8/54.23.0/20.2/45.40.2/4.5/10.12.6/17.6/39.41.4/12.6/32.40.2/4.8/10.8
DTMI-Logit30.4/64.4/71.822.6/55.1/62.82.7/7.1/9.616.1/39.3/43.713.5/33.0/38.12.1/7.1/7.7
DTMI-Logit-SU23.8/63.9/75.516.6/55.9/66.92.0/8.3/11.612.8/42.9/50.29.3/37.2/45.21.8/7.5/10.4
AttackWhite-box Model: VGG16White-box Model: Inc-v3
→ Res50→ Dense121→ Inc-v3→ Res50→ Dense121→ VGG16
DTMI-CE0.6/0.6/0.50.4/0.3/0.40.0/0.0/0.00.8/1.8/2.40.8/2.4/2.90.7/1.3/1.8
DTMI-CE-SU0.2/2.1/2.80.2/2.1/3.20.0/0.2/0.20.4/1.2/2.90.2/1.4/5.00.1/0.8/2.5
DTMI-Logit3.0/9.6/11.33.2/12.0/13.70.1/0.6/0.70.9/2.0/2.81.1/3.3/5.00.6/2.2/3.9
DTMI-Logit-SU3.4/11.7/13.93.3/13.8/16.10.2/0.9/0.80.6/2.3/4.30.5/3.8/7.40.3/1.9/4.4
", + "bbox": [ + 89, + 88, + 877, + 323 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/68eb8c9970a0824396ff48c69e9b4fc49658ee924ed384d8bb2a666117d99104.jpg", + "table_caption": [ + "Table 2. TASR (%) of all black-box models under four attack scenarios using ResNet50, DenseNet121, VGGNet16 and Inception-v3 as white-box models, respectively. We conduct these experiments three times and report average TASR with 20/100/300 iterations, the standard deviation is shown in Appendix. The best results with 300 iterations are in bold." + ], + "table_footnote": [], + "table_body": "
Ensemble AttackBlack-box ModelAverage
Res50Dense121VGG16Inc-v3
DTMI-CE31.155.251.616.138.5
DTMI-CE-SU55.765.068.229.354.5
DTMI-Logit70.282.382.229.165.9
DTMI-Logit-SU75.382.984.234.569.2
", + "bbox": [ + 238, + 380, + 727, + 500 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/e93932439188010d1e309264c2531b8da9000260eefd7400c629ff13ed58911c.jpg", + "table_caption": [ + "Table 3. TASR (%) of one black-box model in ensemble transfer attacks. TASR with 300 iterations is reported. The best results are in bold." + ], + "table_footnote": [], + "table_body": "
AttackDense121VGG16Inc-v3
DTMI-SI/+SU85.7/87.269.0/71.835.8/41.6
DTMI-Adm./+SU89.1/89.475.7/79.142.1/47.1
DTMI-EMI/+SU71.0/79.064.6/82.45.0/14.8
ODI-TMI/+SU89.9/92.881.0/91.766.9/72.0
", + "bbox": [ + 78, + 541, + 468, + 633 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 4. Average TASR (\\%) of different combinational attacks. We use ResNet50 as the white-box model, and report the results with 300 iterations. Logit is used here.", + "bbox": [ + 75, + 636, + 468, + 680 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "tion, the proposed SU further boosts cross-model targeted transferability. However, the improvement of TASR gained from DTMI-Logit-SU is not so significant. This can be explained by the fact that the loss function value of Logit increases infinitely, while the value of cosine similarity is bounded. Thus, it impedes the maximization of feature similarity. Nevertheless, methods that are combined with SU can promote targeted transferability in all cases.", + "bbox": [ + 75, + 714, + 468, + 835 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Combination with existing methods To further boost transferable targeted attacks, we combine our method with other attacks, including SI [13], Admix [24], EMI [25], and ODI [1]. Table 4 reports the results. The attack methods", + "bbox": [ + 75, + 839, + 470, + 901 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "combined with the proposed SU achieve better performance than other attack methods. In particular, compared to ODI, SU achieves an average TASR gain of $6\\%$ . Such remarkable improvements demonstrate that the proposed SU can be easily combined with other existing methods and further improve targeted transferability. In terms of computational efficiency, SU only requires two forward propagations for global and local inputs per iteration, which is lower than SI, Admix, and EMI (which require $\\geq 5$ forward propagations). To compare SU with ODI, we report the computation time (sec) required to generate an adversarial example. DTMI-SU and DTMI-ODI require 2.3 and 2.6 sec, respectively. It indicates that SU requires less computation time than previous methods.", + "bbox": [ + 496, + 544, + 893, + 755 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.3. Ablation Studies", + "text_level": 1, + "bbox": [ + 498, + 768, + 663, + 784 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "In this section, we utilize CE as the classification loss to investigate the effects of each component and various hyperparameters. In addition, we investigate the effects of different regions of random cropping.", + "bbox": [ + 496, + 792, + 892, + 854 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Effect of components. The evaluations are conducted on four attack scenarios using ResNet50, DenseNet121, VGGNet16 and Inceptionv3 as white-box models, respec", + "bbox": [ + 496, + 854, + 893, + 902 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "12287", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/f8fedb410fe06dd0859d8db908ccdeebeb14134d19f8af455c2bc5121fd8d9eb.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
LocalFeature Similarity LossAveraged TASR
--9.8
✓-10.9
✓✓15.6
", + "bbox": [ + 91, + 88, + 450, + 165 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/61a8dd0de1876c46d955e4dbd6720b68feb556dde66ee5fe5befd24994b6cea2.jpg", + "image_caption": [ + "(a) Scale parameter $(s_l,s_{int})$" + ], + "image_footnote": [], + "bbox": [ + 83, + 272, + 269, + 364 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/9c1caf5f98bef99e8fc29b5e2b255499dc038588057b39cea0b14ce66ddf1a07.jpg", + "image_caption": [ + "(b) Layer $l$ and weight $\\lambda$", + "Figure 4. Average TASR with different values of hyper-parameters in the attack. The classification loss is set as CE." + ], + "image_footnote": [], + "bbox": [ + 274, + 272, + 457, + 363 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "tively. We split SU into the local inputs and the feature similarity loss. Table 5 shows the results of different component combinations. As can be seen, both components improve targeted transferability. And the improvement of TASR gained from feature similarity loss is more significant. It demonstrates the effectiveness of each component in the proposed SU attack.", + "bbox": [ + 75, + 444, + 467, + 549 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Effect of hyper-parameters. The evaluations are conducted by using densenet121 as the white-box model and averaging TASR among black-box models. The scale parameter $s$ determines the area of cropped images. When the area is large, SU overlooks the local structure of inputs. Thus, it is vital to study optimal values of $s$ . We fix the weighted parameter $\\lambda = 1.0$ , and the feature extraction layer as layer 3 due to the high transferability of middle layers [30]. Figure 4a shows the results with $s_l \\in [0.1, 0.3, 0.5, 0.7]$ and $s_{int} \\in [0.0, 0.1, 0.2, 0.3]$ . We observe that the smaller the area of cropped images, the higher the performance. It suggests that local image patches that differ significantly from the original images provide more diverse input patterns for perturbation optimization and contribute to targeted transferability. Besides, when $s_l = 0.1$ and $s_{int} = 0.1$ , the optimal result is reached. However, the area relative to the original image may fluctuate within [0.1, 0.2]. To keep it stable, we use the parameters $s = (0.1, 0.0)$ to conduct subsequent experiments. Figure 4b shows the results of performing attacks on different layers and $\\lambda$ . Extracting features from layer 3 is better than other layers. This is because the features captured by shallow layers represent the low-level patterns (such as edges),", + "bbox": [ + 75, + 551, + 467, + 901 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/4c4f6fa68b7079a3d9625d0658a1ff0df2ed65452f386ab6c6193fbeab91ee95.jpg", + "table_caption": [ + "Table 5. Average TASR (\\%) of black-box models for our proposed method with different component combinations. The classification loss is set as CE. $\\checkmark$ indicates that the component is used while $-$ indicates that it is not used. TASR is averaged among four attack scenarios using ResNet50, DenseNet121, VGGNet16 and Inceptionv3 as white-box models, respectively." + ], + "table_footnote": [], + "table_body": "
RegionRes50VGG16Inc-v3
Center33.029.29.9
Corner33.630.910.8
Whole39.432.410.8
Uniform3.11.70.4
", + "bbox": [ + 557, + 88, + 831, + 186 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 6. TASR (\\%) of DTMI-CE-SU with different distributions of local images. The top three rows show different regions of random cropping. The last row denotes the uniform distribution $\\mathcal{U}(0,1)$ of local images.", + "bbox": [ + 498, + 188, + 890, + 244 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "while the deepest layer contains more semantic information hence is more related to the classification task of the white-box model [30]. For the weighted parameter $\\lambda$ , we set $\\lambda \\in [10^{-4}, 10^{-3}, 10^{-2}, 10^{-1}, 10^{0}]$ . When $\\lambda = 10^{-3}$ , SU achieves the best result.", + "bbox": [ + 498, + 277, + 890, + 353 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Effect of different regions. The regions of random cropping determine the distribution of local images. The center may be more related to the object of the image than the corner. Therefore, we conduct experiments on the center, the corner and the whole regions. We also compare the uniform distribution $\\mathcal{U}(0,1)$ of local images. As shown in Table 6, there is no significant performance difference between the center and the corner. The reason is that SU concentrates on the target class regardless of the object related to the original class. Therefore, directly providing more local input patterns within one image leads to better performance in SU. The whole region indeed achieves the best performance. Moreover, the uniform distribution makes it difficult to converge, resulting in the worst performance.", + "bbox": [ + 496, + 357, + 890, + 569 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 592, + 617, + 607 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this paper, we provide new insight into transfer-based targeted attacks: more universal perturbations yield better transferability. Based on this observation, we propose the Self-University (SU) attack, which optimizes perturbations on the global image and more diverse local images, and aligns intermediate features between them. In this way, SU can make perturbations to be agnostic to different image regions, resulting in high self-transferability. We conduct extensive experiments to show that SU can improve targeted transferability regardless of the single-model attack or ensemble-based attack.", + "bbox": [ + 496, + 621, + 890, + 786 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "6. Acknowledgments", + "text_level": 1, + "bbox": [ + 500, + 811, + 678, + 828 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "This project was supported by National Key R&D Program of China (No. 2020AAA0140001), NSFC (No. 62072116), and Science and Technology Commission of Shanghai Municipality (No. 21JC1400600).", + "bbox": [ + 498, + 839, + 890, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "12288", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Junyoung Byun, Seungju Cho, Myung-Joon Kwon, Hee-Seon Kim, and Changick Kim. Improving the transferability of targeted adversarial examples through object-based diverse input. 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Advances in Neural Information Processing Systems, 34:6115-6128, 2021. 1, 3, 4, 5, 6" + ], + "bbox": [ + 78, + 90, + 468, + 738 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "12290", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/Enhancing the Self-Universality for Transferable Targeted Attacks/4a2df1aa-152c-427f-bd2e-28ba0bd1cd5f_model.json b/2023/Enhancing the Self-Universality for Transferable Targeted Attacks/4a2df1aa-152c-427f-bd2e-28ba0bd1cd5f_model.json new file mode 100644 index 0000000000000000000000000000000000000000..3e3d0b0c294f39aeaadc2ae7db2907bb41cea8b9 --- /dev/null +++ b/2023/Enhancing the Self-Universality for Transferable Targeted Attacks/4a2df1aa-152c-427f-bd2e-28ba0bd1cd5f_model.json @@ -0,0 +1,1958 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.001, + 0.812, + 0.047 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.15, + 0.131, + 0.823, + 0.154 + ], + "angle": 0, + "content": "Enhancing the Self-Universality for Transferable Targeted Attacks" + }, + { + "type": "text", + "bbox": [ + 0.174, + 0.18, + 0.796, + 0.236 + ], + "angle": 0, + "content": "Zhipeng Wei\\(^{1,2}\\), Jingjing Chen\\(^{1,2\\dagger}\\), Zuxuan Wu\\(^{1,2}\\), Yu-Gang Jiang\\(^{1,2}\\) \n\\(^{1}\\)Shanghai Key Lab of Intell. Info. Processing, School of CS, Fudan University \n\\(^{2}\\)Shanghai Collaborative Innovation Center of Intelligent Visual Computing" + }, + { + "type": "text", + "bbox": [ + 0.212, + 0.237, + 0.753, + 0.253 + ], + "angle": 0, + "content": "zpwei21@m.fudan.edu.cn,{chenjingjing, zxwu, ygj}@fudan.edu.cn" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.287, + 0.314, + 0.303 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.319, + 0.473, + 0.712 + ], + "angle": 0, + "content": "In this paper, we propose a novel transfer-based targeted attack method that optimizes the adversarial perturbations without any extra training efforts for auxiliary networks on training data. Our new attack method is proposed based on the observation that highly universal adversarial perturbations tend to be more transferable for targeted attacks. Therefore, we propose to make the perturbation to be agnostic to different local regions within one image, which we called as self-universality. Instead of optimizing the perturbations on different images, optimizing on different regions to achieve self-universality can get rid of using extra data. Specifically, we introduce a feature similarity loss that encourages the learned perturbations to be universal by maximizing the feature similarity between adversarial perturbed global images and randomly cropped local regions. With the feature similarity loss, our method makes the features from adversarial perturbations to be more dominant than that of benign images, hence improving targeted transferability. We name the proposed attack method as Self-Universality (SU) attack. Extensive experiments demonstrate that SU can achieve high success rates for transfer-based targeted attacks. On ImageNet-compatible dataset, SU yields an improvement of \\(12\\%\\) compared with existing state-of-the-art methods. Code is available at https://github.com/zhipeng-wei/Self-Universality." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.743, + 0.21, + 0.759 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.769, + 0.47, + 0.876 + ], + "angle": 0, + "content": "It has been demonstrated in recent works that adversarial examples have the properties of transferability, which means an adversarial example generated on one white-box model can be used to fool other black-box models [3, 15, 27, 30, 33]. The existence of transferability brings convenience to performing black-box attacks, hence raising security concerns for deploying deep models in real-world" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.288, + 0.892, + 0.349 + ], + "angle": 0, + "content": "applications [14,22,28,35]. Consequently, considerable research attention has been spent on improving the transferability of adversarial examples for both non-targeted and targeted attacks [4, 29, 36]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.353, + 0.895, + 0.609 + ], + "angle": 0, + "content": "Compared to non-targeted attacks, transfer-based targeted attacks are inherently much more challenging since the goal is to fool deep models into predicting the specific target class. The major difficulty of transfer-based targeted attacks is caused by the fact that the gradient directions from a source image to a target class are usually different among different DNNs [16]. Hence, transfer-based attack methods designed for non-targeted attacks typically work poorly for targeted attacks. To increase the transferability, previous studies make efforts in aligning the feature of the generated adversarial example with the feature distributions of the targeted class, which are learned from class-specific auxiliary networks [7, 8] or generative adversarial networks [18]. However, these works assume that the training dataset is available and require extra training efforts for auxiliary networks, making it hard to apply in real-world scenarios." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.614, + 0.895, + 0.902 + ], + "angle": 0, + "content": "This paper investigates the problem of transfer-based targeted attacks. Specifically, we propose a new method that improves the transferability of adversarial examples in a more efficient way, i.e., without any training efforts for auxiliary networks to learn the feature distributions of the targeted class. Our method is proposed based on the observation that more universal perturbations yield better attack success rates in targeted attacks. To this end, our goal is to enhance the universality of the generated adversarial perturbations, in order to improve its targeted transferability. Note that existing universal adversarial perturbation (UAP) attacks [17] require optimizing the perturbations on an abundant set of images to achieve universality, which is not applicable in our setting. To get rid of using extra data and make transfer-based targeted attacks as convenient as non-targeted attacks, we propose to make the perturbation to be agnostic to different local regions within one image, which we called as self-universality. Then our method optimizes the self-universality of adversarial pertur" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.887, + 0.222, + 0.9 + ], + "angle": 0, + "content": "† Corresponding author." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "12281" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.16, + 0.089, + 0.805, + 0.276 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.281, + 0.895, + 0.339 + ], + "angle": 0, + "content": "Figure 1. Overview of the proposed SU attack. The random cropping is applied to the given benign image to generate the local image patch. After cropping, the local patch is resized to the shape of the benign image. Then both benign and local adversarial images with the shared perturbations are input to a surrogate white-box CNN model. Finally, the gradients obtained from the classification loss and the feature similarity loss are used to optimize perturbations." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.364, + 0.47, + 0.485 + ], + "angle": 0, + "content": "bations instead. To be specific, in addition to classification loss, our Self-Universality (SU) attack method introduces a feature similarity loss that maximizes the feature similarity between adversarial perturbed global images and randomly cropped local regions to achieve self-universality. In this way, our method makes the features from adversarial perturbations to be more dominant than that of benign images, hence improving targeted transferability." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.485, + 0.471, + 0.742 + ], + "angle": 0, + "content": "Figure 1 gives an overview of the proposed Self-Universality (SU) attack. SU firstly applies random cropping on benign images to obtain local cropped patches. Then it resizes local patches to the same size with benign images. Consequently, global and local inputs with shared perturbations are input to the white-box model. Finally, adversarial perturbations are updated by minimizing the classification loss (e.g., Cross Entropy) between inputs and the target class and maximizing the feature similarity loss (e.g., Cosine Similarity) of adversarial intermediate features between local and global inputs. Benefiting from satisfying the prediction of the target class between global and local inputs and approximating adversarial intermediate features between the two, the proposed SU attack can generate perturbations with self-universality, thereby improving the cross-model targeted transferability. We briefly summarize our primary contributions as follows:" + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.748, + 0.47, + 0.809 + ], + "angle": 0, + "content": "- Through experiments, we find that highly universal adversarial perturbations tend to be more transferable for targeted attacks, which brings new insight into the design of transfer-based targeted attack methods." + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.817, + 0.469, + 0.877 + ], + "angle": 0, + "content": "- Based on the finding, we propose a novel Self-Universality (SU) attack method that enhances the universality of adversarial perturbations for better targeted transferability without the requirement for extra data." + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.886, + 0.469, + 0.901 + ], + "angle": 0, + "content": "- We conduct comprehensive experiments to demon" + }, + { + "type": "list", + "bbox": [ + 0.096, + 0.748, + 0.47, + 0.901 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.532, + 0.364, + 0.892, + 0.425 + ], + "angle": 0, + "content": "strate that the proposed SU attack can significantly improve the cross-model targeted transferability of adversarial images. Notably, SU can be easily combined with other existing methods." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.437, + 0.642, + 0.453 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.462, + 0.892, + 0.493 + ], + "angle": 0, + "content": "In this section, we review existing works on non-targeted transferable attacks as well as targeted transferable attacks." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.5, + 0.805, + 0.516 + ], + "angle": 0, + "content": "2.1. Non-targeted Transferable Attacks" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.524, + 0.892, + 0.903 + ], + "angle": 0, + "content": "Non-targeted transferable attacks are based on the Iterative-Fast Gradient Sign Method (I-FGSM) [11], which iteratively calculates the gradient of the classification loss with respect to the input and updates perturbations along the direction of maximizing the loss. The multiple-step update of I-FGSM leads to more wrong predictions of white-box models. However, the generated adversarial examples are hard to attack other black-box models. This phenomenon is called over-fitting to the white-box model [10]. Subsequently, several works perform data augmentation or advanced gradient calculation to overcome the over-fitting problem. Data augmentation creates various input patterns, which generate adversarial perturbations with a generic pattern. For the input images, Diverse Input (DI) [33] performs random resizing and padding, Scale-invariant method (SIM) [13] applies scale transformation, Admix [24] extends SIM by integrating images from other labels. However, these data augmentation approaches neglect to consider more diverse input patterns (e.g., random cropping in this paper), and focus on the loss-preserving transformation [13]. This is because the gradient direction fluctuates violently under more diverse input patterns without specified target classes in non-target attacks. Advanced gradient calculation pays attention to changing gradient calculation methods or designing a new loss function. For changing" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "12282" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.091, + 0.473, + 0.381 + ], + "angle": 0, + "content": "gradient calculation, the momentum term [3] and the Nesterov accelerated gradient [13] can be incorporated with I-FGSM to stabilize gradients. Translation-Invariant (TI) [4] smooths gradients through a predefined convolution kernel in order to mitigate the over-fitting problem. Skip Gradient Method (SGM) [31] modifies the path of gradient backpropagation by skipping residual modules. Variance Tuning [23] utilizes gradients from data points around previous data to avoid over-fitting. For designing a new loss function, Attention-guided Transfer Attack (ATA) [32] and Feature Importance-aware Attack (FIA) [26] disrupt important features that are likely to be utilized in other black-box models. ATA applies Grad-CAM [19] to represent attention weights of features. Different to ATA, FIA computes averaged gradients of features among various augmented inputs as attention weights. However, these new loss functions are restricted to global structures. In contrast, this paper calculates the feature similarity loss between global and local structures of images." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.392, + 0.35, + 0.408 + ], + "angle": 0, + "content": "2.2. Targeted Transferable Attacks" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.416, + 0.473, + 0.765 + ], + "angle": 0, + "content": "The transfer-based targeted attacks are more challenging than the non-targeted attacks due to the requirement of fooling the model into predicting the specified target class. Previous efforts have been devoted into training class-specific auxiliary networks [7, 8] or generative adversarial networks (GANs) [18], in order to learn feature distributions of the targeted class. Feature Distribution Attack (FDA) [8] utilizes the intermediate features of the training dataset from the white-box model to train a binary classifier, which predicts the probability that the current feature belongs to the targeted class. Then, through learning class-wise and layer-wise feature distributions, FDA generates targeted transferable adversarial perturbations by maximizing the probability outputted from the trained binary classifier. Subsequently, \\( FDA^{N} + xent \\) [7] incorporates the CE loss and multi-layer information with FDA, achieving better performance. Transferable targeted perturbations (TTP) [18] trains a generator to synthesize perturbations that seek to have similar features with targeted samples in the latent space of a pretrained discriminator. This series of FDA works and TTP improve the performance of targeted transferable attacks, but require additional training efforts for auxiliary networks on the training dataset." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.765, + 0.473, + 0.904 + ], + "angle": 0, + "content": "To improve the efficiency of targeted transferable attacks, recent works pay more attention to iterative attacks based on I-FGSM. Activation Attack (AA) [9] replace the classification loss with a euclidean distance loss between features of adversarial and targeted images. However, AA depends on the selected examples of the targeted class and achieves low performance on the large resolution image dataset (e.g. ImageNet [2]). Different to AA, Po+Trip [12] utilizes Poincaré distance metric to solve the noise curing." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.091, + 0.895, + 0.334 + ], + "angle": 0, + "content": "They also design a triplet loss for driving adversarial examples away from the original class. However, \\(\\mathrm{Po + Tri}\\) evaluates the attack performance only on easy transfer scenarios, and also achieves poor performance on the targeted scenario used in the Logit attack [36]. Logit [36] attributes the poor performance of I-FGSM based methods to the restricted number of iterations. Thus, Logit enlarges the number of iterations for ensuring the convergence of attacks. In addition, to overcome the vanishing gradient caused by the large iterations, Logit utilizes gradients of the targeted logit output with respect to inputs to update perturbations. Different to them, our method leverages the global and local structures to generate adversarial examples with self-universality, hence improving targeted transferability. Note that the proposed SU attack can be easily combined with existing methods." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.344, + 0.636, + 0.363 + ], + "angle": 0, + "content": "3. Methodology" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.369, + 0.631, + 0.387 + ], + "angle": 0, + "content": "3.1. Preliminary" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.392, + 0.895, + 0.633 + ], + "angle": 0, + "content": "Let \\( f \\) represent the white-box surrogate model, \\( v \\) be the black-box victim model, \\( x \\in \\mathcal{X} \\subset \\mathbf{R}^{H \\times W \\times C} \\) be the benign image with the ground-truth label \\( y \\in \\mathcal{Y} = \\{1, 2, \\dots, K\\} \\), where \\( f \\) and \\( v \\) are trained with the same training dataset, \\( H \\), \\( W \\), \\( C \\) denote the number of height, width and channels respectively, and \\( K \\) is the number of classes. We use \\( f(x), v(x) \\) to be the prediction over the set of classes \\( \\mathcal{V} \\). Given a specified targeted class \\( y_{t} \\), the targeted transferable attacks aim to generate adversarial examples \\( x_{adv} \\) from the white-box model \\( f \\) that satisfy \\( v(x_{adv}) = y_{t} \\). Following previous works, we enforce a \\( L_{\\infty} \\)-norm constraint on perturbations, which can be formulated as \\( ||x_{adv} - x||_{\\infty} = ||\\delta||_{\\infty} \\leq \\epsilon \\), where \\( \\delta \\) is the perturbation, \\( \\epsilon \\) denotes a constant of the norm constraint. Given a classification loss \\( J \\) (e.g. CE loss) of \\( f \\), the targeted attack of I-FGSM can be formulated as:" + }, + { + "type": "equation", + "bbox": [ + 0.617, + 0.642, + 0.891, + 0.657 + ], + "angle": 0, + "content": "\\[\n\\delta_ {0} = 0, g _ {0} = 0, \\tag {1}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.601, + 0.66, + 0.891, + 0.676 + ], + "angle": 0, + "content": "\\[\ng _ {i + 1} = \\nabla_ {\\delta} J (f (x + \\delta_ {i}), y _ {t}), \\tag {2}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.601, + 0.679, + 0.891, + 0.695 + ], + "angle": 0, + "content": "\\[\n\\delta_ {i + 1} = \\delta_ {i} - \\alpha * \\operatorname {s i g n} \\left(g _ {i + 1}\\right), \\tag {3}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.601, + 0.698, + 0.891, + 0.714 + ], + "angle": 0, + "content": "\\[\n\\delta_ {i + 1} = \\operatorname {C l i p} _ {x, \\epsilon} (\\delta_ {i + 1}), \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.895, + 0.903 + ], + "angle": 0, + "content": "where \\(\\delta_{i}, g_{i}\\) denote the adversarial perturbation and the gradient of the \\(i\\)-th iteration, \\(i = [0, \\dots, I - 1]\\) and \\(I\\) is the maximum number of iterations; \\(\\alpha\\) is the step size; the function \\(Clip_{x,\\epsilon}(\\cdot)\\) projects \\(\\delta\\) to the vicinity of \\(x\\) for satisfying the \\(L_{\\infty}\\)-norm constraint. Specifically, I-FGSM first initializes \\(\\delta_0\\) and \\(g_{0}\\) as 0 (Eq.1). Then it calculates the gradients of the loss function with respect to the perturbation (Eq.2), and drives the prediction of \\(f\\) on the adversarial example towards the targeted class by minimizing \\(J(f(x + \\delta_i), y_t)\\) (Eq.3). Finally, it restricts the adversarial perturbation with the \\(L_{\\infty}\\)-norm constraint (Eq.4). Eq.2, 3, 4 are performed alternately until the maximum iteration is reached. Through" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "12283" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.132, + 0.096, + 0.476, + 0.298 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.24, + 0.305, + 0.368, + 0.317 + ], + "angle": 0, + "content": "(a) Universal evaluation" + }, + { + "type": "image", + "bbox": [ + 0.489, + 0.118, + 0.839, + 0.297 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.584, + 0.305, + 0.743, + 0.317 + ], + "angle": 0, + "content": "(b) Feature similarity analysis" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.321, + 0.894, + 0.378 + ], + "angle": 0, + "content": "Figure 2. (a) For each targeted perturbation generated by I-FGSM or DTMI, we calculate the number of successful targeted attacks caused by adding this perturbation to benign images other than the original optimized image. (b) We average the cosine similarity of intermediate features among different benign images or universal adversarial images that are generated by adding the same perturbation to these benign images." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.403, + 0.47, + 0.525 + ], + "angle": 0, + "content": "this greedy update, I-FGSM is easily caught in local maxima and over-fitting to \\( f \\), which results in performing poorly for targeted attacks. Therefore, previous work [36] utilizes the combination of DI [33], TI [4] and MI [3] as the baseline, since it could achieve more stable performances with a large number of iteration compared to I-FGSM. For convenience, we abbreviate the name of this combination as DTMI. DTMI replaces Eq.2 with" + }, + { + "type": "equation", + "bbox": [ + 0.091, + 0.529, + 0.47, + 0.565 + ], + "angle": 0, + "content": "\\[\ng _ {i + 1} = \\mu \\cdot g _ {i} + \\frac {W \\cdot \\nabla_ {\\delta} J (f (T (x + \\delta_ {i} , p)) , y _ {t})}{\\left| \\left| W \\cdot \\nabla_ {\\delta} J (f (T (x + \\delta_ {i} , p)), y _ {t}) \\right| \\right| _ {1}}, \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.568, + 0.47, + 0.614 + ], + "angle": 0, + "content": "where \\( T(x + \\delta_i, p) \\) performs random resizing and padding with a probability \\( p \\) in DI, \\( W \\) is the pre-defined convolution kernel in TI, \\( \\mu \\) is a decay factor in MI." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.621, + 0.411, + 0.637 + ], + "angle": 0, + "content": "3.2. Universality of Targeted Perturbations" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.645, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Transferable targeted attacks aim to generate cross-model perturbations that drive the prediction of different models towards predicting the same specified class. It requires perturbations generated from one white-box model are model-agnostic, i.e., universal to different models. A simple way to meet this requirement is to optimize perturbations on massive models. However, it may be impractical in the real world, because the number of white-box models is usually limited. In contrast, targeted universal adversarial perturbations (UAP) [17] lead to a specific prediction \\( y_{t} \\) of DNNs for almost all images. [34] attributes this phenomenon to the dominant features produced by Targeted UAP. Specifically, let \\( \\delta_{u} \\) denote targeted UAP, they conclude that the predictive logit vectors of \\( \\delta_{u} \\) have a higher linear correlation with that of \\( x + \\delta_{u} \\), while the linear correlation between \\( x \\) and \\( x + \\delta_{u} \\) is low. It suggests that the features of \\( \\delta_{u} \\) represent the feature distribution of the specific" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.403, + 0.892, + 0.524 + ], + "angle": 0, + "content": "targeted class and dominate the prediction of DNNs. Therefore, targeted UAP could transfer to attack other models trained on the same dataset, because these models share the similar feature distribution of the target class. In summary, universality may correlate to transferability in targeted attacks. Motivated by the above analysis, we delve into the divergence between perturbations crafted by I-FGSM and DTMI from the perspective of universality." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.524, + 0.893, + 0.706 + ], + "angle": 0, + "content": "To further verify the findings in the above analysis, we conduct experiments to show the correlation between universality and targeted transferability. We optimize targeted perturbations on the ImageNet-compatible dataset (dataset details are in Section 4.1) by I-FGSM and DTMI using DenseNet121 as the white-box model. Here CE loss is utilized as classification loss. Given a set of benign images \\(\\Phi = \\{x^{1},\\dots,x^{m},\\dots,x^{M}\\}\\), we generate the perturbation for each image in the set. Denote \\(\\delta^m\\) as the generated perturbation for \\(x^{m}\\). To evaluate the universality of \\(\\delta^m\\), we add \\(\\delta^m\\) to all benign images other than \\(x^{m}\\), and calculate the number of successful targeted attacks on DenseNet121 by:" + }, + { + "type": "equation", + "bbox": [ + 0.576, + 0.714, + 0.892, + 0.758 + ], + "angle": 0, + "content": "\\[\n\\sum_ {j = 1, j \\neq m} ^ {M} \\left\\{ \\begin{array}{l l} 1, & \\text {i f} f \\left(x ^ {j} + \\delta^ {m}\\right) = y _ {t}, \\\\ 0, & \\text {o t h e r w i s e .} \\end{array} \\right. \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.891, + 0.81 + ], + "angle": 0, + "content": "The number of successful targeted attacks is used as the metric to evaluate the universality of \\(\\delta^m\\). A higher number denotes better universality." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.811, + 0.892, + 0.902 + ], + "angle": 0, + "content": "Figure 2a shows the comparison of universality between each perturbation crafted by I-FGSM and DTMI. For better visualization, we sort perturbations in descending order based on their universality reported in I-FGSM. Notably, DTMI attains higher universality than I-FGSM for each perturbation. This is because, aided by the diverse input pat" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "12284" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.091, + 0.47, + 0.182 + ], + "angle": 0, + "content": "terns provided by DI, DTMI makes the perturbations to be universal to these input patterns. Since DTMI achieves better targeted transferability than I-FGSM [36], we can basically draw a conclusion that there is a relatively positive correlation between universality and targeted transferability." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.183, + 0.473, + 0.545 + ], + "angle": 0, + "content": "To provide insights on how the targeted perturbation affects the image features, we compare the average cosine similarity of intermediate features between benign images and adversarial images that generated by adding one specific targeted perturbation to these benign images. Specifically, these benign images can be denoted by \\(\\Phi^m\\), which is the set of \\(x^j\\) satisfying \\(f(x^{j} + \\delta^{m}) = y_{t}\\). Adversarial images can be denoted by \\(\\{x^{j} + \\delta^{m}\\}\\) for \\(x_{j}\\in \\Phi^{m}\\). Figure 2b shows the changes in the feature similarity after adding the same perturbation \\(\\delta^m\\). It can be observed that after adding this perturbation, the image features become more similar. This is because the targeted perturbations drive features from different benign images towards the feature distribution of the target class. In other words, compared to benign images, targeted perturbations produce more dominant features. In addition, from Figure 2b, we can also find that compared to I-FGSM, targeted perturbations generated by DTMI make the image features more similar. Since DTMI achieves better targeted transferability than I-FGSM, the result basically indicates that perturbations with highly targeted transferability will produce more dominant features and enjoy higher universality. The above analysis suggests that adversarial examples with high universality tend to be more transferable in targeted attacks." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.555, + 0.339, + 0.571 + ], + "angle": 0, + "content": "3.3. Self-Universality (SU) Attack" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.579, + 0.47, + 0.866 + ], + "angle": 0, + "content": "To enhance the universality of adversarial perturbations for transferable targeted attacks, we propose the Self-Universality (SU) attack method. Instead of optimizing the perturbations on different images to achieve universality, our SU method optimizes the perturbation to be agnostic to different local regions within one image, which is called self-universality. In this way, our method is able to generate the universal perturbations without extra data. To achieve self-universality, our method generates perturbations by incorporating randomly cropped local regions within one image into the iterative attacks. To create local input patterns, we consider the random cropping, which crops images into a local image patch by the scale parameter \\( s = \\{s_l, s_{int}\\} \\). Where \\( s_l \\) denotes the lower bound for the area of the random cropped images, and \\( s_{int} \\) is the interval value between the lower and upper bounds, thus \\( s_l + s_{int} \\) is the upper bound. After cropping images, we resize them to the same shape as benign images. Let \\( Loc(x, s) \\) be the random cropping and the resizing operations*. In addition, we apply the same thresholding operation on all images in the image patches." + }, + { + "type": "page_footnote", + "bbox": [ + 0.076, + 0.875, + 0.47, + 0.903 + ], + "angle": 0, + "content": "*We perform it by RandomResizedCrop in torchvision and ignore the parameter of the random aspect ratio." + }, + { + "type": "title", + "bbox": [ + 0.501, + 0.091, + 0.707, + 0.106 + ], + "angle": 0, + "content": "Algorithm 1 DTMI-SU attack" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.108, + 0.892, + 0.138 + ], + "angle": 0, + "content": "Input: the classification loss function \\( J \\), white-box model \\( f \\), benign image \\( x \\), targeted class \\( y_{t} \\)." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.139, + 0.892, + 0.184 + ], + "angle": 0, + "content": "Parameter: The perturbation budget \\(\\epsilon\\), iteration number I, step size \\(\\alpha\\), scale parameter \\(s = \\{s_l, s_{int}\\}\\), weighted parameter \\(\\lambda\\), and DTMI parameters \\(T(\\cdot, p)\\), \\(W\\), \\(\\mu\\)." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.184, + 0.765, + 0.199 + ], + "angle": 0, + "content": "Output: The adversarial example \\( x_{adv} \\)." + }, + { + "type": "text", + "bbox": [ + 0.511, + 0.216, + 0.71, + 0.232 + ], + "angle": 0, + "content": "1: Initialize \\(\\delta_0\\) and \\(g_{0}\\) by Eq.1" + }, + { + "type": "text", + "bbox": [ + 0.511, + 0.232, + 0.672, + 0.245 + ], + "angle": 0, + "content": "2: for \\( i = 0 \\) to \\( I - 1 \\) do" + }, + { + "type": "text", + "bbox": [ + 0.511, + 0.246, + 0.852, + 0.262 + ], + "angle": 0, + "content": "3: Random cropping and resizing: \\(\\hat{x} = Loc(x,s)\\)" + }, + { + "type": "text", + "bbox": [ + 0.511, + 0.262, + 0.816, + 0.277 + ], + "angle": 0, + "content": "4: \\(\\mathbf{DI}\\colon x^{\\prime} = T(x + \\delta_{i},p);\\hat{x}^{\\prime} = T(\\hat{x} +\\delta_{i},p)\\)" + }, + { + "type": "text", + "bbox": [ + 0.511, + 0.277, + 0.891, + 0.308 + ], + "angle": 0, + "content": "5: Calculate gradients: \\( g_{i+1} = \\nabla_{\\delta}(J(f(x'), y_t) + J(f(\\hat{x}', y_t) - \\lambda \\cdot CS(f_l(x'), f_l(\\hat{x}))) \\)" + }, + { + "type": "text", + "bbox": [ + 0.511, + 0.306, + 0.723, + 0.327 + ], + "angle": 0, + "content": "6: \\(g_{i + 1} = \\mu \\cdot g_i + \\frac{W\\cdot g_{i + 1}}{||W\\cdot g_{i + 1}||_1}\\)" + }, + { + "type": "text", + "bbox": [ + 0.511, + 0.326, + 0.76, + 0.341 + ], + "angle": 0, + "content": "7: Update and Clip \\(\\delta_{i + 1}\\) by Eq.3, 4" + }, + { + "type": "text", + "bbox": [ + 0.511, + 0.341, + 0.584, + 0.354 + ], + "angle": 0, + "content": "8: end for" + }, + { + "type": "text", + "bbox": [ + 0.511, + 0.355, + 0.624, + 0.37 + ], + "angle": 0, + "content": "9: return \\( x + \\delta_I \\)" + }, + { + "type": "list", + "bbox": [ + 0.511, + 0.216, + 0.891, + 0.37 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.419, + 0.892, + 0.57 + ], + "angle": 0, + "content": "tion, motivated by Figure 2b, we propose a feature similarity loss to maximize the cosine similarity of intermediate features between the adversarial global and local inputs. Under this design, SU could generate perturbations with more dominant features. This loss can be formulated by \\( CS(f_{l}(x + \\delta_{i}),f_{l}(Loc(x,s) + \\delta_{i})) \\), where \\( f_{l}(\\cdot) \\) means to extract features from the \\( l \\)-th layer of the white-box model \\( f \\), the function \\( CS(\\cdot ,\\cdot) \\) calculates cosine similarity score of features between adversarial global and local inputs. In summary, the proposed SU replaces Eq.2 with:" + }, + { + "type": "equation", + "bbox": [ + 0.51, + 0.599, + 0.892, + 0.65 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} g _ {i + 1} = \\nabla_ {\\delta} \\left(J \\left(f \\left(x + \\delta_ {i}\\right), y _ {t}\\right) + J \\left(f \\left(L o c (x, s) + \\delta_ {i}\\right), y _ {t}\\right) \\right. \\\\ - \\lambda \\cdot C S \\left(f _ {l} \\left(x + \\delta_ {i}\\right), f _ {l} \\left(L o c (x, s) + \\delta_ {i}\\right)\\right)), \\tag {7} \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.68, + 0.891, + 0.711 + ], + "angle": 0, + "content": "where \\(\\lambda\\) weights the contribution of the classification loss and the proposed similarity loss." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.892, + 0.901 + ], + "angle": 0, + "content": "In this way, the perturbation optimization of SU can improve the self-universality of perturbations, and the maximization of the cosine similarity can align intermediate features between adversarial global and local inputs for improving the dominance of feature representation of perturbations. Following [36], we integrate SU with the baseline DTMI to further boost targeted transferability, which we named DTMI-SU. We show DTMI-SU in Algorithm 1. In the end, SU can generate adversarial perturbations with high dominant features by incorporating local images, as shown in Figure 2b, hence improving targeted transferability." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "12285" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.08, + 0.089, + 0.468, + 0.181 + ], + "angle": 0, + "content": "
ModelLayer 1Layer 2Layer 3Layer 4
Res50Block-1Block-2Block-3Block-4
Den121Block-1Block-2Block-3Block-4
VGG16ReLU-4ReLU-7ReLU-10ReLU-13
Inc-v3Conv-4aMix-5dMix-6eMix-7c
" + }, + { + "type": "table_footnote", + "bbox": [ + 0.077, + 0.183, + 0.47, + 0.226 + ], + "angle": 0, + "content": "Table 1. Intermediate layers for feature extraction. \"Block\" means the basic block in ResNet50 and DenseNet121. \"ReLU-k\" denotes the \\(k\\)-th ReLU layer." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.252, + 0.202, + 0.269 + ], + "angle": 0, + "content": "4. Experiment" + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.278, + 0.284, + 0.294 + ], + "angle": 0, + "content": "4.1. Experimental Settings" + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.303, + 0.268, + 0.317 + ], + "angle": 0, + "content": "4.1.1 Dataset and models" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.328, + 0.471, + 0.451 + ], + "angle": 0, + "content": "Following [36], we attack four diverse classifier architectures: ResNet50 [5], DenseNet121 [6], VGGNet16 [20], and Inception-v3 [21] with the ImageNet-compatible dataset†. The architectures of these four models are more diverse and challenging than the ones used in [12]. The used dataset is first introduced by the NIPS 2017 Competition on Adversarial Attacks and Defenses. It consists of 1,000 images and corresponding labels for targeted attacks." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.473, + 0.231, + 0.488 + ], + "angle": 0, + "content": "4.1.2 Attack setting" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.498, + 0.47, + 0.651 + ], + "angle": 0, + "content": "We use the Targeted Attack Success Rate (TASR) to evaluate the targeted attack on one black-box model, which is the rate of adversarial examples that are successfully classified as the targeted class by the black-box model. Hence, the methods with higher TASR can generate adversarial examples with high targeted transferability. Following [36], we set the maximum perturbation as \\(\\epsilon = 16\\), the step size as \\(\\alpha = 2\\), the maximum number of iterations as \\(I = 300\\). For each model, we select one layer \\(1/2/3/4\\) from shallow to deep layers (as shown in Table 1) to extract features." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.661, + 0.313, + 0.679 + ], + "angle": 0, + "content": "4.2. Performance Comparison" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.685, + 0.47, + 0.791 + ], + "angle": 0, + "content": "Following [36], we adopt the combination of DI, TI and MI (DTMI) as the baseline. The parameters of DTMI are the same as [36]. We then integrate the proposed SU method with several baselines: CE loss with DTMI (DTMI-CE) and Logit loss [36] with DTMI (DTMI-Logit). We exclude \\(\\mathrm{Po + }\\) Trip [12] in the comparison because it has a worse performance than the Logit loss." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.792, + 0.47, + 0.853 + ], + "angle": 0, + "content": "For SU, the weighted parameter \\(\\lambda\\) is set as \\(10^{-3}\\), the scale parameters \\(s\\) is set as \\((0.1, 0)\\), and the layer 3 is used to extract features. These parameters will be discussed in Section 4.3." + }, + { + "type": "image", + "bbox": [ + 0.505, + 0.093, + 0.691, + 0.181 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.561, + 0.185, + 0.636, + 0.198 + ], + "angle": 0, + "content": "(a) TASR \\((\\%)\\)" + }, + { + "type": "image", + "bbox": [ + 0.697, + 0.091, + 0.885, + 0.181 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.743, + 0.186, + 0.84, + 0.198 + ], + "angle": 0, + "content": "(b) Gradient norm" + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.201, + 0.892, + 0.245 + ], + "angle": 0, + "content": "Figure 3. (a) TASR \\((\\%)\\) of attacking ResNet50 from DenseNet121. (b) Gradient norm of performing DTMI-CE and DTMI-CE-SU when using DenseNet121 as the surrogate model." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.278, + 0.893, + 0.732 + ], + "angle": 0, + "content": "Single-model transferable attacks. We conduct single-model transferable experiments by selecting one model as the white-box model to attack the other three black-box models. Table 2 shows the results. We have the following observations. First, the proposed SU method achieves higher TASR than DTMI-CE and DTMI-Logit by a large margin in almost all cases. It suggests that the proposed SU is suitable for different classification loss functions. Second, the attacks using ResNet50 and DenseNet121 as white-box models outperform that using VGGNet16 and Inception-v3, which is also observed in [8, 9, 36]. It may be caused by the skip connection structure, which mitigates the gradient vanishing/exploding problem in a large number of iterations and emphasizes features of lower layers by backpropagating gradients on both residual modules and skip connections. These features tend to transfer among different models [30, 31]. Third, SU performs worse than other methods when using a small number of iterations (e.g. \\( I = 20 \\)). This is because SU requires a large iteration for convergence, illustrated in Figure 3a. Especially for the CE loss, DTMI achieves the convergence at \\( I = 20 \\), while DTMI-SU steadily improves performance as the iteration increases, since SU can eliminate the vanishing gradient caused by CE, as shown in 3b. We also perform experiments with a smaller perturbation budget \\( \\epsilon = 8 \\), which are shown in Appendix. It follows a similar trend as Table 2. These results jointly demonstrate the effectiveness of SU. In addition, we visualize adversarial examples in Appendix. These adversarial examples, which humans can correctly understand, lead to the specific target prediction of DNNs." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.735, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Ensemble model transferable attacks. As mentioned above, the targeted perturbations generated from a set of models are more model-agnostic, and thus can obtain high cross-model transferability. Hence, we select one black-box model to attack, and use the other three models as white-box models. Following [36], we simply assign equal weights to all white-box models. Results are shown in Table 3. As can be seen, compared to single-model transferable attacks, ensemble attacks achieve much better performance. It demonstrates that the model-agnostic perturbations can easily transfer to attack other models. In addition, we also show that the model-agnostic perturbations can easily transfer to attack other models." + }, + { + "type": "page_footnote", + "bbox": [ + 0.077, + 0.863, + 0.47, + 0.903 + ], + "angle": 0, + "content": "\\(\\dagger\\)https://github.com/cleverhans-lab/cleverhans/tree/master/cleverhans_v3.1.0/examples/nips17_adversarial_competition/dataset" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "12286" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.09, + 0.089, + 0.878, + 0.324 + ], + "angle": 0, + "content": "
AttackWhite-box Model: Res50White-box Model: Dense121
→ Dense121→ VGG16→ Inc-v3→ Res50→ VGG16→ Inc-v3
DTMI-CE27.1/39.7/44.318.9/27.6/29.42.2/3.4/4.112.9/16.7/18.48.1/10.6/10.61.7/2.2/3.2
DTMI-CE-SU6.2/27.8/54.23.0/20.2/45.40.2/4.5/10.12.6/17.6/39.41.4/12.6/32.40.2/4.8/10.8
DTMI-Logit30.4/64.4/71.822.6/55.1/62.82.7/7.1/9.616.1/39.3/43.713.5/33.0/38.12.1/7.1/7.7
DTMI-Logit-SU23.8/63.9/75.516.6/55.9/66.92.0/8.3/11.612.8/42.9/50.29.3/37.2/45.21.8/7.5/10.4
AttackWhite-box Model: VGG16White-box Model: Inc-v3
→ Res50→ Dense121→ Inc-v3→ Res50→ Dense121→ VGG16
DTMI-CE0.6/0.6/0.50.4/0.3/0.40.0/0.0/0.00.8/1.8/2.40.8/2.4/2.90.7/1.3/1.8
DTMI-CE-SU0.2/2.1/2.80.2/2.1/3.20.0/0.2/0.20.4/1.2/2.90.2/1.4/5.00.1/0.8/2.5
DTMI-Logit3.0/9.6/11.33.2/12.0/13.70.1/0.6/0.70.9/2.0/2.81.1/3.3/5.00.6/2.2/3.9
DTMI-Logit-SU3.4/11.7/13.93.3/13.8/16.10.2/0.9/0.80.6/2.3/4.30.5/3.8/7.40.3/1.9/4.4
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.326, + 0.895, + 0.37 + ], + "angle": 0, + "content": "Table 2. TASR (%) of all black-box models under four attack scenarios using ResNet50, DenseNet121, VGGNet16 and Inception-v3 as white-box models, respectively. We conduct these experiments three times and report average TASR with 20/100/300 iterations, the standard deviation is shown in Appendix. The best results with 300 iterations are in bold." + }, + { + "type": "table", + "bbox": [ + 0.24, + 0.381, + 0.728, + 0.501 + ], + "angle": 0, + "content": "
Ensemble AttackBlack-box ModelAverage
Res50Dense121VGG16Inc-v3
DTMI-CE31.155.251.616.138.5
DTMI-CE-SU55.765.068.229.354.5
DTMI-Logit70.282.382.229.165.9
DTMI-Logit-SU75.382.984.234.569.2
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.504, + 0.893, + 0.52 + ], + "angle": 0, + "content": "Table 3. TASR (%) of one black-box model in ensemble transfer attacks. TASR with 300 iterations is reported. The best results are in bold." + }, + { + "type": "table", + "bbox": [ + 0.079, + 0.542, + 0.47, + 0.635 + ], + "angle": 0, + "content": "
AttackDense121VGG16Inc-v3
DTMI-SI/+SU85.7/87.269.0/71.835.8/41.6
DTMI-Adm./+SU89.1/89.475.7/79.142.1/47.1
DTMI-EMI/+SU71.0/79.064.6/82.45.0/14.8
ODI-TMI/+SU89.9/92.881.0/91.766.9/72.0
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.637, + 0.47, + 0.681 + ], + "angle": 0, + "content": "Table 4. Average TASR (\\%) of different combinational attacks. We use ResNet50 as the white-box model, and report the results with 300 iterations. Logit is used here." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.715, + 0.47, + 0.837 + ], + "angle": 0, + "content": "tion, the proposed SU further boosts cross-model targeted transferability. However, the improvement of TASR gained from DTMI-Logit-SU is not so significant. This can be explained by the fact that the loss function value of Logit increases infinitely, while the value of cosine similarity is bounded. Thus, it impedes the maximization of feature similarity. Nevertheless, methods that are combined with SU can promote targeted transferability in all cases." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.471, + 0.902 + ], + "angle": 0, + "content": "Combination with existing methods To further boost transferable targeted attacks, we combine our method with other attacks, including SI [13], Admix [24], EMI [25], and ODI [1]. Table 4 reports the results. The attack methods" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.545, + 0.895, + 0.756 + ], + "angle": 0, + "content": "combined with the proposed SU achieve better performance than other attack methods. In particular, compared to ODI, SU achieves an average TASR gain of \\(6\\%\\). Such remarkable improvements demonstrate that the proposed SU can be easily combined with other existing methods and further improve targeted transferability. In terms of computational efficiency, SU only requires two forward propagations for global and local inputs per iteration, which is lower than SI, Admix, and EMI (which require \\(\\geq 5\\) forward propagations). To compare SU with ODI, we report the computation time (sec) required to generate an adversarial example. DTMI-SU and DTMI-ODI require 2.3 and 2.6 sec, respectively. It indicates that SU requires less computation time than previous methods." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.769, + 0.665, + 0.785 + ], + "angle": 0, + "content": "4.3. Ablation Studies" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.794, + 0.893, + 0.856 + ], + "angle": 0, + "content": "In this section, we utilize CE as the classification loss to investigate the effects of each component and various hyperparameters. In addition, we investigate the effects of different regions of random cropping." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.856, + 0.894, + 0.903 + ], + "angle": 0, + "content": "Effect of components. The evaluations are conducted on four attack scenarios using ResNet50, DenseNet121, VGGNet16 and Inceptionv3 as white-box models, respec" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "12287" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.093, + 0.089, + 0.452, + 0.166 + ], + "angle": 0, + "content": "
LocalFeature Similarity LossAveraged TASR
--9.8
✓-10.9
✓✓15.6
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.168, + 0.47, + 0.252 + ], + "angle": 0, + "content": "Table 5. Average TASR (\\%) of black-box models for our proposed method with different component combinations. The classification loss is set as CE. \\(\\checkmark\\) indicates that the component is used while \\(-\\) indicates that it is not used. TASR is averaged among four attack scenarios using ResNet50, DenseNet121, VGGNet16 and Inceptionv3 as white-box models, respectively." + }, + { + "type": "image", + "bbox": [ + 0.084, + 0.273, + 0.27, + 0.365 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.097, + 0.369, + 0.255, + 0.382 + ], + "angle": 0, + "content": "(a) Scale parameter \\((s_l,s_{int})\\)" + }, + { + "type": "image", + "bbox": [ + 0.276, + 0.273, + 0.459, + 0.364 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.301, + 0.369, + 0.433, + 0.382 + ], + "angle": 0, + "content": "(b) Layer \\(l\\) and weight \\(\\lambda\\)" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.385, + 0.468, + 0.412 + ], + "angle": 0, + "content": "Figure 4. Average TASR with different values of hyper-parameters in the attack. The classification loss is set as CE." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.445, + 0.468, + 0.55 + ], + "angle": 0, + "content": "tively. We split SU into the local inputs and the feature similarity loss. Table 5 shows the results of different component combinations. As can be seen, both components improve targeted transferability. And the improvement of TASR gained from feature similarity loss is more significant. It demonstrates the effectiveness of each component in the proposed SU attack." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.553, + 0.468, + 0.902 + ], + "angle": 0, + "content": "Effect of hyper-parameters. The evaluations are conducted by using densenet121 as the white-box model and averaging TASR among black-box models. The scale parameter \\( s \\) determines the area of cropped images. When the area is large, SU overlooks the local structure of inputs. Thus, it is vital to study optimal values of \\( s \\). We fix the weighted parameter \\( \\lambda = 1.0 \\), and the feature extraction layer as layer 3 due to the high transferability of middle layers [30]. Figure 4a shows the results with \\( s_l \\in [0.1, 0.3, 0.5, 0.7] \\) and \\( s_{int} \\in [0.0, 0.1, 0.2, 0.3] \\). We observe that the smaller the area of cropped images, the higher the performance. It suggests that local image patches that differ significantly from the original images provide more diverse input patterns for perturbation optimization and contribute to targeted transferability. Besides, when \\( s_l = 0.1 \\) and \\( s_{int} = 0.1 \\), the optimal result is reached. However, the area relative to the original image may fluctuate within [0.1, 0.2]. To keep it stable, we use the parameters \\( s = (0.1, 0.0) \\) to conduct subsequent experiments. Figure 4b shows the results of performing attacks on different layers and \\( \\lambda \\). Extracting features from layer 3 is better than other layers. This is because the features captured by shallow layers represent the low-level patterns (such as edges)," + }, + { + "type": "table", + "bbox": [ + 0.558, + 0.089, + 0.832, + 0.187 + ], + "angle": 0, + "content": "
RegionRes50VGG16Inc-v3
Center33.029.29.9
Corner33.630.910.8
Whole39.432.410.8
Uniform3.11.70.4
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.189, + 0.892, + 0.245 + ], + "angle": 0, + "content": "Table 6. TASR (\\%) of DTMI-CE-SU with different distributions of local images. The top three rows show different regions of random cropping. The last row denotes the uniform distribution \\(\\mathcal{U}(0,1)\\) of local images." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.279, + 0.892, + 0.354 + ], + "angle": 0, + "content": "while the deepest layer contains more semantic information hence is more related to the classification task of the white-box model [30]. For the weighted parameter \\(\\lambda\\), we set \\(\\lambda \\in [10^{-4}, 10^{-3}, 10^{-2}, 10^{-1}, 10^{0}]\\). When \\(\\lambda = 10^{-3}\\), SU achieves the best result." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.358, + 0.892, + 0.57 + ], + "angle": 0, + "content": "Effect of different regions. The regions of random cropping determine the distribution of local images. The center may be more related to the object of the image than the corner. Therefore, we conduct experiments on the center, the corner and the whole regions. We also compare the uniform distribution \\(\\mathcal{U}(0,1)\\) of local images. As shown in Table 6, there is no significant performance difference between the center and the corner. The reason is that SU concentrates on the target class regardless of the object related to the original class. Therefore, directly providing more local input patterns within one image leads to better performance in SU. The whole region indeed achieves the best performance. Moreover, the uniform distribution makes it difficult to converge, resulting in the worst performance." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.593, + 0.619, + 0.608 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.622, + 0.892, + 0.787 + ], + "angle": 0, + "content": "In this paper, we provide new insight into transfer-based targeted attacks: more universal perturbations yield better transferability. Based on this observation, we propose the Self-University (SU) attack, which optimizes perturbations on the global image and more diverse local images, and aligns intermediate features between them. In this way, SU can make perturbations to be agnostic to different image regions, resulting in high self-transferability. We conduct extensive experiments to show that SU can improve targeted transferability regardless of the single-model attack or ensemble-based attack." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.812, + 0.679, + 0.829 + ], + "angle": 0, + "content": "6. Acknowledgments" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.84, + 0.892, + 0.901 + ], + "angle": 0, + "content": "This project was supported by National Key R&D Program of China (No. 2020AAA0140001), NSFC (No. 62072116), and Science and Technology Commission of Shanghai Municipality (No. 21JC1400600)." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.956 + ], + "angle": 0, + "content": "12288" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.115, + 0.47, + 0.197 + ], + "angle": 0, + "content": "[1] Junyoung Byun, Seungju Cho, Myung-Joon Kwon, Hee-Seon Kim, and Changick Kim. Improving the transferability of targeted adversarial examples through object-based diverse input. 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Info. Processing, School of CS, Fudan University + $^{2}$ Shanghai Collaborative Innovation Center of Intelligent Visual Computing + +zpwei21@m.fudan.edu.cn,{chenjingjing, zxwu, ygj}@fudan.edu.cn + +# Abstract + +In this paper, we propose a novel transfer-based targeted attack method that optimizes the adversarial perturbations without any extra training efforts for auxiliary networks on training data. Our new attack method is proposed based on the observation that highly universal adversarial perturbations tend to be more transferable for targeted attacks. Therefore, we propose to make the perturbation to be agnostic to different local regions within one image, which we called as self-universality. Instead of optimizing the perturbations on different images, optimizing on different regions to achieve self-universality can get rid of using extra data. Specifically, we introduce a feature similarity loss that encourages the learned perturbations to be universal by maximizing the feature similarity between adversarial perturbed global images and randomly cropped local regions. With the feature similarity loss, our method makes the features from adversarial perturbations to be more dominant than that of benign images, hence improving targeted transferability. We name the proposed attack method as Self-Universality (SU) attack. Extensive experiments demonstrate that SU can achieve high success rates for transfer-based targeted attacks. On ImageNet-compatible dataset, SU yields an improvement of $12\%$ compared with existing state-of-the-art methods. Code is available at https://github.com/zhipeng-wei/Self-Universality. + +# 1. Introduction + +It has been demonstrated in recent works that adversarial examples have the properties of transferability, which means an adversarial example generated on one white-box model can be used to fool other black-box models [3, 15, 27, 30, 33]. The existence of transferability brings convenience to performing black-box attacks, hence raising security concerns for deploying deep models in real-world + +applications [14,22,28,35]. Consequently, considerable research attention has been spent on improving the transferability of adversarial examples for both non-targeted and targeted attacks [4, 29, 36]. + +Compared to non-targeted attacks, transfer-based targeted attacks are inherently much more challenging since the goal is to fool deep models into predicting the specific target class. The major difficulty of transfer-based targeted attacks is caused by the fact that the gradient directions from a source image to a target class are usually different among different DNNs [16]. Hence, transfer-based attack methods designed for non-targeted attacks typically work poorly for targeted attacks. To increase the transferability, previous studies make efforts in aligning the feature of the generated adversarial example with the feature distributions of the targeted class, which are learned from class-specific auxiliary networks [7, 8] or generative adversarial networks [18]. However, these works assume that the training dataset is available and require extra training efforts for auxiliary networks, making it hard to apply in real-world scenarios. + +This paper investigates the problem of transfer-based targeted attacks. Specifically, we propose a new method that improves the transferability of adversarial examples in a more efficient way, i.e., without any training efforts for auxiliary networks to learn the feature distributions of the targeted class. Our method is proposed based on the observation that more universal perturbations yield better attack success rates in targeted attacks. To this end, our goal is to enhance the universality of the generated adversarial perturbations, in order to improve its targeted transferability. Note that existing universal adversarial perturbation (UAP) attacks [17] require optimizing the perturbations on an abundant set of images to achieve universality, which is not applicable in our setting. To get rid of using extra data and make transfer-based targeted attacks as convenient as non-targeted attacks, we propose to make the perturbation to be agnostic to different local regions within one image, which we called as self-universality. Then our method optimizes the self-universality of adversarial pertur + +![](images/9cf0e970e901a9cf9489e12017896756a0828c0afd4585fdef40b07e5c10abad.jpg) +Figure 1. Overview of the proposed SU attack. The random cropping is applied to the given benign image to generate the local image patch. After cropping, the local patch is resized to the shape of the benign image. Then both benign and local adversarial images with the shared perturbations are input to a surrogate white-box CNN model. Finally, the gradients obtained from the classification loss and the feature similarity loss are used to optimize perturbations. + +bations instead. To be specific, in addition to classification loss, our Self-Universality (SU) attack method introduces a feature similarity loss that maximizes the feature similarity between adversarial perturbed global images and randomly cropped local regions to achieve self-universality. In this way, our method makes the features from adversarial perturbations to be more dominant than that of benign images, hence improving targeted transferability. + +Figure 1 gives an overview of the proposed Self-Universality (SU) attack. SU firstly applies random cropping on benign images to obtain local cropped patches. Then it resizes local patches to the same size with benign images. Consequently, global and local inputs with shared perturbations are input to the white-box model. Finally, adversarial perturbations are updated by minimizing the classification loss (e.g., Cross Entropy) between inputs and the target class and maximizing the feature similarity loss (e.g., Cosine Similarity) of adversarial intermediate features between local and global inputs. Benefiting from satisfying the prediction of the target class between global and local inputs and approximating adversarial intermediate features between the two, the proposed SU attack can generate perturbations with self-universality, thereby improving the cross-model targeted transferability. We briefly summarize our primary contributions as follows: + +- Through experiments, we find that highly universal adversarial perturbations tend to be more transferable for targeted attacks, which brings new insight into the design of transfer-based targeted attack methods. +- Based on the finding, we propose a novel Self-Universality (SU) attack method that enhances the universality of adversarial perturbations for better targeted transferability without the requirement for extra data. +- We conduct comprehensive experiments to demon + +strate that the proposed SU attack can significantly improve the cross-model targeted transferability of adversarial images. Notably, SU can be easily combined with other existing methods. + +# 2. Related Work + +In this section, we review existing works on non-targeted transferable attacks as well as targeted transferable attacks. + +# 2.1. Non-targeted Transferable Attacks + +Non-targeted transferable attacks are based on the Iterative-Fast Gradient Sign Method (I-FGSM) [11], which iteratively calculates the gradient of the classification loss with respect to the input and updates perturbations along the direction of maximizing the loss. The multiple-step update of I-FGSM leads to more wrong predictions of white-box models. However, the generated adversarial examples are hard to attack other black-box models. This phenomenon is called over-fitting to the white-box model [10]. Subsequently, several works perform data augmentation or advanced gradient calculation to overcome the over-fitting problem. Data augmentation creates various input patterns, which generate adversarial perturbations with a generic pattern. For the input images, Diverse Input (DI) [33] performs random resizing and padding, Scale-invariant method (SIM) [13] applies scale transformation, Admix [24] extends SIM by integrating images from other labels. However, these data augmentation approaches neglect to consider more diverse input patterns (e.g., random cropping in this paper), and focus on the loss-preserving transformation [13]. This is because the gradient direction fluctuates violently under more diverse input patterns without specified target classes in non-target attacks. Advanced gradient calculation pays attention to changing gradient calculation methods or designing a new loss function. For changing + +gradient calculation, the momentum term [3] and the Nesterov accelerated gradient [13] can be incorporated with I-FGSM to stabilize gradients. Translation-Invariant (TI) [4] smooths gradients through a predefined convolution kernel in order to mitigate the over-fitting problem. Skip Gradient Method (SGM) [31] modifies the path of gradient backpropagation by skipping residual modules. Variance Tuning [23] utilizes gradients from data points around previous data to avoid over-fitting. For designing a new loss function, Attention-guided Transfer Attack (ATA) [32] and Feature Importance-aware Attack (FIA) [26] disrupt important features that are likely to be utilized in other black-box models. ATA applies Grad-CAM [19] to represent attention weights of features. Different to ATA, FIA computes averaged gradients of features among various augmented inputs as attention weights. However, these new loss functions are restricted to global structures. In contrast, this paper calculates the feature similarity loss between global and local structures of images. + +# 2.2. Targeted Transferable Attacks + +The transfer-based targeted attacks are more challenging than the non-targeted attacks due to the requirement of fooling the model into predicting the specified target class. Previous efforts have been devoted into training class-specific auxiliary networks [7, 8] or generative adversarial networks (GANs) [18], in order to learn feature distributions of the targeted class. Feature Distribution Attack (FDA) [8] utilizes the intermediate features of the training dataset from the white-box model to train a binary classifier, which predicts the probability that the current feature belongs to the targeted class. Then, through learning class-wise and layer-wise feature distributions, FDA generates targeted transferable adversarial perturbations by maximizing the probability outputted from the trained binary classifier. Subsequently, $FDA^{N} + xent$ [7] incorporates the CE loss and multi-layer information with FDA, achieving better performance. Transferable targeted perturbations (TTP) [18] trains a generator to synthesize perturbations that seek to have similar features with targeted samples in the latent space of a pretrained discriminator. This series of FDA works and TTP improve the performance of targeted transferable attacks, but require additional training efforts for auxiliary networks on the training dataset. + +To improve the efficiency of targeted transferable attacks, recent works pay more attention to iterative attacks based on I-FGSM. Activation Attack (AA) [9] replace the classification loss with a euclidean distance loss between features of adversarial and targeted images. However, AA depends on the selected examples of the targeted class and achieves low performance on the large resolution image dataset (e.g. ImageNet [2]). Different to AA, Po+Trip [12] utilizes Poincaré distance metric to solve the noise curing. + +They also design a triplet loss for driving adversarial examples away from the original class. However, $\mathrm{Po + Tri}$ evaluates the attack performance only on easy transfer scenarios, and also achieves poor performance on the targeted scenario used in the Logit attack [36]. Logit [36] attributes the poor performance of I-FGSM based methods to the restricted number of iterations. Thus, Logit enlarges the number of iterations for ensuring the convergence of attacks. In addition, to overcome the vanishing gradient caused by the large iterations, Logit utilizes gradients of the targeted logit output with respect to inputs to update perturbations. Different to them, our method leverages the global and local structures to generate adversarial examples with self-universality, hence improving targeted transferability. Note that the proposed SU attack can be easily combined with existing methods. + +# 3. Methodology + +# 3.1. Preliminary + +Let $f$ represent the white-box surrogate model, $v$ be the black-box victim model, $x \in \mathcal{X} \subset \mathbf{R}^{H \times W \times C}$ be the benign image with the ground-truth label $y \in \mathcal{Y} = \{1, 2, \dots, K\}$ , where $f$ and $v$ are trained with the same training dataset, $H$ , $W$ , $C$ denote the number of height, width and channels respectively, and $K$ is the number of classes. We use $f(x), v(x)$ to be the prediction over the set of classes $\mathcal{V}$ . Given a specified targeted class $y_{t}$ , the targeted transferable attacks aim to generate adversarial examples $x_{adv}$ from the white-box model $f$ that satisfy $v(x_{adv}) = y_{t}$ . Following previous works, we enforce a $L_{\infty}$ -norm constraint on perturbations, which can be formulated as $||x_{adv} - x||_{\infty} = ||\delta||_{\infty} \leq \epsilon$ , where $\delta$ is the perturbation, $\epsilon$ denotes a constant of the norm constraint. Given a classification loss $J$ (e.g. CE loss) of $f$ , the targeted attack of I-FGSM can be formulated as: + +$$ +\delta_ {0} = 0, g _ {0} = 0, \tag {1} +$$ + +$$ +g _ {i + 1} = \nabla_ {\delta} J (f (x + \delta_ {i}), y _ {t}), \tag {2} +$$ + +$$ +\delta_ {i + 1} = \delta_ {i} - \alpha * \operatorname {s i g n} \left(g _ {i + 1}\right), \tag {3} +$$ + +$$ +\delta_ {i + 1} = \operatorname {C l i p} _ {x, \epsilon} (\delta_ {i + 1}), \tag {4} +$$ + +where $\delta_{i}, g_{i}$ denote the adversarial perturbation and the gradient of the $i$ -th iteration, $i = [0, \dots, I - 1]$ and $I$ is the maximum number of iterations; $\alpha$ is the step size; the function $Clip_{x,\epsilon}(\cdot)$ projects $\delta$ to the vicinity of $x$ for satisfying the $L_{\infty}$ -norm constraint. Specifically, I-FGSM first initializes $\delta_0$ and $g_{0}$ as 0 (Eq.1). Then it calculates the gradients of the loss function with respect to the perturbation (Eq.2), and drives the prediction of $f$ on the adversarial example towards the targeted class by minimizing $J(f(x + \delta_i), y_t)$ (Eq.3). Finally, it restricts the adversarial perturbation with the $L_{\infty}$ -norm constraint (Eq.4). Eq.2, 3, 4 are performed alternately until the maximum iteration is reached. Through + +![](images/8ef664ac2e65f34a3891df8c8abc896cceb0a674acbb8dd55fe7a7db638f8dc7.jpg) +(a) Universal evaluation + +![](images/42c4654e040875b8b4ae0d74da068fdac2f3323f994f1f8fcce1f21cf1df7a67.jpg) +(b) Feature similarity analysis +Figure 2. (a) For each targeted perturbation generated by I-FGSM or DTMI, we calculate the number of successful targeted attacks caused by adding this perturbation to benign images other than the original optimized image. (b) We average the cosine similarity of intermediate features among different benign images or universal adversarial images that are generated by adding the same perturbation to these benign images. + +this greedy update, I-FGSM is easily caught in local maxima and over-fitting to $f$ , which results in performing poorly for targeted attacks. Therefore, previous work [36] utilizes the combination of DI [33], TI [4] and MI [3] as the baseline, since it could achieve more stable performances with a large number of iteration compared to I-FGSM. For convenience, we abbreviate the name of this combination as DTMI. DTMI replaces Eq.2 with + +$$ +g _ {i + 1} = \mu \cdot g _ {i} + \frac {W \cdot \nabla_ {\delta} J (f (T (x + \delta_ {i} , p)) , y _ {t})}{\left| \left| W \cdot \nabla_ {\delta} J (f (T (x + \delta_ {i} , p)), y _ {t}) \right| \right| _ {1}}, \tag {5} +$$ + +where $T(x + \delta_i, p)$ performs random resizing and padding with a probability $p$ in DI, $W$ is the pre-defined convolution kernel in TI, $\mu$ is a decay factor in MI. + +# 3.2. Universality of Targeted Perturbations + +Transferable targeted attacks aim to generate cross-model perturbations that drive the prediction of different models towards predicting the same specified class. It requires perturbations generated from one white-box model are model-agnostic, i.e., universal to different models. A simple way to meet this requirement is to optimize perturbations on massive models. However, it may be impractical in the real world, because the number of white-box models is usually limited. In contrast, targeted universal adversarial perturbations (UAP) [17] lead to a specific prediction $y_{t}$ of DNNs for almost all images. [34] attributes this phenomenon to the dominant features produced by Targeted UAP. Specifically, let $\delta_{u}$ denote targeted UAP, they conclude that the predictive logit vectors of $\delta_{u}$ have a higher linear correlation with that of $x + \delta_{u}$ , while the linear correlation between $x$ and $x + \delta_{u}$ is low. It suggests that the features of $\delta_{u}$ represent the feature distribution of the specific + +targeted class and dominate the prediction of DNNs. Therefore, targeted UAP could transfer to attack other models trained on the same dataset, because these models share the similar feature distribution of the target class. In summary, universality may correlate to transferability in targeted attacks. Motivated by the above analysis, we delve into the divergence between perturbations crafted by I-FGSM and DTMI from the perspective of universality. + +To further verify the findings in the above analysis, we conduct experiments to show the correlation between universality and targeted transferability. We optimize targeted perturbations on the ImageNet-compatible dataset (dataset details are in Section 4.1) by I-FGSM and DTMI using DenseNet121 as the white-box model. Here CE loss is utilized as classification loss. Given a set of benign images $\Phi = \{x^{1},\dots,x^{m},\dots,x^{M}\}$ , we generate the perturbation for each image in the set. Denote $\delta^m$ as the generated perturbation for $x^{m}$ . To evaluate the universality of $\delta^m$ , we add $\delta^m$ to all benign images other than $x^{m}$ , and calculate the number of successful targeted attacks on DenseNet121 by: + +$$ +\sum_ {j = 1, j \neq m} ^ {M} \left\{ \begin{array}{l l} 1, & \text {i f} f \left(x ^ {j} + \delta^ {m}\right) = y _ {t}, \\ 0, & \text {o t h e r w i s e .} \end{array} \right. \tag {6} +$$ + +The number of successful targeted attacks is used as the metric to evaluate the universality of $\delta^m$ . A higher number denotes better universality. + +Figure 2a shows the comparison of universality between each perturbation crafted by I-FGSM and DTMI. For better visualization, we sort perturbations in descending order based on their universality reported in I-FGSM. Notably, DTMI attains higher universality than I-FGSM for each perturbation. This is because, aided by the diverse input pat + +terns provided by DI, DTMI makes the perturbations to be universal to these input patterns. Since DTMI achieves better targeted transferability than I-FGSM [36], we can basically draw a conclusion that there is a relatively positive correlation between universality and targeted transferability. + +To provide insights on how the targeted perturbation affects the image features, we compare the average cosine similarity of intermediate features between benign images and adversarial images that generated by adding one specific targeted perturbation to these benign images. Specifically, these benign images can be denoted by $\Phi^m$ , which is the set of $x^j$ satisfying $f(x^{j} + \delta^{m}) = y_{t}$ . Adversarial images can be denoted by $\{x^{j} + \delta^{m}\}$ for $x_{j}\in \Phi^{m}$ . Figure 2b shows the changes in the feature similarity after adding the same perturbation $\delta^m$ . It can be observed that after adding this perturbation, the image features become more similar. This is because the targeted perturbations drive features from different benign images towards the feature distribution of the target class. In other words, compared to benign images, targeted perturbations produce more dominant features. In addition, from Figure 2b, we can also find that compared to I-FGSM, targeted perturbations generated by DTMI make the image features more similar. Since DTMI achieves better targeted transferability than I-FGSM, the result basically indicates that perturbations with highly targeted transferability will produce more dominant features and enjoy higher universality. The above analysis suggests that adversarial examples with high universality tend to be more transferable in targeted attacks. + +# 3.3. Self-Universality (SU) Attack + +To enhance the universality of adversarial perturbations for transferable targeted attacks, we propose the Self-Universality (SU) attack method. Instead of optimizing the perturbations on different images to achieve universality, our SU method optimizes the perturbation to be agnostic to different local regions within one image, which is called self-universality. In this way, our method is able to generate the universal perturbations without extra data. To achieve self-universality, our method generates perturbations by incorporating randomly cropped local regions within one image into the iterative attacks. To create local input patterns, we consider the random cropping, which crops images into a local image patch by the scale parameter $s = \{s_l, s_{int}\}$ . Where $s_l$ denotes the lower bound for the area of the random cropped images, and $s_{int}$ is the interval value between the lower and upper bounds, thus $s_l + s_{int}$ is the upper bound. After cropping images, we resize them to the same shape as benign images. Let $Loc(x, s)$ be the random cropping and the resizing operations*. In addition, we apply the same thresholding operation on all images in the image patches. + +# Algorithm 1 DTMI-SU attack + +Input: the classification loss function $J$ , white-box model $f$ , benign image $x$ , targeted class $y_{t}$ . + +Parameter: The perturbation budget $\epsilon$ , iteration number I, step size $\alpha$ , scale parameter $s = \{s_l, s_{int}\}$ , weighted parameter $\lambda$ , and DTMI parameters $T(\cdot, p)$ , $W$ , $\mu$ . + +Output: The adversarial example $x_{adv}$ . + +1: Initialize $\delta_0$ and $g_{0}$ by Eq.1 +2: for $i = 0$ to $I - 1$ do +3: Random cropping and resizing: $\hat{x} = Loc(x,s)$ +4: $\mathbf{DI}\colon x^{\prime} = T(x + \delta_{i},p);\hat{x}^{\prime} = T(\hat{x} +\delta_{i},p)$ +5: Calculate gradients: $g_{i+1} = \nabla_{\delta}(J(f(x'), y_t) + J(f(\hat{x}', y_t) - \lambda \cdot CS(f_l(x'), f_l(\hat{x})))$ +6: $g_{i + 1} = \mu \cdot g_i + \frac{W\cdot g_{i + 1}}{||W\cdot g_{i + 1}||_1}$ +7: Update and Clip $\delta_{i + 1}$ by Eq.3, 4 +8: end for +9: return $x + \delta_I$ + +tion, motivated by Figure 2b, we propose a feature similarity loss to maximize the cosine similarity of intermediate features between the adversarial global and local inputs. Under this design, SU could generate perturbations with more dominant features. This loss can be formulated by $CS(f_{l}(x + \delta_{i}),f_{l}(Loc(x,s) + \delta_{i}))$ , where $f_{l}(\cdot)$ means to extract features from the $l$ -th layer of the white-box model $f$ , the function $CS(\cdot ,\cdot)$ calculates cosine similarity score of features between adversarial global and local inputs. In summary, the proposed SU replaces Eq.2 with: + +$$ +\begin{array}{l} g _ {i + 1} = \nabla_ {\delta} \left(J \left(f \left(x + \delta_ {i}\right), y _ {t}\right) + J \left(f \left(L o c (x, s) + \delta_ {i}\right), y _ {t}\right) \right. \\ - \lambda \cdot C S \left(f _ {l} \left(x + \delta_ {i}\right), f _ {l} \left(L o c (x, s) + \delta_ {i}\right)\right)), \tag {7} \\ \end{array} +$$ + +where $\lambda$ weights the contribution of the classification loss and the proposed similarity loss. + +In this way, the perturbation optimization of SU can improve the self-universality of perturbations, and the maximization of the cosine similarity can align intermediate features between adversarial global and local inputs for improving the dominance of feature representation of perturbations. Following [36], we integrate SU with the baseline DTMI to further boost targeted transferability, which we named DTMI-SU. We show DTMI-SU in Algorithm 1. In the end, SU can generate adversarial perturbations with high dominant features by incorporating local images, as shown in Figure 2b, hence improving targeted transferability. + +
ModelLayer 1Layer 2Layer 3Layer 4
Res50Block-1Block-2Block-3Block-4
Den121Block-1Block-2Block-3Block-4
VGG16ReLU-4ReLU-7ReLU-10ReLU-13
Inc-v3Conv-4aMix-5dMix-6eMix-7c
+ +Table 1. Intermediate layers for feature extraction. "Block" means the basic block in ResNet50 and DenseNet121. "ReLU-k" denotes the $k$ -th ReLU layer. + +# 4. Experiment + +# 4.1. Experimental Settings + +# 4.1.1 Dataset and models + +Following [36], we attack four diverse classifier architectures: ResNet50 [5], DenseNet121 [6], VGGNet16 [20], and Inception-v3 [21] with the ImageNet-compatible dataset†. The architectures of these four models are more diverse and challenging than the ones used in [12]. The used dataset is first introduced by the NIPS 2017 Competition on Adversarial Attacks and Defenses. It consists of 1,000 images and corresponding labels for targeted attacks. + +# 4.1.2 Attack setting + +We use the Targeted Attack Success Rate (TASR) to evaluate the targeted attack on one black-box model, which is the rate of adversarial examples that are successfully classified as the targeted class by the black-box model. Hence, the methods with higher TASR can generate adversarial examples with high targeted transferability. Following [36], we set the maximum perturbation as $\epsilon = 16$ , the step size as $\alpha = 2$ , the maximum number of iterations as $I = 300$ . For each model, we select one layer $1/2/3/4$ from shallow to deep layers (as shown in Table 1) to extract features. + +# 4.2. Performance Comparison + +Following [36], we adopt the combination of DI, TI and MI (DTMI) as the baseline. The parameters of DTMI are the same as [36]. We then integrate the proposed SU method with several baselines: CE loss with DTMI (DTMI-CE) and Logit loss [36] with DTMI (DTMI-Logit). We exclude $\mathrm{Po + }$ Trip [12] in the comparison because it has a worse performance than the Logit loss. + +For SU, the weighted parameter $\lambda$ is set as $10^{-3}$ , the scale parameters $s$ is set as $(0.1, 0)$ , and the layer 3 is used to extract features. These parameters will be discussed in Section 4.3. + +![](images/7a90ea67337207534311eea373b1e752fe97a8015bb7fb9a9ea8487de9c163c9.jpg) +(a) TASR $(\%)$ + +![](images/47ae710ec8cb6f7afb578477f572d5681f057e3c2e137f257abb3e42278d4403.jpg) +(b) Gradient norm +Figure 3. (a) TASR $(\%)$ of attacking ResNet50 from DenseNet121. (b) Gradient norm of performing DTMI-CE and DTMI-CE-SU when using DenseNet121 as the surrogate model. + +Single-model transferable attacks. We conduct single-model transferable experiments by selecting one model as the white-box model to attack the other three black-box models. Table 2 shows the results. We have the following observations. First, the proposed SU method achieves higher TASR than DTMI-CE and DTMI-Logit by a large margin in almost all cases. It suggests that the proposed SU is suitable for different classification loss functions. Second, the attacks using ResNet50 and DenseNet121 as white-box models outperform that using VGGNet16 and Inception-v3, which is also observed in [8, 9, 36]. It may be caused by the skip connection structure, which mitigates the gradient vanishing/exploding problem in a large number of iterations and emphasizes features of lower layers by backpropagating gradients on both residual modules and skip connections. These features tend to transfer among different models [30, 31]. Third, SU performs worse than other methods when using a small number of iterations (e.g. $I = 20$ ). This is because SU requires a large iteration for convergence, illustrated in Figure 3a. Especially for the CE loss, DTMI achieves the convergence at $I = 20$ , while DTMI-SU steadily improves performance as the iteration increases, since SU can eliminate the vanishing gradient caused by CE, as shown in 3b. We also perform experiments with a smaller perturbation budget $\epsilon = 8$ , which are shown in Appendix. It follows a similar trend as Table 2. These results jointly demonstrate the effectiveness of SU. In addition, we visualize adversarial examples in Appendix. These adversarial examples, which humans can correctly understand, lead to the specific target prediction of DNNs. + +Ensemble model transferable attacks. As mentioned above, the targeted perturbations generated from a set of models are more model-agnostic, and thus can obtain high cross-model transferability. Hence, we select one black-box model to attack, and use the other three models as white-box models. Following [36], we simply assign equal weights to all white-box models. Results are shown in Table 3. As can be seen, compared to single-model transferable attacks, ensemble attacks achieve much better performance. It demonstrates that the model-agnostic perturbations can easily transfer to attack other models. In addition, we also show that the model-agnostic perturbations can easily transfer to attack other models. + +
AttackWhite-box Model: Res50White-box Model: Dense121
→ Dense121→ VGG16→ Inc-v3→ Res50→ VGG16→ Inc-v3
DTMI-CE27.1/39.7/44.318.9/27.6/29.42.2/3.4/4.112.9/16.7/18.48.1/10.6/10.61.7/2.2/3.2
DTMI-CE-SU6.2/27.8/54.23.0/20.2/45.40.2/4.5/10.12.6/17.6/39.41.4/12.6/32.40.2/4.8/10.8
DTMI-Logit30.4/64.4/71.822.6/55.1/62.82.7/7.1/9.616.1/39.3/43.713.5/33.0/38.12.1/7.1/7.7
DTMI-Logit-SU23.8/63.9/75.516.6/55.9/66.92.0/8.3/11.612.8/42.9/50.29.3/37.2/45.21.8/7.5/10.4
AttackWhite-box Model: VGG16White-box Model: Inc-v3
→ Res50→ Dense121→ Inc-v3→ Res50→ Dense121→ VGG16
DTMI-CE0.6/0.6/0.50.4/0.3/0.40.0/0.0/0.00.8/1.8/2.40.8/2.4/2.90.7/1.3/1.8
DTMI-CE-SU0.2/2.1/2.80.2/2.1/3.20.0/0.2/0.20.4/1.2/2.90.2/1.4/5.00.1/0.8/2.5
DTMI-Logit3.0/9.6/11.33.2/12.0/13.70.1/0.6/0.70.9/2.0/2.81.1/3.3/5.00.6/2.2/3.9
DTMI-Logit-SU3.4/11.7/13.93.3/13.8/16.10.2/0.9/0.80.6/2.3/4.30.5/3.8/7.40.3/1.9/4.4
+ +Table 2. TASR (%) of all black-box models under four attack scenarios using ResNet50, DenseNet121, VGGNet16 and Inception-v3 as white-box models, respectively. We conduct these experiments three times and report average TASR with 20/100/300 iterations, the standard deviation is shown in Appendix. The best results with 300 iterations are in bold. + +
Ensemble AttackBlack-box ModelAverage
Res50Dense121VGG16Inc-v3
DTMI-CE31.155.251.616.138.5
DTMI-CE-SU55.765.068.229.354.5
DTMI-Logit70.282.382.229.165.9
DTMI-Logit-SU75.382.984.234.569.2
+ +Table 3. TASR (%) of one black-box model in ensemble transfer attacks. TASR with 300 iterations is reported. The best results are in bold. + +
AttackDense121VGG16Inc-v3
DTMI-SI/+SU85.7/87.269.0/71.835.8/41.6
DTMI-Adm./+SU89.1/89.475.7/79.142.1/47.1
DTMI-EMI/+SU71.0/79.064.6/82.45.0/14.8
ODI-TMI/+SU89.9/92.881.0/91.766.9/72.0
+ +Table 4. Average TASR (\%) of different combinational attacks. We use ResNet50 as the white-box model, and report the results with 300 iterations. Logit is used here. + +tion, the proposed SU further boosts cross-model targeted transferability. However, the improvement of TASR gained from DTMI-Logit-SU is not so significant. This can be explained by the fact that the loss function value of Logit increases infinitely, while the value of cosine similarity is bounded. Thus, it impedes the maximization of feature similarity. Nevertheless, methods that are combined with SU can promote targeted transferability in all cases. + +Combination with existing methods To further boost transferable targeted attacks, we combine our method with other attacks, including SI [13], Admix [24], EMI [25], and ODI [1]. Table 4 reports the results. The attack methods + +combined with the proposed SU achieve better performance than other attack methods. In particular, compared to ODI, SU achieves an average TASR gain of $6\%$ . Such remarkable improvements demonstrate that the proposed SU can be easily combined with other existing methods and further improve targeted transferability. In terms of computational efficiency, SU only requires two forward propagations for global and local inputs per iteration, which is lower than SI, Admix, and EMI (which require $\geq 5$ forward propagations). To compare SU with ODI, we report the computation time (sec) required to generate an adversarial example. DTMI-SU and DTMI-ODI require 2.3 and 2.6 sec, respectively. It indicates that SU requires less computation time than previous methods. + +# 4.3. Ablation Studies + +In this section, we utilize CE as the classification loss to investigate the effects of each component and various hyperparameters. In addition, we investigate the effects of different regions of random cropping. + +Effect of components. The evaluations are conducted on four attack scenarios using ResNet50, DenseNet121, VGGNet16 and Inceptionv3 as white-box models, respec + +
LocalFeature Similarity LossAveraged TASR
--9.8
✓-10.9
✓✓15.6
+ +![](images/61a8dd0de1876c46d955e4dbd6720b68feb556dde66ee5fe5befd24994b6cea2.jpg) +(a) Scale parameter $(s_l,s_{int})$ + +![](images/9c1caf5f98bef99e8fc29b5e2b255499dc038588057b39cea0b14ce66ddf1a07.jpg) +(b) Layer $l$ and weight $\lambda$ +Figure 4. Average TASR with different values of hyper-parameters in the attack. The classification loss is set as CE. + +tively. We split SU into the local inputs and the feature similarity loss. Table 5 shows the results of different component combinations. As can be seen, both components improve targeted transferability. And the improvement of TASR gained from feature similarity loss is more significant. It demonstrates the effectiveness of each component in the proposed SU attack. + +Effect of hyper-parameters. The evaluations are conducted by using densenet121 as the white-box model and averaging TASR among black-box models. The scale parameter $s$ determines the area of cropped images. When the area is large, SU overlooks the local structure of inputs. Thus, it is vital to study optimal values of $s$ . We fix the weighted parameter $\lambda = 1.0$ , and the feature extraction layer as layer 3 due to the high transferability of middle layers [30]. Figure 4a shows the results with $s_l \in [0.1, 0.3, 0.5, 0.7]$ and $s_{int} \in [0.0, 0.1, 0.2, 0.3]$ . We observe that the smaller the area of cropped images, the higher the performance. It suggests that local image patches that differ significantly from the original images provide more diverse input patterns for perturbation optimization and contribute to targeted transferability. Besides, when $s_l = 0.1$ and $s_{int} = 0.1$ , the optimal result is reached. However, the area relative to the original image may fluctuate within [0.1, 0.2]. To keep it stable, we use the parameters $s = (0.1, 0.0)$ to conduct subsequent experiments. Figure 4b shows the results of performing attacks on different layers and $\lambda$ . Extracting features from layer 3 is better than other layers. This is because the features captured by shallow layers represent the low-level patterns (such as edges), + +Table 5. Average TASR (\%) of black-box models for our proposed method with different component combinations. The classification loss is set as CE. $\checkmark$ indicates that the component is used while $-$ indicates that it is not used. TASR is averaged among four attack scenarios using ResNet50, DenseNet121, VGGNet16 and Inceptionv3 as white-box models, respectively. + +
RegionRes50VGG16Inc-v3
Center33.029.29.9
Corner33.630.910.8
Whole39.432.410.8
Uniform3.11.70.4
+ +Table 6. TASR (\%) of DTMI-CE-SU with different distributions of local images. The top three rows show different regions of random cropping. The last row denotes the uniform distribution $\mathcal{U}(0,1)$ of local images. + +while the deepest layer contains more semantic information hence is more related to the classification task of the white-box model [30]. For the weighted parameter $\lambda$ , we set $\lambda \in [10^{-4}, 10^{-3}, 10^{-2}, 10^{-1}, 10^{0}]$ . When $\lambda = 10^{-3}$ , SU achieves the best result. + +Effect of different regions. The regions of random cropping determine the distribution of local images. The center may be more related to the object of the image than the corner. Therefore, we conduct experiments on the center, the corner and the whole regions. We also compare the uniform distribution $\mathcal{U}(0,1)$ of local images. As shown in Table 6, there is no significant performance difference between the center and the corner. The reason is that SU concentrates on the target class regardless of the object related to the original class. Therefore, directly providing more local input patterns within one image leads to better performance in SU. The whole region indeed achieves the best performance. Moreover, the uniform distribution makes it difficult to converge, resulting in the worst performance. + +# 5. Conclusion + +In this paper, we provide new insight into transfer-based targeted attacks: more universal perturbations yield better transferability. Based on this observation, we propose the Self-University (SU) attack, which optimizes perturbations on the global image and more diverse local images, and aligns intermediate features between them. In this way, SU can make perturbations to be agnostic to different image regions, resulting in high self-transferability. We conduct extensive experiments to show that SU can improve targeted transferability regardless of the single-model attack or ensemble-based attack. + +# 6. Acknowledgments + +This project was supported by National Key R&D Program of China (No. 2020AAA0140001), NSFC (No. 62072116), and Science and Technology Commission of Shanghai Municipality (No. 21JC1400600). + +# References + +[1] Junyoung Byun, Seungju Cho, Myung-Joon Kwon, Hee-Seon Kim, and Changick Kim. Improving the transferability of targeted adversarial examples through object-based diverse input. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 15244-15253, 2022. 7 +[2] Jia Deng, Wei Dong, Richard Socher, Li-Jia Li, K. Li, and Li Fei-Fei. Imagenet: A large-scale hierarchical image database. 2009 IEEE Conference on Computer Vision and Pattern Recognition, pages 248-255, 2009. 3 +[3] Yinpeng Dong, Fangzhou Liao, Tianyu Pang, Hang Su, Jun Zhu, Xiaolin Hu, and Jianguo Li. 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Our new attack method is proposed based on the observation that highly universal adversarial perturbations tend to be more transferable for targeted attacks. Therefore, we propose to make the perturbation to be agnostic to different local regions within one image, which we called as self-universality. Instead of optimizing the perturbations on different images, optimizing on different regions to achieve self-universality can get rid of using extra data. Specifically, we introduce a feature similarity loss that encourages the learned perturbations to be universal by maximizing the feature similarity between adversarial perturbed global images and randomly cropped local regions. With the feature similarity loss, our method makes the features from adversarial perturbations to be more dominant than that of benign images, hence improving targeted transferability. We name the proposed attack method as Self-Universality (SU) attack. Extensive experiments demonstrate that SU can achieve high success rates for transfer-based targeted attacks. On ImageNet-compatible dataset, SU yields an improvement of " + }, + { + "bbox": [ + 47, + 252, + 289, + 563 + ], + "type": "inline_equation", + "content": "12\\%" + }, + { + "bbox": [ + 47, + 252, + 289, + 563 + ], + "type": "text", + "content": " compared with existing state-of-the-art methods. Code is available at https://github.com/zhipeng-wei/Self-Universality." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 588, + 128, + 601 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 588, + 128, + 601 + ], + "spans": [ + { + "bbox": [ + 47, + 588, + 128, + 601 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 609, + 287, + 693 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 609, + 287, + 693 + ], + "spans": [ + { + "bbox": [ + 46, + 609, + 287, + 693 + ], + "type": "text", + "content": "It has been demonstrated in recent works that adversarial examples have the properties of transferability, which means an adversarial example generated on one white-box model can be used to fool other black-box models [3, 15, 27, 30, 33]. The existence of transferability brings convenience to performing black-box attacks, hence raising security concerns for deploying deep models in real-world" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 228, + 545, + 276 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 228, + 545, + 276 + ], + "spans": [ + { + "bbox": [ + 306, + 228, + 545, + 276 + ], + "type": "text", + "content": "applications [14,22,28,35]. Consequently, considerable research attention has been spent on improving the transferability of adversarial examples for both non-targeted and targeted attacks [4, 29, 36]." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 279, + 547, + 482 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 279, + 547, + 482 + ], + "spans": [ + { + "bbox": [ + 304, + 279, + 547, + 482 + ], + "type": "text", + "content": "Compared to non-targeted attacks, transfer-based targeted attacks are inherently much more challenging since the goal is to fool deep models into predicting the specific target class. The major difficulty of transfer-based targeted attacks is caused by the fact that the gradient directions from a source image to a target class are usually different among different DNNs [16]. Hence, transfer-based attack methods designed for non-targeted attacks typically work poorly for targeted attacks. To increase the transferability, previous studies make efforts in aligning the feature of the generated adversarial example with the feature distributions of the targeted class, which are learned from class-specific auxiliary networks [7, 8] or generative adversarial networks [18]. However, these works assume that the training dataset is available and require extra training efforts for auxiliary networks, making it hard to apply in real-world scenarios." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 486, + 547, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 486, + 547, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 486, + 547, + 714 + ], + "type": "text", + "content": "This paper investigates the problem of transfer-based targeted attacks. Specifically, we propose a new method that improves the transferability of adversarial examples in a more efficient way, i.e., without any training efforts for auxiliary networks to learn the feature distributions of the targeted class. Our method is proposed based on the observation that more universal perturbations yield better attack success rates in targeted attacks. To this end, our goal is to enhance the universality of the generated adversarial perturbations, in order to improve its targeted transferability. Note that existing universal adversarial perturbation (UAP) attacks [17] require optimizing the perturbations on an abundant set of images to achieve universality, which is not applicable in our setting. To get rid of using extra data and make transfer-based targeted attacks as convenient as non-targeted attacks, we propose to make the perturbation to be agnostic to different local regions within one image, which we called as self-universality. Then our method optimizes the self-universality of adversarial pertur" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 702, + 135, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 702, + 135, + 712 + ], + "spans": [ + { + "bbox": [ + 58, + 702, + 135, + 712 + ], + "type": "text", + "content": "† Corresponding author." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "12281" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 97, + 70, + 492, + 218 + ], + "blocks": [ + { + "bbox": [ + 97, + 70, + 492, + 218 + ], + "lines": [ + { + "bbox": [ + 97, + 70, + 492, + 218 + ], + "spans": [ + { + "bbox": [ + 97, + 70, + 492, + 218 + ], + "type": "image", + "image_path": "9cf0e970e901a9cf9489e12017896756a0828c0afd4585fdef40b07e5c10abad.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 222, + 547, + 268 + ], + "lines": [ + { + "bbox": [ + 46, + 222, + 547, + 268 + ], + "spans": [ + { + "bbox": [ + 46, + 222, + 547, + 268 + ], + "type": "text", + "content": "Figure 1. Overview of the proposed SU attack. The random cropping is applied to the given benign image to generate the local image patch. After cropping, the local patch is resized to the shape of the benign image. Then both benign and local adversarial images with the shared perturbations are input to a surrogate white-box CNN model. Finally, the gradients obtained from the classification loss and the feature similarity loss are used to optimize perturbations." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 288, + 287, + 384 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 288, + 287, + 384 + ], + "spans": [ + { + "bbox": [ + 46, + 288, + 287, + 384 + ], + "type": "text", + "content": "bations instead. To be specific, in addition to classification loss, our Self-Universality (SU) attack method introduces a feature similarity loss that maximizes the feature similarity between adversarial perturbed global images and randomly cropped local regions to achieve self-universality. In this way, our method makes the features from adversarial perturbations to be more dominant than that of benign images, hence improving targeted transferability." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 384, + 288, + 587 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 384, + 288, + 587 + ], + "spans": [ + { + "bbox": [ + 46, + 384, + 288, + 587 + ], + "type": "text", + "content": "Figure 1 gives an overview of the proposed Self-Universality (SU) attack. SU firstly applies random cropping on benign images to obtain local cropped patches. Then it resizes local patches to the same size with benign images. Consequently, global and local inputs with shared perturbations are input to the white-box model. Finally, adversarial perturbations are updated by minimizing the classification loss (e.g., Cross Entropy) between inputs and the target class and maximizing the feature similarity loss (e.g., Cosine Similarity) of adversarial intermediate features between local and global inputs. Benefiting from satisfying the prediction of the target class between global and local inputs and approximating adversarial intermediate features between the two, the proposed SU attack can generate perturbations with self-universality, thereby improving the cross-model targeted transferability. We briefly summarize our primary contributions as follows:" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 58, + 592, + 287, + 713 + ], + "type": "list", + "angle": 0, + "index": 7, + "blocks": [ + { + "bbox": [ + 58, + 592, + 287, + 640 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 592, + 287, + 640 + ], + "spans": [ + { + "bbox": [ + 58, + 592, + 287, + 640 + ], + "type": "text", + "content": "- Through experiments, we find that highly universal adversarial perturbations tend to be more transferable for targeted attacks, which brings new insight into the design of transfer-based targeted attack methods." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 58, + 647, + 287, + 694 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 647, + 287, + 694 + ], + "spans": [ + { + "bbox": [ + 58, + 647, + 287, + 694 + ], + "type": "text", + "content": "- Based on the finding, we propose a novel Self-Universality (SU) attack method that enhances the universality of adversarial perturbations for better targeted transferability without the requirement for extra data." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 58, + 701, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 701, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 58, + 701, + 287, + 713 + ], + "type": "text", + "content": "- We conduct comprehensive experiments to demon" + } + ] + } + ], + "index": 6 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 325, + 288, + 545, + 336 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 325, + 288, + 545, + 336 + ], + "spans": [ + { + "bbox": [ + 325, + 288, + 545, + 336 + ], + "type": "text", + "content": "strate that the proposed SU attack can significantly improve the cross-model targeted transferability of adversarial images. Notably, SU can be easily combined with other existing methods." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 346, + 392, + 358 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 346, + 392, + 358 + ], + "spans": [ + { + "bbox": [ + 306, + 346, + 392, + 358 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 365, + 545, + 390 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 365, + 545, + 390 + ], + "spans": [ + { + "bbox": [ + 305, + 365, + 545, + 390 + ], + "type": "text", + "content": "In this section, we review existing works on non-targeted transferable attacks as well as targeted transferable attacks." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 396, + 492, + 408 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 396, + 492, + 408 + ], + "spans": [ + { + "bbox": [ + 306, + 396, + 492, + 408 + ], + "type": "text", + "content": "2.1. Non-targeted Transferable Attacks" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 415, + 545, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 415, + 545, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 415, + 545, + 715 + ], + "type": "text", + "content": "Non-targeted transferable attacks are based on the Iterative-Fast Gradient Sign Method (I-FGSM) [11], which iteratively calculates the gradient of the classification loss with respect to the input and updates perturbations along the direction of maximizing the loss. The multiple-step update of I-FGSM leads to more wrong predictions of white-box models. However, the generated adversarial examples are hard to attack other black-box models. This phenomenon is called over-fitting to the white-box model [10]. Subsequently, several works perform data augmentation or advanced gradient calculation to overcome the over-fitting problem. Data augmentation creates various input patterns, which generate adversarial perturbations with a generic pattern. For the input images, Diverse Input (DI) [33] performs random resizing and padding, Scale-invariant method (SIM) [13] applies scale transformation, Admix [24] extends SIM by integrating images from other labels. However, these data augmentation approaches neglect to consider more diverse input patterns (e.g., random cropping in this paper), and focus on the loss-preserving transformation [13]. This is because the gradient direction fluctuates violently under more diverse input patterns without specified target classes in non-target attacks. Advanced gradient calculation pays attention to changing gradient calculation methods or designing a new loss function. For changing" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "12282" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 301 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 301 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 301 + ], + "type": "text", + "content": "gradient calculation, the momentum term [3] and the Nesterov accelerated gradient [13] can be incorporated with I-FGSM to stabilize gradients. Translation-Invariant (TI) [4] smooths gradients through a predefined convolution kernel in order to mitigate the over-fitting problem. Skip Gradient Method (SGM) [31] modifies the path of gradient backpropagation by skipping residual modules. Variance Tuning [23] utilizes gradients from data points around previous data to avoid over-fitting. For designing a new loss function, Attention-guided Transfer Attack (ATA) [32] and Feature Importance-aware Attack (FIA) [26] disrupt important features that are likely to be utilized in other black-box models. ATA applies Grad-CAM [19] to represent attention weights of features. Different to ATA, FIA computes averaged gradients of features among various augmented inputs as attention weights. However, these new loss functions are restricted to global structures. In contrast, this paper calculates the feature similarity loss between global and local structures of images." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 310, + 214, + 323 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 310, + 214, + 323 + ], + "spans": [ + { + "bbox": [ + 47, + 310, + 214, + 323 + ], + "type": "text", + "content": "2.2. Targeted Transferable Attacks" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 329, + 289, + 605 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 329, + 289, + 605 + ], + "spans": [ + { + "bbox": [ + 46, + 329, + 289, + 605 + ], + "type": "text", + "content": "The transfer-based targeted attacks are more challenging than the non-targeted attacks due to the requirement of fooling the model into predicting the specified target class. Previous efforts have been devoted into training class-specific auxiliary networks [7, 8] or generative adversarial networks (GANs) [18], in order to learn feature distributions of the targeted class. Feature Distribution Attack (FDA) [8] utilizes the intermediate features of the training dataset from the white-box model to train a binary classifier, which predicts the probability that the current feature belongs to the targeted class. Then, through learning class-wise and layer-wise feature distributions, FDA generates targeted transferable adversarial perturbations by maximizing the probability outputted from the trained binary classifier. Subsequently, " + }, + { + "bbox": [ + 46, + 329, + 289, + 605 + ], + "type": "inline_equation", + "content": "FDA^{N} + xent" + }, + { + "bbox": [ + 46, + 329, + 289, + 605 + ], + "type": "text", + "content": " [7] incorporates the CE loss and multi-layer information with FDA, achieving better performance. Transferable targeted perturbations (TTP) [18] trains a generator to synthesize perturbations that seek to have similar features with targeted samples in the latent space of a pretrained discriminator. This series of FDA works and TTP improve the performance of targeted transferable attacks, but require additional training efforts for auxiliary networks on the training dataset." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 605, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 605, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 605, + 289, + 715 + ], + "type": "text", + "content": "To improve the efficiency of targeted transferable attacks, recent works pay more attention to iterative attacks based on I-FGSM. Activation Attack (AA) [9] replace the classification loss with a euclidean distance loss between features of adversarial and targeted images. However, AA depends on the selected examples of the targeted class and achieves low performance on the large resolution image dataset (e.g. ImageNet [2]). Different to AA, Po+Trip [12] utilizes Poincaré distance metric to solve the noise curing." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 304, + 72, + 547, + 264 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 264 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 264 + ], + "type": "text", + "content": "They also design a triplet loss for driving adversarial examples away from the original class. However, " + }, + { + "bbox": [ + 304, + 72, + 547, + 264 + ], + "type": "inline_equation", + "content": "\\mathrm{Po + Tri}" + }, + { + "bbox": [ + 304, + 72, + 547, + 264 + ], + "type": "text", + "content": " evaluates the attack performance only on easy transfer scenarios, and also achieves poor performance on the targeted scenario used in the Logit attack [36]. Logit [36] attributes the poor performance of I-FGSM based methods to the restricted number of iterations. Thus, Logit enlarges the number of iterations for ensuring the convergence of attacks. In addition, to overcome the vanishing gradient caused by the large iterations, Logit utilizes gradients of the targeted logit output with respect to inputs to update perturbations. Different to them, our method leverages the global and local structures to generate adversarial examples with self-universality, hence improving targeted transferability. Note that the proposed SU attack can be easily combined with existing methods." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 306, + 272, + 389, + 287 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 272, + 389, + 287 + ], + "spans": [ + { + "bbox": [ + 306, + 272, + 389, + 287 + ], + "type": "text", + "content": "3. Methodology" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 306, + 292, + 386, + 306 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 292, + 386, + 306 + ], + "spans": [ + { + "bbox": [ + 306, + 292, + 386, + 306 + ], + "type": "text", + "content": "3.1. Preliminary" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 310, + 547, + 501 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 310, + 547, + 501 + ], + "spans": [ + { + "bbox": [ + 304, + 310, + 547, + 501 + ], + "type": "text", + "content": "Let " + }, + { + "bbox": [ + 304, + 310, + 547, + 501 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 304, + 310, + 547, + 501 + ], + "type": "text", + "content": " represent the white-box surrogate model, " + }, + { + "bbox": [ + 304, + 310, + 547, + 501 + ], + "type": "inline_equation", + "content": "v" + }, + { + "bbox": [ + 304, + 310, + 547, + 501 + ], + "type": "text", + "content": " be the black-box victim model, " + }, + { + "bbox": [ + 304, + 310, + 547, + 501 + ], + "type": "inline_equation", + "content": "x \\in \\mathcal{X} \\subset \\mathbf{R}^{H \\times W \\times C}" + }, + { + "bbox": [ + 304, + 310, + 547, + 501 + ], + "type": "text", + "content": " be the benign image with the ground-truth label " + }, + { + "bbox": [ + 304, + 310, + 547, + 501 + ], + "type": "inline_equation", + "content": "y \\in \\mathcal{Y} = \\{1, 2, \\dots, K\\}" + }, + { + "bbox": [ + 304, + 310, + 547, + 501 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 310, + 547, + 501 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 304, + 310, + 547, + 501 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 310, + 547, + 501 + ], + "type": "inline_equation", + "content": "v" + }, + { + "bbox": [ + 304, + 310, + 547, + 501 + ], + "type": "text", + "content": " are trained with the same training dataset, " + }, + { + "bbox": [ + 304, + 310, + 547, + 501 + ], + "type": "inline_equation", + "content": "H" + }, + { + "bbox": [ + 304, + 310, + 547, + 501 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 310, + 547, + 501 + ], + "type": "inline_equation", + "content": "W" + }, + { + "bbox": [ + 304, + 310, + 547, + 501 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 310, + 547, + 501 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 304, + 310, + 547, + 501 + ], + "type": "text", + "content": " denote the number of height, width and channels respectively, and " + }, + { + "bbox": [ + 304, + 310, + 547, + 501 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 304, + 310, + 547, + 501 + ], + "type": "text", + "content": " is the number of classes. We use " + }, + { + "bbox": [ + 304, + 310, + 547, + 501 + ], + "type": "inline_equation", + "content": "f(x), v(x)" + }, + { + "bbox": [ + 304, + 310, + 547, + 501 + ], + "type": "text", + "content": " to be the prediction over the set of classes " + }, + { + "bbox": [ + 304, + 310, + 547, + 501 + ], + "type": "inline_equation", + "content": "\\mathcal{V}" + }, + { + "bbox": [ + 304, + 310, + 547, + 501 + ], + "type": "text", + "content": ". Given a specified targeted class " + }, + { + "bbox": [ + 304, + 310, + 547, + 501 + ], + "type": "inline_equation", + "content": "y_{t}" + }, + { + "bbox": [ + 304, + 310, + 547, + 501 + ], + "type": "text", + "content": ", the targeted transferable attacks aim to generate adversarial examples " + }, + { + "bbox": [ + 304, + 310, + 547, + 501 + ], + "type": "inline_equation", + "content": "x_{adv}" + }, + { + "bbox": [ + 304, + 310, + 547, + 501 + ], + "type": "text", + "content": " from the white-box model " + }, + { + "bbox": [ + 304, + 310, + 547, + 501 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 304, + 310, + 547, + 501 + ], + "type": "text", + "content": " that satisfy " + }, + { + "bbox": [ + 304, + 310, + 547, + 501 + ], + "type": "inline_equation", + "content": "v(x_{adv}) = y_{t}" + }, + { + "bbox": [ + 304, + 310, + 547, + 501 + ], + "type": "text", + "content": ". Following previous works, we enforce a " + }, + { + "bbox": [ + 304, + 310, + 547, + 501 + ], + "type": "inline_equation", + "content": "L_{\\infty}" + }, + { + "bbox": [ + 304, + 310, + 547, + 501 + ], + "type": "text", + "content": "-norm constraint on perturbations, which can be formulated as " + }, + { + "bbox": [ + 304, + 310, + 547, + 501 + ], + "type": "inline_equation", + "content": "||x_{adv} - x||_{\\infty} = ||\\delta||_{\\infty} \\leq \\epsilon" + }, + { + "bbox": [ + 304, + 310, + 547, + 501 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 310, + 547, + 501 + ], + "type": "inline_equation", + "content": "\\delta" + }, + { + "bbox": [ + 304, + 310, + 547, + 501 + ], + "type": "text", + "content": " is the perturbation, " + }, + { + "bbox": [ + 304, + 310, + 547, + 501 + ], + "type": "inline_equation", + "content": "\\epsilon" + }, + { + "bbox": [ + 304, + 310, + 547, + 501 + ], + "type": "text", + "content": " denotes a constant of the norm constraint. Given a classification loss " + }, + { + "bbox": [ + 304, + 310, + 547, + 501 + ], + "type": "inline_equation", + "content": "J" + }, + { + "bbox": [ + 304, + 310, + 547, + 501 + ], + "type": "text", + "content": " (e.g. CE loss) of " + }, + { + "bbox": [ + 304, + 310, + 547, + 501 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 304, + 310, + 547, + 501 + ], + "type": "text", + "content": ", the targeted attack of I-FGSM can be formulated as:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 377, + 508, + 545, + 520 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 377, + 508, + 545, + 520 + ], + "spans": [ + { + "bbox": [ + 377, + 508, + 545, + 520 + ], + "type": "interline_equation", + "content": "\\delta_ {0} = 0, g _ {0} = 0, \\tag {1}", + "image_path": "b2f0a8a64dce5de4e93617668083d03f3dbfac6fd0546380489e404cb5fc812b.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 367, + 522, + 545, + 535 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 367, + 522, + 545, + 535 + ], + "spans": [ + { + "bbox": [ + 367, + 522, + 545, + 535 + ], + "type": "interline_equation", + "content": "g _ {i + 1} = \\nabla_ {\\delta} J (f (x + \\delta_ {i}), y _ {t}), \\tag {2}", + "image_path": "a9a6f8b1795fb1c08ab15cd4777eaecd682a4ea77ca3f951100e110cc781b038.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 367, + 537, + 545, + 550 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 367, + 537, + 545, + 550 + ], + "spans": [ + { + "bbox": [ + 367, + 537, + 545, + 550 + ], + "type": "interline_equation", + "content": "\\delta_ {i + 1} = \\delta_ {i} - \\alpha * \\operatorname {s i g n} \\left(g _ {i + 1}\\right), \\tag {3}", + "image_path": "e5ec697c1fd0eaefcd9ff28f664930fab63b1e7bfdfc62d56f62248b0963ae93.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 367, + 552, + 545, + 565 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 367, + 552, + 545, + 565 + ], + "spans": [ + { + "bbox": [ + 367, + 552, + 545, + 565 + ], + "type": "interline_equation", + "content": "\\delta_ {i + 1} = \\operatorname {C l i p} _ {x, \\epsilon} (\\delta_ {i + 1}), \\tag {4}", + "image_path": "c2deb4add0b3cbbdc27c9148913baba592c4d00e181f2734b8da81629394bce8.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 570, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 547, + 715 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 570, + 547, + 715 + ], + "type": "inline_equation", + "content": "\\delta_{i}, g_{i}" + }, + { + "bbox": [ + 304, + 570, + 547, + 715 + ], + "type": "text", + "content": " denote the adversarial perturbation and the gradient of the " + }, + { + "bbox": [ + 304, + 570, + 547, + 715 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 304, + 570, + 547, + 715 + ], + "type": "text", + "content": "-th iteration, " + }, + { + "bbox": [ + 304, + 570, + 547, + 715 + ], + "type": "inline_equation", + "content": "i = [0, \\dots, I - 1]" + }, + { + "bbox": [ + 304, + 570, + 547, + 715 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 570, + 547, + 715 + ], + "type": "inline_equation", + "content": "I" + }, + { + "bbox": [ + 304, + 570, + 547, + 715 + ], + "type": "text", + "content": " is the maximum number of iterations; " + }, + { + "bbox": [ + 304, + 570, + 547, + 715 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 304, + 570, + 547, + 715 + ], + "type": "text", + "content": " is the step size; the function " + }, + { + "bbox": [ + 304, + 570, + 547, + 715 + ], + "type": "inline_equation", + "content": "Clip_{x,\\epsilon}(\\cdot)" + }, + { + "bbox": [ + 304, + 570, + 547, + 715 + ], + "type": "text", + "content": " projects " + }, + { + "bbox": [ + 304, + 570, + 547, + 715 + ], + "type": "inline_equation", + "content": "\\delta" + }, + { + "bbox": [ + 304, + 570, + 547, + 715 + ], + "type": "text", + "content": " to the vicinity of " + }, + { + "bbox": [ + 304, + 570, + 547, + 715 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 304, + 570, + 547, + 715 + ], + "type": "text", + "content": " for satisfying the " + }, + { + "bbox": [ + 304, + 570, + 547, + 715 + ], + "type": "inline_equation", + "content": "L_{\\infty}" + }, + { + "bbox": [ + 304, + 570, + 547, + 715 + ], + "type": "text", + "content": "-norm constraint. Specifically, I-FGSM first initializes " + }, + { + "bbox": [ + 304, + 570, + 547, + 715 + ], + "type": "inline_equation", + "content": "\\delta_0" + }, + { + "bbox": [ + 304, + 570, + 547, + 715 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 570, + 547, + 715 + ], + "type": "inline_equation", + "content": "g_{0}" + }, + { + "bbox": [ + 304, + 570, + 547, + 715 + ], + "type": "text", + "content": " as 0 (Eq.1). Then it calculates the gradients of the loss function with respect to the perturbation (Eq.2), and drives the prediction of " + }, + { + "bbox": [ + 304, + 570, + 547, + 715 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 304, + 570, + 547, + 715 + ], + "type": "text", + "content": " on the adversarial example towards the targeted class by minimizing " + }, + { + "bbox": [ + 304, + 570, + 547, + 715 + ], + "type": "inline_equation", + "content": "J(f(x + \\delta_i), y_t)" + }, + { + "bbox": [ + 304, + 570, + 547, + 715 + ], + "type": "text", + "content": " (Eq.3). Finally, it restricts the adversarial perturbation with the " + }, + { + "bbox": [ + 304, + 570, + 547, + 715 + ], + "type": "inline_equation", + "content": "L_{\\infty}" + }, + { + "bbox": [ + 304, + 570, + 547, + 715 + ], + "type": "text", + "content": "-norm constraint (Eq.4). Eq.2, 3, 4 are performed alternately until the maximum iteration is reached. Through" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "12283" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 80, + 76, + 291, + 236 + ], + "blocks": [ + { + "bbox": [ + 80, + 76, + 291, + 236 + ], + "lines": [ + { + "bbox": [ + 80, + 76, + 291, + 236 + ], + "spans": [ + { + "bbox": [ + 80, + 76, + 291, + 236 + ], + "type": "image", + "image_path": "8ef664ac2e65f34a3891df8c8abc896cceb0a674acbb8dd55fe7a7db638f8dc7.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 146, + 241, + 225, + 251 + ], + "lines": [ + { + "bbox": [ + 146, + 241, + 225, + 251 + ], + "spans": [ + { + "bbox": [ + 146, + 241, + 225, + 251 + ], + "type": "text", + "content": "(a) Universal evaluation" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 299, + 93, + 513, + 235 + ], + "blocks": [ + { + "bbox": [ + 299, + 93, + 513, + 235 + ], + "lines": [ + { + "bbox": [ + 299, + 93, + 513, + 235 + ], + "spans": [ + { + "bbox": [ + 299, + 93, + 513, + 235 + ], + "type": "image", + "image_path": "42c4654e040875b8b4ae0d74da068fdac2f3323f994f1f8fcce1f21cf1df7a67.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 357, + 241, + 454, + 251 + ], + "lines": [ + { + "bbox": [ + 357, + 241, + 454, + 251 + ], + "spans": [ + { + "bbox": [ + 357, + 241, + 454, + 251 + ], + "type": "text", + "content": "(b) Feature similarity analysis" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 46, + 254, + 547, + 299 + ], + "lines": [ + { + "bbox": [ + 46, + 254, + 547, + 299 + ], + "spans": [ + { + "bbox": [ + 46, + 254, + 547, + 299 + ], + "type": "text", + "content": "Figure 2. (a) For each targeted perturbation generated by I-FGSM or DTMI, we calculate the number of successful targeted attacks caused by adding this perturbation to benign images other than the original optimized image. (b) We average the cosine similarity of intermediate features among different benign images or universal adversarial images that are generated by adding the same perturbation to these benign images." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 319, + 287, + 415 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 319, + 287, + 415 + ], + "spans": [ + { + "bbox": [ + 46, + 319, + 287, + 415 + ], + "type": "text", + "content": "this greedy update, I-FGSM is easily caught in local maxima and over-fitting to " + }, + { + "bbox": [ + 46, + 319, + 287, + 415 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 46, + 319, + 287, + 415 + ], + "type": "text", + "content": ", which results in performing poorly for targeted attacks. Therefore, previous work [36] utilizes the combination of DI [33], TI [4] and MI [3] as the baseline, since it could achieve more stable performances with a large number of iteration compared to I-FGSM. For convenience, we abbreviate the name of this combination as DTMI. DTMI replaces Eq.2 with" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 55, + 418, + 287, + 447 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 55, + 418, + 287, + 447 + ], + "spans": [ + { + "bbox": [ + 55, + 418, + 287, + 447 + ], + "type": "interline_equation", + "content": "g _ {i + 1} = \\mu \\cdot g _ {i} + \\frac {W \\cdot \\nabla_ {\\delta} J (f (T (x + \\delta_ {i} , p)) , y _ {t})}{\\left| \\left| W \\cdot \\nabla_ {\\delta} J (f (T (x + \\delta_ {i} , p)), y _ {t}) \\right| \\right| _ {1}}, \\tag {5}", + "image_path": "92ce1aedafa223f1dd0d4788868ac3987da4fee62cc6cadd999a356847c09faf.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 449, + 287, + 486 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 449, + 287, + 486 + ], + "spans": [ + { + "bbox": [ + 47, + 449, + 287, + 486 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 449, + 287, + 486 + ], + "type": "inline_equation", + "content": "T(x + \\delta_i, p)" + }, + { + "bbox": [ + 47, + 449, + 287, + 486 + ], + "type": "text", + "content": " performs random resizing and padding with a probability " + }, + { + "bbox": [ + 47, + 449, + 287, + 486 + ], + "type": "inline_equation", + "content": "p" + }, + { + "bbox": [ + 47, + 449, + 287, + 486 + ], + "type": "text", + "content": " in DI, " + }, + { + "bbox": [ + 47, + 449, + 287, + 486 + ], + "type": "inline_equation", + "content": "W" + }, + { + "bbox": [ + 47, + 449, + 287, + 486 + ], + "type": "text", + "content": " is the pre-defined convolution kernel in TI, " + }, + { + "bbox": [ + 47, + 449, + 287, + 486 + ], + "type": "inline_equation", + "content": "\\mu" + }, + { + "bbox": [ + 47, + 449, + 287, + 486 + ], + "type": "text", + "content": " is a decay factor in MI." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 491, + 251, + 504 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 491, + 251, + 504 + ], + "spans": [ + { + "bbox": [ + 47, + 491, + 251, + 504 + ], + "type": "text", + "content": "3.2. Universality of Targeted Perturbations" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 510, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 510, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 510, + 288, + 715 + ], + "type": "text", + "content": "Transferable targeted attacks aim to generate cross-model perturbations that drive the prediction of different models towards predicting the same specified class. It requires perturbations generated from one white-box model are model-agnostic, i.e., universal to different models. A simple way to meet this requirement is to optimize perturbations on massive models. However, it may be impractical in the real world, because the number of white-box models is usually limited. In contrast, targeted universal adversarial perturbations (UAP) [17] lead to a specific prediction " + }, + { + "bbox": [ + 46, + 510, + 288, + 715 + ], + "type": "inline_equation", + "content": "y_{t}" + }, + { + "bbox": [ + 46, + 510, + 288, + 715 + ], + "type": "text", + "content": " of DNNs for almost all images. [34] attributes this phenomenon to the dominant features produced by Targeted UAP. Specifically, let " + }, + { + "bbox": [ + 46, + 510, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\delta_{u}" + }, + { + "bbox": [ + 46, + 510, + 288, + 715 + ], + "type": "text", + "content": " denote targeted UAP, they conclude that the predictive logit vectors of " + }, + { + "bbox": [ + 46, + 510, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\delta_{u}" + }, + { + "bbox": [ + 46, + 510, + 288, + 715 + ], + "type": "text", + "content": " have a higher linear correlation with that of " + }, + { + "bbox": [ + 46, + 510, + 288, + 715 + ], + "type": "inline_equation", + "content": "x + \\delta_{u}" + }, + { + "bbox": [ + 46, + 510, + 288, + 715 + ], + "type": "text", + "content": ", while the linear correlation between " + }, + { + "bbox": [ + 46, + 510, + 288, + 715 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 46, + 510, + 288, + 715 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 510, + 288, + 715 + ], + "type": "inline_equation", + "content": "x + \\delta_{u}" + }, + { + "bbox": [ + 46, + 510, + 288, + 715 + ], + "type": "text", + "content": " is low. It suggests that the features of " + }, + { + "bbox": [ + 46, + 510, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\delta_{u}" + }, + { + "bbox": [ + 46, + 510, + 288, + 715 + ], + "type": "text", + "content": " represent the feature distribution of the specific" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 319, + 545, + 415 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 319, + 545, + 415 + ], + "spans": [ + { + "bbox": [ + 304, + 319, + 545, + 415 + ], + "type": "text", + "content": "targeted class and dominate the prediction of DNNs. Therefore, targeted UAP could transfer to attack other models trained on the same dataset, because these models share the similar feature distribution of the target class. In summary, universality may correlate to transferability in targeted attacks. Motivated by the above analysis, we delve into the divergence between perturbations crafted by I-FGSM and DTMI from the perspective of universality." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 415, + 546, + 559 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 415, + 546, + 559 + ], + "spans": [ + { + "bbox": [ + 304, + 415, + 546, + 559 + ], + "type": "text", + "content": "To further verify the findings in the above analysis, we conduct experiments to show the correlation between universality and targeted transferability. We optimize targeted perturbations on the ImageNet-compatible dataset (dataset details are in Section 4.1) by I-FGSM and DTMI using DenseNet121 as the white-box model. Here CE loss is utilized as classification loss. Given a set of benign images " + }, + { + "bbox": [ + 304, + 415, + 546, + 559 + ], + "type": "inline_equation", + "content": "\\Phi = \\{x^{1},\\dots,x^{m},\\dots,x^{M}\\}" + }, + { + "bbox": [ + 304, + 415, + 546, + 559 + ], + "type": "text", + "content": ", we generate the perturbation for each image in the set. Denote " + }, + { + "bbox": [ + 304, + 415, + 546, + 559 + ], + "type": "inline_equation", + "content": "\\delta^m" + }, + { + "bbox": [ + 304, + 415, + 546, + 559 + ], + "type": "text", + "content": " as the generated perturbation for " + }, + { + "bbox": [ + 304, + 415, + 546, + 559 + ], + "type": "inline_equation", + "content": "x^{m}" + }, + { + "bbox": [ + 304, + 415, + 546, + 559 + ], + "type": "text", + "content": ". To evaluate the universality of " + }, + { + "bbox": [ + 304, + 415, + 546, + 559 + ], + "type": "inline_equation", + "content": "\\delta^m" + }, + { + "bbox": [ + 304, + 415, + 546, + 559 + ], + "type": "text", + "content": ", we add " + }, + { + "bbox": [ + 304, + 415, + 546, + 559 + ], + "type": "inline_equation", + "content": "\\delta^m" + }, + { + "bbox": [ + 304, + 415, + 546, + 559 + ], + "type": "text", + "content": " to all benign images other than " + }, + { + "bbox": [ + 304, + 415, + 546, + 559 + ], + "type": "inline_equation", + "content": "x^{m}" + }, + { + "bbox": [ + 304, + 415, + 546, + 559 + ], + "type": "text", + "content": ", and calculate the number of successful targeted attacks on DenseNet121 by:" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 352, + 565, + 545, + 600 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 352, + 565, + 545, + 600 + ], + "spans": [ + { + "bbox": [ + 352, + 565, + 545, + 600 + ], + "type": "interline_equation", + "content": "\\sum_ {j = 1, j \\neq m} ^ {M} \\left\\{ \\begin{array}{l l} 1, & \\text {i f} f \\left(x ^ {j} + \\delta^ {m}\\right) = y _ {t}, \\\\ 0, & \\text {o t h e r w i s e .} \\end{array} \\right. \\tag {6}", + "image_path": "d86a0a9fc4230cbd19148497bd9e8f7147a6b2f17b73edec8e837d978b5b9951.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 605, + 545, + 641 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 545, + 641 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 545, + 641 + ], + "type": "text", + "content": "The number of successful targeted attacks is used as the metric to evaluate the universality of " + }, + { + "bbox": [ + 304, + 605, + 545, + 641 + ], + "type": "inline_equation", + "content": "\\delta^m" + }, + { + "bbox": [ + 304, + 605, + 545, + 641 + ], + "type": "text", + "content": ". A higher number denotes better universality." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 642, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 642, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 642, + 545, + 714 + ], + "type": "text", + "content": "Figure 2a shows the comparison of universality between each perturbation crafted by I-FGSM and DTMI. For better visualization, we sort perturbations in descending order based on their universality reported in I-FGSM. Notably, DTMI attains higher universality than I-FGSM for each perturbation. This is because, aided by the diverse input pat" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "12284" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "type": "text", + "content": "terns provided by DI, DTMI makes the perturbations to be universal to these input patterns. Since DTMI achieves better targeted transferability than I-FGSM [36], we can basically draw a conclusion that there is a relatively positive correlation between universality and targeted transferability." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 144, + 289, + 431 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 144, + 289, + 431 + ], + "spans": [ + { + "bbox": [ + 46, + 144, + 289, + 431 + ], + "type": "text", + "content": "To provide insights on how the targeted perturbation affects the image features, we compare the average cosine similarity of intermediate features between benign images and adversarial images that generated by adding one specific targeted perturbation to these benign images. Specifically, these benign images can be denoted by " + }, + { + "bbox": [ + 46, + 144, + 289, + 431 + ], + "type": "inline_equation", + "content": "\\Phi^m" + }, + { + "bbox": [ + 46, + 144, + 289, + 431 + ], + "type": "text", + "content": ", which is the set of " + }, + { + "bbox": [ + 46, + 144, + 289, + 431 + ], + "type": "inline_equation", + "content": "x^j" + }, + { + "bbox": [ + 46, + 144, + 289, + 431 + ], + "type": "text", + "content": " satisfying " + }, + { + "bbox": [ + 46, + 144, + 289, + 431 + ], + "type": "inline_equation", + "content": "f(x^{j} + \\delta^{m}) = y_{t}" + }, + { + "bbox": [ + 46, + 144, + 289, + 431 + ], + "type": "text", + "content": ". Adversarial images can be denoted by " + }, + { + "bbox": [ + 46, + 144, + 289, + 431 + ], + "type": "inline_equation", + "content": "\\{x^{j} + \\delta^{m}\\}" + }, + { + "bbox": [ + 46, + 144, + 289, + 431 + ], + "type": "text", + "content": " for " + }, + { + "bbox": [ + 46, + 144, + 289, + 431 + ], + "type": "inline_equation", + "content": "x_{j}\\in \\Phi^{m}" + }, + { + "bbox": [ + 46, + 144, + 289, + 431 + ], + "type": "text", + "content": ". Figure 2b shows the changes in the feature similarity after adding the same perturbation " + }, + { + "bbox": [ + 46, + 144, + 289, + 431 + ], + "type": "inline_equation", + "content": "\\delta^m" + }, + { + "bbox": [ + 46, + 144, + 289, + 431 + ], + "type": "text", + "content": ". It can be observed that after adding this perturbation, the image features become more similar. This is because the targeted perturbations drive features from different benign images towards the feature distribution of the target class. In other words, compared to benign images, targeted perturbations produce more dominant features. In addition, from Figure 2b, we can also find that compared to I-FGSM, targeted perturbations generated by DTMI make the image features more similar. Since DTMI achieves better targeted transferability than I-FGSM, the result basically indicates that perturbations with highly targeted transferability will produce more dominant features and enjoy higher universality. The above analysis suggests that adversarial examples with high universality tend to be more transferable in targeted attacks." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 439, + 207, + 452 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 439, + 207, + 452 + ], + "spans": [ + { + "bbox": [ + 47, + 439, + 207, + 452 + ], + "type": "text", + "content": "3.3. Self-Universality (SU) Attack" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 458, + 287, + 685 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 458, + 287, + 685 + ], + "spans": [ + { + "bbox": [ + 46, + 458, + 287, + 685 + ], + "type": "text", + "content": "To enhance the universality of adversarial perturbations for transferable targeted attacks, we propose the Self-Universality (SU) attack method. Instead of optimizing the perturbations on different images to achieve universality, our SU method optimizes the perturbation to be agnostic to different local regions within one image, which is called self-universality. In this way, our method is able to generate the universal perturbations without extra data. To achieve self-universality, our method generates perturbations by incorporating randomly cropped local regions within one image into the iterative attacks. To create local input patterns, we consider the random cropping, which crops images into a local image patch by the scale parameter " + }, + { + "bbox": [ + 46, + 458, + 287, + 685 + ], + "type": "inline_equation", + "content": "s = \\{s_l, s_{int}\\}" + }, + { + "bbox": [ + 46, + 458, + 287, + 685 + ], + "type": "text", + "content": ". Where " + }, + { + "bbox": [ + 46, + 458, + 287, + 685 + ], + "type": "inline_equation", + "content": "s_l" + }, + { + "bbox": [ + 46, + 458, + 287, + 685 + ], + "type": "text", + "content": " denotes the lower bound for the area of the random cropped images, and " + }, + { + "bbox": [ + 46, + 458, + 287, + 685 + ], + "type": "inline_equation", + "content": "s_{int}" + }, + { + "bbox": [ + 46, + 458, + 287, + 685 + ], + "type": "text", + "content": " is the interval value between the lower and upper bounds, thus " + }, + { + "bbox": [ + 46, + 458, + 287, + 685 + ], + "type": "inline_equation", + "content": "s_l + s_{int}" + }, + { + "bbox": [ + 46, + 458, + 287, + 685 + ], + "type": "text", + "content": " is the upper bound. After cropping images, we resize them to the same shape as benign images. Let " + }, + { + "bbox": [ + 46, + 458, + 287, + 685 + ], + "type": "inline_equation", + "content": "Loc(x, s)" + }, + { + "bbox": [ + 46, + 458, + 287, + 685 + ], + "type": "text", + "content": " be the random cropping and the resizing operations*. In addition, we apply the same thresholding operation on all images in the image patches." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 306, + 72, + 432, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 72, + 432, + 83 + ], + "spans": [ + { + "bbox": [ + 306, + 72, + 432, + 83 + ], + "type": "text", + "content": "Algorithm 1 DTMI-SU attack" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 306, + 85, + 545, + 109 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 85, + 545, + 109 + ], + "spans": [ + { + "bbox": [ + 306, + 85, + 545, + 109 + ], + "type": "text", + "content": "Input: the classification loss function " + }, + { + "bbox": [ + 306, + 85, + 545, + 109 + ], + "type": "inline_equation", + "content": "J" + }, + { + "bbox": [ + 306, + 85, + 545, + 109 + ], + "type": "text", + "content": ", white-box model " + }, + { + "bbox": [ + 306, + 85, + 545, + 109 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 306, + 85, + 545, + 109 + ], + "type": "text", + "content": ", benign image " + }, + { + "bbox": [ + 306, + 85, + 545, + 109 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 306, + 85, + 545, + 109 + ], + "type": "text", + "content": ", targeted class " + }, + { + "bbox": [ + 306, + 85, + 545, + 109 + ], + "type": "inline_equation", + "content": "y_{t}" + }, + { + "bbox": [ + 306, + 85, + 545, + 109 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 305, + 110, + 545, + 145 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 110, + 545, + 145 + ], + "spans": [ + { + "bbox": [ + 305, + 110, + 545, + 145 + ], + "type": "text", + "content": "Parameter: The perturbation budget " + }, + { + "bbox": [ + 305, + 110, + 545, + 145 + ], + "type": "inline_equation", + "content": "\\epsilon" + }, + { + "bbox": [ + 305, + 110, + 545, + 145 + ], + "type": "text", + "content": ", iteration number I, step size " + }, + { + "bbox": [ + 305, + 110, + 545, + 145 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 305, + 110, + 545, + 145 + ], + "type": "text", + "content": ", scale parameter " + }, + { + "bbox": [ + 305, + 110, + 545, + 145 + ], + "type": "inline_equation", + "content": "s = \\{s_l, s_{int}\\}" + }, + { + "bbox": [ + 305, + 110, + 545, + 145 + ], + "type": "text", + "content": ", weighted parameter " + }, + { + "bbox": [ + 305, + 110, + 545, + 145 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 305, + 110, + 545, + 145 + ], + "type": "text", + "content": ", and DTMI parameters " + }, + { + "bbox": [ + 305, + 110, + 545, + 145 + ], + "type": "inline_equation", + "content": "T(\\cdot, p)" + }, + { + "bbox": [ + 305, + 110, + 545, + 145 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 305, + 110, + 545, + 145 + ], + "type": "inline_equation", + "content": "W" + }, + { + "bbox": [ + 305, + 110, + 545, + 145 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 305, + 110, + 545, + 145 + ], + "type": "inline_equation", + "content": "\\mu" + }, + { + "bbox": [ + 305, + 110, + 545, + 145 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 145, + 468, + 157 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 145, + 468, + 157 + ], + "spans": [ + { + "bbox": [ + 306, + 145, + 468, + 157 + ], + "type": "text", + "content": "Output: The adversarial example " + }, + { + "bbox": [ + 306, + 145, + 468, + 157 + ], + "type": "inline_equation", + "content": "x_{adv}" + }, + { + "bbox": [ + 306, + 145, + 468, + 157 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 312, + 171, + 545, + 293 + ], + "type": "list", + "angle": 0, + "index": 18, + "blocks": [ + { + "bbox": [ + 312, + 171, + 434, + 183 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, 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"\\mathbf{DI}\\colon x^{\\prime} = T(x + \\delta_{i},p);\\hat{x}^{\\prime} = T(\\hat{x} +\\delta_{i},p)" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 312, + 219, + 545, + 243 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 219, + 545, + 243 + ], + "spans": [ + { + "bbox": [ + 312, + 219, + 545, + 243 + ], + "type": "text", + "content": "5: Calculate gradients: " + }, + { + "bbox": [ + 312, + 219, + 545, + 243 + ], + "type": "inline_equation", + "content": "g_{i+1} = \\nabla_{\\delta}(J(f(x'), y_t) + J(f(\\hat{x}', y_t) - \\lambda \\cdot CS(f_l(x'), f_l(\\hat{x})))" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 312, + 242, + 442, + 258 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 242, + 442, + 258 + ], + "spans": [ + { + "bbox": [ + 312, + 242, + 442, + 258 + ], + "type": "text", + "content": "6: " + }, + { + "bbox": [ + 312, + 242, + 442, + 258 + ], + "type": "inline_equation", + "content": "g_{i + 1} = \\mu \\cdot g_i + \\frac{W\\cdot g_{i + 1}}{||W\\cdot g_{i + 1}||_1}" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 312, + 258, + 465, + 270 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 258, + 465, + 270 + ], + "spans": [ + { + "bbox": [ + 312, + 258, + 465, + 270 + ], + "type": "text", + "content": "7: Update and Clip " + }, + { + "bbox": [ + 312, + 258, + 465, + 270 + ], + "type": "inline_equation", + "content": "\\delta_{i + 1}" + }, + { + "bbox": [ + 312, + 258, + 465, + 270 + ], + "type": "text", + "content": " by Eq.3, 4" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 312, + 270, + 357, + 280 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 270, + 357, + 280 + ], + "spans": [ + { + "bbox": [ + 312, + 270, + 357, + 280 + ], + "type": "text", + "content": "8: end for" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 312, + 281, + 381, + 293 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, 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Under this design, SU could generate perturbations with more dominant features. This loss can be formulated by " + }, + { + "bbox": [ + 304, + 331, + 545, + 451 + ], + "type": "inline_equation", + "content": "CS(f_{l}(x + \\delta_{i}),f_{l}(Loc(x,s) + \\delta_{i}))" + }, + { + "bbox": [ + 304, + 331, + 545, + 451 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 331, + 545, + 451 + ], + "type": "inline_equation", + "content": "f_{l}(\\cdot)" + }, + { + "bbox": [ + 304, + 331, + 545, + 451 + ], + "type": "text", + "content": " means to extract features from the " + }, + { + "bbox": [ + 304, + 331, + 545, + 451 + ], + "type": "inline_equation", + "content": "l" + }, + { + "bbox": [ + 304, + 331, + 545, + 451 + ], + "type": "text", + "content": "-th layer of the white-box model " + }, + { + "bbox": [ + 304, + 331, + 545, + 451 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 304, + 331, + 545, + 451 + ], + "type": "text", + "content": ", the function " + }, + { + "bbox": [ + 304, + 331, + 545, + 451 + ], + "type": "inline_equation", + "content": "CS(\\cdot ,\\cdot)" + }, + { + "bbox": [ + 304, + 331, + 545, + 451 + ], + "type": "text", + "content": " calculates cosine similarity score of features between adversarial global and local inputs. In summary, the proposed SU replaces Eq.2 with:" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 312, + 474, + 545, + 514 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 474, + 545, + 514 + ], + "spans": [ + { + "bbox": [ + 312, + 474, + 545, + 514 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} g _ {i + 1} = \\nabla_ {\\delta} \\left(J \\left(f \\left(x + \\delta_ {i}\\right), y _ {t}\\right) + J \\left(f \\left(L o c (x, s) + \\delta_ {i}\\right), y _ {t}\\right) \\right. \\\\ - \\lambda \\cdot C S \\left(f _ {l} \\left(x + \\delta_ {i}\\right), f _ {l} \\left(L o c (x, s) + \\delta_ {i}\\right)\\right)), \\tag {7} \\\\ \\end{array}", + "image_path": "e1ebf59dd459985c844839964d93ac06fb88e0ef3c3a42de9193d8f42e7fa03a.jpg" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 305, + 538, + 545, + 563 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 538, + 545, + 563 + ], + "spans": [ + { + "bbox": [ + 305, + 538, + 545, + 563 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 538, + 545, + 563 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 305, + 538, + 545, + 563 + ], + "type": "text", + "content": " weights the contribution of the classification loss and the proposed similarity loss." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "content": "In this way, the perturbation optimization of SU can improve the self-universality of perturbations, and the maximization of the cosine similarity can align intermediate features between adversarial global and local inputs for improving the dominance of feature representation of perturbations. Following [36], we integrate SU with the baseline DTMI to further boost targeted transferability, which we named DTMI-SU. We show DTMI-SU in Algorithm 1. In the end, SU can generate adversarial perturbations with high dominant features by incorporating local images, as shown in Figure 2b, hence improving targeted transferability." + } + ] + } + ], + "index": 22 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 46, + 693, + 287, + 715 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 693, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 693, + 287, + 715 + ], + "type": "text", + "content": "*We perform it by RandomResizedCrop in torchvision and ignore the parameter of the random aspect ratio." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "12285" + } + ] + } + ], + "index": 23 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 48, + 70, + 286, + 143 + ], + "blocks": [ + { + "bbox": [ + 48, + 70, + 286, + 143 + ], + "lines": [ + { + "bbox": [ + 48, + 70, + 286, + 143 + ], + "spans": [ + { + "bbox": [ + 48, + 70, + 286, + 143 + ], + "type": "table", + "html": "
ModelLayer 1Layer 2Layer 3Layer 4
Res50Block-1Block-2Block-3Block-4
Den121Block-1Block-2Block-3Block-4
VGG16ReLU-4ReLU-7ReLU-10ReLU-13
Inc-v3Conv-4aMix-5dMix-6eMix-7c
", + "image_path": "fa3fb85ed7b92bbadbf5a679e4be0dbbd4d9d79b5bee4ef0b2d8c1afc3e76ea5.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + }, + { + "bbox": [ + 47, + 144, + 287, + 178 + ], + "lines": [ + { + "bbox": [ + 47, + 144, + 287, + 178 + ], + "spans": [ + { + "bbox": [ + 47, + 144, + 287, + 178 + ], + "type": "text", + "content": "Table 1. Intermediate layers for feature extraction. \"Block\" means the basic block in ResNet50 and DenseNet121. \"ReLU-k\" denotes the " + }, + { + "bbox": [ + 47, + 144, + 287, + 178 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 47, + 144, + 287, + 178 + ], + "type": "text", + "content": "-th ReLU layer." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_footnote" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 199, + 123, + 213 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 199, + 123, + 213 + ], + "spans": [ + { + "bbox": [ + 47, + 199, + 123, + 213 + ], + "type": "text", + "content": "4. Experiment" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 220, + 173, + 232 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 220, + 173, + 232 + ], + "spans": [ + { + "bbox": [ + 47, + 220, + 173, + 232 + ], + "type": "text", + "content": "4.1. Experimental Settings" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 239, + 164, + 251 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 239, + 164, + 251 + ], + "spans": [ + { + "bbox": [ + 47, + 239, + 164, + 251 + ], + "type": "text", + "content": "4.1.1 Dataset and models" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 259, + 288, + 357 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 259, + 288, + 357 + ], + "spans": [ + { + "bbox": [ + 46, + 259, + 288, + 357 + ], + "type": "text", + "content": "Following [36], we attack four diverse classifier architectures: ResNet50 [5], DenseNet121 [6], VGGNet16 [20], and Inception-v3 [21] with the ImageNet-compatible dataset†. The architectures of these four models are more diverse and challenging than the ones used in [12]. The used dataset is first introduced by the NIPS 2017 Competition on Adversarial Attacks and Defenses. It consists of 1,000 images and corresponding labels for targeted attacks." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 374, + 141, + 386 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 374, + 141, + 386 + ], + "spans": [ + { + "bbox": [ + 47, + 374, + 141, + 386 + ], + "type": "text", + "content": "4.1.2 Attack setting" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 394, + 287, + 515 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 394, + 287, + 515 + ], + "spans": [ + { + "bbox": [ + 46, + 394, + 287, + 515 + ], + "type": "text", + "content": "We use the Targeted Attack Success Rate (TASR) to evaluate the targeted attack on one black-box model, which is the rate of adversarial examples that are successfully classified as the targeted class by the black-box model. Hence, the methods with higher TASR can generate adversarial examples with high targeted transferability. Following [36], we set the maximum perturbation as " + }, + { + "bbox": [ + 46, + 394, + 287, + 515 + ], + "type": "inline_equation", + "content": "\\epsilon = 16" + }, + { + "bbox": [ + 46, + 394, + 287, + 515 + ], + "type": "text", + "content": ", the step size as " + }, + { + "bbox": [ + 46, + 394, + 287, + 515 + ], + "type": "inline_equation", + "content": "\\alpha = 2" + }, + { + "bbox": [ + 46, + 394, + 287, + 515 + ], + "type": "text", + "content": ", the maximum number of iterations as " + }, + { + "bbox": [ + 46, + 394, + 287, + 515 + ], + "type": "inline_equation", + "content": "I = 300" + }, + { + "bbox": [ + 46, + 394, + 287, + 515 + ], + "type": "text", + "content": ". For each model, we select one layer " + }, + { + "bbox": [ + 46, + 394, + 287, + 515 + ], + "type": "inline_equation", + "content": "1/2/3/4" + }, + { + "bbox": [ + 46, + 394, + 287, + 515 + ], + "type": "text", + "content": " from shallow to deep layers (as shown in Table 1) to extract features." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 523, + 191, + 537 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 523, + 191, + 537 + ], + "spans": [ + { + "bbox": [ + 47, + 523, + 191, + 537 + ], + "type": "text", + "content": "4.2. Performance Comparison" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 542, + 287, + 626 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 542, + 287, + 626 + ], + "spans": [ + { + "bbox": [ + 46, + 542, + 287, + 626 + ], + "type": "text", + "content": "Following [36], we adopt the combination of DI, TI and MI (DTMI) as the baseline. The parameters of DTMI are the same as [36]. We then integrate the proposed SU method with several baselines: CE loss with DTMI (DTMI-CE) and Logit loss [36] with DTMI (DTMI-Logit). We exclude " + }, + { + "bbox": [ + 46, + 542, + 287, + 626 + ], + "type": "inline_equation", + "content": "\\mathrm{Po + }" + }, + { + "bbox": [ + 46, + 542, + 287, + 626 + ], + "type": "text", + "content": " Trip [12] in the comparison because it has a worse performance than the Logit loss." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 627, + 287, + 675 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 627, + 287, + 675 + ], + "spans": [ + { + "bbox": [ + 46, + 627, + 287, + 675 + ], + "type": "text", + "content": "For SU, the weighted parameter " + }, + { + "bbox": [ + 46, + 627, + 287, + 675 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 46, + 627, + 287, + 675 + ], + "type": "text", + "content": " is set as " + }, + { + "bbox": [ + 46, + 627, + 287, + 675 + ], + "type": "inline_equation", + "content": "10^{-3}" + }, + { + "bbox": [ + 46, + 627, + 287, + 675 + ], + "type": "text", + "content": ", the scale parameters " + }, + { + "bbox": [ + 46, + 627, + 287, + 675 + ], + "type": "inline_equation", + "content": "s" + }, + { + "bbox": [ + 46, + 627, + 287, + 675 + ], + "type": "text", + "content": " is set as " + }, + { + "bbox": [ + 46, + 627, + 287, + 675 + ], + "type": "inline_equation", + "content": "(0.1, 0)" + }, + { + "bbox": [ + 46, + 627, + 287, + 675 + ], + "type": "text", + "content": ", and the layer 3 is used to extract features. These parameters will be discussed in Section 4.3." + } + ] + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 309, + 73, + 422, + 143 + ], + "blocks": [ + { + "bbox": [ + 309, + 73, + 422, + 143 + ], + "lines": [ + { + "bbox": [ + 309, + 73, + 422, + 143 + ], + "spans": [ + { + "bbox": [ + 309, + 73, + 422, + 143 + ], + "type": "image", + "image_path": "7a90ea67337207534311eea373b1e752fe97a8015bb7fb9a9ea8487de9c163c9.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 343, + 146, + 389, + 156 + ], + "lines": [ + { + "bbox": [ + 343, + 146, + 389, + 156 + ], + "spans": [ + { + "bbox": [ + 343, + 146, + 389, + 156 + ], + "type": "text", + "content": "(a) TASR " + }, + { + "bbox": [ + 343, + 146, + 389, + 156 + ], + "type": "inline_equation", + "content": "(\\%)" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 11 + }, + { + "type": "image", + "bbox": [ + 426, + 72, + 541, + 143 + ], + "blocks": [ + { + "bbox": [ + 426, + 72, + 541, + 143 + ], + "lines": [ + { + "bbox": [ + 426, + 72, + 541, + 143 + ], + "spans": [ + { + "bbox": [ + 426, + 72, + 541, + 143 + ], + "type": "image", + "image_path": "47ae710ec8cb6f7afb578477f572d5681f057e3c2e137f257abb3e42278d4403.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 454, + 147, + 514, + 156 + ], + "lines": [ + { + "bbox": [ + 454, + 147, + 514, + 156 + ], + "spans": [ + { + "bbox": [ + 454, + 147, + 514, + 156 + ], + "type": "text", + "content": "(b) Gradient norm" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 305, + 159, + 545, + 194 + ], + "lines": [ + { + "bbox": [ + 305, + 159, + 545, + 194 + ], + "spans": [ + { + "bbox": [ + 305, + 159, + 545, + 194 + ], + "type": "text", + "content": "Figure 3. (a) TASR " + }, + { + "bbox": [ + 305, + 159, + 545, + 194 + ], + "type": "inline_equation", + "content": "(\\%)" + }, + { + "bbox": [ + 305, + 159, + 545, + 194 + ], + "type": "text", + "content": " of attacking ResNet50 from DenseNet121. (b) Gradient norm of performing DTMI-CE and DTMI-CE-SU when using DenseNet121 as the surrogate model." + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_caption" + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 220, + 546, + 579 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 220, + 546, + 579 + ], + "spans": [ + { + "bbox": [ + 304, + 220, + 546, + 579 + ], + "type": "text", + "content": "Single-model transferable attacks. We conduct single-model transferable experiments by selecting one model as the white-box model to attack the other three black-box models. Table 2 shows the results. We have the following observations. First, the proposed SU method achieves higher TASR than DTMI-CE and DTMI-Logit by a large margin in almost all cases. It suggests that the proposed SU is suitable for different classification loss functions. Second, the attacks using ResNet50 and DenseNet121 as white-box models outperform that using VGGNet16 and Inception-v3, which is also observed in [8, 9, 36]. It may be caused by the skip connection structure, which mitigates the gradient vanishing/exploding problem in a large number of iterations and emphasizes features of lower layers by backpropagating gradients on both residual modules and skip connections. These features tend to transfer among different models [30, 31]. Third, SU performs worse than other methods when using a small number of iterations (e.g. " + }, + { + "bbox": [ + 304, + 220, + 546, + 579 + ], + "type": "inline_equation", + "content": "I = 20" + }, + { + "bbox": [ + 304, + 220, + 546, + 579 + ], + "type": "text", + "content": "). This is because SU requires a large iteration for convergence, illustrated in Figure 3a. Especially for the CE loss, DTMI achieves the convergence at " + }, + { + "bbox": [ + 304, + 220, + 546, + 579 + ], + "type": "inline_equation", + "content": "I = 20" + }, + { + "bbox": [ + 304, + 220, + 546, + 579 + ], + "type": "text", + "content": ", while DTMI-SU steadily improves performance as the iteration increases, since SU can eliminate the vanishing gradient caused by CE, as shown in 3b. We also perform experiments with a smaller perturbation budget " + }, + { + "bbox": [ + 304, + 220, + 546, + 579 + ], + "type": "inline_equation", + "content": "\\epsilon = 8" + }, + { + "bbox": [ + 304, + 220, + 546, + 579 + ], + "type": "text", + "content": ", which are shown in Appendix. It follows a similar trend as Table 2. These results jointly demonstrate the effectiveness of SU. In addition, we visualize adversarial examples in Appendix. These adversarial examples, which humans can correctly understand, lead to the specific target prediction of DNNs." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 582, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 547, + 715 + ], + "type": "text", + "content": "Ensemble model transferable attacks. As mentioned above, the targeted perturbations generated from a set of models are more model-agnostic, and thus can obtain high cross-model transferability. Hence, we select one black-box model to attack, and use the other three models as white-box models. Following [36], we simply assign equal weights to all white-box models. Results are shown in Table 3. As can be seen, compared to single-model transferable attacks, ensemble attacks achieve much better performance. It demonstrates that the model-agnostic perturbations can easily transfer to attack other models. In addition, we also show that the model-agnostic perturbations can easily transfer to attack other models." + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 47, + 683, + 287, + 715 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 683, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 47, + 683, + 287, + 715 + ], + "type": "inline_equation", + "content": "\\dagger" + }, + { + "bbox": [ + 47, + 683, + 287, + 715 + ], + "type": "text", + "content": "https://github.com/cleverhans-lab/cleverhans/tree/master/cleverhans_v3.1.0/examples/nips17_adversarial_competition/dataset" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "12286" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 55, + 70, + 537, + 256 + ], + "blocks": [ + { + "bbox": [ + 55, + 70, + 537, + 256 + ], + "lines": [ + { + "bbox": [ + 55, + 70, + 537, + 256 + ], + "spans": [ + { + "bbox": [ + 55, + 70, + 537, + 256 + ], + "type": "table", + "html": "
AttackWhite-box Model: Res50White-box Model: Dense121
→ Dense121→ VGG16→ Inc-v3→ Res50→ VGG16→ Inc-v3
DTMI-CE27.1/39.7/44.318.9/27.6/29.42.2/3.4/4.112.9/16.7/18.48.1/10.6/10.61.7/2.2/3.2
DTMI-CE-SU6.2/27.8/54.23.0/20.2/45.40.2/4.5/10.12.6/17.6/39.41.4/12.6/32.40.2/4.8/10.8
DTMI-Logit30.4/64.4/71.822.6/55.1/62.82.7/7.1/9.616.1/39.3/43.713.5/33.0/38.12.1/7.1/7.7
DTMI-Logit-SU23.8/63.9/75.516.6/55.9/66.92.0/8.3/11.612.8/42.9/50.29.3/37.2/45.21.8/7.5/10.4
AttackWhite-box Model: VGG16White-box Model: Inc-v3
→ Res50→ Dense121→ Inc-v3→ Res50→ Dense121→ VGG16
DTMI-CE0.6/0.6/0.50.4/0.3/0.40.0/0.0/0.00.8/1.8/2.40.8/2.4/2.90.7/1.3/1.8
DTMI-CE-SU0.2/2.1/2.80.2/2.1/3.20.0/0.2/0.20.4/1.2/2.90.2/1.4/5.00.1/0.8/2.5
DTMI-Logit3.0/9.6/11.33.2/12.0/13.70.1/0.6/0.70.9/2.0/2.81.1/3.3/5.00.6/2.2/3.9
DTMI-Logit-SU3.4/11.7/13.93.3/13.8/16.10.2/0.9/0.80.6/2.3/4.30.5/3.8/7.40.3/1.9/4.4
", + "image_path": "13dc6379d6546aed6a646b971d2dd217b77b7594dc337d16065eebeff196e581.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 146, + 301, + 445, + 396 + ], + "blocks": [ + { + "bbox": [ + 46, + 258, + 547, + 293 + ], + "lines": [ + { + "bbox": [ + 46, + 258, + 547, + 293 + ], + "spans": [ + { + "bbox": [ + 46, + 258, + 547, + 293 + ], + "type": "text", + "content": "Table 2. TASR (%) of all black-box models under four attack scenarios using ResNet50, DenseNet121, VGGNet16 and Inception-v3 as white-box models, respectively. We conduct these experiments three times and report average TASR with 20/100/300 iterations, the standard deviation is shown in Appendix. The best results with 300 iterations are in bold." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 146, + 301, + 445, + 396 + ], + "lines": [ + { + "bbox": [ + 146, + 301, + 445, + 396 + ], + "spans": [ + { + "bbox": [ + 146, + 301, + 445, + 396 + ], + "type": "table", + "html": "
Ensemble AttackBlack-box ModelAverage
Res50Dense121VGG16Inc-v3
DTMI-CE31.155.251.616.138.5
DTMI-CE-SU55.765.068.229.354.5
DTMI-Logit70.282.382.229.165.9
DTMI-Logit-SU75.382.984.234.569.2
", + "image_path": "68eb8c9970a0824396ff48c69e9b4fc49658ee924ed384d8bb2a666117d99104.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "type": "table", + "bbox": [ + 48, + 429, + 287, + 502 + ], + "blocks": [ + { + "bbox": [ + 47, + 399, + 546, + 411 + ], + "lines": [ + { + "bbox": [ + 47, + 399, + 546, + 411 + ], + "spans": [ + { + "bbox": [ + 47, + 399, + 546, + 411 + ], + "type": "text", + "content": "Table 3. TASR (%) of one black-box model in ensemble transfer attacks. TASR with 300 iterations is reported. The best results are in bold." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 48, + 429, + 287, + 502 + ], + "lines": [ + { + "bbox": [ + 48, + 429, + 287, + 502 + ], + "spans": [ + { + "bbox": [ + 48, + 429, + 287, + 502 + ], + "type": "table", + "html": "
AttackDense121VGG16Inc-v3
DTMI-SI/+SU85.7/87.269.0/71.835.8/41.6
DTMI-Adm./+SU89.1/89.475.7/79.142.1/47.1
DTMI-EMI/+SU71.0/79.064.6/82.45.0/14.8
ODI-TMI/+SU89.9/92.881.0/91.766.9/72.0
", + "image_path": "e93932439188010d1e309264c2531b8da9000260eefd7400c629ff13ed58911c.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_body" + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 504, + 287, + 539 + ], + "lines": [ + { + "bbox": [ + 46, + 504, + 287, + 539 + ], + "spans": [ + { + "bbox": [ + 46, + 504, + 287, + 539 + ], + "type": "text", + "content": "Table 4. Average TASR (\\%) of different combinational attacks. We use ResNet50 as the white-box model, and report the results with 300 iterations. Logit is used here." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 566, + 287, + 662 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 566, + 287, + 662 + ], + "spans": [ + { + "bbox": [ + 46, + 566, + 287, + 662 + ], + "type": "text", + "content": "tion, the proposed SU further boosts cross-model targeted transferability. However, the improvement of TASR gained from DTMI-Logit-SU is not so significant. This can be explained by the fact that the loss function value of Logit increases infinitely, while the value of cosine similarity is bounded. Thus, it impedes the maximization of feature similarity. Nevertheless, methods that are combined with SU can promote targeted transferability in all cases." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 665, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 288, + 714 + ], + "type": "text", + "content": "Combination with existing methods To further boost transferable targeted attacks, we combine our method with other attacks, including SI [13], Admix [24], EMI [25], and ODI [1]. Table 4 reports the results. The attack methods" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 431, + 547, + 598 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 431, + 547, + 598 + ], + "spans": [ + { + "bbox": [ + 304, + 431, + 547, + 598 + ], + "type": "text", + "content": "combined with the proposed SU achieve better performance than other attack methods. In particular, compared to ODI, SU achieves an average TASR gain of " + }, + { + "bbox": [ + 304, + 431, + 547, + 598 + ], + "type": "inline_equation", + "content": "6\\%" + }, + { + "bbox": [ + 304, + 431, + 547, + 598 + ], + "type": "text", + "content": ". Such remarkable improvements demonstrate that the proposed SU can be easily combined with other existing methods and further improve targeted transferability. In terms of computational efficiency, SU only requires two forward propagations for global and local inputs per iteration, which is lower than SI, Admix, and EMI (which require " + }, + { + "bbox": [ + 304, + 431, + 547, + 598 + ], + "type": "inline_equation", + "content": "\\geq 5" + }, + { + "bbox": [ + 304, + 431, + 547, + 598 + ], + "type": "text", + "content": " forward propagations). To compare SU with ODI, we report the computation time (sec) required to generate an adversarial example. DTMI-SU and DTMI-ODI require 2.3 and 2.6 sec, respectively. It indicates that SU requires less computation time than previous methods." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 609, + 406, + 621 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 609, + 406, + 621 + ], + "spans": [ + { + "bbox": [ + 305, + 609, + 406, + 621 + ], + "type": "text", + "content": "4.3. Ablation Studies" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 628, + 546, + 677 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 628, + 546, + 677 + ], + "spans": [ + { + "bbox": [ + 304, + 628, + 546, + 677 + ], + "type": "text", + "content": "In this section, we utilize CE as the classification loss to investigate the effects of each component and various hyperparameters. In addition, we investigate the effects of different regions of random cropping." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 677, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 547, + 715 + ], + "type": "text", + "content": "Effect of components. The evaluations are conducted on four attack scenarios using ResNet50, DenseNet121, VGGNet16 and Inceptionv3 as white-box models, respec" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "12287" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 56, + 70, + 276, + 131 + ], + "blocks": [ + { + "bbox": [ + 56, + 70, + 276, + 131 + ], + "lines": [ + { + "bbox": [ + 56, + 70, + 276, + 131 + ], + "spans": [ + { + "bbox": [ + 56, + 70, + 276, + 131 + ], + "type": "table", + "html": "
LocalFeature Similarity LossAveraged TASR
--9.8
✓-10.9
✓✓15.6
", + "image_path": "f8fedb410fe06dd0859d8db908ccdeebeb14134d19f8af455c2bc5121fd8d9eb.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 51, + 216, + 165, + 289 + ], + "blocks": [ + { + "bbox": [ + 51, + 216, + 165, + 289 + ], + "lines": [ + { + "bbox": [ + 51, + 216, + 165, + 289 + ], + "spans": [ + { + "bbox": [ + 51, + 216, + 165, + 289 + ], + "type": "image", + "image_path": "61a8dd0de1876c46d955e4dbd6720b68feb556dde66ee5fe5befd24994b6cea2.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 59, + 292, + 156, + 302 + ], + "lines": [ + { + "bbox": [ + 59, + 292, + 156, + 302 + ], + "spans": [ + { + "bbox": [ + 59, + 292, + 156, + 302 + ], + "type": "text", + "content": "(a) Scale parameter " + }, + { + "bbox": [ + 59, + 292, + 156, + 302 + ], + "type": "inline_equation", + "content": "(s_l,s_{int})" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 168, + 216, + 280, + 288 + ], + "blocks": [ + { + "bbox": [ + 168, + 216, + 280, + 288 + ], + "lines": [ + { + "bbox": [ + 168, + 216, + 280, + 288 + ], + "spans": [ + { + "bbox": [ + 168, + 216, + 280, + 288 + ], + "type": "image", + "image_path": "9c1caf5f98bef99e8fc29b5e2b255499dc038588057b39cea0b14ce66ddf1a07.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 184, + 292, + 264, + 302 + ], + "lines": [ + { + "bbox": [ + 184, + 292, + 264, + 302 + ], + "spans": [ + { + "bbox": [ + 184, + 292, + 264, + 302 + ], + "type": "text", + "content": "(b) Layer " + }, + { + "bbox": [ + 184, + 292, + 264, + 302 + ], + "type": "inline_equation", + "content": "l" + }, + { + "bbox": [ + 184, + 292, + 264, + 302 + ], + "type": "text", + "content": " and weight " + }, + { + "bbox": [ + 184, + 292, + 264, + 302 + ], + "type": "inline_equation", + "content": "\\lambda" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 46, + 304, + 286, + 326 + ], + "lines": [ + { + "bbox": [ + 46, + 304, + 286, + 326 + ], + "spans": [ + { + "bbox": [ + 46, + 304, + 286, + 326 + ], + "type": "text", + "content": "Figure 4. Average TASR with different values of hyper-parameters in the attack. The classification loss is set as CE." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 352, + 286, + 435 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 352, + 286, + 435 + ], + "spans": [ + { + "bbox": [ + 46, + 352, + 286, + 435 + ], + "type": "text", + "content": "tively. We split SU into the local inputs and the feature similarity loss. Table 5 shows the results of different component combinations. As can be seen, both components improve targeted transferability. And the improvement of TASR gained from feature similarity loss is more significant. It demonstrates the effectiveness of each component in the proposed SU attack." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 437, + 286, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 437, + 286, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 437, + 286, + 714 + ], + "type": "text", + "content": "Effect of hyper-parameters. The evaluations are conducted by using densenet121 as the white-box model and averaging TASR among black-box models. The scale parameter " + }, + { + "bbox": [ + 46, + 437, + 286, + 714 + ], + "type": "inline_equation", + "content": "s" + }, + { + "bbox": [ + 46, + 437, + 286, + 714 + ], + "type": "text", + "content": " determines the area of cropped images. When the area is large, SU overlooks the local structure of inputs. Thus, it is vital to study optimal values of " + }, + { + "bbox": [ + 46, + 437, + 286, + 714 + ], + "type": "inline_equation", + "content": "s" + }, + { + "bbox": [ + 46, + 437, + 286, + 714 + ], + "type": "text", + "content": ". We fix the weighted parameter " + }, + { + "bbox": [ + 46, + 437, + 286, + 714 + ], + "type": "inline_equation", + "content": "\\lambda = 1.0" + }, + { + "bbox": [ + 46, + 437, + 286, + 714 + ], + "type": "text", + "content": ", and the feature extraction layer as layer 3 due to the high transferability of middle layers [30]. Figure 4a shows the results with " + }, + { + "bbox": [ + 46, + 437, + 286, + 714 + ], + "type": "inline_equation", + "content": "s_l \\in [0.1, 0.3, 0.5, 0.7]" + }, + { + "bbox": [ + 46, + 437, + 286, + 714 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 437, + 286, + 714 + ], + "type": "inline_equation", + "content": "s_{int} \\in [0.0, 0.1, 0.2, 0.3]" + }, + { + "bbox": [ + 46, + 437, + 286, + 714 + ], + "type": "text", + "content": ". We observe that the smaller the area of cropped images, the higher the performance. It suggests that local image patches that differ significantly from the original images provide more diverse input patterns for perturbation optimization and contribute to targeted transferability. Besides, when " + }, + { + "bbox": [ + 46, + 437, + 286, + 714 + ], + "type": "inline_equation", + "content": "s_l = 0.1" + }, + { + "bbox": [ + 46, + 437, + 286, + 714 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 437, + 286, + 714 + ], + "type": "inline_equation", + "content": "s_{int} = 0.1" + }, + { + "bbox": [ + 46, + 437, + 286, + 714 + ], + "type": "text", + "content": ", the optimal result is reached. However, the area relative to the original image may fluctuate within [0.1, 0.2]. To keep it stable, we use the parameters " + }, + { + "bbox": [ + 46, + 437, + 286, + 714 + ], + "type": "inline_equation", + "content": "s = (0.1, 0.0)" + }, + { + "bbox": [ + 46, + 437, + 286, + 714 + ], + "type": "text", + "content": " to conduct subsequent experiments. Figure 4b shows the results of performing attacks on different layers and " + }, + { + "bbox": [ + 46, + 437, + 286, + 714 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 46, + 437, + 286, + 714 + ], + "type": "text", + "content": ". Extracting features from layer 3 is better than other layers. This is because the features captured by shallow layers represent the low-level patterns (such as edges)," + } + ] + } + ], + "index": 8 + }, + { + "type": "table", + "bbox": [ + 341, + 70, + 509, + 148 + ], + "blocks": [ + { + "bbox": [ + 46, + 133, + 287, + 199 + ], + "lines": [ + { + "bbox": [ + 46, + 133, + 287, + 199 + ], + "spans": [ + { + "bbox": [ + 46, + 133, + 287, + 199 + ], + "type": "text", + "content": "Table 5. Average TASR (\\%) of black-box models for our proposed method with different component combinations. The classification loss is set as CE. " + }, + { + "bbox": [ + 46, + 133, + 287, + 199 + ], + "type": "inline_equation", + "content": "\\checkmark" + }, + { + "bbox": [ + 46, + 133, + 287, + 199 + ], + "type": "text", + "content": " indicates that the component is used while " + }, + { + "bbox": [ + 46, + 133, + 287, + 199 + ], + "type": "inline_equation", + "content": "-" + }, + { + "bbox": [ + 46, + 133, + 287, + 199 + ], + "type": "text", + "content": " indicates that it is not used. TASR is averaged among four attack scenarios using ResNet50, DenseNet121, VGGNet16 and Inceptionv3 as white-box models, respectively." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 341, + 70, + 509, + 148 + ], + "lines": [ + { + "bbox": [ + 341, + 70, + 509, + 148 + ], + "spans": [ + { + "bbox": [ + 341, + 70, + 509, + 148 + ], + "type": "table", + "html": "
RegionRes50VGG16Inc-v3
Center33.029.29.9
Corner33.630.910.8
Whole39.432.410.8
Uniform3.11.70.4
", + "image_path": "4c4f6fa68b7079a3d9625d0658a1ff0df2ed65452f386ab6c6193fbeab91ee95.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "table_body" + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 149, + 545, + 194 + ], + "lines": [ + { + "bbox": [ + 305, + 149, + 545, + 194 + ], + "spans": [ + { + "bbox": [ + 305, + 149, + 545, + 194 + ], + "type": "text", + "content": "Table 6. TASR (\\%) of DTMI-CE-SU with different distributions of local images. The top three rows show different regions of random cropping. The last row denotes the uniform distribution " + }, + { + "bbox": [ + 305, + 149, + 545, + 194 + ], + "type": "inline_equation", + "content": "\\mathcal{U}(0,1)" + }, + { + "bbox": [ + 305, + 149, + 545, + 194 + ], + "type": "text", + "content": " of local images." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 305, + 220, + 545, + 280 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 220, + 545, + 280 + ], + "spans": [ + { + "bbox": [ + 305, + 220, + 545, + 280 + ], + "type": "text", + "content": "while the deepest layer contains more semantic information hence is more related to the classification task of the white-box model [30]. For the weighted parameter " + }, + { + "bbox": [ + 305, + 220, + 545, + 280 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 305, + 220, + 545, + 280 + ], + "type": "text", + "content": ", we set " + }, + { + "bbox": [ + 305, + 220, + 545, + 280 + ], + "type": "inline_equation", + "content": "\\lambda \\in [10^{-4}, 10^{-3}, 10^{-2}, 10^{-1}, 10^{0}]" + }, + { + "bbox": [ + 305, + 220, + 545, + 280 + ], + "type": "text", + "content": ". When " + }, + { + "bbox": [ + 305, + 220, + 545, + 280 + ], + "type": "inline_equation", + "content": "\\lambda = 10^{-3}" + }, + { + "bbox": [ + 305, + 220, + 545, + 280 + ], + "type": "text", + "content": ", SU achieves the best result." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 283, + 545, + 451 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 283, + 545, + 451 + ], + "spans": [ + { + "bbox": [ + 304, + 283, + 545, + 451 + ], + "type": "text", + "content": "Effect of different regions. The regions of random cropping determine the distribution of local images. The center may be more related to the object of the image than the corner. Therefore, we conduct experiments on the center, the corner and the whole regions. We also compare the uniform distribution " + }, + { + "bbox": [ + 304, + 283, + 545, + 451 + ], + "type": "inline_equation", + "content": "\\mathcal{U}(0,1)" + }, + { + "bbox": [ + 304, + 283, + 545, + 451 + ], + "type": "text", + "content": " of local images. As shown in Table 6, there is no significant performance difference between the center and the corner. The reason is that SU concentrates on the target class regardless of the object related to the original class. Therefore, directly providing more local input patterns within one image leads to better performance in SU. The whole region indeed achieves the best performance. Moreover, the uniform distribution makes it difficult to converge, resulting in the worst performance." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 469, + 378, + 481 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 469, + 378, + 481 + ], + "spans": [ + { + "bbox": [ + 306, + 469, + 378, + 481 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 492, + 545, + 623 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 492, + 545, + 623 + ], + "spans": [ + { + "bbox": [ + 304, + 492, + 545, + 623 + ], + "type": "text", + "content": "In this paper, we provide new insight into transfer-based targeted attacks: more universal perturbations yield better transferability. Based on this observation, we propose the Self-University (SU) attack, which optimizes perturbations on the global image and more diverse local images, and aligns intermediate features between them. In this way, SU can make perturbations to be agnostic to different image regions, resulting in high self-transferability. We conduct extensive experiments to show that SU can improve targeted transferability regardless of the single-model attack or ensemble-based attack." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 643, + 415, + 656 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 643, + 415, + 656 + ], + "spans": [ + { + "bbox": [ + 306, + 643, + 415, + 656 + ], + "type": "text", + "content": "6. Acknowledgments" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 665, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 665, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 665, + 545, + 713 + ], + "type": "text", + "content": "This project was supported by National Key R&D Program of China (No. 2020AAA0140001), NSFC (No. 62072116), and Science and Technology Commission of Shanghai Municipality (No. 21JC1400600)." + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "12288" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 288, + 712 + ], + "type": "list", + "angle": 0, + "index": 14, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 156 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 156 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 156 + ], + "type": "text", + "content": "[1] Junyoung Byun, Seungju Cho, Myung-Joon Kwon, Hee-Seon Kim, and Changick Kim. 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Advances in Neural Information Processing Systems, 34:6115-6128, 2021. 1, 3, 4, 5, 6" + } + ] + } + ], + "index": 9 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "12290" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 9 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Enlarging Instance-Specific and Class-Specific Information for Open-Set Action Recognition/a1eb877e-c60e-4804-81d3-1cd98ec238d0_content_list.json b/2023/Enlarging Instance-Specific and Class-Specific Information for Open-Set Action Recognition/a1eb877e-c60e-4804-81d3-1cd98ec238d0_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..8dc9ad852acc6622fde352b5198c6eaec7d6549d --- /dev/null +++ b/2023/Enlarging Instance-Specific and Class-Specific Information for Open-Set Action Recognition/a1eb877e-c60e-4804-81d3-1cd98ec238d0_content_list.json @@ -0,0 +1,1801 @@ +[ + { + "type": "text", + "text": "Enlarging Instance-specific and Class-specific Information for Open-set Action Recognition", + "text_level": 1, + "bbox": [ + 174, + 130, + 797, + 176 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Jun Cen $^{1,2*}$ Shiwei Zhang $^{2}$ Xiang Wang $^{3}$ Yixuan Pei $^{4}$", + "bbox": [ + 243, + 202, + 723, + 220 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Zhiwu Qing $^{3}$ Yingya Zhang $^{2}$ Qifeng Chen $^{1}$", + "bbox": [ + 292, + 220, + 676, + 239 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1The Hong Kong University of Science and Technology 2Alibaba Group", + "bbox": [ + 191, + 239, + 779, + 256 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "$^{3}$ Huazhong University of Science and Technology $^{4}$ Xi'an Jiaotong University", + "bbox": [ + 171, + 256, + 799, + 275 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "jcenaa@connect.ust.hk, {zhangjin.zsw,yingya.zyy}@alibaba-inc.com,", + "bbox": [ + 197, + 277, + 767, + 292 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "{wxiang,zzw}@hust.edu.cn, peiyixuan@stu.xjtu.edu.cn, cqf@ust.hk", + "bbox": [ + 207, + 295, + 761, + 309 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 344, + 313, + 359 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Open-set action recognition is to reject unknown human action cases which are out of the distribution of the training set. Existing methods mainly focus on learning better uncertainty scores but dismiss the importance of feature representations. We find that features with richer semantic diversity can significantly improve the open-set performance under the same uncertainty scores. In this paper, we begin with analyzing the feature representation behavior in the open-set action recognition (OSAR) problem based on the information bottleneck (IB) theory, and propose to enlarge the instance-specific (IS) and class-specific (CS) information contained in the feature for better performance. To this end, a novel Prototypical Similarity Learning (PSL) framework is proposed to keep the instance variance within the same class to retain more IS information. Besides, we notice that unknown samples sharing similar appearances to known samples are easily misclassified as known classes. To alleviate this issue, video shuffling is further introduced in our PSL to learn distinct temporal information between original and shuffled samples, which we find enlarges the CS information. Extensive experiments demonstrate that the proposed PSL can significantly boost both the open-set and closed-set performance and achieves state-of-the-art results on multiple benchmarks. Code is available at https://github.com/Jun-CEN/PSL.", + "bbox": [ + 76, + 377, + 473, + 753 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 786, + 209, + 801 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Deep learning methods for video action recognition have developed very fast and achieved remarkable performance in recent years [1-4]. However, these methods operate under the closed-set condition, i.e., to classify all videos into", + "bbox": [ + 76, + 813, + 468, + 875 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/03d36989466045e3d8b921c122d254eb2975ce4690521f3eaddc27271b9942d3.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 504, + 344, + 671, + 463 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/17b1e0c3aad89e3277e6caa4f1220ba460d5a5109ce78e7d063708458e4caa29.jpg", + "image_caption": [ + "(a)", + "Figure 1. (a) Richer semantic features brought by the pretraining can significantly improve the open-set performance. (b) Information in the feature is divided into IS and CS information. $s_4$ can be identified as OoD since it has distinct IS information (IS bars in different colors) with $s_1$ and $s_2$ , while $s_5$ has distinct CS information (CS bars in different colors) with all InD samples so it may be OoD. Our PSL aims to learn more IS and CS information (bars in longer lengths) than Cross-Entropy (C.E.). (c) Both enlarged IS and CS information boosts the open-set performance. (d) Our PSL achieves the best OSAR performance." + ], + "image_footnote": [], + "bbox": [ + 503, + 474, + 689, + 593 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/0c0c86e899c2a7f275c2524163186a4ca0ffda8dfd7cf032038f70bdd3d1a457.jpg", + "image_caption": [ + "(b)" + ], + "image_footnote": [], + "bbox": [ + 686, + 345, + 887, + 465 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/28dd088508a878e682ff43ab36a64bbab2776531674a34cfe6338da35eb93cd2.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 669, + 474, + 885, + 592 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "one of the classes encountered during training. This closed-set condition is not practical in the real-world scenario, as videos whose classes are beyond the range of the training set will be misclassified as one of the known classes. Therefore, open-set action recognition (OSAR) is proposed to require the network to correctly classify in-distribution (InD) samples and identify out-of-distribution (OoD) samples. InD and OoD classes refer to classes involved and not involved in the training set, respectively.", + "bbox": [ + 496, + 763, + 893, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 810, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Work done as an intern at Alibaba DAMO Academy.", + "bbox": [ + 94, + 886, + 380, + 900 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "15295", + "bbox": [ + 480, + 944, + 517, + 957 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Open-set video action recognition is systematically studied in the recent work [5], in which they transfer the existing methods for open-set image recognition into the video domain [6-9] as the baselines, and propose their own method to introduce deep evidential learning [10] to calculate the uncertainty and propose a contrastive evidential debiasing module to alleviate the appearance bias issue in the video domain. All of these methods tend to improve the OSAR performance by calculating a better uncertainty score, based on the feature representations extracted by the neural network (NN). However, the main purpose of training in these methods is still to classify InD samples, which determines the learned feature representations are merely sufficient for InD classification. We find that almost all methods have a significantly better open-set performance when the NN is pretrained with a large dataset (Fig. 1 (a)), so we argue that the diversity of feature representation is extremely important for the OSAR task. Therefore, we propose to boost the open-set ability from the feature representation perspective rather than finding a better uncertainty score.", + "bbox": [ + 76, + 90, + 472, + 393 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "We first analyze the feature representation behavior in the open-set problem based on the information bottleneck (IB) theory [11, 12]. We divide the information of the feature into Instance-Specific (IS) and Class-Specific (CS) information. CS information is used for inter-class recognition, so it is similar for samples within the same class but different for samples from other classes. IS information is the special information of each sample within the same class, as two samples cannot be exactly the same even if they belong to the same class. Both CS and IS information are crucial for the open-set task, as illustrated in Fig. 1 (b), where $s_4$ and $s_5$ can be identified as OoD samples based on the IS and CS information, respectively. We find that the closed-set classification setting tends to eliminate IS information during training, and cannot fully extract the minimum sufficient CS information for the classification task, so we aim to enlarge IS and CS information in learned feature representations for better OSAR performance.", + "bbox": [ + 75, + 397, + 472, + 671 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To enlarge the IS information, we propose the Prototypical Similarity Learning (PSL) framework, in which the representation of an instance is encouraged to have less than 1 similarity with the corresponding prototype. In this way, we encourage the IS information to be retained and not eliminated. In addition, [5] finds that OoD videos can be easily classified as InD videos in a similar appearance. To alleviate this issue, we introduce the shuffled video into PSL and make it have less than 1 similarity with the original sample. As the shuffled video almost shares the same appearance information with the original one, we encourage the similarity to be less than 1 so that the network can extract the distinct temporal information among them. We find this technique actually enlarges the CS information in the feature representation. Fig. 1 (c) shows that enlarging the IS informa", + "bbox": [ + 75, + 674, + 472, + 902 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "tion is helpful for the open-set performance, and more CS information can further benefit the open-set and closed-set performance. To summarize, our contributions include:", + "bbox": [ + 496, + 90, + 893, + 136 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- We provide a novel perspective to analyze the open-set recognition task based on the information bottleneck theory, and find that the classical closed-set cross-entropy tends to eliminate the IS information which is helpful to identify OoD samples.", + "- We propose to enlarge the IS and CS information for better OSAR performance. Specifically, PSL is designed to retain the IS information in the features, and we involve video shuffling in PSL to learn more CS information.", + "- Experiments on multiple datasets and backbones show our PSL's superiority over a large margin compared to other state-of-the-art counterparts, as shown in Fig. 1 (d)." + ], + "bbox": [ + 500, + 136, + 893, + 318 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 500, + 330, + 640, + 347 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Action Recognition. Most recent approaches for action recognition are to exploit appearance and motion cues jointly and achieve remarkable success [1-3, 13-16]. Typically, two-stream networks [17-19] consist of two branches that explore spatial information and temporal dynamics, respectively. Some attempts [1, 20, 21] introduce additional temporal mining operations to overcome the limited temporal information extraction ability of 2D CNN. 3D CNN-based methods [2, 3, 22] inflated 2D kernels for joint spatiotemporal modeling. [23] proposes the prototype similarity learning which pushes the learned representation to the corresponding prototype as close as possible, while our PSL keeps the differences among the same class.", + "bbox": [ + 496, + 356, + 893, + 551 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Open-set Action Recognition. The related work of OSAR is limited [5, 24-26]. Recently, [5] systematically studies the OSAR problem and transfers several open-set image recognition methods to the video domain, including SoftMax [6], MC Dropout [7], OpenMax [8], and RPL [27]. In the benchmark of [5], the only two methods designed specifically for the video domain are BNN SVI [24] and their proposed DEAR. BNN SVI is a Bayesian NN application in the OSAR, while DEAR adopts the deep evidential learning [10] to calculate the uncertainty, and utilizes two modules to alleviate the over-confidence prediction and appearance bias problem, respectively. Existing methods pursue better uncertainty scores, while the objective of our PSL is to learn more diverse feature representations for better open-set distinguishability.", + "bbox": [ + 496, + 553, + 893, + 779 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Information Bottleneck Theory. Based on the IB theory [11, 28], the NN intends to extract minimum sufficient information of the inputs for the current task. More recent [12, 29, 30] adopt the IB theory on unsupervised contrastive learning to analyze the representation learning behavior under the corresponding tasks. In this work, we provide a new view to analyze the OSAR problem based on the IB theory.", + "bbox": [ + 496, + 779, + 893, + 902 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "15296", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "3. Information Analysis in OSAR", + "text_level": 1, + "bbox": [ + 76, + 89, + 359, + 107 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Prototypical Learning", + "text_level": 1, + "bbox": [ + 76, + 114, + 284, + 131 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Let $f$ be the encoder to extract the information for an input video sample $x$ and output the feature representation $z = f(x), z \\in \\mathbb{R}^d$ . We first define a prototypical learning (PL) loss [31], which is a general version of the cross-entropy (C.E.) loss:", + "bbox": [ + 75, + 137, + 468, + 213 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {P L} = - \\log \\frac {\\exp \\left(\\frac {z ^ {T} k _ {i}}{\\tau}\\right)}{\\exp \\left(\\frac {z ^ {T} k _ {i}}{\\tau}\\right) + \\sum_ {n \\in K ^ {-}} \\exp \\left(\\frac {z ^ {T} n}{\\tau}\\right)}, \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 120, + 219, + 468, + 268 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $i$ is the ground truth label of $x$ , $k_{i} \\in \\mathbb{R}^{d}$ is the prototype for class $i$ , $\\tau$ is a temperature parameter, $K_{i}^{-} = \\{k_{j} | j \\in \\{1, 2, \\dots, N\\}, j \\neq i\\}$ is the negative prototype set, and $N$ is the number of InD classes. Note that $z$ and $k_{i}$ are normalized by L2 norm, so that $z^{T} k_{i}$ is the cosine similarity. If we regard prototypes as the row vector of the linear classifier $W \\in \\mathbb{R}^{N \\times d}$ , and do not normalize $z$ and $k$ as well as remove $\\tau$ , $\\mathcal{L}_{PL}$ will degenerate to the C.E. loss. We introduce the $\\mathcal{L}_{PL}$ so that we can directly manipulate the feature representation $z$ .", + "bbox": [ + 75, + 268, + 472, + 419 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. Information Analysis of OSAR", + "text_level": 1, + "bbox": [ + 76, + 426, + 349, + 443 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Let $x_{InD}, z_{InD}$ , and $Y$ be the random variables of InD sample, extracted representation of InD sample, and the task to predict the label of $x_{InD}$ , where $z_{InD} = f(x_{InD})$ . Given the joint distribution of $p(x_{InD}, Y)$ , the relevant information between $x_{InD}$ and $Y$ is defined as $I(x_{InD}, Y)$ where $I$ denotes the mutual information [28]. The learned representation $z_{InD}$ satisfies:", + "bbox": [ + 75, + 450, + 468, + 556 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nI \\left(x _ {I n D}; z _ {I n D}\\right) = \\underbrace {I \\left(x _ {I n D} ; z _ {I n D} \\mid Y\\right)} _ {I S} + \\underbrace {I \\left(z _ {I n D} ; Y\\right)} _ {C S}, \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 93, + 556, + 468, + 590 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "in which $I(x_{\\text{InD}}; z_{\\text{InD}}|Y)$ and $I(z_{\\text{InD}}; Y)$ denote the Instance-Specific (IS) and Class-Specific (CS) information respectively. In Fig. 2, IS information is blue and orange areas, and CS information is yellow and green areas. CS information is for the closed-set label prediction task $Y$ , while IS information is the special information of each sample that is not related to $Y$ .", + "bbox": [ + 75, + 592, + 468, + 696 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "To analyze the information about OSAR, we let $T$ be a random variable that represents the task to distinguish OoD samples from InD samples, then we divide the information contained in $z_{InD}$ about $T$ into two parts [12]:", + "bbox": [ + 75, + 696, + 468, + 758 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nI \\left(z _ {I n D}; T\\right) = \\underbrace {I \\left(z _ {I n D} \\mid Y ; T\\right)} _ {I S \\text {a b o u t} T} + \\underbrace {I \\left(z _ {I n D} ; Y ; T\\right)} _ {C S \\text {a b o u t} T}, \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 116, + 758, + 468, + 794 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $I(z_{\\text{InD}} | Y; T)$ and $I(z_{\\text{InD}}; Y; T)$ are the information about the OoD detection task $T$ in IS and CS information (orange and green areas in Fig. 2 respectively). We can see that larger IS and CS information are helpful for OSAR.", + "bbox": [ + 75, + 794, + 468, + 854 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In this paper, we aim to enlarge the information about $T$ contained in CS and IS information for better OSAR performance, as illustrated in Fig. 1 (b) and the enlarged green", + "bbox": [ + 75, + 854, + 468, + 901 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/bb0db8cf4d069bfd820ab3b4e5e877f9e776a22972a4465c38a1257769f6f55a.jpg", + "image_caption": [ + "C.E.", + "Figure 2. The neural network (NN) can only extract limited representations $z_{InD}$ of the InD sample $x_{InD}$ for the current task $Y$ (predict the closed-set label), which is not diverse enough for the task $T$ (distinguish OoD samples), as green and orange areas are small in (a). In our PSL, we encourage the NN to learn a more diverse representation so that more IS and CS information about $T$ are contained." + ], + "image_footnote": [], + "bbox": [ + 509, + 93, + 679, + 215 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/dcd0b41555d4d56953edbbc6a3bb1569dcf8919af70f0f0659eec9f03b39caee.jpg", + "image_caption": [ + "PSL (ours)" + ], + "image_footnote": [], + "bbox": [ + 697, + 94, + 875, + 215 + ], + "page_idx": 2 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "$\\bigcirc \\bigcirc z_{InD} = f(x_{InD})$ , representation of $x_{InD}$ from NN", + "$\\mathbb{Z}_{InD}^{min}$ , minimum sufficient information of $x_{InD}$ about $Y$", + "$\\bigcirc$ $I(z_{InD};Y;T)$ , CS information in $z_{InD}$ about $T$", + "$I(z_{InD}|Y;T)$ , IS information in $z_{InD}$ about $T$", + "Enlarged information that $z_{\\text{InD}}$ contains using our PSL" + ], + "bbox": [ + 506, + 229, + 874, + 316 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "and orange areas in Fig. 2. We first analyze the CS and IS information behaviors under the classical C.E. loss, and find that CS information is encouraged to be maximized but IS information tends to be eliminated in Sec. 3.3. Then we explain this conclusion from the IB theory view in Sec. 3.4.", + "bbox": [ + 496, + 446, + 892, + 523 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.3. CS and IS Information Behavior under C.E.", + "text_level": 1, + "bbox": [ + 498, + 537, + 872, + 554 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "CS information is for closed-set classification task $Y$ , so it is similar for the same class sample, but distinct for the different class sample $(s_1, s_2 / s_3$ in Fig. 1). In contrast, IS information is not related to $Y$ and it is distinct for samples in the same class $(s_1, s_2$ in Fig. 1). Therefore, we have the following proposition which describe the relation between CS/IS information and feature representation similarity.", + "bbox": [ + 496, + 564, + 890, + 670 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Proposition 1 For two feature representations of samples in the same class, more CS information means these two feature representations are more similar, and more IS information decreases their feature similarity.", + "bbox": [ + 496, + 680, + 890, + 742 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "CS information is for the closed-set label prediction task $Y$ , which is fully supervised by C.E. loss, so it is maximized during training. In contrast, Eq. 1 shows that C.E. encourages representations of the same class to be exactly same with the corresponding prototype, and such high similarity eliminates the IS information according to Proposition 1. Therefore, C.E. loss tends to maximize the CS information and eliminate the IS information in the feature representation. We analyze this conclusion based on Information Bottleneck (IB) theory in next Sec. 3.4.", + "bbox": [ + 496, + 750, + 892, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "15297", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.4. IB Theory Analysis for CS and IS Information", + "text_level": 1, + "bbox": [ + 76, + 90, + 468, + 106 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Applying the Data Processing Inequality [32] to the Markov chain $Y \\to x_{inD} \\to z_{InD}$ , we have", + "bbox": [ + 76, + 113, + 468, + 143 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nI \\left(z _ {I n D}; Y\\right) \\leq I \\left(x _ {I n D}; Y\\right). \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 179, + 145, + 468, + 162 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "It means that the compressed representation $z_{InD}$ cannot contain more information of $Y$ compared to the original data $x_{InD}$ .", + "bbox": [ + 75, + 164, + 468, + 209 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "According to the IB theory [11, 28], the NN is to find the optimal solution of $z_{\\text{InD}}$ with minimizing the following Lagrange:", + "bbox": [ + 75, + 209, + 468, + 255 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} \\left[ p \\left(z _ {I n D} \\mid x _ {I n D}\\right) \\right] = I \\left(z _ {I n D}; x _ {I n D}\\right) - \\beta I \\left(z _ {I n D}; Y\\right), \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 88, + 256, + 468, + 273 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\beta$ is the Lagrange multiplier attached to the constrained meaningful condition. Eq. 5 demonstrates the NN is solving a trade-off problem, as the first term tends to keep the information of $x_{InD}$ as less as possible while the second term tends to maximize the information of $Y$ .", + "bbox": [ + 75, + 273, + 468, + 348 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Inspired by [12, 33], the sufficient and minimum sufficient representation of $x_{\\text{InD}}$ about $Y$ can be defined as:", + "bbox": [ + 75, + 349, + 468, + 381 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Definition 1 (Sufficient Representation) A feature representation $z_{InD}^{suf}$ of $x_{InD}$ is sufficient for $Y$ if and only if $I(z_{InD}^{suf};Y) = I(x_{InD};Y)$ .", + "bbox": [ + 76, + 388, + 470, + 436 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Definition 2 (Minimum Sufficient Representation) A sufficient representation $z_{InD}^{min}$ of $x_{InD}$ is minimum if and only if $I(z_{InD}^{min}; x_{InD}) \\leq I(z_{InD}^{suf}; x_{InD}), \\forall z_{InD}^{suf}$ that is sufficient for $Y$ .", + "bbox": [ + 75, + 444, + 472, + 508 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "CS Information Maximization. The goal of training is to optimize $f$ so that $I(z_{InD};Y)$ (CS information) can approximate $I(x_{InD};Y)$ , which stays unchanged as data distribution is fixed during training. Therefore, CS information is supposed to be maximized to the upper bound $I(x_{InD};Y)$ because of Eq. 4. In this way, the closed-set classification task pushes the NN to learn the sufficient representation $z_{InD}^{suf}$ according to definition 1 [30].", + "bbox": [ + 75, + 516, + 468, + 638 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "IS Information Elimination. When $z_{InD}$ is close to the sufficient representation $z_{InD}^{suf}$ , the second term in Eq. 5 will be the fix value $I(x_{InD};Y)$ based on the definition 1. So the key to minimize Eq. 5 is to minimize the first term $I(z_{InD}^{suf};x_{InD})$ . Based on the definition 2, the lower bound of $I(z_{InD}^{suf};x_{InD})$ is $I(z_{InD}^{min};x_{InD})$ , so we can conclude that the learned representation is supposed to be the minimum sufficient representation $z_{InD}^{min}$ [12]. We substitute $I(z_{InD}^{suf};x_{InD})$ and $I(z_{InD}^{min};x_{InD})$ in definition 2 with Eq. 2 and we have", + "bbox": [ + 75, + 638, + 468, + 792 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} I \\left(x _ {I n D}; z _ {I n D} ^ {\\min } \\mid Y\\right) + I \\left(z _ {I n D} ^ {\\min }; Y\\right) \\\\ \\leq I \\left(x _ {I n D}; z _ {I n D} ^ {s u f} | Y\\right) + I \\left(z _ {I n D} ^ {s u f}; Y\\right). \\tag {6} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 158, + 794, + 468, + 834 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "As both $z_{InD}^{min}$ and $z_{InD}^{suf}$ are sufficient, the second term of both sides in Eq. 6 is $I(x_{InD};Y)$ , so we have", + "bbox": [ + 75, + 842, + 468, + 875 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n0 \\leq I \\left(x _ {I n D}; z _ {I n D} ^ {\\text {m i n}} | Y\\right) \\leq I \\left(x _ {I n D}; z _ {I n D} ^ {\\text {s u f}} | Y\\right). \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 125, + 883, + 468, + 902 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Therefore, the learned IS information in $z_{InD}^{min}$ is smaller than any IS information in $z_{InD}^{suf}$ , which could be eliminated to 0 [12] (no blue and orange areas in $z_{InD}^{min}$ in Fig. 2).", + "bbox": [ + 498, + 90, + 890, + 140 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.5. Enlarge CS and IS Information for OSAR", + "text_level": 1, + "bbox": [ + 498, + 147, + 857, + 162 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Based on the analysis in Sec. 3.3 and Sec. 3.4, we show that C.E. tends to maximize the CS information and eliminate the IS information in the feature representation. Both larger IS and CS information are crucial for OSAR according to Eq. 3, but C.E. does not bring the optimal information. On the one hand, IS information is eliminated so we lose a part of information which is beneficial for the OSAR. On the other hand, the learned representation is not sufficient and does not contain enough CS information in practice due to the model capacity and data distribution shift between training and test sets, which can be supported by the fact that test accuracy cannot reach $100\\%$ . Therefore, we propose our method to enlarge the CS and IS information for better OSAR performance in next Sec. 4.", + "bbox": [ + 496, + 170, + 890, + 382 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4. Methods", + "text_level": 1, + "bbox": [ + 498, + 396, + 596, + 411 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4.1. Prototypical Similarity Learning", + "text_level": 1, + "bbox": [ + 498, + 420, + 787, + 436 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "According to Sec. 3.3, we notice that IS information is suppressed by the C.E. loss and a key reason is C.E. encourages feature representations of the same class to be exactly same. Therefore, we argue that the feature representation of the same class samples should have a similarity $s < 1$ . In other words, we aim to keep the intra-class variance which prevents intra-class collapse to retain IS information. Based on the classical PL loss Eq. 1, we develop prototypical similarity learning (PSL):", + "bbox": [ + 496, + 443, + 890, + 580 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {P S L} = - \\log \\frac {\\exp \\left(\\frac {1 - \\left| z ^ {T} k _ {i} - s \\right|}{\\tau}\\right)}{\\exp \\left(\\frac {1 - \\left| z ^ {T} k _ {i} - s \\right|}{\\tau}\\right) + \\sum_ {n \\in K _ {i} ^ {-}} \\exp \\left(\\frac {z ^ {T} n}{\\tau}\\right)}, \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 509, + 583, + 890, + 640 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $s$ and $\\tau$ are fixed hyperparameters. In this way, we expect the prototype $k_{i}$ to act as the CS information for the InD class $i$ , which is used to predict the label, and the dissimilarity between the $z$ and $k_{i}$ represents the IS information. Traditional PL loss (or C.E. loss) encourages the features of samples in the same classes to be as tight as possible, while our PSL aims to keep the variance within the same class.", + "bbox": [ + 496, + 643, + 890, + 763 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "However, we find Eq. 8 will converge to the trivial solution, where the $z$ converges to the training result of Eq. 1 and only $k_{i}$ shifts. To solve this problem, we introduce the similarity between different samples within a mini-batch into the denominator of Eq. 8. In this way, we directly constrain the relationship between sample features instead of only supervising the similarity between the sample feature and its prototype. We name the modified loss as PSL with contrastive terms (CT):", + "bbox": [ + 496, + 763, + 890, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "15298", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/e238f5a8b0f1d50fcf404fec8d8cd134070a55d98285c119b792335724f1fd16.jpg", + "image_caption": [ + "Figure 3. (a) C.E. encourages the sample feature $z$ to be exactly same with the corresponding prototype $k_{i}$ . (b) Our PSL encourages the similarity between $z$ and $k_{i}$ , features of shuffled sample $Q_{shuf}$ and other samples in the same class $Q_{sc}$ to have a similarity less than 1." + ], + "image_footnote": [], + "bbox": [ + 80, + 93, + 468, + 253 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/a8b833f4658139937f81e0958abd4e88842883459f3e42de178ff1ebdf1b6d01.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 496, + 93, + 883, + 252 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\mathcal {L} _ {P S L} ^ {C T} = \\\\ \\frac {\\exp \\left(\\frac {1 - \\left| z ^ {T} k _ {i} - s \\right|}{\\tau}\\right)}{\\exp \\left(\\frac {1 - \\left| z ^ {T} k _ {i} - s \\right|}{\\tau}\\right) + \\sum_ {n \\in Q _ {n}} \\exp \\left(\\frac {z ^ {T} n}{\\tau}\\right) + \\sum_ {p \\in Q _ {s p}} \\exp \\left(\\frac {\\left| z ^ {T} p - s \\right|}{\\tau}\\right)}, \\end{array} \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 76, + 305, + 470, + 396 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $Q_{n} = K_{i}^{-} \\cup Q_{ns}$ . $Q_{ns}$ refers to the negative samples, i.e., samples in other classes, and $Q_{sp}$ refers to the soft positive samples which contains samples in the same class $Q_{sc}$ here. The reason we call soft positive samples is that we think samples in the same class share CS information but have distinct IS information.", + "bbox": [ + 75, + 411, + 468, + 501 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.2. Video Shuffling for PSL", + "text_level": 1, + "bbox": [ + 76, + 513, + 295, + 530 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "PSL aims to keep IS information during training, and in this section we introduce how to enlarge CS information through video shuffling. The appearance bias is a significant problem in the OSAR. For instance, the OoD classes Smile and Chew are easily classified as InD classes ApplyEyeMakeup and ApplyLipstick, as the majority area of all these classes are occupied by a face, as shown in Fig. 7. The NN is confused by the extremely similar spatial information and neglects the minor different temporal information. This phenomenon encourages us to strengthen the temporal information extraction ability of the NN to distinguish classes with very similar appearances but different actions. We find that introducing a simple yet effective way, i.e., to regard the shuffled video $Q_{shuf}$ as the soft positive sample in Eq. 9, is extremely suitable and useful in our PSL framework. In this case, $Q_{sp} = Q_{sc} \\cup Q_{shuf}$ . Shuffled video means shuffling the frames within a single video. As the appearance information of the shuffled video is almost the same as the original video, a smaller than 1 similarity forces the NN to learn the distinct temporal information between them. Unlike existing works which predict the sequence or the type of the shuffled video [34-37], we regard the shuffle video as a whole sample and directly compare its feature representation with the original video in our PSL. We find this", + "bbox": [ + 75, + 537, + 472, + 902 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "technique can improve the closed-set accuracy which indicates more CS information is learned. We summarize the difference between our PSL and classical C.E. in Fig. 3.", + "bbox": [ + 496, + 306, + 892, + 354 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.3. Uncertainty Score", + "text_level": 1, + "bbox": [ + 498, + 364, + 676, + 380 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "As our PSL aims to learn richer CS and IS information in the feature representation, we use the Mahalanobis distance to measure the uncertainty as it can be calculated from the feature representation perspective [38, 39]:", + "bbox": [ + 496, + 387, + 892, + 449 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nu = \\left(z - \\mu_ {m}\\right) ^ {T} \\sum_ {m} ^ {- 1} \\left(z - \\mu_ {m}\\right), \\tag {10}\n$$\n", + "text_format": "latex", + "bbox": [ + 588, + 460, + 890, + 479 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\mu_{m}$ and $\\sum_{m}$ denote the mean and covariance of the whole training set features, and $z$ is the test sample feature.", + "bbox": [ + 498, + 491, + 890, + 522 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "5. Experiments", + "text_level": 1, + "bbox": [ + 500, + 537, + 633, + 555 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Datasets. Following [5], we use UCF101 [40] as the InD dataset for training and closed-set evaluation, and use HMDB51 [41] and MiT-v2 [42] as OoD data for open-set evaluation. Different from [5] which does not clean the OoD data that may contains InD classes, we remove the overlapping classes between InD and OoD dataset during evaluation. See Appendix A for more details.", + "bbox": [ + 496, + 561, + 890, + 667 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Evaluation protocols. For closed-set performance, we evaluate like the traditional way to calculate the top-1 accuracy Acc. $(\\%)$ . For open-set performance, we follow the classical open-set recognition protocol [6,43] to use the obtained uncertainty score Eq. 10 to calculate AUROC $(\\%)$ , AUPR $(\\%)$ and FPR95 $(\\%)$ .", + "bbox": [ + 496, + 669, + 890, + 760 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Implementation details. For Kinetics400 (K400) [3] pretrained model, our implementation setting is the same with [5]. The base learning rate is 0.001 and step-wisely decayed every 20 epochs with total of 50 epochs. We argue that as K400 is extremely large, the K400 pretrained model may already have seen the OoD data used in inference, so", + "bbox": [ + 496, + 760, + 890, + 851 + ], + "page_idx": 4 + }, + { + "type": "page_footnote", + "text": "1We find AUROC in [5] only considers one specific threshold based on their code, and after discussion and agreement they provide the modified correct score in our Tab. 1. See Appendix B for details.", + "bbox": [ + 498, + 862, + 892, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "15299", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/a23f8e3d7140131f311d0d9f8b89b325ae695ab3e93acc6aece6a4be1d52503d.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
DatasetsMethodsw/o K400 Pretrainw/ K400 Pretrain
AUROC↑AUPR↑FPR95↓Acc.↑AUROC↑AUPR↑FPR95↓Acc.↑
UCF101 (InD)OpenMax [8]82.2854.5950.6973.9290.8973.1638.7795.32
MC Dropout [7]75.7541.2154.7873.6388.2367.6238.1295.06
BNN SVI [24]80.1053.4352.3371.5191.8179.6531.4394.71
HMDB51 (OoD)SoftMax [6]79.7252.1353.2273.9291.7577.6928.6095.03
RPL [27]79.6751.8556.4071.4690.5377.8637.0995.59
DEAR [5]80.0049.2353.2871.3384.1675.5489.4094.48
PSL(ours)86.4365.5441.6776.5394.0586.5523.1895.62
Δ(+4.15)(+10.95)(-9.02)(+2.61)(+2.24)(+6.90)(-5.42)(+0.03)
UCF101 (InD)OpenMax [8]84.4376.6947.7473.9293.3488.1428.9595.32
MC Dropout [7]75.6662.2051.5773.6388.7183.3639.4695.06
BNN SVI [24]79.4871.7352.5271.5191.8690.1236.2194.71
MiTv2 (OoD)SoftMax [6]80.5573.1750.4973.9291.9589.1632.0095.03
RPL [27]80.2172.0452.8371.4690.6488.7938.4395.59
DEAR [5]79.0067.1052.4471.3386.0487.3887.4094.48
PSL(ours)86.5379.9540.9976.5395.7594.9618.9695.62
Δ(+2.10)(+3.26)(-6.75)(+2.61)(+2.41)(+4.84)(-9.99)(+0.03)
", + "bbox": [ + 81, + 88, + 885, + 301 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 1. Comparison with state-of-the-art methods on HMDB51 and MiTv2 (OoD) using TSM backbone. Acc. refers to closed-set accuracy. AUROC, AUPR and FPR95 are open-set metrics. Best results are in bold and second best results in italic. The gap between best and second best is in blue. DEAR and our methods contain video-specific operation.", + "bbox": [ + 76, + 301, + 892, + 345 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/5bab0fc96c46516adc715a41287e2c6ef48b0c70a1e2b9851c0df9af2db516cb.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 81, + 349, + 272, + 472 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/fd098bc633ed9b6899e41054a025dfce13ebcd84dc862529d0ccf0febf54e951.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 277, + 349, + 467, + 472 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/81ef902486b45035e37814c29c935d9648187adbdc62c4b608c53a139b739bd4.jpg", + "image_caption": [ + "Figure 4. The uncertainty distribution of InD and OoD samples of (a) Softmax, (b) DEAR, (c) BNN SVI and (d) our PSL method." + ], + "image_footnote": [], + "bbox": [ + 80, + 472, + 272, + 593 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/d45d442a2f6eb36ef94790a2cb2e0edc4d85e4107be2db50b973c8187b5af9f4.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 277, + 472, + 467, + 593 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "we conduct experiments from scratch (no ImageNet pretrained) to ensure that OoD data is absolutely unavailable during training. We use the LARS optimizer [44] and set the base learning rate and momentum as 0.6 and 0.9 with total of 400 epochs. The experiments are conducted on TSM [1], I3D [3] and SlowFast [2]. The batch size for all methods is 256. More details are in Appendix C.", + "bbox": [ + 75, + 650, + 468, + 755 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5.1. Evaluation Results", + "text_level": 1, + "bbox": [ + 76, + 770, + 256, + 784 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Comparison with state-of-the-art. We report the results on HMDB51 (OoD) and MiT-v2 (OoD) in Table 1 using TSM backbone [1]. The evaluation results of other backbones including I3D and SlowFast are in the Appendix D. We can see that for w/ or w/o K400 pretrain, our PSL method has significantly better open-set and closed-set performance than all baselines. The uncertainty distribution", + "bbox": [ + 75, + 794, + 468, + 900 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/e67db6fe4925db7807ee0237e27071e5990aa4d6b9b139f15db3e92dff832ceb.jpg", + "image_caption": [ + "(a) Cross-entropy", + "Figure 5. Feature representation visualization of cross-entropy and our PSL method. OoD samples are in black and InD samples are in other colors. In the red, blue and green circles, it is clear that OoD samples distribute at the edge of InD samples in our PSL, while greatly overlap with each other in the cross-entropy method." + ], + "image_footnote": [], + "bbox": [ + 506, + 349, + 696, + 496 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/c30ffa7f6925d9f5f8ac531f6f0052a4a42e2842269bed4315ce86da26fdc896.jpg", + "image_caption": [ + "(b) PSL (ours)" + ], + "image_footnote": [], + "bbox": [ + 697, + 349, + 885, + 496 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "of InD and OoD samples are depicted in Fig. 4 for MiT-v2 (OoD) with K400 pretrained. Three baseline methods have a clear over confidence problem, i.e., the far left column is extremely high (red circles in Fig. 4), which means a large number of OoD samples have almost 0 uncertainty, while our method significantly alleviates this problem through the distinct representation of OoD samples, illustrated in Fig. 5. Besides, we can find that the open-set performance w/ K400 pretrain is higher than w/o pretrain for almost all methods in Table 1 and Fig. 1 (a), which can testify the importance of richer semantic representation for OSAR.", + "bbox": [ + 496, + 609, + 892, + 776 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Comparison with metric learning methods. Our method concentrates on the feature representation aspect for the OSAR problem, so we also implement several well-known metric learning methods and show the result in Table 3. The evaluation is conducted using TSM model and OoD dataset is HMDB51. We do not use video shuffling in our method for fair comparison. We can see that our method still achieves the best open-set performance. The most im", + "bbox": [ + 496, + 779, + 892, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "15300", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/c44c03511d355fff434f811c28d84e6d1e35410039f27f58cf798a87e3c1679e.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
sQnsQscQshufInDOoDAUROC↑AUPR↑FPR95↓Acc.↑
MeanVarianceMeanVariance
LPLXXXX0.810.00150.630.002980.9552.7952.5172.36
LPSL✓XXX0.790.00160.620.002881.7954.1652.3372.33
LCTPSL✓✓XX0.710.00220.610.003682.6057.3650.0372.17
✓✓✓X0.710.00230.490.003583.4259.0551.3272.28
✓✓✓✓0.740.00160.630.002986.4365.5841.7577.19
", + "bbox": [ + 94, + 88, + 870, + 207 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/60960084174e814b992981c17a7500498e548812c43d41d5fe531b529ea614bc.jpg", + "table_caption": [ + "Table 2. Abaltion results of different components in ${\\mathcal{L}}_{PSL}^{CT}$ ." + ], + "table_footnote": [ + "Table 3. Comparison with different metric learning methods." + ], + "table_body": "
AUROC↑AUPR↑FPR95↓Acc.↑
SoftMax80.9552.7952.5172.36
Triplet [45]81.0254.7553.8875.50
Normface [46]80.9954.9053.1973.34
Circle [47]78.7651.6555.2772.15
Arcface [48]81.2355.0353.6775.95
LSoftMax [49]80.8754.0152.2973.05
PSL(s = 0.8)83.4259.0551.3272.28
PSL(s = 0.6)82.7558.5752.2773.26
", + "bbox": [ + 88, + 227, + 454, + 349 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "important difference between our method and all other metric learning methods is that they aim to push the features of one class as tight as possible like C.E., while our method aims to keep the feature variance within a class to retain IS information. We calculate the mean similarity between the sample feature and the corresponding class center. The mean similarity ranges from 0.77 to 0.82 for other metric learning methods, while mean similarity is 0.71 ( $s = 0.8$ ) and 0.6 ( $s = 0.6$ ) for our PSL. So our method has looser feature distribution within a class, as shown in Fig. 5.", + "bbox": [ + 75, + 378, + 468, + 530 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.2. Ablation Study", + "text_level": 1, + "bbox": [ + 76, + 542, + 230, + 559 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Contrastive terms in $\\mathcal{L}_{PSL}^{CT}$ for IS information. The intuition of PSL is to keep the intra-class variance to retain the IS information which is helpful for OSAR. We expect that the representation $z$ within a class has a similarity $s < 1$ with the prototype $k_{i}$ , so each sample can keep its own IS information. However, we find that the loss $\\mathcal{L}_{PSL}$ may lead the network to find the trivial representation of samples $z$ which is similar to using loss $\\mathcal{L}_{PL}$ , where only $k_{i}$ shifts and $z$ does not. We calculate the mean of similarity $\\text{sim}(z, \\bar{z}_i)$ , where $\\bar{z}_i$ denotes the mean representation of all samples in the same class $i$ , and the mean of similarity with the corresponding prototype $\\text{sim}(z, k_i)$ , as well as the feature variance in all dimensions. Fig. 6 (a) and (b) show that with the hyper-parameter $s$ decreasing, the $\\text{sim}(z, k_i)$ decreases as expected by $\\mathcal{L}_{PSL}$ (green curves), but the $\\text{sim}(z, \\bar{z}_i)$ and variance stay unchanged (blue curves), meaning that the representation of samples are still similar with using $\\mathcal{L}_{PL}$ , and only the prototypes are pushed away by the sample representations. In contrast, with CT in $\\mathcal{L}_{PSL}^{CT}$ , the $\\text{sim}(z, \\bar{z}_i)$ decreases and variance increases with $s$ decreases (red curves), indicating that CT is significantly effective to keep the intra-class variance.", + "bbox": [ + 75, + 566, + 470, + 900 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/152feb23ba7db6e11c1e44b328e9b654ba6af9b1fc9cea71e5304d5cda87d0b7.jpg", + "image_caption": [ + "Figure 6. Mean similarity and variance analysis for CT terms." + ], + "image_footnote": [], + "bbox": [ + 506, + 228, + 691, + 376 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/a68a850b4c3be0ff966023feda67a7cdb1a80476aae3a0b00c963c9811651299.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 692, + 227, + 880, + 376 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "To individually study the effectiveness of $Q_{ns}$ and $Q_{sc}$ in $\\mathcal{L}_{PSL}^{CT}$ , we provide the ablation results in Table 2. For OoD samples, we calculate the similarity with the mean representation of its predicted class. Table 2 shows that using $Q_{ns}$ alone can significantly increase the intra-class variance for both InD and OoD samples, meaning the pushing effect of representations in other classes can implicitly help retain the IS information. On top of that, $Q_{sc}$ can further learn more IS information that is helpful to distinguish OoD samples, as the mean similarity of InD samples stay unchanged, but OoD samples are smaller which means OoD samples are far away from InD samples.", + "bbox": [ + 496, + 412, + 890, + 594 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Shuffled videos for CS information. Tab. 2 shows that $Q_{shuf}$ can improve both closed-set and open-set performance, which proves introducing shuffled videos in PSL can enlarge CS information. Smaller intra-class variance brought by $Q_{shuf}$ testify Proposition 1 that more CS information means more similar features within the same class.", + "bbox": [ + 496, + 595, + 890, + 686 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We draw the uncertainty of all classes in HMDB51, as shown in Fig. 7. Note that some classes in HMDB51 are actually InD as they appear in the UCF101, like the class 3 golf and 4 shoot bow in Fig. 7. We find that in C.E. some OoD classes have extremely low uncertainty, such as class 1 chew and 2 smile, because they are spatially similar to some InD classes like ApplyEyeMakeup and ApplyLipstick in Fig. 7 (a). Comparing (b) and (c) shows that our PSL can increase the average uncertainty of OoD classes (higher yellow points), and some OoD classes which are similar to InD classes like 1 and 2 have much higher uncertainty in our PSL method. After shuffled samples are involved, some InD classes whose uncertainty are increased in (c) like 3 and 4 have lower uncertainty in (d), and the uncertainty of some", + "bbox": [ + 496, + 688, + 892, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "15301", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/5d523ea15bdc4df1542393b1042976962d48fcf29a64ec257e5acdb06cd62b4c.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 89, + 88, + 272, + 215 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/50e5e0570a74c5f12ce4f25e711b674fa204afd5ab1082cd0b973b2191322216.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 274, + 89, + 459, + 215 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/5a0e013a93c29fc56bcd2808d6f44ed69014fda9edfb5b713789aa7f2625a09a.jpg", + "image_caption": [ + "Figure 7. (a) chew and smile are OoD samples from HMDB51, and ApplyEyeMakeup and ApplyLipstick are InD samples from UCF101. (b-d) Uncertainty distribution of each class in HMDB51. Class 1: chew, 2: smile, 3: golf, 4: shoot bow. Classes 1 and 2 are OoD while 3 and 4 are InD." + ], + "image_footnote": [], + "bbox": [ + 81, + 215, + 269, + 337 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/cd41194f660b0ff9bf5afc5f4c7f967af85dbf81ba7b0d270e698f326dfa2b78.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 274, + 215, + 459, + 337 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/c4ab2ab086b9465c927d30057ba79a3fc1da9ea0e09b3ba7f4241d74e4bdc8bf.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
s(Qshuf)s(Qsc)AUROC↑AUPR↑FPR95↓Acc.↑
0.785.2563.9148.3476.98
0.50.786.0364.3643.7076.53
0.383.8060.4248.7675.50
079.5450.5954.4372.59
0.80.886.4365.5841.7576.53
0.90.983.1257.0446.8473.31
1182.0453.8251.8272.89
", + "bbox": [ + 83, + 407, + 460, + 518 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 4. Ablation study of similarity $s$ for ${Q}_{shuf}$ and ${Q}_{sc}$ .", + "bbox": [ + 96, + 520, + 446, + 534 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "OoD classes sharing similar appearance with InD classes like class 1 is further improved.", + "bbox": [ + 75, + 550, + 468, + 579 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "$Q_{sp}$ in Eq. 9 contains $Q_{shuf}$ and $Q_{sc}$ , so we analyze whether should we assign the same $s$ for the shuffled video $Q_{shuf}$ and other videos in the same class $Q_{sc}$ . Tab. 4 shows that the same $s$ have good enough performance. So we set the same $s$ for $Q_{shuf}$ and $Q_{sc}$ in the default setting to reduce the number of hyper-parameters.", + "bbox": [ + 75, + 580, + 468, + 672 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5.3. Discussion", + "text_level": 1, + "bbox": [ + 76, + 680, + 194, + 695 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Both CS and IS information are useful. We provide the closed-set and open-set performance under different hyperparameter $s$ and feature dimension $d$ in Fig. 8. (a) shows that $s = 0.8$ has better open-set performance than $s = 1$ and has comparable closed-set accuracy, which illustrates that retaining the IS information which is eliminated by C.E. $(s = 1)$ is beneficial. When $s < 0.8$ , the NN cannot learn enough CS information, so both closed-set and open-set performance drops. Therefore, a proper mixture of CS and IS information is ideal. (b) shows that when $d$ grows from 4 to 16, more CS information is contained so that both closed-set and open-set performance improves. When $d$ grows from 16 to 128, the feature does not include more CS in", + "bbox": [ + 75, + 703, + 468, + 898 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/9220a62ace11c85ad1b96ae8083dbc023ebf04f764c93f016fac405fc69f5080.jpg", + "image_caption": [ + "(a)" + ], + "image_footnote": [], + "bbox": [ + 506, + 88, + 686, + 215 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/139ec59e1462d2fd9a8807c51b43df4ac7c5063252ed767e06e4dc61e7ec8a9b.jpg", + "image_caption": [ + "(b)" + ], + "image_footnote": [], + "bbox": [ + 692, + 88, + 880, + 218 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/dab39e2182cb473f6318c09e7a0c3943bbe1d18573e3a8098a218ca908287b18.jpg", + "table_caption": [ + "Figure 8. Ablation study of similarity $s$ and feature dimension $d$ ." + ], + "table_footnote": [], + "table_body": "
EpochMeanVarianceAUROC↑Acc-Test.↑Acc-Train.↑
2000.5773.3e-375.0868.3999.85
4000.6023.1e-382.9273.26100
8000.6133.0e-382.5473.29100
", + "bbox": [ + 506, + 243, + 880, + 304 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 5. Training process analysis when $s = {0.6}\\mathrm{\\;w}/\\mathrm{o}{Q}_{shuf}$ .", + "bbox": [ + 513, + 305, + 875, + 319 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "formation as closed-set accuracy is comparable. However, open-set performance keeps increasing which means more IS information is contained based on more feature dimensions. This interesting experiment shows that enough information for closed-set recognition is not enough for open-set recognition because IS information is not related to the closed-set task but useful for the open-set task.", + "bbox": [ + 496, + 333, + 890, + 438 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Feature variance and open-set performance analysis. Fig. 8 (a) shows that when features get looser ( $s = 1 - 0.8$ ), the open-set performance is improved, but if features get continually looser ( $s = 0.8 - 0.1$ ), the open-set performance drops. So there is no strict relation between the feature variance and open-set performance. One may argue that continual training can benefit the open-set performance [50], which is alongside with smaller feature variance [51]. We show that the benefit of continual training comes from better closed-set performance, not tighter features. Tab. 5 shows that when we train the model from 200 to 400 epochs, the closed-set accuracy is higher, and feature is tighter (larger mean similarity and smaller variance), and the open-set performance is better. But from epoch 400 to 800 we find the model is already overfitted to the training set, as the accuracy of test set remains unchanged. So although the features get tighter in the 800 epoch, both the closed-set and open-set performance remain same.", + "bbox": [ + 496, + 439, + 890, + 710 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "6. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 724, + 617, + 739 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We analyze the OSAR problem from the information perspective, and show that cross-entropy tends to eliminate IS information and cannot fully learn CS information which are both useful for the open-set task. So we propose PSL to retain IS information and introduce shuffle videos into PSL to enlarge CS information. Comprehensive experiments demonstrate the effectiveness of our PSL and the importance of IS and CS information in the OSAR task.", + "bbox": [ + 496, + 750, + 890, + 869 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgements This work is supported by Alibaba Group through Alibaba Research Intern Program.", + "bbox": [ + 496, + 869, + 890, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "15302", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Ji Lin, Chuang Gan, and Song Han. TSM: Temporal shift module for efficient video understanding. In ICCV, 2019. 1, 2, 6", + "[2] Christoph Feichtenhofer, Haoqi Fan, Jitendra Malik, and Kaiming He. SlowFast networks for video recognition. 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In ICLR, 2022. 8" + ], + "bbox": [ + 501, + 90, + 890, + 180 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "15304", + "bbox": [ + 480, + 945, + 517, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/Enlarging Instance-Specific and Class-Specific Information for Open-Set Action Recognition/a1eb877e-c60e-4804-81d3-1cd98ec238d0_model.json b/2023/Enlarging Instance-Specific and Class-Specific Information for Open-Set Action Recognition/a1eb877e-c60e-4804-81d3-1cd98ec238d0_model.json new file mode 100644 index 0000000000000000000000000000000000000000..6aac555f4330e29c83213f6f483fcc441251dd74 --- /dev/null +++ b/2023/Enlarging Instance-Specific and Class-Specific Information for Open-Set Action Recognition/a1eb877e-c60e-4804-81d3-1cd98ec238d0_model.json @@ -0,0 +1,2475 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.001, + 0.812, + 0.047 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.175, + 0.131, + 0.798, + 0.177 + ], + "angle": 0, + "content": "Enlarging Instance-specific and Class-specific Information for Open-set Action Recognition" + }, + { + "type": "text", + "bbox": [ + 0.245, + 0.203, + 0.724, + 0.222 + ], + "angle": 0, + "content": "Jun Cen\\(^{1,2*}\\) Shiwei Zhang\\(^{2}\\) Xiang Wang\\(^{3}\\) Yixuan Pei\\(^{4}\\)" + }, + { + "type": "text", + "bbox": [ + 0.294, + 0.222, + 0.677, + 0.24 + ], + "angle": 0, + "content": "Zhiwu Qing\\(^{3}\\) Yingya Zhang\\(^{2}\\) Qifeng Chen\\(^{1}\\)" + }, + { + "type": "text", + "bbox": [ + 0.192, + 0.24, + 0.78, + 0.257 + ], + "angle": 0, + "content": "1The Hong Kong University of Science and Technology 2Alibaba Group" + }, + { + "type": "text", + "bbox": [ + 0.172, + 0.257, + 0.8, + 0.276 + ], + "angle": 0, + "content": "\\(^{3}\\)Huazhong University of Science and Technology \\(^{4}\\)Xi'an Jiaotong University" + }, + { + "type": "text", + "bbox": [ + 0.199, + 0.278, + 0.768, + 0.293 + ], + "angle": 0, + "content": "jcenaa@connect.ust.hk, {zhangjin.zsw,yingya.zyy}@alibaba-inc.com," + }, + { + "type": "text", + "bbox": [ + 0.208, + 0.296, + 0.763, + 0.31 + ], + "angle": 0, + "content": "{wxiang,zzw}@hust.edu.cn, peiyixuan@stu.xjtu.edu.cn, cqf@ust.hk" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.345, + 0.314, + 0.361 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.378, + 0.474, + 0.755 + ], + "angle": 0, + "content": "Open-set action recognition is to reject unknown human action cases which are out of the distribution of the training set. Existing methods mainly focus on learning better uncertainty scores but dismiss the importance of feature representations. We find that features with richer semantic diversity can significantly improve the open-set performance under the same uncertainty scores. In this paper, we begin with analyzing the feature representation behavior in the open-set action recognition (OSAR) problem based on the information bottleneck (IB) theory, and propose to enlarge the instance-specific (IS) and class-specific (CS) information contained in the feature for better performance. To this end, a novel Prototypical Similarity Learning (PSL) framework is proposed to keep the instance variance within the same class to retain more IS information. Besides, we notice that unknown samples sharing similar appearances to known samples are easily misclassified as known classes. To alleviate this issue, video shuffling is further introduced in our PSL to learn distinct temporal information between original and shuffled samples, which we find enlarges the CS information. Extensive experiments demonstrate that the proposed PSL can significantly boost both the open-set and closed-set performance and achieves state-of-the-art results on multiple benchmarks. Code is available at https://github.com/Jun-CEN/PSL." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.787, + 0.21, + 0.803 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.814, + 0.47, + 0.875 + ], + "angle": 0, + "content": "Deep learning methods for video action recognition have developed very fast and achieved remarkable performance in recent years [1-4]. However, these methods operate under the closed-set condition, i.e., to classify all videos into" + }, + { + "type": "image", + "bbox": [ + 0.505, + 0.345, + 0.673, + 0.464 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.583, + 0.467, + 0.605, + 0.477 + ], + "angle": 0, + "content": "(a)" + }, + { + "type": "image", + "bbox": [ + 0.504, + 0.476, + 0.69, + 0.594 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.687, + 0.346, + 0.888, + 0.466 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.791, + 0.467, + 0.808, + 0.476 + ], + "angle": 0, + "content": "(b)" + }, + { + "type": "image", + "bbox": [ + 0.671, + 0.476, + 0.887, + 0.593 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.595, + 0.895, + 0.734 + ], + "angle": 0, + "content": "Figure 1. (a) Richer semantic features brought by the pretraining can significantly improve the open-set performance. (b) Information in the feature is divided into IS and CS information. \\( s_4 \\) can be identified as OoD since it has distinct IS information (IS bars in different colors) with \\( s_1 \\) and \\( s_2 \\), while \\( s_5 \\) has distinct CS information (CS bars in different colors) with all InD samples so it may be OoD. Our PSL aims to learn more IS and CS information (bars in longer lengths) than Cross-Entropy (C.E.). (c) Both enlarged IS and CS information boosts the open-set performance. (d) Our PSL achieves the best OSAR performance." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.895, + 0.903 + ], + "angle": 0, + "content": "one of the classes encountered during training. This closed-set condition is not practical in the real-world scenario, as videos whose classes are beyond the range of the training set will be misclassified as one of the known classes. Therefore, open-set action recognition (OSAR) is proposed to require the network to correctly classify in-distribution (InD) samples and identify out-of-distribution (OoD) samples. InD and OoD classes refer to classes involved and not involved in the training set, respectively." + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.887, + 0.382, + 0.901 + ], + "angle": 0, + "content": "*Work done as an intern at Alibaba DAMO Academy." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.958 + ], + "angle": 0, + "content": "15295" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.473, + 0.395 + ], + "angle": 0, + "content": "Open-set video action recognition is systematically studied in the recent work [5], in which they transfer the existing methods for open-set image recognition into the video domain [6-9] as the baselines, and propose their own method to introduce deep evidential learning [10] to calculate the uncertainty and propose a contrastive evidential debiasing module to alleviate the appearance bias issue in the video domain. All of these methods tend to improve the OSAR performance by calculating a better uncertainty score, based on the feature representations extracted by the neural network (NN). However, the main purpose of training in these methods is still to classify InD samples, which determines the learned feature representations are merely sufficient for InD classification. We find that almost all methods have a significantly better open-set performance when the NN is pretrained with a large dataset (Fig. 1 (a)), so we argue that the diversity of feature representation is extremely important for the OSAR task. Therefore, we propose to boost the open-set ability from the feature representation perspective rather than finding a better uncertainty score." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.398, + 0.473, + 0.672 + ], + "angle": 0, + "content": "We first analyze the feature representation behavior in the open-set problem based on the information bottleneck (IB) theory [11, 12]. We divide the information of the feature into Instance-Specific (IS) and Class-Specific (CS) information. CS information is used for inter-class recognition, so it is similar for samples within the same class but different for samples from other classes. IS information is the special information of each sample within the same class, as two samples cannot be exactly the same even if they belong to the same class. Both CS and IS information are crucial for the open-set task, as illustrated in Fig. 1 (b), where \\( s_4 \\) and \\( s_5 \\) can be identified as OoD samples based on the IS and CS information, respectively. We find that the closed-set classification setting tends to eliminate IS information during training, and cannot fully extract the minimum sufficient CS information for the classification task, so we aim to enlarge IS and CS information in learned feature representations for better OSAR performance." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.675, + 0.473, + 0.903 + ], + "angle": 0, + "content": "To enlarge the IS information, we propose the Prototypical Similarity Learning (PSL) framework, in which the representation of an instance is encouraged to have less than 1 similarity with the corresponding prototype. In this way, we encourage the IS information to be retained and not eliminated. In addition, [5] finds that OoD videos can be easily classified as InD videos in a similar appearance. To alleviate this issue, we introduce the shuffled video into PSL and make it have less than 1 similarity with the original sample. As the shuffled video almost shares the same appearance information with the original one, we encourage the similarity to be less than 1 so that the network can extract the distinct temporal information among them. We find this technique actually enlarges the CS information in the feature representation. Fig. 1 (c) shows that enlarging the IS informa" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.894, + 0.137 + ], + "angle": 0, + "content": "tion is helpful for the open-set performance, and more CS information can further benefit the open-set and closed-set performance. To summarize, our contributions include:" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.137, + 0.894, + 0.213 + ], + "angle": 0, + "content": "- We provide a novel perspective to analyze the open-set recognition task based on the information bottleneck theory, and find that the classical closed-set cross-entropy tends to eliminate the IS information which is helpful to identify OoD samples." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.213, + 0.892, + 0.272 + ], + "angle": 0, + "content": "- We propose to enlarge the IS and CS information for better OSAR performance. Specifically, PSL is designed to retain the IS information in the features, and we involve video shuffling in PSL to learn more CS information." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.273, + 0.892, + 0.319 + ], + "angle": 0, + "content": "- Experiments on multiple datasets and backbones show our PSL's superiority over a large margin compared to other state-of-the-art counterparts, as shown in Fig. 1 (d)." + }, + { + "type": "list", + "bbox": [ + 0.5, + 0.137, + 0.894, + 0.319 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.332, + 0.642, + 0.348 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.357, + 0.895, + 0.553 + ], + "angle": 0, + "content": "Action Recognition. Most recent approaches for action recognition are to exploit appearance and motion cues jointly and achieve remarkable success [1-3, 13-16]. Typically, two-stream networks [17-19] consist of two branches that explore spatial information and temporal dynamics, respectively. Some attempts [1, 20, 21] introduce additional temporal mining operations to overcome the limited temporal information extraction ability of 2D CNN. 3D CNN-based methods [2, 3, 22] inflated 2D kernels for joint spatiotemporal modeling. [23] proposes the prototype similarity learning which pushes the learned representation to the corresponding prototype as close as possible, while our PSL keeps the differences among the same class." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.554, + 0.895, + 0.78 + ], + "angle": 0, + "content": "Open-set Action Recognition. The related work of OSAR is limited [5, 24-26]. Recently, [5] systematically studies the OSAR problem and transfers several open-set image recognition methods to the video domain, including SoftMax [6], MC Dropout [7], OpenMax [8], and RPL [27]. In the benchmark of [5], the only two methods designed specifically for the video domain are BNN SVI [24] and their proposed DEAR. BNN SVI is a Bayesian NN application in the OSAR, while DEAR adopts the deep evidential learning [10] to calculate the uncertainty, and utilizes two modules to alleviate the over-confidence prediction and appearance bias problem, respectively. Existing methods pursue better uncertainty scores, while the objective of our PSL is to learn more diverse feature representations for better open-set distinguishability." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Information Bottleneck Theory. Based on the IB theory [11, 28], the NN intends to extract minimum sufficient information of the inputs for the current task. More recent [12, 29, 30] adopt the IB theory on unsupervised contrastive learning to analyze the representation learning behavior under the corresponding tasks. In this work, we provide a new view to analyze the OSAR problem based on the IB theory." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "15296" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.077, + 0.09, + 0.361, + 0.108 + ], + "angle": 0, + "content": "3. Information Analysis in OSAR" + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.115, + 0.285, + 0.132 + ], + "angle": 0, + "content": "3.1. Prototypical Learning" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.138, + 0.47, + 0.214 + ], + "angle": 0, + "content": "Let \\( f \\) be the encoder to extract the information for an input video sample \\( x \\) and output the feature representation \\( z = f(x), z \\in \\mathbb{R}^d \\). We first define a prototypical learning (PL) loss [31], which is a general version of the cross-entropy (C.E.) loss:" + }, + { + "type": "equation", + "bbox": [ + 0.122, + 0.22, + 0.47, + 0.27 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {P L} = - \\log \\frac {\\exp \\left(\\frac {z ^ {T} k _ {i}}{\\tau}\\right)}{\\exp \\left(\\frac {z ^ {T} k _ {i}}{\\tau}\\right) + \\sum_ {n \\in K ^ {-}} \\exp \\left(\\frac {z ^ {T} n}{\\tau}\\right)}, \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.269, + 0.473, + 0.42 + ], + "angle": 0, + "content": "where \\(i\\) is the ground truth label of \\(x\\), \\(k_{i} \\in \\mathbb{R}^{d}\\) is the prototype for class \\(i\\), \\(\\tau\\) is a temperature parameter, \\(K_{i}^{-} = \\{k_{j} | j \\in \\{1, 2, \\dots, N\\}, j \\neq i\\}\\) is the negative prototype set, and \\(N\\) is the number of InD classes. Note that \\(z\\) and \\(k_{i}\\) are normalized by L2 norm, so that \\(z^{T} k_{i}\\) is the cosine similarity. If we regard prototypes as the row vector of the linear classifier \\(W \\in \\mathbb{R}^{N \\times d}\\), and do not normalize \\(z\\) and \\(k\\) as well as remove \\(\\tau\\), \\(\\mathcal{L}_{PL}\\) will degenerate to the C.E. loss. We introduce the \\(\\mathcal{L}_{PL}\\) so that we can directly manipulate the feature representation \\(z\\)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.428, + 0.351, + 0.444 + ], + "angle": 0, + "content": "3.2. Information Analysis of OSAR" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.451, + 0.47, + 0.557 + ], + "angle": 0, + "content": "Let \\( x_{InD}, z_{InD} \\), and \\( Y \\) be the random variables of InD sample, extracted representation of InD sample, and the task to predict the label of \\( x_{InD} \\), where \\( z_{InD} = f(x_{InD}) \\). Given the joint distribution of \\( p(x_{InD}, Y) \\), the relevant information between \\( x_{InD} \\) and \\( Y \\) is defined as \\( I(x_{InD}, Y) \\) where \\( I \\) denotes the mutual information [28]. The learned representation \\( z_{InD} \\) satisfies:" + }, + { + "type": "equation", + "bbox": [ + 0.094, + 0.558, + 0.47, + 0.592 + ], + "angle": 0, + "content": "\\[\nI \\left(x _ {I n D}; z _ {I n D}\\right) = \\underbrace {I \\left(x _ {I n D} ; z _ {I n D} \\mid Y\\right)} _ {I S} + \\underbrace {I \\left(z _ {I n D} ; Y\\right)} _ {C S}, \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.593, + 0.47, + 0.698 + ], + "angle": 0, + "content": "in which \\( I(x_{\\text{InD}}; z_{\\text{InD}}|Y) \\) and \\( I(z_{\\text{InD}}; Y) \\) denote the Instance-Specific (IS) and Class-Specific (CS) information respectively. In Fig. 2, IS information is blue and orange areas, and CS information is yellow and green areas. CS information is for the closed-set label prediction task \\( Y \\), while IS information is the special information of each sample that is not related to \\( Y \\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.698, + 0.47, + 0.759 + ], + "angle": 0, + "content": "To analyze the information about OSAR, we let \\( T \\) be a random variable that represents the task to distinguish OoD samples from InD samples, then we divide the information contained in \\( z_{InD} \\) about \\( T \\) into two parts [12]:" + }, + { + "type": "equation", + "bbox": [ + 0.117, + 0.76, + 0.469, + 0.795 + ], + "angle": 0, + "content": "\\[\nI \\left(z _ {I n D}; T\\right) = \\underbrace {I \\left(z _ {I n D} \\mid Y ; T\\right)} _ {I S \\text {a b o u t} T} + \\underbrace {I \\left(z _ {I n D} ; Y ; T\\right)} _ {C S \\text {a b o u t} T}, \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.795, + 0.469, + 0.855 + ], + "angle": 0, + "content": "where \\( I(z_{\\text{InD}} | Y; T) \\) and \\( I(z_{\\text{InD}}; Y; T) \\) are the information about the OoD detection task \\( T \\) in IS and CS information (orange and green areas in Fig. 2 respectively). We can see that larger IS and CS information are helpful for OSAR." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.47, + 0.902 + ], + "angle": 0, + "content": "In this paper, we aim to enlarge the information about \\( T \\) contained in CS and IS information for better OSAR performance, as illustrated in Fig. 1 (b) and the enlarged green" + }, + { + "type": "image", + "bbox": [ + 0.51, + 0.094, + 0.681, + 0.216 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.583, + 0.218, + 0.612, + 0.23 + ], + "angle": 0, + "content": "C.E." + }, + { + "type": "image", + "bbox": [ + 0.699, + 0.095, + 0.876, + 0.216 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.765, + 0.218, + 0.834, + 0.23 + ], + "angle": 0, + "content": "PSL (ours)" + }, + { + "type": "text", + "bbox": [ + 0.508, + 0.231, + 0.865, + 0.248 + ], + "angle": 0, + "content": "\\(\\bigcirc \\bigcirc z_{InD} = f(x_{InD})\\) , representation of \\(x_{InD}\\) from NN" + }, + { + "type": "text", + "bbox": [ + 0.508, + 0.248, + 0.875, + 0.266 + ], + "angle": 0, + "content": "\\(\\mathbb{Z}_{InD}^{min}\\), minimum sufficient information of \\(x_{InD}\\) about \\(Y\\)" + }, + { + "type": "text", + "bbox": [ + 0.509, + 0.266, + 0.817, + 0.282 + ], + "angle": 0, + "content": "\\(\\bigcirc\\) \\(I(z_{InD};Y;T)\\) , CS information in \\(z_{InD}\\) about \\(T\\)" + }, + { + "type": "text", + "bbox": [ + 0.509, + 0.283, + 0.81, + 0.299 + ], + "angle": 0, + "content": "\\(I(z_{InD}|Y;T)\\) , IS information in \\(z_{InD}\\) about \\(T\\)" + }, + { + "type": "text", + "bbox": [ + 0.509, + 0.3, + 0.871, + 0.317 + ], + "angle": 0, + "content": "Enlarged information that \\( z_{\\text{InD}} \\) contains using our PSL" + }, + { + "type": "list", + "bbox": [ + 0.508, + 0.231, + 0.875, + 0.317 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.32, + 0.894, + 0.417 + ], + "angle": 0, + "content": "Figure 2. The neural network (NN) can only extract limited representations \\( z_{InD} \\) of the InD sample \\( x_{InD} \\) for the current task \\( Y \\) (predict the closed-set label), which is not diverse enough for the task \\( T \\) (distinguish OoD samples), as green and orange areas are small in (a). In our PSL, we encourage the NN to learn a more diverse representation so that more IS and CS information about \\( T \\) are contained." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.448, + 0.893, + 0.525 + ], + "angle": 0, + "content": "and orange areas in Fig. 2. We first analyze the CS and IS information behaviors under the classical C.E. loss, and find that CS information is encouraged to be maximized but IS information tends to be eliminated in Sec. 3.3. Then we explain this conclusion from the IB theory view in Sec. 3.4." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.539, + 0.874, + 0.555 + ], + "angle": 0, + "content": "3.3. CS and IS Information Behavior under C.E." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.565, + 0.892, + 0.671 + ], + "angle": 0, + "content": "CS information is for closed-set classification task \\( Y \\), so it is similar for the same class sample, but distinct for the different class sample \\( (s_1, s_2 / s_3 \\) in Fig. 1). In contrast, IS information is not related to \\( Y \\) and it is distinct for samples in the same class \\( (s_1, s_2 \\) in Fig. 1). Therefore, we have the following proposition which describe the relation between CS/IS information and feature representation similarity." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.681, + 0.892, + 0.743 + ], + "angle": 0, + "content": "Proposition 1 For two feature representations of samples in the same class, more CS information means these two feature representations are more similar, and more IS information decreases their feature similarity." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.75, + 0.893, + 0.901 + ], + "angle": 0, + "content": "CS information is for the closed-set label prediction task \\( Y \\), which is fully supervised by C.E. loss, so it is maximized during training. In contrast, Eq. 1 shows that C.E. encourages representations of the same class to be exactly same with the corresponding prototype, and such high similarity eliminates the IS information according to Proposition 1. Therefore, C.E. loss tends to maximize the CS information and eliminate the IS information in the feature representation. We analyze this conclusion based on Information Bottleneck (IB) theory in next Sec. 3.4." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "15297" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.077, + 0.091, + 0.47, + 0.107 + ], + "angle": 0, + "content": "3.4. IB Theory Analysis for CS and IS Information" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.114, + 0.47, + 0.145 + ], + "angle": 0, + "content": "Applying the Data Processing Inequality [32] to the Markov chain \\( Y \\to x_{inD} \\to z_{InD} \\), we have" + }, + { + "type": "equation", + "bbox": [ + 0.181, + 0.146, + 0.469, + 0.163 + ], + "angle": 0, + "content": "\\[\nI \\left(z _ {I n D}; Y\\right) \\leq I \\left(x _ {I n D}; Y\\right). \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.165, + 0.469, + 0.21 + ], + "angle": 0, + "content": "It means that the compressed representation \\( z_{InD} \\) cannot contain more information of \\( Y \\) compared to the original data \\( x_{InD} \\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.21, + 0.469, + 0.256 + ], + "angle": 0, + "content": "According to the IB theory [11, 28], the NN is to find the optimal solution of \\( z_{\\text{InD}} \\) with minimizing the following Lagrange:" + }, + { + "type": "equation", + "bbox": [ + 0.089, + 0.257, + 0.469, + 0.274 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} \\left[ p \\left(z _ {I n D} \\mid x _ {I n D}\\right) \\right] = I \\left(z _ {I n D}; x _ {I n D}\\right) - \\beta I \\left(z _ {I n D}; Y\\right), \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.275, + 0.469, + 0.349 + ], + "angle": 0, + "content": "where \\(\\beta\\) is the Lagrange multiplier attached to the constrained meaningful condition. Eq. 5 demonstrates the NN is solving a trade-off problem, as the first term tends to keep the information of \\(x_{InD}\\) as less as possible while the second term tends to maximize the information of \\(Y\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.351, + 0.469, + 0.382 + ], + "angle": 0, + "content": "Inspired by [12, 33], the sufficient and minimum sufficient representation of \\( x_{\\text{InD}} \\) about \\( Y \\) can be defined as:" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.389, + 0.472, + 0.438 + ], + "angle": 0, + "content": "Definition 1 (Sufficient Representation) A feature representation \\( z_{InD}^{suf} \\) of \\( x_{InD} \\) is sufficient for \\( Y \\) if and only if \\( I(z_{InD}^{suf};Y) = I(x_{InD};Y) \\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.445, + 0.473, + 0.509 + ], + "angle": 0, + "content": "Definition 2 (Minimum Sufficient Representation) A sufficient representation \\( z_{InD}^{min} \\) of \\( x_{InD} \\) is minimum if and only if \\( I(z_{InD}^{min}; x_{InD}) \\leq I(z_{InD}^{suf}; x_{InD}), \\forall z_{InD}^{suf} \\) that is sufficient for \\( Y \\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.517, + 0.469, + 0.639 + ], + "angle": 0, + "content": "CS Information Maximization. The goal of training is to optimize \\( f \\) so that \\( I(z_{InD};Y) \\) (CS information) can approximate \\( I(x_{InD};Y) \\), which stays unchanged as data distribution is fixed during training. Therefore, CS information is supposed to be maximized to the upper bound \\( I(x_{InD};Y) \\) because of Eq. 4. In this way, the closed-set classification task pushes the NN to learn the sufficient representation \\( z_{InD}^{suf} \\) according to definition 1 [30]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.639, + 0.469, + 0.793 + ], + "angle": 0, + "content": "IS Information Elimination. When \\( z_{InD} \\) is close to the sufficient representation \\( z_{InD}^{suf} \\), the second term in Eq. 5 will be the fix value \\( I(x_{InD};Y) \\) based on the definition 1. So the key to minimize Eq. 5 is to minimize the first term \\( I(z_{InD}^{suf};x_{InD}) \\). Based on the definition 2, the lower bound of \\( I(z_{InD}^{suf};x_{InD}) \\) is \\( I(z_{InD}^{min};x_{InD}) \\), so we can conclude that the learned representation is supposed to be the minimum sufficient representation \\( z_{InD}^{min} \\) [12]. We substitute \\( I(z_{InD}^{suf};x_{InD}) \\) and \\( I(z_{InD}^{min};x_{InD}) \\) in definition 2 with Eq. 2 and we have" + }, + { + "type": "equation", + "bbox": [ + 0.16, + 0.795, + 0.469, + 0.835 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} I \\left(x _ {I n D}; z _ {I n D} ^ {\\min } \\mid Y\\right) + I \\left(z _ {I n D} ^ {\\min }; Y\\right) \\\\ \\leq I \\left(x _ {I n D}; z _ {I n D} ^ {s u f} | Y\\right) + I \\left(z _ {I n D} ^ {s u f}; Y\\right). \\tag {6} \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.843, + 0.47, + 0.876 + ], + "angle": 0, + "content": "As both \\( z_{InD}^{min} \\) and \\( z_{InD}^{suf} \\) are sufficient, the second term of both sides in Eq. 6 is \\( I(x_{InD};Y) \\), so we have" + }, + { + "type": "equation", + "bbox": [ + 0.126, + 0.884, + 0.469, + 0.903 + ], + "angle": 0, + "content": "\\[\n0 \\leq I \\left(x _ {I n D}; z _ {I n D} ^ {\\text {m i n}} | Y\\right) \\leq I \\left(x _ {I n D}; z _ {I n D} ^ {\\text {s u f}} | Y\\right). \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.091, + 0.892, + 0.141 + ], + "angle": 0, + "content": "Therefore, the learned IS information in \\( z_{InD}^{min} \\) is smaller than any IS information in \\( z_{InD}^{suf} \\), which could be eliminated to 0 [12] (no blue and orange areas in \\( z_{InD}^{min} \\) in Fig. 2)." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.148, + 0.859, + 0.164 + ], + "angle": 0, + "content": "3.5. Enlarge CS and IS Information for OSAR" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.171, + 0.892, + 0.383 + ], + "angle": 0, + "content": "Based on the analysis in Sec. 3.3 and Sec. 3.4, we show that C.E. tends to maximize the CS information and eliminate the IS information in the feature representation. Both larger IS and CS information are crucial for OSAR according to Eq. 3, but C.E. does not bring the optimal information. On the one hand, IS information is eliminated so we lose a part of information which is beneficial for the OSAR. On the other hand, the learned representation is not sufficient and does not contain enough CS information in practice due to the model capacity and data distribution shift between training and test sets, which can be supported by the fact that test accuracy cannot reach \\(100\\%\\). Therefore, we propose our method to enlarge the CS and IS information for better OSAR performance in next Sec. 4." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.397, + 0.598, + 0.412 + ], + "angle": 0, + "content": "4. Methods" + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.421, + 0.788, + 0.437 + ], + "angle": 0, + "content": "4.1. Prototypical Similarity Learning" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.444, + 0.892, + 0.581 + ], + "angle": 0, + "content": "According to Sec. 3.3, we notice that IS information is suppressed by the C.E. loss and a key reason is C.E. encourages feature representations of the same class to be exactly same. Therefore, we argue that the feature representation of the same class samples should have a similarity \\( s < 1 \\). In other words, we aim to keep the intra-class variance which prevents intra-class collapse to retain IS information. Based on the classical PL loss Eq. 1, we develop prototypical similarity learning (PSL):" + }, + { + "type": "equation", + "bbox": [ + 0.511, + 0.584, + 0.891, + 0.641 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {P S L} = - \\log \\frac {\\exp \\left(\\frac {1 - \\left| z ^ {T} k _ {i} - s \\right|}{\\tau}\\right)}{\\exp \\left(\\frac {1 - \\left| z ^ {T} k _ {i} - s \\right|}{\\tau}\\right) + \\sum_ {n \\in K _ {i} ^ {-}} \\exp \\left(\\frac {z ^ {T} n}{\\tau}\\right)}, \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.645, + 0.892, + 0.764 + ], + "angle": 0, + "content": "where \\( s \\) and \\( \\tau \\) are fixed hyperparameters. In this way, we expect the prototype \\( k_{i} \\) to act as the CS information for the InD class \\( i \\), which is used to predict the label, and the dissimilarity between the \\( z \\) and \\( k_{i} \\) represents the IS information. Traditional PL loss (or C.E. loss) encourages the features of samples in the same classes to be as tight as possible, while our PSL aims to keep the variance within the same class." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.892, + 0.901 + ], + "angle": 0, + "content": "However, we find Eq. 8 will converge to the trivial solution, where the \\(z\\) converges to the training result of Eq. 1 and only \\(k_{i}\\) shifts. To solve this problem, we introduce the similarity between different samples within a mini-batch into the denominator of Eq. 8. In this way, we directly constrain the relationship between sample features instead of only supervising the similarity between the sample feature and its prototype. We name the modified loss as PSL with contrastive terms (CT):" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "15298" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.081, + 0.094, + 0.47, + 0.254 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.498, + 0.094, + 0.885, + 0.253 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.253, + 0.894, + 0.283 + ], + "angle": 0, + "content": "Figure 3. (a) C.E. encourages the sample feature \\( z \\) to be exactly same with the corresponding prototype \\( k_{i} \\). (b) Our PSL encourages the similarity between \\( z \\) and \\( k_{i} \\), features of shuffled sample \\( Q_{shuf} \\) and other samples in the same class \\( Q_{sc} \\) to have a similarity less than 1." + }, + { + "type": "equation", + "bbox": [ + 0.078, + 0.306, + 0.472, + 0.397 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\mathcal {L} _ {P S L} ^ {C T} = \\\\ \\frac {\\exp \\left(\\frac {1 - \\left| z ^ {T} k _ {i} - s \\right|}{\\tau}\\right)}{\\exp \\left(\\frac {1 - \\left| z ^ {T} k _ {i} - s \\right|}{\\tau}\\right) + \\sum_ {n \\in Q _ {n}} \\exp \\left(\\frac {z ^ {T} n}{\\tau}\\right) + \\sum_ {p \\in Q _ {s p}} \\exp \\left(\\frac {\\left| z ^ {T} p - s \\right|}{\\tau}\\right)}, \\end{array} \\tag {9}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.412, + 0.47, + 0.502 + ], + "angle": 0, + "content": "where \\( Q_{n} = K_{i}^{-} \\cup Q_{ns} \\). \\( Q_{ns} \\) refers to the negative samples, i.e., samples in other classes, and \\( Q_{sp} \\) refers to the soft positive samples which contains samples in the same class \\( Q_{sc} \\) here. The reason we call soft positive samples is that we think samples in the same class share CS information but have distinct IS information." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.515, + 0.296, + 0.531 + ], + "angle": 0, + "content": "4.2. Video Shuffling for PSL" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.539, + 0.473, + 0.903 + ], + "angle": 0, + "content": "PSL aims to keep IS information during training, and in this section we introduce how to enlarge CS information through video shuffling. The appearance bias is a significant problem in the OSAR. For instance, the OoD classes Smile and Chew are easily classified as InD classes ApplyEyeMakeup and ApplyLipstick, as the majority area of all these classes are occupied by a face, as shown in Fig. 7. The NN is confused by the extremely similar spatial information and neglects the minor different temporal information. This phenomenon encourages us to strengthen the temporal information extraction ability of the NN to distinguish classes with very similar appearances but different actions. We find that introducing a simple yet effective way, i.e., to regard the shuffled video \\( Q_{shuf} \\) as the soft positive sample in Eq. 9, is extremely suitable and useful in our PSL framework. In this case, \\( Q_{sp} = Q_{sc} \\cup Q_{shuf} \\). Shuffled video means shuffling the frames within a single video. As the appearance information of the shuffled video is almost the same as the original video, a smaller than 1 similarity forces the NN to learn the distinct temporal information between them. Unlike existing works which predict the sequence or the type of the shuffled video [34-37], we regard the shuffle video as a whole sample and directly compare its feature representation with the original video in our PSL. We find this" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.308, + 0.893, + 0.355 + ], + "angle": 0, + "content": "technique can improve the closed-set accuracy which indicates more CS information is learned. We summarize the difference between our PSL and classical C.E. in Fig. 3." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.365, + 0.677, + 0.381 + ], + "angle": 0, + "content": "4.3. Uncertainty Score" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.388, + 0.893, + 0.45 + ], + "angle": 0, + "content": "As our PSL aims to learn richer CS and IS information in the feature representation, we use the Mahalanobis distance to measure the uncertainty as it can be calculated from the feature representation perspective [38, 39]:" + }, + { + "type": "equation", + "bbox": [ + 0.589, + 0.461, + 0.892, + 0.48 + ], + "angle": 0, + "content": "\\[\nu = \\left(z - \\mu_ {m}\\right) ^ {T} \\sum_ {m} ^ {- 1} \\left(z - \\mu_ {m}\\right), \\tag {10}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.492, + 0.892, + 0.523 + ], + "angle": 0, + "content": "where \\(\\mu_{m}\\) and \\(\\sum_{m}\\) denote the mean and covariance of the whole training set features, and \\(z\\) is the test sample feature." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.538, + 0.634, + 0.556 + ], + "angle": 0, + "content": "5. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.563, + 0.892, + 0.669 + ], + "angle": 0, + "content": "Datasets. Following [5], we use UCF101 [40] as the InD dataset for training and closed-set evaluation, and use HMDB51 [41] and MiT-v2 [42] as OoD data for open-set evaluation. Different from [5] which does not clean the OoD data that may contains InD classes, we remove the overlapping classes between InD and OoD dataset during evaluation. See Appendix A for more details." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.67, + 0.892, + 0.761 + ], + "angle": 0, + "content": "Evaluation protocols. For closed-set performance, we evaluate like the traditional way to calculate the top-1 accuracy Acc. \\((\\%)\\). For open-set performance, we follow the classical open-set recognition protocol [6,43] to use the obtained uncertainty score Eq. 10 to calculate AUROC \\((\\%)\\), AUPR \\((\\%)\\) and FPR95 \\((\\%)\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.761, + 0.892, + 0.852 + ], + "angle": 0, + "content": "Implementation details. For Kinetics400 (K400) [3] pretrained model, our implementation setting is the same with [5]. The base learning rate is 0.001 and step-wisely decayed every 20 epochs with total of 50 epochs. We argue that as K400 is extremely large, the K400 pretrained model may already have seen the OoD data used in inference, so" + }, + { + "type": "page_footnote", + "bbox": [ + 0.499, + 0.863, + 0.893, + 0.901 + ], + "angle": 0, + "content": "1We find AUROC in [5] only considers one specific threshold based on their code, and after discussion and agreement they provide the modified correct score in our Tab. 1. See Appendix B for details." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "15299" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.082, + 0.089, + 0.887, + 0.302 + ], + "angle": 0, + "content": "
DatasetsMethodsw/o K400 Pretrainw/ K400 Pretrain
AUROC↑AUPR↑FPR95↓Acc.↑AUROC↑AUPR↑FPR95↓Acc.↑
UCF101 (InD)OpenMax [8]82.2854.5950.6973.9290.8973.1638.7795.32
MC Dropout [7]75.7541.2154.7873.6388.2367.6238.1295.06
BNN SVI [24]80.1053.4352.3371.5191.8179.6531.4394.71
HMDB51 (OoD)SoftMax [6]79.7252.1353.2273.9291.7577.6928.6095.03
RPL [27]79.6751.8556.4071.4690.5377.8637.0995.59
DEAR [5]80.0049.2353.2871.3384.1675.5489.4094.48
PSL(ours)86.4365.5441.6776.5394.0586.5523.1895.62
Δ(+4.15)(+10.95)(-9.02)(+2.61)(+2.24)(+6.90)(-5.42)(+0.03)
UCF101 (InD)OpenMax [8]84.4376.6947.7473.9293.3488.1428.9595.32
MC Dropout [7]75.6662.2051.5773.6388.7183.3639.4695.06
BNN SVI [24]79.4871.7352.5271.5191.8690.1236.2194.71
MiTv2 (OoD)SoftMax [6]80.5573.1750.4973.9291.9589.1632.0095.03
RPL [27]80.2172.0452.8371.4690.6488.7938.4395.59
DEAR [5]79.0067.1052.4471.3386.0487.3887.4094.48
PSL(ours)86.5379.9540.9976.5395.7594.9618.9695.62
Δ(+2.10)(+3.26)(-6.75)(+2.61)(+2.41)(+4.84)(-9.99)(+0.03)
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.303, + 0.893, + 0.346 + ], + "angle": 0, + "content": "Table 1. Comparison with state-of-the-art methods on HMDB51 and MiTv2 (OoD) using TSM backbone. Acc. refers to closed-set accuracy. AUROC, AUPR and FPR95 are open-set metrics. Best results are in bold and second best results in italic. The gap between best and second best is in blue. DEAR and our methods contain video-specific operation." + }, + { + "type": "image", + "bbox": [ + 0.083, + 0.351, + 0.273, + 0.473 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.278, + 0.351, + 0.468, + 0.473 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.081, + 0.473, + 0.273, + 0.594 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.278, + 0.473, + 0.468, + 0.594 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.594, + 0.47, + 0.621 + ], + "angle": 0, + "content": "Figure 4. The uncertainty distribution of InD and OoD samples of (a) Softmax, (b) DEAR, (c) BNN SVI and (d) our PSL method." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.651, + 0.47, + 0.756 + ], + "angle": 0, + "content": "we conduct experiments from scratch (no ImageNet pretrained) to ensure that OoD data is absolutely unavailable during training. We use the LARS optimizer [44] and set the base learning rate and momentum as 0.6 and 0.9 with total of 400 epochs. The experiments are conducted on TSM [1], I3D [3] and SlowFast [2]. The batch size for all methods is 256. More details are in Appendix C." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.771, + 0.258, + 0.785 + ], + "angle": 0, + "content": "5.1. Evaluation Results" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.795, + 0.47, + 0.901 + ], + "angle": 0, + "content": "Comparison with state-of-the-art. We report the results on HMDB51 (OoD) and MiT-v2 (OoD) in Table 1 using TSM backbone [1]. The evaluation results of other backbones including I3D and SlowFast are in the Appendix D. We can see that for w/ or w/o K400 pretrain, our PSL method has significantly better open-set and closed-set performance than all baselines. The uncertainty distribution" + }, + { + "type": "image", + "bbox": [ + 0.507, + 0.35, + 0.697, + 0.497 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.553, + 0.498, + 0.661, + 0.512 + ], + "angle": 0, + "content": "(a) Cross-entropy" + }, + { + "type": "image", + "bbox": [ + 0.699, + 0.35, + 0.887, + 0.497 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.75, + 0.498, + 0.838, + 0.51 + ], + "angle": 0, + "content": "(b) PSL (ours)" + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.511, + 0.892, + 0.58 + ], + "angle": 0, + "content": "Figure 5. Feature representation visualization of cross-entropy and our PSL method. OoD samples are in black and InD samples are in other colors. In the red, blue and green circles, it is clear that OoD samples distribute at the edge of InD samples in our PSL, while greatly overlap with each other in the cross-entropy method." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.611, + 0.893, + 0.777 + ], + "angle": 0, + "content": "of InD and OoD samples are depicted in Fig. 4 for MiT-v2 (OoD) with K400 pretrained. Three baseline methods have a clear over confidence problem, i.e., the far left column is extremely high (red circles in Fig. 4), which means a large number of OoD samples have almost 0 uncertainty, while our method significantly alleviates this problem through the distinct representation of OoD samples, illustrated in Fig. 5. Besides, we can find that the open-set performance w/ K400 pretrain is higher than w/o pretrain for almost all methods in Table 1 and Fig. 1 (a), which can testify the importance of richer semantic representation for OSAR." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.893, + 0.901 + ], + "angle": 0, + "content": "Comparison with metric learning methods. Our method concentrates on the feature representation aspect for the OSAR problem, so we also implement several well-known metric learning methods and show the result in Table 3. The evaluation is conducted using TSM model and OoD dataset is HMDB51. We do not use video shuffling in our method for fair comparison. We can see that our method still achieves the best open-set performance. The most im" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "15300" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.095, + 0.089, + 0.872, + 0.208 + ], + "angle": 0, + "content": "
sQnsQscQshufInDOoDAUROC↑AUPR↑FPR95↓Acc.↑
MeanVarianceMeanVariance
LPLXXXX0.810.00150.630.002980.9552.7952.5172.36
LPSL✓XXX0.790.00160.620.002881.7954.1652.3372.33
LCTPSL✓✓XX0.710.00220.610.003682.6057.3650.0372.17
✓✓✓X0.710.00230.490.003583.4259.0551.3272.28
✓✓✓✓0.740.00160.630.002986.4365.5841.7577.19
" + }, + { + "type": "table_caption", + "bbox": [ + 0.308, + 0.208, + 0.66, + 0.222 + ], + "angle": 0, + "content": "Table 2. Abaltion results of different components in \\( {\\mathcal{L}}_{PSL}^{CT} \\) ." + }, + { + "type": "table", + "bbox": [ + 0.089, + 0.228, + 0.455, + 0.35 + ], + "angle": 0, + "content": "
AUROC↑AUPR↑FPR95↓Acc.↑
SoftMax80.9552.7952.5172.36
Triplet [45]81.0254.7553.8875.50
Normface [46]80.9954.9053.1973.34
Circle [47]78.7651.6555.2772.15
Arcface [48]81.2355.0353.6775.95
LSoftMax [49]80.8754.0152.2973.05
PSL(s = 0.8)83.4259.0551.3272.28
PSL(s = 0.6)82.7558.5752.2773.26
" + }, + { + "type": "table_footnote", + "bbox": [ + 0.091, + 0.352, + 0.454, + 0.365 + ], + "angle": 0, + "content": "Table 3. Comparison with different metric learning methods." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.38, + 0.47, + 0.531 + ], + "angle": 0, + "content": "important difference between our method and all other metric learning methods is that they aim to push the features of one class as tight as possible like C.E., while our method aims to keep the feature variance within a class to retain IS information. We calculate the mean similarity between the sample feature and the corresponding class center. The mean similarity ranges from 0.77 to 0.82 for other metric learning methods, while mean similarity is 0.71 (\\(s = 0.8\\)) and 0.6 (\\(s = 0.6\\)) for our PSL. So our method has looser feature distribution within a class, as shown in Fig. 5." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.544, + 0.231, + 0.56 + ], + "angle": 0, + "content": "5.2. Ablation Study" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.568, + 0.471, + 0.901 + ], + "angle": 0, + "content": "Contrastive terms in \\(\\mathcal{L}_{PSL}^{CT}\\) for IS information. The intuition of PSL is to keep the intra-class variance to retain the IS information which is helpful for OSAR. We expect that the representation \\(z\\) within a class has a similarity \\(s < 1\\) with the prototype \\(k_{i}\\), so each sample can keep its own IS information. However, we find that the loss \\(\\mathcal{L}_{PSL}\\) may lead the network to find the trivial representation of samples \\(z\\) which is similar to using loss \\(\\mathcal{L}_{PL}\\), where only \\(k_{i}\\) shifts and \\(z\\) does not. We calculate the mean of similarity \\(\\text{sim}(z, \\bar{z}_i)\\), where \\(\\bar{z}_i\\) denotes the mean representation of all samples in the same class \\(i\\), and the mean of similarity with the corresponding prototype \\(\\text{sim}(z, k_i)\\), as well as the feature variance in all dimensions. Fig. 6 (a) and (b) show that with the hyper-parameter \\(s\\) decreasing, the \\(\\text{sim}(z, k_i)\\) decreases as expected by \\(\\mathcal{L}_{PSL}\\) (green curves), but the \\(\\text{sim}(z, \\bar{z}_i)\\) and variance stay unchanged (blue curves), meaning that the representation of samples are still similar with using \\(\\mathcal{L}_{PL}\\), and only the prototypes are pushed away by the sample representations. In contrast, with CT in \\(\\mathcal{L}_{PSL}^{CT}\\), the \\(\\text{sim}(z, \\bar{z}_i)\\) decreases and variance increases with \\(s\\) decreases (red curves), indicating that CT is significantly effective to keep the intra-class variance." + }, + { + "type": "image", + "bbox": [ + 0.508, + 0.229, + 0.692, + 0.377 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.693, + 0.228, + 0.882, + 0.377 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.511, + 0.378, + 0.88, + 0.392 + ], + "angle": 0, + "content": "Figure 6. Mean similarity and variance analysis for CT terms." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.413, + 0.892, + 0.595 + ], + "angle": 0, + "content": "To individually study the effectiveness of \\( Q_{ns} \\) and \\( Q_{sc} \\) in \\( \\mathcal{L}_{PSL}^{CT} \\), we provide the ablation results in Table 2. For OoD samples, we calculate the similarity with the mean representation of its predicted class. Table 2 shows that using \\( Q_{ns} \\) alone can significantly increase the intra-class variance for both InD and OoD samples, meaning the pushing effect of representations in other classes can implicitly help retain the IS information. On top of that, \\( Q_{sc} \\) can further learn more IS information that is helpful to distinguish OoD samples, as the mean similarity of InD samples stay unchanged, but OoD samples are smaller which means OoD samples are far away from InD samples." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.596, + 0.892, + 0.687 + ], + "angle": 0, + "content": "Shuffled videos for CS information. Tab. 2 shows that \\( Q_{shuf} \\) can improve both closed-set and open-set performance, which proves introducing shuffled videos in PSL can enlarge CS information. Smaller intra-class variance brought by \\( Q_{shuf} \\) testify Proposition 1 that more CS information means more similar features within the same class." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.689, + 0.893, + 0.901 + ], + "angle": 0, + "content": "We draw the uncertainty of all classes in HMDB51, as shown in Fig. 7. Note that some classes in HMDB51 are actually InD as they appear in the UCF101, like the class 3 golf and 4 shoot bow in Fig. 7. We find that in C.E. some OoD classes have extremely low uncertainty, such as class 1 chew and 2 smile, because they are spatially similar to some InD classes like ApplyEyeMakeup and ApplyLipstick in Fig. 7 (a). Comparing (b) and (c) shows that our PSL can increase the average uncertainty of OoD classes (higher yellow points), and some OoD classes which are similar to InD classes like 1 and 2 have much higher uncertainty in our PSL method. After shuffled samples are involved, some InD classes whose uncertainty are increased in (c) like 3 and 4 have lower uncertainty in (d), and the uncertainty of some" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "15301" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.091, + 0.089, + 0.273, + 0.216 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.275, + 0.09, + 0.46, + 0.217 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.083, + 0.217, + 0.27, + 0.338 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.276, + 0.217, + 0.46, + 0.338 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.339, + 0.47, + 0.406 + ], + "angle": 0, + "content": "Figure 7. (a) chew and smile are OoD samples from HMDB51, and ApplyEyeMakeup and ApplyLipstick are InD samples from UCF101. (b-d) Uncertainty distribution of each class in HMDB51. Class 1: chew, 2: smile, 3: golf, 4: shoot bow. Classes 1 and 2 are OoD while 3 and 4 are InD." + }, + { + "type": "table", + "bbox": [ + 0.084, + 0.409, + 0.462, + 0.52 + ], + "angle": 0, + "content": "
s(Qshuf)s(Qsc)AUROC↑AUPR↑FPR95↓Acc.↑
0.785.2563.9148.3476.98
0.50.786.0364.3643.7076.53
0.383.8060.4248.7675.50
079.5450.5954.4372.59
0.80.886.4365.5841.7576.53
0.90.983.1257.0446.8473.31
1182.0453.8251.8272.89
" + }, + { + "type": "table_caption", + "bbox": [ + 0.098, + 0.521, + 0.447, + 0.535 + ], + "angle": 0, + "content": "Table 4. Ablation study of similarity \\( s \\) for \\( {Q}_{shuf} \\) and \\( {Q}_{sc} \\) ." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.551, + 0.469, + 0.58 + ], + "angle": 0, + "content": "OoD classes sharing similar appearance with InD classes like class 1 is further improved." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.581, + 0.469, + 0.673 + ], + "angle": 0, + "content": "\\(Q_{sp}\\) in Eq. 9 contains \\(Q_{shuf}\\) and \\(Q_{sc}\\), so we analyze whether should we assign the same \\(s\\) for the shuffled video \\(Q_{shuf}\\) and other videos in the same class \\(Q_{sc}\\). Tab. 4 shows that the same \\(s\\) have good enough performance. So we set the same \\(s\\) for \\(Q_{shuf}\\) and \\(Q_{sc}\\) in the default setting to reduce the number of hyper-parameters." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.681, + 0.195, + 0.696 + ], + "angle": 0, + "content": "5.3. Discussion" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.704, + 0.47, + 0.9 + ], + "angle": 0, + "content": "Both CS and IS information are useful. We provide the closed-set and open-set performance under different hyperparameter \\( s \\) and feature dimension \\( d \\) in Fig. 8. (a) shows that \\( s = 0.8 \\) has better open-set performance than \\( s = 1 \\) and has comparable closed-set accuracy, which illustrates that retaining the IS information which is eliminated by C.E. \\( (s = 1) \\) is beneficial. When \\( s < 0.8 \\), the NN cannot learn enough CS information, so both closed-set and open-set performance drops. Therefore, a proper mixture of CS and IS information is ideal. (b) shows that when \\( d \\) grows from 4 to 16, more CS information is contained so that both closed-set and open-set performance improves. When \\( d \\) grows from 16 to 128, the feature does not include more CS in" + }, + { + "type": "image", + "bbox": [ + 0.507, + 0.089, + 0.687, + 0.217 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.589, + 0.219, + 0.605, + 0.23 + ], + "angle": 0, + "content": "(a)" + }, + { + "type": "image", + "bbox": [ + 0.694, + 0.089, + 0.882, + 0.219 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.777, + 0.22, + 0.792, + 0.23 + ], + "angle": 0, + "content": "(b)" + }, + { + "type": "table_caption", + "bbox": [ + 0.503, + 0.231, + 0.887, + 0.243 + ], + "angle": 0, + "content": "Figure 8. Ablation study of similarity \\( s \\) and feature dimension \\( d \\)." + }, + { + "type": "table", + "bbox": [ + 0.508, + 0.244, + 0.882, + 0.305 + ], + "angle": 0, + "content": "
EpochMeanVarianceAUROC↑Acc-Test.↑Acc-Train.↑
2000.5773.3e-375.0868.3999.85
4000.6023.1e-382.9273.26100
8000.6133.0e-382.5473.29100
" + }, + { + "type": "table_caption", + "bbox": [ + 0.514, + 0.306, + 0.877, + 0.32 + ], + "angle": 0, + "content": "Table 5. Training process analysis when \\( s = {0.6}\\mathrm{\\;w}/\\mathrm{o}{Q}_{shuf} \\) ." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.334, + 0.892, + 0.439 + ], + "angle": 0, + "content": "formation as closed-set accuracy is comparable. However, open-set performance keeps increasing which means more IS information is contained based on more feature dimensions. This interesting experiment shows that enough information for closed-set recognition is not enough for open-set recognition because IS information is not related to the closed-set task but useful for the open-set task." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.44, + 0.892, + 0.711 + ], + "angle": 0, + "content": "Feature variance and open-set performance analysis. Fig. 8 (a) shows that when features get looser (\\(s = 1 - 0.8\\)), the open-set performance is improved, but if features get continually looser (\\(s = 0.8 - 0.1\\)), the open-set performance drops. So there is no strict relation between the feature variance and open-set performance. One may argue that continual training can benefit the open-set performance [50], which is alongside with smaller feature variance [51]. We show that the benefit of continual training comes from better closed-set performance, not tighter features. Tab. 5 shows that when we train the model from 200 to 400 epochs, the closed-set accuracy is higher, and feature is tighter (larger mean similarity and smaller variance), and the open-set performance is better. But from epoch 400 to 800 we find the model is already overfitted to the training set, as the accuracy of test set remains unchanged. So although the features get tighter in the 800 epoch, both the closed-set and open-set performance remain same." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.725, + 0.619, + 0.74 + ], + "angle": 0, + "content": "6. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.75, + 0.892, + 0.871 + ], + "angle": 0, + "content": "We analyze the OSAR problem from the information perspective, and show that cross-entropy tends to eliminate IS information and cannot fully learn CS information which are both useful for the open-set task. So we propose PSL to retain IS information and introduce shuffle videos into PSL to enlarge CS information. Comprehensive experiments demonstrate the effectiveness of our PSL and the importance of IS and CS information in the OSAR task." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.871, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Acknowledgements This work is supported by Alibaba Group through Alibaba Research Intern Program." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "15302" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.115, + 0.47, + 0.156 + ], + "angle": 0, + "content": "[1] Ji Lin, Chuang Gan, and Song Han. TSM: Temporal shift module for efficient video understanding. In ICCV, 2019. 1, 2, 6" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.161, + 0.47, + 0.202 + ], + "angle": 0, + "content": "[2] Christoph Feichtenhofer, Haoqi Fan, Jitendra Malik, and Kaiming He. 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Existing methods mainly focus on learning better uncertainty scores but dismiss the importance of feature representations. We find that features with richer semantic diversity can significantly improve the open-set performance under the same uncertainty scores. In this paper, we begin with analyzing the feature representation behavior in the open-set action recognition (OSAR) problem based on the information bottleneck (IB) theory, and propose to enlarge the instance-specific (IS) and class-specific (CS) information contained in the feature for better performance. To this end, a novel Prototypical Similarity Learning (PSL) framework is proposed to keep the instance variance within the same class to retain more IS information. Besides, we notice that unknown samples sharing similar appearances to known samples are easily misclassified as known classes. To alleviate this issue, video shuffling is further introduced in our PSL to learn distinct temporal information between original and shuffled samples, which we find enlarges the CS information. Extensive experiments demonstrate that the proposed PSL can significantly boost both the open-set and closed-set performance and achieves state-of-the-art results on multiple benchmarks. Code is available at https://github.com/Jun-CEN/PSL. + +# 1. Introduction + +Deep learning methods for video action recognition have developed very fast and achieved remarkable performance in recent years [1-4]. However, these methods operate under the closed-set condition, i.e., to classify all videos into + +![](images/03d36989466045e3d8b921c122d254eb2975ce4690521f3eaddc27271b9942d3.jpg) + +![](images/17b1e0c3aad89e3277e6caa4f1220ba460d5a5109ce78e7d063708458e4caa29.jpg) +(a) +Figure 1. (a) Richer semantic features brought by the pretraining can significantly improve the open-set performance. (b) Information in the feature is divided into IS and CS information. $s_4$ can be identified as OoD since it has distinct IS information (IS bars in different colors) with $s_1$ and $s_2$ , while $s_5$ has distinct CS information (CS bars in different colors) with all InD samples so it may be OoD. Our PSL aims to learn more IS and CS information (bars in longer lengths) than Cross-Entropy (C.E.). (c) Both enlarged IS and CS information boosts the open-set performance. (d) Our PSL achieves the best OSAR performance. + +![](images/0c0c86e899c2a7f275c2524163186a4ca0ffda8dfd7cf032038f70bdd3d1a457.jpg) +(b) + +![](images/28dd088508a878e682ff43ab36a64bbab2776531674a34cfe6338da35eb93cd2.jpg) + +one of the classes encountered during training. This closed-set condition is not practical in the real-world scenario, as videos whose classes are beyond the range of the training set will be misclassified as one of the known classes. Therefore, open-set action recognition (OSAR) is proposed to require the network to correctly classify in-distribution (InD) samples and identify out-of-distribution (OoD) samples. InD and OoD classes refer to classes involved and not involved in the training set, respectively. + +Open-set video action recognition is systematically studied in the recent work [5], in which they transfer the existing methods for open-set image recognition into the video domain [6-9] as the baselines, and propose their own method to introduce deep evidential learning [10] to calculate the uncertainty and propose a contrastive evidential debiasing module to alleviate the appearance bias issue in the video domain. All of these methods tend to improve the OSAR performance by calculating a better uncertainty score, based on the feature representations extracted by the neural network (NN). However, the main purpose of training in these methods is still to classify InD samples, which determines the learned feature representations are merely sufficient for InD classification. We find that almost all methods have a significantly better open-set performance when the NN is pretrained with a large dataset (Fig. 1 (a)), so we argue that the diversity of feature representation is extremely important for the OSAR task. Therefore, we propose to boost the open-set ability from the feature representation perspective rather than finding a better uncertainty score. + +We first analyze the feature representation behavior in the open-set problem based on the information bottleneck (IB) theory [11, 12]. We divide the information of the feature into Instance-Specific (IS) and Class-Specific (CS) information. CS information is used for inter-class recognition, so it is similar for samples within the same class but different for samples from other classes. IS information is the special information of each sample within the same class, as two samples cannot be exactly the same even if they belong to the same class. Both CS and IS information are crucial for the open-set task, as illustrated in Fig. 1 (b), where $s_4$ and $s_5$ can be identified as OoD samples based on the IS and CS information, respectively. We find that the closed-set classification setting tends to eliminate IS information during training, and cannot fully extract the minimum sufficient CS information for the classification task, so we aim to enlarge IS and CS information in learned feature representations for better OSAR performance. + +To enlarge the IS information, we propose the Prototypical Similarity Learning (PSL) framework, in which the representation of an instance is encouraged to have less than 1 similarity with the corresponding prototype. In this way, we encourage the IS information to be retained and not eliminated. In addition, [5] finds that OoD videos can be easily classified as InD videos in a similar appearance. To alleviate this issue, we introduce the shuffled video into PSL and make it have less than 1 similarity with the original sample. As the shuffled video almost shares the same appearance information with the original one, we encourage the similarity to be less than 1 so that the network can extract the distinct temporal information among them. We find this technique actually enlarges the CS information in the feature representation. Fig. 1 (c) shows that enlarging the IS informa + +tion is helpful for the open-set performance, and more CS information can further benefit the open-set and closed-set performance. To summarize, our contributions include: + +- We provide a novel perspective to analyze the open-set recognition task based on the information bottleneck theory, and find that the classical closed-set cross-entropy tends to eliminate the IS information which is helpful to identify OoD samples. +- We propose to enlarge the IS and CS information for better OSAR performance. Specifically, PSL is designed to retain the IS information in the features, and we involve video shuffling in PSL to learn more CS information. +- Experiments on multiple datasets and backbones show our PSL's superiority over a large margin compared to other state-of-the-art counterparts, as shown in Fig. 1 (d). + +# 2. Related Work + +Action Recognition. Most recent approaches for action recognition are to exploit appearance and motion cues jointly and achieve remarkable success [1-3, 13-16]. Typically, two-stream networks [17-19] consist of two branches that explore spatial information and temporal dynamics, respectively. Some attempts [1, 20, 21] introduce additional temporal mining operations to overcome the limited temporal information extraction ability of 2D CNN. 3D CNN-based methods [2, 3, 22] inflated 2D kernels for joint spatiotemporal modeling. [23] proposes the prototype similarity learning which pushes the learned representation to the corresponding prototype as close as possible, while our PSL keeps the differences among the same class. + +Open-set Action Recognition. The related work of OSAR is limited [5, 24-26]. Recently, [5] systematically studies the OSAR problem and transfers several open-set image recognition methods to the video domain, including SoftMax [6], MC Dropout [7], OpenMax [8], and RPL [27]. In the benchmark of [5], the only two methods designed specifically for the video domain are BNN SVI [24] and their proposed DEAR. BNN SVI is a Bayesian NN application in the OSAR, while DEAR adopts the deep evidential learning [10] to calculate the uncertainty, and utilizes two modules to alleviate the over-confidence prediction and appearance bias problem, respectively. Existing methods pursue better uncertainty scores, while the objective of our PSL is to learn more diverse feature representations for better open-set distinguishability. + +Information Bottleneck Theory. Based on the IB theory [11, 28], the NN intends to extract minimum sufficient information of the inputs for the current task. More recent [12, 29, 30] adopt the IB theory on unsupervised contrastive learning to analyze the representation learning behavior under the corresponding tasks. In this work, we provide a new view to analyze the OSAR problem based on the IB theory. + +# 3. Information Analysis in OSAR + +# 3.1. Prototypical Learning + +Let $f$ be the encoder to extract the information for an input video sample $x$ and output the feature representation $z = f(x), z \in \mathbb{R}^d$ . We first define a prototypical learning (PL) loss [31], which is a general version of the cross-entropy (C.E.) loss: + +$$ +\mathcal {L} _ {P L} = - \log \frac {\exp \left(\frac {z ^ {T} k _ {i}}{\tau}\right)}{\exp \left(\frac {z ^ {T} k _ {i}}{\tau}\right) + \sum_ {n \in K ^ {-}} \exp \left(\frac {z ^ {T} n}{\tau}\right)}, \tag {1} +$$ + +where $i$ is the ground truth label of $x$ , $k_{i} \in \mathbb{R}^{d}$ is the prototype for class $i$ , $\tau$ is a temperature parameter, $K_{i}^{-} = \{k_{j} | j \in \{1, 2, \dots, N\}, j \neq i\}$ is the negative prototype set, and $N$ is the number of InD classes. Note that $z$ and $k_{i}$ are normalized by L2 norm, so that $z^{T} k_{i}$ is the cosine similarity. If we regard prototypes as the row vector of the linear classifier $W \in \mathbb{R}^{N \times d}$ , and do not normalize $z$ and $k$ as well as remove $\tau$ , $\mathcal{L}_{PL}$ will degenerate to the C.E. loss. We introduce the $\mathcal{L}_{PL}$ so that we can directly manipulate the feature representation $z$ . + +# 3.2. Information Analysis of OSAR + +Let $x_{InD}, z_{InD}$ , and $Y$ be the random variables of InD sample, extracted representation of InD sample, and the task to predict the label of $x_{InD}$ , where $z_{InD} = f(x_{InD})$ . Given the joint distribution of $p(x_{InD}, Y)$ , the relevant information between $x_{InD}$ and $Y$ is defined as $I(x_{InD}, Y)$ where $I$ denotes the mutual information [28]. The learned representation $z_{InD}$ satisfies: + +$$ +I \left(x _ {I n D}; z _ {I n D}\right) = \underbrace {I \left(x _ {I n D} ; z _ {I n D} \mid Y\right)} _ {I S} + \underbrace {I \left(z _ {I n D} ; Y\right)} _ {C S}, \tag {2} +$$ + +in which $I(x_{\text{InD}}; z_{\text{InD}}|Y)$ and $I(z_{\text{InD}}; Y)$ denote the Instance-Specific (IS) and Class-Specific (CS) information respectively. In Fig. 2, IS information is blue and orange areas, and CS information is yellow and green areas. CS information is for the closed-set label prediction task $Y$ , while IS information is the special information of each sample that is not related to $Y$ . + +To analyze the information about OSAR, we let $T$ be a random variable that represents the task to distinguish OoD samples from InD samples, then we divide the information contained in $z_{InD}$ about $T$ into two parts [12]: + +$$ +I \left(z _ {I n D}; T\right) = \underbrace {I \left(z _ {I n D} \mid Y ; T\right)} _ {I S \text {a b o u t} T} + \underbrace {I \left(z _ {I n D} ; Y ; T\right)} _ {C S \text {a b o u t} T}, \tag {3} +$$ + +where $I(z_{\text{InD}} | Y; T)$ and $I(z_{\text{InD}}; Y; T)$ are the information about the OoD detection task $T$ in IS and CS information (orange and green areas in Fig. 2 respectively). We can see that larger IS and CS information are helpful for OSAR. + +In this paper, we aim to enlarge the information about $T$ contained in CS and IS information for better OSAR performance, as illustrated in Fig. 1 (b) and the enlarged green + +![](images/bb0db8cf4d069bfd820ab3b4e5e877f9e776a22972a4465c38a1257769f6f55a.jpg) +C.E. +Figure 2. The neural network (NN) can only extract limited representations $z_{InD}$ of the InD sample $x_{InD}$ for the current task $Y$ (predict the closed-set label), which is not diverse enough for the task $T$ (distinguish OoD samples), as green and orange areas are small in (a). In our PSL, we encourage the NN to learn a more diverse representation so that more IS and CS information about $T$ are contained. + +![](images/dcd0b41555d4d56953edbbc6a3bb1569dcf8919af70f0f0659eec9f03b39caee.jpg) +PSL (ours) + +$\bigcirc \bigcirc z_{InD} = f(x_{InD})$ , representation of $x_{InD}$ from NN +$\mathbb{Z}_{InD}^{min}$ , minimum sufficient information of $x_{InD}$ about $Y$ +$\bigcirc$ $I(z_{InD};Y;T)$ , CS information in $z_{InD}$ about $T$ +$I(z_{InD}|Y;T)$ , IS information in $z_{InD}$ about $T$ +Enlarged information that $z_{\text{InD}}$ contains using our PSL + +and orange areas in Fig. 2. We first analyze the CS and IS information behaviors under the classical C.E. loss, and find that CS information is encouraged to be maximized but IS information tends to be eliminated in Sec. 3.3. Then we explain this conclusion from the IB theory view in Sec. 3.4. + +# 3.3. CS and IS Information Behavior under C.E. + +CS information is for closed-set classification task $Y$ , so it is similar for the same class sample, but distinct for the different class sample $(s_1, s_2 / s_3$ in Fig. 1). In contrast, IS information is not related to $Y$ and it is distinct for samples in the same class $(s_1, s_2$ in Fig. 1). Therefore, we have the following proposition which describe the relation between CS/IS information and feature representation similarity. + +Proposition 1 For two feature representations of samples in the same class, more CS information means these two feature representations are more similar, and more IS information decreases their feature similarity. + +CS information is for the closed-set label prediction task $Y$ , which is fully supervised by C.E. loss, so it is maximized during training. In contrast, Eq. 1 shows that C.E. encourages representations of the same class to be exactly same with the corresponding prototype, and such high similarity eliminates the IS information according to Proposition 1. Therefore, C.E. loss tends to maximize the CS information and eliminate the IS information in the feature representation. We analyze this conclusion based on Information Bottleneck (IB) theory in next Sec. 3.4. + +# 3.4. IB Theory Analysis for CS and IS Information + +Applying the Data Processing Inequality [32] to the Markov chain $Y \to x_{inD} \to z_{InD}$ , we have + +$$ +I \left(z _ {I n D}; Y\right) \leq I \left(x _ {I n D}; Y\right). \tag {4} +$$ + +It means that the compressed representation $z_{InD}$ cannot contain more information of $Y$ compared to the original data $x_{InD}$ . + +According to the IB theory [11, 28], the NN is to find the optimal solution of $z_{\text{InD}}$ with minimizing the following Lagrange: + +$$ +\mathcal {L} \left[ p \left(z _ {I n D} \mid x _ {I n D}\right) \right] = I \left(z _ {I n D}; x _ {I n D}\right) - \beta I \left(z _ {I n D}; Y\right), \tag {5} +$$ + +where $\beta$ is the Lagrange multiplier attached to the constrained meaningful condition. Eq. 5 demonstrates the NN is solving a trade-off problem, as the first term tends to keep the information of $x_{InD}$ as less as possible while the second term tends to maximize the information of $Y$ . + +Inspired by [12, 33], the sufficient and minimum sufficient representation of $x_{\text{InD}}$ about $Y$ can be defined as: + +Definition 1 (Sufficient Representation) A feature representation $z_{InD}^{suf}$ of $x_{InD}$ is sufficient for $Y$ if and only if $I(z_{InD}^{suf};Y) = I(x_{InD};Y)$ . + +Definition 2 (Minimum Sufficient Representation) A sufficient representation $z_{InD}^{min}$ of $x_{InD}$ is minimum if and only if $I(z_{InD}^{min}; x_{InD}) \leq I(z_{InD}^{suf}; x_{InD}), \forall z_{InD}^{suf}$ that is sufficient for $Y$ . + +CS Information Maximization. The goal of training is to optimize $f$ so that $I(z_{InD};Y)$ (CS information) can approximate $I(x_{InD};Y)$ , which stays unchanged as data distribution is fixed during training. Therefore, CS information is supposed to be maximized to the upper bound $I(x_{InD};Y)$ because of Eq. 4. In this way, the closed-set classification task pushes the NN to learn the sufficient representation $z_{InD}^{suf}$ according to definition 1 [30]. + +IS Information Elimination. When $z_{InD}$ is close to the sufficient representation $z_{InD}^{suf}$ , the second term in Eq. 5 will be the fix value $I(x_{InD};Y)$ based on the definition 1. So the key to minimize Eq. 5 is to minimize the first term $I(z_{InD}^{suf};x_{InD})$ . Based on the definition 2, the lower bound of $I(z_{InD}^{suf};x_{InD})$ is $I(z_{InD}^{min};x_{InD})$ , so we can conclude that the learned representation is supposed to be the minimum sufficient representation $z_{InD}^{min}$ [12]. We substitute $I(z_{InD}^{suf};x_{InD})$ and $I(z_{InD}^{min};x_{InD})$ in definition 2 with Eq. 2 and we have + +$$ +\begin{array}{l} I \left(x _ {I n D}; z _ {I n D} ^ {\min } \mid Y\right) + I \left(z _ {I n D} ^ {\min }; Y\right) \\ \leq I \left(x _ {I n D}; z _ {I n D} ^ {s u f} | Y\right) + I \left(z _ {I n D} ^ {s u f}; Y\right). \tag {6} \\ \end{array} +$$ + +As both $z_{InD}^{min}$ and $z_{InD}^{suf}$ are sufficient, the second term of both sides in Eq. 6 is $I(x_{InD};Y)$ , so we have + +$$ +0 \leq I \left(x _ {I n D}; z _ {I n D} ^ {\text {m i n}} | Y\right) \leq I \left(x _ {I n D}; z _ {I n D} ^ {\text {s u f}} | Y\right). \tag {7} +$$ + +Therefore, the learned IS information in $z_{InD}^{min}$ is smaller than any IS information in $z_{InD}^{suf}$ , which could be eliminated to 0 [12] (no blue and orange areas in $z_{InD}^{min}$ in Fig. 2). + +# 3.5. Enlarge CS and IS Information for OSAR + +Based on the analysis in Sec. 3.3 and Sec. 3.4, we show that C.E. tends to maximize the CS information and eliminate the IS information in the feature representation. Both larger IS and CS information are crucial for OSAR according to Eq. 3, but C.E. does not bring the optimal information. On the one hand, IS information is eliminated so we lose a part of information which is beneficial for the OSAR. On the other hand, the learned representation is not sufficient and does not contain enough CS information in practice due to the model capacity and data distribution shift between training and test sets, which can be supported by the fact that test accuracy cannot reach $100\%$ . Therefore, we propose our method to enlarge the CS and IS information for better OSAR performance in next Sec. 4. + +# 4. Methods + +# 4.1. Prototypical Similarity Learning + +According to Sec. 3.3, we notice that IS information is suppressed by the C.E. loss and a key reason is C.E. encourages feature representations of the same class to be exactly same. Therefore, we argue that the feature representation of the same class samples should have a similarity $s < 1$ . In other words, we aim to keep the intra-class variance which prevents intra-class collapse to retain IS information. Based on the classical PL loss Eq. 1, we develop prototypical similarity learning (PSL): + +$$ +\mathcal {L} _ {P S L} = - \log \frac {\exp \left(\frac {1 - \left| z ^ {T} k _ {i} - s \right|}{\tau}\right)}{\exp \left(\frac {1 - \left| z ^ {T} k _ {i} - s \right|}{\tau}\right) + \sum_ {n \in K _ {i} ^ {-}} \exp \left(\frac {z ^ {T} n}{\tau}\right)}, \tag {8} +$$ + +where $s$ and $\tau$ are fixed hyperparameters. In this way, we expect the prototype $k_{i}$ to act as the CS information for the InD class $i$ , which is used to predict the label, and the dissimilarity between the $z$ and $k_{i}$ represents the IS information. Traditional PL loss (or C.E. loss) encourages the features of samples in the same classes to be as tight as possible, while our PSL aims to keep the variance within the same class. + +However, we find Eq. 8 will converge to the trivial solution, where the $z$ converges to the training result of Eq. 1 and only $k_{i}$ shifts. To solve this problem, we introduce the similarity between different samples within a mini-batch into the denominator of Eq. 8. In this way, we directly constrain the relationship between sample features instead of only supervising the similarity between the sample feature and its prototype. We name the modified loss as PSL with contrastive terms (CT): + +![](images/e238f5a8b0f1d50fcf404fec8d8cd134070a55d98285c119b792335724f1fd16.jpg) +Figure 3. (a) C.E. encourages the sample feature $z$ to be exactly same with the corresponding prototype $k_{i}$ . (b) Our PSL encourages the similarity between $z$ and $k_{i}$ , features of shuffled sample $Q_{shuf}$ and other samples in the same class $Q_{sc}$ to have a similarity less than 1. + +![](images/a8b833f4658139937f81e0958abd4e88842883459f3e42de178ff1ebdf1b6d01.jpg) + +$$ +\begin{array}{l} \mathcal {L} _ {P S L} ^ {C T} = \\ \frac {\exp \left(\frac {1 - \left| z ^ {T} k _ {i} - s \right|}{\tau}\right)}{\exp \left(\frac {1 - \left| z ^ {T} k _ {i} - s \right|}{\tau}\right) + \sum_ {n \in Q _ {n}} \exp \left(\frac {z ^ {T} n}{\tau}\right) + \sum_ {p \in Q _ {s p}} \exp \left(\frac {\left| z ^ {T} p - s \right|}{\tau}\right)}, \end{array} \tag {9} +$$ + +where $Q_{n} = K_{i}^{-} \cup Q_{ns}$ . $Q_{ns}$ refers to the negative samples, i.e., samples in other classes, and $Q_{sp}$ refers to the soft positive samples which contains samples in the same class $Q_{sc}$ here. The reason we call soft positive samples is that we think samples in the same class share CS information but have distinct IS information. + +# 4.2. Video Shuffling for PSL + +PSL aims to keep IS information during training, and in this section we introduce how to enlarge CS information through video shuffling. The appearance bias is a significant problem in the OSAR. For instance, the OoD classes Smile and Chew are easily classified as InD classes ApplyEyeMakeup and ApplyLipstick, as the majority area of all these classes are occupied by a face, as shown in Fig. 7. The NN is confused by the extremely similar spatial information and neglects the minor different temporal information. This phenomenon encourages us to strengthen the temporal information extraction ability of the NN to distinguish classes with very similar appearances but different actions. We find that introducing a simple yet effective way, i.e., to regard the shuffled video $Q_{shuf}$ as the soft positive sample in Eq. 9, is extremely suitable and useful in our PSL framework. In this case, $Q_{sp} = Q_{sc} \cup Q_{shuf}$ . Shuffled video means shuffling the frames within a single video. As the appearance information of the shuffled video is almost the same as the original video, a smaller than 1 similarity forces the NN to learn the distinct temporal information between them. Unlike existing works which predict the sequence or the type of the shuffled video [34-37], we regard the shuffle video as a whole sample and directly compare its feature representation with the original video in our PSL. We find this + +technique can improve the closed-set accuracy which indicates more CS information is learned. We summarize the difference between our PSL and classical C.E. in Fig. 3. + +# 4.3. Uncertainty Score + +As our PSL aims to learn richer CS and IS information in the feature representation, we use the Mahalanobis distance to measure the uncertainty as it can be calculated from the feature representation perspective [38, 39]: + +$$ +u = \left(z - \mu_ {m}\right) ^ {T} \sum_ {m} ^ {- 1} \left(z - \mu_ {m}\right), \tag {10} +$$ + +where $\mu_{m}$ and $\sum_{m}$ denote the mean and covariance of the whole training set features, and $z$ is the test sample feature. + +# 5. Experiments + +Datasets. Following [5], we use UCF101 [40] as the InD dataset for training and closed-set evaluation, and use HMDB51 [41] and MiT-v2 [42] as OoD data for open-set evaluation. Different from [5] which does not clean the OoD data that may contains InD classes, we remove the overlapping classes between InD and OoD dataset during evaluation. See Appendix A for more details. + +Evaluation protocols. For closed-set performance, we evaluate like the traditional way to calculate the top-1 accuracy Acc. $(\%)$ . For open-set performance, we follow the classical open-set recognition protocol [6,43] to use the obtained uncertainty score Eq. 10 to calculate AUROC $(\%)$ , AUPR $(\%)$ and FPR95 $(\%)$ . + +Implementation details. For Kinetics400 (K400) [3] pretrained model, our implementation setting is the same with [5]. The base learning rate is 0.001 and step-wisely decayed every 20 epochs with total of 50 epochs. We argue that as K400 is extremely large, the K400 pretrained model may already have seen the OoD data used in inference, so + +
DatasetsMethodsw/o K400 Pretrainw/ K400 Pretrain
AUROC↑AUPR↑FPR95↓Acc.↑AUROC↑AUPR↑FPR95↓Acc.↑
UCF101 (InD)OpenMax [8]82.2854.5950.6973.9290.8973.1638.7795.32
MC Dropout [7]75.7541.2154.7873.6388.2367.6238.1295.06
BNN SVI [24]80.1053.4352.3371.5191.8179.6531.4394.71
HMDB51 (OoD)SoftMax [6]79.7252.1353.2273.9291.7577.6928.6095.03
RPL [27]79.6751.8556.4071.4690.5377.8637.0995.59
DEAR [5]80.0049.2353.2871.3384.1675.5489.4094.48
PSL(ours)86.4365.5441.6776.5394.0586.5523.1895.62
Δ(+4.15)(+10.95)(-9.02)(+2.61)(+2.24)(+6.90)(-5.42)(+0.03)
UCF101 (InD)OpenMax [8]84.4376.6947.7473.9293.3488.1428.9595.32
MC Dropout [7]75.6662.2051.5773.6388.7183.3639.4695.06
BNN SVI [24]79.4871.7352.5271.5191.8690.1236.2194.71
MiTv2 (OoD)SoftMax [6]80.5573.1750.4973.9291.9589.1632.0095.03
RPL [27]80.2172.0452.8371.4690.6488.7938.4395.59
DEAR [5]79.0067.1052.4471.3386.0487.3887.4094.48
PSL(ours)86.5379.9540.9976.5395.7594.9618.9695.62
Δ(+2.10)(+3.26)(-6.75)(+2.61)(+2.41)(+4.84)(-9.99)(+0.03)
+ +Table 1. Comparison with state-of-the-art methods on HMDB51 and MiTv2 (OoD) using TSM backbone. Acc. refers to closed-set accuracy. AUROC, AUPR and FPR95 are open-set metrics. Best results are in bold and second best results in italic. The gap between best and second best is in blue. DEAR and our methods contain video-specific operation. + +![](images/5bab0fc96c46516adc715a41287e2c6ef48b0c70a1e2b9851c0df9af2db516cb.jpg) + +![](images/fd098bc633ed9b6899e41054a025dfce13ebcd84dc862529d0ccf0febf54e951.jpg) + +![](images/81ef902486b45035e37814c29c935d9648187adbdc62c4b608c53a139b739bd4.jpg) +Figure 4. The uncertainty distribution of InD and OoD samples of (a) Softmax, (b) DEAR, (c) BNN SVI and (d) our PSL method. + +![](images/d45d442a2f6eb36ef94790a2cb2e0edc4d85e4107be2db50b973c8187b5af9f4.jpg) + +we conduct experiments from scratch (no ImageNet pretrained) to ensure that OoD data is absolutely unavailable during training. We use the LARS optimizer [44] and set the base learning rate and momentum as 0.6 and 0.9 with total of 400 epochs. The experiments are conducted on TSM [1], I3D [3] and SlowFast [2]. The batch size for all methods is 256. More details are in Appendix C. + +# 5.1. Evaluation Results + +Comparison with state-of-the-art. We report the results on HMDB51 (OoD) and MiT-v2 (OoD) in Table 1 using TSM backbone [1]. The evaluation results of other backbones including I3D and SlowFast are in the Appendix D. We can see that for w/ or w/o K400 pretrain, our PSL method has significantly better open-set and closed-set performance than all baselines. The uncertainty distribution + +![](images/e67db6fe4925db7807ee0237e27071e5990aa4d6b9b139f15db3e92dff832ceb.jpg) +(a) Cross-entropy +Figure 5. Feature representation visualization of cross-entropy and our PSL method. OoD samples are in black and InD samples are in other colors. In the red, blue and green circles, it is clear that OoD samples distribute at the edge of InD samples in our PSL, while greatly overlap with each other in the cross-entropy method. + +![](images/c30ffa7f6925d9f5f8ac531f6f0052a4a42e2842269bed4315ce86da26fdc896.jpg) +(b) PSL (ours) + +of InD and OoD samples are depicted in Fig. 4 for MiT-v2 (OoD) with K400 pretrained. Three baseline methods have a clear over confidence problem, i.e., the far left column is extremely high (red circles in Fig. 4), which means a large number of OoD samples have almost 0 uncertainty, while our method significantly alleviates this problem through the distinct representation of OoD samples, illustrated in Fig. 5. Besides, we can find that the open-set performance w/ K400 pretrain is higher than w/o pretrain for almost all methods in Table 1 and Fig. 1 (a), which can testify the importance of richer semantic representation for OSAR. + +Comparison with metric learning methods. Our method concentrates on the feature representation aspect for the OSAR problem, so we also implement several well-known metric learning methods and show the result in Table 3. The evaluation is conducted using TSM model and OoD dataset is HMDB51. We do not use video shuffling in our method for fair comparison. We can see that our method still achieves the best open-set performance. The most im + +
sQnsQscQshufInDOoDAUROC↑AUPR↑FPR95↓Acc.↑
MeanVarianceMeanVariance
LPLXXXX0.810.00150.630.002980.9552.7952.5172.36
LPSL✓XXX0.790.00160.620.002881.7954.1652.3372.33
LCTPSL✓✓XX0.710.00220.610.003682.6057.3650.0372.17
✓✓✓X0.710.00230.490.003583.4259.0551.3272.28
✓✓✓✓0.740.00160.630.002986.4365.5841.7577.19
+ +Table 2. Abaltion results of different components in ${\mathcal{L}}_{PSL}^{CT}$ . + +
AUROC↑AUPR↑FPR95↓Acc.↑
SoftMax80.9552.7952.5172.36
Triplet [45]81.0254.7553.8875.50
Normface [46]80.9954.9053.1973.34
Circle [47]78.7651.6555.2772.15
Arcface [48]81.2355.0353.6775.95
LSoftMax [49]80.8754.0152.2973.05
PSL(s = 0.8)83.4259.0551.3272.28
PSL(s = 0.6)82.7558.5752.2773.26
+ +Table 3. Comparison with different metric learning methods. + +important difference between our method and all other metric learning methods is that they aim to push the features of one class as tight as possible like C.E., while our method aims to keep the feature variance within a class to retain IS information. We calculate the mean similarity between the sample feature and the corresponding class center. The mean similarity ranges from 0.77 to 0.82 for other metric learning methods, while mean similarity is 0.71 ( $s = 0.8$ ) and 0.6 ( $s = 0.6$ ) for our PSL. So our method has looser feature distribution within a class, as shown in Fig. 5. + +# 5.2. Ablation Study + +Contrastive terms in $\mathcal{L}_{PSL}^{CT}$ for IS information. The intuition of PSL is to keep the intra-class variance to retain the IS information which is helpful for OSAR. We expect that the representation $z$ within a class has a similarity $s < 1$ with the prototype $k_{i}$ , so each sample can keep its own IS information. However, we find that the loss $\mathcal{L}_{PSL}$ may lead the network to find the trivial representation of samples $z$ which is similar to using loss $\mathcal{L}_{PL}$ , where only $k_{i}$ shifts and $z$ does not. We calculate the mean of similarity $\text{sim}(z, \bar{z}_i)$ , where $\bar{z}_i$ denotes the mean representation of all samples in the same class $i$ , and the mean of similarity with the corresponding prototype $\text{sim}(z, k_i)$ , as well as the feature variance in all dimensions. Fig. 6 (a) and (b) show that with the hyper-parameter $s$ decreasing, the $\text{sim}(z, k_i)$ decreases as expected by $\mathcal{L}_{PSL}$ (green curves), but the $\text{sim}(z, \bar{z}_i)$ and variance stay unchanged (blue curves), meaning that the representation of samples are still similar with using $\mathcal{L}_{PL}$ , and only the prototypes are pushed away by the sample representations. In contrast, with CT in $\mathcal{L}_{PSL}^{CT}$ , the $\text{sim}(z, \bar{z}_i)$ decreases and variance increases with $s$ decreases (red curves), indicating that CT is significantly effective to keep the intra-class variance. + +![](images/152feb23ba7db6e11c1e44b328e9b654ba6af9b1fc9cea71e5304d5cda87d0b7.jpg) +Figure 6. Mean similarity and variance analysis for CT terms. + +![](images/a68a850b4c3be0ff966023feda67a7cdb1a80476aae3a0b00c963c9811651299.jpg) + +To individually study the effectiveness of $Q_{ns}$ and $Q_{sc}$ in $\mathcal{L}_{PSL}^{CT}$ , we provide the ablation results in Table 2. For OoD samples, we calculate the similarity with the mean representation of its predicted class. Table 2 shows that using $Q_{ns}$ alone can significantly increase the intra-class variance for both InD and OoD samples, meaning the pushing effect of representations in other classes can implicitly help retain the IS information. On top of that, $Q_{sc}$ can further learn more IS information that is helpful to distinguish OoD samples, as the mean similarity of InD samples stay unchanged, but OoD samples are smaller which means OoD samples are far away from InD samples. + +Shuffled videos for CS information. Tab. 2 shows that $Q_{shuf}$ can improve both closed-set and open-set performance, which proves introducing shuffled videos in PSL can enlarge CS information. Smaller intra-class variance brought by $Q_{shuf}$ testify Proposition 1 that more CS information means more similar features within the same class. + +We draw the uncertainty of all classes in HMDB51, as shown in Fig. 7. Note that some classes in HMDB51 are actually InD as they appear in the UCF101, like the class 3 golf and 4 shoot bow in Fig. 7. We find that in C.E. some OoD classes have extremely low uncertainty, such as class 1 chew and 2 smile, because they are spatially similar to some InD classes like ApplyEyeMakeup and ApplyLipstick in Fig. 7 (a). Comparing (b) and (c) shows that our PSL can increase the average uncertainty of OoD classes (higher yellow points), and some OoD classes which are similar to InD classes like 1 and 2 have much higher uncertainty in our PSL method. After shuffled samples are involved, some InD classes whose uncertainty are increased in (c) like 3 and 4 have lower uncertainty in (d), and the uncertainty of some + +![](images/5d523ea15bdc4df1542393b1042976962d48fcf29a64ec257e5acdb06cd62b4c.jpg) + +![](images/50e5e0570a74c5f12ce4f25e711b674fa204afd5ab1082cd0b973b2191322216.jpg) + +![](images/5a0e013a93c29fc56bcd2808d6f44ed69014fda9edfb5b713789aa7f2625a09a.jpg) +Figure 7. (a) chew and smile are OoD samples from HMDB51, and ApplyEyeMakeup and ApplyLipstick are InD samples from UCF101. (b-d) Uncertainty distribution of each class in HMDB51. Class 1: chew, 2: smile, 3: golf, 4: shoot bow. Classes 1 and 2 are OoD while 3 and 4 are InD. + +![](images/cd41194f660b0ff9bf5afc5f4c7f967af85dbf81ba7b0d270e698f326dfa2b78.jpg) + +
s(Qshuf)s(Qsc)AUROC↑AUPR↑FPR95↓Acc.↑
0.785.2563.9148.3476.98
0.50.786.0364.3643.7076.53
0.383.8060.4248.7675.50
079.5450.5954.4372.59
0.80.886.4365.5841.7576.53
0.90.983.1257.0446.8473.31
1182.0453.8251.8272.89
+ +Table 4. Ablation study of similarity $s$ for ${Q}_{shuf}$ and ${Q}_{sc}$ . + +OoD classes sharing similar appearance with InD classes like class 1 is further improved. + +$Q_{sp}$ in Eq. 9 contains $Q_{shuf}$ and $Q_{sc}$ , so we analyze whether should we assign the same $s$ for the shuffled video $Q_{shuf}$ and other videos in the same class $Q_{sc}$ . Tab. 4 shows that the same $s$ have good enough performance. So we set the same $s$ for $Q_{shuf}$ and $Q_{sc}$ in the default setting to reduce the number of hyper-parameters. + +# 5.3. Discussion + +Both CS and IS information are useful. We provide the closed-set and open-set performance under different hyperparameter $s$ and feature dimension $d$ in Fig. 8. (a) shows that $s = 0.8$ has better open-set performance than $s = 1$ and has comparable closed-set accuracy, which illustrates that retaining the IS information which is eliminated by C.E. $(s = 1)$ is beneficial. When $s < 0.8$ , the NN cannot learn enough CS information, so both closed-set and open-set performance drops. Therefore, a proper mixture of CS and IS information is ideal. (b) shows that when $d$ grows from 4 to 16, more CS information is contained so that both closed-set and open-set performance improves. When $d$ grows from 16 to 128, the feature does not include more CS in + +![](images/9220a62ace11c85ad1b96ae8083dbc023ebf04f764c93f016fac405fc69f5080.jpg) +(a) + +![](images/139ec59e1462d2fd9a8807c51b43df4ac7c5063252ed767e06e4dc61e7ec8a9b.jpg) +(b) + +Figure 8. Ablation study of similarity $s$ and feature dimension $d$ . + +
EpochMeanVarianceAUROC↑Acc-Test.↑Acc-Train.↑
2000.5773.3e-375.0868.3999.85
4000.6023.1e-382.9273.26100
8000.6133.0e-382.5473.29100
+ +Table 5. Training process analysis when $s = {0.6}\mathrm{\;w}/\mathrm{o}{Q}_{shuf}$ . + +formation as closed-set accuracy is comparable. However, open-set performance keeps increasing which means more IS information is contained based on more feature dimensions. This interesting experiment shows that enough information for closed-set recognition is not enough for open-set recognition because IS information is not related to the closed-set task but useful for the open-set task. + +Feature variance and open-set performance analysis. Fig. 8 (a) shows that when features get looser ( $s = 1 - 0.8$ ), the open-set performance is improved, but if features get continually looser ( $s = 0.8 - 0.1$ ), the open-set performance drops. So there is no strict relation between the feature variance and open-set performance. One may argue that continual training can benefit the open-set performance [50], which is alongside with smaller feature variance [51]. We show that the benefit of continual training comes from better closed-set performance, not tighter features. Tab. 5 shows that when we train the model from 200 to 400 epochs, the closed-set accuracy is higher, and feature is tighter (larger mean similarity and smaller variance), and the open-set performance is better. But from epoch 400 to 800 we find the model is already overfitted to the training set, as the accuracy of test set remains unchanged. So although the features get tighter in the 800 epoch, both the closed-set and open-set performance remain same. + +# 6. Conclusion + +We analyze the OSAR problem from the information perspective, and show that cross-entropy tends to eliminate IS information and cannot fully learn CS information which are both useful for the open-set task. So we propose PSL to retain IS information and introduce shuffle videos into PSL to enlarge CS information. Comprehensive experiments demonstrate the effectiveness of our PSL and the importance of IS and CS information in the OSAR task. + +Acknowledgements This work is supported by Alibaba Group through Alibaba Research Intern Program. + +# References + +[1] Ji Lin, Chuang Gan, and Song Han. TSM: Temporal shift module for efficient video understanding. In ICCV, 2019. 1, 2, 6 +[2] Christoph Feichtenhofer, Haoqi Fan, Jitendra Malik, and Kaiming He. SlowFast networks for video recognition. In ICCV, 2019. 1, 2, 6 +[3] Joao Carreira and Andrew Zisserman. Quo vadis, action recognition? A new model and the kinetics dataset. In CVPR, 2017. 1, 2, 5, 6 +[4] Ceyuan Yang, Yinghao Xu, Jianping Shi, Bo Dai, and Bolei Zhou. Temporal pyramid network for action recognition. In CVPR, 2020. 1 +[5] Wentao Bao, Qi Yu, and Yu Kong. Evidential deep learning for open set action recognition. In ICCV, 2021. 2, 5, 6 +[6] Dan Hendrycks and Kevin Gimpel. 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(a) Richer semantic features brought by the pretraining can significantly improve the open-set performance. (b) Information in the feature is divided into IS and CS information. " + }, + { + "bbox": [ + 304, + 471, + 547, + 581 + ], + "type": "inline_equation", + "content": "s_4" + }, + { + "bbox": [ + 304, + 471, + 547, + 581 + ], + "type": "text", + "content": " can be identified as OoD since it has distinct IS information (IS bars in different colors) with " + }, + { + "bbox": [ + 304, + 471, + 547, + 581 + ], + "type": "inline_equation", + "content": "s_1" + }, + { + "bbox": [ + 304, + 471, + 547, + 581 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 471, + 547, + 581 + ], + "type": "inline_equation", + "content": "s_2" + }, + { + "bbox": [ + 304, + 471, + 547, + 581 + ], + "type": "text", + "content": ", while " + }, + { + "bbox": [ + 304, + 471, + 547, + 581 + ], + "type": "inline_equation", + "content": "s_5" + }, + { + "bbox": [ + 304, + 471, + 547, + 581 + ], + "type": "text", + "content": " has distinct CS information (CS bars in different colors) with all InD samples so it may be OoD. Our PSL aims to learn more IS and CS information (bars in longer lengths) than Cross-Entropy (C.E.). (c) Both enlarged IS and CS information boosts the open-set performance. (d) Our PSL achieves the best OSAR performance." + } + ] + } + ], + "index": 19, + "angle": 0, + "type": "image_caption" + } + ], + "index": 15 + }, + { + "type": "image", + "bbox": [ + 420, + 274, + 543, + 369 + ], + "blocks": [ + { + "bbox": [ + 420, + 274, + 543, + 369 + ], + "lines": [ + { + "bbox": [ + 420, + 274, + 543, + 369 + ], + "spans": [ + { + "bbox": [ + 420, + 274, + 543, + 369 + ], + "type": "image", + "image_path": "0c0c86e899c2a7f275c2524163186a4ca0ffda8dfd7cf032038f70bdd3d1a457.jpg" + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 484, + 369, + 494, + 376 + ], + "lines": [ + { + "bbox": [ + 484, + 369, + 494, + 376 + ], + "spans": [ + { + "bbox": [ + 484, + 369, + 494, + 376 + ], + "type": "text", + "content": "(b)" + } + ] + } + ], + "index": 17, + "angle": 0, + "type": "image_caption" + } + ], + "index": 16 + }, + { + "type": "image", + "bbox": [ + 410, + 376, + 542, + 469 + ], + "blocks": [ + { + "bbox": [ + 410, + 376, + 542, + 469 + ], + "lines": [ + { + "bbox": [ + 410, + 376, + 542, + 469 + ], + "spans": [ + { + "bbox": [ + 410, + 376, + 542, + 469 + ], + "type": "image", + "image_path": "28dd088508a878e682ff43ab36a64bbab2776531674a34cfe6338da35eb93cd2.jpg" + } + ] + } + ], + "index": 18, + "angle": 0, + "type": "image_body" + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 605, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 547, + 715 + ], + "type": "text", + "content": "one of the classes encountered during training. This closed-set condition is not practical in the real-world scenario, as videos whose classes are beyond the range of the training set will be misclassified as one of the known classes. Therefore, open-set action recognition (OSAR) is proposed to require the network to correctly classify in-distribution (InD) samples and identify out-of-distribution (OoD) samples. InD and OoD classes refer to classes involved and not involved in the training set, respectively." + } + ] + } + ], + "index": 20 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 496, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 702, + 233, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 702, + 233, + 713 + ], + "spans": [ + { + "bbox": [ + 58, + 702, + 233, + 713 + ], + "type": "text", + "content": "*Work done as an intern at Alibaba DAMO Academy." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 294, + 748, + 317, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 758 + ], + "type": "text", + "content": "15295" + } + ] + } + ], + "index": 22 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 289, + 312 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 289, + 312 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 289, + 312 + ], + "type": "text", + "content": "Open-set video action recognition is systematically studied in the recent work [5], in which they transfer the existing methods for open-set image recognition into the video domain [6-9] as the baselines, and propose their own method to introduce deep evidential learning [10] to calculate the uncertainty and propose a contrastive evidential debiasing module to alleviate the appearance bias issue in the video domain. All of these methods tend to improve the OSAR performance by calculating a better uncertainty score, based on the feature representations extracted by the neural network (NN). However, the main purpose of training in these methods is still to classify InD samples, which determines the learned feature representations are merely sufficient for InD classification. We find that almost all methods have a significantly better open-set performance when the NN is pretrained with a large dataset (Fig. 1 (a)), so we argue that the diversity of feature representation is extremely important for the OSAR task. Therefore, we propose to boost the open-set ability from the feature representation perspective rather than finding a better uncertainty score." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 315, + 289, + 532 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 315, + 289, + 532 + ], + "spans": [ + { + "bbox": [ + 46, + 315, + 289, + 532 + ], + "type": "text", + "content": "We first analyze the feature representation behavior in the open-set problem based on the information bottleneck (IB) theory [11, 12]. We divide the information of the feature into Instance-Specific (IS) and Class-Specific (CS) information. CS information is used for inter-class recognition, so it is similar for samples within the same class but different for samples from other classes. IS information is the special information of each sample within the same class, as two samples cannot be exactly the same even if they belong to the same class. Both CS and IS information are crucial for the open-set task, as illustrated in Fig. 1 (b), where " + }, + { + "bbox": [ + 46, + 315, + 289, + 532 + ], + "type": "inline_equation", + "content": "s_4" + }, + { + "bbox": [ + 46, + 315, + 289, + 532 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 315, + 289, + 532 + ], + "type": "inline_equation", + "content": "s_5" + }, + { + "bbox": [ + 46, + 315, + 289, + 532 + ], + "type": "text", + "content": " can be identified as OoD samples based on the IS and CS information, respectively. We find that the closed-set classification setting tends to eliminate IS information during training, and cannot fully extract the minimum sufficient CS information for the classification task, so we aim to enlarge IS and CS information in learned feature representations for better OSAR performance." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 534, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 534, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 534, + 289, + 715 + ], + "type": "text", + "content": "To enlarge the IS information, we propose the Prototypical Similarity Learning (PSL) framework, in which the representation of an instance is encouraged to have less than 1 similarity with the corresponding prototype. In this way, we encourage the IS information to be retained and not eliminated. In addition, [5] finds that OoD videos can be easily classified as InD videos in a similar appearance. To alleviate this issue, we introduce the shuffled video into PSL and make it have less than 1 similarity with the original sample. As the shuffled video almost shares the same appearance information with the original one, we encourage the similarity to be less than 1 so that the network can extract the distinct temporal information among them. We find this technique actually enlarges the CS information in the feature representation. Fig. 1 (c) shows that enlarging the IS informa" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 304, + 72, + 547, + 108 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 108 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 108 + ], + "type": "text", + "content": "tion is helpful for the open-set performance, and more CS information can further benefit the open-set and closed-set performance. To summarize, our contributions include:" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 306, + 108, + 547, + 252 + ], + "type": "list", + "angle": 0, + "index": 7, + "blocks": [ + { + "bbox": [ + 306, + 108, + 547, + 168 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 108, + 547, + 168 + ], + "spans": [ + { + "bbox": [ + 306, + 108, + 547, + 168 + ], + "type": "text", + "content": "- We provide a novel perspective to analyze the open-set recognition task based on the information bottleneck theory, and find that the classical closed-set cross-entropy tends to eliminate the IS information which is helpful to identify OoD samples." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 306, + 168, + 545, + 215 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 168, + 545, + 215 + ], + "spans": [ + { + "bbox": [ + 306, + 168, + 545, + 215 + ], + "type": "text", + "content": "- We propose to enlarge the IS and CS information for better OSAR performance. Specifically, PSL is designed to retain the IS information in the features, and we involve video shuffling in PSL to learn more CS information." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 306, + 216, + 545, + 252 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 216, + 545, + 252 + ], + "spans": [ + { + "bbox": [ + 306, + 216, + 545, + 252 + ], + "type": "text", + "content": "- Experiments on multiple datasets and backbones show our PSL's superiority over a large margin compared to other state-of-the-art counterparts, as shown in Fig. 1 (d)." + } + ] + } + ], + "index": 6 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 306, + 262, + 392, + 275 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 262, + 392, + 275 + ], + "spans": [ + { + "bbox": [ + 306, + 262, + 392, + 275 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 282, + 547, + 437 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 282, + 547, + 437 + ], + "spans": [ + { + "bbox": [ + 304, + 282, + 547, + 437 + ], + "type": "text", + "content": "Action Recognition. Most recent approaches for action recognition are to exploit appearance and motion cues jointly and achieve remarkable success [1-3, 13-16]. Typically, two-stream networks [17-19] consist of two branches that explore spatial information and temporal dynamics, respectively. Some attempts [1, 20, 21] introduce additional temporal mining operations to overcome the limited temporal information extraction ability of 2D CNN. 3D CNN-based methods [2, 3, 22] inflated 2D kernels for joint spatiotemporal modeling. [23] proposes the prototype similarity learning which pushes the learned representation to the corresponding prototype as close as possible, while our PSL keeps the differences among the same class." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 438, + 547, + 617 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 438, + 547, + 617 + ], + "spans": [ + { + "bbox": [ + 304, + 438, + 547, + 617 + ], + "type": "text", + "content": "Open-set Action Recognition. The related work of OSAR is limited [5, 24-26]. Recently, [5] systematically studies the OSAR problem and transfers several open-set image recognition methods to the video domain, including SoftMax [6], MC Dropout [7], OpenMax [8], and RPL [27]. In the benchmark of [5], the only two methods designed specifically for the video domain are BNN SVI [24] and their proposed DEAR. BNN SVI is a Bayesian NN application in the OSAR, while DEAR adopts the deep evidential learning [10] to calculate the uncertainty, and utilizes two modules to alleviate the over-confidence prediction and appearance bias problem, respectively. Existing methods pursue better uncertainty scores, while the objective of our PSL is to learn more diverse feature representations for better open-set distinguishability." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "type": "text", + "content": "Information Bottleneck Theory. Based on the IB theory [11, 28], the NN intends to extract minimum sufficient information of the inputs for the current task. More recent [12, 29, 30] adopt the IB theory on unsupervised contrastive learning to analyze the representation learning behavior under the corresponding tasks. In this work, we provide a new view to analyze the OSAR problem based on the IB theory." + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "15296" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 71, + 220, + 85 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 71, + 220, + 85 + ], + "spans": [ + { + "bbox": [ + 47, + 71, + 220, + 85 + ], + "type": "text", + "content": "3. Information Analysis in OSAR" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 91, + 174, + 104 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 91, + 174, + 104 + ], + "spans": [ + { + "bbox": [ + 47, + 91, + 174, + 104 + ], + "type": "text", + "content": "3.1. Prototypical Learning" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 109, + 287, + 169 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 109, + 287, + 169 + ], + "spans": [ + { + "bbox": [ + 46, + 109, + 287, + 169 + ], + "type": "text", + "content": "Let " + }, + { + "bbox": [ + 46, + 109, + 287, + 169 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 46, + 109, + 287, + 169 + ], + "type": "text", + "content": " be the encoder to extract the information for an input video sample " + }, + { + "bbox": [ + 46, + 109, + 287, + 169 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 46, + 109, + 287, + 169 + ], + "type": "text", + "content": " and output the feature representation " + }, + { + "bbox": [ + 46, + 109, + 287, + 169 + ], + "type": "inline_equation", + "content": "z = f(x), z \\in \\mathbb{R}^d" + }, + { + "bbox": [ + 46, + 109, + 287, + 169 + ], + "type": "text", + "content": ". We first define a prototypical learning (PL) loss [31], which is a general version of the cross-entropy (C.E.) loss:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 74, + 174, + 287, + 213 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 74, + 174, + 287, + 213 + ], + "spans": [ + { + "bbox": [ + 74, + 174, + 287, + 213 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {P L} = - \\log \\frac {\\exp \\left(\\frac {z ^ {T} k _ {i}}{\\tau}\\right)}{\\exp \\left(\\frac {z ^ {T} k _ {i}}{\\tau}\\right) + \\sum_ {n \\in K ^ {-}} \\exp \\left(\\frac {z ^ {T} n}{\\tau}\\right)}, \\tag {1}", + "image_path": "97d7a0678ab988264156173fcab3a260ac7f2d2e75b643367ba1ed4683864c3e.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 213, + 289, + 332 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 213, + 289, + 332 + ], + "spans": [ + { + "bbox": [ + 46, + 213, + 289, + 332 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 213, + 289, + 332 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 213, + 289, + 332 + ], + "type": "text", + "content": " is the ground truth label of " + }, + { + "bbox": [ + 46, + 213, + 289, + 332 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 46, + 213, + 289, + 332 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 213, + 289, + 332 + ], + "type": "inline_equation", + "content": "k_{i} \\in \\mathbb{R}^{d}" + }, + { + "bbox": [ + 46, + 213, + 289, + 332 + ], + "type": "text", + "content": " is the prototype for class " + }, + { + "bbox": [ + 46, + 213, + 289, + 332 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 213, + 289, + 332 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 213, + 289, + 332 + ], + "type": "inline_equation", + "content": "\\tau" + }, + { + "bbox": [ + 46, + 213, + 289, + 332 + ], + "type": "text", + "content": " is a temperature parameter, " + }, + { + "bbox": [ + 46, + 213, + 289, + 332 + ], + "type": "inline_equation", + "content": "K_{i}^{-} = \\{k_{j} | j \\in \\{1, 2, \\dots, N\\}, j \\neq i\\}" + }, + { + "bbox": [ + 46, + 213, + 289, + 332 + ], + "type": "text", + "content": " is the negative prototype set, and " + }, + { + "bbox": [ + 46, + 213, + 289, + 332 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 213, + 289, + 332 + ], + "type": "text", + "content": " is the number of InD classes. Note that " + }, + { + "bbox": [ + 46, + 213, + 289, + 332 + ], + "type": "inline_equation", + "content": "z" + }, + { + "bbox": [ + 46, + 213, + 289, + 332 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 213, + 289, + 332 + ], + "type": "inline_equation", + "content": "k_{i}" + }, + { + "bbox": [ + 46, + 213, + 289, + 332 + ], + "type": "text", + "content": " are normalized by L2 norm, so that " + }, + { + "bbox": [ + 46, + 213, + 289, + 332 + ], + "type": "inline_equation", + "content": "z^{T} k_{i}" + }, + { + "bbox": [ + 46, + 213, + 289, + 332 + ], + "type": "text", + "content": " is the cosine similarity. If we regard prototypes as the row vector of the linear classifier " + }, + { + "bbox": [ + 46, + 213, + 289, + 332 + ], + "type": "inline_equation", + "content": "W \\in \\mathbb{R}^{N \\times d}" + }, + { + "bbox": [ + 46, + 213, + 289, + 332 + ], + "type": "text", + "content": ", and do not normalize " + }, + { + "bbox": [ + 46, + 213, + 289, + 332 + ], + "type": "inline_equation", + "content": "z" + }, + { + "bbox": [ + 46, + 213, + 289, + 332 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 213, + 289, + 332 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 213, + 289, + 332 + ], + "type": "text", + "content": " as well as remove " + }, + { + "bbox": [ + 46, + 213, + 289, + 332 + ], + "type": "inline_equation", + "content": "\\tau" + }, + { + "bbox": [ + 46, + 213, + 289, + 332 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 213, + 289, + 332 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{PL}" + }, + { + "bbox": [ + 46, + 213, + 289, + 332 + ], + "type": "text", + "content": " will degenerate to the C.E. loss. We introduce the " + }, + { + "bbox": [ + 46, + 213, + 289, + 332 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{PL}" + }, + { + "bbox": [ + 46, + 213, + 289, + 332 + ], + "type": "text", + "content": " so that we can directly manipulate the feature representation " + }, + { + "bbox": [ + 46, + 213, + 289, + 332 + ], + "type": "inline_equation", + "content": "z" + }, + { + "bbox": [ + 46, + 213, + 289, + 332 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 338, + 214, + 351 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 338, + 214, + 351 + ], + "spans": [ + { + "bbox": [ + 47, + 338, + 214, + 351 + ], + "type": "text", + "content": "3.2. Information Analysis of OSAR" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 357, + 287, + 441 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 357, + 287, + 441 + ], + "spans": [ + { + "bbox": [ + 46, + 357, + 287, + 441 + ], + "type": "text", + "content": "Let " + }, + { + "bbox": [ + 46, + 357, + 287, + 441 + ], + "type": "inline_equation", + "content": "x_{InD}, z_{InD}" + }, + { + "bbox": [ + 46, + 357, + 287, + 441 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 46, + 357, + 287, + 441 + ], + "type": "inline_equation", + "content": "Y" + }, + { + "bbox": [ + 46, + 357, + 287, + 441 + ], + "type": "text", + "content": " be the random variables of InD sample, extracted representation of InD sample, and the task to predict the label of " + }, + { + "bbox": [ + 46, + 357, + 287, + 441 + ], + "type": "inline_equation", + "content": "x_{InD}" + }, + { + "bbox": [ + 46, + 357, + 287, + 441 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 357, + 287, + 441 + ], + "type": "inline_equation", + "content": "z_{InD} = f(x_{InD})" + }, + { + "bbox": [ + 46, + 357, + 287, + 441 + ], + "type": "text", + "content": ". Given the joint distribution of " + }, + { + "bbox": [ + 46, + 357, + 287, + 441 + ], + "type": "inline_equation", + "content": "p(x_{InD}, Y)" + }, + { + "bbox": [ + 46, + 357, + 287, + 441 + ], + "type": "text", + "content": ", the relevant information between " + }, + { + "bbox": [ + 46, + 357, + 287, + 441 + ], + "type": "inline_equation", + "content": "x_{InD}" + }, + { + "bbox": [ + 46, + 357, + 287, + 441 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 357, + 287, + 441 + ], + "type": "inline_equation", + "content": "Y" + }, + { + "bbox": [ + 46, + 357, + 287, + 441 + ], + "type": "text", + "content": " is defined as " + }, + { + "bbox": [ + 46, + 357, + 287, + 441 + ], + "type": "inline_equation", + "content": "I(x_{InD}, Y)" + }, + { + "bbox": [ + 46, + 357, + 287, + 441 + ], + "type": "text", + "content": " where " + }, + { + "bbox": [ + 46, + 357, + 287, + 441 + ], + "type": "inline_equation", + "content": "I" + }, + { + "bbox": [ + 46, + 357, + 287, + 441 + ], + "type": "text", + "content": " denotes the mutual information [28]. The learned representation " + }, + { + "bbox": [ + 46, + 357, + 287, + 441 + ], + "type": "inline_equation", + "content": "z_{InD}" + }, + { + "bbox": [ + 46, + 357, + 287, + 441 + ], + "type": "text", + "content": " satisfies:" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 57, + 441, + 287, + 468 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 57, + 441, + 287, + 468 + ], + "spans": [ + { + "bbox": [ + 57, + 441, + 287, + 468 + ], + "type": "interline_equation", + "content": "I \\left(x _ {I n D}; z _ {I n D}\\right) = \\underbrace {I \\left(x _ {I n D} ; z _ {I n D} \\mid Y\\right)} _ {I S} + \\underbrace {I \\left(z _ {I n D} ; Y\\right)} _ {C S}, \\tag {2}", + "image_path": "e17c41038c0dd08fdf91cddf5ff7b3a30103ed1475321cdbe9f989271dd4b310.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 469, + 287, + 552 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 469, + 287, + 552 + ], + "spans": [ + { + "bbox": [ + 46, + 469, + 287, + 552 + ], + "type": "text", + "content": "in which " + }, + { + "bbox": [ + 46, + 469, + 287, + 552 + ], + "type": "inline_equation", + "content": "I(x_{\\text{InD}}; z_{\\text{InD}}|Y)" + }, + { + "bbox": [ + 46, + 469, + 287, + 552 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 469, + 287, + 552 + ], + "type": "inline_equation", + "content": "I(z_{\\text{InD}}; Y)" + }, + { + "bbox": [ + 46, + 469, + 287, + 552 + ], + "type": "text", + "content": " denote the Instance-Specific (IS) and Class-Specific (CS) information respectively. In Fig. 2, IS information is blue and orange areas, and CS information is yellow and green areas. CS information is for the closed-set label prediction task " + }, + { + "bbox": [ + 46, + 469, + 287, + 552 + ], + "type": "inline_equation", + "content": "Y" + }, + { + "bbox": [ + 46, + 469, + 287, + 552 + ], + "type": "text", + "content": ", while IS information is the special information of each sample that is not related to " + }, + { + "bbox": [ + 46, + 469, + 287, + 552 + ], + "type": "inline_equation", + "content": "Y" + }, + { + "bbox": [ + 46, + 469, + 287, + 552 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 552, + 287, + 601 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 552, + 287, + 601 + ], + "spans": [ + { + "bbox": [ + 46, + 552, + 287, + 601 + ], + "type": "text", + "content": "To analyze the information about OSAR, we let " + }, + { + "bbox": [ + 46, + 552, + 287, + 601 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 46, + 552, + 287, + 601 + ], + "type": "text", + "content": " be a random variable that represents the task to distinguish OoD samples from InD samples, then we divide the information contained in " + }, + { + "bbox": [ + 46, + 552, + 287, + 601 + ], + "type": "inline_equation", + "content": "z_{InD}" + }, + { + "bbox": [ + 46, + 552, + 287, + 601 + ], + "type": "text", + "content": " about " + }, + { + "bbox": [ + 46, + 552, + 287, + 601 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 46, + 552, + 287, + 601 + ], + "type": "text", + "content": " into two parts [12]:" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 71, + 601, + 287, + 629 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 71, + 601, + 287, + 629 + ], + "spans": [ + { + "bbox": [ + 71, + 601, + 287, + 629 + ], + "type": "interline_equation", + "content": "I \\left(z _ {I n D}; T\\right) = \\underbrace {I \\left(z _ {I n D} \\mid Y ; T\\right)} _ {I S \\text {a b o u t} T} + \\underbrace {I \\left(z _ {I n D} ; Y ; T\\right)} _ {C S \\text {a b o u t} T}, \\tag {3}", + "image_path": "7b7180ebda8bcd4d833dc9ae864095922fae07c03cc0c690f09fdf321cdf33fc.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 629, + 287, + 677 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 629, + 287, + 677 + ], + "spans": [ + { + "bbox": [ + 46, + 629, + 287, + 677 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 629, + 287, + 677 + ], + "type": "inline_equation", + "content": "I(z_{\\text{InD}} | Y; T)" + }, + { + "bbox": [ + 46, + 629, + 287, + 677 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 629, + 287, + 677 + ], + "type": "inline_equation", + "content": "I(z_{\\text{InD}}; Y; T)" + }, + { + "bbox": [ + 46, + 629, + 287, + 677 + ], + "type": "text", + "content": " are the information about the OoD detection task " + }, + { + "bbox": [ + 46, + 629, + 287, + 677 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 46, + 629, + 287, + 677 + ], + "type": "text", + "content": " in IS and CS information (orange and green areas in Fig. 2 respectively). We can see that larger IS and CS information are helpful for OSAR." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 46, + 677, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 287, + 714 + ], + "type": "text", + "content": "In this paper, we aim to enlarge the information about " + }, + { + "bbox": [ + 46, + 677, + 287, + 714 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 46, + 677, + 287, + 714 + ], + "type": "text", + "content": " contained in CS and IS information for better OSAR performance, as illustrated in Fig. 1 (b) and the enlarged green" + } + ] + } + ], + "index": 12 + }, + { + "type": "image", + "bbox": [ + 312, + 74, + 416, + 171 + ], + "blocks": [ + { + "bbox": [ + 312, + 74, + 416, + 171 + ], + "lines": [ + { + "bbox": [ + 312, + 74, + 416, + 171 + ], + "spans": [ + { + "bbox": [ + 312, + 74, + 416, + 171 + ], + "type": "image", + "image_path": "bb0db8cf4d069bfd820ab3b4e5e877f9e776a22972a4465c38a1257769f6f55a.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 356, + 172, + 374, + 182 + ], + "lines": [ + { + "bbox": [ + 356, + 172, + 374, + 182 + ], + "spans": [ + { + "bbox": [ + 356, + 172, + 374, + 182 + ], + "type": "text", + "content": "C.E." + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 304, + 253, + 547, + 330 + ], + "lines": [ + { + "bbox": [ + 304, + 253, + 547, + 330 + ], + "spans": [ + { + "bbox": [ + 304, + 253, + 547, + 330 + ], + "type": "text", + "content": "Figure 2. The neural network (NN) can only extract limited representations " + }, + { + "bbox": [ + 304, + 253, + 547, + 330 + ], + "type": "inline_equation", + "content": "z_{InD}" + }, + { + "bbox": [ + 304, + 253, + 547, + 330 + ], + "type": "text", + "content": " of the InD sample " + }, + { + "bbox": [ + 304, + 253, + 547, + 330 + ], + "type": "inline_equation", + "content": "x_{InD}" + }, + { + "bbox": [ + 304, + 253, + 547, + 330 + ], + "type": "text", + "content": " for the current task " + }, + { + "bbox": [ + 304, + 253, + 547, + 330 + ], + "type": "inline_equation", + "content": "Y" + }, + { + "bbox": [ + 304, + 253, + 547, + 330 + ], + "type": "text", + "content": " (predict the closed-set label), which is not diverse enough for the task " + }, + { + "bbox": [ + 304, + 253, + 547, + 330 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 304, + 253, + 547, + 330 + ], + "type": "text", + "content": " (distinguish OoD samples), as green and orange areas are small in (a). In our PSL, we encourage the NN to learn a more diverse representation so that more IS and CS information about " + }, + { + "bbox": [ + 304, + 253, + 547, + 330 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 304, + 253, + 547, + 330 + ], + "type": "text", + "content": " are contained." + } + ] + } + ], + "index": 23, + "angle": 0, + "type": "image_caption" + } + ], + "index": 13 + }, + { + "type": "image", + "bbox": [ + 427, + 75, + 536, + 171 + ], + "blocks": [ + { + "bbox": [ + 427, + 75, + 536, + 171 + ], + "lines": [ + { + "bbox": [ + 427, + 75, + 536, + 171 + ], + "spans": [ + { + "bbox": [ + 427, + 75, + 536, + 171 + ], + "type": "image", + "image_path": "dcd0b41555d4d56953edbbc6a3bb1569dcf8919af70f0f0659eec9f03b39caee.jpg" + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 468, + 172, + 510, + 182 + ], + "lines": [ + { + "bbox": [ + 468, + 172, + 510, + 182 + ], + "spans": [ + { + "bbox": [ + 468, + 172, + 510, + 182 + ], + "type": "text", + "content": "PSL (ours)" + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "image_caption" + } + ], + "index": 15 + }, + { + "bbox": [ + 310, + 182, + 535, + 251 + ], + "type": "list", + "angle": 0, + "index": 22, + "blocks": [ + { + "bbox": [ + 310, + 182, + 529, + 196 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 310, + 182, + 529, + 196 + ], + "spans": [ + { + "bbox": [ + 310, + 182, + 529, + 196 + ], + "type": "inline_equation", + "content": "\\bigcirc \\bigcirc z_{InD} = f(x_{InD})" + }, + { + "bbox": [ + 310, + 182, + 529, + 196 + ], + "type": "text", + "content": " , representation of " + }, + { + "bbox": [ + 310, + 182, + 529, + 196 + ], + "type": "inline_equation", + "content": "x_{InD}" + }, + { + "bbox": [ + 310, + 182, + 529, + 196 + ], + "type": "text", + "content": " from NN" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 310, + 196, + 535, + 210 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 310, + 196, + 535, + 210 + ], + "spans": [ + { + "bbox": [ + 310, + 196, + 535, + 210 + ], + "type": "inline_equation", + "content": "\\mathbb{Z}_{InD}^{min}" + }, + { + "bbox": [ + 310, + 196, + 535, + 210 + ], + "type": "text", + "content": ", minimum sufficient information of " + }, + { + "bbox": [ + 310, + 196, + 535, + 210 + ], + "type": "inline_equation", + "content": "x_{InD}" + }, + { + "bbox": [ + 310, + 196, + 535, + 210 + ], + "type": "text", + "content": " about " + }, + { + "bbox": [ + 310, + 196, + 535, + 210 + ], + "type": "inline_equation", + "content": "Y" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 311, + 210, + 500, + 223 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 311, + 210, + 500, + 223 + ], + "spans": [ + { + "bbox": [ + 311, + 210, + 500, + 223 + ], + "type": "inline_equation", + "content": "\\bigcirc" + }, + { + "bbox": [ + 311, + 210, + 500, + 223 + ], + "type": "inline_equation", + "content": "I(z_{InD};Y;T)" + }, + { + "bbox": [ + 311, + 210, + 500, + 223 + ], + "type": "text", + "content": " , CS information in " + }, + { + "bbox": [ + 311, + 210, + 500, + 223 + ], + "type": "inline_equation", + "content": "z_{InD}" + }, + { + "bbox": [ + 311, + 210, + 500, + 223 + ], + "type": "text", + "content": " about " + }, + { + "bbox": [ + 311, + 210, + 500, + 223 + ], + "type": "inline_equation", + "content": "T" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 311, + 224, + 495, + 236 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 311, + 224, + 495, + 236 + ], + "spans": [ + { + "bbox": [ + 311, + 224, + 495, + 236 + ], + "type": "inline_equation", + "content": "I(z_{InD}|Y;T)" + }, + { + "bbox": [ + 311, + 224, + 495, + 236 + ], + "type": "text", + "content": " , IS information in " + }, + { + "bbox": [ + 311, + 224, + 495, + 236 + ], + "type": "inline_equation", + "content": "z_{InD}" + }, + { + "bbox": [ + 311, + 224, + 495, + 236 + ], + "type": "text", + "content": " about " + }, + { + "bbox": [ + 311, + 224, + 495, + 236 + ], + "type": "inline_equation", + "content": "T" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 311, + 237, + 533, + 251 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 311, + 237, + 533, + 251 + ], + "spans": [ + { + "bbox": [ + 311, + 237, + 533, + 251 + ], + "type": "text", + "content": "Enlarged information that " + }, + { + "bbox": [ + 311, + 237, + 533, + 251 + ], + "type": "inline_equation", + "content": "z_{\\text{InD}}" + }, + { + "bbox": [ + 311, + 237, + 533, + 251 + ], + "type": "text", + "content": " contains using our PSL" + } + ] + } + ], + "index": 21 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 304, + 354, + 546, + 415 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 354, + 546, + 415 + ], + "spans": [ + { + "bbox": [ + 304, + 354, + 546, + 415 + ], + "type": "text", + "content": "and orange areas in Fig. 2. We first analyze the CS and IS information behaviors under the classical C.E. loss, and find that CS information is encouraged to be maximized but IS information tends to be eliminated in Sec. 3.3. Then we explain this conclusion from the IB theory view in Sec. 3.4." + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 305, + 426, + 534, + 439 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 426, + 534, + 439 + ], + "spans": [ + { + "bbox": [ + 305, + 426, + 534, + 439 + ], + "type": "text", + "content": "3.3. CS and IS Information Behavior under C.E." + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 304, + 447, + 545, + 531 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 447, + 545, + 531 + ], + "spans": [ + { + "bbox": [ + 304, + 447, + 545, + 531 + ], + "type": "text", + "content": "CS information is for closed-set classification task " + }, + { + "bbox": [ + 304, + 447, + 545, + 531 + ], + "type": "inline_equation", + "content": "Y" + }, + { + "bbox": [ + 304, + 447, + 545, + 531 + ], + "type": "text", + "content": ", so it is similar for the same class sample, but distinct for the different class sample " + }, + { + "bbox": [ + 304, + 447, + 545, + 531 + ], + "type": "inline_equation", + "content": "(s_1, s_2 / s_3" + }, + { + "bbox": [ + 304, + 447, + 545, + 531 + ], + "type": "text", + "content": " in Fig. 1). In contrast, IS information is not related to " + }, + { + "bbox": [ + 304, + 447, + 545, + 531 + ], + "type": "inline_equation", + "content": "Y" + }, + { + "bbox": [ + 304, + 447, + 545, + 531 + ], + "type": "text", + "content": " and it is distinct for samples in the same class " + }, + { + "bbox": [ + 304, + 447, + 545, + 531 + ], + "type": "inline_equation", + "content": "(s_1, s_2" + }, + { + "bbox": [ + 304, + 447, + 545, + 531 + ], + "type": "text", + "content": " in Fig. 1). Therefore, we have the following proposition which describe the relation between CS/IS information and feature representation similarity." + } + ] + } + ], + "index": 26 + }, + { + "bbox": [ + 304, + 539, + 545, + 588 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 539, + 545, + 588 + ], + "spans": [ + { + "bbox": [ + 304, + 539, + 545, + 588 + ], + "type": "text", + "content": "Proposition 1 For two feature representations of samples in the same class, more CS information means these two feature representations are more similar, and more IS information decreases their feature similarity." + } + ] + } + ], + "index": 27 + }, + { + "bbox": [ + 304, + 594, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 594, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 594, + 546, + 713 + ], + "type": "text", + "content": "CS information is for the closed-set label prediction task " + }, + { + "bbox": [ + 304, + 594, + 546, + 713 + ], + "type": "inline_equation", + "content": "Y" + }, + { + "bbox": [ + 304, + 594, + 546, + 713 + ], + "type": "text", + "content": ", which is fully supervised by C.E. loss, so it is maximized during training. In contrast, Eq. 1 shows that C.E. encourages representations of the same class to be exactly same with the corresponding prototype, and such high similarity eliminates the IS information according to Proposition 1. Therefore, C.E. loss tends to maximize the CS information and eliminate the IS information in the feature representation. We analyze this conclusion based on Information Bottleneck (IB) theory in next Sec. 3.4." + } + ] + } + ], + "index": 28 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "15297" + } + ] + } + ], + "index": 29 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 287, + 84 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 287, + 84 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 287, + 84 + ], + "type": "text", + "content": "3.4. IB Theory Analysis for CS and IS Information" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 90, + 287, + 114 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 90, + 287, + 114 + ], + "spans": [ + { + "bbox": [ + 47, + 90, + 287, + 114 + ], + "type": "text", + "content": "Applying the Data Processing Inequality [32] to the Markov chain " + }, + { + "bbox": [ + 47, + 90, + 287, + 114 + ], + "type": "inline_equation", + "content": "Y \\to x_{inD} \\to z_{InD}" + }, + { + "bbox": [ + 47, + 90, + 287, + 114 + ], + "type": "text", + "content": ", we have" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 110, + 115, + 287, + 129 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 110, + 115, + 287, + 129 + ], + "spans": [ + { + "bbox": [ + 110, + 115, + 287, + 129 + ], + "type": "interline_equation", + "content": "I \\left(z _ {I n D}; Y\\right) \\leq I \\left(x _ {I n D}; Y\\right). \\tag {4}", + "image_path": "92b1d1e132adc53ea23f94b9be38f05af434e225e591833fd43b5666754a99f6.jpg" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 130, + 287, + 166 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 130, + 287, + 166 + ], + "spans": [ + { + "bbox": [ + 46, + 130, + 287, + 166 + ], + "type": "text", + "content": "It means that the compressed representation " + }, + { + "bbox": [ + 46, + 130, + 287, + 166 + ], + "type": "inline_equation", + "content": "z_{InD}" + }, + { + "bbox": [ + 46, + 130, + 287, + 166 + ], + "type": "text", + "content": " cannot contain more information of " + }, + { + "bbox": [ + 46, + 130, + 287, + 166 + ], + "type": "inline_equation", + "content": "Y" + }, + { + "bbox": [ + 46, + 130, + 287, + 166 + ], + "type": "text", + "content": " compared to the original data " + }, + { + "bbox": [ + 46, + 130, + 287, + 166 + ], + "type": "inline_equation", + "content": "x_{InD}" + }, + { + "bbox": [ + 46, + 130, + 287, + 166 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 166, + 287, + 202 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 166, + 287, + 202 + ], + "spans": [ + { + "bbox": [ + 46, + 166, + 287, + 202 + ], + "type": "text", + "content": "According to the IB theory [11, 28], the NN is to find the optimal solution of " + }, + { + "bbox": [ + 46, + 166, + 287, + 202 + ], + "type": "inline_equation", + "content": "z_{\\text{InD}}" + }, + { + "bbox": [ + 46, + 166, + 287, + 202 + ], + "type": "text", + "content": " with minimizing the following Lagrange:" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 54, + 203, + 287, + 217 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 54, + 203, + 287, + 217 + ], + "spans": [ + { + "bbox": [ + 54, + 203, + 287, + 217 + ], + "type": "interline_equation", + "content": "\\mathcal {L} \\left[ p \\left(z _ {I n D} \\mid x _ {I n D}\\right) \\right] = I \\left(z _ {I n D}; x _ {I n D}\\right) - \\beta I \\left(z _ {I n D}; Y\\right), \\tag {5}", + "image_path": "ad1f2a6a2df2e6f350af6c4311accb3f97270ee03164319adcb27a77f87ba322.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 217, + 287, + 276 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 217, + 287, + 276 + ], + "spans": [ + { + "bbox": [ + 46, + 217, + 287, + 276 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 217, + 287, + 276 + ], + "type": "inline_equation", + "content": "\\beta" + }, + { + "bbox": [ + 46, + 217, + 287, + 276 + ], + "type": "text", + "content": " is the Lagrange multiplier attached to the constrained meaningful condition. Eq. 5 demonstrates the NN is solving a trade-off problem, as the first term tends to keep the information of " + }, + { + "bbox": [ + 46, + 217, + 287, + 276 + ], + "type": "inline_equation", + "content": "x_{InD}" + }, + { + "bbox": [ + 46, + 217, + 287, + 276 + ], + "type": "text", + "content": " as less as possible while the second term tends to maximize the information of " + }, + { + "bbox": [ + 46, + 217, + 287, + 276 + ], + "type": "inline_equation", + "content": "Y" + }, + { + "bbox": [ + 46, + 217, + 287, + 276 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 277, + 287, + 302 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 277, + 287, + 302 + ], + "spans": [ + { + "bbox": [ + 46, + 277, + 287, + 302 + ], + "type": "text", + "content": "Inspired by [12, 33], the sufficient and minimum sufficient representation of " + }, + { + "bbox": [ + 46, + 277, + 287, + 302 + ], + "type": "inline_equation", + "content": "x_{\\text{InD}}" + }, + { + "bbox": [ + 46, + 277, + 287, + 302 + ], + "type": "text", + "content": " about " + }, + { + "bbox": [ + 46, + 277, + 287, + 302 + ], + "type": "inline_equation", + "content": "Y" + }, + { + "bbox": [ + 46, + 277, + 287, + 302 + ], + "type": "text", + "content": " can be defined as:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 308, + 288, + 346 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 308, + 288, + 346 + ], + "spans": [ + { + "bbox": [ + 47, + 308, + 288, + 346 + ], + "type": "text", + "content": "Definition 1 (Sufficient Representation) A feature representation " + }, + { + "bbox": [ + 47, + 308, + 288, + 346 + ], + "type": "inline_equation", + "content": "z_{InD}^{suf}" + }, + { + "bbox": [ + 47, + 308, + 288, + 346 + ], + "type": "text", + "content": " of " + }, + { + "bbox": [ + 47, + 308, + 288, + 346 + ], + "type": "inline_equation", + "content": "x_{InD}" + }, + { + "bbox": [ + 47, + 308, + 288, + 346 + ], + "type": "text", + "content": " is sufficient for " + }, + { + "bbox": [ + 47, + 308, + 288, + 346 + ], + "type": "inline_equation", + "content": "Y" + }, + { + "bbox": [ + 47, + 308, + 288, + 346 + ], + "type": "text", + "content": " if and only if " + }, + { + "bbox": [ + 47, + 308, + 288, + 346 + ], + "type": "inline_equation", + "content": "I(z_{InD}^{suf};Y) = I(x_{InD};Y)" + }, + { + "bbox": [ + 47, + 308, + 288, + 346 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 352, + 289, + 403 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 352, + 289, + 403 + ], + "spans": [ + { + "bbox": [ + 46, + 352, + 289, + 403 + ], + "type": "text", + "content": "Definition 2 (Minimum Sufficient Representation) A sufficient representation " + }, + { + "bbox": [ + 46, + 352, + 289, + 403 + ], + "type": "inline_equation", + "content": "z_{InD}^{min}" + }, + { + "bbox": [ + 46, + 352, + 289, + 403 + ], + "type": "text", + "content": " of " + }, + { + "bbox": [ + 46, + 352, + 289, + 403 + ], + "type": "inline_equation", + "content": "x_{InD}" + }, + { + "bbox": [ + 46, + 352, + 289, + 403 + ], + "type": "text", + "content": " is minimum if and only if " + }, + { + "bbox": [ + 46, + 352, + 289, + 403 + ], + "type": "inline_equation", + "content": "I(z_{InD}^{min}; x_{InD}) \\leq I(z_{InD}^{suf}; x_{InD}), \\forall z_{InD}^{suf}" + }, + { + "bbox": [ + 46, + 352, + 289, + 403 + ], + "type": "text", + "content": " that is sufficient for " + }, + { + "bbox": [ + 46, + 352, + 289, + 403 + ], + "type": "inline_equation", + "content": "Y" + }, + { + "bbox": [ + 46, + 352, + 289, + 403 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 409, + 287, + 506 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 409, + 287, + 506 + ], + "spans": [ + { + "bbox": [ + 46, + 409, + 287, + 506 + ], + "type": "text", + "content": "CS Information Maximization. The goal of training is to optimize " + }, + { + "bbox": [ + 46, + 409, + 287, + 506 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 46, + 409, + 287, + 506 + ], + "type": "text", + "content": " so that " + }, + { + "bbox": [ + 46, + 409, + 287, + 506 + ], + "type": "inline_equation", + "content": "I(z_{InD};Y)" + }, + { + "bbox": [ + 46, + 409, + 287, + 506 + ], + "type": "text", + "content": " (CS information) can approximate " + }, + { + "bbox": [ + 46, + 409, + 287, + 506 + ], + "type": "inline_equation", + "content": "I(x_{InD};Y)" + }, + { + "bbox": [ + 46, + 409, + 287, + 506 + ], + "type": "text", + "content": ", which stays unchanged as data distribution is fixed during training. Therefore, CS information is supposed to be maximized to the upper bound " + }, + { + "bbox": [ + 46, + 409, + 287, + 506 + ], + "type": "inline_equation", + "content": "I(x_{InD};Y)" + }, + { + "bbox": [ + 46, + 409, + 287, + 506 + ], + "type": "text", + "content": " because of Eq. 4. In this way, the closed-set classification task pushes the NN to learn the sufficient representation " + }, + { + "bbox": [ + 46, + 409, + 287, + 506 + ], + "type": "inline_equation", + "content": "z_{InD}^{suf}" + }, + { + "bbox": [ + 46, + 409, + 287, + 506 + ], + "type": "text", + "content": " according to definition 1 [30]." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 506, + 287, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 506, + 287, + 628 + ], + "spans": [ + { + "bbox": [ + 46, + 506, + 287, + 628 + ], + "type": "text", + "content": "IS Information Elimination. When " + }, + { + "bbox": [ + 46, + 506, + 287, + 628 + ], + "type": "inline_equation", + "content": "z_{InD}" + }, + { + "bbox": [ + 46, + 506, + 287, + 628 + ], + "type": "text", + "content": " is close to the sufficient representation " + }, + { + "bbox": [ + 46, + 506, + 287, + 628 + ], + "type": "inline_equation", + "content": "z_{InD}^{suf}" + }, + { + "bbox": [ + 46, + 506, + 287, + 628 + ], + "type": "text", + "content": ", the second term in Eq. 5 will be the fix value " + }, + { + "bbox": [ + 46, + 506, + 287, + 628 + ], + "type": "inline_equation", + "content": "I(x_{InD};Y)" + }, + { + "bbox": [ + 46, + 506, + 287, + 628 + ], + "type": "text", + "content": " based on the definition 1. So the key to minimize Eq. 5 is to minimize the first term " + }, + { + "bbox": [ + 46, + 506, + 287, + 628 + ], + "type": "inline_equation", + "content": "I(z_{InD}^{suf};x_{InD})" + }, + { + "bbox": [ + 46, + 506, + 287, + 628 + ], + "type": "text", + "content": ". Based on the definition 2, the lower bound of " + }, + { + "bbox": [ + 46, + 506, + 287, + 628 + ], + "type": "inline_equation", + "content": "I(z_{InD}^{suf};x_{InD})" + }, + { + "bbox": [ + 46, + 506, + 287, + 628 + ], + "type": "text", + "content": " is " + }, + { + "bbox": [ + 46, + 506, + 287, + 628 + ], + "type": "inline_equation", + "content": "I(z_{InD}^{min};x_{InD})" + }, + { + "bbox": [ + 46, + 506, + 287, + 628 + ], + "type": "text", + "content": ", so we can conclude that the learned representation is supposed to be the minimum sufficient representation " + }, + { + "bbox": [ + 46, + 506, + 287, + 628 + ], + "type": "inline_equation", + "content": "z_{InD}^{min}" + }, + { + "bbox": [ + 46, + 506, + 287, + 628 + ], + "type": "text", + "content": " [12]. We substitute " + }, + { + "bbox": [ + 46, + 506, + 287, + 628 + ], + "type": "inline_equation", + "content": "I(z_{InD}^{suf};x_{InD})" + }, + { + "bbox": [ + 46, + 506, + 287, + 628 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 506, + 287, + 628 + ], + "type": "inline_equation", + "content": "I(z_{InD}^{min};x_{InD})" + }, + { + "bbox": [ + 46, + 506, + 287, + 628 + ], + "type": "text", + "content": " in definition 2 with Eq. 2 and we have" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 97, + 629, + 287, + 661 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 97, + 629, + 287, + 661 + ], + "spans": [ + { + "bbox": [ + 97, + 629, + 287, + 661 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} I \\left(x _ {I n D}; z _ {I n D} ^ {\\min } \\mid Y\\right) + I \\left(z _ {I n D} ^ {\\min }; Y\\right) \\\\ \\leq I \\left(x _ {I n D}; z _ {I n D} ^ {s u f} | Y\\right) + I \\left(z _ {I n D} ^ {s u f}; Y\\right). \\tag {6} \\\\ \\end{array}", + "image_path": "573d358afae492c6b776664f24fde8b5a737bca4ec1fd2359a9b722bc488d924.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 46, + 667, + 287, + 693 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 667, + 287, + 693 + ], + "spans": [ + { + "bbox": [ + 46, + 667, + 287, + 693 + ], + "type": "text", + "content": "As both " + }, + { + "bbox": [ + 46, + 667, + 287, + 693 + ], + "type": "inline_equation", + "content": "z_{InD}^{min}" + }, + { + "bbox": [ + 46, + 667, + 287, + 693 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 667, + 287, + 693 + ], + "type": "inline_equation", + "content": "z_{InD}^{suf}" + }, + { + "bbox": [ + 46, + 667, + 287, + 693 + ], + "type": "text", + "content": " are sufficient, the second term of both sides in Eq. 6 is " + }, + { + "bbox": [ + 46, + 667, + 287, + 693 + ], + "type": "inline_equation", + "content": "I(x_{InD};Y)" + }, + { + "bbox": [ + 46, + 667, + 287, + 693 + ], + "type": "text", + "content": ", so we have" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 77, + 700, + 287, + 715 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 77, + 700, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 77, + 700, + 287, + 715 + ], + "type": "interline_equation", + "content": "0 \\leq I \\left(x _ {I n D}; z _ {I n D} ^ {\\text {m i n}} | Y\\right) \\leq I \\left(x _ {I n D}; z _ {I n D} ^ {\\text {s u f}} | Y\\right). \\tag {7}", + "image_path": "c9507adbfa98d72d9cc2fb280bf4e34eaaf6b13d98b0b8f59892deb11a978463.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 72, + 545, + 111 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 545, + 111 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 545, + 111 + ], + "type": "text", + "content": "Therefore, the learned IS information in " + }, + { + "bbox": [ + 305, + 72, + 545, + 111 + ], + "type": "inline_equation", + "content": "z_{InD}^{min}" + }, + { + "bbox": [ + 305, + 72, + 545, + 111 + ], + "type": "text", + "content": " is smaller than any IS information in " + }, + { + "bbox": [ + 305, + 72, + 545, + 111 + ], + "type": "inline_equation", + "content": "z_{InD}^{suf}" + }, + { + "bbox": [ + 305, + 72, + 545, + 111 + ], + "type": "text", + "content": ", which could be eliminated to 0 [12] (no blue and orange areas in " + }, + { + "bbox": [ + 305, + 72, + 545, + 111 + ], + "type": "inline_equation", + "content": "z_{InD}^{min}" + }, + { + "bbox": [ + 305, + 72, + 545, + 111 + ], + "type": "text", + "content": " in Fig. 2)." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 117, + 525, + 129 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 117, + 525, + 129 + ], + "spans": [ + { + "bbox": [ + 305, + 117, + 525, + 129 + ], + "type": "text", + "content": "3.5. Enlarge CS and IS Information for OSAR" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 135, + 545, + 303 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 135, + 545, + 303 + ], + "spans": [ + { + "bbox": [ + 304, + 135, + 545, + 303 + ], + "type": "text", + "content": "Based on the analysis in Sec. 3.3 and Sec. 3.4, we show that C.E. tends to maximize the CS information and eliminate the IS information in the feature representation. Both larger IS and CS information are crucial for OSAR according to Eq. 3, but C.E. does not bring the optimal information. On the one hand, IS information is eliminated so we lose a part of information which is beneficial for the OSAR. On the other hand, the learned representation is not sufficient and does not contain enough CS information in practice due to the model capacity and data distribution shift between training and test sets, which can be supported by the fact that test accuracy cannot reach " + }, + { + "bbox": [ + 304, + 135, + 545, + 303 + ], + "type": "inline_equation", + "content": "100\\%" + }, + { + "bbox": [ + 304, + 135, + 545, + 303 + ], + "type": "text", + "content": ". Therefore, we propose our method to enlarge the CS and IS information for better OSAR performance in next Sec. 4." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 305, + 314, + 365, + 326 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 314, + 365, + 326 + ], + "spans": [ + { + "bbox": [ + 305, + 314, + 365, + 326 + ], + "type": "text", + "content": "4. Methods" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 305, + 333, + 482, + 346 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 333, + 482, + 346 + ], + "spans": [ + { + "bbox": [ + 305, + 333, + 482, + 346 + ], + "type": "text", + "content": "4.1. Prototypical Similarity Learning" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 351, + 545, + 460 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 351, + 545, + 460 + ], + "spans": [ + { + "bbox": [ + 304, + 351, + 545, + 460 + ], + "type": "text", + "content": "According to Sec. 3.3, we notice that IS information is suppressed by the C.E. loss and a key reason is C.E. encourages feature representations of the same class to be exactly same. Therefore, we argue that the feature representation of the same class samples should have a similarity " + }, + { + "bbox": [ + 304, + 351, + 545, + 460 + ], + "type": "inline_equation", + "content": "s < 1" + }, + { + "bbox": [ + 304, + 351, + 545, + 460 + ], + "type": "text", + "content": ". In other words, we aim to keep the intra-class variance which prevents intra-class collapse to retain IS information. Based on the classical PL loss Eq. 1, we develop prototypical similarity learning (PSL):" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 312, + 462, + 545, + 507 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 462, + 545, + 507 + ], + "spans": [ + { + "bbox": [ + 312, + 462, + 545, + 507 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {P S L} = - \\log \\frac {\\exp \\left(\\frac {1 - \\left| z ^ {T} k _ {i} - s \\right|}{\\tau}\\right)}{\\exp \\left(\\frac {1 - \\left| z ^ {T} k _ {i} - s \\right|}{\\tau}\\right) + \\sum_ {n \\in K _ {i} ^ {-}} \\exp \\left(\\frac {z ^ {T} n}{\\tau}\\right)}, \\tag {8}", + "image_path": "4bfc6622fdbb93b2c66287c1fed3fcec047b95909241df190a8834a296da3a0c.jpg" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 304, + 510, + 545, + 605 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 510, + 545, + 605 + ], + "spans": [ + { + "bbox": [ + 304, + 510, + 545, + 605 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 510, + 545, + 605 + ], + "type": "inline_equation", + "content": "s" + }, + { + "bbox": [ + 304, + 510, + 545, + 605 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 510, + 545, + 605 + ], + "type": "inline_equation", + "content": "\\tau" + }, + { + "bbox": [ + 304, + 510, + 545, + 605 + ], + "type": "text", + "content": " are fixed hyperparameters. In this way, we expect the prototype " + }, + { + "bbox": [ + 304, + 510, + 545, + 605 + ], + "type": "inline_equation", + "content": "k_{i}" + }, + { + "bbox": [ + 304, + 510, + 545, + 605 + ], + "type": "text", + "content": " to act as the CS information for the InD class " + }, + { + "bbox": [ + 304, + 510, + 545, + 605 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 304, + 510, + 545, + 605 + ], + "type": "text", + "content": ", which is used to predict the label, and the dissimilarity between the " + }, + { + "bbox": [ + 304, + 510, + 545, + 605 + ], + "type": "inline_equation", + "content": "z" + }, + { + "bbox": [ + 304, + 510, + 545, + 605 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 510, + 545, + 605 + ], + "type": "inline_equation", + "content": "k_{i}" + }, + { + "bbox": [ + 304, + 510, + 545, + 605 + ], + "type": "text", + "content": " represents the IS information. Traditional PL loss (or C.E. loss) encourages the features of samples in the same classes to be as tight as possible, while our PSL aims to keep the variance within the same class." + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": "However, we find Eq. 8 will converge to the trivial solution, where the " + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "inline_equation", + "content": "z" + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": " converges to the training result of Eq. 1 and only " + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "inline_equation", + "content": "k_{i}" + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": " shifts. To solve this problem, we introduce the similarity between different samples within a mini-batch into the denominator of Eq. 8. In this way, we directly constrain the relationship between sample features instead of only supervising the similarity between the sample feature and its prototype. We name the modified loss as PSL with contrastive terms (CT):" + } + ] + } + ], + "index": 23 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "15298" + } + ] + } + ], + "index": 24 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 49, + 74, + 287, + 201 + ], + "blocks": [ + { + "bbox": [ + 49, + 74, + 287, + 201 + ], + "lines": [ + { + "bbox": [ + 49, + 74, + 287, + 201 + ], + "spans": [ + { + "bbox": [ + 49, + 74, + 287, + 201 + ], + "type": "image", + "image_path": "e238f5a8b0f1d50fcf404fec8d8cd134070a55d98285c119b792335724f1fd16.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 200, + 547, + 224 + ], + "lines": [ + { + "bbox": [ + 46, + 200, + 547, + 224 + ], + "spans": [ + { + "bbox": [ + 46, + 200, + 547, + 224 + ], + "type": "text", + "content": "Figure 3. (a) C.E. encourages the sample feature " + }, + { + "bbox": [ + 46, + 200, + 547, + 224 + ], + "type": "inline_equation", + "content": "z" + }, + { + "bbox": [ + 46, + 200, + 547, + 224 + ], + "type": "text", + "content": " to be exactly same with the corresponding prototype " + }, + { + "bbox": [ + 46, + 200, + 547, + 224 + ], + "type": "inline_equation", + "content": "k_{i}" + }, + { + "bbox": [ + 46, + 200, + 547, + 224 + ], + "type": "text", + "content": ". (b) Our PSL encourages the similarity between " + }, + { + "bbox": [ + 46, + 200, + 547, + 224 + ], + "type": "inline_equation", + "content": "z" + }, + { + "bbox": [ + 46, + 200, + 547, + 224 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 200, + 547, + 224 + ], + "type": "inline_equation", + "content": "k_{i}" + }, + { + "bbox": [ + 46, + 200, + 547, + 224 + ], + "type": "text", + "content": ", features of shuffled sample " + }, + { + "bbox": [ + 46, + 200, + 547, + 224 + ], + "type": "inline_equation", + "content": "Q_{shuf}" + }, + { + "bbox": [ + 46, + 200, + 547, + 224 + ], + "type": "text", + "content": " and other samples in the same class " + }, + { + "bbox": [ + 46, + 200, + 547, + 224 + ], + "type": "inline_equation", + "content": "Q_{sc}" + }, + { + "bbox": [ + 46, + 200, + 547, + 224 + ], + "type": "text", + "content": " to have a similarity less than 1." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 304, + 74, + 541, + 200 + ], + "blocks": [ + { + "bbox": [ + 304, + 74, + 541, + 200 + ], + "lines": [ + { + "bbox": [ + 304, + 74, + 541, + 200 + ], + "spans": [ + { + "bbox": [ + 304, + 74, + 541, + 200 + ], + "type": "image", + "image_path": "a8b833f4658139937f81e0958abd4e88842883459f3e42de178ff1ebdf1b6d01.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 242, + 288, + 314 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 242, + 288, + 314 + ], + "spans": [ + { + "bbox": [ + 47, + 242, + 288, + 314 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\mathcal {L} _ {P S L} ^ {C T} = \\\\ \\frac {\\exp \\left(\\frac {1 - \\left| z ^ {T} k _ {i} - s \\right|}{\\tau}\\right)}{\\exp \\left(\\frac {1 - \\left| z ^ {T} k _ {i} - s \\right|}{\\tau}\\right) + \\sum_ {n \\in Q _ {n}} \\exp \\left(\\frac {z ^ {T} n}{\\tau}\\right) + \\sum_ {p \\in Q _ {s p}} \\exp \\left(\\frac {\\left| z ^ {T} p - s \\right|}{\\tau}\\right)}, \\end{array} \\tag {9}", + "image_path": "98c8a973b6db86af6996fff66aa6f4a759745537760a5a191073aa8e2649d01f.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 326, + 287, + 397 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 326, + 287, + 397 + ], + "spans": [ + { + "bbox": [ + 46, + 326, + 287, + 397 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 326, + 287, + 397 + ], + "type": "inline_equation", + "content": "Q_{n} = K_{i}^{-} \\cup Q_{ns}" + }, + { + "bbox": [ + 46, + 326, + 287, + 397 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 46, + 326, + 287, + 397 + ], + "type": "inline_equation", + "content": "Q_{ns}" + }, + { + "bbox": [ + 46, + 326, + 287, + 397 + ], + "type": "text", + "content": " refers to the negative samples, i.e., samples in other classes, and " + }, + { + "bbox": [ + 46, + 326, + 287, + 397 + ], + "type": "inline_equation", + "content": "Q_{sp}" + }, + { + "bbox": [ + 46, + 326, + 287, + 397 + ], + "type": "text", + "content": " refers to the soft positive samples which contains samples in the same class " + }, + { + "bbox": [ + 46, + 326, + 287, + 397 + ], + "type": "inline_equation", + "content": "Q_{sc}" + }, + { + "bbox": [ + 46, + 326, + 287, + 397 + ], + "type": "text", + "content": " here. The reason we call soft positive samples is that we think samples in the same class share CS information but have distinct IS information." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 407, + 181, + 420 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 407, + 181, + 420 + ], + "spans": [ + { + "bbox": [ + 47, + 407, + 181, + 420 + ], + "type": "text", + "content": "4.2. Video Shuffling for PSL" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 426, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 426, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 426, + 289, + 715 + ], + "type": "text", + "content": "PSL aims to keep IS information during training, and in this section we introduce how to enlarge CS information through video shuffling. The appearance bias is a significant problem in the OSAR. For instance, the OoD classes Smile and Chew are easily classified as InD classes ApplyEyeMakeup and ApplyLipstick, as the majority area of all these classes are occupied by a face, as shown in Fig. 7. The NN is confused by the extremely similar spatial information and neglects the minor different temporal information. This phenomenon encourages us to strengthen the temporal information extraction ability of the NN to distinguish classes with very similar appearances but different actions. We find that introducing a simple yet effective way, i.e., to regard the shuffled video " + }, + { + "bbox": [ + 46, + 426, + 289, + 715 + ], + "type": "inline_equation", + "content": "Q_{shuf}" + }, + { + "bbox": [ + 46, + 426, + 289, + 715 + ], + "type": "text", + "content": " as the soft positive sample in Eq. 9, is extremely suitable and useful in our PSL framework. In this case, " + }, + { + "bbox": [ + 46, + 426, + 289, + 715 + ], + "type": "inline_equation", + "content": "Q_{sp} = Q_{sc} \\cup Q_{shuf}" + }, + { + "bbox": [ + 46, + 426, + 289, + 715 + ], + "type": "text", + "content": ". Shuffled video means shuffling the frames within a single video. As the appearance information of the shuffled video is almost the same as the original video, a smaller than 1 similarity forces the NN to learn the distinct temporal information between them. Unlike existing works which predict the sequence or the type of the shuffled video [34-37], we regard the shuffle video as a whole sample and directly compare its feature representation with the original video in our PSL. We find this" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 243, + 546, + 281 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 243, + 546, + 281 + ], + "spans": [ + { + "bbox": [ + 304, + 243, + 546, + 281 + ], + "type": "text", + "content": "technique can improve the closed-set accuracy which indicates more CS information is learned. We summarize the difference between our PSL and classical C.E. in Fig. 3." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 305, + 289, + 414, + 301 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 289, + 414, + 301 + ], + "spans": [ + { + "bbox": [ + 305, + 289, + 414, + 301 + ], + "type": "text", + "content": "4.3. Uncertainty Score" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 307, + 546, + 356 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 307, + 546, + 356 + ], + "spans": [ + { + "bbox": [ + 304, + 307, + 546, + 356 + ], + "type": "text", + "content": "As our PSL aims to learn richer CS and IS information in the feature representation, we use the Mahalanobis distance to measure the uncertainty as it can be calculated from the feature representation perspective [38, 39]:" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 360, + 365, + 545, + 380 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 360, + 365, + 545, + 380 + ], + "spans": [ + { + "bbox": [ + 360, + 365, + 545, + 380 + ], + "type": "interline_equation", + "content": "u = \\left(z - \\mu_ {m}\\right) ^ {T} \\sum_ {m} ^ {- 1} \\left(z - \\mu_ {m}\\right), \\tag {10}", + "image_path": "ab452c61918483d63bf160579cbd575ee26fa8b8a817c091860049738270ff86.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 389, + 545, + 414 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 389, + 545, + 414 + ], + "spans": [ + { + "bbox": [ + 305, + 389, + 545, + 414 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 389, + 545, + 414 + ], + "type": "inline_equation", + "content": "\\mu_{m}" + }, + { + "bbox": [ + 305, + 389, + 545, + 414 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 389, + 545, + 414 + ], + "type": "inline_equation", + "content": "\\sum_{m}" + }, + { + "bbox": [ + 305, + 389, + 545, + 414 + ], + "type": "text", + "content": " denote the mean and covariance of the whole training set features, and " + }, + { + "bbox": [ + 305, + 389, + 545, + 414 + ], + "type": "inline_equation", + "content": "z" + }, + { + "bbox": [ + 305, + 389, + 545, + 414 + ], + "type": "text", + "content": " is the test sample feature." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 426, + 388, + 440 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 426, + 388, + 440 + ], + "spans": [ + { + "bbox": [ + 306, + 426, + 388, + 440 + ], + "type": "text", + "content": "5. Experiments" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 445, + 545, + 529 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 445, + 545, + 529 + ], + "spans": [ + { + "bbox": [ + 304, + 445, + 545, + 529 + ], + "type": "text", + "content": "Datasets. Following [5], we use UCF101 [40] as the InD dataset for training and closed-set evaluation, and use HMDB51 [41] and MiT-v2 [42] as OoD data for open-set evaluation. Different from [5] which does not clean the OoD data that may contains InD classes, we remove the overlapping classes between InD and OoD dataset during evaluation. See Appendix A for more details." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 530, + 545, + 602 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 530, + 545, + 602 + ], + "spans": [ + { + "bbox": [ + 304, + 530, + 545, + 602 + ], + "type": "text", + "content": "Evaluation protocols. For closed-set performance, we evaluate like the traditional way to calculate the top-1 accuracy Acc. " + }, + { + "bbox": [ + 304, + 530, + 545, + 602 + ], + "type": "inline_equation", + "content": "(\\%)" + }, + { + "bbox": [ + 304, + 530, + 545, + 602 + ], + "type": "text", + "content": ". For open-set performance, we follow the classical open-set recognition protocol [6,43] to use the obtained uncertainty score Eq. 10 to calculate AUROC " + }, + { + "bbox": [ + 304, + 530, + 545, + 602 + ], + "type": "inline_equation", + "content": "(\\%)" + }, + { + "bbox": [ + 304, + 530, + 545, + 602 + ], + "type": "text", + "content": ", AUPR " + }, + { + "bbox": [ + 304, + 530, + 545, + 602 + ], + "type": "inline_equation", + "content": "(\\%)" + }, + { + "bbox": [ + 304, + 530, + 545, + 602 + ], + "type": "text", + "content": " and FPR95 " + }, + { + "bbox": [ + 304, + 530, + 545, + 602 + ], + "type": "inline_equation", + "content": "(\\%)" + }, + { + "bbox": [ + 304, + 530, + 545, + 602 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 602, + 545, + 674 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 602, + 545, + 674 + ], + "spans": [ + { + "bbox": [ + 304, + 602, + 545, + 674 + ], + "type": "text", + "content": "Implementation details. For Kinetics400 (K400) [3] pretrained model, our implementation setting is the same with [5]. The base learning rate is 0.001 and step-wisely decayed every 20 epochs with total of 50 epochs. We argue that as K400 is extremely large, the K400 pretrained model may already have seen the OoD data used in inference, so" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 305, + 683, + 546, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 683, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 683, + 546, + 713 + ], + "type": "text", + "content": "1We find AUROC in [5] only considers one specific threshold based on their code, and after discussion and agreement they provide the modified correct score in our Tab. 1. See Appendix B for details." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "15299" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 50, + 70, + 542, + 239 + ], + "blocks": [ + { + "bbox": [ + 50, + 70, + 542, + 239 + ], + "lines": [ + { + "bbox": [ + 50, + 70, + 542, + 239 + ], + "spans": [ + { + "bbox": [ + 50, + 70, + 542, + 239 + ], + "type": "table", + "html": "
DatasetsMethodsw/o K400 Pretrainw/ K400 Pretrain
AUROC↑AUPR↑FPR95↓Acc.↑AUROC↑AUPR↑FPR95↓Acc.↑
UCF101 (InD)OpenMax [8]82.2854.5950.6973.9290.8973.1638.7795.32
MC Dropout [7]75.7541.2154.7873.6388.2367.6238.1295.06
BNN SVI [24]80.1053.4352.3371.5191.8179.6531.4394.71
HMDB51 (OoD)SoftMax [6]79.7252.1353.2273.9291.7577.6928.6095.03
RPL [27]79.6751.8556.4071.4690.5377.8637.0995.59
DEAR [5]80.0049.2353.2871.3384.1675.5489.4094.48
PSL(ours)86.4365.5441.6776.5394.0586.5523.1895.62
Δ(+4.15)(+10.95)(-9.02)(+2.61)(+2.24)(+6.90)(-5.42)(+0.03)
UCF101 (InD)OpenMax [8]84.4376.6947.7473.9293.3488.1428.9595.32
MC Dropout [7]75.6662.2051.5773.6388.7183.3639.4695.06
BNN SVI [24]79.4871.7352.5271.5191.8690.1236.2194.71
MiTv2 (OoD)SoftMax [6]80.5573.1750.4973.9291.9589.1632.0095.03
RPL [27]80.2172.0452.8371.4690.6488.7938.4395.59
DEAR [5]79.0067.1052.4471.3386.0487.3887.4094.48
PSL(ours)86.5379.9540.9976.5395.7594.9618.9695.62
Δ(+2.10)(+3.26)(-6.75)(+2.61)(+2.41)(+4.84)(-9.99)(+0.03)
", + "image_path": "a23f8e3d7140131f311d0d9f8b89b325ae695ab3e93acc6aece6a4be1d52503d.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 239, + 546, + 274 + ], + "lines": [ + { + "bbox": [ + 47, + 239, + 546, + 274 + ], + "spans": [ + { + "bbox": [ + 47, + 239, + 546, + 274 + ], + "type": "text", + "content": "Table 1. Comparison with state-of-the-art methods on HMDB51 and MiTv2 (OoD) using TSM backbone. Acc. refers to closed-set accuracy. AUROC, AUPR and FPR95 are open-set metrics. Best results are in bold and second best results in italic. The gap between best and second best is in blue. DEAR and our methods contain video-specific operation." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "text" + }, + { + "type": "image", + "bbox": [ + 50, + 277, + 167, + 374 + ], + "blocks": [ + { + "bbox": [ + 50, + 277, + 167, + 374 + ], + "lines": [ + { + "bbox": [ + 50, + 277, + 167, + 374 + ], + "spans": [ + { + "bbox": [ + 50, + 277, + 167, + 374 + ], + "type": "image", + "image_path": "5bab0fc96c46516adc715a41287e2c6ef48b0c70a1e2b9851c0df9af2db516cb.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 170, + 277, + 286, + 374 + ], + "blocks": [ + { + "bbox": [ + 170, + 277, + 286, + 374 + ], + "lines": [ + { + "bbox": [ + 170, + 277, + 286, + 374 + ], + "spans": [ + { + "bbox": [ + 170, + 277, + 286, + 374 + ], + "type": "image", + "image_path": "fd098bc633ed9b6899e41054a025dfce13ebcd84dc862529d0ccf0febf54e951.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + } + ], + "index": 3 + }, + { + "type": "image", + "bbox": [ + 49, + 374, + 167, + 470 + ], + "blocks": [ + { + "bbox": [ + 49, + 374, + 167, + 470 + ], + "lines": [ + { + "bbox": [ + 49, + 374, + 167, + 470 + ], + "spans": [ + { + "bbox": [ + 49, + 374, + 167, + 470 + ], + "type": "image", + "image_path": "81ef902486b45035e37814c29c935d9648187adbdc62c4b608c53a139b739bd4.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 47, + 470, + 287, + 491 + ], + "lines": [ + { + "bbox": [ + 47, + 470, + 287, + 491 + ], + "spans": [ + { + "bbox": [ + 47, + 470, + 287, + 491 + ], + "type": "text", + "content": "Figure 4. The uncertainty distribution of InD and OoD samples of (a) Softmax, (b) DEAR, (c) BNN SVI and (d) our PSL method." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "type": "image", + "bbox": [ + 170, + 374, + 286, + 470 + ], + "blocks": [ + { + "bbox": [ + 170, + 374, + 286, + 470 + ], + "lines": [ + { + "bbox": [ + 170, + 374, + 286, + 470 + ], + "spans": [ + { + "bbox": [ + 170, + 374, + 286, + 470 + ], + "type": "image", + "image_path": "d45d442a2f6eb36ef94790a2cb2e0edc4d85e4107be2db50b973c8187b5af9f4.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_body" + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 515, + 287, + 598 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 515, + 287, + 598 + ], + "spans": [ + { + "bbox": [ + 46, + 515, + 287, + 598 + ], + "type": "text", + "content": "we conduct experiments from scratch (no ImageNet pretrained) to ensure that OoD data is absolutely unavailable during training. We use the LARS optimizer [44] and set the base learning rate and momentum as 0.6 and 0.9 with total of 400 epochs. The experiments are conducted on TSM [1], I3D [3] and SlowFast [2]. The batch size for all methods is 256. More details are in Appendix C." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 610, + 157, + 621 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 610, + 157, + 621 + ], + "spans": [ + { + "bbox": [ + 47, + 610, + 157, + 621 + ], + "type": "text", + "content": "5.1. Evaluation Results" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 629, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 629, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 629, + 287, + 713 + ], + "type": "text", + "content": "Comparison with state-of-the-art. We report the results on HMDB51 (OoD) and MiT-v2 (OoD) in Table 1 using TSM backbone [1]. The evaluation results of other backbones including I3D and SlowFast are in the Appendix D. We can see that for w/ or w/o K400 pretrain, our PSL method has significantly better open-set and closed-set performance than all baselines. The uncertainty distribution" + } + ] + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 310, + 277, + 426, + 393 + ], + "blocks": [ + { + "bbox": [ + 310, + 277, + 426, + 393 + ], + "lines": [ + { + "bbox": [ + 310, + 277, + 426, + 393 + ], + "spans": [ + { + "bbox": [ + 310, + 277, + 426, + 393 + ], + "type": "image", + "image_path": "e67db6fe4925db7807ee0237e27071e5990aa4d6b9b139f15db3e92dff832ceb.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 338, + 394, + 404, + 405 + ], + "lines": [ + { + "bbox": [ + 338, + 394, + 404, + 405 + ], + "spans": [ + { + "bbox": [ + 338, + 394, + 404, + 405 + ], + "type": "text", + "content": "(a) Cross-entropy" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 305, + 404, + 545, + 459 + ], + "lines": [ + { + "bbox": [ + 305, + 404, + 545, + 459 + ], + "spans": [ + { + "bbox": [ + 305, + 404, + 545, + 459 + ], + "type": "text", + "content": "Figure 5. Feature representation visualization of cross-entropy and our PSL method. OoD samples are in black and InD samples are in other colors. In the red, blue and green circles, it is clear that OoD samples distribute at the edge of InD samples in our PSL, while greatly overlap with each other in the cross-entropy method." + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 427, + 277, + 542, + 393 + ], + "blocks": [ + { + "bbox": [ + 427, + 277, + 542, + 393 + ], + "lines": [ + { + "bbox": [ + 427, + 277, + 542, + 393 + ], + "spans": [ + { + "bbox": [ + 427, + 277, + 542, + 393 + ], + "type": "image", + "image_path": "c30ffa7f6925d9f5f8ac531f6f0052a4a42e2842269bed4315ce86da26fdc896.jpg" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 459, + 394, + 512, + 403 + ], + "lines": [ + { + "bbox": [ + 459, + 394, + 512, + 403 + ], + "spans": [ + { + "bbox": [ + 459, + 394, + 512, + 403 + ], + "type": "text", + "content": "(b) PSL (ours)" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_caption" + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 483, + 546, + 615 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 483, + 546, + 615 + ], + "spans": [ + { + "bbox": [ + 304, + 483, + 546, + 615 + ], + "type": "text", + "content": "of InD and OoD samples are depicted in Fig. 4 for MiT-v2 (OoD) with K400 pretrained. Three baseline methods have a clear over confidence problem, i.e., the far left column is extremely high (red circles in Fig. 4), which means a large number of OoD samples have almost 0 uncertainty, while our method significantly alleviates this problem through the distinct representation of OoD samples, illustrated in Fig. 5. Besides, we can find that the open-set performance w/ K400 pretrain is higher than w/o pretrain for almost all methods in Table 1 and Fig. 1 (a), which can testify the importance of richer semantic representation for OSAR." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 617, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 546, + 713 + ], + "type": "text", + "content": "Comparison with metric learning methods. Our method concentrates on the feature representation aspect for the OSAR problem, so we also implement several well-known metric learning methods and show the result in Table 3. The evaluation is conducted using TSM model and OoD dataset is HMDB51. We do not use video shuffling in our method for fair comparison. We can see that our method still achieves the best open-set performance. The most im" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "15300" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 58, + 70, + 533, + 164 + ], + "blocks": [ + { + "bbox": [ + 58, + 70, + 533, + 164 + ], + "lines": [ + { + "bbox": [ + 58, + 70, + 533, + 164 + ], + "spans": [ + { + "bbox": [ + 58, + 70, + 533, + 164 + ], + "type": "table", + "html": "
sQnsQscQshufInDOoDAUROC↑AUPR↑FPR95↓Acc.↑
MeanVarianceMeanVariance
LPLXXXX0.810.00150.630.002980.9552.7952.5172.36
LPSL✓XXX0.790.00160.620.002881.7954.1652.3372.33
LCTPSL✓✓XX0.710.00220.610.003682.6057.3650.0372.17
✓✓✓X0.710.00230.490.003583.4259.0551.3272.28
✓✓✓✓0.740.00160.630.002986.4365.5841.7577.19
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AUROC↑AUPR↑FPR95↓Acc.↑
SoftMax80.9552.7952.5172.36
Triplet [45]81.0254.7553.8875.50
Normface [46]80.9954.9053.1973.34
Circle [47]78.7651.6555.2772.15
Arcface [48]81.2355.0353.6775.95
LSoftMax [49]80.8754.0152.2973.05
PSL(s = 0.8)83.4259.0551.3272.28
PSL(s = 0.6)82.7558.5752.2773.26
", + "image_path": "60960084174e814b992981c17a7500498e548812c43d41d5fe531b529ea614bc.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + }, + { + "bbox": [ + 55, + 278, + 277, + 289 + ], + "lines": [ + { + "bbox": [ + 55, + 278, + 277, + 289 + ], + "spans": [ + { + "bbox": [ + 55, + 278, + 277, + 289 + ], + "type": "text", + "content": "Table 3. Comparison with different metric learning methods." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_footnote" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 300, + 287, + 420 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 300, + 287, + 420 + ], + "spans": [ + { + "bbox": [ + 46, + 300, + 287, + 420 + ], + "type": "text", + "content": "important difference between our method and all other metric learning methods is that they aim to push the features of one class as tight as possible like C.E., while our method aims to keep the feature variance within a class to retain IS information. We calculate the mean similarity between the sample feature and the corresponding class center. The mean similarity ranges from 0.77 to 0.82 for other metric learning methods, while mean similarity is 0.71 (" + }, + { + "bbox": [ + 46, + 300, + 287, + 420 + ], + "type": "inline_equation", + "content": "s = 0.8" + }, + { + "bbox": [ + 46, + 300, + 287, + 420 + ], + "type": "text", + "content": ") and 0.6 (" + }, + { + "bbox": [ + 46, + 300, + 287, + 420 + ], + "type": "inline_equation", + "content": "s = 0.6" + }, + { + "bbox": [ + 46, + 300, + 287, + 420 + ], + "type": "text", + "content": ") for our PSL. So our method has looser feature distribution within a class, as shown in Fig. 5." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 430, + 141, + 443 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 430, + 141, + 443 + ], + "spans": [ + { + "bbox": [ + 47, + 430, + 141, + 443 + ], + "type": "text", + "content": "5.2. Ablation Study" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 449, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 449, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 449, + 288, + 713 + ], + "type": "text", + "content": "Contrastive terms in " + }, + { + "bbox": [ + 46, + 449, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{PSL}^{CT}" + }, + { + "bbox": [ + 46, + 449, + 288, + 713 + ], + "type": "text", + "content": " for IS information. The intuition of PSL is to keep the intra-class variance to retain the IS information which is helpful for OSAR. We expect that the representation " + }, + { + "bbox": [ + 46, + 449, + 288, + 713 + ], + "type": "inline_equation", + "content": "z" + }, + { + "bbox": [ + 46, + 449, + 288, + 713 + ], + "type": "text", + "content": " within a class has a similarity " + }, + { + "bbox": [ + 46, + 449, + 288, + 713 + ], + "type": "inline_equation", + "content": "s < 1" + }, + { + "bbox": [ + 46, + 449, + 288, + 713 + ], + "type": "text", + "content": " with the prototype " + }, + { + "bbox": [ + 46, + 449, + 288, + 713 + ], + "type": "inline_equation", + "content": "k_{i}" + }, + { + "bbox": [ + 46, + 449, + 288, + 713 + ], + "type": "text", + "content": ", so each sample can keep its own IS information. However, we find that the loss " + }, + { + "bbox": [ + 46, + 449, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{PSL}" + }, + { + "bbox": [ + 46, + 449, + 288, + 713 + ], + "type": "text", + "content": " may lead the network to find the trivial representation of samples " + }, + { + "bbox": [ + 46, + 449, + 288, + 713 + ], + "type": "inline_equation", + "content": "z" + }, + { + "bbox": [ + 46, + 449, + 288, + 713 + ], + "type": "text", + "content": " which is similar to using loss " + }, + { + "bbox": [ + 46, + 449, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{PL}" + }, + { + "bbox": [ + 46, + 449, + 288, + 713 + ], + "type": "text", + "content": ", where only " + }, + { + "bbox": [ + 46, + 449, + 288, + 713 + ], + "type": "inline_equation", + "content": "k_{i}" + }, + { + "bbox": [ + 46, + 449, + 288, + 713 + ], + "type": "text", + "content": " shifts and " + }, + { + "bbox": [ + 46, + 449, + 288, + 713 + ], + "type": "inline_equation", + "content": "z" + }, + { + "bbox": [ + 46, + 449, + 288, + 713 + ], + "type": "text", + "content": " does not. We calculate the mean of similarity " + }, + { + "bbox": [ + 46, + 449, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\text{sim}(z, \\bar{z}_i)" + }, + { + "bbox": [ + 46, + 449, + 288, + 713 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 449, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\bar{z}_i" + }, + { + "bbox": [ + 46, + 449, + 288, + 713 + ], + "type": "text", + "content": " denotes the mean representation of all samples in the same class " + }, + { + "bbox": [ + 46, + 449, + 288, + 713 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 449, + 288, + 713 + ], + "type": "text", + "content": ", and the mean of similarity with the corresponding prototype " + }, + { + "bbox": [ + 46, + 449, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\text{sim}(z, k_i)" + }, + { + "bbox": [ + 46, + 449, + 288, + 713 + ], + "type": "text", + "content": ", as well as the feature variance in all dimensions. Fig. 6 (a) and (b) show that with the hyper-parameter " + }, + { + "bbox": [ + 46, + 449, + 288, + 713 + ], + "type": "inline_equation", + "content": "s" + }, + { + "bbox": [ + 46, + 449, + 288, + 713 + ], + "type": "text", + "content": " decreasing, the " + }, + { + "bbox": [ + 46, + 449, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\text{sim}(z, k_i)" + }, + { + "bbox": [ + 46, + 449, + 288, + 713 + ], + "type": "text", + "content": " decreases as expected by " + }, + { + "bbox": [ + 46, + 449, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{PSL}" + }, + { + "bbox": [ + 46, + 449, + 288, + 713 + ], + "type": "text", + "content": " (green curves), but the " + }, + { + "bbox": [ + 46, + 449, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\text{sim}(z, \\bar{z}_i)" + }, + { + "bbox": [ + 46, + 449, + 288, + 713 + ], + "type": "text", + "content": " and variance stay unchanged (blue curves), meaning that the representation of samples are still similar with using " + }, + { + "bbox": [ + 46, + 449, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{PL}" + }, + { + "bbox": [ + 46, + 449, + 288, + 713 + ], + "type": "text", + "content": ", and only the prototypes are pushed away by the sample representations. In contrast, with CT in " + }, + { + "bbox": [ + 46, + 449, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{PSL}^{CT}" + }, + { + "bbox": [ + 46, + 449, + 288, + 713 + ], + "type": "text", + "content": ", the " + }, + { + "bbox": [ + 46, + 449, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\text{sim}(z, \\bar{z}_i)" + }, + { + "bbox": [ + 46, + 449, + 288, + 713 + ], + "type": "text", + "content": " decreases and variance increases with " + }, + { + "bbox": [ + 46, + 449, + 288, + 713 + ], + "type": "inline_equation", + "content": "s" + }, + { + "bbox": [ + 46, + 449, + 288, + 713 + ], + "type": "text", + "content": " decreases (red curves), indicating that CT is significantly effective to keep the intra-class variance." + } + ] + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 310, + 181, + 423, + 298 + ], + "blocks": [ + { + "bbox": [ + 310, + 181, + 423, + 298 + ], + "lines": [ + { + "bbox": [ + 310, + 181, + 423, + 298 + ], + "spans": [ + { + "bbox": [ + 310, + 181, + 423, + 298 + ], + "type": "image", + "image_path": "152feb23ba7db6e11c1e44b328e9b654ba6af9b1fc9cea71e5304d5cda87d0b7.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 312, + 299, + 538, + 310 + ], + "lines": [ + { + "bbox": [ + 312, + 299, + 538, + 310 + ], + "spans": [ + { + "bbox": [ + 312, + 299, + 538, + 310 + ], + "type": "text", + "content": "Figure 6. Mean similarity and variance analysis for CT terms." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 424, + 180, + 539, + 298 + ], + "blocks": [ + { + "bbox": [ + 424, + 180, + 539, + 298 + ], + "lines": [ + { + "bbox": [ + 424, + 180, + 539, + 298 + ], + "spans": [ + { + "bbox": [ + 424, + 180, + 539, + 298 + ], + "type": "image", + "image_path": "a68a850b4c3be0ff966023feda67a7cdb1a80476aae3a0b00c963c9811651299.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 327, + 545, + 471 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 327, + 545, + 471 + ], + "spans": [ + { + "bbox": [ + 304, + 327, + 545, + 471 + ], + "type": "text", + "content": "To individually study the effectiveness of " + }, + { + "bbox": [ + 304, + 327, + 545, + 471 + ], + "type": "inline_equation", + "content": "Q_{ns}" + }, + { + "bbox": [ + 304, + 327, + 545, + 471 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 327, + 545, + 471 + ], + "type": "inline_equation", + "content": "Q_{sc}" + }, + { + "bbox": [ + 304, + 327, + 545, + 471 + ], + "type": "text", + "content": " in " + }, + { + "bbox": [ + 304, + 327, + 545, + 471 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{PSL}^{CT}" + }, + { + "bbox": [ + 304, + 327, + 545, + 471 + ], + "type": "text", + "content": ", we provide the ablation results in Table 2. For OoD samples, we calculate the similarity with the mean representation of its predicted class. Table 2 shows that using " + }, + { + "bbox": [ + 304, + 327, + 545, + 471 + ], + "type": "inline_equation", + "content": "Q_{ns}" + }, + { + "bbox": [ + 304, + 327, + 545, + 471 + ], + "type": "text", + "content": " alone can significantly increase the intra-class variance for both InD and OoD samples, meaning the pushing effect of representations in other classes can implicitly help retain the IS information. On top of that, " + }, + { + "bbox": [ + 304, + 327, + 545, + 471 + ], + "type": "inline_equation", + "content": "Q_{sc}" + }, + { + "bbox": [ + 304, + 327, + 545, + 471 + ], + "type": "text", + "content": " can further learn more IS information that is helpful to distinguish OoD samples, as the mean similarity of InD samples stay unchanged, but OoD samples are smaller which means OoD samples are far away from InD samples." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 472, + 545, + 544 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 472, + 545, + 544 + ], + "spans": [ + { + "bbox": [ + 304, + 472, + 545, + 544 + ], + "type": "text", + "content": "Shuffled videos for CS information. Tab. 2 shows that " + }, + { + "bbox": [ + 304, + 472, + 545, + 544 + ], + "type": "inline_equation", + "content": "Q_{shuf}" + }, + { + "bbox": [ + 304, + 472, + 545, + 544 + ], + "type": "text", + "content": " can improve both closed-set and open-set performance, which proves introducing shuffled videos in PSL can enlarge CS information. Smaller intra-class variance brought by " + }, + { + "bbox": [ + 304, + 472, + 545, + 544 + ], + "type": "inline_equation", + "content": "Q_{shuf}" + }, + { + "bbox": [ + 304, + 472, + 545, + 544 + ], + "type": "text", + "content": " testify Proposition 1 that more CS information means more similar features within the same class." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "text", + "content": "We draw the uncertainty of all classes in HMDB51, as shown in Fig. 7. Note that some classes in HMDB51 are actually InD as they appear in the UCF101, like the class 3 golf and 4 shoot bow in Fig. 7. We find that in C.E. some OoD classes have extremely low uncertainty, such as class 1 chew and 2 smile, because they are spatially similar to some InD classes like ApplyEyeMakeup and ApplyLipstick in Fig. 7 (a). Comparing (b) and (c) shows that our PSL can increase the average uncertainty of OoD classes (higher yellow points), and some OoD classes which are similar to InD classes like 1 and 2 have much higher uncertainty in our PSL method. After shuffled samples are involved, some InD classes whose uncertainty are increased in (c) like 3 and 4 have lower uncertainty in (d), and the uncertainty of some" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "15301" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 55, + 70, + 167, + 171 + ], + "blocks": [ + { + "bbox": [ + 55, + 70, + 167, + 171 + ], + "lines": [ + { + "bbox": [ + 55, + 70, + 167, + 171 + ], + "spans": [ + { + "bbox": [ + 55, + 70, + 167, + 171 + ], + "type": "image", + "image_path": "5d523ea15bdc4df1542393b1042976962d48fcf29a64ec257e5acdb06cd62b4c.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 168, + 71, + 281, + 171 + ], + "blocks": [ + { + "bbox": [ + 168, + 71, + 281, + 171 + ], + "lines": [ + { + "bbox": [ + 168, + 71, + 281, + 171 + ], + "spans": [ + { + "bbox": [ + 168, + 71, + 281, + 171 + ], + "type": "image", + "image_path": "50e5e0570a74c5f12ce4f25e711b674fa204afd5ab1082cd0b973b2191322216.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 50, + 171, + 165, + 267 + ], + "blocks": [ + { + "bbox": [ + 50, + 171, + 165, + 267 + ], + "lines": [ + { + "bbox": [ + 50, + 171, + 165, + 267 + ], + "spans": [ + { + "bbox": [ + 50, + 171, + 165, + 267 + ], + "type": "image", + "image_path": "5a0e013a93c29fc56bcd2808d6f44ed69014fda9edfb5b713789aa7f2625a09a.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 268, + 287, + 321 + ], + "lines": [ + { + "bbox": [ + 46, + 268, + 287, + 321 + ], + "spans": [ + { + "bbox": [ + 46, + 268, + 287, + 321 + ], + "type": "text", + "content": "Figure 7. (a) chew and smile are OoD samples from HMDB51, and ApplyEyeMakeup and ApplyLipstick are InD samples from UCF101. (b-d) Uncertainty distribution of each class in HMDB51. Class 1: chew, 2: smile, 3: golf, 4: shoot bow. Classes 1 and 2 are OoD while 3 and 4 are InD." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 168, + 171, + 281, + 267 + ], + "blocks": [ + { + "bbox": [ + 168, + 171, + 281, + 267 + ], + "lines": [ + { + "bbox": [ + 168, + 171, + 281, + 267 + ], + "spans": [ + { + "bbox": [ + 168, + 171, + 281, + 267 + ], + "type": "image", + "image_path": "cd41194f660b0ff9bf5afc5f4c7f967af85dbf81ba7b0d270e698f326dfa2b78.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + } + ], + "index": 3 + }, + { + "type": "table", + "bbox": [ + 51, + 323, + 282, + 411 + ], + "blocks": [ + { + "bbox": [ + 51, + 323, + 282, + 411 + ], + "lines": [ + { + "bbox": [ + 51, + 323, + 282, + 411 + ], + "spans": [ + { + "bbox": [ + 51, + 323, + 282, + 411 + ], + "type": "table", + "html": "
s(Qshuf)s(Qsc)AUROC↑AUPR↑FPR95↓Acc.↑
0.785.2563.9148.3476.98
0.50.786.0364.3643.7076.53
0.383.8060.4248.7675.50
079.5450.5954.4372.59
0.80.886.4365.5841.7576.53
0.90.983.1257.0446.8473.31
1182.0453.8251.8272.89
", + "image_path": "c4ab2ab086b9465c927d30057ba79a3fc1da9ea0e09b3ba7f4241d74e4bdc8bf.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "table_body" + } + ], + "index": 5 + }, + { + "bbox": [ + 59, + 412, + 273, + 423 + ], + "lines": [ + { + "bbox": [ + 59, + 412, + 273, + 423 + ], + "spans": [ + { + "bbox": [ + 59, + 412, + 273, + 423 + ], + "type": "text", + "content": "Table 4. Ablation study of similarity " + }, + { + "bbox": [ + 59, + 412, + 273, + 423 + ], + "type": "inline_equation", + "content": "s" + }, + { + "bbox": [ + 59, + 412, + 273, + 423 + ], + "type": "text", + "content": " for " + }, + { + "bbox": [ + 59, + 412, + 273, + 423 + ], + "type": "inline_equation", + "content": "{Q}_{shuf}" + }, + { + "bbox": [ + 59, + 412, + 273, + 423 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 59, + 412, + 273, + 423 + ], + "type": "inline_equation", + "content": "{Q}_{sc}" + }, + { + "bbox": [ + 59, + 412, + 273, + 423 + ], + "type": "text", + "content": " ." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 436, + 287, + 459 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 436, + 287, + 459 + ], + "spans": [ + { + "bbox": [ + 46, + 436, + 287, + 459 + ], + "type": "text", + "content": "OoD classes sharing similar appearance with InD classes like class 1 is further improved." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 460, + 287, + 533 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 460, + 287, + 533 + ], + "spans": [ + { + "bbox": [ + 46, + 460, + 287, + 533 + ], + "type": "inline_equation", + "content": "Q_{sp}" + }, + { + "bbox": [ + 46, + 460, + 287, + 533 + ], + "type": "text", + "content": " in Eq. 9 contains " + }, + { + "bbox": [ + 46, + 460, + 287, + 533 + ], + "type": "inline_equation", + "content": "Q_{shuf}" + }, + { + "bbox": [ + 46, + 460, + 287, + 533 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 460, + 287, + 533 + ], + "type": "inline_equation", + "content": "Q_{sc}" + }, + { + "bbox": [ + 46, + 460, + 287, + 533 + ], + "type": "text", + "content": ", so we analyze whether should we assign the same " + }, + { + "bbox": [ + 46, + 460, + 287, + 533 + ], + "type": "inline_equation", + "content": "s" + }, + { + "bbox": [ + 46, + 460, + 287, + 533 + ], + "type": "text", + "content": " for the shuffled video " + }, + { + "bbox": [ + 46, + 460, + 287, + 533 + ], + "type": "inline_equation", + "content": "Q_{shuf}" + }, + { + "bbox": [ + 46, + 460, + 287, + 533 + ], + "type": "text", + "content": " and other videos in the same class " + }, + { + "bbox": [ + 46, + 460, + 287, + 533 + ], + "type": "inline_equation", + "content": "Q_{sc}" + }, + { + "bbox": [ + 46, + 460, + 287, + 533 + ], + "type": "text", + "content": ". Tab. 4 shows that the same " + }, + { + "bbox": [ + 46, + 460, + 287, + 533 + ], + "type": "inline_equation", + "content": "s" + }, + { + "bbox": [ + 46, + 460, + 287, + 533 + ], + "type": "text", + "content": " have good enough performance. So we set the same " + }, + { + "bbox": [ + 46, + 460, + 287, + 533 + ], + "type": "inline_equation", + "content": "s" + }, + { + "bbox": [ + 46, + 460, + 287, + 533 + ], + "type": "text", + "content": " for " + }, + { + "bbox": [ + 46, + 460, + 287, + 533 + ], + "type": "inline_equation", + "content": "Q_{shuf}" + }, + { + "bbox": [ + 46, + 460, + 287, + 533 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 460, + 287, + 533 + ], + "type": "inline_equation", + "content": "Q_{sc}" + }, + { + "bbox": [ + 46, + 460, + 287, + 533 + ], + "type": "text", + "content": " in the default setting to reduce the number of hyper-parameters." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 539, + 119, + 551 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 539, + 119, + 551 + ], + "spans": [ + { + "bbox": [ + 47, + 539, + 119, + 551 + ], + "type": "text", + "content": "5.3. Discussion" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 557, + 287, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 557, + 287, + 712 + ], + "spans": [ + { + "bbox": [ + 46, + 557, + 287, + 712 + ], + "type": "text", + "content": "Both CS and IS information are useful. We provide the closed-set and open-set performance under different hyperparameter " + }, + { + "bbox": [ + 46, + 557, + 287, + 712 + ], + "type": "inline_equation", + "content": "s" + }, + { + "bbox": [ + 46, + 557, + 287, + 712 + ], + "type": "text", + "content": " and feature dimension " + }, + { + "bbox": [ + 46, + 557, + 287, + 712 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 46, + 557, + 287, + 712 + ], + "type": "text", + "content": " in Fig. 8. (a) shows that " + }, + { + "bbox": [ + 46, + 557, + 287, + 712 + ], + "type": "inline_equation", + "content": "s = 0.8" + }, + { + "bbox": [ + 46, + 557, + 287, + 712 + ], + "type": "text", + "content": " has better open-set performance than " + }, + { + "bbox": [ + 46, + 557, + 287, + 712 + ], + "type": "inline_equation", + "content": "s = 1" + }, + { + "bbox": [ + 46, + 557, + 287, + 712 + ], + "type": "text", + "content": " and has comparable closed-set accuracy, which illustrates that retaining the IS information which is eliminated by C.E. " + }, + { + "bbox": [ + 46, + 557, + 287, + 712 + ], + "type": "inline_equation", + "content": "(s = 1)" + }, + { + "bbox": [ + 46, + 557, + 287, + 712 + ], + "type": "text", + "content": " is beneficial. When " + }, + { + "bbox": [ + 46, + 557, + 287, + 712 + ], + "type": "inline_equation", + "content": "s < 0.8" + }, + { + "bbox": [ + 46, + 557, + 287, + 712 + ], + "type": "text", + "content": ", the NN cannot learn enough CS information, so both closed-set and open-set performance drops. Therefore, a proper mixture of CS and IS information is ideal. (b) shows that when " + }, + { + "bbox": [ + 46, + 557, + 287, + 712 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 46, + 557, + 287, + 712 + ], + "type": "text", + "content": " grows from 4 to 16, more CS information is contained so that both closed-set and open-set performance improves. When " + }, + { + "bbox": [ + 46, + 557, + 287, + 712 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 46, + 557, + 287, + 712 + ], + "type": "text", + "content": " grows from 16 to 128, the feature does not include more CS in" + } + ] + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 310, + 70, + 420, + 171 + ], + "blocks": [ + { + "bbox": [ + 310, + 70, + 420, + 171 + ], + "lines": [ + { + "bbox": [ + 310, + 70, + 420, + 171 + ], + "spans": [ + { + "bbox": [ + 310, + 70, + 420, + 171 + ], + "type": "image", + "image_path": "9220a62ace11c85ad1b96ae8083dbc023ebf04f764c93f016fac405fc69f5080.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 360, + 173, + 370, + 182 + ], + "lines": [ + { + "bbox": [ + 360, + 173, + 370, + 182 + ], + "spans": [ + { + "bbox": [ + 360, + 173, + 370, + 182 + ], + "type": "text", + "content": "(a)" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 11 + }, + { + "type": "image", + "bbox": [ + 424, + 70, + 539, + 173 + ], + "blocks": [ + { + "bbox": [ + 424, + 70, + 539, + 173 + ], + "lines": [ + { + "bbox": [ + 424, + 70, + 539, + 173 + ], + "spans": [ + { + "bbox": [ + 424, + 70, + 539, + 173 + ], + "type": "image", + "image_path": "139ec59e1462d2fd9a8807c51b43df4ac7c5063252ed767e06e4dc61e7ec8a9b.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 475, + 174, + 484, + 182 + ], + "lines": [ + { + "bbox": [ + 475, + 174, + 484, + 182 + ], + "spans": [ + { + "bbox": [ + 475, + 174, + 484, + 182 + ], + "type": "text", + "content": "(b)" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_caption" + } + ], + "index": 13 + }, + { + "type": "table", + "bbox": [ + 310, + 193, + 539, + 241 + ], + "blocks": [ + { + "bbox": [ + 307, + 182, + 542, + 192 + ], + "lines": [ + { + "bbox": [ + 307, + 182, + 542, + 192 + ], + "spans": [ + { + "bbox": [ + 307, + 182, + 542, + 192 + ], + "type": "text", + "content": "Figure 8. Ablation study of similarity " + }, + { + "bbox": [ + 307, + 182, + 542, + 192 + ], + "type": "inline_equation", + "content": "s" + }, + { + "bbox": [ + 307, + 182, + 542, + 192 + ], + "type": "text", + "content": " and feature dimension " + }, + { + "bbox": [ + 307, + 182, + 542, + 192 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 307, + 182, + 542, + 192 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 310, + 193, + 539, + 241 + ], + "lines": [ + { + "bbox": [ + 310, + 193, + 539, + 241 + ], + "spans": [ + { + "bbox": [ + 310, + 193, + 539, + 241 + ], + "type": "table", + "html": "
EpochMeanVarianceAUROC↑Acc-Test.↑Acc-Train.↑
2000.5773.3e-375.0868.3999.85
4000.6023.1e-382.9273.26100
8000.6133.0e-382.5473.29100
", + "image_path": "dab39e2182cb473f6318c09e7a0c3943bbe1d18573e3a8098a218ca908287b18.jpg" + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "table_body" + } + ], + "index": 16 + }, + { + "bbox": [ + 314, + 242, + 536, + 253 + ], + "lines": [ + { + "bbox": [ + 314, + 242, + 536, + 253 + ], + "spans": [ + { + "bbox": [ + 314, + 242, + 536, + 253 + ], + "type": "text", + "content": "Table 5. Training process analysis when " + }, + { + "bbox": [ + 314, + 242, + 536, + 253 + ], + "type": "inline_equation", + "content": "s = {0.6}\\mathrm{\\;w}/\\mathrm{o}{Q}_{shuf}" + }, + { + "bbox": [ + 314, + 242, + 536, + 253 + ], + "type": "text", + "content": " ." + } + ] + } + ], + "index": 17, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 304, + 264, + 545, + 347 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 264, + 545, + 347 + ], + "spans": [ + { + "bbox": [ + 304, + 264, + 545, + 347 + ], + "type": "text", + "content": "formation as closed-set accuracy is comparable. However, open-set performance keeps increasing which means more IS information is contained based on more feature dimensions. This interesting experiment shows that enough information for closed-set recognition is not enough for open-set recognition because IS information is not related to the closed-set task but useful for the open-set task." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 348, + 545, + 563 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 348, + 545, + 563 + ], + "spans": [ + { + "bbox": [ + 304, + 348, + 545, + 563 + ], + "type": "text", + "content": "Feature variance and open-set performance analysis. Fig. 8 (a) shows that when features get looser (" + }, + { + "bbox": [ + 304, + 348, + 545, + 563 + ], + "type": "inline_equation", + "content": "s = 1 - 0.8" + }, + { + "bbox": [ + 304, + 348, + 545, + 563 + ], + "type": "text", + "content": "), the open-set performance is improved, but if features get continually looser (" + }, + { + "bbox": [ + 304, + 348, + 545, + 563 + ], + "type": "inline_equation", + "content": "s = 0.8 - 0.1" + }, + { + "bbox": [ + 304, + 348, + 545, + 563 + ], + "type": "text", + "content": "), the open-set performance drops. So there is no strict relation between the feature variance and open-set performance. One may argue that continual training can benefit the open-set performance [50], which is alongside with smaller feature variance [51]. We show that the benefit of continual training comes from better closed-set performance, not tighter features. Tab. 5 shows that when we train the model from 200 to 400 epochs, the closed-set accuracy is higher, and feature is tighter (larger mean similarity and smaller variance), and the open-set performance is better. But from epoch 400 to 800 we find the model is already overfitted to the training set, as the accuracy of test set remains unchanged. So although the features get tighter in the 800 epoch, both the closed-set and open-set performance remain same." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 306, + 574, + 378, + 586 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 574, + 378, + 586 + ], + "spans": [ + { + "bbox": [ + 306, + 574, + 378, + 586 + ], + "type": "text", + "content": "6. Conclusion" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 304, + 594, + 545, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 594, + 545, + 689 + ], + "spans": [ + { + "bbox": [ + 304, + 594, + 545, + 689 + ], + "type": "text", + "content": "We analyze the OSAR problem from the information perspective, and show that cross-entropy tends to eliminate IS information and cannot fully learn CS information which are both useful for the open-set task. So we propose PSL to retain IS information and introduce shuffle videos into PSL to enlarge CS information. Comprehensive experiments demonstrate the effectiveness of our PSL and the importance of IS and CS information in the OSAR task." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 304, + 689, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 689, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 689, + 545, + 713 + ], + "type": "text", + "content": "Acknowledgements This work is supported by Alibaba Group through Alibaba Research Intern Program." + } + ] + } + ], + "index": 22 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "15302" + } + ] + } + ], + "index": 23 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 287, + 711 + ], + "type": "list", + "angle": 0, + "index": 17, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 123 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 123 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 123 + ], + "type": "text", + "content": "[1] Ji Lin, Chuang Gan, and Song Han. 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In ICLR, 2022. 8" + } + ] + } + ], + "index": 18 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "type": "text", + "content": "15304" + } + ] + } + ], + "index": 20 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 9 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Ensemble-Based Blackbox Attacks on Dense Prediction/1f7b1ddd-65c3-47e9-8398-1b94d1c9d1e3_content_list.json b/2023/Ensemble-Based Blackbox Attacks on Dense Prediction/1f7b1ddd-65c3-47e9-8398-1b94d1c9d1e3_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..834fd163cdf306cde8a3ecf13247b1d8bedcf1f8 --- /dev/null +++ b/2023/Ensemble-Based Blackbox Attacks on Dense Prediction/1f7b1ddd-65c3-47e9-8398-1b94d1c9d1e3_content_list.json @@ -0,0 +1,1566 @@ +[ + { + "type": "text", + "text": "Ensemble-based Blackbox Attacks on Dense Prediction", + "text_level": 1, + "bbox": [ + 207, + 130, + 763, + 150 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Zikui Cai*, Yaoteng Tan*, and M. Salman Asif \nUniversity of California Riverside", + "bbox": [ + 299, + 180, + 671, + 215 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "{zcai032,ytan073,sasif}@ucr.edu", + "bbox": [ + 344, + 219, + 620, + 233 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 268, + 313, + 284 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "We propose an approach for adversarial attacks on dense prediction models (such as object detectors and segmentation). It is well known that the attacks generated by a single surrogate model do not transfer to arbitrary (blackbox) victim models. Furthermore, targeted attacks are often more challenging than the untargeted attacks. In this paper, we show that a carefully designed ensemble can create effective attacks for a number of victim models. In particular, we show that normalization of the weights for individual models plays a critical role in the success of the attacks. We then demonstrate that by adjusting the weights of the ensemble according to the victim model can further improve the performance of the attacks. We performed a number of experiments for object detectors and segmentation to highlight the significance of the our proposed methods. Our proposed ensemble-based method outperforms existing blackbox attack methods for object detection and segmentation. Finally, we show that our proposed method can also generate a single perturbation that can fool multiple blackbox detection and segmentation models simultaneously. Code is available at https://github.com/CSIplab/EBAD.", + "bbox": [ + 75, + 301, + 473, + 619 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 650, + 209, + 666 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Computer vision models (e.g., classification, object detection, segmentation, and depth estimation) are known to be vulnerable to carefully crafted adversarial examples [4, 11, 16, 17, 46]. Creating such adversarial attacks is easy for whitebox models, where the victim model is completely known [14, 16, 24, 37, 55]. In contrast, creating adversarial attacks for blackbox models, where the victim model is unknown, remains a challenging task [1, 33, 54]. Most of the existing blackbox attack methods have been developed for classification models [10, 21, 35, 47]. Blackbox attacks for dense prediction models such as object detection and segmentation are relatively less studied [4, 17, 27], and most of the existing ones mainly focus on untargeted", + "bbox": [ + 75, + 676, + 468, + 875 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/93739e57f8193773619599eae7a2b10b2097bfbefc1409edf124328d01dc36bf.jpg", + "image_caption": [ + "Figure 1. Illustration of the targeted ensemble-based blackbox attack. (Top) Attack generated by a single surrogate model does not transfer on the victim blackbox model (person does not map to car). (Bottom) Attack generated by weight balancing and optimization can transfer on a variety of victim models (person is mapped to car)." + ], + "image_footnote": [], + "bbox": [ + 517, + 268, + 883, + 421 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "attacks [17]. Furthermore, a vast majority of these methods are based on transfer attacks, in which a surrogate (white-box) model is used to generate the adversarial example that is tested on the victim model. However, the success rate of such transfer-based attacks is often low, especially for targeted attacks [10, 21, 47].", + "bbox": [ + 496, + 506, + 893, + 595 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "In this paper, we propose and evaluate an ensemble-based blackbox attack method for objection detection and segmentation. Our method is inspired by three key observations: 1) targeted attacks generated by a single surrogate model are rarely successful; 2) attacks generated by an ensemble of surrogate models are highly successful if the contribution from all the models is properly normalized; and 3) attacks generated by an ensemble for a specific victim model can be further improved by adjusting the contributions of different surrogate models. The overall idea of the proposed work is illustrated in Fig. 1. Our proposed method can be viewed as a combination of transfer- and query-based attacks, where we can adjust the contribution based on the feedback from the victim model using a small number of queries (5–20 in our experiments). In contrast, conventional query-based attacks require hundreds or thousands of queries from the victim model [9, 19, 22, 49].", + "bbox": [ + 496, + 598, + 895, + 853 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "We conduct comprehensive experiments to validate our proposed method and achieve state-of-the-art performance for both targeted and untargeted blackbox attacks on ob-", + "bbox": [ + 498, + 854, + 893, + 900 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 810, + 44 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "* Equal contribution", + "bbox": [ + 96, + 886, + 202, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "4045", + "bbox": [ + 482, + 924, + 514, + 936 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "ject detection. Specifically, our proposed method attains $29 - 53\\%$ success rate using only 5 queries for targeted attacks on object detectors, whereas the current state-of-the-art method [4] achieves $20 - 39\\%$ success rate with the same number of queries. Furthermore, we extend our evaluation to untargeted and targeted attacks on blackbox semantic segmentation models. Our method achieves $0.9 - 1.55\\%$ mIoU for untargeted and $69 - 95\\%$ pixel-wise success for targeted attacks. By comparison, the current state-of-the-art method [17] obtains $0.6 - 7.97\\%$ mIoU for untargeted attacks and does not report results for targeted attacks. To the best of our knowledge, our work is the first approach for targeted and query-based attacks for semantic segmentation.", + "bbox": [ + 75, + 90, + 472, + 287 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Below we summarize main contributions of this work.", + "bbox": [ + 96, + 287, + 454, + 301 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- We design a novel framework that can effectively attack blackbox dense prediction models based on an ensemble of surrogate models.", + "- We propose two simple yet highly effective ideas, namely weight balancing and weight optimization, with which we can achieve significantly better attack performance compared to existing methods.", + "- We extensively evaluate our method for targeted and untargeted attacks on object detection and semantic segmentation models and achieve state-of-the-art results.", + "- We demonstrate that our proposed method can generate a single perturbation that can fool multiple blackbox detection and segmentation models simultaneously." + ], + "bbox": [ + 76, + 306, + 468, + 513 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related work", + "text_level": 1, + "bbox": [ + 76, + 527, + 212, + 542 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Blackbox adversarial attacks. In the context of blackbox attacks, the attacker cannot access the model parameters or compute the gradient via backpropagation. Blackbox attack methods can be broadly divided into two groups: transfer-based [25, 33, 39, 40] and query-based attacks [9, 22, 49]. Transfer-based attacks rely on the assumption that surrogate models share similarities with the victim model, such that an adversarial example generated for the surrogate model can also fool the victim model. Query-based methods generate attacks by searching the adversarial examples space based on the feedback obtained from the victim model through queries. They can often achieve higher success rate but may require a large number of queries.", + "bbox": [ + 75, + 551, + 468, + 750 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Ensemble-based attacks. Ensemble-based attacks leverage the idea of transfer attack and assume that if an adversarial example can fool multiple models simultaneously, the chances of fooling an unseen model are higher [14, 33, 56]. Recently, some methods have combined ensemble-based transfer attacks with limited feedback from the victim models to improve the overall success rate [19, 21, 26, 35, 45, 47]. These methods have mainly focused on classification models, and ensemble attacks on dense prediction tasks such as object detection and semantic segmentation are relatively", + "bbox": [ + 75, + 750, + 470, + 901 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "less studied, especially for targeted attacks [52].", + "bbox": [ + 498, + 90, + 816, + 106 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Attacks against object detectors and segmentation. Dense (pixel-level) prediction tasks such as object detection and semantic segmentation have higher task complexities [50] compared to classification tasks. Existing attacks on object detectors mainly focus on whitebox setting, although there are a few exceptions [3, 51]. A recent study [4] generates blackbox attacks on object detectors by using a surrogate ensemble and context-aware attack-based queries. Another approach [51] trains a generative model to generate transferable attacks. While some patch-based attacks [32, 44] are effective, the patches are easily noticeable. Recent works [17, 18] have investigated adversarial robustness for semantic segmentation and proposed a transferable untargeted attack using a single surrogate model. While most existing methods are based on a single surrogate model, we demonstrate that using multiple surrogates with weight balancing/search in the attack generation process, we can generate more effective adversarial examples for both untargeted and targeted scenarios, as well as for various types of dense prediction tasks.", + "bbox": [ + 496, + 107, + 890, + 409 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "3. Method", + "text_level": 1, + "bbox": [ + 500, + 425, + 589, + 440 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "3.1. Preliminaries", + "text_level": 1, + "bbox": [ + 500, + 450, + 638, + 465 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "We consider a per-instance attack scenario in which we generate adversarial perturbation $\\delta$ for a given image $x$ . To keep the perturbation imperceptible, we bound its $\\ell_p$ norm as $\\| \\delta \\|_p \\leq \\varepsilon$ . In our experiments, we mainly use $\\ell_{\\infty}$ or max norm that limits the maximum level of perturbation. Our goal is to find $\\delta$ such that the perturbed image, $x^{\\star} = x + \\delta$ , can disrupt a victim image recognition system $f_{\\mathbf{v}}$ to make wrong predictions. Suppose the original prediction for the clean image $x$ is $y = f_{\\mathbf{v}}(x)$ . The attack goal is $f(x^{\\star}) \\neq y$ for untargeted attack, and $f(x^{\\star}) = y^{\\star}$ for targeted attack, where $y^{\\star}$ is the desired output (e.g., label or bounding box or segmentation map).", + "bbox": [ + 496, + 474, + 890, + 656 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "For classification models, the label $y \\in \\mathbb{R}$ is a scalar. However, dense prediction models can have more complex output space. For object detection, the variable-length output $y \\in \\mathbb{R}^{K \\times 6}$ , where $K$ is the number of detected objects, and each object label and position are encoded in a vector of length 6 that include the object category, bounding box coordinates, and confidence score. Some other tasks like keypoint detection and OCR are similar to object detection. For semantic segmentation, the prediction $y \\in \\mathbb{R}^{H \\times W}$ is per-pixel classification, where $H$ and $W$ are the height and width of the input image, respectively. Depth and optical flow estimation tasks have similar output structure.", + "bbox": [ + 496, + 657, + 890, + 838 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "The adversarial loss functions for object detection and semantic segmentation can be defined using their respective training or prediction loss functions. Let us consider a whitebox model $f$ and an input image $x$ with output", + "bbox": [ + 496, + 839, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "4046", + "bbox": [ + 482, + 924, + 514, + 936 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "$y = f(x)$ . For untargeted attack, we can search for the adversarial example $x^{\\star}$ by solving the following maximization problem:", + "bbox": [ + 76, + 90, + 468, + 135 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nx ^ {\\star} = \\underset {x} {\\operatorname {a r g m a x}} \\mathcal {L} (f (x), y), \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 176, + 148, + 468, + 172 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\mathcal{L}(f(x),y)$ represents the training loss of the model with input $x$ and output $y$ . For targeted attacks, with a target output $y^{\\star}$ , we solve the following minimization problem:", + "bbox": [ + 76, + 185, + 468, + 231 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nx ^ {\\star} = \\underset {x} {\\operatorname {a r g m i n}} \\mathcal {L} (f (x), y ^ {\\star}). \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 174, + 243, + 468, + 267 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Different from classification, which mostly use cross-entropy loss across different models, dense predictions have different loss functions for different models due to the complexity of the output space and diversity of the architectures. For example, two-stage object detector, including Faster RCNN [43], has losses for object classification, bounding box regression, and losses on the region proposal network (RPN). But for one-stage object detectors like YOLO [41,42], they do not have losses corresponding to RPN. Due to the large variability of the loss functions used in different dense prediction models, we use the corresponding training loss $\\mathcal{L}$ for each model as the optimization loss to guide the backpropagation.", + "bbox": [ + 75, + 279, + 468, + 474 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We employ PGD [37] to optimize the perturbation as", + "bbox": [ + 96, + 474, + 446, + 489 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\delta^ {t + 1} = \\Pi_ {\\varepsilon} \\left(\\delta^ {t} - \\lambda \\operatorname {s i g n} \\left(\\nabla_ {\\delta} \\mathcal {L} \\left(f \\left(x + \\delta^ {t}\\right), y ^ {\\star}\\right)\\right)\\right), \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 99, + 502, + 468, + 520 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "for targeted attack and", + "bbox": [ + 76, + 532, + 227, + 546 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\delta^ {t + 1} = \\Pi_ {\\varepsilon} \\left(\\delta^ {t} + \\lambda \\operatorname {s i g n} \\left(\\nabla_ {\\delta} \\mathcal {L} (f (x + \\delta^ {t}), y)\\right)\\right), \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 102, + 559, + 468, + 577 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "for untargeted attack. Here $t$ indicates the attack step, $\\lambda$ is the step size, and $\\Pi_{\\varepsilon}$ projects the perturbation into a $\\ell_p$ norm ball with radius $\\varepsilon$ . In the rest of the paper, we focus on targeted attacks without loss of generalization.", + "bbox": [ + 76, + 589, + 468, + 650 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. Ensemble-based attacks", + "text_level": 1, + "bbox": [ + 76, + 660, + 295, + 674 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In an ensemble-based transfer attack, we use an ensemble of $N$ surrogate (whitebox) models: $\\mathcal{F} = \\{f_1,\\dots ,f_N\\}$ to generate perturbations to attack the victim model $f_{\\mathbf{v}}$ . Note that if the ensemble has a single model, then such an attack becomes a simple transfer attack with a single surrogate model. Let us denote the training loss function for $i$ th model as $\\mathcal{L}_i(f_i(x),y^*)$ . A natural approach to combine the loss functions of all surrogate models is to compute an average or weighted average of the individual loss functions. For instance, we can generate the adversarial image by solving the following optimization problem:", + "bbox": [ + 75, + 684, + 468, + 849 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nx ^ {\\star} (\\alpha) = \\underset {x} {\\arg \\min } \\sum_ {i = 1} ^ {N} \\alpha_ {i} \\mathcal {L} _ {i} \\left(f _ {i} (x), y ^ {\\star}\\right), \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 138, + 863, + 468, + 902 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/889d58ca82bf9620b14c67f1477290eec90f29cb8aa1c102214d9ec432c388bd.jpg", + "image_caption": [ + "Figure 2. Distribution of losses for different object detection models. $\\mathbb{P}(\\mathcal{L}_i(f_i(x),y^\\star))$ . Calculated on 500 images from VOC dataset." + ], + "image_footnote": [], + "bbox": [ + 557, + 93, + 831, + 234 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $x^{\\star}(\\alpha)$ is a function of the weights of the ensemble $\\alpha = \\{\\alpha_{1},\\ldots ,\\alpha_{N}\\}$ . One of our key observations is that the choice of weights plays a critical role in the transfer attack success rate of the ensemble models.", + "bbox": [ + 498, + 270, + 890, + 330 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Weight balancing (victim model agnostic). In ensemble-based transfer attacks, we build on the intuition that if an adversarial example can fool all models simultaneously, it would potentially be more transferable to any unseen victim model. This concept has been empirically corroborated by numerous works [14, 33]. However, most attack methods have only been verified on classification models, all of which use the same cross-entropy loss and yield similar loss values. In contrast, the loss functions for object detectors in an ensemble can differ significantly and cover a large range of values (as shown in Fig. 2). In such cases, models with large loss terms heavily influence the optimization procedure, reducing the attack success rate for models with small losses (see Tab. 1). To overcome this issue, we propose a simple yet effective solution to balance the weights assigned to each model in the ensemble as follows. For each input image $x$ and target output $y^{\\star}$ , we adjust the weight for $i$ th surrogate model loss as", + "bbox": [ + 498, + 330, + 890, + 602 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\alpha_ {i} = \\frac {\\sum_ {i = 1} ^ {N} \\mathcal {L} _ {i} \\left(f _ {i} (x) , y ^ {\\star}\\right)}{N \\mathcal {L} _ {i} \\left(f _ {i} (x) , y ^ {\\star}\\right)}. \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 604, + 613, + 890, + 648 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The weights are adjusted in a whitebox setting as it allows us to measure the loss of each whitebox model accurately. The purpose of weight balancing is to ensure that all surrogate models can be successfully attacked, making the generated example more adversarial for blackbox victim models. Weight optimization (victim model specific). Note that the weight normalization, as discussed above, is agnostic to the victim model. We further observe that such transfer-based attacks can be further improved by optimizing the weights of the ensemble according to the victim model, input image, and target output. In particular, we can change the individual $\\alpha_{i}$ to create the perturbations that reduce the victim model loss $\\mathcal{L}_{\\mathbf{v}}$ . To achieve this goal, we need to solve the following optimization problem with respect to $\\alpha$ :", + "bbox": [ + 498, + 657, + 890, + 868 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\alpha^ {\\star} = \\underset {\\alpha} {\\arg \\min } \\mathcal {L} _ {\\mathrm {v}} \\left(f _ {\\mathrm {v}} \\left(x ^ {\\star} (\\alpha)\\right), y ^ {\\star}\\right). \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 571, + 878, + 890, + 902 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "4047", + "bbox": [ + 480, + 926, + 514, + 936 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The optimization problem in (7) is a nested optimization that we can solve as an alternating minimization routine.", + "bbox": [ + 75, + 90, + 467, + 119 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Step 0. Given input $x$ , output $y^{\\star}$ , and surrogate ensemble $\\mathcal{F}$ , we initialize $\\alpha$ using (6).", + "bbox": [ + 75, + 121, + 467, + 151 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Step 1. Solve (5) to generate an adversarial example $x^{\\star}(\\alpha)$ . Step 2. Test the victim model. Stop if attack is successful; otherwise, change one of the $\\alpha_{i}$ and repeat Step 1.", + "bbox": [ + 75, + 151, + 467, + 196 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In our experiments, we update the $\\alpha_{i}$ in a cyclic manner (one coordinate at a time) as $\\alpha_{i} \\pm \\gamma$ in Step 2, where $\\gamma$ denotes a step size. In every round, we select the value of $\\alpha_{i}$ that provides smallest value of the victim loss. We count the number of queries as the number of times we test the generated adversarial example on the victim model and denote it as $Q$ in our experiments.", + "bbox": [ + 75, + 196, + 467, + 301 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 76, + 316, + 207, + 334 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "To evaluate the effectiveness of our method, we performed extensive experiments on attacking various object detection and semantic segmentation models. We first show that the attacks generated by a single surrogate model fail to transfer to arbitrary victim models. Then we show that the attack transfer rate can be increased by using an ensemble with weight balancing. Additional optimization of the weights surrogates for each victim model can further improve the attack performance. Finally, we show that we can generate single perturbations to fool object detectors and semantic segmentation models simultaneously.", + "bbox": [ + 75, + 343, + 467, + 508 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4.1. Experiment setup", + "text_level": 1, + "bbox": [ + 76, + 520, + 250, + 536 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4.1.1 Object detection", + "text_level": 1, + "bbox": [ + 76, + 542, + 245, + 558 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Models and datasets. We utilize MMDetection [7] toolbox to select various model architectures and weights pre-trained on COCO 2017 dataset [30]. To construct the surrogate ensemble, we start with two widely used models, Faster R-CNN [43] and YOLO [41, 42], and expand the ensemble by appending models with different architectures, including {FCOS [48], Grid R-CNN [36], SSD [31]}. We select different victim models, including {RetinaNet [29], Libra R-CNN [38], FoveaBox [23], FreeAnchor [59], DETR [6]}}. We evaluate attack performance on COCO 2017 [30] and Pascal VOC 2007 [15] datasets. Since the models from this repository are trained on COCO, which contains 80 object categories (a superset of VOC dataset's 20 categories), while testing on VOC dataset, we only return the objects that exist in VOC. We follow the setup in [4] and randomly select 500 images containing multiple (2-6) objects from VOC 2007 test and COCO 2017 validation sets.", + "bbox": [ + 75, + 566, + 467, + 838 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Evaluation metrics. We mainly focus on targeted attacks for object detection since they are more challenging than untargeted or vanishing attacks. We measure the performance of the attack using attack success rate (ASR), which", + "bbox": [ + 75, + 839, + 467, + 900 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "equals the number of successfully attacked images over the total number of attacks. We follow the setting in [4], where if the target label is detected within the victim object region with IOU $>0.3$ , the attack is determined a success.", + "bbox": [ + 496, + 90, + 890, + 150 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Perturbation and query budget. We tested different perturbation levels with $\\ell_{\\infty} = \\{10,20,30\\}$ out of 255. We use at most 10 queries for attacking object detectors, and we show the trends of how ASR increases with the number of queries. To align with [4] that uses 5 attack plans, we set the maximum query budget to $Q = 5$ in Tab. 1.", + "bbox": [ + 496, + 152, + 890, + 242 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Comparing methods. We compare with [4], which is a state-of-the-art transfer-based approach that leverages context information to design attack plans to iteratively attack the victim object. The method generates different perturbations by iterating over a set of predefined attacks, and the total number of queries is the number of attempted attacks. BASES [3] is a recent work on ensemble-based blackbox attacks, which mainly focused on classification tasks and did not consider the loss distributions of different surrogate models. In our experiments, the ensemble with weight optimization and without balancing is equivalent to BASES [3].", + "bbox": [ + 496, + 244, + 890, + 409 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4.1.2 Semantic segmentation", + "text_level": 1, + "bbox": [ + 498, + 434, + 714, + 449 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Models and datasets. We use MMSegmentation [12] toolbox to select different model architectures and weights pre-trained on Cityscapes [13] ( $x \\in \\mathbb{R}^{512 \\times 1024 \\times 3}$ ) and Pascal VOC ( $x \\in \\mathbb{R}^{512 \\times 512 \\times 3}$ ) datasets. We select PSPNet [60] and DeepLabV3 [8] with ResNet50 and ResNet101 [20] backbones as our blackbox victim models. For the surrogate ensemble, we start with the primary semantic segmentation model FCN [34], and expand the ensemble with {UPerNet [53], PSANet [61], GCNet [5], ANN [62], EncNet [57]}. All models are built on ResNet50 [20] backbone trained with the cross-entropy loss. The loss values across all surrogate models have similar range; therefore, the effect of weight balancing for semantic segmentation is not as significant as it is for object detection. We use validation datasets from Cityscapes [13] and Pascal VOC 2012, which contains 500 and 1499 images with 19 and 21 classes, respectively.", + "bbox": [ + 496, + 459, + 890, + 715 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Evaluation metrics. We use different metrics for untargeted and targeted attack performance evaluation. In untargeted experiments, the attack performance is evaluated using the mIoU score (in percentage $\\%$ ), the lower mIoU score the better attack performance. For targeted experiments, we report the pixel success ratio (PSR), which indicates the percentage of pixels successfully assigned the desired label in the target region, the higher the better attack performance.", + "bbox": [ + 496, + 717, + 890, + 838 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Perturbation and query budget. We use the perturbation budget $\\ell_{\\infty} \\leq 8$ out of 255 and query budget $Q = 20$ .", + "bbox": [ + 496, + 839, + 890, + 869 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Comparing methods. We compare with dynamic scale (DS) attack [17] which is the most recent method that", + "bbox": [ + 498, + 869, + 890, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "4048", + "bbox": [ + 480, + 924, + 514, + 936 + ], + "page_idx": 3 + }, + { + "type": "table", + "img_path": "images/b9fe398fba2f48d85812a9ecfdc0c7ea1578f0c04aabec090ef56132da4dfb3a.jpg", + "table_caption": [ + "Table 1. Targeted attack success rate (%) of different methods at different perturbation budgets on VOC dataset. For each perturbation level, the first 4 rows correspond to different settings of our attacks, i.e. with (✓) or without (✗) weight balancing and weight optimization. We show comparison with context-aware attack [4], the state-of-the-art method for query-based blackbox attacks." + ], + "table_footnote": [], + "table_body": "
Perturbation BudgetWeight BalancingWeight OptimizationSurrogate EnsembleBlackbox Victim Models (ASR ↑)
FRCNNYOLOv3RetinaLibraFoveaFreeDETR
l∞=10XX27.991.511.69.29.013.45.6
X✓61.499.424.328.022.431.015.4
✓X71.185.730.933.427.236.012.2
✓✓86.096.953.256.647.257.429.0
Context-aware Attack [4]55.875.622.620.433.639.220.2
l∞=20XX40.192.216.920.415.423.29.7
X✓77.799.841.045.437.847.022.5
✓X82.789.841.050.444.857.021.6
✓✓94.698.066.974.468.079.448.0
Context-aware Attack [4]78.687.235.238.451.656.634.0
l∞=30XX43.491.117.122.617.427.211.4
X✓82.799.647.254.847.057.433.4
✓X85.390.248.856.845.659.629.2
✓✓96.098.178.982.876.883.058.8
Context-aware Attack [4]80.688.042.044.256.863.640.2
", + "bbox": [ + 140, + 137, + 831, + 378 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/bf23be9877ea494142a9129da7d6bf2bd199fdfc91701662f371beca1bf4ab55.jpg", + "image_caption": [ + "(a) $\\ell_{\\infty}\\leq 10$" + ], + "image_footnote": [], + "bbox": [ + 107, + 393, + 346, + 539 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/9b0fe3173b86f53f13c892bf9bc9a9d65eeccca60dfffa7b60d26167ff85ce86.jpg", + "image_caption": [ + "(b) $\\ell_{\\infty}\\leq 20$" + ], + "image_footnote": [], + "bbox": [ + 364, + 393, + 604, + 537 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/644f5928c385c4850f91a9d08c9c0a1f365f494ae69416d37584902a7dc022c4.jpg", + "image_caption": [ + "(c) $\\ell_{\\infty}\\leq 30$", + "Figure 3. Attack success rate (or fooling rate) vs number of queries $(Q)$ . The maximum value of $Q$ is set to 10 for these results." + ], + "image_footnote": [], + "bbox": [ + 625, + 393, + 864, + 539 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "achieves the highest attack transfer rate on semantic segmentation untargeted attacks.", + "bbox": [ + 75, + 609, + 468, + 640 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.2. Attacks against object detection", + "text_level": 1, + "bbox": [ + 76, + 648, + 357, + 666 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Following settings in [4], we randomly select one object from the output of victim model as the victim object and perturb it into a target object that does not exist in the original detection. This approach rules out the possibility of mis-counting existing objects as the target object.", + "bbox": [ + 75, + 672, + 468, + 750 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We report our main results in Tab. 1. The baseline method uses a surrogate ensemble without weight balancing and models are assigned weight of 1. Such a baseline method is same a transfer-based method and results in highly imbalanced success rate for different surrogate models. For instance, at $\\ell_{\\infty} \\leq 10$ , the success rate for YOLOv3 is above $90\\%$ while the success rate for Faster R-CNN is less than $30\\%$ . Low success rate on surrogate side translates to low success rate on blackbox victim side. The main reason for such imbalance is that the loss of dif", + "bbox": [ + 75, + 750, + 470, + 900 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "ferent object detectors can be highly unbalanced (e.g., the loss value for YOLOv3 is nearly $60\\times$ larger than the loss of Faster RCNN for targeted attacks, cf. Fig. 2). With weight balancing, the success rate increases for surrogate and blackbox victim models. The success rate is further increased on surrogate and victim blackbox models if we optimize the weights, same as BASES [3]. Our method (with weight balancing and optimization) achieves a significantly higher ASR compared to context-aware attack across different datasets and different perturbation budgets. On average, our ASR on blackbox victim models is over $4\\times$ better than baseline method and over $1.5\\times$ better than context-aware attack. On whitebox surrogate models, weight balancing and optimization also achieves the highest ASR. Context-aware attack fixes weight ratio for surrogate models, $\\alpha_{\\mathrm{FRCNN}} / \\alpha_{\\mathrm{YOLO}} = 4$ , which is sub-optimal according to our analyses. Even though it achieves much higher performance than baseline, it still largely under-performs our method. Similar trend is observed for COCO dataset (see Tab. S1).", + "bbox": [ + 496, + 608, + 890, + 896 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "4049", + "bbox": [ + 480, + 926, + 514, + 936 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/ae8853e94db1cab6abd77fa2014cc510408b5c1990dcf0932c8ff942c294ee35.jpg", + "table_caption": [ + "Table 2. Targeted ASR (%) for blackbox victim models and whitebox surrogate models with different ensemble sizes (N). On VOC dataset, ${\\ell }_{\\infty } \\leq {10}$ ." + ], + "table_footnote": [], + "table_body": "
NSurrogate EnsembleBlackbox Victim Models (ASR ↑)
FRCNNYOLOv3FCOSGrid R-CNNSSDRetinaLibraFoveaFreeDETR
174.7----31.331.229.840.410.6
286.096.9---53.256.647.257.429.0
387.996.174.2--63.162.057.366.638.0
489.694.775.287.9-68.771.067.674.449.6
589.791.873.586.182.468.970.268.477.653.2
", + "bbox": [ + 161, + 114, + 807, + 215 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/6edf3798048fd7118740e5c0c68af1af5b0b1ff3615566035775c0e142802e82.jpg", + "table_caption": [ + "Table 3. Untargeted attack mIoU scores (%) of ensemble sizes $N = 2,4,6$ on Cityscapes dataset. We compare $Q = 0$ (i.e. direct transfer attack) with $Q = 20$ ensemble attack performance. DS uses DeepLabV3-Res50 (DL3-50) as the surrogate model for attack generation; thus the DS on DL3-50 is a whitebox attack. While our method used an ensemble that does not include any victim models for attack generation, we still achieved comparable mIoU scores to DS on DL3-50. Blue numbers represent whitebox attacks." + ], + "table_footnote": [], + "table_body": "
MethodWhitebox SurrogateBlackbox Victim Models (mIoU ↓)
PSPNet-Res50PSPNet-Res101DeepLabV3-Res50DeepLabV3-Res101
Clean Images-77.9278.2879.1277.12
BaselinePSPNet-Res503.4324.185.0525.74
DeepLabV3-Res504.7621.723.9222.23
DS [17]PSPNet-Res500.828.041.369.00
DeepLabV3-Res501.237.970.617.11
Ours (Q=0)N=25.078.325.198.74
N=44.336.264.326.33
N=63.624.914.024.84
Ours (Q=20)N=21.382.881.153.50
N=40.792.040.731.80
N=60.901.550.941.09
", + "bbox": [ + 107, + 289, + 864, + 474 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/9841868574528a628705e29c53dc9e2b997a3a2b7217379ea4c17287d49e0b92.jpg", + "table_caption": [ + "Table 4. Targeted attack performance on Cityscapes as pixel success rate (higher the better). The attack performance increases as we increase ensemble size $(N)$ and number of queries for weight optimization $(Q)$ . $N = 1$ has zero query. We note PSPNet-Res50 as PSP-r50, and DeepLabV3-Res50 as DL3-r50, similar abbreviations apply to Res101." + ], + "table_footnote": [], + "table_body": "
QNBlackbox Victim Models (PSR ↑)
PSP-r50PSP-r101DL3-r50DL3-r101
0139.1510.2135.027.58
252.1512.2847.9910.59
343.1711.3442.109.87
451.4426.1349.1417.42
552.2423.8851.7516.08
20283.9751.8082.7046.95
388.8864.6385.5560.88
491.5164.2887.1963.88
592.9169.0988.9569.65
", + "bbox": [ + 89, + 578, + 457, + 734 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Fig. 3 shows the effect of the number of queries on the ASR that gradually improves as we optimize the weights. We observe the largest increase in the first two steps and then the improvement plateaus as $Q \\to 10$ .", + "bbox": [ + 76, + 763, + 467, + 823 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We also conducted an experiment to test our method with varying ensemble sizes. The results for $\\ell_{\\infty} \\leq 10$ , $Q = 5$ are presented in Tab. 2. As we increase the number of models in the ensemble from $N = 1$ to $N = 5$ , we observe an increased ASR on all blackbox victim models.", + "bbox": [ + 76, + 825, + 467, + 898 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.3. Attacks against semantic segmentation", + "text_level": 1, + "bbox": [ + 500, + 500, + 831, + 515 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We evaluate the effectiveness of our attack on semantic segmentation in both untargeted and targeted settings. For the sake of consistency and a fair comparison, we adopt adversarial attack settings in DS attack [17].", + "bbox": [ + 498, + 530, + 890, + 590 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Untargeted attacks. We generate adversarial attacks using different ensemble sizes and report mIoU scores on Cityscapes in Tab. 3 and Fig. 4 (and Pascal VOC in supplementary material). In the untargeted setting, semantic segmentation models are attacked to maximize the loss between clean and modified annotation; hence, the lower mIoU implies better attack performance. All of the victim models achieve high performance on clean images. The baseline method (direct transfer attack with one surrogate model using PGD) performs well in the whitebox setting but suffers when the victim uses another backbone. For example, the attacks generated on PSPNet-Res50 achieves $3.43\\%$ mIoU on PSPNet-Res50 but only attains $24.18\\%$ mIoU on PSPNet-Res101. DS attack achieves better results than the baseline method but still suffers from crossbackbone transfers. On the other hand, our method, without weight optimization (i.e., $Q = 0$ ) and using a surrogate ensemble of $N = 2$ models, can achieve results comparable to DS attack, particularly for attacks on Res101 models. As we increase the number of surrogate models to 4 or 6, our", + "bbox": [ + 496, + 598, + 892, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "4050", + "bbox": [ + 480, + 926, + 514, + 936 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/6bebcb55ed5cc7a2bb00b16f301eb8447883c77b2f756dace29bfe42398bf41c.jpg", + "image_caption": [ + "(a) $N = 2$" + ], + "image_footnote": [], + "bbox": [ + 109, + 104, + 330, + 239 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/689f07dde1e9b9fea8f0a1e283c20ccd5c04bcf810a36713d5af13bf6ac958bd.jpg", + "image_caption": [ + "(b) $N = 4$" + ], + "image_footnote": [], + "bbox": [ + 367, + 104, + 588, + 239 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/655a64495db1d8d9e69cb84ac560a39fb6bd7e0960a8532d64dabdbf8f604ad1.jpg", + "image_caption": [ + "(c) $N = 6$", + "Figure 4. mIoU vs number of queries $(Q)$ for different ensemble sizes $(N)$ ." + ], + "image_footnote": [], + "bbox": [ + 627, + 104, + 846, + 239 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "attack performance further improves. Furthermore, when we apply weight optimization (e.g., $Q = 20$ ), the attack improves by updating the weights of the surrogate models, allowing us to outperform DS attack for all victim models. Fig. 4 shows how the mIoU changes with the number of queries. We observe that the mIoU gradually reduces as we query the victim model and optimize the weights. The largest decrease happens in the first 3-4 steps and then the reduction plateaus as $Q \\to 20$ .", + "bbox": [ + 75, + 294, + 468, + 429 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Targeted attack. To evaluate our method in a more challenging setting, we consider a targeted attack scenario, where instead of changing every pixel in the segmentation to some arbitrary label, we focus on attacking a dominant class (i.e., the class occupying the largest area) in the scene to its least likely class $y^{\\star}$ . For each clean image, we first select a region with the dominant class $y$ (e.g., \"road\" or \"building\" for most of the Cityscapes images. See Fig. S3 as an example). Then based on the least-likely class of each pixel in that region, we select the class that appears most frequently as the target label $y^{\\star}$ of the entire region. We use PSR as our evaluation metric, which represents the percentage of pixels in the selected region that are successfully assigned to $y^{\\star}$ . The higher percentage indicates more pixels are successfully attacked to the desired class, which indicates better attack performance. Our targeted attack results are reported in Tab. 4. Results show that as we increase the number of surrogate models ( $N$ ), the ASR improves for most instances without any weight optimization step (i.e., $Q = 0$ ). If we perform weight optimization for $Q = 20$ steps, then the success rate increases for all the models. For instance, with $N = 4$ , the ASR for Res101 models increases from 17–26% to 63–64%.", + "bbox": [ + 75, + 430, + 472, + 777 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.4. Joint attack for multiple models and tasks", + "text_level": 1, + "bbox": [ + 76, + 786, + 434, + 801 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We first show that generally adversarial examples generated for object detection do not transfer to semantic segmentation, and vice versa. Then we show that we can generate single perturbations to fool object detectors and semantic segmentation models simultaneously, by using a surrogate ensemble including both detection and segmentation mod", + "bbox": [ + 75, + 810, + 468, + 901 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "els. We choose targeted attacks in our experiments because they are more challenging than untargeted attacks.", + "bbox": [ + 496, + 294, + 890, + 324 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Experiment setup. On the blackbox (victim) side, we tested RetinaNet as the victim object detector and PSPNet-Res50 as the victim semantic segmentation model. On the whitebox (surrogate) side, we used Faster RCNN, YOLOv3 as the surrogate object detectors and FCN, UPerNet as the surrogate semantic segmentation models. We performed targeted attacks on 500 test images selected from the validation set of CityScapes dataset.", + "bbox": [ + 496, + 325, + 892, + 445 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Results. We present the ASRs for task-specific and joint attacks in Fig. 5. Green curves denote ASR for object detectors, and blue curves denote PSR for semantic segmentation. Fig. 5a presents the results when we generate attacks using an object detector surrogate ensemble. Note that success rate for victim object detector (RetinaNet) increases as we optimize the weights but the success rate for the semantic segmentation model (PSPNet) remains small. Similarly, Fig. 5b presents the results when we generate attacks using a segmentation surrogate ensemble. The success rate for the victim semantic segmentation model increases, but the success rate for the object doctor remains close to zero. Fig. 5c presents the results when we perform a joint attack using an ensemble that consists of both object detectors and segmentation models. The blackbox ASR is high on both detection and segmentation Fig. 5c, and the attack performance improves as we update the weights of the surrogate models. In Fig. 5c, we show the results for different perturbation budgets, with $\\ell_{\\infty} \\leq 10$ , the success rates on detection and segmentation are between $60\\% - 70\\%$ , which are close to in-domain detection attacks in Fig. 5a and indomain segmentation attacks Fig. 5b. When we increase the perturbation to $\\ell_{\\infty} \\leq 20$ , the success rate for both detection and segmentation can surpass $80\\%$ .", + "bbox": [ + 496, + 446, + 892, + 808 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Visualization of adversarial examples. In this example, our goal is to perturb the car in the middle to a traffic light. We assign the target label for car region to traffic light. Fig. 6a shows the results where a single adversarial image generated by the surrogate model can successfully fool the blackbox models RetinaNet and PSPNet.", + "bbox": [ + 496, + 810, + 890, + 898 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "4051", + "bbox": [ + 482, + 926, + 513, + 936 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/c9895fc8f9ffc64509809a6f8e394840ed1ca79e5e91fd28662ee9fe5f222d78.jpg", + "image_caption": [ + "(a) Attacks generated for object detection only, $\\ell_{\\infty}\\leq 10$" + ], + "image_footnote": [], + "bbox": [ + 106, + 97, + 344, + 242 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/70b43ba3141826aa03c9844f8dd9f83cbb4283514c9e04865cee9ba41573286a.jpg", + "image_caption": [ + "(b) Attacks generated for semantic segmentation only, $\\ell_{\\infty}\\leq 10$" + ], + "image_footnote": [], + "bbox": [ + 364, + 97, + 604, + 241 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/eab51f90d6955e39e012ecf8a559c349c8b3bed87ba32017409de27e8338b72b.jpg", + "image_caption": [ + "(c) Attacks generated jointly for object detection and semantic segmentation, $\\ell_{\\infty} \\leq \\{10, 20\\}$" + ], + "image_footnote": [], + "bbox": [ + 625, + 92, + 864, + 236 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/905f8a2ffc1329c97a139fd05c665c859c64411f7aadbda480a39e1c0f0c1cb7.jpg", + "image_caption": [ + "Figure 5. Comparison between task-specific attacks and joint attack performance on blackbox object detector (RetinaNet) and segmentation model (PSPNet). Green curves denote attack success rate for object detectors, and blue curves denote pixel success rate for semantic segmentation. (a) Attacks generated with an object detector surrogate do not transfer for semantic segmentation. (b) Attacks generated with semantic segmentation models surrogate do not transfer for object detectors. (c) Attacks generated by a surrogate of object detectors and semantic segmentation (along with weight balancing and optimization) provide successful attacks for blackbox object detectors and semantic segmentation models.", + "Clean image" + ], + "image_footnote": [], + "bbox": [ + 122, + 367, + 362, + 462 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/27e8259ecbfeda124bfe7e97f1ea359ef857824cd84ca7df8debc2d5193cf486.jpg", + "image_caption": [ + "Detection on clean image" + ], + "image_footnote": [], + "bbox": [ + 364, + 367, + 604, + 462 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/573b7cbcf54cc2ef948a7538892c8567ef92dc5b103ead3cec0525d697dab33a.jpg", + "image_caption": [ + "Segmentation of clean image" + ], + "image_footnote": [], + "bbox": [ + 607, + 368, + 846, + 462 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/b43f6fba2a48d184c208ad4052d0f4f69a7823d152ceff707d33003f8b03c8e1.jpg", + "image_caption": [ + "Perturbed image" + ], + "image_footnote": [], + "bbox": [ + 122, + 478, + 362, + 573 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/1346bccf623f70f2bf29720ef2af1e975b5c36b5328ba3e70d8d0f763a01005e.jpg", + "image_caption": [ + "Detection on perturbed image" + ], + "image_footnote": [], + "bbox": [ + 364, + 478, + 602, + 573 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/e724eeeefabd9a6d6e3e428b62b5f87ef22bdeed147db2c40559790bd30e07c5.jpg", + "image_caption": [ + "Segmentation of perturbed image" + ], + "image_footnote": [], + "bbox": [ + 607, + 478, + 846, + 573 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/930609f2565537a7ef8c1443d370e491b1dea0baca65256d2e4164a47e44e422.jpg", + "image_caption": [ + "(a) Our method can generate attacks to fool multiple blackbox object detector and blackbox semantic segmentation models jointly. First row shows a clean image from Cityscapes dataset, detection with RetinaNet and segmentation with PSPNet. Second row shows the perturbed image using ensemble surrogates {Faster RCNN,YOLOv3,FCN,UPerNet}, and detection and segmentation results on the perturbed image. We generate perturbation to map the Car in the middle to Traffic Light. Image id: lindau_000026_000019", + "(b) Color encoding for segmentation maps in CityScapes dataset", + "Figure 6. Visual adversarial examples of our method that generates successful attacks to fool a blackbox object detector and a blackbox semantic segmentation model using a single perturbed image." + ], + "image_footnote": [], + "bbox": [ + 120, + 641, + 844, + 672 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 76, + 726, + 194, + 739 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We presented a new method to generate targeted attacks for dense prediction task (e.g., object detectors and semantic segmentation) using an ensemble of surrogate models. We demonstrate that (victim model-agnostic) weight balancing and (victim model-specific) weight optimization play a critical role in the success of attacks. We present an extensive set of experiments to demonstrate the performance of our method with different models and datasets. Finally, we show that our approach can create adversarial ex", + "bbox": [ + 75, + 763, + 470, + 900 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "amples to fool multiple blackbox models and tasks jointly.", + "bbox": [ + 498, + 727, + 883, + 743 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Limitations. Our method employs an ensemble of surrogate models to generate attacks, which inevitably incurs higher memory and computational overhead. Moreover, the success of our method hinges on the availability of a diverse set of surrogate models, which could potentially limit its efficacy if such models are not readily obtainable.", + "bbox": [ + 496, + 744, + 890, + 835 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgments. This material is based upon work supported by AFOSR award FA9550-21-1-0330, NSF award 2046293, UC Regents Faculty Development grant. We acknowledge the computing support from Nautilus PRP.", + "bbox": [ + 496, + 839, + 890, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "4052", + "bbox": [ + 482, + 926, + 514, + 936 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 174, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Anurag Arnab, Ondrej Miksik, and Philip HS Torr. On the robustness of semantic segmentation models to adversarial attacks. In Proceedings of the IEEE Conference on Computer Vision and Pattern Recognition, pages 888-897, 2018. 1", + "[2] Zikui Cai, Shantanu Rane, Alejandro E Brito, Chengyu Song, Srikanth V Krishnamurthy, Amit K Roy-Chowdhury, and M Salman Asif. Zero-query transfer attacks on context-aware object detectors. 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In Proceedings of the IEEE/CVF International Conference on Computer Vision, pages 593-602, 2019. 4" + ], + "bbox": [ + 78, + 90, + 468, + 852 + ], + "page_idx": 10 + }, + { + "type": "page_number", + "text": "4055", + "bbox": [ + 482, + 926, + 514, + 936 + ], + "page_idx": 10 + } +] \ No newline at end of file diff --git a/2023/Ensemble-Based Blackbox Attacks on Dense Prediction/1f7b1ddd-65c3-47e9-8398-1b94d1c9d1e3_model.json b/2023/Ensemble-Based Blackbox Attacks on Dense Prediction/1f7b1ddd-65c3-47e9-8398-1b94d1c9d1e3_model.json new file mode 100644 index 0000000000000000000000000000000000000000..9a85c746ef23f7738920991b5f1a42288d0fc2b9 --- /dev/null +++ b/2023/Ensemble-Based Blackbox Attacks on Dense Prediction/1f7b1ddd-65c3-47e9-8398-1b94d1c9d1e3_model.json @@ -0,0 +1,2433 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.0, + 0.812, + 0.045 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.208, + 0.131, + 0.764, + 0.151 + ], + "angle": 0, + "content": "Ensemble-based Blackbox Attacks on Dense Prediction" + }, + { + "type": "text", + "bbox": [ + 0.3, + 0.181, + 0.672, + 0.217 + ], + "angle": 0, + "content": "Zikui Cai*, Yaoteng Tan*, and M. Salman Asif \nUniversity of California Riverside" + }, + { + "type": "text", + "bbox": [ + 0.346, + 0.22, + 0.621, + 0.234 + ], + "angle": 0, + "content": "{zcai032,ytan073,sasif}@ucr.edu" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.269, + 0.314, + 0.285 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.302, + 0.474, + 0.62 + ], + "angle": 0, + "content": "We propose an approach for adversarial attacks on dense prediction models (such as object detectors and segmentation). It is well known that the attacks generated by a single surrogate model do not transfer to arbitrary (blackbox) victim models. Furthermore, targeted attacks are often more challenging than the untargeted attacks. In this paper, we show that a carefully designed ensemble can create effective attacks for a number of victim models. In particular, we show that normalization of the weights for individual models plays a critical role in the success of the attacks. We then demonstrate that by adjusting the weights of the ensemble according to the victim model can further improve the performance of the attacks. We performed a number of experiments for object detectors and segmentation to highlight the significance of the our proposed methods. Our proposed ensemble-based method outperforms existing blackbox attack methods for object detection and segmentation. Finally, we show that our proposed method can also generate a single perturbation that can fool multiple blackbox detection and segmentation models simultaneously. Code is available at https://github.com/CSIplab/EBAD." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.651, + 0.21, + 0.667 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.678, + 0.47, + 0.875 + ], + "angle": 0, + "content": "Computer vision models (e.g., classification, object detection, segmentation, and depth estimation) are known to be vulnerable to carefully crafted adversarial examples [4, 11, 16, 17, 46]. Creating such adversarial attacks is easy for whitebox models, where the victim model is completely known [14, 16, 24, 37, 55]. In contrast, creating adversarial attacks for blackbox models, where the victim model is unknown, remains a challenging task [1, 33, 54]. Most of the existing blackbox attack methods have been developed for classification models [10, 21, 35, 47]. Blackbox attacks for dense prediction models such as object detection and segmentation are relatively less studied [4, 17, 27], and most of the existing ones mainly focus on untargeted" + }, + { + "type": "image", + "bbox": [ + 0.518, + 0.27, + 0.885, + 0.422 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.435, + 0.895, + 0.497 + ], + "angle": 0, + "content": "Figure 1. Illustration of the targeted ensemble-based blackbox attack. (Top) Attack generated by a single surrogate model does not transfer on the victim blackbox model (person does not map to car). (Bottom) Attack generated by weight balancing and optimization can transfer on a variety of victim models (person is mapped to car)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.507, + 0.895, + 0.597 + ], + "angle": 0, + "content": "attacks [17]. Furthermore, a vast majority of these methods are based on transfer attacks, in which a surrogate (white-box) model is used to generate the adversarial example that is tested on the victim model. However, the success rate of such transfer-based attacks is often low, especially for targeted attacks [10, 21, 47]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.599, + 0.896, + 0.854 + ], + "angle": 0, + "content": "In this paper, we propose and evaluate an ensemble-based blackbox attack method for objection detection and segmentation. Our method is inspired by three key observations: 1) targeted attacks generated by a single surrogate model are rarely successful; 2) attacks generated by an ensemble of surrogate models are highly successful if the contribution from all the models is properly normalized; and 3) attacks generated by an ensemble for a specific victim model can be further improved by adjusting the contributions of different surrogate models. The overall idea of the proposed work is illustrated in Fig. 1. Our proposed method can be viewed as a combination of transfer- and query-based attacks, where we can adjust the contribution based on the feedback from the victim model using a small number of queries (5–20 in our experiments). In contrast, conventional query-based attacks require hundreds or thousands of queries from the victim model [9, 19, 22, 49]." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.856, + 0.895, + 0.901 + ], + "angle": 0, + "content": "We conduct comprehensive experiments to validate our proposed method and achieve state-of-the-art performance for both targeted and untargeted blackbox attacks on ob-" + }, + { + "type": "page_footnote", + "bbox": [ + 0.097, + 0.887, + 0.204, + 0.9 + ], + "angle": 0, + "content": "* Equal contribution" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.925, + 0.516, + 0.937 + ], + "angle": 0, + "content": "4045" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.288 + ], + "angle": 0, + "content": "ject detection. Specifically, our proposed method attains \\(29 - 53\\%\\) success rate using only 5 queries for targeted attacks on object detectors, whereas the current state-of-the-art method [4] achieves \\(20 - 39\\%\\) success rate with the same number of queries. Furthermore, we extend our evaluation to untargeted and targeted attacks on blackbox semantic segmentation models. Our method achieves \\(0.9 - 1.55\\%\\) mIoU for untargeted and \\(69 - 95\\%\\) pixel-wise success for targeted attacks. By comparison, the current state-of-the-art method [17] obtains \\(0.6 - 7.97\\%\\) mIoU for untargeted attacks and does not report results for targeted attacks. To the best of our knowledge, our work is the first approach for targeted and query-based attacks for semantic segmentation." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.289, + 0.455, + 0.303 + ], + "angle": 0, + "content": "Below we summarize main contributions of this work." + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.307, + 0.469, + 0.352 + ], + "angle": 0, + "content": "- We design a novel framework that can effectively attack blackbox dense prediction models based on an ensemble of surrogate models." + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.356, + 0.469, + 0.416 + ], + "angle": 0, + "content": "- We propose two simple yet highly effective ideas, namely weight balancing and weight optimization, with which we can achieve significantly better attack performance compared to existing methods." + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.42, + 0.468, + 0.464 + ], + "angle": 0, + "content": "- We extensively evaluate our method for targeted and untargeted attacks on object detection and semantic segmentation models and achieve state-of-the-art results." + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.47, + 0.469, + 0.514 + ], + "angle": 0, + "content": "- We demonstrate that our proposed method can generate a single perturbation that can fool multiple blackbox detection and segmentation models simultaneously." + }, + { + "type": "list", + "bbox": [ + 0.078, + 0.307, + 0.469, + 0.514 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.529, + 0.214, + 0.544 + ], + "angle": 0, + "content": "2. Related work" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.553, + 0.47, + 0.75 + ], + "angle": 0, + "content": "Blackbox adversarial attacks. In the context of blackbox attacks, the attacker cannot access the model parameters or compute the gradient via backpropagation. Blackbox attack methods can be broadly divided into two groups: transfer-based [25, 33, 39, 40] and query-based attacks [9, 22, 49]. Transfer-based attacks rely on the assumption that surrogate models share similarities with the victim model, such that an adversarial example generated for the surrogate model can also fool the victim model. Query-based methods generate attacks by searching the adversarial examples space based on the feedback obtained from the victim model through queries. They can often achieve higher success rate but may require a large number of queries." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.75, + 0.471, + 0.902 + ], + "angle": 0, + "content": "Ensemble-based attacks. Ensemble-based attacks leverage the idea of transfer attack and assume that if an adversarial example can fool multiple models simultaneously, the chances of fooling an unseen model are higher [14, 33, 56]. Recently, some methods have combined ensemble-based transfer attacks with limited feedback from the victim models to improve the overall success rate [19, 21, 26, 35, 45, 47]. These methods have mainly focused on classification models, and ensemble attacks on dense prediction tasks such as object detection and semantic segmentation are relatively" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.092, + 0.818, + 0.107 + ], + "angle": 0, + "content": "less studied, especially for targeted attacks [52]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.108, + 0.892, + 0.41 + ], + "angle": 0, + "content": "Attacks against object detectors and segmentation. Dense (pixel-level) prediction tasks such as object detection and semantic segmentation have higher task complexities [50] compared to classification tasks. Existing attacks on object detectors mainly focus on whitebox setting, although there are a few exceptions [3, 51]. A recent study [4] generates blackbox attacks on object detectors by using a surrogate ensemble and context-aware attack-based queries. Another approach [51] trains a generative model to generate transferable attacks. While some patch-based attacks [32, 44] are effective, the patches are easily noticeable. Recent works [17, 18] have investigated adversarial robustness for semantic segmentation and proposed a transferable untargeted attack using a single surrogate model. While most existing methods are based on a single surrogate model, we demonstrate that using multiple surrogates with weight balancing/search in the attack generation process, we can generate more effective adversarial examples for both untargeted and targeted scenarios, as well as for various types of dense prediction tasks." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.426, + 0.591, + 0.441 + ], + "angle": 0, + "content": "3. Method" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.452, + 0.64, + 0.467 + ], + "angle": 0, + "content": "3.1. Preliminaries" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.476, + 0.892, + 0.657 + ], + "angle": 0, + "content": "We consider a per-instance attack scenario in which we generate adversarial perturbation \\(\\delta\\) for a given image \\(x\\). To keep the perturbation imperceptible, we bound its \\(\\ell_p\\) norm as \\(\\| \\delta \\|_p \\leq \\varepsilon\\). In our experiments, we mainly use \\(\\ell_{\\infty}\\) or max norm that limits the maximum level of perturbation. Our goal is to find \\(\\delta\\) such that the perturbed image, \\(x^{\\star} = x + \\delta\\), can disrupt a victim image recognition system \\(f_{\\mathbf{v}}\\) to make wrong predictions. Suppose the original prediction for the clean image \\(x\\) is \\(y = f_{\\mathbf{v}}(x)\\). The attack goal is \\(f(x^{\\star}) \\neq y\\) for untargeted attack, and \\(f(x^{\\star}) = y^{\\star}\\) for targeted attack, where \\(y^{\\star}\\) is the desired output (e.g., label or bounding box or segmentation map)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.659, + 0.892, + 0.839 + ], + "angle": 0, + "content": "For classification models, the label \\(y \\in \\mathbb{R}\\) is a scalar. However, dense prediction models can have more complex output space. For object detection, the variable-length output \\(y \\in \\mathbb{R}^{K \\times 6}\\), where \\(K\\) is the number of detected objects, and each object label and position are encoded in a vector of length 6 that include the object category, bounding box coordinates, and confidence score. Some other tasks like keypoint detection and OCR are similar to object detection. For semantic segmentation, the prediction \\(y \\in \\mathbb{R}^{H \\times W}\\) is per-pixel classification, where \\(H\\) and \\(W\\) are the height and width of the input image, respectively. Depth and optical flow estimation tasks have similar output structure." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.892, + 0.901 + ], + "angle": 0, + "content": "The adversarial loss functions for object detection and semantic segmentation can be defined using their respective training or prediction loss functions. Let us consider a whitebox model \\( f \\) and an input image \\( x \\) with output" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.925, + 0.516, + 0.937 + ], + "angle": 0, + "content": "4046" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.47, + 0.136 + ], + "angle": 0, + "content": "\\(y = f(x)\\). For untargeted attack, we can search for the adversarial example \\(x^{\\star}\\) by solving the following maximization problem:" + }, + { + "type": "equation", + "bbox": [ + 0.177, + 0.15, + 0.469, + 0.174 + ], + "angle": 0, + "content": "\\[\nx ^ {\\star} = \\underset {x} {\\operatorname {a r g m a x}} \\mathcal {L} (f (x), y), \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.186, + 0.469, + 0.232 + ], + "angle": 0, + "content": "where \\(\\mathcal{L}(f(x),y)\\) represents the training loss of the model with input \\(x\\) and output \\(y\\). For targeted attacks, with a target output \\(y^{\\star}\\), we solve the following minimization problem:" + }, + { + "type": "equation", + "bbox": [ + 0.175, + 0.244, + 0.469, + 0.268 + ], + "angle": 0, + "content": "\\[\nx ^ {\\star} = \\underset {x} {\\operatorname {a r g m i n}} \\mathcal {L} (f (x), y ^ {\\star}). \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.28, + 0.469, + 0.475 + ], + "angle": 0, + "content": "Different from classification, which mostly use cross-entropy loss across different models, dense predictions have different loss functions for different models due to the complexity of the output space and diversity of the architectures. For example, two-stage object detector, including Faster RCNN [43], has losses for object classification, bounding box regression, and losses on the region proposal network (RPN). But for one-stage object detectors like YOLO [41,42], they do not have losses corresponding to RPN. Due to the large variability of the loss functions used in different dense prediction models, we use the corresponding training loss \\(\\mathcal{L}\\) for each model as the optimization loss to guide the backpropagation." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.476, + 0.447, + 0.491 + ], + "angle": 0, + "content": "We employ PGD [37] to optimize the perturbation as" + }, + { + "type": "equation", + "bbox": [ + 0.1, + 0.503, + 0.469, + 0.521 + ], + "angle": 0, + "content": "\\[\n\\delta^ {t + 1} = \\Pi_ {\\varepsilon} \\left(\\delta^ {t} - \\lambda \\operatorname {s i g n} \\left(\\nabla_ {\\delta} \\mathcal {L} \\left(f \\left(x + \\delta^ {t}\\right), y ^ {\\star}\\right)\\right)\\right), \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.534, + 0.228, + 0.547 + ], + "angle": 0, + "content": "for targeted attack and" + }, + { + "type": "equation", + "bbox": [ + 0.104, + 0.56, + 0.469, + 0.578 + ], + "angle": 0, + "content": "\\[\n\\delta^ {t + 1} = \\Pi_ {\\varepsilon} \\left(\\delta^ {t} + \\lambda \\operatorname {s i g n} \\left(\\nabla_ {\\delta} \\mathcal {L} (f (x + \\delta^ {t}), y)\\right)\\right), \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.59, + 0.469, + 0.651 + ], + "angle": 0, + "content": "for untargeted attack. Here \\(t\\) indicates the attack step, \\(\\lambda\\) is the step size, and \\(\\Pi_{\\varepsilon}\\) projects the perturbation into a \\(\\ell_p\\) norm ball with radius \\(\\varepsilon\\). In the rest of the paper, we focus on targeted attacks without loss of generalization." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.661, + 0.297, + 0.675 + ], + "angle": 0, + "content": "3.2. Ensemble-based attacks" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.685, + 0.469, + 0.851 + ], + "angle": 0, + "content": "In an ensemble-based transfer attack, we use an ensemble of \\(N\\) surrogate (whitebox) models: \\(\\mathcal{F} = \\{f_1,\\dots ,f_N\\}\\) to generate perturbations to attack the victim model \\(f_{\\mathbf{v}}\\). Note that if the ensemble has a single model, then such an attack becomes a simple transfer attack with a single surrogate model. Let us denote the training loss function for \\(i\\)th model as \\(\\mathcal{L}_i(f_i(x),y^*)\\). A natural approach to combine the loss functions of all surrogate models is to compute an average or weighted average of the individual loss functions. For instance, we can generate the adversarial image by solving the following optimization problem:" + }, + { + "type": "equation", + "bbox": [ + 0.14, + 0.864, + 0.469, + 0.904 + ], + "angle": 0, + "content": "\\[\nx ^ {\\star} (\\alpha) = \\underset {x} {\\arg \\min } \\sum_ {i = 1} ^ {N} \\alpha_ {i} \\mathcal {L} _ {i} \\left(f _ {i} (x), y ^ {\\star}\\right), \\tag {5}\n\\]" + }, + { + "type": "image", + "bbox": [ + 0.558, + 0.094, + 0.833, + 0.236 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.24, + 0.89, + 0.265 + ], + "angle": 0, + "content": "Figure 2. Distribution of losses for different object detection models. \\(\\mathbb{P}(\\mathcal{L}_i(f_i(x),y^\\star))\\). Calculated on 500 images from VOC dataset." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.271, + 0.891, + 0.331 + ], + "angle": 0, + "content": "where \\(x^{\\star}(\\alpha)\\) is a function of the weights of the ensemble \\(\\alpha = \\{\\alpha_{1},\\ldots ,\\alpha_{N}\\}\\). One of our key observations is that the choice of weights plays a critical role in the transfer attack success rate of the ensemble models." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.332, + 0.892, + 0.603 + ], + "angle": 0, + "content": "Weight balancing (victim model agnostic). In ensemble-based transfer attacks, we build on the intuition that if an adversarial example can fool all models simultaneously, it would potentially be more transferable to any unseen victim model. This concept has been empirically corroborated by numerous works [14, 33]. However, most attack methods have only been verified on classification models, all of which use the same cross-entropy loss and yield similar loss values. In contrast, the loss functions for object detectors in an ensemble can differ significantly and cover a large range of values (as shown in Fig. 2). In such cases, models with large loss terms heavily influence the optimization procedure, reducing the attack success rate for models with small losses (see Tab. 1). To overcome this issue, we propose a simple yet effective solution to balance the weights assigned to each model in the ensemble as follows. For each input image \\( x \\) and target output \\( y^{\\star} \\), we adjust the weight for \\( i \\)th surrogate model loss as" + }, + { + "type": "equation", + "bbox": [ + 0.605, + 0.614, + 0.891, + 0.65 + ], + "angle": 0, + "content": "\\[\n\\alpha_ {i} = \\frac {\\sum_ {i = 1} ^ {N} \\mathcal {L} _ {i} \\left(f _ {i} (x) , y ^ {\\star}\\right)}{N \\mathcal {L} _ {i} \\left(f _ {i} (x) , y ^ {\\star}\\right)}. \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.658, + 0.892, + 0.869 + ], + "angle": 0, + "content": "The weights are adjusted in a whitebox setting as it allows us to measure the loss of each whitebox model accurately. The purpose of weight balancing is to ensure that all surrogate models can be successfully attacked, making the generated example more adversarial for blackbox victim models. Weight optimization (victim model specific). Note that the weight normalization, as discussed above, is agnostic to the victim model. We further observe that such transfer-based attacks can be further improved by optimizing the weights of the ensemble according to the victim model, input image, and target output. In particular, we can change the individual \\(\\alpha_{i}\\) to create the perturbations that reduce the victim model loss \\(\\mathcal{L}_{\\mathbf{v}}\\). To achieve this goal, we need to solve the following optimization problem with respect to \\(\\alpha\\):" + }, + { + "type": "equation", + "bbox": [ + 0.573, + 0.88, + 0.891, + 0.904 + ], + "angle": 0, + "content": "\\[\n\\alpha^ {\\star} = \\underset {\\alpha} {\\arg \\min } \\mathcal {L} _ {\\mathrm {v}} \\left(f _ {\\mathrm {v}} \\left(x ^ {\\star} (\\alpha)\\right), y ^ {\\star}\\right). \\tag {7}\n\\]" + }, + { + "type": "page_number", + "bbox": [ + 0.482, + 0.927, + 0.515, + 0.938 + ], + "angle": 0, + "content": "4047" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.468, + 0.121 + ], + "angle": 0, + "content": "The optimization problem in (7) is a nested optimization that we can solve as an alternating minimization routine." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.122, + 0.468, + 0.152 + ], + "angle": 0, + "content": "Step 0. Given input \\(x\\), output \\(y^{\\star}\\), and surrogate ensemble \\(\\mathcal{F}\\), we initialize \\(\\alpha\\) using (6)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.152, + 0.468, + 0.197 + ], + "angle": 0, + "content": "Step 1. Solve (5) to generate an adversarial example \\(x^{\\star}(\\alpha)\\). Step 2. Test the victim model. Stop if attack is successful; otherwise, change one of the \\(\\alpha_{i}\\) and repeat Step 1." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.198, + 0.468, + 0.303 + ], + "angle": 0, + "content": "In our experiments, we update the \\(\\alpha_{i}\\) in a cyclic manner (one coordinate at a time) as \\(\\alpha_{i} \\pm \\gamma\\) in Step 2, where \\(\\gamma\\) denotes a step size. In every round, we select the value of \\(\\alpha_{i}\\) that provides smallest value of the victim loss. We count the number of queries as the number of times we test the generated adversarial example on the victim model and denote it as \\(Q\\) in our experiments." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.318, + 0.209, + 0.335 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.344, + 0.468, + 0.51 + ], + "angle": 0, + "content": "To evaluate the effectiveness of our method, we performed extensive experiments on attacking various object detection and semantic segmentation models. We first show that the attacks generated by a single surrogate model fail to transfer to arbitrary victim models. Then we show that the attack transfer rate can be increased by using an ensemble with weight balancing. Additional optimization of the weights surrogates for each victim model can further improve the attack performance. Finally, we show that we can generate single perturbations to fool object detectors and semantic segmentation models simultaneously." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.521, + 0.25, + 0.537 + ], + "angle": 0, + "content": "4.1. Experiment setup" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.544, + 0.246, + 0.559 + ], + "angle": 0, + "content": "4.1.1 Object detection" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.568, + 0.468, + 0.839 + ], + "angle": 0, + "content": "Models and datasets. We utilize MMDetection [7] toolbox to select various model architectures and weights pre-trained on COCO 2017 dataset [30]. To construct the surrogate ensemble, we start with two widely used models, Faster R-CNN [43] and YOLO [41, 42], and expand the ensemble by appending models with different architectures, including {FCOS [48], Grid R-CNN [36], SSD [31]}. We select different victim models, including {RetinaNet [29], Libra R-CNN [38], FoveaBox [23], FreeAnchor [59], DETR [6]}}. We evaluate attack performance on COCO 2017 [30] and Pascal VOC 2007 [15] datasets. Since the models from this repository are trained on COCO, which contains 80 object categories (a superset of VOC dataset's 20 categories), while testing on VOC dataset, we only return the objects that exist in VOC. We follow the setup in [4] and randomly select 500 images containing multiple (2-6) objects from VOC 2007 test and COCO 2017 validation sets." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.468, + 0.901 + ], + "angle": 0, + "content": "Evaluation metrics. We mainly focus on targeted attacks for object detection since they are more challenging than untargeted or vanishing attacks. We measure the performance of the attack using attack success rate (ASR), which" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.151 + ], + "angle": 0, + "content": "equals the number of successfully attacked images over the total number of attacks. We follow the setting in [4], where if the target label is detected within the victim object region with IOU \\(>0.3\\), the attack is determined a success." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.153, + 0.892, + 0.243 + ], + "angle": 0, + "content": "Perturbation and query budget. We tested different perturbation levels with \\(\\ell_{\\infty} = \\{10,20,30\\}\\) out of 255. We use at most 10 queries for attacking object detectors, and we show the trends of how ASR increases with the number of queries. To align with [4] that uses 5 attack plans, we set the maximum query budget to \\(Q = 5\\) in Tab. 1." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.245, + 0.892, + 0.41 + ], + "angle": 0, + "content": "Comparing methods. We compare with [4], which is a state-of-the-art transfer-based approach that leverages context information to design attack plans to iteratively attack the victim object. The method generates different perturbations by iterating over a set of predefined attacks, and the total number of queries is the number of attempted attacks. BASES [3] is a recent work on ensemble-based blackbox attacks, which mainly focused on classification tasks and did not consider the loss distributions of different surrogate models. In our experiments, the ensemble with weight optimization and without balancing is equivalent to BASES [3]." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.435, + 0.715, + 0.45 + ], + "angle": 0, + "content": "4.1.2 Semantic segmentation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.46, + 0.892, + 0.717 + ], + "angle": 0, + "content": "Models and datasets. We use MMSegmentation [12] toolbox to select different model architectures and weights pre-trained on Cityscapes [13] (\\(x \\in \\mathbb{R}^{512 \\times 1024 \\times 3}\\)) and Pascal VOC (\\(x \\in \\mathbb{R}^{512 \\times 512 \\times 3}\\)) datasets. We select PSPNet [60] and DeepLabV3 [8] with ResNet50 and ResNet101 [20] backbones as our blackbox victim models. For the surrogate ensemble, we start with the primary semantic segmentation model FCN [34], and expand the ensemble with {UPerNet [53], PSANet [61], GCNet [5], ANN [62], EncNet [57]}. All models are built on ResNet50 [20] backbone trained with the cross-entropy loss. The loss values across all surrogate models have similar range; therefore, the effect of weight balancing for semantic segmentation is not as significant as it is for object detection. We use validation datasets from Cityscapes [13] and Pascal VOC 2012, which contains 500 and 1499 images with 19 and 21 classes, respectively." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.718, + 0.892, + 0.839 + ], + "angle": 0, + "content": "Evaluation metrics. We use different metrics for untargeted and targeted attack performance evaluation. In untargeted experiments, the attack performance is evaluated using the mIoU score (in percentage \\(\\%\\) ), the lower mIoU score the better attack performance. For targeted experiments, we report the pixel success ratio (PSR), which indicates the percentage of pixels successfully assigned the desired label in the target region, the higher the better attack performance." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.892, + 0.87 + ], + "angle": 0, + "content": "Perturbation and query budget. We use the perturbation budget \\(\\ell_{\\infty} \\leq 8\\) out of 255 and query budget \\(Q = 20\\)." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.871, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Comparing methods. We compare with dynamic scale (DS) attack [17] which is the most recent method that" + }, + { + "type": "page_number", + "bbox": [ + 0.482, + 0.925, + 0.516, + 0.937 + ], + "angle": 0, + "content": "4048" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.102, + 0.894, + 0.138 + ], + "angle": 0, + "content": "Table 1. Targeted attack success rate (%) of different methods at different perturbation budgets on VOC dataset. For each perturbation level, the first 4 rows correspond to different settings of our attacks, i.e. with (✓) or without (✗) weight balancing and weight optimization. We show comparison with context-aware attack [4], the state-of-the-art method for query-based blackbox attacks." + }, + { + "type": "table", + "bbox": [ + 0.142, + 0.138, + 0.832, + 0.38 + ], + "angle": 0, + "content": "
Perturbation BudgetWeight BalancingWeight OptimizationSurrogate EnsembleBlackbox Victim Models (ASR ↑)
FRCNNYOLOv3RetinaLibraFoveaFreeDETR
l∞=10XX27.991.511.69.29.013.45.6
X✓61.499.424.328.022.431.015.4
✓X71.185.730.933.427.236.012.2
✓✓86.096.953.256.647.257.429.0
Context-aware Attack [4]55.875.622.620.433.639.220.2
l∞=20XX40.192.216.920.415.423.29.7
X✓77.799.841.045.437.847.022.5
✓X82.789.841.050.444.857.021.6
✓✓94.698.066.974.468.079.448.0
Context-aware Attack [4]78.687.235.238.451.656.634.0
l∞=30XX43.491.117.122.617.427.211.4
X✓82.799.647.254.847.057.433.4
✓X85.390.248.856.845.659.629.2
✓✓96.098.178.982.876.883.058.8
Context-aware Attack [4]80.688.042.044.256.863.640.2
" + }, + { + "type": "image", + "bbox": [ + 0.108, + 0.395, + 0.348, + 0.54 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.191, + 0.546, + 0.263, + 0.559 + ], + "angle": 0, + "content": "(a) \\(\\ell_{\\infty}\\leq 10\\)" + }, + { + "type": "image", + "bbox": [ + 0.366, + 0.395, + 0.605, + 0.539 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.449, + 0.546, + 0.522, + 0.559 + ], + "angle": 0, + "content": "(b) \\(\\ell_{\\infty}\\leq 20\\)" + }, + { + "type": "image", + "bbox": [ + 0.626, + 0.395, + 0.865, + 0.54 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.709, + 0.546, + 0.781, + 0.559 + ], + "angle": 0, + "content": "(c) \\(\\ell_{\\infty}\\leq 30\\)" + }, + { + "type": "image_caption", + "bbox": [ + 0.146, + 0.57, + 0.822, + 0.584 + ], + "angle": 0, + "content": "Figure 3. Attack success rate (or fooling rate) vs number of queries \\((Q)\\). The maximum value of \\(Q\\) is set to 10 for these results." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.61, + 0.47, + 0.641 + ], + "angle": 0, + "content": "achieves the highest attack transfer rate on semantic segmentation untargeted attacks." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.65, + 0.358, + 0.667 + ], + "angle": 0, + "content": "4.2. Attacks against object detection" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.674, + 0.47, + 0.75 + ], + "angle": 0, + "content": "Following settings in [4], we randomly select one object from the output of victim model as the victim object and perturb it into a target object that does not exist in the original detection. This approach rules out the possibility of mis-counting existing objects as the target object." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.75, + 0.471, + 0.901 + ], + "angle": 0, + "content": "We report our main results in Tab. 1. The baseline method uses a surrogate ensemble without weight balancing and models are assigned weight of 1. Such a baseline method is same a transfer-based method and results in highly imbalanced success rate for different surrogate models. For instance, at \\(\\ell_{\\infty} \\leq 10\\), the success rate for YOLOv3 is above \\(90\\%\\) while the success rate for Faster R-CNN is less than \\(30\\%\\). Low success rate on surrogate side translates to low success rate on blackbox victim side. The main reason for such imbalance is that the loss of dif" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.609, + 0.892, + 0.897 + ], + "angle": 0, + "content": "ferent object detectors can be highly unbalanced (e.g., the loss value for YOLOv3 is nearly \\(60\\times\\) larger than the loss of Faster RCNN for targeted attacks, cf. Fig. 2). With weight balancing, the success rate increases for surrogate and blackbox victim models. The success rate is further increased on surrogate and victim blackbox models if we optimize the weights, same as BASES [3]. Our method (with weight balancing and optimization) achieves a significantly higher ASR compared to context-aware attack across different datasets and different perturbation budgets. On average, our ASR on blackbox victim models is over \\(4\\times\\) better than baseline method and over \\(1.5\\times\\) better than context-aware attack. On whitebox surrogate models, weight balancing and optimization also achieves the highest ASR. Context-aware attack fixes weight ratio for surrogate models, \\(\\alpha_{\\mathrm{FRCNN}} / \\alpha_{\\mathrm{YOLO}} = 4\\), which is sub-optimal according to our analyses. Even though it achieves much higher performance than baseline, it still largely under-performs our method. Similar trend is observed for COCO dataset (see Tab. S1)." + }, + { + "type": "page_number", + "bbox": [ + 0.482, + 0.927, + 0.516, + 0.938 + ], + "angle": 0, + "content": "4049" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.087, + 0.102, + 0.882, + 0.114 + ], + "angle": 0, + "content": "Table 2. Targeted ASR (%) for blackbox victim models and whitebox surrogate models with different ensemble sizes (N). On VOC dataset, \\( {\\ell }_{\\infty } \\leq {10} \\) ." + }, + { + "type": "table", + "bbox": [ + 0.162, + 0.115, + 0.808, + 0.216 + ], + "angle": 0, + "content": "
NSurrogate EnsembleBlackbox Victim Models (ASR ↑)
FRCNNYOLOv3FCOSGrid R-CNNSSDRetinaLibraFoveaFreeDETR
174.7----31.331.229.840.410.6
286.096.9---53.256.647.257.429.0
387.996.174.2--63.162.057.366.638.0
489.694.775.287.9-68.771.067.674.449.6
589.791.873.586.182.468.970.268.477.653.2
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.241, + 0.892, + 0.289 + ], + "angle": 0, + "content": "Table 3. Untargeted attack mIoU scores (%) of ensemble sizes \\(N = 2,4,6\\) on Cityscapes dataset. We compare \\(Q = 0\\) (i.e. direct transfer attack) with \\(Q = 20\\) ensemble attack performance. DS uses DeepLabV3-Res50 (DL3-50) as the surrogate model for attack generation; thus the DS on DL3-50 is a whitebox attack. While our method used an ensemble that does not include any victim models for attack generation, we still achieved comparable mIoU scores to DS on DL3-50. Blue numbers represent whitebox attacks." + }, + { + "type": "table", + "bbox": [ + 0.108, + 0.29, + 0.865, + 0.476 + ], + "angle": 0, + "content": "
MethodWhitebox SurrogateBlackbox Victim Models (mIoU ↓)
PSPNet-Res50PSPNet-Res101DeepLabV3-Res50DeepLabV3-Res101
Clean Images-77.9278.2879.1277.12
BaselinePSPNet-Res503.4324.185.0525.74
DeepLabV3-Res504.7621.723.9222.23
DS [17]PSPNet-Res500.828.041.369.00
DeepLabV3-Res501.237.970.617.11
Ours (Q=0)N=25.078.325.198.74
N=44.336.264.326.33
N=63.624.914.024.84
Ours (Q=20)N=21.382.881.153.50
N=40.792.040.731.80
N=60.901.550.941.09
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.512, + 0.47, + 0.573 + ], + "angle": 0, + "content": "Table 4. Targeted attack performance on Cityscapes as pixel success rate (higher the better). The attack performance increases as we increase ensemble size \\((N)\\) and number of queries for weight optimization \\((Q)\\). \\(N = 1\\) has zero query. We note PSPNet-Res50 as PSP-r50, and DeepLabV3-Res50 as DL3-r50, similar abbreviations apply to Res101." + }, + { + "type": "table", + "bbox": [ + 0.091, + 0.579, + 0.458, + 0.735 + ], + "angle": 0, + "content": "
QNBlackbox Victim Models (PSR ↑)
PSP-r50PSP-r101DL3-r50DL3-r101
0139.1510.2135.027.58
252.1512.2847.9910.59
343.1711.3442.109.87
451.4426.1349.1417.42
552.2423.8851.7516.08
20283.9751.8082.7046.95
388.8864.6385.5560.88
491.5164.2887.1963.88
592.9169.0988.9569.65
" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.764, + 0.468, + 0.824 + ], + "angle": 0, + "content": "Fig. 3 shows the effect of the number of queries on the ASR that gradually improves as we optimize the weights. We observe the largest increase in the first two steps and then the improvement plateaus as \\( Q \\to 10 \\)." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.826, + 0.468, + 0.899 + ], + "angle": 0, + "content": "We also conducted an experiment to test our method with varying ensemble sizes. The results for \\(\\ell_{\\infty} \\leq 10\\), \\(Q = 5\\) are presented in Tab. 2. As we increase the number of models in the ensemble from \\(N = 1\\) to \\(N = 5\\), we observe an increased ASR on all blackbox victim models." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.501, + 0.833, + 0.516 + ], + "angle": 0, + "content": "4.3. Attacks against semantic segmentation" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.531, + 0.892, + 0.592 + ], + "angle": 0, + "content": "We evaluate the effectiveness of our attack on semantic segmentation in both untargeted and targeted settings. For the sake of consistency and a fair comparison, we adopt adversarial attack settings in DS attack [17]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.599, + 0.893, + 0.901 + ], + "angle": 0, + "content": "Untargeted attacks. We generate adversarial attacks using different ensemble sizes and report mIoU scores on Cityscapes in Tab. 3 and Fig. 4 (and Pascal VOC in supplementary material). In the untargeted setting, semantic segmentation models are attacked to maximize the loss between clean and modified annotation; hence, the lower mIoU implies better attack performance. All of the victim models achieve high performance on clean images. The baseline method (direct transfer attack with one surrogate model using PGD) performs well in the whitebox setting but suffers when the victim uses another backbone. For example, the attacks generated on PSPNet-Res50 achieves \\(3.43\\%\\) mIoU on PSPNet-Res50 but only attains \\(24.18\\%\\) mIoU on PSPNet-Res101. DS attack achieves better results than the baseline method but still suffers from crossbackbone transfers. On the other hand, our method, without weight optimization (i.e., \\(Q = 0\\)) and using a surrogate ensemble of \\(N = 2\\) models, can achieve results comparable to DS attack, particularly for attacks on Res101 models. As we increase the number of surrogate models to 4 or 6, our" + }, + { + "type": "page_number", + "bbox": [ + 0.482, + 0.927, + 0.516, + 0.938 + ], + "angle": 0, + "content": "4050" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.111, + 0.105, + 0.331, + 0.24 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.197, + 0.244, + 0.258, + 0.255 + ], + "angle": 0, + "content": "(a) \\(N = 2\\)" + }, + { + "type": "image", + "bbox": [ + 0.369, + 0.105, + 0.589, + 0.241 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.455, + 0.244, + 0.516, + 0.255 + ], + "angle": 0, + "content": "(b) \\(N = 4\\)" + }, + { + "type": "image", + "bbox": [ + 0.629, + 0.105, + 0.848, + 0.241 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.715, + 0.244, + 0.774, + 0.255 + ], + "angle": 0, + "content": "(c) \\(N = 6\\)" + }, + { + "type": "image_caption", + "bbox": [ + 0.282, + 0.267, + 0.687, + 0.281 + ], + "angle": 0, + "content": "Figure 4. mIoU vs number of queries \\((Q)\\) for different ensemble sizes \\((N)\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.295, + 0.47, + 0.43 + ], + "angle": 0, + "content": "attack performance further improves. Furthermore, when we apply weight optimization (e.g., \\( Q = 20 \\)), the attack improves by updating the weights of the surrogate models, allowing us to outperform DS attack for all victim models. Fig. 4 shows how the mIoU changes with the number of queries. We observe that the mIoU gradually reduces as we query the victim model and optimize the weights. The largest decrease happens in the first 3-4 steps and then the reduction plateaus as \\( Q \\to 20 \\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.431, + 0.473, + 0.779 + ], + "angle": 0, + "content": "Targeted attack. To evaluate our method in a more challenging setting, we consider a targeted attack scenario, where instead of changing every pixel in the segmentation to some arbitrary label, we focus on attacking a dominant class (i.e., the class occupying the largest area) in the scene to its least likely class \\( y^{\\star} \\). For each clean image, we first select a region with the dominant class \\( y \\) (e.g., \"road\" or \"building\" for most of the Cityscapes images. See Fig. S3 as an example). Then based on the least-likely class of each pixel in that region, we select the class that appears most frequently as the target label \\( y^{\\star} \\) of the entire region. We use PSR as our evaluation metric, which represents the percentage of pixels in the selected region that are successfully assigned to \\( y^{\\star} \\). The higher percentage indicates more pixels are successfully attacked to the desired class, which indicates better attack performance. Our targeted attack results are reported in Tab. 4. Results show that as we increase the number of surrogate models (\\( N \\)), the ASR improves for most instances without any weight optimization step (i.e., \\( Q = 0 \\)). If we perform weight optimization for \\( Q = 20 \\) steps, then the success rate increases for all the models. For instance, with \\( N = 4 \\), the ASR for Res101 models increases from 17–26% to 63–64%." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.787, + 0.436, + 0.803 + ], + "angle": 0, + "content": "4.4. Joint attack for multiple models and tasks" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.811, + 0.47, + 0.902 + ], + "angle": 0, + "content": "We first show that generally adversarial examples generated for object detection do not transfer to semantic segmentation, and vice versa. Then we show that we can generate single perturbations to fool object detectors and semantic segmentation models simultaneously, by using a surrogate ensemble including both detection and segmentation mod" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.295, + 0.892, + 0.325 + ], + "angle": 0, + "content": "els. We choose targeted attacks in our experiments because they are more challenging than untargeted attacks." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.326, + 0.893, + 0.446 + ], + "angle": 0, + "content": "Experiment setup. On the blackbox (victim) side, we tested RetinaNet as the victim object detector and PSPNet-Res50 as the victim semantic segmentation model. On the whitebox (surrogate) side, we used Faster RCNN, YOLOv3 as the surrogate object detectors and FCN, UPerNet as the surrogate semantic segmentation models. We performed targeted attacks on 500 test images selected from the validation set of CityScapes dataset." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.448, + 0.893, + 0.809 + ], + "angle": 0, + "content": "Results. We present the ASRs for task-specific and joint attacks in Fig. 5. Green curves denote ASR for object detectors, and blue curves denote PSR for semantic segmentation. Fig. 5a presents the results when we generate attacks using an object detector surrogate ensemble. Note that success rate for victim object detector (RetinaNet) increases as we optimize the weights but the success rate for the semantic segmentation model (PSPNet) remains small. Similarly, Fig. 5b presents the results when we generate attacks using a segmentation surrogate ensemble. The success rate for the victim semantic segmentation model increases, but the success rate for the object doctor remains close to zero. Fig. 5c presents the results when we perform a joint attack using an ensemble that consists of both object detectors and segmentation models. The blackbox ASR is high on both detection and segmentation Fig. 5c, and the attack performance improves as we update the weights of the surrogate models. In Fig. 5c, we show the results for different perturbation budgets, with \\(\\ell_{\\infty} \\leq 10\\), the success rates on detection and segmentation are between \\(60\\% - 70\\%\\), which are close to in-domain detection attacks in Fig. 5a and indomain segmentation attacks Fig. 5b. When we increase the perturbation to \\(\\ell_{\\infty} \\leq 20\\), the success rate for both detection and segmentation can surpass \\(80\\%\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.811, + 0.892, + 0.9 + ], + "angle": 0, + "content": "Visualization of adversarial examples. In this example, our goal is to perturb the car in the middle to a traffic light. We assign the target label for car region to traffic light. Fig. 6a shows the results where a single adversarial image generated by the surrogate model can successfully fool the blackbox models RetinaNet and PSPNet." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.927, + 0.514, + 0.938 + ], + "angle": 0, + "content": "4051" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.107, + 0.098, + 0.345, + 0.243 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.102, + 0.249, + 0.35, + 0.274 + ], + "angle": 0, + "content": "(a) Attacks generated for object detection only, \\(\\ell_{\\infty}\\leq 10\\)" + }, + { + "type": "image", + "bbox": [ + 0.366, + 0.098, + 0.605, + 0.242 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.361, + 0.249, + 0.608, + 0.275 + ], + "angle": 0, + "content": "(b) Attacks generated for semantic segmentation only, \\(\\ell_{\\infty}\\leq 10\\)" + }, + { + "type": "image", + "bbox": [ + 0.626, + 0.093, + 0.865, + 0.237 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.619, + 0.243, + 0.868, + 0.28 + ], + "angle": 0, + "content": "(c) Attacks generated jointly for object detection and semantic segmentation, \\(\\ell_{\\infty} \\leq \\{10, 20\\}\\)" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.291, + 0.894, + 0.352 + ], + "angle": 0, + "content": "Figure 5. Comparison between task-specific attacks and joint attack performance on blackbox object detector (RetinaNet) and segmentation model (PSPNet). Green curves denote attack success rate for object detectors, and blue curves denote pixel success rate for semantic segmentation. (a) Attacks generated with an object detector surrogate do not transfer for semantic segmentation. (b) Attacks generated with semantic segmentation models surrogate do not transfer for object detectors. (c) Attacks generated by a surrogate of object detectors and semantic segmentation (along with weight balancing and optimization) provide successful attacks for blackbox object detectors and semantic segmentation models." + }, + { + "type": "image", + "bbox": [ + 0.123, + 0.368, + 0.363, + 0.463 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.211, + 0.464, + 0.28, + 0.475 + ], + "angle": 0, + "content": "Clean image" + }, + { + "type": "image", + "bbox": [ + 0.365, + 0.368, + 0.605, + 0.463 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.411, + 0.464, + 0.549, + 0.475 + ], + "angle": 0, + "content": "Detection on clean image" + }, + { + "type": "image", + "bbox": [ + 0.608, + 0.369, + 0.848, + 0.463 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.65, + 0.464, + 0.81, + 0.475 + ], + "angle": 0, + "content": "Segmentation of clean image" + }, + { + "type": "image", + "bbox": [ + 0.123, + 0.479, + 0.363, + 0.574 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.197, + 0.576, + 0.29, + 0.586 + ], + "angle": 0, + "content": "Perturbed image" + }, + { + "type": "image", + "bbox": [ + 0.365, + 0.479, + 0.604, + 0.574 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.398, + 0.576, + 0.561, + 0.586 + ], + "angle": 0, + "content": "Detection on perturbed image" + }, + { + "type": "image", + "bbox": [ + 0.608, + 0.479, + 0.848, + 0.574 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.638, + 0.576, + 0.822, + 0.587 + ], + "angle": 0, + "content": "Segmentation of perturbed image" + }, + { + "type": "image_caption", + "bbox": [ + 0.117, + 0.59, + 0.851, + 0.639 + ], + "angle": 0, + "content": "(a) Our method can generate attacks to fool multiple blackbox object detector and blackbox semantic segmentation models jointly. First row shows a clean image from Cityscapes dataset, detection with RetinaNet and segmentation with PSPNet. Second row shows the perturbed image using ensemble surrogates {Faster RCNN,YOLOv3,FCN,UPerNet}, and detection and segmentation results on the perturbed image. We generate perturbation to map the Car in the middle to Traffic Light. Image id: lindau_000026_000019" + }, + { + "type": "image", + "bbox": [ + 0.121, + 0.642, + 0.846, + 0.673 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.312, + 0.676, + 0.655, + 0.689 + ], + "angle": 0, + "content": "(b) Color encoding for segmentation maps in CityScapes dataset" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.694, + 0.89, + 0.719 + ], + "angle": 0, + "content": "Figure 6. Visual adversarial examples of our method that generates successful attacks to fool a blackbox object detector and a blackbox semantic segmentation model using a single perturbed image." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.727, + 0.196, + 0.741 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.765, + 0.471, + 0.901 + ], + "angle": 0, + "content": "We presented a new method to generate targeted attacks for dense prediction task (e.g., object detectors and semantic segmentation) using an ensemble of surrogate models. We demonstrate that (victim model-agnostic) weight balancing and (victim model-specific) weight optimization play a critical role in the success of attacks. We present an extensive set of experiments to demonstrate the performance of our method with different models and datasets. Finally, we show that our approach can create adversarial ex" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.728, + 0.885, + 0.744 + ], + "angle": 0, + "content": "amples to fool multiple blackbox models and tasks jointly." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.746, + 0.892, + 0.837 + ], + "angle": 0, + "content": "Limitations. Our method employs an ensemble of surrogate models to generate attacks, which inevitably incurs higher memory and computational overhead. Moreover, the success of our method hinges on the availability of a diverse set of surrogate models, which could potentially limit its efficacy if such models are not readily obtainable." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Acknowledgments. This material is based upon work supported by AFOSR award FA9550-21-1-0330, NSF award 2046293, UC Regents Faculty Development grant. 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In Proceedings of the IEEE/CVF International Conference on Computer Vision, pages 593-602, 2019. 4" + }, + { + "type": "list", + "bbox": [ + 0.08, + 0.092, + 0.47, + 0.853 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.927, + 0.515, + 0.938 + ], + "angle": 0, + "content": "4055" + } + ] +] \ No newline at end of file diff --git a/2023/Ensemble-Based Blackbox Attacks on Dense Prediction/1f7b1ddd-65c3-47e9-8398-1b94d1c9d1e3_origin.pdf b/2023/Ensemble-Based Blackbox Attacks on Dense Prediction/1f7b1ddd-65c3-47e9-8398-1b94d1c9d1e3_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..7f12492870c202762c5bd97d6d7b00cc3c0c6a7b --- /dev/null +++ b/2023/Ensemble-Based Blackbox Attacks on Dense Prediction/1f7b1ddd-65c3-47e9-8398-1b94d1c9d1e3_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:6f2186fe89738e490345cd7f7d0b024da3779ea00953d591630717ff06f5d703 +size 1454867 diff --git a/2023/Ensemble-Based Blackbox Attacks on Dense Prediction/full.md b/2023/Ensemble-Based Blackbox Attacks on Dense Prediction/full.md new file mode 100644 index 0000000000000000000000000000000000000000..3844bff253bf9b02cf060c09b8fb62b1cf86276d --- /dev/null +++ b/2023/Ensemble-Based Blackbox Attacks on Dense Prediction/full.md @@ -0,0 +1,327 @@ +# Ensemble-based Blackbox Attacks on Dense Prediction + +Zikui Cai*, Yaoteng Tan*, and M. Salman Asif +University of California Riverside + +{zcai032,ytan073,sasif}@ucr.edu + +# Abstract + +We propose an approach for adversarial attacks on dense prediction models (such as object detectors and segmentation). It is well known that the attacks generated by a single surrogate model do not transfer to arbitrary (blackbox) victim models. Furthermore, targeted attacks are often more challenging than the untargeted attacks. In this paper, we show that a carefully designed ensemble can create effective attacks for a number of victim models. In particular, we show that normalization of the weights for individual models plays a critical role in the success of the attacks. We then demonstrate that by adjusting the weights of the ensemble according to the victim model can further improve the performance of the attacks. We performed a number of experiments for object detectors and segmentation to highlight the significance of the our proposed methods. Our proposed ensemble-based method outperforms existing blackbox attack methods for object detection and segmentation. Finally, we show that our proposed method can also generate a single perturbation that can fool multiple blackbox detection and segmentation models simultaneously. Code is available at https://github.com/CSIplab/EBAD. + +# 1. Introduction + +Computer vision models (e.g., classification, object detection, segmentation, and depth estimation) are known to be vulnerable to carefully crafted adversarial examples [4, 11, 16, 17, 46]. Creating such adversarial attacks is easy for whitebox models, where the victim model is completely known [14, 16, 24, 37, 55]. In contrast, creating adversarial attacks for blackbox models, where the victim model is unknown, remains a challenging task [1, 33, 54]. Most of the existing blackbox attack methods have been developed for classification models [10, 21, 35, 47]. Blackbox attacks for dense prediction models such as object detection and segmentation are relatively less studied [4, 17, 27], and most of the existing ones mainly focus on untargeted + +![](images/93739e57f8193773619599eae7a2b10b2097bfbefc1409edf124328d01dc36bf.jpg) +Figure 1. Illustration of the targeted ensemble-based blackbox attack. (Top) Attack generated by a single surrogate model does not transfer on the victim blackbox model (person does not map to car). (Bottom) Attack generated by weight balancing and optimization can transfer on a variety of victim models (person is mapped to car). + +attacks [17]. Furthermore, a vast majority of these methods are based on transfer attacks, in which a surrogate (white-box) model is used to generate the adversarial example that is tested on the victim model. However, the success rate of such transfer-based attacks is often low, especially for targeted attacks [10, 21, 47]. + +In this paper, we propose and evaluate an ensemble-based blackbox attack method for objection detection and segmentation. Our method is inspired by three key observations: 1) targeted attacks generated by a single surrogate model are rarely successful; 2) attacks generated by an ensemble of surrogate models are highly successful if the contribution from all the models is properly normalized; and 3) attacks generated by an ensemble for a specific victim model can be further improved by adjusting the contributions of different surrogate models. The overall idea of the proposed work is illustrated in Fig. 1. Our proposed method can be viewed as a combination of transfer- and query-based attacks, where we can adjust the contribution based on the feedback from the victim model using a small number of queries (5–20 in our experiments). In contrast, conventional query-based attacks require hundreds or thousands of queries from the victim model [9, 19, 22, 49]. + +We conduct comprehensive experiments to validate our proposed method and achieve state-of-the-art performance for both targeted and untargeted blackbox attacks on ob- + +ject detection. Specifically, our proposed method attains $29 - 53\%$ success rate using only 5 queries for targeted attacks on object detectors, whereas the current state-of-the-art method [4] achieves $20 - 39\%$ success rate with the same number of queries. Furthermore, we extend our evaluation to untargeted and targeted attacks on blackbox semantic segmentation models. Our method achieves $0.9 - 1.55\%$ mIoU for untargeted and $69 - 95\%$ pixel-wise success for targeted attacks. By comparison, the current state-of-the-art method [17] obtains $0.6 - 7.97\%$ mIoU for untargeted attacks and does not report results for targeted attacks. To the best of our knowledge, our work is the first approach for targeted and query-based attacks for semantic segmentation. + +Below we summarize main contributions of this work. + +- We design a novel framework that can effectively attack blackbox dense prediction models based on an ensemble of surrogate models. +- We propose two simple yet highly effective ideas, namely weight balancing and weight optimization, with which we can achieve significantly better attack performance compared to existing methods. +- We extensively evaluate our method for targeted and untargeted attacks on object detection and semantic segmentation models and achieve state-of-the-art results. +- We demonstrate that our proposed method can generate a single perturbation that can fool multiple blackbox detection and segmentation models simultaneously. + +# 2. Related work + +Blackbox adversarial attacks. In the context of blackbox attacks, the attacker cannot access the model parameters or compute the gradient via backpropagation. Blackbox attack methods can be broadly divided into two groups: transfer-based [25, 33, 39, 40] and query-based attacks [9, 22, 49]. Transfer-based attacks rely on the assumption that surrogate models share similarities with the victim model, such that an adversarial example generated for the surrogate model can also fool the victim model. Query-based methods generate attacks by searching the adversarial examples space based on the feedback obtained from the victim model through queries. They can often achieve higher success rate but may require a large number of queries. + +Ensemble-based attacks. Ensemble-based attacks leverage the idea of transfer attack and assume that if an adversarial example can fool multiple models simultaneously, the chances of fooling an unseen model are higher [14, 33, 56]. Recently, some methods have combined ensemble-based transfer attacks with limited feedback from the victim models to improve the overall success rate [19, 21, 26, 35, 45, 47]. These methods have mainly focused on classification models, and ensemble attacks on dense prediction tasks such as object detection and semantic segmentation are relatively + +less studied, especially for targeted attacks [52]. + +Attacks against object detectors and segmentation. Dense (pixel-level) prediction tasks such as object detection and semantic segmentation have higher task complexities [50] compared to classification tasks. Existing attacks on object detectors mainly focus on whitebox setting, although there are a few exceptions [3, 51]. A recent study [4] generates blackbox attacks on object detectors by using a surrogate ensemble and context-aware attack-based queries. Another approach [51] trains a generative model to generate transferable attacks. While some patch-based attacks [32, 44] are effective, the patches are easily noticeable. Recent works [17, 18] have investigated adversarial robustness for semantic segmentation and proposed a transferable untargeted attack using a single surrogate model. While most existing methods are based on a single surrogate model, we demonstrate that using multiple surrogates with weight balancing/search in the attack generation process, we can generate more effective adversarial examples for both untargeted and targeted scenarios, as well as for various types of dense prediction tasks. + +# 3. Method + +# 3.1. Preliminaries + +We consider a per-instance attack scenario in which we generate adversarial perturbation $\delta$ for a given image $x$ . To keep the perturbation imperceptible, we bound its $\ell_p$ norm as $\| \delta \|_p \leq \varepsilon$ . In our experiments, we mainly use $\ell_{\infty}$ or max norm that limits the maximum level of perturbation. Our goal is to find $\delta$ such that the perturbed image, $x^{\star} = x + \delta$ , can disrupt a victim image recognition system $f_{\mathbf{v}}$ to make wrong predictions. Suppose the original prediction for the clean image $x$ is $y = f_{\mathbf{v}}(x)$ . The attack goal is $f(x^{\star}) \neq y$ for untargeted attack, and $f(x^{\star}) = y^{\star}$ for targeted attack, where $y^{\star}$ is the desired output (e.g., label or bounding box or segmentation map). + +For classification models, the label $y \in \mathbb{R}$ is a scalar. However, dense prediction models can have more complex output space. For object detection, the variable-length output $y \in \mathbb{R}^{K \times 6}$ , where $K$ is the number of detected objects, and each object label and position are encoded in a vector of length 6 that include the object category, bounding box coordinates, and confidence score. Some other tasks like keypoint detection and OCR are similar to object detection. For semantic segmentation, the prediction $y \in \mathbb{R}^{H \times W}$ is per-pixel classification, where $H$ and $W$ are the height and width of the input image, respectively. Depth and optical flow estimation tasks have similar output structure. + +The adversarial loss functions for object detection and semantic segmentation can be defined using their respective training or prediction loss functions. Let us consider a whitebox model $f$ and an input image $x$ with output + +$y = f(x)$ . For untargeted attack, we can search for the adversarial example $x^{\star}$ by solving the following maximization problem: + +$$ +x ^ {\star} = \underset {x} {\operatorname {a r g m a x}} \mathcal {L} (f (x), y), \tag {1} +$$ + +where $\mathcal{L}(f(x),y)$ represents the training loss of the model with input $x$ and output $y$ . For targeted attacks, with a target output $y^{\star}$ , we solve the following minimization problem: + +$$ +x ^ {\star} = \underset {x} {\operatorname {a r g m i n}} \mathcal {L} (f (x), y ^ {\star}). \tag {2} +$$ + +Different from classification, which mostly use cross-entropy loss across different models, dense predictions have different loss functions for different models due to the complexity of the output space and diversity of the architectures. For example, two-stage object detector, including Faster RCNN [43], has losses for object classification, bounding box regression, and losses on the region proposal network (RPN). But for one-stage object detectors like YOLO [41,42], they do not have losses corresponding to RPN. Due to the large variability of the loss functions used in different dense prediction models, we use the corresponding training loss $\mathcal{L}$ for each model as the optimization loss to guide the backpropagation. + +We employ PGD [37] to optimize the perturbation as + +$$ +\delta^ {t + 1} = \Pi_ {\varepsilon} \left(\delta^ {t} - \lambda \operatorname {s i g n} \left(\nabla_ {\delta} \mathcal {L} \left(f \left(x + \delta^ {t}\right), y ^ {\star}\right)\right)\right), \tag {3} +$$ + +for targeted attack and + +$$ +\delta^ {t + 1} = \Pi_ {\varepsilon} \left(\delta^ {t} + \lambda \operatorname {s i g n} \left(\nabla_ {\delta} \mathcal {L} (f (x + \delta^ {t}), y)\right)\right), \tag {4} +$$ + +for untargeted attack. Here $t$ indicates the attack step, $\lambda$ is the step size, and $\Pi_{\varepsilon}$ projects the perturbation into a $\ell_p$ norm ball with radius $\varepsilon$ . In the rest of the paper, we focus on targeted attacks without loss of generalization. + +# 3.2. Ensemble-based attacks + +In an ensemble-based transfer attack, we use an ensemble of $N$ surrogate (whitebox) models: $\mathcal{F} = \{f_1,\dots ,f_N\}$ to generate perturbations to attack the victim model $f_{\mathbf{v}}$ . Note that if the ensemble has a single model, then such an attack becomes a simple transfer attack with a single surrogate model. Let us denote the training loss function for $i$ th model as $\mathcal{L}_i(f_i(x),y^*)$ . A natural approach to combine the loss functions of all surrogate models is to compute an average or weighted average of the individual loss functions. For instance, we can generate the adversarial image by solving the following optimization problem: + +$$ +x ^ {\star} (\alpha) = \underset {x} {\arg \min } \sum_ {i = 1} ^ {N} \alpha_ {i} \mathcal {L} _ {i} \left(f _ {i} (x), y ^ {\star}\right), \tag {5} +$$ + +![](images/889d58ca82bf9620b14c67f1477290eec90f29cb8aa1c102214d9ec432c388bd.jpg) +Figure 2. Distribution of losses for different object detection models. $\mathbb{P}(\mathcal{L}_i(f_i(x),y^\star))$ . Calculated on 500 images from VOC dataset. + +where $x^{\star}(\alpha)$ is a function of the weights of the ensemble $\alpha = \{\alpha_{1},\ldots ,\alpha_{N}\}$ . One of our key observations is that the choice of weights plays a critical role in the transfer attack success rate of the ensemble models. + +Weight balancing (victim model agnostic). In ensemble-based transfer attacks, we build on the intuition that if an adversarial example can fool all models simultaneously, it would potentially be more transferable to any unseen victim model. This concept has been empirically corroborated by numerous works [14, 33]. However, most attack methods have only been verified on classification models, all of which use the same cross-entropy loss and yield similar loss values. In contrast, the loss functions for object detectors in an ensemble can differ significantly and cover a large range of values (as shown in Fig. 2). In such cases, models with large loss terms heavily influence the optimization procedure, reducing the attack success rate for models with small losses (see Tab. 1). To overcome this issue, we propose a simple yet effective solution to balance the weights assigned to each model in the ensemble as follows. For each input image $x$ and target output $y^{\star}$ , we adjust the weight for $i$ th surrogate model loss as + +$$ +\alpha_ {i} = \frac {\sum_ {i = 1} ^ {N} \mathcal {L} _ {i} \left(f _ {i} (x) , y ^ {\star}\right)}{N \mathcal {L} _ {i} \left(f _ {i} (x) , y ^ {\star}\right)}. \tag {6} +$$ + +The weights are adjusted in a whitebox setting as it allows us to measure the loss of each whitebox model accurately. The purpose of weight balancing is to ensure that all surrogate models can be successfully attacked, making the generated example more adversarial for blackbox victim models. Weight optimization (victim model specific). Note that the weight normalization, as discussed above, is agnostic to the victim model. We further observe that such transfer-based attacks can be further improved by optimizing the weights of the ensemble according to the victim model, input image, and target output. In particular, we can change the individual $\alpha_{i}$ to create the perturbations that reduce the victim model loss $\mathcal{L}_{\mathbf{v}}$ . To achieve this goal, we need to solve the following optimization problem with respect to $\alpha$ : + +$$ +\alpha^ {\star} = \underset {\alpha} {\arg \min } \mathcal {L} _ {\mathrm {v}} \left(f _ {\mathrm {v}} \left(x ^ {\star} (\alpha)\right), y ^ {\star}\right). \tag {7} +$$ + +The optimization problem in (7) is a nested optimization that we can solve as an alternating minimization routine. + +Step 0. Given input $x$ , output $y^{\star}$ , and surrogate ensemble $\mathcal{F}$ , we initialize $\alpha$ using (6). + +Step 1. Solve (5) to generate an adversarial example $x^{\star}(\alpha)$ . Step 2. Test the victim model. Stop if attack is successful; otherwise, change one of the $\alpha_{i}$ and repeat Step 1. + +In our experiments, we update the $\alpha_{i}$ in a cyclic manner (one coordinate at a time) as $\alpha_{i} \pm \gamma$ in Step 2, where $\gamma$ denotes a step size. In every round, we select the value of $\alpha_{i}$ that provides smallest value of the victim loss. We count the number of queries as the number of times we test the generated adversarial example on the victim model and denote it as $Q$ in our experiments. + +# 4. Experiments + +To evaluate the effectiveness of our method, we performed extensive experiments on attacking various object detection and semantic segmentation models. We first show that the attacks generated by a single surrogate model fail to transfer to arbitrary victim models. Then we show that the attack transfer rate can be increased by using an ensemble with weight balancing. Additional optimization of the weights surrogates for each victim model can further improve the attack performance. Finally, we show that we can generate single perturbations to fool object detectors and semantic segmentation models simultaneously. + +# 4.1. Experiment setup + +# 4.1.1 Object detection + +Models and datasets. We utilize MMDetection [7] toolbox to select various model architectures and weights pre-trained on COCO 2017 dataset [30]. To construct the surrogate ensemble, we start with two widely used models, Faster R-CNN [43] and YOLO [41, 42], and expand the ensemble by appending models with different architectures, including {FCOS [48], Grid R-CNN [36], SSD [31]}. We select different victim models, including {RetinaNet [29], Libra R-CNN [38], FoveaBox [23], FreeAnchor [59], DETR [6]}}. We evaluate attack performance on COCO 2017 [30] and Pascal VOC 2007 [15] datasets. Since the models from this repository are trained on COCO, which contains 80 object categories (a superset of VOC dataset's 20 categories), while testing on VOC dataset, we only return the objects that exist in VOC. We follow the setup in [4] and randomly select 500 images containing multiple (2-6) objects from VOC 2007 test and COCO 2017 validation sets. + +Evaluation metrics. We mainly focus on targeted attacks for object detection since they are more challenging than untargeted or vanishing attacks. We measure the performance of the attack using attack success rate (ASR), which + +equals the number of successfully attacked images over the total number of attacks. We follow the setting in [4], where if the target label is detected within the victim object region with IOU $>0.3$ , the attack is determined a success. + +Perturbation and query budget. We tested different perturbation levels with $\ell_{\infty} = \{10,20,30\}$ out of 255. We use at most 10 queries for attacking object detectors, and we show the trends of how ASR increases with the number of queries. To align with [4] that uses 5 attack plans, we set the maximum query budget to $Q = 5$ in Tab. 1. + +Comparing methods. We compare with [4], which is a state-of-the-art transfer-based approach that leverages context information to design attack plans to iteratively attack the victim object. The method generates different perturbations by iterating over a set of predefined attacks, and the total number of queries is the number of attempted attacks. BASES [3] is a recent work on ensemble-based blackbox attacks, which mainly focused on classification tasks and did not consider the loss distributions of different surrogate models. In our experiments, the ensemble with weight optimization and without balancing is equivalent to BASES [3]. + +# 4.1.2 Semantic segmentation + +Models and datasets. We use MMSegmentation [12] toolbox to select different model architectures and weights pre-trained on Cityscapes [13] ( $x \in \mathbb{R}^{512 \times 1024 \times 3}$ ) and Pascal VOC ( $x \in \mathbb{R}^{512 \times 512 \times 3}$ ) datasets. We select PSPNet [60] and DeepLabV3 [8] with ResNet50 and ResNet101 [20] backbones as our blackbox victim models. For the surrogate ensemble, we start with the primary semantic segmentation model FCN [34], and expand the ensemble with {UPerNet [53], PSANet [61], GCNet [5], ANN [62], EncNet [57]}. All models are built on ResNet50 [20] backbone trained with the cross-entropy loss. The loss values across all surrogate models have similar range; therefore, the effect of weight balancing for semantic segmentation is not as significant as it is for object detection. We use validation datasets from Cityscapes [13] and Pascal VOC 2012, which contains 500 and 1499 images with 19 and 21 classes, respectively. + +Evaluation metrics. We use different metrics for untargeted and targeted attack performance evaluation. In untargeted experiments, the attack performance is evaluated using the mIoU score (in percentage $\%$ ), the lower mIoU score the better attack performance. For targeted experiments, we report the pixel success ratio (PSR), which indicates the percentage of pixels successfully assigned the desired label in the target region, the higher the better attack performance. + +Perturbation and query budget. We use the perturbation budget $\ell_{\infty} \leq 8$ out of 255 and query budget $Q = 20$ . + +Comparing methods. We compare with dynamic scale (DS) attack [17] which is the most recent method that + +Table 1. Targeted attack success rate (%) of different methods at different perturbation budgets on VOC dataset. For each perturbation level, the first 4 rows correspond to different settings of our attacks, i.e. with (✓) or without (✗) weight balancing and weight optimization. We show comparison with context-aware attack [4], the state-of-the-art method for query-based blackbox attacks. + +
Perturbation BudgetWeight BalancingWeight OptimizationSurrogate EnsembleBlackbox Victim Models (ASR ↑)
FRCNNYOLOv3RetinaLibraFoveaFreeDETR
l∞=10XX27.991.511.69.29.013.45.6
X✓61.499.424.328.022.431.015.4
✓X71.185.730.933.427.236.012.2
✓✓86.096.953.256.647.257.429.0
Context-aware Attack [4]55.875.622.620.433.639.220.2
l∞=20XX40.192.216.920.415.423.29.7
X✓77.799.841.045.437.847.022.5
✓X82.789.841.050.444.857.021.6
✓✓94.698.066.974.468.079.448.0
Context-aware Attack [4]78.687.235.238.451.656.634.0
l∞=30XX43.491.117.122.617.427.211.4
X✓82.799.647.254.847.057.433.4
✓X85.390.248.856.845.659.629.2
✓✓96.098.178.982.876.883.058.8
Context-aware Attack [4]80.688.042.044.256.863.640.2
+ +![](images/bf23be9877ea494142a9129da7d6bf2bd199fdfc91701662f371beca1bf4ab55.jpg) +(a) $\ell_{\infty}\leq 10$ + +![](images/9b0fe3173b86f53f13c892bf9bc9a9d65eeccca60dfffa7b60d26167ff85ce86.jpg) +(b) $\ell_{\infty}\leq 20$ + +![](images/644f5928c385c4850f91a9d08c9c0a1f365f494ae69416d37584902a7dc022c4.jpg) +(c) $\ell_{\infty}\leq 30$ +Figure 3. Attack success rate (or fooling rate) vs number of queries $(Q)$ . The maximum value of $Q$ is set to 10 for these results. + +achieves the highest attack transfer rate on semantic segmentation untargeted attacks. + +# 4.2. Attacks against object detection + +Following settings in [4], we randomly select one object from the output of victim model as the victim object and perturb it into a target object that does not exist in the original detection. This approach rules out the possibility of mis-counting existing objects as the target object. + +We report our main results in Tab. 1. The baseline method uses a surrogate ensemble without weight balancing and models are assigned weight of 1. Such a baseline method is same a transfer-based method and results in highly imbalanced success rate for different surrogate models. For instance, at $\ell_{\infty} \leq 10$ , the success rate for YOLOv3 is above $90\%$ while the success rate for Faster R-CNN is less than $30\%$ . Low success rate on surrogate side translates to low success rate on blackbox victim side. The main reason for such imbalance is that the loss of dif + +ferent object detectors can be highly unbalanced (e.g., the loss value for YOLOv3 is nearly $60\times$ larger than the loss of Faster RCNN for targeted attacks, cf. Fig. 2). With weight balancing, the success rate increases for surrogate and blackbox victim models. The success rate is further increased on surrogate and victim blackbox models if we optimize the weights, same as BASES [3]. Our method (with weight balancing and optimization) achieves a significantly higher ASR compared to context-aware attack across different datasets and different perturbation budgets. On average, our ASR on blackbox victim models is over $4\times$ better than baseline method and over $1.5\times$ better than context-aware attack. On whitebox surrogate models, weight balancing and optimization also achieves the highest ASR. Context-aware attack fixes weight ratio for surrogate models, $\alpha_{\mathrm{FRCNN}} / \alpha_{\mathrm{YOLO}} = 4$ , which is sub-optimal according to our analyses. Even though it achieves much higher performance than baseline, it still largely under-performs our method. Similar trend is observed for COCO dataset (see Tab. S1). + +Table 2. Targeted ASR (%) for blackbox victim models and whitebox surrogate models with different ensemble sizes (N). On VOC dataset, ${\ell }_{\infty } \leq {10}$ . + +
NSurrogate EnsembleBlackbox Victim Models (ASR ↑)
FRCNNYOLOv3FCOSGrid R-CNNSSDRetinaLibraFoveaFreeDETR
174.7----31.331.229.840.410.6
286.096.9---53.256.647.257.429.0
387.996.174.2--63.162.057.366.638.0
489.694.775.287.9-68.771.067.674.449.6
589.791.873.586.182.468.970.268.477.653.2
+ +Table 3. Untargeted attack mIoU scores (%) of ensemble sizes $N = 2,4,6$ on Cityscapes dataset. We compare $Q = 0$ (i.e. direct transfer attack) with $Q = 20$ ensemble attack performance. DS uses DeepLabV3-Res50 (DL3-50) as the surrogate model for attack generation; thus the DS on DL3-50 is a whitebox attack. While our method used an ensemble that does not include any victim models for attack generation, we still achieved comparable mIoU scores to DS on DL3-50. Blue numbers represent whitebox attacks. + +
MethodWhitebox SurrogateBlackbox Victim Models (mIoU ↓)
PSPNet-Res50PSPNet-Res101DeepLabV3-Res50DeepLabV3-Res101
Clean Images-77.9278.2879.1277.12
BaselinePSPNet-Res503.4324.185.0525.74
DeepLabV3-Res504.7621.723.9222.23
DS [17]PSPNet-Res500.828.041.369.00
DeepLabV3-Res501.237.970.617.11
Ours (Q=0)N=25.078.325.198.74
N=44.336.264.326.33
N=63.624.914.024.84
Ours (Q=20)N=21.382.881.153.50
N=40.792.040.731.80
N=60.901.550.941.09
+ +Table 4. Targeted attack performance on Cityscapes as pixel success rate (higher the better). The attack performance increases as we increase ensemble size $(N)$ and number of queries for weight optimization $(Q)$ . $N = 1$ has zero query. We note PSPNet-Res50 as PSP-r50, and DeepLabV3-Res50 as DL3-r50, similar abbreviations apply to Res101. + +
QNBlackbox Victim Models (PSR ↑)
PSP-r50PSP-r101DL3-r50DL3-r101
0139.1510.2135.027.58
252.1512.2847.9910.59
343.1711.3442.109.87
451.4426.1349.1417.42
552.2423.8851.7516.08
20283.9751.8082.7046.95
388.8864.6385.5560.88
491.5164.2887.1963.88
592.9169.0988.9569.65
+ +Fig. 3 shows the effect of the number of queries on the ASR that gradually improves as we optimize the weights. We observe the largest increase in the first two steps and then the improvement plateaus as $Q \to 10$ . + +We also conducted an experiment to test our method with varying ensemble sizes. The results for $\ell_{\infty} \leq 10$ , $Q = 5$ are presented in Tab. 2. As we increase the number of models in the ensemble from $N = 1$ to $N = 5$ , we observe an increased ASR on all blackbox victim models. + +# 4.3. Attacks against semantic segmentation + +We evaluate the effectiveness of our attack on semantic segmentation in both untargeted and targeted settings. For the sake of consistency and a fair comparison, we adopt adversarial attack settings in DS attack [17]. + +Untargeted attacks. We generate adversarial attacks using different ensemble sizes and report mIoU scores on Cityscapes in Tab. 3 and Fig. 4 (and Pascal VOC in supplementary material). In the untargeted setting, semantic segmentation models are attacked to maximize the loss between clean and modified annotation; hence, the lower mIoU implies better attack performance. All of the victim models achieve high performance on clean images. The baseline method (direct transfer attack with one surrogate model using PGD) performs well in the whitebox setting but suffers when the victim uses another backbone. For example, the attacks generated on PSPNet-Res50 achieves $3.43\%$ mIoU on PSPNet-Res50 but only attains $24.18\%$ mIoU on PSPNet-Res101. DS attack achieves better results than the baseline method but still suffers from crossbackbone transfers. On the other hand, our method, without weight optimization (i.e., $Q = 0$ ) and using a surrogate ensemble of $N = 2$ models, can achieve results comparable to DS attack, particularly for attacks on Res101 models. As we increase the number of surrogate models to 4 or 6, our + +![](images/6bebcb55ed5cc7a2bb00b16f301eb8447883c77b2f756dace29bfe42398bf41c.jpg) +(a) $N = 2$ + +![](images/689f07dde1e9b9fea8f0a1e283c20ccd5c04bcf810a36713d5af13bf6ac958bd.jpg) +(b) $N = 4$ + +![](images/655a64495db1d8d9e69cb84ac560a39fb6bd7e0960a8532d64dabdbf8f604ad1.jpg) +(c) $N = 6$ +Figure 4. mIoU vs number of queries $(Q)$ for different ensemble sizes $(N)$ . + +attack performance further improves. Furthermore, when we apply weight optimization (e.g., $Q = 20$ ), the attack improves by updating the weights of the surrogate models, allowing us to outperform DS attack for all victim models. Fig. 4 shows how the mIoU changes with the number of queries. We observe that the mIoU gradually reduces as we query the victim model and optimize the weights. The largest decrease happens in the first 3-4 steps and then the reduction plateaus as $Q \to 20$ . + +Targeted attack. To evaluate our method in a more challenging setting, we consider a targeted attack scenario, where instead of changing every pixel in the segmentation to some arbitrary label, we focus on attacking a dominant class (i.e., the class occupying the largest area) in the scene to its least likely class $y^{\star}$ . For each clean image, we first select a region with the dominant class $y$ (e.g., "road" or "building" for most of the Cityscapes images. See Fig. S3 as an example). Then based on the least-likely class of each pixel in that region, we select the class that appears most frequently as the target label $y^{\star}$ of the entire region. We use PSR as our evaluation metric, which represents the percentage of pixels in the selected region that are successfully assigned to $y^{\star}$ . The higher percentage indicates more pixels are successfully attacked to the desired class, which indicates better attack performance. Our targeted attack results are reported in Tab. 4. Results show that as we increase the number of surrogate models ( $N$ ), the ASR improves for most instances without any weight optimization step (i.e., $Q = 0$ ). If we perform weight optimization for $Q = 20$ steps, then the success rate increases for all the models. For instance, with $N = 4$ , the ASR for Res101 models increases from 17–26% to 63–64%. + +# 4.4. Joint attack for multiple models and tasks + +We first show that generally adversarial examples generated for object detection do not transfer to semantic segmentation, and vice versa. Then we show that we can generate single perturbations to fool object detectors and semantic segmentation models simultaneously, by using a surrogate ensemble including both detection and segmentation mod + +els. We choose targeted attacks in our experiments because they are more challenging than untargeted attacks. + +Experiment setup. On the blackbox (victim) side, we tested RetinaNet as the victim object detector and PSPNet-Res50 as the victim semantic segmentation model. On the whitebox (surrogate) side, we used Faster RCNN, YOLOv3 as the surrogate object detectors and FCN, UPerNet as the surrogate semantic segmentation models. We performed targeted attacks on 500 test images selected from the validation set of CityScapes dataset. + +Results. We present the ASRs for task-specific and joint attacks in Fig. 5. Green curves denote ASR for object detectors, and blue curves denote PSR for semantic segmentation. Fig. 5a presents the results when we generate attacks using an object detector surrogate ensemble. Note that success rate for victim object detector (RetinaNet) increases as we optimize the weights but the success rate for the semantic segmentation model (PSPNet) remains small. Similarly, Fig. 5b presents the results when we generate attacks using a segmentation surrogate ensemble. The success rate for the victim semantic segmentation model increases, but the success rate for the object doctor remains close to zero. Fig. 5c presents the results when we perform a joint attack using an ensemble that consists of both object detectors and segmentation models. The blackbox ASR is high on both detection and segmentation Fig. 5c, and the attack performance improves as we update the weights of the surrogate models. In Fig. 5c, we show the results for different perturbation budgets, with $\ell_{\infty} \leq 10$ , the success rates on detection and segmentation are between $60\% - 70\%$ , which are close to in-domain detection attacks in Fig. 5a and indomain segmentation attacks Fig. 5b. When we increase the perturbation to $\ell_{\infty} \leq 20$ , the success rate for both detection and segmentation can surpass $80\%$ . + +Visualization of adversarial examples. In this example, our goal is to perturb the car in the middle to a traffic light. We assign the target label for car region to traffic light. Fig. 6a shows the results where a single adversarial image generated by the surrogate model can successfully fool the blackbox models RetinaNet and PSPNet. + +![](images/c9895fc8f9ffc64509809a6f8e394840ed1ca79e5e91fd28662ee9fe5f222d78.jpg) +(a) Attacks generated for object detection only, $\ell_{\infty}\leq 10$ + +![](images/70b43ba3141826aa03c9844f8dd9f83cbb4283514c9e04865cee9ba41573286a.jpg) +(b) Attacks generated for semantic segmentation only, $\ell_{\infty}\leq 10$ + +![](images/eab51f90d6955e39e012ecf8a559c349c8b3bed87ba32017409de27e8338b72b.jpg) +(c) Attacks generated jointly for object detection and semantic segmentation, $\ell_{\infty} \leq \{10, 20\}$ + +![](images/905f8a2ffc1329c97a139fd05c665c859c64411f7aadbda480a39e1c0f0c1cb7.jpg) +Figure 5. Comparison between task-specific attacks and joint attack performance on blackbox object detector (RetinaNet) and segmentation model (PSPNet). Green curves denote attack success rate for object detectors, and blue curves denote pixel success rate for semantic segmentation. (a) Attacks generated with an object detector surrogate do not transfer for semantic segmentation. (b) Attacks generated with semantic segmentation models surrogate do not transfer for object detectors. (c) Attacks generated by a surrogate of object detectors and semantic segmentation (along with weight balancing and optimization) provide successful attacks for blackbox object detectors and semantic segmentation models. +Clean image + +![](images/27e8259ecbfeda124bfe7e97f1ea359ef857824cd84ca7df8debc2d5193cf486.jpg) +Detection on clean image + +![](images/573b7cbcf54cc2ef948a7538892c8567ef92dc5b103ead3cec0525d697dab33a.jpg) +Segmentation of clean image + +![](images/b43f6fba2a48d184c208ad4052d0f4f69a7823d152ceff707d33003f8b03c8e1.jpg) +Perturbed image + +![](images/1346bccf623f70f2bf29720ef2af1e975b5c36b5328ba3e70d8d0f763a01005e.jpg) +Detection on perturbed image + +![](images/e724eeeefabd9a6d6e3e428b62b5f87ef22bdeed147db2c40559790bd30e07c5.jpg) +Segmentation of perturbed image + +![](images/930609f2565537a7ef8c1443d370e491b1dea0baca65256d2e4164a47e44e422.jpg) +(a) Our method can generate attacks to fool multiple blackbox object detector and blackbox semantic segmentation models jointly. First row shows a clean image from Cityscapes dataset, detection with RetinaNet and segmentation with PSPNet. Second row shows the perturbed image using ensemble surrogates {Faster RCNN,YOLOv3,FCN,UPerNet}, and detection and segmentation results on the perturbed image. We generate perturbation to map the Car in the middle to Traffic Light. Image id: lindau_000026_000019 +(b) Color encoding for segmentation maps in CityScapes dataset +Figure 6. Visual adversarial examples of our method that generates successful attacks to fool a blackbox object detector and a blackbox semantic segmentation model using a single perturbed image. + +# 5. Conclusion + +We presented a new method to generate targeted attacks for dense prediction task (e.g., object detectors and semantic segmentation) using an ensemble of surrogate models. We demonstrate that (victim model-agnostic) weight balancing and (victim model-specific) weight optimization play a critical role in the success of attacks. We present an extensive set of experiments to demonstrate the performance of our method with different models and datasets. Finally, we show that our approach can create adversarial ex + +amples to fool multiple blackbox models and tasks jointly. + +Limitations. Our method employs an ensemble of surrogate models to generate attacks, which inevitably incurs higher memory and computational overhead. Moreover, the success of our method hinges on the availability of a diverse set of surrogate models, which could potentially limit its efficacy if such models are not readily obtainable. + +Acknowledgments. This material is based upon work supported by AFOSR award FA9550-21-1-0330, NSF award 2046293, UC Regents Faculty Development grant. We acknowledge the computing support from Nautilus PRP. + +# References + +[1] Anurag Arnab, Ondrej Miksik, and Philip HS Torr. On the robustness of semantic segmentation models to adversarial attacks. 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In Proceedings of the IEEE/CVF International Conference on Computer Vision, pages 593-602, 2019. 4 \ No newline at end of file diff --git a/2023/Ensemble-Based Blackbox Attacks on Dense Prediction/images.zip b/2023/Ensemble-Based Blackbox Attacks on Dense Prediction/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..cedb7b15262e6f74136533e5ad2bcaec2d773af7 --- /dev/null +++ b/2023/Ensemble-Based Blackbox Attacks on Dense Prediction/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:36606d80f15a4194a88d3af50bdbfc7ad2f1e0ef664fb5a5c42fde587fd71c33 +size 514964 diff --git a/2023/Ensemble-Based Blackbox Attacks on Dense Prediction/layout.json b/2023/Ensemble-Based Blackbox Attacks on Dense Prediction/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..ac05854a189a7a18326de0091c5afb7cdf8c7243 --- /dev/null +++ b/2023/Ensemble-Based Blackbox Attacks on Dense Prediction/layout.json @@ -0,0 +1,9835 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 127, + 103, + 467, + 119 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 127, + 103, + 467, + 119 + ], + "spans": [ + { + "bbox": [ + 127, + 103, + 467, + 119 + ], + "type": "text", + "content": "Ensemble-based Blackbox Attacks on Dense Prediction" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 183, + 143, + 411, + 171 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 183, + 143, + 411, + 171 + ], + "spans": [ + { + "bbox": [ + 183, + 143, + 411, + 171 + ], + "type": "text", + "content": "Zikui Cai*, Yaoteng Tan*, and M. Salman Asif \nUniversity of California Riverside" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 211, + 174, + 380, + 185 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 211, + 174, + 380, + 185 + ], + "spans": [ + { + "bbox": [ + 211, + 174, + 380, + 185 + ], + "type": "text", + "content": "{zcai032,ytan073,sasif}@ucr.edu" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 143, + 213, + 192, + 225 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 213, + 192, + 225 + ], + "spans": [ + { + "bbox": [ + 143, + 213, + 192, + 225 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 239, + 290, + 491 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 239, + 290, + 491 + ], + "spans": [ + { + "bbox": [ + 46, + 239, + 290, + 491 + ], + "type": "text", + "content": "We propose an approach for adversarial attacks on dense prediction models (such as object detectors and segmentation). It is well known that the attacks generated by a single surrogate model do not transfer to arbitrary (blackbox) victim models. Furthermore, targeted attacks are often more challenging than the untargeted attacks. In this paper, we show that a carefully designed ensemble can create effective attacks for a number of victim models. In particular, we show that normalization of the weights for individual models plays a critical role in the success of the attacks. We then demonstrate that by adjusting the weights of the ensemble according to the victim model can further improve the performance of the attacks. We performed a number of experiments for object detectors and segmentation to highlight the significance of the our proposed methods. Our proposed ensemble-based method outperforms existing blackbox attack methods for object detection and segmentation. Finally, we show that our proposed method can also generate a single perturbation that can fool multiple blackbox detection and segmentation models simultaneously. Code is available at https://github.com/CSIplab/EBAD." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 515, + 128, + 528 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 515, + 128, + 528 + ], + "spans": [ + { + "bbox": [ + 47, + 515, + 128, + 528 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 536, + 287, + 693 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 536, + 287, + 693 + ], + "spans": [ + { + "bbox": [ + 46, + 536, + 287, + 693 + ], + "type": "text", + "content": "Computer vision models (e.g., classification, object detection, segmentation, and depth estimation) are known to be vulnerable to carefully crafted adversarial examples [4, 11, 16, 17, 46]. Creating such adversarial attacks is easy for whitebox models, where the victim model is completely known [14, 16, 24, 37, 55]. In contrast, creating adversarial attacks for blackbox models, where the victim model is unknown, remains a challenging task [1, 33, 54]. Most of the existing blackbox attack methods have been developed for classification models [10, 21, 35, 47]. Blackbox attacks for dense prediction models such as object detection and segmentation are relatively less studied [4, 17, 27], and most of the existing ones mainly focus on untargeted" + } + ] + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 317, + 213, + 541, + 334 + ], + "blocks": [ + { + "bbox": [ + 317, + 213, + 541, + 334 + ], + "lines": [ + { + "bbox": [ + 317, + 213, + 541, + 334 + ], + "spans": [ + { + "bbox": [ + 317, + 213, + 541, + 334 + ], + "type": "image", + "image_path": "93739e57f8193773619599eae7a2b10b2097bfbefc1409edf124328d01dc36bf.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 344, + 547, + 393 + ], + "lines": [ + { + "bbox": [ + 305, + 344, + 547, + 393 + ], + "spans": [ + { + "bbox": [ + 305, + 344, + 547, + 393 + ], + "type": "text", + "content": "Figure 1. Illustration of the targeted ensemble-based blackbox attack. (Top) Attack generated by a single surrogate model does not transfer on the victim blackbox model (person does not map to car). (Bottom) Attack generated by weight balancing and optimization can transfer on a variety of victim models (person is mapped to car)." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 401, + 547, + 472 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 401, + 547, + 472 + ], + "spans": [ + { + "bbox": [ + 304, + 401, + 547, + 472 + ], + "type": "text", + "content": "attacks [17]. Furthermore, a vast majority of these methods are based on transfer attacks, in which a surrogate (white-box) model is used to generate the adversarial example that is tested on the victim model. However, the success rate of such transfer-based attacks is often low, especially for targeted attacks [10, 21, 47]." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 474, + 548, + 676 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 474, + 548, + 676 + ], + "spans": [ + { + "bbox": [ + 304, + 474, + 548, + 676 + ], + "type": "text", + "content": "In this paper, we propose and evaluate an ensemble-based blackbox attack method for objection detection and segmentation. Our method is inspired by three key observations: 1) targeted attacks generated by a single surrogate model are rarely successful; 2) attacks generated by an ensemble of surrogate models are highly successful if the contribution from all the models is properly normalized; and 3) attacks generated by an ensemble for a specific victim model can be further improved by adjusting the contributions of different surrogate models. The overall idea of the proposed work is illustrated in Fig. 1. Our proposed method can be viewed as a combination of transfer- and query-based attacks, where we can adjust the contribution based on the feedback from the victim model using a small number of queries (5–20 in our experiments). In contrast, conventional query-based attacks require hundreds or thousands of queries from the victim model [9, 19, 22, 49]." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 677, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 677, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 677, + 547, + 713 + ], + "type": "text", + "content": "We conduct comprehensive experiments to validate our proposed method and achieve state-of-the-art performance for both targeted and untargeted blackbox attacks on ob-" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 496, + 35 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 496, + 35 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 496, + 35 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 59, + 702, + 124, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 702, + 124, + 712 + ], + "spans": [ + { + "bbox": [ + 59, + 702, + 124, + 712 + ], + "type": "text", + "content": "* Equal contribution" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 295, + 732, + 315, + 742 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 732, + 315, + 742 + ], + "spans": [ + { + "bbox": [ + 295, + 732, + 315, + 742 + ], + "type": "text", + "content": "4045" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 228 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 228 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 228 + ], + "type": "text", + "content": "ject detection. Specifically, our proposed method attains " + }, + { + "bbox": [ + 46, + 72, + 289, + 228 + ], + "type": "inline_equation", + "content": "29 - 53\\%" + }, + { + "bbox": [ + 46, + 72, + 289, + 228 + ], + "type": "text", + "content": " success rate using only 5 queries for targeted attacks on object detectors, whereas the current state-of-the-art method [4] achieves " + }, + { + "bbox": [ + 46, + 72, + 289, + 228 + ], + "type": "inline_equation", + "content": "20 - 39\\%" + }, + { + "bbox": [ + 46, + 72, + 289, + 228 + ], + "type": "text", + "content": " success rate with the same number of queries. Furthermore, we extend our evaluation to untargeted and targeted attacks on blackbox semantic segmentation models. Our method achieves " + }, + { + "bbox": [ + 46, + 72, + 289, + 228 + ], + "type": "inline_equation", + "content": "0.9 - 1.55\\%" + }, + { + "bbox": [ + 46, + 72, + 289, + 228 + ], + "type": "text", + "content": " mIoU for untargeted and " + }, + { + "bbox": [ + 46, + 72, + 289, + 228 + ], + "type": "inline_equation", + "content": "69 - 95\\%" + }, + { + "bbox": [ + 46, + 72, + 289, + 228 + ], + "type": "text", + "content": " pixel-wise success for targeted attacks. By comparison, the current state-of-the-art method [17] obtains " + }, + { + "bbox": [ + 46, + 72, + 289, + 228 + ], + "type": "inline_equation", + "content": "0.6 - 7.97\\%" + }, + { + "bbox": [ + 46, + 72, + 289, + 228 + ], + "type": "text", + "content": " mIoU for untargeted attacks and does not report results for targeted attacks. To the best of our knowledge, our work is the first approach for targeted and query-based attacks for semantic segmentation." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 59, + 228, + 278, + 239 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 228, + 278, + 239 + ], + "spans": [ + { + "bbox": [ + 59, + 228, + 278, + 239 + ], + "type": "text", + "content": "Below we summarize main contributions of this work." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 243, + 287, + 407 + ], + "type": "list", + "angle": 0, + "index": 6, + "blocks": [ + { + "bbox": [ + 47, + 243, + 287, + 278 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 243, + 287, + 278 + ], + "spans": [ + { + "bbox": [ + 47, + 243, + 287, + 278 + ], + "type": "text", + "content": "- We design a novel framework that can effectively attack blackbox dense prediction models based on an ensemble of surrogate models." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 281, + 287, + 329 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 281, + 287, + 329 + ], + "spans": [ + { + "bbox": [ + 47, + 281, + 287, + 329 + ], + "type": "text", + "content": "- We propose two simple yet highly effective ideas, namely weight balancing and weight optimization, with which we can achieve significantly better attack performance compared to existing methods." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 332, + 286, + 367 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 332, + 286, + 367 + ], + "spans": [ + { + "bbox": [ + 47, + 332, + 286, + 367 + ], + "type": "text", + "content": "- We extensively evaluate our method for targeted and untargeted attacks on object detection and semantic segmentation models and achieve state-of-the-art results." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 372, + 287, + 407 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 372, + 287, + 407 + ], + "spans": [ + { + "bbox": [ + 47, + 372, + 287, + 407 + ], + "type": "text", + "content": "- We demonstrate that our proposed method can generate a single perturbation that can fool multiple blackbox detection and segmentation models simultaneously." + } + ] + } + ], + "index": 5 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 47, + 418, + 130, + 430 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 418, + 130, + 430 + ], + "spans": [ + { + "bbox": [ + 47, + 418, + 130, + 430 + ], + "type": "text", + "content": "2. Related work" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 437, + 287, + 594 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 437, + 287, + 594 + ], + "spans": [ + { + "bbox": [ + 46, + 437, + 287, + 594 + ], + "type": "text", + "content": "Blackbox adversarial attacks. In the context of blackbox attacks, the attacker cannot access the model parameters or compute the gradient via backpropagation. Blackbox attack methods can be broadly divided into two groups: transfer-based [25, 33, 39, 40] and query-based attacks [9, 22, 49]. Transfer-based attacks rely on the assumption that surrogate models share similarities with the victim model, such that an adversarial example generated for the surrogate model can also fool the victim model. Query-based methods generate attacks by searching the adversarial examples space based on the feedback obtained from the victim model through queries. They can often achieve higher success rate but may require a large number of queries." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 594, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 594, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 288, + 714 + ], + "type": "text", + "content": "Ensemble-based attacks. Ensemble-based attacks leverage the idea of transfer attack and assume that if an adversarial example can fool multiple models simultaneously, the chances of fooling an unseen model are higher [14, 33, 56]. Recently, some methods have combined ensemble-based transfer attacks with limited feedback from the victim models to improve the overall success rate [19, 21, 26, 35, 45, 47]. These methods have mainly focused on classification models, and ensemble attacks on dense prediction tasks such as object detection and semantic segmentation are relatively" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 72, + 500, + 84 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 500, + 84 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 500, + 84 + ], + "type": "text", + "content": "less studied, especially for targeted attacks [52]." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 85, + 545, + 324 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 85, + 545, + 324 + ], + "spans": [ + { + "bbox": [ + 304, + 85, + 545, + 324 + ], + "type": "text", + "content": "Attacks against object detectors and segmentation. Dense (pixel-level) prediction tasks such as object detection and semantic segmentation have higher task complexities [50] compared to classification tasks. Existing attacks on object detectors mainly focus on whitebox setting, although there are a few exceptions [3, 51]. A recent study [4] generates blackbox attacks on object detectors by using a surrogate ensemble and context-aware attack-based queries. Another approach [51] trains a generative model to generate transferable attacks. While some patch-based attacks [32, 44] are effective, the patches are easily noticeable. Recent works [17, 18] have investigated adversarial robustness for semantic segmentation and proposed a transferable untargeted attack using a single surrogate model. While most existing methods are based on a single surrogate model, we demonstrate that using multiple surrogates with weight balancing/search in the attack generation process, we can generate more effective adversarial examples for both untargeted and targeted scenarios, as well as for various types of dense prediction tasks." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 337, + 361, + 349 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 337, + 361, + 349 + ], + "spans": [ + { + "bbox": [ + 306, + 337, + 361, + 349 + ], + "type": "text", + "content": "3. Method" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 357, + 391, + 369 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 357, + 391, + 369 + ], + "spans": [ + { + "bbox": [ + 306, + 357, + 391, + 369 + ], + "type": "text", + "content": "3.1. Preliminaries" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 376, + 545, + 520 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 376, + 545, + 520 + ], + "spans": [ + { + "bbox": [ + 304, + 376, + 545, + 520 + ], + "type": "text", + "content": "We consider a per-instance attack scenario in which we generate adversarial perturbation " + }, + { + "bbox": [ + 304, + 376, + 545, + 520 + ], + "type": "inline_equation", + "content": "\\delta" + }, + { + "bbox": [ + 304, + 376, + 545, + 520 + ], + "type": "text", + "content": " for a given image " + }, + { + "bbox": [ + 304, + 376, + 545, + 520 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 304, + 376, + 545, + 520 + ], + "type": "text", + "content": ". To keep the perturbation imperceptible, we bound its " + }, + { + "bbox": [ + 304, + 376, + 545, + 520 + ], + "type": "inline_equation", + "content": "\\ell_p" + }, + { + "bbox": [ + 304, + 376, + 545, + 520 + ], + "type": "text", + "content": " norm as " + }, + { + "bbox": [ + 304, + 376, + 545, + 520 + ], + "type": "inline_equation", + "content": "\\| \\delta \\|_p \\leq \\varepsilon" + }, + { + "bbox": [ + 304, + 376, + 545, + 520 + ], + "type": "text", + "content": ". In our experiments, we mainly use " + }, + { + "bbox": [ + 304, + 376, + 545, + 520 + ], + "type": "inline_equation", + "content": "\\ell_{\\infty}" + }, + { + "bbox": [ + 304, + 376, + 545, + 520 + ], + "type": "text", + "content": " or max norm that limits the maximum level of perturbation. Our goal is to find " + }, + { + "bbox": [ + 304, + 376, + 545, + 520 + ], + "type": "inline_equation", + "content": "\\delta" + }, + { + "bbox": [ + 304, + 376, + 545, + 520 + ], + "type": "text", + "content": " such that the perturbed image, " + }, + { + "bbox": [ + 304, + 376, + 545, + 520 + ], + "type": "inline_equation", + "content": "x^{\\star} = x + \\delta" + }, + { + "bbox": [ + 304, + 376, + 545, + 520 + ], + "type": "text", + "content": ", can disrupt a victim image recognition system " + }, + { + "bbox": [ + 304, + 376, + 545, + 520 + ], + "type": "inline_equation", + "content": "f_{\\mathbf{v}}" + }, + { + "bbox": [ + 304, + 376, + 545, + 520 + ], + "type": "text", + "content": " to make wrong predictions. Suppose the original prediction for the clean image " + }, + { + "bbox": [ + 304, + 376, + 545, + 520 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 304, + 376, + 545, + 520 + ], + "type": "text", + "content": " is " + }, + { + "bbox": [ + 304, + 376, + 545, + 520 + ], + "type": "inline_equation", + "content": "y = f_{\\mathbf{v}}(x)" + }, + { + "bbox": [ + 304, + 376, + 545, + 520 + ], + "type": "text", + "content": ". The attack goal is " + }, + { + "bbox": [ + 304, + 376, + 545, + 520 + ], + "type": "inline_equation", + "content": "f(x^{\\star}) \\neq y" + }, + { + "bbox": [ + 304, + 376, + 545, + 520 + ], + "type": "text", + "content": " for untargeted attack, and " + }, + { + "bbox": [ + 304, + 376, + 545, + 520 + ], + "type": "inline_equation", + "content": "f(x^{\\star}) = y^{\\star}" + }, + { + "bbox": [ + 304, + 376, + 545, + 520 + ], + "type": "text", + "content": " for targeted attack, where " + }, + { + "bbox": [ + 304, + 376, + 545, + 520 + ], + "type": "inline_equation", + "content": "y^{\\star}" + }, + { + "bbox": [ + 304, + 376, + 545, + 520 + ], + "type": "text", + "content": " is the desired output (e.g., label or bounding box or segmentation map)." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 521, + 545, + 664 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 521, + 545, + 664 + ], + "spans": [ + { + "bbox": [ + 304, + 521, + 545, + 664 + ], + "type": "text", + "content": "For classification models, the label " + }, + { + "bbox": [ + 304, + 521, + 545, + 664 + ], + "type": "inline_equation", + "content": "y \\in \\mathbb{R}" + }, + { + "bbox": [ + 304, + 521, + 545, + 664 + ], + "type": "text", + "content": " is a scalar. However, dense prediction models can have more complex output space. For object detection, the variable-length output " + }, + { + "bbox": [ + 304, + 521, + 545, + 664 + ], + "type": "inline_equation", + "content": "y \\in \\mathbb{R}^{K \\times 6}" + }, + { + "bbox": [ + 304, + 521, + 545, + 664 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 521, + 545, + 664 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 304, + 521, + 545, + 664 + ], + "type": "text", + "content": " is the number of detected objects, and each object label and position are encoded in a vector of length 6 that include the object category, bounding box coordinates, and confidence score. Some other tasks like keypoint detection and OCR are similar to object detection. For semantic segmentation, the prediction " + }, + { + "bbox": [ + 304, + 521, + 545, + 664 + ], + "type": "inline_equation", + "content": "y \\in \\mathbb{R}^{H \\times W}" + }, + { + "bbox": [ + 304, + 521, + 545, + 664 + ], + "type": "text", + "content": " is per-pixel classification, where " + }, + { + "bbox": [ + 304, + 521, + 545, + 664 + ], + "type": "inline_equation", + "content": "H" + }, + { + "bbox": [ + 304, + 521, + 545, + 664 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 521, + 545, + 664 + ], + "type": "inline_equation", + "content": "W" + }, + { + "bbox": [ + 304, + 521, + 545, + 664 + ], + "type": "text", + "content": " are the height and width of the input image, respectively. Depth and optical flow estimation tasks have similar output structure." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "content": "The adversarial loss functions for object detection and semantic segmentation can be defined using their respective training or prediction loss functions. Let us consider a whitebox model " + }, + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "content": " and an input image " + }, + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "content": " with output" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 732, + 315, + 742 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 732, + 315, + 742 + ], + "spans": [ + { + "bbox": [ + 295, + 732, + 315, + 742 + ], + "type": "text", + "content": "4046" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 287, + 107 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 287, + 107 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 287, + 107 + ], + "type": "inline_equation", + "content": "y = f(x)" + }, + { + "bbox": [ + 47, + 72, + 287, + 107 + ], + "type": "text", + "content": ". For untargeted attack, we can search for the adversarial example " + }, + { + "bbox": [ + 47, + 72, + 287, + 107 + ], + "type": "inline_equation", + "content": "x^{\\star}" + }, + { + "bbox": [ + 47, + 72, + 287, + 107 + ], + "type": "text", + "content": " by solving the following maximization problem:" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 108, + 118, + 287, + 137 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 108, + 118, + 287, + 137 + ], + "spans": [ + { + "bbox": [ + 108, + 118, + 287, + 137 + ], + "type": "interline_equation", + "content": "x ^ {\\star} = \\underset {x} {\\operatorname {a r g m a x}} \\mathcal {L} (f (x), y), \\tag {1}", + "image_path": "efcf94986e2ac5594736649da826272d88a410b77a69873c8d023a6397217aac.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 147, + 287, + 183 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 147, + 287, + 183 + ], + "spans": [ + { + "bbox": [ + 47, + 147, + 287, + 183 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 147, + 287, + 183 + ], + "type": "inline_equation", + "content": "\\mathcal{L}(f(x),y)" + }, + { + "bbox": [ + 47, + 147, + 287, + 183 + ], + "type": "text", + "content": " represents the training loss of the model with input " + }, + { + "bbox": [ + 47, + 147, + 287, + 183 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 47, + 147, + 287, + 183 + ], + "type": "text", + "content": " and output " + }, + { + "bbox": [ + 47, + 147, + 287, + 183 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 47, + 147, + 287, + 183 + ], + "type": "text", + "content": ". For targeted attacks, with a target output " + }, + { + "bbox": [ + 47, + 147, + 287, + 183 + ], + "type": "inline_equation", + "content": "y^{\\star}" + }, + { + "bbox": [ + 47, + 147, + 287, + 183 + ], + "type": "text", + "content": ", we solve the following minimization problem:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 107, + 193, + 287, + 212 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 107, + 193, + 287, + 212 + ], + "spans": [ + { + "bbox": [ + 107, + 193, + 287, + 212 + ], + "type": "interline_equation", + "content": "x ^ {\\star} = \\underset {x} {\\operatorname {a r g m i n}} \\mathcal {L} (f (x), y ^ {\\star}). \\tag {2}", + "image_path": "3c67218054ebf2b79c4899ac099387ec45add8223167e13d94675207adcbd511.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 221, + 287, + 376 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 221, + 287, + 376 + ], + "spans": [ + { + "bbox": [ + 46, + 221, + 287, + 376 + ], + "type": "text", + "content": "Different from classification, which mostly use cross-entropy loss across different models, dense predictions have different loss functions for different models due to the complexity of the output space and diversity of the architectures. For example, two-stage object detector, including Faster RCNN [43], has losses for object classification, bounding box regression, and losses on the region proposal network (RPN). But for one-stage object detectors like YOLO [41,42], they do not have losses corresponding to RPN. Due to the large variability of the loss functions used in different dense prediction models, we use the corresponding training loss " + }, + { + "bbox": [ + 46, + 221, + 287, + 376 + ], + "type": "inline_equation", + "content": "\\mathcal{L}" + }, + { + "bbox": [ + 46, + 221, + 287, + 376 + ], + "type": "text", + "content": " for each model as the optimization loss to guide the backpropagation." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 59, + 376, + 273, + 388 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 376, + 273, + 388 + ], + "spans": [ + { + "bbox": [ + 59, + 376, + 273, + 388 + ], + "type": "text", + "content": "We employ PGD [37] to optimize the perturbation as" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 61, + 398, + 287, + 412 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 61, + 398, + 287, + 412 + ], + "spans": [ + { + "bbox": [ + 61, + 398, + 287, + 412 + ], + "type": "interline_equation", + "content": "\\delta^ {t + 1} = \\Pi_ {\\varepsilon} \\left(\\delta^ {t} - \\lambda \\operatorname {s i g n} \\left(\\nabla_ {\\delta} \\mathcal {L} \\left(f \\left(x + \\delta^ {t}\\right), y ^ {\\star}\\right)\\right)\\right), \\tag {3}", + "image_path": "6a15e7afd8157c5eec12a0152f9a08e0b33f6c47c3a1deae8671716fab5e6b01.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 422, + 139, + 433 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 422, + 139, + 433 + ], + "spans": [ + { + "bbox": [ + 47, + 422, + 139, + 433 + ], + "type": "text", + "content": "for targeted attack and" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 63, + 443, + 287, + 457 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 63, + 443, + 287, + 457 + ], + "spans": [ + { + "bbox": [ + 63, + 443, + 287, + 457 + ], + "type": "interline_equation", + "content": "\\delta^ {t + 1} = \\Pi_ {\\varepsilon} \\left(\\delta^ {t} + \\lambda \\operatorname {s i g n} \\left(\\nabla_ {\\delta} \\mathcal {L} (f (x + \\delta^ {t}), y)\\right)\\right), \\tag {4}", + "image_path": "2d14e9dafc92987f6a6f695d4b2efcc2db94d1311411f485d68fd4eef26a88e4.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 467, + 287, + 515 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 467, + 287, + 515 + ], + "spans": [ + { + "bbox": [ + 47, + 467, + 287, + 515 + ], + "type": "text", + "content": "for untargeted attack. Here " + }, + { + "bbox": [ + 47, + 467, + 287, + 515 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 47, + 467, + 287, + 515 + ], + "type": "text", + "content": " indicates the attack step, " + }, + { + "bbox": [ + 47, + 467, + 287, + 515 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 47, + 467, + 287, + 515 + ], + "type": "text", + "content": " is the step size, and " + }, + { + "bbox": [ + 47, + 467, + 287, + 515 + ], + "type": "inline_equation", + "content": "\\Pi_{\\varepsilon}" + }, + { + "bbox": [ + 47, + 467, + 287, + 515 + ], + "type": "text", + "content": " projects the perturbation into a " + }, + { + "bbox": [ + 47, + 467, + 287, + 515 + ], + "type": "inline_equation", + "content": "\\ell_p" + }, + { + "bbox": [ + 47, + 467, + 287, + 515 + ], + "type": "text", + "content": " norm ball with radius " + }, + { + "bbox": [ + 47, + 467, + 287, + 515 + ], + "type": "inline_equation", + "content": "\\varepsilon" + }, + { + "bbox": [ + 47, + 467, + 287, + 515 + ], + "type": "text", + "content": ". In the rest of the paper, we focus on targeted attacks without loss of generalization." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 523, + 181, + 534 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 523, + 181, + 534 + ], + "spans": [ + { + "bbox": [ + 47, + 523, + 181, + 534 + ], + "type": "text", + "content": "3.2. Ensemble-based attacks" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 542, + 287, + 673 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 542, + 287, + 673 + ], + "spans": [ + { + "bbox": [ + 46, + 542, + 287, + 673 + ], + "type": "text", + "content": "In an ensemble-based transfer attack, we use an ensemble of " + }, + { + "bbox": [ + 46, + 542, + 287, + 673 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 542, + 287, + 673 + ], + "type": "text", + "content": " surrogate (whitebox) models: " + }, + { + "bbox": [ + 46, + 542, + 287, + 673 + ], + "type": "inline_equation", + "content": "\\mathcal{F} = \\{f_1,\\dots ,f_N\\}" + }, + { + "bbox": [ + 46, + 542, + 287, + 673 + ], + "type": "text", + "content": " to generate perturbations to attack the victim model " + }, + { + "bbox": [ + 46, + 542, + 287, + 673 + ], + "type": "inline_equation", + "content": "f_{\\mathbf{v}}" + }, + { + "bbox": [ + 46, + 542, + 287, + 673 + ], + "type": "text", + "content": ". Note that if the ensemble has a single model, then such an attack becomes a simple transfer attack with a single surrogate model. Let us denote the training loss function for " + }, + { + "bbox": [ + 46, + 542, + 287, + 673 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 542, + 287, + 673 + ], + "type": "text", + "content": "th model as " + }, + { + "bbox": [ + 46, + 542, + 287, + 673 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_i(f_i(x),y^*)" + }, + { + "bbox": [ + 46, + 542, + 287, + 673 + ], + "type": "text", + "content": ". A natural approach to combine the loss functions of all surrogate models is to compute an average or weighted average of the individual loss functions. For instance, we can generate the adversarial image by solving the following optimization problem:" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 85, + 684, + 287, + 715 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 85, + 684, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 85, + 684, + 287, + 715 + ], + "type": "interline_equation", + "content": "x ^ {\\star} (\\alpha) = \\underset {x} {\\arg \\min } \\sum_ {i = 1} ^ {N} \\alpha_ {i} \\mathcal {L} _ {i} \\left(f _ {i} (x), y ^ {\\star}\\right), \\tag {5}", + "image_path": "ed0e1ea6d45a8f5573e2d8c625608c2e80c1c05a007874b1585536ea53d50a0e.jpg" + } + ] + } + ], + "index": 12 + }, + { + "type": "image", + "bbox": [ + 341, + 74, + 509, + 186 + ], + "blocks": [ + { + "bbox": [ + 341, + 74, + 509, + 186 + ], + "lines": [ + { + "bbox": [ + 341, + 74, + 509, + 186 + ], + "spans": [ + { + "bbox": [ + 341, + 74, + 509, + 186 + ], + "type": "image", + "image_path": "889d58ca82bf9620b14c67f1477290eec90f29cb8aa1c102214d9ec432c388bd.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 190, + 544, + 209 + ], + "lines": [ + { + "bbox": [ + 305, + 190, + 544, + 209 + ], + "spans": [ + { + "bbox": [ + 305, + 190, + 544, + 209 + ], + "type": "text", + "content": "Figure 2. Distribution of losses for different object detection models. " + }, + { + "bbox": [ + 305, + 190, + 544, + 209 + ], + "type": "inline_equation", + "content": "\\mathbb{P}(\\mathcal{L}_i(f_i(x),y^\\star))" + }, + { + "bbox": [ + 305, + 190, + 544, + 209 + ], + "type": "text", + "content": ". Calculated on 500 images from VOC dataset." + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_caption" + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 214, + 545, + 262 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 214, + 545, + 262 + ], + "spans": [ + { + "bbox": [ + 305, + 214, + 545, + 262 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 214, + 545, + 262 + ], + "type": "inline_equation", + "content": "x^{\\star}(\\alpha)" + }, + { + "bbox": [ + 305, + 214, + 545, + 262 + ], + "type": "text", + "content": " is a function of the weights of the ensemble " + }, + { + "bbox": [ + 305, + 214, + 545, + 262 + ], + "type": "inline_equation", + "content": "\\alpha = \\{\\alpha_{1},\\ldots ,\\alpha_{N}\\}" + }, + { + "bbox": [ + 305, + 214, + 545, + 262 + ], + "type": "text", + "content": ". One of our key observations is that the choice of weights plays a critical role in the transfer attack success rate of the ensemble models." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 262, + 545, + 477 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 262, + 545, + 477 + ], + "spans": [ + { + "bbox": [ + 305, + 262, + 545, + 477 + ], + "type": "text", + "content": "Weight balancing (victim model agnostic). In ensemble-based transfer attacks, we build on the intuition that if an adversarial example can fool all models simultaneously, it would potentially be more transferable to any unseen victim model. This concept has been empirically corroborated by numerous works [14, 33]. However, most attack methods have only been verified on classification models, all of which use the same cross-entropy loss and yield similar loss values. In contrast, the loss functions for object detectors in an ensemble can differ significantly and cover a large range of values (as shown in Fig. 2). In such cases, models with large loss terms heavily influence the optimization procedure, reducing the attack success rate for models with small losses (see Tab. 1). To overcome this issue, we propose a simple yet effective solution to balance the weights assigned to each model in the ensemble as follows. For each input image " + }, + { + "bbox": [ + 305, + 262, + 545, + 477 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 305, + 262, + 545, + 477 + ], + "type": "text", + "content": " and target output " + }, + { + "bbox": [ + 305, + 262, + 545, + 477 + ], + "type": "inline_equation", + "content": "y^{\\star}" + }, + { + "bbox": [ + 305, + 262, + 545, + 477 + ], + "type": "text", + "content": ", we adjust the weight for " + }, + { + "bbox": [ + 305, + 262, + 545, + 477 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 305, + 262, + 545, + 477 + ], + "type": "text", + "content": "th surrogate model loss as" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 370, + 486, + 545, + 514 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 370, + 486, + 545, + 514 + ], + "spans": [ + { + "bbox": [ + 370, + 486, + 545, + 514 + ], + "type": "interline_equation", + "content": "\\alpha_ {i} = \\frac {\\sum_ {i = 1} ^ {N} \\mathcal {L} _ {i} \\left(f _ {i} (x) , y ^ {\\star}\\right)}{N \\mathcal {L} _ {i} \\left(f _ {i} (x) , y ^ {\\star}\\right)}. \\tag {6}", + "image_path": "5e26a5de331bb2d3e0e885bc6ac57cc586cbb3ac5a5c3ddadbaa5a88cf54deed.jpg" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 305, + 521, + 545, + 688 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 521, + 545, + 688 + ], + "spans": [ + { + "bbox": [ + 305, + 521, + 545, + 688 + ], + "type": "text", + "content": "The weights are adjusted in a whitebox setting as it allows us to measure the loss of each whitebox model accurately. The purpose of weight balancing is to ensure that all surrogate models can be successfully attacked, making the generated example more adversarial for blackbox victim models. Weight optimization (victim model specific). Note that the weight normalization, as discussed above, is agnostic to the victim model. We further observe that such transfer-based attacks can be further improved by optimizing the weights of the ensemble according to the victim model, input image, and target output. In particular, we can change the individual " + }, + { + "bbox": [ + 305, + 521, + 545, + 688 + ], + "type": "inline_equation", + "content": "\\alpha_{i}" + }, + { + "bbox": [ + 305, + 521, + 545, + 688 + ], + "type": "text", + "content": " to create the perturbations that reduce the victim model loss " + }, + { + "bbox": [ + 305, + 521, + 545, + 688 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathbf{v}}" + }, + { + "bbox": [ + 305, + 521, + 545, + 688 + ], + "type": "text", + "content": ". To achieve this goal, we need to solve the following optimization problem with respect to " + }, + { + "bbox": [ + 305, + 521, + 545, + 688 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 305, + 521, + 545, + 688 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 350, + 696, + 545, + 715 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 350, + 696, + 545, + 715 + ], + "spans": [ + { + "bbox": [ + 350, + 696, + 545, + 715 + ], + "type": "interline_equation", + "content": "\\alpha^ {\\star} = \\underset {\\alpha} {\\arg \\min } \\mathcal {L} _ {\\mathrm {v}} \\left(f _ {\\mathrm {v}} \\left(x ^ {\\star} (\\alpha)\\right), y ^ {\\star}\\right). \\tag {7}", + "image_path": "a84517a26a09a6c722f54c19cfa39cab04196540415922e28656ed33b93d8597.jpg" + } + ] + } + ], + "index": 19 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 734, + 315, + 742 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 734, + 315, + 742 + ], + "spans": [ + { + "bbox": [ + 294, + 734, + 315, + 742 + ], + "type": "text", + "content": "4047" + } + ] + } + ], + "index": 20 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 286, + 95 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 286, + 95 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 286, + 95 + ], + "type": "text", + "content": "The optimization problem in (7) is a nested optimization that we can solve as an alternating minimization routine." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 96, + 286, + 120 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 96, + 286, + 120 + ], + "spans": [ + { + "bbox": [ + 46, + 96, + 286, + 120 + ], + "type": "text", + "content": "Step 0. Given input " + }, + { + "bbox": [ + 46, + 96, + 286, + 120 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 46, + 96, + 286, + 120 + ], + "type": "text", + "content": ", output " + }, + { + "bbox": [ + 46, + 96, + 286, + 120 + ], + "type": "inline_equation", + "content": "y^{\\star}" + }, + { + "bbox": [ + 46, + 96, + 286, + 120 + ], + "type": "text", + "content": ", and surrogate ensemble " + }, + { + "bbox": [ + 46, + 96, + 286, + 120 + ], + "type": "inline_equation", + "content": "\\mathcal{F}" + }, + { + "bbox": [ + 46, + 96, + 286, + 120 + ], + "type": "text", + "content": ", we initialize " + }, + { + "bbox": [ + 46, + 96, + 286, + 120 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 46, + 96, + 286, + 120 + ], + "type": "text", + "content": " using (6)." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 120, + 286, + 156 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 120, + 286, + 156 + ], + "spans": [ + { + "bbox": [ + 46, + 120, + 286, + 156 + ], + "type": "text", + "content": "Step 1. Solve (5) to generate an adversarial example " + }, + { + "bbox": [ + 46, + 120, + 286, + 156 + ], + "type": "inline_equation", + "content": "x^{\\star}(\\alpha)" + }, + { + "bbox": [ + 46, + 120, + 286, + 156 + ], + "type": "text", + "content": ". Step 2. Test the victim model. Stop if attack is successful; otherwise, change one of the " + }, + { + "bbox": [ + 46, + 120, + 286, + 156 + ], + "type": "inline_equation", + "content": "\\alpha_{i}" + }, + { + "bbox": [ + 46, + 120, + 286, + 156 + ], + "type": "text", + "content": " and repeat Step 1." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 156, + 286, + 239 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 156, + 286, + 239 + ], + "spans": [ + { + "bbox": [ + 46, + 156, + 286, + 239 + ], + "type": "text", + "content": "In our experiments, we update the " + }, + { + "bbox": [ + 46, + 156, + 286, + 239 + ], + "type": "inline_equation", + "content": "\\alpha_{i}" + }, + { + "bbox": [ + 46, + 156, + 286, + 239 + ], + "type": "text", + "content": " in a cyclic manner (one coordinate at a time) as " + }, + { + "bbox": [ + 46, + 156, + 286, + 239 + ], + "type": "inline_equation", + "content": "\\alpha_{i} \\pm \\gamma" + }, + { + "bbox": [ + 46, + 156, + 286, + 239 + ], + "type": "text", + "content": " in Step 2, where " + }, + { + "bbox": [ + 46, + 156, + 286, + 239 + ], + "type": "inline_equation", + "content": "\\gamma" + }, + { + "bbox": [ + 46, + 156, + 286, + 239 + ], + "type": "text", + "content": " denotes a step size. In every round, we select the value of " + }, + { + "bbox": [ + 46, + 156, + 286, + 239 + ], + "type": "inline_equation", + "content": "\\alpha_{i}" + }, + { + "bbox": [ + 46, + 156, + 286, + 239 + ], + "type": "text", + "content": " that provides smallest value of the victim loss. We count the number of queries as the number of times we test the generated adversarial example on the victim model and denote it as " + }, + { + "bbox": [ + 46, + 156, + 286, + 239 + ], + "type": "inline_equation", + "content": "Q" + }, + { + "bbox": [ + 46, + 156, + 286, + 239 + ], + "type": "text", + "content": " in our experiments." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 251, + 127, + 265 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 251, + 127, + 265 + ], + "spans": [ + { + "bbox": [ + 47, + 251, + 127, + 265 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 272, + 286, + 403 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 272, + 286, + 403 + ], + "spans": [ + { + "bbox": [ + 46, + 272, + 286, + 403 + ], + "type": "text", + "content": "To evaluate the effectiveness of our method, we performed extensive experiments on attacking various object detection and semantic segmentation models. We first show that the attacks generated by a single surrogate model fail to transfer to arbitrary victim models. Then we show that the attack transfer rate can be increased by using an ensemble with weight balancing. Additional optimization of the weights surrogates for each victim model can further improve the attack performance. Finally, we show that we can generate single perturbations to fool object detectors and semantic segmentation models simultaneously." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 412, + 153, + 425 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 412, + 153, + 425 + ], + "spans": [ + { + "bbox": [ + 47, + 412, + 153, + 425 + ], + "type": "text", + "content": "4.1. Experiment setup" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 430, + 150, + 442 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 430, + 150, + 442 + ], + "spans": [ + { + "bbox": [ + 47, + 430, + 150, + 442 + ], + "type": "text", + "content": "4.1.1 Object detection" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 449, + 286, + 664 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 449, + 286, + 664 + ], + "spans": [ + { + "bbox": [ + 46, + 449, + 286, + 664 + ], + "type": "text", + "content": "Models and datasets. We utilize MMDetection [7] toolbox to select various model architectures and weights pre-trained on COCO 2017 dataset [30]. To construct the surrogate ensemble, we start with two widely used models, Faster R-CNN [43] and YOLO [41, 42], and expand the ensemble by appending models with different architectures, including {FCOS [48], Grid R-CNN [36], SSD [31]}. We select different victim models, including {RetinaNet [29], Libra R-CNN [38], FoveaBox [23], FreeAnchor [59], DETR [6]}}. We evaluate attack performance on COCO 2017 [30] and Pascal VOC 2007 [15] datasets. Since the models from this repository are trained on COCO, which contains 80 object categories (a superset of VOC dataset's 20 categories), while testing on VOC dataset, we only return the objects that exist in VOC. We follow the setup in [4] and randomly select 500 images containing multiple (2-6) objects from VOC 2007 test and COCO 2017 validation sets." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 665, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 286, + 713 + ], + "type": "text", + "content": "Evaluation metrics. We mainly focus on targeted attacks for object detection since they are more challenging than untargeted or vanishing attacks. We measure the performance of the attack using attack success rate (ASR), which" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 72, + 545, + 119 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 119 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 119 + ], + "type": "text", + "content": "equals the number of successfully attacked images over the total number of attacks. We follow the setting in [4], where if the target label is detected within the victim object region with IOU " + }, + { + "bbox": [ + 304, + 72, + 545, + 119 + ], + "type": "inline_equation", + "content": ">0.3" + }, + { + "bbox": [ + 304, + 72, + 545, + 119 + ], + "type": "text", + "content": ", the attack is determined a success." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 121, + 545, + 192 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 121, + 545, + 192 + ], + "spans": [ + { + "bbox": [ + 304, + 121, + 545, + 192 + ], + "type": "text", + "content": "Perturbation and query budget. We tested different perturbation levels with " + }, + { + "bbox": [ + 304, + 121, + 545, + 192 + ], + "type": "inline_equation", + "content": "\\ell_{\\infty} = \\{10,20,30\\}" + }, + { + "bbox": [ + 304, + 121, + 545, + 192 + ], + "type": "text", + "content": " out of 255. We use at most 10 queries for attacking object detectors, and we show the trends of how ASR increases with the number of queries. To align with [4] that uses 5 attack plans, we set the maximum query budget to " + }, + { + "bbox": [ + 304, + 121, + 545, + 192 + ], + "type": "inline_equation", + "content": "Q = 5" + }, + { + "bbox": [ + 304, + 121, + 545, + 192 + ], + "type": "text", + "content": " in Tab. 1." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 194, + 545, + 324 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 194, + 545, + 324 + ], + "spans": [ + { + "bbox": [ + 304, + 194, + 545, + 324 + ], + "type": "text", + "content": "Comparing methods. We compare with [4], which is a state-of-the-art transfer-based approach that leverages context information to design attack plans to iteratively attack the victim object. The method generates different perturbations by iterating over a set of predefined attacks, and the total number of queries is the number of attempted attacks. BASES [3] is a recent work on ensemble-based blackbox attacks, which mainly focused on classification tasks and did not consider the loss distributions of different surrogate models. In our experiments, the ensemble with weight optimization and without balancing is equivalent to BASES [3]." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 344, + 437, + 356 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 344, + 437, + 356 + ], + "spans": [ + { + "bbox": [ + 305, + 344, + 437, + 356 + ], + "type": "text", + "content": "4.1.2 Semantic segmentation" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 364, + 545, + 567 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 364, + 545, + 567 + ], + "spans": [ + { + "bbox": [ + 304, + 364, + 545, + 567 + ], + "type": "text", + "content": "Models and datasets. We use MMSegmentation [12] toolbox to select different model architectures and weights pre-trained on Cityscapes [13] (" + }, + { + "bbox": [ + 304, + 364, + 545, + 567 + ], + "type": "inline_equation", + "content": "x \\in \\mathbb{R}^{512 \\times 1024 \\times 3}" + }, + { + "bbox": [ + 304, + 364, + 545, + 567 + ], + "type": "text", + "content": ") and Pascal VOC (" + }, + { + "bbox": [ + 304, + 364, + 545, + 567 + ], + "type": "inline_equation", + "content": "x \\in \\mathbb{R}^{512 \\times 512 \\times 3}" + }, + { + "bbox": [ + 304, + 364, + 545, + 567 + ], + "type": "text", + "content": ") datasets. We select PSPNet [60] and DeepLabV3 [8] with ResNet50 and ResNet101 [20] backbones as our blackbox victim models. For the surrogate ensemble, we start with the primary semantic segmentation model FCN [34], and expand the ensemble with {UPerNet [53], PSANet [61], GCNet [5], ANN [62], EncNet [57]}. All models are built on ResNet50 [20] backbone trained with the cross-entropy loss. The loss values across all surrogate models have similar range; therefore, the effect of weight balancing for semantic segmentation is not as significant as it is for object detection. We use validation datasets from Cityscapes [13] and Pascal VOC 2012, which contains 500 and 1499 images with 19 and 21 classes, respectively." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 568, + 545, + 664 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 568, + 545, + 664 + ], + "spans": [ + { + "bbox": [ + 304, + 568, + 545, + 664 + ], + "type": "text", + "content": "Evaluation metrics. We use different metrics for untargeted and targeted attack performance evaluation. In untargeted experiments, the attack performance is evaluated using the mIoU score (in percentage " + }, + { + "bbox": [ + 304, + 568, + 545, + 664 + ], + "type": "inline_equation", + "content": "\\%" + }, + { + "bbox": [ + 304, + 568, + 545, + 664 + ], + "type": "text", + "content": " ), the lower mIoU score the better attack performance. For targeted experiments, we report the pixel success ratio (PSR), which indicates the percentage of pixels successfully assigned the desired label in the target region, the higher the better attack performance." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 665, + 545, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 545, + 689 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 545, + 689 + ], + "type": "text", + "content": "Perturbation and query budget. We use the perturbation budget " + }, + { + "bbox": [ + 304, + 665, + 545, + 689 + ], + "type": "inline_equation", + "content": "\\ell_{\\infty} \\leq 8" + }, + { + "bbox": [ + 304, + 665, + 545, + 689 + ], + "type": "text", + "content": " out of 255 and query budget " + }, + { + "bbox": [ + 304, + 665, + 545, + 689 + ], + "type": "inline_equation", + "content": "Q = 20" + }, + { + "bbox": [ + 304, + 665, + 545, + 689 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "type": "text", + "content": "Comparing methods. We compare with dynamic scale (DS) attack [17] which is the most recent method that" + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 732, + 315, + 742 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 732, + 315, + 742 + ], + "spans": [ + { + "bbox": [ + 294, + 732, + 315, + 742 + ], + "type": "text", + "content": "4048" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 86, + 109, + 509, + 300 + ], + "blocks": [ + { + "bbox": [ + 46, + 80, + 547, + 109 + ], + "lines": [ + { + "bbox": [ + 46, + 80, + 547, + 109 + ], + "spans": [ + { + "bbox": [ + 46, + 80, + 547, + 109 + ], + "type": "text", + "content": "Table 1. Targeted attack success rate (%) of different methods at different perturbation budgets on VOC dataset. For each perturbation level, the first 4 rows correspond to different settings of our attacks, i.e. with (✓) or without (✗) weight balancing and weight optimization. We show comparison with context-aware attack [4], the state-of-the-art method for query-based blackbox attacks." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 86, + 109, + 509, + 300 + ], + "lines": [ + { + "bbox": [ + 86, + 109, + 509, + 300 + ], + "spans": [ + { + "bbox": [ + 86, + 109, + 509, + 300 + ], + "type": "table", + "html": "
Perturbation BudgetWeight BalancingWeight OptimizationSurrogate EnsembleBlackbox Victim Models (ASR ↑)
FRCNNYOLOv3RetinaLibraFoveaFreeDETR
l∞=10XX27.991.511.69.29.013.45.6
X✓61.499.424.328.022.431.015.4
✓X71.185.730.933.427.236.012.2
✓✓86.096.953.256.647.257.429.0
Context-aware Attack [4]55.875.622.620.433.639.220.2
l∞=20XX40.192.216.920.415.423.29.7
X✓77.799.841.045.437.847.022.5
✓X82.789.841.050.444.857.021.6
✓✓94.698.066.974.468.079.448.0
Context-aware Attack [4]78.687.235.238.451.656.634.0
l∞=30XX43.491.117.122.617.427.211.4
X✓82.799.647.254.847.057.433.4
✓X85.390.248.856.845.659.629.2
✓✓96.098.178.982.876.883.058.8
Context-aware Attack [4]80.688.042.044.256.863.640.2
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Attack success rate (or fooling rate) vs number of queries " + }, + { + "bbox": [ + 89, + 451, + 503, + 462 + ], + "type": "inline_equation", + "content": "(Q)" + }, + { + "bbox": [ + 89, + 451, + 503, + 462 + ], + "type": "text", + "content": ". The maximum value of " + }, + { + "bbox": [ + 89, + 451, + 503, + 462 + ], + "type": "inline_equation", + "content": "Q" + }, + { + "bbox": [ + 89, + 451, + 503, + 462 + ], + "type": "text", + "content": " is set to 10 for these results." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_caption" + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 483, + 287, + 507 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 483, + 287, + 507 + ], + "spans": [ + { + "bbox": [ + 46, + 483, + 287, + 507 + ], + "type": "text", + "content": "achieves the highest attack transfer rate on semantic segmentation untargeted attacks." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 514, + 219, + 528 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 514, + 219, + 528 + ], + "spans": [ + { + "bbox": [ + 47, + 514, + 219, + 528 + ], + "type": "text", + "content": "4.2. Attacks against object detection" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 533, + 287, + 594 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 533, + 287, + 594 + ], + "spans": [ + { + "bbox": [ + 46, + 533, + 287, + 594 + ], + "type": "text", + "content": "Following settings in [4], we randomly select one object from the output of victim model as the victim object and perturb it into a target object that does not exist in the original detection. This approach rules out the possibility of mis-counting existing objects as the target object." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 46, + 594, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 594, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 288, + 713 + ], + "type": "text", + "content": "We report our main results in Tab. 1. The baseline method uses a surrogate ensemble without weight balancing and models are assigned weight of 1. Such a baseline method is same a transfer-based method and results in highly imbalanced success rate for different surrogate models. For instance, at " + }, + { + "bbox": [ + 46, + 594, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\ell_{\\infty} \\leq 10" + }, + { + "bbox": [ + 46, + 594, + 288, + 713 + ], + "type": "text", + "content": ", the success rate for YOLOv3 is above " + }, + { + "bbox": [ + 46, + 594, + 288, + 713 + ], + "type": "inline_equation", + "content": "90\\%" + }, + { + "bbox": [ + 46, + 594, + 288, + 713 + ], + "type": "text", + "content": " while the success rate for Faster R-CNN is less than " + }, + { + "bbox": [ + 46, + 594, + 288, + 713 + ], + "type": "inline_equation", + "content": "30\\%" + }, + { + "bbox": [ + 46, + 594, + 288, + 713 + ], + "type": "text", + "content": ". Low success rate on surrogate side translates to low success rate on blackbox victim side. The main reason for such imbalance is that the loss of dif" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 482, + 545, + 710 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 482, + 545, + 710 + ], + "spans": [ + { + "bbox": [ + 304, + 482, + 545, + 710 + ], + "type": "text", + "content": "ferent object detectors can be highly unbalanced (e.g., the loss value for YOLOv3 is nearly " + }, + { + "bbox": [ + 304, + 482, + 545, + 710 + ], + "type": "inline_equation", + "content": "60\\times" + }, + { + "bbox": [ + 304, + 482, + 545, + 710 + ], + "type": "text", + "content": " larger than the loss of Faster RCNN for targeted attacks, cf. Fig. 2). With weight balancing, the success rate increases for surrogate and blackbox victim models. The success rate is further increased on surrogate and victim blackbox models if we optimize the weights, same as BASES [3]. Our method (with weight balancing and optimization) achieves a significantly higher ASR compared to context-aware attack across different datasets and different perturbation budgets. On average, our ASR on blackbox victim models is over " + }, + { + "bbox": [ + 304, + 482, + 545, + 710 + ], + "type": "inline_equation", + "content": "4\\times" + }, + { + "bbox": [ + 304, + 482, + 545, + 710 + ], + "type": "text", + "content": " better than baseline method and over " + }, + { + "bbox": [ + 304, + 482, + 545, + 710 + ], + "type": "inline_equation", + "content": "1.5\\times" + }, + { + "bbox": [ + 304, + 482, + 545, + 710 + ], + "type": "text", + "content": " better than context-aware attack. On whitebox surrogate models, weight balancing and optimization also achieves the highest ASR. Context-aware attack fixes weight ratio for surrogate models, " + }, + { + "bbox": [ + 304, + 482, + 545, + 710 + ], + "type": "inline_equation", + "content": "\\alpha_{\\mathrm{FRCNN}} / \\alpha_{\\mathrm{YOLO}} = 4" + }, + { + "bbox": [ + 304, + 482, + 545, + 710 + ], + "type": "text", + "content": ", which is sub-optimal according to our analyses. Even though it achieves much higher performance than baseline, it still largely under-performs our method. Similar trend is observed for COCO dataset (see Tab. S1)." + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 734, + 315, + 742 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 734, + 315, + 742 + ], + "spans": [ + { + "bbox": [ + 294, + 734, + 315, + 742 + ], + "type": "text", + "content": "4049" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 99, + 91, + 494, + 171 + ], + "blocks": [ + { + "bbox": [ + 53, + 80, + 539, + 90 + ], + "lines": [ + { + "bbox": [ + 53, + 80, + 539, + 90 + ], + "spans": [ + { + "bbox": [ + 53, + 80, + 539, + 90 + ], + "type": "text", + "content": "Table 2. Targeted ASR (%) for blackbox victim models and whitebox surrogate models with different ensemble sizes (N). On VOC dataset, " + }, + { + "bbox": [ + 53, + 80, + 539, + 90 + ], + "type": "inline_equation", + "content": "{\\ell }_{\\infty } \\leq {10}" + }, + { + "bbox": [ + 53, + 80, + 539, + 90 + ], + "type": "text", + "content": " ." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 99, + 91, + 494, + 171 + ], + "lines": [ + { + "bbox": [ + 99, + 91, + 494, + 171 + ], + "spans": [ + { + "bbox": [ + 99, + 91, + 494, + 171 + ], + "type": "table", + "html": "
NSurrogate EnsembleBlackbox Victim Models (ASR ↑)
FRCNNYOLOv3FCOSGrid R-CNNSSDRetinaLibraFoveaFreeDETR
174.7----31.331.229.840.410.6
286.096.9---53.256.647.257.429.0
387.996.174.2--63.162.057.366.638.0
489.694.775.287.9-68.771.067.674.449.6
589.791.873.586.182.468.970.268.477.653.2
", + "image_path": "ae8853e94db1cab6abd77fa2014cc510408b5c1990dcf0932c8ff942c294ee35.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "type": "table", + "bbox": [ + 66, + 229, + 529, + 376 + ], + "blocks": [ + { + "bbox": [ + 47, + 190, + 545, + 228 + ], + "lines": [ + { + "bbox": [ + 47, + 190, + 545, + 228 + ], + "spans": [ + { + "bbox": [ + 47, + 190, + 545, + 228 + ], + "type": "text", + "content": "Table 3. Untargeted attack mIoU scores (%) of ensemble sizes " + }, + { + "bbox": [ + 47, + 190, + 545, + 228 + ], + "type": "inline_equation", + "content": "N = 2,4,6" + }, + { + "bbox": [ + 47, + 190, + 545, + 228 + ], + "type": "text", + "content": " on Cityscapes dataset. We compare " + }, + { + "bbox": [ + 47, + 190, + 545, + 228 + ], + "type": "inline_equation", + "content": "Q = 0" + }, + { + "bbox": [ + 47, + 190, + 545, + 228 + ], + "type": "text", + "content": " (i.e. direct transfer attack) with " + }, + { + "bbox": [ + 47, + 190, + 545, + 228 + ], + "type": "inline_equation", + "content": "Q = 20" + }, + { + "bbox": [ + 47, + 190, + 545, + 228 + ], + "type": "text", + "content": " ensemble attack performance. DS uses DeepLabV3-Res50 (DL3-50) as the surrogate model for attack generation; thus the DS on DL3-50 is a whitebox attack. While our method used an ensemble that does not include any victim models for attack generation, we still achieved comparable mIoU scores to DS on DL3-50. Blue numbers represent whitebox attacks." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 66, + 229, + 529, + 376 + ], + "lines": [ + { + "bbox": [ + 66, + 229, + 529, + 376 + ], + "spans": [ + { + "bbox": [ + 66, + 229, + 529, + 376 + ], + "type": "table", + "html": "
MethodWhitebox SurrogateBlackbox Victim Models (mIoU ↓)
PSPNet-Res50PSPNet-Res101DeepLabV3-Res50DeepLabV3-Res101
Clean Images-77.9278.2879.1277.12
BaselinePSPNet-Res503.4324.185.0525.74
DeepLabV3-Res504.7621.723.9222.23
DS [17]PSPNet-Res500.828.041.369.00
DeepLabV3-Res501.237.970.617.11
Ours (Q=0)N=25.078.325.198.74
N=44.336.264.326.33
N=63.624.914.024.84
Ours (Q=20)N=21.382.881.153.50
N=40.792.040.731.80
N=60.901.550.941.09
", + "image_path": "6edf3798048fd7118740e5c0c68af1af5b0b1ff3615566035775c0e142802e82.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "type": "table", + "bbox": [ + 55, + 458, + 280, + 582 + ], + "blocks": [ + { + "bbox": [ + 47, + 405, + 287, + 453 + ], + "lines": [ + { + "bbox": [ + 47, + 405, + 287, + 453 + ], + "spans": [ + { + "bbox": [ + 47, + 405, + 287, + 453 + ], + "type": "text", + "content": "Table 4. Targeted attack performance on Cityscapes as pixel success rate (higher the better). The attack performance increases as we increase ensemble size " + }, + { + "bbox": [ + 47, + 405, + 287, + 453 + ], + "type": "inline_equation", + "content": "(N)" + }, + { + "bbox": [ + 47, + 405, + 287, + 453 + ], + "type": "text", + "content": " and number of queries for weight optimization " + }, + { + "bbox": [ + 47, + 405, + 287, + 453 + ], + "type": "inline_equation", + "content": "(Q)" + }, + { + "bbox": [ + 47, + 405, + 287, + 453 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 47, + 405, + 287, + 453 + ], + "type": "inline_equation", + "content": "N = 1" + }, + { + "bbox": [ + 47, + 405, + 287, + 453 + ], + "type": "text", + "content": " has zero query. We note PSPNet-Res50 as PSP-r50, and DeepLabV3-Res50 as DL3-r50, similar abbreviations apply to Res101." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 55, + 458, + 280, + 582 + ], + "lines": [ + { + "bbox": [ + 55, + 458, + 280, + 582 + ], + "spans": [ + { + "bbox": [ + 55, + 458, + 280, + 582 + ], + "type": "table", + "html": "
QNBlackbox Victim Models (PSR ↑)
PSP-r50PSP-r101DL3-r50DL3-r101
0139.1510.2135.027.58
252.1512.2847.9910.59
343.1711.3442.109.87
451.4426.1349.1417.42
552.2423.8851.7516.08
20283.9751.8082.7046.95
388.8864.6385.5560.88
491.5164.2887.1963.88
592.9169.0988.9569.65
", + "image_path": "9841868574528a628705e29c53dc9e2b997a3a2b7217379ea4c17287d49e0b92.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "table_body" + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 605, + 286, + 652 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 605, + 286, + 652 + ], + "spans": [ + { + "bbox": [ + 47, + 605, + 286, + 652 + ], + "type": "text", + "content": "Fig. 3 shows the effect of the number of queries on the ASR that gradually improves as we optimize the weights. We observe the largest increase in the first two steps and then the improvement plateaus as " + }, + { + "bbox": [ + 47, + 605, + 286, + 652 + ], + "type": "inline_equation", + "content": "Q \\to 10" + }, + { + "bbox": [ + 47, + 605, + 286, + 652 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 654, + 286, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 654, + 286, + 712 + ], + "spans": [ + { + "bbox": [ + 47, + 654, + 286, + 712 + ], + "type": "text", + "content": "We also conducted an experiment to test our method with varying ensemble sizes. The results for " + }, + { + "bbox": [ + 47, + 654, + 286, + 712 + ], + "type": "inline_equation", + "content": "\\ell_{\\infty} \\leq 10" + }, + { + "bbox": [ + 47, + 654, + 286, + 712 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 654, + 286, + 712 + ], + "type": "inline_equation", + "content": "Q = 5" + }, + { + "bbox": [ + 47, + 654, + 286, + 712 + ], + "type": "text", + "content": " are presented in Tab. 2. As we increase the number of models in the ensemble from " + }, + { + "bbox": [ + 47, + 654, + 286, + 712 + ], + "type": "inline_equation", + "content": "N = 1" + }, + { + "bbox": [ + 47, + 654, + 286, + 712 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 47, + 654, + 286, + 712 + ], + "type": "inline_equation", + "content": "N = 5" + }, + { + "bbox": [ + 47, + 654, + 286, + 712 + ], + "type": "text", + "content": ", we observe an increased ASR on all blackbox victim models." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 396, + 509, + 408 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 396, + 509, + 408 + ], + "spans": [ + { + "bbox": [ + 306, + 396, + 509, + 408 + ], + "type": "text", + "content": "4.3. Attacks against semantic segmentation" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 420, + 545, + 468 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 420, + 545, + 468 + ], + "spans": [ + { + "bbox": [ + 305, + 420, + 545, + 468 + ], + "type": "text", + "content": "We evaluate the effectiveness of our attack on semantic segmentation in both untargeted and targeted settings. For the sake of consistency and a fair comparison, we adopt adversarial attack settings in DS attack [17]." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 474, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 474, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 474, + 546, + 713 + ], + "type": "text", + "content": "Untargeted attacks. We generate adversarial attacks using different ensemble sizes and report mIoU scores on Cityscapes in Tab. 3 and Fig. 4 (and Pascal VOC in supplementary material). In the untargeted setting, semantic segmentation models are attacked to maximize the loss between clean and modified annotation; hence, the lower mIoU implies better attack performance. All of the victim models achieve high performance on clean images. The baseline method (direct transfer attack with one surrogate model using PGD) performs well in the whitebox setting but suffers when the victim uses another backbone. For example, the attacks generated on PSPNet-Res50 achieves " + }, + { + "bbox": [ + 304, + 474, + 546, + 713 + ], + "type": "inline_equation", + "content": "3.43\\%" + }, + { + "bbox": [ + 304, + 474, + 546, + 713 + ], + "type": "text", + "content": " mIoU on PSPNet-Res50 but only attains " + }, + { + "bbox": [ + 304, + 474, + 546, + 713 + ], + "type": "inline_equation", + "content": "24.18\\%" + }, + { + "bbox": [ + 304, + 474, + 546, + 713 + ], + "type": "text", + "content": " mIoU on PSPNet-Res101. DS attack achieves better results than the baseline method but still suffers from crossbackbone transfers. On the other hand, our method, without weight optimization (i.e., " + }, + { + "bbox": [ + 304, + 474, + 546, + 713 + ], + "type": "inline_equation", + "content": "Q = 0" + }, + { + "bbox": [ + 304, + 474, + 546, + 713 + ], + "type": "text", + "content": ") and using a surrogate ensemble of " + }, + { + "bbox": [ + 304, + 474, + 546, + 713 + ], + "type": "inline_equation", + "content": "N = 2" + }, + { + "bbox": [ + 304, + 474, + 546, + 713 + ], + "type": "text", + "content": " models, can achieve results comparable to DS attack, particularly for attacks on Res101 models. As we increase the number of surrogate models to 4 or 6, our" + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 734, + 315, + 742 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 734, + 315, + 742 + ], + "spans": [ + { + "bbox": [ + 294, + 734, + 315, + 742 + ], + "type": "text", + "content": "4050" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 67, + 83, + 202, + 190 + ], + "blocks": [ + { + "bbox": [ + 67, + 83, + 202, + 190 + ], + "lines": [ + { + "bbox": [ + 67, + 83, + 202, + 190 + ], + "spans": [ + { + "bbox": [ + 67, + 83, + 202, + 190 + ], + "type": "image", + "image_path": "6bebcb55ed5cc7a2bb00b16f301eb8447883c77b2f756dace29bfe42398bf41c.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 120, + 193, + 157, + 201 + ], + "lines": [ + { + "bbox": [ + 120, + 193, + 157, + 201 + ], + "spans": [ + { + "bbox": [ + 120, + 193, + 157, + 201 + ], + "type": "text", + "content": "(a) " + }, + { + "bbox": [ + 120, + 193, + 157, + 201 + ], + "type": "inline_equation", + "content": "N = 2" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 225, + 83, + 360, + 190 + ], + "blocks": [ + { + "bbox": [ + 225, + 83, + 360, + 190 + ], + "lines": [ + { + "bbox": [ + 225, + 83, + 360, + 190 + ], + "spans": [ + { + "bbox": [ + 225, + 83, + 360, + 190 + ], + "type": "image", + "image_path": "689f07dde1e9b9fea8f0a1e283c20ccd5c04bcf810a36713d5af13bf6ac958bd.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 278, + 193, + 315, + 201 + ], + "lines": [ + { + "bbox": [ + 278, + 193, + 315, + 201 + ], + "spans": [ + { + "bbox": [ + 278, + 193, + 315, + 201 + ], + "type": "text", + "content": "(b) " + }, + { + "bbox": [ + 278, + 193, + 315, + 201 + ], + "type": "inline_equation", + "content": "N = 4" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 384, + 83, + 518, + 190 + ], + "blocks": [ + { + "bbox": [ + 384, + 83, + 518, + 190 + ], + "lines": [ + { + "bbox": [ + 384, + 83, + 518, + 190 + ], + "spans": [ + { + "bbox": [ + 384, + 83, + 518, + 190 + ], + "type": "image", + "image_path": "655a64495db1d8d9e69cb84ac560a39fb6bd7e0960a8532d64dabdbf8f604ad1.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 437, + 193, + 473, + 201 + ], + "lines": [ + { + "bbox": [ + 437, + 193, + 473, + 201 + ], + "spans": [ + { + "bbox": [ + 437, + 193, + 473, + 201 + ], + "type": "text", + "content": "(c) " + }, + { + "bbox": [ + 437, + 193, + 473, + 201 + ], + "type": "inline_equation", + "content": "N = 6" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 172, + 211, + 420, + 222 + ], + "lines": [ + { + "bbox": [ + 172, + 211, + 420, + 222 + ], + "spans": [ + { + "bbox": [ + 172, + 211, + 420, + 222 + ], + "type": "text", + "content": "Figure 4. mIoU vs number of queries " + }, + { + "bbox": [ + 172, + 211, + 420, + 222 + ], + "type": "inline_equation", + "content": "(Q)" + }, + { + "bbox": [ + 172, + 211, + 420, + 222 + ], + "type": "text", + "content": " for different ensemble sizes " + }, + { + "bbox": [ + 172, + 211, + 420, + 222 + ], + "type": "inline_equation", + "content": "(N)" + }, + { + "bbox": [ + 172, + 211, + 420, + 222 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 233, + 287, + 340 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 233, + 287, + 340 + ], + "spans": [ + { + "bbox": [ + 46, + 233, + 287, + 340 + ], + "type": "text", + "content": "attack performance further improves. Furthermore, when we apply weight optimization (e.g., " + }, + { + "bbox": [ + 46, + 233, + 287, + 340 + ], + "type": "inline_equation", + "content": "Q = 20" + }, + { + "bbox": [ + 46, + 233, + 287, + 340 + ], + "type": "text", + "content": "), the attack improves by updating the weights of the surrogate models, allowing us to outperform DS attack for all victim models. Fig. 4 shows how the mIoU changes with the number of queries. We observe that the mIoU gradually reduces as we query the victim model and optimize the weights. The largest decrease happens in the first 3-4 steps and then the reduction plateaus as " + }, + { + "bbox": [ + 46, + 233, + 287, + 340 + ], + "type": "inline_equation", + "content": "Q \\to 20" + }, + { + "bbox": [ + 46, + 233, + 287, + 340 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 341, + 289, + 616 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 341, + 289, + 616 + ], + "spans": [ + { + "bbox": [ + 46, + 341, + 289, + 616 + ], + "type": "text", + "content": "Targeted attack. To evaluate our method in a more challenging setting, we consider a targeted attack scenario, where instead of changing every pixel in the segmentation to some arbitrary label, we focus on attacking a dominant class (i.e., the class occupying the largest area) in the scene to its least likely class " + }, + { + "bbox": [ + 46, + 341, + 289, + 616 + ], + "type": "inline_equation", + "content": "y^{\\star}" + }, + { + "bbox": [ + 46, + 341, + 289, + 616 + ], + "type": "text", + "content": ". For each clean image, we first select a region with the dominant class " + }, + { + "bbox": [ + 46, + 341, + 289, + 616 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 46, + 341, + 289, + 616 + ], + "type": "text", + "content": " (e.g., \"road\" or \"building\" for most of the Cityscapes images. See Fig. S3 as an example). Then based on the least-likely class of each pixel in that region, we select the class that appears most frequently as the target label " + }, + { + "bbox": [ + 46, + 341, + 289, + 616 + ], + "type": "inline_equation", + "content": "y^{\\star}" + }, + { + "bbox": [ + 46, + 341, + 289, + 616 + ], + "type": "text", + "content": " of the entire region. We use PSR as our evaluation metric, which represents the percentage of pixels in the selected region that are successfully assigned to " + }, + { + "bbox": [ + 46, + 341, + 289, + 616 + ], + "type": "inline_equation", + "content": "y^{\\star}" + }, + { + "bbox": [ + 46, + 341, + 289, + 616 + ], + "type": "text", + "content": ". The higher percentage indicates more pixels are successfully attacked to the desired class, which indicates better attack performance. Our targeted attack results are reported in Tab. 4. Results show that as we increase the number of surrogate models (" + }, + { + "bbox": [ + 46, + 341, + 289, + 616 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 341, + 289, + 616 + ], + "type": "text", + "content": "), the ASR improves for most instances without any weight optimization step (i.e., " + }, + { + "bbox": [ + 46, + 341, + 289, + 616 + ], + "type": "inline_equation", + "content": "Q = 0" + }, + { + "bbox": [ + 46, + 341, + 289, + 616 + ], + "type": "text", + "content": "). If we perform weight optimization for " + }, + { + "bbox": [ + 46, + 341, + 289, + 616 + ], + "type": "inline_equation", + "content": "Q = 20" + }, + { + "bbox": [ + 46, + 341, + 289, + 616 + ], + "type": "text", + "content": " steps, then the success rate increases for all the models. For instance, with " + }, + { + "bbox": [ + 46, + 341, + 289, + 616 + ], + "type": "inline_equation", + "content": "N = 4" + }, + { + "bbox": [ + 46, + 341, + 289, + 616 + ], + "type": "text", + "content": ", the ASR for Res101 models increases from 17–26% to 63–64%." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 623, + 266, + 635 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 623, + 266, + 635 + ], + "spans": [ + { + "bbox": [ + 47, + 623, + 266, + 635 + ], + "type": "text", + "content": "4.4. Joint attack for multiple models and tasks" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 642, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 642, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 642, + 287, + 714 + ], + "type": "text", + "content": "We first show that generally adversarial examples generated for object detection do not transfer to semantic segmentation, and vice versa. Then we show that we can generate single perturbations to fool object detectors and semantic segmentation models simultaneously, by using a surrogate ensemble including both detection and segmentation mod" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 233, + 545, + 257 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 233, + 545, + 257 + ], + "spans": [ + { + "bbox": [ + 304, + 233, + 545, + 257 + ], + "type": "text", + "content": "els. We choose targeted attacks in our experiments because they are more challenging than untargeted attacks." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 258, + 546, + 353 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 258, + 546, + 353 + ], + "spans": [ + { + "bbox": [ + 304, + 258, + 546, + 353 + ], + "type": "text", + "content": "Experiment setup. On the blackbox (victim) side, we tested RetinaNet as the victim object detector and PSPNet-Res50 as the victim semantic segmentation model. On the whitebox (surrogate) side, we used Faster RCNN, YOLOv3 as the surrogate object detectors and FCN, UPerNet as the surrogate semantic segmentation models. We performed targeted attacks on 500 test images selected from the validation set of CityScapes dataset." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 354, + 546, + 640 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 354, + 546, + 640 + ], + "spans": [ + { + "bbox": [ + 304, + 354, + 546, + 640 + ], + "type": "text", + "content": "Results. We present the ASRs for task-specific and joint attacks in Fig. 5. Green curves denote ASR for object detectors, and blue curves denote PSR for semantic segmentation. Fig. 5a presents the results when we generate attacks using an object detector surrogate ensemble. Note that success rate for victim object detector (RetinaNet) increases as we optimize the weights but the success rate for the semantic segmentation model (PSPNet) remains small. Similarly, Fig. 5b presents the results when we generate attacks using a segmentation surrogate ensemble. The success rate for the victim semantic segmentation model increases, but the success rate for the object doctor remains close to zero. Fig. 5c presents the results when we perform a joint attack using an ensemble that consists of both object detectors and segmentation models. The blackbox ASR is high on both detection and segmentation Fig. 5c, and the attack performance improves as we update the weights of the surrogate models. In Fig. 5c, we show the results for different perturbation budgets, with " + }, + { + "bbox": [ + 304, + 354, + 546, + 640 + ], + "type": "inline_equation", + "content": "\\ell_{\\infty} \\leq 10" + }, + { + "bbox": [ + 304, + 354, + 546, + 640 + ], + "type": "text", + "content": ", the success rates on detection and segmentation are between " + }, + { + "bbox": [ + 304, + 354, + 546, + 640 + ], + "type": "inline_equation", + "content": "60\\% - 70\\%" + }, + { + "bbox": [ + 304, + 354, + 546, + 640 + ], + "type": "text", + "content": ", which are close to in-domain detection attacks in Fig. 5a and indomain segmentation attacks Fig. 5b. When we increase the perturbation to " + }, + { + "bbox": [ + 304, + 354, + 546, + 640 + ], + "type": "inline_equation", + "content": "\\ell_{\\infty} \\leq 20" + }, + { + "bbox": [ + 304, + 354, + 546, + 640 + ], + "type": "text", + "content": ", the success rate for both detection and segmentation can surpass " + }, + { + "bbox": [ + 304, + 354, + 546, + 640 + ], + "type": "inline_equation", + "content": "80\\%" + }, + { + "bbox": [ + 304, + 354, + 546, + 640 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 642, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 642, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 304, + 642, + 545, + 712 + ], + "type": "text", + "content": "Visualization of adversarial examples. In this example, our goal is to perturb the car in the middle to a traffic light. We assign the target label for car region to traffic light. Fig. 6a shows the results where a single adversarial image generated by the surrogate model can successfully fool the blackbox models RetinaNet and PSPNet." + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 734, + 314, + 742 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 734, + 314, + 742 + ], + "spans": [ + { + "bbox": [ + 295, + 734, + 314, + 742 + ], + "type": "text", + "content": "4051" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 65, + 77, + 211, + 192 + ], + "blocks": [ + { + "bbox": [ + 65, + 77, + 211, + 192 + ], + "lines": [ + { + "bbox": [ + 65, + 77, + 211, + 192 + ], + "spans": [ + { + "bbox": [ + 65, + 77, + 211, + 192 + ], + "type": "image", + "image_path": "c9895fc8f9ffc64509809a6f8e394840ed1ca79e5e91fd28662ee9fe5f222d78.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 62, + 197, + 214, + 217 + ], + "lines": [ + { + "bbox": [ + 62, + 197, + 214, + 217 + ], + "spans": [ + { + "bbox": [ + 62, + 197, + 214, + 217 + ], + "type": "text", + "content": "(a) Attacks generated for object detection only, " + }, + { + "bbox": [ + 62, + 197, + 214, + 217 + ], + "type": "inline_equation", + "content": "\\ell_{\\infty}\\leq 10" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 223, + 77, + 370, + 191 + ], + "blocks": [ + { + "bbox": [ + 223, + 77, + 370, + 191 + ], + "lines": [ + { + "bbox": [ + 223, + 77, + 370, + 191 + ], + "spans": [ + { + "bbox": [ + 223, + 77, + 370, + 191 + ], + "type": "image", + "image_path": "70b43ba3141826aa03c9844f8dd9f83cbb4283514c9e04865cee9ba41573286a.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 220, + 197, + 372, + 217 + ], + "lines": [ + { + "bbox": [ + 220, + 197, + 372, + 217 + ], + "spans": [ + { + "bbox": [ + 220, + 197, + 372, + 217 + ], + "type": "text", + "content": "(b) Attacks generated for semantic segmentation only, " + }, + { + "bbox": [ + 220, + 197, + 372, + 217 + ], + "type": "inline_equation", + "content": "\\ell_{\\infty}\\leq 10" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 383, + 73, + 529, + 187 + ], + "blocks": [ + { + "bbox": [ + 383, + 73, + 529, + 187 + ], + "lines": [ + { + "bbox": [ + 383, + 73, + 529, + 187 + ], + "spans": [ + { + "bbox": [ + 383, + 73, + 529, + 187 + ], + "type": "image", + "image_path": "eab51f90d6955e39e012ecf8a559c349c8b3bed87ba32017409de27e8338b72b.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 378, + 192, + 531, + 221 + ], + "lines": [ + { + "bbox": [ + 378, + 192, + 531, + 221 + ], + "spans": [ + { + "bbox": [ + 378, + 192, + 531, + 221 + ], + "type": "text", + "content": "(c) Attacks generated jointly for object detection and semantic segmentation, " + }, + { + "bbox": [ + 378, + 192, + 531, + 221 + ], + "type": "inline_equation", + "content": "\\ell_{\\infty} \\leq \\{10, 20\\}" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "type": "image", + "bbox": [ + 75, + 291, + 222, + 366 + ], + "blocks": [ + { + "bbox": [ + 46, + 230, + 547, + 278 + ], + "lines": [ + { + "bbox": [ + 46, + 230, + 547, + 278 + ], + "spans": [ + { + "bbox": [ + 46, + 230, + 547, + 278 + ], + "type": "text", + "content": "Figure 5. Comparison between task-specific attacks and joint attack performance on blackbox object detector (RetinaNet) and segmentation model (PSPNet). Green curves denote attack success rate for object detectors, and blue curves denote pixel success rate for semantic segmentation. (a) Attacks generated with an object detector surrogate do not transfer for semantic segmentation. (b) Attacks generated with semantic segmentation models surrogate do not transfer for object detectors. 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"type": "text", + "content": "(a) Our method can generate attacks to fool multiple blackbox object detector and blackbox semantic segmentation models jointly. First row shows a clean image from Cityscapes dataset, detection with RetinaNet and segmentation with PSPNet. Second row shows the perturbed image using ensemble surrogates {Faster RCNN,YOLOv3,FCN,UPerNet}, and detection and segmentation results on the perturbed image. We generate perturbation to map the Car in the middle to Traffic Light. Image id: lindau_000026_000019" + } + ] + } + ], + "index": 19, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 74, + 508, + 517, + 533 + ], + "lines": [ + { + "bbox": [ + 74, + 508, + 517, + 533 + ], + "spans": [ + { + "bbox": [ + 74, + 508, + 517, + 533 + ], + "type": "image", + "image_path": "930609f2565537a7ef8c1443d370e491b1dea0baca65256d2e4164a47e44e422.jpg" + } + ] + } + ], + "index": 20, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 190, + 535, + 400, + 545 + ], + "lines": [ + { + "bbox": [ + 190, + 535, + 400, + 545 + ], + "spans": [ + { + "bbox": [ + 190, + 535, + 400, + 545 + ], + "type": "text", + "content": "(b) Color encoding for segmentation maps in CityScapes dataset" + } + ] + } + ], + "index": 21, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 46, + 549, + 544, + 569 + ], + "lines": [ + { + "bbox": [ + 46, + 549, + 544, + 569 + ], + "spans": [ + { + "bbox": [ + 46, + 549, + 544, + 569 + ], + "type": "text", + "content": "Figure 6. Visual adversarial examples of our method that generates successful attacks to fool a blackbox object detector and a blackbox semantic segmentation model using a single perturbed image." + } + ] + } + ], + "index": 22, + "angle": 0, + "type": "image_caption" + } + ], + "index": 20 + }, + { + "bbox": [ + 47, + 575, + 119, + 586 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 575, + 119, + 586 + ], + "spans": [ + { + "bbox": [ + 47, + 575, + 119, + 586 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 46, + 605, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 605, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 605, + 288, + 713 + ], + "type": "text", + "content": "We presented a new method to generate targeted attacks for dense prediction task (e.g., object detectors and semantic segmentation) using an ensemble of surrogate models. We demonstrate that (victim model-agnostic) weight balancing and (victim model-specific) weight optimization play a critical role in the success of attacks. We present an extensive set of experiments to demonstrate the performance of our method with different models and datasets. Finally, we show that our approach can create adversarial ex" + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 305, + 576, + 541, + 589 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 576, + 541, + 589 + ], + "spans": [ + { + "bbox": [ + 305, + 576, + 541, + 589 + ], + "type": "text", + "content": "amples to fool multiple blackbox models and tasks jointly." + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 304, + 590, + 545, + 662 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 590, + 545, + 662 + ], + "spans": [ + { + "bbox": [ + 304, + 590, + 545, + 662 + ], + "type": "text", + "content": "Limitations. Our method employs an ensemble of surrogate models to generate attacks, which inevitably incurs higher memory and computational overhead. Moreover, the success of our method hinges on the availability of a diverse set of surrogate models, which could potentially limit its efficacy if such models are not readily obtainable." + } + ] + } + ], + "index": 26 + }, + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "content": "Acknowledgments. This material is based upon work supported by AFOSR award FA9550-21-1-0330, NSF award 2046293, UC Regents Faculty Development grant. We acknowledge the computing support from Nautilus PRP." + } + ] + } + ], + "index": 27 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 734, + 315, + 742 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 734, + 315, + 742 + ], + "spans": [ + { + "bbox": [ + 295, + 734, + 315, + 742 + ], + "type": "text", + "content": "4052" + } + ] + } + ], + "index": 28 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 107, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 107, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 107, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 92, + 288, + 713 + ], + "type": "list", + "angle": 0, + "index": 12, + "blocks": [ + { + "bbox": [ + 53, + 92, + 287, + 135 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 92, + 287, + 135 + ], + "spans": [ + { + "bbox": [ + 53, + 92, + 287, + 135 + ], + "type": "text", + "content": "[1] Anurag Arnab, Ondrej Miksik, and Philip HS Torr. 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Tan $^{2}$ , Yuhong Tan $^{1}$ , Siheng Chen $^{1,3*}$ , Yu Guang Wang $^{1}$ , Xinchao Wang $^{2}$ , Yanfeng Wang $^{3,1}$", + "bbox": [ + 274, + 202, + 761, + 239 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "$^{1}$ Shanghai Jiao Tong University, $^{2}$ National University of Singapore, $^{3}$ Shanghai AI Laboratory", + "bbox": [ + 151, + 239, + 885, + 257 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "{xcxwakaka,tyheeer,sihengc,yuguang.wang,wangyanfeng}@sjtu.edu.cn,{robby.tan,xinchao}@nus.edu.sg", + "bbox": [ + 88, + 258, + 941, + 273 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 308, + 313, + 325 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Learning to predict agent motions with relationship reasoning is important for many applications. In motion prediction tasks, maintaining motion equivariance under Euclidean geometric transformations and invariance of agent interaction is a critical and fundamental principle. However, such equivariance and invariance properties are overlooked by most existing methods. To fill this gap, we propose EqMotion, an efficient equivariant motion prediction model with invariant interaction reasoning. To achieve motion equivariance, we propose an equivariant geometric feature learning module to learn a Euclidean transformable feature through dedicated designs of equivariant operations. To reason agent's interactions, we propose an invariant interaction reasoning module to achieve a more stable interaction modeling. To further promote more comprehensive motion features, we propose an invariant pattern feature learning module to learn an invariant pattern feature, which cooperates with the equivariant geometric feature to enhance network expressiveness. We conduct experiments for the proposed model on four distinct scenarios: particle dynamics, molecule dynamics, human skeleton motion prediction and pedestrian trajectory prediction. Experimental results show that our method is not only generally applicable, but also achieves state-of-the-art prediction performances on all the four tasks, improving by 24.0/30.1/8.6/9.2%. Code is available at https://github.com/MediaBrain-SJTU/EqMotion.", + "bbox": [ + 75, + 340, + 473, + 750 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 777, + 209, + 792 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Motion prediction aims to predict future trajectories of multiple interacting agents given their historical observations. It is widely studied in many applications like physics [3, 28], molecule dynamics [7], autonomous driving [35] and humanrobot interaction [38, 68]. In the task of motion prediction, an", + "bbox": [ + 75, + 801, + 470, + 878 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/56c14bbc12890fac2a4e53a7601ef264e20305b1b4f2fc02968ca076c7d214f0.jpg", + "image_caption": [ + "(a) Particle dynamics" + ], + "image_footnote": [], + "bbox": [ + 504, + 306, + 888, + 405 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/f595ab90c833b4b3e777cbcfa7ac2676ef880039cf02eaa409196291a8ff6878.jpg", + "image_caption": [ + "(c) Human skeleton motion", + "(d) Pedestrian trajectories", + "Figure 1. Motion equivariance and interaction invariance under the Euclidean geometric transformation is a fundamental principle for a prediction model, but this principle is often overlooked by previous works. In this work, we propose EqMotion to fill this gap." + ], + "image_footnote": [], + "bbox": [ + 504, + 421, + 885, + 523 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "often-overlooked yet fundamental principle is that a prediction model is required to be equivariant under the Euclidean geometric transformation (including translation, rotation and reflection), and at the same time maintain the interaction relationships invariant. Motion equivariance here means that if an input motion is transformed under a Euclidean transformation, the output motion must be equally transformed under the same transformation. Interaction invariance means that the way agents interact remains unchanged under the input's transformation. Figure 1 shows real-world examples of motion equivariance and interaction invariance.", + "bbox": [ + 496, + 608, + 893, + 773 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Employing this principle in a network design brings at least two benefits. First, the network will be robust to arbitrary Euclidean transformations. Second, the network will have the capability of being generalizable over rotations and translations of the data. This capability makes the network more compact, reducing the network's learning burden and contributing to a more accurate prediction.", + "bbox": [ + 496, + 777, + 893, + 883 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Despite the motion equivariance property being important", + "bbox": [ + 517, + 885, + 890, + 901 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Corresponding author.", + "bbox": [ + 94, + 886, + 220, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "1410", + "bbox": [ + 483, + 944, + 514, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "and fundamental, it is often neglected and not guaranteed by most existing motion prediction methods. The main reason is that these methods transform the input motion sequence directly into abstract feature vectors, where the geometric transformations are not traceable, causing the geometric relationships between agents to be irretrievable. Random augmentation will ease the equivariance problem, but it is still unable to guarantee the equivariance property. [30] uses non-parametric pre and post coordinate processing to achieve equivariance, but its parametric network structures do not satisfy equivariance. Some methods propose equivariant parametric network structures utilizing the higher-order representations of spherical harmonics [14, 61] or proposing an equivariant message passing [58], but they focus on the state-to-state prediction. This means that they use only one historical timestamp to predict one future timestamp. Consequently, these methods have limitations on utilizing motion's temporal information and modeling interaction relationships since a single-state observation is insufficient for both interaction modeling and temporal dependency modeling.", + "bbox": [ + 76, + 90, + 472, + 393 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In this paper, we propose EqMotion, the first motion prediction model that is theoretically equivariant to the input motion under Euclidean geometric transformations based on the parametric network. The proposed EqMotion has three novel designs: equivariant geometric feature learning, invariant pattern feature learning and invariant interaction reasoning. To ensure motion equivariance, we propose an equivariant geometric feature learning module to learn a Euclidean transformable geometric feature through dedicated designs of equivariant operations. The geometric feature preserves motion attributes that are relevant to Euclidean transformations. To promote more comprehensive representation power, we introduce an invariant pattern feature learning module to complement the network with motion attributes that are independent of Euclidean transformations. The pattern features, cooperated into the geometric features, provide expressive motion representations by exploiting motions' spatial-temporal dependencies.", + "bbox": [ + 76, + 396, + 472, + 667 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To further infer the interactions during motion prediction, we propose an invariant interaction reasoning module, which ensures that the captured interaction relationships are invariant to the input motion under Euclidean transformations. The module infers an invariant interaction graph by utilizing invariant factors in motions. The edge weights in the interaction graph categorize agents' interactions into different types, leading to better interaction representation.", + "bbox": [ + 76, + 670, + 472, + 792 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "We conduct extensive experiments on four different scenarios to evaluate our method's effectiveness: particle dynamics, molecule dynamics, 3D human skeleton motion and pedestrian trajectories. Comparing to many task-specific motion prediction methods, our method is generally applicable and achieves state-of-the-art performance in all these tasks by reducing the prediction error by $24.0 / 30.1 / 8.6 / 9.2\\%$", + "bbox": [ + 76, + 795, + 472, + 902 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "respectively. We also present that EqMotion is lightweight, and has a model size less than $30\\%$ of many other models' sizes. We show that EqMotion using only $5\\%$ data can achieve a comparable performance with other methods that take full data. As a summary, here are our contributions:", + "bbox": [ + 496, + 90, + 893, + 167 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- We propose EqMotion, the first motion prediction model that theoretically ensures sequence-to-sequence motion equivariance based on the parametric network. With equivariance, EqMotion promotes more generalization ability of motion feature learning, leading to more robust and accurate prediction.", + "- We propose a novel invariant interaction reasoning module, in which the captured interactions between agents are invariant to the input motion under Euclidean geometric transformations. With this, EqMotion achieves more generalization ability and stability in the interaction reasoning.", + "- We conduct experiments on four types of scenarios and find that EqMotion is applicable to all these different tasks, and importantly outperforms existing state-of-the-art methods on all the tasks." + ], + "bbox": [ + 496, + 167, + 893, + 393 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 500, + 409, + 640, + 425 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Equivariant Networks. Equivariance first draws high attention on the 2D image domain. Since CNN structure is sensitive to rotations, researchers start to explore rotation-equivariant designs like oriented convolutional filters [8,49], log-polar transform [11], circular harmonics [67] or steerable filters [66]. Meanwhile, GNN architectures [73-75] exploring symmetries on both rotation and translation have been emerged. Specifically, [57, 62] achieves partial symmetries by promoting translation equivariance. [14, 61] builds filters using spherical harmonics allowing transformations between high-order representations, achieving the rotation and translation equivariance. [12, 24] construct a Lie convolution to parameterize transformations into Lie algebra form. [10] proposes a series of equivariant layers for point cloud networks. [27] propose geometric vector perceptions for protein structure learning. Recently, EGNN [58] proposes a simple equivariant message passing form without using computationally expensive high-order representations. [23] further extends it by considering geometrical constraints. However, most existing methods are only applicable to state prediction, limiting models from exploiting sequence information. [30] uses pre and post coordinate processing to achieve motion equivariance but its network structure does not satisfy equivariance. In this work, we propose an equivariant model based on the parametric network which is generally applicable to motion prediction tasks and achieves a more precise prediction.", + "bbox": [ + 496, + 431, + 895, + 839 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Motion Prediction. Motion prediction has wide application scenarios. [3, 53, 56] proposes graph neural networks for learning to simulate complex physical systems. [17, 28, 37, 71] both explicitly infer the interactions rela", + "bbox": [ + 496, + 839, + 895, + 902 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "1411", + "bbox": [ + 483, + 944, + 514, + 957 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "tionships and perform prediction in physical systems. For human or vehicle trajectory prediction, social forces [21, 51], Markov [29, 65] process, and RNNs [1, 52, 63] are first methods to employ. Multi-model prediction methods are further proposed like using generator-discriminator structures [20, 22], multi-head output [43, 59], conditional variational autoencoders [32, 45, 55, 69, 71, 72, 76], memory mechanisms [48, 70], Gaussian mixture distribution prediction [17, 37]. The HD map information is specifically considered in the autonomous driving scenario [5, 6, 15, 22, 42, 43, 77]. For 3D human skeleton motion prediction, early methods are based on the state prediction [33, 60]. Later RNN-based models considering the sequential motion states are proposed [13, 26, 50, 64]. [19, 36] use spatial graph convolutions to directly regress the whole sequences. Besides, some methods [4, 40, 46, 47] specifically exploit the correlations between body joints. Multi-scale graphs are built by [9, 39, 41] to capture different body-level dependencies. In this work, we propose a generally applicable motion prediction network which promotes Euclidean equivariance, a fundamental property but neglected by previous methods, to have a more robust and accurate prediction.", + "bbox": [ + 75, + 90, + 472, + 422 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Background and Problem Formulation", + "text_level": 1, + "bbox": [ + 76, + 431, + 426, + 448 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Motion Prediction", + "text_level": 1, + "bbox": [ + 76, + 452, + 253, + 467 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Here we introduce the general problem formulation of motion prediction, which aims to generate future motions given the historical observations. Mathematically, consider $M$ agents in a multi-agent system. Let $\\mathbf{X}_i = [\\mathbf{x}_i^1,\\mathbf{x}_i^2,\\dots \\mathbf{x}_i^{T_{\\mathrm{p}}}]\\in$ $\\mathbb{R}^{T_{\\mathrm{p}}\\times n}$ and $\\mathbf{Y}_i = [\\mathbf{y}_i^1,\\mathbf{y}_i^2,\\dots \\mathbf{y}_i^{T_{\\mathrm{f}}}]\\in \\mathbb{R}^{T_{\\mathrm{f}}\\times n}$ be the ith agent's past and future motion, where $T_{\\mathrm{p}}$ and $T_{\\mathrm{f}}$ are the past and future timestamps and $n$ is the dimension of the system space. $n$ usually equals to 2 or 3 (corresponding to 2D or 3D case). The $t$ th timestamp locations $\\mathbf{x}_i^t$ and $\\mathbf{y}_i^t$ are $n$ dimension vectors. The whole system's past and future motion is represented as $\\mathbb{X} = [\\mathbf{X}_1,\\mathbf{X}_2,\\dots ,\\mathbf{X}_M]\\in \\mathbb{R}^{M\\times T_{\\mathrm{p}}\\times n}$ and $\\mathbb{Y} = [\\mathbf{Y}_1,\\mathbf{Y}_2,\\dots ,\\mathbf{Y}_M]\\in \\mathbb{R}^{M\\times T_{\\mathrm{f}}\\times n}$ . We aim to propose a prediction network $\\mathcal{F}_{\\mathrm{pred}}(\\cdot)$ so that the predicted future motions $\\widehat{\\mathbb{Y}} = \\mathcal{F}_{\\mathrm{pred}}(\\mathbb{X})$ are as close to the ground-truth future motions $\\mathbb{Y}$ as possible.", + "bbox": [ + 75, + 472, + 472, + 704 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. Equivariance and Invariance", + "text_level": 1, + "bbox": [ + 76, + 710, + 336, + 726 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The Euclidean geometric transformation has three basic forms: translation, rotation and reflection. The translation is modeled by a translation vector and rotation (or reflection) is modeled by an orthogonal rotation (or reflection) matrix. Let $\\mathbf{t} \\in \\mathbb{R}^n$ be a translation vector and $\\mathbf{R} \\in \\mathrm{SO}(n)$ be a $n \\times n$ rotation matrix, we have the following definitions for equivariance and invariance:", + "bbox": [ + 75, + 729, + 470, + 835 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Definition 1 Let $\\mathbb{X}$ be an input, $\\mathcal{F}(\\cdot)$ be an operation and $\\mathbb{Z} = \\mathcal{F}(\\mathbb{X})$ be the corresponding output. The operation $\\mathcal{F}(\\cdot)$ is called equivariant under Euclidean transformation if", + "bbox": [ + 75, + 837, + 470, + 883 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbb {Z} \\mathbf {R} + \\mathbf {t} = \\mathcal {F} (\\mathbb {X} \\mathbf {R} + \\mathbf {t}) \\quad \\forall \\mathbf {R} \\in \\mathrm {S O} (n), \\forall \\mathbf {t} \\in \\mathbb {R} ^ {n}.\n$$\n", + "text_format": "latex", + "bbox": [ + 102, + 883, + 441, + 901 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Definition 2 Let $\\mathbb{X}$ be an input, $\\mathcal{F}(\\cdot)$ be an operation and $\\mathbb{Z} = \\mathcal{F}(\\mathbb{X})$ be the corresponding output. The operation $\\mathcal{F}(\\cdot)$ is called invariant under Euclidean transformation if", + "bbox": [ + 496, + 92, + 893, + 138 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbb {Z} = \\mathcal {F} (\\mathbb {X} \\mathbf {R} + \\mathbf {t}) \\quad \\forall \\mathbf {R} \\in \\mathrm {S O} (n), \\forall \\mathbf {t} \\in \\mathbb {R} ^ {n}.\n$$\n", + "text_format": "latex", + "bbox": [ + 547, + 140, + 841, + 156 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Here, when a motion prediction network $\\mathcal{F}_{\\mathrm{pred}}(\\cdot)$ satisfies Definition 1, $\\mathcal{F}_{\\mathrm{pred}}(\\cdot)$ is said motion equivariant. When an interaction reasoning model $\\mathcal{F}_{\\mathrm{reason}}(\\cdot)$ satisfies Definition 2, $\\mathcal{F}_{\\mathrm{reason}}(\\cdot)$ is considered interaction invariant. We also say the output $\\mathbb{Z}$ is equivariant/invariant (to the input motion under Euclidean transformation) if Definition 1/2 is satisfied.", + "bbox": [ + 496, + 160, + 893, + 250 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In the following section, we will introduce our motion prediction network along with geometric features that are equivariant under Euclidean transformations, and pattern features along with the interaction reasoning module are invariant under Euclidean transformations.", + "bbox": [ + 496, + 251, + 893, + 325 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "4. Methodology", + "text_level": 1, + "bbox": [ + 498, + 340, + 633, + 357 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In this section, we present EqMotion, a motion prediction network which is equivariant under Euclidean geometric transformations. The whole network architecture is shown in Figure 2. The core of EqMotion is to successively learn equivariant geometric features and invariant pattern features by mutual cooperation in designed equivariant/invariant operations, which not only provide expressive motion and interaction representations, but also preserve equivariant/invariant properties. For agents' motions $\\mathbb{X} \\in \\mathbb{R}^{M \\times T_{\\mathrm{p}} \\times n}$ , the overall procedure of the proposed EqMotion is formulated as", + "bbox": [ + 496, + 362, + 893, + 513 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbb {G} ^ {(0)}, \\mathbf {H} ^ {(0)} = \\mathcal {F} _ {\\mathrm {I L}} (\\mathbb {X}), \\tag {1a}\n$$\n", + "text_format": "latex", + "bbox": [ + 570, + 513, + 890, + 530 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\left\\{\\mathbf {c} _ {i j} \\right\\} = \\mathcal {F} _ {\\mathrm {I R M}} \\left(\\mathbb {G} ^ {(0)}, \\mathbf {H} ^ {(0)}\\right), \\tag {1b}\n$$\n", + "text_format": "latex", + "bbox": [ + 571, + 534, + 890, + 553 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbb {G} ^ {(\\ell + 1)} = \\mathcal {F} _ {\\mathrm {E G F L}} ^ {(\\ell)} \\left(\\mathbb {G} ^ {(\\ell)}, \\mathbf {H} ^ {(\\ell)}, \\left\\{\\mathbf {c} _ {i j} \\right\\}\\right), \\tag {1c}\n$$\n", + "text_format": "latex", + "bbox": [ + 571, + 556, + 890, + 575 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {H} ^ {(\\ell + 1)} = \\mathcal {F} _ {\\mathrm {I P F L}} ^ {(\\ell)} \\left(\\mathbb {G} ^ {(\\ell)}, \\mathbf {H} ^ {(\\ell)}\\right), \\tag {1d}\n$$\n", + "text_format": "latex", + "bbox": [ + 571, + 578, + 890, + 599 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\widehat {\\mathbb {Y}} = \\mathcal {F} _ {\\mathrm {E O L}} \\left(\\mathbb {G} ^ {(L)}\\right). \\tag {1e}\n$$\n", + "text_format": "latex", + "bbox": [ + 571, + 601, + 890, + 619 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Step (1a) uses an initialization layer $\\mathcal{F}_{\\mathrm{IL}}(\\cdot)$ to obtain initial geometric features $\\mathbb{G}^{(0)}$ and pattern features $\\mathbf{H}^{(0)}$ . For interaction relationship unavailable cases, Step (1b) uses an invariant interaction reasoning module $\\mathcal{F}_{\\mathrm{IRM}}(\\cdot)$ to infer an interaction graph $\\{\\mathbf{c}_{ij}\\}$ whose edge weight $\\mathbf{c}_{ij}$ is the interaction category between agent $i$ and $j$ . Step (1c) uses the $\\ell$ th equivariant geometric feature learning layer $\\mathcal{F}_{\\mathrm{EGFL}}^{(\\ell)}(\\cdot)$ to learn the $(\\ell + 1)$ th geometric feature $\\mathbb{G}^{(\\ell + 1)}$ . Step (1d) uses the $\\ell$ th invariant pattern feature learning layer $\\mathcal{F}_{\\mathrm{IPFL}}^{(\\ell)}(\\cdot)$ to learn the $(\\ell + 1)$ th pattern feature $\\mathbf{H}^{(\\ell + 1)}$ . Step (1c) and Step (1d) will repeat $L$ times. Step (1e) uses an equivariant output layer $\\mathcal{F}_{\\mathrm{EOL}}(\\cdot)$ to obtain the final prediction $\\widehat{\\mathbb{Y}}$ .", + "bbox": [ + 496, + 621, + 893, + 806 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Note that i) to incorporate the geometric feature's equivariance, we need to design equivariant operations for the initialization layer $\\mathcal{F}_{\\mathrm{IL}}(\\cdot)$ and the equivariant geometric feature learning layer $\\mathcal{F}_{\\mathrm{EGFL}}^{(\\ell)}(\\cdot)$ ; ii) to introduce the pattern feature's invariance, we need to design invariant operations for the initialization layer $\\mathcal{F}_{\\mathrm{IL}}(\\cdot)$ and the invariant pattern feature", + "bbox": [ + 496, + 806, + 893, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "1412", + "bbox": [ + 483, + 944, + 514, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/c33d300b2f93111391dc484f51e09a89defc2f12477aaf4000742040a246196e.jpg", + "image_caption": [ + "Figure 2. EqMotion architecture. In EqMotion, we first use a feature initialization layer to initialize geometric features and pattern features. We then successively update the geometric features and the pattern features by the equivariant geometric feature learning and invariant pattern feature learning layers, obtaining expressive feature representation. We further propose an invariant reasoning module to infer an interaction graph used in equivariant geometric feature learning. Finally, we use an equivariant output layer to obtain the final prediction." + ], + "image_footnote": [], + "bbox": [ + 91, + 87, + 877, + 198 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "learning layer $\\mathcal{F}_{\\mathrm{IPFL}}^{(\\ell)}(\\cdot)$ ; and iii) the interaction graph categorizes agent's spatial interaction into different categories for better interaction representing. The interaction graph is invariant due to the reasoning module $\\mathcal{F}_{\\mathrm{IRM}}(\\cdot)$ design. In subsequent sections, we elaborate the details of each step.", + "bbox": [ + 75, + 268, + 472, + 347 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4.1. Feature Initialization", + "text_level": 1, + "bbox": [ + 76, + 356, + 274, + 371 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The feature initialization layer aims to obtain initial geometric features and pattern features while equipping them with different functionality. The initial geometric feature is denoted as $\\mathbb{G}^{(0)} = [\\mathbf{G}_1^{(0)},\\dots ,\\mathbf{G}_M^{(0)}]\\in \\mathbb{R}^{M\\times C\\times n}$ whose $i$ th agent's geometric feature consists of $C$ geometric coordinates. The initial pattern feature is denoted as $\\mathbf{H}^{(0)} = [\\mathbf{h}_1^{(0)},\\dots ,\\mathbf{h}_M^{(0)}]\\in \\mathbb{R}^{M\\times D}$ whose $i$ th agent's pattern feature is a $D$ -dimensional vector. Given the past motions $\\mathbb{X}$ whose the $i$ th agent's motion is $\\mathbf{X}_i\\in \\mathbb{R}^{T_{\\mathrm{p}}\\times n}$ , we obtain two initial features of the $i$ th agent:", + "bbox": [ + 75, + 376, + 472, + 531 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {G} _ {i} ^ {(0)} = \\phi_ {\\mathrm {i n i t \\_ g}} (\\mathbf {X} _ {i} - \\overline {{\\mathbb {X}}}) + \\overline {{\\mathbb {X}}},\n$$\n", + "text_format": "latex", + "bbox": [ + 106, + 532, + 310, + 551 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {V} _ {i} = \\triangle \\mathbf {X} _ {i}, \\rho_ {i} ^ {t} = | | \\mathbf {V} _ {i} ^ {t} | | _ {2}, \\theta_ {i} ^ {t} = \\mathrm {a n g l e} (\\mathbf {V} _ {i} ^ {t}, \\mathbf {V} _ {i} ^ {t - 1}),\n$$\n", + "text_format": "latex", + "bbox": [ + 107, + 554, + 437, + 573 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {h} _ {i} ^ {(0)} = \\phi_ {\\mathrm {i n i t \\_ h}} ([ \\rho_ {i}; \\theta_ {i} ]),\n$$\n", + "text_format": "latex", + "bbox": [ + 107, + 575, + 272, + 595 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\phi_{\\mathrm{init\\_g}}(\\mathbf{X}) = \\mathbf{W}_{\\mathrm{init\\_g}}\\mathbf{X}$ , $\\mathbf{W}_{\\mathrm{init\\_g}} \\in \\mathbb{R}^{C \\times T_p}$ is a linear function, $\\overline{\\mathbb{X}}$ is the mean coordinate of all agents all past timestamps. $\\triangle$ is the difference operator to obtain the velocity $\\mathbf{V}_i \\in \\mathbb{R}^{T_{\\mathrm{p}} \\times n}$ . $\\rho_i \\in \\mathbb{R}^{T_{\\mathrm{p}}}$ is the velocity magnitude sequence and $\\theta_i \\in \\mathbb{R}^{T_{\\mathrm{p}}}$ is the velocity angle sequence. The superscript $(\\cdot)^t$ denotes the $t$ th element, $||\\cdot||_2$ is vector 2-norm, $\\mathrm{angle}(\\cdot)$ is the function calculating the angle between two vectors and $\\phi_{\\mathrm{init\\_h}}(\\cdot)$ is an embedding function implemented by MLP or LSTM. $[\\cdot; \\cdot]$ represents concatenation.", + "bbox": [ + 75, + 597, + 470, + 733 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The geometric feature preserves both equivariant property and motion attributes that are sensitive to Euclidean geometric transforms since we linearly combine the equivariant locations. The pattern feature remains invariant and is sensitive to motion attributes independent of Euclidean geometric transforms.", + "bbox": [ + 75, + 734, + 470, + 825 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4.2. Invariant Reasoning Module", + "text_level": 1, + "bbox": [ + 76, + 835, + 333, + 851 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "For most scenarios, the interaction relationship is implicit and unavailable. Thus, we propose an invariant reasoning module for inferring the interaction category between agents.", + "bbox": [ + 75, + 854, + 470, + 900 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Note that we design the reasoning module to be invariant as the interaction category is independent of Euclidean transformations. The output of the reasoning module is an invariant interaction graph whose edge weight $\\mathbf{c}_{ij} \\in [0,1]^K$ is a categorical vector representing the type of interaction between agent $i$ and $j$ . $K$ is the interaction category number. To obtain the interaction categorical vector, we perform a message passing operation using the agent's initial pattern feature $\\mathbf{h}_i^{(0)}$ and geometric feature $\\mathbf{G}_i^{(0)}$ :", + "bbox": [ + 496, + 268, + 893, + 407 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {m} _ {i j} ^ {\\prime} = \\phi_ {\\mathrm {r m}} \\left(\\left[ \\mathbf {h} _ {i} ^ {(0)}; \\mathbf {h} _ {j} ^ {(0)}; \\left| \\left| \\mathbf {G} _ {i} ^ {(0)} - \\mathbf {G} _ {j} ^ {(0)} \\right| \\right| _ {2, \\text {c o l}} \\right]\\right),\n$$\n", + "text_format": "latex", + "bbox": [ + 529, + 409, + 838, + 431 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {p} _ {i} ^ {\\prime} = \\sum_ {j \\in \\mathcal {N} _ {i}} \\mathbf {m} _ {i j} ^ {\\prime}, \\mathbf {h} _ {i} ^ {\\prime} = \\phi_ {\\mathrm {r h}} \\big ([ \\mathbf {p} _ {i} ^ {\\prime}; \\mathbf {h} _ {i} ^ {(0)} ] \\big),\n$$\n", + "text_format": "latex", + "bbox": [ + 529, + 433, + 790, + 465 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {c} _ {i j} = \\mathrm {s m} \\Big (\\phi_ {\\mathrm {r c}} \\big ([ \\mathbf {h} _ {i} ^ {\\prime}; \\mathbf {h} _ {j} ^ {\\prime}; | | \\mathbf {G} _ {i} ^ {(0)} - \\mathbf {G} _ {j} ^ {(0)} | | _ {2, \\mathrm {c o l}} ] \\big) / \\tau \\Big),\n$$\n", + "text_format": "latex", + "bbox": [ + 529, + 469, + 859, + 494 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $||\\cdot ||_{2,\\mathrm{col}}$ is a column-wise $\\ell_2$ -distance, $\\phi_{\\mathrm{rm}}(\\cdot),\\phi_{\\mathrm{rh}}(\\cdot)$ $\\phi_{\\mathrm{rc}}(\\cdot)$ are learnable functions implemented by MLPs. $\\mathrm{sm}(\\cdot)$ is the softmax function and $\\tau$ is the temperature to control the smoothness of the categorical distribution. The interaction edge weights $\\{\\mathbf{c}_{ij}\\}$ will be end-to-end learned with the whole prediction network.", + "bbox": [ + 496, + 494, + 893, + 585 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4.3. Equivariant Geometric Feature Learning", + "text_level": 1, + "bbox": [ + 498, + 599, + 852, + 616 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The equivariant geometric feature learning process aims to find more representative agents' geometric features by exploiting their spatial and temporal dependencies, while maintaining the equivariance. During the process, we perform i) equivariant inner-agent attention to exploit the temporal dependencies; ii) equivariant inter-agent aggregation to model spatial interactions; and iii) equivariant non-linear function to further enhance the representation ability.", + "bbox": [ + 496, + 619, + 893, + 741 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Equivariant inner-agent attention To exploit the temporal dependency, we perform an attention mechanism on the coordinate dimension of the geometric feature since the coordinate dimension originates from the temporal dimension. Given the $i$ th agent's geometric feature $\\mathbf{G}_i^{(\\ell)} \\in \\mathbb{R}^{C \\times n}$ and pattern feature $\\mathbf{h}_i^{(\\ell)}$ , we have", + "bbox": [ + 496, + 742, + 893, + 837 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {G} _ {i} ^ {(\\ell)} \\leftarrow \\phi_ {\\mathrm {a t t}} ^ {(\\ell)} \\left(\\mathbf {h} _ {i} ^ {(\\ell)}\\right) \\cdot \\left(\\mathbf {G} _ {i} ^ {(\\ell)} - \\overline {{\\mathbb {G}}} ^ {(\\ell)}\\right) + \\overline {{\\mathbb {G}}} ^ {(\\ell)}, \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 550, + 839, + 890, + 861 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\phi_{\\mathrm{att}}^{(\\ell)}(\\cdot):\\mathbb{R}^D\\to \\mathbb{R}^C$ is a function which learns the attention weight for per coordinate, and $\\overline{\\mathbb{G}}^{(\\ell)}$ is the mean", + "bbox": [ + 496, + 864, + 890, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "1413", + "bbox": [ + 483, + 944, + 514, + 955 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "coordinates summing up over all agents and all coordinates.", + "bbox": [ + 76, + 90, + 470, + 106 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The above operation will bring the following benefits: i) The learned attention weight is invariant and the learned dependencies between different timestamps of the motion will not be disturbed by irrelevant Euclidean transformations; and ii) The learned geometric feature is equivariant because of the coordinate-wise linear multiplication.", + "bbox": [ + 75, + 106, + 468, + 196 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Equivariant inter-agent aggregation The equivariant inter-agent aggregation aims to model spatial interactions between agents. The key idea is to use the reasoned or provided interaction category to learn aggregation weights, and then use the weights to aggregate neighboring agents' geometric features. The aggregation operation reads", + "bbox": [ + 75, + 198, + 470, + 287 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\mathbf {e} _ {i j} ^ {(\\ell)} = \\sum_ {k = 1} ^ {K} \\mathbf {c} _ {i j, k} \\phi_ {e, k} ^ {(\\ell)} \\left(\\left[ \\mathbf {h} _ {i} ^ {(\\ell)}; \\mathbf {h} _ {j} ^ {(\\ell)}; \\left\\| \\mathbf {G} _ {i} ^ {(\\ell)} - \\mathbf {G} _ {j} ^ {(\\ell)} \\right\\| _ {2, \\text {c o l}} \\right]\\right), \\tag {3} \\\\ \\mathbf {G} _ {i} ^ {(\\ell)} \\leftarrow \\mathbf {G} _ {i} ^ {(\\ell)} + \\sum_ {j \\in \\mathcal {N} _ {i}} \\mathbf {e} _ {i j} ^ {(\\ell)} \\cdot (\\mathbf {G} _ {i} ^ {(\\ell)} - \\mathbf {G} _ {j} ^ {(\\ell)}), \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 96, + 289, + 468, + 357 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\mathbf{e}_{ij}^{(\\ell)}\\in \\mathbb{R}^C$ is the learned aggregation weights between agent $i$ and $j,||\\cdot ||_{2,\\mathrm{col}}$ is a column-wise $\\ell_2$ -distance, $\\cdot$ is dot product and $\\mathcal{N}_i$ is the $i$ th agent's neighboring set. For the $k$ th interaction category, we assign a function $\\phi_{e,k}^{(\\ell)}(\\cdot)$ that is implemented by MLP to model how the interaction works.", + "bbox": [ + 75, + 358, + 468, + 436 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The social influence from agent $j$ to agent $i$ is modeled by the coordinates' difference between the two agents. The intuition behind this design is that the mutual force between two objects is always in the direction of the line they formed.", + "bbox": [ + 75, + 438, + 468, + 498 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Note that for most scenarios, we do not have an explicit definition of interacted \"neighbors\", thus we use a fully-connected graph structure, which means every agent's neighbors include all other agents. For some special cases with massive nodes, like point clouds, we construct a local neighboring set by choosing neighbors within a distance threshold.", + "bbox": [ + 75, + 500, + 470, + 589 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Equivariant non-linear function According to Eq. (2) and Eq. (3), the operation of inner-agent attention and inter-agent aggregation are linear combinations with agents' coordinates. It is well known that non-linear operation is the key to improving neural networks' expressivity. Therefore, we propose an equivariant non-linear function to enhance the representation ability of our prediction network while preserving equivariance. The key idea is proposing a criterion with the invariance property for splitting different conditions, and for each condition design an equivariant equation. Mathematically, the non-linear function is", + "bbox": [ + 75, + 590, + 470, + 755 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\mathbf {Q} _ {i} ^ {(\\ell)} = \\mathbf {W} _ {\\mathrm {Q}} ^ {(\\ell)} \\left(\\mathbf {G} _ {i} ^ {(\\ell)} - \\overline {{\\mathbb {G}}} ^ {(\\ell)}\\right), \\mathbf {K} _ {i} ^ {(\\ell)} = \\mathbf {W} _ {\\mathrm {K}} ^ {(\\ell)} \\left(\\mathbf {G} _ {i} ^ {(\\ell)} - \\overline {{\\mathbb {G}}} ^ {(\\ell)}\\right), \\\\ \\mathbf {g} _ {i, c} ^ {(\\ell + 1)} = \\left\\{ \\begin{array}{l l} \\mathbf {q} _ {i, c} ^ {(\\ell)} + \\overline {{\\mathbb {G}}} ^ {(\\ell)} & \\text {i f} \\langle \\mathbf {q} _ {i, c} ^ {(\\ell)}, \\mathbf {k} _ {i, c} ^ {(\\ell)} \\rangle \\geq 0, \\\\ \\mathbf {q} _ {i, c} ^ {(\\ell)} - \\langle \\mathbf {q} _ {i, c} ^ {(\\ell)}, \\frac {\\mathbf {k} _ {i , c} ^ {(\\ell)}}{| | \\mathbf {k} _ {i , c} ^ {(\\ell)} | | _ {2}} \\rangle \\frac {\\mathbf {k} _ {i , c} ^ {(\\ell)}}{| | \\mathbf {k} _ {i , c} ^ {(\\ell)} | | _ {2}} + \\overline {{\\mathbb {G}}} ^ {(\\ell)} & \\text {o t h e r w i s e}, \\end{array} \\right. \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 76, + 757, + 486, + 825 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\mathbf{Q}_i^{(\\ell)}$ and $\\mathbf{K}_i^{(\\ell)}$ is the learned query coordinates and key coordinates, $\\mathbf{W}_{\\mathrm{K}}^{(\\ell)}\\in \\mathbb{R}^{C\\times C}$ are learnable matrices for queries and keys. $\\overline{\\mathbb{G}}_{\\nu}^{(\\ell)}$ is the mean coordinates over all agents and all coordinates. $\\mathbf{q}_{i,c}^{(\\ell)}$ , $\\mathbf{k}_{i,c}^{(\\ell)}$ is the $c$ th coordinate of", + "bbox": [ + 75, + 827, + 468, + 902 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "$\\mathbf{Q}_i^{(\\ell)}$ and $\\mathbf{K}_i^{(\\ell)}$ . $\\langle \\cdot, \\cdot \\rangle$ is the vector inner product.", + "bbox": [ + 500, + 88, + 813, + 108 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "For every geometric coordinate $\\mathbf{g}_{i,c}^{(\\ell)}$ , we learn a query coordinate $\\mathbf{q}_{i,c}^{(\\ell)}$ and a key coordinate $\\mathbf{k}_{i,c}^{(\\ell)}$ . We set the criterion as the inner product of the query coordinate and the key coordinate. If the inner product is positive, we directly take the value of the query coordinate as output; otherwise, we clip the query coordinate vector by moving out its parallel components with the key coordinate vector. Finally, we obtain the $i$ th agent's geometric features of the next layer $\\mathbf{G}_i^{(l + 1)}$ by gathering all the coordinates $\\mathbf{g}_{i,c}^{(l + 1)}$ . The non-linear function is equivariant, since the criterion is invariant and the two equations under two conditions are equivariant.", + "bbox": [ + 496, + 108, + 893, + 286 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.4. Invariant Pattern Feature Learning", + "text_level": 1, + "bbox": [ + 498, + 295, + 808, + 311 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The invariant pattern feature learning aims to obtain a more representative agent pattern feature through interacting with neighbors. Here we learn the agent's pattern feature with an invariant message passing mechanism. Specially, we add the relative geometric feature difference into the edge modeling in the message passing to complement the information of relationships between agent absolute locations, which cannot be obtained by solely using the pattern features. Given the $i$ th agent's pattern feature $\\mathbf{h}_i^{(\\ell)} \\in \\mathbb{R}^D$ and geometric feature $\\mathbf{G}_i^{(\\ell)} \\in \\mathbb{R}^{C \\times n}$ , the next layer's pattern feature $\\mathbf{h}_i^{(l+1)}$ is obtained by", + "bbox": [ + 496, + 314, + 893, + 488 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\mathbf {m} _ {i j} ^ {(\\ell)} = \\phi_ {m} ^ {(\\ell)} \\left(\\left[ \\mathbf {h} _ {i} ^ {(\\ell)}; \\mathbf {h} _ {j} ^ {(\\ell)}; | | \\mathbf {G} _ {i} ^ {(\\ell)} - \\mathbf {G} _ {j} ^ {(\\ell)} | | _ {2, \\text {c o l}} \\right]\\right), \\\\ \\mathbf {p} _ {i} ^ {(\\ell)} = \\sum_ {j \\in \\mathcal {N} (i)} \\mathbf {m} _ {i j} ^ {(\\ell)}, \\mathbf {h} _ {i} ^ {(l + 1)} = \\phi_ {h} ^ {(\\ell)} ([ \\mathbf {h} _ {i} ^ {(\\ell)}; \\mathbf {p} _ {i} ^ {(\\ell)} ]). \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 535, + 489, + 854, + 551 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Here $\\mathbf{m}_{ij}^{(\\ell)}$ is the edge features and $\\mathbf{p}_i^{(\\ell)}$ is the aggregated neighboring features in the message passing. $||\\cdot ||_{2,\\mathrm{col}}$ is a column-wise $\\ell_2$ -distance and $[\\cdot ;\\cdot ]$ denotes concatenation. Functions $\\phi_m^{(\\ell)}(\\cdot)$ and $\\phi_h^{(\\ell)}(\\cdot)$ are implemented by MLPs.", + "bbox": [ + 496, + 551, + 893, + 618 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.5. Equivariant Output Layer", + "text_level": 1, + "bbox": [ + 498, + 627, + 740, + 643 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "After total $L$ feature learning layers, we obtain the final $i$ th agent's geometric feature $\\mathbf{G}_i^{(L)}$ and pattern feature $\\mathbf{h}_i^{(L)}$ . We use the geometric feature for the final prediction by a linear operation for equivariance: for the $i$ th agent:", + "bbox": [ + 496, + 647, + 893, + 709 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\widehat {\\mathbf {Y}} _ {i} = \\mathbf {W} _ {\\text {o u t}} (\\mathbf {G} _ {i} ^ {(\\ell)} - \\overline {{\\mathbb {G}}} ^ {(\\ell)}) + \\overline {{\\mathbb {G}}} ^ {(\\ell)},\n$$\n", + "text_format": "latex", + "bbox": [ + 578, + 710, + 810, + 731 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\mathbf{W}_{\\mathrm{out}} \\in \\mathbb{R}^{T_{\\mathrm{f}} \\times D}$ is a learnable weight matrix. Finally, we gather all the agent prediction $\\widehat{\\mathbf{Y}}_i$ to have the final predicted motions $\\widehat{\\mathbb{Y}}$ .", + "bbox": [ + 496, + 732, + 893, + 780 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.6. Theoretical Analysis", + "text_level": 1, + "bbox": [ + 500, + 790, + 692, + 806 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In this section, we analyze our network's equivariance property and the interaction reasoning module's invariance property, as stated in the following theorem. Let $\\mathbb{G}^{(\\ell)}\\in$ $\\mathbb{R}^{M\\times C\\times n}$ be all agents' geometric features, $\\mathbf{H}^{(\\ell)}\\in \\mathbb{R}^{M\\times D}$ be all agents' pattern features at the $\\ell$ th layer, and $\\{\\mathbf{c}_{ij}\\}$ be the set of all the interaction categorical vectors.", + "bbox": [ + 496, + 810, + 893, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "1414", + "bbox": [ + 483, + 944, + 514, + 955 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Theorem 1 For arbitrary translation vector $\\mathbf{t} \\in \\mathbb{R}^n$ and rotation (or reflection) matrix $\\mathbf{R} \\in \\mathrm{SO}(n)$ , the modules with equivariance and invariance in our network satisfy:", + "bbox": [ + 75, + 90, + 468, + 136 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "1. For the initialization layer $\\mathcal{F}_{\\mathrm{IL}}(\\cdot)$ , the initial geometric feature is equivariant and the initial pattern feature is invariant:", + "bbox": [ + 75, + 137, + 468, + 181 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbb {G} ^ {(0)} \\mathbf {R} + \\mathbf {t}, \\mathbf {H} ^ {(0)} = \\mathcal {F} _ {\\mathrm {I L}} (\\mathbb {X} \\mathbf {R} + \\mathbf {t}).\n$$\n", + "text_format": "latex", + "bbox": [ + 153, + 181, + 388, + 200 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "2. The reasoning module $\\mathcal{F}_{\\mathrm{IRM}}(\\cdot)$ along with reasoned interaction categorical vectors $\\{\\mathbf{c}_{ij}\\}$ is invariant:", + "bbox": [ + 75, + 202, + 468, + 233 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\left\\{\\mathbf {c} _ {i j} \\right\\} = \\mathcal {F} _ {\\mathrm {I R M}} \\left(\\mathbb {G} ^ {(0)} \\mathbf {R} + \\mathbf {t}, \\mathbf {H} ^ {(0)}\\right).\n$$\n", + "text_format": "latex", + "bbox": [ + 158, + 234, + 385, + 253 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "3. The $\\ell$ th geometric feature learning layer $\\mathcal{F}_{\\mathrm{EGFL}}^{(\\ell)}(\\cdot)$ is equivariant:", + "bbox": [ + 75, + 256, + 468, + 287 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbb {G} ^ {(l + 1)} \\mathbf {R} + \\mathbf {t} = \\mathcal {F} _ {\\mathrm {E G F L}} ^ {(\\ell)} \\left(\\mathbb {G} ^ {(\\ell)} \\mathbf {R} + \\mathbf {t}, \\mathbf {H} ^ {(\\ell)}, \\left\\{\\mathbf {c} _ {i j} \\right\\}\\right).\n$$\n", + "text_format": "latex", + "bbox": [ + 107, + 289, + 436, + 310 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4. The $\\ell$ th pattern feature learning layer $\\mathcal{F}_{\\mathrm{IPFL}}^{(\\ell)}(\\cdot)$ is invariant:", + "bbox": [ + 75, + 311, + 468, + 342 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {H} ^ {(l + 1)} = \\mathcal {F} _ {\\mathrm {I P F L}} ^ {(\\ell)} (\\mathbb {G} ^ {(\\ell)} \\mathbf {R} + \\mathbf {t}, \\mathbf {H} ^ {(\\ell)}).\n$$\n", + "text_format": "latex", + "bbox": [ + 151, + 343, + 392, + 363 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5. The output layer $\\mathcal{F}_{\\mathrm{EOL}}(\\cdot)$ is equivariant:", + "bbox": [ + 96, + 364, + 385, + 380 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\widehat {\\mathbf {Y}} \\mathbf {R} + \\mathbf {t} = \\mathcal {F} _ {\\mathrm {E O L}} (\\mathbb {G} ^ {(L)} \\mathbf {R} + \\mathbf {t}).\n$$\n", + "text_format": "latex", + "bbox": [ + 166, + 382, + 377, + 400 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "See the detailed proof in Appendix. Theorem 1 presents the equivariance/invariance properties with the Euclidean transformation for each operation in the proposed network. Based on Theorem 1, by combining all network operations together, we can show that the whole network is equivariant:", + "bbox": [ + 75, + 401, + 468, + 477 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Corollary 1 For arbitrary translation vector $\\mathbf{t} \\in \\mathbb{R}^n$ and rotation matrix $\\mathbf{R} \\in \\mathrm{SO}(n)$ , our whole network EqMotion $\\mathcal{F}_{\\mathrm{pred}}(\\cdot)$ satisfies:", + "bbox": [ + 75, + 482, + 468, + 527 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\widehat {\\mathbb {Y}} \\mathbf {R} + \\mathbf {t} = \\mathcal {F} _ {\\mathrm {p r e d}} (\\mathbb {X} \\mathbf {R} + \\mathbf {t}).\n$$\n", + "text_format": "latex", + "bbox": [ + 178, + 529, + 364, + 547 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5. Experiment", + "text_level": 1, + "bbox": [ + 76, + 558, + 200, + 575 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "In this section, we validate our method on four different scenarios: particle dynamics, molecule dynamics, 3D human skeleton motion, and pedestrian trajectories. The detailed dataset description, implementation details, and additional experiment results are elaborated in the Appendix.", + "bbox": [ + 75, + 580, + 468, + 656 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Metric We use: i) Average Displacement Error (ADE) and Final Displacement Error (FDE). ADE/FDE is the $\\ell_2$ distance of the predicted whole motion/endpoint to the ground truth of the whole motion/endpoint; ii) Mean Per Joint Position Error (MPJPE). It records average $\\ell_2$ distance between predicted joints and target ones at each future timestamp.", + "bbox": [ + 75, + 657, + 468, + 748 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5.1. Scenario 1: Particle Dynamic Prediction", + "text_level": 1, + "bbox": [ + 75, + 758, + 421, + 773 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We use the particle $N$ -body simulation [28] in a 3D space similar to [14, 58]. In the Springs simulation, particles are randomly connected by a spring. In the Charged simulation, particles are randomly charged or uncharged.", + "bbox": [ + 75, + 777, + 468, + 840 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Validation on interaction reasoning Since we can get the ground-truth interaction through simulation, we evaluate the ability of interaction reasoning as a category recognition task. To evaluate the robustness of the reasoning result with", + "bbox": [ + 75, + 840, + 468, + 900 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/f1e883ca0155892d5e394df95a02f16c7398806ac35fd101e9de2b2a7dc74e1b.jpg", + "table_caption": [ + "Table 1. Interaction recognition accuracy and consistency (mean ± std in % in 5 independent runs) on the physical simulation." + ], + "table_footnote": [], + "table_body": "
ModelSpringsCharged
AccuracyConsistencyAccuracyConsistency
Corr.(path) [28]58.1 ± 0.099.8 ± 0.157.5 ± 0.187.9 ± 0.1
Corr.(LSTM) [28]53.5 ± 0.592.4 ± 2.157.2 ± 0.491.7 ± 1.1
EGNN [58]61.0 ± 1.3100.0 ± 0.058.2 ± 1.4100.0 ± 0.0
NRI [28]93.0 ± 1.193.7 ± 1.270.0 ± 0.688.5 ± 1.3
dNRI [17]93.3 ± 2.089.6 ± 2.070.4 ± 1.783.6 ± 1.8
Ours97.6 ± 1.1100.0 ± 0.080.9 ± 3.4100.0 ± 0.0
Supervised98.7 ± 0.2100.0 ± 0.097.4 ± 0.2100.0 ± 0.0
", + "bbox": [ + 501, + 118, + 883, + 247 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/c99ac6037ac5632c7029371226f8df24bf8811fe060beff70661f62224c11da9.jpg", + "image_caption": [ + "Figure 3. Comparison of displacement error across different timestamps on the physical simulation." + ], + "image_footnote": [], + "bbox": [ + 506, + 250, + 875, + 388 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "the Euclidean transformation, we introduce recognition \"consistency\", which is the ratio of the same recognition result under 20 random Euclidean transformations. The \"Supervised\" represents an upper bound that uses the ground-truth category to train the model. Table 1 reports the comparison of reasoning results on both springs and charged simulations, for recognizing whether there is a spring connection or electrostatic force. We see that i) our method achieves significant improvement on the recognition accuracy and has more robust reasoning results due to the invariance of our reasoning module; and ii) our method achieves a close performance to the upper bound, reflecting that our method is capable of reasoning a robust and accurate interaction category.", + "bbox": [ + 496, + 430, + 893, + 626 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Validation on future prediction We conduct the experiment to evaluate the prediction performance on the charged settings. Figure 3 compares the displacement error at all future timestamps of different methods. We see that our method (red line) achieves state-of-the-art prediction performance, reflecting our model's efficiency in future prediction.", + "bbox": [ + 496, + 627, + 893, + 718 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5.2. Scenario 2: Molecule Dynamic Prediction", + "text_level": 1, + "bbox": [ + 498, + 729, + 856, + 744 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We adopt the MD17 [7] dataset which contains the motions of different molecules generated via a molecular dynamics simulation environment. The goal is to predict the motions of every atom of the molecule. We randomly pick four kinds of molecules: Aspirin, Benzene, Ethanol and Malonaldehyde and learn a prediction model for each molecule.", + "bbox": [ + 496, + 750, + 893, + 839 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 4 presents the comparison of different motion prediction methods. We achieve state-of-the-art prediction performance on all four molecules. The ADE/FDE across four molecules is decreased by $34.2\\% / 30.1\\%$ on average.", + "bbox": [ + 496, + 840, + 893, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "1415", + "bbox": [ + 483, + 944, + 514, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/261d77cdb50438963b636cd6d014a4f6f4f95d9b052c5ba5f598792db6a9b47e.jpg", + "table_caption": [ + "Table 2. Comparisons of short-term skeleton motion prediction on 11 representative actions and average results across all actions on H3.6M." + ], + "table_footnote": [], + "table_body": "
MotionWalkingEatingSmokingDiscussionDirectionsPhoning
millisecond801603204008016032040080160320400801603204008016032040080160320400
Res-sup. (CVPR'17)29.450.876.081.516.830.656.968.723.042.670.182.732.961.290.996.235.457.376.387.738.069.3115.0126.7
Traj-GCN (ICCV'19)12.323.039.846.18.416.933.240.77.916.231.938.912.527.458.571.79.019.943.453.710.221.042.552.3
DMGNN (CVPR'20)17.330.754.665.211.021.436.243.99.017.632.140.317.334.861.069.813.124.664.781.912.525.848.158.3
MSRGCN (ICCV'21)12.222.738.645.28.417.133.040.48.016.331.338.212.026.857.169.78.619.743.353.810.120.741.551.3
PGBIG (CVPR'22)10.219.834.540.37.015.130.638.16.614.128.234.710.023.853.666.77.217.640.951.58.318.338.748.4
SPGSN (ECCV'22)10.119.434.841.57.114.930.537.96.713.828.034.610.423.853.667.17.417.239.850.38.718.338.748.5
EqMotion (Ours)9.017.532.639.26.313.628.936.55.511.323.029.38.218.942.153.96.315.838.950.17.416.736.947.0
MotionPosingSittingSitting DownWaitingWalking TogetherAverage
millisecond801603204008016032040080160320400801603204008016032040080160320400
", + "bbox": [ + 83, + 93, + 888, + 258 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/2fde0ec58d2c54f9bef589426e63a581e204bdaef5e1445f6ac522761e428327.jpg", + "table_caption": [ + "Table 3. Comparisons of long-term skeleton motion prediction on 8 representative actions and average results across all actions on H3.6M." + ], + "table_footnote": [], + "table_body": "
MotionWalkingEatingSmokingDiscussionGreetingPhoningPosingWalking TogetherAverage
millisecond560ms1000ms560ms1000ms560ms1000ms560ms1000ms560ms1000ms560ms1000ms560ms1000ms560ms1000ms560ms1000ms
Res-Sup. [50]81.7100.779.9100.294.8137.4121.3161.7156.3184.3143.9186.8165.4236.8173.6202.3129.2165.0
Traj-GCN [47]54.159.853.477.850.772.691.6121.5115.4148.869.2103.1114.5173.055.065.681.6114.3
DMGNN [41]71.485.858.186.750.972.281.9138.3144.5170.571.3108.4125.5188.270.586.993.6127.6
MSRGCN [9]52.763.052.577.149.571.688.6117.6116.3147.268.3104.4116.3174.352.965.981.1114.2
PGBIG [44]48.156.451.176.046.569.587.1118.2110.2143.565.9102.7106.1164.851.964.376.9110.3
SPGSN [40]46.953.649.873.446.768.689.7118.6111.0143.266.7102.5110.3165.449.860.977.4109.6
EqMotion (Ours)43.452.848.473.041.063.475.3105.6108.7142.064.7101.084.9139.444.556.073.4106.9
", + "bbox": [ + 81, + 273, + 888, + 362 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/0e35fbb2ffffb01894a3c9a6ae0d543767ff662eba077c8ff0722989e1275efd.jpg", + "table_caption": [ + "Table 4. Prediction ADE/FDE $\\left( {\\times {10}^{-2}}\\right)$ on the MD17 dataset." + ], + "table_footnote": [], + "table_body": "
AspirinBenzeneEthanolMalonaldehyde
Radial Field [31]17.98/26.207.73/12.478.10/10.6116.53/25.10
TFN [61]15.02/21.357.55/12.308.05/10.5715.21/24.32
SE(3)-Trans [14]15.70/22.397.62/12.508.05/10.8615.44/24.47
EGNN [58]14.61/20.657.50/12.168.01/10.2215.21/24.00
LSTM17.59/24.796.06/9.467.73/9.8815.14/22.90
S-LSTM [1]13.12/18.143.06/3.527.23/9.8511.93/18.43
NRI [28]12.60/18.501.89/2.586.69/8.7812.79/19.86
NMMP [22]10.41/14.672.21/3.336.17/7.869.50/14.89
GroupNet [69]10.62/14.002.02/2.956.00/7.887.99/12.49
EqMotion(Ours)5.95/8.381.18/1.735.05/7.025.85/9.02
", + "bbox": [ + 78, + 380, + 470, + 529 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.3. Scenario 3: Human Skeleton Motion Prediction", + "text_level": 1, + "bbox": [ + 76, + 537, + 468, + 553 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We conduct experiments on the Human 3.6M (H3.6M) dataset [25] for 3D human skeleton motion prediction. H3.6M contains 7 subjects performing 15 actions. Following the standard paradigm [41, 50], we train the models on 6 subjects and tested on the specific clips of the 5th subject.", + "bbox": [ + 75, + 560, + 468, + 635 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Short-term motion prediction Short-term motion prediction aims to predict future poses within 400 milliseconds. We compare EqMotion with six state-of-the-art methods. Table 2 presents the comparison of prediction MPJPEs. See the overall result in the Appendix. We see that i) EqMotion obtains superior performance at most timestamps across all the actions; and ii) compared to the baselines, EqMotion achieves much lower MPJPEs by $8.6\\%$ on average.", + "bbox": [ + 75, + 638, + 468, + 758 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Long-term motion prediction Long-term motion prediction aims to predict the poses over 400 milliseconds. Table 3 presents the prediction MPJPEs of various methods. We see that EqMotion achieves more effective prediction on most actions and has lower MPJPEs by $3.8\\%$ on average.", + "bbox": [ + 75, + 761, + 468, + 835 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Visualization results Figure 4 visualizes and compares the predictions on H3.6M. Baselines fail to predict future movements. EqMotion completes the action more precisely.", + "bbox": [ + 75, + 838, + 468, + 883 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "The quantitative and visualization results reveal that Eq-", + "bbox": [ + 96, + 885, + 470, + 900 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/66ac84f39e6d3770a2966afba273266f83058812eefa17690a0814951ee8440a.jpg", + "image_caption": [ + "Figure 4. Qualitative comparison on the action 'Sitting Down' of H3.6M. EqMotion completes the action more accurately." + ], + "image_footnote": [], + "bbox": [ + 501, + 366, + 885, + 479 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Motion outperforms many previous methods that are task-specific, reflecting the effectiveness of EqMotion.", + "bbox": [ + 498, + 522, + 893, + 551 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.4. Scenario 4: Pedestrian Trajectory Prediction", + "text_level": 1, + "bbox": [ + 500, + 563, + 879, + 579 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We conduct experiments on pedestrian trajectory prediction using the ETH-UCY dataset [34, 54], which contains 5 subsets, ETH, HOTEL, UNIV, ZARA1, and ZARA2. Following the standard setting [1, 20, 76], we use 3.2 seconds (8 timestamps) to predict the 4.8 seconds (12 timestamps).", + "bbox": [ + 498, + 583, + 893, + 657 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Here we apply our EqMotion to two prediction modes: deterministic and multi-prediction. Deterministic means the model only outputs a single prediction for each input motion. Multi-prediction means the model has 20 predictions for each input motion. Under multi-prediction, ADE and FDE will be calculated by the best-performed predicted motion. To adapt to multi-prediction, we slightly modify EqMotion to repeat the last feature updating layer and the output layer 20 times in parallel to have a multi-head prediction, see the details in the Appendix. Table 5 compares our method with sixteen baselines. We observe that i) EqMotion achieves state-of-the-art performance with the lowest average ADE and FDE, outperforming many baseline methods that are specifically designed for this task. EqMotion reduces the FDE by $10.4\\%$ and $7.9\\%$ under deterministic and multi-prediction settings; and ii) EqMotion achieves the best or the", + "bbox": [ + 496, + 659, + 893, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "1416", + "bbox": [ + 483, + 944, + 514, + 955 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/201e495356de449f8c2904dae0f0d7d7b37a8bd6f82e3ca1161702c56d4be685.jpg", + "table_caption": [ + "Table 5. Prediction performance on the ETH-UCY dataset. The bold/underline font denotes the best/second best result." + ], + "table_footnote": [], + "table_body": "
Performance (ADE/FDE)
DeterministicETHHotelUnivZara1Zara2Average
S-LSTM [1]1.09/2.350.79/1.760.67/1.400.47/1.000.56/1.170.72/1.54
SGAN-ind [20]1.13/2.211.01/2.180.60/1.280.42/0.910.52/1.110.74/1.54
Traj++ [55]1.02/2.000.33/0.620.53/1.190.44/0.990.32/0.730.53/1.11
TransF [16]1.03/2.100.36/0.710.53/1.320.44/1.000.34/0.760.54/1.17
MemoNet [70]1.00/2.080.35/0.670.55/1.190.46/1.000.37/0.820.55/1.15
EqMotion(Ours)0.96/1.920.30/0.580.50/1.100.39/0.860.30/0.680.49/1.03
Multi-predictionETHHotelUnivZara1Zara2Average
SGAN [20]0.87/1.620.67/1.370.76/0.520.35/0.680.42/0.840.61/1.21
NMMP [22]0.61/1.080.33/0.630.52/1.110.32/0.660.43/0.850.41/0.82
Traj++ [55]0.61/1.020.19/0.280.30/0.540.24/0.420.18/0.310.30/0.51
PECNet [45]0.54/0.870.18/0.240.35/0.600.22/0.390.17/0.300.29/0.48
Agentformer [76]0.45/0.750.14/0.220.25/0.450.18/0.300.14/0.240.23/0.39
GroupNet [69]0.46/0.730.15/0.250.26/0.490.21/0.390.17/0.330.25/0.44
MID [18]0.39/0.660.13/0.220.22/0.450.17/0.300.13/0.270.21/0.38
GP-Graph [2]0.43/0.630.18/0.300.24/0.420.17/0.310.15/0.290.23/0.39
EqMotion(Ours)0.40/0.610.12/0.180.23/0.430.18/0.320.13/0.230.21/0.35
", + "bbox": [ + 76, + 119, + 475, + 335 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/7f3425fe5da172c2e35960b1b3bf3ebd8e06e90231633585b069e99a06256359.jpg", + "table_caption": [ + "Table 6. Ablation study on key modules of EqMotion on H3.6M." + ], + "table_footnote": [], + "table_body": "
EGFLIPFLIRM80ms160ms320ms400msAverage
12.931.968.282.448.9
✓10.122.648.760.735.5
✓✓9.220.845.457.033.1
✓✓✓9.120.143.755.032.0
", + "bbox": [ + 84, + 352, + 460, + 430 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/b41302088839b3d270c27f51fa842ab8baf0e030609ed80dd2973fc9e9f69f0d.jpg", + "table_caption": [ + "Table 7. Ablation study on operations in the equivariant geometric feature learning on H3.6M dataset." + ], + "table_footnote": [], + "table_body": "
Ablation80ms160ms320ms400msAverage
w/o Inner att9.220.544.355.732.4
w/o Inter agg9.722.047.258.934.5
w/o Non-linear9.421.346.758.634.0
EqMotion9.120.143.755.032.0
", + "bbox": [ + 78, + 460, + 468, + 539 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "second best ADE/FDE result on most subsets, reflecting its effectiveness on the pedestrian trajectory prediction.", + "bbox": [ + 75, + 542, + 468, + 574 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5.5. Ablation Studies", + "text_level": 1, + "bbox": [ + 76, + 579, + 240, + 592 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Effect of network modules We explore the effect of three proposed key modules in EqMotion on the H3.6M dataset, including the equivariant geometric feature learning (EGFL), the invariant pattern feature learning (IPFL) and the invariant reasoning module (IRM). Table 6 presents the experimental result. It is observed that i) the proposed three key modules all contribute to an accurate prediction; and ii) the equivariant geometric feature learning module is most important since learning a comprehensive equivariant geometric feature directly for prediction is the most important.", + "bbox": [ + 75, + 598, + 468, + 748 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Effect of equivariant operations We explore the effect of three proposed operations in the equivariant feature learning module in EqMotion, including the inner-agent attention (Inner att), inter-agent aggregation (Inter agg) and non-linear function (Non-linear). Table 7 presents the results. We see that the proposed three key operations all contribute to promoting an accurate prediction.", + "bbox": [ + 75, + 750, + 470, + 854 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Different amounts of training data Figure 5 presents the comparison of model performance under different amounts of training data on H3.6M. We see that i) our method", + "bbox": [ + 75, + 854, + 470, + 900 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/78e38ba1b03658df0374cb61713f5b007d611827bf91a31a1fb41a2ea7a888d2.jpg", + "image_caption": [ + "Figure 5. Comparison of model performance on different amounts of data in short-term prediction on H3.6M dataset." + ], + "image_footnote": [], + "bbox": [ + 521, + 88, + 867, + 239 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/e4c924e8ae3ed1f7112d255ab3bb483ad5a2650ea969fd116e2573f0035707b2.jpg", + "image_caption": [ + "Figure 6. Comparison of model size and MPJPE in short-term prediction on H3.6M dataset. The target means the ideal model." + ], + "image_footnote": [], + "bbox": [ + 522, + 267, + 864, + 417 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "achieves the best prediction performance under all training data ratios; and ii) our method even outperforms some full-data using baselines by only using $5\\%$ of training data since the equivariant design promotes the network generalization ability under Euclidean transformations.", + "bbox": [ + 496, + 454, + 893, + 529 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Model size Figure 6 compares EqMotion to existing methods in terms of the model size and prediction results in short-term prediction on H3.6M. We can observe that EqMotion has the smallest model size (less than $30\\%$ of other models' sizes) with the lowest MPJPE thanks to the equivariant design that compacts the model free from generalizing over rotations and translations of the data.", + "bbox": [ + 496, + 530, + 893, + 635 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "6. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 651, + 617, + 666 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this work, we present EqMotion, a motion prediction network that is theoretically equivariant under Euclidean transformations. EqMotion includes three novel designs: the equivariant geometric feature learning, the invariant pattern feature learning and the invariant reasoning module. We evaluate our method on four different scenarios and our method achieves state-of-the-art prediction performance.", + "bbox": [ + 496, + 672, + 890, + 779 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgements. This project is partially supported by National Natural Science Foundation of China under Grant 62171276, the Science and Technology Commission of Shanghai Municipal under Grant 21511100900 and 22DZ2229005, and the National Research Foundation Singapore under its AI Singapore Programme (Award Number: AISG2-RP-2021-023). Robby T. 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Springer, 2022. 3" + ], + "bbox": [ + 501, + 90, + 893, + 686 + ], + "page_idx": 10 + }, + { + "type": "page_number", + "text": "1420", + "bbox": [ + 483, + 944, + 514, + 955 + ], + "page_idx": 10 + } +] \ No newline at end of file diff --git a/2023/EqMotion_ Equivariant Multi-Agent Motion Prediction With Invariant Interaction Reasoning/f8c65856-4ee9-403e-8f18-e949bafd8ca6_model.json b/2023/EqMotion_ Equivariant Multi-Agent Motion Prediction With Invariant Interaction Reasoning/f8c65856-4ee9-403e-8f18-e949bafd8ca6_model.json new file mode 100644 index 0000000000000000000000000000000000000000..e2e3ad50977b21b45282b83ba6985feb56a89032 --- /dev/null +++ b/2023/EqMotion_ Equivariant Multi-Agent Motion Prediction With Invariant Interaction Reasoning/f8c65856-4ee9-403e-8f18-e949bafd8ca6_model.json @@ -0,0 +1,2873 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.208, + 0.131, + 0.764, + 0.177 + ], + "angle": 0, + "content": "EqMotion: Equivariant Multi-agent Motion Prediction with Invariant Interaction Reasoning" + }, + { + "type": "text", + "bbox": [ + 0.276, + 0.203, + 0.762, + 0.24 + ], + "angle": 0, + "content": "Chenxin Xu\\(^{1,2}\\), Robby T. Tan\\(^{2}\\), Yuhong Tan\\(^{1}\\), Siheng Chen\\(^{1,3*}\\), Yu Guang Wang\\(^{1}\\), Xinchao Wang\\(^{2}\\), Yanfeng Wang\\(^{3,1}\\)" + }, + { + "type": "text", + "bbox": [ + 0.153, + 0.24, + 0.886, + 0.258 + ], + "angle": 0, + "content": "\\(^{1}\\)Shanghai Jiao Tong University, \\(^{2}\\)National University of Singapore, \\(^{3}\\)Shanghai AI Laboratory" + }, + { + "type": "text", + "bbox": [ + 0.089, + 0.26, + 0.942, + 0.275 + ], + "angle": 0, + "content": "{xcxwakaka,tyheeer,sihengc,yuguang.wang,wangyanfeng}@sjtu.edu.cn,{robby.tan,xinchao}@nus.edu.sg" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.309, + 0.314, + 0.326 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.342, + 0.474, + 0.751 + ], + "angle": 0, + "content": "Learning to predict agent motions with relationship reasoning is important for many applications. In motion prediction tasks, maintaining motion equivariance under Euclidean geometric transformations and invariance of agent interaction is a critical and fundamental principle. However, such equivariance and invariance properties are overlooked by most existing methods. To fill this gap, we propose EqMotion, an efficient equivariant motion prediction model with invariant interaction reasoning. To achieve motion equivariance, we propose an equivariant geometric feature learning module to learn a Euclidean transformable feature through dedicated designs of equivariant operations. To reason agent's interactions, we propose an invariant interaction reasoning module to achieve a more stable interaction modeling. To further promote more comprehensive motion features, we propose an invariant pattern feature learning module to learn an invariant pattern feature, which cooperates with the equivariant geometric feature to enhance network expressiveness. We conduct experiments for the proposed model on four distinct scenarios: particle dynamics, molecule dynamics, human skeleton motion prediction and pedestrian trajectory prediction. Experimental results show that our method is not only generally applicable, but also achieves state-of-the-art prediction performances on all the four tasks, improving by 24.0/30.1/8.6/9.2%. Code is available at https://github.com/MediaBrain-SJTU/EqMotion." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.778, + 0.21, + 0.793 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.803, + 0.471, + 0.879 + ], + "angle": 0, + "content": "Motion prediction aims to predict future trajectories of multiple interacting agents given their historical observations. It is widely studied in many applications like physics [3, 28], molecule dynamics [7], autonomous driving [35] and humanrobot interaction [38, 68]. In the task of motion prediction, an" + }, + { + "type": "image", + "bbox": [ + 0.505, + 0.308, + 0.889, + 0.406 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.536, + 0.407, + 0.652, + 0.421 + ], + "angle": 0, + "content": "(a) Particle dynamics" + }, + { + "type": "image", + "bbox": [ + 0.506, + 0.422, + 0.886, + 0.524 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.517, + 0.526, + 0.67, + 0.537 + ], + "angle": 0, + "content": "(c) Human skeleton motion" + }, + { + "type": "image_caption", + "bbox": [ + 0.717, + 0.526, + 0.86, + 0.538 + ], + "angle": 0, + "content": "(d) Pedestrian trajectories" + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.539, + 0.894, + 0.594 + ], + "angle": 0, + "content": "Figure 1. Motion equivariance and interaction invariance under the Euclidean geometric transformation is a fundamental principle for a prediction model, but this principle is often overlooked by previous works. In this work, we propose EqMotion to fill this gap." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.609, + 0.895, + 0.775 + ], + "angle": 0, + "content": "often-overlooked yet fundamental principle is that a prediction model is required to be equivariant under the Euclidean geometric transformation (including translation, rotation and reflection), and at the same time maintain the interaction relationships invariant. Motion equivariance here means that if an input motion is transformed under a Euclidean transformation, the output motion must be equally transformed under the same transformation. Interaction invariance means that the way agents interact remains unchanged under the input's transformation. Figure 1 shows real-world examples of motion equivariance and interaction invariance." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.778, + 0.895, + 0.884 + ], + "angle": 0, + "content": "Employing this principle in a network design brings at least two benefits. First, the network will be robust to arbitrary Euclidean transformations. Second, the network will have the capability of being generalizable over rotations and translations of the data. This capability makes the network more compact, reducing the network's learning burden and contributing to a more accurate prediction." + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.886, + 0.892, + 0.902 + ], + "angle": 0, + "content": "Despite the motion equivariance property being important" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.887, + 0.222, + 0.9 + ], + "angle": 0, + "content": "*Corresponding author." + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "1410" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.473, + 0.395 + ], + "angle": 0, + "content": "and fundamental, it is often neglected and not guaranteed by most existing motion prediction methods. The main reason is that these methods transform the input motion sequence directly into abstract feature vectors, where the geometric transformations are not traceable, causing the geometric relationships between agents to be irretrievable. Random augmentation will ease the equivariance problem, but it is still unable to guarantee the equivariance property. [30] uses non-parametric pre and post coordinate processing to achieve equivariance, but its parametric network structures do not satisfy equivariance. Some methods propose equivariant parametric network structures utilizing the higher-order representations of spherical harmonics [14, 61] or proposing an equivariant message passing [58], but they focus on the state-to-state prediction. This means that they use only one historical timestamp to predict one future timestamp. Consequently, these methods have limitations on utilizing motion's temporal information and modeling interaction relationships since a single-state observation is insufficient for both interaction modeling and temporal dependency modeling." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.397, + 0.473, + 0.669 + ], + "angle": 0, + "content": "In this paper, we propose EqMotion, the first motion prediction model that is theoretically equivariant to the input motion under Euclidean geometric transformations based on the parametric network. The proposed EqMotion has three novel designs: equivariant geometric feature learning, invariant pattern feature learning and invariant interaction reasoning. To ensure motion equivariance, we propose an equivariant geometric feature learning module to learn a Euclidean transformable geometric feature through dedicated designs of equivariant operations. The geometric feature preserves motion attributes that are relevant to Euclidean transformations. To promote more comprehensive representation power, we introduce an invariant pattern feature learning module to complement the network with motion attributes that are independent of Euclidean transformations. The pattern features, cooperated into the geometric features, provide expressive motion representations by exploiting motions' spatial-temporal dependencies." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.671, + 0.473, + 0.793 + ], + "angle": 0, + "content": "To further infer the interactions during motion prediction, we propose an invariant interaction reasoning module, which ensures that the captured interaction relationships are invariant to the input motion under Euclidean transformations. The module infers an invariant interaction graph by utilizing invariant factors in motions. The edge weights in the interaction graph categorize agents' interactions into different types, leading to better interaction representation." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.796, + 0.473, + 0.903 + ], + "angle": 0, + "content": "We conduct extensive experiments on four different scenarios to evaluate our method's effectiveness: particle dynamics, molecule dynamics, 3D human skeleton motion and pedestrian trajectories. Comparing to many task-specific motion prediction methods, our method is generally applicable and achieves state-of-the-art performance in all these tasks by reducing the prediction error by \\(24.0 / 30.1 / 8.6 / 9.2\\%\\)" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.895, + 0.168 + ], + "angle": 0, + "content": "respectively. We also present that EqMotion is lightweight, and has a model size less than \\(30\\%\\) of many other models' sizes. We show that EqMotion using only \\(5\\%\\) data can achieve a comparable performance with other methods that take full data. As a summary, here are our contributions:" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.168, + 0.895, + 0.258 + ], + "angle": 0, + "content": "- We propose EqMotion, the first motion prediction model that theoretically ensures sequence-to-sequence motion equivariance based on the parametric network. With equivariance, EqMotion promotes more generalization ability of motion feature learning, leading to more robust and accurate prediction." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.259, + 0.895, + 0.335 + ], + "angle": 0, + "content": "- We propose a novel invariant interaction reasoning module, in which the captured interactions between agents are invariant to the input motion under Euclidean geometric transformations. With this, EqMotion achieves more generalization ability and stability in the interaction reasoning." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.335, + 0.895, + 0.395 + ], + "angle": 0, + "content": "- We conduct experiments on four types of scenarios and find that EqMotion is applicable to all these different tasks, and importantly outperforms existing state-of-the-art methods on all the tasks." + }, + { + "type": "list", + "bbox": [ + 0.498, + 0.168, + 0.895, + 0.395 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.41, + 0.642, + 0.426 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.433, + 0.897, + 0.84 + ], + "angle": 0, + "content": "Equivariant Networks. Equivariance first draws high attention on the 2D image domain. Since CNN structure is sensitive to rotations, researchers start to explore rotation-equivariant designs like oriented convolutional filters [8,49], log-polar transform [11], circular harmonics [67] or steerable filters [66]. Meanwhile, GNN architectures [73-75] exploring symmetries on both rotation and translation have been emerged. Specifically, [57, 62] achieves partial symmetries by promoting translation equivariance. [14, 61] builds filters using spherical harmonics allowing transformations between high-order representations, achieving the rotation and translation equivariance. [12, 24] construct a Lie convolution to parameterize transformations into Lie algebra form. [10] proposes a series of equivariant layers for point cloud networks. [27] propose geometric vector perceptions for protein structure learning. Recently, EGNN [58] proposes a simple equivariant message passing form without using computationally expensive high-order representations. [23] further extends it by considering geometrical constraints. However, most existing methods are only applicable to state prediction, limiting models from exploiting sequence information. [30] uses pre and post coordinate processing to achieve motion equivariance but its network structure does not satisfy equivariance. In this work, we propose an equivariant model based on the parametric network which is generally applicable to motion prediction tasks and achieves a more precise prediction." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.897, + 0.903 + ], + "angle": 0, + "content": "Motion Prediction. Motion prediction has wide application scenarios. [3, 53, 56] proposes graph neural networks for learning to simulate complex physical systems. [17, 28, 37, 71] both explicitly infer the interactions rela" + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.945, + 0.516, + 0.958 + ], + "angle": 0, + "content": "1411" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.424 + ], + "angle": 0, + "content": "tionships and perform prediction in physical systems. For human or vehicle trajectory prediction, social forces [21, 51], Markov [29, 65] process, and RNNs [1, 52, 63] are first methods to employ. Multi-model prediction methods are further proposed like using generator-discriminator structures [20, 22], multi-head output [43, 59], conditional variational autoencoders [32, 45, 55, 69, 71, 72, 76], memory mechanisms [48, 70], Gaussian mixture distribution prediction [17, 37]. The HD map information is specifically considered in the autonomous driving scenario [5, 6, 15, 22, 42, 43, 77]. For 3D human skeleton motion prediction, early methods are based on the state prediction [33, 60]. Later RNN-based models considering the sequential motion states are proposed [13, 26, 50, 64]. [19, 36] use spatial graph convolutions to directly regress the whole sequences. Besides, some methods [4, 40, 46, 47] specifically exploit the correlations between body joints. Multi-scale graphs are built by [9, 39, 41] to capture different body-level dependencies. In this work, we propose a generally applicable motion prediction network which promotes Euclidean equivariance, a fundamental property but neglected by previous methods, to have a more robust and accurate prediction." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.432, + 0.428, + 0.449 + ], + "angle": 0, + "content": "3. Background and Problem Formulation" + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.453, + 0.254, + 0.468 + ], + "angle": 0, + "content": "3.1. Motion Prediction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.473, + 0.473, + 0.705 + ], + "angle": 0, + "content": "Here we introduce the general problem formulation of motion prediction, which aims to generate future motions given the historical observations. Mathematically, consider \\(M\\) agents in a multi-agent system. Let \\(\\mathbf{X}_i = [\\mathbf{x}_i^1,\\mathbf{x}_i^2,\\dots \\mathbf{x}_i^{T_{\\mathrm{p}}}]\\in\\) \\(\\mathbb{R}^{T_{\\mathrm{p}}\\times n}\\) and \\(\\mathbf{Y}_i = [\\mathbf{y}_i^1,\\mathbf{y}_i^2,\\dots \\mathbf{y}_i^{T_{\\mathrm{f}}}]\\in \\mathbb{R}^{T_{\\mathrm{f}}\\times n}\\) be the ith agent's past and future motion, where \\(T_{\\mathrm{p}}\\) and \\(T_{\\mathrm{f}}\\) are the past and future timestamps and \\(n\\) is the dimension of the system space. \\(n\\) usually equals to 2 or 3 (corresponding to 2D or 3D case). The \\(t\\)th timestamp locations \\(\\mathbf{x}_i^t\\) and \\(\\mathbf{y}_i^t\\) are \\(n\\) dimension vectors. The whole system's past and future motion is represented as \\(\\mathbb{X} = [\\mathbf{X}_1,\\mathbf{X}_2,\\dots ,\\mathbf{X}_M]\\in \\mathbb{R}^{M\\times T_{\\mathrm{p}}\\times n}\\) and \\(\\mathbb{Y} = [\\mathbf{Y}_1,\\mathbf{Y}_2,\\dots ,\\mathbf{Y}_M]\\in \\mathbb{R}^{M\\times T_{\\mathrm{f}}\\times n}\\). We aim to propose a prediction network \\(\\mathcal{F}_{\\mathrm{pred}}(\\cdot)\\) so that the predicted future motions \\(\\widehat{\\mathbb{Y}} = \\mathcal{F}_{\\mathrm{pred}}(\\mathbb{X})\\) are as close to the ground-truth future motions \\(\\mathbb{Y}\\) as possible." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.712, + 0.337, + 0.727 + ], + "angle": 0, + "content": "3.2. Equivariance and Invariance" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.731, + 0.471, + 0.837 + ], + "angle": 0, + "content": "The Euclidean geometric transformation has three basic forms: translation, rotation and reflection. The translation is modeled by a translation vector and rotation (or reflection) is modeled by an orthogonal rotation (or reflection) matrix. Let \\(\\mathbf{t} \\in \\mathbb{R}^n\\) be a translation vector and \\(\\mathbf{R} \\in \\mathrm{SO}(n)\\) be a \\(n \\times n\\) rotation matrix, we have the following definitions for equivariance and invariance:" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.838, + 0.471, + 0.884 + ], + "angle": 0, + "content": "Definition 1 Let \\(\\mathbb{X}\\) be an input, \\(\\mathcal{F}(\\cdot)\\) be an operation and \\(\\mathbb{Z} = \\mathcal{F}(\\mathbb{X})\\) be the corresponding output. The operation \\(\\mathcal{F}(\\cdot)\\) is called equivariant under Euclidean transformation if" + }, + { + "type": "equation", + "bbox": [ + 0.104, + 0.885, + 0.442, + 0.902 + ], + "angle": 0, + "content": "\\[\n\\mathbb {Z} \\mathbf {R} + \\mathbf {t} = \\mathcal {F} (\\mathbb {X} \\mathbf {R} + \\mathbf {t}) \\quad \\forall \\mathbf {R} \\in \\mathrm {S O} (n), \\forall \\mathbf {t} \\in \\mathbb {R} ^ {n}.\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.093, + 0.894, + 0.14 + ], + "angle": 0, + "content": "Definition 2 Let \\(\\mathbb{X}\\) be an input, \\(\\mathcal{F}(\\cdot)\\) be an operation and \\(\\mathbb{Z} = \\mathcal{F}(\\mathbb{X})\\) be the corresponding output. The operation \\(\\mathcal{F}(\\cdot)\\) is called invariant under Euclidean transformation if" + }, + { + "type": "equation", + "bbox": [ + 0.548, + 0.141, + 0.843, + 0.157 + ], + "angle": 0, + "content": "\\[\n\\mathbb {Z} = \\mathcal {F} (\\mathbb {X} \\mathbf {R} + \\mathbf {t}) \\quad \\forall \\mathbf {R} \\in \\mathrm {S O} (n), \\forall \\mathbf {t} \\in \\mathbb {R} ^ {n}.\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.161, + 0.894, + 0.251 + ], + "angle": 0, + "content": "Here, when a motion prediction network \\(\\mathcal{F}_{\\mathrm{pred}}(\\cdot)\\) satisfies Definition 1, \\(\\mathcal{F}_{\\mathrm{pred}}(\\cdot)\\) is said motion equivariant. When an interaction reasoning model \\(\\mathcal{F}_{\\mathrm{reason}}(\\cdot)\\) satisfies Definition 2, \\(\\mathcal{F}_{\\mathrm{reason}}(\\cdot)\\) is considered interaction invariant. We also say the output \\(\\mathbb{Z}\\) is equivariant/invariant (to the input motion under Euclidean transformation) if Definition 1/2 is satisfied." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.252, + 0.894, + 0.327 + ], + "angle": 0, + "content": "In the following section, we will introduce our motion prediction network along with geometric features that are equivariant under Euclidean transformations, and pattern features along with the interaction reasoning module are invariant under Euclidean transformations." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.341, + 0.635, + 0.358 + ], + "angle": 0, + "content": "4. Methodology" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.363, + 0.895, + 0.514 + ], + "angle": 0, + "content": "In this section, we present EqMotion, a motion prediction network which is equivariant under Euclidean geometric transformations. The whole network architecture is shown in Figure 2. The core of EqMotion is to successively learn equivariant geometric features and invariant pattern features by mutual cooperation in designed equivariant/invariant operations, which not only provide expressive motion and interaction representations, but also preserve equivariant/invariant properties. For agents' motions \\(\\mathbb{X} \\in \\mathbb{R}^{M \\times T_{\\mathrm{p}} \\times n}\\), the overall procedure of the proposed EqMotion is formulated as" + }, + { + "type": "equation", + "bbox": [ + 0.571, + 0.514, + 0.892, + 0.531 + ], + "angle": 0, + "content": "\\[\n\\mathbb {G} ^ {(0)}, \\mathbf {H} ^ {(0)} = \\mathcal {F} _ {\\mathrm {I L}} (\\mathbb {X}), \\tag {1a}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.573, + 0.535, + 0.892, + 0.554 + ], + "angle": 0, + "content": "\\[\n\\left\\{\\mathbf {c} _ {i j} \\right\\} = \\mathcal {F} _ {\\mathrm {I R M}} \\left(\\mathbb {G} ^ {(0)}, \\mathbf {H} ^ {(0)}\\right), \\tag {1b}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.572, + 0.557, + 0.892, + 0.577 + ], + "angle": 0, + "content": "\\[\n\\mathbb {G} ^ {(\\ell + 1)} = \\mathcal {F} _ {\\mathrm {E G F L}} ^ {(\\ell)} \\left(\\mathbb {G} ^ {(\\ell)}, \\mathbf {H} ^ {(\\ell)}, \\left\\{\\mathbf {c} _ {i j} \\right\\}\\right), \\tag {1c}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.572, + 0.579, + 0.892, + 0.6 + ], + "angle": 0, + "content": "\\[\n\\mathbf {H} ^ {(\\ell + 1)} = \\mathcal {F} _ {\\mathrm {I P F L}} ^ {(\\ell)} \\left(\\mathbb {G} ^ {(\\ell)}, \\mathbf {H} ^ {(\\ell)}\\right), \\tag {1d}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.572, + 0.602, + 0.892, + 0.621 + ], + "angle": 0, + "content": "\\[\n\\widehat {\\mathbb {Y}} = \\mathcal {F} _ {\\mathrm {E O L}} \\left(\\mathbb {G} ^ {(L)}\\right). \\tag {1e}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.622, + 0.894, + 0.808 + ], + "angle": 0, + "content": "Step (1a) uses an initialization layer \\(\\mathcal{F}_{\\mathrm{IL}}(\\cdot)\\) to obtain initial geometric features \\(\\mathbb{G}^{(0)}\\) and pattern features \\(\\mathbf{H}^{(0)}\\). For interaction relationship unavailable cases, Step (1b) uses an invariant interaction reasoning module \\(\\mathcal{F}_{\\mathrm{IRM}}(\\cdot)\\) to infer an interaction graph \\(\\{\\mathbf{c}_{ij}\\}\\) whose edge weight \\(\\mathbf{c}_{ij}\\) is the interaction category between agent \\(i\\) and \\(j\\). Step (1c) uses the \\(\\ell\\)th equivariant geometric feature learning layer \\(\\mathcal{F}_{\\mathrm{EGFL}}^{(\\ell)}(\\cdot)\\) to learn the \\((\\ell + 1)\\)th geometric feature \\(\\mathbb{G}^{(\\ell + 1)}\\). Step (1d) uses the \\(\\ell\\)th invariant pattern feature learning layer \\(\\mathcal{F}_{\\mathrm{IPFL}}^{(\\ell)}(\\cdot)\\) to learn the \\((\\ell + 1)\\)th pattern feature \\(\\mathbf{H}^{(\\ell + 1)}\\). Step (1c) and Step (1d) will repeat \\(L\\) times. Step (1e) uses an equivariant output layer \\(\\mathcal{F}_{\\mathrm{EOL}}(\\cdot)\\) to obtain the final prediction \\(\\widehat{\\mathbb{Y}}\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.808, + 0.894, + 0.901 + ], + "angle": 0, + "content": "Note that i) to incorporate the geometric feature's equivariance, we need to design equivariant operations for the initialization layer \\(\\mathcal{F}_{\\mathrm{IL}}(\\cdot)\\) and the equivariant geometric feature learning layer \\(\\mathcal{F}_{\\mathrm{EGFL}}^{(\\ell)}(\\cdot)\\); ii) to introduce the pattern feature's invariance, we need to design invariant operations for the initialization layer \\(\\mathcal{F}_{\\mathrm{IL}}(\\cdot)\\) and the invariant pattern feature" + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "1412" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.093, + 0.088, + 0.878, + 0.199 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.199, + 0.894, + 0.255 + ], + "angle": 0, + "content": "Figure 2. EqMotion architecture. In EqMotion, we first use a feature initialization layer to initialize geometric features and pattern features. We then successively update the geometric features and the pattern features by the equivariant geometric feature learning and invariant pattern feature learning layers, obtaining expressive feature representation. We further propose an invariant reasoning module to infer an interaction graph used in equivariant geometric feature learning. Finally, we use an equivariant output layer to obtain the final prediction." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.269, + 0.473, + 0.348 + ], + "angle": 0, + "content": "learning layer \\(\\mathcal{F}_{\\mathrm{IPFL}}^{(\\ell)}(\\cdot)\\); and iii) the interaction graph categorizes agent's spatial interaction into different categories for better interaction representing. The interaction graph is invariant due to the reasoning module \\(\\mathcal{F}_{\\mathrm{IRM}}(\\cdot)\\) design. In subsequent sections, we elaborate the details of each step." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.357, + 0.276, + 0.372 + ], + "angle": 0, + "content": "4.1. Feature Initialization" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.377, + 0.473, + 0.532 + ], + "angle": 0, + "content": "The feature initialization layer aims to obtain initial geometric features and pattern features while equipping them with different functionality. The initial geometric feature is denoted as \\(\\mathbb{G}^{(0)} = [\\mathbf{G}_1^{(0)},\\dots ,\\mathbf{G}_M^{(0)}]\\in \\mathbb{R}^{M\\times C\\times n}\\) whose \\(i\\)th agent's geometric feature consists of \\(C\\) geometric coordinates. The initial pattern feature is denoted as \\(\\mathbf{H}^{(0)} = [\\mathbf{h}_1^{(0)},\\dots ,\\mathbf{h}_M^{(0)}]\\in \\mathbb{R}^{M\\times D}\\) whose \\(i\\)th agent's pattern feature is a \\(D\\) -dimensional vector. Given the past motions \\(\\mathbb{X}\\) whose the \\(i\\)th agent's motion is \\(\\mathbf{X}_i\\in \\mathbb{R}^{T_{\\mathrm{p}}\\times n}\\), we obtain two initial features of the \\(i\\)th agent:" + }, + { + "type": "equation", + "bbox": [ + 0.107, + 0.534, + 0.312, + 0.553 + ], + "angle": 0, + "content": "\\[\n\\mathbf {G} _ {i} ^ {(0)} = \\phi_ {\\mathrm {i n i t \\_ g}} (\\mathbf {X} _ {i} - \\overline {{\\mathbb {X}}}) + \\overline {{\\mathbb {X}}},\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.109, + 0.555, + 0.438, + 0.574 + ], + "angle": 0, + "content": "\\[\n\\mathbf {V} _ {i} = \\triangle \\mathbf {X} _ {i}, \\rho_ {i} ^ {t} = | | \\mathbf {V} _ {i} ^ {t} | | _ {2}, \\theta_ {i} ^ {t} = \\mathrm {a n g l e} (\\mathbf {V} _ {i} ^ {t}, \\mathbf {V} _ {i} ^ {t - 1}),\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.109, + 0.577, + 0.273, + 0.597 + ], + "angle": 0, + "content": "\\[\n\\mathbf {h} _ {i} ^ {(0)} = \\phi_ {\\mathrm {i n i t \\_ h}} ([ \\rho_ {i}; \\theta_ {i} ]),\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.598, + 0.472, + 0.734 + ], + "angle": 0, + "content": "where \\(\\phi_{\\mathrm{init\\_g}}(\\mathbf{X}) = \\mathbf{W}_{\\mathrm{init\\_g}}\\mathbf{X}\\), \\(\\mathbf{W}_{\\mathrm{init\\_g}} \\in \\mathbb{R}^{C \\times T_p}\\) is a linear function, \\(\\overline{\\mathbb{X}}\\) is the mean coordinate of all agents all past timestamps. \\(\\triangle\\) is the difference operator to obtain the velocity \\(\\mathbf{V}_i \\in \\mathbb{R}^{T_{\\mathrm{p}} \\times n}\\). \\(\\rho_i \\in \\mathbb{R}^{T_{\\mathrm{p}}}\\) is the velocity magnitude sequence and \\(\\theta_i \\in \\mathbb{R}^{T_{\\mathrm{p}}}\\) is the velocity angle sequence. The superscript \\((\\cdot)^t\\) denotes the \\(t\\)th element, \\(||\\cdot||_2\\) is vector 2-norm, \\(\\mathrm{angle}(\\cdot)\\) is the function calculating the angle between two vectors and \\(\\phi_{\\mathrm{init\\_h}}(\\cdot)\\) is an embedding function implemented by MLP or LSTM. \\([\\cdot; \\cdot]\\) represents concatenation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.735, + 0.472, + 0.826 + ], + "angle": 0, + "content": "The geometric feature preserves both equivariant property and motion attributes that are sensitive to Euclidean geometric transforms since we linearly combine the equivariant locations. The pattern feature remains invariant and is sensitive to motion attributes independent of Euclidean geometric transforms." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.836, + 0.334, + 0.852 + ], + "angle": 0, + "content": "4.2. Invariant Reasoning Module" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.472, + 0.901 + ], + "angle": 0, + "content": "For most scenarios, the interaction relationship is implicit and unavailable. Thus, we propose an invariant reasoning module for inferring the interaction category between agents." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.27, + 0.895, + 0.409 + ], + "angle": 0, + "content": "Note that we design the reasoning module to be invariant as the interaction category is independent of Euclidean transformations. The output of the reasoning module is an invariant interaction graph whose edge weight \\(\\mathbf{c}_{ij} \\in [0,1]^K\\) is a categorical vector representing the type of interaction between agent \\(i\\) and \\(j\\). \\(K\\) is the interaction category number. To obtain the interaction categorical vector, we perform a message passing operation using the agent's initial pattern feature \\(\\mathbf{h}_i^{(0)}\\) and geometric feature \\(\\mathbf{G}_i^{(0)}\\):" + }, + { + "type": "equation", + "bbox": [ + 0.53, + 0.41, + 0.839, + 0.432 + ], + "angle": 0, + "content": "\\[\n\\mathbf {m} _ {i j} ^ {\\prime} = \\phi_ {\\mathrm {r m}} \\left(\\left[ \\mathbf {h} _ {i} ^ {(0)}; \\mathbf {h} _ {j} ^ {(0)}; \\left| \\left| \\mathbf {G} _ {i} ^ {(0)} - \\mathbf {G} _ {j} ^ {(0)} \\right| \\right| _ {2, \\text {c o l}} \\right]\\right),\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.53, + 0.434, + 0.791, + 0.467 + ], + "angle": 0, + "content": "\\[\n\\mathbf {p} _ {i} ^ {\\prime} = \\sum_ {j \\in \\mathcal {N} _ {i}} \\mathbf {m} _ {i j} ^ {\\prime}, \\mathbf {h} _ {i} ^ {\\prime} = \\phi_ {\\mathrm {r h}} \\big ([ \\mathbf {p} _ {i} ^ {\\prime}; \\mathbf {h} _ {i} ^ {(0)} ] \\big),\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.53, + 0.47, + 0.861, + 0.496 + ], + "angle": 0, + "content": "\\[\n\\mathbf {c} _ {i j} = \\mathrm {s m} \\Big (\\phi_ {\\mathrm {r c}} \\big ([ \\mathbf {h} _ {i} ^ {\\prime}; \\mathbf {h} _ {j} ^ {\\prime}; | | \\mathbf {G} _ {i} ^ {(0)} - \\mathbf {G} _ {j} ^ {(0)} | | _ {2, \\mathrm {c o l}} ] \\big) / \\tau \\Big),\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.496, + 0.894, + 0.587 + ], + "angle": 0, + "content": "where \\(||\\cdot ||_{2,\\mathrm{col}}\\) is a column-wise \\(\\ell_2\\)-distance, \\(\\phi_{\\mathrm{rm}}(\\cdot),\\phi_{\\mathrm{rh}}(\\cdot)\\) \\(\\phi_{\\mathrm{rc}}(\\cdot)\\) are learnable functions implemented by MLPs. \\(\\mathrm{sm}(\\cdot)\\) is the softmax function and \\(\\tau\\) is the temperature to control the smoothness of the categorical distribution. The interaction edge weights \\(\\{\\mathbf{c}_{ij}\\}\\) will be end-to-end learned with the whole prediction network." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.6, + 0.854, + 0.617 + ], + "angle": 0, + "content": "4.3. Equivariant Geometric Feature Learning" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.621, + 0.894, + 0.742 + ], + "angle": 0, + "content": "The equivariant geometric feature learning process aims to find more representative agents' geometric features by exploiting their spatial and temporal dependencies, while maintaining the equivariance. During the process, we perform i) equivariant inner-agent attention to exploit the temporal dependencies; ii) equivariant inter-agent aggregation to model spatial interactions; and iii) equivariant non-linear function to further enhance the representation ability." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.743, + 0.894, + 0.838 + ], + "angle": 0, + "content": "Equivariant inner-agent attention To exploit the temporal dependency, we perform an attention mechanism on the coordinate dimension of the geometric feature since the coordinate dimension originates from the temporal dimension. Given the \\(i\\)th agent's geometric feature \\(\\mathbf{G}_i^{(\\ell)} \\in \\mathbb{R}^{C \\times n}\\) and pattern feature \\(\\mathbf{h}_i^{(\\ell)}\\), we have" + }, + { + "type": "equation", + "bbox": [ + 0.552, + 0.84, + 0.892, + 0.862 + ], + "angle": 0, + "content": "\\[\n\\mathbf {G} _ {i} ^ {(\\ell)} \\leftarrow \\phi_ {\\mathrm {a t t}} ^ {(\\ell)} \\left(\\mathbf {h} _ {i} ^ {(\\ell)}\\right) \\cdot \\left(\\mathbf {G} _ {i} ^ {(\\ell)} - \\overline {{\\mathbb {G}}} ^ {(\\ell)}\\right) + \\overline {{\\mathbb {G}}} ^ {(\\ell)}, \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.865, + 0.892, + 0.901 + ], + "angle": 0, + "content": "where \\(\\phi_{\\mathrm{att}}^{(\\ell)}(\\cdot):\\mathbb{R}^D\\to \\mathbb{R}^C\\) is a function which learns the attention weight for per coordinate, and \\(\\overline{\\mathbb{G}}^{(\\ell)}\\) is the mean" + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "1413" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.471, + 0.107 + ], + "angle": 0, + "content": "coordinates summing up over all agents and all coordinates." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.107, + 0.47, + 0.198 + ], + "angle": 0, + "content": "The above operation will bring the following benefits: i) The learned attention weight is invariant and the learned dependencies between different timestamps of the motion will not be disturbed by irrelevant Euclidean transformations; and ii) The learned geometric feature is equivariant because of the coordinate-wise linear multiplication." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.199, + 0.471, + 0.289 + ], + "angle": 0, + "content": "Equivariant inter-agent aggregation The equivariant inter-agent aggregation aims to model spatial interactions between agents. The key idea is to use the reasoned or provided interaction category to learn aggregation weights, and then use the weights to aggregate neighboring agents' geometric features. The aggregation operation reads" + }, + { + "type": "equation", + "bbox": [ + 0.097, + 0.29, + 0.47, + 0.358 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\mathbf {e} _ {i j} ^ {(\\ell)} = \\sum_ {k = 1} ^ {K} \\mathbf {c} _ {i j, k} \\phi_ {e, k} ^ {(\\ell)} \\left(\\left[ \\mathbf {h} _ {i} ^ {(\\ell)}; \\mathbf {h} _ {j} ^ {(\\ell)}; \\left\\| \\mathbf {G} _ {i} ^ {(\\ell)} - \\mathbf {G} _ {j} ^ {(\\ell)} \\right\\| _ {2, \\text {c o l}} \\right]\\right), \\tag {3} \\\\ \\mathbf {G} _ {i} ^ {(\\ell)} \\leftarrow \\mathbf {G} _ {i} ^ {(\\ell)} + \\sum_ {j \\in \\mathcal {N} _ {i}} \\mathbf {e} _ {i j} ^ {(\\ell)} \\cdot (\\mathbf {G} _ {i} ^ {(\\ell)} - \\mathbf {G} _ {j} ^ {(\\ell)}), \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.359, + 0.469, + 0.438 + ], + "angle": 0, + "content": "where \\(\\mathbf{e}_{ij}^{(\\ell)}\\in \\mathbb{R}^C\\) is the learned aggregation weights between agent \\(i\\) and \\(j,||\\cdot ||_{2,\\mathrm{col}}\\) is a column-wise \\(\\ell_2\\)-distance, \\(\\cdot\\) is dot product and \\(\\mathcal{N}_i\\) is the \\(i\\)th agent's neighboring set. For the \\(k\\)th interaction category, we assign a function \\(\\phi_{e,k}^{(\\ell)}(\\cdot)\\) that is implemented by MLP to model how the interaction works." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.439, + 0.47, + 0.499 + ], + "angle": 0, + "content": "The social influence from agent \\(j\\) to agent \\(i\\) is modeled by the coordinates' difference between the two agents. The intuition behind this design is that the mutual force between two objects is always in the direction of the line they formed." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.5, + 0.471, + 0.59 + ], + "angle": 0, + "content": "Note that for most scenarios, we do not have an explicit definition of interacted \"neighbors\", thus we use a fully-connected graph structure, which means every agent's neighbors include all other agents. For some special cases with massive nodes, like point clouds, we construct a local neighboring set by choosing neighbors within a distance threshold." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.591, + 0.472, + 0.756 + ], + "angle": 0, + "content": "Equivariant non-linear function According to Eq. (2) and Eq. (3), the operation of inner-agent attention and inter-agent aggregation are linear combinations with agents' coordinates. It is well known that non-linear operation is the key to improving neural networks' expressivity. Therefore, we propose an equivariant non-linear function to enhance the representation ability of our prediction network while preserving equivariance. The key idea is proposing a criterion with the invariance property for splitting different conditions, and for each condition design an equivariant equation. Mathematically, the non-linear function is" + }, + { + "type": "equation", + "bbox": [ + 0.077, + 0.758, + 0.487, + 0.827 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\mathbf {Q} _ {i} ^ {(\\ell)} = \\mathbf {W} _ {\\mathrm {Q}} ^ {(\\ell)} \\left(\\mathbf {G} _ {i} ^ {(\\ell)} - \\overline {{\\mathbb {G}}} ^ {(\\ell)}\\right), \\mathbf {K} _ {i} ^ {(\\ell)} = \\mathbf {W} _ {\\mathrm {K}} ^ {(\\ell)} \\left(\\mathbf {G} _ {i} ^ {(\\ell)} - \\overline {{\\mathbb {G}}} ^ {(\\ell)}\\right), \\\\ \\mathbf {g} _ {i, c} ^ {(\\ell + 1)} = \\left\\{ \\begin{array}{l l} \\mathbf {q} _ {i, c} ^ {(\\ell)} + \\overline {{\\mathbb {G}}} ^ {(\\ell)} & \\text {i f} \\langle \\mathbf {q} _ {i, c} ^ {(\\ell)}, \\mathbf {k} _ {i, c} ^ {(\\ell)} \\rangle \\geq 0, \\\\ \\mathbf {q} _ {i, c} ^ {(\\ell)} - \\langle \\mathbf {q} _ {i, c} ^ {(\\ell)}, \\frac {\\mathbf {k} _ {i , c} ^ {(\\ell)}}{| | \\mathbf {k} _ {i , c} ^ {(\\ell)} | | _ {2}} \\rangle \\frac {\\mathbf {k} _ {i , c} ^ {(\\ell)}}{| | \\mathbf {k} _ {i , c} ^ {(\\ell)} | | _ {2}} + \\overline {{\\mathbb {G}}} ^ {(\\ell)} & \\text {o t h e r w i s e}, \\end{array} \\right. \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.828, + 0.47, + 0.904 + ], + "angle": 0, + "content": "where \\(\\mathbf{Q}_i^{(\\ell)}\\) and \\(\\mathbf{K}_i^{(\\ell)}\\) is the learned query coordinates and key coordinates, \\(\\mathbf{W}_{\\mathrm{K}}^{(\\ell)}\\in \\mathbb{R}^{C\\times C}\\) are learnable matrices for queries and keys. \\(\\overline{\\mathbb{G}}_{\\nu}^{(\\ell)}\\) is the mean coordinates over all agents and all coordinates. \\(\\mathbf{q}_{i,c}^{(\\ell)}\\), \\(\\mathbf{k}_{i,c}^{(\\ell)}\\) is the \\(c\\)th coordinate of" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.089, + 0.815, + 0.109 + ], + "angle": 0, + "content": "\\(\\mathbf{Q}_i^{(\\ell)}\\) and \\(\\mathbf{K}_i^{(\\ell)}\\). \\(\\langle \\cdot, \\cdot \\rangle\\) is the vector inner product." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.109, + 0.895, + 0.287 + ], + "angle": 0, + "content": "For every geometric coordinate \\(\\mathbf{g}_{i,c}^{(\\ell)}\\), we learn a query coordinate \\(\\mathbf{q}_{i,c}^{(\\ell)}\\) and a key coordinate \\(\\mathbf{k}_{i,c}^{(\\ell)}\\). We set the criterion as the inner product of the query coordinate and the key coordinate. If the inner product is positive, we directly take the value of the query coordinate as output; otherwise, we clip the query coordinate vector by moving out its parallel components with the key coordinate vector. Finally, we obtain the \\(i\\)th agent's geometric features of the next layer \\(\\mathbf{G}_i^{(l + 1)}\\) by gathering all the coordinates \\(\\mathbf{g}_{i,c}^{(l + 1)}\\). The non-linear function is equivariant, since the criterion is invariant and the two equations under two conditions are equivariant." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.296, + 0.81, + 0.312 + ], + "angle": 0, + "content": "4.4. Invariant Pattern Feature Learning" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.315, + 0.894, + 0.489 + ], + "angle": 0, + "content": "The invariant pattern feature learning aims to obtain a more representative agent pattern feature through interacting with neighbors. Here we learn the agent's pattern feature with an invariant message passing mechanism. Specially, we add the relative geometric feature difference into the edge modeling in the message passing to complement the information of relationships between agent absolute locations, which cannot be obtained by solely using the pattern features. Given the \\(i\\)th agent's pattern feature \\(\\mathbf{h}_i^{(\\ell)} \\in \\mathbb{R}^D\\) and geometric feature \\(\\mathbf{G}_i^{(\\ell)} \\in \\mathbb{R}^{C \\times n}\\), the next layer's pattern feature \\(\\mathbf{h}_i^{(l+1)}\\) is obtained by" + }, + { + "type": "equation", + "bbox": [ + 0.536, + 0.49, + 0.855, + 0.552 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\mathbf {m} _ {i j} ^ {(\\ell)} = \\phi_ {m} ^ {(\\ell)} \\left(\\left[ \\mathbf {h} _ {i} ^ {(\\ell)}; \\mathbf {h} _ {j} ^ {(\\ell)}; | | \\mathbf {G} _ {i} ^ {(\\ell)} - \\mathbf {G} _ {j} ^ {(\\ell)} | | _ {2, \\text {c o l}} \\right]\\right), \\\\ \\mathbf {p} _ {i} ^ {(\\ell)} = \\sum_ {j \\in \\mathcal {N} (i)} \\mathbf {m} _ {i j} ^ {(\\ell)}, \\mathbf {h} _ {i} ^ {(l + 1)} = \\phi_ {h} ^ {(\\ell)} ([ \\mathbf {h} _ {i} ^ {(\\ell)}; \\mathbf {p} _ {i} ^ {(\\ell)} ]). \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.553, + 0.894, + 0.619 + ], + "angle": 0, + "content": "Here \\(\\mathbf{m}_{ij}^{(\\ell)}\\) is the edge features and \\(\\mathbf{p}_i^{(\\ell)}\\) is the aggregated neighboring features in the message passing. \\(||\\cdot ||_{2,\\mathrm{col}}\\) is a column-wise \\(\\ell_2\\)-distance and \\([\\cdot ;\\cdot ]\\) denotes concatenation. Functions \\(\\phi_m^{(\\ell)}(\\cdot)\\) and \\(\\phi_h^{(\\ell)}(\\cdot)\\) are implemented by MLPs." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.628, + 0.741, + 0.644 + ], + "angle": 0, + "content": "4.5. Equivariant Output Layer" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.648, + 0.894, + 0.71 + ], + "angle": 0, + "content": "After total \\(L\\) feature learning layers, we obtain the final \\(i\\)th agent's geometric feature \\(\\mathbf{G}_i^{(L)}\\) and pattern feature \\(\\mathbf{h}_i^{(L)}\\). We use the geometric feature for the final prediction by a linear operation for equivariance: for the \\(i\\)th agent:" + }, + { + "type": "equation", + "bbox": [ + 0.579, + 0.711, + 0.812, + 0.732 + ], + "angle": 0, + "content": "\\[\n\\widehat {\\mathbf {Y}} _ {i} = \\mathbf {W} _ {\\text {o u t}} (\\mathbf {G} _ {i} ^ {(\\ell)} - \\overline {{\\mathbb {G}}} ^ {(\\ell)}) + \\overline {{\\mathbb {G}}} ^ {(\\ell)},\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.733, + 0.894, + 0.781 + ], + "angle": 0, + "content": "where \\(\\mathbf{W}_{\\mathrm{out}} \\in \\mathbb{R}^{T_{\\mathrm{f}} \\times D}\\) is a learnable weight matrix. Finally, we gather all the agent prediction \\(\\widehat{\\mathbf{Y}}_i\\) to have the final predicted motions \\(\\widehat{\\mathbb{Y}}\\)." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.791, + 0.694, + 0.807 + ], + "angle": 0, + "content": "4.6. Theoretical Analysis" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.811, + 0.894, + 0.901 + ], + "angle": 0, + "content": "In this section, we analyze our network's equivariance property and the interaction reasoning module's invariance property, as stated in the following theorem. Let \\(\\mathbb{G}^{(\\ell)}\\in\\) \\(\\mathbb{R}^{M\\times C\\times n}\\) be all agents' geometric features, \\(\\mathbf{H}^{(\\ell)}\\in \\mathbb{R}^{M\\times D}\\) be all agents' pattern features at the \\(\\ell\\)th layer, and \\(\\{\\mathbf{c}_{ij}\\}\\) be the set of all the interaction categorical vectors." + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "1414" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.137 + ], + "angle": 0, + "content": "Theorem 1 For arbitrary translation vector \\(\\mathbf{t} \\in \\mathbb{R}^n\\) and rotation (or reflection) matrix \\(\\mathbf{R} \\in \\mathrm{SO}(n)\\), the modules with equivariance and invariance in our network satisfy:" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.138, + 0.47, + 0.182 + ], + "angle": 0, + "content": "1. For the initialization layer \\(\\mathcal{F}_{\\mathrm{IL}}(\\cdot)\\), the initial geometric feature is equivariant and the initial pattern feature is invariant:" + }, + { + "type": "equation", + "bbox": [ + 0.155, + 0.183, + 0.39, + 0.201 + ], + "angle": 0, + "content": "\\[\n\\mathbb {G} ^ {(0)} \\mathbf {R} + \\mathbf {t}, \\mathbf {H} ^ {(0)} = \\mathcal {F} _ {\\mathrm {I L}} (\\mathbb {X} \\mathbf {R} + \\mathbf {t}).\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.203, + 0.47, + 0.234 + ], + "angle": 0, + "content": "2. The reasoning module \\(\\mathcal{F}_{\\mathrm{IRM}}(\\cdot)\\) along with reasoned interaction categorical vectors \\(\\{\\mathbf{c}_{ij}\\}\\) is invariant:" + }, + { + "type": "equation", + "bbox": [ + 0.16, + 0.236, + 0.386, + 0.254 + ], + "angle": 0, + "content": "\\[\n\\left\\{\\mathbf {c} _ {i j} \\right\\} = \\mathcal {F} _ {\\mathrm {I R M}} \\left(\\mathbb {G} ^ {(0)} \\mathbf {R} + \\mathbf {t}, \\mathbf {H} ^ {(0)}\\right).\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.257, + 0.469, + 0.289 + ], + "angle": 0, + "content": "3. The \\( \\ell \\)th geometric feature learning layer \\( \\mathcal{F}_{\\mathrm{EGFL}}^{(\\ell)}(\\cdot) \\) is equivariant:" + }, + { + "type": "equation", + "bbox": [ + 0.108, + 0.29, + 0.437, + 0.311 + ], + "angle": 0, + "content": "\\[\n\\mathbb {G} ^ {(l + 1)} \\mathbf {R} + \\mathbf {t} = \\mathcal {F} _ {\\mathrm {E G F L}} ^ {(\\ell)} \\left(\\mathbb {G} ^ {(\\ell)} \\mathbf {R} + \\mathbf {t}, \\mathbf {H} ^ {(\\ell)}, \\left\\{\\mathbf {c} _ {i j} \\right\\}\\right).\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.313, + 0.469, + 0.343 + ], + "angle": 0, + "content": "4. The \\( \\ell \\)th pattern feature learning layer \\( \\mathcal{F}_{\\mathrm{IPFL}}^{(\\ell)}(\\cdot) \\) is invariant:" + }, + { + "type": "equation", + "bbox": [ + 0.152, + 0.344, + 0.393, + 0.364 + ], + "angle": 0, + "content": "\\[\n\\mathbf {H} ^ {(l + 1)} = \\mathcal {F} _ {\\mathrm {I P F L}} ^ {(\\ell)} (\\mathbb {G} ^ {(\\ell)} \\mathbf {R} + \\mathbf {t}, \\mathbf {H} ^ {(\\ell)}).\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.366, + 0.386, + 0.381 + ], + "angle": 0, + "content": "5. The output layer \\(\\mathcal{F}_{\\mathrm{EOL}}(\\cdot)\\) is equivariant:" + }, + { + "type": "equation", + "bbox": [ + 0.168, + 0.383, + 0.378, + 0.401 + ], + "angle": 0, + "content": "\\[\n\\widehat {\\mathbf {Y}} \\mathbf {R} + \\mathbf {t} = \\mathcal {F} _ {\\mathrm {E O L}} (\\mathbb {G} ^ {(L)} \\mathbf {R} + \\mathbf {t}).\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.402, + 0.47, + 0.478 + ], + "angle": 0, + "content": "See the detailed proof in Appendix. Theorem 1 presents the equivariance/invariance properties with the Euclidean transformation for each operation in the proposed network. Based on Theorem 1, by combining all network operations together, we can show that the whole network is equivariant:" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.483, + 0.47, + 0.528 + ], + "angle": 0, + "content": "Corollary 1 For arbitrary translation vector \\(\\mathbf{t} \\in \\mathbb{R}^n\\) and rotation matrix \\(\\mathbf{R} \\in \\mathrm{SO}(n)\\), our whole network EqMotion \\(\\mathcal{F}_{\\mathrm{pred}}(\\cdot)\\) satisfies:" + }, + { + "type": "equation", + "bbox": [ + 0.179, + 0.53, + 0.366, + 0.549 + ], + "angle": 0, + "content": "\\[\n\\widehat {\\mathbb {Y}} \\mathbf {R} + \\mathbf {t} = \\mathcal {F} _ {\\mathrm {p r e d}} (\\mathbb {X} \\mathbf {R} + \\mathbf {t}).\n\\]" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.559, + 0.201, + 0.576 + ], + "angle": 0, + "content": "5. Experiment" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.581, + 0.469, + 0.657 + ], + "angle": 0, + "content": "In this section, we validate our method on four different scenarios: particle dynamics, molecule dynamics, 3D human skeleton motion, and pedestrian trajectories. The detailed dataset description, implementation details, and additional experiment results are elaborated in the Appendix." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.658, + 0.47, + 0.749 + ], + "angle": 0, + "content": "Metric We use: i) Average Displacement Error (ADE) and Final Displacement Error (FDE). ADE/FDE is the \\(\\ell_2\\) distance of the predicted whole motion/endpoint to the ground truth of the whole motion/endpoint; ii) Mean Per Joint Position Error (MPJPE). It records average \\(\\ell_2\\) distance between predicted joints and target ones at each future timestamp." + }, + { + "type": "title", + "bbox": [ + 0.076, + 0.759, + 0.423, + 0.775 + ], + "angle": 0, + "content": "5.1. Scenario 1: Particle Dynamic Prediction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.779, + 0.47, + 0.841 + ], + "angle": 0, + "content": "We use the particle \\(N\\)-body simulation [28] in a 3D space similar to [14, 58]. In the Springs simulation, particles are randomly connected by a spring. In the Charged simulation, particles are randomly charged or uncharged." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.841, + 0.469, + 0.901 + ], + "angle": 0, + "content": "Validation on interaction reasoning Since we can get the ground-truth interaction through simulation, we evaluate the ability of interaction reasoning as a category recognition task. To evaluate the robustness of the reasoning result with" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.09, + 0.892, + 0.117 + ], + "angle": 0, + "content": "Table 1. Interaction recognition accuracy and consistency (mean ± std in % in 5 independent runs) on the physical simulation." + }, + { + "type": "table", + "bbox": [ + 0.502, + 0.119, + 0.885, + 0.248 + ], + "angle": 0, + "content": "
ModelSpringsCharged
AccuracyConsistencyAccuracyConsistency
Corr.(path) [28]58.1 ± 0.099.8 ± 0.157.5 ± 0.187.9 ± 0.1
Corr.(LSTM) [28]53.5 ± 0.592.4 ± 2.157.2 ± 0.491.7 ± 1.1
EGNN [58]61.0 ± 1.3100.0 ± 0.058.2 ± 1.4100.0 ± 0.0
NRI [28]93.0 ± 1.193.7 ± 1.270.0 ± 0.688.5 ± 1.3
dNRI [17]93.3 ± 2.089.6 ± 2.070.4 ± 1.783.6 ± 1.8
Ours97.6 ± 1.1100.0 ± 0.080.9 ± 3.4100.0 ± 0.0
Supervised98.7 ± 0.2100.0 ± 0.097.4 ± 0.2100.0 ± 0.0
" + }, + { + "type": "image", + "bbox": [ + 0.508, + 0.251, + 0.877, + 0.39 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.391, + 0.892, + 0.418 + ], + "angle": 0, + "content": "Figure 3. Comparison of displacement error across different timestamps on the physical simulation." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.431, + 0.895, + 0.627 + ], + "angle": 0, + "content": "the Euclidean transformation, we introduce recognition \"consistency\", which is the ratio of the same recognition result under 20 random Euclidean transformations. The \"Supervised\" represents an upper bound that uses the ground-truth category to train the model. Table 1 reports the comparison of reasoning results on both springs and charged simulations, for recognizing whether there is a spring connection or electrostatic force. We see that i) our method achieves significant improvement on the recognition accuracy and has more robust reasoning results due to the invariance of our reasoning module; and ii) our method achieves a close performance to the upper bound, reflecting that our method is capable of reasoning a robust and accurate interaction category." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.628, + 0.894, + 0.719 + ], + "angle": 0, + "content": "Validation on future prediction We conduct the experiment to evaluate the prediction performance on the charged settings. Figure 3 compares the displacement error at all future timestamps of different methods. We see that our method (red line) achieves state-of-the-art prediction performance, reflecting our model's efficiency in future prediction." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.73, + 0.857, + 0.745 + ], + "angle": 0, + "content": "5.2. Scenario 2: Molecule Dynamic Prediction" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.75, + 0.894, + 0.84 + ], + "angle": 0, + "content": "We adopt the MD17 [7] dataset which contains the motions of different molecules generated via a molecular dynamics simulation environment. The goal is to predict the motions of every atom of the molecule. We randomly pick four kinds of molecules: Aspirin, Benzene, Ethanol and Malonaldehyde and learn a prediction model for each molecule." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.841, + 0.894, + 0.901 + ], + "angle": 0, + "content": "Table 4 presents the comparison of different motion prediction methods. We achieve state-of-the-art prediction performance on all four molecules. The ADE/FDE across four molecules is decreased by \\(34.2\\% / 30.1\\%\\) on average." + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "1415" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.078, + 0.08, + 0.89, + 0.093 + ], + "angle": 0, + "content": "Table 2. Comparisons of short-term skeleton motion prediction on 11 representative actions and average results across all actions on H3.6M." + }, + { + "type": "table", + "bbox": [ + 0.084, + 0.094, + 0.89, + 0.259 + ], + "angle": 0, + "content": "
MotionWalkingEatingSmokingDiscussionDirectionsPhoning
millisecond801603204008016032040080160320400801603204008016032040080160320400
Res-sup. (CVPR'17)29.450.876.081.516.830.656.968.723.042.670.182.732.961.290.996.235.457.376.387.738.069.3115.0126.7
Traj-GCN (ICCV'19)12.323.039.846.18.416.933.240.77.916.231.938.912.527.458.571.79.019.943.453.710.221.042.552.3
DMGNN (CVPR'20)17.330.754.665.211.021.436.243.99.017.632.140.317.334.861.069.813.124.664.781.912.525.848.158.3
MSRGCN (ICCV'21)12.222.738.645.28.417.133.040.48.016.331.338.212.026.857.169.78.619.743.353.810.120.741.551.3
PGBIG (CVPR'22)10.219.834.540.37.015.130.638.16.614.128.234.710.023.853.666.77.217.640.951.58.318.338.748.4
SPGSN (ECCV'22)10.119.434.841.57.114.930.537.96.713.828.034.610.423.853.667.17.417.239.850.38.718.338.748.5
EqMotion (Ours)9.017.532.639.26.313.628.936.55.511.323.029.38.218.942.153.96.315.838.950.17.416.736.947.0
MotionPosingSittingSitting DownWaitingWalking TogetherAverage
millisecond801603204008016032040080160320400801603204008016032040080160320400
" + }, + { + "type": "table_caption", + "bbox": [ + 0.08, + 0.261, + 0.889, + 0.274 + ], + "angle": 0, + "content": "Table 3. Comparisons of long-term skeleton motion prediction on 8 representative actions and average results across all actions on H3.6M." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.275, + 0.889, + 0.363 + ], + "angle": 0, + "content": "
MotionWalkingEatingSmokingDiscussionGreetingPhoningPosingWalking TogetherAverage
millisecond560ms1000ms560ms1000ms560ms1000ms560ms1000ms560ms1000ms560ms1000ms560ms1000ms560ms1000ms560ms1000ms
Res-Sup. [50]81.7100.779.9100.294.8137.4121.3161.7156.3184.3143.9186.8165.4236.8173.6202.3129.2165.0
Traj-GCN [47]54.159.853.477.850.772.691.6121.5115.4148.869.2103.1114.5173.055.065.681.6114.3
DMGNN [41]71.485.858.186.750.972.281.9138.3144.5170.571.3108.4125.5188.270.586.993.6127.6
MSRGCN [9]52.763.052.577.149.571.688.6117.6116.3147.268.3104.4116.3174.352.965.981.1114.2
PGBIG [44]48.156.451.176.046.569.587.1118.2110.2143.565.9102.7106.1164.851.964.376.9110.3
SPGSN [40]46.953.649.873.446.768.689.7118.6111.0143.266.7102.5110.3165.449.860.977.4109.6
EqMotion (Ours)43.452.848.473.041.063.475.3105.6108.7142.064.7101.084.9139.444.556.073.4106.9
" + }, + { + "type": "table_caption", + "bbox": [ + 0.09, + 0.366, + 0.456, + 0.38 + ], + "angle": 0, + "content": "Table 4. Prediction ADE/FDE \\( \\left( {\\times {10}^{-2}}\\right) \\) on the MD17 dataset." + }, + { + "type": "table", + "bbox": [ + 0.08, + 0.381, + 0.472, + 0.53 + ], + "angle": 0, + "content": "
AspirinBenzeneEthanolMalonaldehyde
Radial Field [31]17.98/26.207.73/12.478.10/10.6116.53/25.10
TFN [61]15.02/21.357.55/12.308.05/10.5715.21/24.32
SE(3)-Trans [14]15.70/22.397.62/12.508.05/10.8615.44/24.47
EGNN [58]14.61/20.657.50/12.168.01/10.2215.21/24.00
LSTM17.59/24.796.06/9.467.73/9.8815.14/22.90
S-LSTM [1]13.12/18.143.06/3.527.23/9.8511.93/18.43
NRI [28]12.60/18.501.89/2.586.69/8.7812.79/19.86
NMMP [22]10.41/14.672.21/3.336.17/7.869.50/14.89
GroupNet [69]10.62/14.002.02/2.956.00/7.887.99/12.49
EqMotion(Ours)5.95/8.381.18/1.735.05/7.025.85/9.02
" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.539, + 0.469, + 0.554 + ], + "angle": 0, + "content": "5.3. Scenario 3: Human Skeleton Motion Prediction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.561, + 0.47, + 0.636 + ], + "angle": 0, + "content": "We conduct experiments on the Human 3.6M (H3.6M) dataset [25] for 3D human skeleton motion prediction. H3.6M contains 7 subjects performing 15 actions. Following the standard paradigm [41, 50], we train the models on 6 subjects and tested on the specific clips of the 5th subject." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.639, + 0.47, + 0.759 + ], + "angle": 0, + "content": "Short-term motion prediction Short-term motion prediction aims to predict future poses within 400 milliseconds. We compare EqMotion with six state-of-the-art methods. Table 2 presents the comparison of prediction MPJPEs. See the overall result in the Appendix. We see that i) EqMotion obtains superior performance at most timestamps across all the actions; and ii) compared to the baselines, EqMotion achieves much lower MPJPEs by \\(8.6\\%\\) on average." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.762, + 0.47, + 0.837 + ], + "angle": 0, + "content": "Long-term motion prediction Long-term motion prediction aims to predict the poses over 400 milliseconds. Table 3 presents the prediction MPJPEs of various methods. We see that EqMotion achieves more effective prediction on most actions and has lower MPJPEs by \\(3.8\\%\\) on average." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.839, + 0.47, + 0.884 + ], + "angle": 0, + "content": "Visualization results Figure 4 visualizes and compares the predictions on H3.6M. Baselines fail to predict future movements. EqMotion completes the action more precisely." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.886, + 0.471, + 0.901 + ], + "angle": 0, + "content": "The quantitative and visualization results reveal that Eq-" + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.367, + 0.886, + 0.48 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.5, + 0.482, + 0.892, + 0.51 + ], + "angle": 0, + "content": "Figure 4. Qualitative comparison on the action 'Sitting Down' of H3.6M. EqMotion completes the action more accurately." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.523, + 0.894, + 0.553 + ], + "angle": 0, + "content": "Motion outperforms many previous methods that are task-specific, reflecting the effectiveness of EqMotion." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.564, + 0.88, + 0.58 + ], + "angle": 0, + "content": "5.4. Scenario 4: Pedestrian Trajectory Prediction" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.584, + 0.894, + 0.659 + ], + "angle": 0, + "content": "We conduct experiments on pedestrian trajectory prediction using the ETH-UCY dataset [34, 54], which contains 5 subsets, ETH, HOTEL, UNIV, ZARA1, and ZARA2. Following the standard setting [1, 20, 76], we use 3.2 seconds (8 timestamps) to predict the 4.8 seconds (12 timestamps)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.66, + 0.895, + 0.901 + ], + "angle": 0, + "content": "Here we apply our EqMotion to two prediction modes: deterministic and multi-prediction. Deterministic means the model only outputs a single prediction for each input motion. Multi-prediction means the model has 20 predictions for each input motion. Under multi-prediction, ADE and FDE will be calculated by the best-performed predicted motion. To adapt to multi-prediction, we slightly modify EqMotion to repeat the last feature updating layer and the output layer 20 times in parallel to have a multi-head prediction, see the details in the Appendix. Table 5 compares our method with sixteen baselines. We observe that i) EqMotion achieves state-of-the-art performance with the lowest average ADE and FDE, outperforming many baseline methods that are specifically designed for this task. EqMotion reduces the FDE by \\(10.4\\%\\) and \\(7.9\\%\\) under deterministic and multi-prediction settings; and ii) EqMotion achieves the best or the" + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "1416" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.09, + 0.47, + 0.117 + ], + "angle": 0, + "content": "Table 5. Prediction performance on the ETH-UCY dataset. The bold/underline font denotes the best/second best result." + }, + { + "type": "table", + "bbox": [ + 0.078, + 0.12, + 0.477, + 0.337 + ], + "angle": 0, + "content": "
Performance (ADE/FDE)
DeterministicETHHotelUnivZara1Zara2Average
S-LSTM [1]1.09/2.350.79/1.760.67/1.400.47/1.000.56/1.170.72/1.54
SGAN-ind [20]1.13/2.211.01/2.180.60/1.280.42/0.910.52/1.110.74/1.54
Traj++ [55]1.02/2.000.33/0.620.53/1.190.44/0.990.32/0.730.53/1.11
TransF [16]1.03/2.100.36/0.710.53/1.320.44/1.000.34/0.760.54/1.17
MemoNet [70]1.00/2.080.35/0.670.55/1.190.46/1.000.37/0.820.55/1.15
EqMotion(Ours)0.96/1.920.30/0.580.50/1.100.39/0.860.30/0.680.49/1.03
Multi-predictionETHHotelUnivZara1Zara2Average
SGAN [20]0.87/1.620.67/1.370.76/0.520.35/0.680.42/0.840.61/1.21
NMMP [22]0.61/1.080.33/0.630.52/1.110.32/0.660.43/0.850.41/0.82
Traj++ [55]0.61/1.020.19/0.280.30/0.540.24/0.420.18/0.310.30/0.51
PECNet [45]0.54/0.870.18/0.240.35/0.600.22/0.390.17/0.300.29/0.48
Agentformer [76]0.45/0.750.14/0.220.25/0.450.18/0.300.14/0.240.23/0.39
GroupNet [69]0.46/0.730.15/0.250.26/0.490.21/0.390.17/0.330.25/0.44
MID [18]0.39/0.660.13/0.220.22/0.450.17/0.300.13/0.270.21/0.38
GP-Graph [2]0.43/0.630.18/0.300.24/0.420.17/0.310.15/0.290.23/0.39
EqMotion(Ours)0.40/0.610.12/0.180.23/0.430.18/0.320.13/0.230.21/0.35
" + }, + { + "type": "table_caption", + "bbox": [ + 0.081, + 0.339, + 0.465, + 0.351 + ], + "angle": 0, + "content": "Table 6. Ablation study on key modules of EqMotion on H3.6M." + }, + { + "type": "table", + "bbox": [ + 0.086, + 0.353, + 0.462, + 0.431 + ], + "angle": 0, + "content": "
EGFLIPFLIRM80ms160ms320ms400msAverage
12.931.968.282.448.9
✓10.122.648.760.735.5
✓✓9.220.845.457.033.1
✓✓✓9.120.143.755.032.0
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.433, + 0.468, + 0.459 + ], + "angle": 0, + "content": "Table 7. Ablation study on operations in the equivariant geometric feature learning on H3.6M dataset." + }, + { + "type": "table", + "bbox": [ + 0.08, + 0.462, + 0.469, + 0.54 + ], + "angle": 0, + "content": "
Ablation80ms160ms320ms400msAverage
w/o Inner att9.220.544.355.732.4
w/o Inter agg9.722.047.258.934.5
w/o Non-linear9.421.346.758.634.0
EqMotion9.120.143.755.032.0
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.544, + 0.469, + 0.575 + ], + "angle": 0, + "content": "second best ADE/FDE result on most subsets, reflecting its effectiveness on the pedestrian trajectory prediction." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.58, + 0.241, + 0.593 + ], + "angle": 0, + "content": "5.5. Ablation Studies" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.599, + 0.47, + 0.749 + ], + "angle": 0, + "content": "Effect of network modules We explore the effect of three proposed key modules in EqMotion on the H3.6M dataset, including the equivariant geometric feature learning (EGFL), the invariant pattern feature learning (IPFL) and the invariant reasoning module (IRM). Table 6 presents the experimental result. It is observed that i) the proposed three key modules all contribute to an accurate prediction; and ii) the equivariant geometric feature learning module is most important since learning a comprehensive equivariant geometric feature directly for prediction is the most important." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.75, + 0.471, + 0.856 + ], + "angle": 0, + "content": "Effect of equivariant operations We explore the effect of three proposed operations in the equivariant feature learning module in EqMotion, including the inner-agent attention (Inner att), inter-agent aggregation (Inter agg) and non-linear function (Non-linear). Table 7 presents the results. We see that the proposed three key operations all contribute to promoting an accurate prediction." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.471, + 0.901 + ], + "angle": 0, + "content": "Different amounts of training data Figure 5 presents the comparison of model performance under different amounts of training data on H3.6M. We see that i) our method" + }, + { + "type": "image", + "bbox": [ + 0.522, + 0.089, + 0.868, + 0.24 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.24, + 0.892, + 0.267 + ], + "angle": 0, + "content": "Figure 5. Comparison of model performance on different amounts of data in short-term prediction on H3.6M dataset." + }, + { + "type": "image", + "bbox": [ + 0.523, + 0.268, + 0.866, + 0.418 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.418, + 0.892, + 0.446 + ], + "angle": 0, + "content": "Figure 6. Comparison of model size and MPJPE in short-term prediction on H3.6M dataset. The target means the ideal model." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.455, + 0.894, + 0.53 + ], + "angle": 0, + "content": "achieves the best prediction performance under all training data ratios; and ii) our method even outperforms some full-data using baselines by only using \\(5\\%\\) of training data since the equivariant design promotes the network generalization ability under Euclidean transformations." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.531, + 0.895, + 0.636 + ], + "angle": 0, + "content": "Model size Figure 6 compares EqMotion to existing methods in terms of the model size and prediction results in short-term prediction on H3.6M. We can observe that EqMotion has the smallest model size (less than \\(30\\%\\) of other models' sizes) with the lowest MPJPE thanks to the equivariant design that compacts the model free from generalizing over rotations and translations of the data." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.652, + 0.619, + 0.667 + ], + "angle": 0, + "content": "6. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.674, + 0.892, + 0.78 + ], + "angle": 0, + "content": "In this work, we present EqMotion, a motion prediction network that is theoretically equivariant under Euclidean transformations. EqMotion includes three novel designs: the equivariant geometric feature learning, the invariant pattern feature learning and the invariant reasoning module. We evaluate our method on four different scenarios and our method achieves state-of-the-art prediction performance." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.895, + 0.9 + ], + "angle": 0, + "content": "Acknowledgements. This project is partially supported by National Natural Science Foundation of China under Grant 62171276, the Science and Technology Commission of Shanghai Municipal under Grant 21511100900 and 22DZ2229005, and the National Research Foundation Singapore under its AI Singapore Programme (Award Number: AISG2-RP-2021-023). Robby T. 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Tan $^{2}$ , Yuhong Tan $^{1}$ , Siheng Chen $^{1,3*}$ , Yu Guang Wang $^{1}$ , Xinchao Wang $^{2}$ , Yanfeng Wang $^{3,1}$ + +$^{1}$ Shanghai Jiao Tong University, $^{2}$ National University of Singapore, $^{3}$ Shanghai AI Laboratory + +{xcxwakaka,tyheeer,sihengc,yuguang.wang,wangyanfeng}@sjtu.edu.cn,{robby.tan,xinchao}@nus.edu.sg + +# Abstract + +Learning to predict agent motions with relationship reasoning is important for many applications. In motion prediction tasks, maintaining motion equivariance under Euclidean geometric transformations and invariance of agent interaction is a critical and fundamental principle. However, such equivariance and invariance properties are overlooked by most existing methods. To fill this gap, we propose EqMotion, an efficient equivariant motion prediction model with invariant interaction reasoning. To achieve motion equivariance, we propose an equivariant geometric feature learning module to learn a Euclidean transformable feature through dedicated designs of equivariant operations. To reason agent's interactions, we propose an invariant interaction reasoning module to achieve a more stable interaction modeling. To further promote more comprehensive motion features, we propose an invariant pattern feature learning module to learn an invariant pattern feature, which cooperates with the equivariant geometric feature to enhance network expressiveness. We conduct experiments for the proposed model on four distinct scenarios: particle dynamics, molecule dynamics, human skeleton motion prediction and pedestrian trajectory prediction. Experimental results show that our method is not only generally applicable, but also achieves state-of-the-art prediction performances on all the four tasks, improving by 24.0/30.1/8.6/9.2%. Code is available at https://github.com/MediaBrain-SJTU/EqMotion. + +# 1. Introduction + +Motion prediction aims to predict future trajectories of multiple interacting agents given their historical observations. It is widely studied in many applications like physics [3, 28], molecule dynamics [7], autonomous driving [35] and humanrobot interaction [38, 68]. In the task of motion prediction, an + +![](images/56c14bbc12890fac2a4e53a7601ef264e20305b1b4f2fc02968ca076c7d214f0.jpg) +(a) Particle dynamics + +![](images/f595ab90c833b4b3e777cbcfa7ac2676ef880039cf02eaa409196291a8ff6878.jpg) +(c) Human skeleton motion +(d) Pedestrian trajectories +Figure 1. Motion equivariance and interaction invariance under the Euclidean geometric transformation is a fundamental principle for a prediction model, but this principle is often overlooked by previous works. In this work, we propose EqMotion to fill this gap. + +often-overlooked yet fundamental principle is that a prediction model is required to be equivariant under the Euclidean geometric transformation (including translation, rotation and reflection), and at the same time maintain the interaction relationships invariant. Motion equivariance here means that if an input motion is transformed under a Euclidean transformation, the output motion must be equally transformed under the same transformation. Interaction invariance means that the way agents interact remains unchanged under the input's transformation. Figure 1 shows real-world examples of motion equivariance and interaction invariance. + +Employing this principle in a network design brings at least two benefits. First, the network will be robust to arbitrary Euclidean transformations. Second, the network will have the capability of being generalizable over rotations and translations of the data. This capability makes the network more compact, reducing the network's learning burden and contributing to a more accurate prediction. + +Despite the motion equivariance property being important + +and fundamental, it is often neglected and not guaranteed by most existing motion prediction methods. The main reason is that these methods transform the input motion sequence directly into abstract feature vectors, where the geometric transformations are not traceable, causing the geometric relationships between agents to be irretrievable. Random augmentation will ease the equivariance problem, but it is still unable to guarantee the equivariance property. [30] uses non-parametric pre and post coordinate processing to achieve equivariance, but its parametric network structures do not satisfy equivariance. Some methods propose equivariant parametric network structures utilizing the higher-order representations of spherical harmonics [14, 61] or proposing an equivariant message passing [58], but they focus on the state-to-state prediction. This means that they use only one historical timestamp to predict one future timestamp. Consequently, these methods have limitations on utilizing motion's temporal information and modeling interaction relationships since a single-state observation is insufficient for both interaction modeling and temporal dependency modeling. + +In this paper, we propose EqMotion, the first motion prediction model that is theoretically equivariant to the input motion under Euclidean geometric transformations based on the parametric network. The proposed EqMotion has three novel designs: equivariant geometric feature learning, invariant pattern feature learning and invariant interaction reasoning. To ensure motion equivariance, we propose an equivariant geometric feature learning module to learn a Euclidean transformable geometric feature through dedicated designs of equivariant operations. The geometric feature preserves motion attributes that are relevant to Euclidean transformations. To promote more comprehensive representation power, we introduce an invariant pattern feature learning module to complement the network with motion attributes that are independent of Euclidean transformations. The pattern features, cooperated into the geometric features, provide expressive motion representations by exploiting motions' spatial-temporal dependencies. + +To further infer the interactions during motion prediction, we propose an invariant interaction reasoning module, which ensures that the captured interaction relationships are invariant to the input motion under Euclidean transformations. The module infers an invariant interaction graph by utilizing invariant factors in motions. The edge weights in the interaction graph categorize agents' interactions into different types, leading to better interaction representation. + +We conduct extensive experiments on four different scenarios to evaluate our method's effectiveness: particle dynamics, molecule dynamics, 3D human skeleton motion and pedestrian trajectories. Comparing to many task-specific motion prediction methods, our method is generally applicable and achieves state-of-the-art performance in all these tasks by reducing the prediction error by $24.0 / 30.1 / 8.6 / 9.2\%$ + +respectively. We also present that EqMotion is lightweight, and has a model size less than $30\%$ of many other models' sizes. We show that EqMotion using only $5\%$ data can achieve a comparable performance with other methods that take full data. As a summary, here are our contributions: + +- We propose EqMotion, the first motion prediction model that theoretically ensures sequence-to-sequence motion equivariance based on the parametric network. With equivariance, EqMotion promotes more generalization ability of motion feature learning, leading to more robust and accurate prediction. +- We propose a novel invariant interaction reasoning module, in which the captured interactions between agents are invariant to the input motion under Euclidean geometric transformations. With this, EqMotion achieves more generalization ability and stability in the interaction reasoning. +- We conduct experiments on four types of scenarios and find that EqMotion is applicable to all these different tasks, and importantly outperforms existing state-of-the-art methods on all the tasks. + +# 2. Related Work + +Equivariant Networks. Equivariance first draws high attention on the 2D image domain. Since CNN structure is sensitive to rotations, researchers start to explore rotation-equivariant designs like oriented convolutional filters [8,49], log-polar transform [11], circular harmonics [67] or steerable filters [66]. Meanwhile, GNN architectures [73-75] exploring symmetries on both rotation and translation have been emerged. Specifically, [57, 62] achieves partial symmetries by promoting translation equivariance. [14, 61] builds filters using spherical harmonics allowing transformations between high-order representations, achieving the rotation and translation equivariance. [12, 24] construct a Lie convolution to parameterize transformations into Lie algebra form. [10] proposes a series of equivariant layers for point cloud networks. [27] propose geometric vector perceptions for protein structure learning. Recently, EGNN [58] proposes a simple equivariant message passing form without using computationally expensive high-order representations. [23] further extends it by considering geometrical constraints. However, most existing methods are only applicable to state prediction, limiting models from exploiting sequence information. [30] uses pre and post coordinate processing to achieve motion equivariance but its network structure does not satisfy equivariance. In this work, we propose an equivariant model based on the parametric network which is generally applicable to motion prediction tasks and achieves a more precise prediction. + +Motion Prediction. Motion prediction has wide application scenarios. [3, 53, 56] proposes graph neural networks for learning to simulate complex physical systems. [17, 28, 37, 71] both explicitly infer the interactions rela + +tionships and perform prediction in physical systems. For human or vehicle trajectory prediction, social forces [21, 51], Markov [29, 65] process, and RNNs [1, 52, 63] are first methods to employ. Multi-model prediction methods are further proposed like using generator-discriminator structures [20, 22], multi-head output [43, 59], conditional variational autoencoders [32, 45, 55, 69, 71, 72, 76], memory mechanisms [48, 70], Gaussian mixture distribution prediction [17, 37]. The HD map information is specifically considered in the autonomous driving scenario [5, 6, 15, 22, 42, 43, 77]. For 3D human skeleton motion prediction, early methods are based on the state prediction [33, 60]. Later RNN-based models considering the sequential motion states are proposed [13, 26, 50, 64]. [19, 36] use spatial graph convolutions to directly regress the whole sequences. Besides, some methods [4, 40, 46, 47] specifically exploit the correlations between body joints. Multi-scale graphs are built by [9, 39, 41] to capture different body-level dependencies. In this work, we propose a generally applicable motion prediction network which promotes Euclidean equivariance, a fundamental property but neglected by previous methods, to have a more robust and accurate prediction. + +# 3. Background and Problem Formulation + +# 3.1. Motion Prediction + +Here we introduce the general problem formulation of motion prediction, which aims to generate future motions given the historical observations. Mathematically, consider $M$ agents in a multi-agent system. Let $\mathbf{X}_i = [\mathbf{x}_i^1,\mathbf{x}_i^2,\dots \mathbf{x}_i^{T_{\mathrm{p}}}]\in$ $\mathbb{R}^{T_{\mathrm{p}}\times n}$ and $\mathbf{Y}_i = [\mathbf{y}_i^1,\mathbf{y}_i^2,\dots \mathbf{y}_i^{T_{\mathrm{f}}}]\in \mathbb{R}^{T_{\mathrm{f}}\times n}$ be the ith agent's past and future motion, where $T_{\mathrm{p}}$ and $T_{\mathrm{f}}$ are the past and future timestamps and $n$ is the dimension of the system space. $n$ usually equals to 2 or 3 (corresponding to 2D or 3D case). The $t$ th timestamp locations $\mathbf{x}_i^t$ and $\mathbf{y}_i^t$ are $n$ dimension vectors. The whole system's past and future motion is represented as $\mathbb{X} = [\mathbf{X}_1,\mathbf{X}_2,\dots ,\mathbf{X}_M]\in \mathbb{R}^{M\times T_{\mathrm{p}}\times n}$ and $\mathbb{Y} = [\mathbf{Y}_1,\mathbf{Y}_2,\dots ,\mathbf{Y}_M]\in \mathbb{R}^{M\times T_{\mathrm{f}}\times n}$ . We aim to propose a prediction network $\mathcal{F}_{\mathrm{pred}}(\cdot)$ so that the predicted future motions $\widehat{\mathbb{Y}} = \mathcal{F}_{\mathrm{pred}}(\mathbb{X})$ are as close to the ground-truth future motions $\mathbb{Y}$ as possible. + +# 3.2. Equivariance and Invariance + +The Euclidean geometric transformation has three basic forms: translation, rotation and reflection. The translation is modeled by a translation vector and rotation (or reflection) is modeled by an orthogonal rotation (or reflection) matrix. Let $\mathbf{t} \in \mathbb{R}^n$ be a translation vector and $\mathbf{R} \in \mathrm{SO}(n)$ be a $n \times n$ rotation matrix, we have the following definitions for equivariance and invariance: + +Definition 1 Let $\mathbb{X}$ be an input, $\mathcal{F}(\cdot)$ be an operation and $\mathbb{Z} = \mathcal{F}(\mathbb{X})$ be the corresponding output. The operation $\mathcal{F}(\cdot)$ is called equivariant under Euclidean transformation if + +$$ +\mathbb {Z} \mathbf {R} + \mathbf {t} = \mathcal {F} (\mathbb {X} \mathbf {R} + \mathbf {t}) \quad \forall \mathbf {R} \in \mathrm {S O} (n), \forall \mathbf {t} \in \mathbb {R} ^ {n}. +$$ + +Definition 2 Let $\mathbb{X}$ be an input, $\mathcal{F}(\cdot)$ be an operation and $\mathbb{Z} = \mathcal{F}(\mathbb{X})$ be the corresponding output. The operation $\mathcal{F}(\cdot)$ is called invariant under Euclidean transformation if + +$$ +\mathbb {Z} = \mathcal {F} (\mathbb {X} \mathbf {R} + \mathbf {t}) \quad \forall \mathbf {R} \in \mathrm {S O} (n), \forall \mathbf {t} \in \mathbb {R} ^ {n}. +$$ + +Here, when a motion prediction network $\mathcal{F}_{\mathrm{pred}}(\cdot)$ satisfies Definition 1, $\mathcal{F}_{\mathrm{pred}}(\cdot)$ is said motion equivariant. When an interaction reasoning model $\mathcal{F}_{\mathrm{reason}}(\cdot)$ satisfies Definition 2, $\mathcal{F}_{\mathrm{reason}}(\cdot)$ is considered interaction invariant. We also say the output $\mathbb{Z}$ is equivariant/invariant (to the input motion under Euclidean transformation) if Definition 1/2 is satisfied. + +In the following section, we will introduce our motion prediction network along with geometric features that are equivariant under Euclidean transformations, and pattern features along with the interaction reasoning module are invariant under Euclidean transformations. + +# 4. Methodology + +In this section, we present EqMotion, a motion prediction network which is equivariant under Euclidean geometric transformations. The whole network architecture is shown in Figure 2. The core of EqMotion is to successively learn equivariant geometric features and invariant pattern features by mutual cooperation in designed equivariant/invariant operations, which not only provide expressive motion and interaction representations, but also preserve equivariant/invariant properties. For agents' motions $\mathbb{X} \in \mathbb{R}^{M \times T_{\mathrm{p}} \times n}$ , the overall procedure of the proposed EqMotion is formulated as + +$$ +\mathbb {G} ^ {(0)}, \mathbf {H} ^ {(0)} = \mathcal {F} _ {\mathrm {I L}} (\mathbb {X}), \tag {1a} +$$ + +$$ +\left\{\mathbf {c} _ {i j} \right\} = \mathcal {F} _ {\mathrm {I R M}} \left(\mathbb {G} ^ {(0)}, \mathbf {H} ^ {(0)}\right), \tag {1b} +$$ + +$$ +\mathbb {G} ^ {(\ell + 1)} = \mathcal {F} _ {\mathrm {E G F L}} ^ {(\ell)} \left(\mathbb {G} ^ {(\ell)}, \mathbf {H} ^ {(\ell)}, \left\{\mathbf {c} _ {i j} \right\}\right), \tag {1c} +$$ + +$$ +\mathbf {H} ^ {(\ell + 1)} = \mathcal {F} _ {\mathrm {I P F L}} ^ {(\ell)} \left(\mathbb {G} ^ {(\ell)}, \mathbf {H} ^ {(\ell)}\right), \tag {1d} +$$ + +$$ +\widehat {\mathbb {Y}} = \mathcal {F} _ {\mathrm {E O L}} \left(\mathbb {G} ^ {(L)}\right). \tag {1e} +$$ + +Step (1a) uses an initialization layer $\mathcal{F}_{\mathrm{IL}}(\cdot)$ to obtain initial geometric features $\mathbb{G}^{(0)}$ and pattern features $\mathbf{H}^{(0)}$ . For interaction relationship unavailable cases, Step (1b) uses an invariant interaction reasoning module $\mathcal{F}_{\mathrm{IRM}}(\cdot)$ to infer an interaction graph $\{\mathbf{c}_{ij}\}$ whose edge weight $\mathbf{c}_{ij}$ is the interaction category between agent $i$ and $j$ . Step (1c) uses the $\ell$ th equivariant geometric feature learning layer $\mathcal{F}_{\mathrm{EGFL}}^{(\ell)}(\cdot)$ to learn the $(\ell + 1)$ th geometric feature $\mathbb{G}^{(\ell + 1)}$ . Step (1d) uses the $\ell$ th invariant pattern feature learning layer $\mathcal{F}_{\mathrm{IPFL}}^{(\ell)}(\cdot)$ to learn the $(\ell + 1)$ th pattern feature $\mathbf{H}^{(\ell + 1)}$ . Step (1c) and Step (1d) will repeat $L$ times. Step (1e) uses an equivariant output layer $\mathcal{F}_{\mathrm{EOL}}(\cdot)$ to obtain the final prediction $\widehat{\mathbb{Y}}$ . + +Note that i) to incorporate the geometric feature's equivariance, we need to design equivariant operations for the initialization layer $\mathcal{F}_{\mathrm{IL}}(\cdot)$ and the equivariant geometric feature learning layer $\mathcal{F}_{\mathrm{EGFL}}^{(\ell)}(\cdot)$ ; ii) to introduce the pattern feature's invariance, we need to design invariant operations for the initialization layer $\mathcal{F}_{\mathrm{IL}}(\cdot)$ and the invariant pattern feature + +![](images/c33d300b2f93111391dc484f51e09a89defc2f12477aaf4000742040a246196e.jpg) +Figure 2. EqMotion architecture. In EqMotion, we first use a feature initialization layer to initialize geometric features and pattern features. We then successively update the geometric features and the pattern features by the equivariant geometric feature learning and invariant pattern feature learning layers, obtaining expressive feature representation. We further propose an invariant reasoning module to infer an interaction graph used in equivariant geometric feature learning. Finally, we use an equivariant output layer to obtain the final prediction. + +learning layer $\mathcal{F}_{\mathrm{IPFL}}^{(\ell)}(\cdot)$ ; and iii) the interaction graph categorizes agent's spatial interaction into different categories for better interaction representing. The interaction graph is invariant due to the reasoning module $\mathcal{F}_{\mathrm{IRM}}(\cdot)$ design. In subsequent sections, we elaborate the details of each step. + +# 4.1. Feature Initialization + +The feature initialization layer aims to obtain initial geometric features and pattern features while equipping them with different functionality. The initial geometric feature is denoted as $\mathbb{G}^{(0)} = [\mathbf{G}_1^{(0)},\dots ,\mathbf{G}_M^{(0)}]\in \mathbb{R}^{M\times C\times n}$ whose $i$ th agent's geometric feature consists of $C$ geometric coordinates. The initial pattern feature is denoted as $\mathbf{H}^{(0)} = [\mathbf{h}_1^{(0)},\dots ,\mathbf{h}_M^{(0)}]\in \mathbb{R}^{M\times D}$ whose $i$ th agent's pattern feature is a $D$ -dimensional vector. Given the past motions $\mathbb{X}$ whose the $i$ th agent's motion is $\mathbf{X}_i\in \mathbb{R}^{T_{\mathrm{p}}\times n}$ , we obtain two initial features of the $i$ th agent: + +$$ +\mathbf {G} _ {i} ^ {(0)} = \phi_ {\mathrm {i n i t \_ g}} (\mathbf {X} _ {i} - \overline {{\mathbb {X}}}) + \overline {{\mathbb {X}}}, +$$ + +$$ +\mathbf {V} _ {i} = \triangle \mathbf {X} _ {i}, \rho_ {i} ^ {t} = | | \mathbf {V} _ {i} ^ {t} | | _ {2}, \theta_ {i} ^ {t} = \mathrm {a n g l e} (\mathbf {V} _ {i} ^ {t}, \mathbf {V} _ {i} ^ {t - 1}), +$$ + +$$ +\mathbf {h} _ {i} ^ {(0)} = \phi_ {\mathrm {i n i t \_ h}} ([ \rho_ {i}; \theta_ {i} ]), +$$ + +where $\phi_{\mathrm{init\_g}}(\mathbf{X}) = \mathbf{W}_{\mathrm{init\_g}}\mathbf{X}$ , $\mathbf{W}_{\mathrm{init\_g}} \in \mathbb{R}^{C \times T_p}$ is a linear function, $\overline{\mathbb{X}}$ is the mean coordinate of all agents all past timestamps. $\triangle$ is the difference operator to obtain the velocity $\mathbf{V}_i \in \mathbb{R}^{T_{\mathrm{p}} \times n}$ . $\rho_i \in \mathbb{R}^{T_{\mathrm{p}}}$ is the velocity magnitude sequence and $\theta_i \in \mathbb{R}^{T_{\mathrm{p}}}$ is the velocity angle sequence. The superscript $(\cdot)^t$ denotes the $t$ th element, $||\cdot||_2$ is vector 2-norm, $\mathrm{angle}(\cdot)$ is the function calculating the angle between two vectors and $\phi_{\mathrm{init\_h}}(\cdot)$ is an embedding function implemented by MLP or LSTM. $[\cdot; \cdot]$ represents concatenation. + +The geometric feature preserves both equivariant property and motion attributes that are sensitive to Euclidean geometric transforms since we linearly combine the equivariant locations. The pattern feature remains invariant and is sensitive to motion attributes independent of Euclidean geometric transforms. + +# 4.2. Invariant Reasoning Module + +For most scenarios, the interaction relationship is implicit and unavailable. Thus, we propose an invariant reasoning module for inferring the interaction category between agents. + +Note that we design the reasoning module to be invariant as the interaction category is independent of Euclidean transformations. The output of the reasoning module is an invariant interaction graph whose edge weight $\mathbf{c}_{ij} \in [0,1]^K$ is a categorical vector representing the type of interaction between agent $i$ and $j$ . $K$ is the interaction category number. To obtain the interaction categorical vector, we perform a message passing operation using the agent's initial pattern feature $\mathbf{h}_i^{(0)}$ and geometric feature $\mathbf{G}_i^{(0)}$ : + +$$ +\mathbf {m} _ {i j} ^ {\prime} = \phi_ {\mathrm {r m}} \left(\left[ \mathbf {h} _ {i} ^ {(0)}; \mathbf {h} _ {j} ^ {(0)}; \left| \left| \mathbf {G} _ {i} ^ {(0)} - \mathbf {G} _ {j} ^ {(0)} \right| \right| _ {2, \text {c o l}} \right]\right), +$$ + +$$ +\mathbf {p} _ {i} ^ {\prime} = \sum_ {j \in \mathcal {N} _ {i}} \mathbf {m} _ {i j} ^ {\prime}, \mathbf {h} _ {i} ^ {\prime} = \phi_ {\mathrm {r h}} \big ([ \mathbf {p} _ {i} ^ {\prime}; \mathbf {h} _ {i} ^ {(0)} ] \big), +$$ + +$$ +\mathbf {c} _ {i j} = \mathrm {s m} \Big (\phi_ {\mathrm {r c}} \big ([ \mathbf {h} _ {i} ^ {\prime}; \mathbf {h} _ {j} ^ {\prime}; | | \mathbf {G} _ {i} ^ {(0)} - \mathbf {G} _ {j} ^ {(0)} | | _ {2, \mathrm {c o l}} ] \big) / \tau \Big), +$$ + +where $||\cdot ||_{2,\mathrm{col}}$ is a column-wise $\ell_2$ -distance, $\phi_{\mathrm{rm}}(\cdot),\phi_{\mathrm{rh}}(\cdot)$ $\phi_{\mathrm{rc}}(\cdot)$ are learnable functions implemented by MLPs. $\mathrm{sm}(\cdot)$ is the softmax function and $\tau$ is the temperature to control the smoothness of the categorical distribution. The interaction edge weights $\{\mathbf{c}_{ij}\}$ will be end-to-end learned with the whole prediction network. + +# 4.3. Equivariant Geometric Feature Learning + +The equivariant geometric feature learning process aims to find more representative agents' geometric features by exploiting their spatial and temporal dependencies, while maintaining the equivariance. During the process, we perform i) equivariant inner-agent attention to exploit the temporal dependencies; ii) equivariant inter-agent aggregation to model spatial interactions; and iii) equivariant non-linear function to further enhance the representation ability. + +Equivariant inner-agent attention To exploit the temporal dependency, we perform an attention mechanism on the coordinate dimension of the geometric feature since the coordinate dimension originates from the temporal dimension. Given the $i$ th agent's geometric feature $\mathbf{G}_i^{(\ell)} \in \mathbb{R}^{C \times n}$ and pattern feature $\mathbf{h}_i^{(\ell)}$ , we have + +$$ +\mathbf {G} _ {i} ^ {(\ell)} \leftarrow \phi_ {\mathrm {a t t}} ^ {(\ell)} \left(\mathbf {h} _ {i} ^ {(\ell)}\right) \cdot \left(\mathbf {G} _ {i} ^ {(\ell)} - \overline {{\mathbb {G}}} ^ {(\ell)}\right) + \overline {{\mathbb {G}}} ^ {(\ell)}, \tag {2} +$$ + +where $\phi_{\mathrm{att}}^{(\ell)}(\cdot):\mathbb{R}^D\to \mathbb{R}^C$ is a function which learns the attention weight for per coordinate, and $\overline{\mathbb{G}}^{(\ell)}$ is the mean + +coordinates summing up over all agents and all coordinates. + +The above operation will bring the following benefits: i) The learned attention weight is invariant and the learned dependencies between different timestamps of the motion will not be disturbed by irrelevant Euclidean transformations; and ii) The learned geometric feature is equivariant because of the coordinate-wise linear multiplication. + +Equivariant inter-agent aggregation The equivariant inter-agent aggregation aims to model spatial interactions between agents. The key idea is to use the reasoned or provided interaction category to learn aggregation weights, and then use the weights to aggregate neighboring agents' geometric features. The aggregation operation reads + +$$ +\begin{array}{l} \mathbf {e} _ {i j} ^ {(\ell)} = \sum_ {k = 1} ^ {K} \mathbf {c} _ {i j, k} \phi_ {e, k} ^ {(\ell)} \left(\left[ \mathbf {h} _ {i} ^ {(\ell)}; \mathbf {h} _ {j} ^ {(\ell)}; \left\| \mathbf {G} _ {i} ^ {(\ell)} - \mathbf {G} _ {j} ^ {(\ell)} \right\| _ {2, \text {c o l}} \right]\right), \tag {3} \\ \mathbf {G} _ {i} ^ {(\ell)} \leftarrow \mathbf {G} _ {i} ^ {(\ell)} + \sum_ {j \in \mathcal {N} _ {i}} \mathbf {e} _ {i j} ^ {(\ell)} \cdot (\mathbf {G} _ {i} ^ {(\ell)} - \mathbf {G} _ {j} ^ {(\ell)}), \\ \end{array} +$$ + +where $\mathbf{e}_{ij}^{(\ell)}\in \mathbb{R}^C$ is the learned aggregation weights between agent $i$ and $j,||\cdot ||_{2,\mathrm{col}}$ is a column-wise $\ell_2$ -distance, $\cdot$ is dot product and $\mathcal{N}_i$ is the $i$ th agent's neighboring set. For the $k$ th interaction category, we assign a function $\phi_{e,k}^{(\ell)}(\cdot)$ that is implemented by MLP to model how the interaction works. + +The social influence from agent $j$ to agent $i$ is modeled by the coordinates' difference between the two agents. The intuition behind this design is that the mutual force between two objects is always in the direction of the line they formed. + +Note that for most scenarios, we do not have an explicit definition of interacted "neighbors", thus we use a fully-connected graph structure, which means every agent's neighbors include all other agents. For some special cases with massive nodes, like point clouds, we construct a local neighboring set by choosing neighbors within a distance threshold. + +Equivariant non-linear function According to Eq. (2) and Eq. (3), the operation of inner-agent attention and inter-agent aggregation are linear combinations with agents' coordinates. It is well known that non-linear operation is the key to improving neural networks' expressivity. Therefore, we propose an equivariant non-linear function to enhance the representation ability of our prediction network while preserving equivariance. The key idea is proposing a criterion with the invariance property for splitting different conditions, and for each condition design an equivariant equation. Mathematically, the non-linear function is + +$$ +\begin{array}{l} \mathbf {Q} _ {i} ^ {(\ell)} = \mathbf {W} _ {\mathrm {Q}} ^ {(\ell)} \left(\mathbf {G} _ {i} ^ {(\ell)} - \overline {{\mathbb {G}}} ^ {(\ell)}\right), \mathbf {K} _ {i} ^ {(\ell)} = \mathbf {W} _ {\mathrm {K}} ^ {(\ell)} \left(\mathbf {G} _ {i} ^ {(\ell)} - \overline {{\mathbb {G}}} ^ {(\ell)}\right), \\ \mathbf {g} _ {i, c} ^ {(\ell + 1)} = \left\{ \begin{array}{l l} \mathbf {q} _ {i, c} ^ {(\ell)} + \overline {{\mathbb {G}}} ^ {(\ell)} & \text {i f} \langle \mathbf {q} _ {i, c} ^ {(\ell)}, \mathbf {k} _ {i, c} ^ {(\ell)} \rangle \geq 0, \\ \mathbf {q} _ {i, c} ^ {(\ell)} - \langle \mathbf {q} _ {i, c} ^ {(\ell)}, \frac {\mathbf {k} _ {i , c} ^ {(\ell)}}{| | \mathbf {k} _ {i , c} ^ {(\ell)} | | _ {2}} \rangle \frac {\mathbf {k} _ {i , c} ^ {(\ell)}}{| | \mathbf {k} _ {i , c} ^ {(\ell)} | | _ {2}} + \overline {{\mathbb {G}}} ^ {(\ell)} & \text {o t h e r w i s e}, \end{array} \right. \\ \end{array} +$$ + +where $\mathbf{Q}_i^{(\ell)}$ and $\mathbf{K}_i^{(\ell)}$ is the learned query coordinates and key coordinates, $\mathbf{W}_{\mathrm{K}}^{(\ell)}\in \mathbb{R}^{C\times C}$ are learnable matrices for queries and keys. $\overline{\mathbb{G}}_{\nu}^{(\ell)}$ is the mean coordinates over all agents and all coordinates. $\mathbf{q}_{i,c}^{(\ell)}$ , $\mathbf{k}_{i,c}^{(\ell)}$ is the $c$ th coordinate of + +$\mathbf{Q}_i^{(\ell)}$ and $\mathbf{K}_i^{(\ell)}$ . $\langle \cdot, \cdot \rangle$ is the vector inner product. + +For every geometric coordinate $\mathbf{g}_{i,c}^{(\ell)}$ , we learn a query coordinate $\mathbf{q}_{i,c}^{(\ell)}$ and a key coordinate $\mathbf{k}_{i,c}^{(\ell)}$ . We set the criterion as the inner product of the query coordinate and the key coordinate. If the inner product is positive, we directly take the value of the query coordinate as output; otherwise, we clip the query coordinate vector by moving out its parallel components with the key coordinate vector. Finally, we obtain the $i$ th agent's geometric features of the next layer $\mathbf{G}_i^{(l + 1)}$ by gathering all the coordinates $\mathbf{g}_{i,c}^{(l + 1)}$ . The non-linear function is equivariant, since the criterion is invariant and the two equations under two conditions are equivariant. + +# 4.4. Invariant Pattern Feature Learning + +The invariant pattern feature learning aims to obtain a more representative agent pattern feature through interacting with neighbors. Here we learn the agent's pattern feature with an invariant message passing mechanism. Specially, we add the relative geometric feature difference into the edge modeling in the message passing to complement the information of relationships between agent absolute locations, which cannot be obtained by solely using the pattern features. Given the $i$ th agent's pattern feature $\mathbf{h}_i^{(\ell)} \in \mathbb{R}^D$ and geometric feature $\mathbf{G}_i^{(\ell)} \in \mathbb{R}^{C \times n}$ , the next layer's pattern feature $\mathbf{h}_i^{(l+1)}$ is obtained by + +$$ +\begin{array}{l} \mathbf {m} _ {i j} ^ {(\ell)} = \phi_ {m} ^ {(\ell)} \left(\left[ \mathbf {h} _ {i} ^ {(\ell)}; \mathbf {h} _ {j} ^ {(\ell)}; | | \mathbf {G} _ {i} ^ {(\ell)} - \mathbf {G} _ {j} ^ {(\ell)} | | _ {2, \text {c o l}} \right]\right), \\ \mathbf {p} _ {i} ^ {(\ell)} = \sum_ {j \in \mathcal {N} (i)} \mathbf {m} _ {i j} ^ {(\ell)}, \mathbf {h} _ {i} ^ {(l + 1)} = \phi_ {h} ^ {(\ell)} ([ \mathbf {h} _ {i} ^ {(\ell)}; \mathbf {p} _ {i} ^ {(\ell)} ]). \\ \end{array} +$$ + +Here $\mathbf{m}_{ij}^{(\ell)}$ is the edge features and $\mathbf{p}_i^{(\ell)}$ is the aggregated neighboring features in the message passing. $||\cdot ||_{2,\mathrm{col}}$ is a column-wise $\ell_2$ -distance and $[\cdot ;\cdot ]$ denotes concatenation. Functions $\phi_m^{(\ell)}(\cdot)$ and $\phi_h^{(\ell)}(\cdot)$ are implemented by MLPs. + +# 4.5. Equivariant Output Layer + +After total $L$ feature learning layers, we obtain the final $i$ th agent's geometric feature $\mathbf{G}_i^{(L)}$ and pattern feature $\mathbf{h}_i^{(L)}$ . We use the geometric feature for the final prediction by a linear operation for equivariance: for the $i$ th agent: + +$$ +\widehat {\mathbf {Y}} _ {i} = \mathbf {W} _ {\text {o u t}} (\mathbf {G} _ {i} ^ {(\ell)} - \overline {{\mathbb {G}}} ^ {(\ell)}) + \overline {{\mathbb {G}}} ^ {(\ell)}, +$$ + +where $\mathbf{W}_{\mathrm{out}} \in \mathbb{R}^{T_{\mathrm{f}} \times D}$ is a learnable weight matrix. Finally, we gather all the agent prediction $\widehat{\mathbf{Y}}_i$ to have the final predicted motions $\widehat{\mathbb{Y}}$ . + +# 4.6. Theoretical Analysis + +In this section, we analyze our network's equivariance property and the interaction reasoning module's invariance property, as stated in the following theorem. Let $\mathbb{G}^{(\ell)}\in$ $\mathbb{R}^{M\times C\times n}$ be all agents' geometric features, $\mathbf{H}^{(\ell)}\in \mathbb{R}^{M\times D}$ be all agents' pattern features at the $\ell$ th layer, and $\{\mathbf{c}_{ij}\}$ be the set of all the interaction categorical vectors. + +Theorem 1 For arbitrary translation vector $\mathbf{t} \in \mathbb{R}^n$ and rotation (or reflection) matrix $\mathbf{R} \in \mathrm{SO}(n)$ , the modules with equivariance and invariance in our network satisfy: + +1. For the initialization layer $\mathcal{F}_{\mathrm{IL}}(\cdot)$ , the initial geometric feature is equivariant and the initial pattern feature is invariant: + +$$ +\mathbb {G} ^ {(0)} \mathbf {R} + \mathbf {t}, \mathbf {H} ^ {(0)} = \mathcal {F} _ {\mathrm {I L}} (\mathbb {X} \mathbf {R} + \mathbf {t}). +$$ + +2. The reasoning module $\mathcal{F}_{\mathrm{IRM}}(\cdot)$ along with reasoned interaction categorical vectors $\{\mathbf{c}_{ij}\}$ is invariant: + +$$ +\left\{\mathbf {c} _ {i j} \right\} = \mathcal {F} _ {\mathrm {I R M}} \left(\mathbb {G} ^ {(0)} \mathbf {R} + \mathbf {t}, \mathbf {H} ^ {(0)}\right). +$$ + +3. The $\ell$ th geometric feature learning layer $\mathcal{F}_{\mathrm{EGFL}}^{(\ell)}(\cdot)$ is equivariant: + +$$ +\mathbb {G} ^ {(l + 1)} \mathbf {R} + \mathbf {t} = \mathcal {F} _ {\mathrm {E G F L}} ^ {(\ell)} \left(\mathbb {G} ^ {(\ell)} \mathbf {R} + \mathbf {t}, \mathbf {H} ^ {(\ell)}, \left\{\mathbf {c} _ {i j} \right\}\right). +$$ + +4. The $\ell$ th pattern feature learning layer $\mathcal{F}_{\mathrm{IPFL}}^{(\ell)}(\cdot)$ is invariant: + +$$ +\mathbf {H} ^ {(l + 1)} = \mathcal {F} _ {\mathrm {I P F L}} ^ {(\ell)} (\mathbb {G} ^ {(\ell)} \mathbf {R} + \mathbf {t}, \mathbf {H} ^ {(\ell)}). +$$ + +5. The output layer $\mathcal{F}_{\mathrm{EOL}}(\cdot)$ is equivariant: + +$$ +\widehat {\mathbf {Y}} \mathbf {R} + \mathbf {t} = \mathcal {F} _ {\mathrm {E O L}} (\mathbb {G} ^ {(L)} \mathbf {R} + \mathbf {t}). +$$ + +See the detailed proof in Appendix. Theorem 1 presents the equivariance/invariance properties with the Euclidean transformation for each operation in the proposed network. Based on Theorem 1, by combining all network operations together, we can show that the whole network is equivariant: + +Corollary 1 For arbitrary translation vector $\mathbf{t} \in \mathbb{R}^n$ and rotation matrix $\mathbf{R} \in \mathrm{SO}(n)$ , our whole network EqMotion $\mathcal{F}_{\mathrm{pred}}(\cdot)$ satisfies: + +$$ +\widehat {\mathbb {Y}} \mathbf {R} + \mathbf {t} = \mathcal {F} _ {\mathrm {p r e d}} (\mathbb {X} \mathbf {R} + \mathbf {t}). +$$ + +# 5. Experiment + +In this section, we validate our method on four different scenarios: particle dynamics, molecule dynamics, 3D human skeleton motion, and pedestrian trajectories. The detailed dataset description, implementation details, and additional experiment results are elaborated in the Appendix. + +Metric We use: i) Average Displacement Error (ADE) and Final Displacement Error (FDE). ADE/FDE is the $\ell_2$ distance of the predicted whole motion/endpoint to the ground truth of the whole motion/endpoint; ii) Mean Per Joint Position Error (MPJPE). It records average $\ell_2$ distance between predicted joints and target ones at each future timestamp. + +# 5.1. Scenario 1: Particle Dynamic Prediction + +We use the particle $N$ -body simulation [28] in a 3D space similar to [14, 58]. In the Springs simulation, particles are randomly connected by a spring. In the Charged simulation, particles are randomly charged or uncharged. + +Validation on interaction reasoning Since we can get the ground-truth interaction through simulation, we evaluate the ability of interaction reasoning as a category recognition task. To evaluate the robustness of the reasoning result with + +Table 1. Interaction recognition accuracy and consistency (mean ± std in % in 5 independent runs) on the physical simulation. + +
ModelSpringsCharged
AccuracyConsistencyAccuracyConsistency
Corr.(path) [28]58.1 ± 0.099.8 ± 0.157.5 ± 0.187.9 ± 0.1
Corr.(LSTM) [28]53.5 ± 0.592.4 ± 2.157.2 ± 0.491.7 ± 1.1
EGNN [58]61.0 ± 1.3100.0 ± 0.058.2 ± 1.4100.0 ± 0.0
NRI [28]93.0 ± 1.193.7 ± 1.270.0 ± 0.688.5 ± 1.3
dNRI [17]93.3 ± 2.089.6 ± 2.070.4 ± 1.783.6 ± 1.8
Ours97.6 ± 1.1100.0 ± 0.080.9 ± 3.4100.0 ± 0.0
Supervised98.7 ± 0.2100.0 ± 0.097.4 ± 0.2100.0 ± 0.0
+ +![](images/c99ac6037ac5632c7029371226f8df24bf8811fe060beff70661f62224c11da9.jpg) +Figure 3. Comparison of displacement error across different timestamps on the physical simulation. + +the Euclidean transformation, we introduce recognition "consistency", which is the ratio of the same recognition result under 20 random Euclidean transformations. The "Supervised" represents an upper bound that uses the ground-truth category to train the model. Table 1 reports the comparison of reasoning results on both springs and charged simulations, for recognizing whether there is a spring connection or electrostatic force. We see that i) our method achieves significant improvement on the recognition accuracy and has more robust reasoning results due to the invariance of our reasoning module; and ii) our method achieves a close performance to the upper bound, reflecting that our method is capable of reasoning a robust and accurate interaction category. + +Validation on future prediction We conduct the experiment to evaluate the prediction performance on the charged settings. Figure 3 compares the displacement error at all future timestamps of different methods. We see that our method (red line) achieves state-of-the-art prediction performance, reflecting our model's efficiency in future prediction. + +# 5.2. Scenario 2: Molecule Dynamic Prediction + +We adopt the MD17 [7] dataset which contains the motions of different molecules generated via a molecular dynamics simulation environment. The goal is to predict the motions of every atom of the molecule. We randomly pick four kinds of molecules: Aspirin, Benzene, Ethanol and Malonaldehyde and learn a prediction model for each molecule. + +Table 4 presents the comparison of different motion prediction methods. We achieve state-of-the-art prediction performance on all four molecules. The ADE/FDE across four molecules is decreased by $34.2\% / 30.1\%$ on average. + +Table 2. Comparisons of short-term skeleton motion prediction on 11 representative actions and average results across all actions on H3.6M. + +
MotionWalkingEatingSmokingDiscussionDirectionsPhoning
millisecond801603204008016032040080160320400801603204008016032040080160320400
Res-sup. (CVPR'17)29.450.876.081.516.830.656.968.723.042.670.182.732.961.290.996.235.457.376.387.738.069.3115.0126.7
Traj-GCN (ICCV'19)12.323.039.846.18.416.933.240.77.916.231.938.912.527.458.571.79.019.943.453.710.221.042.552.3
DMGNN (CVPR'20)17.330.754.665.211.021.436.243.99.017.632.140.317.334.861.069.813.124.664.781.912.525.848.158.3
MSRGCN (ICCV'21)12.222.738.645.28.417.133.040.48.016.331.338.212.026.857.169.78.619.743.353.810.120.741.551.3
PGBIG (CVPR'22)10.219.834.540.37.015.130.638.16.614.128.234.710.023.853.666.77.217.640.951.58.318.338.748.4
SPGSN (ECCV'22)10.119.434.841.57.114.930.537.96.713.828.034.610.423.853.667.17.417.239.850.38.718.338.748.5
EqMotion (Ours)9.017.532.639.26.313.628.936.55.511.323.029.38.218.942.153.96.315.838.950.17.416.736.947.0
MotionPosingSittingSitting DownWaitingWalking TogetherAverage
millisecond801603204008016032040080160320400801603204008016032040080160320400
+ +Table 3. Comparisons of long-term skeleton motion prediction on 8 representative actions and average results across all actions on H3.6M. + +
MotionWalkingEatingSmokingDiscussionGreetingPhoningPosingWalking TogetherAverage
millisecond560ms1000ms560ms1000ms560ms1000ms560ms1000ms560ms1000ms560ms1000ms560ms1000ms560ms1000ms560ms1000ms
Res-Sup. [50]81.7100.779.9100.294.8137.4121.3161.7156.3184.3143.9186.8165.4236.8173.6202.3129.2165.0
Traj-GCN [47]54.159.853.477.850.772.691.6121.5115.4148.869.2103.1114.5173.055.065.681.6114.3
DMGNN [41]71.485.858.186.750.972.281.9138.3144.5170.571.3108.4125.5188.270.586.993.6127.6
MSRGCN [9]52.763.052.577.149.571.688.6117.6116.3147.268.3104.4116.3174.352.965.981.1114.2
PGBIG [44]48.156.451.176.046.569.587.1118.2110.2143.565.9102.7106.1164.851.964.376.9110.3
SPGSN [40]46.953.649.873.446.768.689.7118.6111.0143.266.7102.5110.3165.449.860.977.4109.6
EqMotion (Ours)43.452.848.473.041.063.475.3105.6108.7142.064.7101.084.9139.444.556.073.4106.9
+ +Table 4. Prediction ADE/FDE $\left( {\times {10}^{-2}}\right)$ on the MD17 dataset. + +
AspirinBenzeneEthanolMalonaldehyde
Radial Field [31]17.98/26.207.73/12.478.10/10.6116.53/25.10
TFN [61]15.02/21.357.55/12.308.05/10.5715.21/24.32
SE(3)-Trans [14]15.70/22.397.62/12.508.05/10.8615.44/24.47
EGNN [58]14.61/20.657.50/12.168.01/10.2215.21/24.00
LSTM17.59/24.796.06/9.467.73/9.8815.14/22.90
S-LSTM [1]13.12/18.143.06/3.527.23/9.8511.93/18.43
NRI [28]12.60/18.501.89/2.586.69/8.7812.79/19.86
NMMP [22]10.41/14.672.21/3.336.17/7.869.50/14.89
GroupNet [69]10.62/14.002.02/2.956.00/7.887.99/12.49
EqMotion(Ours)5.95/8.381.18/1.735.05/7.025.85/9.02
+ +# 5.3. Scenario 3: Human Skeleton Motion Prediction + +We conduct experiments on the Human 3.6M (H3.6M) dataset [25] for 3D human skeleton motion prediction. H3.6M contains 7 subjects performing 15 actions. Following the standard paradigm [41, 50], we train the models on 6 subjects and tested on the specific clips of the 5th subject. + +Short-term motion prediction Short-term motion prediction aims to predict future poses within 400 milliseconds. We compare EqMotion with six state-of-the-art methods. Table 2 presents the comparison of prediction MPJPEs. See the overall result in the Appendix. We see that i) EqMotion obtains superior performance at most timestamps across all the actions; and ii) compared to the baselines, EqMotion achieves much lower MPJPEs by $8.6\%$ on average. + +Long-term motion prediction Long-term motion prediction aims to predict the poses over 400 milliseconds. Table 3 presents the prediction MPJPEs of various methods. We see that EqMotion achieves more effective prediction on most actions and has lower MPJPEs by $3.8\%$ on average. + +Visualization results Figure 4 visualizes and compares the predictions on H3.6M. Baselines fail to predict future movements. EqMotion completes the action more precisely. + +The quantitative and visualization results reveal that Eq- + +![](images/66ac84f39e6d3770a2966afba273266f83058812eefa17690a0814951ee8440a.jpg) +Figure 4. Qualitative comparison on the action 'Sitting Down' of H3.6M. EqMotion completes the action more accurately. + +Motion outperforms many previous methods that are task-specific, reflecting the effectiveness of EqMotion. + +# 5.4. Scenario 4: Pedestrian Trajectory Prediction + +We conduct experiments on pedestrian trajectory prediction using the ETH-UCY dataset [34, 54], which contains 5 subsets, ETH, HOTEL, UNIV, ZARA1, and ZARA2. Following the standard setting [1, 20, 76], we use 3.2 seconds (8 timestamps) to predict the 4.8 seconds (12 timestamps). + +Here we apply our EqMotion to two prediction modes: deterministic and multi-prediction. Deterministic means the model only outputs a single prediction for each input motion. Multi-prediction means the model has 20 predictions for each input motion. Under multi-prediction, ADE and FDE will be calculated by the best-performed predicted motion. To adapt to multi-prediction, we slightly modify EqMotion to repeat the last feature updating layer and the output layer 20 times in parallel to have a multi-head prediction, see the details in the Appendix. Table 5 compares our method with sixteen baselines. We observe that i) EqMotion achieves state-of-the-art performance with the lowest average ADE and FDE, outperforming many baseline methods that are specifically designed for this task. EqMotion reduces the FDE by $10.4\%$ and $7.9\%$ under deterministic and multi-prediction settings; and ii) EqMotion achieves the best or the + +Table 5. Prediction performance on the ETH-UCY dataset. The bold/underline font denotes the best/second best result. + +
Performance (ADE/FDE)
DeterministicETHHotelUnivZara1Zara2Average
S-LSTM [1]1.09/2.350.79/1.760.67/1.400.47/1.000.56/1.170.72/1.54
SGAN-ind [20]1.13/2.211.01/2.180.60/1.280.42/0.910.52/1.110.74/1.54
Traj++ [55]1.02/2.000.33/0.620.53/1.190.44/0.990.32/0.730.53/1.11
TransF [16]1.03/2.100.36/0.710.53/1.320.44/1.000.34/0.760.54/1.17
MemoNet [70]1.00/2.080.35/0.670.55/1.190.46/1.000.37/0.820.55/1.15
EqMotion(Ours)0.96/1.920.30/0.580.50/1.100.39/0.860.30/0.680.49/1.03
Multi-predictionETHHotelUnivZara1Zara2Average
SGAN [20]0.87/1.620.67/1.370.76/0.520.35/0.680.42/0.840.61/1.21
NMMP [22]0.61/1.080.33/0.630.52/1.110.32/0.660.43/0.850.41/0.82
Traj++ [55]0.61/1.020.19/0.280.30/0.540.24/0.420.18/0.310.30/0.51
PECNet [45]0.54/0.870.18/0.240.35/0.600.22/0.390.17/0.300.29/0.48
Agentformer [76]0.45/0.750.14/0.220.25/0.450.18/0.300.14/0.240.23/0.39
GroupNet [69]0.46/0.730.15/0.250.26/0.490.21/0.390.17/0.330.25/0.44
MID [18]0.39/0.660.13/0.220.22/0.450.17/0.300.13/0.270.21/0.38
GP-Graph [2]0.43/0.630.18/0.300.24/0.420.17/0.310.15/0.290.23/0.39
EqMotion(Ours)0.40/0.610.12/0.180.23/0.430.18/0.320.13/0.230.21/0.35
+ +Table 6. Ablation study on key modules of EqMotion on H3.6M. + +
EGFLIPFLIRM80ms160ms320ms400msAverage
12.931.968.282.448.9
✓10.122.648.760.735.5
✓✓9.220.845.457.033.1
✓✓✓9.120.143.755.032.0
+ +Table 7. Ablation study on operations in the equivariant geometric feature learning on H3.6M dataset. + +
Ablation80ms160ms320ms400msAverage
w/o Inner att9.220.544.355.732.4
w/o Inter agg9.722.047.258.934.5
w/o Non-linear9.421.346.758.634.0
EqMotion9.120.143.755.032.0
+ +second best ADE/FDE result on most subsets, reflecting its effectiveness on the pedestrian trajectory prediction. + +# 5.5. Ablation Studies + +Effect of network modules We explore the effect of three proposed key modules in EqMotion on the H3.6M dataset, including the equivariant geometric feature learning (EGFL), the invariant pattern feature learning (IPFL) and the invariant reasoning module (IRM). Table 6 presents the experimental result. It is observed that i) the proposed three key modules all contribute to an accurate prediction; and ii) the equivariant geometric feature learning module is most important since learning a comprehensive equivariant geometric feature directly for prediction is the most important. + +Effect of equivariant operations We explore the effect of three proposed operations in the equivariant feature learning module in EqMotion, including the inner-agent attention (Inner att), inter-agent aggregation (Inter agg) and non-linear function (Non-linear). Table 7 presents the results. We see that the proposed three key operations all contribute to promoting an accurate prediction. + +Different amounts of training data Figure 5 presents the comparison of model performance under different amounts of training data on H3.6M. We see that i) our method + +![](images/78e38ba1b03658df0374cb61713f5b007d611827bf91a31a1fb41a2ea7a888d2.jpg) +Figure 5. Comparison of model performance on different amounts of data in short-term prediction on H3.6M dataset. + +![](images/e4c924e8ae3ed1f7112d255ab3bb483ad5a2650ea969fd116e2573f0035707b2.jpg) +Figure 6. Comparison of model size and MPJPE in short-term prediction on H3.6M dataset. The target means the ideal model. + +achieves the best prediction performance under all training data ratios; and ii) our method even outperforms some full-data using baselines by only using $5\%$ of training data since the equivariant design promotes the network generalization ability under Euclidean transformations. + +Model size Figure 6 compares EqMotion to existing methods in terms of the model size and prediction results in short-term prediction on H3.6M. We can observe that EqMotion has the smallest model size (less than $30\%$ of other models' sizes) with the lowest MPJPE thanks to the equivariant design that compacts the model free from generalizing over rotations and translations of the data. + +# 6. Conclusion + +In this work, we present EqMotion, a motion prediction network that is theoretically equivariant under Euclidean transformations. EqMotion includes three novel designs: the equivariant geometric feature learning, the invariant pattern feature learning and the invariant reasoning module. We evaluate our method on four different scenarios and our method achieves state-of-the-art prediction performance. + +Acknowledgements. This project is partially supported by National Natural Science Foundation of China under Grant 62171276, the Science and Technology Commission of Shanghai Municipal under Grant 21511100900 and 22DZ2229005, and the National Research Foundation Singapore under its AI Singapore Programme (Award Number: AISG2-RP-2021-023). Robby T. Tan's work is supported by MOE AcRF Tier, A-0009455-01-00. + +# References + +[1] Alexandre Alahi, Kratarth Goel, Vignesh Ramanathan, Alexandre Robicquet, Li Fei-Fei, and Silvio Savarese. Social lstm: Human trajectory prediction in crowded spaces. 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In motion prediction tasks, maintaining motion equivariance under Euclidean geometric transformations and invariance of agent interaction is a critical and fundamental principle. However, such equivariance and invariance properties are overlooked by most existing methods. To fill this gap, we propose EqMotion, an efficient equivariant motion prediction model with invariant interaction reasoning. To achieve motion equivariance, we propose an equivariant geometric feature learning module to learn a Euclidean transformable feature through dedicated designs of equivariant operations. To reason agent's interactions, we propose an invariant interaction reasoning module to achieve a more stable interaction modeling. To further promote more comprehensive motion features, we propose an invariant pattern feature learning module to learn an invariant pattern feature, which cooperates with the equivariant geometric feature to enhance network expressiveness. We conduct experiments for the proposed model on four distinct scenarios: particle dynamics, molecule dynamics, human skeleton motion prediction and pedestrian trajectory prediction. Experimental results show that our method is not only generally applicable, but also achieves state-of-the-art prediction performances on all the four tasks, improving by 24.0/30.1/8.6/9.2%. Code is available at https://github.com/MediaBrain-SJTU/EqMotion." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 616, + 128, + 628 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 616, + 128, + 628 + ], + "spans": [ + { + "bbox": [ + 47, + 616, + 128, + 628 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 635, + 288, + 696 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 635, + 288, + 696 + ], + "spans": [ + { + "bbox": [ + 46, + 635, + 288, + 696 + ], + "type": "text", + "content": "Motion prediction aims to predict future trajectories of multiple interacting agents given their historical observations. It is widely studied in many applications like physics [3, 28], molecule dynamics [7], autonomous driving [35] and humanrobot interaction [38, 68]. In the task of motion prediction, an" + } + ] + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 309, + 243, + 544, + 321 + ], + "blocks": [ + { + "bbox": [ + 309, + 243, + 544, + 321 + ], + "lines": [ + { + "bbox": [ + 309, + 243, + 544, + 321 + ], + "spans": [ + { + "bbox": [ + 309, + 243, + 544, + 321 + ], + "type": "image", + "image_path": "56c14bbc12890fac2a4e53a7601ef264e20305b1b4f2fc02968ca076c7d214f0.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 328, + 322, + 399, + 333 + ], + "lines": [ + { + "bbox": [ + 328, + 322, + 399, + 333 + ], + "spans": [ + { + "bbox": [ + 328, + 322, + 399, + 333 + ], + "type": "text", + "content": "(a) Particle dynamics" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 309, + 334, + 542, + 415 + ], + "blocks": [ + { + "bbox": [ + 309, + 334, + 542, + 415 + ], + "lines": [ + { + "bbox": [ + 309, + 334, + 542, + 415 + ], + "spans": [ + { + "bbox": [ + 309, + 334, + 542, + 415 + ], + "type": "image", + "image_path": "f595ab90c833b4b3e777cbcfa7ac2676ef880039cf02eaa409196291a8ff6878.jpg" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 316, + 416, + 410, + 425 + ], + "lines": [ + { + "bbox": [ + 316, + 416, + 410, + 425 + ], + "spans": [ + { + "bbox": [ + 316, + 416, + 410, + 425 + ], + "type": "text", + "content": "(c) Human skeleton motion" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 438, + 416, + 526, + 426 + ], + "lines": [ + { + "bbox": [ + 438, + 416, + 526, + 426 + ], + "spans": [ + { + "bbox": [ + 438, + 416, + 526, + 426 + ], + "type": "text", + "content": "(d) Pedestrian trajectories" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 305, + 426, + 547, + 470 + ], + "lines": [ + { + "bbox": [ + 305, + 426, + 547, + 470 + ], + "spans": [ + { + "bbox": [ + 305, + 426, + 547, + 470 + ], + "type": "text", + "content": "Figure 1. Motion equivariance and interaction invariance under the Euclidean geometric transformation is a fundamental principle for a prediction model, but this principle is often overlooked by previous works. In this work, we propose EqMotion to fill this gap." + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_caption" + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 482, + 547, + 613 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 482, + 547, + 613 + ], + "spans": [ + { + "bbox": [ + 304, + 482, + 547, + 613 + ], + "type": "text", + "content": "often-overlooked yet fundamental principle is that a prediction model is required to be equivariant under the Euclidean geometric transformation (including translation, rotation and reflection), and at the same time maintain the interaction relationships invariant. Motion equivariance here means that if an input motion is transformed under a Euclidean transformation, the output motion must be equally transformed under the same transformation. Interaction invariance means that the way agents interact remains unchanged under the input's transformation. Figure 1 shows real-world examples of motion equivariance and interaction invariance." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 616, + 547, + 700 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 616, + 547, + 700 + ], + "spans": [ + { + "bbox": [ + 304, + 616, + 547, + 700 + ], + "type": "text", + "content": "Employing this principle in a network design brings at least two benefits. First, the network will be robust to arbitrary Euclidean transformations. Second, the network will have the capability of being generalizable over rotations and translations of the data. This capability makes the network more compact, reducing the network's learning burden and contributing to a more accurate prediction." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 317, + 701, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 701, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 317, + 701, + 545, + 714 + ], + "type": "text", + "content": "Despite the motion equivariance property being important" + } + ] + } + ], + "index": 18 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 494, + 37 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 702, + 135, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 702, + 135, + 712 + ], + "spans": [ + { + "bbox": [ + 58, + 702, + 135, + 712 + ], + "type": "text", + "content": "*Corresponding author." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "text", + "content": "1410" + } + ] + } + ], + "index": 20 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 289, + 312 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 289, + 312 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 289, + 312 + ], + "type": "text", + "content": "and fundamental, it is often neglected and not guaranteed by most existing motion prediction methods. The main reason is that these methods transform the input motion sequence directly into abstract feature vectors, where the geometric transformations are not traceable, causing the geometric relationships between agents to be irretrievable. Random augmentation will ease the equivariance problem, but it is still unable to guarantee the equivariance property. [30] uses non-parametric pre and post coordinate processing to achieve equivariance, but its parametric network structures do not satisfy equivariance. Some methods propose equivariant parametric network structures utilizing the higher-order representations of spherical harmonics [14, 61] or proposing an equivariant message passing [58], but they focus on the state-to-state prediction. This means that they use only one historical timestamp to predict one future timestamp. Consequently, these methods have limitations on utilizing motion's temporal information and modeling interaction relationships since a single-state observation is insufficient for both interaction modeling and temporal dependency modeling." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 314, + 289, + 529 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 314, + 289, + 529 + ], + "spans": [ + { + "bbox": [ + 47, + 314, + 289, + 529 + ], + "type": "text", + "content": "In this paper, we propose EqMotion, the first motion prediction model that is theoretically equivariant to the input motion under Euclidean geometric transformations based on the parametric network. The proposed EqMotion has three novel designs: equivariant geometric feature learning, invariant pattern feature learning and invariant interaction reasoning. To ensure motion equivariance, we propose an equivariant geometric feature learning module to learn a Euclidean transformable geometric feature through dedicated designs of equivariant operations. The geometric feature preserves motion attributes that are relevant to Euclidean transformations. To promote more comprehensive representation power, we introduce an invariant pattern feature learning module to complement the network with motion attributes that are independent of Euclidean transformations. The pattern features, cooperated into the geometric features, provide expressive motion representations by exploiting motions' spatial-temporal dependencies." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 531, + 289, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 531, + 289, + 628 + ], + "spans": [ + { + "bbox": [ + 47, + 531, + 289, + 628 + ], + "type": "text", + "content": "To further infer the interactions during motion prediction, we propose an invariant interaction reasoning module, which ensures that the captured interaction relationships are invariant to the input motion under Euclidean transformations. The module infers an invariant interaction graph by utilizing invariant factors in motions. The edge weights in the interaction graph categorize agents' interactions into different types, leading to better interaction representation." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 630, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 630, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 47, + 630, + 289, + 715 + ], + "type": "text", + "content": "We conduct extensive experiments on four different scenarios to evaluate our method's effectiveness: particle dynamics, molecule dynamics, 3D human skeleton motion and pedestrian trajectories. Comparing to many task-specific motion prediction methods, our method is generally applicable and achieves state-of-the-art performance in all these tasks by reducing the prediction error by " + }, + { + "bbox": [ + 47, + 630, + 289, + 715 + ], + "type": "inline_equation", + "content": "24.0 / 30.1 / 8.6 / 9.2\\%" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 304, + 72, + 547, + 133 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 133 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 133 + ], + "type": "text", + "content": "respectively. We also present that EqMotion is lightweight, and has a model size less than " + }, + { + "bbox": [ + 304, + 72, + 547, + 133 + ], + "type": "inline_equation", + "content": "30\\%" + }, + { + "bbox": [ + 304, + 72, + 547, + 133 + ], + "type": "text", + "content": " of many other models' sizes. We show that EqMotion using only " + }, + { + "bbox": [ + 304, + 72, + 547, + 133 + ], + "type": "inline_equation", + "content": "5\\%" + }, + { + "bbox": [ + 304, + 72, + 547, + 133 + ], + "type": "text", + "content": " data can achieve a comparable performance with other methods that take full data. As a summary, here are our contributions:" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 133, + 547, + 312 + ], + "type": "list", + "angle": 0, + "index": 8, + "blocks": [ + { + "bbox": [ + 304, + 133, + 547, + 204 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 133, + 547, + 204 + ], + "spans": [ + { + "bbox": [ + 304, + 133, + 547, + 204 + ], + "type": "text", + "content": "- We propose EqMotion, the first motion prediction model that theoretically ensures sequence-to-sequence motion equivariance based on the parametric network. With equivariance, EqMotion promotes more generalization ability of motion feature learning, leading to more robust and accurate prediction." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 205, + 547, + 265 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 205, + 547, + 265 + ], + "spans": [ + { + "bbox": [ + 304, + 205, + 547, + 265 + ], + "type": "text", + "content": "- We propose a novel invariant interaction reasoning module, in which the captured interactions between agents are invariant to the input motion under Euclidean geometric transformations. With this, EqMotion achieves more generalization ability and stability in the interaction reasoning." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 265, + 547, + 312 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 265, + 547, + 312 + ], + "spans": [ + { + "bbox": [ + 304, + 265, + 547, + 312 + ], + "type": "text", + "content": "- We conduct experiments on four types of scenarios and find that EqMotion is applicable to all these different tasks, and importantly outperforms existing state-of-the-art methods on all the tasks." + } + ] + } + ], + "index": 7 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 306, + 324, + 392, + 337 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 324, + 392, + 337 + ], + "spans": [ + { + "bbox": [ + 306, + 324, + 392, + 337 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 342, + 548, + 665 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 342, + 548, + 665 + ], + "spans": [ + { + "bbox": [ + 304, + 342, + 548, + 665 + ], + "type": "text", + "content": "Equivariant Networks. Equivariance first draws high attention on the 2D image domain. Since CNN structure is sensitive to rotations, researchers start to explore rotation-equivariant designs like oriented convolutional filters [8,49], log-polar transform [11], circular harmonics [67] or steerable filters [66]. Meanwhile, GNN architectures [73-75] exploring symmetries on both rotation and translation have been emerged. Specifically, [57, 62] achieves partial symmetries by promoting translation equivariance. [14, 61] builds filters using spherical harmonics allowing transformations between high-order representations, achieving the rotation and translation equivariance. [12, 24] construct a Lie convolution to parameterize transformations into Lie algebra form. [10] proposes a series of equivariant layers for point cloud networks. [27] propose geometric vector perceptions for protein structure learning. Recently, EGNN [58] proposes a simple equivariant message passing form without using computationally expensive high-order representations. [23] further extends it by considering geometrical constraints. However, most existing methods are only applicable to state prediction, limiting models from exploiting sequence information. [30] uses pre and post coordinate processing to achieve motion equivariance but its network structure does not satisfy equivariance. In this work, we propose an equivariant model based on the parametric network which is generally applicable to motion prediction tasks and achieves a more precise prediction." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 665, + 548, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 548, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 548, + 715 + ], + "type": "text", + "content": "Motion Prediction. Motion prediction has wide application scenarios. [3, 53, 56] proposes graph neural networks for learning to simulate complex physical systems. [17, 28, 37, 71] both explicitly infer the interactions rela" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 296, + 748, + 315, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 748, + 315, + 758 + ], + "spans": [ + { + "bbox": [ + 296, + 748, + 315, + 758 + ], + "type": "text", + "content": "1411" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 335 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 335 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 335 + ], + "type": "text", + "content": "tionships and perform prediction in physical systems. For human or vehicle trajectory prediction, social forces [21, 51], Markov [29, 65] process, and RNNs [1, 52, 63] are first methods to employ. Multi-model prediction methods are further proposed like using generator-discriminator structures [20, 22], multi-head output [43, 59], conditional variational autoencoders [32, 45, 55, 69, 71, 72, 76], memory mechanisms [48, 70], Gaussian mixture distribution prediction [17, 37]. The HD map information is specifically considered in the autonomous driving scenario [5, 6, 15, 22, 42, 43, 77]. For 3D human skeleton motion prediction, early methods are based on the state prediction [33, 60]. Later RNN-based models considering the sequential motion states are proposed [13, 26, 50, 64]. [19, 36] use spatial graph convolutions to directly regress the whole sequences. Besides, some methods [4, 40, 46, 47] specifically exploit the correlations between body joints. Multi-scale graphs are built by [9, 39, 41] to capture different body-level dependencies. In this work, we propose a generally applicable motion prediction network which promotes Euclidean equivariance, a fundamental property but neglected by previous methods, to have a more robust and accurate prediction." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 342, + 261, + 355 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 342, + 261, + 355 + ], + "spans": [ + { + "bbox": [ + 47, + 342, + 261, + 355 + ], + "type": "text", + "content": "3. Background and Problem Formulation" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 358, + 155, + 370 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 358, + 155, + 370 + ], + "spans": [ + { + "bbox": [ + 47, + 358, + 155, + 370 + ], + "type": "text", + "content": "3.1. Motion Prediction" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 374, + 289, + 558 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 374, + 289, + 558 + ], + "spans": [ + { + "bbox": [ + 46, + 374, + 289, + 558 + ], + "type": "text", + "content": "Here we introduce the general problem formulation of motion prediction, which aims to generate future motions given the historical observations. Mathematically, consider " + }, + { + "bbox": [ + 46, + 374, + 289, + 558 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 46, + 374, + 289, + 558 + ], + "type": "text", + "content": " agents in a multi-agent system. Let " + }, + { + "bbox": [ + 46, + 374, + 289, + 558 + ], + "type": "inline_equation", + "content": "\\mathbf{X}_i = [\\mathbf{x}_i^1,\\mathbf{x}_i^2,\\dots \\mathbf{x}_i^{T_{\\mathrm{p}}}]\\in" + }, + { + "bbox": [ + 46, + 374, + 289, + 558 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^{T_{\\mathrm{p}}\\times n}" + }, + { + "bbox": [ + 46, + 374, + 289, + 558 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 374, + 289, + 558 + ], + "type": "inline_equation", + "content": "\\mathbf{Y}_i = [\\mathbf{y}_i^1,\\mathbf{y}_i^2,\\dots \\mathbf{y}_i^{T_{\\mathrm{f}}}]\\in \\mathbb{R}^{T_{\\mathrm{f}}\\times n}" + }, + { + "bbox": [ + 46, + 374, + 289, + 558 + ], + "type": "text", + "content": " be the ith agent's past and future motion, where " + }, + { + "bbox": [ + 46, + 374, + 289, + 558 + ], + "type": "inline_equation", + "content": "T_{\\mathrm{p}}" + }, + { + "bbox": [ + 46, + 374, + 289, + 558 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 374, + 289, + 558 + ], + "type": "inline_equation", + "content": "T_{\\mathrm{f}}" + }, + { + "bbox": [ + 46, + 374, + 289, + 558 + ], + "type": "text", + "content": " are the past and future timestamps and " + }, + { + "bbox": [ + 46, + 374, + 289, + 558 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 46, + 374, + 289, + 558 + ], + "type": "text", + "content": " is the dimension of the system space. " + }, + { + "bbox": [ + 46, + 374, + 289, + 558 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 46, + 374, + 289, + 558 + ], + "type": "text", + "content": " usually equals to 2 or 3 (corresponding to 2D or 3D case). The " + }, + { + "bbox": [ + 46, + 374, + 289, + 558 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 374, + 289, + 558 + ], + "type": "text", + "content": "th timestamp locations " + }, + { + "bbox": [ + 46, + 374, + 289, + 558 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_i^t" + }, + { + "bbox": [ + 46, + 374, + 289, + 558 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 374, + 289, + 558 + ], + "type": "inline_equation", + "content": "\\mathbf{y}_i^t" + }, + { + "bbox": [ + 46, + 374, + 289, + 558 + ], + "type": "text", + "content": " are " + }, + { + "bbox": [ + 46, + 374, + 289, + 558 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 46, + 374, + 289, + 558 + ], + "type": "text", + "content": " dimension vectors. The whole system's past and future motion is represented as " + }, + { + "bbox": [ + 46, + 374, + 289, + 558 + ], + "type": "inline_equation", + "content": "\\mathbb{X} = [\\mathbf{X}_1,\\mathbf{X}_2,\\dots ,\\mathbf{X}_M]\\in \\mathbb{R}^{M\\times T_{\\mathrm{p}}\\times n}" + }, + { + "bbox": [ + 46, + 374, + 289, + 558 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 374, + 289, + 558 + ], + "type": "inline_equation", + "content": "\\mathbb{Y} = [\\mathbf{Y}_1,\\mathbf{Y}_2,\\dots ,\\mathbf{Y}_M]\\in \\mathbb{R}^{M\\times T_{\\mathrm{f}}\\times n}" + }, + { + "bbox": [ + 46, + 374, + 289, + 558 + ], + "type": "text", + "content": ". We aim to propose a prediction network " + }, + { + "bbox": [ + 46, + 374, + 289, + 558 + ], + "type": "inline_equation", + "content": "\\mathcal{F}_{\\mathrm{pred}}(\\cdot)" + }, + { + "bbox": [ + 46, + 374, + 289, + 558 + ], + "type": "text", + "content": " so that the predicted future motions " + }, + { + "bbox": [ + 46, + 374, + 289, + 558 + ], + "type": "inline_equation", + "content": "\\widehat{\\mathbb{Y}} = \\mathcal{F}_{\\mathrm{pred}}(\\mathbb{X})" + }, + { + "bbox": [ + 46, + 374, + 289, + 558 + ], + "type": "text", + "content": " are as close to the ground-truth future motions " + }, + { + "bbox": [ + 46, + 374, + 289, + 558 + ], + "type": "inline_equation", + "content": "\\mathbb{Y}" + }, + { + "bbox": [ + 46, + 374, + 289, + 558 + ], + "type": "text", + "content": " as possible." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 563, + 206, + 575 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 563, + 206, + 575 + ], + "spans": [ + { + "bbox": [ + 47, + 563, + 206, + 575 + ], + "type": "text", + "content": "3.2. Equivariance and Invariance" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 578, + 288, + 662 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 578, + 288, + 662 + ], + "spans": [ + { + "bbox": [ + 46, + 578, + 288, + 662 + ], + "type": "text", + "content": "The Euclidean geometric transformation has three basic forms: translation, rotation and reflection. The translation is modeled by a translation vector and rotation (or reflection) is modeled by an orthogonal rotation (or reflection) matrix. Let " + }, + { + "bbox": [ + 46, + 578, + 288, + 662 + ], + "type": "inline_equation", + "content": "\\mathbf{t} \\in \\mathbb{R}^n" + }, + { + "bbox": [ + 46, + 578, + 288, + 662 + ], + "type": "text", + "content": " be a translation vector and " + }, + { + "bbox": [ + 46, + 578, + 288, + 662 + ], + "type": "inline_equation", + "content": "\\mathbf{R} \\in \\mathrm{SO}(n)" + }, + { + "bbox": [ + 46, + 578, + 288, + 662 + ], + "type": "text", + "content": " be a " + }, + { + "bbox": [ + 46, + 578, + 288, + 662 + ], + "type": "inline_equation", + "content": "n \\times n" + }, + { + "bbox": [ + 46, + 578, + 288, + 662 + ], + "type": "text", + "content": " rotation matrix, we have the following definitions for equivariance and invariance:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 663, + 288, + 700 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 663, + 288, + 700 + ], + "spans": [ + { + "bbox": [ + 46, + 663, + 288, + 700 + ], + "type": "text", + "content": "Definition 1 Let " + }, + { + "bbox": [ + 46, + 663, + 288, + 700 + ], + "type": "inline_equation", + "content": "\\mathbb{X}" + }, + { + "bbox": [ + 46, + 663, + 288, + 700 + ], + "type": "text", + "content": " be an input, " + }, + { + "bbox": [ + 46, + 663, + 288, + 700 + ], + "type": "inline_equation", + "content": "\\mathcal{F}(\\cdot)" + }, + { + "bbox": [ + 46, + 663, + 288, + 700 + ], + "type": "text", + "content": " be an operation and " + }, + { + "bbox": [ + 46, + 663, + 288, + 700 + ], + "type": "inline_equation", + "content": "\\mathbb{Z} = \\mathcal{F}(\\mathbb{X})" + }, + { + "bbox": [ + 46, + 663, + 288, + 700 + ], + "type": "text", + "content": " be the corresponding output. The operation " + }, + { + "bbox": [ + 46, + 663, + 288, + 700 + ], + "type": "inline_equation", + "content": "\\mathcal{F}(\\cdot)" + }, + { + "bbox": [ + 46, + 663, + 288, + 700 + ], + "type": "text", + "content": " is called equivariant under Euclidean transformation if" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 63, + 700, + 270, + 714 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 63, + 700, + 270, + 714 + ], + "spans": [ + { + "bbox": [ + 63, + 700, + 270, + 714 + ], + "type": "interline_equation", + "content": "\\mathbb {Z} \\mathbf {R} + \\mathbf {t} = \\mathcal {F} (\\mathbb {X} \\mathbf {R} + \\mathbf {t}) \\quad \\forall \\mathbf {R} \\in \\mathrm {S O} (n), \\forall \\mathbf {t} \\in \\mathbb {R} ^ {n}.", + "image_path": "5ad9f38e1d064569698ebdcdb22154e6808157639f360ee4e407317bae408e44.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 73, + 547, + 110 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 73, + 547, + 110 + ], + "spans": [ + { + "bbox": [ + 304, + 73, + 547, + 110 + ], + "type": "text", + "content": "Definition 2 Let " + }, + { + "bbox": [ + 304, + 73, + 547, + 110 + ], + "type": "inline_equation", + "content": "\\mathbb{X}" + }, + { + "bbox": [ + 304, + 73, + 547, + 110 + ], + "type": "text", + "content": " be an input, " + }, + { + "bbox": [ + 304, + 73, + 547, + 110 + ], + "type": "inline_equation", + "content": "\\mathcal{F}(\\cdot)" + }, + { + "bbox": [ + 304, + 73, + 547, + 110 + ], + "type": "text", + "content": " be an operation and " + }, + { + "bbox": [ + 304, + 73, + 547, + 110 + ], + "type": "inline_equation", + "content": "\\mathbb{Z} = \\mathcal{F}(\\mathbb{X})" + }, + { + "bbox": [ + 304, + 73, + 547, + 110 + ], + "type": "text", + "content": " be the corresponding output. The operation " + }, + { + "bbox": [ + 304, + 73, + 547, + 110 + ], + "type": "inline_equation", + "content": "\\mathcal{F}(\\cdot)" + }, + { + "bbox": [ + 304, + 73, + 547, + 110 + ], + "type": "text", + "content": " is called invariant under Euclidean transformation if" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 335, + 111, + 515, + 124 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 335, + 111, + 515, + 124 + ], + "spans": [ + { + "bbox": [ + 335, + 111, + 515, + 124 + ], + "type": "interline_equation", + "content": "\\mathbb {Z} = \\mathcal {F} (\\mathbb {X} \\mathbf {R} + \\mathbf {t}) \\quad \\forall \\mathbf {R} \\in \\mathrm {S O} (n), \\forall \\mathbf {t} \\in \\mathbb {R} ^ {n}.", + "image_path": "357c7c9cb9d6cc5ed0f0502a9ea26a74baefc5a2067c05329a8952eb235b4cf6.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 127, + 547, + 198 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 127, + 547, + 198 + ], + "spans": [ + { + "bbox": [ + 304, + 127, + 547, + 198 + ], + "type": "text", + "content": "Here, when a motion prediction network " + }, + { + "bbox": [ + 304, + 127, + 547, + 198 + ], + "type": "inline_equation", + "content": "\\mathcal{F}_{\\mathrm{pred}}(\\cdot)" + }, + { + "bbox": [ + 304, + 127, + 547, + 198 + ], + "type": "text", + "content": " satisfies Definition 1, " + }, + { + "bbox": [ + 304, + 127, + 547, + 198 + ], + "type": "inline_equation", + "content": "\\mathcal{F}_{\\mathrm{pred}}(\\cdot)" + }, + { + "bbox": [ + 304, + 127, + 547, + 198 + ], + "type": "text", + "content": " is said motion equivariant. When an interaction reasoning model " + }, + { + "bbox": [ + 304, + 127, + 547, + 198 + ], + "type": "inline_equation", + "content": "\\mathcal{F}_{\\mathrm{reason}}(\\cdot)" + }, + { + "bbox": [ + 304, + 127, + 547, + 198 + ], + "type": "text", + "content": " satisfies Definition 2, " + }, + { + "bbox": [ + 304, + 127, + 547, + 198 + ], + "type": "inline_equation", + "content": "\\mathcal{F}_{\\mathrm{reason}}(\\cdot)" + }, + { + "bbox": [ + 304, + 127, + 547, + 198 + ], + "type": "text", + "content": " is considered interaction invariant. We also say the output " + }, + { + "bbox": [ + 304, + 127, + 547, + 198 + ], + "type": "inline_equation", + "content": "\\mathbb{Z}" + }, + { + "bbox": [ + 304, + 127, + 547, + 198 + ], + "type": "text", + "content": " is equivariant/invariant (to the input motion under Euclidean transformation) if Definition 1/2 is satisfied." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 199, + 547, + 258 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 199, + 547, + 258 + ], + "spans": [ + { + "bbox": [ + 304, + 199, + 547, + 258 + ], + "type": "text", + "content": "In the following section, we will introduce our motion prediction network along with geometric features that are equivariant under Euclidean transformations, and pattern features along with the interaction reasoning module are invariant under Euclidean transformations." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 270, + 388, + 283 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 270, + 388, + 283 + ], + "spans": [ + { + "bbox": [ + 305, + 270, + 388, + 283 + ], + "type": "text", + "content": "4. Methodology" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 287, + 547, + 407 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 287, + 547, + 407 + ], + "spans": [ + { + "bbox": [ + 304, + 287, + 547, + 407 + ], + "type": "text", + "content": "In this section, we present EqMotion, a motion prediction network which is equivariant under Euclidean geometric transformations. The whole network architecture is shown in Figure 2. The core of EqMotion is to successively learn equivariant geometric features and invariant pattern features by mutual cooperation in designed equivariant/invariant operations, which not only provide expressive motion and interaction representations, but also preserve equivariant/invariant properties. For agents' motions " + }, + { + "bbox": [ + 304, + 287, + 547, + 407 + ], + "type": "inline_equation", + "content": "\\mathbb{X} \\in \\mathbb{R}^{M \\times T_{\\mathrm{p}} \\times n}" + }, + { + "bbox": [ + 304, + 287, + 547, + 407 + ], + "type": "text", + "content": ", the overall procedure of the proposed EqMotion is formulated as" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 349, + 407, + 545, + 420 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 349, + 407, + 545, + 420 + ], + "spans": [ + { + "bbox": [ + 349, + 407, + 545, + 420 + ], + "type": "interline_equation", + "content": "\\mathbb {G} ^ {(0)}, \\mathbf {H} ^ {(0)} = \\mathcal {F} _ {\\mathrm {I L}} (\\mathbb {X}), \\tag {1a}", + "image_path": "2f53b7dca1ab3cb989d1e180fe47847ce69970c50dc1991b6cc985a457af6ea4.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 350, + 423, + 545, + 438 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 350, + 423, + 545, + 438 + ], + "spans": [ + { + "bbox": [ + 350, + 423, + 545, + 438 + ], + "type": "interline_equation", + "content": "\\left\\{\\mathbf {c} _ {i j} \\right\\} = \\mathcal {F} _ {\\mathrm {I R M}} \\left(\\mathbb {G} ^ {(0)}, \\mathbf {H} ^ {(0)}\\right), \\tag {1b}", + "image_path": "b4b5cd5d72cea632ba2713bae648236536ce41da073c93b344adb96c34504645.jpg" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 350, + 441, + 545, + 456 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 350, + 441, + 545, + 456 + ], + "spans": [ + { + "bbox": [ + 350, + 441, + 545, + 456 + ], + "type": "interline_equation", + "content": "\\mathbb {G} ^ {(\\ell + 1)} = \\mathcal {F} _ {\\mathrm {E G F L}} ^ {(\\ell)} \\left(\\mathbb {G} ^ {(\\ell)}, \\mathbf {H} ^ {(\\ell)}, \\left\\{\\mathbf {c} _ {i j} \\right\\}\\right), \\tag {1c}", + "image_path": "be7bf9951695bdf2c30fe31bf928fbd83c13df07c7228896142e431149a8e7d3.jpg" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 350, + 458, + 545, + 475 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 350, + 458, + 545, + 475 + ], + "spans": [ + { + "bbox": [ + 350, + 458, + 545, + 475 + ], + "type": "interline_equation", + "content": "\\mathbf {H} ^ {(\\ell + 1)} = \\mathcal {F} _ {\\mathrm {I P F L}} ^ {(\\ell)} \\left(\\mathbb {G} ^ {(\\ell)}, \\mathbf {H} ^ {(\\ell)}\\right), \\tag {1d}", + "image_path": "9b22af720103d8069293801146ad1662132a80dd8d1509deafa865e659e2c67e.jpg" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 350, + 476, + 545, + 491 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 350, + 476, + 545, + 491 + ], + "spans": [ + { + "bbox": [ + 350, + 476, + 545, + 491 + ], + "type": "interline_equation", + "content": "\\widehat {\\mathbb {Y}} = \\mathcal {F} _ {\\mathrm {E O L}} \\left(\\mathbb {G} ^ {(L)}\\right). \\tag {1e}", + "image_path": "9643bf46355bf30ff4830a6810eb7ae8c99596a963b8243e15b6d0dc79a1276f.jpg" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 492, + 547, + 639 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 492, + 547, + 639 + ], + "spans": [ + { + "bbox": [ + 304, + 492, + 547, + 639 + ], + "type": "text", + "content": "Step (1a) uses an initialization layer " + }, + { + "bbox": [ + 304, + 492, + 547, + 639 + ], + "type": "inline_equation", + "content": "\\mathcal{F}_{\\mathrm{IL}}(\\cdot)" + }, + { + "bbox": [ + 304, + 492, + 547, + 639 + ], + "type": "text", + "content": " to obtain initial geometric features " + }, + { + "bbox": [ + 304, + 492, + 547, + 639 + ], + "type": "inline_equation", + "content": "\\mathbb{G}^{(0)}" + }, + { + "bbox": [ + 304, + 492, + 547, + 639 + ], + "type": "text", + "content": " and pattern features " + }, + { + "bbox": [ + 304, + 492, + 547, + 639 + ], + "type": "inline_equation", + "content": "\\mathbf{H}^{(0)}" + }, + { + "bbox": [ + 304, + 492, + 547, + 639 + ], + "type": "text", + "content": ". For interaction relationship unavailable cases, Step (1b) uses an invariant interaction reasoning module " + }, + { + "bbox": [ + 304, + 492, + 547, + 639 + ], + "type": "inline_equation", + "content": "\\mathcal{F}_{\\mathrm{IRM}}(\\cdot)" + }, + { + "bbox": [ + 304, + 492, + 547, + 639 + ], + "type": "text", + "content": " to infer an interaction graph " + }, + { + "bbox": [ + 304, + 492, + 547, + 639 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{c}_{ij}\\}" + }, + { + "bbox": [ + 304, + 492, + 547, + 639 + ], + "type": "text", + "content": " whose edge weight " + }, + { + "bbox": [ + 304, + 492, + 547, + 639 + ], + "type": "inline_equation", + "content": "\\mathbf{c}_{ij}" + }, + { + "bbox": [ + 304, + 492, + 547, + 639 + ], + "type": "text", + "content": " is the interaction category between agent " + }, + { + "bbox": [ + 304, + 492, + 547, + 639 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 304, + 492, + 547, + 639 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 492, + 547, + 639 + ], + "type": "inline_equation", + "content": "j" + }, + { + "bbox": [ + 304, + 492, + 547, + 639 + ], + "type": "text", + "content": ". Step (1c) uses the " + }, + { + "bbox": [ + 304, + 492, + 547, + 639 + ], + "type": "inline_equation", + "content": "\\ell" + }, + { + "bbox": [ + 304, + 492, + 547, + 639 + ], + "type": "text", + "content": "th equivariant geometric feature learning layer " + }, + { + "bbox": [ + 304, + 492, + 547, + 639 + ], + "type": "inline_equation", + "content": "\\mathcal{F}_{\\mathrm{EGFL}}^{(\\ell)}(\\cdot)" + }, + { + "bbox": [ + 304, + 492, + 547, + 639 + ], + "type": "text", + "content": " to learn the " + }, + { + "bbox": [ + 304, + 492, + 547, + 639 + ], + "type": "inline_equation", + "content": "(\\ell + 1)" + }, + { + "bbox": [ + 304, + 492, + 547, + 639 + ], + "type": "text", + "content": "th geometric feature " + }, + { + "bbox": [ + 304, + 492, + 547, + 639 + ], + "type": "inline_equation", + "content": "\\mathbb{G}^{(\\ell + 1)}" + }, + { + "bbox": [ + 304, + 492, + 547, + 639 + ], + "type": "text", + "content": ". Step (1d) uses the " + }, + { + "bbox": [ + 304, + 492, + 547, + 639 + ], + "type": "inline_equation", + "content": "\\ell" + }, + { + "bbox": [ + 304, + 492, + 547, + 639 + ], + "type": "text", + "content": "th invariant pattern feature learning layer " + }, + { + "bbox": [ + 304, + 492, + 547, + 639 + ], + "type": "inline_equation", + "content": "\\mathcal{F}_{\\mathrm{IPFL}}^{(\\ell)}(\\cdot)" + }, + { + "bbox": [ + 304, + 492, + 547, + 639 + ], + "type": "text", + "content": " to learn the " + }, + { + "bbox": [ + 304, + 492, + 547, + 639 + ], + "type": "inline_equation", + "content": "(\\ell + 1)" + }, + { + "bbox": [ + 304, + 492, + 547, + 639 + ], + "type": "text", + "content": "th pattern feature " + }, + { + "bbox": [ + 304, + 492, + 547, + 639 + ], + "type": "inline_equation", + "content": "\\mathbf{H}^{(\\ell + 1)}" + }, + { + "bbox": [ + 304, + 492, + 547, + 639 + ], + "type": "text", + "content": ". Step (1c) and Step (1d) will repeat " + }, + { + "bbox": [ + 304, + 492, + 547, + 639 + ], + "type": "inline_equation", + "content": "L" + }, + { + "bbox": [ + 304, + 492, + 547, + 639 + ], + "type": "text", + "content": " times. Step (1e) uses an equivariant output layer " + }, + { + "bbox": [ + 304, + 492, + 547, + 639 + ], + "type": "inline_equation", + "content": "\\mathcal{F}_{\\mathrm{EOL}}(\\cdot)" + }, + { + "bbox": [ + 304, + 492, + 547, + 639 + ], + "type": "text", + "content": " to obtain the final prediction " + }, + { + "bbox": [ + 304, + 492, + 547, + 639 + ], + "type": "inline_equation", + "content": "\\widehat{\\mathbb{Y}}" + }, + { + "bbox": [ + 304, + 492, + 547, + 639 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 639, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 639, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 639, + 547, + 713 + ], + "type": "text", + "content": "Note that i) to incorporate the geometric feature's equivariance, we need to design equivariant operations for the initialization layer " + }, + { + "bbox": [ + 304, + 639, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{F}_{\\mathrm{IL}}(\\cdot)" + }, + { + "bbox": [ + 304, + 639, + 547, + 713 + ], + "type": "text", + "content": " and the equivariant geometric feature learning layer " + }, + { + "bbox": [ + 304, + 639, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{F}_{\\mathrm{EGFL}}^{(\\ell)}(\\cdot)" + }, + { + "bbox": [ + 304, + 639, + 547, + 713 + ], + "type": "text", + "content": "; ii) to introduce the pattern feature's invariance, we need to design invariant operations for the initialization layer " + }, + { + "bbox": [ + 304, + 639, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{F}_{\\mathrm{IL}}(\\cdot)" + }, + { + "bbox": [ + 304, + 639, + 547, + 713 + ], + "type": "text", + "content": " and the invariant pattern feature" + } + ] + } + ], + "index": 20 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "text", + "content": "1412" + } + ] + } + ], + "index": 21 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 56, + 69, + 537, + 157 + ], + "blocks": [ + { + "bbox": [ + 56, + 69, + 537, + 157 + ], + "lines": [ + { + "bbox": [ + 56, + 69, + 537, + 157 + ], + "spans": [ + { + "bbox": [ + 56, + 69, + 537, + 157 + ], + "type": "image", + "image_path": "c33d300b2f93111391dc484f51e09a89defc2f12477aaf4000742040a246196e.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 157, + 547, + 201 + ], + "lines": [ + { + "bbox": [ + 46, + 157, + 547, + 201 + ], + "spans": [ + { + "bbox": [ + 46, + 157, + 547, + 201 + ], + "type": "text", + "content": "Figure 2. EqMotion architecture. In EqMotion, we first use a feature initialization layer to initialize geometric features and pattern features. We then successively update the geometric features and the pattern features by the equivariant geometric feature learning and invariant pattern feature learning layers, obtaining expressive feature representation. We further propose an invariant reasoning module to infer an interaction graph used in equivariant geometric feature learning. Finally, we use an equivariant output layer to obtain the final prediction." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 213, + 289, + 275 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 213, + 289, + 275 + ], + "spans": [ + { + "bbox": [ + 46, + 213, + 289, + 275 + ], + "type": "text", + "content": "learning layer " + }, + { + "bbox": [ + 46, + 213, + 289, + 275 + ], + "type": "inline_equation", + "content": "\\mathcal{F}_{\\mathrm{IPFL}}^{(\\ell)}(\\cdot)" + }, + { + "bbox": [ + 46, + 213, + 289, + 275 + ], + "type": "text", + "content": "; and iii) the interaction graph categorizes agent's spatial interaction into different categories for better interaction representing. The interaction graph is invariant due to the reasoning module " + }, + { + "bbox": [ + 46, + 213, + 289, + 275 + ], + "type": "inline_equation", + "content": "\\mathcal{F}_{\\mathrm{IRM}}(\\cdot)" + }, + { + "bbox": [ + 46, + 213, + 289, + 275 + ], + "type": "text", + "content": " design. In subsequent sections, we elaborate the details of each step." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 282, + 168, + 294 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 282, + 168, + 294 + ], + "spans": [ + { + "bbox": [ + 47, + 282, + 168, + 294 + ], + "type": "text", + "content": "4.1. Feature Initialization" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 298, + 289, + 421 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 298, + 289, + 421 + ], + "spans": [ + { + "bbox": [ + 46, + 298, + 289, + 421 + ], + "type": "text", + "content": "The feature initialization layer aims to obtain initial geometric features and pattern features while equipping them with different functionality. The initial geometric feature is denoted as " + }, + { + "bbox": [ + 46, + 298, + 289, + 421 + ], + "type": "inline_equation", + "content": "\\mathbb{G}^{(0)} = [\\mathbf{G}_1^{(0)},\\dots ,\\mathbf{G}_M^{(0)}]\\in \\mathbb{R}^{M\\times C\\times n}" + }, + { + "bbox": [ + 46, + 298, + 289, + 421 + ], + "type": "text", + "content": " whose " + }, + { + "bbox": [ + 46, + 298, + 289, + 421 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 298, + 289, + 421 + ], + "type": "text", + "content": "th agent's geometric feature consists of " + }, + { + "bbox": [ + 46, + 298, + 289, + 421 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 46, + 298, + 289, + 421 + ], + "type": "text", + "content": " geometric coordinates. The initial pattern feature is denoted as " + }, + { + "bbox": [ + 46, + 298, + 289, + 421 + ], + "type": "inline_equation", + "content": "\\mathbf{H}^{(0)} = [\\mathbf{h}_1^{(0)},\\dots ,\\mathbf{h}_M^{(0)}]\\in \\mathbb{R}^{M\\times D}" + }, + { + "bbox": [ + 46, + 298, + 289, + 421 + ], + "type": "text", + "content": " whose " + }, + { + "bbox": [ + 46, + 298, + 289, + 421 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 298, + 289, + 421 + ], + "type": "text", + "content": "th agent's pattern feature is a " + }, + { + "bbox": [ + 46, + 298, + 289, + 421 + ], + "type": "inline_equation", + "content": "D" + }, + { + "bbox": [ + 46, + 298, + 289, + 421 + ], + "type": "text", + "content": " -dimensional vector. Given the past motions " + }, + { + "bbox": [ + 46, + 298, + 289, + 421 + ], + "type": "inline_equation", + "content": "\\mathbb{X}" + }, + { + "bbox": [ + 46, + 298, + 289, + 421 + ], + "type": "text", + "content": " whose the " + }, + { + "bbox": [ + 46, + 298, + 289, + 421 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 298, + 289, + 421 + ], + "type": "text", + "content": "th agent's motion is " + }, + { + "bbox": [ + 46, + 298, + 289, + 421 + ], + "type": "inline_equation", + "content": "\\mathbf{X}_i\\in \\mathbb{R}^{T_{\\mathrm{p}}\\times n}" + }, + { + "bbox": [ + 46, + 298, + 289, + 421 + ], + "type": "text", + "content": ", we obtain two initial features of the " + }, + { + "bbox": [ + 46, + 298, + 289, + 421 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 298, + 289, + 421 + ], + "type": "text", + "content": "th agent:" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 65, + 422, + 190, + 437 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 422, + 190, + 437 + ], + "spans": [ + { + "bbox": [ + 65, + 422, + 190, + 437 + ], + "type": "interline_equation", + "content": "\\mathbf {G} _ {i} ^ {(0)} = \\phi_ {\\mathrm {i n i t \\_ g}} (\\mathbf {X} _ {i} - \\overline {{\\mathbb {X}}}) + \\overline {{\\mathbb {X}}},", + "image_path": "be8f792ce976ad270bc2fb3b8645b7e70539dd8b8ace6ec4f190bf46b5dfff81.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 66, + 439, + 268, + 454 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 66, + 439, + 268, + 454 + ], + "spans": [ + { + "bbox": [ + 66, + 439, + 268, + 454 + ], + "type": "interline_equation", + "content": "\\mathbf {V} _ {i} = \\triangle \\mathbf {X} _ {i}, \\rho_ {i} ^ {t} = | | \\mathbf {V} _ {i} ^ {t} | | _ {2}, \\theta_ {i} ^ {t} = \\mathrm {a n g l e} (\\mathbf {V} _ {i} ^ {t}, \\mathbf {V} _ {i} ^ {t - 1}),", + "image_path": "5f60ddb4f2796a169a1a42b8da5de2119bab8941b6420b81e9d36ba62101c39b.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 66, + 456, + 167, + 472 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 66, + 456, + 167, + 472 + ], + "spans": [ + { + "bbox": [ + 66, + 456, + 167, + 472 + ], + "type": "interline_equation", + "content": "\\mathbf {h} _ {i} ^ {(0)} = \\phi_ {\\mathrm {i n i t \\_ h}} ([ \\rho_ {i}; \\theta_ {i} ]),", + "image_path": "a208cc80c608d1cf599425857bdaa86810c1de7c4711e1a955fd7eb3ca0c6c47.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 473, + 288, + 581 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 473, + 288, + 581 + ], + "spans": [ + { + "bbox": [ + 46, + 473, + 288, + 581 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 473, + 288, + 581 + ], + "type": "inline_equation", + "content": "\\phi_{\\mathrm{init\\_g}}(\\mathbf{X}) = \\mathbf{W}_{\\mathrm{init\\_g}}\\mathbf{X}" + }, + { + "bbox": [ + 46, + 473, + 288, + 581 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 473, + 288, + 581 + ], + "type": "inline_equation", + "content": "\\mathbf{W}_{\\mathrm{init\\_g}} \\in \\mathbb{R}^{C \\times T_p}" + }, + { + "bbox": [ + 46, + 473, + 288, + 581 + ], + "type": "text", + "content": " is a linear function, " + }, + { + "bbox": [ + 46, + 473, + 288, + 581 + ], + "type": "inline_equation", + "content": "\\overline{\\mathbb{X}}" + }, + { + "bbox": [ + 46, + 473, + 288, + 581 + ], + "type": "text", + "content": " is the mean coordinate of all agents all past timestamps. " + }, + { + "bbox": [ + 46, + 473, + 288, + 581 + ], + "type": "inline_equation", + "content": "\\triangle" + }, + { + "bbox": [ + 46, + 473, + 288, + 581 + ], + "type": "text", + "content": " is the difference operator to obtain the velocity " + }, + { + "bbox": [ + 46, + 473, + 288, + 581 + ], + "type": "inline_equation", + "content": "\\mathbf{V}_i \\in \\mathbb{R}^{T_{\\mathrm{p}} \\times n}" + }, + { + "bbox": [ + 46, + 473, + 288, + 581 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 46, + 473, + 288, + 581 + ], + "type": "inline_equation", + "content": "\\rho_i \\in \\mathbb{R}^{T_{\\mathrm{p}}}" + }, + { + "bbox": [ + 46, + 473, + 288, + 581 + ], + "type": "text", + "content": " is the velocity magnitude sequence and " + }, + { + "bbox": [ + 46, + 473, + 288, + 581 + ], + "type": "inline_equation", + "content": "\\theta_i \\in \\mathbb{R}^{T_{\\mathrm{p}}}" + }, + { + "bbox": [ + 46, + 473, + 288, + 581 + ], + "type": "text", + "content": " is the velocity angle sequence. The superscript " + }, + { + "bbox": [ + 46, + 473, + 288, + 581 + ], + "type": "inline_equation", + "content": "(\\cdot)^t" + }, + { + "bbox": [ + 46, + 473, + 288, + 581 + ], + "type": "text", + "content": " denotes the " + }, + { + "bbox": [ + 46, + 473, + 288, + 581 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 473, + 288, + 581 + ], + "type": "text", + "content": "th element, " + }, + { + "bbox": [ + 46, + 473, + 288, + 581 + ], + "type": "inline_equation", + "content": "||\\cdot||_2" + }, + { + "bbox": [ + 46, + 473, + 288, + 581 + ], + "type": "text", + "content": " is vector 2-norm, " + }, + { + "bbox": [ + 46, + 473, + 288, + 581 + ], + "type": "inline_equation", + "content": "\\mathrm{angle}(\\cdot)" + }, + { + "bbox": [ + 46, + 473, + 288, + 581 + ], + "type": "text", + "content": " is the function calculating the angle between two vectors and " + }, + { + "bbox": [ + 46, + 473, + 288, + 581 + ], + "type": "inline_equation", + "content": "\\phi_{\\mathrm{init\\_h}}(\\cdot)" + }, + { + "bbox": [ + 46, + 473, + 288, + 581 + ], + "type": "text", + "content": " is an embedding function implemented by MLP or LSTM. " + }, + { + "bbox": [ + 46, + 473, + 288, + 581 + ], + "type": "inline_equation", + "content": "[\\cdot; \\cdot]" + }, + { + "bbox": [ + 46, + 473, + 288, + 581 + ], + "type": "text", + "content": " represents concatenation." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 582, + 288, + 654 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 582, + 288, + 654 + ], + "spans": [ + { + "bbox": [ + 46, + 582, + 288, + 654 + ], + "type": "text", + "content": "The geometric feature preserves both equivariant property and motion attributes that are sensitive to Euclidean geometric transforms since we linearly combine the equivariant locations. The pattern feature remains invariant and is sensitive to motion attributes independent of Euclidean geometric transforms." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 662, + 204, + 674 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 662, + 204, + 674 + ], + "spans": [ + { + "bbox": [ + 47, + 662, + 204, + 674 + ], + "type": "text", + "content": "4.2. Invariant Reasoning Module" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 677, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 288, + 713 + ], + "type": "text", + "content": "For most scenarios, the interaction relationship is implicit and unavailable. Thus, we propose an invariant reasoning module for inferring the interaction category between agents." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 213, + 547, + 323 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 213, + 547, + 323 + ], + "spans": [ + { + "bbox": [ + 304, + 213, + 547, + 323 + ], + "type": "text", + "content": "Note that we design the reasoning module to be invariant as the interaction category is independent of Euclidean transformations. The output of the reasoning module is an invariant interaction graph whose edge weight " + }, + { + "bbox": [ + 304, + 213, + 547, + 323 + ], + "type": "inline_equation", + "content": "\\mathbf{c}_{ij} \\in [0,1]^K" + }, + { + "bbox": [ + 304, + 213, + 547, + 323 + ], + "type": "text", + "content": " is a categorical vector representing the type of interaction between agent " + }, + { + "bbox": [ + 304, + 213, + 547, + 323 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 304, + 213, + 547, + 323 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 213, + 547, + 323 + ], + "type": "inline_equation", + "content": "j" + }, + { + "bbox": [ + 304, + 213, + 547, + 323 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 304, + 213, + 547, + 323 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 304, + 213, + 547, + 323 + ], + "type": "text", + "content": " is the interaction category number. To obtain the interaction categorical vector, we perform a message passing operation using the agent's initial pattern feature " + }, + { + "bbox": [ + 304, + 213, + 547, + 323 + ], + "type": "inline_equation", + "content": "\\mathbf{h}_i^{(0)}" + }, + { + "bbox": [ + 304, + 213, + 547, + 323 + ], + "type": "text", + "content": " and geometric feature " + }, + { + "bbox": [ + 304, + 213, + 547, + 323 + ], + "type": "inline_equation", + "content": "\\mathbf{G}_i^{(0)}" + }, + { + "bbox": [ + 304, + 213, + 547, + 323 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 324, + 324, + 513, + 342 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 324, + 324, + 513, + 342 + ], + "spans": [ + { + "bbox": [ + 324, + 324, + 513, + 342 + ], + "type": "interline_equation", + "content": "\\mathbf {m} _ {i j} ^ {\\prime} = \\phi_ {\\mathrm {r m}} \\left(\\left[ \\mathbf {h} _ {i} ^ {(0)}; \\mathbf {h} _ {j} ^ {(0)}; \\left| \\left| \\mathbf {G} _ {i} ^ {(0)} - \\mathbf {G} _ {j} ^ {(0)} \\right| \\right| _ {2, \\text {c o l}} \\right]\\right),", + "image_path": "320d7c40ec82ab85be2044a2aab7298e9ebf36db1b72a5fb241b42b014765461.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 324, + 343, + 484, + 369 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 324, + 343, + 484, + 369 + ], + "spans": [ + { + "bbox": [ + 324, + 343, + 484, + 369 + ], + "type": "interline_equation", + "content": "\\mathbf {p} _ {i} ^ {\\prime} = \\sum_ {j \\in \\mathcal {N} _ {i}} \\mathbf {m} _ {i j} ^ {\\prime}, \\mathbf {h} _ {i} ^ {\\prime} = \\phi_ {\\mathrm {r h}} \\big ([ \\mathbf {p} _ {i} ^ {\\prime}; \\mathbf {h} _ {i} ^ {(0)} ] \\big),", + "image_path": "4bc6a33f3541e1288f682d3474163b24b02cadae32eaa0f092d95c682046423f.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 324, + 372, + 526, + 392 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 324, + 372, + 526, + 392 + ], + "spans": [ + { + "bbox": [ + 324, + 372, + 526, + 392 + ], + "type": "interline_equation", + "content": "\\mathbf {c} _ {i j} = \\mathrm {s m} \\Big (\\phi_ {\\mathrm {r c}} \\big ([ \\mathbf {h} _ {i} ^ {\\prime}; \\mathbf {h} _ {j} ^ {\\prime}; | | \\mathbf {G} _ {i} ^ {(0)} - \\mathbf {G} _ {j} ^ {(0)} | | _ {2, \\mathrm {c o l}} ] \\big) / \\tau \\Big),", + "image_path": "d022e9acb573cefbcd016fac9a0683461076261f23b5de95c97b3af0f2246294.jpg" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 392, + 547, + 464 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 392, + 547, + 464 + ], + "spans": [ + { + "bbox": [ + 304, + 392, + 547, + 464 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 392, + 547, + 464 + ], + "type": "inline_equation", + "content": "||\\cdot ||_{2,\\mathrm{col}}" + }, + { + "bbox": [ + 304, + 392, + 547, + 464 + ], + "type": "text", + "content": " is a column-wise " + }, + { + "bbox": [ + 304, + 392, + 547, + 464 + ], + "type": "inline_equation", + "content": "\\ell_2" + }, + { + "bbox": [ + 304, + 392, + 547, + 464 + ], + "type": "text", + "content": "-distance, " + }, + { + "bbox": [ + 304, + 392, + 547, + 464 + ], + "type": "inline_equation", + "content": "\\phi_{\\mathrm{rm}}(\\cdot),\\phi_{\\mathrm{rh}}(\\cdot)" + }, + { + "bbox": [ + 304, + 392, + 547, + 464 + ], + "type": "inline_equation", + "content": "\\phi_{\\mathrm{rc}}(\\cdot)" + }, + { + "bbox": [ + 304, + 392, + 547, + 464 + ], + "type": "text", + "content": " are learnable functions implemented by MLPs. " + }, + { + "bbox": [ + 304, + 392, + 547, + 464 + ], + "type": "inline_equation", + "content": "\\mathrm{sm}(\\cdot)" + }, + { + "bbox": [ + 304, + 392, + 547, + 464 + ], + "type": "text", + "content": " is the softmax function and " + }, + { + "bbox": [ + 304, + 392, + 547, + 464 + ], + "type": "inline_equation", + "content": "\\tau" + }, + { + "bbox": [ + 304, + 392, + 547, + 464 + ], + "type": "text", + "content": " is the temperature to control the smoothness of the categorical distribution. The interaction edge weights " + }, + { + "bbox": [ + 304, + 392, + 547, + 464 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{c}_{ij}\\}" + }, + { + "bbox": [ + 304, + 392, + 547, + 464 + ], + "type": "text", + "content": " will be end-to-end learned with the whole prediction network." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 305, + 475, + 522, + 488 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 475, + 522, + 488 + ], + "spans": [ + { + "bbox": [ + 305, + 475, + 522, + 488 + ], + "type": "text", + "content": "4.3. Equivariant Geometric Feature Learning" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 491, + 547, + 587 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 491, + 547, + 587 + ], + "spans": [ + { + "bbox": [ + 304, + 491, + 547, + 587 + ], + "type": "text", + "content": "The equivariant geometric feature learning process aims to find more representative agents' geometric features by exploiting their spatial and temporal dependencies, while maintaining the equivariance. During the process, we perform i) equivariant inner-agent attention to exploit the temporal dependencies; ii) equivariant inter-agent aggregation to model spatial interactions; and iii) equivariant non-linear function to further enhance the representation ability." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 588, + 547, + 663 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 588, + 547, + 663 + ], + "spans": [ + { + "bbox": [ + 304, + 588, + 547, + 663 + ], + "type": "text", + "content": "Equivariant inner-agent attention To exploit the temporal dependency, we perform an attention mechanism on the coordinate dimension of the geometric feature since the coordinate dimension originates from the temporal dimension. Given the " + }, + { + "bbox": [ + 304, + 588, + 547, + 663 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 304, + 588, + 547, + 663 + ], + "type": "text", + "content": "th agent's geometric feature " + }, + { + "bbox": [ + 304, + 588, + 547, + 663 + ], + "type": "inline_equation", + "content": "\\mathbf{G}_i^{(\\ell)} \\in \\mathbb{R}^{C \\times n}" + }, + { + "bbox": [ + 304, + 588, + 547, + 663 + ], + "type": "text", + "content": " and pattern feature " + }, + { + "bbox": [ + 304, + 588, + 547, + 663 + ], + "type": "inline_equation", + "content": "\\mathbf{h}_i^{(\\ell)}" + }, + { + "bbox": [ + 304, + 588, + 547, + 663 + ], + "type": "text", + "content": ", we have" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 337, + 665, + 545, + 682 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 337, + 665, + 545, + 682 + ], + "spans": [ + { + "bbox": [ + 337, + 665, + 545, + 682 + ], + "type": "interline_equation", + "content": "\\mathbf {G} _ {i} ^ {(\\ell)} \\leftarrow \\phi_ {\\mathrm {a t t}} ^ {(\\ell)} \\left(\\mathbf {h} _ {i} ^ {(\\ell)}\\right) \\cdot \\left(\\mathbf {G} _ {i} ^ {(\\ell)} - \\overline {{\\mathbb {G}}} ^ {(\\ell)}\\right) + \\overline {{\\mathbb {G}}} ^ {(\\ell)}, \\tag {2}", + "image_path": "99c083ee485f055bf55e316fbf792aa5e39c07d45b14d8c2e19551f68af0c77e.jpg" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 304, + 685, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 685, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 685, + 545, + 713 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 685, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\phi_{\\mathrm{att}}^{(\\ell)}(\\cdot):\\mathbb{R}^D\\to \\mathbb{R}^C" + }, + { + "bbox": [ + 304, + 685, + 545, + 713 + ], + "type": "text", + "content": " is a function which learns the attention weight for per coordinate, and " + }, + { + "bbox": [ + 304, + 685, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\overline{\\mathbb{G}}^{(\\ell)}" + }, + { + "bbox": [ + 304, + 685, + 545, + 713 + ], + "type": "text", + "content": " is the mean" + } + ] + } + ], + "index": 21 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "text", + "content": "1413" + } + ] + } + ], + "index": 22 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 288, + 84 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 288, + 84 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 288, + 84 + ], + "type": "text", + "content": "coordinates summing up over all agents and all coordinates." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 84, + 287, + 156 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 84, + 287, + 156 + ], + "spans": [ + { + "bbox": [ + 46, + 84, + 287, + 156 + ], + "type": "text", + "content": "The above operation will bring the following benefits: i) The learned attention weight is invariant and the learned dependencies between different timestamps of the motion will not be disturbed by irrelevant Euclidean transformations; and ii) The learned geometric feature is equivariant because of the coordinate-wise linear multiplication." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 157, + 288, + 228 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 157, + 288, + 228 + ], + "spans": [ + { + "bbox": [ + 46, + 157, + 288, + 228 + ], + "type": "text", + "content": "Equivariant inter-agent aggregation The equivariant inter-agent aggregation aims to model spatial interactions between agents. The key idea is to use the reasoned or provided interaction category to learn aggregation weights, and then use the weights to aggregate neighboring agents' geometric features. The aggregation operation reads" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 59, + 229, + 287, + 283 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 229, + 287, + 283 + ], + "spans": [ + { + "bbox": [ + 59, + 229, + 287, + 283 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\mathbf {e} _ {i j} ^ {(\\ell)} = \\sum_ {k = 1} ^ {K} \\mathbf {c} _ {i j, k} \\phi_ {e, k} ^ {(\\ell)} \\left(\\left[ \\mathbf {h} _ {i} ^ {(\\ell)}; \\mathbf {h} _ {j} ^ {(\\ell)}; \\left\\| \\mathbf {G} _ {i} ^ {(\\ell)} - \\mathbf {G} _ {j} ^ {(\\ell)} \\right\\| _ {2, \\text {c o l}} \\right]\\right), \\tag {3} \\\\ \\mathbf {G} _ {i} ^ {(\\ell)} \\leftarrow \\mathbf {G} _ {i} ^ {(\\ell)} + \\sum_ {j \\in \\mathcal {N} _ {i}} \\mathbf {e} _ {i j} ^ {(\\ell)} \\cdot (\\mathbf {G} _ {i} ^ {(\\ell)} - \\mathbf {G} _ {j} ^ {(\\ell)}), \\\\ \\end{array}", + "image_path": "1fe5210e8b327e8bcba326c71e18e952bbb40b71e0bd872f4e74eb731fa62b9b.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 284, + 287, + 346 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 284, + 287, + 346 + ], + "spans": [ + { + "bbox": [ + 46, + 284, + 287, + 346 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 284, + 287, + 346 + ], + "type": "inline_equation", + "content": "\\mathbf{e}_{ij}^{(\\ell)}\\in \\mathbb{R}^C" + }, + { + "bbox": [ + 46, + 284, + 287, + 346 + ], + "type": "text", + "content": " is the learned aggregation weights between agent " + }, + { + "bbox": [ + 46, + 284, + 287, + 346 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 284, + 287, + 346 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 284, + 287, + 346 + ], + "type": "inline_equation", + "content": "j,||\\cdot ||_{2,\\mathrm{col}}" + }, + { + "bbox": [ + 46, + 284, + 287, + 346 + ], + "type": "text", + "content": " is a column-wise " + }, + { + "bbox": [ + 46, + 284, + 287, + 346 + ], + "type": "inline_equation", + "content": "\\ell_2" + }, + { + "bbox": [ + 46, + 284, + 287, + 346 + ], + "type": "text", + "content": "-distance, " + }, + { + "bbox": [ + 46, + 284, + 287, + 346 + ], + "type": "inline_equation", + "content": "\\cdot" + }, + { + "bbox": [ + 46, + 284, + 287, + 346 + ], + "type": "text", + "content": " is dot product and " + }, + { + "bbox": [ + 46, + 284, + 287, + 346 + ], + "type": "inline_equation", + "content": "\\mathcal{N}_i" + }, + { + "bbox": [ + 46, + 284, + 287, + 346 + ], + "type": "text", + "content": " is the " + }, + { + "bbox": [ + 46, + 284, + 287, + 346 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 284, + 287, + 346 + ], + "type": "text", + "content": "th agent's neighboring set. For the " + }, + { + "bbox": [ + 46, + 284, + 287, + 346 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 284, + 287, + 346 + ], + "type": "text", + "content": "th interaction category, we assign a function " + }, + { + "bbox": [ + 46, + 284, + 287, + 346 + ], + "type": "inline_equation", + "content": "\\phi_{e,k}^{(\\ell)}(\\cdot)" + }, + { + "bbox": [ + 46, + 284, + 287, + 346 + ], + "type": "text", + "content": " that is implemented by MLP to model how the interaction works." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 347, + 287, + 395 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 347, + 287, + 395 + ], + "spans": [ + { + "bbox": [ + 46, + 347, + 287, + 395 + ], + "type": "text", + "content": "The social influence from agent " + }, + { + "bbox": [ + 46, + 347, + 287, + 395 + ], + "type": "inline_equation", + "content": "j" + }, + { + "bbox": [ + 46, + 347, + 287, + 395 + ], + "type": "text", + "content": " to agent " + }, + { + "bbox": [ + 46, + 347, + 287, + 395 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 347, + 287, + 395 + ], + "type": "text", + "content": " is modeled by the coordinates' difference between the two agents. The intuition behind this design is that the mutual force between two objects is always in the direction of the line they formed." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 396, + 288, + 467 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 396, + 288, + 467 + ], + "spans": [ + { + "bbox": [ + 46, + 396, + 288, + 467 + ], + "type": "text", + "content": "Note that for most scenarios, we do not have an explicit definition of interacted \"neighbors\", thus we use a fully-connected graph structure, which means every agent's neighbors include all other agents. For some special cases with massive nodes, like point clouds, we construct a local neighboring set by choosing neighbors within a distance threshold." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 468, + 288, + 598 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 468, + 288, + 598 + ], + "spans": [ + { + "bbox": [ + 46, + 468, + 288, + 598 + ], + "type": "text", + "content": "Equivariant non-linear function According to Eq. (2) and Eq. (3), the operation of inner-agent attention and inter-agent aggregation are linear combinations with agents' coordinates. It is well known that non-linear operation is the key to improving neural networks' expressivity. Therefore, we propose an equivariant non-linear function to enhance the representation ability of our prediction network while preserving equivariance. The key idea is proposing a criterion with the invariance property for splitting different conditions, and for each condition design an equivariant equation. Mathematically, the non-linear function is" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 600, + 298, + 654 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 600, + 298, + 654 + ], + "spans": [ + { + "bbox": [ + 47, + 600, + 298, + 654 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\mathbf {Q} _ {i} ^ {(\\ell)} = \\mathbf {W} _ {\\mathrm {Q}} ^ {(\\ell)} \\left(\\mathbf {G} _ {i} ^ {(\\ell)} - \\overline {{\\mathbb {G}}} ^ {(\\ell)}\\right), \\mathbf {K} _ {i} ^ {(\\ell)} = \\mathbf {W} _ {\\mathrm {K}} ^ {(\\ell)} \\left(\\mathbf {G} _ {i} ^ {(\\ell)} - \\overline {{\\mathbb {G}}} ^ {(\\ell)}\\right), \\\\ \\mathbf {g} _ {i, c} ^ {(\\ell + 1)} = \\left\\{ \\begin{array}{l l} \\mathbf {q} _ {i, c} ^ {(\\ell)} + \\overline {{\\mathbb {G}}} ^ {(\\ell)} & \\text {i f} \\langle \\mathbf {q} _ {i, c} ^ {(\\ell)}, \\mathbf {k} _ {i, c} ^ {(\\ell)} \\rangle \\geq 0, \\\\ \\mathbf {q} _ {i, c} ^ {(\\ell)} - \\langle \\mathbf {q} _ {i, c} ^ {(\\ell)}, \\frac {\\mathbf {k} _ {i , c} ^ {(\\ell)}}{| | \\mathbf {k} _ {i , c} ^ {(\\ell)} | | _ {2}} \\rangle \\frac {\\mathbf {k} _ {i , c} ^ {(\\ell)}}{| | \\mathbf {k} _ {i , c} ^ {(\\ell)} | | _ {2}} + \\overline {{\\mathbb {G}}} ^ {(\\ell)} & \\text {o t h e r w i s e}, \\end{array} \\right. \\\\ \\end{array}", + "image_path": "6f50457d89d50d44983596a8884e2d17b1a87f334057de8f631ea2c42b00c493.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 655, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 655, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 655, + 287, + 715 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 655, + 287, + 715 + ], + "type": "inline_equation", + "content": "\\mathbf{Q}_i^{(\\ell)}" + }, + { + "bbox": [ + 46, + 655, + 287, + 715 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 655, + 287, + 715 + ], + "type": "inline_equation", + "content": "\\mathbf{K}_i^{(\\ell)}" + }, + { + "bbox": [ + 46, + 655, + 287, + 715 + ], + "type": "text", + "content": " is the learned query coordinates and key coordinates, " + }, + { + "bbox": [ + 46, + 655, + 287, + 715 + ], + "type": "inline_equation", + "content": "\\mathbf{W}_{\\mathrm{K}}^{(\\ell)}\\in \\mathbb{R}^{C\\times C}" + }, + { + "bbox": [ + 46, + 655, + 287, + 715 + ], + "type": "text", + "content": " are learnable matrices for queries and keys. " + }, + { + "bbox": [ + 46, + 655, + 287, + 715 + ], + "type": "inline_equation", + "content": "\\overline{\\mathbb{G}}_{\\nu}^{(\\ell)}" + }, + { + "bbox": [ + 46, + 655, + 287, + 715 + ], + "type": "text", + "content": " is the mean coordinates over all agents and all coordinates. " + }, + { + "bbox": [ + 46, + 655, + 287, + 715 + ], + "type": "inline_equation", + "content": "\\mathbf{q}_{i,c}^{(\\ell)}" + }, + { + "bbox": [ + 46, + 655, + 287, + 715 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 655, + 287, + 715 + ], + "type": "inline_equation", + "content": "\\mathbf{k}_{i,c}^{(\\ell)}" + }, + { + "bbox": [ + 46, + 655, + 287, + 715 + ], + "type": "text", + "content": " is the " + }, + { + "bbox": [ + 46, + 655, + 287, + 715 + ], + "type": "inline_equation", + "content": "c" + }, + { + "bbox": [ + 46, + 655, + 287, + 715 + ], + "type": "text", + "content": "th coordinate of" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 70, + 498, + 86 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 70, + 498, + 86 + ], + "spans": [ + { + "bbox": [ + 306, + 70, + 498, + 86 + ], + "type": "inline_equation", + "content": "\\mathbf{Q}_i^{(\\ell)}" + }, + { + "bbox": [ + 306, + 70, + 498, + 86 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 306, + 70, + 498, + 86 + ], + "type": "inline_equation", + "content": "\\mathbf{K}_i^{(\\ell)}" + }, + { + "bbox": [ + 306, + 70, + 498, + 86 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 306, + 70, + 498, + 86 + ], + "type": "inline_equation", + "content": "\\langle \\cdot, \\cdot \\rangle" + }, + { + "bbox": [ + 306, + 70, + 498, + 86 + ], + "type": "text", + "content": " is the vector inner product." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 86, + 547, + 227 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 86, + 547, + 227 + ], + "spans": [ + { + "bbox": [ + 304, + 86, + 547, + 227 + ], + "type": "text", + "content": "For every geometric coordinate " + }, + { + "bbox": [ + 304, + 86, + 547, + 227 + ], + "type": "inline_equation", + "content": "\\mathbf{g}_{i,c}^{(\\ell)}" + }, + { + "bbox": [ + 304, + 86, + 547, + 227 + ], + "type": "text", + "content": ", we learn a query coordinate " + }, + { + "bbox": [ + 304, + 86, + 547, + 227 + ], + "type": "inline_equation", + "content": "\\mathbf{q}_{i,c}^{(\\ell)}" + }, + { + "bbox": [ + 304, + 86, + 547, + 227 + ], + "type": "text", + "content": " and a key coordinate " + }, + { + "bbox": [ + 304, + 86, + 547, + 227 + ], + "type": "inline_equation", + "content": "\\mathbf{k}_{i,c}^{(\\ell)}" + }, + { + "bbox": [ + 304, + 86, + 547, + 227 + ], + "type": "text", + "content": ". We set the criterion as the inner product of the query coordinate and the key coordinate. If the inner product is positive, we directly take the value of the query coordinate as output; otherwise, we clip the query coordinate vector by moving out its parallel components with the key coordinate vector. Finally, we obtain the " + }, + { + "bbox": [ + 304, + 86, + 547, + 227 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 304, + 86, + 547, + 227 + ], + "type": "text", + "content": "th agent's geometric features of the next layer " + }, + { + "bbox": [ + 304, + 86, + 547, + 227 + ], + "type": "inline_equation", + "content": "\\mathbf{G}_i^{(l + 1)}" + }, + { + "bbox": [ + 304, + 86, + 547, + 227 + ], + "type": "text", + "content": " by gathering all the coordinates " + }, + { + "bbox": [ + 304, + 86, + 547, + 227 + ], + "type": "inline_equation", + "content": "\\mathbf{g}_{i,c}^{(l + 1)}" + }, + { + "bbox": [ + 304, + 86, + 547, + 227 + ], + "type": "text", + "content": ". The non-linear function is equivariant, since the criterion is invariant and the two equations under two conditions are equivariant." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 234, + 495, + 247 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 234, + 495, + 247 + ], + "spans": [ + { + "bbox": [ + 305, + 234, + 495, + 247 + ], + "type": "text", + "content": "4.4. Invariant Pattern Feature Learning" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 249, + 547, + 387 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 249, + 547, + 387 + ], + "spans": [ + { + "bbox": [ + 304, + 249, + 547, + 387 + ], + "type": "text", + "content": "The invariant pattern feature learning aims to obtain a more representative agent pattern feature through interacting with neighbors. Here we learn the agent's pattern feature with an invariant message passing mechanism. Specially, we add the relative geometric feature difference into the edge modeling in the message passing to complement the information of relationships between agent absolute locations, which cannot be obtained by solely using the pattern features. Given the " + }, + { + "bbox": [ + 304, + 249, + 547, + 387 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 304, + 249, + 547, + 387 + ], + "type": "text", + "content": "th agent's pattern feature " + }, + { + "bbox": [ + 304, + 249, + 547, + 387 + ], + "type": "inline_equation", + "content": "\\mathbf{h}_i^{(\\ell)} \\in \\mathbb{R}^D" + }, + { + "bbox": [ + 304, + 249, + 547, + 387 + ], + "type": "text", + "content": " and geometric feature " + }, + { + "bbox": [ + 304, + 249, + 547, + 387 + ], + "type": "inline_equation", + "content": "\\mathbf{G}_i^{(\\ell)} \\in \\mathbb{R}^{C \\times n}" + }, + { + "bbox": [ + 304, + 249, + 547, + 387 + ], + "type": "text", + "content": ", the next layer's pattern feature " + }, + { + "bbox": [ + 304, + 249, + 547, + 387 + ], + "type": "inline_equation", + "content": "\\mathbf{h}_i^{(l+1)}" + }, + { + "bbox": [ + 304, + 249, + 547, + 387 + ], + "type": "text", + "content": " is obtained by" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 328, + 388, + 523, + 437 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 328, + 388, + 523, + 437 + ], + "spans": [ + { + "bbox": [ + 328, + 388, + 523, + 437 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\mathbf {m} _ {i j} ^ {(\\ell)} = \\phi_ {m} ^ {(\\ell)} \\left(\\left[ \\mathbf {h} _ {i} ^ {(\\ell)}; \\mathbf {h} _ {j} ^ {(\\ell)}; | | \\mathbf {G} _ {i} ^ {(\\ell)} - \\mathbf {G} _ {j} ^ {(\\ell)} | | _ {2, \\text {c o l}} \\right]\\right), \\\\ \\mathbf {p} _ {i} ^ {(\\ell)} = \\sum_ {j \\in \\mathcal {N} (i)} \\mathbf {m} _ {i j} ^ {(\\ell)}, \\mathbf {h} _ {i} ^ {(l + 1)} = \\phi_ {h} ^ {(\\ell)} ([ \\mathbf {h} _ {i} ^ {(\\ell)}; \\mathbf {p} _ {i} ^ {(\\ell)} ]). \\\\ \\end{array}", + "image_path": "e54b894e642cce333712ec71ee9ca371b541195c53662d4e9f5c6e4d5abf9683.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 437, + 547, + 490 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 437, + 547, + 490 + ], + "spans": [ + { + "bbox": [ + 304, + 437, + 547, + 490 + ], + "type": "text", + "content": "Here " + }, + { + "bbox": [ + 304, + 437, + 547, + 490 + ], + "type": "inline_equation", + "content": "\\mathbf{m}_{ij}^{(\\ell)}" + }, + { + "bbox": [ + 304, + 437, + 547, + 490 + ], + "type": "text", + "content": " is the edge features and " + }, + { + "bbox": [ + 304, + 437, + 547, + 490 + ], + "type": "inline_equation", + "content": "\\mathbf{p}_i^{(\\ell)}" + }, + { + "bbox": [ + 304, + 437, + 547, + 490 + ], + "type": "text", + "content": " is the aggregated neighboring features in the message passing. " + }, + { + "bbox": [ + 304, + 437, + 547, + 490 + ], + "type": "inline_equation", + "content": "||\\cdot ||_{2,\\mathrm{col}}" + }, + { + "bbox": [ + 304, + 437, + 547, + 490 + ], + "type": "text", + "content": " is a column-wise " + }, + { + "bbox": [ + 304, + 437, + 547, + 490 + ], + "type": "inline_equation", + "content": "\\ell_2" + }, + { + "bbox": [ + 304, + 437, + 547, + 490 + ], + "type": "text", + "content": "-distance and " + }, + { + "bbox": [ + 304, + 437, + 547, + 490 + ], + "type": "inline_equation", + "content": "[\\cdot ;\\cdot ]" + }, + { + "bbox": [ + 304, + 437, + 547, + 490 + ], + "type": "text", + "content": " denotes concatenation. Functions " + }, + { + "bbox": [ + 304, + 437, + 547, + 490 + ], + "type": "inline_equation", + "content": "\\phi_m^{(\\ell)}(\\cdot)" + }, + { + "bbox": [ + 304, + 437, + 547, + 490 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 437, + 547, + 490 + ], + "type": "inline_equation", + "content": "\\phi_h^{(\\ell)}(\\cdot)" + }, + { + "bbox": [ + 304, + 437, + 547, + 490 + ], + "type": "text", + "content": " are implemented by MLPs." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 497, + 453, + 510 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 497, + 453, + 510 + ], + "spans": [ + { + "bbox": [ + 305, + 497, + 453, + 510 + ], + "type": "text", + "content": "4.5. Equivariant Output Layer" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 513, + 547, + 562 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 513, + 547, + 562 + ], + "spans": [ + { + "bbox": [ + 304, + 513, + 547, + 562 + ], + "type": "text", + "content": "After total " + }, + { + "bbox": [ + 304, + 513, + 547, + 562 + ], + "type": "inline_equation", + "content": "L" + }, + { + "bbox": [ + 304, + 513, + 547, + 562 + ], + "type": "text", + "content": " feature learning layers, we obtain the final " + }, + { + "bbox": [ + 304, + 513, + 547, + 562 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 304, + 513, + 547, + 562 + ], + "type": "text", + "content": "th agent's geometric feature " + }, + { + "bbox": [ + 304, + 513, + 547, + 562 + ], + "type": "inline_equation", + "content": "\\mathbf{G}_i^{(L)}" + }, + { + "bbox": [ + 304, + 513, + 547, + 562 + ], + "type": "text", + "content": " and pattern feature " + }, + { + "bbox": [ + 304, + 513, + 547, + 562 + ], + "type": "inline_equation", + "content": "\\mathbf{h}_i^{(L)}" + }, + { + "bbox": [ + 304, + 513, + 547, + 562 + ], + "type": "text", + "content": ". We use the geometric feature for the final prediction by a linear operation for equivariance: for the " + }, + { + "bbox": [ + 304, + 513, + 547, + 562 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 304, + 513, + 547, + 562 + ], + "type": "text", + "content": "th agent:" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 354, + 563, + 496, + 579 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 354, + 563, + 496, + 579 + ], + "spans": [ + { + "bbox": [ + 354, + 563, + 496, + 579 + ], + "type": "interline_equation", + "content": "\\widehat {\\mathbf {Y}} _ {i} = \\mathbf {W} _ {\\text {o u t}} (\\mathbf {G} _ {i} ^ {(\\ell)} - \\overline {{\\mathbb {G}}} ^ {(\\ell)}) + \\overline {{\\mathbb {G}}} ^ {(\\ell)},", + "image_path": "391043be4b8a5045bf1df62ff9c6765964c9c52e81e703c6c1c3cbb7213c28dd.jpg" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 580, + 547, + 618 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 580, + 547, + 618 + ], + "spans": [ + { + "bbox": [ + 304, + 580, + 547, + 618 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 580, + 547, + 618 + ], + "type": "inline_equation", + "content": "\\mathbf{W}_{\\mathrm{out}} \\in \\mathbb{R}^{T_{\\mathrm{f}} \\times D}" + }, + { + "bbox": [ + 304, + 580, + 547, + 618 + ], + "type": "text", + "content": " is a learnable weight matrix. Finally, we gather all the agent prediction " + }, + { + "bbox": [ + 304, + 580, + 547, + 618 + ], + "type": "inline_equation", + "content": "\\widehat{\\mathbf{Y}}_i" + }, + { + "bbox": [ + 304, + 580, + 547, + 618 + ], + "type": "text", + "content": " to have the final predicted motions " + }, + { + "bbox": [ + 304, + 580, + 547, + 618 + ], + "type": "inline_equation", + "content": "\\widehat{\\mathbb{Y}}" + }, + { + "bbox": [ + 304, + 580, + 547, + 618 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 306, + 626, + 424, + 639 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 626, + 424, + 639 + ], + "spans": [ + { + "bbox": [ + 306, + 626, + 424, + 639 + ], + "type": "text", + "content": "4.6. Theoretical Analysis" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 304, + 642, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 642, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 642, + 547, + 713 + ], + "type": "text", + "content": "In this section, we analyze our network's equivariance property and the interaction reasoning module's invariance property, as stated in the following theorem. Let " + }, + { + "bbox": [ + 304, + 642, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\mathbb{G}^{(\\ell)}\\in" + }, + { + "bbox": [ + 304, + 642, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^{M\\times C\\times n}" + }, + { + "bbox": [ + 304, + 642, + 547, + 713 + ], + "type": "text", + "content": " be all agents' geometric features, " + }, + { + "bbox": [ + 304, + 642, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{H}^{(\\ell)}\\in \\mathbb{R}^{M\\times D}" + }, + { + "bbox": [ + 304, + 642, + 547, + 713 + ], + "type": "text", + "content": " be all agents' pattern features at the " + }, + { + "bbox": [ + 304, + 642, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\ell" + }, + { + "bbox": [ + 304, + 642, + 547, + 713 + ], + "type": "text", + "content": "th layer, and " + }, + { + "bbox": [ + 304, + 642, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{c}_{ij}\\}" + }, + { + "bbox": [ + 304, + 642, + 547, + 713 + ], + "type": "text", + "content": " be the set of all the interaction categorical vectors." + } + ] + } + ], + "index": 21 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "text", + "content": "1414" + } + ] + } + ], + "index": 22 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 108 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 108 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 108 + ], + "type": "text", + "content": "Theorem 1 For arbitrary translation vector " + }, + { + "bbox": [ + 46, + 72, + 287, + 108 + ], + "type": "inline_equation", + "content": "\\mathbf{t} \\in \\mathbb{R}^n" + }, + { + "bbox": [ + 46, + 72, + 287, + 108 + ], + "type": "text", + "content": " and rotation (or reflection) matrix " + }, + { + "bbox": [ + 46, + 72, + 287, + 108 + ], + "type": "inline_equation", + "content": "\\mathbf{R} \\in \\mathrm{SO}(n)" + }, + { + "bbox": [ + 46, + 72, + 287, + 108 + ], + "type": "text", + "content": ", the modules with equivariance and invariance in our network satisfy:" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 109, + 287, + 144 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 109, + 287, + 144 + ], + "spans": [ + { + "bbox": [ + 46, + 109, + 287, + 144 + ], + "type": "text", + "content": "1. For the initialization layer " + }, + { + "bbox": [ + 46, + 109, + 287, + 144 + ], + "type": "inline_equation", + "content": "\\mathcal{F}_{\\mathrm{IL}}(\\cdot)" + }, + { + "bbox": [ + 46, + 109, + 287, + 144 + ], + "type": "text", + "content": ", the initial geometric feature is equivariant and the initial pattern feature is invariant:" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 94, + 144, + 238, + 159 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 94, + 144, + 238, + 159 + ], + "spans": [ + { + "bbox": [ + 94, + 144, + 238, + 159 + ], + "type": "interline_equation", + "content": "\\mathbb {G} ^ {(0)} \\mathbf {R} + \\mathbf {t}, \\mathbf {H} ^ {(0)} = \\mathcal {F} _ {\\mathrm {I L}} (\\mathbb {X} \\mathbf {R} + \\mathbf {t}).", + "image_path": "b09d07cf1d2ffdee2f53148cb6daa47908881e8ca179d4a9720b36b2e758b475.jpg" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 160, + 287, + 185 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 160, + 287, + 185 + ], + "spans": [ + { + "bbox": [ + 46, + 160, + 287, + 185 + ], + "type": "text", + "content": "2. The reasoning module " + }, + { + "bbox": [ + 46, + 160, + 287, + 185 + ], + "type": "inline_equation", + "content": "\\mathcal{F}_{\\mathrm{IRM}}(\\cdot)" + }, + { + "bbox": [ + 46, + 160, + 287, + 185 + ], + "type": "text", + "content": " along with reasoned interaction categorical vectors " + }, + { + "bbox": [ + 46, + 160, + 287, + 185 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{c}_{ij}\\}" + }, + { + "bbox": [ + 46, + 160, + 287, + 185 + ], + "type": "text", + "content": " is invariant:" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 97, + 186, + 236, + 201 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 97, + 186, + 236, + 201 + ], + "spans": [ + { + "bbox": [ + 97, + 186, + 236, + 201 + ], + "type": "interline_equation", + "content": "\\left\\{\\mathbf {c} _ {i j} \\right\\} = \\mathcal {F} _ {\\mathrm {I R M}} \\left(\\mathbb {G} ^ {(0)} \\mathbf {R} + \\mathbf {t}, \\mathbf {H} ^ {(0)}\\right).", + "image_path": "a91fedf62e9ee9a0723f72421fe4fac84ec6149228e31f5b4848dccf74b29b7f.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 203, + 287, + 228 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 203, + 287, + 228 + ], + "spans": [ + { + "bbox": [ + 46, + 203, + 287, + 228 + ], + "type": "text", + "content": "3. The " + }, + { + "bbox": [ + 46, + 203, + 287, + 228 + ], + "type": "inline_equation", + "content": "\\ell" + }, + { + "bbox": [ + 46, + 203, + 287, + 228 + ], + "type": "text", + "content": "th geometric feature learning layer " + }, + { + "bbox": [ + 46, + 203, + 287, + 228 + ], + "type": "inline_equation", + "content": "\\mathcal{F}_{\\mathrm{EGFL}}^{(\\ell)}(\\cdot)" + }, + { + "bbox": [ + 46, + 203, + 287, + 228 + ], + "type": "text", + "content": " is equivariant:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 66, + 229, + 267, + 246 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 66, + 229, + 267, + 246 + ], + "spans": [ + { + "bbox": [ + 66, + 229, + 267, + 246 + ], + "type": "interline_equation", + "content": "\\mathbb {G} ^ {(l + 1)} \\mathbf {R} + \\mathbf {t} = \\mathcal {F} _ {\\mathrm {E G F L}} ^ {(\\ell)} \\left(\\mathbb {G} ^ {(\\ell)} \\mathbf {R} + \\mathbf {t}, \\mathbf {H} ^ {(\\ell)}, \\left\\{\\mathbf {c} _ {i j} \\right\\}\\right).", + "image_path": "b54f53dd180eee985c6347a6fe2f0b7e13dba1e7f581b9820cce77886d7064db.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 247, + 287, + 271 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 247, + 287, + 271 + ], + "spans": [ + { + "bbox": [ + 46, + 247, + 287, + 271 + ], + "type": "text", + "content": "4. The " + }, + { + "bbox": [ + 46, + 247, + 287, + 271 + ], + "type": "inline_equation", + "content": "\\ell" + }, + { + "bbox": [ + 46, + 247, + 287, + 271 + ], + "type": "text", + "content": "th pattern feature learning layer " + }, + { + "bbox": [ + 46, + 247, + 287, + 271 + ], + "type": "inline_equation", + "content": "\\mathcal{F}_{\\mathrm{IPFL}}^{(\\ell)}(\\cdot)" + }, + { + "bbox": [ + 46, + 247, + 287, + 271 + ], + "type": "text", + "content": " is invariant:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 93, + 272, + 240, + 288 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 93, + 272, + 240, + 288 + ], + "spans": [ + { + "bbox": [ + 93, + 272, + 240, + 288 + ], + "type": "interline_equation", + "content": "\\mathbf {H} ^ {(l + 1)} = \\mathcal {F} _ {\\mathrm {I P F L}} ^ {(\\ell)} (\\mathbb {G} ^ {(\\ell)} \\mathbf {R} + \\mathbf {t}, \\mathbf {H} ^ {(\\ell)}).", + "image_path": "0626951a41c553632ff99d8e247b1ec3a7fd258900bcba75e980bea3076a6142.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 59, + 289, + 236, + 301 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 289, + 236, + 301 + ], + "spans": [ + { + "bbox": [ + 59, + 289, + 236, + 301 + ], + "type": "text", + "content": "5. The output layer " + }, + { + "bbox": [ + 59, + 289, + 236, + 301 + ], + "type": "inline_equation", + "content": "\\mathcal{F}_{\\mathrm{EOL}}(\\cdot)" + }, + { + "bbox": [ + 59, + 289, + 236, + 301 + ], + "type": "text", + "content": " is equivariant:" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 102, + 303, + 231, + 317 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 102, + 303, + 231, + 317 + ], + "spans": [ + { + "bbox": [ + 102, + 303, + 231, + 317 + ], + "type": "interline_equation", + "content": "\\widehat {\\mathbf {Y}} \\mathbf {R} + \\mathbf {t} = \\mathcal {F} _ {\\mathrm {E O L}} (\\mathbb {G} ^ {(L)} \\mathbf {R} + \\mathbf {t}).", + "image_path": "a73dadece8a7dd2efcfbf0163eadbed8640ae4e59deea406760019a590cd406c.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 318, + 287, + 378 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 318, + 287, + 378 + ], + "spans": [ + { + "bbox": [ + 46, + 318, + 287, + 378 + ], + "type": "text", + "content": "See the detailed proof in Appendix. Theorem 1 presents the equivariance/invariance properties with the Euclidean transformation for each operation in the proposed network. Based on Theorem 1, by combining all network operations together, we can show that the whole network is equivariant:" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 46, + 382, + 287, + 418 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 382, + 287, + 418 + ], + "spans": [ + { + "bbox": [ + 46, + 382, + 287, + 418 + ], + "type": "text", + "content": "Corollary 1 For arbitrary translation vector " + }, + { + "bbox": [ + 46, + 382, + 287, + 418 + ], + "type": "inline_equation", + "content": "\\mathbf{t} \\in \\mathbb{R}^n" + }, + { + "bbox": [ + 46, + 382, + 287, + 418 + ], + "type": "text", + "content": " and rotation matrix " + }, + { + "bbox": [ + 46, + 382, + 287, + 418 + ], + "type": "inline_equation", + "content": "\\mathbf{R} \\in \\mathrm{SO}(n)" + }, + { + "bbox": [ + 46, + 382, + 287, + 418 + ], + "type": "text", + "content": ", our whole network EqMotion " + }, + { + "bbox": [ + 46, + 382, + 287, + 418 + ], + "type": "inline_equation", + "content": "\\mathcal{F}_{\\mathrm{pred}}(\\cdot)" + }, + { + "bbox": [ + 46, + 382, + 287, + 418 + ], + "type": "text", + "content": " satisfies:" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 109, + 419, + 223, + 434 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 109, + 419, + 223, + 434 + ], + "spans": [ + { + "bbox": [ + 109, + 419, + 223, + 434 + ], + "type": "interline_equation", + "content": "\\widehat {\\mathbb {Y}} \\mathbf {R} + \\mathbf {t} = \\mathcal {F} _ {\\mathrm {p r e d}} (\\mathbb {X} \\mathbf {R} + \\mathbf {t}).", + "image_path": "1b0f81c0b694624f6e9eff4f146c7ad679614792b13186270ec3f5b570098d0b.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 47, + 442, + 123, + 456 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 442, + 123, + 456 + ], + "spans": [ + { + "bbox": [ + 47, + 442, + 123, + 456 + ], + "type": "text", + "content": "5. Experiment" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 46, + 460, + 287, + 520 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 460, + 287, + 520 + ], + "spans": [ + { + "bbox": [ + 46, + 460, + 287, + 520 + ], + "type": "text", + "content": "In this section, we validate our method on four different scenarios: particle dynamics, molecule dynamics, 3D human skeleton motion, and pedestrian trajectories. The detailed dataset description, implementation details, and additional experiment results are elaborated in the Appendix." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 46, + 521, + 287, + 593 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 521, + 287, + 593 + ], + "spans": [ + { + "bbox": [ + 46, + 521, + 287, + 593 + ], + "type": "text", + "content": "Metric We use: i) Average Displacement Error (ADE) and Final Displacement Error (FDE). ADE/FDE is the " + }, + { + "bbox": [ + 46, + 521, + 287, + 593 + ], + "type": "inline_equation", + "content": "\\ell_2" + }, + { + "bbox": [ + 46, + 521, + 287, + 593 + ], + "type": "text", + "content": " distance of the predicted whole motion/endpoint to the ground truth of the whole motion/endpoint; ii) Mean Per Joint Position Error (MPJPE). It records average " + }, + { + "bbox": [ + 46, + 521, + 287, + 593 + ], + "type": "inline_equation", + "content": "\\ell_2" + }, + { + "bbox": [ + 46, + 521, + 287, + 593 + ], + "type": "text", + "content": " distance between predicted joints and target ones at each future timestamp." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 46, + 601, + 258, + 613 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 601, + 258, + 613 + ], + "spans": [ + { + "bbox": [ + 46, + 601, + 258, + 613 + ], + "type": "text", + "content": "5.1. Scenario 1: Particle Dynamic Prediction" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 46, + 616, + 287, + 666 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 616, + 287, + 666 + ], + "spans": [ + { + "bbox": [ + 46, + 616, + 287, + 666 + ], + "type": "text", + "content": "We use the particle " + }, + { + "bbox": [ + 46, + 616, + 287, + 666 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 616, + 287, + 666 + ], + "type": "text", + "content": "-body simulation [28] in a 3D space similar to [14, 58]. In the Springs simulation, particles are randomly connected by a spring. In the Charged simulation, particles are randomly charged or uncharged." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 46, + 666, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 666, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 666, + 287, + 713 + ], + "type": "text", + "content": "Validation on interaction reasoning Since we can get the ground-truth interaction through simulation, we evaluate the ability of interaction reasoning as a category recognition task. To evaluate the robustness of the reasoning result with" + } + ] + } + ], + "index": 19 + }, + { + "type": "table", + "bbox": [ + 307, + 94, + 541, + 196 + ], + "blocks": [ + { + "bbox": [ + 305, + 71, + 545, + 92 + ], + "lines": [ + { + "bbox": [ + 305, + 71, + 545, + 92 + ], + "spans": [ + { + "bbox": [ + 305, + 71, + 545, + 92 + ], + "type": "text", + "content": "Table 1. Interaction recognition accuracy and consistency (mean ± std in % in 5 independent runs) on the physical simulation." + } + ] + } + ], + "index": 20, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 307, + 94, + 541, + 196 + ], + "lines": [ + { + "bbox": [ + 307, + 94, + 541, + 196 + ], + "spans": [ + { + "bbox": [ + 307, + 94, + 541, + 196 + ], + "type": "table", + "html": "
ModelSpringsCharged
AccuracyConsistencyAccuracyConsistency
Corr.(path) [28]58.1 ± 0.099.8 ± 0.157.5 ± 0.187.9 ± 0.1
Corr.(LSTM) [28]53.5 ± 0.592.4 ± 2.157.2 ± 0.491.7 ± 1.1
EGNN [58]61.0 ± 1.3100.0 ± 0.058.2 ± 1.4100.0 ± 0.0
NRI [28]93.0 ± 1.193.7 ± 1.270.0 ± 0.688.5 ± 1.3
dNRI [17]93.3 ± 2.089.6 ± 2.070.4 ± 1.783.6 ± 1.8
Ours97.6 ± 1.1100.0 ± 0.080.9 ± 3.4100.0 ± 0.0
Supervised98.7 ± 0.2100.0 ± 0.097.4 ± 0.2100.0 ± 0.0
", + "image_path": "f1e883ca0155892d5e394df95a02f16c7398806ac35fd101e9de2b2a7dc74e1b.jpg" + } + ] + } + ], + "index": 21, + "angle": 0, + "type": "table_body" + } + ], + "index": 21 + }, + { + "type": "image", + "bbox": [ + 310, + 198, + 536, + 308 + ], + "blocks": [ + { + "bbox": [ + 310, + 198, + 536, + 308 + ], + "lines": [ + { + "bbox": [ + 310, + 198, + 536, + 308 + ], + "spans": [ + { + "bbox": [ + 310, + 198, + 536, + 308 + ], + "type": "image", + "image_path": "c99ac6037ac5632c7029371226f8df24bf8811fe060beff70661f62224c11da9.jpg" + } + ] + } + ], + "index": 22, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 309, + 545, + 331 + ], + "lines": [ + { + "bbox": [ + 305, + 309, + 545, + 331 + ], + "spans": [ + { + "bbox": [ + 305, + 309, + 545, + 331 + ], + "type": "text", + "content": "Figure 3. Comparison of displacement error across different timestamps on the physical simulation." + } + ] + } + ], + "index": 23, + "angle": 0, + "type": "image_caption" + } + ], + "index": 22 + }, + { + "bbox": [ + 304, + 341, + 547, + 496 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 341, + 547, + 496 + ], + "spans": [ + { + "bbox": [ + 304, + 341, + 547, + 496 + ], + "type": "text", + "content": "the Euclidean transformation, we introduce recognition \"consistency\", which is the ratio of the same recognition result under 20 random Euclidean transformations. The \"Supervised\" represents an upper bound that uses the ground-truth category to train the model. Table 1 reports the comparison of reasoning results on both springs and charged simulations, for recognizing whether there is a spring connection or electrostatic force. We see that i) our method achieves significant improvement on the recognition accuracy and has more robust reasoning results due to the invariance of our reasoning module; and ii) our method achieves a close performance to the upper bound, reflecting that our method is capable of reasoning a robust and accurate interaction category." + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 304, + 497, + 547, + 569 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 497, + 547, + 569 + ], + "spans": [ + { + "bbox": [ + 304, + 497, + 547, + 569 + ], + "type": "text", + "content": "Validation on future prediction We conduct the experiment to evaluate the prediction performance on the charged settings. Figure 3 compares the displacement error at all future timestamps of different methods. We see that our method (red line) achieves state-of-the-art prediction performance, reflecting our model's efficiency in future prediction." + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 305, + 578, + 524, + 590 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 578, + 524, + 590 + ], + "spans": [ + { + "bbox": [ + 305, + 578, + 524, + 590 + ], + "type": "text", + "content": "5.2. Scenario 2: Molecule Dynamic Prediction" + } + ] + } + ], + "index": 26 + }, + { + "bbox": [ + 304, + 594, + 547, + 665 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 594, + 547, + 665 + ], + "spans": [ + { + "bbox": [ + 304, + 594, + 547, + 665 + ], + "type": "text", + "content": "We adopt the MD17 [7] dataset which contains the motions of different molecules generated via a molecular dynamics simulation environment. The goal is to predict the motions of every atom of the molecule. We randomly pick four kinds of molecules: Aspirin, Benzene, Ethanol and Malonaldehyde and learn a prediction model for each molecule." + } + ] + } + ], + "index": 27 + }, + { + "bbox": [ + 304, + 666, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 666, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 666, + 547, + 713 + ], + "type": "text", + "content": "Table 4 presents the comparison of different motion prediction methods. We achieve state-of-the-art prediction performance on all four molecules. The ADE/FDE across four molecules is decreased by " + }, + { + "bbox": [ + 304, + 666, + 547, + 713 + ], + "type": "inline_equation", + "content": "34.2\\% / 30.1\\%" + }, + { + "bbox": [ + 304, + 666, + 547, + 713 + ], + "type": "text", + "content": " on average." + } + ] + } + ], + "index": 28 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "text", + "content": "1415" + } + ] + } + ], + "index": 29 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 51, + 74, + 544, + 205 + ], + "blocks": [ + { + "bbox": [ + 47, + 63, + 544, + 73 + ], + "lines": [ + { + "bbox": [ + 47, + 63, + 544, + 73 + ], + "spans": [ + { + "bbox": [ + 47, + 63, + 544, + 73 + ], + "type": "text", + "content": "Table 2. Comparisons of short-term skeleton motion prediction on 11 representative actions and average results across all actions on H3.6M." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 51, + 74, + 544, + 205 + ], + "lines": [ + { + "bbox": [ + 51, + 74, + 544, + 205 + ], + "spans": [ + { + "bbox": [ + 51, + 74, + 544, + 205 + ], + "type": "table", + "html": "
MotionWalkingEatingSmokingDiscussionDirectionsPhoning
millisecond801603204008016032040080160320400801603204008016032040080160320400
Res-sup. (CVPR'17)29.450.876.081.516.830.656.968.723.042.670.182.732.961.290.996.235.457.376.387.738.069.3115.0126.7
Traj-GCN (ICCV'19)12.323.039.846.18.416.933.240.77.916.231.938.912.527.458.571.79.019.943.453.710.221.042.552.3
DMGNN (CVPR'20)17.330.754.665.211.021.436.243.99.017.632.140.317.334.861.069.813.124.664.781.912.525.848.158.3
MSRGCN (ICCV'21)12.222.738.645.28.417.133.040.48.016.331.338.212.026.857.169.78.619.743.353.810.120.741.551.3
PGBIG (CVPR'22)10.219.834.540.37.015.130.638.16.614.128.234.710.023.853.666.77.217.640.951.58.318.338.748.4
SPGSN (ECCV'22)10.119.434.841.57.114.930.537.96.713.828.034.610.423.853.667.17.417.239.850.38.718.338.748.5
EqMotion (Ours)9.017.532.639.26.313.628.936.55.511.323.029.38.218.942.153.96.315.838.950.17.416.736.947.0
MotionPosingSittingSitting DownWaitingWalking TogetherAverage
millisecond801603204008016032040080160320400801603204008016032040080160320400
", + "image_path": "261d77cdb50438963b636cd6d014a4f6f4f95d9b052c5ba5f598792db6a9b47e.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "type": "table", + "bbox": [ + 50, + 217, + 544, + 287 + ], + "blocks": [ + { + "bbox": [ + 48, + 206, + 544, + 217 + ], + "lines": [ + { + "bbox": [ + 48, + 206, + 544, + 217 + ], + "spans": [ + { + "bbox": [ + 48, + 206, + 544, + 217 + ], + "type": "text", + "content": "Table 3. Comparisons of long-term skeleton motion prediction on 8 representative actions and average results across all actions on H3.6M." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 50, + 217, + 544, + 287 + ], + "lines": [ + { + "bbox": [ + 50, + 217, + 544, + 287 + ], + "spans": [ + { + "bbox": [ + 50, + 217, + 544, + 287 + ], + "type": "table", + "html": "
MotionWalkingEatingSmokingDiscussionGreetingPhoningPosingWalking TogetherAverage
millisecond560ms1000ms560ms1000ms560ms1000ms560ms1000ms560ms1000ms560ms1000ms560ms1000ms560ms1000ms560ms1000ms
Res-Sup. [50]81.7100.779.9100.294.8137.4121.3161.7156.3184.3143.9186.8165.4236.8173.6202.3129.2165.0
Traj-GCN [47]54.159.853.477.850.772.691.6121.5115.4148.869.2103.1114.5173.055.065.681.6114.3
DMGNN [41]71.485.858.186.750.972.281.9138.3144.5170.571.3108.4125.5188.270.586.993.6127.6
MSRGCN [9]52.763.052.577.149.571.688.6117.6116.3147.268.3104.4116.3174.352.965.981.1114.2
PGBIG [44]48.156.451.176.046.569.587.1118.2110.2143.565.9102.7106.1164.851.964.376.9110.3
SPGSN [40]46.953.649.873.446.768.689.7118.6111.0143.266.7102.5110.3165.449.860.977.4109.6
EqMotion (Ours)43.452.848.473.041.063.475.3105.6108.7142.064.7101.084.9139.444.556.073.4106.9
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AspirinBenzeneEthanolMalonaldehyde
Radial Field [31]17.98/26.207.73/12.478.10/10.6116.53/25.10
TFN [61]15.02/21.357.55/12.308.05/10.5715.21/24.32
SE(3)-Trans [14]15.70/22.397.62/12.508.05/10.8615.44/24.47
EGNN [58]14.61/20.657.50/12.168.01/10.2215.21/24.00
LSTM17.59/24.796.06/9.467.73/9.8815.14/22.90
S-LSTM [1]13.12/18.143.06/3.527.23/9.8511.93/18.43
NRI [28]12.60/18.501.89/2.586.69/8.7812.79/19.86
NMMP [22]10.41/14.672.21/3.336.17/7.869.50/14.89
GroupNet [69]10.62/14.002.02/2.956.00/7.887.99/12.49
EqMotion(Ours)5.95/8.381.18/1.735.05/7.025.85/9.02
", + "image_path": "0e35fbb2ffffb01894a3c9a6ae0d543767ff662eba077c8ff0722989e1275efd.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "table_body" + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 426, + 287, + 438 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 426, + 287, + 438 + ], + "spans": [ + { + "bbox": [ + 47, + 426, + 287, + 438 + ], + "type": "text", + "content": "5.3. Scenario 3: Human Skeleton Motion Prediction" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 444, + 287, + 503 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 444, + 287, + 503 + ], + "spans": [ + { + "bbox": [ + 46, + 444, + 287, + 503 + ], + "type": "text", + "content": "We conduct experiments on the Human 3.6M (H3.6M) dataset [25] for 3D human skeleton motion prediction. H3.6M contains 7 subjects performing 15 actions. Following the standard paradigm [41, 50], we train the models on 6 subjects and tested on the specific clips of the 5th subject." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 506, + 287, + 601 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 506, + 287, + 601 + ], + "spans": [ + { + "bbox": [ + 46, + 506, + 287, + 601 + ], + "type": "text", + "content": "Short-term motion prediction Short-term motion prediction aims to predict future poses within 400 milliseconds. We compare EqMotion with six state-of-the-art methods. Table 2 presents the comparison of prediction MPJPEs. See the overall result in the Appendix. We see that i) EqMotion obtains superior performance at most timestamps across all the actions; and ii) compared to the baselines, EqMotion achieves much lower MPJPEs by " + }, + { + "bbox": [ + 46, + 506, + 287, + 601 + ], + "type": "inline_equation", + "content": "8.6\\%" + }, + { + "bbox": [ + 46, + 506, + 287, + 601 + ], + "type": "text", + "content": " on average." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 603, + 287, + 662 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 603, + 287, + 662 + ], + "spans": [ + { + "bbox": [ + 46, + 603, + 287, + 662 + ], + "type": "text", + "content": "Long-term motion prediction Long-term motion prediction aims to predict the poses over 400 milliseconds. Table 3 presents the prediction MPJPEs of various methods. We see that EqMotion achieves more effective prediction on most actions and has lower MPJPEs by " + }, + { + "bbox": [ + 46, + 603, + 287, + 662 + ], + "type": "inline_equation", + "content": "3.8\\%" + }, + { + "bbox": [ + 46, + 603, + 287, + 662 + ], + "type": "text", + "content": " on average." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 664, + 287, + 700 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 664, + 287, + 700 + ], + "spans": [ + { + "bbox": [ + 46, + 664, + 287, + 700 + ], + "type": "text", + "content": "Visualization results Figure 4 visualizes and compares the predictions on H3.6M. Baselines fail to predict future movements. EqMotion completes the action more precisely." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 59, + 701, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 701, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 59, + 701, + 288, + 713 + ], + "type": "text", + "content": "The quantitative and visualization results reveal that Eq-" + } + ] + } + ], + "index": 11 + }, + { + "type": "image", + "bbox": [ + 307, + 290, + 542, + 380 + ], + "blocks": [ + { + "bbox": [ + 307, + 290, + 542, + 380 + ], + "lines": [ + { + "bbox": [ + 307, + 290, + 542, + 380 + ], + "spans": [ + { + "bbox": [ + 307, + 290, + 542, + 380 + ], + "type": "image", + "image_path": "66ac84f39e6d3770a2966afba273266f83058812eefa17690a0814951ee8440a.jpg" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 306, + 381, + 545, + 403 + ], + "lines": [ + { + "bbox": [ + 306, + 381, + 545, + 403 + ], + "spans": [ + { + "bbox": [ + 306, + 381, + 545, + 403 + ], + "type": "text", + "content": "Figure 4. Qualitative comparison on the action 'Sitting Down' of H3.6M. EqMotion completes the action more accurately." + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_caption" + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 414, + 547, + 437 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 414, + 547, + 437 + ], + "spans": [ + { + "bbox": [ + 305, + 414, + 547, + 437 + ], + "type": "text", + "content": "Motion outperforms many previous methods that are task-specific, reflecting the effectiveness of EqMotion." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 446, + 538, + 459 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 446, + 538, + 459 + ], + "spans": [ + { + "bbox": [ + 306, + 446, + 538, + 459 + ], + "type": "text", + "content": "5.4. Scenario 4: Pedestrian Trajectory Prediction" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 462, + 547, + 521 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 462, + 547, + 521 + ], + "spans": [ + { + "bbox": [ + 305, + 462, + 547, + 521 + ], + "type": "text", + "content": "We conduct experiments on pedestrian trajectory prediction using the ETH-UCY dataset [34, 54], which contains 5 subsets, ETH, HOTEL, UNIV, ZARA1, and ZARA2. Following the standard setting [1, 20, 76], we use 3.2 seconds (8 timestamps) to predict the 4.8 seconds (12 timestamps)." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 522, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 522, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 522, + 547, + 713 + ], + "type": "text", + "content": "Here we apply our EqMotion to two prediction modes: deterministic and multi-prediction. Deterministic means the model only outputs a single prediction for each input motion. Multi-prediction means the model has 20 predictions for each input motion. Under multi-prediction, ADE and FDE will be calculated by the best-performed predicted motion. To adapt to multi-prediction, we slightly modify EqMotion to repeat the last feature updating layer and the output layer 20 times in parallel to have a multi-head prediction, see the details in the Appendix. Table 5 compares our method with sixteen baselines. We observe that i) EqMotion achieves state-of-the-art performance with the lowest average ADE and FDE, outperforming many baseline methods that are specifically designed for this task. EqMotion reduces the FDE by " + }, + { + "bbox": [ + 304, + 522, + 547, + 713 + ], + "type": "inline_equation", + "content": "10.4\\%" + }, + { + "bbox": [ + 304, + 522, + 547, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 522, + 547, + 713 + ], + "type": "inline_equation", + "content": "7.9\\%" + }, + { + "bbox": [ + 304, + 522, + 547, + 713 + ], + "type": "text", + "content": " under deterministic and multi-prediction settings; and ii) EqMotion achieves the best or the" + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "text", + "content": "1416" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 47, + 95, + 291, + 266 + ], + "blocks": [ + { + "bbox": [ + 47, + 71, + 287, + 92 + ], + "lines": [ + { + "bbox": [ + 47, + 71, + 287, + 92 + ], + "spans": [ + { + "bbox": [ + 47, + 71, + 287, + 92 + ], + "type": "text", + "content": "Table 5. Prediction performance on the ETH-UCY dataset. The bold/underline font denotes the best/second best result." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 47, + 95, + 291, + 266 + ], + "lines": [ + { + "bbox": [ + 47, + 95, + 291, + 266 + ], + "spans": [ + { + "bbox": [ + 47, + 95, + 291, + 266 + ], + "type": "table", + "html": "
Performance (ADE/FDE)
DeterministicETHHotelUnivZara1Zara2Average
S-LSTM [1]1.09/2.350.79/1.760.67/1.400.47/1.000.56/1.170.72/1.54
SGAN-ind [20]1.13/2.211.01/2.180.60/1.280.42/0.910.52/1.110.74/1.54
Traj++ [55]1.02/2.000.33/0.620.53/1.190.44/0.990.32/0.730.53/1.11
TransF [16]1.03/2.100.36/0.710.53/1.320.44/1.000.34/0.760.54/1.17
MemoNet [70]1.00/2.080.35/0.670.55/1.190.46/1.000.37/0.820.55/1.15
EqMotion(Ours)0.96/1.920.30/0.580.50/1.100.39/0.860.30/0.680.49/1.03
Multi-predictionETHHotelUnivZara1Zara2Average
SGAN [20]0.87/1.620.67/1.370.76/0.520.35/0.680.42/0.840.61/1.21
NMMP [22]0.61/1.080.33/0.630.52/1.110.32/0.660.43/0.850.41/0.82
Traj++ [55]0.61/1.020.19/0.280.30/0.540.24/0.420.18/0.310.30/0.51
PECNet [45]0.54/0.870.18/0.240.35/0.600.22/0.390.17/0.300.29/0.48
Agentformer [76]0.45/0.750.14/0.220.25/0.450.18/0.300.14/0.240.23/0.39
GroupNet [69]0.46/0.730.15/0.250.26/0.490.21/0.390.17/0.330.25/0.44
MID [18]0.39/0.660.13/0.220.22/0.450.17/0.300.13/0.270.21/0.38
GP-Graph [2]0.43/0.630.18/0.300.24/0.420.17/0.310.15/0.290.23/0.39
EqMotion(Ours)0.40/0.610.12/0.180.23/0.430.18/0.320.13/0.230.21/0.35
", + "image_path": "201e495356de449f8c2904dae0f0d7d7b37a8bd6f82e3ca1161702c56d4be685.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "type": "table", + "bbox": [ + 52, + 279, + 282, + 341 + ], + "blocks": [ + { + "bbox": [ + 49, + 268, + 284, + 277 + ], + "lines": [ + { + "bbox": [ + 49, + 268, + 284, + 277 + ], + "spans": [ + { + "bbox": [ + 49, + 268, + 284, + 277 + ], + "type": "text", + "content": "Table 6. Ablation study on key modules of EqMotion on H3.6M." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 52, + 279, + 282, + 341 + ], + "lines": [ + { + "bbox": [ + 52, + 279, + 282, + 341 + ], + "spans": [ + { + "bbox": [ + 52, + 279, + 282, + 341 + ], + "type": "table", + "html": "
EGFLIPFLIRM80ms160ms320ms400msAverage
12.931.968.282.448.9
✓10.122.648.760.735.5
✓✓9.220.845.457.033.1
✓✓✓9.120.143.755.032.0
", + "image_path": "7f3425fe5da172c2e35960b1b3bf3ebd8e06e90231633585b069e99a06256359.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "type": "table", + "bbox": [ + 48, + 365, + 287, + 427 + ], + "blocks": [ + { + "bbox": [ + 47, + 342, + 286, + 363 + ], + "lines": [ + { + "bbox": [ + 47, + 342, + 286, + 363 + ], + "spans": [ + { + "bbox": [ + 47, + 342, + 286, + 363 + ], + "type": "text", + "content": "Table 7. Ablation study on operations in the equivariant geometric feature learning on H3.6M dataset." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 48, + 365, + 287, + 427 + ], + "lines": [ + { + "bbox": [ + 48, + 365, + 287, + 427 + ], + "spans": [ + { + "bbox": [ + 48, + 365, + 287, + 427 + ], + "type": "table", + "html": "
Ablation80ms160ms320ms400msAverage
w/o Inner att9.220.544.355.732.4
w/o Inter agg9.722.047.258.934.5
w/o Non-linear9.421.346.758.634.0
EqMotion9.120.143.755.032.0
", + "image_path": "b41302088839b3d270c27f51fa842ab8baf0e030609ed80dd2973fc9e9f69f0d.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "table_body" + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 430, + 287, + 455 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 430, + 287, + 455 + ], + "spans": [ + { + "bbox": [ + 46, + 430, + 287, + 455 + ], + "type": "text", + "content": "second best ADE/FDE result on most subsets, reflecting its effectiveness on the pedestrian trajectory prediction." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 459, + 147, + 469 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 459, + 147, + 469 + ], + "spans": [ + { + "bbox": [ + 47, + 459, + 147, + 469 + ], + "type": "text", + "content": "5.5. Ablation Studies" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 474, + 287, + 593 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 474, + 287, + 593 + ], + "spans": [ + { + "bbox": [ + 46, + 474, + 287, + 593 + ], + "type": "text", + "content": "Effect of network modules We explore the effect of three proposed key modules in EqMotion on the H3.6M dataset, including the equivariant geometric feature learning (EGFL), the invariant pattern feature learning (IPFL) and the invariant reasoning module (IRM). Table 6 presents the experimental result. It is observed that i) the proposed three key modules all contribute to an accurate prediction; and ii) the equivariant geometric feature learning module is most important since learning a comprehensive equivariant geometric feature directly for prediction is the most important." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 594, + 288, + 677 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 594, + 288, + 677 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 288, + 677 + ], + "type": "text", + "content": "Effect of equivariant operations We explore the effect of three proposed operations in the equivariant feature learning module in EqMotion, including the inner-agent attention (Inner att), inter-agent aggregation (Inter agg) and non-linear function (Non-linear). Table 7 presents the results. We see that the proposed three key operations all contribute to promoting an accurate prediction." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 677, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 288, + 713 + ], + "type": "text", + "content": "Different amounts of training data Figure 5 presents the comparison of model performance under different amounts of training data on H3.6M. We see that i) our method" + } + ] + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 319, + 70, + 531, + 190 + ], + "blocks": [ + { + "bbox": [ + 319, + 70, + 531, + 190 + ], + "lines": [ + { + "bbox": [ + 319, + 70, + 531, + 190 + ], + "spans": [ + { + "bbox": [ + 319, + 70, + 531, + 190 + ], + "type": "image", + "image_path": "78e38ba1b03658df0374cb61713f5b007d611827bf91a31a1fb41a2ea7a888d2.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 190, + 545, + 211 + ], + "lines": [ + { + "bbox": [ + 305, + 190, + 545, + 211 + ], + "spans": [ + { + "bbox": [ + 305, + 190, + 545, + 211 + ], + "type": "text", + "content": "Figure 5. Comparison of model performance on different amounts of data in short-term prediction on H3.6M dataset." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 11 + }, + { + "type": "image", + "bbox": [ + 320, + 212, + 529, + 331 + ], + "blocks": [ + { + "bbox": [ + 320, + 212, + 529, + 331 + ], + "lines": [ + { + "bbox": [ + 320, + 212, + 529, + 331 + ], + "spans": [ + { + "bbox": [ + 320, + 212, + 529, + 331 + ], + "type": "image", + "image_path": "e4c924e8ae3ed1f7112d255ab3bb483ad5a2650ea969fd116e2573f0035707b2.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 331, + 545, + 353 + ], + "lines": [ + { + "bbox": [ + 305, + 331, + 545, + 353 + ], + "spans": [ + { + "bbox": [ + 305, + 331, + 545, + 353 + ], + "type": "text", + "content": "Figure 6. Comparison of model size and MPJPE in short-term prediction on H3.6M dataset. The target means the ideal model." + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_caption" + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 360, + 547, + 419 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 360, + 547, + 419 + ], + "spans": [ + { + "bbox": [ + 304, + 360, + 547, + 419 + ], + "type": "text", + "content": "achieves the best prediction performance under all training data ratios; and ii) our method even outperforms some full-data using baselines by only using " + }, + { + "bbox": [ + 304, + 360, + 547, + 419 + ], + "type": "inline_equation", + "content": "5\\%" + }, + { + "bbox": [ + 304, + 360, + 547, + 419 + ], + "type": "text", + "content": " of training data since the equivariant design promotes the network generalization ability under Euclidean transformations." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 420, + 547, + 503 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 420, + 547, + 503 + ], + "spans": [ + { + "bbox": [ + 304, + 420, + 547, + 503 + ], + "type": "text", + "content": "Model size Figure 6 compares EqMotion to existing methods in terms of the model size and prediction results in short-term prediction on H3.6M. We can observe that EqMotion has the smallest model size (less than " + }, + { + "bbox": [ + 304, + 420, + 547, + 503 + ], + "type": "inline_equation", + "content": "30\\%" + }, + { + "bbox": [ + 304, + 420, + 547, + 503 + ], + "type": "text", + "content": " of other models' sizes) with the lowest MPJPE thanks to the equivariant design that compacts the model free from generalizing over rotations and translations of the data." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 516, + 378, + 528 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 516, + 378, + 528 + ], + "spans": [ + { + "bbox": [ + 306, + 516, + 378, + 528 + ], + "type": "text", + "content": "6. Conclusion" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 533, + 545, + 617 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 533, + 545, + 617 + ], + "spans": [ + { + "bbox": [ + 304, + 533, + 545, + 617 + ], + "type": "text", + "content": "In this work, we present EqMotion, a motion prediction network that is theoretically equivariant under Euclidean transformations. EqMotion includes three novel designs: the equivariant geometric feature learning, the invariant pattern feature learning and the invariant reasoning module. We evaluate our method on four different scenarios and our method achieves state-of-the-art prediction performance." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 617, + 547, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 547, + 712 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 547, + 712 + ], + "type": "text", + "content": "Acknowledgements. This project is partially supported by National Natural Science Foundation of China under Grant 62171276, the Science and Technology Commission of Shanghai Municipal under Grant 21511100900 and 22DZ2229005, and the National Research Foundation Singapore under its AI Singapore Programme (Award Number: AISG2-RP-2021-023). Robby T. Tan's work is supported by MOE AcRF Tier, A-0009455-01-00." + } + ] + } + ], + "index": 19 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "text", + "content": "1417" + } + ] + } + ], + "index": 20 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 288, + 713 + ], + "type": "list", + "angle": 0, + "index": 14, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 147 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 147 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 147 + ], + "type": "text", + "content": "[1] Alexandre Alahi, Kratarth Goel, Vignesh Ramanathan, Alexandre Robicquet, Li Fei-Fei, and Silvio Savarese. 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In deep neural networks, models usually end with a $k$ -way fully connected layer with softmax to handle different classification tasks. The learning objective of these methods can be summarized as mapping the learned feature representations to the samples' label space. While in metric learning approaches, the main objective is to learn a transformation function that maps training data points from the original space to a new space where similar points are closer while dissimilar points become farther apart. Different from previous methods, our EBVs generate normalized vector embeddings as \"predefined classifiers\" which are required to not only be with the equal status between each other, but also be as orthogonal as possible. By minimizing the spherical distance of the embedding of an input between its categorical EBV in training, the predictions can be obtained by identifying the categorical EBV with the smallest distance during inference. Various experiments on the ImageNet-1K dataset and other downstream tasks demonstrate that our method outperforms the general fully connected classifier while it does not introduce huge additional computation compared with classical metric learning methods. Our EBVs won the first place in the 2022 DIGIX Global AI Challenge, and our code is open-source and available at https://github.com/NJUST-VIPGroup/Equiangular-Basis-Vectors.", + "bbox": [ + 75, + 317, + 473, + 676 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 77, + 700, + 208, + 714 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "The pattern classification field developed around the end of the twentieth century aims to deal with the specific problem of assigning input signals to two or more classes [56]. In recent years, deep learning models have brought breakthroughs in processing image, video, audio, text, and other", + "bbox": [ + 75, + 723, + 470, + 793 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "*Corresponding author. This work was supported by National Key R&D Program of China (2021YFA1001100), National Natural Science Foundation of China under Grant (62272231), Natural Science Foundation of Jiangsu Province of China under Grant (BK20210340), the Fundamental Research Funds for the Central Universities (No. NJ2022028), and CAAI-Huawei MindSpore Open Fund.", + "bbox": [ + 75, + 798, + 470, + 866 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/454be30ec200476950ac985528eff7f73c2e6f51f10f3e4323187bd821a8371b.jpg", + "image_caption": [ + "(a) Fully Connected Layers with Softmax" + ], + "image_footnote": [], + "bbox": [ + 584, + 289, + 823, + 420 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/d4275b04165c0bb888f9afd59f701f7f617e49539ed17f0ef8f1781f7fc5ac32.jpg", + "image_caption": [ + "(b) Metric Learning", + "(c) Equiangular Basis Vectors", + "Figure 1. Comparisons between typical classification paradigms and our proposed Equiangular Basis Vectors (EBVs). (a) A general classifier ends with $k$ -way fully connected layers with softmax. When adding more categories, the trainable parameters of the classifier grow linearly. (b) Taking triplet embedding [60] as an example of classical metric learning methods, the complexity is $\\mathcal{O}(M^3)$ when given $M$ images and it will grows to $\\mathcal{O}((M + m')^3)$ when adding a new category with $m'$ images. (c) Our proposed EBVs. EBVs predefine fixed normalized vector embeddings for different categories and these embeddings will not be changed during the training stage. The trainable parameters of the network will not be changed with the growth of the number of categories while the complexity only grows from $\\mathcal{O}(M)$ to $\\mathcal{O}(M + m')$ ." + ], + "image_footnote": [], + "bbox": [ + 505, + 440, + 905, + 549 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "data [10, 19, 27, 58]. Aided by the rapid gains in hardware, deep learning methods today can easily overfit one million images [9] and easily overcomes the obstacle to the quality of handcrafted features in previous pattern classification tasks. Many approaches based on deep learning spring up like mushrooms and had been used to solve classification problems in various scenarios and settings such as remote sensing [38], few-shot [52], long-tailed [72], etc.", + "bbox": [ + 497, + 755, + 895, + 866 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 129, + 49, + 200, + 84 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation.", + "bbox": [ + 252, + 48, + 791, + 61 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "Except for this watermark, it is identical to the accepted version;", + "bbox": [ + 332, + 61, + 709, + 74 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 304, + 74, + 739, + 87 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "11755", + "bbox": [ + 465, + 885, + 505, + 897 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Figure 1 illustrates two typical classification paradigms. Nowadays, a large amount of deep learning methods [38, 72] adopt a trainable fully connected layer with softmax as the classifier. However, since the number of categories is fixed, the trainable parameters of the classifier rise as the number of categories becomes larger. For example, the memory consumption of a fully connected layer $\\mathbf{W} \\in \\mathbb{R}^{d \\times N}$ linearly scales up with the growth of the category number $N$ and so is the cost to compute the matrix multiplication between the fully connected layer and the $d$ -dimensional features. While some other methods based on classical metric learning [23, 30, 60-62] have to consider all the training samples and design positive/negative pairs then optimize a class center for each category, which requires a significant amount of extra computation for large-scale datasets, especially for those pre-training tasks.", + "bbox": [ + 75, + 125, + 472, + 347 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In this paper, we propose Equiangular Basis Vectors (EBVs) to replace the fully connected layer associated with softmax within classification tasks in deep neural networks. EBVs predefine fixed normalized vector embeddings with equal status (equal angles) which will not be changed during the training stage. Specifically, EBVs pre-set a $d$ -dimensional unit hypersphere, and for each category in the classification task, EBVs assign the category a $d$ -dimensional normalized embedding on the surface of the hypersphere and we term these embedding as basis vectors. The spherical distance of each basis vector pair satisfies an artificially made rule to make the relationship between any two vectors as close to orthogonal as possible. In order to keep the trainable parameters of the deep neural networks constant with the growth of the category number $N$ , we then propose the definition of EBVs based on Tammes Problem [55] and Equiangular Lines [57] in Section 3.2.", + "bbox": [ + 75, + 351, + 472, + 586 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "The learning objective of each category in our proposed EBVs is also different from previous classification methods. Compared with deep models that end with a fully connected layer to handle the classification tasks [19, 27], the meaning of the parameter weights within the fully connected layer in EBVs is not the relevance of a feature representation to a particular category but a fixed matrix which embed feature representations to a new space. Also, compared with regression methods [34,51], EBVs do not need to learn the unified representations for different categories and optimize the distance between the representation of input images and category centers, which helps reduce the computational consumption for the extra unified representations learning. In contrast to classical metric learning approaches [14, 23, 50, 61], our EBVs do not need to measure the similarity among different training samples and constrain distance between each category, which will introduce a large amount of computational consumption for large-scale datasets. In our proposed method, the representations of different images learned by EBVs will be embedded into a normalized hypersphere and the learning", + "bbox": [ + 75, + 589, + 472, + 866 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "objective is altered to minimize the spherical distance of the learned representations with different predefined basis vectors. In addition, the spherical distance between each predefined basis vector is carefully constrained so that there is no need to spend extra cost in the optimization of these basis vectors. To quantitatively prove both the effectiveness and efficiency of our proposed EBVs, we evaluate EBVs on diverse computer vision tasks with large-scale datasets, including classification on ImageNet-1K, object detection on COCO, as well as semantic segmentation on ADE20K.", + "bbox": [ + 497, + 125, + 894, + 264 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related work", + "text_level": 1, + "bbox": [ + 499, + 277, + 638, + 292 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.1. Deep networks for image classification", + "text_level": 1, + "bbox": [ + 499, + 301, + 830, + 315 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Image classification is the task of categorizing images into one of several predefined classes, which has been a fundamental problem in computer vision for a long time [4, 36]. It also forms the basis for many other computer vision tasks, e.g., object detection [37], localization [28] and segmentation [39]. To solve the image classification problem, a dual-stage approach was used before the rise of deep learning. Specifically, handcrafted features were first extracted from images using feature descriptors. Then, a trainable classifier is adopted to perform the classification task with these input features [44]. The major hindrance of this approach was that the accuracy of the classification task was profoundly dependent on the design of the feature extraction stage, and this usually proved to be a formidable task [29].", + "bbox": [ + 497, + 323, + 894, + 516 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In recent years, deep learning models that exploit multiple layers of nonlinear information processing, for feature extraction and transformation as well as for pattern analysis and classification, have been shown to overcome these challenges [44]. With the holding of ImageNet Large Scale Visual Recognition Challenge (ILSVRC) [49], a growing number of deep networks demonstrate superior classification performance [10, 15, 19, 27, 32, 33, 42]. Among them, Deep Convolutional Neural Networks (DCNNs) and Vision Transformers (ViTs) [10] have become the leading architectures for most image classification task in recent years. In addition, selected representative examples of other improvement attempts related to the following different aspects: network architecture, nonlinear activation functions, supervision components, regularization mechanisms and optimization techniques. Our proposed Equiangular Basis Vectors (EBVs) are different from these aspects as we do not change the overall architecture and training techniques but the optimization objectives for classification since we preliminary design fixed normalized vector embeddings for each predefined category.", + "bbox": [ + 497, + 517, + 895, + 793 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.2. Learning objectives", + "text_level": 1, + "bbox": [ + 499, + 802, + 687, + 817 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Besides traditional classifiers, machine learning or deep learning methods such as clustering [1,45], regression [34, 51], metric learning [14,50,61], sparse learning [48,67] can", + "bbox": [ + 499, + 824, + 894, + 866 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "11756", + "bbox": [ + 465, + 885, + 505, + 897 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "be used to handle the classification tasks while the learning objectives of these methods vary considerably. In this section, we only discuss the learning objective of our EBVs with two prominent training paradigms of deep learning for the classification tasks, i.e., general $k$ -way classification layers [27] and classical deep metric learning [3, 66].", + "bbox": [ + 75, + 125, + 470, + 209 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Regarding deep learning for classification, the $k$ -way classification layer (always associated with softmax) is the most popular used approach for training deep models. It employs a single linear layer or multiple non-linear layers to map the learned deep representations to the semantic categories in the label space. The corresponding learning objective is minimizing the losses (e.g., the cross-entropy loss [8]) between the mapped categorical signals (aka. predictions) with the ground truth categories. Compared with that, the learning objective of our EBVs is to make the vectorized embedding of input as close as possible to its categorical equiangular basis vector correspondingly.", + "bbox": [ + 75, + 212, + 470, + 378 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The learning objective of classical deep metric learning seems similar to ours. However, there are several crucial and fundamental differences. Firstly, although deep metric learning minimizes the distances between sample vectors belonging to the same category and meanwhile maximizes the distances between samples from different categories, all these sample vectors are constantly changing during the model training process. But, in our method, the equiangular basis vectors corresponding to the categories are predefined, i.e., they are fixed. More importantly, these equiangular basis vectors in the spherical space are forced to be with equal status and be as orthogonal as possible to each other, which could contribute to strong model discriminative ability and good classification accuracy. In practice, both with equal status and being orthogonal of vectors are strict conditions w.r.t. optimization. Thus, our EBVs predefine the satisfied categorical basis vectors and our learning objective focuses on only optimizing the learned feature representations to prevent the model from being unable to converge (when EBVs can also change under such strict conditions). Secondly, the learning objective of deep metric learning is upon massive training samples, while our learning objective is for the training sample and its fixed categorical vectorized embedding, i.e., EBV. It could bring the computational economy, especially for the large-scale training data scenario, cf. Section 3.5. In addition, compared with several specific metric learning approaches, e.g., the center loss [62], the prototypical network [52] and the nearest class mean approach [40], our method is still quite distant from them. Specifically, the basic idea of these works is to construct the \"center\" of samples belonging to a category to represent its semantics and then leverage the centers to optimize sample distances for classification. Similarly, since these categorical centers are always changing during training, these approaches will also encounter the same problems as aforementioned.", + "bbox": [ + 75, + 382, + 470, + 866 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Methodology", + "text_level": 1, + "bbox": [ + 499, + 124, + 633, + 140 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Preliminaries", + "text_level": 1, + "bbox": [ + 499, + 148, + 638, + 162 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The proposed Equiangular Basis Vectors (EBVs) are based on the study with regard to Equiangular Lines [21, 22,57] and the Tammes Problem [55].", + "bbox": [ + 497, + 169, + 892, + 213 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "A set of lines passing through the origin in $\\mathbb{R}^d (d\\in$ $\\{2,3,4,5,\\ldots \\})$ is called equiangular if they are pairwise separated by the same angle. The study of equiangular lines was initiated by Haantjes [22] and it plays an important role in the coding theory [53] and quantum information theory [46].", + "bbox": [ + 497, + 213, + 892, + 296 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The problem of how to determine the maximum number $N(d)$ of equiangular lines in a given dimension $d$ was formally posed by Van Lint and Seidel [57] and has gained a major breakthrough by Jiang et al. [21] last year — Fix $0 < \\alpha < 1$ , let $N_{\\alpha}(d)$ denote the maximum number of lines through the origin in $\\mathbb{R}^d$ with pairwise common angle $\\arccos \\alpha$ , let $k$ denote the minimum number (if it exists) of vertices in a graph whose adjacency matrix has spectral radius exactly $(1 - \\alpha) / (2\\alpha)$ . If $k < \\infty$ , then $N_{\\alpha}(d) = \\lfloor k(d - 1) / (k - 1)\\rfloor$ for all sufficiently large $d$ , and otherwise $N_{\\alpha}(d) = d + o(d)$ . In particular, $N_{1 / (2k - 1)}(d) = \\lfloor k(d - 1) / (k - 1)\\rfloor$ for every integer $k \\geq 2$ and all sufficiently large $d$ [21].", + "bbox": [ + 497, + 298, + 892, + 464 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In simple terms, with a fixed common angle, the maximum number $N(d)$ of equiangular lines is linearly correlated with the dimension $d$ as $d \\to \\infty$ while there is still no precise lower bound for $N(d)$ with smaller values of $d$ [13]. Therefore, we further refer to the Tammes Problem. Let $a_{n}$ be the maximal number with the property that one can place on a unit hypersphere $S^{d} \\in \\mathbb{R}^{d}(d \\in \\{3,4,5,\\ldots\\})$ $n$ points so that the spherical distance of any two points is at least $a_{n}$ . The problem of finding $a_{n}$ together with the corresponding arrangement of each point is known as the Tammes Problem [55] or the optimal spherical code [12]. It is easy to find that the number of these points will be close to infinity as $a_{n}$ tends to zero.", + "bbox": [ + 497, + 465, + 894, + 644 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. Definition of Equiangular Basis Vectors", + "text_level": 1, + "bbox": [ + 499, + 657, + 836, + 672 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In order to predefine fixed $d$ -dimensional embeddings for as many categories as possible but still keep these embeddings at a distance from each other on a unit hypersphere $S^d \\in \\mathbb{R}^d$ , we therefore propose Equiangular Basis Vectors (EBVs). Specifically, we fix $0 \\leq \\alpha < 1$ and let $\\mathcal{N}_{\\alpha}(d)$ denote the range of values for the number of coordinate vectors in $\\mathbb{R}^d$ with the pairwise common angle between $\\arccos \\alpha$ and $\\arccos -\\alpha$ . The problem of our proposed EBVs is to calculate the coordinates of each vector in the vector set $\\mathcal{W}$ when given fixed $\\alpha, d$ and $N \\in \\mathcal{N}_{\\alpha}(d)$ if possible, i.e., solve the set $\\mathcal{W}$ which satisfies:", + "bbox": [ + 497, + 680, + 892, + 831 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\forall \\boldsymbol {w} _ {i}, \\boldsymbol {w} _ {j} \\in \\mathcal {W}, i \\neq j, - \\alpha \\leq \\frac {\\boldsymbol {w} _ {i} \\cdot \\boldsymbol {w} _ {j}}{\\| \\boldsymbol {w} _ {i} \\| \\| \\boldsymbol {w} _ {j} \\|} \\leq \\alpha , \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 521, + 840, + 892, + 870 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "11757", + "bbox": [ + 465, + 885, + 504, + 897 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\pmb{w}_i\\in \\mathbb{R}^d$ , card(W) $= N$ and $\\| \\cdot \\|$ denotes the Euclidean norm. Let $\\phi$ denote the spherical distance function, which can also be replaced by the cosine similarity function. EBVs produce a distribution over classes for a query point $\\pmb {v}\\in \\mathbb{R}^{d}$ based on softmax over cosine similarity to the $N$ fixed coordinate vectors in the embedding space:", + "bbox": [ + 75, + 124, + 473, + 209 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\np (y = k | \\boldsymbol {v}) = \\frac {\\exp (- \\phi (\\boldsymbol {v} , \\boldsymbol {w} _ {k}))}{\\sum_ {k ^ {\\prime}} \\exp (- \\phi (\\boldsymbol {v} , \\boldsymbol {w} _ {k ^ {\\prime}}))}, \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 139, + 216, + 470, + 248 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $y = k \\in \\{1, 2, \\dots, N\\}$ denotes the corresponding coordinate vector, which can also be seen as the corresponding label. While $k'$ represents the associated basis vectors in $\\mathcal{W}$ . Relations between $\\alpha$ , $d$ and $N$ are described in the supplementary materials. With such a set $\\mathcal{W}$ , the maximum number of categories it can handle is $N$ . Additionally, training with any category number less than $N$ , it is sufficient to randomly select any of the same numbers of coordinate vectors in $\\mathcal{W}$ , since these vectors are exactly equivalent.", + "bbox": [ + 75, + 254, + 472, + 381 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.3. How to generate EBVs?", + "text_level": 1, + "bbox": [ + 77, + 387, + 295, + 402 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The basic idea of our Equiangular Basis Vectors (EBVs) is to generate fixed normalized vector embeddings with equal status (equal angles) as \"predefined classifiers\" for all the relevant categories. The question then comes to how to calculate the predefined EBVs which satisfy Eq. (1). Therefore, we will discuss how to generate the proposed EBVs when given fixed $\\alpha$ , $d$ and $N \\in \\mathcal{N}_{\\alpha}(d)$ in this section.", + "bbox": [ + 75, + 408, + 468, + 505 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Assuming each $\\boldsymbol{w}_i \\in \\mathcal{W}$ ( $i = \\{1, 2, \\dots, N\\}$ ) as a line, we can construct the Grassmannian Matrices to solve the set $\\mathcal{W}$ [11]. Specifically, we assemble the vectors in $\\mathcal{W}$ into a matrix $\\boldsymbol{W} \\in \\mathbb{R}^{d \\times N}$ , where $\\boldsymbol{W} = [\\boldsymbol{w}_1; \\boldsymbol{w}_2; \\dots; \\boldsymbol{w}_N]$ . Then, the mutual-coherence of $\\boldsymbol{W}$ is defined by:", + "bbox": [ + 75, + 505, + 472, + 574 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mu (\\boldsymbol {W}) = \\max _ {1 \\leq i, j \\leq N, i \\neq j} \\frac {\\left| \\boldsymbol {w} _ {i} ^ {\\top} \\cdot \\boldsymbol {w} _ {j} \\right|}{\\left\\| \\boldsymbol {w} _ {i} \\right\\| \\left\\| \\boldsymbol {w} _ {j} \\right\\|} = \\max _ {1 \\leq i, j \\leq N, i \\neq j} \\cos \\theta_ {i j}, \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 80, + 592, + 468, + 637 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "which is transformed to the smallest possible mutualcoherence possible [11]. Therefore, the lower bound for $\\alpha$ is $\\sqrt{\\frac{N - d}{d(N - 1)}}$ and the upper bound for $\\mathcal{N}_{\\alpha}(d)$ is $1 + \\frac{d - 1}{1 - \\alpha^2d}$ ( $d \\leq N, 1 - \\alpha^2 d > 0$ ). In addition, such matrix is possible only if $N < \\min(d(d + 1)/2, (N - d)(N - d + 1)/2)$ . Construction of such a matrix has a strong connection with the packing of vectors/subspaces in the $\\mathbb{R}^d$ -space. In the case of $N = d$ , we can simply construct a unitary matrix, while in other cases, it will be very hard to construct such a general Grassmannian matrix [11].", + "bbox": [ + 75, + 637, + 468, + 782 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In the definition of our proposed EBVs, whether the angle between any two basis vectors $\\pmb{w}_i, \\pmb{w}_j \\in \\mathcal{W} (i \\neq j)$ is $\\arccos \\alpha$ or $\\arccos -\\alpha$ is equivalent. It is clear that we can not construct the Grassmannian matrix in a situation such as $N = 30,000$ and $d = 200$ . However, it is still possible for us to construct $\\mathcal{W}$ which satisfies Eq. (1). Therefore, as", + "bbox": [ + 75, + 783, + 468, + 866 + ], + "page_idx": 3 + }, + { + "type": "code", + "sub_type": "algorithm", + "code_caption": [ + "Algorithm 1 Generation of EBVs in a PyTorch-like style" + ], + "code_body": "#d:Dim for each coordinate vectors \n#N:The number of coordinate vectors \n# $\\alpha$ : Threshold of $\\hat{\\pmb{w}}_i\\cdot \\hat{\\pmb{w}}_j,i\\neq j$ \n#W:The EBVs matrix $W\\in \\mathbb{R}^{d\\times N}$ \n#slice: In the case of $N\\gg d$ ,optimize W by slicing \n#λ: Learning rate. \nInitialize W randomly; \nwhile True: #Normalize each row in W \n $W =$ Normalize(W) \nfor i in [N/slice]: start $=$ i\\* slice end $= \\min (N$ $(\\mathrm{i} + 1)^{*}$ slice) E $=$ Fonehot(arange(start, end), N) C $=$ (W[start:end]@W.T).abs()-E loss $=$ ReLU(C-α).sum() # Cutout the gradient of vector pairs which satisfies $-\\alpha \\leq \\hat{\\pmb{w}}_i\\cdot \\hat{\\pmb{w}}_j\\leq \\alpha$ loss.backup() if max(α,C.max()) < α + o(α): Save(W) break \n $W = W - \\lambda *W.\\mathrm{grad}\\#$ Update W", + "bbox": [ + 500, + 141, + 788, + 406 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "an alternative, we adopt Stochastic Gradient Descent [47] to search the set $\\mathcal{W}$ that satisfies the definition of EBVs when given fixed $\\alpha$ , $d$ and $N$ . Specifically, we random initialize a matrix $\\pmb{W} \\in \\mathbb{R}^{d \\times N}$ with normalized rows such that the angle between any two vectors $\\hat{\\pmb{w}}_i$ , $\\hat{\\pmb{w}}_j \\in \\mathbb{R}^d$ , $i, j \\in \\{1, 2, \\dots, N\\}$ , $i \\neq j$ , $\\hat{\\pmb{w}}_i = \\frac{\\pmb{w}_i}{\\|\\pmb{w}_i\\|}$ can be represented as $\\arccos(\\hat{\\pmb{w}}_i \\cdot \\hat{\\pmb{w}}_j)$ . Then, we cut out the gradient of those vector pairs which satisfies $-\\alpha \\leq \\hat{\\pmb{w}}_i \\cdot \\hat{\\pmb{w}}_j \\leq \\alpha$ and optimize the remaining vector pairs. The optimization function of the generation of EBVs can be formulated by:", + "bbox": [ + 497, + 429, + 890, + 570 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\underset {\\boldsymbol {W}} {\\arg \\min } \\sum_ {i = 1} ^ {N - 1} \\sum_ {j > i} ^ {N} \\max \\left(\\hat {\\boldsymbol {w}} _ {i} \\cdot \\hat {\\boldsymbol {w}} _ {j} - \\alpha , 0\\right). \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 539, + 578, + 890, + 606 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Algorithm 1 provides the code of a simple generation method of the proposed EBVs in a PyTorch-like style. It is also worth mentioning that the EBVs matrix $W$ will not be changed in the following training stage within all the tasks.", + "bbox": [ + 497, + 615, + 890, + 671 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.4. How to achieve the learning objective of EBVs?", + "text_level": 1, + "bbox": [ + 499, + 678, + 890, + 694 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Equiangular Basis Vectors (EBVs) provide fixed learning targets for each independent optimization objective, i.e., semantic categories. In the following, we introduce how to achieve the learning objective of EBVs for all the training samples. Generally, a deep network is performed to extract the high-dimensional features, and a fully connected classification layer is then deployed to map the features to semantic categories. While in our proposed EBVs, each category will be bound to a unique normalized $d$ -dimensional basis vector in $\\mathcal{W}$ . Thus, for a training sample $x$ , we directly use a unified deep model to generate a $d$ -dimensional embedding $\\pmb{v}$ , as well as optimizing the cosine distance between $\\pmb{v}$ and", + "bbox": [ + 497, + 700, + 894, + 866 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "11758", + "bbox": [ + 465, + 885, + 505, + 897 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "the relevant basis vector. Below we analyze the underlying distance/loss function used in the training stage.", + "bbox": [ + 75, + 125, + 468, + 153 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "For our EBVs, many existing distance functions including squared Euclidean distance, Mahalanobis distance, or cosine distance are permissible. However, a particular class of distance functions, e.g., regular Bregman divergences [2], seems hard to explain and optimize in the proposed EBVs settings. In addition, intuitively, the straightforward way is to optimize the spherical distance between any two vectors on the surface of the hyper-sphere. Therefore, we adopt the cosine distance as the distance metric, which is widely used for measuring whether two inputs are similar or dissimilar and have been widely used in the Tammes problem [55].", + "bbox": [ + 75, + 154, + 470, + 306 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Implementations Suppose we have $M$ sample-label pairs $\\{(x_{1},y_{1}),(x_{2},y_{2}),\\ldots ,(x_{M},y_{M})\\}$ in $N$ classes and their $d$ -dimensional features $\\pmb{v}_1,\\pmb{v}_2,\\dots ,\\pmb{v}_M$ with $\\boldsymbol {v}_i = f_\\theta (\\boldsymbol {x}_i)$ where $f_{\\theta}(\\cdot)$ represents a feature extractor. A straightforward way to achieve the learning objective of EBVs is to directly optimize the cosine similarity between each $\\pmb{v}_i$ and the corresponding basis vector $\\hat{w}_{y_i}\\in \\mathcal{W}$", + "bbox": [ + 75, + 325, + 468, + 421 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "However, the basis vector itself is not correlated with the training data since it is predefined. Fitting the training samples directly to the corresponding basis vectors might disrupt the representation learning. Therefore, we consider the conventional parametric softmax formulation, of which for image $x_{i}$ with embedding $v_{i}$ , the probability of it being recognized as the $y_{i}$ category can be formulated as:", + "bbox": [ + 75, + 422, + 468, + 517 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nP (y = y _ {i} | \\boldsymbol {v} _ {i}) = \\frac {\\exp \\left(\\boldsymbol {m} _ {i} ^ {\\top} \\boldsymbol {v} _ {i}\\right)}{\\sum_ {j = 1} ^ {N} \\exp \\left(\\boldsymbol {m} _ {j} ^ {\\top} \\boldsymbol {v} _ {i}\\right)}, \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 147, + 529, + 468, + 566 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $m_j$ is a weight vector for the $j$ -th class. Thus, according to Eq. (2) and Eq. (5), the probability of the embedding $v_i$ being recognized as category $y_i$ in our proposed EBVs can be formulated as:", + "bbox": [ + 75, + 574, + 468, + 629 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nP _ {\\mathrm {E B V s}} (y = y _ {i} \\mid \\boldsymbol {v} _ {i}) = \\frac {\\exp \\left(\\hat {\\boldsymbol {w}} _ {i} \\hat {\\boldsymbol {v}} _ {i} / \\tau\\right)}{\\sum_ {j = 1} ^ {N} \\exp \\left(\\hat {\\boldsymbol {w}} _ {j} \\hat {\\boldsymbol {v}} _ {i} / \\tau\\right)}, \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 127, + 638, + 468, + 672 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\hat{\\pmb{v}}_i$ denotes the $\\ell_{2}$ -normalized of the embedding $\\pmb{v}_i$ and $\\tau$ is a hyper-parameter of temperature [17,20,64] which usually used in unsupervised learning. The learning objective is then to maximize the joint probability $\\prod_{i=1}^{M} P_{\\pmb{\\theta}}(y_i | f_{\\pmb{\\theta}}(x_i))$ , or equivalently to minimize the negative log-likelihood over the training set which can be formulated as:", + "bbox": [ + 75, + 682, + 468, + 764 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nJ (\\boldsymbol {\\theta}) = - \\sum_ {i = 1} ^ {M} \\log P _ {\\mathrm {E B V s}} (y = y _ {i} | f _ {\\boldsymbol {\\theta}} (x _ {i})). \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 122, + 776, + 468, + 801 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "With this optimization approach, we relax the learning objective to make the angle between the embedding $\\pmb{v}$ of a training sample and its corresponding basis vector smaller than the angle between $\\pmb{v}$ and the other basis vectors.", + "bbox": [ + 75, + 809, + 468, + 866 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.5. Merits of our EBVs", + "text_level": 1, + "bbox": [ + 499, + 125, + 687, + 138 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We briefly summarize the merits of our proposed EBVs in this section. First of all, the embedding dimension of EBVs can be manually altered and the trainable parameters of the classifier will not grow linearly when the number of categories increases. Specifically, if the embedding dimension of each image is $d'$ and the number of categories is $N$ , the trainable parameters of a general classifier are $d' \\times N$ . However, with our proposed EBVs, as the dimension of the embedding for each category is fixed as $d$ , then the trainable parameters of the classifier are $d' \\times d$ . What's more, $d$ can be set at least close to $\\sqrt{2N}$ when $N$ is very large according to Section 3.3. Experimental results can be found in Table 2 and the supplementary materials.", + "bbox": [ + 497, + 148, + 892, + 328 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Secondly, as the proposed EBVs are generated before the training step and the fixed $d$ -dimensional embedding of each category will not be changed throughout the optimization process, EBVs will not introduce a large amount of computation during the training stage like the metric learning. In particular, metric learning methods such as pairwise/triplet embedding [60] are time-consuming, where the complexity can be $\\mathcal{O}(K^2)$ and $\\mathcal{O}(K^3)$ when given $K$ images from $N$ categories. However, the complexity of our proposed EBVs equals $\\mathcal{O}(K)$ . In addition, EBVs are not sensitive to the optimizers and previous training tricks while they can still achieve state-of-the-art performance as the results shown in Table 1 and the supplementary materials. Also, further results on the downstream tasks can be found in Section 4 and the supplementary materials.", + "bbox": [ + 497, + 330, + 892, + 536 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 499, + 555, + 631, + 570 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In this section, quantitative and qualitative experiments are exhibited on models that end with a $k$ -way fully connected layer with softmax and our proposed method to demonstrate the effectiveness of the proposed Equiangular Basis Vectors (EBVs). All experiments are conducted with 8 RTX 3090 GPUs.", + "bbox": [ + 497, + 580, + 892, + 662 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.1. Quantitative results on image classification", + "text_level": 1, + "bbox": [ + 499, + 676, + 862, + 692 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.1.1 Dataset and settings", + "text_level": 1, + "bbox": [ + 499, + 701, + 692, + 714 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We conduct the general image classification task on the ImageNet-1K [9] dataset, which contains 1.28M training images and 50K validation images from 1,000 different object classes. Then, we report ImageNet-1K top-1 accuracy on the validation set under a single crop setting.", + "bbox": [ + 497, + 726, + 892, + 795 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In order to demonstrate the effectiveness of the proposed EBVs, we follow the state-of-the-art training methods provided by TorchVision [59] and timm [63]. For fair comparisons, we offer the following diverse training settings for the general classification task.", + "bbox": [ + 497, + 796, + 892, + 866 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "11759", + "bbox": [ + 465, + 885, + 504, + 897 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/5d77342f3967f9e2d70501f7ffb903d17afb09d06586b3bfa6df4f1996449cab.jpg", + "table_caption": [ + "Table 1. Comparisons on the ImageNet-1K validation set. \"FC\" denotes models ending with a 1000-way fully connected layer with softmax. The test size for each image is set as \"224^2\" if there is one result while it is set as \"224^2/256^2\" if there exist two results." + ], + "table_footnote": [ + "* represents the result of the model with a general fully connected layer with softmax is provided by TorchVision [59]." + ], + "table_body": "
BackboneMethodOptimizerLREpochSettingParams.GFLOPsTest size#Forward passTop-1 Acc (%)
ResNet-50FCSGD0.190A025.6M4.12242600k77.15
ResNet-50FCSGD0.55/100A125.6M4.12242/2562131k76.88/77.92
EBVs77.55/78.73
ResNet-50FCSGD0.55/100A225.6M4.12242/2562131k77.71/78.59
EBVs78.14/78.99
ResNet-50*FCSGD0.55/600A225.6M4.12242/2562755k79.51/-\n79.73/80.45
EBVs
ResNet-50FCAdamW0.00172.57/73.79
FC0.015/100A125.6M4.12242/2562131k72.51/74.03
EBVs0.0175.62/77.14
ResNet-50FCAdamW0.00175.42/76.48
FC0.015/100A225.6M4.12242/2562131kNaN
EBVs0.0176.46/77.52
Swin-TFCAdamW0.0015/100A128.3M4.52242131k75.64
EBVs78.37
Swin-TFCAdamW0.0015/100A228.3M4.52242131k79.12
EBVs79.34
", + "bbox": [ + 77, + 160, + 889, + 419 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Setting A0 The official training setting provided in ResNet [19]. A $224 \\times 224$ crop is randomly sampled from an image or its horizontal flip, with the per-pixel mean subtracted [27]. It trains the backbone by using SGD optimizer with momentum as 0.9, weight decay as $1 \\times 10^{-4}$ and batch size as 256. The training iteration is up to $60 \\times 10^{4}$ . The standard color augmentation in [27] is used. It adopts the standard 10-crop testing [27] in the validation stage.", + "bbox": [ + 75, + 457, + 470, + 568 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Setting A1 We employ an AdamW [35] or an SGD [47] optimizer for 100 epochs using a cosine decay learning rate scheduler and 5 epochs of linear warm-up. The batch size is set as 1024 and the initial learning rate for the AdamW optimizer is 0.01 or 0.001 while it is set as 0.5 for the SGD optimizer. A $224 \\times 224$ crop is randomly sampled from each image and the weight decay is set as $2 \\times 10^{-5}$ . We perform TrivialAugment [41], which is extremely simple and can be considered \"parameter-free\". We also adopt random erasing [71] and the probability is set as 0.1.", + "bbox": [ + 75, + 585, + 468, + 724 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Setting A2 On the basis of Setting A1, we add label-smoothing [54] and the value is set as 0.1. We also perform mixup [69] and cutmix [68]. The setting of hyper-parameters of the two techniques is the same with TorchVision [59].", + "bbox": [ + 75, + 741, + 468, + 796 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We adopt ResNet-50 [19] and Swin-T [32] as the typical backbone for Convolutional Neural Networks (CNNs) and Vision Transformers [10]. The hyper-parameters $\\tau$ for the proposed EBVs are set as 0.07 for all the following experiments unless otherwise specified.", + "bbox": [ + 75, + 796, + 470, + 866 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.1.2 Main results", + "text_level": 1, + "bbox": [ + 497, + 457, + 640, + 469 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 1 presents comparisons between deep networks ending with FC, i.e., a 1000-way classification layer with softmax and our proposed EBVs. The fixed $\\alpha$ , $d$ and $N$ of EBVs are set as 0.004, 1000 and 1000, respectively. When adopting ResNet-50 as the backbone, EBVs outperform FC among all the settings. In addition, when adopting AdamW as the optimizer, EBVs gain $3.11\\% / 1.04\\%$ improvement over FC under Setting A1 and Setting A2 when using $224^2 / 256^2$ testing. EBVs still gain around $2.7\\% / 0.2\\%$ improvement on Swin-T under Setting A1 and Setting A2. As previous training techniques summarised by both TorchVision [59] and timm [63] are under the setting of FC, we suspect it will have some impact on the performance of EBVs. We further conduct ablation studies in the supplementary materials.", + "bbox": [ + 497, + 479, + 892, + 674 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.1.3 Ablation studies", + "text_level": 1, + "bbox": [ + 497, + 691, + 665, + 704 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We conduct ablation studies on the dimension $d$ of each basis vector to demonstrate the merits of our proposed EBVs. Table 2 reports ImageNet-1K top-1 accuracy on the validation set with different dimensions $d$ . Taking $d = 100$ as an example, the dimension of the embedding of an image is set as 100. We adopt ResNet-50 as the backbone and the setting of all the experiments follows Setting A2. We use SGD [47] as the optimizer and the initial learning rate is set as 0.01. The test size of each image is set as $224^2$ and $256^2$ . The Min. Ang. which represents the minimum angle between each two basis vectors is defined as $\\min_{1 \\leq i,j \\leq N, i \\neq j} \\min(\\pi - \\arccos(\\hat{w}_i)$", + "bbox": [ + 497, + 713, + 892, + 866 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "11760", + "bbox": [ + 465, + 885, + 505, + 897 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/e23a264ed70e0dbd1aaab4deff2948a404cc93c86349ec83e9d90df351105112.jpg", + "table_caption": [ + "Table 2. Ablation studies on the dimension of our proposed EBVs. \"EBVs Dim.\" denotes the embedding dimension for each category. The test size for each image is set as $224^2$ and $256^2$ ." + ], + "table_footnote": [], + "table_body": "
EBVs Dim.Epoch Min.Ang.Ave.Del.Ang.Top-1 Acc (%)
1005/10082.24°4.84°76.10/76.83
2005/10085.41°3.37°77.04/77.83
3005/10086.67°2.64°77.25/78.08
4005/10087.48°2.18°77.20/78.38
5005/10087.99°1.82°77.39/78.34
10005/10089.98°0.01°78.14/78.99
20005/10089.98°0.01°77.87/78.58
1005/30082.24°4.84°78.33/79.25
10005/30089.98°0.01°79.10/79.96
", + "bbox": [ + 78, + 173, + 475, + 326 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/beac3d97fa08613538d2b242ce3c2f288e791be1237133849e56d7e839b2cfda.jpg", + "table_caption": [ + "Table 3. Object detection and instance segmentation on the COCO 2017 dataset. Models are based on Mask R-CNN [18] and “ $1 \\times$ ” denotes we train models for 12 epochs while “ $3 \\times$ ” denotes 36 epochs. “ $\\mathrm{AP}^{\\mathrm{b}}$ ” and “ $\\mathrm{AP}^{\\mathrm{m}}$ ” refer to bounding box AP and mask AP, respectively. Results shaded in gray denote models ending with the general fully connected classifier while others denote models ending with our proposed EBVs." + ], + "table_footnote": [], + "table_body": "
BackboneSchedule\\(AP^b\\)\\(AP_{50}^b\\)\\(AP_{75}^b\\)\\(AP^m\\)\\(AP_{50}^m\\)\\(AP_{75}^m\\)
ResNet-501×38.2 58.8 41.4 34.7 55.7 37.2
ResNet-50 (EBVs)1×38.3 59.0 42.0 35.2 56.2 37.7
ResNet-503×40.9 61.3 44.8 37.1 58.3 39.9
ResNet-50 (EBVs)3×41.1 61.7 44.9 37.7 58.9 40.5
Swin-T1×42.7 65.2 46.8 39.3 62.2 42.2
Swin-T (EBVs)1×42.8 65.3 47.2 39.4 62.2 42.6
", + "bbox": [ + 78, + 440, + 473, + 554 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "$\\hat{\\boldsymbol{w}}_j)$ , $\\operatorname{arccos}(\\hat{\\boldsymbol{w}}_i \\cdot \\hat{\\boldsymbol{w}}_j)$ , where $N$ represents the number of categories. While the Ave. Del. Ang. which represents the average angle between each of two basis vectors is defined as $\\frac{N(N-1)}{2} \\sum_{i=1}^{N-1} \\sum_{j=i+1}^{N} \\left| \\operatorname{arccos}(\\hat{\\boldsymbol{w}}_i \\cdot \\hat{\\boldsymbol{w}}_j) - \\frac{\\pi}{2} \\right|$ . For a clearer representation, we adopt an angle instead of a radian. It can be seen from Table 2 that dimension has an impact on the performance of a model when training with limited cycles. However, this gap decreases a lot when adopting longer training cycles. Taking $d = 100$ and $d = 1000$ as an example, the top-1 accuracy under $d = 1000$ gains $2.04\\% / 2.16\\%$ improvement over $d = 100$ when training with 105 epochs while this gap is reduced to $0.77\\% / 0.71\\%$ when training with 305 epochs.", + "bbox": [ + 75, + 580, + 468, + 762 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.2. Empirical evaluations on object detection", + "text_level": 1, + "bbox": [ + 75, + 774, + 428, + 789 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Settings Object detection and instance segmentation experiments are conducted on the COCO 2017 benchmark [31], which contains $118\\mathrm{K}$ images in the training set and $5\\mathrm{K}$ images in the validation set. We consider Mask R-CNN [18] in MMdetection [5] as the detection framework and adopt", + "bbox": [ + 75, + 796, + 470, + 866 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/eec6d90ae0dfed84cebc1c4079fa29fa211ce028b1a3aed45def4e2c772b401f.jpg", + "table_caption": [ + "Table 4. Results of semantic segmentation on the ADE20K validation set. Results shaded in gray denote models ending with the general fully connected classifier while others denote models ending with our proposed EBVs. “ $1 \\times$ ” denotes we train models for 80,000 steps while “ $2 \\times$ ” denotes 160,000 steps." + ], + "table_footnote": [], + "table_body": "
BackboneSchedulemIoUmIoU(ms+flip)
ResNet-181×38.7639.81
ResNet-18 (EBVs)1×38.9840.09
ResNet-182×39.2339.97
ResNet-18 (EBVs)2×39.7540.91
ResNet-501×40.7041.81
ResNet-50 (EBVs)1×42.7344.19
ResNet-502×42.0542.78
ResNet-50 (EBVs)2×42.4443.94
Swin-T2×44.4145.79
Swin-T (EBVs)2×44.3045.88
", + "bbox": [ + 502, + 198, + 889, + 374 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "ResNet [19] and Swin Transformer [32] as backbones. For fair comparisons, we utilize the same settings according to MMdetection and previous work. We scaled the image to a maximum of 800 on the short side and 1333 on the long side. We adopt $50\\%$ scale horizontal flip and use SGD [47] with momentum $= 0.9$ as the optimizer, the initial learning rate is 0.02. The weight decay equals 0.0001 while the batch size is 16 for experiments under the backbone of ResNet. For experiments on Swin Transformer, we use Adam [24] as the optimizer and the initial learning rate is 0.0001. The weight decay is changed to 0.05. To demonstrate the effectiveness of the proposed EBVs, we replace both instance-level and pixel-level classifiers in the detection framework with EBVs. In order to control the parameters of each backbone for fair comparisons, the dimension $d$ of the basis vectors is kept consistent with the number of categories. All backbone models are pre-trained on the ImageNet-1K training set.", + "bbox": [ + 497, + 397, + 894, + 633 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Results Table 3 presents comparisons between the general framework and our proposed EBVs. When adopting ResNet-50 as the backbone, the framework ending with EBVs outperforms those ending with fully connected layers among six evaluation indicators. While adopting Swin-T as the backbone, the framework ending with EBVs also achieves comparative results with state-of-the-art performance.", + "bbox": [ + 497, + 653, + 892, + 751 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.3. Empirical evaluations on semantic segmentation", + "text_level": 1, + "bbox": [ + 497, + 760, + 890, + 788 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Settings Semantic segmentation experiments are conducted on the ADE20K [73], which contains 20,000 images in the training set and 2,000 images in the validation set. We adopt FPN [25] and UperNet [65] in MMSEG [6] as segmentation framework and adopt ResNet [19] and Swin Trans", + "bbox": [ + 497, + 796, + 894, + 866 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "11761", + "bbox": [ + 465, + 885, + 502, + 897 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/a57eff453f219621b701e140d9732c9f33a2e144b6fb7a6dadcdcd04c339d08f.jpg", + "image_caption": [ + "Figure 2. Representation structure of ResNet-50. Left: Similarity between layers within ResNet-50 ends with a general fully connected classifier (FC). It shows that the last few layers share minimal similarity with the shallow layers while a few shallow layers also share minimal similarity with all the other layers. Middle: Similarity between layers within ResNet-50 ends with EBVs. Only the last few layers share minimal similarity with other layers. Right: Similarity between layers across ResNet-50 ends with a general fully connected layer with softmax and our proposed EBVs. Around $10\\%$ initial layers share a little similarity while the last few layers share the least similarity." + ], + "image_footnote": [], + "bbox": [ + 109, + 133, + 327, + 292 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/041aea74dcbd9ed5dde9e6bf8be810725005b24b6e9044fd86f1be6aa3588b4b.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 346, + 131, + 561, + 292 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/3ff2a477372a0afa4eda9646fd301c05972614d7324bf639750f290e9040e36d.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 579, + 131, + 860, + 292 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "former [32] as backbones. For fair comparisons, we utilize the same settings in MMSEG. For experiments on ResNet, we use SGD [47] as the optimizer. The initial learning rate equals 0.01, weight decay equals 0.0005, momentum equals 0.9 and batch size is set as 16. For experiments on Swin Transformer, we use AdamW [35] as the optimizer and the initial learning rate is 0.00006 while the weight decay is set as 0.01. To perform our proposed method, We modify pixel-level classifiers in both the decode head and auxiliary head to EBVs. All backbone models are pre-trained on the ImageNet-1K training set.", + "bbox": [ + 75, + 376, + 472, + 529 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Results According to Table 4, we find that EBVs surpass the framework ending with fully connected layers as the classifier under the backbone of ResNet. Additionally, when the training step is set as 80,000, EBVs gain a higher mIoU score than the general framework trained for 160,000 steps. While adopting Swin-T as the backbone, the framework ending with EBVs still achieving comparative performance.", + "bbox": [ + 75, + 549, + 470, + 647 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Discussions", + "text_level": 1, + "bbox": [ + 75, + 661, + 198, + 676 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We explore whether there are differences in the way EBVs represent and solve image tasks compared to a fully connected layer with softmax in this section. In order to answer this question, we have to analyze the features in the hidden layers as features are usually spread across neurons. However, different layers generally have different numbers of neurons. Recently, Raghu et al. [43] and Zhen et al. [70] applied the Centered Kernel Alignment (CKA) [7, 26] to solve the above task. CKA is effective because it involves no constraint on the number of neurons. It is also independent of the orthogonal transformations of representations [70]. Therefore, we adopt CKA to analyze the above question.", + "bbox": [ + 75, + 685, + 470, + 851 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We pick ResNet-50 as the backbone while the experi", + "bbox": [ + 95, + 852, + 470, + 866 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "ments on Swin-T can be found in the supplementary materials. One model ends with a general fully connected (FC) classifier and another model ends with our proposed EBVs. Both of the models are pre-trained on the ImageNet-1K [9] training dataset. We use 49 convolutional layers and the last fully connected layer. We plot CKA similarities between all pairs of layers within the whole ImageNet-1K validation dataset in Figure 2. As shown in Figure 2, for the ResNet-50 model ending with a general FC classifier, the feature similarity shows that around $10\\%$ initial convolutional layers almost share no similarity with all the other layers while they themselves share a high similarity. If we change the last layer and the learning objective with our proposed EBVs, these shallow layers then share a relatively higher similarity.", + "bbox": [ + 497, + 376, + 895, + 571 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "6. Conclusion", + "text_level": 1, + "bbox": [ + 499, + 580, + 618, + 593 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this paper, we proposed Equiangular Basis Vectors (EBVs) for classification tasks. Different from previous classifiers and classical metric learning methods, EBVs predefined a fixed embedding for all the semantic categories. The learning objective of EBVs then changed to minimize the spherical distance of the embedding of input and each basis vector. Various experiments on the ImageNet-1K [9], COCO 2017 [31] and ADE20K [73] datasets and ablation studies also demonstrated the effectiveness of our proposed EBVs. In the future, we would like to explore relations between each basis vector pair and embed hierarchies when generating the proposed EBVs as the normal Euclidean space could not naturally embed hierarchies on datasets with known semantic hierarchies [16]. We also would like to explore the performance of EBVs in the case when the number of categories became very large. In addition, EBVs could also be regarded as advanced classifiers, it is interesting to adopt EBVs in other related tasks, e.g., incremental learning, few-shot learning, etc.", + "bbox": [ + 497, + 603, + 895, + 866 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "11762", + "bbox": [ + 465, + 885, + 505, + 897 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 124, + 173, + 138 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] L Douglas Baker and Andrew Kachites McCallum. 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Vis., 127(3):302-321, 2019. 7, 8" + ], + "bbox": [ + 78, + 125, + 470, + 631 + ], + "page_idx": 10 + }, + { + "type": "page_number", + "text": "11765", + "bbox": [ + 465, + 885, + 504, + 897 + ], + "page_idx": 10 + } +] \ No newline at end of file diff --git a/2023/Equiangular Basis Vectors/d0d8b892-8a3a-423d-9839-0349feda6f33_model.json b/2023/Equiangular Basis Vectors/d0d8b892-8a3a-423d-9839-0349feda6f33_model.json new file mode 100644 index 0000000000000000000000000000000000000000..f81a2b1c41de2ffb70e1da30c7593d28d1548216 --- /dev/null +++ b/2023/Equiangular Basis Vectors/d0d8b892-8a3a-423d-9839-0349feda6f33_model.json @@ -0,0 +1,2257 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.13, + 0.051, + 0.201, + 0.085 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.253, + 0.049, + 0.792, + 0.062 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation." + }, + { + "type": "header", + "bbox": [ + 0.334, + 0.062, + 0.71, + 0.075 + ], + "angle": 0, + "content": "Except for this watermark, it is identical to the accepted version;" + }, + { + "type": "header", + "bbox": [ + 0.305, + 0.075, + 0.74, + 0.088 + ], + "angle": 0, + "content": "the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.35, + 0.163, + 0.621, + 0.182 + ], + "angle": 0, + "content": "Equiangular Basis Vectors" + }, + { + "type": "text", + "bbox": [ + 0.297, + 0.209, + 0.68, + 0.224 + ], + "angle": 0, + "content": "Yang Shen Xuhao Sun Xiu-Shen Wei*" + }, + { + "type": "text", + "bbox": [ + 0.088, + 0.225, + 0.882, + 0.242 + ], + "angle": 0, + "content": "School of Computer Science and Engineering, Nanjing University of Science and Technology, China" + }, + { + "type": "text", + "bbox": [ + 0.318, + 0.243, + 0.65, + 0.257 + ], + "angle": 0, + "content": "{shenyang.98,sunxh,weixs}@njust.edu.cn" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.289, + 0.314, + 0.303 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.318, + 0.474, + 0.678 + ], + "angle": 0, + "content": "We propose Equiangular Basis Vectors (EBVs) for classification tasks. In deep neural networks, models usually end with a \\(k\\)-way fully connected layer with softmax to handle different classification tasks. The learning objective of these methods can be summarized as mapping the learned feature representations to the samples' label space. While in metric learning approaches, the main objective is to learn a transformation function that maps training data points from the original space to a new space where similar points are closer while dissimilar points become farther apart. Different from previous methods, our EBVs generate normalized vector embeddings as \"predefined classifiers\" which are required to not only be with the equal status between each other, but also be as orthogonal as possible. By minimizing the spherical distance of the embedding of an input between its categorical EBV in training, the predictions can be obtained by identifying the categorical EBV with the smallest distance during inference. Various experiments on the ImageNet-1K dataset and other downstream tasks demonstrate that our method outperforms the general fully connected classifier while it does not introduce huge additional computation compared with classical metric learning methods. Our EBVs won the first place in the 2022 DIGIX Global AI Challenge, and our code is open-source and available at https://github.com/NJUST-VIPGroup/Equiangular-Basis-Vectors." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.701, + 0.21, + 0.715 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.724, + 0.471, + 0.794 + ], + "angle": 0, + "content": "The pattern classification field developed around the end of the twentieth century aims to deal with the specific problem of assigning input signals to two or more classes [56]. In recent years, deep learning models have brought breakthroughs in processing image, video, audio, text, and other" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.799, + 0.471, + 0.867 + ], + "angle": 0, + "content": "*Corresponding author. This work was supported by National Key R&D Program of China (2021YFA1001100), National Natural Science Foundation of China under Grant (62272231), Natural Science Foundation of Jiangsu Province of China under Grant (BK20210340), the Fundamental Research Funds for the Central Universities (No. NJ2022028), and CAAI-Huawei MindSpore Open Fund." + }, + { + "type": "image", + "bbox": [ + 0.586, + 0.29, + 0.824, + 0.421 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.571, + 0.421, + 0.842, + 0.435 + ], + "angle": 0, + "content": "(a) Fully Connected Layers with Softmax" + }, + { + "type": "image", + "bbox": [ + 0.507, + 0.441, + 0.907, + 0.55 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.529, + 0.55, + 0.664, + 0.563 + ], + "angle": 0, + "content": "(b) Metric Learning" + }, + { + "type": "image_caption", + "bbox": [ + 0.705, + 0.55, + 0.9, + 0.563 + ], + "angle": 0, + "content": "(c) Equiangular Basis Vectors" + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.576, + 0.896, + 0.743 + ], + "angle": 0, + "content": "Figure 1. Comparisons between typical classification paradigms and our proposed Equiangular Basis Vectors (EBVs). (a) A general classifier ends with \\( k \\)-way fully connected layers with softmax. When adding more categories, the trainable parameters of the classifier grow linearly. (b) Taking triplet embedding [60] as an example of classical metric learning methods, the complexity is \\( \\mathcal{O}(M^3) \\) when given \\( M \\) images and it will grows to \\( \\mathcal{O}((M + m')^3) \\) when adding a new category with \\( m' \\) images. (c) Our proposed EBVs. EBVs predefine fixed normalized vector embeddings for different categories and these embeddings will not be changed during the training stage. The trainable parameters of the network will not be changed with the growth of the number of categories while the complexity only grows from \\( \\mathcal{O}(M) \\) to \\( \\mathcal{O}(M + m') \\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.756, + 0.896, + 0.868 + ], + "angle": 0, + "content": "data [10, 19, 27, 58]. Aided by the rapid gains in hardware, deep learning methods today can easily overfit one million images [9] and easily overcomes the obstacle to the quality of handcrafted features in previous pattern classification tasks. Many approaches based on deep learning spring up like mushrooms and had been used to solve classification problems in various scenarios and settings such as remote sensing [38], few-shot [52], long-tailed [72], etc." + }, + { + "type": "page_number", + "bbox": [ + 0.466, + 0.887, + 0.506, + 0.898 + ], + "angle": 0, + "content": "11755" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.126, + 0.473, + 0.348 + ], + "angle": 0, + "content": "Figure 1 illustrates two typical classification paradigms. Nowadays, a large amount of deep learning methods [38, 72] adopt a trainable fully connected layer with softmax as the classifier. However, since the number of categories is fixed, the trainable parameters of the classifier rise as the number of categories becomes larger. For example, the memory consumption of a fully connected layer \\( \\mathbf{W} \\in \\mathbb{R}^{d \\times N} \\) linearly scales up with the growth of the category number \\( N \\) and so is the cost to compute the matrix multiplication between the fully connected layer and the \\( d \\)-dimensional features. While some other methods based on classical metric learning [23, 30, 60-62] have to consider all the training samples and design positive/negative pairs then optimize a class center for each category, which requires a significant amount of extra computation for large-scale datasets, especially for those pre-training tasks." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.352, + 0.473, + 0.587 + ], + "angle": 0, + "content": "In this paper, we propose Equiangular Basis Vectors (EBVs) to replace the fully connected layer associated with softmax within classification tasks in deep neural networks. EBVs predefine fixed normalized vector embeddings with equal status (equal angles) which will not be changed during the training stage. Specifically, EBVs pre-set a \\(d\\)-dimensional unit hypersphere, and for each category in the classification task, EBVs assign the category a \\(d\\)-dimensional normalized embedding on the surface of the hypersphere and we term these embedding as basis vectors. The spherical distance of each basis vector pair satisfies an artificially made rule to make the relationship between any two vectors as close to orthogonal as possible. In order to keep the trainable parameters of the deep neural networks constant with the growth of the category number \\(N\\), we then propose the definition of EBVs based on Tammes Problem [55] and Equiangular Lines [57] in Section 3.2." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.59, + 0.473, + 0.868 + ], + "angle": 0, + "content": "The learning objective of each category in our proposed EBVs is also different from previous classification methods. Compared with deep models that end with a fully connected layer to handle the classification tasks [19, 27], the meaning of the parameter weights within the fully connected layer in EBVs is not the relevance of a feature representation to a particular category but a fixed matrix which embed feature representations to a new space. Also, compared with regression methods [34,51], EBVs do not need to learn the unified representations for different categories and optimize the distance between the representation of input images and category centers, which helps reduce the computational consumption for the extra unified representations learning. In contrast to classical metric learning approaches [14, 23, 50, 61], our EBVs do not need to measure the similarity among different training samples and constrain distance between each category, which will introduce a large amount of computational consumption for large-scale datasets. In our proposed method, the representations of different images learned by EBVs will be embedded into a normalized hypersphere and the learning" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.126, + 0.895, + 0.266 + ], + "angle": 0, + "content": "objective is altered to minimize the spherical distance of the learned representations with different predefined basis vectors. In addition, the spherical distance between each predefined basis vector is carefully constrained so that there is no need to spend extra cost in the optimization of these basis vectors. To quantitatively prove both the effectiveness and efficiency of our proposed EBVs, we evaluate EBVs on diverse computer vision tasks with large-scale datasets, including classification on ImageNet-1K, object detection on COCO, as well as semantic segmentation on ADE20K." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.279, + 0.64, + 0.293 + ], + "angle": 0, + "content": "2. Related work" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.302, + 0.831, + 0.317 + ], + "angle": 0, + "content": "2.1. Deep networks for image classification" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.324, + 0.895, + 0.517 + ], + "angle": 0, + "content": "Image classification is the task of categorizing images into one of several predefined classes, which has been a fundamental problem in computer vision for a long time [4, 36]. It also forms the basis for many other computer vision tasks, e.g., object detection [37], localization [28] and segmentation [39]. To solve the image classification problem, a dual-stage approach was used before the rise of deep learning. Specifically, handcrafted features were first extracted from images using feature descriptors. Then, a trainable classifier is adopted to perform the classification task with these input features [44]. The major hindrance of this approach was that the accuracy of the classification task was profoundly dependent on the design of the feature extraction stage, and this usually proved to be a formidable task [29]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.518, + 0.897, + 0.794 + ], + "angle": 0, + "content": "In recent years, deep learning models that exploit multiple layers of nonlinear information processing, for feature extraction and transformation as well as for pattern analysis and classification, have been shown to overcome these challenges [44]. With the holding of ImageNet Large Scale Visual Recognition Challenge (ILSVRC) [49], a growing number of deep networks demonstrate superior classification performance [10, 15, 19, 27, 32, 33, 42]. Among them, Deep Convolutional Neural Networks (DCNNs) and Vision Transformers (ViTs) [10] have become the leading architectures for most image classification task in recent years. In addition, selected representative examples of other improvement attempts related to the following different aspects: network architecture, nonlinear activation functions, supervision components, regularization mechanisms and optimization techniques. Our proposed Equiangular Basis Vectors (EBVs) are different from these aspects as we do not change the overall architecture and training techniques but the optimization objectives for classification since we preliminary design fixed normalized vector embeddings for each predefined category." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.804, + 0.689, + 0.818 + ], + "angle": 0, + "content": "2.2. Learning objectives" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.825, + 0.895, + 0.868 + ], + "angle": 0, + "content": "Besides traditional classifiers, machine learning or deep learning methods such as clustering [1,45], regression [34, 51], metric learning [14,50,61], sparse learning [48,67] can" + }, + { + "type": "page_number", + "bbox": [ + 0.466, + 0.887, + 0.506, + 0.898 + ], + "angle": 0, + "content": "11756" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.126, + 0.471, + 0.21 + ], + "angle": 0, + "content": "be used to handle the classification tasks while the learning objectives of these methods vary considerably. In this section, we only discuss the learning objective of our EBVs with two prominent training paradigms of deep learning for the classification tasks, i.e., general \\(k\\)-way classification layers [27] and classical deep metric learning [3, 66]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.213, + 0.471, + 0.38 + ], + "angle": 0, + "content": "Regarding deep learning for classification, the \\(k\\)-way classification layer (always associated with softmax) is the most popular used approach for training deep models. It employs a single linear layer or multiple non-linear layers to map the learned deep representations to the semantic categories in the label space. The corresponding learning objective is minimizing the losses (e.g., the cross-entropy loss [8]) between the mapped categorical signals (aka. predictions) with the ground truth categories. Compared with that, the learning objective of our EBVs is to make the vectorized embedding of input as close as possible to its categorical equiangular basis vector correspondingly." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.383, + 0.471, + 0.867 + ], + "angle": 0, + "content": "The learning objective of classical deep metric learning seems similar to ours. However, there are several crucial and fundamental differences. Firstly, although deep metric learning minimizes the distances between sample vectors belonging to the same category and meanwhile maximizes the distances between samples from different categories, all these sample vectors are constantly changing during the model training process. But, in our method, the equiangular basis vectors corresponding to the categories are predefined, i.e., they are fixed. More importantly, these equiangular basis vectors in the spherical space are forced to be with equal status and be as orthogonal as possible to each other, which could contribute to strong model discriminative ability and good classification accuracy. In practice, both with equal status and being orthogonal of vectors are strict conditions w.r.t. optimization. Thus, our EBVs predefine the satisfied categorical basis vectors and our learning objective focuses on only optimizing the learned feature representations to prevent the model from being unable to converge (when EBVs can also change under such strict conditions). Secondly, the learning objective of deep metric learning is upon massive training samples, while our learning objective is for the training sample and its fixed categorical vectorized embedding, i.e., EBV. It could bring the computational economy, especially for the large-scale training data scenario, cf. Section 3.5. In addition, compared with several specific metric learning approaches, e.g., the center loss [62], the prototypical network [52] and the nearest class mean approach [40], our method is still quite distant from them. Specifically, the basic idea of these works is to construct the \"center\" of samples belonging to a category to represent its semantics and then leverage the centers to optimize sample distances for classification. Similarly, since these categorical centers are always changing during training, these approaches will also encounter the same problems as aforementioned." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.125, + 0.635, + 0.141 + ], + "angle": 0, + "content": "3. Methodology" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.149, + 0.64, + 0.163 + ], + "angle": 0, + "content": "3.1. Preliminaries" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.171, + 0.894, + 0.214 + ], + "angle": 0, + "content": "The proposed Equiangular Basis Vectors (EBVs) are based on the study with regard to Equiangular Lines [21, 22,57] and the Tammes Problem [55]." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.214, + 0.894, + 0.298 + ], + "angle": 0, + "content": "A set of lines passing through the origin in \\(\\mathbb{R}^d (d\\in\\) \\(\\{2,3,4,5,\\ldots \\})\\) is called equiangular if they are pairwise separated by the same angle. The study of equiangular lines was initiated by Haantjes [22] and it plays an important role in the coding theory [53] and quantum information theory [46]." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.299, + 0.893, + 0.465 + ], + "angle": 0, + "content": "The problem of how to determine the maximum number \\( N(d) \\) of equiangular lines in a given dimension \\( d \\) was formally posed by Van Lint and Seidel [57] and has gained a major breakthrough by Jiang et al. [21] last year — Fix \\( 0 < \\alpha < 1 \\), let \\( N_{\\alpha}(d) \\) denote the maximum number of lines through the origin in \\( \\mathbb{R}^d \\) with pairwise common angle \\( \\arccos \\alpha \\), let \\( k \\) denote the minimum number (if it exists) of vertices in a graph whose adjacency matrix has spectral radius exactly \\( (1 - \\alpha) / (2\\alpha) \\). If \\( k < \\infty \\), then \\( N_{\\alpha}(d) = \\lfloor k(d - 1) / (k - 1)\\rfloor \\) for all sufficiently large \\( d \\), and otherwise \\( N_{\\alpha}(d) = d + o(d) \\). In particular, \\( N_{1 / (2k - 1)}(d) = \\lfloor k(d - 1) / (k - 1)\\rfloor \\) for every integer \\( k \\geq 2 \\) and all sufficiently large \\( d \\) [21]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.466, + 0.895, + 0.645 + ], + "angle": 0, + "content": "In simple terms, with a fixed common angle, the maximum number \\( N(d) \\) of equiangular lines is linearly correlated with the dimension \\( d \\) as \\( d \\to \\infty \\) while there is still no precise lower bound for \\( N(d) \\) with smaller values of \\( d \\) [13]. Therefore, we further refer to the Tammes Problem. Let \\( a_{n} \\) be the maximal number with the property that one can place on a unit hypersphere \\( S^{d} \\in \\mathbb{R}^{d}(d \\in \\{3,4,5,\\ldots\\}) \\) \\( n \\) points so that the spherical distance of any two points is at least \\( a_{n} \\). The problem of finding \\( a_{n} \\) together with the corresponding arrangement of each point is known as the Tammes Problem [55] or the optimal spherical code [12]. It is easy to find that the number of these points will be close to infinity as \\( a_{n} \\) tends to zero." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.659, + 0.838, + 0.673 + ], + "angle": 0, + "content": "3.2. Definition of Equiangular Basis Vectors" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.681, + 0.894, + 0.832 + ], + "angle": 0, + "content": "In order to predefine fixed \\(d\\)-dimensional embeddings for as many categories as possible but still keep these embeddings at a distance from each other on a unit hypersphere \\(S^d \\in \\mathbb{R}^d\\), we therefore propose Equiangular Basis Vectors (EBVs). Specifically, we fix \\(0 \\leq \\alpha < 1\\) and let \\(\\mathcal{N}_{\\alpha}(d)\\) denote the range of values for the number of coordinate vectors in \\(\\mathbb{R}^d\\) with the pairwise common angle between \\(\\arccos \\alpha\\) and \\(\\arccos -\\alpha\\). The problem of our proposed EBVs is to calculate the coordinates of each vector in the vector set \\(\\mathcal{W}\\) when given fixed \\(\\alpha, d\\) and \\(N \\in \\mathcal{N}_{\\alpha}(d)\\) if possible, i.e., solve the set \\(\\mathcal{W}\\) which satisfies:" + }, + { + "type": "equation", + "bbox": [ + 0.522, + 0.842, + 0.893, + 0.871 + ], + "angle": 0, + "content": "\\[\n\\forall \\boldsymbol {w} _ {i}, \\boldsymbol {w} _ {j} \\in \\mathcal {W}, i \\neq j, - \\alpha \\leq \\frac {\\boldsymbol {w} _ {i} \\cdot \\boldsymbol {w} _ {j}}{\\| \\boldsymbol {w} _ {i} \\| \\| \\boldsymbol {w} _ {j} \\|} \\leq \\alpha , \\tag {1}\n\\]" + }, + { + "type": "page_number", + "bbox": [ + 0.466, + 0.887, + 0.505, + 0.898 + ], + "angle": 0, + "content": "11757" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.125, + 0.474, + 0.21 + ], + "angle": 0, + "content": "where \\(\\pmb{w}_i\\in \\mathbb{R}^d\\) , card(W) \\(= N\\) and \\(\\| \\cdot \\|\\) denotes the Euclidean norm. Let \\(\\phi\\) denote the spherical distance function, which can also be replaced by the cosine similarity function. EBVs produce a distribution over classes for a query point \\(\\pmb {v}\\in \\mathbb{R}^{d}\\) based on softmax over cosine similarity to the \\(N\\) fixed coordinate vectors in the embedding space:" + }, + { + "type": "equation", + "bbox": [ + 0.141, + 0.217, + 0.471, + 0.249 + ], + "angle": 0, + "content": "\\[\np (y = k | \\boldsymbol {v}) = \\frac {\\exp (- \\phi (\\boldsymbol {v} , \\boldsymbol {w} _ {k}))}{\\sum_ {k ^ {\\prime}} \\exp (- \\phi (\\boldsymbol {v} , \\boldsymbol {w} _ {k ^ {\\prime}}))}, \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.255, + 0.473, + 0.382 + ], + "angle": 0, + "content": "where \\( y = k \\in \\{1, 2, \\dots, N\\} \\) denotes the corresponding coordinate vector, which can also be seen as the corresponding label. While \\( k' \\) represents the associated basis vectors in \\( \\mathcal{W} \\). Relations between \\( \\alpha \\), \\( d \\) and \\( N \\) are described in the supplementary materials. With such a set \\( \\mathcal{W} \\), the maximum number of categories it can handle is \\( N \\). Additionally, training with any category number less than \\( N \\), it is sufficient to randomly select any of the same numbers of coordinate vectors in \\( \\mathcal{W} \\), since these vectors are exactly equivalent." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.388, + 0.296, + 0.403 + ], + "angle": 0, + "content": "3.3. How to generate EBVs?" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.409, + 0.47, + 0.506 + ], + "angle": 0, + "content": "The basic idea of our Equiangular Basis Vectors (EBVs) is to generate fixed normalized vector embeddings with equal status (equal angles) as \"predefined classifiers\" for all the relevant categories. The question then comes to how to calculate the predefined EBVs which satisfy Eq. (1). Therefore, we will discuss how to generate the proposed EBVs when given fixed \\(\\alpha\\), \\(d\\) and \\(N \\in \\mathcal{N}_{\\alpha}(d)\\) in this section." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.506, + 0.473, + 0.576 + ], + "angle": 0, + "content": "Assuming each \\( \\boldsymbol{w}_i \\in \\mathcal{W} \\) (\\( i = \\{1, 2, \\dots, N\\} \\)) as a line, we can construct the Grassmannian Matrices to solve the set \\( \\mathcal{W} \\) [11]. Specifically, we assemble the vectors in \\( \\mathcal{W} \\) into a matrix \\( \\boldsymbol{W} \\in \\mathbb{R}^{d \\times N} \\), where \\( \\boldsymbol{W} = [\\boldsymbol{w}_1; \\boldsymbol{w}_2; \\dots; \\boldsymbol{w}_N] \\). Then, the mutual-coherence of \\( \\boldsymbol{W} \\) is defined by:" + }, + { + "type": "equation", + "bbox": [ + 0.081, + 0.593, + 0.47, + 0.638 + ], + "angle": 0, + "content": "\\[\n\\mu (\\boldsymbol {W}) = \\max _ {1 \\leq i, j \\leq N, i \\neq j} \\frac {\\left| \\boldsymbol {w} _ {i} ^ {\\top} \\cdot \\boldsymbol {w} _ {j} \\right|}{\\left\\| \\boldsymbol {w} _ {i} \\right\\| \\left\\| \\boldsymbol {w} _ {j} \\right\\|} = \\max _ {1 \\leq i, j \\leq N, i \\neq j} \\cos \\theta_ {i j}, \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.638, + 0.47, + 0.783 + ], + "angle": 0, + "content": "which is transformed to the smallest possible mutualcoherence possible [11]. Therefore, the lower bound for \\(\\alpha\\) is \\(\\sqrt{\\frac{N - d}{d(N - 1)}}\\) and the upper bound for \\(\\mathcal{N}_{\\alpha}(d)\\) is \\(1 + \\frac{d - 1}{1 - \\alpha^2d}\\) (\\(d \\leq N, 1 - \\alpha^2 d > 0\\)). In addition, such matrix is possible only if \\(N < \\min(d(d + 1)/2, (N - d)(N - d + 1)/2)\\). Construction of such a matrix has a strong connection with the packing of vectors/subspaces in the \\(\\mathbb{R}^d\\)-space. In the case of \\(N = d\\), we can simply construct a unitary matrix, while in other cases, it will be very hard to construct such a general Grassmannian matrix [11]." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.784, + 0.47, + 0.868 + ], + "angle": 0, + "content": "In the definition of our proposed EBVs, whether the angle between any two basis vectors \\(\\pmb{w}_i, \\pmb{w}_j \\in \\mathcal{W} (i \\neq j)\\) is \\(\\arccos \\alpha\\) or \\(\\arccos -\\alpha\\) is equivalent. It is clear that we can not construct the Grassmannian matrix in a situation such as \\(N = 30,000\\) and \\(d = 200\\). However, it is still possible for us to construct \\(\\mathcal{W}\\) which satisfies Eq. (1). Therefore, as" + }, + { + "type": "code_caption", + "bbox": [ + 0.501, + 0.126, + 0.88, + 0.14 + ], + "angle": 0, + "content": "Algorithm 1 Generation of EBVs in a PyTorch-like style" + }, + { + "type": "algorithm", + "bbox": [ + 0.501, + 0.142, + 0.789, + 0.407 + ], + "angle": 0, + "content": "#d:Dim for each coordinate vectors \n#N:The number of coordinate vectors \n# \\(\\alpha\\) : Threshold of \\(\\hat{\\pmb{w}}_i\\cdot \\hat{\\pmb{w}}_j,i\\neq j\\) \n#W:The EBVs matrix \\(W\\in \\mathbb{R}^{d\\times N}\\) \n#slice: In the case of \\(N\\gg d\\) ,optimize W by slicing \n#λ: Learning rate. \nInitialize W randomly; \nwhile True: #Normalize each row in W \n\\(W =\\) Normalize(W) \nfor i in [N/slice]: start \\(=\\) i\\* slice end \\(= \\min (N\\) \\((\\mathrm{i} + 1)^{*}\\) slice) E \\(=\\) Fonehot(arange(start, end), N) C \\(=\\) (W[start:end]@W.T).abs()-E loss \\(=\\) ReLU(C-α).sum() # Cutout the gradient of vector pairs which satisfies \\(-\\alpha \\leq \\hat{\\pmb{w}}_i\\cdot \\hat{\\pmb{w}}_j\\leq \\alpha\\) loss.backup() if max(α,C.max()) < α + o(α): Save(W) break \n\\(W = W - \\lambda *W.\\mathrm{grad}\\#\\) Update W" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.43, + 0.892, + 0.571 + ], + "angle": 0, + "content": "an alternative, we adopt Stochastic Gradient Descent [47] to search the set \\(\\mathcal{W}\\) that satisfies the definition of EBVs when given fixed \\(\\alpha\\), \\(d\\) and \\(N\\). Specifically, we random initialize a matrix \\(\\pmb{W} \\in \\mathbb{R}^{d \\times N}\\) with normalized rows such that the angle between any two vectors \\(\\hat{\\pmb{w}}_i\\), \\(\\hat{\\pmb{w}}_j \\in \\mathbb{R}^d\\), \\(i, j \\in \\{1, 2, \\dots, N\\}\\), \\(i \\neq j\\), \\(\\hat{\\pmb{w}}_i = \\frac{\\pmb{w}_i}{\\|\\pmb{w}_i\\|}\\) can be represented as \\(\\arccos(\\hat{\\pmb{w}}_i \\cdot \\hat{\\pmb{w}}_j)\\). Then, we cut out the gradient of those vector pairs which satisfies \\(-\\alpha \\leq \\hat{\\pmb{w}}_i \\cdot \\hat{\\pmb{w}}_j \\leq \\alpha\\) and optimize the remaining vector pairs. The optimization function of the generation of EBVs can be formulated by:" + }, + { + "type": "equation", + "bbox": [ + 0.54, + 0.579, + 0.892, + 0.607 + ], + "angle": 0, + "content": "\\[\n\\underset {\\boldsymbol {W}} {\\arg \\min } \\sum_ {i = 1} ^ {N - 1} \\sum_ {j > i} ^ {N} \\max \\left(\\hat {\\boldsymbol {w}} _ {i} \\cdot \\hat {\\boldsymbol {w}} _ {j} - \\alpha , 0\\right). \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.616, + 0.892, + 0.672 + ], + "angle": 0, + "content": "Algorithm 1 provides the code of a simple generation method of the proposed EBVs in a PyTorch-like style. It is also worth mentioning that the EBVs matrix \\( W \\) will not be changed in the following training stage within all the tasks." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.679, + 0.891, + 0.695 + ], + "angle": 0, + "content": "3.4. How to achieve the learning objective of EBVs?" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.701, + 0.895, + 0.868 + ], + "angle": 0, + "content": "Equiangular Basis Vectors (EBVs) provide fixed learning targets for each independent optimization objective, i.e., semantic categories. In the following, we introduce how to achieve the learning objective of EBVs for all the training samples. Generally, a deep network is performed to extract the high-dimensional features, and a fully connected classification layer is then deployed to map the features to semantic categories. While in our proposed EBVs, each category will be bound to a unique normalized \\(d\\)-dimensional basis vector in \\(\\mathcal{W}\\). Thus, for a training sample \\(x\\), we directly use a unified deep model to generate a \\(d\\)-dimensional embedding \\(\\pmb{v}\\), as well as optimizing the cosine distance between \\(\\pmb{v}\\) and" + }, + { + "type": "page_number", + "bbox": [ + 0.466, + 0.887, + 0.506, + 0.898 + ], + "angle": 0, + "content": "11758" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.127, + 0.47, + 0.154 + ], + "angle": 0, + "content": "the relevant basis vector. Below we analyze the underlying distance/loss function used in the training stage." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.155, + 0.471, + 0.307 + ], + "angle": 0, + "content": "For our EBVs, many existing distance functions including squared Euclidean distance, Mahalanobis distance, or cosine distance are permissible. However, a particular class of distance functions, e.g., regular Bregman divergences [2], seems hard to explain and optimize in the proposed EBVs settings. In addition, intuitively, the straightforward way is to optimize the spherical distance between any two vectors on the surface of the hyper-sphere. Therefore, we adopt the cosine distance as the distance metric, which is widely used for measuring whether two inputs are similar or dissimilar and have been widely used in the Tammes problem [55]." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.326, + 0.47, + 0.422 + ], + "angle": 0, + "content": "Implementations Suppose we have \\(M\\) sample-label pairs \\(\\{(x_{1},y_{1}),(x_{2},y_{2}),\\ldots ,(x_{M},y_{M})\\}\\) in \\(N\\) classes and their \\(d\\) -dimensional features \\(\\pmb{v}_1,\\pmb{v}_2,\\dots ,\\pmb{v}_M\\) with \\(\\boldsymbol {v}_i = f_\\theta (\\boldsymbol {x}_i)\\) where \\(f_{\\theta}(\\cdot)\\) represents a feature extractor. A straightforward way to achieve the learning objective of EBVs is to directly optimize the cosine similarity between each \\(\\pmb{v}_i\\) and the corresponding basis vector \\(\\hat{w}_{y_i}\\in \\mathcal{W}\\)" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.423, + 0.47, + 0.519 + ], + "angle": 0, + "content": "However, the basis vector itself is not correlated with the training data since it is predefined. Fitting the training samples directly to the corresponding basis vectors might disrupt the representation learning. Therefore, we consider the conventional parametric softmax formulation, of which for image \\( x_{i} \\) with embedding \\( v_{i} \\), the probability of it being recognized as the \\( y_{i} \\) category can be formulated as:" + }, + { + "type": "equation", + "bbox": [ + 0.149, + 0.53, + 0.47, + 0.567 + ], + "angle": 0, + "content": "\\[\nP (y = y _ {i} | \\boldsymbol {v} _ {i}) = \\frac {\\exp \\left(\\boldsymbol {m} _ {i} ^ {\\top} \\boldsymbol {v} _ {i}\\right)}{\\sum_ {j = 1} ^ {N} \\exp \\left(\\boldsymbol {m} _ {j} ^ {\\top} \\boldsymbol {v} _ {i}\\right)}, \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.575, + 0.47, + 0.63 + ], + "angle": 0, + "content": "where \\( m_j \\) is a weight vector for the \\( j \\)-th class. Thus, according to Eq. (2) and Eq. (5), the probability of the embedding \\( v_i \\) being recognized as category \\( y_i \\) in our proposed EBVs can be formulated as:" + }, + { + "type": "equation", + "bbox": [ + 0.129, + 0.639, + 0.47, + 0.673 + ], + "angle": 0, + "content": "\\[\nP _ {\\mathrm {E B V s}} (y = y _ {i} \\mid \\boldsymbol {v} _ {i}) = \\frac {\\exp \\left(\\hat {\\boldsymbol {w}} _ {i} \\hat {\\boldsymbol {v}} _ {i} / \\tau\\right)}{\\sum_ {j = 1} ^ {N} \\exp \\left(\\hat {\\boldsymbol {w}} _ {j} \\hat {\\boldsymbol {v}} _ {i} / \\tau\\right)}, \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.683, + 0.47, + 0.766 + ], + "angle": 0, + "content": "where \\(\\hat{\\pmb{v}}_i\\) denotes the \\(\\ell_{2}\\)-normalized of the embedding \\(\\pmb{v}_i\\) and \\(\\tau\\) is a hyper-parameter of temperature [17,20,64] which usually used in unsupervised learning. The learning objective is then to maximize the joint probability \\(\\prod_{i=1}^{M} P_{\\pmb{\\theta}}(y_i | f_{\\pmb{\\theta}}(x_i))\\), or equivalently to minimize the negative log-likelihood over the training set which can be formulated as:" + }, + { + "type": "equation", + "bbox": [ + 0.124, + 0.777, + 0.47, + 0.802 + ], + "angle": 0, + "content": "\\[\nJ (\\boldsymbol {\\theta}) = - \\sum_ {i = 1} ^ {M} \\log P _ {\\mathrm {E B V s}} (y = y _ {i} | f _ {\\boldsymbol {\\theta}} (x _ {i})). \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.811, + 0.47, + 0.867 + ], + "angle": 0, + "content": "With this optimization approach, we relax the learning objective to make the angle between the embedding \\( \\pmb{v} \\) of a training sample and its corresponding basis vector smaller than the angle between \\( \\pmb{v} \\) and the other basis vectors." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.126, + 0.688, + 0.139 + ], + "angle": 0, + "content": "3.5. Merits of our EBVs" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.149, + 0.894, + 0.329 + ], + "angle": 0, + "content": "We briefly summarize the merits of our proposed EBVs in this section. First of all, the embedding dimension of EBVs can be manually altered and the trainable parameters of the classifier will not grow linearly when the number of categories increases. Specifically, if the embedding dimension of each image is \\( d' \\) and the number of categories is \\( N \\), the trainable parameters of a general classifier are \\( d' \\times N \\). However, with our proposed EBVs, as the dimension of the embedding for each category is fixed as \\( d \\), then the trainable parameters of the classifier are \\( d' \\times d \\). What's more, \\( d \\) can be set at least close to \\( \\sqrt{2N} \\) when \\( N \\) is very large according to Section 3.3. Experimental results can be found in Table 2 and the supplementary materials." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.331, + 0.893, + 0.538 + ], + "angle": 0, + "content": "Secondly, as the proposed EBVs are generated before the training step and the fixed \\(d\\)-dimensional embedding of each category will not be changed throughout the optimization process, EBVs will not introduce a large amount of computation during the training stage like the metric learning. In particular, metric learning methods such as pairwise/triplet embedding [60] are time-consuming, where the complexity can be \\(\\mathcal{O}(K^2)\\) and \\(\\mathcal{O}(K^3)\\) when given \\(K\\) images from \\(N\\) categories. However, the complexity of our proposed EBVs equals \\(\\mathcal{O}(K)\\). In addition, EBVs are not sensitive to the optimizers and previous training tricks while they can still achieve state-of-the-art performance as the results shown in Table 1 and the supplementary materials. Also, further results on the downstream tasks can be found in Section 4 and the supplementary materials." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.556, + 0.632, + 0.571 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.581, + 0.893, + 0.663 + ], + "angle": 0, + "content": "In this section, quantitative and qualitative experiments are exhibited on models that end with a \\(k\\)-way fully connected layer with softmax and our proposed method to demonstrate the effectiveness of the proposed Equiangular Basis Vectors (EBVs). All experiments are conducted with 8 RTX 3090 GPUs." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.678, + 0.863, + 0.693 + ], + "angle": 0, + "content": "4.1. Quantitative results on image classification" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.702, + 0.694, + 0.715 + ], + "angle": 0, + "content": "4.1.1 Dataset and settings" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.727, + 0.894, + 0.796 + ], + "angle": 0, + "content": "We conduct the general image classification task on the ImageNet-1K [9] dataset, which contains 1.28M training images and 50K validation images from 1,000 different object classes. Then, we report ImageNet-1K top-1 accuracy on the validation set under a single crop setting." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.798, + 0.894, + 0.867 + ], + "angle": 0, + "content": "In order to demonstrate the effectiveness of the proposed EBVs, we follow the state-of-the-art training methods provided by TorchVision [59] and timm [63]. For fair comparisons, we offer the following diverse training settings for the general classification task." + }, + { + "type": "page_number", + "bbox": [ + 0.466, + 0.887, + 0.505, + 0.898 + ], + "angle": 0, + "content": "11759" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.124, + 0.894, + 0.152 + ], + "angle": 0, + "content": "Table 1. Comparisons on the ImageNet-1K validation set. \"FC\" denotes models ending with a 1000-way fully connected layer with softmax. The test size for each image is set as \"224^2\" if there is one result while it is set as \"224^2/256^2\" if there exist two results." + }, + { + "type": "table", + "bbox": [ + 0.078, + 0.161, + 0.89, + 0.42 + ], + "angle": 0, + "content": "
BackboneMethodOptimizerLREpochSettingParams.GFLOPsTest size#Forward passTop-1 Acc (%)
ResNet-50FCSGD0.190A025.6M4.12242600k77.15
ResNet-50FCSGD0.55/100A125.6M4.12242/2562131k76.88/77.92
EBVs77.55/78.73
ResNet-50FCSGD0.55/100A225.6M4.12242/2562131k77.71/78.59
EBVs78.14/78.99
ResNet-50*FCSGD0.55/600A225.6M4.12242/2562755k79.51/-\n79.73/80.45
EBVs
ResNet-50FCAdamW0.00172.57/73.79
FC0.015/100A125.6M4.12242/2562131k72.51/74.03
EBVs0.0175.62/77.14
ResNet-50FCAdamW0.00175.42/76.48
FC0.015/100A225.6M4.12242/2562131kNaN
EBVs0.0176.46/77.52
Swin-TFCAdamW0.0015/100A128.3M4.52242131k75.64
EBVs78.37
Swin-TFCAdamW0.0015/100A228.3M4.52242131k79.12
EBVs79.34
" + }, + { + "type": "table_footnote", + "bbox": [ + 0.091, + 0.422, + 0.803, + 0.436 + ], + "angle": 0, + "content": "* represents the result of the model with a general fully connected layer with softmax is provided by TorchVision [59]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.458, + 0.471, + 0.569 + ], + "angle": 0, + "content": "Setting A0 The official training setting provided in ResNet [19]. A \\(224 \\times 224\\) crop is randomly sampled from an image or its horizontal flip, with the per-pixel mean subtracted [27]. It trains the backbone by using SGD optimizer with momentum as 0.9, weight decay as \\(1 \\times 10^{-4}\\) and batch size as 256. The training iteration is up to \\(60 \\times 10^{4}\\). The standard color augmentation in [27] is used. It adopts the standard 10-crop testing [27] in the validation stage." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.586, + 0.47, + 0.725 + ], + "angle": 0, + "content": "Setting A1 We employ an AdamW [35] or an SGD [47] optimizer for 100 epochs using a cosine decay learning rate scheduler and 5 epochs of linear warm-up. The batch size is set as 1024 and the initial learning rate for the AdamW optimizer is 0.01 or 0.001 while it is set as 0.5 for the SGD optimizer. A \\(224 \\times 224\\) crop is randomly sampled from each image and the weight decay is set as \\(2 \\times 10^{-5}\\). We perform TrivialAugment [41], which is extremely simple and can be considered \"parameter-free\". We also adopt random erasing [71] and the probability is set as 0.1." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.742, + 0.47, + 0.797 + ], + "angle": 0, + "content": "Setting A2 On the basis of Setting A1, we add label-smoothing [54] and the value is set as 0.1. We also perform mixup [69] and cutmix [68]. The setting of hyper-parameters of the two techniques is the same with TorchVision [59]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.798, + 0.471, + 0.867 + ], + "angle": 0, + "content": "We adopt ResNet-50 [19] and Swin-T [32] as the typical backbone for Convolutional Neural Networks (CNNs) and Vision Transformers [10]. The hyper-parameters \\(\\tau\\) for the proposed EBVs are set as 0.07 for all the following experiments unless otherwise specified." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.458, + 0.642, + 0.47 + ], + "angle": 0, + "content": "4.1.2 Main results" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.48, + 0.893, + 0.675 + ], + "angle": 0, + "content": "Table 1 presents comparisons between deep networks ending with FC, i.e., a 1000-way classification layer with softmax and our proposed EBVs. The fixed \\(\\alpha\\), \\(d\\) and \\(N\\) of EBVs are set as 0.004, 1000 and 1000, respectively. When adopting ResNet-50 as the backbone, EBVs outperform FC among all the settings. In addition, when adopting AdamW as the optimizer, EBVs gain \\(3.11\\% / 1.04\\%\\) improvement over FC under Setting A1 and Setting A2 when using \\(224^2 / 256^2\\) testing. EBVs still gain around \\(2.7\\% / 0.2\\%\\) improvement on Swin-T under Setting A1 and Setting A2. As previous training techniques summarised by both TorchVision [59] and timm [63] are under the setting of FC, we suspect it will have some impact on the performance of EBVs. We further conduct ablation studies in the supplementary materials." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.692, + 0.667, + 0.705 + ], + "angle": 0, + "content": "4.1.3 Ablation studies" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.714, + 0.894, + 0.868 + ], + "angle": 0, + "content": "We conduct ablation studies on the dimension \\(d\\) of each basis vector to demonstrate the merits of our proposed EBVs. Table 2 reports ImageNet-1K top-1 accuracy on the validation set with different dimensions \\(d\\). Taking \\(d = 100\\) as an example, the dimension of the embedding of an image is set as 100. We adopt ResNet-50 as the backbone and the setting of all the experiments follows Setting A2. We use SGD [47] as the optimizer and the initial learning rate is set as 0.01. The test size of each image is set as \\(224^2\\) and \\(256^2\\). The Min. Ang. which represents the minimum angle between each two basis vectors is defined as \\(\\min_{1 \\leq i,j \\leq N, i \\neq j} \\min(\\pi - \\arccos(\\hat{w}_i)\\)" + }, + { + "type": "page_number", + "bbox": [ + 0.466, + 0.887, + 0.506, + 0.898 + ], + "angle": 0, + "content": "11760" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.124, + 0.471, + 0.163 + ], + "angle": 0, + "content": "Table 2. Ablation studies on the dimension of our proposed EBVs. \"EBVs Dim.\" denotes the embedding dimension for each category. The test size for each image is set as \\(224^2\\) and \\(256^2\\)." + }, + { + "type": "table", + "bbox": [ + 0.079, + 0.174, + 0.477, + 0.327 + ], + "angle": 0, + "content": "
EBVs Dim.Epoch Min.Ang.Ave.Del.Ang.Top-1 Acc (%)
1005/10082.24°4.84°76.10/76.83
2005/10085.41°3.37°77.04/77.83
3005/10086.67°2.64°77.25/78.08
4005/10087.48°2.18°77.20/78.38
5005/10087.99°1.82°77.39/78.34
10005/10089.98°0.01°78.14/78.99
20005/10089.98°0.01°77.87/78.58
1005/30082.24°4.84°78.33/79.25
10005/30089.98°0.01°79.10/79.96
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.341, + 0.471, + 0.43 + ], + "angle": 0, + "content": "Table 3. Object detection and instance segmentation on the COCO 2017 dataset. Models are based on Mask R-CNN [18] and “\\(1 \\times\\)” denotes we train models for 12 epochs while “\\(3 \\times\\)” denotes 36 epochs. “\\(\\mathrm{AP}^{\\mathrm{b}}\\)” and “\\(\\mathrm{AP}^{\\mathrm{m}}\\)” refer to bounding box AP and mask AP, respectively. Results shaded in gray denote models ending with the general fully connected classifier while others denote models ending with our proposed EBVs." + }, + { + "type": "table", + "bbox": [ + 0.08, + 0.441, + 0.475, + 0.555 + ], + "angle": 0, + "content": "
BackboneSchedule\\(AP^b\\)\\(AP_{50}^b\\)\\(AP_{75}^b\\)\\(AP^m\\)\\(AP_{50}^m\\)\\(AP_{75}^m\\)
ResNet-501×38.2 58.8 41.4 34.7 55.7 37.2
ResNet-50 (EBVs)1×38.3 59.0 42.0 35.2 56.2 37.7
ResNet-503×40.9 61.3 44.8 37.1 58.3 39.9
ResNet-50 (EBVs)3×41.1 61.7 44.9 37.7 58.9 40.5
Swin-T1×42.7 65.2 46.8 39.3 62.2 42.2
Swin-T (EBVs)1×42.8 65.3 47.2 39.4 62.2 42.6
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.581, + 0.47, + 0.763 + ], + "angle": 0, + "content": "\\(\\hat{\\boldsymbol{w}}_j)\\), \\(\\operatorname{arccos}(\\hat{\\boldsymbol{w}}_i \\cdot \\hat{\\boldsymbol{w}}_j)\\), where \\(N\\) represents the number of categories. While the Ave. Del. Ang. which represents the average angle between each of two basis vectors is defined as \\(\\frac{N(N-1)}{2} \\sum_{i=1}^{N-1} \\sum_{j=i+1}^{N} \\left| \\operatorname{arccos}(\\hat{\\boldsymbol{w}}_i \\cdot \\hat{\\boldsymbol{w}}_j) - \\frac{\\pi}{2} \\right|\\). For a clearer representation, we adopt an angle instead of a radian. It can be seen from Table 2 that dimension has an impact on the performance of a model when training with limited cycles. However, this gap decreases a lot when adopting longer training cycles. Taking \\(d = 100\\) and \\(d = 1000\\) as an example, the top-1 accuracy under \\(d = 1000\\) gains \\(2.04\\% / 2.16\\%\\) improvement over \\(d = 100\\) when training with 105 epochs while this gap is reduced to \\(0.77\\% / 0.71\\%\\) when training with 305 epochs." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.775, + 0.43, + 0.79 + ], + "angle": 0, + "content": "4.2. Empirical evaluations on object detection" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.797, + 0.471, + 0.868 + ], + "angle": 0, + "content": "Settings Object detection and instance segmentation experiments are conducted on the COCO 2017 benchmark [31], which contains \\(118\\mathrm{K}\\) images in the training set and \\(5\\mathrm{K}\\) images in the validation set. We consider Mask R-CNN [18] in MMdetection [5] as the detection framework and adopt" + }, + { + "type": "table_caption", + "bbox": [ + 0.498, + 0.124, + 0.894, + 0.189 + ], + "angle": 0, + "content": "Table 4. Results of semantic segmentation on the ADE20K validation set. Results shaded in gray denote models ending with the general fully connected classifier while others denote models ending with our proposed EBVs. “\\(1 \\times\\)” denotes we train models for 80,000 steps while “\\(2 \\times\\)” denotes 160,000 steps." + }, + { + "type": "table", + "bbox": [ + 0.504, + 0.199, + 0.89, + 0.375 + ], + "angle": 0, + "content": "
BackboneSchedulemIoUmIoU(ms+flip)
ResNet-181×38.7639.81
ResNet-18 (EBVs)1×38.9840.09
ResNet-182×39.2339.97
ResNet-18 (EBVs)2×39.7540.91
ResNet-501×40.7041.81
ResNet-50 (EBVs)1×42.7344.19
ResNet-502×42.0542.78
ResNet-50 (EBVs)2×42.4443.94
Swin-T2×44.4145.79
Swin-T (EBVs)2×44.3045.88
" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.398, + 0.895, + 0.634 + ], + "angle": 0, + "content": "ResNet [19] and Swin Transformer [32] as backbones. For fair comparisons, we utilize the same settings according to MMdetection and previous work. We scaled the image to a maximum of 800 on the short side and 1333 on the long side. We adopt \\(50\\%\\) scale horizontal flip and use SGD [47] with momentum \\(= 0.9\\) as the optimizer, the initial learning rate is 0.02. The weight decay equals 0.0001 while the batch size is 16 for experiments under the backbone of ResNet. For experiments on Swin Transformer, we use Adam [24] as the optimizer and the initial learning rate is 0.0001. The weight decay is changed to 0.05. To demonstrate the effectiveness of the proposed EBVs, we replace both instance-level and pixel-level classifiers in the detection framework with EBVs. In order to control the parameters of each backbone for fair comparisons, the dimension \\(d\\) of the basis vectors is kept consistent with the number of categories. All backbone models are pre-trained on the ImageNet-1K training set." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.654, + 0.894, + 0.752 + ], + "angle": 0, + "content": "Results Table 3 presents comparisons between the general framework and our proposed EBVs. When adopting ResNet-50 as the backbone, the framework ending with EBVs outperforms those ending with fully connected layers among six evaluation indicators. While adopting Swin-T as the backbone, the framework ending with EBVs also achieves comparative results with state-of-the-art performance." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.761, + 0.892, + 0.789 + ], + "angle": 0, + "content": "4.3. Empirical evaluations on semantic segmentation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.797, + 0.895, + 0.868 + ], + "angle": 0, + "content": "Settings Semantic segmentation experiments are conducted on the ADE20K [73], which contains 20,000 images in the training set and 2,000 images in the validation set. We adopt FPN [25] and UperNet [65] in MMSEG [6] as segmentation framework and adopt ResNet [19] and Swin Trans" + }, + { + "type": "page_number", + "bbox": [ + 0.466, + 0.887, + 0.504, + 0.898 + ], + "angle": 0, + "content": "11761" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.11, + 0.134, + 0.329, + 0.293 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.347, + 0.133, + 0.563, + 0.293 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.58, + 0.133, + 0.862, + 0.293 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.298, + 0.894, + 0.364 + ], + "angle": 0, + "content": "Figure 2. Representation structure of ResNet-50. Left: Similarity between layers within ResNet-50 ends with a general fully connected classifier (FC). It shows that the last few layers share minimal similarity with the shallow layers while a few shallow layers also share minimal similarity with all the other layers. Middle: Similarity between layers within ResNet-50 ends with EBVs. Only the last few layers share minimal similarity with other layers. Right: Similarity between layers across ResNet-50 ends with a general fully connected layer with softmax and our proposed EBVs. Around \\(10\\%\\) initial layers share a little similarity while the last few layers share the least similarity." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.377, + 0.473, + 0.53 + ], + "angle": 0, + "content": "former [32] as backbones. For fair comparisons, we utilize the same settings in MMSEG. For experiments on ResNet, we use SGD [47] as the optimizer. The initial learning rate equals 0.01, weight decay equals 0.0005, momentum equals 0.9 and batch size is set as 16. For experiments on Swin Transformer, we use AdamW [35] as the optimizer and the initial learning rate is 0.00006 while the weight decay is set as 0.01. To perform our proposed method, We modify pixel-level classifiers in both the decode head and auxiliary head to EBVs. All backbone models are pre-trained on the ImageNet-1K training set." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.55, + 0.472, + 0.648 + ], + "angle": 0, + "content": "Results According to Table 4, we find that EBVs surpass the framework ending with fully connected layers as the classifier under the backbone of ResNet. Additionally, when the training step is set as 80,000, EBVs gain a higher mIoU score than the general framework trained for 160,000 steps. While adopting Swin-T as the backbone, the framework ending with EBVs still achieving comparative performance." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.662, + 0.199, + 0.677 + ], + "angle": 0, + "content": "5. Discussions" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.686, + 0.472, + 0.852 + ], + "angle": 0, + "content": "We explore whether there are differences in the way EBVs represent and solve image tasks compared to a fully connected layer with softmax in this section. In order to answer this question, we have to analyze the features in the hidden layers as features are usually spread across neurons. However, different layers generally have different numbers of neurons. Recently, Raghu et al. [43] and Zhen et al. [70] applied the Centered Kernel Alignment (CKA) [7, 26] to solve the above task. CKA is effective because it involves no constraint on the number of neurons. It is also independent of the orthogonal transformations of representations [70]. Therefore, we adopt CKA to analyze the above question." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.853, + 0.472, + 0.867 + ], + "angle": 0, + "content": "We pick ResNet-50 as the backbone while the experi" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.377, + 0.896, + 0.572 + ], + "angle": 0, + "content": "ments on Swin-T can be found in the supplementary materials. One model ends with a general fully connected (FC) classifier and another model ends with our proposed EBVs. Both of the models are pre-trained on the ImageNet-1K [9] training dataset. We use 49 convolutional layers and the last fully connected layer. We plot CKA similarities between all pairs of layers within the whole ImageNet-1K validation dataset in Figure 2. As shown in Figure 2, for the ResNet-50 model ending with a general FC classifier, the feature similarity shows that around \\(10\\%\\) initial convolutional layers almost share no similarity with all the other layers while they themselves share a high similarity. If we change the last layer and the learning objective with our proposed EBVs, these shallow layers then share a relatively higher similarity." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.581, + 0.619, + 0.595 + ], + "angle": 0, + "content": "6. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.604, + 0.896, + 0.867 + ], + "angle": 0, + "content": "In this paper, we proposed Equiangular Basis Vectors (EBVs) for classification tasks. Different from previous classifiers and classical metric learning methods, EBVs predefined a fixed embedding for all the semantic categories. The learning objective of EBVs then changed to minimize the spherical distance of the embedding of input and each basis vector. Various experiments on the ImageNet-1K [9], COCO 2017 [31] and ADE20K [73] datasets and ablation studies also demonstrated the effectiveness of our proposed EBVs. In the future, we would like to explore relations between each basis vector pair and embed hierarchies when generating the proposed EBVs as the normal Euclidean space could not naturally embed hierarchies on datasets with known semantic hierarchies [16]. We also would like to explore the performance of EBVs in the case when the number of categories became very large. In addition, EBVs could also be regarded as advanced classifiers, it is interesting to adopt EBVs in other related tasks, e.g., incremental learning, few-shot learning, etc." + }, + { + "type": "page_number", + "bbox": [ + 0.466, + 0.887, + 0.506, + 0.898 + ], + "angle": 0, + "content": "11762" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.125, + 0.174, + 0.139 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.148, + 0.47, + 0.198 + ], + "angle": 0, + "content": "[1] L Douglas Baker and Andrew Kachites McCallum. Distributional clustering of words for text classification. In ACM SIGIR Conf. on Research and Development in Information Retrieval, pages 96-103, 1998. 2" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.2, + 0.472, + 0.248 + ], + "angle": 0, + "content": "[2] Arindam Banerjee, Srujana Merugu, Inderjit S Dhillon, Joydeep Ghosh, and John Lafferty. Clustering with Bregman divergences. Journal of Mach. 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In deep neural networks, models usually end with a $k$ -way fully connected layer with softmax to handle different classification tasks. The learning objective of these methods can be summarized as mapping the learned feature representations to the samples' label space. While in metric learning approaches, the main objective is to learn a transformation function that maps training data points from the original space to a new space where similar points are closer while dissimilar points become farther apart. Different from previous methods, our EBVs generate normalized vector embeddings as "predefined classifiers" which are required to not only be with the equal status between each other, but also be as orthogonal as possible. By minimizing the spherical distance of the embedding of an input between its categorical EBV in training, the predictions can be obtained by identifying the categorical EBV with the smallest distance during inference. Various experiments on the ImageNet-1K dataset and other downstream tasks demonstrate that our method outperforms the general fully connected classifier while it does not introduce huge additional computation compared with classical metric learning methods. Our EBVs won the first place in the 2022 DIGIX Global AI Challenge, and our code is open-source and available at https://github.com/NJUST-VIPGroup/Equiangular-Basis-Vectors. + +# 1. Introduction + +The pattern classification field developed around the end of the twentieth century aims to deal with the specific problem of assigning input signals to two or more classes [56]. In recent years, deep learning models have brought breakthroughs in processing image, video, audio, text, and other + +*Corresponding author. This work was supported by National Key R&D Program of China (2021YFA1001100), National Natural Science Foundation of China under Grant (62272231), Natural Science Foundation of Jiangsu Province of China under Grant (BK20210340), the Fundamental Research Funds for the Central Universities (No. NJ2022028), and CAAI-Huawei MindSpore Open Fund. + +![](images/454be30ec200476950ac985528eff7f73c2e6f51f10f3e4323187bd821a8371b.jpg) +(a) Fully Connected Layers with Softmax + +![](images/d4275b04165c0bb888f9afd59f701f7f617e49539ed17f0ef8f1781f7fc5ac32.jpg) +(b) Metric Learning +(c) Equiangular Basis Vectors +Figure 1. Comparisons between typical classification paradigms and our proposed Equiangular Basis Vectors (EBVs). (a) A general classifier ends with $k$ -way fully connected layers with softmax. When adding more categories, the trainable parameters of the classifier grow linearly. (b) Taking triplet embedding [60] as an example of classical metric learning methods, the complexity is $\mathcal{O}(M^3)$ when given $M$ images and it will grows to $\mathcal{O}((M + m')^3)$ when adding a new category with $m'$ images. (c) Our proposed EBVs. EBVs predefine fixed normalized vector embeddings for different categories and these embeddings will not be changed during the training stage. The trainable parameters of the network will not be changed with the growth of the number of categories while the complexity only grows from $\mathcal{O}(M)$ to $\mathcal{O}(M + m')$ . + +data [10, 19, 27, 58]. Aided by the rapid gains in hardware, deep learning methods today can easily overfit one million images [9] and easily overcomes the obstacle to the quality of handcrafted features in previous pattern classification tasks. Many approaches based on deep learning spring up like mushrooms and had been used to solve classification problems in various scenarios and settings such as remote sensing [38], few-shot [52], long-tailed [72], etc. + +Figure 1 illustrates two typical classification paradigms. Nowadays, a large amount of deep learning methods [38, 72] adopt a trainable fully connected layer with softmax as the classifier. However, since the number of categories is fixed, the trainable parameters of the classifier rise as the number of categories becomes larger. For example, the memory consumption of a fully connected layer $\mathbf{W} \in \mathbb{R}^{d \times N}$ linearly scales up with the growth of the category number $N$ and so is the cost to compute the matrix multiplication between the fully connected layer and the $d$ -dimensional features. While some other methods based on classical metric learning [23, 30, 60-62] have to consider all the training samples and design positive/negative pairs then optimize a class center for each category, which requires a significant amount of extra computation for large-scale datasets, especially for those pre-training tasks. + +In this paper, we propose Equiangular Basis Vectors (EBVs) to replace the fully connected layer associated with softmax within classification tasks in deep neural networks. EBVs predefine fixed normalized vector embeddings with equal status (equal angles) which will not be changed during the training stage. Specifically, EBVs pre-set a $d$ -dimensional unit hypersphere, and for each category in the classification task, EBVs assign the category a $d$ -dimensional normalized embedding on the surface of the hypersphere and we term these embedding as basis vectors. The spherical distance of each basis vector pair satisfies an artificially made rule to make the relationship between any two vectors as close to orthogonal as possible. In order to keep the trainable parameters of the deep neural networks constant with the growth of the category number $N$ , we then propose the definition of EBVs based on Tammes Problem [55] and Equiangular Lines [57] in Section 3.2. + +The learning objective of each category in our proposed EBVs is also different from previous classification methods. Compared with deep models that end with a fully connected layer to handle the classification tasks [19, 27], the meaning of the parameter weights within the fully connected layer in EBVs is not the relevance of a feature representation to a particular category but a fixed matrix which embed feature representations to a new space. Also, compared with regression methods [34,51], EBVs do not need to learn the unified representations for different categories and optimize the distance between the representation of input images and category centers, which helps reduce the computational consumption for the extra unified representations learning. In contrast to classical metric learning approaches [14, 23, 50, 61], our EBVs do not need to measure the similarity among different training samples and constrain distance between each category, which will introduce a large amount of computational consumption for large-scale datasets. In our proposed method, the representations of different images learned by EBVs will be embedded into a normalized hypersphere and the learning + +objective is altered to minimize the spherical distance of the learned representations with different predefined basis vectors. In addition, the spherical distance between each predefined basis vector is carefully constrained so that there is no need to spend extra cost in the optimization of these basis vectors. To quantitatively prove both the effectiveness and efficiency of our proposed EBVs, we evaluate EBVs on diverse computer vision tasks with large-scale datasets, including classification on ImageNet-1K, object detection on COCO, as well as semantic segmentation on ADE20K. + +# 2. Related work + +# 2.1. Deep networks for image classification + +Image classification is the task of categorizing images into one of several predefined classes, which has been a fundamental problem in computer vision for a long time [4, 36]. It also forms the basis for many other computer vision tasks, e.g., object detection [37], localization [28] and segmentation [39]. To solve the image classification problem, a dual-stage approach was used before the rise of deep learning. Specifically, handcrafted features were first extracted from images using feature descriptors. Then, a trainable classifier is adopted to perform the classification task with these input features [44]. The major hindrance of this approach was that the accuracy of the classification task was profoundly dependent on the design of the feature extraction stage, and this usually proved to be a formidable task [29]. + +In recent years, deep learning models that exploit multiple layers of nonlinear information processing, for feature extraction and transformation as well as for pattern analysis and classification, have been shown to overcome these challenges [44]. With the holding of ImageNet Large Scale Visual Recognition Challenge (ILSVRC) [49], a growing number of deep networks demonstrate superior classification performance [10, 15, 19, 27, 32, 33, 42]. Among them, Deep Convolutional Neural Networks (DCNNs) and Vision Transformers (ViTs) [10] have become the leading architectures for most image classification task in recent years. In addition, selected representative examples of other improvement attempts related to the following different aspects: network architecture, nonlinear activation functions, supervision components, regularization mechanisms and optimization techniques. Our proposed Equiangular Basis Vectors (EBVs) are different from these aspects as we do not change the overall architecture and training techniques but the optimization objectives for classification since we preliminary design fixed normalized vector embeddings for each predefined category. + +# 2.2. Learning objectives + +Besides traditional classifiers, machine learning or deep learning methods such as clustering [1,45], regression [34, 51], metric learning [14,50,61], sparse learning [48,67] can + +be used to handle the classification tasks while the learning objectives of these methods vary considerably. In this section, we only discuss the learning objective of our EBVs with two prominent training paradigms of deep learning for the classification tasks, i.e., general $k$ -way classification layers [27] and classical deep metric learning [3, 66]. + +Regarding deep learning for classification, the $k$ -way classification layer (always associated with softmax) is the most popular used approach for training deep models. It employs a single linear layer or multiple non-linear layers to map the learned deep representations to the semantic categories in the label space. The corresponding learning objective is minimizing the losses (e.g., the cross-entropy loss [8]) between the mapped categorical signals (aka. predictions) with the ground truth categories. Compared with that, the learning objective of our EBVs is to make the vectorized embedding of input as close as possible to its categorical equiangular basis vector correspondingly. + +The learning objective of classical deep metric learning seems similar to ours. However, there are several crucial and fundamental differences. Firstly, although deep metric learning minimizes the distances between sample vectors belonging to the same category and meanwhile maximizes the distances between samples from different categories, all these sample vectors are constantly changing during the model training process. But, in our method, the equiangular basis vectors corresponding to the categories are predefined, i.e., they are fixed. More importantly, these equiangular basis vectors in the spherical space are forced to be with equal status and be as orthogonal as possible to each other, which could contribute to strong model discriminative ability and good classification accuracy. In practice, both with equal status and being orthogonal of vectors are strict conditions w.r.t. optimization. Thus, our EBVs predefine the satisfied categorical basis vectors and our learning objective focuses on only optimizing the learned feature representations to prevent the model from being unable to converge (when EBVs can also change under such strict conditions). Secondly, the learning objective of deep metric learning is upon massive training samples, while our learning objective is for the training sample and its fixed categorical vectorized embedding, i.e., EBV. It could bring the computational economy, especially for the large-scale training data scenario, cf. Section 3.5. In addition, compared with several specific metric learning approaches, e.g., the center loss [62], the prototypical network [52] and the nearest class mean approach [40], our method is still quite distant from them. Specifically, the basic idea of these works is to construct the "center" of samples belonging to a category to represent its semantics and then leverage the centers to optimize sample distances for classification. Similarly, since these categorical centers are always changing during training, these approaches will also encounter the same problems as aforementioned. + +# 3. Methodology + +# 3.1. Preliminaries + +The proposed Equiangular Basis Vectors (EBVs) are based on the study with regard to Equiangular Lines [21, 22,57] and the Tammes Problem [55]. + +A set of lines passing through the origin in $\mathbb{R}^d (d\in$ $\{2,3,4,5,\ldots \})$ is called equiangular if they are pairwise separated by the same angle. The study of equiangular lines was initiated by Haantjes [22] and it plays an important role in the coding theory [53] and quantum information theory [46]. + +The problem of how to determine the maximum number $N(d)$ of equiangular lines in a given dimension $d$ was formally posed by Van Lint and Seidel [57] and has gained a major breakthrough by Jiang et al. [21] last year — Fix $0 < \alpha < 1$ , let $N_{\alpha}(d)$ denote the maximum number of lines through the origin in $\mathbb{R}^d$ with pairwise common angle $\arccos \alpha$ , let $k$ denote the minimum number (if it exists) of vertices in a graph whose adjacency matrix has spectral radius exactly $(1 - \alpha) / (2\alpha)$ . If $k < \infty$ , then $N_{\alpha}(d) = \lfloor k(d - 1) / (k - 1)\rfloor$ for all sufficiently large $d$ , and otherwise $N_{\alpha}(d) = d + o(d)$ . In particular, $N_{1 / (2k - 1)}(d) = \lfloor k(d - 1) / (k - 1)\rfloor$ for every integer $k \geq 2$ and all sufficiently large $d$ [21]. + +In simple terms, with a fixed common angle, the maximum number $N(d)$ of equiangular lines is linearly correlated with the dimension $d$ as $d \to \infty$ while there is still no precise lower bound for $N(d)$ with smaller values of $d$ [13]. Therefore, we further refer to the Tammes Problem. Let $a_{n}$ be the maximal number with the property that one can place on a unit hypersphere $S^{d} \in \mathbb{R}^{d}(d \in \{3,4,5,\ldots\})$ $n$ points so that the spherical distance of any two points is at least $a_{n}$ . The problem of finding $a_{n}$ together with the corresponding arrangement of each point is known as the Tammes Problem [55] or the optimal spherical code [12]. It is easy to find that the number of these points will be close to infinity as $a_{n}$ tends to zero. + +# 3.2. Definition of Equiangular Basis Vectors + +In order to predefine fixed $d$ -dimensional embeddings for as many categories as possible but still keep these embeddings at a distance from each other on a unit hypersphere $S^d \in \mathbb{R}^d$ , we therefore propose Equiangular Basis Vectors (EBVs). Specifically, we fix $0 \leq \alpha < 1$ and let $\mathcal{N}_{\alpha}(d)$ denote the range of values for the number of coordinate vectors in $\mathbb{R}^d$ with the pairwise common angle between $\arccos \alpha$ and $\arccos -\alpha$ . The problem of our proposed EBVs is to calculate the coordinates of each vector in the vector set $\mathcal{W}$ when given fixed $\alpha, d$ and $N \in \mathcal{N}_{\alpha}(d)$ if possible, i.e., solve the set $\mathcal{W}$ which satisfies: + +$$ +\forall \boldsymbol {w} _ {i}, \boldsymbol {w} _ {j} \in \mathcal {W}, i \neq j, - \alpha \leq \frac {\boldsymbol {w} _ {i} \cdot \boldsymbol {w} _ {j}}{\| \boldsymbol {w} _ {i} \| \| \boldsymbol {w} _ {j} \|} \leq \alpha , \tag {1} +$$ + +where $\pmb{w}_i\in \mathbb{R}^d$ , card(W) $= N$ and $\| \cdot \|$ denotes the Euclidean norm. Let $\phi$ denote the spherical distance function, which can also be replaced by the cosine similarity function. EBVs produce a distribution over classes for a query point $\pmb {v}\in \mathbb{R}^{d}$ based on softmax over cosine similarity to the $N$ fixed coordinate vectors in the embedding space: + +$$ +p (y = k | \boldsymbol {v}) = \frac {\exp (- \phi (\boldsymbol {v} , \boldsymbol {w} _ {k}))}{\sum_ {k ^ {\prime}} \exp (- \phi (\boldsymbol {v} , \boldsymbol {w} _ {k ^ {\prime}}))}, \tag {2} +$$ + +where $y = k \in \{1, 2, \dots, N\}$ denotes the corresponding coordinate vector, which can also be seen as the corresponding label. While $k'$ represents the associated basis vectors in $\mathcal{W}$ . Relations between $\alpha$ , $d$ and $N$ are described in the supplementary materials. With such a set $\mathcal{W}$ , the maximum number of categories it can handle is $N$ . Additionally, training with any category number less than $N$ , it is sufficient to randomly select any of the same numbers of coordinate vectors in $\mathcal{W}$ , since these vectors are exactly equivalent. + +# 3.3. How to generate EBVs? + +The basic idea of our Equiangular Basis Vectors (EBVs) is to generate fixed normalized vector embeddings with equal status (equal angles) as "predefined classifiers" for all the relevant categories. The question then comes to how to calculate the predefined EBVs which satisfy Eq. (1). Therefore, we will discuss how to generate the proposed EBVs when given fixed $\alpha$ , $d$ and $N \in \mathcal{N}_{\alpha}(d)$ in this section. + +Assuming each $\boldsymbol{w}_i \in \mathcal{W}$ ( $i = \{1, 2, \dots, N\}$ ) as a line, we can construct the Grassmannian Matrices to solve the set $\mathcal{W}$ [11]. Specifically, we assemble the vectors in $\mathcal{W}$ into a matrix $\boldsymbol{W} \in \mathbb{R}^{d \times N}$ , where $\boldsymbol{W} = [\boldsymbol{w}_1; \boldsymbol{w}_2; \dots; \boldsymbol{w}_N]$ . Then, the mutual-coherence of $\boldsymbol{W}$ is defined by: + +$$ +\mu (\boldsymbol {W}) = \max _ {1 \leq i, j \leq N, i \neq j} \frac {\left| \boldsymbol {w} _ {i} ^ {\top} \cdot \boldsymbol {w} _ {j} \right|}{\left\| \boldsymbol {w} _ {i} \right\| \left\| \boldsymbol {w} _ {j} \right\|} = \max _ {1 \leq i, j \leq N, i \neq j} \cos \theta_ {i j}, \tag {3} +$$ + +which is transformed to the smallest possible mutualcoherence possible [11]. Therefore, the lower bound for $\alpha$ is $\sqrt{\frac{N - d}{d(N - 1)}}$ and the upper bound for $\mathcal{N}_{\alpha}(d)$ is $1 + \frac{d - 1}{1 - \alpha^2d}$ ( $d \leq N, 1 - \alpha^2 d > 0$ ). In addition, such matrix is possible only if $N < \min(d(d + 1)/2, (N - d)(N - d + 1)/2)$ . Construction of such a matrix has a strong connection with the packing of vectors/subspaces in the $\mathbb{R}^d$ -space. In the case of $N = d$ , we can simply construct a unitary matrix, while in other cases, it will be very hard to construct such a general Grassmannian matrix [11]. + +In the definition of our proposed EBVs, whether the angle between any two basis vectors $\pmb{w}_i, \pmb{w}_j \in \mathcal{W} (i \neq j)$ is $\arccos \alpha$ or $\arccos -\alpha$ is equivalent. It is clear that we can not construct the Grassmannian matrix in a situation such as $N = 30,000$ and $d = 200$ . However, it is still possible for us to construct $\mathcal{W}$ which satisfies Eq. (1). Therefore, as + +Algorithm 1 Generation of EBVs in a PyTorch-like style +#d:Dim for each coordinate vectors +#N:The number of coordinate vectors +# $\alpha$ : Threshold of $\hat{\pmb{w}}_i\cdot \hat{\pmb{w}}_j,i\neq j$ +#W:The EBVs matrix $W\in \mathbb{R}^{d\times N}$ +#slice: In the case of $N\gg d$ ,optimize W by slicing +#λ: Learning rate. +Initialize W randomly; +while True: #Normalize each row in W + $W =$ Normalize(W) +for i in [N/slice]: start $=$ i\* slice end $= \min (N$ $(\mathrm{i} + 1)^{*}$ slice) E $=$ Fonehot(arange(start, end), N) C $=$ (W[start:end]@W.T).abs()-E loss $=$ ReLU(C-α).sum() # Cutout the gradient of vector pairs which satisfies $-\alpha \leq \hat{\pmb{w}}_i\cdot \hat{\pmb{w}}_j\leq \alpha$ loss.backup() if max(α,C.max()) < α + o(α): Save(W) break + $W = W - \lambda *W.\mathrm{grad}\#$ Update W + +an alternative, we adopt Stochastic Gradient Descent [47] to search the set $\mathcal{W}$ that satisfies the definition of EBVs when given fixed $\alpha$ , $d$ and $N$ . Specifically, we random initialize a matrix $\pmb{W} \in \mathbb{R}^{d \times N}$ with normalized rows such that the angle between any two vectors $\hat{\pmb{w}}_i$ , $\hat{\pmb{w}}_j \in \mathbb{R}^d$ , $i, j \in \{1, 2, \dots, N\}$ , $i \neq j$ , $\hat{\pmb{w}}_i = \frac{\pmb{w}_i}{\|\pmb{w}_i\|}$ can be represented as $\arccos(\hat{\pmb{w}}_i \cdot \hat{\pmb{w}}_j)$ . Then, we cut out the gradient of those vector pairs which satisfies $-\alpha \leq \hat{\pmb{w}}_i \cdot \hat{\pmb{w}}_j \leq \alpha$ and optimize the remaining vector pairs. The optimization function of the generation of EBVs can be formulated by: + +$$ +\underset {\boldsymbol {W}} {\arg \min } \sum_ {i = 1} ^ {N - 1} \sum_ {j > i} ^ {N} \max \left(\hat {\boldsymbol {w}} _ {i} \cdot \hat {\boldsymbol {w}} _ {j} - \alpha , 0\right). \tag {4} +$$ + +Algorithm 1 provides the code of a simple generation method of the proposed EBVs in a PyTorch-like style. It is also worth mentioning that the EBVs matrix $W$ will not be changed in the following training stage within all the tasks. + +# 3.4. How to achieve the learning objective of EBVs? + +Equiangular Basis Vectors (EBVs) provide fixed learning targets for each independent optimization objective, i.e., semantic categories. In the following, we introduce how to achieve the learning objective of EBVs for all the training samples. Generally, a deep network is performed to extract the high-dimensional features, and a fully connected classification layer is then deployed to map the features to semantic categories. While in our proposed EBVs, each category will be bound to a unique normalized $d$ -dimensional basis vector in $\mathcal{W}$ . Thus, for a training sample $x$ , we directly use a unified deep model to generate a $d$ -dimensional embedding $\pmb{v}$ , as well as optimizing the cosine distance between $\pmb{v}$ and + +the relevant basis vector. Below we analyze the underlying distance/loss function used in the training stage. + +For our EBVs, many existing distance functions including squared Euclidean distance, Mahalanobis distance, or cosine distance are permissible. However, a particular class of distance functions, e.g., regular Bregman divergences [2], seems hard to explain and optimize in the proposed EBVs settings. In addition, intuitively, the straightforward way is to optimize the spherical distance between any two vectors on the surface of the hyper-sphere. Therefore, we adopt the cosine distance as the distance metric, which is widely used for measuring whether two inputs are similar or dissimilar and have been widely used in the Tammes problem [55]. + +Implementations Suppose we have $M$ sample-label pairs $\{(x_{1},y_{1}),(x_{2},y_{2}),\ldots ,(x_{M},y_{M})\}$ in $N$ classes and their $d$ -dimensional features $\pmb{v}_1,\pmb{v}_2,\dots ,\pmb{v}_M$ with $\boldsymbol {v}_i = f_\theta (\boldsymbol {x}_i)$ where $f_{\theta}(\cdot)$ represents a feature extractor. A straightforward way to achieve the learning objective of EBVs is to directly optimize the cosine similarity between each $\pmb{v}_i$ and the corresponding basis vector $\hat{w}_{y_i}\in \mathcal{W}$ + +However, the basis vector itself is not correlated with the training data since it is predefined. Fitting the training samples directly to the corresponding basis vectors might disrupt the representation learning. Therefore, we consider the conventional parametric softmax formulation, of which for image $x_{i}$ with embedding $v_{i}$ , the probability of it being recognized as the $y_{i}$ category can be formulated as: + +$$ +P (y = y _ {i} | \boldsymbol {v} _ {i}) = \frac {\exp \left(\boldsymbol {m} _ {i} ^ {\top} \boldsymbol {v} _ {i}\right)}{\sum_ {j = 1} ^ {N} \exp \left(\boldsymbol {m} _ {j} ^ {\top} \boldsymbol {v} _ {i}\right)}, \tag {5} +$$ + +where $m_j$ is a weight vector for the $j$ -th class. Thus, according to Eq. (2) and Eq. (5), the probability of the embedding $v_i$ being recognized as category $y_i$ in our proposed EBVs can be formulated as: + +$$ +P _ {\mathrm {E B V s}} (y = y _ {i} \mid \boldsymbol {v} _ {i}) = \frac {\exp \left(\hat {\boldsymbol {w}} _ {i} \hat {\boldsymbol {v}} _ {i} / \tau\right)}{\sum_ {j = 1} ^ {N} \exp \left(\hat {\boldsymbol {w}} _ {j} \hat {\boldsymbol {v}} _ {i} / \tau\right)}, \tag {6} +$$ + +where $\hat{\pmb{v}}_i$ denotes the $\ell_{2}$ -normalized of the embedding $\pmb{v}_i$ and $\tau$ is a hyper-parameter of temperature [17,20,64] which usually used in unsupervised learning. The learning objective is then to maximize the joint probability $\prod_{i=1}^{M} P_{\pmb{\theta}}(y_i | f_{\pmb{\theta}}(x_i))$ , or equivalently to minimize the negative log-likelihood over the training set which can be formulated as: + +$$ +J (\boldsymbol {\theta}) = - \sum_ {i = 1} ^ {M} \log P _ {\mathrm {E B V s}} (y = y _ {i} | f _ {\boldsymbol {\theta}} (x _ {i})). \tag {7} +$$ + +With this optimization approach, we relax the learning objective to make the angle between the embedding $\pmb{v}$ of a training sample and its corresponding basis vector smaller than the angle between $\pmb{v}$ and the other basis vectors. + +# 3.5. Merits of our EBVs + +We briefly summarize the merits of our proposed EBVs in this section. First of all, the embedding dimension of EBVs can be manually altered and the trainable parameters of the classifier will not grow linearly when the number of categories increases. Specifically, if the embedding dimension of each image is $d'$ and the number of categories is $N$ , the trainable parameters of a general classifier are $d' \times N$ . However, with our proposed EBVs, as the dimension of the embedding for each category is fixed as $d$ , then the trainable parameters of the classifier are $d' \times d$ . What's more, $d$ can be set at least close to $\sqrt{2N}$ when $N$ is very large according to Section 3.3. Experimental results can be found in Table 2 and the supplementary materials. + +Secondly, as the proposed EBVs are generated before the training step and the fixed $d$ -dimensional embedding of each category will not be changed throughout the optimization process, EBVs will not introduce a large amount of computation during the training stage like the metric learning. In particular, metric learning methods such as pairwise/triplet embedding [60] are time-consuming, where the complexity can be $\mathcal{O}(K^2)$ and $\mathcal{O}(K^3)$ when given $K$ images from $N$ categories. However, the complexity of our proposed EBVs equals $\mathcal{O}(K)$ . In addition, EBVs are not sensitive to the optimizers and previous training tricks while they can still achieve state-of-the-art performance as the results shown in Table 1 and the supplementary materials. Also, further results on the downstream tasks can be found in Section 4 and the supplementary materials. + +# 4. Experiments + +In this section, quantitative and qualitative experiments are exhibited on models that end with a $k$ -way fully connected layer with softmax and our proposed method to demonstrate the effectiveness of the proposed Equiangular Basis Vectors (EBVs). All experiments are conducted with 8 RTX 3090 GPUs. + +# 4.1. Quantitative results on image classification + +# 4.1.1 Dataset and settings + +We conduct the general image classification task on the ImageNet-1K [9] dataset, which contains 1.28M training images and 50K validation images from 1,000 different object classes. Then, we report ImageNet-1K top-1 accuracy on the validation set under a single crop setting. + +In order to demonstrate the effectiveness of the proposed EBVs, we follow the state-of-the-art training methods provided by TorchVision [59] and timm [63]. For fair comparisons, we offer the following diverse training settings for the general classification task. + +Table 1. Comparisons on the ImageNet-1K validation set. "FC" denotes models ending with a 1000-way fully connected layer with softmax. The test size for each image is set as "224^2" if there is one result while it is set as "224^2/256^2" if there exist two results. + +
BackboneMethodOptimizerLREpochSettingParams.GFLOPsTest size#Forward passTop-1 Acc (%)
ResNet-50FCSGD0.190A025.6M4.12242600k77.15
ResNet-50FCSGD0.55/100A125.6M4.12242/2562131k76.88/77.92
EBVs77.55/78.73
ResNet-50FCSGD0.55/100A225.6M4.12242/2562131k77.71/78.59
EBVs78.14/78.99
ResNet-50*FCSGD0.55/600A225.6M4.12242/2562755k79.51/- +79.73/80.45
EBVs
ResNet-50FCAdamW0.00172.57/73.79
FC0.015/100A125.6M4.12242/2562131k72.51/74.03
EBVs0.0175.62/77.14
ResNet-50FCAdamW0.00175.42/76.48
FC0.015/100A225.6M4.12242/2562131kNaN
EBVs0.0176.46/77.52
Swin-TFCAdamW0.0015/100A128.3M4.52242131k75.64
EBVs78.37
Swin-TFCAdamW0.0015/100A228.3M4.52242131k79.12
EBVs79.34
+ +* represents the result of the model with a general fully connected layer with softmax is provided by TorchVision [59]. + +Setting A0 The official training setting provided in ResNet [19]. A $224 \times 224$ crop is randomly sampled from an image or its horizontal flip, with the per-pixel mean subtracted [27]. It trains the backbone by using SGD optimizer with momentum as 0.9, weight decay as $1 \times 10^{-4}$ and batch size as 256. The training iteration is up to $60 \times 10^{4}$ . The standard color augmentation in [27] is used. It adopts the standard 10-crop testing [27] in the validation stage. + +Setting A1 We employ an AdamW [35] or an SGD [47] optimizer for 100 epochs using a cosine decay learning rate scheduler and 5 epochs of linear warm-up. The batch size is set as 1024 and the initial learning rate for the AdamW optimizer is 0.01 or 0.001 while it is set as 0.5 for the SGD optimizer. A $224 \times 224$ crop is randomly sampled from each image and the weight decay is set as $2 \times 10^{-5}$ . We perform TrivialAugment [41], which is extremely simple and can be considered "parameter-free". We also adopt random erasing [71] and the probability is set as 0.1. + +Setting A2 On the basis of Setting A1, we add label-smoothing [54] and the value is set as 0.1. We also perform mixup [69] and cutmix [68]. The setting of hyper-parameters of the two techniques is the same with TorchVision [59]. + +We adopt ResNet-50 [19] and Swin-T [32] as the typical backbone for Convolutional Neural Networks (CNNs) and Vision Transformers [10]. The hyper-parameters $\tau$ for the proposed EBVs are set as 0.07 for all the following experiments unless otherwise specified. + +# 4.1.2 Main results + +Table 1 presents comparisons between deep networks ending with FC, i.e., a 1000-way classification layer with softmax and our proposed EBVs. The fixed $\alpha$ , $d$ and $N$ of EBVs are set as 0.004, 1000 and 1000, respectively. When adopting ResNet-50 as the backbone, EBVs outperform FC among all the settings. In addition, when adopting AdamW as the optimizer, EBVs gain $3.11\% / 1.04\%$ improvement over FC under Setting A1 and Setting A2 when using $224^2 / 256^2$ testing. EBVs still gain around $2.7\% / 0.2\%$ improvement on Swin-T under Setting A1 and Setting A2. As previous training techniques summarised by both TorchVision [59] and timm [63] are under the setting of FC, we suspect it will have some impact on the performance of EBVs. We further conduct ablation studies in the supplementary materials. + +# 4.1.3 Ablation studies + +We conduct ablation studies on the dimension $d$ of each basis vector to demonstrate the merits of our proposed EBVs. Table 2 reports ImageNet-1K top-1 accuracy on the validation set with different dimensions $d$ . Taking $d = 100$ as an example, the dimension of the embedding of an image is set as 100. We adopt ResNet-50 as the backbone and the setting of all the experiments follows Setting A2. We use SGD [47] as the optimizer and the initial learning rate is set as 0.01. The test size of each image is set as $224^2$ and $256^2$ . The Min. Ang. which represents the minimum angle between each two basis vectors is defined as $\min_{1 \leq i,j \leq N, i \neq j} \min(\pi - \arccos(\hat{w}_i)$ + +Table 2. Ablation studies on the dimension of our proposed EBVs. "EBVs Dim." denotes the embedding dimension for each category. The test size for each image is set as $224^2$ and $256^2$ . + +
EBVs Dim.Epoch Min.Ang.Ave.Del.Ang.Top-1 Acc (%)
1005/10082.24°4.84°76.10/76.83
2005/10085.41°3.37°77.04/77.83
3005/10086.67°2.64°77.25/78.08
4005/10087.48°2.18°77.20/78.38
5005/10087.99°1.82°77.39/78.34
10005/10089.98°0.01°78.14/78.99
20005/10089.98°0.01°77.87/78.58
1005/30082.24°4.84°78.33/79.25
10005/30089.98°0.01°79.10/79.96
+ +Table 3. Object detection and instance segmentation on the COCO 2017 dataset. Models are based on Mask R-CNN [18] and “ $1 \times$ ” denotes we train models for 12 epochs while “ $3 \times$ ” denotes 36 epochs. “ $\mathrm{AP}^{\mathrm{b}}$ ” and “ $\mathrm{AP}^{\mathrm{m}}$ ” refer to bounding box AP and mask AP, respectively. Results shaded in gray denote models ending with the general fully connected classifier while others denote models ending with our proposed EBVs. + +
BackboneSchedule\(AP^b\)\(AP_{50}^b\)\(AP_{75}^b\)\(AP^m\)\(AP_{50}^m\)\(AP_{75}^m\)
ResNet-501×38.2 58.8 41.4 34.7 55.7 37.2
ResNet-50 (EBVs)1×38.3 59.0 42.0 35.2 56.2 37.7
ResNet-503×40.9 61.3 44.8 37.1 58.3 39.9
ResNet-50 (EBVs)3×41.1 61.7 44.9 37.7 58.9 40.5
Swin-T1×42.7 65.2 46.8 39.3 62.2 42.2
Swin-T (EBVs)1×42.8 65.3 47.2 39.4 62.2 42.6
+ +$\hat{\boldsymbol{w}}_j)$ , $\operatorname{arccos}(\hat{\boldsymbol{w}}_i \cdot \hat{\boldsymbol{w}}_j)$ , where $N$ represents the number of categories. While the Ave. Del. Ang. which represents the average angle between each of two basis vectors is defined as $\frac{N(N-1)}{2} \sum_{i=1}^{N-1} \sum_{j=i+1}^{N} \left| \operatorname{arccos}(\hat{\boldsymbol{w}}_i \cdot \hat{\boldsymbol{w}}_j) - \frac{\pi}{2} \right|$ . For a clearer representation, we adopt an angle instead of a radian. It can be seen from Table 2 that dimension has an impact on the performance of a model when training with limited cycles. However, this gap decreases a lot when adopting longer training cycles. Taking $d = 100$ and $d = 1000$ as an example, the top-1 accuracy under $d = 1000$ gains $2.04\% / 2.16\%$ improvement over $d = 100$ when training with 105 epochs while this gap is reduced to $0.77\% / 0.71\%$ when training with 305 epochs. + +# 4.2. Empirical evaluations on object detection + +Settings Object detection and instance segmentation experiments are conducted on the COCO 2017 benchmark [31], which contains $118\mathrm{K}$ images in the training set and $5\mathrm{K}$ images in the validation set. We consider Mask R-CNN [18] in MMdetection [5] as the detection framework and adopt + +Table 4. Results of semantic segmentation on the ADE20K validation set. Results shaded in gray denote models ending with the general fully connected classifier while others denote models ending with our proposed EBVs. “ $1 \times$ ” denotes we train models for 80,000 steps while “ $2 \times$ ” denotes 160,000 steps. + +
BackboneSchedulemIoUmIoU(ms+flip)
ResNet-181×38.7639.81
ResNet-18 (EBVs)1×38.9840.09
ResNet-182×39.2339.97
ResNet-18 (EBVs)2×39.7540.91
ResNet-501×40.7041.81
ResNet-50 (EBVs)1×42.7344.19
ResNet-502×42.0542.78
ResNet-50 (EBVs)2×42.4443.94
Swin-T2×44.4145.79
Swin-T (EBVs)2×44.3045.88
+ +ResNet [19] and Swin Transformer [32] as backbones. For fair comparisons, we utilize the same settings according to MMdetection and previous work. We scaled the image to a maximum of 800 on the short side and 1333 on the long side. We adopt $50\%$ scale horizontal flip and use SGD [47] with momentum $= 0.9$ as the optimizer, the initial learning rate is 0.02. The weight decay equals 0.0001 while the batch size is 16 for experiments under the backbone of ResNet. For experiments on Swin Transformer, we use Adam [24] as the optimizer and the initial learning rate is 0.0001. The weight decay is changed to 0.05. To demonstrate the effectiveness of the proposed EBVs, we replace both instance-level and pixel-level classifiers in the detection framework with EBVs. In order to control the parameters of each backbone for fair comparisons, the dimension $d$ of the basis vectors is kept consistent with the number of categories. All backbone models are pre-trained on the ImageNet-1K training set. + +Results Table 3 presents comparisons between the general framework and our proposed EBVs. When adopting ResNet-50 as the backbone, the framework ending with EBVs outperforms those ending with fully connected layers among six evaluation indicators. While adopting Swin-T as the backbone, the framework ending with EBVs also achieves comparative results with state-of-the-art performance. + +# 4.3. Empirical evaluations on semantic segmentation + +Settings Semantic segmentation experiments are conducted on the ADE20K [73], which contains 20,000 images in the training set and 2,000 images in the validation set. We adopt FPN [25] and UperNet [65] in MMSEG [6] as segmentation framework and adopt ResNet [19] and Swin Trans + +![](images/a57eff453f219621b701e140d9732c9f33a2e144b6fb7a6dadcdcd04c339d08f.jpg) +Figure 2. Representation structure of ResNet-50. Left: Similarity between layers within ResNet-50 ends with a general fully connected classifier (FC). It shows that the last few layers share minimal similarity with the shallow layers while a few shallow layers also share minimal similarity with all the other layers. Middle: Similarity between layers within ResNet-50 ends with EBVs. Only the last few layers share minimal similarity with other layers. Right: Similarity between layers across ResNet-50 ends with a general fully connected layer with softmax and our proposed EBVs. Around $10\%$ initial layers share a little similarity while the last few layers share the least similarity. + +![](images/041aea74dcbd9ed5dde9e6bf8be810725005b24b6e9044fd86f1be6aa3588b4b.jpg) + +![](images/3ff2a477372a0afa4eda9646fd301c05972614d7324bf639750f290e9040e36d.jpg) + +former [32] as backbones. For fair comparisons, we utilize the same settings in MMSEG. For experiments on ResNet, we use SGD [47] as the optimizer. The initial learning rate equals 0.01, weight decay equals 0.0005, momentum equals 0.9 and batch size is set as 16. For experiments on Swin Transformer, we use AdamW [35] as the optimizer and the initial learning rate is 0.00006 while the weight decay is set as 0.01. To perform our proposed method, We modify pixel-level classifiers in both the decode head and auxiliary head to EBVs. All backbone models are pre-trained on the ImageNet-1K training set. + +Results According to Table 4, we find that EBVs surpass the framework ending with fully connected layers as the classifier under the backbone of ResNet. Additionally, when the training step is set as 80,000, EBVs gain a higher mIoU score than the general framework trained for 160,000 steps. While adopting Swin-T as the backbone, the framework ending with EBVs still achieving comparative performance. + +# 5. Discussions + +We explore whether there are differences in the way EBVs represent and solve image tasks compared to a fully connected layer with softmax in this section. In order to answer this question, we have to analyze the features in the hidden layers as features are usually spread across neurons. However, different layers generally have different numbers of neurons. Recently, Raghu et al. [43] and Zhen et al. [70] applied the Centered Kernel Alignment (CKA) [7, 26] to solve the above task. CKA is effective because it involves no constraint on the number of neurons. It is also independent of the orthogonal transformations of representations [70]. Therefore, we adopt CKA to analyze the above question. + +We pick ResNet-50 as the backbone while the experi + +ments on Swin-T can be found in the supplementary materials. One model ends with a general fully connected (FC) classifier and another model ends with our proposed EBVs. Both of the models are pre-trained on the ImageNet-1K [9] training dataset. We use 49 convolutional layers and the last fully connected layer. We plot CKA similarities between all pairs of layers within the whole ImageNet-1K validation dataset in Figure 2. As shown in Figure 2, for the ResNet-50 model ending with a general FC classifier, the feature similarity shows that around $10\%$ initial convolutional layers almost share no similarity with all the other layers while they themselves share a high similarity. If we change the last layer and the learning objective with our proposed EBVs, these shallow layers then share a relatively higher similarity. + +# 6. Conclusion + +In this paper, we proposed Equiangular Basis Vectors (EBVs) for classification tasks. Different from previous classifiers and classical metric learning methods, EBVs predefined a fixed embedding for all the semantic categories. The learning objective of EBVs then changed to minimize the spherical distance of the embedding of input and each basis vector. Various experiments on the ImageNet-1K [9], COCO 2017 [31] and ADE20K [73] datasets and ablation studies also demonstrated the effectiveness of our proposed EBVs. In the future, we would like to explore relations between each basis vector pair and embed hierarchies when generating the proposed EBVs as the normal Euclidean space could not naturally embed hierarchies on datasets with known semantic hierarchies [16]. We also would like to explore the performance of EBVs in the case when the number of categories became very large. In addition, EBVs could also be regarded as advanced classifiers, it is interesting to adopt EBVs in other related tasks, e.g., incremental learning, few-shot learning, etc. + +# References + +[1] L Douglas Baker and Andrew Kachites McCallum. Distributional clustering of words for text classification. 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Vis., 127(3):302-321, 2019. 7, 8 \ No newline at end of file diff --git a/2023/Equiangular Basis Vectors/images.zip b/2023/Equiangular Basis Vectors/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..32863bf0777b592e23eaf6a9ee7a1606553cc703 --- /dev/null +++ b/2023/Equiangular Basis Vectors/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:7d4f5c8b7da7dfe2b3d9390bceefcebbb4cf1595fa65856bc60173441b7276d7 +size 374892 diff --git a/2023/Equiangular Basis Vectors/layout.json b/2023/Equiangular Basis Vectors/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..86c233917f10ad154657cb54b7fd5d9c209f0d30 --- /dev/null +++ b/2023/Equiangular Basis Vectors/layout.json @@ -0,0 +1,10963 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 208, + 137, + 369, + 153 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 208, + 137, + 369, + 153 + ], + "spans": [ + { + "bbox": [ + 208, + 137, + 369, + 153 + ], + "type": "text", + "content": "Equiangular Basis Vectors" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 176, + 175, + 404, + 188 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 176, + 175, + 404, + 188 + ], + "spans": [ + { + "bbox": [ + 176, + 175, + 404, + 188 + ], + "type": "text", + "content": "Yang Shen Xuhao Sun Xiu-Shen Wei*" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 52, + 189, + 524, + 203 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 52, + 189, + 524, + 203 + ], + "spans": [ + { + "bbox": [ + 52, + 189, + 524, + 203 + ], + "type": "text", + "content": "School of Computer Science and Engineering, Nanjing University of Science and Technology, China" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 189, + 204, + 386, + 216 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 189, + 204, + 386, + 216 + ], + "spans": [ + { + "bbox": [ + 189, + 204, + 386, + 216 + ], + "type": "text", + "content": "{shenyang.98,sunxh,weixs}@njust.edu.cn" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 139, + 243, + 186, + 255 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 139, + 243, + 186, + 255 + ], + "spans": [ + { + "bbox": [ + 139, + 243, + 186, + 255 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 45, + 267, + 282, + 570 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 267, + 282, + 570 + ], + "spans": [ + { + "bbox": [ + 45, + 267, + 282, + 570 + ], + "type": "text", + "content": "We propose Equiangular Basis Vectors (EBVs) for classification tasks. In deep neural networks, models usually end with a " + }, + { + "bbox": [ + 45, + 267, + 282, + 570 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 45, + 267, + 282, + 570 + ], + "type": "text", + "content": "-way fully connected layer with softmax to handle different classification tasks. The learning objective of these methods can be summarized as mapping the learned feature representations to the samples' label space. While in metric learning approaches, the main objective is to learn a transformation function that maps training data points from the original space to a new space where similar points are closer while dissimilar points become farther apart. Different from previous methods, our EBVs generate normalized vector embeddings as \"predefined classifiers\" which are required to not only be with the equal status between each other, but also be as orthogonal as possible. By minimizing the spherical distance of the embedding of an input between its categorical EBV in training, the predictions can be obtained by identifying the categorical EBV with the smallest distance during inference. Various experiments on the ImageNet-1K dataset and other downstream tasks demonstrate that our method outperforms the general fully connected classifier while it does not introduce huge additional computation compared with classical metric learning methods. Our EBVs won the first place in the 2022 DIGIX Global AI Challenge, and our code is open-source and available at https://github.com/NJUST-VIPGroup/Equiangular-Basis-Vectors." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 590, + 124, + 602 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 590, + 124, + 602 + ], + "spans": [ + { + "bbox": [ + 46, + 590, + 124, + 602 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 45, + 609, + 280, + 668 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 609, + 280, + 668 + ], + "spans": [ + { + "bbox": [ + 45, + 609, + 280, + 668 + ], + "type": "text", + "content": "The pattern classification field developed around the end of the twentieth century aims to deal with the specific problem of assigning input signals to two or more classes [56]. In recent years, deep learning models have brought breakthroughs in processing image, video, audio, text, and other" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 45, + 672, + 280, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 672, + 280, + 730 + ], + "spans": [ + { + "bbox": [ + 45, + 672, + 280, + 730 + ], + "type": "text", + "content": "*Corresponding author. This work was supported by National Key R&D Program of China (2021YFA1001100), National Natural Science Foundation of China under Grant (62272231), Natural Science Foundation of Jiangsu Province of China under Grant (BK20210340), the Fundamental Research Funds for the Central Universities (No. NJ2022028), and CAAI-Huawei MindSpore Open Fund." + } + ] + } + ], + "index": 12 + }, + { + "type": "image", + "bbox": [ + 348, + 244, + 490, + 354 + ], + "blocks": [ + { + "bbox": [ + 348, + 244, + 490, + 354 + ], + "lines": [ + { + "bbox": [ + 348, + 244, + 490, + 354 + ], + "spans": [ + { + "bbox": [ + 348, + 244, + 490, + 354 + ], + "type": "image", + "image_path": "454be30ec200476950ac985528eff7f73c2e6f51f10f3e4323187bd821a8371b.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 339, + 354, + 500, + 366 + ], + "lines": [ + { + "bbox": [ + 339, + 354, + 500, + 366 + ], + "spans": [ + { + "bbox": [ + 339, + 354, + 500, + 366 + ], + "type": "text", + "content": "(a) Fully Connected Layers with Softmax" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_caption" + } + ], + "index": 13 + }, + { + "type": "image", + "bbox": [ + 301, + 371, + 539, + 463 + ], + "blocks": [ + { + "bbox": [ + 301, + 371, + 539, + 463 + ], + "lines": [ + { + "bbox": [ + 301, + 371, + 539, + 463 + ], + "spans": [ + { + "bbox": [ + 301, + 371, + 539, + 463 + ], + "type": "image", + "image_path": "d4275b04165c0bb888f9afd59f701f7f617e49539ed17f0ef8f1781f7fc5ac32.jpg" + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 314, + 463, + 395, + 474 + ], + "lines": [ + { + "bbox": [ + 314, + 463, + 395, + 474 + ], + "spans": [ + { + "bbox": [ + 314, + 463, + 395, + 474 + ], + "type": "text", + "content": "(b) Metric Learning" + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 419, + 463, + 535, + 474 + ], + "lines": [ + { + "bbox": [ + 419, + 463, + 535, + 474 + ], + "spans": [ + { + "bbox": [ + 419, + 463, + 535, + 474 + ], + "type": "text", + "content": "(c) Equiangular Basis Vectors" + } + ] + } + ], + "index": 17, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 296, + 484, + 533, + 625 + ], + "lines": [ + { + "bbox": [ + 296, + 484, + 533, + 625 + ], + "spans": [ + { + "bbox": [ + 296, + 484, + 533, + 625 + ], + "type": "text", + "content": "Figure 1. Comparisons between typical classification paradigms and our proposed Equiangular Basis Vectors (EBVs). (a) A general classifier ends with " + }, + { + "bbox": [ + 296, + 484, + 533, + 625 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 296, + 484, + 533, + 625 + ], + "type": "text", + "content": "-way fully connected layers with softmax. When adding more categories, the trainable parameters of the classifier grow linearly. (b) Taking triplet embedding [60] as an example of classical metric learning methods, the complexity is " + }, + { + "bbox": [ + 296, + 484, + 533, + 625 + ], + "type": "inline_equation", + "content": "\\mathcal{O}(M^3)" + }, + { + "bbox": [ + 296, + 484, + 533, + 625 + ], + "type": "text", + "content": " when given " + }, + { + "bbox": [ + 296, + 484, + 533, + 625 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 296, + 484, + 533, + 625 + ], + "type": "text", + "content": " images and it will grows to " + }, + { + "bbox": [ + 296, + 484, + 533, + 625 + ], + "type": "inline_equation", + "content": "\\mathcal{O}((M + m')^3)" + }, + { + "bbox": [ + 296, + 484, + 533, + 625 + ], + "type": "text", + "content": " when adding a new category with " + }, + { + "bbox": [ + 296, + 484, + 533, + 625 + ], + "type": "inline_equation", + "content": "m'" + }, + { + "bbox": [ + 296, + 484, + 533, + 625 + ], + "type": "text", + "content": " images. (c) Our proposed EBVs. EBVs predefine fixed normalized vector embeddings for different categories and these embeddings will not be changed during the training stage. The trainable parameters of the network will not be changed with the growth of the number of categories while the complexity only grows from " + }, + { + "bbox": [ + 296, + 484, + 533, + 625 + ], + "type": "inline_equation", + "content": "\\mathcal{O}(M)" + }, + { + "bbox": [ + 296, + 484, + 533, + 625 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 296, + 484, + 533, + 625 + ], + "type": "inline_equation", + "content": "\\mathcal{O}(M + m')" + }, + { + "bbox": [ + 296, + 484, + 533, + 625 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 18, + "angle": 0, + "type": "image_caption" + } + ], + "index": 15 + }, + { + "bbox": [ + 296, + 636, + 533, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 636, + 533, + 730 + ], + "spans": [ + { + "bbox": [ + 296, + 636, + 533, + 730 + ], + "type": "text", + "content": "data [10, 19, 27, 58]. Aided by the rapid gains in hardware, deep learning methods today can easily overfit one million images [9] and easily overcomes the obstacle to the quality of handcrafted features in previous pattern classification tasks. Many approaches based on deep learning spring up like mushrooms and had been used to solve classification problems in various scenarios and settings such as remote sensing [38], few-shot [52], long-tailed [72], etc." + } + ] + } + ], + "index": 19 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 77, + 42, + 119, + 71 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 77, + 42, + 119, + 71 + ], + "spans": [ + { + "bbox": [ + 77, + 42, + 119, + 71 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 150, + 41, + 471, + 52 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 150, + 41, + 471, + 52 + ], + "spans": [ + { + "bbox": [ + 150, + 41, + 471, + 52 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 198, + 52, + 422, + 63 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 198, + 52, + 422, + 63 + ], + "spans": [ + { + "bbox": [ + 198, + 52, + 422, + 63 + ], + "type": "text", + "content": "Except for this watermark, it is identical to the accepted version;" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 181, + 63, + 440, + 74 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 181, + 63, + 440, + 74 + ], + "spans": [ + { + "bbox": [ + 181, + 63, + 440, + 74 + ], + "type": "text", + "content": "the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 277, + 746, + 301, + 756 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 277, + 746, + 301, + 756 + ], + "spans": [ + { + "bbox": [ + 277, + 746, + 301, + 756 + ], + "type": "text", + "content": "11755" + } + ] + } + ], + "index": 20 + } + ], + "page_size": [ + 595, + 842 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 45, + 106, + 281, + 293 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 106, + 281, + 293 + ], + "spans": [ + { + "bbox": [ + 45, + 106, + 281, + 293 + ], + "type": "text", + "content": "Figure 1 illustrates two typical classification paradigms. Nowadays, a large amount of deep learning methods [38, 72] adopt a trainable fully connected layer with softmax as the classifier. However, since the number of categories is fixed, the trainable parameters of the classifier rise as the number of categories becomes larger. For example, the memory consumption of a fully connected layer " + }, + { + "bbox": [ + 45, + 106, + 281, + 293 + ], + "type": "inline_equation", + "content": "\\mathbf{W} \\in \\mathbb{R}^{d \\times N}" + }, + { + "bbox": [ + 45, + 106, + 281, + 293 + ], + "type": "text", + "content": " linearly scales up with the growth of the category number " + }, + { + "bbox": [ + 45, + 106, + 281, + 293 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 45, + 106, + 281, + 293 + ], + "type": "text", + "content": " and so is the cost to compute the matrix multiplication between the fully connected layer and the " + }, + { + "bbox": [ + 45, + 106, + 281, + 293 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 45, + 106, + 281, + 293 + ], + "type": "text", + "content": "-dimensional features. While some other methods based on classical metric learning [23, 30, 60-62] have to consider all the training samples and design positive/negative pairs then optimize a class center for each category, which requires a significant amount of extra computation for large-scale datasets, especially for those pre-training tasks." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 45, + 296, + 281, + 494 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 296, + 281, + 494 + ], + "spans": [ + { + "bbox": [ + 45, + 296, + 281, + 494 + ], + "type": "text", + "content": "In this paper, we propose Equiangular Basis Vectors (EBVs) to replace the fully connected layer associated with softmax within classification tasks in deep neural networks. EBVs predefine fixed normalized vector embeddings with equal status (equal angles) which will not be changed during the training stage. Specifically, EBVs pre-set a " + }, + { + "bbox": [ + 45, + 296, + 281, + 494 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 45, + 296, + 281, + 494 + ], + "type": "text", + "content": "-dimensional unit hypersphere, and for each category in the classification task, EBVs assign the category a " + }, + { + "bbox": [ + 45, + 296, + 281, + 494 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 45, + 296, + 281, + 494 + ], + "type": "text", + "content": "-dimensional normalized embedding on the surface of the hypersphere and we term these embedding as basis vectors. The spherical distance of each basis vector pair satisfies an artificially made rule to make the relationship between any two vectors as close to orthogonal as possible. In order to keep the trainable parameters of the deep neural networks constant with the growth of the category number " + }, + { + "bbox": [ + 45, + 296, + 281, + 494 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 45, + 296, + 281, + 494 + ], + "type": "text", + "content": ", we then propose the definition of EBVs based on Tammes Problem [55] and Equiangular Lines [57] in Section 3.2." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 45, + 496, + 281, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 496, + 281, + 730 + ], + "spans": [ + { + "bbox": [ + 45, + 496, + 281, + 730 + ], + "type": "text", + "content": "The learning objective of each category in our proposed EBVs is also different from previous classification methods. Compared with deep models that end with a fully connected layer to handle the classification tasks [19, 27], the meaning of the parameter weights within the fully connected layer in EBVs is not the relevance of a feature representation to a particular category but a fixed matrix which embed feature representations to a new space. Also, compared with regression methods [34,51], EBVs do not need to learn the unified representations for different categories and optimize the distance between the representation of input images and category centers, which helps reduce the computational consumption for the extra unified representations learning. In contrast to classical metric learning approaches [14, 23, 50, 61], our EBVs do not need to measure the similarity among different training samples and constrain distance between each category, which will introduce a large amount of computational consumption for large-scale datasets. In our proposed method, the representations of different images learned by EBVs will be embedded into a normalized hypersphere and the learning" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 296, + 106, + 532, + 223 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 106, + 532, + 223 + ], + "spans": [ + { + "bbox": [ + 296, + 106, + 532, + 223 + ], + "type": "text", + "content": "objective is altered to minimize the spherical distance of the learned representations with different predefined basis vectors. In addition, the spherical distance between each predefined basis vector is carefully constrained so that there is no need to spend extra cost in the optimization of these basis vectors. To quantitatively prove both the effectiveness and efficiency of our proposed EBVs, we evaluate EBVs on diverse computer vision tasks with large-scale datasets, including classification on ImageNet-1K, object detection on COCO, as well as semantic segmentation on ADE20K." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 297, + 234, + 380, + 246 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 234, + 380, + 246 + ], + "spans": [ + { + "bbox": [ + 297, + 234, + 380, + 246 + ], + "type": "text", + "content": "2. Related work" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 297, + 254, + 494, + 266 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 254, + 494, + 266 + ], + "spans": [ + { + "bbox": [ + 297, + 254, + 494, + 266 + ], + "type": "text", + "content": "2.1. Deep networks for image classification" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 296, + 272, + 532, + 435 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 272, + 532, + 435 + ], + "spans": [ + { + "bbox": [ + 296, + 272, + 532, + 435 + ], + "type": "text", + "content": "Image classification is the task of categorizing images into one of several predefined classes, which has been a fundamental problem in computer vision for a long time [4, 36]. It also forms the basis for many other computer vision tasks, e.g., object detection [37], localization [28] and segmentation [39]. To solve the image classification problem, a dual-stage approach was used before the rise of deep learning. Specifically, handcrafted features were first extracted from images using feature descriptors. Then, a trainable classifier is adopted to perform the classification task with these input features [44]. The major hindrance of this approach was that the accuracy of the classification task was profoundly dependent on the design of the feature extraction stage, and this usually proved to be a formidable task [29]." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 296, + 436, + 533, + 668 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 436, + 533, + 668 + ], + "spans": [ + { + "bbox": [ + 296, + 436, + 533, + 668 + ], + "type": "text", + "content": "In recent years, deep learning models that exploit multiple layers of nonlinear information processing, for feature extraction and transformation as well as for pattern analysis and classification, have been shown to overcome these challenges [44]. With the holding of ImageNet Large Scale Visual Recognition Challenge (ILSVRC) [49], a growing number of deep networks demonstrate superior classification performance [10, 15, 19, 27, 32, 33, 42]. Among them, Deep Convolutional Neural Networks (DCNNs) and Vision Transformers (ViTs) [10] have become the leading architectures for most image classification task in recent years. In addition, selected representative examples of other improvement attempts related to the following different aspects: network architecture, nonlinear activation functions, supervision components, regularization mechanisms and optimization techniques. Our proposed Equiangular Basis Vectors (EBVs) are different from these aspects as we do not change the overall architecture and training techniques but the optimization objectives for classification since we preliminary design fixed normalized vector embeddings for each predefined category." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 297, + 676, + 409, + 688 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 676, + 409, + 688 + ], + "spans": [ + { + "bbox": [ + 297, + 676, + 409, + 688 + ], + "type": "text", + "content": "2.2. Learning objectives" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 297, + 694, + 532, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 694, + 532, + 730 + ], + "spans": [ + { + "bbox": [ + 297, + 694, + 532, + 730 + ], + "type": "text", + "content": "Besides traditional classifiers, machine learning or deep learning methods such as clustering [1,45], regression [34, 51], metric learning [14,50,61], sparse learning [48,67] can" + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 277, + 746, + 301, + 756 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 277, + 746, + 301, + 756 + ], + "spans": [ + { + "bbox": [ + 277, + 746, + 301, + 756 + ], + "type": "text", + "content": "11756" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 595, + 842 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 45, + 106, + 280, + 176 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 106, + 280, + 176 + ], + "spans": [ + { + "bbox": [ + 45, + 106, + 280, + 176 + ], + "type": "text", + "content": "be used to handle the classification tasks while the learning objectives of these methods vary considerably. In this section, we only discuss the learning objective of our EBVs with two prominent training paradigms of deep learning for the classification tasks, i.e., general " + }, + { + "bbox": [ + 45, + 106, + 280, + 176 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 45, + 106, + 280, + 176 + ], + "type": "text", + "content": "-way classification layers [27] and classical deep metric learning [3, 66]." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 45, + 179, + 280, + 319 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 179, + 280, + 319 + ], + "spans": [ + { + "bbox": [ + 45, + 179, + 280, + 319 + ], + "type": "text", + "content": "Regarding deep learning for classification, the " + }, + { + "bbox": [ + 45, + 179, + 280, + 319 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 45, + 179, + 280, + 319 + ], + "type": "text", + "content": "-way classification layer (always associated with softmax) is the most popular used approach for training deep models. It employs a single linear layer or multiple non-linear layers to map the learned deep representations to the semantic categories in the label space. The corresponding learning objective is minimizing the losses (e.g., the cross-entropy loss [8]) between the mapped categorical signals (aka. predictions) with the ground truth categories. Compared with that, the learning objective of our EBVs is to make the vectorized embedding of input as close as possible to its categorical equiangular basis vector correspondingly." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 45, + 322, + 280, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 322, + 280, + 730 + ], + "spans": [ + { + "bbox": [ + 45, + 322, + 280, + 730 + ], + "type": "text", + "content": "The learning objective of classical deep metric learning seems similar to ours. However, there are several crucial and fundamental differences. Firstly, although deep metric learning minimizes the distances between sample vectors belonging to the same category and meanwhile maximizes the distances between samples from different categories, all these sample vectors are constantly changing during the model training process. But, in our method, the equiangular basis vectors corresponding to the categories are predefined, i.e., they are fixed. More importantly, these equiangular basis vectors in the spherical space are forced to be with equal status and be as orthogonal as possible to each other, which could contribute to strong model discriminative ability and good classification accuracy. In practice, both with equal status and being orthogonal of vectors are strict conditions w.r.t. optimization. Thus, our EBVs predefine the satisfied categorical basis vectors and our learning objective focuses on only optimizing the learned feature representations to prevent the model from being unable to converge (when EBVs can also change under such strict conditions). Secondly, the learning objective of deep metric learning is upon massive training samples, while our learning objective is for the training sample and its fixed categorical vectorized embedding, i.e., EBV. It could bring the computational economy, especially for the large-scale training data scenario, cf. Section 3.5. In addition, compared with several specific metric learning approaches, e.g., the center loss [62], the prototypical network [52] and the nearest class mean approach [40], our method is still quite distant from them. Specifically, the basic idea of these works is to construct the \"center\" of samples belonging to a category to represent its semantics and then leverage the centers to optimize sample distances for classification. Similarly, since these categorical centers are always changing during training, these approaches will also encounter the same problems as aforementioned." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 297, + 105, + 377, + 118 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 105, + 377, + 118 + ], + "spans": [ + { + "bbox": [ + 297, + 105, + 377, + 118 + ], + "type": "text", + "content": "3. Methodology" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 297, + 125, + 380, + 137 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 125, + 380, + 137 + ], + "spans": [ + { + "bbox": [ + 297, + 125, + 380, + 137 + ], + "type": "text", + "content": "3.1. Preliminaries" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 296, + 143, + 531, + 180 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 143, + 531, + 180 + ], + "spans": [ + { + "bbox": [ + 296, + 143, + 531, + 180 + ], + "type": "text", + "content": "The proposed Equiangular Basis Vectors (EBVs) are based on the study with regard to Equiangular Lines [21, 22,57] and the Tammes Problem [55]." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 296, + 180, + 531, + 250 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 180, + 531, + 250 + ], + "spans": [ + { + "bbox": [ + 296, + 180, + 531, + 250 + ], + "type": "text", + "content": "A set of lines passing through the origin in " + }, + { + "bbox": [ + 296, + 180, + 531, + 250 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^d (d\\in" + }, + { + "bbox": [ + 296, + 180, + 531, + 250 + ], + "type": "inline_equation", + "content": "\\{2,3,4,5,\\ldots \\})" + }, + { + "bbox": [ + 296, + 180, + 531, + 250 + ], + "type": "text", + "content": " is called equiangular if they are pairwise separated by the same angle. The study of equiangular lines was initiated by Haantjes [22] and it plays an important role in the coding theory [53] and quantum information theory [46]." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 296, + 251, + 531, + 391 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 251, + 531, + 391 + ], + "spans": [ + { + "bbox": [ + 296, + 251, + 531, + 391 + ], + "type": "text", + "content": "The problem of how to determine the maximum number " + }, + { + "bbox": [ + 296, + 251, + 531, + 391 + ], + "type": "inline_equation", + "content": "N(d)" + }, + { + "bbox": [ + 296, + 251, + 531, + 391 + ], + "type": "text", + "content": " of equiangular lines in a given dimension " + }, + { + "bbox": [ + 296, + 251, + 531, + 391 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 296, + 251, + 531, + 391 + ], + "type": "text", + "content": " was formally posed by Van Lint and Seidel [57] and has gained a major breakthrough by Jiang et al. [21] last year — Fix " + }, + { + "bbox": [ + 296, + 251, + 531, + 391 + ], + "type": "inline_equation", + "content": "0 < \\alpha < 1" + }, + { + "bbox": [ + 296, + 251, + 531, + 391 + ], + "type": "text", + "content": ", let " + }, + { + "bbox": [ + 296, + 251, + 531, + 391 + ], + "type": "inline_equation", + "content": "N_{\\alpha}(d)" + }, + { + "bbox": [ + 296, + 251, + 531, + 391 + ], + "type": "text", + "content": " denote the maximum number of lines through the origin in " + }, + { + "bbox": [ + 296, + 251, + 531, + 391 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^d" + }, + { + "bbox": [ + 296, + 251, + 531, + 391 + ], + "type": "text", + "content": " with pairwise common angle " + }, + { + "bbox": [ + 296, + 251, + 531, + 391 + ], + "type": "inline_equation", + "content": "\\arccos \\alpha" + }, + { + "bbox": [ + 296, + 251, + 531, + 391 + ], + "type": "text", + "content": ", let " + }, + { + "bbox": [ + 296, + 251, + 531, + 391 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 296, + 251, + 531, + 391 + ], + "type": "text", + "content": " denote the minimum number (if it exists) of vertices in a graph whose adjacency matrix has spectral radius exactly " + }, + { + "bbox": [ + 296, + 251, + 531, + 391 + ], + "type": "inline_equation", + "content": "(1 - \\alpha) / (2\\alpha)" + }, + { + "bbox": [ + 296, + 251, + 531, + 391 + ], + "type": "text", + "content": ". If " + }, + { + "bbox": [ + 296, + 251, + 531, + 391 + ], + "type": "inline_equation", + "content": "k < \\infty" + }, + { + "bbox": [ + 296, + 251, + 531, + 391 + ], + "type": "text", + "content": ", then " + }, + { + "bbox": [ + 296, + 251, + 531, + 391 + ], + "type": "inline_equation", + "content": "N_{\\alpha}(d) = \\lfloor k(d - 1) / (k - 1)\\rfloor" + }, + { + "bbox": [ + 296, + 251, + 531, + 391 + ], + "type": "text", + "content": " for all sufficiently large " + }, + { + "bbox": [ + 296, + 251, + 531, + 391 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 296, + 251, + 531, + 391 + ], + "type": "text", + "content": ", and otherwise " + }, + { + "bbox": [ + 296, + 251, + 531, + 391 + ], + "type": "inline_equation", + "content": "N_{\\alpha}(d) = d + o(d)" + }, + { + "bbox": [ + 296, + 251, + 531, + 391 + ], + "type": "text", + "content": ". In particular, " + }, + { + "bbox": [ + 296, + 251, + 531, + 391 + ], + "type": "inline_equation", + "content": "N_{1 / (2k - 1)}(d) = \\lfloor k(d - 1) / (k - 1)\\rfloor" + }, + { + "bbox": [ + 296, + 251, + 531, + 391 + ], + "type": "text", + "content": " for every integer " + }, + { + "bbox": [ + 296, + 251, + 531, + 391 + ], + "type": "inline_equation", + "content": "k \\geq 2" + }, + { + "bbox": [ + 296, + 251, + 531, + 391 + ], + "type": "text", + "content": " and all sufficiently large " + }, + { + "bbox": [ + 296, + 251, + 531, + 391 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 296, + 251, + 531, + 391 + ], + "type": "text", + "content": " [21]." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 296, + 392, + 532, + 543 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 392, + 532, + 543 + ], + "spans": [ + { + "bbox": [ + 296, + 392, + 532, + 543 + ], + "type": "text", + "content": "In simple terms, with a fixed common angle, the maximum number " + }, + { + "bbox": [ + 296, + 392, + 532, + 543 + ], + "type": "inline_equation", + "content": "N(d)" + }, + { + "bbox": [ + 296, + 392, + 532, + 543 + ], + "type": "text", + "content": " of equiangular lines is linearly correlated with the dimension " + }, + { + "bbox": [ + 296, + 392, + 532, + 543 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 296, + 392, + 532, + 543 + ], + "type": "text", + "content": " as " + }, + { + "bbox": [ + 296, + 392, + 532, + 543 + ], + "type": "inline_equation", + "content": "d \\to \\infty" + }, + { + "bbox": [ + 296, + 392, + 532, + 543 + ], + "type": "text", + "content": " while there is still no precise lower bound for " + }, + { + "bbox": [ + 296, + 392, + 532, + 543 + ], + "type": "inline_equation", + "content": "N(d)" + }, + { + "bbox": [ + 296, + 392, + 532, + 543 + ], + "type": "text", + "content": " with smaller values of " + }, + { + "bbox": [ + 296, + 392, + 532, + 543 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 296, + 392, + 532, + 543 + ], + "type": "text", + "content": " [13]. Therefore, we further refer to the Tammes Problem. Let " + }, + { + "bbox": [ + 296, + 392, + 532, + 543 + ], + "type": "inline_equation", + "content": "a_{n}" + }, + { + "bbox": [ + 296, + 392, + 532, + 543 + ], + "type": "text", + "content": " be the maximal number with the property that one can place on a unit hypersphere " + }, + { + "bbox": [ + 296, + 392, + 532, + 543 + ], + "type": "inline_equation", + "content": "S^{d} \\in \\mathbb{R}^{d}(d \\in \\{3,4,5,\\ldots\\})" + }, + { + "bbox": [ + 296, + 392, + 532, + 543 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 296, + 392, + 532, + 543 + ], + "type": "text", + "content": " points so that the spherical distance of any two points is at least " + }, + { + "bbox": [ + 296, + 392, + 532, + 543 + ], + "type": "inline_equation", + "content": "a_{n}" + }, + { + "bbox": [ + 296, + 392, + 532, + 543 + ], + "type": "text", + "content": ". The problem of finding " + }, + { + "bbox": [ + 296, + 392, + 532, + 543 + ], + "type": "inline_equation", + "content": "a_{n}" + }, + { + "bbox": [ + 296, + 392, + 532, + 543 + ], + "type": "text", + "content": " together with the corresponding arrangement of each point is known as the Tammes Problem [55] or the optimal spherical code [12]. It is easy to find that the number of these points will be close to infinity as " + }, + { + "bbox": [ + 296, + 392, + 532, + 543 + ], + "type": "inline_equation", + "content": "a_{n}" + }, + { + "bbox": [ + 296, + 392, + 532, + 543 + ], + "type": "text", + "content": " tends to zero." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 297, + 554, + 498, + 566 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 554, + 498, + 566 + ], + "spans": [ + { + "bbox": [ + 297, + 554, + 498, + 566 + ], + "type": "text", + "content": "3.2. Definition of Equiangular Basis Vectors" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 296, + 573, + 531, + 700 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 573, + 531, + 700 + ], + "spans": [ + { + "bbox": [ + 296, + 573, + 531, + 700 + ], + "type": "text", + "content": "In order to predefine fixed " + }, + { + "bbox": [ + 296, + 573, + 531, + 700 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 296, + 573, + 531, + 700 + ], + "type": "text", + "content": "-dimensional embeddings for as many categories as possible but still keep these embeddings at a distance from each other on a unit hypersphere " + }, + { + "bbox": [ + 296, + 573, + 531, + 700 + ], + "type": "inline_equation", + "content": "S^d \\in \\mathbb{R}^d" + }, + { + "bbox": [ + 296, + 573, + 531, + 700 + ], + "type": "text", + "content": ", we therefore propose Equiangular Basis Vectors (EBVs). Specifically, we fix " + }, + { + "bbox": [ + 296, + 573, + 531, + 700 + ], + "type": "inline_equation", + "content": "0 \\leq \\alpha < 1" + }, + { + "bbox": [ + 296, + 573, + 531, + 700 + ], + "type": "text", + "content": " and let " + }, + { + "bbox": [ + 296, + 573, + 531, + 700 + ], + "type": "inline_equation", + "content": "\\mathcal{N}_{\\alpha}(d)" + }, + { + "bbox": [ + 296, + 573, + 531, + 700 + ], + "type": "text", + "content": " denote the range of values for the number of coordinate vectors in " + }, + { + "bbox": [ + 296, + 573, + 531, + 700 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^d" + }, + { + "bbox": [ + 296, + 573, + 531, + 700 + ], + "type": "text", + "content": " with the pairwise common angle between " + }, + { + "bbox": [ + 296, + 573, + 531, + 700 + ], + "type": "inline_equation", + "content": "\\arccos \\alpha" + }, + { + "bbox": [ + 296, + 573, + 531, + 700 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 296, + 573, + 531, + 700 + ], + "type": "inline_equation", + "content": "\\arccos -\\alpha" + }, + { + "bbox": [ + 296, + 573, + 531, + 700 + ], + "type": "text", + "content": ". The problem of our proposed EBVs is to calculate the coordinates of each vector in the vector set " + }, + { + "bbox": [ + 296, + 573, + 531, + 700 + ], + "type": "inline_equation", + "content": "\\mathcal{W}" + }, + { + "bbox": [ + 296, + 573, + 531, + 700 + ], + "type": "text", + "content": " when given fixed " + }, + { + "bbox": [ + 296, + 573, + 531, + 700 + ], + "type": "inline_equation", + "content": "\\alpha, d" + }, + { + "bbox": [ + 296, + 573, + 531, + 700 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 296, + 573, + 531, + 700 + ], + "type": "inline_equation", + "content": "N \\in \\mathcal{N}_{\\alpha}(d)" + }, + { + "bbox": [ + 296, + 573, + 531, + 700 + ], + "type": "text", + "content": " if possible, i.e., solve the set " + }, + { + "bbox": [ + 296, + 573, + 531, + 700 + ], + "type": "inline_equation", + "content": "\\mathcal{W}" + }, + { + "bbox": [ + 296, + 573, + 531, + 700 + ], + "type": "text", + "content": " which satisfies:" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 310, + 708, + 531, + 733 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 310, + 708, + 531, + 733 + ], + "spans": [ + { + "bbox": [ + 310, + 708, + 531, + 733 + ], + "type": "interline_equation", + "content": "\\forall \\boldsymbol {w} _ {i}, \\boldsymbol {w} _ {j} \\in \\mathcal {W}, i \\neq j, - \\alpha \\leq \\frac {\\boldsymbol {w} _ {i} \\cdot \\boldsymbol {w} _ {j}}{\\| \\boldsymbol {w} _ {i} \\| \\| \\boldsymbol {w} _ {j} \\|} \\leq \\alpha , \\tag {1}", + "image_path": "1de2bc564977bb7973691b4f8493800b3d1b6aac96a7b85fe01f2f0a5791c207.jpg" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 277, + 746, + 300, + 756 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 277, + 746, + 300, + 756 + ], + "spans": [ + { + "bbox": [ + 277, + 746, + 300, + 756 + ], + "type": "text", + "content": "11757" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 595, + 842 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 45, + 105, + 282, + 176 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 105, + 282, + 176 + ], + "spans": [ + { + "bbox": [ + 45, + 105, + 282, + 176 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 45, + 105, + 282, + 176 + ], + "type": "inline_equation", + "content": "\\pmb{w}_i\\in \\mathbb{R}^d" + }, + { + "bbox": [ + 45, + 105, + 282, + 176 + ], + "type": "text", + "content": " , card(W) " + }, + { + "bbox": [ + 45, + 105, + 282, + 176 + ], + "type": "inline_equation", + "content": "= N" + }, + { + "bbox": [ + 45, + 105, + 282, + 176 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 45, + 105, + 282, + 176 + ], + "type": "inline_equation", + "content": "\\| \\cdot \\|" + }, + { + "bbox": [ + 45, + 105, + 282, + 176 + ], + "type": "text", + "content": " denotes the Euclidean norm. Let " + }, + { + "bbox": [ + 45, + 105, + 282, + 176 + ], + "type": "inline_equation", + "content": "\\phi" + }, + { + "bbox": [ + 45, + 105, + 282, + 176 + ], + "type": "text", + "content": " denote the spherical distance function, which can also be replaced by the cosine similarity function. EBVs produce a distribution over classes for a query point " + }, + { + "bbox": [ + 45, + 105, + 282, + 176 + ], + "type": "inline_equation", + "content": "\\pmb {v}\\in \\mathbb{R}^{d}" + }, + { + "bbox": [ + 45, + 105, + 282, + 176 + ], + "type": "text", + "content": " based on softmax over cosine similarity to the " + }, + { + "bbox": [ + 45, + 105, + 282, + 176 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 45, + 105, + 282, + 176 + ], + "type": "text", + "content": " fixed coordinate vectors in the embedding space:" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 83, + 182, + 280, + 209 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 83, + 182, + 280, + 209 + ], + "spans": [ + { + "bbox": [ + 83, + 182, + 280, + 209 + ], + "type": "interline_equation", + "content": "p (y = k | \\boldsymbol {v}) = \\frac {\\exp (- \\phi (\\boldsymbol {v} , \\boldsymbol {w} _ {k}))}{\\sum_ {k ^ {\\prime}} \\exp (- \\phi (\\boldsymbol {v} , \\boldsymbol {w} _ {k ^ {\\prime}}))}, \\tag {2}", + "image_path": "d8db90efb690ca7df60e2cac389b31d250a230baadaabe5447e73b2c0d25611f.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 45, + 214, + 281, + 321 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 214, + 281, + 321 + ], + "spans": [ + { + "bbox": [ + 45, + 214, + 281, + 321 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 45, + 214, + 281, + 321 + ], + "type": "inline_equation", + "content": "y = k \\in \\{1, 2, \\dots, N\\}" + }, + { + "bbox": [ + 45, + 214, + 281, + 321 + ], + "type": "text", + "content": " denotes the corresponding coordinate vector, which can also be seen as the corresponding label. While " + }, + { + "bbox": [ + 45, + 214, + 281, + 321 + ], + "type": "inline_equation", + "content": "k'" + }, + { + "bbox": [ + 45, + 214, + 281, + 321 + ], + "type": "text", + "content": " represents the associated basis vectors in " + }, + { + "bbox": [ + 45, + 214, + 281, + 321 + ], + "type": "inline_equation", + "content": "\\mathcal{W}" + }, + { + "bbox": [ + 45, + 214, + 281, + 321 + ], + "type": "text", + "content": ". Relations between " + }, + { + "bbox": [ + 45, + 214, + 281, + 321 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 45, + 214, + 281, + 321 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 45, + 214, + 281, + 321 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 45, + 214, + 281, + 321 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 45, + 214, + 281, + 321 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 45, + 214, + 281, + 321 + ], + "type": "text", + "content": " are described in the supplementary materials. With such a set " + }, + { + "bbox": [ + 45, + 214, + 281, + 321 + ], + "type": "inline_equation", + "content": "\\mathcal{W}" + }, + { + "bbox": [ + 45, + 214, + 281, + 321 + ], + "type": "text", + "content": ", the maximum number of categories it can handle is " + }, + { + "bbox": [ + 45, + 214, + 281, + 321 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 45, + 214, + 281, + 321 + ], + "type": "text", + "content": ". Additionally, training with any category number less than " + }, + { + "bbox": [ + 45, + 214, + 281, + 321 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 45, + 214, + 281, + 321 + ], + "type": "text", + "content": ", it is sufficient to randomly select any of the same numbers of coordinate vectors in " + }, + { + "bbox": [ + 45, + 214, + 281, + 321 + ], + "type": "inline_equation", + "content": "\\mathcal{W}" + }, + { + "bbox": [ + 45, + 214, + 281, + 321 + ], + "type": "text", + "content": ", since these vectors are exactly equivalent." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 326, + 176, + 339 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 326, + 176, + 339 + ], + "spans": [ + { + "bbox": [ + 46, + 326, + 176, + 339 + ], + "type": "text", + "content": "3.3. How to generate EBVs?" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 45, + 344, + 279, + 426 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 344, + 279, + 426 + ], + "spans": [ + { + "bbox": [ + 45, + 344, + 279, + 426 + ], + "type": "text", + "content": "The basic idea of our Equiangular Basis Vectors (EBVs) is to generate fixed normalized vector embeddings with equal status (equal angles) as \"predefined classifiers\" for all the relevant categories. The question then comes to how to calculate the predefined EBVs which satisfy Eq. (1). Therefore, we will discuss how to generate the proposed EBVs when given fixed " + }, + { + "bbox": [ + 45, + 344, + 279, + 426 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 45, + 344, + 279, + 426 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 45, + 344, + 279, + 426 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 45, + 344, + 279, + 426 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 45, + 344, + 279, + 426 + ], + "type": "inline_equation", + "content": "N \\in \\mathcal{N}_{\\alpha}(d)" + }, + { + "bbox": [ + 45, + 344, + 279, + 426 + ], + "type": "text", + "content": " in this section." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 45, + 426, + 281, + 484 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 426, + 281, + 484 + ], + "spans": [ + { + "bbox": [ + 45, + 426, + 281, + 484 + ], + "type": "text", + "content": "Assuming each " + }, + { + "bbox": [ + 45, + 426, + 281, + 484 + ], + "type": "inline_equation", + "content": "\\boldsymbol{w}_i \\in \\mathcal{W}" + }, + { + "bbox": [ + 45, + 426, + 281, + 484 + ], + "type": "text", + "content": " (" + }, + { + "bbox": [ + 45, + 426, + 281, + 484 + ], + "type": "inline_equation", + "content": "i = \\{1, 2, \\dots, N\\}" + }, + { + "bbox": [ + 45, + 426, + 281, + 484 + ], + "type": "text", + "content": ") as a line, we can construct the Grassmannian Matrices to solve the set " + }, + { + "bbox": [ + 45, + 426, + 281, + 484 + ], + "type": "inline_equation", + "content": "\\mathcal{W}" + }, + { + "bbox": [ + 45, + 426, + 281, + 484 + ], + "type": "text", + "content": " [11]. Specifically, we assemble the vectors in " + }, + { + "bbox": [ + 45, + 426, + 281, + 484 + ], + "type": "inline_equation", + "content": "\\mathcal{W}" + }, + { + "bbox": [ + 45, + 426, + 281, + 484 + ], + "type": "text", + "content": " into a matrix " + }, + { + "bbox": [ + 45, + 426, + 281, + 484 + ], + "type": "inline_equation", + "content": "\\boldsymbol{W} \\in \\mathbb{R}^{d \\times N}" + }, + { + "bbox": [ + 45, + 426, + 281, + 484 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 45, + 426, + 281, + 484 + ], + "type": "inline_equation", + "content": "\\boldsymbol{W} = [\\boldsymbol{w}_1; \\boldsymbol{w}_2; \\dots; \\boldsymbol{w}_N]" + }, + { + "bbox": [ + 45, + 426, + 281, + 484 + ], + "type": "text", + "content": ". Then, the mutual-coherence of " + }, + { + "bbox": [ + 45, + 426, + 281, + 484 + ], + "type": "inline_equation", + "content": "\\boldsymbol{W}" + }, + { + "bbox": [ + 45, + 426, + 281, + 484 + ], + "type": "text", + "content": " is defined by:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 48, + 499, + 279, + 537 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 499, + 279, + 537 + ], + "spans": [ + { + "bbox": [ + 48, + 499, + 279, + 537 + ], + "type": "interline_equation", + "content": "\\mu (\\boldsymbol {W}) = \\max _ {1 \\leq i, j \\leq N, i \\neq j} \\frac {\\left| \\boldsymbol {w} _ {i} ^ {\\top} \\cdot \\boldsymbol {w} _ {j} \\right|}{\\left\\| \\boldsymbol {w} _ {i} \\right\\| \\left\\| \\boldsymbol {w} _ {j} \\right\\|} = \\max _ {1 \\leq i, j \\leq N, i \\neq j} \\cos \\theta_ {i j}, \\tag {3}", + "image_path": "47c30322c67a5fe2e86551b7213fa4ebf63c0c17396a0292bf13af296dbf6b45.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 45, + 537, + 279, + 659 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 537, + 279, + 659 + ], + "spans": [ + { + "bbox": [ + 45, + 537, + 279, + 659 + ], + "type": "text", + "content": "which is transformed to the smallest possible mutualcoherence possible [11]. Therefore, the lower bound for " + }, + { + "bbox": [ + 45, + 537, + 279, + 659 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 45, + 537, + 279, + 659 + ], + "type": "text", + "content": " is " + }, + { + "bbox": [ + 45, + 537, + 279, + 659 + ], + "type": "inline_equation", + "content": "\\sqrt{\\frac{N - d}{d(N - 1)}}" + }, + { + "bbox": [ + 45, + 537, + 279, + 659 + ], + "type": "text", + "content": " and the upper bound for " + }, + { + "bbox": [ + 45, + 537, + 279, + 659 + ], + "type": "inline_equation", + "content": "\\mathcal{N}_{\\alpha}(d)" + }, + { + "bbox": [ + 45, + 537, + 279, + 659 + ], + "type": "text", + "content": " is " + }, + { + "bbox": [ + 45, + 537, + 279, + 659 + ], + "type": "inline_equation", + "content": "1 + \\frac{d - 1}{1 - \\alpha^2d}" + }, + { + "bbox": [ + 45, + 537, + 279, + 659 + ], + "type": "text", + "content": " (" + }, + { + "bbox": [ + 45, + 537, + 279, + 659 + ], + "type": "inline_equation", + "content": "d \\leq N, 1 - \\alpha^2 d > 0" + }, + { + "bbox": [ + 45, + 537, + 279, + 659 + ], + "type": "text", + "content": "). In addition, such matrix is possible only if " + }, + { + "bbox": [ + 45, + 537, + 279, + 659 + ], + "type": "inline_equation", + "content": "N < \\min(d(d + 1)/2, (N - d)(N - d + 1)/2)" + }, + { + "bbox": [ + 45, + 537, + 279, + 659 + ], + "type": "text", + "content": ". Construction of such a matrix has a strong connection with the packing of vectors/subspaces in the " + }, + { + "bbox": [ + 45, + 537, + 279, + 659 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^d" + }, + { + "bbox": [ + 45, + 537, + 279, + 659 + ], + "type": "text", + "content": "-space. In the case of " + }, + { + "bbox": [ + 45, + 537, + 279, + 659 + ], + "type": "inline_equation", + "content": "N = d" + }, + { + "bbox": [ + 45, + 537, + 279, + 659 + ], + "type": "text", + "content": ", we can simply construct a unitary matrix, while in other cases, it will be very hard to construct such a general Grassmannian matrix [11]." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 45, + 660, + 279, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 660, + 279, + 730 + ], + "spans": [ + { + "bbox": [ + 45, + 660, + 279, + 730 + ], + "type": "text", + "content": "In the definition of our proposed EBVs, whether the angle between any two basis vectors " + }, + { + "bbox": [ + 45, + 660, + 279, + 730 + ], + "type": "inline_equation", + "content": "\\pmb{w}_i, \\pmb{w}_j \\in \\mathcal{W} (i \\neq j)" + }, + { + "bbox": [ + 45, + 660, + 279, + 730 + ], + "type": "text", + "content": " is " + }, + { + "bbox": [ + 45, + 660, + 279, + 730 + ], + "type": "inline_equation", + "content": "\\arccos \\alpha" + }, + { + "bbox": [ + 45, + 660, + 279, + 730 + ], + "type": "text", + "content": " or " + }, + { + "bbox": [ + 45, + 660, + 279, + 730 + ], + "type": "inline_equation", + "content": "\\arccos -\\alpha" + }, + { + "bbox": [ + 45, + 660, + 279, + 730 + ], + "type": "text", + "content": " is equivalent. It is clear that we can not construct the Grassmannian matrix in a situation such as " + }, + { + "bbox": [ + 45, + 660, + 279, + 730 + ], + "type": "inline_equation", + "content": "N = 30,000" + }, + { + "bbox": [ + 45, + 660, + 279, + 730 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 45, + 660, + 279, + 730 + ], + "type": "inline_equation", + "content": "d = 200" + }, + { + "bbox": [ + 45, + 660, + 279, + 730 + ], + "type": "text", + "content": ". However, it is still possible for us to construct " + }, + { + "bbox": [ + 45, + 660, + 279, + 730 + ], + "type": "inline_equation", + "content": "\\mathcal{W}" + }, + { + "bbox": [ + 45, + 660, + 279, + 730 + ], + "type": "text", + "content": " which satisfies Eq. (1). Therefore, as" + } + ] + } + ], + "index": 8 + }, + { + "type": "code", + "bbox": [ + 298, + 119, + 469, + 342 + ], + "blocks": [ + { + "bbox": [ + 298, + 106, + 523, + 117 + ], + "lines": [ + { + "bbox": [ + 298, + 106, + 523, + 117 + ], + "spans": [ + { + "bbox": [ + 298, + 106, + 523, + 117 + ], + "type": "text", + "content": "Algorithm 1 Generation of EBVs in a PyTorch-like style" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "code_caption" + }, + { + "bbox": [ + 298, + 119, + 469, + 342 + ], + "lines": [ + { + "bbox": [ + 298, + 119, + 469, + 342 + ], + "spans": [ + { + "bbox": [ + 298, + 119, + 469, + 342 + ], + "type": "text", + "content": "#d:Dim for each coordinate vectors \n#N:The number of coordinate vectors \n# " + }, + { + "bbox": [ + 298, + 119, + 469, + 342 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 298, + 119, + 469, + 342 + ], + "type": "text", + "content": " : Threshold of " + }, + { + "bbox": [ + 298, + 119, + 469, + 342 + ], + "type": "inline_equation", + "content": "\\hat{\\pmb{w}}_i\\cdot \\hat{\\pmb{w}}_j,i\\neq j" + }, + { + "bbox": [ + 298, + 119, + 469, + 342 + ], + "type": "text", + "content": " \n#W:The EBVs matrix " + }, + { + "bbox": [ + 298, + 119, + 469, + 342 + ], + "type": "inline_equation", + "content": "W\\in \\mathbb{R}^{d\\times N}" + }, + { + "bbox": [ + 298, + 119, + 469, + 342 + ], + "type": "text", + "content": " \n#slice: In the case of " + }, + { + "bbox": [ + 298, + 119, + 469, + 342 + ], + "type": "inline_equation", + "content": "N\\gg d" + }, + { + "bbox": [ + 298, + 119, + 469, + 342 + ], + "type": "text", + "content": " ,optimize W by slicing \n#λ: Learning rate. \nInitialize W randomly; \nwhile True: #Normalize each row in W \n" + }, + { + "bbox": [ + 298, + 119, + 469, + 342 + ], + "type": "inline_equation", + "content": "W =" + }, + { + "bbox": [ + 298, + 119, + 469, + 342 + ], + "type": "text", + "content": " Normalize(W) \nfor i in [N/slice]: start " + }, + { + "bbox": [ + 298, + 119, + 469, + 342 + ], + "type": "inline_equation", + "content": "=" + }, + { + "bbox": [ + 298, + 119, + 469, + 342 + ], + "type": "text", + "content": " i\\* slice end " + }, + { + "bbox": [ + 298, + 119, + 469, + 342 + ], + "type": "inline_equation", + "content": "= \\min (N" + }, + { + "bbox": [ + 298, + 119, + 469, + 342 + ], + "type": "inline_equation", + "content": "(\\mathrm{i} + 1)^{*}" + }, + { + "bbox": [ + 298, + 119, + 469, + 342 + ], + "type": "text", + "content": " slice) E " + }, + { + "bbox": [ + 298, + 119, + 469, + 342 + ], + "type": "inline_equation", + "content": "=" + }, + { + "bbox": [ + 298, + 119, + 469, + 342 + ], + "type": "text", + "content": " Fonehot(arange(start, end), N) C " + }, + { + "bbox": [ + 298, + 119, + 469, + 342 + ], + "type": "inline_equation", + "content": "=" + }, + { + "bbox": [ + 298, + 119, + 469, + 342 + ], + "type": "text", + "content": " (W[start:end]@W.T).abs()-E loss " + }, + { + "bbox": [ + 298, + 119, + 469, + 342 + ], + "type": "inline_equation", + "content": "=" + }, + { + "bbox": [ + 298, + 119, + 469, + 342 + ], + "type": "text", + "content": " ReLU(C-α).sum() # Cutout the gradient of vector pairs which satisfies " + }, + { + "bbox": [ + 298, + 119, + 469, + 342 + ], + "type": "inline_equation", + "content": "-\\alpha \\leq \\hat{\\pmb{w}}_i\\cdot \\hat{\\pmb{w}}_j\\leq \\alpha" + }, + { + "bbox": [ + 298, + 119, + 469, + 342 + ], + "type": "text", + "content": " loss.backup() if max(α,C.max()) < α + o(α): Save(W) break \n" + }, + { + "bbox": [ + 298, + 119, + 469, + 342 + ], + "type": "inline_equation", + "content": "W = W - \\lambda *W.\\mathrm{grad}\\#" + }, + { + "bbox": [ + 298, + 119, + 469, + 342 + ], + "type": "text", + "content": " Update W" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "code_body" + } + ], + "index": 10, + "sub_type": "algorithm" + }, + { + "bbox": [ + 296, + 362, + 530, + 480 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 362, + 530, + 480 + ], + "spans": [ + { + "bbox": [ + 296, + 362, + 530, + 480 + ], + "type": "text", + "content": "an alternative, we adopt Stochastic Gradient Descent [47] to search the set " + }, + { + "bbox": [ + 296, + 362, + 530, + 480 + ], + "type": "inline_equation", + "content": "\\mathcal{W}" + }, + { + "bbox": [ + 296, + 362, + 530, + 480 + ], + "type": "text", + "content": " that satisfies the definition of EBVs when given fixed " + }, + { + "bbox": [ + 296, + 362, + 530, + 480 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 296, + 362, + 530, + 480 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 296, + 362, + 530, + 480 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 296, + 362, + 530, + 480 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 296, + 362, + 530, + 480 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 296, + 362, + 530, + 480 + ], + "type": "text", + "content": ". Specifically, we random initialize a matrix " + }, + { + "bbox": [ + 296, + 362, + 530, + 480 + ], + "type": "inline_equation", + "content": "\\pmb{W} \\in \\mathbb{R}^{d \\times N}" + }, + { + "bbox": [ + 296, + 362, + 530, + 480 + ], + "type": "text", + "content": " with normalized rows such that the angle between any two vectors " + }, + { + "bbox": [ + 296, + 362, + 530, + 480 + ], + "type": "inline_equation", + "content": "\\hat{\\pmb{w}}_i" + }, + { + "bbox": [ + 296, + 362, + 530, + 480 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 296, + 362, + 530, + 480 + ], + "type": "inline_equation", + "content": "\\hat{\\pmb{w}}_j \\in \\mathbb{R}^d" + }, + { + "bbox": [ + 296, + 362, + 530, + 480 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 296, + 362, + 530, + 480 + ], + "type": "inline_equation", + "content": "i, j \\in \\{1, 2, \\dots, N\\}" + }, + { + "bbox": [ + 296, + 362, + 530, + 480 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 296, + 362, + 530, + 480 + ], + "type": "inline_equation", + "content": "i \\neq j" + }, + { + "bbox": [ + 296, + 362, + 530, + 480 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 296, + 362, + 530, + 480 + ], + "type": "inline_equation", + "content": "\\hat{\\pmb{w}}_i = \\frac{\\pmb{w}_i}{\\|\\pmb{w}_i\\|}" + }, + { + "bbox": [ + 296, + 362, + 530, + 480 + ], + "type": "text", + "content": " can be represented as " + }, + { + "bbox": [ + 296, + 362, + 530, + 480 + ], + "type": "inline_equation", + "content": "\\arccos(\\hat{\\pmb{w}}_i \\cdot \\hat{\\pmb{w}}_j)" + }, + { + "bbox": [ + 296, + 362, + 530, + 480 + ], + "type": "text", + "content": ". Then, we cut out the gradient of those vector pairs which satisfies " + }, + { + "bbox": [ + 296, + 362, + 530, + 480 + ], + "type": "inline_equation", + "content": "-\\alpha \\leq \\hat{\\pmb{w}}_i \\cdot \\hat{\\pmb{w}}_j \\leq \\alpha" + }, + { + "bbox": [ + 296, + 362, + 530, + 480 + ], + "type": "text", + "content": " and optimize the remaining vector pairs. The optimization function of the generation of EBVs can be formulated by:" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 321, + 487, + 530, + 511 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 321, + 487, + 530, + 511 + ], + "spans": [ + { + "bbox": [ + 321, + 487, + 530, + 511 + ], + "type": "interline_equation", + "content": "\\underset {\\boldsymbol {W}} {\\arg \\min } \\sum_ {i = 1} ^ {N - 1} \\sum_ {j > i} ^ {N} \\max \\left(\\hat {\\boldsymbol {w}} _ {i} \\cdot \\hat {\\boldsymbol {w}} _ {j} - \\alpha , 0\\right). \\tag {4}", + "image_path": "d6df82d7b64cb8f5284e79073c5a59a540892f7f75dc0786eb07e31af8fa05e4.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 296, + 518, + 530, + 565 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 518, + 530, + 565 + ], + "spans": [ + { + "bbox": [ + 296, + 518, + 530, + 565 + ], + "type": "text", + "content": "Algorithm 1 provides the code of a simple generation method of the proposed EBVs in a PyTorch-like style. It is also worth mentioning that the EBVs matrix " + }, + { + "bbox": [ + 296, + 518, + 530, + 565 + ], + "type": "inline_equation", + "content": "W" + }, + { + "bbox": [ + 296, + 518, + 530, + 565 + ], + "type": "text", + "content": " will not be changed in the following training stage within all the tasks." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 297, + 571, + 530, + 585 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 571, + 530, + 585 + ], + "spans": [ + { + "bbox": [ + 297, + 571, + 530, + 585 + ], + "type": "text", + "content": "3.4. How to achieve the learning objective of EBVs?" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 296, + 590, + 532, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 590, + 532, + 730 + ], + "spans": [ + { + "bbox": [ + 296, + 590, + 532, + 730 + ], + "type": "text", + "content": "Equiangular Basis Vectors (EBVs) provide fixed learning targets for each independent optimization objective, i.e., semantic categories. In the following, we introduce how to achieve the learning objective of EBVs for all the training samples. Generally, a deep network is performed to extract the high-dimensional features, and a fully connected classification layer is then deployed to map the features to semantic categories. While in our proposed EBVs, each category will be bound to a unique normalized " + }, + { + "bbox": [ + 296, + 590, + 532, + 730 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 296, + 590, + 532, + 730 + ], + "type": "text", + "content": "-dimensional basis vector in " + }, + { + "bbox": [ + 296, + 590, + 532, + 730 + ], + "type": "inline_equation", + "content": "\\mathcal{W}" + }, + { + "bbox": [ + 296, + 590, + 532, + 730 + ], + "type": "text", + "content": ". Thus, for a training sample " + }, + { + "bbox": [ + 296, + 590, + 532, + 730 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 296, + 590, + 532, + 730 + ], + "type": "text", + "content": ", we directly use a unified deep model to generate a " + }, + { + "bbox": [ + 296, + 590, + 532, + 730 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 296, + 590, + 532, + 730 + ], + "type": "text", + "content": "-dimensional embedding " + }, + { + "bbox": [ + 296, + 590, + 532, + 730 + ], + "type": "inline_equation", + "content": "\\pmb{v}" + }, + { + "bbox": [ + 296, + 590, + 532, + 730 + ], + "type": "text", + "content": ", as well as optimizing the cosine distance between " + }, + { + "bbox": [ + 296, + 590, + 532, + 730 + ], + "type": "inline_equation", + "content": "\\pmb{v}" + }, + { + "bbox": [ + 296, + 590, + 532, + 730 + ], + "type": "text", + "content": " and" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 277, + 746, + 301, + 756 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 277, + 746, + 301, + 756 + ], + "spans": [ + { + "bbox": [ + 277, + 746, + 301, + 756 + ], + "type": "text", + "content": "11758" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 595, + 842 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 45, + 106, + 279, + 129 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 106, + 279, + 129 + ], + "spans": [ + { + "bbox": [ + 45, + 106, + 279, + 129 + ], + "type": "text", + "content": "the relevant basis vector. Below we analyze the underlying distance/loss function used in the training stage." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 45, + 130, + 280, + 258 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 130, + 280, + 258 + ], + "spans": [ + { + "bbox": [ + 45, + 130, + 280, + 258 + ], + "type": "text", + "content": "For our EBVs, many existing distance functions including squared Euclidean distance, Mahalanobis distance, or cosine distance are permissible. However, a particular class of distance functions, e.g., regular Bregman divergences [2], seems hard to explain and optimize in the proposed EBVs settings. In addition, intuitively, the straightforward way is to optimize the spherical distance between any two vectors on the surface of the hyper-sphere. Therefore, we adopt the cosine distance as the distance metric, which is widely used for measuring whether two inputs are similar or dissimilar and have been widely used in the Tammes problem [55]." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 45, + 274, + 279, + 355 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 274, + 279, + 355 + ], + "spans": [ + { + "bbox": [ + 45, + 274, + 279, + 355 + ], + "type": "text", + "content": "Implementations Suppose we have " + }, + { + "bbox": [ + 45, + 274, + 279, + 355 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 45, + 274, + 279, + 355 + ], + "type": "text", + "content": " sample-label pairs " + }, + { + "bbox": [ + 45, + 274, + 279, + 355 + ], + "type": "inline_equation", + "content": "\\{(x_{1},y_{1}),(x_{2},y_{2}),\\ldots ,(x_{M},y_{M})\\}" + }, + { + "bbox": [ + 45, + 274, + 279, + 355 + ], + "type": "text", + "content": " in " + }, + { + "bbox": [ + 45, + 274, + 279, + 355 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 45, + 274, + 279, + 355 + ], + "type": "text", + "content": " classes and their " + }, + { + "bbox": [ + 45, + 274, + 279, + 355 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 45, + 274, + 279, + 355 + ], + "type": "text", + "content": " -dimensional features " + }, + { + "bbox": [ + 45, + 274, + 279, + 355 + ], + "type": "inline_equation", + "content": "\\pmb{v}_1,\\pmb{v}_2,\\dots ,\\pmb{v}_M" + }, + { + "bbox": [ + 45, + 274, + 279, + 355 + ], + "type": "text", + "content": " with " + }, + { + "bbox": [ + 45, + 274, + 279, + 355 + ], + "type": "inline_equation", + "content": "\\boldsymbol {v}_i = f_\\theta (\\boldsymbol {x}_i)" + }, + { + "bbox": [ + 45, + 274, + 279, + 355 + ], + "type": "text", + "content": " where " + }, + { + "bbox": [ + 45, + 274, + 279, + 355 + ], + "type": "inline_equation", + "content": "f_{\\theta}(\\cdot)" + }, + { + "bbox": [ + 45, + 274, + 279, + 355 + ], + "type": "text", + "content": " represents a feature extractor. A straightforward way to achieve the learning objective of EBVs is to directly optimize the cosine similarity between each " + }, + { + "bbox": [ + 45, + 274, + 279, + 355 + ], + "type": "inline_equation", + "content": "\\pmb{v}_i" + }, + { + "bbox": [ + 45, + 274, + 279, + 355 + ], + "type": "text", + "content": " and the corresponding basis vector " + }, + { + "bbox": [ + 45, + 274, + 279, + 355 + ], + "type": "inline_equation", + "content": "\\hat{w}_{y_i}\\in \\mathcal{W}" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 45, + 356, + 279, + 436 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 356, + 279, + 436 + ], + "spans": [ + { + "bbox": [ + 45, + 356, + 279, + 436 + ], + "type": "text", + "content": "However, the basis vector itself is not correlated with the training data since it is predefined. Fitting the training samples directly to the corresponding basis vectors might disrupt the representation learning. Therefore, we consider the conventional parametric softmax formulation, of which for image " + }, + { + "bbox": [ + 45, + 356, + 279, + 436 + ], + "type": "inline_equation", + "content": "x_{i}" + }, + { + "bbox": [ + 45, + 356, + 279, + 436 + ], + "type": "text", + "content": " with embedding " + }, + { + "bbox": [ + 45, + 356, + 279, + 436 + ], + "type": "inline_equation", + "content": "v_{i}" + }, + { + "bbox": [ + 45, + 356, + 279, + 436 + ], + "type": "text", + "content": ", the probability of it being recognized as the " + }, + { + "bbox": [ + 45, + 356, + 279, + 436 + ], + "type": "inline_equation", + "content": "y_{i}" + }, + { + "bbox": [ + 45, + 356, + 279, + 436 + ], + "type": "text", + "content": " category can be formulated as:" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 88, + 446, + 279, + 477 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 88, + 446, + 279, + 477 + ], + "spans": [ + { + "bbox": [ + 88, + 446, + 279, + 477 + ], + "type": "interline_equation", + "content": "P (y = y _ {i} | \\boldsymbol {v} _ {i}) = \\frac {\\exp \\left(\\boldsymbol {m} _ {i} ^ {\\top} \\boldsymbol {v} _ {i}\\right)}{\\sum_ {j = 1} ^ {N} \\exp \\left(\\boldsymbol {m} _ {j} ^ {\\top} \\boldsymbol {v} _ {i}\\right)}, \\tag {5}", + "image_path": "46cc8e8c28d7a69974c6658d0b9fe70e1e352e8b4e588ca67df8fbc3b343691b.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 45, + 484, + 279, + 530 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 484, + 279, + 530 + ], + "spans": [ + { + "bbox": [ + 45, + 484, + 279, + 530 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 45, + 484, + 279, + 530 + ], + "type": "inline_equation", + "content": "m_j" + }, + { + "bbox": [ + 45, + 484, + 279, + 530 + ], + "type": "text", + "content": " is a weight vector for the " + }, + { + "bbox": [ + 45, + 484, + 279, + 530 + ], + "type": "inline_equation", + "content": "j" + }, + { + "bbox": [ + 45, + 484, + 279, + 530 + ], + "type": "text", + "content": "-th class. Thus, according to Eq. (2) and Eq. (5), the probability of the embedding " + }, + { + "bbox": [ + 45, + 484, + 279, + 530 + ], + "type": "inline_equation", + "content": "v_i" + }, + { + "bbox": [ + 45, + 484, + 279, + 530 + ], + "type": "text", + "content": " being recognized as category " + }, + { + "bbox": [ + 45, + 484, + 279, + 530 + ], + "type": "inline_equation", + "content": "y_i" + }, + { + "bbox": [ + 45, + 484, + 279, + 530 + ], + "type": "text", + "content": " in our proposed EBVs can be formulated as:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 76, + 538, + 279, + 566 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 76, + 538, + 279, + 566 + ], + "spans": [ + { + "bbox": [ + 76, + 538, + 279, + 566 + ], + "type": "interline_equation", + "content": "P _ {\\mathrm {E B V s}} (y = y _ {i} \\mid \\boldsymbol {v} _ {i}) = \\frac {\\exp \\left(\\hat {\\boldsymbol {w}} _ {i} \\hat {\\boldsymbol {v}} _ {i} / \\tau\\right)}{\\sum_ {j = 1} ^ {N} \\exp \\left(\\hat {\\boldsymbol {w}} _ {j} \\hat {\\boldsymbol {v}} _ {i} / \\tau\\right)}, \\tag {6}", + "image_path": "380a5fbc20da11e70f88cec2c0fc9aad1a30afcf7c4c59dd95cf3b82125e4168.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 45, + 575, + 279, + 644 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 575, + 279, + 644 + ], + "spans": [ + { + "bbox": [ + 45, + 575, + 279, + 644 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 45, + 575, + 279, + 644 + ], + "type": "inline_equation", + "content": "\\hat{\\pmb{v}}_i" + }, + { + "bbox": [ + 45, + 575, + 279, + 644 + ], + "type": "text", + "content": " denotes the " + }, + { + "bbox": [ + 45, + 575, + 279, + 644 + ], + "type": "inline_equation", + "content": "\\ell_{2}" + }, + { + "bbox": [ + 45, + 575, + 279, + 644 + ], + "type": "text", + "content": "-normalized of the embedding " + }, + { + "bbox": [ + 45, + 575, + 279, + 644 + ], + "type": "inline_equation", + "content": "\\pmb{v}_i" + }, + { + "bbox": [ + 45, + 575, + 279, + 644 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 45, + 575, + 279, + 644 + ], + "type": "inline_equation", + "content": "\\tau" + }, + { + "bbox": [ + 45, + 575, + 279, + 644 + ], + "type": "text", + "content": " is a hyper-parameter of temperature [17,20,64] which usually used in unsupervised learning. The learning objective is then to maximize the joint probability " + }, + { + "bbox": [ + 45, + 575, + 279, + 644 + ], + "type": "inline_equation", + "content": "\\prod_{i=1}^{M} P_{\\pmb{\\theta}}(y_i | f_{\\pmb{\\theta}}(x_i))" + }, + { + "bbox": [ + 45, + 575, + 279, + 644 + ], + "type": "text", + "content": ", or equivalently to minimize the negative log-likelihood over the training set which can be formulated as:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 73, + 654, + 279, + 675 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 73, + 654, + 279, + 675 + ], + "spans": [ + { + "bbox": [ + 73, + 654, + 279, + 675 + ], + "type": "interline_equation", + "content": "J (\\boldsymbol {\\theta}) = - \\sum_ {i = 1} ^ {M} \\log P _ {\\mathrm {E B V s}} (y = y _ {i} | f _ {\\boldsymbol {\\theta}} (x _ {i})). \\tag {7}", + "image_path": "3ac699251332e0e295da56afe053fe6aabf6e2f6f0397ec081531ebf77f3cdea.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 45, + 682, + 279, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 682, + 279, + 730 + ], + "spans": [ + { + "bbox": [ + 45, + 682, + 279, + 730 + ], + "type": "text", + "content": "With this optimization approach, we relax the learning objective to make the angle between the embedding " + }, + { + "bbox": [ + 45, + 682, + 279, + 730 + ], + "type": "inline_equation", + "content": "\\pmb{v}" + }, + { + "bbox": [ + 45, + 682, + 279, + 730 + ], + "type": "text", + "content": " of a training sample and its corresponding basis vector smaller than the angle between " + }, + { + "bbox": [ + 45, + 682, + 279, + 730 + ], + "type": "inline_equation", + "content": "\\pmb{v}" + }, + { + "bbox": [ + 45, + 682, + 279, + 730 + ], + "type": "text", + "content": " and the other basis vectors." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 297, + 106, + 409, + 117 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 106, + 409, + 117 + ], + "spans": [ + { + "bbox": [ + 297, + 106, + 409, + 117 + ], + "type": "text", + "content": "3.5. Merits of our EBVs" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 296, + 125, + 531, + 277 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 125, + 531, + 277 + ], + "spans": [ + { + "bbox": [ + 296, + 125, + 531, + 277 + ], + "type": "text", + "content": "We briefly summarize the merits of our proposed EBVs in this section. First of all, the embedding dimension of EBVs can be manually altered and the trainable parameters of the classifier will not grow linearly when the number of categories increases. Specifically, if the embedding dimension of each image is " + }, + { + "bbox": [ + 296, + 125, + 531, + 277 + ], + "type": "inline_equation", + "content": "d'" + }, + { + "bbox": [ + 296, + 125, + 531, + 277 + ], + "type": "text", + "content": " and the number of categories is " + }, + { + "bbox": [ + 296, + 125, + 531, + 277 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 296, + 125, + 531, + 277 + ], + "type": "text", + "content": ", the trainable parameters of a general classifier are " + }, + { + "bbox": [ + 296, + 125, + 531, + 277 + ], + "type": "inline_equation", + "content": "d' \\times N" + }, + { + "bbox": [ + 296, + 125, + 531, + 277 + ], + "type": "text", + "content": ". However, with our proposed EBVs, as the dimension of the embedding for each category is fixed as " + }, + { + "bbox": [ + 296, + 125, + 531, + 277 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 296, + 125, + 531, + 277 + ], + "type": "text", + "content": ", then the trainable parameters of the classifier are " + }, + { + "bbox": [ + 296, + 125, + 531, + 277 + ], + "type": "inline_equation", + "content": "d' \\times d" + }, + { + "bbox": [ + 296, + 125, + 531, + 277 + ], + "type": "text", + "content": ". What's more, " + }, + { + "bbox": [ + 296, + 125, + 531, + 277 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 296, + 125, + 531, + 277 + ], + "type": "text", + "content": " can be set at least close to " + }, + { + "bbox": [ + 296, + 125, + 531, + 277 + ], + "type": "inline_equation", + "content": "\\sqrt{2N}" + }, + { + "bbox": [ + 296, + 125, + 531, + 277 + ], + "type": "text", + "content": " when " + }, + { + "bbox": [ + 296, + 125, + 531, + 277 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 296, + 125, + 531, + 277 + ], + "type": "text", + "content": " is very large according to Section 3.3. Experimental results can be found in Table 2 and the supplementary materials." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 296, + 278, + 531, + 452 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 278, + 531, + 452 + ], + "spans": [ + { + "bbox": [ + 296, + 278, + 531, + 452 + ], + "type": "text", + "content": "Secondly, as the proposed EBVs are generated before the training step and the fixed " + }, + { + "bbox": [ + 296, + 278, + 531, + 452 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 296, + 278, + 531, + 452 + ], + "type": "text", + "content": "-dimensional embedding of each category will not be changed throughout the optimization process, EBVs will not introduce a large amount of computation during the training stage like the metric learning. In particular, metric learning methods such as pairwise/triplet embedding [60] are time-consuming, where the complexity can be " + }, + { + "bbox": [ + 296, + 278, + 531, + 452 + ], + "type": "inline_equation", + "content": "\\mathcal{O}(K^2)" + }, + { + "bbox": [ + 296, + 278, + 531, + 452 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 296, + 278, + 531, + 452 + ], + "type": "inline_equation", + "content": "\\mathcal{O}(K^3)" + }, + { + "bbox": [ + 296, + 278, + 531, + 452 + ], + "type": "text", + "content": " when given " + }, + { + "bbox": [ + 296, + 278, + 531, + 452 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 296, + 278, + 531, + 452 + ], + "type": "text", + "content": " images from " + }, + { + "bbox": [ + 296, + 278, + 531, + 452 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 296, + 278, + 531, + 452 + ], + "type": "text", + "content": " categories. However, the complexity of our proposed EBVs equals " + }, + { + "bbox": [ + 296, + 278, + 531, + 452 + ], + "type": "inline_equation", + "content": "\\mathcal{O}(K)" + }, + { + "bbox": [ + 296, + 278, + 531, + 452 + ], + "type": "text", + "content": ". In addition, EBVs are not sensitive to the optimizers and previous training tricks while they can still achieve state-of-the-art performance as the results shown in Table 1 and the supplementary materials. Also, further results on the downstream tasks can be found in Section 4 and the supplementary materials." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 297, + 468, + 376, + 480 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 468, + 376, + 480 + ], + "spans": [ + { + "bbox": [ + 297, + 468, + 376, + 480 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 296, + 489, + 531, + 558 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 489, + 531, + 558 + ], + "spans": [ + { + "bbox": [ + 296, + 489, + 531, + 558 + ], + "type": "text", + "content": "In this section, quantitative and qualitative experiments are exhibited on models that end with a " + }, + { + "bbox": [ + 296, + 489, + 531, + 558 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 296, + 489, + 531, + 558 + ], + "type": "text", + "content": "-way fully connected layer with softmax and our proposed method to demonstrate the effectiveness of the proposed Equiangular Basis Vectors (EBVs). All experiments are conducted with 8 RTX 3090 GPUs." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 297, + 570, + 513, + 583 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 570, + 513, + 583 + ], + "spans": [ + { + "bbox": [ + 297, + 570, + 513, + 583 + ], + "type": "text", + "content": "4.1. Quantitative results on image classification" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 297, + 591, + 412, + 602 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 591, + 412, + 602 + ], + "spans": [ + { + "bbox": [ + 297, + 591, + 412, + 602 + ], + "type": "text", + "content": "4.1.1 Dataset and settings" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 296, + 612, + 531, + 670 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 612, + 531, + 670 + ], + "spans": [ + { + "bbox": [ + 296, + 612, + 531, + 670 + ], + "type": "text", + "content": "We conduct the general image classification task on the ImageNet-1K [9] dataset, which contains 1.28M training images and 50K validation images from 1,000 different object classes. Then, we report ImageNet-1K top-1 accuracy on the validation set under a single crop setting." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 296, + 671, + 531, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 671, + 531, + 730 + ], + "spans": [ + { + "bbox": [ + 296, + 671, + 531, + 730 + ], + "type": "text", + "content": "In order to demonstrate the effectiveness of the proposed EBVs, we follow the state-of-the-art training methods provided by TorchVision [59] and timm [63]. For fair comparisons, we offer the following diverse training settings for the general classification task." + } + ] + } + ], + "index": 18 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 277, + 746, + 300, + 756 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 277, + 746, + 300, + 756 + ], + "spans": [ + { + "bbox": [ + 277, + 746, + 300, + 756 + ], + "type": "text", + "content": "11759" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 595, + 842 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 46, + 135, + 529, + 353 + ], + "blocks": [ + { + "bbox": [ + 45, + 104, + 531, + 127 + ], + "lines": [ + { + "bbox": [ + 45, + 104, + 531, + 127 + ], + "spans": [ + { + "bbox": [ + 45, + 104, + 531, + 127 + ], + "type": "text", + "content": "Table 1. Comparisons on the ImageNet-1K validation set. \"FC\" denotes models ending with a 1000-way fully connected layer with softmax. The test size for each image is set as \"224^2\" if there is one result while it is set as \"224^2/256^2\" if there exist two results." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 46, + 135, + 529, + 353 + ], + "lines": [ + { + "bbox": [ + 46, + 135, + 529, + 353 + ], + "spans": [ + { + "bbox": [ + 46, + 135, + 529, + 353 + ], + "type": "table", + "html": "
BackboneMethodOptimizerLREpochSettingParams.GFLOPsTest size#Forward passTop-1 Acc (%)
ResNet-50FCSGD0.190A025.6M4.12242600k77.15
ResNet-50FCSGD0.55/100A125.6M4.12242/2562131k76.88/77.92
EBVs77.55/78.73
ResNet-50FCSGD0.55/100A225.6M4.12242/2562131k77.71/78.59
EBVs78.14/78.99
ResNet-50*FCSGD0.55/600A225.6M4.12242/2562755k79.51/-\n79.73/80.45
EBVs
ResNet-50FCAdamW0.00172.57/73.79
FC0.015/100A125.6M4.12242/2562131k72.51/74.03
EBVs0.0175.62/77.14
ResNet-50FCAdamW0.00175.42/76.48
FC0.015/100A225.6M4.12242/2562131kNaN
EBVs0.0176.46/77.52
Swin-TFCAdamW0.0015/100A128.3M4.52242131k75.64
EBVs78.37
Swin-TFCAdamW0.0015/100A228.3M4.52242131k79.12
EBVs79.34
", + "image_path": "5d77342f3967f9e2d70501f7ffb903d17afb09d06586b3bfa6df4f1996449cab.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + }, + { + "bbox": [ + 54, + 355, + 477, + 367 + ], + "lines": [ + { + "bbox": [ + 54, + 355, + 477, + 367 + ], + "spans": [ + { + "bbox": [ + 54, + 355, + 477, + 367 + ], + "type": "text", + "content": "* represents the result of the model with a general fully connected layer with softmax is provided by TorchVision [59]." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_footnote" + } + ], + "index": 1 + }, + { + "bbox": [ + 45, + 385, + 280, + 479 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 385, + 280, + 479 + ], + "spans": [ + { + "bbox": [ + 45, + 385, + 280, + 479 + ], + "type": "text", + "content": "Setting A0 The official training setting provided in ResNet [19]. A " + }, + { + "bbox": [ + 45, + 385, + 280, + 479 + ], + "type": "inline_equation", + "content": "224 \\times 224" + }, + { + "bbox": [ + 45, + 385, + 280, + 479 + ], + "type": "text", + "content": " crop is randomly sampled from an image or its horizontal flip, with the per-pixel mean subtracted [27]. It trains the backbone by using SGD optimizer with momentum as 0.9, weight decay as " + }, + { + "bbox": [ + 45, + 385, + 280, + 479 + ], + "type": "inline_equation", + "content": "1 \\times 10^{-4}" + }, + { + "bbox": [ + 45, + 385, + 280, + 479 + ], + "type": "text", + "content": " and batch size as 256. The training iteration is up to " + }, + { + "bbox": [ + 45, + 385, + 280, + 479 + ], + "type": "inline_equation", + "content": "60 \\times 10^{4}" + }, + { + "bbox": [ + 45, + 385, + 280, + 479 + ], + "type": "text", + "content": ". The standard color augmentation in [27] is used. It adopts the standard 10-crop testing [27] in the validation stage." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 45, + 493, + 279, + 610 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 493, + 279, + 610 + ], + "spans": [ + { + "bbox": [ + 45, + 493, + 279, + 610 + ], + "type": "text", + "content": "Setting A1 We employ an AdamW [35] or an SGD [47] optimizer for 100 epochs using a cosine decay learning rate scheduler and 5 epochs of linear warm-up. The batch size is set as 1024 and the initial learning rate for the AdamW optimizer is 0.01 or 0.001 while it is set as 0.5 for the SGD optimizer. A " + }, + { + "bbox": [ + 45, + 493, + 279, + 610 + ], + "type": "inline_equation", + "content": "224 \\times 224" + }, + { + "bbox": [ + 45, + 493, + 279, + 610 + ], + "type": "text", + "content": " crop is randomly sampled from each image and the weight decay is set as " + }, + { + "bbox": [ + 45, + 493, + 279, + 610 + ], + "type": "inline_equation", + "content": "2 \\times 10^{-5}" + }, + { + "bbox": [ + 45, + 493, + 279, + 610 + ], + "type": "text", + "content": ". We perform TrivialAugment [41], which is extremely simple and can be considered \"parameter-free\". We also adopt random erasing [71] and the probability is set as 0.1." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 45, + 624, + 279, + 671 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 624, + 279, + 671 + ], + "spans": [ + { + "bbox": [ + 45, + 624, + 279, + 671 + ], + "type": "text", + "content": "Setting A2 On the basis of Setting A1, we add label-smoothing [54] and the value is set as 0.1. We also perform mixup [69] and cutmix [68]. The setting of hyper-parameters of the two techniques is the same with TorchVision [59]." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 45, + 671, + 280, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 671, + 280, + 730 + ], + "spans": [ + { + "bbox": [ + 45, + 671, + 280, + 730 + ], + "type": "text", + "content": "We adopt ResNet-50 [19] and Swin-T [32] as the typical backbone for Convolutional Neural Networks (CNNs) and Vision Transformers [10]. The hyper-parameters " + }, + { + "bbox": [ + 45, + 671, + 280, + 730 + ], + "type": "inline_equation", + "content": "\\tau" + }, + { + "bbox": [ + 45, + 671, + 280, + 730 + ], + "type": "text", + "content": " for the proposed EBVs are set as 0.07 for all the following experiments unless otherwise specified." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 296, + 385, + 381, + 395 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 385, + 381, + 395 + ], + "spans": [ + { + "bbox": [ + 296, + 385, + 381, + 395 + ], + "type": "text", + "content": "4.1.2 Main results" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 296, + 404, + 531, + 568 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 404, + 531, + 568 + ], + "spans": [ + { + "bbox": [ + 296, + 404, + 531, + 568 + ], + "type": "text", + "content": "Table 1 presents comparisons between deep networks ending with FC, i.e., a 1000-way classification layer with softmax and our proposed EBVs. The fixed " + }, + { + "bbox": [ + 296, + 404, + 531, + 568 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 296, + 404, + 531, + 568 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 296, + 404, + 531, + 568 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 296, + 404, + 531, + 568 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 296, + 404, + 531, + 568 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 296, + 404, + 531, + 568 + ], + "type": "text", + "content": " of EBVs are set as 0.004, 1000 and 1000, respectively. When adopting ResNet-50 as the backbone, EBVs outperform FC among all the settings. In addition, when adopting AdamW as the optimizer, EBVs gain " + }, + { + "bbox": [ + 296, + 404, + 531, + 568 + ], + "type": "inline_equation", + "content": "3.11\\% / 1.04\\%" + }, + { + "bbox": [ + 296, + 404, + 531, + 568 + ], + "type": "text", + "content": " improvement over FC under Setting A1 and Setting A2 when using " + }, + { + "bbox": [ + 296, + 404, + 531, + 568 + ], + "type": "inline_equation", + "content": "224^2 / 256^2" + }, + { + "bbox": [ + 296, + 404, + 531, + 568 + ], + "type": "text", + "content": " testing. EBVs still gain around " + }, + { + "bbox": [ + 296, + 404, + 531, + 568 + ], + "type": "inline_equation", + "content": "2.7\\% / 0.2\\%" + }, + { + "bbox": [ + 296, + 404, + 531, + 568 + ], + "type": "text", + "content": " improvement on Swin-T under Setting A1 and Setting A2. As previous training techniques summarised by both TorchVision [59] and timm [63] are under the setting of FC, we suspect it will have some impact on the performance of EBVs. We further conduct ablation studies in the supplementary materials." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 296, + 582, + 396, + 593 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 582, + 396, + 593 + ], + "spans": [ + { + "bbox": [ + 296, + 582, + 396, + 593 + ], + "type": "text", + "content": "4.1.3 Ablation studies" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 296, + 601, + 531, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 601, + 531, + 730 + ], + "spans": [ + { + "bbox": [ + 296, + 601, + 531, + 730 + ], + "type": "text", + "content": "We conduct ablation studies on the dimension " + }, + { + "bbox": [ + 296, + 601, + 531, + 730 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 296, + 601, + 531, + 730 + ], + "type": "text", + "content": " of each basis vector to demonstrate the merits of our proposed EBVs. Table 2 reports ImageNet-1K top-1 accuracy on the validation set with different dimensions " + }, + { + "bbox": [ + 296, + 601, + 531, + 730 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 296, + 601, + 531, + 730 + ], + "type": "text", + "content": ". Taking " + }, + { + "bbox": [ + 296, + 601, + 531, + 730 + ], + "type": "inline_equation", + "content": "d = 100" + }, + { + "bbox": [ + 296, + 601, + 531, + 730 + ], + "type": "text", + "content": " as an example, the dimension of the embedding of an image is set as 100. We adopt ResNet-50 as the backbone and the setting of all the experiments follows Setting A2. We use SGD [47] as the optimizer and the initial learning rate is set as 0.01. The test size of each image is set as " + }, + { + "bbox": [ + 296, + 601, + 531, + 730 + ], + "type": "inline_equation", + "content": "224^2" + }, + { + "bbox": [ + 296, + 601, + 531, + 730 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 296, + 601, + 531, + 730 + ], + "type": "inline_equation", + "content": "256^2" + }, + { + "bbox": [ + 296, + 601, + 531, + 730 + ], + "type": "text", + "content": ". The Min. Ang. which represents the minimum angle between each two basis vectors is defined as " + }, + { + "bbox": [ + 296, + 601, + 531, + 730 + ], + "type": "inline_equation", + "content": "\\min_{1 \\leq i,j \\leq N, i \\neq j} \\min(\\pi - \\arccos(\\hat{w}_i)" + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 277, + 746, + 301, + 756 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 277, + 746, + 301, + 756 + ], + "spans": [ + { + "bbox": [ + 277, + 746, + 301, + 756 + ], + "type": "text", + "content": "11760" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 595, + 842 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 47, + 146, + 283, + 275 + ], + "blocks": [ + { + "bbox": [ + 45, + 104, + 280, + 137 + ], + "lines": [ + { + "bbox": [ + 45, + 104, + 280, + 137 + ], + "spans": [ + { + "bbox": [ + 45, + 104, + 280, + 137 + ], + "type": "text", + "content": "Table 2. Ablation studies on the dimension of our proposed EBVs. \"EBVs Dim.\" denotes the embedding dimension for each category. The test size for each image is set as " + }, + { + "bbox": [ + 45, + 104, + 280, + 137 + ], + "type": "inline_equation", + "content": "224^2" + }, + { + "bbox": [ + 45, + 104, + 280, + 137 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 45, + 104, + 280, + 137 + ], + "type": "inline_equation", + "content": "256^2" + }, + { + "bbox": [ + 45, + 104, + 280, + 137 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 47, + 146, + 283, + 275 + ], + "lines": [ + { + "bbox": [ + 47, + 146, + 283, + 275 + ], + "spans": [ + { + "bbox": [ + 47, + 146, + 283, + 275 + ], + "type": "table", + "html": "
EBVs Dim.Epoch Min.Ang.Ave.Del.Ang.Top-1 Acc (%)
1005/10082.24°4.84°76.10/76.83
2005/10085.41°3.37°77.04/77.83
3005/10086.67°2.64°77.25/78.08
4005/10087.48°2.18°77.20/78.38
5005/10087.99°1.82°77.39/78.34
10005/10089.98°0.01°78.14/78.99
20005/10089.98°0.01°77.87/78.58
1005/30082.24°4.84°78.33/79.25
10005/30089.98°0.01°79.10/79.96
", + "image_path": "e23a264ed70e0dbd1aaab4deff2948a404cc93c86349ec83e9d90df351105112.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "type": "table", + "bbox": [ + 47, + 371, + 282, + 467 + ], + "blocks": [ + { + "bbox": [ + 45, + 287, + 280, + 362 + ], + "lines": [ + { + "bbox": [ + 45, + 287, + 280, + 362 + ], + "spans": [ + { + "bbox": [ + 45, + 287, + 280, + 362 + ], + "type": "text", + "content": "Table 3. Object detection and instance segmentation on the COCO 2017 dataset. Models are based on Mask R-CNN [18] and “" + }, + { + "bbox": [ + 45, + 287, + 280, + 362 + ], + "type": "inline_equation", + "content": "1 \\times" + }, + { + "bbox": [ + 45, + 287, + 280, + 362 + ], + "type": "text", + "content": "” denotes we train models for 12 epochs while “" + }, + { + "bbox": [ + 45, + 287, + 280, + 362 + ], + "type": "inline_equation", + "content": "3 \\times" + }, + { + "bbox": [ + 45, + 287, + 280, + 362 + ], + "type": "text", + "content": "” denotes 36 epochs. “" + }, + { + "bbox": [ + 45, + 287, + 280, + 362 + ], + "type": "inline_equation", + "content": "\\mathrm{AP}^{\\mathrm{b}}" + }, + { + "bbox": [ + 45, + 287, + 280, + 362 + ], + "type": "text", + "content": "” and “" + }, + { + "bbox": [ + 45, + 287, + 280, + 362 + ], + "type": "inline_equation", + "content": "\\mathrm{AP}^{\\mathrm{m}}" + }, + { + "bbox": [ + 45, + 287, + 280, + 362 + ], + "type": "text", + "content": "” refer to bounding box AP and mask AP, respectively. Results shaded in gray denote models ending with the general fully connected classifier while others denote models ending with our proposed EBVs." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 47, + 371, + 282, + 467 + ], + "lines": [ + { + "bbox": [ + 47, + 371, + 282, + 467 + ], + "spans": [ + { + "bbox": [ + 47, + 371, + 282, + 467 + ], + "type": "table", + "html": "
BackboneSchedule\\(AP^b\\)\\(AP_{50}^b\\)\\(AP_{75}^b\\)\\(AP^m\\)\\(AP_{50}^m\\)\\(AP_{75}^m\\)
ResNet-501×38.2 58.8 41.4 34.7 55.7 37.2
ResNet-50 (EBVs)1×38.3 59.0 42.0 35.2 56.2 37.7
ResNet-503×40.9 61.3 44.8 37.1 58.3 39.9
ResNet-50 (EBVs)3×41.1 61.7 44.9 37.7 58.9 40.5
Swin-T1×42.7 65.2 46.8 39.3 62.2 42.2
Swin-T (EBVs)1×42.8 65.3 47.2 39.4 62.2 42.6
", + "image_path": "beac3d97fa08613538d2b242ce3c2f288e791be1237133849e56d7e839b2cfda.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 45, + 489, + 279, + 642 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 489, + 279, + 642 + ], + "spans": [ + { + "bbox": [ + 45, + 489, + 279, + 642 + ], + "type": "inline_equation", + "content": "\\hat{\\boldsymbol{w}}_j)" + }, + { + "bbox": [ + 45, + 489, + 279, + 642 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 45, + 489, + 279, + 642 + ], + "type": "inline_equation", + "content": "\\operatorname{arccos}(\\hat{\\boldsymbol{w}}_i \\cdot \\hat{\\boldsymbol{w}}_j)" + }, + { + "bbox": [ + 45, + 489, + 279, + 642 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 45, + 489, + 279, + 642 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 45, + 489, + 279, + 642 + ], + "type": "text", + "content": " represents the number of categories. While the Ave. Del. Ang. which represents the average angle between each of two basis vectors is defined as " + }, + { + "bbox": [ + 45, + 489, + 279, + 642 + ], + "type": "inline_equation", + "content": "\\frac{N(N-1)}{2} \\sum_{i=1}^{N-1} \\sum_{j=i+1}^{N} \\left| \\operatorname{arccos}(\\hat{\\boldsymbol{w}}_i \\cdot \\hat{\\boldsymbol{w}}_j) - \\frac{\\pi}{2} \\right|" + }, + { + "bbox": [ + 45, + 489, + 279, + 642 + ], + "type": "text", + "content": ". For a clearer representation, we adopt an angle instead of a radian. It can be seen from Table 2 that dimension has an impact on the performance of a model when training with limited cycles. However, this gap decreases a lot when adopting longer training cycles. Taking " + }, + { + "bbox": [ + 45, + 489, + 279, + 642 + ], + "type": "inline_equation", + "content": "d = 100" + }, + { + "bbox": [ + 45, + 489, + 279, + 642 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 45, + 489, + 279, + 642 + ], + "type": "inline_equation", + "content": "d = 1000" + }, + { + "bbox": [ + 45, + 489, + 279, + 642 + ], + "type": "text", + "content": " as an example, the top-1 accuracy under " + }, + { + "bbox": [ + 45, + 489, + 279, + 642 + ], + "type": "inline_equation", + "content": "d = 1000" + }, + { + "bbox": [ + 45, + 489, + 279, + 642 + ], + "type": "text", + "content": " gains " + }, + { + "bbox": [ + 45, + 489, + 279, + 642 + ], + "type": "inline_equation", + "content": "2.04\\% / 2.16\\%" + }, + { + "bbox": [ + 45, + 489, + 279, + 642 + ], + "type": "text", + "content": " improvement over " + }, + { + "bbox": [ + 45, + 489, + 279, + 642 + ], + "type": "inline_equation", + "content": "d = 100" + }, + { + "bbox": [ + 45, + 489, + 279, + 642 + ], + "type": "text", + "content": " when training with 105 epochs while this gap is reduced to " + }, + { + "bbox": [ + 45, + 489, + 279, + 642 + ], + "type": "inline_equation", + "content": "0.77\\% / 0.71\\%" + }, + { + "bbox": [ + 45, + 489, + 279, + 642 + ], + "type": "text", + "content": " when training with 305 epochs." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 45, + 652, + 255, + 665 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 652, + 255, + 665 + ], + "spans": [ + { + "bbox": [ + 45, + 652, + 255, + 665 + ], + "type": "text", + "content": "4.2. Empirical evaluations on object detection" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 45, + 671, + 280, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 671, + 280, + 730 + ], + "spans": [ + { + "bbox": [ + 45, + 671, + 280, + 730 + ], + "type": "text", + "content": "Settings Object detection and instance segmentation experiments are conducted on the COCO 2017 benchmark [31], which contains " + }, + { + "bbox": [ + 45, + 671, + 280, + 730 + ], + "type": "inline_equation", + "content": "118\\mathrm{K}" + }, + { + "bbox": [ + 45, + 671, + 280, + 730 + ], + "type": "text", + "content": " images in the training set and " + }, + { + "bbox": [ + 45, + 671, + 280, + 730 + ], + "type": "inline_equation", + "content": "5\\mathrm{K}" + }, + { + "bbox": [ + 45, + 671, + 280, + 730 + ], + "type": "text", + "content": " images in the validation set. We consider Mask R-CNN [18] in MMdetection [5] as the detection framework and adopt" + } + ] + } + ], + "index": 6 + }, + { + "type": "table", + "bbox": [ + 299, + 167, + 529, + 315 + ], + "blocks": [ + { + "bbox": [ + 296, + 104, + 531, + 159 + ], + "lines": [ + { + "bbox": [ + 296, + 104, + 531, + 159 + ], + "spans": [ + { + "bbox": [ + 296, + 104, + 531, + 159 + ], + "type": "text", + "content": "Table 4. Results of semantic segmentation on the ADE20K validation set. Results shaded in gray denote models ending with the general fully connected classifier while others denote models ending with our proposed EBVs. “" + }, + { + "bbox": [ + 296, + 104, + 531, + 159 + ], + "type": "inline_equation", + "content": "1 \\times" + }, + { + "bbox": [ + 296, + 104, + 531, + 159 + ], + "type": "text", + "content": "” denotes we train models for 80,000 steps while “" + }, + { + "bbox": [ + 296, + 104, + 531, + 159 + ], + "type": "inline_equation", + "content": "2 \\times" + }, + { + "bbox": [ + 296, + 104, + 531, + 159 + ], + "type": "text", + "content": "” denotes 160,000 steps." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 299, + 167, + 529, + 315 + ], + "lines": [ + { + "bbox": [ + 299, + 167, + 529, + 315 + ], + "spans": [ + { + "bbox": [ + 299, + 167, + 529, + 315 + ], + "type": "table", + "html": "
BackboneSchedulemIoUmIoU(ms+flip)
ResNet-181×38.7639.81
ResNet-18 (EBVs)1×38.9840.09
ResNet-182×39.2339.97
ResNet-18 (EBVs)2×39.7540.91
ResNet-501×40.7041.81
ResNet-50 (EBVs)1×42.7344.19
ResNet-502×42.0542.78
ResNet-50 (EBVs)2×42.4443.94
Swin-T2×44.4145.79
Swin-T (EBVs)2×44.3045.88
", + "image_path": "eec6d90ae0dfed84cebc1c4079fa29fa211ce028b1a3aed45def4e2c772b401f.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "table_body" + } + ], + "index": 8 + }, + { + "bbox": [ + 296, + 335, + 532, + 533 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 335, + 532, + 533 + ], + "spans": [ + { + "bbox": [ + 296, + 335, + 532, + 533 + ], + "type": "text", + "content": "ResNet [19] and Swin Transformer [32] as backbones. For fair comparisons, we utilize the same settings according to MMdetection and previous work. We scaled the image to a maximum of 800 on the short side and 1333 on the long side. We adopt " + }, + { + "bbox": [ + 296, + 335, + 532, + 533 + ], + "type": "inline_equation", + "content": "50\\%" + }, + { + "bbox": [ + 296, + 335, + 532, + 533 + ], + "type": "text", + "content": " scale horizontal flip and use SGD [47] with momentum " + }, + { + "bbox": [ + 296, + 335, + 532, + 533 + ], + "type": "inline_equation", + "content": "= 0.9" + }, + { + "bbox": [ + 296, + 335, + 532, + 533 + ], + "type": "text", + "content": " as the optimizer, the initial learning rate is 0.02. The weight decay equals 0.0001 while the batch size is 16 for experiments under the backbone of ResNet. For experiments on Swin Transformer, we use Adam [24] as the optimizer and the initial learning rate is 0.0001. The weight decay is changed to 0.05. To demonstrate the effectiveness of the proposed EBVs, we replace both instance-level and pixel-level classifiers in the detection framework with EBVs. In order to control the parameters of each backbone for fair comparisons, the dimension " + }, + { + "bbox": [ + 296, + 335, + 532, + 533 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 296, + 335, + 532, + 533 + ], + "type": "text", + "content": " of the basis vectors is kept consistent with the number of categories. All backbone models are pre-trained on the ImageNet-1K training set." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 296, + 550, + 531, + 633 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 550, + 531, + 633 + ], + "spans": [ + { + "bbox": [ + 296, + 550, + 531, + 633 + ], + "type": "text", + "content": "Results Table 3 presents comparisons between the general framework and our proposed EBVs. When adopting ResNet-50 as the backbone, the framework ending with EBVs outperforms those ending with fully connected layers among six evaluation indicators. While adopting Swin-T as the backbone, the framework ending with EBVs also achieves comparative results with state-of-the-art performance." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 296, + 640, + 530, + 664 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 640, + 530, + 664 + ], + "spans": [ + { + "bbox": [ + 296, + 640, + 530, + 664 + ], + "type": "text", + "content": "4.3. Empirical evaluations on semantic segmentation" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 296, + 671, + 532, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 671, + 532, + 730 + ], + "spans": [ + { + "bbox": [ + 296, + 671, + 532, + 730 + ], + "type": "text", + "content": "Settings Semantic segmentation experiments are conducted on the ADE20K [73], which contains 20,000 images in the training set and 2,000 images in the validation set. We adopt FPN [25] and UperNet [65] in MMSEG [6] as segmentation framework and adopt ResNet [19] and Swin Trans" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 277, + 746, + 299, + 756 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 277, + 746, + 299, + 756 + ], + "spans": [ + { + "bbox": [ + 277, + 746, + 299, + 756 + ], + "type": "text", + "content": "11761" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 595, + 842 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 65, + 112, + 195, + 246 + ], + "blocks": [ + { + "bbox": [ + 65, + 112, + 195, + 246 + ], + "lines": [ + { + "bbox": [ + 65, + 112, + 195, + 246 + ], + "spans": [ + { + "bbox": [ + 65, + 112, + 195, + 246 + ], + "type": "image", + "image_path": "a57eff453f219621b701e140d9732c9f33a2e144b6fb7a6dadcdcd04c339d08f.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 45, + 250, + 531, + 306 + ], + "lines": [ + { + "bbox": [ + 45, + 250, + 531, + 306 + ], + "spans": [ + { + "bbox": [ + 45, + 250, + 531, + 306 + ], + "type": "text", + "content": "Figure 2. Representation structure of ResNet-50. Left: Similarity between layers within ResNet-50 ends with a general fully connected classifier (FC). It shows that the last few layers share minimal similarity with the shallow layers while a few shallow layers also share minimal similarity with all the other layers. Middle: Similarity between layers within ResNet-50 ends with EBVs. Only the last few layers share minimal similarity with other layers. Right: Similarity between layers across ResNet-50 ends with a general fully connected layer with softmax and our proposed EBVs. Around " + }, + { + "bbox": [ + 45, + 250, + 531, + 306 + ], + "type": "inline_equation", + "content": "10\\%" + }, + { + "bbox": [ + 45, + 250, + 531, + 306 + ], + "type": "text", + "content": " initial layers share a little similarity while the last few layers share the least similarity." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 206, + 111, + 334, + 246 + ], + "blocks": [ + { + "bbox": [ + 206, + 111, + 334, + 246 + ], + "lines": [ + { + "bbox": [ + 206, + 111, + 334, + 246 + ], + "spans": [ + { + "bbox": [ + 206, + 111, + 334, + 246 + ], + "type": "image", + "image_path": "041aea74dcbd9ed5dde9e6bf8be810725005b24b6e9044fd86f1be6aa3588b4b.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 345, + 111, + 512, + 246 + ], + "blocks": [ + { + "bbox": [ + 345, + 111, + 512, + 246 + ], + "lines": [ + { + "bbox": [ + 345, + 111, + 512, + 246 + ], + "spans": [ + { + "bbox": [ + 345, + 111, + 512, + 246 + ], + "type": "image", + "image_path": "3ff2a477372a0afa4eda9646fd301c05972614d7324bf639750f290e9040e36d.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 45, + 317, + 281, + 446 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 317, + 281, + 446 + ], + "spans": [ + { + "bbox": [ + 45, + 317, + 281, + 446 + ], + "type": "text", + "content": "former [32] as backbones. For fair comparisons, we utilize the same settings in MMSEG. For experiments on ResNet, we use SGD [47] as the optimizer. The initial learning rate equals 0.01, weight decay equals 0.0005, momentum equals 0.9 and batch size is set as 16. For experiments on Swin Transformer, we use AdamW [35] as the optimizer and the initial learning rate is 0.00006 while the weight decay is set as 0.01. To perform our proposed method, We modify pixel-level classifiers in both the decode head and auxiliary head to EBVs. All backbone models are pre-trained on the ImageNet-1K training set." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 45, + 463, + 280, + 545 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 463, + 280, + 545 + ], + "spans": [ + { + "bbox": [ + 45, + 463, + 280, + 545 + ], + "type": "text", + "content": "Results According to Table 4, we find that EBVs surpass the framework ending with fully connected layers as the classifier under the backbone of ResNet. Additionally, when the training step is set as 80,000, EBVs gain a higher mIoU score than the general framework trained for 160,000 steps. While adopting Swin-T as the backbone, the framework ending with EBVs still achieving comparative performance." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 45, + 557, + 118, + 570 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 557, + 118, + 570 + ], + "spans": [ + { + "bbox": [ + 45, + 557, + 118, + 570 + ], + "type": "text", + "content": "5. Discussions" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 45, + 577, + 280, + 717 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 577, + 280, + 717 + ], + "spans": [ + { + "bbox": [ + 45, + 577, + 280, + 717 + ], + "type": "text", + "content": "We explore whether there are differences in the way EBVs represent and solve image tasks compared to a fully connected layer with softmax in this section. In order to answer this question, we have to analyze the features in the hidden layers as features are usually spread across neurons. However, different layers generally have different numbers of neurons. Recently, Raghu et al. [43] and Zhen et al. [70] applied the Centered Kernel Alignment (CKA) [7, 26] to solve the above task. CKA is effective because it involves no constraint on the number of neurons. It is also independent of the orthogonal transformations of representations [70]. Therefore, we adopt CKA to analyze the above question." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 57, + 718, + 280, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 57, + 718, + 280, + 730 + ], + "spans": [ + { + "bbox": [ + 57, + 718, + 280, + 730 + ], + "type": "text", + "content": "We pick ResNet-50 as the backbone while the experi" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 296, + 317, + 533, + 481 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 317, + 533, + 481 + ], + "spans": [ + { + "bbox": [ + 296, + 317, + 533, + 481 + ], + "type": "text", + "content": "ments on Swin-T can be found in the supplementary materials. One model ends with a general fully connected (FC) classifier and another model ends with our proposed EBVs. Both of the models are pre-trained on the ImageNet-1K [9] training dataset. We use 49 convolutional layers and the last fully connected layer. We plot CKA similarities between all pairs of layers within the whole ImageNet-1K validation dataset in Figure 2. As shown in Figure 2, for the ResNet-50 model ending with a general FC classifier, the feature similarity shows that around " + }, + { + "bbox": [ + 296, + 317, + 533, + 481 + ], + "type": "inline_equation", + "content": "10\\%" + }, + { + "bbox": [ + 296, + 317, + 533, + 481 + ], + "type": "text", + "content": " initial convolutional layers almost share no similarity with all the other layers while they themselves share a high similarity. If we change the last layer and the learning objective with our proposed EBVs, these shallow layers then share a relatively higher similarity." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 297, + 489, + 368, + 500 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 489, + 368, + 500 + ], + "spans": [ + { + "bbox": [ + 297, + 489, + 368, + 500 + ], + "type": "text", + "content": "6. Conclusion" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 296, + 508, + 533, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 508, + 533, + 730 + ], + "spans": [ + { + "bbox": [ + 296, + 508, + 533, + 730 + ], + "type": "text", + "content": "In this paper, we proposed Equiangular Basis Vectors (EBVs) for classification tasks. Different from previous classifiers and classical metric learning methods, EBVs predefined a fixed embedding for all the semantic categories. The learning objective of EBVs then changed to minimize the spherical distance of the embedding of input and each basis vector. Various experiments on the ImageNet-1K [9], COCO 2017 [31] and ADE20K [73] datasets and ablation studies also demonstrated the effectiveness of our proposed EBVs. In the future, we would like to explore relations between each basis vector pair and embed hierarchies when generating the proposed EBVs as the normal Euclidean space could not naturally embed hierarchies on datasets with known semantic hierarchies [16]. We also would like to explore the performance of EBVs in the case when the number of categories became very large. In addition, EBVs could also be regarded as advanced classifiers, it is interesting to adopt EBVs in other related tasks, e.g., incremental learning, few-shot learning, etc." + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 277, + 746, + 301, + 756 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 277, + 746, + 301, + 756 + ], + "spans": [ + { + "bbox": [ + 277, + 746, + 301, + 756 + ], + "type": "text", + "content": "11762" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 595, + 842 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 105, + 103, + 117 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 105, + 103, + 117 + ], + "spans": [ + { + "bbox": [ + 47, + 105, + 103, + 117 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 124, + 280, + 728 + ], + "type": "list", + "angle": 0, + "index": 15, + "blocks": [ + { + "bbox": [ + 51, + 124, + 279, + 166 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 51, + 124, + 279, + 166 + ], + "spans": [ + { + "bbox": [ + 51, + 124, + 279, + 166 + ], + "type": "text", + "content": "[1] L Douglas Baker and Andrew Kachites McCallum. 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To address this issue, many lightweight super-resolution models have been proposed. However, these models still contain time-consuming components that increase inference latency, limiting their real-world applications on mobile devices. In this paper, we propose a novel model for single-image super-resolution based on Equivalent Transformation and Dual Stream network construction (ETDS). ET method is proposed to transform time-consuming operators into time-friendly operations, such as convolution and ReLU, on mobile devices. Then, a dual stream network is designed to alleviate redundant parameters resulting from the use of ET and enhance the feature extraction ability. Taking full advantage of the advance of ET and the dual stream network structure, we develop the efficient SR model ETDS for mobile devices. The experimental results demonstrate that our ETDS achieves superior inference speed and reconstruction quality compared to previous lightweight SR methods on mobile devices. The code is available at https://github.com/ECNUSR/ETDS.", + "bbox": [ + 73, + 358, + 473, + 676 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 686, + 209, + 704 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Image super-resolution (SR) aims to reconstruct high-resolution images (HR) from low-resolution images (LR). Over the years, numerous deep-learning methods have been proposed [3, 6, 17, 18, 33, 35, 36] with good fidelity and perceptual quality. However, these methods are not efficient and lightweight when it comes to mobile platforms where SR application becomes increasingly ubiquitous. Thus, it is essential to devise an approach that takes into account the restrictions of mobile platforms.", + "bbox": [ + 75, + 713, + 468, + 849 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Generally, mobile platforms have limitations such as a restricted amount of RAM, lower memory bandwidth,", + "bbox": [ + 76, + 849, + 468, + 878 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/777bfb15aaaa8a30a43870e697161f696fcd04e7893bd360cb15254a0027b4b1.jpg", + "image_caption": [ + "Figure 1. Comparisons of PSNR performance and the inference latency of different models. The inference latency is tested on Dimensity 8100 SoC, NNAPI driver, INT8 precision and upsampling from $360 \\times 640$ to $1080 \\times 1920$ . PSNR indexes are evaluated on Set5 [2]." + ], + "image_footnote": [], + "bbox": [ + 509, + 347, + 857, + 526 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "lower computational speed and insufficient support for many common deep learning layers and operators. To take the particularities into consideration, the recently proposed SR models [27, 34] designed for mobile devices adopt a neat topology [34] as the base model to ensure low inference latency. ABPN [8] further boosted efficiency by employing the repeat operator instead of the time-consuming nearest neighbor interpolation. Nevertheless, in-depth investigation reveals that some time-consuming components in current mobile SR models, such as the global residual connection and clip operator, are indispensable for overall reconstruction quality. Therefore, to accelerate the inference on mobile devices and achieve a competitive reconstruction quality and inference latency, it is necessary to seek time-friendly surrogates for these time-consuming operators.", + "bbox": [ + 496, + 612, + 893, + 852 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "To this end, we propose Equivalent Transformation (ET), a method that speeds up the model by substituting time-consuming operators with time-friendly ones without im", + "bbox": [ + 496, + 854, + 893, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 810, + 44 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Corresponding author.", + "bbox": [ + 94, + 886, + 220, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "14102", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "pairing reconstruction quality. As shown in Fig. 1, the proposed ET can be directly applied to existing models (e.g., ECBSR [34] and ABPN [8]) and reduce inference latency without retraining. However, ET introduces some redundant and unlearnable parameters. To fully utilize these parameters, we design the dual stream network that makes the redundant parameters partially learnable, to boost the feature extraction ability. Finally, we propose a mobile image SR model named ETDS that employs the dual stream network in the training stage and transforms it into an equivalent plain network by ET in the inference stage. As shown in Fig. 1, our ETDS not only achieves high reconstruction quality but also maintains low inference speed.", + "bbox": [ + 75, + 90, + 472, + 287 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In summary, the main contributions of this paper are as follows:", + "bbox": [ + 76, + 287, + 470, + 316 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "1) We propose ET, a method that can transform time-consuming operators and speed up the inference without impairing reconstruction quality. It can be applied to existing models to accelerate the inference.", + "2) We design a dual stream network to alleviate the redundancy yielded from ET by making redundant parameters partially learnable.", + "3) We propose an efficient and lightweight network named ETDS for real-time SR on mobile devices based on ET and dual stream networks. Experiments demonstrate that state-of-the-art models equipped with ET have at most $80\\%$ improvement in inference latency and ETDS achieves $34\\%$ inference latency improvement and 0.42dB PSNR performance improvement." + ], + "bbox": [ + 86, + 323, + 467, + 551 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 76, + 571, + 218, + 585 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Due to the rapid development of convolutional neural networks (CNN), CNN-based methods [6, 18, 24, 35, 36] have become mainstream methods for SR tasks. SRCNN [6] pioneered the application of convolutional neural networks on the SR task, surpassing the performance of traditional methods. In EDSR [18], a very deep network was utilized and the batch normalization layers in the residual block were removed. SwinIR [17] first attempted to apply the Swin-Transformer [20] on the SR task, showing the potential of Transformer-based networks [26]. To enlarge the receptive field, the hybrid attention block (HAB) was proposed by HAT [3], which achieved state-of-the-art performance. However, these models have high requirements for memory and computational resources which are not easily attainable in real-world applications.", + "bbox": [ + 75, + 597, + 468, + 824 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To realize lightweight SR for GPU servers, many approaches tried to reduce the number of parameters and FLOPs. CARN [1] attempted to apply group convolutions. IMDN [10] employed a progressive refinement module to improve the information extraction ability and reduced the", + "bbox": [ + 75, + 824, + 468, + 902 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "number of layers and channels. For further improvement in the efficiency of feature extraction, in RFDN [19], $1 \\times 1$ convolutions were utilized to replace the $3 \\times 3$ convolutions on the split channel of the IMDB [10] module. RLFN [15] replaced the progressive refinement module with a simpler residual module, which further improved the running speed and achieved great performance. MemSR [30] optimized the network in terms of memory by removing the residual structure in the model and proposed a novel knowledge distillation method to improve the performance.", + "bbox": [ + 496, + 90, + 890, + 241 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Due to the particularity of the mobile platforms, most models for GPU servers are not directly applicable to mobile devices whose applications require to be carried out in a timely fashion with restricted computational resources. To solve this problem, current methods mainly optimized the network from three aspects, i.e., neat network topology, computation reduction and operator substitution. ECBSR [34], which proposed an Edge-oriented Convolutional Block (ECB) to achieve better performance, used relatively neat topology for low inference latency on mobile devices and introduced reparameterization techniques to achieve computation reduction for SR task. Following [34], RepSR [27] optimized the performance and training efficiency of the reparameterization module in ECBSR to achieve further computation reduction. ABPN [8] first attempted to apply operator substitution and used the faster repeat operator instead of nearest neighbor interpolation in global residual connections. Inspired by the reparameterization technique, we propose ET, which substitutes more types of operators to achieve low inference latency. Our proposed ETDS optimized the network from all three aspects, where ET optimized the network by achieving operator substitution and computation reduction while the dual stream network adopted a neat topology.", + "bbox": [ + 496, + 243, + 892, + 604 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "3. Methodology", + "text_level": 1, + "bbox": [ + 500, + 619, + 635, + 637 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In this section, we examine the current mobile superresolution models in Sec. 3.1, and then propose a novel method, Equivalent Transformation (ET), which substitutes time-consuming operators with time-friendly ones in 3.2. However, applying ET comes at the cost of introducing redundant parameters. To address this, we carefully design a dual stream network that alleviates redundancy and enhances feature extraction ability in Sec. 3.3.", + "bbox": [ + 496, + 645, + 890, + 767 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "3.1. Analysis of Current Mobile SR Models", + "text_level": 1, + "bbox": [ + 498, + 776, + 834, + 792 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In order to design more efficient super-resolution models for mobile devices, we analyze the speed bottleneck of current mobile SR models on two of the most popular mobile phone $\\mathrm{SoCs}^1$ . As shown in Tab. 1, convolution and ReLU operations have lower inference latency than most other op", + "bbox": [ + 496, + 800, + 890, + 877 + ], + "page_idx": 1 + }, + { + "type": "page_footnote", + "text": "1www counterpointresearch.com/global-smartphone-ap-market-share/", + "bbox": [ + 517, + 887, + 888, + 898 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "14103", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 1 + }, + { + "type": "table", + "img_path": "images/3f95c467bb35b6141d1707eb69eef9c4b4936173afc29ae40694c2ad5727188c.jpg", + "table_caption": [ + "Table 1. Average inference latency (ms) of common components in mobile SR models. The average inference latency of all components is tested on SR models with a channel size of 32, an input of size $360 \\times 640$ and a scale factor of 3. For operators in the same type, the results of higher latency are marked in bold." + ], + "table_footnote": [], + "table_body": "
TypeOperatorLatency (ms)
Dimensity 8100Snapdragon 870Snapdragon 865
Convolution1 × 1 Convolution2.244
3 × 3 Convolution10.41821
Transposed Convolution7.379
ActivationReLU0.060.60.6
PReLU2.264.83.8
LeakyReLU2.265.64.2
Sigmoid0.120.60.8
Tanh0.30.81
InterpolationNearest neighbor262427
Bilinear676568
OthersAdd6.534
Concatenate22.867
Multiply6.534
Repeat16.31914
Clip6.99194
PixelShuffle4.234
", + "bbox": [ + 81, + 162, + 465, + 392 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "erations, and PixelShuffle [23] is more efficient than transposed convolution, which indicates PixelShuffle and ReLU are better choices for mobile platforms. Hereafter, plain network refers to a network that only contains time-friendly operators (i.e., convolution, ReLU activation functions and PixelShuffle), which has low inference latency on mobile devices.", + "bbox": [ + 75, + 406, + 467, + 511 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "To transform current mobile models into plain models, we may encounter the following challenges:", + "bbox": [ + 76, + 513, + 467, + 542 + ], + "page_idx": 2 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "1) To avoid the rescaling problem in the INT8 quantization models, it is necessary to add the clip operator at the end of the model. However, the clip operator is also time-consuming (see Tab. 1), which requires a more efficient and equivalent alternative.", + "2) To compensate for the PSNR performance drop brought by the removal of global residual connections, it is necessary to find an equivalent way to transform the global residual connection into an efficient operator." + ], + "bbox": [ + 86, + 545, + 468, + 696 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "To tackle these challenges, we propose ET, which substitutes some time-consuming operators with time-friendly ones without reducing the reconstruction quality, thereby improving the running speed.", + "bbox": [ + 75, + 698, + 467, + 758 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. Equivalent Transformation", + "text_level": 1, + "bbox": [ + 76, + 770, + 321, + 786 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Formal Definitions. A convolution operation is formulated as $z = W \\otimes x + b$ , where $x \\in \\mathbb{R}^{c_i \\times h \\times w}$ and $z \\in \\mathbb{R}^{c_o \\times h \\times w}$ are the input and output tensors respectively, $W \\in \\mathbb{R}^{c_o \\times k \\times k \\times c_i}$ , $b \\in \\mathbb{R}^{c_o}$ are the kernel and the bias of the convolution, and $k$ is the kernel size, $c_i, c_o$ are the numbers of the input and output channels, and $h, w$ are the input height and width. $I$ is the identity kernel of the convolution", + "bbox": [ + 76, + 794, + 468, + 900 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "operation, and $O$ is the kernel of zero elements, satisfying", + "bbox": [ + 498, + 90, + 880, + 106 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nI \\otimes x = x, \\quad O \\otimes x = 0, \\forall x \\in \\mathbb {R} ^ {c _ {i} \\times h \\times w}. \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 555, + 114, + 890, + 132 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "For input features and convolution kernels, the concatenation operation requires all but the concatenated dimension to be consistent. The channel dimension concatenation operation of feature vectors $x$ and $y$ is defined as $\\begin{bmatrix} x \\\\ y \\end{bmatrix}$ . The concatenation operation of the convolution kernels $W_{h,1}$ and $W_{h,2}$ in the horizontal direction (i.e., input-dimension concatenation) is defined as $[W_{h,1}, W_{h,2}]$ , which satisfies", + "bbox": [ + 496, + 143, + 890, + 263 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\left[ W _ {h, 1}, W _ {h, 2} \\right] \\otimes \\left[ \\begin{array}{l} x \\\\ y \\end{array} \\right] = W _ {h, 1} \\otimes x + W _ {h, 2} \\otimes y. \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 540, + 272, + 890, + 306 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Likewise, the concatenation operation of the convolution kernels $W_{v,1}$ and $W_{v,2}$ in the vertical direction, i.e., output-dimension concatenation is defined as $\\begin{bmatrix} W_{v,1} \\\\ W_{v,2} \\end{bmatrix}$ , which satisfies", + "bbox": [ + 496, + 314, + 890, + 385 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\left[ \\begin{array}{l} W _ {v, 1} \\\\ W _ {v, 2} \\end{array} \\right] \\otimes x = \\left[ \\begin{array}{l} W _ {v, 1} \\otimes x \\\\ W _ {v, 2} \\otimes x \\end{array} \\right]. \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 599, + 385, + 890, + 419 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "More details will be found in Appendix.", + "bbox": [ + 500, + 422, + 764, + 436 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "ET for Repeat Operator. Given an input tensor $x \\in \\mathbb{R}^{c \\times h \\times w}$ , the repeat operator $\\text{repeat}(x, n)$ constructs a new tensor $z \\in \\mathbb{R}^{(nc) \\times h \\times w}$ by replicating the input $n$ times along the channel dimension. This operation can be expressed as a convolution layer. Precisely, Eq. (1) and (3) yield", + "bbox": [ + 496, + 436, + 890, + 527 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\operatorname {r e p e a t} (x, n) = \\left[ \\begin{array}{c} x \\\\ \\vdots \\\\ x \\end{array} \\right] = \\left[ \\begin{array}{c} I \\otimes x \\\\ \\vdots \\\\ I \\otimes x \\end{array} \\right] = \\left[ \\begin{array}{c} I \\\\ \\vdots \\\\ I \\end{array} \\right] \\otimes x \\tag {4} \\\\ = \\operatorname {r e p e a t} (I, n) \\otimes x, \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 544, + 536, + 890, + 613 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\text{repeat}(I, n)$ is a constant. Thus, the repeat operator is equivalently transformed into a convolution layer, whose kernel and bias are $\\text{repeat}(I, n)$ and a zero vector, respectively.", + "bbox": [ + 496, + 623, + 890, + 681 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "ET for Add Operator. The add operator refers to the element-wise addition operation of two feature vectors and is an indispensable part of residual connections, i.e., $z = x + y$ . From Eq. (1) and (2), we have:", + "bbox": [ + 496, + 683, + 890, + 744 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nx + y = I \\otimes x + I \\otimes y = [ I, I ] \\otimes \\left[ \\begin{array}{l} x \\\\ y \\end{array} \\right]. \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 557, + 753, + 890, + 786 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Thus, the add operator is equivalently transformed into a convolution layer with a concatenate operator, whose kernel and bias are $[I, I]$ and a zero vector, respectively. Notably, this proposed convolution layer can be eliminated later by reparameterization techniques.", + "bbox": [ + 496, + 794, + 890, + 869 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "ET for Concatenate Operator. In our model, the concatenate operator always follows the convolution layers.", + "bbox": [ + 498, + 869, + 890, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "14104", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We integrate the convolution-concatenate structure, i.e., the concatenate operator and its preceding convolution layer, which can be simplified with Eq. (2) and (3) as follows:", + "bbox": [ + 76, + 90, + 468, + 137 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nz = \\left[ \\begin{array}{c} W _ {1} \\otimes x + b _ {1} \\\\ W _ {2} \\otimes y + b _ {2} \\end{array} \\right] = \\left[ \\begin{array}{c c} W _ {1} & O \\\\ O & W _ {2} \\end{array} \\right] \\otimes \\left[ \\begin{array}{c} x \\\\ y \\end{array} \\right] + \\left[ \\begin{array}{c} b _ {1} \\\\ b _ {2} \\end{array} \\right]. \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 89, + 143, + 468, + 180 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Following Eq. (6), the convolution-concatenate structure is transformed into a concatenate-convolution structure, with the kernel and bias as follows:", + "bbox": [ + 76, + 186, + 468, + 231 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\left[ \\begin{array}{c c} W _ {1} & O \\\\ O & W _ {2} \\end{array} \\right] \\quad \\text {a n d} \\quad \\left[ \\begin{array}{l} b _ {1} \\\\ b _ {2} \\end{array} \\right]. \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 181, + 237, + 468, + 272 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In particular, when the residual branch does not have a convolution layer, it can be expressed as:", + "bbox": [ + 76, + 279, + 468, + 310 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nz = \\left[ \\begin{array}{c} W \\otimes x + b \\\\ y \\end{array} \\right] = \\left[ \\begin{array}{c c} W & O \\\\ O & I \\end{array} \\right] \\otimes \\left[ \\begin{array}{c} x \\\\ y \\end{array} \\right] + \\left[ \\begin{array}{c} b \\\\ 0 \\end{array} \\right]. \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 116, + 316, + 468, + 353 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "When $x = y$ , Eq. (8) can be further rewritten as:", + "bbox": [ + 76, + 359, + 395, + 375 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nz = \\left[ \\begin{array}{c} W \\otimes x + b \\\\ x \\end{array} \\right] = \\left[ \\begin{array}{c} W \\\\ I \\end{array} \\right] \\otimes x + \\left[ \\begin{array}{c} b \\\\ 0 \\end{array} \\right], \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 140, + 382, + 468, + 417 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where the kernel is $\\left[ \\begin{array}{l}W\\\\ I \\end{array} \\right]$ and thus the concatenate operator is eliminated.", + "bbox": [ + 76, + 425, + 468, + 469 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "ET for Clip Operator. The clip operator is expressed as:", + "bbox": [ + 76, + 472, + 468, + 498 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\operatorname {c l i p} (x) = \\left\\{ \\begin{array}{l l} 0, & x \\leq 0, \\\\ x, & 0 < x \\leq 2 5 5, \\\\ 2 5 5, & x > 2 5 5, \\end{array} \\right. \\tag {10}\n$$\n", + "text_format": "latex", + "bbox": [ + 151, + 498, + 468, + 546 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "which avoids the loss of precision and subsequent additional inverse scaling operations caused by mismatched normalization of the INT8 quantization model [12]. Nevertheless, as shown in Tab. 1, the clip operator is extremely time-consuming on many mobile SoCs, so it is of great necessity to find a time-friendly substitution for the clip operator.", + "bbox": [ + 76, + 550, + 468, + 640 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "To equivalently transform the clip operator with ReLU, we reformulate clip operator as:", + "bbox": [ + 76, + 641, + 467, + 670 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\operatorname {c l i p} (x) = \\operatorname {R e L U} (- \\operatorname {R e L U} (- x + 2 5 5) + 2 5 5). \\tag {11}\n$$\n", + "text_format": "latex", + "bbox": [ + 104, + 680, + 468, + 698 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "To speed up this process, we further rewrite it as:", + "bbox": [ + 76, + 707, + 401, + 720 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\left\\{ \\begin{array}{l l} y = & \\operatorname {R e L U} (- I \\otimes x + 2 5 5), \\\\ c l i p (x) = & \\operatorname {R e L U} (- I \\otimes y + 2 5 5). \\end{array} \\right. \\tag {12}\n$$\n", + "text_format": "latex", + "bbox": [ + 147, + 729, + 468, + 772 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Using Eq. (12), the clip operator is transformed into two convolutions with ReLU, whose kernels are $-I$ and bias is a vector with all elements equal to 255. Remark that the first convolution layer in Eq. (12) is eliminated by reparameterization techniques [5].", + "bbox": [ + 76, + 779, + 468, + 854 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "ET for Equivalent Plain Model Conversion. As depicted in Fig. 2, the model is converted into an equivalent plain model by ET as following:", + "bbox": [ + 76, + 854, + 468, + 900 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/59f6d1975d519faadfd1e91349866a0ec9b3ce51ae72d4cad240447b246410b6.jpg", + "image_caption": [ + "Figure 2. Illustration of converting the general model into the equivalent plain model using ET. The beige convolution indicates that the convolution kernel is assigned a specific value. Rep refers to the reparameterization technique." + ], + "image_footnote": [], + "bbox": [ + 501, + 90, + 888, + 319 + ], + "page_idx": 3 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- The repeat operator and the add operator are converted into a single convolution and a concatenate operator respectively (see Step 1 and Step 2).", + "- The concatenate operator with the preceding convolutions from two branches is converted into a convolution. Notably, the global residual connection does not contain negative values, so the ReLU function is omitted (see Step 3).", + "- The two convolutions introduced by previous steps are converted into a convolution using reparameterization techniques (see Step 4).", + "- The convolution-concatenate structure is converted into a concatenate-convolution one, thus the concatenate operator is converted and moves forward till it reaches the skip connection starting point, that is, $x$ equals $y$ . In this situation, the concatenate operator is further eliminated (see Step 5 and Step 6).", + "- The clip operator is converted into the convolution (see Step 7)." + ], + "bbox": [ + 517, + 393, + 890, + 685 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Remark 1 Although $ET$ speeds up inference by transforming time-consuming operators into time-friendly ones, it introduces some redundant parameters. For instance, in the transformed convolution kernel $\\mathrm{diag}(W, I)$ derived from Eq. (8). All learnable parameters appear in $W$ . If the redundant parameters are effectively utilized, better reconstruction performance can be achieved.", + "bbox": [ + 498, + 698, + 890, + 804 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.3. Dual Stream Network", + "text_level": 1, + "bbox": [ + 500, + 816, + 702, + 830 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "To alleviate the side effects of the redundant parameters of ET, we design a dual stream network where the two branches learn the low-frequency and high-frequency contents of the image separately and utilize the parameters to", + "bbox": [ + 498, + 839, + 890, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "14105", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/daf35378cd2414e3c9483385e5c31e2e32e06ef0ba9c5d827745e79b08432eca.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 81, + 89, + 883, + 224 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/c38885220b3bd666d9c8b90aaa8f9edc40866df1e243e1aa8b56f76615dab007.jpg", + "image_caption": [ + "Figure 3. Network architecture of ETDS during training and inference stages. The residual branch for extracting low-frequency contents only contains a few parameters, and most of the parameters are used to extract high-frequency contents." + ], + "image_footnote": [], + "bbox": [ + 81, + 233, + 890, + 329 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "the fullest. The transformed convolution kernel in Eq. (8) is $\\left[ \\begin{array}{cc}K_b & K_{r2b}\\\\ K_{b2r} & K_r \\end{array} \\right]$ , where $K_{b}$ and $K_{r}$ denote the modules that constitute the backbone branch and residual branch, respectively. $K_{r2b}$ is the module that transfers information from the residual branch to the backbone branch, and $K_{b2r}$ transfers information reversely. The residual branch consisting of $K_{r}$ and the backbone branch consisting of $K_{b}$ extract low-frequency and high-frequency information respectively.", + "bbox": [ + 75, + 392, + 468, + 541 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Initially, $K_{r}$ , $K_{r2b}$ and $K_{b2r}$ are not learnable. Furthermore, we have analyzed the possible impacts of making them learnable on the reconstruction quality and found that when $K_{r}$ and $K_{r2b}$ are learnable, they can extract low-frequency information more effectively and transfer more residual information to the backbone branch, respectively. However, when $K_{b2r}$ is learnable, the backbone branch may take less important low-frequency information into consideration, which reduces the number of parameters for extracting high-frequency components, and potentially compromising the performance.", + "bbox": [ + 75, + 542, + 468, + 707 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "As shown in Fig. 3, $K_{r}$ and $K_{r2b}$ in our dual stream network contain learnable parameters, while parameters in $K_{b2r}$ remain fixed. In the training phase, we encourage the residual branch to learn as many low-frequency contents as possible, that is, to minimize the $L_{1}$ distance between the output of the residual branch $(I_{LF})$ and the ground truth $(I_{GT})$ :", + "bbox": [ + 75, + 708, + 468, + 813 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {L F} = \\left\\| I _ {G T} - I _ {L F} \\right\\| _ {1}. \\tag {13}\n$$\n", + "text_format": "latex", + "bbox": [ + 191, + 813, + 468, + 829 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The backbone branch learns high-frequency contents, and its output $(I_{HF})$ compensates for the gap between $I_{GT}$ and $I_{LF}$ :", + "bbox": [ + 76, + 832, + 468, + 878 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {H F} = \\left\\| I _ {G T} - I _ {L F} - I _ {H F} \\right\\| _ {1}. \\tag {14}\n$$\n", + "text_format": "latex", + "bbox": [ + 166, + 885, + 468, + 901 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "To train the dual stream network, we use the overall loss function:", + "bbox": [ + 498, + 392, + 890, + 420 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {D S} = \\mathcal {L} _ {H F} + \\alpha \\times \\mathcal {L} _ {L F}, \\tag {15}\n$$\n", + "text_format": "latex", + "bbox": [ + 606, + 422, + 890, + 436 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "which drives more parameters to extract high-frequency contents to improve the overall performance. In the inference stage, as shown in Fig. 3, the dual stream network can be equivalently transformed into a plain network, which ensures low inference latency.", + "bbox": [ + 496, + 444, + 890, + 518 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 500, + 532, + 633, + 550 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.1. Datasets and Metrics", + "text_level": 1, + "bbox": [ + 500, + 558, + 697, + 571 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Our model ETDS is trained on DIV2K dataset [25] with 800 training images. The performance is evaluated on 5 benchmark datasets (i.e., Set5 [2], Set14 [32], BSDS100 [21], Urban100 [9] and DIV2K100 [25]). PSNR and SSIM [29] are used to evaluate the reconstruction quality and calculated on the Y channel in the YCbCr space.", + "bbox": [ + 496, + 580, + 890, + 672 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.2. Implementation Details", + "text_level": 1, + "bbox": [ + 500, + 681, + 717, + 696 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "ETDS is implemented on PyTorch-based [22] BasicSR [28] framework and trained on an NVIDIA 2080Ti GPU. In the training phase, 32 patches of $64 \\times 64$ LR image are used as input. Random rotation, horizontal flipping, and channel shuffle are applied for data augmentation. We train our model by the ADAM [14] optimizer with $\\beta_{1} = 0.9$ , $\\beta_{2} = 0.999$ , and $\\epsilon = 10^{-8}$ . We set $\\mathcal{L}_{\\mathrm{DS}}$ as the loss function with $\\alpha = 0.5$ . In accordance with previous works, our model is trained for $1600k$ iterations with a learning rate of $5e^{-4}$ . For the first $100k$ iterations, $K_{r}$ and $K_{r2b}$ are initialized by setting $K_{r} = I$ and $K_{r2b} = O$ . In the testing phase, we test the inference latency on three SoCs (i.e., Dimensity 8100, Snapdragon 888, and Snapdragon 8 Gen 1) with the", + "bbox": [ + 496, + 703, + 892, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "14106", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/cc6366a5335d5f46fa093fa8a1777dce8e0f4b00f65ab646650db0b790e50717.jpg", + "image_caption": [ + "(a)" + ], + "image_footnote": [], + "bbox": [ + 81, + 89, + 343, + 244 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/dcd00be26e6a0999c9b2fc3f601004b9d2ef260cb459d864a3a72d8506f4e502.jpg", + "image_caption": [ + "(b)", + "Figure 4. The effect of the numbers of channels and layers on inference latency of the plain model. (a) shows the inference latency with the number of channels between 4 and 24. (b) shows the inference latency with the number of channels between 4 and 64, divisible by 4. (c) shows the inference latency with the number of layers between 1 and 10." + ], + "image_footnote": [], + "bbox": [ + 351, + 88, + 616, + 244 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/bf1e483e16a8306be5bec537a92b6b801913e2dbce1e1d4ace198a1526487cf7.jpg", + "image_caption": [ + "(c)" + ], + "image_footnote": [], + "bbox": [ + 627, + 89, + 890, + 244 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "AI Benchmark application [11, 13]. All inference latencies and multiply-accumulate operations (MACs) are tested with inputs of $360 \\times 640$ .", + "bbox": [ + 75, + 316, + 468, + 361 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.3. Hardware-Friendly Number of Channels", + "text_level": 1, + "bbox": [ + 76, + 372, + 428, + 387 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "As shown in Fig. 4, the numbers of channels and layers have a significant impact on the model's efficiency. Observing Fig. 4 (a)(b), we can see that the models have lower inference latency on mobile devices when the number of channels is a multiple of 4, due to the processing unit alignment [31], the memory alignment, and other hardware optimizations [4]. Fig. 4 (c) supports that the inference latency is proportional to the number of layers.", + "bbox": [ + 75, + 396, + 468, + 517 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "As a result, for a lower inference latency, ETDS is designed with 16, 32, and 48 channels and the number of layers in the model is designed for balancing the performance and inference latency. Also, for the equivalently transformed models (e.g., $\\mathrm{ECBSR + ET}$ and $\\mathrm{ABPN + ET}$ ), extra channels are added to ensure that the number of channels is a multiple of 4.", + "bbox": [ + 75, + 517, + 468, + 623 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.4. Comparisons to Previous Works", + "text_level": 1, + "bbox": [ + 76, + 633, + 361, + 648 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We compare our ETDS with representative real-time SR models on mobile devices, including Bicubic, ESPCN [23], FSRCNN [7], ABPN [8], and ECBSR [34]. Since ESPCN, FSRCNN, and ECBSR only process on a single channel of the input image, some preprocessing and postprocessing, such as color space conversion and upsampling of the other two channels are omitted. For a fair comparison, these models are retrained in the RGB color space.", + "bbox": [ + 75, + 657, + 468, + 777 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We train four different sizes of our model, denoted as ETDS-T, ETDS-S, ETDS-M and ETDS-L for different computational use cases, with channels 16, 32, 32 and 48, and layers 5, 4, 6, and 7, respectively. The performance comparison is summarized in Tab. 2. In addition to PSNR/SSIM indexes, we also list the number of parameters and MACs for a more comprehensive comparison.", + "bbox": [ + 75, + 779, + 468, + 883 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Quantitative Results. The quantitative comparison is", + "bbox": [ + 96, + 885, + 468, + 900 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "presented in Tab. 2. From Tab. 2, our model achieves not only lower inference latency than other models in most cases but also higher PSNR/SSIM indexes. For instance, as shown in Tab. 2 (latency column i), our ETDS-S runs $1.2\\mathrm{ms}$ faster than ECBSR-M4C16 on the $\\times 3$ task, and its PSNR index on the Urban100 dataset is $0.29\\mathrm{dB}$ higher. ETDS-L's inference latency on the $\\times 3$ task is $3.5\\mathrm{ms}$ faster than the ABPN-M6C40's, and PSNR on Set5. Notably, although our model consists of slightly more parameters and MACs, it is still faster than the state-of-the-art models. This phenomenon occurs due to two-fold aspects. 1). Under different contexts, the same operations may have different inference latency. 2). Some operations are not measured in parameters and MACs metrics. For instance, ReLU does not influence parameters and concatenation does not influence MACs.", + "bbox": [ + 496, + 316, + 890, + 556 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Qualitative Results. The qualitative comparison results are depicted in Fig. 5. We can see that the texture of the wall in thimagese images generated by ESPCN [23] and FSRCNN [7] is blurred, and images generated by ECBSR-M6C40 [34] and ABPN-M6C40 [8] are slightly distorted. Obviously, our ETDS-T produces the least distorted and blurred images with the best PSNR/SSIM results.", + "bbox": [ + 496, + 559, + 890, + 664 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.5. Ablation Studies", + "text_level": 1, + "bbox": [ + 500, + 678, + 663, + 693 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "In this section, we propose a series of ablation studies on the design of the proposed ETDS. All the ablation experiments are conducted on the $\\times 4$ task. We report PSNR values on the Y channel in the YCbCr space.", + "bbox": [ + 496, + 703, + 890, + 763 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Ablation Studies for Equivalent Transformation. We validate the effectiveness of ET through a series of ablation studies. Additionally, we apply ET to both ECBSR and ABPN to further demonstrate its effectiveness. Note that ETDS does not have a repeat operator and we do not apply ET for the concatenate operator for ECBSR and ABPN because the improvement on the NNAPI driver is insignificant. Our results in Tab. Tab. 3 show that applying ET to these operators results in reduced latency.", + "bbox": [ + 496, + 763, + 890, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "14107", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/861a2577225553959326ee5339e6dd67e83129a348765ebca20a9746fb9131f3.jpg", + "table_caption": [ + "Table 2. Performance comparison of different SR models on five benchmark datasets. PSNR/SSIM on the Y channel is reported on each dataset. Inference latency i, ii, iii and iv denotes the inference latency of the models using NNAPI driver on Dimensity 8100 SoC, MediaTek Neuron driver on Dimensity 8100 SoC, Qualcomm QNN GPU driver on Snapdragon 888 SoC, and NNAPI on Snapdragon 8 Gen 1 SoC respectively." + ], + "table_footnote": [], + "table_body": "
ScaleModelParams (K)MACs (G)Latency (ms)Set5Set14B100Urban100DIV2K100
iiiiiiivPSNR/SSIMPSNR/SSIMPSNR/SSIMPSNR/SSIMPSNR/SSIM
×2Bicubic******33.95/0.933430.54/0.875129.74/0.850327.07/0.845632.67/0.9078
ESPCN26.806.156.304.8391-36.87/0.955932.62/0.908631.40/0.889829.61/0.897334.78/0.9347
ETDS-T (Ours)13.943.194.853.81125-37.18/0.957832.76/0.910331.62/0.893030.10/0.905835.09/0.9375
FSRCNN24.6815.0510.45.8941456237.00/0.956832.68/0.909431.51/0.891329.92/0.902234.97/0.9363
ECBSR-M4C1611.552.646.154.5718931.637.18/0.957732.79/0.910531.61/0.892830.18/0.906435.10/0.9375
ETDS-S (Ours)41.519.528.065.77169-37.38/0.958732.96/0.912431.77/0.895130.62/0.912135.36/0.9396
ECBSR-M4C3241.529.539.706.6437231.437.39/0.958733.03/0.912631.79/0.895330.69/0.912835.39/0.9398
ABPN-M4C2833.467.6710.06.6620728.537.36/0.958532.96/0.912131.75/0.894930.55/0.911135.31/0.9392
ETDS-M (Ours)60.0113.7710.26.73288-37.54/0.959333.09/0.913331.86/0.896330.87/0.914935.50/0.9406
ECBSR-M6C4092.3721.2218.110.965346.237.61/0.959633.18/0.913931.94/0.897231.09/0.917435.61/0.9415
ABPN-M6C4093.4021.4518.711.243531.937.58/0.959433.16/0.91431.92/0.897131.04/0.916935.59/0.9414
ETDS-L (Ours)152.1834.9720.612.1469-37.64/0.959733.24/0.914531.98/0.897731.22/0.918835.69/0.9421
×3Bicubic******30.61/0.871927.79/0.781127.31/0.745324.58/0.739629.80/0.8341
ESPCN31.137.149.798.381104432.85/0.911529.41/0.823628.40/0.787626.22/0.800231.24/0.8670
ETDS-T (Ours)16.923.868.645.3614049.233.14/0.916029.53/0.827428.54/0.792026.48/0.811131.43/0.8713
FSRCNN24.6830.7313.77.32456135033.01/0.914529.52/0.826428.50/0.790326.40/0.807431.38/0.8699
ECBSR-M4C1613.723.1416.211.021669.433.07/0.914929.53/0.826928.57/0.792126.61/0.813631.44/0.8712
ETDS-S (Ours)46.7910.7312.27.7318549.233.49/0.919429.76 0.831428.71/0.796126.90/0.822131.69/0.8756
ECBSR-M4C3245.8510.5219.713.135469.233.56/0.920529.78/0.831928.73/0.796526.98/0.823931.73/0.8761
ABPN-M4C2842.549.7620.513.827562.833.53/0.920029.78/0.831728.72/0.796626.94/0.823231.71/0.8758
ETDS-M (Ours)65.2914.9814.48.762604933.65/0.921429.86/0.833328.78/0.798127.12/0.827831.81/0.8776
ECBSR-M6C4097.7922.4628.117.471375.333.67/0.921129.92/0.833928.85/0.799427.36/0.833331.88/0.8784
ABPN-M6C40104.1023.9129.218.24806633.71/0.921329.92/0.833928.85/0.799427.37/0.833631.89/0.8786
ETDS-L (Ours)159.7736.7125.414.244451.833.88/0.923530.00/0.835928.90/0.801027.45/0.835932.00/0.8807
×4Bicubic******28.60/0.814026.21/0.708826.04/0.673323.23/0.661328.23/0.7775
ESPCN37.208.5411.88.1412079.830.66/0.868827.66/0.758126.94/0.715224.56/0.726329.46/0.8133
ETDS-T (Ours)21.364.8810.96.9416377.430.87/0.873827.75/0.761827.04/0.719424.71/0.735029.59/0.8172
FSRCNN24.6852.68----30.76/0.872127.74/0.760927.01/0.718124.66/0.733029.56/0.8163
ECBSR-M4C1616.773.8323.913.727819130.87/0.874127.80/0.762627.06/0.719524.75/0.736429.61/0.8176
ETDS-S (Ours)54.1112.4114.69.0220377.431.19/0.880628.01/0.767827.18/0.724025.03/0.747929.80/0.8224
ECBSR-M4C3251.9211.9128.016.339919131.24/0.881528.04/0.768627.21/0.724825.07/0.749429.84/0.8231
ABPN-M4C2862.0514.2430.317.433518731.32/0.883328.10/0.769727.23/0.725425.12/0.751129.86/0.8237
ETDS-M (Ours)72.6116.6616.69.9826778.931.41/0.884328.13/0.770527.27/0.726525.20/0.754429.92/0.8250
ECBSR-M6C40105.3724.2036.820.774919531.41/0.883128.20/0.771627.33/0.728025.37/0.760129.97/0.8259
ABPN-M6C40125.8728.9139.122.453819131.62/0.887628.27/0.773727.35/0.729325.41/0.761630.04/0.8277
ETDS-L (Ours)169.9739.0527.615.344785.331.69/0.888928.31/0.775127.37/0.730225.47/0.764330.09/0.8289
", + "bbox": [ + 80, + 146, + 888, + 577 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/c89380adc00125307cb19a762388b42e0c4d8f7ba0ed60fbed4fd63e722dab80.jpg", + "table_caption": [ + "Table 3. Ablation operation for each operator. All indicators are tested using NNAPI driver on Dimensity 8100 SoC." + ], + "table_footnote": [], + "table_body": "
ModelSizeImprovement
addconcatenateclip
ETDST21.03%28.92%0.26%
S16.74%26.61%0.86%
M8.33%34.47%0.76%
L7.29%27.64%0.50%
repeataddclip
ECBSRM4C1647.95%7.38%1.23%
M4C3239.01%11.35%-0.35%
M6C4029.92%10.24%0.54%
ABPNM4C2837.46%10.75%1.30%
M6C4027.30%10.20%0.77%
", + "bbox": [ + 109, + 628, + 436, + 792 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Ablation Studies for Global Residual Connection. Here we investigate the effect of the global residual connection. Tab. 4 shows the results of the experiments. The PSNR value is improved by 0.04dB on Set5, when adding a global residual connection composed of nearest neighbor interpolation to Plain-M6C32.", + "bbox": [ + 76, + 809, + 468, + 900 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/d4fe7d8c49f787e5b9ec916b061ece9d7ee2743c04dd742973ccb726fa2788f2.jpg", + "table_caption": [ + "Table 4. PSNR/SSIM results for different variants of ETDS-M." + ], + "table_footnote": [], + "table_body": "
VariantModificationsSet5Urban100
PSNR/SSIMPSNR/SSIM
IPlain-M6C3231.32/0.883025.10/0.7505
IIPlain-M6C32 w/ interpolation31.36/0.883325.13/0.7519
IIIETDS-M w/o Kr2b module31.36/0.883525.16/0.7526
IVETDS-M31.41/0.884325.20/0.7544
VETDS-M w/ Kb2r module31.38/0.883725.17/0.7530
VIETDS-M w/o LDS31.35/0.883725.14/0.7521
", + "bbox": [ + 504, + 608, + 890, + 705 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Ablation Studies for $K_{r}$ , $K_{r2b}$ and $K_{b2r}$ . We train $K_{r}$ , $K_{r2b}$ , and $K_{b2r}$ one after another in an incremental way. The variants are recorded as Variant III, Variant IV, and Variant V in Tab. 4. Variant IV refers to our ETDS-M. From Tab. 4, the performance of Variant II, III and IV increases sequentially, indicating that the learnability of $K_{r}$ and $K_{r2b}$ is beneficial to improve the performance. However, Variant V's performance is worse than Variant IV's, which may indicate that introducing a learnable $K_{b2r}$ could lead to a degradation in performance. The $K_{b2r}$ module connects the low-frequency constraints to the backbone branch during backpropagation which causes the backbone branch to", + "bbox": [ + 496, + 719, + 890, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "14108", + "bbox": [ + 480, + 945, + 517, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/5407a0144381de1f836b934a0c11d437bc422b2480bcd8724306eed71f24a570.jpg", + "image_caption": [ + "img_088 from Urban100" + ], + "image_footnote": [], + "bbox": [ + 81, + 90, + 328, + 281 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/af6df120cf019b57a035b052ab349219b9558bc34493f4e01b1c0b5a63eb03ef.jpg", + "image_caption": [ + "ESPCN" + ], + "image_footnote": [], + "bbox": [ + 80, + 303, + 189, + 386 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/2356df50b90919ad7cc1f7c005df684a7be3956feef236a5078686771a006c0f.jpg", + "image_caption": [ + "ESRCNN" + ], + "image_footnote": [], + "bbox": [ + 218, + 303, + 326, + 386 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/d4331471852ab6af0c9b23336e5a178699ce02dfafbb9fc79064368fb9a6ac46.jpg", + "image_caption": [ + "20.41/0.5572", + "ECBSR-M6C40", + "21.03/0.6680" + ], + "image_footnote": [], + "bbox": [ + 81, + 410, + 189, + 492 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/20bb1d1b964fd58ef7fe9ee5ea5cc5b11bdc2e91132f942d45d9257a15b135b6.jpg", + "image_caption": [ + "20.53/0.5825", + "ABPN-M6C40", + "21.12/0.6593" + ], + "image_footnote": [], + "bbox": [ + 218, + 410, + 326, + 492 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/53e638c2f2772b45d7a0ca419c8e1538e878c34773396357c0691a1b31e1f4a3.jpg", + "image_caption": [ + "Ground Truth" + ], + "image_footnote": [], + "bbox": [ + 357, + 90, + 465, + 172 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/9cdbc4dd61c2a27f601d212c7647984ec4ec03ced82d4f90c00a45ac52589fdf.jpg", + "image_caption": [ + "PSNR/SSIM", + "Bicubic" + ], + "image_footnote": [], + "bbox": [ + 357, + 196, + 465, + 279 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/ebe42bbfd98a9f73cdd84e338b692cf1969140659ab0a12391fc83a9102432c5.jpg", + "image_caption": [ + "19.17/0.4514", + "Plain-M6C32" + ], + "image_footnote": [], + "bbox": [ + 357, + 303, + 465, + 386 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/7c2c698439c5564a2df8ffdc04bee4861055814667a33e41760894a9c4298ba9.jpg", + "image_caption": [ + "21.08/0.6193", + "ETDS-L", + "21.77/0.7050" + ], + "image_footnote": [], + "bbox": [ + 357, + 410, + 465, + 492 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/86b4e7a4904148a1a049daf42d7389d007c2c6385de7ba32a55b0f944464b326.jpg", + "image_caption": [ + "Figure 5. Qualitative comparison of real-time SR models on Set5 for $\\times 4$ upscaling task.", + "Figure 6. Channel masking experiments with Plain-M6C32 model, ETDS and Variant V. In order to understand the meaning of each channel, the visualization images of some channels are shown in this figure." + ], + "image_footnote": [], + "bbox": [ + 76, + 571, + 467, + 731 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "pay extra attention to low-frequency information, thereby reducing the model's ability to extract high-frequency information.", + "bbox": [ + 75, + 809, + 467, + 853 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Ablation Studies for Dual Stream Constraint $\\mathcal{L}_{\\mathrm{DS}}$ . For ETDS-M, the PSNR value is 0.06dB higher than the one without $\\mathcal{L}_{\\mathrm{DS}}$ (Tab. 4 Variant VI), which supports the", + "bbox": [ + 75, + 854, + 468, + 900 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "benefit of the dual stream constraint $\\mathcal{L}_{\\mathrm{DS}}$", + "bbox": [ + 500, + 90, + 772, + 104 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Analysis of Dual Stream Network. We conduct the channel mask experiments [16] on ETDS-M, Plain-M6C32 and Variant V models, and then analyze how each channel contributes to the performance. From Fig. 6, the low-frequency information of ETDS-M is mainly concentrated in the last three channels (i.e., the residual branch), while the high-frequency information is distributed in the remaining channels (i.e., the backbone branch) corresponding to our design in Sec. 3.3. In addition, the extraction of the low-frequency channel of ETDS-M is more effective than the Plain-M6C32 model. This may be the reason why ETDS-M has better performance than the Plain-M6C32 model. On top of that, Variant V does better in extracting low-frequency information than ETDS-M, but worse in PSNR performance, which confirms that the learnability of $K_{b2r}$ compromises the ability to extract high-frequency information.", + "bbox": [ + 496, + 106, + 890, + 361 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.6. Limitations", + "text_level": 1, + "bbox": [ + 500, + 372, + 625, + 386 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "While our method achieves a better trade-off between performance and latency on mobile devices, it also has its limitations. Firstly, ET is only appropriate for relatively simple network architectures. More complex structures would require a more complicated ET process, which could potentially introduce an excessive number of redundant parameters. Secondly, due to its simplified structure, very deep networks still pose a challenge for ETDS, and its performance may not reach the level of its EDSR counterpart.", + "bbox": [ + 496, + 395, + 890, + 546 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 560, + 617, + 575 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "This paper has presented ETDS for mobile image superresolution via Equivalent Transformation and dual stream network construction. ET method is applied to substitute time-consuming operators, including add, repeat, clip and concatenate, with time-friendly ones (convolution and ReLU), which can alleviate the inference latency. We have developed a dual stream network, which successfully eliminated most of the redundant parameters brought by the implementation of ET. Our approach represents an innovative integration of the ET method with a dual-stream network for mobile devices. Extensive experiments have demonstrated that ETDS can outperform the state-of-the-art lightweight SR models in terms of inference latency and reconstruction quality.", + "bbox": [ + 496, + 585, + 890, + 797 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgements. This work was supported in part by \"Digital Silk Road\" Shanghai International Joint Lab of Trustworthy Intelligent Software (Grant No. 22510750100), and Shanghai Trusted Industry Internet Software Collaborative Innovation Center.", + "bbox": [ + 496, + 811, + 890, + 886 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "14109", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 174, + 106 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Namhyuk Ahn, Byungkon Kang, and Kyung-Ah Sohn. 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Computer Vision Foundation / IEEE Computer Society, 2018. 1, 2" + ], + "bbox": [ + 501, + 92, + 890, + 849 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "14111", + "bbox": [ + 480, + 945, + 517, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/Equivalent Transformation and Dual Stream Network Construction for Mobile Image Super-Resolution/dacaf17d-de1f-48bb-830c-55e8de8a8f85_model.json b/2023/Equivalent Transformation and Dual Stream Network Construction for Mobile Image Super-Resolution/dacaf17d-de1f-48bb-830c-55e8de8a8f85_model.json new file mode 100644 index 0000000000000000000000000000000000000000..c9faf9a06f8758857982f36a2d339b1b8f20d39c --- /dev/null +++ b/2023/Equivalent Transformation and Dual Stream Network Construction for Mobile Image Super-Resolution/dacaf17d-de1f-48bb-830c-55e8de8a8f85_model.json @@ -0,0 +1,2409 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.0, + 0.812, + 0.045 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.088, + 0.13, + 0.882, + 0.175 + ], + "angle": 0, + "content": "Equivalent Transformation and Dual Stream Network Construction for Mobile Image Super-Resolution" + }, + { + "type": "text", + "bbox": [ + 0.086, + 0.203, + 0.92, + 0.291 + ], + "angle": 0, + "content": "Jiahao Chao\\(^{1}\\), Zhou Zhou\\(^{1}\\), Hongfan Gao\\(^{1}\\), Jiali Gong\\(^{1}\\), Zhengfeng Yang\\(^{1*}\\), Zhenbing Zeng\\(^{2}\\), Lydia Dehbi\\(^{1}\\) \n\\(^{1}\\)East China Normal University; \n\\(^{2}\\)Chengdu Institute of Computer Applications of Chinese Academy of Sciences \n{jhchao502, zhouzhou, hfgao, gongjl}@stu.ecnu.edu.cn, zfyang@sei.ecnu.edu.cn, zbzeng@shu.edu.cn, dehbilydia@sei.ecnu.edu.cn" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.327, + 0.313, + 0.344 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.075, + 0.359, + 0.474, + 0.678 + ], + "angle": 0, + "content": "In recent years, there has been an increasing demand for real-time super-resolution networks on mobile devices. To address this issue, many lightweight super-resolution models have been proposed. However, these models still contain time-consuming components that increase inference latency, limiting their real-world applications on mobile devices. In this paper, we propose a novel model for single-image super-resolution based on Equivalent Transformation and Dual Stream network construction (ETDS). ET method is proposed to transform time-consuming operators into time-friendly operations, such as convolution and ReLU, on mobile devices. Then, a dual stream network is designed to alleviate redundant parameters resulting from the use of ET and enhance the feature extraction ability. Taking full advantage of the advance of ET and the dual stream network structure, we develop the efficient SR model ETDS for mobile devices. The experimental results demonstrate that our ETDS achieves superior inference speed and reconstruction quality compared to previous lightweight SR methods on mobile devices. The code is available at https://github.com/ECNUSR/ETDS." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.688, + 0.21, + 0.705 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.714, + 0.47, + 0.85 + ], + "angle": 0, + "content": "Image super-resolution (SR) aims to reconstruct high-resolution images (HR) from low-resolution images (LR). Over the years, numerous deep-learning methods have been proposed [3, 6, 17, 18, 33, 35, 36] with good fidelity and perceptual quality. However, these methods are not efficient and lightweight when it comes to mobile platforms where SR application becomes increasingly ubiquitous. Thus, it is essential to devise an approach that takes into account the restrictions of mobile platforms." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.85, + 0.47, + 0.88 + ], + "angle": 0, + "content": "Generally, mobile platforms have limitations such as a restricted amount of RAM, lower memory bandwidth," + }, + { + "type": "image", + "bbox": [ + 0.51, + 0.348, + 0.859, + 0.527 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.538, + 0.895, + 0.608 + ], + "angle": 0, + "content": "Figure 1. Comparisons of PSNR performance and the inference latency of different models. The inference latency is tested on Dimensity 8100 SoC, NNAPI driver, INT8 precision and upsampling from \\(360 \\times 640\\) to \\(1080 \\times 1920\\). PSNR indexes are evaluated on Set5 [2]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.613, + 0.895, + 0.853 + ], + "angle": 0, + "content": "lower computational speed and insufficient support for many common deep learning layers and operators. To take the particularities into consideration, the recently proposed SR models [27, 34] designed for mobile devices adopt a neat topology [34] as the base model to ensure low inference latency. ABPN [8] further boosted efficiency by employing the repeat operator instead of the time-consuming nearest neighbor interpolation. Nevertheless, in-depth investigation reveals that some time-consuming components in current mobile SR models, such as the global residual connection and clip operator, are indispensable for overall reconstruction quality. Therefore, to accelerate the inference on mobile devices and achieve a competitive reconstruction quality and inference latency, it is necessary to seek time-friendly surrogates for these time-consuming operators." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.856, + 0.895, + 0.903 + ], + "angle": 0, + "content": "To this end, we propose Equivalent Transformation (ET), a method that speeds up the model by substituting time-consuming operators with time-friendly ones without im" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.887, + 0.222, + 0.9 + ], + "angle": 0, + "content": "*Corresponding author." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "14102" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.288 + ], + "angle": 0, + "content": "pairing reconstruction quality. As shown in Fig. 1, the proposed ET can be directly applied to existing models (e.g., ECBSR [34] and ABPN [8]) and reduce inference latency without retraining. However, ET introduces some redundant and unlearnable parameters. To fully utilize these parameters, we design the dual stream network that makes the redundant parameters partially learnable, to boost the feature extraction ability. Finally, we propose a mobile image SR model named ETDS that employs the dual stream network in the training stage and transforms it into an equivalent plain network by ET in the inference stage. As shown in Fig. 1, our ETDS not only achieves high reconstruction quality but also maintains low inference speed." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.289, + 0.472, + 0.318 + ], + "angle": 0, + "content": "In summary, the main contributions of this paper are as follows:" + }, + { + "type": "text", + "bbox": [ + 0.089, + 0.324, + 0.468, + 0.383 + ], + "angle": 0, + "content": "1) We propose ET, a method that can transform time-consuming operators and speed up the inference without impairing reconstruction quality. It can be applied to existing models to accelerate the inference." + }, + { + "type": "text", + "bbox": [ + 0.088, + 0.387, + 0.468, + 0.432 + ], + "angle": 0, + "content": "2) We design a dual stream network to alleviate the redundancy yielded from ET by making redundant parameters partially learnable." + }, + { + "type": "text", + "bbox": [ + 0.088, + 0.435, + 0.468, + 0.553 + ], + "angle": 0, + "content": "3) We propose an efficient and lightweight network named ETDS for real-time SR on mobile devices based on ET and dual stream networks. Experiments demonstrate that state-of-the-art models equipped with ET have at most \\(80\\%\\) improvement in inference latency and ETDS achieves \\(34\\%\\) inference latency improvement and 0.42dB PSNR performance improvement." + }, + { + "type": "list", + "bbox": [ + 0.088, + 0.324, + 0.468, + 0.553 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.572, + 0.22, + 0.587 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.598, + 0.47, + 0.825 + ], + "angle": 0, + "content": "Due to the rapid development of convolutional neural networks (CNN), CNN-based methods [6, 18, 24, 35, 36] have become mainstream methods for SR tasks. SRCNN [6] pioneered the application of convolutional neural networks on the SR task, surpassing the performance of traditional methods. In EDSR [18], a very deep network was utilized and the batch normalization layers in the residual block were removed. SwinIR [17] first attempted to apply the Swin-Transformer [20] on the SR task, showing the potential of Transformer-based networks [26]. To enlarge the receptive field, the hybrid attention block (HAB) was proposed by HAT [3], which achieved state-of-the-art performance. However, these models have high requirements for memory and computational resources which are not easily attainable in real-world applications." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.825, + 0.47, + 0.903 + ], + "angle": 0, + "content": "To realize lightweight SR for GPU servers, many approaches tried to reduce the number of parameters and FLOPs. CARN [1] attempted to apply group convolutions. IMDN [10] employed a progressive refinement module to improve the information extraction ability and reduced the" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.242 + ], + "angle": 0, + "content": "number of layers and channels. For further improvement in the efficiency of feature extraction, in RFDN [19], \\( 1 \\times 1 \\) convolutions were utilized to replace the \\( 3 \\times 3 \\) convolutions on the split channel of the IMDB [10] module. RLFN [15] replaced the progressive refinement module with a simpler residual module, which further improved the running speed and achieved great performance. MemSR [30] optimized the network in terms of memory by removing the residual structure in the model and proposed a novel knowledge distillation method to improve the performance." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.244, + 0.893, + 0.606 + ], + "angle": 0, + "content": "Due to the particularity of the mobile platforms, most models for GPU servers are not directly applicable to mobile devices whose applications require to be carried out in a timely fashion with restricted computational resources. To solve this problem, current methods mainly optimized the network from three aspects, i.e., neat network topology, computation reduction and operator substitution. ECBSR [34], which proposed an Edge-oriented Convolutional Block (ECB) to achieve better performance, used relatively neat topology for low inference latency on mobile devices and introduced reparameterization techniques to achieve computation reduction for SR task. Following [34], RepSR [27] optimized the performance and training efficiency of the reparameterization module in ECBSR to achieve further computation reduction. ABPN [8] first attempted to apply operator substitution and used the faster repeat operator instead of nearest neighbor interpolation in global residual connections. Inspired by the reparameterization technique, we propose ET, which substitutes more types of operators to achieve low inference latency. Our proposed ETDS optimized the network from all three aspects, where ET optimized the network by achieving operator substitution and computation reduction while the dual stream network adopted a neat topology." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.62, + 0.637, + 0.638 + ], + "angle": 0, + "content": "3. Methodology" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.646, + 0.892, + 0.768 + ], + "angle": 0, + "content": "In this section, we examine the current mobile superresolution models in Sec. 3.1, and then propose a novel method, Equivalent Transformation (ET), which substitutes time-consuming operators with time-friendly ones in 3.2. However, applying ET comes at the cost of introducing redundant parameters. To address this, we carefully design a dual stream network that alleviates redundancy and enhances feature extraction ability in Sec. 3.3." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.777, + 0.836, + 0.794 + ], + "angle": 0, + "content": "3.1. Analysis of Current Mobile SR Models" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.801, + 0.892, + 0.878 + ], + "angle": 0, + "content": "In order to design more efficient super-resolution models for mobile devices, we analyze the speed bottleneck of current mobile SR models on two of the most popular mobile phone \\(\\mathrm{SoCs}^1\\). As shown in Tab. 1, convolution and ReLU operations have lower inference latency than most other op" + }, + { + "type": "page_footnote", + "bbox": [ + 0.518, + 0.888, + 0.89, + 0.9 + ], + "angle": 0, + "content": "1www counterpointresearch.com/global-smartphone-ap-market-share/" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "14103" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.09, + 0.47, + 0.16 + ], + "angle": 0, + "content": "Table 1. Average inference latency (ms) of common components in mobile SR models. The average inference latency of all components is tested on SR models with a channel size of 32, an input of size \\(360 \\times 640\\) and a scale factor of 3. For operators in the same type, the results of higher latency are marked in bold." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.164, + 0.466, + 0.393 + ], + "angle": 0, + "content": "
TypeOperatorLatency (ms)
Dimensity 8100Snapdragon 870Snapdragon 865
Convolution1 × 1 Convolution2.244
3 × 3 Convolution10.41821
Transposed Convolution7.379
ActivationReLU0.060.60.6
PReLU2.264.83.8
LeakyReLU2.265.64.2
Sigmoid0.120.60.8
Tanh0.30.81
InterpolationNearest neighbor262427
Bilinear676568
OthersAdd6.534
Concatenate22.867
Multiply6.534
Repeat16.31914
Clip6.99194
PixelShuffle4.234
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.407, + 0.468, + 0.512 + ], + "angle": 0, + "content": "erations, and PixelShuffle [23] is more efficient than transposed convolution, which indicates PixelShuffle and ReLU are better choices for mobile platforms. Hereafter, plain network refers to a network that only contains time-friendly operators (i.e., convolution, ReLU activation functions and PixelShuffle), which has low inference latency on mobile devices." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.514, + 0.468, + 0.544 + ], + "angle": 0, + "content": "To transform current mobile models into plain models, we may encounter the following challenges:" + }, + { + "type": "text", + "bbox": [ + 0.088, + 0.546, + 0.47, + 0.62 + ], + "angle": 0, + "content": "1) To avoid the rescaling problem in the INT8 quantization models, it is necessary to add the clip operator at the end of the model. However, the clip operator is also time-consuming (see Tab. 1), which requires a more efficient and equivalent alternative." + }, + { + "type": "text", + "bbox": [ + 0.088, + 0.623, + 0.47, + 0.697 + ], + "angle": 0, + "content": "2) To compensate for the PSNR performance drop brought by the removal of global residual connections, it is necessary to find an equivalent way to transform the global residual connection into an efficient operator." + }, + { + "type": "list", + "bbox": [ + 0.088, + 0.546, + 0.47, + 0.697 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.699, + 0.468, + 0.76 + ], + "angle": 0, + "content": "To tackle these challenges, we propose ET, which substitutes some time-consuming operators with time-friendly ones without reducing the reconstruction quality, thereby improving the running speed." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.771, + 0.322, + 0.787 + ], + "angle": 0, + "content": "3.2. Equivalent Transformation" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.795, + 0.47, + 0.901 + ], + "angle": 0, + "content": "Formal Definitions. A convolution operation is formulated as \\( z = W \\otimes x + b \\), where \\( x \\in \\mathbb{R}^{c_i \\times h \\times w} \\) and \\( z \\in \\mathbb{R}^{c_o \\times h \\times w} \\) are the input and output tensors respectively, \\( W \\in \\mathbb{R}^{c_o \\times k \\times k \\times c_i} \\), \\( b \\in \\mathbb{R}^{c_o} \\) are the kernel and the bias of the convolution, and \\( k \\) is the kernel size, \\( c_i, c_o \\) are the numbers of the input and output channels, and \\( h, w \\) are the input height and width. \\( I \\) is the identity kernel of the convolution" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.092, + 0.882, + 0.107 + ], + "angle": 0, + "content": "operation, and \\( O \\) is the kernel of zero elements, satisfying" + }, + { + "type": "equation", + "bbox": [ + 0.556, + 0.116, + 0.892, + 0.133 + ], + "angle": 0, + "content": "\\[\nI \\otimes x = x, \\quad O \\otimes x = 0, \\forall x \\in \\mathbb {R} ^ {c _ {i} \\times h \\times w}. \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.144, + 0.892, + 0.265 + ], + "angle": 0, + "content": "For input features and convolution kernels, the concatenation operation requires all but the concatenated dimension to be consistent. The channel dimension concatenation operation of feature vectors \\( x \\) and \\( y \\) is defined as \\( \\begin{bmatrix} x \\\\ y \\end{bmatrix} \\). The concatenation operation of the convolution kernels \\( W_{h,1} \\) and \\( W_{h,2} \\) in the horizontal direction (i.e., input-dimension concatenation) is defined as \\( [W_{h,1}, W_{h,2}] \\), which satisfies" + }, + { + "type": "equation", + "bbox": [ + 0.541, + 0.273, + 0.892, + 0.307 + ], + "angle": 0, + "content": "\\[\n\\left[ W _ {h, 1}, W _ {h, 2} \\right] \\otimes \\left[ \\begin{array}{l} x \\\\ y \\end{array} \\right] = W _ {h, 1} \\otimes x + W _ {h, 2} \\otimes y. \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.315, + 0.892, + 0.386 + ], + "angle": 0, + "content": "Likewise, the concatenation operation of the convolution kernels \\( W_{v,1} \\) and \\( W_{v,2} \\) in the vertical direction, i.e., output-dimension concatenation is defined as \\( \\begin{bmatrix} W_{v,1} \\\\ W_{v,2} \\end{bmatrix} \\), which satisfies" + }, + { + "type": "equation", + "bbox": [ + 0.601, + 0.386, + 0.891, + 0.42 + ], + "angle": 0, + "content": "\\[\n\\left[ \\begin{array}{l} W _ {v, 1} \\\\ W _ {v, 2} \\end{array} \\right] \\otimes x = \\left[ \\begin{array}{l} W _ {v, 1} \\otimes x \\\\ W _ {v, 2} \\otimes x \\end{array} \\right]. \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.423, + 0.766, + 0.438 + ], + "angle": 0, + "content": "More details will be found in Appendix." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.438, + 0.892, + 0.528 + ], + "angle": 0, + "content": "ET for Repeat Operator. Given an input tensor \\( x \\in \\mathbb{R}^{c \\times h \\times w} \\), the repeat operator \\( \\text{repeat}(x, n) \\) constructs a new tensor \\( z \\in \\mathbb{R}^{(nc) \\times h \\times w} \\) by replicating the input \\( n \\) times along the channel dimension. This operation can be expressed as a convolution layer. Precisely, Eq. (1) and (3) yield" + }, + { + "type": "equation", + "bbox": [ + 0.545, + 0.537, + 0.891, + 0.614 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\operatorname {r e p e a t} (x, n) = \\left[ \\begin{array}{c} x \\\\ \\vdots \\\\ x \\end{array} \\right] = \\left[ \\begin{array}{c} I \\otimes x \\\\ \\vdots \\\\ I \\otimes x \\end{array} \\right] = \\left[ \\begin{array}{c} I \\\\ \\vdots \\\\ I \\end{array} \\right] \\otimes x \\tag {4} \\\\ = \\operatorname {r e p e a t} (I, n) \\otimes x, \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.624, + 0.892, + 0.683 + ], + "angle": 0, + "content": "where \\( \\text{repeat}(I, n) \\) is a constant. Thus, the repeat operator is equivalently transformed into a convolution layer, whose kernel and bias are \\( \\text{repeat}(I, n) \\) and a zero vector, respectively." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.684, + 0.892, + 0.745 + ], + "angle": 0, + "content": "ET for Add Operator. The add operator refers to the element-wise addition operation of two feature vectors and is an indispensable part of residual connections, i.e., \\( z = x + y \\). From Eq. (1) and (2), we have:" + }, + { + "type": "equation", + "bbox": [ + 0.558, + 0.754, + 0.892, + 0.787 + ], + "angle": 0, + "content": "\\[\nx + y = I \\otimes x + I \\otimes y = [ I, I ] \\otimes \\left[ \\begin{array}{l} x \\\\ y \\end{array} \\right]. \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.795, + 0.892, + 0.87 + ], + "angle": 0, + "content": "Thus, the add operator is equivalently transformed into a convolution layer with a concatenate operator, whose kernel and bias are \\([I, I]\\) and a zero vector, respectively. Notably, this proposed convolution layer can be eliminated later by reparameterization techniques." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.871, + 0.892, + 0.901 + ], + "angle": 0, + "content": "ET for Concatenate Operator. In our model, the concatenate operator always follows the convolution layers." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "14104" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.47, + 0.138 + ], + "angle": 0, + "content": "We integrate the convolution-concatenate structure, i.e., the concatenate operator and its preceding convolution layer, which can be simplified with Eq. (2) and (3) as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.091, + 0.145, + 0.47, + 0.181 + ], + "angle": 0, + "content": "\\[\nz = \\left[ \\begin{array}{c} W _ {1} \\otimes x + b _ {1} \\\\ W _ {2} \\otimes y + b _ {2} \\end{array} \\right] = \\left[ \\begin{array}{c c} W _ {1} & O \\\\ O & W _ {2} \\end{array} \\right] \\otimes \\left[ \\begin{array}{c} x \\\\ y \\end{array} \\right] + \\left[ \\begin{array}{c} b _ {1} \\\\ b _ {2} \\end{array} \\right]. \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.187, + 0.469, + 0.232 + ], + "angle": 0, + "content": "Following Eq. (6), the convolution-concatenate structure is transformed into a concatenate-convolution structure, with the kernel and bias as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.182, + 0.238, + 0.469, + 0.273 + ], + "angle": 0, + "content": "\\[\n\\left[ \\begin{array}{c c} W _ {1} & O \\\\ O & W _ {2} \\end{array} \\right] \\quad \\text {a n d} \\quad \\left[ \\begin{array}{l} b _ {1} \\\\ b _ {2} \\end{array} \\right]. \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.28, + 0.469, + 0.311 + ], + "angle": 0, + "content": "In particular, when the residual branch does not have a convolution layer, it can be expressed as:" + }, + { + "type": "equation", + "bbox": [ + 0.117, + 0.318, + 0.469, + 0.354 + ], + "angle": 0, + "content": "\\[\nz = \\left[ \\begin{array}{c} W \\otimes x + b \\\\ y \\end{array} \\right] = \\left[ \\begin{array}{c c} W & O \\\\ O & I \\end{array} \\right] \\otimes \\left[ \\begin{array}{c} x \\\\ y \\end{array} \\right] + \\left[ \\begin{array}{c} b \\\\ 0 \\end{array} \\right]. \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.361, + 0.397, + 0.376 + ], + "angle": 0, + "content": "When \\(x = y\\), Eq. (8) can be further rewritten as:" + }, + { + "type": "equation", + "bbox": [ + 0.141, + 0.383, + 0.469, + 0.419 + ], + "angle": 0, + "content": "\\[\nz = \\left[ \\begin{array}{c} W \\otimes x + b \\\\ x \\end{array} \\right] = \\left[ \\begin{array}{c} W \\\\ I \\end{array} \\right] \\otimes x + \\left[ \\begin{array}{c} b \\\\ 0 \\end{array} \\right], \\tag {9}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.426, + 0.469, + 0.47 + ], + "angle": 0, + "content": "where the kernel is \\(\\left[ \\begin{array}{l}W\\\\ I \\end{array} \\right]\\) and thus the concatenate operator is eliminated." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.473, + 0.469, + 0.499 + ], + "angle": 0, + "content": "ET for Clip Operator. The clip operator is expressed as:" + }, + { + "type": "equation", + "bbox": [ + 0.152, + 0.499, + 0.469, + 0.547 + ], + "angle": 0, + "content": "\\[\n\\operatorname {c l i p} (x) = \\left\\{ \\begin{array}{l l} 0, & x \\leq 0, \\\\ x, & 0 < x \\leq 2 5 5, \\\\ 2 5 5, & x > 2 5 5, \\end{array} \\right. \\tag {10}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.551, + 0.469, + 0.641 + ], + "angle": 0, + "content": "which avoids the loss of precision and subsequent additional inverse scaling operations caused by mismatched normalization of the INT8 quantization model [12]. Nevertheless, as shown in Tab. 1, the clip operator is extremely time-consuming on many mobile SoCs, so it is of great necessity to find a time-friendly substitution for the clip operator." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.642, + 0.468, + 0.671 + ], + "angle": 0, + "content": "To equivalently transform the clip operator with ReLU, we reformulate clip operator as:" + }, + { + "type": "equation", + "bbox": [ + 0.106, + 0.681, + 0.469, + 0.699 + ], + "angle": 0, + "content": "\\[\n\\operatorname {c l i p} (x) = \\operatorname {R e L U} (- \\operatorname {R e L U} (- x + 2 5 5) + 2 5 5). \\tag {11}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.708, + 0.402, + 0.722 + ], + "angle": 0, + "content": "To speed up this process, we further rewrite it as:" + }, + { + "type": "equation", + "bbox": [ + 0.148, + 0.731, + 0.469, + 0.773 + ], + "angle": 0, + "content": "\\[\n\\left\\{ \\begin{array}{l l} y = & \\operatorname {R e L U} (- I \\otimes x + 2 5 5), \\\\ c l i p (x) = & \\operatorname {R e L U} (- I \\otimes y + 2 5 5). \\end{array} \\right. \\tag {12}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.78, + 0.469, + 0.855 + ], + "angle": 0, + "content": "Using Eq. (12), the clip operator is transformed into two convolutions with ReLU, whose kernels are \\(-I\\) and bias is a vector with all elements equal to 255. Remark that the first convolution layer in Eq. (12) is eliminated by reparameterization techniques [5]." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.856, + 0.469, + 0.901 + ], + "angle": 0, + "content": "ET for Equivalent Plain Model Conversion. As depicted in Fig. 2, the model is converted into an equivalent plain model by ET as following:" + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.091, + 0.889, + 0.32 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.326, + 0.892, + 0.381 + ], + "angle": 0, + "content": "Figure 2. Illustration of converting the general model into the equivalent plain model using ET. The beige convolution indicates that the convolution kernel is assigned a specific value. Rep refers to the reparameterization technique." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.394, + 0.892, + 0.439 + ], + "angle": 0, + "content": "- The repeat operator and the add operator are converted into a single convolution and a concatenate operator respectively (see Step 1 and Step 2)." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.441, + 0.892, + 0.516 + ], + "angle": 0, + "content": "- The concatenate operator with the preceding convolutions from two branches is converted into a convolution. Notably, the global residual connection does not contain negative values, so the ReLU function is omitted (see Step 3)." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.518, + 0.892, + 0.563 + ], + "angle": 0, + "content": "- The two convolutions introduced by previous steps are converted into a convolution using reparameterization techniques (see Step 4)." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.565, + 0.892, + 0.655 + ], + "angle": 0, + "content": "- The convolution-concatenate structure is converted into a concatenate-convolution one, thus the concatenate operator is converted and moves forward till it reaches the skip connection starting point, that is, \\( x \\) equals \\( y \\). In this situation, the concatenate operator is further eliminated (see Step 5 and Step 6)." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.656, + 0.891, + 0.686 + ], + "angle": 0, + "content": "- The clip operator is converted into the convolution (see Step 7)." + }, + { + "type": "list", + "bbox": [ + 0.518, + 0.394, + 0.892, + 0.686 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.699, + 0.892, + 0.805 + ], + "angle": 0, + "content": "Remark 1 Although \\( ET \\) speeds up inference by transforming time-consuming operators into time-friendly ones, it introduces some redundant parameters. For instance, in the transformed convolution kernel \\( \\mathrm{diag}(W, I) \\) derived from Eq. (8). All learnable parameters appear in \\( W \\). If the redundant parameters are effectively utilized, better reconstruction performance can be achieved." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.817, + 0.704, + 0.832 + ], + "angle": 0, + "content": "3.3. Dual Stream Network" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.84, + 0.892, + 0.901 + ], + "angle": 0, + "content": "To alleviate the side effects of the redundant parameters of ET, we design a dual stream network where the two branches learn the low-frequency and high-frequency contents of the image separately and utilize the parameters to" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "14105" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.083, + 0.09, + 0.885, + 0.226 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.083, + 0.234, + 0.891, + 0.33 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.345, + 0.893, + 0.374 + ], + "angle": 0, + "content": "Figure 3. Network architecture of ETDS during training and inference stages. The residual branch for extracting low-frequency contents only contains a few parameters, and most of the parameters are used to extract high-frequency contents." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.393, + 0.47, + 0.542 + ], + "angle": 0, + "content": "the fullest. The transformed convolution kernel in Eq. (8) is \\(\\left[ \\begin{array}{cc}K_b & K_{r2b}\\\\ K_{b2r} & K_r \\end{array} \\right]\\), where \\(K_{b}\\) and \\(K_{r}\\) denote the modules that constitute the backbone branch and residual branch, respectively. \\(K_{r2b}\\) is the module that transfers information from the residual branch to the backbone branch, and \\(K_{b2r}\\) transfers information reversely. The residual branch consisting of \\(K_{r}\\) and the backbone branch consisting of \\(K_{b}\\) extract low-frequency and high-frequency information respectively." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.543, + 0.47, + 0.708 + ], + "angle": 0, + "content": "Initially, \\( K_{r} \\), \\( K_{r2b} \\) and \\( K_{b2r} \\) are not learnable. Furthermore, we have analyzed the possible impacts of making them learnable on the reconstruction quality and found that when \\( K_{r} \\) and \\( K_{r2b} \\) are learnable, they can extract low-frequency information more effectively and transfer more residual information to the backbone branch, respectively. However, when \\( K_{b2r} \\) is learnable, the backbone branch may take less important low-frequency information into consideration, which reduces the number of parameters for extracting high-frequency components, and potentially compromising the performance." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.709, + 0.47, + 0.814 + ], + "angle": 0, + "content": "As shown in Fig. 3, \\( K_{r} \\) and \\( K_{r2b} \\) in our dual stream network contain learnable parameters, while parameters in \\( K_{b2r} \\) remain fixed. In the training phase, we encourage the residual branch to learn as many low-frequency contents as possible, that is, to minimize the \\( L_{1} \\) distance between the output of the residual branch \\( (I_{LF}) \\) and the ground truth \\( (I_{GT}) \\):" + }, + { + "type": "equation", + "bbox": [ + 0.192, + 0.814, + 0.469, + 0.83 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {L F} = \\left\\| I _ {G T} - I _ {L F} \\right\\| _ {1}. \\tag {13}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.833, + 0.469, + 0.879 + ], + "angle": 0, + "content": "The backbone branch learns high-frequency contents, and its output \\((I_{HF})\\) compensates for the gap between \\(I_{GT}\\) and \\(I_{LF}\\):" + }, + { + "type": "equation", + "bbox": [ + 0.167, + 0.886, + 0.469, + 0.902 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {H F} = \\left\\| I _ {G T} - I _ {L F} - I _ {H F} \\right\\| _ {1}. \\tag {14}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.393, + 0.892, + 0.421 + ], + "angle": 0, + "content": "To train the dual stream network, we use the overall loss function:" + }, + { + "type": "equation", + "bbox": [ + 0.607, + 0.423, + 0.891, + 0.438 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {D S} = \\mathcal {L} _ {H F} + \\alpha \\times \\mathcal {L} _ {L F}, \\tag {15}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.445, + 0.892, + 0.52 + ], + "angle": 0, + "content": "which drives more parameters to extract high-frequency contents to improve the overall performance. In the inference stage, as shown in Fig. 3, the dual stream network can be equivalently transformed into a plain network, which ensures low inference latency." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.534, + 0.634, + 0.551 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.559, + 0.698, + 0.573 + ], + "angle": 0, + "content": "4.1. Datasets and Metrics" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.581, + 0.892, + 0.673 + ], + "angle": 0, + "content": "Our model ETDS is trained on DIV2K dataset [25] with 800 training images. The performance is evaluated on 5 benchmark datasets (i.e., Set5 [2], Set14 [32], BSDS100 [21], Urban100 [9] and DIV2K100 [25]). PSNR and SSIM [29] are used to evaluate the reconstruction quality and calculated on the Y channel in the YCbCr space." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.682, + 0.718, + 0.698 + ], + "angle": 0, + "content": "4.2. Implementation Details" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.704, + 0.893, + 0.901 + ], + "angle": 0, + "content": "ETDS is implemented on PyTorch-based [22] BasicSR [28] framework and trained on an NVIDIA 2080Ti GPU. In the training phase, 32 patches of \\(64 \\times 64\\) LR image are used as input. Random rotation, horizontal flipping, and channel shuffle are applied for data augmentation. We train our model by the ADAM [14] optimizer with \\(\\beta_{1} = 0.9\\), \\(\\beta_{2} = 0.999\\), and \\(\\epsilon = 10^{-8}\\). We set \\(\\mathcal{L}_{\\mathrm{DS}}\\) as the loss function with \\(\\alpha = 0.5\\). In accordance with previous works, our model is trained for \\(1600k\\) iterations with a learning rate of \\(5e^{-4}\\). For the first \\(100k\\) iterations, \\(K_{r}\\) and \\(K_{r2b}\\) are initialized by setting \\(K_{r} = I\\) and \\(K_{r2b} = O\\). In the testing phase, we test the inference latency on three SoCs (i.e., Dimensity 8100, Snapdragon 888, and Snapdragon 8 Gen 1) with the" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "14106" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.09, + 0.344, + 0.245 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.219, + 0.248, + 0.237, + 0.26 + ], + "angle": 0, + "content": "(a)" + }, + { + "type": "image", + "bbox": [ + 0.352, + 0.089, + 0.617, + 0.245 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.494, + 0.247, + 0.512, + 0.259 + ], + "angle": 0, + "content": "(b)" + }, + { + "type": "image", + "bbox": [ + 0.629, + 0.09, + 0.891, + 0.246 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.775, + 0.248, + 0.792, + 0.26 + ], + "angle": 0, + "content": "(c)" + }, + { + "type": "image_caption", + "bbox": [ + 0.075, + 0.263, + 0.894, + 0.304 + ], + "angle": 0, + "content": "Figure 4. The effect of the numbers of channels and layers on inference latency of the plain model. (a) shows the inference latency with the number of channels between 4 and 24. (b) shows the inference latency with the number of channels between 4 and 64, divisible by 4. (c) shows the inference latency with the number of layers between 1 and 10." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.317, + 0.47, + 0.362 + ], + "angle": 0, + "content": "AI Benchmark application [11, 13]. All inference latencies and multiply-accumulate operations (MACs) are tested with inputs of \\(360 \\times 640\\)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.373, + 0.429, + 0.388 + ], + "angle": 0, + "content": "4.3. Hardware-Friendly Number of Channels" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.397, + 0.47, + 0.518 + ], + "angle": 0, + "content": "As shown in Fig. 4, the numbers of channels and layers have a significant impact on the model's efficiency. Observing Fig. 4 (a)(b), we can see that the models have lower inference latency on mobile devices when the number of channels is a multiple of 4, due to the processing unit alignment [31], the memory alignment, and other hardware optimizations [4]. Fig. 4 (c) supports that the inference latency is proportional to the number of layers." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.518, + 0.47, + 0.624 + ], + "angle": 0, + "content": "As a result, for a lower inference latency, ETDS is designed with 16, 32, and 48 channels and the number of layers in the model is designed for balancing the performance and inference latency. Also, for the equivalently transformed models (e.g., \\(\\mathrm{ECBSR + ET}\\) and \\(\\mathrm{ABPN + ET}\\)), extra channels are added to ensure that the number of channels is a multiple of 4." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.635, + 0.362, + 0.65 + ], + "angle": 0, + "content": "4.4. Comparisons to Previous Works" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.659, + 0.469, + 0.779 + ], + "angle": 0, + "content": "We compare our ETDS with representative real-time SR models on mobile devices, including Bicubic, ESPCN [23], FSRCNN [7], ABPN [8], and ECBSR [34]. Since ESPCN, FSRCNN, and ECBSR only process on a single channel of the input image, some preprocessing and postprocessing, such as color space conversion and upsampling of the other two channels are omitted. For a fair comparison, these models are retrained in the RGB color space." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.78, + 0.469, + 0.885 + ], + "angle": 0, + "content": "We train four different sizes of our model, denoted as ETDS-T, ETDS-S, ETDS-M and ETDS-L for different computational use cases, with channels 16, 32, 32 and 48, and layers 5, 4, 6, and 7, respectively. The performance comparison is summarized in Tab. 2. In addition to PSNR/SSIM indexes, we also list the number of parameters and MACs for a more comprehensive comparison." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.886, + 0.469, + 0.901 + ], + "angle": 0, + "content": "Quantitative Results. The quantitative comparison is" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.317, + 0.892, + 0.557 + ], + "angle": 0, + "content": "presented in Tab. 2. From Tab. 2, our model achieves not only lower inference latency than other models in most cases but also higher PSNR/SSIM indexes. For instance, as shown in Tab. 2 (latency column i), our ETDS-S runs \\(1.2\\mathrm{ms}\\) faster than ECBSR-M4C16 on the \\(\\times 3\\) task, and its PSNR index on the Urban100 dataset is \\(0.29\\mathrm{dB}\\) higher. ETDS-L's inference latency on the \\(\\times 3\\) task is \\(3.5\\mathrm{ms}\\) faster than the ABPN-M6C40's, and PSNR on Set5. Notably, although our model consists of slightly more parameters and MACs, it is still faster than the state-of-the-art models. This phenomenon occurs due to two-fold aspects. 1). Under different contexts, the same operations may have different inference latency. 2). Some operations are not measured in parameters and MACs metrics. For instance, ReLU does not influence parameters and concatenation does not influence MACs." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.56, + 0.892, + 0.665 + ], + "angle": 0, + "content": "Qualitative Results. The qualitative comparison results are depicted in Fig. 5. We can see that the texture of the wall in thimagese images generated by ESPCN [23] and FSRCNN [7] is blurred, and images generated by ECBSR-M6C40 [34] and ABPN-M6C40 [8] are slightly distorted. Obviously, our ETDS-T produces the least distorted and blurred images with the best PSNR/SSIM results." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.679, + 0.665, + 0.694 + ], + "angle": 0, + "content": "4.5. Ablation Studies" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.704, + 0.891, + 0.764 + ], + "angle": 0, + "content": "In this section, we propose a series of ablation studies on the design of the proposed ETDS. All the ablation experiments are conducted on the \\(\\times 4\\) task. We report PSNR values on the Y channel in the YCbCr space." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Ablation Studies for Equivalent Transformation. We validate the effectiveness of ET through a series of ablation studies. Additionally, we apply ET to both ECBSR and ABPN to further demonstrate its effectiveness. Note that ETDS does not have a repeat operator and we do not apply ET for the concatenate operator for ECBSR and ABPN because the improvement on the NNAPI driver is insignificant. Our results in Tab. Tab. 3 show that applying ET to these operators results in reduced latency." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "14107" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.089, + 0.892, + 0.146 + ], + "angle": 0, + "content": "Table 2. Performance comparison of different SR models on five benchmark datasets. PSNR/SSIM on the Y channel is reported on each dataset. Inference latency i, ii, iii and iv denotes the inference latency of the models using NNAPI driver on Dimensity 8100 SoC, MediaTek Neuron driver on Dimensity 8100 SoC, Qualcomm QNN GPU driver on Snapdragon 888 SoC, and NNAPI on Snapdragon 8 Gen 1 SoC respectively." + }, + { + "type": "table", + "bbox": [ + 0.081, + 0.147, + 0.89, + 0.578 + ], + "angle": 0, + "content": "
ScaleModelParams (K)MACs (G)Latency (ms)Set5Set14B100Urban100DIV2K100
iiiiiiivPSNR/SSIMPSNR/SSIMPSNR/SSIMPSNR/SSIMPSNR/SSIM
×2Bicubic******33.95/0.933430.54/0.875129.74/0.850327.07/0.845632.67/0.9078
ESPCN26.806.156.304.8391-36.87/0.955932.62/0.908631.40/0.889829.61/0.897334.78/0.9347
ETDS-T (Ours)13.943.194.853.81125-37.18/0.957832.76/0.910331.62/0.893030.10/0.905835.09/0.9375
FSRCNN24.6815.0510.45.8941456237.00/0.956832.68/0.909431.51/0.891329.92/0.902234.97/0.9363
ECBSR-M4C1611.552.646.154.5718931.637.18/0.957732.79/0.910531.61/0.892830.18/0.906435.10/0.9375
ETDS-S (Ours)41.519.528.065.77169-37.38/0.958732.96/0.912431.77/0.895130.62/0.912135.36/0.9396
ECBSR-M4C3241.529.539.706.6437231.437.39/0.958733.03/0.912631.79/0.895330.69/0.912835.39/0.9398
ABPN-M4C2833.467.6710.06.6620728.537.36/0.958532.96/0.912131.75/0.894930.55/0.911135.31/0.9392
ETDS-M (Ours)60.0113.7710.26.73288-37.54/0.959333.09/0.913331.86/0.896330.87/0.914935.50/0.9406
ECBSR-M6C4092.3721.2218.110.965346.237.61/0.959633.18/0.913931.94/0.897231.09/0.917435.61/0.9415
ABPN-M6C4093.4021.4518.711.243531.937.58/0.959433.16/0.91431.92/0.897131.04/0.916935.59/0.9414
ETDS-L (Ours)152.1834.9720.612.1469-37.64/0.959733.24/0.914531.98/0.897731.22/0.918835.69/0.9421
×3Bicubic******30.61/0.871927.79/0.781127.31/0.745324.58/0.739629.80/0.8341
ESPCN31.137.149.798.381104432.85/0.911529.41/0.823628.40/0.787626.22/0.800231.24/0.8670
ETDS-T (Ours)16.923.868.645.3614049.233.14/0.916029.53/0.827428.54/0.792026.48/0.811131.43/0.8713
FSRCNN24.6830.7313.77.32456135033.01/0.914529.52/0.826428.50/0.790326.40/0.807431.38/0.8699
ECBSR-M4C1613.723.1416.211.021669.433.07/0.914929.53/0.826928.57/0.792126.61/0.813631.44/0.8712
ETDS-S (Ours)46.7910.7312.27.7318549.233.49/0.919429.76 0.831428.71/0.796126.90/0.822131.69/0.8756
ECBSR-M4C3245.8510.5219.713.135469.233.56/0.920529.78/0.831928.73/0.796526.98/0.823931.73/0.8761
ABPN-M4C2842.549.7620.513.827562.833.53/0.920029.78/0.831728.72/0.796626.94/0.823231.71/0.8758
ETDS-M (Ours)65.2914.9814.48.762604933.65/0.921429.86/0.833328.78/0.798127.12/0.827831.81/0.8776
ECBSR-M6C4097.7922.4628.117.471375.333.67/0.921129.92/0.833928.85/0.799427.36/0.833331.88/0.8784
ABPN-M6C40104.1023.9129.218.24806633.71/0.921329.92/0.833928.85/0.799427.37/0.833631.89/0.8786
ETDS-L (Ours)159.7736.7125.414.244451.833.88/0.923530.00/0.835928.90/0.801027.45/0.835932.00/0.8807
×4Bicubic******28.60/0.814026.21/0.708826.04/0.673323.23/0.661328.23/0.7775
ESPCN37.208.5411.88.1412079.830.66/0.868827.66/0.758126.94/0.715224.56/0.726329.46/0.8133
ETDS-T (Ours)21.364.8810.96.9416377.430.87/0.873827.75/0.761827.04/0.719424.71/0.735029.59/0.8172
FSRCNN24.6852.68----30.76/0.872127.74/0.760927.01/0.718124.66/0.733029.56/0.8163
ECBSR-M4C1616.773.8323.913.727819130.87/0.874127.80/0.762627.06/0.719524.75/0.736429.61/0.8176
ETDS-S (Ours)54.1112.4114.69.0220377.431.19/0.880628.01/0.767827.18/0.724025.03/0.747929.80/0.8224
ECBSR-M4C3251.9211.9128.016.339919131.24/0.881528.04/0.768627.21/0.724825.07/0.749429.84/0.8231
ABPN-M4C2862.0514.2430.317.433518731.32/0.883328.10/0.769727.23/0.725425.12/0.751129.86/0.8237
ETDS-M (Ours)72.6116.6616.69.9826778.931.41/0.884328.13/0.770527.27/0.726525.20/0.754429.92/0.8250
ECBSR-M6C40105.3724.2036.820.774919531.41/0.883128.20/0.771627.33/0.728025.37/0.760129.97/0.8259
ABPN-M6C40125.8728.9139.122.453819131.62/0.887628.27/0.773727.35/0.729325.41/0.761630.04/0.8277
ETDS-L (Ours)169.9739.0527.615.344785.331.69/0.888928.31/0.775127.37/0.730225.47/0.764330.09/0.8289
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.591, + 0.471, + 0.619 + ], + "angle": 0, + "content": "Table 3. Ablation operation for each operator. All indicators are tested using NNAPI driver on Dimensity 8100 SoC." + }, + { + "type": "table", + "bbox": [ + 0.11, + 0.63, + 0.437, + 0.793 + ], + "angle": 0, + "content": "
ModelSizeImprovement
addconcatenateclip
ETDST21.03%28.92%0.26%
S16.74%26.61%0.86%
M8.33%34.47%0.76%
L7.29%27.64%0.50%
repeataddclip
ECBSRM4C1647.95%7.38%1.23%
M4C3239.01%11.35%-0.35%
M6C4029.92%10.24%0.54%
ABPNM4C2837.46%10.75%1.30%
M6C4027.30%10.20%0.77%
" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.81, + 0.47, + 0.901 + ], + "angle": 0, + "content": "Ablation Studies for Global Residual Connection. Here we investigate the effect of the global residual connection. Tab. 4 shows the results of the experiments. The PSNR value is improved by 0.04dB on Set5, when adding a global residual connection composed of nearest neighbor interpolation to Plain-M6C32." + }, + { + "type": "table_caption", + "bbox": [ + 0.508, + 0.59, + 0.882, + 0.604 + ], + "angle": 0, + "content": "Table 4. PSNR/SSIM results for different variants of ETDS-M." + }, + { + "type": "table", + "bbox": [ + 0.505, + 0.609, + 0.892, + 0.707 + ], + "angle": 0, + "content": "
VariantModificationsSet5Urban100
PSNR/SSIMPSNR/SSIM
IPlain-M6C3231.32/0.883025.10/0.7505
IIPlain-M6C32 w/ interpolation31.36/0.883325.13/0.7519
IIIETDS-M w/o Kr2b module31.36/0.883525.16/0.7526
IVETDS-M31.41/0.884325.20/0.7544
VETDS-M w/ Kb2r module31.38/0.883725.17/0.7530
VIETDS-M w/o LDS31.35/0.883725.14/0.7521
" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Ablation Studies for \\( K_{r} \\), \\( K_{r2b} \\) and \\( K_{b2r} \\). We train \\( K_{r} \\), \\( K_{r2b} \\), and \\( K_{b2r} \\) one after another in an incremental way. The variants are recorded as Variant III, Variant IV, and Variant V in Tab. 4. Variant IV refers to our ETDS-M. From Tab. 4, the performance of Variant II, III and IV increases sequentially, indicating that the learnability of \\( K_{r} \\) and \\( K_{r2b} \\) is beneficial to improve the performance. However, Variant V's performance is worse than Variant IV's, which may indicate that introducing a learnable \\( K_{b2r} \\) could lead to a degradation in performance. The \\( K_{b2r} \\) module connects the low-frequency constraints to the backbone branch during backpropagation which causes the backbone branch to" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.946, + 0.519, + 0.957 + ], + "angle": 0, + "content": "14108" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.091, + 0.329, + 0.282 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.13, + 0.287, + 0.281, + 0.3 + ], + "angle": 0, + "content": "img_088 from Urban100" + }, + { + "type": "image", + "bbox": [ + 0.081, + 0.304, + 0.191, + 0.387 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.114, + 0.388, + 0.16, + 0.397 + ], + "angle": 0, + "content": "ESPCN" + }, + { + "type": "image_caption", + "bbox": [ + 0.097, + 0.398, + 0.176, + 0.41 + ], + "angle": 0, + "content": "20.41/0.5572" + }, + { + "type": "image", + "bbox": [ + 0.22, + 0.304, + 0.328, + 0.387 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.242, + 0.388, + 0.303, + 0.397 + ], + "angle": 0, + "content": "ESRCNN" + }, + { + "type": "image_caption", + "bbox": [ + 0.235, + 0.398, + 0.314, + 0.409 + ], + "angle": 0, + "content": "20.53/0.5825" + }, + { + "type": "image", + "bbox": [ + 0.082, + 0.411, + 0.191, + 0.493 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.088, + 0.494, + 0.186, + 0.504 + ], + "angle": 0, + "content": "ECBSR-M6C40" + }, + { + "type": "image_caption", + "bbox": [ + 0.096, + 0.505, + 0.176, + 0.516 + ], + "angle": 0, + "content": "21.03/0.6680" + }, + { + "type": "image", + "bbox": [ + 0.22, + 0.411, + 0.328, + 0.493 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.23, + 0.494, + 0.319, + 0.504 + ], + "angle": 0, + "content": "ABPN-M6C40" + }, + { + "type": "image_caption", + "bbox": [ + 0.233, + 0.505, + 0.314, + 0.516 + ], + "angle": 0, + "content": "21.12/0.6593" + }, + { + "type": "image", + "bbox": [ + 0.358, + 0.091, + 0.466, + 0.174 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.371, + 0.175, + 0.453, + 0.185 + ], + "angle": 0, + "content": "Ground Truth" + }, + { + "type": "image_caption", + "bbox": [ + 0.374, + 0.186, + 0.45, + 0.196 + ], + "angle": 0, + "content": "PSNR/SSIM" + }, + { + "type": "image", + "bbox": [ + 0.358, + 0.198, + 0.466, + 0.28 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.389, + 0.281, + 0.436, + 0.292 + ], + "angle": 0, + "content": "Bicubic" + }, + { + "type": "image_caption", + "bbox": [ + 0.374, + 0.292, + 0.452, + 0.303 + ], + "angle": 0, + "content": "19.17/0.4514" + }, + { + "type": "image", + "bbox": [ + 0.358, + 0.304, + 0.466, + 0.387 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.371, + 0.388, + 0.452, + 0.398 + ], + "angle": 0, + "content": "Plain-M6C32" + }, + { + "type": "image_caption", + "bbox": [ + 0.373, + 0.399, + 0.451, + 0.41 + ], + "angle": 0, + "content": "21.08/0.6193" + }, + { + "type": "image", + "bbox": [ + 0.358, + 0.411, + 0.466, + 0.493 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.385, + 0.494, + 0.441, + 0.504 + ], + "angle": 0, + "content": "ETDS-L" + }, + { + "type": "image_caption", + "bbox": [ + 0.372, + 0.505, + 0.452, + 0.516 + ], + "angle": 0, + "content": "21.77/0.7050" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.529, + 0.47, + 0.557 + ], + "angle": 0, + "content": "Figure 5. Qualitative comparison of real-time SR models on Set5 for \\(\\times 4\\) upscaling task." + }, + { + "type": "image", + "bbox": [ + 0.078, + 0.572, + 0.468, + 0.732 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.737, + 0.47, + 0.793 + ], + "angle": 0, + "content": "Figure 6. Channel masking experiments with Plain-M6C32 model, ETDS and Variant V. In order to understand the meaning of each channel, the visualization images of some channels are shown in this figure." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.81, + 0.468, + 0.854 + ], + "angle": 0, + "content": "pay extra attention to low-frequency information, thereby reducing the model's ability to extract high-frequency information." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.469, + 0.901 + ], + "angle": 0, + "content": "Ablation Studies for Dual Stream Constraint \\(\\mathcal{L}_{\\mathrm{DS}}\\). For ETDS-M, the PSNR value is 0.06dB higher than the one without \\(\\mathcal{L}_{\\mathrm{DS}}\\) (Tab. 4 Variant VI), which supports the" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.092, + 0.774, + 0.106 + ], + "angle": 0, + "content": "benefit of the dual stream constraint \\(\\mathcal{L}_{\\mathrm{DS}}\\)" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.107, + 0.892, + 0.362 + ], + "angle": 0, + "content": "Analysis of Dual Stream Network. We conduct the channel mask experiments [16] on ETDS-M, Plain-M6C32 and Variant V models, and then analyze how each channel contributes to the performance. From Fig. 6, the low-frequency information of ETDS-M is mainly concentrated in the last three channels (i.e., the residual branch), while the high-frequency information is distributed in the remaining channels (i.e., the backbone branch) corresponding to our design in Sec. 3.3. In addition, the extraction of the low-frequency channel of ETDS-M is more effective than the Plain-M6C32 model. This may be the reason why ETDS-M has better performance than the Plain-M6C32 model. On top of that, Variant V does better in extracting low-frequency information than ETDS-M, but worse in PSNR performance, which confirms that the learnability of \\( K_{b2r} \\) compromises the ability to extract high-frequency information." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.373, + 0.627, + 0.387 + ], + "angle": 0, + "content": "4.6. Limitations" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.396, + 0.892, + 0.547 + ], + "angle": 0, + "content": "While our method achieves a better trade-off between performance and latency on mobile devices, it also has its limitations. Firstly, ET is only appropriate for relatively simple network architectures. More complex structures would require a more complicated ET process, which could potentially introduce an excessive number of redundant parameters. Secondly, due to its simplified structure, very deep networks still pose a challenge for ETDS, and its performance may not reach the level of its EDSR counterpart." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.561, + 0.619, + 0.576 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.586, + 0.892, + 0.798 + ], + "angle": 0, + "content": "This paper has presented ETDS for mobile image superresolution via Equivalent Transformation and dual stream network construction. ET method is applied to substitute time-consuming operators, including add, repeat, clip and concatenate, with time-friendly ones (convolution and ReLU), which can alleviate the inference latency. We have developed a dual stream network, which successfully eliminated most of the redundant parameters brought by the implementation of ET. Our approach represents an innovative integration of the ET method with a dual-stream network for mobile devices. Extensive experiments have demonstrated that ETDS can outperform the state-of-the-art lightweight SR models in terms of inference latency and reconstruction quality." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.812, + 0.892, + 0.887 + ], + "angle": 0, + "content": "Acknowledgements. This work was supported in part by \"Digital Silk Road\" Shanghai International Joint Lab of Trustworthy Intelligent Software (Grant No. 22510750100), and Shanghai Trusted Industry Internet Software Collaborative Innovation Center." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "14109" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.079, + 0.09, + 0.176, + 0.107 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.115, + 0.47, + 0.226 + ], + "angle": 0, + "content": "[1] Namhyuk Ahn, Byungkon Kang, and Kyung-Ah Sohn. Fast, accurate, and lightweight super-resolution with cascading residual network. In Vittorio Ferrari, Martial Hebert, Cristian Sminchisescu, and Yair Weiss, editors, Computer Vision - ECCV 2018 - 15th European Conference, Munich, Germany, September 8-14, 2018, Proceedings, Part X, volume 11214 of Lecture Notes in Computer Science, pages 256-272. 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To address this issue, many lightweight super-resolution models have been proposed. However, these models still contain time-consuming components that increase inference latency, limiting their real-world applications on mobile devices. In this paper, we propose a novel model for single-image super-resolution based on Equivalent Transformation and Dual Stream network construction (ETDS). ET method is proposed to transform time-consuming operators into time-friendly operations, such as convolution and ReLU, on mobile devices. Then, a dual stream network is designed to alleviate redundant parameters resulting from the use of ET and enhance the feature extraction ability. Taking full advantage of the advance of ET and the dual stream network structure, we develop the efficient SR model ETDS for mobile devices. The experimental results demonstrate that our ETDS achieves superior inference speed and reconstruction quality compared to previous lightweight SR methods on mobile devices. The code is available at https://github.com/ECNUSR/ETDS. + +# 1. Introduction + +Image super-resolution (SR) aims to reconstruct high-resolution images (HR) from low-resolution images (LR). Over the years, numerous deep-learning methods have been proposed [3, 6, 17, 18, 33, 35, 36] with good fidelity and perceptual quality. However, these methods are not efficient and lightweight when it comes to mobile platforms where SR application becomes increasingly ubiquitous. Thus, it is essential to devise an approach that takes into account the restrictions of mobile platforms. + +Generally, mobile platforms have limitations such as a restricted amount of RAM, lower memory bandwidth, + +![](images/777bfb15aaaa8a30a43870e697161f696fcd04e7893bd360cb15254a0027b4b1.jpg) +Figure 1. Comparisons of PSNR performance and the inference latency of different models. The inference latency is tested on Dimensity 8100 SoC, NNAPI driver, INT8 precision and upsampling from $360 \times 640$ to $1080 \times 1920$ . PSNR indexes are evaluated on Set5 [2]. + +lower computational speed and insufficient support for many common deep learning layers and operators. To take the particularities into consideration, the recently proposed SR models [27, 34] designed for mobile devices adopt a neat topology [34] as the base model to ensure low inference latency. ABPN [8] further boosted efficiency by employing the repeat operator instead of the time-consuming nearest neighbor interpolation. Nevertheless, in-depth investigation reveals that some time-consuming components in current mobile SR models, such as the global residual connection and clip operator, are indispensable for overall reconstruction quality. Therefore, to accelerate the inference on mobile devices and achieve a competitive reconstruction quality and inference latency, it is necessary to seek time-friendly surrogates for these time-consuming operators. + +To this end, we propose Equivalent Transformation (ET), a method that speeds up the model by substituting time-consuming operators with time-friendly ones without im + +pairing reconstruction quality. As shown in Fig. 1, the proposed ET can be directly applied to existing models (e.g., ECBSR [34] and ABPN [8]) and reduce inference latency without retraining. However, ET introduces some redundant and unlearnable parameters. To fully utilize these parameters, we design the dual stream network that makes the redundant parameters partially learnable, to boost the feature extraction ability. Finally, we propose a mobile image SR model named ETDS that employs the dual stream network in the training stage and transforms it into an equivalent plain network by ET in the inference stage. As shown in Fig. 1, our ETDS not only achieves high reconstruction quality but also maintains low inference speed. + +In summary, the main contributions of this paper are as follows: + +1) We propose ET, a method that can transform time-consuming operators and speed up the inference without impairing reconstruction quality. It can be applied to existing models to accelerate the inference. +2) We design a dual stream network to alleviate the redundancy yielded from ET by making redundant parameters partially learnable. +3) We propose an efficient and lightweight network named ETDS for real-time SR on mobile devices based on ET and dual stream networks. Experiments demonstrate that state-of-the-art models equipped with ET have at most $80\%$ improvement in inference latency and ETDS achieves $34\%$ inference latency improvement and 0.42dB PSNR performance improvement. + +# 2. Related Work + +Due to the rapid development of convolutional neural networks (CNN), CNN-based methods [6, 18, 24, 35, 36] have become mainstream methods for SR tasks. SRCNN [6] pioneered the application of convolutional neural networks on the SR task, surpassing the performance of traditional methods. In EDSR [18], a very deep network was utilized and the batch normalization layers in the residual block were removed. SwinIR [17] first attempted to apply the Swin-Transformer [20] on the SR task, showing the potential of Transformer-based networks [26]. To enlarge the receptive field, the hybrid attention block (HAB) was proposed by HAT [3], which achieved state-of-the-art performance. However, these models have high requirements for memory and computational resources which are not easily attainable in real-world applications. + +To realize lightweight SR for GPU servers, many approaches tried to reduce the number of parameters and FLOPs. CARN [1] attempted to apply group convolutions. IMDN [10] employed a progressive refinement module to improve the information extraction ability and reduced the + +number of layers and channels. For further improvement in the efficiency of feature extraction, in RFDN [19], $1 \times 1$ convolutions were utilized to replace the $3 \times 3$ convolutions on the split channel of the IMDB [10] module. RLFN [15] replaced the progressive refinement module with a simpler residual module, which further improved the running speed and achieved great performance. MemSR [30] optimized the network in terms of memory by removing the residual structure in the model and proposed a novel knowledge distillation method to improve the performance. + +Due to the particularity of the mobile platforms, most models for GPU servers are not directly applicable to mobile devices whose applications require to be carried out in a timely fashion with restricted computational resources. To solve this problem, current methods mainly optimized the network from three aspects, i.e., neat network topology, computation reduction and operator substitution. ECBSR [34], which proposed an Edge-oriented Convolutional Block (ECB) to achieve better performance, used relatively neat topology for low inference latency on mobile devices and introduced reparameterization techniques to achieve computation reduction for SR task. Following [34], RepSR [27] optimized the performance and training efficiency of the reparameterization module in ECBSR to achieve further computation reduction. ABPN [8] first attempted to apply operator substitution and used the faster repeat operator instead of nearest neighbor interpolation in global residual connections. Inspired by the reparameterization technique, we propose ET, which substitutes more types of operators to achieve low inference latency. Our proposed ETDS optimized the network from all three aspects, where ET optimized the network by achieving operator substitution and computation reduction while the dual stream network adopted a neat topology. + +# 3. Methodology + +In this section, we examine the current mobile superresolution models in Sec. 3.1, and then propose a novel method, Equivalent Transformation (ET), which substitutes time-consuming operators with time-friendly ones in 3.2. However, applying ET comes at the cost of introducing redundant parameters. To address this, we carefully design a dual stream network that alleviates redundancy and enhances feature extraction ability in Sec. 3.3. + +# 3.1. Analysis of Current Mobile SR Models + +In order to design more efficient super-resolution models for mobile devices, we analyze the speed bottleneck of current mobile SR models on two of the most popular mobile phone $\mathrm{SoCs}^1$ . As shown in Tab. 1, convolution and ReLU operations have lower inference latency than most other op + +Table 1. Average inference latency (ms) of common components in mobile SR models. The average inference latency of all components is tested on SR models with a channel size of 32, an input of size $360 \times 640$ and a scale factor of 3. For operators in the same type, the results of higher latency are marked in bold. + +
TypeOperatorLatency (ms)
Dimensity 8100Snapdragon 870Snapdragon 865
Convolution1 × 1 Convolution2.244
3 × 3 Convolution10.41821
Transposed Convolution7.379
ActivationReLU0.060.60.6
PReLU2.264.83.8
LeakyReLU2.265.64.2
Sigmoid0.120.60.8
Tanh0.30.81
InterpolationNearest neighbor262427
Bilinear676568
OthersAdd6.534
Concatenate22.867
Multiply6.534
Repeat16.31914
Clip6.99194
PixelShuffle4.234
+ +erations, and PixelShuffle [23] is more efficient than transposed convolution, which indicates PixelShuffle and ReLU are better choices for mobile platforms. Hereafter, plain network refers to a network that only contains time-friendly operators (i.e., convolution, ReLU activation functions and PixelShuffle), which has low inference latency on mobile devices. + +To transform current mobile models into plain models, we may encounter the following challenges: + +1) To avoid the rescaling problem in the INT8 quantization models, it is necessary to add the clip operator at the end of the model. However, the clip operator is also time-consuming (see Tab. 1), which requires a more efficient and equivalent alternative. +2) To compensate for the PSNR performance drop brought by the removal of global residual connections, it is necessary to find an equivalent way to transform the global residual connection into an efficient operator. + +To tackle these challenges, we propose ET, which substitutes some time-consuming operators with time-friendly ones without reducing the reconstruction quality, thereby improving the running speed. + +# 3.2. Equivalent Transformation + +Formal Definitions. A convolution operation is formulated as $z = W \otimes x + b$ , where $x \in \mathbb{R}^{c_i \times h \times w}$ and $z \in \mathbb{R}^{c_o \times h \times w}$ are the input and output tensors respectively, $W \in \mathbb{R}^{c_o \times k \times k \times c_i}$ , $b \in \mathbb{R}^{c_o}$ are the kernel and the bias of the convolution, and $k$ is the kernel size, $c_i, c_o$ are the numbers of the input and output channels, and $h, w$ are the input height and width. $I$ is the identity kernel of the convolution + +operation, and $O$ is the kernel of zero elements, satisfying + +$$ +I \otimes x = x, \quad O \otimes x = 0, \forall x \in \mathbb {R} ^ {c _ {i} \times h \times w}. \tag {1} +$$ + +For input features and convolution kernels, the concatenation operation requires all but the concatenated dimension to be consistent. The channel dimension concatenation operation of feature vectors $x$ and $y$ is defined as $\begin{bmatrix} x \\ y \end{bmatrix}$ . The concatenation operation of the convolution kernels $W_{h,1}$ and $W_{h,2}$ in the horizontal direction (i.e., input-dimension concatenation) is defined as $[W_{h,1}, W_{h,2}]$ , which satisfies + +$$ +\left[ W _ {h, 1}, W _ {h, 2} \right] \otimes \left[ \begin{array}{l} x \\ y \end{array} \right] = W _ {h, 1} \otimes x + W _ {h, 2} \otimes y. \tag {2} +$$ + +Likewise, the concatenation operation of the convolution kernels $W_{v,1}$ and $W_{v,2}$ in the vertical direction, i.e., output-dimension concatenation is defined as $\begin{bmatrix} W_{v,1} \\ W_{v,2} \end{bmatrix}$ , which satisfies + +$$ +\left[ \begin{array}{l} W _ {v, 1} \\ W _ {v, 2} \end{array} \right] \otimes x = \left[ \begin{array}{l} W _ {v, 1} \otimes x \\ W _ {v, 2} \otimes x \end{array} \right]. \tag {3} +$$ + +More details will be found in Appendix. + +ET for Repeat Operator. Given an input tensor $x \in \mathbb{R}^{c \times h \times w}$ , the repeat operator $\text{repeat}(x, n)$ constructs a new tensor $z \in \mathbb{R}^{(nc) \times h \times w}$ by replicating the input $n$ times along the channel dimension. This operation can be expressed as a convolution layer. Precisely, Eq. (1) and (3) yield + +$$ +\begin{array}{l} \operatorname {r e p e a t} (x, n) = \left[ \begin{array}{c} x \\ \vdots \\ x \end{array} \right] = \left[ \begin{array}{c} I \otimes x \\ \vdots \\ I \otimes x \end{array} \right] = \left[ \begin{array}{c} I \\ \vdots \\ I \end{array} \right] \otimes x \tag {4} \\ = \operatorname {r e p e a t} (I, n) \otimes x, \\ \end{array} +$$ + +where $\text{repeat}(I, n)$ is a constant. Thus, the repeat operator is equivalently transformed into a convolution layer, whose kernel and bias are $\text{repeat}(I, n)$ and a zero vector, respectively. + +ET for Add Operator. The add operator refers to the element-wise addition operation of two feature vectors and is an indispensable part of residual connections, i.e., $z = x + y$ . From Eq. (1) and (2), we have: + +$$ +x + y = I \otimes x + I \otimes y = [ I, I ] \otimes \left[ \begin{array}{l} x \\ y \end{array} \right]. \tag {5} +$$ + +Thus, the add operator is equivalently transformed into a convolution layer with a concatenate operator, whose kernel and bias are $[I, I]$ and a zero vector, respectively. Notably, this proposed convolution layer can be eliminated later by reparameterization techniques. + +ET for Concatenate Operator. In our model, the concatenate operator always follows the convolution layers. + +We integrate the convolution-concatenate structure, i.e., the concatenate operator and its preceding convolution layer, which can be simplified with Eq. (2) and (3) as follows: + +$$ +z = \left[ \begin{array}{c} W _ {1} \otimes x + b _ {1} \\ W _ {2} \otimes y + b _ {2} \end{array} \right] = \left[ \begin{array}{c c} W _ {1} & O \\ O & W _ {2} \end{array} \right] \otimes \left[ \begin{array}{c} x \\ y \end{array} \right] + \left[ \begin{array}{c} b _ {1} \\ b _ {2} \end{array} \right]. \tag {6} +$$ + +Following Eq. (6), the convolution-concatenate structure is transformed into a concatenate-convolution structure, with the kernel and bias as follows: + +$$ +\left[ \begin{array}{c c} W _ {1} & O \\ O & W _ {2} \end{array} \right] \quad \text {a n d} \quad \left[ \begin{array}{l} b _ {1} \\ b _ {2} \end{array} \right]. \tag {7} +$$ + +In particular, when the residual branch does not have a convolution layer, it can be expressed as: + +$$ +z = \left[ \begin{array}{c} W \otimes x + b \\ y \end{array} \right] = \left[ \begin{array}{c c} W & O \\ O & I \end{array} \right] \otimes \left[ \begin{array}{c} x \\ y \end{array} \right] + \left[ \begin{array}{c} b \\ 0 \end{array} \right]. \tag {8} +$$ + +When $x = y$ , Eq. (8) can be further rewritten as: + +$$ +z = \left[ \begin{array}{c} W \otimes x + b \\ x \end{array} \right] = \left[ \begin{array}{c} W \\ I \end{array} \right] \otimes x + \left[ \begin{array}{c} b \\ 0 \end{array} \right], \tag {9} +$$ + +where the kernel is $\left[ \begin{array}{l}W\\ I \end{array} \right]$ and thus the concatenate operator is eliminated. + +ET for Clip Operator. The clip operator is expressed as: + +$$ +\operatorname {c l i p} (x) = \left\{ \begin{array}{l l} 0, & x \leq 0, \\ x, & 0 < x \leq 2 5 5, \\ 2 5 5, & x > 2 5 5, \end{array} \right. \tag {10} +$$ + +which avoids the loss of precision and subsequent additional inverse scaling operations caused by mismatched normalization of the INT8 quantization model [12]. Nevertheless, as shown in Tab. 1, the clip operator is extremely time-consuming on many mobile SoCs, so it is of great necessity to find a time-friendly substitution for the clip operator. + +To equivalently transform the clip operator with ReLU, we reformulate clip operator as: + +$$ +\operatorname {c l i p} (x) = \operatorname {R e L U} (- \operatorname {R e L U} (- x + 2 5 5) + 2 5 5). \tag {11} +$$ + +To speed up this process, we further rewrite it as: + +$$ +\left\{ \begin{array}{l l} y = & \operatorname {R e L U} (- I \otimes x + 2 5 5), \\ c l i p (x) = & \operatorname {R e L U} (- I \otimes y + 2 5 5). \end{array} \right. \tag {12} +$$ + +Using Eq. (12), the clip operator is transformed into two convolutions with ReLU, whose kernels are $-I$ and bias is a vector with all elements equal to 255. Remark that the first convolution layer in Eq. (12) is eliminated by reparameterization techniques [5]. + +ET for Equivalent Plain Model Conversion. As depicted in Fig. 2, the model is converted into an equivalent plain model by ET as following: + +![](images/59f6d1975d519faadfd1e91349866a0ec9b3ce51ae72d4cad240447b246410b6.jpg) +Figure 2. Illustration of converting the general model into the equivalent plain model using ET. The beige convolution indicates that the convolution kernel is assigned a specific value. Rep refers to the reparameterization technique. + +- The repeat operator and the add operator are converted into a single convolution and a concatenate operator respectively (see Step 1 and Step 2). +- The concatenate operator with the preceding convolutions from two branches is converted into a convolution. Notably, the global residual connection does not contain negative values, so the ReLU function is omitted (see Step 3). +- The two convolutions introduced by previous steps are converted into a convolution using reparameterization techniques (see Step 4). +- The convolution-concatenate structure is converted into a concatenate-convolution one, thus the concatenate operator is converted and moves forward till it reaches the skip connection starting point, that is, $x$ equals $y$ . In this situation, the concatenate operator is further eliminated (see Step 5 and Step 6). +- The clip operator is converted into the convolution (see Step 7). + +Remark 1 Although $ET$ speeds up inference by transforming time-consuming operators into time-friendly ones, it introduces some redundant parameters. For instance, in the transformed convolution kernel $\mathrm{diag}(W, I)$ derived from Eq. (8). All learnable parameters appear in $W$ . If the redundant parameters are effectively utilized, better reconstruction performance can be achieved. + +# 3.3. Dual Stream Network + +To alleviate the side effects of the redundant parameters of ET, we design a dual stream network where the two branches learn the low-frequency and high-frequency contents of the image separately and utilize the parameters to + +![](images/daf35378cd2414e3c9483385e5c31e2e32e06ef0ba9c5d827745e79b08432eca.jpg) + +![](images/c38885220b3bd666d9c8b90aaa8f9edc40866df1e243e1aa8b56f76615dab007.jpg) +Figure 3. Network architecture of ETDS during training and inference stages. The residual branch for extracting low-frequency contents only contains a few parameters, and most of the parameters are used to extract high-frequency contents. + +the fullest. The transformed convolution kernel in Eq. (8) is $\left[ \begin{array}{cc}K_b & K_{r2b}\\ K_{b2r} & K_r \end{array} \right]$ , where $K_{b}$ and $K_{r}$ denote the modules that constitute the backbone branch and residual branch, respectively. $K_{r2b}$ is the module that transfers information from the residual branch to the backbone branch, and $K_{b2r}$ transfers information reversely. The residual branch consisting of $K_{r}$ and the backbone branch consisting of $K_{b}$ extract low-frequency and high-frequency information respectively. + +Initially, $K_{r}$ , $K_{r2b}$ and $K_{b2r}$ are not learnable. Furthermore, we have analyzed the possible impacts of making them learnable on the reconstruction quality and found that when $K_{r}$ and $K_{r2b}$ are learnable, they can extract low-frequency information more effectively and transfer more residual information to the backbone branch, respectively. However, when $K_{b2r}$ is learnable, the backbone branch may take less important low-frequency information into consideration, which reduces the number of parameters for extracting high-frequency components, and potentially compromising the performance. + +As shown in Fig. 3, $K_{r}$ and $K_{r2b}$ in our dual stream network contain learnable parameters, while parameters in $K_{b2r}$ remain fixed. In the training phase, we encourage the residual branch to learn as many low-frequency contents as possible, that is, to minimize the $L_{1}$ distance between the output of the residual branch $(I_{LF})$ and the ground truth $(I_{GT})$ : + +$$ +\mathcal {L} _ {L F} = \left\| I _ {G T} - I _ {L F} \right\| _ {1}. \tag {13} +$$ + +The backbone branch learns high-frequency contents, and its output $(I_{HF})$ compensates for the gap between $I_{GT}$ and $I_{LF}$ : + +$$ +\mathcal {L} _ {H F} = \left\| I _ {G T} - I _ {L F} - I _ {H F} \right\| _ {1}. \tag {14} +$$ + +To train the dual stream network, we use the overall loss function: + +$$ +\mathcal {L} _ {D S} = \mathcal {L} _ {H F} + \alpha \times \mathcal {L} _ {L F}, \tag {15} +$$ + +which drives more parameters to extract high-frequency contents to improve the overall performance. In the inference stage, as shown in Fig. 3, the dual stream network can be equivalently transformed into a plain network, which ensures low inference latency. + +# 4. Experiments + +# 4.1. Datasets and Metrics + +Our model ETDS is trained on DIV2K dataset [25] with 800 training images. The performance is evaluated on 5 benchmark datasets (i.e., Set5 [2], Set14 [32], BSDS100 [21], Urban100 [9] and DIV2K100 [25]). PSNR and SSIM [29] are used to evaluate the reconstruction quality and calculated on the Y channel in the YCbCr space. + +# 4.2. Implementation Details + +ETDS is implemented on PyTorch-based [22] BasicSR [28] framework and trained on an NVIDIA 2080Ti GPU. In the training phase, 32 patches of $64 \times 64$ LR image are used as input. Random rotation, horizontal flipping, and channel shuffle are applied for data augmentation. We train our model by the ADAM [14] optimizer with $\beta_{1} = 0.9$ , $\beta_{2} = 0.999$ , and $\epsilon = 10^{-8}$ . We set $\mathcal{L}_{\mathrm{DS}}$ as the loss function with $\alpha = 0.5$ . In accordance with previous works, our model is trained for $1600k$ iterations with a learning rate of $5e^{-4}$ . For the first $100k$ iterations, $K_{r}$ and $K_{r2b}$ are initialized by setting $K_{r} = I$ and $K_{r2b} = O$ . In the testing phase, we test the inference latency on three SoCs (i.e., Dimensity 8100, Snapdragon 888, and Snapdragon 8 Gen 1) with the + +![](images/cc6366a5335d5f46fa093fa8a1777dce8e0f4b00f65ab646650db0b790e50717.jpg) +(a) + +![](images/dcd00be26e6a0999c9b2fc3f601004b9d2ef260cb459d864a3a72d8506f4e502.jpg) +(b) +Figure 4. The effect of the numbers of channels and layers on inference latency of the plain model. (a) shows the inference latency with the number of channels between 4 and 24. (b) shows the inference latency with the number of channels between 4 and 64, divisible by 4. (c) shows the inference latency with the number of layers between 1 and 10. + +![](images/bf1e483e16a8306be5bec537a92b6b801913e2dbce1e1d4ace198a1526487cf7.jpg) +(c) + +AI Benchmark application [11, 13]. All inference latencies and multiply-accumulate operations (MACs) are tested with inputs of $360 \times 640$ . + +# 4.3. Hardware-Friendly Number of Channels + +As shown in Fig. 4, the numbers of channels and layers have a significant impact on the model's efficiency. Observing Fig. 4 (a)(b), we can see that the models have lower inference latency on mobile devices when the number of channels is a multiple of 4, due to the processing unit alignment [31], the memory alignment, and other hardware optimizations [4]. Fig. 4 (c) supports that the inference latency is proportional to the number of layers. + +As a result, for a lower inference latency, ETDS is designed with 16, 32, and 48 channels and the number of layers in the model is designed for balancing the performance and inference latency. Also, for the equivalently transformed models (e.g., $\mathrm{ECBSR + ET}$ and $\mathrm{ABPN + ET}$ ), extra channels are added to ensure that the number of channels is a multiple of 4. + +# 4.4. Comparisons to Previous Works + +We compare our ETDS with representative real-time SR models on mobile devices, including Bicubic, ESPCN [23], FSRCNN [7], ABPN [8], and ECBSR [34]. Since ESPCN, FSRCNN, and ECBSR only process on a single channel of the input image, some preprocessing and postprocessing, such as color space conversion and upsampling of the other two channels are omitted. For a fair comparison, these models are retrained in the RGB color space. + +We train four different sizes of our model, denoted as ETDS-T, ETDS-S, ETDS-M and ETDS-L for different computational use cases, with channels 16, 32, 32 and 48, and layers 5, 4, 6, and 7, respectively. The performance comparison is summarized in Tab. 2. In addition to PSNR/SSIM indexes, we also list the number of parameters and MACs for a more comprehensive comparison. + +Quantitative Results. The quantitative comparison is + +presented in Tab. 2. From Tab. 2, our model achieves not only lower inference latency than other models in most cases but also higher PSNR/SSIM indexes. For instance, as shown in Tab. 2 (latency column i), our ETDS-S runs $1.2\mathrm{ms}$ faster than ECBSR-M4C16 on the $\times 3$ task, and its PSNR index on the Urban100 dataset is $0.29\mathrm{dB}$ higher. ETDS-L's inference latency on the $\times 3$ task is $3.5\mathrm{ms}$ faster than the ABPN-M6C40's, and PSNR on Set5. Notably, although our model consists of slightly more parameters and MACs, it is still faster than the state-of-the-art models. This phenomenon occurs due to two-fold aspects. 1). Under different contexts, the same operations may have different inference latency. 2). Some operations are not measured in parameters and MACs metrics. For instance, ReLU does not influence parameters and concatenation does not influence MACs. + +Qualitative Results. The qualitative comparison results are depicted in Fig. 5. We can see that the texture of the wall in thimagese images generated by ESPCN [23] and FSRCNN [7] is blurred, and images generated by ECBSR-M6C40 [34] and ABPN-M6C40 [8] are slightly distorted. Obviously, our ETDS-T produces the least distorted and blurred images with the best PSNR/SSIM results. + +# 4.5. Ablation Studies + +In this section, we propose a series of ablation studies on the design of the proposed ETDS. All the ablation experiments are conducted on the $\times 4$ task. We report PSNR values on the Y channel in the YCbCr space. + +Ablation Studies for Equivalent Transformation. We validate the effectiveness of ET through a series of ablation studies. Additionally, we apply ET to both ECBSR and ABPN to further demonstrate its effectiveness. Note that ETDS does not have a repeat operator and we do not apply ET for the concatenate operator for ECBSR and ABPN because the improvement on the NNAPI driver is insignificant. Our results in Tab. Tab. 3 show that applying ET to these operators results in reduced latency. + +Table 2. Performance comparison of different SR models on five benchmark datasets. PSNR/SSIM on the Y channel is reported on each dataset. Inference latency i, ii, iii and iv denotes the inference latency of the models using NNAPI driver on Dimensity 8100 SoC, MediaTek Neuron driver on Dimensity 8100 SoC, Qualcomm QNN GPU driver on Snapdragon 888 SoC, and NNAPI on Snapdragon 8 Gen 1 SoC respectively. + +
ScaleModelParams (K)MACs (G)Latency (ms)Set5Set14B100Urban100DIV2K100
iiiiiiivPSNR/SSIMPSNR/SSIMPSNR/SSIMPSNR/SSIMPSNR/SSIM
×2Bicubic******33.95/0.933430.54/0.875129.74/0.850327.07/0.845632.67/0.9078
ESPCN26.806.156.304.8391-36.87/0.955932.62/0.908631.40/0.889829.61/0.897334.78/0.9347
ETDS-T (Ours)13.943.194.853.81125-37.18/0.957832.76/0.910331.62/0.893030.10/0.905835.09/0.9375
FSRCNN24.6815.0510.45.8941456237.00/0.956832.68/0.909431.51/0.891329.92/0.902234.97/0.9363
ECBSR-M4C1611.552.646.154.5718931.637.18/0.957732.79/0.910531.61/0.892830.18/0.906435.10/0.9375
ETDS-S (Ours)41.519.528.065.77169-37.38/0.958732.96/0.912431.77/0.895130.62/0.912135.36/0.9396
ECBSR-M4C3241.529.539.706.6437231.437.39/0.958733.03/0.912631.79/0.895330.69/0.912835.39/0.9398
ABPN-M4C2833.467.6710.06.6620728.537.36/0.958532.96/0.912131.75/0.894930.55/0.911135.31/0.9392
ETDS-M (Ours)60.0113.7710.26.73288-37.54/0.959333.09/0.913331.86/0.896330.87/0.914935.50/0.9406
ECBSR-M6C4092.3721.2218.110.965346.237.61/0.959633.18/0.913931.94/0.897231.09/0.917435.61/0.9415
ABPN-M6C4093.4021.4518.711.243531.937.58/0.959433.16/0.91431.92/0.897131.04/0.916935.59/0.9414
ETDS-L (Ours)152.1834.9720.612.1469-37.64/0.959733.24/0.914531.98/0.897731.22/0.918835.69/0.9421
×3Bicubic******30.61/0.871927.79/0.781127.31/0.745324.58/0.739629.80/0.8341
ESPCN31.137.149.798.381104432.85/0.911529.41/0.823628.40/0.787626.22/0.800231.24/0.8670
ETDS-T (Ours)16.923.868.645.3614049.233.14/0.916029.53/0.827428.54/0.792026.48/0.811131.43/0.8713
FSRCNN24.6830.7313.77.32456135033.01/0.914529.52/0.826428.50/0.790326.40/0.807431.38/0.8699
ECBSR-M4C1613.723.1416.211.021669.433.07/0.914929.53/0.826928.57/0.792126.61/0.813631.44/0.8712
ETDS-S (Ours)46.7910.7312.27.7318549.233.49/0.919429.76 0.831428.71/0.796126.90/0.822131.69/0.8756
ECBSR-M4C3245.8510.5219.713.135469.233.56/0.920529.78/0.831928.73/0.796526.98/0.823931.73/0.8761
ABPN-M4C2842.549.7620.513.827562.833.53/0.920029.78/0.831728.72/0.796626.94/0.823231.71/0.8758
ETDS-M (Ours)65.2914.9814.48.762604933.65/0.921429.86/0.833328.78/0.798127.12/0.827831.81/0.8776
ECBSR-M6C4097.7922.4628.117.471375.333.67/0.921129.92/0.833928.85/0.799427.36/0.833331.88/0.8784
ABPN-M6C40104.1023.9129.218.24806633.71/0.921329.92/0.833928.85/0.799427.37/0.833631.89/0.8786
ETDS-L (Ours)159.7736.7125.414.244451.833.88/0.923530.00/0.835928.90/0.801027.45/0.835932.00/0.8807
×4Bicubic******28.60/0.814026.21/0.708826.04/0.673323.23/0.661328.23/0.7775
ESPCN37.208.5411.88.1412079.830.66/0.868827.66/0.758126.94/0.715224.56/0.726329.46/0.8133
ETDS-T (Ours)21.364.8810.96.9416377.430.87/0.873827.75/0.761827.04/0.719424.71/0.735029.59/0.8172
FSRCNN24.6852.68----30.76/0.872127.74/0.760927.01/0.718124.66/0.733029.56/0.8163
ECBSR-M4C1616.773.8323.913.727819130.87/0.874127.80/0.762627.06/0.719524.75/0.736429.61/0.8176
ETDS-S (Ours)54.1112.4114.69.0220377.431.19/0.880628.01/0.767827.18/0.724025.03/0.747929.80/0.8224
ECBSR-M4C3251.9211.9128.016.339919131.24/0.881528.04/0.768627.21/0.724825.07/0.749429.84/0.8231
ABPN-M4C2862.0514.2430.317.433518731.32/0.883328.10/0.769727.23/0.725425.12/0.751129.86/0.8237
ETDS-M (Ours)72.6116.6616.69.9826778.931.41/0.884328.13/0.770527.27/0.726525.20/0.754429.92/0.8250
ECBSR-M6C40105.3724.2036.820.774919531.41/0.883128.20/0.771627.33/0.728025.37/0.760129.97/0.8259
ABPN-M6C40125.8728.9139.122.453819131.62/0.887628.27/0.773727.35/0.729325.41/0.761630.04/0.8277
ETDS-L (Ours)169.9739.0527.615.344785.331.69/0.888928.31/0.775127.37/0.730225.47/0.764330.09/0.8289
+ +Table 3. Ablation operation for each operator. All indicators are tested using NNAPI driver on Dimensity 8100 SoC. + +
ModelSizeImprovement
addconcatenateclip
ETDST21.03%28.92%0.26%
S16.74%26.61%0.86%
M8.33%34.47%0.76%
L7.29%27.64%0.50%
repeataddclip
ECBSRM4C1647.95%7.38%1.23%
M4C3239.01%11.35%-0.35%
M6C4029.92%10.24%0.54%
ABPNM4C2837.46%10.75%1.30%
M6C4027.30%10.20%0.77%
+ +Ablation Studies for Global Residual Connection. Here we investigate the effect of the global residual connection. Tab. 4 shows the results of the experiments. The PSNR value is improved by 0.04dB on Set5, when adding a global residual connection composed of nearest neighbor interpolation to Plain-M6C32. + +Table 4. PSNR/SSIM results for different variants of ETDS-M. + +
VariantModificationsSet5Urban100
PSNR/SSIMPSNR/SSIM
IPlain-M6C3231.32/0.883025.10/0.7505
IIPlain-M6C32 w/ interpolation31.36/0.883325.13/0.7519
IIIETDS-M w/o Kr2b module31.36/0.883525.16/0.7526
IVETDS-M31.41/0.884325.20/0.7544
VETDS-M w/ Kb2r module31.38/0.883725.17/0.7530
VIETDS-M w/o LDS31.35/0.883725.14/0.7521
+ +Ablation Studies for $K_{r}$ , $K_{r2b}$ and $K_{b2r}$ . We train $K_{r}$ , $K_{r2b}$ , and $K_{b2r}$ one after another in an incremental way. The variants are recorded as Variant III, Variant IV, and Variant V in Tab. 4. Variant IV refers to our ETDS-M. From Tab. 4, the performance of Variant II, III and IV increases sequentially, indicating that the learnability of $K_{r}$ and $K_{r2b}$ is beneficial to improve the performance. However, Variant V's performance is worse than Variant IV's, which may indicate that introducing a learnable $K_{b2r}$ could lead to a degradation in performance. The $K_{b2r}$ module connects the low-frequency constraints to the backbone branch during backpropagation which causes the backbone branch to + +![](images/5407a0144381de1f836b934a0c11d437bc422b2480bcd8724306eed71f24a570.jpg) +img_088 from Urban100 + +![](images/af6df120cf019b57a035b052ab349219b9558bc34493f4e01b1c0b5a63eb03ef.jpg) +ESPCN + +![](images/2356df50b90919ad7cc1f7c005df684a7be3956feef236a5078686771a006c0f.jpg) +ESRCNN + +![](images/d4331471852ab6af0c9b23336e5a178699ce02dfafbb9fc79064368fb9a6ac46.jpg) +20.41/0.5572 +ECBSR-M6C40 +21.03/0.6680 + +![](images/20bb1d1b964fd58ef7fe9ee5ea5cc5b11bdc2e91132f942d45d9257a15b135b6.jpg) +20.53/0.5825 +ABPN-M6C40 +21.12/0.6593 + +![](images/53e638c2f2772b45d7a0ca419c8e1538e878c34773396357c0691a1b31e1f4a3.jpg) +Ground Truth + +![](images/9cdbc4dd61c2a27f601d212c7647984ec4ec03ced82d4f90c00a45ac52589fdf.jpg) +PSNR/SSIM +Bicubic + +![](images/ebe42bbfd98a9f73cdd84e338b692cf1969140659ab0a12391fc83a9102432c5.jpg) +19.17/0.4514 +Plain-M6C32 + +![](images/7c2c698439c5564a2df8ffdc04bee4861055814667a33e41760894a9c4298ba9.jpg) +21.08/0.6193 +ETDS-L +21.77/0.7050 + +![](images/86b4e7a4904148a1a049daf42d7389d007c2c6385de7ba32a55b0f944464b326.jpg) +Figure 5. Qualitative comparison of real-time SR models on Set5 for $\times 4$ upscaling task. +Figure 6. Channel masking experiments with Plain-M6C32 model, ETDS and Variant V. In order to understand the meaning of each channel, the visualization images of some channels are shown in this figure. + +pay extra attention to low-frequency information, thereby reducing the model's ability to extract high-frequency information. + +Ablation Studies for Dual Stream Constraint $\mathcal{L}_{\mathrm{DS}}$ . For ETDS-M, the PSNR value is 0.06dB higher than the one without $\mathcal{L}_{\mathrm{DS}}$ (Tab. 4 Variant VI), which supports the + +benefit of the dual stream constraint $\mathcal{L}_{\mathrm{DS}}$ + +Analysis of Dual Stream Network. We conduct the channel mask experiments [16] on ETDS-M, Plain-M6C32 and Variant V models, and then analyze how each channel contributes to the performance. From Fig. 6, the low-frequency information of ETDS-M is mainly concentrated in the last three channels (i.e., the residual branch), while the high-frequency information is distributed in the remaining channels (i.e., the backbone branch) corresponding to our design in Sec. 3.3. In addition, the extraction of the low-frequency channel of ETDS-M is more effective than the Plain-M6C32 model. This may be the reason why ETDS-M has better performance than the Plain-M6C32 model. On top of that, Variant V does better in extracting low-frequency information than ETDS-M, but worse in PSNR performance, which confirms that the learnability of $K_{b2r}$ compromises the ability to extract high-frequency information. + +# 4.6. Limitations + +While our method achieves a better trade-off between performance and latency on mobile devices, it also has its limitations. Firstly, ET is only appropriate for relatively simple network architectures. More complex structures would require a more complicated ET process, which could potentially introduce an excessive number of redundant parameters. Secondly, due to its simplified structure, very deep networks still pose a challenge for ETDS, and its performance may not reach the level of its EDSR counterpart. + +# 5. Conclusion + +This paper has presented ETDS for mobile image superresolution via Equivalent Transformation and dual stream network construction. ET method is applied to substitute time-consuming operators, including add, repeat, clip and concatenate, with time-friendly ones (convolution and ReLU), which can alleviate the inference latency. We have developed a dual stream network, which successfully eliminated most of the redundant parameters brought by the implementation of ET. Our approach represents an innovative integration of the ET method with a dual-stream network for mobile devices. Extensive experiments have demonstrated that ETDS can outperform the state-of-the-art lightweight SR models in terms of inference latency and reconstruction quality. + +Acknowledgements. This work was supported in part by "Digital Silk Road" Shanghai International Joint Lab of Trustworthy Intelligent Software (Grant No. 22510750100), and Shanghai Trusted Industry Internet Software Collaborative Innovation Center. + +# References + +[1] Namhyuk Ahn, Byungkon Kang, and Kyung-Ah Sohn. Fast, accurate, and lightweight super-resolution with cascading residual network. In Vittorio Ferrari, Martial Hebert, Cristian Sminchisescu, and Yair Weiss, editors, Computer Vision - ECCV 2018 - 15th European Conference, Munich, Germany, September 8-14, 2018, Proceedings, Part X, volume 11214 of Lecture Notes in Computer Science, pages 256-272. Springer, 2018. 2 +[2] Marco Bevilacqua, Aline Roumy, Christine Guillemot, and Marie-Line Alberi-Morel. 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To address this issue, many lightweight super-resolution models have been proposed. However, these models still contain time-consuming components that increase inference latency, limiting their real-world applications on mobile devices. In this paper, we propose a novel model for single-image super-resolution based on Equivalent Transformation and Dual Stream network construction (ETDS). ET method is proposed to transform time-consuming operators into time-friendly operations, such as convolution and ReLU, on mobile devices. Then, a dual stream network is designed to alleviate redundant parameters resulting from the use of ET and enhance the feature extraction ability. Taking full advantage of the advance of ET and the dual stream network structure, we develop the efficient SR model ETDS for mobile devices. The experimental results demonstrate that our ETDS achieves superior inference speed and reconstruction quality compared to previous lightweight SR methods on mobile devices. 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Thus, it is essential to devise an approach that takes into account the restrictions of mobile platforms." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 673, + 287, + 696 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 673, + 287, + 696 + ], + "spans": [ + { + "bbox": [ + 47, + 673, + 287, + 696 + ], + "type": "text", + "content": "Generally, mobile platforms have limitations such as a restricted amount of RAM, lower memory bandwidth," + } + ] + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 312, + 275, + 525, + 417 + ], + "blocks": [ + { + "bbox": [ + 312, + 275, + 525, + 417 + ], + "lines": [ + { + "bbox": [ + 312, + 275, + 525, + 417 + ], + "spans": [ + { + "bbox": [ + 312, + 275, + 525, + 417 + ], + "type": "image", + "image_path": "777bfb15aaaa8a30a43870e697161f696fcd04e7893bd360cb15254a0027b4b1.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 426, + 547, + 481 + ], + "lines": [ + { + "bbox": [ + 304, + 426, + 547, + 481 + ], + "spans": [ + { + "bbox": [ + 304, + 426, + 547, + 481 + ], + "type": "text", + "content": "Figure 1. Comparisons of PSNR performance and the inference latency of different models. The inference latency is tested on Dimensity 8100 SoC, NNAPI driver, INT8 precision and upsampling from " + }, + { + "bbox": [ + 304, + 426, + 547, + 481 + ], + "type": "inline_equation", + "content": "360 \\times 640" + }, + { + "bbox": [ + 304, + 426, + 547, + 481 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 304, + 426, + 547, + 481 + ], + "type": "inline_equation", + "content": "1080 \\times 1920" + }, + { + "bbox": [ + 304, + 426, + 547, + 481 + ], + "type": "text", + "content": ". PSNR indexes are evaluated on Set5 [2]." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 485, + 547, + 675 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 485, + 547, + 675 + ], + "spans": [ + { + "bbox": [ + 304, + 485, + 547, + 675 + ], + "type": "text", + "content": "lower computational speed and insufficient support for many common deep learning layers and operators. To take the particularities into consideration, the recently proposed SR models [27, 34] designed for mobile devices adopt a neat topology [34] as the base model to ensure low inference latency. ABPN [8] further boosted efficiency by employing the repeat operator instead of the time-consuming nearest neighbor interpolation. Nevertheless, in-depth investigation reveals that some time-consuming components in current mobile SR models, such as the global residual connection and clip operator, are indispensable for overall reconstruction quality. Therefore, to accelerate the inference on mobile devices and achieve a competitive reconstruction quality and inference latency, it is necessary to seek time-friendly surrogates for these time-consuming operators." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 677, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 547, + 715 + ], + "type": "text", + "content": "To this end, we propose Equivalent Transformation (ET), a method that speeds up the model by substituting time-consuming operators with time-friendly ones without im" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 496, + 35 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 496, + 35 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 496, + 35 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 702, + 135, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 702, + 135, + 712 + ], + "spans": [ + { + "bbox": [ + 58, + 702, + 135, + 712 + ], + "type": "text", + "content": "*Corresponding author." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "14102" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 228 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 228 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 228 + ], + "type": "text", + "content": "pairing reconstruction quality. As shown in Fig. 1, the proposed ET can be directly applied to existing models (e.g., ECBSR [34] and ABPN [8]) and reduce inference latency without retraining. However, ET introduces some redundant and unlearnable parameters. To fully utilize these parameters, we design the dual stream network that makes the redundant parameters partially learnable, to boost the feature extraction ability. Finally, we propose a mobile image SR model named ETDS that employs the dual stream network in the training stage and transforms it into an equivalent plain network by ET in the inference stage. As shown in Fig. 1, our ETDS not only achieves high reconstruction quality but also maintains low inference speed." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 228, + 288, + 251 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 228, + 288, + 251 + ], + "spans": [ + { + "bbox": [ + 47, + 228, + 288, + 251 + ], + "type": "text", + "content": "In summary, the main contributions of this paper are as follows:" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 53, + 256, + 286, + 437 + ], + "type": "list", + "angle": 0, + "index": 5, + "blocks": [ + { + "bbox": [ + 54, + 256, + 286, + 303 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 54, + 256, + 286, + 303 + ], + "spans": [ + { + "bbox": [ + 54, + 256, + 286, + 303 + ], + "type": "text", + "content": "1) We propose ET, a method that can transform time-consuming operators and speed up the inference without impairing reconstruction quality. It can be applied to existing models to accelerate the inference." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 53, + 306, + 286, + 342 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 306, + 286, + 342 + ], + "spans": [ + { + "bbox": [ + 53, + 306, + 286, + 342 + ], + "type": "text", + "content": "2) We design a dual stream network to alleviate the redundancy yielded from ET by making redundant parameters partially learnable." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 53, + 344, + 286, + 437 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 344, + 286, + 437 + ], + "spans": [ + { + "bbox": [ + 53, + 344, + 286, + 437 + ], + "type": "text", + "content": "3) We propose an efficient and lightweight network named ETDS for real-time SR on mobile devices based on ET and dual stream networks. Experiments demonstrate that state-of-the-art models equipped with ET have at most " + }, + { + "bbox": [ + 53, + 344, + 286, + 437 + ], + "type": "inline_equation", + "content": "80\\%" + }, + { + "bbox": [ + 53, + 344, + 286, + 437 + ], + "type": "text", + "content": " improvement in inference latency and ETDS achieves " + }, + { + "bbox": [ + 53, + 344, + 286, + 437 + ], + "type": "inline_equation", + "content": "34\\%" + }, + { + "bbox": [ + 53, + 344, + 286, + 437 + ], + "type": "text", + "content": " inference latency improvement and 0.42dB PSNR performance improvement." + } + ] + } + ], + "index": 4 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 47, + 453, + 134, + 464 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 453, + 134, + 464 + ], + "spans": [ + { + "bbox": [ + 47, + 453, + 134, + 464 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 473, + 287, + 653 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 473, + 287, + 653 + ], + "spans": [ + { + "bbox": [ + 46, + 473, + 287, + 653 + ], + "type": "text", + "content": "Due to the rapid development of convolutional neural networks (CNN), CNN-based methods [6, 18, 24, 35, 36] have become mainstream methods for SR tasks. SRCNN [6] pioneered the application of convolutional neural networks on the SR task, surpassing the performance of traditional methods. In EDSR [18], a very deep network was utilized and the batch normalization layers in the residual block were removed. SwinIR [17] first attempted to apply the Swin-Transformer [20] on the SR task, showing the potential of Transformer-based networks [26]. To enlarge the receptive field, the hybrid attention block (HAB) was proposed by HAT [3], which achieved state-of-the-art performance. However, these models have high requirements for memory and computational resources which are not easily attainable in real-world applications." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "type": "text", + "content": "To realize lightweight SR for GPU servers, many approaches tried to reduce the number of parameters and FLOPs. CARN [1] attempted to apply group convolutions. IMDN [10] employed a progressive refinement module to improve the information extraction ability and reduced the" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 72, + 545, + 191 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 191 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 191 + ], + "type": "text", + "content": "number of layers and channels. For further improvement in the efficiency of feature extraction, in RFDN [19], " + }, + { + "bbox": [ + 304, + 72, + 545, + 191 + ], + "type": "inline_equation", + "content": "1 \\times 1" + }, + { + "bbox": [ + 304, + 72, + 545, + 191 + ], + "type": "text", + "content": " convolutions were utilized to replace the " + }, + { + "bbox": [ + 304, + 72, + 545, + 191 + ], + "type": "inline_equation", + "content": "3 \\times 3" + }, + { + "bbox": [ + 304, + 72, + 545, + 191 + ], + "type": "text", + "content": " convolutions on the split channel of the IMDB [10] module. RLFN [15] replaced the progressive refinement module with a simpler residual module, which further improved the running speed and achieved great performance. MemSR [30] optimized the network in terms of memory by removing the residual structure in the model and proposed a novel knowledge distillation method to improve the performance." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 193, + 546, + 479 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 193, + 546, + 479 + ], + "spans": [ + { + "bbox": [ + 304, + 193, + 546, + 479 + ], + "type": "text", + "content": "Due to the particularity of the mobile platforms, most models for GPU servers are not directly applicable to mobile devices whose applications require to be carried out in a timely fashion with restricted computational resources. To solve this problem, current methods mainly optimized the network from three aspects, i.e., neat network topology, computation reduction and operator substitution. ECBSR [34], which proposed an Edge-oriented Convolutional Block (ECB) to achieve better performance, used relatively neat topology for low inference latency on mobile devices and introduced reparameterization techniques to achieve computation reduction for SR task. Following [34], RepSR [27] optimized the performance and training efficiency of the reparameterization module in ECBSR to achieve further computation reduction. ABPN [8] first attempted to apply operator substitution and used the faster repeat operator instead of nearest neighbor interpolation in global residual connections. Inspired by the reparameterization technique, we propose ET, which substitutes more types of operators to achieve low inference latency. Our proposed ETDS optimized the network from all three aspects, where ET optimized the network by achieving operator substitution and computation reduction while the dual stream network adopted a neat topology." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 491, + 389, + 505 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 491, + 389, + 505 + ], + "spans": [ + { + "bbox": [ + 306, + 491, + 389, + 505 + ], + "type": "text", + "content": "3. Methodology" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 511, + 545, + 608 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 511, + 545, + 608 + ], + "spans": [ + { + "bbox": [ + 304, + 511, + 545, + 608 + ], + "type": "text", + "content": "In this section, we examine the current mobile superresolution models in Sec. 3.1, and then propose a novel method, Equivalent Transformation (ET), which substitutes time-consuming operators with time-friendly ones in 3.2. However, applying ET comes at the cost of introducing redundant parameters. To address this, we carefully design a dual stream network that alleviates redundancy and enhances feature extraction ability in Sec. 3.3." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 615, + 511, + 628 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 615, + 511, + 628 + ], + "spans": [ + { + "bbox": [ + 305, + 615, + 511, + 628 + ], + "type": "text", + "content": "3.1. Analysis of Current Mobile SR Models" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 634, + 545, + 695 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 634, + 545, + 695 + ], + "spans": [ + { + "bbox": [ + 304, + 634, + 545, + 695 + ], + "type": "text", + "content": "In order to design more efficient super-resolution models for mobile devices, we analyze the speed bottleneck of current mobile SR models on two of the most popular mobile phone " + }, + { + "bbox": [ + 304, + 634, + 545, + 695 + ], + "type": "inline_equation", + "content": "\\mathrm{SoCs}^1" + }, + { + "bbox": [ + 304, + 634, + 545, + 695 + ], + "type": "text", + "content": ". As shown in Tab. 1, convolution and ReLU operations have lower inference latency than most other op" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 317, + 703, + 544, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 703, + 544, + 712 + ], + "spans": [ + { + "bbox": [ + 317, + 703, + 544, + 712 + ], + "type": "text", + "content": "1www counterpointresearch.com/global-smartphone-ap-market-share/" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "14103" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 50, + 129, + 285, + 311 + ], + "blocks": [ + { + "bbox": [ + 47, + 71, + 287, + 126 + ], + "lines": [ + { + "bbox": [ + 47, + 71, + 287, + 126 + ], + "spans": [ + { + "bbox": [ + 47, + 71, + 287, + 126 + ], + "type": "text", + "content": "Table 1. Average inference latency (ms) of common components in mobile SR models. The average inference latency of all components is tested on SR models with a channel size of 32, an input of size " + }, + { + "bbox": [ + 47, + 71, + 287, + 126 + ], + "type": "inline_equation", + "content": "360 \\times 640" + }, + { + "bbox": [ + 47, + 71, + 287, + 126 + ], + "type": "text", + "content": " and a scale factor of 3. For operators in the same type, the results of higher latency are marked in bold." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 50, + 129, + 285, + 311 + ], + "lines": [ + { + "bbox": [ + 50, + 129, + 285, + 311 + ], + "spans": [ + { + "bbox": [ + 50, + 129, + 285, + 311 + ], + "type": "table", + "html": "
TypeOperatorLatency (ms)
Dimensity 8100Snapdragon 870Snapdragon 865
Convolution1 × 1 Convolution2.244
3 × 3 Convolution10.41821
Transposed Convolution7.379
ActivationReLU0.060.60.6
PReLU2.264.83.8
LeakyReLU2.265.64.2
Sigmoid0.120.60.8
Tanh0.30.81
InterpolationNearest neighbor262427
Bilinear676568
OthersAdd6.534
Concatenate22.867
Multiply6.534
Repeat16.31914
Clip6.99194
PixelShuffle4.234
", + "image_path": "3f95c467bb35b6141d1707eb69eef9c4b4936173afc29ae40694c2ad5727188c.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 322, + 286, + 405 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 322, + 286, + 405 + ], + "spans": [ + { + "bbox": [ + 46, + 322, + 286, + 405 + ], + "type": "text", + "content": "erations, and PixelShuffle [23] is more efficient than transposed convolution, which indicates PixelShuffle and ReLU are better choices for mobile platforms. Hereafter, plain network refers to a network that only contains time-friendly operators (i.e., convolution, ReLU activation functions and PixelShuffle), which has low inference latency on mobile devices." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 407, + 286, + 430 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 407, + 286, + 430 + ], + "spans": [ + { + "bbox": [ + 47, + 407, + 286, + 430 + ], + "type": "text", + "content": "To transform current mobile models into plain models, we may encounter the following challenges:" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 53, + 432, + 287, + 552 + ], + "type": "list", + "angle": 0, + "index": 6, + "blocks": [ + { + "bbox": [ + 53, + 432, + 287, + 491 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 432, + 287, + 491 + ], + "spans": [ + { + "bbox": [ + 53, + 432, + 287, + 491 + ], + "type": "text", + "content": "1) To avoid the rescaling problem in the INT8 quantization models, it is necessary to add the clip operator at the end of the model. However, the clip operator is also time-consuming (see Tab. 1), which requires a more efficient and equivalent alternative." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 53, + 493, + 287, + 552 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 493, + 287, + 552 + ], + "spans": [ + { + "bbox": [ + 53, + 493, + 287, + 552 + ], + "type": "text", + "content": "2) To compensate for the PSNR performance drop brought by the removal of global residual connections, it is necessary to find an equivalent way to transform the global residual connection into an efficient operator." + } + ] + } + ], + "index": 5 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 46, + 553, + 286, + 601 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 553, + 286, + 601 + ], + "spans": [ + { + "bbox": [ + 46, + 553, + 286, + 601 + ], + "type": "text", + "content": "To tackle these challenges, we propose ET, which substitutes some time-consuming operators with time-friendly ones without reducing the reconstruction quality, thereby improving the running speed." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 610, + 197, + 623 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 610, + 197, + 623 + ], + "spans": [ + { + "bbox": [ + 47, + 610, + 197, + 623 + ], + "type": "text", + "content": "3.2. Equivalent Transformation" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 629, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 629, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 629, + 287, + 713 + ], + "type": "text", + "content": "Formal Definitions. A convolution operation is formulated as " + }, + { + "bbox": [ + 47, + 629, + 287, + 713 + ], + "type": "inline_equation", + "content": "z = W \\otimes x + b" + }, + { + "bbox": [ + 47, + 629, + 287, + 713 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 47, + 629, + 287, + 713 + ], + "type": "inline_equation", + "content": "x \\in \\mathbb{R}^{c_i \\times h \\times w}" + }, + { + "bbox": [ + 47, + 629, + 287, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 629, + 287, + 713 + ], + "type": "inline_equation", + "content": "z \\in \\mathbb{R}^{c_o \\times h \\times w}" + }, + { + "bbox": [ + 47, + 629, + 287, + 713 + ], + "type": "text", + "content": " are the input and output tensors respectively, " + }, + { + "bbox": [ + 47, + 629, + 287, + 713 + ], + "type": "inline_equation", + "content": "W \\in \\mathbb{R}^{c_o \\times k \\times k \\times c_i}" + }, + { + "bbox": [ + 47, + 629, + 287, + 713 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 629, + 287, + 713 + ], + "type": "inline_equation", + "content": "b \\in \\mathbb{R}^{c_o}" + }, + { + "bbox": [ + 47, + 629, + 287, + 713 + ], + "type": "text", + "content": " are the kernel and the bias of the convolution, and " + }, + { + "bbox": [ + 47, + 629, + 287, + 713 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 47, + 629, + 287, + 713 + ], + "type": "text", + "content": " is the kernel size, " + }, + { + "bbox": [ + 47, + 629, + 287, + 713 + ], + "type": "inline_equation", + "content": "c_i, c_o" + }, + { + "bbox": [ + 47, + 629, + 287, + 713 + ], + "type": "text", + "content": " are the numbers of the input and output channels, and " + }, + { + "bbox": [ + 47, + 629, + 287, + 713 + ], + "type": "inline_equation", + "content": "h, w" + }, + { + "bbox": [ + 47, + 629, + 287, + 713 + ], + "type": "text", + "content": " are the input height and width. " + }, + { + "bbox": [ + 47, + 629, + 287, + 713 + ], + "type": "inline_equation", + "content": "I" + }, + { + "bbox": [ + 47, + 629, + 287, + 713 + ], + "type": "text", + "content": " is the identity kernel of the convolution" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 72, + 539, + 84 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 539, + 84 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 539, + 84 + ], + "type": "text", + "content": "operation, and " + }, + { + "bbox": [ + 305, + 72, + 539, + 84 + ], + "type": "inline_equation", + "content": "O" + }, + { + "bbox": [ + 305, + 72, + 539, + 84 + ], + "type": "text", + "content": " is the kernel of zero elements, satisfying" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 340, + 91, + 545, + 105 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 340, + 91, + 545, + 105 + ], + "spans": [ + { + "bbox": [ + 340, + 91, + 545, + 105 + ], + "type": "interline_equation", + "content": "I \\otimes x = x, \\quad O \\otimes x = 0, \\forall x \\in \\mathbb {R} ^ {c _ {i} \\times h \\times w}. \\tag {1}", + "image_path": "ddd66fcfc1f78188916608aa21aef256f028bd057960ff34f67c67cfe77f3a03.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 114, + 545, + 209 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 114, + 545, + 209 + ], + "spans": [ + { + "bbox": [ + 304, + 114, + 545, + 209 + ], + "type": "text", + "content": "For input features and convolution kernels, the concatenation operation requires all but the concatenated dimension to be consistent. The channel dimension concatenation operation of feature vectors " + }, + { + "bbox": [ + 304, + 114, + 545, + 209 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 304, + 114, + 545, + 209 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 114, + 545, + 209 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 304, + 114, + 545, + 209 + ], + "type": "text", + "content": " is defined as " + }, + { + "bbox": [ + 304, + 114, + 545, + 209 + ], + "type": "inline_equation", + "content": "\\begin{bmatrix} x \\\\ y \\end{bmatrix}" + }, + { + "bbox": [ + 304, + 114, + 545, + 209 + ], + "type": "text", + "content": ". The concatenation operation of the convolution kernels " + }, + { + "bbox": [ + 304, + 114, + 545, + 209 + ], + "type": "inline_equation", + "content": "W_{h,1}" + }, + { + "bbox": [ + 304, + 114, + 545, + 209 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 114, + 545, + 209 + ], + "type": "inline_equation", + "content": "W_{h,2}" + }, + { + "bbox": [ + 304, + 114, + 545, + 209 + ], + "type": "text", + "content": " in the horizontal direction (i.e., input-dimension concatenation) is defined as " + }, + { + "bbox": [ + 304, + 114, + 545, + 209 + ], + "type": "inline_equation", + "content": "[W_{h,1}, W_{h,2}]" + }, + { + "bbox": [ + 304, + 114, + 545, + 209 + ], + "type": "text", + "content": ", which satisfies" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 331, + 216, + 545, + 243 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 331, + 216, + 545, + 243 + ], + "spans": [ + { + "bbox": [ + 331, + 216, + 545, + 243 + ], + "type": "interline_equation", + "content": "\\left[ W _ {h, 1}, W _ {h, 2} \\right] \\otimes \\left[ \\begin{array}{l} x \\\\ y \\end{array} \\right] = W _ {h, 1} \\otimes x + W _ {h, 2} \\otimes y. \\tag {2}", + "image_path": "08787e37cf0f4a31f775169b4f2bcaa7b5bf64f3382531bad406d33b8a07a9d2.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 249, + 545, + 305 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 249, + 545, + 305 + ], + "spans": [ + { + "bbox": [ + 304, + 249, + 545, + 305 + ], + "type": "text", + "content": "Likewise, the concatenation operation of the convolution kernels " + }, + { + "bbox": [ + 304, + 249, + 545, + 305 + ], + "type": "inline_equation", + "content": "W_{v,1}" + }, + { + "bbox": [ + 304, + 249, + 545, + 305 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 249, + 545, + 305 + ], + "type": "inline_equation", + "content": "W_{v,2}" + }, + { + "bbox": [ + 304, + 249, + 545, + 305 + ], + "type": "text", + "content": " in the vertical direction, i.e., output-dimension concatenation is defined as " + }, + { + "bbox": [ + 304, + 249, + 545, + 305 + ], + "type": "inline_equation", + "content": "\\begin{bmatrix} W_{v,1} \\\\ W_{v,2} \\end{bmatrix}" + }, + { + "bbox": [ + 304, + 249, + 545, + 305 + ], + "type": "text", + "content": ", which satisfies" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 367, + 305, + 545, + 332 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 367, + 305, + 545, + 332 + ], + "spans": [ + { + "bbox": [ + 367, + 305, + 545, + 332 + ], + "type": "interline_equation", + "content": "\\left[ \\begin{array}{l} W _ {v, 1} \\\\ W _ {v, 2} \\end{array} \\right] \\otimes x = \\left[ \\begin{array}{l} W _ {v, 1} \\otimes x \\\\ W _ {v, 2} \\otimes x \\end{array} \\right]. \\tag {3}", + "image_path": "c2d84f32be7e87c1d16d452fbe47d916b603571ec67b41e2dd93d2f302c70167.jpg" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 306, + 335, + 468, + 346 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 335, + 468, + 346 + ], + "spans": [ + { + "bbox": [ + 306, + 335, + 468, + 346 + ], + "type": "text", + "content": "More details will be found in Appendix." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 346, + 545, + 418 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 346, + 545, + 418 + ], + "spans": [ + { + "bbox": [ + 304, + 346, + 545, + 418 + ], + "type": "text", + "content": "ET for Repeat Operator. Given an input tensor " + }, + { + "bbox": [ + 304, + 346, + 545, + 418 + ], + "type": "inline_equation", + "content": "x \\in \\mathbb{R}^{c \\times h \\times w}" + }, + { + "bbox": [ + 304, + 346, + 545, + 418 + ], + "type": "text", + "content": ", the repeat operator " + }, + { + "bbox": [ + 304, + 346, + 545, + 418 + ], + "type": "inline_equation", + "content": "\\text{repeat}(x, n)" + }, + { + "bbox": [ + 304, + 346, + 545, + 418 + ], + "type": "text", + "content": " constructs a new tensor " + }, + { + "bbox": [ + 304, + 346, + 545, + 418 + ], + "type": "inline_equation", + "content": "z \\in \\mathbb{R}^{(nc) \\times h \\times w}" + }, + { + "bbox": [ + 304, + 346, + 545, + 418 + ], + "type": "text", + "content": " by replicating the input " + }, + { + "bbox": [ + 304, + 346, + 545, + 418 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 304, + 346, + 545, + 418 + ], + "type": "text", + "content": " times along the channel dimension. This operation can be expressed as a convolution layer. Precisely, Eq. (1) and (3) yield" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 333, + 425, + 545, + 486 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 333, + 425, + 545, + 486 + ], + "spans": [ + { + "bbox": [ + 333, + 425, + 545, + 486 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\operatorname {r e p e a t} (x, n) = \\left[ \\begin{array}{c} x \\\\ \\vdots \\\\ x \\end{array} \\right] = \\left[ \\begin{array}{c} I \\otimes x \\\\ \\vdots \\\\ I \\otimes x \\end{array} \\right] = \\left[ \\begin{array}{c} I \\\\ \\vdots \\\\ I \\end{array} \\right] \\otimes x \\tag {4} \\\\ = \\operatorname {r e p e a t} (I, n) \\otimes x, \\\\ \\end{array}", + "image_path": "00d77a9e4e5e8ab05158059c5b50bd3fe20928cd9fa38d4f19659781d1a3cea9.jpg" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 494, + 545, + 540 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 494, + 545, + 540 + ], + "spans": [ + { + "bbox": [ + 304, + 494, + 545, + 540 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 494, + 545, + 540 + ], + "type": "inline_equation", + "content": "\\text{repeat}(I, n)" + }, + { + "bbox": [ + 304, + 494, + 545, + 540 + ], + "type": "text", + "content": " is a constant. Thus, the repeat operator is equivalently transformed into a convolution layer, whose kernel and bias are " + }, + { + "bbox": [ + 304, + 494, + 545, + 540 + ], + "type": "inline_equation", + "content": "\\text{repeat}(I, n)" + }, + { + "bbox": [ + 304, + 494, + 545, + 540 + ], + "type": "text", + "content": " and a zero vector, respectively." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 541, + 545, + 590 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 541, + 545, + 590 + ], + "spans": [ + { + "bbox": [ + 304, + 541, + 545, + 590 + ], + "type": "text", + "content": "ET for Add Operator. The add operator refers to the element-wise addition operation of two feature vectors and is an indispensable part of residual connections, i.e., " + }, + { + "bbox": [ + 304, + 541, + 545, + 590 + ], + "type": "inline_equation", + "content": "z = x + y" + }, + { + "bbox": [ + 304, + 541, + 545, + 590 + ], + "type": "text", + "content": ". From Eq. (1) and (2), we have:" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 341, + 597, + 545, + 623 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 341, + 597, + 545, + 623 + ], + "spans": [ + { + "bbox": [ + 341, + 597, + 545, + 623 + ], + "type": "interline_equation", + "content": "x + y = I \\otimes x + I \\otimes y = [ I, I ] \\otimes \\left[ \\begin{array}{l} x \\\\ y \\end{array} \\right]. \\tag {5}", + "image_path": "930d552cd04962c69d9da5f5740d66c0bcaa535987b6c395c2cfc4fb9d7ed646.jpg" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 304, + 629, + 545, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 629, + 545, + 689 + ], + "spans": [ + { + "bbox": [ + 304, + 629, + 545, + 689 + ], + "type": "text", + "content": "Thus, the add operator is equivalently transformed into a convolution layer with a concatenate operator, whose kernel and bias are " + }, + { + "bbox": [ + 304, + 629, + 545, + 689 + ], + "type": "inline_equation", + "content": "[I, I]" + }, + { + "bbox": [ + 304, + 629, + 545, + 689 + ], + "type": "text", + "content": " and a zero vector, respectively. Notably, this proposed convolution layer can be eliminated later by reparameterization techniques." + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "type": "text", + "content": "ET for Concatenate Operator. In our model, the concatenate operator always follows the convolution layers." + } + ] + } + ], + "index": 23 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "14104" + } + ] + } + ], + "index": 24 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 287, + 109 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 287, + 109 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 287, + 109 + ], + "type": "text", + "content": "We integrate the convolution-concatenate structure, i.e., the concatenate operator and its preceding convolution layer, which can be simplified with Eq. (2) and (3) as follows:" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 55, + 114, + 287, + 143 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 55, + 114, + 287, + 143 + ], + "spans": [ + { + "bbox": [ + 55, + 114, + 287, + 143 + ], + "type": "interline_equation", + "content": "z = \\left[ \\begin{array}{c} W _ {1} \\otimes x + b _ {1} \\\\ W _ {2} \\otimes y + b _ {2} \\end{array} \\right] = \\left[ \\begin{array}{c c} W _ {1} & O \\\\ O & W _ {2} \\end{array} \\right] \\otimes \\left[ \\begin{array}{c} x \\\\ y \\end{array} \\right] + \\left[ \\begin{array}{c} b _ {1} \\\\ b _ {2} \\end{array} \\right]. \\tag {6}", + "image_path": "e17b82dcbd1f5be00cc4883b99ea1f885012ee8bc3d15d2dc0983f72bc0c8ad8.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 148, + 287, + 183 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 148, + 287, + 183 + ], + "spans": [ + { + "bbox": [ + 47, + 148, + 287, + 183 + ], + "type": "text", + "content": "Following Eq. (6), the convolution-concatenate structure is transformed into a concatenate-convolution structure, with the kernel and bias as follows:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 111, + 188, + 287, + 216 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 111, + 188, + 287, + 216 + ], + "spans": [ + { + "bbox": [ + 111, + 188, + 287, + 216 + ], + "type": "interline_equation", + "content": "\\left[ \\begin{array}{c c} W _ {1} & O \\\\ O & W _ {2} \\end{array} \\right] \\quad \\text {a n d} \\quad \\left[ \\begin{array}{l} b _ {1} \\\\ b _ {2} \\end{array} \\right]. \\tag {7}", + "image_path": "5aa05bff01e8048e65e01a574bd7e29674f3e9bdd961d0b9788942f5daec774d.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 221, + 287, + 246 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 221, + 287, + 246 + ], + "spans": [ + { + "bbox": [ + 47, + 221, + 287, + 246 + ], + "type": "text", + "content": "In particular, when the residual branch does not have a convolution layer, it can be expressed as:" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 71, + 251, + 287, + 280 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 71, + 251, + 287, + 280 + ], + "spans": [ + { + "bbox": [ + 71, + 251, + 287, + 280 + ], + "type": "interline_equation", + "content": "z = \\left[ \\begin{array}{c} W \\otimes x + b \\\\ y \\end{array} \\right] = \\left[ \\begin{array}{c c} W & O \\\\ O & I \\end{array} \\right] \\otimes \\left[ \\begin{array}{c} x \\\\ y \\end{array} \\right] + \\left[ \\begin{array}{c} b \\\\ 0 \\end{array} \\right]. \\tag {8}", + "image_path": "ad949d22e7490adbf3de49f83f3fe18255567258c6e6f3299a69c8954031e88b.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 285, + 242, + 297 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 285, + 242, + 297 + ], + "spans": [ + { + "bbox": [ + 47, + 285, + 242, + 297 + ], + "type": "text", + "content": "When " + }, + { + "bbox": [ + 47, + 285, + 242, + 297 + ], + "type": "inline_equation", + "content": "x = y" + }, + { + "bbox": [ + 47, + 285, + 242, + 297 + ], + "type": "text", + "content": ", Eq. (8) can be further rewritten as:" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 86, + 303, + 287, + 331 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 86, + 303, + 287, + 331 + ], + "spans": [ + { + "bbox": [ + 86, + 303, + 287, + 331 + ], + "type": "interline_equation", + "content": "z = \\left[ \\begin{array}{c} W \\otimes x + b \\\\ x \\end{array} \\right] = \\left[ \\begin{array}{c} W \\\\ I \\end{array} \\right] \\otimes x + \\left[ \\begin{array}{c} b \\\\ 0 \\end{array} \\right], \\tag {9}", + "image_path": "f3140a38116eefd3bbeeddae33776538ff710ad08947d151c457164a7692361b.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 337, + 287, + 372 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 337, + 287, + 372 + ], + "spans": [ + { + "bbox": [ + 47, + 337, + 287, + 372 + ], + "type": "text", + "content": "where the kernel is " + }, + { + "bbox": [ + 47, + 337, + 287, + 372 + ], + "type": "inline_equation", + "content": "\\left[ \\begin{array}{l}W\\\\ I \\end{array} \\right]" + }, + { + "bbox": [ + 47, + 337, + 287, + 372 + ], + "type": "text", + "content": " and thus the concatenate operator is eliminated." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 374, + 287, + 395 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 374, + 287, + 395 + ], + "spans": [ + { + "bbox": [ + 47, + 374, + 287, + 395 + ], + "type": "text", + "content": "ET for Clip Operator. The clip operator is expressed as:" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 93, + 395, + 287, + 433 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 93, + 395, + 287, + 433 + ], + "spans": [ + { + "bbox": [ + 93, + 395, + 287, + 433 + ], + "type": "interline_equation", + "content": "\\operatorname {c l i p} (x) = \\left\\{ \\begin{array}{l l} 0, & x \\leq 0, \\\\ x, & 0 < x \\leq 2 5 5, \\\\ 2 5 5, & x > 2 5 5, \\end{array} \\right. \\tag {10}", + "image_path": "285d31ddd490d9f34e743daa3adb760020355bdf4125a7a8251bcc453c811f88.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 47, + 436, + 287, + 507 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 436, + 287, + 507 + ], + "spans": [ + { + "bbox": [ + 47, + 436, + 287, + 507 + ], + "type": "text", + "content": "which avoids the loss of precision and subsequent additional inverse scaling operations caused by mismatched normalization of the INT8 quantization model [12]. Nevertheless, as shown in Tab. 1, the clip operator is extremely time-consuming on many mobile SoCs, so it is of great necessity to find a time-friendly substitution for the clip operator." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 47, + 508, + 286, + 531 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 508, + 286, + 531 + ], + "spans": [ + { + "bbox": [ + 47, + 508, + 286, + 531 + ], + "type": "text", + "content": "To equivalently transform the clip operator with ReLU, we reformulate clip operator as:" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 64, + 539, + 287, + 553 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 64, + 539, + 287, + 553 + ], + "spans": [ + { + "bbox": [ + 64, + 539, + 287, + 553 + ], + "type": "interline_equation", + "content": "\\operatorname {c l i p} (x) = \\operatorname {R e L U} (- \\operatorname {R e L U} (- x + 2 5 5) + 2 5 5). \\tag {11}", + "image_path": "be50c223595871fb3cd300eaa5c6c109066cd468e68fe470dc4923947c60af40.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 47, + 560, + 246, + 571 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 560, + 246, + 571 + ], + "spans": [ + { + "bbox": [ + 47, + 560, + 246, + 571 + ], + "type": "text", + "content": "To speed up this process, we further rewrite it as:" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 90, + 578, + 287, + 612 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 90, + 578, + 287, + 612 + ], + "spans": [ + { + "bbox": [ + 90, + 578, + 287, + 612 + ], + "type": "interline_equation", + "content": "\\left\\{ \\begin{array}{l l} y = & \\operatorname {R e L U} (- I \\otimes x + 2 5 5), \\\\ c l i p (x) = & \\operatorname {R e L U} (- I \\otimes y + 2 5 5). \\end{array} \\right. \\tag {12}", + "image_path": "956e7824043ba8aa00c1cbc699c6a15488c9a00202cb2d42014c4e63950c6991.jpg" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 47, + 617, + 287, + 677 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 617, + 287, + 677 + ], + "spans": [ + { + "bbox": [ + 47, + 617, + 287, + 677 + ], + "type": "text", + "content": "Using Eq. (12), the clip operator is transformed into two convolutions with ReLU, whose kernels are " + }, + { + "bbox": [ + 47, + 617, + 287, + 677 + ], + "type": "inline_equation", + "content": "-I" + }, + { + "bbox": [ + 47, + 617, + 287, + 677 + ], + "type": "text", + "content": " and bias is a vector with all elements equal to 255. Remark that the first convolution layer in Eq. (12) is eliminated by reparameterization techniques [5]." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 47, + 677, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 677, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 677, + 287, + 713 + ], + "type": "text", + "content": "ET for Equivalent Plain Model Conversion. As depicted in Fig. 2, the model is converted into an equivalent plain model by ET as following:" + } + ] + } + ], + "index": 17 + }, + { + "type": "image", + "bbox": [ + 307, + 72, + 544, + 253 + ], + "blocks": [ + { + "bbox": [ + 307, + 72, + 544, + 253 + ], + "lines": [ + { + "bbox": [ + 307, + 72, + 544, + 253 + ], + "spans": [ + { + "bbox": [ + 307, + 72, + 544, + 253 + ], + "type": "image", + "image_path": "59f6d1975d519faadfd1e91349866a0ec9b3ce51ae72d4cad240447b246410b6.jpg" + } + ] + } + ], + "index": 18, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 258, + 545, + 301 + ], + "lines": [ + { + "bbox": [ + 305, + 258, + 545, + 301 + ], + "spans": [ + { + "bbox": [ + 305, + 258, + 545, + 301 + ], + "type": "text", + "content": "Figure 2. Illustration of converting the general model into the equivalent plain model using ET. The beige convolution indicates that the convolution kernel is assigned a specific value. Rep refers to the reparameterization technique." + } + ] + } + ], + "index": 19, + "angle": 0, + "type": "image_caption" + } + ], + "index": 18 + }, + { + "bbox": [ + 317, + 312, + 545, + 543 + ], + "type": "list", + "angle": 0, + "index": 25, + "blocks": [ + { + "bbox": [ + 317, + 312, + 545, + 347 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 312, + 545, + 347 + ], + "spans": [ + { + "bbox": [ + 317, + 312, + 545, + 347 + ], + "type": "text", + "content": "- The repeat operator and the add operator are converted into a single convolution and a concatenate operator respectively (see Step 1 and Step 2)." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 317, + 349, + 545, + 408 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 349, + 545, + 408 + ], + "spans": [ + { + "bbox": [ + 317, + 349, + 545, + 408 + ], + "type": "text", + "content": "- The concatenate operator with the preceding convolutions from two branches is converted into a convolution. Notably, the global residual connection does not contain negative values, so the ReLU function is omitted (see Step 3)." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 317, + 410, + 545, + 445 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 410, + 545, + 445 + ], + "spans": [ + { + "bbox": [ + 317, + 410, + 545, + 445 + ], + "type": "text", + "content": "- The two convolutions introduced by previous steps are converted into a convolution using reparameterization techniques (see Step 4)." + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 317, + 447, + 545, + 518 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 447, + 545, + 518 + ], + "spans": [ + { + "bbox": [ + 317, + 447, + 545, + 518 + ], + "type": "text", + "content": "- The convolution-concatenate structure is converted into a concatenate-convolution one, thus the concatenate operator is converted and moves forward till it reaches the skip connection starting point, that is, " + }, + { + "bbox": [ + 317, + 447, + 545, + 518 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 317, + 447, + 545, + 518 + ], + "type": "text", + "content": " equals " + }, + { + "bbox": [ + 317, + 447, + 545, + 518 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 317, + 447, + 545, + 518 + ], + "type": "text", + "content": ". In this situation, the concatenate operator is further eliminated (see Step 5 and Step 6)." + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 317, + 519, + 545, + 543 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 519, + 545, + 543 + ], + "spans": [ + { + "bbox": [ + 317, + 519, + 545, + 543 + ], + "type": "text", + "content": "- The clip operator is converted into the convolution (see Step 7)." + } + ] + } + ], + "index": 24 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 305, + 553, + 545, + 637 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 553, + 545, + 637 + ], + "spans": [ + { + "bbox": [ + 305, + 553, + 545, + 637 + ], + "type": "text", + "content": "Remark 1 Although " + }, + { + "bbox": [ + 305, + 553, + 545, + 637 + ], + "type": "inline_equation", + "content": "ET" + }, + { + "bbox": [ + 305, + 553, + 545, + 637 + ], + "type": "text", + "content": " speeds up inference by transforming time-consuming operators into time-friendly ones, it introduces some redundant parameters. For instance, in the transformed convolution kernel " + }, + { + "bbox": [ + 305, + 553, + 545, + 637 + ], + "type": "inline_equation", + "content": "\\mathrm{diag}(W, I)" + }, + { + "bbox": [ + 305, + 553, + 545, + 637 + ], + "type": "text", + "content": " derived from Eq. (8). All learnable parameters appear in " + }, + { + "bbox": [ + 305, + 553, + 545, + 637 + ], + "type": "inline_equation", + "content": "W" + }, + { + "bbox": [ + 305, + 553, + 545, + 637 + ], + "type": "text", + "content": ". If the redundant parameters are effectively utilized, better reconstruction performance can be achieved." + } + ] + } + ], + "index": 26 + }, + { + "bbox": [ + 306, + 647, + 430, + 658 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 647, + 430, + 658 + ], + "spans": [ + { + "bbox": [ + 306, + 647, + 430, + 658 + ], + "type": "text", + "content": "3.3. Dual Stream Network" + } + ] + } + ], + "index": 27 + }, + { + "bbox": [ + 305, + 665, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 665, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 665, + 545, + 713 + ], + "type": "text", + "content": "To alleviate the side effects of the redundant parameters of ET, we design a dual stream network where the two branches learn the low-frequency and high-frequency contents of the image separately and utilize the parameters to" + } + ] + } + ], + "index": 28 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "14105" + } + ] + } + ], + "index": 29 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 50, + 71, + 541, + 178 + ], + "blocks": [ + { + "bbox": [ + 50, + 71, + 541, + 178 + ], + "lines": [ + { + "bbox": [ + 50, + 71, + 541, + 178 + ], + "spans": [ + { + "bbox": [ + 50, + 71, + 541, + 178 + ], + "type": "image", + "image_path": "daf35378cd2414e3c9483385e5c31e2e32e06ef0ba9c5d827745e79b08432eca.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 50, + 185, + 545, + 261 + ], + "blocks": [ + { + "bbox": [ + 50, + 185, + 545, + 261 + ], + "lines": [ + { + "bbox": [ + 50, + 185, + 545, + 261 + ], + "spans": [ + { + "bbox": [ + 50, + 185, + 545, + 261 + ], + "type": "image", + "image_path": "c38885220b3bd666d9c8b90aaa8f9edc40866df1e243e1aa8b56f76615dab007.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 273, + 546, + 296 + ], + "lines": [ + { + "bbox": [ + 46, + 273, + 546, + 296 + ], + "spans": [ + { + "bbox": [ + 46, + 273, + 546, + 296 + ], + "type": "text", + "content": "Figure 3. Network architecture of ETDS during training and inference stages. The residual branch for extracting low-frequency contents only contains a few parameters, and most of the parameters are used to extract high-frequency contents." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_caption" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 311, + 287, + 429 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 311, + 287, + 429 + ], + "spans": [ + { + "bbox": [ + 46, + 311, + 287, + 429 + ], + "type": "text", + "content": "the fullest. The transformed convolution kernel in Eq. (8) is " + }, + { + "bbox": [ + 46, + 311, + 287, + 429 + ], + "type": "inline_equation", + "content": "\\left[ \\begin{array}{cc}K_b & K_{r2b}\\\\ K_{b2r} & K_r \\end{array} \\right]" + }, + { + "bbox": [ + 46, + 311, + 287, + 429 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 311, + 287, + 429 + ], + "type": "inline_equation", + "content": "K_{b}" + }, + { + "bbox": [ + 46, + 311, + 287, + 429 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 311, + 287, + 429 + ], + "type": "inline_equation", + "content": "K_{r}" + }, + { + "bbox": [ + 46, + 311, + 287, + 429 + ], + "type": "text", + "content": " denote the modules that constitute the backbone branch and residual branch, respectively. " + }, + { + "bbox": [ + 46, + 311, + 287, + 429 + ], + "type": "inline_equation", + "content": "K_{r2b}" + }, + { + "bbox": [ + 46, + 311, + 287, + 429 + ], + "type": "text", + "content": " is the module that transfers information from the residual branch to the backbone branch, and " + }, + { + "bbox": [ + 46, + 311, + 287, + 429 + ], + "type": "inline_equation", + "content": "K_{b2r}" + }, + { + "bbox": [ + 46, + 311, + 287, + 429 + ], + "type": "text", + "content": " transfers information reversely. The residual branch consisting of " + }, + { + "bbox": [ + 46, + 311, + 287, + 429 + ], + "type": "inline_equation", + "content": "K_{r}" + }, + { + "bbox": [ + 46, + 311, + 287, + 429 + ], + "type": "text", + "content": " and the backbone branch consisting of " + }, + { + "bbox": [ + 46, + 311, + 287, + 429 + ], + "type": "inline_equation", + "content": "K_{b}" + }, + { + "bbox": [ + 46, + 311, + 287, + 429 + ], + "type": "text", + "content": " extract low-frequency and high-frequency information respectively." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 430, + 287, + 560 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 430, + 287, + 560 + ], + "spans": [ + { + "bbox": [ + 46, + 430, + 287, + 560 + ], + "type": "text", + "content": "Initially, " + }, + { + "bbox": [ + 46, + 430, + 287, + 560 + ], + "type": "inline_equation", + "content": "K_{r}" + }, + { + "bbox": [ + 46, + 430, + 287, + 560 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 430, + 287, + 560 + ], + "type": "inline_equation", + "content": "K_{r2b}" + }, + { + "bbox": [ + 46, + 430, + 287, + 560 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 430, + 287, + 560 + ], + "type": "inline_equation", + "content": "K_{b2r}" + }, + { + "bbox": [ + 46, + 430, + 287, + 560 + ], + "type": "text", + "content": " are not learnable. Furthermore, we have analyzed the possible impacts of making them learnable on the reconstruction quality and found that when " + }, + { + "bbox": [ + 46, + 430, + 287, + 560 + ], + "type": "inline_equation", + "content": "K_{r}" + }, + { + "bbox": [ + 46, + 430, + 287, + 560 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 430, + 287, + 560 + ], + "type": "inline_equation", + "content": "K_{r2b}" + }, + { + "bbox": [ + 46, + 430, + 287, + 560 + ], + "type": "text", + "content": " are learnable, they can extract low-frequency information more effectively and transfer more residual information to the backbone branch, respectively. However, when " + }, + { + "bbox": [ + 46, + 430, + 287, + 560 + ], + "type": "inline_equation", + "content": "K_{b2r}" + }, + { + "bbox": [ + 46, + 430, + 287, + 560 + ], + "type": "text", + "content": " is learnable, the backbone branch may take less important low-frequency information into consideration, which reduces the number of parameters for extracting high-frequency components, and potentially compromising the performance." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 561, + 287, + 644 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 561, + 287, + 644 + ], + "spans": [ + { + "bbox": [ + 46, + 561, + 287, + 644 + ], + "type": "text", + "content": "As shown in Fig. 3, " + }, + { + "bbox": [ + 46, + 561, + 287, + 644 + ], + "type": "inline_equation", + "content": "K_{r}" + }, + { + "bbox": [ + 46, + 561, + 287, + 644 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 561, + 287, + 644 + ], + "type": "inline_equation", + "content": "K_{r2b}" + }, + { + "bbox": [ + 46, + 561, + 287, + 644 + ], + "type": "text", + "content": " in our dual stream network contain learnable parameters, while parameters in " + }, + { + "bbox": [ + 46, + 561, + 287, + 644 + ], + "type": "inline_equation", + "content": "K_{b2r}" + }, + { + "bbox": [ + 46, + 561, + 287, + 644 + ], + "type": "text", + "content": " remain fixed. In the training phase, we encourage the residual branch to learn as many low-frequency contents as possible, that is, to minimize the " + }, + { + "bbox": [ + 46, + 561, + 287, + 644 + ], + "type": "inline_equation", + "content": "L_{1}" + }, + { + "bbox": [ + 46, + 561, + 287, + 644 + ], + "type": "text", + "content": " distance between the output of the residual branch " + }, + { + "bbox": [ + 46, + 561, + 287, + 644 + ], + "type": "inline_equation", + "content": "(I_{LF})" + }, + { + "bbox": [ + 46, + 561, + 287, + 644 + ], + "type": "text", + "content": " and the ground truth " + }, + { + "bbox": [ + 46, + 561, + 287, + 644 + ], + "type": "inline_equation", + "content": "(I_{GT})" + }, + { + "bbox": [ + 46, + 561, + 287, + 644 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 117, + 644, + 287, + 657 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 117, + 644, + 287, + 657 + ], + "spans": [ + { + "bbox": [ + 117, + 644, + 287, + 657 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {L F} = \\left\\| I _ {G T} - I _ {L F} \\right\\| _ {1}. \\tag {13}", + "image_path": "53f40a36bb28227d6d78409ee05346b220a594aea308604384f6f2ac1934b292.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 659, + 287, + 696 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 659, + 287, + 696 + ], + "spans": [ + { + "bbox": [ + 47, + 659, + 287, + 696 + ], + "type": "text", + "content": "The backbone branch learns high-frequency contents, and its output " + }, + { + "bbox": [ + 47, + 659, + 287, + 696 + ], + "type": "inline_equation", + "content": "(I_{HF})" + }, + { + "bbox": [ + 47, + 659, + 287, + 696 + ], + "type": "text", + "content": " compensates for the gap between " + }, + { + "bbox": [ + 47, + 659, + 287, + 696 + ], + "type": "inline_equation", + "content": "I_{GT}" + }, + { + "bbox": [ + 47, + 659, + 287, + 696 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 659, + 287, + 696 + ], + "type": "inline_equation", + "content": "I_{LF}" + }, + { + "bbox": [ + 47, + 659, + 287, + 696 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 102, + 701, + 287, + 714 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 102, + 701, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 102, + 701, + 287, + 714 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {H F} = \\left\\| I _ {G T} - I _ {L F} - I _ {H F} \\right\\| _ {1}. \\tag {14}", + "image_path": "b2da02594a5ea260c6f838cca91f0721d71b5adb83d0be6a209b2704abde811e.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 311, + 545, + 333 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 311, + 545, + 333 + ], + "spans": [ + { + "bbox": [ + 305, + 311, + 545, + 333 + ], + "type": "text", + "content": "To train the dual stream network, we use the overall loss function:" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 371, + 335, + 545, + 346 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 371, + 335, + 545, + 346 + ], + "spans": [ + { + "bbox": [ + 371, + 335, + 545, + 346 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {D S} = \\mathcal {L} _ {H F} + \\alpha \\times \\mathcal {L} _ {L F}, \\tag {15}", + "image_path": "dfd94ba9a25586940a665117a4c542b53812b00be21152c04f6bbb112cd1e0c0.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 352, + 545, + 411 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 352, + 545, + 411 + ], + "spans": [ + { + "bbox": [ + 304, + 352, + 545, + 411 + ], + "type": "text", + "content": "which drives more parameters to extract high-frequency contents to improve the overall performance. In the inference stage, as shown in Fig. 3, the dual stream network can be equivalently transformed into a plain network, which ensures low inference latency." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 422, + 388, + 436 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 422, + 388, + 436 + ], + "spans": [ + { + "bbox": [ + 306, + 422, + 388, + 436 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 442, + 427, + 453 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 442, + 427, + 453 + ], + "spans": [ + { + "bbox": [ + 306, + 442, + 427, + 453 + ], + "type": "text", + "content": "4.1. Datasets and Metrics" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 460, + 545, + 533 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 460, + 545, + 533 + ], + "spans": [ + { + "bbox": [ + 304, + 460, + 545, + 533 + ], + "type": "text", + "content": "Our model ETDS is trained on DIV2K dataset [25] with 800 training images. The performance is evaluated on 5 benchmark datasets (i.e., Set5 [2], Set14 [32], BSDS100 [21], Urban100 [9] and DIV2K100 [25]). PSNR and SSIM [29] are used to evaluate the reconstruction quality and calculated on the Y channel in the YCbCr space." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 540, + 439, + 552 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 540, + 439, + 552 + ], + "spans": [ + { + "bbox": [ + 306, + 540, + 439, + 552 + ], + "type": "text", + "content": "4.2. Implementation Details" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 557, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 557, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 557, + 546, + 713 + ], + "type": "text", + "content": "ETDS is implemented on PyTorch-based [22] BasicSR [28] framework and trained on an NVIDIA 2080Ti GPU. In the training phase, 32 patches of " + }, + { + "bbox": [ + 304, + 557, + 546, + 713 + ], + "type": "inline_equation", + "content": "64 \\times 64" + }, + { + "bbox": [ + 304, + 557, + 546, + 713 + ], + "type": "text", + "content": " LR image are used as input. Random rotation, horizontal flipping, and channel shuffle are applied for data augmentation. We train our model by the ADAM [14] optimizer with " + }, + { + "bbox": [ + 304, + 557, + 546, + 713 + ], + "type": "inline_equation", + "content": "\\beta_{1} = 0.9" + }, + { + "bbox": [ + 304, + 557, + 546, + 713 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 557, + 546, + 713 + ], + "type": "inline_equation", + "content": "\\beta_{2} = 0.999" + }, + { + "bbox": [ + 304, + 557, + 546, + 713 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 304, + 557, + 546, + 713 + ], + "type": "inline_equation", + "content": "\\epsilon = 10^{-8}" + }, + { + "bbox": [ + 304, + 557, + 546, + 713 + ], + "type": "text", + "content": ". We set " + }, + { + "bbox": [ + 304, + 557, + 546, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{DS}}" + }, + { + "bbox": [ + 304, + 557, + 546, + 713 + ], + "type": "text", + "content": " as the loss function with " + }, + { + "bbox": [ + 304, + 557, + 546, + 713 + ], + "type": "inline_equation", + "content": "\\alpha = 0.5" + }, + { + "bbox": [ + 304, + 557, + 546, + 713 + ], + "type": "text", + "content": ". In accordance with previous works, our model is trained for " + }, + { + "bbox": [ + 304, + 557, + 546, + 713 + ], + "type": "inline_equation", + "content": "1600k" + }, + { + "bbox": [ + 304, + 557, + 546, + 713 + ], + "type": "text", + "content": " iterations with a learning rate of " + }, + { + "bbox": [ + 304, + 557, + 546, + 713 + ], + "type": "inline_equation", + "content": "5e^{-4}" + }, + { + "bbox": [ + 304, + 557, + 546, + 713 + ], + "type": "text", + "content": ". For the first " + }, + { + "bbox": [ + 304, + 557, + 546, + 713 + ], + "type": "inline_equation", + "content": "100k" + }, + { + "bbox": [ + 304, + 557, + 546, + 713 + ], + "type": "text", + "content": " iterations, " + }, + { + "bbox": [ + 304, + 557, + 546, + 713 + ], + "type": "inline_equation", + "content": "K_{r}" + }, + { + "bbox": [ + 304, + 557, + 546, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 557, + 546, + 713 + ], + "type": "inline_equation", + "content": "K_{r2b}" + }, + { + "bbox": [ + 304, + 557, + 546, + 713 + ], + "type": "text", + "content": " are initialized by setting " + }, + { + "bbox": [ + 304, + 557, + 546, + 713 + ], + "type": "inline_equation", + "content": "K_{r} = I" + }, + { + "bbox": [ + 304, + 557, + 546, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 557, + 546, + 713 + ], + "type": "inline_equation", + "content": "K_{r2b} = O" + }, + { + "bbox": [ + 304, + 557, + 546, + 713 + ], + "type": "text", + "content": ". In the testing phase, we test the inference latency on three SoCs (i.e., Dimensity 8100, Snapdragon 888, and Snapdragon 8 Gen 1) with the" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "14106" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 50, + 71, + 210, + 194 + ], + "blocks": [ + { + "bbox": [ + 50, + 71, + 210, + 194 + ], + "lines": [ + { + "bbox": [ + 50, + 71, + 210, + 194 + ], + "spans": [ + { + "bbox": [ + 50, + 71, + 210, + 194 + ], + "type": "image", + "image_path": "cc6366a5335d5f46fa093fa8a1777dce8e0f4b00f65ab646650db0b790e50717.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 134, + 196, + 145, + 205 + ], + "lines": [ + { + "bbox": [ + 134, + 196, + 145, + 205 + ], + "spans": [ + { + "bbox": [ + 134, + 196, + 145, + 205 + ], + "type": "text", + "content": "(a)" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 215, + 70, + 377, + 194 + ], + "blocks": [ + { + "bbox": [ + 215, + 70, + 377, + 194 + ], + "lines": [ + { + "bbox": [ + 215, + 70, + 377, + 194 + ], + "spans": [ + { + "bbox": [ + 215, + 70, + 377, + 194 + ], + "type": "image", + "image_path": "dcd00be26e6a0999c9b2fc3f601004b9d2ef260cb459d864a3a72d8506f4e502.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 302, + 195, + 313, + 205 + ], + "lines": [ + { + "bbox": [ + 302, + 195, + 313, + 205 + ], + "spans": [ + { + "bbox": [ + 302, + 195, + 313, + 205 + ], + "type": "text", + "content": "(b)" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 45, + 208, + 547, + 240 + ], + "lines": [ + { + "bbox": [ + 45, + 208, + 547, + 240 + ], + "spans": [ + { + "bbox": [ + 45, + 208, + 547, + 240 + ], + "type": "text", + "content": "Figure 4. The effect of the numbers of channels and layers on inference latency of the plain model. (a) shows the inference latency with the number of channels between 4 and 24. (b) shows the inference latency with the number of channels between 4 and 64, divisible by 4. (c) shows the inference latency with the number of layers between 1 and 10." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 384, + 71, + 545, + 194 + ], + "blocks": [ + { + "bbox": [ + 384, + 71, + 545, + 194 + ], + "lines": [ + { + "bbox": [ + 384, + 71, + 545, + 194 + ], + "spans": [ + { + "bbox": [ + 384, + 71, + 545, + 194 + ], + "type": "image", + "image_path": "bf1e483e16a8306be5bec537a92b6b801913e2dbce1e1d4ace198a1526487cf7.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 474, + 196, + 484, + 205 + ], + "lines": [ + { + "bbox": [ + 474, + 196, + 484, + 205 + ], + "spans": [ + { + "bbox": [ + 474, + 196, + 484, + 205 + ], + "type": "text", + "content": "(c)" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 251, + 287, + 286 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 251, + 287, + 286 + ], + "spans": [ + { + "bbox": [ + 46, + 251, + 287, + 286 + ], + "type": "text", + "content": "AI Benchmark application [11, 13]. All inference latencies and multiply-accumulate operations (MACs) are tested with inputs of " + }, + { + "bbox": [ + 46, + 251, + 287, + 286 + ], + "type": "inline_equation", + "content": "360 \\times 640" + }, + { + "bbox": [ + 46, + 251, + 287, + 286 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 295, + 262, + 307 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 295, + 262, + 307 + ], + "spans": [ + { + "bbox": [ + 47, + 295, + 262, + 307 + ], + "type": "text", + "content": "4.3. Hardware-Friendly Number of Channels" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 314, + 287, + 410 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 314, + 287, + 410 + ], + "spans": [ + { + "bbox": [ + 46, + 314, + 287, + 410 + ], + "type": "text", + "content": "As shown in Fig. 4, the numbers of channels and layers have a significant impact on the model's efficiency. Observing Fig. 4 (a)(b), we can see that the models have lower inference latency on mobile devices when the number of channels is a multiple of 4, due to the processing unit alignment [31], the memory alignment, and other hardware optimizations [4]. Fig. 4 (c) supports that the inference latency is proportional to the number of layers." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 410, + 287, + 494 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 410, + 287, + 494 + ], + "spans": [ + { + "bbox": [ + 46, + 410, + 287, + 494 + ], + "type": "text", + "content": "As a result, for a lower inference latency, ETDS is designed with 16, 32, and 48 channels and the number of layers in the model is designed for balancing the performance and inference latency. Also, for the equivalently transformed models (e.g., " + }, + { + "bbox": [ + 46, + 410, + 287, + 494 + ], + "type": "inline_equation", + "content": "\\mathrm{ECBSR + ET}" + }, + { + "bbox": [ + 46, + 410, + 287, + 494 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 410, + 287, + 494 + ], + "type": "inline_equation", + "content": "\\mathrm{ABPN + ET}" + }, + { + "bbox": [ + 46, + 410, + 287, + 494 + ], + "type": "text", + "content": "), extra channels are added to ensure that the number of channels is a multiple of 4." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 47, + 502, + 221, + 514 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 502, + 221, + 514 + ], + "spans": [ + { + "bbox": [ + 47, + 502, + 221, + 514 + ], + "type": "text", + "content": "4.4. Comparisons to Previous Works" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 46, + 521, + 287, + 616 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 521, + 287, + 616 + ], + "spans": [ + { + "bbox": [ + 46, + 521, + 287, + 616 + ], + "type": "text", + "content": "We compare our ETDS with representative real-time SR models on mobile devices, including Bicubic, ESPCN [23], FSRCNN [7], ABPN [8], and ECBSR [34]. Since ESPCN, FSRCNN, and ECBSR only process on a single channel of the input image, some preprocessing and postprocessing, such as color space conversion and upsampling of the other two channels are omitted. For a fair comparison, these models are retrained in the RGB color space." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 46, + 617, + 287, + 700 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 617, + 287, + 700 + ], + "spans": [ + { + "bbox": [ + 46, + 617, + 287, + 700 + ], + "type": "text", + "content": "We train four different sizes of our model, denoted as ETDS-T, ETDS-S, ETDS-M and ETDS-L for different computational use cases, with channels 16, 32, 32 and 48, and layers 5, 4, 6, and 7, respectively. The performance comparison is summarized in Tab. 2. In addition to PSNR/SSIM indexes, we also list the number of parameters and MACs for a more comprehensive comparison." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 59, + 701, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 701, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 59, + 701, + 287, + 713 + ], + "type": "text", + "content": "Quantitative Results. The quantitative comparison is" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 251, + 545, + 441 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 251, + 545, + 441 + ], + "spans": [ + { + "bbox": [ + 304, + 251, + 545, + 441 + ], + "type": "text", + "content": "presented in Tab. 2. From Tab. 2, our model achieves not only lower inference latency than other models in most cases but also higher PSNR/SSIM indexes. For instance, as shown in Tab. 2 (latency column i), our ETDS-S runs " + }, + { + "bbox": [ + 304, + 251, + 545, + 441 + ], + "type": "inline_equation", + "content": "1.2\\mathrm{ms}" + }, + { + "bbox": [ + 304, + 251, + 545, + 441 + ], + "type": "text", + "content": " faster than ECBSR-M4C16 on the " + }, + { + "bbox": [ + 304, + 251, + 545, + 441 + ], + "type": "inline_equation", + "content": "\\times 3" + }, + { + "bbox": [ + 304, + 251, + 545, + 441 + ], + "type": "text", + "content": " task, and its PSNR index on the Urban100 dataset is " + }, + { + "bbox": [ + 304, + 251, + 545, + 441 + ], + "type": "inline_equation", + "content": "0.29\\mathrm{dB}" + }, + { + "bbox": [ + 304, + 251, + 545, + 441 + ], + "type": "text", + "content": " higher. ETDS-L's inference latency on the " + }, + { + "bbox": [ + 304, + 251, + 545, + 441 + ], + "type": "inline_equation", + "content": "\\times 3" + }, + { + "bbox": [ + 304, + 251, + 545, + 441 + ], + "type": "text", + "content": " task is " + }, + { + "bbox": [ + 304, + 251, + 545, + 441 + ], + "type": "inline_equation", + "content": "3.5\\mathrm{ms}" + }, + { + "bbox": [ + 304, + 251, + 545, + 441 + ], + "type": "text", + "content": " faster than the ABPN-M6C40's, and PSNR on Set5. Notably, although our model consists of slightly more parameters and MACs, it is still faster than the state-of-the-art models. This phenomenon occurs due to two-fold aspects. 1). Under different contexts, the same operations may have different inference latency. 2). Some operations are not measured in parameters and MACs metrics. For instance, ReLU does not influence parameters and concatenation does not influence MACs." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 443, + 545, + 526 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 443, + 545, + 526 + ], + "spans": [ + { + "bbox": [ + 304, + 443, + 545, + 526 + ], + "type": "text", + "content": "Qualitative Results. The qualitative comparison results are depicted in Fig. 5. We can see that the texture of the wall in thimagese images generated by ESPCN [23] and FSRCNN [7] is blurred, and images generated by ECBSR-M6C40 [34] and ABPN-M6C40 [8] are slightly distorted. Obviously, our ETDS-T produces the least distorted and blurred images with the best PSNR/SSIM results." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 537, + 406, + 549 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 537, + 406, + 549 + ], + "spans": [ + { + "bbox": [ + 306, + 537, + 406, + 549 + ], + "type": "text", + "content": "4.5. Ablation Studies" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 557, + 545, + 605 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 557, + 545, + 605 + ], + "spans": [ + { + "bbox": [ + 304, + 557, + 545, + 605 + ], + "type": "text", + "content": "In this section, we propose a series of ablation studies on the design of the proposed ETDS. All the ablation experiments are conducted on the " + }, + { + "bbox": [ + 304, + 557, + 545, + 605 + ], + "type": "inline_equation", + "content": "\\times 4" + }, + { + "bbox": [ + 304, + 557, + 545, + 605 + ], + "type": "text", + "content": " task. We report PSNR values on the Y channel in the YCbCr space." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": "Ablation Studies for Equivalent Transformation. We validate the effectiveness of ET through a series of ablation studies. Additionally, we apply ET to both ECBSR and ABPN to further demonstrate its effectiveness. Note that ETDS does not have a repeat operator and we do not apply ET for the concatenate operator for ECBSR and ABPN because the improvement on the NNAPI driver is insignificant. Our results in Tab. Tab. 3 show that applying ET to these operators results in reduced latency." + } + ] + } + ], + "index": 19 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "14107" + } + ] + } + ], + "index": 20 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 49, + 116, + 544, + 457 + ], + "blocks": [ + { + "bbox": [ + 47, + 70, + 545, + 115 + ], + "lines": [ + { + "bbox": [ + 47, + 70, + 545, + 115 + ], + "spans": [ + { + "bbox": [ + 47, + 70, + 545, + 115 + ], + "type": "text", + "content": "Table 2. Performance comparison of different SR models on five benchmark datasets. PSNR/SSIM on the Y channel is reported on each dataset. Inference latency i, ii, iii and iv denotes the inference latency of the models using NNAPI driver on Dimensity 8100 SoC, MediaTek Neuron driver on Dimensity 8100 SoC, Qualcomm QNN GPU driver on Snapdragon 888 SoC, and NNAPI on Snapdragon 8 Gen 1 SoC respectively." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 49, + 116, + 544, + 457 + ], + "lines": [ + { + "bbox": [ + 49, + 116, + 544, + 457 + ], + "spans": [ + { + "bbox": [ + 49, + 116, + 544, + 457 + ], + "type": "table", + "html": "
ScaleModelParams (K)MACs (G)Latency (ms)Set5Set14B100Urban100DIV2K100
iiiiiiivPSNR/SSIMPSNR/SSIMPSNR/SSIMPSNR/SSIMPSNR/SSIM
×2Bicubic******33.95/0.933430.54/0.875129.74/0.850327.07/0.845632.67/0.9078
ESPCN26.806.156.304.8391-36.87/0.955932.62/0.908631.40/0.889829.61/0.897334.78/0.9347
ETDS-T (Ours)13.943.194.853.81125-37.18/0.957832.76/0.910331.62/0.893030.10/0.905835.09/0.9375
FSRCNN24.6815.0510.45.8941456237.00/0.956832.68/0.909431.51/0.891329.92/0.902234.97/0.9363
ECBSR-M4C1611.552.646.154.5718931.637.18/0.957732.79/0.910531.61/0.892830.18/0.906435.10/0.9375
ETDS-S (Ours)41.519.528.065.77169-37.38/0.958732.96/0.912431.77/0.895130.62/0.912135.36/0.9396
ECBSR-M4C3241.529.539.706.6437231.437.39/0.958733.03/0.912631.79/0.895330.69/0.912835.39/0.9398
ABPN-M4C2833.467.6710.06.6620728.537.36/0.958532.96/0.912131.75/0.894930.55/0.911135.31/0.9392
ETDS-M (Ours)60.0113.7710.26.73288-37.54/0.959333.09/0.913331.86/0.896330.87/0.914935.50/0.9406
ECBSR-M6C4092.3721.2218.110.965346.237.61/0.959633.18/0.913931.94/0.897231.09/0.917435.61/0.9415
ABPN-M6C4093.4021.4518.711.243531.937.58/0.959433.16/0.91431.92/0.897131.04/0.916935.59/0.9414
ETDS-L (Ours)152.1834.9720.612.1469-37.64/0.959733.24/0.914531.98/0.897731.22/0.918835.69/0.9421
×3Bicubic******30.61/0.871927.79/0.781127.31/0.745324.58/0.739629.80/0.8341
ESPCN31.137.149.798.381104432.85/0.911529.41/0.823628.40/0.787626.22/0.800231.24/0.8670
ETDS-T (Ours)16.923.868.645.3614049.233.14/0.916029.53/0.827428.54/0.792026.48/0.811131.43/0.8713
FSRCNN24.6830.7313.77.32456135033.01/0.914529.52/0.826428.50/0.790326.40/0.807431.38/0.8699
ECBSR-M4C1613.723.1416.211.021669.433.07/0.914929.53/0.826928.57/0.792126.61/0.813631.44/0.8712
ETDS-S (Ours)46.7910.7312.27.7318549.233.49/0.919429.76 0.831428.71/0.796126.90/0.822131.69/0.8756
ECBSR-M4C3245.8510.5219.713.135469.233.56/0.920529.78/0.831928.73/0.796526.98/0.823931.73/0.8761
ABPN-M4C2842.549.7620.513.827562.833.53/0.920029.78/0.831728.72/0.796626.94/0.823231.71/0.8758
ETDS-M (Ours)65.2914.9814.48.762604933.65/0.921429.86/0.833328.78/0.798127.12/0.827831.81/0.8776
ECBSR-M6C4097.7922.4628.117.471375.333.67/0.921129.92/0.833928.85/0.799427.36/0.833331.88/0.8784
ABPN-M6C40104.1023.9129.218.24806633.71/0.921329.92/0.833928.85/0.799427.37/0.833631.89/0.8786
ETDS-L (Ours)159.7736.7125.414.244451.833.88/0.923530.00/0.835928.90/0.801027.45/0.835932.00/0.8807
×4Bicubic******28.60/0.814026.21/0.708826.04/0.673323.23/0.661328.23/0.7775
ESPCN37.208.5411.88.1412079.830.66/0.868827.66/0.758126.94/0.715224.56/0.726329.46/0.8133
ETDS-T (Ours)21.364.8810.96.9416377.430.87/0.873827.75/0.761827.04/0.719424.71/0.735029.59/0.8172
FSRCNN24.6852.68----30.76/0.872127.74/0.760927.01/0.718124.66/0.733029.56/0.8163
ECBSR-M4C1616.773.8323.913.727819130.87/0.874127.80/0.762627.06/0.719524.75/0.736429.61/0.8176
ETDS-S (Ours)54.1112.4114.69.0220377.431.19/0.880628.01/0.767827.18/0.724025.03/0.747929.80/0.8224
ECBSR-M4C3251.9211.9128.016.339919131.24/0.881528.04/0.768627.21/0.724825.07/0.749429.84/0.8231
ABPN-M4C2862.0514.2430.317.433518731.32/0.883328.10/0.769727.23/0.725425.12/0.751129.86/0.8237
ETDS-M (Ours)72.6116.6616.69.9826778.931.41/0.884328.13/0.770527.27/0.726525.20/0.754429.92/0.8250
ECBSR-M6C40105.3724.2036.820.774919531.41/0.883128.20/0.771627.33/0.728025.37/0.760129.97/0.8259
ABPN-M6C40125.8728.9139.122.453819131.62/0.887628.27/0.773727.35/0.729325.41/0.761630.04/0.8277
ETDS-L (Ours)169.9739.0527.615.344785.331.69/0.888928.31/0.775127.37/0.730225.47/0.764330.09/0.8289
", + "image_path": "861a2577225553959326ee5339e6dd67e83129a348765ebca20a9746fb9131f3.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "type": "table", + "bbox": [ + 67, + 498, + 267, + 628 + ], + "blocks": [ + { + "bbox": [ + 47, + 468, + 288, + 490 + ], + "lines": [ + { + "bbox": [ + 47, + 468, + 288, + 490 + ], + "spans": [ + { + "bbox": [ + 47, + 468, + 288, + 490 + ], + "type": "text", + "content": "Table 3. Ablation operation for each operator. All indicators are tested using NNAPI driver on Dimensity 8100 SoC." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 67, + 498, + 267, + 628 + ], + "lines": [ + { + "bbox": [ + 67, + 498, + 267, + 628 + ], + "spans": [ + { + "bbox": [ + 67, + 498, + 267, + 628 + ], + "type": "table", + "html": "
ModelSizeImprovement
addconcatenateclip
ETDST21.03%28.92%0.26%
S16.74%26.61%0.86%
M8.33%34.47%0.76%
L7.29%27.64%0.50%
repeataddclip
ECBSRM4C1647.95%7.38%1.23%
M4C3239.01%11.35%-0.35%
M6C4029.92%10.24%0.54%
ABPNM4C2837.46%10.75%1.30%
M6C4027.30%10.20%0.77%
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VariantModificationsSet5Urban100
PSNR/SSIMPSNR/SSIM
IPlain-M6C3231.32/0.883025.10/0.7505
IIPlain-M6C32 w/ interpolation31.36/0.883325.13/0.7519
IIIETDS-M w/o Kr2b module31.36/0.883525.16/0.7526
IVETDS-M31.41/0.884325.20/0.7544
VETDS-M w/ Kb2r module31.38/0.883725.17/0.7530
VIETDS-M w/o LDS31.35/0.883725.14/0.7521
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We train " + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "inline_equation", + "content": "K_{r}" + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "inline_equation", + "content": "K_{r2b}" + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "inline_equation", + "content": "K_{b2r}" + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "content": " one after another in an incremental way. The variants are recorded as Variant III, Variant IV, and Variant V in Tab. 4. Variant IV refers to our ETDS-M. From Tab. 4, the performance of Variant II, III and IV increases sequentially, indicating that the learnability of " + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "inline_equation", + "content": "K_{r}" + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "inline_equation", + "content": "K_{r2b}" + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "content": " is beneficial to improve the performance. However, Variant V's performance is worse than Variant IV's, which may indicate that introducing a learnable " + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "inline_equation", + "content": "K_{b2r}" + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "content": " could lead to a degradation in performance. 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Qualitative comparison of real-time SR models on Set5 for " + }, + { + "bbox": [ + 46, + 418, + 287, + 441 + ], + "type": "inline_equation", + "content": "\\times 4" + }, + { + "bbox": [ + 46, + 418, + 287, + 441 + ], + "type": "text", + "content": " upscaling task." + } + ] + } + ], + "index": 26, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 47, + 453, + 286, + 579 + ], + "lines": [ + { + "bbox": [ + 47, + 453, + 286, + 579 + ], + "spans": [ + { + "bbox": [ + 47, + 453, + 286, + 579 + ], + "type": "image", + "image_path": "86b4e7a4904148a1a049daf42d7389d007c2c6385de7ba32a55b0f944464b326.jpg" + } + ] + } + ], + "index": 27, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 583, + 287, + 628 + ], + "lines": [ + { + "bbox": [ + 46, + 583, + 287, + 628 + ], + "spans": [ + { + "bbox": [ + 46, + 583, + 287, + 628 + ], + "type": "text", + "content": "Figure 6. Channel masking experiments with Plain-M6C32 model, ETDS and Variant V. In order to understand the meaning of each channel, the visualization images of some channels are shown in this figure." + } + ] + } + ], + "index": 28, + "angle": 0, + "type": "image_caption" + } + ], + "index": 27 + }, + { + "bbox": [ + 46, + 641, + 286, + 676 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 641, + 286, + 676 + ], + "spans": [ + { + "bbox": [ + 46, + 641, + 286, + 676 + ], + "type": "text", + "content": "pay extra attention to low-frequency information, thereby reducing the model's ability to extract high-frequency information." + } + ] + } + ], + "index": 29 + }, + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "text", + "content": "Ablation Studies for Dual Stream Constraint " + }, + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{DS}}" + }, + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "text", + "content": ". For ETDS-M, the PSNR value is 0.06dB higher than the one without " + }, + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{DS}}" + }, + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "text", + "content": " (Tab. 4 Variant VI), which supports the" + } + ] + } + ], + "index": 30 + }, + { + "bbox": [ + 306, + 72, + 473, + 83 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 72, + 473, + 83 + ], + "spans": [ + { + "bbox": [ + 306, + 72, + 473, + 83 + ], + "type": "text", + "content": "benefit of the dual stream constraint " + }, + { + "bbox": [ + 306, + 72, + 473, + 83 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{DS}}" + } + ] + } + ], + "index": 31 + }, + { + "bbox": [ + 304, + 84, + 545, + 286 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 84, + 545, + 286 + ], + "spans": [ + { + "bbox": [ + 304, + 84, + 545, + 286 + ], + "type": "text", + "content": "Analysis of Dual Stream Network. We conduct the channel mask experiments [16] on ETDS-M, Plain-M6C32 and Variant V models, and then analyze how each channel contributes to the performance. From Fig. 6, the low-frequency information of ETDS-M is mainly concentrated in the last three channels (i.e., the residual branch), while the high-frequency information is distributed in the remaining channels (i.e., the backbone branch) corresponding to our design in Sec. 3.3. In addition, the extraction of the low-frequency channel of ETDS-M is more effective than the Plain-M6C32 model. This may be the reason why ETDS-M has better performance than the Plain-M6C32 model. On top of that, Variant V does better in extracting low-frequency information than ETDS-M, but worse in PSNR performance, which confirms that the learnability of " + }, + { + "bbox": [ + 304, + 84, + 545, + 286 + ], + "type": "inline_equation", + "content": "K_{b2r}" + }, + { + "bbox": [ + 304, + 84, + 545, + 286 + ], + "type": "text", + "content": " compromises the ability to extract high-frequency information." + } + ] + } + ], + "index": 32 + }, + { + "bbox": [ + 306, + 295, + 383, + 306 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 295, + 383, + 306 + ], + "spans": [ + { + "bbox": [ + 306, + 295, + 383, + 306 + ], + "type": "text", + "content": "4.6. Limitations" + } + ] + } + ], + "index": 33 + }, + { + "bbox": [ + 304, + 313, + 545, + 433 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 313, + 545, + 433 + ], + "spans": [ + { + "bbox": [ + 304, + 313, + 545, + 433 + ], + "type": "text", + "content": "While our method achieves a better trade-off between performance and latency on mobile devices, it also has its limitations. Firstly, ET is only appropriate for relatively simple network architectures. More complex structures would require a more complicated ET process, which could potentially introduce an excessive number of redundant parameters. Secondly, due to its simplified structure, very deep networks still pose a challenge for ETDS, and its performance may not reach the level of its EDSR counterpart." + } + ] + } + ], + "index": 34 + }, + { + "bbox": [ + 306, + 444, + 378, + 456 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 444, + 378, + 456 + ], + "spans": [ + { + "bbox": [ + 306, + 444, + 378, + 456 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 35 + }, + { + "bbox": [ + 304, + 464, + 545, + 632 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 464, + 545, + 632 + ], + "spans": [ + { + "bbox": [ + 304, + 464, + 545, + 632 + ], + "type": "text", + "content": "This paper has presented ETDS for mobile image superresolution via Equivalent Transformation and dual stream network construction. ET method is applied to substitute time-consuming operators, including add, repeat, clip and concatenate, with time-friendly ones (convolution and ReLU), which can alleviate the inference latency. We have developed a dual stream network, which successfully eliminated most of the redundant parameters brought by the implementation of ET. Our approach represents an innovative integration of the ET method with a dual-stream network for mobile devices. Extensive experiments have demonstrated that ETDS can outperform the state-of-the-art lightweight SR models in terms of inference latency and reconstruction quality." + } + ] + } + ], + "index": 36 + }, + { + "bbox": [ + 304, + 643, + 545, + 702 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 643, + 545, + 702 + ], + "spans": [ + { + "bbox": [ + 304, + 643, + 545, + 702 + ], + "type": "text", + "content": "Acknowledgements. This work was supported in part by \"Digital Silk Road\" Shanghai International Joint Lab of Trustworthy Intelligent Software (Grant No. 22510750100), and Shanghai Trusted Industry Internet Software Collaborative Innovation Center." + } + ] + } + ], + "index": 37 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "14109" + } + ] + } + ], + "index": 38 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 107, + 84 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 107, + 84 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 107, + 84 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 288, + 712 + ], + "type": "list", + "angle": 0, + "index": 11, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 178 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 178 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 178 + ], + "type": "text", + "content": "[1] Namhyuk Ahn, Byungkon Kang, and Kyung-Ah Sohn. 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Comparison of EvShutter to state-of-the-art event-based RS correction method [28]. Our method introduces a novel event transformation, which allows us to correct RS artifacts in the presence of non-linear motion or large displacements." + ], + "image_footnote": [], + "bbox": [ + 78, + 395, + 228, + 515 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/b2738cd95759a26437c0d04dad23ca6964130c29fee4d5ff8daa28ac7b3c1088.jpg", + "image_caption": [ + "EvShutter" + ], + "image_footnote": [], + "bbox": [ + 232, + 395, + 380, + 515 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/2d25beea17eb81277f5de824e7bf3bffd36f2dcc253e3abe89829acccb84d07a.jpg", + "image_caption": [ + "EvUnroll [28]" + ], + "image_footnote": [], + "bbox": [ + 385, + 393, + 637, + 515 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/fe831c2acb3c481e0da625f010d209da1f54cfbf3d29ba0abe16d44447cbcd05.jpg", + "image_caption": [ + "EvShutter" + ], + "image_footnote": [], + "bbox": [ + 638, + 393, + 890, + 515 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 583, + 313, + 598 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Widely used Rolling Shutter (RS) CMOS sensors capture high resolution images at the expense of introducing distortions and artifacts in the presence of motion. In such situations, RS distortion correction algorithms are critical. Recent methods rely on a constant velocity assumption and require multiple frames to predict the dense displacement field. In this work, we introduce a new method, called Eventful Shutter (EvShutter), that corrects RS artifacts using a single RGB image and event information with high temporal resolution. The method firstly removes blur using a novel flow-based deblurring module and then compensates RS using a double encoder hourglass network. In contrast to previous methods, it does not rely on a constant velocity assumption and uses a simple architecture thanks to an event transformation dedicated to RS, called Filter and Flip (FnF), that transforms input events to encode only", + "bbox": [ + 73, + 616, + 470, + 859 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "the changes between GS and RS images. To evaluate the proposed method and facilitate future research, we collect the first dataset with real events and high-quality RS images with optional blur, called RS-ERGB. We generate the RS images from GS images using a newly proposed simulator based on adaptive interpolation. The simulator permits the use of inexpensive cameras with long exposure to capture high-quality GS images. We show that on this realistic dataset the proposed method outperforms the state-of-the-art image- and event-based methods by 9.16 dB and 0.75 dB respectively in terms of PSNR and an improvement of $23\\%$ and $21\\%$ in LPIPS.", + "bbox": [ + 500, + 584, + 893, + 765 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 500, + 797, + 630, + 813 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Most consumer cameras like cell phones or action cameras use a rolling shutter (RS) sensor which instead of capturing the whole frame in a single shot as in a global shutter (GS) camera, it acquires each row sequentially as shown in Fig. 2. Specifically, it obtains each row $y$ at time", + "bbox": [ + 498, + 825, + 893, + 900 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 236, + 0, + 810, + 44 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "The evaluation code and the dataset can be found here https://github.com/juliuserbach/EvShutter", + "bbox": [ + 76, + 875, + 467, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "13904", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/375ae97a0e8d6baeaa4952e1bb2b6233fc1ead868a7aaf773f62e0d65a9baa0f.jpg", + "image_caption": [ + "Figure 2. Rolling Shutter Explained. While recording with a RS camera (left), image rows are exposed sequentially, while in the case of a GS camera (right) they are exposed all at the same time." + ], + "image_footnote": [], + "bbox": [ + 94, + 87, + 297, + 200 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/be616edbbe694b75a57965dbdafbe4f211d5af4b1f7af4066f4ab79ec0c6e800.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 316, + 87, + 452, + 200 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "$t_{y} = y \\cdot t_{H} / H$ , where $H$ is the height of an image and $t_{H}$ is the mid-exposure time of the last row. RS cameras are often preferred due to their high spatial resolution and high frame rates at low cost. Global shutter sensors have a more complicated circuitry, and therefore a smaller resolution than rolling shutter sensors of the same physical size. A larger sensor size in turn increases the cost of the lens. However, in the presence of fast camera or object movement, RS sensors can produce skew distortion in images (see Fig. 1) and jello artifacts in videos.", + "bbox": [ + 75, + 262, + 467, + 412 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To correct such artifacts, RS correction methods are widely used. Conventional methods attempt to recover the corresponding GS image from the RS output by first estimating the camera motion or dense displacement field during the image acquisition and sequentially applying motion compensation to align all the pixels to a fixed timestamp. However, these methods make strong assumptions on the motion type and are prone to fail in the presence of complex motion patterns like local or non-linear motion, which no longer satisfy the assumptions.", + "bbox": [ + 75, + 414, + 467, + 565 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In this work, we address the fundamental problem of modeling scene changes during image acquisition by using the high temporal information provided by an auxiliary event camera. Instead of measuring synchronous frames of absolute brightness, event cameras only measure asynchronous brightness changes at each pixel with a high temporal resolution in the order of microseconds [3]. Unlike image-based methods, event cameras allow to estimate the motion without relying on a constant speed assumption and synthesizing images by directly adding the brightness changes registered by the events to an image. This enables exciting computational photography applications such as event-guided image deblurring [12, 18, 24], video interpolation [8, 22, 23] and high dynamic range imaging [6, 16].", + "bbox": [ + 75, + 566, + 467, + 779 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In this paper, we propose a RS compensation method, called Eventful Shutter (EvShutter), that only requires a single RS image and the corresponding events. The method firstly removes blur using a novel flow-based deblurring module and then compensates RS using an hourglass network with two encoders relying on complementary geometric and synthesis-based interpolation approaches. The proposed method is the first method that does not rely on", + "bbox": [ + 75, + 780, + 467, + 901 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "constant velocity assumption and uses a simple architecture thanks to the newly introduced event transformation, that we call Filter and Flip (FnF). FnF transforms the input events to encode just changes between GS and RS images. To train and evaluate the proposed method, we collect the first dataset with real events and high quality RS images (optionally with blur), called RS-ERGB. The RS images are generated from GS images using our new simulator based on adaptive interpolation. This pipeline allows the use of an inexpensive high speed camera and the use of long exposures while capturing the GS images.", + "bbox": [ + 496, + 90, + 890, + 257 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Contributions of this work are as follows", + "text_level": 1, + "bbox": [ + 517, + 257, + 799, + 270 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "1. Eventful Shutter (EvShutter): the first event-assisted RS distortion compensation and deblurring method that avoids constant speed motion assumptions.", + "2. Filter and Flip (FnF): an event transformation module that transforms the input event stream to encode only the brightness change from GS to RS image and simplifies the architecture of downstream modules.", + "3. Rolling Shutter Events and RGB (RS-ERGB) dataset and simulator: the first dataset with real events and RS images with optional blur generated using a new realistic RS-simulator, based on adaptive interpolation." + ], + "bbox": [ + 511, + 272, + 890, + 438 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 500, + 452, + 640, + 468 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Previous works on RS correction attempt to recover the GS image by estimating the camera motion or dense displacement field during image acquisition and applying motion compensation to align all the pixels to a fixed timesamp. They can be classified according to their motion estimation method into following categories: gyro-based, single image-based, multiple image-based and event-based. Below we describe each category in detail.", + "bbox": [ + 496, + 477, + 890, + 598 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Gyroscope-based methods [7, 13] utilize a gyro sensor to estimate the rotational motion of the camera. These methods are widely used in mobile devices, due to their speed and reliability. However, they assume a static scene and a simplified rotational camera motion. hence, they can not correct RS distortions due to moving objects (e.g. see Fig. 1), or in the presence of more complex camera motion where the purely rotational assumption is violated.", + "bbox": [ + 496, + 598, + 890, + 718 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Single image-based methods infer the motion from a single RS image by relying on a prior model of the scene. Methods in [14, 19] assume the presence of multiple straight lines in the scenes (Manhattan world assumption) for motion estimation. These hand-crafted priors fail when the scene deviates from the assumed model. Recent methods [21, 31] rely on deep learning to automatically learn scene priors that are used to estimate the camera motion. While these methods are more robust, they are still limited to certain scene types with static scene and constant depth (except [31]).", + "bbox": [ + 496, + 719, + 890, + 883 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Multiple image-based methods estimate the motion be", + "bbox": [ + 517, + 885, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "13905", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "tween sequential RS images and use it to approximate the motion during image exposure relying on a parametric motion model. While early methods [2, 5] use image feature matching to estimate a rotational or planar homography, more recent methods [1, 15, 27] compute the dense optical flow between RS images and can correct RS distortion due to object motion. However, they suffer from limitations of image-based motion estimation: they do not work with a single image, image blur and illumination changes. Moreover, they lack the exact information about the motion during exposure and can fail in the presence of large displacements in between frames and highly non-linear motion.", + "bbox": [ + 75, + 90, + 472, + 271 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Event-based method. Recently, [28] developed an event-assisted RS compensation method based on the work of [23]. To ensure that interpolation in a given row is performed from mid-exposure time of that same row to mid-exposure time of the latent GS image their method uses additional conditioning mechanisms and assumptions in the sub-modules, notably constant velocity assumption similar to images-based methods [1, 15, 27]. In contrast, we eliminate the need of additional strong assumptions and conditioning in downstream modules by introducing a simple yet effective event transformation that modifies the input events to encode the transformation from GS to RS image.", + "bbox": [ + 75, + 272, + 472, + 450 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "RS Deblur. Besides RS distortion, in presence of fast motion RS images often suffers from blur. In those cases, RS restoration methods needs to simultaneously perform deblur and distortion correction. [27] directly incorporate a deblurring stream in the RS correction network, while [28] adds an optional deblur module before the RS correction.", + "bbox": [ + 75, + 453, + 472, + 542 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Datasets. BS-RSCD [27] dataset is recorded by using a beamsplitter setup with temporally and geometrically synchronized GS and RS cameras. Other datasets, such as Fastec-RS [15] or Gev-RS [28] are collected by first using a high speed GS camera and later synthesizing RS images by sequentially copying rows from the high frame rate GS images. For Gev-RS events are simulated from high speed GS images using V2E [10]. Unfortunately, training with synthetic events often does not generalize well to real event data. Moreover, RS images synthesized by the above method suffer from noise, low contrast and have small resolution, due to very short exposure time in the high speed cameras. We address two of the above problems by capturing a new dataset with real events using GS RGB and event cameras arranged in a beamsplitter setup and introducing new high fidelity simulator that generates high quality RS images with optional blur from GS images.", + "bbox": [ + 75, + 544, + 472, + 801 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Method", + "text_level": 1, + "bbox": [ + 76, + 819, + 169, + 834 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1.Eventful Shutter (EvShutter) Network", + "text_level": 1, + "bbox": [ + 76, + 844, + 408, + 861 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "At first, we perform event-assisted deblurring of the input RS image $I_{blur}^{rs}$ image using a pre-processing deblurring", + "bbox": [ + 76, + 869, + 468, + 902 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "module inspired by [24]. Next, we compensate RS distortion to obtain at a GS estimate at reference time $t_{ref}$ using the pipeline shown in Fig. 3. As shown in the Fig. 3, instead of directly feeding all the raw events $E_{0\\rightarrow t_H}$ to the network as in [28], we firstly pre-process them by using the proposed Filter and Flip (FnF) transformation, described in details in Sec. 3.2. Next, we encode the transformed events $E_{gs\\rightarrow rs}$ into a voxel grid representation $V_{gs\\rightarrow rs}$ as described in [32]. Then we feed the voxel grid and the RS image $I^{rs}$ to an hourglass network composed of a warping encoder and a synthesis encoder using complementary interpolation approaches as in [22, 23]. Lastly, the fusion decoder progressively combines multi-scale images and warping and synthesis features to produce the final GS image $I^{gs}$ . Below we explain the main modules of the proposed method.", + "bbox": [ + 496, + 90, + 890, + 330 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Deblurring. Besides the RS distortion, RS images can suffer from motion blur due to camera or object motion during the exposure time. Therefore, we propose to deblur RS images using events before passing them to our RS distortion compensation method. The overall pipeline of the deblurring is shown in Fig. 4. First, we filter out all events triggered not during the exposure time of the corresponding image rows and then, we shift them according to the row-wise delay, similar to [28]. This allows the use of GS event-based deblurring methods, such as [24]. The original method estimates a deblur operator directly from events using offsets and masks of deformable convolutions [29]. However, we found that it is possible to estimate better deblur operators from more a explicit motion representation, such as optical flow. To estimate flow, we re-use the same network and weights as in the main RS distortion compensation pipeline.", + "bbox": [ + 496, + 333, + 890, + 589 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Warping Encoder. The warping-based encoder takes the voxel grid $V_{gs \\to rs}$ and estimates optical flow $\\mathcal{F}_{gs \\to rs}$ relating the latent GS image to RS image using a flow network from [23]. Note that because the transformed events only encode changes from GS to RS image we can directly estimate optical flow between them without relying on a constant speed assumption. In other words, we can directly estimate row-wise flow, where each row $y$ represents the pixel displacement from time $t_{ref}$ to time $y \\cdot t_H / H$ . In contrast in [1, 15, 26, 28], the authors predict optical flow between frames or during the exposure time of the frame using events and approximate the displacement between RS and GS by multiplying with a row dependent coefficient, which is only accurate for linear motions. The estimated flow is used to warp multi-scale features extracted from the RS image $I^{rs}$ using the image encoder resulting in multi-scale warping interpolation features $\\mathbf{F}_{\\rightarrow \\mathrm{gs}}^{\\mathbf{w}} = (F_{\\rightarrow gs}^{w(0)}, F_{\\rightarrow gs}^{w(1)}, F_{\\rightarrow gs}^{w(2)})$ . Similarly, a multi-scale image pyramid computed from the RS image is warped to get $\\mathbf{I}_{\\rightarrow \\mathrm{gs}}^{\\mathrm{rs}} = (I_{\\rightarrow gs}^{rs(0)}, I_{\\rightarrow gs}^{rs(1)}, I_{\\rightarrow gs}^{rs(2)})$ . The warping is performed by using", + "bbox": [ + 496, + 590, + 890, + 902 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "13906", + "bbox": [ + 480, + 945, + 519, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/a59f8edf354aa5e0e9886c53267995101c63b28ee386af5abd26c6e6f3b01bc4.jpg", + "image_caption": [ + "Figure 3. RS distortion compensation pipeline. At first the proposed method pre-processes input events with $FnF$ transformation to encode only the brightness change between GS and RS frames. The transformed events are then passed to double encoder hourglass network with complementary warping and synthesis encoders relying on different interpolation principles. Then multi-scale features and images from both encoders are fused in the decoder to produce a GS image. The first fusion block of the decoder is shown in detail." + ], + "image_footnote": [], + "bbox": [ + 81, + 90, + 890, + 375 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/61c7432c3c7f537fe4be7efc37e2c5027ed95afa2daf142f28ce6d4346e09c6c.jpg", + "image_caption": [ + "Figure 4. RS deblurring pipeline. First we filter out all the events which are not triggered during the exposure time, then we deblur the RS image using an improved version of [24], that relies on optical flow estimation to predict deblur kernels." + ], + "image_footnote": [], + "bbox": [ + 122, + 465, + 429, + 614 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "differentiable backward interpolation. To downscale images and optical flow we perform average pooling and in case of flow we additionally divide the flow by the downscale factor.", + "bbox": [ + 75, + 690, + 468, + 751 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Synthesis-based Encoder. The synthesis-based encoder takes both voxel grid $V_{gs \\to rs}$ and RS image $I^{rs}$ as inputs and computes multi-scale synthesis interpolation features $\\mathbf{F}^s$ . Intuitively, this encoder integrates brightness changes from the event stream and adds them to the RS image. Notice that, in contrast to the warping encoder, this module can handle illumination changes and fill motion occlusions.", + "bbox": [ + 75, + 758, + 468, + 864 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Fusion Decoder: The fusion decoder progressively combines synthesis $\\mathbf{F}^s$ and warping-based $\\mathbf{F}_{\\rightarrow gs}^{w}$ features, orig-", + "bbox": [ + 76, + 869, + 468, + 902 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/6e1ac7f3966be9de00c1414819b30c66389a742a83c1e4ba767da61231dcf9be.jpg", + "image_caption": [ + "Figure 5. Event transformation workflow. Top row: Event stream is transformed by first applying and event filtering followed by a flipping step around an arbitrary reference time. Bottom row: An example of events. Right: Animation (best viewed with Acrobot Reader) between RS-input and GS estimations at different reference times." + ], + "image_footnote": [], + "bbox": [ + 504, + 472, + 888, + 618 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "inal RS image $I^{rs}$ and warped RS image $I_{\\rightarrow gs}^{rs}$ on multiple scales to reconstruct the GS image $I^{gs}$ . We use shortcut connections from the original RS image to help the decoder to reconstruct static parts of the image. To select the most informative features on each scale the decoder relies on Squeeze-and-excitation (SE) blocks [9] attenuating channels, and modulated deformable convolutions [29], attenuating the feature maps spatially.", + "bbox": [ + 496, + 723, + 892, + 845 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "13907", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. Filter and Flip (FnF) Transformation", + "text_level": 1, + "bbox": [ + 76, + 90, + 398, + 107 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The auxiliary event camera records an event stream $E_{0 \\to t_H}$ encoding all brightness changes from time 0 to $t_H$ . However, to recover the GS image $I^{gs}$ corresponding to a given RS image $I^{rs}$ , we are only interested on those events $E_{gs \\to rs}$ encoding brightness changes between latent GS and observed RS image. In this work, we propose a well-suited RS event transformation called Filter and Flip (FnF), which transforms the event stream $E_{0 \\to t_H}$ to $E_{gs \\to rs}$ through two steps: filtering and flipping steps as shown in Fig. 5 and described below.", + "bbox": [ + 75, + 113, + 468, + 263 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Filtering step. For each row $y$ , we only keep those events triggered between time $t_y$ and the reference time $t_{ref}$ , where $t_y$ is mid-exposure time of row $y$ in observed RS image.", + "bbox": [ + 75, + 265, + 468, + 325 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Flipping step. We reverse all events before the reference time $t_{ref}$ by inverting their polarities and recomputing their timestamps such that they are flipped around $t_{ref}$ as shown in Fig. 5. This process ensures that the events encode changes in the direction from GS-frame to RS-frame and that the transformed events start at the time, which matches the GS-frame and end at the RS-time.", + "bbox": [ + 75, + 325, + 468, + 430 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Applying the event transformation eliminates the need in time conditioning mechanisms and additional assumptions in the downstream modules. For example, in contrast to [28], the proposed method does not require constant speed assumption in the flow estimation module and attention mechanisms in the synthesis-based encoder, which allows re-using already pretrained modules on widely used GS images. Also, notice, that the FnF transformation can be adapted to arbitrary reference times.", + "bbox": [ + 75, + 431, + 468, + 566 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In order to allow a good comparison to other works, we set $t_{ref} = t_H / 2$ , which corresponds to the mid-exposure time of the central row.", + "bbox": [ + 75, + 566, + 468, + 611 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.3. RS-ERGB Dataset", + "text_level": 1, + "bbox": [ + 76, + 619, + 256, + 635 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "To bridge the sim-to-real gap from synthetic to real events we build a hybrid imaging system of a high speed GS RGB-camera and an event camera in a beam splitter setup. We use hardware temporal synchronization and geometrically align events and images as described in the Supp. Mat. With this setup we capture the first RS dataset with real events and high quality images. We generate high quality RS images with optional blur using our novel simulator based on adaptive interpolation described below.", + "bbox": [ + 75, + 643, + 468, + 779 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "High quality RS simulator. Our proposed pipeline allows to record GS sequences at lower speed than previous methods (160 fps compared to [15, 28] that record GS sequence at 2400 or 5700 fps). This allows us to use a longer exposure and as a result, acquire images of higher quality. Then we adaptively interpolate captured images using Super Slomo [11], so that the maximum displacement between interpolated frames is at most 1 pixel similar to", + "bbox": [ + 75, + 780, + 468, + 900 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/06b51f2e5d82233a6b853affd0784b0ad0bc23bf1951f36e342bdcb95eaa6448.jpg", + "image_caption": [ + "Figure 6. Synthetic RS-images from a sequence of GS-Images $I_{i}$ . Each row is constructed separately by computing the weighted average of the GS-frames, which are assumed to be a close approximation of the latent GS-frames." + ], + "image_footnote": [], + "bbox": [ + 501, + 87, + 893, + 204 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Vid2E [4]. This procedure ensures that a sufficient temporal resolution is achieved to synthesize realistic blur and RS effect. As shown in Fig. 7, using a fixed interpolation factor can give unrealistic results as the amount of motion can differ significantly by region and scene. The resulting interpolated video sequence can be thought of as discrete approximation of latent GS-images $I_{i}$ of the true latent frames $I_{\\text{latent}}(t,x,y)$ . To synthesize a row $y_{rs}$ of a RS-image the integral of $I_{\\text{latent}}(t,x,y = y_{rs})$ has to be computed over the exposure time for this row, as", + "bbox": [ + 498, + 280, + 892, + 431 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nI _ {r s} \\left(t _ {\\text {s t a r t}}, t _ {\\text {e n d}}, y _ {i}\\right) = \\frac {1}{t _ {\\text {e n d}} - t _ {\\text {s t a r t}}} \\int_ {t _ {\\text {s t a r t}}} ^ {t _ {\\text {e n d}}} I _ {\\text {l a t e n t}} (t, y _ {i}) d t. \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 504, + 444, + 890, + 505 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We use a discrete approximation instead and compute a weighted average of the approximated latent frames $I_{i}$ as shown in Fig. 6. Using this procedure a synthetic exposure time and readout time $T$ are chosen to synthesize corresponding RS frames. Notice that exposure time and readout time can be set separately allowing us to create blurry RS images with sharp RS ground truth for the task of RS deblurring. Video interpolation has already been used in the past to generate more realistic blur from videos [17], but to the best of our knowledge, we are the first to use an adaptive upsampling scheme to get consistently realistic results. Examples of our dataset with different amounts of blur and a comparison to a version without adaptive interpolation can be seen in the Supp. Mat..", + "bbox": [ + 496, + 506, + 890, + 717 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Comparison to Gev-RS [28] is shown in Tab. 1. Compared to Gev-RS, our dataset has real events and the RS and GS image have better quality and resolution, despite using a lower end camera ${}^{2}$ ,since our new synthesis procedure allows using lower frame rate with longer exposure.", + "bbox": [ + 496, + 717, + 890, + 792 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 500, + 808, + 632, + 825 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In this section, first, we ablate the key contributions of the proposed EvShutter method. Second, we benchmark", + "bbox": [ + 498, + 834, + 893, + 864 + ], + "page_idx": 4 + }, + { + "type": "page_footnote", + "text": "2 Phantom VEO 640 is used for collecting Gev-RS cost $60\\mathrm{k}$ while Blackfly S used for collecting our datasets costs just $500$ .", + "bbox": [ + 500, + 875, + 890, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "13908", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/4f1097efdd78c67a4e4a23129c10ad156c80d02369f96b499c5101ff0b6c4c47.jpg", + "image_caption": [ + "Figure 7. Benefit of the proposed RS simulator In contrast to a simulator with fixed interpolation rate, the proposed simulator with an adaptive interpolation does not suffer from aliasing artifacts regardless of the motion speed." + ], + "image_footnote": [], + "bbox": [ + 80, + 88, + 452, + 246 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/2f11e95f30ef03c409328d2902599cf8a7c094ad4f35f5085fc45936d7bb4203.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
RS-ERGB (ours)Gev-RS [28]
Event datareal (Prophesee Gen4M)synthetic
GS camera160 fps5.7k fps
Blackfly SPhantom VEO 640
№ sequence3429
Image qualityhighlow
Resolution970×625640×360
", + "bbox": [ + 78, + 333, + 478, + 435 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "the EvShutter against state-of-the-art image-based [15,27] and event-based [28] methods on our RS-ERGB dataset, as well as on the public Fastec-RS dataset [15].", + "bbox": [ + 76, + 484, + 468, + 529 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Details of the objective loss, training procedure and runtime comparisons together with ablation on additional design choices can be found in the Supp. Mat.", + "bbox": [ + 76, + 530, + 468, + 575 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.1. Ablation Study", + "text_level": 1, + "bbox": [ + 76, + 587, + 228, + 603 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "FnF event transformation. To evaluate the proposed FnF transformation Tab. 2 we dissect our pipeline in purely warping-based, purely synthesis-based and the full pipeline.", + "bbox": [ + 76, + 611, + 468, + 656 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We compare the purely warping-based method to a version that relies on a constant velocity assumption similar to EvUnroll [28] by applying a row-wise scaling to the optical flow computed from $t_{GS}$ to $t_0$ and from $t_{GS}$ to $t_H$ . Our FnF transformation improves the warping-based method by 0.77 dB in PSNR and 0.0104 in LPIPS [25].", + "bbox": [ + 75, + 657, + 468, + 746 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We also test the purely synthesis based module with and without the FnF transformation. As shown in Tab. 2 the synthesis module with the transformation outperforms the version without by $3.92\\mathrm{dB}$ in PSNR and 0.0376 in LPIPS.", + "bbox": [ + 76, + 748, + 468, + 808 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "The overall architecture also benefits from the FnF transformation by 2.61 dB in PSNR and 0.0203 in LPIPS.", + "bbox": [ + 76, + 809, + 468, + 838 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Importance of optical flow in RS deblur module. We show benefits of estimating the deblur operator from optical flow instead of raw events in Tab. 3. By introducing the optical flow explicitly to the deblurring network we observe", + "bbox": [ + 75, + 840, + 468, + 900 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/857052aa1af78ca7bb1b69064b0d2163cf105ff0d79efe9817b6af236ca8b5ca.jpg", + "table_caption": [ + "Table 1. Details of our RS-ERGB compared to Gev-RS [28]. Best-suited properties are shown in bold." + ], + "table_footnote": [], + "table_body": "
MethodPSNR↑LPIPS↓SSIM↑
Warping
Linearized flow28.390.17210.870
FnF-Transform29.160.16170.883
Synthesis
w/o FnF-Transform25.870.22330.807
FnF-Transform29.790.18570.867
Warping & Synthesis
Linearized flow28.970.17030.870
FnF-Transform31.580.15000.897
", + "bbox": [ + 500, + 87, + 890, + 246 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "an improvement of $1.4\\mathrm{dB}$ in PSNR without effectively increasing the capacity, since we reuse the optical flow module from the RS correction pipeline. Furthermore, we visualized the offsets and masks of the deformable kernels in Fig. 9 and observed that in the case of large motions the kernels did not follow the motion in the original implementation of [24], but with our flow based adaption the deformable kernel is well aligned with the motion. For the sake of completeness we also add the results for deblurring of the EvUnroll [28] deblur module finetuned on our data.", + "bbox": [ + 496, + 335, + 890, + 487 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/0314f6751010145fb53f22540b09daaf8bebc5d3a550b877d485839971a25dab.jpg", + "table_caption": [ + "Table 2. Importance of FnF event transformation. The transformation improves performance of synthesis encoder and warping encoder. In the warping encoder it allows to avoid constant speed motion assumption. Ablation is made on the RS-ERGB validation set and best method is shown in bold." + ], + "table_footnote": [], + "table_body": "
MethodPSNR↑LPIPS↓SSIM↑
EDDMA [24]34.920.05880.936
EDDMA [24]+Flow36.320.04880.951
EvUnroll + Deblur [28]35.640.04990.934
", + "bbox": [ + 501, + 496, + 890, + 563 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 3. Importance of optical flow in RS deblur module. For this experiment we generate RS images with 50ms exposure and compare RS-Deblurring results without RS correction. Best method is shown in bold. We also show performance of EvUnroll deblur module for reference.", + "bbox": [ + 498, + 573, + 890, + 641 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.2. Comparison with SOTA methods", + "text_level": 1, + "bbox": [ + 500, + 665, + 790, + 681 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "RS-ERGB dataset. We compare our method to the state-of-the-art image-based methods DSUN [15], RSCD [27] and the recent event-based EvUnroll [28] on RS-ERGB-Sharp dataset without blur and RSCD [27] and EvUnroll [28] on the RS-ERGB-Blurry dataset with blur. All methods were finetuned on our datasets. For more details please refer to the Supp. Mat. The results are reported in Tab. 4 and qualitative comparisons are shown in Fig. 8. On the RS-ERGB dataset, we outperform the best image-based method DSUN [15] by 9.16 dB in terms of PSNR and 0.0966 in LPIPS and the event-based method EvUnroll [28] by 0.75 dB in PSNR and 0.0966 in LPIPS. On the RS-ERGB-Blurry dataset, we outperform EvUnroll [28] by 0.48 dB in PSNR and 0.053 in LPIPS. The image based", + "bbox": [ + 496, + 688, + 890, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "13909", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/970e0194a189a82c909cec4d774aab631f4d178e19bbc304281d9a3855c792ea.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 86, + 104, + 250, + 179 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/68eb3c3cfaf1eab4ddf16b7bacd60cbba7783fb78f6359295fd8c81c3e0d2527.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 250, + 104, + 411, + 179 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/2106ce3ccbfcbe184bb5ad94f36eed187001d24d2d266b7787841e2a3c2a23f5.jpg", + "image_caption": [ + "RS-ERGB-Sharp" + ], + "image_footnote": [], + "bbox": [ + 411, + 104, + 573, + 179 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/29f633ae1f5536178f6fe54de6fc52857a3dff8ab13d2cb594cc72640e4117e4.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 573, + 104, + 736, + 179 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/65c25a7b0f114d0128cdd723084b49d4f6399df80632a08f04da863ae7614cb0.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 736, + 104, + 900, + 179 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/2f65dca1ae397b497e11e4784a8d774698d1e63d7a687fb0d3f91186b5e2bb49.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 86, + 180, + 250, + 323 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/7055d5ff2563883574ed78ca0c9a22e799d1eb2aac3069011844d9051c65b79c.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 250, + 180, + 395, + 323 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/2e7d47b3051d533c1efb032dc60cb02bcf6b0be1acb67d3a24e01241be17ef6d.jpg", + 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+ "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/733481a8c27dd4a5a6c41afa872949181e6740fcdf5f82c73f85c80469fbda55.jpg", + "image_caption": [ + "RS-ERGB-Blurry" + ], + "image_footnote": [], + "bbox": [ + 411, + 343, + 573, + 429 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/d2ebb2cc8f4a13fddb71e1cf224bad1456b224d70b1a853653275103cd18b278.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 573, + 343, + 736, + 429 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/78a55870cdd8ae7b0988798b8c005b008cc35c6f07c43a988662def1235893d6.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 736, + 343, + 900, + 429 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/74cbabb627089f03b9dca46173450377649a4231278460fd310cf3c1cc245813.jpg", + "image_caption": [ + "Input RS-image" + ], + "image_footnote": [], + "bbox": [ + 86, + 435, + 250, + 511 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/45a523cf3270beeb0023d0a6d3d401d706041443bd28ab5602dfb183ecce8125.jpg", + "image_caption": [ + "DSUN [15] (i)" + ], + "image_footnote": [], + "bbox": [ + 250, + 433, + 411, + 511 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/0e9137a7c24300925e397ed0a8904dfa6006e795675e3ff771c5d65adfdb75ab.jpg", + "image_caption": [ + "EvUnroll [28] (i+e)" + ], + "image_footnote": [], + "bbox": [ + 411, + 433, + 573, + 511 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/bbfe492e6cfc5b07b2e55eae3afe5e2621466ecfc03aea0e5c95a3ea617e8379.jpg", + "image_caption": [ + "EvShutter (Ours) $(\\mathrm{i} + \\mathrm{e})$" + ], + "image_footnote": [], + "bbox": [ + 573, + 433, + 736, + 511 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/d9a8e8b67a376724c3df8a458c0cc823b0b96af6332a3a85c6e20a65eaa5f6b9.jpg", + "image_caption": [ + "Ground truth" + ], + "image_footnote": [], + "bbox": [ + 736, + 433, + 900, + 511 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/5f118937660988ec5b12d6a953897b3e2eb1d693044206dc6a82ec5d602f7519.jpg", + "image_caption": [ + "Figure 8. Quantitative results on RS-ERGB-Sharp and ER-ERGB-Blurry datasets. Image-based methods are marked by (i) and event and image based methods are marked by $(\\mathrm{i + e})$ . The best method is shown in bold.", + "Figure 9. Visualization of deformable convolutions offsets in deblurring module for the original method [24](left), and our method (right), where offset are computed from optical flow." + ], + "image_footnote": [], + "bbox": [ + 78, + 593, + 272, + 736 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/6e3a24295e703785aad2877caa27e3dd17cb092c37612f58348327854048e1a3.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 274, + 593, + 468, + 736 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "method RSCD [27] seems not able to handle the difficult combination of large RS distortion and blur. Our method improves current image-based SOTA methods especially in areas with large displacements between RS and GS-frame. DSUN [15] is able to reconstruct the overall shape of the object, but produces strong artifacts. EvUnroll [28] is able to", + "bbox": [ + 75, + 799, + 468, + 890 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "recover the structure of the GS images very well, but seems to heavily rely on their synthesis branch in areas with large non linear motion. We hypothesize that the fusion in RGB space makes it more difficult to combine the fine detail and texture from the warping branch with the coarse structurally correct results from the synthesis branch, which often lack precise colors. Additional comparisons can be found in the Supp. Mat..", + "bbox": [ + 496, + 595, + 890, + 717 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Fastec-RS dataset To compare the proposed method to other SOTA on the public Fastec-RS dataset [15] we synthesized events from the original high speed sequences shared by the authors using ESIM [20] with the same parameters as in [28] and re-train our method from scratch. We run JCD [27] and DSUN [15] using the publicly available checkpoints. For [26, 30], we extract the metrics from the JCD paper [27] and for EvUnroll [28] and SUNet [1] from their respective papers. The results are reported in Tab. 5. The proposed method outperforms the best image-based approach by $4.07\\mathrm{dB}$ in PSNR and the event-based approach by $1.09\\mathrm{dB}$ in PSNR, 0.023 in terms of LPIPS and 0.03 in", + "bbox": [ + 496, + 719, + 892, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "13910", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/19e1a3f8d098ec708dcbf40ea1e5d68ac33daa823e7a5a03c53d1c51251a1e3a.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 86, + 88, + 289, + 207 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/2de3b47b211a417cad147e88fde520a9f8d5371821777f169ddcdb18b2d8f168.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 292, + 88, + 491, + 207 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/2bba678d3699ef4c589f6022ae989fbcf26269d3bf9e3eb064c0b6ace8287457.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 493, + 88, + 697, + 207 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/e65885285938758351dfe3a8ab9f289f2c94c78418f82070a951f5aa4bad16dd.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 697, + 88, + 900, + 207 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/010cd0b8b4d1efdf009b3fd94926873a5c64e3cc647f17e0be3c988681112bdf.jpg", + "image_caption": [ + "Input RS-image" + ], + "image_footnote": [], + "bbox": [ + 86, + 210, + 289, + 328 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/189794c3318147ef2ad5227ac5a18c3c0946fcfab05595d7c6dfcfd12d5421a5.jpg", + "image_caption": [ + "EvUnroll original [28]" + ], + "image_footnote": [], + "bbox": [ + 292, + 210, + 491, + 328 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/49787c3836d5c0c72d7ce4e1e34de6425e5d7dcfd55cc73853f6e0a3740b90d6.jpg", + "image_caption": [ + "Figure 10. Qualitative comparison on Real Events and RS images from EvUnroll [28]. Note that no ground truth data is provided for this dataset." + ], + "image_footnote": [], + "bbox": [ + 493, + 210, + 697, + 328 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/6177c7cf3a5a852b4107152faf811c296f5ff4fbe8189d61773d8733c335a550.jpg", + "image_caption": [ + "EvUnroll trained on RS-ERGB", + "Ours" + ], + "image_footnote": [], + "bbox": [ + 697, + 210, + 900, + 328 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/3098c48911ae51856e9ae11404a26abf3695183e163a3e02d8cfff6b9d1dae90.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodPSNR [dB]↑LPIPS↓SSIM↑
RS-ERGB-Sharp
DSUN [15] (i)22.970.26700.7976
RSCD [27] (i)22.620.27590.7884
EvUnroll [28] (i+e)31.380.23340.8614
EvShutter (Ours) (i+e)32.130.17040.8866
RS-ERGB-Blurry
RSCD [27] (i)17.870.37130.7109
EvUnroll [28] (i+e)31.070.25760.8592
EvShutter (Ours) (i+e)31.550.20460.8780
", + "bbox": [ + 78, + 411, + 468, + 555 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "SSIM. Additionally, some qualitative examples are shown in the Supp. Mat.. Similarly, to the results on the RS-ERGB dataset we observe that our method performs better at object boundaries, where the displacement is not homogeneous. We obtain sharper and less \"wobbly\" results.", + "bbox": [ + 75, + 618, + 468, + 694 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/ee7a732a75149bbd74742876a5af316b73f4397d36ed37c8bf9256d2c8f2d7b8.jpg", + "table_caption": [ + "Table 4. RS correction on RS-ERGB dataset with real events. The best method is shown in bold. Image-base methods are marked by (i) and image and event-based methods by $(\\mathrm{i + e})$" + ], + "table_footnote": [], + "table_body": "
MethodPSNR ↑LPIPS↓SSIM↑
DSUN [15] (i)26.520.1220.79
RSCD [27] (i)24.840.1070.78
SUNet [1] (i)28.34-0.84
ESTRNN [26] (i)27.410.1890.84
EvUnroll [28] (i+e)31.320.0840.88
EvShutter (Ours) (i+e)32.410.0610.91
", + "bbox": [ + 78, + 705, + 468, + 815 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 5. RS correction on Fastec-RS dataset with synthetic events. The best method is shown in bold. Image-base methods are marked by (i) and image and event-based methods by $(\\mathrm{i + e})$", + "bbox": [ + 75, + 825, + 468, + 868 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Qualitative comparison on real RS dataset from [28] For qualitative comparison on real data, we evaluated our method on the dataset published in [28], which features real events and real RS images, but no ground truth. In Fig. 10, we compare to the results from EvUnroll [28] trained on their synthetic dataset with synthetic events and their model trained on our RS-ERGB dataset, see Fig. 10. We observe that by training on our RS-ERGB dataset with real events EvUnroll [28] greatly improves their performance. This shows the benefits of the proposed dataset with real events and the novel RS image simulator. Our method performs even better and does not suffer from strong ghosting artifacts as the EvUnroll [28]. Additional examples can be found in Supp. Mat.", + "bbox": [ + 496, + 414, + 890, + 625 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 638, + 617, + 654 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "This paper proposes a method for RS distortion correction and deblurring. The method estimates deblurring operator from event-based optical flow and then compensates RS using a double encoder hourglass network. In contrast to previous methods, it does not rely on a constant velocity assumption and uses a simple architecture thanks to the proposed event transformation. Additionally, we propose the first RS dataset with optional blur containing real events and simulated high-quality RS images and show that training on this dataset increases performance of methods in real case scenarios. We carefully ablate each of the contributions and demonstrate the qualitative and quantitative performance boost compared to previous state-of-the-art methods.", + "bbox": [ + 496, + 664, + 890, + 875 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "13911", + "bbox": [ + 480, + 945, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Bin Fan, Yuchao Dai, and Mingyi He. Sunet: symmetric undistortion network for rolling shutter correction. 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In CVPR, 2018. 6" + ], + "bbox": [ + 501, + 92, + 893, + 900 + ], + "page_idx": 8 + }, + { + "type": "page_number", + "text": "13912", + "bbox": [ + 480, + 945, + 519, + 955 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[26] Zhihang Zhong, Ye Gao, Yinqiang Zheng, and Bo Zheng. Efficient spatio-temporal recurrent neural network for video deblurring. In European Conference on Computer Vision, pages 191-207. Springer, 2020. 3, 7, 8", + "[27] Zhihang Zhong, Yinqiang Zheng, and Imari Sato. Towards rolling shutter correction and deblurring in dynamic scenes. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 9219-9228, 2021. 3, 6, 7, 8", + "[28] Xinyu Zhou, Peiqi Duan, Yi Ma, and Boxin Shi. Evunroll: Neuromorphic events based rolling shutter image correction. 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Unsupervised event-based optical flow using motion compensation. In Proceedings of the European Conference on Computer Vision (ECCV) Workshops, pages 0–0, 2018. 3" + ], + "bbox": [ + 78, + 90, + 470, + 542 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "13913", + "bbox": [ + 480, + 945, + 517, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/EvShutter_ Transforming Events for Unconstrained Rolling Shutter Correction/65a66f35-8745-4d12-9133-82f4227811f2_model.json b/2023/EvShutter_ Transforming Events for Unconstrained Rolling Shutter Correction/65a66f35-8745-4d12-9133-82f4227811f2_model.json new file mode 100644 index 0000000000000000000000000000000000000000..1da0c225d32a6e05d45fa465ba9d0a36963e689d --- /dev/null +++ b/2023/EvShutter_ Transforming Events for Unconstrained Rolling Shutter Correction/65a66f35-8745-4d12-9133-82f4227811f2_model.json @@ -0,0 +1,2310 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.237, + 0.0, + 0.812, + 0.045 + ], + "angle": 0, + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.086, + 0.131, + 0.885, + 0.152 + ], + "angle": 0, + "content": "EvShutter: Transforming Events for Unconstrained Rolling Shutter Correction" + }, + { + "type": "text", + "bbox": [ + 0.151, + 0.181, + 0.264, + 0.198 + ], + "angle": 0, + "content": "Julius Erbach" + }, + { + "type": "text", + "bbox": [ + 0.308, + 0.181, + 0.444, + 0.199 + ], + "angle": 0, + "content": "Stepan Tulyakov" + }, + { + "type": "text", + "bbox": [ + 0.491, + 0.182, + 0.614, + 0.198 + ], + "angle": 0, + "content": "Patricia Vitoria" + }, + { + "type": "text", + "bbox": [ + 0.66, + 0.182, + 0.818, + 0.197 + ], + "angle": 0, + "content": "Alfredo Bochicchio" + }, + { + "type": "text", + "bbox": [ + 0.439, + 0.2, + 0.533, + 0.217 + ], + "angle": 0, + "content": "Yuanyou Li" + }, + { + "type": "text", + "bbox": [ + 0.299, + 0.218, + 0.667, + 0.234 + ], + "angle": 0, + "content": "Huawei Technologies, Zurich Research Center" + }, + { + "type": "image_caption", + "bbox": [ + 0.086, + 0.26, + 0.226, + 0.273 + ], + "angle": 0, + "content": "Rolling Shutter Image" + }, + { + "type": "image", + "bbox": [ + 0.081, + 0.274, + 0.229, + 0.395 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.277, + 0.26, + 0.322, + 0.271 + ], + "angle": 0, + "content": "Events" + }, + { + "type": "image", + "bbox": [ + 0.232, + 0.273, + 0.384, + 0.395 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.442, + 0.26, + 0.58, + 0.273 + ], + "angle": 0, + "content": "Rolling Shutter Image" + }, + { + "type": "image", + "bbox": [ + 0.387, + 0.273, + 0.638, + 0.395 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.736, + 0.26, + 0.78, + 0.271 + ], + "angle": 0, + "content": "Events" + }, + { + "type": "image", + "bbox": [ + 0.64, + 0.273, + 0.891, + 0.395 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.08, + 0.396, + 0.229, + 0.516 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.11, + 0.518, + 0.198, + 0.532 + ], + "angle": 0, + "content": "EvUnroll [28]" + }, + { + "type": "image", + "bbox": [ + 0.233, + 0.396, + 0.382, + 0.516 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.268, + 0.518, + 0.332, + 0.531 + ], + "angle": 0, + "content": "EvShutter" + }, + { + "type": "image", + "bbox": [ + 0.386, + 0.395, + 0.638, + 0.516 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.467, + 0.518, + 0.555, + 0.532 + ], + "angle": 0, + "content": "EvUnroll [28]" + }, + { + "type": "image", + "bbox": [ + 0.64, + 0.395, + 0.891, + 0.516 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.726, + 0.518, + 0.79, + 0.53 + ], + "angle": 0, + "content": "EvShutter" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.545, + 0.894, + 0.574 + ], + "angle": 0, + "content": "Figure 1. Comparison of EvShutter to state-of-the-art event-based RS correction method [28]. Our method introduces a novel event transformation, which allows us to correct RS artifacts in the presence of non-linear motion or large displacements." + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.584, + 0.314, + 0.599 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.075, + 0.617, + 0.471, + 0.86 + ], + "angle": 0, + "content": "Widely used Rolling Shutter (RS) CMOS sensors capture high resolution images at the expense of introducing distortions and artifacts in the presence of motion. In such situations, RS distortion correction algorithms are critical. Recent methods rely on a constant velocity assumption and require multiple frames to predict the dense displacement field. In this work, we introduce a new method, called Eventful Shutter (EvShutter), that corrects RS artifacts using a single RGB image and event information with high temporal resolution. The method firstly removes blur using a novel flow-based deblurring module and then compensates RS using a double encoder hourglass network. In contrast to previous methods, it does not rely on a constant velocity assumption and uses a simple architecture thanks to an event transformation dedicated to RS, called Filter and Flip (FnF), that transforms input events to encode only" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.585, + 0.894, + 0.766 + ], + "angle": 0, + "content": "the changes between GS and RS images. To evaluate the proposed method and facilitate future research, we collect the first dataset with real events and high-quality RS images with optional blur, called RS-ERGB. We generate the RS images from GS images using a newly proposed simulator based on adaptive interpolation. The simulator permits the use of inexpensive cameras with long exposure to capture high-quality GS images. We show that on this realistic dataset the proposed method outperforms the state-of-the-art image- and event-based methods by 9.16 dB and 0.75 dB respectively in terms of PSNR and an improvement of \\(23\\%\\) and \\(21\\%\\) in LPIPS." + }, + { + "type": "title", + "bbox": [ + 0.501, + 0.799, + 0.631, + 0.814 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.826, + 0.894, + 0.901 + ], + "angle": 0, + "content": "Most consumer cameras like cell phones or action cameras use a rolling shutter (RS) sensor which instead of capturing the whole frame in a single shot as in a global shutter (GS) camera, it acquires each row sequentially as shown in Fig. 2. Specifically, it obtains each row \\( y \\) at time" + }, + { + "type": "page_footnote", + "bbox": [ + 0.078, + 0.875, + 0.468, + 0.9 + ], + "angle": 0, + "content": "The evaluation code and the dataset can be found here https://github.com/juliuserbach/EvShutter" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "13904" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.095, + 0.088, + 0.298, + 0.201 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.318, + 0.088, + 0.454, + 0.201 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.211, + 0.47, + 0.253 + ], + "angle": 0, + "content": "Figure 2. Rolling Shutter Explained. While recording with a RS camera (left), image rows are exposed sequentially, while in the case of a GS camera (right) they are exposed all at the same time." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.263, + 0.468, + 0.413 + ], + "angle": 0, + "content": "\\( t_{y} = y \\cdot t_{H} / H \\), where \\( H \\) is the height of an image and \\( t_{H} \\) is the mid-exposure time of the last row. RS cameras are often preferred due to their high spatial resolution and high frame rates at low cost. Global shutter sensors have a more complicated circuitry, and therefore a smaller resolution than rolling shutter sensors of the same physical size. A larger sensor size in turn increases the cost of the lens. However, in the presence of fast camera or object movement, RS sensors can produce skew distortion in images (see Fig. 1) and jello artifacts in videos." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.415, + 0.468, + 0.566 + ], + "angle": 0, + "content": "To correct such artifacts, RS correction methods are widely used. Conventional methods attempt to recover the corresponding GS image from the RS output by first estimating the camera motion or dense displacement field during the image acquisition and sequentially applying motion compensation to align all the pixels to a fixed timestamp. However, these methods make strong assumptions on the motion type and are prone to fail in the presence of complex motion patterns like local or non-linear motion, which no longer satisfy the assumptions." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.568, + 0.468, + 0.78 + ], + "angle": 0, + "content": "In this work, we address the fundamental problem of modeling scene changes during image acquisition by using the high temporal information provided by an auxiliary event camera. Instead of measuring synchronous frames of absolute brightness, event cameras only measure asynchronous brightness changes at each pixel with a high temporal resolution in the order of microseconds [3]. Unlike image-based methods, event cameras allow to estimate the motion without relying on a constant speed assumption and synthesizing images by directly adding the brightness changes registered by the events to an image. This enables exciting computational photography applications such as event-guided image deblurring [12, 18, 24], video interpolation [8, 22, 23] and high dynamic range imaging [6, 16]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.781, + 0.468, + 0.902 + ], + "angle": 0, + "content": "In this paper, we propose a RS compensation method, called Eventful Shutter (EvShutter), that only requires a single RS image and the corresponding events. The method firstly removes blur using a novel flow-based deblurring module and then compensates RS using an hourglass network with two encoders relying on complementary geometric and synthesis-based interpolation approaches. The proposed method is the first method that does not rely on" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.258 + ], + "angle": 0, + "content": "constant velocity assumption and uses a simple architecture thanks to the newly introduced event transformation, that we call Filter and Flip (FnF). FnF transforms the input events to encode just changes between GS and RS images. To train and evaluate the proposed method, we collect the first dataset with real events and high quality RS images (optionally with blur), called RS-ERGB. The RS images are generated from GS images using our new simulator based on adaptive interpolation. This pipeline allows the use of an inexpensive high speed camera and the use of long exposures while capturing the GS images." + }, + { + "type": "title", + "bbox": [ + 0.519, + 0.258, + 0.8, + 0.271 + ], + "angle": 0, + "content": "Contributions of this work are as follows" + }, + { + "type": "text", + "bbox": [ + 0.513, + 0.273, + 0.892, + 0.317 + ], + "angle": 0, + "content": "1. Eventful Shutter (EvShutter): the first event-assisted RS distortion compensation and deblurring method that avoids constant speed motion assumptions." + }, + { + "type": "text", + "bbox": [ + 0.512, + 0.318, + 0.891, + 0.377 + ], + "angle": 0, + "content": "2. Filter and Flip (FnF): an event transformation module that transforms the input event stream to encode only the brightness change from GS to RS image and simplifies the architecture of downstream modules." + }, + { + "type": "text", + "bbox": [ + 0.512, + 0.379, + 0.892, + 0.439 + ], + "angle": 0, + "content": "3. Rolling Shutter Events and RGB (RS-ERGB) dataset and simulator: the first dataset with real events and RS images with optional blur generated using a new realistic RS-simulator, based on adaptive interpolation." + }, + { + "type": "list", + "bbox": [ + 0.512, + 0.273, + 0.892, + 0.439 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.453, + 0.642, + 0.469 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.478, + 0.892, + 0.599 + ], + "angle": 0, + "content": "Previous works on RS correction attempt to recover the GS image by estimating the camera motion or dense displacement field during image acquisition and applying motion compensation to align all the pixels to a fixed timesamp. They can be classified according to their motion estimation method into following categories: gyro-based, single image-based, multiple image-based and event-based. Below we describe each category in detail." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.599, + 0.892, + 0.719 + ], + "angle": 0, + "content": "Gyroscope-based methods [7, 13] utilize a gyro sensor to estimate the rotational motion of the camera. These methods are widely used in mobile devices, due to their speed and reliability. However, they assume a static scene and a simplified rotational camera motion. hence, they can not correct RS distortions due to moving objects (e.g. see Fig. 1), or in the presence of more complex camera motion where the purely rotational assumption is violated." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.892, + 0.885 + ], + "angle": 0, + "content": "Single image-based methods infer the motion from a single RS image by relying on a prior model of the scene. Methods in [14, 19] assume the presence of multiple straight lines in the scenes (Manhattan world assumption) for motion estimation. These hand-crafted priors fail when the scene deviates from the assumed model. Recent methods [21, 31] rely on deep learning to automatically learn scene priors that are used to estimate the camera motion. While these methods are more robust, they are still limited to certain scene types with static scene and constant depth (except [31])." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.886, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Multiple image-based methods estimate the motion be" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "13905" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.272 + ], + "angle": 0, + "content": "tween sequential RS images and use it to approximate the motion during image exposure relying on a parametric motion model. While early methods [2, 5] use image feature matching to estimate a rotational or planar homography, more recent methods [1, 15, 27] compute the dense optical flow between RS images and can correct RS distortion due to object motion. However, they suffer from limitations of image-based motion estimation: they do not work with a single image, image blur and illumination changes. Moreover, they lack the exact information about the motion during exposure and can fail in the presence of large displacements in between frames and highly non-linear motion." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.273, + 0.473, + 0.452 + ], + "angle": 0, + "content": "Event-based method. Recently, [28] developed an event-assisted RS compensation method based on the work of [23]. To ensure that interpolation in a given row is performed from mid-exposure time of that same row to mid-exposure time of the latent GS image their method uses additional conditioning mechanisms and assumptions in the sub-modules, notably constant velocity assumption similar to images-based methods [1, 15, 27]. In contrast, we eliminate the need of additional strong assumptions and conditioning in downstream modules by introducing a simple yet effective event transformation that modifies the input events to encode the transformation from GS to RS image." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.454, + 0.473, + 0.544 + ], + "angle": 0, + "content": "RS Deblur. Besides RS distortion, in presence of fast motion RS images often suffers from blur. In those cases, RS restoration methods needs to simultaneously perform deblur and distortion correction. [27] directly incorporate a deblurring stream in the RS correction network, while [28] adds an optional deblur module before the RS correction." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.545, + 0.473, + 0.803 + ], + "angle": 0, + "content": "Datasets. BS-RSCD [27] dataset is recorded by using a beamsplitter setup with temporally and geometrically synchronized GS and RS cameras. Other datasets, such as Fastec-RS [15] or Gev-RS [28] are collected by first using a high speed GS camera and later synthesizing RS images by sequentially copying rows from the high frame rate GS images. For Gev-RS events are simulated from high speed GS images using V2E [10]. Unfortunately, training with synthetic events often does not generalize well to real event data. Moreover, RS images synthesized by the above method suffer from noise, low contrast and have small resolution, due to very short exposure time in the high speed cameras. We address two of the above problems by capturing a new dataset with real events using GS RGB and event cameras arranged in a beamsplitter setup and introducing new high fidelity simulator that generates high quality RS images with optional blur from GS images." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.82, + 0.17, + 0.835 + ], + "angle": 0, + "content": "3. Method" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.845, + 0.409, + 0.862 + ], + "angle": 0, + "content": "3.1.Eventful Shutter (EvShutter) Network" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.47, + 0.903 + ], + "angle": 0, + "content": "At first, we perform event-assisted deblurring of the input RS image \\( I_{blur}^{rs} \\) image using a pre-processing deblurring" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.332 + ], + "angle": 0, + "content": "module inspired by [24]. Next, we compensate RS distortion to obtain at a GS estimate at reference time \\( t_{ref} \\) using the pipeline shown in Fig. 3. As shown in the Fig. 3, instead of directly feeding all the raw events \\( E_{0\\rightarrow t_H} \\) to the network as in [28], we firstly pre-process them by using the proposed Filter and Flip (FnF) transformation, described in details in Sec. 3.2. Next, we encode the transformed events \\( E_{gs\\rightarrow rs} \\) into a voxel grid representation \\( V_{gs\\rightarrow rs} \\) as described in [32]. Then we feed the voxel grid and the RS image \\( I^{rs} \\) to an hourglass network composed of a warping encoder and a synthesis encoder using complementary interpolation approaches as in [22, 23]. Lastly, the fusion decoder progressively combines multi-scale images and warping and synthesis features to produce the final GS image \\( I^{gs} \\). Below we explain the main modules of the proposed method." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.334, + 0.892, + 0.59 + ], + "angle": 0, + "content": "Deblurring. Besides the RS distortion, RS images can suffer from motion blur due to camera or object motion during the exposure time. Therefore, we propose to deblur RS images using events before passing them to our RS distortion compensation method. The overall pipeline of the deblurring is shown in Fig. 4. First, we filter out all events triggered not during the exposure time of the corresponding image rows and then, we shift them according to the row-wise delay, similar to [28]. This allows the use of GS event-based deblurring methods, such as [24]. The original method estimates a deblur operator directly from events using offsets and masks of deformable convolutions [29]. However, we found that it is possible to estimate better deblur operators from more a explicit motion representation, such as optical flow. To estimate flow, we re-use the same network and weights as in the main RS distortion compensation pipeline." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.591, + 0.892, + 0.903 + ], + "angle": 0, + "content": "Warping Encoder. The warping-based encoder takes the voxel grid \\( V_{gs \\to rs} \\) and estimates optical flow \\( \\mathcal{F}_{gs \\to rs} \\) relating the latent GS image to RS image using a flow network from [23]. Note that because the transformed events only encode changes from GS to RS image we can directly estimate optical flow between them without relying on a constant speed assumption. In other words, we can directly estimate row-wise flow, where each row \\( y \\) represents the pixel displacement from time \\( t_{ref} \\) to time \\( y \\cdot t_H / H \\). In contrast in [1, 15, 26, 28], the authors predict optical flow between frames or during the exposure time of the frame using events and approximate the displacement between RS and GS by multiplying with a row dependent coefficient, which is only accurate for linear motions. The estimated flow is used to warp multi-scale features extracted from the RS image \\( I^{rs} \\) using the image encoder resulting in multi-scale warping interpolation features \\( \\mathbf{F}_{\\rightarrow \\mathrm{gs}}^{\\mathbf{w}} = (F_{\\rightarrow gs}^{w(0)}, F_{\\rightarrow gs}^{w(1)}, F_{\\rightarrow gs}^{w(2)}) \\). Similarly, a multi-scale image pyramid computed from the RS image is warped to get \\( \\mathbf{I}_{\\rightarrow \\mathrm{gs}}^{\\mathrm{rs}} = (I_{\\rightarrow gs}^{rs(0)}, I_{\\rightarrow gs}^{rs(1)}, I_{\\rightarrow gs}^{rs(2)}) \\). The warping is performed by using" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.946, + 0.52, + 0.957 + ], + "angle": 0, + "content": "13906" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.092, + 0.891, + 0.375 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.389, + 0.893, + 0.445 + ], + "angle": 0, + "content": "Figure 3. RS distortion compensation pipeline. At first the proposed method pre-processes input events with \\( FnF \\) transformation to encode only the brightness change between GS and RS frames. The transformed events are then passed to double encoder hourglass network with complementary warping and synthesis encoders relying on different interpolation principles. Then multi-scale features and images from both encoders are fused in the decoder to produce a GS image. The first fusion block of the decoder is shown in detail." + }, + { + "type": "image", + "bbox": [ + 0.124, + 0.467, + 0.43, + 0.616 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.626, + 0.47, + 0.682 + ], + "angle": 0, + "content": "Figure 4. RS deblurring pipeline. First we filter out all the events which are not triggered during the exposure time, then we deblur the RS image using an improved version of [24], that relies on optical flow estimation to predict deblur kernels." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.691, + 0.47, + 0.752 + ], + "angle": 0, + "content": "differentiable backward interpolation. To downscale images and optical flow we perform average pooling and in case of flow we additionally divide the flow by the downscale factor." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.759, + 0.47, + 0.865 + ], + "angle": 0, + "content": "Synthesis-based Encoder. The synthesis-based encoder takes both voxel grid \\( V_{gs \\to rs} \\) and RS image \\( I^{rs} \\) as inputs and computes multi-scale synthesis interpolation features \\( \\mathbf{F}^s \\). Intuitively, this encoder integrates brightness changes from the event stream and adds them to the RS image. Notice that, in contrast to the warping encoder, this module can handle illumination changes and fill motion occlusions." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.469, + 0.903 + ], + "angle": 0, + "content": "Fusion Decoder: The fusion decoder progressively combines synthesis \\(\\mathbf{F}^s\\) and warping-based \\(\\mathbf{F}_{\\rightarrow gs}^{w}\\) features, orig-" + }, + { + "type": "image", + "bbox": [ + 0.505, + 0.473, + 0.889, + 0.619 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.63, + 0.893, + 0.713 + ], + "angle": 0, + "content": "Figure 5. Event transformation workflow. Top row: Event stream is transformed by first applying and event filtering followed by a flipping step around an arbitrary reference time. Bottom row: An example of events. Right: Animation (best viewed with Acrobot Reader) between RS-input and GS estimations at different reference times." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.724, + 0.893, + 0.846 + ], + "angle": 0, + "content": "inal RS image \\( I^{rs} \\) and warped RS image \\( I_{\\rightarrow gs}^{rs} \\) on multiple scales to reconstruct the GS image \\( I^{gs} \\). We use shortcut connections from the original RS image to help the decoder to reconstruct static parts of the image. To select the most informative features on each scale the decoder relies on Squeeze-and-excitation (SE) blocks [9] attenuating channels, and modulated deformable convolutions [29], attenuating the feature maps spatially." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "13907" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.077, + 0.091, + 0.4, + 0.108 + ], + "angle": 0, + "content": "3.2. Filter and Flip (FnF) Transformation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.114, + 0.47, + 0.265 + ], + "angle": 0, + "content": "The auxiliary event camera records an event stream \\( E_{0 \\to t_H} \\) encoding all brightness changes from time 0 to \\( t_H \\). However, to recover the GS image \\( I^{gs} \\) corresponding to a given RS image \\( I^{rs} \\), we are only interested on those events \\( E_{gs \\to rs} \\) encoding brightness changes between latent GS and observed RS image. In this work, we propose a well-suited RS event transformation called Filter and Flip (FnF), which transforms the event stream \\( E_{0 \\to t_H} \\) to \\( E_{gs \\to rs} \\) through two steps: filtering and flipping steps as shown in Fig. 5 and described below." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.266, + 0.47, + 0.326 + ], + "angle": 0, + "content": "Filtering step. For each row \\(y\\), we only keep those events triggered between time \\(t_y\\) and the reference time \\(t_{ref}\\), where \\(t_y\\) is mid-exposure time of row \\(y\\) in observed RS image." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.326, + 0.469, + 0.431 + ], + "angle": 0, + "content": "Flipping step. We reverse all events before the reference time \\( t_{ref} \\) by inverting their polarities and recomputing their timestamps such that they are flipped around \\( t_{ref} \\) as shown in Fig. 5. This process ensures that the events encode changes in the direction from GS-frame to RS-frame and that the transformed events start at the time, which matches the GS-frame and end at the RS-time." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.432, + 0.469, + 0.567 + ], + "angle": 0, + "content": "Applying the event transformation eliminates the need in time conditioning mechanisms and additional assumptions in the downstream modules. For example, in contrast to [28], the proposed method does not require constant speed assumption in the flow estimation module and attention mechanisms in the synthesis-based encoder, which allows re-using already pretrained modules on widely used GS images. Also, notice, that the FnF transformation can be adapted to arbitrary reference times." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.568, + 0.469, + 0.612 + ], + "angle": 0, + "content": "In order to allow a good comparison to other works, we set \\( t_{ref} = t_H / 2 \\), which corresponds to the mid-exposure time of the central row." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.621, + 0.257, + 0.636 + ], + "angle": 0, + "content": "3.3. RS-ERGB Dataset" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.645, + 0.469, + 0.78 + ], + "angle": 0, + "content": "To bridge the sim-to-real gap from synthetic to real events we build a hybrid imaging system of a high speed GS RGB-camera and an event camera in a beam splitter setup. We use hardware temporal synchronization and geometrically align events and images as described in the Supp. Mat. With this setup we capture the first RS dataset with real events and high quality images. We generate high quality RS images with optional blur using our novel simulator based on adaptive interpolation described below." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.781, + 0.469, + 0.901 + ], + "angle": 0, + "content": "High quality RS simulator. Our proposed pipeline allows to record GS sequences at lower speed than previous methods (160 fps compared to [15, 28] that record GS sequence at 2400 or 5700 fps). This allows us to use a longer exposure and as a result, acquire images of higher quality. Then we adaptively interpolate captured images using Super Slomo [11], so that the maximum displacement between interpolated frames is at most 1 pixel similar to" + }, + { + "type": "image", + "bbox": [ + 0.502, + 0.088, + 0.895, + 0.205 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.215, + 0.894, + 0.271 + ], + "angle": 0, + "content": "Figure 6. Synthetic RS-images from a sequence of GS-Images \\( I_{i} \\). Each row is constructed separately by computing the weighted average of the GS-frames, which are assumed to be a close approximation of the latent GS-frames." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.281, + 0.893, + 0.432 + ], + "angle": 0, + "content": "Vid2E [4]. This procedure ensures that a sufficient temporal resolution is achieved to synthesize realistic blur and RS effect. As shown in Fig. 7, using a fixed interpolation factor can give unrealistic results as the amount of motion can differ significantly by region and scene. The resulting interpolated video sequence can be thought of as discrete approximation of latent GS-images \\(I_{i}\\) of the true latent frames \\(I_{\\text{latent}}(t,x,y)\\). To synthesize a row \\(y_{rs}\\) of a RS-image the integral of \\(I_{\\text{latent}}(t,x,y = y_{rs})\\) has to be computed over the exposure time for this row, as" + }, + { + "type": "equation", + "bbox": [ + 0.505, + 0.445, + 0.891, + 0.506 + ], + "angle": 0, + "content": "\\[\nI _ {r s} \\left(t _ {\\text {s t a r t}}, t _ {\\text {e n d}}, y _ {i}\\right) = \\frac {1}{t _ {\\text {e n d}} - t _ {\\text {s t a r t}}} \\int_ {t _ {\\text {s t a r t}}} ^ {t _ {\\text {e n d}}} I _ {\\text {l a t e n t}} (t, y _ {i}) d t. \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.507, + 0.892, + 0.718 + ], + "angle": 0, + "content": "We use a discrete approximation instead and compute a weighted average of the approximated latent frames \\( I_{i} \\) as shown in Fig. 6. Using this procedure a synthetic exposure time and readout time \\( T \\) are chosen to synthesize corresponding RS frames. Notice that exposure time and readout time can be set separately allowing us to create blurry RS images with sharp RS ground truth for the task of RS deblurring. Video interpolation has already been used in the past to generate more realistic blur from videos [17], but to the best of our knowledge, we are the first to use an adaptive upsampling scheme to get consistently realistic results. Examples of our dataset with different amounts of blur and a comparison to a version without adaptive interpolation can be seen in the Supp. Mat.." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.718, + 0.892, + 0.794 + ], + "angle": 0, + "content": "Comparison to Gev-RS [28] is shown in Tab. 1. Compared to Gev-RS, our dataset has real events and the RS and GS image have better quality and resolution, despite using a lower end camera \\( {}^{2} \\) ,since our new synthesis procedure allows using lower frame rate with longer exposure." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.809, + 0.633, + 0.826 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.835, + 0.894, + 0.865 + ], + "angle": 0, + "content": "In this section, first, we ablate the key contributions of the proposed EvShutter method. Second, we benchmark" + }, + { + "type": "page_footnote", + "bbox": [ + 0.5, + 0.875, + 0.892, + 0.901 + ], + "angle": 0, + "content": "2 Phantom VEO 640 is used for collecting Gev-RS cost \\(60\\mathrm{k}\\) while Blackfly S used for collecting our datasets costs just \\(500\\)." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "13908" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.081, + 0.089, + 0.454, + 0.247 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.258, + 0.471, + 0.313 + ], + "angle": 0, + "content": "Figure 7. Benefit of the proposed RS simulator In contrast to a simulator with fixed interpolation rate, the proposed simulator with an adaptive interpolation does not suffer from aliasing artifacts regardless of the motion speed." + }, + { + "type": "table", + "bbox": [ + 0.079, + 0.334, + 0.48, + 0.436 + ], + "angle": 0, + "content": "
RS-ERGB (ours)Gev-RS [28]
Event datareal (Prophesee Gen4M)synthetic
GS camera160 fps5.7k fps
Blackfly SPhantom VEO 640
№ sequence3429
Image qualityhighlow
Resolution970×625640×360
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.447, + 0.468, + 0.474 + ], + "angle": 0, + "content": "Table 1. Details of our RS-ERGB compared to Gev-RS [28]. Best-suited properties are shown in bold." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.485, + 0.469, + 0.53 + ], + "angle": 0, + "content": "the EvShutter against state-of-the-art image-based [15,27] and event-based [28] methods on our RS-ERGB dataset, as well as on the public Fastec-RS dataset [15]." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.531, + 0.469, + 0.577 + ], + "angle": 0, + "content": "Details of the objective loss, training procedure and runtime comparisons together with ablation on additional design choices can be found in the Supp. Mat." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.588, + 0.23, + 0.604 + ], + "angle": 0, + "content": "4.1. Ablation Study" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.612, + 0.469, + 0.657 + ], + "angle": 0, + "content": "FnF event transformation. To evaluate the proposed FnF transformation Tab. 2 we dissect our pipeline in purely warping-based, purely synthesis-based and the full pipeline." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.658, + 0.469, + 0.747 + ], + "angle": 0, + "content": "We compare the purely warping-based method to a version that relies on a constant velocity assumption similar to EvUnroll [28] by applying a row-wise scaling to the optical flow computed from \\( t_{GS} \\) to \\( t_0 \\) and from \\( t_{GS} \\) to \\( t_H \\). Our FnF transformation improves the warping-based method by 0.77 dB in PSNR and 0.0104 in LPIPS [25]." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.749, + 0.469, + 0.809 + ], + "angle": 0, + "content": "We also test the purely synthesis based module with and without the FnF transformation. As shown in Tab. 2 the synthesis module with the transformation outperforms the version without by \\(3.92\\mathrm{dB}\\) in PSNR and 0.0376 in LPIPS." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.81, + 0.469, + 0.839 + ], + "angle": 0, + "content": "The overall architecture also benefits from the FnF transformation by 2.61 dB in PSNR and 0.0203 in LPIPS." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.841, + 0.469, + 0.901 + ], + "angle": 0, + "content": "Importance of optical flow in RS deblur module. We show benefits of estimating the deblur operator from optical flow instead of raw events in Tab. 3. By introducing the optical flow explicitly to the deblurring network we observe" + }, + { + "type": "table", + "bbox": [ + 0.501, + 0.088, + 0.892, + 0.247 + ], + "angle": 0, + "content": "
MethodPSNR↑LPIPS↓SSIM↑
Warping
Linearized flow28.390.17210.870
FnF-Transform29.160.16170.883
Synthesis
w/o FnF-Transform25.870.22330.807
FnF-Transform29.790.18570.867
Warping & Synthesis
Linearized flow28.970.17030.870
FnF-Transform31.580.15000.897
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.257, + 0.892, + 0.326 + ], + "angle": 0, + "content": "Table 2. Importance of FnF event transformation. The transformation improves performance of synthesis encoder and warping encoder. In the warping encoder it allows to avoid constant speed motion assumption. Ablation is made on the RS-ERGB validation set and best method is shown in bold." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.337, + 0.892, + 0.488 + ], + "angle": 0, + "content": "an improvement of \\(1.4\\mathrm{dB}\\) in PSNR without effectively increasing the capacity, since we reuse the optical flow module from the RS correction pipeline. Furthermore, we visualized the offsets and masks of the deformable kernels in Fig. 9 and observed that in the case of large motions the kernels did not follow the motion in the original implementation of [24], but with our flow based adaption the deformable kernel is well aligned with the motion. For the sake of completeness we also add the results for deblurring of the EvUnroll [28] deblur module finetuned on our data." + }, + { + "type": "table", + "bbox": [ + 0.502, + 0.497, + 0.891, + 0.564 + ], + "angle": 0, + "content": "
MethodPSNR↑LPIPS↓SSIM↑
EDDMA [24]34.920.05880.936
EDDMA [24]+Flow36.320.04880.951
EvUnroll + Deblur [28]35.640.04990.934
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.574, + 0.892, + 0.642 + ], + "angle": 0, + "content": "Table 3. Importance of optical flow in RS deblur module. For this experiment we generate RS images with 50ms exposure and compare RS-Deblurring results without RS correction. Best method is shown in bold. We also show performance of EvUnroll deblur module for reference." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.666, + 0.791, + 0.682 + ], + "angle": 0, + "content": "4.2. Comparison with SOTA methods" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.689, + 0.892, + 0.901 + ], + "angle": 0, + "content": "RS-ERGB dataset. We compare our method to the state-of-the-art image-based methods DSUN [15], RSCD [27] and the recent event-based EvUnroll [28] on RS-ERGB-Sharp dataset without blur and RSCD [27] and EvUnroll [28] on the RS-ERGB-Blurry dataset with blur. All methods were finetuned on our datasets. For more details please refer to the Supp. Mat. The results are reported in Tab. 4 and qualitative comparisons are shown in Fig. 8. On the RS-ERGB dataset, we outperform the best image-based method DSUN [15] by 9.16 dB in terms of PSNR and 0.0966 in LPIPS and the event-based method EvUnroll [28] by 0.75 dB in PSNR and 0.0966 in LPIPS. On the RS-ERGB-Blurry dataset, we outperform EvUnroll [28] by 0.48 dB in PSNR and 0.053 in LPIPS. The image based" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "13909" + } + ], + [ + { + "type": "image_caption", + "bbox": [ + 0.438, + 0.09, + 0.551, + 0.105 + ], + "angle": 0, + "content": "RS-ERGB-Sharp" + }, + { + "type": "image", + "bbox": [ + 0.087, + 0.106, + 0.251, + 0.18 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.251, + 0.105, + 0.412, + 0.18 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.412, + 0.105, + 0.574, + 0.18 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.574, + 0.105, + 0.737, + 0.18 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.737, + 0.105, + 0.901, + 0.18 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.087, + 0.181, + 0.25, + 0.324 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.25, + 0.181, + 0.396, + 0.324 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.412, + 0.181, + 0.574, + 0.324 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.574, + 0.181, + 0.716, + 0.324 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.716, + 0.181, + 0.884, + 0.324 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.437, + 0.33, + 0.554, + 0.344 + ], + "angle": 0, + "content": "RS-ERGB-Blurry" + }, + { + "type": "image", + "bbox": [ + 0.088, + 0.344, + 0.251, + 0.43 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.251, + 0.344, + 0.412, + 0.43 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.412, + 0.344, + 0.575, + 0.43 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.575, + 0.344, + 0.738, + 0.43 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.738, + 0.344, + 0.901, + 0.43 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.088, + 0.436, + 0.25, + 0.512 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.251, + 0.434, + 0.412, + 0.512 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.412, + 0.434, + 0.575, + 0.512 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.575, + 0.434, + 0.738, + 0.512 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.738, + 0.434, + 0.901, + 0.512 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.116, + 0.515, + 0.223, + 0.529 + ], + "angle": 0, + "content": "Input RS-image" + }, + { + "type": "image_caption", + "bbox": [ + 0.282, + 0.515, + 0.379, + 0.529 + ], + "angle": 0, + "content": "DSUN [15] (i)" + }, + { + "type": "image_caption", + "bbox": [ + 0.435, + 0.515, + 0.566, + 0.529 + ], + "angle": 0, + "content": "EvUnroll [28] (i+e)" + }, + { + "type": "image_caption", + "bbox": [ + 0.582, + 0.515, + 0.743, + 0.529 + ], + "angle": 0, + "content": "EvShutter (Ours) \\((\\mathrm{i} + \\mathrm{e})\\)" + }, + { + "type": "image_caption", + "bbox": [ + 0.786, + 0.515, + 0.872, + 0.527 + ], + "angle": 0, + "content": "Ground truth" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.542, + 0.892, + 0.57 + ], + "angle": 0, + "content": "Figure 8. Quantitative results on RS-ERGB-Sharp and ER-ERGB-Blurry datasets. Image-based methods are marked by (i) and event and image based methods are marked by \\((\\mathrm{i + e})\\) . The best method is shown in bold." + }, + { + "type": "image", + "bbox": [ + 0.08, + 0.594, + 0.273, + 0.737 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.275, + 0.594, + 0.469, + 0.737 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.748, + 0.47, + 0.79 + ], + "angle": 0, + "content": "Figure 9. Visualization of deformable convolutions offsets in deblurring module for the original method [24](left), and our method (right), where offset are computed from optical flow." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.8, + 0.47, + 0.891 + ], + "angle": 0, + "content": "method RSCD [27] seems not able to handle the difficult combination of large RS distortion and blur. Our method improves current image-based SOTA methods especially in areas with large displacements between RS and GS-frame. DSUN [15] is able to reconstruct the overall shape of the object, but produces strong artifacts. EvUnroll [28] is able to" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.597, + 0.892, + 0.718 + ], + "angle": 0, + "content": "recover the structure of the GS images very well, but seems to heavily rely on their synthesis branch in areas with large non linear motion. We hypothesize that the fusion in RGB space makes it more difficult to combine the fine detail and texture from the warping branch with the coarse structurally correct results from the synthesis branch, which often lack precise colors. Additional comparisons can be found in the Supp. Mat.." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.893, + 0.901 + ], + "angle": 0, + "content": "Fastec-RS dataset To compare the proposed method to other SOTA on the public Fastec-RS dataset [15] we synthesized events from the original high speed sequences shared by the authors using ESIM [20] with the same parameters as in [28] and re-train our method from scratch. We run JCD [27] and DSUN [15] using the publicly available checkpoints. For [26, 30], we extract the metrics from the JCD paper [27] and for EvUnroll [28] and SUNet [1] from their respective papers. The results are reported in Tab. 5. The proposed method outperforms the best image-based approach by \\(4.07\\mathrm{dB}\\) in PSNR and the event-based approach by \\(1.09\\mathrm{dB}\\) in PSNR, 0.023 in terms of LPIPS and 0.03 in" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "13910" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.088, + 0.089, + 0.29, + 0.208 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.293, + 0.089, + 0.493, + 0.208 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.495, + 0.089, + 0.698, + 0.208 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.699, + 0.089, + 0.901, + 0.208 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.088, + 0.211, + 0.29, + 0.329 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.135, + 0.333, + 0.242, + 0.347 + ], + "angle": 0, + "content": "Input RS-image" + }, + { + "type": "image", + "bbox": [ + 0.293, + 0.211, + 0.493, + 0.329 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.321, + 0.333, + 0.47, + 0.347 + ], + "angle": 0, + "content": "EvUnroll original [28]" + }, + { + "type": "image", + "bbox": [ + 0.495, + 0.211, + 0.698, + 0.329 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.495, + 0.333, + 0.7, + 0.346 + ], + "angle": 0, + "content": "EvUnroll trained on RS-ERGB" + }, + { + "type": "image", + "bbox": [ + 0.699, + 0.211, + 0.901, + 0.329 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.771, + 0.334, + 0.804, + 0.345 + ], + "angle": 0, + "content": "Ours" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.36, + 0.892, + 0.387 + ], + "angle": 0, + "content": "Figure 10. Qualitative comparison on Real Events and RS images from EvUnroll [28]. Note that no ground truth data is provided for this dataset." + }, + { + "type": "table", + "bbox": [ + 0.079, + 0.412, + 0.47, + 0.556 + ], + "angle": 0, + "content": "
MethodPSNR [dB]↑LPIPS↓SSIM↑
RS-ERGB-Sharp
DSUN [15] (i)22.970.26700.7976
RSCD [27] (i)22.620.27590.7884
EvUnroll [28] (i+e)31.380.23340.8614
EvShutter (Ours) (i+e)32.130.17040.8866
RS-ERGB-Blurry
RSCD [27] (i)17.870.37130.7109
EvUnroll [28] (i+e)31.070.25760.8592
EvShutter (Ours) (i+e)31.550.20460.8780
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.567, + 0.469, + 0.609 + ], + "angle": 0, + "content": "Table 4. RS correction on RS-ERGB dataset with real events. The best method is shown in bold. Image-base methods are marked by (i) and image and event-based methods by \\((\\mathrm{i + e})\\)" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.619, + 0.469, + 0.695 + ], + "angle": 0, + "content": "SSIM. Additionally, some qualitative examples are shown in the Supp. Mat.. Similarly, to the results on the RS-ERGB dataset we observe that our method performs better at object boundaries, where the displacement is not homogeneous. We obtain sharper and less \"wobbly\" results." + }, + { + "type": "table", + "bbox": [ + 0.08, + 0.706, + 0.469, + 0.816 + ], + "angle": 0, + "content": "
MethodPSNR ↑LPIPS↓SSIM↑
DSUN [15] (i)26.520.1220.79
RSCD [27] (i)24.840.1070.78
SUNet [1] (i)28.34-0.84
ESTRNN [26] (i)27.410.1890.84
EvUnroll [28] (i+e)31.320.0840.88
EvShutter (Ours) (i+e)32.410.0610.91
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.827, + 0.469, + 0.869 + ], + "angle": 0, + "content": "Table 5. RS correction on Fastec-RS dataset with synthetic events. The best method is shown in bold. Image-base methods are marked by (i) and image and event-based methods by \\((\\mathrm{i + e})\\)" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.415, + 0.892, + 0.626 + ], + "angle": 0, + "content": "Qualitative comparison on real RS dataset from [28] For qualitative comparison on real data, we evaluated our method on the dataset published in [28], which features real events and real RS images, but no ground truth. In Fig. 10, we compare to the results from EvUnroll [28] trained on their synthetic dataset with synthetic events and their model trained on our RS-ERGB dataset, see Fig. 10. We observe that by training on our RS-ERGB dataset with real events EvUnroll [28] greatly improves their performance. This shows the benefits of the proposed dataset with real events and the novel RS image simulator. Our method performs even better and does not suffer from strong ghosting artifacts as the EvUnroll [28]. Additional examples can be found in Supp. Mat." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.64, + 0.619, + 0.655 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.665, + 0.892, + 0.875 + ], + "angle": 0, + "content": "This paper proposes a method for RS distortion correction and deblurring. The method estimates deblurring operator from event-based optical flow and then compensates RS using a double encoder hourglass network. In contrast to previous methods, it does not rely on a constant velocity assumption and uses a simple architecture thanks to the proposed event transformation. Additionally, we propose the first RS dataset with optional blur containing real events and simulated high-quality RS images and show that training on this dataset increases performance of methods in real case scenarios. We carefully ablate each of the contributions and demonstrate the qualitative and quantitative performance boost compared to previous state-of-the-art methods." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.946, + 0.518, + 0.957 + ], + "angle": 0, + "content": "13911" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.116, + 0.47, + 0.171 + ], + "angle": 0, + "content": "[1] Bin Fan, Yuchao Dai, and Mingyi He. Sunet: symmetric undistortion network for rolling shutter correction. 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In Proceedings of the European Conference on Computer Vision (ECCV) Workshops, pages 0–0, 2018. 3" + }, + { + "type": "list", + "bbox": [ + 0.08, + 0.092, + 0.471, + 0.543 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.946, + 0.519, + 0.957 + ], + "angle": 0, + "content": "13913" + } + ] +] \ No newline at end of file diff --git a/2023/EvShutter_ Transforming Events for Unconstrained Rolling Shutter Correction/65a66f35-8745-4d12-9133-82f4227811f2_origin.pdf b/2023/EvShutter_ Transforming Events for Unconstrained Rolling Shutter Correction/65a66f35-8745-4d12-9133-82f4227811f2_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..fa8081fd8a193f963276ae37d4a5d49030a65b93 --- /dev/null +++ b/2023/EvShutter_ Transforming Events for Unconstrained Rolling Shutter Correction/65a66f35-8745-4d12-9133-82f4227811f2_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:bb7d587cc4fe8675d8c1d5ad4fb76736bb92caaf0ae510e5d9bc002f90425d90 +size 2303758 diff --git a/2023/EvShutter_ Transforming Events for Unconstrained Rolling Shutter Correction/full.md b/2023/EvShutter_ Transforming Events for Unconstrained Rolling Shutter Correction/full.md new file mode 100644 index 0000000000000000000000000000000000000000..b2b81aee5cb760d1f5b28ae0700fd2bd9c765295 --- /dev/null +++ b/2023/EvShutter_ Transforming Events for Unconstrained Rolling Shutter Correction/full.md @@ -0,0 +1,321 @@ +# EvShutter: Transforming Events for Unconstrained Rolling Shutter Correction + +Julius Erbach + +Stepan Tulyakov + +Patricia Vitoria + +Alfredo Bochicchio + +Yuanyou Li + +Huawei Technologies, Zurich Research Center + +![](images/fde9c7a6480e28fe33f54d632956ac3832e6c443b04def3f6f606251e11570fc.jpg) +Rolling Shutter Image + +![](images/d9d0fb8056938f5e6fc6248f4ef8a0a25434bc967c77d61465b3d78910e7a7dc.jpg) +Events + +![](images/bd683f0986e9a9e29278666355e4d63131c1147ef079a81ac68638371770ab9e.jpg) +Rolling Shutter Image + +![](images/d94103058d1b826c6519249bfdbf4239c4f763b17ae23c7af543b8fb394a482a.jpg) +Events + +![](images/9032c25cd9ac525fbeaab607bc9c22906fb8493c7e748dc2402f5760d3edf2c4.jpg) +EvUnroll [28] +Figure 1. Comparison of EvShutter to state-of-the-art event-based RS correction method [28]. Our method introduces a novel event transformation, which allows us to correct RS artifacts in the presence of non-linear motion or large displacements. + +![](images/b2738cd95759a26437c0d04dad23ca6964130c29fee4d5ff8daa28ac7b3c1088.jpg) +EvShutter + +![](images/2d25beea17eb81277f5de824e7bf3bffd36f2dcc253e3abe89829acccb84d07a.jpg) +EvUnroll [28] + +![](images/fe831c2acb3c481e0da625f010d209da1f54cfbf3d29ba0abe16d44447cbcd05.jpg) +EvShutter + +# Abstract + +Widely used Rolling Shutter (RS) CMOS sensors capture high resolution images at the expense of introducing distortions and artifacts in the presence of motion. In such situations, RS distortion correction algorithms are critical. Recent methods rely on a constant velocity assumption and require multiple frames to predict the dense displacement field. In this work, we introduce a new method, called Eventful Shutter (EvShutter), that corrects RS artifacts using a single RGB image and event information with high temporal resolution. The method firstly removes blur using a novel flow-based deblurring module and then compensates RS using a double encoder hourglass network. In contrast to previous methods, it does not rely on a constant velocity assumption and uses a simple architecture thanks to an event transformation dedicated to RS, called Filter and Flip (FnF), that transforms input events to encode only + +the changes between GS and RS images. To evaluate the proposed method and facilitate future research, we collect the first dataset with real events and high-quality RS images with optional blur, called RS-ERGB. We generate the RS images from GS images using a newly proposed simulator based on adaptive interpolation. The simulator permits the use of inexpensive cameras with long exposure to capture high-quality GS images. We show that on this realistic dataset the proposed method outperforms the state-of-the-art image- and event-based methods by 9.16 dB and 0.75 dB respectively in terms of PSNR and an improvement of $23\%$ and $21\%$ in LPIPS. + +# 1. Introduction + +Most consumer cameras like cell phones or action cameras use a rolling shutter (RS) sensor which instead of capturing the whole frame in a single shot as in a global shutter (GS) camera, it acquires each row sequentially as shown in Fig. 2. Specifically, it obtains each row $y$ at time + +![](images/375ae97a0e8d6baeaa4952e1bb2b6233fc1ead868a7aaf773f62e0d65a9baa0f.jpg) +Figure 2. Rolling Shutter Explained. While recording with a RS camera (left), image rows are exposed sequentially, while in the case of a GS camera (right) they are exposed all at the same time. + +![](images/be616edbbe694b75a57965dbdafbe4f211d5af4b1f7af4066f4ab79ec0c6e800.jpg) + +$t_{y} = y \cdot t_{H} / H$ , where $H$ is the height of an image and $t_{H}$ is the mid-exposure time of the last row. RS cameras are often preferred due to their high spatial resolution and high frame rates at low cost. Global shutter sensors have a more complicated circuitry, and therefore a smaller resolution than rolling shutter sensors of the same physical size. A larger sensor size in turn increases the cost of the lens. However, in the presence of fast camera or object movement, RS sensors can produce skew distortion in images (see Fig. 1) and jello artifacts in videos. + +To correct such artifacts, RS correction methods are widely used. Conventional methods attempt to recover the corresponding GS image from the RS output by first estimating the camera motion or dense displacement field during the image acquisition and sequentially applying motion compensation to align all the pixels to a fixed timestamp. However, these methods make strong assumptions on the motion type and are prone to fail in the presence of complex motion patterns like local or non-linear motion, which no longer satisfy the assumptions. + +In this work, we address the fundamental problem of modeling scene changes during image acquisition by using the high temporal information provided by an auxiliary event camera. Instead of measuring synchronous frames of absolute brightness, event cameras only measure asynchronous brightness changes at each pixel with a high temporal resolution in the order of microseconds [3]. Unlike image-based methods, event cameras allow to estimate the motion without relying on a constant speed assumption and synthesizing images by directly adding the brightness changes registered by the events to an image. This enables exciting computational photography applications such as event-guided image deblurring [12, 18, 24], video interpolation [8, 22, 23] and high dynamic range imaging [6, 16]. + +In this paper, we propose a RS compensation method, called Eventful Shutter (EvShutter), that only requires a single RS image and the corresponding events. The method firstly removes blur using a novel flow-based deblurring module and then compensates RS using an hourglass network with two encoders relying on complementary geometric and synthesis-based interpolation approaches. The proposed method is the first method that does not rely on + +constant velocity assumption and uses a simple architecture thanks to the newly introduced event transformation, that we call Filter and Flip (FnF). FnF transforms the input events to encode just changes between GS and RS images. To train and evaluate the proposed method, we collect the first dataset with real events and high quality RS images (optionally with blur), called RS-ERGB. The RS images are generated from GS images using our new simulator based on adaptive interpolation. This pipeline allows the use of an inexpensive high speed camera and the use of long exposures while capturing the GS images. + +# Contributions of this work are as follows + +1. Eventful Shutter (EvShutter): the first event-assisted RS distortion compensation and deblurring method that avoids constant speed motion assumptions. +2. Filter and Flip (FnF): an event transformation module that transforms the input event stream to encode only the brightness change from GS to RS image and simplifies the architecture of downstream modules. +3. Rolling Shutter Events and RGB (RS-ERGB) dataset and simulator: the first dataset with real events and RS images with optional blur generated using a new realistic RS-simulator, based on adaptive interpolation. + +# 2. Related Work + +Previous works on RS correction attempt to recover the GS image by estimating the camera motion or dense displacement field during image acquisition and applying motion compensation to align all the pixels to a fixed timesamp. They can be classified according to their motion estimation method into following categories: gyro-based, single image-based, multiple image-based and event-based. Below we describe each category in detail. + +Gyroscope-based methods [7, 13] utilize a gyro sensor to estimate the rotational motion of the camera. These methods are widely used in mobile devices, due to their speed and reliability. However, they assume a static scene and a simplified rotational camera motion. hence, they can not correct RS distortions due to moving objects (e.g. see Fig. 1), or in the presence of more complex camera motion where the purely rotational assumption is violated. + +Single image-based methods infer the motion from a single RS image by relying on a prior model of the scene. Methods in [14, 19] assume the presence of multiple straight lines in the scenes (Manhattan world assumption) for motion estimation. These hand-crafted priors fail when the scene deviates from the assumed model. Recent methods [21, 31] rely on deep learning to automatically learn scene priors that are used to estimate the camera motion. While these methods are more robust, they are still limited to certain scene types with static scene and constant depth (except [31]). + +Multiple image-based methods estimate the motion be + +tween sequential RS images and use it to approximate the motion during image exposure relying on a parametric motion model. While early methods [2, 5] use image feature matching to estimate a rotational or planar homography, more recent methods [1, 15, 27] compute the dense optical flow between RS images and can correct RS distortion due to object motion. However, they suffer from limitations of image-based motion estimation: they do not work with a single image, image blur and illumination changes. Moreover, they lack the exact information about the motion during exposure and can fail in the presence of large displacements in between frames and highly non-linear motion. + +Event-based method. Recently, [28] developed an event-assisted RS compensation method based on the work of [23]. To ensure that interpolation in a given row is performed from mid-exposure time of that same row to mid-exposure time of the latent GS image their method uses additional conditioning mechanisms and assumptions in the sub-modules, notably constant velocity assumption similar to images-based methods [1, 15, 27]. In contrast, we eliminate the need of additional strong assumptions and conditioning in downstream modules by introducing a simple yet effective event transformation that modifies the input events to encode the transformation from GS to RS image. + +RS Deblur. Besides RS distortion, in presence of fast motion RS images often suffers from blur. In those cases, RS restoration methods needs to simultaneously perform deblur and distortion correction. [27] directly incorporate a deblurring stream in the RS correction network, while [28] adds an optional deblur module before the RS correction. + +Datasets. BS-RSCD [27] dataset is recorded by using a beamsplitter setup with temporally and geometrically synchronized GS and RS cameras. Other datasets, such as Fastec-RS [15] or Gev-RS [28] are collected by first using a high speed GS camera and later synthesizing RS images by sequentially copying rows from the high frame rate GS images. For Gev-RS events are simulated from high speed GS images using V2E [10]. Unfortunately, training with synthetic events often does not generalize well to real event data. Moreover, RS images synthesized by the above method suffer from noise, low contrast and have small resolution, due to very short exposure time in the high speed cameras. We address two of the above problems by capturing a new dataset with real events using GS RGB and event cameras arranged in a beamsplitter setup and introducing new high fidelity simulator that generates high quality RS images with optional blur from GS images. + +# 3. Method + +# 3.1.Eventful Shutter (EvShutter) Network + +At first, we perform event-assisted deblurring of the input RS image $I_{blur}^{rs}$ image using a pre-processing deblurring + +module inspired by [24]. Next, we compensate RS distortion to obtain at a GS estimate at reference time $t_{ref}$ using the pipeline shown in Fig. 3. As shown in the Fig. 3, instead of directly feeding all the raw events $E_{0\rightarrow t_H}$ to the network as in [28], we firstly pre-process them by using the proposed Filter and Flip (FnF) transformation, described in details in Sec. 3.2. Next, we encode the transformed events $E_{gs\rightarrow rs}$ into a voxel grid representation $V_{gs\rightarrow rs}$ as described in [32]. Then we feed the voxel grid and the RS image $I^{rs}$ to an hourglass network composed of a warping encoder and a synthesis encoder using complementary interpolation approaches as in [22, 23]. Lastly, the fusion decoder progressively combines multi-scale images and warping and synthesis features to produce the final GS image $I^{gs}$ . Below we explain the main modules of the proposed method. + +Deblurring. Besides the RS distortion, RS images can suffer from motion blur due to camera or object motion during the exposure time. Therefore, we propose to deblur RS images using events before passing them to our RS distortion compensation method. The overall pipeline of the deblurring is shown in Fig. 4. First, we filter out all events triggered not during the exposure time of the corresponding image rows and then, we shift them according to the row-wise delay, similar to [28]. This allows the use of GS event-based deblurring methods, such as [24]. The original method estimates a deblur operator directly from events using offsets and masks of deformable convolutions [29]. However, we found that it is possible to estimate better deblur operators from more a explicit motion representation, such as optical flow. To estimate flow, we re-use the same network and weights as in the main RS distortion compensation pipeline. + +Warping Encoder. The warping-based encoder takes the voxel grid $V_{gs \to rs}$ and estimates optical flow $\mathcal{F}_{gs \to rs}$ relating the latent GS image to RS image using a flow network from [23]. Note that because the transformed events only encode changes from GS to RS image we can directly estimate optical flow between them without relying on a constant speed assumption. In other words, we can directly estimate row-wise flow, where each row $y$ represents the pixel displacement from time $t_{ref}$ to time $y \cdot t_H / H$ . In contrast in [1, 15, 26, 28], the authors predict optical flow between frames or during the exposure time of the frame using events and approximate the displacement between RS and GS by multiplying with a row dependent coefficient, which is only accurate for linear motions. The estimated flow is used to warp multi-scale features extracted from the RS image $I^{rs}$ using the image encoder resulting in multi-scale warping interpolation features $\mathbf{F}_{\rightarrow \mathrm{gs}}^{\mathbf{w}} = (F_{\rightarrow gs}^{w(0)}, F_{\rightarrow gs}^{w(1)}, F_{\rightarrow gs}^{w(2)})$ . Similarly, a multi-scale image pyramid computed from the RS image is warped to get $\mathbf{I}_{\rightarrow \mathrm{gs}}^{\mathrm{rs}} = (I_{\rightarrow gs}^{rs(0)}, I_{\rightarrow gs}^{rs(1)}, I_{\rightarrow gs}^{rs(2)})$ . The warping is performed by using + +![](images/a59f8edf354aa5e0e9886c53267995101c63b28ee386af5abd26c6e6f3b01bc4.jpg) +Figure 3. RS distortion compensation pipeline. At first the proposed method pre-processes input events with $FnF$ transformation to encode only the brightness change between GS and RS frames. The transformed events are then passed to double encoder hourglass network with complementary warping and synthesis encoders relying on different interpolation principles. Then multi-scale features and images from both encoders are fused in the decoder to produce a GS image. The first fusion block of the decoder is shown in detail. + +![](images/61c7432c3c7f537fe4be7efc37e2c5027ed95afa2daf142f28ce6d4346e09c6c.jpg) +Figure 4. RS deblurring pipeline. First we filter out all the events which are not triggered during the exposure time, then we deblur the RS image using an improved version of [24], that relies on optical flow estimation to predict deblur kernels. + +differentiable backward interpolation. To downscale images and optical flow we perform average pooling and in case of flow we additionally divide the flow by the downscale factor. + +Synthesis-based Encoder. The synthesis-based encoder takes both voxel grid $V_{gs \to rs}$ and RS image $I^{rs}$ as inputs and computes multi-scale synthesis interpolation features $\mathbf{F}^s$ . Intuitively, this encoder integrates brightness changes from the event stream and adds them to the RS image. Notice that, in contrast to the warping encoder, this module can handle illumination changes and fill motion occlusions. + +Fusion Decoder: The fusion decoder progressively combines synthesis $\mathbf{F}^s$ and warping-based $\mathbf{F}_{\rightarrow gs}^{w}$ features, orig- + +![](images/6e1ac7f3966be9de00c1414819b30c66389a742a83c1e4ba767da61231dcf9be.jpg) +Figure 5. Event transformation workflow. Top row: Event stream is transformed by first applying and event filtering followed by a flipping step around an arbitrary reference time. Bottom row: An example of events. Right: Animation (best viewed with Acrobot Reader) between RS-input and GS estimations at different reference times. + +inal RS image $I^{rs}$ and warped RS image $I_{\rightarrow gs}^{rs}$ on multiple scales to reconstruct the GS image $I^{gs}$ . We use shortcut connections from the original RS image to help the decoder to reconstruct static parts of the image. To select the most informative features on each scale the decoder relies on Squeeze-and-excitation (SE) blocks [9] attenuating channels, and modulated deformable convolutions [29], attenuating the feature maps spatially. + +# 3.2. Filter and Flip (FnF) Transformation + +The auxiliary event camera records an event stream $E_{0 \to t_H}$ encoding all brightness changes from time 0 to $t_H$ . However, to recover the GS image $I^{gs}$ corresponding to a given RS image $I^{rs}$ , we are only interested on those events $E_{gs \to rs}$ encoding brightness changes between latent GS and observed RS image. In this work, we propose a well-suited RS event transformation called Filter and Flip (FnF), which transforms the event stream $E_{0 \to t_H}$ to $E_{gs \to rs}$ through two steps: filtering and flipping steps as shown in Fig. 5 and described below. + +Filtering step. For each row $y$ , we only keep those events triggered between time $t_y$ and the reference time $t_{ref}$ , where $t_y$ is mid-exposure time of row $y$ in observed RS image. + +Flipping step. We reverse all events before the reference time $t_{ref}$ by inverting their polarities and recomputing their timestamps such that they are flipped around $t_{ref}$ as shown in Fig. 5. This process ensures that the events encode changes in the direction from GS-frame to RS-frame and that the transformed events start at the time, which matches the GS-frame and end at the RS-time. + +Applying the event transformation eliminates the need in time conditioning mechanisms and additional assumptions in the downstream modules. For example, in contrast to [28], the proposed method does not require constant speed assumption in the flow estimation module and attention mechanisms in the synthesis-based encoder, which allows re-using already pretrained modules on widely used GS images. Also, notice, that the FnF transformation can be adapted to arbitrary reference times. + +In order to allow a good comparison to other works, we set $t_{ref} = t_H / 2$ , which corresponds to the mid-exposure time of the central row. + +# 3.3. RS-ERGB Dataset + +To bridge the sim-to-real gap from synthetic to real events we build a hybrid imaging system of a high speed GS RGB-camera and an event camera in a beam splitter setup. We use hardware temporal synchronization and geometrically align events and images as described in the Supp. Mat. With this setup we capture the first RS dataset with real events and high quality images. We generate high quality RS images with optional blur using our novel simulator based on adaptive interpolation described below. + +High quality RS simulator. Our proposed pipeline allows to record GS sequences at lower speed than previous methods (160 fps compared to [15, 28] that record GS sequence at 2400 or 5700 fps). This allows us to use a longer exposure and as a result, acquire images of higher quality. Then we adaptively interpolate captured images using Super Slomo [11], so that the maximum displacement between interpolated frames is at most 1 pixel similar to + +![](images/06b51f2e5d82233a6b853affd0784b0ad0bc23bf1951f36e342bdcb95eaa6448.jpg) +Figure 6. Synthetic RS-images from a sequence of GS-Images $I_{i}$ . Each row is constructed separately by computing the weighted average of the GS-frames, which are assumed to be a close approximation of the latent GS-frames. + +Vid2E [4]. This procedure ensures that a sufficient temporal resolution is achieved to synthesize realistic blur and RS effect. As shown in Fig. 7, using a fixed interpolation factor can give unrealistic results as the amount of motion can differ significantly by region and scene. The resulting interpolated video sequence can be thought of as discrete approximation of latent GS-images $I_{i}$ of the true latent frames $I_{\text{latent}}(t,x,y)$ . To synthesize a row $y_{rs}$ of a RS-image the integral of $I_{\text{latent}}(t,x,y = y_{rs})$ has to be computed over the exposure time for this row, as + +$$ +I _ {r s} \left(t _ {\text {s t a r t}}, t _ {\text {e n d}}, y _ {i}\right) = \frac {1}{t _ {\text {e n d}} - t _ {\text {s t a r t}}} \int_ {t _ {\text {s t a r t}}} ^ {t _ {\text {e n d}}} I _ {\text {l a t e n t}} (t, y _ {i}) d t. \tag {1} +$$ + +We use a discrete approximation instead and compute a weighted average of the approximated latent frames $I_{i}$ as shown in Fig. 6. Using this procedure a synthetic exposure time and readout time $T$ are chosen to synthesize corresponding RS frames. Notice that exposure time and readout time can be set separately allowing us to create blurry RS images with sharp RS ground truth for the task of RS deblurring. Video interpolation has already been used in the past to generate more realistic blur from videos [17], but to the best of our knowledge, we are the first to use an adaptive upsampling scheme to get consistently realistic results. Examples of our dataset with different amounts of blur and a comparison to a version without adaptive interpolation can be seen in the Supp. Mat.. + +Comparison to Gev-RS [28] is shown in Tab. 1. Compared to Gev-RS, our dataset has real events and the RS and GS image have better quality and resolution, despite using a lower end camera ${}^{2}$ ,since our new synthesis procedure allows using lower frame rate with longer exposure. + +# 4. Experiments + +In this section, first, we ablate the key contributions of the proposed EvShutter method. Second, we benchmark + +![](images/4f1097efdd78c67a4e4a23129c10ad156c80d02369f96b499c5101ff0b6c4c47.jpg) +Figure 7. Benefit of the proposed RS simulator In contrast to a simulator with fixed interpolation rate, the proposed simulator with an adaptive interpolation does not suffer from aliasing artifacts regardless of the motion speed. + +
RS-ERGB (ours)Gev-RS [28]
Event datareal (Prophesee Gen4M)synthetic
GS camera160 fps5.7k fps
Blackfly SPhantom VEO 640
№ sequence3429
Image qualityhighlow
Resolution970×625640×360
+ +the EvShutter against state-of-the-art image-based [15,27] and event-based [28] methods on our RS-ERGB dataset, as well as on the public Fastec-RS dataset [15]. + +Details of the objective loss, training procedure and runtime comparisons together with ablation on additional design choices can be found in the Supp. Mat. + +# 4.1. Ablation Study + +FnF event transformation. To evaluate the proposed FnF transformation Tab. 2 we dissect our pipeline in purely warping-based, purely synthesis-based and the full pipeline. + +We compare the purely warping-based method to a version that relies on a constant velocity assumption similar to EvUnroll [28] by applying a row-wise scaling to the optical flow computed from $t_{GS}$ to $t_0$ and from $t_{GS}$ to $t_H$ . Our FnF transformation improves the warping-based method by 0.77 dB in PSNR and 0.0104 in LPIPS [25]. + +We also test the purely synthesis based module with and without the FnF transformation. As shown in Tab. 2 the synthesis module with the transformation outperforms the version without by $3.92\mathrm{dB}$ in PSNR and 0.0376 in LPIPS. + +The overall architecture also benefits from the FnF transformation by 2.61 dB in PSNR and 0.0203 in LPIPS. + +Importance of optical flow in RS deblur module. We show benefits of estimating the deblur operator from optical flow instead of raw events in Tab. 3. By introducing the optical flow explicitly to the deblurring network we observe + +Table 1. Details of our RS-ERGB compared to Gev-RS [28]. Best-suited properties are shown in bold. + +
MethodPSNR↑LPIPS↓SSIM↑
Warping
Linearized flow28.390.17210.870
FnF-Transform29.160.16170.883
Synthesis
w/o FnF-Transform25.870.22330.807
FnF-Transform29.790.18570.867
Warping & Synthesis
Linearized flow28.970.17030.870
FnF-Transform31.580.15000.897
+ +an improvement of $1.4\mathrm{dB}$ in PSNR without effectively increasing the capacity, since we reuse the optical flow module from the RS correction pipeline. Furthermore, we visualized the offsets and masks of the deformable kernels in Fig. 9 and observed that in the case of large motions the kernels did not follow the motion in the original implementation of [24], but with our flow based adaption the deformable kernel is well aligned with the motion. For the sake of completeness we also add the results for deblurring of the EvUnroll [28] deblur module finetuned on our data. + +Table 2. Importance of FnF event transformation. The transformation improves performance of synthesis encoder and warping encoder. In the warping encoder it allows to avoid constant speed motion assumption. Ablation is made on the RS-ERGB validation set and best method is shown in bold. + +
MethodPSNR↑LPIPS↓SSIM↑
EDDMA [24]34.920.05880.936
EDDMA [24]+Flow36.320.04880.951
EvUnroll + Deblur [28]35.640.04990.934
+ +Table 3. Importance of optical flow in RS deblur module. For this experiment we generate RS images with 50ms exposure and compare RS-Deblurring results without RS correction. Best method is shown in bold. We also show performance of EvUnroll deblur module for reference. + +# 4.2. Comparison with SOTA methods + +RS-ERGB dataset. We compare our method to the state-of-the-art image-based methods DSUN [15], RSCD [27] and the recent event-based EvUnroll [28] on RS-ERGB-Sharp dataset without blur and RSCD [27] and EvUnroll [28] on the RS-ERGB-Blurry dataset with blur. All methods were finetuned on our datasets. For more details please refer to the Supp. Mat. The results are reported in Tab. 4 and qualitative comparisons are shown in Fig. 8. On the RS-ERGB dataset, we outperform the best image-based method DSUN [15] by 9.16 dB in terms of PSNR and 0.0966 in LPIPS and the event-based method EvUnroll [28] by 0.75 dB in PSNR and 0.0966 in LPIPS. On the RS-ERGB-Blurry dataset, we outperform EvUnroll [28] by 0.48 dB in PSNR and 0.053 in LPIPS. The image based + +![](images/970e0194a189a82c909cec4d774aab631f4d178e19bbc304281d9a3855c792ea.jpg) + +![](images/68eb3c3cfaf1eab4ddf16b7bacd60cbba7783fb78f6359295fd8c81c3e0d2527.jpg) + +![](images/2106ce3ccbfcbe184bb5ad94f36eed187001d24d2d266b7787841e2a3c2a23f5.jpg) +RS-ERGB-Sharp + +![](images/29f633ae1f5536178f6fe54de6fc52857a3dff8ab13d2cb594cc72640e4117e4.jpg) + +![](images/65c25a7b0f114d0128cdd723084b49d4f6399df80632a08f04da863ae7614cb0.jpg) + +![](images/2f65dca1ae397b497e11e4784a8d774698d1e63d7a687fb0d3f91186b5e2bb49.jpg) + +![](images/7055d5ff2563883574ed78ca0c9a22e799d1eb2aac3069011844d9051c65b79c.jpg) + +![](images/2e7d47b3051d533c1efb032dc60cb02bcf6b0be1acb67d3a24e01241be17ef6d.jpg) + +![](images/f5c1a80a2d5ee186098ea3c041ed42725b3a18aa9342edd1ca7024dde97f1e71.jpg) + +![](images/d46dbbaf6a4f28c2a189973e7d0c13fbbc5797da30f628375ddb54b8c8511ed5.jpg) + +![](images/f2e1f792d12ce081d6043639dda0f48352fe0c3eb5c04461b5844eb9fb02388d.jpg) + +![](images/d7c9066d790a7b534181d29b1e8a6511fd12afb27ea9c5aef17d98653debbae5.jpg) + +![](images/733481a8c27dd4a5a6c41afa872949181e6740fcdf5f82c73f85c80469fbda55.jpg) +RS-ERGB-Blurry + +![](images/d2ebb2cc8f4a13fddb71e1cf224bad1456b224d70b1a853653275103cd18b278.jpg) + +![](images/78a55870cdd8ae7b0988798b8c005b008cc35c6f07c43a988662def1235893d6.jpg) + +![](images/74cbabb627089f03b9dca46173450377649a4231278460fd310cf3c1cc245813.jpg) +Input RS-image + +![](images/45a523cf3270beeb0023d0a6d3d401d706041443bd28ab5602dfb183ecce8125.jpg) +DSUN [15] (i) + +![](images/0e9137a7c24300925e397ed0a8904dfa6006e795675e3ff771c5d65adfdb75ab.jpg) +EvUnroll [28] (i+e) + +![](images/bbfe492e6cfc5b07b2e55eae3afe5e2621466ecfc03aea0e5c95a3ea617e8379.jpg) +EvShutter (Ours) $(\mathrm{i} + \mathrm{e})$ + +![](images/d9a8e8b67a376724c3df8a458c0cc823b0b96af6332a3a85c6e20a65eaa5f6b9.jpg) +Ground truth + +![](images/5f118937660988ec5b12d6a953897b3e2eb1d693044206dc6a82ec5d602f7519.jpg) +Figure 8. Quantitative results on RS-ERGB-Sharp and ER-ERGB-Blurry datasets. Image-based methods are marked by (i) and event and image based methods are marked by $(\mathrm{i + e})$ . The best method is shown in bold. +Figure 9. Visualization of deformable convolutions offsets in deblurring module for the original method [24](left), and our method (right), where offset are computed from optical flow. + +![](images/6e3a24295e703785aad2877caa27e3dd17cb092c37612f58348327854048e1a3.jpg) + +method RSCD [27] seems not able to handle the difficult combination of large RS distortion and blur. Our method improves current image-based SOTA methods especially in areas with large displacements between RS and GS-frame. DSUN [15] is able to reconstruct the overall shape of the object, but produces strong artifacts. EvUnroll [28] is able to + +recover the structure of the GS images very well, but seems to heavily rely on their synthesis branch in areas with large non linear motion. We hypothesize that the fusion in RGB space makes it more difficult to combine the fine detail and texture from the warping branch with the coarse structurally correct results from the synthesis branch, which often lack precise colors. Additional comparisons can be found in the Supp. Mat.. + +Fastec-RS dataset To compare the proposed method to other SOTA on the public Fastec-RS dataset [15] we synthesized events from the original high speed sequences shared by the authors using ESIM [20] with the same parameters as in [28] and re-train our method from scratch. We run JCD [27] and DSUN [15] using the publicly available checkpoints. For [26, 30], we extract the metrics from the JCD paper [27] and for EvUnroll [28] and SUNet [1] from their respective papers. The results are reported in Tab. 5. The proposed method outperforms the best image-based approach by $4.07\mathrm{dB}$ in PSNR and the event-based approach by $1.09\mathrm{dB}$ in PSNR, 0.023 in terms of LPIPS and 0.03 in + +![](images/19e1a3f8d098ec708dcbf40ea1e5d68ac33daa823e7a5a03c53d1c51251a1e3a.jpg) + +![](images/2de3b47b211a417cad147e88fde520a9f8d5371821777f169ddcdb18b2d8f168.jpg) + +![](images/2bba678d3699ef4c589f6022ae989fbcf26269d3bf9e3eb064c0b6ace8287457.jpg) + +![](images/e65885285938758351dfe3a8ab9f289f2c94c78418f82070a951f5aa4bad16dd.jpg) + +![](images/010cd0b8b4d1efdf009b3fd94926873a5c64e3cc647f17e0be3c988681112bdf.jpg) +Input RS-image + +![](images/189794c3318147ef2ad5227ac5a18c3c0946fcfab05595d7c6dfcfd12d5421a5.jpg) +EvUnroll original [28] + +![](images/49787c3836d5c0c72d7ce4e1e34de6425e5d7dcfd55cc73853f6e0a3740b90d6.jpg) +Figure 10. Qualitative comparison on Real Events and RS images from EvUnroll [28]. Note that no ground truth data is provided for this dataset. + +![](images/6177c7cf3a5a852b4107152faf811c296f5ff4fbe8189d61773d8733c335a550.jpg) +EvUnroll trained on RS-ERGB +Ours + +
MethodPSNR [dB]↑LPIPS↓SSIM↑
RS-ERGB-Sharp
DSUN [15] (i)22.970.26700.7976
RSCD [27] (i)22.620.27590.7884
EvUnroll [28] (i+e)31.380.23340.8614
EvShutter (Ours) (i+e)32.130.17040.8866
RS-ERGB-Blurry
RSCD [27] (i)17.870.37130.7109
EvUnroll [28] (i+e)31.070.25760.8592
EvShutter (Ours) (i+e)31.550.20460.8780
+ +SSIM. Additionally, some qualitative examples are shown in the Supp. Mat.. Similarly, to the results on the RS-ERGB dataset we observe that our method performs better at object boundaries, where the displacement is not homogeneous. We obtain sharper and less "wobbly" results. + +Table 4. RS correction on RS-ERGB dataset with real events. The best method is shown in bold. Image-base methods are marked by (i) and image and event-based methods by $(\mathrm{i + e})$ + +
MethodPSNR ↑LPIPS↓SSIM↑
DSUN [15] (i)26.520.1220.79
RSCD [27] (i)24.840.1070.78
SUNet [1] (i)28.34-0.84
ESTRNN [26] (i)27.410.1890.84
EvUnroll [28] (i+e)31.320.0840.88
EvShutter (Ours) (i+e)32.410.0610.91
+ +Table 5. RS correction on Fastec-RS dataset with synthetic events. The best method is shown in bold. Image-base methods are marked by (i) and image and event-based methods by $(\mathrm{i + e})$ + +Qualitative comparison on real RS dataset from [28] For qualitative comparison on real data, we evaluated our method on the dataset published in [28], which features real events and real RS images, but no ground truth. In Fig. 10, we compare to the results from EvUnroll [28] trained on their synthetic dataset with synthetic events and their model trained on our RS-ERGB dataset, see Fig. 10. We observe that by training on our RS-ERGB dataset with real events EvUnroll [28] greatly improves their performance. This shows the benefits of the proposed dataset with real events and the novel RS image simulator. Our method performs even better and does not suffer from strong ghosting artifacts as the EvUnroll [28]. Additional examples can be found in Supp. Mat. + +# 5. Conclusion + +This paper proposes a method for RS distortion correction and deblurring. The method estimates deblurring operator from event-based optical flow and then compensates RS using a double encoder hourglass network. In contrast to previous methods, it does not rely on a constant velocity assumption and uses a simple architecture thanks to the proposed event transformation. Additionally, we propose the first RS dataset with optional blur containing real events and simulated high-quality RS images and show that training on this dataset increases performance of methods in real case scenarios. We carefully ablate each of the contributions and demonstrate the qualitative and quantitative performance boost compared to previous state-of-the-art methods. + +# References + +[1] Bin Fan, Yuchao Dai, and Mingyi He. Sunet: symmetric undistortion network for rolling shutter correction. 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Comparison of EvShutter to state-of-the-art event-based RS correction method [28]. Our method introduces a novel event transformation, which allows us to correct RS artifacts in the presence of non-linear motion or large displacements." + } + ] + } + ], + "index": 25, + "angle": 0, + "type": "image_caption" + } + ], + "index": 17 + }, + { + "type": "image", + "bbox": [ + 142, + 313, + 233, + 408 + ], + "blocks": [ + { + "bbox": [ + 142, + 313, + 233, + 408 + ], + "lines": [ + { + "bbox": [ + 142, + 313, + 233, + 408 + ], + "spans": [ + { + "bbox": [ + 142, + 313, + 233, + 408 + ], + "type": "image", + "image_path": "b2738cd95759a26437c0d04dad23ca6964130c29fee4d5ff8daa28ac7b3c1088.jpg" + } + ] + } + ], + "index": 19, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 164, + 410, + 203, + 420 + ], + "lines": [ + { + "bbox": [ + 164, + 410, + 203, + 420 + ], + "spans": [ + { + "bbox": [ + 164, + 410, + 203, + 420 + ], + "type": "text", + "content": "EvShutter" + } + ] + } + ], + "index": 20, + "angle": 0, + "type": "image_caption" + } + ], + "index": 19 + }, + { + "type": "image", + "bbox": [ + 236, + 312, + 390, + 408 + ], + "blocks": [ + { + "bbox": [ + 236, + 312, + 390, + 408 + ], + "lines": [ + { + "bbox": [ + 236, + 312, + 390, + 408 + ], + "spans": [ + { + "bbox": [ + 236, + 312, + 390, + 408 + ], + "type": "image", + "image_path": "2d25beea17eb81277f5de824e7bf3bffd36f2dcc253e3abe89829acccb84d07a.jpg" + } + ] + } + ], + "index": 21, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 285, + 410, + 339, + 421 + ], + "lines": [ + { + "bbox": [ + 285, + 410, + 339, + 421 + ], + "spans": [ + { + "bbox": [ + 285, + 410, + 339, + 421 + ], + "type": "text", + "content": "EvUnroll [28]" + } + ] + } + ], + "index": 22, + "angle": 0, + "type": "image_caption" + } + ], + "index": 21 + }, + { + "type": "image", + "bbox": [ + 391, + 312, + 545, + 408 + ], + "blocks": [ + { + "bbox": [ + 391, + 312, + 545, + 408 + ], + "lines": [ + { + "bbox": [ + 391, + 312, + 545, + 408 + ], + "spans": [ + { + "bbox": [ + 391, + 312, + 545, + 408 + ], + "type": "image", + "image_path": "fe831c2acb3c481e0da625f010d209da1f54cfbf3d29ba0abe16d44447cbcd05.jpg" + } + ] + } + ], + "index": 23, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 444, + 410, + 483, + 419 + ], + "lines": [ + { + "bbox": [ + 444, + 410, + 483, + 419 + ], + "spans": [ + { + "bbox": [ + 444, + 410, + 483, + 419 + ], + "type": "text", + "content": "EvShutter" + } + ] + } + ], + "index": 24, + "angle": 0, + "type": "image_caption" + } + ], + "index": 23 + }, + { + "bbox": [ + 143, + 462, + 192, + 474 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 462, + 192, + 474 + ], + "spans": [ + { + "bbox": [ + 143, + 462, + 192, + 474 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 26 + }, + { + "bbox": [ + 45, + 488, + 288, + 681 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 488, + 288, + 681 + ], + "spans": [ + { + "bbox": [ + 45, + 488, + 288, + 681 + ], + "type": "text", + "content": "Widely used Rolling Shutter (RS) CMOS sensors capture high resolution images at the expense of introducing distortions and artifacts in the presence of motion. In such situations, RS distortion correction algorithms are critical. Recent methods rely on a constant velocity assumption and require multiple frames to predict the dense displacement field. In this work, we introduce a new method, called Eventful Shutter (EvShutter), that corrects RS artifacts using a single RGB image and event information with high temporal resolution. The method firstly removes blur using a novel flow-based deblurring module and then compensates RS using a double encoder hourglass network. In contrast to previous methods, it does not rely on a constant velocity assumption and uses a simple architecture thanks to an event transformation dedicated to RS, called Filter and Flip (FnF), that transforms input events to encode only" + } + ] + } + ], + "index": 27 + }, + { + "bbox": [ + 306, + 463, + 547, + 606 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 463, + 547, + 606 + ], + "spans": [ + { + "bbox": [ + 306, + 463, + 547, + 606 + ], + "type": "text", + "content": "the changes between GS and RS images. To evaluate the proposed method and facilitate future research, we collect the first dataset with real events and high-quality RS images with optional blur, called RS-ERGB. We generate the RS images from GS images using a newly proposed simulator based on adaptive interpolation. The simulator permits the use of inexpensive cameras with long exposure to capture high-quality GS images. We show that on this realistic dataset the proposed method outperforms the state-of-the-art image- and event-based methods by 9.16 dB and 0.75 dB respectively in terms of PSNR and an improvement of " + }, + { + "bbox": [ + 306, + 463, + 547, + 606 + ], + "type": "inline_equation", + "content": "23\\%" + }, + { + "bbox": [ + 306, + 463, + 547, + 606 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 306, + 463, + 547, + 606 + ], + "type": "inline_equation", + "content": "21\\%" + }, + { + "bbox": [ + 306, + 463, + 547, + 606 + ], + "type": "text", + "content": " in LPIPS." + } + ] + } + ], + "index": 28 + }, + { + "bbox": [ + 306, + 632, + 386, + 644 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 632, + 386, + 644 + ], + "spans": [ + { + "bbox": [ + 306, + 632, + 386, + 644 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 29 + }, + { + "bbox": [ + 305, + 654, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 654, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 654, + 547, + 713 + ], + "type": "text", + "content": "Most consumer cameras like cell phones or action cameras use a rolling shutter (RS) sensor which instead of capturing the whole frame in a single shot as in a global shutter (GS) camera, it acquires each row sequentially as shown in Fig. 2. Specifically, it obtains each row " + }, + { + "bbox": [ + 305, + 654, + 547, + 713 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 305, + 654, + 547, + 713 + ], + "type": "text", + "content": " at time" + } + ] + } + ], + "index": 30 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 145, + 0, + 496, + 35 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 0, + 496, + 35 + ], + "spans": [ + { + "bbox": [ + 145, + 0, + 496, + 35 + ], + "type": "text", + "content": "This CVPR paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 693, + 286, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 693, + 286, + 712 + ], + "spans": [ + { + "bbox": [ + 47, + 693, + 286, + 712 + ], + "type": "text", + "content": "The evaluation code and the dataset can be found here https://github.com/juliuserbach/EvShutter" + } + ] + } + ], + "index": 31 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "13904" + } + ] + } + ], + "index": 32 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 58, + 69, + 182, + 159 + ], + "blocks": [ + { + "bbox": [ + 58, + 69, + 182, + 159 + ], + "lines": [ + { + "bbox": [ + 58, + 69, + 182, + 159 + ], + "spans": [ + { + "bbox": [ + 58, + 69, + 182, + 159 + ], + "type": "image", + "image_path": "375ae97a0e8d6baeaa4952e1bb2b6233fc1ead868a7aaf773f62e0d65a9baa0f.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 167, + 287, + 200 + ], + "lines": [ + { + "bbox": [ + 46, + 167, + 287, + 200 + ], + "spans": [ + { + "bbox": [ + 46, + 167, + 287, + 200 + ], + "type": "text", + "content": "Figure 2. Rolling Shutter Explained. While recording with a RS camera (left), image rows are exposed sequentially, while in the case of a GS camera (right) they are exposed all at the same time." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 194, + 69, + 277, + 159 + ], + "blocks": [ + { + "bbox": [ + 194, + 69, + 277, + 159 + ], + "lines": [ + { + "bbox": [ + 194, + 69, + 277, + 159 + ], + "spans": [ + { + "bbox": [ + 194, + 69, + 277, + 159 + ], + "type": "image", + "image_path": "be616edbbe694b75a57965dbdafbe4f211d5af4b1f7af4066f4ab79ec0c6e800.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 208, + 286, + 327 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 208, + 286, + 327 + ], + "spans": [ + { + "bbox": [ + 46, + 208, + 286, + 327 + ], + "type": "inline_equation", + "content": "t_{y} = y \\cdot t_{H} / H" + }, + { + "bbox": [ + 46, + 208, + 286, + 327 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 208, + 286, + 327 + ], + "type": "inline_equation", + "content": "H" + }, + { + "bbox": [ + 46, + 208, + 286, + 327 + ], + "type": "text", + "content": " is the height of an image and " + }, + { + "bbox": [ + 46, + 208, + 286, + 327 + ], + "type": "inline_equation", + "content": "t_{H}" + }, + { + "bbox": [ + 46, + 208, + 286, + 327 + ], + "type": "text", + "content": " is the mid-exposure time of the last row. RS cameras are often preferred due to their high spatial resolution and high frame rates at low cost. Global shutter sensors have a more complicated circuitry, and therefore a smaller resolution than rolling shutter sensors of the same physical size. A larger sensor size in turn increases the cost of the lens. However, in the presence of fast camera or object movement, RS sensors can produce skew distortion in images (see Fig. 1) and jello artifacts in videos." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 328, + 286, + 448 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 328, + 286, + 448 + ], + "spans": [ + { + "bbox": [ + 46, + 328, + 286, + 448 + ], + "type": "text", + "content": "To correct such artifacts, RS correction methods are widely used. Conventional methods attempt to recover the corresponding GS image from the RS output by first estimating the camera motion or dense displacement field during the image acquisition and sequentially applying motion compensation to align all the pixels to a fixed timestamp. However, these methods make strong assumptions on the motion type and are prone to fail in the presence of complex motion patterns like local or non-linear motion, which no longer satisfy the assumptions." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 449, + 286, + 617 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 449, + 286, + 617 + ], + "spans": [ + { + "bbox": [ + 46, + 449, + 286, + 617 + ], + "type": "text", + "content": "In this work, we address the fundamental problem of modeling scene changes during image acquisition by using the high temporal information provided by an auxiliary event camera. Instead of measuring synchronous frames of absolute brightness, event cameras only measure asynchronous brightness changes at each pixel with a high temporal resolution in the order of microseconds [3]. Unlike image-based methods, event cameras allow to estimate the motion without relying on a constant speed assumption and synthesizing images by directly adding the brightness changes registered by the events to an image. This enables exciting computational photography applications such as event-guided image deblurring [12, 18, 24], video interpolation [8, 22, 23] and high dynamic range imaging [6, 16]." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 618, + 286, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 618, + 286, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 618, + 286, + 714 + ], + "type": "text", + "content": "In this paper, we propose a RS compensation method, called Eventful Shutter (EvShutter), that only requires a single RS image and the corresponding events. The method firstly removes blur using a novel flow-based deblurring module and then compensates RS using an hourglass network with two encoders relying on complementary geometric and synthesis-based interpolation approaches. The proposed method is the first method that does not rely on" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 72, + 545, + 204 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 204 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 204 + ], + "type": "text", + "content": "constant velocity assumption and uses a simple architecture thanks to the newly introduced event transformation, that we call Filter and Flip (FnF). FnF transforms the input events to encode just changes between GS and RS images. To train and evaluate the proposed method, we collect the first dataset with real events and high quality RS images (optionally with blur), called RS-ERGB. The RS images are generated from GS images using our new simulator based on adaptive interpolation. This pipeline allows the use of an inexpensive high speed camera and the use of long exposures while capturing the GS images." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 317, + 204, + 489, + 214 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 204, + 489, + 214 + ], + "spans": [ + { + "bbox": [ + 317, + 204, + 489, + 214 + ], + "type": "text", + "content": "Contributions of this work are as follows" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 313, + 216, + 545, + 347 + ], + "type": "list", + "angle": 0, + "index": 12, + "blocks": [ + { + "bbox": [ + 313, + 216, + 545, + 251 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 313, + 216, + 545, + 251 + ], + "spans": [ + { + "bbox": [ + 313, + 216, + 545, + 251 + ], + "type": "text", + "content": "1. Eventful Shutter (EvShutter): the first event-assisted RS distortion compensation and deblurring method that avoids constant speed motion assumptions." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 313, + 251, + 545, + 298 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 313, + 251, + 545, + 298 + ], + "spans": [ + { + "bbox": [ + 313, + 251, + 545, + 298 + ], + "type": "text", + "content": "2. Filter and Flip (FnF): an event transformation module that transforms the input event stream to encode only the brightness change from GS to RS image and simplifies the architecture of downstream modules." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 313, + 300, + 545, + 347 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 313, + 300, + 545, + 347 + ], + "spans": [ + { + "bbox": [ + 313, + 300, + 545, + 347 + ], + "type": "text", + "content": "3. Rolling Shutter Events and RGB (RS-ERGB) dataset and simulator: the first dataset with real events and RS images with optional blur generated using a new realistic RS-simulator, based on adaptive interpolation." + } + ] + } + ], + "index": 11 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 306, + 358, + 392, + 371 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 358, + 392, + 371 + ], + "spans": [ + { + "bbox": [ + 306, + 358, + 392, + 371 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 378, + 545, + 474 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 378, + 545, + 474 + ], + "spans": [ + { + "bbox": [ + 304, + 378, + 545, + 474 + ], + "type": "text", + "content": "Previous works on RS correction attempt to recover the GS image by estimating the camera motion or dense displacement field during image acquisition and applying motion compensation to align all the pixels to a fixed timesamp. They can be classified according to their motion estimation method into following categories: gyro-based, single image-based, multiple image-based and event-based. Below we describe each category in detail." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 474, + 545, + 569 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 474, + 545, + 569 + ], + "spans": [ + { + "bbox": [ + 304, + 474, + 545, + 569 + ], + "type": "text", + "content": "Gyroscope-based methods [7, 13] utilize a gyro sensor to estimate the rotational motion of the camera. These methods are widely used in mobile devices, due to their speed and reliability. However, they assume a static scene and a simplified rotational camera motion. hence, they can not correct RS distortions due to moving objects (e.g. see Fig. 1), or in the presence of more complex camera motion where the purely rotational assumption is violated." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 570, + 545, + 700 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 545, + 700 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 545, + 700 + ], + "type": "text", + "content": "Single image-based methods infer the motion from a single RS image by relying on a prior model of the scene. Methods in [14, 19] assume the presence of multiple straight lines in the scenes (Manhattan world assumption) for motion estimation. These hand-crafted priors fail when the scene deviates from the assumed model. Recent methods [21, 31] rely on deep learning to automatically learn scene priors that are used to estimate the camera motion. While these methods are more robust, they are still limited to certain scene types with static scene and constant depth (except [31])." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 317, + 701, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 701, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 317, + 701, + 545, + 713 + ], + "type": "text", + "content": "Multiple image-based methods estimate the motion be" + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "13905" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 215 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 215 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 215 + ], + "type": "text", + "content": "tween sequential RS images and use it to approximate the motion during image exposure relying on a parametric motion model. While early methods [2, 5] use image feature matching to estimate a rotational or planar homography, more recent methods [1, 15, 27] compute the dense optical flow between RS images and can correct RS distortion due to object motion. However, they suffer from limitations of image-based motion estimation: they do not work with a single image, image blur and illumination changes. Moreover, they lack the exact information about the motion during exposure and can fail in the presence of large displacements in between frames and highly non-linear motion." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 216, + 289, + 357 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 216, + 289, + 357 + ], + "spans": [ + { + "bbox": [ + 46, + 216, + 289, + 357 + ], + "type": "text", + "content": "Event-based method. Recently, [28] developed an event-assisted RS compensation method based on the work of [23]. To ensure that interpolation in a given row is performed from mid-exposure time of that same row to mid-exposure time of the latent GS image their method uses additional conditioning mechanisms and assumptions in the sub-modules, notably constant velocity assumption similar to images-based methods [1, 15, 27]. In contrast, we eliminate the need of additional strong assumptions and conditioning in downstream modules by introducing a simple yet effective event transformation that modifies the input events to encode the transformation from GS to RS image." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 359, + 289, + 430 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 359, + 289, + 430 + ], + "spans": [ + { + "bbox": [ + 46, + 359, + 289, + 430 + ], + "type": "text", + "content": "RS Deblur. Besides RS distortion, in presence of fast motion RS images often suffers from blur. In those cases, RS restoration methods needs to simultaneously perform deblur and distortion correction. [27] directly incorporate a deblurring stream in the RS correction network, while [28] adds an optional deblur module before the RS correction." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 431, + 289, + 635 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 431, + 289, + 635 + ], + "spans": [ + { + "bbox": [ + 46, + 431, + 289, + 635 + ], + "type": "text", + "content": "Datasets. BS-RSCD [27] dataset is recorded by using a beamsplitter setup with temporally and geometrically synchronized GS and RS cameras. Other datasets, such as Fastec-RS [15] or Gev-RS [28] are collected by first using a high speed GS camera and later synthesizing RS images by sequentially copying rows from the high frame rate GS images. For Gev-RS events are simulated from high speed GS images using V2E [10]. Unfortunately, training with synthetic events often does not generalize well to real event data. Moreover, RS images synthesized by the above method suffer from noise, low contrast and have small resolution, due to very short exposure time in the high speed cameras. We address two of the above problems by capturing a new dataset with real events using GS RGB and event cameras arranged in a beamsplitter setup and introducing new high fidelity simulator that generates high quality RS images with optional blur from GS images." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 649, + 104, + 661 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 649, + 104, + 661 + ], + "spans": [ + { + "bbox": [ + 47, + 649, + 104, + 661 + ], + "type": "text", + "content": "3. Method" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 669, + 250, + 682 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 669, + 250, + 682 + ], + "spans": [ + { + "bbox": [ + 47, + 669, + 250, + 682 + ], + "type": "text", + "content": "3.1.Eventful Shutter (EvShutter) Network" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 689, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 715 + ], + "type": "text", + "content": "At first, we perform event-assisted deblurring of the input RS image " + }, + { + "bbox": [ + 47, + 689, + 287, + 715 + ], + "type": "inline_equation", + "content": "I_{blur}^{rs}" + }, + { + "bbox": [ + 47, + 689, + 287, + 715 + ], + "type": "text", + "content": " image using a pre-processing deblurring" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 72, + 545, + 262 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 262 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 262 + ], + "type": "text", + "content": "module inspired by [24]. Next, we compensate RS distortion to obtain at a GS estimate at reference time " + }, + { + "bbox": [ + 304, + 72, + 545, + 262 + ], + "type": "inline_equation", + "content": "t_{ref}" + }, + { + "bbox": [ + 304, + 72, + 545, + 262 + ], + "type": "text", + "content": " using the pipeline shown in Fig. 3. As shown in the Fig. 3, instead of directly feeding all the raw events " + }, + { + "bbox": [ + 304, + 72, + 545, + 262 + ], + "type": "inline_equation", + "content": "E_{0\\rightarrow t_H}" + }, + { + "bbox": [ + 304, + 72, + 545, + 262 + ], + "type": "text", + "content": " to the network as in [28], we firstly pre-process them by using the proposed Filter and Flip (FnF) transformation, described in details in Sec. 3.2. Next, we encode the transformed events " + }, + { + "bbox": [ + 304, + 72, + 545, + 262 + ], + "type": "inline_equation", + "content": "E_{gs\\rightarrow rs}" + }, + { + "bbox": [ + 304, + 72, + 545, + 262 + ], + "type": "text", + "content": " into a voxel grid representation " + }, + { + "bbox": [ + 304, + 72, + 545, + 262 + ], + "type": "inline_equation", + "content": "V_{gs\\rightarrow rs}" + }, + { + "bbox": [ + 304, + 72, + 545, + 262 + ], + "type": "text", + "content": " as described in [32]. Then we feed the voxel grid and the RS image " + }, + { + "bbox": [ + 304, + 72, + 545, + 262 + ], + "type": "inline_equation", + "content": "I^{rs}" + }, + { + "bbox": [ + 304, + 72, + 545, + 262 + ], + "type": "text", + "content": " to an hourglass network composed of a warping encoder and a synthesis encoder using complementary interpolation approaches as in [22, 23]. Lastly, the fusion decoder progressively combines multi-scale images and warping and synthesis features to produce the final GS image " + }, + { + "bbox": [ + 304, + 72, + 545, + 262 + ], + "type": "inline_equation", + "content": "I^{gs}" + }, + { + "bbox": [ + 304, + 72, + 545, + 262 + ], + "type": "text", + "content": ". Below we explain the main modules of the proposed method." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 264, + 545, + 467 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 264, + 545, + 467 + ], + "spans": [ + { + "bbox": [ + 304, + 264, + 545, + 467 + ], + "type": "text", + "content": "Deblurring. Besides the RS distortion, RS images can suffer from motion blur due to camera or object motion during the exposure time. Therefore, we propose to deblur RS images using events before passing them to our RS distortion compensation method. The overall pipeline of the deblurring is shown in Fig. 4. First, we filter out all events triggered not during the exposure time of the corresponding image rows and then, we shift them according to the row-wise delay, similar to [28]. This allows the use of GS event-based deblurring methods, such as [24]. The original method estimates a deblur operator directly from events using offsets and masks of deformable convolutions [29]. However, we found that it is possible to estimate better deblur operators from more a explicit motion representation, such as optical flow. To estimate flow, we re-use the same network and weights as in the main RS distortion compensation pipeline." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 468, + 545, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 468, + 545, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 468, + 545, + 715 + ], + "type": "text", + "content": "Warping Encoder. The warping-based encoder takes the voxel grid " + }, + { + "bbox": [ + 304, + 468, + 545, + 715 + ], + "type": "inline_equation", + "content": "V_{gs \\to rs}" + }, + { + "bbox": [ + 304, + 468, + 545, + 715 + ], + "type": "text", + "content": " and estimates optical flow " + }, + { + "bbox": [ + 304, + 468, + 545, + 715 + ], + "type": "inline_equation", + "content": "\\mathcal{F}_{gs \\to rs}" + }, + { + "bbox": [ + 304, + 468, + 545, + 715 + ], + "type": "text", + "content": " relating the latent GS image to RS image using a flow network from [23]. Note that because the transformed events only encode changes from GS to RS image we can directly estimate optical flow between them without relying on a constant speed assumption. In other words, we can directly estimate row-wise flow, where each row " + }, + { + "bbox": [ + 304, + 468, + 545, + 715 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 304, + 468, + 545, + 715 + ], + "type": "text", + "content": " represents the pixel displacement from time " + }, + { + "bbox": [ + 304, + 468, + 545, + 715 + ], + "type": "inline_equation", + "content": "t_{ref}" + }, + { + "bbox": [ + 304, + 468, + 545, + 715 + ], + "type": "text", + "content": " to time " + }, + { + "bbox": [ + 304, + 468, + 545, + 715 + ], + "type": "inline_equation", + "content": "y \\cdot t_H / H" + }, + { + "bbox": [ + 304, + 468, + 545, + 715 + ], + "type": "text", + "content": ". In contrast in [1, 15, 26, 28], the authors predict optical flow between frames or during the exposure time of the frame using events and approximate the displacement between RS and GS by multiplying with a row dependent coefficient, which is only accurate for linear motions. The estimated flow is used to warp multi-scale features extracted from the RS image " + }, + { + "bbox": [ + 304, + 468, + 545, + 715 + ], + "type": "inline_equation", + "content": "I^{rs}" + }, + { + "bbox": [ + 304, + 468, + 545, + 715 + ], + "type": "text", + "content": " using the image encoder resulting in multi-scale warping interpolation features " + }, + { + "bbox": [ + 304, + 468, + 545, + 715 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_{\\rightarrow \\mathrm{gs}}^{\\mathbf{w}} = (F_{\\rightarrow gs}^{w(0)}, F_{\\rightarrow gs}^{w(1)}, F_{\\rightarrow gs}^{w(2)})" + }, + { + "bbox": [ + 304, + 468, + 545, + 715 + ], + "type": "text", + "content": ". Similarly, a multi-scale image pyramid computed from the RS image is warped to get " + }, + { + "bbox": [ + 304, + 468, + 545, + 715 + ], + "type": "inline_equation", + "content": "\\mathbf{I}_{\\rightarrow \\mathrm{gs}}^{\\mathrm{rs}} = (I_{\\rightarrow gs}^{rs(0)}, I_{\\rightarrow gs}^{rs(1)}, I_{\\rightarrow gs}^{rs(2)})" + }, + { + "bbox": [ + 304, + 468, + 545, + 715 + ], + "type": "text", + "content": ". The warping is performed by using" + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 749, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 749, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 749, + 318, + 757 + ], + "type": "text", + "content": "13906" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 50, + 72, + 545, + 297 + ], + "blocks": [ + { + "bbox": [ + 50, + 72, + 545, + 297 + ], + "lines": [ + { + "bbox": [ + 50, + 72, + 545, + 297 + ], + "spans": [ + { + "bbox": [ + 50, + 72, + 545, + 297 + ], + "type": "image", + "image_path": "a59f8edf354aa5e0e9886c53267995101c63b28ee386af5abd26c6e6f3b01bc4.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 308, + 546, + 352 + ], + "lines": [ + { + "bbox": [ + 46, + 308, + 546, + 352 + ], + "spans": [ + { + "bbox": [ + 46, + 308, + 546, + 352 + ], + "type": "text", + "content": "Figure 3. RS distortion compensation pipeline. At first the proposed method pre-processes input events with " + }, + { + "bbox": [ + 46, + 308, + 546, + 352 + ], + "type": "inline_equation", + "content": "FnF" + }, + { + "bbox": [ + 46, + 308, + 546, + 352 + ], + "type": "text", + "content": " transformation to encode only the brightness change between GS and RS frames. The transformed events are then passed to double encoder hourglass network with complementary warping and synthesis encoders relying on different interpolation principles. Then multi-scale features and images from both encoders are fused in the decoder to produce a GS image. The first fusion block of the decoder is shown in detail." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 75, + 369, + 263, + 487 + ], + "blocks": [ + { + "bbox": [ + 75, + 369, + 263, + 487 + ], + "lines": [ + { + "bbox": [ + 75, + 369, + 263, + 487 + ], + "spans": [ + { + "bbox": [ + 75, + 369, + 263, + 487 + ], + "type": "image", + "image_path": "61c7432c3c7f537fe4be7efc37e2c5027ed95afa2daf142f28ce6d4346e09c6c.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 495, + 287, + 540 + ], + "lines": [ + { + "bbox": [ + 46, + 495, + 287, + 540 + ], + "spans": [ + { + "bbox": [ + 46, + 495, + 287, + 540 + ], + "type": "text", + "content": "Figure 4. RS deblurring pipeline. First we filter out all the events which are not triggered during the exposure time, then we deblur the RS image using an improved version of [24], that relies on optical flow estimation to predict deblur kernels." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 547, + 287, + 595 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 547, + 287, + 595 + ], + "spans": [ + { + "bbox": [ + 46, + 547, + 287, + 595 + ], + "type": "text", + "content": "differentiable backward interpolation. To downscale images and optical flow we perform average pooling and in case of flow we additionally divide the flow by the downscale factor." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 601, + 287, + 685 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 601, + 287, + 685 + ], + "spans": [ + { + "bbox": [ + 46, + 601, + 287, + 685 + ], + "type": "text", + "content": "Synthesis-based Encoder. The synthesis-based encoder takes both voxel grid " + }, + { + "bbox": [ + 46, + 601, + 287, + 685 + ], + "type": "inline_equation", + "content": "V_{gs \\to rs}" + }, + { + "bbox": [ + 46, + 601, + 287, + 685 + ], + "type": "text", + "content": " and RS image " + }, + { + "bbox": [ + 46, + 601, + 287, + 685 + ], + "type": "inline_equation", + "content": "I^{rs}" + }, + { + "bbox": [ + 46, + 601, + 287, + 685 + ], + "type": "text", + "content": " as inputs and computes multi-scale synthesis interpolation features " + }, + { + "bbox": [ + 46, + 601, + 287, + 685 + ], + "type": "inline_equation", + "content": "\\mathbf{F}^s" + }, + { + "bbox": [ + 46, + 601, + 287, + 685 + ], + "type": "text", + "content": ". Intuitively, this encoder integrates brightness changes from the event stream and adds them to the RS image. Notice that, in contrast to the warping encoder, this module can handle illumination changes and fill motion occlusions." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 689, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 715 + ], + "type": "text", + "content": "Fusion Decoder: The fusion decoder progressively combines synthesis " + }, + { + "bbox": [ + 47, + 689, + 287, + 715 + ], + "type": "inline_equation", + "content": "\\mathbf{F}^s" + }, + { + "bbox": [ + 47, + 689, + 287, + 715 + ], + "type": "text", + "content": " and warping-based " + }, + { + "bbox": [ + 47, + 689, + 287, + 715 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_{\\rightarrow gs}^{w}" + }, + { + "bbox": [ + 47, + 689, + 287, + 715 + ], + "type": "text", + "content": " features, orig-" + } + ] + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 309, + 374, + 544, + 490 + ], + "blocks": [ + { + "bbox": [ + 309, + 374, + 544, + 490 + ], + "lines": [ + { + "bbox": [ + 309, + 374, + 544, + 490 + ], + "spans": [ + { + "bbox": [ + 309, + 374, + 544, + 490 + ], + "type": "image", + "image_path": "6e1ac7f3966be9de00c1414819b30c66389a742a83c1e4ba767da61231dcf9be.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 498, + 546, + 564 + ], + "lines": [ + { + "bbox": [ + 304, + 498, + 546, + 564 + ], + "spans": [ + { + "bbox": [ + 304, + 498, + 546, + 564 + ], + "type": "text", + "content": "Figure 5. Event transformation workflow. Top row: Event stream is transformed by first applying and event filtering followed by a flipping step around an arbitrary reference time. Bottom row: An example of events. Right: Animation (best viewed with Acrobot Reader) between RS-input and GS estimations at different reference times." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_caption" + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 573, + 546, + 670 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 573, + 546, + 670 + ], + "spans": [ + { + "bbox": [ + 304, + 573, + 546, + 670 + ], + "type": "text", + "content": "inal RS image " + }, + { + "bbox": [ + 304, + 573, + 546, + 670 + ], + "type": "inline_equation", + "content": "I^{rs}" + }, + { + "bbox": [ + 304, + 573, + 546, + 670 + ], + "type": "text", + "content": " and warped RS image " + }, + { + "bbox": [ + 304, + 573, + 546, + 670 + ], + "type": "inline_equation", + "content": "I_{\\rightarrow gs}^{rs}" + }, + { + "bbox": [ + 304, + 573, + 546, + 670 + ], + "type": "text", + "content": " on multiple scales to reconstruct the GS image " + }, + { + "bbox": [ + 304, + 573, + 546, + 670 + ], + "type": "inline_equation", + "content": "I^{gs}" + }, + { + "bbox": [ + 304, + 573, + 546, + 670 + ], + "type": "text", + "content": ". We use shortcut connections from the original RS image to help the decoder to reconstruct static parts of the image. To select the most informative features on each scale the decoder relies on Squeeze-and-excitation (SE) blocks [9] attenuating channels, and modulated deformable convolutions [29], attenuating the feature maps spatially." + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "13907" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 244, + 85 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 244, + 85 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 244, + 85 + ], + "type": "text", + "content": "3.2. Filter and Flip (FnF) Transformation" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 90, + 287, + 209 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 90, + 287, + 209 + ], + "spans": [ + { + "bbox": [ + 46, + 90, + 287, + 209 + ], + "type": "text", + "content": "The auxiliary event camera records an event stream " + }, + { + "bbox": [ + 46, + 90, + 287, + 209 + ], + "type": "inline_equation", + "content": "E_{0 \\to t_H}" + }, + { + "bbox": [ + 46, + 90, + 287, + 209 + ], + "type": "text", + "content": " encoding all brightness changes from time 0 to " + }, + { + "bbox": [ + 46, + 90, + 287, + 209 + ], + "type": "inline_equation", + "content": "t_H" + }, + { + "bbox": [ + 46, + 90, + 287, + 209 + ], + "type": "text", + "content": ". However, to recover the GS image " + }, + { + "bbox": [ + 46, + 90, + 287, + 209 + ], + "type": "inline_equation", + "content": "I^{gs}" + }, + { + "bbox": [ + 46, + 90, + 287, + 209 + ], + "type": "text", + "content": " corresponding to a given RS image " + }, + { + "bbox": [ + 46, + 90, + 287, + 209 + ], + "type": "inline_equation", + "content": "I^{rs}" + }, + { + "bbox": [ + 46, + 90, + 287, + 209 + ], + "type": "text", + "content": ", we are only interested on those events " + }, + { + "bbox": [ + 46, + 90, + 287, + 209 + ], + "type": "inline_equation", + "content": "E_{gs \\to rs}" + }, + { + "bbox": [ + 46, + 90, + 287, + 209 + ], + "type": "text", + "content": " encoding brightness changes between latent GS and observed RS image. In this work, we propose a well-suited RS event transformation called Filter and Flip (FnF), which transforms the event stream " + }, + { + "bbox": [ + 46, + 90, + 287, + 209 + ], + "type": "inline_equation", + "content": "E_{0 \\to t_H}" + }, + { + "bbox": [ + 46, + 90, + 287, + 209 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 46, + 90, + 287, + 209 + ], + "type": "inline_equation", + "content": "E_{gs \\to rs}" + }, + { + "bbox": [ + 46, + 90, + 287, + 209 + ], + "type": "text", + "content": " through two steps: filtering and flipping steps as shown in Fig. 5 and described below." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 210, + 287, + 258 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 210, + 287, + 258 + ], + "spans": [ + { + "bbox": [ + 46, + 210, + 287, + 258 + ], + "type": "text", + "content": "Filtering step. For each row " + }, + { + "bbox": [ + 46, + 210, + 287, + 258 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 46, + 210, + 287, + 258 + ], + "type": "text", + "content": ", we only keep those events triggered between time " + }, + { + "bbox": [ + 46, + 210, + 287, + 258 + ], + "type": "inline_equation", + "content": "t_y" + }, + { + "bbox": [ + 46, + 210, + 287, + 258 + ], + "type": "text", + "content": " and the reference time " + }, + { + "bbox": [ + 46, + 210, + 287, + 258 + ], + "type": "inline_equation", + "content": "t_{ref}" + }, + { + "bbox": [ + 46, + 210, + 287, + 258 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 210, + 287, + 258 + ], + "type": "inline_equation", + "content": "t_y" + }, + { + "bbox": [ + 46, + 210, + 287, + 258 + ], + "type": "text", + "content": " is mid-exposure time of row " + }, + { + "bbox": [ + 46, + 210, + 287, + 258 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 46, + 210, + 287, + 258 + ], + "type": "text", + "content": " in observed RS image." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 258, + 287, + 341 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 258, + 287, + 341 + ], + "spans": [ + { + "bbox": [ + 46, + 258, + 287, + 341 + ], + "type": "text", + "content": "Flipping step. We reverse all events before the reference time " + }, + { + "bbox": [ + 46, + 258, + 287, + 341 + ], + "type": "inline_equation", + "content": "t_{ref}" + }, + { + "bbox": [ + 46, + 258, + 287, + 341 + ], + "type": "text", + "content": " by inverting their polarities and recomputing their timestamps such that they are flipped around " + }, + { + "bbox": [ + 46, + 258, + 287, + 341 + ], + "type": "inline_equation", + "content": "t_{ref}" + }, + { + "bbox": [ + 46, + 258, + 287, + 341 + ], + "type": "text", + "content": " as shown in Fig. 5. This process ensures that the events encode changes in the direction from GS-frame to RS-frame and that the transformed events start at the time, which matches the GS-frame and end at the RS-time." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 342, + 287, + 449 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 342, + 287, + 449 + ], + "spans": [ + { + "bbox": [ + 46, + 342, + 287, + 449 + ], + "type": "text", + "content": "Applying the event transformation eliminates the need in time conditioning mechanisms and additional assumptions in the downstream modules. For example, in contrast to [28], the proposed method does not require constant speed assumption in the flow estimation module and attention mechanisms in the synthesis-based encoder, which allows re-using already pretrained modules on widely used GS images. Also, notice, that the FnF transformation can be adapted to arbitrary reference times." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 449, + 287, + 484 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 449, + 287, + 484 + ], + "spans": [ + { + "bbox": [ + 46, + 449, + 287, + 484 + ], + "type": "text", + "content": "In order to allow a good comparison to other works, we set " + }, + { + "bbox": [ + 46, + 449, + 287, + 484 + ], + "type": "inline_equation", + "content": "t_{ref} = t_H / 2" + }, + { + "bbox": [ + 46, + 449, + 287, + 484 + ], + "type": "text", + "content": ", which corresponds to the mid-exposure time of the central row." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 491, + 157, + 503 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 491, + 157, + 503 + ], + "spans": [ + { + "bbox": [ + 47, + 491, + 157, + 503 + ], + "type": "text", + "content": "3.3. RS-ERGB Dataset" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 510, + 287, + 617 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 510, + 287, + 617 + ], + "spans": [ + { + "bbox": [ + 46, + 510, + 287, + 617 + ], + "type": "text", + "content": "To bridge the sim-to-real gap from synthetic to real events we build a hybrid imaging system of a high speed GS RGB-camera and an event camera in a beam splitter setup. We use hardware temporal synchronization and geometrically align events and images as described in the Supp. Mat. With this setup we capture the first RS dataset with real events and high quality images. We generate high quality RS images with optional blur using our novel simulator based on adaptive interpolation described below." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 618, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 618, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 618, + 287, + 713 + ], + "type": "text", + "content": "High quality RS simulator. Our proposed pipeline allows to record GS sequences at lower speed than previous methods (160 fps compared to [15, 28] that record GS sequence at 2400 or 5700 fps). This allows us to use a longer exposure and as a result, acquire images of higher quality. Then we adaptively interpolate captured images using Super Slomo [11], so that the maximum displacement between interpolated frames is at most 1 pixel similar to" + } + ] + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 307, + 69, + 547, + 162 + ], + "blocks": [ + { + "bbox": [ + 307, + 69, + 547, + 162 + ], + "lines": [ + { + "bbox": [ + 307, + 69, + 547, + 162 + ], + "spans": [ + { + "bbox": [ + 307, + 69, + 547, + 162 + ], + "type": "image", + "image_path": "06b51f2e5d82233a6b853affd0784b0ad0bc23bf1951f36e342bdcb95eaa6448.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 170, + 547, + 214 + ], + "lines": [ + { + "bbox": [ + 305, + 170, + 547, + 214 + ], + "spans": [ + { + "bbox": [ + 305, + 170, + 547, + 214 + ], + "type": "text", + "content": "Figure 6. Synthetic RS-images from a sequence of GS-Images " + }, + { + "bbox": [ + 305, + 170, + 547, + 214 + ], + "type": "inline_equation", + "content": "I_{i}" + }, + { + "bbox": [ + 305, + 170, + 547, + 214 + ], + "type": "text", + "content": ". Each row is constructed separately by computing the weighted average of the GS-frames, which are assumed to be a close approximation of the latent GS-frames." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 222, + 546, + 342 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 222, + 546, + 342 + ], + "spans": [ + { + "bbox": [ + 305, + 222, + 546, + 342 + ], + "type": "text", + "content": "Vid2E [4]. This procedure ensures that a sufficient temporal resolution is achieved to synthesize realistic blur and RS effect. As shown in Fig. 7, using a fixed interpolation factor can give unrealistic results as the amount of motion can differ significantly by region and scene. The resulting interpolated video sequence can be thought of as discrete approximation of latent GS-images " + }, + { + "bbox": [ + 305, + 222, + 546, + 342 + ], + "type": "inline_equation", + "content": "I_{i}" + }, + { + "bbox": [ + 305, + 222, + 546, + 342 + ], + "type": "text", + "content": " of the true latent frames " + }, + { + "bbox": [ + 305, + 222, + 546, + 342 + ], + "type": "inline_equation", + "content": "I_{\\text{latent}}(t,x,y)" + }, + { + "bbox": [ + 305, + 222, + 546, + 342 + ], + "type": "text", + "content": ". To synthesize a row " + }, + { + "bbox": [ + 305, + 222, + 546, + 342 + ], + "type": "inline_equation", + "content": "y_{rs}" + }, + { + "bbox": [ + 305, + 222, + 546, + 342 + ], + "type": "text", + "content": " of a RS-image the integral of " + }, + { + "bbox": [ + 305, + 222, + 546, + 342 + ], + "type": "inline_equation", + "content": "I_{\\text{latent}}(t,x,y = y_{rs})" + }, + { + "bbox": [ + 305, + 222, + 546, + 342 + ], + "type": "text", + "content": " has to be computed over the exposure time for this row, as" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 309, + 352, + 545, + 400 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 309, + 352, + 545, + 400 + ], + "spans": [ + { + "bbox": [ + 309, + 352, + 545, + 400 + ], + "type": "interline_equation", + "content": "I _ {r s} \\left(t _ {\\text {s t a r t}}, t _ {\\text {e n d}}, y _ {i}\\right) = \\frac {1}{t _ {\\text {e n d}} - t _ {\\text {s t a r t}}} \\int_ {t _ {\\text {s t a r t}}} ^ {t _ {\\text {e n d}}} I _ {\\text {l a t e n t}} (t, y _ {i}) d t. \\tag {1}", + "image_path": "b5945feb488accc995ccb66a051457bc7c35a7bffd729b649fd7b3351a550505.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 401, + 545, + 568 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 401, + 545, + 568 + ], + "spans": [ + { + "bbox": [ + 304, + 401, + 545, + 568 + ], + "type": "text", + "content": "We use a discrete approximation instead and compute a weighted average of the approximated latent frames " + }, + { + "bbox": [ + 304, + 401, + 545, + 568 + ], + "type": "inline_equation", + "content": "I_{i}" + }, + { + "bbox": [ + 304, + 401, + 545, + 568 + ], + "type": "text", + "content": " as shown in Fig. 6. Using this procedure a synthetic exposure time and readout time " + }, + { + "bbox": [ + 304, + 401, + 545, + 568 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 304, + 401, + 545, + 568 + ], + "type": "text", + "content": " are chosen to synthesize corresponding RS frames. Notice that exposure time and readout time can be set separately allowing us to create blurry RS images with sharp RS ground truth for the task of RS deblurring. Video interpolation has already been used in the past to generate more realistic blur from videos [17], but to the best of our knowledge, we are the first to use an adaptive upsampling scheme to get consistently realistic results. Examples of our dataset with different amounts of blur and a comparison to a version without adaptive interpolation can be seen in the Supp. Mat.." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 568, + 545, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 568, + 545, + 628 + ], + "spans": [ + { + "bbox": [ + 304, + 568, + 545, + 628 + ], + "type": "text", + "content": "Comparison to Gev-RS [28] is shown in Tab. 1. Compared to Gev-RS, our dataset has real events and the RS and GS image have better quality and resolution, despite using a lower end camera " + }, + { + "bbox": [ + 304, + 568, + 545, + 628 + ], + "type": "inline_equation", + "content": "{}^{2}" + }, + { + "bbox": [ + 304, + 568, + 545, + 628 + ], + "type": "text", + "content": " ,since our new synthesis procedure allows using lower frame rate with longer exposure." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 640, + 387, + 654 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 640, + 387, + 654 + ], + "spans": [ + { + "bbox": [ + 306, + 640, + 387, + 654 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 661, + 547, + 685 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 661, + 547, + 685 + ], + "spans": [ + { + "bbox": [ + 305, + 661, + 547, + 685 + ], + "type": "text", + "content": "In this section, first, we ablate the key contributions of the proposed EvShutter method. Second, we benchmark" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 306, + 693, + 545, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 693, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 306, + 693, + 545, + 713 + ], + "type": "text", + "content": "2 Phantom VEO 640 is used for collecting Gev-RS cost " + }, + { + "bbox": [ + 306, + 693, + 545, + 713 + ], + "type": "inline_equation", + "content": "60\\mathrm{k}" + }, + { + "bbox": [ + 306, + 693, + 545, + 713 + ], + "type": "text", + "content": " while Blackfly S used for collecting our datasets costs just " + }, + { + "bbox": [ + 306, + 693, + 545, + 713 + ], + "type": "inline_equation", + "content": "500" + }, + { + "bbox": [ + 306, + 693, + 545, + 713 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "13908" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 49, + 70, + 277, + 195 + ], + "blocks": [ + { + "bbox": [ + 49, + 70, + 277, + 195 + ], + "lines": [ + { + "bbox": [ + 49, + 70, + 277, + 195 + ], + "spans": [ + { + "bbox": [ + 49, + 70, + 277, + 195 + ], + "type": "image", + "image_path": "4f1097efdd78c67a4e4a23129c10ad156c80d02369f96b499c5101ff0b6c4c47.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 204, + 288, + 247 + ], + "lines": [ + { + "bbox": [ + 46, + 204, + 288, + 247 + ], + "spans": [ + { + "bbox": [ + 46, + 204, + 288, + 247 + ], + "type": "text", + "content": "Figure 7. Benefit of the proposed RS simulator In contrast to a simulator with fixed interpolation rate, the proposed simulator with an adaptive interpolation does not suffer from aliasing artifacts regardless of the motion speed." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 48, + 264, + 293, + 345 + ], + "blocks": [ + { + "bbox": [ + 48, + 264, + 293, + 345 + ], + "lines": [ + { + "bbox": [ + 48, + 264, + 293, + 345 + ], + "spans": [ + { + "bbox": [ + 48, + 264, + 293, + 345 + ], + "type": "table", + "html": "
RS-ERGB (ours)Gev-RS [28]
Event datareal (Prophesee Gen4M)synthetic
GS camera160 fps5.7k fps
Blackfly SPhantom VEO 640
№ sequence3429
Image qualityhighlow
Resolution970×625640×360
", + "image_path": "2f11e95f30ef03c409328d2902599cf8a7c094ad4f35f5085fc45936d7bb4203.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 384, + 287, + 419 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 384, + 287, + 419 + ], + "spans": [ + { + "bbox": [ + 47, + 384, + 287, + 419 + ], + "type": "text", + "content": "the EvShutter against state-of-the-art image-based [15,27] and event-based [28] methods on our RS-ERGB dataset, as well as on the public Fastec-RS dataset [15]." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 420, + 287, + 456 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 420, + 287, + 456 + ], + "spans": [ + { + "bbox": [ + 47, + 420, + 287, + 456 + ], + "type": "text", + "content": "Details of the objective loss, training procedure and runtime comparisons together with ablation on additional design choices can be found in the Supp. Mat." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 465, + 140, + 478 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 465, + 140, + 478 + ], + "spans": [ + { + "bbox": [ + 47, + 465, + 140, + 478 + ], + "type": "text", + "content": "4.1. Ablation Study" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 484, + 287, + 520 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 484, + 287, + 520 + ], + "spans": [ + { + "bbox": [ + 47, + 484, + 287, + 520 + ], + "type": "text", + "content": "FnF event transformation. To evaluate the proposed FnF transformation Tab. 2 we dissect our pipeline in purely warping-based, purely synthesis-based and the full pipeline." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 521, + 287, + 591 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 521, + 287, + 591 + ], + "spans": [ + { + "bbox": [ + 46, + 521, + 287, + 591 + ], + "type": "text", + "content": "We compare the purely warping-based method to a version that relies on a constant velocity assumption similar to EvUnroll [28] by applying a row-wise scaling to the optical flow computed from " + }, + { + "bbox": [ + 46, + 521, + 287, + 591 + ], + "type": "inline_equation", + "content": "t_{GS}" + }, + { + "bbox": [ + 46, + 521, + 287, + 591 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 46, + 521, + 287, + 591 + ], + "type": "inline_equation", + "content": "t_0" + }, + { + "bbox": [ + 46, + 521, + 287, + 591 + ], + "type": "text", + "content": " and from " + }, + { + "bbox": [ + 46, + 521, + 287, + 591 + ], + "type": "inline_equation", + "content": "t_{GS}" + }, + { + "bbox": [ + 46, + 521, + 287, + 591 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 46, + 521, + 287, + 591 + ], + "type": "inline_equation", + "content": "t_H" + }, + { + "bbox": [ + 46, + 521, + 287, + 591 + ], + "type": "text", + "content": ". Our FnF transformation improves the warping-based method by 0.77 dB in PSNR and 0.0104 in LPIPS [25]." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 593, + 287, + 640 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 593, + 287, + 640 + ], + "spans": [ + { + "bbox": [ + 47, + 593, + 287, + 640 + ], + "type": "text", + "content": "We also test the purely synthesis based module with and without the FnF transformation. As shown in Tab. 2 the synthesis module with the transformation outperforms the version without by " + }, + { + "bbox": [ + 47, + 593, + 287, + 640 + ], + "type": "inline_equation", + "content": "3.92\\mathrm{dB}" + }, + { + "bbox": [ + 47, + 593, + 287, + 640 + ], + "type": "text", + "content": " in PSNR and 0.0376 in LPIPS." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 641, + 287, + 664 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 641, + 287, + 664 + ], + "spans": [ + { + "bbox": [ + 47, + 641, + 287, + 664 + ], + "type": "text", + "content": "The overall architecture also benefits from the FnF transformation by 2.61 dB in PSNR and 0.0203 in LPIPS." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 666, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 666, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 666, + 287, + 713 + ], + "type": "text", + "content": "Importance of optical flow in RS deblur module. We show benefits of estimating the deblur operator from optical flow instead of raw events in Tab. 3. By introducing the optical flow explicitly to the deblurring network we observe" + } + ] + } + ], + "index": 11 + }, + { + "type": "table", + "bbox": [ + 306, + 69, + 545, + 195 + ], + "blocks": [ + { + "bbox": [ + 47, + 354, + 286, + 375 + ], + "lines": [ + { + "bbox": [ + 47, + 354, + 286, + 375 + ], + "spans": [ + { + "bbox": [ + 47, + 354, + 286, + 375 + ], + "type": "text", + "content": "Table 1. Details of our RS-ERGB compared to Gev-RS [28]. Best-suited properties are shown in bold." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 306, + 69, + 545, + 195 + ], + "lines": [ + { + "bbox": [ + 306, + 69, + 545, + 195 + ], + "spans": [ + { + "bbox": [ + 306, + 69, + 545, + 195 + ], + "type": "table", + "html": "
MethodPSNR↑LPIPS↓SSIM↑
Warping
Linearized flow28.390.17210.870
FnF-Transform29.160.16170.883
Synthesis
w/o FnF-Transform25.870.22330.807
FnF-Transform29.790.18570.867
Warping & Synthesis
Linearized flow28.970.17030.870
FnF-Transform31.580.15000.897
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MethodPSNR↑LPIPS↓SSIM↑
EDDMA [24]34.920.05880.936
EDDMA [24]+Flow36.320.04880.951
EvUnroll + Deblur [28]35.640.04990.934
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Comparison with SOTA methods" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 545, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 545, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 545, + 545, + 713 + ], + "type": "text", + "content": "RS-ERGB dataset. We compare our method to the state-of-the-art image-based methods DSUN [15], RSCD [27] and the recent event-based EvUnroll [28] on RS-ERGB-Sharp dataset without blur and RSCD [27] and EvUnroll [28] on the RS-ERGB-Blurry dataset with blur. All methods were finetuned on our datasets. For more details please refer to the Supp. Mat. The results are reported in Tab. 4 and qualitative comparisons are shown in Fig. 8. On the RS-ERGB dataset, we outperform the best image-based method DSUN [15] by 9.16 dB in terms of PSNR and 0.0966 in LPIPS and the event-based method EvUnroll [28] by 0.75 dB in PSNR and 0.0966 in LPIPS. 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Quantitative results on RS-ERGB-Sharp and ER-ERGB-Blurry datasets. Image-based methods are marked by (i) and event and image based methods are marked by " + }, + { + "bbox": [ + 46, + 429, + 545, + 451 + ], + "type": "inline_equation", + "content": "(\\mathrm{i + e})" + }, + { + "bbox": [ + 46, + 429, + 545, + 451 + ], + "type": "text", + "content": " . The best method is shown in bold." + } + ] + } + ], + "index": 27, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 48, + 470, + 167, + 583 + ], + "lines": [ + { + "bbox": [ + 48, + 470, + 167, + 583 + ], + "spans": [ + { + "bbox": [ + 48, + 470, + 167, + 583 + ], + "type": "image", + "image_path": "5f118937660988ec5b12d6a953897b3e2eb1d693044206dc6a82ec5d602f7519.jpg" + } + ] + } + ], + "index": 28, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 592, + 287, + 625 + ], + "lines": [ + { + "bbox": [ + 46, + 592, + 287, + 625 + ], + "spans": [ + { + "bbox": [ + 46, + 592, + 287, + 625 + ], + "type": "text", + "content": "Figure 9. Visualization of deformable convolutions offsets in deblurring module for the original method [24](left), and our method (right), where offset are computed from optical flow." + } + ] + } + ], + "index": 30, + "angle": 0, + "type": "image_caption" + } + ], + "index": 28 + }, + { + "type": "image", + "bbox": [ + 168, + 470, + 287, + 583 + ], + "blocks": [ + { + "bbox": [ + 168, + 470, + 287, + 583 + ], + "lines": [ + { + "bbox": [ + 168, + 470, + 287, + 583 + ], + "spans": [ + { + "bbox": [ + 168, + 470, + 287, + 583 + ], + "type": "image", + "image_path": "6e3a24295e703785aad2877caa27e3dd17cb092c37612f58348327854048e1a3.jpg" + } + ] + } + ], + "index": 29, + "angle": 0, + "type": "image_body" + } + ], + "index": 29 + }, + { + "bbox": [ + 46, + 633, + 287, + 705 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 633, + 287, + 705 + ], + "spans": [ + { + "bbox": [ + 46, + 633, + 287, + 705 + ], + "type": "text", + "content": "method RSCD [27] seems not able to handle the difficult combination of large RS distortion and blur. Our method improves current image-based SOTA methods especially in areas with large displacements between RS and GS-frame. DSUN [15] is able to reconstruct the overall shape of the object, but produces strong artifacts. EvUnroll [28] is able to" + } + ] + } + ], + "index": 31 + }, + { + "bbox": [ + 304, + 472, + 545, + 568 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 472, + 545, + 568 + ], + "spans": [ + { + "bbox": [ + 304, + 472, + 545, + 568 + ], + "type": "text", + "content": "recover the structure of the GS images very well, but seems to heavily rely on their synthesis branch in areas with large non linear motion. We hypothesize that the fusion in RGB space makes it more difficult to combine the fine detail and texture from the warping branch with the coarse structurally correct results from the synthesis branch, which often lack precise colors. Additional comparisons can be found in the Supp. Mat.." + } + ] + } + ], + "index": 32 + }, + { + "bbox": [ + 304, + 570, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 546, + 713 + ], + "type": "text", + "content": "Fastec-RS dataset To compare the proposed method to other SOTA on the public Fastec-RS dataset [15] we synthesized events from the original high speed sequences shared by the authors using ESIM [20] with the same parameters as in [28] and re-train our method from scratch. We run JCD [27] and DSUN [15] using the publicly available checkpoints. For [26, 30], we extract the metrics from the JCD paper [27] and for EvUnroll [28] and SUNet [1] from their respective papers. The results are reported in Tab. 5. The proposed method outperforms the best image-based approach by " + }, + { + "bbox": [ + 304, + 570, + 546, + 713 + ], + "type": "inline_equation", + "content": "4.07\\mathrm{dB}" + }, + { + "bbox": [ + 304, + 570, + 546, + 713 + ], + "type": "text", + "content": " in PSNR and the event-based approach by " + }, + { + "bbox": [ + 304, + 570, + 546, + 713 + ], + "type": "inline_equation", + "content": "1.09\\mathrm{dB}" + }, + { + "bbox": [ + 304, + 570, + 546, + 713 + ], + "type": "text", + "content": " in PSNR, 0.023 in terms of LPIPS and 0.03 in" + } + ] + } + ], + "index": 33 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "13910" + } + ] + } + ], + "index": 34 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 53, + 70, + 177, + 164 + ], + "blocks": [ + { + "bbox": [ + 53, + 70, + 177, + 164 + ], + "lines": [ + { + "bbox": [ + 53, + 70, + 177, + 164 + ], + "spans": [ + { + "bbox": [ + 53, + 70, + 177, + 164 + ], + "type": "image", + "image_path": "19e1a3f8d098ec708dcbf40ea1e5d68ac33daa823e7a5a03c53d1c51251a1e3a.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 179, + 70, + 301, + 164 + ], + "blocks": [ + { + "bbox": [ + 179, + 70, + 301, + 164 + ], + "lines": [ + { + "bbox": [ + 179, + 70, + 301, + 164 + ], + "spans": [ + { + "bbox": [ + 179, + 70, + 301, + 164 + ], + "type": "image", + "image_path": "2de3b47b211a417cad147e88fde520a9f8d5371821777f169ddcdb18b2d8f168.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 302, + 70, + 427, + 164 + ], + "blocks": [ + { + "bbox": [ + 302, + 70, + 427, + 164 + ], + "lines": [ + { + "bbox": [ + 302, + 70, + 427, + 164 + ], + "spans": [ + { + "bbox": [ + 302, + 70, + 427, + 164 + ], + "type": "image", + "image_path": "2bba678d3699ef4c589f6022ae989fbcf26269d3bf9e3eb064c0b6ace8287457.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 427, + 70, + 551, + 164 + ], + "blocks": [ + { + "bbox": [ + 427, + 70, + 551, + 164 + ], + "lines": [ + { + "bbox": [ + 427, + 70, + 551, + 164 + ], + "spans": [ + { + "bbox": [ + 427, + 70, + 551, + 164 + ], + "type": "image", + "image_path": "e65885285938758351dfe3a8ab9f289f2c94c78418f82070a951f5aa4bad16dd.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + } + ], + "index": 3 + }, + { + "type": "image", + "bbox": [ + 53, + 167, + 177, + 260 + ], + "blocks": [ + { + "bbox": [ + 53, + 167, + 177, + 260 + ], + "lines": [ + { + "bbox": [ + 53, + 167, + 177, + 260 + ], + "spans": [ + { + "bbox": [ + 53, + 167, + 177, + 260 + ], + "type": "image", + "image_path": "010cd0b8b4d1efdf009b3fd94926873a5c64e3cc647f17e0be3c988681112bdf.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 82, + 263, + 148, + 274 + ], + "lines": [ + { + "bbox": [ + 82, + 263, + 148, + 274 + ], + "spans": [ + { + "bbox": [ + 82, + 263, + 148, + 274 + ], + "type": "text", + "content": "Input RS-image" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "type": "image", + "bbox": [ + 179, + 167, + 301, + 260 + ], + "blocks": [ + { + "bbox": [ + 179, + 167, + 301, + 260 + ], + "lines": [ + { + "bbox": [ + 179, + 167, + 301, + 260 + ], + "spans": [ + { + "bbox": [ + 179, + 167, + 301, + 260 + ], + "type": "image", + "image_path": "189794c3318147ef2ad5227ac5a18c3c0946fcfab05595d7c6dfcfd12d5421a5.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 196, + 263, + 287, + 274 + ], + "lines": [ + { + "bbox": [ + 196, + 263, + 287, + 274 + ], + "spans": [ + { + "bbox": [ + 196, + 263, + 287, + 274 + ], + "type": "text", + "content": "EvUnroll original [28]" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_caption" + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 302, + 167, + 427, + 260 + ], + "blocks": [ + { + "bbox": [ + 302, + 167, + 427, + 260 + ], + "lines": [ + { + "bbox": [ + 302, + 167, + 427, + 260 + ], + "spans": [ + { + "bbox": [ + 302, + 167, + 427, + 260 + ], + "type": "image", + "image_path": "49787c3836d5c0c72d7ce4e1e34de6425e5d7dcfd55cc73853f6e0a3740b90d6.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 285, + 545, + 306 + ], + "lines": [ + { + "bbox": [ + 46, + 285, + 545, + 306 + ], + "spans": [ + { + "bbox": [ + 46, + 285, + 545, + 306 + ], + "type": "text", + "content": "Figure 10. Qualitative comparison on Real Events and RS images from EvUnroll [28]. Note that no ground truth data is provided for this dataset." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 427, + 167, + 551, + 260 + ], + "blocks": [ + { + "bbox": [ + 302, + 263, + 428, + 274 + ], + "lines": [ + { + "bbox": [ + 302, + 263, + 428, + 274 + ], + "spans": [ + { + "bbox": [ + 302, + 263, + 428, + 274 + ], + "type": "text", + "content": "EvUnroll trained on RS-ERGB" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 427, + 167, + 551, + 260 + ], + "lines": [ + { + "bbox": [ + 427, + 167, + 551, + 260 + ], + "spans": [ + { + "bbox": [ + 427, + 167, + 551, + 260 + ], + "type": "image", + "image_path": "6177c7cf3a5a852b4107152faf811c296f5ff4fbe8189d61773d8733c335a550.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 471, + 264, + 492, + 273 + ], + "lines": [ + { + "bbox": [ + 471, + 264, + 492, + 273 + ], + "spans": [ + { + "bbox": [ + 471, + 264, + 492, + 273 + ], + "type": "text", + "content": "Ours" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "type": "table", + "bbox": [ + 48, + 326, + 287, + 440 + ], + "blocks": [ + { + "bbox": [ + 48, + 326, + 287, + 440 + ], + "lines": [ + { + "bbox": [ + 48, + 326, + 287, + 440 + ], + "spans": [ + { + "bbox": [ + 48, + 326, + 287, + 440 + ], + "type": "table", + "html": "
MethodPSNR [dB]↑LPIPS↓SSIM↑
RS-ERGB-Sharp
DSUN [15] (i)22.970.26700.7976
RSCD [27] (i)22.620.27590.7884
EvUnroll [28] (i+e)31.380.23340.8614
EvShutter (Ours) (i+e)32.130.17040.8866
RS-ERGB-Blurry
RSCD [27] (i)17.870.37130.7109
EvUnroll [28] (i+e)31.070.25760.8592
EvShutter (Ours) (i+e)31.550.20460.8780
", + "image_path": "3098c48911ae51856e9ae11404a26abf3695183e163a3e02d8cfff6b9d1dae90.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "table_body" + } + ], + "index": 13 + }, + { + "bbox": [ + 46, + 490, + 287, + 550 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 490, + 287, + 550 + ], + "spans": [ + { + "bbox": [ + 46, + 490, + 287, + 550 + ], + "type": "text", + "content": "SSIM. Additionally, some qualitative examples are shown in the Supp. Mat.. Similarly, to the results on the RS-ERGB dataset we observe that our method performs better at object boundaries, where the displacement is not homogeneous. We obtain sharper and less \"wobbly\" results." + } + ] + } + ], + "index": 15 + }, + { + "type": "table", + "bbox": [ + 48, + 559, + 287, + 646 + ], + "blocks": [ + { + "bbox": [ + 46, + 449, + 287, + 482 + ], + "lines": [ + { + "bbox": [ + 46, + 449, + 287, + 482 + ], + "spans": [ + { + "bbox": [ + 46, + 449, + 287, + 482 + ], + "type": "text", + "content": "Table 4. RS correction on RS-ERGB dataset with real events. The best method is shown in bold. Image-base methods are marked by (i) and image and event-based methods by " + }, + { + "bbox": [ + 46, + 449, + 287, + 482 + ], + "type": "inline_equation", + "content": "(\\mathrm{i + e})" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 48, + 559, + 287, + 646 + ], + "lines": [ + { + "bbox": [ + 48, + 559, + 287, + 646 + ], + "spans": [ + { + "bbox": [ + 48, + 559, + 287, + 646 + ], + "type": "table", + "html": "
MethodPSNR ↑LPIPS↓SSIM↑
DSUN [15] (i)26.520.1220.79
RSCD [27] (i)24.840.1070.78
SUNet [1] (i)28.34-0.84
ESTRNN [26] (i)27.410.1890.84
EvUnroll [28] (i+e)31.320.0840.88
EvShutter (Ours) (i+e)32.410.0610.91
", + "image_path": "ee7a732a75149bbd74742876a5af316b73f4397d36ed37c8bf9256d2c8f2d7b8.jpg" + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "table_body" + } + ], + "index": 16 + }, + { + "bbox": [ + 46, + 654, + 287, + 688 + ], + "lines": [ + { + "bbox": [ + 46, + 654, + 287, + 688 + ], + "spans": [ + { + "bbox": [ + 46, + 654, + 287, + 688 + ], + "type": "text", + "content": "Table 5. RS correction on Fastec-RS dataset with synthetic events. The best method is shown in bold. Image-base methods are marked by (i) and image and event-based methods by " + }, + { + "bbox": [ + 46, + 654, + 287, + 688 + ], + "type": "inline_equation", + "content": "(\\mathrm{i + e})" + } + ] + } + ], + "index": 17, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 304, + 328, + 545, + 495 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 328, + 545, + 495 + ], + "spans": [ + { + "bbox": [ + 304, + 328, + 545, + 495 + ], + "type": "text", + "content": "Qualitative comparison on real RS dataset from [28] For qualitative comparison on real data, we evaluated our method on the dataset published in [28], which features real events and real RS images, but no ground truth. In Fig. 10, we compare to the results from EvUnroll [28] trained on their synthetic dataset with synthetic events and their model trained on our RS-ERGB dataset, see Fig. 10. We observe that by training on our RS-ERGB dataset with real events EvUnroll [28] greatly improves their performance. This shows the benefits of the proposed dataset with real events and the novel RS image simulator. Our method performs even better and does not suffer from strong ghosting artifacts as the EvUnroll [28]. Additional examples can be found in Supp. Mat." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 306, + 506, + 378, + 518 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 506, + 378, + 518 + ], + "spans": [ + { + "bbox": [ + 306, + 506, + 378, + 518 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 526, + 545, + 693 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 526, + 545, + 693 + ], + "spans": [ + { + "bbox": [ + 304, + 526, + 545, + 693 + ], + "type": "text", + "content": "This paper proposes a method for RS distortion correction and deblurring. The method estimates deblurring operator from event-based optical flow and then compensates RS using a double encoder hourglass network. In contrast to previous methods, it does not rely on a constant velocity assumption and uses a simple architecture thanks to the proposed event transformation. Additionally, we propose the first RS dataset with optional blur containing real events and simulated high-quality RS images and show that training on this dataset increases performance of methods in real case scenarios. We carefully ablate each of the contributions and demonstrate the qualitative and quantitative performance boost compared to previous state-of-the-art methods." + } + ] + } + ], + "index": 20 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "type": "text", + "content": "13911" + } + ] + } + ], + "index": 21 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 288, + 713 + ], + "type": "list", + "angle": 0, + "index": 13, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 135 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 135 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 135 + ], + "type": "text", + "content": "[1] Bin Fan, Yuchao Dai, and Mingyi He. 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